Electrode active material, electrode mixture, electrode layer, battery and method for producing the same

Abstract

A primary objective of the present disclosure is to provide an electrode active material whose volume change due to charge and discharge is small. The present disclosure achieves the objective by providing an electrode active material having a type II silicon clathrate crystal phase, a void being present within a primary particle; and a void fraction P1 of a void having a pore diameter of 5 nm or less than 0.015 cm 3 / g or more and 0.05 cm 3 / g or less.

Description

Technical FieldThe disclosure herein relates to an electrode active material, an electrode mixture, an electrode layer, a battery, and a method for manufacturing the same.Prior ArtIn recent years, development of a battery has been actively advanced. For example, development of a battery using battery electric vehicles (BEV), plug-in hybrid electric vehicles (PHEV), or hybrid electric vehicles (HEV) has continued in the automotive industry. As an electrode active material used for a battery, Si (silicon) is known. For example, Patent Literature 1 discloses an electrode active material having a type II silicon clathrate crystal phase and a void within a primary particle.List of Citer ListsPatent LiteraturePatent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2023-044620SUMMARY OF THE DISCLOSURETechnical ProblemThe theoretical capacity of Si is large, and it is advantageous that a battery has a high energy density. On the other hand, the volume change of Si in charging and discharging is large. For example, when the volume change during charging and discharging is large, there is a problem that the function of an electrode tends to be deteriorated in repeated charging and discharging.The disclosure mentioned here has been made in view of the above circumstances, and a main object thereof is to provide an electrode active material whose volume change due to charging and discharging is small.Solution of the Problem[1] An electrode active material comprising a type II silicon clathrate crystal phase, wherein a void inside a primary particle is specified; and a void ratio P 1 of a void having a pore diameter of 5 nm or less is 0.015 cm 3 / g or more and 0.05 cm 3 / g or less.[2] The electrode active material according to [1], wherein a ratio of the void fraction P is 1 to a void fraction P is 2 of a void having a pore diameter of 10 nm or less, that is, P is 1 / P is 2, 50% or more.[3] The electrode active material according to [1] or [2], wherein a void ratio P 2 of a void having a pore diameter of 10 nm or less is 0.03 cm 3 / g or more and 0.08 cm 3 / g or less.[4] The electrode active material according to any one of [1] to [3], wherein a ratio of the void fraction P is 1 to a void fraction P is 3 of a void having a pore diameter of 100 nm or less, that is, P is 1 / P is 3, 6,5% or more.[5] The electrode active material according to any one of [1] to [4], wherein the void ratio P 3 of a void having a pore diameter of 100 nm or less is 0.1 cm 3 / g or more and 0.5 cm 3 / g or less.[6] The electrode active material according to any one of [1] to [5], wherein the electrode active material has the type II silicon clathrate crystal phase as a main phase.[7] A mixture of electrodes comprising the electrode active material according to any one of [1] to [6], and at least one of a conductive material and a binder.[8] The mixture according to [7] further comprises a solid electrolyte.[9] The electrode mixture according to [8], wherein the solid electrolyte contained in the electrode mixture is a sulfide solid electrolyte.

[10] An electrode layer for use in a battery, the electrode layer comprising:an electrode active material having a type II silicon clathrate crystal phase and a void within a primary particle, whereina void ratio Q 1 of a void having a pore diameter of 5 nm or less is 0.008 cm 3 / g or more and 0.04 cm 3 / g or less.

[11] The electrode layer according to

[10] , wherein a ratio of the void fraction Q is 1 to a void fraction Q is 2 of a void having a pore diameter of 10 nm or less, that is, Q is 1 / Q is 2, 50% or more.

[12] The electrode layer according to

[10] or

[11] , wherein a void ratio Q 2 of a void having a pore diameter of 10 nm or less is 0.01 cm 3 / g or more and 0.05 cm 3 / g or less.

[13] The electrode layer according to any one of

[10] to

[12] , wherein a ratio of the void fraction Q is 1 to a void fraction Q is 3 of a void having a pore diameter of 100 nm or less, that is, Q is 1 / Q is 3, 10% or more.

[14] The electrode layer according to any one of

[10] to

[13] , wherein a void ratio Q 3 of a void having a pore diameter of 100 nm or less is 0.07 cm 3 / g or more and 0.2 cm 3 / g or less.

[15] A battery comprising a cathode layer, an anode layer and an electrolyte layer disposed between the cathode layer and the anode layer, wherein the cathode layer or the anode layer is the electrode layer according to any one of

[10] to

[14] .

[16] A method for producing an electrode active material, the method comprising:an alloying step for obtaining a Na-Si alloy by reacting a Na source and a Si source;a burning step of burning the Na-Si alloy to reduce the amount of Na in the Na-Si alloy and have a precursor active material containing a type II silicon clathrate crystal phase; anda liquid treatment step of performing liquid treatment on the precursor active material using hydrofluoric acid, whereina hydrogen fluoride concentration in the hydrofluoric acid is 3% by weight or more; anda treatment time in the liquid treatment step is 3 hours or more and less than 24 hours.

[17] The method for producing an electrode active material according to

[16] , wherein in the electrode active material, a void ratio P 1 of a void having a pore diameter of 5 nm or less is 0.015 cm 3 / g or more and 0.05 cm 3 / g or less.

[18] A method of making an electrode mixture, the method comprising:a manufacturing step of manufacturing an electrode active material by the method of manufacturing an electrode active material according to

[16] or

[17] ; anda mixing step of mixing the electrode active material and at least one of a conductive material and a binder to obtain an electrode mixture.

[19] A method of forming an electrode layer, the method comprising:a manufacturing step of manufacturing an electrode active material by the method of manufacturing an electrode active material according to

[16] or

[17] ;a mixing step of mixing the electrode active material and at least one of a conductive material and a binder to obtain an electrode mixture; anda step of forming an electrode layer using the electrode mixture.

[20] A method of manufacturing a battery, the method comprising:a manufacturing step of manufacturing an electrode active material by the method of manufacturing an electrode active material according to

[16] or

[17] ;a mixing step of mixing the electrode active material and at least one of a conductive material and a binder to obtain an electrode mixture; anda step of forming an electrode layer using the electrode mixture.Advantageous Effects of the DisclosureThe disclosure herein exhibits an effect of, for example, obtaining an electrode active material whose volume change by charging and discharging is small.Brief Description of the DrawingsFIGS. 1A and 1B are schematic perspective views explaining the crystal phase of Si. FIG. 2 is a schematic cross-sectional view illustrating the battery mentioned here. FIG. 3 is a flowchart illustrating the method for producing the electrode active material in the disclosure mentioned herein. FIG. 4 is an XRD pattern of an active material before and after liquid treatment with an HF aqueous solution.DESCRIPTION OF THE EMBODIMENTSThe electrode active material, the electrode mixture, the electrode layer, the battery and the method for producing mentioned here are explained in more detail below.A. Electrode Active MaterialThe electrode active material mentioned here has a type II silicon clathrate crystal phase and a void within a primary particle. Also, a void ratio P 1 of a void having a pore diameter of 5 nm or less is large.According to the disclosure mentioned here, the void ratio P 1 is large, so that the volume change of the electrode active material by charging and discharging is small. The present inventors have obtained through previous studies the finding that fracture of a void by a pressing process was prevented by increasing the void ratio of a minute void having a pore diameter of 100 nm or less. In addition, it has been found that by increasing the void ratio of a minute void having a pore diameter of 10 nm or less, the fill ratio of the deposited Li in a void can be increased while at the same time significantly inhibiting the breakage of the void by the pressing operation, thereby effectively suppressing the volume change by charging and discharging.In contrast, in the disclosure mentioned herein, it has been found that, for example, by a positive liquid treatment with hydrofluoric acid, the void ratio P 1 of a minute void having a pore diameter of 5 nm or less can be increased. As a reason for this, it is presumed that the deposited Li is preferentially filled into the minute cavity having the pore diameter of 5 nm or less upon charging. It is presumed that, by positively performing the liquid treatment with hydrofluoric acid, the crystal phase of the type I silicon clathrate crystal phase contained in the electrode active material disappears simultaneously with the etching of the surface of the electrode active material, and thereby the void ratio P 1 increases. As the void ratio P 1 increases, the volume change by charging and discharging can be effectively suppressed.In addition, the electrode active material referred to herein includes a type II silicon clathrate crystal phase. As shown in FIG. 1A, in the type II silicon clathrate crystal phase, a plurality of Si elements form a polyhedron (cage) having pentagonals and hexagon. This polyhedron has an internal space containing metal ions, for example, Li ions. The metal ions are stored in this space to prevent the volume change by the charge and discharge. In particular, in an all-solid battery, in order to suppress the volume change by charging and discharging, it is generally necessary to act a high retaining pressure, but by using the electrode active material mentioned herein, the retaining pressure can be reduced, and as a result, the enlargement of the retaining device can be suppressed. As shown in FIG. 1B, a plurality of Si elements in the diamond-like silicon crystal phase form a tetrahedron. The tetrahedron does not have an internal space that can contain metal ions such as Li ions, and therefore its volume change due to charge and discharge by the diamond-like silicon crystal phase cannot be easily suppressed compared to the type II silicon clathrate crystal phase.The form of the active material mentioned here is generally a granular form. The active material may be a primary particle, and may be a secondary particle, that is, aggregation of the primary particle. In both cases, a void is present within a primary particle.It is preferable that the electrode active material has a lot of voids having a pore diameter of 5 nm or less. The void ratio P 1 of a void having a pore diameter of 5 nm or less is typically 0.015 cm 3 / g or more, may be 0.020 cm 3 / g or more, and may be 0.023 cm 3 / g or more. The void ratio P 1 is typically 0.05 cm3 / g or less, may be 0.04 cm3 / g or less, and may be 0.035 cm3 / g or less. The void ratio referred to herein means an integrating hole volume, and can be obtained by, for example, a BET measurement, a gas absorption method, a mercury porosimeter measurement, 3D-SEM, and 3D-TEM.It is preferable that the electrode active material has a lot of voids having a pore diameter of 10 nm or less. The void ratio P 2 of a void having a pore diameter of 10 nm or less is, for example, 0.03 cm 3 / g or more, may be 0.035 cm 3 / g or more, and may be 0.04 cm 3 / g or more. The void ratio P 2 is, for example, 0.08 cm 3 / g or less, may be 0.07 cm 3 / g or less, and may be 0.06 cm 3 / g or less. Also, the ratio of the void ratio P 1 to the void ratio P 2, that is, P 1 / P 2 is, for example, 50% or more, may be 55% or more, and may be 57% or more. For example, P 1 / P 2 is 80% or less, may be 70% or less, and may be 65% or less.It is preferable that the electrode active material has a lot of voids having a pore diameter of 100 nm or less. The void ratio P 3 of a void having a pore diameter of 100 nm or less is, for example, 0.1 cm 3 / g or more, may be 0.2 cm 3 / g or more, and may be 0.32 cm 3 / g or more. The void ratio P 3 is, for example, 0.5 cm 3 / g or less, may be 0.45 cm 3 / g or less, and may be 0.38 cm 3 / g or less. Also, the ratio of the void ratio P 1 to the void ratio P 3, that is, P 1 / P 3 is, for example, 6.0% or more, may be 6.5% or more, and may be 6.9% or more. For example, P 1 / P 3 is 15% or less, may be 12% or less, and may be 10% or less.The electrode active material preferably has a cavity within the primary particle. The ratio of the void (void ratio) in the primary particle is, for example, 4% or more and may be 10% or more. The void ratio is, for example, 40% or less and may be 20% or less. The void ratio can be obtained by the following methods, for example. First, the electrode layer including the electrode active material is subjected to ion milling processing to take out the cross section. Then, the cross section is observed with an SEM (scanning electron microscope) to obtain an image of the particles. From the obtained image, a silicon portion and the cavity portion are distinguished and binarized using image analysis software. The areas of the silicon portion and the cavity portion are obtained, and the cavity ratio (%) is calculated from the following equation.The average particle size (D 50) of the electrode active material is not particularly limited, and is, for example, 0.1 μm or more and 50 μm or less, and may be 0.5 μm or more and 30 μm or less. The average particle size (D 50) can be calculated, for example, by measurement with a scanning electron microscope (SEM). Also, the BET specific surface area of the electrode active material is not particularly limited, and is, for example, 30 m 2 / g or more, may be 40 m 2 / g or more, 50 m 2 / g or more, and 60 m 2 / g or more. The specific surface area of the BET electrode active material is, for example, 150 m 2 / g or less.The electrode active material has a type II silicon clathrate crystal phase. Preferably, the electrode active material has the type II silicon clathrate crystal phase as a main phase. "Main phase" means that the peak belonging to this crystal phase has the highest diffraction intensity among the peaks observed in X-ray diffraction measurement. The proportion of the type II silicon clathrate crystal phase having the electrode active material is, for example, 80% by weight or more, may be 85% by weight or more, may be 90% by weight or more, and may be 95% by weight or more. Also, the proportion of the type II silicon clathrate crystal phase having the electrode active material may be 100% by weight, and may be less than 100% by weight. The proportion of the crystal phase can be obtained by performing Rietveld analysis on the XRD measurement result and using the analysis result and a reference intensity ratio (RIR) method.The type II silicon clathrate crystal phase is normally a space group Fd-3m. In an X-ray diffraction measurement using a CuKα ray, the type II silicon clathrate crystal phase has typical peaks at positions 2θ=20.09°, 21.00°, 26.51°, 31.72°, 36.26°, and 53.01°. Each of these peaks may shift in the range of ±0.50°, in the range of ±0.30°, and in the range of ±0.10°.In the type II silicon clathrate crystal phase, a peak at 2θ=20.09°±0.50° is regarded as the peak A and a peak at 2θ=31.72°±0.50° is regarded as the peak B. The intensity of the peak A is considered as I A and the intensity of the peak B is considered as I B. The maximum intensity at 2θ=22° to 23° is regarded as I M. Since 2θ=22° to 23° is the range where peaks of the crystal phase relating to Si do not normally occur, it can be used as a base.The value of I / I Am is preferably greater than 1. When the value of I / I is AM1 or less, it can be considered that the type II silicon clathrate crystal phase is not substantially formed. The value of I A / I AM is, for example, 1.75 or more, and may be 1.80 or more. The value of I A / I AM is, for example, 10 or less, and may be 5 or less.The value of I B / I AM is preferably greater than 1. When the value of I is B / I AM1 or less, it can be considered that the type II silicon clathrate crystal phase is not substantially formed. The value of I B / I AM is, for example, 1.35 or more, and may be 1.40 or more. The value of I B / I AM is, for example, 7 or less, and may be 4 or less.The electrode active material referred to herein may or may not have a crystal phase of the type I silicon clathrate crystal phase. "Do not have a crystal phase" means that the peaks of this crystal phase are not confirmed by an X-ray diffraction measurement. The crystal phase of the type I silicon clathrate crystal phase is usually of the space group Pm-3n. The type I silicon clathrate crystal phase crystal phase has typical peaks at positions 2θ=19,44°, 21.32°, 30.33°, 31.60°, 32.82°, 36.29°, 52.39° and 55.49° in X-ray diffraction measurement using a CuKα ray. Each of these peaks may shift in the range of ±0.50°, in the range of ±0.30°, and in the range of ±0.10°.The electrode active material referred to herein may include a diamond-like silicon crystal phase, but need not. In an X-ray diffraction measurement using a CuKα ray, the diamond-like silicon crystal phase has typical peaks at positions 2θ=22.44°, 47.31°, 56.10°, 69.17° and 76.37°. Each of these peaks may shift in the range of ±0.50°, in the range of ±0.30°, and in the range of ±0.10°.When a peak C at 2θ=22.44°±0.50° is regarded as a peak of the diamond-like silicon crystal phase, the intensity of the peak C is regarded as I C. I A / I C is, for example, greater than 1, may be 1.5 or more, may be 2 or more, and may be 3 or more. The advantageous range of I B / I C is the same as the advantageous range of I A / I C.The composition of the electrode active material in the disclosure mentioned here is not particularly limited, but is preferably represented by Na x Si 136(0 ≤ x ≤ 24). The "x" may be 0 and may be greater than 0. Meanwhile, the "x" may be 20 or less, 10 or less, and 5 or less. The composition of the electrode active material can be obtained by, for example, EDX, XRD, XRF, ICP, and an atomic absorption method. Incidentally, an oxidized film generally inevitably forms on the surface of the electrode active material. For this reason, the electrode active material may contain a small amount of O (oxygen). In addition, the electrode active material may contain a small amount of C (carbon) derived from the production steps.The electrode active material referred to herein is normally used for a battery. The electrode active material mentioned here may be both an anode active material and a cathode active material, the former being advantageous. Examples of methods for producing the electrode active material may include the methods described later under "E. Methods for producing electrode active material".B. Electrode MixtureThe electrode mixture mentioned here contains the above-described electrode active material and at least one of the two materials, namely a conductive material and a binder.According to the disclosure mentioned herein, the use of the above-described electrode active material enables the mixture of the electrodes to have a smaller volume change due to charging and discharging.The mixture contains the electrode active material and at least one conductive material or a binder. The electrode active material has the same proportions as those described in "A. Electrode active material" above. The electrode active material can be both an anode active material and a cathode active material, the former being advantageous. In other words, the electrode mixture may be an anode mixture and a cathode mixture, the former being advantageous.The proportion of the electrode active material in the mixture of the electrodes is, for example, 20% by weight or more, may be 30% by weight or more, and may be 40% by weight or more. If the proportion of the electrode active material is too small, there is a possibility that a sufficient energy density is not obtained. The proportion of the electrode active material is, for example, 80% by weight or less, may be 70% by weight or less, and may be 60% by weight or less. When the proportion of the electrode active material is too high, there is a possibility that the ion conductivity and the electron conductivity in the electrode mixture are relatively deteriorated.The mixture of electrodes includes at least one conductive material and a binder. Examples of the conductive material may include a carbon material, a metal particle, and a conductive polymer. Examples of the carbon material may include a particulate material such as acetylene black (AB) and ketjen black (KB), and a fiber carbon material such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF). In addition, the binder may include, for example, a rubber-based binder and a fluoride-based binder.The electrode mixture may further include a solid electrolyte. Examples of the solid electrolyte may include an inorganic solid electrolyte such as a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, and a halide solid electrolyte; and an organic polymer electrolyte such as a polymer electrolyte. Examples of sulfide solid electrolytes may include a solid electrolyte including a Li element, an X element (X is at least one kind of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and an S element. In addition, the sulfide solid electrolyte may further include at least an O element and a halogen element. Examples of the halogen element may include an F element, a Cl element, a Br element, and an I element. The sulfide solid electrolyte may be made of (amorphous) glass and may be a glass ceramic. Examples of the sulfide solid electrolyte may include Li 2 S-P 2 S 5, LiI-Li 2 S-P 2 S 5, LiI-LiBr-Li 2 S-P 2 S 5, Li 2 S-SiS2, Li 2 S-GeS 2 and Li 2 S-P 2 S 5- GeS 2. In addition, the electrode mixture may contain a dispersion medium.C. Electrode LayerThe electrode layer mentioned here is an electrode layer using a battery, and has an electrode active material containing a type II silicon clathrate crystal phase and a void inside a primary particle. In addition, there is a large void ratio Q 1 of a void having a pore diameter of 5 nm or less.According to the disclosure mentioned here, since the void ratio Q 1 is large, the electrode layer has less volume change due to charging and discharging.It is preferable that the electrode layer has a lot of voids having a pore diameter of 5 nm or less. The void ratio Q 1 of a void having a pore diameter of 5 nm or less is normally 0.008 cm 3 / g or more, may be 0.010 cm 3 / g or more, and may be 0.013 cm 3 / g or more. The void ratio Q 1 is typically 0.04 cm 3 / g or less, and may be 0.03 cm 3 / g or less.It is preferable that the electrode layer has a lot of voids having a pore diameter of 10 nm or less. The void ratio Q 2 of a void having a pore diameter of 10 nm or less is, for example, 0.01 cm 3 / g or more, may be 0.015 cm 3 / g or more, and may be 0.021 cm 3 / g or more. The void ratio Q 2 is, for example, 0.05 cm 3 / g or less, and may be 0.04 cm 3 / g or less. Also, the ratio of the void ratio Q 1 to the void ratio Q 2, that is, Q 1 / Q 2 is, for example, 50% or more, and may be 56.9% or more. The Q 1 / Q 2 is, for example, 90% or less, but may be 80% or less.It is preferable that the electrode layer has a lot of voids having a pore diameter of 100 nm or less. The void ratio Q 3 of a void having a pore diameter of 100 nm or less is, for example, 0.07 cm 3 / g or more, may be 0.08 cm 3 / g or more, and may be 0.09 cm 3 / g or more. The void ratio Q 3 is, for example, 0.2 cm 3 / g or less, may be 0.15 cm 3 / g or less, and may be 0.12 cm 3 / g or less. Also, the ratio of the void ratio Q 1 to the void ratio Q 3, that is, Q 1 / Q 3 is, for example, 10% or more, may be 12% or more, and may be 13% or more. For example, Q is 1 / Q is 325 % or less, may be 23% or less, and may be 20% or less.The electrode layer contains an electrode active material and at least one of two materials: a conductive material and a binder. The electrode layer can also contain an electrolyte. The materials, compositions and other constituents have the same proportion as those described above under "A. electrode active material" and "B. electrode mixture". The electrode layer may be both an anode layer and a cathode layer, the former being advantageous. The thickness of the electrode layer is, for example, 0.1 μm or more and 1000 μm or less, may be 0.1 μm or more and 500 μm or less, and may be 0.1 μm or more and 100 μm or less. Examples of methods for manufacturing the electrode layer may also include a manufacturing method described later under "F. Method for manufacturing the electrode layer".D. BatteryFIG. 2 is a schematic cross-sectional view illustrating the battery mentioned here. The battery 10 shown in FIG. 2 includes a cathode layer 1, an anode layer 2, an electrolyte layer 3 disposed between the cathode layer 1 and the anode layer 2, a cathode current collector 4 for collecting currents of the cathode layer 1, and an anode current collector 5 for collecting currents of the anode layer 2. In the disclosure mentioned here, the cathode layer 1 or the anode layer 2 is the electrode layer described above under "C. electrode layer".According to the disclosure herein, the use of the above-described electrode layer enables a battery to have a smaller volume change by charging and discharging. As described above, the electrode layer may be an anode layer and a cathode layer, the former being advantageous. Details of the battery when the electrode layer is an anode layer will be explained below.1. Anode LayerThe anode layer is a layer containing at least one anode active material. The anode layer has the same proportion as the layer described above under "C. electrode layer"; therefore, the descriptions are omitted here.2. Cathode LayerThe cathode layer is a layer containing at least one cathode active material. In addition, the cathode layer may contain at least an electrolyte, a conductive material, and a binder as needed.Examples of the cathode active material may include an oxide active material. Examples of the oxide active material may include a rock salt bed type active material such as LiCoO 2, LiMnO 2, LiNiO 2, LiVO 2 and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2; a spinel type active material such as LiMn 2 O 4, Li 4 Ti 5 O 12 and Li(Ni 0,5 Mn 1,5) O 4; and an olivine type active material such as LiFePO 4, LiMnPO 4, LiNiPO_NERmn_and LiCoPO_NERmn_.On the surface of the oxide active material, a coating layer containing an oxide containing Li may be formed. This is because the reaction of the oxide active material and the solid electrolyte (particularly, a sulfide solid electrolyte) is inhibited. Examples of the conductive Li ion oxide may include LiMnO 3. The thickness of the coating layer is, for example, 1 nm or more and 30 nm or less. Li 2 S can be used, for example, as cathodic active material.Examples of the form of the cathodic active material may have a granular form. The average particle size (D 50) of the cathodic active material is not particularly limited, and is, for example, 10 nm or more, and may be 100 nm or more. The average particle size (D 50) of the cathode active material is, for example, 50 μm or less, and may be 20 μm or less.The electrolyte used for the cathode layer has the same proportion as that described in "3rd electrolyte layer". Also, the conductive material and the binder used for the cathode layer have the same contents as those described under "B. electrode mixture" above; therefore, the descriptions are omitted here. The thickness of the cathode layer is, for example, 0.1 μm or more and 1000 μm or less, may be 0.1 μm or more and 500 μm or less, and may be 0.1 μm or more and 100 μm or less.3. Electrolyte LayerThe electrolyte layer is a layer formed between the cathode layer and the anode layer and contains at least one electrolyte. The electrolyte may be a solid electrolyte or an electrolyte solution (liquid electrolyte).The solid electrolyte has the same proportions as in the above-described "B electrode layer"; therefore, the descriptions are omitted here. The liquid electrolyte preferably contains a supporting electrolyte (lithium salt) and a solvent. Examples of the supporting electrolyte of the electrolyte having lithium ion conductivity may include an inorganic lithium salt such as LiPF 6, LiB 4, LiClO 4, and LiAsF 6 ; and an organic lithium salt such as LiCF 3 SO 3, LiN(CF 3 SO 2)2, LiN(C 2 F 5 SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3. Examples of the solvent used for the electrolyte may include a cyclic ester (cyclic carbonate) such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC); and a chain ester (chain carbonate) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylmethyl carbonate (EMC). Preferably, the liquid electrolyte contains two or more kinds of the solvent.The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less, may be 0.1 μm or more and 500 μm or less, and may be 0.1 μm or more and 100 μm or less.4. Other ProceduresThe battery referred to herein preferably includes a cathode current collector for collecting currents from the cathode layer and an anode current collector for collecting currents from the anode layer. Examples of the material of the cathode current collector may include SUS, aluminum, nickel, iron, titanium, and carbon. Examples of the material of the anode current collector may include SUS, copper, nickel, and carbon.The battery herein may further include a holding device that applies a holding pressure along the thickness direction of the cathode layer, the electrolyte layer, and the anode layer. Particularly, when the electrolyte layer is a solid electrolyte layer, it is preferable to apply a restraint pressure to form an excellent ion conduction path and electron conduction path. The holding pressure is, for example, 0.1 MPa or more, may be 1 MPa or more, and may be 5 MPa or more. For example, the holding pressure is 100 MPa or less, may be 50 MPa or less, and may be 20 MPa or less.5. A battery batteryThe type of the battery in the disclosure mentioned here is not particularly limited, but is typically a lithium ion battery. Also, the battery mentioned here may be a liquid battery in which the electrolyte layer contains a liquid electrolyte, and an all-solid-state battery in which the electrolyte layer contains a solid electrolyte. The all-solid-state battery can be a semi-solid-state battery or a pure all-solid-state battery. In the disclosure mentioned here, the semi-solid battery is a battery in which the electrolyte layer includes an inorganic solid electrolyte and a liquid member (for example, an ionic solution). In the disclosure mentioned here, the all solid state battery is a battery whose electrolyte layer has only the inorganic solid electrolyte as an electrolyte. Also, the battery mentioned here may be a primary battery and a secondary battery, but preferably a secondary battery among them. This is because it can be repeatedly charged and discharged, and can be used as, for example, an automobile-mounted battery.Examples of the application of the battery may include a power source for vehicles, for example, hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), battery electric vehicles (BEV), gasoline-powered cars, and diesel-powered cars. In particular, it is preferably used as a power source for driving hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and battery electric vehicles (BEV). The battery can also be used as a power source for vehicles (e.g., railway vehicles, ships, and aircraft) other than vehicles, and as a power source for electronic products, e.g., information processing apparatuses.E. Method for Producing Electrode Active MaterialFIG. 3 is a flowchart for illustrating the method for producing the electrode active material in the disclosure mentioned here. In the manufacturing method shown in FIG. 3, a Na-Si alloy is first obtained by reacting a Na source and a Si source (an alloying step). Subsequently, the Na-Si alloy is fired to reduce the amount of Na in the Na-Si alloy and form a precursor active material having a type II silicon clathrate crystal phase (a firing step). Subsequently, liquid treatment of the precursor active material is performed using hydrofluoric acid to obtain an electrode active material (a liquid treatment step). In the disclosure mentioned herein, the concentration of hydrofluoric acid is 3% by weight or more, and the treatment time in the liquid treatment step is 3 hours or more and less than 24 hours.According to the disclosure mentioned herein, by performing the liquid treatment step, an electrode active material whose volume change by charging and discharging is small can be obtained.1. Alloying StepThe alloying step referred to herein is to obtain a Na-Si alloy by reacting a Na source and a Si source.The Si source is a particle containing at least Si. The Si source may be a simple substance of Si or an alloy of Si with other metals. When the Si source is an alloy, the alloy preferably contains Si as a main component. The content of Si in the alloy is, for example, 50 at % or more, may be 70 at % or more, and may be 90 at % or more.The Si source is advantageously a porous Si which has a quantity of hollow space within the primary particle. Examples of methods for manufacturing the Si source (porous Si) may include a method in which an alloy of Li with Si (Li-Si alloy) is prepared, and then Li is removed from the Li-Si alloy. The Li-Si alloy can be obtained by mixing Li and Si, for example. The ratio of Li to Si, that is, Li / Si is, for example, 1.0 or more, may be 2.0 or more, 3.0 or more, and 4.0 or more. Meanwhile, Li / Si is, for example, 8.0 or less. Examples of the method for removing Li from the Li-Si alloy may include a method in which the Li-Si alloy is reacted with a Li extractant. Examples of the Li extractant may include alcohol such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol; and acid such as acetic acid, formic acid, propionic acid, and oxalic acid.Examples of methods for manufacturing the Si source (porous Si) may also include a method in which an alloy of Mg with Si (Mg-Si alloy) is prepared, and then Mg is removed from the Mg-Si alloy. The Mg-Si alloy can be obtained, for example, by heating a mixture of Mg and Si. The ratio of Mg to Si, that is, Mg / Si is, for example, 1.0 or more, may be 1.5 or more, and may be 2.0 or more. Meanwhile, Mg / Si is, for example, 6.0 or less. Examples of methods for removing Mg from the Mg-Si alloy may include a method in which Mg in the Mg-Si alloy is converted into MgO by heating the Mg-Si alloy in an oxygen-containing inert gas atmosphere, and then MgO is removed by an acid solution. Examples of the acidic solution may include an aqueous solution containing hydrochloric acid (HCl) and hydrogen fluoride (HF).Examples of the method for manufacturing the Si source (porous Si) may also include a method in which an alloy of Mg with Si (Mg-Si alloy) is made and then Mg is removed from the Mg-Si alloy, and thereafter an alloy of Li with Si obtained by removing Mg (Li-Si alloy) is made and then Li is removed from the Li-Si alloy.Meanwhile, the Na source contains at least Na. Examples of the Na source may include a metal-Na, NaH, and a metal-Na dispersion in which metal-Na particles are dispersed in an oil.Examples of methods for obtaining the Na-Si alloy by bringing the Na source and the Si source together may include a method of heating a mixture containing the Na source and the Si source. The heating temperature is, for example, 300° C. or more, may be 310° C. or more, 320° C. or more, and 340° C. or more. Meanwhile, the temperature is 800° C. or less, may be 600° C. or less, and may be 450° C. or less, for example. In addition, the alloying step is preferably carried out under an inert atmosphere, for example Ar.The Na-Si alloy preferably has a Zintl phase. The Zintl phase has typical peaks at positions 2θ=16.10°, 16.56°, 17.64°, 20.16°, 27.96°, 33.60°, 35.68°, 40.22°, and 41.14° in X-ray diffraction measurement using a CuKα ray. Each of these peaks may shift in the range of ±0.50° and may shift in the range of ±0.30°. The Na-Si alloy preferably has the Zintl phase as the main phase.The composition of the Na-Si alloy is not particularly limited, but is preferably represented by the composition of Na z Si 136(121 ≤ z ≤ 151). The "z" may be 126 or more, and may be 131 or more. Meanwhile, the "z" may be 141 or less. In addition to Na and Si, other elements may be contained in the Na-Si alloy. Examples of the additional element may include Li, K, Rb, Cs, Ba, Ga, and Ge.2. Firing StepThe firing step mentioned here is a step of firing the Na-Si alloy to reduce the amount of Na in the Na-Si alloy and form a precursor active material having a type II silicon clathrate crystal phase.The firing conditions of the Na-Si alloy are appropriately adjusted to obtain the desired precursor active material. The firing temperature is, for example, 300° C. or more and 400° C. or less. The firing time is, for example, 5 hours or more and 120 hours or less. The firing step can be carried out in a reduced-pressure atmosphere, but also in a normal-pressure atmosphere.In the firing step, a scavenger that traps Na in the Na-Si alloy is preferably used. Examples of the capturing agent may include a Na getter agent that reacts with a vapor of Na geneVerhältnis of the Na-Si alloy. The Na getter agent is deposited, for example, in a state of not being in contact with the Na-Si alloy. Examples of the Na getter agent may include SiO, MoO 3, FeO, and FeO 34. In the case of using the Na getter agent, the firing step is preferably performed in a reduced-pressure atmosphere.Other examples of the capturing agent may include a Na capturing agent that directly reacts with the Na-Si alloy and receives Na. The Na scavenger is applied, for example, in a state of being in contact with the Na-Si alloy. Examples of the Na scavenger may include CaCl 2, AlF 3, CaBr 2, Cal 2, Fe 3 O 4, FeO, MgCl 2, ZnO, ZnCl 2 and MnCl 2. In the case where the Na scavenger is used, the firing step may be performed in a reduced-pressure atmosphere and in a normal-pressure atmosphere.3. Liquid Treatment StepThe liquid treatment step mentioned here is a step of performing liquid treatment of the precursor active material using hydrofluoric acid. The hydrofluoric acid is an aqueous solution in which a hydrogen fluoride (HF) is dissolved in water.The concentration of the hydrogen fluoride in the hydrofluoric acid is typically 3% by weight or more, may be 4% by weight or more, and may be 5% by weight or more. The hydrogen fluoride concentration in the hydrofluoric acid is, for example, 10% by weight or less. Also, the treatment time of the liquid treatment is typically 3 hours or more, may be 4 hours or more, and may be 5 hours or more. Meanwhile, the treatment time of the liquid treatment is typically less than 24 hours, may be 15 hours or less, and may be 10 hours or less. The temperature of the liquid treatment is not particularly limited, but for example, it is a normal temperature.Examples of methods for performing liquid treatment of the precursor active material with the hydrofluoric acid may include a method in which the precursor active material is impregnated with the hydrofluoric acid, and a method in which the hydrofluoric acid acts on the precursor active material.4. Electrode Active MaterialThe electrode active material obtained by the above-described steps includes the type II silicon clathrate crystal phase. In addition, in the electrode active material, it is preferable that the void ratio P 1 of a void having a pore diameter of 5 nm or less is 0.015 cm 3 / g or more and 0.05 cm 3 / g or less. Preferably, the proportions of the electrode active material are the same as those described in "A. Electrode active material" above.F. Methods for Making Electrode MixturesThe disclosure herein includes a method for producing an electrode mixture, the method including: a production step of producing an electrode active material by the above-described method for producing an electrode active material; and a mixing step of mixing the electrode active material and at least one of a conductive material and a binder to obtain an electrode mixture.According to the disclosure mentioned here, by using the above-described electrode active material, a mixture of electrodes whose volume change by charging and discharging is small can be obtained. The step of preparing has the same proportions as those described in "E. Methods of Preparing Electrode Active Material" above.The mixture generally contains the electrode active material and at least one of the two materials, namely a conductive material and a binder. The conductive material and the binder have the same proportions as those described under "B. electrode mixture" above. The mixture may or may not further comprise a dispersion medium. In addition, the electrode mixture is generally obtained by mixing the electrode active material and at least one of the conductive material and the binder. There are no particular restrictions on the methods of mixing, and known methods can be used. It is also advantageous that the electrode mixture to be obtained has the same proportions as described above under "B electrode mixture".G. Method for Producing Electrode LayerThe disclosure herein has a method for manufacturing an electrode layer, the method including: a manufacturing step of manufacturing an electrode active material by the above-described method of manufacturing an electrode active material; a mixing step of mixing the electrode active material and at least one of a conductive material and a binder to obtain an electrode mixture; and an electrode layer forming step of forming an electrode layer using the electrode mixture.According to the disclosure mentioned here, by using the above-described electrode active material, an electrode layer whose volume change by charging and discharging is small can be obtained. The preparing step and the mixing step have the same proportion as those described above under "E. Method for preparing electrode active material" and "F. Method for preparing electrode mixture".The step of forming the electrode layer is a step of forming an electrode layer using the electrode mixture. There are no particular restrictions on the methods for forming the electrode layer, and known methods can be used. Examples of methods for forming the electrode layer may include a method in which the electrode mixture acts on the current collector of the electrode. In the formation of the electrode layer, a pressing treatment in which the electrode layer is pressed in a thickness direction may be performed. Examples of the pressing treatment may include a roll pressing and a flat plate pressing. When the electrode mixture is a slurry containing a dispersion medium, drying is preferably performed after the electrode mixture is knitted on the current collector.The step of forming the electrode layer may be a step of forming a cathode layer and a step of forming an anode layer.H. Method for Manufacturing BatteriesThe disclosure herein has a method for manufacturing a battery, the method including: a manufacturing step of manufacturing an electrode active material by the above-described method of manufacturing an electrode active material; a mixing step of mixing the electrode active material and at least one of a conductive material and a binder to obtain an electrode mixture; and an electrode layer forming step of forming an electrode layer using the electrode mixture.According to the disclosure mentioned here, by using the above-described electrode active material, a battery whose volume change by charging and discharging is small can be obtained. The step of preparing, mixing, and forming the electrode layer has the same proportion as those described above under "E. Method for preparing electrode active material", "F. Method for preparing electrode mixture", and "G. Method for preparing electrode layer". The method for manufacturing a battery referred to herein may further include an additional step of forming an electrolyte layer, for example. It is also advantageous that the battery to be obtained has the same proportions as those described above under "D. Battery".Incidentally, the disclosure mentioned here is not limited to the embodiments. The embodiments are exemplary, and all other variations are intended to be within the technical scope of the disclosure herein when they have substantially the same constitution as and effect similar to the technical idea described in the claims of the present disclosure.Examples[Comparative Example 1]Metal-Li and Si powders were weighed in the ratio of 4:1 and reacted by mixing with a mortar under Ar atmosphere at room temperature for 0.5 hour. Li 4 Si was obtained in this manner. The obtained Li 4 Si was reacted with ethanol under an Ar atmosphere. The obtained reaction product was considered to include Si and CH 3 CH 2 OLi. This reaction product was filtered, and the filtered solid portion was dried at 120° C. for 3 hours or longer to obtain powdery porous Si.Using the obtained porous Si, a Na-Si alloy was prepared using NaH as a Na source. Incidentally, as NaH, NaH washed with hexane in advance was used. The NaH and the porous Si were weighed in a molar ratio of 1.05:1 and mixed using a cutter mill. The mixture of NaH and porous Si was heated under Ar atmosphere and at 475°C for 40 hours in a heating furnace to obtain a powdery Na-Si alloy.Using the obtained Na-Si alloy and also using AlF 3 as the Na scavenger, a silicon clathrate was prepared in a solid phase method. The Na-Si alloy and the AlF 3 were weighed in a molar ratio of 1:0.35 and mixed using a cutter mill to obtain a reaction raw material. The obtained powdery reaction raw material was placed in a stainless steel reaction vessel and reacted by heating under Ar atmosphere at 310° C. and for 60 hours in a heating furnace to obtain a precursor active material.The obtained precursor active material was considered to have NaF and Al as byproducts. Subsequently, the precursor active material was washed using a mixture in which HNO 3 and H 2 O were mixed in a 10:90 volume ratio. Thereby, the by-products in the reaction product were eliminated. After washing, the filtered and separated solid portion was dried at 120° C. for 3 hours or longer to obtain the powder. Further, 5 g of the obtained powder was weighed and taken out, and liquid treatment was performed using an HF aqueous solution having a concentration of 3% by weight for 1 hour. After the liquid treatment, the filtered and separated solid portion was dried at 120° C. for 3 hours or longer to obtain an electrode active material.[Comparative Example 2]An electrode active material was obtained in the same manner as in Comparative Example 1, except that the metal Li and Si powder were used in a molar ratio of 4.75:1 using the powder of porous Si, and heating was performed under an Ar atmosphere, at 400° C., and for 40 hours in a heating furnace using the powder of Na-Si alloy.[Example 1]An electrode active material was obtained in the same manner as in Comparative Example 1 except that the metal Li and Si powder were used in the molar ratio of 4.75:1 upon preparation of the powder of porous Si, and the treatment time was changed to 3 hours upon liquid treatment with the HF aqueous solution.[Example 2]An electrode active material was obtained in the same manner as in Comparative Example 1 except that the metal Li and Si powder were used in the molar ratio of 4.75:1 upon preparation of the powder of porous Si, and the treatment time was changed to 5 hours upon liquid treatment with the HF aqueous solution.[Example 3]An electrode active material was obtained in the same manner as in Comparative Example 1, except that the treatment time was changed to 5 hours upon liquid treatment with the HF aqueous solution.[Comparative Example 3]An electrode active material was obtained in the same manner as in Comparative Example 1, except that the metal Li and Si powder were used in the molar ratio of 4.75:1 using the porous Si powder, the concentration was changed to 1 % by weight using the liquid treatment with the HF aqueous solution, and the treatment time was changed to 5 hours.[Comparative Example 4]An electrode active material was obtained in the same manner as in Comparative Example 1 except that the metal Li and Si powder were used in the molar ratio of 4.75:1 upon preparation of the powder of porous Si, and the treatment time was changed to 24 hours upon liquid treatment with the HF aqueous solution.[Comparative Example 5]Crystal Si (SIEPB23, manufactured by Kojundo Chemical Laboratory Co., Ltd.) was prepared, and sputtering was performed by mechanical grinding. Specifically, 1 g of crystal Si and 53 g of zirconia balls having a diameter of φ1 mm were placed in a container and sealed, and mechanical milling was performed using a planetary ball mill (from Fritsch) at 200 U / min and 3 hours. Thereafter, the liquid treatment was preformed using an aqueous HF solution having a concentration of 3% by weight. After the liquid treatment, the filtered and separated solid portion was dried at 120° C. for 3 hours or longer to obtain an electrode active material. The conditions of liquid treatment to the electrode active materials in Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 1. [Table 1] Table 1] [Table 1] Table 1]Comparative Example 131Clathrate15Comparative Example 231Clathrate13Example 133Clathrate16Example 235Clathrate13Example 335Clathrate12Comparative Example 315Clathrate14Comparative Example 4324Clathrate16Comparative Example 535Diamond0[Evaluation]<XRD Measurement>On the electrode active materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4, X-ray diffraction measurement (XRD) was performed using CuKα radiation, respectively. As a result, it was confirmed that all the electrode active materials had the type II silicon clathrate crystal phase as the main phase.In the type II silicon clathrate crystal phase, an intensity of the peak A in the vicinity of 2θ=20.09° was regarded as I A and an intensity of the peak B in the vicinity of 2θ=31.72° was regarded as I B. In addition, the maximum intensity at 2θ=22° to 23° was regarded as I M and I / I Am and I / I BM were obtained. As a result, I / I Am was larger than 1 and I / I BM was larger than 1 in all the electrode active materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4.Also, in Examples 1 to 3 and Comparative Examples 1 to 4, the ratio of the type I silicon clathrate crystal phase before the liquid treatment with the HF aqueous solution was obtained by a RIR (Reference Intensity Ratio) method. The results are shown in Table 1. As shown in Table 1, it was confirmed that the precursor active material before the liquid treatment with the HF aqueous solution had a crystal phase of the type I silicon clathrate crystal phase. In addition, as shown in FIG. 4, it was confirmed that the crystal phase disappeared from the type I silicon clathrate crystal phase before and after the liquid treatment with the HF aqueous solution.< Of Void Portion>The void fractions of the electrode active materials obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were obtained. Specifically, the void fraction P 1 having a pore diameter of 5 nm or less, the void fraction P 2 having a pore diameter of 10 nm or less, and the void fraction P 3 having a pore diameter of 100 nm or less were obtained using a highly accurate gas absorption amount measurement apparatus (BELSORP MAXII). The results are shown in Table 2.<Specific Measurement of Surface>The BET specific surface area of the electrode active materials obtained in Examples 1 to 3 and Comparative Examples 1 to 5 was each determined using the specific surface area measuring apparatus. The results are shown in Table 2. [Table 2] [Table 2]Comparative Example 10,00800,01950,39040,92,0554,6Comparative Example 20,01360,08540,25315,95,3863,0Example 10,0230,0400,3357,56,9764,7Example 20,0350,0580,3860,39,2180,4Example 30,02570,04000,3264,28,0252,5Comparative Example 30,01460,01650,23288,46,2861,5Comparative Example 40,00030,00540,1025,90,3163Comparative Example 50,00130,03670,4733,50,2748As shown in Table 2, it was confirmed that the void ratio P 1 having a pore diameter of 5 nm or less was larger in the electrode active materials obtained in Examples 1 to 3 than in the electrode active materials obtained in Comparative Examples 1 to 5. The crystal phase of the type I silicon clathrate crystal phase is more easily soluble in the HF aqueous solution than the crystal phase of the type II silicon clathrate, and thus it was presumed that the type I silicon clathrate crystal phase disappeared due to the liquid treatment with the HF aqueous solution and the void ratio P 1 having the pore diameter of 5 nm or less increased.< Of All All Solid State Batteries>Using the electrode active materials obtained in Examples 1 to 3 and Comparative Examples 1 and 2 as the anode active material, an all-solid battery was produced. The method for preparation was as follows.(1) Manufacturing AnodesThe obtained electrode active material, a sulfide solid electrolyte (LiS PS 225- based glass ceramic), a conductive material (VGCF), a butyl butyrate solution containing a PVDF-based binder in a ratio of 5 wt %, and butyl butyrate were added to a container made of polypropylene and stirred for 30 seconds with an ultrasonic dispersion device (UH-50 from SMT Corporation). Then, the container was shaken for 30 minutes with a shaker (TTM-1 manufactured by SIBATA SCIENTIFIC TECHNOLOGY LTD.). The product acted on an anodic current collector (Cu foil of UACJ) by a blade method using an applicator and was dried on a hot plate at 100° C. for 30 minutes. Thus, an anode comprising a current collector and an anode layer was obtained.(2) Manufacturing the CathodeA cathode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2, average particle diameter 6 μm), a sulfide solid electrolyte (Li S-P S 225- based glass ceramic), a conductive material (VGCF), a butyl butyrate solution containing a PVDF-based binder in a ratio of 5 wt %, and butyl butyrate solution were added to a polypropylene container and shaken for 30 seconds with an ultrasonic disperser (UH-50 from SMT Corporation). Then, the container was shaken for 3 minutes with a shaker (TTM-1 by SIBATA SCIENTIFIC TECHNOLOGY LTD.), further shaken for 30 seconds with the ultrasonic disperser, and then shaken for 3 minutes with the shaker. The product acted on a cathode current collector (Al foil of SHOWA DENKO K.K.) by a blade method using an applicator and was dried on a hot plate at 100°C for 30 minutes. Thus, a cathode comprising a cathode current collector and a cathode layer was obtained. Incidentally, the area of the cathode was made smaller than the area of the anode.(3) Manufacturing of solid electrolyte layerA sulfide solid electrolyte (LiS-PS 225- based glass ceramic), a heptane solution containing a butylene rubber based binder in a ratio of 5 wt %, and heptane were added to a container made of polypropylene and stirred for 30 seconds with an ultrasonic disperser (UH-50 from SMT Corporation). Then, the container was shaken for 30 minutes with a shaker (TTM-1 manufactured by SIBATA SCIENTIFIC TECHNOLOGY LTD.). The product acted on a peel (Al) film by a blade method using an applicator and was dried on a hot plate at 100°C for 30 minutes. In this way, a transfer member having the peel sheet and the solid electrolyte layer was obtained.(4) Manufacturing of all solid batteriesA solid electrolyte layer for adhesion was applied on the cathode layer and installed in a rolling machine, then pressed at 100 kN / cm and 165° C. In this way, a first layered body was obtained.Then, the anode was set in the roll pressing machine and pressed at 60 kN / cm and 25° C. In this way, a pressed anode was obtained. Thereafter, in order from the anode layer side, the solid electrolyte layer for joining and the transfer member were applied. At this time, the solid electrolyte layer for connection and the solid electrolyte layer in the transfer member were deposited so as to face each other. The obtained laminated body was installed in a planar uniaxial pressing machine and pressed at 100 MPa and 25° C. for 10 seconds. Thereafter, the peel off film was peeled off from the solid electrolyte layer. In this way, a second layered body was obtained.Subsequently, the solid electrolyte layer for adhesion in the first laminate and the solid electrolyte layer in the second laminate were coated so as to face each other, installed in a planar uniaxial pressing machine, and pressed at 200 MPa and 120° C. for 1 minute. Thus, a solid battery was obtained.(5) Measurement of Void Content and Volume Expansion RatioThe void ratio of the pressed anode was obtained. Specifically, the void ratio Q 1 having a pore diameter of 5 nm or less, the void ratio Q 2 having a pore diameter of 10 nm or less, and the void ratio Q 3 having a pore diameter of 100 nm or less were obtained using a highly accurate gas absorption amount measuring apparatus (BELSORP MAXII from microtrac bel). The results are shown in Table 3. In addition, the obtained all solid battery was charged, and the volume expansion ratio was measured. The test conditions were the holding pressure (constant ratio) of 5 MPa, the charge at 0.1 C, and the cut-off voltage of 4.55 V. The holding pressure at 4.55 V was measured, the amount of the holding pressure increase against the state before charging was obtained, and the ratio of the volume expansion was obtained. The results are shown in Table 3. Incidentally, the results of the volume expansion ratio in Table 3 are the relative values when the result of Comparative Example 1 is regarded as 100. Also, the changes of the void ratio by pressing are shown in Table 4. [Table 3] [Table 3]Comparative Example 10,00480,01040,08646,25,57100Comparative Example 20,00770,03510,08721,98,8582Example 10,01320,02320,0973156,913,5661Example 20,02330,03230,119172,119,5748Example 30,01550,02120,0937173,116,5452 [Table 4][Table 4]Comparative Example 1605322Comparative Example 2574134Example 1575829Example 2675631Example 3605329As shown in Table 3, it was confirmed that the void ratio Q 1 having a pore diameter of 5 nm or less was larger in the electrode active materials obtained in Examples 1 to 3 than in the electrode active materials obtained in Comparative Examples 1 and 2. As shown in Table 4, it was also confirmed that Q 1 / P 1 was larger than Q 2 / P 2, and that the cavity having a pore diameter of 5 nm or less could not be easily crushed by pressing. As shown in Table 3, it was also confirmed that the ratio of the volume expansion in Examples 1 to 3 was decreased as compared with Comparative Examples 1 and 2. In particular, the volume expansion ratio of Examples 2 and 3 was significantly reduced as compared with Comparative Example 1.Reference Character List1 Cathode layer 2 Anode layer 3 Electrolyte layer 4 Cathode current collector 5 Anode current collector 10 BatteryReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 2023-044620

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Claims

An electrode active material characterized by comprising a type II silicon clathrate crystal phase, wherein a void is contained within a primary particle; and a void ratio P 1 of a void having a pore diameter of 5 nm or less is 0.015 cm 3 / g or more and 0.05 cm 3 / g or less.The electrode active material according to claim 1, characterized in that a ratio of the void fraction P 1 to a void fraction P 2 of a void having a pore diameter of 10 nm or less, that is, P 1 / P 2, 50 % or more.The electrode active material according to claim 1 or 2, characterized in that a ratio of the void fraction P 1 to a void fraction P 3 of a void having a pore diameter of 100 nm or less, that is, P 1 / P 3, 6,5 % or more.The electrode active material according to any one of claims 1 to 3, characterized in that the electrode active material contains the type II silicon clathrate crystal phase as a main phase.An electrode layer for use in a battery, the electrode layer characterized by comprising: an electrode active material having a type II silicon clathrate crystal phase and a void within a primary particle, wherein a void ratio Q 1 of a void having a pore diameter of 5 nm or less is 0.008 cm 3 / g or more and 0.04 cm 3 / g or less.The electrode layer according to claim 5, characterized in that a ratio of the void fraction Q 1 to a void fraction Q 2 of a void having a pore diameter of 10 nm or less, that is, Q 1 / Q 2, 50 % or more.The electrode layer according to claim 5 or 6, characterized in that a ratio of a void fraction Q 1 to a void fraction Q 3 of a void having a pore diameter of 100 nm or less, that is, Q 1 / Q 3, 10 % or more is.A battery comprising a cathode layer, an anode layer and an electrolyte layer applied between the cathode layer and the anode layer, characterized in that the cathode layer or the anode layer is the electrode layer according to any one of claims 5 to 7.A method for producing an electrode active material, the method being characterized by comprising: an alloying step of obtaining a Na-Si alloy by reacting a Na source and a Si source; a firing step of firing the Na-Si alloy to reduce the amount of Na in the Na-Si alloy and form a precursor active material having a type II silicon clathrate crystal phase; and a liquid treatment step of performing liquid treatment of the precursor active material using hydrofluoric acid, wherein a hydrogen fluoride concentration in the hydrofluoric acid is 3% by weight or more; and a treatment time in the liquid treatment step is 3 hours or more and less than 24 hours.The method for producing an electrode active material according to claim 9, characterized in that in the electrode active material, a void fraction P 1 of a void having a pore diameter of 5 nm or less is 0.015 cm 3 / g or more and 0.05 cm 3 / g or less.

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