All-solid-state batteries

Abstract

This all-solid-state battery is equipped with a positive electrode which has a positive electrode active material layer, a negative electrode which has a negative electrode active material layer, and a solid electrolyte layer located between the positive electrode active material layer and the negative electrode active material layer. The negative electrode active material layer contains a titanium compound. The solid electrolyte layer contains an LAGP compound represented by Li1+xAlxGe2-x(PO4)3(x is a number which satisfies 0<x<1). The interior of the negative electrode active material layer and / or the interface between the negative electrode active material layer and the solid electrolyte layer contain an LATGP compound represented by Li1+yAlyTizGe2-y-z(PO4)3(y and z are numbers which satisfy 0<y<1 and 0<z<1).

Description

Technical Field

[0001] The present invention relates to all-solid-state batteries. This application claims priority based on Japanese Patent Application No. 2021-111458 filed in Japan on July 5, 2021, and incorporates its content herein.

Background Art

[0002] Lithium-ion secondary batteries, which are representative of secondary batteries, are widely used in various applications such as notebook computers, mobile phones, digital cameras, and automobiles because they are lightweight, small-sized, and have a high capacity. Currently, commonly used lithium-ion secondary batteries use a liquid electrolyte containing a lithium salt in an organic solvent. Therefore, for lithium-ion secondary batteries, strict safety measures against flammability, liquid leakage, short circuit, overcharging, etc. are required. From such a perspective, in recent years, research and development on all-solid-state batteries using a solid electrolyte as an electrolyte have been actively conducted.

[0003] An all-solid-state battery is composed of a laminate having a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer containing a solid electrolyte between the positive electrode active material layer and the negative electrode active material layer, and is roughly classified according to the type of the solid electrolyte. The types of solid electrolytes mainly include oxide-based and sulfide-based. In particular, oxide-based solid electrolytes are excellent in chemical stability. As an all-solid-state battery using an oxide-based solid electrolyte, for example, an all-solid-state battery using a solid electrolyte having a NASICON-type crystal structure has been reported.

[0004] For example, in Patent Document 1, there is disclosed a laminate for an all-solid-state lithium secondary battery including an active material layer and a solid electrolyte layer sintered and joined to the active material layer, wherein when analyzed by X-ray diffraction method, no components other than the components of the active material layer and the components of the solid electrolyte layer are detected.

[0005] Also, in Patent Document 2, the general formula Li 1+x Alx Ge 2-x A sintered battery is disclosed, which contains a solid electrolyte material represented by (PO4)3 (0≦x≦2) and an active material material containing Li, Ti, and O, and is characterized in that when analyzed by X-ray diffraction, components other than the solid electrolyte material and the active material material are detected at the interface between the solid electrolyte material and the active material material.

[0006] Furthermore, Patent Document 3 discloses an all-solid-state battery comprising a negative electrode layer, a solid electrolyte layer laminated on the negative electrode layer, and an intervening layer interposed between the negative electrode layer and the solid electrolyte layer, wherein the intervening layer contains a second solid electrolyte material different from a first solid electrolyte material contained in the solid electrolyte layer, and the second solid electrolyte material has a wider potential window than the first solid electrolyte material. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2007-5279 [Patent Document 2] Japanese Patent Publication No. 2012-104280 [Patent Document 3] International Publication No. 2013 / 137224 [Overview of the project] [Problems that the invention aims to solve]

[0008] As described above, controlling the interface composition at the interface between the solid electrolyte layer and the active material layer is effective in improving the discharge characteristics of all-solid-state batteries. However, depending on the material composition of the interface, the interface resistance may increase, which can lead to a decrease in discharge capacity during high-rate discharge and other deteriorations in discharge characteristics. In this respect, further improvements are needed in the material composition at the interface between the solid electrolyte layer and the active material layer to obtain higher discharge characteristics.

[0009] The present invention has been made to solve the above problems, and an object thereof is to provide an all-solid-state battery having a high discharge capacity during high-rate discharge and excellent discharge characteristics.

Means for Solving the Problems

[0010] As a result of intensive studies, the present inventors have found that the negative electrode active material layer contains at least a titanium compound, and the solid electrolyte layer contains Li 1+x Al x Ge 2-x (PO4)3 (0 < x < 1). In an all-solid-state battery containing a LAGP compound represented by this, by including Li 1+y Al y Ti z Ge 2-y-z (PO4)3 (0 < y < 1, 0 < z < 1) represented by LATGP compound in either one or both of the negative electrode active material layer and the interface between the negative electrode active material layer and the solid electrolyte layer, it has been found that the discharge capacity during high-rate discharge increases. That is, the present invention provides the following means to solve the above problems.

[0011] [1] A positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a solid electrolyte layer between the positive electrode active material layer and the negative electrode active material layer, The negative electrode active material layer contains at least a titanium compound, The solid electrolyte layer contains a LAGP compound represented by the following formula (1), Li 1+x Al x Ge 2-x (PO4)3 (1) (However, in formula (1), x is a number satisfying 0 < x < 1.) An all-solid-state battery in which either one or both of the negative electrode active material layer and the interface between the negative electrode active material layer and the solid electrolyte layer contain a LATGP compound represented by the following formula (2). Li 1+y Al y Ti z Ge 2-y-z (PO4)3 (2) (However, in formula (2), y and z are numbers that satisfy 0 < y < 1 and 0 < z < 1.)

[0012] [2] The titanium compound includes either one or both of TiO2 and Li4Ti5O, the all-solid-state battery according to [1] above. 12

[0013] [3] In the formula (2), y and z are numbers that satisfy 0.11 ≤ y + z ≤ 1 and 0.01 ≤ z / y ≤ 9, the all-solid-state battery according to [1] or [2] above.

[0014] [4] The negative electrode active material layer includes either one or both of a carbon-based material and the LAGP compound represented by the formula (1), the all-solid-state battery according to any one of [1] to [3] above.

[0015] [5] The solid electrolyte layer has a porosity of 40% or less, the all-solid-state battery according to any one of [1] to [4] above. [Advantages of the Invention]

[0016] According to the present invention, it is possible to provide an all-solid-state battery having a high discharge capacity during high-rate discharge and excellent discharge characteristics. [Brief Description of the Drawings]

[0017] [Figure 1] It is a cross-sectional schematic view of the all-solid-state battery according to this embodiment. [Figure 2] It is a cross-sectional schematic view of the solid electrolyte layer of the all-solid-state battery according to this embodiment and the negative electrode active material layer and the positive electrode active material layer around it. [Figure 3] It is a cross-sectional schematic view of the solid electrolyte layer of the all-solid-state battery according to the first modification example and the negative electrode active material layer and the positive electrode active material layer around it. [Figure 4] It is a cross-sectional schematic view of the solid electrolyte layer of the all-solid-state battery according to the second modification example and the negative electrode active material layer and the positive electrode active material layer around it. [Modes for Carrying Out the Invention] ​

[0018] The present embodiment will be described in detail below with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience to clearly illustrate the features of the present invention, and the dimensional ratios of each component may differ from those in reality. The materials, dimensions, etc., exemplified in the following description are examples only, and the present invention is not limited to them. It can be implemented with appropriate modifications without altering its essence.

[0019] [All-solid battery] Figure 1 is a schematic cross-sectional view of the all-solid-state battery 10 according to this embodiment. The all-solid-state battery 10 has a laminate 4, a positive electrode terminal 5, and a negative electrode terminal 6. The positive electrode terminal 5 and the negative electrode terminal 6 are in contact with opposing surfaces of the laminate 4, respectively. The positive electrode terminal 5 and the negative electrode terminal 6 extend in a direction that intersects (is perpendicular to) the laminate surface of the laminate 4.

[0020] The laminate 4 has a positive electrode 1, a negative electrode 2, and a solid electrolyte layer 3. The number of layers for the positive electrode 1 and negative electrode 2 is irrelevant. The solid electrolyte layer 3 is located between the positive electrode 1 and the negative electrode 2, between the positive electrode 1 and the negative electrode terminal 6, and between the negative electrode 2 and the positive electrode terminal 5. One end of the positive electrode 1 is connected to the positive electrode terminal 5. One end of the negative electrode 2 is connected to the negative electrode terminal 6.

[0021] The all-solid-state battery 10 charges or discharges by the exchange of ions between the positive electrode 1 and the negative electrode 2 via the solid electrolyte layer 3. Figure 1 shows a stacked battery, but a wound-type battery may also be used. The all-solid-state battery 10 can be used in, for example, laminated batteries, prismatic batteries, cylindrical batteries, coin-type batteries, button-type batteries, etc.

[0022] "Solid electrolyte layer" The solid electrolyte layer 3 contains a solid electrolyte. The solid electrolyte is a material that can move ions by an externally applied electric field. The solid electrolyte layer 3 has lithium ion conductivity and inhibits electron movement. The solid electrolyte layer 3 is, for example, a sintered body obtained by sintering.

[0023] The solid electrolyte layer 3 contains an LAGP compound represented by the following formula (1). Li 1+x Al x Ge 2-x (PO4)3(1) However, in formula (1), x is a number satisfying 0 < x < 1. Although x is not particularly limited, it is preferably a number satisfying 0.1 ≤ x ≤ 0.9.

[0024] The solid electrolyte layer 3 may be a sintered body of the powder of the above LAGP compound. The solid electrolyte layer 3 may contain substances other than the LAGP compound. For example, the solid electrolyte layer 3 can contain a binder for the solid electrolyte. The binder for the solid electrolyte can use the same material as the subsequent binder for the positive electrode and the binder for the negative electrode. In the solid electrolyte layer 3, the content of the LAGP compound is not particularly limited, but it is preferably 80% by mass or more. Also, the solid electrolyte contained in the solid electrolyte layer 3 may be a single body of one type of LAGP compound or a mixture containing the LAGP compound and other solid electrolytes. As other solid electrolytes, general solid electrolytes such as oxide-based lithium ion conductors having any one of the crystal structures of the NASICON type, garnet type, and perovskite type can be included. As the oxide-based lithium ion conductor having a NASICON-type crystal structure, a solid electrolyte containing at least Li and M (M is at least one of Ti, Zr, Ge, Hf, Sn) and P and O (for example, Li 1+x Al x Ti 2-x (PO4)3; LATP) can be used. As the oxide-based lithium ion conductor having a garnet-type crystal structure, a solid electrolyte containing at least Li, Zr, La, and O (for example, Li7La3Zr2O 12 ; LLZ) can be used. As the oxide-based lithium ion conductor having a perovskite-type structure, a solid electrolyte containing at least Li, Ti, La, and O (for example, Li 3x La 2 / 3-x TiO3; LLTO) can be mentioned.

[0025] The solid electrolyte layer 3 may have a porosity of 40% or less. Porosity is the percentage of the area of ​​the space where the solid electrolyte is not present relative to the observed area when observing the cross-section of the solid electrolyte layer. A scanning electron microscope (SEM) can be used to observe the cross-section of the solid electrolyte layer. The porosity of the solid electrolyte layer 3 is not particularly limited, but is more preferably 30% or less, and even more preferably 20% or less.

[0026] "Positive electrode" As shown in Figure 1, the positive electrode 1 includes, for example, a positive electrode current collector layer 1A containing at least a conductive material and a positive electrode active material layer 1B containing at least a positive electrode active material.

[0027] (Positive electrode current collector layer) The positive electrode current collector layer 1A comprises at least a conductive material. Furthermore, the positive electrode current collector layer 1A may also comprise a positive electrode binder and the aforementioned solid electrolyte (LAGP compound). The positive electrode current collector layer 1A may be in the form of powder, foil, punched, or expanded material.

[0028] Examples of conductive materials include silver, palladium, gold, platinum, aluminum, copper, nickel, and carbon. The content of conductive material in the positive electrode current collector layer 1A is not particularly limited, but is preferably 10% by mass or more. Examples of the carbon mentioned above include graphite, carbon black, acetylene black, Ketjenblack, graphene, carbon nanotubes, and vapor-processed carbon fibers (VGCF).

[0029] The positive electrode binder may be included in a range that does not impair the function of the positive electrode current collector layer 1A. The content of the positive electrode binder in the positive electrode current collector layer 1A can be, for example, in the range of 0.5 to 30 mass%. If the content of the positive electrode binder is less than 0.5 mass%, the bonding of the various materials constituting the positive electrode current collector layer 1A may be insufficient, and the internal resistance of the positive electrode current collector layer 1A may increase. If it is more than 30 mass%, the positive electrode binder becomes a resistive component, and the internal resistance of the positive electrode current collector layer 1A may increase. Note that the positive electrode binder may be omitted if it is not needed.

[0030] For the positive electrode binder, for example, organic binders and inorganic binders can be used. Examples of organic binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) cellulose, polyvinyl butyral, ethylcellulose, styrene-butadiene rubber (SBR), ethylene-propylene rubber, polyacrylate (PAA) polyimide resin (PI), and polyamide-imide resin (PAI). In addition, conductive polymers with electronic conductivity or ionic conductive polymers may be used as organic binders. Examples of conductive polymers with electronic conductivity include polyacetylene. In this case, since the organic binder also functions as conductive additive particles, it may not be necessary to add a conductive additive. As ion-conducting polymers, for example, those that conduct lithium ions can be used, and examples include composites of monomers of polymer compounds (polyether polymer compounds such as polyethylene oxide and polypropylene oxide, polyphosphozenes, etc.) and lithium salts such as LiClO4, LiBF4, LiPF6, or alkali metal salts mainly composed of lithium. As polymerization initiators used in the composites, for example, photopolymerization initiators or thermal polymerization initiators that are compatible with the above monomers can be used. Examples of inorganic binders include lithium halides, silicate compounds, phosphate compounds, and low-melting-point glasses. The properties required of a cathode binder include oxidation-reduction resistance and good adhesion.

[0031] Furthermore, the positive electrode current collector layer 1A may contain a solid electrolyte to an extent that does not impair its function as a positive electrode current collector layer. The solid electrolyte is preferably the LAGP compound contained in the solid electrolyte layer 3 described above. In addition, if a firing process is included in the manufacturing of the all-solid-state battery, the solid electrolyte contained in the positive electrode current collector layer 1A can alleviate the shrinkage stress of the positive electrode current collector layer 1A due to firing, thereby suppressing cracks and fractures that may occur.

[0032] (Cathode active material layer) The positive electrode active material layer 1B is formed on one or both sides of the positive electrode current collector layer 1A. The positive electrode active material layer 1B contains at least positive electrode active material. The positive electrode active material layer 1B may also contain a conductive additive, a positive electrode binder, and the above-mentioned solid electrolyte (LAGP compound).

[0033] (Cathode active material) The positive electrode active material is not particularly limited as long as it can reversibly carry out lithium ion release and intercalation, and lithium ion desorption and insertion. For example, positive electrode active materials used in known lithium-ion secondary batteries can be used.

[0034] The positive electrode active material is, for example, a transition metal oxide, a composite transition metal oxide, etc.

[0035] The positive electrode active material is a transition metal oxide represented by, for example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese spinel (LiMn2O4), and the general formula: LiNi x Co y Mn z M a Composite transition metal oxides represented by O2 (x+y+z+a=1, 0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦a≦1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), lithium vanadium compounds (LiV2O5, Li3V2(PO4)3, LiVOPO4), olivine-type LiMPO4 (where M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, V, Nb, Ti, Al, Zr), LiNix Co y Al z It is O2(0.9 < x + y + z < 1.1) or the like.

[0036] As the positive electrode active material in the present disclosure, it is preferable to use a phosphate compound, and it is preferably any one or more of lithium vanadium phosphate (LiVOPO4, Li3V2(PO4)3, Li4(VO)(PO4)2), lithium vanadium pyrophosphate (Li2VOP2O7, Li2VP2O7), and Li9V3(P2O7)3(PO4)2, and particularly preferably one or both of LiVOPO4 and Li3V2(PO4)3. The content of the positive electrode active material in the positive electrode active material layer 1B is not particularly limited, but is preferably 40% by mass or more.

[0037] The conductive assistant contained in the positive electrode active material layer 1B is not particularly limited as long as it improves the electron conductivity in the positive electrode active material layer 1B, and known conductive assistants can be used. Examples of the conductive assistant include carbon-based materials such as graphite, carbon black, acetylene black, ketjen black, graphene, carbon nanotubes, and vapor-grown carbon fibers (VGCF), metals such as gold, platinum, silver, palladium, aluminum, copper, nickel, stainless steel, and iron, conductive oxides such as ITO, or mixtures thereof. The conductive assistant may be in the form of powder or fiber. It is preferable to use a carbon-based material as the conductive assistant.

[0038] The positive electrode binder joins the positive electrode current collector layer 1A and the positive electrode active material layer 1B, the positive electrode active material layer 1B and the solid electrolyte layer 3, and various materials constituting the positive electrode active material layer 1B.

[0039] The positive electrode binder may be included in a range that does not impair the function of the positive electrode active material layer 1B. The content of the positive electrode binder in the positive electrode active material layer 1B can be, for example, in the range of 0.5 to 70% by mass. The content of the positive electrode binder in the positive electrode active material layer 1B may also be, for example, in the range of 0.5 to 30% by volume of the positive electrode active material layer. If the content of the positive electrode binder is sufficiently low, the resistance of the positive electrode active material layer 1B will be sufficiently low. The positive electrode binder may be omitted if it is not needed.

[0040] As the positive electrode binder, an organic binder or an inorganic binder can be used, similar to the positive electrode binder contained in the positive electrode current collector layer 1A.

[0041] Furthermore, the positive electrode active material layer 1B may contain a solid electrolyte to an extent that does not impair its function as a positive electrode active material layer. The solid electrolyte content of the positive electrode active material layer 1B can be, for example, in the range of 1 to 50% by mass. The solid electrolyte is preferably the LAGP compound contained in the solid electrolyte layer 3 described above. The solid electrolyte contained in the positive electrode active material layer 1B improves the lithium ion conductivity within the positive electrode active material layer 1B. In addition, if a firing process is included in the manufacturing of an all-solid-state battery, the solid electrolyte contained in the positive electrode active material layer 1B can alleviate the shrinkage stress of the positive electrode active material layer 1B due to firing, thereby suppressing cracks and fractures that may occur.

[0042] "Negative electrode" As shown in Figure 1, the negative electrode 2 includes, for example, a negative electrode current collector layer 2A containing at least a conductive material and a negative electrode active material layer 2B containing at least a negative electrode active material.

[0043] (Negative electrode current collector layer) The negative electrode current collector layer 2A is the same as the positive electrode current collector layer 1A.

[0044] (Negative electrode active material layer) The negative electrode active material layer 2B is formed on one or both sides of the negative electrode current collector layer 2A. The negative electrode active material layer 2B contains at least a negative electrode active material. Furthermore, the negative electrode active material layer 2B may also contain a conductive additive, a negative electrode binder, and the above-mentioned solid electrolyte (LAGP compound). In addition, the LATGP compound is contained within the negative electrode active material layer 2B and at either one or both of the interfaces between the negative electrode active material layer 2B and the solid electrolyte layer 3.

[0045] The negative electrode active material includes a titanium compound. The titanium compound is not particularly limited as long as it is a compound capable of intercalating and releasing ions. Examples of titanium compounds include TiO2 and Li4Ti5O. 12 These can be used. Examples of TiO2 include those having anatase-type crystal structure, brookite-type crystal structure, and rutile-type crystal structure, but in the embodiments of this disclosure, the titanium compound is not limited to one of these types. These titanium compounds may be used individually or in combination of two types.

[0046] The conductive additive contained in the negative electrode active material layer 2B can be the same material as that used in the positive electrode active material layer 1B. It is preferable to use a carbon-based material as the conductive additive.

[0047] The negative electrode binder bonds the negative electrode current collector layer 2A to the negative electrode active material layer 2B, the negative electrode active material layer 2B to the solid electrolyte layer 3, and the various materials that make up the negative electrode active material layer 2B.

[0048] The negative electrode binder may be included within a range that does not impair the function of the negative electrode active material layer 2B. The content of the negative electrode binder can be within the range of 0.5 to 70% by mass of the negative electrode active material layer 2B, similar to the positive electrode active material layer 1B. The same material as the positive electrode binder can be used for the negative electrode binder. However, the negative electrode binder may be omitted if it is not needed.

[0049] Furthermore, the negative electrode active material layer 2B can contain a solid electrolyte to such an extent that the function as a negative electrode active material layer is not impaired. For example, the content of the solid electrolyte in the negative electrode active material layer 2B can be, for example, within the range of 1 to 50% by mass. The solid electrolyte is preferably the LAGP compound contained in the solid electrolyte layer 3 described above. The solid electrolyte contained in the negative electrode active material layer 2B improves the lithium ion conductivity within the negative electrode active material layer 2B. Also, when the firing process is included in the manufacture of the all-solid-state battery, the solid electrolyte contained in the negative electrode active material layer 2B relaxes the shrinkage stress of the negative electrode active material layer 2B due to firing, and can suppress cracks and fractures caused thereby.

[0050] (LATGP compound) The LATGP compound is represented by the following formula (2). Li 1+y Al y Ti z Ge 2-y-z (PO4)3(2) However, in formula (2), y and z are numbers satisfying 0 < y < 1 and 0 < z < 1. Although y and z are not particularly limited, it is preferable that they are further numbers satisfying 0.11 ≦ y + z ≦ 1 and 0.01 ≦ z / y ≦ 9.

[0051] Figure 2 is a schematic cross-sectional view of the solid electrolyte layer and the surrounding negative electrode active material layer and positive electrode active material layer of the all-solid-state battery according to this embodiment. In Figure 2, the solid electrolyte layer 3 is a sintered body of LAGP compound powder 30. The positive electrode active material layer 1B contains positive electrode active material powder 40 and conductive additive powder 41. The negative electrode active material layer 2B contains titanium compound powder 20, LATGP compound 21, conductive additive powder 22, and LAGP compound powder 30. The LATGP compound 21 is contained within the negative electrode active material layer 2B in a manner that covers at least a portion of the titanium compound powder 20. As a result, the titanium compound powder 20 and the LAGP compound powder 30 are in contact via the LATGP compound 21. Since both the LATGP compound 21 and the LAGP compound powder 30 contain Li, Al, Ge, and PO4, they have high affinity, and since the LATGP compound 21 contains Ti, it has high affinity with the titanium compound powder 20. Furthermore, since the LATGP compound 21 has a NASICON-type structure, the diffusion rate of lithium ions is fast. Therefore, when the titanium compound powder 20 and the LATGP compound powder 30 come into contact via the LATGP compound 21, the LATGP compound 21 functions as a lithium ion conduction path, and the diffusion rate of lithium ions from the negative electrode active material layer 2B to the solid electrolyte layer 3 during discharge is increased. As a result, the discharge capacity at high rates is increased. The coverage rate of the titanium compound powder 20 by the LATGP compound 21 is not particularly limited, but is preferably 1% or more, more preferably 30% or more, and preferably 50% or more. Also, the thickness of the LATGP compound 21 covering the titanium compound powder 20 is not particularly limited, but is preferably in the range of 1 nm to 1 μm, more preferably in the range of 1 nm to 100 nm, and more preferably in the range of 1 nm to 50 nm. The coverage and thickness of the LATGP compound 21 can be measured by performing elemental analysis of the surface of the titanium compound powder 20 using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS).

[0052] Titanium compound powder 20, in which at least a portion of the surface is coated with LATGP compound 21, can be produced, for example, by the sol-gel method. A Li source, Al source, Ti source, Ge source, and PO4 source are weighed to obtain a desired LATGP compound composition and dissolved in an organic solvent to obtain solution A. Alternatively, titanium compound powder 20 is dispersed in a phosphate solution obtained by dissolving phosphate in deionized water to obtain solution B. Solution A is added to solution B and stirred to generate a sol of LATGP precursor on the surface of titanium compound powder 20. This titanium compound powder 20 is washed and then calcined at a temperature of 400°C to 550°C to obtain titanium compound powder 20 coated with LATGP compound 21.

[0053] There are no particular restrictions on the materials used as Li sources, Al sources, Ti sources, Ge sources, and PO4 sources. As Li sources, Al sources, Ti sources, and Ge sources, metal alkoxides, carbonates, nitrates, acetates, oxides, hydroxides, chlorides, phosphates, etc., can be used. Phosphates also act as PO4 sources. As PO4 sources, phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, etc., can be used.

[0054] Another method for producing the titanium compound powder 20 coated with LATGP compound 21 is, for example, a spray drying method. A mixture is obtained by mixing a dispersion containing pre-prepared fine powder of LATGP compound 21 with the titanium compound powder 20. The resulting mixture is dried with a spray dryer to obtain a dried powder. The resulting dried powder is calcined to sinter the titanium compound powder 20 and the fine powder of LATGP compound 21.

[0055] While there are no particular limitations on the method for coating the titanium compound powder with the LATGP compound, the sol-gel method is preferred from the viewpoint of coating performance and adhesion. The sol-gel method allows for easy control of the thickness of the LATGP compound and is suitable for coating with a relatively thin thickness of 100 nm or less.

[0056] (Manufacturing method for all-solid-state batteries) Next, the manufacturing method of the all-solid-state battery 10 will be described. First, the laminate 4 is manufactured. The laminate 4 is manufactured, for example, by a co-firing method or a sequential firing method.

[0057] The simultaneous firing method is a method of producing a laminate 4 by stacking the materials that form each layer and then firing them all at once. The sequential firing method is a method of firing each layer as it is formed. The simultaneous firing method can produce the laminate 4 with fewer steps than the sequential firing method. In addition, the laminate 4 produced by the simultaneous firing method is denser than the laminate 4 produced using the sequential firing method. The following explanation will use the simultaneous firing method as an example.

[0058] First, the materials for the positive electrode current collector layer 1A, positive electrode active material layer 1B, solid electrolyte layer 3, negative electrode active material layer 2B, and negative electrode current collector layer 2A that constitute the laminate 4 are made into a paste. As the negative electrode active material, a titanium compound powder is used in which at least a portion of the surface is coated with LATGP compound 21.

[0059] The method for forming a paste from each material is not particularly limited; for example, a method of mixing the powders of each material with a vehicle to obtain a paste can be used. Here, "vehicle" is a general term for the medium in the liquid phase. The vehicle includes solvents and binders.

[0060] Next, a green sheet is prepared. The green sheet is obtained by applying a paste prepared for each material onto a substrate such as a PET (polyethylene terephthalate) film, drying it as needed, and then peeling off the substrate. The method of applying the paste is not particularly limited, and known methods such as screen printing, coating, transfer, and doctor blade can be used.

[0061] Next, the green sheets prepared for each material are stacked in the desired order and number of layers to create a laminated sheet. When stacking the green sheets, alignment and cutting are performed as needed. For example, when creating a parallel or series-parallel battery, the green sheets are stacked after alignment so that the end face of the positive electrode current collector layer 1A and the end face of the negative electrode current collector layer 2A do not coincide.

[0062] The laminated sheet may be manufactured by creating a positive electrode unit and a negative electrode unit and then laminating these units. The positive electrode unit is a laminated sheet in which a solid electrolyte layer 3, a positive electrode active material layer 1B, a positive electrode current collector layer 1A, and a positive electrode active material layer 1B are laminated in this order. The negative electrode unit is a laminated sheet in which a solid electrolyte layer 3, a negative electrode active material layer 2B, a negative electrode current collector layer 2A, and a negative electrode active material layer 2B are laminated in this order. The laminated sheets are arranged so that the solid electrolyte layer 3 of the positive electrode unit and the negative electrode active material layer 2B of the negative electrode unit face each other, or so that the positive electrode active material layer 1B of the positive electrode unit and the solid electrolyte layer 3 of the negative electrode unit face each other.

[0063] Next, the fabricated laminated sheets are pressed together to improve the adhesion of each layer. Pressurization can be performed using, for example, a die press, a hot water isostatic press (WIP), a cold water isostatic press (CIP), or a hydrostatic press. It is preferable to perform the pressurization while heating. The heating temperature during pressing should be, for example, 40 to 95°C. Then, the pressed laminate is cut into chips using a dicing device. Finally, the chips are degreased and fired to obtain a laminate 4 made of sintered material.

[0064] The binder degreasing process can be performed as a separate step from the firing process. Performing the binder degreasing process allows the binder components contained in the chip to be thermally decomposed before the firing process, thereby suppressing the rapid decomposition of the binder components during the firing process. The atmosphere and heating conditions for the binder degreasing process are not limited, but for example, it can be performed by heating at a temperature of 300°C or higher for 0.1 to 10 hours in an air atmosphere, nitrogen atmosphere, argon atmosphere, or oxygen atmosphere. There is no particular upper limit to the temperature of the degreasing process, but it is preferable to perform it below the sintering temperature.

[0065] The firing process is carried out, for example, by placing the chips on a ceramic base. The firing is carried out, for example, by heating to 600-1000°C under a nitrogen atmosphere. The firing time is, for example, 0.1-3 hours. The sintering process can be carried out in any reducing atmosphere other than a nitrogen atmosphere, for example, an argon atmosphere or a nitrogen-hydrogen mixed atmosphere.

[0066] Alternatively, the sintered laminate 4 (sintered body) may be placed in a cylindrical container with an abrasive such as alumina and barrel polished. This allows for chamfering of the corners of the laminate. Polishing may also be performed using sandblasting. Sandblasting is preferred because it allows for the removal of only specific parts.

[0067] Positive electrode terminals 5 and negative electrode terminals 6 are formed on the opposing sides of the fabricated laminate 4. The positive electrode terminals 5 and negative electrode terminals 6 can be formed using methods such as sputtering, dipping, screen printing, and spray coating, respectively. By going through the above steps, an all-solid-state battery 10 can be manufactured. If the positive electrode terminals 5 and negative electrode terminals 6 are to be formed only in predetermined areas, the area is masked with tape or the like before the above process is performed.

[0068] In this embodiment, the all-solid-state battery 10 has high discharge capacity and improved discharge characteristics because the titanium compound powder 20, which is the negative electrode active material, and the LAGP compound powder 30, which is the solid electrolyte, are in contact via the LATGP compound 21. 12 When either or both of these titanium compounds are present, the amount of lithium ions inserted and removed during the charge-discharge reaction is large, resulting in a higher charge-discharge capacity of the negative electrode active material layer 2B.

[0069] Furthermore, in the all-solid-state battery 10 of this embodiment, if the LATGP compound 21 contains Al and Ti such that y and z in equation (2) above satisfy 0.11≦y+z≦1 and 0.01≦z / y≦9, the lithium ion conductivity of the LATGP compound is further improved, resulting in a higher discharge capacity during high-rate discharge and further improved discharge characteristics. Furthermore, in the all-solid-state battery 10 of this embodiment, if the negative electrode active material layer 2B contains a carbon-based material, the electronic conductivity within the negative electrode active material layer 2B is improved, resulting in an even higher discharge capacity during high-rate discharge and further improved discharge characteristics. Furthermore, in the all-solid-state battery 10 of this embodiment, if the negative electrode active material layer 2B contains a LAGP compound, the lithium ion conductivity within the negative electrode active material layer 2B is improved, resulting in an even higher discharge capacity during high-rate discharge and further improved discharge characteristics.

[0070] Furthermore, in the all-solid-state battery 10 of this embodiment, if the porosity of the solid electrolyte layer 3 is 40% or less, the ionic conductivity of lithium ions in the solid electrolyte layer 3 can be further increased, resulting in an even higher discharge capacity during high-rate discharge and further improved discharge characteristics.

[0071] We have described in detail specific examples of all-solid-state batteries according to this embodiment. The present invention is not limited to these examples, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims. For example, in the example shown in Figure 2, the LATGP compound 21 is included in the negative electrode active material layer 2B by coating at least a portion of the surface of the titanium compound powder 20, but the location in which the LATGP compound 21 is included is not limited to this.

[0072] Figure 3 is a schematic cross-sectional view of the solid electrolyte layer and the surrounding negative electrode active material layer and positive electrode active material layer of an all-solid-state battery according to the first modified example. The all-solid-state battery according to the first modified example shown in Figure 3 differs from the all-solid-state battery shown in Figure 2 in that, instead of the titanium compound powder 20 being coated with LATGP compound 21, an intermediate layer 25 containing LATGP compound 21 is formed between the interface between the solid electrolyte layer 3 and the negative electrode active material layer 2B. The thickness of the intermediate layer 25 is not particularly limited, but is preferably in the range of 0.01 μm to 2.0 μm, more preferably in the range of 0.01 μm to 1.2 μm, and particularly preferably in the range of 0.1 μm to 0.5 μm.

[0073] In the modified example 1, instead of coating the surface of the titanium compound powder 20 with the LATGP compound 21 when manufacturing the negative electrode unit, a LATGP compound paste is prepared, and the LATGP compound paste is applied to the surface of the solid electrolyte layer 3 and dried.

[0074] In the all-solid-state battery according to Modification 1, the negative electrode active material layer 2B containing titanium compound powder 20 and the solid electrolyte layer 3 containing LAGP compound powder 30 are in contact via an intermediate layer 25 containing a LATGP compound, resulting in a high discharge capacity during high-rate discharge and improved discharge characteristics.

[0075] Figure 4 is a schematic cross-sectional view of the solid electrolyte layer and the surrounding negative electrode active material layer and positive electrode active material layer of an all-solid-state battery according to a second modification. The all-solid-state battery according to the second modification shown in Figure 4 differs from the all-solid-state battery shown in Figure 2 in that the titanium compound powder 20 is coated with LATGP compound 21, and an intermediate layer 25 containing LATGP compound is formed between the interface between the solid electrolyte layer 3 and the negative electrode active material layer 2B.

[0076] The all-solid-state battery according to Modification 2 can be manufactured by coating the surface of the titanium compound powder 20 with LATGP compound 21 when manufacturing the negative electrode unit, preparing a LATGP compound paste, applying the LATGP compound paste to the surface of the solid electrolyte layer 3, and drying it.

[0077] In the all-solid-state battery according to Modification 2, the titanium compound powder 20 and the solid electrolyte LAGP compound powder 30 are in contact via the LATGP compound 21, resulting in a high discharge capacity and improved discharge characteristics during high-rate discharge. Furthermore, since the negative electrode active material layer 2B containing the titanium compound powder 20 and the solid electrolyte layer 3 containing the LAGP compound powder 30 are in contact via an intermediate layer 25 containing the LATGP compound, the discharge capacity and improved discharge characteristics are achieved during high-rate discharge.

[0078] In the all-solid-state battery 10 of this embodiment, the LATGP compound 21 may be contained in at least a portion of the surface of the titanium compound powder 20 and in the interface between the solid electrolyte layer 3 and the negative electrode active material layer 2B. Furthermore, the LATGP compound 21 may also be contained within the solid electrolyte layer 3. [Examples]

[0079] [Example 1] (1) Preparation of a solid electrolyte sheet A solid electrolyte paste was prepared as follows: Li was used as the solid electrolyte. 1.5 Al 0.5 Ge 1.5 (PO4)3 powder was used. This Li 1.5 Al 0.5 Ge 1.5To 100 parts by mass of (PO4)3 powder, 100 parts by mass of ethanol and 200 parts by mass of toluene were added as solvents and wet-mixed in a ball mill. Subsequently, 16 parts by mass of polyvinyl butyral as a binder for the solid electrolyte and 4.8 parts by mass of benzyl butyl phthalate as a plasticizer were further added, and the mixture was mixed and dispersed to obtain a solid electrolyte paste.

[0080] Next, the obtained solid electrolyte paste was applied onto a PET film using the doctor blade method, and the resulting coating was dried at 80°C for 5 minutes to obtain a PET film with a solid electrolyte layer. The obtained PET film with a solid electrolyte layer was peeled from the PET sheet to prepare a solid electrolyte sheet. The thickness of the solid electrolyte sheet was set to 15 μm.

[0081] (2) Fabrication of the positive electrode unit The positive electrode active material paste was prepared as follows: Li3V2(PO4)3 powder was used as the positive electrode active material, acetylene black powder was used as the conductive additive, and the same as used in (1) above was used as the solid electrolyte. The Li3V2(PO4)3 powder, acetylene black powder, and solid electrolyte powder were mixed in a mass ratio of 45:10:45. Next, 15 parts by mass of ethyl cellulose as a positive electrode binder and 65 parts by mass of dihydroterpineol as a solvent were added to 100 parts by mass of this mixed powder and mixed to obtain the positive electrode active material paste.

[0082] The positive electrode current collector paste was prepared as follows: Cu powder and acetylene black powder were used as the current collector, and the same as used in (1) above was used as the solid electrolyte. The Cu powder, acetylene black powder, and solid electrolyte powder were mixed in a mass ratio of 40:10:50. Next, 10 parts by mass of ethyl cellulose as a positive electrode binder and 50 parts by mass of dihydroterpineol as a solvent were added to 100 parts by mass of this mixed powder and mixed to prepare the positive electrode current collector paste.

[0083] A solid electrolyte paste for screen printing was prepared as follows: The same solid electrolyte used in (1) above was used as the solid electrolyte. To 100 parts by mass of this solid electrolyte powder, 10 parts by mass of ethylcellulose was added as a binder and 50 parts by mass of dihydroterpineol was added as a solvent and mixed to prepare a solid electrolyte paste for screen printing.

[0084] Next, a positive electrode active material paste was printed to a thickness of 10 μm onto the solid electrolyte layer of the PET film with a solid electrolyte layer obtained in (1) above using a screen printing method, and dried at 80°C for 5 minutes to form a positive electrode active material layer. Then, a positive electrode current collector paste was printed to a thickness of 5 μm onto the positive electrode active material layer using a screen printing method, and dried at 80°C for 5 minutes to form a positive electrode current collector layer. Then, a positive electrode active material paste was printed again to a thickness of 10 μm onto the positive electrode current collector layer using a screen printing method, and dried at 80°C for 5 minutes to form a positive electrode active material layer. This formed a positive electrode on the solid electrolyte layer. Next, a solid electrolyte paste for screen printing was screen printed onto the region of the solid electrolyte layer where the positive electrode was not formed, so as to be at approximately the same height as the positive electrode, and dried at 80°C for 10 minutes to form a side margin layer containing a solid electrolyte. After that, the PET film was peeled off. In this way, a positive electrode unit was obtained in which a positive electrode was formed on the main surface of the solid electrolyte layer, with a positive electrode active material layer / positive electrode current collector layer / positive electrode active material layer stacked in that order, and a side margin layer.

[0085] (3) Fabrication of the negative electrode unit The negative electrode active material paste was prepared as follows. Anatase-type TiO2 powder was used as the negative electrode active material. To 100 parts by mass of this TiO2 powder, 15 parts by mass of ethylcellulose was added as a negative electrode binder and 65 parts by mass of dihydroterpineol was added as a solvent and mixed to obtain the negative electrode active material paste.

[0086] The negative electrode current collector paste was prepared as follows: Cu powder and acetylene black powder were used as the current collector, and the same as used in (1) above was used as the solid electrolyte. The Cu powder, acetylene black powder, and solid electrolyte were mixed in a mass ratio of 40:10:50. Next, 10 parts by mass of ethyl cellulose as a negative electrode binder and 50 parts by mass of dihydroterpineol as a solvent were added to 100 parts by mass of this mixed powder and mixed to prepare the negative electrode current collector paste.

[0087] The LATGP compound paste was prepared as follows. First, the LATGP compound was prepared as follows. As starting materials, lithium acetate (CH3COOLi), aluminum s-butoxide (Al(OC4H9)3), titanium(IV) tetrabutoxide (Ti[O(CH2)3CH3]4), tetraethoxygermanium (Ge(OC2H5)4), ammonium dihydrogen phosphate (NH4H2PO4), n-butyl alcohol (n-C4H9OH), and deionized water (H2O) were prepared. The lithium acetate, aluminum s-butoxide, titanium(IV) tetrabutoxide, tetraethoxygermanium, and ammonium dihydrogen phosphate were weighed so that the molar ratio of Li:Al:Ti:Ge:PO4 was 1.5:0.5:0.01:1.49:3.0. Next, the lithium acetate, aluminum s-butoxide, titanium(IV) tetrabutoxide, and tetraethoxygermanium were dissolved in n-butyl alcohol. This was designated as solution A. Next, ammonium dihydrogen phosphate was dissolved in deionized water. This was designated as solution B. Solution A was added to solution B and stirred with a magnetic stirrer for 2 hours to prepare a sol of the LATGP compound precursor. After washing the precursor sol with ethanol and deionized water, the LATGP precursor sol was collected by suction filtration and dried at 100°C. The obtained powder was calcined at 500°C in an air atmosphere for 4 hours to obtain the LATGP compound powder. The particle size of the obtained LATGP compound powder was measured using a laser diffraction / scattering particle size distribution analyzer, and the average particle size was found to be 100 nm. The composition of the LATGP compound powder was determined by dissolving the LATGP compound powder in acid and quantifying the content of Li, Al, Ti, Ge, and P in the obtained solution by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The composition of the obtained LATGP compound powder was Li 1.5 Al 0.5 Ti 0.01 Ge 1.49 (PO4)3 was 3.

[0088] To 100 parts by mass of LATGP compound powder, 100 parts by mass of ethanol and 200 parts by mass of toluene were added as solvents and wet-mixed in a ball mill. Subsequently, 16 parts by mass of polyvinyl butyral as a solid electrolyte binder and 4.8 parts by mass of benzyl butyl phthalate as a plasticizer were added, and the mixture was mixed and dispersed to obtain a LATGP compound paste. In subsequent steps, if a thinner LATGP compound layer was desired, the amount of LATGP compound powder was reduced to produce a paste with a lower solid content of LATGP compound powder. On the other hand, if a thicker LATGP compound layer was desired, the amount of LATGP compound powder was increased to produce a paste with a higher solid content of LATGP compound powder.

[0089] Next, LATGP compound paste was printed onto the solid electrolyte layer of the PET film with a solid electrolyte layer obtained in (1) above using a screen printing method, and dried at 80°C for 5 minutes to form a 2 μm thick LATGP compound layer. Then, negative electrode active material paste was printed onto the LATGP compound layer using a screen printing method, and dried at 80°C for 5 minutes to form a 10 μm thick negative electrode active material layer. Then, negative electrode current collector paste was printed onto the negative electrode active material layer using a screen printing method, and dried at 80°C for 5 minutes to form a 5 μm thick negative electrode current collector layer. Then, negative electrode active material paste was printed again onto the negative electrode current collector layer using a screen printing method, and dried at 80°C for 5 minutes to form a 10 μm thick negative electrode active material layer. Then, LATGP compound paste was printed again onto the negative electrode active material layer using a screen printing method, and dried at 80°C for 5 minutes to form a 2 μm thick LATGP compound layer. This formed a negative electrode sandwiched between LATGP compound layers on top of a solid electrolyte layer. Next, the solid electrolyte paste used in (2) above was screen printed onto the region of the solid electrolyte layer where the negative electrode sandwiched between LATGP compound layers was not formed, so as to be at approximately the same height as the negative electrode sandwiched between LATGP compound layers, and dried at 80°C for 10 minutes to form a side margin layer containing the solid electrolyte. After that, the PET film was peeled off. In this way, a negative electrode unit was obtained in which a negative electrode was formed on the main surface of the solid electrolyte layer, with the LATGP compound layer / negative electrode active material layer / negative electrode current collector layer / negative electrode active material layer / LATGP compound layer stacked in this order, and a side margin layer was formed.

[0090] (4) Fabrication of all-solid-state batteries Five solid electrolyte sheets prepared in (1) above were stacked, and 25 positive electrode units prepared in (2) above and 25 negative electrode units prepared in (3) above were stacked alternately on top of them, with the positive electrode units having the positive electrode active material facing upwards and the negative electrode units having the LATGP compound layer facing upwards. At this time, the positive electrode units and negative electrode units were stacked with a staggered arrangement so that the positive electrode current collector layer of the positive electrode unit extended only to one end face, and the negative electrode current collector layer of the negative electrode unit extended only to the opposite end face. Finally, six solid electrolyte sheets were stacked on top of the stacked negative electrode units. The resulting laminate was formed by thermocompression bonding and then cut to produce laminated chips. The obtained laminated chips were subjected to binder degreasing and firing to sinter the laminated chips. The binder degreasing and firing were performed in a nitrogen atmosphere by raising the temperature to a firing temperature of 800°C at a heating rate of 200°C / hour and holding it at that temperature for 2 hours.

[0091] A positive electrode terminal was formed on the side of the sintered body where the positive electrode current collector was exposed, and a negative electrode terminal was formed on the side of the negative electrode current collector that was exposed, thereby fabricating an all-solid-state battery.

[0092] (5) Evaluation (Porosity of the solid electrolyte layer, thickness of the LATGP compound layer) The all-solid-state battery was cut along the stacking direction, and a polished cross-section was obtained using a cross-section polisher (CP). The obtained cross-section was observed using a scanning electron microscope (SEM), and the porosity of the solid electrolyte layer and the thickness of the LATGP compound layer were measured. The porosity of the solid electrolyte layer was calculated using the following procedure. First, an SEM image of the solid electrolyte layer taken at 5000x magnification was binarized so that the void areas were black and the solid electrolyte areas were white, and the number of pixels in each area was measured. Then, the porosity of the solid electrolyte layer per layer was calculated by calculating the number of pixels in the black area relative to the total number of pixels in the solid electrolyte layer. The porosity of a total of 20 solid electrolyte layers was calculated using the same procedure. The thickness of the LATGP compound layer was calculated using the following procedure. In an SEM image taken at 2000x magnification, the thickness was measured at 5 locations within the same LATGP compound layer, and the average value was taken as the thickness of the LATGP compound layer per layer. The thickness of a total of 20 LATGP compound layers was measured using the same measurement method. The average values ​​are shown in Table 1A below.

[0093] (Discharge characteristics) The discharge characteristics of the all-solid-state battery were evaluated using the ratio of the discharge capacity at a discharge rate of 10C to the discharge capacity at a discharge rate of 0.1C (10C / 0.1C rate characteristics). All-solid-state batteries were charged using constant current (CC charging) at a rate of 0.1C until the battery voltage reached 3.2V in an environment of 25°C. Then, they were discharged using a constant current at a rate of 0.1C until the battery voltage reached 0V (CC discharge), and the discharge capacity at 0C was measured. Next, the all-solid-state batteries were charged again under the same conditions and discharged at a discharge rate of 10C until the battery voltage reached 0V, and the discharge capacity at 10C was measured. The results are shown in Table 1A below.

[0094] [Examples 2-6, Comparative Example 1] Examples 2-6 involved fabricating and evaluating all-solid-state batteries in the same manner as in Example 1, except that the composition of the LATGP compound powder was as shown in Table 1A below. Comparative Example 1 involved fabricating and evaluating an all-solid-state battery in the same manner as in Example 1, except that a LATGP compound layer was not formed on the negative electrode unit. The results are shown in Table 1A.

[0095] [Examples 7-11, Comparative Example 2] Examples 7-11 use Li as the solid electrolyte. 1.7 Al 0.7 Ge 1.3 A solid-state battery was prepared and evaluated in the same manner as in Example 1, except that (PO4)3 powder was used and the composition of the LATGP compound powder was as shown in Table 1A below. Comparative Example 2 used Li as the solid electrolyte. 1.7 Al 0.3 Ge 1.3 An all-solid-state battery was fabricated and evaluated in the same manner as in Example 1, except that (PO4)3 powder was used and a LATGP compound layer was not formed on the negative electrode unit. The results are shown in Table 1A.

[0096] [Examples 12-16, Comparative Example 3] Examples 12-16 use Li as the solid electrolyte. 1.3 Al 0.3 Ge 1.7 A solid-state battery was prepared and evaluated in the same manner as in Example 1, except that (PO4)3 powder was used and the composition of the LATGP compound powder was as shown in Table 1A below. Comparative Example 3 used Li as the solid electrolyte. 1.3 Al 0.3 Ge 1.7 An all-solid-state battery was fabricated and evaluated in the same manner as in Example 1, except that (PO4)3 powder was used and a LATGP compound layer was not formed on the negative electrode unit. The results are shown in Table 1A.

[0097] [Examples 17-21, Comparative Example 4] Examples 17-21 use Li as the solid electrolyte. 1.2 Al 0.2 Ge 1.8 A solid-state battery was prepared and evaluated in the same manner as in Example 1, except that (PO4)3 powder was used and the composition of the LATGP compound powder was as shown in Table 1B below. Comparative Example 4 used Li as the solid electrolyte. 1.2 Al 0.2 Ge 1.8An all-solid-state battery was fabricated and evaluated in the same manner as in Example 1, except that (PO4)3 powder was used and a LATGP compound layer was not formed on the negative electrode unit. The results are shown in Table 1B.

[0098] [Examples 22-26, Comparative Example 5] Examples 22-26 use Li as the solid electrolyte. 1.1 Al 0.1 Ge 1.9 A solid-state battery was prepared and evaluated in the same manner as in Example 1, except that (PO4)3 powder was used and the composition of the LATGP compound powder was as shown in Table 1B below. Comparative Example 5 used Li as the solid electrolyte. 1.1 Al 0.1 Ge 1.9 An all-solid-state battery was fabricated and evaluated in the same manner as in Example 1, except that (PO4)3 powder was used and a LATGP compound layer was not formed on the negative electrode unit. The results are shown in Table 1B.

[0099] [Comparative Examples 6-11] Comparative Example 6 uses Li as the solid electrolyte. 2.0 Al 1.0 Ge 1.0 All-solid-state batteries were fabricated and evaluated in the same manner as in Example 1, except that (PO4)3 powder was used and a LATGP compound layer was not formed on the negative electrode unit. Comparative Examples 7-11 used Li as the solid electrolyte. 2.0 Al 1.0 Ge 1.0 All-solid-state batteries were fabricated and evaluated in the same manner as in Example 1, except that (PO4)3 powder was used and the composition of the LATGP compound powder was as shown in Table 1B below. The results are shown in Table 1B.

[0100] [Examples 27-28] In Example 27, an all-solid-state battery was fabricated and evaluated in the same manner as in Comparative Example 1, except that TiO2 powder coated with a LATGP compound was used as the negative electrode active material. The results are shown in Table 1B. The TiO2 powder coated with the LATGP compound was prepared by the following procedure. The starting materials prepared were lithium acetate (CH3COOLi), aluminum s-butoxide (Al(OC4H9)3), titanium(IV) tetrabutoxide (Ti[O(CH2)3CH3]4), tetraethoxygermanium (Ge(OC2H5)4), ammonium dihydrogen phosphate (NH4H2PO4), n-butyl alcohol (n-C4H9OH), deionized water (H2O), and anatase-type titanium dioxide (TiO2). First, lithium acetate, aluminum s-butoxide, titanium(IV) tetrabutoxide, tetraethoxygermanium, and ammonium dihydrogen phosphate were weighed in such a molar ratio of Li:Al:Ti:Ge:PO4 as 1.5:0.5:0.01:1.49:3.0. Next, lithium acetate, aluminum s-butoxide, titanium(IV) tetrabutoxide, and tetraethoxygermanium were dissolved in n-butyl alcohol. This is designated as solution A. Then, ammonium dihydrogen phosphate was dissolved in deionized water, and TiO2 powder was added to this solution and dispersed using a magnetic stirrer (this is designated as solution B). Solution A was added to solution B and stirred with a magnetic stirrer for 2 hours to generate a sol of LATGP compound precursor on the surface of the TiO2 powder. The TiO2 powder coated with the precursor sol was washed with ethanol and deionized water, collected by suction filtration, and dried at 100°C. The obtained powder was calcined in an air atmosphere at 500°C for 4 hours to obtain TiO2 powder coated with a LATGP compound. After embedding the TiO2 powder coated with the obtained LATGP compound in resin, thin sections were prepared, and STEM images were observed and elemental mapping was performed using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS). It was confirmed that more than 50% of the surface of the TiO2 powder was coated with the LATGP compound, and that the thickness of the LATGP compound was 50 nm or less.

[0101] In Example 28, an all-solid-state battery was fabricated and evaluated in the same manner as in Example 1, except that the negative electrode active material used was TiO2 powder coated with the LATGP compound from Example 27. The results are shown in Table 1B.

[0102] [Table 1A]

[0103] [Table 1B]

[0104] The results shown in Tables 1A and 1B indicate that the all-solid-state batteries of Examples 1-26, which have a LATGP compound layer between the negative electrode active material layer containing TiO2 and the solid electrolyte layer containing the LAGP compound, exhibit higher 10C / 0.1C rate characteristics and superior discharge characteristics compared to the all-solid-state batteries of Comparative Examples 1-6, which do not have a LATGP compound layer. 1+x Al x Ge 2-x The all-solid-state batteries of Examples 1 to 26, in which x in (PO4)3) is less than 1, show improved 10C / 1C rate characteristics and superior discharge characteristics compared to the all-solid-state batteries of Comparative Examples 7 to 11, where x is 1. Furthermore, the all-solid-state battery of Example 27, which uses TiO2 coated with a LATGP compound, also shows superior discharge characteristics compared to the all-solid-state battery of Comparative Example 1. Moreover, the all-solid-state battery of Example 28, which has a negative electrode active material layer containing TiO2 coated with a LATGP compound and a LATGP compound layer, shows even superior discharge characteristics.

[0105] [Examples 29-32, Comparative Example 12] Example 29 uses Li4Ti5O as the negative electrode active material. 12 A solid-state battery was prepared and evaluated in the same manner as in Example 1, except that powder was used. Comparative Example 12 used Li4Ti5O as the negative electrode active material. 12A all-solid-state battery was fabricated and evaluated in the same manner as in Example 1, except that powder was used and the LATGP compound layer was not formed on the negative electrode unit. The results are shown in Table 2 below together with the results of Example 1.

[0106] In Example 30, TiO2 powder was used as the negative electrode active material and acetylene black powder was used as the conductive assistant. The TiO2 powder and the acetylene black powder were mixed so that the weight ratio was 90:10. Next, 15 parts by mass of ethyl cellulose was added as a binder for the negative electrode and 65 parts by mass of dihydroterpineol was added as a solvent to 100 parts by mass of this mixed powder and mixed to obtain a negative electrode active material paste. A all-solid-state battery was fabricated and evaluated in the same manner as in Example 1, except for the preparation of this negative electrode active material paste. The results are shown in Table 2 below.

[0107] In Example 31, the negative electrode active material paste was prepared as follows. First, TiO2 powder, acetylene black powder, and a solid electrolyte (LAGP:Li 1.5 Al 0.5 Ge 1.5 (PO4)3) powder were mixed so that the mass ratio was 45:10:45. Next, 15 parts by mass of ethyl cellulose was added as a binder for the negative electrode and 65 parts by mass of dihydroterpineol was added as a solvent to 100 parts by mass of this mixed powder and mixed to obtain a negative electrode active material paste. A all-solid-state battery was fabricated and evaluated in the same manner as in Example 1, except for the preparation of this negative electrode active material paste. The results are shown in Table 2 below.

[0108] In Example 32, the negative electrode active material paste was prepared as follows. First, the TiO2 powder coated with the LATGP compound prepared in Example 28, acetylene black powder, and a solid electrolyte powder (LAGP:Li 1.5 Al 0.5 Ge 1.5(PO4)3) powder was mixed with the other powder in a mass ratio of 45:10:45. Next, 15 parts by mass of ethyl cellulose as a negative electrode binder and 65 parts by mass of dihydroterpineol as a solvent were added to 100 parts by mass of this mixed powder and mixed to obtain a negative electrode active material paste. An all-solid-state battery was prepared and evaluated in the same manner as in Example 1, except for the preparation of the negative electrode active material paste. The results are shown in Table 2 below.

[0109] [Table 2]

[0110] From the results in Table 2, Li4Ti5O was selected as the negative electrode active material. 12 Even when using powder, the all-solid-state battery of Example 29, which has a LATGP compound layer, exhibits superior discharge characteristics compared to the all-solid-state battery of Comparative Example 12, which does not have a LATGP compound layer. Furthermore, the results from Examples 30 and 31 show that adding acetylene black (carbon) and a solid electrolyte to the negative electrode active material layer further improves the 10C / 0.1C rate characteristics. Additionally, the results from Example 32 show that an all-solid-state battery using TiO2 coated with a LATGP compound as the negative electrode active material, and further including acetylene black and a solid electrolyte in the negative electrode active material layer, exhibits even greater discharge characteristics.

[0111] [Examples 33-38] In fabricating the all-solid-state battery, the only difference was that the porosity of the solid electrolyte layer was changed by adjusting the mass of the polyvinyl butyral binder in the solid electrolyte sheet. The all-solid-state battery was then fabricated and evaluated in the same manner as in Example 1. The results, along with those of Example 1, are shown in Table 3 below.

[0112] [Table 3]

[0113] The results in Table 3 show that as the porosity of the solid electrolyte layer decreases, the 10C / 0.1C rate characteristics improve, and the discharge characteristics of the all-solid-state battery tend to improve.

[0114] [Examples 39-46] Examples 39-46 were manufactured and evaluated in the same manner as in Example 1, except that the thickness of the LATGP compound layer in the sintered all-solid-state battery was set to the thickness shown in Table 4 below. The thickness of the LATGP compound layer was adjusted by changing various factors, such as the solid content concentration of the LATGP compound paste used in screen printing and the printing thickness of the LATGP compound layer during printing. In particular, in Examples 39-43, where the thickness of the LATGP compound layer was less than 1 μm, the stirring time in the preparation of the LATGP compound powder was changed to 10 minutes to produce fine particles of LATGP compound powder with an average particle size of 5 nm. Furthermore, the thickness of the LATGP compound layer after firing was adjusted to less than 1 μm by using a LATGP compound paste with a solid content concentration of 5-50% in screen printing. The solid content concentration of the LATGP compound paste was adjusted by appropriately changing the proportions of LATGP compound powder by mass, solvent, solid electrolyte binder, and plasticizer. The results, along with those of Example 1, are shown in Table 4.

[0115] [Table 4]

[0116] From the results in Table 4, it can be seen that the 10C / 0.1C rate characteristics are high when the thickness of the LATGP compound layer (intermediate layer) formed between the solid electrolyte layer and the negative electrode active material layer is 2.0 μm or less, even higher in the range of 0.01 μm to 1.2 μm, and particularly high in the range of 0.10 μm to 0.50 μm. [Explanation of symbols]

[0117] 1...Positive electrode, 1A...Positive electrode current collector layer, 1B...Positive electrode active material layer, 2...Negative electrode, 2A...Negative electrode current collector layer, 2B...Negative electrode active material layer, 3...Solid electrolyte layer, 4...Laminate, 5...Positive electrode terminal, 6...Negative electrode terminal, 20...Titanium compound powder, 21...LATGP compound, 22...Conductive additive powder, 25...Intermediate layer, 30...LAGP compound powder, 31...Void, 40...Positive electrode active material powder, 41...Conductive additive powder

Claims

1. The device comprises a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a solid electrolyte layer between the positive electrode active material layer and the negative electrode active material layer. The negative electrode active material layer contains a titanium compound, The solid electrolyte layer contains a LAGP compound represented by the following formula (1): Li １＋ｘ Al ｘ Ge ２－ｘ (PO) ４ ) ３ (1) (However, in equation (1), x is a number that satisfies 0 < x < 1.) An all-solid-state battery in which either or both of the negative electrode active material layer and the interface between the negative electrode active material layer and the solid electrolyte layer contain a LATGP compound represented by the following formula (2). Li １＋ｙ Al ｙ Ti ｚ Ge ２－ｙ－ｚ (PO) ４ ) ３ (2) (However, in equation (2), y and z are numbers that satisfy 0 < y < 1, 0 < z < 1, 0.11 ≤ y + z ≤ 1, and 0.01 ≤ z / y ≤ 9.)

2. The aforementioned titanium compound is TiO ２ and Li ４ Ti ５ O １２ The all-solid-state battery according to claim 1, comprising either one or both of the following.

3. The all-solid-state battery according to claim 1, wherein the negative electrode active material layer comprises either or both a carbon-based material and a LAGP compound represented by formula (1).

4. The all-solid-state battery according to claim 1, wherein the solid electrolyte layer has a porosity of 40% or less.

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