Method for producing porous silicon material, porous silicon material, electrode, and power storage device

Abstract

A method for producing a porous silicon material according to the present disclosure comprises: a precursor step for obtaining a precursor of a silicon alloy by melting, rapidly cooling, and solidifying a raw material that contains 1-4 at% of Ti and 15-35 at% of Si, with the balance including Al, where the total of Si, Ti, and Al is taken as 100 at%; and a porosity-increasing step for obtaining a porous silicon material by removing Al components contained in the silicon alloy.

Description

Method for manufacturing porous silicon material, porous silicon material, electrode, and energy storage device

[0001] This disclosure relates to a method for manufacturing porous silicon materials, porous silicon materials, electrodes, and energy storage devices.

[0002] Conventionally, silicon materials have been proposed as negative electrode materials for energy storage devices. Silicon absorbs lithium ions during charging. 3.75 While forming a Si alloy exhibits a high theoretical capacity of 3579 mAh / g, it expands by approximately 300% during charging (Li absorption), degrading its charge-discharge characteristics. Therefore, suppressing the expansion and contraction of the electrodes during charging and discharging is a major challenge. To address this, we have proposed porous silicon materials obtained by melting and rapidly solidifying a raw material containing Ti in the range of 5 at% to 20 at%, Al in the range of 50 at% to 80 at%, with the remainder being Si, or a raw material containing Ti in the range of 5 at% to 15 at%, Al in the range of 10 at% to 50 at%, with the remainder being Si, to form a silicon alloy, and then removing the Al component contained in the silicon alloy (for example, Patent Documents 1 and 2). Such porous silicon materials can further suppress the degradation of charge-discharge characteristics. Furthermore, as electrodes for energy storage devices, we have proposed one that contains porous silicon material in an amount of 50% to 70% by mass, a binder in an amount of 15% to 30% by mass, and a conductive material in an amount of 10% to 25% by mass (for example, Patent Document 3). Such electrodes can further enhance the electrochemical properties of energy storage devices.

[0003] Japanese Patent Publication No. 2022-150481, Japanese Patent Publication No. 2023-68494, Japanese Patent Publication No. 2024-102802

[0004] However, while the aforementioned Patent Documents 1 to 3 can suppress the deterioration of charge / discharge characteristics and improve the electrochemical characteristics of energy storage devices, further improvements were desired.

[0005] This disclosure is made to address these challenges and primarily aims to improve the electrochemical properties of energy storage devices.

[0006] To achieve the above-mentioned objectives, the inventors conducted diligent research. They conceived of a method to produce a porous silicon material by melting and rapidly solidifying a raw material containing Ti in the range of 1 at% to 4 at%, Si in the range of 15 at% to 35 at%, with the remainder being Al, to obtain a silicon alloy, and then removing the Al component contained in the silicon alloy. They then found that using the obtained porous silicon material as an active material could further improve the electrochemical properties of energy storage devices, and thus completed this disclosure.

[0007] In other words, the method for producing a porous silicon material according to the present disclosure includes a precursor step of melting and rapidly solidifying a raw material in which, when the total amount of Si, Ti, and Al is set to 100 at%, Ti is in the range of 1 at% to 4 at%, Si is in the range of 15 at% to 35 at%, and the remainder is Al, in order to obtain a silicon alloy precursor, and a porosity-forming step of removing the Al component contained in the silicon alloy to obtain a porous silicon material.

[0008] The porous silicon material of this disclosure has a pore size distribution range of 1 nm to 500 nm determined by the mercury intrusion method, contains a three-dimensional network structure of silicon skeleton having voids, contains a Ti(Al,Si)2 compound, and has an average porosity of 50% to 80% by volume.

[0009] The electrode of this disclosure contains the above-mentioned porous silicon material as an active material, wherein the active material is contained in an amount of 50% to 70% by mass, the conductive material in an amount of 10% to 25% by mass, and the remainder is the binder, based on the total amount of the active material, binder, and conductive material.

[0010] The energy storage device of this disclosure comprises a negative electrode containing the above-mentioned porous silicon material as a negative electrode active material, a positive electrode containing a positive electrode active material, and an ion-conducting medium interposed between the negative electrode and the positive electrode for conducting carrier ions.

[0011] This disclosure can further enhance the electrochemical properties of energy storage devices. The reason for this effect is presumed to be as follows. For example, when a raw material containing Ti in the range of 1 at% to 4 at%, Si in the range of 15 at% to 35 at%, with the remainder being Al, is melted and rapidly cooled and solidified, first Ti(Al,Si)2 compound crystallizes from the liquid phase as the primary crystal, and then primary Al, eutectic Al, and dendritic eutectic Si crystallize, or primary Si, eutectic Al, and dendritic eutectic Si crystallize. The silicon alloy thus obtained, after the Al component is removed, becomes a highly conductive porous silicon material with a three-dimensional network structure of Si skeleton and dispersed Ti(Al,Si)2 compound, which is a highly conductive compound. Furthermore, because the silicon alloy contains a large amount of Al, after the Al component is removed, a high average porosity, such as 50% to 80% by volume, can be achieved, thereby mitigating the expansion and contraction of Si during charging and discharging. Therefore, it is presumed that the electrochemical properties of the energy storage device, such as high-rate characteristics and charge-discharge cycle characteristics, can be further enhanced in this disclosure.

[0012] Al-Si-Ti phase diagram at 2.5 at%Ti. Explanatory diagram showing an example of the structure of the energy storage device 10. Schematic diagram of the atomization apparatus. XRD measurement results of atomized powder and porous silicon in Experimental Example 2. Surface SEM image of atomized powder in Experimental Example 2. Surface SEM image of porous silicon in Experimental Example 2. Pore distribution of porous silicon in Experimental Example 2 by mercury adsorption method. Cross-sectional SEM image of porous silicon in Experimental Example 2. Cross-sectional STEM image of porous silicon in Experimental Example 2.

[0013] (Method for manufacturing porous silicon material) The method for manufacturing a porous silicon material according to this disclosure includes a precursor step and a porosity-forming step. In the precursor step, raw materials containing Si, Al, and Ti are melted and rapidly cooled and solidified to obtain a silicon alloy precursor. In the porosity-forming step, the Al component contained in the silicon alloy is removed to obtain a porous silicon material. First, the raw material composition will be described.

[0014] Figure 1 is an Al-Si-Ti phase diagram for 2.5 at% Ti. In Figure 1, the equilibrium state is shown with a solid line, and the non-equilibrium state due to rapid solidification is shown with a dashed line. Figure 1 also shows a schematic diagram of the phase transformation behavior when rapid solidification occurs from the molten state in 25 at% Si. Generally, when a molten material with a eutectic composition where the liquidus line is minimal in the equilibrium phase diagram of a eutectic A-B alloy is solidified, a eutectic structure is formed in which phases A and B are separated in a fibrous (lamellar) manner. At this time, the size of the lamellar structure formed becomes finer as the cooling rate increases, and at cooling rates of 1000°C / sec or higher, a nano-sized structure is formed. If only element A can be selectively removed from this eutectic structure by acid treatment, a material consisting of element B with a eutectic structure can be obtained. The microstructure changes by adjusting the composition of elements A and B near the eutectic composition, resulting in a porous body with a structure in which crystallized phases consisting of element B are linked. In Al-Si-Ti alloys, for example, Al can be considered as element A, and Si and Ti as elements B. Incidentally, as can be seen from reference 1 (X. Ao, H. Xia, J. Liu, Q. He, S. Lin, A numerical study of irregular eutectic in Al-Si alloys Under a large undercooling, Comput. Mater. Sci. 186 (2021) 110049, https: / / doi.org / 10.1016 / j.commatsci.2020.110049.), the eutectic point of Al-Si eutectic alloys shifts to the high-Si side upon rapid cooling. Consequently, in Al-xSi-2.5at%Ti alloy, as can be seen from the non-equilibrium phase diagram shown by the dashed line in Figure 1, the eutectic point also shifts to the high-Si side (from e to e'). Near the eutectic composition corresponding to the eutectic point e', when the raw materials are melted and rapidly solidified, as shown in Figure 1, Ti(Al,Si)2 compounds first crystallize from the liquid phase (L) as the primary crystal. Subsequently, similar to Al-Si binary alloys, at Si compositions lower than the eutectic point (hypoeutectic composition), primary Al, eutectic Al, and dendritic eutectic Si crystallize. On the other hand, at Si compositions higher than the eutectic point (hypereutectic composition), Si crystallizes as the primary crystal, followed by eutectic Al and dendritic eutectic Si crystallization.Since primary Al and eutectic Al in the crystalline phase dissolve in acid, it is presumed that after acid treatment, silicon alloys become porous bodies with a three-dimensional network structure mainly composed of remaining Ti(Al,Si)2 compounds and dendritic eutectic Si frameworks.

[0015] (Precursor step) In the precursor step, a raw material is used in which, when the total amount of Si, Ti, and Al is set to 100 at%, Ti is contained in a range of 1 at% to 4 at%, Si is contained in a range of 15 at% to 35 at%, and the remainder is Al. The raw material may contain unavoidable impurities. Unavoidable impurities are components that inevitably remain during the purification of any of Si, Ti, or Al, and examples include Fe, C, Cu, Ni, and P. It is preferable that the amount of unavoidable impurities be as small as possible; for example, when the total amount of Si, Ti, and Al is set to 100 at%, it is preferable that it be 5 at% or less, and more preferably 2 at% or less. The blending ratio of Ti is preferably 1.5 at% or more, and may be 2 at% or more. Also, the blending ratio of Ti is preferably 3.5 at% or less, and may be 3 at% or less. The blending ratio of Si is preferably 17.5 at% or more, and may be 20 at% or more. Furthermore, the Si content is preferably less than 35 at%, more preferably 32.5 at% or less, and may be 30 at% or less. Silicon alloys containing Ti and Si within these ranges 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. The cooling rate is preferably rapid, for example, 10 2 ℃ / s or more 10 8 The range may be less than or equal to °C / s.

[0016] In this process, when melting the raw materials, high-frequency crucible melting in an inert gas atmosphere such as Ar or nitrogen is preferred, but any melting method may be used. In the precursor process, the alloy obtained from the raw materials may be atomized. In this atomization process, the molten silicon alloy raw material may be cast into a mold, and the resulting ingot may be crushed to atomize it. Alternatively, the method for atomizing the silicon alloy may be to atomize the molten silicon alloy using one or more of the following methods: gas atomization, water atomization, and roll quenching. These methods are also suitable for rapidly cooling and solidifying the molten silicon alloy. The gas atomization and water atomization methods yield alloy powder. On the other hand, the roll quenching method yields a thin strip alloy, which may then be crushed into powder. The powder obtained by the roll quenching method has a fine alloy structure, so porous silicon with fine pores can be obtained after the dissolution treatment. Of these, the gas atomization method is more preferred for atomizing the silicon alloy. In gas atomization, it is preferable to use a nitrogen or Ar atmosphere when forming the molten metal, and to use an Ar, He, or nitrogen atmosphere when atomizing the material.

[0017] In the precursor step, it is preferable to atomize the silicon alloy into particles with an average particle size in the range of 0.1 μm to 100 μm. For example, these particles are preferably 0.5 μm or larger, and may be 1 μm or larger. For example, these particles are preferably 10 μm or smaller, and may be 5 μm or smaller. The silicon alloy particles can be appropriately selected according to the characteristics required for the energy storage device. Here, the average particle size of the particles is determined by observing the particles with a scanning electron microscope (SEM), summing the major axis of each particle as its diameter, dividing by the number of particles, and averaging the result. The particles obtained in this atomization process will be the average particle size of the porous particle aggregate to be ultimately obtained.

[0018] In this precursor step, in addition to Si, Ti, and Al, raw materials containing a second element may also be used. Examples of the second element include one or more of Ca, Cu, Mg, Na, Sr, and P. The amount of the second element is preferably less than the amount of Al or Ti, 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.

[0019] (Porous Formation Process) In the porous formation process, the Al component is removed from the silicon alloy particles prepared above. This process may also be used to remove substances other than Si. Examples of substances other than Si include Al and its compounds, Ti and its compounds. In this process, it is preferable to selectively remove the Al component, i.e., the Al phase and its compounds, using 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. This acid or alkali is preferably 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 Ti and its compounds, and can be in the range of 1 mol / L to 5 mol / L, for example. This removal process may be carried out at room temperature, or with heating, or a combination of these. When heating is used, for example, the temperature may be 30°C or higher or 50°C or higher, or 100°C or lower or 95°C or lower. Furthermore, the removal process is preferably carried out by immersing the silicon alloy particles in an acid or alkaline solution, allowing them to stand in the immersed state as needed, and then stirring. The standing time and stirring time may be, for example, 30 minutes or more and 1 hour or more, or 5 hours or less and 2 hours or less, respectively. The resulting porous silicon material is then washed and dried.

[0020] In the porosity formation process, substances other than Si may be removed in the range of 85% by mass or more and 100% by mass or less. For example, Al, Ti, and other oxygen may remain, but when used as an electrode active material, it is preferable to have less from the viewpoint of charge-discharge capacity. Also, components such as Al and Ti preferably contain a predetermined amount or more from the viewpoint of reinforcing the silicon skeleton and improving durability. In this process, a porous silicon material containing a Ti(Al,Si)₂ compound may be obtained. Also, in this process, in addition to the Ti(Al,Si)₂ compound, a porous silicon material containing a SiTi compound and / or an AlSiTi compound other than the Ti(Al,Si)₂ compound may be obtained. Examples of the SiTi compound include Si x Ti y (x, y are arbitrary numbers), such as Si₃Ti₅ and Si₄Ti₅. Examples of the AlSiTi compound include Al a Si b Ti c compound (a, b, c are arbitrary numbers), such as Ti 33 Al 15 Si 52 (τ₂), etc. The Ti(Al,Si)₂ compound, the SiTi compound, and the AlSiTi compound may be hardly soluble in an acid or an alkali.

[0021] In the porosity formation process, when the total of Si and the Ti(Al,Si)₂ compound is 100% by mass, it is preferable to obtain a porous silicon material containing the Ti(Al,Si)₂ compound in the range of 30% by mass or less. In the porous silicon material, the ratio of the Ti(Al,Si)₂ compound is preferably 25% by mass or less or 20% by mass or less, and may be 5% by mass or more or 10% by mass or more. The porous silicon material is preferably mainly composed of Si and the Ti(Al,Si)₂ compound. For example, when the total of Si and the Ti(Al,Si)₂ compound is 100% by mass, it is more preferable that the ratio of other substances is 10% by mass or less or 5% by mass or less.

[0022] In the porosity process, a porous silicon material with an average porosity in the range of 50% to 80% by volume may be obtained. This average porosity shall be the value measured by a mercury porosimeter. This average porosity is preferably, for example, more than 50% by volume, and may be 55% by volume or more. Also, the average porosity is preferably, for example, 75% by volume or less, and may be 70% by volume or less. A larger average porosity makes it easier to respond to volume changes during occlusion of carrier ions, and a smaller average porosity results in a larger amount of Si present per unit volume, which is preferable.

[0023] (Porous silicon material) The porous silicon material of the present disclosure may be produced by the manufacturing method described above. Here, detailed descriptions of each physical property of the porous silicon material and the like are omitted on the assumption that they are the same as those of the manufacturing method described above. The distribution range of the pore diameter determined by the mercury intrusion method for this porous silicon material is in the range of 1 nm or more and 500 nm or less. This pore diameter may be 10 nm or more, 50 nm or more, or 70 nm or more. Also, this pore diameter is preferably 200 nm or less, and may be 150 nm or less, or 100 nm or less. In this porous silicon material, the average pore diameter determined by the mercury intrusion method may be in the range of 5 nm or more and 500 nm or less, or in the range of 10 nm or more and 250 nm or less.

[0024] The porous silicon material contains a skeletal silicon having a three-dimensional network structure with voids and contains a Ti(Al,Si)₂ compound. This Ti(Al,Si)₂ compound is dispersed throughout the porous silicon material and is presumed to play a role in assisting the conductivity of the porous silicon material and reinforcing the silicon skeleton. It is preferable that this porous silicon material contains the Ti(Al,Si)₂ compound in the range of 30% by mass or less. The content of the Ti(Al,Si)₂ compound may be, for example, 25% by mass or less or 20% by mass or less, and may be 5% by mass or more or 10% by mass or more. From the viewpoint of assisting conductivity and reinforcing the skeleton, a larger amount of the Ti(Al,Si)₂ compound is preferable, and from the viewpoint of the charge-discharge capacity of the energy storage device, a smaller amount is preferable.

[0025] The porous silicon material has an average porosity in the range of 50 vol% to 80 vol%. This average porosity may be, for example, greater than 50 vol% or greater than 55 vol%, or less than or equal to 75 vol% or 70 vol%. From the viewpoint of volume change of the material, a higher average porosity is preferable, and from the viewpoint of charge / discharge capacity of the energy storage device, a lower average porosity is preferable. This average porosity shall be the value measured with a mercury porosimeter.

[0026] The porous silicon material preferably has an average particle size of 0.1 μm or more, more preferably 0.5 μm or more, and may be 1 μm or more. Furthermore, the porous silicon material preferably has an average particle size of 100 μm or less, more preferably 10 μm or less, and may be 5 μm or less.

[0027] The porous silicon material may contain Ti in the range of 0.1 at% to 15 at%, Si in the range of 80 at% to 98 at%, and the remainder being Al, when the total amount of Si, Ti, and Al is considered to be 100 at%. The Ti content may be, for example, 0.5 at% or more, 1 at% or more, or 10 at% or less, or 5 at% or less. The Si content may be, for example, 85 at% or more, 90 at% or more, or 97 at% or less, or 96 at% or less. 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 conductivity assistance and structural reinforcement. A higher Al and Ti content is preferable from the viewpoint of conductivity assistance and structural reinforcement, and a lower Al and Ti content is preferable from the viewpoint of charge / discharge capacity of the energy storage device, since these are components that do not charge or discharge. Furthermore, the porous silicon material may also contain a second element in addition to Si, Ti, and Al. Examples of the second element include one or more of Ca, Cu, Mg, Na, Sr, and P. The amount of the second element is preferably less than the amount of Al and Ti, for example, it is preferably in the range of 15% by mass or less relative to the total amount of the porous silicon material. In addition to Si, Ti, and Al, the porous silicon material may also contain unavoidable impurities. It is preferable that the amount of the second element and unavoidable impurities be as low as possible.

[0028] (Electrode) The electrode of the present disclosure is an electrode for a power storage device including the above-described porous silicon material as an electrode active material (hereinafter also referred to as an active material). This electrode becomes either a positive electrode or a negative electrode based on the potential of the counter electrode with respect to the potential of the electrode active material. When lithium is used as a carrier, it is preferably a negative electrode. This electrode can be used, for example, in a lithium-ion secondary battery, a hybrid capacitor, an air battery, or the like. This electrode may have a reduced porosity of the porous silicon material by compression during production. For example, when using porous silicon particles as a negative electrode active material of a lithium-ion secondary battery, the smaller the pores, the more uniformly alloying occurs when lithium ions alloy, reducing stress concentration and preventing deterioration of the electrode itself. The average porosity of the porous silicon material after compression may be appropriately adjusted according to the characteristics required for the electrode for the power storage device. For example, it may be 5% by volume or more, or 10% by volume or more. Further, the average porosity of the porous silicon material after compression may be, for example, 30% by volume or less, or 20% by volume or less.

[0029] The electrode may be formed by creating the porous silicon material described above on a current collector and fixing it to the current collector. This electrode may be manufactured by mixing the porous silicon material with a conductive material and a binder in a solvent as needed to form a paste, which is then applied to the current collector, or by mixing the porous silicon material with a conductive material and a binder as needed and pressing it onto the current collector. The conductive material is not particularly limited as long as it is an electronically conductive material that does not adversely affect 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 metals (copper, nickel, aluminum, silver, gold, etc.). The binder plays the role of binding the active material particles and conductive material particles together. For example, imide resins such as polyimide (PI), 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. The solvent is preferably one that functions as a binder solvent that dissolves the binder. Examples of coating methods include roller coating such as applicator roll coating, screen coating, doctor blade method, spin coating, and bar coating, and any thickness and shape can be achieved using any of these methods.The current collector can be appropriately selected according to the potential of the active material, etc. For example, aluminum, titanium, stainless steel, nickel, iron, copper, calcined carbon, conductive polymers, conductive glass, etc., can be used, as well as aluminum, copper, etc., whose surfaces have 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. Examples of current collector shapes include foil, film, sheet, net, punched or expanded materials, lath, porous materials, foams, and fiber clusters. The thickness of the current collector can be, for example, 1 to 500 μm. The amount of active material composite formed can be appropriately set according to the desired performance required for the energy storage device.

[0030] The electrode preferably contains 50% to 70% by mass of active material and 10% to 30% by mass (preferably 25% by mass or less) of conductive material, with the remainder being the binder, relative to the total amount of active material, binder, and conductive material. In such a formulation, the active material, binder, and conductive material are suitably arranged, and the electrochemical properties can be further enhanced. In particular, when the porous silicon material of this disclosure is used as the active material, the expansion and contraction during charging and discharging are suppressed by the pores of the porous silicon active material, and the conductivity of the entire electrode is significantly improved by the composite of Ti(Al,Si)2 silicide and conductive material, thereby further enhancing electrochemical properties such as capacity, high-rate characteristics, and charge-discharge cycle characteristics. The active material blending ratio is more preferably 55% to 65% by mass, and the conductive material blending ratio is more preferably 15% to 25% by mass. The conductive material is preferably a carbon material, such as graphite, natural graphite (scaly graphite, flake graphite), artificial graphite, acetylene black, carbon black, Ketjenblack, carbon nanotubes, carbon nanowires, graphene, needle coke, or carbon fibers. The conductive material preferably has an average particle size of 0.1 μm or more and 10 μm or less. Furthermore, the conductive material preferably contains 60 at% or more of carbon in terms of elemental ratio, excluding unavoidable impurities such as oxygen.

[0031] In this electrode, the electrode active material may include, in addition to the porous silicon material, an active material other than the porous silicon material, within a range that allows for both low confinement pressure and capacity retention. For example, the electrode active material may be a carbonaceous material or Li4Ti5O 12 These may also be included. However, from the viewpoint of further increasing the battery capacity, it is preferable that, with the total electrode active material being 100% by mass, porous silicon material accounts for 50% or more by mass, preferably 90% or more by mass.

[0032] (Energy Storage Device) The energy storage device of this disclosure comprises a negative electrode containing the above-mentioned porous silicon material as a negative electrode active material, a positive electrode containing a positive electrode active material, and an ion-conducting medium interposed between the negative electrode and the positive electrode to conduct carrier ions. This energy storage device may use alkali metal ions such as lithium, sodium, or potassium as carrier ions. This energy storage device may be any of the following: a lithium-ion secondary battery, a hybrid capacitor, or an air battery. The negative electrode may be the electrode for the energy storage device described above. In the positive electrode, the positive electrode active material can be a sulfide containing a transition metal element or an oxide containing lithium and a transition metal element. Specifically, transition metal sulfides such as TiS2, TiS3, MoS3, and FeS2, and a basic composition formula of Li (1-x) MnO2 (0 < x < 1, etc., the same applies below) and Li (1-x) Lithium manganese composite oxides such as Mn2O4, with the basic composition formula Li (1-x) Lithium cobalt composite oxides such as CoO2, with the basic composition formula Li (1-x) Lithium nickel composite oxides such as NiO2, with the basic composition formula Li (1-x) Ni a Co b Mn c Lithium nickel cobalt manganese composite oxides such as O2 (a + b + c = 1), lithium vanadium composite oxides with a basic composition formula such as LiV2O3, and transition metal oxides with a basic composition formula such as V2O5 can be used. Among these, lithium transition metal composite oxides, such as LiCoO2, LiNiO2, LiMnO2, Li (1-x) Ni1 / 3 Co 1 / 3 Mn 1 / 3 O2 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 the amount is 1500m or more per gram. 2 It is more preferable that the amount is 1 / g or more. The specific surface area is 1000 m². 2 At concentrations of 1 / g or higher, the discharge capacity can be further increased. The specific surface area of ​​this activated carbon is 3000 m² due to its ease of manufacture. 2 It is preferable that it be less than or equal to 2000m 2 It is more preferable that the value be less than or equal to / g. The conductive material, binder, solvent, current collector, etc. used in the positive electrode can be any of the examples given above for the electrode.

[0033] 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. Of these, it is preferable from the viewpoint of electrical properties to use a combination of one or more salts selected from the group consisting of inorganic salts such as LiPF6, LiBF4, LiAsF6, and LiClO4, and organic salts such as LiCF3SO3, LiN(CF3SO2)2, and LiC(CF3SO2)3.The support 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 more in which the support salt dissolves allows for a sufficient current density to be obtained, while a concentration of 5 mol / L or less 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.

[0034] 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.

[0035] 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.

[0036] 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 2 is an explanatory diagram showing an example of the structure of the 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 13 and a current collector 14. The negative electrode 15 has a negative electrode active material 16 and a current collector 17. The negative electrode active material 16 is the porous silicon material 21 described above and has voids 23.

[0037] As detailed above, this disclosure can further enhance the electrochemical properties of energy storage devices. The reason for this effect is presumed to be as follows. For example, silicon anodes for lithium-ion secondary batteries have a theoretical capacity of 4199 mAh / g, which is about 10 times higher than the theoretical capacity of general graphite (372 mAh / g), and further increases in capacity and energy density are expected. On the other hand, silicon that has absorbed lithium ions is Li 4.4The silicon material expands in volume to approximately four times its original size compared to silicon before lithium absorption. According to this disclosure, by using an acid or alkali that dissolves Al components other than silicon contained in the silicon alloy, these can be selectively removed, making it possible to easily produce a porous silicon material with small pore size and large porosity. Furthermore, the microstructure contains a compound containing Ti, which strengthens the silicon skeleton, thus further suppressing capacity degradation associated with skeleton fluctuations due to repeated charge and discharge cycles. In such a porous silicon material with small pore size and large porosity, when used in energy storage devices such as lithium-ion secondary batteries, volume expansion and contraction are greatly mitigated, improving charge and discharge characteristics such as charge-discharge cycle characteristics, thus making it easy to obtain a high-performance energy storage device. In particular, when a raw material containing Ti in the range of 1 at% to 4 at%, Si in the range of 15 at% to 35 at%, with the remainder being Al, is melted and rapidly cooled and solidified, first, Ti(Al,Si)2 compound crystallizes from the liquid phase as the primary crystal, and then primary Al, eutectic Al, and dendritic eutectic Si crystallize, or primary Si, eutectic Al, and dendritic eutectic Si crystallize. As a result, after the Al component is removed, a highly conductive porous silicon material is obtained in which Ti(Al,Si)2 compound, which has a three-dimensional network structure of Si skeleton and is a highly conductive compound, is dispersed. Furthermore, because it contains a large amount of Al, after the Al component is removed, a high average porosity, such as 50% to 80% by volume, can be achieved, thereby mitigating the expansion and contraction of Si during charging and discharging. Therefore, it is presumed that in this disclosure, electrochemical properties such as high-rate characteristics and charge-discharge cycle characteristics can be further enhanced in energy storage devices.

[0038] 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.

[0039] This disclosure may be as shown in any of the following [1] to

[11] . [1] A method for producing a porous silicon material, comprising: a precursor step of melting and rapidly solidifying a raw material containing 1 at% to 4 at% of Ti, 15 at% to 35 at% of Si, and the remainder being Al, when the total amount of Si, Ti, and Al is 100 at%, to obtain a silicon alloy precursor; and a porosity step of removing the Al component contained in the silicon alloy to obtain a porous silicon material. [2] The method for producing a porous silicon material according to [1], wherein in the precursor step, the raw material contains 1.5 at% to 4 at% of Ti, 20 at% to 30 at% of Si, and the remainder being Al. [3] The method for producing a porous silicon material according to [1] or [2], wherein in the porosity step, the Al component is selectively removed by an acid or alkali. [4] A method for producing a porous silicon material according to any one of [1] to [3], wherein the porous step is to obtain the porous silicon material containing the Ti(Al,Si)2 compound. [5] A method for producing a porous silicon material according to any one of [1] to [4], wherein the precursor step is to obtain the precursor having an average particle size in the range of 0.1 μm to 10 μm. [6] A porous silicon material having a pore size distribution range of 1 nm to 500 nm determined by mercury intrusion, containing a three-dimensional network structure of silicon skeleton having voids, containing a Ti(Al,Si)2 compound, and having an average porosity of 50 volume% to 80 volume%. [7] A porous silicon material according to [6], containing a Ti(Al,Si)2 compound in an amount of 5 mass% to 20 mass%. [8] A porous silicon material according to [6] or [7], wherein when the total amount of Si, Ti and Al is 100 at%, Ti is contained in an amount of 0.1 at% to 15 at%, Si is contained in an amount of 80 at% to 98 at%, and the remainder is Al. [9] An electrode containing the porous silicon material according to any one of [6] to [8] as an active material, wherein the active material is contained in an amount of 50% to 70% by mass, the conductive material is contained in an amount of 10% to 25% by mass, and the remainder is the binder, with respect to the total amount of the active material, binder and conductive material.

[10] A power storage device comprising a negative electrode containing a porous silicon material as described in any one of [6] to [8] as a negative electrode active material, a positive electrode containing a positive electrode active material, and an ion-conducting medium interposed between the negative electrode and the positive electrode to conduct carrier ions.

[11] A power storage device comprising a negative electrode which is an electrode as described in [9], a positive electrode containing a positive electrode active material, and an ion-conducting medium interposed between the negative electrode and the positive electrode to conduct carrier ions.

[0040] The following describes specific examples of how the porous silicon carbon electrode and energy storage device described herein have been fabricated. Experimental Examples 1 to 3 correspond to embodiments of the present disclosure, and Experimental Examples 4 to 8 correspond to comparative examples.

[0041] [Experimental Example 1] (Precursor Process) 75.4% by mass of lumpy Al, 20.3% by mass of lumpy Si, and 4.3% by mass of sponge Ti were prepared. These were mixed and then melted in a nitrogen-inert atmosphere using high-frequency heating to obtain a molten alloy. Al-Si-Ti alloy powder with an average particle size (d50) of 3 μm was obtained from this molten alloy by gas atomization using nitrogen-inert gas. Figure 3 is a schematic diagram of the atomization apparatus. The quenching rate was 10 2 ~10 4 The temperature was set to °C / s. The atomized powder in Experimental Example 1 has an atomic composition of Al-20at%Si-2.5at%Ti (atomized Al-20Si-2.5Ti alloy).

[0042] (Porous Formation Process) Next, 20 g of atomized Al-Si-Ti alloy powder was immersed in 800 ml of 3 mol / L hydrochloric acid solution at room temperature (25°C) for 1 hour, and then stirred at 90°C for 1 hour. The resulting particles (etched particles) were then washed several times with pure water and filtered. Subsequently, porous silicon particles were obtained by drying in a vacuum drying oven set at a furnace temperature of 30°C for 2 hours.

[0043] (Electrode Fabrication Process) 1.5 g of the obtained porous silicon particles and 0.5 g of carbon black with an average particle size of 48 nm as a conductive material were mixed. Then, 3.0 g of N-methylpyrrolidone (NMP) as a binder solvent was added and stirred to obtain a mixture of porous silicon particles, carbon material, and binder solvent (solvent mixing treatment). 2.85 g of binder solution was added to the mixture obtained in the solvent mixing treatment and stirred to obtain a composite slurry containing porous silicon particles, conductive material, binder solvent, and binder (binder mixing treatment). As the binder solution, a polyimide-based binder solution containing polyamic acid, a precursor of polyimide, and NMP, with a solid content concentration of 18.5% by mass, was used. The obtained composite slurry was coated onto a 20 μm thick copper foil, dried, and then rolled to obtain an electrode with a thickness of 50 μm. In this way, the electrode of Experimental Example 1 was fabricated. In Experimental Example 1, the electrode contains 60% by mass of porous silicon particles, 20% by mass of carbon material, and 20% by mass of binder, relative to the total amount of porous silicon particles, conductive material, and binder.

[0044] (Preparation of evaluation cell) First, the electrode prepared using the procedure described above was punched out into a circle with a diameter of 16 mm to serve as the negative electrode. The obtained negative electrode and a circular metal Li counter electrode with a diameter of 21 mm were stacked with a porous polyethylene separator in between. Then, the electrolyte was poured in to prepare a Tom cell-type half cell. The electrolyte was prepared by mixing fluoroethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC) in a volume ratio of 1.5:1.5:4:3, and then adding LiPF6 to a concentration of 1 mol / L.

[0045] (Electrochemical measurement of evaluation cells) For the half-cells obtained as described above, charge and discharge were repeated for 5 cycles at a current density (0.1C) of 10% of the rated capacity (1C) specified by the initial discharge capacity, within the battery voltage range of 0.005 to 1.5V, and the discharge capacity after 5 cycles was taken as the initial discharge capacity (Q1). However, for Experimental Example 4 described below, the discharge capacity of the first cycle was taken as the initial discharge capacity (Q1). Charge and discharge at 0.1C was continued, and the discharge capacity (Q) after 50 cycles was taken. 50 ) to find Q 50The capacity retention rate [%], expressed as / Q1 × 100, was calculated, and the cycle characteristics were evaluated. In addition, in the battery voltage range of 0.005 to 1.5V, 10 charge-discharge cycles were performed at 0.1C, followed by 5 charge-discharge cycles at 0.5C and 5 charge-discharge cycles at 2C. The average values ​​of the discharge capacity were calculated as the discharge capacity at 0.5C and 2C, respectively, and the rate characteristics were evaluated.

[0046] [Experimental Example 2] The process was the same as in Experimental Example 1, except that the amount of solid Al used in the precursor process was 70.4% by mass, solid Si was 25.3% by mass, and sponge Ti was 4.3% by mass. The atomized powder in Experimental Example 2 has an atomic composition of Al-25at%Si-2.5at%Ti (atomized Al-25Si-2.5Ti alloy).

[0047] [Experimental Example 3] The process was the same as in Experimental Example 1, except that the amount of solid Al used in the precursor process was 65.4% by mass, solid Si was 30.3% by mass, and sponge Ti was 4.3% by mass. The atomized powder in Experimental Example 3 has an atomic composition of Al-30at%Si-2.5at%Ti (atomized Al-30Si-2.5Ti alloy).

[0048] [Experimental Example 4] The procedure was the same as in Experimental Example 1, except that the precursor step and porosity creation step were omitted and the electrode fabrication step was performed using bulk Si powder with an average particle size of 5 μm.

[0049] [Experimental Example 5] The process was the same as in Experimental Example 1, except that the amount of solid Al used in the molten alloy in the precursor step was 87.6% by mass, the amount of solid Si was 12.4% by mass, and sponge Ti was not used.

[0050] [Experimental Example 6] The process was the same as in Experimental Example 1, except that the amount of solid Al used in the molten alloy in the precursor step was 79.4% by mass, the amount of solid Si was 20.6% by mass, and sponge Ti was not used.

[0051] [Experimental Example 7] The process was the same as in Experimental Example 1, except that the amount of solid Al used in the molten alloy in the precursor step was 74.2% by mass, the amount of solid Si was 25.8% by mass, and sponge Ti was not used.

[0052] [Experimental Example 8] The process was the same as in Experimental Example 1, except that the amount of solid Al used in the precursor step was 45.5% by mass, solid Si was 37.7% by mass, and sponge Ti was 16.8% by weight.

[0053] [Results and Discussion] Figure 4 shows the XRD measurement results for the atomized powder and porous silicon from Experimental Example 2. Figure 4 also shows the XRD measurement results for the bulk silicon from Experimental Example 4. From Figure 4, it was confirmed that Ti(Al,Si)2 compounds crystallize near the ternary eutectic composition of Al-xSi-2.5at%Ti, as inferred from Figure 1.

[0054] Figure 5 shows a surface SEM image of the atomized powder from Experimental Example 2. Figure 6 shows a surface SEM image of the porous silicon from Experimental Example 2. From Figures 5 and 6, it can be seen that the atomized powder retains its shape and becomes porous even after acid treatment.

[0055] Figure 7 shows the pore distribution of the porous silicon of Experimental Example 2 obtained by the mercury adsorption method. Figure 8 shows a cross-sectional SEM image of the porous silicon of Experimental Example 2. Figure 9 shows a cross-sectional scanning transmission electron microscope (STEM) image of the porous silicon of Experimental Example 2. Figure 9A is a dark-field (DF)-STEM image, Figure 9B is a DF-STEM image of the dashed frame in Figure 9A, Figure 9C is an elemental mapping image of Al, Figure 9D is an elemental mapping image of Si, and Figure 9E is an elemental mapping image of Ti. As shown in Figure 7, the porosity of the porous silicon of Experimental Example 2 was 63 volume%, and the average pore diameter was approximately 80 nm. Furthermore, from the XRD results in Figure 4, the cross-sectional SEM image in Figure 8, and the cross-sectional STEM image and elemental mapping images in Figure 9, it was inferred that in Experimental Example 2, Ti(Al,Si)2 crystallized as a primary crystal within the dendritic eutectic Si.

[0056] Table 1 shows the elemental composition, phase composition (compound composition ratio), porosity by mercury intrusion method, and average pore size for the atomized powders and acid-treated porous silicon particles of Experimental Examples 1-3 and 5-8. Table 1 also shows the results for pure Si in Experimental Example 4. In Experimental Examples 1-3, it was inferred that after acid treatment, the Al and AlTi compounds in the atomized Al-Si-Ti alloy dissolved, resulting in a structure (porous silicon) that was mainly Si and contained a Ti(Al,Si)2 phase. In the porous silicon of Experimental Examples 1-3, the atomic composition was 93-95 at% Si, 3.6-5.6 at% Al, and 1.0-1.2 at% Ti, and the proportion of the Ti(Al,Si)2 silicide phase, determined using XRD results, was 12-15 mass%. Furthermore, in the porous silicon of Experimental Examples 1 to 3, the porosity was 58 to 68 volume%, and the average pore diameter was 70 to 95 nm, indicating high porosity. On the other hand, in Experimental Examples 5 to 7, a binary atomized Al-Si alloy was acid-treated, and the atomic composition of the porous silicon after acid treatment was 87 to 96 at% Si and 3.4 to 6.0 at% Al. In addition, in the porous silicon of Experimental Examples 5 to 7, the porosity was 63 to 76 volume%, and the average pore diameter was 75 to 150 nm. In Experimental Example 8, similar to Experimental Examples 1 to 3, it was inferred that the Al-40at%Si-10at%Ti alloy was formed by the dissolution of Al and AlTi compounds after acid treatment. In the porous silicon of Experimental Example 8, the atomic composition was 70 at% Si, 6.3 at% Al, and 17 at% Ti. The proportion of the (Al,Si)2 silicide phase, determined using XRD results, was 40 mass%. In addition, the porosity of the porous silicon of Experimental Example 8 was 47 volume%, and the average pore diameter was 85 nm.

[0057] Table 2 shows the electrochemical measurement results using porous silicon in Experimental Examples 1-3 and 5-8, along with the electrochemical measurement results using pure Si in Experimental Example 4. In Experimental Examples 1-3, the initial discharge capacity at a 0.1C rate was 2245-2612 mAh / g, and the capacity retention rate after 50 cycles was 76-79%. The rate characteristics were 1662-1812 mAh / g at a 0.5C rate and 1029-1245 mAh / g at a 2C rate. In Experimental Examples 1-3, it was found that a discharge capacity of 1000 mAh / g or more could be maintained even at a 2C rate. In Experimental Example 4, the initial discharge capacity was 2804 mAh / g, and the capacity retention rate after 50 cycles deteriorated to 5.9%. This was presumed to be due to electrode breakdown caused by the expansion and contraction of Si during the charge-discharge cycle. In Experimental Examples 5-7, the initial discharge capacity at a 0.1C rate was 2084-2434 mAh / g, and the capacity retention rate after 50 cycles was 68-75%. The rate characteristics were 1215-1453 mAh / g at a 0.5C rate and 198-564 mAh / g at a 2C rate. In Experimental Examples 5-7, there was no significant difference in capacity degradation due to the 0.1C cycle test compared to Experimental Examples 1-3. However, at higher rates of 0.5C and 2C, the discharge capacity decreased significantly, and at a 2C rate, a discharge capacity of 564 mAh / g or less could be obtained. In Experimental Example 8, the initial discharge capacity at a 0.1C rate was 1231 mAh / g, and the capacity retention rate after 50 cycles was 63%. The rate characteristics for Experimental Example 8 were 924 mAh / g at a 0.5C rate and 698 mAh / g at a 2C rate.

[0058] The porous silicon in Experimental Examples 1-3 and 8 all contain silicide compounds, but the porous silicon in Experimental Examples 1-3 had a relatively large initial discharge capacity at 0.1C. This was presumed to be because the porous silicon in Experimental Examples 1-3 contains a large amount of Si phase, which has a large discharge capacity. In this regard, Si undergoes a charging (Li insertion) reaction through the reaction shown in the following formula (1), and Li 3.75 This results in a Si (x = 3.75) compound. Si is theoretically known to have a capacity of 3579 mAh / g. On the other hand, in Si-M silicide compounds (where M is a transition metal), the charging (Li insertion) reaction proceeds by the reaction shown in equation (2) below, and Li (0.1~0.3)It is known that the resulting compound is an MSi2 (x = 0.1–0.3) compound. The discharge capacity of Ti(Al,Si)2 silicide was estimated to be approximately 400 mAh / g based on the elemental ratio of the Li–Si compound when Li was inserted into the Si–Ti silicide compound, and the discharge capacity, as reported in Reference 2 (PK Lee, MH Tahmasebi, S. Ran, ST Boles, DYW Yu, Small 14 (2018), e1802051. DOI: 10.1002 / smll.201802051). Si + xLi + xe - →Li x Si...Formula (1) MSi2+xLi+xe - →Li x MSi2...Formula (2)

[0059] Furthermore, the porous silicon used in Experimental Examples 1-3 showed a high volume retention rate after cycling. This was presumed to be because the porous silicon in Experimental Examples 1-3 had a higher porosity than that in Experimental Example 8, resulting in a greater suppression of particle expansion during Li insertion.

[0060] From the above, it was confirmed that the porous silicon materials of Experimental Examples 1 to 3 can further enhance electrochemical properties such as high-rate characteristics and charge-discharge cycle characteristics. Furthermore, as shown in Figure 1, regarding the raw material composition, it was inferred that not only when the composition is the same as in Experimental Examples 1 to 3, but also when the total amount of Si, Ti, and Al is set to 100 at%, Ti is included in the range of 1 at% to 4 at%, Si is included in the range of 15 at% to 35 at%, and the remainder is Al (see, for example, the shaded area in Figure 1), the same phase transformation behavior as in Experimental Examples 1 to 3 is observed, and the same porous silicon materials as in Experimental Examples 1 to 3 can be obtained. However, as shown in Figure 1, even when Si exceeds 35 at%, the same phase transformation behavior as in Experimental Examples 1 to 3 is observed, but coarsening of the primary Si is predicted, which is inferred to reduce the effect of conductivity improvement by the Ti(Al,Si)2 compound. For this reason, it was inferred that Si should be 35 at% or less.

[0061]

[0062]

[0063] This application is based on the priority claim of Japanese Patent Application No. 2024-191073, filed on 30 October 2024, the entire contents of which are incorporated herein by reference.

[0064] This disclosure can be used, for example, in the field of energy storage devices.

[0065] 10 Energy storage device, 12 Positive electrode, 13 Positive electrode active material, 14 Current collector, 15 Negative electrode, 16 Negative electrode active material, 17 Current collector, 18 Ion conducting medium, 21 Porous silicon material, 23 Void.

Claims

1. A method for producing a porous silicon material, comprising: a precursor step of melting and rapidly solidifying a raw material containing 1 at% to 4 at% of Ti, 15 at% to 35 at% of Si, and the remainder being Al, when the total amount of Si, Ti, and Al is 100 at%, to obtain a silicon alloy precursor; and a porosity-forming step of removing the Al component contained in the silicon alloy to obtain a porous silicon material.

2. The method for producing a porous silicon material according to claim 1, wherein the precursor step uses a raw material containing Ti in an amount of 1.5 at% to 4 at%, Si in an amount of 20 at% to 30 at%, and the remainder being Al.

3. The method for producing a porous silicon material according to claim 1 or 2, wherein the Al component is selectively removed by an acid or alkali in the porosification step.

4. The method for producing a porous silicon material according to claim 1 or 2, wherein the porous step yields the porous silicon material containing a Ti(Al,Si)2 compound.

5. The method for producing a porous silicon material according to claim 1 or 2, wherein the precursor step yields the precursor having an average particle size in the range of 0.1 μm to 10 μm.

6. A porous silicon material having a pore size distribution range of 1 nm to 500 nm determined by mercury intrusion, containing a three-dimensional network structure of silicon skeleton with voids, containing a Ti(Al,Si)2 compound, and having an average porosity of 50% to 80% by volume.

7. The porous silicon material according to claim 6, comprising a Ti(Al,Si)2 compound in an amount of 5% by mass or more and 20% by mass or less.

8. The porous silicon material according to claim 6 or 7, wherein, when the total amount of Si, Ti, and Al is 100 at%, Ti is contained in an amount of 0.1 at% to 15 at%, Si is contained in an amount of 80 at% to 98 at%, and the remainder is Al.

9. An electrode comprising the porous silicon material described in claim 6 or 7 as an active material, wherein the active material is present in an amount of 50% by mass or more and 70% by mass or less, the conductive material is present in an amount of 10% by mass or more and 25% by mass or less, and the remainder is the binder, based on the total amount of the active material, binder and conductive material.

10. An energy storage device comprising: a negative electrode containing the porous silicon material described in claim 6 or 7 as a negative electrode active material; a positive electrode containing a positive electrode active material; and an ion conducting medium interposed between the negative electrode and the positive electrode for conducting carrier ions.

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