Negative electrode active material, solid-state battery, and method for manufacturing negative electrode active material

Abstract

The negative electrode active material (1000) of the present disclosure includes: a graphite particle (100) having a void (102) inside; and a first solid electrolyte (103). The void diameter of the void (102) is 1 nm to 300 nm. The first solid electrolyte (103) is positioned in the void (102). The graphite particle (100) has, for example, a plurality of voids inside. The average void diameter of the graphite particle (100) obtained by a mercury intrusion method is, for example, 1 nm to 300 nm.

Description

TECHNICAL FIELD

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

[0002] In the case of an all-solid-state lithium ion battery, it is required to effectively supply both electrons and lithium ions to an active material in an electrode layer. In an all-solid-state lithium ion battery, an active material is dispersed, for example, in an electrode layer. In a general negative electrode layer, both an electron conduction path in which active material particles are in contact with each other and an ion conduction path in which solid electrolytes are connected to each other are preferably taken into account.

[0003] As a negative electrode active material, graphite particles are sometimes used. Graphite has a layered structure including carbon. By a reaction in which lithium ions are inserted into or detached from the layered structure of graphite, a battery having a high capacity is realized. However, graphite has electron conductivity (electronic conductivity), but lacks ion conductivity (ionic conductivity). In order to compensate for the ion conductivity of graphite, in a general negative electrode layer, graphite particles are sometimes complexed with a solid electrolyte. In addition, graphite particles are sometimes complexed with a binder. The binder is suitable for binding particles to form a film.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 8-195219 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] In the prior art, a new type of negative electrode active material is desired.

[0009] MEANS FOR SOLVING THE PROBLEMS

[0010] The negative electrode active material of the present disclosure includes:

[0011] a graphite particle having a void inside; and

[0012] a first solid electrolyte,

[0013] a void diameter of the void is 1 nm to 300 nm,

[0014] the first solid electrolyte is located in the void.

[0015] EFFECTS OF THE INVENTION

[0016] According to the present disclosure, a new type of negative electrode active material can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a cross-sectional view showing a schematic configuration of the negative electrode active material in Embodiment 1.

[0018] Figure 2 is a flowchart regarding a manufacturing method of the negative electrode active material in Embodiment 1.

[0019] Figure 3 is a cross-sectional view showing a schematic configuration of the solid-state battery in Embodiment 2.

[0020] Figure 4 is a scanning electron microscope (SEM) image of a cross section of the graphite particle used in Example 1.

[0021] Figure 5 is a SEM image of a cross section of the negative electrode active material of Example 1.

[0022] Figure 6 is a SEM image of a void of the graphite particle in the negative electrode active material of Example 1.

[0023] Figure 7 is a SEM image of another void of the graphite particle in the negative electrode active material of Example 1.

[0024] Figure 8 is a graph showing a relationship between diameters of voids in the negative electrode active material and graphite particles of Example 1 and Log differential void volume.

[0025] Figure 9 is a SEM image of a surface of the graphite particle used in Example 1.

[0026] Figure 10 is a SEM image of a surface of the negative electrode active material of Example 1. DETAILED DESCRIPTION

[0027] (Cognitions that became the basis of the present disclosure)

[0028] In the negative electrode layer containing the graphite particle and the solid electrolyte, the solid electrolyte lacks electronic conductivity. Thus, if the addition amount of the solid electrolyte with respect to the graphite particle increases, the volume ratio of the graphite in the negative electrode layer decreases, and the capacity of the negative electrode layer decreases. In addition, since the contact of the graphite particles with each other is hindered, the electronic conductivity of the negative electrode layer also decreases. That is, when the graphite particles are complexed with the solid electrolyte in the negative electrode layer, the electronic conductivity and the ionic conductivity show a trade-off relationship in the negative electrode layer. In this case, it is required to increase the capacity of the negative electrode layer while maintaining the balance of the electronic conductivity and the ionic conductivity.

[0029] Patent Document 1 discloses the following matter: in an electrode of an existing all-solid lithium secondary battery, in order to increase the utilization rate of an active material, the average particle diameter of the active material, the average particle diameter of a solid electrolyte, and the mixing ratio of the active material and the solid electrolyte are adjusted.

[0030] In Patent Document 1, it is disclosed that the average particle diameter of each of the active material and the solid electrolyte is adjusted to be in the range of 0.1 μm to 50 μm. In order to increase the capacity of the negative electrode layer, it is considered that the average particle diameter of the active material is increased within the above range. However, in this case, the conduction of ions inside the active material is slow, and thus the rate characteristics at the time of charge and discharge of the battery are reduced. On the other hand, if the average particle diameter of the active material is decreased, the area of the outer surface of the active material increases. Thus, the contact area of the active material and the solid electrolyte increases, and the electronic conductivity of the negative electrode layer decreases. The active material having a small average particle diameter sometimes also increases the viscosity of a coating liquid. Thus, in the case where a negative electrode layer is produced using a coating liquid containing the active material, a problem in the process can occur. In this way, by adjusting the average particle diameter of the active material, it is difficult to produce a battery having excellent rate characteristics at the time of charge and discharge.

[0031] (Summary of one aspect of the present disclosure)

[0032] The negative electrode active material of the first aspect of the present disclosure includes:

[0033] graphite particles having a void inside; and

[0034] a first solid electrolyte,

[0035] the void diameter of the void is 1 nm to 300 nm,

[0036] the first solid electrolyte is located in the void.

[0037] According to the first aspect, a novel negative electrode active material can be provided. The negative electrode active material has high electronic conductivity due to the graphite particles. In addition, in the negative electrode active material, the insertion and extraction of lithium ions are efficiently performed. Thus, the negative electrode active material is suitable for improving the rate characteristics of a battery.

[0038] In the second aspect of the present disclosure, for example, the negative electrode active material according to the first aspect, in which the graphite particles can have a plurality of voids inside, and the average void diameter of the graphite particles, which is obtained by a mercury intrusion method, can also be 1 nm to 300 nm. According to such a configuration, the negative electrode active material is suitable for improving the rate characteristics of a battery.

[0039] In the third aspect of the present disclosure, the negative electrode active material according to the first or second aspect, wherein the graphite particle can also be a collection of a plurality of primary particles including graphite. According to such a configuration, the negative electrode active material can be easily produced using the graphite particle.

[0040] In the fourth aspect of the present disclosure, the negative electrode active material according to the third aspect, wherein the plurality of primary particles can have a shape of a plate or a flake, and the plurality of primary particles can be stacked in the graphite particle. According to such a configuration, the negative electrode active material can be easily produced using the graphite particle.

[0041] In the fifth aspect of the present disclosure, the negative electrode active material according to any one of the first to fourth aspects, wherein the first solid electrolyte can include lithium, phosphorus, sulfur, and halogen. According to such a configuration, the negative electrode active material has high ion conductivity.

[0042] In the sixth aspect of the present disclosure, the negative electrode active material according to any one of the first to fifth aspects, wherein the first solid electrolyte can be represented by the following composition formula (1),

[0043] Li α PS β X γ Formula (1)

[0044] α, β, and γ can satisfy 5.5 ≤ α ≤ 6.5, 4.5 ≤ β ≤ 5.5, and 0.5 ≤ γ ≤ 1.5, and X can include at least one selected from F, Cl, Br, and I. According to such a configuration, the negative electrode active material has high ion conductivity.

[0045] In the seventh aspect of the present disclosure, the negative electrode active material according to any one of the first to sixth aspects, wherein the first solid electrolyte can have a sulfide silver germanium type crystal structure. According to such a configuration, the negative electrode active material has high ion conductivity.

[0046] In the eighth aspect of the present disclosure, the negative electrode active material according to any one of the first to seventh aspects, wherein the void diameter of the void can be 70 nm or less. According to such a configuration, when the negative electrode active material is used to produce a negative electrode layer, the ion conduction path in the negative electrode active material can be easily maintained.

[0047] In a 9th aspect of the present disclosure, the negative electrode active material according to any one of the 1st to 8th aspects can further include a 2nd solid electrolyte attached to the outer surface of the graphite particle, and the 2nd solid electrolyte can also have a coverage rate of 10% or less on the outer surface. According to such a 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.

[0048] In a 10th aspect of the present disclosure, the negative electrode active material according to any one of the 1st to 9th aspects can also have a ratio of the mass of the 1st solid electrolyte to the mass of the graphite particle of 0.3 to 20 mass%. According to such a configuration, in the negative electrode active material, ion conductivity can be improved while suppressing a decrease in capacity density.

[0049] In an 11th aspect of the present disclosure, the negative electrode active material according to any one of the 1st to 10th aspects can also have a median particle diameter of the graphite particle of 300 nm to 30 μm. According to such a configuration, the graphite particle can be easily handled. In addition, the 1st solid electrolyte can be easily introduced into the inside of the graphite particle.

[0050] A solid-state battery according to a 12th aspect of the present disclosure includes:

[0051] a negative electrode layer including the negative electrode active material according to any one of the 1st to 11th aspects;

[0052] a positive electrode layer; and

[0053] a solid electrolyte layer between the positive electrode layer and the negative electrode layer.

[0054] According to the 12th aspect, the solid-state battery has a high-rate characteristic.

[0055] In a 13th aspect of the present disclosure, the solid-state battery according to the 12th aspect can further include a solid electrolyte having a different composition from the 1st solid electrolyte in the negative electrode layer. According to such a configuration, ion conductivity of the negative electrode layer can be easily improved.

[0056] In a 14th aspect of the present disclosure, the solid-state battery according to the 12th or 13th aspect can include a solid electrolyte having lithium ion conductivity in the solid electrolyte layer. According to such a configuration, the solid-state battery has a high-rate characteristic.

[0057] A method of manufacturing a negative electrode active material according to a 15th aspect of the present disclosure includes:

[0058] The graphite particle having a void inside is brought into contact with a solution containing a solid electrolyte, thereby introducing the above-mentioned solution into the above-mentioned void; and

[0059] The solvent contained in the above-mentioned solution is removed from the above-mentioned solution introduced into the above-mentioned void, and the above-mentioned solid electrolyte is precipitated.

[0060] According to the 15th aspect, it is possible to easily produce a negative electrode active material suitable for improving the rate characteristics of a battery.

[0061] Hereinafter, the embodiments of the present disclosure will be described while referring to the drawings.

[0062] (Embodiment 1)

[0063] Figure 1 is a cross-sectional view showing the schematic configuration of the negative electrode active material 1000 in Embodiment 1.

[0064] The negative electrode active material 1000 in Embodiment 1 is used in a solid-state battery, for example. The negative electrode active material 1000 contains a graphite particle 100 and a first solid electrolyte 103.

[0065] The graphite particle 100 can function as an active material. The graphite particle 100 has a void 102 inside thereof. The graphite particle 100 can also have a plurality of voids 102 inside thereof. The first solid electrolyte 103 is located in the void 102. In other words, the first solid electrolyte 103 is filled into the void 102.

[0066] The void diameter of the void 102 is 1 nm to 300 nm. The first solid electrolyte 103 is located in the void 102 having a void diameter of 1 nm to 300 nm, which can be determined using mercury intrusion method, for example.

[0067] In the mercury intrusion method, high-pressure mercury is injected into a sample having a void. The void distribution can be obtained from the relationship between the pressure applied to the mercury and the amount of mercury injected into the sample. In detail, the diameter D of the void into which the mercury is injected in the sample can be obtained from the following relationship (I). In the relationship (I), γ is the surface tension of mercury. θ is the contact angle of mercury with the wall surface of the sample. P is the pressure applied to the mercury.

[0068] D = -4γcosθ ÷ P (I)

[0069] The pressure P is changed in stages, and the amount of mercury injected is measured for each pressure P. The amount of mercury injected can be regarded as the cumulative value of the volume of the void up to the diameter D corresponding to a certain pressure P. Thus, for each diameter D, the void distribution in which the amount of the void is determined can be obtained. The void distribution is a graph showing the relationship between the diameter D of the void and the Log differential void volume, for example.

[0070] For example, the mercury intrusion method 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, respectively. As the graphite particles 100 in which the first solid electrolyte 103 is not present in the voids 102, the graphite particles 100 before the first solid electrolyte 103 is introduced into the voids 102 or the graphite particles 100 obtained by removing the first solid electrolyte 103 from the negative electrode active material 1000 can be used. The first solid electrolyte 103 can be removed from the negative electrode active material 1000, for example, using a solvent or the like. By the mercury intrusion method, the void distribution indicating the relationship between the diameter of the void and the Log differential void volume can be obtained for the negative electrode active material 1000 and the graphite particles 100, respectively. The diameter of the void in the void distribution of the graphite particles 100 corresponds to the void diameter of the voids 102.

[0071] 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 present in the voids 102 of the graphite particles 100 in the negative electrode active material 1000. For example, the Log differential void volume at a certain diameter in the range of 1 nm to 300 nm is determined for the void distribution of each of the negative electrode active material 1000 and the graphite particles 100. In the case where the Log differential void volume of the negative electrode active material 1000 at the certain diameter is smaller than the Log differential void volume of the graphite particles 100, it can be judged that the first solid electrolyte 103 is present in the voids 102 of the graphite particles 100. In addition, in the case where 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 judged that the first solid electrolyte 103 is present in the voids 102 of the graphite particles 100.

[0072] The fact that the first solid electrolyte 103 is present in the voids 102 of the graphite particles 100 can also be determined by observing the cross section of the negative electrode active material 1000 with an electron microscope.

[0073] For example, the negative electrode active material 1000 is processed so that the cross section of the negative electrode active material 1000 is exposed. The processing of the negative electrode active material 1000 can be performed by a cross section polisher (registered trademark), for example. According to the cross section polisher, a smooth cross section can be formed for 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). Thereby, an SEM image of the cross section of the negative electrode active material 1000 can be obtained.

[0074] Next, the graphite particles 100, the voids 102, and the first solid electrolyte 103 are determined from the obtained SEM image. These determinations can be made on the basis of the contrast of the image, or on the basis of the results of elemental analysis such as energy dispersive X-ray analysis (EDS). Thereby, it is possible to determine that the first solid electrolyte 103 is present in the voids 102 of the graphite particles 100.

[0075] The negative electrode active material 1000 in Embodiment 1 contains the first solid electrolyte 103 in the voids 102 of the graphite particles 100. Thereby, the negative electrode active material 1000 has a tendency to have high ion conductivity and high electron conductivity.

[0076] The voids 102 in which the first solid electrolyte 103 is present have a void diameter of 1 nm to 300 nm. In the voids 102 having a void diameter of 1 nm or more, the first solid electrolyte 103 can be easily introduced. In the voids 102 having a void diameter of 300 nm or less, the first solid electrolyte 103 is difficult to be excessively introduced. Thus, when the voids 102 in which the first solid electrolyte 103 is present have a void diameter of 300 nm or less, the negative electrode active material 1000 is suitable for increasing the capacity density of the negative electrode layer.

[0077] The voids 102 in which the first solid electrolyte 103 is present can also have a void diameter of 70 nm or less. Alternatively, the voids 102 can be filled with the first solid electrolyte 103. In other words, the voids 102 can be filled with the first solid electrolyte 103. In the negative electrode active material 1000, all of the voids 102 having a void diameter of 70 nm or less can be filled with the first solid electrolyte 103. When a full solid battery is produced using the negative electrode active material 1000, the negative electrode material containing the negative electrode active material 1000 is sometimes compression molded. If the negative electrode material is compression molded, it is possible that the negative electrode active material 1000 is deformed. By the deformation of the negative electrode active material 1000, it is possible that the space in which the first solid electrolyte 103 is not present disappears. In the case where 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. Thereby, the ion conduction path in the negative electrode layer can be sufficiently maintained.

[0078] In the negative electrode active material 1000, the voids 102 can also be connected to the outside of the negative electrode active material 1000. In the case where a battery is produced using a negative electrode material containing the 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 the solid electrolyte layer. Thereby, ion conduction to the inside of the graphite particles 100 can be efficiently performed.

[0079] The average void diameter S of the graphite particle 100, which is obtained by the mercury intrusion method, is not particularly limited, and is, for example, 1 nm to 300 nm. The average void diameter S can be 10 nm or more, can be 50 nm or more, can be 100 nm or more, or can be 150 nm or more. The average void diameter S can be 250 nm or less, or can be 200 nm or less.

[0080] The average void diameter S of the graphite particle 100 can be determined, for example, by the following method. First, for the graphite particle 100 in which the first solid electrolyte 103 is not present in the void 102, the mercury intrusion method is used for measurement. As the graphite particle 100 in which the first solid electrolyte 103 is not present in the void 102, the graphite particle 100 before the first solid electrolyte 103 is introduced into the void 102, or the graphite particle 100 obtained by removing the first solid electrolyte 103 from the negative electrode active material 1000 can be used. By the mercury intrusion method, for the graphite particle 100, a void distribution indicating the relationship between the diameter of the void and the Log differential void volume can be obtained. Next, the peak of the void distribution of the graphite particle 100 is determined. The diameter at the peak of the void distribution can be regarded as the average void diameter S. The diameter at the peak of the void distribution corresponds to the mode diameter of the void.

[0081] The graphite particle 100 is, for example, a collection of a plurality of primary particles 101 including graphite. In other words, the graphite particle 100 is a secondary particle formed of a plurality of primary particles 101. In the graphite particle 100, the plurality of primary particles 101 can be in contact with each other. The primary particle 101 can form an interlayer compound including carbon. In the graphite particle 100, for example, a void 102 is formed between the plurality of primary particles 101.

[0082] The shape of the primary particle 101 is not particularly limited, and is, for example, a plate shape or a flake shape. The shape of the primary particle 101 can also be a needle shape, a spherical shape, an ellipsoidal shape, or the like. In the graphite particle 100, a plurality of primary particles 101 of a plate shape or a flake shape can also be stacked. That is, the graphite particle 100 can also have a stacked structure formed of a plurality of primary particles 101 of a plate shape or a flake shape. In this stacked structure, for example, a void 102 is formed between two primary particles 101 of the plurality of primary particles 101. The void 102 extends, for example, in a direction orthogonal to the stacking direction of the plurality of primary particles 101.

[0083] As an example, the graphite particle 100 can have a plurality of voids 102 arranged in a stacking direction of the plurality of primary particles 101. Each of the plurality of voids 102 can be independent of each other. However, at least one of the plurality of voids 102 can be connected to another void 102. The plurality of voids 102 can also be formed continuously in three dimensions. At least one of the plurality of voids 102 can also penetrate the graphite particle 100.

[0084] For example, the graphite particle 100 is spherical or spheroidal. At this time, in a central portion of the graphite particle 100, the plurality of primary particles 101 are overlapped and integrated in a manner that a principal surface of the plate-like or flaky primary particle 101 extends in a diameter direction of the graphite particle 100. At a peripheral portion of the graphite particle 100, the plate-like or flaky primary particle 101 is bent while the plurality of primary particles 101 are overlapped and integrated. A part of the plurality of primary particles 101 is overlapped with another primary particle 101 while being folded. The void 102 is formed between the primary particle 101 and the primary particle 101, and between the folded primary particles 101. The "principal surface" refers to a surface having the largest area.

[0085] The primary particle 101 can also contain graphite as a main component, for example, substantially formed of graphite. The "main component" refers to a component contained most in the primary particle 101 in terms of mass ratio. The "substantially formed of" refers to excluding other components that change the essential characteristics of the material mentioned. However, the primary particle 101 can contain impurities in addition to graphite.

[0086] The shape of the graphite particle 100 is not particularly limited, for example, spherical or spheroidal. In the case of the spherical or spheroidal graphite particle 100, protrusions from the surface of the particle are less. Thus, according to the coating liquid containing such a graphite particle 100, there is a tendency to be able to reduce the resistance at the time of coating. According to the coating liquid, it is possible to easily produce a negative electrode layer in which the graphite particles 100 are densely packed. However, the graphite particle 100 can have protrusions due to the plate-like primary particles 101.

[0087] The median particle diameter of the graphite particle 100 is not particularly limited, for example, 300 nm to 30 μm. The graphite particle 100 having a median particle diameter of 300 nm or more can be easily handled, and is suitable for the production of the negative electrode active material 1000. The graphite particle 100 having a median particle diameter of 30 μm or less can easily introduce the first solid electrolyte 103 into the inside. The median particle diameter of the graphite particle 100 can also be 1 μm to 10 μm.

[0088] Generally, the "median diameter" refers to the particle diameter at which the cumulative volume in the volume-based particle size distribution is 50%. The volume-based particle size distribution is measured, for example, using a laser diffraction analyzer.

[0089] The graphite particles 100 containing a plurality of voids 102 can be regarded as a porous material. The specific surface area of ​​the graphite particles 100 is not particularly limited, and is, for example, 5 m 2 / g or more. In the specific surface area of ​​5m 2 In graphite particles 100 having a specific surface area of ​​100 or greater, the inner surface of the graphite particles 100 surrounding the voids 102 can be covered with a sufficient amount of the first solid electrolyte 103. The larger the specific surface area of ​​the graphite particles 100, the greater the area of ​​the inner surface of the graphite particles 100 that can be covered by the first solid electrolyte 103. The specific surface area of ​​the graphite particles 100 can be measured, for example, by mercury intrusion porosimetry. The specific surface area of ​​the graphite particles 100 can also be obtained by converting adsorption isotherm data obtained by a gas adsorption method using nitrogen gas using the BET (Brunauer-Emmett-Teller) method.

[0090] The porosity of graphite particles 100 may be 5% or greater. In graphite particles 100 having a porosity of 5% or greater, the inner surface of the graphite particles 100 may be coated with a sufficient amount of the first solid electrolyte 103. The upper limit of the porosity of graphite particles 100 is not particularly limited, but is, for example, 50%. Graphite particles 100 having a porosity of 50% or less tend to have sufficiently high strength. The porosity of graphite particles 100 can be measured, for example, by mercury intrusion porosimetry. The porosity of graphite particles 100 can also be calculated from the volume of voids 102 obtained by a gas adsorption method using nitrogen gas.

[0091] The shape of the first solid electrolyte 103 is not particularly limited, and may be needle-shaped, spherical, ellipsoidal, or the like. The shape of the first solid electrolyte 103 may also be particulate. The first solid electrolyte 103 may also have the shape of a film covering the inner surface of the graphite particle 100. As for the film-shaped first solid electrolyte 103, there is a tendency to promote ion conduction within the surface of the first solid electrolyte 103. The size of the first solid electrolyte 103 is not particularly limited, and may be 1 nm to 100 nm, or 1 nm to 70 nm. When the size of the first solid electrolyte 103 is 1 nm to 100 nm, the first solid electrolyte 103 can fully maintain ion conductivity and easily enter the voids 102 of the graphite particle 100.

[0092] The shape of the first solid electrolyte 103 can be determined by observing a cross section of the negative electrode active material 1000 using an electron microscope. The size of the first solid electrolyte 103 can be determined, for example, using a mercury intrusion method by the following method. First, the mercury intrusion method is performed on 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, respectively. By the mercury intrusion method, the void distribution indicating the relationship between the diameter of the void and the differential void volume can be obtained for the negative electrode active material 1000 and the graphite particles 100, respectively. The value obtained 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 can be regarded as the size of the first solid electrolyte 103.

[0093] In the case where the shape of the first solid electrolyte 103 is particle-like, the median particle diameter of the first solid electrolyte 103 can be 1 nm to 100 nm, or 1 nm to 70 nm.

[0094] The negative electrode active material 1000 can further include a second solid electrolyte attached to the outer surface of the graphite particles 100, or can not include the second solid electrolyte. The coverage rate of the second solid electrolyte to the outer surface of the graphite particles 100 is not particularly limited, and is, for example, 10% or less. The coverage rate can be 5% or less, 3% or less, or 1% or less.

[0095] The coverage rate of the second solid electrolyte to the outer surface of the graphite particles 100 can be determined by the following method. First, the surface of the negative electrode active material 1000 is observed with a scanning electron microscope. The area Al 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 by image processing. The ratio of the area A2 to the area Al can be regarded as the coverage rate of the second solid electrolyte to the outer surface of the graphite particles 100.

[0096] The second solid electrolyte is generally formed when the first solid electrolyte 103 is introduced into the voids 102 of the graphite particles 100. Thus, 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 sometimes has low crystallinity because it is introduced into the minute voids 102. A solid electrolyte having low crystallinity has a tendency to have poor ion conductivity as compared with a solid electrolyte having high crystallinity. Thus, the negative electrode material used to produce the negative electrode layer of the all-solid battery can further contain a solid electrolyte having higher ion conductivity than the first solid electrolyte 103. If the coverage rate of the second solid electrolyte with respect to the outer surfaces of the graphite particles 100 is 10% or less, the solid electrolyte having high ion conductivity is likely to come into contact with the outer surfaces of the graphite particles 100 in the negative electrode material. Thus, according to such a negative electrode active material 1000, it is possible to easily produce a negative electrode layer having high ion conductivity.

[0097] In the negative electrode active material 1000, the ratio P1 of the mass of the first solid electrolyte 103 with respect to the mass of the graphite particles 100 is not particularly limited and can be 0.3 to 20 mass%, can be 0.3 to 10 mass%, or can be 1.0 to 6.0 mass%. By the ratio P1 being 0.3 mass% or more, it is possible to sufficiently increase the ion conduction path in the negative electrode active material 1000. By the ratio P1 being 20 mass% or less, it is possible to sufficiently suppress the decrease in the capacity density of the negative electrode active material 1000. In addition, in the negative electrode active material 1000, the ratio P2 of the total of the mass of the first solid electrolyte 103 and the mass of the second solid electrolyte with respect to the mass of the graphite particles 100 can be 0.3 to 20 mass%, can be 0.3 to 10 mass%, or can be 1.0 to 6.0 mass%.

[0098] The first solid electrolyte 103 has, for example, lithium ion conductivity. The first solid electrolyte 103 contains, for example, at least one selected from inorganic solid electrolytes and organic solid electrolytes. The first solid electrolyte 103 can also contain a sulfide solid electrolyte. The sulfide solid electrolyte is suitable for combination with the graphite particles 100 as a low-potential negative electrode material because of its excellent reduction stability.

[0099] The sulfide solid electrolyte contained in the first solid electrolyte 103 can contain lithium, phosphorus, sulfur, and a halogen. The first solid electrolyte 103 is represented, for example, by the following composition formula (1).

[0100] Li α PS β X γ Formula (1)

[0101] In formula (1), a, β, and γ satisfy 5.5 ≤ a ≤ 6.5, 4.5 ≤ β ≤ 5.5, and 0.5 ≤ γ ≤ 1.5. X includes at least one selected from F, Cl, Br, and I. X can be Cl or Br, or can be Cl. The first solid electrolyte 103 can also be Li6PS5X. The solid electrolyte represented by composition formula (1) has, for example, a crystal structure of argyrodite type. That is, the first solid electrolyte 103 can have a crystal structure of argyrodite type. Such a negative electrode active material 1000 including the first solid electrolyte 103 has a tendency to have high ionic conductivity.

[0102] As the sulfide solid electrolyte other than the solid electrolyte represented by composition formula (1), Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 , and the like can be exemplified. LiX, Li2O, MO q , Li p MO q , and the like can also be added to the above. Here, the element X in "LiX" is at least one element selected from F, Cl, Br, and I. The element M in "MO q " and "Li p MO q " is at least one element selected from P, Si, Ge, B, Al, Ga, In, Fe, and Zn. p and q in "MO q " and "Li p MO q " are each independently a natural number.

[0103] The first solid electrolyte 103 can also include at least one selected from an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte.

[0104] As the oxide solid electrolyte, for example, a NASICON-type solid electrolyte represented by LiTi2(PO4)3 and element-substituted products thereof; a perovskite-type solid electrolyte of (LaLi)TiO3 system; a LISICON-type solid electrolyte represented by Li 14 ZnGe4O 16 , Li4SiO4, LiGeO4, and element-substituted products thereof; a garnet-type solid electrolyte represented by Li7La3Zr2O 12Li3N and H-substituted products thereof; Li3PO4 and N-substituted products thereof; and a glass or a glass ceramic, etc. obtained by adding Li2SO4, Li2CO3, etc. to a base material including LiBO2, Li3BO3, etc. Li-B-O compound.

[0105] As the polymer solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used. The polymer compound can have an oxirane structure. By having the oxirane structure, the polymer compound can contain a large amount of the lithium salt, and thus the ion conductivity can be further improved. 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 kind of lithium salt selected from the above can be used alone, or a mixture of two or more kinds of lithium salts selected from the above can be used.

[0106] As the complex hydride solid electrolyte, for example, LiBH4-LiI, LiBH4-P2S5, etc. can be used.

[0107] The shape of the negative electrode active material 1000 is not particularly limited, and is, for example, spherical or ellipsoidal. The shape of the negative electrode active material 1000 can also be particulate. In the case where the shape of the negative electrode active material 1000 is particulate, the median particle diameter of the negative electrode active material 1000 is not particularly limited, and is, for example, 300 nm to 30 μm.

[0108] Next, the manufacturing method of the negative electrode active material 1000 will be described. Figure 2 is a flowchart regarding the manufacturing method of the negative electrode active material 1000 in Embodiment 1. First, in step S11, a solution L containing the first solid electrolyte 103 is prepared. Specific examples of the solution L are described in Non-Patent Literature, J. Mater. Chem. A, 2019, 7, 558-566, etc. The concentration of the first solid electrolyte 103 in the solution L is not particularly limited, and is, for example, 1 mass% to 20 mass%.

[0109] A method of producing a sulfide solid electrolyte represented by Li6PS5Br from a solution is disclosed in the above non-patent literature. In detail, the non-patent literature discloses the following matter: the solvent contained in the solution is removed by volatilizing the solvent from the solution containing the above solid electrolyte, and further, heat treatment is performed, whereby the solid electrolyte is produced. The present inventors have made intensive studies, and as a result, have found that other solid electrolytes having a kesterite-type crystal structure can also be synthesized by the method described in the non-patent literature. As the other solid electrolytes, for example, Li6PS5Cl can be cited.

[0110] Next, in step S12, the graphite particle 100 having the void 102 inside is brought into contact with a solution L. The solution L, for example, does not contain the particles of the first solid electrolyte 103. Thus, when the graphite particle 100 is brought into contact with the solution L, the solution L can easily penetrate into the minute void 102 of the graphite particle 100. In detail, the solution L easily penetrates into the inside of the graphite particle 100 by capillary phenomenon. Thereby, the solution L is introduced into the void 102. The method of bringing the graphite particle 100 into contact with the solution L is not particularly limited. For example, the graphite particle 100 can be brought into contact with the solution L by kneading the graphite particle 100 and the solution L. The ratio of the mass of the first solid electrolyte 103 to the total value of the mass of the graphite particle 100 and the mass of the first solid electrolyte 103 is not particularly limited when the graphite particle 100 is brought into contact with the solution L, and is, for example, more than 0.2 mass% and 20 mass% or less.

[0111] The method of producing the graphite particle 100 having the void 102 inside is not particularly limited. The graphite particle 100 can be produced, for example, by subjecting a plurality of primary particles 101 to a known spheroidization treatment. As one example, the plurality of primary particles 101 are dispersed in a stream of an inert gas, and they are made to collide with each other in the stream, whereby the graphite particle 100 can be produced. The spheroidization treatment can be performed using a commercially available device.

[0112] Next, in step S13, the solvent contained in the solution L is removed. Thereby, the first solid electrolyte 103 is precipitated in the void 102. The removal of the solvent is performed, for example, by volatilizing the solvent. As one example, the graphite particles 100 can be kneaded with the solution L while volatilizing the solvent of the solution L. The solvent of the solution L that permeates the inside of the graphite particles 100 is difficult to volatilize compared to the solvent of the solution L that exists outside the graphite particles 100. Thus, if the solvent contained in the solution L is volatilized, there is a tendency that the first solid electrolyte 103 is concentrated in the void 102 of the graphite particles 100. When the solvent of the solution L is volatilized, the first solid electrolyte 103 hardly exists outside the graphite particles 100, but is supported on the graphite particles 100 in the void 102. Thus, according to this method, the negative electrode active material 1000 that hardly contains the second solid electrolyte attached on the outer surface of the graphite particles 100 can be easily produced.

[0113] Next, in step S14, the graphite particles 100 can be subjected to a heat treatment. The conditions of the heat treatment can be appropriately set depending on the composition of the first solid electrolyte 103, and the like. The temperature of the heat treatment is not particularly limited, and is, for example, 100°C or higher. The time of the heat treatment is not particularly limited, and is, for example, 1 hour or more. The heat treatment can be performed under a reduced pressure atmosphere, or can be performed under a vacuum atmosphere. By subjecting the graphite particles 100 to the heat treatment, there is a tendency that the crystallinity of the first solid electrolyte 103 is improved.

[0114] The manufacturing method of the negative electrode active material 1000 is not limited to Figure 2 the flowchart. For example, the negative electrode active material 1000 can be produced by using a dispersion liquid of the first solid electrolyte 103 instead of the solution L1.

[0115] (Embodiment 2)

[0116] Hereinafter, Embodiment 2 will be described. The description overlapping with Embodiment 1 described above is appropriately omitted.

[0117] Figure 3 is a cross-sectional view that shows the schematic configuration of the solid battery 2000 in Embodiment 2.

[0118] The solid battery 2000 in Embodiment 2 includes a negative electrode layer 201, a solid electrolyte layer 202, and a positive electrode layer 203.

[0119] The negative electrode layer 201 has a negative electrode material including the negative electrode active material 1000.

[0120] The solid electrolyte layer 202 is located between the positive electrode layer 203 and the negative electrode layer 201.

[0121] When a full-solid battery is produced using the negative electrode active material 1000, the negative electrode material including the negative electrode active material 1000 is sometimes compression-molded. If the negative electrode material is compression-molded, it is possible that the negative electrode active material 1000 deforms. By the negative electrode active material 1000 deforming, it is possible that the volume of the space in which the first solid electrolyte 103 is not present decreases and the space disappears. Thus, of the negative electrode active material 1000 present within the negative electrode layer 201, it is possible that all the voids 102 are filled with the first solid electrolyte 103. Figure 3 The state after the disappearance of the space in which the first solid electrolyte 103 is not present with respect to the negative electrode active material 1000 is shown. In other words, in the negative electrode active material 1000 of Figure 3 In the negative electrode active material 1000 of, all the voids 102 are filled with the first solid electrolyte 103. However, of the negative electrode active material 1000 within the negative electrode layer 201, all the voids 102 can not be filled with the first solid electrolyte 103.

[0122] In the negative electrode material, a plurality of negative electrode active materials 1000 can be connected to each other, thereby forming an electron conduction path.

[0123] The negative electrode material can further include a solid electrolyte 105 in addition to the negative electrode active material 1000. In this specification, the solid electrolyte 105 is sometimes referred to as a "third solid electrolyte". The third solid electrolyte 105, for example, fills between a plurality of negative electrode active materials 1000. The third solid electrolyte 105 can have the shape of a particle. A plurality of particles of the third solid electrolyte 105 can be compressed and thereby bonded to each other, thereby forming an ion conduction path.

[0124] The third solid electrolyte 105 can be in contact with the second solid electrolyte of the negative electrode active material 1000, or can not be in contact with the second solid electrolyte of the negative electrode active material 1000. If the third solid electrolyte 105 is in contact with the second solid electrolyte, ion conduction to the inside of the graphite particle 100 can be effectively produced.

[0125] The third solid electrolyte 105, for example, has lithium ion conductivity. The third solid electrolyte 105, for example, includes at least one selected from among inorganic solid electrolytes and organic solid electrolytes. The third solid electrolyte 105 can include at least one selected from among sulfide solid electrolytes, oxide solid electrolytes, halide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes, or can include a sulfide solid electrolyte. As the sulfide solid electrolyte, oxide solid electrolyte, polymer solid electrolyte, and complex hydride solid electrolyte, the electrolytes described above with respect to the first solid electrolyte 103 can be used. Specific examples of the halide solid electrolyte will be described below with respect to the solid electrolyte layer 202.

[0126] In order to achieve a good dispersion state, the third solid electrolyte 105 is preferably made of a soft material. In this regard, it is appropriate to select at least one of a sulfide solid electrolyte and a halide solid electrolyte as the third solid electrolyte 105.

[0127] The composition of the third solid electrolyte 105 can be the same as or different from that of the first solid electrolyte 103. As one example, in order to easily introduce the first solid electrolyte 103 into the minute interstice 102 of the graphite particle 100, the composition of the first solid electrolyte 103 can be adjusted. In order to make the third solid electrolyte 105 have high ion conductivity, the composition of the third solid electrolyte 105 can also be adjusted.

[0128] The shape of the third solid electrolyte 105 is not particularly limited and can be needle-shaped, spherical, ellipsoidal, scale-like, or the like. The shape of the third solid electrolyte 105 can also be particulate.

[0129] In the case where the shape of the third solid electrolyte 105 is particulate (for example, spherical), the median particle diameter of the third solid electrolyte 105 can also be 0.3 μm to 100 μm. In the case where the median particle diameter is 0.3 μm or more, the contact interface between the particles of the third solid electrolyte 105 does not excessively increase, and an increase in ion resistance inside the negative electrode layer 201 can be suppressed. Thus, the operation of the battery at high power can be achieved.

[0130] In the case where the median particle diameter of the third solid electrolyte 105 is 100 μm or less, the negative electrode active material 1000 and the third solid electrolyte 105 easily form a good dispersion state in the negative electrode material. Thus, the high capacity of the battery becomes easy.

[0131] The median particle diameter of the third solid electrolyte 105 can also be smaller than that of the negative electrode active material 1000. Thereby, in the negative electrode material, the negative electrode active material 1000 and the third solid electrolyte 105 can form a more good dispersion state.

[0132] The negative electrode material can further include another active material other than the negative electrode active material 1000. The shape of the other active material is not particularly limited and can be needle-shaped, spherical, ellipsoidal, or the like. The shape of the other active material can be particulate.

[0133] The median particle diameter of the other active material can also be 0.1 μm to 100 μm.

[0134] When the median particle size of the other active material is 0.1 μm or larger, the other active material and the third solid electrolyte 105 are easily well dispersed in the negative electrode material. As a result, the charging characteristics of the battery are improved.

[0135] When the median particle size of the other active materials is 100 μm or less, the diffusion rate of lithium in the active materials can be sufficiently ensured, thereby enabling high-power operation of the battery.

[0136] The median particle size of other active materials may be larger than the median particle size of the third solid electrolyte 105. This allows the active materials and the third solid electrolyte 105 to be well dispersed.

[0137] Other active materials include materials having the characteristics of embedding and de-embedding metal ions (such as lithium ions). As other active materials, metal materials, carbon materials, oxides, nitrides, tin compounds, silicon compounds, etc. can be used. The metal material can be a simple metal or an alloy. As examples of metal materials, lithium metal, lithium alloys, etc. can be listed. As examples of carbon materials, natural graphite, coke, carbon in the process of graphitization, carbon fiber, spherical carbon, artificial graphite, amorphous carbon, etc. can be listed. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, and tin compounds can be preferably used. Other active materials can include a single active material or a plurality of active materials with different compositions.

[0138] The particles of the negative electrode active material 1000 and the third solid electrolyte 105 are as follows: Figure 3 The negative electrode material may include a plurality of negative electrode active materials 1000 and a plurality of third solid electrolyte particles 105 .

[0139] 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 as or different from each other.

[0140] When the total amount of the negative electrode material is set to 100% by mass, the content of the negative electrode active material 1000 can be 40% to 90% by mass, or 40% to 80% by mass. By appropriately adjusting the content of the negative electrode active material 1000, the negative electrode active material 1000 and the third solid electrolyte 105 can be easily dispersed.

[0141] The negative electrode material can also include only the negative electrode active material 1000 and the third solid electrolyte 105. In other words, the negative electrode material can also be formed substantially of the negative electrode active material 1000 and the third solid electrolyte 105. According to such a configuration, it is possible to increase the energy density of the battery. "Include only the negative electrode active material 1000 and the third solid electrolyte 105" means that, except for inevitable impurities, no other material is intentionally included in the negative electrode material.

[0142] As for the mass ratio "w1: 100-w1" of the active material to the third solid electrolyte 105 in the negative electrode layer 201, it is possible to satisfy 40 ≤ w1 ≤ 90, and it is also possible to satisfy 40 ≤ w1 ≤ 80. In the case where 40 ≤ w1 is satisfied, it is possible to sufficiently ensure the energy density of the solid battery 2000. In addition, in the case where w1 ≤ 90 is satisfied, it is possible to achieve the operation of the solid battery 2000 at high power.

[0143] The thickness of the negative electrode layer 201 can be 10 μm to 500 μm. In the case where the thickness of the negative electrode layer 201 is 10 μm or more, it is possible to sufficiently ensure the energy density of the solid battery 2000. In the case where the thickness of the negative electrode layer 201 is 500 μm or less, it is possible to achieve the operation of the solid battery 2000 at high power.

[0144] The solid electrolyte layer 202 is a layer including a solid electrolyte.

[0145] As the solid electrolyte included in the solid electrolyte layer 202, for example, an inorganic solid electrolyte having lithium ion conductivity is used. As the inorganic solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, or the like is used.

[0146] As the solid electrolyte included in the solid electrolyte layer 202, a halide solid electrolyte can be used.

[0147] The halide solid electrolyte is represented by the following composition formula (2), for example. In the composition formula (2), α, β, and γ are each independently a value greater than 0. M includes at least one element selected from metal elements other than Li and semimetal elements. X includes at least one selected from F, Cl, Br, and I.

[0148] Li α M β X γ Formula (2)

[0149] The semi-metal elements include B, Si, Ge, As, Sb, and Te. The metal elements include all elements included in Groups 1 to 12 of the periodic table except hydrogen, and all elements included in Groups 13 to 16 except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. That is, the metal elements are a group of elements that can become cations when forming halide compounds and inorganic compounds.

[0150] As the halide solid electrolyte, Li3YX6, Li2MgX4, Li2FeX4, Li(Al, Ga, In)X4, Li3(Al, Ga, In)X6, or the like can be used.

[0151] According to the above configuration, the power density of the solid-state battery 2000 can be improved. In addition, 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.

[0152] In the present disclosure, when an element in the formula is expressed as “(Al, Ga, In)” and the like, the notation indicates at least one element selected from the group of elements within the parentheses. That is, “(Al, Ga, In)” is synonymous with “at least one selected from Al, Ga, and In”. The same applies to other elements. The halide solid electrolyte exhibits excellent ionic conductivity.

[0153] In the composition formula (2), M can also include Y (= yttrium). That is, the halide solid electrolyte contained in the solid electrolyte layer 202 can also include Y as a metal element.

[0154] The halide solid electrolyte including Y can also be a compound represented by the following composition formula (3).

[0155] Li a M b Y c X6 Formula (3)

[0156] The composition formula (3) satisfies a + mb + 3c = 6, and c > 0. In the composition formula (3), M contains at least one element selected from metal elements other than Li and Y and semi-metal elements. m is the valence number of M. X contains at least one selected from F, Cl, Br, and I. M contains at least one selected from Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb. As the halide solid electrolyte containing Y, specifically, 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.

[0157] According to the above constitution, the power density of the solid-state battery 2000 can be further improved.

[0158] The solid electrolyte contained in the solid electrolyte layer 202 can also contain a sulfide solid electrolyte. As the sulfide solid electrolyte, the electrolyte described above with respect to the first solid electrolyte 103 can be used.

[0159] The solid electrolyte contained in the solid electrolyte layer 202 can also contain at least one selected from 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, the electrolyte described above with respect to the first solid electrolyte 103 can be used.

[0160] The solid electrolyte layer 202 can contain only one kind of solid electrolyte selected from the above-described solid electrolytes, or can contain two or more kinds of solid electrolytes selected from the above-described solid electrolytes. The plurality of solid electrolytes have mutually different compositions. For example, the solid electrolyte layer 202 can contain a halide solid electrolyte and a sulfide solid electrolyte.

[0161] The thickness of the solid electrolyte layer 202 can be 1 μm to 300 μm. In the case where the thickness of the solid electrolyte layer 202 is 1 μm or more, the negative electrode layer 201 and the positive electrode layer 203 are less likely to short-circuit. In the case where the thickness of the solid electrolyte layer 202 is 300 μm or less, the solid battery 2000 can operate at high power.

[0162] The positive electrode layer 203 serves as a counter electrode of the negative electrode layer 201 and contributes to the operation of the solid battery 2000.

[0163] The positive electrode layer 203 can also contain a material having the property of intercalating and deintercalating metal ions (e.g., lithium ions), such as a positive electrode active material. As the positive electrode active material, for example, a metal complex oxide, a transition metal fluoride, a polyanion material, a fluorinated polyanion material, a transition metal sulfide, a transition metal oxysulfide, and a transition metal oxynitride, or the like can be used. In particular, in the case where a lithium-containing transition metal oxide is used as the positive electrode active material, the manufacturing cost can be reduced, and the average discharge voltage can be increased.

[0164] The metal complex oxide selected as the positive electrode active material contained in the positive electrode layer 203 can contain Li and at least one element selected from Mn, Co, Ni, and Al. As such a material, Li(NiCoAl)O2, Li(NiCoMn)O2, LiCoO2, and the like can be listed. For example, the positive electrode active material can be Li(NiCoMn)O2.

[0165] The positive electrode layer 203 can also contain a solid electrolyte. According to the above configuration, the lithium ion conductivity inside the positive electrode layer 203 can be increased, and the solid battery 2000 can operate at high power. As the solid electrolyte in the positive electrode layer 203, the materials exemplified as the solid electrolyte contained in the solid electrolyte layer 202 can be used.

[0166] The median particle diameter of the particles of the active material contained in the positive electrode layer 203 can be 0.1 μm to 100 μm. In the case where the median particle diameter of the particles of the active material is 0.1 μm or more, the active material particles and the solid electrolyte can form a good dispersion state. Thus, the charge capacity of the solid battery 2000 is increased. In the case where the median particle diameter of the particles of the active material is 100 μm or less, the diffusion speed of lithium inside the particles of the active material can be sufficiently ensured. Thus, the solid battery 2000 can operate at high power.

[0167] The median particle diameter of the particles of the active material can also be greater than the median particle diameter of the particles of the solid electrolyte. Thus, a good dispersion state of the active material and the solid electrolyte can be formed.

[0168] As for the mass ratio of the active material to the solid electrolyte contained in the positive electrode layer 203, "w2: 100 - w2", 40 ≤ w2 ≤ 90 can be satisfied. In the case where 40 ≤ w2 is satisfied, the energy density of the solid-state battery 2000 can be sufficiently ensured. In the case where w2 ≤ 90 is satisfied, the operation of the solid-state battery 2000 at high power can be achieved.

[0169] The thickness of the positive electrode layer 203 can be 10 μm to 500 μm. In the case where the thickness of the positive electrode layer 203 is 10 μm or more, the energy density of the solid-state battery 2000 can be sufficiently ensured. In the case where the thickness of the positive electrode layer 203 is 500 μm or less, the operation of the solid-state battery 2000 at high power can be achieved.

[0170] In order to improve the adhesion of the particles to each other, a binder can be contained in at least one of the negative electrode layer 201, the solid electrolyte layer 202, and the positive electrode layer 203. The binder is, for example, used to improve the adhesion of the materials constituting the electrode. As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aromatic polyamide resin, polyamide, polyimide, polyamide-imide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinyl pyrrolidone, polyether, polyether sulfone, hexafluorinated polypropylene, styrene-butadiene rubber, carboxymethyl cellulose, and the like can be listed. As the binder, a copolymer of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluorinated propylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluorinated propylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene can be used. In addition, two or more of these can be mixed and used as the binder.

[0171] In order to improve the electron conductivity, at least one of the negative electrode layer 201 and the positive electrode layer 203 can also contain a conductive aid. As the conductive aid, for example, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black and Ketjen black, conductive fiber such as carbon fiber or metal fiber, metal powder such as fluorinated carbon and aluminum, conductive whisker such as zinc oxide or potassium titanate, conductive metal oxide such as titanium oxide, conductive high molecular compound such as polyaniline, polypyrrole, and polythiophene, and the like can be used. In the case where a carbon conductive aid is used, cost reduction can be achieved.

[0172] The solid-state battery 2000 can also 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, a stacked type, and the like.

[0173] Example

[0174] Hereinafter, the present disclosure will be described in detail using examples and comparative examples. The present disclosure is not limited to the following examples.

[0175] Example 1

[0176] [Preparation of solution containing sulfide solid electrolyte]

[0177] In an argon glove box under an Ar atmosphere with a dew point of -60°C or less, Li2S, P2S5, and super-dehydrated tetrahydrofuran (THF) were mixed. The molar ratio of Li2S and P2S5 was 3:1. The THF did not contain a stabilizer. By stirring the resulting mixture overnight, a THF suspension containing Li3PS4 was obtained.

[0178] Next, Li2S and LiCl were dissolved in super-dehydrated ethanol (EtOH) to obtain an EtOH solution. The molar ratio of Li2S and LiCl was 1:1. Next, by mixing the THF suspension with the EtOH solution, a THF-EtOH solution containing Li6PS5Cl was obtained. 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%.

[0179] [Graphite particles and solid electrolyte are compounded]

[0180] Next, spherical graphite particles having voids inside were prepared. The median particle diameter of the graphite particles was 8 μm. The average void diameter of the graphite particles, which was obtained by the mercury intrusion method, was 190 nm. Next, in an argon glove box, the graphite particles and the THF-EtOH solution containing Li6PS5Cl were weighed in a mass ratio of graphite particles:Li6PS5Cl = 97.5:2.5. Next, by mixing them in an agate mortar, the graphite particles were brought into contact with the THF-EtOH solution. Further, they were kneaded while volatilizing the solvent contained in the THF-EtOH solution. Next, the resulting composite was heat-treated at 150°C under a vacuum atmosphere for 2 hours. Thus, the negative electrode active material of Example 1 was obtained. The negative electrode active material of Example 1 contained Li6PS5Cl as a solid electrolyte.

[0181] Example 2

[0182] The negative electrode active material of Example 2 was obtained by the same method 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.

[0183] Example 3

[0184] The negative electrode active material of Example 3 was obtained by the same method as in Example 1 except that LiBr was used instead of LiCl. The negative electrode active material of Example 3 contained Li6PS5Br as a solid electrolyte.

[0185] Example 4

[0186] The negative electrode active material of Example 4 was obtained by the same method 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.

[0187] Comparative Example 1

[0188] The negative electrode active material of Comparative Example 1 was obtained by the same method as in Example 1 except that the plate-like graphite particles having no voids having a void diameter of 1 nm to 300 nm were used. The median particle diameter of the graphite particles used in Comparative Example 1 was 3 μm.

[0189] Comparative Example 2

[0190] The negative electrode active material of Comparative Example 2 was obtained by the same method as in Example 1 except that the THF suspension containing Li3PS4was used instead of the THF-EtOH solution containing Li6PS5Cl, and the graphite particles and the THF suspension containing Li3PS4were weighed in a mass ratio of graphite particles:Li3PS4= 97.5:2.5.

[0191] [Observation of the cross section of the particles using SEM]

[0192] The cross section of the graphite particles used in Example 1 was observed using SEM (SU-70 manufactured by Hitachi High-Technologies Corporation). Figure 4 is an SEM image of the cross section of the graphite particles used in Example 1. As is apparent from Figure 4 , the graphite particles are a collection of plate-like primary particles capable of forming an intercalation compound containing carbon. In the graphite particles, voids exist between the plurality of primary particles.

[0193] Next, the cross section of the negative electrode active material of Example 1 was observed using SEM. Figure 5 is an SEM image of the cross section of the negative electrode active material of Example 1. As is apparent from Figure 5 , in the negative electrode active material, precipitates of the solid electrolyte (white portions) exist in the voids inside the graphite particles.

[0194] Next, for the cross section of the negative electrode active material of Example 1, elemental analysis was performed using EDS. Figure 6This is a SEM image of voids in graphite particles in the negative electrode active material of Example 1 and is an enlarged view of a cross section of the negative electrode active material. Figure 6 The results obtained by plotting the information on the locations of P, S, and Cl obtained from the above elemental analysis are also shown. Figure 6 The inner surface of the void shown here contains P, S, and Cl due to Li6PS5Cl.

[0195] Figure 7 This is a SEM image of other 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. Figure 7 The results obtained by mapping the information on the locations of P, S, and Cl obtained by the above-mentioned elemental analysis are also shown. Figure 7 The voids shown are completely filled with precipitates containing P, S, and Cl. In other words, the voids are filled with Li6PS5Cl.

[0196] [Measurement by mercury intrusion porosimetry]

[0197] 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 (AutoPore IV9500 manufactured by Shimadzu Corporation). Figure 8 This is a graph showing the relationship between the diameter of the voids in the negative electrode active material and graphite particles of Example 1 and the Log differential void volume. Figure 8 It can be seen that the graphite particle void distribution has a peak at a void diameter of 190 nm. The graphite particle void distribution is a gentle curve from 5 nm to 190 nm. Furthermore, the measurement results show that the void fraction of the graphite particles is 25%.

[0198] Depend on Figure 8 It can be seen that the diameter at the peak of the void distribution of the negative electrode active material is approximately 10 nm smaller than the diameter at the peak of the void distribution of the graphite particles. Furthermore, within the diameter range of 12 nm to 70 nm, the Log differential void volume of the negative electrode active material is smaller than that of the graphite particles. These results indicate that the formation of a solid electrolyte within the voids of the graphite particles reduces the void diameter of the graphite particles. In other words, it can be seen that in the negative electrode active material of Example 1, the solid electrolyte is located within the voids of the graphite particles. Some of the voids in the graphite particles are blocked by the solid electrolyte.

[0199] [Observation of the Particle Surface Using SEM]

[0200] The surfaces of the graphite particles used in Example 1 and the negative electrode active material of Example 1 were observed using SEM. Figure 9is an SEM image of the surface of the graphite particles used in Example 1. Figure 10 is an SEM image of the surface of the negative electrode active material of Example 1. The scale bar indicates 500 nm. Figure 9 and 10 It is understood that the surface of the negative electrode active material is almost the same as the surface of the graphite particles except that minute particles are partially present. Figure 10 The precipitates of are solid electrolytes. The coverage of the outer surface of the graphite particles by the solid electrolytes is 1% or less.

[0201] [Evaluation of the negative electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 2]

[0202] By the same method as in Example 1, the observation by SEM and the measurement by the mercury press-in method were performed on the negative electrode active materials of Examples 2 to 4 and Comparative Examples 1 to 2. Based on the obtained results, it was determined whether the solid electrolytes were present in the voids of the graphite particles. The results are shown in Table 1. In Table 1, "Yes" means that the solid electrolytes were present in the voids of the graphite particles having a void diameter of 1 nm to 300 nm. "No" means that the solid electrolytes were not present in the voids of the graphite particles having a void diameter of 1 nm to 300 nm, or that there were no voids having a void diameter of 1 nm to 300 nm in the interior of the graphite particles.

[0203] In addition, the negative electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 2 were each pressure-formed under a pressure of 600 MPa. The cross sections of the negative electrode active materials after the pressure formation were observed by SEM. Further, the shapes of the sulfide solid electrolytes in the voids of the graphite particles were confirmed in the SEM images. In Table 1, the negative electrode active materials in which the sulfide solid electrolytes were continuously present in the SEM images with a length of 500 nm or more were evaluated as a round mark (O). The negative electrode active materials in which the sulfide solid electrolytes were not continuously present in the SEM images with a length of 500 nm or more were evaluated as a cross mark (X). When the sulfide solid electrolytes were continuously present in the voids of the graphite particles with a length of 500 nm or more, it was inferred that there were sufficient ion conduction paths in the negative electrode active material.

[0204] Further, by the same method as in Example 1, the coverage of the outer surface of the graphite particles by the solid electrolytes was calculated for the negative electrode active materials of Examples 2 to 4 and Comparative Examples 1 to 2. The results are shown in Table 1.

[0205] Table 1

[0206]

[0207] (*1) presence or absence of voids having a void diameter of 1 nm to 300 nm (*2) whether or not the sulfide solid electrolyte is continuously present in the voids of the graphite particles of the negative electrode active material after pressure molding in a length of 500 nm or more

[0208] As for the negative electrode active materials of Examples 1 to 4, the solid electrolyte is present in the voids of the graphite particles. In particular, as for the negative electrode active materials of Examples 1 to 4, the solid electrolyte is continuously present in the voids of the graphite particles in a length of 500 nm or more after pressure molding. From this result, it is known that the solid electrolyte has a sufficient path length for ion conduction in the negative electrode active materials of Examples 1 to 4. Furthermore, in the negative electrode active materials of Examples 1 to 3, the solid electrolyte has a low coverage rate for the outer surface of the graphite particles, which is superior to the negative electrode active material of Example 4.

[0209] As for Comparative Example 1, the graphite particles do not have voids, and thus the solid electrolyte is not present in the interior of the graphite particles. In Comparative Example 1, the solid electrolyte is precipitated on the outer surface of the graphite particles.

[0210] As for Comparative Example 2, Li3PS4 is present in the form of a solid in the THF suspension. Thus, Li3PS4 is not introduced into the voids of the graphite particles. In Comparative Example 2, the solid electrolyte is present on the outer surface of the graphite particles.

[0211] Industrial applicability

[0212] The negative electrode active material of the present disclosure can be used, for example, in a full solid secondary battery or the like.

Claims

1. A negative electrode active material comprising: Graphite particles having voids inside; and 1st solid electrolyte, The diameter of the voids is 1 nm to 300 nm. The first solid electrolyte is located in the void and has a film shape covering the inner surface of the void. The first solid electrolyte exists continuously in the gaps between the graphite particles with a length of 500 nm or more.

2. The negative electrode active material according to claim 1, wherein The graphite particles have a plurality of voids inside them. The average pore diameter of the graphite particles determined by mercury intrusion porosimetry is 1 nm to 300 nm.

3. The negative electrode active material according to claim 1, wherein The graphite particles are aggregates of a plurality of primary particles containing graphite.

4. The negative electrode active material according to claim 3, wherein The shapes of the plurality of primary particles are plate-like or scale-like, In the graphite particles, a plurality of the primary particles are stacked.

5. The negative electrode active material according to claim 1, wherein The first solid electrolyte contains lithium, phosphorus, sulfur, and halogen.

6. The negative electrode active material according to claim 1, wherein The first solid electrolyte is represented by the following composition formula (1): Li α PS β X γ Formula (1) α, β and γ satisfy 5.5≤α≤6.5, 4.5≤β≤5.5 and 0.5≤γ≤1.5, X contains at least one selected from F, Cl, Br, and I.

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

8. The negative electrode active material according to claim 1, wherein The void diameter of the void is 70 nm or less.

9. The negative electrode active material according to claim 1, further comprising a second solid electrolyte attached to the outer surface of the graphite particles. The coverage of the outer surface by the second solid electrolyte is 10% or less.

10. The negative electrode active material according to claim 1, wherein The ratio of the mass of the first solid electrolyte to the mass of the graphite particles is 0.3% by mass to 20% by mass.

11. The negative electrode active material according to claim 1, wherein The median particle size of the graphite particles is 300 nm to 30 μm.

12. A solid battery comprising: A negative electrode layer comprising the negative electrode active material according to any one of claims 1 to 11; a positive electrode layer; and A solid electrolyte layer is located between the positive electrode layer and the negative electrode layer.

13. The solid battery according to claim 12, wherein The negative electrode layer further includes a solid electrolyte having a composition different from that of the first solid electrolyte.

14. The solid state battery according to claim 12, wherein The solid electrolyte layer includes a solid electrolyte having lithium ion conductivity.

15. A method for producing a negative electrode active material, comprising: contacting graphite particles having voids therein with a solution containing a solid electrolyte, thereby introducing the solution into the voids; removing the solvent contained in the solution from the solution introduced into the gap to precipitate the solid electrolyte; and The pressure molding is performed so that the solid electrolyte exists continuously in the gaps between the graphite particles with a length of 500 nm or more.

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