All-solid-state batteries

Abstract

This all-solid-state battery is provided with an electrode layer, a solid electrolyte layer, and an intermediate layer that is at least partially arranged between the electrode layer and the solid electrolyte layer; the electrode layer comprises a collector layer and an active material layer; the active material layer contains an active material and a carbon material; the intermediate layer has ion conductivity; and the carbon content in the intermediate layer is lower than the carbon content in the active material layer.

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state battery. This application claims priority based on Japanese Patent Application No. 2019-201864, filed on November 7, 2019, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, electronics technology has made remarkable advances, leading to efforts to make portable electronic devices smaller, lighter, thinner, and more multifunctional. Accordingly, there is a strong demand for smaller, lighter, thinner, and more reliable batteries, which serve as the power source for such electronic devices. Currently, commonly used lithium-ion secondary batteries have traditionally used electrolytes (electrolytic solutions) such as organic solvents as a medium for ion migration. However, batteries with such a configuration pose a risk of electrolyte leakage. Furthermore, because organic solvents and other materials used in the electrolyte solutions are flammable, there is a demand for safer batteries.

[0003] Therefore, as one measure to improve the safety of batteries, the use of a solid electrolyte instead of a liquid electrolyte has been proposed. Furthermore, the development of all-solid-state batteries, which use a solid electrolyte as the electrolyte and also have other solid components, is underway.

[0004] Patent Document 1 proposes an all-solid-state battery that uses an oxide-based solid electrolyte that is stable in air and is produced by an industrially applicable mass-production method in which each component is formed into a sheet, stacked, and then fired simultaneously. However, in order to put the battery into practical use, it was necessary to improve the strength of the battery body while also improving its battery characteristics in order to ensure durability against vibrations and shocks that may occur in the living environment.

[0005] For example, Patent Document 2 states that an all-solid-state battery with improved capacity can be obtained by using a carbon material with a high sintering initiation temperature. However, the method described in Patent Document 2 was unable to obtain a sintered body with sufficient strength. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2007 / 135790 [Patent Document 2] International Publication No. 2013 / 038948 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above problems, and aims to provide an all-solid-state battery having excellent element strength. We discovered that the presence of carbon material at the interface between the active material layer and the solid electrolyte prevents the carbon material from bonding to the solid electrolyte, creating gaps, which act as starting points for cracks and fractures. [Means for solving the problem]

[0008] An all-solid-state battery according to one aspect of the present invention includes an electrode layer, a solid electrolyte layer, and an intermediate layer at least partially between the electrode layer and the solid electrolyte layer, the electrode layer including a current collector layer and an active material layer, the active material layer including an active material and a carbon material, the intermediate layer having ionic conductivity, and a carbon content in the intermediate layer that is lower than the carbon content in the active material layer.

[0009] Furthermore, in the all-solid-state battery according to the above embodiment, the ratio T1 / T2 of the thickness T1 of the intermediate layer to the thickness T2 of the active material layer may be 0.05≦T1 / T2≦1.2.

[0010] Furthermore, in the all-solid-state battery according to the above embodiment, the carbon content in the intermediate layer may be 100 ppm or more and 50,000 ppm or less.

[0011] Furthermore, in the all-solid-state battery according to the above aspect, the intermediate layer may be composed of an active material and elements contained in the solid electrolyte layer.

[0012] Furthermore, in the all-solid-state battery according to the above embodiment, the carbon material may be distributed in the active material layer so that the content thereof increases with increasing distance from the surface in contact with the intermediate layer.

[0013] Furthermore, in the all-solid-state battery according to the above aspect, the carbon contents of the active material layer, the solid electrolyte layer, and the intermediate layer may be greatest in the order of the active material layer, the intermediate layer, and the solid electrolyte layer.

[0014] Furthermore, in the all-solid-state battery according to the above embodiment, the current collector layer may contain carbon.

[0015] Furthermore, in the all-solid-state battery according to the above aspect, the carbon material may be graphite or carbon nanotubes. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide an all-solid-state battery having excellent element strength. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view of an all-solid-state battery according to an embodiment of the present invention; [Figure 2] FIG. 2 is an enlarged view of a main part of the all-solid-state battery according to the present embodiment. [Figure 3] FIG. 2 is an enlarged view of a main part of an all-solid-state battery according to a first modified example. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the all-solid-state battery of the present invention will be described in detail with appropriate reference to the drawings. The drawings used in the following description may show, for the sake of convenience, the characteristic parts enlarged to make the features of the present invention easier to understand. Therefore, the dimensional ratios of the respective components shown in the drawings may be different from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be appropriately changed and implemented within the scope of not changing the gist thereof.

[0019] First, the directions are defined. The direction in which the positive electrode layer 1 and the negative electrode layer 2 described later are laminated is defined as the z direction. Also, one of the in-plane directions in which the positive electrode layer 1 and the negative electrode layer 2 described later extend is defined as the x direction, and the direction orthogonal to the x direction is defined as the y direction.

[0020] (All-solid-state battery) FIG. 1 is an enlarged cross-sectional schematic view of the main part of an all-solid-state battery according to the first embodiment. As shown in FIG. 1, the all-solid-state battery 10 has a laminate 5. The laminate 5 includes a plurality of electrode layers. The all-solid-state battery according to the present embodiment has a plurality of first electrode layers, a plurality of second electrode layers, and a solid electrolyte layer 4 located between the first electrode layer and the second electrode layer. And an intermediate layer 3 is provided at least in part of the portions where the first electrode layer and the solid electrolyte layer 4 are in contact, and the second electrode layer and the solid electrolyte layer 4 are in contact. The positive electrode layer 1 is an example of the first electrode layer, and the negative electrode layer 2 is an example of the second electrode layer. Either the first electrode layer or the second electrode layer functions as a positive electrode, and the other functions as a negative electrode. The positive electrode layer 1 and the negative electrode layer 2 are respectively connected to external terminals of corresponding polarities, and the positive electrode layer 1 and the negative electrode layer 2 do not contact each other.

[0021] The positive electrode layers 1 are respectively connected to the first external terminals 6, and the negative electrode layers 2 are respectively connected to the second external terminals 7. The first external terminals 6 and the second external terminals 7 are electrical contacts with the outside.

[0022] (Laminate) The laminate 5 has a plurality of positive electrode layers 1, a plurality of negative electrode layers 2, a plurality of intermediate layers 3, and a plurality of solid electrolyte layers 4. Between each positive electrode layer 1 and negative electrode layer 2, an intermediate layer 3 and a solid electrolyte layer 4 are located. The all-solid-state battery 10 is charged and discharged by the exchange of lithium ions between the positive electrode layer 1 and the negative electrode layer 2 via the solid electrolyte layer 4.

[0023] (Positive and negative electrode layers) For example, there are multiple positive electrode layers 1 and multiple negative electrode layers 2 in the laminate 5. The positive electrode layers 1 and the negative electrode layers 2 are alternately stacked in the z direction with the solid electrolyte layer 4 sandwiched therebetween. Each positive electrode layer 1 and negative electrode layer 2 extends in the xy plane. A first end of the positive electrode layer 1 is connected to the first external terminal 6, and a second end thereof extends toward the second external terminal 7. The second end of the positive electrode layer 1 is not connected to the second external terminal 7. A first end of the negative electrode layer 2 is connected to the second external terminal 7, and a second end thereof extends toward the first external terminal 6. The second end of the negative electrode layer 2 is not connected to the first external terminal 6. A material similar to the solid electrolyte layer 4 exists between the positive electrode layer 1 and the second external terminal 7 and between the negative electrode layer 2 and the first external terminal 6.

[0024] The positive electrode layer 1 has a positive electrode current collector layer 1A and a positive electrode active material layer 1B. The negative electrode layer 2 has a negative electrode current collector layer 2A and a negative electrode active material layer 2B.

[0025] The positive electrode current collector layer 1A and the negative electrode current collector layer 2A extend in the xy plane. The positive electrode current collector layer 1A and the negative electrode current collector layer 2A contain a material with excellent conductivity. When the all-solid-state battery 10 is divided along the xy plane, the positive electrode current collector layer 1A and the negative electrode current collector layer 2A are portions containing 50% or more of a material with excellent conductivity. Examples of materials with excellent conductivity include silver, palladium, gold, platinum, aluminum, copper, and nickel. Copper does not easily react with the positive electrode active material, the negative electrode active material, and the solid electrolyte. For example, using copper for the positive electrode current collector layer 1A and the negative electrode current collector layer 2A can reduce the internal resistance of the all-solid-state battery 10. The materials constituting the positive electrode current collector layer 1A and the negative electrode current collector layer 2A may be the same or different.

[0026] The positive electrode current collector layer 1A may contain a positive electrode active material, which will be described later. The negative electrode current collector layer 2A may contain a negative electrode active material, which will be described later. The content ratio of the active materials contained in each current collector layer is not particularly limited as long as they function as current collectors. The volume ratio of the conductive material to the positive electrode active material in the positive electrode current collector layer 1A is, for example, within a range of 90:10 to 70:30. Similarly, the volume ratio of the conductive material to the negative electrode active material in the negative electrode current collector layer 2A is, for example, within a range of 90:10 to 70:30. When the positive electrode current collector layer 1A and the negative electrode current collector layer 2A contain a positive electrode active material and a negative electrode active material, respectively, the adhesion between the positive electrode current collector layer 1A and the positive electrode active material layer 1B and the adhesion between the negative electrode current collector layer 2A and the negative electrode active material layer 2B are improved.

[0027] The positive electrode active material layer 1B and the negative electrode active material layer 2B extend in the xy plane. 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 may not be present on the side of the positive electrode current collector layer 1A on which the opposing negative electrode layer 2 is not present. 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 may not be present on the side of the negative electrode current collector layer 2A on which the opposing positive electrode layer 1 is not present. For example, the positive electrode layer 1 or the negative electrode layer 2 located in the uppermost or lowermost layer of the laminate 4 may not have the positive electrode active material layer 1B or the negative electrode active material layer 2B on one side.

[0028] The positive electrode active material layer 1B and the negative electrode active material layer 2B contain an active material that donates and accepts electrons during charge and discharge, and a carbon material that facilitates electron movement. The positive electrode active material layer 1B contains a positive electrode active material. The negative electrode active material layer 2B contains a negative electrode active material. The positive electrode active material layer 1B and the negative electrode active material layer 2B may each contain a conductive additive, an ion-conducting additive, a binder, etc. It is preferable that the positive electrode active material and the negative electrode active material be able to efficiently insert and extract lithium ions. The carbon content contained in the positive electrode active material layer 1B and the negative electrode active material layer 2B can be, for example, 5,000 ppm or more and 100,000 ppm or less. By setting it within this range, a solid-state battery with excellent body strength can be obtained while improving the capacity. Further, this carbon content is preferably 10,000 ppm or more and 70,000 ppm or less, and more preferably 20,000 ppm or more and 50,000 ppm or less.

[0029] The positive electrode active material and the negative electrode active material are, for example, transition metal oxides and transition metal composite oxides. Specifically, the positive electrode active material and the negative electrode active material are, for example, lithium manganese composite oxide Li2Mn a Ma 1-a O3 (0.8 ≦ a ≦ 1, Ma = Co, Ni), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese spinel (LiMn2O4), general formula: LiNi x Co y Mn z O2 (x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1), lithium vanadium compound (LiV2O5), olivine type LiMbPO4 (where Mb is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr), lithium vanadium phosphate (Li3V2(PO4)3, Li2VTi(PO4)3, LiVOPO4), Li2MnO3-LiMcO2 (Mc = Mn, Co, Ni) represented by an Li-excess type solid solution positive electrode, titanium oxide (TiO2, Li4Ti5O 12 )、Li s Ni t Co u Al v O2 (0.9 < s < 1.3, 0.9 < t + u + v < 1.1) and other composite metal oxides.

[0030] The positive electrode active material and the negative electrode active material may be used alone or in combination of two or more of those exemplified above.

[0031] The carbon material is used under conditions that do not cause combustion or volatilization when fired. For example, graphite, carbon nanotubes, graphene, acetylene black, ketjen black, etc. are used and fired in a reducing atmosphere to prevent the carbon material from volatilizing.

[0032] The shape of the carbon material is not limited and may be flat, tubular, needle-like, spherical, or the like, but materials with a large aspect ratio, as shown in FIG. 2, are preferred.

[0033] 2 is an enlarged view of the vicinity of the positive electrode layer 1 of the all-solid-state battery according to this embodiment. Carbon material 11 is distributed mainly in the positive electrode active material layer 1B. The size of the carbon material is, for example, a major axis of 0.2 to 40 μm and a minor axis of 0.1 to 5 μm.

[0034] The size of the carbon material is measured by first polishing or cutting the all-solid-state battery to expose a cross section, then taking an SEM image of the cross section. From the SEM image, carbon material with a minor axis of 0.1 μm or more is marked by image processing or visual inspection, and the particle size is analyzed by image analysis to determine the major and minor axes.

[0035] Particle size analysis is performed by image analysis, and the average major axis and average minor axis obtained are calculated as the size of the carbon material in this embodiment.

[0036] It is preferable that the distribution of the carbon material 11 is similar on the negative electrode layer 2 side.

[0037] There is no clear distinction between the active materials constituting the positive electrode active material layer 1B and the negative electrode active material layer 2B. By comparing the potentials of two types of compounds, the compound exhibiting a more noble potential can be used as the positive electrode active material, and the compound exhibiting a more base potential can be used as the negative electrode active material.

[0038] (Solid electrolyte layer) The solid electrolyte layers 4 are located between each of the positive electrode layers 1 and negative electrode layers 2. The solid electrolyte layers 4 adjacent in the z direction are connected between the positive electrode layer 1 and the second external terminal 7 and between the negative electrode layer 2 and the first external terminal 6 by the same material as the solid electrolyte layers 4.

[0039] The solid electrolyte layer 4 includes a solid electrolyte. The solid electrolyte is a substance (e.g., particles) that can move ions when an externally applied electric field is applied. For example, lithium ions move within the solid electrolyte when an externally applied electric field is applied. The solid electrolyte is also an insulator that inhibits the movement of electrons. The solid electrolyte layer 4 may contain a carbon material. The carbon content of the solid electrolyte layer 4 may be, for example, 100 ppm or more and 10,000 ppm or less.

[0040] The solid electrolyte contains, for example, lithium. The solid electrolyte may be, for example, an oxide-based material or a sulfide-based material. The solid electrolyte may be, for example, a perovskite-type compound, a lithizone-type compound, a garnet-type compound, a nasizone-type compound, a thiolithizone-type compound, a glass compound, or a phosphate compound. La 0.5 Li 0.5 TiO3 is an example of a perovskite compound. 14 Zn(GeO4)4 is an example of a lysicone-type compound. Li7La3Zr2O 12 is an example of a garnet-type compound. LiZr2(PO4)3, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 1.55 Al 0.2 Zr 1.7 Si 0.25 P 9.75 O 12 , Li 1.4 Na 0.1 Zr 1.5 Al 0.5 (PO4)3, Li 1.4 Ca 0.25 Er 0.3 Zr1.7 (PO4) 3.2 , Li 1.4 Ca 0.25 Yb 0.3 Zr 1.7 (PO4) 3.2 is an example of a Nasicon-type compound. 3.25 Ge 0.25 P 0.75 S4 and Li3PS4 are examples of thiolithium-type compounds. Li2S-P2S5 and Li2O-V2O5-SiO2 are examples of glass compounds. Li3PO4 and Li 3.5 Si 0.5 P 0.5 O4, Li 2.9 PO 3.3 N 0.46 is an example of a phosphate compound. The solid electrolyte may contain one or more of these compounds.

[0041] The shape of the solid electrolyte is not particularly limited. The shape of the solid electrolyte may be, for example, spherical, ellipsoidal, needle-like, plate-like, scale-like, tubular, wire-like, rod-like, or amorphous. The particle size of the solid electrolyte is, for example, 0.1 μm to 10 μm, and may be 0.3 μm to 9 μm. The particle size is measured by first polishing or cutting the all-solid-state battery to expose a cross section, then subjecting the battery to heat treatment or chemical treatment to highlight the grain boundaries, and then photographing an SEM cross-sectional image. The grain boundaries of the solid electrolyte are then marked in the obtained SEM image by image processing or visual inspection, and the particle size is then analyzed by image analysis to determine the particle size.

[0042] (middle class) The intermediate layer 3 extends in the xy plane and is disposed so as to be in contact with at least a portion between the positive electrode layer 1 and the solid electrolyte layer 4, and between the negative electrode layer 2 and the solid electrolyte layer 4. The intermediate layer 3 plays an important role in improving the bond between the positive electrode layer 1 and the solid electrolyte layer 4, and between the negative electrode layer 2 and the solid electrolyte layer 4. The intermediate layer 3 exhibits good ionic conductivity because it facilitates the movement of lithium ions between the positive electrode layer 1 and the solid electrolyte layer 4 and between the negative electrode layer 2 and the solid electrolyte layer 4. The bond between the positive electrode layer 1 or the negative electrode layer 2, which is in contact with the intermediate layer, and the solid electrolyte layer 4 is good, and lithium ions can easily move at the interface.

[0043] The composition of the intermediate layer 3 disposed between the positive electrode layer 1 and the solid electrolyte layer 4 and the composition of the intermediate layer 3 disposed between the negative electrode layer 2 and the solid electrolyte layer 4 may be the same or different. It is important that the composition of the intermediate layer 3 has good interfacial bonding with the compositions of the adjacent layers and that lithium ions move easily at the interface.

[0044] In this embodiment, the all-solid-state battery 10 includes a solid electrolyte layer 4, an electrode layer (positive electrode layer 1 or negative electrode layer 2), and an intermediate layer at least partially between the electrode layer and the solid electrolyte layer. The electrode layer (positive electrode layer 1 or negative electrode layer 2) includes a current collector layer (positive electrode current collector layer 1A or negative electrode current collector layer 2A) and an active material layer (positive electrode active material layer 1B or negative electrode active material layer 2B). The active material layer (positive electrode active material layer 1B or negative electrode active material layer 2B) contains an active material and a carbon material. The intermediate layer 3 has ionic conductivity, and the carbon content in the intermediate layer 3 is lower than the carbon content in the active material layer. The ionic conductivity of the intermediate layer 3 is 1×10 -6 It is preferably S / cm or more.

[0045] According to this configuration, the presence of the intermediate layer allows the active material layer containing the active material and the carbon material to be strongly bonded to the solid electrolyte layer via the intermediate layer, thereby improving the strength of the body of the all-solid-state battery. This is thought to be because the placement of an intermediate layer between the active material layer and the solid electrolyte layer, which contains less carbon than the active material layer, reduces gaps that may occur at the interface between the carbon material and the solid electrolyte, thereby strongly bonding the active material layer and the solid electrolyte layer via the intermediate layer and improving the element strength of the all-solid-state battery.

[0046] Furthermore, the ratio T1 / T2 of the thickness T1 of the intermediate layer 3 to the thickness T2 of the active material layer (positive electrode active material layer 1B or negative electrode active material layer 2B) in contact with the intermediate layer is preferably 0.05≦T1 / T2≦1.2.

[0047] According to this configuration, T1 / T2 satisfies the relationship 0.05≦T1 / T2≦1.2, so that the active material layer and the intermediate layer can be strongly bonded to each other, and the element strength of the all-solid-state battery can be improved without reducing the energy density.

[0048] If T1 / T2 is less than 0.05, the bond between the active material layer and the intermediate layer is insufficient, resulting in weak element strength. If T1 / T2 is more than 1.2, the lithium ion conductive layer becomes too thick, which undesirably leads to an increase in the internal resistance of the all-solid-state battery.

[0049] Furthermore, the carbon content in the intermediate layer 3 is preferably 100 ppm or more and 50,000 ppm or less.

[0050] According to this configuration, the intermediate layer 3 has a carbon content of 100 ppm or more and 50,000 ppm or less, so that the active material layer containing the active material and the carbon material and the solid electrolyte layer can be strongly bonded via the intermediate layer, thereby improving the strength of the body of the all-solid-state battery.

[0051] Furthermore, the intermediate layer 3 is preferably composed of elements contained in the adjacent active material layer (positive electrode active material layer 1B or negative electrode active material layer 2B) and the solid electrolyte layer 4.

[0052] According to this configuration, the intermediate layer 3 is composed of an active material (positive electrode active material layer 1B or negative electrode active material layer 2B) and an element contained in the solid electrolyte layer 4, thereby enabling the active material layer (positive electrode active material layer 1B or negative electrode active material layer 2B) containing the active material and the carbon material to be more strongly bonded to the solid electrolyte layer 4 via the intermediate layer, thereby improving the element strength of the all-solid-state battery.

[0053] Furthermore, it is preferable that the carbon material content in the active material layer (positive electrode active material layer 1B or negative electrode active material layer 2B) increases with increasing distance from the surface in contact with the intermediate layer.

[0054] According to this configuration, by reducing the carbon content in the active material layer near the intermediate layer, the active material layer containing the active material and the carbon material can be strongly bonded to the intermediate layer, thereby improving the strength of the body of the all-solid-state battery.

[0055] 3 is an enlarged view of the vicinity of the positive electrode layer 1 of the all-solid-state battery according to the first modified example, and shows that the distribution of the carbon material in the active material layer (positive electrode active material layer 1B or negative electrode active material layer 2B) increases with increasing distance from the surface in contact with the intermediate layer 3. When the positive electrode active material layer 1B is divided into two equal parts in the z direction (thickness direction), it is preferable that the carbon material content be higher on the positive electrode current collector 1A side than on the intermediate layer 3 side.

[0056] The carbon contents of the active material layer, the solid electrolyte layer, and the intermediate layer preferably increase in the order of the active material layer, the intermediate layer, and the solid electrolyte layer.

[0057] According to this configuration, distortion due to differences in shrinkage behavior during firing caused by differences in carbon content at the interface between the active material layer and the intermediate layer and at the interface between the intermediate layer and the solid electrolyte layer is less likely to occur, and bonding strength can be increased.

[0058] The carbon material contained in the active material layer preferably contains at least one material selected from graphite and carbon nanotubes.

[0059] According to this configuration, graphite and carbon nanotubes have stronger mechanical strength as carbon materials themselves than amorphous carbon, and are less likely to volatilize during the de-bindering and firing process, so defects are less likely to occur in the active material layer, thereby improving the strength of the body of the all-solid-state battery.

[0060] (Margin layer) When an electrode layer or an intermediate layer is printed on a solid electrolyte sheet by screen printing, a step occurs between the non-printed portion and the portion where the electrode layer or intermediate layer is printed. In order to eliminate the step, it is preferable to print a margin layer paste on the non-printed portion and provide a margin layer to eliminate the step between the non-printed portion and the portion where the electrode layer or intermediate layer is printed.

[0061] This process reduces stress when stacking sheets to produce a laminate, resulting in a high-quality laminate. In addition, the presence of the margin layer eliminates the step between the solid electrolyte layer 4 and the positive electrode layer 1, and between the solid electrolyte layer 4 and the negative electrode layer 2, increasing the density between the solid electrolyte layer 4 and each electrode layer and making it less likely for delamination or warping to occur during firing of the all-solid-state battery.

[0062] (Terminal) The first external terminal 6 and the second external terminal 7 are made of, for example, a material with excellent conductivity. The first external terminal 6 and the second external terminal 7 are made of, for example, silver, gold, platinum, aluminum, copper, tin, or nickel. The first external terminal 6 and the second external terminal 7 may be a single layer or multiple layers.

[0063] (protective layer) The all-solid-state secondary battery 10 may have a protective layer on the outer periphery that electrically, physically, and chemically protects the laminate 4 and the terminals. The protective layer is preferably made of a material that is excellent in insulation, durability, and moisture resistance, and is environmentally safe. The protective layer is, for example, glass, ceramics, thermosetting resin, or photocurable resin. The protective layer may be made of one type of material, or a combination of two or more types. The protective layer may be a single layer or multiple layers. The protective layer is preferably an organic-inorganic hybrid made by mixing a thermosetting resin and ceramic powder.

[0064] Next, a method for manufacturing the all-solid-state secondary battery according to this embodiment will be described. The all-solid-state secondary battery 10 may be fabricated by a co-firing method or a sequential firing method. The co-firing method is a method in which materials for forming each layer are stacked and then fired all at once. The sequential firing method is a method in which each layer is fired as it is stacked. The co-firing method has a simpler working process than the sequential firing method. Furthermore, the laminate 4 fabricated by the co-firing method is denser than the laminate 4 fabricated by the sequential firing method. Below, an example in which the co-firing method is used will be described.

[0065] First, pastes for the layers constituting the laminate 4 are prepared. Materials for the positive electrode current collector layer 1A, the positive electrode active material layer 1B, the solid electrolyte layer 3, the negative electrode active material layer 2B, and the negative electrode current collector layer 2A are each made into a paste. The method for making the paste is not particularly limited. For example, a paste can be obtained by mixing powders of the respective materials into a vehicle. A vehicle is a general term for a medium in a liquid phase. The vehicle includes a solvent and a binder.

[0066] A filler is added to the voids of at least one of the positive electrode active material layer 1B and the negative electrode active material layer 2B. Examples of the filler include a binder remover, a resin material, and a carbon material. All fillers volatilize during firing. The carbon material used as the filler volatilizes during firing and can be distinguished from the conductive additive. Examples of the filler include flake graphite and a pore-forming material. Examples of the pore-forming material include resin particles such as polyethylene and polypropylene. The filler has an anisotropic shape. The aspect ratio, calculated by dividing the length of the filler in the major axis direction by the length of the minor axis direction, is 2 or more and 29 or less. The filler volatilizes during firing to form anisotropic voids V1.

[0067] Next, a green sheet is produced. The green sheet is obtained by processing the paste into a sheet shape. The green sheet is obtained, for example, by applying the paste to a substrate such as PET (polyethylene terephthalate) in a desired order, drying it as necessary, and then peeling it off from the substrate. The method for applying the paste is not particularly limited. For example, known methods such as screen printing, coating, transfer, doctor blade, etc. can be used.

[0068] When preparing the green sheets for the positive electrode active material layer 1B and the negative electrode active material layer 2B, the carbon material can be oriented in the in-plane direction by controlling the coating speed or by coating through a mesh with openings. When the carbon material is oriented in the in-plane direction, the carbon material is oriented in the in-plane direction in the prepared positive electrode active material layer 1B and the negative electrode active material layer 2B.

[0069] The green sheets thus produced are stacked in the desired order and in the desired number of layers. Alignment, cutting, and other processes are performed as necessary to produce a laminate. When producing a parallel-type or series-parallel-type battery, the positive electrode current collector layer and the negative electrode current collector layer are aligned so that the end faces of the positive electrode current collector layer and the negative electrode current collector layer do not coincide with each other.

[0070] The laminate may be produced after preparing the positive electrode active material layer unit and the negative electrode active material layer unit described below.

[0071] First, the paste for the solid electrolyte layer is formed into a sheet on a PET film by the doctor blade method and dried. Next, the paste for the positive electrode active material layer is printed on the green sheet for the solid electrolyte layer by screen printing and dried.

[0072] Next, a paste for a positive electrode current collector layer is printed by screen printing on the dried paste for a positive electrode active material layer and dried. A paste for a positive electrode active material layer is then printed again by screen printing on the dried paste for a positive electrode current collector layer and dried. The PET film is then peeled off to produce a positive electrode unit. The positive electrode unit is composed of 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 stacked in this order.

[0073] The negative electrode unit is also fabricated in the same manner. The negative electrode unit is formed by laminating the solid electrolyte layer 3 / negative electrode active material layer 2B / negative electrode current collector layer 2A / negative electrode active material layer 2B in this order.

[0074] Next, the positive electrode unit and the negative electrode unit are stacked. The positive electrode unit and the negative electrode unit are stacked so that the solid electrolyte layers of the respective units do not face each other. The stacked laminate is composed of positive electrode active material layer 1B / positive electrode current collector layer 1A / positive electrode active material layer 1B / solid electrolyte layer 3 / negative electrode active material layer 2B / negative electrode current collector layer 2A / negative electrode active material layer 2B / solid electrolyte layer 3 in this order. The positive electrode unit and the negative electrode unit are stacked with a shift so that the positive electrode current collector layer 1A is exposed at a first end face of the laminate and the negative electrode current collector layer 2A is exposed at a second end face opposite the first end face. For example, solid electrolyte layer sheets of a predetermined thickness are further stacked on the top and bottom layers in the stacking direction and dried.

[0075] Next, the produced laminate is pressure-bonded together. The pressure-bonding is performed while heating. The heating temperature is, for example, 40 to 95°C. Next, the pressure-bonded laminate is sintered. For example, the sintering is performed by heating in a temperature range of 500°C or higher and 1000°C or lower in a nitrogen atmosphere. The firing time is, for example, 0.1 to 3 hours. A laminate 4 is obtained by sintering.

[0076] The sintered body may be placed in a cylindrical container together with an abrasive such as alumina and barrel polished. The corners of the sintered body are chamfered by polishing. Polishing may also be performed by sandblasting or the like.

[0077] Then, a first external terminal 6 and a second external terminal 7 are attached to the laminate 5. The first external terminal 6 and the second external terminal 7 are formed so as to be in electrical contact with the positive electrode current collector layer 1A or the negative electrode current collector layer 2A, respectively. For example, the first external terminal 6 is connected to the positive electrode current collector layer 1A exposed from the side surface of the laminate 4, and the second external terminal 7 is connected to the negative electrode current collector layer 2A exposed from the side surface of the laminate 4. The first external terminal 6 and the second external terminal 7 can be produced by, for example, a sputtering method, a screen printing method, a dipping method, a spray coating method, or the like. In the screen printing method and the dipping method, an external electrode paste containing a metal powder, a resin, and a solvent is produced, and this is used to form the first external terminal 6 and the second external terminal 7. Next, a baking process is performed to remove the solvent, and a plating process is performed to form terminal electrodes on the surfaces of the first external terminal 6 and the second external terminal 7. On the other hand, sputtering makes it possible to directly form the external electrodes and terminal electrodes, eliminating the need for baking and plating processes.

[0078] The all-solid-state battery 10 may be sealed, for example, in a coin cell to improve moisture resistance and impact resistance. The sealing method is not particularly limited, and for example, the fired laminate may be sealed with a resin. Alternatively, the laminate may be sealed by applying or dip-coating an insulating paste such as Al2O3 around the laminate and then heat-treating the insulating paste.

[0079] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and can be modified in various ways. [Example]

[0080] The present invention will be described in more detail below using examples and comparative examples based on the above-described embodiment, but the present invention is not limited to these examples. Note that the "parts" used in the amounts of materials used to prepare the paste mean "parts by mass" unless otherwise specified.

[0081] Example 1 The all-solid-state battery of Example 1 was fabricated as follows.

[0082] (Preparation of active material) The active material used was lithium vanadium titanium phosphate, prepared by the following method. Starting materials were Li2CO3, V2O5, TiO2, and NH4H2PO4. The materials were wet-mixed in a ball mill for 16 hours, dehydrated, and dried. The resulting powder was then calcined at 850°C for 2 hours in a nitrogen-hydrogen mixed gas. The calcined product was then wet-pulverized in a ball mill, dehydrated, and dried to obtain the active material. X-ray diffraction confirmed that the powder had the same crystal structure as Li3VTi(PO4)3.

[0083] (Preparation of Paste for Active Material Layer) The active material layer paste was prepared by adding 96 parts of the obtained active material powder and 4 parts of flat-shaped carbon material (graphite: TIMREX (registered trademark) Graphite: KS-6L) powder, 15 parts of ethyl cellulose as a binder, and 65 parts of dihydroterpineol as a solvent, and mixing and dispersing them.

[0084] (Preparation of solid electrolyte) As a solid electrolyte, LATP-based Nasicon-type compounds (e.g., Li 1.3 Al 0.3 Ti 1.7The solid electrolyte powder was obtained by wet-mixing Li2CO3, Al2O3, TiO2, and NH4H2PO4 as starting materials in a ball mill for 16 hours, dehydrating and drying the mixture, and then calcining the resulting powder at 800°C for 2 hours in air. After calcining, the powder was wet-pulverized in a ball mill for 16 hours, and then dehydrating and drying to obtain the solid electrolyte powder. The crystal structure of the resulting powder was confirmed to be the same as that of the LATP-based solid electrolyte using an X-ray diffraction (XRD) analyzer.

[0085] (Preparation of paste for solid electrolyte layer) The paste for the solid electrolyte layer was prepared by adding 100 parts of solid electrolyte powder, 100 parts of ethanol and 200 parts of toluene as solvents, and wet-mixing them in a ball mill, and then adding 16 parts of a polyvinyl butyral binder and 4.8 parts of benzyl butyl phthalate and mixing them to prepare a paste for the solid electrolyte layer.

[0086] (Production of solid electrolyte layer sheet) The paste for the solid electrolyte layer was formed into a sheet using a doctor blade method with a PET film as a substrate, to obtain a sheet for the solid electrolyte layer having a thickness of 15 μm.

[0087] (Preparation of paste for current collector layer) To prepare the current collector, Cu and the active material, lithium vanadium titanium phosphate, were mixed in a volume ratio of 80 / 20, and then 100 parts of this mixture, 10 parts of ethyl cellulose as a binder, and 50 parts of dihydroterpineol as a solvent were added and mixed / dispersed to prepare a paste for the current collector layer.

[0088] (Preparation of intermediate layer substrate) The intermediate layer substrate was prepared by wet mixing the vanadium titanium lithium phosphate powder prepared as the active material with the LATP-based Nasicon-type compound powder prepared as the solid electrolyte in a ball mill for 16 hours, dehydrating and drying the resulting powder, which was then calcined in a nitrogen-hydrogen mixed gas at 850°C for 2 hours. The calcined product was then wet-pulverized in a ball mill, dehydrating and drying to obtain the intermediate layer substrate powder.

[0089] (Preparation of Intermediate Layer Paste) The intermediate layer paste was prepared by adding 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent to 100 parts of the intermediate layer base powder, and mixing and dispersing the mixture.

[0090] (Preparation of margin layer paste) The margin layer paste was prepared by adding 100 parts of LATP-based Nasicon-type compound powder to 100 parts of ethanol and 100 parts of toluene as solvents and wet mixing them in a ball mill, then adding 16 parts of polyvinyl butyral-based binder and 4.8 parts of benzyl butyl phthalate and mixing to produce the margin layer paste.

[0091] (Preparation of external terminal paste) A thermosetting external electrode paste was prepared by mixing and dispersing silver powder, epoxy resin, and a solvent.

[0092] Using these pastes, all-solid-state batteries were fabricated as follows.

[0093] (Fabrication of positive electrode layer unit) A 0.2 μm thick intermediate layer (referred to as the first positive electrode intermediate layer) was formed on the solid electrolyte layer sheet using screen printing and dried at 80°C for 10 minutes. Next, a 5 μm thick positive electrode active material layer (referred to as the first positive electrode active material layer) was formed thereon using screen printing and dried at 80°C for 10 minutes. A 5 μm thick positive electrode current collector layer was further formed thereon using screen printing and dried at 80°C for 10 minutes. A 5 μm thick positive electrode active material layer (referred to as the second positive electrode active material layer) was further formed thereon using screen printing and dried at 80°C for 10 minutes. A 0.2 μm thick intermediate layer (referred to as the second positive electrode intermediate layer) was further formed thereon using screen printing and dried at 80°C for 10 minutes, thereby producing a positive electrode layer on the solid electrolyte layer sheet. Next, a margin layer having a height approximately flush with the positive electrode layer was formed on the outer periphery of one end of the positive electrode layer using screen printing and dried at 80°C for 10 minutes. Next, the PET film was peeled off to obtain a sheet of the positive electrode layer unit.

[0094] (Fabrication of negative electrode layer unit) A 0.2 μm thick intermediate layer (referred to as the first negative electrode intermediate layer) was formed on the solid electrolyte layer sheet using screen printing and dried at 80°C for 10 minutes. Next, a 5 μm thick negative electrode active material layer (referred to as the first negative electrode active material layer) was formed thereon using screen printing and dried at 80°C for 10 minutes. A 5 μm thick negative electrode current collector layer was further formed thereon using screen printing and dried at 80°C for 10 minutes. A 5 μm thick negative electrode active material layer (referred to as the second negative electrode active material layer) was further formed thereon using screen printing and dried at 80°C for 10 minutes. A 0.2 μm thick intermediate layer (referred to as the second negative electrode intermediate layer) was further formed thereon using screen printing and dried at 80°C for 10 minutes, thereby producing a negative electrode layer on the solid electrolyte layer sheet. Next, a margin layer having a height approximately flush with the negative electrode layer was formed on the outer periphery of one end of the negative electrode layer using screen printing and dried at 80°C for 10 minutes. Next, the PET film was peeled off to obtain a sheet of the negative electrode layer unit.

[0095] (Preparation of laminate) A laminated substrate was produced by stacking multiple positive electrode layer units and negative electrode layer units alternately while offsetting each other so that one end of each unit did not coincide. Furthermore, multiple solid electrolyte sheets were stacked on both main surfaces of the laminated substrate as outer layers, forming 200 μm outer layers. This was then thermocompressed using a mold press and cut to produce an unfired all-solid-state battery laminate. The laminate was then de-bindered and fired to obtain an all-solid-state battery laminate. The firing was carried out in nitrogen by increasing the temperature at a rate of 200°C / hour to a firing temperature of 750°C, maintaining the temperature for 2 hours, and then removing the laminate after natural cooling.

[0096] (External electrode formation process) An external terminal paste was applied to the end faces of the laminate of the all-solid-state battery, and thermally cured at 150° C. for 30 minutes to form a pair of external electrodes.

[0097] The dimensions of the fabricated all-solid-state battery were approximately 4.5 mm x 3.2 mm x 1.1 mm.

[0098] Examples 2 to 6 The all-solid-state batteries according to Examples 2 to 6 were fabricated in the same manner as in Example 1, except that the printing thickness of the intermediate layer was adjusted so that the ratio T1 / T2 of the thickness T1 of the intermediate layer after firing to the thickness T2 of the active material layer would be the values ​​shown in Table 1.

[0099] Examples 7 to 10 The all-solid-state batteries according to Examples 7 to 10 were fabricated in the same manner as in Example 4, except that a carbon material was added to the intermediate layer paste or the conditions for removing the binder were adjusted so that the carbon content in the intermediate layer was the value shown in Table 1.

[0100] Example 11 The all-solid-state battery of Example 11 used LiCoPO4 prepared by the following method as the positive electrode active material. The starting materials were Li2CO3, CoO, and NH4H2PO4, which were wet-mixed in a ball mill for 16 hours. The resulting powder was dehydrated and dried, and then calcined at 850°C for 2 hours in an air atmosphere. The calcined product was wet-pulverized in a ball mill, then dehydrated and dried to obtain a positive electrode active material powder. The crystal structure of the prepared powder was confirmed to be the same as that of LiCoPO4 using an X-ray diffractometer.

[0101] The positive electrode intermediate layer substrate was prepared by wet-mixing LiCoPO4 powder prepared as the positive electrode active material with LATP-based solid electrolyte powder prepared as the solid electrolyte in a ball mill for 16 hours, dehydrating and drying the resulting powder, and calcining it in a nitrogen-hydrogen mixed gas at 850°C for 2 hours. The calcined product was then wet-pulverized in a ball mill and dehydrating and drying to obtain the positive electrode intermediate layer substrate powder, which was then used to prepare a positive electrode intermediate layer paste and form the positive electrode intermediate layer.

[0102] An all-solid-state battery was fabricated in the same manner as in Example 3, except that the obtained electrode active material and positive electrode intermediate layer substrate were used.

[0103] Example 12 The solid-state battery of Example 12 used an LZP-based Nasicon-type compound prepared as follows for the solid electrolyte. The starting materials were Li2CO3, ZrO2, CaCO3, and NH4H2PO4. The mixture was wet-mixed in a ball mill for 16 hours, then dehydrated and dried. The resulting powder was then calcined in air at 900°C for 2 hours. After calcination, the mixture was wet-pulverized in a ball mill for 16 hours, then dehydrated and dried to obtain a solid electrolyte powder. X-ray diffractometer (XRD) confirmed that the crystal structure of the resulting powder was the same as that of LiZr2(PO4)3.

[0104] Then, an all-solid-state battery was fabricated in the same manner as in Example 4, except that the fabricated LZP-based Nasicon-type compound was used and the firing temperature was set to 1000°C.

[0105] Example 13 The all-solid-state battery of Example 13 used Li3Fe2(PO4)3 prepared by the following method as the positive electrode active material. The preparation method involved wet-mixing Li2CO3, Fe2O3, and NH4H2PO4 as starting materials in a ball mill for 16 hours, dehydrating and drying the resulting powder, and calcining it at 850°C for 2 hours in an air atmosphere. The calcined product was then wet-pulverized in a ball mill and dehydrating and drying to obtain a positive electrode active material powder. The crystal structure of the prepared powder was confirmed to be the same as that of Li3Fe2(PO4)3 using an X-ray diffractometer.

[0106] Next, to prepare the positive electrode intermediate layer substrate, LiCoPO4 powder prepared as the positive electrode active material and LATP-based solid electrolyte powder prepared as the solid electrolyte were wet mixed in a ball mill for 16 hours, and the resulting powder after dehydration and drying was calcined in a nitrogen-hydrogen mixed gas at 850°C for 2 hours. The calcined product was wet-pulverized in a ball mill, and then dehydration and drying were performed to obtain the positive electrode intermediate layer substrate powder.

[0107] The negative electrode active material was Li4Ti5O prepared by the following method. 12The method of preparation was to use Li2CO3 and TiO2 as starting materials, wet mix them in a ball mill for 16 hours, dehydrate and dry the resulting powder, and then calcined it in the air at 1000°C for 2 hours. The calcined product was then wet pulverized in a ball mill, and then dehydrated and dried to obtain the negative electrode active material powder. The crystal structure of the powder was Li4Ti5O 12 It was confirmed using an X-ray diffraction apparatus that the results were the same as those shown in the above.

[0108] Next, to prepare the negative electrode intermediate layer substrate, LiCoPO4 powder prepared as the negative electrode active material and LATP-based solid electrolyte powder prepared as the solid electrolyte were wet mixed in a ball mill for 16 hours, and the resulting powder after dehydration and drying was calcined in a nitrogen-hydrogen mixed gas at 850°C for 2 hours. The calcined product was wet-pulverized in a ball mill, and then dehydration and drying were performed to obtain the negative electrode intermediate layer substrate powder.

[0109] The obtained positive electrode active material and negative electrode active material. An all-solid-state battery was produced in the same manner as in Example 3, except that an intermediate layer base material was used.

[0110] Example 14 The all-solid-state battery according to Example 14 was produced in the same manner as in Example 4, except that a substrate obtained by the following production method was used to produce the intermediate layer substrate.

[0111] The intermediate layer substrate was prepared by wet-mixing the Li3VTi(PO4)3 powder and ZrO2 powder prepared as the positive and negative electrode active materials in a ball mill for 16 hours, dehydrating and drying the resulting powder, and calcining it in a nitrogen-hydrogen mixed gas at 850°C for 2 hours. The calcined product was then wet-pulverized in a ball mill, dehydrating and drying to obtain the intermediate layer substrate powder.

[0112] (Examples 15 to 17) The all-solid-state batteries according to Examples 15 to 17 were fabricated in the same manner as in Example 4, except that the carbon materials used in preparing the paste for the positive electrode active material layer and the paste for the negative electrode active material layer were spherical 1 (graphite), tubular, and spherical 2 (amorphous carbon) listed in Table 1, respectively.

[0113] Example 18 The all-solid-state battery according to Example 18 was fabricated so that the carbon material content in the positive electrode active material layer and the negative electrode active material layer increased with increasing distance from the surface in contact with the intermediate layer.

[0114] Specifically, to prepare a paste for a positive electrode active material layer and a paste for a negative electrode active material layer, 95 parts of Li3VTi(PO4)3 powder and 5 parts of a flat-shaped carbon material (graphite: TIMREX (registered trademark) Graphite: KS-6L) powder were added with 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent, and the mixture was mixed and dispersed to prepare a paste for a positive electrode active material layer and a paste for a negative electrode active material layer (Paste A). To prepare a paste for a positive electrode active material layer and a paste for a negative electrode active material layer (Paste B), 97 parts of Li3VTi(PO4)3 powder and 3 parts of a flat-shaped carbon material (graphite: TIMREX (registered trademark) Graphite: KS-6L) powder were added with 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent, and the mixture was mixed and dispersed to prepare a paste for a positive electrode active material layer and a paste for a negative electrode active material layer.

[0115] Using these pastes, a 1.5 μm thick intermediate layer (referred to as a first positive electrode intermediate layer) was formed on a solid electrolyte layer sheet by screen printing, and then dried at 80°C for 10 minutes. Next, Paste B was printed thereon by screen printing to form a 2.5 μm thick positive electrode active material layer (referred to as a first positive electrode active material layer B), and then dried at 80°C for 10 minutes. Paste A was then printed thereon by screen printing to form a 2.5 μm thick positive electrode active material layer (referred to as a first positive electrode active material layer A), and then dried at 80°C for 10 minutes. A 5 μm thick positive electrode current collector layer was then formed thereon by screen printing, and then dried at 80°C for 10 minutes. Paste A was then printed thereon by screen printing to form a 2.5 μm thick positive electrode active material layer (referred to as a second positive electrode active material layer A), and then dried at 80°C for 10 minutes. Furthermore, paste B was printed thereon using screen printing to form a 2.5 μm thick positive electrode active material layer (referred to as second positive electrode active material layer B), which was then dried at 80°C for 10 minutes. Furthermore, a 1.5 μm thick intermediate layer (referred to as second positive electrode intermediate layer) was again formed thereon using screen printing, which was then dried at 80°C for 10 minutes, thereby producing a positive electrode layer on the solid electrolyte layer sheet. Next, a margin layer of approximately the same height as the positive electrode layer was formed on the outer periphery of one end of the positive electrode layer using screen printing, which was then dried at 80°C for 10 minutes. Next, the PET film was peeled off to obtain a positive electrode layer unit sheet. A negative electrode layer unit sheet was also produced in the same manner as the positive electrode layer unit sheet.

[0116] An all-solid-state battery was fabricated in the same manner as in Example 3 except for the steps described above.

[0117] (Comparative Example 1) The all-solid-state battery according to Comparative Example 1 was fabricated in the same manner as in Example 1, except that no intermediate layer was printed, the binder was removed, and the firing process was performed under conditions of atmosphere and firing temperature profile so as to prevent element diffusion between the active material layer and the solid electrolyte layer.

[0118] (Examples 19 to 30) Examples 19 to 21 show the results of measuring the carbon content of the active material layer and solid electrolyte layer in addition to the intermediate layer for the all-solid-state batteries fabricated in Examples 8 to 10. In addition, in Examples 22 to 30, all-solid-state batteries were fabricated in the same manner as in Example 4, except that a carbon material was added to the intermediate layer paste, active material layer paste, and solid electrolyte layer paste, or the binder removal conditions were adjusted so that the carbon contents of the intermediate layer, active material layer, and solid electrolyte layer were the values ​​shown in Table 2, respectively.

[0119] (evaluation) The all-solid-state batteries fabricated in the present examples and comparative examples were evaluated for the following battery characteristics.

[0120] [Carbon content in intermediate layer, active material layer, and solid electrolyte layer] In the all-solid-state battery produced in this example, the amounts of carbon contained in the intermediate layer, active material layer, and solid electrolyte layer were measured as follows.

[0121] First, the all-solid-state battery was polished while embedded in a resin such as epoxy resin to expose the cross section of the intermediate layer. To measure the largest possible area, it is preferable to polish the surface obliquely, close to horizontal, rather than perpendicular to the stacking direction. Next, the carbon content (concentration) was measured using EPMA (WDS = wavelength dispersive spectroscopy). The measurement conditions were an acceleration voltage of 10 kV, a measurement current of 500 nA, a peak measurement time of 80 seconds, a background measurement time of 20 seconds, and a minimum spot diameter. To eliminate the influence of measurement errors due to hydrocarbon contamination inside the device, measurements were performed using a liquid nitrogen trap. The same procedure was performed on the active material layer and solid electrolyte layer.

[0122] [Three-point bending test] The strength of the all-solid-state battery was evaluated by a three-point bending test in accordance with JIS R 1601.

[0123] [Internal resistance] The internal resistance was measured using the AC impedance method. At 30°C, an impedance analyzer was used to apply an AC voltage of 10 mV amplitude at frequencies from 10 mV to 1 MHz with a closed circuit voltage of 0 V, and the impedance was measured from the response current. The measured impedance was plotted on a Nyquist diagram and calculated by fitting with an RC parallel circuit.

[0124] (result) Table 1 shows the results of the three-point bending test and the internal resistance of the all-solid-state batteries according to Examples 1 to 18 and Comparative Example 1. Table 2 also shows the results of the three-point bending test and the internal resistance of the all-solid-state batteries according to Examples 19 to 30.

[0125] [Table 1]

[0126] [Table 2]

[0127] In the all-solid-state batteries according to Examples 1 to 30, better results than the all-solid-state battery according to Comparative Example 1 were confirmed in the three-point bending test.

[0128] Furthermore, in the all-solid-state batteries according to Examples 1 to 6, particularly when the ratio T1 / T2 of the thickness T1 of the intermediate layer to the thickness T2 of the active material layer satisfies 0.05≦T1 / T2≦1.2, better three-point bending test results and internal resistance were confirmed. This is because when T1 / T2 is less than 0.05, the bonding between the active material layer and the solid electrolyte layer is insufficient, and the element strength is weaker, compared to when T1 / T2 is 0.05 or more, resulting in poor three-point bending test results. When T1 / T2 is greater than 1.2, the distance between the positive and negative electrodes is longer than when T1 / T2 is 1.2 or more, making it more difficult for lithium ions to move, which is thought to contribute to an increase in the internal resistance of the all-solid-state battery.

[0129] Furthermore, in the all-solid-state batteries according to Examples 4 and 7 to 10, better results in the three-point bending test were confirmed, particularly when the carbon content in the intermediate layer was 100 ppm or more and 5,000 ppm or less. This is thought to be because cracks are more likely to occur at the interface between the intermediate layer and the active material layer when the carbon content is less than 100 ppm compared to when it is 100 ppm or more, and cracks are more likely to occur at the interface between the intermediate layer and the solid electrolyte layer when the carbon content is more than 5,000 ppm compared to when it is 5,000 ppm or less.

[0130] The all-solid-state battery according to Example 11 is an all-solid-state battery in which the positive electrode active material is changed and the positive electrode active material and the negative electrode active material are different. The all-solid-state battery according to Example 12 is an all-solid-state battery in which the solid electrolyte is changed. The all-solid-state battery according to Example 13 is an all-solid-state battery in which the positive electrode active material and the negative electrode active material are changed and the positive electrode active material and the negative electrode active material are different. As such, even when the positive electrode active material, solid electrolyte, and negative electrode active material were changed to various substrates, the three-point bending test results were confirmed to be better than those of the all-solid-state battery according to Comparative Example 1.

[0131] On the other hand, it was confirmed that the results of the three-point bending test were inferior for the all-solid-state battery of Example 14 compared to Example 4. This is thought to be because the constituent elements of the intermediate layer include an element (Zr) that is not contained in the adjacent active material layer or solid electrolyte layer, which reduces the adhesion between the active material layer of the intermediate layer and the solid electrolyte layer, resulting in the inferior results of the three-point bending test.

[0132] Furthermore, the all-solid-state batteries according to Examples 15 to 17 are all-solid-state batteries in which the carbon material was changed from that of Example 4. These all-solid-state batteries were confirmed to have better three-point bending test results than the all-solid-state battery according to Comparative Example 1. It was confirmed that Example 17, which used amorphous carbon as a carbon material, had slightly worse three-point bending test results than Examples 4, 15, and 16. This is thought to be because amorphous carbon has weaker mechanical strength than graphite and carbon nanotubes, and is more likely to volatilize during the de-bindering and calcination process, which makes it easier for defects to form in the active material layer, resulting in slightly worse three-point bending test results.

[0133] The all-solid-state battery of Example 18 is an all-solid-state battery in which the distribution of the carbon material in the active material layer increases with increasing distance from the surface in contact with the intermediate layer. It was confirmed that the three-point bending test results were superior to those of Example 3, in which the distribution of the carbon material was uniform. This is thought to be because by reducing the carbon content in the active material layer near the intermediate layer, it is possible to strongly bond the active material layer containing the active material and the carbon material to the intermediate layer.

[0134] In the all-solid-state batteries according to Examples 19 to 21, the carbon content in the intermediate layer was 2.3% to 16.7% relative to the carbon content in the active material layer, and 2.9 to 25 times relative to the carbon content in the solid electrolyte layer. In the all-solid-state batteries according to Examples 22 to 27, the carbon content in the intermediate layer was 25% to 90.9% relative to the carbon content in the active material layer, and 7.1 to 166.7 times relative to the carbon content in the solid electrolyte layer. In the all-solid-state batteries according to Examples 28 to 30, the carbon content in the intermediate layer was 2.5% to 17.5% relative to the carbon content in the active material layer, and 0.5 to 0.74 times relative to the carbon content in the solid electrolyte layer. In the all-solid-state batteries according to Examples 19 to 30, in which the carbon content in the intermediate layer was about 2% to about 90% compared to the carbon content in the active material layer, better results in the three-point bending test were confirmed than in the all-solid-state battery according to Comparative Example 1. In the all-solid-state batteries according to Examples 19 to 30, in which the carbon content in the intermediate layer was 0.5 to approximately 166 times that of the carbon content in the solid electrolyte layer, better results in the three-point bending test were confirmed than in the all-solid-state battery according to Comparative Example 1.

[0135] In both cases where the carbon content in the intermediate layer was greater than the carbon content in the solid electrolyte layer (Examples 19 to 27) and conversely, where it was smaller (Examples 28 to 30), the three-point bending test results were found to be superior to those of the all-solid-state battery according to Comparative Example 1. Comparing Examples 19 to 21 with Examples 28 to 30, when the carbon content in the intermediate layer was 7000 ppm or less, the configuration in which the carbon content was greatest in the active material layer, intermediate layer, and solid electrolyte layer, in that order, showed better results in the three-point bending test than the configuration in which the carbon content was greatest in the active material layer, solid electrolyte layer, and intermediate layer, in that order.

[0136] Although the present invention has been described in detail above, the above-described embodiments and examples are merely illustrative, and the invention disclosed herein includes various modifications and variations of the above-described specific examples. [Explanation of symbols]

[0137] 1...positive electrode layer, 1A...positive electrode current collector layer, 1B...positive electrode active material layer, 2...negative electrode layer, 2A...Negative electrode current collector layer, 2B...Negative electrode active material layer, 3. Middle class 4...Solid electrolyte layer, 5...Laminate, 6...First external terminal, 7...Second external terminal, 11...carbon materials,

Claims

1. an electrode layer, a solid electrolyte layer, and an intermediate layer at least partially between the electrode layer and the solid electrolyte layer; the electrode layer includes a current collector layer and an active material layer, the active material layer contains an active material and a carbon material, the intermediate layer has ionic conductivity, the intermediate layer contains the active material and carbon derived from a solid electrolyte constituting the solid electrolyte layer, the carbon content in the intermediate layer is less than the carbon content in the active material layer, the carbon contents of the active material layer, the solid electrolyte layer, and the intermediate layer are greatest in the active material layer, the intermediate layer, and the solid electrolyte layer in that order; the carbon content of the solid electrolyte layer is 100 ppm or more and 10,000 ppm or less; The all-solid-state battery, wherein the carbon content in the intermediate layer is 100 ppm or more and 50,000 ppm or less.

2. 2. The all-solid-state battery according to claim 1, wherein a ratio T1 / T2 of a thickness T1 of the intermediate layer to a thickness T2 of the active material layer satisfies 0.05≦T1 / T2≦1.

2.

3. 3. The all-solid-state battery according to claim 1, wherein the intermediate layer is composed of elements contained in the active material layer and the solid electrolyte layer.

4. The all-solid-state battery according to claim 1 , wherein the carbon material content in the active material layer increases with increasing distance from a surface in contact with the intermediate layer.

5. The all-solid-state battery according to claim 1 , wherein the current collector layer contains carbon.

6. The all-solid-state battery according to claim 1 , wherein the carbon material contains at least one material selected from the group consisting of graphite and carbon nanotubes.

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