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: a layer containing metallic Ag or a Li-Ag alloy; and a compound expressed by the formula LiαTi5O12 (4≤α≤7).

Description

[Technical Field]

[0001] This invention relates to an all-solid-state battery. This application claims priority based on Japanese Patent Application No. 2022-029207, filed in Japan on February 28, 2022, the contents of which 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 materials that can be used and therefore different performance characteristics due to the 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] To make all-solid-state batteries smaller and lighter, it is necessary to increase their energy density.

[0007] This 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] To solve the above problems, the following means are provided.

[0009] (1) The all-solid-state battery according to the first embodiment comprises 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 contains a solid electrolyte having a γ-Li3PO4 type crystal structure. The negative electrode has a layer containing a metal made of Ag or a Li-Ag alloy, and Li α Ti5O 12 It contains a compound represented by (4 ≤ α ≤ 7).

[0010] (2) In the all-solid-state battery according to the above embodiment, the negative electrode comprises a first layer and a second layer, the first layer is a layer containing a metal made of Ag or a Li-Ag alloy, the second layer is in contact with at least one main surface of the first layer, and the second layer is Li α Ti5O 12 The compound may be represented by (4 ≤ α ≤ 7).

[0011] (3) In the all-solid-state battery according to the above embodiment, the average thickness of the second layer may be 1 μm or more and 4 μm or less.

[0012] (4) In the all-solid-state battery according to the above embodiment, the first layer may have a layer containing a Li-Ag alloy.

[0013] (5) In the all-solid-state battery according to the above embodiment, the first layer is Li α Ti5O 12 The compound may also be represented by (4 ≤ α ≤ 7).

[0014] (6) In the all-solid-state battery according to the above embodiment, the total volume ratio of the metal made of Ag and the Li-Ag alloy in the first layer may be 45% or more and 90% or less.

[0015] (7) In the all-solid-state battery according to the above aspect, the solid electrolyte is Li 3+x Si x P 1-x It may contain O4 (0.2 ≤ x ≤ 0.6).

[0016] (8) In the all-solid-state battery according to the above aspect, the positive electrode may contain lithium cobaltate.

[0017] (9) 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 contacting at least one main surface of the third layer.

Advantages of the Invention

[0018] The all-solid-state battery according to the above aspect has a high energy density.

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 characteristic part of the all-solid-state battery according to the first embodiment. [Figure 3] It is an enlarged cross-sectional view of a characteristic part of another example of the all-solid-state battery according to the first embodiment. [Figure 4] It is an enlarged cross-sectional view of a characteristic part of the positive electrode of another example of the all-solid-state battery according to the first embodiment. [Figure 5] [[ID=IP=43]]It is an enlarged cross-sectional view of a characteristic part of the positive electrode of another example of the all-solid-state battery according to the first embodiment.

Modes for Carrying Out the Invention

[0020] The present embodiment will be described in detail below with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience to clearly illustrate the features of the present invention, and the dimensional ratios of each component may differ from those in reality. The materials, dimensions, etc., exemplified in the following description are examples only, and the present invention is not limited to them. It can be implemented with appropriate modifications without altering its essence.

[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. The all-solid-state battery 10 shown in Figure 1 is a stacked type battery, but the all-solid-state battery 10 may also be a wound type battery. The all-solid-state battery 10 is used in laminate 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 characteristic part 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 a third layer. The positive electrode active material layer 1B is an example of a fourth layer.

[0026] [Positive electrode current collector layer] The positive electrode current collector layer 1A includes, for example, a positive electrode current collector 11 and a positive electrode active material 12. In this case, the area between the xy plane passing through the top and the xy plane passing through the bottom of the positive electrode current collector 11 is considered to be the positive electrode current collector layer 1A.

[0027] The positive electrode current collector 11 comprises a metal or alloy containing, for example, one selected from the group consisting of Ag, Pd, Au, and Pt. The positive electrode current collector 11 is, for example, an Ag-AgPd alloy. The positive electrode current collector 11 may be the same as or different from the negative electrode current collector 21, which will be described later.

[0028] The positive electrode current collector 11 consists of, for example, multiple current collector particles. The multiple current collector particles are connected to each other and electrically connected in the xy plane.

[0029] The positive electrode active material 12 is mixed together with the positive electrode current collector 11 in the positive electrode current collector layer 1A. 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, the transfer of electrons between the positive electrode active material 12 and the positive electrode current collector 11 becomes smoother. The positive electrode active material 12 contains a transition metal oxide that includes one or more 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. Lithium cobalt oxide is Li x Lithium manganese is denoted as CoO2, and Li x It is represented as Mn2O4. x is between 0.4 and 1.2, and the value of x fluctuates within this range during charging and discharging. The chemical formulas used herein do not necessarily have to be stoichiometric compositions, and a deviation of about 10% is acceptable.

[0030] Figure 2 shows an example in which the positive electrode current collector 11 consists of multiple current collector particles, but is not limited to this case. Figure 3 is an enlarged view of a characteristic part of another example of an all-solid-state battery according to the first embodiment. The positive electrode current collector layer 1C shown in Figure 3 consists of foil-like positive electrode current collectors 11 that spread in the xy plane. The positive electrode current collectors 11 may also be in the form of a punched film or an expanded film that spreads in the xy plane. The positive electrode current collector layer 1C may consist of positive electrode current collectors 11.

[0031] [Cathode active material layer] The positive electrode active material layer 1B 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 xy plane passing through the outermost part 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.

[0032] (Cathode active material) The positive electrode active material comprises 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 cobaltate, lithium manganeseate, and preferably lithium cobaltate. Lithium cobaltate is Li x Lithium manganese is denoted as CoO2, and Li x It is represented as Mn2O4. x is between 0.4 and 1.2, and the value of x fluctuates within this range during charging and discharging.

[0033] (Conductive additive) 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 powder or fibrous form.

[0034] (Binding agent) 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.

[0035] 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 volume% to 30 volume% 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% is approximately equal to the area% of the cross-section measured by a scanning electron microscope, for example. Therefore, the area ratio of the cross-section measured by a scanning electron microscope can be directly considered as the volume ratio.

[0036] 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, the binder also functions as a conductive additive, so it is not necessary to add a conductive additive. Examples of ionic conductive polymers with ionic conductivity include those that conduct lithium ions, such as monomers of polymer compounds (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide, polyphosphozenes, etc.) and lithium salts such as LiClO4, LiBF4, 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.

[0037] Up to this point, we have shown specific examples of positive electrodes, but the positive electrode is not limited to these examples. For example, the positive electrode 1 may be a single layer in which the positive electrode current collector 11 and the positive electrode active material 12 are mixed. Also, for example, Figures 4 and 5 are cross-sectional views of another example of a positive electrode according to the first embodiment.

[0038] The positive electrode shown in Figure 4 has a positive electrode current collector layer 1D and a positive electrode active material layer 1B. The positive electrode current collector layer 1D has 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 contains, for example, 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 the 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.

[0039] The positive electrode shown in Figure 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 consists of the oxide 13. The example shown in Figure 5 corresponds to the case where the thickness of the oxide 13 is thicker than the example shown in Figure 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.

[0040] "Solid electrolyte layer" The solid electrolyte layer 3 contains a solid electrolyte. The solid electrolyte is a material that can move ions by an externally applied electric field. For example, the solid electrolyte layer 3 conducts lithium ions and inhibits electron movement. The solid electrolyte layer 3 is, for example, a sintered body obtained by sintering.

[0041] The solid electrolyte layer 3 includes, for example, a solid electrolyte having a γ-Li3PO4 type crystal structure. Solid electrolytes having a γ-Li3PO4 type crystal structure have 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-xO4, Li 3+x Ge x P 1-x O4, Li 3+x Ge x V 1-x O4, preferably Li 3+x Si x P 1-x The electrolyte is O4. x satisfies 0.4 ≤ x ≤ 0.8, preferably 0.2 ≤ x ≤ 0.6. The solid electrolyte may also be a ternary lithium oxide containing Si, V, and Ge, etc.

[0042] "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 negative electrode active material (see Figure 2). 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 in contact with at least one main surface of the first layer. The negative electrode 2 has a layer containing a metal made of Ag or a Li-Ag alloy, and Li α Ti5O 12 It has a compound represented by (4≦α≦7).

[0043] [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 negative electrode current collector layer 2A is considered to be the space between the xy plane passing through the top and the xy plane passing through the bottom of the negative electrode current collector 21. The negative electrode current collector layer 2A is a layer containing a metal made of Ag.

[0044] The negative electrode current collector 21 includes, for example, a metal composed of Ag (elemental silver) or a Li-Ag alloy. A Li-Ag alloy is an alloy formed by the combination of Li and Ag, and the composition ratio of Li and Ag is not specified. The negative electrode current collector 21 may contain both a metal composed of Ag and a Li-Ag alloy. If the negative electrode current collector 21 contains Ag or a Li-Ag alloy, the negative electrode active material 22 contains Li α Ti5O 12 Even in this case, Ag also exhibits its function as an active material.

[0045] The total volume ratio (Va) of Ag and Li-Ag alloy in the negative electrode current collector layer 2A is, for example, between 45% and 90%. The volume ratio is determined from images obtained using a scanning electron microscope, as described above.

[0046] As shown in Figure 3, the negative electrode current collector layer 2C may consist 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 it may be in the form of punching or expanding.

[0047] 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 within the negative electrode current collector layer 2A 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 described later, for example Li α Ti5O 12 It includes compounds represented by (4 ≤ α ≤ 7).

[0048] [Negative electrode active material layer] The negative electrode active material layer 2B is in contact with at least one main surface of the negative electrode current collector layer 2A. 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. If the negative electrode active material layer 2B contains a solid electrolyte, the xy plane passing through the outermost part 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.

[0049] The average thickness of the negative electrode active material layer 2B is, for example, 4 μm or less, preferably 1 μm to 4 μm. The average thickness of the negative electrode active material layer 2B is determined from scanning electron microscope images. For example, the distance of the perpendicular line drawn between the xy plane passing through the outermost part of the negative electrode current collector 21 and the xy plane passing through the outermost part of the negative electrode active material 22 is measured in any 10 images, and the average of these distances is considered to be the average thickness of the negative electrode active material layer 2B. If the average thickness of the negative electrode active material layer 2B is thin, the physical distance between the negative electrode current collector 21 and the solid electrolyte becomes shorter, and lithium ions are conducted to the vicinity of the negative electrode current collector 21. As a result, the Ag used in the negative electrode current collector 21 functions as an active material, and the output voltage of the all-solid-state battery increases.

[0050] (Negative electrode active material) 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 negative electrode active material is Li xα Ti5O 12 Therefore, α satisfies the condition of being between 4 and 7, and the value of α fluctuates within this range during charging and discharging. The negative electrode active material is, for example, Li4Ti5O in the basic uncharged state. 12 It is represented as such, and the composition ratio of Li changes with charging and discharging.

[0051] (Conductive additive) 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.

[0052] (Binding agent) 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.

[0053] Figure 2 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 2 may be a single layer in which the negative electrode current collector 21 and the negative electrode active material 22 are mixed.

[0054] "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.

[0055] 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.

[0056] 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 made into a paste. In the example shown in Figure 4, the positive electrode current collector 11 is coated with oxide 13 before being made into a paste. In the example shown in Figure 5, the materials constituting the intermediate layer 1F are also made into a paste.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] The laminated sheet may be manufactured by creating 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 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 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.

[0061] 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°C to 95°C. Then, the pressed laminate is cut using a dicing device to form chips. Finally, the chips are subjected to a debinder treatment and firing to obtain a laminate 4 made of sintered material.

[0062] The debinding process can be carried out as a separate process 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 in an atmospheric environment at a temperature of 300°C to 800°C for 0.1 hours to 10 hours. 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 a mixture thereof.

[0063] The firing process is carried out, for example, by placing the chips on a ceramic base. The firing is carried out, for example, by heating to a temperature of 600°C to 1000°C in an atmospheric environment. The firing time is, for example, 0.1 hours to 3 hours. 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.

[0064] 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.

[0065] Terminal electrodes 5 and 6 are formed on opposite sides of the fabricated laminate 4, respectively. The terminal electrodes 5 and 6 can be formed using methods such as sputtering, dipping, screen printing, and spray coating. 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.

[0066] The all-solid-state battery according to this embodiment has a high energy density. This is because the Ag or Li-Ag alloy of the negative electrode 2 also functions as the negative electrode active material, so the potential of the negative electrode 2 is approximately 0V (vs Li + This is thought to be because the potential is approximately 0V at negative electrode 2 and approximately 3.6V (vs Li + Positive electrode 1 (Li) x CoO2 and Li x The all-solid-state battery 10 is driven by the potential difference between it and Mn2O4, which increases the output voltage of the all-solid-state battery. The energy amount of the all-solid-state battery 10 can be determined by the product of the output voltage of the all-solid-state battery 10 and the capacity of the all-solid-state battery. The energy density of the all-solid-state battery 10 can be compared in terms of energy amount 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.

[0067] Here, the energy density of the all-solid-state battery 10 is such that the negative electrode current collector is Ag or Li-Ag alloy, and the negative electrode active material is Li α Ti5O 12 The value increases in this case. The principle is not clear, but for example, if the negative electrode current collector is AgPd and the negative electrode active material is Li α Ti5O 12 In this case, the AgPd in ​​the negative electrode current collector does not function as an active material, and the output voltage of the all-solid-state battery 10 decreases.

[0068] 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]

[0069] "Example 1" (Preparation of positive electrode paste) For the preparation of the positive electrode current collector layer paste, a powder mixture of Ag and LiMn2O4 in a volume ratio of 80:20 was used. Ethyl cellulose and dihydroterpineol were added to this powder and mixed. Ethyl cellulose acted as a binder, and dihydroterpineol acted as a solvent.

[0070] The positive electrode active material layer paste was prepared by mixing LiMn2O4 with ethylcellulose and dihydroterpineol. LiMn2O4 is the positive electrode active material.

[0071] (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 prepared. Then, 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. Then, 16 parts by mass of polyvinyl butyral binder and 4.8 parts by mass of benzyl butyl phthalate were further added and mixed to prepare a solid electrolyte layer paste.

[0072] (Preparation of negative electrode paste) The negative electrode current collector layer paste is made using Ag and Li4Ti5O 12 (=Li 4 / 3 Ti 5 / 3 A powder was used, which was a mixture of O4 and another substance in a volume ratio of 80:20. Ethyl cellulose and dihydroterpineol were added to this powder and mixed to prepare a negative electrode current collector layer paste. 4 / 3 Ti 5 / 3 O4 is the negative electrode active material.

[0073] The negative electrode active material layer paste is Li 4 / 3 Ti 5 / 3It was prepared by adding ethylcellulose and dihydroterpineol to O4 and mixing them.

[0074] (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.

[0075] Furthermore, using a similar procedure, a negative electrode unit was obtained in which a negative electrode active material layer / negative electrode current collector layer / negative electrode active material layer was stacked in this order on the main surface of the solid electrolyte layer.

[0076] 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 such that the current collector layer of the odd-numbered electrode units extended only to one end face, and the current collector layer of the even-numbered electrode units extended only to the opposite end face. Six solid electrolyte layer sheets were then stacked on top of these stacked units. 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.

[0077] A solid-state battery was fabricated by attaching terminal electrodes 5 and 6 to a sintered laminate (sintered body) using a known method. The volume ratio of each layer remained unchanged between the paste state before sintering and the state after sintering.

[0078] The fabricated all-solid-state battery was then cut along the stacking direction, and cross-sectional observation was performed 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 volume ratio (Va) of Ag 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 Li-Ag alloy in the cross-section observed with the scanning electron microscope. The distinction between Ag and Li-Ag alloy and other materials can be identified from the contrast of the images.

[0079] Next, the output voltage and capacity of the all-solid-state battery fabricated under the same conditions were measured. The capacity was the discharge capacity. One cycle consisted of constant current charging (CC charging) at a constant current of 100 μA until the battery voltage reached 3.9 V in a 60°C environment, followed by discharge (CC discharge) at a constant current of 100 μA until the battery voltage reached 0 V. This process was repeated 10 times, and the discharge capacity (μAh) after 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. 12 We confirmed that the Li composition ratio fluctuates between 4 and 7 depending on the charge and discharge cycle.

[0080] Examples 2-4 Examples 2-4 differ from Example 1 in that the thickness of the negative electrode active material layer was varied. The thickness of the negative electrode active material layer was adjusted by the thickness of the paste used when fabricating the negative electrode active material layer. The thickness of the negative electrode active material layer was 4 μm for Example 2, 3 μm for Example 3, and 1 μm for Example 4. The energy amount of the all-solid-state battery was determined under the same conditions as in Example 1.

[0081] Example 5 Example 5 differs from Example 4 in that the positive electrode active material was changed from LiMn2O4 to LiCoO2. Other conditions were the same as in Example 4, and the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0082] Examples 6-9 Examples 6-9 use Li as the solid electrolyte. 3.5 Si 0.5 P 0.5 O4 to Li 3.5 Si 0.5 V 0.5 The difference from each of Examples 1 to 4 is that O4 was used instead. 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 10-12 Examples 10 to 12 differ from Example 1 in that the configuration of the positive electrode current collector layer is changed. In Example 10, when preparing the positive electrode current collector layer paste, a powder was used which consisted of Ag, Pd, and LiMn2O4 mixed in a volume ratio of 64:16:20. In Example 11, a powder was used in which Au and LiMn2O4 were mixed in a volume ratio of 80:20 when preparing the positive electrode current collector layer paste. In Example 10, a powder was used in which Pt and LiMn2O4 were mixed in a volume ratio of 80:20 when preparing the positive electrode current collector layer paste. Other conditions were determined in the same manner as in Example 1, to find the thickness of the negative electrode active material layer and the energy content of the all-solid-state battery.

[0084] Examples 13-16 Examples 13-16 differ from Example 4 in that the mixing ratio of Li2CO3, SiO2, and Li3PO4 was changed during the preparation of the solid electrolyte layer paste. Examples 13-16 also differ from Example 1 in the composition ratio of the solid electrolyte layer. Under the same conditions as in Example 4, 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" Comparative Example 1 involves the use of Ag, Pd, and Li in the preparation of the positive electrode current collector layer paste and the negative electrode current collector layer paste. 4 / 3 Ti 5 / 3 This example differs from Example 1 in that it uses a powder mixed with O4 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 of the all-solid-state battery were determined. In the completed negative electrode current collector layer, Ag and Pd formed an AgPd alloy.

[0086] "Comparative Example 2" Comparative Example 2 differs from Example 1 in that a powder mixture of Ag, Pd, and LiMn2O4 in a volume ratio of 64:16:20 was used to prepare the positive electrode current collector layer paste and the negative electrode current collector layer paste, and LiMn2O4 was used for the negative electrode active material layer. 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. In the completed negative electrode current collector layer, Ag and Pd formed an AgPd alloy.

[0087] The results of Examples 1-16 and Comparative Examples 1 and 2 are summarized in Table 1 below.

[0088] [Table 1]

[0089] [Table 2]

[0090] Examples 1-16, in which the negative electrode current collector was Ag, showed a higher output voltage compared to Comparative Example 1, in which the negative electrode current collector was an AgPd alloy. This is thought to be because in Examples 1-16, the Ag constituting the negative electrode current collector also functioned as the negative electrode active material, whereas in Comparative Example 1, the Ag constituting the negative electrode current collector did not exhibit this function. Furthermore, comparing Examples 1 and 13-16, the amount of energy also changed depending on the composition of the solid electrolyte.

[0091] Next, in Examples 17 to 27, Comparative Example 3, and Comparative Example 4, the parameters of each layer were changed based on Example 5, in which the positive electrode active material was LiCoO2.

[0092] Examples 17-19 Examples 17-19 differ from Example 5 in that the thickness of the negative electrode active material layer was varied. The thickness of the negative electrode active material layer was adjusted by the thickness of the paste used when fabricating the negative electrode active material layer. The thickness of the negative electrode active material layer was 3 μm for Example 17, 4 μm for Example 18, and 6 μm for Example 19. The energy amount of the all-solid-state battery was determined under the same conditions as in Example 1.

[0093] Examples 20-23 Examples 20-23 show Ag and Li4Ti5O in the negative electrode current collector layer. 12 (=Li 4 / 3 Ti 5 / 3 The difference from Example 5 is that the volume ratio with O4 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] Example 20 involves Ag and Li4Ti5O 12 (=Li 4 / 3 Ti 5 / 3 The volume ratio with O4 is Ag:Li4Ti5O 12 The ratio was set to 45:55. Example 21 involves Ag and Li4Ti5O 12 (=Li 4 / 3 Ti 5 / 3 The volume ratio with O4 is Ag:Li4Ti5O 12 The ratio was set to 50:50. Example 22 involves Ag and Li4Ti5O 12 (=Li 4 / 3 Ti 5 / 3 The volume ratio with O4 is Ag:Li4Ti5O 12 The ratio was set to 90:10. Example 23 is Ag and Li4Ti5O 12 (=Li 4 / 3 Ti 5 / 3 The volume ratio with O4 is Ag:Li4Ti5O 12= 100:0. That is, in Example 23, Li4Ti5O was not added when preparing the negative electrode current collector layer paste. 12 was not added.

[0095] "Example 24" In Example 24, the negative electrode paste was prepared as a single layer instead of laminating a separately prepared negative electrode current collector paste and a negative electrode active material layer paste. The negative electrode paste was prepared by mixing a powder obtained by mixing Ag and Li4Ti5O 12 (= Li 4 / 3 Ti 5 / 3 O4) in a volume ratio of 80:20, and adding ethyl cellulose and dihydroterpineol and mixing them. Then, the negative electrode unit in the production of the all-solid-state battery was formed as a single layer composed of the negative electrode paste on one side of the solid electrolyte layer. Under the same conditions as in Example 1, the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0096] "Examples 25 to 27" In Examples 25 to 27, the difference from Examples 5, 17, and 18 respectively is that the solid electrolyte was changed from Li 3.5 Si 0.5 P 0.5 O4 to Li 3.5 Si 0.5 V 0.5 O4. Under the same conditions as in Example 1, the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0097] "Comparative Example 3" The difference between Comparative Example 3 and Comparative Example 1 is that the positive electrode active material was changed from LiMn2O4 to LiCoO2. Under the same conditions as in Example 1, the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0098] "Comparative Example 4" The difference between Comparative Example 4 and Comparative Example 2 is that the positive electrode active material was changed from LiMn2O4 to LiCoO2. Under the same conditions as in Example 1, the thickness of the negative electrode active material layer and the energy amount of the all-solid-state battery were determined.

[0099]

Table 3

[0100]

Table 4

[0101] Next, in Examples 28 to 33, Li-Ag alloy was added to the negative electrode current collector layer, and the same examination was conducted. However, the handling of the Li-Ag alloy was carried out in a glove box with a dew point of -50°C, and the co-firing was carried out by heating up to a firing temperature of 800°C at a heating rate of 1200°C / hour in an argon atmosphere, holding at that temperature for 20 minutes, and then naturally cooling after firing.

[0102] 「Example 28」 Example 28 is different from Example 5 in that part of Ag was changed to Li-Ag alloy (Li 3.1 Ag) when manufacturing the negative electrode current collector layer. The amount of Li in the Li-Ag alloy was determined by quantitative analysis of X-ray diffraction (XRD). Under the same conditions as in Example 1, the energy amount of the all-solid-state battery was determined.

[0103] 「Examples 29 and 30」 Examples 29 and 30 are different from Example 28 in that the thickness of the negative electrode active material layer was changed. Also, each of Examples 29 and 30 is different from Examples 17 and 18 respectively in that part of Ag was changed to Li-Ag alloy (Li 3.1 Ag) when manufacturing the negative electrode current collector layer. The thickness of the negative electrode active material layer was 3 μm in Example 29 and 4 μm in Example 30. In Examples 28 to 30, the negative electrode active material layer was manufactured with Ag, Li-Ag alloy (Li 3.1 Ag), and Li 4 / 3 Ti 5 / 3 O4 in a volume ratio of 5:75:20. Under the same conditions as in Example 1, the energy amount of the all-solid-state battery was determined.

[0104] 「Examples 31 to 33」 Examples 31 to 33 are the Li-Ag alloy (Li 3.1Ag) to Li-Ag alloy (Li 4.7 The difference from each of Examples 28-30 is that Ag was changed to Li-Ag alloy (Li 4.7 Ag) and Li 4 / 3 Ti 5 / 3 A negative electrode active material layer was prepared using O4 and a volume ratio of 3:77:20. The energy content of the all-solid-state battery was determined under the same conditions as in Example 1.

[0105] [Table 5] [Explanation of Symbols]

[0106] 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. The sintered body comprises a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode. The solid electrolyte layer is γ-Li ３ PO ４ It contains a solid electrolyte having a crystal structure of the type, The negative electrode comprises a layer containing a metal or Li-Ag alloy made of Ag, and Li α Ti ５ O １２ An all-solid-state battery comprising a compound represented by (4 ≤ α ≤ 7).

2. The all-solid-state battery according to claim 1, wherein the negative electrode comprises a layer containing a Li-Ag alloy and a compound represented by Li α Ti 5 O 12 (4 ≤ α ≤ 7).

3. The all-solid-state battery according to claim 1, wherein the negative electrode does not contain a LiPd alloy.

4. The negative electrode comprises a first layer and a second layer, The first layer is a layer containing a metal or Li-Ag alloy made of Ag, The second layer is in contact with at least one main surface of the first layer, The second layer is Li α Ti ５ O １２ The all-solid-state battery according to claim 1, comprising a compound represented by (4 ≤ α ≤ 7).

5. The all-solid-state battery according to claim 4, wherein the average thickness of the second layer is 1 μm or more and 4 μm or less.

6. The all-solid-state battery according to claim 4, wherein the first layer has a layer containing a Li-Ag alloy.

7. The first layer is Li α Ti ５ O １２ The all-solid-state battery according to claim 4, comprising a compound represented by (4 ≤ α ≤ 7).

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

9. The solid electrolyte is Li ３＋ｘ Si ｘ P １－ｘ O ４ The all-solid-state battery according to claim 1, including (0.2 ≤ x ≤ 0.6).

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

11. 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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