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

Abstract

The main purpose of the present disclosure is to provide an electrode active material having little change in volume due to charge and discharge. In the present disclosure, the problem is solved by providing an electrode active material containing Si, having Si-H bonds present on the surface thereof, and having a ratio of the amount of hydrogen (wt%) to the BET specific surface area (m2 / g) of greater than 0.0034.

Description

Technical Field The present disclosure relates to an electrode active material, an electrode mixture, a battery, and methods for manufacturing them. Background Art In recent years, the development of batteries has been actively carried out. For example, in the automotive industry, the development of batteries for electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), or hybrid vehicles (HEVs) is being promoted. In addition, as an electrode active material for batteries, Si (silicon) is known. For example, Patent Document 1 discloses an electrode active material having a crystalline phase of a type II silicon clathrate and having voids inside primary particles. Prior Art Documents Patent Document 1: Japanese Unexamined Patent Application Publication No. 2023-044620 Summary of the Invention Si has a large theoretical capacity and is effective for increasing the energy density of batteries. On the other hand, Si has a large volume change during charge and discharge. If the volume change during charge and discharge is large, there are problems such as the function of the electrode being easily degraded during repeated charge and discharge. The present disclosure has been made in view of the above actual situation, and a main object thereof is to provide an electrode active material with a small volume change caused by charge and discharge.

[0001] An electrode active material containing Si, Si-H bonds are present on the surface of the above electrode active material, The ratio of the hydrogen amount (m 2 / g) to the BET specific surface area (wt%) is greater than 0.0034.

[0002] For the electrode active material according to [1], the above ratio is 0.0039 or more.

[0003] For the electrode active material according to [1] or [2], the above ratio is 0.05 or less.

[0004] For the electrode active material according to any one of [1] to [3], the above BET specific surface area is 50 m 2 / g or more.

[0005] For the electrode active material according to any one of [1] to [4], the above hydrogen amount is 0.20 wt% or more.

[0006] For the electrode active material according to any one of [1] to [5], the above ratio is 0.0060 or more, and the above hydrogen amount is 0.40 wt% or more.

[0007] The electrode active material according to any one of [1] to [5], the above ratio is greater than 0.0034 and less than 0.0046, and the above hydrogen content is 0.30% by weight or less.

[0008] The electrode active material according to any one of [1] to [7], the above electrode active material has a crystalline phase of type II silicon clathrate as the main phase.

[0009] The electrode active material according to any one of [1] to [8], the above electrode active material has voids inside the primary particles.

[0010] The electrode active material according to [9], the proportion of the above voids is 4% or more and 40% or less.

[0011] An electrode mixture, comprising: the electrode active material according to any one of [1] to

[10] , and at least one selected from a conductive material and a binder.

[0012] The electrode mixture according to

[11] , the above electrode mixture further contains a solid electrolyte.

[0013] The electrode mixture according to

[12] , the above solid electrolyte contained in the above electrode mixture is a sulfide solid electrolyte.

[0014] A battery, having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the above positive electrode layer and the above negative electrode layer, The above positive electrode layer or the above negative electrode layer contains the electrode mixture according to any one of

[11] to

[13] .

[0015] The battery according to

[14] , the above negative electrode layer contains the above electrode mixture.

[0016] The battery according to

[14] or

[15] , the above electrolyte layer contains a solid electrolyte.

[0017] The battery according to

[16] , the above solid electrolyte contained in the above electrolyte layer is a sulfide solid electrolyte, The thickness of the above electrolyte layer is 0.1 μm or more and 100 μm or less.

[0018] The battery according to any one of

[14] to

[17] , the above positive electrode layer contains a rock salt layer-structured active material.

[0019] A method for manufacturing an electrode active material, having an alloying step, a firing step, and a liquid treatment step, In the above alloying step, a Na source and a Si source are reacted to obtain a Na-Si alloy, In the above firing process, the above Na-Si alloy is fired to reduce the amount of Na in the above Na-Si alloy, forming a precursor active material having a crystalline phase of a type-II silicon clathrate. In the above liquid treatment process, the above precursor active material is subjected to liquid treatment with hydrofluoric acid to obtain an electrode active material, and in the above liquid treatment process, the liquid treatment conditions are adjusted so that the proportion of the hydrogen amount (wt%) relative to the BET specific surface area (m 2 / g) is greater than 0.0034.

[0020] According to the method for manufacturing an electrode active material described in

[19] , the concentration of hydrogen fluoride in the above hydrofluoric acid is 3 wt% or more, the treatment time in the above liquid treatment process is 3 hours or more.

[0021] A method for manufacturing an electrode active material, having an alloying process and a firing process, in the above alloying process, a Na-Si alloy is obtained by reacting a Na source and a Si source, in the above firing process, the above Na-Si alloy is fired to reduce the amount of Na in the above Na-Si alloy, forming an electrode active material having a crystalline phase of a type-II silicon clathrate, and in the above alloying process, metallic Na particles are used as the above Na source.

[0022] According to the method for manufacturing an electrode active material described in

[21] , the average particle size of the above metallic Na particles is 10 μm or less.

[0023] A method for manufacturing an electrode mixture, having a preparation process and a mixing process, in the above preparation process, an electrode active material is prepared by the method for manufacturing an electrode active material described in any one of

[19] to

[22] , in the above mixing process, the above electrode active material and at least one selected from a conductive material and a binder are mixed to obtain an electrode mixture.

[0024] A method for manufacturing a battery, having a preparation process, a mixing process, and an electrode layer forming process, in the above preparation process, an electrode active material is prepared by the method for manufacturing an electrode active material described in any one of

[19] to

[22] , in the above mixing process, the above electrode active material and at least one selected from a conductive material and a binder are mixed to obtain an electrode mixture, in the above electrode layer forming process, an electrode layer is formed using the above electrode mixture. In the present disclosure, an effect of obtaining an electrode active material with a small volume change caused by charge and discharge is achieved. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a schematic perspective view illustrating the crystal phase of Si. Figure 2 It is an explanatory view illustrating the hydrogen termination of the present disclosure. Figure 3 It is a schematic cross-sectional view illustrating the battery of the present disclosure. Figure 4 It is a flowchart illustrating the manufacturing method of the electrode active material of the present disclosure. Figure 5 It is a flowchart illustrating the manufacturing method of the electrode active material of the present disclosure. DESCRIPTION OF REFERENCE NUMERALS 1... positive electrode layer 2... negative electrode layer 3... electrolyte layer 4... positive electrode current collector 5... negative electrode current collector 10... battery DETAILED DESCRIPTION Hereinafter, the electrode active material, electrode binder, battery, and their manufacturing methods of the present disclosure will be described in detail. A. Electrode Active Material The electrode active material of the present disclosure contains Si. Moreover, Si-H bonds exist on the surface of the electrode active material. In addition, in the electrode active material, the proportion of the hydrogen amount (wt%) with respect to the BET specific surface area (m 2 / g) is in a predetermined range. According to the present disclosure, since Si-H bonds exist on the surface of the electrode active material and the proportion of the hydrogen amount with respect to the BET specific surface area is in a predetermined range, an electrode active material with a small volume change caused by charge and discharge is obtained. Here, if the surface of the electrode active material (Si-based active material) is oxidized, the polarity increases, the affinity with the solid electrolyte increases, and the dispersibility becomes high. On the contrary, generally, since the polarity of the conductive material is low, if the surface of the electrode active material (Si-based active material) is oxidized, the dispersibility of the electrode active material and the conductive material decreases. In the electrode layer, usually, the content of the conductive material is less than the content of the solid electrolyte. Therefore, if the dispersibility of the electrode active material and the conductive material decreases, reaction non-uniformity is likely to occur, and it becomes difficult to suppress the volume change caused by charge and discharge. In contrast, in the present disclosure, for example, by hydrogen-terminating the surface of the electrode active material, Si-H bonds are introduced onto the surface of the electrode active material, and the dispersibility of the electrode active material and the conductive material is improved. As a result, the reaction uniformity in the electrode layer is improved, and the volume change caused by charge and discharge can be suppressed. In addition, the electrode active material of the present disclosure has a crystalline phase such as a type-II silicon clathrate. As Figure 1 (a) shows, in the crystalline phase of the type-II silicon clathrate, a polyhedron (cage) containing pentagons or hexagons is formed by a plurality of Si atoms. The polyhedron has a space inside that can accommodate metal ions such as Li ions. By inserting metal ions into this space, volume changes caused by charge and discharge can be suppressed. Especially in a solid-state battery, in order to suppress volume changes caused by charge and discharge, it is generally necessary to apply a high constraint pressure. However, by using the electrode active material of the present disclosure, a reduction in the constraint pressure can be achieved. As a result, enlargement of the constraint jig can be suppressed. On the other hand, as Figure 1 (b) shows, in the crystalline phase of diamond-type silicon, a tetrahedron is formed by a plurality of Si atoms. Since the tetrahedron does not have a space inside that can accommodate metal ions such as Li ions, it is difficult to suppress volume changes caused by charge and discharge in the crystalline phase of diamond-type silicon compared to the crystalline phase of the type-II silicon clathrate. On the other hand, an electrode active material having a crystalline phase of diamond-type silicon has the advantage of being easy to manufacture compared to an electrode active material having a type-II silicon clathrate. In addition, the electrode active material of the present disclosure may also have a crystalline phase of a type-I silicon clathrate. Furthermore, the crystalline phases of the type-I silicon clathrate and the type-II silicon clathrate are sometimes collectively referred to as a silicon clathrate-type crystalline phase. The electrode active material of the present disclosure has Si-H bonds on its surface. The Si-H bonds are formed, for example, by treating the surface of the electrode active material with hydrofluoric acid. As Figure 2 (a) shows, a natural oxide film exists on the surface of the electrode active material (Si-based active material). If the surface of such an electrode active material is treated with hydrofluoric acid, then as Figure 2 (b) shows, the surface of the electrode active material is etched (SiO2 + 6HF(aq) → H2SiF6), and Si combines with H present around it, thereby forming Si-H bonds (hydrogen capping). The presence of Si-H bonds can be confirmed by infrared spectroscopy (IR method). The peak of the Si-H bond usually appears in the range of 2100 cm -1 to 2300 cm -1 . In the present disclosure, the peak of the Si-H bond is sometimes referred to as peak α. On the other hand, the peak of the Si-OH bond usually appears in the range of 3610 cm -1 to 3670 cm -1 . In the present disclosure, the peak of the Si-OH bond is sometimes referred to as peak β. Let the peak intensities of peak α and peak β be I α and I β . The ratio of I α to I β (I α / I β)There is no particular limitation. For example, it can be greater than 0.63, can be 0.65 or more, can be 0.70 or more, or can be 0.80 or more. In the present disclosure, the amount of hydrogen (% by weight) relative to the BET specific surface area (m 2 / g) is greater than 0.0034. The above ratio can be 0.0039 or more, can be 0.0046 or more, can be 0.0050 or more, or can be 0.0060 or more. If the above ratio is too small, it is difficult to improve the dispersibility of the electrode active material and the conductive material. On the other hand, the above ratio is, for example, 0.05 or less, can be 0.04 or less, or can be 0.03 or less. The BET specific surface area of the electrode active material is not particularly limited. For example, it can be 30 m 2 / g or more, can be 40 m 2 / g or more, can be 50 m 2 / g or more, or can be 60 m 2 / g or more. On the other hand, the BET specific surface area of the electrode active material is, for example, 150 m 2 / g or less. In addition, the amount of hydrogen in the electrode active material is, for example, 0.20% by weight or more, can be 0.30% by weight or more, can be 0.40% by weight or more, or can be 0.50% by weight or more. On the other hand, the amount of hydrogen in the electrode active material is, for example, 3.0% by weight or less. In the present disclosure, it can also be that the ratio of the amount of hydrogen (% by weight) relative to the BET specific surface area (m 2 / g) is 0.0060 or more, and the amount of hydrogen in the electrode active material is 0.40% by weight or more. In this case, the volume change caused by charge and discharge can be significantly reduced. In addition, it can also be that the ratio of the amount of hydrogen (% by weight) relative to the BET specific surface area (m 2 / g) is greater than 0.0034 and less than 0.0046, and the amount of hydrogen in the electrode active material is 0.30% by weight or less. In this case, the volume change caused by charge and discharge can also be significantly reduced. The electrode active material has a crystalline phase of, for example, type II silicon clathrate. Among them, the electrode active material preferably has a crystalline phase of type II silicon clathrate as the main phase. The "main phase" means that the peak belonging to this crystalline phase has the largest diffraction intensity among the peaks observed by X-ray diffraction measurement. The proportion of the crystalline phase of type II silicon clathrate contained in the electrode active material is, for example, 80% by weight or more, can be 85% by weight or more, can be 90% by weight or more, or can be 95% by weight or more. In addition, the proportion of the crystalline phase of type II silicon clathrate contained in the electrode active material can be 100% by weight, or can be less than 100% by weight. The proportion of the crystalline phase can be obtained by performing Rietveld analysis on the XRD measurement results and using the analysis results and the RIR method (Reference IntenSity Ratio method). The crystalline phase of type II silicon clathrate generally belongs to the space group (Fd-3m). In X-ray diffraction measurement using CuKα radiation, the crystalline phase of type II silicon clathrate has typical peaks at positions of 2θ = 20.09°, 21.00°, 26.51°, 31.72°, 36.26°, and 53.01°. These peak positions can vary before and after in the range of ±0.50°, can vary before and after in the range of ±0.30°, or can vary before and after in the range of ±0.10°. In the crystalline phase of type II silicon clathrate, the peak located at 2θ = 20.09° ± 0.50° is designated as peak A, and the peak located at 2θ = 31.72° ± 0.50° is designated as peak B. In addition, the intensity of peak A is designated as I A , and the intensity of peak B is designated as I B . In addition, the maximum intensity at 2θ = 22° to 23° is designated as I M . At 2θ = 22° to 23°, it is usually a range where no peaks of the crystalline phase related to Si appear, so it can be used as a reference. I A / I M The value is preferably greater than 1. When the value of I A / I M is 1 or less, it can be judged that the crystalline phase of type II silicon clathrate is substantially not formed. The value of I A / I M is, for example, 1.75 or more, and can also be 1.80 or more. On the other hand, the value of I A / I M is, for example, 10 or less, and can also be 5 or less. I B / I M The value is preferably greater than 1. When the value of I B / I MWhen the value is less than 1, it can be determined that the crystalline phase of the type-II silicon clathrate is not substantially formed. I B / I M The value is, for example, 1.35 or more, and can also be 1.40 or more. On the other hand, I B / I M the value is, for example, 7 or less, and can also be 4 or less. The electrode active material of the present disclosure may or may not have a crystalline phase of type-I silicon clathrate. "Not having a crystalline phase" means that no peak of this crystalline phase can be confirmed in X-ray diffraction measurement. On the other hand, the electrode active material of the present disclosure may also have a crystalline phase of type-I silicon clathrate as the main phase. The crystalline phase of type-I silicon clathrate generally belongs to the space group (Pm-3n). In X-ray diffraction measurement using CuKα radiation, the crystalline phase of type-I silicon clathrate has typical peaks at positions of 2θ = 19.44°, 21.32°, 30.33°, 31.60°, 32.82°, 36.29°, 52.39°, and 55.49°. These peak positions can vary before and after in the range of ±0.50°, can vary before and after in the range of ±0.30°, and can also vary before and after in the range of ±0.10°. The electrode active material of the present disclosure may or may not have a crystalline phase of diamond-type silicon. On the other hand, the electrode active material of the present disclosure may also have a crystalline phase of diamond-type silicon as the main phase. In addition, in X-ray diffraction measurement using CuKα radiation, the crystalline phase of diamond-type silicon has typical peaks at positions of 2θ = 28.44°, 47.31°, 56.10°, 69.17°, and 76.37°. These peak positions can vary before and after in the range of ±0.50°, can vary before and after in the range of ±0.30°, and can also vary before and after in the range of ±0.10°. When observing a peak C at 2θ = 28.44° ± 0.50° as the peak of the crystalline phase of diamond-type silicon, the intensity of peak C is set as I C 。I A / I C For example, it is greater than 1, can be 1.5 or more, can be 2 or more, and can also be 3 or more. I B / I C The preferred range of is the same as that of I A / I C the preferred range of. The composition of the electrode active material of the present disclosure is not particularly limited, but is preferably composed of Na x Si 136It is represented by (0 ≤ x ≤ 24). x can be 0 or greater than 0. On the other hand, x can be 20 or less, 10 or less, or 5 or less. The composition of the electrode active material can be determined, for example, by EDX, XRD, XRF, ICP, or atomic absorption spectrometry. Furthermore, an inevitable oxide film is generally formed on the surface of the electrode active material. Therefore, the electrode active material may also contain a trace amount of O (oxygen). In addition, the electrode active material may also contain a trace amount of C (carbon) from the manufacturing process. The electrode active material of the present disclosure may be primary particles or secondary particles formed by aggregation of primary particles. The average particle diameter (D 50 ) is not particularly limited. For example, it is 0.1 μm or more and 50 μm or less, and may also be 0.5 μm or more and 30 μm or less. The average particle diameter (D 50 ) can be calculated, for example, based on measurement by a scanning electron microscope (SEM). The electrode active material preferably has voids inside the primary particles. The proportion of voids (void fraction) in the primary particles is, for example, 4% or more and may also be 10% or more. In addition, the above void fraction is, for example, 40% or less and may also be 20% or less. The void fraction can be determined, for example, in the following order. First, the electrode layer containing the electrode active material is processed by ion milling to expose the cross section. Then, the cross section is observed with an SEM (scanning electron microscope) to obtain a photograph of the particles. Using image analysis software, the silicon part and the void part are strictly distinguished based on the obtained photograph and binarized. The areas of the silicon part and the void part are determined, and the void fraction (%) is calculated from the following formula. Void fraction (%) = 100 × (void part area) / ((silicon part area) + (void part area)) The electrode active material preferably has voids with a pore diameter of 5 nm or less. The void volume P1 of the voids with a pore diameter of 5 nm or less is, for example, 0.015 cc / g or more, may be 0.020 cc / g or more, or may also be 0.023 cc / g or more. On the other hand, the void volume P1 is, for example, 0.05 cc / g or less, may be 0.04 cc / g or less, or may also be 0.035 cc / g or less. The void volume in the present disclosure refers to the cumulative pore volume and can be determined, for example, by BET measurement, gas adsorption method, mercury porosimetry, 3D-SEM, or 3D-TEM. The electrode active material preferably has many voids with a pore diameter of 10 nm or less. The void volume P2 of the voids with a pore diameter of 10 nm or less is, for example, 0.03 cc / g or more, may be 0.035 cc / g or more, or may be 0.04 cc / g or more. On the other hand, the void volume P2 is, for example, 0.08 cc / g or less, may be 0.07 cc / g or less, or may be 0.06 cc / g or less. In addition, the ratio (P1 / P2) of the void volume P1 to the void volume P2 is, for example, 50% or more, may be 55% or more, or may be 57% or more. On the other hand, P1 / P2 is, for example, 80% or less, may be 70% or less, or may be 65% or less. The electrode active material preferably has many voids with a pore diameter of 100 nm or less. The void volume P3 of the voids with a pore diameter of 100 nm or less is, for example, 0.1 cc / g or more, may be 0.2 cc / g or more, or may be 0.32 cc / g or more. On the other hand, the void volume P3 is, for example, 0.5 cc / g or less, may be 0.45 cc / g or less, or may be 0.38 cc / g or less. In addition, the ratio (P1 / P3) of the void volume P1 to the void volume P3 is, for example, 6.0% or more, may be 6.5% or more, or may be 6.9% or more. On the other hand, P1 / P3 is, for example, 15% or less, may be 12% or less, or may be 10% or less. The electrode active material of the present disclosure is generally used in a battery. The electrode active material of the present disclosure may be a negative electrode active material or a positive electrode active material, but the former is preferred. As a method for manufacturing the electrode active material, for example, the manufacturing method described in "D. Method for Manufacturing Electrode Active Material" described later can be cited. B. Electrode binder The electrode binder of the present disclosure contains: the above electrode active material, and at least one selected from a conductive material and a binder. According to the present disclosure, by using the above electrode active material, an electrode binder with a small volume change caused by charge and discharge is obtained. The electrode binder contains an electrode active material and at least one selected from a conductive material and a binder. Regarding the electrode active material, it is the same as the content described in the above "A. Electrode Active Material". The electrode active material may be a negative electrode active material or a positive electrode active material, but the former is preferred. That is, the electrode binder may be a negative electrode binder or a positive electrode binder, but the former is preferred. The proportion of the electrode active material in the electrode mixture is, for example, 20% by weight or more, may be 30% by weight or more, or may be 40% by weight or more. If the proportion of the electrode active material is too small, sufficient energy density may not be obtained. On the other hand, the proportion of the electrode active material is, for example, 80% by weight or less, may be 70% by weight or less, or may be 60% by weight or less. If the proportion of the electrode active material is too large, the ionic conductivity and electronic conductivity in the electrode mixture may relatively decrease. The electrode mixture contains at least one of a conductive material and a binder. As the conductive material, for example, carbon materials, metal particles, and conductive polymers can be cited. As the carbon materials, for example, particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), carbon fibers, carbon nanotubes (CNT), and fibrous carbon materials such as carbon nanofibers (CNF) can be cited. In addition, as the binder, for example, rubber-based binders and fluoride-based binders can be cited. The electrode mixture may further contain a solid electrolyte. As the solid electrolyte, inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, and organic polymer electrolytes such as polymer electrolytes can be cited. As the sulfide solid electrolyte, for example, a solid electrolyte containing Li element, X element (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In), and S element can be cited. In addition, the sulfide solid electrolyte may further contain at least one of O element and halogen element. As the halogen element, for example, F element, Cl element, Br element, and I element can be cited. The sulfide solid electrolyte may be glass (amorphous) or glass-ceramics. As the sulfide solid electrolyte, for example, Li2S-P2S5, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-SiS2, Li2S-GeS2, Li2S-P2S5-GeS2 can be cited. In addition, the electrode mixture may further contain a dispersion medium. C. Battery Figure 3 is a schematic cross-sectional view illustrating the battery of the present disclosure. Figure 3 The battery 10 shown has a positive electrode layer 1, a negative electrode layer 2, an electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive electrode current collector 4 for collecting current of the positive electrode layer 1, and a negative electrode current collector 5 for collecting current of the negative electrode layer 2. In the present disclosure, the positive electrode layer 1 or the negative electrode layer 2 contains the electrode mixture described in the above "B. Electrode Mixture". According to the present disclosure, by using the above electrode mixture, a battery with a small volume change caused by charge and discharge is obtained. As described above, the electrode mixture can be a negative electrode mixture or a positive electrode mixture, but the former is preferred. Hereinafter, the details of the battery in the case where the electrode mixture is a negative electrode mixture will be described. 1. Negative electrode layer The negative electrode layer of the present disclosure contains the above electrode mixture (negative electrode mixture). Regarding the electrode mixture, it is the same as the content described in the above "B. Electrode mixture", so the description here is omitted. In addition, the negative electrode layer may also contain an electrolyte as needed. Regarding the electrolyte, it is the same as the content described in "3. Electrolyte layer". The thickness of the negative 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, or may be 0.1 μm or more and 100 μm or less. In addition, as a method for forming the negative electrode layer, for example, a method of applying the electrode mixture (negative electrode mixture) to the negative electrode current collector can be cited. 2. Positive electrode layer The positive electrode layer is a layer containing at least a positive electrode active material. In addition, the positive electrode layer may also contain at least one of an electrolyte, a conductive material, and a binder as needed. As the positive electrode active material, for example, an oxide active material can be cited. As the oxide active material, for example, rock salt layered active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., spinel-type active materials such as LiMn2O4, Li4Ti5O 12 , Li(Ni 0.5 Mn 1.5 )O4, etc., and olivine-type active materials such as LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4 can be cited. A coating containing a Li-ion conductive oxide can also be formed on the surface of the oxide active material. Because it can inhibit the reaction between the oxide active material and the solid electrolyte (especially the sulfide solid electrolyte). As the Li-ion conductive oxide, for example, LiNbO3 can be cited. The thickness of the coating is, for example, 1 nm or more and 30 nm or less. In addition, as the positive electrode active material, for example, Li2S can also be used. As the shape of the positive electrode active material, for example, a particle shape can be cited. The average particle size (D 50 ) of the positive electrode active material is not particularly limited, for example, it is 10 nm or more, and may also be 100 nm or more. On the other hand, the average particle size (D 50 ) of the positive electrode active material is, for example, 50 μm or less, and may also be 20 μm or less. Regarding the electrolyte for the positive electrode layer, it is the same as that described in "3. Electrolyte layer". In addition, regarding the conductive material and binder for the positive electrode layer, they are the same as those described in the above "B. Electrode binder", so the description here is omitted. The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less, can be 0.1 μm or more and 500 μm or less, or can be 0.1 μm or more and 100 μm or less. 3. Electrolyte layer The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer and contains at least an electrolyte. The electrolyte can be a solid electrolyte or a liquid electrolyte (electrolyte solution). Regarding the solid electrolyte, it is the same as that described in the above "B. Electrode binder", so the description here is omitted. On the other hand, the electrolyte solution preferably contains a supporting salt and a solvent. As the supporting salt (lithium salt) of the electrolyte solution having lithium ion conductivity, for example, inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAsF6, etc., and organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, LiC(CF3SO2)3, etc. can be cited. As the solvent for the electrolyte solution, for example, cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc., and chain-like esters (chain-like carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be cited. The electrolyte solution preferably contains two or more solvents. The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less, can be 0.1 μm or more and 500 μm or less, or can be 0.1 μm or more and 100 μm or less. 4. Other components The battery of the present disclosure preferably has a positive electrode current collector for collecting current from the positive electrode layer and a negative electrode current collector for collecting current from the negative electrode layer. As the material of the positive electrode current collector, for example, SUS, aluminum, nickel, iron, titanium, and carbon can be cited. On the other hand, as the material of the negative electrode current collector, for example, SUS, copper, nickel, and carbon can be cited. The battery of the present disclosure may also have a restraining jig, and the restraining jig applies a restraining pressure to the positive electrode layer, the electrolyte layer, and the negative electrode layer in the thickness direction. Especially when the electrolyte layer is a solid electrolyte layer, in order to form good ion conduction paths and electron conduction paths, it is preferable to apply a restraining pressure. The restraining pressure is, for example, 0.1 MPa or more, can be 1 MPa or more, or can be 5 MPa or more. On the other hand, the restraining pressure is, for example, 100 MPa or less, can be 50 MPa or less, or can be 20 MPa or less. 5. Battery The type of the battery of the present disclosure is not particularly limited, and typically it is a lithium ion battery. In addition, the battery of the present disclosure may be a liquid battery in which the electrolyte layer contains an electrolytic solution, or may be a solid battery in which the electrolyte layer contains a solid electrolyte. The solid battery may be a semi-solid battery or a all-solid battery. In the present disclosure, a semi-solid battery is a battery in which the electrolyte layer has an inorganic solid electrolyte and a liquid component (such as an ionic liquid). In the present disclosure, an all-solid battery is a battery in which the electrolyte layer has only an inorganic solid electrolyte as the electrolyte. In addition, the battery in the present disclosure may be a primary battery or a secondary battery, and a secondary battery is preferred. Because it can be charged and discharged repeatedly, it is useful as, for example, a vehicle-mounted battery. As uses of the battery, for example, power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles can be cited. It is particularly preferably used as a drive power source for a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), or a battery electric vehicle (BEV). In addition, the battery can be used as a power source for a moving body other than a vehicle (such as a railway, a ship, and an aircraft), or can be used as a power source for an electrical product such as an information processing device. D. Method for manufacturing electrode active material The method for manufacturing the electrode active material of the present disclosure can be roughly divided into two embodiments. 1. First embodiment Figure 4 is a flowchart illustrating the method for manufacturing the electrode active material of the first embodiment. In Figure 4 the manufacturing method shown, first, a Na source and a Si source are reacted to obtain a Na-Si alloy (alloying step). Next, 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 crystalline phase of type II silicon clathrate (firing step). Next, the precursor active material is subjected to liquid treatment using hydrofluoric acid to obtain an electrode active material (liquid treatment step). In the liquid treatment step, the liquid treatment conditions are adjusted so that the ratio of the hydrogen amount (wt%) to the BET specific surface area (m 2 / g) is greater than 0.0034. According to the first embodiment, by performing the liquid treatment step, an electrode active material with a small volume change caused by charge and discharge can be obtained. (1) Alloying step The alloying step of the first embodiment is a step of reacting a Na source and a Si source to obtain a Na-Si alloy. The Si source is particles containing at least Si. The Si source can be elemental Si or an alloy of Si and other metals. When the Si source is an alloy, the alloy preferably contains Si as the main component. The proportion of Si in the alloy is, for example, 50 atomic% or more, can be 70 atomic% or more, or can be 90 atomic% or more. The Si source is preferably porous silicon having many voids inside the primary particles. As a method for manufacturing the Si source (porous silicon), for example, a method of manufacturing an alloy of Li and Si (Li-Si alloy) and then removing Li from the Li-Si alloy can be cited. The Li-Si alloy is obtained, for example, by mixing Li and Si. The ratio of Li to Si (Li / Si) is, for example, 1.0 or more, can be 2.0 or more, can be 3.0 or more, or can be 4.0 or more. On the other hand, Li / Si is, for example, 8.0 or less. As a method for removing Li from the Li-Si alloy, for example, a method of reacting the Li-Si alloy with a Li extraction material can be cited. As the Li extraction material, for example, alcohols such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol; acids such as acetic acid, formic acid, propionic acid, and oxalic acid can be cited. In addition, as a method for manufacturing the Si source (porous silicon), for example, a method of manufacturing an alloy of Mg and Si (Mg-Si alloy) and then removing Mg from the Mg-Si alloy can be cited. The Mg-Si alloy is obtained, for example, by heating a mixture of Mg and Si. The ratio of Mg to Si (Mg / Si) is, for example, 1.0 or more, can be 1.5 or more, or can be 2.0 or more. On the other hand, Mg / Si is, for example, 6.0 or less. As a method for removing Mg from the Mg-Si alloy, for example, a method of heating the Mg-Si alloy in an inert gas atmosphere containing oxygen to convert Mg in the Mg-Si alloy into MgO and then removing MgO with an acid solution can be cited. As the acid solution, for example, an aqueous solution containing hydrochloric acid (HCl) and hydrogen fluoride (HF) can be cited. In addition, as a method for manufacturing the Si source (porous silicon), for example, a method of manufacturing an alloy of Mg and Si (Mg-Si alloy), then removing Mg from the Mg-Si alloy, then manufacturing an alloy of Si and Li from which Mg has been removed (Li-Si alloy), and then removing Li from the Li-Si alloy can be cited. On the other hand, the Na source contains at least Na. As the Na source, for example, metallic Na, NaH, and a metallic Na dispersion in which particles of metallic Na are dispersed in oil can be cited. As a method for obtaining a Na-Si alloy by reacting a Na source and a Si source, for example, a method of heating a mixture containing a Na source and a Si source can be cited. The heating temperature is, for example, 300 °C or higher, can be 310 °C or higher, can be 320 °C or higher, or can be 340 °C or higher. On the other hand, the heating temperature is, for example, 800 °C or lower, can be 600 °C or lower, or can be 450 °C or lower. In addition, the alloying step is preferably carried out in an inert atmosphere such as an Ar atmosphere. The Na-Si alloy preferably has a Zintl phase. In X-ray diffraction measurement using CuKα radiation, the Zintl phase has typical peaks at positions of 2θ = 16.10°, 16.56°, 17.64°, 20.16°, 27.96°, 33.60°, 35.68°, 40.22°, 41.14°. These peak positions can vary before and after in the range of ±0.50°, or can also vary before and after 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 preferably consists of Na z Si 136 The composition (121 ≤ z ≤ 151) represents. z can be 126 or higher, or can be 131 or higher. On the other hand, z can also be 141 or lower. Other elements other than Na and Si may also be present in the Na-Si alloy. As other elements, for example, Li, K, Rb, Cs, Ba, Ga, Ge can be cited. (2) Firing process The firing process of the first embodiment is a process of firing the above Na-Si alloy to reduce the amount of Na in the above Na-Si alloy and form a precursor active material having a crystalline phase of type II silicon clathrate. 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 higher and 400 °C or lower. On the other hand, the firing time is, for example, 5 hours or longer and 120 hours or shorter. The firing process can be carried out in a reduced-pressure atmosphere or in an atmospheric-pressure atmosphere. In the firing process, it is preferable to use a scavenger that captures Na in the Na-Si alloy. As an example of the scavenger, a Na getter that reacts with the vapor of Na generated from the Na-Si alloy can be cited. The Na getter is, for example, arranged in a state not in contact with the Na-Si alloy. As the Na getter, for example, SiO, MoO3, FeO, Fe3O4 can be cited. In the case of using a Na getter, the firing process is preferably carried out in a reduced-pressure atmosphere. As other examples of the scavenger, a Na scavenger that directly reacts with the Na—Si alloy to receive Na can be cited. The Na scavenger is arranged, for example, in a state of being in contact with the Na—Si alloy. As the Na scavenger, for example, CaCl2, AlF3, CaBr2, CaI2, Fe3O4, FeO, MgCl2, ZnO, ZnCl2, and MnCl2 can be cited. When a Na scavenger is used, the firing step can be carried out in a reduced-pressure atmosphere or in an atmospheric-pressure atmosphere. (3) Liquid treatment step The liquid treatment step of the first embodiment is a step of obtaining an electrode active material by subjecting the above-mentioned precursor active material to liquid treatment with hydrofluoric acid. Hydrofluoric acid refers to an aqueous solution obtained by dissolving hydrogen fluoride (HF) in water. In addition, in the liquid treatment step, the liquid treatment conditions are adjusted so that the proportion of the hydrogen amount (wt%) relative to the BET specific surface area (m 2 / g) is greater than 0.0034. The concentration of hydrogen fluoride in the hydrofluoric acid is, for example, 1 wt%, may be 2 wt% or more, may be 3 wt% or more, may be 4 wt% or more, or may be 5 wt% or more. On the other hand, the concentration of hydrogen fluoride in the hydrofluoric acid is, for example, 10 wt% or less. In addition, the treatment time of the liquid treatment is, for example, 1 hour or more, may be 2 hours or more, may be 3 hours or more, may be 4 hours or more, or may be 5 hours or more. On the other hand, the treatment time of the liquid treatment is, for example, less than 24 hours, may be 15 hours or less, or may be 10 hours or less. The temperature of the liquid treatment is not particularly limited and is, for example, room temperature. As a method of subjecting the precursor active material to liquid treatment with hydrofluoric acid, for example, a method of immersing the precursor active material in hydrofluoric acid and a method of coating the precursor active material with hydrofluoric acid can be cited. (4) Electrode active material The electrode active material obtained through the above-mentioned respective steps has, for example, a crystal phase of a type-II silicon clathrate. In addition, by changing the firing conditions, an electrode active material having a crystal phase of a type-I silicon clathrate can also be obtained. In addition, in the present disclosure, the above-mentioned liquid treatment step can also be performed on a precursor active material having a diamond-type crystal phase. In addition, the surface of the electrode active material has Si—H bonds. The preferred mode of the electrode active material is the same as the content described in the above-mentioned "A. Electrode active material". 2. Second embodiment Figure 5 is a flowchart exemplifying a method for manufacturing an electrode active material of the second embodiment. In Figure 5In the manufacturing method shown, first, a Na source and a Si source are reacted to obtain a Na—Si alloy (alloying step). Next, the Na—Si alloy is fired to reduce the amount of Na in the Na—Si alloy, thereby forming an electrode active material having a crystalline phase of a type-II silicon clathrate (firing step). In the alloying step, metallic Na particles are used as the above-described Na source. According to the second embodiment, by using metallic Na particles as the Na source, an electrode active material with a small volume change caused by charge and discharge can be obtained. (1) Alloying step The alloying step of the second embodiment is a step of reacting a Na source and a Si source to obtain a Na—Si alloy. Moreover, metallic Na particles are used as the Na source. The average particle diameter (D 50 ) is not particularly limited. For example, it may be 10 μm or less, may be 5 μm or less, may be 3 μm or less, or may be 500 nm or less. Regarding the alloying step of the second embodiment, except for using metallic Na particles as the Na source, the content described in the first embodiment above is the same. (2) Firing step The firing step of the second embodiment is a step of firing the above-described Na—Si alloy to reduce the amount of Na in the Na—Si alloy, thereby forming an electrode active material having a crystalline phase of a type-II silicon clathrate. Regarding the firing step, the content described in the first embodiment above is the same. (3) Others In the manufacturing method of the electrode active material according to the second embodiment, a liquid treatment step of subjecting the electrode active material to liquid treatment with hydrofluoric acid may be provided after the alloying step. Regarding the liquid treatment step, the content described in the first embodiment above is the same. In addition, regarding the preferred mode of the electrode active material obtained by the manufacturing method of the electrode active material according to the second embodiment, the content described in "A. Electrode active material" above is the same. E. Manufacturing method of electrode mixture In the present disclosure, a manufacturing method of an electrode mixture is provided, which includes: a preparation step of preparing an electrode active material by the above-described manufacturing method of the electrode active material; and a mixing step of mixing the above-described electrode active material with at least one selected from a conductive material and a binder to obtain an electrode mixture. According to the present disclosure, by using the above-described electrode active material, an electrode mixture with a small volume change caused by charge and discharge can be obtained. Regarding the preparation step, the content described in "D. Manufacturing method of electrode active material" above is the same. The electrode mixture usually contains an electrode active material and at least one selected from a conductive material and a binder. Regarding the conductive material and the binder, they are the same as those described in the above "B. Electrode mixture". The electrode mixture may or may not have a dispersion medium. Additionally, the electrode mixture is usually obtained by mixing the electrode active material with at least one selected from the conductive material and the binder. The mixing method is not particularly limited, and known methods can be employed. Moreover, regarding the preferred manner of the obtained electrode mixture, it is the same as that described in the above "B. Electrode mixture". F. Battery manufacturing method In the present disclosure, a battery manufacturing method is provided, which includes: a preparation step of preparing an electrode active material by the above-described method for manufacturing an electrode active material; a mixing step of mixing the above-described electrode active material with at least one selected from a conductive material and a binder to obtain an electrode mixture; and an electrode layer forming step of forming an electrode layer using the above-described electrode mixture. According to the present disclosure, by using the above-described electrode active material, a battery with a small volume change caused by charge and discharge can be obtained. Regarding the preparation step and the mixing step, they are the same as those described in the above "D. Method for manufacturing an electrode active material" and the above "E. Method for manufacturing an electrode mixture". The electrode layer forming step is a step of forming an electrode layer using the above-described electrode mixture. The method for forming the electrode layer is not particularly limited, and known methods can be employed. As a method for forming the electrode layer, for example, a method of coating the electrode mixture on an electrode current collector can be cited. When forming the electrode layer, a pressing treatment for pressing the electrode layer in the thickness direction can also be performed. As the pressing treatment, for example, roll pressing and flat pressing can be cited. Additionally, when the electrode mixture is a slurry containing a dispersion medium, drying is preferably performed after coating the electrode current collector. The electrode layer forming step can be a positive electrode layer forming step for forming a positive electrode layer or a negative electrode layer forming step for forming a negative electrode layer. The battery manufacturing method of the present disclosure may also have other steps such as an electrolyte layer forming step for forming an electrolyte layer. Moreover, regarding the preferred manner of the obtained battery, it is the same as that described in the above "C. Battery". Furthermore, the present disclosure is not limited to the above-described embodiments. The above-described embodiments are illustrative, and solutions having substantially the same technical idea as that described in the scope of the patent claim of the present disclosure and solutions having the same function and effect are all included in the technical scope of the present disclosure.

Examples

Claims

1. An electrode active material comprising Si, There are Si-H bonds on the surface of the electrode active material. The ratio of hydrogen content to BET specific surface area is greater than 0.0034. in, The unit of the hydrogen content is weight %, and the unit of the BET specific surface area is m 2 / g. 2 . The electrode active material according to claim 1 , wherein the ratio is 0.0039 or more. The electrode active material according to claim 1 , wherein the ratio is 0.05 or less.

4. The electrode active material according to claim 1, wherein the BET specific surface area is 50 m 2 / g or above. The electrode active material according to claim 1 , wherein the amount of hydrogen is 0.20 wt % or more. 6 . The electrode active material according to claim 1 , wherein the ratio is 0.0060 or more, and the amount of hydrogen is 0.40 wt % or more. 7 . The electrode active material according to claim 1 , wherein the ratio is greater than 0.0034 and less than 0.0046, and the amount of hydrogen is less than 0.30 wt %. 8 . The electrode active material according to claim 1 , which has a crystal phase of type II silicon inclusion compound as a main phase. 9 . The electrode active material according to claim 1 , which has voids inside primary particles. 10 . The electrode active material according to claim 9 , wherein the ratio of the voids is 4% or more and 40% or less.

11. An electrode mixture comprising: The electrode active material according to any one of claims 1 to 10, and At least one selected from a conductive material and an adhesive. 12 . The electrode mixture according to claim 11 , further comprising a solid electrolyte. 13 . The electrode mixture according to claim 12 , wherein the solid electrolyte contained in the electrode mixture is a sulfide solid electrolyte.

14. A battery comprising a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, The positive electrode layer or the negative electrode layer contains the electrode mixture according to claim 11. 15 . The battery according to claim 14 , wherein the negative electrode layer contains the electrode mixture.

16. The battery according to claim 14, wherein the electrolyte layer contains a solid electrolyte.

17. The battery according to claim 16, The solid electrolyte contained in the electrolyte layer is a sulfide solid electrolyte, The electrolyte layer has a thickness of 0.1 μm or more and 100 μm or less.

18. The battery according to claim 17, wherein the positive electrode layer contains a rock salt layered active material.

19. A method for producing an electrode active material, comprising an alloying step, a sintering step and a liquid treatment step, In the alloying step, a Na source and a Si source are reacted to obtain a Na-Si alloy. In the calcining step, the Na—Si alloy is calcined to reduce the amount of Na in the Na—Si alloy, thereby forming a precursor active material having a crystal phase of a type II silicon clathrate. In the liquid treatment step, the precursor active material is subjected to liquid treatment using hydrofluoric acid to obtain an electrode active material, and In the liquid treatment step, the liquid treatment conditions are adjusted so that the ratio of the amount of hydrogen to the BET specific surface area is greater than 0.0034, wherein: The unit of the hydrogen content is weight %, and the unit of the BET specific surface area is m 2 / g.

20. The method for producing an electrode active material according to claim 19, The concentration of hydrogen fluoride in the hydrofluoric acid is 3% by weight or more, The treatment time in the liquid treatment step is 3 hours or more.

21. A method for producing an electrode active material, comprising an alloying step and a sintering step. In the alloying step, a Na source and a Si source are reacted to obtain a Na-Si alloy. In the sintering step, the Na-Si alloy is sintered to reduce the amount of Na in the Na-Si alloy, thereby forming an electrode active material having a crystal phase of a type II silicon inclusion compound, and In the alloying step, metal Na particles are used as the Na source. 22 . The method for producing an electrode active material according to claim 21 , wherein the average particle size of the metal Na particles is 10 μm or less.

23. A method for producing an electrode mixture, comprising a preparation step and a mixing step. In the preparation step, the electrode active material is prepared by the method for producing an electrode active material according to any one of claims 19 to 22, In the mixing step, the electrode active material and at least one selected from a conductive material and a binder are mixed to obtain an electrode mixture.

24. A method for manufacturing a battery, comprising a preparation step, a mixing step and an electrode layer forming step, In the preparation step, the electrode active material is prepared by the method for producing an electrode active material according to any one of claims 19 to 22, In the mixing step, the electrode active material and at least one selected from a conductive material and a binder are mixed to obtain an electrode mixture. In the electrode layer forming step, an electrode layer is formed using the electrode mixture.

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