Lithium-based solid electrolyte, method for manufacturing lithium-based solid electrolyte, modified positive electrode active material, modified negative electrode active material, all-solid-state secondary battery, electrode sheet for all-solid-state secondary battery, solid electrolyte sheet, electrode for all-solid-state secondary battery

Abstract

The present invention addresses the problem of providing: a lithium-based solid electrolyte which has excellent ion conductivity; a method for producing a lithium-based solid electrolyte; a modified positive electrode active material; a modified negative electrode active material; an all-solid-state secondary battery; an electrode sheet for all-solid-state secondary batteries; a solid electrolyte sheet; and an electrode for all-solid-state secondary batteries.　A lithium-based solid electrolyte according to the present invention contains lithium tetraborate in an amorphous state, water and a lithium salt. With respect to this lithium-based solid electrolyte, the content of water is 45% by mass or less relative to the total mass of this lithium-based solid electrolyte.

Description

[Technical Field]

[0001] The present invention relates to a lithium-based solid electrolyte, a method for producing a lithium-based solid electrolyte, a modified positive electrode active material, a modified negative electrode active material, an all-solid-state secondary battery, an electrode sheet for an all-solid-state secondary battery, a solid electrolyte sheet, and an electrode for an all-solid-state 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. In all-solid-state batteries, a solid electrolyte with good ionic conductivity is required to obtain the desired charge and discharge characteristics. For example, Patent Document 1 discloses a lithium-containing oxide-based solid electrolyte that can be used in all-solid-state lithium-ion secondary batteries. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-052755 [Overview of the project] [Problems that the invention aims to solve]

[0004] In Patent Document 1, the conductivity is 10 -5 S·cm -1 While the current level of conductivity has been disclosed, there is a growing demand for further improvements in conductivity these days.

[0005] The object of this invention is to provide a lithium-based solid electrolyte with excellent ionic conductivity. Furthermore, the present invention aims to provide a method for producing a lithium-based solid electrolyte, a modified positive electrode active material, a modified negative electrode active material, an all-solid-state secondary battery, an electrode sheet for an all-solid-state secondary battery, a solid electrolyte sheet, and an electrode for an all-solid-state secondary battery. [Means for solving the problem]

[0006] The inventors of this invention have diligently conducted research to solve the above problems and have completed the present invention with the following configuration.

[0007] [1] A lithium-based solid electrolyte comprising amorphous lithium tetraborate, water, and a lithium salt, wherein the water content is 45% by mass or less relative to the total mass of the lithium-based solid electrolyte. [2] The lithium-based solid electrolyte according to [1], wherein the lithium tetraborate has an OH structure. [3] The lithium-based solid electrolyte according to [1] or [2], wherein the molar ratio of the lithium salt content to the lithium tetraborate content is 0.001 to 1.5, and the molar ratio of the water content to the lithium tetraborate content is 1 to 12. [4] A lithium-based solid electrolyte according to any of [1] to [3], wherein the lithium salt is a compound represented by formula (1) described later. [5] A lithium-based solid electrolyte according to any one of [1] to [4], wherein when a cross-section of a molded body obtained by pressurizing the lithium-based solid electrolyte is observed with a scanning electron microscope, the region containing the lithium salt is present in a network-like structure. [6] A lithium-based solid electrolyte comprising amorphous lithium tetraborate and a lithium salt, wherein when a cross-section of a molded body obtained by pressurizing the lithium-based solid electrolyte is observed with a scanning electron microscope, the region containing the lithium salt is found to be in a network-like structure. [7] The lithium-based solid electrolyte according to [6], wherein the lithium tetraborate has a hydroxyl group. [8] The lithium-based solid electrolyte according to [6] or [7], wherein the lithium salt is a compound represented by formula (1) described later. A method for producing a lithium-based solid electrolyte according to any one of [9], [1] to [8], comprising: step 1 of subjecting a lithium-based oxide containing Li and B to mechanical milling; step 2 of mixing the product obtained in step 1 with water; and step 3 of removing water from the dispersion obtained in step 2 to obtain a lithium-based solid electrolyte, wherein the method satisfies any of the requirements 1 to 3 described later.

[10] The method for producing a lithium-based solid electrolyte according to [9], wherein in step 3, the dispersion obtained in step 2 is dried under conditions of 20 Pa or less and 40°C or less to obtain a lithium-based solid electrolyte.

[11] A method for producing a lithium-based solid electrolyte according to [9] or

[10] , which satisfies requirement 1 above and further comprises step 0, in which a lithium-based oxide containing Li and B is subjected to mechanical milling in an environment in which the lithium salt is absent, prior to step 1 above.

[12] A modified positive electrode active material comprising a positive electrode active material and a coating layer disposed on the positive electrode active material, wherein the coating layer contains a lithium-based solid electrolyte as described in any of [1] to [8].

[13] A modified negative electrode active material comprising a negative electrode active material and a coating layer disposed on the negative electrode active material, wherein the coating layer contains a lithium-based solid electrolyte as described in any of [1] to [8].

[14] An all-solid-state secondary battery comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer in this order, wherein at least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer contains a lithium-based solid electrolyte as described in any of [1] to [8]. An electrode sheet for an all-solid-state secondary battery, comprising a lithium-based solid electrolyte as described in any of

[15] , [1], to [8]. A solid electrolyte sheet containing a lithium-based solid electrolyte as described in any of

[16] , [1], to [8].

[17] An electrode for an all-solid-state secondary battery, comprising an active material and an active material layer containing a lithium-based solid electrolyte as described in any of [1] to [8], and a current collector. [Effects of the Invention]

[0008] According to the present invention, a lithium-based solid electrolyte with excellent ionic conductivity can be provided. Furthermore, according to the present invention, a method for producing a lithium-based solid electrolyte, a modified positive electrode active material, a modified negative electrode active material, an all-solid-state secondary battery, an electrode sheet for an all-solid-state secondary battery, a solid electrolyte sheet, and an electrode for an all-solid-state secondary battery can also be provided. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows an example of an X-ray diffraction pattern to explain requirement α. [Figure 2] Figure 2 shows an example of the reduction two-body distribution function G(r) obtained by X-ray total scattering measurement of a specific lithium tetraborate, which will be described later. [Figure 3] Figure 3 shows an example of the X-ray total scattering profile of a specific lithium tetraborate, which will be discussed later. [Figure 4] Figure 4 shows an example of a structure factor S(Q) based on the total X-ray scattering profile obtained in Figure 3. [Figure 5] Figure 5 shows an example of a Raman spectrum to illustrate requirement δ. [Figure 6] Figure 6 is a conceptual diagram showing the state of water contained in the lithium-based solid electrolyte of the present invention. [Figure 7] Figure 7 shows an example of a spectrum obtained when a solid-state 7Li-NMR (Nuclear Magnetic Resonance) measurement of the first embodiment of the lithium-based solid electrolyte of the present invention is performed at 20°C or 120°C. [Figure 8] Figure 8 shows an example of a spectrum obtained when solid-state 7Li-NMR measurements of lithium tetraborate crystals were performed at 20°C or 120°C. [Figure 9] Figure 9 shows an example of a spectrum obtained when a solid-state 7Li-NMR measurement of the first embodiment of the lithium-based solid electrolyte of the present invention is performed at 20°C. [Figure 10] Figure 10 shows the waveforms separated from the peaks shown in Figure 9. [Figure 11]Figure 11 shows an example of a spectrum obtained by 1H-NMR measurement of the first embodiment of the lithium-based solid electrolyte of the present invention. [Figure 12] Figure 12 shows an example of a Raman spectrum of the first embodiment of the lithium-based solid electrolyte of the present invention. [Figure 13] Figure 13 shows the Raman spectrum of a typical lithium tetraborate crystal. [Figure 14] Figure 14 shows an example of a mapping image obtained by measuring the cross-section of a molded body obtained by molding a second embodiment of the lithium-based solid electrolyte of the present invention using scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX). [Figure 15] Figure 15 shows an example of calculation results based on first-principles molecular dynamics for the lithium-based solid electrolyte of the present invention. [Figure 16] Figure 16 is a schematic cross-sectional view showing an all-solid-state lithium-ion secondary battery according to a preferred embodiment of the present invention. [Figure 17] Figure 17 shows an example of a chart obtained by thermogravimetric differential thermal analysis (TG-DTA) of the lithium-based solid electrolyte of the present invention. [Figure 18] Figure 18 shows an example of a chart obtained by thermogravimetric mass spectrometry (TG-MS) of the lithium-based solid electrolyte of the present invention. [Figure 19] Figure 19 shows an example of a spectrum obtained by 19F-NMR measurement of the lithium-based solid electrolyte of the present invention. [Figure 20] Figure 20 shows the reduced two-body distribution function G(r) obtained from X-ray total scattering measurements of the crystalline powder of Comparative Example 1. [Figure 21] Figure 21 shows the X-ray diffraction pattern of the crystalline powder of Comparative Example 1. [Figure 22] Figure 22 shows the X-ray diffraction pattern of the lithium-based solid electrolyte of Example 4. [Modes for carrying out the invention]

[0010] The present invention will be described in detail below. In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively.

[0011] A key feature of the first embodiment of the lithium-based solid electrolyte of the present invention is that it is used by mixing amorphous lithium tetraborate with predetermined components (a predetermined amount of water and a lithium salt). When amorphous lithium tetraborate and the predetermined components are used together, a soft hydration layer is easily formed on the surface of the lithium tetraborate, and it is presumed that this hydration layer contains a large amount of lithium derived from the lithium salt, resulting in good ionic conductivity. A feature of the second embodiment of the lithium-based solid electrolyte of the present invention is that in the molded body obtained by pressurizing the lithium-based solid electrolyte, the region where the lithium salt is present exists in a network structure. In the above molded body, the region where the lithium salt is present (particularly the region where the lithium salt anion is present) forms a continuous phase, forming a network structure surrounding the lithium tetraborate particles, and is presumed to function as an excellent ion conduction path, resulting in good ion conductivity. The following describes in detail each embodiment of the lithium-based solid electrolyte of the present invention.

[0012] <<First Embodiment>> The first embodiment of the lithium-based solid electrolyte of the present invention (hereinafter also referred to as the "first lithium-based solid electrolyte") comprises amorphous lithium tetraborate, a predetermined amount of water, and a lithium salt. The following provides a detailed description of each component.

[0013] (Amorphous lithium tetraborate) The lithium tetraborate contained in the first lithium-based solid electrolyte is usually a compound represented as Li2B4O7, and is mainly composed of Li, B, and O, but in the present invention, it may deviate from the above standard value. More specifically, as lithium tetraborate, Li 2+x B 4+y O 7+zA compound represented by (-0.3 < x < 0.3, -0.3 < y < 0.3, -0.3 < z < 0.3) is preferred. Moreover, lithium tetraborate contained in the first lithium-based solid electrolyte is in an amorphous state. Amorphous lithium tetraborate (hereinafter also referred to as "specific lithium tetraborate") means lithium tetraborate that satisfies the following requirement α.

[0014] Requirement α: In the X-ray diffraction pattern obtained from X-ray diffraction measurement using the CuKα ray of amorphous lithium tetraborate, there is no peak top in the range of 21.6 to 22.0° with a full width at half maximum of 0.65° or less, no peak top in the range of 2,5.4 to 25.8° with a full width at half maximum of 0.65° or less, no peak top in the range of 33.4 to 33.8° with a full width at half maximum of 0.65° or less, and no peak top in the range of 34.4 to 34.8° with a full width at half maximum of 0.65° or less, or In the X-ray diffraction pattern, when at least one specific peak selected from the group consisting of the first peak, the second peak, the third peak, and the fourth peak exists, the intensity ratio calculated by at least one of the following intensity measurement methods for the specific peak is 5.0 or less. Intensity measurement method: Calculate the average intensity 1 in the range of +0.45° to +0.55° from the diffraction angle 2θ of the peak top of the specific peak, calculate the average intensity 2 in the range of -0.55° to -0.45° from the diffraction angle -0.55° to -0.45° of the peak top of the specific peak, calculate the additive average value of the average intensity 1 and the average intensity 2, and use the ratio of the peak intensity at the peak top of the specific peak to the additive average value as the intensity ratio.

[0015] Specific lithium tetraborate may further separately satisfy the following requirement β. Requirement β: In the reduced pair distribution function G(r) obtained from the X-ray total scattering measurement of specific lithium tetraborate, there are a first peak with a peak top located in the range of r = 1.43 ± 0.2 Å and a second peak with a peak top located in the range of r = 2.40 ± 0.2 Å. The G(r) at the peak top of the first peak shows a value exceeding 1.0, and the G(r) at the peak top of the second peak shows a value of 0.8 or more. It is preferable that the specific lithium tetraborate satisfies the above requirement β. That is, it is preferable that the lithium tetraborate contained in the first lithium-based solid electrolyte satisfies the above requirement α and also satisfies the above requirement β.

[0016] The specific lithium tetraborate may further separately satisfy at least one of the following requirement γ and requirement δ. It is preferable that the specific lithium tetraborate satisfies at least one of the above requirement γ and requirement δ. That is, it is more preferable that the lithium tetraborate contained in the first lithium-based solid electrolyte satisfies the above requirement α, satisfies the above requirement β, and satisfies at least one of the above requirement γ and requirement δ.

[0017] Requirement γ: In the reduced pair distribution function G(r) obtained from the X-ray total scattering measurement of specific lithium tetraborate, the absolute value of G(r) is less than 1.0 in the range where r is more than 5 Å and 10 Å or less.

[0018] Requirement δ: In the Raman spectrum of amorphous lithium tetraborate, there is no peak top at 710 - 730 cm[[ID=XX]] -1 [[ID=XX]]has a peak top, and a full width at half maximum of 5 cm[[ID=XX]] -1 [[ID=XX]]or more for the first peak, no peak top at 770 - 790 cm[[ID=XX]] -1 [[ID=XX]]has a peak top, and a full width at half maximum of 5 cm[[ID=XX]] -1 [[ID=XX]]or more for the second peak, and no peak top at 1020 - 1040 cm[[ID=XX]] -1 [[ID=XX]]has a peak top, and a full width at half maximum of 5 cm[[ID=XX]] -1 [[ID=XX]]or more for the third peak, or In the above Raman spectrum, if there is at least one specific peak selected from the group consisting of the first peak, the second peak, and the third peak, the intensity ratio calculated by the following intensity measurement method for at least one of the specific peaks is 5.0 or less. Intensity measurement method: 400-600 cm² of the Raman spectrum shown above. -1 The point showing the minimum value M1 of Raman intensity in the wavenumber region, and the above Raman spectrum at 1300-1500 cm⁻¹ -1 A straight line is obtained by connecting the point showing the minimum value M2 of the Raman intensity in the wavenumber region, and within the region from the wavenumber showing the minimum value M1 to the wavenumber showing the minimum value M2, 710 to 730 cm² -1 770-790cm -1 , and 1020~1040cm -1 The average difference between the Raman intensity of the above line and the Raman intensity of the Raman spectrum at each wavenumber in the region outside the specified region is calculated. The absolute difference between the Raman intensity of the above peak and the Raman intensity of the above line at the wavenumber that shows the peak top of the specific peak is calculated, and the ratio of the absolute value of the above difference to the average difference is defined as the intensity ratio.

[0019] -Requirement α- The following explains requirement α. First, requirement α is satisfied if, in the X-ray diffraction pattern obtained from X-ray diffraction measurements using CuKα radiation of a specific lithium tetraborate, none of the following are present: a first peak with its peak top located in the range of 21.6-22.0° and a full width at half maximum (FMAX) of 0.65° or less; a second peak with its peak top located in the range of 25.4-25.8° and a FMAX of 0.65° or less; a third peak with its peak top located in the range of 33.4-33.8° and a FMAX of 0.65° or less; and a fourth peak with its peak top located in the range of 34.4-34.8° and a FMAX of 0.65° or less. The full width at half maximum (FWHM) of a peak refers to the width (°) at the point where the peak intensity is half.

[0020] Furthermore, if the X-ray diffraction pattern obtained from X-ray diffraction measurements using CuKα rays of a specific lithium tetraborate contains at least one specific peak selected from the group consisting of a first peak, a second peak, a third peak, and a fourth peak, and the intensity ratio calculated by the intensity measurement method described later for at least one of the specific peaks is 5.0 or less, then requirement α is also satisfied.

[0021] The strength measurement method is explained below in Figure 1. Figure 1 shows an example of a specific peak appearing in the diffraction pattern obtained from X-ray diffraction measurements using CuKα radiation of a specific lithium tetraborate. In the diffraction pattern shown in Figure 1, a specific peak with a peak top intensity of intensity 1 is shown. In the intensity measurement method, as shown in Figure 1, the average intensity 1 is calculated in the range of +0.45° to +0.55° from the diffraction angle 2θ of the peak top of the specific peak, and then the average intensity 2 is calculated in the range of -0.55° to -0.45° from the diffraction angle 2θ of the peak top of the specific peak. Next, the average value of average intensity 1 and average intensity 2 is calculated, and the ratio of intensity 1 to the average value is determined as the intensity ratio. If the above requirement α is met, it means that the lithium tetraborate contains no or very little crystalline structure, and is in an amorphous state. In other words, the first to fourth peaks described in requirement α are mainly peaks originating from the crystal structure in the specific lithium tetraborate. If these peaks are absent, it is presumed that the specific lithium tetraborate lacks the predetermined crystal structure and is in an amorphous state, thus making it easier to form a hydrate layer with excellent ion conductivity, as described above. Furthermore, even if at least one of the first to fourth peaks is present, if the intensity ratio of any one of the present specific peaks is below a predetermined value, it indicates that the specific lithium tetraborate has almost no crystal structure, and as described above, it is presumed that it is easier to form a hydrate layer with excellent ion conductivity. In addition, in the specific lithium tetraborate, peaks may occur due to factors other than those originating from predetermined regular structures such as the crystal structure of lithium tetraborate. Other factors include, for example, peaks originating from regular structures within impurities, and such peaks may overlap with the first to fourth peaks described above. When an amorphous state is achieved that is presumed to allow the formation of a hydrate layer with excellent ionic conductivity, all of the first to fourth peaks often decrease. Even if, as mentioned above, a peak due to other factors happens to overlap with one of the first to fourth peaks, resulting in the appearance of a single large peak, the existence of a specific peak with an intensity ratio below a predetermined value indicates that the specific lithium tetraborate is in an amorphous state that is presumed to allow the formation of a hydrate layer with excellent ionic conductivity.

[0022] The above X-ray diffraction measurement was performed using CuKα radiation under measurement conditions of 0.01° / step and 3° / min.

[0023] Regarding the above requirement α, in the X-ray diffraction pattern obtained from X-ray diffraction measurements using CuKα rays of a specific lithium tetraborate, it is more preferable that the intensity ratio of at least one of the specific peaks is 3.0 or less, either because the first, second, third, and fourth peaks are absent, or because a specific peak selected from the group consisting of the first, second, third, and fourth peaks is present. In particular, it is even more preferable that the intensity ratio of at least one of the specific peaks is 2.0 or less, either because the first, second, third, and fourth peaks are absent, or because a specific peak selected from the group consisting of the first, second, third, and fourth peaks is present.

[0024] Furthermore, in the above X-ray diffraction pattern for requirement α, 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 determination of requirement α is made. Furthermore, in the above X-ray diffraction pattern for requirement α, 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 determination of requirement α is made. Furthermore, in the above X-ray diffraction pattern for requirement α, 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 determination of requirement α is made. Furthermore, in the above X-ray diffraction pattern for requirement α, 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 determination of requirement α is made.

[0025] -Requirement β- Requirement β will be explained using Figures 2 to 4. Figure 2 shows an example of a reduction two-body distribution function G(r) obtained by X-ray total scattering measurements of a specific lithium tetraborate. The vertical axis in Figure 2 represents the reduction two-body 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 measurements will be performed at SPring-8 BL04B2 (acceleration voltage 61.4 keV, wavelength 0.2019 Å). Furthermore, the reduced two-body distribution function G(r) is obtained by transforming the scattering intensity I obtained from the experiment using the following procedure. First, scattering intensity I obs It is expressed by equation (1). Also, the structure factor S(Q) is I coh It is obtained by dividing it by the product of the number of atoms N and the atomic scattering factor f. I obs =I coh +I incoh +I 蛍光 (1)

[0026]

number

[0027] PDF (Pair Distribution Function) analysis requires the use of a structure factor S(Q). In equation (2) above, the required intensity is coherent scattering I coh That is all. Incoherent scattering I incoh and X-ray 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 this. An example of the total scattering measurement results and extracted structure factor S(Q) for specific lithium tetraborate is shown in Figures 3 and 4. Coherent scattering is represented by Debye's scattering equation (3) (N: total number of atoms, f: atomic scattering factor, r ij (Interatomic distance between atoms at :ij).

[0028]

number

[0029] 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) can be expressed as equation (4).

[0030]

number

[0031] Letting the average atomic density be ρ0, equation (4) can be rearranged to obtain equation (5).

[0032]

number

[0033] From equation (5) and equation (2), we obtain equation (6).

[0034]

number

[0035] The two-body distribution function g(r) is given by equation (7).

[0036]

number

[0037] From equations (6) and (7) above, equation (8) is obtained.

[0038]

number

[0039] 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 2). 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.

[0040] In requirement β, as shown in Figure 2, the reduced dibody distribution function G(r) obtained from X-ray total scattering measurement 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 other words, in the reduction dibody distribution function G(r) obtained from the X-ray total scattering measurement of specific lithium tetraborate, a first peak is observed where the G(r) of the peak top (hereinafter also referred to as the "first peak top") is greater than 1.0 and the first peak top is located in the range of 1.43 ± 0.2 Å, and a second peak is observed where the G(r) of the peak top (hereinafter also referred to as the "second peak top") is greater than 0.8 and the second peak top is located in the range of 2.40 ± 0.2 Å. In Figure 2, 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. Near 1.43 Å, there is a peak attributed to the B (boron)-O (oxygen) interatomic distance. Near 2.40 Å, there are peaks attributed to the B (boron)-B (boron) and O (oxygen)-O (oxygen) interatomic distances. In other words, the observation of these two peaks (the first and second peaks) means that a periodic structure corresponding to these two interatomic distances exists in the specific lithium tetraborate. Note that the BO interatomic distance represents the distance between chemically bonded B and O atoms, the BB interatomic distance represents the distance between adjacent B atoms, and the OO interatomic distance represents the distance between adjacent O atoms. Specific lithium tetraborate that satisfies the above requirement γ is thought to have a short-range ordered structure related to the interatomic distances of BO, BB, and OO.

[0041] -Requirements γ- The above requirement γ will be explained below. The reduction dibody distribution function G(r) obtained by X-ray total scattering measurement of specific lithium tetraborate in requirement γ is the same as that for requirement β above. In requirement γ, as shown in Figure 2, the absolute value of G(r) is less than 1.0 (corresponding to the dashed line) 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 is almost no long-range ordered structure in the specific lithium tetraborate. Therefore, if the specific lithium tetraborate satisfies requirement β, the specific lithium tetraborate itself exhibits elastic properties that make it easily plastically deformable.

[0042] Furthermore, in the reduction dibody distribution function G(r) obtained from X-ray total scattering measurements of specific lithium tetraborate, peaks other than the first and second peaks may be present in the range where r is 5 Å or less.

[0043] -Requirement δ- The above requirement δ will be explained below. First, in the Raman spectrum of specific lithium tetraborate, 710-730 cm⁻¹ -1It has a peak top and a full width at half maximum of 5 cm. -1 The first peak, as described above, is 770-790 cm. -1 It has a peak top and a full width at half maximum of 5 cm. -1 The second peak mentioned above, and 1020-1040cm -1 It has a peak top and a full width at half maximum of 5 cm. -1 If none of the above third peaks exist, then requirement δ is satisfied. Note that the full width at half maximum of the peak is the width at half the peak height (cm). -1 ) means.

[0044] Furthermore, if the Raman spectrum of a specific lithium tetraborate contains at least one specific peak selected from the group consisting of a first peak, a second peak, and a third peak, requirement T is also satisfied if the intensity ratio calculated by the following intensity measurement method for at least one of the specific peaks is 5.0 or less. In particular, it is preferable that the above intensity ratio is satisfied for all of the specific peaks. The method for measuring strength is explained below in Figure 5. Figure 5 shows an example of a Raman spectrum of a specific lithium tetraborate, with the vertical axis representing Raman intensity and the horizontal axis representing Raman shift. For clarity, Figure 5 shows an example with a single specific peak. In the intensity measurement method, first, the Raman spectrum of a specific lithium tetraborate is measured at 400-600 cm⁻¹. -1 The point showing the minimum value M1 of Raman intensity in the wavenumber region, and the above Raman spectrum at 1300-1500 cm⁻¹ -1 A straight line is obtained by connecting the point showing the minimum value M2 of the Raman intensity in the wavenumber region. Specifically, as shown in Figure 5, a straight line shown by the dashed line is obtained by connecting point P1 showing the minimum value M1 and point P2 showing the minimum value M2. Next, within the region from the wavenumber showing the minimum value M1 (W1 in Figure 5) to the wavenumber showing the minimum value M2 (W2 in Figure 5), we consider the range from 710 to 730 cm². -1 770-790cm -1 , and 1020~1040cm -1The average difference between the Raman intensity of the above line and the Raman intensity of the Raman spectrum at each wavenumber in the region other than the specified region (hereinafter also referred to as the "specific region") is calculated. The above average difference is calculated from the 2cm distance between W1 and W2 in the specified region. -1 This is calculated by determining the absolute difference between the Raman intensity of the line and the Raman intensity of the Raman spectrum at each wavenumber, and then averaging the absolute values ​​of these differences. Next, the absolute value of the difference between the Raman intensity of the peak at the wavenumber indicating the peak top of the specific peak and the Raman intensity of the straight line is calculated, and the ratio of the absolute value of this difference to the average difference is calculated as the intensity ratio. More specifically, as shown in Figure 5, the absolute value of the difference (|S1-S2|) between the Raman intensity S1 of the peak at wavenumber W3 indicating the peak top and the Raman intensity S2 of the straight line at wavenumber W3 is calculated, and it is checked whether the absolute value of the obtained difference is 5.0 times or less of the average difference.

[0045] If the above requirement δ is met, it means that the lithium tetraborate contains no or very little crystalline structure, and is in an amorphous state. In other words, the first to third peaks described in requirement δ are peaks mainly derived from the crystal structure in the specific lithium tetraborate. If these peaks are absent, it is presumed that the specific lithium tetraborate lacks the predetermined crystal structure and is in an amorphous state, thus making it easier to form a hydrate layer with excellent ion conductivity, as described above. Furthermore, even if at least one of the first to third peaks is present, if the intensity ratio of any one of the present specific peaks is below a predetermined value, it indicates that the specific lithium tetraborate has almost no crystal structure, and as described above, it is presumed that it is easier to form a hydrate layer with excellent ion conductivity. In addition, in the specific lithium tetraborate, peaks may occur due to factors other than those derived from predetermined regular structures such as the crystal structure of lithium tetraborate. Other factors include, for example, peaks derived from regular structures within impurities, and such peaks may overlap with the first to third peaks described above. When an amorphous state is achieved that is presumed to allow the formation of a hydrate layer with excellent ionic conductivity, all of the first to third peaks often decrease. Even if, as mentioned above, a peak due to other factors happens to overlap with one of the first to third peaks, resulting in the appearance of a single large peak, the existence of a specific peak with an intensity ratio below a predetermined value indicates that the specific lithium tetraborate is in an amorphous state that is presumed to allow the formation of a hydrate layer with excellent ionic conductivity.

[0046] In the Raman spectrum of the specified lithium tetraborate described above, if the first, second, and third peaks are absent, or if a specific peak selected from the group consisting of the first, second, and third peaks is present, it is more preferable that the intensity ratio of at least one of the specific peaks is 3.0 or less. In particular, if the first, second, and third peaks are absent, or if a specific peak selected from the group consisting of the first, second, and third peaks is present, it is even more preferable that the intensity ratio of at least one of the specific peaks is 2.0 or less, and it is especially preferable that the first peak, second peak, and third peak are absent.

[0047] Furthermore, Raman imaging will be performed as the method for measuring the Raman spectrum. Raman imaging is a microspectroscopy technique that combines Raman spectroscopy with microscopy techniques. Specifically, it is a technique that detects measurement light containing Raman scattered light by scanning excitation light on the sample, and visualizes the distribution of components based on the intensity of the measurement light. The Raman imaging measurement conditions are as follows: 27°C, air, excitation light of 532 nm, objective lens of 100x, point scanning mapping method, 1 μm step, exposure time per point of 1 second, number of integrations of 1, and measurement range of 70 μm × 50 μm. However, the measurement range may be narrower depending on the film thickness of the sample. Furthermore, the Raman spectrum data is subjected to principal component analysis (PCA) to remove noise. Specifically, in the PCA process, the spectrum is recombined using components with an autocorrelation coefficient of 0.6 or higher.

[0048] The bulk modulus of the specific lithium tetraborate is not particularly limited, but is preferably 45 GPa or less, and more preferably 40 GPa or less, in terms of superior effects of the present invention. The lower limit is not particularly limited, but is preferably 5 GPa or more. The above measurement of bulk modulus is performed using the ultrasonic attenuation method. Specifically, first, a suspension is prepared by suspending specific lithium tetraborate in pure water. The content of specific lithium tetraborate in the suspension is set to 1.2% by mass relative to the total mass of the suspension. Next, the ultrasonic attenuation spectrum of the above suspension is measured, and the bulk modulus of specific lithium tetraborate is determined by fitting using the scattering attenuation theory formula. When performing the above fitting, the particle size distribution, density (2.3 g / ml), and Poisson's ratio (0.12) of specific lithium tetraborate are used. For fitting using the above scattering decay theory formula, the bulk modulus is calculated using equations (7), (12), and (13) described in Kohjiro Kubo et al., Ultrasonics 62 (2015) 186-194. Furthermore, the particle size distribution of specific lithium tetraborate is obtained by acquiring particle images using a flow-type particle image analysis method, and then obtaining a histogram (particle size distribution) of the particle diameter of specific lithium tetraborate. The above particle diameter corresponds to the equivalent diameter of a circle.

[0049] The median diameter (D50) of the specific lithium tetraborate is not particularly limited, but 0.01 to 20 μm is preferred, and 0.1 to 2.0 μm is more preferred, in terms of achieving superior effects of the present invention. The above median diameter (D50) was measured by acquiring particle images using flow-type particle image analysis, calculating the particle size distribution of specific lithium tetraborate, and analyzing the obtained distribution. The above particle size corresponds to the equivalent diameter of a circle.

[0050] For superior effects of the present invention, it is preferable that the specific lithium tetraborate has an O (oxygen)-H (hydrogen) structure. The OH structure exists as a hydroxyl group or as a substructure of a water molecule. Based on X-ray total scattering measurements, specific lithium tetraborate in an amorphous state is thought to maintain a BO3-BO4 linked structure (diborate structure) as shown in the structural formula below. Therefore, if specific lithium tetraborate has a hydroxyl group, it is presumed that the hydroxyl group is bonded to one of the boron atoms located around the structural formula below, forming a substructure called "B-OH". It is also presumed that water molecules are present in the hydration layer formed at the interface of the specific lithium tetraborate particles. It is presumed that one or both of these OH structures contribute to the good conductivity of Li ions. Furthermore, the presence of an OH structure in a specific lithium tetraborate can be confirmed by measuring the infrared absorption spectrum of the first lithium-based solid electrolyte, as will be described later.

[0051] [ka]

[0052] The content of specific lithium tetraborate in the first lithium-based solid electrolyte is not particularly limited, but is, for example, 80% by mass or less, preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less, particularly preferably 30% by mass or less, and most preferably 25% by mass or less, relative to the total mass of the first lithium-based solid electrolyte. Furthermore, the lower limit of the content of specific lithium tetraborate is not particularly limited, but is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more, relative to the total mass of the lithium-based solid electrolyte.

[0053] The method for producing specific lithium tetraborate will be described in detail later, but it is preferable that it be produced by a manufacturing method that includes mechanical milling. An example of the mechanical milling treatment performed on lithium tetraborate is the mechanical milling treatment performed in step 1A described later, and the details will be described later. It is hypothesized that mechanical milling of lithium tetraborate can make it amorphous, thereby facilitating the formation of a hydrated layer with excellent ionic conductivity.

[0054] (water) The first lithium-based solid electrolyte contains water. Furthermore, the water content in the first lithium-based solid electrolyte is 45% by mass or less relative to the total mass of the lithium-based solid electrolyte. A first lithium-based solid electrolyte containing water with the above water content is in a solid state and allows ions to move within it. In addition, it is presumed that a first lithium-based solid electrolyte containing water with the above water content will have excellent ionic conductivity because a hydration layer will be formed that functions as an ion conduction path, allowing Li ions and other elements to move. Furthermore, it is hypothesized that if highly polar water is included in the first lithium-based solid electrolyte, the water and lithium salt interact, making it easier for Li and anions to dissociate, thereby improving the conductivity of Li ions. It is also possible that some of the water dissociates and binds to its surroundings in the form of hydroxyl groups. The water content in the first lithium-based solid electrolyte is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less, relative to the total mass of the lithium-based solid electrolyte. While there is no particular lower limit to the water content, it is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more, relative to the total mass of the lithium-based solid electrolyte.

[0055] Furthermore, in terms of achieving superior effects of the present invention, the molar ratio of water to specific lithium tetraborate in the first lithium-based solid electrolyte (moles of water / molars of specific lithium tetraborate) is preferably 1 to 12, and more preferably 1 to 10. In some cases, the above molar ratio of water to specific lithium tetraborate is more preferably 2 to 12. The above molar ratio of water to specific lithium tetraborate is even more preferably 2 to 10, even more preferably 2 to 8, particularly preferably 2 to 7, and most preferably 3 to 7.

[0056] The water content and molar amount in a first-lithium solid electrolyte can be determined using known methods. For example, as described later, the content of various elements in the first-lithium solid electrolyte can be identified by the elemental analysis methods described later, and the water content and molar amount can be determined from the structure of the compound used.

[0057] The state of water contained in the first lithium-based solid electrolyte will be explained. As shown conceptually in Figure 6, the water contained in the first lithium-based solid electrolyte can be classified as follows, depending on whether or not it desorbs (vaporizes) from the first lithium-based solid electrolyte when dried under predetermined conditions. Water in its first state: It vaporizes when dried under atmospheric pressure and 100°C conditions (first condition). Water in the second state: It does not vaporize when dried under the first condition, but it vaporizes when dried under the conditions of 20 Pa and 40°C (second condition). Water in the third state: It does not vaporize when dried under the first and second conditions, but it vaporizes when dried under the conditions of 20 Pa and 100°C (third condition). Water in state 4: Does not evaporate under any of the drying conditions 1 through 3. Furthermore, the detachment of water from the first lithium-based solid electrolyte also includes cases where water is constrained by its surroundings, and detaches from the first lithium-based solid electrolyte when those constraints are relaxed.

[0058] When using the first lithium-based solid electrolyte in a battery, it is preferable from the viewpoint of battery characteristics that the first lithium-based solid electrolyte does not contain water in the first state or water in the second state. However, when a molded body obtained by pressurizing the first lithium-based solid electrolyte is used in a battery, water in the second state may be present. Furthermore, when using the first lithium-based solid electrolyte in a battery, it is preferable that the first lithium-based solid electrolyte contains water in the third state described above, from the viewpoint of having a good balance between ionic conductivity and cycle characteristics.

[0059] (Lithium salt) The first lithium-based solid electrolyte contains a lithium salt. The type of lithium salt is not particularly limited, and examples of lithium salts are given in step 1A, which will be described in detail later. The content of lithium salt in the first lithium-based solid electrolyte is not particularly limited. In the first lithium-based solid electrolyte, the mass ratio of the lithium salt content to the content of the specified lithium tetraborate (mass of lithium salt content / mass of specified lithium tetraborate content) is not particularly limited. In particular, in terms of achieving superior effects of the present invention, the molar ratio of the lithium salt to the specified lithium tetraborate (moles of lithium salt / molars of specified lithium tetraborate) in the first lithium-based solid electrolyte is preferably 0.001 to 1.5, more preferably 0.001 to 1.2, even more preferably 0.01 to 1.2, even more preferably 0.1 to 1.2, particularly preferably 0.3 to 1.2, extremely preferably 0.5 to 1.2, and most preferably 0.5 to 1.0.

[0060] The first lithium-based solid electrolyte contains specific lithium tetraborate and therefore contains the elements Li, B, and O. Furthermore, the first lithium-based solid electrolyte preferably contains one or more specific elements selected from the group consisting of Group 4, Group 15, Group 16, Group 17 elements of the periodic table, Si, C, Sc, and Y, and more preferably contains two or more specific elements. In addition, for superior effects of the present invention, the first lithium-based solid electrolyte preferably contains one or more (more preferably two or more) specific elements selected from the group consisting of F, Cl, Br, I, S, P, Si, Se, Te, C, Sb, As, Sc, Y, Zr, Ti, Hf, and N. The elements of Group 4 of the periodic table include Ti, Zr, Hr, 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 number of specific elements contained in the first lithium-based solid electrolyte may be three or more. In particular, in terms of achieving superior effects of the present invention, it is preferable that the number of specific elements contained in the lithium-based solid electrolyte be two or more, more preferably two to five, and even more preferably two to four. The first lithium-based solid electrolyte preferably contains two or more specific elements selected from the group consisting of F, S, N, P, C, Cl, and I, more preferably contains two or more specific elements selected from the group consisting of F, S, C, and N, and even more preferably contains three specific elements: F, S, and N. The specific elements mentioned above often originate from elements found in lithium salts, for example.

[0061] In the first lithium-based solid electrolyte, when the molar amount of B in the lithium-based solid electrolyte is set to 4.00 and the molar amount of Li is expressed accordingly, it is preferable that the molar amount of Li be between 1.58 and 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 be between 1.58 and 3.49. In particular, in terms of the superior effects of the present invention, when the molar amount of B in a lithium-based solid electrolyte is set to 4.00 and the molar amount of Li is expressed as such, the molar amount of Li is more preferably 1.58 to 3.00, even more preferably 1.90 to 3.00, even more preferably 2.00 to 3.00, especially preferably 2.30 to 3.00, and most preferably 2.50 to 3.00.

[0062] In the first lithium-based solid electrolyte, when the molar amount of B in the lithium-based solid electrolyte is set to 4.00 and the molar amount of O is expressed as such, it is preferable that the molar amount of O is between 6.23 and 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 between 6.23 and 25.00. In particular, in terms of the superior effects of the present invention, when the molar amount of B in the lithium-based solid electrolyte is set to 4.00 and the molar amount of O is expressed as such, the molar amount of O is more preferably 8.00 to 23.00, even more preferably 10.00 to 23.00, and particularly preferably 10.00 to 17.00.

[0063] In the first lithium-based solid electrolyte, when the molar amount of B in the lithium-based solid electrolyte is set to 4.00 and the molar amount of a specific element is expressed, it is preferable that the molar amount of each specific element is 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 specific element are between 0.001 and 10.00. In particular, in terms of the superior effects of the present invention, when the molar amount of B in a lithium-based solid electrolyte is set to 4.00 and the molar amount of a specific element is expressed, the molar amounts of each specific element are more preferably 0.001 to 6.0, even more preferably 0.01 to 5.0, even more preferably 0.01 to 4.0, particularly preferably 0.01 to 3.0, and most preferably 0.01 to 2.0. As described above, it is preferable that the first lithium-based solid electrolyte contains two or more specific elements. For example, if the first lithium-based solid electrolyte contains two specific elements, specific element A and specific element B which is a different type of element from specific element A, then when the molar amount of B in the lithium-based solid electrolyte is 4.00, the molar amounts of specific element A and specific element B are each 0.001 to 10.00. Also, for example, if the first lithium-based solid electrolyte contains three specific elements, specific element A, specific element B which is a different type of element from specific element A, and specific element C which is a different type of element from specific elements A and B, then when the molar amount of B in the lithium-based solid electrolyte is 4.00, the molar amounts of specific element A, specific element B, and specific element C are each 0.001 to 10.00.

[0064] The molar ratios and content of each component in the first lithium-based solid electrolyte can be determined using known methods. For example, the content of various elements in the first lithium-based solid electrolyte can be identified, and the molar ratios and content of each component can be determined from the structure of the compound used. As for elemental analysis methods, for example, Na and B can be analyzed by ICP-OES (Inductively coupled plasma optical emission spectrometry), N can be analyzed by the inert gas fusion method, and F and S can be analyzed by combustion ion chromatography. For O, the analytical masses of elements other than O can be added together and calculated as the difference from the total powder amount. Note that the method for calculating the content of each element is not limited to the above, and the content of other elements can be estimated from the analytical results of one element, taking into account the structure of the compound used.

[0065] (Characteristics of lithium-based solid electrolytes) ·TG-MS measurement A more advantageous aspect of the present invention is that, when thermogravimetric mass spectrometry (TG-MS) is performed on a molded body obtained by pressurizing the first lithium-based solid electrolyte, it is preferable that a component with a molecular weight of 18 is detected in the temperature range above 100°C, and more preferably that a component with a molecular weight of 18 is detected in the temperature range above 120°C. When TG-MS results for molded lithium-based solid electrolytes detect a component with a molecular weight of 18 in the temperature range above 100°C, it is presumed that water (particularly water in the third and fourth states described above) is present in the lithium-based solid electrolyte. The water present in the lithium-based solid electrolyte (particularly water in the third and fourth states described above) is thought to contribute to the ionic conductivity. The TG-MS measurement method for molded lithium-based solid electrolytes will be described in detail in the examples below.

[0066] · 7 Li-NMR measurement The present invention offers superior effects, particularly in the solid of the first lithium-based solid electrolyte. 7 The solid lithium-based solid electrolyte is defined as the solid of the first lithium-based solid electrolyte, with respect to the full width at half maximum of the peaks in the spectrum obtained when the chemical shift in the spectrum is in the range of -100 to +100 ppm, as measured by Li-NMR at 20°C. 7 When Li-NMR measurements are performed at 120°C, the ratio of the full width at half maximum (FMAX) of peaks appearing in the chemical shift range of -100 to +100 ppm in the obtained spectrum 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 full width at half maximum (FWHM) of a peak refers to the width (ppm) at half the peak height (H / 2).

[0067] The above characteristics will be explained below using Figure 7. Figure 7 shows the solid of the first lithium-based solid electrolyte. 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 shown at the bottom of Figure 7 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 7 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 is high, the resulting peaks are sharper. In the embodiment shown in Figure 7, when comparing the spectrum at 20°C and the spectrum at 120°C, the spectrum at 120°C is sharper. In other words, in the lithium-based solid electrolyte shown in Figure 7, Li + This indicates that the mobility of is increased. Such lithium-based solid electrolytes, due to their amorphous structure, become more easily plastically deformable, and Li + It is believed that the effects of the present invention are further enhanced by the superior hopping properties. For example, regarding lithium tetraborate crystals, solid 7 When Li-NMR measurements are performed at 20°C or 120°C, the spectrum measured at 20°C, shown as a solid line in the lower part of Figure 8, and the spectrum measured at 120°C, shown as a dashed line in the upper part of Figure 8, tend to have approximately the same shape.

[0068] The above solid 7 The Li-NMR measurement conditions are as follows: Specifically, measurements are performed using a 4mm HX CP-MAS probe with a single-pulse method, 90° pulse width: 3.2μs, observation frequency: 155.546MHz, observation width: 1397.6ppm, repetition time: 15sec, integration: 1, and MAS rotation speed: 0Hz.

[0069] Furthermore, the first lithium-based solid electrolyte offers superior effects. 7When a Li-NMR measurement is performed at 20°C, the spectrum obtained is preferably obtained by waveform separation of the first peak appearing in the range of -100 to +100 ppm, and a second peak with a full width at half maximum of 5 ppm or less is present in the chemical shift range of -3 to 3 ppm, and the ratio of the area intensity of the second peak to the area intensity of the first peak is preferably 0.5% or more. The above area intensity ratio is more preferably 2% or more, and even more preferably 15% or more. There is no particular upper limit to the above area intensity ratio, but it is often 50% or less.

[0070] The above characteristics will be explained below using Figures 9 and 10. Figure 9 shows the solid of the first lithium-based solid electrolyte. 7 An example of a spectrum obtained when Li-NMR measurement is performed at 20°C is shown. As shown in Figure 9, in the first lithium-based solid electrolyte, a peak (corresponding to the first peak) is observed in the range of -100 to +100 ppm, and within this first peak, a small peak is observed near the chemical shift of 0 ppm, as enclosed by a dashed line. 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 10 shows the waveform separation of the first peak. As shown in Figure 10, 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. In the first lithium-based solid electrolyte, the ratio of the area intensity of the second peak (represented by the solid line in Figure 10) to the area intensity of the first peak (the peak before waveform separation) shown in Figure 9, {(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.

[0071] · 1 H-NMR measurement The present invention offers superior effects compared to the first lithium-based solid electrolyte. 1 It is preferable that the chemical shift in the spectrum obtained by 1H-NMR measurement shows both sharp and broad peaks in the range of -200 to +200 ppm. A "sharp peak" refers to a peak with a full width at half maximum of 50 ppm or less, while a "broad peak" refers to a peak with a full width at half maximum of 50 ppm or more. The above characteristics will be explained below using Figure 11. In Figure 11, the first lithium-based solid electrolyte is subjected to 20°C. 1 An example of a spectrum obtained by 1H-NMR measurement is shown. Generally, 1 In 1H-NMR measurements, sharper peaks are obtained when hydrogen atoms have high mobility. In the spectrum shown in Figure 11, a peak appears that is a combination of a sharp peak and a broad peak. In other words, in the lithium-based solid electrolyte shown in Figure 11, there are hydrogen atoms with relatively high mobility corresponding to the sharp peak and hydrogen atoms with relatively low mobility corresponding to the broad peak. It is presumed that these relatively mobile hydrogen atoms in lithium-based solid electrolytes are contained in the hydration layer described above and are involved in the conduction of lithium ions. For example, regarding lithium tetraborate crystals, 1 When 1H-NMR measurements are performed at 20°C, sharp peaks do not appear in the chemical shift range of -200 to +200 ppm, and only broad peaks tend to appear.

[0072] the above 1 The H-NMR measurement conditions are as follows: Specifically, measurements were performed using a 4mm HX CP-MAS probe at a measurement temperature of 20°C, using the composite pulse method, with a 90° pulse width of 2.5 μs, an observation frequency of 400.23092 MHz, an observation width of 694.043 ppm, a repetition time of 20 sec, 16 integration cycles, and a MAS rotation speed of 0 Hz.

[0073] · 19 F-NMR measurement A more advantageous aspect of the present invention is that when the lithium salt contains a fluorine atom, the first lithium-based solid electrolyte 19 It is preferable that the spectrum obtained by F-NMR measurement shows a sharp peak with a chemical shift in the range of -200 to +300 ppm and a full width at half maximum of 20 ppm or less. While lithium salts or lithium salt anions are thought to contribute to ionic conductivity, the appearance of sharp peaks in the above range in lithium-based solid electrolytes suggests that the mobility of these lithium salts or lithium salt anions is relatively high.

[0074] the above 19 The F-NMR measurement conditions are as follows: Specifically, measurements are performed using a 4mm HXCP-MAS probe with a single-pulse method, 90° pulse width: 3.5μs, observation frequency: 376.59246MHz, observation width: 603.497ppm, repetition time: 10sec, integration: 1, and MAS rotation speed: 0Hz.

[0075] TG-DTA measurement In terms of superior effects of the present invention, it is preferable that the mass loss rate when the first lithium-based solid electrolyte is heated to 800°C is 20 to 40% by mass. In particular, in terms of superior effects of the present invention, a mass loss rate of 25 to 35% by mass is more preferable. The mass reduction of the first lithium-based solid electrolyte that occurs during the heating process described above is thought to be due to the removal of some of the water contained in the lithium-based solid electrolyte. The fact that it exhibits a predetermined mass reduction rate as described above indicates that the lithium-based solid electrolyte contains a predetermined amount of water, and it is thought that the conductivity of lithium ions is improved by the presence of this predetermined amount of water. When performing the above heat treatment, the material should be heated at a heating rate of 20°C / second within the range of 25°C to 800°C. A known thermogravimetric differential thermal analysis (TG-DTA) instrument can be used for measurement. The above mass reduction rate is calculated by {(mass at 25°C - mass at 800°C) / mass at 25°C} × 100. Furthermore, in order to carry out the above heat treatment, the first lithium-based solid electrolyte is vacuum-dried at 40°C for 2 hours, and then measured under atmospheric conditions.

[0076] Ionic conductivity A further advantage of the present invention is that the ionic conductivity at -10°C of the molded body obtained by pressurizing the first lithium-based solid electrolyte is 1 × 10⁻⁶ -5 Preferably, S / cm or higher, 1 × 10 -4 It is more preferable that the S / cm or higher. There is no particular upper limit, but 1 × 10 -3 The values ​​are often less than S / cm. When a molded body of a lithium-based solid electrolyte exhibits the above-mentioned ionic conductivity under temperature conditions of -10°C, it is suggested that substances other than water in the first and second states that contribute to ionic conductivity are present in the lithium-based solid electrolyte, and that good ionic conduction paths are formed. Such a lithium-based solid electrolyte is considered to have excellent ionic conductivity even at room temperature (27°C). The method for measuring the ionic conductivity at -10°C of a molded body obtained by pressurizing a lithium-based solid electrolyte will be described in detail in the examples described later.

[0077] ·SEM-EDX analysis In the case of the first lithium-based solid electrolyte, it is preferable that, in terms of superior effects of the present invention, when the cross-section of the molded body obtained by pressurizing the first lithium-based solid electrolyte is observed with a scanning electron microscope (SEM), the region where the lithium salt is present exists in a mesh-like pattern. The above characteristics and their measurement methods will be described in detail in the second embodiment described later.

[0078] • Infrared absorption spectrum A more advantageous aspect of the present invention is that in the infrared absorption spectrum of the first lithium-based solid electrolyte, 800-1600 cm⁻¹ -1 For the maximum absorption intensity in the wavenumber region, 3000-3500 cm -1It is preferable that the ratio of the maximum absorption intensities in the wavenumber region is 1 / 5 or more. In particular, for the effects of the present invention to be even better, the above ratio is preferably 3 / 10 or more, and more preferably 2 / 5 or more. There is no particular upper limit, but it is preferably 1 or less. Infrared absorption spectrum 3000-3500 cm -1 In the wavenumber region, the OH stretching vibration mode was observed, between 800 and 1600 cm². -1 A BO ​​stretching vibration mode is observed in the wavenumber region. The absorption intensity originating from the above OH stretching vibration mode is due to hydroxyl groups or water contained in the lithium-based solid electrolyte. In particular, in the first lithium-based solid electrolyte, when the absorption intensity originating from the above OH stretching vibration mode is strongly observed, it is thought that the specific lithium tetraborate contained in the first lithium-based solid electrolyte often has a large number of OH structures. In such a lithium-based solid electrolyte, lithium ions move more easily, and as a result, ionic conductivity is thought to improve. Note: 800-1600cm -1 In the wavenumber region, oscillation modes originating from lithium salts can also be observed.

[0079] The infrared absorption spectrum measurement conditions described above are as follows: Specifically, the objective lens is a 32x Cassegrain type (NA 0.65), the detector is an MCT-A, and the measurement range is 650-4000 cm. -1 , resolution: 4cm -1 The sample cell is a diamond cell. Furthermore, the obtained infrared absorption spectrum is corrected to remove signals from atmospheric water and CO2, and then offset correction is applied to the background to set the absorption intensity to zero. Furthermore, when measuring the infrared absorption spectrum of the first lithium-based solid electrolyte, the sample is vacuum-dried at 40°C for 2 hours before being measured in air.

[0080] • Raman spectrum Furthermore, the present invention offers superior effects, particularly in the Raman spectrum of the first lithium-based solid electrolyte at 600-850 cm⁻¹. -1The coefficient of determination obtained by performing linear regression analysis using the least squares method in the wavenumber domain is preferably 0.9400 or higher. Furthermore, the coefficient of determination is more preferably 0.9600 or higher, as this indicates superior effectiveness of the present invention. There is no particular upper limit, but 1.0000 is a possible value.

[0081] The above characteristics will be explained below using Figure 12. Figure 12 shows an example of a Raman spectrum of a lithium-ion solid electrolyte. The vertical axis represents Raman intensity, and the horizontal axis represents Raman shift. (600–850 cm⁻¹) -1 In the wavenumber domain, the coefficient of determination (coefficient of determination R) obtained by performing linear regression analysis using the least squares method is obtained. 2 This calculates the 600-850 cm⁻¹ range of the Raman spectrum in Figure 12. -1 In the wavenumber domain, the regression line (thick dashed line in Figure 12) is obtained using the least squares method, and the coefficient of determination R of that regression line is calculated. 2 The coefficient of determination is calculated. The coefficient of determination takes a value between 0 (no linear correlation) and 1 (perfect linear correlation of the measured values), depending on the linear correlation of the measured values. In the first lithium-based solid electrolyte, as shown in Figure 2, 600-850 cm⁻¹ -1 In the wavenumber domain, virtually no peaks are observed, resulting in a high coefficient of determination. Note that the coefficient of determination R 2 This corresponds to the square of the correlation coefficient (Pearson's product-moment correlation coefficient). More specifically, in this specification, the coefficient of determination R 2 It 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.

[0082]

number

[0083] On the other hand, Figure 13 shows the Raman spectrum of a typical lithium tetraborate crystal. As shown in Figure 13, 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 domain. When there is such a peak, 600-850cm -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 first lithium-based solid electrolyte contains almost no crystalline structure like that found in typical lithium tetraborate crystals. Therefore, as a result, the first lithium-based solid electrolyte is Li + It is thought to possess excellent hopping properties.

[0084] • Karl Fischer measurement In terms of the superior effects of the present invention, when a molded body obtained by pressurizing a first lithium-based solid electrolyte is dried by a predetermined method, and the amount of water vaporized from the obtained molded body is measured based on the Karl Fischer method, it is preferable that the amount of water vaporized from the first lithium-based solid electrolyte B during heating from room temperature to 200°C is greater than the amount of water vaporized from the first lithium-based solid electrolyte A during heating from room temperature (27°C) to 100°C. The fact that water content B is greater than water content A indicates that the first lithium-based solid electrolyte contains water that is more strongly bound to its surroundings compared to water in the first state, and it is thought that the presence of such a predetermined amount of water contributes to the conductivity of lithium ions. The drying method for the molded body obtained by pressurizing the first lithium-based solid electrolyte, and the method for measuring the moisture content based on the Karl Fischer method, will be described in the examples below.

[0085] ·Requirement T In terms of achieving superior effects of the present invention, the first lithium-based solid electrolyte is preferably satisfied with the following requirement T. Requirement T: In the Raman spectrum of a lithium-based solid electrolyte, there is no peak top at 710 - 730 cm -1 with a full width at half maximum of 5 cm -1 or more for the first peak, no peak top at 770 - 790 cm -1 with a full width at half maximum of 5 cm -1 or more for the second peak, and no peak top at 1020 - 1040 cm -1 with a full width at half maximum of 5 cm -1 or more for the third peak, or, in the above Raman spectrum, when at least one specific peak selected from the group consisting of the first peak, the second peak, and the third peak exists, the intensity ratio calculated by at least one of the following intensity measurement methods for the specific peak is 5.0 or less. Intensity measurement method: Connect the point indicating the minimum value M1 of the Raman intensity in the wavenumber range of 400 - 600 cm -1 of the above Raman spectrum and the point indicating the minimum value M2 of the Raman intensity in the wavenumber range of 1300 - 1500 cm -1 of the above Raman spectrum to obtain a straight line. Among the regions from the wavenumber indicating the minimum value M1 to the wavenumber indicating the minimum value M2, for each wavenumber in the region other than the regions of 710 - 730 cm -1 , 770 - 790 cm -1 , and 1020 - 1040 cm -1 , calculate the average difference value between the Raman intensity of the straight line and the Raman intensity of the Raman spectrum, calculate the absolute value of the difference between the Raman intensity of the peak at the wavenumber indicating the peak top of the above specific peak and the Raman intensity of the straight line, and take the ratio of the absolute value of the difference to the average difference value as the intensity ratio.

[0086] Requirement T is a requirement evaluated by the same procedure except that the first lithium-based solid electrolyte is used as the measurement object of Requirement δ described above, and its evaluation method is as described above.

[0087] [[ID=3�]] In the Raman spectrum of the lithium-based solid electrolyte described above, if the first, second, and third peaks are absent, or if a specific peak selected from the group consisting of the first, second, and third peaks is present, it is more preferable that the intensity ratio of at least one of the specific peaks is 3.0 or less. In particular, if the first, second, and third peaks are absent, or if a specific peak selected from the group consisting of the first, second, and third peaks is present, it is even more preferable that the intensity ratio of at least one of the specific peaks is 2.0 or less, and it is especially preferable that the first, second, and third peaks are absent.

[0088] ·Requirement X The first lithium-based solid electrolyte is preferable in that it satisfies the following requirement X, which provides superior effects for the present invention. Requirement X: In the reduction dibody distribution function G(r) obtained from X-ray total scattering measurements of lithium-based solid electrolytes, there exists a first peak whose peak top is located in the range of r = 1.43 ± 0.2 Å, and a second peak whose peak top is located in the range of r = 2.40 ± 0.2 Å, the G(r) at the peak top of the first peak is greater than 1.0 (preferably 1.2 or greater), and the G(r) at the peak top of the second peak is greater than 0.8 (preferably greater than 1.0). Requirement X corresponds to requirement β described above, and its technical meaning, as stated above, is that a periodic structure corresponding to the interatomic distances of B (boron)-O (oxygen), B (boron)-B (boron), and O (oxygen)-O (oxygen) exists in the lithium-based solid electrolyte. In requirement X, as described above, it is preferable that the G(r) at the peak top of the first peak is 1.2 or higher, and that the G(r) at the peak top of the second peak is greater than 1.0. The method for measuring requirement X is as described above for requirement β.

[0089] Requirement Y The first lithium-based solid electrolyte is preferable in that it satisfies the following requirement Y, which provides superior effects for the present invention. Requirement Y: In the X-ray diffraction pattern obtained from X-ray diffraction measurements of lithium-based solid electrolytes using CuKα radiation, none of the following are present: a first peak with its peak top located in the range of 21.6–22.0° and a full width at half maximum (FMAX) of 0.65° or less; a second peak with its peak top located in the range of 25.4–25.8° and a FMAX of 0.65° or less; a third peak with its peak top located in the range of 33.4–33.8° and a FMAX of 0.65° or less; or a fourth peak with its peak top located in the range of 34.4–34.8° and a FMAX of 0.65° or less. In an X-ray diffraction pattern, if there is at least one specific peak selected from the group consisting of a first peak, a second peak, a third peak, and a fourth peak, the intensity ratio calculated by the following intensity measurement method for at least one of the specific peaks is 5.0 or less. Intensity measurement method: The average intensity 1 is calculated from the diffraction angle 2θ of the peak top of the specific peak in the range of +0.45° to +0.55°. The average intensity 2 is calculated from the diffraction angle 2θ of the peak top of the specific peak in the range of -0.55° to -0.45°. The sum of average intensity 1 and average intensity 2 is calculated, and the ratio of the peak intensity at the peak top of the specific peak to the sum of the sum is defined as the intensity ratio.

[0090] Requirement Y is evaluated using the same procedure as requirement α, except that the first lithium-based solid electrolyte is used as the object to be measured, and the evaluation method is as described above.

[0091] In the X-ray diffraction pattern obtained from the first embodiment of the lithium-based solid electrolyte using CuKα radiation, it is more preferable that the intensity ratio of at least one of the specific peaks is 3.0 or less, if the first, second, third, and fourth peaks are absent, or if a specific peak selected from the group consisting of the first, second, third, and fourth peaks is present. In particular, if the first, second, third, and fourth peaks are absent, or if a specific peak selected from the group consisting of the first, second, third, and fourth peaks is present, it is even more preferable that the intensity ratio of at least one of the specific peaks is 2.0 or less.

[0092] <<Second Embodiment>> A second embodiment of the lithium-based solid electrolyte of the present invention (hereinafter also referred to as the "second lithium-based solid electrolyte") comprises amorphous lithium tetraborate and a lithium salt. Furthermore, in the case of the second lithium-based solid electrolyte, when the cross-section of the molded body obtained by pressurizing the second lithium-based solid electrolyte is observed with a scanning electron microscope (SEM), regions where lithium salts are present are found to exist in a network-like pattern.

[0093] One method for observing the cross-section of a molded body of a lithium-2 solid electrolyte using a scanning electron microscope (SEM) is to detect elements derived from the lithium salt, such as the specified elements mentioned above, by energy dispersive X-ray spectrometry (EDX), and to obtain a mapping image showing the compositional distribution in the cross-section. The elements to be detected can be appropriately selected depending on the type of lithium salt, but sulfur, nitrogen, or halogen atoms are preferred, with sulfur being more preferred. The method for forming the cross-section of the molded body of the second lithium-based solid electrolyte is not particularly limited, but it is preferable to form the cross-section using a cross-section polisher (CCP) device.

[0094] The above characteristics will be explained below using Figure 14. Figure 14 shows an example of a mapping image of a cross-section of a molded body of a lithium-ion solid electrolyte obtained by SEM-EDX analysis. In the mapping image shown in Figure 14, regions where lithium salts are present are represented by bright areas, and regions where lithium salts are absent (regions where specific lithium tetraborate is present) are represented by dark areas. The bright areas form a continuous, mesh-like phase surrounding the dark areas. In a molded body of a lithium-ion solid electrolyte, the lithium salts contributing to ion conduction form a mesh-like structure, which is thought to create good ion conduction paths connecting the electrodes, thus providing the effects of the present invention. A method for analyzing the cross-section of a molded lithium-based solid electrolyte using SEM-EDX, and a method for preparing the cross-section of a molded lithium-based solid electrolyte, will be described in detail in the examples described later.

[0095] The second lithium-based solid electrolyte contains amorphous lithium tetraborate (specific lithium tetraborate). The type, characteristics, and content of specific lithium tetraborate contained in the second lithium-based solid electrolyte are as described in the first embodiment, including preferred embodiments.

[0096] The second lithium-based solid electrolyte contains a lithium salt. The type, characteristics, and content of lithium salts contained in the second lithium-based solid electrolyte are as described in the first embodiment, including preferred embodiments.

[0097] The second lithium-based solid electrolyte contains specific lithium tetraborate and therefore contains the elements Li, B, and O. Furthermore, it is preferable that the second lithium-based solid electrolyte further contains specific elements selected from the group consisting of Group 4 elements, Group 15 elements, Group 16 elements, Group 17 elements, Si, C, Sc, and Y. The types of specific elements contained in the second lithium-based solid electrolyte, as well as the molar amounts of Li, B, O, and the specific elements contained in the second lithium-based solid electrolyte, are as described in the first embodiment, including preferred embodiments.

[0098] The lithium-2 solid electrolyte may contain water, and it is preferable that it contains water. The water content in the second lithium-based solid electrolyte is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less, particularly preferably 30% by mass or less, and most preferably 25% by mass or less, relative to the total mass of the lithium-based solid electrolyte. Furthermore, there is no particular lower limit to the water content, but it is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more, relative to the total mass of the lithium-based solid electrolyte. The water content is as described in the first embodiment, and the measurement method is also as described in the first embodiment.

[0099] The molar ratios and content of each component in a lithium-2 solid electrolyte can be determined using known methods. For example, the content of various elements in a lithium-2 solid electrolyte can be identified, and the molar ratios and content of each component can be determined from the structure of the compound used. As for elemental analysis methods, for example, Na and B can be analyzed by ICP-OES (Inductively coupled plasma optical emission spectrometry), N can be analyzed by the inert gas fusion method, and F and S can be analyzed by combustion ion chromatography. For O, the analytical masses of elements other than O can be added together and calculated as the difference from the total powder amount. Note that the method for calculating the content of each element is not limited to the above, and the content of other elements can be estimated from the analytical results of one element, taking into account the structure of the compound used.

[0100] (Characteristics of lithium-based solid electrolytes) ·TG-MS measurement A more advantageous aspect of the present invention is that, when thermogravimetric mass spectrometry (TG-MS) is performed on a molded body obtained by pressurizing a second lithium-based solid electrolyte, it is preferable that a component with a molecular weight of 18 is detected in the temperature range above 100°C, and more preferably that a component with a molecular weight of 18 is detected in the temperature range above 120°C. The above characteristics are as described in the first embodiment, and the measurement method is also as described in the first embodiment.

[0101] · 7 Li-NMR measurement The present invention offers superior effects compared to the solid lithium-ion solid electrolyte. 7 The solid lithium-ion solid electrolyte is defined as the solid lithium-ion solid electrolyte whose chemical shift in the spectrum obtained by Li-NMR measurement at 20°C is in the range of -100 to +100 ppm, and its full width at half maximum is shown for the solid lithium-ion solid electrolyte. 7 When Li-NMR measurements are performed at 120°C, the ratio of the full width at half maximum (FMAX) of peaks appearing in the chemical shift range of -100 to +100 ppm in the obtained spectrum 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 full width at half maximum (FWHM) of a peak refers to the width (ppm) at half the peak height (H / 2).

[0102] Furthermore, the present invention offers superior effects, particularly in the case of a second lithium-based solid electrolyte. 7 When a Li-NMR measurement is performed at 20°C, the spectrum obtained is preferably obtained by waveform separation of the first peak appearing in the range of -100 to +100 ppm, and a second peak with a full width at half maximum of 5 ppm or less is present in the chemical shift range of -3 to 3 ppm, and the ratio of the area intensity of the second peak to the area intensity of the first peak is preferably 0.5% or more. The above area intensity ratio is more preferably 2% or more, and even more preferably 15% or more. There is no particular upper limit to the above area intensity ratio, but it is often 50% or less. The above characteristics are as described in the first embodiment, and the measurement method is also as described in the first embodiment.

[0103] · 1 H-NMR measurement The present invention offers superior effects compared to the second lithium-based solid electrolyte. 1 It is preferable that the chemical shift in the spectrum obtained by 1H-NMR measurement shows both sharp and broad peaks in the range of -200 to +200 ppm. The above characteristics are as described in the first embodiment, and the measurement method is also as described in the first embodiment.

[0104] · 19 F-NMR measurement A more advantageous aspect of the present invention is that when the lithium salt contains a fluorine atom, the second lithium-based solid electrolyte 19 It is preferable that a sharp peak appears in the chemical shift range of -200 to +300 ppm in the spectrum obtained by F-NMR measurement. The above characteristics are as described in the first embodiment, and the measurement method is also as described in the first embodiment.

[0105] TG-DTA measurement Furthermore, in terms of achieving superior effects of the present invention, it is preferable that the mass loss rate when the second lithium-based solid electrolyte is heated to 800°C is 20 to 40% by mass. In particular, in terms of achieving superior effects of the present invention, a mass loss rate of 25 to 35% by mass is more preferable. The above characteristics are as described in the first embodiment, and the measurement method is also as described in the first embodiment.

[0106] Ionic conductivity A further advantage of the present invention is that the ionic conductivity at -10°C of a molded body obtained by pressurizing a second lithium-based solid electrolyte is 1 × 10⁻⁶ -5 Preferably, S / cm or higher, 1 × 10 -4 It is more preferable that the S / cm or higher. There is no particular upper limit, but 1 × 10 -3The values ​​are often less than S / cm. The above characteristics are as described in the first embodiment, and the measurement method is also as described in the first embodiment.

[0107] • Infrared absorption spectrum Furthermore, a more superior aspect of the present invention is that in the infrared absorption spectrum of the second lithium-based solid electrolyte, 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 is preferably 1 / 5 or more. In particular, the above ratio is preferably 3 / 10 or more, and more preferably 2 / 5 or more, in terms of superior effects of the present invention. There is no particular upper limit, but 1 or less is preferred. The above characteristics are as described in the first embodiment, and the measurement method is also as described in the first embodiment.

[0108] • Raman spectrum Furthermore, in terms of the superior effects of the present invention, the Raman spectrum of the second lithium-based solid electrolyte is 600-850 cm⁻¹. -1 The coefficient of determination obtained by performing linear regression analysis using the least squares method in the wavenumber domain is preferably 0.9400 or higher. Furthermore, the coefficient of determination is more preferably 0.9600 or higher, as this indicates superior effectiveness of the present invention. There is no particular upper limit, but 1.0000 is a possible value. The above characteristics are as described in the first embodiment, and the measurement method is also as described in the first embodiment.

[0109] • Karl Fischer measurement In terms of the superior effects of the present invention, when a molded body obtained by pressurizing a second lithium-based solid electrolyte is dried by a predetermined method, and the amount of water vaporized from the obtained molded body is measured based on the Karl Fischer method, it is preferable that the amount of water vaporized from the first lithium-based solid electrolyte B during heating from room temperature to 200°C is greater than the amount of water vaporized from the first lithium-based solid electrolyte A during heating from room temperature (27°C) to 100°C. The above characteristics are as described in the first embodiment, and the measurement method is also as described in the first embodiment.

[0110] ·Requirement T Furthermore, in terms of achieving superior effects of the present invention, it is preferable that the second lithium-based solid electrolyte satisfies requirement T. The following requirement T is the same as requirement T defined in the first embodiment described above, and the measurement method is also as described in the first embodiment. Requirement T: Raman spectrum of lithium-based solid electrolytes, 710-730 cm⁻¹ -1 It has a peak top and a full width at half maximum of 5 cm. -1 The first peak, as described above, is 770-790 cm. -1 It has a peak top and a full width at half maximum of 5 cm. -1 The second peak mentioned above, and 1020-1040cm -1 It has a peak top and a full width at half maximum of 5 cm. -1 Either none of the above third peaks exist, or In the above Raman spectrum, if there is at least one specific peak selected from the group consisting of the first peak, the second peak, and the third peak, the intensity ratio calculated by the following intensity measurement method for at least one of the specific peaks is 5.0 or less. Intensity measurement method: 400-600 cm² of the Raman spectrum shown above. -1 The point showing the minimum value M1 of Raman intensity in the wavenumber region, and the above Raman spectrum at 1300-1500 cm⁻¹ -1 A straight line is obtained by connecting the point showing the minimum value M2 of the Raman intensity in the wavenumber region, and within the region from the wavenumber showing the minimum value M1 to the wavenumber showing the minimum value M2, 710 to 730 cm² -1 770-790cm -1 , and 1020~1040cm -1 The average difference between the Raman intensity of the above line and the Raman intensity of the Raman spectrum at each wavenumber in the region outside the specified region is calculated. The absolute difference between the Raman intensity of the above peak and the Raman intensity of the above line at the wavenumber that shows the peak top of the specific peak is calculated, and the ratio of the absolute value of the above difference to the average difference is defined as the intensity ratio.

[0111] In the Raman spectrum of the lithium-based solid electrolyte described above, if the first, second, and third peaks are absent, or if a specific peak selected from the group consisting of the first, second, and third peaks is present, it is more preferable that the intensity ratio of at least one of the specific peaks is 3.0 or less. In particular, if the first, second, and third peaks are absent, or if a specific peak selected from the group consisting of the first, second, and third peaks is present, it is even more preferable that the intensity ratio of at least one of the specific peaks is 2.0 or less, and it is especially preferable that the first, second, and third peaks are absent.

[0112] ·Requirement X The second lithium-based solid electrolyte is preferable in that it satisfies the following requirement X, which provides superior effects of the present invention. The following requirement X is the same as the requirement X defined in the first embodiment described above, and the measurement method is also as described in the first embodiment. Requirement X: In the reduction dibody distribution function G(r) obtained from X-ray total scattering measurements of lithium-based solid electrolytes, there exists a first peak whose peak top is located in the range of r = 1.43 ± 0.2 Å, and a second peak whose peak top is located in the range of r = 2.40 ± 0.2 Å, the G(r) at the peak top of the first peak is greater than 1.0 (preferably 1.2 or greater), and the G(r) at the peak top of the second peak is greater than 0.8 (preferably greater than 1.0).

[0113] Requirement Y The second lithium-based solid electrolyte is preferable in that it satisfies the following requirement Y, which provides superior effects of the present invention. The following requirement Y is the same as the requirement Y defined in the first embodiment described above, and the measurement method is also as described in the first embodiment. Requirement Y: In the X-ray diffraction pattern obtained from X-ray diffraction measurements of lithium-based solid electrolytes using CuKα radiation, none of the following are present: a first peak with its peak top located in the range of 21.6–22.0° and a full width at half maximum (FMAX) of 0.65° or less; a second peak with its peak top located in the range of 25.4–25.8° and a FMAX of 0.65° or less; a third peak with its peak top located in the range of 33.4–33.8° and a FMAX of 0.65° or less; or a fourth peak with its peak top located in the range of 34.4–34.8° and a FMAX of 0.65° or less. In an X-ray diffraction pattern, if there is at least one specific peak selected from the group consisting of a first peak, a second peak, a third peak, and a fourth peak, the intensity ratio calculated by the following intensity measurement method for at least one of the specific peaks is 5.0 or less. Intensity measurement method: The average intensity 1 is calculated from the diffraction angle 2θ of the peak top of the specific peak in the range of +0.45° to +0.55°. The average intensity 2 is calculated from the diffraction angle 2θ of the peak top of the specific peak in the range of -0.55° to -0.45°. The sum of average intensity 1 and average intensity 2 is calculated, and the ratio of the peak intensity at the peak top of the specific peak to the sum of the sum is defined as the intensity ratio.

[0114] In the X-ray diffraction pattern obtained from the X-ray diffraction measurement using CuKα rays of the second embodiment of the lithium-based solid electrolyte described above, if the first, second, third, and fourth peaks are absent, or if a specific peak selected from the group consisting of the first, second, third, and fourth peaks is present, it is more preferable that the intensity ratio of at least one of the specific peaks is 3.0 or less. In particular, if the first, second, third, and fourth peaks are absent, or if a specific peak selected from the group consisting of the first, second, third, and fourth peaks is present, it is even more preferable that the intensity ratio of at least one of the specific peaks is 2.0 or less.

[0115] Figure 15 shows an example of calculation results performed based on first-principles molecular dynamics (MD) for a lithium-based solid electrolyte included in the present invention. Figure 15 shows the arrangement of Li, S, F, H, B, O, and N atoms in the lithium-based solid electrolyte of the present invention (first and second embodiments) using Li(FSO2)2N (hereinafter also referred to as "LiFSI") as the lithium salt. The dashed lines in the figure represent hydrogen bonds, Coulomb forces, etc. As shown in Figure 15, in the lithium-based solid electrolyte of the present invention, it is considered that an ion conduction path (indicated as A2 in the figure) containing water (H2O) and anions contained in LiSFI is formed between specific lithium tetraborate particles (indicated as A1 in the figure). Furthermore, as shown in Figure 15, it is considered that a portion of the BO3 and BO4 structures present on the particle surface of the BO3-BO4 linked structure constituting the specific lithium tetraborate particles interacts with H2O and plays a role in the above-mentioned ion conduction path. Furthermore, some of the BO3 and BO4 structures present on the particle surface may have dangling bonds, for example, due to elemental defects. Furthermore, a B-OH substructure may be formed through the interaction between H2O and parts of the BO3 and BO4 structures present on the particle surface. This B-OH substructure is thought to play a role in part of the ion conduction path. In addition, this B-OH substructure is thought to improve dispersibility in water in steps 2, 2A, 2B, and 2C of the lithium-based solid electrolyte manufacturing method described later. Furthermore, it is possible that Li and water (H2O) are strongly interacting (the Li-O bond distance is calculated to be approximately 1.8 Å), where strong Coulomb forces are acting to bind the water, contributing to solidification. Note that the structure and number of water (H2O) and LiSFI molecules in the region indicated by A2 are based on hypothetical settings and calculations, and are not limited to these.

[0116] The ion conduction paths described above may contain other components in addition to the anions found in H2O and LiSFI. These other components may include, for example, the BO3-BO4 linked structure found in certain lithium tetraborate particles, or molecules with structures different from the BO3-BO4 linked structure. Examples of molecules with different structures include B(OH)3 and B(OH)4. - Furthermore, BO3-BO4 structures that differ in structure or number of links from the BO3-BO4 linked structures present in lithium tetraborate crystals can be considered as candidates. As mentioned above, some of the H2O contained in the ion conduction path may be in a dissociated state. In the ion conduction path described above, H2O, anions contained in LiSFI, and the other components (if present) form a pseudo-bridged structure or a three-dimensional structure through chemical reactions via hydrogen bonding or the like. As a result, it is believed that the lithium-based solid electrolyte proceeds in a direction toward pseudo-solidification or solidification. Furthermore, the presence of BO4 is considered desirable for the formation of the pseudo-crosslinked structure or three-dimensional structure described above. The above explanation is based on estimations derived from calculation results for specific lithium-based solid electrolytes included in the present invention, and the present invention is not limited to the above-described content.

[0117] <<Method for manufacturing lithium-based solid electrolytes>> The method for manufacturing the lithium-based solid electrolyte of the present invention (first and second embodiments) is not particularly limited, but a manufacturing method having the following steps 1A to 3A is preferred in that it can produce the lithium-based solid electrolyte of the present invention with good productivity. Step 1A: A step of mechanically milling a lithium-based oxide (preferably lithium tetraborate) containing Li and B 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 remove water from the dispersion obtained in Step 2A to obtain a lithium-based solid electrolyte. The following details the steps of the above manufacturing method.

[0118] Step 1A is a step of subjecting the lithium-based oxide (preferably lithium tetraborate) to mechanical milling in the presence of a lithium salt. The following sections will detail the materials used in process 1A, followed by a detailed description of the procedure.

[0119] Examples of lithium salts include lithium salts containing one or more of the specified elements mentioned above, lithium salts containing two or more of the specified elements are preferred, and compounds represented by formula (1) are more 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.

[0120] The following are examples of lithium salts. (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. (L-2) Fluorine-containing organic lithium salts: perfluoroalkanesulfonates such as LiCF3SO3; perfluoroalkanesulfonylimide salts such as LiN(CF3SO2)2, LiN(CF3CF2SO2)2, lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide, LiN(FSO2)2, and LiN(CF3SO2)(C4F9SO2); perfluoroalkanesulfonylmethide salts such as LiC(CF3SO2)3; fluoroalkylphosphate salts 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]. (L-3) Oxalatoborate salts: lithium bis(oxalato)borate and lithium difluorooxalatoborate. In addition to the above, LiF, LiCl, LiBr, LiI, Li2SO4, LiNO3, Li2CO3, CH3COOLi, LiAsF6, LiSbF6, LiAlCl4, and LiB(C6H5)4 can be mentioned. Among them, LiPF6, LiBF4, LiAsF6, LiSbF6, LiClO4, Li(R f1 SO3), LiN(R f1 SO2)2, LiN(FSO2)2, LiN(R f1 SO2)(R f2 SO2), LiCl, LiB, or LiI is preferable, and LiPF6, LiBF4, LiN(R f1 SO2)2, LiN(FSO2)2, or LiN(R f1 SO2)(R f2 SO2) is more preferable. Here, R f1 and R f2 each independently represent a perfluoroalkyl group.

[0121] The usage amount of the lithium salt is not particularly limited, and the usage amount is appropriately adjusted so that the lithium-based solid electrolyte of the present invention described above can be obtained. Among them, the amount of the lithium salt used is preferably 1 to 300 parts by mass, more preferably 100 to 200 parts by mass with respect to 100 parts by mass of the lithium-based oxide.

[0122] Examples of the lithium-based oxide containing Li and B include, for example, Li2B4O7, LiBO5, LiB3O5, Li3B 11 O 18 , Li2B7O 12 , LiB2O3(OH)H2O, Li4B8O 13 (OH)2(H2O)3, Li4B7O 12 Cl, and Li3B7O 12 and the like. Among them, Li2B4O7 (lithium tetraborate) is preferred.

[0123] For the purpose of expanding the potential window and the like when using the lithium solid electrolyte as a battery, a liquid selected from the group consisting of an organic solvent and an ionic liquid may be used in addition to water and the Li salt. Examples of the organic solvent include, for example, acetamide, acetonitrile, ethylene carbonate, vinylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, γ-butyrolactone, fluoroethylene carbonate, and 1,3-propane sultone. Examples of ionic liquids include imidazolium, pyrrolidinium, piperidinium, ammonium, 1-ethyl-3-methylimidazolium, diethylmethyl-2-methoxyethylammonium, N-methyl-N-propylpiperidinium, N-methyl-N-propylpyridinium, 1-butyl-1-2,3-dimethylimidazolium, 1-methyltetrahydrothiophenium, 1-ethyltetrahydrothiophenium, ethylmethylpropylsulfonium, butyldimethylsulfonium, 1-propyltetrahydrothiophenium, 1-methyl[1,4]-thioxonium, 1-butyltetrahydrothiophenium, diethylethylsulfonium, 1-propyl-2,3,5-trimethylpyrazolium, bistrifluoromethanesulfonamide, dicyanamide, hexafluorophosphate, and tetrachloroaluminate.

[0124] Mechanical milling is a process in which a sample is pulverized while applying mechanical energy. Examples of mechanical milling processes include ball mills, vibratory mills, turbo mills, and disc mills, with ball mills being preferred because they can produce the lithium-based solid electrolyte of the present invention with high productivity. Examples of ball mills include vibratory ball mills, rotary ball mills, and planetary ball mills, with planetary ball mills being more preferred.

[0125] The optimal conditions for ball milling are selected based on the raw materials used. The material of the grinding balls (media) used in the ball mill is not particularly limited, but examples include agate, silicon nitride, stabilized zirconia (YSZ), alumina, and iron-based alloys. Stabilized zirconia (YSZ) is preferred because it allows for the productive manufacture of the lithium-based solid electrolyte of the present invention. The average particle size of the grinding balls is not particularly limited, but from the standpoint of enabling productive manufacturing of the lithium-based solid electrolyte of the present invention, it is preferably 1 to 10 mm, and more preferably 3 to 7 mm. The above average particle size is calculated by measuring the diameters of any 50 grinding balls and averaging them. If the grinding balls are not perfectly spherical, the major axis is used as the diameter. The number of grinding balls used in the ball mill is not particularly limited, but 10 to 100 balls are preferred, and 40 to 60 balls are more preferred, in order to enable productive production of the lithium-based solid electrolyte of the present invention.

[0126] The material of the grinding pot used in the ball mill is not particularly limited, but examples include agate, silicon nitride, stabilized zirconia (YSZ), alumina, and iron-based alloys. Stabilized zirconia (YSZ) is preferred because it allows for the productive manufacture of the lithium-based solid electrolyte of the present invention.

[0127] While there are no particular restrictions on the rotational speed when performing the ball milling, 200 to 700 rpm is preferred, and 350 to 550 rpm is more preferred, in order to efficiently produce the lithium-based solid electrolyte of the present invention. The processing time for the ball mill is not particularly limited, but 10 to 200 hours is preferred, and 20 to 140 hours is more preferred, from the standpoint of being able to produce the lithium-based solid electrolyte of the present invention with high productivity. The atmosphere in which the ball mill is performed may be open air or an inert gas atmosphere (e.g., argon, helium, and nitrogen).

[0128] Step 2A is a step in which the product obtained in Step 1A is mixed with water. By performing this step, the lithium-based oxide containing Li and B that has undergone mechanical milling in Step 1A is mixed with water to produce the lithium-based solid electrolyte of the present invention which is rich in O (oxygen). In step 2A, by preparing a mixture containing a lithium-based oxide that has undergone mechanical milling and water, a composition with good manufacturability can be obtained. Furthermore, by forcibly adsorbing water onto the lithium-based oxide that has undergone mechanical milling, the water content is increased, which is expected to improve ionic conductivity. While there are no particular restrictions on the amount of water used, for the best results of the present invention, the amount of water used is preferably 10 to 200 parts by mass, and more preferably 50 to 150 parts by mass, per 100 parts by mass of the product obtained in step 1A.

[0129] 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 then mixed. When mixing, ultrasonic treatment may be applied as needed. While there are no particular restrictions on the duration of the ultrasonic treatment, 10 minutes to 5 hours is preferred in that it yields superior results for the present invention.

[0130] Step 3A is a step in which water is removed from the dispersion obtained in Step 2A to obtain a lithium-based solid electrolyte. In this step, water contained in the dispersion is removed to obtain a lithium-based solid electrolyte containing water. In this step, water may be removed from the dispersion such that a lithium-based solid electrolyte is formed and water remains in the lithium-based solid electrolyte. Specifically, water may be removed so that at least water in the first to fourth states described above remains in the lithium-based solid electrolyte. Furthermore, water may be removed so that at least water in the second to fourth states remains in the lithium-based solid electrolyte, or so that at least water in the third to fourth states remains in the lithium-based solid electrolyte, or so that at least water in the fourth state remains in the lithium-based solid electrolyte. In other words, step 3A above may be a step in which a portion of the water in the dispersion is removed to obtain a predetermined lithium-based solid electrolyte containing the water described above. The method for removing water from the dispersion obtained in step 2A is not particularly limited; the water may be evaporated by heat treatment or by vacuum drying. By adjusting the amount of water removed within the above range, the water content in the lithium-based solid electrolyte can be adjusted as appropriate. In this step, it is preferable to dry the above dispersion under vacuum conditions to obtain a lithium-based solid electrolyte containing water. Vacuum conditions mean performing the drying process under a predetermined reduced pressure environment and a predetermined temperature. More specific vacuum conditions include, for example, a pressure of 2000 Pa or less (preferably 200 Pa or less, more preferably 20 Pa or less) and a temperature of 60°C or less (preferably 40°C or less). The lower limit of the above pressure is not particularly limited, for example, 10 Pa or more. Similarly, the lower limit of the above temperature is not particularly limited, for example, 0°C or higher. The processing time for the vacuum drying treatment can be appropriately selected depending on the pressure and temperature, the amount of water contained in the dispersion, and the water content of the target lithium-based solid electrolyte, for example, 120 to 1080 minutes, with 300 to 900 minutes being preferred.

[0131] Furthermore, before step 1A described above, step 0 may be performed in which a lithium-based oxide (preferably lithium tetraborate) is subjected to mechanical milling in an environment where lithium salts are not present. The preferred mode of the mechanical milling process performed in step 0 is the same as the preferred mode of the mechanical milling process performed in step 1A.

[0132] Another preferred embodiment of the method for producing the lithium-based solid electrolyte of the present invention is a manufacturing method having the following steps 1B to 3B. Step 1B: A process of mechanically milling a lithium-based oxide (preferably lithium tetraborate). 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 lithium-based solid electrolyte. The difference between Step 1B and Step 1A is that in Step 1A, the mechanical milling treatment is carried out in the presence of a lithium salt, while in Step 1B, the mechanical milling treatment is carried out without using a lithium salt. The preferred embodiment of the mechanical milling treatment carried out in Step 1B is the same as the preferred embodiment of the mechanical milling treatment carried out in Step 1A.

[0133] The difference between Step 2B and Step 2A is that in Step 2B, the product obtained in Step 1B, water, and a lithium salt are mixed. The lithium salt used in Step 2B is the same as the lithium salt used in Step 1A. The amount of the lithium salt used in Step 2B is preferably 1 to 300 parts by mass, more preferably 100 to 200 parts by mass, based on 100 parts by mass of the product obtained in Step 1B. The procedure of Step 2B is not particularly limited, and it may be a method (Method 1) of mixing the product obtained in Step 1B, water, and a lithium salt together, or a method (Method 2) of mixing the product obtained in Step 1B and water to prepare a dispersion liquid and then mixing the obtained dispersion liquid and the lithium salt, or a method (Method 3) of mixing the product obtained in Step 1B and water to prepare Dispersion Liquid 1, mixing the lithium salt and water to prepare Solution 2, and then mixing Dispersion Liquid 1 and Solution 2. When mixing the product obtained in Step 1B and water, dispersion treatment such as ultrasonic treatment may be appropriately carried out. Among them, Method 3 is preferred in terms of more excellent effects of the present invention. [[ID=I6]]In Method 2, when mixing the product obtained in Step 1B and water to prepare a dispersion liquid and then mixing the lithium salt, if the amount of the lithium salt is too large, the resulting liquid is likely to gel, and it is difficult to increase the mixing amount of the lithium salt. On the contrary, in Method 3, even if the product obtained in Step 1B and the lithium salt are mixed in an equimolar amount, the liquid is less likely to gel, and it is easy to increase the mixing amount of the lithium salt.

[0134] The procedures of Step 3B and Step 3A are the same. [[ID=I22]]

[0135] Another preferred embodiment of the method for producing the lithium-based solid electrolyte of the present invention is a method having the following steps 1C to 3C. Step 1C: A process of mechanically milling a lithium-based oxide (preferably lithium tetraborate). Step 2C: A step in which the product obtained in Step 1C is mixed with water. Step 3C: A step to obtain a lithium-based solid electrolyte by removing water from the dispersion obtained in Step 2C and mixing the resulting product with a lithium salt. The procedure for process 1C and process 1B is the same. The procedure for process 2C and process 2A is the same. The difference between step 3C and step 3A is that step 3C involves mixing the product obtained by removing water from the dispersion obtained in step 2C with the lithium salt. In step 3C, the method for removing water from the dispersion obtained in step 2C is the same as in step 3A, including preferred embodiments. The lithium salt used in process 3C is the same as the lithium salt used in process 1A. The amount of lithium salt used in step 3C is preferably 1 to 300 parts by mass, and more preferably 100 to 200 parts by mass, per 100 parts by mass of the product obtained by removing water from the dispersion obtained in step 2C. 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.

[0136] In other words, preferred embodiments of the lithium-based solid electrolyte manufacturing method of the present invention include: Step 1 involves mechanically milling a lithium-based oxide (more preferably lithium tetraborate), Step 2 involves mixing the product obtained in Step 1 with water, The process includes step 3, which involves removing water from the dispersion obtained in step 2 to obtain a lithium-based solid electrolyte. A manufacturing method that satisfies any of the following requirements 1 to 3 is listed. Requirement 1: The mechanical milling process in step 1 is carried out in the presence of a lithium salt containing one or more of the specified elements mentioned above. Requirement 2: In step 2, the product is mixed with water and a lithium salt containing one or more of the specified elements. Requirement 3: In step 3, the product obtained by removing water from the dispersion obtained in step 2 is mixed with a lithium salt containing one or more of the specified elements to obtain a lithium-based solid electrolyte. The preferred configurations of the processes to be carried out in each step and the components to be used are as described above.

[0137] <Dispersion> The dispersion of the present invention comprises the lithium-based solid electrolyte of the present invention described above and a solvent (e.g., an organic solvent, water). The dispersion of the present invention is liquid and can be applied to various substrates, and is useful for producing a solid electrolyte layer. In this specification, the dispersion of the present invention means an embodiment in which the solvent content in the dispersion is 80% by mass or more.

[0138] The dispersion of the present invention may contain other components besides the lithium-based solid electrolyte and solvent of the present invention. Other components include binders. Examples of binders include various organic polymer compounds. The organic polymer compounds constituting the binder may be particulate or non-particulate.

[0139] Other components include solid electrolytes other than the lithium-based solid electrolyte of the present invention. "Other solid electrolytes" refers to solid electrolytes capable of ion movement within their structure. Inorganic solid electrolytes are preferred as the solid electrolyte. Other solid electrolytes that can be used include sulfide-based inorganic solid electrolytes, oxide-based inorganic solid electrolytes, halide-based inorganic solid electrolytes, and hydride-based solid electrolytes.

[0140] The method for producing the dispersion of the present invention is not particularly limited, and examples include the production method having steps 1A and 2A described above, and the production method having steps 1B and 2B.

[0141] <Application> The lithium-based solid electrolyte of the present invention exhibits excellent ionic conductivity and can therefore be applied to various applications. For example, the lithium-based solid electrolyte of the present invention can be used in various batteries (e.g., all-solid-state secondary batteries, solid oxide fuel cells, solid oxide steam electrolysis). Among these, the lithium-based solid electrolyte of the present invention is particularly preferred for use in all-solid-state lithium-ion secondary batteries. More specifically, the lithium-based solid electrolyte of the present invention is preferably used to form a solid electrolyte contained in at least one of the positive electrode active material layer, solid electrolyte layer, and negative electrode active material layer in an all-solid-state secondary battery. In particular, the lithium-based solid electrolyte of the present invention is preferably used to form a solid electrolyte contained in the positive electrode active material layer, solid electrolyte layer, and negative electrode active material layer in an all-solid-state lithium-ion secondary battery. Furthermore, the lithium-based solid electrolyte of the present invention is preferably used as a solid electrolyte contained in any of the positive electrode active material layer, solid electrolyte layer, and negative electrode active material layer in an all-solid-state lithium-ion secondary battery. Furthermore, the lithium-based solid electrolyte of the present invention is suitably used as a coating material for coating the surface of a positive electrode active material. In other words, one preferred embodiment of the present invention is a modified positive electrode active material having a positive electrode active material and a coating layer disposed on the positive electrode active material, wherein the coating layer contains the lithium-based solid electrolyte of the present invention. Furthermore, the lithium-based solid electrolyte of the present invention is suitably used as a coating material for coating the surface of the negative electrode active material. In other words, one preferred embodiment of the present invention is a modified negative electrode active material having a negative electrode active material and a coating layer disposed on the negative electrode active material, wherein the coating layer contains the lithium-based solid electrolyte of the present invention.

[0142] When using the lithium-based solid electrolyte of the present invention, it is preferable to apply pressure treatment to the lithium-based solid electrolyte of the present invention and mold it into a predetermined shape before use. The method of pressurization is not particularly limited, and one example is using a known press device. The pressure applied during the pressurization process is not particularly limited, and the optimal pressure can be selected as appropriate. However, a pressure of 5 to 1500 MPa is preferred, and 10 to 600 MPa is more preferred, as this yields superior effects of the present invention. While there are no particular restrictions on the pressurization time, from the standpoint of achieving superior effects and productivity, 1 second to 0.5 hours is preferred, and 2 seconds to 0.2 hours is more preferred. Furthermore, heat treatment may be performed during the pressurization process. The heating temperature during the heat treatment is not particularly limited, but 40 to 400°C is preferred, and 50 to 350°C is more preferred. The heating time during the heat treatment is preferably 1 minute to 6 hours. The atmosphere under pressurization is not particularly limited and includes atmospheric air, dry air (dew point below -20°C), and an inert gas atmosphere (e.g., argon, helium, and nitrogen).

[0143] The ionic conductivity (at 27°C) of the lithium-based solid electrolyte of the present invention is not particularly limited, but from the standpoint of application to various uses, 1.0 × 10⁻⁶ is preferred. -5 Preferably S / cm or higher, 1.0 × 10 -4 A value of S / cm or higher is preferable. There is no particular upper limit, but 1.0 × 10 -2 The values ​​are often less than S / cm.

[0144] The dispersion of the present invention, which contains the lithium-based solid electrolyte of the present invention, can be suitably used as a dispersion for forming a solid electrolyte layer. The method for forming a solid electrolyte layer using the above-mentioned dispersion for forming a solid electrolyte layer is not particularly limited, but one method is to apply the dispersion for forming a solid electrolyte layer to an object to be formed. If necessary, the formed coating film may be subjected to pressure treatment.

[0145] The method for applying the dispersion for forming the solid electrolyte layer is not particularly limited and includes, for example, spray coating, spin coating, dip coating, slit coating, stripe coating, aerosol deposition method, thermal spraying, and bar coating. Furthermore, after applying the dispersion for forming the solid electrolyte layer, the resulting coating film may be subjected to a drying treatment as needed. The drying temperature is not particularly limited, but the lower limit is preferably 30°C or higher, more preferably 60°C or higher, and even more preferably 80°C or higher. The upper limit of the drying temperature is preferably 300°C or lower, and more preferably 250°C or lower.

[0146] The method for applying pressure to the coating is not particularly limited, but one method is to use a known press device (for example, a hydraulic cylinder press). The pressure applied during the pressurization process is not particularly limited, but 5 to 1500 MPa is preferred, and 300 to 600 MPa is more preferred, as it results in superior ionic conductivity of the formed solid electrolyte layer. The pressurization time is not particularly limited, but 1 minute to 6 hours is preferred, and 1 to 20 minutes is more preferred, in terms of superior ionic conductivity of the formed solid electrolyte layer and productivity. Furthermore, heat treatment may be performed during the pressurization process. The heating temperature during the heat treatment is not particularly limited, but 30 to 300°C is preferred, and the heating time is more preferably 1 minute to 6 hours. The atmosphere under pressurization is not particularly limited and includes atmospheric air, dry air (dew point below -20°C), and an inert gas atmosphere (e.g., argon, helium, and nitrogen).

[0147] The lithium-based solid electrolyte of the present invention is also preferably used as a component of an electrode-forming composition. In other words, the electrode-forming composition of the present invention is preferably a composition containing the lithium-based solid electrolyte of the present invention described above and an active material. The mixing ratio of lithium-based solid electrolyte and active material in the electrode-forming composition is not particularly limited, and the content ratio of lithium-based solid electrolyte to active material (mass of lithium-based solid electrolyte / mass of active material) is not particularly limited, but is preferably 0.01 to 50, and more preferably 0.05 to 20.

[0148] The lithium-based solid electrolyte contained in the electrode formation composition is as described above. Examples of active materials include negative electrode active materials and positive electrode active materials. The active materials are described in detail below.

[0149] (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.

[0150] 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 calcining 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, cellulosic carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, dehydrated PVA (polyvinyl alcohol)-based carbon fibers, lignin carbon fibers, glassy carbon fibers, and activated carbon fibers, as well as mesophase microspheres, graphite whiskers, and flat graphite. These carbonaceous materials can also be 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.

[0151] 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 nonmetalloid 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.

[0152] 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 selected from groups 13(IIIB) to 15(VB) of the periodic table (for example, Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi) or a combination of two or more of these elements (compounds), 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.

[0153] 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 described above 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., a metal oxide) may also preferably contain the element titanium (titanium oxide). Specifically, Li4Ti5O 12 Lithium titanate (LTO) is preferred 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 improves the lifespan of all-solid-state lithium-ion secondary batteries. Another preferred negative electrode active material containing titanium is TiNb2O7 (titanium-niobium oxide [TNO]).

[0154] The lithium alloy used 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 in all-solid-state lithium-ion secondary batteries; for example, lithium aluminum alloy can be used.

[0155] The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is one that is commonly used as a negative electrode active material in all-solid-state lithium-ion secondary batteries. Examples of the above negative electrode active material include negative electrode active materials (alloys) containing silicon or tin, as well as various metals such as Al and In. A negative electrode active material containing silicon (silicon-containing active material) that enables a higher battery capacity is preferred, and a silicon-containing active material in which the silicon content is 50 mol% or more of the total constituent elements is more preferred. Generally, negative electrodes containing these negative electrode active materials (for example, Si negative electrodes containing silicon element-containing active materials, Sn negative electrodes containing active materials containing tin elements) can occlude more Li ions than carbon negative electrodes (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 made longer.

[0156] 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 silicon elements and tin elements 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) that can be alloyed with lithium in order to generate Si 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 above silicon elements and tin elements.

[0157] In terms of battery capacity, a negative electrode active material that can be alloyed with lithium is preferable as the negative electrode active material, the above silicon material or silicon-containing alloy (alloy containing a silicon element) is more preferable, and silicon (Si) or silicon-containing alloy is even more preferable.

[0158] The shape of the negative electrode active material is not particularly limited, but a particulate shape is preferable. The volume average particle diameter of the negative electrode active material is not particularly limited, but 0.1 to 60 μm is preferable, 0.5 to 20 μm is more preferable, and 1.0 to 15 μm is even more preferable. The measurement of the volume average particle diameter is performed according to 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.

[0159] The negative electrode active material may be used alone or in combination of two or more types.

[0160] 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 12 Examples include Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, SiO2, TiO2, ZrO2, Al2O3, and B2O3. 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.

[0161] (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 the transition metal element M aA transition metal oxide containing one or more elements selected from Co, Ni, Fe, Mn, Cu, and V is more preferable. b (Elements from Group 1 (Ia), Group 2 (IIa), Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, and B, other than lithium, may be mixed.) a A concentration of 0 to 30 mol% is preferred relative to the amount (100 mol%). Li / M a A more preferable product is one synthesized by mixing the elements so that their molar ratio is between 0.3 and 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.

[0162] (MA) Examples of transition metal oxides having a layered rock salt structure include LiCoO2 (lithium cobaltate [LCO]), LiNi2O2 (lithium nickelate), 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. (MB) Examples of transition metal oxides having a spinel-type structure include LiMn2O4(LMO), LiCoMnO4, Li2FeMn3O8, Li2CuMn3O8, Li2CrMn3O8, and LiNi 0.5 Mn 1.5 O4 (LNMO) is one example. Examples of (MC) lithium-containing transition metal phosphate compounds include olivine-type iron phosphates such as LiFePO4 and Li3Fe2(PO4)3, iron pyrophosphates such as LiFeP2O7, cobalt phosphates such as LiCoPO4, and monoclinic NASICON-type vanadium phosphates such as Li3V2(PO4)3 (lithium vanadium phosphate). 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. Examples of (ME) lithium-containing transition metal silicate compounds include Li2FeSiO4, Li2MnSiO4, and Li2CoSiO4.

[0163] The shape of the positive electrode active material is not particularly limited, but particulate is preferred. The volume-average particle diameter of the positive electrode active material is not particularly limited, but 0.1 to 50 μm is preferred. The volume-average particle diameter of the positive electrode active material particles can be measured in the same manner as the volume-average particle diameter of the negative electrode active material. 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.

[0164] The positive electrode active material, like the negative electrode active material, may be surface-coated with the above-mentioned surface coating agent, sulfur, or phosphorus, and furthermore, with active light.

[0165] The positive electrode active material may be used alone or in combination of two or more types.

[0166] The electrode-forming composition may contain other components besides the lithium-based solid electrolyte and the active material. The electrode-forming composition may contain a conductive additive. 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. Note that conductive additives are substances that do not function as active materials because lithium is not inserted or released when the battery is charged or discharged. Therefore, among conductive additives, those that can function as active materials in the active material layer when the battery is charged or discharged are classified as active materials, not conductive additives. Whether or not a substance functions as an active material when the battery is charged or discharged is not unique, but is determined by its combination with the active material.

[0167] Other components include the aforementioned binder and lithium salt.

[0168] The electrode-forming composition may contain a dispersion medium. Examples of dispersion media include water and various organic solvents.

[0169] The electrode-forming composition may also contain, in addition to the above-mentioned components, ionic liquids, thickeners, crosslinking agents (those that undergo crosslinking reactions by radical polymerization, condensation polymerization, or ring-opening polymerization), polymerization initiators (such as those that generate acids or radicals by heat or light), defoaming agents, leveling agents, dehydrating agents, and antioxidants.

[0170] The method for forming electrodes (negative electrode active material layer and positive electrode active material layer) using the above electrode-forming composition is not particularly limited, but one method is to apply the electrode-forming composition to form the electrodes. If necessary, the formed coating film may be subjected to pressure treatment.

[0171] The method for applying the electrode-forming composition is not particularly limited and includes, for example, spray coating, spin coating, dip coating, slit coating, stripe coating, aerosol deposition method, thermal spraying, and bar coating. Furthermore, after applying the electrode-forming composition, the resulting coating film may be subjected to a drying treatment as needed. The drying temperature is not particularly limited, but the lower limit is preferably 30°C or higher, more preferably 60°C or higher, and even more preferably 80°C or higher. The upper limit of the drying temperature is preferably 300°C or lower, and more preferably 250°C or lower.

[0172] The method for applying pressure to the coating is not particularly limited, but one method is to use a known press device (for example, a hydraulic cylinder press). The pressure applied during the pressurization process is not particularly limited, but 5 to 1500 MPa is preferred, and 300 to 600 MPa is more preferred. While there are no particular restrictions on the pressurization time, from a productivity standpoint, 1 minute to 6 hours is preferred, and 1 to 20 minutes is more preferred. Furthermore, heat treatment may be performed during the pressurization process. The heating temperature during the heat treatment is not particularly limited, but 30 to 300°C is preferred, and the heating time is preferably 1 minute to 6 hours. The atmosphere under pressurization is not particularly limited and includes atmospheric air, dry air (dew point below -20°C), and an inert gas atmosphere (e.g., argon, helium, and nitrogen).

[0173] <Solid Electrolyte Sheet> The lithium-based solid electrolyte of the present invention may be contained in a solid electrolyte sheet. The above-mentioned solid electrolyte sheet is preferably used as a solid electrolyte sheet for all-solid-state batteries. The above-mentioned solid electrolyte sheet can be formed by molding the lithium-based solid electrolyte of the present invention into a sheet. The molding method is not particularly limited; for example, a sheet may be formed by press molding a dispersion containing the lithium-based solid electrolyte of the present invention.

[0174] <Electrode sheets for all-solid-state secondary batteries> The lithium-based solid electrolyte of the present invention may be included in an electrode sheet for an all-solid-state secondary battery. In particular, the lithium-based solid electrolyte of the present invention may be included in an electrode sheet for an all-solid-state lithium-ion secondary battery. The following section will primarily detail electrode sheets for all-solid-state lithium-ion secondary batteries. The electrode sheet for all-solid-state lithium-ion secondary batteries of the present invention is a sheet-like molded body capable of forming an electrode active material layer for an all-solid-state lithium-ion secondary battery, and is preferably used as an electrode, or as a laminate of an electrode and a solid electrolyte layer.

[0175] The electrode sheet for all-solid-state lithium-ion secondary batteries of the present invention (also simply referred to as "electrode sheet") may be any electrode sheet having an active material electrode layer selected from the group consisting of a negative electrode active material layer and a positive electrode active material layer (hereinafter also simply referred to as "active material electrode layer"). The sheet may be one in which the active material electrode layer is formed on a substrate (current collector), or it may be a sheet without a substrate, formed solely from the active material electrode layer. This electrode sheet is usually a sheet having a current collector and an active material electrode layer, but embodiments having a current collector, an active material electrode layer, and a solid electrolyte layer in that order are also included, as well as embodiments having a current collector, an active material electrode layer, a solid electrolyte layer, and an active material electrode layer in that order. The electrode sheet of the present invention may have other layers as described above. The thickness of each layer constituting the electrode sheet of the present invention is the same as the thickness of each layer described later in the all-solid-state lithium-ion secondary battery. The all-solid-state lithium-ion secondary battery sheet of the present invention contains at least one layer of the active material electrode layer which comprises the lithium-based solid electrolyte of the present invention.

[0176] The method for manufacturing the electrode sheet for all-solid-state lithium-ion secondary batteries of the present invention is not particularly limited, and can be manufactured, for example, by forming an active material electrode layer using the electrode-forming composition of the present invention. For example, one method involves applying an electrode-forming composition onto a current collector (which may be via other layers) to form a coating film, and then applying pressure to the coating film. Methods for applying the electrode-forming composition and for applying pressure treatment to the coating film include the methods described in the section on electrode-forming compositions.

[0177] <All-solid-state secondary battery> The all-solid-state secondary battery of the present invention comprises a positive electrode active material layer, a negative electrode active material layer facing the positive electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer. The positive electrode active material layer is preferably formed on a positive electrode current collector and constitutes the positive electrode. The negative electrode active material layer is preferably formed on a negative electrode current collector and constitutes the negative electrode. Preferably, at least one of the negative electrode active material layer, the positive electrode active material layer, and the solid electrolyte layer contains the lithium-based solid electrolyte of the present invention. In other words, the present invention also relates to an electrode for an all-solid-state secondary battery, comprising an active material, an active material layer containing the lithium-based solid electrolyte of the present invention, and a current collector. The following will primarily describe in detail the all-solid-state lithium-ion secondary battery of the present invention. The all-solid-state lithium-ion secondary battery of the present invention comprises a positive electrode active material layer, a negative electrode active material layer facing the positive electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer. The positive electrode active material layer is preferably formed on a positive electrode current collector and constitutes the positive electrode. The negative electrode active material layer is preferably formed on a negative electrode current collector and constitutes the negative electrode. At least one of the negative electrode active material layer, the positive electrode active material layer, and the solid electrolyte layer contains the lithium-based solid electrolyte of the present invention.

[0178] The thicknesses of the negative electrode active material layer, the solid electrolyte layer, and the positive electrode active material layer are not particularly limited. Considering the dimensions of a typical all-solid-state lithium-ion secondary battery, the thickness of each layer is preferably 10 to 1000 μm, and more preferably 20 μm or more and less than 500 μm. It is even more preferable that the thickness of at least one of the positive electrode active material layer and the negative electrode active material layer be 50 μm or more and less than 500 μm. The positive electrode active material layer and the negative electrode active material layer may each have a current collector on the side opposite to the solid electrolyte layer.

[0179] The all-solid-state lithium-ion secondary battery of the present invention may be used as an all-solid-state lithium-ion secondary battery with the above structure in place, depending on the application. However, to form a dry cell, it is preferable to enclose it in a suitable housing. The housing may be made of metal or resin (plastic). Examples of metal housings include aluminum alloy housings and stainless steel housings. It is preferable to divide the metal housing into a positive electrode housing and a negative electrode housing, and to electrically connect them to the positive electrode current collector and the negative electrode current collector, respectively. It is preferable that the positive electrode housing and the negative electrode housing are joined together and integrated via a gasket to prevent short circuits.

[0180] A preferred embodiment of the all-solid-state lithium-ion secondary battery of the present invention will be described below with reference to Figure 16, but the present invention is not limited thereto. Figure 16 is a schematic cross-sectional view showing an all-solid-state lithium-ion secondary battery according to a preferred embodiment of the present invention. The all-solid-state lithium-ion secondary battery 10 of this embodiment 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. At least one of the negative electrode active material layer 2, the positive electrode active material layer 4, and the solid electrolyte layer 3 contains the lithium-based solid electrolyte of the present invention. Each layer is in contact with the others and has an adjacent structure. By adopting this structure, during charging, electrons (e - ) is supplied, and lithium ions (Li+ ) 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, 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 the discharge occurs.

[0181] The negative electrode active material layer 2 contains the negative electrode active material described above. The positive electrode active material layer 4 contains the positive electrode active material described above.

[0182] The positive electrode current collector 5 and the negative electrode current collector 1 are preferably made of electron conductors. Materials for forming 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). Materials for forming 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.

[0183] The shape of the current collector is usually that of a film sheet, but it may also be in other shapes. The thickness of the current collector is not particularly limited, but 1 to 500 μm is preferred. Furthermore, it is preferable to create an uneven surface on the current collector surface through surface treatment.

[0184] The method for manufacturing the all-solid-state lithium-ion secondary battery described above is not particularly limited and includes known methods. Among these, the method using the electrode-forming composition and / or solid electrolyte layer-forming dispersion described above is preferred. For example, a positive electrode active material layer can be formed by applying a positive electrode forming composition containing positive electrode active material to a metal foil, which is a positive electrode current collector. Next, a solid electrolyte layer can be formed by applying a dispersion for forming a solid electrolyte layer on top of this positive electrode active material layer. Furthermore, a negative electrode active material layer can be formed by applying a negative electrode forming composition containing negative electrode active material on top of the solid electrolyte layer. Finally, a negative electrode current collector (metal foil) can be placed on top of the negative electrode active material layer, and the resulting laminate can be subjected to a pressurizing treatment to obtain an all-solid-state lithium-ion secondary battery in which a solid electrolyte layer is sandwiched between the positive electrode active material layer and the negative electrode active material layer. This can then be sealed in a housing to obtain a desired all-solid-state lithium-ion secondary battery. Furthermore, 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 a positive electrode current collector can be stacked on top to manufacture an all-solid-state lithium-ion secondary battery.

[0185] Alternatively, a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer may be manufactured separately and then laminated together to produce an all-solid-state lithium-ion secondary battery.

[0186] It is preferable to initialize all-solid-state lithium-ion secondary batteries after manufacturing or before use. Initialization is not particularly limited and can be performed, for example, by performing initial charging and discharging under increased press pressure, and then releasing the pressure until it reaches the general operating pressure of the all-solid-state lithium-ion secondary battery.

[0187] <Applications of all-solid-state rechargeable batteries> The all-solid-state secondary battery of the present invention (particularly the all-solid-state lithium-ion secondary battery) 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 notebook 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. [Examples]

[0188] The features of the present invention will be further described below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted restrictively by the specific examples shown below.

[0189] <Example 1> A lithium compound was obtained by ball milling Li2B4O7(247) powder (Rare Metallic) using a ball mill (Fritsch P-7) under the following conditions: pot: stabilized zirconia (YSZ) (45 ml), grinding balls: stabilized zirconia (YSZ) (average particle size: 5 mm, number: 50), rotation speed: 370 rpm (revolutions per minute), amount of LBO powder (powdered Li2B4O7 crystals (Rare Metallic)): 1 g, atmosphere: air, ball mill processing time: 100 hours. The particle size distribution of the obtained lithium compound was approximately a few μm to 10 μm, and the median diameter (D50) was 1.5 μm. 0.05 g of the lithium salt Li(FSO2)2N(LiFSI) was added to the obtained lithium compound, and the mixture was ball-milled for a further 100 hours. The resulting powder was added to water to a powder concentration of 42% by mass and sonicated for 30 minutes. Next, the obtained dispersion was transferred to a glass petri dish and dried in air at 120°C for 2 hours to obtain a lithium-based solid electrolyte film. Subsequently, the obtained film was peeled off to obtain powder. After the obtained powder was allowed to stand in air for a certain period of time, the following evaluation was performed.

[0190] Furthermore, using the lithium-based solid electrolyte obtained above, X-ray total scattering measurements were performed at SPring-8 BL04B2 (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 then 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) was greater than 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) was greater than 1.0. The absolute values ​​of G(r) in the range of r from 5 Å to 10 Å were confirmed to be less than 1.0 in all regions except 3.50±0.2 Å, 3.99±0.2 Å, 5.85±0.2 Å, 6.20±0.2 Å, 7.25±0.2 Å, 9.50±0.2 Å, and 9.75±0.2 Å. From the above results, it was confirmed that the lithium-based solid electrolyte obtained by adding LiFSI and dispersing it in water was amorphous. On the other hand, the peaks attributed to the BO-to-BO distance and BB-to-BB distance, which are observed in typical lithium tetraborate crystals, were maintained in the lithium-based solid electrolyte. 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 is maintained in lithium-based solid electrolytes.

[0191] The solid lithium-based solid electrolyte obtained above 7The total width at half maximum (FMAX 1) of the peaks in the spectrum obtained when the chemical shift in the spectrum is in the range of -100 to +100 ppm, when measured at 20°C, is relative to the solid state of lithium-based solid electrolytes. 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%. solid 7 When 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%.

[0192] Using the lithium-based solid electrolyte 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 maximum absorption intensities in the wavenumber region was 0.72.

[0193] In the Raman spectrum of the obtained lithium-based solid electrolyte, 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. The obtained lithium-based solid electrolyte was heated from 25°C to 800°C using a TG-DTA apparatus under the conditions described later, and the mass loss rate was measured to be 29.8%.

[0194] For the analysis of each element in the obtained lithium-based solid electrolyte, 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.

[0195] <Example 2> A lithium compound was obtained by ball milling Li2B4O7(247) powder (Rare Metallic) using a ball mill (Fritsch P-7) under the following conditions: pot: stabilized zirconia (YSZ) (45 ml), grinding balls: stabilized zirconia (YSZ) (average particle size: 5 mm, number: 50), rotation speed: 370 rpm, amount of LBO powder (powdered Li2B4O7 crystals (Rare Metallic)): 1 g, atmosphere: air, ball mill processing time: 100 hours. The obtained lithium compound was added to water at a powder concentration of 42% by mass and subjected to sonication for 30 minutes. Next, 0.05 g of Li(FSO2)2N(LiFSI) was added to the resulting dispersion, and the mixture was sonicated for a further 30 minutes. Next, the obtained dispersion was transferred to a glass petri dish and dried in air at 120°C for 2 hours to obtain a lithium-based solid electrolyte film. Subsequently, the obtained film was peeled off to obtain powder. After the obtained powder was allowed to stand in air for a certain period of time, various evaluations were performed in the same manner as in Example 1. The results are summarized in the table below.

[0196] <Example 3> Using a ball mill (Fritsch P-7), Li2B4O7(247) powder (Rare Metallic) was ball-milled under the following conditions: pot: stabilized zirconia (YSZ) (45 ml), grinding balls: stabilized zirconia (YSZ) (average particle size: 5 mm, weight: 70 g), rotation speed: 530 rpm, amount of LBO powder (powdered Li2B4O7 crystals (Rare Metallic)): 4.2 g, atmosphere: air, ball mill processing time: 100 hours to obtain a lithium compound. The obtained lithium compound was added to water at a powder concentration of 42% by mass and sonicated for 60 minutes to obtain dispersion 1. Next, 2.32 g of Li(FSO2)2N(LiFSI) was added to water at a powder 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 a powder (lithium-based solid electrolyte). After the obtained powder was allowed to stand in the atmosphere for a certain period of time, various evaluations were performed in the atmosphere as in Example 1. The results are summarized in the table below.

[0197] <Example 4> Using a ball mill (Fritsch P-7), Li2B4O7(247) powder (Rare Metallic) was ball-milled under the following conditions: pot: stabilized zirconia (YSZ) (45 ml), grinding balls: stabilized zirconia (YSZ) (average particle size: 5 mm, weight: 70 g), rotation speed: 530 rpm, amount of LBO powder (powdered Li2B4O7 crystals (Rare Metallic)): 4.2 g, atmosphere: air, ball mill processing time: 100 hours to obtain a lithium compound. The obtained lithium compound was added to water at a powder concentration of 42% by mass and sonicated for 60 minutes to obtain dispersion 3. Next, 3.25 g of Li(FSO2)2N(LiFSI) was added to water at a powder 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 a powder (lithium-based solid electrolyte). After the obtained powder was allowed to stand in the atmosphere for a certain period of time, various evaluations were performed in the atmosphere as in Example 1. The results are summarized in the table below.

[0198] <Example 5> Using a ball mill (Fritsch P-7), Li2B4O7(247) powder (Rare Metallic) was ball-milled under the following conditions: pot: stabilized zirconia (YSZ) (45 ml), grinding balls: stabilized zirconia (YSZ) (average particle size: 5 mm, weight: 70 g), rotation speed: 530 rpm, amount of LBO powder (powdered Li2B4O7 crystals (Rare Metallic)): 4.2 g, atmosphere: air, ball mill processing time: 100 hours to obtain a lithium compound. The obtained lithium compound was added to water at a powder concentration of 42% by mass and sonicated for 60 minutes to obtain dispersion 5. Next, 4.65 g of Li(FSO2)2N(LiFSI) was added to water at a powder 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 a powder (lithium-based solid electrolyte). Immediately after vacuum drying, various evaluations were performed under air using the obtained powder in the same manner as in Example 1. The results are summarized in the table below.

[0199] <Example 6> Using a ball mill (Fritsch P-7), Li2B4O7(247) powder (Rare Metallic) was ball-milled under the following conditions: pot: stabilized zirconia (YSZ) (45 ml), grinding balls: stabilized zirconia (YSZ) (average particle size: 5 mm, weight: 70 g), rotation speed: 530 rpm, amount of LBO powder (powdered Li2B4O7 crystals (Rare Metallic)): 4.2 g, atmosphere: air, ball mill processing time: 100 hours to obtain a lithium compound. The obtained lithium compound was added to water at a powder concentration of 42% by mass and sonicated for 60 minutes to obtain dispersion 7. Next, 7.13 g of Li(F3CSO2)2N(LiTFSI) was added to water at a powder 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 a powder (lithium-based solid electrolyte). After the obtained powder was allowed to stand in the atmosphere for a certain period of time, various evaluations were performed in the atmosphere as in Example 1. The results are summarized in the table below. In Example 6, the amount of carbon shown in Table 1, described later, was estimated from the analytical mass of sulfur, taking into account the atomic weights of each component in the Li salt.

[0200] <Comparative Example 1> A comparative compact was obtained by compacting powdered Li2B4O7 crystals (LBO powder) (manufactured by Rare Metallic) at an effective pressure of 200 MPa at 27°C (room temperature). The ionic conductivity of the obtained compact could not be detected.

[0201] <Reference example 1> A lithium compound was obtained by ball milling Li2B4O7 (LBO) powder (Rare Metallic) using a ball mill (Fritsch P-7) under the following conditions: pot: stabilized zirconia (YSZ) (45 ml), grinding balls: stabilized zirconia (YSZ) (average particle size: 5 mm, number: 50), rotation speed: 500 rpm, amount of LBO powder (powdered Li2B4O7 crystals (Rare Metallic)): 2 g, atmosphere: air, ball mill processing time: 100 hours. After the obtained lithium compound was allowed to stand in air for a certain period of time, various evaluations were performed in the same manner as in Example 1.

[0202] The obtained lithium compound had a particle size distribution of several μm to approximately 10 μm, and a median diameter (D50) of 1.5 μm. The bulk modulus of the obtained lithium compound was 36 GPa. For reference, the bulk modulus of the LBO powder before ball milling was 47 GPa. The bulk modulus of the lithium compound was measured using the ultrasonic attenuation method. Specifically, a suspension was prepared by first suspending the lithium compound in pure water. The lithium compound content in the suspension was 1.2% by mass relative to the total mass of the suspension. Next, the ultrasonic attenuation spectrum of the above suspension was measured, and the bulk modulus (GPa) of the lithium compound was determined by fitting using the scattering attenuation theory formula. When calculating the bulk modulus, the density of the specific solid electrolyte was set to 2.3 g / mL and the Poisson's ratio to 0.12 for the fitting. Furthermore, the bulk modulus was calculated using equations (7), (12), and (13) described in Kohjiro Kubo et al., Ultrasonics 62 (2015), pp. 186-194.

[0203] <Various evaluations> (Ionic conductivity measurement (1)) The lithium-based solid electrolytes obtained in each example were compacted at 27°C (room temperature) under an effective pressure of 200 MPa to obtain compacted bodies. In foil was placed on the front and back surfaces of the obtained compacted bodies, and the ionic conductivity was estimated from the analysis of the arc diameter of the Cole-Cole plot (Nyquist plot) obtained by AC impedance measurement via two In electrodes (measurement temperature 27°C or 60°C, applied voltage 50 mV, measurement frequency range 1 Hz to 1 MHz). The obtained ionic conductivity values ​​at measurement temperatures of 27°C and 60°C are shown in Table 2 below.

[0204] (Water content) The water content in the lithium-based solid electrolyte obtained in each example was determined from the measurement results of the lithium-based solid electrolyte using elemental analysis methods and the types of components used. The water content relative to the total mass of the lithium-based solid electrolyte obtained in Examples 1 to 6, as determined by the method described above, is summarized in Table 2 below.

[0205] (SEM-EDX analysis) 400 mg of the lithium-based solid electrolyte obtained in Example 5 was compacted into a powder pellet (10 mm in diameter, 2 mm thick) using a pressure molder at 27°C with an effective pressure of 200 MPa. The obtained powder pellet was placed in a battery jig and dried for 48 hours in an airtight container containing silica gel desiccant while a confinement pressure of 60 MPa was applied. The dried compacted powder was cut, and the exposed rough surface was polished using a cross-section polisher (CCP) under the following conditions. • Device: JEOL Ltd. "SM-9020CP" Processing time: 4.5 hours ·Processing temperature: -120℃ • Processing range: 500 μm (width at half maximum) Next, by detecting the K-line spectra of sulfur, boron, nitrogen, oxygen, and fluorine using the SEM-EDX instrument described below, a mapping image showing the compositional distribution in the exposed cross-section was obtained. • Field emission electron probe microanalyzer (FE-EPMA): JXA-8530F, manufactured by JEOL Ltd. • Acceleration voltage: 10kV • Observation magnification: 100 to 1000 times The cross-sectional structure and composition of the compacted powder were observed and analyzed from the mapping images obtained using the above-mentioned device.

[0206] Figure 14 shows the mapping image obtained by the SEM-EDX analysis described above. In the obtained mapping image, the regions where sulfur was detected by SEM-EDX analysis are shown as bright areas, and a network structure is formed in which particulate dark areas are surrounded by bright areas that form a continuous phase. In the lithium-based solid electrolyte obtained in Example 5, sulfur is contained in the lithium salt, but not in lithium tetraborate or water. From this, observation by SEM-EDX analysis confirmed that a network structure is formed in the region where lithium salt is present in the cross-section of the molded body obtained by pressurizing the lithium-based solid electrolyte obtained in Example 5. As shown in Figure 14, it is presumed that the wide network structure containing lithium salt functions as an excellent ion conduction path, resulting in excellent ion conductivity. Similar to Example 5, compacts were prepared using the lithium-based solid electrolytes obtained in Examples 1-4 and 6. SEM-EDX analysis of the cross-section of the obtained compacts confirmed that a network structure was formed in the regions where lithium salts were present.

[0207] (TG-DTA) The lithium-based solid electrolyte obtained in Example 5 was compacted into a powder using a pressure molder at 27°C under an effective pressure of 200 MPa to produce a compacted powder (pellet) (10 mm in diameter, 1 mm thick). The obtained compacted powder was placed in a battery jig and freeze-dried under a confinement pressure of 60 MPa for 18 hours. The freeze-dried compacted powder was pulverized, and thermogravimetric differential thermal analysis (TG-DTA) was performed on 20 mg of the resulting powder under the following conditions. • Equipment: MacScience "TG-DTA 2000S" • Temperature program: 25℃ (room temperature) - 800℃ (slope: 10℃ / min) • Measurement environment: Under air • Sample weight: 20 mg • Measuring container: Deep dish made of Pt (platinum).

[0208] Figure 17 shows the chart obtained from the TG-DTA measurement described above. In the obtained chart, a combustion peak appeared at a temperature of around 149°C. This combustion peak is presumed to originate from the combustion of the Li salt (LiFSI). When TG-DTA measurement was performed on LiFSI alone under the above measurement conditions, the combustion peak of LiFSI appeared at around 120°C. Therefore, it is presumed that in the compacted lithium-based solid electrolyte of Example 5, the combustion peak shifted to a higher temperature as a result of the interaction between the Li salt and BM-LBO247 (ball-milled Li2B4O7) and / or water.

[0209] (TG-MS) A compacted lithium-based solid electrolyte obtained in Example 5 was prepared according to the method described above (TG-DTA), and the obtained compacted powder was freeze-dried. The freeze-dried compacted powder was pulverized, and thermogravimetric mass spectrometry (TG-MS) was performed on the obtained powder under the following conditions. • Equipment: NETCH STA2500 and JEOL JMS-Q1050GC • Temperature program: 40℃-500℃ (Slope: 5℃ / min) • Measurement atmosphere: He • Sample weight: 84.46 mg • Measuring container: Aluminum deep dish ·Mass spectrometer: Quadrupole mass spectrometer (QMS) • Ionizer: EI 70eV capillary (0.32mm inner diameter blank tube) • Scan range: 10-1000Da Transfer line temperature: 300℃

[0210] Figure 18 shows the chart obtained from the TG-MS measurement described above. The chart shows a weight decrease between 100 and 137°C, during which a component with a molecular weight of 18 was mainly detected. Thus, the detection of a component with a molecular weight of 18, presumed to be water, in the temperature range above 100°C suggests that water (particularly water in the third and fourth states) is present in the compacted lithium-based solid electrolyte obtained in Example 5. Furthermore, a rapid weight decrease was observed from 137°C. At this temperature, a component presumed to mainly originate from the combustion of Li salt (LiFSI) was detected, but a component with a molecular weight of 18 was also detected. From this, it is highly probable that water confined by the Li salt vaporized along with the combustion of the Li salt. The TG-MS measurements described above suggest that water (particularly water in the third and fourth states) may be confined in the region where the Li salt is present in the lithium-based solid electrolyte of the present invention.

[0211] ( 1 (H-NMR) The lithium-based solid electrolyte powder obtained in Example 5 was placed in a sealed test tube under a nitrogen atmosphere and subjected to the conditions described above. 1 1H-NMR measurements were performed. Figure 11 shows the above 1 The spectrum obtained by 1H-NMR measurement is shown. From the obtained spectrum, both sharp and broad peaks were observed. From this, it is inferred that the lithium-based solid electrolyte of Example 5 contains hydrogen atoms with relatively high mobility corresponding to the sharp peak and hydrogen atoms with relatively low mobility corresponding to the broad peak.

[0212] ( 19 F-NMR) The lithium-based solid electrolyte powder obtained in Example 5 was placed in a sealed test tube under a nitrogen atmosphere and solidified under the conditions described above. 19 F-NMR measurements were performed. Figure 19 shows the above 19The spectrum obtained by F-NMR measurement is shown. The results of the above measurement show a sharp peak in the chemical shift range of -200 to +300 ppm, suggesting the presence of a lithium salt or anion with relatively high mobility that contributes to ionic conductivity.

[0213] (X-ray total scattering measurement) X-ray total scattering measurements were performed at SPring-8 BL04B2 (acceleration voltage: 61.4 keV, wavelength: 0.2019 Å) using the lithium-based solid electrolyte of each example, the crystalline powder of the comparative example, and the lithium compound of the reference example. The samples were sealed in 2 mmφ or 1 mmφ Kapton capillaries for the experiment. The obtained data were then Fourier transformed as described above to obtain the reduced two-body distribution function. The analysis revealed that in the reduced two-body distribution function G(r) obtained from X-ray total scattering measurements, there was 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. If the G(r) at the peak top of both the first and second peaks was greater than 1.0, the "Short-range G(r)" column in Table 2 was marked "A," and all other cases were marked "B." Furthermore, in Examples 1-6 shown in Table 2 (described later) and Examples 9-13 shown in Table 6 (described later), the G(r) value at the peak top of the first peak was 1.2 or higher. Furthermore, in the above reduction dibody distribution function G(r), if 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-range G(r)" column in Table 2 is set to "A", and in all other cases, it is set to "B".

[0214] (X-ray diffraction measurement) X-ray diffraction measurements were performed using CuKα radiation for the lithium-based solid electrolyte of the example, the crystalline powder of the comparative example, and the lithium compound of the reference example. The measurement conditions were 0.01° / step and 3° / min. Based on the measurement results, the diffraction pattern obtained was designated as "A" if it satisfied the above-mentioned requirement Y, and as "B" if it did not. In addition, in Examples 1 to 6 shown in Table 2 and Examples 7 to 13 shown in Table 6, the X-ray diffraction patterns either did not contain any of the first, second, third, and fourth peaks, or the intensity ratio of at least one specific peak selected from the group consisting of the first, second, third, and fourth peaks was 2.0 or less.

[0215] In Table 1, the "Elemental Analysis" column shows the composition of the lithium-based solid electrolyte obtained in each example, as determined by the elemental analysis method described above, expressed as the molar content of each element as a relative value when the content of B is set to "4.00". In the table, the "Water (%)" column indicates the water content (unit: mass%) in the lithium-based solid electrolyte obtained in each example. In the table, the "Percentage of Full Width at Half Maximum (%)" column represents the solid state of lithium-based solid electrolytes. 7 The total width at half maximum 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 state of lithium-based solid electrolytes. 7 This value represents the percentage of the full width at half maximum (FMAX) of peaks in the spectrum obtained when Li-NMR measurements are performed at 120°C, where the chemical shift falls within the range of -100 to +100 ppm.

[0216] In the table, the "Area Intensity Ratio" column represents the ratio of the area intensity of the second peak to the area intensity of the first peak, as described above. The "Value (%)" column shows a specific numerical value, and the "Range" column indicates which range each example and comparative example falls into according to the following criteria (area intensity ratio range). Note that in Examples 3, 5, and 6, the "Value (%)" column does not show a numerical value, but rather the "Range" column indicates which range it belonged to. (Ratio range 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%

[0217] In the table, the "Maximum Absorption Intensity Ratio" column represents the infrared absorption spectrum of lithium-based solid electrolytes, specifically the range from 800 to 1600 cm⁻¹. -1 For the maximum absorption intensity in the wavenumber region, 3000-3500 cm -1 This represents the ratio of maximum absorption intensities in the wavenumber region. The "Value" column shows a specific numerical value, and the "Range" column indicates which range the values ​​for each example and comparative example belong to according to the following criteria (maximum absorption intensity ratio range). Note that in Examples 3, 5, and 6, the "Value" column does not show a numerical value, but the "Range" column indicates which range it belonged to. (Maximum absorption intensity ratio range) A: When the maximum absorption intensity ratio range is 0.20 or greater. B: When the maximum absorption intensity ratio range is less than 0.20

[0218] In the table, the "Maximum Absorption Intensity Ratio (N2 Atmosphere, Heated at 90°C)" column indicates that the obtained lithium-based solid electrolyte was heated at 90°C for 5 minutes, and the infrared absorption spectrum of the lithium-based solid electrolyte after heat treatment was measured. The obtained infrared absorption spectrum was measured between 800 and 1600 cm⁻¹. -1 For the maximum absorption intensity in the wavenumber region, 3000-3500 cm -1 This represents the ratio of the maximum absorption intensities in the wavenumber region. In the table, the "Coefficient of Determination" column represents the Raman spectrum from 600 to 850 cm⁻¹ for Examples 1 and 2. -1 This represents the coefficient of determination obtained by performing a linear regression analysis using the least squares method in the wavenumber domain. In the table, the "Requirement T" column is marked "A" if the above requirement T is met, and "B" if it is not met. Note that in the Raman spectra of the lithium-based solid electrolytes of Examples 1-6, the range specified by requirement T is 710-730 cm⁻¹. -1 It has a peak top and a full width at half maximum of 5 cm. -1 The first peak, as described above, is 770-790 cm. -1 It has a peak top and a full width at half maximum of 5 cm. -1 The second peak mentioned above, and 1020-1040cm -1 It has a peak top and a full width at half maximum of 5 cm. -1 None of the above third peaks were present. In the table, the "Mass Loss Rate (%)" column represents the mass loss rate when the lithium-based solid electrolyte is heated to 800°C, as described above. In the table, "-" indicates that a measurement value is not shown.

[0219] In Examples 1 to 6, the lithium compounds obtained by ball milling Li2B4O7(247) powder (made by Rare Metallic) all satisfied all of the above-mentioned requirements α, β, γ, and δ. More specifically, in Examples 1 to 6, the Raman spectra of lithium compounds obtained by ball milling Li2B4O7(247) powder (made by Rare Metallic) did not contain any of the first to third peaks defined by requirement δ. Furthermore, in Examples 1 to 6, the X-ray diffraction patterns obtained from CuKα-ray X-ray diffraction measurements of lithium compounds obtained by ball milling Li2B4O7(247) powder (made by Rare Metallic) showed that none of the first to fourth peaks defined by requirement α were present, or at least one specific peak selected from the group consisting of the first, second, third, and fourth peaks was present, and the intensity ratio calculated by at least one intensity measurement method for that specific peak was 2.0 or less.

[0220] [Table 1]

[0221] [Table 2]

[0222] As shown in the table above, the lithium-based solid electrolyte of the present invention exhibited the desired effects. In particular, the invention described in Patent Document 1 has an ionic conductivity of 10 -5 S·cm -1 In contrast to the previous method, it has been confirmed that the present invention exhibits superior ionic conductivity. As shown in Table 1, it was confirmed that the Li content was higher in Examples 3 to 6. The reason for the increase in Li content is that in Examples 3 to 6, a method was used in which 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). This method allows for a larger amount of Li(FSO2)2N(LiFSI) to be mixed, which is presumed to have increased the amount of Li incorporated into the lithium-based solid electrolyte. Furthermore, as shown in Table 2, it was confirmed that the ionic conductivity was also improved in Examples 3 to 6. The reason for the improved ionic conductivity is presumed to be that the Li composition ratio (content ratio) increased, and the increased Li included highly mobile Li, resulting in an overall increase in highly mobile Li.

[0223] Furthermore, as shown in the "Maximum Absorption Intensity Ratio" and "Maximum Absorption Intensity Ratio (N2 atmosphere, heated at 90°C)" columns of Table 2, in Example 4, the heat treatment resulted in 800-1600 cm⁻¹ -1 For the maximum absorption intensity in the wavenumber region, 3000-3500 cm -1 The ratio of maximum absorption intensities in the wavenumber region was reduced. This is presumed to be due to the vaporization of water (mainly water in the first state) contained in the lithium-based solid electrolyte.

[0224] In the reduced dibody distribution function G(r) obtained from the X-ray total scattering measurement of the crystalline powder of Comparative Example 1, there was a first peak located at 1.40 Å (corresponding to proximity of BO) and a second peak located at 2.40 Å (corresponding to proximity of BB), and the G(r) values ​​at the peak tops of both the first and second peaks were greater than or equal to 1.0 (see Figure 20). In addition, there were peaks located at 3.65 Å, 5.22 Å, 5.51 Å, and 8.54 Å, and the G(r) values ​​at the peak tops of each of these peaks were greater than or equal to 1.0 (see Figure 20). In contrast, the reduced dibody distribution function G(r) obtained from the X-ray total scattering measurement of the lithium compound in Reference Example 1 had a first peak (corresponding to proximity of BO) with its peak top located at 1.40 Å, and a second peak (corresponding to proximity of BB) with its peak top located at 2.40 Å, and the G(r) values ​​at the peak tops of both the first and second peaks were greater than 1.0. On the other hand, in the range where r is greater than 5 Å and less than or equal to 10 Å, the absolute value of G(r) was less than 1.0. These results confirm that mechanical milling reduces the peaks of long-range ordered structures in the range of r greater than 5 Å and less than or equal to 10 Å. On the other hand, the peaks attributed to the BO-to-BO distance and BB-to-BB distance, which are observed in typical lithium tetraborate crystals, were maintained even after mechanical milling. From these results, it is considered that the structure in which BO4 tetrahedra and BO3 triangles exist in a 1:1 ratio (diborate structure), which is present in typical lithium tetraborate crystals, is maintained after mechanical milling.

[0225] Figure 21 shows the X-ray diffraction pattern of the crystalline powder of Comparative Example 1. As shown in Figure 21, Comparative Example 1 did not satisfy the above-mentioned requirement Y, and several narrow peaks were observed. 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°, with the intensities of these three peaks being almost equivalent. These peaks originate from the crystalline components. In contrast, Figure 22 shows the X-ray diffraction pattern of the lithium-based solid electrolyte of Example 4. As shown in Figure 22, in Example 4, the requirement was met even when the intensity ratio specified in requirement Y above was changed from 5.0 to 2.0. In Figure 21, it can be seen that the crystalline components present were amorphous by the mechanical milling process, and the sharp peaks originating from the lithium tetraborate crystals disappeared and became broader.

[0226] (Ionic conductivity measurement (2)) The lithium-based solid electrolyte compacted powder (pellets) (10 mmφ, 0.9 mm thick) obtained in Example 4 was vacuum-dried at 27°C under a constraint of 60 MPa, and the pressure change and ionic conductivity with respect to the vacuum drying time were evaluated. The method for preparing the compacted powder and evaluating its ionic conductivity was the same as described above (Ionic Conductivity Measurement (1)), except that the In electrode was replaced with a Ti electrode. The results are shown in Table 3.

[0227] [Table 3]

[0228] The lithium-based solid electrolyte of Example 4 showed an infrared absorption spectrum of 3000-3500 cm⁻¹. -1 The increased OH stretching peak suggests the presence of numerous OH groups or water molecules. Furthermore, as mentioned above, the presence of water molecules in states 1 through 4 is also inferred. In the above evaluation, in order to confirm the presence of substances with good ionic conductivity other than water in the first and second states, the pellets were first dried under conditions where it was thought that mainly the water in the first state would vaporize, and then dried under conditions with increased intensity, and the ionic conductivity at each stage was evaluated.

[0229] As shown in Table 3, after a drying time of 5 minutes, the pressure is 200 Pa, and it is thought that the water in the first state is mainly in a vaporized state, but the ionic conductivity is 3.8 × 10⁻⁶. -3 The result was S / cm. Subsequently, after vacuum drying for 1080 minutes at a pressure of 15 Pa, the ionic conductivity was 5.7 × 10⁻⁶ even in the state where the water in the first and second states was thought to have vaporized. -4 It was found to exhibit S / cm, confirming the existence of a substance with good ionic conductivity other than water in the first and second states. Although this substance is not yet clear, it is presumed to be water (particularly water in the third and fourth states). Furthermore, although the phenomena occurring during the drying process are not clear, as shown in Table 3, at a drying time of 50 minutes and a pressure of 10 Pa, it is presumed that water (especially water in the third and fourth states) remains and gradually desorbs under these conditions. Moreover, at a drying time of 1080 minutes and a pressure of 15 Pa, it is presumed that water with properties that make it more difficult to vaporize (especially water in the fourth state) remains. The results above suggest that lithium-based solid electrolytes possess water with good ionic conductivity (particularly water in the third and fourth states), as evidenced by the excellent ionic conductivity observed even after extended drying times. Furthermore, when the temperature was raised to 100°C while maintaining the pressure and dried, and the ionic conductivity was measured, it was found to be 1.2 × 10⁻⁶. ―5 The reading was S / cm. Thus, ionic conductivity is observed even when it is assumed that only water in the fourth state is present in a lithium-based solid electrolyte.

[0230] (Ionic conductivity measurement (3)) The lithium-based solid electrolyte obtained in Example 5 was compacted using a pressure molder at 27°C and an effective pressure of 200 MPa to produce compacted powder (pellets) (10 mm in diameter, 0.8 mm thick). The obtained compacted powder was clamped in a battery jig and vacuum-dried for 15 hours at 40°C and 20 Pa under a confinement pressure of 60 MPa. The ionic conductivity was then measured under the temperature conditions shown in the table below. The measurement of the ionic conductivity of the compacted powder was carried out according to the method described in (Ionic Conductivity Measurement (1)) above, except that the In electrode was replaced with the Al electrode of the battery jig. The ionic conductivity values ​​obtained at each temperature are shown in Table 4, which will be described later.

[0231] [Table 4]

[0232] As shown in Table 4, under temperature conditions below 0°C, it is presumed that at least the water in the first state contained in the compacted powder is frozen, and under temperature conditions of -10°C, the water in the second state is also frozen. -4The measurement of ionic conductivity in S / cm suggests the presence of a substance with good ionic conductivity other than water in the first and second states. Although this substance is not yet clear, it is presumed to be water (particularly water in the third and fourth states). The results above suggest that lithium-based solid electrolytes possess excellent ionic conductivity, even under temperature conditions of -10°C, indicating the presence of water with good ionic conductivity (particularly water in the third and fourth states).

[0233] (Karl Fischer measurement) 200 mg of each lithium-based solid electrolyte powder obtained in Example 5 was pressed using a uniaxial press (200 MPa, 2 minutes) to obtain compacted powder. The obtained compacted powder was placed in a sealed cell and dried for one month at atmospheric pressure using silica gel enclosed in the cell under a pressure of 60 MPa. The cell was opened under an argon atmosphere, and approximately 5-10 mg of the dried sample was placed in a measurement vial, which was then sealed. A blank vial sealed in the same environment in which the above sample was collected and sealed was also prepared. The vial was placed in the moisture vaporizer attached to the Karl Fischer measuring instrument and heated from room temperature (27°C) to 300°C to vaporize the moisture. Subsequently, the amount of vaporized moisture was measured using the Karl Fischer titration method with a coulometric moisture meter. The above measurements showed that the amount of water vaporized from the lithium-based solid electrolyte during heating from room temperature to 200°C was greater than the amount of water vaporized from the lithium-based solid electrolyte during heating from room temperature to 100°C (A). This suggests the presence of water in the lithium-based solid electrolyte that is more strongly bound to its surroundings compared to water in the first state.

[0234] <Example 7> Using a ball mill (Fritsch P-7), Li2B4O7(247) powder (Rare Metallic) was ball-milled under the following conditions: pot: stabilized zirconia (YSZ) (45 ml), grinding balls: stabilized zirconia (YSZ) (average particle size: 5 mm, weight: 70 g), rotation speed: 530 rpm, amount of LBO powder (powdered Li2B4O7 crystals (Rare Metallic)): 4.2 g, atmosphere: air, ball mill processing time: 100 hours to obtain a lithium compound. The obtained lithium compound was added to water at a powder concentration of 42% by mass and sonicated for 60 minutes to obtain dispersion 9. Next, 7.12 g of Li(F3CSO2)2N(LiTFSI) was added to water at a powder 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 a lithium-based solid electrolyte powder. After the obtained powder was allowed to stand in the atmosphere for a certain period of time, various evaluations were performed in the atmosphere as in Example 1.

[0235] <Example 8> A lithium-based solid electrolyte powder was obtained in the same manner as in Example 7, except that the water and Li(F3CSO2)2N(LiTFSI) content in the obtained lithium-based solid electrolyte was changed to the amounts shown in the table below. After the obtained powder was left to stand in the atmosphere for a certain period of time, various evaluations were performed in the atmosphere as in Example 1.

[0236] <Examples 9-13> A lithium-based solid electrolyte powder was obtained in the same manner as in Example 7, except that Li(F3CSO2)2N(LiTFSI) was changed to Li(FSO2)2N(LiFSI), and the water and Li(FSO2)2N(LiFSI) content in the resulting lithium-based solid electrolyte was changed to the amounts shown in the table below. The obtained powder was left to stand in the atmosphere for a certain period of time, and then various evaluations were performed in the atmosphere as in Example 1. In addition, for the lithium-based solid electrolyte powder obtained in Example 13, various evaluations in the atmosphere were performed immediately after the vacuum drying treatment described above.

[0237] In Table 5, the "BM-LBO247," "Li salt," and "Water" columns represent the respective components in the powder obtained in each example and Reference Example 1. Specifically, "BM-LBO247" represents ball-milled Li2B4O7, and "Li salt" represents the lithium salts (Li(F3CSO2)2N(LiTFSI), Li(FSO2)2N(LiFSI)) used in each example. The "Molar Ratio" column in the table represents the relative molar ratio of each component when the molar amount of BM-LBO247 is set to 1. For example, in the powder obtained in Example 7, the molar ratio of Li salt to BM-LBO247 is 1, and the molar ratio of water to BM-LBO247 is 12. The "Mass Ratio" column in the table represents the relative mass ratio of each component when the total mass of BM-LBO247, Li salt, and water is set to 100. For example, the mass ratio of BM-LBO247, Li salt, and water in the powder obtained in Example 7 is 26:44:30.

[0238] The above molar ratios and mass ratios were calculated using the following method. For the analysis of each element in the obtained powder, 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. For oxygen, the analytical masses of elements other than oxygen were added together and calculated as the difference from the total powder weight. In Examples 7 and 8, the amount of carbon was estimated from the analytical mass of sulfur, taking into account the atomic weights of each element in the Li salt. The molar ratio of BM-LBO247 to Li salt in the powder was calculated from the molar ratio of elements found only in BM-LBO247 (e.g., B) and elements found only in Li salt (e.g., specific elements). The molar ratio of BM-LBO247 to water was calculated by subtracting the molar ratios of O contained in BM-LBO247 and Li salt from the molar ratio of O in the powder to determine the molar amount of O derived from water. The resulting molar amount of O derived from water and the molar amount of BM-LBO247 were then used to calculate the molar ratio. Based on the calculated molar amounts and molecular weights of each component, the mass ratio of each component was calculated.

[0239] In Examples 7 to 13, the lithium compounds obtained by ball milling Li2B4O7(247) powder (made by Rare Metallic) all satisfied the requirements α, β, γ, and δ described above. More specifically, in Examples 7 to 13, the Raman spectra of lithium compounds obtained by ball milling Li2B4O7(247) powder (made by Rare Metallic) did not contain any of the first to third peaks defined by requirement δ. Furthermore, in Examples 7 to 13, the X-ray diffraction patterns obtained from CuKα-ray X-ray diffraction measurements of lithium compounds obtained by ball milling Li2B4O7(247) powder (made by Rare Metallic) showed that none of the first to fourth peaks defined by requirement α were present, or at least one specific peak selected from the group consisting of the first, second, third, and fourth peaks was present, and the intensity ratio calculated by at least one intensity measurement method for that specific peak was 2.0 or less.

[0240] Furthermore, the lithium-based solid electrolytes obtained in Examples 7 to 13 satisfied requirements T, X, and Y described above.

[0241] [Table 5]

[0242] [Table 6]

[0243] As shown in the table above, the lithium-based solid electrolyte of the present invention exhibited the desired effects.

[0244] <Example 21> Using a ball mill (Fritsch P-7), Li2B4O7(247) powder (Rare Metallic) was ball-milled under the following conditions: pot: stabilized zirconia (YSZ) (45 ml), grinding balls: stabilized zirconia (YSZ) (average particle size: 5 mm, weight: 70 g), rotation speed: 530 rpm, amount of LBO powder (powdered Li2B4O7 crystals (Rare Metallic)): 4.2 g, atmosphere: air, ball mill processing time: 100 hours to obtain a lithium compound. The lithium compounds obtained from multiple pots were collected, and 5 g of the collected lithium compound was added to water at a powder concentration of 42% by mass and sonicated for 60 minutes to obtain dispersion A1. Next, 2.5 g of LiCl was added to water at a powder concentration of 40% by mass, and sonicated for 60 minutes to obtain solution A2. The obtained dispersion A1 and solution A2 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 3.5 hours to obtain a powder (lithium-based solid electrolyte). The obtained powder was left to stand in the atmosphere for a certain period of time, and the following evaluation was performed in the atmosphere as in Example 1.

[0245] <Examples 22-27> A lithium-based solid electrolyte powder was obtained in the same manner as in Example 21, except that LiCl was replaced with a Li salt listed in the table below, and the content of each Li salt and water in the resulting lithium-based solid electrolyte was changed to the amounts listed in the table below. After the obtained powder was left to stand in the atmosphere for a certain period of time, the following evaluation was performed in the atmosphere as in Example 1.

[0246] In Table 7, the "BM-LBO247" column, the "Li salt" column, and the "Water" column represent the respective components in the powder obtained in each example. Specifically, "BM-LBO247" represents ball-milled Li2B4O7, and "Li salt" represents the lithium salts (LiCl, LiI, Li2SO4, LiFSI) used in each example. The "Molar Ratio" column in the table represents the relative molar ratio of each component when the molar amount of BM-LBO247 is set to 1.

[0247] Table 7 shows the ionic conductivity values ​​at a measurement temperature of 27°C for compacts obtained by compacting the lithium-based solid electrolytes obtained in each example at an effective pressure of 200 MPa at 27°C (room temperature). The ionic conductivity of each compact was measured according to the method described in (Ionic Conductivity Measurement (1)) above. The water content in the lithium-based solid electrolytes obtained in Examples 21-27 was measured in the same manner as in Examples 1-6, and in all cases it was 20-40% by mass relative to the total mass of the lithium-based solid electrolyte. Furthermore, similar to Example 5, compacts were prepared using the lithium-based solid electrolytes obtained in Examples 21-27, and SEM-EDX analysis of the cross-section of the obtained compacts confirmed that a network structure was formed in the regions where lithium salts were present.

[0248] In Examples 21-27, the lithium compounds obtained by ball milling Li2B4O7(247) powder (made by Rare Metallic) all satisfied the requirements α, β, γ, and δ described above. More specifically, in Examples 21-27, the Raman spectra of lithium compounds obtained by ball-milling Li2B4O7(247) powder (made by Rare Metallic) did not contain any of the first to third peaks defined by requirement δ. Furthermore, in Examples 21 to 27, the X-ray diffraction patterns obtained from CuKα-ray X-ray diffraction measurements of lithium compounds obtained by ball milling Li2B4O7(247) powder (made by Rare Metallic) showed that none of the first to fourth peaks defined by requirement α were present, or at least one specific peak selected from the group consisting of the first, second, third, and fourth peaks was present, and the intensity ratio calculated by at least one intensity measurement method for that specific peak was 2.0 or less.

[0249] Furthermore, the lithium-based solid electrolytes obtained in Examples 21-27 satisfied requirements T, X, and Y described above.

[0250] [Table 7]

[0251] As shown in the table above, the lithium-based solid electrolyte of the present invention exhibited the desired effects. [Explanation of symbols]

[0252] 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. A lithium-based solid electrolyte comprising amorphous lithium tetraborate, water, and a lithium salt, A lithium-based solid electrolyte in which the water content is 45% by mass or less relative to the total mass of the lithium-based solid electrolyte.

2. The lithium-based solid electrolyte according to claim 1, wherein the lithium tetraborate has an O-H structure.

3. The molar ratio of the lithium salt content to the lithium tetraborate content is 0.001 to 1.

5. The lithium-based solid electrolyte according to claim 1, wherein the molar ratio of the water content to the lithium tetraborate content is 1 to 12.

4. The lithium-based solid electrolyte according to claim 2, wherein the lithium salt is a compound represented by formula (1). Formula (1) LiN(R ｆ１ SO ２ ) (Caution ｆ２ SO ２ ) R ｆ１ and R ｆ２ Each of these independently represents either a fluorine atom or a perfluoroalkyl group.

5. The lithium-based solid electrolyte according to claim 1, wherein 400 mg of the lithium-based solid electrolyte is compacted using a pressure molder at 27°C under an effective pressure of 200 MPa to produce a molded body with a diameter of 10 mmφ and a thickness of 2 mm, and when the cross-section of the obtained molded body is observed with a scanning electron microscope, the region where the lithium salt is present is found to be in a mesh-like pattern.

6. A lithium-based solid electrolyte comprising amorphous lithium tetraborate, water, and a lithium salt, A lithium-based solid electrolyte is produced by compacting 400 mg of the lithium-based solid electrolyte using a pressure molding machine at 27°C under an effective pressure of 200 MPa to produce a molded body with a diameter of 10 mmφ and a thickness of 2 mm, and observing the cross-section of the obtained molded body with a scanning electron microscope, wherein the region where the lithium salt is present is found to be in a mesh-like pattern.

7. The lithium-based solid electrolyte according to claim 6, wherein the lithium tetraborate has a hydroxyl group.

8. The lithium-based solid electrolyte according to claim 6, wherein the lithium salt is a compound represented by formula (1). Formula (1) LiN(R ｆ１ SO ２ )(R ｆ２ SO ２ ) R ｆ１ and R ｆ２ Each of these independently represents either a fluorine atom or a perfluoroalkyl group.

9. A method for producing a lithium-based solid electrolyte according to any one of claims 1 to 8, Step 1 involves mechanically milling a lithium-based oxide containing Li and B, Step 2 involves mixing the product obtained in step 1 with water, The process includes step 3, which involves removing water from the dispersion obtained in step 2 to obtain a lithium-based solid electrolyte. A method for producing a lithium-based solid electrolyte that satisfies any of the following requirements 1 to 3. Requirement 1: The mechanical milling process of step 1 is carried out in the presence of a lithium salt containing one or more specific elements selected from the group consisting of F, Cl, Br, I, S, P, Si, Se, Te, C, Sb, As, Sc, Y, Zr, Ti, Hf, and N. Requirement 2: In step 2, the product, water, and lithium salt are mixed. Requirement 3: In step 3, the product obtained by removing water from the dispersion obtained in step 2 is mixed with the lithium salt to obtain the lithium-based solid electrolyte.

10. A method for producing a lithium-based solid electrolyte according to claim 9, wherein in step 3, the dispersion obtained in step 2 is dried under conditions of 20 Pa or less and 40°C or less to obtain a lithium-based solid electrolyte.

11. The above requirement 1 is met, A method for producing a lithium-based solid electrolyte according to claim 9, further comprising step 0, which involves mechanically milling a lithium-based oxide containing Li and B in an environment where the lithium salt is absent, prior to step 1.

12. It comprises a positive electrode active material and a coating layer disposed on the positive electrode active material, A modified positive electrode active material wherein the coating layer contains a lithium-based solid electrolyte according to any one of claims 1 to 8.

13. It comprises a negative electrode active material and a coating layer disposed on the negative electrode active material, A modified negative electrode active material wherein the coating layer contains a lithium-based solid electrolyte according to any one of claims 1 to 8.

14. An all-solid-state secondary battery comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer in this order, An all-solid-state secondary battery wherein at least one of the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer contains a lithium-based solid electrolyte according to any one of claims 1 to 8.

15. An electrode sheet for an all-solid-state secondary battery, comprising a lithium-based solid electrolyte according to any one of claims 1 to 8.

16. A solid electrolyte sheet comprising a lithium-based solid electrolyte according to any one of claims 1 to 8.

17. An active material and an active material layer comprising a lithium-based solid electrolyte according to any one of claims 1 to 8, Having a current collector, Electrode for all-solid-state secondary batteries.

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