Electrode, power storage device, and method for manufacturing electrode

Abstract

To increase the mass energy density while suppressing the decrease in discharge capacity.SOLUTION: A power storage device disclosed herein includes an electrode and an ion-conducting medium in contact with the electrode and conducting carrier ions. The electrode includes a current collector having a metal layer composed of metal particles, and an active material layer formed on the surface of the metal layer and containing active material particles, and the average particle size d [nm] of the metal particles and the average particle size D [μm] of the active material particles satisfy the relationship (D-11)×(d-150)>0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Disclosed herein are an electrode, an electricity storage device, and a method for manufacturing the electrode. [Background technology]

[0002] Conventionally, electrodes for power storage devices consist of an insulating layer with a thickness of 1 to 10 μm and a tensile strength of 150 MPa or more and a 0.2 to 1.5 μm thick insulating layer with an electrical resistivity of 8.0 × 10 -8 One proposed electrode includes a current collector having a conductive layer of Ω·m or less, and an active material layer formed on the surface of the conductive layer (see, for example, Patent Document 1). This electrode is said to have an improved weight energy density due to the weight reduction of the current collector. Another proposed electrode for an electricity storage device includes a current collector having a titanium layer of 2 to 6 μm in thickness and an aluminum layer of 0.1 μm or more in thickness but less than the thickness of the titanium layer, and an active material layer formed on the surface of the aluminum layer (see, for example, Patent Document 2). This electrode is said to have an improved volume energy density due to the thinning of the current collector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2020-503639 [Patent Document 2] Japanese Patent Publication No. 2020-098683 Summary of the Invention [Problem to be solved by the invention]

[0004] However, although the energy density is improved by improving the current collector in Patent Documents 1 and 2, the discharge capacity is reduced, and further improvements are desired.

[0005] The present disclosure has been made to solve such problems, and has as its main object to increase the mass energy density while suppressing a decrease in discharge capacity. [Means for solving the problem]

[0006] As a result of intensive research to achieve the above-mentioned object, the inventors have found that an electrode comprising a current collector having a metal layer made of metal particles and an active material layer containing active material particles formed on the surface of the metal layer, in which the particle size of the metal particles and the particle size of the active material particles satisfy a predetermined relationship, can increase the mass energy density while suppressing a decrease in discharge capacity, and have completed the electrode, electricity storage device, and method for manufacturing an electrode disclosed herein.

[0007] That is, the electrode of the present disclosure is a current collector having a metal layer made of metal particles; an active material layer formed on the surface of the metal layer and including active material particles; wherein the average particle size d [nm] of the metal particles and the average particle size D [μm] of the active material particles satisfy (D-11)×(d-150)>0.

[0008] The electricity storage device of the present disclosure includes: The electrode as described above; an ion-conducting medium in contact with the electrode and conducting carrier ions; It is equipped with the following.

[0009] The method for manufacturing an electrode according to the present disclosure includes: a metal layer forming step of forming a metal layer composed of metal particles on a surface of a substrate by electron beam deposition; an active material layer forming step of forming an active material layer containing active material particles on the surface of the metal layer; In the active material layer forming step, the active material particles are used such that the average particle size d [nm] of the metal particles and the average particle size D [μm] of the active material particles satisfy (D-11) × (d-150) > 0. [Effects of the Invention]

[0010] The electrode, power storage device, and electrode manufacturing method disclosed herein can increase mass energy density while suppressing a decrease in discharge capacity. The reason for this is presumed to be as follows. For example, a metal layer composed of metal particles can be formed into a relatively thin film by electron beam deposition or the like, which is suitable for reducing the weight of the current collector and can increase mass energy density. Furthermore, it is presumed that the particle size of the metal particles and the particle size of the active material particles satisfying a predetermined relationship reduces interfacial contact resistance, thereby suppressing a decrease in discharge capacity. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is an explanatory diagram showing an example of the structure of the electricity storage device 10. [Figure 2] SEM image of the metal layer (aluminum layer) surface in Experimental Example 1. [Figure 3] 10 is a graph showing the relationship between the thickness of the metal layer and the normalized mass energy density. [Figure 4] 10 is a graph showing the relationship between the thickness of a resin layer and the normalized mass energy density. [Figure 5] Charge and discharge curves for experimental examples 1, 2, and 5. DETAILED DESCRIPTION OF THE INVENTION

[0012] (electrode) The electrode of the present disclosure is an electrode used in an electricity storage device. The electricity storage device may be, for example, any of a lithium ion secondary battery, a hybrid capacitor, an air battery, etc. Furthermore, this electrode may be a positive electrode or a negative electrode, but when lithium is used as a carrier, it is preferably a positive electrode. This electrode includes a current collector and an active material layer.

[0013] The current collector has a metal layer composed of metal particles as a conductive layer. Examples of metals include those used in current collectors of electricity storage devices, such as copper, nickel, stainless steel, titanium, and aluminum, with aluminum being more preferred. The average particle size d [nm] of the metal particles may be, for example, 1 nm or more, 10 nm or more, or 50 nm or more. This average particle size d may be 1,000 nm or less, 500 nm or less, or 300 nm or less. The average particle size d of the metal particles is the number-based average diameter of the equivalent circle diameter determined by observing the metal particles on the surface of the metal layer at 50,000 times magnification using a scanning electron microscope (SEM), or an equivalent value. The metal layer may be formed by densely packing these metal particles so that there are no gaps when viewed from above. The metal layer can be formed, for example, by physical vapor deposition such as electron beam evaporation, sputtering, or the like. The thickness t [μm] of the metal layer is preferably thicker from the viewpoint of electrical conductivity, for example, 0.1 μm or more, 0.15 μm or more, or 0.2 μm or more. From the viewpoint of energy density, the thickness t is preferably thinner, for example, 3 μm or less, 1.5 μm or less, 1.2 μm or less, or 1.0 μm or less. The thickness t of the metal layer is determined by measuring the step between the metal layer and the resin layer five times using a fully automatic micro-profile measuring device and calculating the average value, or a value equivalent thereto. The ratio t / d of the thickness t [μm] of the metal layer to the average particle size d [nm] of the metal particles may be, for example, 1 / 1000 or more, 2 / 1000 or more, or 3 / 1000 or more. This ratio t / d may be 30 / 1000 or less, or 15 / 1000 or less.

[0014] The current collector may have a resin layer as a base material, and may also have the above-described metal layer on the surface of the base material. The base material may have a metal layer on one side or may have metal layers on both sides. The base material may be conductive or insulating. The base material is preferably a resin layer having flexibility or flexibility. The base material may be, for example, polyethylene terephthalate or polyimide. The thickness T [μm] of the base material is preferably thicker from the viewpoint of mechanical strength, and may be, for example, 5 μm or more, 10 μm or more, or 12 μm or more. This thickness T is preferably thinner from the viewpoint of energy density, and may be, for example, 50 μm or less, 30 μm or less, or 25 μm or less. The thickness T of the base material is a value obtained by measuring the thickness of the base material 5 times using a constant pressure thickness measuring device and calculating the average value thereof, or something equivalent thereto. The base material may be a thin metal layer (for example, a titanium layer) having a thickness of about 2 to 6 μm from the viewpoint of increasing the volume energy density, etc., but from the viewpoint of reducing the amount of metal used, a resin layer is desirable.

[0015] Examples of the shape of the current collector include foil shape, film shape, sheet shape, net shape, punched or expanded shape, lath body, porous body, foam body, and formed body of fiber group. The thickness of the current collector is, for example, the thickness obtained by adding the thickness of the base material and the thickness of the metal layer, and may be, for example, 5 μm or more and 50 μm or less.

[0016] The active material layer is formed on the surface of the above-described metal layer. The active material layer contains active material particles. The active material particles may be, for example, a positive electrode active material, a negative electrode active material, or a carbon material used in a capacitor or a lithium ion capacitor.

[0017] In the active material particles, examples of the positive electrode active material include sulfides containing a transition metal element and oxides containing lithium and a transition metal element. Specifically, transition metal sulfides such as TiS2, TiS3, MoS3, FeS2, basic composition formula Li (1-x) MnO2 (0 <x <1, etc., the same below), Li (1-x) Mn2O4 and the like, lithium manganese composite oxides having a basic composition formula of Li(1-x) Lithium cobalt composite oxides such as CoO2, with the basic composition formula Li (1-x) Lithium nickel composite oxide such as NiO2, the basic composition formula is Li (1-x) Ni a Co b Mn c Lithium nickel cobalt manganese composite oxides with a basic composition formula of LiV2O3, etc., and transition metal oxides with a basic composition formula of V2O5, etc., can be used. Among these, lithium transition metal composite oxides, such as LiCoO2, LiNiO2, LiMnO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 is preferred. The term "basic composition formula" means that other elements may be included.

[0018] In the active material particles, examples of the negative electrode active material include inorganic compounds such as lithium, lithium alloys, and tin compounds, carbon materials capable of absorbing and releasing lithium ions, composite oxides containing multiple elements, and conductive polymers. Examples of carbon materials include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Of these, graphites such as artificial graphite and natural graphite are preferred because they have an operating potential close to that of metallic lithium and allow charging and discharging at a high operating voltage. Examples of composite oxides include lithium titanium composite oxide and lithium vanadium composite oxide. Of these, carbon materials are preferred as the negative electrode active material from the standpoint of safety.

[0019] In the active material particles, carbon materials used in capacitors and lithium ion capacitors include activated carbons, cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, and polyacenes. Among these, activated carbons with a high specific surface area are preferred. Activated carbons as carbon materials have a specific surface area of ​​1000 m 2 / g or more, and 1500m 2 / g or more is more preferable.2 / g or more, the discharge capacity can be further increased. The specific surface area of ​​this activated carbon is 3000 m 2 / g or less, and 2 It is more preferable that the saturation coefficient is 1 / g or less.

[0020] The average particle size D [μm] of the active material particles may be, for example, 1 μm or more, 2 μm or more, or 5 μm or more. This average particle size D may be, for example, 50 μm or less, 30 μm or less, or 20 μm or less. The average particle size D of the active material particles is the volume-based median diameter D50 measured in powder form by laser diffraction / scattering, or an equivalent thereof. The average particle size D of the active material particles is a value measured on primary particles that do not contain binders, etc., rather than on secondary particles granulated by mixing the active material with binders, etc.

[0021] The active material layer may contain, for example, active material particles and, if necessary, a binder and / or a conductive material. Examples of binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber; thermoplastic resins such as polypropylene and polyethylene; ethylene propylene diene rubber (EPDM), sulfonated EPDM rubber; and natural butyl rubber (NBR). Other examples include aqueous binders such as cellulose-based binders and styrene butadiene rubber (SBR). Examples of conductive materials include graphite such as natural graphite (scale graphite, flake graphite) and artificial graphite, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.). Among these, carbon black and acetylene black are preferred as conductive materials from the viewpoints of electronic conductivity and coatability. The thickness of the active material layer may be appropriately selected depending on the characteristics required for the power storage device. The active material layer may be formed, for example, by mixing active material particles with, if necessary, a binder and / or conductive material, adding an appropriate solvent to form a paste-like electrode mixture, applying it to the surface of the metal layer, drying it, and compressing it to increase electrode density as needed. Examples of solvents that can be used include organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. Alternatively, a dispersant, thickener, etc. may be added to water, and the active material may be slurried with a latex such as SBR. Examples of thickeners include polysaccharides such as carboxymethyl cellulose and methyl cellulose, either alone or in combination. Application methods include roller coating (e.g., applicator roll), screen coating, doctor blade coating, spin coating, and bar coating. Any of these methods can be used to form a desired thickness and shape.

[0022] In this electrode, the average particle size d [nm] of the metal particles and the average particle size D [μm] of the active material particles satisfy the relationship (D-11) × (d-150) > 0. This is thought to reduce the contact resistance at the interface, thereby suppressing the decrease in discharge capacity.

[0023] This electrode may have an average particle size d of less than 150 nm of metal particles and an average particle size D of less than 11 μm of active material particles. In this case, in order to suppress a decrease in discharge capacity, it is preferable that the thickness t of the metal layer is relatively thin, for example, preferably 1 μm or less, more preferably 0.7 μm or less, and even more preferably 0.3 μm or less.

[0024] This electrode may have an average particle size d of more than 150 nm and an average particle size D of more than 11 μm of the active material particles. In this case, in order to suppress a decrease in discharge capacity, it is preferable that the thickness t of the metal layer is relatively large, for example, preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more.

[0025] In this electrode, the ratio d / D of the average particle size d [nm] of the metal particles to the average particle size D [μm] of the active material particles may be 20 or less, or may be less than 20. This ratio d / D may be 1 or more, or 5 or more.

[0026] (Electricity storage device) The electricity storage device of the present disclosure includes the above-described electrode and an ion-conductive medium in contact with the above-described electrode and conducting carrier ions. The counter electrode may be selected appropriately depending on the characteristics required of the electricity storage device. This electricity storage device may include a positive electrode, a negative electrode, and an ion-conductive medium interposed between the positive electrode and the negative electrode and conducting carrier ions.

[0027] The ion-conducting medium may be a non-aqueous electrolyte solution containing a supporting salt, a non-aqueous gel electrolyte solution, etc. Examples of the solvent for the non-aqueous electrolyte include carbonates, esters, ethers, nitriles, furans, sulfolanes, and dioxolanes, which may be used alone or in combination. Specific examples of carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate; chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate; cyclic esters such as γ-butyl lactone and γ-valerolactone; chain 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; sulfolanes such as sulfolane and tetramethylsulfolane; and dioxolanes such as 1,3-dioxolane and methyldioxolane. Among these, a combination of cyclic carbonates and chain carbonates is preferred. This combination not only provides excellent cycle characteristics, which represent battery characteristics during repeated charge and discharge, but also allows for a well-balanced electrolyte viscosity, the resulting battery's electrical capacity, and battery output. Examples of supporting salts include LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiSbF6, LiSiF6, LiAlF4, LiSCN, LiClO4, LiCl, LiF, LiBr, LiI, and LiAlCl4. The concentration of this supporting salt in the nonaqueous 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. A supporting salt concentration of 0.1 mol / L or more can achieve sufficient current density, while a supporting salt concentration of 5 mol / L or less can further stabilize the electrolyte. A phosphorus-based or halogen-based flame retardant may be added to the non-aqueous electrolyte.

[0028] Instead of a liquid ion-conducting medium, a solid ion-conducting polymer can be used as the ion-conducting medium. Examples of the ion-conducting polymer include polymer gels composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinylpyrrolidone, or vinylidene fluoride and a supporting salt. Furthermore, a combination of an ion-conducting polymer and a nonaqueous electrolyte can also be used. In addition to ion-conducting polymers, other ion-conducting media include inorganic solid electrolytes, mixed materials of organic polymer electrolytes and inorganic solid electrolytes, and inorganic solid powders bound by an organic binder.

[0029] The counter electrode may be formed, for example, by closely adhering an active material to a current collector. Alternatively, the active material may be mixed with, if necessary, a conductive material and a binder, and an appropriate solvent added to form a paste-like electrode mixture. This paste is then applied to the surface of the current collector, dried, and compressed, if necessary, to increase electrode density. The active material, conductive material, binder, solvent, and application method for the counter electrode may be any of the active materials, conductive materials, binders, solvents, and application methods exemplified for the electrodes described above. Examples of the counter electrode current collector include copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymers, conductive glass, and Al-Cd alloys. For example, copper surfaces treated with carbon, nickel, titanium, silver, or the like to improve adhesion, conductivity, and reduction resistance may also be used. The above-described electrodes may also be used as counter electrodes.

[0030] The electricity storage device may include a separator between the electrode and the counter electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the electricity storage device, and examples thereof include polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and thin microporous films of olefin resins such as polyethylene and polypropylene. These may be used alone or in combination.

[0031] The shape of the electricity storage device is not particularly limited, and examples thereof include coin, button, sheet, laminate, cylindrical, flat, and rectangular shapes. FIG. 1 is an explanatory diagram showing an example of the structure of an electricity storage device 10. The electricity storage device 10 includes the above-described electrode 12, counter electrode 15, and ion-conducting medium 18. The electrode 12 is, for example, a positive electrode and includes an active material layer 13 and a current collector 14. The current collector 14 includes a substrate 21 made of a resin such as polyethylene terephthalate and a metal layer 22 formed on the substrate 21 and including metal particles 22p such as aluminum particles. The thickness T of the substrate 21 is, for example, 5 μm to 50 μm, and the thickness t of the metal layer 22 is, for example, 0.1 μm to 3 μm. The active material layer 13 includes active material particles 13p such as lithium transition metal composite oxide particles. The average particle size d [nm] of the metal particles 22p and the average particle size D [μm] of the active material particles 13p satisfy the relationship (D-11) × (d-150) > 0. The counter electrode 15 is, for example, a negative electrode, and has an active material layer 16 containing an active material such as graphite, and a current collector 17 such as copper foil.

[0032] (Electrode manufacturing method) The method for manufacturing an electrode according to the present disclosure includes a metal layer forming step and an active material layer forming step. The method for manufacturing an electrode according to the present disclosure may be a method for manufacturing the electrode described above. Here, the configuration of the electrode is the same as that of the electrode described above, and detailed description thereof will be omitted.

[0033] In the metal layer formation process, a metal layer composed of metal particles is formed on the surface of a substrate by electron beam (EB) deposition. The substrate may be, for example, a polyethylene terephthalate layer or a polyimide layer having a thickness T of 5 μm to 50 μm. Electron beam deposition is a method in which an electron beam generated from an electron gun is irradiated onto a metal target material in a vacuum, causing it to heat and evaporate, thereby forming a thin film composed of metal particles on the substrate. The target material may be selected appropriately depending on the metal layer to be formed, and may be, for example, aluminum metal. In electron beam deposition, the particle size of the metal particles can be controlled by controlling deposition conditions such as the deposition speed and vacuum level. Electron beam deposition may be performed under deposition conditions that result in metal particles with an average particle size d of 1 nm to 1000 nm. The deposition speed may be, for example, 1 Å / sec or more, 3 Å / sec or more, or 5 Å / sec or more. The deposition speed may be, for example, 20 Å / sec or less, 15 Å / sec or less, or 10 Å / sec. The slower the film formation speed, the smaller the particle size of the metal particles tends to be. Although it depends on the degree of vacuum, for example, if the film formation speed is less than 8 Å / sec, metal particles with an average particle size d of less than 150 nm are generated, and if the film formation speed exceeds 8 Å / sec, metal particles with an average particle size d of more than 150 nm are generated. -5 Pa or more, 10 -4 The degree of vacuum may be, for example, 10 -1 Pa or less, 10 -2 Pa or less, 10 -3 The vacuum pressure may be set to 0.1 Pa or less. The lower the degree of vacuum, the smaller the particle size of the metal particles tends to be. Furthermore, in electron beam evaporation, the thickness of the metal layer can be controlled according to the evaporation time (electron beam irradiation time). The electron beam irradiation time may be set, for example, so that the thickness t of the metal layer is 0.1 μm or more and 3 μm or less.

[0034] In the active material layer forming step, an active material layer containing active material particles is formed on the surface of the metal layer. The active material layer may be formed, for example, by mixing the active material particles with, if necessary, a binder and / or a conductive material, adding an appropriate solvent to form a paste-like electrode mixture, applying it to the surface of the metal layer, drying it, and compressing it as needed to increase the electrode density. In the active material layer forming step, active material particles are used in which the average particle size d [nm] of the metal particles and the average particle size D [μm] of the active material particles satisfy (D-11) × (d-150) > 0. In this way, the above-mentioned electrode is obtained.

[0035] The electrode, electricity storage device, and electrode manufacturing method of the present embodiment described above can suppress a decrease in discharge capacity while increasing mass energy density. The reason for this is presumed to be as follows. For example, a metal layer composed of metal particles can be formed into a relatively thin film by electron beam deposition or the like, which is suitable for reducing the weight of the current collector and can increase mass energy density. Furthermore, it is presumed that when the particle size of the metal particles and the particle size of the active material particles satisfy a predetermined relationship, the interaction between their morphologies reduces interfacial contact resistance, thereby suppressing a decrease in discharge capacity.

[0036] Generally, aluminum foils with a thickness of several tens of micrometers are used as positive electrode current collectors in lithium-ion batteries. However, the current collector foil accounts for approximately one-quarter of the total metal weight of the battery, making it a significant factor in resource conservation. In this disclosure, for example, by significantly reducing the amount of aluminum used in the current collector, it is believed possible to fabricate batteries that are lighter, have higher mass energy density, and are safer. However, thinning the aluminum layer can impair the electronic conductivity and good interface with the positive electrode composite layer required of the current collector foil, making it difficult to maintain battery functionality simply by thinning the aluminum layer. In this disclosure, it is believed possible to fabricate thin, uniform metal thin films, such as those with a thickness of 1 μm or less, by using a flexible resin layer as a substrate and controlling the deposition speed and vacuum level through electron beam deposition. At the same time, the favorable interaction between the particle morphology of the aluminum layer and the particle morphology of the positive electrode composite layer is believed to reduce the contact resistance between the current collector and the positive electrode composite layer, enabling the fabrication of a high-quality positive electrode without sacrificing battery performance. Furthermore, by wet-coating a composite layer containing active material particles on a metal layer composed of metal particles, the bonding interface between the composite layer and the metal layer is optimized, improving adhesion, reducing contact resistance, and further improving battery performance. Furthermore, by thinning the metal layer, it is believed possible to reduce the amount of metal used in the positive electrode current collector to 1 / 15 or less. Furthermore, by using a resin substrate and forming an aluminum thin film on this, it is possible to fabricate an extremely thin metal film that would be difficult to support as metal alone. The surface interaction between these layers is believed to enable the fabrication of a homogeneous aluminum thin film that does not peel or crack from the base resin. Furthermore, by using a current collector with a thin metal layer and a resin layer, it is believed possible to realize an energy storage device that combines lightweight design with excellent battery performance. The thin metal film current collector contributes to resource conservation, avoiding resource risks, and reducing the overall weight of the battery, which is expected to lead to an improvement in mass energy density. Furthermore, the thin metal film current collector fabricated on resin is flexible and can be deformed into various shapes, and is less likely to break than a collector made of metal alone. This thinness of the current collector makes it possible to apply it to a variety of battery configurations.

[0037] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure.

[0038] The present disclosure may be any of the following [1] to

[10] . [1] An electrode comprising: a current collector having a metal layer composed of metal particles; and an active material layer formed on the surface of the metal layer and containing active material particles, wherein the average particle size d [nm] of the metal particles and the average particle size D [μm] of the active material particles satisfy the relationship (D-11) × (d-150) > 0. [2] The electrode according to [1], wherein the average particle size d of the metal particles is 10 nm or more and 1000 nm or less. [3] The electrode according to [1] or [2], wherein the average particle size D of the active material particles is 5 μm or more and 20 μm or less. [4] The electrode according to any one of [1] to [3], wherein the thickness t of the metal layer is 0.2 μm or more and 1.0 μm or less. [5] The electrode according to any one of [1] to [4], wherein the metal particles are aluminum particles. [6] The electrode according to any one of [1] to [5], wherein the current collector has a resin layer as a substrate, and the metal layer is provided on the surface of the substrate. [7] The electrode according to [6], wherein the substrate is polyethylene terephthalate or polyimide. [8] The electrode according to [6] or [7], wherein the thickness T of the substrate is 12 μm or more and 25 μm or less. [9] An electricity storage device comprising: the electrode according to any one of [1] to [8]; and an ion-conductive medium in contact with the electrode and conducting carrier ions.

[10] A method for manufacturing an electrode, comprising: a metal layer forming step of forming a metal layer composed of metal particles on a surface of a substrate by electron beam evaporation; and an active material layer forming step of forming an active material layer containing active material particles on the surface of the metal layer, wherein in the active material layer forming step, active material particles are used such that the average particle size d [nm] of the metal particles and the average particle size D [μm] of the active material particles satisfy (D-11) × (d-150) > 0. [Example]

[0039] Specific examples of implementing the electricity storage device of the present disclosure will be described below as examples. Experimental Examples 1 to 4, 6, and 16 to 18 correspond to working examples of the present disclosure, Experimental Examples 5, 8 to 13, and 15 correspond to comparative examples, and Experimental Examples 7 and 14 correspond to reference examples.

[0040] [Experimental Example 1] (Preparation of positive electrode current collector) A polyethylene terephthalate (PET) sheet with a thickness T of 25 μm was placed on the deposition substrate and placed in the EB deposition device. After that, aluminum was used as the deposition source, and 2.4 × 10 -4 Electron beam (EB) deposition was performed at a deposition rate of 6 to 7 Å / sec under 100 Pa. This resulted in a current collector in which an aluminum layer (metal layer) with a thickness t of 0.2 μm was formed on the PET sheet.

[0041] (Observation of the positive electrode current collector surface using a scanning electron microscope (SEM)) The results of SEM observation of aluminum particles on the surface of the aluminum layer of the positive electrode current collector are shown in Figure 2. As shown in Figure 2, the metal layer formed on the resin by electron beam evaporation had a structure in which metal particles were densely accumulated, with uniform particle diameters. Ten aluminum particles were randomly selected from each 50,000x SEM image, and the average particle diameter was calculated. This was then repeated for three images, resulting in the final average aluminum particle diameter d.

[0042] (Preparation of electrode mixture slurry and fabrication of positive electrode) As the positive electrode active material, LiNi with an average primary particle size D of 5 to 10 μm 0.5 Co 0.2 Mn 0.3 A positive electrode slurry was prepared by mixing 90% by mass of O2 (manufactured by Toda Kogyo Co., Ltd.), 6% by mass of a conductive material containing fibrous graphite and expanded graphite, and 4% by mass of polyvinylidene fluoride as a binder, followed by the addition of N-methyl-2-pyrrolidone (NMP). This slurry was applied to the previously prepared aluminum thin film current collector for the positive electrode and dried by heating. The resulting coated sheet was passed through a roll press to densify it, yielding a positive electrode.

[0043] (Calculation of mass energy density) The positive electrode was cut into a rectangle measuring 56 mm x 25 mm, and the rest was peeled off, leaving an electrode area of ​​40 mm x 25 mm in the center. The thickness and mass of this were measured, and the mass energy density (Ah / g) per positive electrode was calculated.

[0044] (Fabrication of a single-electrode laminated battery with lithium metal as the counter electrode) The electrode composite coating area of ​​the positive electrode was 40 mm long, and an aluminum tab was attached to the remaining excess current collector. A 25 mm x 45 mm piece of metallic lithium was attached to the center of a 74 mm x 25 mm piece of copper foil to form a counter electrode, with nickel tabs attached to the copper foil at both ends. The positive electrode and counter electrode were placed opposite each other with a separator in between to form a laminated electrode assembly. This electrode assembly was sealed in an aluminum laminated bag, impregnated with a nonaqueous electrolyte, and then sealed to form a single-electrode laminated battery for evaluation. The nonaqueous electrolyte used was a 1M solution of LiPF6 in a mixed solvent of 30 vol% ethylene carbonate (EC), 40 vol% dimethyl carbonate (DMC), and 30 vol% ethyl methyl carbonate (EMC).

[0045] (Electrode performance test) The laminated battery described above was used as a test battery to carry out a battery performance test. The charge / discharge test of the test battery was carried out as follows, at a temperature of 25°C and in a range of 2.5V to 4.2V relative to lithium. CC charging and CC discharging were carried out at a constant current of 0.1C, and this was repeated for three cycles.

[0046] [Experimental Examples 2, 3, and 4] Experimental Examples 2, 3, and 4 were the same as Experimental Example 1, except that the deposition time was changed to make the thickness t of the aluminum layer 0.4 μm, 0.6 μm, and 1.0 μm, respectively.

[0047] [Experimental Example 5] The same procedure as in Experimental Example 1 was carried out except that a commercially available aluminum foil having a thickness of 15 μm was used as the current collector.

[0048] [Experimental Example 6] Experimental Example 6 was the same as Experimental Example 1, except that the deposition time was changed so that the thickness t of the aluminum layer of the current collector was set to 0.1 μm.

[0049] [Experimental Example 7] In Experimental Example 7, an aluminum current collector was produced by depositing aluminum to a thickness t of 1.5 μm using the same method as in Experimental Example 1, except that the deposition time was changed. In Experimental Example 7, peeling of the aluminum occurred from the edges and cracks and peeling occurred on the entire aluminum surface, making it impossible to obtain a thin film usable as a current collector.

[0050] [Experimental Examples 8, 9, and 10] In Experimental Example 8, a polyethylene terephthalate (PET) sheet having a thickness T of 25 μm was placed on a deposition substrate, and the substrate was placed in an EB deposition apparatus. After that, aluminum was used as the deposition source, and 2.4 × 10 -4 EB deposition was performed under 10 Pa at a deposition rate of 9 to 10 Å / sec. This resulted in a current collector in which an aluminum layer (metal layer) with a thickness t of 0.2 μm was formed on a PET sheet. Experimental Example 1 was repeated except for using the current collector thus obtained. Experimental Examples 9 and 10 were repeated in the same manner as Experimental Example 8 except for changing the deposition time to set the thickness t of the aluminum layer of the current collector to 0.4 μm and 1 μm, respectively.

[0051] [Experimental Examples 11, 12, and 13] In Experimental Example 11, in preparing the electrode mixture slurry, LiNi 0.5 Co 0.2 Mn 0.3 O2 (manufactured by Toda Kogyo Co., Ltd.) was used. Other than that, the experiment was the same as in Experimental Example 1. Experimental Examples 12 and 13 were the same as Experimental Example 11, except that the deposition time was changed so that the thickness t of the aluminum layer of the current collector was 0.4 μm and 1 μm, respectively.

[0052] [Experimental Example 14] In Experimental Example 14, an aluminum current collector was produced by vapor-depositing aluminum until the thickness t reached 0.2 μm using the same method as in Experimental Example 1, except that the thickness T of the PET sheet was set to 5 μm. An attempt was made to coat this current collector with the positive electrode composite using the same procedure as in Experimental Example 1, but the produced current collector was thin and warped or kinked, making coating difficult.

[0053] [Experimental Example 15] The same procedure as in Experimental Example 11 was carried out except that a commercially available aluminum foil having a thickness of 15 μm was used as the current collector.

[0054] [Experimental Examples 16, 17, and 18] In Experimental Example 16, in producing a current collector, a polyethylene terephthalate (PET) sheet having a thickness T of 25 μm was placed on a deposition substrate, which was then placed in an EB deposition apparatus. After that, aluminum was used as the deposition source, and 2.4 × 10 -4 EB deposition was performed under 100 Pa at a deposition rate of 9 to 10 Å / sec. This resulted in a current collector with an aluminum layer (metal layer) with a thickness t of 0.2 μm formed on the PET sheet. In addition, in preparing the electrode mixture slurry, LiNi 0.5 Co 0.2 Mn 0.3 O2 (manufactured by Toda Kogyo Kogyo Co., Ltd.) was used. Other than that, the same procedures as in Experimental Example 1 were carried out. Experimental Examples 17 and 18 were carried out in the same manner as in Experimental Example 16, except that the deposition time was changed so that the thickness t of the aluminum layer of the current collector was 0.4 μm and 1.0 μm, respectively.

[0055] [Results and Discussion] Table 1 summarizes the normalized mass energy density and normalized discharge capacity for Experimental Examples 1 to 18. The normalized mass energy density was determined by normalizing the mass energy density of Experimental Example 5, which used 15 μm aluminum foil as the current collector, to 1. The normalized discharge capacity was determined by normalizing the discharge capacity of Experimental Example 5 to 1.

[0056] The relationship between the normalized mass energy density and the thickness of the metal layer (aluminum) is shown in Figure 3. The relationship between the normalized mass energy density and the thickness of the resin layer is shown in Figure 4. In Figure 3, the thickness of the resin layer is set to 25 μm, and in Figure 4, the thickness of the metal layer is set to 0.2 μm.

[0057] Figure 5 shows charge-discharge curves obtained by CCCV charging at a constant current of 0.2 C followed by CCCV discharging at a constant current of 0.1 C for Experimental Examples 1, 2, and 5. It was found that the positive electrodes of Experimental Examples 1 and 2 exhibited stable charge-discharge behavior. Experimental Examples 3 to 4, 6, and 16 to 18 also exhibited stable charge-discharge behavior.

[0058] As shown in Table 1, among Experimental Examples 1 to 18, Experimental Examples 1 to 4, 6, 8 to 13, and 16 to 18, which used current collectors with a metal layer formed on a resin layer, had higher mass energy densities than Experimental Example 5 and Experimental Example 15, which used conventional metal foil current collectors. Experimental Examples 8 to 13, which did not satisfy (D-11) × (d-150) > 0, exhibited low normalized discharge capacities of 0.93 or less. In contrast, Experimental Examples 1 to 4, 6, and 16 to 18, which satisfied (D-11) × (d-150) > 0, exhibited high normalized discharge capacities of 0.94 or more, demonstrating that discharge capacity degradation could be suppressed. In particular, Experimental Examples 1 to 4 and Experimental Examples 16 to 18 exhibited high normalized discharge capacities of 0.98 or more, demonstrating that discharge capacity degradation could be further suppressed. The discharge capacity of Experimental Example 6 was relatively low, presumably because the metal layer thickness t was thin, making the electronic conductivity of the current collector rate-determining. From this, it was inferred that, from the viewpoint of electronic conductivity, the thickness t of the metal layer is preferably greater than 0.1 μm. In Experimental Example 7, the metal layer thickness t could not be increased to 1.5 μm. However, it was inferred that an aluminum layer could be formed without cracking or peeling by adjusting the film formation method and film formation conditions. However, from the viewpoint of ease of metal layer formation, it was inferred that the metal layer thickness t is preferably less than 1.5 μm. Furthermore, as shown in Figure 3, the thinner the metal layer thickness t, the higher the mass energy density. Therefore, it was inferred that the metal layer thickness t is preferably less than 1.5 μm from the viewpoint of mass energy density. In Experimental Example 14, the resin layer thickness T was thin at 5 μm, and the overall thickness of the current collector was also thin, so the current collector sagged and twisted, making it impossible to coat the composite layer. However, it was inferred that the composite layer could be coated by using a resin layer made of a high-strength material. However, from the viewpoint of ease of coating the composite layer, it was inferred that the resin layer thickness T is preferably greater than 5 μm. On the other hand, as shown in FIG. 4, the thinner the thickness T of the resin layer, the higher the mass energy density can be, and therefore it was inferred that the thickness T of the resin layer is preferably, for example, 25 μm or less.

[0059] [Table 1] [Industrial Applicability]

[0060] The present disclosure is applicable to the technical field of electricity storage devices. [Explanation of symbols]

[0061] 10 Energy storage device, 12 Electrode (positive electrode), 13 Active material layer, 13p Active material particles, 14 Current collector, 15 Counter electrode (negative electrode), 16 Active material layer, 17 Current collector, 21 Substrate, 22 Metal layer, 22p Metal particles, d, D Average particle diameter, t, T Thickness.

Claims

1. a current collector having a metal layer made of metal particles; an active material layer formed on the surface of the metal layer and including active material particles; wherein an average particle size d [nm] of the metal particles and an average particle size D [μm] of the active material particles satisfy (D-11)×(d-150)>0.

2. The electrode according to claim 1 , wherein the metal particles have an average particle size d of 10 nm or more and 1000 nm or less.

3. 3. The electrode according to claim 1, wherein the active material particles have an average particle size D of 5 μm or more and 20 μm or less.

4. The electrode according to claim 1 or 2, wherein the thickness t of the metal layer is 0.2 μm or more and 1.0 μm or less.

5. 3. The electrode according to claim 1, wherein the metal particles are aluminum.

6. The electrode according to claim 1 or 2, wherein the current collector has a resin layer as a substrate, and the metal layer is provided on a surface of the substrate.

7. 7. The electrode of claim 6, wherein the substrate is polyethylene terephthalate or polyimide.

8. The electrode according to claim 6 , wherein the thickness T of the substrate is 12 μm or more and 25 μm or less.

9. The electrode according to claim 1 or 2; an ion-conducting medium in contact with the electrode and conducting carrier ions; An electricity storage device comprising:

10. a metal layer forming step of forming a metal layer composed of metal particles on a surface of a substrate by electron beam deposition; an active material layer forming step of forming an active material layer containing active material particles on the surface of the metal layer; wherein in the active material layer forming step, the active material particles are used such that an average particle size d [nm] of the metal particles and an average particle size D [μm] of the active material particles satisfy (D-11) × (d-150) > 0.

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