Storage method for power storage device and storage system for power storage device

Abstract

This power storage device is provided with: a container that is filled with an electrolyte solution; metal atoms that are ionized in the electrolyte solution and are involved in charging and discharging; and an electrode that is disposed in the electrolyte solution. This power storage device is configured such that a layer of the metal atoms, in which the metal atoms are deposited, is formed on the surface of the electrode during charging. A storage method for the power storage device includes: a step of charging the power storage device; and a step of maintaining the temperature of the power storage device at a predetermined storage temperature of 25°C to 65°C inclusive by setting the power storage device after charging in an open circuit state.

Description

Method for storing an electricity storage device and system for storing an electricity storage device

[0001] The present application relates to a method for storing an electricity storage device and a system for storing an electricity storage device.

[0002] Known examples of chargeable and dischargeable electricity storage devices include secondary batteries, electric double layer capacitors, etc. Known secondary batteries include, for example, lithium ion batteries in which lithium ions are involved in charging and discharging.

[0003] Conventional lithium-ion batteries have generally been stored at temperatures lower than room temperature. The reason for this is that if they are left in a high-temperature environment above room temperature for a long period of time, internal chemical reactions may be accelerated, making them more susceptible to self-discharge, and a coating may form on the electrode surface, causing performance degradation. For example, Patent Document 1 listed below discloses a technology for storing lithium-ion batteries at temperatures between 0°C and -40°C. JP 2011-210612 A

[0004] Conventional lithium-ion batteries such as those disclosed in Patent Document 1 are charged by intercalation, in which lithium ions enter between the layers of the crystalline electrode material. In contrast, the inventors of the present invention, through extensive research into electricity storage devices, have developed an electricity storage device that is charged by an electrode reaction different from intercalation.

[0005] The inventors of the present invention have found that self-discharge of such an electricity storage device can be suppressed by storing it at a temperature range other than the above-mentioned low temperature. If self-discharge during long-term storage of an electricity storage device can be suppressed, the power of the electricity storage device can be used more effectively.

[0006] An object of the present application is to provide a technology for suppressing self-discharge of an electricity storage device by storing the electricity storage device for a long period of time at a temperature suitable for the electricity storage device.

[0007] The present invention is based on the findings that the inventor of the present invention independently obtained in the course of researching electricity storage devices that are charged by electrode reactions different from intercalation, and can be realized, for example, in the following forms.

[0008] One aspect of the present invention is provided as a method for storing an electricity storage device. This storage method includes the steps of charging an electricity storage device including a container filled with an electrolyte solution, metal atoms that ionize in the electrolyte solution and participate in charge and discharge, and electrodes disposed in the electrolyte solution, the electricity storage device being configured such that, during charging, a layer of the metal atoms precipitates on a surface of the electrode, and placing the charged electricity storage device in an open-circuit state and maintaining the temperature of the electricity storage device at a predetermined storage temperature of 25°C or higher and 65°C or lower.

[0009] In an electricity storage device to which this storage method is applied, charging is achieved by forming a layer of metal atoms involved in charging and discharging on the surface of the electrodes. According to findings obtained through original research by the inventors of the present invention, in such an electricity storage device, the higher the environmental temperature is at 25°C or higher in an unloaded state, the more effectively self-discharge is suppressed. Furthermore, if the environmental temperature is 65°C or higher, problems such as deterioration of the electrolyte may occur. According to the storage method for an electricity storage device of the above embodiment, the electricity storage device is stored at an environmental temperature of 25°C or higher and 65°C or lower in an unloaded state, thereby suppressing self-discharge and deterioration of the electricity storage device.

[0010] The present invention can be realized in various forms other than a method for storing an electricity storage device. For example, the present invention can be realized in the form of a storage system or storage device for storing an electricity storage device, or a mobile body, fixed facility, building, etc. to which the configuration of such a system or device is applied. Furthermore, in addition to a method for storing an electricity storage device, the present invention can also be realized in the form of a method for managing the temperature of an electricity storage device, a method for controlling the temperature for storing an electricity storage device, a control program for executing such a method, a recording medium on which such a program is recorded, etc.

[0011] 1 is a schematic diagram showing the configuration of a storage system according to a first embodiment. FIG. 1 is a schematic diagram showing the configuration of an electricity storage device according to a first embodiment. FIG. 2 is a schematic diagram showing the configuration of a carbon nanostructure according to a first embodiment. FIG. 3 is a process flow diagram showing the procedure of a storage method for an electricity storage device. FIG. 4 is an explanatory diagram showing photographed images of active material layers according to an example and a comparative example. FIG. 5 is a reference diagram for explaining a method of calculating a self-discharge rate SD. FIG. 6 is a first explanatory diagram showing the change over time in open-circuit voltage of secondary batteries according to an example and a comparative example. FIG. 7 is a second explanatory diagram showing the change over time in open-circuit voltage of secondary batteries according to an example and a comparative example. FIG. 8 is a third explanatory diagram showing the change over time in open-circuit voltage of secondary batteries according to an example and a comparative example. FIG. 9 is an explanatory diagram showing a histogram of self-discharge rate for each storage temperature according to an example and a comparative example. FIG. 10 is an explanatory diagram showing a Cole-Cole plot obtained for a secondary battery according to an example. FIG. 11 is an explanatory diagram showing a Cole-Cole plot obtained for a secondary battery according to a comparative example. FIG. 12 is a schematic diagram showing the configuration of a first electrode included in an electricity storage device according to a second embodiment. FIG. 13 is an explanatory diagram showing a photographed image of an example of a first electrode according to the second embodiment. 10 is a schematic diagram showing the configuration of a first electrode included in an electricity storage device of a third embodiment. An explanatory diagram showing a photographed image of an example of the first electrode of the third embodiment. An explanatory diagram showing the configuration of a first electrode included in an electricity storage device of a fourth embodiment. An explanatory diagram showing a photographed image of an example of the first electrode of the fourth embodiment. An explanatory diagram showing the configuration of a first electrode included in an electricity storage device of a fifth embodiment. An explanatory diagram showing a photographed image of an example of the first electrode of the fifth embodiment. An explanatory diagram showing a Raman spectroscopy spectrum of the first electrode of the fifth embodiment. An explanatory diagram showing the configuration of an electricity storage device of a sixth embodiment. An explanatory diagram showing a photographed image of an example of the first electrode of the fifth embodiment. An explanatory diagram showing the Raman spectroscopy spectrum of the first electrode of the fifth embodiment. An explanatory diagram showing the configuration of an electricity storage device of a sixth embodiment. An explanatory diagram showing a photographed image of an example of the metal substrate of the sixth embodiment. An explanatory diagram showing a schematic diagram of a first example of the configuration of the convex structure portion of the metal substrate of the seventh embodiment. An explanatory diagram showing a photographed image of a second example of the configuration of the convex structure portion of the metal substrate of the seventh embodiment. An explanatory diagram showing a photographed image of an example of the metal substrate of the seventh embodiment. An explanatory diagram showing the configuration of an electricity storage device of an eighth embodiment. An explanatory diagram showing an example of change in X-ray diffraction due to heat treatment of the metal substrate of the eighth embodiment. FIG. 13 is an explanatory diagram showing an example of a change in a two-dimensional diffraction image of Debye rings due to heat treatment of a metal substrate according to the eighth embodiment.

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

[0013] 1. First Embodiment: 1-1. Configuration of Storage System: Fig. 1 is a schematic diagram showing the configuration of a storage system 100 for an electricity storage device 10 in a first embodiment. The electricity storage device 10 to be stored in the storage system 100 of this embodiment is a lithium ion battery that is charged by an electrode reaction different from intercalation. The configuration of the electricity storage device 10 and the electrode reaction in the electricity storage device 10 will be described later.

[0014] The storage system 100 can store the charged electricity storage device 10 in a state in which self-discharge is suppressed and deterioration of internal chemical substances is suppressed. The storage system 100 includes a storage unit 101 that stores the electricity storage device 10, a temperature monitoring unit 102 that monitors the temperature of the electricity storage device 10 stored in the storage unit 101, and a temperature control unit 103 that adjusts the temperature inside the storage unit 101. The storage system 100 also includes a control unit 105 that controls the storage system 100.

[0015] The storage unit 101 has an airtight internal space in which the power storage devices 10 are stored. The storage unit 101 can store one or more power storage devices 10. The storage unit 101 may be provided with shelves or the like for placing the power storage devices 10 therein.

[0016] The internal space of the storage unit 101 is preferably insulated from the external environment. Therefore, the outer wall section that partitions the internal space of the storage unit 101 is preferably made of a material with high thermal insulation properties. The outer wall section may have a configuration in which a thermal insulation layer is provided inside.

[0017] In this embodiment, after being charged, the power storage device 10 is stored in the storage unit 101 in an unloaded, open-circuit state in which the terminals are opened and the electrical connection is cut off. In the storage unit 101, the power storage device 10 may be stored in a state in which it is electrically connected to an electric circuit that monitors the state of charge (SOC) of the power storage device 10, a charging device that can charge the power storage device 10, or the like.

[0018] The temperature monitoring unit 102 includes, for example, a temperature sensor, and outputs a signal representing the temperature of the power storage device 10 stored in the storage unit 101 to the control unit 105. In this embodiment, the temperature monitoring unit 102 measures the environmental temperature inside the storage unit 101, which directly affects the temperature of the power storage device 10, as a temperature representing the temperature of the power storage device 10, and outputs the measured temperature to the control unit 105.

[0019] In another embodiment, the temperature monitoring unit 102 may be configured to directly measure the temperature of each power storage device 10 housed in the storage unit 101. In another embodiment, the temperature monitoring unit 102 may be configured to measure the air temperature outside the storage unit 101 and calculate an estimated value of the environmental temperature inside the storage unit 101 from that temperature.

[0020] The temperature control unit 103 is provided in the storage unit 101, and adjusts the temperature of the power storage devices 10 housed in the storage unit 101 under the control of the control unit 105. In this embodiment, the temperature control unit 103 is configured by a heater and an air conditioner, and adjusts the environmental temperature inside the storage unit 101.

[0021] In another embodiment, the temperature control unit 103 may adjust the temperature of the power storage device 10 by heating or cooling the power storage device 10 stored in the storage unit 101. For example, the temperature control unit 103 may adjust the temperature of the power storage device 10 by supplying a refrigerant with an adjusted temperature to a refrigerant flow path provided inside a jacket that covers the power storage device 10. Furthermore, the temperature control unit 103 may adjust the temperature of the power storage device 10 by using a heater element or a Peltier element attached to the power storage device 10.

[0022] The control unit 105 is configured by, for example, a microcomputer including a central processing unit (CPU) and a main memory device (RAM). The control unit 105 drives the temperature control unit 103 based on the measurement results by the temperature monitoring unit 102 to adjust the temperature of the power storage device 10 stored in the storage unit 101. In this embodiment, the control unit 105 maintains the temperature of the power storage device 10 at a predetermined storage temperature of 25° C. or higher and 65° C. or lower. The temperature range of the storage temperature will be described in detail later.

[0023] 2 is a schematic diagram showing the configuration of the electricity storage device 10 according to the first embodiment. In this embodiment, the electricity storage device 10 is a lithium-ion battery as described above, and therefore includes lithium (Li) atoms as metal atoms that ionize in the electrolytic solution and participate in charging and discharging.

[0024] 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. 2, the container 11 is illustrated by a dashed line, and the separator 15 is illustrated by a broken line.

[0025] The container 11 has an internal space filled with the electrolyte solution 12. The container 11 is liquid-tight and made of a material that is not easily reactive with the electrolyte solution 12. The electrolyte solution 12 has the 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 Li ions between the first electrode 20 and the second electrode 30.

[0026] The lithium salt of the electrolyte 12 is, for example, LiN(SO ２ R Ａ ) (SO ２ R Ｂ ) can be used. Ａ " and "R Ｂ " represents a fluorine atom (F) or a fluorocarbon. Ａ " and "R Ｂ " may be the same atom or a group having the same structure. In the electrolyte solution 12 of this embodiment, the lithium salt is lithium bis(fluorosulfonyl)imide (LiN(FSO ２ ) ２ , LiFSI) is used.

[0027] Other examples of lithium salts include lithium bis(trifluoromethanesulfonyl)imide (LiN(CF ３ SO ２ ) ２, LiTFSI), lithium bis(perfluoroethylsulfonyl)imide (LiN(SO ２ C ２ F ５ ) ２ , LiBETI), CTFSI-Li, or other lithium imide salts can be used. The lithium salt is not limited to lithium imide salts, and can be, for example, lithium hexafluorophosphate (LiPF ６ The lithium salt may be a derivative of any of the lithium salts described above, or may be a mixture of any combination of the lithium salts described above or their derivatives.

[0028] In this embodiment, the organic solvent of the electrolytic solution 12 is 1,2-dimethoxyethane (DME, C ４ H １０ O ２ As the organic solvent for the electrolytic solution 12, for example, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE, C ５ H ４ F ８ O) and 1,2-diethoxyethane (DEE,C ６ H １４ O ２ ), triglyme (triglyme, CH ３ OCH ２ CH ２ OCH ２ CH ２ OCH ２ CH ２ OCH ３ ), tetraglyme (dimethoxytetraethylene glycol tetraglyme, C １０ H ２２ O ５), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), bis(2,2,2-trifluoroethyl) ether (BTFE), tris[(trifluoroethoxy)methane] (TFEO), etc., can be used as the organic solvent. In addition, derivatives of the above-mentioned substances can be used, or a mixture of any combination of the above-mentioned substances and derivatives of the above-mentioned substances can also be used.

[0029] An additive may be further added to the electrolytic solution 12. Examples of the additive include vinylene carbonate (VC) and lithium nitrate (LiNO ３ ), boroxine compounds including triisopropoxyboroxine (TiPBx), derivatives thereof, and mixtures of any combinations thereof can be used. The additive may be added to the electrolytic solution 12 at a concentration of 0.1% by mass or more and 2.0% by mass or less, for example.

[0030] The separator 15 divides the internal space of the container 11 into a first electrode chamber 16 that houses the first electrode 20 and a second electrode chamber 17 that houses the second electrode 30. The separator 15 is electrically insulating and ion conductive, electrically insulating the first electrode 20 from the second electrode 30, and allowing metal ions (Li ions in this embodiment) transmitted via the electrolyte solution 12 to pass through. The separator 15 is made of, for example, a resin film or nonwoven fabric having a porous structure.

[0031] The first electrode 20 constitutes a negative electrode. The first electrode 20 includes a current collector 21 and an active material layer 25. The current collector 21 of the first electrode 20 is formed of a metal substrate 23. In this embodiment, the metal substrate 23 has a smooth surface.

[0032] In this embodiment, the metal substrate 23 is made of a metal foil of copper (Cu). The metal substrate 23 may be made of Cu, a Cu alloy, or a metal other than Cu. The metal substrate 23 may be made of, for example, aluminum (Al) or an Al alloy.

[0033] The metal substrate 23 does not have to be made of metal foil, but may be made of, for example, a metal sheet or a metal film. The metal substrate 23 does not have to be configured in a flat plate shape, but may be bent into various shapes, such as a cylindrical shape or a corrugated shape.

[0034] The active material layer 25 of the first electrode 20 is provided on the plate surface of the metal substrate 23. The active material layer 25 is preferably provided on both surfaces of the metal substrate 23. The active material layer 25 contains carbon (C) as an active material and is conductive. In this embodiment, the active material layer 25 includes carbon nanostructures CN. Details of the carbon nanostructures CN will be described later.

[0035] The second electrode 30 constitutes the positive electrode of the electricity storage device 10. The second electrode 30 has a current collector 31 and an active material layer 35. The current collector 31 is made of, for example, a metal foil such as Al or titanium (Ti). The current collector 31 may be made of another metal or may have a form other than a metal foil. The 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.

[0036] The active material layer 35 of the second electrode 30 is formed on the surface of the current collector 31. The active material layer 35 is preferably formed on both sides of the current collector 31. The active material layer 35 contains an active material including metal ion atoms involved in charge and discharge (Li atoms in this embodiment), a conductive additive, and a binder. The active material layer 35 may also contain a thickener.

[0037] As the active material of the second electrode 30, for example, a ternary material can be used, such as lithium cobalt oxide (LiCoO ２, LCO), lithium manganese oxide (LMO), and lithium nickel oxide (NCA) can be used. As the conductive additive, for example, acetylene black, carbon black (CB), carbon nanotubes (CNT), acetylene black (AB), and mixtures thereof can be used. As the binder, for example, polyvinylidene fluoride (PVDF) and styrene butadiene rubber (SBR) can be used. As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

[0038] Fig. 3 is a schematic diagram showing the configuration of the carbon nanostructure CN included in the active material layer 25 of the first electrode 20. For convenience, in Fig. 3, graphene GF constituting the carbon nanostructure CN is shown in the form of a substantially rectangular sheet.

[0039] Graphene GF as a main component and carbon nanostructures CN are disposed all over the surface of the metal substrate 23 of the first electrode 20. Graphene GF, also known as a "graphene sheet," is a sheet-like material with a thickness equivalent to one carbon atom, composed of a six-membered carbon ring structure, i.e., a hexagonal lattice structure with carbon atoms at the vertices. Carbon nanostructures CN are graphite-like materials and therefore have higher electrical conductivity than carbon materials such as activated carbon.

[0040] In this embodiment, the carbon nanostructure CN has a configuration in which the graphene GF extends elongatedly with its base end facing the metal substrate 23. The carbon nanostructure CN has a multilayer structure in which a plurality of graphene GFs are stacked in the thickness direction.

[0041] The graphene GF does not have to be entirely composed of single crystals of six-membered carbon rings. In other words, the graphene GF may not have a complete graphene structure, but may be a thin film mainly composed of carbon with a six-membered ring structure. The graphene GF may have a mosaic structure mainly composed of carbon with a six-membered ring structure. The mosaic structure means a structure in which a plurality of regions composed of six-membered carbon ring structures are discretely arranged.

[0042] The carbon nanostructures CN can be formed by a known CVD (chemical vapor deposition) method on the surface of the metal substrate 23. The CVD method capable of forming the carbon nanostructures CN is described in, for example, Japanese Patent Application Laid-Open No. 2024-016510.

[0043] Although not shown in the figure, the surface of the metal substrate 23 is covered with an amorphous carbon layer. In the CVD method, after the amorphous carbon layer is formed on the surface of the metal substrate 23, carbon nanostructures CN are formed so as to extend upward in elongated shapes, with the amorphous carbon layer serving as the starting point for growth.

[0044] In this embodiment, the carbon nanostructure CN is composed of carbon nanowalls extending from the smooth surface of the metal substrate 23. The carbon nanowalls have a structure in which graphene GF is stacked in the thickness direction.

[0045] Carbon nanowalls may be formed in the shape of needles, plates, or pleats. In this specification, the term "carbon nanowall" is used to broadly encompass not only wall-like structures connected in a strip shape, but also similar structures mainly composed of graphene, such as so-called carbon nanoflakes and carbon nanoflowers.

[0046] 1-3. Battery Reaction in the Electricity Storage Device: The electricity storage device 10 is configured so that, during charging, metal atoms involved in charging and discharging are precipitated on the surface of the first electrode 20, forming a layer of these metal atoms. The electrode reaction during charging and discharging of the electricity storage device 10 of this embodiment, which is a lithium ion battery, can be represented, for example, by the following reaction formula:

[0047] The positive electrode material is LiCoO ２ In this case, the electrode reaction at the second electrode 30, which is the positive electrode, is expressed by the following chemical formula (1): where x represents the proportion of reacting atoms and is a real number greater than 0 and less than 1.

[0048] [Chemical formula 1] Li １－ｘ CoO ２ + xLi ＋ + xe －⇔ LiCoO ２ …(1)

[0049] In contrast, the electrode reaction at the first electrode 20, which is the negative electrode, is represented by the following chemical formula (2): As shown in chemical formula (2), when the electricity storage device 10 is charged, Li is precipitated on the surface of the first electrode 20, and a Li layer is formed.

[0050] [Chemical formula 2] Li ＋ + e － ⇔ Li … (2)

[0051] Generally, the charge capacity of conventional lithium-ion batteries, which are charged by intercalation, in which metal ions involved in charging and discharging are inserted into gaps in the crystalline structure of the electrode, is limited by the crystalline structure of the electrode. In contrast, with the power storage device 10 of this embodiment, as shown in the above chemical formula (2), theoretically, charging is possible as long as Li can be deposited on the surface of the first electrode 20. Therefore, with the power storage device 10 of this embodiment, a higher charge capacity can be achieved than with power storage devices in which intercalation occurs in the electrode during charging.

[0052] Furthermore, as will be described later, the energy storage device 10 of this embodiment, which is charged by the above-mentioned electrode reaction, can effectively suppress self-discharge when stored at a storage temperature of 25°C or higher, unlike conventional lithium-ion batteries.

[0053] 1-4. Storage Method of Electricity Storage Device: A storage method of the electricity storage device 10 using the storage system 100 will be described with reference to FIG.

[0054] In step 1, the stored power storage device 10 is charged. In this embodiment, the power storage device 10 is fully charged. The power storage device 10 is preferably charged in a room temperature environment of, for example, 18°C ​​or higher and lower than 35°C, and more preferably charged at an ambient temperature of 25°C.

[0055] In step 2, the charged electricity storage device 10 is stored in the storage section 101 of the storage system 100. After storing the electricity storage device 10, the storage section 101 is preferably sealed.

[0056] In step 3, the temperature of the power storage device 10 housed in the storage unit 101 is maintained at a predetermined storage temperature under the control of the control unit 105. In this embodiment, the temperature control unit 103 adjusts the environmental temperature of the storage unit 101, thereby maintaining the power storage device 10 at the storage temperature. The storage temperature is, for example, a value of 25°C or higher and 65°C or lower.

[0057] As shown in the experimental examples described below, the self-discharge of the electricity storage device 10 of this embodiment is suppressed more at temperatures of 25°C or higher than at temperatures of 0°C or lower. Furthermore, as shown in the experimental examples, the higher the storage temperature, the more the self-discharge of the electricity storage device 10 is suppressed. Therefore, the storage temperature is preferably 30°C or higher, and more preferably room temperature or higher. Here, "room temperature" means, for example, a temperature of 18°C ​​or higher and lower than 35°C. The storage temperature is more preferably 35°C or higher, and even more preferably 38°C or higher. The storage temperature is even more preferably 40°C or higher.

[0058] In general, in an energy storage device that realizes charging by intercalation at electrodes, such as a conventional lithium-ion battery, when the ambient temperature rises above room temperature, the release of metal ions from the electrodes is promoted, and the self-discharge rate tends to increase. For example, it is known that in a high-temperature environment where the temperature is 35°C or higher, such as in summer, 45% or more of the stored energy may be lost due to self-discharge. It is also known that conventional energy storage devices deteriorate significantly when stored at an ambient temperature of 40°C or higher.

[0059] For this reason, some electric vehicles equipped with conventional power storage devices employ a configuration in which the power storage device is cooled by a cooling means such as a fan, etc. However, in such a configuration, for example, in summer, in order to cool the conventional power storage device to a temperature at which self-discharge and degradation of the device can be suppressed, for example, 35°C or less, the amount of power consumed for cooling may increase significantly, making the configuration inefficient.

[0060] In contrast, in a configuration in which a layer of metal atoms involved in charging and discharging is formed on the surface of the first electrode 20 during charging, as in the electricity storage device 10 of this embodiment, the metal atoms precipitated on the first electrode 20 can remain stable on the electrode. Therefore, with the electricity storage device 10 of this embodiment, self-discharge and deterioration are suppressed even in high-temperature environments of 25°C or higher, 30°C or higher, or 35°C or higher. While the conventional electricity storage devices described above are expected to be stored at temperatures of 35°C or lower, with the electricity storage device 10 of this embodiment, self-discharge and deterioration are suppressed even in an environmental temperature of 50°C without cooling.

[0061] Therefore, the electricity storage device 10 of this embodiment can achieve the above-mentioned high storage temperature. Achieving a high storage temperature means that the amount of storage temperature adjustment can be reduced, even in an environment where the outside air temperature is high, such as in summer. Therefore, an increase in energy consumption for adjusting the storage temperature of the electricity storage device 10 can be suppressed, which is efficient.

[0062] In the electricity storage device 10 of this embodiment, if the storage temperature exceeds 65°C, the electrolyte solution 12 may begin to deteriorate. Therefore, in this embodiment, the storage temperature is set to 65°C or lower. In order to more reliably suppress deterioration of the electrolyte solution 12, the storage temperature is preferably 50°C or lower. From the viewpoint of more reliably suppressing deterioration of the electrolyte solution 12 and suppressing energy consumption for temperature adjustment by the temperature control unit 103, the storage temperature is more preferably 45°C or lower.

[0063] When the power storage device 10 is to be used, it is removed from the storage unit 101 (step 4). As described above, in the storage system 100, the storage unit 101 is maintained at a predetermined storage temperature, so that the power storage device 10 is prevented from self-discharging or deteriorating, and a good state of charge is maintained even after a long storage period, so that it can be used quickly and smoothly.

[0064] 1-5. Experimental Example Regarding Self-Discharge of Electricity Storage Device An experimental example verifying the self-discharge suppression effect of the electricity storage device E1 as an example and the electricity storage device C1 as a comparative example will be described with reference to FIGS. 5 to 12 in this order.

[0065] (1) Energy storage device of this experimental example: Energy storage device E1 of this example was fabricated as a lithium ion battery coin cell having the configuration shown in the following Table 1. Energy storage device C1 of the comparative example was fabricated to have substantially the same configuration as energy storage device E1 of the example, except for the difference in the configuration of the active material layer of the negative electrode, which is the first electrode.

[0066]

[0067] 5 shows photographed images I1a and I1b of the active material layer of an electricity storage device E1 fabricated as an example of this embodiment. Photographed image I1a of Example E1 is an image of the active material layer viewed with a scanning electron microscope in a direction perpendicular to the thickness direction of the metal substrate of the electrode. Photographed image I1b of the Example is an image of the active material layer viewed with a scanning electron microscope in the thickness direction of the metal substrate of the electrode.

[0068] 5 shows a photographed image I1c of the active material layer of an electricity storage device C1 fabricated as a comparative example, which is an image of the active material layer viewed through a scanning electron microscope in the thickness direction of the metal substrate of the electrode.

[0069] As shown in Table 1 and photographed images I1a and I1b, the active material layer of the electricity storage device E1 of the example was composed of carbon nanowalls. These carbon nanowalls were formed on the smooth surface of Cu foil, which was the metal substrate constituting the current collector, by a CVD method under the conditions shown in Table 2 below. In this CVD method, hydrogen was plasma-treated using a microwave power source. The "pressure" in Table 2 is the pressure inside the treatment chamber. Furthermore, the "heating temperature" in Table 2 is the temperature of the metal substrate measured with a thermocouple. The flow rate unit "sccm" in this specification may be converted to 1 mL / min.

[0070]

[0071] The carbon nanowalls constituting the negative electrode active material layer of the example power storage device E1 were formed with a substantially uniform height of about 1.0 μm. In the example power storage device E1, it was confirmed that, during charging, a layer of Li atoms was formed on the surface layer of the first electrode due to the electrode reaction represented by the above chemical formula (2).

[0072] See photographed image I1c. In the comparative example of the power storage device C1, the negative electrode active material layer was formed as a graphite layer in which graphite particles were spread on the smooth surface of a Cu foil. In the case of the negative electrode configuration of the comparative example of the power storage device C1, charging was performed by intercalation, in which Li ions were inserted into gaps in the crystalline structure of the graphite of the negative electrode.

[0073] (2) Self-discharge rate for each storage temperature: A method for calculating the self-discharge rate SD, which is an index showing the self-discharge suppression performance of an electricity storage device in this experimental example, will be described with reference to Fig. 6. Fig. 6 shows an example of the change over time in open-circuit voltage when a charged electricity storage device is kept in an open-circuit state and at a constant storage temperature.

[0074] The lower the self-discharge rate SD, the more suppressed the self-discharge of the power storage device is. To calculate the self-discharge rate SD, first, a fully charged power storage device is placed in an open-circuit state with electrical connections cut off, and stored for a predetermined period of time in an environment maintained at a constant humidity and a constant storage temperature. Next, the initial open-circuit voltage V0 of the power storage device and the open-circuit voltage V1 of the secondary battery after the storage period are determined, and the self-discharge rate SD [%] of the secondary battery is calculated using the following formula (A). Note that ΔV in FIG. 6 refers to the amount of voltage drop due to self-discharge and is the value obtained by subtracting V1 from V0.

[0075] [Math 1] SD [%] = (V0-V1) / V0×100...(A)

[0076] In this experimental example, the electricity storage device E1 of the example and the electricity storage device C1 of the comparative example, which were brought into a fully charged state, were placed in an airtight storage compartment of an environmental tester (SH-242 manufactured by Espec Corporation) in an open-circuit state for three days (approximately 72 hours), and the change in open-circuit voltage over time was measured while the temperature inside the storage compartment was kept constant at either 40° C., 25° C., or −10° C. In both cases, the humidity inside the storage compartment was kept at 50% RH.

[0077] 7, 8, and 9 are graphs showing the changes over time in the open-circuit voltage of electricity storage devices E1 and C1 stored in a storage facility at storage temperatures of 40° C., 25° C., and −10° C. Solid line graphs G1, G2, and G3 in FIGS. 7, 8, and 9 show the open-circuit voltage of electricity storage device E1 of the example, and dashed line graphs G1a, G2a, and G3a show the open-circuit voltage of electricity storage device C1 of the comparative example. Table 3 below summarizes the ΔV and self-discharge rate SD obtained for storage temperatures of 40° C., 25° C., and −10° C.

[0078]

[0079] As shown in Figure 7, at a storage temperature of 40°C, the open-circuit voltage of the comparative example power storage device C1 dropped sharply within a few hours after being stored in the storage facility. As a result, the voltage drop ΔV of the comparative example power storage device C1 was approximately 0.19 V, and the self-discharge rate SD was approximately 45%. In contrast, the open-circuit voltage of the example power storage device E1 was maintained approximately constant during the storage period. As a result, the voltage drop ΔV of the example power storage device E1 was approximately 0.022 V, and the self-discharge rate SD was approximately 0.14%.

[0080] As shown in Figure 8, at a storage temperature of 25°C, the decrease in open-circuit voltage was suppressed in almost the same way during storage time for both the comparative example power storage device C1 and the example power storage device E1. However, the example power storage device E1 always had a higher open-circuit voltage than the comparative example power storage device C1, and the difference was significantly large. The voltage drop ΔV for the comparative example power storage device C1 was approximately 0.02 V, and the self-discharge rate SD was approximately 0.5%. The voltage drop ΔV for the example power storage device E1 was approximately 0.022 V, and the self-discharge rate SD was approximately 0.5%.

[0081] As shown in Fig. 9, at a storage temperature of -10°C, the voltage drop ΔV was smaller for the power storage device E1 of the example than for the open-circuit voltage of the power storage device C1 of the comparative example. Furthermore, the open-circuit voltage of the power storage device C1 of the comparative example dropped sharply around the time 20 hours had elapsed, whereas the open-circuit voltage of the power storage device E1 of the example dropped gradually at a substantially constant rate. The voltage drop ΔV for the power storage device C1 of the comparative example was approximately 0.13 V, and the self-discharge rate SD was approximately 3.1%. The voltage drop ΔV for the power storage device E1 of the example was approximately 0.009 V, and the self-discharge rate SD was approximately 2.2%.

[0082] FIG. 10 shows a histogram comparing the self-discharge rates SD obtained for the electricity storage device E1 of the example and the electricity storage device C1 of the comparative example at storage temperatures of 40°C, 25°C, and -10°C.

[0083] The power storage device C1 of the comparative example had a self-discharge rate SD that was approximately equal to that of the power storage device E1 of the example at a storage temperature of 25° C. However, at a storage temperature of −10° C., the self-discharge rate SD of the power storage device C1 of the comparative example was higher than that of the power storage device E1 of the example. Furthermore, at a storage temperature of 40° C., the self-discharge rate SD of the power storage device C1 of the comparative example was much higher than that of the power storage device E1 of the example, and the open-circuit voltage was reduced to nearly half.

[0084] In contrast, in the electricity storage device E1 of the example, the self-discharge rate SD was kept to a value of less than 2.5% over the range of -10°C to 40°C. Furthermore, in the electricity storage device E1 of the example, the self-discharge rate SD decreased as the storage temperature increased. In the electricity storage device E1 of the example, the self-discharge rate SD was 0.5% or less at a storage temperature of 25°C or higher, and the self-discharge rate SD decreased to the 0.1% range at a storage temperature of 40°C.

[0085] Thus, the difference in self-discharge between the electricity storage device E1 of the example and the electricity storage device C1 of the comparative example became significantly large at a storage temperature of 40° C. Below, the difference between the electricity storage device E1 of the example and the electricity storage device C1 of the comparative example at a storage temperature of 40° C. was verified using an AC impedance method.

[0086] (3) Analysis by AC Impedance Method: Fig. 11 shows a Cole-Cole plot obtained by AC impedance method for the electricity storage device E1 of the example. Fig. 12 shows a Cole-Cole plot obtained by AC impedance method for the electricity storage device C1 of the comparative example.

[0087] 11 and 12, the graphs for the initial state when the fully charged power storage devices E1 and C1 are in an open-circuit state and storage at a storage temperature of 40° C. is started are shown by dashed lines, and the graphs for three days after the start of storage are shown by solid lines. Ｔｏｔａｌ , W Ｗａｒｂｕｒｇ is plotted against the solid line graph after three days have passed.

[0088] Table 4 below lists the resistances Rs, Rp, Rn, and R obtained in the Cole-Cole plots shown in FIGS. 11 and 12. Ｔｏｔａｌ and Warburg impedance W Ｗａｒｂｕｒｇ The values ​​of are summarized.

[0089]

[0090] As shown in FIG. 11 and Table 4, in the electricity storage device E1 of the example, the resistance Rs did not change during the storage period of 3 days, and the electrode resistance Rp of the positive electrode hardly changed. Ｗａｒｂｕｒｇ The total resistance R Ｔｏｔａｌ also decreased.

[0091] On the other hand, as shown in FIG. 12 and Table 4, in the comparative example of the electricity storage device C1, the resistance Rs increased slightly, the electrode resistance Rp at the positive electrode increased significantly, and the resistance Rn also increased, and the Warburg impedance W Ｗａｒｂｕｒｇ As a result, in the comparative example of the electricity storage device C1, the total resistance R Ｔｏｔａｌ increased significantly.

[0092] In this way, in the electricity storage device E1 of the example, the Warburg impedance W Ｗａｒｂｕｒｇand total resistance R Ｔｏｔａｌ From this, it is presumed that the reason why the self-discharge rate SD value was kept low at a storage temperature of 40°C in the electricity storage device E1 of the example is that the Li atoms that were precipitated on the surface of the negative electrode by the chemical reaction of charging formed a metal layer and continued to exist on the surface of the negative electrode in a stable state.

[0093] On the other hand, in the comparative example of the electricity storage device C1, the Warburg impedance W Ｗａｒｂｕｒｇ and total resistance R Ｔｏｔａｌ From this, it is presumed that the reason why the self-discharge rate SD at a storage temperature of 40°C in the electricity storage device C1 of the comparative example became significantly large is because the release of Li ions that had entered the crystal structure of the graphite of the negative electrode by intercalation was promoted in a high-temperature environment.

[0094] (4) Summary of Experimental Examples: As described above, in the comparative example electricity storage device C1, the self-discharge rate SD was lowest at 25°C and the self-discharge rate SD increased rapidly at 40°C, indicating that a storage temperature of 25°C or less tends to be preferable for the comparative example electricity storage device C1. In contrast, in the example electricity storage device E1, the self-discharge rate SD decreased as the storage temperature increased within the temperature range of -10°C to 40°C. From these results, it can be seen that for the example electricity storage device E1, the higher the storage temperature, the more self-discharge can be suppressed, and that a storage temperature of 25°C or higher can more effectively suppress self-discharge.

[0095] 1-6. Summary of First Embodiment As described above, according to the storage system 100 and storage method for the electricity storage device 10 of the first embodiment, the electricity storage device 10 is stored at a storage temperature of 25°C or higher and 65°C or lower, which is suitable for the electricity storage device 10, and therefore self-discharge of the electricity storage device 10 can be effectively suppressed. This makes it possible to achieve highly efficient power utilization in the electricity storage device 10. Furthermore, deterioration of the electricity storage device 10 due to being placed in a high-temperature environment can also be suppressed.

[0096] 2. Second embodiment: Fig. 13 is a schematic cross-sectional view illustrating a cross-sectional structure of a first electrode 20A included in an electricity storage device 10A that is a storage target in a storage system and storage method according to a second embodiment. Fig. 13 illustrates a cross-sectional structure of the first electrode 20A at an arbitrary cross section along the thickness direction.

[0097] The storage system and storage method of the second embodiment are the same as those described in the first embodiment ( FIGS. 1 and 4 ), except for the configuration of the power storage device 10A to be stored. The power storage device 10A of the second embodiment has almost the same configuration as the power storage device 10 of the first embodiment, except for the configuration of the first electrode 20A.

[0098] The first electrode 20A of the power storage device 10A has a configuration in which an active material layer 25A is formed on the surface of a metal substrate 23A. The surface of the first electrode 20A has a fine uneven structure in which a plurality of minute particles 40 constituting the active material layer 25A are densely arranged. Each particle 40 of the first electrode 20A has a particle-like outer periphery when viewed in the thickness direction of the metal substrate 23A.

[0099] In this specification, the term "granular material" refers to a portion that can be recognized as having a particle-like shape when viewed from a certain direction, and is a concept that includes protruding portions that are approximately spherical. Also, in this specification, the term "particle" refers to a concept that means minute lumps of various shapes, which do not necessarily have an approximately spherical shape, and is a concept that includes shapes that have a random uneven structure on the surface.

[0100] Carbon nanostructures CNa are formed over the entire surface layer of the granules 40. The carbon nanostructures CNa are made of graphene GF as described in FIG. 3 and extend in elongated shapes outward from the granules 40. The carbon nanostructures CNa extend from an amorphous carbon layer AC that covers the surface of a particle structure 41, which is a densely formed protrusion on the surface of the metal substrate 23A. The particle structure 41 of the metal substrate 23A has a configuration in which minute metal particles MP are gathered in clusters.

[0101] The method for forming the granular material 40 of the first electrode 20A is described in detail in Japanese Patent Application Laid-Open No. 2024-16510. The granular material 40 of the first electrode 20A is formed by forming a particle structure 41 on the surface of the metal substrate 23A and then generating carbon nanostructures CNa on the surface of the particle structure 41.

[0102] The particle structure 41 of the metal substrate 23A is formed by performing a surface treatment on the base material of the metal substrate 23A having a smooth surface. The surface treatment is, for example, electrolytic deposition. The particle structure 41 is formed by immersing the base material of the metal substrate 23A and an electrode plate in an electrolyte, applying a voltage with the electrode plate as the anode and the base material of the metal substrate 23A as the cathode, and thereby precipitating metal ions contained in the electrode plate onto the surface of the base material of the metal substrate 23A.

[0103] The carbon nanostructures CNa are formed by a plasma treatment by a CVD method on the surface of the metal substrate 23A on which the particle structures 41 are formed. In this plasma treatment, a carbon-based gas containing carbon and hydrogen (H ２ ) and a reaction contributing gas such as argon (Ar) are used.

[0104] In the plasma treatment, the metal substrate 23A is placed in a reaction chamber, and while the metal substrate 23A is heated to a temperature of 700° C. or less using a heater, a raw material gas is supplied and a high-frequency voltage is applied between the metal substrate 23A and an electrode in the reaction chamber. This generates a high-density capacitively coupled plasma in the reaction chamber, and radicals generated in the plasma form carbon nanostructures CNa on the surface of the metal substrate 23A.

[0105] The power storage device 10A of the second embodiment has the first electrode 20A configured as described above, and is therefore capable of charging and discharging through the electrode reactions of the chemical formulas (1) and (2) described in the first embodiment. When the power storage device 10A is charged, Li, which is involved in charging and discharging, precipitates and forms a layer of Li on the granules 40 of the first electrode 20.

[0106] The average particle size of the granules 40 in the first electrode 20A is preferably 0.1 μm to 10.0 μm, more preferably 0.5 μm to 5.0 μm, and even more preferably 1.0 μm to 3.0 μm. By setting the average particle size of the granules 40 within this preferred range, deposition of metal atoms involved in charging and discharging onto the surface of the first electrode 20A during charging of the electricity storage device 10A is facilitated, and the generation of dendrites can be suppressed.

[0107] 14 shows photographed images I2a, I2b, I2c, and I2d illustrating an example of the first electrode 20A of the second embodiment. The photographed direction of the photographed images I2a and I2c is a direction perpendicular to the thickness direction of the metal substrate 23A, and the photographed direction of the photographed images I2b and I2d is the thickness direction of the metal substrate 23A.

[0108] The captured images I2a and I2b show the surface of the metal substrate 23A before the carbon nanostructures CNa were formed. In this example, the metal substrate 23A in the captured images I2a and I2b is a Cu foil. The surface of the metal substrate 23A had an uneven structure in which particle structures 41, each of which was made of metal particles MP gathered in clusters, were densely arranged.

[0109] The captured images I2c and I2d show granules 40 having carbon nanostructures CNa formed on the surface of particle structure 41. Table 5 below shows the processing conditions for the plasma processing that formed the carbon nanostructures CNa in the captured images I2c and I2d.

[0110]

[0111] A lithium-ion battery coin cell was fabricated using the active material layer 25A shown in photographed images I2c and I2d under the conditions of Table 1 described in the first embodiment. In this lithium-ion battery, during charging, a layer of Li was formed on the granules 40 of the first electrode 20A due to the electrode reaction of chemical formula (2) described in the first embodiment.

[0112] The power storage device 10A of the second embodiment shares a charge / discharge mechanism with the power storage device 10 of the first embodiment, and also shares a suitable storage temperature at which self-discharge is suppressed with the power storage device 10 of the first embodiment. Therefore, even with the power storage device 10A of the second embodiment, self-discharge and performance degradation can be suppressed by storing the power storage device 10A in a storage system at a storage temperature similar to that of the power storage device 10 of the first embodiment. In addition, the storage system and storage method of the second embodiment can achieve various effects similar to those described in the first embodiment.

[0113] 15 is a schematic cross-sectional view illustrating a cross-sectional structure of a first electrode 20B included in an electricity storage device 10B that is a storage target of a storage system and a storage method according to a third embodiment. Fig. 15 illustrates a cross-sectional structure of the first electrode 20B taken along an arbitrary cross section along the thickness direction.

[0114] The storage system and storage method of the third embodiment are the same as those described in the first embodiment ( FIGS. 1 and 4 ), except for the configuration of the electricity storage device 10B to be stored. The electricity storage device 10B of the third embodiment has almost the same configuration as the electricity storage device 10 of the first embodiment, except for the configuration of the active material layer 25B of the first electrode 20B.

[0115] The active material layer 25B of the first electrode 20B of the third embodiment has an amorphous carbon layer AC covering the surface of the metal substrate 23B and carbon nanostructures CNb formed on the amorphous carbon layer AC. The amorphous carbon layer AC is a thin film layer made of carbon and is the starting point for the growth of the carbon nanostructures CNb. The formation of the amorphous carbon layer AC is favorable, improving the state of formation of the carbon nanostructures CNb.

[0116] The carbon nanostructures CNb of the third embodiment are minute structures made entirely of carbon, and are formed so as to be distributed over the entire surface of the amorphous carbon layer AC. Because the carbon nanostructures CNb are graphite-like substances, they have higher electrical conductivity than carbon materials such as activated carbon.

[0117] The carbon nanostructure CNb has a base 43 that extends elongatedly in the thickness direction of the metal substrate 23B, and a plurality of extension portions 44 that extend from the base 43. Most of the extension portions 44 are formed so as to branch out in a branch-like manner on the upper end side of the base 43.

[0118] As will be shown in a photographed image later, the base 43 is arranged in a random mesh pattern on the surface of the metal substrate 23B. The base 43 has a multilayer structure in which a plurality of graphene GFs, as described in FIG. 3, are stacked in the thickness direction. The number of stacked graphene GFs in the base 43 varies. The base 43 is formed in a needle, plate, or pleat shape. The base 43 can also be interpreted as a structure similar to a carbon nanowall.

[0119] Each extension 44 is made of carbon and is formed in a needle, column, plate, or pleat shape. Most of the extensions 44 are randomly distributed on the surface of the upper end of the base 43. By forming each extension 44 on the base 43, the gaps between the carbon nanostructures CNb near the surface of the active material layer 25 are reduced.

[0120] The height of the carbon nanostructures CNb corresponds to the height from the lower end of the base 43 on the metal substrate 23B side to the upper end of the extension 44. The height of the carbon nanostructures CNb is preferably 0.5 μm or more, and more preferably 0.8 μm or more. Furthermore, the height of the carbon nanostructures CNb is further preferably 1.0 μm or more, and even more preferably 1.2 μm or more.

[0121] However, the taller the carbon nanostructures CNb, the longer the time required to form them. Therefore, from the viewpoint of increasing the productivity of the electrode 20, it is preferable that the average height of the carbon nanostructures CNb be 10.0 μm or less. It is more preferable that the average height of the carbon nanostructures CNb be 8.0 μm or less, and even more preferable that the average height of the carbon nanostructures CNb be 5.0 μm or less. It is even more preferable that the average height of the carbon nanostructures CNb be 3.0 μm or less.

[0122] Details of the manufacturing method of the carbon nanostructures CNb constituting the active material layer 25B of the third embodiment are disclosed in the specification of Japanese Patent Application No. 2022-212870. The carbon nanostructures CNb of the third embodiment are formed by two types of CVD methods. These two types of CVD methods are radical-injection plasma-enhanced (RI-PE) CVD and capacitively coupled plasma (CPP) CVD.

[0123] To fabricate carbon nanostructures CNb, a first plasma treatment is performed using the RI-PECVD method. In this first plasma treatment, microwaves having a frequency of 2.00 to 3.00 GHz are generated at a power of 300 to 500 W in a plasma generation chamber to which a radical source gas is supplied, generating a surface wave plasma containing radicals, which is then introduced into a reaction chamber. Furthermore, a source gas, such as a carbon-based gas, is supplied to the reaction chamber at a flow rate of 80 to 120 sccm, and a reaction contributing gas is supplied at a flow rate of 40 to 60 sccm. The pressure in the reaction chamber is controlled to, for example, approximately 0.5 to 1.5 Pa.

[0124] While the source gas is being supplied to the reaction chamber, a high-frequency voltage having a frequency of 80 to 120 MHz is applied between the partition wall of the reaction chamber and the metal substrate 23B with a power of, for example, 300 to 500 W to generate capacitively coupled plasma CCP. As a result, an amorphous carbon layer AC is formed on the surface of the metal substrate 23B, and a base 43 grows on the amorphous carbon layer AC. The processing time for the first plasma treatment is, for example, about 5 to 15 minutes.

[0125] Next, a second plasma treatment is performed by the CPP-CVD method. In the second plasma treatment, the metal substrate 23B on which the base 43 is formed is heated to a temperature of 600 to 800°C by a heater in the reaction chamber. Then, a carbonaceous gas as a source gas is supplied to the reaction chamber at a flow rate of 80 to 120 sccm, and a reaction contributing gas is supplied at a flow rate of 40 to 60 sccm. The pressure in the reaction chamber is controlled to, for example, 5 to 15 Pa.

[0126] In this state, a high frequency voltage of, for example, 2000 to 3000 W and a frequency of 12 to 15 MHz is applied between the metal substrate 23B and the upper electrode placed above the metal substrate 23B, thereby forming a plurality of extensions 44 on the surface of each base 43 formed on the metal substrate 23B.

[0127] The power storage device 10B of the third embodiment can be charged and discharged by the electrode reactions of the chemical formulas (1) and (2) described in the first embodiment. When the power storage device 10A is charged, Li, which is involved in charging and discharging, precipitates on the carbon nanostructures CNb that constitute the active material layer 25B of the first electrode 20, forming a layer of Li. Li precipitates in the gaps between the base portions 43 of the carbon nanostructures CNb and in the gaps between the extension portions 44, and also precipitates above the carbon nanostructures CNb to form a layer.

[0128] 16 shows images I3a, I3b, I3c, and I3d illustrating an example of the active material layer 25B according to the third embodiment. The images I3a and I3c were taken in the thickness direction, while the images I3b and I3d were taken in a direction perpendicular to the thickness direction of the metal substrate 23B. The metal substrate 23B in this example is a Cu foil.

[0129] The photographed images I3a and I3b shown on the left side of Fig. 16 show a first state in which base 43 of carbon nanostructure CNb has been formed. The photographed images I3c and I3d shown on the right side of Fig. 16 show a second state in which extensions have been formed on the surface of base 43. Table 6 below shows the processing conditions for the first plasma treatment (RI-PECVD) for forming base 43 and the processing conditions for the second plasma treatment (CCP-CVD) for forming extension 44.

[0130]

[0131] A lithium-ion battery coin cell was fabricated using the active material layer 25B shown in images I3c and I3d under the conditions of Table 1 described in the first embodiment. In this lithium-ion battery, Li precipitated on the first electrode 20B during charging due to the electrode reaction of chemical formula (2) described in the first embodiment. Li precipitated in the gaps between the base portions 43 of the carbon nanostructures CNb and in the gaps between the extension portions 44, and also precipitated above the carbon nanostructures CNb to form a layer.

[0132] The power storage device 10B of the third embodiment shares a charge / discharge mechanism with the power storage device 10 of the first embodiment, and also shares a suitable storage temperature at which self-discharge is suppressed with the power storage device 10 of the first embodiment. Therefore, even with the power storage device 10B of the third embodiment, self-discharge and performance degradation can be suppressed by storing the power storage device 10B in a storage system at a storage temperature similar to that of the power storage device 10 of the first embodiment. In addition, the storage system and storage method of the third embodiment can achieve various effects similar to those described in the first embodiment.

[0133] 17 is a schematic cross-sectional view illustrating a cross-sectional structure of a first electrode 20C included in an electricity storage device 10C that is a storage target of a storage system and a storage method according to a fourth embodiment. Fig. 17 illustrates a cross-sectional structure of the first electrode 20C taken along an arbitrary cross section along the thickness direction.

[0134] The storage system and storage method of the fourth embodiment are the same as those described in the first embodiment ( FIGS. 1 and 4 ), except for the configuration of the power storage device 10C to be stored. The power storage device 10C of the fourth embodiment has almost the same configuration as the power storage device 10 of the first embodiment, except for the configuration of the first electrode 20C.

[0135] The first electrode 20C of the power storage device 10C has a metal substrate 23C having a plurality of protrusions 46 on its plate surface. Each protrusion 46 is composed of fine metal particles MP. The protrusions 46 include those composed of a single metal particle MP and those composed of a plurality of metal particles MP densely packed together. The metal particles MP and the protrusions 46 are composed of the same metal as the metal substrate 23C. On the surface of the metal substrate 23C, regions where the protrusions 46 are densely packed and regions where the number of protrusions 46 is small are distributed throughout.

[0136] In order to obtain protrusions 46 of appropriate dimensions, the particle diameter of the metal particles MP when viewed in the thickness direction of the metal substrate 23C is preferably 5 nm or more and 55 nm or less. Furthermore, the average particle diameter of the metal particles MP is preferably 8 nm or more and 30 nm or less. In this specification, the term "particle diameter" refers to the maximum value of the particle diameters in all directions measured in multiple images taken directly facing the metal substrate 23C using, for example, a scanning electron microscope or the like.

[0137] In order to realize an appropriate distribution density of the convex portions 46, the distribution density of the metal particles MP in the metal substrate 23C should be 1 particle / μm ２ More than 1000 pieces / μm ２ Here, the "distribution density of metal particles MP" corresponds to the number of metal particles MP distributed per unit area of ​​the metal substrate 23C, which can be observed when viewed in the thickness direction of the metal substrate 23C.

[0138] The height of the protrusions 46 when viewed in a direction perpendicular to the thickness direction of the metal substrate 23C is preferably 5 nm to 300 nm. The height of the protrusions 46 is measured as the distance from the flat surface at the bottom of the protrusions 46 to the top of the protrusions 46 on an image taken from a direction perpendicular to the thickness direction of an arbitrary region of the metal substrate 23C using, for example, a scanning electron microscope.

[0139] On the surface of the metal substrate 23C, a plurality of carbon nanostructures CNc are arranged, each of which is mainly composed of graphene GF as described in Fig. 3 and extends linearly on the surface of the metal substrate 23C. Here, the "main component" may be, for example, a component whose content ratio in the whole is 50 mass% or more. Furthermore, "linear" may also be referred to as fibrous, thread-like, or string-like, and it is preferable that the length is at least 7 to 8 times the diameter.

[0140] The carbon nanostructure CNc preferably includes a carbon nanotube-like structure in which a graphene sheet is rolled into a cylindrical shape. The carbon nanostructure CNc is a graphite-like substance, and therefore has higher electrical conductivity than carbon materials such as activated carbon.

[0141] The diameter of the carbon nanostructure CNc may be, for example, 1 nm or more and 15 nm or less, and the length of the carbon nanostructure CNc when stretched out straight may be, for example, 100 nm or more and 2000 nm or less.

[0142] Carbon nanostructures CNc constitute the active material layer 25C of the first electrode 20C. As shown in the photographed image I4 of the example in Figure 18, which will be referred to later, the carbon nanostructures CNc extend linearly on the surface of the metal substrate 23C when viewed in the thickness direction of the metal substrate 23C, and are distributed throughout the surface of the metal substrate 23C. The carbon nanostructures CNc are randomly distributed on the surface of the metal substrate 23C. The carbon nanostructures CNc can also be interpreted as extending in a manner that threads between the protrusions 46. The carbon nanostructures CNc may include those that extend through regions above the protrusions 46.

[0143] The manufacturing method of the protrusions 46 and the carbon nanostructures CNc is disclosed in the specification of Japanese Patent Application No. 2023-069934. The protrusions 46 can be formed by plasma treatment of the smooth surface of the metal substrate 23C by the RI-PECVD method. The carbon nanostructures CNc can be generated by plasma treatment of the metal substrate 23C on which the protrusions 46 have been formed by the CPP-CVD method.

[0144] The following describes the plasma treatment by the RI-PECVD method for forming the convex portions 46. In this plasma treatment, first, microwaves with a power of 300 to 500 W and a frequency of 2.00 to 3.00 GHz are introduced into the plasma generation chamber, and a radical source gas such as hydrogen is supplied to generate surface wave plasma containing radicals.

[0145] Next, the surface wave plasma generated in the plasma generation chamber is introduced into the reaction chamber where the base material of the metal substrate 23C is placed, and raw material gas is supplied. A high-frequency voltage with a power of, for example, 300 to 500 W and a frequency of 80 to 120 MHz is applied by the power supply unit. This generates a capacitively coupled plasma in the reaction chamber. During this plasma processing, the pressure in the reaction chamber is controlled to, for example, about 1.0 to 3.0 Pa.

[0146] When the capacitively coupled plasma containing radicals comes into contact with the base material of the metal substrate 23C, metal particles constituting the base material of the metal substrate 23C are scattered and re-adhere to the metal substrate 23C. This forms the convex portions 46 composed of the metal particles MP described above. The processing time for this plasma treatment is, for example, about 5 to 15 minutes.

[0147] The plasma processing of the CCP-CVD method for producing carbon nanostructures CNc will be described. First, the metal substrate 23C on which the protrusions 46 are formed is placed in a reaction chamber and heated to a temperature of, for example, 600 to 800° C. by a heater. Then, methane (CH ４ ) and hexafluoroethane (C ２ F ６ ) and carbon-based gases such as H ２ A source gas containing a carbon-based gas and a reaction contributing gas such as Ar is supplied. The flow rate of the carbon-based gas may be, for example, 80 to 120 sccm, and the flow rate of the reaction contributing gas may be, for example, 40 to 60 sccm. The pressure in the reaction chamber is controlled to be 30 Pa or more and 50 Pa or less.

[0148] In this state, a high-frequency voltage of, for example, 300 to 700 W and a frequency of 12 to 15 MHz is applied between the metal substrate 23C and an upper electrode placed above the metal substrate 23C. As a result, carbon nanostructures CNc are generated starting from the protrusions 46 formed on the metal substrate 23C. The processing time for this plasma treatment is, for example, about 5 to 15 minutes.

[0149] The electricity storage device 10C of the fourth embodiment can be charged and discharged by the electrode reactions of chemical formulas (1) and (2) described in the first embodiment. When the electricity storage device 10C is charged, Li, which is involved in charging and discharging, precipitates on the surface of the first electrode 20C to form a Li layer. This is because the carbon nanostructure CNc functions as an active material, promoting the precipitation of lithium on the surface layer of the first electrode 20C. In addition, the precipitation of Li on the surface of the first electrode 20C is promoted from the protrusions 46 of the metal substrate 23C. This is based on findings derived by the inventor of the present invention from experimental results based on nucleation theory.

[0150] 18 shows a captured image I4 illustrating an example of the first electrode 20C of the fourth embodiment. The captured image I4 was taken in the thickness direction of the metal substrate 23C. The metal substrate 23C in the captured image I4 is a Cu foil. As shown in the captured image I4, convex portions 46 composed of metal particles MP are formed on the surface of the metal substrate 23C, and linear carbon nanostructures CNc are distributed over the entire surface of the metal substrate 23C. The convex portions 46 of the metal substrate 23C in the captured image I4 and the processing conditions of the plasma processing for forming the carbon nanostructures CNc are shown in Table 7 below.

[0151]

[0152] A coin cell of a lithium ion battery was fabricated using the first electrode 20C shown in photographed image I4 under the conditions of Table 1 described in the first embodiment. During charging of this lithium ion battery, a layer of Li was formed on the surface of the first electrode 20C due to the electrode reaction of chemical formula (2) described in the first embodiment.

[0153] The power storage device 10C of the fourth embodiment shares a charge / discharge mechanism with the power storage device 10 of the first embodiment, and also shares a suitable storage temperature at which self-discharge is suppressed with the power storage device 10 of the first embodiment. Even with the power storage device 10C of the fourth embodiment, self-discharge and performance degradation can be suppressed by storing the power storage device 10C in a storage system at a storage temperature similar to that of the power storage device 10 of the first embodiment. In addition, the storage system and storage method of the fourth embodiment can achieve various effects similar to those described in the first embodiment.

[0154] 19 is a schematic cross-sectional view illustrating a cross-sectional structure of a first electrode 20D included in an electricity storage device 10D that is a storage target of a storage system and a storage method according to a fifth embodiment. Fig. 19 illustrates a cross-sectional structure of the first electrode 20D at an arbitrary cross section along the thickness direction.

[0155] The storage system and storage method of the fifth embodiment are the same as those described in the first embodiment ( FIGS. 1 and 4 ), except that the configuration of the storage target power storage device 10D is different. The power storage device 10D of the fifth embodiment has almost the same configuration as the power storage device 10 of the first embodiment, except that it includes a first electrode 20D with a different configuration.

[0156] The first electrode 20D has a configuration in which an active material layer 25D is formed on the surface of a metal substrate 23D. A fine uneven structure CS on the order of microns is formed on the surface of the metal substrate 23D. The active material layer 25D is formed as a thin film so as to densely cover the surface of the uneven structure CS. The average thickness of the active material layer 25D may be, for example, 0.1 μm to 15.0 μm.

[0157] The active material layer 25D has a surface uneven structure CSs with smaller unevenness dimensions than the uneven structure CS of the metal substrate 23D. To improve the battery performance of the power storage device 10D, it is preferable that the surface of the active material layer 25D has a dense distribution of multiple granular surface protrusions 48 with a width of 0.1 μm or more and 10.0 μm or less when viewed in the thickness direction of the metal substrate 23D. The "width of the surface protrusions 48" refers to the maximum value of the widths of each surface protrusion 48 measured in all directions perpendicular to the thickness direction of the metal substrate 23D. Note that minute voids VD may be formed inside the uneven structure CS of the metal substrate 23D and the active material layer 25D during their formation process.

[0158] The active material layer 25D is primarily composed of a carbon nanostructure CNd composed of nanographene and amorphous carbon. The active material layer 25D is configured by depositing nanographene and amorphous carbon particles. The nanographene and amorphous carbon particles include those having a spherical shape and those having a plate-like shape. The surface protrusions 48 of the active material layer 25D described above include those composed of a single particle and those composed of a random collection of multiple particles. Hydroxyl groups may remain inside the active material layer 25D as impurities introduced during the manufacturing process.

[0159] A manufacturing method of the first electrode 20D is disclosed in the specification of Japanese Patent Application No. 2023-128891. The concavo-convex structure CS and the active material layer 25D of the metal substrate 23D in the first electrode 20D are formed by plasma treatment. The first electrode 20D is formed by immersing the metal substrate 23D in a solution containing alcohols stored in a reaction chamber, generating plasma using a plasma electrode installed above the liquid surface of the solution while supplying a reactive gas to the reaction chamber, and irradiating the plasma onto the metal substrate 23D in the solution.

[0160] The alcohol contained in the solution is, for example, ethanol (C ２ H ６Ｏ The reaction gas may be, for example, Ar or H ２In the plasma processing, the reaction gas is supplied to the reaction chamber at a flow rate of, for example, about 1 to 10 slm. The unit "slm" indicates the flow rate per minute at 1 atmosphere (atm) and 0°C. The pressure in the reaction chamber is, for example, 0.5 x 10 ５ ~1.5 x 10 ５ The pressure is controlled to about Pa.

[0161] The plasma electrode is made of a carbon substrate such as sintered graphite. The distance between the tip of the plasma electrode and the liquid surface of the solution may be, for example, about 1 to 10 mm. The high-frequency voltage for generating plasma may be, for example, 5 to 15 kV, and the frequency may be, for example, 50 to 80 Hz.

[0162] When plasma irradiation of the metal substrate 23D in the solution begins, the alcohols and hydrocarbons in the solution are decomposed, generating hydrogen atoms and radicals in the solution. The hydrogen atoms and radicals erode the surface of the metal substrate 23D, forming a fine concave-convex structure CS. While the plasma is being irradiated, the hydrogen atoms and radicals continue to erode the surface of the metal substrate 23D, and the recesses and protrusions of the concave-convex structure CS become larger. During this time, as hydrogen atoms enter the interior of the metal substrate 23D, tiny cavities VD are formed within the concave-convex structure CS.

[0163] During the formation of the concave-convex structure CS, carbon atoms generated in the solution by decomposition of alcohol due to plasma irradiation precipitate as nanographene and amorphous carbon particles, which begin to adhere to the surface of the concave-convex structure CS of the metal substrate 23D. In parallel with the growth of the concave-convex structure CS on the surface of the metal substrate 23D, nanographene and amorphous carbon particles are deposited to cover the surface of the concave-convex structure CS, thereby forming an active material layer 25D that covers the surface of the concave-convex structure CS. During this growth process, tiny voids VD may also be formed inside the active material layer 25D.

[0164] The power storage device 10D of the fifth embodiment has the first electrode 20D described above, and is therefore capable of charging and discharging through the electrode reactions of the chemical formulas (1) and (2) described in the first embodiment. When the power storage device 10D is charged, Li, which is involved in charging and discharging, is deposited on the first electrode 20D to form a Li layer.

[0165] 20a shows a photographed image I5 of active material layer 25D of first electrode 20D as an example, photographed in the thickness direction of metal substrate 23D. Metal substrate 23D in photographed image I5 is a Cu foil. The processing conditions for the plasma treatment for forming first electrode 20D are shown in Table 8 below. In active material layer 25D in photographed image I5, a plurality of granular surface protrusions 48 having a width of 0.1 μm or more and 10.0 μm or less were densely distributed.

[0166]

[0167] FIG. 20b shows the Raman spectrum of the active material layer 25D of the captured image I5. In this graph, the D band (1340 cm －１ ) and G band (1580 cm －１ ) was observed. This result indicates that active material layer 25D is formed mainly from a carbon nanostructure made of nanographene or amorphous carbon.

[0168] A lithium-ion battery coin cell was fabricated using the first electrode 20D shown in photographed image I5 under the conditions of Table 1 described in the first embodiment. During charging of this lithium-ion battery, a layer of Li was formed on the surface of the first electrode 20D due to the electrode reaction of chemical formula (2) described in the first embodiment.

[0169] The power storage device 10D of the fifth embodiment shares a charge / discharge mechanism with the power storage device 10 of the first embodiment, and also shares a temperature suitable for storage at which self-discharge is suppressed with the power storage device 10 of the first embodiment. Therefore, even with the power storage device 10D of the fifth embodiment, self-discharge and performance degradation can be suppressed by storing the power storage device 10D in a storage system at a storage temperature similar to that of the power storage device 10 of the first embodiment. In addition, the storage system and storage method of the fifth embodiment can achieve various effects similar to those described in the first embodiment.

[0170] 6. Sixth Embodiment: Fig. 21 is a schematic diagram illustrating a storage system and a power storage device 10E that is the storage target of a storage method according to a sixth embodiment. The storage system and storage method according to the second embodiment are the same as those described in the first embodiment (Figs. 1 and 4), except that the configuration of the power storage device 10E that is the storage target is different. The power storage device 10E of the sixth embodiment has substantially the same configuration as the power storage device 10 of the first embodiment, except that the configuration of the first electrode 20E is different.

[0171] The first electrode 20E of the electricity storage device 10E of the sixth embodiment is composed of a metal substrate 23E that functions as a current collector. No active material layer is provided on the metal substrate 23E. As shown in the balloon in Fig. 21 , the metal substrate 23E has a plurality of protrusions 46a formed of fine metal particles MP on its plate surface. When the electricity storage device 10E is charged, Li precipitates on the surfaces of the protrusions 46a.

[0172] In order to smoothly deposit Li during charging, the area of ​​the projection region of the protrusion 46a projected onto the surface of the metal substrate 23E must be 10 nm ２ 10000nm or more ２ The density of the protrusions 46a on the surface of the metal substrate 23E is preferably 1 / μm or less. ２ More than 1000 pieces / μm ２Alternatively, it is preferable that the average value of the maximum length of the projected region of the convex portion 46a projected onto the surface of the metal substrate 23E is 10 nm or more and 200 nm or less, and the area occupied by the projected region is 1 / 10 or more of the area of ​​the surface of the metal substrate 23E.

[0173] The method for forming the protrusions 46a of the metal substrate 23E is also substantially the same as the method for forming the protrusions 46 described in the fourth embodiment. The protrusions 46a of the metal substrate 23E can be formed by a CVD method on the metal substrate 23E. The method for forming the protrusions 46a of the metal substrate 23E is the same as the method for forming the "protrusions PR1" disclosed in Japanese Patent Application Laid-Open No. 2022-187895.

[0174] The electricity storage device 10E of the sixth embodiment can be charged and discharged by the electrode reactions of the chemical formulas (1) and (2) described in the first embodiment. When the electricity storage device 10E is charged, Li involved in charging and discharging is precipitated from the protrusions 46a of the metal substrate 23E as starting points, and a layer of Li is formed on the surface of the first electrode 20E.

[0175] 22 shows a captured image I6 illustrating an example of the first electrode 20E according to the sixth embodiment. The captured image I6 was taken in the thickness direction of the metal substrate 23E. The metal substrate 23E in the captured image I6 is a Cu foil, and the metal particles MP are Cu particles. As shown in the captured image I6, convex portions 46a formed by the metal particles MP are distributed over the entire surface of the metal substrate 23E.

[0176] A coin cell of a lithium ion battery was fabricated using the first electrode 20E shown in photographed image I6 under the conditions of Table 1 described in the first embodiment. During charging of the lithium ion battery, a layer of Li was formed on the surface of the first electrode 20E due to the electrode reaction of chemical formula (2) described in the first embodiment.

[0177] The electricity storage device 10E of the sixth embodiment shares a charge / discharge mechanism with the electricity storage device 10 of the first embodiment, and also shares a suitable storage temperature at which self-discharge is suppressed with the electricity storage device 10 of the first embodiment. Therefore, even with the electricity storage device 10E of the sixth embodiment, self-discharge and performance degradation can be suppressed by storing the electricity storage device 10E in a storage system at a storage temperature similar to that of the electricity storage device 10 of the first embodiment. In addition, the storage system and storage method of the sixth embodiment can achieve various effects similar to those described in the first embodiment.

[0178] 23a and 23b are schematic cross-sectional views each illustrating a cross-sectional structure of a first electrode 20F included in an electricity storage device 10F that is a storage target in a storage system and a storage method according to a seventh embodiment. Each of Figs. 23a and 23b illustrates a cross-sectional structure of the first electrode 20F taken along an arbitrary cross section along the thickness direction.

[0179] The storage system and storage method of the seventh embodiment are the same as those described in the first embodiment ( FIGS. 1 and 4 ), except for the configuration of the energy storage device 10F to be stored. The energy storage device 10F of the seventh embodiment is substantially the same in configuration as the energy storage device 10E of the sixth embodiment, except for the surface structure of the metal substrate 23F of the first electrode 20F.

[0180] In this embodiment, a fine uneven structure is formed on the outer surface of the metal substrate 23F. The uneven structure includes a plurality of convex structures 52 having a maximum width Wmax of 0.5 μm or more and 30.0 μm or less. The convex structures 52 are portions that protrude in the thickness direction of the metal substrate 23F. As will be described later, the convex structures 52 are composed of one or more metal particles MP. The metal particles MP are composed of the same type of metal as the metal that constitutes the metal substrate 23F. When the metal substrate 23F is composed of an alloy, the metal particles MP are composed of the same type of metal as the main metal of the alloy.

[0181] The maximum width Wmax of the convex structure portion 52 corresponds to the maximum width of the convex structure portion 52 in any direction, as measured in an image of the metal substrate 23F taken in its thickness direction using, for example, a scanning electron microscope, etc. "All directions" refers to all directions perpendicular to the thickness direction of the metal substrate 23F.

[0182] The lower limit of the maximum width Wmax of the convex structure 52 is preferably 0.6 μm or more, and more preferably 0.8 μm or more. The upper limit of the maximum width Wmax of the convex structure 52 is preferably 28.0 μm or less, and more preferably 25.0 μm or less. In addition to the convex structure 52 within the above-mentioned range of the maximum width Wmax, the surface of the metal substrate 23F may also include convex portions having a width smaller than the lower limit of the above-mentioned range of the maximum width Wmax.

[0183] Figures 23a and 23b each show examples of the convex structure 52 having different shapes. Figure 23a shows a first convex body 52a as a first example of the convex structure 52. Figure 23b shows a second convex body 52b as a second example of the convex structure 52, and a third convex body 52c as a third example of the convex structure 52. The example forms of the convex structure 52 will be described below in order.

[0184] 23a. The first convex body 52a, which is a first embodiment of the convex structure 52, is formed by a dense accumulation of multiple minute metal particles MP having a particle diameter Pp of 0.5 μm or more and 5.0 μm or less. In this specification, the term "particle diameter" refers to the maximum value of the particle diameters in all directions measured in multiple images taken directly facing the metal substrate 23F using a scanning electron microscope or the like.

[0185] The first convex body 52a has a structure in which multiple tiny metal particles MP are gathered in a tuft-like shape, and an uneven structure in which the tiny metal particles MP are densely arranged is formed on the surface, giving it a structure that protrudes from the surrounding area as a whole.

[0186] In the first convex bodies 52a, the maximum width Wmax of the convex structure 52 corresponds to the maximum distance between the ends of the plurality of metal particles MP constituting the first convex bodies 52a in a direction perpendicular to the thickness direction of the metal substrate 23F. The lower limit of the particle diameter Pp of each metal particle MP constituting the first convex bodies 52a is preferably 0.6 μm or more, and more preferably 0.8 μm or more. The upper limit of the particle diameter Pp of the metal particles MP is preferably 4.0 μm or less, and more preferably 3.0 μm or less.

[0187] The first convex body 52a has a height Hp of 1.0 μm or more and 15.0 μm or less. The height Hp of the first convex body 52a corresponds to the distance in the thickness direction of the metal substrate 23F between the bottom and top ends of the first convex body 52a, as measured, for example, in an image captured with a scanning electron microscope from a direction perpendicular to the thickness direction of the metal substrate 23F. The lower limit of the height Hp of the first convex body 52a is preferably 2.0 μm or more, and more preferably 4.0 μm or more. The upper limit of the height Hp of the first convex body 52a may be 12.0 μm or less, or may be 10.0 μm or less.

[0188] See Figure 23b. The second convex body 52b, which is a second embodiment of the convex structure 52, and the third convex body 52c, which is a third embodiment, have in common the fact that they are composed of metal particles MP recognized as individual particles, but they differ in size and shape. The second convex body 52b and the third convex body 52c differ in particular in their height. The height of the convex bodies 52b and 52c corresponds to the distance in the thickness direction of the metal substrate 23F between the bottom and top ends of the convex bodies 52b and 52c, as measured, for example, in an image captured by a scanning electron microscope from a direction perpendicular to the thickness direction of the metal substrate 23F.

[0189] The particle diameter Pq of the second convex bodies 52b is 0.5 μm or more and 5.0 μm or less, and the height Hq is approximately equal to or less than the particle diameter Pq. In the second convex bodies 52b, the particle diameter Pq corresponds to the maximum width Wmax of the convex structure 52. The lower limit of the particle diameter Pq of the second convex bodies 52b is preferably 0.6 μm or more, and more preferably 0.8 μm or more. The upper limit of the particle diameter Pq of the second convex bodies 52b may be 4.5 μm or less, or may be 4.0 μm or less.

[0190] The third convex bodies 52c have a vertically elongated shape. The third convex bodies 52c have a particle diameter Pr of 0.5 μm or more and 8.0 μm or less, and have a height Hr greater than the particle diameter Pr. The particle diameter Pr of the third convex bodies 52c corresponds to the maximum width Wmax of the convex structure portion 52. The lower limit of the particle diameter of the third convex bodies 52c is preferably 0.6 μm or more, and more preferably 0.8 μm or more. The upper limit of the particle diameter of the third convex bodies 52c may be 7.0 μm or less, or may be 5.0 μm or less.

[0191] The height Hr of the third convex body 52c may be, for example, 1.0 μm or more and 12.0 μm or less. The lower limit of the height Hr of the third convex body 52c may be 2.0 μm or more, or 3.0 μm or more. The upper limit of the height Hr of the third convex body 52c may be 10.0 μm or less, or 8.0 μm or less.

[0192] The uneven structure on the surface of the metal substrate 23F may have, for example, a configuration in which the first convex bodies 52a are densely arranged on the surface of the metal substrate 23F. The uneven structure on the surface of the metal substrate 23F may have a configuration in which the second convex bodies 52b and the third convex bodies 52c are arranged between the first convex bodies 52a. The uneven structure on the surface of the metal substrate 23F may have a configuration in which the second convex bodies 52b or the third convex bodies 52c are distributed over the entire surface of the metal substrate 23F. The uneven structure on the surface of the metal substrate 23F may have a configuration in which the first convex bodies 52a and the third convex bodies 52c are arranged between the second convex bodies 52b arranged over the entire surface of the metal substrate 23F. The uneven structure on the surface of the metal substrate 23F may have a configuration in which the first convex bodies 52a, the second convex bodies 52b, and the third convex bodies 52c are mixed. The uneven structure on the surface of the metal substrate 23F may be configured to include, in addition to the convex structure portion 52, particle-like convex portions that are smaller than the second convex bodies 52b and the third convex bodies 52c.

[0193] The area of ​​the projected region of the convex structure 52 including the convex bodies 52a, 52b, and 52c projected in the thickness direction of the metal substrate 23F is 0.01 μm ２ Larger than 10,000 μm ２ Furthermore, the density of the projected area of ​​the convex structure 52 when the metal substrate 23F is projected in the thickness direction is 1 piece / mm ２ Above, 108 pieces / mm ２ The convex structure 52 having such dimensions can be easily formed by surface treatment using electrolytic deposition on the base material of the metal substrate 23F.

[0194] A method for forming the convex structure portion 52 is disclosed in Japanese Patent Application Laid-Open No. 2024-016511. When the metal substrate 23F is made of Cu, an uneven structure including the convex structure portion 52 can be formed on the surface of the metal substrate 23F by performing electrolytic deposition under the following conditions. In the electrolytic deposition, for example, sulfuric acid (H O ) having a concentration of about 0.5 to 2.0 M (volume molar concentration mol / L) is used as an electrolyte. ２ SO ４) is used. Furthermore, an electrode plate made of crude copper is used as the anode, and the base material of the metal substrate 23F is used as the cathode, and a voltage of approximately 0.5 to 2.0 V is applied, and a current of approximately 80.0 to 200.0 mA is passed through it. As a result, the Cu on the electrode plate is oxidized and elutes as Cu ions into the electrolyte, which migrate toward the base material of the metal substrate 23F and are reduced and precipitated on the surface of the base material of the metal substrate 23F. The precipitated Cu particles form protruding structures 52 one after another on the base material surface.

[0195] The electricity storage device 10F of the seventh embodiment can be charged and discharged by the electrode reactions of the chemical formulas (1) and (2) described in the first embodiment. When the electricity storage device 10F is charged, Li involved in charging and discharging is precipitated from the convex structure portion 52 of the metal substrate 23F as an origin, and a layer of Li is formed on the surface of the first electrode 20F.

[0196] 24 shows photographed images I7a, I7b, I7c, and I7d illustrating examples of the convex structure portion 52 of the first electrode 20F according to the seventh embodiment. The photographed direction of the photographed images I7a and I7c is perpendicular to the thickness direction of the metal substrate 23F. The photographed direction of the photographed images I7b and I7d is the thickness direction of the metal substrate 23F.

[0197] The photographed images I7a and I7b in the upper column of Fig. 24 show an example of a first convex body 52a, which is a first embodiment of the convex structure portion 52. The first convex body 52a is composed of a plurality of minute metal particles MP densely stacked on top of each other. The photographed images I7c and I7d in the lower column of Fig. 24 show a second convex body 52b, which is a second embodiment of the convex structure portion 52, and a third convex body 52c, which is a third embodiment. The second convex body 52b and the third convex body 52c are composed of metal particles MP that are recognized as individual particles.

[0198] The first convex body 52a, the second convex body 52b, and the third convex body 52c in the photographed images I7a, I7b, I7c, and I7d were produced by performing a surface treatment by electrolytic deposition on a Cu foil serving as the metal substrate 23F. In the electrolytic deposition for forming the second convex body 52b and the third convex body 52c, 1.5 M H ２ SO ４A DC voltage of 1.0 V was applied to the Cu foil in the electrolyte solution, and a current of 128 mA was passed through the Cu foil. The distance between the substrate and the electrode was 3.5 cm.

[0199] A lithium-ion battery coin cell was fabricated using the first electrode 20F shown in photographed images I7a, I7b, I7c, and I7d under the conditions of Table 1 described in the first embodiment. During charging of the lithium-ion battery, a layer of Li was formed on the surface of the first electrode 20F due to the electrode reaction of chemical formula (2) described in the first embodiment.

[0200] The energy storage device 10F of the seventh embodiment shares a charge / discharge mechanism with the energy storage device 10 of the first embodiment, and also shares a suitable storage temperature at which self-discharge is suppressed with the energy storage device 10 of the first embodiment. Therefore, even with the energy storage device 10F of the seventh embodiment, self-discharge and performance degradation can be suppressed by storing the energy storage device 10F in a storage system at a storage temperature similar to that of the energy storage device 10 of the first embodiment. In addition, the storage system and storage method of the seventh embodiment can achieve various effects similar to those described in the first embodiment.

[0201] 8. Eighth Embodiment: A storage system and a metal substrate 23G of a first electrode 20G included in an electricity storage device 10G that is the target of storage in a storage method according to an eighth embodiment will be described with reference to FIGS. 25, 26, and 27.

[0202] 25 is a schematic diagram showing the configuration of an electricity storage device 10G according to an eighth embodiment. The electricity storage device 10G has substantially the same configuration as the electricity storage device 10E according to the sixth embodiment, except that it includes a metal substrate 23G having smooth surfaces and having been subjected to a heat treatment described below.

[0203] Through extensive research, the inventors of the present invention have found that if a metal substrate heat-treated under an atmospheric gas is used as an electrode for an electricity storage device, high charge / discharge performance can be achieved by the electrode reactions of chemical formulas (1) and (2) described in the first embodiment, even without providing an active material layer or a textured structure. Details of this finding are disclosed in the specification of Japanese Patent Application No. 2024-023186.

[0204] The heat treatment of the metal substrate 23G is performed in an atmosphere gas at a predetermined temperature for a predetermined time. In this embodiment, a reducing gas is used as the atmosphere gas. For example, 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 ) etc. may also be used.

[0205] The reducing gas is not limited to the above-mentioned examples, and may be any gas that can cause a reduction reaction of the base material of the metal substrate 23G 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.

[0206] As the atmospheric gas, an inert gas may be used instead of the reducing gas. Examples of the inert gas include argon (Ar), helium (He), xenon (Xe), and nitrogen (N ２ ) can be used.

[0207] In the heat treatment, 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 23G. 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 －６If 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.

[0208] The treatment temperature in the heat treatment of this embodiment may be, for example, 400° C. or higher and 1000° C. or lower. The treatment temperature in the heat treatment is preferably 500° C. or higher, and more preferably 600° C. or higher. The treatment temperature in the heat treatment is further preferably 700° C. or higher, and more preferably 800° C. or higher.

[0209] The treatment time of the heat treatment may be determined appropriately depending on the type of metal constituting the metal substrate, the treatment temperature in the heat treatment, etc. The treatment time of the heat treatment may be determined as the time required for the metal structure of the metal substrate to undergo a predetermined change or the time required for most of the metal oxide in the metal substrate to be reduced.

[0210] The heat treatment time may be set to a time longer than the reduction time of the metal oxide, but from the viewpoint of suppressing an increase in manufacturing costs due to a longer process time, 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.

[0211] As will be described below, the metal substrate 23G that has been subjected to the above heat treatment has a two-dimensional diffraction image of the Debye rings obtained by a two-dimensional X-ray detector as a discontinuous arc-shaped image with an array of points or line segments.

[0212] 26 and 27 show the change in X-ray diffraction (XRD) of the metal substrate 23G when subjected to the heat treatment. FIG. 26 shows the X-ray diffraction patterns of a Cu foil as an example of the metal substrate 23G before and after the heat treatment. In FIG. 26, the numbers in parentheses after Cu refer to Miller indices. FIG. 27 shows two-dimensional diffraction images of the Debye rings obtained by a two-dimensional X-ray detector of the same Cu foil before and after the heat treatment. The specific conditions for the heat treatment performed on the Cu foil as an example of the metal substrate 23G that was the subject of the X-ray diffraction in FIGS. 26 and 27 are shown in Table 9 below.

[0213]

[0214] The X-ray diffraction pattern shown in FIG. 26 shows that the number of prominent peaks was reduced after the heat treatment under the conditions of Table 5. For example, after the heat treatment, the Cu(220) peak was reduced to an almost negligible level. As a result, the I200 / I220 ratio, which is the ratio of the Cu(200) peak to the Cu(220) peak, increased from 1 before the heat treatment to 2000 after the heat treatment. Furthermore, the Cu(200) peak and the Cu(400) peak were significantly smaller after the heat treatment. This change in the X-ray diffraction pattern indicates that the metal particles constituting the metal substrate were coarsened by the heat treatment.

[0215] In the two-dimensional diffraction image before heat treatment shown in Figure 27, the Debye rings corresponding to the peaks shown in Figure 26 were confirmed as clear, continuous solid line images. In contrast, in the two-dimensional diffraction image after 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 heat treatment recrystallized the metal crystal structure in the metal substrate into a preferred orientation crystal structure. The blurred two-dimensional diffraction image shown in Figure 27 can be said to indicate the history of the metal substrate undergoing heat treatment.

[0216] A lithium-ion battery coin cell was fabricated using the heat-treated Cu foil metal substrate 23G as the first electrode under the conditions of Table 1 described in the first embodiment. In this lithium-ion battery, a Li layer was formed on the surface of the first electrode during charging due to the electrode reaction of chemical formula (2) described in the first embodiment.

[0217] The energy storage device 10G of the eighth embodiment shares a charge / discharge mechanism with the energy storage device 10 of the first embodiment, and also shares a suitable storage temperature at which self-discharge is suppressed with the energy storage device 10 of the first embodiment. Therefore, even for the energy storage device 10G including the heat-treated metal substrate 23G of the eighth embodiment, self-discharge and performance degradation can be suppressed by storing the energy storage device 10 of the first embodiment in a storage system at a storage temperature similar to that of the energy storage device 10 of the first embodiment. In addition, the storage system and storage method of the eighth embodiment can achieve various effects similar to those described in the first embodiment.

[0218] 9. 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 configurations and examples described as other embodiments within the above-described embodiments.

[0219] The storage system and storage method for an electricity storage device described in each of the above embodiments may be applied to a mobile body such as an automobile. In this case, for an electricity storage device in a mobile body that has been stopped for a long period of time, the temperature of the electricity storage device may be controlled to be maintained at the above-mentioned storage temperature by air-cooling means using a fan or refrigerant provided in the mobile body. Furthermore, the temperature control based on the above-mentioned storage temperature may be applied to an electricity storage device that supplies power to a moving mobile body or is being charged by a moving mobile body.

[0220] In each of the above embodiments, the storage temperature may be set according to the season and the outside air temperature. For example, when the outside air temperature is 30 to 45°C, such as in summer, the storage temperature of the power storage device 10 may be set to, for example, 35 to 50°C, and when the outside air temperature is 20°C or lower, such as in winter, the storage temperature of the power storage device 10 may be set to, for example, 25 to 35°C. In the storage system 100, the control unit 105 may automatically set the storage temperature as described above based on the detection results of the outside air temperature sensor. This can significantly reduce the amount of energy consumed to maintain the storage temperature, which is efficient.

[0221] In each of the above embodiments, the power storage device may be configured as a secondary battery other than a lithium ion battery or another power storage device. The power storage device may be configured as, for example, an electric double layer capacitor. The power storage device may also be configured to involve metal ions other than Li ions in charging and discharging. The power storage device may also be configured to involve metal ions such as sodium (Na) ions, potassium (K) ions, and magnesium (Mg) ions in charging and discharging. In the power storage device, the metal substrate of the first electrode may be made of a metal other than Cu. The metal substrate may be made of, for example, a Cu alloy, Al, an Al alloy, or another metal.

[0222] In the above-described first, second, third, fourth, fifth, sixth, and seventh embodiments, the energy storage devices 10, 10A, 10B, 10C, 10D, 10E, and 10F have at least one of a first configuration having an active material layer of carbon nanostructures mainly composed of graphene on the plate surface of the metal substrate, and a second configuration having an uneven structure on the plate surface of the metal substrate, and thus can be interpreted as being configured so that, during charging, a layer of metal atoms formed by the deposition of metal atoms is formed on the surface of the electrode.

[0223] 10. Example of embodiment: The present invention can be realized in the following embodiments.

[0224] [First Aspect] The first aspect is provided as a method for storing an electricity storage device. The storage method of the first aspect includes the steps of: charging an electricity storage device comprising a container filled with an electrolyte solution, metal atoms that ionize in the electrolyte solution and participate in charging and discharging; and electrodes disposed in the electrolyte solution, wherein the metal atoms are deposited to form a layer of the metal atoms on the surface of the electrodes during charging; and placing the charged electricity storage device in an open-circuit state and maintaining the temperature of the electricity storage device at a predetermined storage temperature of 25°C or higher and 65°C or lower. According to findings obtained through independent research by the inventors of the present invention, in an electricity storage device to which the storage method of the first aspect is applied, self-discharge is more effectively suppressed in an unloaded state at an environmental temperature of 25°C or higher. Furthermore, if the environmental temperature exceeds 65°C, problems such as deterioration of the electrolyte solution may occur. According to the storage method of the first aspect, the electricity storage device is stored in an unloaded state at an environmental temperature of 25°C or higher and 65°C or lower, thereby suppressing self-discharge and deterioration of the electricity storage device.

[0225] [Second Aspect] In the storage method of the first aspect, the storage temperature may be equal to or higher than 35° C. and equal to or lower than 50° C. According to the storage method of the second aspect, self-discharge and deterioration of the electricity storage device can be more effectively suppressed.

[0226] [Third Aspect] In the storage method according to the first or second aspect, the metal atoms may be lithium atoms, the electrode may have a metal substrate functioning as a current collector, and the electricity storage device may have an active material layer of carbon nanostructures mainly composed of graphene on the plate surface of the metal substrate. According to the storage method of the third aspect, it is possible to effectively suppress self-discharge and deterioration of electricity storage devices including lithium-ion batteries.

[0227] [Fourth Mode] In the storage method according to the third mode, the carbon nanostructures may be carbon nanowalls extending from the smooth surface of the metal substrate. According to the storage method of the fourth mode, it is possible to effectively suppress self-discharge and deterioration of an electricity storage device that uses carbon nanowalls as an active material.

[0228] [Fifth Mode] In the storage method of the third mode, the surface of the active material layer may have a fine uneven structure in which a plurality of minute granules are densely arranged, and the carbon nanostructures, which extend thinly outward from the granules, may be arranged over the entire surface of the granules. According to the storage method of the fifth mode, it is possible to effectively suppress self-discharge and deterioration of an electricity storage device having an active material layer in which a fine uneven structure is formed by granules having carbon nanostructures formed over the entire surface.

[0229] [Sixth Aspect] In the storage method of the third aspect, the carbon nanostructure may have a base portion where the graphene is laminated and extends elongatedly in a thickness direction of the metal substrate, and a plurality of extension portions made of carbon and extending from the base portion. According to the storage method of the sixth aspect, it is possible to effectively suppress self-discharge and deterioration of an electricity storage device to which an active material layer including a carbon nanostructure having a base portion and extension portions is applied.

[0230] [Seventh Mode] In the storage method of the third mode, the metal substrate may have a plurality of protrusions on the plate surface, and when viewed in the thickness direction of the metal substrate, a plurality of the carbon nanostructures extending linearly on the plate surface of the metal substrate may be distributed on the surface of the metal substrate. According to the storage method of the seventh mode, it is possible to effectively suppress self-discharge and deterioration of an electricity storage device including an electrode having protrusions and a plurality of linearly extending carbon nanostructures on the surface of the metal substrate.

[0231] [Eighth Aspect] In the storage method of the third aspect, a fine uneven structure may be formed on the surface of the metal substrate, and the active material layer containing the carbon nanostructure composed of nanographene and amorphous carbon as a main component may be formed so as to densely cover the surface of the uneven structure. According to the storage method of the eighth aspect, it is possible to effectively suppress self-discharge and deterioration of an electricity storage device having an active material layer containing the carbon nanostructure composed of nanographene and amorphous carbon as a main component, which covers the uneven structure on the surface of the metal substrate.

[0232] [Ninth embodiment] In the storage method according to the first embodiment or the second embodiment, the metal atoms are lithium atoms, the electrode has a metal substrate that functions as a current collector, the metal substrate has a plurality of protrusions on its plate surface where the lithium atoms are precipitated, and the area of ​​a projected region of the protrusions projected onto the plate surface of the metal substrate is 10 nm ２ 10000nm or more ２ and the density of the protrusions on the plate surface is 1 piece / μm ２ More than 1000 pieces / μm ２ According to the storage method of the ninth aspect, it is possible to effectively suppress self-discharge and deterioration of an electricity storage device that includes, as a current collector, a metal substrate having a plurality of protrusions on its plate surface.

[0233] [Tenth Mode] In the storage method according to any one of the first, second, and ninth modes, the metal atoms are lithium atoms, the electrode has a metal substrate that functions as a current collector, the metal substrate has a plurality of protrusions on its plate surface where the lithium atoms are precipitated, the average maximum length of the projected regions when the protrusions are projected onto the plate surface may be 10 nm or more and 200 nm or less, and the area occupied by the projected regions may be 1 / 10 or more of the area of ​​the plate surface. According to the tenth mode storage method, it is possible to more effectively suppress self-discharge and deterioration of an electricity storage device that includes a metal substrate having a plurality of protrusions on its plate surface as a current collector.

[0234] [11th embodiment] In the storage method according to the first or second embodiment, the metal atoms may be lithium atoms, the electrode may have a metal substrate that functions as a current collector, and the metal substrate may have a fine uneven structure on its plate surface that is made up of metal particles, has a maximum width of 0.5 μm to 30.0 μm, and is made up of a plurality of protrusions on whose surface the lithium atoms precipitate during charging. According to the storage method of the 11th embodiment, it is possible to more effectively suppress self-discharge and deterioration of an electricity storage device that includes, as a current collector, a metal substrate having a plurality of protrusions on its plate surface.

[0235] [Twelfth Mode] In the storage method according to the first or second mode, the metal atoms may be lithium atoms, the electrode may have a metal substrate that functions as a current collector, and a two-dimensional diffraction image of the Debye rings of the metal substrate obtained by a two-dimensional X-ray detector may be a discontinuous arc-shaped image in which points or line segments are arranged. According to the storage method of the twelfth mode, it is possible to more effectively suppress self-discharge and deterioration of an electricity storage device that includes a metal substrate that has been subjected to a predetermined heat treatment as a current collector.

[0236] [Thirteenth Aspect] The thirteenth aspect is provided as a storage system for storing an electricity storage device. The storage system of the thirteenth aspect includes a storage unit that houses an electricity storage device including metal atoms that ionize in an electrolyte and participate in charge and discharge, and a metal substrate that forms a current collector, and is configured so that, during charging, a layer of metal atoms formed by the deposition of the metal atoms is formed on the surface of the electrode, a temperature monitoring unit that monitors the temperature within the storage unit, and a temperature control unit that adjusts the temperature of the electricity storage device housed in the storage unit to maintain it at a predetermined storage temperature of 25°C or higher and 65°C or lower based on the detection result of the temperature monitoring unit. The storage system of the thirteenth aspect can suppress self-discharge in the electricity storage device and deterioration of the electricity storage device.

[0237] REFERENCE SIGNS LIST 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G...electricity storage device, 11...container, 12...electrolyte, 15...separator, 16...first electrode chamber, 17...second electrode chamber, 20, 20A, 20B, 20C, 20D, 20E, 20F, 20G...first electrode, 21...current collector, 23, 23A, 23B, 23C, 23D, 23E, 23F, 23G, 23F...metal substrate, 25, 25A, 25B, 25C, 25D...active material layer, 30...second electrode, 31...current collector, 35...active material layer, 40...granular body , 41...particle structure, 43...base, 44...extension, 46...protrusion, 46a...protrusion, 48...surface protrusion, 52...protrusion structure, 52a...first protrusion, 52b...second protrusion, 52c...third protrusion, 100...storage system, 101...storage unit, 102...temperature monitoring unit, 103...temperature control unit, 105...control unit, AC...amorphous carbon layer, VD...cavity, GF...graphene, CN, CNa, CNb, CNc, CNd...carbon nanostructure, CS...uneven structure, CSs...surface uneven structure, MP...metal particle

Claims

1. A method for storing an electricity storage device, comprising: a step of charging the electricity storage device, the electricity storage device comprising a container filled with an electrolyte, metal atoms that ionize in the electrolyte and participate in charging and discharging, and electrodes placed in the electrolyte, wherein the metal atoms are configured to deposit a layer of the metal atoms on the surface of the electrodes during charging; and a step of placing the charged electricity storage device in an open-circuit state and maintaining the temperature of the electricity storage device at a predetermined storage temperature of 25°C or higher and 65°C or lower.

2. A storage method according to claim 1, wherein the storage temperature is between 35°C and 50°C.

3. A storage method according to claim 1 or claim 2, wherein the metal atoms are lithium atoms, the electrode has a metal substrate that functions as a current collector, and the electricity storage device has an active material layer of a carbon nanostructure composed primarily of graphene on the plate surface of the metal substrate.

4. A storage method according to claim 3, wherein the carbon nanostructures are carbon nanowalls extending from the smooth surface of the metal substrate.

5. A storage method according to claim 3, wherein the surface of the active material layer has a fine uneven structure in which a plurality of minute particles are densely arranged, and the carbon nanostructures are arranged over the entire surface of the particles, extending in elongated shapes outward from the particles.

6. A storage method according to claim 3, wherein the carbon nanostructure has a base portion on which the graphene is laminated and extends in an elongated manner in the thickness direction of the metal substrate, and a plurality of extension portions made of carbon and extending from the base portion.

7. A storage method according to claim 3, wherein the metal substrate has a plurality of convex portions on the plate surface, and when the metal substrate is viewed in the thickness direction, a plurality of the carbon nanostructures extending linearly on the plate surface of the metal substrate are distributed on the surface of the metal substrate.

8. A storage method according to claim 3, wherein a fine uneven structure is formed on the surface of the metal substrate, and an active material layer mainly composed of the carbon nanostructure made of nanographene and amorphous carbon is formed so as to densely cover the surface of the uneven structure.

9. A storage method according to claim 1 or claim 2, wherein the metal atoms are lithium atoms, the electrode has a metal substrate that functions as a current collector, the metal substrate has a plurality of protrusions on the plate surface where the lithium atoms are precipitated, and the area of ​​the projection region obtained by projecting the protrusions onto the plate surface of the metal substrate is 10 nm ２ 10000nm or more ２ the density of the protrusions on the plate surface is 1 / μm ２ More than 1000 pieces / μm ２ The storage method is as follows.

10. A storage method according to claim 1 or claim 2, wherein the metal atoms are lithium atoms, the electrode has a metal substrate that functions as a current collector, the metal substrate has a plurality of protrusions on its plate surface where the lithium atoms are precipitated, the average maximum length of the projection areas of the protrusions projected onto the plate surface is 10 nm or more and 200 nm or less, and the area occupied by the projection areas is 1 / 10 or more of the area of ​​the plate surface.

11. A storage method according to claim 1 or claim 2, wherein the metal atoms are lithium atoms, the electrode has a metal substrate that functions as a current collector, and the metal substrate has a fine uneven structure on its plate surface that is made up of metal particles, has a maximum width of 0.5 μm or more and 30.0 μm or less, and is made up of a plurality of protrusions on whose surface the lithium atoms precipitate during charging.

12. A storage method according to claim 1 or claim 2, wherein the metal atoms are lithium atoms, the electrode has a metal substrate that functions as a current collector, and the metal substrate is such 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.

13. A storage system for storing an electricity storage device comprising metal atoms that ionize in an electrolyte and participate in charging and discharging, and a metal substrate that forms a current collector, wherein the metal atoms precipitate to form a layer of metal atoms on the surface of the electrode during charging, the storage system comprising: a storage unit that houses the electricity storage device; a temperature monitoring unit that monitors the temperature within the storage unit; and a temperature control unit that adjusts the temperature of the electricity storage device housed in the storage unit to maintain it at a predetermined storage temperature of 25°C or higher and 65°C or lower, based on the detection results of the temperature monitoring unit.

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