JP7768524B2 - Method for manufacturing an electrode for an electric storage device and apparatus for manufacturing an electrode for an electric storage device - Google Patents

Description

The technology disclosed herein relates to electrodes for electricity storage devices, secondary batteries, methods for manufacturing electrodes for electricity storage devices, and manufacturing apparatuses for electrodes for electricity storage devices.

Secondary batteries are known as chargeable and dischargeable electricity storage devices. Typically, in electrodes for electricity storage devices, an active material layer composed of substances involved in the charge and discharge reactions of the electricity storage device is formed on the surface of a current collector. For example, Patent Documents 1 and 2 listed below disclose lithium-ion secondary batteries having an active material layer containing lithium (Li) in the positive electrode and an active material layer containing carbon (C) as an active material in the form of graphite, carbon nanowalls, or the like in the negative electrode.

It is generally known that the composition of the active material layer has a significant impact on the battery performance of an electricity storage device. For example, there is technical knowledge that applying a carbon nanostructure such as a carbon nanowall to the active material layer, as in Patent Document 2, improves the battery performance of an electricity storage device compared to applying graphite to the active material layer, as in Patent Document 1.

Patent No. 2668678 JP 2010-9980 A

The conventional structure in which graphite is applied to the active material layer, as in Patent Document 1, may not be able to fully achieve the high battery performance targets required for future energy storage devices.

On the other hand, when carbon nanowalls are applied to the active material layer, as in Patent Document 2, the production of the carbon nanowalls is time-consuming, which may significantly increase the production costs of the electricity storage device. Furthermore, when electrodes with carbon nanowalls applied to the active material layer are rolled up for transportation or storage during the production process of the electricity storage device, the carbon nanowalls on the surface may be destroyed or fall off due to compressive stress or shear stress.

As such, there is still room for improvement in electrodes for electricity storage devices that use carbon as an active material. The purpose of this disclosure is to provide an electrode for electricity storage devices that has a structure different from conventional ones and includes an active material layer that can achieve high battery performance.

Through extensive research into carbon nanostructures that can be used in active material layers, the inventors of the present invention have succeeded in developing an electrode for an electricity storage device that can be easily manufactured using a non-traditional method and can dramatically improve battery performance. The technology disclosed herein can be realized, for example, in the following forms:

One aspect of the present invention is provided as an electrode for an electricity storage device. This electrode for an electricity storage device comprises a metal substrate that constitutes a current collector and has a finely textured structure formed on its surface; and an active material layer that is primarily composed of a carbon nanostructure composed of nanographene and amorphous carbon and is formed so as to densely cover the surface of the textured structure, and in which metal atoms involved in the charging and discharging of the electricity storage device are precipitated on the surface when the electricity storage device is charged.

This type of electrode for an electricity storage device uses a carbon nanostructure composed of nanographene and amorphous carbon as the active material, thereby improving the battery performance of the electricity storage device. Furthermore, because the surface of the active material layer is formed with irregularities, the surface area of the active material layer is increased, allowing for a greater amount of metal to precipitate during charging of the electricity storage device, thereby increasing the charge capacity of the electricity storage device. Furthermore, the irregular structure of the active material layer forms numerous protrusions on the surface of the active material layer, promoting metal precipitation on the surface of the active material layer during charging of the electricity storage device. This further improves the battery performance of the electricity storage device. Additionally, because the active material layer is formed like a thin film that densely covers the surface of the metal substrate, it is less likely to be destroyed or shed during the manufacturing process of the electricity storage device, unlike carbon nanowalls that grow to extend from the surface of the metal substrate.

The present invention can be realized in various forms other than an electrode for an electricity storage device, a secondary battery, a method for manufacturing an electrode for an electricity storage device, and an apparatus for manufacturing an electrode for an electricity storage device. For example, the present invention can be realized in the form of various electricity storage devices other than secondary batteries, active material layers used in such electricity storage devices, methods for manufacturing active material layers, and apparatus for manufacturing active material layers. The present invention can also be realized in the form of an apparatus or system including an electricity storage device.

FIG. 1 is a schematic diagram showing the configuration of a secondary battery. FIG. 2 is a schematic cross-sectional view showing the configuration of a metal substrate and an active material layer. FIG. 1 is a process flow diagram showing a manufacturing process of a secondary battery. FIG. 1 is a schematic diagram showing the configuration of a plasma processing apparatus. FIG. 3 is a schematic diagram showing the configuration of an electrode holding unit of a first configuration example. FIG. 10 is a schematic diagram showing the configuration of an electrode holding unit in a second configuration example. 3A and 3B are schematic diagrams illustrating the mechanism by which an active material layer is formed by plasma treatment. FIG. 4 is an explanatory diagram showing photographed images of the process of forming an active material layer according to an example. FIG. 4 is an explanatory diagram showing a photographed image of an active material layer according to an example. FIG. 3 is an explanatory diagram showing a Raman spectrum of an active material layer according to an example. FIG. 10 is an explanatory diagram showing a list of photographed images of active material layers of comparative examples. FIG. 4 is an explanatory diagram showing the results of an evaluation test of the battery performance of the examples. FIG. 4 is an explanatory diagram showing the results of an evaluation test of the battery performance of the first comparative example. FIG. 10 is an explanatory diagram showing the results of an evaluation test of the battery performance of the second comparative example. FIG. 10 is an explanatory diagram showing the results of an evaluation test of the battery performance of the third comparative example. FIG. 4 is an explanatory diagram showing the results of an evaluation test of the battery performance of an example and a comparative example.

Hereinafter, with reference to the drawings, embodiments of an electrode for an electricity storage device, a secondary battery, a method for manufacturing an electrode for an electricity storage device, and an apparatus for manufacturing an electrode for an electricity storage device according to the present invention will be described.

1. Embodiment:
1-1. Secondary battery and electrode configuration:
Fig. 1 is a schematic diagram showing the configuration of a secondary battery 10 according to this embodiment. For convenience, in Fig. 1, a container 11 is shown by a dashed line and a separator 15 is shown by a two-dot chain line.

The secondary battery 10 is a type of chargeable and dischargeable power storage device, and is a lithium-ion secondary battery in which lithium (Li) ions are involved in charging and discharging. The secondary battery 10 includes a container 11, an electrolyte 12, a separator 15, a first electrode 20, and a second electrode 30.

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 a solution in which a lithium salt is dissolved in an organic solvent, and is capable of transferring lithium ions. For example, lithium hexafluorophosphate (LiPF ₆ ) can be used as the lithium salt of the electrolyte solution 12. For example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be used as the organic solvent.

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 made of a thin film material, such as a resin film or nonwoven fabric with a porous structure, and is electrically insulating and ion-conductive. The separator 15 electrically insulates the first electrode 20 from the second electrode 30 and allows metal ions transmitted via the electrolyte solution 12 to pass through.

The first electrode 20 corresponds to the electrode for the electricity storage device in this embodiment. In the following description, the first electrode 20 will also be simply referred to as the "electrode 20." In the secondary battery 10 of this embodiment, the electrode 20 constitutes the negative electrode. The electrode 20 includes a metal substrate 21 and an active material layer 22.

The metal substrate 21 constitutes a current collector. In this embodiment, the metal substrate 21 is made of a metal foil of copper (Cu) or a Cu alloy. If the metal substrate 21 is made of Cu or a Cu alloy, high battery performance can be achieved in the electricity storage device.

In other embodiments, the metal substrate 21 may be made of a metal other than Cu or a Cu alloy. The metal substrate 21 may be made of, for example, nickel (Ni), a Ni alloy, aluminum (Al), an Al alloy, etc. The metal substrate 21 does not have to be made of metal foil, but may be made of, for example, a thin metal plate. The metal substrate 21 does not have to be made in a flat plate shape, but may be bent into various shapes, such as a cylindrical or corrugated shape. The metal substrate 21 may have a porous structure.

The active material layer 22 is provided on both the first surface 21a and the second surface 21b of the metal substrate 21. The configuration of the active material layer 22 will be described in detail below. As will be described below, a fine uneven structure is formed on the first surface 21a and the second surface 21b of the metal substrate 21, and therefore, for convenience, the first surface 21a and the second surface 21b are illustrated in Figure 1 with dashed lines.

The second electrode 30 constitutes the positive electrode of the secondary battery 10. The second electrode 30 has a positive electrode current collector 31 and a positive electrode active material layer 32. The positive electrode current collector 31 is made of a metal foil such as aluminum (Al) or titanium (Ti). The positive electrode current collector 31 may be made of other metals or may have a form other than a metal foil. The positive electrode current collector 31 does not have to be made in a flat shape, and may be bent into various shapes such as a cylindrical or wavy shape.

The positive electrode active material layer 32 is formed on each of the first surface 31a and the second surface 31b of the positive electrode current collector 31. The positive electrode active material layer 32 contains a positive electrode active material including metal atoms involved in charging and discharging, a conductive additive, and a binder. The positive electrode active material layer 32 may also contain a thickener.

In this embodiment, the metal atom involved in charge and discharge is a Li atom. As the positive electrode active material, for example, a ternary substance such as lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LMO), or lithium nickel oxide (NCA) can be used.

As a conductive additive, for example, acetylene black or carbon black can be used. As a binder, for example, polyvinylidene fluoride (PVDF) or styrene butadiene rubber (SBR) can be used. As a thickener, for example, carboxymethyl cellulose (CMC) can be used.

The configuration of the active material layer 22 of the electrode 20 will be described with reference to Figure 2. Figure 2 is a schematic cross-sectional view showing the metal substrate 21 and the active material layer 22 at an arbitrary cut surface along the thickness direction of the metal substrate 21. While Figure 2 shows the first surface 21a of the metal substrate 21, the configuration described below is common to both the first surface 21a and the second surface 21b of the metal substrate 21.

A microscopic uneven structure 23 on the micron scale is formed on the first surface 21a and second surface 21b of the metal substrate 21. The active material layer 22 is formed as a thin film so as to densely cover the surface of the uneven structure 23. The average thickness of the active material layer 22 may be, for example, 0.1 μm to 15.0 μm.

The active material layer 22 has a surface uneven structure 24 that is finer than the uneven structure 23 of the metal substrate 21. In order to improve the battery performance of the energy storage device, it is preferable that the surface of the active material layer 22 has a dense distribution of multiple granular protrusions 24t, each having a width of 0.1 μm or more and 10.0 μm or less, when viewed in the thickness direction of the metal substrate 21. The "width of a protrusion 24t" refers to the maximum width of a single protrusion 24t measured in all directions perpendicular to the thickness direction of the metal substrate 21. Note that minute cavities 25 may be formed inside the uneven structure 23 of the metal substrate 21 and the active material layer 22 during their formation process.

The active material layer 22 is primarily composed of a carbon nanostructure composed of nanographene and amorphous carbon. The active material layer 22 is configured by depositing nanographene and amorphous carbon particles. The nanographene and amorphous carbon particles include those with a spherical shape and those with a plate-like shape. The protrusions 24t of the active material layer 22 described above include those composed of individual particles and those composed of randomly aggregated particles.

The active material layer 22 is formed by plasma treatment, which will be described later. However, hydroxyl groups may remain inside the active material layer 22 as impurities introduced by the plasma treatment. The method for forming the active material layer 22 will be described later in the description of the method for manufacturing the secondary battery 10.

1-2. Charging and discharging reactions in electricity storage devices:
The chemical reactions occurring during charging and discharging of the secondary battery 10 can be expressed, for example, by the following reaction formula: When the positive electrode material is _LiCoO2 , the reaction formula at the second electrode 30, which is the positive electrode, is expressed by the following formula (1): x represents the proportion of reacting atoms and is a real number greater than 0 and less than 1.
Li _1-x CoO ₂ + xLi ⁺ + xe ^- ⇔ LiCoO ₂ …(1)

When the metal involved in charging and discharging is Li, the reaction formula at the negative electrode 20 is expressed by the following formula (2): In the active material layer 22 mainly composed of carbon nanostructures, when the secondary battery 10 is charged, Li is precipitated on the surface of the active material layer 22 of the electrode 20 due to the reaction shown in formula (2).
Li ⁺ + e ^- ⇔ Li...(2)

In the case of a conventional negative electrode having graphite as an active material disposed on the surface of a flat metal substrate, in principle, one lithium ion is absorbed per six carbon atoms during charging, forming lithium carbide (LiC ₆ ). Therefore, the reaction formula for this conventional configuration, as a comparative example, is expressed as the following formula (3):
xLi+ + C ₆ + xe ^- ⇔ Li _x C ₆ ...(3)

As shown in formula (3) in the comparative example above, in the case of a conventional electrode that uses graphite as the negative electrode active material, the number of lithium ions that can be absorbed during charging is determined by the number of carbon atoms contained in the active material layer. In contrast, with a secondary battery 10 having the electrode 20 of this embodiment, as shown in formula (2) above, charging is theoretically possible as long as Li can be precipitated in the electrode 20. Therefore, the electrode 20 of this embodiment can achieve a higher charge capacity in power storage devices such as the secondary battery 10.

Furthermore, as described above, in the electrode 20 of this embodiment, the active material layer 22 is formed so as to cover the surface of the uneven structure 23 of the metal substrate 21, and has a surface uneven structure 24 that is finer than the uneven structure 23 of the metal substrate 21. As a result, the surface area of the active material layer 22 on which Li can be deposited is significantly increased. Therefore, the electrode 20 of this embodiment can achieve a high charge capacity in the secondary battery 10.

A large number of protrusions 24t that constitute the surface uneven structure 24 are formed on the surface of the active material layer 22. According to nucleation theory, the protrusions 24t on the surface of the active material layer 22 serve as starting points for Li precipitation, thereby promoting Li precipitation on the surface of the active material layer 22. Therefore, the electrode 20 of this embodiment can improve the battery performance of the secondary battery 10, such as the charge capacity and specific capacity.

Furthermore, if the protrusions 24t are uniformly distributed on the surface of the active material layer 22, Li can be uniformly precipitated on the surface of the active material layer 22. This prevents dendrites from forming on the electrode 20 due to repeated charging and discharging of the secondary battery 10, and prevents damage and deterioration of the electricity storage device caused by dendrites.

1-3. Secondary battery manufacturing method:
3 is a process flow diagram showing the manufacturing process of the secondary battery 10. Processes P1 to P5 are manufacturing processes for the electrode 20. In this embodiment, a plurality of electrodes 20 are manufactured continuously.

In process P1, a base material BM of the metal substrate 21 is prepared. In this embodiment, the base material BM has a strip-like configuration in which multiple pieces are connected together so that multiple electrodes 20 can be continuously manufactured. The above-mentioned fine uneven surface structure 23 has not yet been formed on the base material BM, and the surface of the base material BM is configured to be flat.

In steps P2 to P4, an active material layer 22 is formed on the surface of the substrate BM by plasma treatment, as described below. This plasma treatment forms a fine uneven structure 23 on the surface of the substrate BM, and the active material layer 22 is formed to cover the surface of the uneven structure 23.

In this embodiment, plasma treatment is performed by a plasma treatment apparatus 50 of the first configuration example or a plasma treatment apparatus 50a of the second configuration example. Each of the plasma treatment apparatuses 50 and 50a is an example of an apparatus for forming an active material layer 22 on the base material BM of a metal substrate 21, and corresponds to an electrode 20 manufacturing apparatus. Below, the plasma treatment apparatus 50 of the first configuration example will be described, followed by a description of the plasma treatment apparatus 50a of the second configuration example, and then the details of steps P2 to P4 for the plasma treatment will be described.

Figure 4 is a schematic diagram showing the configuration of a plasma processing apparatus 50 according to a first configuration example. The plasma processing apparatus 50 performs plasma processing to form an active material layer 22 on a strip-shaped substrate BM being transported in the longitudinal direction. The plasma processing apparatus 50 includes a reaction chamber 51, a liquid supply unit 52, a liquid drainage unit 53, a substrate transport unit 55, and a plasma generation unit 60.

The reaction chamber 51 is configured to be liquid-tight so that the solution LQ can be stored inside. The reaction chamber 51 is also configured to be airtight so that plasma can be generated in the region above the stored solution LQ.

The solution LQ contains alcohols. The alcohol concentration of the solution LQ may be, for example, about 50 to 100 mass %. The C atoms contained in the solution LQ constitute the active material of the active material layer 22. The alcohol contained in the solution LQ may be, for example, a primary alcohol. In this embodiment, the alcohol contained in the solution LQ is ethanol (C ₂ H ₆ O).

The alcohol of the solution LQ is not limited to ethanol. In other embodiments, the alcohol of the solution LQ may be, for example, butanol (C ₄ H ₁₀ O) or hexanol (C ₆ H ₁₄ O). The solution LQ may also be a mixture of multiple types of alcohol. The solution LQ may be, for example, a mixture of ethanol and methanol (CH ₃ OH). Alternatively, the solution LQ may be a mixture of a hydrocarbon such as hexane (C ₆ H ₁₄ ) or benzene (C ₆ H ₆ ) with an alcohol such as ethanol.

A liquid supply unit 52 and a liquid drainage unit 53 are connected to the bottom of the reaction chamber 51. The liquid supply unit 52 supplies solution LQ to the reaction chamber 51, and the liquid drainage unit 53 discharges the solution LQ to the outside of the reaction chamber 51. During plasma processing, the amount of solution LQ stored in the reaction chamber 51 and the concentration of the solution LQ are controlled to predetermined target values by controlling the liquid supply unit 52 and the liquid drainage unit 53.

The substrate conveying unit 55 conveys the substrate BM of the metal substrate 21. As described above, in this embodiment, the substrate BM of the metal substrate 21 is strip-shaped, and the substrate conveying unit 55 conveys the substrate BM in its longitudinal direction. Figure 4 shows an arrow indicating the conveying direction MD of the substrate BM.

The substrate transport unit 55 includes a substrate supply unit 56, multiple transport rollers 57, and a recovery unit 58. The substrate supply unit 56 stores a roll BMr in which substrate BM is wound in a roll shape in the longitudinal direction, and unwinds a strip of substrate BM from the roll BMr and sends it into the reaction chamber 51.

Multiple transport rollers 57 are installed within the reaction chamber 51 and form a transport path for the substrate BM. The substrate BM sent out from the substrate supply unit 56 is introduced into the area above the solution LQ in the reaction chamber 51. The multiple transport rollers 57 are installed to transport the substrate BM into the solution LQ, immerse it in the solution LQ, and then transport it back to the area above the solution LQ in the reaction chamber 51. Furthermore, the transport rollers 57 in the solution LQ are installed below the plasma electrode 65 so that the substrate BM is positioned along the liquid surface of the solution LQ.

As will be described in more detail below, in the plasma processing apparatus 50, while the substrate BM is immersed in the solution LQ, plasma generated by the plasma electrode 65 is irradiated onto the upper surface to form an active material layer 22. After the active material layer 22 is formed, the substrate BM is sent out of the reaction chamber 51 by the transport rollers 57 and collected by the collection unit 58. The collection unit 58 is configured to wind up the substrate BM on which the active material layer 22 has been formed into a roll and collect it.

The plasma generating unit 60 is located above the reaction chamber 51 and generates plasma within the reaction chamber 51. The plasma generating unit 60 includes a gas supply unit 61, an exhaust unit 62, a plasma electrode 65, an electrode holder 66, and a plasma power supply unit 67.

The gas supply unit 61 is connected to the top of the reaction chamber 51 and supplies a reactive gas for generating plasma to the region above the solution LQ in the reaction chamber 51. In this embodiment, the gas supply unit 61 supplies argon (Ar) as the reactive gas. Note that the reactive gas is not limited to argon. For example, hydrogen may also be used as the reactive gas.

The gas supply unit 61 supplies the reaction gas at a flow rate of, for example, approximately 1 to 10 slm. The unit "slm" indicates the flow rate per minute at 1 atmosphere (atm) and 0°C.

The exhaust unit 62 is connected to the top of the reaction chamber 51 and exhausts gas from the region above the solution LQ inside the reaction chamber 51. During plasma processing, the exhaust unit 62 controls the air pressure inside the reaction chamber 51 to a predetermined target value. The target value of the air pressure inside the reaction chamber 51 may be, for example, approximately 0.5×10 ⁵ to 1.5×10 ⁵ Pa.

The plasma electrode 65 is installed in an area above the solution LQ within the reaction chamber 51. The plasma electrode 65 is made of a carbon substrate such as a graphite sintered body. The plasma electrode 65 has a cylindrical shape, and is installed so that its tip faces the surface of the substrate BM immersed in the solution LQ above the liquid surface of the solution LQ.

The distance Da between the tip of the plasma electrode 65 and the liquid surface of the solution LQ may be, for example, approximately 1 to 10 mm. Furthermore, the distance Db between the tip of the plasma electrode 65 and the surface of the substrate BM may be, for example, approximately 5 to 20 mm. The plasma electrode 65 is held by an electrode holder 66. The electrode holder 66 will be described later.

The substrate BM, which is immersed in the solution LQ and being transported, is grounded via the transport roller 57. The plasma electrode 65 is connected to a plasma power supply unit 67. The plasma power supply unit 67 applies a high-frequency voltage to generate plasma between the plasma electrode 65 and the substrate BM. The high-frequency voltage may be, for example, 5 to 15 kV, and the frequency may be 50 to 80 Hz. The frequency for generating plasma is not limited to the aforementioned frequencies and may be, for example, a frequency in the range of several Hz to several hundred Hz. It may also be a frequency in the GHz range, which corresponds to microwaves.

The electrode holder 66 in the first configuration example will be described with reference to Figure 5A. Figure 5A schematically illustrates the electrode holder 66 viewed from above and the substrate BM being transported below it in the transport direction MD. In Figure 5A, the position of the tip of the plasma electrode 65 is indicated by a dashed line, and its movement direction is indicated by a dashed arrow.

In the plasma processing apparatus 50 of the first configuration example, the electrode holding unit 66 is configured as a moving mechanism that can move one plasma electrode 65 along the surface of the base material BM in the width direction of the base material BM. This allows the plasma irradiation area on the base material BM to be moved in the width direction of the base material BM, making it possible to form the active material layer 22 across the entire width of the base material BM.

In plasma processing using the plasma processing apparatus 50 of the first configuration example, the process of forming an active material layer 22 across the width of the substrate BM by scanning the plasma electrode 65 and the process of transporting the substrate BM in the transport direction MD by the substrate transport unit 55 are repeated alternately. This allows the active material layer 22 to be efficiently formed over the entire surface of the substrate BM.

The configuration of the plasma processing apparatus 50a of the second configuration example will be described with reference to Figure 5B. The configuration of the plasma processing apparatus 50a of the second configuration example is substantially the same as the configuration of the plasma processing apparatus 50 of the first configuration example, except that it is equipped with multiple plasma electrodes 65 and the configuration of the electrode holder 66a is different. Figure 5B, like Figure 5A, schematically illustrates the electrode holder 66a of the second configuration example when viewed from above and below, and the substrate BM being transported below it in the transport direction MD.

The electrode holder 66a holds multiple plasma electrodes 65 arranged in the width direction of the substrate BM. The plasma electrodes 65 are arranged at a predetermined interval so that the active material layer 22 can be formed without gaps during plasma treatment. The plasma electrodes 65 are arranged at intervals of, for example, 1 to 50 mm. In this embodiment, the plasma electrodes 65 are arranged at equal intervals.

In other embodiments, the multiple plasma electrodes 65 do not have to be arranged in a row. The multiple plasma electrodes 65 may be arranged, for example, in a staggered pattern. Furthermore, the multiple plasma electrodes 65 do not have to be arranged parallel to the width direction of the substrate BM, and may be arranged, for example, in a direction diagonally intersecting the conveyance direction MD. The multiple plasma electrodes 65 do not have to be arranged at equal intervals.

In the second configuration example of the plasma processing apparatus 50a, during plasma processing, each of the multiple plasma electrodes 65 can simultaneously generate plasma between itself and the substrate BM. This allows the active material layer 22 to be formed simultaneously across the array direction of the plasma electrodes 65. This reduces the time required to form the active material layer 22.

In plasma processing using the plasma processing apparatus 50a of the second configuration example, the active material layer 22 is formed by the multiple plasma electrodes 65 in the arrangement direction of the plasma electrodes 65, while the substrate BM is transported in the transport direction MD by the substrate transport unit 55. This allows the active material layer 22 to be efficiently formed over the entire surface of the substrate BM.

Returning to Figure 3, the process of forming an active material layer 22 on the substrate BM by plasma treatment in the plasma treatment device 50, 50a will be described. In process P2, the substrate BM is transported by the substrate transport unit 55, and the substrate BM is immersed in the solution LQ in the reaction chamber 51.

In process P3, the plasma generation unit 60 of the plasma processing apparatus 50, 50a generates plasma in the reaction chamber 51. First, the gas supply unit 61 supplies a reactive gas into the reaction chamber 51. Next, through control of the gas supply unit 61 and the exhaust unit 62, when the reactive gas concentration in the reaction chamber 51 reaches a predetermined concentration and pressure, the plasma power supply unit 67 applies a high-frequency voltage between the plasma electrode 65 and the substrate BM, causing a discharge from the plasma electrode 65. This generates plasma from the tip of the plasma electrode 65 toward the surface of the substrate BM in the solution LQ, and as shown by the dashed line in Figure 4, the plasma is irradiated onto the surface of the substrate BM in the solution LQ. In process P4, an active material layer 22 is formed on the surface of the substrate BM by the plasma irradiation.

With reference to Figure 6, the mechanism by which the active material layer 22 is formed by irradiating the substrate BM with plasma will be described. Figures 6(a) to 6(c) schematically show the change over time in the appearance of the solution LQ and the surface of the substrate BM in the solution LQ after plasma treatment has begun. Note that the mechanism described below is based on the considerations of the inventors of the present invention derived from the examples described below.

When plasma irradiation of the substrate BM in the solution LQ begins, as shown in Figure 6(a), the alcohols and hydrocarbons in the solution LQ are decomposed, generating hydrogen atoms H and radicals RD in the solution LQ. Then, as shown in Figure 6(b), the surface of the substrate BM is eroded by the hydrogen atoms H and radicals RD, forming a fine uneven structure 23. While the plasma is being irradiated, the erosion of the surface of the substrate BM by the hydrogen atoms H and radicals RD continues, and the recesses and protrusions of the uneven structure 23 become larger, as shown in Figures 6(b) and 6(c). During this time, hydrogen atoms H may enter the interior of the metal substrate 21, forming tiny cavities 25 within the uneven structure 23.

Furthermore, as shown in FIG. 6(b), during the formation of the uneven structure 23, carbon atoms generated in the solution LQ by decomposition of the alcohol due to plasma irradiation precipitate as nanographene and amorphous carbon particles CP, which begin to adhere to the surface of the uneven structure 23 of the substrate BM. Then, as shown in FIGS. 6(b) and 6(c), in parallel with the growth of the uneven structure 23 on the surface of the substrate BM, nanographene and amorphous carbon particles CP are deposited to cover the surface of the uneven structure 23, thereby forming the active material layer 22. During this growth process, tiny cavities 25 may also form inside the active material layer 22.

The degree of unevenness of the active material layer 22 and the amount of carbon nanostructure deposition can be adjusted by the plasma irradiation time. The plasma irradiation time for forming the active material layer 22 should be at least 1 second. The plasma irradiation time may be, for example, approximately 1 to 60 minutes.

The active material layer 22 can be formed more efficiently and in a shorter time in the region of the substrate BM located directly below the plasma electrode 65. In the plasma processing apparatus 50, 50a, the region where the active material layer 22 is formed is expanded by alternately shifting the plasma irradiation region on the surface of the substrate BM and irradiating the plasma for a predetermined period of time.

See Figure 4. In the plasma processing device 50, 50a, the first plasma treatment is performed on the substrate BM, forming an active material layer 22 on one side of the substrate BM. To form active material layers 22 on both sides of the substrate BM, the substrate BM with the active material layer 22 formed on only one side, which has been recovered in the recovery unit 58, is set in the substrate supply unit 56 as a roll BMr, and a second plasma treatment is performed.

When the substrate BM is subjected to the second plasma treatment, it is transported so that the surface opposite to that of the first transport faces upward in the solution LQ. Therefore, during the first plasma treatment, it is preferable that the substrate BM is wound up in the recovery section 58 so that it is upside down compared to when it was forming the roll body BMr stored in the substrate supply section 56.

See Figure 3. In process P5, multiple first electrodes 20 are individually cut out from a strip-shaped substrate BM with active material layers 22 formed on both sides. The first electrodes 20 are completed through processes P1 to P5.

In process P6, the second electrode 30, which will serve as the positive electrode, is manufactured. In the following process P7, as shown in FIG. 1, the first electrode 20 and the second electrode 30 are assembled into a container 11 filled with an electrolyte 12. Through these processes, the secondary battery 10 is completed.

1-4. Summary:
As described above, the electrode 20 of this embodiment includes an active material layer 22 having a novel structure, which is primarily composed of a carbon nanostructure formed of nanographene and amorphous carbon and is formed so as to cover the surface of the concave-convex structure 23 of the metal substrate 21. With this electrode 20, the charge-discharge performance of the secondary battery 10 can be significantly improved, as will be shown in the examples described below.

Furthermore, with the electrode 20 manufacturing method and the plasma processing apparatus 50, 50a, which are the electrode 20 manufacturing apparatus of this embodiment, the active material layer 22 can be easily formed along with the uneven structure 23 on the metal substrate 21 by plasma processing. Therefore, the electrode 20 can be manufactured efficiently. With the plasma processing apparatus 50 of the first configuration example, the active material layer 22 can be formed over the entire substrate BM for forming multiple electrodes 20 by transporting the strip-shaped substrate BM and moving the plasma electrode 65 using the electrode holder 66. Furthermore, with the plasma processing apparatus 50a of the second configuration example, the active material layer 22 can be formed over the entire substrate BM for forming multiple electrodes 20 by irradiating plasma from each of the multiple plasma electrodes 65 and transporting the strip-shaped substrate BM. Therefore, using the plasma processing apparatus 50, 50a, multiple electrodes 20 can be manufactured continuously, allowing for even more efficient electrode 20 manufacturing.

Here, for example, in the manufacturing process of a conventional secondary battery having an active material layer of carbon nanowalls, when the electrode on which the active material layer is formed is rolled up for transportation, storage, etc., some of the carbon nanowalls may be damaged or fall off. In contrast, with the electrode 20 of this embodiment, the active material layer 22 has a thin-film configuration, so deterioration and fall-off of the active material layer 22 are suppressed even when the electrode is rolled up for transportation or storage during the manufacturing process of the secondary battery 10. Therefore, the electrode 20 of this embodiment is easy to handle, facilitating mass production of the electrode 20.

2. Working Example:
2-1. Plasma treatment:
An example of the process for forming the active material layer 22 by the plasma treatment described in the above embodiment will be described with reference to Figure 7. Figure 7 shows images taken for each plasma irradiation time when the plasma treatment described in the above embodiment was performed under the treatment conditions shown in Table 1 below. Each image in Figure 7 is an image of the surface of the base material BM of the metal substrate 21 taken from the side. The plasma irradiation time is displayed in the upper left corner of each image.

When plasma irradiation began, the surface of the substrate BM was flat. 0.5 minutes after the start of plasma irradiation, irregularities began to form on the surface of the substrate BM. This is presumably due to erosion by hydrogen atoms and radicals in the solution LQ. As the plasma irradiation time continued, the irregularities on the surface of the substrate BM gradually increased. When the plasma irradiation time reached 10 minutes, several tiny cavities were observed within the irregular structure. Furthermore, during this experiment, it was confirmed that the concentrations of C atoms and O atoms increased near the surface of the substrate BM between 1 and 10 minutes of plasma irradiation. This indicates that an active material layer 22 was being formed while an irregular structure 23 was being formed on the surface of the substrate BM.

2-2. Examples of active material layers:
8 shows a photograph of the active material layer 22 of the electrode 20 of Example E1 taken in the thickness direction of the metal substrate 21. The active material layer 22 of Example E1 was formed by plasma treatment under the conditions shown in Table 1 above. The plasma irradiation time was 30 minutes. As shown in this photograph, in the active material layer 22 of Example E1, when viewed in the thickness direction of the metal substrate 21, a plurality of granular protrusions 24t having a width of 0.1 μm or more and 10.0 μm or less were densely distributed.

9 is a graph showing the Raman spectrum of the active material layer 22 of Example E1. In this graph, peaks of the D band (1340 cm ⁻¹ ) and the G band (1580 cm ⁻¹ ) were observed. This result indicates that the active material layer 22 is formed mainly from carbon nanostructures composed of nanographene and amorphous carbon.

2-3. Comparative Example of Active Material Layer:
FIG. 10 shows a list of photographed images of the electrodes of comparative examples C1, C2, and C3.

Figures 10(a) and (b) each show photographed images of the surface of the electrode of Comparative Example C1. Figure 10(a) is an image taken directly facing the surface of the electrode of Comparative Example C1 using a scanning electron microscope. Figure 10(b) is an image taken at a higher magnification than the image of Figure 10(a).

The electrode of Comparative Example C1 did not have an active material layer and was composed only of a metal substrate that constituted the current collector. The metal substrate of Comparative Example C1 was composed of the same copper foil as the base material BM of the metal substrate 21 of Example E1 before the active material layer 22 was formed. Therefore, the surface of Comparative Example C1 was composed of a flat surface, as shown in the images of Figures 10(a) and (b).

Figure 10(c) shows an image of the electrode of Comparative Example C2. Figure 10(c) is an image taken directly on the surface of the active material layer of Comparative Example C2 using a scanning electron microscope. The electrode of Comparative Example C2 is configured by providing a graphite active material layer on the surface of a metal substrate with a flat surface similar to that of Comparative Example C1. Figure 10(c) shows the granular graphite that makes up the active material layer.

Figures 10(d) and (e) show images of the electrode of Comparative Example C3. Figure 10(d) is an image of the surface layer of the electrode of Comparative Example C1 taken with a scanning electron microscope from a direction perpendicular to the thickness direction of the electrode. Figure 10(e) is an image of the surface of the electrode of Comparative Example C1 taken with a scanning electron microscope from directly facing it.

The electrode of Comparative Example C3 was constructed by providing carbon nanowalls as an active material layer on the surface of a metal substrate with a flat surface similar to that of Comparative Example C1. The white folds in the image in Figure 10(d) and the white mesh-like streaks in the image in Figure 10(e) are carbon nanowalls. The carbon nanowalls were formed by CVD in a random mesh pattern across the entire surface of the metal substrate, with a nearly uniform height of approximately 1.0 μm.

2-4. Battery performance of Examples and Comparative Examples:
11 to 15, the results of evaluation tests on the battery performance of secondary batteries using the negative electrodes of Example E1 and Comparative Examples C1, C2, and C3 will be described.

Figure 11 shows a graph obtained for a secondary battery using the electrode of Example E1. Figures 12, 13, and 14 show graphs obtained for secondary batteries using the electrodes of Comparative Examples C1, C2, and C3, respectively. In Figures 11 to 14, the relationship between the voltage and charge capacity of the secondary battery is shown by a solid line during charging and by a dashed line during discharging.

Figure 15 shows the charge capacity and specific capacity of secondary batteries using Example E1 and Comparative Examples C2 and C3, respectively, as bar graphs. In this evaluation test, the charge current and discharge current were both 0.5 mA.

The secondary batteries used in Example E1 and Comparative Examples C1, C2, and C3 were lithium-ion secondary batteries and were fabricated with the configurations shown in Table 2 below.

As shown in Figures 11 and 15, the secondary battery using Example E1 had a charge capacity of 14.2 [mAh] and a specific capacity of 10.8 [mAh/cm ² ]. In contrast, as shown in Figure 12, the secondary battery using Comparative Example C1, which had an electrode composed only of a metal substrate with a flat surface as the negative electrode, was unable to charge or discharge. As shown in Figures 13 and 15, the secondary battery using Comparative Example C2, which had a graphite active material layer, had a charge capacity of 4.0 [mAh] and a specific capacity of 2.0 [mAh/cm ² ]. As shown in Figures 14 and 15, the secondary battery using Comparative Example C3, which had a carbon nanowall active material layer, had a charge capacity of 12.6 [mAh] and a specific capacity of 9.4 [mAh/cm ² ].

As such, the secondary battery 10 using the electrode 20 of Example E1 exhibited significantly improved battery performance compared not only with the secondary battery using the electrode of Comparative Example C1, which does not have an active material layer, but also with the secondary batteries using Comparative Examples C2 and C3, which have a carbon active material layer.

As described above, the electrodes for electricity storage devices according to the present invention can significantly improve the battery performance of electricity storage devices, including secondary batteries. Furthermore, the manufacturing method and manufacturing apparatus for electrodes for electricity storage devices according to the present invention can easily manufacture electrodes for electricity storage devices.

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

3-1. Other embodiment 1:
A secondary battery using the electrode 20 of the above embodiment may be configured so that metal ions other than lithium ions are involved in charging and discharging. For example, a secondary battery using the electrode 20 of the above embodiment may be configured so that sodium (Na) ions, potassium (K) ions, magnesium (Mg) ions, etc. are involved in charging and discharging.

3-2. Other embodiment 2:
In the electrode 20, the active material layer 22 may be formed on at least one of the first surface 21 a and the second surface 21 b of the metal substrate 21, and may be formed only on the first surface 21 a, for example. The electrode 20 may be applied to an electricity storage device other than a secondary battery. For example, the electrode 20 may be applied to a capacitor.

3-3. Other embodiment 3:
The plasma processing apparatus 50, 50a does not have to be configured to continuously produce multiple electrodes 20, but may be configured to produce electrodes 20 one by one. In this case, the plasma processing apparatus 50, 50a does not have to be configured to transport the strip-shaped substrate BM using the transport rollers 57. For example, the plasma processing apparatus 50, 50a may be configured to support the substrate BM of one metal substrate 21 by a support portion installed in the solution LQ. Even with such a configuration, it is possible to produce electrodes 20 for small-sized secondary batteries 10.

3-4. Other embodiment 4:
The configuration of the plasma processing apparatus that performs the plasma processing to form the active material layer 22 is not limited to the first or second configuration examples described in the above embodiment. The plasma processing apparatus may have, for example, a configuration in which multiple electrode holders 66a of the second configuration example are arranged in the transport direction MD of the substrate BM. Furthermore, the plasma processing apparatus may include a movement mechanism that holds a group of multiple plasma electrodes 65 movably in a direction intersecting the transport direction MD of the substrate BM.

3-5. Other embodiment 5:
The plasma treatment described in the above embodiment may be applied to a method for manufacturing an electric storage device other than a secondary battery. Furthermore, the plasma treatment is not limited to an electric storage device, and may be applied to a method for manufacturing various electrodes.

4. Example of form:
The present invention can be realized in the following aspects.

[First embodiment] The first embodiment is provided as an electrode for an electricity storage device. The electrode for an electricity storage device of the first embodiment comprises a metal substrate constituting a current collector and having a finely textured structure formed on its surface, and an active material layer mainly composed of a carbon nanostructure formed of nanographene and amorphous carbon, formed so as to densely cover the surface of the textured structure, and in which metal atoms involved in charging and discharging of the electricity storage device are precipitated on its surface when the electricity storage device is charged.
According to the first embodiment of the electrode for an electricity storage device, a carbon nanostructure composed of nanographene and amorphous carbon is used as the active material, thereby improving the battery performance of the electricity storage device. Furthermore, because the surface of the active material layer is formed unevenly, the surface area of the active material layer is increased, which increases the amount of metal deposited during charging of the electricity storage device and increases the charge capacity of the electricity storage device. Furthermore, the uneven structure of the active material layer forms numerous protrusions on the surface of the active material layer, which promotes metal deposition on the surface of the active material layer during charging of the electricity storage device. This further improves the battery performance of the electricity storage device. Additionally, because the active material layer is formed like a thin film that densely covers the surface of the metal substrate, it is less likely to be destroyed or detached during the manufacturing process of the electricity storage device, unlike carbon nanowalls that grow to extend from the surface of the metal substrate.

[Second embodiment] In the electrode for an electricity storage device of the first embodiment, a plurality of protrusions each having a width of 0.1 μm or more and 10.0 μm or less may be densely distributed on the surface of the active material layer when viewed in the thickness direction of the metal substrate.
According to the second embodiment of the electrode for an electricity storage device, the surface area of the active material layer can be further increased, and more protrusions can be formed on the surface of the active material layer, thereby further improving the battery performance of the electricity storage device.

[Third Aspect] In the third aspect of the electrode for an electricity storage device, the metal substrate may be made of copper or a copper alloy.
The electricity storage device electrode of the third aspect can achieve higher battery performance in an electricity storage device.

[Fourth Aspect] The fourth aspect is provided as a secondary battery. The secondary battery of the fourth aspect may include a container filled with an electrolyte, an electrically insulating and ionically conductive separator that divides the interior space of the container into a first electrode chamber and a second electrode chamber, a first electrode contained in the first electrode chamber and configured as the electricity storage device electrode according to any one of the above aspects, and a second electrode contained in the second electrode chamber and containing metal atoms that ionize and migrate to the first electrode during charging.
According to the secondary battery of the fourth aspect, the battery performance can be improved by using the electrode for an electricity storage device of the above aspect.

[Fifth Aspect] The fifth aspect is provided as a method for manufacturing an electrode for an electricity storage device. The manufacturing method of the fifth aspect includes the steps of: immersing a metal substrate base material constituting a current collector in an alcohol solution; generating plasma by applying a high-frequency voltage between a plasma electrode disposed above the solution and the base material in the solution while supplying a reactive gas for generating plasma onto the solution; and forming a fine uneven structure on the surface of the base material by the plasma, while forming an active material layer containing carbon nanostructures mainly composed of nanographene and amorphous carbon, the active material layer containing metal atoms involved in charging and discharging of the electricity storage device, so as to densely cover the surface of the uneven structure.
According to the fifth embodiment, the active material layer of carbon nanostructures can be formed while forming a textured structure on the surface of the metal substrate by plasma treatment, thereby enabling the easy and efficient production of an electrode for an electricity storage device that can improve the battery performance of the electricity storage device.

[Sixth Aspect] The manufacturing method of the sixth aspect may further comprise a step of moving the plasma electrode along the surface of the substrate in the solution to move the plasma irradiation area on the surface of the substrate.
According to the sixth embodiment of the manufacturing method, the plasma irradiation area where the active material layer is formed on the surface of the substrate can be moved, so that an electrode with a large area can be manufactured more efficiently.

[Seventh Aspect] The seventh aspect is provided as an apparatus for manufacturing an electrode for an electricity storage device. The manufacturing apparatus of the seventh aspect includes a reaction chamber storing an alcohol solution in which a metal substrate base material constituting a current collector is immersed, a plasma electrode disposed above the solution in the reaction chamber so as to face the surface of the base material immersed in the solution, a gas supply unit supplying a reactive gas for generating plasma to the region above the solution in the reaction chamber, and a plasma power supply unit applying a high-frequency voltage between the plasma electrode and the base material to generate the plasma. The plasma generated between the plasma electrode and the base material forms a fine uneven structure on the surface of the base material, and an active material layer is formed on the surface of the uneven structure, the active material layer mainly composed of carbon nanostructures formed of nanographene and amorphous carbon, and metal atoms involved in the charging and discharging of the electricity storage device are precipitated on the surface of the active material layer during charging of the electricity storage device.
According to the seventh embodiment, the manufacturing apparatus can form an active material layer of carbon nanostructures while forming a textured structure on the surface of a metal substrate by plasma treatment, thereby easily manufacturing an electrode for an electricity storage device that can improve the battery performance of the electricity storage device.

[Eighth Mode] The manufacturing apparatus of the seventh mode may further include a moving mechanism that moves the plasma electrode along the surface of the substrate in the solution.
According to the eighth embodiment of the manufacturing apparatus, the plasma electrode is moved by the moving mechanism, thereby moving the plasma irradiation area where the active material layer is formed on the surface of the substrate, thereby enabling electrodes with a large area to be manufactured more efficiently.

[Ninth Form] The manufacturing apparatus of the seventh or eighth form may have a plurality of the plasma electrodes arranged along the surface of the substrate, and may be configured to be able to simultaneously generate plasma between each of the plurality of plasma electrodes and the substrate.
According to the manufacturing apparatus of the ninth embodiment, a wide area on the surface of the substrate can be irradiated with plasma at once by using a plurality of plasma electrodes, and therefore electrodes with large electrode areas can be manufactured more efficiently.

10... Secondary battery, 11... Container, 12... Electrolyte, 15... Separator, 16... First electrode chamber, 17... Second electrode chamber, 20... First electrode, 21... Metal substrate, 21a... First surface, 21b... Second surface, 22... Active material layer, 23... Uneven structure, 24... Surface uneven structure, 24t... Convex portion, 25... Cavity, 30... Second electrode, 31... Positive electrode current collector, 31a... First surface, 31b... Second surface, 32... Positive electrode active material layer, 50, 50a... Plasma Plasma treatment device, 51...reaction chamber, 52...liquid supply unit, 53...liquid drainage unit, 55...substrate transport unit, 56...substrate supply unit, 57...transport roller, 58...recovery unit, 60...plasma generation unit, 61...gas supply unit, 62...exhaust unit, 65...plasma electrode, 66, 66a...electrode holder, 67...plasma power supply unit, BM...substrate, BMr...roll body, CP...particle, H...hydrogen atom, LQ...solution, MD...transport direction, RD...radical

Claims (5)

A method for manufacturing an electrode for an electricity storage device, comprising:
a step of immersing a base material of a metal substrate constituting a current collector in an alcohol solution;
generating plasma by applying a high frequency voltage between a plasma electrode disposed above the solution and the substrate in the solution while supplying a reactive gas for generating plasma onto the solution;
forming an active material layer, which is mainly composed of a carbon nanostructure composed of nanographene and amorphous carbon, and in which metal atoms involved in charging and discharging of the electricity storage device are deposited on the surface during charging of the electricity storage device, so as to densely cover the surface of the uneven structure while forming a fine uneven structure on the surface of the base material by the plasma;
A manufacturing method comprising: The manufacturing method according to claim 1,
The manufacturing method further comprises a step of moving the plasma electrode along the surface of the substrate in the solution to move a plasma irradiation area on the surface of the substrate. An apparatus for manufacturing an electrode for an electricity storage device, comprising:
a reaction chamber storing an alcohol solution in which the base material of the metal substrate constituting the current collector is immersed;
a plasma electrode disposed in a region above the solution in the reaction chamber so as to face a surface of the substrate immersed in the solution;
a gas supply unit that supplies a reactive gas for generating plasma to a region above the solution in the reaction chamber;
a plasma power supply unit that applies a high-frequency voltage between the plasma electrode and the substrate to generate the plasma;
Equipped with
The manufacturing apparatus is configured such that a fine uneven structure is formed on the surface of the substrate by plasma generated between the plasma electrode and the substrate, and an active material layer is formed so as to cover the surface of the uneven structure, the active material layer being composed primarily of a carbon nanostructure made of nanographene and amorphous carbon, and in which metal atoms involved in the charging and discharging of the energy storage device are precipitated on the surface when the energy storage device is charged. The manufacturing apparatus according to claim 3, further comprising:
The manufacturing apparatus includes a moving mechanism that moves the plasma electrode along the surface of the substrate in the solution. The manufacturing apparatus according to claim 3 or claim 4,
A manufacturing apparatus having a plurality of the plasma electrodes arranged along the surface of the substrate, and configured to be able to simultaneously generate plasma between each of the plurality of plasma electrodes and the substrate.