Method for manufacturing porous silicon, porous silicon, negative electrode layer, and secondary battery

Abstract

This invention provides porous silicon with a high porosity, determined from the pore volume measured by the BJH method. [Solution] The method includes the steps of bringing a raw material containing silicate into contact with an alkaline earth metal gas, and bringing the raw material that has been in contact with the alkaline earth metal gas into contact with an acid.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing porous silicon, porous silicon, a negative electrode layer, and a secondary battery.

Background Art

[0002] Silicon has attracted attention as a negative electrode active material because it has a high theoretical capacity. In particular, by using porous silicon as the negative electrode active material, it is possible to achieve a high energy density of the battery. As a method for manufacturing porous silicon, an intermediate product containing Si and MgO is produced by reducing SiO2 using Mg vapor generated by heating metallic Mg, and the intermediate product is washed with an acid to remove MgO, thereby obtaining porous silicon.

[0003] Patent Document 1 contemplates reducing in such a manner that Mg2Si and SiO2 are not generated in the above-described method for manufacturing porous silicon, and under reduced pressure and under conditions of a Mg vapor pressure below the equilibrium pressure of the reaction formula (Mg2Si ⇔ 2Mg(g) + Si), by bringing Mg vapor into contact with a raw material containing SiO2, a reduction step of obtaining an intermediate product containing Si and MgO, and a washing step of removing MgO from the intermediate product are provided, and a method for manufacturing porous silicon is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Means for Solving the Problems

[0006] As a result of intensive studies by the present inventors to achieve the above object, it has been found that porous silicon having a high porosity determined from the pore volume measured by the BJH method can be produced by using a silicate, and the present disclosure has been completed. The present disclosure includes the following. <1> A method for producing porous silicon, comprising a step of bringing a raw material containing a silicate into contact with an alkaline earth metal gas, and a step of bringing the raw material brought into contact with the alkaline earth metal gas into contact with an acid. <2> The method for producing porous silicon according to <1>, wherein the silicate is an alkali metal silicate. <3> The method for producing porous silicon according to <1>, wherein the silicate is at least one compound selected from the group consisting of sodium silicate and lithium silicate. <4> The method for producing porous silicon according to <1>, wherein the silicate is sodium silicate. <5> The method for producing porous silicon according to any one of <1> to <4>, wherein the alkaline earth metal gas is magnesium gas. <6> Porous silicon having a porosity of 66% or more determined from the pore volume measured by the Barrett-Joyner-Halenda method (BJH method) and containing 0.5% by mass or more of an alkali metal. <7> The porous silicon according to <6>, wherein the alkali metal is at least one element selected from the group consisting of sodium and lithium. <8> The pore volume is 0.8 cm 3It is 1 / g or more. <6> or <7> Porous silicon as described above. <9> The average pore size is 15 nm or less. <6> ~ <8> Porous silicon as described in any one of the following. <10> BET specific surface area 70m 2 It is 1 / g or more. <6> ~ <9> Porous silicon as described in any one of the following. <11> A negative electrode current collector and a negative electrode current collector arranged on one or both sides thereof <6> ~ <10> A negative electrode layer comprising a negative electrode active material layer containing porous silicon as described in any one of the following, as the negative electrode active material. <12> A secondary battery comprising: a negative electrode layer according to claim 11; a positive electrode layer including a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material disposed on one or both sides of the positive electrode current collector; and an electrolyte layer disposed between the negative electrode layer and the positive electrode layer. <13> The electrolyte layer includes a solid electrolyte. <12> The secondary battery described above. [Effects of the Invention]

[0007] The method for producing porous silicon according to this disclosure makes it possible to produce porous silicon with a high porosity, which can be determined from the pore volume measured by the BJH method. In other words, the porous silicon of this disclosure has the characteristic of having a high porosity, which can be determined from the pore volume measured by the BJH method. Furthermore, the negative electrode layer and secondary battery of this disclosure can have porous silicon with a high porosity, which can be determined from the pore volume measured by the BJH method, as the negative electrode active material. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view of a main part illustrating one embodiment of the secondary battery of the present disclosure. [Figure 2] This is a characteristic diagram showing the porosity of porous silicon in the examples and comparative examples. [Figure 3] This is a characteristic diagram showing the average pore diameter measured for the porous silicon of the examples and comparative examples. [Figure 4] This is a characteristic diagram showing the BET specific surface area measured for the porous silicon of the examples and comparative examples. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure are described below. The description is illustrative and does not limit the scope of this disclosure.

[0010] In this specification, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise within this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in numerical ranges described within this specification, the upper or lower limit of that range may be replaced with the values ​​shown in the examples.

[0011] In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their intended purpose is achieved.

[0012] In this specification, when embodiments are described with reference to the drawings, the configuration of the embodiments is not limited to the configuration shown in the drawings. Furthermore, the sizes of the members in each figure are conceptual, and the relative relationships between the sizes of the members are not limited thereto.

[0013] In this specification, each component may contain multiple substances. In this embodiment, when referring to the amount of each component in the composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

[0014] [Method for manufacturing porous silicon] The method for producing porous silicon according to this disclosure includes the steps of contacting a silicate-containing raw material with an alkaline earth metal gas, and contacting the raw material that has been contacted with the alkaline earth metal gas with an acid. According to the method for producing porous silicon according to this disclosure, porous silicon with a high porosity, determined from the pore volume measured by the BJH method, can be produced. Here, the BJH method is performed using a BELSORP MAX X-034 manufactured by MicrotracBEL. The pore volume of porous silicon produced by the method for producing porous silicon according to this disclosure can be measured using this BJH method. The porosity of porous silicon produced by the method for producing porous silicon according to this disclosure can then be determined based on the pore volume Vp measured by the BJH method. Specifically, the porosity is calculated using the true density of Si = 2.33 g / cm³. 3 Therefore, it can be calculated as Vp / (Vp+1 / 2.33)*100.

[0015] Silicates are salts composed of silicic acid and metal oxides. Silicic acid is SiO₂ x (OH) 4-2x ] n (x is an integer between 1 and 2, and n is any integer) This is a general term for compounds. Silicic acid includes orthosilicic acid, pyrosilicic acid, metasilicic acid, and metadisiliic acid. Among silicates, when the metal oxide is an alkali metal oxide, it is represented by the general formula M2O·SiO2 (or, in the case of a hydrate, the general formula M2O·xSiO2·yH2O (x and y are integers representing the molar ratio of silicon dioxide to coordinate water, and M is an alkali metal)). Examples of alkali metals include lithium, sodium, potassium, etc. In particular, in the method for producing porous silicon of this disclosure, the silicate is preferably an alkali metal silicate, more preferably at least one compound selected from the group consisting of sodium silicate and lithium silicate, and particularly preferably sodium silicate.

[0016] The size of the raw material containing silicate according to the present disclosure is not particularly limited. The average primary particle diameter of the raw material containing silicate may be, for example, 10 nm or more, 30 nm or more, 50 nm or more, 100 nm or more, or 150 nm or more, and may be 10 μm or less, 5 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less. In addition, a part of the raw material containing silicate may form secondary particles. In this case, the average secondary particle diameter may be, for example, 100 nm or more, 1 μm or more, or 2 μm or more, and may be 20 μm or less, 15 μm or less, or 10 μm or less. The average primary particle diameter and the average secondary particle diameter can be appropriately adjusted, for example, by appropriately changing the production conditions of the raw material containing silicate or performing a classification treatment. The average primary particle diameter and the average secondary particle diameter of the raw material containing silicate are the particle diameters (median diameters) at 50% of the integrated value in the volume-based particle size distribution determined by the laser diffraction scattering method, i.e., the value of D50 is used.

[0017] In the method for producing porous silicon according to the present disclosure, first, a step of bringing a raw material containing silicate into contact with an alkaline earth metal gas (hereinafter, reduction step) is performed, and then, a step of bringing the raw material after the reduction step into contact with an acid (hereinafter, washing step) is performed.

[0018] <Reduction step> In the reduction step, an alkaline earth metal gas is brought into contact with the raw material containing silicate to reduce silicic acid and metal oxides in the raw material. For example, when the raw material containing silicate is represented as M x Si y O z (M is a metal) and Mg gas is used as the alkaline earth metal gas, in the reduction step, an intermediate product containing Si and MgO is obtained as follows. Equation: M x Si y O z +aMg→ySi+aMgO+M x O z-a As shown in this equation, metal oxides such as MgO and M x O z-a are generated as intermediate products by the reduction step.

[0019] Here, the reduction process is not particularly limited, but a vacuum furnace can be used. In a vacuum furnace, for example, the internal pressure is reduced and the furnace is heated to a temperature at which alkaline earth metal gas is generated from alkaline earth metals. The generated alkaline earth metal gas diffuses into the furnace and the reduction reaction proceeds upon contact with the raw materials.

[0020] (Method for generating alkaline earth metal gases) In this disclosure, alkaline earth metals include beryllium, magnesium, calcium, strontium, barium, and radium. In particular, in this disclosure, it is preferable to use one element selected from the group consisting of beryllium, magnesium, calcium, and strontium, more preferably one element selected from the group consisting of magnesium and calcium, and most preferably magnesium. The method for generating alkaline earth metal gas is not particularly limited. For example, a method for generating alkaline earth metal gas is to heat an alkaline earth metal or an alloy thereof.

[0021] For example, when using magnesium as an alkaline earth metal, you can use metallic magnesium (hereinafter referred to as metallic Mg), Mg2Si, MgCa alloy, MgCu2, MgNi2, and MgSn alloy (hereinafter collectively referred to as Mg alloy). To generate magnesium gas, you can raise the temperature of these materials to, for example, 600°C, 650°C, 700°C, or 800°C.

[0022] (Temperature conditions) The temperature of the reduction reaction described above is not particularly limited, but can be, for example, 500°C to 900°C, preferably 550°C to 750°C, and more preferably 600°C to 700°C. In particular, by setting the reduction reaction temperature to 600°C to 700°C, the average pore size of the porous silicon produced can be made smaller.

[0023] (Reaction time) The reaction time for the reduction reaction described above can be appropriately selected according to the pressure and temperature conditions described above. For example, the reaction time for the reduction reaction can be 1 to 48 hours, preferably 3 to 24 hours, and more preferably 5 to 18 hours.

[0024] <Washing process> In the method for producing porous silicon according to this disclosure, a washing step is then performed. In the washing step, the intermediate product obtained in the reduction step is treated with an acid or the like to remove MgO and M x O z-a This is a step to remove MgO and M from the intermediate product. x O z-a By removing the material, the desired porous silicon is obtained. The acid used in the cleaning process is not particularly limited, and can be MgO and M x O z-a Any acid capable of removing the substance is acceptable. Examples of acids used in the cleaning process include hydrochloric acid, nitric acid, and sulfuric acid. The concentration of the acid used in the cleaning process can be appropriately selected depending on the type of acid.

[0025] The cleaning process may include, if necessary, a further cleaning of the solid matter after acid cleaning using distilled water or alcohol. The cleaning process may also include, if necessary, a drying process for the cleaned solid matter.

[0026] [Porous Silicone] The porous silicon of this disclosure has a porosity of 66% or more, determined from the pore volume measured by the Barrett-Joyner-Halenda method (BJH method), and contains 0.5% by mass or more of alkali metals. While such porous silicon of this disclosure is not particularly limited, it can, for example, be manufactured by the method for manufacturing the porous silicon of this disclosure described above. The porous silicon of this disclosure has a higher porosity compared to porous silicon manufactured from silicon oxide (SiO or SiO2). Porous silicon manufactured from SiO has a porosity of 48.3%, and porous silicon manufactured from SiO2 has a porosity of approximately 65.1%. Compared to these, the porous silicon of this disclosure achieves a porosity of 66% or more. In addition, the porous silicon of this disclosure preferably has a porosity of 70% or more, more preferably 71% or more, and even more preferably 72% or more.

[0027] Because the porous silicon of this disclosure has the high porosity described above, it is preferable to use it as a negative electrode active material in secondary batteries such as lithium-ion secondary batteries. Because the porous silicon of this disclosure has a high porosity, expansion and contraction during charging and discharging in the negative electrode layer using the porous silicon as the negative electrode active material is suppressed. Therefore, by using the porous silicon of this disclosure, stable battery characteristics can be maintained. The secondary battery such as a lithium-ion secondary battery using the porous silicon of this disclosure may be either a liquid-type secondary battery with an electrolyte or a solid-state battery with a solid electrolyte layer, and an all-solid-state battery with a negative electrode layer containing the porous silicon of this disclosure is a preferred embodiment. Solid-state batteries include all-solid-state batteries having a solid electrolyte as an electrolyte between electrodes, and semi-solid-state batteries having a gel layer containing an electrolyte and a polymer between the electrodes and the solid electrolyte, and the solid electrolyte may contain less than 10% by mass of electrolyte relative to the total amount of electrolyte. The solid electrolyte may also be a composite solid electrolyte containing an inorganic solid electrolyte and a polymer electrolyte.

[0028] The porous silicon of this disclosure is manufactured from raw materials containing silicates and therefore contains metals derived from silicates. In particular, when alkali metal silicates are used as the silicates included in the raw materials, the porous silicon of this disclosure may contain 0.5% by mass or more of alkali metals. Examples of alkali metals include lithium, sodium, potassium, etc. In particular, in the porous silicon of this disclosure, the silicate is preferably an alkali metal silicate, more preferably at least one compound selected from the group consisting of sodium silicate and lithium silicate, and particularly preferably sodium silicate. Therefore, the porous silicon of this disclosure may contain 0.5% by mass or more of sodium and lithium as alkali metals. However, in the porous silicon of this disclosure, since alkali metals are residues of alkali metal oxides contained in silicates, it is preferable that the alkali metal content be lower, for example, preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, even more preferably 2% by mass or less, and even more preferably 1.5% by mass or less. In the porous silicon of this disclosure, if the alkali metal content is within this range, the alkali metal oxides contained in the raw material will sufficiently form pores, and the high porosity described above can be achieved.

[0029] Furthermore, the porous silicon of this disclosure has a pore volume of 0.8 cm³ as measured by the BJH method. 3 It is preferable that it be 0.9 cm or more. 3 It is more preferable that it be 1.0 cm or more per gram. 3 It is even more preferable that it be 1.1 cm or more. 3 It is even more preferable that the porosity is 1 / g or more. The above-mentioned porosity can be achieved by having the pore volume of the porous silicon of this disclosure be in this range.

[0030] Furthermore, the porous silicon of this disclosure preferably has an average pore diameter of 15 nm or less, more preferably 13 nm or less, and even more preferably 12 nm or less. Having an average pore diameter within this range in the porous silicon of this disclosure allows for a negative electrode layer with excellent resistance to the pressure applied during the secondary battery manufacturing process. That is, a negative electrode layer using this porous silicon as the negative electrode active material can maintain the high porosity described above even when pressed at a predetermined pressure during the secondary battery manufacturing process. The average pore diameter of the porous silicon can be measured by performing mesopore analysis using the BJH method on the adsorption isotherm obtained by gas adsorption measurement using the analysis software BEL Master.

[0031] Furthermore, the porous silicon of this disclosure has a BET specific surface area of ​​70 m². 2 It is preferable that it be 1 / g or more, and 90m 2 It is more preferable that it be 100m or more per gram. 2 It is even more preferable that it be 150m or more / g. 2 It is even more preferable that it be 200m or more / g. 2 It is even more preferable that the BET specific surface area of ​​the porous silicon is within the above range, which allows for a negative electrode layer with excellent resistance to the pressure applied during the secondary battery manufacturing process. In other words, in a negative electrode layer using the porous silicon as the negative electrode active material, the high porosity described above can be maintained even when pressed at a predetermined pressure during the secondary battery manufacturing process. Here, the BET specific surface area of ​​the porous silicon is the value measured using BELSORP MAX manufactured by MicrotracBEL.

[0032] [Negative electrode layer] The negative electrode layer of this disclosure comprises a negative electrode current collector and a negative electrode active material layer containing the porous silicon of this disclosure, disposed on one or both sides of the negative electrode current collector. The negative electrode layer of this disclosure can suppress expansion and contraction during charging and discharging by containing the porous silicon described above. The negative electrode layer of this disclosure may contain any components other than the porous silicon described above.

[0033] <Solid electrolyte> The negative electrode active material layer can contain a solid electrolyte as an optional component. Examples of the solid electrolyte contained in the negative electrode active material layer include the following substances. The solid electrolyte according to the present disclosure preferably contains at least one type of solid electrolyte selected from the group of solid electrolytes consisting of sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes. In particular, as the solid electrolyte according to the present disclosure, it is preferable to use at least one solid electrolyte selected from the group consisting of sulfide solid electrolytes and halide solid electrolytes.

[0034] As the sulfide solid electrolyte, it is preferable to contain sulfur (S) as the main component of the anion element, and in addition to S, it is preferably further contained, for example, Li element, A element, and S element. The A element is at least one selected from the group consisting of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In. The sulfide solid electrolyte may further contain at least one of O and halogen elements. Examples of the halogen element (X) include F, Cl, Br, I, etc. The composition of the sulfide solid electrolyte is not particularly limited, and examples thereof include xLi2S·(100 - x)P2S5 (70 ≤ x ≤ 80), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.7 ≤ x ≤ 0.8, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30).

[0035] The sulfide solid electrolyte may have a composition represented by the following general formula (1). Li 4-x Ge 1-x P x S4(0 < x < 1) ··· Formula (1) In formula (1), at least a portion of Ge may be substituted with at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. Also, at least a portion of P may be substituted with at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. A portion of Li may be substituted with at least one selected from the group consisting of Na, K, Mg, Ca, and Zn. A portion of S may be substituted with a halogen. The halogen is at least one of F, Cl, Br, and I.

[0036] The oxide solid electrolyte preferably contains oxygen (O) as the main component of the anionic element, and may also contain, for example, Li, the element Q (where Q represents at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O. Examples of oxide solid electrolytes include garnet-type solid electrolytes, perovskite-type solid electrolytes, NASICON-type solid electrolytes, Li-PO-based solid electrolytes, and Li-BO-based solid electrolytes. An example of a garnet-type solid electrolyte is Li7La3Zr2O 12 Li 7-x La3(Zr 2-x Nb x )O 12 (0≦x≦2), Li5La3Nb2O 12 Examples include the following. Perovskite-type solid electrolytes include (Li,La)TiO3, (Li,La)NbO3, and (Li,Sr)(Ta,Zr)O3. Nasicone-type solid electrolytes include the following: Li(Al,Ti)(PO4)3 and Li(Al,Ga)(PO4)3. Li-PO-based solid electrolytes include Li3PO4 and LIPON (a compound in which some of the O in Li3PO4 is replaced with N), and Li-BO-based solid electrolytes include Li3BO3 and a compound in which some of the O in Li3BO3 is replaced with C.

[0037] As a halide solid electrolyte, a solid electrolyte containing Li, M, and X (where M represents at least one of Ti, Al, and Y, and X represents F, Cl, or Br) is preferred. Specifically, Li 6-3zY z X6 (where X represents Cl or Br, and z satisfies 0 < z < 2), Li 6-(4-x)b (Ti 1-x Al x ) b F6 (0 < x < 1, 0 < b ≤ 1.5) is preferred. Li 6-3z Y z Among X6, Li3YX6 (where X represents Cl or Br) is more preferred and Li3YCl6 is even more preferred in terms of excellent lithium ion conductivity. Also, Li 6-(4-x)b (Ti 1-x Al x ) b F6 (0 < x < 1, 0 < b ≤ 1.5) is preferably included together with a solid electrolyte such as a sulfide solid electrolyte, for example, from the viewpoint of suppressing the oxidative decomposition of the sulfide solid electrolyte.

[0038] <Conductive aid Also, the negative electrode active material layer can contain a conductive aid as an optional component. Examples of the conductive aid include carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotube (CNT), and carbon nanofiber (CNF); and metal materials such as nickel, aluminum, and stainless steel. The conductive aid may be, for example, particulate or fibrous, and its size is not particularly limited. Only one kind of conductive aid may be used alone, or two or more kinds may be used in combination.

[0039] The negative electrode active material layer can be produced by applying a slurry obtained by mixing the porous silicon of the present disclosure and optional components such as a solid electrolyte and a conductive aid onto a negative electrode current collector. Here, the slurry can be prepared by adding and kneading porous silicon, an optional solid electrolyte, a conductive aid, etc. to a solvent in which a resin is dissolved or dispersed.

[0040] <Resin The resin is not particularly limited, and various resins known as constituent materials for secondary batteries can be used. For example, the resin may be at least one selected from butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, styrene butadiene rubber (SBR) binders, polyvinylidene fluoride (PVdF) binders, polytetrafluoroethylene (PTFE) binders, polyimide (PI) binders, carboxymethylcellulose (CMC) binders, polyacrylate binders, polyacrylic acid ester binders, etc. PVdF binders, in particular, have high performance. The PVdF binder may be a copolymer having units derived from monomers other than VdF. The polymer may be used alone or in combination of two or more types.

[0041] Here, the content of porous silicon in the negative electrode active material layer may be, for example, 40% or more by mass, 50% or more by mass, 60% or more by mass, or 70% or more by mass, with the entire negative electrode active material layer (total solid content) being 100% by mass, or it may be 100% or less by mass or 90% or less by mass. The shape of the negative electrode active material layer is not particularly limited, and for example, it may be a sheet-like negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer is not particularly limited, and for example, it may be 0.1 μm or more, 1 μm or more, or 10 μm or more, or it may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0042] Furthermore, the negative electrode layer of this disclosure may contain a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. In particular, a higher effect is more easily obtained when the negative electrode active material layer contains at least a solid electrolyte. That is, it is preferable that the negative electrode layer of this disclosure contains the porous silicon described above and a solid electrolyte disposed around it. It is preferable that the negative electrode active material layer contains a solid electrolyte, in particular a sulfide solid electrolyte, and moreover a sulfide solid electrolyte containing Li, S, and P as constituent elements.

[0043] As the negative electrode current collector, any of the materials commonly used as negative electrode current collectors in batteries can be used. The negative electrode current collector may be in the form of foil, plate, mesh, perforated metal, or foam. The negative electrode current collector may be a metal foil or metal mesh, or a carbon sheet. The negative electrode current collector may consist of multiple foils or sheets. Examples of metals constituting the negative electrode current collector include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. In particular, from the viewpoint of ensuring reduction resistance and avoiding alloying with lithium, the negative electrode current collector may contain at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector may have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the negative electrode current collector may be a metal foil or substrate on which the above metals are plated or vapor-deposited. Also, if the negative electrode current collector consists of multiple metal foils, there may be some kind of layer between the multiple metal foils. The thickness of the negative electrode current collector is not particularly limited. For example, it may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0044] [Secondary battery] The secondary battery of this disclosure comprises a negative electrode layer, a positive electrode layer including a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material disposed on one or both sides of the positive electrode current collector, and an electrolyte layer disposed between the negative electrode layer and the positive electrode layer. As described above, the secondary battery of this disclosure has a negative electrode layer that can suppress expansion and contraction during charging and discharging, and therefore can maintain excellent battery characteristics.

[0045] In the secondary battery of this disclosure, the positive electrode layer only needs to be capable of functioning appropriately as the positive electrode of the secondary battery, and its composition is not particularly limited. The positive electrode active material layer includes at least a positive electrode active material and may optionally include an electrolyte, a conductive additive, and a binder. The positive electrode active material layer may also contain various other additives. As the positive electrode active material, known positive electrode active materials for secondary batteries can be used. As the positive electrode active material, for example, at least one selected from various lithium-containing compounds, elemental sulfur and sulfur compounds, etc. Lithium-containing compounds as positive electrode active materials include lithium cobaltate, lithium nickelate, Li 1±α Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O 2±δ Lithium manganate, spinel-type lithium compounds (Li 1+x Mn 2-x-y M y Various lithium-containing oxides may be used, such as heteroatom-substituted Li-Mn spinel (e.g., O4, where M is one or more selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate, and metallic lithium phosphate (e.g., LiMPO4, where M is one or more selected from Fe, Mn, Co, and Ni). In particular, a higher effect can be expected when the positive electrode active material contains a lithium-containing oxide that includes at least Li, at least one of Ni, Co, and Mn, and O as constituent elements. The positive electrode active material may be used alone or in combination of two or more types.

[0046] The shape of the positive electrode active material can be any shape that is common for positive electrode active materials in batteries. The positive electrode active material may be, for example, particulate. The positive electrode active material may be solid, hollow, have voids, or be porous. The positive electrode active material may be primary particles or secondary particles formed by the aggregation of multiple primary particles. In addition, a protective layer containing an ion-conducting oxide may be formed on the surface of the positive electrode active material. This makes it easier to suppress reactions between the positive electrode active material and sulfides (e.g., sulfide solid electrolytes). Examples of ion-conducting oxides include Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, and Li4Ti5O 12 Examples include Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, and Li2WO4.

[0047] The electrolyte contained in the positive electrode active material layer may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. In particular, a higher effect can be expected when the positive electrode active material layer contains at least a solid electrolyte. As the solid electrolyte, those listed in the [negative electrode layer] section above can be used. As the conductive additive contained in the positive electrode active material layer, those listed in the [negative electrode layer] section above can be used. As the resin contained in the positive electrode active material layer, those listed in the [negative electrode layer] section above can be used.

[0048] The positive electrode current collector can be any of the commonly used positive electrode current collectors for batteries. The positive electrode current collector may be in the form of foil, plate, mesh, perforated metal, or foam. The positive electrode current collector may be composed of metal foil or metal mesh. Metal foil, in particular, offers superior handling. The positive electrode current collector may consist of multiple foils. Examples of metals that can constitute the positive electrode current collector include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. In particular, the positive electrode current collector may contain Al to ensure oxidation resistance. The positive electrode current collector may have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the positive electrode current collector may be a metal foil or substrate on which the above metals are plated or vapor-deposited.

[0049] The electrolyte layer in the secondary battery of this disclosure may be a layer that does not contain a liquid electrolyte but contains a solid electrolyte, a layer that does not contain a solid electrolyte but contains a liquid electrolyte (non-aqueous electrolyte), or a layer that contains both a solid electrolyte and a liquid electrolyte. As one embodiment of the secondary battery of this disclosure, the lithium-ion secondary battery 1 shown in Figure 1 comprises a positive electrode layer 2 including a positive electrode current collector 5 and a positive electrode active material layer 6, a negative electrode layer 3 including a negative electrode current collector 7 and a negative electrode active material layer 8, and an electrolyte layer 4 disposed between the positive electrode layer 2 and the negative electrode layer 3. When the electrolyte layer 4 contains a liquid electrolyte, it is preferable that the electrolyte layer 4 has a separator that holds the liquid electrolyte and insulates the positive electrode layer 2 and the negative electrode layer 3. Furthermore, when the electrolyte layer 4 contains a solid electrolyte, the electrolyte layer 4 may optionally contain a binder or the like in addition to the solid electrolyte. In particular, when using the negative electrode active material and negative electrode of this disclosure, it is preferable that the electrolyte layer 4 does not contain a liquid electrolyte but contains a solid electrolyte, or contains both a liquid electrolyte and a solid electrolyte.

[0050] The liquid electrolyte can be any non-aqueous electrolyte typically used in non-aqueous lithium-ion secondary batteries. The non-aqueous electrolyte may be a composition containing a supporting salt in a non-aqueous solvent. Examples of non-aqueous solvents include organic electrolytes, fluorinated solvents, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and materials selected from the group consisting of two or more combinations thereof. Examples of supporting salts include materials selected from the group consisting of Li(FSO2)2N, LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, lithium compounds (lithium salts) of LiI, and materials selected from the group consisting of two or more combinations thereof.

[0051] The separator used in the liquid electrolyte can be any separator commonly used in non-aqueous lithium-ion secondary batteries, such as those containing resins like polyethylene (PE), polypropylene (PP), polyester, and polyamide. The separator may have a single-layer structure or a multi-layer structure. [Examples]

[0052] The present disclosure will be described in more detail below using examples, but the technical scope of the present disclosure is not limited to the following examples.

[0053] <Example 1> <Manufacturing of porous silicon> Sodium metasilicate (Na2SiO3, manufactured by Kojun Chemical Laboratory Co., Ltd.) was ground in a mortar for 3 minutes in a glove box filled with argon gas. The particle size of the ground sodium metasilicate was measured by surface SEM observation and found to be an average of 9.8 μm. Next, 1 g of the ground sodium metasilicate was weighed and placed in a vacuum reactor. In addition, 2.55 g of Mg2Si was placed below the position of the sodium metasilicate in the vacuum reactor. The vacuum reactor was removed from the glove box and calcined at 850°C for 12 hours under vacuum conditions (approximately 80 Pa) (reduction process). The heating rate in the vacuum reactor was set to 10°C / min. Next, the powder after the reaction was allowed to cool naturally. 1 g of the obtained powder was mixed with 88.5 ml of a 6% by mass HCl aqueous solution and stirred for 1 hour to perform a washing process. This process was carried out in a simple glove box with argon gas introduced. Afterwards, the powder was dried in a vacuum dryer at 120°C for 12 hours in a glove box filled with argon gas. The porous silicon of Example 1 was thus produced.

[0054] <Example 2> Porous silicon was produced in the same manner as in Example 1, except that sodium metasilicate was calcined at 800°C for 12 hours.

[0055] <Example 3> Porous silicon was produced in the same manner as in Example 1, except that sodium metasilicate was calcined at 700°C for 12 hours.

[0056] <Example 4> Porous silicon was produced in the same manner as in Example 1, except that the sodium metasilicate was not crushed in a mortar. The average particle size of the sodium metasilicate used in this example was 30 μm.

[0057] <Comparative Example 1> Porous silicon was manufactured in the same manner as in Example 1, except that SiO2 (Kishida Chemical Co., Ltd., product code: 010-70255) was used instead of sodium metasilicate.

[0058] <Comparative Example 2> Porous silicon was produced in the same manner as in Comparative Example 1, except that SiO2 was fired under the conditions of 700 °C for 12 hours.

[0059] <Physical Property Measurement> For each of the porous silicons of Examples 1 to 4, Comparative Example 1, and Comparative Example 2, the BET specific surface area, pore volume Vp, average pore diameter, and BJH pore distribution peak were measured, and the porosity was calculated from the pore volume Vp. In addition, for each of the porous silicons of Examples 1 to 4, the amount of remaining sodium was measured. [BET Specific Surface Area] Nitrogen gas adsorption measurement was performed using BELSORP MAX X manufactured by MicrotracBEL, and the specific surface area was calculated by analyzing the obtained adsorption isotherm by the BET method in the range of 0.1 < P / P0 < 0.25. [Pore Volume Vp] Calculated from mesopore analysis using the BJH method of the gas adsorption measurement result (adsorption side). [Average Pore Diameter] Calculated from mesopore analysis using the BJH method of the gas adsorption measurement result (adsorption side). [BJH Pore Distribution Peak] From the analysis using the BJH method of the gas adsorption measurement result (adsorption side), the dp showing the maximum value in the pore distribution graph with the obtained pore diameter dp on the horizontal axis and dVp / dlog(dp) on the vertical axis was calculated as the peak. [Porosity] From the analysis using the BJH method of the gas adsorption measurement result, using the obtained pore volume Vp, the true density of Si = 2.33 g / cm 3 Therefore, it was calculated from the following formula: Vp / (Vp + 1 / 2.33) * 100. [Amount of Remaining Sodium] The powder was dissolved, and using ICPS-8100 manufactured by SHIMADZU, it was quantified by ICP emission spectrometry (ICP-AES measurement). The sample was dissolved by acid treatment with nitric acid and hydrofluoric acid, and the Na concentration was calculated by comparison with the calibration curve of Na.

[0060] <Results> Table 1 shows the results of measuring the above-mentioned physical properties of the porous silicon of Examples 1 to 4, Comparative Example 1, and Comparative Example 2.

[0061] [Table 1]

[0062] Furthermore, Figure 2 shows the porosity of the porous silicon for Examples 1 to 4, Comparative Example 1, and Comparative Example 2. In addition, Figure 3 shows the average pore diameter measured for the porous silicon for Examples 1 to 4, Comparative Example 1, and Comparative Example 2. Furthermore, Figure 4 shows the BET specific surface area measured for the porous silicon for Examples 1 to 4, Comparative Example 1, and Comparative Example 2.

[0063] As shown in Table 1 and Figure 2, it was found that using a raw material containing silicates allows for the production of porous silicon with a higher porosity compared to using a raw material containing SiO2. Furthermore, as shown in Table 1 and Figure 3, it was found that the average pore size of the porous silicon depends on the firing temperature when it comes into contact with alkyl earth metal gas, regardless of whether the raw material contains silicates or SiO2. In addition, as shown in Table 1 and Figure 4, it was found that using a raw material containing silicates allows for the production of porous silicon with a higher BET specific surface area compared to using a raw material containing SiO2. These results demonstrate that using a raw material containing silicates can yield porous silicon with a high porosity, and that using this porous silicon allows for the production of a secondary battery with reduced expansion and contraction during charging and discharging, and that a secondary battery equipped with this anode layer can maintain excellent battery performance. [Explanation of symbols]

[0064] 1...Lithium-ion secondary battery, 2...Positive electrode layer, 3...Negative electrode layer, 4...Electrolyte layer, 5...Positive electrode current collector, 6...Positive electrode active material layer, 7...Negative electrode current collector, 8...Negative electrode active material layer

Claims

1. A process of contacting a raw material containing silicate with an alkaline earth metal gas, A step of bringing the raw material that has been brought into contact with the alkaline earth metal gas into contact with an acid, A method for producing porous silicon containing [the specified material].

2. The method for producing porous silicon according to claim 1, wherein the silicate is an alkali metal silicate.

3. The method for producing porous silicon according to claim 1, wherein the silicate is at least one compound selected from the group consisting of sodium silicate and lithium silicate.

4. The method for producing porous silicon according to claim 1, wherein the silicate is sodium silicate.

5. The method for producing porous silicon according to claim 1, wherein the alkaline earth metal gas is magnesium gas.

6. Porous silicon having a porosity of 66% or more, determined from the pore volume measured by the Barrett-Joyner-Halenda method (BJH method), and containing 0.5% by mass or more of alkali metals.

7. The porous silicon according to claim 6, wherein the alkali metal is at least one element selected from the group consisting of sodium and lithium.

8. The aforementioned pore volume is 0.8 cm³. ３ The porous silicon according to claim 6, wherein the amount is 1 / g or more.

9. The porous silicon according to claim 6, wherein the average pore diameter is 15 nm or less.

10. BET specific surface area is 70 m² ２ The porous silicon according to claim 6, wherein the amount is 1 / g or more.

11. A negative electrode current collector, and a negative electrode active material layer disposed on one or both sides of the negative electrode current collector, the negative electrode active material layer containing porous silicon as described in any one of claims 6 to 10, A negative electrode layer containing this layer.

12. The negative electrode layer according to claim 11, A positive electrode layer comprising a positive electrode current collector and a positive electrode active material layer containing positive electrode active material disposed on one or both sides of the positive electrode current collector, An electrolyte layer disposed between the negative electrode layer and the positive electrode layer, A secondary battery equipped with the following features.

13. The secondary battery according to claim 12, wherein the electrolyte layer includes a solid electrolyte.

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