Anode active material, solid-state battery, and method for producing anode active material

Abstract

A negative electrode active material 1000 according to the present disclosure comprises: graphite particles 100 each having a void 102 therein; and a first solid electrolyte 103. The void 102 has a void diameter of 1 to 300 nm, inclusive. The first solid electrolyte 103 is positioned in the void 102. Each of the graphite particles 100 has, for example, a plurality of voids therein. The average void diameter in the graphite particles 100 as measured by mercury intrusion porosimetry is, for example, 1 to 300 nm, inclusive.

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode active material, a solid-state battery, and a method for producing a negative electrode active material. [Background technology]

[0002] In all-solid-state lithium-ion batteries, both electrons and lithium ions are required to be efficiently supplied to the active material in the electrode layer. In all-solid-state lithium-ion batteries, the active material is, for example, dispersed in the electrode layer. In a typical negative electrode layer, it is desirable to have both an electron conduction path formed by contact between active material particles and an ion conduction path formed by connecting solid electrolyte particles.

[0003] Graphite particles are sometimes used as anode active materials. Graphite has a layered structure containing carbon. High-capacity batteries are realized through reactions in which lithium ions are inserted into or extracted from the graphite layer structure. However, while graphite has electronic conductivity, it has poor ionic conductivity. To compensate for the ionic conductivity of graphite, graphite particles are sometimes composited with a solid electrolyte in a typical anode layer. Furthermore, graphite particles are sometimes composited with a binder. The binder is suitable for binding the particles together to form a membrane. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-195219 Summary of the Invention [Problem to be solved by the invention]

[0005] In the prior art, new negative electrode active materials are desired. [Means for solving the problem]

[0006] The negative electrode active material of the present disclosure is graphite particles having voids therein; a first solid electrolyte; Including, The void diameter is 1 nm or more and 300 nm or less, The first solid electrolyte is located in the void. [Effects of the Invention]

[0007] According to the present disclosure, a novel negative electrode active material can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of the negative electrode active material according to the first embodiment. [Figure 2] FIG. 2 is a flowchart showing a method for producing the negative electrode active material according to the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing a schematic configuration of a solid-state battery according to the second embodiment. [Figure 4] FIG. 4 is a scanning electron microscope (SEM) image of a cross section of the graphite particle used in Example 1. [Figure 5] FIG. 5 is an SEM image of a cross section of the negative electrode active material of Example 1. [Figure 6] FIG. 6 is an SEM image of the voids in the graphite particles in the negative electrode active material of Example 1. [Figure 7] FIG. 7 is an SEM image of another void in the graphite particles in the negative electrode active material of Example 1. [Figure 8] FIG. 8 is a graph showing the relationship between the pore diameter and the Log differential pore volume in the negative electrode active material and graphite particles of Example 1. [Figure 9] FIG. 9 is an SEM image of the surface of the graphite particles used in Example 1. [Figure 10] FIG. 10 is an SEM image of the surface of the negative electrode active material of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Findings that formed the basis of this disclosure) In a negative electrode layer containing graphite particles and a solid electrolyte, the solid electrolyte has poor electronic conductivity. Therefore, increasing the amount of solid electrolyte added relative to the graphite particles reduces the volume ratio of graphite in the negative electrode layer, resulting in a decrease in the capacity of the negative electrode layer. Furthermore, the electronic conductivity of the negative electrode layer also decreases due to the prevention of contact between the graphite particles. In other words, when graphite particles are combined with a solid electrolyte in the negative electrode layer, a trade-off occurs between electronic conductivity and ionic conductivity in the negative electrode layer. In this case, it is necessary to improve the capacity of the negative electrode layer while maintaining a balance between electronic conductivity and ionic conductivity.

[0010] Patent Document 1 discloses that in order to improve the utilization rate of the active material in the electrodes of conventional all-solid-state lithium secondary batteries, the average particle size of the active material, the average particle size of the solid electrolyte, and the mixing ratio of the active material and the solid electrolyte are adjusted.

[0011] Patent Document 1 discloses adjusting the average particle diameters of the active material and solid electrolyte to a range of 0.1 μm to 50 μm. Increasing the average particle diameter of the active material within this range is considered to improve the capacity of the negative electrode layer. However, in this case, the rate characteristics of the battery during charge and discharge deteriorate due to slow ion conduction within the active material. On the other hand, decreasing the average particle diameter of the active material increases the outer surface area of ​​the active material. This increases the contact area between the active material and the solid electrolyte, reducing the electronic conductivity of the negative electrode layer. Active materials with small average particle diameters can also increase the viscosity of the coating liquid. Therefore, when preparing a negative electrode layer using a coating liquid containing this active material, process issues may arise. As such, it is difficult to prepare a battery with excellent rate characteristics during charge and discharge by adjusting the average particle diameter of the active material.

[0012] (Summary of one aspect of the present disclosure) The negative electrode active material according to the first embodiment of the present disclosure comprises: graphite particles having voids therein; a first solid electrolyte; Including, The void diameter is 1 nm or more and 300 nm or less, The first solid electrolyte is located in the void.

[0013] According to the first aspect, a novel negative electrode active material can be provided. This negative electrode active material has high electronic conductivity due to the graphite particles. Furthermore, the negative electrode active material efficiently intercalates and deintercalates lithium ions. Therefore, this negative electrode active material is suitable for improving the rate characteristics of batteries.

[0014] In a second aspect of the present disclosure, for example, in the negative electrode active material according to the first aspect, the graphite particles may have a plurality of voids therein, and the average void diameter of the graphite particles may be 1 nm or more and 300 nm or less as determined by mercury intrusion porosimetry. With this configuration, the negative electrode active material is suitable for improving the rate characteristics of a battery.

[0015] In the third aspect of the present disclosure, for example, in the negative electrode active material according to the first or second aspect, the graphite particles may be an aggregate of a plurality of primary particles containing graphite. With this configuration, the negative electrode active material can be easily produced using the graphite particles.

[0016] In a fourth aspect of the present disclosure, for example, in the negative electrode active material according to the third aspect, the primary particles may be plate-like or scaly, and the graphite particles may be stacked. With this configuration, the negative electrode active material can be easily produced using the graphite particles.

[0017] In a fifth aspect of the present disclosure, for example, in the negative electrode active material according to any one of the first to fourth aspects, the first solid electrolyte may contain lithium, phosphorus, sulfur, and a halogen. With this configuration, the negative electrode active material has high ionic conductivity.

[0018] In a sixth aspect of the present disclosure, for example, in the negative electrode active material according to any one of the first to fifth aspects, the first solid electrolyte may be represented by the following composition formula (1): Li α PS β X γ ...Equation (1) α, β, and γ may satisfy 5.5≦α≦6.5, 4.5≦β≦5.5, and 0.5≦γ≦1.5, and X may contain at least one selected from the group consisting of F, Cl, Br, and I. With this configuration, the negative electrode active material has high ionic conductivity.

[0019] In a seventh aspect of the present disclosure, for example, in the negative electrode active material according to any one of the first to sixth aspects, the first solid electrolyte may have an argyrodite-type crystal structure, and the negative electrode active material has high ionic conductivity.

[0020] In an eighth aspect of the present disclosure, for example, in the negative electrode active material according to any one of the first to seventh aspects, the voids may have a void diameter of 70 nm or less. With this configuration, when a negative electrode layer is fabricated using the negative electrode active material, ion conduction paths in the negative electrode active material are likely to be maintained.

[0021] In a ninth aspect of the present disclosure, for example, the negative electrode active material according to any one of the first to eighth aspects may further include a second solid electrolyte adhered to the outer surfaces of the graphite particles, and the coverage of the outer surfaces with the second solid electrolyte may be 10% or less. With this configuration, by using a solid electrolyte having high ion conductivity together with the negative electrode active material, a negative electrode layer having high ion conductivity can be easily produced.

[0022] In a tenth aspect of the present disclosure, for example, in the negative electrode active material according to any one of the first to ninth aspects, the ratio of the mass of the first solid electrolyte to the mass of the graphite particles may be 0.3 mass % or more and 20 mass % or less. With this configuration, the negative electrode active material can improve ionic conductivity while suppressing a decrease in capacity density.

[0023] In an eleventh aspect of the present disclosure, for example, in the negative electrode active material according to any one of the first to tenth aspects, the graphite particles may have a median diameter of 300 nm or more and 30 μm or less. This configuration allows the graphite particles to be easily handled. Furthermore, the first solid electrolyte can be easily introduced into the graphite particles.

[0024] A solid state battery according to a twelfth aspect of the present disclosure includes: a negative electrode layer including the negative electrode active material according to any one of the first to eleventh aspects; a positive electrode layer; a solid electrolyte layer located between the positive electrode layer and the negative electrode layer; Equipped with.

[0025] According to the twelfth aspect, the solid state battery has high rate characteristics.

[0026] In a thirteenth aspect of the present disclosure, for example, in the solid state battery according to the twelfth aspect, the anode layer may further include a solid electrolyte having a different composition from the first solid electrolyte, which can easily improve the ionic conductivity of the anode layer.

[0027] In a fourteenth aspect of the present disclosure, for example, in the solid state battery according to the twelfth or thirteenth aspect, the solid electrolyte layer may contain a solid electrolyte having lithium ion conductivity. With this configuration, the solid state battery has high rate characteristics.

[0028] A method for producing a negative electrode active material according to a fifteenth aspect of the present disclosure includes: bringing graphite particles having voids therein into contact with a solution containing a solid electrolyte, thereby introducing the solution into the voids; removing a solvent contained in the solution from the solution introduced into the gap to precipitate the solid electrolyte; Includes.

[0029] According to the fifteenth aspect, a negative electrode active material suitable for improving the rate characteristics of a battery can be easily produced.

[0030] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0031] (Embodiment 1) FIG. 1 is a cross-sectional view showing a schematic configuration of a negative electrode active material 1000 according to the first embodiment.

[0032] The negative electrode active material 1000 according to the first embodiment is used in, for example, a solid-state battery. The negative electrode active material 1000 includes graphite particles 100 and a first solid electrolyte 103.

[0033] The graphite particle 100 can function as an active material. The graphite particle 100 has a void 102 therein. The graphite particle 100 may have a plurality of voids 102 therein. A first solid electrolyte 103 is located in the void 102. In other words, the first solid electrolyte 103 fills the void 102.

[0034] The void diameter of the voids 102 is not less than 1 nm and not more than 300 nm. Whether the first solid electrolyte 103 is located in the voids 102 having a void diameter of not less than 1 nm and not more than 300 nm can sometimes be determined using, for example, mercury intrusion porosimetry.

[0035] In mercury intrusion porosimetry, high-pressure mercury is injected into a sample containing voids. The void distribution can be determined from the relationship between the pressure applied to the mercury and the amount of mercury injected into the sample. Specifically, the diameter D of the voids in the sample into which mercury has been injected can be determined from the following relational expression (I): In relational expression (I), γ is the surface tension of mercury, θ is the contact angle between the mercury and the wall surface of the sample, and P is the pressure applied to the mercury. D=-4γcosθ÷P (I)

[0036] The pressure P is changed in stages, and the amount of injected mercury is measured for each pressure P. The amount of injected mercury can be considered as the cumulative value of the void volume up to the diameter D corresponding to a specific pressure P. This makes it possible to obtain a void distribution in which the amount of voids is specified for each diameter D. The void distribution is, for example, a graph showing the relationship between the void diameter D and the Log differential void volume.

[0037] For example, mercury porosimetry is used to measure the negative electrode active material 1000 and the graphite particles 100 in which the first solid electrolyte 103 is not present in the voids 102. The graphite particles 100 in which the first solid electrolyte 103 is not present in the voids 102 may be graphite particles 100 before the first solid electrolyte 103 is introduced into the voids 102, or graphite particles 100 obtained by removing the first solid electrolyte 103 from the negative electrode active material 1000. The first solid electrolyte 103 can be removed from the negative electrode active material 1000 using, for example, a solvent. Mercury porosimetry can be used to obtain a pore distribution showing the relationship between the pore diameter and the Log differential pore volume for each of the negative electrode active material 1000 and the graphite particles 100. The pore diameter in the pore distribution of the graphite particles 100 corresponds to the pore size of the pores 102.

[0038] Based on the void distribution of the negative electrode active material 1000 and the void distribution of the graphite particles 100, it can be determined that the first solid electrolyte 103 is located in the voids 102 of the graphite particles 100 in the negative electrode active material 1000. For example, for the void distribution of each of the negative electrode active material 1000 and the graphite particles 100, a Log differential void volume at a specific diameter in the range of 1 nm to 300 nm is determined. If the Log differential void volume of the negative electrode active material 1000 at the specific diameter is smaller than the Log differential void volume of the graphite particles 100, it can be determined that the first solid electrolyte 103 is located in the voids 102 of the graphite particles 100. Furthermore, if the diameter at the peak of the void distribution of the negative electrode active material 1000 is smaller than the diameter at the peak of the void distribution of the graphite particles 100, it can also be determined that the first solid electrolyte 103 is located in the voids 102 of the graphite particles 100.

[0039] The fact that first solid electrolyte 103 is located in voids 102 of graphite particles 100 can also be identified by observing a cross section of negative electrode active material 1000 with an electron microscope.

[0040] For example, the negative electrode active material 1000 is processed to expose a cross section of the negative electrode active material 1000. The processing of the negative electrode active material 1000 can be performed, for example, by a cross section polisher (registered trademark). The cross section polisher can form a smooth cross section of the negative electrode active material 1000. Next, the cross section of the negative electrode active material 1000 is observed with a scanning electron microscope (SEM). This allows an SEM image of the cross section of the negative electrode active material 1000 to be obtained.

[0041] Next, the graphite particles 100, voids 102, and first solid electrolyte 103 are identified from the obtained SEM image. These identifications may be made based on the contrast of the image, or may be made based on the results of elemental analysis such as energy dispersive X-ray analysis (EDS). This makes it possible to identify that the first solid electrolyte 103 is located in the voids 102 of the graphite particles 100.

[0042] Negative electrode active material 1000 in the first embodiment contains first solid electrolyte 103 in voids 102 of graphite particles 100. This tends to give negative electrode active material 1000 high ionic conductivity and high electronic conductivity.

[0043] The voids 102 in which the first solid electrolyte 103 is located have a void diameter of 1 nm or more and 300 nm or less. The first solid electrolyte 103 can be easily introduced into the voids 102 with a void diameter of 1 nm or more. The first solid electrolyte 103 is unlikely to be excessively introduced into the voids 102 with a void diameter of 300 nm or less. Therefore, when the void diameter of the voids 102 in which the first solid electrolyte 103 is located is 300 nm or less, the negative electrode active material 1000 is suitable for improving the capacity density of the negative electrode layer.

[0044] The voids 102 in which the first solid electrolyte 103 is located may have a void diameter of 70 nm or less. Furthermore, the voids 102 may be filled with the first solid electrolyte 103. In other words, the voids 102 may be filled with the first solid electrolyte 103. In the anode active material 1000, all of the voids 102 having a void diameter of 70 nm or less may be filled with the first solid electrolyte 103. When an all-solid-state battery is produced using the anode active material 1000, the anode material containing the anode active material 1000 may be compression-molded. Compression-molding the anode material may cause deformation of the anode active material 1000. Deformation of the anode active material 1000 may cause the space where the first solid electrolyte 103 is not present to disappear. When the voids 102 having a void diameter of 70 nm or less are filled with the first solid electrolyte 103, the disappearance of the voids 102 is suppressed. This allows the ion conduction path in the anode layer to be sufficiently maintained.

[0045] In the negative electrode active material 1000, the voids 102 may be connected to the outside of the negative electrode active material 1000. When a battery is fabricated using a negative electrode material containing this negative electrode active material 1000, the first solid electrolyte 103 contained in the negative electrode active material 1000 can easily come into contact with other solid electrolytes contained in the negative electrode material or with solid electrolytes contained in the solid electrolyte layer. This allows for efficient ion conduction into the graphite particles 100.

[0046] When graphite particles 100 have multiple voids therein, the average void diameter S of graphite particles 100 determined by mercury intrusion porosimetry is not particularly limited and is, for example, 1 nm or more and 300 nm or less. The average void diameter S may be 10 nm or more, 50 nm or more, 100 nm or more, or 150 nm or more. The average void diameter S may be 250 nm or less, or 200 nm or less.

[0047] The average pore diameter S of the graphite particles 100 can be determined, for example, by the following method. First, measurement is performed by mercury porosimetry on graphite particles 100 in which the first solid electrolyte 103 is not present in the pores 102. Graphite particles 100 in which the first solid electrolyte 103 is not present in the pores 102 can be graphite particles 100 before the first solid electrolyte 103 is introduced into the pores 102, or graphite particles 100 obtained by removing the first solid electrolyte 103 from the negative electrode active material 1000. Mercury porosimetry can be used to obtain a pore distribution for the graphite particles 100, which indicates the relationship between the pore diameter and the Log differential pore volume. Next, the peak of the pore distribution of the graphite particles 100 is identified. The diameter at the peak of the pore distribution can be considered as the average pore diameter S. The diameter at the peak of the pore distribution corresponds to the mode diameter of the pores.

[0048] The graphite particle 100 is, for example, an aggregate of a plurality of primary particles 101 containing graphite. In other words, the graphite particle 100 is a secondary particle made up of a plurality of primary particles 101. In the graphite particle 100, the plurality of primary particles 101 may be in contact with each other. The primary particles 101 can form an intercalation compound containing carbon. In the graphite particle 100, for example, voids 102 are formed between the plurality of primary particles 101.

[0049] The shape of the primary particles 101 is not particularly limited and may be, for example, plate-like or scale-like. The shape of the primary particles 101 may also be needle-like, spherical, oval-spherical, or the like. In the graphite particle 100, a plurality of plate-like or scale-like primary particles 101 may be stacked. That is, the graphite particle 100 may have a layered structure made of a plurality of plate-like or scale-like primary particles 101. In this layered structure, for example, a void 102 is formed between two of the plurality of primary particles 101. The void 102 extends, for example, in a direction perpendicular to the stacking direction of the plurality of primary particles 101.

[0050] As an example, the graphite particle 100 may have a plurality of voids 102, and the plurality of voids 102 may be aligned in the stacking direction of the plurality of primary particles 101. The plurality of voids 102 may be independent of each other. However, at least one void 102 of the plurality of voids 102 may be connected to another void 102. The plurality of voids 102 may be formed three-dimensionally and continuously. At least one void 102 of the plurality of voids 102 may penetrate the graphite particle 100.

[0051] For example, the graphite particle 100 is spherical or ellipsoidal. In this case, at the center of the graphite particle 100, a plurality of plate-like or scale-like primary particles 101 are overlapped and united so that the main surfaces of the plate-like or scale-like primary particles 101 extend in the diameter direction of the graphite particle 100. At the outer periphery of the graphite particle 100, the plate-like or scale-like primary particles 101 are curved and overlapped and united. Some of the plurality of primary particles 101 are folded and overlap one another. Voids 102 are formed between the primary particles 101 and between the folded primary particles 101. The "main surface" means the surface having the largest area.

[0052] The primary particles 101 may contain graphite as a main component, for example, may consist essentially of graphite. "Main component" refers to the component that is contained in the primary particles 101 in the largest amount by mass. "Consist essentially of" means that other components that alter the essential characteristics of the referenced material are excluded. However, the primary particles 101 may contain impurities in addition to graphite.

[0053] The shape of the graphite particles 100 is not particularly limited and may be, for example, spherical or ellipsoidal. Spherical or ellipsoidal graphite particles 100 have few protrusions protruding from the particle surface. Therefore, a coating liquid containing such graphite particles 100 tends to reduce the resistance during coating. This coating liquid makes it easy to produce a negative electrode layer in which the graphite particles 100 are packed at a high density. However, the graphite particles 100 may have protrusions resulting from the plate-like primary particles 101.

[0054] The median diameter of the graphite particles 100 is not particularly limited and is, for example, 300 nm or more and 30 μm or less. Graphite particles 100 with a median diameter of 300 nm or more are easy to handle and suitable for producing a negative electrode active material 1000. Graphite particles 100 with a median diameter of 30 μm or less allow first solid electrolyte 103 to be easily introduced therein. The median diameter of the graphite particles 100 may be 1 μm or more and 10 μm or less.

[0055] Generally, the term "median diameter" refers to the particle size where the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measurement device.

[0056] The graphite particles 100 containing a plurality of voids 102 can be considered as a porous material. The specific surface area of ​​the graphite particles 100 is not particularly limited, and may be, for example, 5 m 2 / g or more. The specific surface area is 5m 2 / g or more, the inner surface of the graphite particle 100 surrounding the voids 102 can be coated with a sufficient amount of the first solid electrolyte 103. The larger the specific surface area of ​​the graphite particle 100, the greater the area of ​​the inner surface of the graphite particle 100 that can be coated with the first solid electrolyte 103. The specific surface area of ​​the graphite particle 100 can be measured, for example, by mercury intrusion porosimetry. The specific surface area of ​​the graphite particle 100 can also be obtained by converting data on an adsorption isotherm obtained by a gas adsorption method using nitrogen gas using the Brunauer-Emmett-Teller (BET) method.

[0057] The porosity of the graphite particle 100 may be 5% or more. In graphite particles 100 with a porosity of 5% or more, the inner surface of the graphite particle 100 can be coated with a sufficient amount of first solid electrolyte 103. The upper limit of the porosity of the graphite particle 100 is not particularly limited and is, for example, 50%. Graphite particles 100 with a porosity of 50% or less tend to have sufficiently high strength. The porosity of the graphite particle 100 can be measured, for example, by mercury intrusion porosimetry. The porosity of the graphite particle 100 can also be calculated from the volume of pores 102 obtained by gas adsorption using nitrogen gas.

[0058] The shape of the first solid electrolyte 103 is not particularly limited and may be acicular, spherical, oval, or the like. The first solid electrolyte 103 may be particulate. The first solid electrolyte 103 may have the shape of a film that covers the inner surface of the graphite particle 100. A film-like first solid electrolyte 103 tends to promote ion conduction within the plane of the first solid electrolyte 103. The size of the first solid electrolyte 103 is not particularly limited and may be 1 nm or more and 100 nm or less, or 1 nm or more and 70 nm or less. When the size of the first solid electrolyte 103 is 1 nm or more and 100 nm or less, the first solid electrolyte 103 can easily enter the voids 102 of the graphite particle 100 while maintaining sufficient ion conductivity.

[0059] The shape of the first solid electrolyte 103 can be identified by observing a cross section of the negative electrode active material 1000 with an electron microscope. The size of the first solid electrolyte 103 can be measured by the following method using mercury porosimetry, for example. First, the negative electrode active material 1000 and the graphite particles 100 in which the first solid electrolyte 103 is not present in the voids 102 are each measured by mercury porosimetry. Mercury porosimetry can be used to obtain a void distribution that shows the relationship between the void diameter and the Log differential void volume for each of the negative electrode active material 1000 and the graphite particles 100. The size of the first solid electrolyte 103 can be determined by subtracting the diameter at the peak of the void distribution of the negative electrode active material 1000 from the diameter at the peak of the void distribution of the graphite particles 100.

[0060] When first solid electrolyte 103 is in the form of particles, the median diameter of first solid electrolyte 103 may be 1 nm or more and 100 nm or less, or may be 1 nm or more and 70 nm or less.

[0061] The negative electrode active material 1000 may or may not further include a second solid electrolyte attached to the outer surfaces of the graphite particles 100. The coverage of the outer surfaces of the graphite particles 100 with the second solid electrolyte is not particularly limited and is, for example, 10% or less. This coverage may be 5% or less, 3% or less, or 1% or less.

[0062] The coverage of the outer surfaces of the graphite particles 100 with the second solid electrolyte can be measured by the following method. First, the surface of the negative electrode active material 1000 is observed with a scanning electron microscope. By image processing, the area A1 of the negative electrode active material 1000 and the area A2 of the second solid electrolyte shown in the obtained electron microscope image are calculated. The ratio of area A2 to area A1 can be considered to be the coverage of the outer surfaces of the graphite particles 100 with the second solid electrolyte.

[0063] The second solid electrolyte is usually formed when the first solid electrolyte 103 is introduced into the voids 102 of the graphite particles 100. Therefore, the composition of the second solid electrolyte is, for example, the same as that of the first solid electrolyte 103. The first solid electrolyte 103 may have low crystallinity because it is introduced into the minute voids 102. A solid electrolyte with low crystallinity tends to have lower ionic conductivity than a solid electrolyte with high crystallinity. Therefore, the negative electrode material for preparing the negative electrode layer of the all-solid-state battery may further contain a solid electrolyte having higher ionic conductivity than the first solid electrolyte 103. If the coverage of the outer surface of the graphite particles 100 with the second solid electrolyte is 10% or less, the solid electrolyte having high ionic conductivity in the negative electrode material is likely to come into contact with the outer surface of the graphite particles 100. Therefore, such a negative electrode active material 1000 makes it easy to prepare a negative electrode layer with high ionic conductivity.

[0064] In the negative electrode active material 1000, the ratio P1 of the mass of the first solid electrolyte 103 to the mass of the graphite particles 100 is not particularly limited and may be 0.3 mass% to 20 mass% or less, 0.3 mass% to 10 mass% or less, or 1.0 mass% to 6.0 mass% or less. When the ratio P1 is 0.3 mass% or more, the ion conduction paths in the negative electrode active material 1000 can be sufficiently increased. When the ratio P1 is 20 mass% or less, a decrease in the capacity density of the negative electrode active material 1000 can be sufficiently suppressed. Furthermore, in the negative electrode active material 1000, the ratio P2 of the sum of the mass of the first solid electrolyte 103 and the mass of the second solid electrolyte to the mass of the graphite particles 100 can be 0.3 mass% to 20 mass% or less, 0.3 mass% to 10 mass% or less, or 1.0 mass% to 6.0 mass% or less.

[0065] The first solid electrolyte 103 has, for example, lithium ion conductivity. The first solid electrolyte 103 includes, for example, at least one selected from the group consisting of inorganic solid electrolytes and organic solid electrolytes. The first solid electrolyte 103 may include a sulfide solid electrolyte. The sulfide solid electrolyte has excellent reduction stability and is therefore suitable for combination with the graphite particles 100, which are a low-potential negative electrode material.

[0066] The sulfide solid electrolyte contained in the first solid electrolyte 103 may contain lithium, phosphorus, sulfur, and a halogen. The first solid electrolyte 103 is represented by, for example, the following composition formula (1). Li α PS β X γ ...Equation (1)

[0067] In formula (1), α, β, and γ satisfy the relationships 5.5≦α≦6.5, 4.5≦β≦5.5, and 0.5≦γ≦1.5. X includes at least one selected from the group consisting of F, Cl, Br, and I. X may be Cl or Br, or may be Cl. The first solid electrolyte 103 may be Li6PS5X. The solid electrolyte represented by composition formula (1) has, for example, an argyrodite-type crystal structure. That is, the first solid electrolyte 103 may have an argyrodite-type crystal structure. A negative electrode active material 1000 including such a first solid electrolyte 103 tends to have high ionic conductivity.

[0068] Examples of sulfide solid electrolytes other than those represented by the composition formula (1) include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 These include LiX, LiO, MO q , Li p MO q The element X in "LiX" is at least one element selected from the group consisting of F, Cl, Br, and I. q " and "Li p MO q "The element M is at least one element selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q " p and q in this expression are independent natural numbers.

[0069] The first solid electrolyte 103 may include at least one selected from the group consisting of an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte.

[0070] Examples of oxide solid electrolytes include NASICON-type solid electrolytes, such as LiTi2(PO4)3 and its elemental substitution products, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGeO 16 , Li4SiO4, LiGeO4 and their element-substituted LISICON-type solid electrolytes, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those substituted with LiN and its element, LiN and its H-substituted compounds, LiPO4 and its N-substituted compounds, and glass or glass ceramics containing a base material containing Li-BO compounds such as LiBO2 and LiBO3 to which a material such as LiSO4 or LiCO3 has been added can be used.

[0071] As the polymer solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used. The polymer compound may have an ethylene oxide structure. By having an ethylene oxide structure, the polymer compound can contain a large amount of lithium salt, thereby further increasing ionic conductivity. As the lithium salt, LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, etc. can be used. As the lithium salt, one type of lithium salt selected from these may be used alone, or a mixture of two or more types of lithium salts selected from these may be used.

[0072] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0073] The shape of the negative electrode active material 1000 is not particularly limited and may be, for example, spherical or oval. The shape of the negative electrode active material 1000 may be particulate. When the negative electrode active material 1000 is particulate, the median diameter of the negative electrode active material 1000 is not particularly limited and may be, for example, 300 nm or more and 30 μm or less.

[0074] Next, a method for manufacturing the negative electrode active material 1000 will be described. FIG. 2 is a flowchart showing the method for manufacturing the negative electrode active material 1000 according to the first embodiment. First, in step S11, a solution L containing a first solid electrolyte 103 is prepared. Specific examples of the solution L are described in non-patent documents such as J. Mater. Chem. A, 2019, 7, 558-566. The concentration of the first solid electrolyte 103 in the solution L is not particularly limited and is, for example, 1% by mass or more and 20% by mass or less.

[0075] The above-mentioned non-patent document discloses a method for preparing a sulfide solid electrolyte represented by Li6PS5Br from a solution. Specifically, the non-patent document discloses that the solid electrolyte is prepared by volatilizing and removing the solvent contained in the solution containing the solid electrolyte, followed by heat treatment. After extensive research, the present inventors have found that other solid electrolytes having an argyrodite-type crystal structure can also be synthesized by the method described in the non-patent document. Examples of other solid electrolytes include Li6PS5Cl.

[0076] Next, in step S12, graphite particles 100 having voids 102 therein are brought into contact with solution L. Solution L does not contain, for example, particles of first solid electrolyte 103. Therefore, when graphite particles 100 are brought into contact with solution L, solution L can easily penetrate into minute voids 102 of graphite particles 100. Specifically, solution L easily penetrates into the interior of graphite particles 100 due to capillary action. As a result, solution L is introduced into voids 102. The method for bringing graphite particles 100 into contact with solution L is not particularly limited. For example, graphite particles 100 may be brought into contact with solution L by kneading graphite particles 100 and solution L. When graphite particles 100 are brought into contact with solution L, the ratio of the mass of first solid electrolyte 103 to the total value of the mass of graphite particles 100 and the mass of first solid electrolyte 103 is not particularly limited, and is, for example, more than 0.2 mass % and not more than 20 mass %.

[0077] The method for producing graphite particles 100 having voids 102 therein is not particularly limited. Graphite particles 100 can be produced, for example, by subjecting a plurality of primary particles 101 to a known spheroidizing treatment. As an example, graphite particles 100 can be produced by dispersing a plurality of primary particles 101 in an inert gas flow and causing these particles to collide with each other in the air flow. The spheroidizing treatment can be carried out using a commercially available device.

[0078] Next, in step S13, the solvent contained in the solution L is removed. As a result, the first solid electrolyte 103 is precipitated in the voids 102. The solvent is removed, for example, by volatilizing the solvent. As an example, the solvent of the solution L may be volatilized while kneading the graphite particles 100 and the solution L. The solvent of the solution L that has penetrated the interior of the graphite particles 100 is less likely to volatilize than the solvent of the solution L present outside the graphite particles 100. Therefore, when the solvent contained in the solution L is volatilized, the first solid electrolyte 103 tends to be concentrated in the voids 102 of the graphite particles 100. When the solvent of the solution L is volatilized, the first solid electrolyte 103 is hardly present outside the graphite particles 100, but is supported by the graphite particles 100 in the voids 102. Therefore, this method makes it possible to easily produce an anode active material 1000 that hardly contains the second solid electrolyte attached to the outer surfaces of the graphite particles 100.

[0079] Next, in step S14, the graphite particles 100 may be heat-treated. The conditions for the heat treatment can be set appropriately depending on the composition of the first solid electrolyte 103, etc. The temperature for the heat treatment is not particularly limited and is, for example, 100°C or higher. The time for the heat treatment is not particularly limited and is, for example, 1 hour or longer. The heat treatment may be performed in a reduced pressure atmosphere or a vacuum atmosphere. Heat-treating the graphite particles 100 tends to improve the crystallinity of the first solid electrolyte 103.

[0080] The method for producing the negative electrode active material 1000 is not limited to the flowchart of Fig. 2. For example, the negative electrode active material 1000 may be produced by using a dispersion of the first solid electrolyte 103 instead of the solution L1.

[0081] (Embodiment 2) The following describes the second embodiment. Explanations that overlap with the first embodiment will be omitted where appropriate.

[0082] FIG. 3 is a cross-sectional view showing a schematic configuration of a solid-state battery 2000 according to the second embodiment.

[0083] The solid state battery 2000 in the second embodiment includes an anode layer 201 , a solid electrolyte layer 202 , and a cathode layer 203 .

[0084] The negative electrode layer 201 has a negative electrode material including a negative electrode active material 1000 .

[0085] The solid electrolyte layer 202 is located between the positive electrode layer 203 and the negative electrode layer 201 .

[0086] When an all-solid-state battery is fabricated using the anode active material 1000, the anode material containing the anode active material 1000 may be compression-molded. Compression-molding the anode material may cause the anode active material 1000 to deform. The deformation of the anode active material 1000 may reduce the volume of spaces where the first solid electrolyte 103 is not present, resulting in the loss of these spaces. Therefore, in the anode active material 1000 present in the anode layer 201, all of the voids 102 may be filled with the first solid electrolyte 103. FIG. 3 illustrates the anode active material 1000 in a state in which the spaces where the first solid electrolyte 103 is not present have disappeared. In other words, in the anode active material 1000 of FIG. 3, all of the voids 102 are filled with the first solid electrolyte 103. However, in the anode active material 1000 in the anode layer 201, not all of the voids 102 may be filled with the first solid electrolyte 103.

[0087] In the negative electrode material, a plurality of negative electrode active materials 1000 may be in contact with each other, thereby forming an electron conduction path.

[0088] The negative electrode material may further include a solid electrolyte 105 in addition to the negative electrode active material 1000. In this specification, the solid electrolyte 105 may be referred to as a "third solid electrolyte." The third solid electrolyte 105 may fill spaces between a plurality of negative electrode active materials 1000, for example. The third solid electrolyte 105 may have a particle shape. A large number of particles of the third solid electrolyte 105 may be compressed and bonded to each other, thereby forming an ion conduction path.

[0089] The third solid electrolyte 105 may or may not be in contact with the second solid electrolyte of the negative electrode active material 1000. When the third solid electrolyte 105 is in contact with the second solid electrolyte, ion conduction into the inside of the graphite particle 100 can occur efficiently.

[0090] The third solid electrolyte 105 has, for example, lithium ion conductivity. The third solid electrolyte 105 includes, for example, at least one selected from the group consisting of inorganic solid electrolytes and organic solid electrolytes. The third solid electrolyte 105 may include at least one selected from the group consisting of sulfide solid electrolytes, oxide solid electrolytes, halide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes, or may include a sulfide solid electrolyte. As the sulfide solid electrolyte, oxide solid electrolyte, polymer solid electrolyte, and complex hydride solid electrolyte, those described above for the first solid electrolyte 103 can be used. Specific examples of halide solid electrolytes will be described later for the solid electrolyte layer 202.

[0091] To achieve a good dispersion state, it is desirable that the third solid electrolyte 105 be made of a soft material. In this respect, at least one selected from the group consisting of sulfide solid electrolytes and halide solid electrolytes is suitable as the third solid electrolyte 105.

[0092] The composition of third solid electrolyte 105 may be the same as or different from that of first solid electrolyte 103. As an example, the composition of first solid electrolyte 103 may be adjusted so that first solid electrolyte 103 can be easily introduced into minute voids 102 of graphite particles 100. The composition of third solid electrolyte 105 may be adjusted so that third solid electrolyte 105 has high ionic conductivity.

[0093] The shape of third solid electrolyte 105 is not particularly limited, and may be needle-like, spherical, oval-spherical, scale-like, etc. Third solid electrolyte 105 may also be particulate.

[0094] When the third solid electrolyte 105 is particulate (e.g., spherical), the median diameter of the third solid electrolyte 105 may be 0.3 μm or more and 100 μm or less. When the median diameter is 0.3 μm or more, the number of contact interfaces between the particles of the third solid electrolyte 105 does not increase too much, and an increase in the ionic resistance inside the anode layer 201 can be suppressed. This enables the battery to operate at high power.

[0095] When the median diameter of third solid electrolyte 105 is 100 μm or less, negative electrode active material 1000 and third solid electrolyte 105 tend to be well dispersed in the negative electrode material, which facilitates achieving a high capacity battery.

[0096] The median diameter of the third solid electrolyte 105 may be smaller than the median diameter of the negative electrode active material 1000. This allows the negative electrode active material 1000 and the third solid electrolyte 105 to form a better dispersed state in the negative electrode material.

[0097] The negative electrode material may further contain an active material other than the negative electrode active material 1000. The shape of the other active material is not particularly limited and may be acicular, spherical, oval spherical, etc. The shape of the other active material may be particulate.

[0098] The median diameter of the other active material may be 0.1 μm or more and 100 μm or less.

[0099] When the median diameter of the other active material is 0.1 μm or more, the other active material and the third solid electrolyte 105 tend to form a good dispersion state in the negative electrode material, which results in improved charging characteristics of the battery.

[0100] When the median diameter of the other active material is 100 μm or less, the diffusion rate of lithium within the active material is sufficiently ensured, enabling the battery to operate at high power.

[0101] The median diameter of the other active material may be larger than the median diameter of the third solid electrolyte 105. This allows the active material and the third solid electrolyte 105 to form a good dispersed state.

[0102] The other active materials include materials that have the property of absorbing and releasing metal ions (e.g., lithium ions). Examples of the other active materials that can be used include metal materials, carbon materials, oxides, nitrides, tin compounds, and silicon compounds. The metal materials may be simple metals or alloys. Examples of metal materials include lithium metal and lithium alloys. Examples of carbon materials include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, and tin compounds are preferably used. The other active materials may include a single active material or multiple active materials having different compositions.

[0103] The particles of the negative electrode active material 1000 and the third solid electrolyte 105 may be in contact with each other, as shown in Figure 3. The negative electrode material may include a plurality of particles of the negative electrode active material 1000 and a plurality of particles of the third solid electrolyte 105.

[0104] In the negative electrode material, the content of the third solid electrolyte 105 and the content of the negative electrode active material 1000 may be the same or different.

[0105] When the total amount of the negative electrode material is taken as 100 mass %, the content of the negative electrode active material 1000 may be 40 mass % or more and 90 mass % or less, or 40 mass % or more and 80 mass % or less. By appropriately adjusting the content of the negative electrode active material 1000, the negative electrode active material 1000 and the third solid electrolyte 105 are likely to form a well-dispersed state.

[0106] The negative electrode material may contain only the negative electrode active material 1000 and the third solid electrolyte 105. In other words, the negative electrode material may consist essentially of the negative electrode active material 1000 and the third solid electrolyte 105. This configuration can improve the energy density of the battery. "Containing only the negative electrode active material 1000 and the third solid electrolyte 105" means that, except for unavoidable impurities, no other materials are intentionally included in the negative electrode material.

[0107] The mass ratio "w1:100-w1" between the active material in the negative electrode layer 201 and the third solid electrolyte 105 may satisfy 40≦w1≦90, or 40≦w1≦80. When 40≦w1 is satisfied, the energy density of the solid battery 2000 is sufficiently ensured. Furthermore, when w1≦90 is satisfied, the solid battery 2000 can operate at high output.

[0108] The thickness of the negative electrode layer 201 may be 10 μm or more and 500 μm or less. When the thickness of the negative electrode layer 201 is 10 μm or more, the energy density of the solid battery 2000 is sufficiently ensured. When the thickness of the negative electrode layer 201 is 500 μm or less, the solid battery 2000 can operate at high output.

[0109] The solid electrolyte layer 202 is a layer containing a solid electrolyte.

[0110] For example, an inorganic solid electrolyte having lithium ion conductivity is used as the solid electrolyte contained in the solid electrolyte layer 202. Examples of the inorganic solid electrolyte that can be used include a sulfide solid electrolyte, an oxide solid electrolyte, and a halide solid electrolyte.

[0111] The solid electrolyte contained in the solid electrolyte layer 202 may be a halide solid electrolyte.

[0112] The halide solid electrolyte is represented, for example, by the following composition formula (2). In composition formula (2), α, β, and γ each independently have a value greater than 0. M includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li. X includes at least one element selected from the group consisting of F, Cl, Br, and I.

[0113] Li α M β X γ ...Equation (2)

[0114] Metalloid elements include B, Si, Ge, As, Sb, and Te. Metal elements include all elements in groups 1 to 12 of the periodic table except for hydrogen, and all elements in groups 13 to 16 except for B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metal elements are a group of elements that can become cations when forming inorganic compounds with halides.

[0115] Examples of halide solid electrolytes that can be used include Li3YX6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, and Li3(Al,Ga,In)X6.

[0116] The above configuration can improve the output density of the solid-state battery 2000. Furthermore, the thermal stability of the solid-state battery 2000 can be improved, and the generation of harmful gases such as hydrogen sulfide can be suppressed.

[0117] In this disclosure, when an element in a formula is expressed as "(Al, Ga, In)", this notation indicates at least one element selected from the group of elements in parentheses. That is, "(Al, Ga, In)" is synonymous with "at least one element selected from the group consisting of Al, Ga, and In". The same applies to other elements. Halide solid electrolytes exhibit excellent ionic conductivity.

[0118] In composition formula (2), M may contain Y (=yttrium). That is, the halide solid electrolyte contained in solid electrolyte layer 202 may contain Y as a metal element.

[0119] The halide solid electrolyte containing Y may be a compound represented by the following composition formula (3).

[0120] Li a M b Y c X6...Formula (3)

[0121] Composition formula (3) satisfies a+mb+3c=6 and c>0. In composition formula (3), M includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li and Y. m is the valence of M. X includes at least one element selected from the group consisting of F, Cl, Br, and I. M includes at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb. Specific examples of Y-containing halide solid electrolytes include Li3YF6, Li3YCl6, Li3YBr6, Li3YI6, Li3YBrCl5, Li3YBr3Cl3, Li3YBr5Cl, Li3YBr5I, Li3YBr3I3, Li3YBrI5, Li3YClI5, Li3YCl3I3, Li3YCl5I, Li3YBr2Cl2I2, Li3YBrCl4I, Li 2.7 Y 1.1 Cl6, Li 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.5 Y 0.3 Zr 0.7 Cl6 and the like can be used.

[0122] According to the above configuration, the output density of the solid state battery 2000 can be further improved.

[0123] The solid electrolyte contained in solid electrolyte layer 202 may include a sulfide solid electrolyte. As the sulfide solid electrolyte, the same as those described above for first solid electrolyte 103 can be used.

[0124] The solid electrolyte contained in the solid electrolyte layer 202 may include at least one selected from the group consisting of an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. As the oxide solid electrolyte, the polymer solid electrolyte, and the complex hydride solid electrolyte, those described above for the first solid electrolyte 103 can be used.

[0125] The solid electrolyte layer 202 may contain only one solid electrolyte selected from the above-mentioned group of solid electrolytes, or may contain two or more solid electrolytes selected from the above-mentioned group of solid electrolytes. The multiple solid electrolytes have different compositions. For example, the solid electrolyte layer 202 may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0126] The thickness of the solid electrolyte layer 202 may be 1 μm or more and 300 μm or less. When the thickness of the solid electrolyte layer 202 is 1 μm or more, the anode layer 201 and the cathode layer 203 are less likely to short-circuit. When the thickness of the solid electrolyte layer 202 is 300 μm or less, the solid battery 2000 can operate at high output.

[0127] The positive electrode layer 203 contributes to the operation of the solid-state battery 2000 as a counter electrode to the negative electrode layer 201 .

[0128] The positive electrode layer 203 may include a material having the property of absorbing and releasing metal ions (e.g., lithium ions), such as a positive electrode active material. Examples of the positive electrode active material that can be used include metal composite oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, using a lithium-containing transition metal oxide as the positive electrode active material can reduce manufacturing costs and increase the average discharge voltage.

[0129] The metal composite oxide selected as the positive electrode active material contained in the positive electrode layer 203 may contain Li and at least one element selected from the group consisting of Mn, Co, Ni, and Al. Examples of such materials include Li(NiCoAl)O2, Li(NiCoMn)O2, and LiCoO2. For example, the positive electrode active material may be Li(NiCoMn)O2.

[0130] The positive electrode layer 203 may contain a solid electrolyte. The above configuration increases the lithium ion conductivity inside the positive electrode layer 203, enabling the solid battery 2000 to operate at high power. The solid electrolyte in the positive electrode layer 203 may be any of the materials exemplified as the solid electrolyte contained in the solid electrolyte layer 202.

[0131] The median diameter of the active material particles contained in the positive electrode layer 203 may be 0.1 μm or more and 100 μm or less. When the median diameter of the active material particles is 0.1 μm or more, the active material particles and the solid electrolyte can form a well-dispersed state. This improves the charge capacity of the solid battery 2000. When the median diameter of the active material particles is 100 μm or less, the diffusion rate of lithium within the active material particles is sufficiently ensured. This enables the solid battery 2000 to operate at high power.

[0132] The median diameter of the active material particles may be larger than the median diameter of the solid electrolyte particles, thereby achieving a good dispersion state between the active material and the solid electrolyte.

[0133] The mass ratio "w2:100-w2" of the active material to the solid electrolyte contained in the positive electrode layer 203 may satisfy 40≦w2≦90. When 40≦w2 is satisfied, the energy density of the solid battery 2000 is sufficiently ensured. Furthermore, when w2≦90 is satisfied, the solid battery 2000 can operate at high output.

[0134] The thickness of the positive electrode layer 203 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode layer 203 is 10 μm or more, the energy density of the solid battery 2000 is sufficiently ensured. When the thickness of the positive electrode layer 203 is 500 μm or less, the solid battery 2000 can operate at high output.

[0135] At least one of the negative electrode layer 201, the solid electrolyte layer 202, and the positive electrode layer 203 may contain a binder to improve adhesion between particles. The binder is used, for example, to improve the binding properties of the materials constituting the electrodes. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl ester of acrylic acid, polyethyl ester of acrylic acid, polyhexyl ester of acrylic acid, polymethacrylic acid, polymethyl ester of methacrylic acid, polyethyl ester of methacrylic acid, polyhexyl ester of methacrylic acid, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose. The binder may be a copolymer of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. Alternatively, a mixture of two or more materials selected from these may be used as the binder.

[0136] At least one of the negative electrode layer 201 and the positive electrode layer 203 may contain a conductive additive to enhance electronic conductivity. Examples of conductive additives that can be used include graphites (natural graphite or artificial graphite), carbon blacks (acetylene black, ketjen black, etc.), conductive fibers (carbon fiber or metal fiber, etc.), metal powders (carbon fluoride, aluminum, etc.), conductive whiskers (zinc oxide, potassium titanate, etc.), conductive metal oxides (titanium oxide, etc.), and conductive polymer compounds (polyaniline, polypyrrole, polythiophene, etc.). Using a carbon conductive additive can reduce costs.

[0137] The solid-state battery 2000 can be configured as a battery of various shapes, such as a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminated type. [Example]

[0138] The present disclosure will be described in detail below using examples and comparative examples, but the present disclosure is not limited to the following examples.

[0139] Example 1 [Preparation of a solution containing sulfide solid electrolyte] Li2S, P2S5, and ultra-dehydrated tetrahydrofuran (THF) were mixed in an argon glove box with an Ar atmosphere at a dew point of -60 °C or less. The molar ratio of Li2S to P2S5 was 3:1. The THF did not contain any stabilizers. The resulting mixture was stirred overnight to obtain a THF suspension containing Li3PS4.

[0140] Next, Li2S and LiCl were dissolved in ultra-dehydrated ethanol (EtOH) to obtain an EtOH solution. The molar ratio of Li2S to LiCl was 1:1. Next, the THF suspension and the EtOH solution were mixed to obtain a THF-EtOH solution containing Li6PS5Cl. In this solution, the molar ratio of Li2S, P2S5, and LiCl used as raw materials was 5:1:2. The concentration of Li6PS5Cl in this solution was 4.5 mass%.

[0141] [Composite of graphite particles and solid electrolyte] Next, spherical graphite particles with internal voids were prepared. The median diameter of the graphite particles was 8 μm. The average void diameter of the graphite particles, as determined by mercury intrusion porosimetry, was 190 nm. Next, in an argon glove box, the graphite particles and a THF-EtOH solution containing Li6PS5Cl were weighed in a mass ratio of graphite particles:Li6PS5Cl = 97.5:2.5. Next, these were mixed in an agate mortar to bring the graphite particles into contact with the THF-EtOH solution. Furthermore, while kneading these, the solvent contained in the THF-EtOH solution was volatilized. Next, the obtained composite was heat-treated at 150°C for 2 hours in a vacuum atmosphere. This resulted in the negative electrode active material of Example 1. The negative electrode active material of Example 1 contained Li6PS5Cl as a solid electrolyte.

[0142] Example 2 The negative electrode active material of Example 2 was obtained in the same manner as in Example 1, except that the graphite particles and the THF-EtOH solution containing Li6PS5Cl were weighed in a mass ratio of graphite particles:Li6PS5Cl=95.0:5.0.

[0143] Example 3 Except for using LiBr instead of LiCl, the negative electrode active material of Example 3 was obtained in the same manner as in Example 1. The negative electrode active material of Example 3 contained Li6PS5Br as a solid electrolyte.

[0144] Example 4 The negative electrode active material of Example 4 was obtained in the same manner as in Example 1, except that the graphite particles and the THF-EtOH solution containing Li6PS5Cl were weighed in a mass ratio of graphite particles:Li6PS5Cl=88.0:12.0.

[0145] Comparative Example 1 The negative electrode active material of Comparative Example 1 was obtained by the same method as in Example 1, except that void-free plate-like graphite particles having a void diameter of 1 nm to 300 nm were used. The median diameter of the graphite particles used in Comparative Example 1 was 3 μm.

[0146] Comparative Example 2 The negative electrode active material of Comparative Example 2 was obtained in the same manner as in Example 1, except that a THF suspension containing Li3PS4 was used instead of a THF-EtOH solution containing Li6PS5Cl, and the graphite particles and the THF suspension containing Li3PS4 were weighed in a mass ratio of graphite particles:Li3PS4 = 97.5:2.5.

[0147] [Observation of particle cross section using SEM] The cross section of the graphite particles used in Example 1 was observed with an SEM (SU-70 manufactured by Hitachi High-Technologies Corporation). FIG. 4 is an SEM image of the cross section of the graphite particles used in Example 1. As can be seen from FIG. 4, the graphite particles were aggregates of plate-like primary particles capable of forming an intercalation compound containing carbon. In the graphite particles, voids existed between multiple primary particles.

[0148] Next, a cross section of the negative electrode active material of Example 1 was observed by SEM. Fig. 5 is an SEM image of the cross section of the negative electrode active material of Example 1. As can be seen from Fig. 5, in the negative electrode active material, precipitates of the solid electrolyte (white portions) were present in the voids inside the graphite particles.

[0149] Next, elemental analysis was performed on a cross section of the negative electrode active material of Example 1 using EDS. FIG. 6 is an SEM image of the voids in the graphite particles in the negative electrode active material of Example 1, and is an enlarged view of the cross section of the negative electrode active material. FIG. 6 also shows the results of mapping the information on the locations of P, S, and Cl obtained by the above elemental analysis. P, S, and Cl were present on the inner surface of the voids shown in FIG. 6 due to Li6PS5Cl.

[0150] FIG. 7 is an SEM image of another void in the graphite particles in the negative electrode active material of Example 1, and is an enlarged cross-section of the negative electrode active material. FIG. 7 also shows the results of mapping the information on the locations of P, S, and Cl obtained by the elemental analysis. The void shown in FIG. 7 was completely filled with precipitates containing P, S, and Cl. In other words, the void was filled with Li6PS5Cl.

[0151] [Measurement by mercury porosimetry] The graphite particles used in Example 1 and the negative electrode active material of Example 1 were measured by mercury intrusion porosimetry using a mercury porosimeter (Shimadzu Autopore IV9500). Figure 8 is a graph showing the relationship between the pore diameter and the Log differential pore volume in the negative electrode active material and graphite particles of Example 1. As can be seen from Figure 8, the pore distribution of the graphite particles has a peak at a pore diameter (pore diameter) of 190 nm. The pore distribution of the graphite particles was a gentle curve from pore diameters of 5 nm to 190 nm. Furthermore, the measurement results showed that the porosity of the graphite particles was 25%.

[0152] As can be seen from FIG. 8, the diameter at the peak of the void distribution of the negative electrode active material was approximately 10 nm smaller than the diameter at the peak of the void distribution of the graphite particles. Furthermore, in the diameter range of 12 nm to 70 nm, the Log differential void volume of the negative electrode active material was smaller than the Log differential void volume of the graphite particles. These results indicate that the solid electrolyte was formed in the voids of the graphite particles, thereby reducing the void diameter of the voids of the graphite particles. In other words, it can be seen that in the negative electrode active material of Example 1, the solid electrolyte was located in the voids of the graphite particles. Some of the voids in the graphite particles were blocked by the solid electrolyte.

[0153] [Observation of particle surfaces using SEM] The surfaces of the graphite particles used in Example 1 and the negative electrode active material of Example 1 were observed by SEM. FIG. 9 is an SEM image of the surface of the graphite particles used in Example 1. FIG. 10 is an SEM image of the surface of the negative electrode active material of Example 1. As can be seen from FIGS. 9 and 10, the surface of the negative electrode active material was almost the same as the surface of the graphite particles, except for the partial presence of small particles. The precipitate in FIG. 10 was a solid electrolyte. The coverage of the outer surfaces of the graphite particles with this solid electrolyte was 1% or less.

[0154] [Evaluation of Negative Electrode Active Materials of Examples 1 to 4 and Comparative Examples 1 and 2] Using the same method as in Example 1, the negative electrode active materials of Examples 2 to 4 and Comparative Examples 1 and 2 were observed using an SEM and measured using mercury intrusion porosimetry. Based on the obtained results, it was determined whether or not the solid electrolyte was located in the voids of the graphite particles. The results are shown in Table 1. In Table 1, "present" means that the solid electrolyte was located in the voids in the graphite particles having a void diameter of 1 nm or more and 300 nm or less. "absent" means that the solid electrolyte was not located in the voids in the graphite particles having a void diameter of 1 nm or more and 300 nm or less, or that no voids having a void diameter of 1 nm or more and 300 nm or less existed inside the graphite particles.

[0155] Furthermore, each of the negative electrode active materials of Examples 1 to 4 and Comparative Examples 1 and 2 was pressure-molded at a pressure of 600 MPa. The cross section of the negative electrode active material after pressure molding was observed using an SEM. Furthermore, the shape of the sulfide solid electrolyte in the voids of the graphite particles was confirmed using SEM images. In Table 1, negative electrode active materials in which the sulfide solid electrolyte was present continuously over a length of 500 nm or more in the SEM images were evaluated as a circle (◯). Negative electrode active materials in which the sulfide solid electrolyte was not present continuously over a length of 500 nm or more in the SEM images were evaluated as a cross (×). When the sulfide solid electrolyte was present continuously over a length of 500 nm or more in the voids of the graphite particles, it was estimated that sufficient ion conduction paths existed in the negative electrode active material.

[0156] Furthermore, the coverage of the outer surfaces of the graphite particles with the solid electrolyte was calculated for the negative electrode active materials of Examples 2 to 4 and Comparative Examples 1 and 2 by the same method as in Example 1. The results are shown in Table 1.

[0157] [Table 1]

[0158] In the negative electrode active materials of Examples 1 to 4, the solid electrolyte was located in the voids of the graphite particles. In particular, in the negative electrode active materials of Examples 1 to 4, after pressure molding, the solid electrolyte was continuously present in the voids of the graphite particles with a length of 500 nm or more. As can be seen from these results, the solid electrolyte in the negative electrode active materials of Examples 1 to 4 had a sufficient path length for ion conduction. Furthermore, in the negative electrode active materials of Examples 1 to 3, the coverage of the outer surfaces of the graphite particles with the solid electrolyte was low, which was superior to that of the negative electrode active material of Example 4.

[0159] In Comparative Example 1, the graphite particles did not have voids, so the solid electrolyte was not present inside the graphite particles, whereas in Comparative Example 1, the solid electrolyte was precipitated on the outer surfaces of the graphite particles.

[0160] In Comparative Example 2, Li3PS4 was present as a solid in the THF suspension. Therefore, Li3PS4 was not introduced into the voids of the graphite particles. In Comparative Example 2, the solid electrolyte was present on the outer surface of the graphite particles. [Industrial Applicability]

[0161] The negative electrode active material of the present disclosure can be used, for example, in all-solid-state secondary batteries.

Claims

1. graphite particles having a plurality of voids therein; a first solid electrolyte; Including, the graphite particles are aggregates of a plurality of primary particles containing graphite, The graphite particles have a median diameter of 300 nm or more and 30 μm or less, the graphite particles have an average void diameter of 1 nm or more and 300 nm or less, as determined by mercury intrusion porosimetry; the first solid electrolyte is located in the void; the first solid electrolyte is a precipitate deposited in the voids of the graphite particles and has the shape of a film covering the inner surfaces of the voids; the first solid electrolyte includes a sulfide solid electrolyte; the first solid electrolyte is present continuously in the voids of the graphite particles with a length of 500 nm or more, a ratio of the mass of the first solid electrolyte to the mass of the graphite particles is 0.3 mass% or more and 20 mass% or less; Negative electrode active material.

2. The primary particles are plate-like or scale-like, In the graphite particles, a plurality of the primary particles are stacked. The negative electrode active material according to claim 1 .

3. The first solid electrolyte contains lithium, phosphorus, sulfur, and a halogen. The negative electrode active material according to claim 1 or 2.

4. The first solid electrolyte is represented by the following composition formula (1): Li α PS β X γ ... Equation (1) α, β, and γ satisfy the following relationships: 5.5≦α≦6.5, 4.5≦β≦5.5, and 0.5≦γ≦1.5; X comprises at least one selected from the group consisting of F, Cl, Br and I; The negative electrode active material according to claim 1 .

5. The first solid electrolyte has an argyrodite-type crystal structure. The negative electrode active material according to claim 1 .

6. Further comprising a second solid electrolyte attached to the outer surface of the graphite particles, a coverage of the outer surface with the second solid electrolyte of 10% or less; The negative electrode active material according to claim 1 .

7. A negative electrode layer comprising the negative electrode active material according to claim 1 ; a positive electrode layer; a solid electrolyte layer located between the positive electrode layer and the negative electrode layer; Equipped with solid state battery.

8. the negative electrode layer further includes a solid electrolyte having a different composition from the first solid electrolyte; The solid-state battery according to claim 7 .

9. The solid electrolyte layer contains a solid electrolyte having lithium ion conductivity. The solid state battery according to claim 7 or 8.

10. A method for producing a negative electrode active material according to any one of claims 1 to 6, comprising: The manufacturing method includes: bringing the graphite particles having the plurality of voids therein into contact with a solution containing a solid electrolyte, thereby introducing the solution into the voids; removing a solvent contained in the solution from the solution introduced into the void to precipitate the solid electrolyte, thereby forming the first solid electrolyte; Including, A method for producing a negative electrode active material.

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