Electrode active material and battery

Abstract

A main object of the present disclosure is to provide an electrode active material having a small volume change due to charge and discharge.SOLUTION: In the present disclosure, the problem is solved by providing an electrode active material that contains a Si element and has voids inside primary particles, wherein the voids include first voids having a pore diameter of 30 nm or more and 100 nm or less and second voids having a pore diameter of 1 nm or more and 5 nm or less, and a ratio (A / B) of the amount of the first voids to the amount of the second voids is larger than 0.10 and smaller than 17.00, where A represents the amount of the first voids and B represents the amount of the second voids.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to electrode active materials and batteries. [Background technology]

[0002] In recent years, the development of batteries has been actively pursued. For example, in the automotive industry, development of batteries for use in electric vehicles (BEVs) and hybrid electric vehicles (HEVs) is progressing. In addition, Si is known as an active material (electrode active material) used in batteries.

[0003] For example, Patent Document 1 discloses an active material having a silicon clathrate type II crystalline phase, having voids inside primary particles, and having a void volume A of voids with a pore diameter of 100 nm or less, which is greater than 0.15 cc / g and less than 0.40 cc / g. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-044620 Summary of the Invention [Problem to be solved by the invention]

[0005] Silicon has a large theoretical capacity and is effective in increasing the energy density of batteries. However, silicon undergoes large volume changes during charging and discharging. While attempts have been made to suppress the amount of volume change by providing voids inside the primary particles, as in Patent Document 1, there is still room for further improvement in the amount of volume change.

[0006] The present disclosure has been made in view of the above circumstances, and has as its main object to provide an electrode active material that undergoes little volume change upon charge and discharge. [Means for solving the problem]

[0007] [1] An electrode active material containing Si element and having voids inside primary particles, The voids include first voids having a pore diameter of 30 nm or more and 100 nm or less, and second voids having a pore diameter of 1 nm or more and 5 nm or less, An electrode active material in which, when the amount of the first voids is A and the amount of the second voids is B, the ratio of A to B (A / B) is greater than 0.10 and smaller than 17.00.

[0008] [2] The electrode active material according to [1], wherein the A / B is 10.00 or less.

[0009] [3] The electrode active material according to [1] or [2], wherein the A / B ratio is 3.00 or more.

[0010] [4] The electrode active material according to any one of [1] to [3], which has a silicon clathrate II type crystalline phase as a main phase.

[0011] [5] A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, A battery, wherein the negative electrode active material layer contains the electrode active material according to any one of [1] to [4] as a negative electrode active material. [Effects of the Invention]

[0012] The present disclosure has an effect of being able to obtain an electrode active material that undergoes little volume change upon charge and discharge. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram illustrating the crystalline phase of an electrode active material. [Figure 2] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] The electrode active material and battery according to the present disclosure will be described in detail below.

[0015] A. Electrode active material The electrode active material according to the present disclosure contains elemental Si and has voids inside primary particles. The voids in the electrode active material according to the present disclosure include first voids having a pore diameter of 30 nm or more and 100 nm or less and second voids having a pore diameter of 1 nm or more and 5 nm or less, and when the amount of the first voids is A and the amount of the second voids is B, the ratio of A to B (A / B) is greater than 0.10 and less than 17.00.

[0016] According to the present disclosure, the electrode active material has predetermined first voids and second voids, and the ratio of the amount A of the first voids to the amount B of the second voids is greater than 0.10 and less than 17.00, thereby reducing the volume change due to charging and discharging.

[0017] As in Patent Document 1, porous Si having voids inside primary particles has been investigated to suppress volume change. It is believed that the presence of dense voids with a size (pore diameter) of 100 nm or less can uniformly mitigate volume change due to discharge. Meanwhile, the present inventors conducted extensive research into the size of the voids and found that volume change can be further suppressed by adjusting the amount of relatively coarse voids (first voids) with a size of 30 nm to 100 nm and the amount of relatively fine voids (second voids) with a size of 1 nm to 5 nm to a predetermined ratio. While the first voids have ample room to absorb expansion and contraction, there is a risk that reactions may concentrate in their vicinity. As a result, if the proportion of the first voids is too high, volume change may not be sufficiently suppressed for the entire active material. In contrast, the presence of second voids can uniformly promote reactions in the active material, thereby demonstrating sufficient volume change suppression for the entire active material.

[0018] The electrode active material in the present disclosure contains elemental Si and has voids inside the primary particles, and corresponds to so-called porous Si (p-Si).

[0019] The electrode active material according to the present disclosure has, as the voids, first voids having a pore diameter of 30 nm or more and 100 nm or less, and second voids having a pore diameter of 1 nm or more and 5 nm or less. Furthermore, when the amount of the first voids is A and the amount of the second voids is B, the ratio of A to B (A / B) is greater than 0.10 and less than 17.00. The presence of voids in the electrode active material, as well as the presence of the first voids and the second voids, can be confirmed by observation with a scanning electron microscope (SEM).

[0020] A / B may be 0.50 or more, 1.00 or more, 3.00 or more, or 5.00 or more. Also, A / B may be 16.00 or less, 15.00 or less, 13.00 or less, 10.00 or less, or 8.00 or less. The first void volume A and the second void volume B can be determined, for example, by mercury porosimeter measurement, BET measurement, gas adsorption method, 3D-SEM, or 3D-TEM.

[0021] The amount of the first voids is not particularly limited as long as it satisfies the above A / B. The amount of the first voids is, for example, 0.050 cc / g or more, or may be 0.100 cc / g or more, or may be 0.150 cc / g or more. On the other hand, the amount of the first voids is, for example, 0.300 cc / g or less, or may be 0.250 cc / g or less, or may be 0.200 cc / g or less.

[0022] The amount of the second voids is not particularly limited as long as it satisfies the above A / B. The amount of the second voids is, for example, 0.005 cc / g or more, or may be 0.010 cc / g or more, or 0.030 cc / g or more, or 0.050 cc / g or more. On the other hand, the amount of the second voids is, for example, 0.150 cc / g or less, or may be 0.100 cc / g or less, or may be 0.20 cc / g or less.

[0023] The electrode active material may also have third pores as the pores, each having a pore diameter greater than 5 nm and smaller than 30 nm. The electrode active material may also have fourth pores as the pores, each having a pore diameter greater than 100 nm. The amount of the third pores is not particularly limited, but is, for example, 0.050 cc / g or more and 0.250 cc / g or less. The amount of the fourth pores is not particularly limited, but is, for example, 0.200 cc / g or more and 0.400 cc / g or less. The amounts of the third pores and the fourth pores can be determined in the same manner as the amounts of the first pores and the second pores described above.

[0024] The porosity of the electrode active material is not particularly limited, but may be, for example, 4% or more, or 10% or more. The porosity may also be, for example, 40% or less, or 20% or less. The porosity can be determined, for example, by the following procedure. First, a cross-sectional image of the electrode active material is obtained using an SEM. From the obtained image, the silicon portion and the void portion are clearly distinguished using image analysis software, and the image is binarized. The areas of the silicon portion and the void portion are determined, and the porosity (%) is calculated using the following formula: Porosity (%) = 100 × (area of ​​void part) / ((area of ​​silicon part) + (area of ​​void part))

[0025] The electrode active material in the present disclosure contains elemental Si. The electrode active material may be simple Si, an alloy containing Si as a main component (Si alloy), or a Si oxide. The proportion of elemental Si in the Si alloy is, for example, 50 mol% or more and 95 mol% or less.

[0026] The electrode active material of the present disclosure may also have a specific crystalline phase. That is, the electrode active material may be crystalline porous Si. Porous Si may have a diamond-type crystalline phase as shown in FIG. 1(a), a silicon clathrate I crystalline phase as shown in FIG. 1(b), or a silicon clathrate II crystalline phase as shown in FIG. 1(c). Porous Si having a clathrate crystalline phase is referred to as porous clathrate Si. The electrode active material of the present disclosure may have one or more of the above-mentioned crystalline phases. The crystalline phase of the electrode active material can be confirmed by X-ray diffraction measurement (XRD measurement) using CuKα radiation. Here, as shown in FIG. 1(a), in the diamond-type crystalline phase, multiple Si elements form tetrahedra. The tetrahedra do not have any internal spaces that can encapsulate metal ions such as Li ions. In contrast, as shown in Figures 1(b) and (c), the crystalline phases of silicon clathrate type I and type II have cage-shaped skeletal atoms, which can accommodate metal ions such as Li ions, and are therefore thought to be able to further suppress the expansion and contraction of the composite particles. Therefore, the electrode active material of the present disclosure preferably has at least one of the crystalline phases of silicon clathrate type I and type II. In particular, the electrode active material of the present disclosure preferably has the crystalline phase of silicon clathrate type II as the main phase. The "main phase" refers to the peak belonging to that crystalline phase having the highest diffraction intensity among the peaks observed in X-ray diffraction measurement. The proportion of the crystalline phase of silicon clathrate type II contained in the electrode active material is, for example, 80% by weight or more, or may be 85% by weight or more, 90% by weight or more, or even 95% by weight or more. The proportion of the crystalline phase of silicon clathrate type II contained in the electrode active material may be 100% by weight or less. The proportion of the crystalline phase can be determined by using the RIR method (Reference Intensity Ratio method).

[0027] In X-ray diffraction measurements using CuKα radiation, the diamond-type crystalline phase exhibits typical peaks at 2θ = 28.44°, 47.31°, 56.10°, 69.17°, and 76.37°. In X-ray diffraction measurements using CuKα radiation, the silicon clathrate I crystalline phase exhibits typical peaks at 2θ = 19.44°, 21.32°, 30.33°, 31.60°, 32.82°, 36.29°, 52.39°, and 55.49°. In X-ray diffraction measurements using CuKα radiation, the silicon clathrate II crystalline phase exhibits typical peaks at 2θ = 20.09°, 21.00°, 26.51°, 31.72°, 36.26°, and 53.01°. The above-mentioned peak positions may vary within a range of ±0.50°, ±0.30°, or ±0.10°.

[0028] As described above, the voids in the present disclosure can be observed by SEM. However, the spaces (distances between atoms) in the cage structures of the silicon clathrates I and II are generally on the order of Å and therefore cannot be observed by SEM. Therefore, the spaces in the cage structures do not constitute the voids in the present disclosure.

[0029] The electrode active material in the present disclosure may be primary particles or secondary particles formed by aggregation of primary particles. The average particle size of the primary particles is, for example, 150 nm or more, 200 nm or more, or 500 nm or more. On the other hand, the average particle size of the primary particles is, for example, 3000 nm or less, 1500 nm or less, or 1000 nm or less. The average particle size of the secondary particles is, for example, 1 μm or more, 2 μm or more, or 5 μm or more. On the other hand, the average particle size of the secondary particles is, for example, 60 μm or less, or 40 μm or less. The average particle size can be determined, for example, by observation using an SEM. A large number of samples is preferably used, for example, 20 or more, 50 or more, or even 100 or more.

[0030] Porous Si can be produced, for example, by preparing an alloy of Li and Si (LiSi alloy) and then removing Li from the LiSi alloy. The LiSi alloy can be obtained, for example, by mixing Li and Si. Removing Li from the LiSi alloy can be achieved, for example, by reacting the LiSi alloy with a Li extractant. Examples of Li extractants include alcohols such as methanol and acids such as acetic acid. The amount of the first pores and the amount of the second pores can be adjusted by changing the ratio of Li to Si and the conditions for Li extraction.

[0031] Examples of methods for producing crystalline porous Si include mixing and heating a Si source with a Na source such as NaH to produce a Na-Si alloy, and then heating the Na-Si alloy to reduce the amount of Na in the Na-Si alloy and generate a silicon clathrate-type crystalline phase. Porous clathrate Si can be produced by using the above-mentioned porous Si as the Si. Furthermore, as described in the Examples below, in the production of porous clathrate Si, it is expected that washing with an acid such as HF will be performed to remove by-products. In this regard, the amount of first pores and the amount of second pores can be adjusted by changing the washing conditions.

[0032] The electrode active material of the present disclosure may be used as either a positive electrode active material or a negative electrode active material in a battery, but the latter is preferred because it allows for the production of a battery with a higher capacity.

[0033] B.Battery Fig. 2 is a schematic cross-sectional view illustrating a battery according to the present disclosure. The battery 10 shown in Fig. 2 includes a positive electrode active material layer 1, a negative electrode active material layer 2, an electrolyte layer 3 disposed between the positive electrode active material layer 1 and the negative electrode active material layer 2, a positive electrode current collector 4 that collects current from the positive electrode active material layer 1, and a negative electrode current collector 5 that collects current from the negative electrode active material layer 2. In particular, according to the present disclosure, the negative electrode active material layer 2 contains the above-described electrode active material as the negative electrode active material.

[0034] According to the present disclosure, since the negative electrode active material layer contains the above-described electrode active material, a battery can be obtained that undergoes small volume changes due to charging and discharging.

[0035] 1.Negative electrode active material layer The negative electrode active material layer contains the above-mentioned electrode active material as the negative electrode active material. The electrode active material is the same as that described in "A. Electrode Active Material." The proportion of the negative electrode active material in the negative electrode active material layer is, for example, 20% by weight or more, or may be 30% by weight or more, or 40% by weight or more. If the proportion of the negative electrode active material is too low, sufficient energy density may not be obtained. On the other hand, the proportion of the negative electrode active material is, for example, 80% by weight or less, or may be 70% by weight or less, or may be 60% by weight or less. If the proportion of the negative electrode active material is too high, the ionic conductivity and electronic conductivity of the negative electrode active material layer may relatively decrease.

[0036] The negative electrode active material layer may contain at least one of an electrolyte, a conductive material, and a binder, as needed. Examples of electrolytes include those described in "3. Electrolyte Layer" below. Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF). Examples of binders include rubber-based binders and fluoride-based binders.

[0037] The thickness of the negative electrode active material layer is, for example, 1 μm or more and 100 μm or less.

[0038] 2. Positive electrode active material layer The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer may also contain at least one of an electrolyte, a conductive material, and a binder, as needed. The electrolyte, conductive material, and binder are the same as those described in "1. Negative electrode active material layer."

[0039] Examples of the positive electrode active material include oxide active materials, such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, LiMn2O4, Li4Ti5O 12 , Li(Ni 0.5 Mn 1.5 )O4, and olivine type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0040] A coating layer containing a Li-ion conductive oxide may be formed on the surface of the oxide active material. This is because it can suppress the reaction between the oxide active material and the solid electrolyte (especially the sulfide solid electrolyte). Examples of Li-ion conductive oxides include LiNbO3 and Li4Ti5O 12 and Li3PO4. The thickness of the coating layer is, for example, 1 nm or more and 30 nm or less.

[0041] The positive electrode active material may be in the form of particles, for example. 50 ) is not particularly limited, but may be, for example, 10 nm or more, or may be 100 nm or more. On the other hand, the average particle diameter (D 50 ) is, for example, 50 μm or less, and may be 20 μm or less. 50 ) can be calculated, for example, from measurements using a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM). The proportion of the positive electrode active material in the positive electrode active material layer is, for example, 50% by weight or more and 80% by weight or less.

[0042] The thickness of the positive electrode active material layer is, for example, 1 μm or more and 100 μm or less.

[0043] 3. Electrolyte layer The electrolyte layer is a layer disposed between the positive electrode active material layer and the negative electrode active material layer, and contains at least an electrolyte. The electrolyte layer may also contain a binder as needed. The binder is the same as that described in "1. Negative electrode active material layer."

[0044] The electrolyte may be a solid electrolyte or a liquid electrolyte (electrolytic solution). Examples of solid electrolytes include 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. An electrolyte layer containing an inorganic solid electrolyte as the electrolyte is called a solid electrolyte layer. The sulfide solid electrolyte preferably contains sulfur (S) as the main anion element. The oxide solid electrolyte preferably contains oxygen (O) as the main anion element. The halide solid electrolyte preferably contains halogen as the main anion element. Among these, the sulfide solid electrolyte is preferred.

[0045] Examples of sulfide solid electrolytes include solid electrolytes containing Li, X (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and a halogen. Examples of halogen include F, Cl, Br, and I. The sulfide solid electrolyte may be glass (amorphous) or glass ceramic. Examples of sulfide solid electrolytes include Li2S-P2S5, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-SiS2, Li2S-GeS2, and Li2S-P2S5-GeS2.

[0046] The electrolyte preferably contains a supporting salt and a solvent. Examples of supporting salts (lithium salts) for the lithium ion conductive electrolyte include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(FSO2)2, and LiC(CF3SO2)3. Examples of solvents used in the electrolyte include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), and chain esters (chain carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The electrolyte preferably contains two or more solvents.

[0047] The thickness of the electrolyte layer is, for example, not less than 1 μm and not more than 100 μm.

[0048] 4. Other configurations The battery according to the present disclosure preferably includes a positive electrode current collector that collects current from the positive electrode active material layer and a negative electrode current collector that collects current from the negative electrode active material layer. Examples of materials for the positive electrode current collector include metals such as SUS, Ni, Cr, Au, Pt, Fe, Ti, and Zn. A plating layer or vapor deposition layer of Ni, Cr, and C may be formed on the surface of the positive electrode current collector. Examples of materials for the negative electrode current collector include Cu and Cu alloys. A plating layer or vapor deposition layer of Ni, Cr, and C may be formed on the surface of the negative electrode current collector.

[0049] The battery according to the present disclosure may further include a restraining jig that applies a restraining pressure to the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer in the thickness direction. In particular, when the electrolyte layer is a solid electrolyte layer, it is preferable to apply a restraining pressure to form good ion conduction paths and electron conduction paths. The restraining pressure is, for example, 0.1 MPa or more and 100 MPa or less.

[0050] 5.Battery The type of battery in the present disclosure is not particularly limited, but is typically a lithium ion battery. The battery in the present disclosure may be a liquid battery or a solid-state battery. A battery having the above-described solid electrolyte layer is referred to as a solid-state battery. The solid-state battery may be a semi-solid-state battery or an all-solid-state battery. When the solid electrolyte layer in a solid-state battery contains only the above-described inorganic solid electrolyte as the electrolyte, the solid-state battery is referred to as an all-solid-state battery.

[0051] Furthermore, the battery in the present disclosure may be a primary battery or a secondary battery, but a secondary battery is preferable because it can be repeatedly charged and discharged and is useful as, for example, an in-vehicle battery.

[0052] The use of the battery in the present disclosure is not particularly limited, but examples include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, it is preferable that the battery be used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery in the present disclosure may also be used as a power source for mobile objects other than vehicles (e.g., trains, ships, and aircraft), or as a power source for electrical appliances such as information processing devices.

[0053] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0054] [Example 1] (Preparation of electrode active material) Metallic Li and Si powders were weighed out in a molar ratio of 4:1 and mixed in a mortar under an Ar atmosphere at room temperature for 0.5 hours. This resulted in Li4Si. The resulting Li4Si was then reacted with ethanol under an Ar atmosphere. The resulting reaction product is believed to contain Si and CH3CHOLi. The reaction product was filtered, and the filtered solid was dried at 120°C for at least 3 hours to obtain powdered porous Si. Na-Si alloy was produced using the resulting Si and NaH as a Na source. Note that the NaH used was previously washed with hexane. NaH and porous Si were weighed out in a molar ratio of 1.05:1 and mixed using a cutter mill. The mixture of NaH and porous Si was heated in a heating furnace under an Ar atmosphere at 475°C for 40 hours to obtain powdered Na-Si alloy.

[0055] The resulting Na-Si alloy was used in a solid-phase silicon clathrate synthesis process, using AlF3 as a sodium trap. The Na-Si alloy and AlF3 were weighed out at a molar ratio of 1:0.35 and mixed using a cutter mill to obtain a reaction material. The resulting powdered reaction material was placed in a stainless steel reaction vessel and heated in an Ar atmosphere at 310°C for 60 hours in a heating furnace. The resulting reaction product is believed to contain the target active material and by-products NaF and Al. The reaction product was washed using a mixed solvent of HNO3 and HO in a volume ratio of 10:90. This removed by-products from the reaction product. After washing, the mixture was filtered, and the filtered solid was dried at 120°C for at least 3 hours to obtain a powder. The resulting powder was washed by immersing it in an HF aqueous solution for 3 hours (HF washing). This produced an electrode active material with voids inside the primary particles. Note that the temperature of the HF aqueous solution during washing was not controlled, and the process was carried out at room temperature (25°C). In this regard, it is believed that the temperature of the HF aqueous solution rose to around 40°C due to heat generation caused by cleaning. Furthermore, although no specific data is shown, when XRD measurement was performed on the prepared electrode active material, it was found that the electrode active material had a silicon clathrate II type crystalline phase as the main phase. The same is true for Examples 2 to 4 and Comparative Examples 1 and 2 described below.

[0056] (Preparation of evaluation battery) First, a positive electrode was prepared as follows. Butyl butyrate, 5 wt% butyl butyrate solution of PVDF-based binder, positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2 (average particle size 6 μm), sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), and conductive additive (VGCF) were added to a polypropylene container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). Next, the container was shaken for 3 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.) and then stirred for 30 seconds using the ultrasonic disperser. The mixture was further shaken for 3 minutes using the shaker to obtain a positive electrode slurry. The positive electrode slurry was applied to a positive electrode current collector (Al foil; manufactured by Showa Denko) using an applicator by the blade method. The mixture was then dried on a hot plate at 100 °C for 30 minutes. This resulted in a positive electrode having a positive electrode current collector and a positive electrode active material layer.

[0057] Next, a negative electrode was prepared as follows. Butyl butyrate, a 5 wt% butyl butyrate solution of a PVDF-based binder, a conductive additive (VGCF), the electrode active material (porous Si), and a sulfide solid electrolyte (LiS-P2S5-based glass ceramic) were added to a polypropylene container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The container was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.) to obtain a negative electrode slurry. The negative electrode slurry was applied to a negative electrode current collector (Cu foil; manufactured by UACJ) using an applicator by the blade method. The coating was then dried on a hot plate at 100°C for 30 minutes. This resulted in a negative electrode comprising a negative electrode current collector and a negative electrode active material layer. The negative electrode was pressed using a roll press at 60 kN / cm and 25°C.

[0058] Next, a transfer member having a solid electrolyte layer was prepared as follows. Heptane, a 5 wt% heptane solution of a BR-based binder, and a sulfide solid electrolyte (Li2S-P2S5-based glass ceramic) were added and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The container was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.). This resulted in a slurry. The slurry was applied to a substrate (Al foil) using an applicator by the blade method. The mixture was then dried on a hot plate at 100°C for 30 minutes. This resulted in a transfer member having a substrate and a solid electrolyte layer.

[0059] The positive electrode and the transfer member were stacked so that the positive electrode active material layer and the solid electrolyte layer faced each other. This was pressed using a roll press at 100 kN / cm and 165°C. After pressing, the substrate was peeled off to obtain a positive electrode laminate. The negative electrode and the transfer member were stacked so that the negative electrode active material layer and the solid electrolyte layer faced each other. This was pressed using a flat uniaxial press at 100 MPa and 25°C for 10 seconds. After pressing, the substrate was peeled off to obtain a negative electrode laminate. The negative electrode laminate and the positive electrode laminate were fabricated so that the area of ​​the negative electrode laminate was larger than that of the positive electrode laminate. The positive electrode laminate and the negative electrode laminate were stacked so that the solid electrolyte layers faced each other, and pressed using a flat uniaxial press at 200 MPa and 120°C for 1 minute. This produced an evaluation battery (all-solid-state battery).

[0060] [Example 2] An electrode active material (negative electrode active material: porous Si) and an all-solid-state battery were produced in the same manner as in Example 1, except that the immersion time for HF cleaning was changed to 1 hour and the temperature of the HF aqueous solution during immersion was maintained at 10°C using cooling water.

[0061] [Example 3] An electrode active material (negative electrode active material: porous Si) and an all-solid-state battery were produced in the same manner as in Example 1, except that the temperature of the HF aqueous solution during immersion was maintained at 10°C using cooling water during HF cleaning.

[0062] [Example 4] The firing time for the mixture of Na-Si alloy and AlF was changed to 345°C for 20 hours. The HF cleaning immersion time was changed to 5 hours, and the temperature of the HF aqueous solution during immersion was maintained at 0°C using ice water. Other than these, an electrode active material and an all-solid-state battery were fabricated in the same manner as in Example 1.

[0063] [Comparative Example 1] An electrode active material and an all-solid-state battery were produced in the same manner as in Example 1, except that the immersion time for HF cleaning was changed to 1 hour.

[0064] Comparative Example 2 An electrode active material and an all-solid-state battery were produced in the same manner as in Example 1, except that the molar ratio of metallic Li and Si powder was changed to 4.75:1 and the immersion time for HF cleaning was changed to 1 hour.

[0065] [evaluation] (Measurement of void volume) For the electrode active materials prepared in each of the Examples and Comparative Examples, the first void volume A and the second void volume B were measured using a BELSORP MAXII from Microtracbel. From the obtained measured values, the ratio of the first void volume A to the second void volume B was calculated. The results are shown in Table 1. The first void volume A was calculated by subtracting the amount of pores with a pore diameter of less than 30 nm from the amount of pores with a pore diameter of more than 100 nm.

[0066] (Expansion rate measurement) The all-solid-state batteries produced in each example and comparative example were restrained using a restraining jig and charged at a constant current and constant voltage up to 4.55 V at a 10-hour rate (1 / 10C). The expansion coefficient was calculated from the amount of change in the restraining pressure. The expansion coefficient of Comparative Example 1 was set to 100 and evaluated relatively. The results are shown in Table 1.

[0067] [Table 1]

[0068] As shown in Table 1, Examples 1 to 4 had significantly smaller expansion coefficients than Comparative Examples 1 and 2, confirming that the electrode active material of the present disclosure has a small volume change due to charge and discharge. [Explanation of symbols]

[0069] 1...Cathode active material layer 2...Negative electrode active material layer 3...electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...battery

Claims

1. An electrode active material containing Si element and having voids inside primary particles, The voids include first voids having a pore diameter of 30 nm or more and 100 nm or less, and second voids having a pore diameter of 1 nm or more and 5 nm or less, an electrode active material, wherein, when the amount of the first voids is A and the amount of the second voids is B, a ratio of A to B (A / B) is greater than 0.10 and smaller than 17.

00.

2. 2. The electrode active material according to claim 1, wherein A / B is 10.00 or less.

3. 2. The electrode active material according to claim 1, wherein the A / B ratio is 3.00 or more.

4. 2. The electrode active material according to claim 1, which has a silicon clathrate II type crystalline phase as a main phase.

5. A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, A battery, wherein the negative electrode active material layer contains the electrode active material according to any one of claims 1 to 4 as a negative electrode active material.

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