Electrode for energy storage device, energy storage device, and method for manufacturing electrode for energy storage device

Abstract

To further improve bondability of an active material layer of a porous body containing Si to a current collector.SOLUTION: An electricity storage device electrode includes: an active material layer that has a plate-like porous silicon material including at least Si and Al and having voids as an electrode active material; a current collector; and a film body of a metal M that is interposed between the active material layer and the current collector and forms an eutectic alloy with an element constituting the current collector and Si.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses electrodes for energy storage devices, energy storage devices, and methods for manufacturing electrodes for energy storage devices. [Background technology]

[0002] Conventionally, porous silicon particles have been proposed as silicon anode materials, obtained by a manufacturing method that includes a particle formation step of dissolving a silicon alloy containing 50% or more by mass of Al, which is a primary element, and 50% or less by mass of Si, and forming particles, and a porosity formation step of removing the primary element from the silicon alloy to obtain porous silicon particles (see, for example, Patent Document 1). These porous silicon particles have an average particle size in the range of 0.1 μm to 100 μm, contain a three-dimensional network structure of silicon skeleton with voids, have an average porosity in the range of 50% by volume to 95% by volume, and contain 85% or more by mass of Si and 15% or less by mass of Al in terms of the ratio of elements excluding oxygen. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-123517 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, the porous silicon particles described in Patent Document 1 above are relatively fine and have a high porosity, making coating for use as electrodes difficult. Furthermore, these porous silicon particles presented challenges in bonding between the active material layer containing the porous silicon particles and the current collector.

[0005] This disclosure has been made in view of the above issues, and its main objective is to provide an electrode for an energy storage device, an energy storage device, and a method for manufacturing an electrode for an energy storage device that can further improve the bonding between a porous active material layer containing Si and a current collector. [Means for Solving the Problem]

[0006] As a result of intensive research to achieve the above object, the present inventors have found that after melting a silicon alloy containing at least Al and Si to obtain a plate-shaped precursor, joining the precursor and a current collector via a predetermined film body and removing an Al-containing compound can further improve the bonding performance between the active material layer and the current collector, and thus have completed the electrode for an electricity storage device, the electricity storage device, and the method for producing an electrode for an electricity storage device of the present disclosure.

[0007] That is, the electrode for an electricity storage device of the present disclosure is: an active material layer containing, as an electrode active material, a plate-shaped porous silicon material that contains at least Si and Al and has voids; a current collector; and a film body of a metal M that is interposed between the active material layer and the current collector and forms a eutectic alloy with the element constituting the current collector and Si, comprising the above components.

[0008] The electricity storage device of the present disclosure is: a positive electrode containing a positive electrode active material; a negative electrode that is the electrode for an electricity storage device described above; and an ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts lithium ions, comprising the above components.

[0009] The method for producing an electrode for an electricity storage device of the present disclosure is: a bonding step of, in a state where a film body of a metal M that forms a eutectic alloy with the element constituting the current collector and Si is interposed between a precursor that is a plate-shaped silicon alloy containing at least Si and Al and having no voids and the current collector, heating and pressure-bonding the precursor and the current collector at a bonding temperature exceeding 150°C; and an electrode-forming step of removing an Al component contained in the silicon alloy to form an active material layer of a porous silicon material having a plate shape, comprising the above steps. [Effect of the Invention]

[0010] This disclosure can further improve the bonding strength between a porous material layer containing Si and a current collector. The reason for this effect is presumed to be as follows. For example, when bonding a current collector to porous silicon, pressure bonding can be considered, but the porosity of the porous material may decrease due to the pressure, and there is a limit to the amount of pressure that can be applied. Also, when making Si porous using Al, Al may be removed with an acid or alkali, but if Al is removed after pressure bonding the current collector before porosity creation, the bonding strength of the current collector may decrease. In this disclosure, the active material layer and the current collector are bonded via a film of metal M that forms a eutectic alloy with the elements constituting the current collector and Si, so the decrease in bonding strength due to the removal of Al can be further suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] An explanatory diagram showing an example of the structure of the energy storage device 10. [Figure 2] Al-Si binary system phase diagram. [Figure 3] An explanatory diagram showing an example of a manufacturing method for electrodes used in energy storage devices. [Figure 4] Evaluation results of the porous silicon material in Reference Example 2. [Figure 5] Evaluation results of the electrodes in Reference Example 2. [Figure 6] An explanatory diagram showing an example of the manufacturing method for Experimental Examples 1-6 and 8. [Figure 7] Observational photographs of the acid treatment in Experimental Examples 1-3 and 8. [Figure 8] An SEM image of a cross-section of Experimental Example 2 and an explanatory diagram showing an example of its microstructure. [Modes for carrying out the invention]

[0012] (Electrodes for energy storage devices) The electrode for an energy storage device according to this disclosure comprises an active material layer, a current collector, and a film between the active material layer and the current collector. The active material layer contains at least Si and Al, and has a plate-shaped porous silicon material with voids as the electrode active material. The film is composed of the elements constituting the current collector and a metal M that forms a eutectic alloy with Si. This electrode becomes either a positive or negative electrode based on the potential of the counter electrode relative to the potential of the electrode active material, but it is preferable to make it a negative electrode when lithium is used as the carrier. This electrode can be used, for example, in lithium-ion secondary batteries, hybrid capacitors, air batteries, etc. The porous silicon material includes a three-dimensional network structure of silicon with voids, and Al may be present inside or outside this silicon skeleton.

[0013] The active material layer has a plate-shaped porous silicon material containing at least Si and Al and having voids, as the electrode active material. The active material layer may have a one-piece shape and not contain a binder. Similarly, the plate-shaped porous silicon material may have a one-piece shape and not contain a binder. It is preferable that the active material layer does not contain conductive material or binder, as this can further increase the capacity. The plate-shaped porous silicon material preferably has a thickness in the range of 10 μm to 50 μm. A thickness of 10 μm or more is preferable from the viewpoint of increasing the capacity, and a thickness of 50 μm or less is preferable from the viewpoint of the strength of the plate-shaped material. A thickness in the range of 20 μm to 40 μm is more preferable. The thickness of the porous silicon material may be appropriately selected according to the required battery characteristics. The plate-shaped porous silicon material may have a current collector heat-pressed onto one surface with a film interposed therebetween. Heat-pressing is preferable because the film easily increases the bonding strength. The conditions for this heat-pressing will be described in detail later.

[0014] The active material layer may consist of a porous silicon material having a porosity in the range of 10% to 50% by volume. This porosity is preferably 40% by volume or less, more preferably 35% by volume or less, and may be 30% by volume or less. Furthermore, the porosity is preferably 15% by volume or more, more preferably 20% by volume or more, and may be 25% by volume or more. From the viewpoint of silicon volume change, a larger porosity is preferable, while from the viewpoint of charge / discharge capacity of the energy storage device, a smaller porosity is preferable. This porosity is measured using a mercury porosimeter.

[0015] The active material layer may consist of a porous silicon material in which the pore size distribution range determined by the mercury intrusion method is in the range of 1 nm to 500 nm. This pore size may be 10 nm or more, 50 nm or more, or 100 nm or more. Furthermore, this pore size is preferably 250 nm or less, but may also be 200 nm or less, or 150 nm or less. In this porous silicon material, the average pore size determined by the mercury intrusion method may be in the range of 5 nm to 500 nm, or in the range of 10 nm to 250 nm.

[0016] The active material layer may have a porous silicon material containing two types of structures: coarse grains (microscale) containing primary silicon that crystallizes upon cooling, and fine grains (nanoscale) containing eutectic silicon with Al. It is presumed that this structure can alleviate the stress of volume expansion during charging and discharging. The coarse grains can be, for example, granular portions in the range of 1 μm to 5 μm. The fine grains can be, for example, granular portions in the range of 10 nm to 100 nm.

[0017] The active material layer preferably has a porous silicon material containing 75 at% or more Si when the total amount of Si and Al, excluding oxygen and unavoidable impurities, is set to 100 at%. The Si content is more preferably 80 at% or more, even more preferably 85 at% or more, and may be 90 at% or more or 98 at% or more. A higher Si content is preferable from the viewpoint of charge / discharge capacity, and a lower Si content is preferable from the viewpoint of relative skeletal reinforcement. The Al content is preferably in the range of 0.5 at% to 15 at%, preferably 12.5 at% or less, more preferably 10 at% or less, and may be 7.5 at% or less. Furthermore, the Al content is preferably 1 at% or more, more preferably 2 at% or more, and may be 2.5 at% or more. A higher Al content is preferable from the viewpoint of supplementing skeletal reinforcement, and a lower Al content is preferable from the viewpoint of charge / discharge capacity of the energy storage device, since Al is a component that does not charge or discharge. Furthermore, the porous silicon material may contain one or more of the secondary elements Ti, Sn, Ca, Cu, Mg, Na, Sr, and P in a range of 15% by mass or less. In addition, the porous silicon material may contain unavoidable impurities in addition to Si and Al. Unavoidable impurities are components that inevitably remain during the purification of Si, Al, etc., and examples include Fe, C, Cu, Ni, and P. The amount of unavoidable impurities is preferably 2 at% or less, and more preferably 1 at% or less. It is preferable that the amount of secondary elements and unavoidable impurities be as low as possible.

[0018] The current collector is a component that has excellent electron conductivity and extracts current to the outside, and is formed on one surface of the active material layer. The current collector is integrated with the active material layer via a film composed of at least metal M. This current collector can be made of, for example, aluminum, titanium, stainless steel, nickel, iron, copper, calcined carbon, conductive polymer, conductive glass, etc., or aluminum or copper whose surface has been treated with carbon, nickel, titanium, or silver for the purpose of improving adhesion, conductivity, and oxidation resistance. It is also possible to oxidize the surface of these materials. Of these, the current collector preferably contains Cu, and may be a Cu alloy, but pure copper is more preferable. The shape of the current collector can be foil, film, sheet, net, punched or expanded, lath, porous, foam, or fiber group formed, but foil is more preferable. The thickness of the current collector can be, for example, 1 to 500 μm, but thicknesses of 30 μm or less, 20 μm or less, or 15 μm or less are preferred.

[0019] The film is interposed between the active material layer and the current collector and is composed of a metal M that forms a eutectic alloy with the elements constituting the current collector and Si. This film is directly adjacent to the current collector. Furthermore, this film may be in direct contact with the active material layer, or it may be formed via a predetermined interlayer. The metal M of this film may be, for example, Sn. Sn can form a eutectic alloy with both the Si in the active material layer and the Cu in the current collector. Sn is also preferable because it can improve bonding properties, such as exhibiting fluidity even at lower temperatures, for example, below 250°C. The thickness of this film is preferably in the range of 50 nm to 300 nm. A thickness of 50 nm or more allows for sufficient improvement of bonding properties, while a thickness of 300 nm or less reduces the amount of components that do not affect charge / discharge capacity, which is preferable from the viewpoint of energy density. The thickness of the film is preferably, for example, 75 nm or more, and may be 100 nm or more. Furthermore, the thickness of this film is preferably 250 nm or less, and may be 200 nm or less. Also, the electrode for this energy storage device may have a Si film with a thickness of 300 nm or less formed as an interlayer between the film and the active material layer. The active material layer is, for example, made by removing Al from a precursor SiAl alloy, but the presence of a Si film as an interlayer is more preferable as it can further improve the bonding between the active material layer and the film. This interlayer may have a thickness of 50 nm or more, or 100 nm or more. Also, the thickness of the interlayer may be 350 nm or less, or 200 nm or less. The thickness of the interlayer is preferably within a range that does not affect the porosity of the active material layer.

[0020] (Energy storage device) The electricity storage device of the present disclosure includes an electrode for an electricity storage device that includes an active material layer containing the above-mentioned porous silicon material, a current collector, and a membrane body. This electricity storage device may include a positive electrode, a negative electrode, and an ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts carrier ions. The porous silicon material can be used as a negative electrode active material. It is preferable that the electricity storage device includes the above-described electrode for an electricity storage device as the negative electrode. The electricity storage device may be any one of a lithium ion secondary battery, a hybrid capacitor, an air battery, and the like. In the positive electrode, as the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used. Specifically, transition metal sulfides such as TiS₂, TiS₃, MoS₃, and FeS₂, Li (1-x) MnO₂ (0<x<1, the same applies hereinafter) or Li (1-x) Mn₂O₄ or other lithium manganese composite oxides, wherein the basic composition formula is Li (1-x) CoO₂ or other lithium cobalt composite oxides, wherein the basic composition formula is Li (1-x) NiO₂ or other lithium nickel composite oxides, wherein the basic composition formula is Li (1-x) Ni a Co b Mn c O₂ (a+b+c=1) or other lithium nickel cobalt manganese composite oxides, lithium vanadium composite oxides having a basic composition formula such as LiV₂O₃, transition metal oxides having a basic composition formula such as V₂O₅, and the like can be used. Among these, lithium transition metal composite oxides, for example, LiCoO₂, LiNiO₂, LiMnO₂, Li (1-x) Ni 1 / 3 Co 1 / 3 Mn 1 / 3O2 is preferred. Note that the "basic composition formula" means that other elements such as Al and Mg may also be included. Alternatively, the positive electrode active material may be a carbonaceous material used in capacitors, lithium-ion capacitors, etc. Examples of carbonaceous materials include activated carbon, coke, glassy carbon, graphite, non-graphitizable carbon, pyrolytic carbon, carbon fibers, carbon nanotubes, and polyacenes. Of these, activated carbon, which exhibits a high specific surface area, is preferred. Activated carbon as a carbonaceous material has a specific surface area of ​​1000 m². 2 It is preferable that it be 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 / g, and 2000m 2 It is more preferable that the value be less than or equal to / g.

[0021] The positive electrode of the energy storage device can be manufactured by either mixing the positive electrode active material described above with a conductive material and binder and a solvent as needed to form a paste, which is then applied to a current collector, or by mixing the positive electrode active material with a conductive material and binder as needed and pressing it onto a current collector. In this electrode, the content of the positive electrode active material is preferably higher, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more. The conductive material is not particularly limited as long as it is an electronically conductive material that does not adversely affect the battery performance. For example, one or more of the following can be used: graphite such as natural graphite (scaly graphite, flake graphite) or artificial graphite, acetylene black, carbon black, Ketjenblack, carbon whiskers, needle coke, carbon fiber, or a mixture of two or more metals (copper, nickel, aluminum, silver, gold, etc.). The binder serves to bind the active material particles and conductive material particles together. For example, fluororesins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber, or thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM rubber, and natural butyl rubber (NBR) can be used individually or as a mixture of two or more. Water-based binders such as cellulose-based or aqueous dispersions of styrene-butadiene rubber (SBR) can also be used. As a solvent, organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran can be used. Alternatively, a dispersant and a thickener may be added to water, and the active material may be slurryed with a latex such as SBR. Coating methods include roller coating using applicator rolls, screen coating, doctor blade method, spin coating, and bar coating, and any thickness and shape can be achieved using any of these methods. Current collectors used in the positive electrode can be those exemplified in the electrodes for energy storage devices described above.

[0022] As the ion-conducting medium, non-aqueous electrolytes containing supporting salts or non-aqueous gel electrolytes can be used. Examples of solvents for non-aqueous electrolytes 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, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate; linear 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; 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. Of these, a combination of cyclic carbonates and linear carbonates is preferred. This combination not only provides excellent cycle characteristics, which represent the battery characteristics during repeated charge and discharge cycles, but also allows for a balanced relationship between the viscosity of the electrolyte, the electrical capacity of the resulting battery, and the 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. From the viewpoint of electrical characteristics, it is preferable to use a combination of one or more salts selected from the group consisting of inorganic salts such as LiPF6, LiBF4, LiAsF6, and LiClO4, and organic salts such as LiCF3SO3, LiN(CF3SO2)2, and LiC(CF3SO2)3.The supporting salt is preferably at a concentration of 0.1 mol / L or more and 5 mol / L or less in the non-aqueous electrolyte, and more preferably at a concentration of 0.5 mol / L or more and 2 mol / L or less. A concentration of 0.1 mol / L or higher allows for sufficient current density, while a concentration of 5 mol / L or lower allows for greater stability of the electrolyte. Furthermore, flame retardants such as phosphorus-based or halogen-based agents may be added to this non-aqueous electrolyte.

[0023] Furthermore, instead of a liquid ion-conducting medium, a solid ion-conducting polymer can be used as the ion-conducting medium. Examples of ion-conducting polymers include polymer gels composed of polymers such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinylpyrrolidone, and vinylidene fluoride, along with supporting salts. In addition, a combination of an ion-conducting polymer and a non-aqueous electrolyte can also be used. Moreover, in addition to ion-conducting polymers, inorganic solid electrolytes, mixed materials of organic polymer electrolytes and inorganic solid electrolytes, or inorganic solid powders bound together by an organic binder can be used as the ion-conducting medium.

[0024] The energy storage device may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as its composition can withstand the operating range of lithium secondary batteries, but examples include polymer nonwoven fabrics such as polypropylene nonwoven fabric or polyphenylene sulfide nonwoven fabric, and thin microporous membranes of olefin resins such as polyethylene or polypropylene. These may be used individually or in combination.

[0025] The shape of this energy storage device is not particularly limited, but examples include coin-shaped, button-shaped, sheet-shaped, laminated, cylindrical, flat, and rectangular shapes. It may also be applied to larger devices used in electric vehicles, etc. Figure 1 is an explanatory diagram showing an example of the structure of an energy storage device 10. This energy storage device 10 has a positive electrode 12, a negative electrode 15, and an ion conducting medium 18. The positive electrode 12 has a positive electrode active material layer 13 and a current collector 14. The negative electrode 15 has a negative electrode active material layer 16 and a current collector 17. The negative electrode 15 is an electrode for the energy storage device described above and comprises a negative electrode active material layer 16 having a plate-shaped porous silicon material 21 as an electrode active material that contains at least Si and Al and has voids 23, a current collector 17, and a film body 25 of metal M interposed between the negative electrode active material layer 16 and the current collector 17, which forms a eutectic alloy with the elements constituting the current collector 17 and Si. Furthermore, an interlayer 24 made of Si may be formed between the film 25 and the negative electrode active material layer 16.

[0026] (All-solid-state lithium-ion rechargeable battery) This energy storage device is preferably an all-solid-state lithium-ion secondary battery. All-solid-state batteries are preferable because they can further suppress performance changes due to the electrolyte and enhance safety. This all-solid-state lithium-ion secondary battery may comprise a positive electrode containing a positive electrode active material, a negative electrode which is the electrode for the energy storage device described above, and a solid electrolyte interposed between the positive and negative electrodes to conduct lithium ions. The positive electrode can be any of those shown in the energy storage device described above. The negative electrode can be the electrode for the energy storage device described above.

[0027] The solid electrolyte may be, for example, a garnet-type oxide containing at least Li, La, and Zr. This solid electrolyte has a basic composition of Li 7.0+x-y (La 3-x ,A x )(Zr 2-y ,T y )O 12may be satisfied. However, A is at least one of Sr and Ca, T is at least one of Nb and Ta, which satisfy 0<x≦1.0 and 0<y<0.75. Alternatively, the solid electrolyte has a basic composition (Li 7-3z+x-y M z )(La 3-x A x )(Zr 2-y T y )O 12 and (Li 7-3z+x-y M z )(La 3-x A x )(Y 2-y T y )O 12 may be a garnet-type oxide represented by. In the formula, the element M is at least one of Al and Ga, the element A is at least one of Ca and Sr, and T is at least one of Nb and Ta, which may satisfy 0≦z≦0.2, 0≦x≦0.2 and 0≦y≦2. In this basic composition formula, it is more preferable to satisfy 0.05≦z≦0.1. In this basic composition formula, it is more preferable to satisfy 0.05≦x≦0.1. Further, in this basic composition formula, it is more preferable to satisfy 0.1≦y≦0.8. In such a range, more favorable ionic conductivity can be obtained.

[0028] Alternatively, examples of the solid electrolyte include common Li 14 Zn(GeO4)4 called Li3N and LISICON, sulfide Li 3.25 Ge 0.25 P 0.75 S4, perovskite-type La 0.5 Li 0.5 TiO3, (La 2 / 3 Li 3x □ 1 / 3-2x )TiO3 (□: atomic vacancy), garnet-type Li7La3Zr2O 12 , LiTi2(PO4)3 called NASICON-type, Li 1.3 M 0.3 Ti 1.7 (PO3)4 (M=Sc, Al), and the like. Further, Li7P3S obtained from glass with a composition of 80Li2S·20P2S5 (mol%), which is a glass-ceramic11 Furthermore, Li, a sulfide-based substance with high conductivity. 10 Ge2PS2 is another example. Examples of glass-based inorganic solid electrolytes include Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li4SiO4, Li2S-P2S5, Li3PO4-Li4SiO4, Li3BO4-Li4SiO4, and those using SiO2, GeO2, B2O3, and P2O5 as glass-based materials with Li2O as a network modifier. Other examples of thiolysicone solid electrolytes include Li2S-GeS2 systems, Li2S-GeS2-ZnS systems, Li2S-Ga2S2 systems, Li2S-GeS2-Ga2S3 systems, Li2S-GeS2-P2S5 systems, Li2S-GeS2-SbS5 systems, Li2S-GeS2-Al2S3 systems, Li2S-SiS2 systems, Li2S-P2S5 systems, Li2S-Al2S3 systems, LiS-SiS2-Al2S3 systems, and Li2S-SiS2-P2S5 systems. These solid electrolytes may be formed in a plate shape and placed between the positive and negative electrodes.

[0029] Furthermore, the all-solid-state lithium-ion secondary battery may be equipped with a restraining member that restrains the laminate, which is made up of a positive electrode, a solid electrolyte, and a negative electrode, in the stacking direction. This restraining member may, for example, include a pair of plate-like parts that sandwich the laminate from both ends in the stacking direction, a rod-like part that connects the pair of plate-like parts, and an adjustment part connected to the rod-like part that adjusts the distance between the pair of plate-like parts by a screw structure or the like.

[0030] (Method for manufacturing electrodes for energy storage devices) The method for manufacturing electrodes for energy storage devices described in this disclosure may also be used to manufacture the electrodes for energy storage devices described above. Here, the physical properties of the porous silicon material are assumed to be the same as those of the electrodes for energy storage devices described above, and a detailed explanation thereof is omitted. The method for manufacturing electrodes for energy storage devices described in this disclosure includes a bonding step and an electrode formation step. The method for manufacturing electrodes for energy storage devices may also include a precursor step in which a precursor is prepared before the bonding step. This precursor step can be omitted by preparing a pre-fabricated precursor. In the method for manufacturing electrodes for energy storage devices, in the bonding step, a film of metal M, which is a plate-shaped silicon alloy containing at least Si and Al and having no voids, is interposed between the precursor and the current collector, and the current collector is heated and pressed together at a bonding temperature of over 150°C. In the electrode formation step, the Al component contained in the silicon alloy is removed to obtain a porous silicon material having a plate-like shape as part of the electrodes for energy storage devices. First, the raw material composition will be described.

[0031] Figure 2 is an Al-Si binary phase diagram. Generally, in the equilibrium phase diagram of a eutectic Si-Al alloy, when a molten state with a eutectic composition where the liquidus line is minimal is solidified, a eutectic structure is formed in which the Si phase and Al phase separate in a fibrous (lamellar) manner. At this time, the size of the formed lamellar structure becomes finer as the cooling rate increases, and at cooling rates of 1000 K / s or higher, a nano-sized structure is formed. If only the Al element can be selectively removed from this eutectic structure, a material consisting of Si element with a eutectic structure can be obtained. In the case of Si-Al alloys, 13Si-87Al is close to the eutectic composition. In this case, it is difficult to obtain a self-supporting film when Al is dissolved, but if an alloy is made around 50Si-50Al, primary Si that does not alloy with eutectic Sj and Al grows. This primary Si forms the framework that maintains the sheet-like structure of the electrode. During electrochemical reactions, the pores formed by the eutectic Si act to mitigate the expansion and contraction of the electrode.

[0032] (Precursor process) In the precursor process, it is preferable to use a raw material in which, when the total amount of Si and Al is set to 100 at%, Al is in the range of 30 at% to 70 at%, with the remainder being Si. The raw material may contain unavoidable impurities. It is preferable that the amount of unavoidable impurities be as low as possible. The Al content ratio is preferably 65 at% or less, more preferably 60 at% or less, and may also be 55 at% or less. Furthermore, the Al content ratio is preferably 35 at% or more, more preferably 40 at% or more, and may also be 45 at% or more. Silicon alloys containing Al in this range are preferable because they allow for a higher porosity and the acquisition of voids of a more suitable shape and size. When the Al content is high, rapid cooling after melting to form an alloy causes a large amount of single-phase Al to precipitate, thus forming many voids. It is preferable that the cooling rate be as rapid as possible, for example, 10 2 ℃ / s or more 10 8 The range may be less than or equal to °C / s.

[0033] In this process, when dissolving the raw materials, high-frequency melting in an inert gas atmosphere such as Ar is preferred, but any melting method may be used. In the precursor process, the molten silicon alloy may be cooled by a roll quenching method to obtain a plate-like (including thin-film) precursor. Since the precursor obtained by the roll quenching method has a fine alloy structure, porous silicon with fine pores can be obtained after the dissolution treatment.

[0034] In this precursor process, a single-roll quenching apparatus as shown in Figure 3A may be used. Figure 3 is an explanatory diagram showing an example of a method for manufacturing electrodes for energy storage devices, where Figure 3A is the process for forming the precursor 30, Figure 3B is the process for forming the interlayer film 24, Figure 3C is the process for forming the film body 25, Figure 3D is the heat-pressure bonding process with the current collector 17, and Figure 3E is the electrode formation process. In this process, a plate-shaped precursor 30 may be obtained by spraying a molten raw material containing Si and Al onto a cooling roll in a reduced-pressure chamber containing an oxygen removal material and cooling it. When quenching a liquid with a cooling roll, parameters that affect the cooling rate include the temperature and thermal conductivity of the molten liquid, the hole diameter d at the nozzle tip, the gap size g between the roll and the nozzle, and the roll rotation speed r. The hole diameter d at the nozzle tip can be, for example, in the range of 0.1 mm to 5 mm, or in the range of 0.2 mm to 2 mm. The gap size g can be in the range of 0.1 mm to 5 mm, or in the range of 0.2 mm to 2 mm. The roll rotation speed r can be in the range of 1000 rpm to 5000 rpm, or it may be in the range of 2000 rpm to 4000 rpm. The chamber is 10 -3 It is preferable to reduce the pressure to below Pa. It is also preferable to introduce an inert gas into the chamber. For example, Ar is preferred as the inert gas. The internal pressure may be, for example, 30 cmHg or more, or 40 cmHg or more. It is also preferable that the internal pressure be 100 cmHg or less. The raw material is heated until it melts, and Ar gas is injected to spray the molten material from the nozzle tip toward the cooling roll, thereby obtaining a rapidly cooled and solidified precursor 30.

[0035] In the precursor step, a plate-shaped precursor 30 with a thickness in the range of 10 μm to 50 μm may be obtained. This thickness may be 20 μm to 40 μm. The thickness of the precursor 30 should be appropriately selected according to the performance required for the energy storage device. In the precursor step, it is preferable to obtain a plate-shaped precursor having an integrated shape that does not contain conductive material or binder.

[0036] In this precursor step, a raw material containing a second element, in addition to Al and Si, may be used, which includes one or more of the following: Ti, Sn, Ca, Cu, Mg, Na, Sr, and P. Of these, one or more of Ca, Na, and Sr are preferred as the second element. The amount of the second element is preferably less than the amount of Al, for example, preferably in the range of 10% by mass or less, and more preferably in the range of 5% by mass or less, relative to the total silicon alloy.

[0037] (Joining process) In the bonding process, the precursor 30 and the current collector 17 are heated and pressed together at a bonding temperature exceeding 150°C. The bonding temperature may be, for example, 200°C or higher, or 250°C or higher. Alternatively, this bonding temperature may be 300°C or lower, or 250°C or lower. A higher bonding temperature can increase the bonding strength, while a lower bonding temperature is preferable from the viewpoint of energy consumption. The pressure applied in this process is preferably 10 MPa or higher, more preferably 25 MPa or higher, and may be 40 MPa or higher. Alternatively, this pressure may be 100 MPa or lower. A higher pressure can increase the bonding strength, while a lower pressure is preferable from the viewpoint of energy consumption. The bonding temperature and applied pressure should be appropriately selected according to the desired bonding properties.

[0038] In this step, a film 25 of metal M, which forms a eutectic alloy with the elements constituting the current collector 17 and Si, is interposed between the precursor 30 and the current collector 17, and these are heated and pressed together. The current collector 17 may be any of the materials described above as appropriate. The current collector 17 is preferably made of Cu, and may be a Cu alloy, but is more preferably made of pure copper. The shape of the current collector 17 is not particularly limited, but is preferably foil-shaped. The thickness of the current collector 17 may be, for example, in the range of 1 μm to 50 μm, or 30 μm or less, 20 μm or less, or 15 μm or less. In the bonding step, it is preferable to use a film 25 made of Sn. In this step, it is also preferable to use a film 25 with a thickness in the range of 50 nm to 300 nm. An intermediate film 24 containing Si may also be interposed between the precursor 30 and the film 25. In other words, in the bonding process, an interlayer 24 with a thickness of 300 nm or less may be formed between the film body 25 and the precursor 30, and then the precursor 30 and the current collector 17 may be heat-pressed together. The interlayer 24 is preferably a Si film. Furthermore, the thickness of the interlayer 24 is preferably 50 nm or more. The interlayer 24 and the film body 25 can be formed by, for example, chemical vapor deposition or physical vapor deposition such as sputtering, with sputtering being preferred.

[0039] (Electrode process) In the electrode formation process, substances other than Si are removed from the precursor 30 of the crimped body with the current collector 17 prepared above, and the precursor 30 is treated to become a porous silicon material. According to this process, since an electrode made of porous silicon material is obtained with the current collector 17 already bonded, the reduction in porosity caused by crimping the current collector 17 after the material has been made into a porous silicon material can be further suppressed. Examples of substances other than Si to be removed include Al and its compounds. In this process, it is preferable to selectively remove the Al component, i.e., the Al phase and its compounds, with an acid or alkali. The acid or alkali used is preferably one that dissolves elements and / or compounds other than silicon in the silicon alloy without dissolving silicon, and examples include hydrochloric acid, sulfuric acid, and sodium hydroxide. It is preferable that this acid or alkali be an aqueous solution. The concentration of the acid or alkali is not particularly limited as long as it can remove Al and its compounds, and can be, for example, in the range of 1 mol / L to 5 mol / L. This removal treatment may be carried out by heating, for example, at 30°C to 60°C. The obtained electrode for the energy storage device is then washed and dried.

[0040] In the electrode preparation process, substances other than Si may be removed in a range of 85% to 100% by mass. For example, Al and other oxygen may remain, but from the viewpoint of charge / discharge capacity, it is preferable to have less when used as an electrode active material. Furthermore, components such as Al reinforce the silicon skeleton, and from the viewpoint of improving durability, it is preferable that they be included in a predetermined amount or more. In this electrode preparation process, it is preferable to obtain an electrode containing a porous silicon material in which Al is contained in a range of 0.5at% to 15at% when the total amount of Si and Al is 100at%. In this porous silicon material, Al may be contained in a range of 1.0at% or more, or 2.0at% or more. Furthermore, Al may be contained in a range of 10at% or less, or 7.5at% or less.

[0041] In the electrode formation process, a porous silicon material with a porosity in the range of 10% to 50% by volume may be obtained. This porosity is measured using a mercury porosimeter. This porosity is preferably, for example, 15% or more by volume, and may be 20% or more by volume. Alternatively, the porosity is preferably, for example, 50% or less by volume, and may be 40% or less by volume or 30% or less by volume. A larger porosity is preferable because it responds more easily to volume changes during carrier ion absorption, while a smaller porosity is preferable because it increases the amount of Si present per unit volume.

[0042] As detailed above, the electrode for the energy storage device, the energy storage device, and the method for manufacturing the electrode for the energy storage device of this embodiment can further improve the bonding strength between the porous active material layer containing Si and the current collector. The reason for this effect is presumed to be as follows. For example, when bonding a current collector to porous silicon, pressure bonding can be considered, but pressure can reduce the porosity of the porous material, and there are limits to the amount of pressure that can be applied. Also, when making Si porous using Al, Al may be removed with acid or alkali, but if Al is removed after pressure bonding the current collector before porosity, the bonding strength of the current collector may decrease. Here, the active material layer and the current collector are bonded via a film of metal M that forms a eutectic alloy with the elements constituting the current collector and Si, and then Al is removed to obtain a porous silicon material. Therefore, the decrease in bonding strength due to the removal of Al can be further suppressed. Furthermore, since this porous silicon material is a self-supporting film, it can be used as an electrode as is without adding conductive materials or binders. Therefore, it becomes possible to provide an electrode with high energy density. Furthermore, by optimizing the size and mixing ratio of the constituent silicon, when used in lithium-ion batteries, volume expansion and contraction are mitigated, improving cycle characteristics, thus easily obtaining high-performance energy storage devices.

[0043] 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.

[0044] This disclosure may be any of the following [1] to

[15] . [1] An active material layer having a plate-shaped porous silicon material containing at least Si and Al and having voids as an electrode active material, Current collector and, A film of metal M interposed between the active material layer and the current collector, which forms a eutectic alloy with the elements constituting the current collector and Si, An electrode for an energy storage device equipped with the following features. [2] The porous silicon material has a one-piece shape and does not contain a binder; an electrode for an energy storage device according to [1]. [3] The film material is made of Sn, and is an electrode for an energy storage device according to [1] or [2]. [4] The electrode for an energy storage device according to any one of [1] to [3], wherein the film has a thickness in the range of 50 nm to 300 nm. [5] An electrode for an energy storage device according to any one of [1] to [4], wherein a Si film with a thickness of 300 nm or less is formed between the film body and the active material layer. [6] An electrode for an energy storage device according to any one of [1] to [5], having one or more of the features of (1) to (5). (1) The porous silicon material contains Si in an amount of 90 at% or more when the total amount of Si and Al is set to 100 at%. (2) The porous silicon material has a void ratio in the range of 10 volume% to 50 volume%. (3) The plate-like body of the porous silicon material has a thickness in the range of 10 μm to 50 μm. (4) The porous silicon plate-like body has the current collector heated and pressed onto one surface with the film body interposed between them. (5) The current collector contains Cu. [7] A positive electrode containing a positive electrode active material, A negative electrode which is an electrode for an energy storage device as described in any one of [1] to [6], An ion-conducting medium interposed between the positive electrode and the negative electrode, which conducts lithium ions, A power storage device equipped with [a specific feature / ability]. [8] A bonding step in which a plate-shaped silicon alloy precursor containing at least Si and Al and having no voids is interposed between the precursor and the current collector, and a film of metal M which forms a eutectic alloy with the elements constituting the current collector and Si is interposed between the precursor and the current collector, and the precursor and the current collector are heated and pressed together at a bonding temperature of more than 150°C, The electrode preparation step involves removing the Al component contained in the silicon alloy to form an active material layer of a porous silicon material having a plate-like shape, A method for manufacturing electrodes for energy storage devices, including [9] The method for manufacturing an electrode for an energy storage device according to [8], wherein the bonding step is performed using the film body made of Sn.

[10] The method for manufacturing an electrode for an energy storage device according to [8] or [9], wherein the bonding step uses the film body having a thickness in the range of 50 nm to 300 nm.

[11] A method for manufacturing an electrode for an energy storage device according to any one of [8] to

[10] , wherein the bonding step uses the precursor having an integral shape and not containing a binder.

[12] A method for manufacturing an electrode for an energy storage device according to any one of [8] to

[11] , wherein in the bonding step, a Si film with a thickness of 300 nm or less is formed between the film body and the precursor, and then the precursor and the current collector are heated and pressed together.

[13] The electrode for an energy storage device according to any one of [8] to

[12] , wherein the bonding step uses one or more of the members from (6) to (8). (6) The precursor contains Si in an amount of 30 at% to 70 at% when the total amount of Si and Al is 100 at%. (7) The precursor has a thickness in the range of 10 μm or more and 50 μm or less. (8) The current collector contains Cu.

[14] A method for producing a porous silicon material according to any one of [8] to

[13] , wherein the electrode formation step selectively removes the Al component with an acid or alkali. A method for producing a porous silicon material according to any one of

[15] [8] to

[14] , A precursor step to obtain a plate-shaped silicon alloy precursor, comprising: melting a raw material containing at least Si and Al; and cooling the molten raw material by spraying it onto a cooling roll in a chamber under reduced pressure containing an oxygen removal material; A method for manufacturing electrodes for energy storage devices, including [Examples]

[0045] The following describes specific examples of the electrodes and energy storage devices for energy storage devices described herein, presented as experimental examples. Experimental Examples 1 to 7 are embodiments of the present disclosure, and Experimental Examples 8 to 7 are comparative examples.

[0046] (Fabrication of ribbon-shaped Al-Si ingots) First, Al-Si ingots were prepared and their composition was investigated. The ingot compositions are summarized in Table 1. The raw materials, Al (high-purity chemical, 99.5% granular) and Si (high-purity chemical, 99.999% granular), were weighed to achieve the desired composition (Table 1) (Reference Examples 1-4). The weighed raw materials were placed in the copper hearth inside the chamber of the arc melting furnace (Nisshin Giken NEV-ACD1). Furthermore, a Ti lump was also placed as an oxygen getter. The chamber was heated for 10°C. -3 After evacuating to below Pa, Ar was introduced to 40 cmHg, and the Ti mass was melted by arc discharge to remove residual oxygen. Then, the raw materials were melted to obtain an Al-Si alloy ingot. At this time, in order to improve the uniformity of the sample, the process of turning the ingot over and remelting it was repeated more than three times.

[0047] Next, the synthesized ingot was rapidly cooled and solidified using the single-roll liquid quenching apparatus shown in Figure 3. When liquid quenching with a single roll, parameters that affect the cooling rate include the temperature and thermal conductivity of the molten liquid, the diameter d of the nozzle tip, the gap size g between the roll and the nozzle, and the roll rotation speed r. The temperature and thermal conductivity of the molten liquid are sample-dependent parameters, but the rest can be adjusted by setting the apparatus. In this case, the settings were adjusted to (1) nozzle tip diameter d = 0.5 mm, (2) gap size g = 0.5 mm, and (3) roll rotation speed r = 3000 rpm. The fabricated ingot was placed in a quartz nozzle and connected to a high-frequency dissolution apparatus. The chamber was heated to 10 -3 After evacuating to below Pa, Ar gas was introduced to 50 cmHg. The current was gradually increased, and the sample was heated until it melted while monitoring the temperature with an infrared thermometer. The melt was then sprayed from the nozzle tip toward the copper roll using Ar gas to obtain a rapidly solidified ribbon sample (plate-shaped precursor). In this case, the thickness of the precursor was set to 30 μm.

[0048] (Electrochemical evaluation) A 1 mg sample was weighed and placed on a copper current collector foil to serve as the working electrode. The electrolyte used was 1 M LiPF6 dissolved in ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), and lithium metal was used as the counter electrode via a polyethylene microporous membrane separator. The resulting test cell was charged and discharged at a current density of 1 / 20C, a lower potential limit of 50 mV, and an upper potential limit of 2 V.

[0049] (Electrode observation) After inserting 3000 mAh / g of lithium, the battery was disassembled in a glove box under an argon atmosphere, and the silicon negative electrode was washed three times with dimethyl carbonate (DMC). The sample was then dried under reduced pressure at room temperature. This sample was then introduced into a scanning electron microscope (SEM) using an air-free holder, and the electrode cross-section was observed. In the case of Experimental Example 1, due to the high battery resistance, lithium was inserted up to 2800 mAh / g before SEM observation.

[0050] (Measurement of physical properties of porous silicon materials) Porous silicon materials treated with acid were observed and analyzed using a scanning electron microscope (SEM, HITACHI S-4300) and energy-dispersive X-ray spectroscopy (EDAX, HITACHI S-4300). Pore distribution and average porosity were also measured using a mercury porosimeter (CANTAChrome POWERMASTER60GT).

[0051] Figure 4 shows the evaluation results for the porous silicon material of Reference Example 2. Figure 4A is the XRD chart of the raw alloy, Figure 4B is the XRD chart of the porous silicon ribbon after acid treatment, Figure 4C is the SEM image of the raw alloy, Figure 4D is the SEM image of the porous silicon ribbon after acid treatment, and Figure 4E is the surface SEM image of the porous silicon ribbon after acid treatment. Figure 5 shows the evaluation results for the electrode of Reference Example 2. Figure 5A is the charge-discharge curve, Figure 5B is the initial cross-sectional SEM image, and Figure 5C is the cross-sectional SEM image when 3000 mAh / g of Li was inserted. Table 1 summarizes the composition of each sample, the crystal phase and crystallinity after acid treatment, and the shape after acid treatment. Table 1 also summarizes the charge-discharge evaluation results, including the initial Li insertion capacity A (mAh / g), initial Li removal capacity B (mAh / g), initial charging efficiency (B / A × 100%), and electrode expansion rate (volume %) when 3000 mAh / g of Li was inserted.

[0052] As shown in Table 1, in Reference Examples 1-3, with starting compositions of Al70Si30, Al50Si50, and Al30Si70, the material had a long ribbon-like or ribbon-like shape after cooling and acid treatment. Furthermore, high-crystallinity silicon was detected in Reference Examples 1-3, indicating high crystallinity. In addition, observation of the cross-sections of Reference Examples 1-3 revealed two types of structures: coarse grains (microscale) containing primary silicon that crystallizes during cooling, and fine grains (nanoscale) containing eutectic silicon with Al. On the other hand, Reference Example 4, with a low Al content, was powdery, had poor shape retention, and low crystallinity. In addition, observation of the cross-section of Reference Example 4 revealed no fine grains, but a shape of connected coarse grains (microscale). Furthermore, in Reference Examples 2-4, the initial Li insertion capacity was 3000 mAh / g or more, the initial Li desorption capacity was 2500 mAh / g or more, and the initial charge / discharge efficiency was 70% or more, all of which were high. On the other hand, in Reference Example 1, the Li insertion limit was 2800 mAh / g, and the insertion capacity, desorption capacity, and initial charge-discharge efficiency were all relatively low. It was observed that this was due to the high amount of Al and high resistance in Reference Example 1. Furthermore, while Reference Examples 1-3 showed good electrode expansion rates, Reference Example 4 had a volume expansion of more than 50 volume%, indicating a large volume change. It was inferred that an Al composition in the range of 30-70 at% was optimal.

[0053] [Table 1]

[0054] (Consideration of the bonding strength with the current collector) Based on the above-mentioned reference examples, the bonding of Al50Si50 (Reference Example 2) and Al30Si70 (Reference Example 3), which maintained their ribbon shape, with Cu foil as a current collector was investigated. Ribbon-shaped samples (precursors) obtained in the same manner as in the above reference examples were cut to a length of 10 mm and set in the deposition apparatus chamber, resulting in a 5 × 10 -4The pressure was reduced to below Pa, and an electron beam was irradiated onto a Si or Sn deposition source to first form a Si film of 0-300 nm on the surface of a precursor plate-like material. Then, a Sn film of 50-300 nm thickness was deposited on top of it. After the Si / Sn film-deposited samples were placed on a Cu foil (20 μm thick), they were bonded by heating and pressing at a pressure of 50 MPa and 100-250°C for 30 minutes (Experimental Examples 1-6). For comparison, samples with only Sn film deposited (Experimental Example 7), a sample with no film deposited (Experimental Example 8), and a sample with only Si film deposited (Experimental Example 9) were prepared and bonded under the same conditions as in Experimental Example 1. Figure 6 is an explanatory diagram showing the preparation conditions for each sample, with Figure 6A being an explanatory diagram for Experimental Example 8 and Figure 6B being an explanatory diagram for Experimental Examples 1-6.

[0055] The obtained samples were immersed in a 1N hydrochloric acid aqueous solution in a petri dish and treated at room temperature for 1 to 5 hours while being stirred at 300 rpm with a rotor to selectively remove Al. Afterward, the samples were washed three or more times with distilled water to obtain a self-supporting porous silicon anode with an integrated Cu foil. Figure 7 shows photographs of the acid treatment in Experimental Examples 1-3 and 8, with Figure 7A showing the observation after 1 hour and Figure 7B showing the observation after 5 hours. Figure 8 is an SEM image of the cross-section of Experimental Example 2 and an explanatory diagram showing an example of its microstructure. Table 2 summarizes the initial composition, interface structure, and peeling time due to acid treatment for Experimental Examples 1-10, as well as the average porosity (volume %) of the porous silicon material determined by the mercury intrusion method and the Al and Si composition (at%) after acid treatment measured by EDAX. Note that the porous silicon materials in Experimental Examples 1-6 had an average porosity of 25-50 volume% and Si content of 95 at% or more. As shown in Table 2, in Experimental Example 8, where Si or Sn were deposited without deposition, the self-supporting silicon film peeled off within 1 hour of immersion in hydrochloric acid solution, and sufficient interfacial strength could not be obtained. In contrast, in Experimental Example 9, where Si was deposited without Sn, the interfacial strength improved, but peeling occurred within 2 hours. On the other hand, in Experimental Examples 1-7, where Sn was deposited, no peeling occurred for up to 4 hours, indicating improved interfacial strength. Furthermore, when a Si film was interposed between the silicon self-supporting film and the Sn film during film formation, regardless of the Si / Sn film thickness, no peeling occurred even after immersion in hydrochloric acid solution for 5 hours, indicating further improvement in interfacial strength (see Figure 7).

[0056] Next, to clarify the effect of heating temperature during bonding, a 100 nm Si film was formed on the surface of Al50Si50, and then a 200 nm thick Sn film was deposited on top of it, and the materials were bonded at various temperatures. Table 3 summarizes the test results for Experimental Examples 2, 10-12. At bonding temperatures below 150°C, sufficient strength could not be obtained, but it was found that the interfacial strength improved when the bonding temperature was increased above 150°C and even above 200°C. Since Sn is a metal that can form eutectic alloys with Si and Cu, it is preferable for bonding porous silicon materials and current collectors (Cu), and it was found that the presence of this Sn film can further increase the structural strength of electrodes for energy storage devices.

[0057] Furthermore, the porous silicon material forming the active material layer was found to have a one-piece shape and not contain a binder, which was considered preferable from the viewpoint of charge and discharge capacity. The Sn film was also found to have a bonding temperature in the range of over 150°C and 250°C or less, as this facilitated heat bonding. Additionally, the Sn film was found to have a good thickness in the range of 50 nm to 300 nm. Furthermore, the formation of a Si film with a thickness of 50 nm to 300 nm between the Sn film and the porous silicon material was considered preferable from the viewpoint of bonding strength. It was confirmed that sufficient bonding strength could be achieved even without this Si film. Finally, it was found that the precursor of the porous silicon material preferably contained Si in a range of 30 at% to 70 at% when the total amount of Si and Al is considered to be 100 at%. Finally, the plate-like porous silicon material was found to preferably have a thickness in the range of 10 μm to 50 μm.

[0058] [Table 2]

[0059] [Table 3]

[0060] It goes without saying that this disclosure is not limited in any way to the experimental examples described above, and can be implemented in various forms as long as they fall within the technical scope of this disclosure. [Industrial applicability]

[0061] This disclosure is applicable to the field of secondary batteries. [Explanation of Symbols]

[0062] 10 Energy storage device, 12 Positive electrode, 13 Positive electrode active material layer, 14 Current collector, 15 Negative electrode, 16 Negative electrode active material layer, 17 Current collector, 18 Ion conducting medium, 21 Porous silicon material, 23 Void, 24 Si film, 25 Film, 30 Precursor.

Claims

1. An active material layer having a plate-shaped porous silicon material containing at least Si and Al and having voids as an electrode active material, Current collector and, The current collector is interposed between the active material layer and the current collector, and comprises a film of metal M that forms a eutectic alloy with the elements constituting the current collector and Si, The aforementioned film body is directly adjacent to the current collector, A Si film with a thickness of 300 nm or less is formed as an interlayer between the aforementioned film body and the active material layer. The aforementioned film body has a thickness in the range of 50 nm to 300 nm. The porous silicon material contains Al in a range of 0.5 at% to 15 at% when the total amount of Si and Al is 100 at%. The porous silicon material has a void ratio in the range of 10 volume% to 50 volume%, The plate-like body of the porous silicon material has a thickness in the range of 10 μm to 50 μm. Electrodes for energy storage devices.

2. The electrode for an energy storage device according to claim 1, wherein the porous silicon material has a one-piece shape and does not contain a binder.

3. The electrode for an energy storage device according to claim 1 or 2, wherein the film body is made of Sn.

4. The electrode for an energy storage device according to claim 1 or 2, wherein the Si film has a thickness of 50 nm or more.

5. An electrode for an energy storage device according to claim 1 or 2, having one or more of the features of (1) to (3). (1) The porous silicon material contains Si in an amount of 90 at% or more when the total amount of Si and Al is set to 100 at%. (2) The porous silicon plate-like body has the current collector heated and pressed onto one surface with the film body interposed between them. (3) The current collector contains Cu.

6. A positive electrode containing a positive electrode active material, A negative electrode which is an electrode for an energy storage device according to claim 1 or 2, An ion-conducting medium interposed between the positive electrode and the negative electrode, which conducts lithium ions, A power storage device equipped with [a specific feature / ability].

7. A bonding step in which a precursor, which is a plate-shaped silicon alloy containing at least Si and Al and having no voids, and a current collector are interposed with a film of metal M which forms a eutectic alloy with the elements constituting the current collector and Si, and the precursor and the current collector are heated and pressed together at a bonding temperature of over 150°C. The process includes an electrode preparation step of removing the Al component contained in the silicon alloy to form an active material layer of a porous silicon material having a plate-like shape, The aforementioned film body is directly adjacent to the current collector, A method for manufacturing an electrode for an energy storage device, wherein the film body is in direct contact with the active material layer, or a Si film is formed as an interlayer between the film body and the active material layer.

8. The method for manufacturing an electrode for an energy storage device according to claim 7, wherein the bonding step uses the film body made of Sn.

9. The method for manufacturing an electrode for an energy storage device according to claim 7 or 8, wherein the bonding step uses the film body having a thickness in the range of 50 nm to 300 nm.

10. The method for manufacturing an electrode for an energy storage device according to claim 7 or 8, wherein the bonding step and the electrode formation step are used to produce an electrode for an energy storage device according to claim 1 or 2.

Images