solid-state batteries

Abstract

To provide a solid state battery that can more sufficiently suppress a decrease in the utilization rate of a negative electrode active material even when a garnet-type solid electrolyte is contained in a negative electrode layer.SOLUTION: A solid state battery includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the negative electrode layer includes a negative electrode active material that contains Li (lithium), M [M is one or more elements selected from the group consisting of W (tungsten), Mo (molybdenum), Ta (tantalum) and Zr (zirconium)], and O (oxygen), and in which the molar ratio (Li / M) of the Li content to the M content is greater than 2.0, and a garnet-type solid electrolyte.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a solid-state battery. [Background technology]

[0002] In recent years, there has been a significant increase in demand for batteries (especially secondary batteries) as power sources for portable electronic devices such as mobile phones and portable personal computers. Secondary batteries used for such applications have traditionally used non-aqueous electrolytes (electrolytic solutions) such as organic solvents as a medium for ion migration. Attempts have been made to improve battery characteristics such as average discharge potential and charge / discharge hysteresis in such non-aqueous electrolyte secondary batteries by using Li4WO5 as the negative electrode active material (see, for example, Patent Document 1).

[0003] However, batteries with the above configuration have the risk of electrolyte leakage, and the organic solvents used in the electrolyte are flammable. For this reason, the use of a solid electrolyte instead of an electrolyte has been proposed. Development of sintered solid-state secondary batteries (so-called "solid-state batteries"), which use a solid electrolyte as the electrolyte and also have other solid components, is underway.

[0004] A solid-state battery includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer laminated between the positive electrode layer and the negative electrode layer. In such a solid-state battery, a solid electrolyte having a garnet structure (e.g., LLZ) has been reported to have relatively high ionic conductivity and a wide potential window (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-201223 [Non-patent literature]

[0006] [Non-Patent Document 1] R. Murugan et al., Angew. Chem. Int. Ed., 2007, 46, 7778-7781 Summary of the Invention [Problem to be solved by the invention]

[0007] The inventors of the present invention have found that in the above-mentioned conventional solid state batteries, the reactivity between the garnet-type solid electrolyte and the electrode active material is very high, and sufficient battery performance cannot be obtained.

[0008] Specifically, when a garnet-type solid electrolyte is contained in the negative electrode layer together with a negative electrode active material in a solid-state battery, the garnet-type solid electrolyte reacts with the negative electrode active material during sintering, resulting in a decrease in the utilization rate of the negative electrode active material. Therefore, a negative electrode active material that has a sufficiently low reactivity with the garnet-type solid electrolyte during sintering has been desired.

[0009] An object of the present invention is to provide a solid-state battery that can more sufficiently suppress a decrease in the utilization rate of the negative electrode active material even when the negative electrode layer contains a garnet-type solid electrolyte. [Means for solving the problem]

[0010] The present invention provides a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; The negative electrode layer relates to a solid-state battery comprising a negative electrode active material that contains Li (lithium), M [M is one or more elements selected from the group consisting of W (tungsten), Mo (molybdenum), Ta (tantalum), and Zr (zirconium)], and O (oxygen), and in which the molar ratio of the Li content to the M content (Li / M) is greater than 2.0, and a garnet-type solid electrolyte.

[0011] The present invention is based on the discovery that a specific negative electrode active material is an electrode material that can withstand co-sintering with a garnet-type solid electrolyte. Specifically, the inventors of the present invention found that by using a garnet-type solid electrolyte in combination with a specific negative electrode active material, the reaction between them can be sufficiently suppressed. [Effects of the Invention]

[0012] The solid state battery according to the present invention can more sufficiently suppress the reaction between the garnet-type solid electrolyte and the negative electrode active material in the negative electrode layer. In the solid state battery of the present invention, even though the negative electrode layer contains a garnet-type solid electrolyte, it is possible to more sufficiently suppress the decrease in the utilization rate of the negative electrode active material. [Brief explanation of the drawings]

[0013] [Figure 1] 1 shows X-ray diffraction patterns (i.e., XRD patterns) measured in the examples. [Figure 2A] 1 shows charge / discharge curves of the solid battery produced in Example 4. [Figure 2B] 1 shows charge / discharge curves of the solid battery produced in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Solid battery] The present invention provides a solid-state battery. In the present specification, the term "solid-state battery" broadly refers to a battery whose components (particularly the electrolyte layer) are made of solids, and in the narrow sense refers to an "all-solid-state battery" whose components (particularly all components) are made of solids. In the present specification, the term "solid-state battery" encompasses so-called "secondary batteries" that can be repeatedly charged and discharged, and "primary batteries" that can only be discharged. The term "solid-state battery" is preferably a "secondary battery." The term "secondary battery" should not be overly limited by its name, and can also encompass electrochemical devices such as "power storage devices," for example.

[0015] The solid-state battery of the present invention includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, and typically has a laminated structure in which a solid electrolyte layer is disposed between the positive electrode layer and the negative electrode layer. The positive electrode layer and the negative electrode layer may each be laminated in two or more layers, as long as a solid electrolyte layer is disposed between them. The solid electrolyte layer is in contact with the positive electrode layer and the negative electrode layer and sandwiched therebetween. The positive electrode layer and the solid electrolyte layer may be sintered together as a sintered body, and / or the negative electrode layer and the solid electrolyte layer may be sintered together as a sintered body. "Sintered together as a sintered body" means that two or more adjacent or contacting members (particularly layers) are joined by sintering. Here, the two or more members (particularly layers) may all be sintered bodies but sintered together as a sintered body. The solid-state battery of the present invention may be referred to as a "sintered solid-state battery" or a "co-sintered solid-state battery" in the sense that the positive electrode layer and the solid electrolyte layer are sintered together as sintered bodies, and the negative electrode layer and the solid electrolyte layer are sintered together as sintered bodies.

[0016] (negative electrode layer) The negative electrode layer is a layer capable of absorbing and releasing metal ions, preferably lithium ions, and includes a negative electrode active material and a solid electrolyte.

[0017] The negative electrode active material contains Li (lithium), M [M is one or more elements selected from the group consisting of W (tungsten), Mo (molybdenum), Ta (tantalum), and Zr (zirconium)], and O (oxygen), and has a molar ratio (Li / M) of the Li content to the M content of greater than 2.0. If the negative electrode active material does not contain M, or if the Li / M ratio in the negative electrode active material is 2.0 or less, the solid electrolyte reacts with the negative electrode active material during sintering, resulting in a decrease in the utilization rate of the negative electrode active material.

[0018] The negative electrode active material preferably contains W as the above-mentioned M from the viewpoint of suppressing the reaction between the solid electrolyte and the negative electrode active material. The charge / discharge capacity of this negative electrode active material is expressed by the redox of W. "Containing W as M" means, for example, that in the general formula (N) described below, β with respect to W (i.e., the number corresponding to β with respect to W) satisfies 0<β<1.5, preferably 0.4≦β≦1.2, more preferably 0.6≦β≦1.02, and even more preferably 0.7≦β≦1.02. From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, M is more preferably W.

[0019] The negative electrode active material preferably has a chemical composition represented by general formula (N) from the viewpoint of suppressing the reaction between the solid electrolyte and the negative electrode active material.

[0020] [ka]

[0021] In formula (N), M is the same as M described above. From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, M preferably contains W, and more preferably contains W. When M contains W (tungsten), M may contain W (tungsten) in combination with one or more elements Mx selected from the group consisting of Mo (molybdenum), Ta (tantalum), and Zr (zirconium). M' is one or more elements selected from the group consisting of Na (sodium), K (potassium), Ca (calcium), Ti (titanium), V (vanadium), Sn (tin), Nb (niobium), Zn (zinc), Mn (manganese), Mg (magnesium), Al (aluminum), and Ga (gallium). M' may also be a metal element that can substitute for a portion of Li.

[0022] α satisfies 2<α<10, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, α preferably satisfies 3≦α≦8, more preferably 3≦α≦5.5, even more preferably 3.9≦α≦5.5, particularly preferably 3.9≦α≦5.0, and most preferably 3.9≦α≦4.5. β satisfies 0<β<1.5, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, it preferably satisfies 0.4≦β≦1.2, more preferably 0.6≦β≦1.05, even more preferably 0.7≦β≦1.02, particularly preferably 0.9≦β≦1.03, and most preferably 1. When M contains two or more elements, the total number of β for each element (i.e., the number corresponding to β for each element) may be within the above-mentioned β range. When M contains two or more elements, each of the β for each element (i.e., the number corresponding to β for each element) may independently be 0.01 or more and 1.2 or less, particularly 0.05 or more and 1.05 or less. In particular, when M contains a combination of W (tungsten) and one or more elements Mx selected from the group consisting of Mo (molybdenum), Ta (tantalum), and Zr (zirconium), the β for W (hereinafter, β) may be 0.01 or more and 1.2 or less, particularly 0.05 or more and 1.05 or less. W ) and β with respect to Mx (hereinafter, β Mx From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, it is preferable that the temperature (temperature) is within the following range: β W is between 0.5 and 1.1, in particular between 0.7 and 1.0; β Mx is 0.05 or more and 0.4 or less, particularly 0.1 or more and 0.3 or less; when Mx contains two or more elements, β Mx (i.e., β for each element Mx The total number of the numbers corresponding to the above β Mx It is sufficient if it is within the range.

[0023] γ satisfies 0≦γ<3, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, preferably satisfies 0≦γ≦2, more preferably 0≦γ≦1, even more preferably 0≦γ≦0.4, and particularly preferably 0. When M′ contains two or more elements, the total number of γ for each element (i.e., the number corresponding to γ ​​for each element) may be within the above range of γ. ω satisfies 4<ω<9, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, ω preferably satisfies 4<ω≦7 (particularly 5, 6, or 7), more preferably 4.5≦ω≦6.5 (particularly 5 or 6), even more preferably 4.5≦ω≦5.5, and even more preferably 5.

[0024] α / β is a value corresponding to the molar ratio (Li / M) of the Li content to the M content described above, and is greater than 2. From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, α / β is preferably 2<α / β≦7, more preferably 3≦α / β≦6.5, even more preferably 3.8≦α / β≦6.5, particularly preferably 3.8≦α / β≦5.5, and most preferably 3.8≦α / β≦5.0.

[0025] The chemical composition of the negative electrode active material may be an average chemical composition. The average chemical composition of the negative electrode active material may be directly measured by breaking the solid-state battery and using TEM-EELS (electron energy loss spectroscopy) or Auger electron spectroscopy. In the negative electrode layer, the average chemical composition of the negative electrode active material and the average chemical composition of the solid electrolyte (described later) can be measured separately based on their compositions in the composition analysis described above. (An element contained only in the solid electrolyte can be detected, and the portion where that element is not detected can be regarded as the negative electrode active material. For example, if the solid electrolyte contains La and the electrode active material does not contain La, the portion where La is not detected is regarded as the negative electrode active material, and the portion where La is detected is regarded as the solid electrolyte.)

[0026] Specific examples of the negative electrode active material represented by the general formula (N) include Li4WO5, Li 3.8 W 1.03 O5, Li6WO6, Li4(W 0.8 Mo 0.2)O5, Li 4.4 (W 0.8 Zr 0.2 )O5, Li 4.1 (W 0.9 Ta 0.1 )O5, Li 4.23 W 0.96 O5, and Li 3.84 Mg 0.2 W 0.96 Examples include O5.

[0027] From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, the negative electrode active material preferably has one or more crystal structures selected from the group consisting of a low-temperature phase Li4WO5-type crystal structure, a high-temperature phase Li4WO5-type crystal structure, and a Li6WO6-type crystal structure, more preferably a low-temperature phase Li4WO5-type crystal structure or a high-temperature phase Li4WO5-type crystal structure, and even more preferably a high-temperature phase Li4WO5-type crystal structure.

[0028] In the present invention, the anode active material having a low-temperature phase Li4WO5-type structure means that the anode active material has a crystal structure that can be assigned to ICDD Card No. 01-074-6445. For example, the anode active material having a low-temperature phase Li4WO5-type structure means that the anode active material (particularly particles thereof) exhibits one or more main peaks in X-ray diffraction at a predetermined incident angle that correspond to Miller indices specific to the so-called low-temperature phase Li4WO5-type crystal structure. The low-temperature phase Li4WO5-type structure is the so-called α-Li4WO5-type structure.

[0029] In the present invention, when a negative electrode active material has a high-temperature phase Li4WO5-type structure, it means that the negative electrode active material has a crystal structure that can be assigned to any of ICDD Card Nos. 01-074-6193, 00-021-0530, or 04-010-6772. For example, when a negative electrode active material has a high-temperature phase Li4WO5-type structure, it means that the negative electrode active material (particularly particles thereof) exhibits one or more major peaks in X-ray diffraction at a predetermined angle of incidence that correspond to Miller indices specific to the so-called high-temperature phase Li4WO5-type crystal structure. The high-temperature phase Li4WO5-type structure includes the so-called β-Li4WO5-type structure and structures similar thereto. Examples of such similar structures include, among the above-mentioned crystal structures, crystal structures that can be assigned to any of ICDD Card Nos. 00-021-0530 or 04-010-6772.

[0030] In the present invention, the anode active material having a Li6WO6-type structure means that the anode active material has a crystal structure that can be assigned to ICDD Card No. 01-073-6224. For example, the anode active material having a Li6WO6-type structure means that the anode active material (particularly particles thereof) exhibits one or more main peaks in X-ray diffraction at a predetermined incident angle that correspond to Miller indices specific to the so-called Li6WO6-type crystal structure.

[0031] The lattice constant of the negative electrode active material in the present invention changes with charge and discharge (Li insertion and removal). Therefore, it does not necessarily have to have a lattice constant exactly equal to that of the ICDD card, but only needs to have a lattice constant that is close to that of the ICDD card. In the present invention, "close" means that the lattice constant is within a range of ±10% of that of the ICDD card.

[0032] From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, it is preferable that the negative electrode active material has a single-phase structure of a high-temperature phase Li4WO5-type crystal structure. The single-phase structure of a high-temperature phase Li4WO5-type crystal structure is a structure in which, in X-ray diffraction (XRD using CuKα radiation), the intensity of the strongest peak specific to each crystal structure (the peak at an incident angle 2θ of approximately 18°) is 1. H is a crystal structure in which the intensity of the strongest peak (peak at an incident angle of 2θ = 18°) specific to the high-temperature phase Li4WO5-type crystal structure is 80% or more of the sum of the intensities of all the strongest peaks. For example, a single-phase structure of the high-temperature phase Li4WO5-type crystal structure is one in which the intensity of the strongest peak (peak at an incident angle of 2θ = 18°) specific to the high-temperature phase Li4WO5-type crystal structure is 80% or more of the sum of the intensities of all the strongest peaks in the high-temperature phase Li4WO5-type crystal structure in X-ray diffraction (XRD using CuKα radiation) compared to a mixed phase structure of the high-temperature phase Li4WO5-type crystal structure and the low-temperature phase Li4WO5-type crystal structure. H and the intensity I of the strongest peak specific to the low-temperature phase Li4WO5-type crystal structure (for example, the peak near the incident angle 2θ = 44°). L But, I H / (I H +I L ) ≧ 0.80. On the other hand, I H and I L I H / (I H +I L )<0.80 is considered to be a mixed phase.

[0033] The negative electrode active material may have the above-described chemical composition and crystalline structure in the solid-state battery after the negative electrode layer is sintered together with the positive electrode layer and the solid electrolyte layer.

[0034] The negative electrode active material can be produced, for example, by the following method. First, raw material compounds containing predetermined metal atoms are weighed so as to have a predetermined chemical composition, and water is added and mixed to obtain a slurry. The slurry is dried, calcined at 700°C to 1000°C for 4 to 24 hours, and then pulverized to obtain the negative electrode active material.

[0035] The average particle size of the negative electrode active material is not particularly limited and may be, for example, 0.01 μm or more and 20 μm or less, and preferably 0.1 μm or more and 5 μm or less.

[0036] The average particle size (arithmetic mean) of the negative electrode active material can be determined by, for example, randomly selecting 10 to 100 particles from an SEM image and simply averaging their particle sizes.

[0037] The particle diameter is the diameter of a spherical particle when the particle is assumed to be perfectly spherical. Such particle diameter can be determined, for example, by cutting out a cross section of a solid-state battery, taking a cross-sectional SEM image using an SEM, calculating the cross-sectional area S of the particle using image analysis software (e.g., "A-zo-kun" (manufactured by Asahi Kasei Engineering Co., Ltd.)), and then calculating the particle diameter R using the following formula:

[0038]

number

[0039] The average particle size of the negative electrode active material in the negative electrode layer can be measured by specifying the negative electrode active material by its composition when measuring the chemical composition described above.

[0040] The volume proportion of the negative electrode active material in the negative electrode layer is not particularly limited, and from the viewpoint of further improving the utilization rate of the negative electrode active material, it is preferably 20% or more and 80% or less, more preferably 30% or more and 75% or less, and even more preferably 30% or more and 60% or less.

[0041] The volume fraction of the negative electrode active material in the negative electrode layer can be measured from SEM images after FIB cross-section processing. Specifically, the cross-section of the negative electrode layer is observed using SEM-EDX. Elements contained only in the solid electrolyte are detected, and the area where these elements are not detected can be considered to be the negative electrode active material. For example, if the solid electrolyte contains La but the electrode active material does not contain La, the area where W is detected by EDX but La is not detected is determined to be the negative electrode active material, and the volume fraction of the negative electrode active material can be measured by calculating the area ratio of the above area.

[0042] The particle shape of the negative electrode active material in the negative electrode layer is not particularly limited, and may be, for example, any of spherical, flat, and irregular particle shapes.

[0043] The solid electrolyte contained in the negative electrode layer is a solid electrolyte having a garnet structure. If the negative electrode layer contains another solid electrolyte (e.g., a Nasicon-type solid electrolyte) instead of the garnet-type solid electrolyte, the solid electrolyte reacts with the negative electrode active material during sintering, resulting in a decrease in the utilization rate of the negative electrode active material.

[0044] The term "solid electrolyte having a garnet-type structure" means that the solid electrolyte has a garnet-type crystal structure, and in a broad sense, means that the solid electrolyte has a crystal structure that can be recognized as a garnet-type crystal structure by those skilled in the field of solid-state batteries. In a narrow sense, the term "solid electrolyte having a garnet-type structure" means that the solid electrolyte exhibits, in X-ray diffraction, one or more major peaks corresponding to Miller indices specific to the so-called garnet-type crystal structure at a predetermined angle of incidence.

[0045] The garnet-type solid electrolyte is not particularly limited as long as it has a garnet-type crystal structure. From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, the garnet-type solid electrolyte preferably contains Li (lithium), La (lanthanum), Zr (zirconium), and O (oxygen), and more preferably further contains W.

[0046] Garnet-type solid electrolytes have the general formula (G): [ka]

[0047] In formula (G), A represents one or more elements capable of forming a solid solution in the Li site of the oxide having a garnet-type crystal structure. Specifically, A represents one or more elements selected from the group consisting of Ga (gallium), Al (aluminum), Mg (magnesium), Zn (zinc), and Sc (scandium). From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, A is preferably one or more elements selected from the group consisting of Ga (gallium), Al (aluminum), and Sc (scandium), or is absent (i.e., x = 0), more preferably contains Ga or is absent (i.e., x = 0), and even more preferably is absent (i.e., x = 0). When A contains Ga, A may contain a combination of Ga and one or more elements Ax selected from the group consisting of Al, Mg, Zn, and Sc (particularly the group consisting of Al and Sc). B I is one or more elements selected from the group consisting of elements that can take a trivalent valence among elements belonging to Groups 1 to 3 that can take an octacoordinated arrangement with oxygen. I Specifically, B is one or more elements selected from the group consisting of La (lanthanum), Y (yttrium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holminium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium). I Preferably, B contains La (lanthanum) from the viewpoint of further suppressing side reactions during firing and a decrease in the ionic conductivity of the garnet-type oxide, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material. I From the same viewpoint, it is more preferable that the oxide contains La (lanthanum). B IIis one or more elements selected from the group consisting of elements belonging to Groups 1 to 3 that can form an octacoordinate with oxygen and can have a valence other than trivalent. II For details, see the bivalent B II Ca (calcium), Sr (strontium) and Ba (barium) as well as tetravalent B II and Ce (cerium) as the element B. II is preferably absent (ie, y=0) from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material. D I is one or more elements selected from the group consisting of transition elements that can be hexacoordinated with oxygen and elements that can be tetravalent among the typical elements belonging to groups 12 to 15. I Specifically, D is one or more elements selected from the group consisting of Zr (zirconium), Ti (titanium), Hf (hafnium), Ge (germanium), and Sn (tin). I Preferably, D contains Zr (zirconium) from the viewpoint of further suppressing side reactions during firing and a decrease in the ionic conductivity of the garnet-type oxide, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material. I From the same viewpoint, it is more preferable that the alloy contains Zr (zirconium). D II is one or more elements selected from the group consisting of transition elements that can be hexacoordinated with oxygen and elements that can have a valence other than tetravalent among the typical elements belonging to groups 12 to 15. II For details, see trivalent D II Sc (Scandium) as pentavalent D II Ta (tantalum), Nb (niobium), Sb (antimony) and Bi (bismuth) as well as hexavalent D II The element is one or more elements selected from the group consisting of Mo (molybdenum), W (tungsten), and Te (tellurium). IIFrom the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, is preferably one or more elements selected from the group consisting of Nb (niobium), Ta (tantalum), W (tungsten), and Bi (bismuth), or is absent (i.e., z=0). II From the same viewpoint, more preferably, it contains W (tungsten), and further preferably, it contains Ta (tantalum) and W (tungsten).

[0048] In formula (G), α satisfies 3.0≦α≦8.0, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, α preferably satisfies 5.5≦α≦7.0, more preferably 6.0≦α≦6.8, even more preferably 6.2≦α≦6.8, and particularly preferably 6.2≦α≦6.7. β satisfies 2.5≦β≦3.5, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, it preferably satisfies 2.6≦β≦3.4, more preferably 2.7≦β≦3.3, even more preferably 2.8≦β≦3.2, particularly preferably 2.9≦β≦3.1, and most preferably 3.0. I When contains two or more elements, "β-y" is the sum of the numbers for each element. γ satisfies 1.5≦γ≦2.5, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, preferably satisfies 1.6≦γ≦2.4, more preferably 1.7≦γ≦2.3, even more preferably 1.8≦γ≦2.2, particularly preferably 1.9≦γ≦2.1, and most preferably 2.0. I When two or more elements are included, "γ-z" is the sum of the numbers for the respective elements. "γ-z" is usually 1.0 or more and 2.5 or less, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, it is preferably 1.2 or more and 2.2 or less, more preferably 1.3 or more and 1.7 or less. ω satisfies 11≦ω≦13, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, preferably satisfies 11≦ω≦12.5, more preferably 11.5≦ω≦12.5, and even more preferably "12-σ". δ indicates the amount of oxygen vacancy and may be 0. δ usually satisfies 0≦δ<1. The amount of oxygen vacancy δ cannot be quantitatively analyzed even using the latest equipment, so it may be considered to be 0. x satisfies 0≦x≦1.0, and from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, preferably satisfies 0≦x≦0.8, more preferably 0≦x≦0.6, even more preferably 0≦x≦0.4, particularly preferably 0≦x≦0.2, and most preferably 0. When A contains two or more elements, the total number of x for each element (i.e., the number corresponding to x for each element) may be within the above range of x. When A contains two or more elements, each of x for each element (i.e., the number corresponding to x for each element) may independently be 0.01 or more and 0.5 or less, particularly 0.03 or more and 0.18 or less. In particular, when A contains a combination of Ga and one or more elements Ax selected from the group consisting of Al, Mg, Zn, and Sc (particularly the group consisting of Al and Sc), x for Ga (hereinafter, x Ga ) and x with respect to Ax (hereafter, x Ax From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, it is preferable that the temperature (temperature) is within the following range: x Ga is between 0.01 and 0.3, in particular between 0.03 and 0.18; x Ax is 0.01 or more and 0.3 or less, particularly 0.03 or more and 0.18 or less; when Ax contains two or more elements, x for each element Ax (i.e., x for each element Ax The total number of (number equivalent to) is the above x Ax It is sufficient if it is within the range. y is a value smaller than β, and usually satisfies 0≦y≦1.0. From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, y preferably satisfies 0≦y≦0.8, more preferably 0≦y≦0.6, even more preferably 0≦y≦0.4, particularly preferably 0≦y≦0.2, and most preferably 0. II When contains two or more elements, the total number of y for each element (that is, the number corresponding to y for each element) may be within the above range of y. z is a value equal to or less than γ, and usually satisfies 0≦z≦2.2. From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, z preferably satisfies 0≦z≦2.0, more preferably 0≦z≦1.0, even more preferably 0.2≦z≦0.8, and particularly preferably satisfies 0.3≦z≦0.6. II When D contains two or more elements, the total number of z for each element (i.e., the number corresponding to z for each element) may be within the above range of z. II When D contains two or more elements, z for each element (i.e., the number corresponding to z for each element) may independently be 0.01 or more and 1.0 or less, particularly 0.05 or more and 0.5 or less. II If includes Ta and W, then z with respect to Ta (hereinafter, z Ta ) and z with respect to W (hereafter, z W From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, it is preferable that the temperature (temperature) is within the following range: z Ta is between 0.1 and 1.0, in particular between 0.2 and 0.6; z W is 0.01 or more and 0.5 or less, particularly 0.08 or more and 0.2 or less.

[0049] Specific examples of the garnet-type solid electrolyte represented by the general formula (G) include, for example, Li 6.6 La3(Zr 1.6 Ta 0.4 )O 12 , (Li 6.4 Ga 0.05 Al 0.15 )La3Zr2O 12, (Li 6.4 Al 0.2 )La3Zr2O 12 , (Li 6.4 Ga 0.15 Sc 0.05 )La3Zr2O 12 , Li 6.75 La3(Zr 1.75 Nb 0.25 )O 12 , Li 6.4 La3(Zr 1.5 Ta 0.4 W 0.1 )O 12 , Li 6.3 La3(Zr 1.45 Ta 0.4 W 0.15 )O 12 , Li 6.53 La3(Zr 1.53 Ta 0.4 Bi 0.07 )O 12 etc.

[0050] The chemical composition of the solid electrolyte may be an average chemical composition. The average chemical composition of the solid electrolyte (particularly a solid electrolyte having a garnet structure) in the anode layer refers to the average value of the chemical composition of the solid electrolyte in the thickness direction of the anode layer. The average chemical composition of the solid electrolyte can be analyzed and measured by breaking the solid battery and performing EDX composition analysis using SEM-EDX (energy dispersive X-ray spectroscopy) in a field of view that includes the entire thickness direction of the anode layer. In the negative electrode layer, the average chemical composition of the negative electrode active material and the average chemical composition of the solid electrolyte can be measured separately based on their compositions in the composition analysis.

[0051] The solid electrolyte of the negative electrode layer can be obtained by the same method as that for the negative electrode active material, except that a raw material compound containing a predetermined metal atom is used, or can be obtained as a commercially available product.

[0052] The chemical composition and crystalline structure of the solid electrolyte in the negative electrode layer usually remain substantially unchanged by sintering, and the solid electrolyte preferably has the above-described average chemical composition and crystalline structure in the solid-state battery after sintering the negative electrode layer together with the positive electrode layer and the solid electrolyte layer.

[0053] The volume ratio of the solid electrolyte having a garnet structure in the negative electrode layer is not particularly limited, and from the viewpoint of a balance between further improving the utilization rate of the negative electrode active material and increasing the energy density of the solid-state battery, it is preferably 10% or more and 50% or less, and more preferably 20% or more and 40% or less.

[0054] The volume fraction of the garnet-type solid electrolyte in the negative electrode layer can be measured by the same method as the volume fraction of the negative electrode active material. The presence of a garnet-type solid electrolyte can be determined by detecting the elements contained in the garnet-type solid electrolyte using EDX or the like. For example, if the solid electrolyte contains Zr or La, the determination is based on the portion where Zr and / or La are detected by EDX.

[0055] The present invention does not preclude the negative electrode layer from containing a solid electrolyte other than the garnet-type solid electrolyte as the solid electrolyte, but from the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, it is preferable that the negative electrode layer does not contain any other solid electrolyte.

[0056] In the present invention, the negative electrode layer contains the above-described negative electrode active material and the above-described garnet-type solid electrolyte in combination, whereby the reaction between the negative electrode active material and the garnet-type solid electrolyte can be sufficiently suppressed, and as a result, the decrease in the utilization rate of the negative electrode active material can be sufficiently suppressed.

[0057] From the viewpoint of further suppressing the reaction between the solid electrolyte and the negative electrode active material, in each of a more preferred embodiment A, a further preferred embodiment B, and a most preferred embodiment C, the negative electrode layer contains the following negative electrode active material and garnet-type solid electrolyte in combination:

[0058] Implementation Example A Negative electrode active material A: Among the above-mentioned negative electrode active materials, a negative electrode active material having a chemical composition represented by the same general formula as the above-mentioned general formula (N) and having a single-phase structure of a high-temperature phase Li4WO5 type structure. In other words, the negative electrode active material A may be a negative electrode active material that has a chemical composition represented by the above general formula (N) and has a single-phase structure of a high-temperature phase Li4WO5-type crystal structure. Garnet-type solid electrolyte A: A garnet-type solid electrolyte having a chemical composition represented by the above general formula (G).

[0059] Implementation Example B Negative electrode active material B: Among the above-mentioned negative electrode active materials, a negative electrode active material having the following chemical composition and a single-phase structure of a high-temperature phase Li4WO5 type structure: Chemical composition: A chemical composition represented by the same general formula as the above general formula (N), except that α / β satisfies 3.8≦α / β≦6.5 and M is W. In other words, the negative electrode active material B may be a negative electrode active material in which, in the above-mentioned general formula (N), α / β satisfies 3.8≦α / β≦6.5 and M is W, and which has a single-phase structure of a high-temperature phase Li4WO5-type crystal structure. Garnet-type solid electrolyte B: Among the above-mentioned garnet-type solid electrolytes, a garnet-type solid electrolyte having the following chemical composition: Chemical composition = A chemical composition represented by the same general formula as the above general formula (G) except that condition (s1) is satisfied: Condition (s1): A contains Ga or does not contain Ga (i.e., x=0). For example, x=0 or A contains Ga and does not contain Ga. <x≦1.0であってもよい。 In other words, the garnet-type solid electrolyte B may be a garnet-type solid electrolyte that satisfies the above condition (s1) in the above general formula (G).

[0060] Implementation Example C Negative electrode active material C: Among the above-mentioned negative electrode active materials, a negative electrode active material having the following chemical composition and a single-phase structure of a high-temperature phase Li4WO5 type structure: Chemical composition: A chemical composition represented by the same general formula as the above general formula (N), except that α / β satisfies 3.8≦α / β≦6.5 and M is W. In other words, the negative electrode active material C may be a negative electrode active material in which, in the above-mentioned general formula (N), α / β satisfies 3.8≦α / β≦6.5 and M is W, and which has a single-phase structure of a high-temperature phase Li4WO5-type crystal structure. Garnet-type solid electrolyte C: Among the above-mentioned garnet-type solid electrolytes, a garnet-type solid electrolyte having the following chemical composition: Chemical composition = A chemical composition represented by the same general formula as the above general formula (G) except that the condition (s1) and the condition (s2) are satisfied: Condition (s1): A contains Ga or does not contain Ga (i.e., x=0); for example, x=0 or A contains Ga and does not contain Ga. <x≦1.0であってもよい。 Condition(s2):D II includes Ta (tantalum) and W (tungsten). In other words, the garnet-type solid electrolyte C may be a garnet-type solid electrolyte that satisfies the above conditions (s1) and (s2) in the above general formula (G).

[0061] The negative electrode layer may further contain a sintering aid and / or a conductive aid.

[0062] By including a sintering aid in the negative electrode layer, densification becomes possible even during sintering at a lower temperature, and element diffusion at the interface between the negative electrode active material and the solid electrolyte layer can be suppressed. Sintering aids known in the field of solid-state batteries can be used. From the viewpoint of further improving the utilization rate of the negative electrode active material, the inventors have conducted studies and found that the composition of the sintering aid preferably contains at least Li (lithium), B (boron), and O (oxygen), with the molar ratio of Li to B (Li / B) being 2.0 or more. These sintering aids have low melting points, and by promoting liquid phase sintering, the negative electrode layer can be densified at a lower temperature. Furthermore, by using the above composition, side reactions between the sintering aid and the garnet-type solid electrolyte during sintering can be further suppressed. Examples of sintering aids that satisfy these requirements include Li3BO3, (Li 2.7 Al 0.3 )BO3, Li 2.4 Al 0.2 BO3, Li 2.8 (B 0.8 C 0.2 Among these, Li has particularly high ionic conductivity. 2.4 Al 0.2 It is particularly preferred to use BO3.

[0063] The volume fraction of the sintering aid in the negative electrode layer is not particularly limited, and from the viewpoint of a balance between further improving the utilization rate of the negative electrode active material and increasing the energy density of the solid-state battery, it is preferably 0.1% or more and 10% or less, and more preferably 1% or more and 7% or less.

[0064] The volume fraction of the sintering aid in the negative electrode layer can be measured in the same manner as the volume fraction of the negative electrode active material. When the above-mentioned sintering aid is used, B (boron) can be detected by EDX and the region of the sintering aid can be determined.

[0065] The conductive additive in the negative electrode layer may be any conductive additive known in the field of solid-state batteries. From the viewpoint of further improving ionic conductivity and further suppressing the growth of Li dendrites, preferred conductive additives include metal materials such as Ag (silver), Au (gold), Pd (palladium), Pt (platinum), Cu (copper), Sn (tin), and Ni (nickel); and carbon materials such as acetylene black, Ketjen black, Super P (registered trademark), and carbon nanotubes such as VGCF (registered trademark). The shape of the carbon material is not particularly limited, and any shape, such as spherical, plate-like, or fibrous, may be used.

[0066] The volume proportion of the conductive additive in the negative electrode layer is not particularly limited, but from the viewpoint of further improving the utilization rate of the active material, it is preferably 10% or more and 50% or less, and more preferably 20% or more and 40% or less.

[0067] The thickness of the negative electrode layer is usually 2 to 100 μm, and from the viewpoint of further improving the utilization rate of the active material, it is preferably 1 to 30 μm. The thickness of the negative electrode layer is the average value of thicknesses measured at any 10 points on the SEM image.

[0068] In the negative electrode layer, the porosity is not particularly limited, and from the viewpoint of further improving the utilization rate of the active material, it is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0069] The porosity of the negative electrode layer was measured from an SEM image after FIB cross-section processing.

[0070] In the negative electrode layer, the negative electrode active material and the solid electrolyte (and optionally the conductive additive and sintering additive) may all be in the form of a sintered body. For example, when the negative electrode layer contains the negative electrode active material, the solid electrolyte, the conductive additive, and the sintering additive, the negative electrode layer may be in the form of a sintered body in which the negative electrode active material particles are bonded together by the solid electrolyte, the conductive additive, and the sintering additive, and the negative electrode active material particles, the solid electrolyte, the conductive additive, and the sintering additive are joined to each other by sintering.

[0071] (positive electrode layer) In the present invention, the positive electrode layer is not particularly limited. For example, the positive electrode layer contains a positive electrode active material. The positive electrode layer may be in the form of a sintered body containing positive electrode active material particles.

[0072] The positive electrode layer is a layer capable of absorbing and releasing metal ions, preferably a layer capable of absorbing and releasing lithium ions. The positive electrode active material is not particularly limited, and positive electrode active materials known in the field of solid-state batteries can be used. Examples of the positive electrode active material include lithium-containing phosphate compound particles having a Nasicon structure, lithium-containing phosphate compound particles having an olivine structure, lithium-containing layered oxide particles, and lithium-containing oxide particles having a spinel structure. Specific examples of lithium-containing phosphate compounds having a Nasicon structure that are preferably used include Li3V2(PO4)3, etc. Specific examples of lithium-containing phosphate compounds having an olivine structure that are preferably used include LiFePO4 and LiMnPO4, etc. Specific examples of lithium-containing layered oxide particles that are preferably used include LiCoO2, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 Specific examples of lithium-containing oxides having a spinel structure that are preferably used include LiMnO, LiNi 0.5 Mn 1.5 O4, Li4Ti5O 12 The positive electrode active material is LiCoO2, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 It is more preferable to use a lithium-containing layered oxide such as O2. Only one type of these positive electrode active material particles may be used, or a mixture of two or more types may be used.

[0073] The positive electrode active material in the positive electrode layer having a Nasicon structure means that the positive electrode active material (particularly its particles) has a Nasicon crystal structure, and in a broad sense, it means that the positive electrode active material has a crystal structure that can be recognized as a Nasicon crystal structure by those skilled in the art of solid-state batteries. In a narrow sense, the positive electrode active material in the positive electrode layer having a Nasicon structure means that the positive electrode active material (particularly its particles) shows one or more main peaks in X-ray diffraction at a predetermined incident angle, which correspond to Miller indices specific to the so-called Nasicon crystal structure. Preferred examples of positive electrode active materials having a Nasicon structure include the compounds exemplified above.

[0074] The positive electrode active material in the positive electrode layer having an olivine structure means that the positive electrode active material (particularly particles thereof) has an olivine crystal structure, and in a broad sense, means that the positive electrode active material has a crystal structure that can be recognized as an olivine crystal structure by those skilled in the field of solid-state batteries. In a narrow sense, the positive electrode active material in the positive electrode layer having an olivine structure means that the positive electrode active material (particularly particles thereof) exhibits, in X-ray diffraction, one or more main peaks corresponding to Miller indices specific to the so-called olivine crystal structure at a predetermined angle of incidence. Preferred positive electrode active materials having an olivine structure include the compounds exemplified above.

[0075] The positive electrode active material in the positive electrode layer having a spinel structure means that the positive electrode active material (particularly its particles) has a spinel crystal structure, and in a broad sense, means that the positive electrode active material has a crystal structure that can be recognized as a spinel crystal structure by those skilled in the field of solid-state batteries. In a narrow sense, the positive electrode active material in the positive electrode layer having a spinel structure means that the positive electrode active material (particularly its particles) exhibits one or more main peaks corresponding to Miller indices specific to the so-called spinel crystal structure at a predetermined incident angle in X-ray diffraction. Preferred positive electrode active materials having a spinel structure include the compounds exemplified above.

[0076] The chemical composition of the positive electrode active material may be an average chemical composition. The average chemical composition of the positive electrode active material means the average value of the chemical composition of the positive electrode active material in the thickness direction of the positive electrode layer. The average chemical composition of the positive electrode active material can be analyzed and measured by breaking the solid-state battery and performing EDX composition analysis using SEM-EDX (energy dispersive X-ray spectroscopy) in a field of view that includes the entire positive electrode layer in the thickness direction.

[0077] The positive electrode active material can be obtained by the same method as the negative electrode active material, except that a raw material compound containing a predetermined metal atom is used, or can be obtained as a commercially available product.

[0078] The chemical composition and crystalline structure of the positive electrode active material in the positive electrode layer usually remain substantially unchanged by sintering, and the positive electrode active material may have the above-described chemical composition and crystalline structure in the solid-state battery after sintering the positive electrode layer together with the negative electrode layer and the solid electrolyte layer.

[0079] The average particle size of the positive electrode active material is not particularly limited and may be, for example, 0.01 μm or more and 10 μm or less, and preferably 0.05 μm or more and 4 μm or less.

[0080] The average particle size of the positive electrode active material can be determined by the same method as that for the average particle size of the negative electrode active material in the negative electrode layer.

[0081] The average particle size of the positive electrode active material in the positive electrode layer is directly reflected by the average particle size of the positive electrode active material used during manufacturing, especially when LCO is used for the positive electrode particles.

[0082] The particle shape of the positive electrode active material in the positive electrode layer is not particularly limited, and may be, for example, any of spherical, flat, and irregular particle shapes.

[0083] The volume ratio of the positive electrode active material in the positive electrode layer is not particularly limited, but is preferably 30% or more and 90% or less, and more preferably 40% or more and 70% or less.

[0084] The positive electrode layer may further contain, in addition to the positive electrode active material, for example, a solid electrolyte, a sintering aid, and / or a conductive aid.

[0085] The type of solid electrolyte contained in the positive electrode layer is not particularly limited. For example, a solid electrolyte having a garnet structure (Li 6.4 Ga 0.2 )La3Zr2O 12 , Li 6.4 La3(Zr 1. 6Ta 0.4 )O 12 , (Li 6.4 Al 0.2 )La3Zr2O 12 , Li 6.5 La3(Zr 1.5 Mo 0.25 )O 12 , a solid electrolyte Li with a LISICON-type structure 3+x (V 1-x Si x )O4, a solid electrolyte with a perovskite structure, La 2 / 3-x Li 3x Examples include TiO3, solid electrolytes having an amorphous structure Li3BO3-Li4SiO4, etc. Among these, it is particularly preferable to use solid electrolytes having a garnet structure and solid electrolytes having a LISICON structure.

[0086] The solid electrolyte for the positive electrode layer can be obtained by the same method as for the negative electrode active material, except that a raw material compound containing a predetermined metal atom is used, or can be obtained as a commercially available product.

[0087] The chemical composition and crystalline structure of the solid electrolyte in the positive electrode layer typically remain substantially unchanged by sintering, and the solid electrolyte may have the average chemical composition and crystalline structure described above in the solid-state battery after sintering the positive electrode layer together with the negative electrode layer and the solid electrolyte layer.

[0088] The volume ratio of the solid electrolyte in the positive electrode layer is not particularly limited, but is preferably 20% to 60%, more preferably 30% to 45%, from the viewpoint of a balance for increasing the energy density of the solid battery.

[0089] As the sintering aid in the positive electrode layer, the same compounds as the sintering aid in the negative electrode layer can be used.

[0090] The volume proportion of the sintering aid in the positive electrode layer is not particularly limited, but is preferably 0.1% to 20%, more preferably 1% to 10%, from the viewpoint of a balance for increasing the energy density of the solid-state battery.

[0091] As the conductive additive in the positive electrode layer, the same compounds as the conductive additive in the negative electrode layer can be used.

[0092] The volume ratio of the conductive additive in the positive electrode layer is not particularly limited, but is preferably 10% to 50%, more preferably 20% to 40%, from the viewpoint of a balance for increasing the energy density of the solid battery.

[0093] In the positive electrode layer, the porosity is not particularly limited, but is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0094] The porosity of the positive electrode layer is a value measured in the same manner as the porosity of the negative electrode layer.

[0095] (solid electrolyte layer) In the present invention, the solid electrolyte layer is not particularly limited. The solid electrolyte layer preferably contains a solid electrolyte having a garnet structure from the viewpoint of further suppressing side reactions with the negative electrode active material during firing and further improving the utilization rate of the active material. The solid electrolyte layer may be in the form of a sintered body containing the solid electrolyte.

[0096] The garnet-type solid electrolyte contained in the solid electrolyte layer is the same as the solid electrolyte having a garnet-type structure contained in the anode layer, and may be selected from the same range as the solid electrolyte having a garnet-type structure described in the description of the anode layer. When both the solid electrolyte layer and the anode layer contain solid electrolytes having a garnet-type structure, the solid electrolyte having a garnet-type structure contained in the solid electrolyte layer and the solid electrolyte having a garnet-type structure contained in the anode layer may have the same chemical composition or may have different chemical compositions.

[0097] The garnet-type solid electrolyte contained in the solid electrolyte layer is not particularly limited as long as it has a garnet-type crystal structure, and preferably has a chemical composition within the range of the chemical composition represented by the above-mentioned general formula (G), similar to the garnet-type solid electrolyte contained in the negative electrode layer. When the solid electrolyte layer contains a solid electrolyte having such a chemical composition, it is possible to achieve a further improvement in the utilization rate of the negative electrode active material in the interface region between the negative electrode layer and the solid electrolyte layer.

[0098] The chemical composition of the solid electrolyte in the solid electrolyte layer may be an average chemical composition. The average chemical composition of the solid electrolyte (particularly a solid electrolyte having a garnet-type structure) in the solid electrolyte layer means the average value of the chemical composition of the solid electrolyte in the thickness direction of the solid electrolyte layer. The average chemical composition of the solid electrolyte can be analyzed and measured by breaking the solid battery and performing EDX composition analysis using SEM-EDX (energy dispersive X-ray spectroscopy) in a field of view that includes the entire thickness direction of the solid electrolyte layer.

[0099] The chemical composition and crystalline structure of the solid electrolyte in the solid electrolyte layer usually remain substantially unchanged by sintering, and the solid electrolyte may have the above-described chemical composition and crystalline structure in the solid-state battery after sintering the solid electrolyte layer together with the anode layer and the cathode layer.

[0100] The volume ratio of the solid electrolyte in the solid electrolyte layer is not particularly limited, but is preferably 10% to 100%, more preferably 20% to 100%, and even more preferably 30% to 100%.

[0101] The volume fraction of the solid electrolyte in the solid electrolyte layer can be measured by the same method as that for the volume fraction of the solid electrolyte in the negative electrode layer.

[0102] The solid electrolyte layer may further contain, in addition to the solid electrolyte, for example, a sintering aid. At least one of the anode layer and the solid electrolyte layer, preferably both, preferably further contains a sintering aid. "At least one of the anode layer and the solid electrolyte layer further contains a sintering aid" means that either the anode layer or the solid electrolyte layer may further contain a sintering aid, or both of them may further contain a sintering aid.

[0103] As the sintering aid in the solid electrolyte layer, the same compounds as the sintering aid in the negative electrode layer can be used.

[0104] The volume fraction of the sintering aid in the solid electrolyte layer is not particularly limited, and from the viewpoint of a balance between further improving the utilization rate of the negative electrode active material and increasing the energy density of the solid-state battery, it is preferably 0.1% or more and 20% or less, and more preferably 1% or more and 10% or less.

[0105] The thickness of the solid electrolyte layer is usually 0.1 μm or more and 30 μm or less, and from the viewpoint of thinning the solid electrolyte layer, it is preferably 1 μm or more and 20 μm or less.

[0106] The thickness of the solid electrolyte layer is the average value of thicknesses measured at 10 arbitrary points on the SEM image.

[0107] In the solid electrolyte layer, the porosity is not particularly limited, but is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0108] The porosity of the solid electrolyte layer is a value measured by the same method as for the porosity of the negative electrode layer.

[0109] The solid-state battery of the present invention may further include any of the components that conventional solid-state batteries may include, such as a positive electrode current collecting layer, a negative electrode current collecting layer, a protective layer, and end electrodes.

[0110] [Solid-state battery manufacturing method] The solid-state battery can be manufactured by, for example, the so-called green sheet method, the printing method, or a combination of these methods.

[0111] The green sheet method will now be described. First, a paste is prepared by appropriately mixing a solvent, binder, etc. with the positive electrode active material. The paste is applied to a sheet and dried to form a first green sheet for forming the positive electrode layer. The first green sheet may contain a solid electrolyte, a conductive additive, and / or a sintering additive.

[0112] A paste is prepared by appropriately mixing the negative electrode active material with a solid electrolyte, a solvent, a binder, etc. The paste is applied to a sheet and dried to form a second green sheet for forming the negative electrode layer. The second green sheet may contain a conductive additive and / or a sintering additive.

[0113] A paste is prepared by appropriately mixing a solvent, a binder, etc. with the solid electrolyte. The paste is applied and dried to prepare a third green sheet for forming the solid electrolyte layer. The third green sheet may contain a sintering aid, etc.

[0114] The solvent and binder used to prepare the first to third green sheets are not particularly limited. For example, a solvent that can be used in the production of a positive electrode layer, a negative electrode layer, or a solid electrolyte layer in the field of solid-state batteries is used as the solvent. Specific examples of the solvent typically include solvents that can be used with the binders described below. Examples of such solvents include alcohols such as 2-propanol. Examples of the binder include binders that can be used in the production of a positive electrode layer, a negative electrode layer, or a solid electrolyte layer in the field of solid-state batteries. Specific examples of such binders include butyral resins and acrylic resins.

[0115] Next, the first to third green sheets are appropriately stacked to produce a laminate. The produced laminate may be pressed. A preferred pressing method is isostatic pressing. The laminate is then heated to a temperature of, for example, 300°C to 500°C to remove the binder, and then sintered at 600 to 900°C to produce a solid-state battery.

[0116] The printing method is explained below. The term "printing" is used in the context of a concept that includes coating. The printing method is similar to the green sheet method except for the following points. Ink for each layer is prepared having the same composition as the paste for each layer used to obtain the green sheet, except that the solvent and resin are blended in amounts suitable for use as an ink. · Each layer is printed using ink and laminated to create a laminate.

[0117] The present invention will be described in more detail below based on specific examples, but the present invention is not limited to the following examples and can be implemented with appropriate modifications within the scope that does not change the gist of the present invention. [Example]

[0118] <Experimental Example 1> (Production of garnet-type solid electrolytes) Raw materials, including lithium hydroxide monohydrate (LiOH·H2O), lanthanum hydroxide (La(OH)3), zirconium oxide (ZrO2), and tantalum oxide (Ta2O5), were weighed to produce the solid electrolyte with the composition shown in Table 1. Water was then added, the mixture was sealed in a 100 ml polyethylene pot, and the pot was rotated at 150 rpm on a pot rack for 16 hours to mix the raw materials. The lithium source, lithium hydroxide monohydrate (LiOH·H2O), was added in an amount 3% by mass in excess of the target composition to account for Li deficiency during sintering. The resulting slurry was then dried and pre-sintered in oxygen gas at 900°C for 5 hours. The pre-sintered material was then added to a toluene-acetone mixed solvent, ground in a planetary ball mill for 6 hours, and then dried to obtain the solid electrolyte powder with the composition shown in Table 1.

[0119] (Manufacturing Nasicon-type solid electrolytes) Raw materials containing lithium carbonate (Li2CO3), aluminum oxide (Al2O3), germanium oxide (GeO2), and ammonium dihydrogen phosphate ((NH4)H2PO4) were weighed to obtain the solid electrolyte composition shown in Table 1 and mixed thoroughly in a mortar. The mixture was calcined at 400°C for two hours in an air atmosphere. Water was added to the calcined powder, which was then sealed in a 100 ml polyethylene pot and rotated on a pot rack at 150 rpm for 16 hours to pulverize the calcined powder. The resulting slurry was then dried and calcined in oxygen gas at 850°C for five hours. A toluene-acetone mixed solvent was then added to the calcined material, which was then pulverized in a planetary ball mill for six hours and then dried to obtain the solid electrolyte powder with the composition shown in Table 1.

[0120] (Production of electrode active materials) Raw materials containing lithium carbonate (Li2CO3) and tungsten oxide (WO3) were weighed out so that the composition of the negative electrode active material had the Li / W ratio shown in Table 1, and then thoroughly mixed in a mortar. For Example 3, the materials were weighed out so that the Li / W ratio was 6.0. Next, ethanol was added, and the mixture was sealed in a 100 ml polyethylene pot. The pot was rotated on a pot rack at 150 rpm for 16 hours to mix the raw materials. The resulting slurry was dried and then sintered in air under the following conditions: The negative electrode active materials of Comparative Examples 1 and 2 and Example 2 were sintered at 650°C for 5 hours. The negative electrode active materials of Comparative Example 4 and Examples 1 and 3 were sintered at 750°C for 5 hours. A toluene-acetone mixed solvent was then added to the resulting sintered product, which was then pulverized in a planetary ball mill for 6 hours and then dried to obtain the negative electrode active material powders shown in Table 1. The electrode active material (purity of 99% or more) having the composition shown in Comparative Example 3 was obtained by pulverizing a commercially available product in a planetary ball mill for 6 hours and then drying it.

[0121] (Examples 1 to 3 and Comparative Examples 1 to 4) The solid electrolyte and electrode active material shown in Table 1 were mixed and sintered at 800°C to prepare a sample, which was then analyzed by XRD to evaluate whether the solid electrolyte and electrode active material had decomposed. If no peaks derived from either or both of the solid electrolyte and the electrode active material were observed after sintering, it was judged as "decomposition occurred," and if peaks derived from both the solid electrolyte and the electrode active material were observed after sintering, it was judged as "no decomposition."

[0122] FIG. 1 shows the XRD patterns after sintering of Comparative Example 1 and Example 1, as well as the XRD pattern of either the solid electrolyte or the electrode active material after sintering. From Comparative Example 1, when an electrode active material with a Li / W ratio of 2 was used, the peak derived from the garnet-type solid electrolyte completely disappeared after sintering, indicating that the solid electrolyte decomposed during sintering. When an active material with a Li / W ratio of 2 or less was used, the garnet-type solid electrolyte decomposed during sintering (Table 1). When a negative electrode active material with a Li / W ratio of 2 was used, as in Comparative Example 1, decomposition of the solid electrolyte (LLZ) proceeded during sintering, and La2Zr2O7, which has no ionic conductivity, was produced.

[0123] From Example 1, when an electrode active material with a Li / W ratio of more than 2 (for example, 4) was used, peaks derived from both the electrode active material and the garnet-type solid electrolyte were observed after sintering, and it was found that side reactions between the two were unlikely to proceed. When a negative electrode active material with a Li / W ratio of more than 2 (for example, 4) was used as in Example 1, it was found that both the negative electrode active material and the solid electrolyte (LLZ) remained even after sintering. Since side reactions were unlikely to proceed during sintering, good charge / discharge characteristics were likely to be obtained.

[0124] From the above, it was found that when an electrode active material with a Li / W ratio of more than 2 is used, side reactions during sintering with the garnet-type solid electrolyte can be extremely suppressed. From Comparative Example 4, it was found that when a NASICON type solid electrolyte was used as the solid electrolyte, the reaction proceeded even when an electrode active material with a Li / W ratio of more than 2 was used. Therefore, it was found that the effects of the present invention can be obtained by combining an electrode active material having a Li / W ratio of more than 2 with a garnet-type solid electrolyte.

[0125] [Table 1]

[0126] In Table 1, "high-temperature phase Li4WO5" refers to a "single-phase structure of the high-temperature phase Li4WO5-type crystal structure." The crystal structures were determined by the above-mentioned method based on the peaks and their intensities specific to each crystal structure in X-ray diffraction (XRD using CuKα radiation). The same applies to Tables 2 and 3 below.

[0127] <Experimental Example 2> (Production of garnet-type solid electrolytes) A solid electrolyte powder having the composition shown in Table 2 was obtained by the same method as the method for producing a garnet-type solid electrolyte in Experimental Example 1, except that raw materials were selected and weighed so that the composition of the garnet-type solid electrolyte would be as shown in Table 2. The raw materials used were the same as those described in "Production of Garnet-Type Solid Electrolyte" in Experimental Example 1, as well as gallium oxide (Ga2O3), aluminum oxide (Al2O3), scandium oxide (Sc2O3), niobium oxide (Nb2O5), tungsten oxide (WO3), and bismuth oxide (Bi2O3).

[0128] (Production of negative electrode active material) Raw materials containing lithium carbonate (Li2CO3), tungsten oxide (WO3), molybdenum oxide (MoO3), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), and magnesium oxide (MgO) were weighed out so that the composition of the negative electrode active material would have the element ratios shown in Table 2. For Example 6, the materials were weighed out so that the Li / W ratio was 3.7. For Example 7, the materials were weighed out so that the Li / W ratio was 6.0. For Example 11, the materials were weighed out so that the Li / W ratio was 4.4. Next, ethanol was added, and the mixture was placed in a 100 ml polyethylene pot. The pot was rotated at 150 rpm on a pot rack for 16 hours to mix the raw materials. The resulting slurry was then dried and sintered in air under the following conditions. The negative electrode active materials of Comparative Examples 5 and 6 and Examples 5 and 6 were sintered at 650°C for 5 hours. The negative electrode active materials of Comparative Example 4 and Examples 4, 7, 8, 9, 10, 11, and 12 were sintered at 750°C for 5 hours. A toluene-acetone mixed solvent was then added to the resulting sintered product, which was then pulverized in a planetary ball mill for 6 hours and dried to obtain the negative electrode active material powders shown in Table 1. The electrode active material (purity of 99% or more) having the composition shown in Comparative Example 7 was obtained by pulverizing a commercially available product in a planetary ball mill for 6 hours and then drying it.

[0129] (Manufacturing of solid electrolyte layers (garnet-type solid electrolyte substrates)) The composition of the garnet-type solid electrolyte is "(Li 6.4 Ga 0.05 Al 0.15 )La3Zr2O 12 The garnet-type solid electrolyte was prepared by the same method as in Experimental Example 1, except that the raw materials were selected and weighed so that "(Li 6.4 Ga 0.05 Al 0.15 )La3Zr2O 12 A garnet-type solid electrolyte powder having the composition " was obtained. The resulting garnet-type solid electrolyte powder, butyral resin, and alcohol were mixed in a mass ratio of 200:15:140, and then the alcohol was removed on a hot plate at 80°C to obtain a solid electrolyte powder coated with butyral resin as a binder. The butyral resin-coated solid electrolyte powder was then pressed into tablets at 90 MPa using a tablet press. The resulting solid electrolyte tablets were thoroughly covered with mother powder and sintered at 500°C in an oxygen atmosphere to remove the butyral resin. The tablets were then sintered at approximately 1200°C for 3 hours in an oxygen atmosphere. The temperature was then lowered to obtain a sintered solid electrolyte. The surface of the resulting sintered body was polished to obtain a garnet-type solid electrolyte substrate (solid electrolyte layer).

[0130] (Production of sintering aid powder) Lithium hydroxide monohydrate (LiOH·H2O), boron oxide (B2O3), and aluminum oxide (Al2O3) were weighed appropriately, mixed in a mortar, and then pre-sintered at 650°C for 5 hours. The pre-sintered powder obtained was crushed and mixed in a mortar, and then sintered at 680°C for 40 hours. A toluene-acetone mixed solvent was added to the sintered powder obtained, and it was crushed for 6 hours using a planetary ball mill and dried to obtain a powder with the composition formula Li 2.4 Al 0.2 A sintering aid powder represented by BO3 was prepared.

[0131] (Examples 4 to 12 and Comparative Examples 5 to 7: Production of Solid-State Batteries) The solid electrolyte powder, negative electrode active material powder, sintering aid powder, and conductive aid powder (Ag particles) listed in Table 2 were weighed out in a volume ratio of 35:30:5:30 and kneaded with alcohol and a binder to prepare a negative electrode layer paste. The negative electrode layer paste was then applied to a solid electrolyte layer (i.e., a solid electrolyte substrate) and dried to obtain a laminate. The laminate was heated to 400°C to remove the binder, and then heat-treated at 800°C for 2 hours in an air atmosphere to produce a solid electrolyte layer and negative electrode layer laminate. Metallic lithium was then attached as a counter electrode and reference electrode to the surface of the solid electrolyte layer opposite the surface of the negative electrode layer of the laminate, and the resulting laminate was sealed in a 2032-type coin cell to produce a solid-state battery.

[0132] (Solid-state battery evaluation; utilization rate of negative electrode active material) The solid state batteries fabricated in each of the comparative examples and examples were evaluated at 25° C. according to the following criteria. Charging was performed at a constant current and constant potential, with the lower limit of charging being 0.2 V (vs. Li / Li + The charge termination condition was when the charge current attenuated to 0.02 C. Discharge was performed at a constant current, and the discharge termination potential was 3.0 V (vs. Li / Li + ) The constant current value for charge and discharge was 0.1 C. The utilization rate of the negative electrode active material was calculated from the measured initial reversible capacity and the theoretical value of the initial reversible capacity according to the following formula, and was evaluated according to the following criteria. The theoretical value of the initial reversible capacity was taken as the amount of electricity when a two-electron reaction proceeded with respect to W. In addition, in the present invention, charging corresponds to a reduction reaction in which lithium ions are inserted into the negative electrode active material, and discharging corresponds to an oxidation reaction in which lithium ions are desorbed from the negative electrode active material.

[0133]

number

[0134] ◎◎; 80% or more (best); ◎: 72% or more but less than 80% (excellent); ○; 60% or more but less than 72% (good); △: 50% or more but less than 60% (no practical problems); ×: Less than 50% (problems in practical use).

[0135] Description of Figures 2A and 2B 2A and 2B show the charge-discharge curves of the solid-state batteries fabricated in Example 4 and Comparative Example 2, respectively. The charge-discharge curve in FIG. 2B reveals that in Comparative Example 2, the utilization rate was approximately 5% or less, making charge and discharge impossible. On the other hand, the charge-discharge curve in FIG. 2A reveals that in Example 4, a capacity component resulting from the Li insertion / deintercalation reaction into the high-temperature phase Li4WO5 was observed in the potential range of 0.2 V to 3.0 V (vs. Li / Li+), demonstrating that the battery functions as a solid-state battery.

[0136] The utilization rate of the negative electrode active material was 5% or less when a negative electrode active material with a Li / W ratio of 2 or less was used. From Experimental Example 1, this is thought to be due to (1) a side reaction occurring between the negative electrode active material and the garnet-type solid electrolyte during sintering, causing the negative electrode active material to be deactivated, and / or (2) the solid electrolyte decomposing, preventing the formation of ion paths in the electrode mixture. It was found that the use of a negative electrode active material with a Li / W ratio of more than 2 (e.g., 4 or more) makes it possible to charge and discharge solid-state batteries. In particular, it was found that a high reversible capacity can be obtained by using a high-temperature phase Li4WO5 crystal structure for the negative electrode active material.

[0137] [Table 2]

[0138] <Experimental Example 3> (Examples 13 to 19: Production of solid state batteries) A solid state battery was produced in the same manner as in Experimental Example 2, except that the negative electrode active material and solid electrolyte had the compositions shown in Table 3. The negative electrode active material was fired under the same conditions as in Example 4.

[0139] (Solid-state battery evaluation; utilization rate of negative electrode active material) In the same manner as in Experimental Example 2, the utilization rate of the negative electrode active material was calculated and evaluated.

[0140] It was found that, as long as the solid electrolyte has a garnet-type crystal structure, the solid-state battery can operate satisfactorily regardless of the solid electrolyte composition used. It was found that the inclusion of W in the garnet-type solid electrolyte is preferable because it results in a higher utilization rate.

[0141] [Table 3] [Industrial Applicability]

[0142] The solid-state battery of the present invention can be used in various fields where battery use or power storage is anticipated. By way of example only, a solid-state battery according to an embodiment of the present invention can be used in electronics packaging. The solid-state battery according to one embodiment of the present invention can also be used in the electrical, information, and communications fields where mobile devices and the like are used (e.g., the electrical and electronic equipment fields including small electronic devices such as mobile phones, smartphones, smart watches, laptops, digital cameras, activity monitors, arm computers, electronic paper, wearable devices, RFID tags, card-type electronic money, and smart watches, or the mobile device field), household and small industrial applications (e.g., power tools, golf carts, and household, nursing care, and industrial robots), large industrial applications (e.g., forklifts, elevators, and harbor cranes), transportation systems (e.g., hybrid cars, electric cars, buses, trains, electrically assisted bicycles, and electric motorcycles), power system applications (e.g., various power generation systems, road conditioners, smart grids, and general household energy storage systems), medical applications (medical devices such as earphones and hearing aids), pharmaceutical applications (medical management systems), IoT fields, and space and deep-sea applications (e.g., space probes, submersible research vessels, and the like).

Claims

1. A solid-state battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the negative electrode layer includes a negative electrode active material and a garnet-type solid electrolyte, The negative electrode active material is a low-temperature phase Li (lithium) alloy containing Li, M (wherein M is one or more elements selected from the group consisting of W (tungsten), Mo (molybdenum), Ta (tantalum), and Zr (zirconium), including W), and O (oxygen), in which the molar ratio (Li / M) of the Li content to the M content is greater than 2.

0. ４ WO ５ type crystal structure, high temperature phase Li ４ WO ５ type crystal structure, and Li ６ WO ６ a negative electrode active material having one or more crystal structures selected from the group consisting of a C1-type crystal structure, The garnet-type solid electrolyte contains, in its chemical composition, Li (lithium), La (lanthanum), Zr (zirconium), and O (oxygen), The solid-state battery is a co-sintered solid-state battery.

2. The negative electrode active material is represented by the general formula (N): 【Chemistry 1】 (In formula (N), M is one or more elements selected from the group consisting of W (tungsten), Mo (molybdenum), Ta (tantalum), and Zr (zirconium), and includes W; M' is one or more elements selected from the group consisting of Na (sodium), K (potassium), Ca (calcium), Ti (titanium), V (vanadium), Sn (tin), Nb (niobium), Zn (zinc), Mn (manganese), Mg (magnesium), Al (aluminum), and Ga (gallium); α and β satisfy the following: 3≦α≦8, 0<β<1.5, and α / β>2; γ satisfies 0≦γ<3; ω satisfies 4<ω<9) The solid-state battery according to claim 1 , having a chemical composition represented by:

3. A solid-state battery as described in claim 2, wherein α further satisfies 3≦α≦5.

5.

4. The negative electrode active material is a low-temperature phase Li ４ WO ５ Li-type crystal structure or high temperature phase ４ WO ５ The solid state battery according to any one of claims 1 to 3, having a crystalline structure.

5. 5. The solid state battery according to claim 1, wherein the garnet-type solid electrolyte further contains W (tungsten) in its chemical composition.

6. The garnet-type solid electrolyte has the general formula (G): 【Chemistry 2】 [In formula (G), A represents one or more elements capable of forming a solid solution in the Li site of the oxide having a garnet-type crystal structure; B Ｉ is one or more elements selected from the group consisting of elements that can take a trivalent valence and belong to Groups 1 to 3 and can take an eight-coordination with oxygen; B ＩＩ is one or more elements selected from the group consisting of elements belonging to Groups 1 to 3 that can be eight-coordinated with oxygen and can have a valence other than trivalent; D Ｉ is one or more elements selected from the group consisting of transition elements capable of forming hexacoordinate bonds with oxygen and elements capable of forming a tetravalent valence among the typical elements belonging to Groups 12 to 15; D ＩＩ is one or more elements selected from the group consisting of transition elements capable of forming a hexacoordinate with oxygen and elements capable of forming a valence other than tetravalent among the typical elements belonging to Groups 12 to 15; α satisfies 3.0≦α≦8.0; β satisfies 2.5≦β≦3.5; γ satisfies 1.5≦γ≦2.5; ω satisfies 11≦ω≦13; x satisfies 0≦x≦1.0; y satisfies 0≦y≦1.0; z satisfies 0≦z≦2.

2. The solid state battery according to any one of claims 1 to 5, having a chemical composition represented by the formula:

7. The negative electrode active material has a chemical composition represented by the general formula (N) and is a high-temperature phase Li ４ WO ５ The solid-state battery according to claim 6 dependent on claim 3, having a single-phase structure of a type crystalline structure.

8. The negative electrode active material is represented by the general formula (N), in which the α / β satisfies 3.8≦α / β≦6.5, and the M is W (tungsten), The solid state battery according to claim 7, wherein the garnet-type solid electrolyte satisfies the following condition (s1) in the general formula (G): Condition (s1): x=0, or A contains Ga and 0<x≦1.

0.

9. The negative electrode active material is represented by the general formula (N), in which the α / β satisfies 3.8≦α / β≦6.5, and the M is W (tungsten), The solid-state battery according to claim 7, wherein the garnet-type solid electrolyte satisfies the following conditions (s1) and (s2) in the general formula (G): Condition (s1): x = 0, or A contains Ga and 0 < x ≦ 1.0; Condition (s2): ＩＩ includes Ta (tantalum) and W (tungsten).

10. 10. The solid state battery according to claim 1, wherein the solid electrolyte layer contains a garnet-type solid electrolyte.

11. 11. The solid state battery according to claim 1, wherein the positive electrode layer and the negative electrode layer are layers capable of absorbing and releasing lithium ions.

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