Positive electrode, solid-state battery, and method for manufacturing the solid-state battery

Abstract

The present invention aims to provide a positive electrode that is less susceptible to volume changes in the positive electrode active material when used in a solid-state battery, thereby contributing to improved energy efficiency. A positive electrode for a solid-state battery, comprising: a positive electrode mixture layer formed by filling pores of a metal porous body with a positive electrode mixture containing a positive electrode active material, a solid electrolyte, and a conductive additive; the positive electrode mixture layer includes a first layer and a second layer provided closer to the solid electrolyte layer than the first layer, a mass fraction of the conductive additive contained in the second layer relative to the mass of the positive electrode composite material contained in the second layer is higher than a mass fraction of the conductive additive contained in the first layer relative to the mass of the positive electrode composite material contained in the first layer.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode, a solid-state battery, and a method for manufacturing a solid-state battery. [Background technology]

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. Solid-state batteries have high energy density and are used in a wide range of applications. In particular, lithium-ion secondary batteries are becoming increasingly important as power sources for electric vehicles (EVs), hybrid electric vehicles (HEVs), and other vehicles.

[0003] A known solid-state battery configuration is one in which lithium is used as the negative electrode of a lithium secondary battery to increase capacity. In this regard, Patent Document 1 discloses that the negative electrode contains lithium, and the through-holes of the current collector in the positive electrode are filled with a positive electrode active material and a conductive additive. The positive electrode mixture layer in Patent Document 1 occludes lithium ions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-142796 Summary of the Invention [Problem to be solved by the invention]

[0005] To contribute to further energy efficiency, solid-state batteries are also required to maintain their battery life even after repeated charge and discharge. For example, a required characteristic for this purpose is the control of structural changes in the positive electrode, such as volume changes of the positive electrode active material caused by the absorption of lithium ions and the like by the positive electrode active material during repeated charge and discharge of the solid-state battery. Volume changes in the positive electrode active material can easily form gaps between layers, which can increase the resistance of the solid-state battery and reduce the electron transport path. In particular, volume changes in the positive electrode active material are likely to occur in high-capacity positive electrodes.

[0006] In light of this background, an object of the present invention is to provide a positive electrode that is less susceptible to the influence of volume changes of the positive electrode active material when used in a solid-state battery, thereby contributing to improved energy efficiency. [Means for solving the problem]

[0007] In order to achieve the above object, a positive electrode according to claim 1 of the present invention is a positive electrode for a solid-state battery, and includes a positive electrode composite layer formed by filling pores of a porous metal body with a positive electrode composite including a positive electrode active material, a solid electrolyte, and a conductive additive, the positive electrode composite layer including a first layer and a second layer provided closer to the solid electrolyte layer than the first layer, and the mass fraction of the conductive additive contained in the second layer relative to the mass of the positive electrode composite contained in the second layer is higher than the mass fraction of the conductive additive contained in the first layer relative to the mass of the positive electrode composite contained in the first layer.

[0008] According to this configuration, since the mass fraction of the conductive additive is high in the second layer of the positive electrode composite layer, the influence of volumetric changes of the positive electrode active material on the second layer is reduced, and the occurrence of gaps at the positive electrode interface is suppressed. Therefore, when used in a solid-state battery, the influence of volumetric changes of the positive electrode active material can be reduced.

[0009] The invention according to claim 2 of the present invention is the positive electrode according to claim 1, wherein the mass fraction of the conductive additive contained in the second layer relative to the mass of the positive electrode composite contained in the second layer is 8 times or more and 10 times or less, relative to the mass fraction of the conductive additive contained in the first layer relative to the mass of the positive electrode composite contained in the first layer.

[0010] This configuration makes it possible to both suppress the occurrence of gaps at the positive electrode interface when a volume change occurs in the positive electrode active material and suppress a decrease in energy density.

[0011] The invention according to claim 3 of the present invention is the positive electrode according to claim 1, wherein the specific surface area of ​​the conductive additive contained in the second layer is 150 m 2 / g or more 800m 2 / g.

[0012] This configuration makes it possible to both suppress the occurrence of gaps at the positive electrode interface when a volume change occurs in the positive electrode active material and realize a positive electrode composite slurry that is easy to apply to a metal porous body.

[0013] A fourth aspect of the present invention provides the positive electrode according to the first aspect, wherein the positive electrode active material is MnO2.

[0014] According to this configuration, a positive electrode in which the positive electrode active material is MnO2 can be suitably used.

[0015] A solid state battery according to claim 5 of the present invention is a solid state battery comprising the positive electrode according to any one of claims 1 to 4, a solid electrolyte layer, and a negative electrode containing lithium.

[0016] In this solid-state battery, the higher mass fraction of the conductive additive in the second layer of the positive electrode composite layer reduces the effect of volumetric changes in the positive electrode active material on the second layer, thereby suppressing the occurrence of gaps at the positive electrode interface, etc. Therefore, the effect of volumetric changes in the positive electrode active material can be made less likely to occur.

[0017] A method for manufacturing a solid-state battery according to claim 6 of the present invention is a method for manufacturing a solid-state battery, the method including: applying a first positive electrode composite containing a positive electrode active material, a solid electrolyte, and a conductive additive to a first metal porous body; applying a second positive electrode composite containing a positive electrode active material, a solid electrolyte, and a conductive additive to a second metal porous body; and joining the second metal porous body to a surface of the first metal porous body that faces the solid electrolyte layer, wherein the mass fraction of the conductive additive contained in the second positive electrode composite relative to the mass of the second positive electrode composite is higher than the mass fraction of the conductive additive contained in the first positive electrode composite relative to the mass of the first positive electrode composite.

[0018] In a solid-state battery manufactured by this manufacturing method, the mass fraction of the conductive additive in the second positive electrode composite is high, so that the effect of volumetric changes in the positive electrode active material on the second positive electrode composite is reduced, and the occurrence of gaps at the positive electrode interface is suppressed. Therefore, the effect of volumetric changes in the positive electrode active material can be made less likely to occur.

[0019] A method for manufacturing a solid-state battery according to claim 7 of the present invention is a method for manufacturing a solid-state battery, comprising: a step of applying a first cathode composite containing a cathode active material, a solid electrolyte, and a conductive additive to a metal porous body; and a step of applying a second cathode composite containing a cathode active material, a solid electrolyte, and a conductive additive to a surface of the metal porous body coated with the first cathode composite, the surface facing the solid electrolyte layer, wherein the mass fraction of the conductive additive contained in the second cathode composite relative to the mass of the second cathode composite is higher than the mass fraction of the conductive additive contained in the first cathode composite relative to the mass of the first cathode composite.

[0020] In a solid-state battery manufactured by this manufacturing method, the mass fraction of the conductive additive in the second positive electrode composite is high, so that the effect of volumetric changes in the positive electrode active material on the second positive electrode composite is reduced, and the occurrence of gaps at the positive electrode interface is suppressed. Therefore, the effect of volumetric changes in the positive electrode active material can be made less likely to occur. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a solid-state battery. [Figure 2] FIG. 1 is a diagram showing the capacity of a solid-state battery for each C-rate. [Figure 3] 1A to 1C are diagrams illustrating a method for manufacturing a positive electrode. [Figure 4] 10A and 10B are diagrams illustrating a first filling step and a second filling step in another method for manufacturing a solid state battery. [Figure 5] FIG. 1 is a diagram showing the capacity of coin-type cells for each cycle in Example 1, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0022] Preferred embodiments of the present invention will now be described in detail.

[0023] [Solid battery] FIG. 1 is a cross-sectional view schematically illustrating a solid-state battery 1. The solid-state battery of this embodiment may be any of coin, button, cylindrical, rectangular, and laminate types. The solid-state battery of this embodiment can be used in a wide range of applications, including mobile devices such as mobile phones and laptops, and in-vehicle applications. FIG. 1 illustrates the solid-state battery as a single unit cell. The solid-state battery 1 includes a positive electrode 10, a solid electrolyte layer 20, and a negative electrode 30. In the solid-state battery 1 shown in FIG. 1, a negative electrode 30 is provided above and below the positive electrode 10, and a solid electrolyte layer 20 is provided above and below the positive electrode 10 so as to be sandwiched between each negative electrode 30 and the positive electrode 10.

[0024] In the solid-state battery 1 of this embodiment, metallic lithium is contained in the negative electrode 30, and lithium ions are absorbed into the positive electrode active material contained in the positive electrode 10 during repeated charge and discharge. When metallic lithium is contained in the negative electrode of a solid-state battery, the energy density of the solid-state battery can be improved. On the other hand, when metallic lithium is contained in the negative electrode, the state of the interfaces with the positive electrode and the negative electrode becomes unstable due to structural changes in the solid electrolyte layer that accompany charge and discharge. In solid-state batteries, interfacial instability associated with charging and discharging is thought to be caused by the following reasons. When the positive electrode active material contained in the positive electrode absorbs lithium ions, the positive electrode active material may expand or crystallize and shrink, resulting in a volume change in the positive electrode active material. When this volume change occurs, gaps form at the interface between the positive electrode and the solid electrolyte layer, making it difficult for lithium ions to conduct at the interface, increasing resistance and easily causing interfacial instability. Furthermore, as the positive electrode expands and contracts, structural changes occur within the positive electrode, interrupting the electron path and increasing resistance. In contrast, the positive electrode of this embodiment is less susceptible to the influence of volume changes in the positive electrode active material, and therefore, destabilization of the interface can be suppressed even when charge and discharge are repeated.

[0025] [Positive electrode] The positive electrode 10 includes a porous metal body 11 as a current collector and a positive electrode mixture 12 . The metal porous body 11 has pores that are continuous with one another. In this embodiment, the pores of the metal porous body 11 are filled with a positive electrode composite 12. Examples of the metal porous body include mesh, woven fabric, nonwoven fabric, embossed body, punched body, expanded body, and foamed body. Examples of metals used for the metal porous body include nickel, aluminum, stainless steel, titanium, and silver.

[0026] The positive electrode composite 12 includes a positive electrode active material, a solid electrolyte, a binder, and a conductive additive. Examples of the positive electrode active material include lithium-free materials such as MnO2 and sulfur, with MnO2 being particularly preferred. Furthermore, the MnO2 is preferably, for example, a ramsdellite-type material. When ramsdellite-type MnO2 is used as the positive electrode active material, the energy density can be improved. When the positive electrode active material is MnO2, repeated charge and discharge as a solid-state battery tends to cause the positive electrode active material to absorb lithium ions and crystallize, resulting in shrinkage. This tends to create gaps at the interface between the positive electrode 10 and the solid electrolyte layer 20, making the interface unstable. On the other hand, in the positive electrode 10 of this embodiment, the current collector is a porous metal body 11, so gaps are less likely to form at the interface. The layer formed by filling the pores of porous metal body 11 with positive electrode mixture 12 can also be regarded as positive electrode mixture layer 13 .

[0027] The positive electrode composite 12 of this embodiment is composed of a first positive electrode composite 121 that is separated from the solid electrolyte layer 20 in the vertical direction in the drawing, and a second positive electrode composite 122 that is located between the solid electrolyte layer 20 and the first positive electrode composite 121 in the vertical direction and adjacent to the solid electrolyte layer 20 in the vertical direction. The second positive electrode composite 122 is provided above and below the first positive electrode composite 121. The layer formed by filling the pores of the metal porous body 11 with the first positive electrode composite material 121 can also be regarded as a first positive electrode composite layer 131. The layer formed by filling the pores of the metal porous body 11 with the second positive electrode composite material 122 can also be regarded as a second positive electrode composite layer 132.

[0028] The first positive electrode composite layer 131 preferably comprises 65 parts by mass or more and 75 parts by mass or less of a positive electrode active material, 23 parts by mass or more and 33 parts by mass or less of a solid electrolyte, 1 part by mass of a binder, and 1 part by mass of a conductive additive. The thickness of the first positive electrode composite layer 131 is not particularly limited because various embodiments are used depending on the specifications of the cell, but is preferably, for example, 10 μm or more and 100 μm or less. The electrical resistance of first positive electrode mixture layer 131 is determined by impedance measurement. The electronic conductivity of first positive electrode mixture layer 131 is determined by measuring the electrical resistivity of first positive electrode mixture layer 131. The thickness and density of first positive electrode mixture layer 131 are determined by using a scanning electron microscope (SEM) after CP processing.

[0029] The second positive electrode composite layer 132 preferably comprises 60 parts by mass or more and 80 parts by mass or less of a positive electrode active material, 8 parts by mass or more and 30 parts by mass or less of a solid electrolyte, 1 part by mass of a binder, and 8 parts by mass or more and 10 parts by mass or less of a conductive additive. The thickness of the second positive electrode composite layer 132 is not particularly limited because various embodiments are used depending on the specifications of the cell, but is preferably, for example, 10 μm or more and 100 μm or less. The methods for measuring the electrical resistance, electronic conductivity, thickness, and density of second positive electrode mixture layer 132 are the same as those for first positive electrode mixture layer 131.

[0030] In the positive electrode 10 of this embodiment, the mass fraction of the conductive additive contained in the second positive electrode composite 122 relative to the mass of the second positive electrode composite 122 is higher than the mass fraction of the conductive additive contained in the first positive electrode composite 121 relative to the mass of the first positive electrode composite 121. In this case, the influence of volumetric changes in the positive electrode active material is less likely to occur. Specifically, when the proportion of the conductive additive in the positive electrode 10 near the interface with the solid electrolyte layer 20 is high, even if a volumetric change occurs in the positive electrode active material, the presence of the conductive additive near the interface makes it less likely for gaps to occur at the interface. This suppresses interfacial instability, such as interruption of the electron transfer path at the interface or an increase in interfacial resistance, resulting in a solid battery with excellent cycle characteristics. That is, in this embodiment, the mass fraction of the conductive additive in the second positive electrode composite 122 is increased to suppress the occurrence of gaps at the interface between the positive electrode 10 and the solid electrolyte layer 20.

[0031] (Conductive additive) Examples of the conductive additive contained in the positive electrode mixture 12 include acetylene black (AB), furnace black (FB), thermal black, lamp black, channel black, roller black, disc black, carbon black (CB), carbon fiber, carbon nanotubes (CNT), carbon nanohorns, graphite, graphene, glassy carbon, and amorphous carbon.

[0032] (binder) The binder is not particularly limited, but examples thereof include resin materials such as styrene butadiene rubber, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, polyvinylidene chloride, polyvinyl chloride, polyurethane, vinylon, polybenzimidazole, polyimide, polyphenylene sulfite, polyether ether ketone, cellulose, and acrylic resin.

[0033] [Solid electrolyte layer] The solid electrolyte layer 20 includes a solid electrolyte 21. Examples of the solid electrolyte 21 include sulfide-based solid electrolyte materials, oxide-based solid electrolyte materials, halide-based solid electrolyte materials, inorganic solid electrolyte materials such as lithium-containing salts, polymer-based solid electrolyte materials such as polyethylene oxide, and gel-based solid electrolyte materials containing lithium-containing salts or lithium-ion conductive ionic liquids. Examples of sulfide-based solid electrolyte materials include LPS-based halogens (Cl, Br, I), Li2S-P2S5, and Li2S-P2S5-LiI. The term "Li2S-P2S5" refers to a sulfide-based solid electrolyte material made using a raw material composition containing Li2S and P2S5, and the same applies to other terms. Examples of oxide-based solid electrolyte materials include NASICON-type oxides, garnet-type oxides, and perovskite-type oxides. Examples of NASICON-type oxides include oxides containing Li, Al, Ti, P, and O (e.g., Li 1.5 A l0.5 Ti 1.5(PO4)3). Examples of garnet-type oxides include oxides containing Li, La, Zr, and O (e.g., Li7La3Zr2O 12 Examples of perovskite oxides include oxides containing Li, La, Ti, and O (for example, LiLaTiO3). The solid electrolyte contained in positive electrode composite 12 may be the same material as solid electrolyte 21 contained in solid electrolyte layer 20 .

[0034] The solid electrolyte layer 20 preferably comprises 90 parts by mass or more and 97 parts by mass or less of the solid electrolyte 21 and 3 parts by mass or more and 10 parts by mass or less of the binder. The thickness of the solid electrolyte layer 20 is not particularly limited because various embodiments are used depending on the specifications of the cell, but is preferably, for example, 10 μm or more and 50 μm or less. The methods for measuring the electrical resistance, electronic conductivity, thickness, and density of solid electrolyte layer 20 are the same as those for positive electrode mixture layer 13.

[0035] The particle size of the solid electrolyte 21 is preferably greater than 0.5 μm and less than 5 μm. If the particle size of the solid electrolyte 21 is 0.5 μm or less, the solid electrolyte 21 is likely to be insufficiently dispersed when preparing a slurry of the solid electrolyte 21, and the viscosity of the slurry is difficult to adjust, making it difficult to apply the slurry. If the particle size of the solid electrolyte 21 is 5 μm or more, the solid electrolyte 21 is unlikely to be uniformly disposed within the pores of the porous metal body 11, and therefore, uneven application of the solid electrolyte 21 to the porous metal body 11 is likely to occur. Furthermore, uneven application of the solid electrolyte 21 to the porous metal body 11 is likely to increase electrical resistance.

[0036] [Negative electrode] The negative electrode 30 has a porous metal body 31 as a current collector and a vapor deposition portion 32 . The porous metal body 31 has pores that are continuous with one another. Examples of the porous metal body include mesh, woven fabric, nonwoven fabric, embossed body, punched body, expanded body, and foam. Examples of metals used for the porous metal body include nickel, aluminum, stainless steel, titanium, copper, and silver. The vapor-deposited portion 32 is a metal portion that is vapor-deposited on the surface of the metal porous body 31. In this embodiment, lithium metal is vapor-deposited on the metal porous body 31 to form a thin film of lithium metal on the surface of the metal porous body 31, thereby suppressing an increase in electrical resistance. In this embodiment, the vapor-deposited portion 32 is provided with an amount of lithium metal that corresponds to the upper limit of the number of lithium ions that can be occluded by the positive electrode active material contained in the positive electrode composite 12.

[0037] The thickness of the negative electrode 30 is not particularly limited, as various embodiments are used depending on the specifications of the cell, but it is preferably, for example, 10 μm or more and 50 μm or less. The methods for measuring the electrical resistance, electronic conductivity, thickness, and density of negative electrode 30 are the same as those for positive electrode mixture layer 13 .

[0038] [Characteristics of the positive electrode] Next, the characteristic configuration of the positive electrode 10 in the solid state battery 1 of this embodiment will be described.

[0039] (mass fraction of conductive additive) In the present embodiment, the mass fraction of the conductive additive contained in the second positive electrode composite 122 relative to the mass of the second positive electrode composite 122 is preferably 8 to 10 times the mass fraction of the conductive additive contained in the first positive electrode composite 121 relative to the mass of the first positive electrode composite 121. Hereinafter, the ratio of the mass fraction of the conductive additive contained in the second positive electrode composite 122 relative to the mass of the second positive electrode composite 122 relative to the mass fraction of the conductive additive contained in the first positive electrode composite 121 relative to the mass of the first positive electrode composite 121 may be referred to as the ratio of the conductive additive of the second positive electrode composite 122 to the conductive additive of the first positive electrode composite 121.

[0040] If the ratio of the conductive additive in the second positive electrode composite 122 to the conductive additive in the first positive electrode composite 121 is less than 8 times, the conductive additive in the second positive electrode composite 122 will be insufficient, and the occurrence of gaps at the interface between the positive electrode 10 and the solid electrolyte layer 20 may not be sufficiently suppressed. If the ratio of the conductive additive in the second positive electrode composite 122 to the conductive additive in the first positive electrode composite 121 is greater than 10, the conductive additive contained in the second positive electrode composite layer 132 will be in excess, which may reduce the capacity of the positive electrode 10 and decrease the energy density of the solid battery 1. Furthermore, in producing the slurry for the second positive electrode composite 122, the conductive additive with a large specific surface area tends to absorb the solvent, making it difficult to knead and apply the slurry.

[0041] (Specific surface area of ​​conductive additive) The specific surface area of ​​the conductive additive contained in the positive electrode mixture 12 is 150 m 2 / g or more 800m 2 / g, and preferably less than 300m 2 / g or more 800m 2 More preferably, it is less than / g. The specific surface area of ​​the conductive additive is 150m 2 If the specific surface area of ​​the conductive additive is less than 800 m / g, the conductive additive is less likely to come into contact with the particles of the positive electrode mixture 12, and therefore, the occurrence of gaps at the interface between the positive electrode 10 and the solid electrolyte layer 20 may not be sufficiently suppressed. 2 / g or more, in the preparation of the slurry of the positive electrode composite 12, agglomerates of the conductive additive grow due to the intermolecular forces between particles of the conductive additive, and the viscosity of the slurry of the positive electrode composite 12 increases, making it difficult to apply the slurry to the metal porous body 11.

[0042] FIG. 2 is a diagram showing the relationship between the C rate and the capacity of a first solid state battery and a second solid state battery each having a positive electrode composite containing a different conductive additive. In the first solid state battery, the mass fraction of the conductive additive contained in the first positive electrode composite 121 relative to the mass of the first positive electrode composite 121 is 1 wt %, and the mass fraction of the conductive additive contained in the second positive electrode composite 122 relative to the mass of the second positive electrode composite 122 is 2.5 wt %. That is, in the first solid state battery, the ratio of the conductive additive in the second positive electrode composite 122 to the conductive additive in the first positive electrode composite 121 is 2.5 times. Also, in the first solid state battery, the specific surface area of ​​the conductive additive contained in the positive electrode composite 122 is 45 m 2 / g. In the second solid state battery, the mass fraction of the conductive additive contained in the first positive electrode composite 121 relative to the mass of the first positive electrode composite 121 is 1 wt %, and the mass fraction of the conductive additive contained in the second positive electrode composite 122 relative to the mass of the second positive electrode composite 122 is 8.0 wt %. That is, in the second solid state battery, the ratio of the conductive additive in the second positive electrode composite 122 to the conductive additive in the first positive electrode composite 121 is 8 times. Also, in the second solid state battery, the specific surface area of ​​the conductive additive contained in the positive electrode composite 122 is 300 m 2 / g.

[0043] Using the first and second solid-state batteries described above, a charge-discharge test was conducted at a temperature of 60°C, a 0.05 C rate, and a cutoff potential of 2.0 V to 4.0 V. The above operation was performed at C rates of 0.5 C, 1.0 C, 2.0 C, and 3.0 C, and the capacity upon charge and discharge was measured for each C rate. The measurement results are shown in Figure 2. The capacity shown in Figure 2 is the ratio of the capacity after charge and discharge at each C rate to the capacity before charge and discharge. In the second solid-state battery, compared to the first solid-state battery, the capacity tends to be less likely to decrease even when the C rate is increased, and it was confirmed that a high capacity is maintained even when the C rate is high. From this result, it can be seen that the positive electrode 10 in which the ratio of the conductive additive in the second positive electrode composite 122 to the conductive additive in the first positive electrode composite 121 is 8 times or more, and the conductive additive contained in the positive electrode composite 12 in which the specific surface area is 150 m 2 It can be seen that the solid state battery 1 including the positive electrode 10 having a volumetric capacity of 1000 vol% or more is less affected by the volume change of the positive electrode active material and has excellent durability (charge / discharge cycle characteristics).

[0044] [Solid-state battery manufacturing method] Next, a method for manufacturing the solid state battery 1 will be described. The solid state battery 1 of this embodiment is manufactured by a cathode manufacturing process for manufacturing a cathode 10, a first lamination process for laminating a solid electrolyte layer 20 on the cathode 10, and a second lamination process for laminating a cathode 30 on the laminate. The cathode manufacturing process also includes a slurry manufacturing process for manufacturing a slurry of the cathode composite 12, a first filling process for filling and applying a first cathode composite 121 into pores of a first porous metal body 111 (described later), a second filling process for filling and applying a second cathode composite 122 into pores of a second porous metal body 112 (described later), and a joining process for joining the first porous metal body 111 and the second porous metal body 112.

[0045] (Slurry manufacturing process) In manufacturing the positive electrode 10, first, a slurry of the positive electrode composite 12 containing a positive electrode active material, a solid electrolyte, a conductive additive, a binder, and a solvent is manufactured. In this embodiment, two types of slurries are manufactured: a slurry of the first positive electrode composite 121 and a slurry of the second positive electrode composite 122.

[0046] (1st filling process) FIG. 3(A) is a diagram for explaining the first filling step. Next, the slurry of the positive electrode composite 12 is filled and coated into the pores of the porous metal body 11. In this embodiment, the porous metal body 11 includes a first porous metal body 111 to be filled and coated with a slurry of the first positive electrode composite 121, and a second porous metal body 112 to be filled and coated with a slurry of the second positive electrode composite 122.

[0047] As shown in FIG. 3(A), two coaters 40 are used to fill and coat the pores of the first porous metal body 111 with the first positive electrode composite 121. The interiors of these two coaters 40 are filled with a slurry of the first positive electrode composite 121. The coaters 40 are provided on both outer sides of the first porous metal body 111 in the thickness direction, and discharge the slurry of the first positive electrode composite 121 onto both sides of the first porous metal body 111, thereby filling and coating the pores of the first porous metal body 111 with the slurry. The coaters 40 discharge the slurry while moving in the longitudinal direction of the first porous metal body 111 (the vertical direction in the illustrated example), thereby filling and coating the slurry of the first porous metal body 111 along the longitudinal direction. Here, a single sheet of first porous metal body 111 is filled with a slurry of first positive electrode composite material 121 by coating.

[0048] (2nd filling process) FIG. 3(B) is a diagram illustrating the second filling step. As shown in FIG. 3(B), two coaters 40 are also used to fill and coat the pores of the second porous metal body 112 with the second positive electrode composite 122. The interiors of these two coaters 40 are filled with a slurry of the second positive electrode composite 122. The coaters 40 are provided on both outer sides of the second porous metal body 112 in the thickness direction, and discharge the slurry of the second positive electrode composite 122 onto both sides of the second porous metal body 112, thereby filling and coating the pores of the second porous metal body 112 with the slurry. The coaters 40 discharge the slurry while moving in the longitudinal direction of the second porous metal body 112, thereby filling and coating the slurry of the second positive electrode composite 122 along the longitudinal direction of the second porous metal body 112. Here, the two second porous metal bodies 112 are each filled with the slurry of the second positive electrode composite material 122 by coating. Thereafter, the one first porous metal body 111 and the two second porous metal bodies 112 filled and coated with the slurry are dried.

[0049] (Joining process) FIG. 3(C) is a diagram illustrating the bonding process. As shown in FIG. 3(C), second porous metal bodies 112 are placed on both sides of a first porous metal body 111. Then, in this state, the first porous metal body 111 and the second porous metal body 112 are sandwiched and pressed between a roll press 50, which is a pressure device. As a result, one first porous metal body 111 and two second porous metal bodies 112 are bonded together to form one porous metal body 11, with the packing density of the first positive electrode composite 121 and the second positive electrode composite 122 improved. In this manner, a positive electrode 10 (see FIG. 1) is manufactured in which a first positive electrode composite layer 131 is sandwiched between second positive electrode composite layers 132.

[0050] Thereafter, solid electrolyte layers 20 are laminated on both sides of the positive electrode 10 and then pressed by a roll press to form a laminate. Furthermore, negative electrodes 30 are laminated on both sides of this laminate and then pressed by a roll press. In this way, the solid battery 1 shown in FIG. 1 is manufactured.

[0051] [Other manufacturing methods for solid-state batteries] Next, a description will be given of another method for manufacturing the solid state battery 1. The method for manufacturing the solid state battery 1 of this embodiment is not limited to the example shown in FIG. In another manufacturing method for a solid battery 1 described below, the first filling step and the second filling step in the positive electrode manufacturing process are different from those in the above-described manufacturing method for the solid battery 1. Furthermore, in another manufacturing method for a solid battery 1 described below, the positive electrode manufacturing process does not include a joining step. Furthermore, in another manufacturing method for a solid battery 1 described below, the slurry manufacturing step, the first stacking step, and the second stacking step in the positive electrode manufacturing process are the same as those in the above-described manufacturing method for the solid battery 1.

[0052] FIG. 4 is a diagram for explaining the first filling step and the second filling step in another method for manufacturing the solid state battery 1. In FIG. In the first filling step and the second filling step in another manufacturing method of solid state battery 1, a single porous metal body 11 is filled and coated with a slurry of first positive electrode composite 121 and a slurry of second positive electrode composite 122.

[0053] 4(A), two first coaters 41 are used to fill and coat the pores of the porous metal body 11 with the first positive electrode composite 121. The interiors of these two first coaters 41 are filled with a slurry of the first positive electrode composite 121. The two first coaters 41 are opposed to each other in the left-right direction in the figure and are spaced apart in the left-right direction. Two second coaters 42 are used to fill and coat the pores of the porous metal body 11 with the second positive electrode composite 122. The two second coaters 42 are filled with a slurry of the second positive electrode composite 122. The two second coaters 42 face each other in the left-right direction in the figure and are spaced apart in the left-right direction.

[0054] Furthermore, the porous metal body 11 moves from below the first coaters 41 to above them, and reaches a position between the two first coaters 41. At this time, the two first coaters 41 eject a slurry of the first positive electrode composite 121 onto both sides of the porous metal body 11, thereby filling and applying the slurry into the pores of the porous metal body 11. Furthermore, as the porous metal body 11 moves upward while the slurry is being ejected from the first coaters 41, the porous metal body 11 is filled with the slurry of the first positive electrode composite 121 along the longitudinal direction. Meanwhile, the porous metal body 11 has not yet reached the second coater 42.

[0055] Next, the porous metal body 11 continues to move upward and reaches a position between two second coaters 42, as shown in FIG. 4(B). At this time, the two second coaters 42 discharge a slurry of the second positive electrode composite 122 onto both sides of the porous metal body 11, thereby filling and coating the slurry of the second positive electrode composite 122 in portions of the pores of the porous metal body 11 that are positioned outward in the left-right direction from the portions of the porous metal body 11 that have been filled and coated with the slurry of the first positive electrode composite 121. Furthermore, as the porous metal body 11 moves upward while the slurry is being discharged from the second coater 42, the slurry of the second positive electrode composite 122 is filled and coated in portions of the porous metal body 11 that are outward in the left-right direction from the portions of the porous metal body 11 that have been filled and coated with the slurry of the first positive electrode composite 121, across the longitudinal direction of the porous metal body 11.

[0056] Note that first coater 41 may discharge the slurry onto porous metal body 11 at a higher pressure than second coater 42. In this manner, the slurry of first positive electrode composite 121 is filled and applied to the central portion in the left-right direction of the inside of the pores of porous metal body 11. In the above example, the porous metal body 11 is provided so as to be movable, but this is not limiting. The first coater 41 and the second coater 42 may move, so that the slurry of the first positive electrode composite 121 and the slurry of the second positive electrode composite 122 may be filled along the longitudinal direction of the porous metal body 11.

[0057] Next, the metal porous body 11 is dried and then pressed by a roll press, thereby improving the packing density of the first positive electrode composite 121 and the second positive electrode composite 122, and producing a positive electrode 10 (see FIG. 1) in which the first positive electrode composite layer 131 is sandwiched between the second positive electrode composite layers 132. [Example]

[0058] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0059] [Example 1] (Fabrication of coin-type cells (solid-state batteries)) The positive electrode active material was 65 parts by mass of ramsdellite-type MnO2, 33 parts by mass of solid electrolyte, 1 part by mass of binder, and a sintered body having a specific surface area of ​​300 m 2 1 part by mass of a conductive additive having a concentration of 1 / g was used to prepare a slurry of a first positive electrode composite 121 (see FIG. 1). Next, the obtained slurry was filled and coated into a sheet of a first porous metal body 111 made of aluminum by the method shown in FIG. 3(A) as a first filling step. Next, 60 parts by mass of ramsdellite-type MnO2 as a positive electrode active material, 30 parts by mass of a solid electrolyte, 2 parts by mass of a binder, and a sintered body having a specific surface area of ​​300 m 2 8 parts by mass of a conductive additive having a conductivity of 1 / g was used to prepare a slurry of the second positive electrode composite 122. Next, the obtained slurry was filled and coated into a sheet of second porous metal body 112 made of aluminum by the method shown in FIG.

[0060] Next, the second porous metal body 112 is laminated on the first porous metal body 111, and pressure is applied by the method shown in FIG. 3(C) as a bonding step, thereby forming a laminate with a weight per unit area of ​​30 mg / cm. 2 Thus, a positive electrode having first positive electrode composite material layer 131 and second positive electrode composite material layer 132 formed thereon was produced.

[0061] Next, a solid electrolyte slurry was prepared using 90 parts by mass of the solid electrolyte and 10 parts by mass of the binder, and the obtained slurry was applied to the positive electrode and dried, and then pressed by a roll press to produce a laminate in which the solid electrolyte layer 20 was laminated on the positive electrode. Next, lithium metal was vapor-deposited on the surface of a copper porous metal body 31 (see FIG. 1 ), thereby producing a negative electrode 30 having a vapor-deposited portion 32. The produced negative electrode 30 was then stacked on a laminate in which a solid electrolyte layer 20 was stacked on a positive electrode, dried, and then pressed with a roll press to produce a coin-shaped cell of Example 1 having a diameter of 10 mm as a solid-state battery.

[0062] [Comparative Example 1] The positive electrode active material is ramsdellite-type MnO2 65 parts by mass, solid electrolyte 33 parts by mass, binder 1 part by mass, and a specific surface area of ​​45 m 2 The resulting slurry was laminated on an aluminum foil as a current collector, dried, and then pressed with a roll press to a weight of 30 mg / cm. 2 A positive electrode was fabricated. Next, a solid electrolyte slurry was prepared using 90 parts by mass of the solid electrolyte and 10 parts by mass of the binder, and the obtained slurry was applied to the positive electrode and dried, and then pressed with a roll press to produce a laminate in which the solid electrolyte layer was laminated on the positive electrode. Next, a copper foil current collector was laminated on the surface of the lithium metal to form a negative electrode. The negative electrode was then laminated on a laminate consisting of a positive electrode and a solid electrolyte layer, dried, and then pressed using a roll press to produce a coin-shaped cell of Comparative Example 1 with a diameter of 10 mm as a solid-state battery. The positive electrode of this coin-shaped cell consisted of a single positive electrode composite layer.

[0063] Comparative Example 2 The positive electrode active material is ramsdellite-type MnO2 65 parts by mass, solid electrolyte 33 parts by mass, binder 1 part by mass, and a specific surface area of ​​45 m 2 A positive electrode composite slurry was prepared using 1 part by mass of a conductive additive having a porosity of 1000 mg / g. Next, the obtained slurry was applied by filling the pores of a porous metal body made of aluminum using the method shown in FIG. 3(A). The porous metal body was then dried and pressed with a roll press to a weight of 30 mg / cm. 2 A positive electrode was fabricated. Next, a coin-shaped cell of Comparative Example 2 having a diameter of 10 mm was produced by forming a solid electrolyte layer and a negative electrode on the obtained positive electrode in the same manner as in Example 1. The positive electrode of this coin-shaped cell is the same as in Example 1 in that the pores of the metal porous body are filled with a positive electrode composite, but differs from Example 1 in that the positive electrode is made of a single positive electrode composite layer, i.e., second positive electrode composite layer 132 (see FIG. 1 ) is not provided on the positive electrode.

[0064] [Coin cell evaluation] Using the obtained coin-type cell, a charge-discharge test was carried out at a temperature of 60°C at a rate of 0.05 C with a cutoff potential of 2.0 V to 4.0 V. The above operation was carried out at C rates of 1.0 C, 2.0 C, and 3.0 C, and the capacity during charge-discharge was measured for each cycle.

[0065] Fig. 5 is a diagram showing the capacity of the coin cells for each cycle when they were charged and discharged for five cycles at a rate of 0.05 C in Example 1, Comparative Example 1, and Comparative Example 2. The capacity shown in Fig. 5 is the ratio of the capacity of the coin cell after charging and discharging to the capacity of the coin cell before charging and discharging. It was confirmed that in Example 1, the capacity tends to be less likely to decrease even with repeated cycles than in Comparative Examples 1 and 2, and that a high capacity is maintained even with repeated cycles. This shows that in a solid battery in which a positive electrode composite layer with a high mass fraction of conductive additive is provided on the solid electrolyte layer side, the presence of the conductive additive near the positive electrode interface makes it less susceptible to the effects of volume changes in the positive electrode active material, and excellent durability (charge-discharge cycle characteristics) can be obtained.

[0066] From the above results, it was found that the present invention can provide a positive electrode that is less susceptible to the influence of volume changes in the positive electrode active material. [Explanation of symbols]

[0067] 1…solid battery 10...Positive electrode 11...Porous metal body 12...Positive electrode mixture 121...First positive electrode composite 122...Second positive electrode composite 20…Solid electrolyte layer 30...Negative electrode

Claims

1. A positive electrode of a solid-state battery, a positive electrode mixture layer formed by filling pores of a metal porous body with a positive electrode mixture containing a positive electrode active material, a solid electrolyte, and a conductive additive; the positive electrode mixture layer includes a first layer and a second layer provided closer to the solid electrolyte layer than the first layer, a mass fraction of the conductive additive contained in the second layer relative to the mass of the positive electrode composite material contained in the second layer is higher than a mass fraction of the conductive additive contained in the first layer relative to the mass of the positive electrode composite material contained in the first layer.

2. 2. The positive electrode according to claim 1, wherein a mass fraction of the conductive additive contained in the second layer relative to a mass of the positive electrode composite contained in the second layer is 8 times or more and 10 times or less than a mass fraction of the conductive additive contained in the first layer relative to a mass of the positive electrode composite contained in the first layer.

3. The specific surface area of ​​the conductive additive contained in the second layer is 150 m ２ / g or more 800m ２ 10. The positive electrode of claim 1, wherein the SiO2 content is less than 1000 kJ / g.

4. The positive electrode active material is MnO ２ The positive electrode according to claim 1 ,

5. A solid-state battery comprising the positive electrode according to claim 1 , a solid electrolyte layer, and a negative electrode containing lithium.

6. A method for manufacturing a solid-state battery, comprising: a step of applying a first positive electrode composite material containing a positive electrode active material, a solid electrolyte, and a conductive additive to a first porous metal body; a step of applying a second positive electrode composite material containing a positive electrode active material, a solid electrolyte, and a conductive additive to a second porous metal body; and joining the second porous metal body to a surface of the first porous metal body that faces the solid electrolyte layer, a mass fraction of the conductive additive contained in the second positive electrode composite relative to a mass of the second positive electrode composite is higher than a mass fraction of the conductive additive contained in the first positive electrode composite relative to a mass of the first positive electrode composite.

7. A method for manufacturing a solid-state battery, comprising: a step of applying a first positive electrode composite material containing a positive electrode active material, a solid electrolyte, and a conductive additive to a metal porous body; applying a second positive electrode composite including a positive electrode active material, a solid electrolyte, and a conductive additive to a surface of the metal porous body coated with the first positive electrode composite, the surface being located on the solid electrolyte layer side; a mass fraction of the conductive additive contained in the second positive electrode composite relative to a mass of the second positive electrode composite is higher than a mass fraction of the conductive additive contained in the first positive electrode composite relative to a mass of the first positive electrode composite.

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