All-solid-state lithium-ion secondary battery and method for manufacturing all-solid-state lithium-ion secondary battery

Abstract

The present invention provides: an all-solid-state lithium-ion secondary battery comprising a positive electrode layer, a solid-state electrolyte layer, and a negative electrode layer that are arranged in that order, the solid-state electrolyte layer including a non-crystalline solid-state electrolyte that includes a lithium-containing oxide that includes Li, B, and O, and a lithium salt, the ratio of the lithium salt content to the lithium-containing oxide content in the non-crystalline solid-state electrolyte being 0.001–1.5 in a molar ratio, and moisture that is included in a laminated body composed of a positive electrode active material layer, the solid-state electrolyte layer, and a negative electrode active material layer being in a specific state; and a method for manufacturing the same.

Description

All-solid-state lithium-ion secondary battery and method for manufacturing the same

[0001] The present invention relates to an all-solid-state lithium-ion secondary battery and a method for manufacturing an all-solid-state lithium-ion secondary battery.

[0002] Conventionally, liquid electrolytes with high ionic conductivity have been used in lithium-ion secondary batteries. However, liquid electrolytes are flammable, which poses safety issues. Furthermore, because they are liquid, they are difficult to compact, and capacity limitations become an issue when batteries are made larger. In contrast, all-solid-state lithium-ion secondary batteries are one of the next-generation batteries that can solve these issues. The basic structure of an all-solid-state lithium-ion secondary battery is shown in Figure 1. Viewed from the negative electrode side, an all-solid-state lithium-ion secondary battery 10 has a negative electrode current collector 1, a negative electrode active material layer 2, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector 5, in this order. Each layer is in contact with each other, forming an adjacent structure. By adopting such a structure, electrons (e － ) is supplied to the solid electrolyte layer 3, and lithium ions (Li ＋ On the other hand, during discharge, the lithium ions (Li ＋ ) is returned to the positive electrode side through the solid electrolyte layer 3, and electrons are supplied to the operating part 6. In the illustrated example, a light bulb is used as a model for the operating part 6, and it is lit by discharge.

[0003] As described above, all-solid-state lithium-ion secondary batteries require excellent lithium-ion conductivity in the solid electrolyte layer to achieve the desired charge / discharge characteristics. Sulfide-based solid electrolytes or oxide-based solid electrolytes are typically used as the solid electrolytes constituting the solid electrolyte layer. Because sulfide-based solid electrolytes are soft and plastically deformable, particles bond together simply by pressure molding. Therefore, sulfide-based solid electrolytes have low interfacial resistance between particles and excellent ionic conductivity. However, sulfide-based solid electrolytes have the problem of reacting with water to generate toxic hydrogen sulfide. In contrast, oxide-based solid electrolytes have the advantage of being highly safe. However, oxide-based solid electrolytes are hard and resistant to plastic deformation. Increasing the interparticle bonding strength of oxide-based solid electrolytes requires a high-temperature sintering process, which is limiting in terms of battery production efficiency and energy costs. For example, Patent Document 1 discloses a solid electrolyte formed from a lithium-containing oxide with a specific elemental composition and describes that this solid electrolyte exhibits high ionic conductivity. However, using this lithium-containing oxide as a solid electrolyte sheet requires a high-temperature sintering process. As a technique for addressing this problem, for example, Patent Document 2 discloses a technique for reducing the lithium ion conductivity at 25° C. to 1.0×10 －６ Patent Document 2 discloses a composite containing a lithium compound having a densitometric value of 0.5 S / cm or more and lithium tetraborate, whose reduced pair distribution function G(r) obtained from X-ray total scattering measurement shows a specific profile. According to the technology described in Patent Document 2, although this composite is composed of a lithium-containing oxide, the lithium tetraborate plastically deforms between the lithium compounds to connect the lithium compounds, and therefore, this composite can be formed into a lithium ion conductor showing good lithium ion conductivity by pressure treatment without being subjected to high-temperature sintering treatment.

[0004] JP 2018-052755 A International Publication No. 2021 / 193204

[0005] The composite described in Patent Document 2 is composed of a lithium-containing oxide, yet is soft, and can ensure interparticle bonding without being subjected to a sintering treatment or without incorporating a binder such as an organic polymer, thereby possessing properties that have not been achieved by oxide-based solid electrolytes to date. However, as a result of further investigations by the present inventors, it has become clear that the lithium ion conductivity is currently insufficient for practical use as a solid electrolyte layer in an all-solid-state lithium ion secondary battery, and that there is room for improvement for practical use.

[0006] The lithium ion conductivity of the solid electrolyte used in an all-solid-state lithium ion secondary battery is an essential property for the battery to function as a battery. Furthermore, since secondary batteries are used by repeatedly charging and discharging, the property of not deteriorating battery performance even after repeated charging and discharging (cyclability) is also an important property required for an all-solid-state lithium ion secondary battery.

[0007] An object of the present invention is to provide an all-solid-state lithium ion secondary battery that uses a lithium-containing oxide in a solid electrolyte layer, and that has excellent interparticle binding properties even without being subjected to high-temperature sintering treatment or even without incorporating a binder such as an organic polymer, and that has higher lithium ion conductivity, excellent safety, and excellent cycle characteristics; and a method for producing the same.

[0008] The object of the present invention has been achieved by the following means.

[0009] [1] An all-solid-state lithium ion secondary battery comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order, wherein the solid electrolyte layer contains an amorphous solid electrolyte containing a lithium-containing oxide containing Li, B, and O and a lithium salt, and the ratio of the content of the lithium salt to the content of the lithium-containing oxide in the amorphous solid electrolyte is 0.001 to 1.5 in terms of molar ratio, and wherein a laminate including the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer has a water content of 7.0% by mass or less as determined by Karl Fischer titration at 100°C, and a difference between the water contents as determined by Karl Fischer titration at 100°C and 300°C is 0.1 to 5.0% by mass. [2] An all-solid-state lithium ion secondary battery comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order, wherein the solid electrolyte layer contains an amorphous solid electrolyte containing a lithium-containing oxide containing Li, B, and O and a lithium salt, and the ratio of the content of the lithium salt to the content of the lithium-containing oxide in this amorphous solid electrolyte is 0.001 to 1.5 in molar ratio, and the all-solid-state lithium ion secondary battery is a laminate obtained by vacuum drying a laminate consisting of a positive electrode active material layer, the solid electrolyte layer, and a negative electrode active material layer. [3] The lithium-containing oxide is Li ２＋ｘ B ４＋ｙ O ７＋ｚ [4] The all-solid-state lithium-ion secondary battery according to any one of [1] to [3], wherein the lithium salt is represented by the following formula (1): Formula (1): LiN(R ｆ１ SO ２ ) (R ｆ２ SO ２ ) In the formula, R ｆ１ and R ｆ２each independently represent a halogen atom or a perfluoroalkyl group. [5] The all-solid-state lithium-ion secondary battery according to any one of [1] to [4], wherein the lithium-containing oxide has been subjected to mechanical milling treatment. [6] The all-solid-state lithium-ion secondary battery according to any one of [1] to [5], wherein the all-solid-state lithium-ion secondary battery is obtained by sealing a laminate having the positive electrode layer, the solid electrolyte layer, and the negative electrode layer arranged in this order. [7] A method for producing the all-solid-state lithium-ion secondary battery according to any one of [1] to [6], comprising forming a laminate including the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer, and then subjecting the laminate to a vacuum drying treatment.

[0010] In the present invention and the specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0011] The all-solid-state lithium-ion secondary battery of the present invention uses a lithium-containing oxide in a solid electrolyte layer, and the solid electrolyte layer has excellent interparticle binding properties, high lithium ion conductivity, excellent safety, and excellent cycle characteristics even without being subjected to high-temperature sintering treatment or without incorporating a binder such as an organic polymer. Furthermore, the manufacturing method for the all-solid-state lithium-ion secondary battery of the present invention is a manufacturing method suitable for obtaining the above-mentioned all-solid-state lithium-ion secondary battery of the present invention.

[0012] Fig. 1 is a cross-sectional view showing a schematic example of the configuration of an all-solid-state lithium ion secondary battery. Fig. 2 is a diagram showing an example of an X-ray diffraction pattern for explaining the X-ray diffraction characteristics of the solid electrolyte (I) used in the present invention. Fig. 3 is a diagram showing an example of the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I) used in the present invention. Fig. 4 is a diagram showing the solid of the solid electrolyte (I) used in the present invention. ７ 5 shows an example of a spectrum obtained when Li-NMR measurement is performed at 20° C. or 120° C. FIG. ７6 shows an example of a spectrum obtained when Li-NMR measurement is performed at 20° C. or 120° C. FIG. ７ FIG. 7 is a diagram showing an example of a spectrum obtained when Li-NMR measurement is performed at 20° C. FIG. 7 is a diagram showing waveform separation of the peaks shown in FIG. 6. FIG. 8 is a diagram showing an example of a Raman spectrum of the solid electrolyte (I) used in the present invention. FIG. 9 is a diagram showing the Raman spectrum of lithium tetraborate crystal. FIG. 10 is a diagram showing the Raman spectrum of powdered Li ２ B ４ O ７ 11 shows the reduced pair distribution function G(r) obtained by X-ray total scattering measurement of the crystal. ２ B ４ O ７ FIG. 1 shows the X-ray diffraction pattern of the crystal.

[0013] [All-Solid-State Lithium-Ion Secondary Battery] The all-solid-state lithium-ion secondary battery of the present invention (hereinafter also referred to as the "secondary battery of the present invention") comprises a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order. The solid electrolyte layer is formed using an amorphous solid electrolyte of a specific composition, as described below. In the secondary battery of the present invention, the water content (water content determined by Karl Fischer titration at 100°C) of a laminate (laminate structure excluding a current collector) comprising a positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer, which constitutes a laminate structure of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer, based on Karl Fischer titration at 100°C, is 7.0 mass% or less. The water content based on Karl Fischer titration can be determined by the method described in the Examples below. The moisture content of the laminate consisting of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer, as determined by Karl Fischer titration at 100°C, is preferably 6.0% by mass or less, more preferably 5.0% by mass or less, even more preferably 4.0% by mass or less, more preferably 3.0% by mass or less, even more preferably 2.0% by mass or less, still more preferably 1.5% by mass or less, and also preferably 1.0% by mass or less. This moisture content is usually 0.2% by mass or more, preferably 0.4% by mass or more, more preferably 0.6% by mass or more, and even more preferably 0.7% by mass or more. Therefore, the moisture content of the laminate including the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer, as determined by Karl Fischer titration at 100°C, is preferably 0.2 to 6.0 mass%, more preferably 0.2 to 5.0 mass%, even more preferably 0.4 to 4.0 mass%, even more preferably 0.4 to 3.0 mass%, even more preferably 0.4 to 2.0 mass%, even more preferably 0.6 to 2.0 mass%, and even more preferably 0.7 to 1.5 mass%. Furthermore, in the secondary battery of the present invention, the moisture content of the laminate including the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer, as determined by Karl Fischer titration at 300°C, is preferably 0.1 to 12.0 mass%, more preferably 0.5 to 10.0 mass%, even more preferably 1.0 to 8.0 mass%, even more preferably 1.5 to 5.0 mass%, and even more preferably 1.5 to 3.0 mass%.In the secondary battery of the present invention, the difference in water content between the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer, as determined by Karl Fischer titration at 100°C and 300°C ([water content determined by Karl Fischer titration at 300°C] - [water content determined by Karl Fischer titration at 100°C]), is 0.1 to 5.0% by mass. This difference in water content is preferably 0.5 to 5.0% by mass, more preferably 1.0 to 5.0% by mass, even more preferably 2.0 to 5.0% by mass, even more preferably 3.0 to 5.0% by mass, and even more preferably 3.0 to 4.0% by mass. The difference in water content is also preferably 0.1 to 4.0% by mass, also preferably 0.5 to 4.0% by mass, also preferably 0.5 to 3.0% by mass, also preferably 0.5 to 2.0% by mass, and even preferably 0.5 to 1.5% by mass.

[0014] Each layer of the secondary battery of the present invention will be described.

[0015] <Solid Electrolyte Layer> The solid electrolyte layer constituting the secondary battery of the present invention is a layer formed by forming a solid electrolyte of a specific composition in an amorphous state (synonymous with amorphous state or amorphous state), or a mixture of this solid electrolyte and other components, into a layer, and typically through a vacuum drying process. This amorphous solid electrolyte of a specific composition before layer formation contains a lithium-containing oxide (hereinafter also referred to as "lithium-containing oxide") containing Li, B, and O, a lithium salt, and water. In the amorphous solid electrolyte before layer formation, the ratio of the lithium salt content to the lithium-containing oxide content (lithium salt / lithium-containing oxide) is 0.001 to 1.5 in molar ratio. Therefore, in the secondary battery of the present invention, the ratio of the lithium salt content to the lithium-containing oxide content in the solid electrolyte layer is also 0.001 to 1.5 in molar ratio. Furthermore, in the amorphous solid electrolyte before layer formation, the ratio of the water content to the lithium-containing oxide content (water / lithium-containing oxide) is preferably 1 to 12 in molar ratio. Hereinafter, the amorphous solid electrolyte having a specific composition will also be referred to as “solid electrolyte (I).” The solid electrolyte (I) is usually an inorganic solid electrolyte.

[0016] The solid electrolyte (I) is in an amorphous state and exhibits elastic properties that are prone to plastic deformation. As a result, in a solid electrolyte layer containing the solid electrolyte (I) formed through pressure treatment, drying treatment, etc., the adhesion between the solid electrolytes (I) and / or between the solid electrolyte (I) and other ion conductors is improved, interfacial resistance can be reduced, and better ion conductivity can be obtained. By forming a solid electrolyte layer using this solid electrolyte (I), a lithium ion conductor that exhibits excellent lithium ion conductivity can be formed by pressure treatment, etc., even though it is a highly safe oxide-based solid electrolyte, without being subjected to high-temperature sintering treatment.

[0017] The water contained in the solid electrolyte (I) includes at least bound water. While the reason why the solid electrolyte (I) exhibits high lithium ion conductivity is unclear, it is believed that in the amorphous solid electrolyte (I), a soft hydration layer is likely to form on the surface of the lithium-containing oxide, and this hydration layer contains a large amount of lithium derived from the lithium salt, resulting in enhanced ionic conductivity. Here, in the present invention and specification, "bound water" refers to water other than water present as free water or OH groups bound to the lithium-containing oxide. Even if the solid electrolyte (I) contains the above amount of water, it is in the form of solid particles (including a state in which solid particles are bound to each other). In other words, the solid electrolyte (I) contains bound water that is not removed or is difficult to remove under normal drying conditions. Note that as long as the solid electrolyte (I) can maintain its solid particle state, some of the water contained in the solid electrolyte (I) may be free water. When the solid electrolyte (I) contains free water, at least a portion of the free water is removed by a drying treatment described later of a solid electrolyte layer (a laminate consisting of a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer) formed using this solid electrolyte (I). Furthermore, depending on the interaction of the bound water with the lithium-containing oxide or the lithium salt and the level of the above-mentioned drying treatment conditions, a portion of the bound water may be removed.

[0018] In the present invention, the solid electrolyte (I) being in an "amorphous state" means that it satisfies the following X-ray diffraction characteristics.

[0019] (X-ray diffraction characteristics) In the X-ray diffraction pattern obtained by X-ray diffraction measurement of the solid electrolyte (I) using CuKα rays, none of the following peaks is present: a first peak having a peak top in the range of a diffraction angle 2θ of 21.6 to 22.0° and a full width at half maximum of 0.65° or less; a second peak having a peak top in the range of a diffraction angle 2θ of 25.4 to 25.8° and a full width at half maximum of 0.65° or less; a third peak having a peak top in the range of a diffraction angle 2θ of 33.4 to 33.8° and a full width at half maximum of 0.65° or less; and a fourth peak having a peak top in the range of a diffraction angle 2θ of 34.4 to 34.8° and a full width at half maximum of 0.65° or less; or In the X-ray diffraction pattern, when at least one peak (hereinafter referred to as "peak X") among the first peak, second peak, third peak, and fourth peak is present, at least one peak among peak X has an intensity ratio of 5.0 or less as calculated by the intensity measurement method described below.

[0020] -Intensity measurement method- The average intensity (Av1) in the range of +0.45° to +0.55° from the diffraction angle 2θ at the peak top of Peak X is calculated, and the average intensity (Av2) in the range of -0.55° to -0.45° from the diffraction angle 2θ at the peak top of Peak X is calculated, and the arithmetic average value of Av1 and Av2 is calculated. The ratio of the peak intensity at the peak top of Peak X to this arithmetic average value (peak intensity at the peak top of Peak X / arithmetic average value) is defined as the intensity ratio.

[0021] The X-ray diffraction characteristics will be described in more detail. In the X-ray diffraction pattern obtained from X-ray diffraction measurement of the solid electrolyte (I) using CuKα radiation, if none of the first peak, second peak, third peak, and fourth peak is present, the X-ray diffraction characteristics are satisfied, and the solid electrolyte (I) is in an amorphous state. In addition, in the X-ray diffraction pattern obtained from X-ray diffraction measurement of the solid electrolyte (I) using CuKα radiation, if the peak X is present, and at least one peak of the peak X has an intensity ratio of 5.0 or less obtained by the intensity measurement method, the X-ray diffraction characteristics are also satisfied, and the solid electrolyte (I) is in an amorphous state. Here, the full width at half maximum (FWHM) of the peak means the peak width (°) at 1 / 2 of the peak intensity at the peak top.

[0022] The intensity measurement method will be described in more detail with reference to FIG. 2. FIG. 2 is a diagram showing an example of peak X appearing in a diffraction pattern obtained by X-ray diffraction measurement of solid electrolyte (I) using CuKα radiation. In the diffraction pattern shown in FIG. 2, a specific peak whose peak top intensity exhibits intensity 1 is shown. In the intensity measurement method, as shown in FIG. 2, an average intensity (Av1) in the range of +0.45° to +0.55° from the diffraction angle 2θ of the peak top of peak X is calculated, and an average intensity (Av2) in the range of −0.55° to −0.45° from the diffraction angle 2θ of the peak top of peak X is further calculated. Next, the arithmetic average values ​​of Av1 and Av2 are calculated, and the ratio of intensity 1 to the arithmetic average value is determined as the intensity ratio. When the above X-ray diffraction characteristics are satisfied, this means that there is no crystalline structure, or almost no crystalline structure, in the solid electrolyte (I), and the solid electrolyte is in an amorphous state. In other words, the first to fourth peaks are mainly peaks derived from the crystalline structure in the solid electrolyte (e.g., the crystalline structure of lithium tetraborate), and the absence of these peaks indicates an amorphous state. Even if at least one of the first to fourth peaks is present, the intensity ratio of at least one of the peaks X present is 5.0 or less, which means that the solid electrolyte (I) is substantially free of a crystalline structure that inhibits the effects of the present invention. For example, a peak derived from a specific component (e.g., a lithium salt) may overlap with any of the first to fourth peaks described above. However, in an amorphous solid electrolyte, all of the first to fourth peaks are usually reduced. Therefore, even if a peak derived from the specific component happens to overlap with any of the first to fourth peaks and a single large peak appears, the presence of at least one peak X with an intensity ratio below a predetermined value indicates that the solid electrolyte (I) is in an amorphous state.

[0023] The X-ray diffraction measurement is carried out using CuKα rays under measurement conditions of 0.01° / step and 3° / min.

[0024] In the X-ray diffraction pattern obtained by X-ray diffraction measurement of the solid electrolyte (I) using CuKα radiation, none of the above-mentioned first peak, second peak, third peak, and fourth peak is present, or even if at least one peak X among the above-mentioned first peak, second peak, third peak, and fourth peak is present, it is preferable that the intensity ratio of at least one peak among the peaks X is 3.0 or less. Among these, it is more preferable that none of the above-mentioned first peak, second peak, third peak, and fourth peak is present, or even if at least one peak X among the above-mentioned first peak, second peak, third peak, and fourth peak is present, the intensity ratio of at least one peak among the peaks X is 2.0 or less.

[0025] In the X-ray diffraction pattern, if two or more peaks have their peak tops in the range of 21.6 to 22.0° and their full width at half maximum is 0.65° or less, the peak with the highest diffracted X-ray intensity is selected as the first peak, and the X-ray diffraction characteristics are determined. In the X-ray diffraction pattern, if two or more peaks have their peak tops in the range of 25.4 to 25.8° and their full width at half maximum is 0.65° or less, the peak with the highest diffracted X-ray intensity is selected as the second peak, and the X-ray diffraction characteristics are determined. In the X-ray diffraction pattern, if two or more peaks have their peak tops in the range of 33.4 to 33.8° and their full width at half maximum is 0.65° or less, the peak with the highest diffracted X-ray intensity is selected as the third peak, and the X-ray diffraction characteristics are determined. Furthermore, in the X-ray diffraction pattern, if there are two or more peaks whose peak tops are located in the range of 34.4 to 34.8° and whose full width at half maximum is 0.65° or less, the peak with the greatest diffracted X-ray intensity is selected as the fourth peak, and the X-ray diffraction characteristics are determined.

[0026] (X-ray total scattering characteristics) The solid electrolyte (I) preferably satisfies the following requirement A-1 as an X-ray total scattering characteristic. Furthermore, when the solid electrolyte (I) satisfies the above X-ray diffraction characteristics, the solid electrolyte (I) usually satisfies the following requirement A-2.

[0027] - Requirement A-1 - In the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I), there is a first peak whose peak top is located in the range of r 1.43±0.2 Å and a second peak whose peak top is located in the range of r 2.40±0.2 Å, and the G(r) at the peak top of the first peak exceeds 1.0, and the G(r) at the peak top of the second peak is 0.8 or more.

[0028] - Requirement A-2 - In the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I), the absolute value of G(r) is less than 1.0 when r is in the range of more than 5 Å and not more than 10 Å.

[0029] When the solid electrolyte (I) satisfies requirements A-1 and A-2, it has a short-range ordered structure related to the interatomic distances of B-O and B-B, but has almost no long-range ordered structure, and therefore the oxide solid electrolyte itself is softer than conventional lithium-containing oxides and exhibits elastic properties that make it more susceptible to plastic deformation. As a result, it is presumed that in a layer containing the solid electrolyte (I) formed by pressure treatment or the like, adhesion between the solid electrolytes (I) and / or adhesion between the solid electrolyte (I) and other ion conductors is improved, interfacial resistance can be reduced, and better ion conductivity can be obtained. Requirements A-1 and A-2 will be described in more detail with reference to the drawings.

[0030] FIG. 3 shows an example of the reduced pair distribution function G(r) obtained by X-ray total scattering measurement of the solid electrolyte (I). The vertical axis of FIG. 3 is the reduced pair distribution function obtained by Fourier transform of the X-ray scattering, and indicates the probability that an atom exists at a position of distance r. The X-ray total scattering measurement can be performed using an SPring-8 BL04B2 (accelerating voltage 61.4 keV, wavelength 0.2019 Å). The reduced pair distribution function G(r) can be obtained by converting the scattering intensity I obtained by the experiment using the following procedure. First, the scattering intensity I ｏｂｓ is expressed by the following formula (1): The structure factor S(Q) is expressed by the following formula (2): ｃｏｈ is obtained by dividing by the product of the number of atoms N and the square of the atomic scattering factor f. ｏｂｓ =I ｃｏｈ +I ｉｎｃｏｈ +I蛍光 (1)

[0031]

[0032] The structure factor S(Q) is used for PDF (Pair Distribution Function) analysis. In the above formula (2), the required intensity is the coherent scattering I ｃｏｈ Incoherent scattering I ｉｎｃｏｈ and X-ray fluorescence I 蛍光 is the scattering intensity I obtained by blank measurement, subtraction using the theoretical formula, and discriminator of the detector. ｏｂｓ Coherent scattering I ｃｏｈ is expressed by Debye's scattering formula (the following formula (3)) (N: total number of atoms, f: atomic scattering factor, r ｉｊ : interatomic distance between i and j).

[0033]

[0034] If we focus on an arbitrary atom and let the atomic density at a distance r be ρ(r), the number of atoms present within a sphere with a radius of r-r+d(r) is 4πr ２ Since ρ(r)dr, the above formula (3) can be expressed as the following formula (4).

[0035]

[0036] The average density of atoms is ρ ０ Then, by transforming the above equation (4), the following equation (5) is obtained.

[0037]

[0038] From the above formula (5) and formula (2), the following formula (6) is obtained.

[0039]

[0040] The pair distribution function g(r) is expressed by the following equation (7).

[0041]

[0042] From the above formulas (6) and (7), the following formula (8) is obtained.

[0043]

[0044] As described above, the pair distribution function can be determined by the Fourier transform of the structure factor S(Q). To facilitate observation of medium- and long-range order, the pair distribution function is transformed as G(r) = 4πr(g(r) - 1), resulting in the reduced pair distribution function (Figure 3). g(r), which oscillates around 0, represents the density difference from the average density at each interatomic distance. If there is a correlation at a specific interatomic distance, the average density will be higher than 1. Therefore, it reflects the element distance and coordination number corresponding to the local to medium distance. As order disappears, ρ(r) approaches the average density, and g(r) approaches 1. Therefore, in an amorphous structure, the larger r is, the less order there is, so g(r) becomes 1, i.e., G(r) becomes 0.

[0045] In requirement A-1, as shown in FIG. 3, in the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I), there is a first peak P1 whose peak top is located in the range of r = 1.43 ± 0.2 Å, and a second peak P2 whose peak top is located in the range of r = 2.40 ± 0.2 Å, and the G(r) at the peak top of the first peak P1 is greater than 1.0 (preferably 1.2 or greater), and the G(r) at the peak top of the second peak P2 is greater than 0.8 (preferably greater than 1.0). In FIG. 3, the peak top of the first peak P1 is located at 1.43 Å, and the peak top of the second peak P2 is located at 2.40 Å. At the position of 1.43 Å, there is a peak assigned to the interatomic distance of B (boron)-O (oxygen). Furthermore, at the position of 2.40 Å, there is a peak assigned to the interatomic distance of B (boron)-B (boron). In other words, the observation of the two peaks (first peak and second peak) means that a periodic structure corresponding to the two interatomic distances is present in the solid electrolyte (I).

[0046] In requirement A-2, the absolute value of G(r) is less than 1.0 when r is in the range of more than 5 Å and not more than 10 Å, as shown in Figure 3. As described above, the absolute value of G(r) being less than 1.0 when r is in the range of more than 5 Å and not more than 10 Å means that there is almost no long-range ordered structure in the solid electrolyte (I).

[0047] In the reduced pair distribution function G(r), there may be peaks other than the first peak and the second peak in the range of r being 5 Å or less.

[0048] There is no particular limitation on the method for making the solid electrolyte (I) amorphous. For example, in preparing the solid electrolyte (I), a method is used in which a lithium-containing oxide that has been subjected to mechanical milling is used as a raw material. This mechanical milling may be performed in the presence of a lithium salt.

[0049] -Mechanical milling treatment- Mechanical milling treatment is a treatment in which a sample is pulverized while applying mechanical energy. Examples of mechanical milling treatment include a ball mill, a vibration mill, a turbo mill, and a disk mill. From the viewpoint of obtaining an amorphous solid electrolyte (I) with good productivity, a ball mill is preferred. Examples of ball mills include a vibration ball mill, a rotary ball mill, and a planetary ball mill. A planetary ball mill is more preferred.

[0050] The conditions for the ball mill treatment are adjusted appropriately depending on the object to be treated. The material of the milling balls (media) is not particularly limited, and examples thereof include agate, silicon nitride, zirconia, alumina, and iron-based alloys, with stabilized zirconia (YSZ) being preferred. The average particle size of the milling balls is not particularly limited, and is preferably 1 to 10 mm, more preferably 3 to 7 mm, from the viewpoint of enabling the solid electrolyte (I) to be produced with good productivity. The average particle size is determined by measuring the diameters of 50 randomly selected milling balls and calculating the arithmetic mean. When the milling balls are not spherical, the major axis is taken as the diameter. The number of milling balls is not particularly limited.

[0051] The material of the grinding pot in the ball mill treatment is not particularly limited, and examples thereof include agate, silicon nitride, zirconia, alumina, and iron-based alloys, with stabilized zirconia (YSZ) being preferred.

[0052] The rotation speed of the ball mill treatment is not particularly limited and can be, for example, 200 to 700 rpm, more preferably 350 to 550 rpm. The treatment time of the ball mill is not particularly limited and can be, for example, 10 to 200 hours, more preferably 20 to 140 hours. The ball mill treatment may be performed in air or in an inert gas (e.g., argon, helium, nitrogen, etc.) atmosphere.

[0053] In the production of the solid electrolyte (I), it is preferable to carry out the following steps 1A to 3A. Step 1A: A step of subjecting a lithium-containing oxide to mechanical milling treatment in the presence of a lithium salt. Step 2A: A step of mixing the product obtained in step 1A with water. Step 3A: A step of removing water from the dispersion obtained in step 2A to obtain the solid electrolyte (I).

[0054] In step 1A, the amount of the lithium salt used is not particularly limited, and is appropriately adjusted so as to obtain the solid electrolyte (I) defined in the present invention.

[0055] In the above-mentioned step 2A, the amount of water used is not particularly limited. For example, the amount of water used can be 10 to 200 parts by mass, and more preferably 50 to 150 parts by mass, per 100 parts by mass of the product obtained in step 1A. The method for mixing the product obtained in step 1A with water is not particularly limited, and they may be mixed all at once, or water may be added stepwise to the product obtained in step 1A and mixed. When mixing, ultrasonic treatment may be performed as necessary. The time for ultrasonic treatment is not particularly limited, and may be, for example, 10 minutes to 5 hours.

[0056] Step 3A is a step of removing water from the dispersion obtained in Step 2A to obtain a solid electrolyte (I). The method for removing water from the dispersion obtained in Step 2A is not particularly limited, and water may be removed by a heat treatment or a vacuum drying treatment.

[0057] Before the step 1A, a step 0 may be carried out in which the lithium-containing oxide is subjected to mechanical milling in an environment in which no lithium salt is present.

[0058] In the production of the solid electrolyte (I), it is also preferable to carry out the following steps 1B to 3B instead of the above steps 1A to 3A. Step 1B: A step of subjecting the lithium-containing oxide to mechanical milling treatment; Step 2B: A step of mixing the product obtained in step 1B with water and a lithium salt; and Step 3B: A step of removing water from the dispersion obtained in step 2B to obtain the solid electrolyte (I).

[0059] The difference between step 1B and step 1A is that in step 1A, mechanical milling is performed in the presence of a lithium salt, whereas in step 1B, mechanical milling is performed without using a lithium salt. Therefore, in step 2B, the product obtained in step 1B is mixed with water and a lithium salt. The procedure of step 2B is not particularly limited, and may be a method of mixing the product obtained in step 1B, water, and a lithium salt all at once (method 1), a method of mixing the product obtained in step 1B with water to prepare a dispersion, and then mixing the resulting dispersion with a lithium salt (method 2), or a method of mixing the product obtained in step 1B with water to prepare dispersion 1, mixing a lithium salt with water to prepare solution 2, and then mixing dispersion 1 with solution 2 (method 3). When mixing the product obtained in step 1B with water, a dispersion treatment such as ultrasonic treatment may be appropriately performed. In Method 2, when mixing the dispersion liquid obtained by mixing the product obtained in Step 1B with water and a lithium salt, if the amount of lithium salt is too large, the resulting liquid is likely to gel, and the amount of lithium salt to be mixed is limited. In contrast, in Method 3, even when the product obtained in Step 1B and the lithium salt are mixed in approximately equimolar amounts, gelation of the liquid is unlikely to occur, and a larger amount of lithium salt can be mixed. From this perspective, Method 3 is preferred. The procedures of Step 3B and Step 3A are the same.

[0060] In the production of the solid electrolyte (I), it is also preferable to carry out the following steps 1C to 3C instead of the above steps 1A to 3A. Step 1C: A step of subjecting the lithium-containing oxide to mechanical milling treatment. Step 2C: A step of mixing the product obtained in step 1C with water. Step 3C: A step of mixing the product obtained by removing water from the dispersion obtained in step 2C with a lithium salt to obtain the solid electrolyte (I).

[0061] The procedures of Step 1C and Step 1B are the same. The procedures of Step 2C and Step 2A are the same. Step 3C differs from Steps 3A and 3B in that a product obtained by removing water from the dispersion obtained in Step 2C is mixed with a lithium salt. In Step 3C, the amount of lithium salt used is not particularly limited and is appropriately adjusted so as to obtain the solid electrolyte (I) defined in the present invention. The method for mixing the product obtained by removing water from the dispersion obtained in Step 2C with the lithium salt is not particularly limited, and a method in which a solution obtained by dissolving the lithium salt in water is impregnated into the product and the two are mixed may be used.

[0062] (Component Composition of Solid Electrolyte (I)) As described above, the solid electrolyte (I) used in the present invention is an amorphous solid electrolyte, and in this solid electrolyte (I), the ratio of the content of the lithium salt to the content of the lithium-containing oxide is 0.001 to 1.5 in molar ratio, and the ratio of the content of the water is 1 to 12 in molar ratio. The ratio of the content of the lithium salt to the content of the lithium-containing oxide in the solid electrolyte (I) is preferably 0.001 to 1.2 in molar ratio, more preferably 0.01 to 1.2, even more preferably 0.1 to 1.2, and particularly preferably 0.5 to 1.2. Furthermore, the ratio of the content of the water to the content of the lithium-containing oxide in the solid electrolyte (I) is more preferably 2 to 12 in molar ratio, and even more preferably 3 to 11. Moreover, this molar ratio is also preferably 2 to 10, also preferably 2 to 8, also preferably 2 to 7, and also preferably 3 to 7. The molar amounts of the lithium-containing oxide, lithium salt, and water in the solid electrolyte (I) can be determined based on elemental analysis. The molar amount of water can also be determined by the Karl Fischer method or the like.

[0063] The water content of the solid electrolyte (I) is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and even more preferably 35% by mass or less. The water content of the solid electrolyte (I) is also preferably 30% by mass or less, and even more preferably 25% by mass or less. The water content of the solid electrolyte (I) is usually 5% by mass or more, preferably 10% by mass or more, and even more preferably 15% by mass or more. Therefore, the water content of the solid electrolyte (I) is preferably 5 to 50% by mass, more preferably 5 to 45% by mass, even more preferably 10 to 40% by mass, even more preferably 10 to 35% by mass, even preferably 10 to 30% by mass, even preferably 15 to 30% by mass, and even preferably 15 to 25% by mass. The lithium-containing oxide content of the solid electrolyte (I) is preferably 20 to 80% by mass, more preferably 20 to 75% by mass, and even more preferably 25 to 70% by mass. The content of the lithium salt in the solid electrolyte (I) is preferably 0.5 to 60 mass%, more preferably 1.0 to 55 mass%, even more preferably 2.0 to 50 mass%, and also preferably 5.0 to 50 mass%.

[0064] - Lithium-containing oxide - As described above, the lithium-containing oxide constituting the solid electrolyte (I) contains Li, B, and O. The lithium-containing oxide is Li ２＋ｘ B ４＋ｙ O ７＋ｚ (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3) is preferred. That is, when the molar amount of B is 4.00 and the molar amount of Li is expressed, it is preferred that the molar amount of Li is 1.58 to 2.49 (i.e., 1.7×4 / 4.3 to 2.3×4 / 3.7) and the molar amount of O is 6.23 to 7.89 (i.e., 6.7×4 / 4.3 to 7.3×4 / 3.7). In other words, when the molar amount of B contained is 4.00, it is preferred that the relative value of the molar amount of Li contained is 1.58 to 2.49 and the molar amount of O is 6.23 to 7.89. Typical examples of such lithium-containing oxides include lithium tetraborate (Li ２ B ４ O ７The lithium-containing oxide may be Li １＋ｘ B ３＋ｙ O ５＋ｚ A compound represented by (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3) is also preferred. As such a lithium-containing oxide, lithium triborate (LiB ３ O ５ The lithium-containing oxide may be Li ３＋ｘ B １１＋ｙ O １８＋ｚ Compounds represented by (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3) are also preferred. As such lithium-containing oxides, typically Li ３ B １１ O １８ The lithium-containing oxide may be Li ３＋ｘ B ７＋ｙ O １２＋ｚ Compounds represented by (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3) are also preferred. As such lithium-containing oxides, typically Li ３ B ７ O １２ Therefore, the lithium-containing oxide can be ２＋ｘ B ４＋ｙ O ７＋ｚ , the above Li １＋ｘ B ３＋ｙ O ５＋ｚ , Li ３＋ｘ B １１＋ｙ O １８＋ｚ , and Li ３＋ｘ B ７＋ｙ O １２＋ｚ In place of the lithium-containing oxide, or together with the lithium-containing oxide, LiBO may be used as the lithium-containing oxide. ５ , Li ２ B ７ O １２ , LiB ２ O ３ (OH)H ２ O and Li ４ B ８ O １３ (OH) ２(H ２ O) ３ At least one of the following may also be used. In the solid electrolyte (I), the lithium-containing oxide is in an amorphous state. That is, so that the solid electrolyte (I) is in the above-mentioned amorphous state, the lithium-containing oxide is also in a desired amorphous state in the solid electrolyte (I). Among them, the lithium-containing oxide is preferably lithium tetraborate in an amorphous state.

[0065] - Lithium Salt - The lithium salt constituting the solid electrolyte (I) used in the present invention is not particularly limited, and Li ＋ and an anion, and Li ＋ and an organic anion are preferred, and Li ＋ and a salt composed of an organic anion having a halogen atom is more preferred. The lithium salt constituting the solid electrolyte (I) used in the present invention preferably contains two or more specific elements selected from the group consisting of elements of Group 3 of the periodic table, elements of Group 4 of the periodic table, elements of Group 13 of the periodic table, elements of Group 14 of the periodic table, elements of Group 15 of the periodic table, elements of Group 16 of the periodic table, elements of Group 17 of the periodic table, and H. As the lithium salt constituting the solid electrolyte (I) used in the present invention, for example, a compound represented by formula (1) is preferred. Formula (1) LiN(R ｆ１ SO ２ ) (R ｆ２ SO ２ ) R ｆ１ and R ｆ２ R each independently represents a halogen atom or a perfluoroalkyl group. ｆ１ and R ｆ２ When R is a perfluoroalkyl group, the number of carbon atoms in the perfluoroalkyl group is not particularly limited. ｆ１ and R ｆ２ is preferably a halogen atom or a perfluoroalkyl group having 1 to 6 carbon atoms, more preferably a halogen atom or a perfluoroalkyl group having 1 to 2 carbon atoms, and even more preferably a halogen atom. When the volume of the terminal group increases, steric hindrance increases, which becomes a factor that inhibits ion conduction. ｆ１ and R ｆ２When is a perfluoroalkyl group, it is preferable that the number of carbon atoms is small.

[0066] The lithium salt that can be contained in the solid electrolyte (I) used in the present invention is not limited to the compound represented by the above formula (1). Examples of the lithium salt that can be contained in the solid electrolyte (I) used in the present invention are shown below.

[0067] (L-1) Inorganic lithium salt: LiPF ６ , LiBF ４ , LiAsF ６ , and LiSbF ６ Inorganic fluoride salts such as LiClO ４ , LiBrO ４ , and LiIO ４ perhalogenates such as LiAlCl ４ Inorganic chloride salts such as

[0068] (L-2) Fluorine-containing organic lithium salt: LiCF ３ SO ３ perfluoroalkanesulfonates such as LiN(CF ３ SO ２ ) ２ , LiN(CF ３ CF ２ SO ２ ) ２ , LiN(FSO ２ ) ２ (In this specification, Li(FSO ２ ) ２ N), and LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ Fluorosulfonylimide salts or perfluoroalkanesulfonylimide salts such as LiC(CF ３ SO ２ ) ３ perfluoroalkanesulfonylmethide salts such as Li[PF ５ (CF ２ CF ２ CF ３ ) )], Li[PF ４ (CF ２ CF ２ CF ３ )２ ], Li[PF ３ (CF ２ CF ２ CF ３ ) ３ ], Li[PF ５ (CF ２ CF ２ CF ２ CF ３ ) )], Li[PF ４ (CF ２ CF ２ CF ２ CF ３ ) ２ ] and Li[PF ３ (CF ２ CF ２ CF ２ CF ３ ) ３ Fluoroalkyl fluorophosphates (preferably perfluoroalkyl fluorophosphates) such as:

[0069] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate and lithium difluorooxalatoborate.

[0070] In addition to the above, LiF, LiCl, LiBr, LiI, Li ２ SO ４ , LiNO ３ , Li ２ CO ３ , C.H. ３ COOLi, LiAsF ６ , LiSbF ６ , LiAlCl ４ , and LiB(C ６ H ５ ) ４ Among them, LiPF ６ , LiBF ４ , LiAsF ６ , LiSbF ６ , LiClO ４ , Li(R ｆ１ SO ２ ), LiN(R ｆ１ SO ２ ) ２ , LiN(FSO ２ ) ２ , or LiN(R ｆ１SO ２ ) (R ｆ２ SO ２ ) is preferred, and LiPF ６ , LiBF ４ , LiN(R ｆ１ SO ２ ) ２ , LiN(FSO ２ ) ２ , or LiN(R ｆ１ SO ２ ) (R ｆ２ SO ２ In these examples, R ｆ１ and R ｆ２ each independently represents a perfluoroalkyl group, preferably having 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and even more preferably 1 or 2. In addition, as the lithium salt, LiNO ３ and 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide lithium are also preferred.

[0071] (Elemental Composition of Solid Electrolyte (I)) The component composition of the solid electrolyte (I) has been described based on the compounds constituting the solid electrolyte (I). Next, the solid electrolyte (I) will be described from the perspective of a preferred elemental composition. That is, in one embodiment of the secondary battery of the present invention, the solid electrolyte (I) does not have a "lithium-containing oxide" or a "lithium salt" as a specific item, and can be specified by its elemental composition, for example, as follows: The solid electrolyte (I) used in the present invention preferably has a molar amount of Li of 1.58 to 3.49 (preferably 1.58 to 3.00, more preferably 1.90 to 3.00, and even more preferably 2.00 to 3.00) when the molar amount of B in the solid electrolyte (I) is 4.00. Furthermore, when the molar amount of B in the solid electrolyte (I) is 4.00, the molar amount of O is preferably 6.23 to 25.00 (preferably 6.50 to 23.00, more preferably 8.00 to 23.00, even more preferably 10.00 to 23.00, and even more preferably 10.00 to 18.00). Furthermore, when the molar amount of B in the solid electrolyte (I) is 4.00, the molar amounts of elements other than B, Li, and O are each preferably 0.001 to 10.00 (preferably 0.001 to 6.00, more preferably 0.01 to 5.00).

[0072] The content of each element is determined by ordinary elemental analysis. As an elemental analysis method, for example, Li and B are analyzed by ICP-OES (inductively coupled plasma optical emission spectrometry), N and the like are analyzed by an inert gas fusion method, and, for example, F and S are analyzed by combustion ion chromatography. O can be calculated by adding up the analyzed masses of elements other than O and calculating the difference from the total amount of powder. Note that the method for calculating the content of each element is not limited to the above, and the content of one element may be estimated from the analysis results of the content of other elements, taking into account the structure of the compound used. From the content of each element calculated by elemental analysis, the molar amounts of Li, O, and other elements are calculated when the molar amount of B is 4.00.

[0073] In a preferred embodiment of the solid electrolyte (I), in addition to Li, B, and O, the solid electrolyte (I) further contains one or more elements (E) selected from Group 4 elements of the periodic table, Group 15 elements of the periodic table, Group 16 elements of the periodic table, Group 17 elements of the periodic table, Si, C, Sc, and Y, more preferably two or more elements. Among these, it is preferable to contain one or more elements (E) selected from F, Cl, Br, I, S, P, Si, Se, Te, C, Sb, As, Sc, Y, Zr, Ti, Hf, and N, and it is preferable to contain two or more elements. Examples of Group 4 elements of the periodic table include Ti, Zr, Hf, and Rf. Examples of Group 15 elements of the periodic table include N, P, As, Sb, Bi, and Mc. Examples of Group 16 elements of the periodic table include S, Se, Te, Po, and Lv. Examples of Group 17 elements of the periodic table include F, Cl, Br, I, At, and Ts. The number of types of element (E) contained in the solid electrolyte (I) may be three or more, preferably two to five, and more preferably two to four. A second embodiment of the solid electrolyte (I) preferably contains two or more elements (E) selected from F, S, N, P, and C, more preferably two or more elements (E) selected from F, S, C, and N, and even more preferably three elements (E) of F, S, and N.

[0074] In the solid electrolyte (I) containing one or more (preferably two or more) of the above element (E), when the molar amount of B in the solid electrolyte (I) is 4.00 and the molar amount of Li is expressed, the molar amount of Li is preferably 1.58 to 3.49. In other words, when the molar amount of B contained is 4.00, the relative value of the molar amount of Li contained is preferably 1.58 to 3.49. In particular, when the molar amount of B contained in the solid electrolyte (I) is 4.00 and the molar amount of Li is expressed, the molar amount of Li is preferably 1.58 to 3.00, more preferably 1.90 to 3.00, and even more preferably 2.00 to 3.00.

[0075] In the solid electrolyte (I) containing one or more (preferably two or more) of the above element (E), when the molar amount of B in the solid electrolyte (I) is 4.00 and the molar amount of O is expressed, the molar amount of O is preferably 6.23 to 25.00. In other words, when the molar amount of B contained is 4.00, the relative value of the molar amount of O contained is preferably 6.23 to 25.00. In particular, when the molar amount of B contained in the solid electrolyte (I) is 4.00 and the molar amount of O is expressed, the molar amount of O is preferably 6.50 to 23.00, more preferably 8.00 to 23.00, more preferably 10.00 to 23.00, and even more preferably 10.00 to 18.00.

[0076] In the solid electrolyte (I) containing one or more (preferably two or more) of the above-mentioned element (E), when the molar amount of B in the solid electrolyte (I) is 4.00 and the molar amount of the element (E) is expressed, the molar amount of each element (E) is preferably 0.001 to 10.00. In other words, when the molar amount of B contained is 4.00, the relative value of the molar amount of each element (E) contained is preferably 0.001 to 10.00. In particular, when the molar amount of B contained in the solid electrolyte (I) is 4.00 and the molar amount of the element (E) is expressed, the molar amount of each element (E) is preferably 0.001 to 6.00, and more preferably 0.01 to 5.00.

[0077] One preferred embodiment of the elemental composition of the solid electrolyte (I) containing one or more (preferably two or more) of the above element (E) is a solid electrolyte containing Li, B, O, F, S, and N, in which, when the molar amount of B is 4.00, the molar amount of Li is 1.58 to 3.49 (preferably 1.58 to 3.00, more preferably 1.90 to 3.00, and even more preferably 2.00 to 3.00), and the molar amount of O is 6.23 to 25.00 (preferably 6.50 to 23.00). 00, more preferably 8.00 to 23.00, even more preferably 10.00 to 23.00, and still more preferably 10.00 to 18.00), the molar amount of F is 0.001 to 10.00 (preferably 0.01 to 10.00), the molar amount of S is 0.001 to 2.00 (preferably 0.01 to 2.00), and the molar amount of N is 0.001 to 1.00 (preferably 0.005 to 1.00).

[0078] The solid electrolyte (I) used in the present invention is in the amorphous state described above, and as a result, the solid electrolyte (I) preferably exhibits the following properties in addition to the above-mentioned X-ray diffraction properties:

[0079] (solid ７ Li-NMR spectrum characteristics) The solid electrolyte (I) is a solid electrolyte (I). ７ Li-NMR measurement is carried out at 20°C and 120°C, and the full width at half maximum ratio calculated from the obtained spectrum by the following method is preferably 50% or less, more preferably 40% or less, and even more preferably 35% or less. There is no particular lower limit, but it is often 10% or more. The above full width at half maximum ratio is determined by the solid electrolyte (I). ７ Li-NMR measurements are performed at 20°C and 120°C, respectively, and the full width at half maximum (FWHM 1) of a peak appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained by measurement at 20°C and the full width at half maximum (FWHM 2) of a peak appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained by measurement at 120°C are determined. The full width at half maximum (FWHM) of a peak is then calculated as a percentage {(FWHM 2 / FWHM 1) x 100}. The full width at half maximum (FWHM) of a peak means the width (ppm) at half the height (H) of the peak (H / 2). The above characteristics will be explained below with reference to FIG. 4. In FIG. 4, the solid electrolyte (I) ７ The following shows an example of the spectrum obtained when Li-NMR measurement was performed at 20°C or 120°C. The solid line spectrum shown at the bottom of FIG. ７ The spectrum obtained when Li-NMR measurement was performed at 20°C, and the spectrum shown by the dashed line at the top of Figure 4 is the spectrum of the solid ７ This is the spectrum obtained when Li-NMR measurement was performed at 120°C. ７ In Li-NMR measurement, Li ＋When the mobility of Li is high, the peak obtained is sharper. In the embodiment shown in FIG. 4, when the spectrum at 20° C. is compared with the spectrum at 120° C., the spectrum at 120° C. is sharper. In other words, in the embodiment shown in FIG. 4, due to the presence of Li defects, etc., ＋ This indicates that the mobility of Li is increased. Such a solid electrolyte (I) is prone to plastic deformation due to the above-mentioned defect structure, and ＋ For reference, the solid state hopping of a typical lithium tetraborate crystal is ７ When Li-NMR measurements are performed at 20°C or 120°C, the spectrum measured at 20°C, represented by the solid line in the lower part of Fig. 5, and the spectrum measured at 120°C, represented by the dashed line in the upper part of Fig. 5, tend to have approximately the same shape. In other words, lithium tetraborate crystals are free of Li defects and, as a result, have a high elastic modulus and are not prone to plastic deformation.

[0080] The above solid ７ The Li-NMR measurement conditions are as follows: a 4 mm HX CP-MAS probe is used, and the measurement is performed using a single pulse method, with a 90° pulse width of 3.2 μs, an observation frequency of 155.546 MHz, an observation width of 1397.6 ppm, a repetition time of 15 sec, integration once, and a MAS rotation speed of 0 Hz.

[0081] The solid electrolyte (I) used in the present invention is a solid ７ When a spectrum obtained by Li-NMR measurement at 20°C is subjected to waveform separation of a first peak appearing in the range of -100 to +100 ppm, it is preferable that a second peak having a chemical shift in the range of -3 to 3 ppm and a full width at half maximum of 5 ppm or less is present, and the ratio of the area intensity of the second peak to the area intensity of the first peak is 0.5% or more. The ratio of the area intensity is more preferably 2% or more, more preferably 5% or more, even more preferably 10% or more, and even more preferably 15% or more. In an embodiment of the present invention in which the solid electrolyte (I) contains water, the solid of the solid electrolyte (I) ７The Li-NMR spectrum characteristics tend to be as described above. There is no particular upper limit to the ratio of the area intensity, but it is often 50% or less.

[0082] The above characteristics will be explained below with reference to Fig. 6 and Fig. 7. Fig. 6 shows the solid electrolyte (I) ７ An example of a spectrum obtained when Li-NMR measurement was performed at 20°C is shown in Figure 6. As shown in Figure 6, a peak (corresponding to the first peak) is observed in the range of -100 to +100 ppm for the solid electrolyte (I), and within this first peak, a small peak is observed near the chemical shift of 0 ppm, as surrounded by a dashed line. As described above, Li ＋ When the mobility of the first peak is high, the peak is observed sharply, which is thought to be the influence of the second peak. Next, FIG. 7 shows the waveform separation of the first peak. As shown in FIG. 7, the first peak is separated into a small peak (corresponding to the second peak) represented by a solid line and a large peak represented by a dashed line. The second peak appears in a chemical shift range of -3 to 3 ppm and has a full width at half maximum of 5 ppm or less. For the solid electrolyte (I), the ratio of the area intensity of the second peak represented by the solid line in FIG. 7 to the area intensity of the first peak (the peak before waveform separation) represented by FIG. 6 ((area intensity of the second peak / area intensity of the first peak) × 100) is preferably within the above range. Examples of waveform separation methods include methods using known software, such as WaveMetrics' graph processing software Igor Pro.

[0083] (Raman Spectral Characteristics) The solid electrolyte (I) has a Raman spectrum of 600 to 850 cm －１ The coefficient of determination obtained by linear regression analysis by the least squares method in the wavenumber region of 0.9400 or more is preferably 0.9600 or more, more preferably 0.9800 or more. There is no particular upper limit, but it is usually 1.0000 or less.

[0084] The Raman spectral characteristics are described with reference to FIG. 8 . First, the Raman spectrum of the solid electrolyte (I) is acquired. Raman imaging is used to measure the Raman spectrum. Raman imaging is a microspectroscopic technique that combines Raman spectroscopy with microscopy. Specifically, it involves scanning excitation light over a sample to detect measurement light containing Raman scattered light and visualizing the distribution of components based on the intensity of the measurement light. The Raman imaging measurement conditions are: 27°C, atmospheric air, 532 nm excitation light, 100x objective lens, mapping point scanning, 1 μm steps, 1 second exposure time per point, 1 integration, and a measurement range of 70 μm × 50 μm. Furthermore, principal component analysis (PCA) is performed on the Raman spectral data to remove noise. Specifically, in the PCA process, spectra are recombined using components with an autocorrelation coefficient of 0.6 or higher.

[0085] An example of the Raman spectrum of the solid electrolyte (I) is shown in Fig. 8. In the graph shown in Fig. 8, the vertical axis represents the Raman intensity and the horizontal axis represents the Raman shift. －１ The coefficient of determination (coefficient of determination R ２ ) is calculated from 600 to 850 cm of the Raman spectrum in FIG. －１ In the wavenumber region, a regression line (thick line in FIG. 8) is obtained by the least squares method, and the coefficient of determination R ２ The coefficient of determination is calculated between 0 (no linear correlation) and 1 (perfect linear correlation of the measured values) depending on the linear correlation of the measured values. In the solid electrolyte (I), as shown in FIG. 8, －１ As a result, a high coefficient of determination is observed. ２ corresponds to the square of the correlation coefficient (Pearson's product-moment correlation coefficient). More specifically, in this specification, the coefficient of determination R ２ is calculated by the following formula: １ and y １represents the wave number in the Raman spectrum and the Raman intensity corresponding to that wave number, and x ２ is the (additive) mean of the wavenumber, and y ２ represents the (additive) average of the Raman intensities.

[0086]

[0087] On the other hand, for reference, the Raman spectrum of a typical lithium tetraborate crystal is shown in Figure 9. As shown in Figure 9, in the case of a typical lithium tetraborate crystal, the peak at 716 to 726 cm －１ , and 771-785 cm －１ When such a peak is present, a peak is observed in the wave number region of 600 to 850 cm －１ When a linear regression analysis by the least squares method is performed in the wave number region, the coefficient of determination is calculated, and the coefficient of determination is less than 0.9400. In other words, the coefficient of determination being 0.9400 or more indicates that the solid electrolyte (I) contains almost no crystalline structure. As a result, the solid electrolyte (I) has the property of being easily plastically deformed and the property of Li ＋ It is believed that the hopping property is excellent.

[0088] (Infrared absorption spectrum characteristics) The solid electrolyte (I) has an infrared absorption spectrum of 800 to 1600 cm －１ 3000 to 3500 cm for the maximum absorption intensity in the wave number region －１ The ratio of the maximum absorption intensity in the wave number region (3000 to 3500 cm －１ Maximum absorption intensity in the wavenumber region / 800 to 1600 cm －１ The ratio of the maximum absorption intensity in the wave number region of 3000 to 3500 cm of the infrared absorption spectrum is preferably 1 / 5 or more (0.2 or more). In particular, the ratio is preferably 3 / 10 or more, and more preferably 2 / 5 or more. There is no particular upper limit, but it is preferably 1 or less. －１ The OH stretching vibration mode is observed in the wavenumber region of 800 to 1600 cm －１In the wavenumber region of 800 to 1600 cm, the B-O stretching vibration mode is observed. In the solid electrolyte (I), a strong absorption intensity due to the OH stretching vibration mode is observed, which indicates that a large number of OH groups and a large amount of water are contained. In such a solid electrolyte (I), lithium ions tend to move easily, and as a result, ionic conductivity tends to improve. －１ In the wavenumber region, vibrational modes originating from lithium salts can also be observed.

[0089] The infrared absorption spectrum measurement conditions can be as follows: Objective lens: 32x Cassegrain type (NA 0.65), Detector: MCT-A, Measurement range: 650 to 4000 cm －１ , resolution: 4cm －１ The infrared absorption spectrum obtained was compared with that of atmospheric water and CO. ２ Correction is performed to remove signals from the sample, and then offset correction is performed on the background to set the absorption intensity to 0. After vacuum drying at 40° C. for 2 hours, measurement is performed under atmospheric pressure.

[0090] The ionic conductivity (27°C) of the solid electrolyte (I) is not particularly limited, and from the viewpoint of application to various uses, it is 1.0 × 10 －５ S / cm or more is preferable, and 1.0 × 10 －４ S / cm or more is more preferable, and 1.0 × 10 －３ S / cm or more is more preferable, and 3.0×10 －３ The upper limit is not particularly limited, but is preferably 1.0 × 10 －２ In many cases, it is less than 1000 S / cm.

[0091] Furthermore, it is also preferable that the solid electrolyte (I) exhibits the following characteristics or physical properties.

[0092] (Mass Loss Rate) When the solid electrolyte (I) is heated to 800°C, the mass loss rate is preferably 20 to 40% by mass, more preferably 25 to 35% by mass. The mass loss caused by the heating is believed to be due to the removal of at least the water contained in the solid electrolyte (I). The inclusion of such water in the solid electrolyte (I) can further improve lithium ion conductivity. In the heat treatment, the solid electrolyte (I) is heated at a temperature increase rate of 20°C / sec from 25°C to 800°C. A known thermogravimetric differential thermal analysis (TG-DTA) device can be used to measure the mass loss. The mass loss rate is calculated by {(mass at 25°C - mass at 800°C) / mass at 25°C} x 100. To measure the mass loss rate, the solid electrolyte (I) is previously subjected to vacuum drying at 40°C for 2 hours. The mass loss rate is measured in the atmosphere.

[0093] The solid electrolyte layer constituting the secondary battery of the present invention may contain other components in addition to the solid electrolyte (I). For example, the solid electrolyte layer may contain a binder made of an organic polymer. The organic polymer constituting the binder may be particulate or non-particulate. The inclusion of a binder more reliably prevents cracks and the like from occurring in the solid electrolyte layer or electrode layer. The solid electrolyte layer may also contain a solid electrolyte other than the solid electrolyte (I). The other solid electrolyte refers to a solid electrolyte capable of transporting lithium ions therein. The solid electrolyte is preferably an inorganic solid electrolyte. Examples of the other solid electrolyte include sulfide-based solid electrolytes, oxide-based solid electrolytes, halide-based solid electrolytes, and hydride-based solid electrolytes. From the perspective of safety, at least one of oxide-based solid electrolytes, halide-based solid electrolytes, and hydride-based solid electrolytes is preferred, with oxide-based solid electrolytes being more preferred. In the solid electrolyte layer, the content of the solid electrolyte (I) is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, also preferably 80% by mass or more, and also preferably 90% by mass.

[0094] The thickness of the solid electrolyte layer constituting the secondary battery of the present invention is not particularly limited, and can be, for example, 10 to 1000 μm, preferably 50 to 400 μm.

[0095] <Positive Electrode Layer> The positive electrode layer is generally composed of a positive electrode current collector and a positive electrode active material layer. However, when the positive electrode current collector also functions as the positive electrode active material layer (in other words, when the positive electrode active material layer also functions as the positive electrode current collector), it does not need to be composed of two layers, i.e., a positive electrode current collector and a positive electrode active material layer, and may have a single-layer configuration. Furthermore, the positive electrode active material layer usually contains a solid electrolyte (preferably an inorganic solid electrolyte) together with the positive electrode active material, but it does not necessarily contain a solid electrolyte. The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, preferably 80% by mass or more, and even preferably 90% by mass.

[0096] When the positive electrode active material layer contains a solid electrolyte, the type of the solid electrolyte is not particularly limited. From the viewpoint of prioritizing flexibility, a sulfide-based solid electrolyte can be used, and from the viewpoint of prioritizing higher safety, an oxide-based solid electrolyte can be used. From the viewpoint of achieving a high level of both flexibility and safety, it is preferable to use the above-mentioned solid electrolyte (I). In this way, the solid electrolyte (I) also acts as a binder for the solid particles contained in the positive electrode layer, and the positive electrode layer can be made more flexible.

[0097] The positive electrode active material itself used in the positive electrode layer can be any positive electrode active material that can be used in ordinary lithium ion secondary batteries. Preferred forms of the positive electrode active material are described below.

[0098] (Positive Electrode Active Material) The positive electrode active material is preferably one that can reversibly insert and / or release lithium ions. The positive electrode active material is not particularly limited, and a transition metal oxide is preferred, and a transition metal oxide containing a transition metal element Ma (one or more elements selected from Co, Ni, Fe, Mn, Cu, and V) is more preferred. In addition, this transition metal oxide may be mixed with an element Mb (a metal element in Group 1 (Ia) of the periodic table other than lithium, an element in Group 2 (IIa), an element such as Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, or B). The amount of the mixed element is preferably 0 to 30 mol% relative to the amount of the transition metal element Ma (100 mol%). More preferably, the mixed material is synthesized by mixing so that the molar ratio of Li / Ma is 0.3 to 2.2. Specific examples of the transition metal oxide include (MA) transition metal oxides having a layered rock salt structure, (MB) transition metal oxides having a spinel structure, (MC) lithium-containing transition metal phosphate compounds, (MD) lithium-containing transition metal halide phosphate compounds, and (ME) lithium-containing transition metal silicate compounds. Among these, (MA) transition metal oxides having a layered rock salt structure are preferred, and LiCoO ２ or LiNi １／３ Co １／３ Mn １／３ O ２ is more preferred.

[0099] (MA) Examples of transition metal oxides having a layered rock salt structure include LiCoO ２ (lithium cobalt oxide [LCO]), LiNiO ２ (lithium nickel oxide), LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ (nickel cobalt lithium aluminum oxide [NCA]), LiNi １／３ Co １／３ Mn １／３ O ２ (Lithium nickel manganese cobalt oxide [NMC]) and LiNi ０．５ Mn ０．５ O ２ (lithium manganese nickel oxide).

[0100] (MB) Examples of transition metal oxides having a spinel structure include LiMn ２ O ４ (LMO), LiNi ０．５ Mn １．５ O ４ ([LNMO]), LiCoMnO ４ , Li ２ FeMn ３ O ８ , Li ２ CuMn ３ O ８ , Li ２ CrMn ３ O ８ , and Li ２ NiMn ３ O ８ Examples include:

[0101] (MC) Examples of lithium-containing transition metal phosphate compounds include LiFePO ４ and Li ３ Fe ２ (P.O. ４ ) ３ Olivine-type iron phosphate salts such as Li ２ CoP ２ O ７ (LCP) and LiFeP ２ O ７ Iron pyrophosphate salts such as LiCoPO ４ Cobalt phosphate salts such as Li ３ V ２ (P.O. ４ ) ３ Examples of suitable vanadium phosphate salts include monoclinic NASICON type vanadium phosphate salts such as (lithium vanadium phosphate).

[0102] (MD) Examples of lithium-containing transition metal halide phosphate compounds include Li ２ FePO ４ Fluorophosphate iron salts such as F, Li ２ MnPO ４ Fluorophosphate manganese salts such as F, and Li ２ CoPO ４ Examples of suitable phosphates include cobalt fluorides such as F.

[0103] (ME) Examples of lithium-containing transition metal silicate compounds include Li２ FeSiO ４ , Li ２ MnSiO ４ , and Li ２ CoSiO ４ Examples include:

[0104] The shape of the positive electrode active material is not particularly limited, and is usually particulate. The volume average particle diameter of the positive electrode active material is not particularly limited, and is preferably, for example, 0.1 to 50 μm. The volume average particle diameter of the positive electrode active material particles can be determined in the same manner as the volume average particle diameter of the negative electrode active material described below. The positive electrode active material obtained by the calcination method may be used after washing with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent.

[0105] The positive electrode active material may be surface-coated with a surface coating agent, sulfur or phosphorus, or further with actinic rays, in the same manner as the negative electrode active material described below.

[0106] The positive electrode active material may be used alone or in combination of two or more kinds.

[0107] (Positive electrode current collector) The current collector constituting the positive electrode layer is an electron conductor. The positive electrode current collector is usually in the form of a film sheet. Examples of materials constituting the positive electrode current collector include aluminum, aluminum alloys, stainless steel, nickel, and titanium, with aluminum or aluminum alloys being preferred. Note that examples of the positive electrode current collector include aluminum or stainless steel surfaces treated with carbon, nickel, titanium, or silver (thin films formed thereon).

[0108] The thickness of the positive electrode active material layer constituting the secondary battery of the present invention is not particularly limited and may be, for example, 5 to 500 μm, preferably 20 to 200 μm. The thickness of the positive electrode current collector constituting the secondary battery of the present invention is also not particularly limited and may be, for example, 10 to 100 μm, preferably 10 to 50 μm.

[0109] <Negative Electrode Layer> The negative electrode layer is generally composed of a negative electrode current collector and a negative electrode active material layer. However, when the negative electrode current collector also functions as the negative electrode active material layer (in other words, when the negative electrode active material layer also functions as the negative electrode current collector), the negative electrode layer does not necessarily have to be composed of two layers, i.e., the negative electrode current collector and the negative electrode active material layer, and may have a single-layer configuration. Furthermore, the negative electrode active material layer usually contains a solid electrolyte (preferably an inorganic solid electrolyte) together with the negative electrode active material, but it does not necessarily contain a solid electrolyte. The content of the negative electrode active material in the negative electrode active material layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, preferably 80% by mass or more, and even preferably 90% by mass.

[0110] When the negative electrode active material layer contains a solid electrolyte, the type of the solid electrolyte is not particularly limited. From the viewpoint of prioritizing flexibility, a sulfide-based solid electrolyte can be used, and from the viewpoint of prioritizing higher safety, an oxide-based solid electrolyte can be used. From the viewpoint of achieving a high level of both flexibility and safety, it is preferable to use the above-mentioned solid electrolyte (I). In this way, the solid electrolyte (I) also acts as a binder for the solid particles contained in the negative electrode layer, and the negative electrode layer can be made more flexible.

[0111] The negative electrode active material itself used in the negative electrode layer can be any negative electrode active material that can be used in ordinary lithium ion secondary batteries. Preferred forms of the negative electrode active material are described below.

[0112] (Negative electrode active material) The negative electrode active material is preferably one that can reversibly insert and release lithium ions. The negative electrode active material is not particularly limited, and examples thereof include carbonaceous materials, oxides of metals or semimetals, lithium alone, lithium alloys, and negative electrode active materials that can form alloys with lithium.

[0113] The carbonaceous material used as the negative electrode active material is a material essentially composed of carbon. Examples include carbon black such as petroleum pitch and acetylene black (AB), graphite (natural graphite and artificial graphite such as vapor-grown graphite), and carbonaceous materials obtained by calcining various synthetic resins such as PAN (polyacrylonitrile)-based resins or furfuryl alcohol resins. Further examples include various carbon fibers such as PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, dehydrated PVA (polyvinyl alcohol)-based carbon fibers, lignin carbon fibers, glassy carbon fibers, and activated carbon fibers, as well as mesophase microspheres, graphite whiskers, and flat graphite. These carbonaceous materials can also be divided into difficult-to-graphitize carbonaceous materials (also called hard carbon) and graphite-based carbonaceous materials depending on the degree of graphitization. Furthermore, the carbonaceous material preferably has the interplanar spacing, density, or crystallite size described in JP-A-62-022066, JP-A-2-006856, and JP-A-3-045473. The carbonaceous material does not need to be a single material, and a mixture of natural graphite and artificial graphite described in JP-A-5-090844 and graphite having a coating layer described in JP-A-6-004516 can also be used. As the carbonaceous material, hard carbon or graphite is preferred, and graphite is more preferred.

[0114] The oxide of a metal element or a metalloid element used as the negative electrode active material is not particularly limited as long as it is an oxide capable of absorbing and releasing lithium, and examples thereof include oxides of metal elements (metal oxides), composite oxides of metal elements, composite oxides of metal elements and metalloid elements, and oxides of metalloid elements (metalloid oxides). Composite oxides of metal elements and composite oxides of metal elements and metalloid elements are collectively referred to as metal composite oxides. Among these oxides, amorphous oxides are preferred, and chalcogenides, which are reaction products of metal elements and elements of Group 16 of the periodic table, are also preferred. In the present invention, the term "metalloid element" refers to an element that exhibits properties intermediate between metal elements and nonmetallic elements, and typically includes six elements: boron, silicon, germanium, arsenic, antimony, and tellurium, and three elements: selenium, polonium, and astatine. Furthermore, "amorphous" refers to an element that has a broad scattering band with a peak in the 2θ range of 20 to 40° in an X-ray diffraction method using CuKα radiation, and may also have crystalline diffraction lines. The strongest intensity of the crystalline diffraction lines observed at 2θ values ​​of 40 to 70° is preferably 100 times or less, more preferably 5 times or less, the diffraction line intensity at the apex of a broad scattering band observed at 2θ values ​​of 20 to 40°, and even more preferably no crystalline diffraction lines.

[0115] Among the compound group consisting of the amorphous oxides and chalcogenides, amorphous oxides or the chalcogenides of metalloid elements are more preferred, and (composite) oxides or chalcogenides consisting of one element selected from Groups 13 (IIIB) to 15 (VB) of the periodic table (e.g., Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi) or a combination of two or more of these elements are even more preferred. ２ O ３ , GeO, PbO, PbO ２ , Pb ２ O ３ , Pb ２ O ４ , Pb ３ O ４ , Sb ２ O ３ , Sb ２ O ４ , Sb２ O ８ Bi ２ O ３ , Sb ２ O ８ Si ２ O ３ , Sb ２ O ５ , Bi ２ O ３ , Bi ２ O ４ , GeS, PbS, PbS ２ , Sb ２ S ３ or Sb ２ S ５ As a negative electrode active material that can be used in combination with the amorphous oxide negative electrode active material mainly containing Sn, Si, or Ge, a carbonaceous material that can occlude and / or release lithium ions or lithium metal, lithium alone, a lithium alloy, or a negative electrode active material that can be alloyed with lithium is preferred.

[0116] The oxides of metal elements or semimetal elements (particularly metal (composite) oxides) and the chalcogenides preferably contain at least one of titanium and lithium as a constituent component in terms of high current density charge / discharge characteristics. Examples of metal composite oxides containing lithium (lithium composite metal oxides) include composite oxides of lithium oxide and the metal oxides, metal composite oxides, or chalcogenides. More specifically, Li ２ SnO ２ The negative electrode active material (for example, a metal oxide) preferably contains titanium element (titanium oxide). Specifically, Li ４ Ti ５ O １２ Lithium titanate (LTO) is preferred in that it has excellent rapid charge / discharge characteristics due to small volume fluctuations during absorption and desorption of lithium ions, and it can suppress electrode deterioration and improve the life of the all-solid-state lithium ion secondary battery.

[0117] The lithium alloy as the negative electrode active material is not particularly limited as long as it is an alloy that is commonly used as a negative electrode active material for all-solid-state lithium ion secondary batteries, and examples thereof include lithium aluminum alloys.

[0118] The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is one commonly used as a negative electrode active material for all-solid-state lithium-ion secondary batteries. Examples of the negative electrode active material include negative electrode active materials (alloys) containing silicon or tin, as well as metals such as Al and In. A negative electrode active material containing silicon (silicon-containing active material) is preferred, as it enables higher battery capacity. A silicon-containing active material having a silicon content of 50 mol% or more of the total constituent elements is more preferred. Generally, negative electrodes containing these negative electrode active materials (e.g., Si negative electrodes containing silicon-containing active materials, Sn negative electrodes containing tin-containing active materials) can absorb more Li ions than carbon negative electrodes (e.g., graphite and acetylene black). That is, the amount of Li ions absorbed per unit mass increases. This increases the battery capacity. As a result, the battery operating time can be extended.

[0119] Examples of silicon-containing active materials include silicon materials such as Si and SiOx (0<x≦1), and silicon-containing alloys containing titanium, vanadium, chromium, manganese, nickel, copper, or lanthanum (e.g., LaSi ２ , VSi ２ , La—Si, Gd—Si, and Ni—Si), or textured active materials (e.g., LaSi ２ / Si). Other examples include SnSiO ３ , and SnSiS ３ Examples of the active material containing silicon and tin include: SiOx itself can be used as a negative electrode active material (semi-metal oxide); and since SiOx generates Si during operation of an all-solid-state lithium-ion secondary battery, it can be used as a negative electrode active material (precursor material) that can be alloyed with lithium. Examples of the negative electrode active material containing tin include Sn, SnO, and SnO. ２ , SnS, SnS ２ and active materials containing the silicon and tin elements.

[0120] In terms of battery capacity, the negative electrode active material is preferably a negative electrode active material that can be alloyed with lithium, more preferably the above-mentioned silicon material or silicon-containing alloy (alloy containing silicon element), and even more preferably silicon (Si) or a silicon-containing alloy.

[0121] It is also preferable to use titanium-niobium composite oxide as the negative electrode active material. Titanium-niobium composite oxide has a high theoretical volumetric capacity density, and is expected to enable a long life and rapid charging. Examples of titanium-niobium composite oxides include TiNb ２ O ７ etc.

[0122] The shape of the negative electrode active material is not particularly limited, but particulate is preferred. The volume-average particle diameter of the negative electrode active material is not particularly limited, but is preferably 0.1 to 60 μm, more preferably 0.5 to 20 μm, and even more preferably 1.0 to 15 μm. The volume-average particle diameter is measured using the following procedure. The negative electrode active material is diluted with water (or heptane in the case of a water-unstable substance) in a 20 mL sample bottle to prepare a 1 mass % dispersion. The diluted dispersion sample is irradiated with 1 kHz ultrasound for 10 minutes and used for testing immediately thereafter. Using this dispersion sample, data is acquired 50 times using a laser diffraction / scattering particle size distribution analyzer at 25°C using a quartz measurement cell to obtain the volume-average particle diameter. For other detailed conditions, please refer to the description in JIS Z 8828:2013, "Particle Size Analysis - Dynamic Light Scattering Method," as necessary. Five samples are prepared for each level, and the average value is used.

[0123] The negative electrode active material may be used alone or in combination of two or more kinds.

[0124] The surface of the negative electrode active material may be coated with another metal oxide. Examples of the surface coating agent include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specific examples include titanate spinel, tantalum-based oxides, niobium-based oxides, and lithium niobate-based compounds, such as Li ４ Ti ５ O １２ , Li ２ Ti ２ O ５ , LiTaO３ , LiNbO ３ , LiAlO ２ , Li ２ ZrO ３ , Li ２ WO ４ , Li ２ TiO ３ , Li ２ B ４ O ７ , Li ３ P.O. ４ , Li ２ MoO ４ , Li ３ BO ３ , LiBO ２ , Li ２ CO ３ , Li ２ SiO ３ , SiO ２ , TiO ２ , ZrO ２ , Al ２ O ３ , B ２ O ３ , and Li ３ AlF ６ The surface of the electrode containing the negative electrode active material may be surface-treated with sulfur or phosphorus. Furthermore, the particle surface of the negative electrode active material may be surface-treated with actinic rays or an active gas (e.g., plasma) before or after the surface coating.

[0125] (Negative electrode current collector) The current collector constituting the negative electrode layer is an electron conductor. The negative electrode current collector is usually in the form of a film sheet. Examples of materials constituting the negative electrode current collector include aluminum, copper, copper alloy, stainless steel, nickel, and titanium, and aluminum, copper, copper alloy, or stainless steel is preferred. Note that examples of the negative electrode current collector include aluminum, copper, copper alloy, or stainless steel whose surface is treated with carbon, nickel, titanium, or silver.

[0126] The thickness of the negative electrode active material layer constituting the secondary battery of the present invention is not particularly limited and may be, for example, 5 to 500 μm, preferably 20 to 200 μm. The thickness of the negative electrode current collector constituting the secondary battery of the present invention is also not particularly limited and may be, for example, 10 to 100 μm, preferably 10 to 50 μm.

[0127] The positive electrode layer and the negative electrode layer may contain components (other components) other than the solid electrolyte and the active material in their active material layers. For example, a conductive additive may be included. Examples of conductive additives include electron-conductive materials such as graphites (e.g., natural graphite and artificial graphite), carbon blacks (e.g., acetylene black, ketjen black, and furnace black), amorphous carbon (e.g., needle coke), fibrous carbon (e.g., vapor-grown carbon fiber and carbon nanotubes), and carbonaceous materials (e.g., graphene and fullerene). Conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylene derivatives may also be used. In addition to the above conductive additives, conventional conductive additives that do not contain carbon atoms, such as metal powder or metal fiber, may also be used. A conductive additive refers to a material that does not intercalate or deintercalate Li during charging and discharging of the battery and does not function as an active material. Therefore, among the conductive additives, those that can function as an active material in the active material layer when the battery is charged and discharged are classified as active materials rather than as conductive additives. Whether or not a conductive additive functions as an active material when the battery is charged and discharged is not uniquely determined, but is determined by the combination with the active material.

[0128] Other components include the binder and lithium salts described above.

[0129] <Manufacturing of All-Solid-State Lithium-Ion Secondary Battery> The secondary battery of the present invention can be manufactured by referring to a conventional manufacturing method for an all-solid-state secondary battery, except that the solid electrolyte (I) is used for at least the solid electrolyte layer. In order to reduce the moisture content of the laminate comprising the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer in the resulting secondary battery to the level specified in the present invention, it is preferable to form a laminate comprising the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer using the solid electrolyte (I), and then subject it to a vacuum drying treatment or the like, which will be described later. A preferred embodiment of the manufacturing method for the secondary battery of the present invention will be described.

[0130] The method for manufacturing a secondary battery of the present invention includes obtaining a laminate comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order. Furthermore, in order to ensure that the water content of the laminate comprising the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer is within the range specified in the present invention, the method for manufacturing a secondary battery of the present invention preferably includes a step of subjecting the laminate comprising the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer to a drying treatment. This drying step may be performed at any stage after the formation of the laminate. To more reliably achieve the water content specified in the present invention, it is preferable to subject the laminate comprising at least the positive electrode layer, the solid electrolyte layer, and the negative electrode layer arranged in this order to the drying treatment while it is placed in a battery cell. The drying method is not particularly limited, and the moisture content of the laminate comprising the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer can be reduced to the range specified in the present invention by, for example, using a desiccator, subjecting it to vacuum drying (preferably vacuum freeze drying), or subjecting it to heat treatment. The secondary battery of the present invention is preferably formed by sealing a laminate having the above-mentioned cathode layer, solid electrolyte layer, and anode layer arranged in this order. By sealing, it is possible to more reliably prevent moisture from entering the solid electrolyte layer after the drying step, thereby further improving cycle characteristics. The sealing method is not particularly limited as long as it completely blocks or suppresses the intrusion of moisture (air). For example, a method of sealing the laminate by closing the lid of a housing (battery cell) that houses the laminate having the above-mentioned cathode layer, solid electrolyte layer, and anode layer arranged in this order via a gasket such as an O-ring can be used.

[0131] Furthermore, the method for forming a laminate having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order is not particularly limited. For example, a positive electrode-forming composition (slurry) containing a positive electrode active material is applied to a metal foil positive electrode current collector to form a positive electrode active material layer. Next, a solid electrolyte layer-forming dispersion (slurry) containing a solid electrolyte is applied to the positive electrode active material layer to form a solid electrolyte layer. Further, a negative electrode-forming composition (slurry) containing a negative electrode active material is applied to the solid electrolyte layer to form a negative electrode active material layer. Finally, a negative electrode current collector (metal foil) is superimposed on the negative electrode active material layer. The entire structure is dried and subjected to pressure treatment as necessary to obtain an all-solid-state lithium-ion secondary battery as shown in FIG. 1 . Alternatively, an all-solid-state lithium-ion secondary battery can be produced by reversing the layer formation method, forming a negative electrode active material layer, a solid electrolyte layer, and a positive electrode active material layer on a negative electrode current collector, and then subjecting the entire structure to pressure treatment as necessary.

[0132] Alternatively, the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer may be separately prepared, stacked, dried, and pressurized as necessary to produce an all-solid-state lithium-ion secondary battery. In this case, a support such as a nonwoven fabric may be provided as necessary during the formation of each layer, making each layer a self-supporting film. The secondary battery of the present invention is not limited to the method described above, as long as the secondary battery defined in the present invention can be obtained.

[0133] In the production of the secondary battery of the present invention, even if a sulfide-based solid electrolyte is not used as the solid electrolyte, the oxide-based solid electrolyte (I) that can be easily plastically deformed by pressure allows for the formation of layers with reduced interfacial resistance between solid particles or between layers. The solid electrolyte (I) itself is soft and plastically deformable, and acts as a binder, contributing to improved adhesion between solid particles or between layers, so it is possible to form layers without using a binder such as an organic polymer.

[0134] The secondary battery of the present invention is preferably initialized after manufacture or before use. The initialization method is not particularly limited, and can be performed, for example, by performing initial charge / discharge under an increased pressure and then releasing the pressure until the pressure falls within the range of the pressure conditions during use of the secondary battery.

[0135] <Applications of All-Solid-State Lithium-Ion Secondary Battery> The secondary battery of the present invention can be used in a variety of applications. While there are no particular limitations on the application, examples of applications include electronic devices such as notebook computers, pen-input PCs, mobile PCs, e-book players, mobile phones, cordless phone handsets, pagers, handheld terminals, mobile fax machines, mobile copiers, mobile printers, headphone stereos, video camcorders, LCD TVs, handheld vacuum cleaners, portable CD players, mini-discs, electric shavers, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, and backup power supplies. Other consumer applications include automobiles, electric vehicles, motors, lighting fixtures, toys, game consoles, road conditioners, clocks, flash devices, cameras, and medical devices (pacemakers, hearing aids, shoulder massagers, etc.). Furthermore, the secondary battery can be used for various military and space applications. It can also be combined with solar cells.

[0136] The present invention will be described in more detail based on examples, but the present invention is not to be construed as being limited to these examples.

[0137] [Reference Example 1] Powdered Li was mixed using a ball mill (P-7 manufactured by Fritsch). ２ B ４ O ７ Crystals (LBO powder) (manufactured by Rare Metallic Co., Ltd.) were ball milled under the following conditions: pot: stabilized zirconia (YSZ) (45 mL), milling balls: YSZ (average particle size: 5 mm, number: 50), rotation speed: 370 rpm (revolutions per minute), amount of LBO powder: 1 g, atmosphere: air, and ball mill treatment time: 100 hours, to obtain a finely divided lithium-containing oxide (hereinafter also referred to as "fine lithium-containing oxide"). 0.05 g of LiFSI (chemical formula: Li(FSO ２ ) ２N) was added (5% by mass relative to the fine particles of the lithium-containing oxide), and the mixture was ball milled for another 100 hours. The obtained powder was added to water so that the powder concentration was 42% by mass, and ultrasonically dispersed for 30 minutes. Subsequently, the obtained dispersion was transferred to a glass petri dish and dried at 120°C for 2 hours in the atmosphere to obtain a solid electrolyte film. Subsequently, the obtained film was peeled off to obtain a powdered solid electrolyte (I)-1.

[0138] <Preparation and Evaluation of a Compacted Solid Electrolyte> The powdered solid electrolyte (I)-1 obtained above was compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a compacted solid electrolyte (compacted powder 1). The compacted powder 1 had a cylindrical shape with a diameter of 10 mm and a thickness of 0.5 to 1 mm. The ionic conductivity of the compacted powder 1 obtained was measured, and the ionic conductivity of the compacted powder 1 was found to be 1.5 x 10 at 27°C. －４ S / cm and 4.0 × 10 at 60°C －４ S / cm.

[0139] The ionic conductivity of the solid electrolyte (I)-1 was calculated by placing two electrodes made of In foil so as to sandwich the powder compact 1, measuring the AC impedance between the two In electrodes in a measurement frequency range of 1 Hz to 1 MHz under conditions of a measurement temperature of 27°C or 60°C and an applied voltage of 50 mV, and analyzing the arc diameter of the obtained Cole-Cole plot (Nyquist plot).

[0140] X-ray diffraction measurement of solid electrolyte (I)-1 was carried out using CuKα radiation as described above. The measurement conditions were 0.01° / step, 3° / min. As a result, it was found that the X-ray diffraction characteristics described above were satisfied, and solid electrolyte (I)-1 was found to be in an amorphous state.

[0141] Using the solid electrolyte (I)-1 obtained above, X-ray total scattering measurements were performed using an SPring-8L04B2 (accelerating voltage: 61.4 keV, wavelength: 0.2019 Å). The sample was sealed in a 2 mmφ or 1 mmφ Kapton capillary, and the experiment was performed. The obtained data was Fourier transformed as described above to obtain a reduced pair distribution function. As a result of the analysis, in the reduced pair distribution function G(r) obtained from the X-ray total scattering measurements, within the r range of 1 to 5 Å, a first peak with a peak top of G(r) exceeding 1.0 and located at 1.43 Å, and a second peak with a peak top of G(r) exceeding 1.0 and located at 2.40 Å, were confirmed. On the other hand, in the solid electrolyte (I)-1, the peaks attributed to the B-O distance and the B-B distance observed in a typical lithium tetraborate crystal were maintained. A typical lithium tetraborate crystal has a peak top of BO. ４ Tetrahedron and BO ３ It is assumed that the structure is a diborate structure in which triangles exist in a 1:1 ratio, and that this structure is maintained in solid electrolyte (I)-1.

[0142] The solid electrolyte (I)-1 obtained above ７ The solid electrolyte (I)-1 is measured by Li-NMR at 20°C. ... ７ The ratio of the full width at half maximum (full width at half maximum 2) of the peak appearing in the chemical shift range of −100 to +100 ppm in the spectrum obtained by Li-NMR measurement at 120° C. {(full width at half maximum 2 / full width at half maximum 1)×100} was 33%. ７ When a spectrum obtained by Li-NMR measurement at 20°C was subjected to waveform separation of a first peak appearing in the range of -100 to +100 ppm, a second peak having a full width at half maximum of 5 ppm or less in a chemical shift range of -3 to 3 ppm was found, and the ratio of the area intensity of the second peak to the area intensity of the first peak was 4%.

[0143] The solid electrolyte (I)-1 obtained above was subjected to infrared absorption spectroscopy under the conditions described above. In the obtained infrared absorption spectrum, －１ 3000 to 3500 cm for the maximum absorption intensity in the wave number region －１ The ratio of the maximum absorption intensities in the wave number region of 0.72 was found to be 0.72.

[0144] In the Raman spectrum of the solid electrolyte (I)-1 obtained above, －１ The coefficient of determination obtained by linear regression analysis by the least squares method in the wavenumber region of 0.9974 was 0.9974. The mass loss rate when the solid electrolyte (I)-1 was heated from 25°C to 800°C as described above was 29.8%.

[0145] Regarding the analysis of each element in the obtained solid electrolyte (I)-1, lithium and boron were quantitatively analyzed by ICP-OES, and fluorine and sulfur were quantitatively analyzed by combustion ion chromatography (combustion IC). N was estimated from the analyzed mass of sulfur taking into account the atomic weight of each element in the Li salt, and O was calculated as the difference from the total amount of powder by adding up the analyzed masses of elements other than O. The results are shown in the table below.

[0146] [Reference Example 2] 1 g of the fine particles of the lithium-containing oxide used in Reference Example 1 was added to water so that the concentration of the fine particles was 42 mass %, and ultrasonic dispersion was performed for 30 minutes. 0.05 g of LiFSI (chemical formula: Li(FSO ２ ) ２ N) was added (5% by mass relative to the fine particles of the lithium-containing oxide), and ultrasonic dispersion was further carried out for 30 minutes. The obtained dispersion was transferred to a glass petri dish and dried at 120°C for 2 hours in the atmosphere to obtain a solid electrolyte film. Subsequently, the obtained film was peeled off to obtain a powdery solid electrolyte (I)-2. Various evaluations were carried out on the solid electrolyte (I)-2 in the atmosphere in the same manner as in Reference Example 1. The results are summarized in the table below.

[0147] [Reference Example 3] Powdered Li was mixed using a ball mill (P-7 manufactured by Fritsch). ２ B ４ O ７(LBO powder) (manufactured by Rare Metallic) was ball milled under the following conditions: pot: YSZ (45 ml), milling balls: YSZ (average particle size: 5 mm, weight: 70 g), rotation speed: 530 rpm (revolutions per minute), LBO powder amount: 4.2 g, atmosphere: air, ball mill treatment time: 100 hours, to obtain a fine lithium-containing oxide. The obtained fine lithium-containing oxide was added to water so that the concentration of the fine lithium-containing oxide was 42 mass%, and the mixture was ultrasonically treated for 60 minutes to obtain dispersion 1. Next, 3.25 g of LiFSI (chemical formula: Li(FSO ２ ) ２ N) was added to water to a concentration of 87% by mass, and the mixture was subjected to ultrasonic treatment for 60 minutes to obtain Solution 2. The obtained Dispersion 1 and Solution 2 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-3. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were performed in the atmosphere using solid electrolyte (I)-3 in the same manner as in Reference Example 1. The results are summarized in the table below.

[0148] Reference Example 4 Dispersion 3 was obtained in the same manner as in the preparation of Dispersion 1 in Reference Example 3. Next, 2.32 g of LiFSI (chemical formula: Li(FSO ２ ) ２ N) was added to water at a concentration of 87% by mass and subjected to ultrasonic treatment for 60 minutes to obtain Solution 4. The obtained Dispersion 3 and Solution 4 were mixed and stirred and mixed with a magnetic stirrer for 60 minutes. Subsequently, the obtained dispersion was vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-4. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were performed in the atmosphere using solid electrolyte (I)-4 in the same manner as in Reference Example 1. The results are summarized in the table below.

[0149] [Reference Example 5] Dispersion 5 was obtained in the same manner as in the preparation of Dispersion 1 in Reference Example 3. Next, 4.65 g of LiFSI (chemical formula: Li(FSO ２ ) ２N) was added to water at a concentration of 87% by mass and subjected to ultrasonic treatment for 60 minutes to obtain Solution 6. The obtained Dispersion 5 and Solution 6 were mixed and stirred and mixed with a magnetic stirrer for 60 minutes. Subsequently, the obtained dispersion was vacuum-dried at 40°C and 10 Pa for 15 hours to obtain a powdered solid electrolyte (I)-5. The obtained powder was immediately subjected to various evaluations in the atmosphere in the same manner as in Reference Example 1. The results are summarized in the table below.

[0150] Reference Example 6 Dispersion 7 was obtained in the same manner as in the preparation of Dispersion 1 in Reference Example 3. Next, 7.13 g of LiTFSI (chemical formula: Li(F ３ CSO ２ ) ２ N) was added to water at a concentration of 87% by mass and ultrasonically treated for 60 minutes to obtain Solution 8. The obtained Dispersion 7 and Solution 8 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-6. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were performed in the atmosphere using solid electrolyte (I)-6 in the same manner as in Reference Example 1. The results are summarized in the table below. In Reference Example 6, the carbon content shown in Table 1 below was estimated from the analyzed mass of sulfur, taking into account the atomic weight of each atom in the lithium salt.

[0151] Comparative Example 1 The LBO powder (powdered Li without ball milling) used in Example 1 was ２ B ４ O ７ As a result of elemental analysis of the LBO powder, the composition of the obtained powder was １．９６ B ４．００ O ６．８０The LBO powder was compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a comparative powder compact C1. The ionic conductivity of the obtained powder compact C1 was undetectable. Furthermore, X-ray total scattering measurement was performed using the LBO powder in the same manner as in Reference Example 1 to obtain the reduced pair distribution function G(r). FIG. 10 shows the reduced pair distribution function G(r) obtained from the LBO powder. As a result of analysis, the reduced pair distribution function G(r) obtained from the X-ray total scattering measurement of the LBO powder contained a first peak (corresponding to B-O proximity) with a peak top at 1.40 Å and a second peak (corresponding to B-B proximity) with a peak top at 2.40 Å, and the G(r) values ​​of the first and second peaks were 1.0 or greater (see FIG. 10). Furthermore, peaks with tops at 3.65 Å, 5.22 Å, 5.51 Å, and 8.54 Å were present, and the absolute value of G(r) at the peak top of each peak clearly exceeded 1.0 (see FIG. 10 ). Furthermore, X-ray diffraction measurement of the LBO powder was performed as described above. The measurement conditions were 0.01° / step and 3° / min. FIG. 11 shows the X-ray diffraction pattern of the LBO powder of Comparative Reference Example 1. As shown in FIG. 11 , multiple narrow peaks were observed in the LBO powder used in Comparative Reference Example 1. More specifically, the strongest peak corresponding to the (1,1,2) plane was observed at a 2θ value of 21.78°. Other major diffraction peaks were observed at 25.54° corresponding to the (2,0,2) plane, 33.58° corresponding to the (2,1,3) plane, and 34.62° corresponding to the (3,1,2) plane, and the intensities of these three peaks were almost equal. These peaks were derived from crystalline components.

[0152] Comparative Example 2: The fine particles of the lithium-containing oxide prepared in Example 1 (powdered Li ２ B ４ O ７ As a result of elemental analysis of the fine particles of lithium-containing oxide (crystals ball-milled), the composition of the fine particles of lithium-containing oxide was １．９４ B ４．００ O ６．８０Next, the fine particles of the lithium-containing oxide were compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a reference compact (compacted powder R1). The ionic conductivity of the obtained compacted powder R1 was 7.5 x 10 at 27°C. －９ S / cm and 7.5 × 10 at 60 °C －８ The viscosity was S / cm.

[0153] In the table below, when the reduced pair distribution function G(r) obtained from X-ray total scattering measurement as described above has a first peak whose peak top is located in the r range of 1.43±0.2 Å and a second peak whose peak top is located in the r range of 2.40±0.2 Å, and the G(r) at the peak top of the first peak and the G(r) at the peak top of the second peak are greater than 1.0, the column for "short-distance G(r)" is marked with "A," and otherwise the column is marked with "B." Note that in Reference Examples 1 to 4 shown in the table below and Reference Examples 9 to 12 described below, the value of G(r) at the peak top of the first peak was 1.2 or greater. Furthermore, when the absolute value of G(r) is less than 1.0 in the r range of greater than 5 Å and not more than 10 Å, the column for "long-distance G(r)" in the table below is marked with "A," and when the absolute value of G(r) does not satisfy the criteria of less than 1.0, the column is marked with "B." Furthermore, as a result of the X-ray diffraction measurement using the above-mentioned CuKα ray, cases where the above-mentioned X-ray diffraction characteristics were satisfied were rated as "A", and cases where the above-mentioned X-ray diffraction characteristics were not satisfied were rated as "B". Note that in Reference Examples 1 to 6 shown in the table below and Reference Examples 7 to 13 described later, none of the first peak, second peak, third peak, and fourth peak was present in the X-ray diffraction pattern, or the intensity ratio of at least one of the first peak, second peak, third peak, and fourth peak was 2.0 or less.

[0154] In the table below, the column "Elemental Analysis" shows the composition of the solid electrolyte (I) obtained in each Reference Example and the lithium-containing oxide in each Comparative Reference Example as a molar amount of each element, as a relative value with the content of B set to "4.00".

[0155] In the table below, the "area intensity ratio" is the solid ７In Li-NMR measurement, this is the ratio of the area intensity of the second peak to the area intensity of the first peak, and the evaluation results are based on the following criteria: <Criteria for area intensity ratio> A: When the area intensity ratio is 15% or more B: When the area intensity ratio is 0.5% or more and less than 15% C: When the area intensity ratio is less than 0.5%

[0156] In the table below, the "maximum absorption intensity ratio" column indicates whether or not the above-mentioned infrared absorption spectrum characteristics are satisfied. －１ Maximum absorption intensity in the wavenumber region of 800 to 1600 cm －１ A value of 0.20 or more for the maximum absorption intensity in the wave number region of [A] is indicated as A, and a value of less than 0.20 is indicated as B. In the table below, "-" means that the measured value is not shown.

[0157]

[0158]

[0159] As shown in the table above, the solid electrolytes (I)-1, (I)-2, (I)-3, (I)-4, (I)-5, and (I)-6 of Reference Examples 1 to 6 were found to have excellent ionic conductivity. Furthermore, the results of elemental analysis confirmed that the solid electrolytes in Reference Examples 3 to 6 had a higher Li content. In Reference Examples 3 to 6, an aqueous solution containing a mechanically milled lithium compound was mixed with an aqueous solution containing a lithium salt (Method 3 in Step 2B described above), allowing for the mixing of a larger amount of lithium salt. It is presumed that this resulted in an increased amount of Li incorporated into the solid electrolyte. Furthermore, it was also found that Reference Examples 3, 4, and 5, which used LiFSI as the lithium salt, had improved ionic conductivity. This is presumed to be due to the presence of highly mobile Li in the increased Li.

[0160] <Effect of Water in Solid Electrolyte> A compact (pellet) (10 mmφ, 0.9 mmt) of solid electrolyte (I)-3 obtained in Reference Example 3 was vacuum-dried at 27°C under a restraint of 60 MPa, and the pressure change and ionic conductivity with respect to the vacuum drying time were investigated. The method for producing the compact and the evaluation of ionic conductivity were the same as described above, except that the In electrode was changed to a Ti electrode. The results are shown in Table 3.

[0161]

[0162] The solid electrolyte (I)-3 of Reference Example 3 has a peak intensity of 3000 to 3500 cm in the infrared absorption spectrum. －１ The OH stretching peak increases, suggesting the presence of numerous OH groups and water. Regarding water, the presence of both free and bound water is suspected. In the above, the pellets were first dried under vacuum drying conditions that would volatilize the free water, and then under more severe drying conditions, and the ionic conductivity at each stage was evaluated.

[0163] As shown in the table above, the pressure was 200 Pa after 5 minutes of drying, and the free water was considered to be in a vaporized state. However, the ionic conductivity was 3.8 × 10 －３ Even with a drying time of 1080 minutes and a pressure of 15 Pa, the ionic conductivity was 5.7 × 10 －４ This result indicates that bound water exists in addition to free water, and that this contributes to ionic conductivity.

[0164] [Reference Example 7] Dispersion 9 having a concentration of lithium-containing oxide fine particles of 42 mass % was obtained in the same manner as in the preparation of dispersion 1 in Reference Example 3. Next, 7.12 g of LiTFSI (chemical formula: Li(F ３ CSO ２ ) ２N was added to water to a concentration of 87% by mass, and the mixture was subjected to ultrasonic treatment for 60 minutes to obtain Solution 10. The obtained Dispersion 9 and Solution 10 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-7. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were performed in the atmosphere using solid electrolyte (I)-7 in the same manner as in Reference Example 1. The results are summarized in the table below.

[0165] [Reference Example 8] A solid electrolyte (I)-8 was obtained in the same manner as in Reference Example 7, except that the contents of water and LiTFSI in the obtained solid electrolyte (I) were changed to the amounts shown in the table below, and various evaluations were carried out under air in the same manner as in Reference Example 1. The results are summarized in the table below.

[0166] [Reference Examples 9 to 13] Solid electrolytes (I)-9 to (I)-13 were obtained in the same manner as in Reference Example 7, except that LiTFSI was changed to LiFSI and the contents of water and LiFSI in the resulting solid electrolyte (I) were changed to the amounts shown in the table below. Various evaluations were carried out in the atmosphere in the same manner as in Reference Example 1. The results are summarized in the table below. However, in Reference Example 13, the powder obtained after vacuum drying was immediately evaluated in the atmosphere.

[0167] In the table below, the "Lithium-containing oxide fine particles" column, the "Lithium salt" column, and the "Water" column represent relative molar ratios. For example, in Reference Example 7, the molar ratio of lithium salt to lithium-containing oxide fine particles is 1, and the molar ratio of water to lithium-containing oxide fine particles is 11. The molar ratios were calculated by the following method. The analysis of each element was performed by quantitatively analyzing lithium and boron using ICP-OES, and fluorine and sulfur using combustion ion chromatography (combustion IC). N was estimated from the analyzed mass of sulfur taking into account the atomic weight of each element in the Li salt, and O was calculated as the difference from the total amount of solid electrolyte by adding up the analyzed masses of elements other than O. In Reference Examples 7 and 8, the carbon amount was estimated from the analyzed mass of sulfur taking into account the atomic weight of each element in the lithium salt. The molar ratio of lithium-containing oxide fine particles to lithium salt in the solid electrolyte was calculated from the molar ratio of an element (e.g., B) that is only present in the lithium-containing oxide fine particles and an element that is only present in the lithium salt. Furthermore, the molar ratio of the fine particles of the lithium-containing oxide to water was calculated by subtracting the molar ratios of O contained in the fine particles of the lithium-containing oxide and the lithium salt from the molar ratio of O in the solid electrolyte to calculate the molar amount of O derived from water, and then using the obtained molar amount of O derived from water and the molar amount of the fine particles of the lithium-containing oxide.

[0168]

[0169] The content (mass %) of each component in the solid electrolyte (I) was calculated based on the molar amount and molecular weight shown in Table 4. The results are shown in Table A below.

[0170]

[0171]

[0172] As shown in the above table, the solid electrolytes of each Reference Example had the desired characteristics or properties and exhibited excellent ionic conductivity.

[0173] [Production Example 1] Production of all-solid-state lithium-ion secondary battery <Preparation of fine particles of lithium-containing oxide> Powdered Li ２ B ４ O ７45 g of crystals (LBO powder) (manufactured by Rare Metallic), 770 g of zirconia beads, and 3 mL of water were placed in a 500 mL zirconia pot and sealed with a Teflon ring and a zirconia lid. The LBO powder was milled in a planetary ball mill at 300 rpm for 45 hours to obtain fine particles of a lithium-containing oxide.

[0174] <Preparation of Solid Electrolyte Slurry> 10 g of the fine particles of the lithium-containing oxide, 15 g of water, and 11 g of LiFSI were mixed in a beaker and ultrasonically treated for 30 minutes using an ultrasonic cleaner to obtain a dispersion. This dispersion was further stirred for 30 minutes using a magnetic stirrer to obtain solid electrolyte slurry 1. This solid electrolyte slurry 1 was vacuum dried at 40°C and 20 Pa for 15 hours to obtain a powder. The obtained powder was stored in a desiccator (5%) for several days and then analyzed under atmospheric pressure. It was confirmed that the powder had the above-mentioned X-ray diffraction characteristics and was in an amorphous state. Furthermore, the ionic conductivity was measured using the above-mentioned method to find a value of 4.5 x 10 －３ S / cm. The molar ratio of the LiFSI content to the lithium-containing oxide content was 1, and the molar ratio of the water content to the lithium-containing oxide content was 9. The element composition (molar ratio) was approximately as follows: Li:B:O:F:S:N=3:4:20:2:2:1.

[0175] <Preparation of Positive Electrode Slurry> 5.2 g of the above solid electrolyte slurry 1 was mixed with the positive electrode active material LiCoO ２ 5.0 g of the above and 4.8 g of a 6 mass % aqueous dispersion of carbon nanotubes (CNT) (manufactured by KJ Specialty Paper Co., Ltd.) as a conductive additive were added, and the mixture was stirred with a magnetic stirrer for 30 minutes to obtain positive electrode slurry 1.

[0176] <Preparation of negative electrode slurry> 7.6 g of the above solid electrolyte slurry 1 was mixed with a negative electrode active material TiNb ２ O ７ 5.0 g of the above and 9.8 g of a 6 mass % aqueous dispersion of CNT (manufactured by KJ Specialty Paper Co., Ltd.) as a conductive additive were added, and the mixture was stirred with a magnetic stirrer for 30 minutes to obtain negative electrode slurry 1.

[0177] <Preparation of Positive Electrode Laminate [Solid Electrolyte Layer / Positive Electrode Active Material Layer / Al Current Collector]> The above-mentioned positive electrode slurry 1 was applied to a 50 μm thick A4-size Al foil using a desktop coater at an applicator gap of 100 μm and a coating speed of 30 mm / s. After leaving at room temperature for 1 hour, the above-mentioned solid electrolyte slurry 1 was applied in a multilayer on the positive electrode slurry coating using a desktop coater at an applicator gap of 200 μm and a coating speed of 90 mm / s. The multilayer coating was stored in a desiccator at a relative humidity of 5% or less for 12 hours to dry, and then punched out to a diameter of 10 mm using a hand punch to obtain a positive electrode laminate (solid electrolyte layer / positive electrode active material layer / Al current collector). The thickness of the solid electrolyte layer was approximately 60 μm.

[0178] <Preparation of Negative Electrode Laminate [Solid Electrolyte Layer / Negative Electrode Active Material Layer / Al Current Collector]> The above-mentioned negative electrode slurry 1 was applied to a 50 μm-thick A4-size Al foil using a desktop coater at an applicator gap of 200 μm and a coating speed of 30 mm / s. After leaving it at room temperature for 1 hour, the above-mentioned solid electrolyte slurry 1 was applied in a multilayer on the negative electrode slurry coating using a desktop coater at an applicator gap of 300 μm and a coating speed of 90 mm / s. The multilayer coating was stored in a desiccator at a relative humidity of 5% or less for 12 hours to dry, and then punched out to a diameter of 10 mm using a hand punch to obtain a negative electrode laminate (solid electrolyte layer / negative electrode active material layer / Al current collector). The thickness of the solid electrolyte layer was approximately 60 μm.

[0179] <Manufacturing of All-Solid-State Lithium-Ion Secondary Battery> (Example 1) The above-mentioned negative electrode side laminate was placed on a 10 mm diameter SUS (stainless steel) stand of an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.) with the solid electrolyte layer facing up. The above-mentioned positive electrode side laminate was placed on top of this solid electrolyte layer with the solid electrolyte layer facing down. In this way, a laminate with a positive electrode side laminate / negative electrode side laminate structure (this laminate is referred to as a cell) was obtained. Next, a Teflon tube with an inner diameter of 10.2 mm was inserted from the positive electrode current collector side of the cell, and a polished Ti plate with a diameter of 10 mm and a thickness of 2 mm was inserted through the hole at the top of the Teflon tube, and the polished Ti plate was placed on top of the positive electrode laminate. Furthermore, a Ti rod with a diameter of 10 mm and a height of 2 cm was placed on top of the polished Ti plate. Next, the upper housing of the KP-SolidCell was inserted and sealed with a double O-ring, four-point bolts, and wing nuts. The cell was constrained from above and below with a torque of 5 Nm (equivalent to 30 MPa) using a confining pressure application mechanism installed on top of the KP-Solid Cell. Next, the KP-Solid Cell was opened, the cell was removed, and excess liquid components that had seeped out due to the application of confining pressure were wiped off. Next, the cell was set in the KP-Solid Cell in the same manner as above, and the cell was constrained from above and below. Next, with the top lid open, the KP-Solid Cell was subjected to a 2-hour freeze-vacuum drying treatment (10 Pa, 40°C) to thoroughly remove moisture from inside the cell. After removing the KP-Solid Cell from the vacuum dryer, the top lid was closed and sealed using a double O-ring. After leaving it for 40 hours, it was made into the battery of Example 1.

[0180] (Examples 2 to 4, Comparative Example 1) In the production of the battery of Example 1, the amount (number of particles) of silica gel (manufactured by Fujifilm Wako Pure Chemical Industries, medium granular (blue)) to be placed in the cavity of the KP-SolidCell after placing the Ti rod on the polished Ti plate, and the vacuum drying treatment time in the freeze-vacuum drying treatment were set as shown in the table below, and a battery was obtained in the same manner as in Example 1.

[0181] The resulting battery (amount of positive electrode active material: 2 mg / cm ２ The cycle characteristics at 25°C under a confining pressure of 30 MPa were measured as described in the following test example.

[0182] [Test Example] Cycle Characteristics Test The battery obtained above was subjected to repeated charging and discharging under the following conditions: a confining pressure (30 MPa) was applied to the battery at a temperature of 27°C using a 580-NOHFR battery manufactured by Toyo Corporation. Charging was performed at a constant current value I until the battery voltage reached 2.8 V. β After the voltage reached 2.8 V, the voltage was kept constant (2.8 V) and the current was charged at a rate of 2.4 C. After charging, the circuit was opened and the battery was left for 10 minutes, after which the current was charged at a constant value I β The battery was discharged at 1000 kJ / s until the battery voltage reached 1.5 V. This cycle of charging and discharging was considered as one cycle. After discharging, the circuit was opened and the battery was left for 10 minutes, after which the next charging and discharging were carried out, and the charging and discharging were repeated under the same conditions. β As an initialization of the battery, the charge / discharge cycle test was performed by setting the charge / discharge current at 0.2 C in the first cycle and setting the current at 3 C in the subsequent cycles.

[0183] The results are shown in the table below. In the table below, the "moisture content in KF measurement" in Example 1 and Comparative Example 1 refers to the moisture content (% by mass) of the laminate consisting of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer, and was determined as follows. The resulting battery was disassembled under an Ar atmosphere, the cells were removed, and approximately 5 to 10 mg of the laminate consisting of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer was sealed in a dedicated vial as a sample. In addition, a vial containing only the Ar atmosphere was also sealed as a blank. The vials were placed in a moisture vaporizer for Karl Fischer measurement and heated to 100°C or 300°C to vaporize the moisture. The moisture content of each sample was then measured by Karl Fischer titration using a coulometric moisture analyzer. The moisture content of the blank was subtracted from the moisture content, and the resulting value was divided by the sample weight to determine the moisture content (% by mass) of the laminate consisting of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer.

[0184]

[0185] As shown in the above table, it was found that the charge-discharge cycle characteristics can be effectively improved by subjecting the laminate consisting of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer that constitute the battery to a vacuum drying treatment to reduce the moisture content.

[0186] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0187] This application claims priority based on Japanese Patent Application No. 2022-089965, filed in Japan on June 1, 2022, the contents of which are incorporated herein by reference.

[0188] REFERENCE SIGNS LIST 1 negative electrode current collector 2 negative electrode active material layer 3 solid electrolyte layer 4 positive electrode active material layer 5 positive electrode current collector 6 operating part 10 all-solid-state lithium ion secondary battery

Claims

1. An all-solid-state lithium ion secondary battery having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order, the solid electrolyte layer includes an amorphous solid electrolyte including a lithium-containing oxide including Li, B, and O and a lithium salt, and in the amorphous solid electrolyte, a ratio of the content of the lithium salt to the content of the lithium-containing oxide is 0.001 to 1.5 in terms of molar ratio; An all-solid-state lithium-ion secondary battery, in which a laminate consisting of a positive electrode active material layer, the solid electrolyte layer, and a negative electrode active material layer has a moisture content based on Karl Fischer titration at 100°C of 7.0% by mass or less, and a difference in moisture content based on Karl Fischer titration at 100°C and 300°C is 0.1 to 5.0% by mass.

2. An all-solid-state lithium ion secondary battery having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer arranged in this order, the solid electrolyte layer includes an amorphous solid electrolyte including a lithium-containing oxide including Li, B, and O and a lithium salt, and in the amorphous solid electrolyte, a ratio of the content of the lithium salt to the content of the lithium-containing oxide is 0.001 to 1.5 in terms of molar ratio; An all-solid-state lithium-ion secondary battery, comprising a laminate including a positive electrode active material layer, the solid electrolyte layer, and a negative electrode active material layer, the laminate being subjected to a vacuum drying treatment.

3. The lithium-containing oxide is Li ２＋ｘ B ４＋ｙ O ７＋ｚ The all-solid-state lithium ion secondary battery according to claim 1 or 2, comprising: However, −0.3<x<0.3, −0.3<y<0.3, and −0.3<z<0.

3.

4. The all-solid-state lithium ion secondary battery according to claim 1 or 2, wherein the lithium salt is represented by the following formula (1): Formula (1) LiN(R ｆ１ SO ２ ) (R ｆ２ SO ２ ) In the formula, R ｆ１ and R ｆ２ each independently represents a halogen atom or a perfluoroalkyl group.

5. 3. The all-solid-state lithium-ion secondary battery according to claim 1, wherein the lithium-containing oxide is subjected to a mechanical milling treatment.

6. 3. The all-solid-state lithium ion secondary battery according to claim 1, wherein the all-solid-state lithium ion secondary battery is formed by sealing a laminate in which the positive electrode layer, the solid electrolyte layer, and the negative electrode layer are arranged in this order.

7. 3. The method for producing an all-solid-state lithium-ion secondary battery according to claim 1, further comprising forming a laminate including the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer, and then subjecting the laminate to a vacuum drying treatment.