All-solid-state batteries

Abstract

To provide an all-solid battery with a low internal resistance.SOLUTION: An all-solid battery comprises a sintered body having a positive electrode, a negative electrode, and a solid electrolyte layer between the positive and negative electrodes. The positive electrode contains LiCoO2. The solid electrolyte layer contains Li3+xSixP1-xO4 (0.4≤x≤0.8).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an all-solid-state battery. [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. Due to differences in manufacturing methods, each type of solid-state battery has different applicable materials and performance characteristics.

[0004] For example, Patent Document 1 discloses a sintered all-solid-state battery using an oxide-based solid electrolyte. The all-solid-state battery described in Patent Document 1 presents several materials applicable to the positive electrode active material layer and the solid electrolyte layer. [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] Some of the all-solid-state batteries described in Patent Document 1 had high internal resistance.

[0007] This invention has been made in view of the above problems, and aims to provide an all-solid-state battery with low internal resistance. [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 aspect includes a sintered body having a positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode. The positive electrode contains LiCoO2, and the solid electrolyte layer contains Li , [Figure 4] , [Figure 3] , [Figure 5] , , Si x P 1-x O4 (0.4 ≤ x ≤ 0.8).

[0010] (2) In the all-solid-state battery according to the above aspect, the positive electrode may further include a metal or alloy containing any one selected from the group consisting of Ag, Pd, Au, and Pt.

[0011] (3) In the all-solid-state battery according to the above aspect, the positive electrode includes a positive electrode current collector layer and a positive electrode active material layer in contact with the solid electrolyte layer. The positive electrode current collector layer may include LiCoO2 and a metal or alloy containing any one selected from the group consisting of Ag, Pd, Au, and Pt.

Advantages of the Invention

[0012] The all-solid-state battery according to the above aspect has a low internal resistance.

Brief Description of the Drawings

[0013] [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] 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 6] This is an enlarged cross-sectional view of a feature portion of another example of an all-solid-state battery according to the first embodiment. [Modes for carrying out the invention]

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] "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.

[0020] [Positive electrode current collector layer] The positive electrode current collector layer 1A includes, for example, a 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 current collector 11 is considered to be the positive electrode current collector layer 1A.

[0021] The current collector 11 consists of multiple current collector particles. The multiple current collector particles are connected to each other and electrically connected in the xy plane. The positive electrode 1 comprises a metal or alloy as the current collector 11, which includes one selected from the group consisting of Ag, Pd, Au, and Pt. These metals or alloys do not melt and are resistant to oxidation even when the laminate 4 is heated in an atmospheric environment. Examples of current collectors 11 include AgPd alloy, Au, and Pt.

[0022] The positive electrode active material 12 is mixed together with the current collector 11 within the positive electrode current collector layer 1A. The positive electrode active material 12 is in contact with the current collector 11. The presence of the positive electrode active material 12 within the positive electrode current collector layer 1A facilitates the transfer of electrons from the positive electrode active material 12 to the current collector 11. The positive electrode 1 contains lithium cobalt oxide as the positive electrode active material 12. Lithium cobalt oxide is denoted as LiCoO2, and deviations from the stoichiometric composition are permitted.

[0023] Figure 2 shows an example in which the 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 current collectors 11. The current collectors 11 may be in the form of foil, punched film, or expanded material extending in the xy plane.

[0024] [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 the solid electrolyte described above. 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 (the xy plane passing through the outermost part of the positive electrode current collector) is considered to be the positive electrode active material layer 1B.

[0025] (Cathode active material) The positive electrode active material is lithium cobalt oxide. Lithium cobalt oxide is denoted as LiCoO2, and deviations from the stoichiometric composition are acceptable.

[0026] (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 the form of a powder or fibers.

[0027] (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.

[0028] 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.

[0029] 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.

[0030] Up to this point, we have shown specific examples of positive electrodes, but positive electrodes are not limited to these examples. For example, Figures 4 and 5 are cross-sectional views of another example of a positive electrode according to the first embodiment.

[0031] The positive electrode shown in FIG. 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 current collector 11, a positive electrode active material 12, and an oxide 13. The oxide 13 is, for example, an oxide containing Ag, and is AgCoO2. The oxide 13 prevents the oxidation of Ag contained in the current collector 11. When there is an oxide 13 between the current collector 11 and the positive electrode active material 12, the cycle characteristics of the all-solid-state battery 10 are improved.

[0032] The positive electrode shown in FIG. 5 has a positive electrode current collector layer 1E, an intermediate layer 1F, and a positive electrode active material layer 1B. The positive electrode current collector layer 1E has a current collector 11 and an oxide 13. The intermediate layer 1F is composed of the oxide 13. The example shown in FIG. 5 corresponds to the case where the thickness of the oxide 13 is thicker than that of the example shown in FIG. 4. The oxide 13 prevents the oxidation of Ag contained in the current collector 11, and the cycle characteristics of the all-solid-state battery 10 are improved.

[0033] "Solid electrolyte layer" The solid electrolyte layer 3 contains a solid electrolyte. The solid electrolyte is a substance that can move ions by an externally applied electric field. For example, the solid electrolyte layer � conducts lithium ions and inhibits the movement of electrons. The solid electrolyte layer 3 is, for example, a sintered body obtained by sintering.

[0034] The solid electrolyte layer 3 contains Li 3+x Si x P 1-x O4 (0.4 ≤ x ≤ 0.8). Li 3+x Si x P 1-x O4 (0.4 ≤ x ≤ 0.8) has a γ-Li3PO4 structure and is excellent in ionic conductivity.

[0035] "Negative electrode" The negative electrode 2 has, for example, a negative electrode current collector layer 2A and a negative electrode active material layer 2B containing a negative electrode active material.

[0036] [Negative electrode current collector] The negative electrode current collector layer 2A includes, for example, a current collector 21 and a negative electrode active material 22. In this case, the area between the xy plane passing through the top and the xy plane passing through the bottom of the current collector 21 is considered to be the negative electrode current collector layer 2A. The current collector 21 is made of the same material as the current collector 11. As shown in Figure 3, the negative electrode current collector layer 2C may be a foil in which the current collector 21 extends within the xy plane, or it may be in the form of punching or expanding.

[0037] The negative electrode active material 22 is mixed together with the current collector 21 in the negative electrode current collector layer 2A. The negative electrode active material 22 is in contact with the current collector 21. When the negative electrode active material 22 is contained in the negative electrode current collector layer 2A, the transfer of electrons from the negative electrode active material 22 to the 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.

[0038] [Negative electrode active material layer] 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 area between the xy plane passing through the outermost part of the negative electrode active material and the boundary with the negative electrode current collector layer 2A (the xy plane passing through the outermost part of the negative electrode current collector) is considered to be the negative electrode active material layer 2B.

[0039] (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. An example of a negative electrode active material is Li4Ti5O 12 These are LiTiO2, Li2TiO3, and Li2TiSiO5.

[0040] (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.

[0041] (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.

[0042] Figure 2 shows an example in which the negative electrode 2 consists of a negative electrode current collector layer 2A and a negative electrode active material layer 2B, but the invention is not limited to this case. Figure 6 is an enlarged view of a characteristic part of another example of an all-solid-state battery according to the first embodiment. The negative electrode 2D shown in Figure 6 has a current collector 21 and a solid electrolyte 23. The current collector 21 is an AgPd alloy. The AgPd alloy also functions as an active material. When the AgPd alloy functions as the negative electrode active material, the all-solid-state battery has a high capacity and the energy density of the all-solid-state battery is improved.

[0043] "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.

[0044] 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.

[0045] 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 4, the current collector 11 is coated with oxide 13 before being paste-formed. In the example shown in Figure 5, the materials constituting the intermediate layer 1F are also paste-formed.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 a mixture thereof.

[0052] 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 600-1000°C under a nitrogen atmosphere. The firing time is, for example, 0.1-3 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.

[0053] 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.

[0054] 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.

[0055] The all-solid-state battery according to this embodiment has low internal resistance. This is because of the Li used in the solid electrolyte layer 3. 3+x Si x P 1-x This is thought to be because O4 and LiCoO2 used in the positive electrode active material layer 1B do not react well. For example, if LiCoO2 is changed to LiMn2O4, an intermediate product is formed between the solid electrolyte layer 3 and the positive electrode active material layer 1B. This intermediate product is LiMn2O4 or Li2MnO3 containing excess Li, and is formed when Li in the solid electrolyte diffuses into the positive electrode active material layer 1B and reacts with the positive electrode active material. This intermediate product and the solid electrolyte lacking Li cause an increase in the internal resistance of the all-solid-state battery. In contrast, Li 3+x Si x P 1-x O4 and LiCoO2 do not react readily, and intermediate products are unlikely to form.

[0056] 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]

[0057] "Example 1" (Preparation of positive electrode paste) For the preparation of the positive electrode current collector layer paste, a powder mixture of Ag, Pd, and LiCoO2 in a mass ratio of 40:10:50 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.

[0058] The positive electrode active material layer paste was prepared by adding ethylcellulose and dihydroterpineol to LiCoO2 and mixing them together.

[0059] (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.

[0060] (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 prepared by mixing O4 and other substances in a mass ratio of 40:10:50. Ethyl cellulose and dihydroterpineol were added to this powder and mixed.

[0061] (Fabrication of all-solid-state batteries) Next, the positive electrode unit and negative electrode unit were fabricated using the following procedure. First, a paste for the positive electrode active material was printed on the solid electrolyte layer sheet using screen printing to a thickness of 5 μm. Next, the printed paste for the positive electrode active material was dried at 80°C for 5 minutes. Then, a paste for the current collector was printed on the dried paste for the positive electrode active material using screen printing to a thickness of 5 μm. Next, the printed paste for the positive electrode current collector was dried at 80°C for 5 minutes. Then, the paste for the positive electrode active material was printed again on the dried paste for the positive electrode current collector 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.

[0062] 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.

[0063] The laminate was fabricated by stacking five solid electrolyte layer sheets to form a solid electrolyte unit. Fifty electrode units (25 positive electrode units and 25 negative electrode units) were stacked alternately, sandwiching the solid electrolyte unit between them. At this time, the units were stacked with a staggered arrangement such that the current collector layer of odd-numbered electrode units extended only to one end face, and the current collector layer of 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, the stacked units were formed by thermocompression bonding and then cut to produce laminated chips. Subsequently, the laminated chips were co-fired to obtain the laminate. Co-fired firing was performed in a nitrogen atmosphere, 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.

[0064] A solid-state battery was fabricated by attaching terminal electrodes 5 and 6 to a sintered laminate (sintered body) using a known method. The resulting solid-state battery had the configuration shown in Figure 6.

[0065] 100 similar samples were created, and their internal resistance was determined. The internal resistance was calculated as the average of these samples. The internal resistance was determined by dividing the voltage drop (V) from the pause to the start of discharge by the discharge current (A) when the battery was charged with a constant current at a rate of 0.2C until the battery voltage reached 4.0V under constant current charge (CC charge) at a rate of 0.2C in an environment of 25°C, then paused for 1 minute, and then discharged with a constant current at a rate of 0.2C until the battery voltage reached 0V (CC discharge).

[0066] Example 2 Example 2 differs from Example 1 in that a powder mixture of Au and LiCoO2 in a mass ratio of 50:50 was used when preparing the positive electrode current collector paste. The internal resistance was determined under the same conditions as in Example 1.

[0067] "Example 3" Example 3 differs from Example 1 in that a powder mixture of Pt and LiCoO2 in a mass ratio of 50:50 was used when preparing the positive electrode current collector paste. The internal resistance was determined under the same conditions as in Example 1.

[0068] "Example 4" Example 4 differs from Example 1 in that when preparing the positive electrode current collector paste, a powder mixture of Ag and Pd in ​​a mass ratio of 80:20 was used (LiCoO2 was not added). The internal resistance was determined under the same conditions as in Example 1.

[0069] Examples 5-9 Examples 5-9 differ from Example 1 in that the mixing ratio of Li2CO3, SiO2, and Li3PO4 was changed during the preparation of the solid electrolyte layer paste. Examples 5-9 also differ from Example 1 in the composition ratio of the solid electrolyte layer. Other conditions were the same as in Example 1 for determining the internal resistance.

[0070] "Comparative Example 1" Comparative Example 1 differs from Example 1 in the following respects. The internal resistance of Comparative Example 1 was determined in the same way as in Example 1. Difference 1: For the preparation of the positive electrode current collector layer paste, a powder mixture of Ag and Pd in ​​a mass ratio of 80:20 was used. Difference 2: The solid electrolyte used in the solid electrolyte paste is Li 3.5 Ge 0.5 V 0.5 I changed it to O4. Difference 3: The negative electrode paste consisted of two layers: a negative electrode current collector layer paste and a negative electrode active material layer paste. The negative electrode current collector layer paste used a powder mixture of Ag and Pd in ​​a mass ratio of 80:20. The negative electrode active material layer paste used Li4Ti5O 12 (Li 4 / 3 Ti 5 / 3 Ethylcellulose and dihydroterpineol were added to O4) and mixed. The all-solid-state battery after fabrication had the configuration shown in Figure 3.

[0071] "Comparative Example 2" Comparative Example 2 uses LiMn2O4 as the positive electrode active material and Li as the solid electrolyte. 3.5 Si 0.5 P 0.5 The difference from Comparative Example 1 is that O4 was used. The internal resistance of Comparative Example 2 was determined in the same way as in Example 1.

[0072] "Comparative Example 3" Comparative Example 3 differs from Example 1 in that the positive electrode active material is LiMn2O4. The internal resistance of Comparative Example 3 was determined in the same way as in Example 1.

[0073] The results of Examples 1-3 and Comparative Examples 1-3 are summarized in Table 1 below.

[0074] [Table 1]

[0075] Comparing Example 1 with Comparative Examples 1 and 3, Example 1 had lower internal resistance than Comparative Examples 1 and 3. This is thought to be because Comparative Examples 1 and 3 reacted with the positive electrode active material and solid electrolyte, producing intermediate products. Furthermore, in Examples 1-9 and Comparative Example 3, where the AgPd alloy functions as the negative electrode active material, Li 4 / 3 Ti 5 / 3Compared to Comparative Examples 1 and 2, in which O4 functions as the negative electrode active material, the output voltage was higher. Furthermore, comparing Example 1 and Example 4, the internal resistance decreased when the positive electrode current collector layer contained the positive electrode active material. Additionally, comparing Examples 1 and 5-9, the internal resistance also changed depending on the composition of the solid electrolyte. [Explanation of Symbols]

[0076] 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 layer, 4... Laminate, 5,6... Terminal electrode, 10... All-solid battery, 11,21... 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 positive electrode is LiCoO ２ Includes, The solid electrolyte layer is Li ３＋ｘ Si ｘ P １－ｘ O ４ All-solid-state batteries including (0.55 ≤ x ≤ 0.70).

2. The all-solid-state battery according to claim 1, wherein the positive electrode further comprises a metal or alloy containing any one selected from the group consisting of Ag, Pd, Au, and Pt.

3. The positive electrode comprises a positive electrode current collector layer and a positive electrode active material layer in contact with the solid electrolyte layer. The positive electrode current collector layer is made of LiCoO ２ The all-solid-state battery according to claim 1 or 2, comprising a metal or alloy containing any one selected from the group consisting of Ag, Pd, Au, and Pt.

4. The all-solid-state battery according to any one of claims 1 to 3, wherein the surface of the LiCoO2 is coated with an oxide containing Ag.

Images