Electrode active material, electrode layer, and solid-state battery

Abstract

The invention relates to an electrode active material, an electrode layer and a solid state battery. An electrode active material includes primary particles containing a silicon element, the primary particles being provided in the form of secondary particles by a binder. The primary particles are porous and the average pore size of the pores of the primary particles is greater than 4.1 nm. The molecular diameter D50 in the molecular diameter distribution of the adhesive is less than 1, 859 nm. The molecular diameter D50 is equal to or greater than the average pore size.

Description

Technical Field

[0001] This disclosure relates to an electrode active material, an electrode layer, and a solid-state battery. Background Technology

[0002] Various technologies for electrodes and batteries have been proposed, such as those disclosed in Japanese Unexamined Patent Application Publication No. 2024-017797 (JP 2024-017797A). Summary of the Invention

[0003] JP 2024-017797A discloses a negative electrode layer for a secondary battery, comprising an active material layer containing composite particles (in which multiple porous silicon particles are bonded together by a binder) as the active material, and the porosity of the active material layer is greater than 15%. JP 2024-017797A describes that when the negative electrode layer has the aforementioned specific porosity, it is possible to reduce the change in negative electrode thickness during charging, and the porous silicon particles containing pores with a diameter of 55 nm or less easily maintain porosity even after pressing. However, there is still room for improvement in preventing electrode expansion during charge and discharge.

[0004] This disclosure is made in view of the above circumstances, and its main purpose is to provide an electrode active material capable of preventing electrode expansion associated with charge and discharge.

[0005] That is, the contents of this disclosure include the following aspects.

[0006] <1> A first aspect of this disclosure relates to an electrode active material comprising primary particles containing silicon, said primary particles being provided in the form of secondary particles via a binder.

[0007] The primary particles are porous and the average pore diameter of the primary particles is greater than 4.1 nm.

[0008] The molecular diameter D50 in the molecular diameter distribution of the adhesive is less than 1,859 nm.

[0009] The molecular diameter D50 is equal to or greater than the average pore size.

[0010] <2> According to <1> In the electrode active material,

[0011] The average pore size of the pores in the primary particles can be greater than 5 nm and less than 30 nm; and

[0012] The molecular diameter D50 in the molecular diameter distribution of the adhesive can be greater than 25 nm and less than 1,000 nm.

[0013] <3> A second aspect of this disclosure relates to an electrode layer comprising, according to <1> or <2> The electrode active material mentioned above.

[0014] <4> A third aspect of this disclosure relates to a solid-state battery comprising, according to <1> or <2> The electrode layer of the electrode active material.

[0015] <5> According to <4> In the solid-state battery, the electrode layer can be a negative electrode layer.

[0016] Using the electrode active material described in this disclosure, electrode expansion associated with charge and discharge can be prevented. Attached Figure Description

[0017] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, wherein like symbols denote like elements, and wherein:

[0018] Figure 1 This is a schematic cross-sectional view illustrating one example of a solid-state battery according to the present disclosure;

[0019] Figure 2 These are diagrams illustrating the results of the embodiments and comparative examples; and

[0020] Figure 3 The figure shows the results of the embodiments and comparative examples. Detailed Implementation

[0021] Embodiments of this disclosure are described below. It should be noted that those skilled in the art can identify, based on relevant technologies in the related fields, matters not specifically mentioned herein but necessary for implementing this disclosure (e.g., electrode active materials, electrode layers, and general configurations and manufacturing processes of solid-state batteries that are not features of this disclosure) as design considerations. This disclosure can be implemented based on the content disclosed herein and well-known technical knowledge in the related fields.

[0022] A. Electrode active materials

[0023] This disclosure provides an electrode active material comprising primary particles containing silicon (hereinafter sometimes referred to as "Si-based primary particles"), which are provided as secondary particles via a binder. The primary particles are porous, with an average pore size greater than 4.1 nm. The molecular diameter D50 in the molecular diameter distribution of the binder is less than 1,859 nm. The molecular diameter D50 is equal to or greater than the average pore size.

[0024] That is, the electrode active material of this disclosure is an electrode active material comprising porous Si-based primary particles (hereinafter sometimes referred to as "porous Si-based primary particles"), which are provided in the form of secondary particles by means of a binder and satisfy the following conditions (1) to (3):

[0025] (1) The average pore diameter of the pores in the porous Si primary particles is greater than 4.1 nm;

[0026] (2) The molecular diameter D50 in the molecular diameter distribution of the adhesive is less than 1,859 nm; and

[0027] (3) The molecular diameter D50 of the adhesive is equal to or greater than the average pore size of the porous Si primary particles.

[0028] It has been found that in electrode active materials in which multiple porous Si primary particles are bonded by the binder, when the porous Si primary particles and the binder are combined to satisfy the conditions (1) to (3) above, electrode expansion associated with charge and discharge can be prevented.

[0029] When the average pore size of the porous Si primary particles is less than 4.1 nm, the pores are compressed during the densification process of the electrode layer, therefore it is considered that the expansion of the electrode layer cannot be prevented. Furthermore, when the molecular diameter D50 in the molecular diameter distribution of the adhesive is greater than 1,859 nm, the expansion of the electrode layer cannot be prevented. Moreover, even if the average pore size of the porous Si primary particles is greater than 4.1 nm and the molecular diameter D50 of the adhesive is less than 1,859 nm, when the molecular diameter D50 of the adhesive is less than the average pore size of the porous Si primary particles, adhesive molecules enter the pores of the porous Si primary particles to fill them, therefore it is considered that the expansion of the electrode layer cannot be prevented.

[0030] The average pore size of the porous Si primary particles only needs to be greater than 4.1 nm, but can be greater than 5 nm and less than 30 nm, because a higher expansion absorption effect can be expected.

[0031] The molecular diameter D50 in the molecular diameter distribution of the adhesive only needs to be less than 1,859 nm, but can be above 25 nm and below 1,000 nm, because a higher swelling absorption effect can be expected.

[0032] The average pore size of the porous Si primary particles can be greater than 5 nm and less than 30 nm, and the molecular diameter D50 in the molecular diameter distribution of the adhesive can be greater than 25 nm and less than 1,000 nm.

[0033] In this disclosure, the average pore size of the porous Si primary particles is a value calculated by measuring the pore size distribution using a gas adsorption capacity measuring device (e.g., the fully automated gas adsorption capacity measuring device "autosorb-iQ" manufactured by Anton Paar) using the DFT method.

[0034] It should be noted that the average pore size can also be calculated by measuring the pore size distribution using a BET device, measuring it using a mercury porosity meter, analyzing cross-sectional images using a scanning electron microscope (SEM), or analyzing cross-sectional images using a transmission electron microscope (TEM).

[0035] Furthermore, in this disclosure, the molecular diameter D50 in the molecular diameter distribution of the adhesive is the value of the median diameter, which is the molecular diameter at the cumulative 50% in the volume-based particle size distribution and can be determined by dynamic light scattering.

[0036] It should be noted that the molecular diameter D50 can also be calculated by laser diffraction scattering, electrosensory region method, cross-sectional image analysis using SEM, cross-sectional image analysis using TEM, etc.

[0037] The porous Si-based primary particles have a porous structure, i.e., multiple pores (voids). As long as the average pore diameter falls within the aforementioned range, the porosity of the porous Si-based primary particles is not particularly limited, and can, for example, be greater than 1% or greater than 10%. Furthermore, the porosity of the porous Si-based primary particles can be less than 80% or less than 60%. The porosity can be calculated, for example, by cross-sectional observation using SEM.

[0038] The composition of the porous Si-based primary particles is not particularly limited as long as they contain silicon, and examples of the composition include elemental Si, Si alloys, Si oxides, and Si carbides. The Si alloys are alloys with Si as the main component. Examples of metals other than Si in the Si alloys include Li, Sn, Fe, Co, Ni, Ti, Cr, Na, W, Mo, V, Nb, Zr, and Hf. The Si alloys may contain only one type of metal other than Si, or they may contain two or more types of metals other than Si. Examples of Si oxides include SiO. Furthermore, examples of Si carbides include SiC. Additionally, the porous Si-based primary particles may contain other elements such as B and P.

[0039] The porous Si-based primary particles can be crystalline or amorphous. When the porous Si-based primary particles are crystalline, the crystalline layers of the porous Si-based primary particles are not particularly limited.

[0040] One type of porous Si-based primary particle can be used alone, or two or more types of porous Si-based primary particles can be used in combination.

[0041] The average particle size (D50) of the porous Si primary particles is not particularly limited, for example, it can be above 10 nm or above 50 nm, and it can be below 10 μm or below 1 μm.

[0042] Here, the average particle size (D50) of the porous Si primary particles is the value of the median diameter (D50), which is the particle size at the 50% cumulative value in the volume-based particle size distribution determined by laser diffraction-scattering particle size distribution measurement.

[0043] The adhesive binds and bonds the porous Si-based primary particles. The type of adhesive is not particularly limited, as long as the molecular diameter D50 in the molecular diameter distribution falls within the aforementioned range. Specific examples of the adhesive include styrene-butadiene rubber (SBR), nitrile rubber (NBR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), butyl rubber (IIR), nitrile rubber (ABR), polyimide (IR), carboxymethyl cellulose (CMC), polyacrylate, polyacrylate, styrene-isoprene-styrene block copolymer (SIS), and ethylene propylene diene monomer (EPDM). Only one type of adhesive can be used alone, or two or more types of adhesives can be used in combination.

[0044] When using an electrode mixture slurry to form the electrode layer, from the perspective of maintaining the particle shape of secondary particles, a binder with poor solubility in the solvent of the electrode mixture slurry can be selected. For example, when using an organic solvent such as mesitylene or tetrahydronaphthalene as the solvent of the electrode mixture slurry, a vinyl-based binder such as PVdF can be used as the binder.

[0045] The ratio of the porous Si-based primary particles to the binder in the secondary particles is not particularly limited. When all electrode active material is considered as 100% by mass, for example, the binder is 1% by mass or more, and can be 5% by mass or more. Furthermore, the binder is 30% by mass or less, and can be 25% by mass or less.

[0046] The particle size of the secondary particles is not particularly limited. For example, the average particle size (D50) is 100 nm or more, and can be 1 μm or more. Furthermore, the average particle size (D50) is 20 μm or less, and can be 15 μm or less. The average particle size (D50) of the secondary particles is the value of the median diameter (D50), which is the particle size at the 50% cumulative value in a volume-based particle size distribution determined by laser diffraction-scattering particle size distribution measurement.

[0047] For example, the electrode active material of this disclosure can be prepared as follows: First, a binder solution is prepared by dissolving or dispersing a binder in an organic solvent. Then, the porous Si-based primary particles are placed into the binder solution to prepare a primary particle slurry. The obtained primary particle slurry is spray-dried (spray drying) to provide the porous Si-based primary particles in the form of secondary particles. The conditions of the spray drying are not particularly limited, as long as they enable the porous Si-based primary particles to be provided in the form of secondary particles.

[0048] The electrode active material described in this disclosure can be used as a negative electrode active material or as a positive electrode active material, but when the electrode active material described in this disclosure is used as a negative electrode active material, a higher effect can be expected.

[0049] B. Electrode layer

[0050] The electrode layer of this disclosure contains the aforementioned "A. Electrode active material". When the electrode active material of this disclosure is used as a negative electrode active material, the electrode layer of this disclosure is a negative electrode layer. When the electrode active material of this disclosure is used as a positive electrode active material, the electrode layer of this disclosure is a positive electrode layer.

[0051] The proportion of electrode active material in the electrode layer is not particularly limited. For example, when the entire electrode layer is considered as 100% by mass, the proportion of electrode active material in the electrode layer is 40% by mass or more, and can be 55% by mass or more. Furthermore, the proportion of electrode active material in the electrode layer is 99% by mass or less, and can be 80% by mass or less.

[0052] The electrode layer may contain only the electrode active material, or may contain other components as needed, such as at least one of a solid electrolyte, a conductive material, and an adhesive other than the adhesive constituting the electrode active material (which may be referred to below as "electrode layer adhesive").

[0053] Examples of the solid electrolyte include: inorganic solid electrolytes such as sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, and complex hydride solid electrolytes; and organic solid electrolytes such as gel electrolytes. Among them, the solid electrolyte may be a sulfide solid electrolyte. The reason is that it has a high ionic conductivity. The sulfide solid electrolyte is an electrolyte containing S element as the main component of the anion component.

[0054] The sulfide solid electrolyte generally contains at least Li element and S element. The sulfide solid electrolyte may also contain Me element (Me is at least one type of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In). In addition, the sulfide solid electrolyte may contain halogen elements such as F, Cl, Br, and I.

[0055] The sulfide solid electrolyte may be a glassy (amorphous) sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. The sulfide solid electrolyte may have a crystalline phase. Examples of the crystalline phase include thio-LISICON type crystalline phase, argyrodite type crystalline phase, and LGPS type crystalline phase.

[0056] The composition of the sulfide solid electrolyte is not particularly limited, and examples of the composition include xLi2S·(1 - x)P2S5 (0.5 ≤ x < 1) and yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.5 ≤ x < 1, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30). In these compositions, x may satisfy 0.7 ≤ x ≤ 0.8. In addition, Li 7-x PS 6-x X x can be given as another example of the composition of the sulfide solid electrolyte. X is at least one of F, Cl, Br, and I, and x satisfies 0 ≤ x < 2. In addition, Li 4-x Me 1-x P x S4 (0 < x < 1) can be given as another example of the composition of the sulfide solid electrolyte. Me is at least one of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi. Examples of the sulfide solid electrolyte include LiI - LiBr - Li2S - P2S5, LiI - Li2S - P2S5, LiI - Li2S - P2O5, and LiI - Li3PO4 - P2S5.

[0057] Examples of the oxide solid electrolytes include substances having a garnet-type crystal structure containing Li, La, A (A being at least one of Zr, Nb, Ta, and Al), and O. Examples of the oxide solid electrolytes include Li₂O-B₂O₃-P₂O₅, Li₂O-SiO₂, Li₂O-B₂O₃, and Li₂O-P₂O₃. 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O 12 Li 3.6 Si 0.6 P 0.4 O4, Li4SiO4, Li3PO4 and Li 3+x PO 4-x N x (1≤x≤3).

[0058] Examples of the halide solid electrolytes include solid electrolytes containing Li, M, and X (M represents at least one of Ti, Al, and Y, and X represents F, Cl, or Br).

[0059] A single type of solid electrolyte can be used, or two or more types of solid electrolytes can be used in combination. For example, when the entire electrode layer is considered as 100% by mass, the proportion of the solid electrolyte in the electrode layer is 1% by mass or more, and can be 20% by mass or more. Furthermore, the proportion of the solid electrolyte in the electrode layer is 60% by mass or less, and can be 45% by mass or less.

[0060] Examples of the conductive materials include carbon materials, metallic materials, and conductive polymers. The conductive materials may be, for example, particle-shaped or fiber-shaped. Examples of carbon materials include particulate carbon materials, such as acetylene black (AB) and Ketjen black (KB), and fibrous carbon materials, such as vapor-grown carbon fibers (VGCF), carbon nanotubes (CNTs), and carbon nanofibers (CNFs). One type of conductive material may be used alone, or two or more types of conductive materials may be used in combination.

[0061] For example, when the entire electrode layer is considered as 100% by mass, the proportion of the conductive material in the electrode layer is 0.1% by mass or more, and may be 1.0% by mass or more. Furthermore, the proportion of the conductive material in the electrode layer is 5% by mass or less, and may be 3% by mass or less.

[0062] The electrode layer binder may be of the same or different type as the binder contained in the electrode active material described above. However, as mentioned above, when the electrode layer is formed using the electrode mixture slurry, although the binder constituting the electrode active material may be of a type with poor solubility in the solvent of the electrode mixture slurry, the electrode layer binder may be of a type that is soluble or dispersed in the solvent of the electrode mixture slurry. For example, when an organic solvent such as mesitylene or tetrahydronaphthalene is used as the solvent of the electrode mixture slurry, SBR can be used as the electrode layer binder.

[0063] For example, when all electrode layers are considered as 100% by mass, the proportion of the electrode layer adhesive in the electrode layers is 0.5% by mass or more, and may be 1.5% by mass or more. Furthermore, the proportion of the electrode layer adhesive in the electrode layers is 5% by mass or less, and may be 3% by mass or less.

[0064] The electrode layer described in this disclosure is typically used in batteries. The type of battery is not particularly limited, and because it is particularly effective at preventing electrode swelling associated with charging and discharging, better results can be expected when the electrode layer is used as an electrode layer in a solid-state battery.

[0065] The thickness of the electrode layer is, for example, 0.1 μm or more and 1,000 μm or less, and may be 1 μm or more and 500 μm or more and 30 μm or more and 100 μm or less.

[0066] The method for manufacturing the electrode layer is not particularly limited; for example, the following method can be provided: First, the electrode active material and, if necessary, the solid electrolyte, the conductive material, the electrode layer binder, etc., are mixed together with a solvent to prepare the electrode mixture slurry. Next, the electrode layer is formed by coating the electrode mixture slurry onto an electrode current collector and drying the electrode mixture slurry. If necessary, the electrode layer can be densified by pressing in the thickness direction.

[0067] C. Solid-state batteries

[0068] Figure 1 This is a schematic cross-sectional view illustrating an example of a solid-state battery in this disclosure. Figure 1 The solid-state battery 10 shown includes 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 the current of the positive electrode layer 1, and a negative electrode current collector 5 for collecting the current of the negative electrode layer 2. In this disclosure, the positive electrode layer 1 or the negative electrode layer 2 is the electrode layer described in "B. Electrode Layer" above.

[0069] By using the electrode layer comprising the electrode active material of this disclosure, a solid-state battery with minimal electrode expansion related to charge and discharge can be obtained. In the solid-state battery of this disclosure, the electrode layer comprising the electrode active material of this disclosure can be a negative electrode layer or a positive electrode layer, but when the electrode layer is a negative electrode layer, higher performance can be expected.

[0070] The solid-state battery described in this disclosure can be a semi-solid-state battery or an all-solid-state battery. In this disclosure, a semi-solid-state battery is a battery in which the electrolyte layer comprises a solid electrolyte and a liquid component (e.g., an ionic liquid). In this disclosure, an all-solid-state battery is a battery in which the electrolyte layer comprises only a solid electrolyte as the electrolyte.

[0071] 1. Negative electrode layer

[0072] The case where the negative electrode layer is the electrode layer described in this disclosure is similar to the case described in "B. Electrode Layer" above, so its description is omitted here. Here, when the positive electrode layer is the electrode layer described in "B. Electrode Layer" above, the negative electrode layer will be described.

[0073] The negative electrode layer contains at least a negative electrode active material. Examples of the negative electrode active material include Si-based active materials, carbon-based active materials, oxide-based active materials, and Li-based active materials.

[0074] Examples of the Si-based active materials include elemental Si, Si alloys, Si oxides, and Si carbides, which are exemplified as the porous Si-based primary particles in “A. Electrode Active Materials” above.

[0075] Examples of the carbon-based active materials include graphite, hard carbon, and soft carbon.

[0076] Examples of the oxide-based active materials include lithium titanate.

[0077] Examples of the Li-based active materials include elemental Li and Li alloys. Examples of metallic elements other than lithium included in the Li alloys include Mg, Ag, In, Sn, Si, Ga, Au, and Pt.

[0078] The negative electrode layer may, as needed, comprise at least one of a solid electrolyte, a conductive material, and an electrode layer adhesive. The solid electrolyte, the conductive material, and the electrode layer adhesive are similar to those described in “B. Electrode Layer” above, and therefore their description is omitted here.

[0079] 2. Positive electrode layer

[0080] The case where the positive electrode layer is the electrode layer described in this disclosure is similar to the case described in "B. Electrode Layer" above, so its description is omitted here. Here, when the negative electrode layer is the electrode layer described in "B. Electrode Layer" above, the positive electrode layer will be described.

[0081] The positive electrode layer comprises at least a positive electrode active material. Examples of the positive electrode active material include oxide active materials. Examples of oxide active materials include rock salt layer type active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and LiNi 0.8 Co 0.15 Mn 0.05 O2, spinel-type active materials such as LiMn2O4, Li4Ti5O 12 and Li(Ni 0.5 Mn 1.5 O4, as well as olivine-type active materials such as LiFePO4, LiMnPO4, LiNiPO4 and LiCoPO4.

[0082] A coating containing a Li ion-conducting compound can be formed on the surface of the positive electrode active material. This is to suppress the reaction between the positive electrode active material and the solid electrolyte (particularly the sulfide solid electrolyte). Examples of the Li ion-conducting compound include B₂O₃, Li₂B₄O₇, LiBPO₄, Li₃PO₄, LiPO₃, and LiNbO₃. The thickness of the coating is, for example, 1 nm or more and 30 nm or less. The coverage of the Li ion-conducting compound covering the positive electrode active material is, for example, 70% or more, and can be 90% or more or 100%. The method of coating with the Li ion-conducting compound is not particularly limited, and conventional and known methods can be appropriately employed.

[0083] The positive electrode layer may, as needed, comprise at least one of a solid electrolyte, a conductive material, and an electrode layer adhesive. The solid electrolyte, the conductive material, and the electrode layer adhesive are similar to those described in “B. Electrode Layer” above, and therefore their description is omitted here.

[0084] 3. Electrolyte layer

[0085] The electrolyte layer is formed between the positive electrode layer and the negative electrode layer, and is a solid electrolyte layer containing at least a solid electrolyte. The solid electrolyte is similar to that described in "B. Electrode Layer" above, therefore its description is omitted here.

[0086] A single type of solid electrolyte can be used alone, or two or more types of solid electrolytes can be used in combination. Furthermore, when using two or more types of solid electrolytes, they can be mixed, or a multilayer structure can be obtained by forming two or more layers of solid electrolyte.

[0087] The proportion of the solid electrolyte in the electrolyte layer is not particularly limited, and may be, for example, 50% by mass or more, or may fall within the range of 60% by mass or more and 100% by mass, or fall within the range of 70% by mass or more and 100% by mass, or may be 100% by mass. The solid electrolyte may contain less than 10% by mass of electrolyte relative to the total amount of electrolyte. It should be noted that the solid electrolyte may be a composite solid electrolyte comprising an inorganic solid electrolyte and a polymer electrolyte.

[0088] The electrolyte layer may include an adhesive, etc., as needed. Examples of adhesives that can be included in the electrode layer described above include... When the electrolyte layer includes an adhesive, the content of the adhesive relative to the total amount of the electrolyte layer can be from 0% by mass to 10% by mass.

[0089] The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1,000 μm or less, or 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less.

[0090] 4. Other configurations

[0091] The solid-state battery described in this disclosure may include a positive current collector for collecting current from the positive electrode layer and a negative current collector for collecting current from the negative electrode layer.

[0092] Examples of materials for the positive electrode current collector include SUS, Cr, Au, Pt, Zn, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the positive electrode current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the positive electrode current collector can be foil or plate. The positive electrode current collector can have the following configuration: a buffer layer, an elastic layer, or a positive temperature coefficient (PTC) thermistor layer is disposed on the surface.

[0093] Examples of materials for the negative electrode current collector include SUS, aluminum, copper, nickel, iron, titanium, and carbon. Examples of shapes for the negative electrode current collector include foil and plate. The shape of the negative electrode current collector in a top view is not particularly limited, and examples of shapes include circles, ellipses, rectangles, and any polygon. Furthermore, the thickness of the negative electrode current collector varies depending on the shape and can, for example, range from 1 μm to 50 μm. The negative electrode current collector may have the following configuration: a buffer layer, an elastic layer, or a PTC thermistor layer is disposed on the surface.

[0094] The solid-state battery described in this disclosure may further include a constraint clamp that applies a constraint pressure along the thickness direction to the positive electrode layer, the electrolyte layer, and the negative electrode layer. The constraint pressure is, for example, 0.1 MPa or more, and may be 1 MPa or more, or 5 MPa or more. Alternatively, the constraint pressure is, for example, 100 MPa or less, and may be 50 MPa or less, or 20 MPa or less.

[0095] 5. Solid-state batteries

[0096] The type of solid-state battery described in this disclosure is not particularly limited, and is typically a lithium-ion battery. Furthermore, the solid-state battery in this disclosure can be a primary or secondary battery, and particularly a secondary battery. This is because the battery can be repeatedly charged and discharged, and is effective, for example, as a vehicle battery.

[0097] The shape of the battery is not particularly limited, and can be, for example, coin-shaped, cylindrical, rectangular, sheet-shaped, button-shaped, flat, or stacked.

[0098] Examples of applications for the solid-state battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. Specifically, the solid-state battery can be used as a drive power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Furthermore, the solid-state battery can be used as a power source for mobile bodies other than vehicles (e.g., railway vehicles, ships, or aircraft), or as a power source for electrical products such as information processing equipment.

[0099] It should be noted that this disclosure is not limited to the embodiments described above. The embodiments described above are merely examples; therefore, any of those embodiments that have substantially the same configuration as the technical concept disclosed in the claims of this disclosure to achieve similar functions and effects are included within the technical scope of this disclosure.

[0100] Solid-state battery fabrication

[0101] Example 1

[0102] Preparation of electrode active materials

[0103] A porous Si particle slurry was prepared by placing porous Si-based primary particles (average pore size 21.9 nm) into a solution obtained by dissolving or dispersing a binder (PVdF, molecular diameter D50 of 25.3 nm) in an organic solvent. Using the obtained porous Si particle slurry, the porous Si-based primary particles were then supplied as secondary particles via spray drying to obtain an electrode active material.

[0104] The molecular diameter D50 in the molecular diameter distribution of PVdF was determined using dynamic light scattering. Furthermore, the average pore size of the porous Si primary particles was determined using a fully automated gas adsorption capacity measuring device ("autosorb-iQ" manufactured by Anton Paar).

[0105] Preparation of negative electrode

[0106] The obtained electrode active material, along with the electrode layer binder (SBR), conductive material, and solid electrolyte, is added to an organic solvent (tetrahydronaphthalene). After addition, the mixture is kneaded using an ultrasonic homogenizer to prepare a negative electrode slurry. The obtained negative electrode slurry is then coated onto a Cu foil to prepare a negative electrode in which the negative electrode layer is stacked on the negative electrode current collector (Cu foil).

[0107] Preparation of positive electrode

[0108] By combining adhesives, conductive materials, solid electrolytes, and positive electrode active materials (LiNi) 0.8 Co 0.15 Mn 0.05 O2) is added to an organic solvent and kneaded using an ultrasonic homogenizer to prepare a positive electrode hybrid material slurry. The obtained positive electrode hybrid material slurry is coated onto an Al foil to prepare a positive electrode in which the positive electrode layer is stacked on the positive electrode current collector (Al foil).

[0109] Preparation of electrolyte layer

[0110] A binder and a solid electrolyte are added to an organic solvent. After addition, the mixture is kneaded using an ultrasonic homogenizer to obtain an electrolyte mixture slurry. The obtained electrolyte mixture slurry is then coated onto an Al foil to prepare an electrolyte sheet in which a solid electrolyte layer is stacked on the Al foil.

[0111] Solid-state battery fabrication

[0112] The layers prepared as described above are shaped (cut) into strips.

[0113] The positive electrode and the electrolyte sheet are stacked such that the surface of the positive electrode layer of the positive electrode and the surface of the electrolyte layer of the electrolyte sheet face each other, and then rolled at 165°C and 50 kN / cm. Next, the aluminum foil of the electrolyte sheet is removed, and the electrolyte layer is transferred onto the positive electrode layer of the positive electrode.

[0114] On the other hand, the negative electrode and the electrolyte sheet are stacked such that the surface of the negative electrode layer of the negative electrode and the surface of the electrolyte layer of the electrolyte sheet face each other, and then rolled at 25°C and 50 kN / cm. Next, the Al foil of the electrolyte sheet is removed, and the electrolyte layer is transferred onto the negative electrode layer of the negative electrode.

[0115] Subsequently, the negative electrode with the electrolyte layer transferred onto it is stamped to φ13.00 mm, and the positive electrode with the electrolyte layer transferred onto it is stamped to φ11.28 mm. The negative electrode layer and the positive electrode layer with the electrolyte layer transferred onto it are uniaxially pressed with the negative and positive electrode layers stacked facing each other. In this way, the negative electrode current collector, the negative electrode layer, the electrolyte layer, the positive electrode layer, and the positive electrode current collector are stacked in the aforementioned order to provide a battery.

[0116] Furthermore, after attaching the current extraction tabs to the positive and negative electrodes, the battery is sealed in an aluminum laminate using a vacuum laminator. Finally, the battery is constrained in the thickness direction under a pressure of 5 MPa, thereby fabricating a solid-state battery.

[0117] Examples 2 to 10 and Comparative Examples 1 to 12

[0118] Solid-state batteries were prepared in a similar manner to Example 1, except that PVdF with a molecular diameter D50 as shown in Table 1 and porous Si-based primary particles with an average pore size as shown in Table 1 were used to prepare electrode active materials.

[0119] Evaluation of electrode expansion rate

[0120] The solid-state batteries of Examples 1 to 10 and Comparative Examples 1 to 12 were disassembled and cut before and after charging and discharging, and then subjected to ion milling. Composite electron images of the processed cross-sections were obtained by SEM, and the electrode expansion rate was calculated from the negative electrode layer thickness before and after charging and discharging [(negative electrode layer thickness after charging and discharging) / (negative electrode layer thickness before charging and discharging)×100%]. The results are shown in Table 1.

[0121] In addition, Figure 2 The figure shows the relationship between the average pore size of the primary particles in the porous Si system and the expansion rate of the electrode. Figure 3The relationship between the molecular diameter D50 in the molecular diameter distribution of the adhesive and the electrode expansion rate is shown in the figure.

[0122] It should be noted that Table 1, Figure 2 and Figure 3 The electrode expansion rate is a relative value when the result of Comparative Example 1 is taken as 100.

[0123]

[0124] As shown in Table 1, Figure 2 and Figure 3 As shown, it was confirmed that the electrode expansion rate of Examples 1 to 10 was less than that of any one of Comparative Examples 1 to 12.

[0125] Specifically, in Comparative Examples 1 and 2, in which the average pore size of the porous Si-based primary particles used to prepare the electrode active material is 4.1 nm or less, and in Comparative Examples 11 and 12, in which the molecular diameter D50 of the binder used to prepare the electrode active material is 1,859 nm or more, even if the molecular diameter D50 of the binder is equal to or greater than the average pore size of the porous Si-based primary particles, the electrode expansion rate is increased compared to Examples 1 to 10.

[0126] Furthermore, in Comparative Examples 3 to 10, where the molecular diameter D50 of the adhesive is smaller than the average pore size of the porous Si primary particles, the electrode expansion rate increased even when the average pore size of the porous Si primary particles was greater than 4.1 nm and the molecular diameter D50 of the adhesive was less than 1,859 nm, compared to Examples 1 to 10.

Claims

1. An electrode active material comprising primary particles containing silicon element, the primary particles being provided in a form of secondary particles by a binder, wherein: the primary particles are porous and an average pore diameter of the pores of the primary particles is greater than 4.1 nm; a molecular diameter D50 in a molecular diameter distribution of the binder is less than 1,859 nm; and the molecular diameter D50 is equal to or greater than the average pore diameter.

2. The electrode active material according to claim 1, wherein: the average pore diameter of the pores of the primary particles is 5 nm or more and 30 nm or less; and the molecular diameter D50 in the molecular diameter distribution of the binder is 25 nm or more and 1,000 nm or less.

3. An electrode layer comprising the electrode active material according to claim 1.

4. A solid-state battery comprising an electrode layer containing the electrode active material according to claim 1.

5. The solid-state battery according to claim 4, wherein the electrode layer is a negative electrode layer. ​ ​ ​ ​ ​

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