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

[Technical Field]

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

[0002] Traditionally, lithium-ion secondary batteries have used liquid electrolytes with high ionic conductivity. However, liquid electrolytes are flammable, posing safety challenges. Furthermore, their liquid nature makes them difficult to miniaturize, and capacity limitations become a problem when batteries are enlarged. In contrast, all-solid-state lithium-ion secondary batteries are one of the next-generation batteries that can solve these problems. The basic structure of an all-solid-state lithium-ion secondary battery is shown in Figure 1. The all-solid-state lithium-ion secondary battery 10 has, when viewed from the negative electrode side, 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 the others and has an adjacent structure. By adopting such a structure, during charging, electrons (e - ) is supplied, and lithium ions (Li) that have moved through the solid electrolyte layer 3 are supplied there. + ) accumulates. On the other hand, during discharge, lithium ions (Li) accumulated on the negative electrode are released. + The discharge is returned to the positive electrode side through the solid electrolyte layer 3, and electrons are supplied to the working part 6. In the illustrated example, a light bulb is used as a model for the working part 6, and it is designed to light up when discharge occurs.

[0003] As described above, in all-solid-state lithium-ion secondary batteries, excellent lithium-ion conductivity is required in the solid electrolyte layer in order to obtain the desired charge-discharge characteristics. The solid electrolytes used to constitute the solid electrolyte layer are mainly sulfide-based solid electrolytes or oxide-based solid electrolytes. Sulfide-based solid electrolytes are soft and plastically deformable, so the 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 produce toxic hydrogen sulfide. In contrast, oxide-based solid electrolytes have the advantage of high safety. However, oxide-based solid electrolytes are hard and difficult to plastically deform. To improve the bonding between particles of oxide-based solid electrolytes, high-temperature sintering is required, which imposes constraints in terms of battery production efficiency and energy costs. For example, Patent Document 1 discloses a solid electrolyte formed from a lithium-containing oxide of a specific elemental composition, and it is stated that this solid electrolyte exhibits high ionic conductivity. However, in order to use this lithium-containing oxide as a solid electrolyte sheet, high-temperature sintering is required. As a technology that addresses this problem, for example, Patent Document 2 describes a lithium ion conductivity of 1.0 × 10 at 25°C. -6 A composite is described that includes a lithium compound with a lithium content of S / cm or higher and lithium tetraborate, whose reduced two-body distribution function G(r) obtained from X-ray total scattering measurements exhibits a specific profile. According to the technology described in Patent Document 2, although this composite is composed of lithium-containing oxides, lithium tetraborate undergoes plastic deformation between the lithium compounds to connect them, and therefore, this composite can form a lithium ion conductor exhibiting good lithium ion conductivity by pressurization treatment without requiring high-temperature sintering treatment. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-052755 [Patent Document 2] International Publication No. 2021 / 193204 [Overview of the project] [Problems that the invention aims to solve]

[0005] The composite described in Patent Document 2 above is composed of lithium-containing oxides, yet is soft, and can ensure interparticle bonding without sintering or the addition of binders such as organic polymers, possessing properties that conventional oxide-based solid electrolytes have not been able to achieve. However, as the inventors have continued their investigations, they have found that the lithium ion conductivity is not yet sufficient for practical use as a solid electrolyte layer in all-solid-state lithium-ion secondary batteries, and there is room for improvement before practical application.

[0006] The lithium-ion conductivity of the solid electrolyte used in all-solid-state lithium-ion secondary batteries is an essential characteristic for the battery to function. Furthermore, since secondary batteries are used through repeated charging and discharging, the characteristic of not losing battery performance even after repeated charging and discharging (cycle characteristics) is also an important characteristic required of all-solid-state lithium-ion secondary batteries.

[0007] The present invention aims to provide an all-solid-state lithium-ion secondary battery using a lithium-containing oxide as the solid electrolyte layer, wherein the solid electrolyte layer exhibits excellent interparticle bonding even without high-temperature sintering treatment and without the inclusion of a binder such as an organic polymer, resulting in higher lithium-ion conductivity, superior safety, and excellent cycle characteristics, as well as a method for manufacturing the same. [Means for solving the problem]

[0008] The problems of the present invention were solved by the following means.

[0009] [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 above solid electrolyte layer contains an amorphous solid electrolyte containing a lithium-containing oxide containing Li, B, and O and a lithium salt. In this amorphous solid electrolyte, the value of the 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. A all-solid-state lithium-ion secondary battery, wherein the laminated body composed of a positive electrode active material layer, the solid electrolyte layer, and a negative electrode active material layer has a water content of 7.0% by mass or less based on the Karl Fischer titration method at 100 °C, and the difference in the water content based on the Karl Fischer titration method at 100 °C and 300 °C is 0.1 to 5.0% by mass. 〔2〕 A all-solid-state lithium-ion secondary battery in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are arranged in this order. The above solid electrolyte layer contains an amorphous solid electrolyte containing a lithium-containing oxide containing Li, B, and O and a lithium salt. In this amorphous solid electrolyte, the value of the 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. A all-solid-state lithium-ion secondary battery, wherein the laminated body composed of a positive electrode active material layer, the solid electrolyte layer, and a negative electrode active material layer is a laminated body that has been vacuum-dried. 〔3〕 The above lithium-containing oxide contains Li 2+x B 4+y O 7+z The all-solid-state lithium-ion secondary battery according to 〔1〕 or 〔2〕. However, -0.3 < x < 0.3, -0.3 < y < 0.3, -0.3 < z < 0.3. 〔4〕 The all-solid-state lithium-ion secondary battery according to any one of 〔1〕 to 〔3〕, wherein the above lithium salt is represented by the following formula (1). Formula (1) LiN(R f1 SO2)(R f2 SO2) In the formula, R f1 and R f2 each independently represents a halogen atom or a perfluoroalkyl group. 〔5〕 An all-solid-state lithium-ion secondary battery according to any one of [1] to [4], wherein the lithium-containing oxide described above has been subjected to mechanical milling. [6] The all-solid-state lithium-ion secondary battery described above is a sealed laminate in which the positive electrode layer, solid electrolyte layer, and negative electrode layer are arranged in that order, as described in any of [1] to [5]. [7] A method for manufacturing an all-solid-state lithium-ion secondary battery according to any one of [1] to [6], comprising forming a laminate containing 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 this invention or specification, a numerical range represented using "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. [Effects of the Invention]

[0011] The all-solid-state lithium-ion secondary battery of the present invention uses a lithium-containing oxide as the solid electrolyte layer. This solid electrolyte layer exhibits excellent interparticle bonding even without high-temperature sintering and without the inclusion of a binder such as an organic polymer, resulting in higher lithium-ion conductivity, superior safety, and excellent cycle characteristics. Furthermore, the manufacturing method for the all-solid-state lithium-ion secondary battery of the present invention is a suitable manufacturing method for obtaining the all-solid-state lithium-ion secondary battery of the present invention described above. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of the configuration of an all-solid-state lithium-ion secondary battery. [Figure 2] Figure 2 shows an example of an X-ray diffraction pattern to illustrate the X-ray diffraction characteristics of the solid electrolyte (I) used in the present invention. [Figure 3]Figure 3 shows an example of the reduction two-body distribution function G(r) obtained from X-ray total scattering measurements of the solid electrolyte (I) used in the present invention. [Figure 4] Figure 4 shows an example of a spectrum obtained when solid-state 7Li-NMR measurement of the solid electrolyte (I) used in the present invention is performed at 20°C or 120°C. [Figure 5] Figure 5 shows an example of a spectrum obtained when solid-state 7Li-NMR measurements of lithium tetraborate crystals are performed at 20°C or 120°C. [Figure 6] Figure 6 shows an example of a spectrum obtained when solid-state 7Li-NMR measurement of the solid electrolyte (I) used in the present invention is performed at 20°C. [Figure 7] Figure 7 shows the waveforms separated from the peaks shown in Figure 6. [Figure 8] Figure 8 shows an example of the Raman spectrum of the solid electrolyte (I) used in the present invention. [Figure 9] Figure 9 shows the Raman spectrum of a lithium tetraborate crystal. [Figure 10] Figure 10 shows the reduction dibody distribution function G(r) obtained by X-ray total scattering measurement of powdered Li2B4O7 crystals. [Figure 11] Figure 11 shows the X-ray diffraction pattern of powdered Li2B4O7 crystals. [Modes for carrying out the invention]

[0013] [All-solid-state lithium-ion rechargeable 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 a solid electrolyte of a specific composition in an amorphous state, as described later. The secondary battery of the present invention has a laminated structure consisting of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, wherein the laminated structure (laminated structure excluding the current collector) consisting of 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 based on Karl Fischer titration at 100°C. The water content based on Karl Fischer titration can be determined by the method described in the examples below. The water content of the laminated structure consisting of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer, based on 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, even more preferably 3.0% by mass or less, even more preferably 2.0% by mass or less, even more preferably 1.5% by mass or less, and also preferably 1.0% by mass or less. The water 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 water 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 0.2 to 6.0% by mass, more preferably 0.2 to 5.0% by mass, even more preferably 0.4 to 4.0% by mass, even more preferably 0.4 to 3.0% by mass, even more preferably 0.4 to 2.0% by mass, even more preferably 0.6 to 2.0% by mass, and even more preferably 0.7 to 1.5% by mass. Furthermore, the secondary battery of the present invention preferably has a water content of 0.1 to 12.0% by mass, more preferably 0.5 to 10.0% by mass, even more preferably 1.0 to 8.0% by mass, even more preferably 1.5 to 5.0% by mass, and even more preferably 1.5 to 3.0% by mass, based on Karl Fischer titration at 300°C, for the laminate comprising the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer of the present invention. The secondary battery of the present invention has a difference in water content of a laminate consisting of a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, based on Karl Fischer titration at 100°C and 300°C ([water content based on Karl Fischer titration at 300°C] - [water content based on Karl Fischer titration at 100°C]), which 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 also preferably 3.0 to 4.0% by mass. Furthermore, the above difference in water content is also preferably 0.1 to 4.0% by mass, preferably 0.5 to 4.0% by mass, preferably 0.5 to 3.0% by mass, preferably 0.5 to 2.0% by mass, and also preferably 0.5 to 1.5% by mass.

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

[0015] <Solid electrolyte layer> The solid electrolyte layer constituting the secondary battery of the present invention is formed by molding a solid electrolyte of a specific composition in an amorphous state (synonymous with non-crystalline state or amorphous state), or a mixture of this solid electrolyte and other components, into layers, and is usually formed by vacuum drying. The solid electrolyte of a specific composition in an amorphous state 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. Hereafter, the solid electrolyte of the specific composition in the amorphous state described above will also be referred to as "solid electrolyte (I)". Solid electrolyte (I) is usually an inorganic solid electrolyte.

[0016] The solid electrolyte (I) is amorphous and exhibits elastic properties that make it easily plastically deformable. As a result, in a solid electrolyte layer containing solid electrolyte (I) formed through pressurization, drying, etc., the adhesion between solid electrolyte (I) particles and / or between solid electrolyte (I) and other ion conductors is improved, reducing interfacial resistance and resulting in superior ion conductivity. By forming a solid electrolyte layer using this solid electrolyte (I), it is possible to form a lithium ion conductor that exhibits excellent lithium ion conductivity through pressurization, etc., without subjecting it to high-temperature sintering, even though it is a highly safe oxide-based solid electrolyte.

[0017] The water contained in the solid electrolyte (I) includes at least bound water. The reason why the solid electrolyte (I) exhibits high lithium ion conductivity is not clear, but it is thought that in the amorphous state of the solid electrolyte (I), a soft hydration layer easily forms 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 higher ionic conductivity. Here, in this invention and its specification, "bound water" means water other than water that exists as free water, or OH groups bonded to lithium-containing oxides. Even if the solid electrolyte (I) contains the above amount of water, it is in the state 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 the state of solid particles, some of the water contained in the solid electrolyte (I) may be free water. If the solid electrolyte (I) contains free water, at least some of the free water is removed by the drying treatment of the 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), as described later. Furthermore, depending on the interaction of the bound water with lithium-containing oxides or lithium salts, and depending on the level of the above drying treatment conditions, some of the bound water may be removed.

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

[0019] (X-ray diffraction properties) In the X-ray diffraction pattern obtained from X-ray diffraction measurements of solid electrolyte (I) using CuKα radiation, if any of the following are absent, or if none of the following exist: a first peak with its peak top located in the diffraction angle 2θ range of 21.6 to 22.0° and a full width at half maximum (FMAX) of 0.65° or less; a second peak with its peak top located in the diffraction angle 2θ range of 25.4 to 25.8° and a FMAX of 0.65° or less; a third peak with its peak top located in the diffraction angle 2θ range of 33.4 to 33.8° and a FMAX of 0.65° or less; or a fourth peak with its peak top located in the diffraction angle 2θ range of 34.4 to 34.8° and a FMAX of 0.65° or less, In the X-ray diffraction pattern, if at least one of the above-mentioned first, second, third, and fourth peaks (hereinafter referred to as "peak X") is present, then at least one of the peaks X has an intensity ratio of 5.0 or less calculated by the intensity measurement method described below.

[0020] -Strength Measurement Method- The average intensity (Av1) is calculated for the range of +0.45° to +0.55° from the diffraction angle 2θ at the peak top of Peak X, and the average intensity (Av2) is calculated for the range of -0.55° to -0.45° from the diffraction angle 2θ at the peak top of Peak X. The sum of Av1 and Av2 is then calculated. The ratio of the peak intensity at the peak top of Peak X to this sum of values ​​(peak intensity at the peak top of Peak X / sum of values) is defined as the intensity ratio.

[0021] The X-ray diffraction characteristics will be explained in more detail. If none of the above-mentioned first, second, third, and fourth peaks are present in the X-ray diffraction pattern obtained from X-ray diffraction measurements of solid electrolyte (I) using CuKα rays, then the above-mentioned X-ray diffraction characteristics are satisfied, and solid electrolyte (I) is in an amorphous state. Furthermore, in the X-ray diffraction pattern obtained from X-ray diffraction measurements of solid electrolyte (I) using CuKα rays, if the above-mentioned peak X is present, and at least one of the peaks of peak X satisfies the above-mentioned X-ray diffraction characteristics if the intensity ratio obtained by the above-mentioned intensity measurement method is 5.0 or less, then the above-mentioned 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 a peak refers to the peak width (°) at the point where the peak intensity is halfway across the peak top.

[0022] The above method for measuring strength will be explained in more detail with reference to Figure 2. Figure 2 shows an example of peak X appearing in the diffraction pattern obtained from X-ray diffraction measurements of solid electrolyte (I) using CuKα rays. In the diffraction pattern shown in Figure 2, a specific peak with a peak top intensity of 1 is shown. In the intensity measurement method, as shown in Figure 2, the 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 then the 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 calculated. Next, the average value of Av1 and Av2 is calculated, and the value of the ratio of intensity 1 to the average value is determined as the intensity ratio. If the above X-ray diffraction characteristics are satisfied, it means that there is no or almost no crystalline structure in the solid electrolyte (I), and that it is in an amorphous state. In other words, the first to fourth peaks described above are mainly peaks originating from the crystal structure in the solid electrolyte (for example, the crystal structure of lithium tetraborate), and the absence of these peaks means that the electrolyte is amorphous. Furthermore, even if at least one of the first to fourth peaks is present, the fact that the intensity ratio of at least one of the present peaks X is 5.0 or less means that there are almost no crystal structures in the solid electrolyte (I) that would hinder the effects of the present invention. Note that, for example, a peak originating from a specific component (for example, 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, so even if a peak due to the specific component mentioned above happens to overlap with any of the first to fourth peaks and a 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 amorphous.

[0023] The above X-ray diffraction measurement was performed using CuKα radiation under measurement conditions of 0.01° / step and 3° / min.

[0024] In the X-ray diffraction pattern obtained from X-ray diffraction measurements of solid electrolyte (I) using CuKα rays, it is preferable that none of the above-mentioned first, second, third, and fourth peaks are present, or, even if at least one of the above-mentioned first, second, third, and fourth peaks X is present, the intensity ratio of at least one of the peaks X is 3.0 or less. In particular, it is more preferable that none of the above-mentioned first, second, third, and fourth peaks are present, or that even if at least one of the above-mentioned first, second, third, and fourth peaks X is present, the intensity ratio of at least one of the peaks X is 2.0 or less.

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

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

[0027] -Requirement A-1- In the reduction dibody distribution function G(r) obtained from X-ray total scattering measurements of solid electrolyte (I), there is a first peak with its peak top located in the range of r = 1.43 ± 0.2 Å, and a second peak with its peak top located in the range of r = 2.40 ± 0.2 Å. The G(r) at the peak top of the first peak is greater than 1.0, and the G(r) at the peak top of the second peak is greater than 0.8.

[0028] -Requirement A-2- In the reduction dibody distribution function G(r) obtained from X-ray total scattering measurements of solid electrolyte (I), the absolute value of G(r) is less than 1.0 in the range where r is greater than 5 Å and less than or equal to 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 BO and BB, but hardly any long-range ordered structure. As a result, the oxide solid electrolyte itself exhibits elastic properties that are softer and more easily plastically deformed than conventional lithium-containing oxides. Consequently, it is presumed that in layers containing the solid electrolyte (I) formed by pressurization or the like, the adhesion between the solid electrolytes (I) and / or between the solid electrolyte (I) and other ion conductors is improved, reducing interfacial resistance and resulting in superior ion conductivity. Requirements A-1 and A-2 will be explained in more detail with reference to the drawings.

[0030] Figure 3 shows an example of a reduction dibody distribution function G(r) obtained by X-ray total scattering measurement of a solid electrolyte (I). The vertical axis of Figure 3 represents the reduction dibody distribution function obtained by Fourier transforming the X-ray scattering, and indicates the probability that an atom exists at a distance r. X-ray total scattering measurement can be performed at SPring-8 BL04B2 (acceleration voltage 61.4 keV, wavelength 0.2019 Å). The reduction dibody distribution function G(r) is obtained by transforming the scattering intensity I obtained experimentally using the following procedure. First, scattering intensity I obs It is expressed by the following equation (1). Furthermore, the structure factor S(Q) is expressed by the following equation (2), as shown by coherent scattering I coh It can be obtained by dividing it by the product of the number of atoms N and the square of the atomic scattering factor f. I obs =I coh +I incoh +I 蛍光 (1)

[0031]

number

[0032] The structure factor S(Q) is used for PDF (Pair Distribution Function) analysis. In equation (2) above, the required intensity is coherent scattering I coh That is all. Incoherent scattering I incoh and X-ray fluorescence I 蛍光 The scattering intensity I is determined by blank measurement, subtraction using a theoretical formula, and the detector's discriminator. obs It can be subtracted from it. Coherent scattering I coh It can be expressed by Debye's scattering equation (equation (3) below) (N: total number of atoms, f: atomic scattering factor, r ij (Interatomic distance between :ij).

[0033]

number

[0034] If we focus on any atom and let ρ(r) be the atomic density at a distance r, then the number of atoms in a sphere of radius r-r+d(r) is 4πr. 2 Since ρ(r)dr, equation (3) above can be expressed as equation (4) below.

[0035]

number

[0036] Letting the average atomic density be ρ0, we can rearrange equation (4) above to obtain equation (5) below.

[0037]

number

[0038] From equation (5) and equation (2) above, we obtain the following equation (6).

[0039]

number

[0040] The two-body distribution function g(r) is given by equation (7) below.

[0041]

number

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

[0043]

number

[0044] As described above, the two-body distribution function can be obtained by the Fourier transform of the structure factor S(Q). To make it easier to observe medium / long-range order, the two-body distribution function is transformed to G(r) = 4πr(g(r) - 1), resulting in the reduced two-body distribution function (Figure 3). g(r), which oscillates around 0, represents the density difference from the average density at each interatomic distance, and will be higher than the average density of 1 if there is a correlation at a particular interatomic distance. Therefore, it reflects the distance and coordination number of the elements corresponding to the local to medium distances. As order disappears, ρ(r) approaches the average density, and g(r) approaches 1. Therefore, in amorphous structures, as r increases, order disappears, and g(r) becomes 1, i.e., G(r) becomes 0.

[0045] In requirement A-1, as shown in Figure 3, the reduced dibody distribution function G(r) obtained from the X-ray total scattering measurement of the solid electrolyte (I) has 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, with the G(r) at the peak top of the first peak P1 being greater than 1.0 (preferably 1.2 or greater), and the G(r) at the peak top of the second peak P2 being greater than 0.8 (preferably greater than 1.0). In Figure 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 attributed to the interatomic distance between boron (B) and oxygen (O). Also, at the position of 2.40 Å, there is a peak attributed to the interatomic distance between boron (B) and boron (B). Therefore, the observation of these two peaks (the first and second peaks) indicates that a periodic structure corresponding to these two interatomic distances exists in the solid electrolyte (I).

[0046] Furthermore, in requirement A-2, as shown in Figure 3, the absolute value of G(r) is less than 1.0 in the range where r is greater than 5 Å and less than or equal to 10 Å. As described above, the fact that the absolute value of G(r) is less than 1.0 in the range where r is greater than 5 Å and less than or equal to 10 Å means that there are almost no long-range ordered structures in the solid electrolyte (I).

[0047] Furthermore, in the reduction dibody distribution function G(r) described above, there may be peaks other than the first peak and other than the second peak in the range where r is 5 Å or less.

[0048] There are no particular restrictions on the method for making the solid electrolyte (I) amorphous. For example, in the preparation of the solid electrolyte (I), one method is to use a lithium-containing oxide that has undergone mechanical milling as the raw material. This mechanical milling treatment may be carried out in the presence of a lithium salt.

[0049] -Mechanical milling process- Mechanical milling is a process in which a sample is pulverized while applying mechanical energy. Examples of mechanical milling methods include ball mills, vibratory mills, turbo mills, and disc mills, with ball mills being preferred because they offer efficient production of amorphous solid electrolyte (I). Examples of ball mills include vibratory ball mills, rotary ball mills, and planetary ball mills, with planetary ball mills being more preferred.

[0050] The conditions for the ball milling process are adjusted as appropriate depending on the material being processed. The material of the grinding balls (media) is not particularly limited, and examples include agate, silicon nitride, zirconia, alumina, and iron-based alloys, with stabilized zirconia (YSZ) being preferred. The average particle size of the grinding balls is not particularly limited, but is preferably 1 to 10 mm, and more preferably 3 to 7 mm, from the standpoint of being able to produce solid electrolyte (I) with good productivity. The above average particle size is obtained by measuring the diameters of 50 randomly selected grinding balls and taking their arithmetic mean. If the grinding balls are not perfectly spherical, the major axis is used as the diameter. The number of grinding balls is not particularly limited.

[0051] There are no particular restrictions on the material of the grinding pot in the ball milling process. Examples include agate, silicon nitride, zirconia, alumina, and iron-based alloys, with stabilized zirconia (YSZ) being preferred.

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

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

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

[0055] In step 2A described above, the amount of water used is not particularly limited. For example, the amount of water used can be 10 to 200 parts by mass per 100 parts by mass of the product obtained in step 1A, and it is more preferable to use 50 to 150 parts by mass of water. The method of mixing the product obtained in step 1A with water is not particularly limited; it may be mixed all at once, or water may be added to the product obtained in step 1A in stages and mixed. When mixing, sonication may be performed as needed. The duration of sonication is not particularly limited and can be, for example, 10 minutes to 5 hours.

[0056] Step 3A is a step to remove 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; water may be removed by heat treatment or by vacuum drying treatment.

[0057] Before step 1A described above, step 0 may be performed, in which a lithium-containing oxide is subjected to mechanical milling in an environment where lithium salts are not present.

[0058] In the production of the solid electrolyte (I), it is also preferable to perform the following steps 1B to 3B instead of the above steps 1A to 3A. Process 1B: Process of applying mechanical milling to lithium-containing oxide. Step 2B: A step in which the product obtained in Step 1B is mixed with water and lithium salt. Step 3B: A step to remove water from the dispersion obtained in Step 2B to obtain a solid electrolyte (I).

[0059] The difference between process 1B and process 1A is that in process 1A, mechanical milling is performed in the presence of lithium salt, whereas in process 1B, mechanical milling is performed without using lithium salt. Therefore, in process 2B, the product obtained in process 1B is mixed with water and lithium salt. The procedure for step 2B is not particularly limited. It may be a method in which the product obtained in step 1B, water, and lithium salt are mixed together (Method 1), or a method in which the product obtained in step 1B and water are mixed to prepare a dispersion, and then the resulting dispersion is mixed with the lithium salt (Method 2), or a method in which the product obtained in step 1B and water are mixed to prepare dispersion 1, the lithium salt and water are mixed to prepare solution 2, and then dispersion 1 and solution 2 are mixed (Method 3). When mixing the product obtained in step 1B with water, a dispersion treatment such as sonication may be performed as appropriate. In Method 2, when mixing the dispersion obtained by mixing the product obtained in Step 1B with water and the lithium salt, if there is too much lithium salt, the resulting liquid is prone to gelation, thus limiting the amount of lithium salt that can be mixed. In contrast, in Method 3, even if the product obtained in Step 1B and the lithium salt are mixed in equimolar amounts, gelation of the liquid is less likely to occur, and a larger amount of lithium salt can be mixed. From this viewpoint, Method 3 is preferred. The procedures for process 3B and process 3A are the same.

[0060] In the production of solid electrolyte (I), it is also preferable to perform the following steps 1C to 3C instead of the above steps 1A to 3A. Process 1C: Process of applying mechanical milling to lithium-containing oxide. Step 2C: A step in which the product obtained in Step 1C is mixed with water. Step 3C: A step in which water is removed from the dispersion obtained in Step 2C, and the resulting product is mixed with a lithium salt to obtain a solid electrolyte (I).

[0061] The procedures for process 1C and process 1B are the same. The procedures for process 2C and process 2A are the same. Step 3C differs from steps 3A and 3B in that it involves mixing the product obtained by removing water from the dispersion obtained in step 2C with the lithium salt. In step 3C, the amount of lithium salt used is not particularly limited and is adjusted as appropriate to obtain the solid electrolyte (I) as 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 of impregnating the product with a solution of lithium salt dissolved in water and then mixing the two is also possible.

[0062] (Component composition of solid electrolyte (I)) As described above, the solid electrolyte (I) used in the present invention is an amorphous solid electrolyte, in which the ratio of lithium salt content to lithium oxide content is 0.001 to 1.5 in molar ratio, and the ratio of water content is 1 to 12 in molar ratio. The ratio of the lithium salt content to the lithium-containing oxide content 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 water content to the lithium-containing oxide content in the solid electrolyte (I) is more preferably 2 to 12 in molar ratio, and even more preferably 3 to 11. This molar ratio is also preferably 2 to 10, 2 to 8, 2 to 7, and 3 to 7. The molar amounts of lithium-containing oxides, lithium salts, and water in solid electrolyte (I) can be determined based on elemental analysis. The molar amount of water can also be determined by methods such as the Karl Fischer method.

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

[0064] -Lithium-containing oxide- The lithium-containing oxide constituting the solid electrolyte (I) contains Li, B, and O as described above. The above lithium-containing oxide is Li 2+x B 4+y O 7+z A compound represented by (-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 represented, 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 preferably 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, 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. As such a lithium-containing oxide, typically, lithium tetraborate (Li2B4O7) can be mentioned. Also, the above lithium-containing oxide is Li 1+x B 3+y O 5+zCompounds represented by (-0.3 < x < 0.3, -0.3 < y < 0.3, -0.3 < z < 0.3) are also preferred. Typical examples of such lithium-containing oxides include lithium triborate (LiB3O5). Also, the above lithium-containing oxide is 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. Typical examples of such lithium-containing oxides include Li3B 11 O 18 and the like. Also, the above lithium-containing oxide is 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. Typical examples of such lithium-containing oxides include Li3B7O 12 and the like. Therefore, the above lithium-containing oxide is preferably at least one of the above Li 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 . Also, instead of the above lithium-containing oxide, or together with the above lithium-containing oxide, at least one of LiBO5, Li2B7O 12 , LiB2O3(OH)H2O, and Li4B8O 13 (OH)¬2(H2O)3 and the like can also be used. In the solid electrolyte (I), the lithium-containing oxide is in an amorphous state. That is, the lithium-containing oxide in the solid electrolyte (I) is also in the desired amorphous state so that the solid electrolyte (I) becomes the above-described amorphous state. Among them, the lithium-containing oxide is preferably amorphous lithium tetraborate.

[0065] -Lithium salt- The lithium salt constituting the solid electrolyte (I) used in the present invention is not particularly limited, Li + A salt composed of Li and anions is an example, Li + A salt composed of Li and an organic anion is preferred. + More preferably, a salt composed of an organic anion having a halogen atom is 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 Group 3, Group 4, Group 13, Group 14, Group 15, Group 16, Group 17 elements 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. Equation (1) LiN(R f1 SO2)(R f2 SO2) R f1 and R f2 Each of these independently represents either a halogen atom or a perfluoroalkyl group. R f1 and R f2 When is a perfluoroalkyl group, the number of carbon atoms in the perfluoroalkyl group is not particularly limited. R f1 and R f2 R 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. As the volume of the terminal group increases, steric hindrance increases, which becomes a factor that inhibits ion conduction, f1 and R f2 If it is a perfluoroalkyl group, a smaller number of carbon atoms is preferable.

[0066] The lithium salts that may be included in the solid electrolyte (I) used in the present invention are not limited to the compound represented by formula (1) above. Examples of lithium salts that may be included in the solid electrolyte (I) used in the present invention are given below.

[0067] (L-1) Inorganic lithium salts: Inorganic fluoride salts such as LiPF6, LiBF4, LiAsF6, and LiSbF6; perhalates such as LiClO4, LiBrO4, and LiIO4; inorganic chloride salts such as LiAlCl4.

[0068] (L-2) Fluorine-containing organolithium salts: Perfluoroalkanesulfonates such as LiCF3SO3; fluorosulfonylimide salts or perfluoroalkanesulfonylimide salts such as LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(FSO2)2 (also referred to as Li(FSO2)2N in this specification), and LiN(CF3SO2)(C4F9SO2); perfluoroalkanesulfonylmethide salts such as LiC(CF3SO2)3; fluoroalkyl fluoride phosphates (preferably perfluoroalkyl fluoride phosphates) such as Li[PF5(CF2CF2CF3)], Li[PF4(CF2CF2CF3)2], Li[PF3(CF2CF2CF3)3], Li[PF5(CF2CF2CF2CF3)], Li[PF4(CF2CF2CF2CF3)2], and Li[PF3(CF2CF2CF2CF3)3].

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

[0070] Other examples include LiF, LiCl, LiBr, LiI, Li2SO4, LiNO3, Li2CO3, CH3COOLi, LiAsF6, LiSbF6, LiAlCl4, and LiB(C6H5)4. Among them, LiPF6, LiBF4, LiAsF6, LiSbF6, LiClO4, Li(R f1 SO2), LiN(R f1 SO2)2, LiN(FSO2)2, or LiN(Rf1 SO2)(R f2 SO2 is preferred, LiPF6, LiBF4, LiN(R f1 SO2)2, LiN(FSO2)2, or LiN(R f1 SO2)(R f2 SO2) is more preferable. In these examples, R f1 and R f2 Each of these independently represents a perfluoroalkyl group, preferably with 1 to 6 carbon atoms, more preferably 1 to 4, and even more preferably 1 or 2 carbon atoms. LiNO3 and 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide lithium are also preferred as lithium salts.

[0071] (Elemental composition of solid electrolyte (I)) The component composition of the solid electrolyte (I) was described based on the compounds that constitute the solid electrolyte (I). Next, the solid electrolyte (I) will be described from the viewpoint of a preferred elemental composition. That is, in one embodiment of the secondary battery of the present invention, the solid electrolyte (I) can be specified by its elemental composition, for example, as follows, without specifying "lithium-containing oxide" and "lithium salt". In the present invention, the solid electrolyte (I) 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 preferably 0.001 to 10.00 each (preferably 0.001 to 6.00, more preferably 0.01 to 5.00).

[0072] The content of each element is determined by standard elemental analysis. For example, Li and B are analyzed by ICP-OES (Inductively coupled plasma optical emission spectrometry), N is analyzed by the inert gas fusion method, and F and S are analyzed by combustion ion chromatography. For O, the analytical masses of elements other than O are added together and the difference from the total powder volume is calculated. Note that the method for calculating the content of each element is not limited to the above; the content of other elements may be estimated from the analytical results of one element, taking into account the structure of the compound used. Based on the content of each element calculated by elemental analysis, the molar amounts of Li, O, and other elements are calculated, assuming that 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, Group 15, Group 16, Group 17 of the periodic table, Si, C, Sc, and Y, and more preferably two or more. In particular, 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 more preferably two or more. The elements of Group 4 of the periodic table include Ti, Zr, Hf, and Rf. The elements of Group 15 of the periodic table include N, P, As, Sb, Bi, and Mc. The elements of Group 16 of the periodic table include S, Se, Te, Po, and Lv. The elements of Group 17 of the periodic table include F, Cl, Br, I, At, and Ts. The solid electrolyte (I) may contain three or more types of elements (E), preferably two to five, and more preferably two to four. The second embodiment of the solid electrolyte (I) preferably contains two or more elements (E) selected from F, S, N, P, and C, more preferably contains two or more elements (E) selected from F, S, C, and N, and even more preferably contains three elements (E) of F, S, and N.

[0074] In a 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 set to 4.00 and the molar amount of Li is expressed, it is preferable that the molar amount of Li is 1.58 to 3.49. In other words, when the molar amount of B is set to 4.00, it is preferable that the relative value of the molar amount of Li is 1.58 to 3.49. In particular, when the molar amount of B in the solid electrolyte (I) is set to 4.00 and the molar amount of Li is expressed, it is preferable that the molar amount of Li is 1.58 to 3.00, more preferably 1.90 to 3.00, and even more preferably 2.00 to 3.00.

[0075] In a 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 set to 4.00 and the molar amount of O is expressed, it is preferable that the molar amount of O is 6.23 to 25.00. In other words, when the molar amount of B is set to 4.00, it is preferable that the relative value of the molar amount of O is 6.23 to 25.00. In particular, when the molar amount of B in the solid electrolyte (I) is set to 4.00 and the molar amount of O is expressed, it is preferable that the molar amount of O is 6.50 to 23.00, more preferably 8.00 to 23.00, even more preferably 10.00 to 23.00, and still preferable 10.00 to 18.00.

[0076] In a solid electrolyte (I) containing one or more (preferably two or more) of the above-mentioned element (E), when the molar amount of element (E) is expressed with the molar amount of B in the solid electrolyte (I) set to 4.00, it is preferable that the molar amounts of each element (E) are between 0.001 and 10.00. In other words, when the molar amount of B is set to 4.00, it is preferable that the relative values ​​of the molar amounts of each element (E) are between 0.001 and 10.00. In particular, when the molar amount of element (E) is expressed with the molar amount of B in the solid electrolyte (I) set to 4.00, it is preferable that the molar amounts of each element (E) are between 0.001 and 6.00, and more preferably between 0.01 and 5.00.

[0077] One preferred embodiment of the elemental composition of a solid electrolyte (I) containing one or more (preferably two or more) of the above-mentioned element (E) is a solid electrolyte (I) containing Li, B, O, F, S, and N, wherein 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). Examples of solid electrolytes include those having a molecular weight of 00 (more preferably 8.00-23.00, even more preferably 10.00-23.00, even more preferably 10.00-18.00), a molar amount of F of 0.001-10.00 (preferably 0.01-10.00), a molar amount of S of 0.001-2.00 (preferably 0.01-2.00), and a molar amount of N of 0.001-1.00 (preferably 0.005-1.00).

[0078] The solid electrolyte (I) used in the present invention is in the amorphous state described above, and as a result, it is preferable that this solid electrolyte (I) exhibits the following characteristics in addition to the X-ray diffraction characteristics described above.

[0079] (solid 7 Li-NMR spectral properties) Solid electrolyte (I) is a solid solid electrolyte (I) 7Li-NMR measurements are performed at 20°C and 120°C, and the full width at half maximum (FMAX) calculated from the obtained spectra using the method described below 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 is for solid electrolytes (I). 7 Li-NMR measurements are performed at 20°C and 120°C, respectively. The total width at half maximum (FWHM) of the peaks appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained at 20°C (FWHM1) and the total width at half maximum (FWHM2) of the peaks appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained at 120°C (FWHM2) are determined. The FWHM is then calculated as the percentage of the ratio of FWHM2 to FWHM1 {(FWHM2 / FWHM1) × 100}. The peak's total width at half maximum (FWHM) represents the width (ppm) at half the peak height (H / 2). The above characteristics will be explained below using Figure 4. Figure 4 shows the solid electrolyte (I) 7 An example of a spectrum obtained when Li-NMR measurements are performed at 20°C or 120°C is shown. The solid line spectrum at the bottom of Figure 4 represents the solid state. 7 The spectrum obtained when Li-NMR measurement was performed at 20°C is shown, with the dashed line spectrum at the top of Figure 4 representing the solid state. 7 This spectrum was obtained when Li-NMR measurements were performed at 120°C. Generally, solid 7 In Li-NMR measurements, Li + When the mobility of the element is high, the resulting peaks are sharper. In the embodiment shown in Figure 4, comparing the spectrum at 20°C and the spectrum at 120°C, the spectrum at 120°C is sharper. In other words, in the embodiment shown in Figure 4, due to the presence of Li defects, + This indicates that the mobility of is increased. Such a solid electrolyte (I) becomes more easily plastically deformed due to the defect structure described above, and Li + It is thought to have excellent hopping ability. For reference, it should be noted that for a general lithium tetraborate crystal, in the solid state 7 When Li-NMR measurement is performed at 20 °C or 120 °C, the spectrum measured at 20 °C represented by a solid line shown at the lower side of FIG. 5 and the spectrum measured at 120 °C represented by a broken line shown at the upper side of FIG. 5 tend to have substantially the same shape. That is, in the lithium tetraborate crystal, there are no Li defects, and as a result, the elastic modulus is high and plastic deformation is difficult.

[0080] The above solid 7 The conditions for the solid Li-NMR measurement are as follows. Using a 4 mm HX CP-MAS probe, measure by the single pulse method, 90° pulse width: 3.2 μs, observation frequency: 155.546 MHz, observation width: 1397.6 ppm, repetition time: 15 sec, integration: 1 time, MAS rotation speed: 0 Hz.

[0081] In addition, the solid electrolyte (I) used in the present invention, in the solid state 7 When the first peak appearing in the range of -100 to +100 ppm in the spectrum obtained when Li-NMR measurement is performed at 20 °C is waveform-separated, it preferably has a second peak with a chemical shift in the range of -3 to 3 ppm and a full width at half maximum of 5 ppm or less, 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 above area intensity is more preferably 2% or more, more preferably 5% or more, further preferably 10% or more, and further preferably 15% or more. In the form of the present invention where the solid electrolyte (I) contains water, the solid 7 Li-NMR spectrum characteristics of the solid electrolyte (I) tend to be as described above. The upper limit of the ratio of the above area intensity is not particularly limited, but it is often 50% or less.

[0082] Hereinafter, the above characteristics will be described with reference to FIGS. 6 and 7. In FIG. 6, the solid of the solid electrolyte (I) 7An example of a spectrum obtained when Li-NMR measurement is performed at 20°C is shown. 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 a small peak is observed around the chemical shift of 0 ppm, as enclosed by a dashed line, within this first peak. As mentioned above, Li + When the kinetic activity is high, the peak is observed to be sharp, which is thought to be the reason for this effect. Next, Figure 7 shows the waveform separation of the first peak. As shown in Figure 7, the first peak is waveform-separated into a small peak represented by a solid line (corresponding to the second peak) and a larger peak represented by a dashed line. The second peak appears in the chemical shift range of -3 to 3 ppm and is a peak with a full width at half maximum of 5 ppm or less. For the solid electrolyte (I), it is preferable that the ratio of the area intensity of the second peak, represented by the solid line in Figure 7, to the area intensity of the first peak (peak before waveform separation), represented by Figure 6, {(area intensity of the second peak / area intensity of the first peak) × 100}, is within the above range. One method for waveform separation is to use well-known software, such as WaveMetrics' graphing software, Igor Pro.

[0083] (Raman spectral properties) Solid electrolyte (I) is measured in the Raman spectrum of solid electrolyte (I) at 600-850 cm⁻¹. -1 In the wavenumber domain, the coefficient of determination obtained by performing linear regression analysis using the least squares method is preferably 0.9400 or higher, more preferably 0.9600 or higher, and also preferably 0.9800 or higher. There is no particular upper limit, but it is usually 1.0000 or lower.

[0084] The above Raman spectral characteristics will be explained with reference to Figure 8. First, obtain the Raman spectrum of the solid electrolyte (I). As a measurement method for the Raman spectrum, Raman imaging is performed. Raman imaging is a microscopic spectroscopic technique that combines Raman spectroscopy with microscopy techniques. Specifically, it is a technique in which excitation light is scanned on a sample to detect measurement light including Raman scattered light, and the distribution of components and the like are visualized based on the intensity of the measurement light. As the measurement conditions for Raman imaging, at 27 °C, under the atmosphere, the excitation light is 532 nm, the objective lens is 100 times magnification, the mapping method of point scanning, 1 μm step, the exposure time per point is 1 second, the number of integrations is 1 time, and the measurement range is set to a range of 70 μm × 50 μm. In addition, the Raman spectrum data is subjected to principal component analysis (PCA) processing to remove noise. Specifically, in the principal component analysis processing, the spectrum is recombined using components with an autocorrelation coefficient of 0.6 or more.

[0085] FIG. 8 shows an example of the Raman spectrum of the solid electrolyte (I). In the graph shown in FIG. 8, the vertical axis represents the Raman intensity and the horizontal axis represents the Raman shift. In the wavenumber range of 600 to 850 cm -1 of the Raman spectrum shown in FIG. 8, the coefficient of determination (coefficient of determination R 2 ) obtained by performing linear regression analysis by the least squares method is calculated. That is, in the wavenumber range of 600 to 850 cm -1 of the Raman spectrum in FIG. 8, a regression line (thick line in FIG. 8) is obtained by the least squares method, and the coefficient of determination R 2 of the regression line is calculated. The coefficient of determination takes a value between 0 (no linear correlation) and 1 (perfect linear correlation of the measured values) according to the linear correlation of the measured values. In the solid electrolyte (I), as shown in FIG. 8, peaks are hardly observed in the wavenumber range of 600 to 850 cm -1 , and as a result, a high coefficient of determination is shown. Note that the coefficient of determination R 2 corresponds to the square of the correlation coefficient (Pearson product-moment correlation coefficient). More specifically, in this specification, the coefficient of determination R 2It is calculated by the following formula. In the formula, x1 and y1 represent the wave number in the Raman spectrum and the Raman intensity corresponding to that wave number, x2 represents the (arithmetic) mean of the wave numbers, and y2 represents the (arithmetic) mean of the Raman intensity.

[0086]

number

[0087] On the other hand, for reference, Figure 9 shows the Raman spectrum of a typical lithium tetraborate crystal. As shown in Figure 9, in the case of a typical lithium tetraborate crystal, the spectrum is 716-726 cm⁻¹, which is due to its structure. -1 , and 771~785cm -1 A peak is observed in the wavenumber region. When such a peak is present, the frequency range is 600-850 cm. -1 In the wavenumber domain, when linear regression analysis is performed using the least squares method and the coefficient of determination is calculated, the coefficient of determination is less than 0.9400. In other words, a coefficient of determination of 0.9400 or higher indicates that the solid electrolyte (I) contains almost no crystalline structure. Therefore, as a result, the solid electrolyte (I) has the property of being easily plastically deformable, and Li + It is thought to possess excellent hopping properties.

[0088] (Infrared absorption spectral characteristics) Solid electrolyte (I) exhibits an infrared absorption spectrum of 800–1600 cm⁻¹. -1 For the maximum absorption intensity in the wavenumber region, 3000-3500 cm -1 The ratio of the maximum absorption intensity in the wavenumber region (3000-3500 cm²) -1 Maximum absorption intensity in the wavenumber region: 800-1600 cm² -1 The maximum absorption intensity in the wavenumber region is preferably 1 / 5 or more (0.2 or more). In particular, the above ratio is preferably 3 / 10 or more, and more preferably 2 / 5 or more. There is no particular upper limit, but 1 or less is preferred. Infrared absorption spectrum 3000-3500 cm -1In the wavenumber region, the OH stretching vibration mode was observed, between 800 and 1600 cm². -1 In the wavenumber region, BO stretching vibration modes are observed. In solid electrolyte (I), strong absorption intensities originating from OH stretching vibration modes are observed, indicating the presence of numerous OH groups and a large amount of water. In such solid electrolytes (I), lithium ions move more easily, resulting in a tendency for improved ionic conductivity. Note: 800-1600cm -1 In the wavenumber region, oscillation modes originating from lithium salts can also be observed.

[0089] The infrared absorption spectrum measurement conditions described above can be as follows. Objective lens: 32x Cassegrain type (NA 0.65), Detector: MCT-A, Measurement range: 650~4000cm -1 , resolution: 4cm -1 The sample cell is a diamond cell. The obtained infrared absorption spectra are corrected to remove signals from atmospheric water and CO2, and then offset to reduce the background to zero absorption intensity. Furthermore, measurements are performed in the atmosphere after vacuum drying at 40°C for 2 hours.

[0090] The ionic conductivity (27°C) of the solid electrolyte (I) is not particularly limited, and from the standpoint of its application to various uses, 1.0 × 10⁻⁶ is appropriate. -5 Preferably S / cm or higher, 1.0 × 10 -4 S / cm or higher is more preferable, 1.0 × 10 -3 S / cm or more is more preferable, 3.0 × 10 -3 A value of S / cm or higher is particularly preferred. There is no particular upper limit, but 1.0 × 10 -2 The values ​​are often less than S / cm.

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

[0092] (mass reduction rate) The mass loss rate when the solid electrolyte (I) is heated to 800°C is preferably 20 to 40% by mass, and more preferably 25 to 35% by mass. The mass loss that occurs due to the above heating is thought to be due to the removal of at least water contained in the solid electrolyte (I). The presence of such water in the solid electrolyte (I) can further improve the conductivity of lithium ions. In the above heat treatment, heating is performed at a heating rate of 20°C / second in the range of 25°C to 800°C. A known thermogravimetric differential thermal analysis (TG-DTA) instrument can be used to measure the mass loss. The above mass loss rate is {(mass at 25°C - mass at 800°C) / mass at 25°C} × 100 It is calculated by [this method]. For the measurement of the mass loss rate, the solid electrolyte (I) is subjected to vacuum drying at 40°C for 2 hours beforehand. The measurement of the mass loss rate is performed under atmospheric conditions.

[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. Including a binder makes it possible to more reliably prevent cracks or other damage from occurring in the solid electrolyte layer or electrode layer. Furthermore, the solid electrolyte layer may contain other solid electrolytes besides solid electrolyte (I). Other solid electrolytes refer to solid electrolytes that can move lithium ions within themselves. Inorganic solid electrolytes are preferred as the solid electrolyte. Examples of other solid electrolytes include sulfide-based solid electrolytes, oxide-based solid electrolytes, halide-based solid electrolytes, and hydride-based solid electrolytes. Considering safety, at least one of oxide-based solid electrolytes, halide-based solid electrolytes, and hydride-based solid electrolytes is preferred, and oxide-based solid electrolytes are more preferred. In the solid electrolyte layer, the content of solid electrolyte (I) is preferably 50% by mass or more, more preferably 60% by mass or more, even 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, with 50 to 400 μm being preferred.

[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, if the positive electrode current collector also functions as the positive electrode active material layer (in other words, if the positive electrode active material layer also functions as the positive electrode current collector), it is not necessary for the positive electrode layer to consist of two layers, and a single layer configuration is acceptable. Furthermore, the positive electrode active material layer usually contains a solid electrolyte (preferably an inorganic solid electrolyte) along with the positive electrode active material, but it does not necessarily have to 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, and also preferably 80% by mass or more, and also preferably 90% by mass.

[0096] When the positive electrode active material layer contains a solid electrolyte, the type of solid electrolyte is not particularly limited. From the viewpoint of prioritizing flexibility, a sulfide-based solid electrolyte can be used, while 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 solid electrolyte (I) described above. In this way, the solid electrolyte (I) also acts as a binder for the solid particles contained in the positive electrode layer, making the positive electrode layer more flexible.

[0097] The positive electrode active material used in the positive electrode layer can be a wide range of positive electrode active materials that can be used in ordinary lithium-ion secondary batteries. Preferred forms of the positive electrode active material are described below.

[0098] (Cathode 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, but transition metal oxides are preferred, and transition metal oxides containing the transition metal element Ma (one or more elements selected from Co, Ni, Fe, Mn, Cu, and V) are more preferred. In addition, the element Mb (metal elements of Group 1 (Ia) of the periodic table other than lithium, elements of Group 2 (IIa), and elements such as Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, and B) may be mixed with this transition metal oxide. The amount of Mb mixed is preferably 0 to 30 mol% relative to the amount of the transition metal element Ma (100 mol%). It is more preferable to synthesize a mixture such that the Li / Ma molar ratio is 0.3 to 2.2. Specific examples of transition metal oxides 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 halogenated phosphate compounds, and (ME) lithium-containing transition metal silicate compounds. Among these, (MA) transition metal oxides having a layered rock salt structure are preferred, such as LiCoO2 or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 is more preferable.

[0099] (MA) Examples of transition metal oxides having a layered rock salt structure include LiCoO2 (lithium cobaltate [LCO]), LiNiO2 (lithium nickelate), and LiNi 0.85 Co 0.10 Al 0.05 O2 (Lithium nickel-cobalt aluminum oxide [NCA]), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (lithium nickel manganese cobalt oxide [NMC]), and LiNi 0.5 Mn 0.5 O2 (lithium manganese nickelate) is one example.

[0100] (MB) Examples of transition metal oxides having a spinel-type structure include LiMn2O4(LMO) and LiNi 0.5 Mn1.5 Examples include O4([LNMO]), LiCoMnO4, Li2FeMn3O8, Li2CuMn3O8, Li2CrMn3O8, and Li2NiMn3O8.

[0101] Examples of (MC) lithium-containing transition metal phosphate compounds include olivine-type iron phosphate salts such as LiFePO4 and Li3Fe2(PO4)3, iron pyrophosphate salts such as Li2CoP2O7(LCP) and LiFeP2O7, cobalt phosphate salts such as LiCoPO4, and monoclinic NASICON-type vanadium phosphate salts such as Li3V2(PO4)3 (lithium vanadium phosphate).

[0102] Examples of (MD) lithium-containing transition metal halide phosphoric acid compounds include iron phosphate fluorides such as Li2FePO4F, manganese phosphate fluorides such as Li2MnPO4F, and cobalt phosphate fluorides such as Li2CoPO4F.

[0103] Examples of (ME) lithium-containing transition metal silicate compounds include Li2FeSiO4, Li2MnSiO4, and Li2CoSiO4.

[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, but 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, as described later. The positive electrode active material obtained by the calcination method may be used after being washed with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent.

[0105] The positive electrode active material, like the negative electrode active material described later, may be surface-coated with the surface coating agent described below, sulfur, or phosphorus, or even with active light.

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

[0107] (Positive electrode current collector) The current collector that makes up the positive electrode layer is an electron conductor. Furthermore, the positive electrode current collector is usually in the form of a film sheet. Examples of materials that make up the positive electrode current collector include aluminum, aluminum alloy, stainless steel, nickel, and titanium, with aluminum or aluminum alloy being preferred. Furthermore, a positive electrode current collector may also be made of aluminum or stainless steel treated with carbon, nickel, titanium, or silver (forming a thin film).

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

[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, if the negative electrode current collector also functions as the negative electrode active material layer (in other words, if the negative electrode active material layer also functions as the negative electrode current collector), it is not necessary for the negative electrode layer to consist of two layers, and a single-layer configuration is acceptable. Furthermore, the negative electrode active material layer usually contains a solid electrolyte (preferably an inorganic solid electrolyte) along with the negative electrode active material, but it does not necessarily have to 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, also preferably 80% by mass or more, and also preferably 90% by mass.

[0110] When the negative electrode active material layer contains a solid electrolyte, the type of solid electrolyte is not particularly limited. From the viewpoint of prioritizing flexibility, a sulfide-based solid electrolyte can be used, while 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 solid electrolyte (I) described above. In this way, the solid electrolyte (I) also acts as a binder for the solid particles contained in the negative electrode layer, making the negative electrode layer more flexible.

[0111] The negative electrode active material used in the negative electrode layer can be a wide range of negative electrode active materials 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 includes, for example, carbonaceous materials, oxides of metals or metalloid elements, elemental lithium, lithium alloys, and negative electrode active materials that can form alloys with lithium.

[0113] Carbonaceous materials used as negative electrode active materials are materials that consist substantially of carbon. Examples include petroleum pitch, carbon black such as acetylene black (AB), graphite (natural graphite and artificial graphite such as vapor-grown graphite), and carbonaceous materials obtained by firing various synthetic resins such as PAN (polyacrylonitrile) resins or furfuryl alcohol resins. Furthermore, examples include various types of 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-based 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 classified into hard carbonaceous materials (also called non-graphitizable carbonaceous materials) and graphitized carbonaceous materials, depending on the degree of graphitization. Furthermore, the carbonaceous material preferably has the interplanar spacing, density, or crystallite size described in Japanese Patent Publication No. 62-022066, Japanese Patent Publication No. 2-006856, and Japanese Patent Publication No. 3-045473. The carbonaceous material does not need to be a single material; a mixture of natural graphite and artificial graphite described in Japanese Patent Publication No. 5-090844, and graphite having a coating layer described in Japanese Patent Publication No. 6-004516 can also be used. As the carbonaceous material, hard carbon or graphite is preferred, with graphite being more preferred.

[0114] The oxides of metal elements or metalloid elements that can be used as negative electrode active materials are not particularly limited as long as they are oxides capable of intercalating and releasing lithium, and include metal oxides, composite oxides of metal elements, composite oxides of metal elements and metalloid elements, and metalloid oxides. Composite oxides of metal elements and composite oxides of metal elements and metalloid elements are collectively referred to as metal composite oxides. Amorphous oxides are preferred among these oxides, 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, a metalloid element refers to an element that exhibits properties intermediate between a metallic element and a nonmetallic element, and typically includes six elements: boron, silicon, germanium, arsenic, antimony, and tellurium, and further includes three elements: selenium, polonium, and astatine. Furthermore, amorphous refers to a material that, in X-ray diffraction using CuKα rays, has a broad scattering band with a peak in the region of 20 to 40° 2θ, and may also have crystalline diffraction lines. Preferably, the strongest intensity of the crystalline diffraction lines observed in the 2θ range of 40 to 70° is 100 times or less, more preferably 5 times or less, than the intensity of the diffraction line at the peak of the broad scattering band observed in the 2θ range of 20 to 40°, and even more preferably has no crystalline diffraction lines.

[0115] Among the group of compounds consisting of amorphous oxides and chalcogenides described above, amorphous oxides of metalloid elements or the chalcogenides described above are more preferred, and oxides consisting of one element alone or a combination of two or more elements selected from groups 13(IIIB) to 15(VB) of the periodic table (for example, Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi), or chalcogenides are even more preferred. Preferred amorphous oxides and chalcogenides include Ga2O3, GeO, PbO, PbO2, Pb2O3, Pb2O4, Pb3O4, Sb2O3, Sb2O4, Sb2O8Bi2O3, Sb2O8Si2O3, Sb2O5, Bi2O3, Bi2O4, GeS, PbS, PbS2, Sb2S3, or Sb2S5. Preferred negative electrode active materials that can be used in combination with amorphous oxide negative electrode active materials centered on Sn, Si, or Ge include carbonaceous materials capable of intercalating and / or releasing lithium ions or lithium metal, elemental lithium, lithium alloys, or negative electrode active materials that can be alloyed with lithium.

[0116] In terms of high current density charge-discharge characteristics, it is preferable that the oxides of metallic or metalloid elements (particularly metallic (composite) oxides) and the chalcogenides contain at least one of titanium and lithium as constituent components. Examples of lithium-containing metal composite oxides (lithium composite metal oxides) include composite oxides of lithium oxide with the above-mentioned metal oxide, the above-mentioned metal composite oxide, or the above-mentioned chalcogenide. More specifically, Li2SnO2 is an example. The negative electrode active material (e.g., metal oxide) may also preferably contain titanium (titanium oxide). Specifically, Li4Ti5O 12 Lithium titanate [LTO] is preferable because it exhibits excellent rapid charge-discharge characteristics due to its small volume fluctuation during lithium ion intercalation and deintercalation, which suppresses electrode degradation and enables an improvement in the lifespan of all-solid-state lithium-ion secondary batteries.

[0117] The lithium alloy as the negative electrode active material is not particularly limited as long as it is an alloy commonly used as the negative electrode active material of an all-solid-state lithium-ion secondary battery. For example, a lithium aluminum alloy can be mentioned.

[0118] The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is commonly used as the negative electrode active material of an all-solid-state lithium-ion secondary battery. Examples of the negative electrode active material include a negative electrode active material (alloy) containing a silicon element or a tin element, and each metal such as Al and In. A negative electrode active material containing a silicon element (silicon element-containing active material) that enables a higher battery capacity is preferable, and a silicon element-containing active material with a silicon element content of 50 mol% or more of all constituent elements is more preferable. Generally, a negative electrode containing these negative electrode active materials (for example, a Si negative electrode containing a silicon element-containing active material, a Sn negative electrode containing an active material containing a tin element) can occlude more Li ions than a carbon negative electrode (such as graphite and acetylene black). That is, the amount of Li ions occluded per unit mass increases. Therefore, the battery capacity can be increased. As a result, there is an advantage that the battery driving time can be lengthened.

[0119] Examples of the silicon element-containing active material include silicon materials such as Si and SiOx (0 < x ≤ 1), and further, silicon-containing alloys containing titanium, vanadium, chromium, manganese, nickel, copper, or lanthanum (for example, LaSi2, VSi2, La-Si, Gd-Si, and Ni-Si), or organized active materials (for example, LaSi2 / Si). In addition, active materials containing a silicon element and a tin element such as SnSiO3 and SnSiS3 can be mentioned. Note that SiOx can be used as a negative electrode active material (semimetal oxide) itself, and can also be used as a negative electrode active material (its precursor material) capable of alloying with lithium because Si is generated by the operation of an all-solid-state lithium-ion secondary battery. Examples of the negative electrode active material having a tin element include Sn, SnO, SnO2, SnS, SnS2, and the active materials containing the silicon element and the tin element described above.

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

[0121] It is also preferable to use a titanium-niobium composite oxide as the negative electrode active material. Titanium-niobium composite oxides have a high theoretical volumetric capacity density and are expected to enable long life and rapid charging. Examples of titanium-niobium composite oxides include TiNb2O7.

[0122] The shape of the negative electrode active material is not particularly limited, but particulate is preferred. The volume-average particle size 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. A 1% by mass dispersion of the negative electrode active material is prepared by diluting it with water (or heptane if the substance is unstable in water) in a 20 mL sample bottle. 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 a temperature of 25°C with a quartz cell to obtain the volume-average particle size. For other detailed conditions, refer to JIS Z 8828:2013 "Particle size analysis - Dynamic light scattering method" as needed. Five samples are prepared for each level and their average value is adopted.

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

[0124] The surface of the negative electrode active material may be coated with another metal oxide. Examples of surface coating agents include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specifically, these include spinel titanate, tantalum oxides, niobium oxides, and lithium niobate compounds, for example, Li4Ti5O 12Examples include Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, SiO2, TiO2, ZrO2, Al2O3, B2O3, and Li3AlF6. Furthermore, the electrode surface 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 active light or an active gas (e.g., plasma) before or after the above-mentioned surface coating.

[0125] (Negative electrode current collector) The current collector that makes up the negative electrode layer is an electron conductor. Furthermore, the negative electrode current collector is usually in the form of a film sheet. Examples of materials that make up the negative electrode current collector include aluminum, copper, copper alloys, stainless steel, nickel, and titanium, with aluminum, copper, copper alloys, or stainless steel being preferred. Furthermore, negative electrode current collectors may also be made of aluminum, copper, copper alloys, or stainless steel with a surface treatment of 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 can be, for example, 5 to 500 μm, with 20 to 200 μm being preferred. Furthermore, the thickness of the negative electrode current collector constituting the secondary battery of the present invention is not particularly limited and can be, for example, 10 to 100 μm, with 10 to 50 μm being preferred.

[0127] The positive electrode layer and the negative electrode layer may contain components other than solid electrolytes and active materials (other components) in their active material layers. For example, they may contain conductive additives. As conductive additives, those commonly known as conductive additives can be used. Examples of conductive additives include graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, Ketjen black, and furnace black, amorphous carbon such as needle coke, fibrous carbon such as vapor-grown carbon fibers and carbon nanotubes, and carbonaceous materials such as graphene and fullerene. Conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylene derivatives may also be used. In addition to the conductive additives mentioned above, ordinary conductive additives that do not contain carbon atoms, such as metal powders or metal fibers, may also be used. A conductive additive is a substance that does not function as an active material because it does not cause the insertion and release of lithium (Li) during the charging and discharging of a battery. Therefore, among conductive additives, those that can function as an active material in the active material layer during the charging and discharging of a battery are classified as active materials, not conductive additives. Whether or not a substance functions as an active material during the charging and discharging of a battery is not unique, but is determined by its combination with the active material.

[0128] Other components include the aforementioned binder and lithium salt.

[0129] <Manufacturing of all-solid-state lithium-ion secondary batteries> The secondary battery of the present invention can be manufactured by referring to a conventional method for manufacturing an all-solid-state secondary battery, except that at least the solid electrolyte layer uses a solid electrolyte (I). In order to reduce the water content of the laminate consisting of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer to the level specified in the present invention, it is preferable in the manufacturing of the secondary battery of the present invention to first form the laminate containing the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer using a solid electrolyte (I), and then subject it to a vacuum drying treatment or the like, as described later. A preferred embodiment of the method for manufacturing the secondary battery of the present invention will now be described.

[0130] The method for manufacturing a secondary battery of the present invention includes obtaining a laminate in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are arranged in this order. Furthermore, in order to make the amount of water in the laminate consisting of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer the amount specified in the present invention, it is preferable that the manufacturing of the secondary battery of the present invention includes a step of subjecting the laminate containing 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 amount of water specified in the present invention, it is preferable to subject the laminate, in which the positive electrode layer, the solid electrolyte layer, and the negative electrode layer are arranged in this order, to a drying treatment while it is placed inside a battery cell. The drying method is not particularly limited, and for example, 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 can be reduced to the range specified in the present invention by using a desiccator, vacuum drying (preferably freeze-vacuum drying), or heat treatment. The secondary battery of the present invention preferably comprises a laminate in which the positive electrode layer, solid electrolyte layer, and negative electrode layer are arranged in this order and sealed. By sealing, it is possible to more reliably prevent moisture from entering the solid electrolyte layer after the drying process, thereby further improving the cycle characteristics. The sealing method is not particularly limited, as long as it completely blocks or suppresses the entry of moisture (air). For example, one method is to seal the laminate by closing the lid of the housing (battery cell) that houses the laminate in which the positive electrode layer, solid electrolyte layer, and negative electrode layer are arranged in this order, via a gasket such as an O-ring.

[0131] Furthermore, there are no particular limitations on the method for forming a laminate in which the positive electrode layer, solid electrolyte layer, and negative electrode layer are arranged in this order. For example, a positive electrode active material layer can be formed by applying a positive electrode forming composition (slurry) containing positive electrode active material onto a metal foil which is a positive electrode current collector. Next, a solid electrolyte layer can be formed by applying a solid electrolyte layer dispersion (slurry) containing a solid electrolyte onto this positive electrode active material layer. Then, a negative electrode forming composition (slurry) containing negative electrode active material can be applied onto the solid electrolyte layer to form a negative electrode active material layer, and a negative electrode current collector (metal foil) can be placed on top of the negative electrode active material layer. If necessary, the entire structure can be dried and subjected to pressurization to obtain an all-solid-state lithium-ion secondary battery as shown in Figure 1. Alternatively, by reversing the formation method of each layer, a negative electrode active material layer, a solid electrolyte layer, and a positive electrode active material layer can be formed on a negative electrode current collector, and the entire assembly can be subjected to pressurization treatment as needed to manufacture an all-solid-state lithium-ion secondary battery.

[0132] Alternatively, a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer can be manufactured separately, stacked, and dried and pressurized as necessary to produce an all-solid-state lithium-ion secondary battery. In this case, during the formation of each layer, a support such as a nonwoven fabric can be placed as needed to make each layer a self-supporting membrane. Furthermore, the manufacturing method of the secondary battery of the present invention is not limited in any way to those described above, as long as a secondary battery as defined in the present invention can be obtained.

[0133] In the manufacturing of the secondary battery of the present invention, even without using a sulfide-based solid electrolyte, it is possible to form layers with suppressed interfacial resistance between solid particles or between layers by the action of the oxide-based solid electrolyte (I) which can be easily plastically deformed by pressure. Because the solid electrolyte (I) itself is soft and plastically deformable, acting like a binder and contributing to improved bonding between solid particles or between layers, 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 manufacturing or before use. The method of initialization is not particularly limited, and can be performed, for example, by performing the initial charge and discharge under increased press pressure, and then releasing the pressure until it falls within the range of pressure conditions for use of the secondary battery.

[0135] <Applications of all-solid-state lithium-ion secondary batteries> The secondary battery of the present invention can be applied to a variety of uses. There are no particular limitations on the applications, but for example, when incorporated into electronic devices, examples include laptop computers, pen-input computers, mobile computers, e-book players, mobile phones, cordless phone handsets, pagers, handheld terminals, portable fax machines, portable copiers, portable printers, headphone stereos, video cameras, LCD televisions, handheld vacuum cleaners, portable CDs, MiniDiscs, 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, strobes, cameras, and medical devices (pacemakers, hearing aids, shoulder massagers, etc.). Furthermore, it 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 limited to these examples. [Examples]

[0137] [Reference example 1] Using a ball mill (Fritsch P-7), powdered Li2B4O7 crystals (LBO powder) (Rare Metallic Co., Ltd.) were ball-milled under the following conditions: pot: stabilized zirconia (YSZ) (45 mL), grinding balls: YSZ (average particle size: 5 mm, number: 50), rotation speed: 370 rpm (revolutions per minute), LBO powder amount: 1 g, atmosphere: air, ball mill processing time: 100 hours, to obtain finely milled lithium-containing oxide (hereinafter also referred to as "fine lithium-containing oxide particles"). To 1 g of the obtained lithium-containing oxide fine material, 0.05 g of LiFSI (chemical formula: Li(FSO2)2N) as a lithium salt was added (5% by mass relative to the lithium-containing oxide fine material), and the mixture was ball-milled for another 100 hours. The resulting powder was added to water to a powder concentration of 42% by mass and ultrasonically dispersed for 30 minutes. Subsequently, the resulting dispersion was transferred to a glass petri dish and dried under air at 120°C for 2 hours to obtain a solid electrolyte film. Subsequently, the obtained film was peeled off to obtain powdered solid electrolyte (I)-1.

[0138] <Fabrication and evaluation of molded bodies of solid electrolytes> 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 solid electrolyte molded body (compacted body 1). The shape of compacted body 1 is cylindrical with a diameter of 10 mm and a thickness of 0.5 to 1 mm. The ionic conductivity of the obtained compacted body 1 was measured, and the ionic conductivity of compacted body 1 at 27°C was 1.5 × 10⁻¹⁰. -4 It is S / cm, and at 60℃ it is 4.0 × 10 -4 The value was S / cm.

[0139] The ionic conductivity of the above solid electrolyte (I)-1 was calculated by arranging electrodes consisting of two In foils so as to sandwich the compacted powder 1, measuring the AC impedance between the two In electrodes in the measurement frequency range of 1 Hz to 1 MHz under the 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 resulting Cole-Cole plot (Nyquist plot).

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

[0141] Using the solid electrolyte (I)-1 obtained above, X-ray total scattering measurements were performed at SPring-8L04B2 (acceleration voltage: 61.4 keV, wavelength: 0.2019 Å). The samples were sealed in 2 mmφ or 1 mmφ Kapton capillaries for the experiment. The obtained data were Fourier transformed as described above to obtain the reduced two-body distribution function. Analysis revealed that in the reduced dibody distribution function G(r) obtained from X-ray total scattering measurements, a first peak was identified at 1.43 Å, where the peak top of G(r) exceeded 1.0 in the range of r from 1 to 5 Å, and a second peak was identified at 2.40 Å, where the peak top of G(r) also exceeded 1.0. On the other hand, in solid electrolyte (I)-1, the peaks attributed to the BO-to-BO distance and BB-to-BB distance, which are observed in typical lithium tetraborate crystals, were maintained. Typical lithium tetraborate crystals have a structure in which BO4 tetrahedra and BO3 triangles exist in a 1:1 ratio (diborate structure), and it was presumed that this structure was maintained in solid electrolyte (I)-1.

[0142] The solid electrolyte (I)-1 obtained above 7 The total width at half maximum (FMAX1) of the peaks in the spectrum obtained when Li-NMR measurements are performed at 20°C, where the chemical shift is in the range of -100 to +100 ppm, is relative to the solid electrolyte (I)-1. 7 When Li-NMR measurements were performed at 120°C, the percentage of peaks with a chemical shift in the range of -100 to +100 ppm in the resulting spectrum, specifically the percentage of the total width at half maximum (FMAX²) {(FMAX² / FMAX¹) × 100}, was 33%. Also, solid 7When the spectrum obtained by Li-NMR measurement at 20°C showed a first peak appearing in the range of -100 to +100 ppm, waveform separation revealed a second peak with a chemical shift in the range of -3 to 3 ppm and a full width at half maximum of 5 ppm or less. The ratio of the area intensity of the second peak to the area intensity of the first peak was 4%.

[0143] Using the solid electrolyte (I)-1 obtained above, infrared absorption spectroscopy was performed under the conditions described above, and in the obtained infrared absorption spectrum, 800-1600 cm⁻¹ -1 For the maximum absorption intensity in the wavenumber region, 3000-3500 cm -1 The ratio of the maximum absorption intensities in the wavenumber region was 0.72.

[0144] In the Raman spectrum of solid electrolyte (I)-1 obtained above, at 600-850 cm⁻¹ -1 The coefficient of determination obtained by performing a linear regression analysis using the least squares method in the wavenumber domain was 0.9974. As described above, the mass loss rate of solid electrolyte (I)-1 when heated from 25°C to 800°C was 29.8%.

[0145] For 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). For nitrogen, it was estimated from the analytical mass of sulfur, taking into account the atomic weights of each element in the Li salt, and for oxygen, the analytical masses of elements other than oxygen were added together and calculated as the difference from the total powder amount. The results are shown in the table below.

[0146] [Reference example 2] One g of the lithium-containing oxide fine particles used in Reference Example 1 was added to water to a concentration of 42% by mass, and ultrasonically dispersed for 30 minutes. To the resulting dispersion, 0.05 g of LiFSI (chemical formula: Li(FSO2)2N) as a lithium salt was added (5% by mass relative to the lithium-containing oxide fine particles), and ultrasonically dispersed for another 30 minutes. The obtained dispersion was transferred to a glass petri dish and dried in air at 120°C for 2 hours to obtain a solid electrolyte film. Subsequently, the obtained film was peeled off to obtain powdered solid electrolyte (I)-2. Solid electrolyte (I)-2 was subjected to various evaluations in air in the same manner as in Reference Example 1. The results are summarized in the table below.

[0147] [Reference example 3] Using a ball mill (Fritsch P-7), powdered Li2B4O7 (LBO powder) (manufactured by Rare Metallic) was ball-milled under the following conditions: pot: YSZ (45 ml), grinding 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 processing time: 100 hours, to obtain fine lithium-containing oxide particles. The obtained lithium-containing oxide fine particles were added to water to a concentration of 42% by mass, and the mixture was sonicated for 60 minutes to obtain dispersion 1. Next, 3.25 g of LiFSI (chemical formula: Li(FSO2)2N) as a lithium salt was added to water to a concentration of 87% by mass, and sonicated 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. Subsequently, the obtained dispersion was vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-3. The obtained powder was left 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 the preparation of dispersion 1 in Reference Example 3. Next, 2.32 g of LiFSI (chemical formula: Li(FSO2)2N) as a lithium salt was added to water at a concentration of 87% by mass, and sonicated for 60 minutes to obtain solution 4. The obtained dispersion 3 and solution 4 were mixed and stirred 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 left 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 the preparation of dispersion 1 in Reference Example 3. Next, 4.65 g of LiFSI (chemical formula: Li(FSO2)2N) as a lithium salt was added to water at a concentration of 87% by mass, and sonicated for 60 minutes to obtain solution 6. The obtained dispersion 5 and solution 6 were mixed and stirred 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)-5. The obtained powder was immediately subjected to various evaluations under air 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 the preparation of dispersion 1 in Reference Example 3. Next, 7.13 g of LiTFSI (chemical formula: Li(F3CSO2)2N) as a lithium salt was added to water at a concentration of 87% by mass, and sonicated 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. Subsequently, the obtained dispersion was vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-6. The obtained powder was left 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 amount of carbon shown in Table 1 below was estimated from the analytical mass of sulfur, taking into account the atomic weights of each component in the lithium salt.

[0151] [Comparison Example 1] Elemental analysis was performed on the LBO powder (unball-milled powdered Li2B4O7 crystals) used in Reference Example 1, and the composition of the obtained LBO powder was Li 1.96 B 4.00 O 6.80 The LBO powder was compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a comparative compact C1. The ionic conductivity of the obtained compact C1 could not be detected. Furthermore, in the same manner as in Reference Example 1, X-ray total scattering measurements were performed using LBO powder to obtain the reduced dibody distribution function G(r). Figure 10 shows the reduced dibody distribution function G(r) obtained from LBO powder. Analysis revealed that the reduced dibody distribution function G(r) obtained from X-ray total scattering measurements of LBO powder had two peaks: a first peak located at 1.40 Å (corresponding to proximity to BO) and a second peak located at 2.40 Å (corresponding to proximity to BB). The G(r) values ​​at the peak tops of both the first and second peaks were greater than 1.0 (see Figure 10). In addition, there were peaks located at 3.65 Å, 5.22 Å, 5.51 Å, and 8.54 Å, and the absolute values ​​of the G(r) values ​​at the peak tops of each of these peaks were clearly greater than 1.0 (see Figure 10). Furthermore, X-ray diffraction measurements were performed on the LBO powder as described above. The measurement conditions were 0.01° / step and 3° / min. Figure 11 shows the X-ray diffraction pattern of the LBO powder used in Comparative Reference Example 1. As shown in Figure 11, the LBO powder used in Comparative Reference Example 1 showed multiple narrow peaks. 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 included a peak corresponding to the (2,0,2) plane at 25.54°, a peak corresponding to the (2,1,3) plane at 33.58°, and a peak corresponding to the (3,1,2) plane at 34.62°. The intensities of these three peaks were almost equivalent. These peaks originate from the crystalline components.

[0152] [Comparison Example 2] As a result of elemental analysis of the fine material of the lithium-containing oxide prepared in Reference Example 1 (powdered Li2B4O7 crystals ball-milled), the composition of the fine material of the lithium-containing oxide was Li 1.94 B 4.00 O 6.80 . Next, the fine material of the lithium-containing oxide was compacted at an effective pressure of 220 MPa at 27 °C (room temperature) to obtain a reference compact (compact R1). The ionic conductivity of the obtained compact R1 was 7.5×10 -9 S / cm at 27 °C and 7.5×10 -8 S / cm at 60 °C.

[0153] In the table below, in the reduced pair distribution function G(r) obtained from the X-ray total scattering measurement as described above, there are a first peak with the peak top located in the range of r = 1.43 ± 0.2 Å and a second peak with the peak top located in the range of r = 2.40 ± 0.2 Å. When the G(r) of the peak top of the first peak and the G(r) of the peak top of the second peak are greater than 1.0, the "Short-distance G(r)" column is designated as "A", and in other cases as "B". In Reference Examples 1 to 4 shown in the table below and Reference Examples 9 to 12 described later, the value of G(r) of the peak top of the first peak was 1.2 or more. In addition, in the reduced pair distribution function G(r), when the absolute value of G(r) is less than 1.0 in the range where r is greater than 5 Å and less than or equal to 10 Å, the "Long-distance G(r)" column in the table below is designated as "A", and when the absolute value of G(r) does not satisfy less than 1.0, it is designated as "B". In addition, as a result of the X-ray diffraction measurement using the above-mentioned CuKα ray, when the above X-ray diffraction characteristics are satisfied, it is designated as "A", and when not satisfied, it is designated as "B". In Reference Examples 1 to 6 shown in the table below and Reference Examples 7 to 13 described later, in the X-ray diffraction pattern, none of the first peak, the second peak, the third peak, and the fourth peak exist, or the intensity ratio of at least one of the first peak, the second peak, the third peak, and the fourth peak is 2.0 or less.

[0154] In the table below, the "Elemental Analysis" column shows the composition of the solid electrolyte (I) obtained in each reference example and the lithium-containing oxide in each comparative reference example, expressed as the molar amount of each element, with the content of B set to "4.00".

[0155] In the table below, "area intensity ratio" refers to the solid as described above. 7 In Li-NMR measurements, this is the ratio of the area intensity of the second peak to the area intensity of the first peak, and the evaluation results based on the following criteria are described. <Criteria for the ratio of area intensity> A: When the area intensity ratio is 15% or more B: When the area intensity ratio is 0.5% or more but 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 infrared absorption spectral characteristics described above are met, [3000~3500 cm] -1 [Maximum absorption intensity in the wavenumber region] / [800~1600cm] -1 A was indicated as A if the maximum absorption intensity in the wavenumber region was 0.20 or greater, and B if it was less than 0.20. In the table below, "-" indicates that a measurement value is not shown.

[0157] [Table 1]

[0158] [Table 2]

[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 1-6 exhibit excellent ionic conductivity. Furthermore, elemental analysis confirmed that Reference Examples 3-6 have a higher Li content in the solid electrolytes. In Reference Examples 3-6, 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 a greater amount of lithium salt to be mixed, which is presumed to have resulted in an increase in the amount of Li incorporated into the solid electrolyte. In addition, Reference Examples 3, 4, and 5, which used LiFSI as the lithium salt, showed improved ionic conductivity. This is presumed to be because the increased amount of Li includes highly mobile Li.

[0160] <Effect of water in solid electrolytes> The compacted powder (pellets) (10 mmφ, 0.9 mmt) of solid electrolyte (I)-3 obtained in Reference Example 3 was vacuum-dried at 27°C under a constraint of 60 MPa, and the pressure change and ionic conductivity with respect to vacuum drying time were investigated. The method for preparing the compacted powder 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] [Table 3]

[0162] The solid electrolyte (I)-3 in Reference Example 3 has an infrared absorption spectrum of 3000-3500 cm⁻¹. -1 The increased OH stretching peak suggests the presence of numerous OH groups and water. Furthermore, the presence of both free water and bound water is inferred. In the above study, the pellets were dried under conditions where free water was thought to volatilize first, and then under even harsher drying conditions. The ionic conductivity at each stage was then evaluated.

[0163] As shown in the table above, the drying time is 5 minutes and the pressure is 200 Pa, so the free water is considered to be in a vaporized state, but the ionic conductivity is 3.8 × 10⁻⁶. -3 It showed a high value of S / cm, and even after a drying time of 1080 minutes and a pressure of 15 Pa, the ionic conductivity was 5.7 × 10⁻⁶. -4 The result showed S / cm. This result indicates the presence of bound water in addition to free water, and that this contributes to ionic conductivity.

[0164] [Reference example 7] A dispersion 9 was obtained in the same manner as the preparation of dispersion 1 in Reference Example 3 above, with a concentration of lithium-containing oxide fine particles of 42% by mass. Next, 7.12 g of LiTFSI (chemical formula: Li(F3CSO2)2N) as a lithium salt was added to water to a concentration of 87% by mass, and sonicated 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. Subsequently, the obtained dispersion was vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-7. The obtained powder was left 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] Solid electrolyte (I)-8 was obtained in the same manner as in Reference Example 7, except that the water and LiTFSI content in the resulting solid electrolyte (I) was changed to the amounts shown in the table below. Various evaluations were then performed in air in the same manner as in Reference Example 1. The results are summarized in the table below.

[0166] [Reference examples 9-13] Solid electrolytes (I)-9 to (I)-13 were obtained in the same manner as in Reference Example 7, except that LiTFSI was replaced with LiFSI, and the water and LiFSI content in the resulting solid electrolyte (I) was adjusted to the amounts shown in the table below. Various evaluations were then performed in air 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 by vacuum drying was evaluated immediately in air.

[0167] In the following table, the columns of "Fine Particles of Lithium-Containing Oxide", "Lithium Salt", and "Water" represent the relative molar ratios. For example, in Reference Example 7, the molar ratio of the lithium salt to the fine particles of the lithium-containing oxide is 1, and the molar ratio of water to the fine particles of the lithium-containing oxide is 11. The above molar ratios were calculated by the following method. The analysis of each element was performed as follows: lithium and boron were quantitatively analyzed by ICP-OES, fluorine and sulfur were quantitatively analyzed by combustion ion chromatography (combustion IC), for N, an estimate was made from the analyzed mass of sulfur considering the atomic weights in the Li salt, and for O, the analyzed masses of the elements other than O were added together and calculated as the difference from the total amount of the solid electrolyte. In Reference Examples 7 and 8, the carbon content was estimated from the analyzed mass of sulfur considering the atomic weights in the lithium salt. The molar ratio of the fine particles of the lithium-containing oxide to the lithium salt in the solid electrolyte was calculated from the molar ratio of an element present only in the fine particles of the lithium-containing oxide (e.g., B) to an element present only in the lithium salt. Also, the molar ratio of the fine particles of the lithium-containing oxide to water was calculated by subtracting the molar ratio 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] [Table 4]

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

[0170] [Table A]

[0171] [Table 5]

[0172] As shown in the table above, the solid electrolytes in each reference example possessed the desired properties or characteristics and exhibited excellent ionic conductivity.

[0173] [Manufacturing Example 1] Manufacturing of all-solid-state lithium-ion secondary batteries <Preparation of lithium-containing oxide fine particles> 45 g of powdered Li2B4O7 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 pulverized using a planetary ball milling apparatus at 300 rpm for 45 hours to obtain fine lithium-containing oxide particles.

[0174] <Preparation of Solid Electrolyte Slurry> 10 g of the lithium-containing oxide fine material, 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 with a magnetic stirrer for 30 minutes 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. After storing the obtained powder in a desiccator (5%) for several days, it was analyzed under air and found to have the X-ray diffraction characteristics described above, confirming that it was amorphous. Furthermore, when the ionic conductivity was measured using the method described above, it was found to be 4.5 × 10⁻⁶. -3 The concentration was S / cm. Furthermore, the molar ratio of LiFSI content to lithium-containing oxide content was 1, and the molar ratio of water content was 9. The elemental 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> To 5.2 g of the above-mentioned solid electrolyte slurry 1, 5.0 g of positive electrode active material LiCoO2 and 4.8 g of a 6% by mass aqueous dispersion of carbon nanotubes (CNT) (manufactured by KJ Special 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> To 7.6 g of the above-mentioned solid electrolyte slurry 1, 5.0 g of the negative electrode active material TiNb2O7 and 9.8 g of a 6% by mass aqueous dispersion of CNTs (manufactured by KJ Special 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 the positive electrode laminate [solid electrolyte layer / positive electrode active material layer / Al current collector]> The above positive electrode slurry 1 was applied to a 50 μm thick A4 size Al foil using a desktop coating machine with an applicator gap of 100 μm and a coating speed of 30 mm / s. After standing at room temperature for 1 hour, the above solid electrolyte slurry 1 was applied as a double layer to the positive electrode slurry film using a desktop coating machine with an applicator gap of 200 μm and a coating speed of 90 mm / s. The double-layered film was dried in a desiccator with a relative humidity of 5% or less for 12 hours, and then punched out to a diameter of 10 mm with a hand punch to obtain the positive electrode side 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 the 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-sized Al foil using a desktop coating machine with an applicator gap of 200 μm and a coating speed of 30 mm / s. After standing at room temperature for 1 hour, the above-mentioned solid electrolyte slurry 1 was applied as a double layer to the negative electrode slurry film using a desktop coating machine with an applicator gap of 300 μm and a coating speed of 90 mm / s. The double-layered film was dried in a desiccator with a relative humidity of 5% or less for 12 hours, and then punched out to a diameter of 10 mm using a hand punch to obtain the negative electrode side laminate (solid electrolyte layer / negative electrode 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 batteries> (Example 1) The negative electrode stack described above was placed with the solid electrolyte layer facing upwards on a 10mm diameter SUS (stainless steel) stand of an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.). The positive electrode stack described above was then placed on top of this solid electrolyte layer with the solid electrolyte layer facing downwards. In this way, a stack with the positive electrode stack / negative electrode stack structure (this stack is called 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, placing the polished Ti plate 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 fitted and sealed with double O-rings, four bolts, and wing nuts. The restraining pressure application mechanism installed on top of the KP-SolidCell restrained the cell from above and below with a torque of 5 Nm (equivalent to 30 MPa). Next, the KP-SolidCell was released and the cell was removed, and any excess liquid components that had seeped out due to the application of restraining pressure were wiped away. Then, the cell was set in the KP-SolidCell in the same manner as above and restrained from above and below. Next, with the top lid open, the KP-SolidCell 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-SolidCell from the vacuum dryer, the top lid was closed and sealed using a double O-ring. After standing for 40 hours, it was used as the battery of Example 1.

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

[0181] The resulting battery (positive electrode active material amount 2 mg / cm³) 2 The cycle characteristics at 25°C with a confinement pressure of 30 MPa were tested as described in the test example below.

[0182] [Test Example] Cycle Characteristics Test The batteries obtained as described above were subjected to a confinement pressure (30 MPa), and repeatedly charged and discharged using a Toyo Technica 580-NOHFR under the following conditions at a temperature of 27°C. Charging is performed using a constant current value I until the battery voltage reaches 2.8V. β The process was carried out, and after reaching 2.8V, the voltage was kept constant (2.8V), and the process continued until the current value reached a rate of 2.4C. After charging, the circuit is disconnected and left for 10 minutes, then a constant current value I β Then, I discharged the battery until the voltage dropped to 1.5V. This entire charging and discharging cycle constitutes one cycle. After discharging, the circuit was opened and left for 10 minutes before proceeding to the next charge cycle, repeating the charging and discharging process under the same conditions. Furthermore, in the above charging and discharging, the current value I β As part of the battery initialization, the first charge / discharge cycle was performed with the current set to 0.2C, and subsequent charge / discharge cycles were performed with the current set to 3C.

[0183] The results are shown in the table below. In the table below, "Water content in KF measurement" in Example 1 and Comparative Example 1 refers to the water content (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 obtained batteries were disassembled under an Ar atmosphere to remove the cells, and approximately 5-10 mg of the laminated portion 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 blank sample of only the Ar atmosphere was also sealed in a dedicated vial. A vial was placed in a Karl Fischer moisture vaporizer, heated to 100°C or 300°C to vaporize the water, and then the water content of each sample was measured using the Karl Fischer titration method with a coulometric moisture meter. The water content of the blank was subtracted from this water content, and the resulting value was divided by the sample volume to obtain the water content (mass%) of the laminate consisting of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer.

[0184] [Table 6]

[0185] As shown in the table above, it was found that the charge-discharge cycle characteristics can be effectively improved by vacuum-drying 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 reduce the moisture content.

[0186] Although we have described the present invention along with its embodiments, we do not intend to limit our invention in any detail of the description unless specifically designated, and we believe that it should be interpreted broadly without contradicting 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 as part of this specification. [Explanation of symbols]

[0188] 1 Negative electrode current collector 2 Negative electrode active material layer 3 Solid electrolyte layer 4 Cathode active material layer 5 Positive electrode current collector 6. Operating parts 10. All-solid-state lithium-ion secondary batteries

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 comprises an amorphous solid electrolyte containing a lithium-containing oxide and a lithium salt, wherein the content of the amorphous solid electrolyte in the solid electrolyte layer is 90% by mass or more, 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 molar ratio. An all-solid-state lithium-ion secondary battery, wherein the laminate comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer has a water content of 7.0% by mass or less at 100°C based on Karl Fischer titration, and the difference in water content based on Karl Fischer titration at 100°C and 300°C is 0.1 to 5.0% by mass.

2. 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, comprising: However, -0.3 < x < 0.3, -0.3 < y < 0.3, and -0.3 < z < 0.

3.

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

4. 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, solid electrolyte layer, and negative electrode layer are arranged in that order.

5. The all-solid-state lithium-ion secondary battery according to claim 1, wherein the solid electrolyte layer does not contain any solid electrolyte other than the amorphous solid electrolyte.

6. A method for manufacturing an all-solid-state lithium-ion secondary battery according to any one of claims 1 to 5, comprising forming a laminate containing 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.

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