All-solid-state batteries

Abstract

An all-solid-state battery comprising 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 positive electrode contains an Ag-containing compound, a Li-containing transition metal oxide, and an oxide having a different composition from Li transition metal oxide; the oxide contains Ag; and at least some of the Ag-containing compound and the Li transition metal oxide are present on the interior of the positive electrode with the oxide therebetween.

Description

[Technical Field]

[0001] This invention relates to an all-solid-state battery. This application claims priority based on Japanese Patent Application No. 2022-029456, filed in Japan on February 28, 2022, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] In recent years, advancements in electronics technology have been remarkable, leading to the miniaturization, weight reduction, thinning, and increased functionality of portable electronic devices. Consequently, there is a strong demand for smaller, lighter, thinner batteries and improved reliability for the batteries that power these devices, and all-solid-state batteries, which use solid electrolytes, are attracting attention.

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

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

[0005] [Patent Document 1] International Publication No. 2007 / 135790 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Minimal performance degradation after multiple charge-discharge cycles is crucial for batteries, and there is a demand for all-solid-state batteries with superior cycle characteristics.

[0007] This invention has been made in view of the above problems, and aims to improve the cycle characteristics of all-solid-state batteries. [Means for solving the problem]

[0008] To solve the above problems, the following means are provided.

[0009] (1) A solid-state battery according to a first embodiment, comprising a sintered body having a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode, wherein the positive electrode comprises an Ag-containing compound, a Li-containing transition metal oxide, and an oxide having a different composition from the Li transition metal oxide, the oxide containing Ag, and at least a portion of the Ag-containing compound and the Li transition metal oxide is present inside the positive electrode via the oxide.

[0010] (2) In the all-solid-state battery according to the above embodiment, the oxide may include the transition metal element that constitutes the Li transition metal oxide.

[0011] (3) In the all-solid-state battery according to the above embodiment, the minimum thickness of the oxide, which is connected to at least a portion of the Ag-containing compound and the Li transition metal oxide, may be 0.01 μm or more and 2.0 μm or less.

[0012] (4) In the all-solid-state battery according to the above embodiment, the contact rate between the Li transition metal oxide and the Ag-containing compound in the cross-section of the positive electrode may be 0.1% or more and 10% or less.

[0013] (5) In the all-solid-state battery according to the above embodiment, the compound containing Ag may be selected from Ag or Ag / Pd.

[0014] (6) In the all-solid-state battery according to the above aspect, the positive electrode includes a first layer and a second layer provided on at least one main surface of the first layer, and the first layer may include a compound containing Ag, the Li-containing transition metal oxide, and the oxide.

[0015] (7) In the all-solid-state battery according to the above aspect, the second layer may contain the Li transition metal oxide.

[0016] (8) In the all-solid-state battery according to the above aspect, the first layer and the second layer may contain a Li transition metal oxide having the same composition.

[0017] (9) In the all-solid-state battery according to the above aspect, the positive electrode may contain lithium cobaltate.

Advantages of the Invention

[0018] The all-solid-state battery according to the above aspect can improve cycle characteristics.

Brief Description of the Drawings

[0019] [Figure 1] It is a cross-sectional view of the all-solid-state battery according to the first embodiment. [Figure 2] It is an enlarged cross-sectional view of a part of the positive electrode according to the first embodiment. [Figure 3] It is an enlarged cross-sectional view of a part of another example of the positive electrode according to the first embodiment. [Figure 4] It is an enlarged cross-sectional view of a part of the negative electrode according to the first embodiment. [Figure 5] It is an enlarged cross-sectional view of a part of another example of the negative electrode according to the first embodiment.

Modes for Carrying Out the Invention

[0021] The directions are defined as follows: The stacking direction of the laminate 4 is defined as the z-direction, one direction in the plane perpendicular to the z-direction is defined as the x-direction, and the direction perpendicular to both the x-direction and the z-direction is defined as the y-direction. Hereafter, one direction in the z-direction may be referred to as "up," and the opposite direction may be referred to as "down." Up and down do not necessarily coincide with the direction in which gravity acts.

[0022] Figure 1 is a schematic cross-sectional view 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, respectively. The terminal electrodes 5 and 6 extend in the z direction, which intersects (is perpendicular to) the laminate surface of the laminate 4.

[0023] 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 laminating and sintering the positive electrode 1, the negative electrode 2, and the solid electrolyte layer 3. The number of layers for the positive electrode 1 and the negative electrode 2 is not limited. 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, there is, for example, the same solid electrolyte as 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.

[0024] The all-solid-state battery 10 charges or discharges by the exchange of ions between the positive electrode 1 and the negative electrode 2 via the solid electrolyte layer 3. Figure 1 shows a stacked battery, but a wound-type battery may also be used. The all-solid-state battery 10 is used in, for example, laminated batteries, prismatic batteries, cylindrical batteries, coin-type batteries, button-type batteries, etc. The all-solid-state battery 10 may also be a liquid-injection type in which the solid electrolyte layer 3 is dissolved or dispersed in a solvent.

[0025] "Positive electrode" Figure 2 is an enlarged view of a part of the positive electrode 1 according to the first embodiment. In terms of structure, the positive electrode 1 has, for example, a positive electrode current collector layer 1A (sometimes referred to as the "first layer" in this specification) and a positive electrode active material layer 1B (sometimes referred to as the "second layer" in this specification). In terms of composition, the positive electrode 1 has, for example, a compound containing Ag, a Li-containing transition metal oxide, and an oxide having a different composition from the Li-containing transition metal oxide (hereinafter referred to as the "oxide"). The aforementioned oxide contains Ag. At least a portion of the Ag-containing compound and the Li-containing transition metal oxide are present inside the positive electrode (for example, inside the positive electrode current collector layer or inside the positive electrode current collector layer and the positive electrode active material layer) via the oxide.

[0026] [Positive electrode current collector layer] The positive electrode current collector layer (first layer) 1A comprises, for example, a positive electrode current collector 11 (which may be referred to herein as an "Ag-containing compound"), a positive electrode active material 12 (which may be referred to herein as a "Li transition metal oxide"), and an oxide 13 (oxide) having a different composition from the Li transition metal oxide. In this case, the area between the xy plane passing through the top and the xy plane passing through the bottom of the oxide 13 having a different composition from the Li transition metal oxide is considered to be the positive electrode current collector layer 1A.

[0027] The positive electrode current collector 11 contains Ag. The positive electrode current collector 11 contains, for example, a metal or alloy containing Ag. The metal or alloy of Ag does not melt and is not easily oxidized even when the laminate 4 is heated in an atmospheric environment. The positive electrode current collector 11 is, for example, an Ag, AgPd alloy.

[0028] The positive electrode current collector 11 consists of, for example, a plurality of conductive particles. The plurality of conductive particles are connected to each other and electrically connected in the xy plane. The positive electrode current collector 11 is not limited to this example and may take the form of, for example, a foil, a punched film, or an expanded film that extends in the xy plane.

[0029] The positive electrode active material 12 is mixed together with the positive electrode current collector 11 within the positive electrode current collector layer 1A. The presence of the positive electrode active material 12 within the positive electrode current collector layer 1A facilitates the transfer of electrons between the positive electrode active material 12 and the positive electrode current collector 11.

[0030] The positive electrode active material 12 is not particularly limited as long as it is capable of reversibly releasing and intercalating lithium ions, and desorption and insertion of lithium ions. For example, positive electrode active materials used in known lithium-ion secondary batteries can be used.

[0031] The positive electrode active material 12 is, for example, a composite transition metal oxide (including Li transition metal oxide). Preferably, the positive electrode active material 12 is a transition metal oxide containing one or more selected from the group consisting of Co, Ni, Mn, Fe, and V. Preferably, the positive electrode active material 12 is lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium vanadium composite oxide, lithium titanium composite oxide, manganese dioxide, titanium oxide, niobium oxide, vanadium oxide, tungsten oxide, etc. For example, the positive electrode active material 12 is LiCoO2, LiMnO2. These compounds may have deviations from the stoichiometric composition. For example, the positive electrode active material 12 is Li x It may be lithium cobalt oxide represented as CoO2, in which x fluctuates in the range of 0.4 to 1.2 with the charging and discharging of the all-solid-state battery.

[0032] Furthermore, lithium-free positive electrode active materials can also be used as the positive electrode active material 12. These positive electrode active materials can be used by first placing a negative electrode active material doped with metallic lithium or lithium ions in the negative electrode and starting the battery from discharge. For example, lithium-free metal oxides (such as MnO2 and V2O5) are examples of such positive electrode active materials.

[0033] The oxide 13 (oxide) having a different composition from the Li transition metal oxide is located between the positive electrode current collector 11 and the positive electrode active material 12. The oxide 13 having a different composition from the Li transition metal oxide is an oxide containing Ag. The oxide 13 having a different composition from the Li transition metal oxide prevents oxidation of the Ag contained in the positive electrode current collector 11, thereby improving the cycle characteristics of the all-solid-state battery 10.

[0034] The oxide 13 having a different composition from the Li transition metal oxide preferably contains the constituent elements that make up the positive electrode active material 12. For example, if the positive electrode active material 12 is LiCoO2, the oxide 13 having a different composition from the Li transition metal oxide is preferably AgCoO2. For example, if the positive electrode active material 12 is LiMn2O4, the oxide 13 having a different composition from the Li transition metal oxide is preferably AgMn2O4.

[0035] The thickness of the oxide 13 having a different composition from the Li transition metal oxide is, for example, 0.01 μm or more. Preferably, the thickness of the oxide 13 having a different composition from the Li transition metal oxide is 0.1 μm or more. The thickness of the oxide 13 having a different composition from the Li transition metal oxide can be determined from a scanning electron microscope image. First, a first imaginary line is drawn in the image, passing through the top of the positive electrode current collector 11. Next, a second imaginary line is drawn, passing through the top of the oxide 13 having a different composition from the Li transition metal oxide. The width between the first and second imaginary lines is taken as the thickness of the oxide 13 having a different composition from the Li transition metal oxide in that image. This process is performed on 10 images, and the average value is defined as "the thickness of the oxide 13 having a different composition from the Li transition metal oxide (thickness of the oxide via the Ag-containing compound and at least a part of the Li transition metal oxide)". In this example, the first and second virtual lines are defined as lines passing through the top of the positive electrode current collector 11 and lines passing through the top of the oxide 13 having a different composition from the Li transition metal oxide, respectively. However, they may also be defined as lines passing through the bottom of each respective element.

[0036] [Cathode active material layer] The positive electrode active material layer 1B (second layer) is formed on one or both sides of the positive electrode current collector layer 1A. The positive electrode active material layer 1B contains positive electrode active material. The positive electrode active material layer 1B may also contain a conductive additive, a binder, and a solid electrolyte as described later. If the positive electrode active material layer 1B contains a solid electrolyte, the area between the xy plane passing through the outermost part of the positive electrode active material and the boundary with the positive electrode current collector layer 1A is considered to be the positive electrode active material layer 1B.

[0037] The positive electrode active material contained in the positive electrode active material layer 1B is the same as the positive electrode active material 12 contained in the positive electrode current collector layer 1A.

[0038] The conductive additive is not particularly limited as long as it improves the electronic conductivity within the positive electrode active material layer 1B, and known conductive additives can be used. Examples of conductive additives 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, or mixtures thereof. The conductive additive may be in the form of a powder or fibers.

[0039] The binder joins the positive electrode current collector layer 1A to the positive electrode active material layer 1B, the positive electrode active material layer 1B to the solid electrolyte layer 3, and the various materials that make up the positive electrode active material layer 1B to each other.

[0040] The binder can be used within a range that does not impair the function of the positive electrode active material layer 1B. The binder may be omitted if it is not needed. The binder content in the positive electrode active material layer 1B is, for example, 0.5 to 30 volume percent of the positive electrode active material layer. If the binder content is sufficiently low, the resistance of the positive electrode active material layer 1B will be sufficiently low. Here, the volume percent is approximately equal to the area percent of the cross-section measured by, for example, a scanning electron microscope. Therefore, the area ratio of the cross-section measured by a scanning electron microscope can be directly considered as the volume ratio.

[0041] The binder can be any material capable of the above-mentioned bonding, such as fluororesins like polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). In addition to the above, other binders such as cellulose, styrene-butadiene rubber, ethylene-propylene rubber, polyimide resin, and polyamide-imide resin may also be used. Furthermore, conductive polymers with electronic conductivity or ionic conductive polymers with ionic conductivity may be used as binders. Examples of conductive polymers with electronic conductivity include polyacetylene. In this case, since the binder also functions as a conductive additive, it is not necessary to add a conductive additive. Examples of ionic conductive polymers with ionic conductivity include those that conduct lithium ions, and include composites of monomers of polymer compounds (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide, polyphosphozenes, etc.) and lithium salts such as LiClO4, LiBF4, and LiPF6, or alkali metal salts mainly composed of lithium. Polymerization initiators used in compounding include, for example, photopolymerization initiators or thermal polymerization initiators compatible with the above-mentioned monomers. Required properties for the binder include oxidation / reduction resistance and good adhesion.

[0042] Up to this point, specific examples of positive electrodes have been shown, but positive electrodes are not limited to these examples. For example, the positive electrode current collector layer (first layer) may consist only of the positive electrode current collector 11 (a compound containing Ag). In this case, the oxide 13 (oxide) having a different composition from the Li transition metal oxide is located between the positive electrode current collector layer (first layer) and the positive electrode active material layer (second layer). Alternatively, the positive electrode may be a single layer in which the positive electrode current collector 11 (a compound containing Ag), the positive electrode active material 12 (a Li transition metal oxide), and the oxide 13 (oxide) having a different composition from the Li transition metal oxide are mixed.

[0043] FIG. 3 is a cross-sectional view taken along the stacking direction of another example of the positive electrode according to the first embodiment. The positive electrode shown in FIG. 3 includes a positive electrode current collector layer 1C, an intermediate layer 1D, and a positive electrode active material layer 1B. The positive electrode current collector layer 1C includes a positive electrode current collector 11 and an oxide 13 (oxide) having a composition different from that of the Li-transition metal oxide. The intermediate layer 1D is made of an oxide 13 (oxide) having a composition different from that of the Li-transition metal oxide. The example shown in FIG. 3 corresponds to the case where the thickness of the oxide 13 (oxide) having a composition different from that of the Li-transition metal oxide is thicker than that of the example shown in FIG. 2.

[0044] "Solid electrolyte layer" The solid electrolyte layer 3 contains a solid electrolyte. The solid electrolyte is a substance capable of moving 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.

[0045] [[ID=ID=10]]The solid electrolyte layer 3 contains, for example, a solid electrolyte having a γ-Li3PO4-type crystal structure. The solid electrolyte having a γ-Li3PO4-type crystal structure has excellent ionic conductivity. The solid electrolyte is, for example, Li 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., and preferably Li 3+x [[ID=ID=36]]Si x P 1-x O4. x satisfies 0.4 ≤ x ≤ 0.8. The solid electrolyte may also be a ternary lithium oxide containing Si, V, Ge, etc.

[0046] "Negative electrode" FIG. 4 is an enlarged view of a part of the negative electrode 2 according to the first embodiment. 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.

[0047] 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 negative electrode current collector layer 2A is considered to be the area between the xy plane passing through the top and the xy plane passing through the bottom of the negative electrode current collector 21.

[0048] The negative electrode current collector 21 comprises a metal or alloy containing, for example, one selected from the group consisting of Ag, Pd, Au, and Pt. For example, AgPd alloy, Au, and Pt are preferred for the negative electrode current collector 21.

[0049] The negative electrode current collector 21 consists of, for example, a plurality of conductive particles. The plurality of conductive particles are connected to each other and electrically connected in the xy plane. The negative electrode current collector 21 is not limited to this example and may take the form of, for example, a foil, a punched film, or an expanded film that extends in the xy plane.

[0050] The negative electrode active material 22 is, for example, mixed together with the negative electrode current collector 21 in the negative electrode current collector layer 2A. 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, the transfer of electrons between the negative electrode active material 22 and the negative electrode current collector 21 becomes smoother. 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.

[0051] The negative electrode active material layer 2B is formed on one or both sides of the negative electrode current collector layer 2A. The negative electrode active material layer 2B contains negative electrode active material. The negative electrode active material layer 2B may also contain a conductive additive, a binder, and the solid electrolyte described above. When the negative electrode active material layer 2B contains a solid electrolyte, the area between the xy plane passing through the outermost part of the negative electrode active material and the interface with the negative electrode current collector layer 2A is considered to be the negative electrode active material layer 2B.

[0052] The negative electrode active material is a compound capable of intercalating and releasing ions. The negative electrode active material is a compound exhibiting a lower potential than the positive electrode active material. The same material as the positive electrode active material can be used as the negative electrode active material. The negative electrode active material and positive electrode active material used in the all-solid-state battery 10 are determined by considering the potentials of the negative electrode active material and the positive electrode active material. For example, the negative electrode active material is Li4Ti5O 12These are LiTiO2, Li2TiO3, and Li2TiSiO5.

[0053] The conductive additive improves the electronic conductivity of the negative electrode active material layer 2B. The conductive additive can be made from the same material as that used for the positive electrode active material layer 1B.

[0054] The binder joins the negative electrode current collector layer 2A to the negative electrode active material layer 2B, the negative electrode active material layer 2B to the solid electrolyte layer 3, and the various materials constituting the negative electrode active material layer 2B to each other. The binder can be the same material as that used for the positive electrode active material layer 1B. The binder content ratio can also be the same as that of the positive electrode active material layer 1B. If the binder is not needed, it does not need to be included.

[0055] Figure 4 shows an example where the negative electrode 2 consists of a negative electrode current collector layer 2A and a negative electrode active material layer 2B, but it is not limited to this case. For example, the negative electrode current collector layer 2A may consist only of the negative electrode current collector 21.

[0056] Figure 5 is an enlarged view of a part of another example of the negative electrode according to the first embodiment. The negative electrode 2C shown in Figure 5 has a negative electrode current collector 21 and a solid electrolyte 23. The negative electrode current collector 21 is, for example, a metal or alloy containing Ag. Ag also functions as an active material. When Ag functions as a negative electrode active material, the potential window of the all-solid-state battery is widened, and charge-discharge reactions occur between high potential (approximately 3.8V) and low potential (approximately 0V). As a result, the all-solid-state battery has a high capacity and an improved energy density.

[0057] "Manufacturing method for all-solid-state batteries" Next, the manufacturing method of the all-solid-state battery 10 will be described. First, the laminate 4 is manufactured. The laminate 4 is manufactured, for example, by a co-firing method or a sequential firing method.

[0058] The simultaneous firing method is a method of producing a laminate 4 by stacking the materials that form each layer and then firing them all at once. The sequential firing method is a method of firing each layer as it is formed. The simultaneous firing method can produce the laminate 4 with fewer steps than the sequential firing method. In addition, the laminate 4 produced by the simultaneous firing method is denser than the laminate 4 produced using the sequential firing method. The following explanation will use the simultaneous firing method as an example.

[0059] First, the materials constituting the laminate 4—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—are paste-formed. In the example shown in Figure 2, the positive electrode current collector 11 is coated with an oxide 13 having a different composition from the Li transition metal oxide before being paste-formed. In the example shown in Figure 3, the materials constituting the intermediate layer 1D are also paste-formed.

[0060] The method for forming a paste from each material is not particularly limited; for example, a method of mixing the powders of each material with a vehicle to obtain a paste can be used. Here, "vehicle" is a general term for the medium in the liquid phase. The vehicle includes solvents and binders.

[0061] 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 needed, and then peeling off the substrate. The method of applying the paste is not particularly limited, and known methods such as screen printing, coating, transfer, and doctor blade can be used.

[0062] Next, the green sheets prepared for each material are stacked in the desired order and number of layers to create a laminated sheet. When stacking the green sheets, alignment and cutting are performed as needed. For example, when creating a parallel or series-parallel battery, the green sheets are stacked after alignment 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.

[0063] The laminated sheet may be manufactured by fabricating a positive electrode unit and a negative electrode unit and then laminating these units. The positive electrode unit is a laminated 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 Figure 3, an intermediate layer 1D is laminated between the positive electrode current collector layer 1A and the positive electrode active material layer 1B. The negative electrode unit is a laminated 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 solid electrolyte layer 3 of the positive electrode unit and the negative electrode active material layer 2B of the negative electrode unit are laminated facing each other, or the positive electrode active material layer 1B of the positive electrode unit and the solid electrolyte layer 3 of the negative electrode unit are laminated facing each other.

[0064] Next, the fabricated laminated sheets are pressed together to improve the adhesion of each layer. Pressurization can be performed using, for example, a die press, hot water isostatic press (WIP), cold water isostatic press (CIP), or hydrostatic press. It is preferable to perform the pressurization while heating. The heating temperature during pressing should be, for example, 40 to 95°C. Then, the pressed laminate is cut into chips using a dicing device. Finally, the chips are subjected to a debinder treatment and firing to obtain a laminate 4 made of sintered material.

[0065] The debinding process can be carried out as a separate step from the firing process. Performing the debinding process allows the binder components contained in the chip to be thermally decomposed before the firing process, thereby suppressing the rapid decomposition of the binder components during the firing process. The debinding process can be carried out, for example, by heating at a temperature of 300 to 800°C for 0.1 to 10 hours in an atmospheric environment. The atmosphere during the debinding process is an oxygen partial pressure environment in which the materials constituting the positive electrode, negative electrode, and solid electrolyte do not oxidize or are unlikely to oxidize, and the type of gas can be arbitrarily selected so that the materials constituting the positive electrode, negative electrode, and solid electrolyte do not react with the atmospheric gas. For example, it may be carried out in a nitrogen atmosphere, argon atmosphere, nitrogen-hydrogen mixed atmosphere, water vapor atmosphere, or an atmosphere of a mixture thereof.

[0066] The firing process is carried out, for example, by placing the chip on a ceramic base. The firing is carried out, for example, by heating to 600-1000°C in an atmospheric environment. The atmosphere during the sintering process is an oxygen partial pressure environment in which the materials constituting the positive electrode, negative electrode, and solid electrolyte do not oxidize or are unlikely to oxidize, and the type of gas can be arbitrarily selected so that the materials constituting the positive electrode, negative electrode, and solid electrolyte do not react with the atmospheric gas. For example, it may be carried out in a nitrogen atmosphere, argon atmosphere, nitrogen-hydrogen mixed atmosphere, water vapor atmosphere, or an atmosphere of a mixture thereof.

[0067] Alternatively, the sintered laminate 4 (sintered body) may be placed in a cylindrical container with an abrasive such as alumina and barrel polished. This allows for chamfering of the corners of the laminate. Polishing may also be performed using sandblasting. Sandblasting is preferred because it allows for the removal of only specific parts.

[0068] Terminal electrodes 5 and 6 are formed on the opposing sides of the fabricated laminate 4. The terminal electrodes 5 and 6 can be formed using methods such as sputtering, dipping, screen printing, and spray coating, respectively. By going through the above steps, an all-solid-state battery 10 can be manufactured. If the terminal electrodes 5 and 6 are to be formed only in predetermined areas, the area is masked with tape or the like before the above process is performed.

[0069] The all-solid-state battery according to this embodiment exhibits excellent cycle characteristics. Although the reason for this is not clear, it is thought that the oxide 13, which has a different composition from the Li transition metal oxide, functions as a coating that prevents the oxidation of Ag during charging and discharging. Ag contained in the positive electrode is oxidized at a potential of 3.84V or higher. The energy used in the oxidation reaction of Ag means that energy is consumed in reactions other than the charging and discharging reactions of the all-solid-state battery, resulting in poor energy efficiency. By pre-forming the oxide 13, which has a different composition from the Li transition metal oxide, between the positive electrode current collector 11 and the positive electrode active material 12, the oxidation of Ag can be suppressed. As a result, the cycle characteristics of the all-solid-state battery are thought to be improved.

[0070] Although embodiments of the present invention have been described in detail above with reference to the drawings, the configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications to the configurations are possible without departing from the spirit of the present invention. [Examples]

[0071] "Example 1" (Preparation of positive electrode paste) First, Ag powder and Pd powder were prepared in a volume ratio of Ag powder:Pd powder = 80:20. Next, AgCoO2 powder, which is an oxide with a different composition from Li transition metal oxides, was prepared. Then, these powders were put into a mechanochemical reactor (manufactured by Hosokawa Micron Corporation, product name: Circulating Mechanofusion® System AMS). An AgCoO2 film was then formed on the surface of the AgPd powder by mechanochemical reaction. Then, this powder and LiCoO2, which is the positive electrode active material, were mixed in a volume ratio of 50:50 to produce a positive electrode current collector layer paste. Ethyl cellulose is the binder and dihydroterpineol is the solvent.

[0072] The positive electrode active material layer paste was prepared by adding ethylcellulose and dihydroterpineol to LiCoO2 and mixing them. LiCoO2 is the positive electrode active material.

[0073] (Preparation of solid electrolyte layer paste) Li2CO3, SiO2, and Li3PO4 were used as starting materials and mixed in a molar ratio of 2:1:1. The mixing was performed wet for 16 hours using a ball mill with water as the dispersion medium. The mixture was calcined at 950°C for 2 hours. 3.5 Si 0.5 P 0.5 O4 was produced. Then, 100 parts by mass of the calcined powder, 100 parts by mass of ethanol, and 200 parts by mass of toluene were added to a ball mill and wet-mixed. Next, 16 parts by mass of polyvinyl butyral binder and 4.8 parts by mass of benzyl butyl phthalate were added and mixed to prepare a solid electrolyte layer paste.

[0074] (Preparation of negative electrode paste) The negative electrode paste is made of Ag, Pd, and Li 3.5 Si 0.5 P 0.5 A powder was used, which was a mixture of O4 and Ag in a volume ratio of 40:10:50. Ethyl cellulose and dihydroterpineol were added to this powder and mixed. Ag functions as both a negative electrode current collector and a negative electrode active material. The function of Ag as a negative electrode active material results in an output voltage of nearly 3.8V for the all-solid-state battery.

[0075] (Fabrication of all-solid-state batteries) Next, the positive electrode unit and negative electrode unit were fabricated using the following procedure. First, a positive electrode active material layer paste was printed on the solid electrolyte layer sheet using screen printing to a thickness of 5 μm. 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 on the dried positive electrode active material layer paste using screen printing to a thickness of 5 μm. 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 on the dried positive electrode current collector layer paste using screen printing to a thickness of 5 μm, and dried. After that, the PET film was peeled off. In this way, a positive electrode unit was obtained in which the 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] Next, a negative electrode paste was printed to a thickness of 10 μm onto the main surface of the solid electrolyte layer. Then, the printed negative electrode paste was dried at 80°C for 5 minutes. A negative electrode unit was fabricated using this procedure.

[0077] Next, a solid electrolyte unit was fabricated by stacking five solid electrolyte layer sheets. The laminate was made by alternately stacking 50 electrode units (25 positive electrode units and 25 negative electrode units) with the solid electrolyte unit in between. At this time, the units were stacked with a staggered arrangement so that the odd-numbered electrode units extended only on one end face, and the even-numbered electrode units extended only on the opposite end face. Six solid electrolyte layer sheets were then stacked on top of this stacked unit. After that, this was formed by thermocompression bonding and then cut to produce laminated chips. Subsequently, the laminated chips were co-fired to obtain a laminate. Co-fired firing was performed in an atmospheric environment by raising the temperature to 800°C at a heating rate of 200°C / hour, holding it at that temperature for 2 hours, and then allowing it to cool naturally.

[0078] A solid-state battery was fabricated by attaching terminal electrodes 5 and 6 to a sintered laminate (sintered body) using a known method. The cross-section of the fabricated solid-state battery was examined with a scanning electron microscope, and the film thickness of the oxide having a different composition from the Li transition metal oxide was measured. The film thickness of the oxide having a different composition from the Li transition metal oxide in Example 1 was 0.01 μm. Furthermore, the volume ratio of each layer did not change between the paste state before sintering and the state after sintering. Ag exists as elemental Ag and as a constituent element of AgPd alloys.

[0079] The cycle characteristics of the all-solid-state battery fabricated under the same conditions were then measured. The cycle characteristics were measured by clamping the first and second external terminals with a spring probe and repeating charge-discharge tests at a temperature of 60°C. The measurement conditions were a current of 100 μA during both charging and discharging, and termination voltages of 3.9 V and 0 V during charging and discharging, respectively. The capacity at the 10th discharge, when the discharge capacity stabilized, was defined as the initial discharge capacity. The cycle characteristics were calculated by dividing the discharge capacity at the 500th cycle by the discharge capacity at the 10th cycle.

[0080] Examples 2-5 Examples 2-5 differ from Example 1 in that the film thickness of the oxide having a different composition from the Li transition metal oxide was varied. The film thickness of the oxide having a different composition from the Li transition metal oxide was controlled by increasing the amount of AgCoO2 added during the mechanochemical reaction. The film thickness of the oxide with a different composition from the Li transition metal oxide in Example 2 was 0.1 μm. The film thickness of the oxide with a different composition from the Li transition metal oxide in Example 3 was 0.5 μm. The film thickness of the oxide with a different composition from the Li transition metal oxide in Example 4 was 1.0 μm. The film thickness of the oxide with a different composition from the Li transition metal oxide in Example 5 was 2.0 μm. The cycle characteristics were determined under the same conditions as in Example 1.

[0081] "Example 6" Example 6 differs from Example 1 in that the positive electrode active material in the positive electrode current collector layer paste and the positive electrode active material layer paste is changed from LiCoO2 to LiMn2O4. The cycle characteristics were determined under the same conditions as in Example 1.

[0082] Example 7 Example 7 differs from Example 1 in that the positive electrode active material in the positive electrode current collector layer paste and positive electrode active material layer paste is changed from LiCoO2 to LiMn2O4, and AgCoO2, which is an oxide with a different composition from Li transition metal oxides, is changed to AgMn2O4. The cycle characteristics were determined under the same conditions as in Example 1.

[0083] "Example 8" Example 8 differs from Example 1 in that AgCoO2, which has a different composition from the Li transition metal oxide, is replaced with AgMn2O4. The cycle characteristics were determined under the same conditions as in Example 1.

[0084] "Example 9" to "Example 10" Example 9 differs from Example 1 in that the film thickness of the oxide having a different composition from the Li transition metal oxide was varied. The film thickness of the oxide having a different composition from the Li transition metal oxide was controlled by increasing the amount of AgCoO2 added during the mechanochemical reaction. The film thickness of the oxide with a different composition from the Li transition metal oxide in Example 9 was 0.009 μm. The film thickness of the oxide with a different composition from the Li transition metal oxide in Example 10 was 2.1 μm.

[0085] "Example 11" to "Example 14" Example 11 differs from Example 1 in that the contact rate between the positive electrode active material and the positive electrode current collector was changed. The contact rate between the positive electrode active material and the positive electrode current collector was adjusted by changing the time during the mechanochemical reaction. Specifically, by shortening the time during the mechanochemical reaction, the amount of AgCoO2 film formed by contact with the surface of the AgPd powder was reduced, thereby increasing the contact rate between the positive electrode active material and the positive electrode current collector that was not coated with the AgCoO2 film. Conversely, by lengthening the time during the mechanochemical reaction, the amount of AgCoO2 film formed by contact with the surface of the AgPd powder was increased, thereby decreasing the contact rate between the positive electrode active material and the positive electrode current collector that was not coated with the AgCoO2 film. The film thickness of the oxide with a different composition from the Li transition metal oxide in Example 9 was 0.009 μm. The film thickness of the oxide with a different composition from the Li transition metal oxide in Example 10 was 2.1 μm.

[0086] Examples 15 to 18 Example 15 differs from Example 1 in that the positive electrode current collector was changed from AgPd to Ag. Examples 16-18 differ from Example 15 in that the film thickness of the oxide having a different composition from the Li transition metal oxide was changed. The film thickness of the oxide having a different composition from the Li transition metal oxide was controlled by increasing the amount of AgCoO2 added during the mechanochemical reaction. In Example 15, the film thickness of the oxide with a different composition from the Li transition metal oxide was 0.01 μm. In Example 16, the film thickness of the oxide with a different composition from the Li transition metal oxide was 0.1 μm. In Example 17, the film thickness of the oxide with a different composition from the Li transition metal oxide was 0.5 μm. In Example 18, the film thickness of the oxide with a different composition from the Li transition metal oxide was 1.0 μm. The cycle characteristics were determined under the same conditions as in Example 1.

[0087] "Comparative Example 1" Comparative Example 1 differs from Example 1 in that it does not form an oxide with a different composition from the Li transition metal oxide, and the positive electrode active material contained in the positive electrode current collector layer paste and positive electrode active material layer paste is changed from LiCoO2 to LiMn2O4. The cycle characteristics were determined under the same conditions as in Example 1.

[0088] "Comparative Example 2" Comparative Example 2 differs from Example 1 in that it did not form an oxide with a different composition from the Li transition metal oxide. The cycle characteristics were determined under the same conditions as in Example 1.

[0089] "Comparative Example 3" Comparative Example 3 differs from Example 15 in that it did not form an oxide with a different composition from the Li transition metal oxide. The cycle characteristics were determined under the same conditions as in Example 15.

[0090] The results of Examples 1-18 and Comparative Examples 1-3 are summarized in Table 1 below.

[0091] [Table 1]

[0092] Examples 1-18 exhibited superior cycle characteristics compared to Comparative Examples 1-3. This is thought to be because the oxide (oxide) having a different composition from the Li transition metal oxide suppressed the oxidation of Ag during charging and discharging. [Industrial applicability]

[0093] This can improve the cycle characteristics of all-solid-state batteries compared to conventional methods. [Explanation of Symbols]

[0094] 1 positive electrode 1A, 1C Positive electrode current collector layer (first layer) 1B Cathode active material layer (2nd layer) 1D middle layer 2, 2C negative electrode 2A negative electrode current collector layer 2B Negative electrode active material layer 3 Solid electrolyte layer 4 Laminate 5, 6 terminal electrode 10 All-solid-state battery 11. Positive electrode current collector (compound containing Ag) 21 Negative electrode current collector 12 Cathode active material (Li transition metal oxide) 13. Oxides (oxides) having a different composition from Li transition metal oxides 22 Negative electrode active material 23 Solid electrolyte

Claims

1. The sintered body comprises a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode. The positive electrode comprises a compound containing Ag, a Li-containing transition metal oxide, and an oxide having a different composition from the Li-containing transition metal oxide. The aforementioned oxide includes Ag, An all-solid-state battery in which at least a portion of the Ag-containing compound and the Li-containing transition metal oxide are present inside the positive electrode via the oxide.

2. The all-solid-state battery according to claim 1, wherein the oxide includes a transition metal element constituting the Li-containing transition metal oxide.

3. The all-solid-state battery according to claim 1, wherein the minimum thickness of the oxide, which is mediated by at least a portion of the Ag-containing compound and the Li-containing transition metal oxide, is 0.01 μm or more and 2.0 μm or less.

4. The all-solid-state battery according to claim 1, wherein the compound containing Ag is selected from Ag or Ag / Pd.

5. The positive electrode comprises a first layer and a second layer on at least one main surface of the first layer. The all-solid-state battery according to claim 1, wherein the first layer comprises the Ag-containing compound, the Li-containing transition metal oxide, and the oxide.

6. The all-solid-state battery according to claim 5, wherein the second layer contains the Li-containing transition metal oxide.

7. The all-solid-state battery according to claim 5, wherein the first layer and the second layer each contain the Li-containing transition metal oxide having the same composition.

8. The all-solid-state battery according to claim 1, wherein the positive electrode contains lithium cobalt oxide.

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