Porous silicon material, power storage device, and method for producing porous silicon material

Abstract

To enhance charge and discharge properties of a porous silicon material.SOLUTION: A porous silicon material disclosed herein comprises Si, Al, and a transition metal element M, has a porosity of 45 vol.% or more according to a mercury intrusion method, is in particulate form, and exhibits a number average particle size derived from a particle size distribution within 0.5 μm or more and 12 μm or less.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] Disclosed herein are porous silicon materials, power storage devices, and methods for making the porous silicon materials. [Background technology]

[0002] Conventionally, porous silicon materials used in electricity storage devices have been produced by a manufacturing method including a precursor process in which a raw material containing Cr in the range of 1 at% to 20 at% and Al in the range of 40 at% to 90 at% and the remainder Si, where Si, Al, and Cr together make up 100 at%, is melted and rapidly solidified to obtain a silicon alloy precursor, and a porosity process in which the Al component contained in the silicon alloy is removed to obtain a porous silicon material (see, for example, Patent Document 1). Among these porous silicon materials, those containing Si can further suppress deterioration of charge / discharge characteristics. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-92861 Summary of the Invention [Problem to be solved by the invention]

[0004] Silicon anodes have a theoretical capacity 10 times greater than that of graphite anodes currently in practical use, but suffer from poor cycle characteristics due to their large expansion and contraction during charge and discharge. The porous silicon material in Patent Document 1 contains Al, Cr, etc., which increases its strength and further prevents deterioration of charge and discharge characteristics, but this is still insufficient, and further improvement is desired.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and has as its main object to provide a porous silicon material, an electricity storage device, and a method for manufacturing a porous silicon material that can further improve the charge / discharge characteristics of the porous silicon material. [Means for solving the problem]

[0006] As a result of intensive research to achieve the above-mentioned object, the present inventors have found that the charge-discharge characteristics of a particulate porous silicon material can be further improved by setting the particle size within a more suitable range in a particulate porous material containing Al, Si, and a transition metal element M, and have completed the porous silicon material, electricity storage device, and method for producing a porous silicon material of the present disclosure.

[0007] That is, the porous silicon material of the present disclosure has: containing Si, Al, and a transition metal element M, The porosity determined by mercury porosimetry is 45% by volume or more, It is particulate, and the number average particle size obtained from the particle size distribution is in the range of 0.5 μm to 12 μm.

[0008] The electricity storage device of the present disclosure includes: a positive electrode including a positive electrode active material; a negative electrode containing the porous silicon material as a negative electrode active material; an ion conductive medium interposed between the positive electrode and the negative electrode and conducting lithium ions; It is equipped with the following.

[0009] The method for producing a porous silicon material of the present disclosure includes: The basic composition formula is Al 100-x-y Si x M y(However, the mother alloy melt is quenched under the condition that M is a transition metal element, 10 ≦ x ≦ 40, 0 < y ≦ 5, 0 < x / y ≦ 0.2), so that Si, Al, and at least one of transition metal silicide, transition metal aluminum, and aluminum transition metal silicide are phase-separated into a conductive phase, and by selectively removing the Al component, the porosity determined by the mercury intrusion method is 45% by volume or more, and it is in a particulate state, and the porous silicon material having a number average value of the particle size obtained from the particle size distribution in the range of 0.5 μm or more and 12 μm or less is obtained. A porous process, is included.

Advantages of the Invention

[0010] The present disclosure can further improve the charge-discharge characteristics of the porous silicon material. The reason for obtaining such an effect is presumed as follows. For example, in an electrode using Si as an active material, a larger capacity can be obtained compared to a graphite electrode, but there is a problem that the pore structure is broken due to residual stress caused by volume change of Si during charge and discharge, and the rate characteristics and capacity retention rate may decrease. In the porous silicon material, even if the porosity in the silicon negative electrode is the same, the pore structure is less likely to break because the stress applied to each pore is dispersed when there are more small pores than when there are a few large pores. Also, high skeleton strength is important for maintaining the pore structure. In the present disclosure, it is presumed that the charge-discharge characteristics of the porous silicon material can be further improved by adopting a suitable particle size range capable of maintaining the pore structure based on these relationships.

Brief Description of the Drawings

[0011] [Figure 1] Al-Si-Cr phase diagram at 25 at% Si. [Figure 2] Schematic diagram of the microstructure formation process of the outermost surface layer during the cooling process of the melt droplet. [Figure 3] Explanation diagram of the eutectic composition range in the Al-Si-Cr system composition. [Figure 4] Explanation diagram showing an example of the structure of the power storage device 10. [Figure 5]1 shows particle size distribution measurement results for porous silicon materials of Experimental Examples 1 to 3. [Figure 6] 1 is a cross-sectional SEM photograph of the porous silicon materials of Experimental Examples 1 to 3. [Figure 7] 1 is a graph showing the relationship between current density and capacity retention rate after 50 cycles in Experimental Examples 1-1, 1-2, and 2-2. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Method of manufacturing porous silicon material) The method for producing a porous silicon material according to the present disclosure includes a porosity-forming step. The porosity-forming step may include a precursor treatment and a removal treatment. In the precursor treatment, a silicon alloy precursor is obtained by melting and rapidly solidifying an Al-Si-M ternary alloy raw material having a composition in which an Al phase, a Si phase, and a silicide phase containing at least an AlSiM compound (M is a transition metal element) appear at room temperature in the equilibrium diagram. The silicide phase contains at least an AlSiM compound containing Al, Si, and M. Examples of M include Cr. In the removal treatment, a portion of the Al component contained in the silicon alloy is removed to obtain a porous silicon material. The porous silicon material obtained by this method for producing a porous silicon material has a structure having a skeleton in which Si and an M silicide containing at least an AlSiM compound coexist, for example. Such a structure is also referred to as a coexisting structure. Examples of such structures include MSi2, M(Al,Si)2, and Al. 13 Since M silicide phases such as Si4M4 are electrically conductive, the coexistence of silicide as a conductive phase in the Si skeleton, which acts as a conduction path, can improve conductivity. Furthermore, because the strength of M silicide is about twice that of Si, the coexistence of M silicide as a reinforcing phase in the Si skeleton is also expected to improve the skeleton strength.

[0013] Figure 1 shows the Al-Si-Cr phase diagram for 25 at% Si. Figure 2 is a schematic diagram of the microstructure formation process of the outermost surface layer during the cooling process of a melt droplet. The formation of a coexistence structure due to Cr addition is influenced by the precipitation order of each phase in the Al-Si-Cr system. Here, we explain the cooling of an alloy melt using the gas atomization method as an example. In the gas atomization method, high-temperature melt is injected into a high-pressure gas through a hole at the tip of a nozzle. When the melt (Figure 1(1)) is cooled to the temperature shown in Figure 1(2), CrSi2 first crystallizes from the low-temperature droplet surface (Figure 2(2)). However, the CrSi2 gradually coarsens in the coexistence temperature range with the melt (Figure 1(3)) (Figure 2(3)). If the CrSi2 coarsens too much, the resulting silicon powder is surrounded by a shell of inactive CrSi2 (Figure 2(3-2)), which is undesirable because it reduces the conduction path for carrier ions (Li) on the active material surface. However, in the AlSiCr phase diagram, when cooled to the temperature shown in Figure 1(4), CrSi2 decomposes (peritectic reaction) and simultaneously Si and Al 13 This is more preferable because Si4Cr4 precipitates (eutectic reaction) and a conductive path for active carrier ions (i.e., Si phase) is formed on the surface of the active material. Furthermore, this peritectic reaction generally proceeds as follows: L + CrSi2 ⇒ Al 13 This refers to a reaction in which a melt reacts with a solid phase to produce another solid phase, such as Si4Cr4. However, since the reaction proceeds from the surface of the solid phase particle, as shown in Figure 2 (4), fine CrSi2 particles are surrounded by Al 13 A structure is formed in which a shell of Si4Cr4 and Si is coated. In this way, in the temperature range of Figure 1 (5), CrSi2 (which may actually be Cr(Al,Si)2) becomes Al. 13 Since a reaction occurs in which Cr4Si4 and Si are decomposed, the Si and Al atoms are separated from the CrSi2 crystal nucleus that was initially generated. 13 The Cr4Si4 nanoparticles coexist in close proximity, forming cluster particles dispersed in the melt (Fig. 2(5)). Finally, the Al melt solidifies, and the Si and Al clusters disintegrate. 13The Cr4Si4 nanoparticles are linked together to form a structure in which Si and Cr silicide coexist in the framework, and by removing Al from this by acid treatment, a composite porous material with a coexisting structure is obtained. Note that if the cooling rate is sufficiently high, cooling occurs before the peritectic reaction is completed, so some of the CrSi2 near the particle surface is thought to remain as a non-equilibrium phase. During the cooling process described above, Al surrounds the fine CrSi2 particles due to the peritectic reaction. 13 The formation of a structure in which Si4Cr4 and Si cores are coated results in a finer microstructure. 13 In addition to the fineness of Si4Cr4, the Al alloy that is the source of pores is also refined. 13 Because the difference in precipitation temperatures between Si4Cr4 and Al is relatively small (up to 350°C), the crystal growth of these particles is small, allowing for the creation of a nano-sized microstructure. The solidification structure forms a lamellar structure consisting of SiCr compounds, AlSiCr compounds, AlCr compounds, eutectic Si, primary Si, and primary Al. Compounds that dissolve in acid include primary Al, AlSiCr compounds, and AlCr compounds. It is estimated that the structure obtained after acid treatment will be a skeletal porous body consisting of the remaining SiCr compounds, eutectic Si, and primary Si, as well as undissolved primary Al, AlSiCr compounds, and AlCr compounds.

[0014] Figure 3 is an explanatory diagram of the range of eutectic compositions in Al-Si-Cr system compositions. To realize a coexistence structure, as mentioned above, it is necessary to go through a state in which cluster particles of Si and Cr silicide are dispersed in the Al melt or a state close to that, and the ideal composition range is one in which Si and Cr silicide precipitate simultaneously through a eutectic reaction. 100-x-y Si x Cr y In the basic composition, when the Si content x is less than 18 at%, the composition does not show a eutectic reaction between Si and silicide. On the other hand, when the Si content x is 18 at% or more, especially 25 at% or more, depending on the Cr content y, the following reactions occur: L ⇒ Si + CrSi2 (eutectic reaction 1) and L ⇒ Si + Al 13There exists a composition that causes the eutectic reaction of Si4Cr4 (eutectic reaction 2). Figure 3 shows the relationship between the amount of Si x and the amount of Cr y that causes these eutectic reactions 1 and 2. In the composition region shown by the diagonal lines, Si and CrSi2 crystallize at relatively close temperatures, and the reaction CrSi2 + L ⇒ Al occurs. 13 It is presumed that this is a more preferable composition range because a peritectic reaction of Si4Cr4 occurs, resulting in a finer pore structure. 100-x-y Si x Cr y In this case, the ranges are 18≦x≦40 and 0.1≦y≦15. Furthermore, based on Fig. 3, the Cr content is preferably 0.1 at% or more, more preferably 0.5 at% or more, and even more preferably 1 at% or more, relative to the total of Al and Si. Furthermore, in Fig. 3, within the composition region indicated by diagonal lines, the composition region where Cr is 10 at% or less, that is, the composition region surrounded by a thick line and colored gray, is more preferable from the viewpoint of increasing the capacity of the electricity storage device, because the amount of silicide that does not contribute to the charge / discharge reaction does not become too large.

[0015] (precursor treatment) In the precursor treatment, a silicon alloy precursor is obtained by melting an Al-Si-M ternary alloy raw material having a composition in which an Al phase, a Si phase, and an M silicide phase appear, followed by rapid solidification. The silicon alloy precursor may, for example, be one in which Si and an M silicide coexist in the framework portion that forms the pores. In this process, a raw material containing M in the range of 0.1 at% to 20 at% and Al in the range of 40 at% to 90 at% and the remainder being Si, when the total of Si, Al, and M is taken as 100 at%, may be used. In the raw material composition, M is 0.1 at% or more, preferably 0.5 at% or more, and more preferably 1 at% or more. As described above, the raw material composition is based on the basic composition formula Al 100-x-y Si x M yIn this case, it is more preferable that x / y is in the range of 18≦x≦40 and 0.1≦y≦15. Of these, it is more preferable that x / y≧8 is satisfied. The value of x / y may be 10 or more or 20 or more. The value of x / y may be 50 or less or 40 or less. The raw material may contain unavoidable impurities. Examples of unavoidable impurities include components that inevitably remain during the refining of Si, Al, or M, such as Fe, C, Cu, Ni, and P. The amount of unavoidable impurities is preferably as small as possible, and for example, when the total amount of Si, Al, and M is 100 at%, it is preferably 5 at% or less, and more preferably 2 at% or less. The compounding ratio of M is, for example, preferably 0.1 at% or more, and may be 0.5 at% or more. The compounding ratio of M is preferably 10 at% or less, and may be 5 at% or less, or may be 3 at% or less. The Al compounding ratio is preferably 50 at% or more, and may be 55 at% or more or 60 at% or more. The Al compounding ratio is preferably 85 at% or less, more preferably 80 at% or less, and may be 77.5 at% or less. The Si compounding ratio is, for example, preferably 15 at% or more, more preferably 18 at% or more, and may be 20 at% or more or 25 at% or more. The Si compounding ratio is, for example, preferably 59 at% or less, more preferably 50 at% or less, and may be 40 at% or less or 30 at% or less. Silicon alloys containing Al and M within these ranges are preferred because they can further increase the porosity and obtain voids with more suitable shapes and sizes. When the Al content is high, rapid cooling after melting the alloy results in the precipitation of a large single phase of Al, allowing the formation of many voids. The cooling rate is preferably more rapid, for example, 10% or less from the molten state. 2 ℃ / s or more 10 8 °C / s or less.

[0016] In this process, when melting the raw materials, high-frequency crucible melting in an inert gas atmosphere such as Ar is preferred, but any melting method can be used. To produce a master alloy, the raw material powder must be melted. High-frequency melting is more preferred for producing a uniform sample, but melting can also be performed simply by heating and melting in an electric furnace or using an electron beam. In the precursor process, the alloy obtained from the raw materials may be granulated. This granulation process may involve casting a molten silicon alloy raw material into a mold and crushing the resulting ingot into particles. The silicon alloy may also be granulated by one or more of the following methods: gas atomization, water atomization, and roll quenching. Gas atomization and water atomization produce alloy powder. On the other hand, roll quenching produces a thin ribbon alloy, which may then be crushed and powdered. The powder obtained by roll quenching has a fine alloy structure, so porous silicon with fine pores can be obtained after the leaching process. Of these, gas atomization is more preferred as a method for granulating the silicon alloy. In gas atomization, it is preferable to carry out the molten metal in an Ar atmosphere, and the granulation in an Ar or He atmosphere.

[0017] In the precursor treatment, the silicon alloy is preferably granulated to have a particle size having a number average particle size in the range of 0.5 μm to 12 μm. The silicon alloy particles preferably have a number average particle size of 3 μm or more, and more preferably 5 μm or more. The number average particle size is more preferably 10 μm or less, and even more preferably 8 μm or less. In this process, the silicon alloy particles may be classified to have a particle size of 15 μm or less, 10 μm or less, or 5 μm or less. In this process, the silicon alloy particles may be classified to have a number average particle size of 0.5 μm or more, 3 μm or more, or 5 μm or more. The silicon alloy particles may be appropriately selected depending on the characteristics required for the power storage device. The silicon alloy particles preferably have a particle size D90 in the range of 2 μm to 15 μm, more preferably 4 μm or more, and even more preferably 12 μm or less. Here, the numerical average particle size is determined by dispersing the particles in a solvent such as water, measuring the particle size distribution, and calculating the numerical average value. This particle size distribution is measured using a laser analysis scattering method. The particles obtained by this particle formation process will have the average particle size of the aggregate of porous particles that are ultimately to be obtained.

[0018] In this precursor process, a raw material containing a second element including one or more of Ca, Mg, Na, Sr, and P in addition to Al, Si, and M may be used. Among these, the second element is preferably one or more of Ca, Na, and Sr. The content of the second element is preferably less than that of Al and M, for example, preferably in the range of 10% by mass or less, more preferably 5% by mass or less, based on the total silicon alloy. In this precursor process, a raw material having a composition in which a portion of M is replaced with another transition metal element may be used. In this case, the content of the other transition metal element may be half or less of that of M, 20% or less, or 10% or less, in terms of molar ratio. Examples of the other transition metal element include Ti, V, Nb, Mo, Ni, Mn, Fe, Co, and Zn.

[0019] (Removal process) The removal process removes Al components contained in the silicon alloy. Examples of Al components removed in this process include Al and its compounds. This removal process is preferably performed under conditions where the increase in oxygen is 7 at% or less. The increase in oxygen may be 5 at% or less, 4 at% or less, or 2 at% or less. A smaller increase in oxygen is desirable. If it is assumed that the amount of Si remains unchanged before and after the removal process, the change in oxygen may be calculated from the ratio of the amount of oxygen (elemental ratio) after the removal process to the amount of Si (elemental ratio), using the amount of Si (elemental ratio) before the removal process as a reference. Specifically, the increase in oxygen GO [at%] is calculated using the formula GO = O2 × S1 / S2 - O1. The elemental ratios of Al, Si, M, and O determined by EDX for the silicon alloy before the removal process are A1 [at%], S1 [at%], M1 [at%], and O1 [at%], respectively (where A1 + S1 + M1 = 100), and the elemental ratios of Al, Si, and M determined by EDX for the porous silicon material after the removal process are A2 [at%], S2 [at%], M2 [at%], and O2 [at%], respectively (where A2 + S2 + M2 = 100). Note that, for example, because Si does not dissolve in hydrochloric acid, if the removal process is performed by acid treatment with hydrochloric acid, it can be assumed that the amount of Si remains unchanged before and after the removal process.

[0020] This removal treatment may be performed under conditions where the reduction in M ​​is 60% or less of the amount of M that would be reduced if M were completely removed. The reduction in M ​​may be 55% or less, or 50% or less of the amount of M that would be reduced if M were completely removed. Although a smaller reduction in M ​​is preferable, it may be 5% or more, 20% or more, or 30% or more of the amount of M that would be reduced if M were completely removed. Furthermore, the removal treatment may be performed under conditions where the reduction in M ​​is 0.5 at% or more less than the amount of M that would be reduced if M were completely removed. The reduction in M ​​may be 0.6 at% or more less, or 0.7 at% or more less than the amount of M that would be reduced if M were completely removed. Furthermore, the reduction in M ​​may be 1.0 at% or less less, 0.9 at% or less less, or 0.8 at% or less less than the amount of M that would be reduced if M were completely removed. The reduction in M ​​may be, for example, -0.6 at% or less. The smaller the reduction in M, the better, but it may be, for example, -0.1 at% or more, -0.3 at% or more, or -0.4 at% or more. This porosity-forming step may be performed under conditions such that the reduction in Al exceeds 90% of the reduction in Al that would occur if Al were completely removed, or may be performed under conditions such that the reduction in Al is 95 at% or more. The reduction in Al may be, for example, -40 at% to -75 at% or -50 at% to -70 at%.

[0021] Here, when it is assumed that the amount of Si is unchanged before and after the removal treatment, the amount of decrease in M ​​and the amount of decrease in Al may be calculated from the ratio of the amount (element ratio) of M or Al after the removal treatment to the amount (element ratio) of Si, using the amount (element ratio) of Si before the removal treatment as a reference. Specifically, the amount of decrease in M ​​LM [at %] is a value calculated using the formula LM = M2 × S1 / S2 - M1, and the amount of decrease in Al LA [at %] is a value calculated using the formula LA = A2 × S1 / S2 - A1. The element ratios of Al, Si, and M determined by EDX for the silicon alloy before the removal process are A1 [at%], S1 [at%], and M1 [at%], respectively (where A1 + S1 + M1 = 100), and the element ratios of Al, Si, and M determined by EDX for the porous silicon material after the removal process are A2 [at%], S2 [at%], and M2 [at%], respectively (where A2 + S2 + M2 = 100). Note that, for example, because Si does not dissolve in hydrochloric acid, if the removal process is performed by acid treatment with hydrochloric acid, it can be assumed that the amount of Si remains unchanged before and after the removal process.

[0022] In the removal treatment, it is preferable to selectively remove the Al component, i.e., the Al phase and its compounds, using an acid or alkali. The removal treatment using an acid is also called an acid treatment, and the removal treatment using an alkali is also called an alkali treatment. The acid or alkali used is preferably one that elutes elements and / or compounds other than silicon in the silicon alloy but does not elute silicon, and examples thereof include hydrochloric acid, sulfuric acid, and sodium hydroxide. This acid or alkali is preferably in the form of an aqueous solution. The concentration of the acid or alkali is not particularly limited as long as it is within a range that can remove the Al component, and may be, for example, 0.01 mol / L or more, 0.02 mol / L or more, or 0.05 mol / L or more. The concentration of the acid or alkali may be, for example, 5 mol / L or less, 3 mol / L or less, or 1.5 mol / L or less. The acid or alkali concentration is preferably low from the viewpoint of suppressing oxygen uptake into the porous silicon material, and may be, for example, less than 1 mol / L, more preferably less than 0.5 mol / L, even more preferably less than 0.2 mol / L, or may be 0.1 mol / L or less. The temperature during the removal treatment may be, for example, less than 40°C, 35°C or less, or 30°C or less. The temperature during the removal treatment may be, for example, 0°C or higher, 5°C or higher, or 10°C or higher. The removal treatment time may be, for example, 1 hour or more, or 2 hours or more. The removal treatment time may be, for example, 24 hours or less, 12 hours or less, or 10 hours or less. This removal treatment is preferably performed by immersing the silicon alloy in an acid or alkali solution and stirring as necessary. The obtained porous silicon material is then washed and dried.

[0023] (porous silicon material) The porous silicon material of the present disclosure may be one produced by the manufacturing method described above. This porous silicon material has a skeleton in which Si and M silicide containing at least an AlSiM compound coexist. M silicide is a semiconductor with relatively high conductivity, so it is expected to have the effect of reducing resistance. In particular, since such M silicide coexists with Si and exists along the skeleton that serves as a conduction path, it is presumed that electrical conduction is efficient and resistivity can be further reduced. The M silicide phase may be an MSi compound or an AlMSi compound, but an AlMSi compound is preferred. The M silicide phase can be CrSi2, Cr(Si,Al)2, Al 13 Cr4Si4, Cr(Si,Al)2, Al 13The porous silicon material may be one or more of Cr4Si4. The M silicide may exist in an amorphous state. The porous silicon material may contain an Al phase. Since Al has high conductivity as a metal phase, it is expected to have the effect of reducing resistance. Furthermore, since Al has charge / discharge capacity as an active material in an electricity storage device, it is expected to have the effect of mitigating the decrease in capacity due to the coexistence of a conductive phase.

[0024] This porous silicon material preferably has an oxygen content of 15 at% or less when the total of Si, Al, and M is taken as 100 at%. Furthermore, the porous silicon material preferably has an O / M ratio, which is the elemental ratio of oxygen to M, of 10 or less. The smaller the oxygen content, or the lower the ratio of the oxygen content to the M content, the lower the resistivity tends to be, presumably due to the presence of less insulating phases such as SiO2. This oxygen content is preferably 10 at% or less, and may be 7.5 at% or less, or 5 at% or less. This oxygen content may be 1 at% or more, 3 at% or more, or 5 at% or more. The O / M ratio may be 7.5 at% or less, 5 at% or less, or 4 at% or less. This O / M ratio may be 0.5 or more, or 1 or more.

[0025] In this porous silicon material, from the viewpoint of reducing resistivity, a high Al content is preferable. For example, when the total of Si, Al, and M is taken as 100 at%, the Al content may be 6 at% or more, 7 at% or more, or 10 at% or more. The Al content may be, for example, 25 at% or less, 20 at% or less, or 15 at% or less. When the total of Si, Al, and M is taken as 100 at%, the Si content of this porous silicon material may be 93 at% or less, 92 at% or less, or 90 at% or less. The Si content may be 50 at% or more, 70 at% or more, or 75 at% or more. When the total of Si, Al, and M is taken as 100 at%, the M content of this porous silicon material may be more than 0 at% but not more than 5 at%, and the Al / M ratio, which is the elemental ratio of Al to M, may be 2 or more and 10 or less. The Al / M ratio may be 7.5 or less, or 5 or less. The Al / M ratio may be 1 or greater.

[0026] In this porous silicon material, when the total of the Si phase, M silicide phase, SiO2 phase, and Al phase is taken as 100 mol%, the content of the M silicide phase may be 6 mol% or less, 5 mol% or less, or 3 mol% or less. The content of the M silicide phase may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more. In this porous silicon material, the content of the Si phase may be 96 mol% or less, 90 mol% or less, or 85 mol% or less. The content of the Si phase may be 65 mol% or more, 70 mol% or more, or 75 mol% or more. In this porous silicon material, the content of the SiO2 phase may be 15 mol% or less, 12 mol% or less, or 10 mol% or less. The content of the SiO2 phase may be 0.5 mol% or more, 1 mol% or more, or 3 mol% or more. It is preferable that this porous silicon material does not contain an Al phase. "Al phase-free" means that no Al phase peak is observed in X-ray diffraction (XRD) analysis. Even if this porous silicon material contains an Al phase, it is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 3 mol% or less. The contents of the Si phase, M silicide phase, SiO2 phase, and Al phase may be determined, for example, as follows: After heat treatment at 600°C, the porous silicon material is subjected to XRD analysis to determine the ratios of the Si phase, M(Al,Si)2 phase, and Al phase. The ratio of the SiO2 phase to the M(Al,Si)2 phase is then determined from the elemental ratio of M to O. The content of each phase may then be calculated by defining the total of the Si phase, M(Al,Si)2 phase, Al phase, and SiO2 phase as 100 mol%. Note that if XRD analysis confirms that the sample does not contain an Al phase, the content may be calculated from the elemental ratios of Al, Si, M, and O, assuming that the phases present in the sample are Si, M(Al,Si)2, and SiO2. In this case, it may be assumed that the Si phase contains (is substituted with) 5 at % Al, and the remaining Al is entirely contained in the M(Al,Si)2 phase. 80 Si 20When an AlSi alloy that does not contain the transition metal element M, such as the one described above, is acid-treated, XRD results show only the Si phase and no Al phase, but composition analysis confirms the presence of approximately 5 at% Al. Similar results were obtained when using AlSi alloys with different compositions, and it is thought that Al is in solid solution in the Si phase. It is also inferred that in AlSiM systems, it can be assumed that the Si phase contains 5 at% Al.

[0027] The porous silicon material preferably has a particle size ranging from 0.5 μm to 12 μm in number average. The particles of this porous silicon material preferably have a particle size ranging from 3 μm to 5 μm in number average, and more preferably 5 μm to 10 μm in number average. The particle size range is preferably 10 μm to 8 μm in number average, and even more preferably 8 μm to 10 μm in number average. The porous silicon material preferably has a porosity of 45% by volume or more, and may be 55% by volume or more, 65% by volume or more, or 70% by volume or more. The porosity is a value measured using a mercury porosimeter. The porosity may be, for example, 85% by volume or less, 80% by volume or less, or 75% by volume or less. A larger porosity is preferable because the material is more responsive to volume changes during occlusion of carrier ions, whereas a smaller porosity increases the amount of Si present per unit volume, which is preferable.

[0028] In this porous silicon material, the average pore diameter may be 100 nm or less. In addition, in this porous silicon material, the pore diameter range may be 1 nm or more and 300 nm or less. The average pore diameter and pore size are values ​​measured with a mercury porosimeter. The average pore diameter may be 65 nm or less, or 60 nm or less. In addition, the average pore diameter may be 10 nm or more, 20 nm or more, or 30 nm or more. The pore diameter range may be, for example, 5 nm or more, 10 nm or more, or 20 nm or more. In addition, the pore diameter range may be, for example, 200 nm or less, or 100 nm or less. A small pore diameter is preferable because the pores are less likely to collapse. In addition, a large pore diameter is preferable because volume change when carrier ions are absorbed can be further suppressed.

[0029] The porous silicon material may have a resistivity of 10,000 Ωcm or less. The resistivity of the porous silicon material is determined by a four-terminal method. When the porous silicon material is a powder, the porous silicon powder is pressed at 200 MPa to produce a green compact, and the resistivity of this green compact determined by the four-terminal method is used as the resistivity of the porous silicon material. This resistivity may be 2,000 Ωcm or less, 1,000 Ωcm or less, 500 Ωcm or less, or 200 Ωcm or less.

[0030] The porous silicon material may contain skeletal silicon with a three-dimensional network structure having voids, and may contain SiM compounds and / or AlSiM compounds as M silicides. The M silicides are presumed to reinforce the silicon skeleton. A larger amount of M silicide is preferable from the viewpoint of supplementing the reinforcement of the skeleton, while a smaller amount is preferable from the viewpoint of the charge / discharge capacity of the power storage device.

[0031] The porous silicon material preferably has 20% or more by volume of pores of 1 μm or less measured by mercury intrusion porosimetry. It is preferable that the porous silicon material has a greater number of such fine pores. It is more preferable that the porous silicon material has 30% or more by volume of pores of 1 μm or less measured by mercury intrusion porosimetry, more preferably 40% or more by volume, even more preferably 45% or more by volume. Furthermore, the porous silicon material may have 90% or less by volume of pores of 1 μm or less measured by mercury intrusion porosimetry.

[0032] When the porous silicon material is used as an electrode and subjected to a confining pressure of 1 GPa, the amount of pore change is preferably less than 25 vol%, more preferably less than 20 vol%, and even more preferably less than 10 vol%. From the viewpoint of skeletal strength, it is preferable that the amount of pore reduction in the porous silicon material when subjected to a confining pressure is as small as possible.

[0033] This porous silicon material may contain one or more of Ca, Mg, Na, Sr, and P as a second element in a range of 15 mass% or less. Furthermore, the porous silicon material may contain unavoidable impurities in addition to Si, Al, and M. It is preferable that the amount of the second element and the unavoidable impurities is as small as possible. Furthermore, this porous silicon material may have a portion of M substituted with another transition metal element. In this case, the amount of the other transition metal element M may be half or less of M, 20% or less, or 10% or less in molar ratio. Examples of the other transition metal element include Ti, V, Nb, Mo, Ni, Mn, Fe, Co, and Zn.

[0034] (Electrodes for electricity storage devices) An electrode for a power storage device includes the porous silicon material described above as an electrode active material. This electrode functions as either a positive electrode or a negative electrode depending on the potential of the electrode active material relative to the potential of the counter electrode. When lithium is used as a carrier, the electrode is preferably a negative electrode. This electrode can be used, for example, in lithium ion secondary batteries, hybrid capacitors, and air batteries. The electrode for a power storage device may be one in which the porosity of the porous silicon material is compressed to a range of 5% to 50% by volume. In this electrode, the porosity of the porous silicon material may be reduced by compression during fabrication. For example, when porous silicon particles are used as a negative electrode active material in a lithium ion secondary battery, smaller pores allow lithium ions to alloy more uniformly, thereby reducing stress concentration and preventing deterioration of the electrode itself. The porosity of the compressed porous silicon material can be appropriately adjusted depending on the properties required of the power storage device electrode, and may be, for example, 5% by volume or more or 10% by volume or more. The porosity of the compressed porous silicon material may also be, for example, 30% by volume or less or 20% by volume or less.

[0035] The electrode for a power storage device may be formed by forming the porous silicon material on a current collector and then adhering the material to the current collector. This electrode can be produced by either mixing the porous silicon material with a solvent and, if necessary, a conductive material and a binder 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 if necessary and then pressing the mixture onto the current collector. In this electrode, the content of the porous silicon material is preferably as high as possible, 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 electron-conductive material that does not adversely affect battery performance. For example, a mixture of one or more of graphite, such as natural graphite (e.g., scaly graphite or flake graphite) or artificial graphite, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (e.g., copper, nickel, aluminum, silver, and gold), can be used. The binder serves to bind the active material particles and conductive material particles together. Examples of binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-containing rubber; thermoplastic resins such as polypropylene and polyethylene; polyimide (PI), ethylene propylene diene rubber (EPDM), sulfonated EPDM rubber, and natural butyl rubber (NBR), either alone or in combination. Water-based binders such as cellulose-based binders and aqueous dispersions of styrene butadiene rubber (SBR) can also be used. Examples of solvents that can be used include organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. Alternatively, dispersants, thickeners, and the like can be added to water to form a slurry of the active material with a latex such as SBR. Examples of application methods include roller coating such as an applicator roll, screen coating, doctor blade method, spin coating, and bar coater, and any of these can be used to obtain a desired thickness and shape.The current collector may be appropriately selected according to the potential of the active material or the like. For example, in addition to aluminum, titanium, stainless steel, nickel, iron, copper, fired carbon, conductive polymers, conductive glass, etc., for the purpose of improving adhesion, conductivity and oxidation resistance, those obtained by treating the surface of aluminum or copper with carbon, nickel, titanium, silver, etc. can be used. It is also possible to oxidize-treat their surfaces. Regarding the shape of the current collector, examples include foil-like, film-like, sheet-like, net-like, punched or expanded ones, lath bodies, porous bodies, foams, formed bodies of fiber groups, etc. The thickness of the current collector is, for example, 1 to 500 μm. The formation amount of the active material composite may be appropriately set according to the desired performance required for the power storage device.

[0036] In this electrode, the electrode active material may contain an active material other than the porous silicon material in addition to the porous silicon material within the range where both low restraint pressure and capacity retention rate can be achieved. For example, as the electrode active material, a carbonaceous material, Li4Ti5O 12 etc. may be included. However, from the perspective of further increasing the battery capacity, taking the total electrode active material as 100% by mass, for example, the porous silicon material preferably occupies 50% by mass or more, preferably 90% by mass or more.

[0037] (Power storage device) The power storage device of the present disclosure includes an electrode having the above-described porous silicon material. This power storage device may include a positive electrode, a negative electrode, and an ion conduction medium interposed between the positive electrode and the negative electrode and conducting carrier ions. The porous silicon material can be used as a negative electrode active material. This power storage device may be any one of a lithium ion secondary battery, a hybrid capacitor, an air battery, etc. In the positive electrode, as the positive electrode active material, sulfides containing transition metal elements, oxides containing lithium and transition metal elements, etc. can be used. Specifically, transition metal sulfides such as CrS2, CrS3, MoS3, FeS2, basic composition formula Li (1-x) MnO2 (0 < x < 1, etc., the same 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 oxide such as NiO2, the basic composition formula is Li (1-x) Ni a Co b Mn c Lithium nickel cobalt manganese composite oxides with a basic composition formula of LiV2O3, etc., and transition metal oxides with a basic composition formula of V2O5, etc., can be used. Among these, lithium transition metal composite oxides, such as LiCoO2, LiNiO2, LiMnO2, and Li (1-x) Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. are preferred. The term "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 carbons, cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, and polyacenes. Among these, activated carbons exhibiting a high specific surface area are preferred. Activated carbons as carbonaceous materials have a specific surface area of ​​1000 m 2 / g or more, and 1500m 2 / g or more is more preferable. 2 / g or more, the discharge capacity can be further increased. The specific surface area of ​​this activated carbon is 3000 m 2 / g or less, and 2 The conductive material, binder, solvent, current collector, and the like used in the positive electrode can be appropriately selected from those exemplified for the electrode described above.

[0038] The ion-conducting medium may be a non-aqueous electrolyte solution containing a supporting salt, a non-aqueous gel electrolyte solution, etc. Examples of the solvent for the non-aqueous electrolyte include carbonates, esters, ethers, nitriles, furans, sulfolanes, and dioxolanes, which may be used alone or in combination. Specific examples of carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate; chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate; cyclic esters such as γ-butyl lactone and γ-valerolactone; chain esters such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate; ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; furans such as tetrahydrofuran and methyltetrahydrofuran; sulfolanes such as sulfolane and tetramethylsulfolane; and dioxolanes such as 1,3-dioxolane and methyldioxolane. Among these, a combination of cyclic carbonates and chain carbonates is preferred. This combination not only provides excellent cycle characteristics, which represent battery characteristics during repeated charge and discharge, but also allows for a well-balanced electrolyte viscosity, the resulting battery's electrical capacity, and battery output. Examples of supporting salts include LiPF, LiBF, LiAsF, LiCF, SO, LiN(CF, SO), LiC(CF, SO), LiSbF, LiSiF, LiAlF, LiSCN, LiClO, LiCl, LiF, LiBr, LiI, and LiAlCl. Among these, a combination of one or more salts selected from the group consisting of inorganic salts such as LiPF, LiBF, LiAsF, and LiClO, and organic salts such as LiCF, SO, LiN(CF, SO), and LiC(CF, SO) is preferred from the standpoint of electrical properties.The concentration of this supporting salt in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. When the supporting salt is dissolved at a concentration of 0.1 mol / L or more, a sufficient current density can be obtained, and when it is 5 mol / L or less, the electrolyte can be more stable. In addition, a phosphorus-based, halogen-based, or other flame retardant may be added to this non-aqueous electrolyte.

[0039] Instead of a liquid ion-conducting medium, a solid ion-conducting polymer can be used as the ion-conducting medium. Examples of the ion-conducting polymer include polymer gels composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinylpyrrolidone, or vinylidene fluoride and a supporting salt. Furthermore, a combination of an ion-conducting polymer and a nonaqueous electrolyte can also be used. In addition to ion-conducting polymers, other ion-conducting media include inorganic solid electrolytes, mixed materials of organic polymer electrolytes and inorganic solid electrolytes, and inorganic solid powders bound by an organic binder.

[0040] The power storage device may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium secondary battery, and examples thereof include polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and thin microporous films of olefin resins such as polyethylene and polypropylene. These may be used alone or in combination.

[0041] The shape of the electricity storage device is not particularly limited, and examples thereof include coin, button, sheet, laminate, cylindrical, flat, and rectangular shapes. The device may also be applied to large devices used in electric vehicles and the like. FIG. 3 is an explanatory diagram showing an example of the structure of an electricity storage device 10. The electricity storage device 10 includes a positive electrode 12, a negative electrode 15, and an ion-conducting medium 18. The positive electrode 12 includes a positive electrode active material 13 and a current collector 14. The negative electrode 15 includes a negative electrode active material 16 and a current collector 17. The negative electrode active material 16 is the porous silicon material 20 described above, which includes a skeleton 25 in which Si 22 and M silicide 24 coexist, and voids 26. The porous silicon material 20 has a porosity of 45% by volume or more as determined by mercury intrusion porosimetry, is particulate, and the number-average particle size obtained from the particle size distribution is in the range of 0.5 μm to 12 μm.

[0042] This power storage device preferably has a higher initial capacity. For example, the initial capacity per unit active material weight at a low rate is preferably 1500 mAh / g or more, more preferably 1800 mAh / g or more, and even more preferably 2000 mAh / g or more. Furthermore, the initial capacity at a low rate is preferably 1000 mAh / g or more, more preferably 1200 mAh / g or more, and even more preferably 1500 mAh / g or more, for example, per unit electrode weight. Furthermore, the initial capacity at a high rate is preferably 500 mAh / g or more, more preferably 700 mAh / g or more, and even more preferably 1000 mAh / g or more, for example, per unit active material weight. Furthermore, the initial capacity at a high rate is preferably 450 mAh / g or more, more preferably 700 mAh / g or more, and even more preferably 1000 mAh / g or more, for example, per unit electrode weight. It is preferable that the power storage device have a high capacity retention rate after cycling. For example, the capacity retention rate after 50 cycles at a low rate is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more, and for example, the capacity retention rate after 50 cycles at a high rate is preferably 40% or more, more preferably 45% or more, and even more preferably 50% or more.

[0043] (All-solid-state lithium-ion secondary battery) This power storage device is preferably a all-solid-state lithium-ion secondary battery. In an all-solid-state battery, changes in performance due to the electrolyte can be more effectively suppressed, and furthermore, safety can be enhanced, which is preferable. This all-solid-state lithium-ion secondary battery may include a positive electrode containing a positive electrode active material, a negative electrode using the porous silicon material described above as a negative electrode active material, and a solid electrolyte interposed between the positive electrode and the negative electrode for conducting lithium ions. The positive electrode can use any of those shown in the power storage device described above. Also, the negative electrode can be one using the porous silicon material described above as a negative electrode active material.

[0044] 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 12 . However, A is one or more of Sr and Ca, T is one or more of Nb and Ta, and it satisfies 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 , or (Li 7-3z+x-y M z )(La 3-x A x )(Y 2-y T y )O 12The garnet-type oxide may be represented by the formula (1). In the formula, element M may be one or more of Al and Ga, element A may be one or more of Ca and Sr, and T may be one or more of Nb and Ta, and 0≦z≦0.2, 0≦x≦0.2, and 0≦y≦2 may be satisfied. In this basic composition formula, it is more preferable that 0.05≦z≦0.1 be satisfied. In this basic composition formula, it is more preferable that 0.05≦x≦0.1 be satisfied. Furthermore, in this basic composition formula, it is more preferable that 0.1≦y≦0.8 be satisfied. In these ranges, the ionic conductivity can be more favorably achieved.

[0045] Alternatively, the solid electrolyte may be, for example, a common LiN or LISICON. 14 Zn(GeO4)4, Li sulfide 3.25 Ge 0.25 P 0.75 S4, perovskite-type La 0.5 Li 0.5 CrO3, (La 2 / 3 Li 3x □ 1 / 3-2x )CrO3 (□: atomic vacancy), garnet-type Li7La3Zr2O 12 , LiCr2(PO4)3, called NASICON type, Li 1.3 M 0.3 Cr 1.7 (PO3)4 (M = Sc, Al), etc. Also, Li7P3S obtained from glass ceramics with a composition of 80Li2S 20P2S5 (mol%) 11 Furthermore, Li, a sulfide-based material with high conductivity, 10Examples 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 that use SiO2, GeO2, B2O3, or P2O5 as the glass-based substance and Li2O as the network modifier. Examples of thiolithium solid electrolytes include Li2S-GeS2, Li2S-GeS2-ZnS, Li2S-Ga2S2, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-SbS5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S-P2S5, Li2S-Al2S3, LiS-SiS2-Al2S3, Li2S-SiS2-P2S5, etc. These solid electrolytes may be formed into a plate shape and placed between the positive electrode and the negative electrode.

[0046] The all-solid-state lithium-ion secondary battery may also include a restraining member that restrains a stack of a positive electrode, a solid electrolyte, and a negative electrode in the stacking direction. This restraining member may include, for example, a pair of plate-like members that sandwich the stack from both ends of the stack in the stacking direction, a rod-like member that connects the pair of plate-like members, and an adjustment member that is connected to the rod-like members and adjusts the gap between the pair of plate-like members by a screw structure or the like.

[0047] As described above in detail, the present disclosure can further improve the charge / discharge characteristics of porous silicon materials. The reason for this effect is believed to be as follows. For example, while electrodes using Si as the active material can achieve a higher capacity than graphite electrodes, there is a problem in that the pore structure is destroyed by residual stress caused by volumetric changes in Si due to expansion and contraction during charge / discharge, which can lead to reduced rate characteristics and capacity retention. Even if the porosity of a porous silicon material is the same in a silicon negative electrode, a porous silicon material containing many small pores is more resistant to destruction than a porous silicon material containing only a few large pores, because the stress acting on each pore is dispersed more effectively. Furthermore, high skeletal strength is also important for maintaining the pore structure. Based on these relationships, the present disclosure believes that the charge / discharge characteristics of porous silicon materials can be further improved by adopting a suitable particle size range that allows the pore structure to be maintained.

[0048] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure.

[0049] For example, the present disclosure may be any of the following [1] to

[10] . [1] Contains Si, Al, and a transition metal element M, The porosity determined by mercury porosimetry is 45% by volume or more, A porous silicon material that is particulate and has a numerical average particle size obtained from particle size distribution in the range of 0.5 μm to 12 μm. [2] The porous silicon material according to [1], which satisfies one or more of the following (1) to (4): (1) The number average particle size is 3 μm or more. (2) The number average particle size is 5 μm or more. (3) The number average particle size is 10 μm or less. (4) The number average particle size is 8 μm or less. [3] The porous silicon material according to [1] or [2], wherein the particle diameter D90 is in the range of 2 μm or more and 15 μm or less. [4] The porous silicon material according to [3], satisfying one or more of the following (5) to (6). (5) The particle size D90 is 4 μm or more. (6) The particle size D90 is 12 μm or less. [5] When the total of Si, Al, and transition element M is 100 at%, oxygen is 10 at% or less, and The porous silicon material according to any one of [1] to [4], wherein the O / M ratio, which is the ratio of oxygen to the transition element M, is 10 or less. [6] The transition metal element M is Cr, and CrSi2, Cr(Si,Al)2, and Al 13 The porous silicon material according to any one of [1] to [5], containing one or more of Cr4Si4. [7] A positive electrode containing a positive electrode active material, A negative electrode containing the porous silicon material according to any one of [1] to [6] as a negative electrode active material, An ion conduction medium interposed between the positive electrode and the negative electrode and conducting lithium ions, And a power storage device provided with the above. [8] By rapidly cooling a master alloy melt having a basic composition formula of Al 100-x-y Si x M y (However, M is a transition metal element, satisfying 10 ≤ x ≤ 40, 0 < y ≤ 5, 0 < x / y ≤ 0.2), phase separation is performed into a conductive phase containing one or more of Si, Al, transition metal silicide, transition metal aluminum, and aluminum transition metal silicide, and by selectively removing the Al component, the porosity obtained by the mercury intrusion method is 45% by volume or more, in the form of particles, and the number average value of the particle size obtained from the particle size distribution is in the range of 0.5 μm or more and 12 μm or less. A porous silicon material is obtained. A method for producing a porous silicon material including the above. <00003​​​​The method for producing a porous silicon material according to [8] or [9], wherein the porous silicon material contains one or more of Cr4Si4, and the content thereof is 6 mol% or less. [Example]

[0050] Specific examples of fabricating porous silicon and electricity storage devices according to the present disclosure are described below as experimental examples. Experimental Examples 1 to 5 correspond to working examples of the present disclosure, and Experimental Examples 3 and 6 correspond to comparative examples.

[0051] [Preparation of porous silicon materials] The raw materials of Al, Si and Cr are treated as the basic composition formula Al 100-x-y Si x Cr y The alloy was weighed to have the composition (x = 10 to 40, y = 0 to 10) and melted in an arc melting furnace. -3 After reducing the pressure to below 1 Pa, the pressure was replaced with Ar gas. To prepare the master alloy, it was necessary to melt the raw material powder, and high-frequency melting was performed to prepare a uniform sample. The obtained master alloy was heated to 1000-1300°C in an Ar atmosphere to melt it, and then gas atomized to 1000°C. 2 The resulting alloy was rapidly solidified at a rate of 1000 K / sec or more to obtain an AlSiCr alloy powder (precursor treatment). The resulting alloy was immersed in a 0.1 to 3 mol / L aqueous hydrochloric acid solution and subjected to acid treatment (removal treatment) at a temperature between room temperature (25°C) and 80°C for 1 to 48 hours to selectively remove the Al component. The residue was transferred to a filter, and the acid was removed by pressure filtration. The residue was then washed with distilled water at least four times, and the washing water was removed by the same pressure filtration method to obtain porous silicon (porosity formation process).

[0052] (Experimental Examples 1 to 7) Experimental Examples 1 to 3 represent porous silicon materials produced under the conditions of a master alloy composition where x = 30 and y = 1 in the above basic composition formula, a hydrochloric acid concentration of 0.1 mol / L, an acid treatment temperature of 25°C, and acid treatment times of 20, 26, and 34 hours. Experimental Examples 4 to 6 represent porous silicon materials produced in the same manner as Experimental Example 1, except that the master alloy composition was a composition where x = 30 and y = 3 in the above basic composition formula, and the acid treatment times were 22, 28, and 34 hours. The precursor obtained in the precursor treatment was classified, and the number-average particle sizes obtained from the particle size distribution were 2.9 μm, 7.2 μm, and 13.9 μm, respectively. Experimental Examples 1 to 3 represent porous silicon materials produced under the same conditions as Experimental Example 1, except that the master alloy composition was a composition where x = 30 and y = 3 in the above basic composition formula, and the acid treatment times were 22, 28, and 34 hours. The precursor obtained in the precursor treatment was classified, and the number-average particle sizes obtained from the particle size distribution were 2.9 μm, 7.2 μm, and 13.9 μm, respectively. The precursor obtained in the precursor treatment was classified, and the particles having a number average particle size obtained from the particle size distribution of 2.9 μm, 7.2 μm, and 14.1 μm were designated Experimental Examples 4 to 6. A porous silicon material was prepared in the same manner as Experimental Example 1, except that the particle size was classified to have a number average particle size obtained from the particle size distribution of 9 μm, designated Experimental Example 7.

[0053] (XRD measurement) The atomized powder before acid treatment and the porous silicon powder after acid treatment were subjected to X-ray diffraction measurement using an X-ray diffractometer (Rigaku Corporation, Ultima IV) with a Cu tube in the range of 2θ = 20° to 60° at a rate of 20° / min. 13 The proportions of the Cr4Si4 and Cr(Al,Si)2 phases were calculated by mass ratio from the XRD peak intensity ratio of each phase using an alumina standard material. The proportions of each phase were measured after heat treatment at 600°C to crystallize the amorphous phase.

[0054] (SEM / EDX measurement) The atomized powder before the acid treatment and the porous silicon powder after the acid treatment were pressure-molded into a disk shape using a carbide mold, and the pressed surface was observed using a scanning electron microscope (SEM, Hitachi S-4300) and energy dispersive X-ray analysis (EDX, Hitachi S-4300) to perform composition analysis. In addition, the porous silicon powder after the acid treatment was embedded in resin, and a cross section was extracted by polishing, and SEM observation was performed using the above-mentioned scanning electron microscope.

[0055] (Particle size distribution measurement) The particle size distribution of the porous silicon powder after acid treatment was measured. Particle size distribution was measured using a Microtrac-Bell MT3300EX (measurable range: 0.02 μm to 2000 μm) and evaluated by laser diffraction scattering method using a wet sample in which the powder was dispersed in water. The numerical average value of the particle size obtained from the particle size distribution was taken as the average particle size.

[0056] (Pore distribution measurement) The pore size distribution of the porous silicon powder after acid treatment was measured using a mercury porosimeter (Quantachrome POREMASTER 60GT). The average pore size was calculated from the volume fraction of pores of each size in the pore size distribution data. Generally, porous material powders contain both intraparticle and interparticle pores, but the pore size distribution data does not allow for a distinction between the two. Here, by comparing the pore size distribution measurement results of the atomized powder before acid treatment, pore size distributions of 300 nm or less were determined to be intraparticle pores, and the two were distinguished to determine the intraparticle porosity and average pore size. Although not shown, the pore size distribution showed peaks in the 700-800 nm range and around 100 nm. Based on a comparison with the pore size distribution data of the atomized powder before acid treatment and SEM images, the peak near 100 nm was determined to be the peak of intraparticle pores, and using 300 nm, the boundary between the two peaks, as the standard, pores of 300 nm or less were determined to be intraparticle pores, as described above. Note that by comparing the pore size distribution data of the sample before and after acid treatment, it is possible to distinguish between intraparticle pores and interparticle pores and determine the intraparticle porosity and average pore size.

[0057] (STEM / EDX measurement) The porous silicon powder after the acid treatment was subjected to elemental image mapping and structure observation using a scanning transmission electron microscope (STEM, JEOL JEM2100F).

[0058] (Battery characteristic evaluation) Battery characteristics were evaluated using the acid-treated porous silicon powder. 60 parts by mass of porous silicon powder as the negative electrode active material, 20 parts by mass of acetylene black (AB) as the conductive material, and 20 parts by mass of polyimide (PI) as the binder were weighed and mixed, and the viscosity was adjusted with N-methyl-2-pyrrolidone (NMP). The resulting slurry was applied to an 18 μm-thick copper current collector foil using a doctor blade method, vacuum dried at 150 °C for 10 hours, and then heat-treated at 400 °C to prepare a first composite electrode. A second composite electrode was prepared using the same process as the first composite electrode, except that 80 parts by mass of porous silicon powder as the negative electrode active material, 10 parts by mass of AB as the conductive material, and 10 parts by mass of PI as the binder were weighed. The first composite electrode using the active material of Experimental Example 1 is referred to as Experimental Example 1-1, and the second composite electrode using the active material of Experimental Example 1 is referred to as Experimental Example 1-2. A lithium secondary battery was fabricated using a small Tom cell-type battery cell by placing a porous polyethylene separator between the negative electrode made by punching out the composite electrode with a 16 mm diameter punch and metallic lithium as the counter electrode, and injecting an electrolyte. The electrolyte used was a mixed solvent containing 1.5 parts by volume of fluoroethylene carbonate (FEC), 3 parts by volume of ethylene carbonate (EC), 4 parts by volume of dimethyl carbonate (DMC), and 3 parts by volume of ethyl methyl carbonate (EMC), to which LiPF6 was added at a concentration of 1 mol / L.

[0059] The resulting lithium secondary batteries were repeatedly charged and discharged 100 times at a predetermined current density within a battery voltage range of 0.005 V to 1.5 V. The rate characteristics were evaluated by charging and discharging the batteries at current densities of 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g, and 4 A / g. The reaction in which the porous silicon powder absorbs lithium is referred to as charging, and the reaction in which the porous silicon powder releases lithium is referred to as discharging. The initial discharge capacity and capacity after 50 cycles per unit active material mass or unit electrode weight at 0.1 A / g, and the initial discharge capacity and capacity after 50 cycles per unit active material mass or unit electrode weight at 1 A / g were determined.

[0060] (Resistivity measurement) The electrode was subjected to the same dry heat treatment as the first composite electrode except that the electrode composite was applied to a glass substrate, and the resistivity was evaluated using the electrode. The resistivity was measured at 25°C.

[0061] (Results and Discussion) Figure 5 shows the particle size distribution measurement results for the porous silicon materials of Experimental Examples 1 to 3. Figure 6 shows cross-sectional SEM photographs of the porous silicon materials of Experimental Examples 1 to 3. Figure 7 shows the relationship between current density and capacity retention after 50 cycles for Experimental Examples 1-1, 1-2, and 2-2. Tables 1 to 3 summarize the experimental results for Experimental Examples 1 to 7. Table 4 summarizes the measurement results for Experimental Examples 1-1 to 6-2. As shown in Tables 1 and 2, by adjusting the acid treatment conditions, the changes due to acid treatment in Experimental Examples 1 to 3 and Experimental Examples 4 to 6, which have different particle sizes, were controlled to approximately the same values, and the element ratios and phase proportions of the porous silicon materials were kept to approximately the same values. As shown in Table 2, even when the particle size increased, the pore structure did not change much, and the porosity was approximately the same. On the other hand, it was confirmed that the pore size became coarser as the particle size increased, and the average pore diameter also tended to increase as the particle size increased.

[0062] As shown in Figure 5 and Table 4, in Experimental Example 1, the particle size was in the range of 1 μm to 8 μm, the average particle size was 2.9 μm, and the D90 was 4.5 μm. In Experimental Example 2, the particle size was in the range of 1 μm to 20 μm, the average particle size was 7.2 μm, and the D90 was 10.8 μm. In Experimental Example 3, the particle size was in the range of 4 μm to 25 μm, the average particle size was 13.9 μm, and the D90 was 18.4 μm. Furthermore, Experimental Examples 4 to 6 showed the same trends as Experimental Examples 1 to 3. As shown in Figure 6, when the cross-sectional structure of the porous bodies classified into different sizes was observed using a scanning electron microscope (SEM), it was confirmed that pores of approximately tens to hundreds of nanometers were formed. Furthermore, the SEM observation results were similar to the measurement results using a mercury porosimeter.

[0063] As shown in Table 3, the resistivity of the electrode varied depending on the conductive material content and particle size. An electrode fabricated using porous powder with an average particle size of 3 μm, classified to 5 μm or less, exhibited a low resistivity of 5 Ωcm in Experimental Example 1-1, which contained 20% conductive material by mass. However, in Experimental Example 1-2, in which the conductive material content was reduced to half, 10% by mass, the resistivity increased by about two orders of magnitude. When comparing electrodes with the same conductive material content, it was confirmed that the larger the particle size of the porous powder, the lower the electrode resistivity tended to be.

[0064] As shown in Figure 7, comparing Experimental Examples 1-1, 1-2, and 2-2, a tendency for capacity to decrease with increasing current during charging and discharging was observed. However, the electrode of Experimental Example 1-1, which contained 20% conductive material by mass, showed a small capacity decrease rate with increasing current. On the other hand, in Experimental Example 1-2, in which the conductive material content was halved, the capacity decrease rate with increasing current increased. This tendency was particularly pronounced in electrodes made with high-resistivity powders of 5 μm or less, but in electrodes made with low-resistivity particles of 12 μm or less, the capacity did not decrease significantly with increasing current. When the amount of conductive material was 20% by mass, active materials with an average particle size of 7 μm or less achieved relatively high capacity and good cycle characteristics at a low rate of 0.1 A / g. On the other hand, when the average particle size increased to 14 μm, the cycle characteristics deteriorated. Furthermore, when the conductive material content was reduced to 10% by mass, the capacity per electrode increased, but even when active materials with a small average particle size were used, the cycle characteristics were not good at a high rate of 1 A / g. In particular, it was found that the capacity significantly decreased with the active material with a high resistivity and an average particle size of 3 μm, making it difficult to obtain the benefits of increasing the active material content. However, in electrodes using active material with a relatively low resistivity and an average particle size of 7 μm, a high capacity was maintained, demonstrating that the benefits of increasing the capacity per electrode were fully obtained.

[0065] Furthermore, as shown in Tables 1 and 2, Experimental Examples 4 to 6, which had a high Cr content, showed a large change in oxygen content due to acid treatment and a tendency for the SiO2 phase ratio to be higher than Experimental Examples 1 to 3. Furthermore, as shown in Table 4, Experimental Examples 4 to 6, which had a high Cr content, showed a tendency for the initial capacity to be lower than Experimental Examples 1 to 3, but a tendency for the capacity retention rate to be higher. This is presumed to be the effect of the Cr silicide strengthening the Si pore structure. From the viewpoint of capacity, a lower oxygen content is presumed to be preferable, and when the total of Si, Al, and Cr is taken as 100 at%, it is presumed to be preferably 15 at% or less, and more preferably 10 at% or less. Furthermore, it is presumed that the O / Cr ratio is preferably 10 at% or less, and more preferably 5 at% or less.

[0066] From the above, it was inferred that the particulate porous silicon material preferably has a particle size distribution with a number average particle size in the range of 0.5 μm to 12 μm. It was also inferred that this number average particle size is more preferably 3 μm or more, and even more preferably 5 μm or more. It was also inferred that this number average particle size is more preferably 10 μm or less, and even more preferably 8 μm or less. It was also inferred that the porosity of this porous silicon material, as determined by mercury intrusion porosimetry, is preferably 45 vol% or more, more preferably 55 vol% or more, 65 vol% or more, 70 vol% or more, etc. Furthermore, it was inferred that the particle size D90 of this porous silicon material is preferably in the range of 2 μm to 15 μm, more preferably 4 μm or more, and even more preferably 12 μm or less. Furthermore, it was estimated that when the total of Si, Al, and the transition element M in this porous silicon material is taken as 100 at%, the oxygen content is 15 at% or less, more preferably 10 at% or less, and even more preferably 7.5 at% or less. Furthermore, it was estimated that the O / M ratio, which is the ratio of oxygen to the transition element M, in this porous silicon material is preferably 10 or less, more preferably 5 or less, and even more preferably 4.5 or less. Furthermore, it is preferable that the transition metal element M is Cr, and this porous silicon material is composed of CrSi2, Cr(Si,Al)2, and Al. 13 It was found that it is preferable to include at least one of Cr4Si4 in the range of 6 mol% or less.

[0067] [Table 1]

[0068] [Table 2]

[0069] [Table 3]

[0070] [Table 4]

[0071] It goes without saying that the present disclosure is not limited to the above-described experimental examples, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure. [Industrial Applicability]

[0072] The present disclosure is applicable to the technical field of secondary batteries. [Explanation of symbols]

[0073] 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, 20 Porous silicon material, 22 Si, 24 M silicide, 25 Framework, 26 Porosity.

Claims

1. containing Si, Al, and a transition metal element M; The porosity determined by mercury porosimetry is 45% by volume or more, It is particulate, and the number average particle size obtained from the particle size distribution is in the range of 0.5 μm to 12 μm. Porous silicon material.

2. The porous silicon material according to claim 1, which satisfies one or more of the following (1) to (4): (1) The number average particle size is 3 μm or more. (2) The number average particle size is 5 μm or more. (3) The number average particle size is 10 μm or less. (4) The number average particle size is 8 μm or less.

3. 3. The porous silicon material according to claim 1, wherein the particle diameter D90 is in the range of 2 μm or more and 15 μm or less.

4. The porous silicon material according to claim 3, which satisfies one or more of the following (5) to (6): (5) The particle diameter D90 is 4 μm or more. (6) The particle diameter D90 is 12 μm or less.

5. When the total of Si, Al, and the transition element M is 100 at%, oxygen is 15 at% or less, 3. The porous silicon material according to claim 1, wherein the O / M ratio, which is the ratio of oxygen to the transition element M, is 10 or less.

6. the transition metal element M is Cr, CrSi 2 , Cr(Si,Al) 2 and Al 13 Cr 4 Si 4 3. The porous silicon material according to claim 1, comprising one or more of:

7. a positive electrode including a positive electrode active material; a negative electrode containing the porous silicon material according to claim 1 or 2 as a negative electrode active material; an ion conductive medium interposed between the positive electrode and the negative electrode and conducting lithium ions; An electricity storage device comprising:

8. The basic composition formula is Al 100-x-y Si x M y a porosity forming step of rapidly cooling a molten master alloy of the formula (where M is a transition metal element and satisfies 10≦x≦40, 0<y≦5, 0<x / y≦0.2), thereby separating the molten master alloy into a conductive phase containing Si, Al, and one or more of a transition metal silicide, a transition metal aluminum, and an aluminum transition metal silicide, and selectively removing the Al component to obtain a porous silicon material having a porosity of 45 vol% or more as determined by mercury intrusion porosimetry, which is particulate and has a number-average particle size obtained from a particle size distribution in the range of 0.5 μm to 12 μm; A method for producing a porous silicon material, comprising:

9. The method for producing a porous silicon material according to claim 8 , wherein the Al component is removed with hydrochloric acid having a concentration of less than 0.5 mol / L in the porosity-forming step.

10. The conductive phase is CrSi 2 , Cr(Si,Al) 2 , Al 13 Cr 4 Si 4 The method for producing a porous silicon material according to claim 8 or 9, wherein the porous silicon material contains one or more of the following, and the content thereof is 6 mol % or less.

Images