Energy storage device and method for manufacturing an energy storage device

Abstract

To more improve an energy density per unit volume while securing a capacitance in a power storage device having a columnar electrode.SOLUTION: A power storage device comprises: an arrangement body in which a columnar electrode containing an electrode active material, a separation membrane that is formed on an outer peripheral side of the columnar electrode and has insulation property and ion conduction, and a columnar electrode formed on the outer peripheral side of the separation membrane and including an opposite electrode containing an opposite active material are arranged in a predetermined direction; and a conductive part that is in contact with an arrangement surface along an arrangement direction of the arrangement body, and has a lamination body containing a structure in which a plurality of two-lamination bodies into which the conductive part is sandwiched between two arrangement bodies is laminated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses an energy storage device and a method for manufacturing the energy storage device. [Background technology]

[0002] Conventionally, as a secondary battery with high energy density, which is an energy storage device, a structure has been proposed that comprises a plurality of columnar electrodes, a separation membrane provided so as to surround each columnar electrode, and a positive electrode provided so as to fill the space between adjacent separation membranes (see, for example, Patent Document 1). This secondary battery has a structure in which columnar electrodes surrounded by separation membranes are arranged within the positive electrode. Furthermore, as an energy storage device, a structure has been proposed that comprises a fibrous first electrode containing an active material, a second electrode containing an active material located between a plurality of fibrous first electrodes, and a separation membrane that has ion conductivity, covers the first electrode, and insulates the first electrode from the second electrode, wherein the plurality of fibrous first electrodes are arranged in a predetermined direction, and the ratio D / L of the diameter D of the first electrode to the thickness L of the separation membrane is 3.3 or more (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-152229 [Patent Document 2] Japanese Patent Publication No. 2019-160733 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in energy storage devices equipped with columnar electrodes, such as those described in Patent Documents 1 and 2, current collection at the counter electrode was sometimes insufficient, preventing them from fully realizing their theoretical capacity. Furthermore, adding a current collector to the energy storage device sometimes reduced the energy density per unit volume. Thus, there was a need to improve the energy density per unit volume while ensuring an appropriate capacity in energy storage devices equipped with columnar electrodes.

[0005] This disclosure has been made in view of these challenges, and its main objective is to provide an energy storage device equipped with columnar electrodes that can improve the energy density per unit volume while ensuring capacity, and a method for manufacturing the energy storage device. [Means for solving the problem]

[0006] Through diligent research to achieve the above-mentioned objectives, the inventors discovered that by arranging conductive parts at appropriate intervals between arrays of columnar batteries, it is possible to further improve the energy density per unit volume while ensuring the capacity of the energy storage device, and thus completed the invention disclosed herein.

[0007] In other words, the energy storage device disclosed herein is An array of columnar battery bodies arranged in a predetermined direction, each comprising a columnar electrode containing an electrode active material, a separation membrane formed on the outer circumference of the columnar electrode having insulating and ion conductive properties, and a counter electrode formed on the outer circumference of the separation membrane containing a counter electrode active material. The array comprises a conductive portion that contacts the array surface along the array direction, The laminate has a structure in which multiple two-layer bodies are stacked, each in which the conductive portion is sandwiched between two of the aforementioned array bodies.

[0008] The method for manufacturing the energy storage device disclosed herein is: a two-layer body step of obtaining a two-layer body, the two-layer body comprising: an array body in which columnar battery bodies are arranged in a predetermined direction, the columnar battery bodies each including a columnar electrode containing an electrode active material, a separation membrane formed on an outer peripheral side of the columnar electrode and having insulating properties and ion conductivity, and a counter electrode formed on an outer peripheral side of the separation membrane and containing a counter electrode active material; and a conductive part in contact with one array surface along the arrangement direction of the array bodies, wherein the conductive part is sandwiched between the two array bodies; a laminating step of obtaining a laminate comprising a structure in which a plurality of the two-layer bodies are laminated; which comprises the above steps. [Advantageous Effects of Invention]

[0009] The present disclosure can further improve the energy density per unit volume while securing capacity in an electricity storage device having columnar electrodes. The reason why such an effect is obtained is presumed as follows. For example, this electricity storage device has a structure in which a plurality of two-layer bodies are laminated, each two-layer body having the conductive part sandwiched between two array bodies obtained by arranging the columnar battery bodies in the predetermined direction. In this electricity storage device, by providing the conductive part only on one array surface of each array body, the current collection of the counter electrodes is improved to secure capacity, and by further suppressing arrangement of excessive conductive parts, the energy density can be further improved. [Brief Description of Drawings]

[0010] [Figure 1] An explanatory diagram showing an example of an electricity storage device 10. [Figure 2] An explanatory diagram showing an example of another electricity storage device 10B. [Figure 3] An explanatory diagram showing an example of other conductive parts 21B, 21C, 21D. [Figure 4] An explanatory diagram showing an example of a method for manufacturing the electricity storage devices 10 and 10B. [Figure 5] Schematic diagrams showing laminates of Experimental Examples 1 to 4. [Figure 6] A graph showing the relationship between discharge capacity and discharge current for Experimental Examples 1 to 4. [Mode for Carrying Out the Invention]

[0011] (Energy storage device) The energy storage device of the present disclosure, as described in the embodiments, comprises a plurality of columnar electrodes, a separator membrane, a counter electrode, and a conductive part. This energy storage device may include an electrode current collector electrically connected to the columnar electrodes, or a counter electrode current collector electrically connected to the counter electrode and the conductive part. This energy storage device may be, for example, an electric double-layer capacitor, a hybrid capacitor, a pseudo-electric double-layer capacitor, an alkali metal secondary battery, or an alkali metal ion battery. The carrier ions of the energy storage device include alkali metal ions such as lithium ions, sodium ions, and potassium ions, and group 2 ions such as magnesium ions, strontium ions, and calcium ions. The counter electrode may be located around the columnar electrodes or may be filled in the space between the columnar electrodes. Furthermore, this energy storage device may have a structure in which a plurality of columnar electrodes are bound together adjacent to the counter electrode via a separator membrane. In addition, this energy storage device may contain an electrolyte in one or more of the columnar electrodes, counter electrode, and separator membrane. The columnar electrode may have a current-collecting component, such as a current-collecting wire, embedded in it, or it may not have such a component. Furthermore, the columnar electrode may be the positive electrode or the negative electrode depending on the potential relationship with the counter electrode, but it is preferable to make it the negative electrode. The same applies to the counter electrode; it may be the positive electrode or the negative electrode, but it is preferable to make it the positive electrode. For the sake of explanation, a lithium-ion secondary battery in which the columnar electrode is the negative electrode, the counter electrode is the positive electrode, and lithium ions are used as carriers will be described below as the main example.

[0012] Here, the energy storage device disclosed in this embodiment will be described with reference to the drawings. Figure 1 is an explanatory diagram showing an example of an energy storage device 10. Figure 2 is an explanatory diagram showing an example of another energy storage device 10B. Figure 3 is an explanatory diagram showing an example of another conductive part 21B, 21C, 21D. In Figure 2, the same reference numerals are used for components similar to those in Figure 1. The energy storage device 10 comprises a columnar electrode 12, a separator membrane 15, a counter electrode 16, a conductive part 21, an electrode current collector 25, and a counter electrode current collector 26. A single cell 11 is composed of a columnar electrode 12, a separator membrane 15, and a counter electrode 16. This energy storage device 10 comprises a columnar electrode 12 containing an electrode active material, and a counter electrode 16 containing a counter electrode active material formed around the columnar electrode 12 via a separator membrane 15. The energy storage device 10 may include an array 30 in which a plurality of single cells 11, which are columnar battery bodies including columnar electrodes 12 on which a separator membrane 15 and a counter electrode 16 are formed, are arranged in a predetermined direction. Furthermore, the energy storage device 10 has a laminate 41 which includes a structure in which a plurality of two-layer bodies 32 are stacked, with a conductive portion 21 sandwiched between two arrays 30. In the laminate 41, the conductive portion 21 is not sandwiched between the two-layer bodies 32. A structure in which the conductive portion 21 is disposed on one of the array surfaces 33 of the array 30 is referred to as a single-layer body 31. The energy storage device 10B has a laminate 41B which includes a structure in which a single-layer body 31 is stacked with the array 30 facing the outermost array surface 33 of a laminate 41 which is made up of a plurality of stacked two-layer bodies 32. Since the energy storage device 10B is the same as the energy storage device 10 except that it has a structure in which a single layer 31 is laminated on the outermost array surface 33 of which two layers 32 are stacked, the explanation will mainly focus on the energy storage device 10 and omit a detailed explanation of the 10B. The laminate 41 and laminate 41B are collectively referred to as the laminate. Note that in Figures 1 to 5, for convenience, the outer shape of the single cell 11 included in the array 30 is shown as cylindrical, but after press molding the outer shape of the single cell 11 may disappear, and the array 30 may have a structure in which the outer shape of the single cell 11 is lost and counter electrodes 16 are filled between columnar electrodes 12.

[0013] The columnar electrode 12 is a columnar member containing electrode active material. Here, "columnar" includes not only those with a non-bending thickness but also those with a bendable, fibrous thickness. The columnar electrode 12 only needs to be columnar, and its cross-section may be circular or polygonal. The energy storage device 10 has a structure in which a plurality of columnar electrodes 12 are arranged at intervals in a predetermined direction. The outer circumference of the columnar electrode 12, excluding the ends connected to the electrode current collector 25, is covered with a separation membrane 15. For example, n columnar electrodes 12 may be connected in parallel to the electrode current collector 25. The diameter D of the cross-section perpendicular to the longitudinal direction of the columnar electrode 12 is preferably 5 μm or more, more preferably 10 μm or more, and may be 15 μm or more or 30 μm or more. Furthermore, the diameter D of the columnar electrode 12 is preferably 800 μm or less, more preferably 500 μm or less, and may be 400 μm or less. When the diameter D is 5 μm or more, the strength of the electrode structure can be ensured, enabling stable charging and discharging. When the diameter D is 800 μm or less, the migration distance of the carrier ions does not become too long, and high output performance can be obtained. When the diameter D is in the range of 10 to 500 μm, the energy density per unit volume can be further increased. Alternatively, in this range, the migration distance of the carrier ions can be further shortened, allowing for charging and discharging with a larger current. The length of the columnar body in the longitudinal direction can be appropriately determined depending on the application of the energy storage device, for example, it may be in the range of 20 mm to 200 mm. When the length of the columnar body is 20 mm or more, the battery capacity can be further increased, which is preferable, and when it is 200 mm or less, the electrical resistance of the negative electrode can be further reduced, which is preferable.

[0014] The columnar electrode 12 preferably contains a carbon material as the electrode active material, and may be one or more of a bundle of carbon fibers 14 and a single piece of carbon material as the electrode active material. The carbon material is preferred for the columnar electrode 12 because it has high conductivity. Examples of carbon materials include one or more of graphites, cokes, glassy carbons, non-graphitizable carbons, and pyrolytic carbons. Of these, graphites such as artificial graphite and natural graphite are preferred. Alternatively, the carbon fiber 14 may have a graphite structure. Such carbon fiber 14 preferably has crystals oriented in the longitudinal direction, which is the fiber direction. Furthermore, when viewed in cross-section in a direction perpendicular to the longitudinal direction (fiber direction), it is preferable that the crystals are oriented radially from the center toward the outer surface. The diameter d of the carbon fiber 14 may be, for example, 5 μm or more, 7 μm or more, or 10 μm or more. Furthermore, the diameter d of the carbon fiber 11 may be in the range of 50 μm or less, 25 μm or less, or 20 μm or less. The columnar electrode 12 may be obtained by twisting together a plurality of carbon fibers 14, or by binding together a plurality of carbon fibers 14 with a binder. The binder is preferably one that has conductivity for carrier ions, and examples include polyvinylidene fluoride (PVdF), copolymer of PVdF and hexafluoropropylene (PVdF-HFP), polymethyl methacrylate (PMMA), and copolymer of PMMA and acrylic polymer. In addition, the columnar electrode 12 may be a single piece formed by carbonizing a raw material of carbon material into a columnar shape, or it may be a carbonized carbon material solidified with a binder or the like.

[0015] Alternatively, the columnar electrode 12 may be formed from a composite oxide capable of intercalating and deintercalating carrier ions. Examples of composite oxides include lithium titanium composite oxide and lithium vanadium composite oxide. The negative electrode made of this composite oxide may have a conductive component formed on at least a portion of its surface. This conductive component can further enhance conductivity. This conductive component is not particularly limited as long as it is a highly conductive material, but for example, it may be a metal.

[0016] The separation membrane 15 has ionic conductivity for carrier ions (e.g., lithium ions) and insulates the columnar electrode 12 from the counter electrode 16, and is provided on the outer circumference of the columnar electrode 12. The separation membrane 15 is formed over the entire outer surface of the columnar electrode 12 facing the counter electrode 16, preventing short circuits between the columnar electrode 12 and the counter electrode 16. This separation membrane 15 may be formed, for example, by creating a self-supporting membrane from a raw material solution containing a resin and covering the surface of the columnar electrode 12 with this self-supporting membrane, or by immersing the columnar electrode 12 in a raw material solution and coating its surface. Examples of the resin for this separation membrane 15 include polyvinylidene fluoride (PVdF), a copolymer of PVdF and hexafluoropropylene (PVdF-HFP), polymethyl methacrylate (PMMA), and a copolymer of PMMA and an acrylic polymer. For example, in the copolymer of PVdF and HFP, a portion of the electrolyte swells and gels the membrane, becoming an ion-conducting membrane. The thickness of the separation membrane 15 is preferably 2 μm or more, more preferably 5 μm or more, and may also be 8 μm or more. A thickness of 2 μm or more is preferable for ensuring insulation. In particular, a thickness of 2 μm or more for the separation membrane 15 is easier to manufacture. Furthermore, the thickness of the separation membrane 15 is preferably 15 μm or less, and more preferably 10 μm or less. A thickness of 15 μm or less is preferable because it can suppress a decrease in ion conductivity and further reduce the volume it occupies in the cell. In the range of 2 to 15 μm for the thickness of the separation membrane 15, both ion conductivity and insulation are suitable.

[0017] The separation membrane 15 may contain an electrolyte that conducts carrier ions. Examples of this electrolyte include non-aqueous solvents. Examples of solvents for the electrolyte include solvents for non-aqueous electrolytes. Examples of these solvents include carbonates, esters, ethers, nitriles, furans, sulfolanes, and dioxolanes, which can be used individually or in combination. Specifically, examples of carbonates include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, as well as linear carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate, and γ-butyl Examples of electrolytes include cyclic esters such as rulactone and γ-valerolactone, linear esters such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane, nitriles such as acetonitrile and benzonitrile, furans such as tetrahydrofuran and methyltetrahydrofuran, sulforanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. The electrolyte may also contain a support salt containing ions that are carriers for the energy storage device 10. Examples of support salts include LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiSbF6, LiSiF6, LiAlF4, LiSCN, LiClO4, LiCl, LiF, LiBr, LiI, and LiAlCl4. Of these, it is preferable from the viewpoint of electrical properties to use a combination of one or more salts selected from the group consisting of inorganic salts such as LiPF6, LiBF4, and LiClO4, and organic salts such as LiCF3SO3, LiN(CF3SO2)2, and LiC(CF3SO2)3. The concentration of this supporting salt in the electrolyte is preferably 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less.

[0018] The counter electrode 16 contains a counter electrode active material and is formed on the outer peripheral side of the separation membrane 15. The counter electrode 16 may be provided so as to fill a space between adjacent columnar electrodes 12. The counter electrode 16 may include a counter electrode active material, optionally a conductive material, and a binder. When producing the electricity storage device 10, the counter electrode 16 may enclose the columnar electrodes 12 and have a hexagonal outer profile in cross section (see FIG. 1). This shape is preferable because when the columnar electrodes 12 each having a positive electrode active material formed on the outer periphery thereof are bound together, the counter electrode 16 is easily filled between the columnar electrodes 12. The counter electrode 16 only needs to be present between the plurality of columnar electrodes 12, and is not limited to having a hexagonal outer profile as shown in FIG. 1. The counter electrode 16 may contain a conductive material and have conductivity itself. For example, the counter electrode 16 may be formed by forming the separation membrane 15 on the outer periphery of the columnar electrodes 12 and then applying a raw material of the counter electrode 16 to the outer periphery of the separation membrane 15.

[0019] For example, the counter electrode 16 may be formed of a counter electrode mixture obtained by mixing a counter electrode active material, a conductive material, and optionally a binder. Examples of the counter electrode active material include a positive electrode active material capable of intercalating and deintercalating lithium serving as a carrier. Examples of the positive electrode active material include compounds containing lithium and a transition metal, such as oxides containing lithium and a transition metal element, and phosphate compounds containing lithium and a transition metal element. Specifically, the basic composition formula is Li (1-x) MnO2 (where 0≦x≦1, the same applies hereinafter), Li (1-x) Mn2O4 lithium manganese composite oxides, the basic composition formula being Li (1-x) CoO2 lithium cobalt composite oxides, the basic composition formula being Li (1-x) NiO2 lithium nickel composite oxides, the basic composition formula being Li (1-x) Co a Ni b Mn c O2 (a>0, b>0, c>0, a+b+c=1), Li (1-x) Co a Ni b Mn cA lithium cobalt nickel manganese composite oxide having a basic composition formula such as O4 (0<a<1, 0<b<1, 1≦c<2, a+b+c=2), a lithium vanadium composite oxide having a basic composition formula such as LiV2O3, a transition metal oxide having a basic composition formula such as V2O5, or the like can be used. Further, a lithium iron phosphate compound having a basic composition formula of LiFePO4 or the like can be used as the positive electrode active material. Among these, lithium cobalt nickel manganese composite oxides, for example, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2 and LiNi 0.4 Co 0.3 Mn 0.3 O2 and the like are preferable. Note that the "basic composition formula" means that the composition may contain other elements, for example, components such as Al and Mg.

[0020] The conductive material contained in the counter electrode 16 is not particularly limited as long as it is an electronically conductive material that does not adversely affect battery performance. For example, one or a mixture of two or more of graphites such as natural graphite (flaky graphite, scaly graphite) and artificial graphite, acetylene black, carbon black, Ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.) can be used. The binder serves to hold active material particles and conductive material particles together and maintain a predetermined shape, and for example, fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber, thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR), or the like can be used alone or as a mixture of two or more thereof. Also, an aqueous dispersion of a cellulose-based binder or styrene butadiene rubber (SBR), which is an aqueous binder, or the like can be used.

[0021] In the counter electrode 16, the content of the positive electrode active material is preferably higher, preferably 70% by mass or more, and more preferably 80% by mass or more, relative to the total mass of the counter electrode 16. The content of the conductive material is preferably in the range of 0% by mass or more and 20% by mass or less, and more preferably in the range of 0% by mass or more and 10% by mass or less, relative to the total mass of the counter electrode 16. Within this range, a decrease in battery capacity can be suppressed and sufficient conductivity can be provided. Furthermore, the content of the binder is preferably in the range of 0.1% by mass or more and 5% by mass or less, and more preferably in the range of 0.2% by mass or more and 3% by mass or less, relative to the total mass of the counter electrode 16.

[0022] The conductive part 21 is a component that contacts the array surface 33 along the array direction A of the array 30, and is a conductive component disposed inside the laminate 41. The conductive part 21 is disposed to contact one of the array surfaces 33 of the array 30. The conductive part 21 is made of a material with a lower volume resistivity than the counter electrode 16, and is a component that improves the current collection efficiency of the counter electrode 16. The conductive part 21 may be a metal foil, for example, aluminum or stainless steel can be used, and aluminum is preferred. The thickness of the conductive part 21 is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 6 μm or more. Furthermore, the thickness of the conductive part 21 is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less. A thickness of 3 μm or more is preferred from the viewpoint of handling strength of the component and improved conductivity, and a thickness of 15 μm or less is preferred from the viewpoint of volume energy density because the presence of components that do not contribute to charging and discharging is reduced. The conductive portion 21 preferably has a thickness in the range of 5 μm to 10 μm. It is preferable that multiple conductive portions 21 exist inside the energy storage device 10, but they may all have the same thickness or different thicknesses. The conductive portion 21 may or may not be disposed on the outermost surface of the laminate 41, but it is preferable that it is not disposed on the outermost surface, as this can further increase the energy density per unit volume.

[0023] The conductive part 21 may be a sheet-like member that contacts the arrangement surface 33 along the arrangement direction of the arrangement 30. The conductive part 21 may have a smooth surface or a textured surface. The conductive part 21 may also have through holes on its surface. The through holes may be rectangular, circular, or elliptical. As shown in Figure 3, the conductive part 21 may be a conductive part 21B with multiple groove-shaped holes, a conductive part 21C with multiple circular holes, or a conductive part 21D with a mesh-like opening. The conductive part 21 may also be coated with a conductive material on its surface. As the conductive material, one or more types of materials such as graphite (scaly graphite, flake graphite) or artificial graphite, acetylene black, carbon black, Ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.) can be used. The binder used to coat the conductive material can be, for example, PTFE, PVdF, fluororesin, or thermoplastic resins such as polypropylene or polyethylene, EPDM, NBR, etc., either alone or as a mixture of two or more.

[0024] The electrode current collector 25 is a conductive material and is electrically connected to the columnar electrode 12. This electrode current collector 25 is positioned on the side where the columnar electrode 12 is exposed. The electrode current collector 25 can be made of materials such as carbon paper, aluminum, copper, titanium, stainless steel, nickel, iron, platinum, calcined carbon, conductive polymer, conductive glass, etc., or materials such as aluminum or copper whose surfaces have been treated with carbon, nickel, titanium, silver, platinum, gold, etc., for the purpose of improving adhesion, conductivity, and oxidation (reduction) resistance. The shape of the electrode current collector 25 is not particularly limited as long as it can be connected to the columnar electrode 12, and examples include plate-shaped, foil-shaped, film-shaped, sheet-shaped, net-shaped, punched or expanded, lath-shaped, porous, foam-shaped, and fiber-group-shaped materials.

[0025] The counter electrode current collector 26 is a conductive component that collects current from the counter electrode 16 and is electrically connected to the outer surface of the counter electrode 16 and the end of the conductive part 21. The counter electrode current collector 26 can use the same material and shape as the electrode current collector 25, for example. In Figure 1, the counter electrode current collector 26 is shown to be disposed on the lower side of the energy storage device 10, but it may also be disposed on the side.

[0026] In this energy storage device 10, the volumetric energy density is preferably higher, for example, preferably 500 Wh / L or more, more preferably 550 Wh / L or more, and even more preferably 600 Wh / L or more. In this energy storage device 10, the positive-negative electrode capacity ratio (negative electrode capacity / positive electrode capacity), which is the ratio of the capacity of the negative electrode active material to the capacity of the positive electrode active material, is preferably in the range of 1.0 to 1.5, and more preferably in the range of 1.2 or less. The formation thickness of the counter electrode 16 is appropriately set according to the diameter D of the columnar electrode 12 and the positive-negative electrode capacity ratio, but may be, for example, in the range of 5 μm to 50 μm. The formation thickness of the counter electrode 16 refers to, for example, the maximum thickness of the portion formed on the columnar electrode 12.

[0027] (Manufacturing method for energy storage devices) The manufacturing method disclosed herein may be the manufacturing method for the energy storage device 10 described above. This manufacturing method includes a two-layer process and a lamination process. Furthermore, it may further include an arrangement process after the lamination process in which electrode current collectors 25 and counter electrode current collectors 26 are arranged. Figure 4 is an explanatory diagram showing an example of a manufacturing method for the energy storage device 10, where Figure 4A is the arrangement process of a single-layer body 31, Figure 4B is an explanatory diagram of the single-layer body 31, Figure 4C is the manufacturing process of a two-layer body 32, Figure 4D is the lamination process of the laminated body 41B, and Figure 4E is an explanatory diagram of an example of the lamination process of the laminated body 41. In this manufacturing method, the materials and sizes described above for the energy storage device are used as appropriate, and their explanation is omitted. Also, in Figure 4, for convenience, the number of single cells 11 is shown as 4, but the number of single cells 11 is arbitrary.

[0028] (2-layer process) In the two-layer process, a process is performed to obtain a two-layer body 31 in which a conductive part 21 is sandwiched between two arrays 30. The two-layer body 32 may be manufactured by first manufacturing a single-layer body 31 and then further stacking arrays 30 (Figure 4C). The single-layer body 31 may be manufactured by first arranging single cells 11 in the arrangement direction A and pressing them together to create an array 30, and then pressing the single-layer body 31 onto the conductive part 21 (Figure 4A). Alternatively, the single-layer body 31 may be manufactured by arranging single cells 11 on the conductive part 21 in the arrangement direction A and pressing the whole thing together (Figure 4A). Or, the two-layer body 32 may be manufactured by first manufacturing an array 30, and then arranging arrays 30 on both sides of the conductive part 21 and pressing them together. The arrays 30, single-layer body 31, and two-layer body 32 may be manufactured by pressing the single cells 11 and conductive part 21 together. The pressing conditions can be determined empirically and appropriately based on the characteristics required for the energy storage device 10.

[0029] (Lamination process) In the lamination process, a process is performed to obtain a laminate that includes a structure in which multiple 2-layer bodies 32 are stacked. In the lamination process, a laminate is obtained in which no conductive parts 21 are sandwiched between the 2-layer bodies 32. The number of stacked 2-layer bodies 32 can be appropriately determined according to the characteristics such as the capacity required for the energy storage device 10. In this process, multiple 2-layer bodies 32 may be stacked to form a laminate 41, or a single-layer body 31 may be further stacked on the outermost arrangement surface 33 of the laminate 41 to obtain a laminate 41B. Alternatively, a single-layer body 31 may be stacked on only one side of the laminate 41, resulting in a structure in which the conductive parts 21 are not provided on only one side of the outermost arrangement surface 33 of the laminate 41B. The laminate may be pressed to compress the 2-layer bodies 32 and single-layer bodies 31. The pressing conditions can be appropriately determined empirically based on the characteristics required for the energy storage device 10.

[0030] According to the energy storage device 10 and its manufacturing method of this embodiment, as detailed above, in an energy storage device having columnar electrodes, it is possible to further improve the energy density per unit volume while ensuring capacity. The reason for obtaining such an effect is presumed to be as follows. For example, among the components that constitute a battery structure, a conductor that collects current from the counter electrode is sometimes placed within the structure, but generally it is placed between the arrays of columnar batteries. Generally, if conductive parts are placed all between the arrays, current collection performance is improved, but since the conductive parts are components that do not participate in charging and discharging, the energy density per unit volume decreases. In this energy storage device 10, there is a structure in which multiple two-layer bodies are stacked, in which a conductive part is sandwiched between two arrays of columnar battery bodies arranged in a predetermined direction. In this energy storage device 10, by providing the conductive part 21 only on one of the array surfaces 33 of the array 30, current collection from the counter electrode 16 is improved to ensure capacity, and the energy density can be further improved by further suppressing the placement of excessive conductive parts 21.

[0031] It goes without saying that this disclosure is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of this disclosure.

[0032] For example, in the embodiment described above, lithium ions were used as the carriers for the energy storage device, but the invention is not limited to lithium ions. Alkali metal ions such as sodium ions and potassium ions, or group 2 element ions such as calcium ions and magnesium ions may also be used. Furthermore, the positive electrode active material may contain carrier ions. In addition, a non-aqueous electrolyte was used, but an aqueous electrolyte may also be used.

[0033] In the embodiments described above, the columnar electrode 12 was shown as being cylindrical, but it is not limited to this and may be shaped as a square prism or a hexagonal prism. Also, although the counter electrode 16 was shown with a hexagonal prism outer diameter, it may be shaped as a square prism or a cylinder.

[0034] In the embodiments described above, the counter electrode active material was a transition metal composite oxide, but it is not particularly limited and may be, for example, a carbon material used in capacitors. Examples of carbon materials, though not particularly limited, include activated carbon, coke, glassy carbon, graphite, non-graphitizable carbon, pyrolytic carbon, carbon fibers, carbon nanotubes, and polyacenes. Of these, activated carbon exhibiting a high specific surface area is preferred. Activated carbon as a carbon material has a specific surface area of ​​1000 m². 2 Preferably, it is 1500m or more per gram. 2 It is more preferable that the amount is greater than or equal to / g. The specific surface area is 1000m². 2 At concentrations of 1 / g or higher, the discharge capacity can be further increased. The specific surface area of ​​this activated carbon is 3000 m² due to its ease of manufacture. 2 It is preferable that it be less than or equal to / g, and 2000m 2 It is more preferable that the value is less than or equal to / g. Furthermore, while it is thought that the positive electrode stores energy by adsorbing and desorbing at least one of the anions and cations contained in the ion-conducting medium, it is also possible to store energy by inserting and desorbing at least one of the anions and cations contained in the ion-conducting medium.

[0035] This disclosure may be any of the following [1] to

[10] . [1] An array of columnar battery bodies arranged in a predetermined direction, each comprising a columnar electrode containing an electrode active material, a separation membrane formed on the outer circumference of the columnar electrode having insulating and ion conductive properties, and a counter electrode formed on the outer circumference of the separation membrane containing a counter electrode active material. The array comprises a conductive portion that contacts the array surface along the array direction, An energy storage device having a laminate including a structure in which multiple two-layer bodies are stacked, each having the conductive portion sandwiched between two of the aforementioned array bodies. [2] The energy storage device according to [1], wherein the conductive portion is a sheet-like member that contacts the arrangement surface. [3] The conductive portion may have a smooth surface or a textured surface and may have through holes on its surface, as described in [1] or [2]. [4] The energy storage device according to any one of [1] to [3], wherein the conductive portion has a thickness in the range of 5 μm or more and 10 μm or less. [5] The energy storage device according to any one of [1] to [4], wherein the conductive portion is not disposed on the outermost surface of the laminate. [6] The energy storage device according to any one of [1] to [5], wherein the conductive portion is also disposed on the outermost surface of the laminate. [7] The energy storage device according to any one of [1] to [6], wherein the conductive portion is not sandwiched between the two layers. [8] The energy storage device according to any one of [1] to [7], wherein the conductive portion is coated with a conductive material on its surface. [9] A two-layer body step to obtain a two-layer body having a columnar battery body arranged in a predetermined direction, the columnar battery body comprising a columnar electrode containing an electrode active material, a separation membrane formed on the outer circumference of the columnar electrode having insulating and ion conductive properties, and a counter electrode formed on the outer circumference of the separation membrane containing a counter electrode active material, and a conductive portion in contact with one of the arrangement surfaces along the arrangement direction of the arrangement body, wherein the conductive portion is sandwiched between two of the arrangement bodies, A lamination step to obtain a laminate including a structure in which multiple of the aforementioned two-layer bodies are stacked, A method for manufacturing an energy storage device, including the device itself.

[10] The method for manufacturing an energy storage device according to [9], wherein in the lamination step, the laminate is obtained in which the conductive portion is not sandwiched between the two layers. [Examples]

[0036] The following describes specific examples of the energy storage devices described above as experimental examples. Experimental Examples 1 and 2 correspond to embodiments of this disclosure, while Experimental Examples 3 and 4 correspond to comparative examples.

[0037] (Manufacturing of energy storage devices) A columnar electrode (negative electrode) was formed by twisting together 400 carbon fibers (manufactured by Nippon Graphite Fiber Co., Ltd.) with a diameter d of 7 μm, to create a carbon fiber bundle with a diameter D of 156.5 μm. This columnar electrode was coated with a solution of vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) dissolved in N-methylpyrrolidone (NMP) using a dipping method, and then dried to uniformly coat the surface of the negative electrode with a polymer film as a separation film with a thickness of 5 μm. Next, the positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode composite paste was prepared by mixing O2, acetylene black (Denka HS-100) as a conductive material, and polyvinylidene fluoride (Kureha PVdF7305) as a binder in a mass ratio of 90:4:4, to which N-methylpyrrolidone was added. The above polymer-coated negative electrode was dip-coated with the positive electrode slurry to form a positive electrode composite layer with a thickness of 35 μm. The negative electrode / polymer film / positive electrode composite layer thus formed in a concentric pattern was cut to a length of 11 cm to form columnar single cells.

[0038] (Experimental Examples 1 and 2) The fabricated single cells were arranged and stacked according to the fabrication procedure shown in Figure 3 to create an energy storage device. A 7 μm thick aluminum foil was used as the conductive part, and a predetermined number of single cells were arranged in a row on this foil and pressed together to create a raft-like arrangement, forming a single layer. In addition, the same number of single cells were arranged in a row on the surface of a conductive part without an arrangement, and pressed together to create a two-layer structure. The predetermined number of arrangements was set to 18, and two two-layer structures were stacked and pressed together to form Experimental Example 1. Figure 5 is a schematic diagram showing the laminates of Experimental Examples 1 to 4. A Cu foil (10 μm thick) was placed on the end face of the columnar electrodes of the obtained laminate as an electrode current collector, and it was pressed onto the end face of all columnar electrodes to electrically connect the two. In addition, an Al foil (7 μm thick) was placed on the counter electrode current collector surface of the laminate as a counter electrode current collector, and it was pressed onto each connection point to electrically connect them. Then, the laminate, in which the electrode current collector and counter electrode current collector were connected, was placed in a case, and after pouring in the electrolyte (1M-LiPF6, EC / DMC / EMC=3 / 4 / 3 (volume ratio)), it was sealed to fabricate the lithium-ion secondary battery as an energy storage device for Experimental Example 1. Furthermore, for Experimental Example 2, an additional layer was laminated and pressed so that single cells faced each other on each of the two outermost arrangement surfaces of the two-layer structure (see Figure 5).

[0039] (Experimental Examples 3 and 4) Experimental Example 3 involved stacking four single-layer structures similar to those in Experimental Example 1, with conductive sections placed on the array surfaces without array elements. Experimental Example 4 involved stacking four array elements and forming conductive sections on the two outermost array surfaces (see Figure 5). All fabricated energy storage devices had the same number of single cells and theoretical capacity.

[0040] (Charge / Discharge Test) Using the energy storage devices from Experimental Examples 1-4, charge-discharge tests were conducted at 20°C and 2.5V-4.2V, and the discharge capacity was measured. The discharge capacity was defined as the capacity when discharged at discharge currents of 10mA, 20mA, 40mA, 100mA, 300mA, and 400mA. The maximum theoretical capacity of Experimental Examples 1-4 is 72mAh.

[0041] (Energy density) The volume of the energy storage devices in Experimental Examples 1-4 was calculated, and the energy density per unit volume (Wh / L) was calculated by dividing the discharge capacity when discharged with a discharge current of 10 mA by the above volume.

[0042] (Results and Discussion) Figure 6 shows the relationship between discharge current and discharge capacity for experimental examples 1 to 4. Table 1 summarizes the relationship between discharge current (mA) and discharge capacity (mAh) shown in Figure 6. Table 2 summarizes the battery volume and energy density per unit volume for each experimental example. As shown in Figure 6 and Table 1, experimental example 4, which lacked conductive parts between the array elements, showed a low discharge capacity. On the other hand, experimental examples 1 to 3 achieved higher discharge capacities. This was presumed to be due to the high current collection efficiency of the counter electrode caused by the conductive parts between the array elements, thus improving the discharge capacity. Furthermore, in experimental example 3, which had conductive parts on both sides of the array plane, the energy density per unit volume was below 500 Wh / L, as shown in Table 2, indicating that the energy density was insufficient. In contrast, experimental example 2 showed a volumetric energy density exceeding 500 Wh / L, specifically over 550 Wh / L. In particular, experimental example 1 exceeded the target value of 600 Wh / L for energy density per unit volume, demonstrating the ability to achieve a previously unseen range of high energy density. From the standpoint of energy density, Experimental Example 1, which consists of only two layers stacked together with conductive material present only on one of the array surfaces, was found to be preferable to Experimental Example 2, which has one layer on the outermost surface. The reason for this is that, for example, in Experimental Examples 2 and 3, the presence of conductive material on the outermost surface may cause damage to the electrodes due to shearing of the conductive material during stacking and compression.

[0043] [Table 1]

[0044] [Table 2]

[0045] Furthermore, a thinner conductive portion allows for a higher volumetric energy density (Wh / L). It was estimated that the conductive portion thickness should be in the range of 5 μm to 10 μm, more preferably 6 μm to 8 μm. In addition, while sheet-like conductive portions were used in Experimental Examples 1-4, rectangular or circular holes may also be used, or a mesh-like structure may be used, and similar effects to those in the above-described examples can be obtained.

[0046] It goes without saying that this disclosure is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of this disclosure. [Explanation of symbols]

[0047] 10,10B Energy storage device, 11 Single cell, 12 Columnar electrode, 14 Carbon fiber, 15 Separation membrane, 16 Counter electrode, 21,21B,21C,21D Conductive part, 25 Electrode current collector, 26 Counter electrode current collector, 30 Array, 31 Single layer, 32 Double layer, 33 Array plane, 41,41B Laminate, d,D Diameter.

Claims

1. An array of columnar battery bodies arranged in a predetermined direction, each comprising a columnar electrode containing an electrode active material, a separation membrane formed on the outer circumference of the columnar electrode having insulating and ion conductive properties, and a counter electrode formed on the outer circumference of the separation membrane containing a counter electrode active material. The array comprises a conductive portion that contacts the array surface along the array direction, The laminate includes a structure in which multiple two-layer bodies are stacked, each having the conductive portion sandwiched between two of the aforementioned array bodies. The conductive portion is not disposed on the outermost surface of the laminate. An energy storage device in which the conductive portion is not sandwiched between the two layers.

2. The energy storage device according to claim 1, wherein the conductive portion is a sheet-like member that contacts the arrangement surface.

3. The energy storage device according to claim 1 or 2, wherein the conductive portion has a smooth surface or a textured surface, and may have through holes on its surface.

4. The energy storage device according to claim 1 or 2, wherein the conductive portion has a thickness in the range of 5 μm to 10 μm.

5. The energy storage device according to claim 1 or 2, wherein the conductive portion is coated with a conductive material on its surface.

6. A two-layer body is obtained by arranging columnar battery bodies in a predetermined direction, each comprising a columnar electrode containing an electrode active material, a separation membrane formed on the outer circumference of the columnar electrode having insulating and ion conductive properties, and a counter electrode formed on the outer circumference of the separation membrane containing a counter electrode active material, and having a conductive portion in contact with one of the arrangement surfaces along the arrangement direction of the arrangement, wherein the conductive portion is sandwiched between two of the arrangement bodies. The process includes a lamination step to obtain a laminate containing a structure in which multiple of the aforementioned two layers are stacked, A method for manufacturing an energy storage device, wherein in the lamination process, the conductive portion is not disposed on the outermost surface of the laminate, and the conductive portion is not sandwiched between the two layers to obtain the laminate.

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