All-solid-state batteries

Abstract

An all-solid-state battery according to the present embodiment comprises a sintered body that has a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein the solid electrolyte layer contains a solid electrolyte having a γ-Li3PO4 crystal structure, and the negative electrode includes elemental Ag or an Ag alloy and at least one compound among LiαTiO3 (2≤α≤2.8) and LiβTiSiO5 (2≤β≤4).

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state battery. This application claims priority to Japanese Patent Application No. 2022-029203, filed on February 28, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, electronics technology has made remarkable progress, with efforts being made to make portable electronic devices smaller, lighter, thinner, and more multifunctional. Accordingly, there is a strong demand for smaller, lighter, thinner, and more reliable batteries that serve as the power source for electronic devices, and all-solid-state batteries that use solid electrolytes have attracted attention.

[0003] There are two types of all-solid-state batteries: thin-film and bulk. Thin-film batteries are manufactured using thin-film technologies such as physical vapor deposition (PVD) and the sol-gel method. Bulk batteries are manufactured using methods such as powder molding and sintering. Each type of all-solid-state battery has different performance characteristics due to differences in the materials that can be used due to differences in manufacturing methods. For example, bulk batteries using sintered bodies require the use of materials that can withstand sintering, but each layer can be made thick, resulting in high capacity.

[0004] For example, Patent Document 1 discloses a sintered all-solid-state battery that uses an oxide-based solid electrolyte as the solid electrolyte. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2007 / 135790 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to make all-solid-state batteries smaller and lighter, there is a need to increase the energy density of all-solid-state batteries.

[0007] The present invention has been made in view of the above problems, and aims to increase the energy density of all-solid-state batteries. [Means for solving the problem]

[0008] In order to solve the above problems, the following means are provided.

[0009] (1) A first aspect of the all-solid-state battery includes a sintered body. The sintered body has a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode. The solid electrolyte layer includes a solid electrolyte having a γ-Li3PO4 type crystal structure. The negative electrode includes a mixture of Ag or an Ag alloy and Li α TiO3 (2≦α≦2.8) and Li β and TiSiO5 (2≦β≦4).

[0010] (2) In the all-solid-state battery according to the above aspect, the negative electrode may include a first layer and a second layer, and the second layer may have an average thickness of 1 μm or more and 4 μm or less. The second layer may be closer to the solid electrolyte layer than the first layer and contact at least one main surface of the first layer.

[0011] (3) In the all-solid-state battery according to the above aspect, the first layer comprises Ag or an Ag alloy and Li α TiO3 (2≦α≦2.8) and Li β and TiSiO5 (2≦β≦4).

[0012] (4) In the all-solid-state battery according to the above aspect, the total volume ratio of Ag and Ag alloy in the first layer may be 45% or more and 90% or less.

[0013] (5) In the all-solid-state battery according to the above aspect, the Ag alloy may be a LiAg alloy or an AgPd alloy.

[0014] (6) In the all-solid-state battery according to the above aspect, the second layer is Li α TiO3 (2≦α≦2.8) and Liβ and TiSiO5 (2≦β≦4).

[0015] (7) In the all-solid-state battery according to the above aspect, the first layer and the second layer are Li α TiO3 (2≦α≦2.8) and Li β It may contain a compound having the same composition as TiSiO5 (2≦β≦4).

[0016] (8) In the all-solid-state battery according to the above aspect, the solid electrolyte contained in the solid electrolyte layer is Li 3+x Si x P 1-x It may also contain O4 (0.2≦x≦0.6).

[0017] (9) In the all-solid-state battery according to the above aspect, the positive electrode active material contained in the positive electrode may contain lithium cobalt oxide.

[0018] (10) In the all-solid-state battery according to the above aspect, the positive electrode may include a third layer containing Ag and a fourth layer in contact with at least one main surface of the third layer. [Effects of the Invention]

[0019] The all-solid-state battery according to the above aspect can increase the energy density. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a cross-sectional view of an all-solid-state battery according to a first embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a characteristic portion of the all-solid-state battery according to the first embodiment. [Figure 3] FIG. 3 is an enlarged cross-sectional view of a characteristic portion of another example of the all-solid-state battery according to the first embodiment. [Figure 4] FIG. 3 is an enlarged cross-sectional view of a characteristic portion of a positive electrode of another example of the all-solid-state battery according to the first embodiment. [Figure 5]FIG. 3 is an enlarged cross-sectional view of a characteristic portion of a positive electrode of another example of the all-solid-state battery according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present embodiment will be described in detail below with reference to the accompanying drawings. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional proportions of each component may differ from the actual proportions. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications may be made within the scope of the present invention.

[0022] The directions are defined as follows. The stacking direction of the laminate 4 is the z direction, one direction in the plane perpendicular to the z direction is the x direction, and the direction perpendicular to the x and z directions is the y direction. Hereinafter, one direction in the z direction may be expressed as "up" and the direction opposite to this direction as "down". Up and down do not necessarily coincide with the direction in which gravity is applied.

[0023] 1 is a cross-sectional schematic diagram of an all-solid-state battery 10 according to this embodiment. The all-solid-state battery 10 has a laminate 4 and terminal electrodes 5 and 6. The terminal electrodes 5 and 6 are in contact with opposing surfaces of the laminate 4. The terminal electrodes 5 and 6 extend in the z direction intersecting (orthogonal to) the laminate surface of the laminate 4.

[0024] The laminate 4 has a positive electrode 1, a negative electrode 2, and a solid electrolyte layer 3. The laminate 4 is a sintered body formed by stacking and sintering the positive electrode 1, the negative electrode 2, and the solid electrolyte layer 3. The number of positive electrode 1 and negative electrode 2 layers is not important. The solid electrolyte layer 3 is located at least between the positive electrode 1 and the negative electrode 2. Between the positive electrode 1 and the terminal electrode 6 and between the negative electrode 2 and the terminal electrode 5, for example, there is a solid electrolyte identical to the solid electrolyte layer 3. One end of the positive electrode 1 is connected to the terminal electrode 5. One end of the negative electrode 2 is connected to the terminal electrode 6.

[0025] The all-solid-state battery 10 is charged or discharged by exchanging ions between the positive electrode 1 and the negative electrode 2 via the solid electrolyte layer 3. The all-solid-state battery 10 shown in FIG. 1 is a laminated type battery, but the all-solid-state battery 10 may also be a wound type battery. The all-solid-state battery 10 is used, for example, in laminated batteries, prismatic batteries, cylindrical batteries, coin batteries, button batteries, etc. The all-solid-state battery 10 may also be an injection type battery in which the solid electrolyte layer 3 is dissolved or dispersed in a solvent.

[0026] "Positive electrode" 2 is an enlarged view of a characteristic portion of the all-solid-state battery 10 according to the first embodiment. The positive electrode 1 has, for example, a positive electrode current collector layer 1A and a positive electrode active material layer 1B. The positive electrode current collector layer 1A is an example of the third layer. The positive electrode active material layer 1B is an example of the fourth layer.

[0027] [Positive electrode current collector layer] Positive electrode current collector layer 1A has, for example, positive electrode current collector 11 and positive electrode active material 12. In this case, the space between an xy plane passing through the top of positive electrode current collector 11 and an xy plane passing through the bottom thereof is considered to be positive electrode current collector layer 1A.

[0028] The positive electrode current collector 11 includes, for example, a metal or alloy containing any one selected from the group consisting of Ag, Pd, Au, and Pt. The positive electrode current collector 11 is, for example, Ag or an AgPd alloy. The positive electrode current collector 11 may be the same as or different from the negative electrode current collector 21 described below.

[0029] The positive electrode current collector 11 is made of, for example, a plurality of current collector particles that are connected to one another and electrically connected in the xy plane.

[0030] The positive electrode active material 12 is present in the positive electrode current collector layer 1A together with the positive electrode current collector 11. The positive electrode active material 12 is in contact with the positive electrode current collector 11. When the positive electrode active material 12 is contained in the positive electrode current collector layer 1A, electrons are smoothly exchanged between the positive electrode active material 12 and the positive electrode current collector 11. The positive electrode active material 12 contains a transition metal oxide containing at least one selected from the group consisting of Co, Ni, Mn, Fe, and V. The positive electrode active material 12 is, for example, lithium cobalt oxide or lithium manganese oxide, and is preferably lithium cobalt oxide. The lithium cobalt oxide is Li x Lithium manganese oxide is expressed as CoO2, and Li x It is expressed as Mn2O4, where x is between 0.4 and 1.2, and the value of x varies within this range during charge and discharge. The chemical formula in this specification does not necessarily have to be a stoichiometric composition, and deviations of about 10% are allowed.

[0031] FIG. 2 shows an example in which the positive electrode current collector 11 is made up of a plurality of current collector particles, but this is not limited to this. FIG. 3 is an enlarged view of a characteristic portion of another example of the all-solid-state battery according to the first embodiment. The positive electrode current collector layer 1C shown in FIG. 3 is made up of a foil-shaped positive electrode current collector 11 extending in the xy plane. The positive electrode current collector 11 may be in the form of a punched film or an expanded film extending in the xy plane. The positive electrode current collector layer 1C may be made up of the positive electrode current collector 11.

[0032] [Cathode active material layer] The positive electrode active material layer 1B is formed on one or both surfaces of the positive electrode current collector layer 1A. The positive electrode active material layer 1B contains a positive electrode active material. The positive electrode active material layer 1B may contain a conductive additive, a binder, and a solid electrolyte described below. When the positive electrode active material layer 1B contains a solid electrolyte, the xy plane passing through the outermost portion of the positive electrode active material is considered to be the boundary between the positive electrode active material layer 1B and the solid electrolyte layer 3.

[0033] (Cathode active material) The positive electrode active material includes a transition metal oxide containing one or more atoms selected from the group consisting of Co, Ni, Mn, Fe, and V. The positive electrode active material 12 is, for example, lithium cobalt oxide, lithium manganese oxide, or the like, and is preferably lithium cobalt oxide. Lithium cobalt oxide is Li x Lithium manganese oxide is expressed as CoO2, and Li x It is expressed as Mn2O4, where x is between 0.4 and 1.2, and the value of x fluctuates within this range during charging and discharging.

[0034] (Conductive additive) The conductive additive is not particularly limited as long as it improves the electronic conductivity in the positive electrode active material layer 1B, and known conductive additives can be used. Examples of the conductive additive include carbon-based materials such as graphite, carbon black, graphene, and carbon nanotubes; metals such as gold, platinum, silver, palladium, aluminum, copper, nickel, stainless steel, and iron; conductive oxides such as ITO; and mixtures thereof. The conductive additive may be in the form of powder or fiber.

[0035] (binding material) The binder bonds the positive electrode current collector layer 1A and the positive electrode active material layer 1B, the positive electrode active material layer 1B and the solid electrolyte layer 3, and the various materials constituting the positive electrode active material layer 1B together.

[0036] The binder can be used within a range that does not impair the functionality of the positive electrode active material layer 1B. If the binder is unnecessary, it need not be contained. The content of the binder in the positive electrode active material layer 1B is, for example, 0.5 volume % or more and 30 volume % or less of the positive electrode active material layer. If the content of the binder is sufficiently low, the resistance of the positive electrode active material layer 1B becomes sufficiently low. Here, the volume % is approximately equal to the area % in a cross section measured with a scanning electron microscope, for example. Therefore, the area ratio in a cross section measured with a scanning electron microscope can be regarded as the volume ratio.

[0037] The binder may be any material capable of forming the above-described bond, such as fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Other binders may also be used, such as cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide resin, and polyamide-imide resin. Alternatively, a conductive polymer with electronic conductivity or an ionic conductive polymer with ionic conductivity may be used. An example of an electronic conductive polymer is polyacetylene. In this case, the binder also functions as a conductive additive, so no conductive additive is required. Examples of ionic conductive polymers that can conduct lithium ions include those that are composites of polymer monomers (polyether polymers such as polyethylene oxide and polypropylene oxide, polyphosphazene, etc.) with lithium salts or lithium-based alkali metal salts such as LiClO4, LiBF4, and LiPF6. The polymerization initiator used for the composite is, for example, a photopolymerization initiator or a thermal polymerization initiator that is compatible with the above-mentioned monomers. The properties required for the binder include oxidation / reduction resistance and good adhesiveness.

[0038] Although specific examples of the positive electrode have been shown so far, the positive electrode is not limited to these examples. For example, the positive electrode may be a single layer in which a positive electrode current collector 11 and a positive electrode active material 12 are mixed. For example, Figures 4 and 5 are cross-sectional views of other examples of the positive electrode according to the first embodiment.

[0039] The positive electrode shown in FIG. 4 includes a positive electrode current collector layer 1D and a positive electrode active material layer 1B. The positive electrode current collector layer 1D includes a positive electrode current collector 11, a positive electrode active material 12, and an oxide 13. The oxide 13 is, for example, an oxide containing Ag, such as AgCoO2 or AgMn2O4. The oxide 13 includes, for example, both the constituent elements of the positive electrode current collector 11 and the constituent elements of the positive electrode active material 12. The oxide 13 prevents oxidation of Ag contained in the positive electrode current collector 11. The presence of the oxide 13 between the positive electrode current collector 11 and the positive electrode active material 12 improves the cycle characteristics of the all-solid-state battery 10.

[0040] The positive electrode shown in FIG. 5 has a positive electrode current collector layer 1E, an intermediate layer 1F, and a positive electrode active material layer 1B. The positive electrode current collector layer 1E has a positive electrode current collector 11 and an oxide 13. The intermediate layer 1F is made of the oxide 13. The example shown in FIG. 5 corresponds to a case where the thickness of the oxide 13 is thicker than the example shown in FIG. 4. The oxide 13 prevents oxidation of Ag contained in the positive electrode current collector 11, improving the cycle characteristics of the all-solid-state battery 10.

[0041] "Solid electrolyte layer" The solid electrolyte layer 3 includes a solid electrolyte. A solid electrolyte is a substance that can move ions by an externally applied electric field. For example, the solid electrolyte layer 3 conducts lithium ions and inhibits the movement of electrons. The solid electrolyte layer 3 is, for example, a sintered body obtained by sintering.

[0042] The solid electrolyte layer 3 includes, for example, a solid electrolyte having a γ-Li3PO4 type crystal structure. The solid electrolyte having a γ-Li3PO4 type crystal structure has excellent ion conductivity. 3+x Si x P 1-x O4, Li 3+x Si x V 1-x O4, Li 3+x Ge x P 1-x O4, Li 3+x Ge x V 1-x O4, etc., preferably Li 3+x Si x P 1-x O4, where x satisfies 0.4≦x≦0.8, and preferably 0.2≦x≦0.6. The solid electrolyte may also be a ternary lithium oxide containing Si, V, and Ge.

[0043] "Negative electrode" The negative electrode 2 has, for example, a negative electrode current collector layer 2A and a negative electrode active material layer 2B containing a negative electrode active material (see FIG. 2). α TiO3 (2≦α≦2.8) and Liβ and at least one compound of TiSiO5 (2≦β≦4). Ag may exist as a single element or as part of an alloy. The negative electrode current collector layer 2A is an example of the first layer. The negative electrode active material layer 2B is an example of the second layer. The second layer is closer to the solid electrolyte layer 3 than the first layer.

[0044] [Negative electrode current collector] The negative electrode current collector layer 2A includes, for example, a negative electrode current collector 21 and a negative electrode active material 22. In this case, the space between the xy plane passing through the top of the negative electrode current collector 21 and the xy plane passing through the bottom thereof is regarded as the negative electrode current collector layer 2A.

[0045] The negative electrode current collector 21 comprises, for example, Ag alone or an Ag alloy. Ag may be present as a single element or as part of an alloy. Examples of Ag alloys include AgPd alloys and Li-Ag alloys. The composition ratio of each component in the alloy is not important. The negative electrode current collector 21 is, for example, Ag, AgPd alloys, Li-Ag alloys, and mixtures thereof. The negative electrode current collector 21 may be the same as or different from the positive electrode current collector 11. The negative electrode current collector 21 also functions as a negative electrode active material.

[0046] The total volume ratio (Va) of Ag and Ag alloy in the negative electrode current collector layer 2A is, for example, 45% to 90%. The volume ratio is determined from an image obtained using a scanning electron microscope, as described above.

[0047] 3, the negative electrode current collector layer 2C may be made of a negative electrode current collector 21. In this case, the negative electrode current collector 21 may be a foil extending in the xy plane, or may be in the form of a punch or an expanded material.

[0048] The negative electrode active material 22 is, for example, mixed in the negative electrode current collector layer 2A together with the negative electrode current collector 21. The negative electrode active material 22 is in contact with the negative electrode current collector 21. When the negative electrode active material 22 is contained in the negative electrode current collector layer 2A, electrons are smoothly exchanged within the negative electrode current collector layer 2A. The negative electrode active material 22 is the same as the negative electrode active material contained in the negative electrode active material layer 2B, which will be described later.

[0049] [Negative electrode active material layer] The negative electrode active material layer 2B is formed on one or both surfaces of the negative electrode current collector layer 2A. The negative electrode active material layer 2B is closer to the solid electrolyte layer 3 than the negative electrode current collector layer 2A. The negative electrode active material layer 2B contains a negative electrode active material. For example, the negative electrode active material layer 2B is formed by dissolving the Li contained in the negative electrode current collector layer 2A. α TiO3 (2≦α≦2.8) or Li β It contains a compound having the same composition as TiSiO5 (2≦β≦4). The negative electrode active material layer 2B may contain a conductive additive, a binder, and the above-mentioned solid electrolyte. When the negative electrode active material layer 2B contains a solid electrolyte, the xy plane passing through the outermost portion of the negative electrode active material is considered to be the boundary between the negative electrode active material layer 2B and the solid electrolyte layer 3.

[0050] The average thickness of the negative electrode active material layer 2B is, for example, 4 μm or less, preferably 1 μm or more and 4 μm or less. The average thickness of the negative electrode active material layer 2B is determined from a scanning electron microscope image. For example, the distance of a perpendicular line drawn between an xy plane passing through the outermost portion of the negative electrode current collector 21 and an xy plane passing through the outermost portion of the negative electrode active material 22 is measured for any 10 images, and the average is regarded as the thickness of the negative electrode active material layer 2B. When the average thickness of the negative electrode active material layer 2B is small, the physical distance between the negative electrode current collector 21 and the solid electrolyte is shortened, and lithium ions are conducted to the vicinity of the negative electrode current collector 21. As a result, the negative electrode current collector 21 also functions as an active material, and the output voltage of the all-solid-state battery is increased.

[0051] (Negative electrode active material) The negative electrode active material is a compound that can absorb and release ions. The negative electrode active material is a compound that exhibits a lower potential than the positive electrode active material. The negative electrode active material is a compound that exhibits a lower potential than the positive electrode active material. α TiO3 and Li β The negative electrode active material contains at least one of TiSiO5 and TiSiO5. α is 2 or more and 2.8 or less, and β is 2 or more and 4 or less. The values ​​of α and β vary within this range with charge and discharge. For example, the composition ratio of Li in the negative electrode active material varies from, for example, a base state of an uncharged battery with charge and discharge. For example, the negative electrode active material may contain a plurality of active material materials. For example, the negative electrode active material may contain Li α TiO3 and Li γ Ti5O 12(4≦γ≦7) may be used as a mixture, and Li β TiSiO5 and Li γ Ti5O 12 (4≦γ≦7) may be used as a mixture, and Li α TiO3 and Li β A mixture with TiSiO5 is also possible.

[0052] (Conductive additive) The conductive additive improves the electronic conductivity of the negative electrode active material layer 2 B. The conductive additive may be the same material as that used for the positive electrode active material layer 1 B.

[0053] (binding material) The binder bonds the negative electrode current collector layer 2A and the negative electrode active material layer 2B, the negative electrode active material layer 2B and the solid electrolyte layer 3, and the various materials constituting the negative electrode active material layer 2B together. The binder may be the same material as that used for the positive electrode active material layer 1B. The binder content may also be the same as that used for the positive electrode active material layer 1B. If a binder is not required, it need not be included.

[0054] 2 shows an example in which the negative electrode 2 is composed of a negative electrode current collector layer 2A and a negative electrode active material layer 2B, but this is not limiting. For example, the negative electrode 2 may be a single layer in which the negative electrode current collector 21 and the negative electrode active material 22 are mixed.

[0055] "Manufacturing method for all-solid-state batteries" Next, a description will be given of a method for manufacturing the all-solid-state battery 10. First, the laminate 4 is produced. The laminate 4 is produced by, for example, a co-firing method or a sequential firing method.

[0056] The co-firing method is a method in which the materials for forming each layer are stacked and then fired all at once to produce the laminate 4. The sequential firing method is a method in which firing is performed after each layer is formed. The co-firing method can produce the laminate 4 with fewer steps than the sequential firing method. Furthermore, the laminate 4 produced by the co-firing method is denser than the laminate 4 produced by the sequential firing method. Below, an example in which the co-firing method is used will be explained.

[0057] First, the materials for the positive electrode current collector layer 1A, the positive electrode active material layer 1B, the solid electrolyte layer 3, the negative electrode active material layer 2B, and the negative electrode current collector layer 2A that constitute the laminate 4 are made into a paste. In the example shown in FIG. 4, the positive electrode current collector 11 is coated with an oxide 13 and then made into a paste. In the example shown in FIG. 5, the materials for the intermediate layer 1F are also made into a paste.

[0058] The method for forming each material into a paste is not particularly limited, and for example, a method of mixing powders of each material with a vehicle to obtain a paste is used. Here, the vehicle is a general term for a medium in a liquid phase. The vehicle includes a solvent and a binder.

[0059] Next, a green sheet is prepared. The green sheet is obtained by applying a paste prepared for each material onto a substrate such as a PET (polyethylene terephthalate) film, drying it as necessary, and then peeling off the substrate. The method for applying the paste is not particularly limited, and known methods such as screen printing, coating, transfer, and doctor blade can be used.

[0060] Next, the green sheets prepared for each material are stacked in the desired order and number of layers to prepare a laminated sheet. When stacking the green sheets, alignment and cutting are performed as necessary. For example, when preparing a parallel or series-parallel battery, alignment is performed so that the end face of the positive electrode current collector layer 1A and the end face of the negative electrode current collector layer 2A do not coincide, and the respective green sheets are stacked.

[0061] The laminate sheet may be fabricated by fabricating a positive electrode unit and a negative electrode unit and then laminating these units. The positive electrode unit is a laminate sheet in which a solid electrolyte layer 3, a positive electrode active material layer 1B, a positive electrode current collector layer 1A, and a positive electrode active material layer 1B are laminated in this order. In the example shown in FIG. 5, an intermediate layer 1F is laminated between the positive electrode current collector layer 1A and the positive electrode active material layer 1B. The negative electrode unit is a laminate sheet in which a solid electrolyte layer 3, a negative electrode active material layer 2B, a negative electrode current collector layer 2A, and a negative electrode active material layer 2B are laminated in this order. The positive electrode unit and the negative electrode active material layer 2B of the negative electrode unit are laminated so that they face each other, or so that the positive electrode active material layer 1B of the positive electrode unit and the solid electrolyte layer 3 of the negative electrode unit face each other.

[0062] Next, the produced laminated sheet is pressed together to increase the adhesion of each layer. Pressing can be performed, for example, by a mold press, hot isostatic pressing (WIP), cold isostatic pressing (CIP), isostatic pressing, or the like. Pressing is preferably performed while heating. The heating temperature during pressing is, for example, 40°C or higher and 95°C or lower. Next, the pressed laminate is cut into chips using a dicing device. The chips are then subjected to a binder removal treatment and sintering to obtain a laminate 4 made of a sintered body.

[0063] The binder removal process can be performed as a separate process from the firing process. The binder removal process thermally decomposes the binder components contained in the chips before the firing process, preventing the binder components from rapidly decomposing during the firing process. The binder removal process is performed, for example, by heating in an air atmosphere at a temperature of 300°C to 800°C for 0.1 to 10 hours. The atmosphere for the binder removal process is an oxygen partial pressure environment in which the materials constituting the positive electrode, negative electrode, and solid electrolyte do not or do not easily oxidize or reduce, and the type of gas can be selected arbitrarily so that the materials constituting the positive electrode, negative electrode, and solid electrolyte do not react with the atmospheric gas. For example, the binder removal process may be performed in a nitrogen atmosphere, an argon atmosphere, a nitrogen-hydrogen mixed atmosphere, a water vapor atmosphere, or a mixture thereof.

[0064] The firing step is performed, for example, by placing the chip on a ceramic base. Firing is performed, for example, by heating to 600°C or higher and 1000°C or lower in an air atmosphere. The firing time is, for example, 0.1 hour or higher and 3 hours or lower. The atmosphere for the sintering step is an oxygen partial pressure environment in which the materials constituting the positive electrode, negative electrode, and solid electrolyte do not or do not easily oxidize or reduce, and the type of gas can be selected arbitrarily so that the materials constituting the positive electrode, negative electrode, and solid electrolyte do not react with the atmospheric gas. For example, the sintering step may be performed in a nitrogen atmosphere, an argon atmosphere, a nitrogen-hydrogen mixed atmosphere, a water vapor atmosphere, or a mixture thereof.

[0065] Alternatively, the sintered laminate 4 (sintered body) may be placed in a cylindrical container together with an abrasive such as alumina and barrel polished. This allows the corners of the laminate to be chamfered. Polishing may also be performed using sandblasting. Sandblasting is preferred because it allows only specific portions to be polished.

[0066] Terminal electrodes 5 and 6 are formed on the opposing side surfaces of the fabricated laminate 4. The terminal electrodes 5 and 6 can be formed by means of sputtering, dipping, screen printing, spray coating, or the like. Through the above-described steps, the all-solid-state battery 10 can be fabricated. When the terminal electrodes 5 and 6 are formed only on predetermined portions, the portions are masked with tape or the like and the above-described process is carried out.

[0067] The all-solid-state battery according to this embodiment has a high energy density. This is because the Ag element contained in the negative electrode 2 functions as a negative electrode active material, and the potential of the negative electrode 2 is approximately 0 V (vs. Li + This is thought to be because the potential of the negative electrode 2 is approximately 0 V and the potential of the negative electrode 3 is approximately 3.6 V (vs Li + / Li) positive electrode 1 (Li x CoO2 and Li xThe all-solid-state battery 10 is driven by the potential difference between the solid-state battery 10 and the Mn2O4), which increases the output voltage of the all-solid-state battery. The amount of energy of the all-solid-state battery 10 is calculated by multiplying the output voltage of the all-solid-state battery 10 by the capacity of the all-solid-state battery. The energy density of the all-solid-state battery 10 can be compared in terms of the amount of energy if the volume of the all-solid-state battery is the same. Therefore, the all-solid-state battery according to this embodiment has a high energy density.

[0068] Here, the energy density of the all-solid-state battery 10 is α TiO3 and Li β The reason why the energy density is increased when at least one of TiSiO5 and TiSiO5 is contained in the negative electrode active material is not clear. When these materials are contained in the negative electrode active material, Ag or a compound containing Ag contained in the negative electrode current collector also functions as an active material, thereby increasing the energy density of the all-solid-state battery 10.

[0069] The above describes the embodiments of the present invention in detail with reference to the drawings. However, each configuration and combination thereof in each embodiment is an example, and additions, omissions, substitutions, and other modifications of the configurations are possible within the scope that does not deviate from the spirit of the present invention. [Example]

[0070] "Example 1" (Preparation of positive electrode paste) To prepare the positive electrode current collector layer paste, powders of Ag and Pd mixed in a volume ratio of 80:20 were used. Ethyl cellulose and dihydroterpineol were added to this powder and mixed. Ethyl cellulose was the binder, and dihydroterpineol was the solvent.

[0071] The positive electrode active material layer paste was prepared by adding ethyl cellulose and dihydroterpineol to LiMn2O4, which is the positive electrode active material, and mixing them.

[0072] (Preparation of solid electrolyte layer paste) The starting materials were Li2CO3, SiO2, and Li3PO4, mixed in a molar ratio of 2:1:1. The mixture was wet mixed for 16 hours using a ball mill with water as the dispersion medium. The mixture was calcined at 950°C for 2 hours, and Li 3.5 Si 0.5 P 0.5 O4 was prepared. 100 parts by mass of this calcined powder, 100 parts by mass of ethanol, and 200 parts by mass of toluene were added to a ball mill and wet mixed. 16 parts by mass of a polyvinyl butyral binder and 4.8 parts by mass of benzyl butyl phthalate were then added and mixed to prepare a solid electrolyte layer paste.

[0073] (Preparation of negative electrode paste) To prepare the negative electrode current collector layer paste, a powder of Ag and Pd mixed in a volume ratio of 80:20 was used. Ethyl cellulose and dihydroterpineol were added to this powder and mixed to prepare the negative electrode current collector layer paste.

[0074] The negative electrode active material layer paste was prepared by adding ethyl cellulose and dihydroterpineol to Li2TiO3 and mixing them.

[0075] (Fabrication of all-solid-state batteries) Next, a positive electrode unit and a negative electrode unit were fabricated by the following procedure. First, a positive electrode active material layer paste was printed to a thickness of 5 μm on the above-mentioned solid electrolyte layer sheet using screen printing. Next, the printed positive electrode active material layer paste was dried at 80°C for 5 minutes. Then, a positive electrode current collector layer paste was printed to a thickness of 5 μm on the dried positive electrode active material layer paste using screen printing. Next, the printed positive electrode current collector layer paste was dried at 80°C for 5 minutes. Then, a positive electrode active material layer paste was printed again to a thickness of 5 μm on the dried positive electrode current collector layer paste using screen printing and dried. Then, the PET film was peeled off. In this way, a positive electrode unit was obtained in which a positive electrode active material layer / positive electrode current collector layer / positive electrode active material layer were laminated in this order on the main surface of the solid electrolyte layer.

[0076] In addition, a negative electrode unit was obtained in the same manner, in which a negative electrode active material layer / a negative electrode current collector layer / a negative electrode active material layer were laminated in this order on the main surface of the solid electrolyte layer.

[0077] Next, a solid electrolyte unit was fabricated by stacking five solid electrolyte layer sheets. The stack was fabricated by alternately stacking 50 electrode units (25 positive electrode units and 25 negative electrode units) with the solid electrolyte unit sandwiched between them. The units were stacked with the current collector layers of odd-numbered electrode units extending only to one end face, and the current collector layers of even-numbered electrode units extending only to the opposite end face. Six solid electrolyte layer sheets were stacked on top of the stacked units. This was then molded by thermocompression bonding and cut to fabricate a laminated chip. The laminated chips were then co-fired to obtain a laminate. The co-firing was performed in an air atmosphere, with the temperature rising at a rate of 200°C / hour to a firing temperature of 800°C, and the temperature was maintained for 2 hours. The resulting product was then naturally cooled.

[0078] Terminal electrodes 5 and 6 were attached to the sintered laminate (sintered body) by a known method to fabricate an all-solid-state battery. The volume ratio of each layer was unchanged between the paste state before sintering and the state after sintering. Ag exists both as a single Ag and as an element contained in an AgPd alloy.

[0079] The fabricated all-solid-state battery was then cut along the lamination direction, and the cross section was observed using a scanning electron microscope. The thickness of the negative electrode active material layer was then measured. The thickness of the negative electrode active material layer in Example 1 was 6 μm. The total volume ratio (Va) of Ag and Ag alloy in the negative electrode current collector layer was also determined. The volume ratio (Va) of the negative electrode was determined as the area ratio of Ag and Ag alloy in the cross section observed with a scanning electron microscope. The Ag and Ag alloy can be distinguished from other substances based on the contrast of the image. Furthermore, when extracting only the volume ratio of Ag from Ag and Ag alloy, the composition ratio can be quantitatively analyzed using energy dispersive X-ray spectroscopy (EDS), and the volume ratio of Ag alone can be determined by calculating the product of that ratio and the volume ratio of Ag and Ag alloy.

[0080] Next, the output voltage and capacity of the all-solid-state battery fabricated under the same conditions were measured. The capacity is the discharge capacity, and in an environment of 60°C, the battery was charged at a constant current of 100 μA (CC charging) until the battery voltage reached 3.9 V, and then discharged at a constant current of 100 μA (CC discharging) until the battery voltage reached 0 V. This process was repeated 10 times, and the discharge capacity (μAh) at the 10th cycle was measured. The energy amount (μWh) was then calculated from the product of the output voltage and capacity of the all-solid-state battery. It was confirmed that the Li composition ratio of Li2TiO3 varied between 2 and 2.8 depending on the charge and discharge.

[0081] "Examples 2 to 4" Examples 2 to 4 differ from Example 1 in that the thickness of the negative electrode active material layer was changed. The thickness of the negative electrode active material layer was adjusted by the thickness of the paste used when producing the negative electrode active material layer. The thickness of the negative electrode active material layer was 4 μm in Example 2, 3 μm in Example 3, and 1 μm in Example 4. The other conditions were the same as in Example 1, and the energy amount of the all-solid-state battery was determined.

[0082] "Examples 5 to 8" In Examples 5 to 8, when preparing the negative electrode active material layer paste, Li 4 / 3 Ti 5 / 3 This differs from Example 1 in that O4 and Li2TiO3 are mixed. Example 5 is Li 4 / 3 Ti 5 / 3 The volume ratio of O4 to Li2TiO3 was 80:20. Example 6 is Li 4 / 3 Ti 5 / 3 The volume ratio of O4 to Li2TiO3 was 60:40. Example 7 is Li 4 / 3 Ti 5 / 3 The volume ratio of O4 to Li2TiO3 was 40:60. Example 8 is Li 4 / 3 Ti 5 / 3 The volume ratio of O4 to Li2TiO3 was 20:80. Other conditions were the same as in Example 1, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0083] "Examples 9 to 12" Examples 9 to 12 differ from Examples 1 to 4 in that Li2TiSiO5 was used instead of Li2TiO3 when preparing the negative electrode active material layer paste. Other conditions were the same as in Example 1, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined. It was confirmed that the Li composition ratio of Li2TiSiO5 varied within a range of 2 to 4 depending on charge and discharge.

[0084] "Examples 13 to 16" Examples 13 to 16 differ from Example 1 in that Li2TiSiO5 and Li2TiO3 were mixed together when preparing the negative electrode active material layer paste. In Example 13, the volume ratio of Li2TiSiO5 to Li2TiO3 was 80:20. In Example 14, the volume ratio of Li2TiSiO5 to Li2TiO3 was 60:40. In Example 15, the volume ratio of Li2TiSiO5 to Li2TiO3 was 40:60. In Example 16, the volume ratio of Li2TiSiO5 to Li2TiO3 was 20:80. Other conditions were the same as in Example 1, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0085] "Comparative Example 1" In Comparative Example 1, when preparing the negative electrode active material layer paste, Li2TiO3 was used instead of Li 4 / 3 Ti 5 / 3 The difference from Example 1 is that O4 was used. Other conditions were the same as in Example 1, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0086] The results of Examples 1 to 16 and Comparative Example 1 are summarized in Table 1 below.

[0087] [Table 1]

[0088] Examples 1 to 17, which contained at least one of Li2TiO3 and Li2TiSiO5 as the negative electrode active material, had higher energy density than Comparative Example 1, which did not contain either of these.

[0089] Next, in Examples 17 to 36 and Comparative Example 2, the positive electrode active material was LiCoO2, and the parameters of each layer were changed.

[0090] "Example 17" Example 17 differs from Example 4 in that the positive electrode active material was LiCoO2, and the negative electrode current collector layer paste was prepared using a powder mixture of Ag, Pd, and Li2TiO3 in a volume ratio of 64:16:20. Other conditions were the same as in Example 1, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0091] "Examples 18 to 20" Examples 18 to 20 differ from Example 17 in that the thickness of the negative electrode active material layer was changed. The thickness of the negative electrode active material layer was adjusted by the thickness of the paste used when producing the negative electrode active material layer. The thickness of the negative electrode active material layer was 3 μm in Example 18, 4 μm in Example 19, and 6 μm in Example 20. The other conditions were the same as in Example 1, and the energy amount of the all-solid-state battery was determined.

[0092] "Examples 21 to 24" Each of Examples 21 to 24 differs from each of Examples 17 to 20 in that Li2TiSiO5 was used instead of Li2TiO3 when preparing the negative electrode active material layer paste. Other conditions were the same as in Example 1, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0093] "Examples 25 to 28" Examples 25 to 28 differ from Example 17 in that the volume ratio of Ag, Pd, and Li2TiO3 in the negative electrode current collector layer was changed. Other conditions were the same as in Example 1, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0094] In Example 25, the volume ratio of Ag, Pd, and Li2TiO3 was Ag:Pd:Li2TiO3=72:18:10. In Example 26, the volume ratio of Ag, Pd, and Li2TiO3 was Ag:Pd:Li2TiO3=40:10:50. In Example 27, the volume ratio of Ag, Pd, and Li2TiO3 was Ag:Pd:Li2TiO3 = 36:9:55. In Example 28, the volume ratio of Ag to Pd was Ag:Pd = 80: 20. That is, in Example 28, Li2TiO3 was not added when preparing the negative electrode current collector layer paste.

[0095] "Examples 29 to 32" Examples 29 to 32 differ from Examples 25 to 28 in that Li2TiSiO5 was used instead of Li2TiO3 when preparing the negative electrode active material layer paste. Other conditions for Examples 29 to 32 were the same as those for Examples 25 to 28, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0096] "Example 33" In Example 33, the negative electrode paste was produced as a single layer, rather than by laminating a negative electrode current collector paste and a negative electrode active material layer paste, which were separately produced. The negative electrode paste was produced by adding ethyl cellulose and dihydroterpineol to a powder mixture of Ag, Pd, and Li2TiO3 in a volume ratio of 64:16:20. The negative electrode unit used in the production of the all-solid-state battery was a single layer made of the negative electrode paste, which was formed on one side of the solid electrolyte layer. The other conditions were the same as in Example 1, and the thickness of the negative electrode active material layer and the energy content of the all-solid-state battery were determined.

[0097] "Example 34" Example 34 differs from Example 33 in that LiTiSiO was used instead of LiTiO when preparing the negative electrode paste. Other conditions in Example 34 were the same as those in Example 33, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0098] "Example 35" In Example 35, the solid electrolyte was Li 3.5 Si 0.5 P 0.5 O4 to Li 3.5 Si 0.5 V 0.5 The difference from Example 17 is that the negative electrode active material layer was changed to O4. Other conditions were the same as in Example 1, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0099] "Example 36" In Example 36, the solid electrolyte was Li 3.5 Si 0.5 P 0.5 O4 to Li 3.5 Si 0.5 V 0.5 The difference from Example 21 is that the negative electrode active material layer was changed to O4. Other conditions were the same as in Example 1, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0100] "Comparative Example 2" In Comparative Example 2, when preparing the negative electrode active material layer paste, Li2TiO3 was used instead of Li 4 / 3 Ti 5 / 3 The difference from Example 17 is that O4 was used. Other conditions were the same as in Example 17, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0101] [Table 2]

[0102] Next, in Examples 38 to 49, a Li-Ag alloy was added to the negative electrode current collector layer and similar studies were performed. However, the Li-Ag alloy was handled in a glove box with a dew point of −50°C, and the co-firing was performed by heating the alloy in an argon atmosphere at a rate of 1200°C / hour up to a firing temperature of 800°C, maintaining the temperature for 20 minutes, and then allowing it to cool naturally after firing.

[0103] "Example 38" In Example 38, when preparing the negative electrode current collector layer, Ag was replaced with a Li-Ag alloy (Li 3.1The difference from Example 17 is that Li-Ag alloy was added. The amount of Li in the Li-Ag alloy was determined by quantitative analysis using X-ray diffraction (XRD). The negative electrode active material layer contained Li-Ag alloy, Ag, Pd, and Li2TiO3 in a volume ratio of 4:60:16:20. The other conditions were the same as in Example 1, and the energy amount of the all-solid-state battery was determined.

[0104] "Examples 39 and 40" Examples 39 and 40 differ from Example 38 in that the thickness of the negative electrode active material layer was changed. The thickness of the negative electrode active material layer was 3 μm in Example 39 and 4 μm in Example 40. The other conditions were the same as in Example 1, and the energy amount of the all-solid-state battery was determined.

[0105] "Examples 41 to 43" In Examples 41 to 43, the composition ratio of the Li-Ag alloy was 4.7 The difference from each of Examples 38 to 40 is that Ag was used. Other conditions were the same as in Example 1, and the energy amount of the all-solid-state battery was determined.

[0106] "Examples 44 to 49" Examples 44 to 49 differ from Examples 38 to 43 in that the negative electrode active material layer was changed from Li2TiO3 to Li2TiSiO5. Other conditions were the same as in Example 1, and the energy amount of the all-solid-state battery was determined.

[0107] [Table 3] [Explanation of symbols]

[0108] 1...Positive electrode, 1A,1C,1D,1E...Positive electrode current collector layer, 1B...Positive electrode active material layer, 1F...Intermediate layer, 2,2D...Negative electrode, 2A,2C...Negative electrode current collector layer, 2B...Negative electrode active material layer, 3...Solid electrolyte material layer, 4... laminate, 5,6... terminal electrode, 10... all-solid battery, 11... positive electrode current collector, 21... negative electrode current collector, 12... positive electrode active material, 13... oxide, 22... negative electrode active material, 23... solid electrolyte

Claims

1. a sintered body having a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode; The solid electrolyte layer is made of γ-Li ３ P.O. ４ a solid electrolyte having a crystal structure of the type The negative electrode is composed of Ag alone or an Ag alloy and Li α TiO ３ (2≦α≦2.8) and Li β TiSiO ５ and at least one compound selected from the group consisting of (2≦β≦4).

2. the negative electrode comprises a first layer and a second layer; the second layer is closer to the solid electrolyte layer than the first layer and is in contact with at least one main surface of the first layer; The all-solid-state battery according to claim 1 , wherein the second layer has a thickness of 1 μm or more and 4 μm or less.

3. The first layer is composed of Ag or an Ag alloy and Li α TiO ３ (2≦α≦2.8) and Li β TiSiO ５ 3. The all-solid-state battery according to claim 2, comprising at least one compound selected from the group consisting of (2≦β≦4).

4. 4. The all-solid-state battery according to claim 3, wherein a total volume ratio of Ag and Ag alloy in the first layer is 45% or more and 90% or less.

5. 2. The all-solid-state battery according to claim 1, wherein the Ag alloy is a LiAg alloy or an AgPd alloy.

6. The second layer is Li α TiO ３ (2≦α≦2.8) and Li β TiSiO ５ 3. The all-solid-state battery according to claim 2, comprising at least one compound selected from the group consisting of (2≦β≦4).

7. The first layer and the second layer are Li α TiO ３ (2≦α≦2.8) and Li β TiSiO ５ The all-solid-state battery according to claim 2 , comprising a compound having the same composition as (2≦β≦4).

8. The solid electrolyte is Li ３＋ｘ Si ｘ P １－ｘ O ４ 2. The all-solid-state battery of claim 1, comprising: (0.2≦x≦0.6).

9. 10. The all-solid-state battery of claim 1, wherein the positive electrode comprises lithium cobalt oxide.

10. 2. The all-solid-state battery according to claim 1, wherein the positive electrode comprises a third layer containing Ag and a fourth layer in contact with at least one main surface of the third layer.

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