JP7751264B2 - Secondary battery, electrode for secondary battery, method for manufacturing secondary battery, and method for manufacturing electrode for secondary battery - Google Patents

Description

This application relates to a secondary battery, an electrode for a secondary battery, a method for manufacturing a secondary battery, and a method for manufacturing an electrode for a secondary battery.

Secondary batteries are known as one type of chargeable and dischargeable electricity storage device. Typically, the electrodes of secondary batteries have an active material layer formed on the surface of a current collector, which is composed of a substance involved in the battery reaction of the secondary battery. For example, in the lithium-ion secondary batteries disclosed in Patent Documents 1 and 2 listed below, an active material layer containing lithium (Li) is provided on the positive electrode, and an active material layer composed of carbon (C) is provided on the negative electrode.

Until now, in the technical field of secondary batteries, it has been common knowledge that the active material layer of the electrode has a significant impact on battery performance, and extensive research has been conducted into various active material layers to improve the performance of secondary batteries. As an example of the results of this research, it has been found that in lithium-ion secondary batteries, battery performance is improved when the negative electrode active material layer is made of carbon nanowalls, as in Patent Document 2, rather than when it is made of graphite, as in Patent Document 1.

Patent No. 2668678 JP 2010-9980 A

However, as mentioned above, even if an active material layer of carbon nanowalls is applied to a lithium-ion secondary battery, the battery performance still does not fully achieve the high battery performance required of secondary batteries. This is also true when a substance other than carbon nanowalls is used as the active material in secondary batteries other than lithium-ion secondary batteries.

Furthermore, depending on the type of active material layer, mass production of electrodes for secondary batteries may be difficult. For example, in the manufacturing process of lithium-ion secondary batteries, when electrodes having an active material layer of carbon nanowalls are rolled up for transportation or storage, the carbon nanowalls may be destroyed or fall off due to compressive stress or shear stress.

The above-mentioned issues are not limited to lithium-ion secondary batteries, but are common to various types of secondary batteries. The present application aims to provide an electrode for a secondary battery that can achieve high battery performance, has a simple configuration, and is easy to manufacture, as well as a secondary battery equipped with such an electrode.

Through extensive research into electrodes for electricity storage devices, the inventors of the present invention made a discovery that overturned conventional technical knowledge about the active material layer described above, and succeeded in developing an electrode for secondary batteries that has a simpler configuration than conventional ones, is easy to manufacture, and can dramatically improve battery performance. The present invention can be realized, for example, in the following forms:

One aspect of the present invention is provided as a secondary battery. This secondary battery comprises a container filled with an electrolyte solution, an electrically insulating and ionically conductive separator that divides the interior space of the container into a first electrode chamber and a second electrode chamber, a first electrode formed from a metal substrate and housed in the first electrode chamber, and a second electrode housed in the second electrode chamber and containing metal atoms that ionize and migrate to the first electrode. The metal substrate has a fine uneven structure on its outer surface, which is made up of metal particles and has a plurality of protrusions with a maximum width of 0.5 μm to 30.0 μm, and the metal atoms precipitate on the surfaces of the protrusions during charging.

The inventors of the present invention have discovered that if the first electrode is formed from a metal substrate having an uneven structure with protrusions of the above dimensions formed on its outer surface, the battery performance of the secondary battery can be improved compared to when an active material layer is present, even without an active material layer on the surface. This type of secondary battery has a novel configuration in which an active material layer is not provided on the first electrode, making it possible to improve charge capacity and battery performance. Furthermore, because this type of secondary battery does not require an active material layer to be provided on the first electrode, the manufacturing process for the secondary battery can be simplified accordingly.

The present invention can be realized in various forms other than secondary batteries. For example, the present invention can be realized in the form of electrodes for secondary batteries, methods for manufacturing secondary batteries, methods for manufacturing electrodes for secondary batteries, and manufacturing apparatuses for carrying out these manufacturing methods. The present invention can also be realized in the form of devices or systems powered by power from secondary batteries, power generation devices or power generation systems equipped with secondary batteries, etc.

FIG. 1 is a schematic diagram showing the configuration of a secondary battery. FIG. 2 is a schematic cross-sectional view showing a first example of a protrusion on a metal substrate. FIG. 10 is a schematic cross-sectional view showing a second example of a convex portion of a metal substrate. 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 surface treatment apparatus. FIG. 10 is an explanatory diagram showing a photographed image in the embodiment. FIG. 10 is an explanatory diagram showing a photographed image of a comparative example. FIG. 4 is an explanatory diagram showing the results of an evaluation test of the battery performance of the first embodiment. FIG. 10 is an explanatory diagram showing the results of an evaluation test of the battery performance of the second embodiment. 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 the secondary battery, electrode for the secondary battery, method for manufacturing a secondary battery, and method for manufacturing an electrode for a secondary battery according to the present invention will be described.

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

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

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 secondary battery of 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 is composed of a metal substrate 21.

In this embodiment, the metal substrate 21 is made of copper (Cu) metal foil. Cu makes it easy to form the uneven structure described below on the outer surface and improves the battery performance of the secondary battery 10. Cu is also easy to obtain and process. The metal substrate 21 may be made of a Cu alloy. Note that the metal substrate 21 does not have to be made of metal foil and may be made of, for example, a thin metal plate. The metal substrate 21 does not have to be made in a flat plate shape and may be bent into various shapes, such as a cylindrical or wavy shape.

The metal substrate 21 functions as a current collector for the electrode 20. In conventional secondary batteries, an active material layer composed of materials involved in charging and discharging is typically provided on the surface of the current collector. In contrast, no such active material layer is formed on the surface of the metal substrate 21 of this embodiment. Instead, a fine uneven structure 23 is formed on the outer surface of the metal substrate 21 of this embodiment. The uneven structure 23 is provided on both the first surface 21a and the second surface 21b of the metal substrate 21.

The uneven structure 23 includes a plurality of protrusions 24 having a maximum width Wmax of 0.5 μm or more and 30.0 μm or less. The protrusions 24 are portions that protrude in the thickness direction of the metal substrate 21. As will be described later, the protrusions 24 are composed of one or more metal particles. "Metal particles" refer to metal lumps having a particulate shape. These metal particles are composed of the same type of metal as the metal that composes the metal substrate 21. If the metal substrate 21 is composed of an alloy, the metal particles are composed of the same type of metal as the main metal of the alloy.

The maximum width Wmax of the protrusions 24 corresponds to the maximum width of the protrusions 24 in any direction, as measured in an image taken directly facing the surface of the metal substrate 21, for example, using a scanning electron microscope. The direction "facing the surface of the metal substrate 21" corresponds to the thickness direction of the metal substrate 21. "All directions" corresponds to all directions perpendicular to the thickness direction of the metal substrate 21. These definitions also apply to the following explanations.

The lower limit of the maximum width Wmax of the convex portions 24 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 portions 24 is preferably 28.0 μm or less, and more preferably 25.0 μm or less. In addition to convex portions 24 within the above-mentioned range of maximum width Wmax, the uneven structure 23 may also include convex portions having a width smaller than the lower limit of the above-mentioned range of maximum width Wmax.

As described above, no active material layer is formed on the metal substrate 21, and each convex portion 24 of the uneven structure 23 is directly immersed in the electrolyte solution 12 in the secondary battery 10 before charging. "Before charging" here refers to a state in which the secondary battery 10 has never been charged since manufacture. As will be described later, when the secondary battery 10 is charged, metal atoms (Li in this embodiment) that have ionized and migrated from the second electrode 30 are deposited on the surface of the convex portions 24 of the uneven structure 23.

Details of the structure of the convex portions 24 and the method for forming the uneven structure 23 on the metal substrate 21 will be described later.

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 containing Li atoms, a conductive additive, and a binder. The positive electrode active material layer 32 may also contain a thickener. Examples of the positive electrode active material include ternary materials such as lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LMO), and lithium nickel oxide (NCA). Examples of the conductive additive include acetylene black and carbon black. Examples of the binder include polyvinylidene fluoride (PVDF) and styrene butadiene rubber (SBR). Examples of the thickener include carboxymethyl cellulose (CMC).

With reference to Figures 2 and 3, an example of the structure of the convex portions 24 that make up the uneven structure 23 of the metal substrate 21 will be described. Figures 2 and 3 are schematic cross-sectional views that show a portion of the cross-sectional structure of the metal substrate 21 at an arbitrary cross section along the thickness direction.

Figures 2 and 3 each show examples of different shapes of the convex portion 24. Figure 2 shows a protrusion 24a as a first example of the convex portion 24. Figure 3 shows a first granular body 24b as a second example of the convex portion 24, and a second granular body 24c as a third example of the convex portion 24. The following describes the examples of the convex portion 24 in order.

See Figure 2. The protrusion 24a, which is a first example of the convex portion 24, is composed of a densely stacked collection of multiple minute metal particles 25 with a particle diameter Rp of 0.5 μm or more and 5.0 μm or less. The protrusion 24a has a structure in which multiple minute metal particles 25 are gathered in clusters, and an uneven structure in which the minute metal particles 25 are densely arranged is formed on the surface, giving it a structure that protrudes from the surrounding area as a whole.

In this specification, the term "particle" refers to tiny lumps of various shapes, and is not necessarily limited to roughly spherical shapes, but also includes irregular shapes with randomly uneven structures on the surface. Furthermore, in this specification, "particle diameter" refers to the maximum diameter of the particle in all directions, measured in multiple images taken directly facing the metal substrate 21 using, for example, a scanning electron microscope.

In the protrusions 24a, the maximum width Wmax of the convex portions 24 described above corresponds to the maximum distance between the ends of the multiple metal particles 25 that make up the protrusions 24a in a direction perpendicular to the thickness direction of the metal substrate 21. The lower limit of the particle diameter Rp of each metal particle 25 that makes up the protrusions 24a is preferably 0.6 μm or more, and more preferably 0.8 μm or more. The upper limit of the particle diameter Rp of the metal particles 25 is preferably 4.0 μm or less, and more preferably 3.0 μm or less.

The protrusions 24a have a height Hp of 1.0 μm or more and 15.0 μm or less. The height Hp of the protrusions 24a corresponds to the distance in the thickness direction of the metal substrate 21 between the bottom and top ends of the protrusions 24a, as measured, for example, in an image captured using a scanning electron microscope from a direction perpendicular to the thickness direction of the metal substrate 21. The lower limit of the height Hp of the protrusions 24a is preferably 2.0 μm or more, and more preferably 4.0 μm or more. The upper limit of the height Hp of the protrusions 24a may be 12.0 μm or less, or may be 10.0 μm or less.

See Figure 3. The first granular body 24b, which is a second embodiment of the convex portion 24, and the second granular body 24c, which is a third embodiment, have in common that they are composed of metal particles 25 recognized as individual particles, but they differ in size and shape. The first granular body 24a and the second granular body 24b differ in particular in their height. The height of the granular bodies 24b and 24c corresponds to the distance in the thickness direction of the metal substrate 21 between the bottom and top ends of the granular bodies 24b and 24c, measured, for example, in an image captured by a scanning electron microscope from a direction perpendicular to the thickness direction of the metal substrate 21.

The particle diameter Rq of the first granules 24b is 0.5 μm or more and 5.0 μm or less, and their height Hq is approximately equal to or less than the particle diameter Rq. For the first granules 24b, the particle diameter Rq corresponds to the maximum width Wmax of the convex portions 24. The lower limit of the particle diameter Rq of the first granules 24b is preferably 0.6 μm or more, and more preferably 0.8 μm or more. The upper limit of the particle diameter Rq of the first granules 24b may be 4.5 μm or less, or may be 4.0 μm or less.

The second granules 24c have a vertically elongated shape. The second granules 24c have a particle diameter Rr of 0.5 μm or more and 8.0 μm or less, and a height Hr greater than the particle diameter Rr. The particle diameter Rr of the second granules 24c corresponds to the maximum width Wmax of the convex portion 24. The lower limit of the particle diameter of the second granules 24c is preferably 0.6 μm or more, and more preferably 0.8 μm or more. The upper limit of the particle diameter of the second granules 24c may be 7.0 μm or less, or may be 5.0 μm or less.

The height Hr of the second granular body 24c may be, for example, 1.0 μm or more and 12.0 μm or less. The lower limit of the height Hr of the second granular body 24c may be 2.0 μm or more, or 3.0 μm or more. The upper limit of the height Hr of the second granular body 24c may be 10.0 μm or less, or 8.0 μm or less.

The uneven structure 23 may have, for example, a configuration in which protrusions 24a are densely arranged on the surface of the metal substrate 21. The uneven structure 23 may have a configuration in which first granules 24b and second granules 24c are arranged between the protrusions 24a. The uneven structure 23 may have a configuration in which the first granules 24b or the second granules 24c are distributed across the entire surface of the metal substrate 21. The uneven structure 23 may have a configuration in which the protrusions 24a and the second granules 24c are arranged between the first granules 24b arranged across the entire surface of the metal substrate 21. The uneven structure 23 may have a configuration in which the protrusions 24a, the first granules 24b, and the second granules 24c are mixed. The uneven structure 23 may have a configuration in which, in addition to the protrusions 24, particulate protrusions smaller than the first granules 24b and the second granules 24c are included.

The area of the projected region of the convex portions 24 including the protrusions 24a and the particles 24b, 24c projected in the thickness direction of the metal substrate 21 is greater than 0.01 ^μm2 and less than 10,000 ^μm2 . Furthermore, the density of the projected region of the convex portions 24 when projected in the thickness direction of the metal substrate 21 is greater than 1/ ^mm2 and less than ¹⁰⁸ / ^mm2 . Convex portions 24 with such dimensions can be easily formed by surface treatment using electrolytic deposition on the base material of the metal substrate 21.

1-2. Battery reaction in secondary batteries:
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)

In contrast, the reaction formula at the negative electrode 20 is expressed by the following formula (2): As shown in formula (2), when the secondary battery 10 is charged, Li is deposited on the surface of the protrusions 24 of the electrode 20.
Li ⁺ + e ^- ⇔ Li...(2)

As shown in equation (2) above, the secondary battery 10 of this embodiment is theoretically capable of being charged as long as Li can be precipitated on the electrode 20, and a high charge capacity can be obtained.

The inventors of the present invention have discovered that when an uneven structure 23 having protrusions 24 of the above-mentioned dimensions is formed on the outer surface of the metal substrate 21 that constitutes the electrode 20, the deposition of Li on the surface of the metal substrate 21 is promoted. According to considerations based on nucleation theory, the reason for this promotion of Li deposition is believed to be that the protrusions 24 of the uneven structure 23 act as starting points for Li deposition.

As such, according to the secondary battery 10 of this embodiment, even though the electrode 20 does not have an active material layer, the presence of the convex portions 24 of the uneven structure 23 of the metal substrate 21 promotes Li deposition on the surface of the metal substrate 21, thereby improving battery performance such as charge capacity and specific capacity. Furthermore, according to the secondary battery 10 of this embodiment, the active material layer on the surface of the electrode 20 can be omitted, thereby simplifying the configuration of the secondary battery 10 and reducing the amount of material used in manufacturing the secondary battery 10.

In addition, according to the secondary battery 10 of this embodiment, the convex portions 24 of the uneven structure 23 are uniformly distributed on the surface of the metal substrate 21, allowing Li to be uniformly deposited on the surface of the metal substrate 21. This prevents dendrites from being generated in the electrode 20, and prevents damage and deterioration of the secondary battery 10 due to dendrites.

Here, for example, in the manufacturing process of conventional secondary batteries having an active material layer of carbon nanowalls, when an 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, even if the electrode is rolled up and transported or stored in the manufacturing process of the secondary battery 10, problems such as deterioration or fall-off of the active material layer do not occur. Therefore, the electrode 20 of this embodiment is easy to handle, facilitating mass production of the electrode 20.

1-3. Secondary battery manufacturing method:
4 is a process flow diagram showing the manufacturing process of the secondary battery 10. Processes P1 and P2 are processes for manufacturing the electrode 20.

In process P1, a base material BM of the metal substrate 21 is prepared. The base material BM is, for example, a metal foil or a thin metal plate, and has a flat surface. In this embodiment, the base material BM is copper foil. In process P2, the base material BM is subjected to surface treatment by electrolytic deposition, thereby forming the above-mentioned uneven structure 23 on both sides.

Figure 5 is a schematic diagram showing the configuration of the surface treatment device 50 used in process P2. The surface treatment device 50 includes, as a transport section for the substrate BM, a feed roller 51 around which the substrate BM before treatment is wound, multiple guide rollers 52 that guide the transport of the substrate BM, and a take-up roller 53 that winds up the substrate BM after surface treatment. The surface treatment device 50 also includes, as a section for performing electrolytic deposition, an electrolytic bath 55 filled with electrolyte 56 and an electrode plate 58 installed in the electrolytic bath 55. Although not shown, the surface treatment device 50 also includes a power supply section that applies electricity to the electrode plate 58 and the substrate BM.

The substrate BM is unwound from a feed roller 51 and guided by multiple guide rollers 52 before being transported to a take-up roller 53. One of the guide rollers 52 is installed inside the electrolytic bath 55. This transports the substrate BM into the electrolytic bath 55, where it is immersed in the electrolyte 56 inside the electrolytic bath 55, then turns around inside the electrolytic bath 55 and transported out of the electrolytic bath 55. While the substrate BM passes through the electrolyte 56 in the electrolytic bath 55, the surface of the substrate BM is subjected to a surface treatment by electrolytic deposition, as described below.

The electrolytic solution 56 in the electrolytic bath 55 is a solution capable of dissolving metal atoms of the same type as the metal constituting the base material BM, and may be, for example, sulfuric acid (H ₂ SO ₄ ). The electrolytic solution 56 may have a concentration of, for example, about 0.5 to 2.0 M (volume molar concentration mol/L).

The electrode plate 58 in the electrolytic bath 55 contains metal atoms of the same type as the metal that constitutes the substrate BM. In this embodiment, the electrode plate 58 is made of blister copper. The electrode plate 58 is installed so that it faces the surface of the substrate BM as it is transported through the electrolytic bath 55. The electrode plate 58 is preferably installed approximately parallel to the surface of the substrate BM. The distance between the electrode plate 58 and the substrate BM may be, for example, approximately 2.0 to 6.0 cm.

During transport of the substrate BM, a voltage is applied from the power supply unit to the electrode plate 58 as the anode and the substrate BM as the cathode, causing a current to flow. The applied voltage may be, for example, about 0.5 to 2.0 V. The current may be, for example, about 80.0 to 200.0 mA, and the current density may be about 15.0 to 30.0 mA/ ^cm² . The ambient temperature may be room temperature or may be within a range of 10 to 30°C. The treatment conditions in the surface treatment device 50, such as the type and concentration of the electrolytic solution 56, the applied voltage, and the transport speed of the substrate BM, are appropriately adjusted so that convex portions 24 of the above-mentioned size are formed.

During electrolytic deposition in the surface treatment device 50, Cu on the electrode plate 58 is oxidized and dissolved into the electrolyte 56 as Cu ions, which then migrate toward the substrate BM and are reduced and precipitated on the surface of the substrate BM. The precipitated Cu particles form protrusions 24 one after another on the substrate BM surface. The protrusions 24 are formed so as to be distributed across the entire surface of the substrate BM.

The surface treatment device 50 may be configured such that multiple guide rollers 52 are arranged in one electrolytic bath 55, thereby allowing the substrate BM to be repeatedly immersed in the electrolytic solution 56 for one electrolytic bath 55 multiple times. Alternatively, the surface treatment device 50 may have a multi-stage configuration with multiple electrolytic baths 55, each with a guide roller 52 arranged in it, and the substrate BM transported so as to be repeatedly immersed in the electrolytic solution 56 of each electrolytic bath 55. In this case, too, the treatment conditions, such as the type and concentration of the electrolytic solution 56 in each electrolytic bath 55, the energization voltage, and the transport speed of the substrate BM, are adjusted appropriately so that protrusions 24 of the above-mentioned size are formed.

The surface treatment in process P2 is preferably performed on both sides of the substrate BM. In the surface treatment device 50, the take-up roller 53 on which the substrate BM, which has been surface-treated on one side, is wound is replaced as the feed roller 51, and the substrate BM is transported again into the electrolytic bath 55, whereby the surface treatment is performed on the other side. This completes the production of a metal substrate 21 having a fine uneven structure 23 on both sides.

See Figure 4. In the following process P3, the second electrode 30, which will serve as the positive electrode, is manufactured. In process P4, as shown in Figure 1, the first electrode 20 and the second electrode 30 are assembled into a container 11 filled with electrolyte 12. The metal substrate 21 that constitutes the first electrode 20 is housed in the container 11 with the convex portions 24 of the uneven structure 23 directly immersed in the electrolyte 12. Through these processes, the secondary battery 10 is completed.

As described above, the manufacturing process for the secondary battery 10 of this embodiment allows for efficient production of a metal substrate 21 having a concave-convex structure 23 on both sides through surface treatment by electrolytic deposition. Furthermore, because it is not necessary to provide an active material layer on the metal substrate 21, the number of steps can be reduced accordingly, enabling lower manufacturing costs for the secondary battery 10.

As described above, the electrode 20 prepared in steps P1 and P2 is easy to handle, even when rolled up and transported, because the active material layer is not damaged or removed. This improves the mass productivity of the electrode 20 and facilitates the manufacture of secondary batteries 10 using the electrode 20.

Referring to Figures 6 and 7, examples E1 and E2 of the electrode 20 of this embodiment and comparative examples C1, C2, and C3 will be described.

Figures 6 (a) and (b) each show photographed images of the uneven structure 23 of the metal substrate 21 of Example E1. Figures 6 (c) and (d) each show photographed images of the surface of the uneven structure 23 of Example E2. Figures 6 (a) and 6 (c) are images taken with a scanning electron microscope of the convex portions 24 when viewed from a direction perpendicular to the thickness direction of the metal substrate 21. Figures 6 (b) and 6 (d) are images taken with a scanning electron microscope of the surface of the metal substrate 21 in the thickness direction of the metal substrate 21. The images of Figures 6 (b) and 6 (d) correspond to images of the projected area obtained by projecting the convex portions 24 in the thickness direction of the metal substrate 21.

The metal substrate 21 of Examples E1 and E2 was prepared by using copper foil as the substrate and performing the above-described electrolytic deposition surface treatment. In Example E2, a 1.5 M _H2SO4 solution was used as the electrolyte, and a DC voltage of 1.0 _V was applied to the substrate in the electrolyte, allowing a current of 128 mA to flow. The distance between the substrate and the electrode was 3.5 cm. This electrolytic deposition was performed in a room temperature environment. The transport speed of the substrate in the electrolyte was appropriately adjusted according to the target dimensions of the convex portion 24 based on the results of a previous experiment.

As shown in Figures 6 (a) and (b), the uneven structure 23 of Example E1 had, as the convex portions 24, a plurality of protrusions 24a formed by densely packed metal particles 25. In Example E1, the plurality of protrusions 24a were distributed adjacent to one another across the entire surface of the metal substrate 21. The maximum width Wmax of each protrusion 24a was generally within the range of 1.0 to 30.0 μm. The height Hp of each protrusion 24a was generally within the range of 1.0 to 15.0 μm. The particle diameter Rp of the metal particles 25 constituting the protrusions 24a was generally within the range of 0.5 to 5.0 μm.

6 (c) and (d), the uneven structure 23 of Example E2 had first granular bodies 24b and second granular bodies 24c as the convex portions 24. In Example E2, the second granular bodies 24c were mixed in with the first granular bodies 24b distributed over the entire surface of the metal substrate 21.

The particle diameter Rq of the first granules 24b was generally within the range of 0.5 to 5.0 μm. The height Hq of the first granules 24b was generally within the range of 0.1 to 5.0 μm.

The particle diameter Rr of the second granules 24c was generally within the range of 0.5 to 8.0 μm. Furthermore, the height Hr of the second granules 24c was generally within the range of 1.0 to 15.0 μm. Many of the second granules 24c had a vertically elongated oval spherical shape.

In both Examples E1 and E2, the area of the projected region of the protrusions 24 projected in the thickness direction of the metal substrate 21 was within the range of more than 0.01 μm ² and not more than 10,000 μm ^2. Furthermore, the density of the projected region of the protrusions 24 when projected in the thickness direction of the metal substrate 21 was within the range of 1 piece/mm ² or more and less than 10 ⁸ pieces/mm ² .

Figures 7(a) and (b) each show photographed images of the surface of the metal substrate constituting the electrode of Comparative Example C1. Figure 7(a) is an image taken directly facing the surface of the metal substrate of Comparative Example C1 using a scanning electron microscope. Figure 7(b) is an image taken at a higher magnification than the image of Figure 7(a).

The electrode of Comparative Example C1, like Examples E1 and E2, did not have an active material layer and was composed of a metal substrate that constituted a current collector. The metal substrate of Comparative Example C1 had almost the same configuration as the metal substrates of Examples E1 and E2, except that it was not subjected to surface treatment by electrolytic deposition as in Examples E1 and E2. As shown in the images in Figures 7(a) and (b), the metal substrate of Comparative Example C1 had a flat surface with almost no irregularities.

Figure 7(c) shows an image of the electrode of Comparative Example C2. Figure 7(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 7(c) shows the graphite particles that make up the active material layer.

Figures 7(d) and (e) show images of the electrode of Comparative Example C3. Figure 7(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 7(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 7(d) and the white mesh-like streaks in the image in Figure 7(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.

Figures 8 to 13 are explanatory diagrams showing the results of evaluation tests of the battery performance of secondary batteries using the electrodes of Examples E1 and E2 and Comparative Examples C1, C2, and C3 as the negative electrodes. Figures 8 and 9 show graphs obtained for secondary batteries using the electrodes of Examples E1 and E2, respectively. Figures 10, 11, and 12 show graphs obtained for secondary batteries using the electrodes of Comparative Examples C1, C2, and C3, respectively. In Figures 8 to 12, the relationship between the voltage and charge capacity of the secondary battery is shown as a solid line during charging and as a dashed-dotted line during discharging. Figure 13 shows the charge capacity and specific capacity of secondary batteries using Example E1 and Comparative Examples C2 and C3, respectively, as bar graphs. In these evaluation tests, the charge current and discharge current were both 0.5 mA.

The secondary batteries used in Examples E1 and E2 and Comparative Examples C1, C2, and C3 were lithium-ion secondary batteries, and were fabricated with the configurations shown in Table 1 below.

As shown in Figure 10, a secondary battery using an electrode composed only of a metal substrate with a flat surface (Comparative Example C1) as the negative electrode was unable to charge or discharge. This result shows that a metal substrate without an uneven structure on its outer surface does not function as an electrode for a secondary battery.

11 and 13, the secondary battery using Comparative Example C2 with a graphite active material layer had a charge capacity of 4.0 mAh and a specific capacity of 2.0 mAh/ ^cm2 . Also, as shown in Figures 12 and 13, the secondary battery using Comparative Example C3 with a uniformly thick carbon nanowall active material layer had a charge capacity of 12.6 mAh and a specific capacity of 9.4 mAh/ ^cm2 .

The results of Comparative Examples C1, C2, and C3 show that providing an active material layer on a flat metal substrate allows it to function as an electrode in a secondary battery. It also shows that using carbon nanowalls in the negative electrode active material layer can significantly improve the battery performance of a secondary battery compared to using graphite in the active material layer.

However, as shown in Figures 8 and 9, the charge capacity of both the secondary batteries using Examples E1 and E2 was approximately 14.0 [mAh]. Also, as shown in Figure 13, the secondary battery using Example E1 had a specific capacity of 10.5 [mAh/ ^cm2 ]. Although not shown in Figure 13, the secondary battery using Example E2 also achieved a similar specific capacity.

As such, in both Examples E1 and E2, the battery performance was clearly significantly improved compared to the secondary batteries using Comparative Examples C2 and C3, which had an active material layer. This result is thought to be due to the fact that the convex portions 24 of the uneven structure 23 formed on the metal substrate 21 of Examples E1 and E2 were able to promote Li deposition more effectively than the active material layer. This result overturns the conventional wisdom that an active material layer is necessary for electrodes in secondary batteries. Furthermore, the fact that battery performance is actually improved without an active material layer is a new discovery that would not be easily arrived at based on conventional technical common sense.

As described above, the secondary battery electrode according to the present invention and the secondary battery using the same can significantly improve the battery performance of the secondary battery. Furthermore, the secondary battery electrode according to the present invention has a simple configuration that does not include an active material layer, which facilitates the manufacture of the secondary battery electrode and the secondary battery.

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

2-1. Other embodiment 1:
The metal substrate 21 in the above embodiment may be made of a metal other than Cu, for example, a Cu alloy, Al, or an Al alloy.

2-2. Other embodiment 2:
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.

2-3. Other embodiment 3:
The convex portions 24 of the uneven structure 23 may have a structure different from the protrusions 24a and the granular bodies 24b and 24c. The convex portions 24 of the uneven structure 23 may be configured in, for example, a substantially semicircular shape or a substantially conical shape.

2-4. Other embodiment 4:
In the manufacturing method of the secondary battery 10 described in the above embodiment, in step P2, the uneven structure 23 may be formed on the base material BM of the metal substrate 21 by a method other than electrolytic deposition. The uneven structure 23 of the metal substrate 21 may be formed, for example, by a surface treatment using a CVD method or an oxidation treatment of the metal substrate.

3. Example of form:
The present invention can be realized in the following forms.

[First Aspect] The first aspect is provided as a secondary battery. The secondary battery of the first aspect includes a container filled with an electrolyte solution, an electrically insulating and ionically conductive separator that divides the interior space of the container into a first electrode chamber and a second electrode chamber, a first electrode formed of a metal substrate and housed in the first electrode chamber, and a second electrode housed in the second electrode chamber and containing metal atoms that ionize and migrate to the first electrode. The metal substrate has a fine uneven structure on its outer surface that is composed of a plurality of protrusions made of metal particles and having a maximum width of 0.5 μm to 30.0 μm, and the metal atoms precipitate on the surfaces of the protrusions during charging.
The secondary battery of the first aspect has a novel and simple configuration in which a metal substrate is provided with a concave-convex structure including protrusions made of metal particles, and the first electrode does not have an active material layer, thereby improving charge capacity and battery performance. Furthermore, since the secondary battery of the first aspect does not require an active material layer to be provided on the first electrode, the manufacturing process of the secondary battery can be simplified and the manufacturing cost of the secondary battery can be reduced.

[Second embodiment] In the secondary battery of the first embodiment, the convex portion may include a protrusion formed by a plurality of metal particles having a particle diameter of 0.5 μm or more and 5.0 μm or less, densely packed together.
According to the secondary battery of the second embodiment, the convex portions can be easily formed by protrusions formed by densely gathering fine metal particles, and the battery performance can be further improved.

[Third Mode] In the secondary battery of the second mode, the protrusion may have a height of 1.0 μm or more and 15.0 μm or less.
According to the secondary battery of the third embodiment, the protrusions can further promote the deposition of metal atoms involved in the battery reaction on the first electrode, thereby further improving the battery performance.

[Fourth form] In the secondary battery described in any one of the first, second, and third forms, the convex portion may include elongated granular bodies having a particle diameter of 0.5 μm or more and 5.0 μm or less and a height greater than the particle diameter.
According to the secondary battery of the fourth embodiment, the presence of granular materials that form the convex portions makes it possible to further improve the battery performance.

[Fifth Mode] In the secondary battery according to any one of the first, second, third, and fourth modes, the area of the projected region of the convex portion projected in the thickness direction of the metal substrate may be greater than 0.01 ^μm2 and less than 10,000 ^μm2 , and the density of the projected region of the convex portion when projected in the thickness direction of the metal substrate may be greater than 1/ ^mm2 and less than ¹⁰⁸ / ^mm2 .
According to the secondary battery of the fifth embodiment, a large number of protrusions can be formed on the electrode surface, thereby further improving the battery performance.

[Sixth aspect] In the secondary battery according to any one of the first, second, third, fourth, and fifth aspects, the metal substrate may be made of copper or a copper alloy.
According to the secondary battery of the sixth embodiment, it is easy to form an uneven structure on the outer surface of the metal substrate, and the battery performance can be easily improved.

[Seventh Aspect] The seventh aspect is provided as a metal substrate used as an electrode of a secondary battery. The metal substrate of the seventh aspect has a fine uneven structure formed by a plurality of protrusions formed of metal particles and having a maximum width of 0.5 μm to 30.0 μm, and is housed in a container of the secondary battery filled with an electrolyte solution, with the protrusions directly immersed in the electrolyte solution.
The metal substrate of the seventh embodiment can be used as an electrode for a secondary battery having no active material layer on its outer surface, and can realize high battery performance in the secondary battery.

[Eighth Aspect] The eighth aspect is provided as a method for manufacturing a secondary battery, which includes the steps of: forming a fine uneven structure on the surface of a metal substrate, the fine uneven structure including a plurality of protrusions formed of metal particles and having a maximum width of 0.5 μm to 30.0 μm; and assembling the metal substrate as an electrode of the secondary battery in a container filled with an electrolyte solution and immersing the protrusions in the electrolyte solution.
According to the manufacturing method of the eighth embodiment, a secondary battery having high battery performance can be obtained by a simple manufacturing process that does not include a step of providing an active material layer on the outer surface of a metal substrate.

[9th form] In the manufacturing method of the 8th form, the step of forming the uneven structure may include a step of forming the convex portions by precipitating metal particles on the outer surface of the metal substrate by electrolytic deposition.
According to the manufacturing method of the ninth embodiment, it is possible to easily form a concave-convex structure that contributes to the charging and discharging of the secondary battery on both sides of the metal substrate, and therefore it is possible to more easily manufacture a secondary battery with high battery performance.

[Tenth Form] The tenth form is a method for manufacturing an electrode for a secondary battery, comprising the steps of: preparing a base material for a metal substrate that constitutes the electrode; and immersing the base material in an electrolyte in an electrolytic bath and forming, by electrolytic deposition, a fine uneven structure on the base material, the fine uneven structure being composed of metal particles and including a plurality of convex portions each having a maximum width of 0.5 μm or more and 30.0 μm or less. The metal substrate is accommodated in a container for the secondary battery in a state in which the convex portions are directly immersed in the electrolyte.
According to the manufacturing method of the tenth embodiment, it is possible to easily form an uneven structure on the outer surface of the metal substrate, which contributes to the charging and discharging of the secondary battery.

REFERENCE SIGNS LIST 10... secondary battery, 11... container, 12... electrolyte, 15... separator, 16... first electrode chamber, 17... second electrode chamber, 20... electrode (first electrode), 21... metal substrate, 21a... first surface, 21b... second surface, 23... uneven structure, 24... convex portion, 24a... protrusion, 24b... first granular body, 24c... second granular body, 25... metal particle, 30... second electrode, 31... positive electrode current collector, 32... positive electrode active material layer, 50... surface treatment device, 51... feed roller, 52... guide roller, 53... winding roller, 55... electrolytic bath, 56... electrolyte, 58... electrode plate, BM... substrate

Claims (15)

A secondary battery,
a container filled with an electrolyte;
a separator having electrical insulation and ion conductivity, which divides the internal space of the container into a first electrode chamber and a second electrode chamber;
a first electrode made of a metal substrate and accommodated in the first electrode chamber;
a second electrode accommodated in the second electrode chamber and including metal atoms that are ionized and move to the first electrode;
Equipped with
the metal substrate has, on its outer surface, a fine uneven structure formed of a plurality of protrusions made of metal particles and having a maximum width of 0.5 μm or more and 30.0 μm or less;
The metal atoms are deposited on the surfaces of the protrusions during charging. 2. The secondary battery according to claim 1,
The metal substrate is made of copper or a copper alloy, and the metal particles are copper. 2. The secondary battery according to claim 1,
The uneven structure is
A first configuration in which the protrusions, each of which is made up of a cluster of metal particles, are densely distributed adjacent to one another; or
a second structure in which the convex portions constituted by first granular bodies whose height is equal to or smaller than the particle diameter and the convex portions constituted by elongated second granular bodies whose height is greater than the particle diameter are mixed and densely distributed;
A secondary battery having either one of the above. 4. The secondary battery according to claim 3,
the concave-convex structure has the first configuration,
The secondary battery, wherein the protrusions are configured by a plurality of metal particles having a particle diameter of 0.5 μm or more and 5.0 μm or less densely gathered together. 5. The secondary battery according to claim 4,
The secondary battery, wherein the protrusion has a height of 1.0 μm or more and 15.0 μm or less. 4. The secondary battery according to claim 3,
the concave-convex structure has the second configuration,
The first granular material has a particle diameter of 0.5 μm or more and 5.0 μm or less, and the second granular material has a particle diameter of 0.5 μm or more and 8.0 μm or less. The secondary battery according to any one of claims 1 to 6,
The area of a projected region obtained by projecting the convex portion in the thickness direction of the metal substrate is
greater than 0.01 μm ² and less than or equal to 10,000 μm ² ;
The density of the projected area of the convex portion when the metal substrate is projected in the thickness direction is
A secondary battery having a density of 1 particle/ ^mm2 or more and less than ¹⁰⁸ particles/ ^mm2 . A metal substrate used as the first electrode of the secondary battery according to any one of claims 1 to 6 ,
The fine uneven structure is formed on the outer surface by a plurality of the protrusions ,
The metal substrate is accommodated in the container of the secondary battery with the protrusions directly immersed in the electrolyte. The metal substrate according to claim 8,
A metal substrate made of copper or a copper alloy, wherein the metal particles are copper. The metal substrate according to claim 8,
The uneven structure is
A first configuration in which the protrusions, each of which is made up of a cluster of metal particles, are densely distributed adjacent to one another; or
a second structure in which the convex portions constituted by first granular bodies whose height is smaller than the particle diameter and the convex portions constituted by second granular bodies whose height is larger than the particle diameter are mixed and densely distributed;
A metal substrate having either one of the following: A method for manufacturing a secondary battery,
forming a fine uneven structure on the outer surface of a metal substrate, the fine uneven structure including a plurality of protrusions, each protrusion being made of metal particles and having a maximum width of 0.5 μm or more and 30.0 μm or less;
a step of assembling the metal substrate as an electrode of the secondary battery in a container filled with an electrolyte solution and immersing the convex portion in the electrolyte solution;
A manufacturing method comprising: The method of claim 11,
The manufacturing method, wherein the step of forming the uneven structure includes a step of forming the convex portions by depositing metal particles on the outer surface of the metal substrate by electrolytic deposition. A method for manufacturing an electrode for a secondary battery, comprising:
preparing a base material for a metal substrate that constitutes the electrode;
a step of immersing the substrate in an electrolytic solution in an electrolytic bath and forming, by electrolytic deposition, a fine uneven structure on the substrate, the fine uneven structure including a plurality of protrusions, each of which is made of metal particles and has a maximum width of 0.5 μm or more and 30.0 μm or less, arranged thereon;
Equipped with
The metal substrate is accommodated in a container of the secondary battery with the protrusions directly immersed in the electrolyte. The manufacturing method according to any one of claims 11 to 13,
The manufacturing method, wherein the metal substrate is made of copper or a copper alloy, and the metal particles are copper. 14. A method for producing a semiconductor device according to any one of claims 11 to 13, comprising:
The uneven structure is
A first configuration in which the protrusions, each of which is made up of a cluster of metal particles, are densely distributed adjacent to one another; or
a second structure in which the convex portions constituted by first granular bodies whose height is smaller than the particle diameter and the convex portions constituted by second granular bodies whose height is larger than the particle diameter are mixed and densely distributed;
A manufacturing method comprising either one of the following: