Sulfide solid electrolyte, and electrode mixture and lithium-ion battery using same

Abstract

Provided are a sulfide solid electrolyte having high ionic conductivity, excellent moldability, and an argyrodite-type crystal structure, and an electrode mixture using the same and lithium-ion battery using these. The sulfide solid electrolyte comprises structure c1, which exhibits a diffraction peak with a peak top at a diffraction angle of 2θ = 25.5 ± 0.5° in the powder X-ray diffraction measurement using CuKα rays and has a crystallite size of 35 nm or more as determined using Scherrer's equation on the basis of the diffraction peak, and structure c2, which has a crystallite size of less than 35 nm. The structures c1 and c2 have an argyrodite-type crystal structure. The content ratio of the structure c2 to the total content of structures c1 and c2 is greater than 33.7% and less than 65.0%.

Description

Sulfide solid electrolyte, and electrode composite material and lithium-ion battery using the same

[0001] This invention relates to a sulfide solid electrolyte, and to an electrode composite material and lithium-ion battery using the same.

[0002] In recent years, with the rapid proliferation of information-related devices and communication equipment such as personal computers, video cameras, and mobile phones, the development of batteries used as power sources has become increasingly important. Traditionally, batteries used in such applications have employed electrolytes containing flammable organic solvents. However, because the electrolyte is both liquid and flammable, there are safety concerns regarding leakage, ignition, etc., when used in batteries. In particular, in automotive applications, there is a demand for higher capacity and higher output, and concerns about the safety of conventional batteries using electrolytes are growing. Therefore, by making batteries entirely solid, it is possible to eliminate the use of flammable organic solvents within the battery, simplify safety devices, and improve manufacturing costs and productivity. As a result, development is underway on all-solid-state batteries, in which the electrolyte is replaced with a solid electrolyte layer.

[0003] Sulfide solid electrolytes are known as solid electrolytes used in lithium-ion batteries. Various crystal structures are known for sulfide solid electrolytes, one of which is the argyrodite type crystal structure. Sulfide solid electrolytes having an argyrodite type crystal structure are known to have high stability and high ionic conductivity (for example, Patent Documents 1 and 2).

[0004] Furthermore, Patent Document 3 discloses sulfide solid electrolyte glass ceramics that have high ionic conductivity, exhibiting a peak with a predetermined intensity at a predetermined diffraction angle in X-ray diffraction measurements, and having a crystallite size of 30 nm or more.

[0005] International Publication No. 2022 / 190940 Brochure International Publication No. 2018 / 164224 Brochure International Publication No. 2023 / 190862 Brochure

[0006] This invention has been made in view of the above circumstances, and provides a sulfide solid electrolyte having an argyrodite-type crystal structure that has high ionic conductivity and excellent moldability, as well as an electrode composite material and a lithium-ion battery using the same.

[0007] The solid electrolyte according to the present invention has a diffraction peak with a peak top at a diffraction angle 2θ = 25.5 ± 0.5°, as measured by powder X-ray diffraction using CuKα rays, and has a structure c whose crystallite size, determined using Scherrer's formula based on the diffraction peak, is 35 nm or larger. １ and structure c with a crystallite size of less than 35 nm ２ Includes the structure c １ and c ２ It has an argyrodite-type crystal structure, and the structure c １ and c ２ The structure c relative to the total content ２ The sulfide solid electrolyte has a content ratio of more than 33.7% but less than 65.0%.

[0008] The electrode composite material according to the present invention is an electrode composite material comprising the above-mentioned sulfide solid electrolyte and electrode active material, and the lithium-ion battery according to the present invention is a lithium-ion battery comprising at least one of the above-mentioned sulfide solid electrolyte and electrode composite material.

[0009] According to the present invention, it is possible to provide a sulfide solid electrolyte having an argyrodite-type crystal structure that has high ionic conductivity and excellent moldability, as well as an electrode composite material and a lithium-ion battery using the same.

[0010] This is the X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Example 1.

[0011] The embodiments of the present invention (hereinafter sometimes referred to as "these embodiments") will be described below. In this specification, the upper and lower limit values ​​related to numerical ranges such as "greater than or equal to," "less than or equal to," and "~" can be arbitrarily combined, and the values ​​of the examples can also be used as the upper and lower limit values. Furthermore, any provisions that are considered preferable can be adopted arbitrarily. That is, one provision that is considered preferable can be adopted in combination with one or more other provisions that are considered preferable. Combinations of preferred provisions are considered even more preferable.

[0012] (Knowledge gained by the inventors to arrive at the present invention) The inventors diligently studied to solve the above problems and, as a result, discovered the following, and completed the present invention.

[0013] To improve the battery characteristics of lithium-ion batteries using solid electrolytes, especially all-solid-state batteries, high ionic conductivity of the solid electrolyte itself is important. However, it is also crucial to consider the state of the solid electrolyte when it is used in the solid electrolyte layer, positive electrode, and negative electrode. In the solid electrolyte layer, the particles of the solid electrolyte are in close contact with each other. In the positive and negative electrodes, the particles of the solid electrolyte and electrode active material are in close contact with each other. By creating many inter-particle junctions and junctions, ion conduction paths can be secured, resulting in superior battery performance. Furthermore, when forming the positive and negative electrode layers, the sulfide solid electrolyte is deformed by pressing or other processes, improving the adhesion between sulfide solid electrolytes and between the sulfide solid electrolyte and electrode active material. Thus, to obtain superior battery characteristics, the solid electrolyte must possess not only high ionic conductivity but also the ability to secure ion conduction paths by creating many inter-particle junctions and junctions, i.e., moldability.

[0014] Accordingly, the present inventors focused on the crystallite diameter of sulfide solid electrolytes, and studied the influence of the crystallite diameter on ionic conductivity and moldability. As described in Patent Document 3, an increase in crystallite diameter reduces the proportion of crystal grain boundaries that suppress diffusion of lithium ions, so the ionic conductivity of the sulfide solid electrolyte increases. That is, in order to improve the ionic conductivity of the sulfide solid electrolyte, the larger the crystallite diameter, the more advantageous it is. On the other hand, amid demands for further improvement in moldability, sulfide solid electrolytes having a large crystallite diameter sometimes cannot cope with the improvement in moldability. That is, it has been found that there is a trade-off relationship between improving ionic conductivity and improving moldability. It has also been found that such a tendency is remarkable in sulfide solid electrolytes having an argyrodite-type crystal structure.

[0015] It is generally known that a sulfide solid electrolyte having an argyrodite-type crystal structure has diffraction peaks with peak tops at diffraction angles 2θ = 15.5°, 18.0°, 25.5°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0° (all diffraction angles fluctuate within a range of ±0.5°) and the like. The present inventors focused on a diffraction peak having a peak top at diffraction angle 2θ = 25.5° and advanced research, and found that the sulfide solid electrolyte of the present embodiment has a diffraction peak having a peak top at diffraction angle 2θ = 25.5±0.5° as the diffraction peak corresponding to said diffraction peak, and when the diffraction peak having a peak top at diffraction angle 2θ = 25.5±0.5° was analyzed by a predetermined method, it was found that the diffraction peak is constituted by two diffraction peaks. Said two diffraction peaks are derived from a structure c having an argyrodite-type crystal structure and different crystallite diameters, one large and one small １ and c ２ . It was also found that having two types of structures having an argyrodite-type crystal structure and different crystallite diameters, one large and one small, and further including these two types of structures in a specific ratio is effective for improving ionic conductivity and moldability in a well-balanced manner.

[0016] Patent Document 1 focuses on a specific diffraction peak measured by X-ray diffraction, sets the relationship between the peak intensities of two peaks separated by waveform separation of the diffraction peak within a predetermined range, and attempts to suppress the generation of hydrogen sulfide by adjusting the balance between the argyrodite crystal structure and other crystal structures. Patent Document 2 attempts to obtain a sulfide solid electrolyte with small particle size and high ionic conductivity by setting the intensity ratio of diffraction peaks within a predetermined range measured by X-ray diffraction within a specific range in a sulfide solid electrolyte having a predetermined average particle size. However, these patent documents do not consider the problem of improving ionic conductivity and moldability at all, nor do they consider that ionic conductivity and moldability can be improved by including two types of argyrodite crystal structures with different crystallite sizes in a specific ratio.

[0017] Furthermore, Patent Document 3 focuses on the crystallite size when improving ionic conductivity. However, similar to Patent Documents 1 and 2, it does not consider that ionic conductivity and moldability can be improved by the crystallite size. Also, Patent Document 3 discloses an invention relating to glass ceramics, and since sulfide solid electrolytes having an argyrodite-type crystal structure are not obtained by crystallizing amorphous solid electrolytes, they do not fall under the category of glass ceramics.

[0018] Based on the above investigations, the inventors have found that by including two structures of different sizes with specific crystallite sizes in a specific ratio, it is possible to obtain a sulfide solid electrolyte having an argyrodite-type crystal structure that exhibits excellent moldability and high ionic conductivity.

[0019] (Regarding various embodiments of this embodiment) The sulfide solid electrolyte according to the first embodiment of this embodiment has a diffraction peak with a peak top at a diffraction angle 2θ = 25.5 ± 0.5° in powder X-ray diffraction measurement using CuKα rays, and has a structure c whose crystallite size, determined using Scherrer's formula based on the diffraction peak, is 35 nm or larger. １ and structure c with a crystallite size of less than 35 nm ２ Includes the structure c １ and c２ It has an argyrodite-type crystal structure, and the structure c １ and c ２ The structure c relative to the total content ２ It is a sulfide solid electrolyte whose content ratio is greater than 33.7% but less than 65.0%.

[0020] The sulfide solid electrolyte of this embodiment has a structure c with a crystallite size of 35 nm or more. １ and structure c with a crystallite size of less than 35 nm ２ The structure of the sulfide solid electrolyte of this embodiment is c １ and c ２ The crystallite size is determined by the method based on the following research.

[0021] The present inventors have identified a diffraction peak having a peak top at a diffraction angle 2θ = 25.5 ± 0.5° (hereinafter referred to as "diffraction peak P"). ０ It is also called ). We proceeded with the analysis of ) using various methods. And the diffraction peak P ０ Based on this, we were able to determine the crystallite size using Scherrer's formula and perform the analysis with high accuracy. More specifically, the diffraction peak P ０ This is assumed to consist of two diffraction peaks, and these two diffraction peaks are fitted with a Gaussian function to separate the waveforms of the diffraction peaks, and the two resulting diffraction peaks ("diffraction peak P") are then separated. １ " and "Diffraction peak P ２ Based on the peak shape having ) the Scherrer equation, each diffraction peak P １ and P ２ The corresponding crystallite size was calculated. Then, the diffraction peak P with low peak intensity was found. １ However, the crystallite size is large, that is, the crystallite size is 35 nm or larger. １ This is caused by the diffraction peak P, which has a large peak intensity. ２ However, structure c has a small crystallite size, that is, a crystallite size of less than 35 nm. ２ Analysis revealed that this was caused by the diffraction peak P. ０By fitting with a Gaussian function, the waveform separation of diffraction peaks can be performed with extremely high accuracy, thus enabling the above-mentioned structures of different sizes c １ and c ２ The configuration having this feature is considered to represent a more precise understanding of the sulfide solid electrolyte structure.

[0022] In this embodiment, diffraction peaks of the sulfide solid electrolyte were detected with peak tops at diffraction angles 2θ = 25.5 ± 0.5°, as well as at least one of the following diffraction angles: 2θ = 15.5°, 18.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0° (all diffraction angles fluctuate within a range of ±0.5°). Therefore, the structure c constituting the sulfide solid electrolyte is detected. １ and c ２ It can be considered that it has an argyrodite-type crystal structure.

[0023] Through the above research, the composition of the sulfide solid electrolyte can be accurately determined, and the sulfide solid electrolyte of this embodiment exhibits diffraction peak P ０ It has a diffraction peak P ０ P is the diffraction peak. １ and P ２ It is composed of these diffraction peaks P １ and P ２ Each of these structures has a crystallite size of 35 nm or more. １ and structure c with a crystallite size of less than 35 nm ２ This is a diffraction peak caused by structure c １ and c ２ It was found that it possesses a structure that includes an argyrodite-type crystal structure.

[0024] Furthermore, the sulfide solid electrolyte of this embodiment has structure c １ and structure c ２ In relation to structure c １ and c ２ Structure c relative to the total content ２The content ratio of must be greater than 33.7% and less than 65.0%. The crystallite size is the diameter of the crystallites that make up the particles of the sulfide solid electrolyte, and is an indicator of the degree of presence of grain boundaries, which are the interfaces between crystallites present in the particles of the sulfide solid electrolyte. As the crystallite size increases, the number of grain boundaries decreases, making it easier for lithium ions to move within the particles of the sulfide solid electrolyte. However, the sulfide solid electrolyte becomes harder, which reduces the adhesion between the sulfide solid electrolyte particles and between the sulfide solid electrolyte and the electrode active material, making it easier to form. On the other hand, as the crystallite size decreases, the number of grain boundaries increases, which correlates with improved adhesion between the sulfide solid electrolyte particles and between the sulfide solid electrolyte and the electrode active material, making it easier to form. However, it becomes more difficult for lithium ions to move within the particles of the sulfide solid electrolyte. Two structures c with different predetermined crystallite sizes １ and c ２ Having the above ratio results in the structure c with a large crystallite size as described above. １ and structure c with a small crystallite size ２ By leveraging the mutual advantages of these materials, it is possible to achieve both the ease of lithium ion movement and the securing of ion conduction paths by increasing the number of bonding points and bonding surfaces between particles through improved adhesion. As a result, a high level of both ionic conductivity and moldability can be achieved.

[0025] The solid electrolyte according to the second embodiment of this invention is the solid electrolyte of the first embodiment described above, wherein the structure c １ The crystallite size of is 50 nm or more and 200 nm or less, and the structure c ２ The crystallite size of the material is between 10 nm and 30 nm.

[0026] structure c １ and c ２ If the crystallite size is within the above range, it is possible to improve ionic conductivity and moldability in a balanced manner.

[0027] The solid electrolyte according to the third embodiment of this embodiment is the solid electrolyte according to the first or second embodiment described above, wherein the constituent atoms include lithium atoms, phosphorus atoms, and sulfur atoms, and the solid electrolyte according to the fourth embodiment is the solid electrolyte according to the third embodiment described above, wherein the solid electrolyte further includes halogen atoms.

[0028] The sulfide solid electrolyte of this embodiment, by containing lithium atoms, phosphorus atoms, and sulfur atoms as constituent atoms, easily improves ionic conductivity, and by further containing halogen atoms, the ionic conductivity can be further improved.

[0029] The fifth embodiment of this solid electrolyte is characterized in that, in any one of the first to fourth embodiments described above, the ionic conductivity when molded at 400 MPa is 3.0 mS / cm or higher.

[0030] The sulfide solid electrolyte of this embodiment has high ionic conductivity under conditions that simulate actual use, such as molding at 400 MPa. Because the sulfide solid electrolyte of this embodiment has an argyrodite crystal structure, it has high ionic conductivity itself, but its excellent moldability allows for an increase in interparticle bonding points and bonding surfaces due to the close contact between sulfide solid electrolyte particles, thereby securing ion conduction paths and achieving superior battery performance.

[0031] The electrode composite material according to the sixth embodiment of this embodiment is an electrode composite material comprising a sulfide solid electrolyte according to any one of the first to fifth embodiments described above, and an electrode active material.

[0032] The sulfide solid electrolyte of this embodiment has high moldability, and by increasing the number of bonding points and bonding surfaces between particles through close contact with the electrode active material, excellent battery performance can be obtained by securing ion conduction paths. Furthermore, since the sulfide solid electrolyte of this embodiment has high ionic conductivity, the electrode composite material containing it also exhibits high ionic conductivity. As a result, excellent battery performance can be obtained by using the electrode composite material of this embodiment in a lithium-ion battery.

[0033] The lithium-ion battery according to the seventh embodiment of this embodiment is a battery comprising at least one of the sulfide solid electrolyte according to any one of the first to fifth embodiments described above and the electrode composite material according to the sixth embodiment described above.

[0034] The sulfide solid electrolyte of this embodiment exhibits excellent ionic conductivity and moldability. Therefore, by employing the sulfide solid electrolyte, or an electrode composite material using it, in a lithium-ion battery, a battery with superior performance can be achieved.

[0035] The solid electrolyte of this embodiment will be described in more detail below, following the embodiments described above.

[0036] In this specification, "solid electrolyte" means an electrolyte that maintains a solid state at 25°C under a nitrogen atmosphere. The sulfide solid electrolyte in this embodiment is a solid electrolyte containing at least sulfur atoms, and preferably further contains lithium atoms in order to have a higher ionic conductivity. The ionic conductivity due to lithium atoms, which is exhibited by using lithium atoms as the conductive species, becomes higher. Furthermore, the sulfide solid electrolyte in this embodiment preferably contains lithium atoms, phosphorus atoms and sulfur atoms, and more preferably further contains halogen atoms.

[0037] The term "solid electrolyte" includes both crystalline solid electrolytes and amorphous solid electrolytes. In this specification, a crystalline solid electrolyte is a solid electrolyte in which peaks originating from the solid electrolyte are observed in the X-ray diffraction pattern in X-ray diffraction measurements, regardless of whether or not peaks originating from the raw materials of the solid electrolyte are present. That is, a crystalline solid electrolyte includes a crystalline structure derived from the solid electrolyte, and may be partially or entirely derived from the solid electrolyte. Furthermore, a crystalline solid electrolyte may contain an amorphous solid electrolyte as long as it has the above-described X-ray diffraction pattern. Therefore, crystalline solid electrolytes include so-called glass ceramics obtained by heating an amorphous solid electrolyte above its crystallization temperature. In this specification, an amorphous solid electrolyte is a solid electrolyte in which, in the X-ray diffraction pattern in X-ray diffraction measurements, substantially no peaks other than those originating from the material are observed, regardless of whether or not peaks originating from the raw materials of the solid electrolyte are present.

[0038] [Sulfide Solid Electrolyte] The sulfide solid electrolyte of this embodiment has a diffraction peak with a peak top at a diffraction angle 2θ = 25.5 ± 0.5° in powder X-ray diffraction measurement using CuKα rays, and has a structure c whose crystallite size, determined using Scherrer's formula based on the diffraction peak, is 35 nm or larger. １ and structure c with a crystallite size of less than 35 nm ２ Includes the structure c １ and c ２ It has an argyrodite-type crystal structure, and the structure c １ and c ２ The structure c relative to the total content ２ It is a sulfide solid electrolyte whose content ratio is greater than 33.7% but less than 65.0%.

[0039] (Structure c １ and c ２ (crystallite size) As previously described, diffraction peak P ０By assuming that it consists of two diffraction peaks and fitting each diffraction peak with a Gaussian function, the waveform separation of the diffraction peaks can be performed with high accuracy. In other words, the structure of the sulfide solid electrolyte in this embodiment can be determined with higher accuracy. And as the structure of the sulfide solid electrolyte determined in this way, the diffraction peak P １ and P ２ The crystallite size, determined using Scherrer's formula based on these diffraction peaks, corresponds to the structure c. １ and c ２ This results in a highly precise crystallite size.

[0040] structure c １ The crystallite size is determined by the diffraction peak (diffraction peak P) having its peak top at the diffraction angle 2θ = 25.5 ± 0.5°. ０ For this, two Gaussian functions are fitted, and the diffraction peak P with the smallest peak intensity is found. １ The crystallite size is calculated using Scherrer's formula from the peak shape having the following characteristics, and structure c ２ The crystallite size is determined by the diffraction peak P, which has a large peak intensity. ２ The crystallite size is calculated from the peak shape using Scherrer's formula as shown below.

[0041] Scherrer's formula is the following equation: Crystallite size (L) = Kλ / (β × cosθ) K: Scherrer's constant, 0.9 was used. λ: 1.5418 Å (Cu-Kα line) β: Calculated from β = w - B. w: The full width at half maximum (FWHW) of each diffraction peak after waveform separation of the diffraction peak with a peak top at 25.5 ± 0.5° obtained by measurement into two diffraction peaks. B: Instrument constant (Powder X-ray diffraction (XRD) measurement was performed on a standard material (silicon) using the same method as the powder X-ray diffraction (XRD) measurement of the sulfide solid electrolyte, and B = 0.087° was determined from the peak at 2θ = 28.5°.) Furthermore, the above w (FWHW obtained by measurement) was determined from the FWHW (full width at half maximum) obtained by peak fitting using the solver function in the following procedure for the diffraction peak with a peak top at the diffraction angle 2θ = 25.5 ± 0.5° obtained by powder X-ray diffraction (XRD) of the sulfide solid electrolyte. First, the initial values ​​were set as follows: Background: The average value of the intensity at diffraction angles of peak top ± 1°. Structure c １ and c ２ The intensity of each is set to 2 / 3 and 1 / 3 of (maximum intensity of diffraction peak - background). Structure c １ and c ２ The full width at half maximum (FWHM) is set to 0.1° and 0.2°, respectively. Next, the Solver function of the spreadsheet software Excel (Microsoft Corporation) is used to determine "structure c １ The full width at half maximum of the diffraction peak < structure c ２ The constraint condition is set to be the "full width at half maximum of the diffraction peak", and the background and structure c １ and c ２ The peak intensity and FWHW (full width at half maximum) were used as variables, the solution method was set to GRG nonlinearity, and the analysis was performed to minimize the error between the fitting result and the measured value, and the solution was determined.

[0042] Structure c calculated in this manner １The crystallite diameter may be 35 nm or more. From the viewpoint of improving ionic conductivity and moldability in a well-balanced manner, it is preferably 50 nm or more, more preferably 55 nm or more, still more preferably 60 nm or more. As the upper limit, it is preferably 500 nm or less, more preferably 350 nm or less, still more preferably 200 nm or less, even more preferably 170 nm or less. Further, structure c ２ The crystallite diameter may be less than 35 nm. From the viewpoint of improving ionic conductivity and moldability in a well-balanced manner, it is preferably 32.5 nm or less, more preferably 30 nm or less, still more preferably 27.5 nm or less. As the lower limit, it is preferably 10 nm or more, more preferably 12.5 nm or more, still more preferably 15 nm or more.

[0043] (Structure c １ and c ２ crystal structure possessed) In the sulfide solid electrolyte of the present embodiment, structure c １ and c ２ have an argyrodite-type crystal structure. Therefore, it can be said that the sulfide solid electrolyte of the present embodiment has an argyrodite-type crystal structure. The argyrodite-type crystal structure has the space group F-43m, and is a cubic crystal structure that basically has a structural skeleton of Li ７ PS ６ . Examples of the compositional formula of the argyrodite-type crystal structure include Li ７－ｘ P １－ｙ Si ｙ S ６ , Li ７＋ｘ P １－ｙ Si ｙ S ６ (wherein x is -0.6 to 0.6 and y is 0.1 to 0.6). The argyrodite-type crystal structure represented by these compositional formulas is cubic or orthorhombic, preferably cubic, and has a peak appearing mainly at 2θ=25.5°, and at least any one of positions 2θ=15.5°, 18.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0° in X-ray diffraction measurement using CuKα radiation.

[0044] As the compositional formula of the argyrodite-type crystal structure, Li ７－ｘ－２ｙ PS６－ｘ－ｙ Cl ｘ Examples include (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5). The argyrodite crystal structure represented by this compositional formula is preferably cubic, and in X-ray diffraction measurements using CuKα rays, peaks appear mainly at 2θ = 25.5°, as well as at least one of 2θ = 15.5°, 18.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Furthermore, the compositional formula for the argyrodite crystal structure is Li ７－ｘ PS ６－ｘ Ha ｘ (Ha is Cl or Br, and x is preferably 0.2 to 1.8) is also an example. The argyrodite crystal structure represented by this compositional formula is preferably cubic, and in X-ray diffraction measurements using CuKα rays, it has peaks that appear mainly at 2θ = 25.5°, as well as at least one of 2θ = 15.5°, 18.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0°.

[0045] Here, structure c １ and c ２ Since it preferably contains lithium atoms, phosphorus atoms and sulfur atoms, and more preferably halogen atoms, the above "Li ７－ｘ P １－ｙ Si ｙ S ６ Li ７＋ｘ P １－ｙ Si ｙ S ６ In the empirical formula (where x is -0.6 to 0.6 and y is 0.1 to 0.6), if an atom other than a chlorine atom is used as the halogen atom, then "Li ７－ｘ－２ｙ PS ６－ｘ－ｙ Cl ｘ The composition formula (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5) may not always be applicable. The above composition formula is a representative example, and depending on the types of atoms that make up the sulfide solid electrolyte of this embodiment, it may not be applicable to the above composition formula. However, if it has the same diffraction peak as the diffraction peak described as having the above "argyrodite type crystal structure", then structure c １ and c ２Furthermore, the sulfide solid electrolyte of this embodiment preferably has an argyrodite-type crystal structure formed of atoms including lithium atoms, phosphorus atoms, and sulfur atoms, and more preferably halogen atoms.

[0046] (Diffraction peak with peak top at diffraction angle 2θ = 25.5 ± 0.5°) Diffraction peak with peak top at diffraction angle 2θ = 25.5 ± 0.5° (diffraction peak P ０ There are no particular restrictions on the full width at half maximum (FWHM) of the diffraction peak P. ０ If the full width at half maximum is within the above range, then structure c １ and c ２ This makes it easier to form the above-mentioned predetermined content ratio. Therefore, the ionic conductivity and moldability of the sulfide solid electrolyte of this embodiment can be improved in a balanced manner. Here, diffraction peak P ０ The full width at half maximum (FWHW) was determined from the FWHW obtained by fitting the peak shape using a pseudo-Voigt function with the Solver function of Microsoft Excel, using data obtained from powder X-ray diffraction (XRD) measurements of sulfide solid electrolytes.

[0047] The diffraction peak P in the pseudo-Voigt function of the sulfide solid electrolyte of this embodiment ０ When the peak shape is fitted with a pseudo-Voigt function, the proportion of the Lorentz function among the Gaussian function and Lorentz function convolved into the pseudo-Voigt function is preferably greater than 0.550, more preferably 0.600 or more, even more preferably 0.630 or more, with an upper limit of preferably 0.995 or less, more preferably 0.990 or less, and even more preferably 0.985 or less. When the proportion of the Lorentz function is within the above range, structure c １ and c ２ Because it becomes easier to form the material with the predetermined content ratio mentioned above, it is possible to improve ionic conductivity and moldability in a balanced way.

[0048] (Constituent Atoms) The sulfide solid electrolyte of this embodiment is a solid electrolyte in which lithium atoms are the conductive species and which have ionic conductivity due to lithium atoms, and therefore contains at least lithium atoms. From the viewpoint of improving ionic conductivity, the sulfide solid electrolyte of this embodiment preferably contains lithium atoms, phosphorus atoms and sulfur atoms, and more preferably further contains halogen atoms. Preferred halogen atoms include fluorine atoms, chlorine atoms, bromine atoms and iodine atoms, more preferably chlorine atoms, bromine atoms and iodine atoms, and even more preferably chlorine atoms and bromine atoms. By including halogen atoms, structure c １ and c ２ Since it becomes easier to form the material with the predetermined content ratio described above, it is possible to improve ionic conductivity and moldability in a balanced manner. In the solid electrolyte of this embodiment, the halogen atoms may be included individually or in combination of multiple types.

[0049] In the solid electrolyte of this embodiment, when lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms are included, the composition ratio (molar ratio) of these atoms is preferably 1.0 to 1.8: 0.1 to 0.8: 1.0 to 2.0: 0.01 to 0.6, more preferably 1.1 to 1.7: 0.2 to 0.6: 1.2 to 1.8: 0.05 to 0.5, and even more preferably 1.2 to 1.6: 0.25 to 0.5: 1.3 to 1.7: 0.08 to 0.4.

[0050] When bromine and chlorine are used in combination as halogen atoms, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, bromine, and chlorine is preferably 1.0 to 1.8:0.1 to 0.8:1.0 to 2.0:0.01 to 0.3:0.01 to 0.3, more preferably 1.1 to 1.7:0.2 to 0.6:1.2 to 1.8:0.02 to 0.25:0.02 to 0.25, even more preferably 1.2 to 1.6:0.25 to 0.5:1.3 to 1.7:0.03 to 0.2:0.03 to 0.2, and even more preferably 1.35 to 1.45:0.3 to 0.45:1.4 to 1.7:0.04 to 0.18:0.04 to 0.18.

[0051] The sulfide solid electrolyte of this embodiment achieves the above structure c by setting the composition ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range. １ and c ２ This makes it easier to obtain a product that possesses these properties, and allows for a good balance of improved ionic conductivity and moldability. The types of atoms and composition ratio (molar ratio) of the solid electrolyte constituting this embodiment can be confirmed, for example, by an ICP emission spectrometer. Note that the atomic composition ratio (molar ratio) of the sulfide solid electrolyte in this embodiment is approximately the same as the atomic composition ratio (molar ratio) calculated from the solid electrolyte raw materials contained in the raw material components used during manufacturing. Therefore, instead of confirming with the above-mentioned analyzer, the atomic composition ratio (molar ratio) can be calculated from the amount of solid electrolyte raw materials used.

[0052] (Properties of the sulfide solid electrolyte) The ionic conductivity of the sulfide solid electrolyte of this embodiment when molded at 400 MPa is 3.0 mS / cm or more, 3.5 mS / cm or more, 4.0 mS / cm or more, further 4.2 mS / cm or more, 4.4 mS / cm or more, 4.5 mS / cm or more, 4.8 mS / cm or more, and 5.0 mS / cm or more, with upper limits of typically 12.5 mS / cm or less, further 12.0 mS / cm or less, 11.5 mS / cm or less, and 11.0 mS / cm or less. Thus, the sulfide solid electrolyte of this embodiment has high ionic conductivity. Here, the molding method at 400 MPa is not particularly limited as long as it is compression molding at a molding pressure of 400 MPa, but from the viewpoint of obtaining stable measurement results, it is preferable to perform uniaxial compression molding at a molding pressure of 400 MPa, and the molding time is preferably 30 seconds or more. A more specific method is, for example, the method in the example.

[0053] Furthermore, the deformation rate of the sulfide solid electrolyte in this embodiment is less than 3.16 GPa, and further, 3.15 GPa or less, 3.10 GPa or less, 3.05 GPa or less, 3.00 GPa or less, and 2.95 GPa or less. Here, the deformation rate is a value determined by the following method. Thus, because the sulfide solid electrolyte in this embodiment has a small deformation rate, it exhibits excellent moldability. (Method for determining the deformation rate) The object to be measured was filled into a cylindrical jig with a diameter of 10 mm, and a compression test was performed using a material testing machine such as a compression tester to compress the sample at a speed of 0.2 mm / min until the stress reached 550 MPa (the thickness of the object to be measured after compression was about 1 mm). A stress-strain curve was created using the thickness of the sample at a stress of 100 MPa as the reference, and the gradient of stress with respect to strain when the stress was between 400 and 550 MPa was defined as the deformation rate.

[0054] (Method for producing sulfide solid electrolyte) There are no particular restrictions on the method for producing the sulfide solid electrolyte of this embodiment, as long as a product having the configuration required for the sulfide solid electrolyte of this embodiment is obtained. Various production methods such as conventional solid-phase methods and liquid-phase methods (for example, methods using complexing agents) can be employed. However, a preferred production method includes, for example, heat-treating a raw material-containing material in a solvent using a pressure vessel or under reflux, removing the solvent, and calcining the heat-treated product obtained by the heat-treating process. This production method makes it possible to produce the sulfide solid electrolyte of this embodiment more efficiently.

[0055] (Heat treatment) This manufacturing method includes heat treatment of the raw material-containing material in a solvent using a pressure vessel or under reflux. The raw material-containing material may contain solid electrolyte raw materials selected according to the solid electrolyte to be obtained, preferably a material containing multiple types of solid electrolyte raw materials containing at least one atom selected from lithium atoms, phosphorus atoms and sulfur atoms, and more preferably a material containing multiple types of solid electrolyte raw materials containing at least one atom selected from lithium atoms, phosphorus atoms, sulfur atoms and halogen atoms.

[0056] (Materials contained in raw materials) Examples of solid electrolyte materials contained in raw materials include lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; and phosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ A raw material containing at least two atoms selected from the above atoms, such as phosphorus sulfide (F), and fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ Typical examples include halogen molecules such as phosphorus molecules and sulfur molecules, and raw materials consisting of one type of atom selected from the above atoms.

[0057] Among the above, solid electrolyte raw materials containing lithium atoms, sulfur atoms, and phosphorus atoms include lithium sulfide; diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ Phosphorus sulfides such as ) are preferred, and among phosphorus sulfides, diphosphorus pentasulfide is preferred.

[0058] Among the above, lithium sulfide and phosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) Phosphorus sulfide, fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ Halogen molecules such as ) and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide are preferred. Furthermore, when introducing oxygen atoms into a sulfide solid electrolyte, phosphorus compounds such as lithium oxide, lithium hydroxide, and lithium phosphate are preferred.

[0059] Among the above, halogen molecules and lithium halides can both be preferably used as solid electrolyte raw materials containing halogen atoms. The halogen atoms contained in the raw material are as described above as halogen atoms that the sulfide solid electrolyte of this embodiment may contain, with fluorine atoms, chlorine atoms, bromine atoms and iodine atoms being preferred, chlorine atoms, bromine atoms and iodine atoms being more preferred, and chlorine atoms and bromine atoms being even more preferred. Therefore, it is preferable to use solid electrolyte raw materials containing such halogen atoms. By including halogen atoms, it is possible to improve the ionic conductivity of the sulfide solid electrolyte, as well as the structure c １ and c ２ It can efficiently promote the formation of the argyrodite-type crystal structure that it possesses, and structure c ２ This makes it easier to adjust the content ratio within a predetermined range, thereby efficiently and effectively improving the ionic conductivity and moldability of the resulting sulfide solid electrolyte in a balanced manner.

[0060] Lithium chloride, lithium bromide, and lithium iodide are more preferred as lithium halides, and it is preferable to use at least one of lithium chloride and lithium bromide, and it is even more preferable to use lithium chloride and lithium bromide in combination. As halogen molecules, chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ) is more preferable, and it is preferable to use at least one of chlorine and bromine, and it is even more preferable to use chlorine and bromine in combination.

[0061] Preferred combinations of solid electrolyte raw materials to be included in the raw material include, for example, combinations of lithium sulfide, phosphorus sulfide, and lithium halide; combinations of lithium sulfide, phosphorus sulfide, and halogen molecules; and combinations of lithium sulfide, phosphorus sulfide, lithium halide, and halogen molecules. More preferably, combinations of lithium sulfide, diphosphorus pentasulfide, and lithium halide; and combinations of lithium sulfide, diphosphorus pentasulfide, and halogen molecules are mentioned. In the above combinations, lithium chloride, lithium bromide, and lithium iodide are preferred as lithium halides, and chlorine, bromine, and iodine are preferred as halogen molecules. For solid electrolyte raw materials containing halogen atoms, please refer to the description of solid electrolyte raw materials containing halogen atoms above. By using such solid electrolyte raw materials, it is possible not only to improve the ionic conductivity of the sulfide solid electrolyte, but also to improve the structure c １ and c ２ It can efficiently promote the formation of the argyrodite-type crystal structure that it possesses, and structure c ２ This makes it easier to adjust the content ratio within a predetermined range, thereby efficiently and effectively improving the ionic conductivity and moldability of the resulting sulfide solid electrolyte in a balanced manner.

[0062] A solid electrolyte raw material containing at least two atoms selected from the above atoms, wherein the raw material contains various phosphorus fluorides (PF ３ , PF ５ ), various phosphorus chlorides (PCL ３ , PCL ５ , P ２ Cl ４ ), various phosphorus bromides (PBr ３ , PBr ５ ), various phosphorus iodides (PI ３ , P ２ I ４ ) and other phosphorus halides; thiophosphoryl fluoride (PSF ３ ), thiophosphoryl chloride (PSCl ３ ), thiophosphoryl bromide (PSBr ３ ), thiophosphoryl iodide (PSI ３ ), thiophosphoryl fluoride dichloride (PSCl２ F), dibromide fluoride thiophosphoryl (PSBr ２ Examples include halogenated thiophosphoryls such as F).

[0063] Other solid electrolyte raw materials contained in the raw material include, for example, solid electrolyte raw materials containing at least one atom selected from the above atoms and also containing atoms other than said atoms, more specifically lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; alkali metal sulfides such as sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, and tin sulfide (SnS, SnS ２ ), metal sulfides such as aluminum sulfide and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; alkali metal halides other than lithium, such as sodium iodide, sodium fluoride, sodium chloride, and sodium bromide; metal halides such as aluminum halide, silicon halide, germanium halide, arsenic halide, selenium halide, tin halide, antimony halide, tellurium halide, and bismuth halide; phosphorus oxychloride (POCl) ３ ), phosphorus oxybromide (POBr ３ Examples include phosphorus oxyhalogenates such as ) and others. Furthermore, when introducing oxygen atoms into a solid electrolyte, phosphorus compounds such as lithium oxide, lithium hydroxide, and lithium phosphate are preferred.

[0064] In this embodiment, PS ４ Li including structure ３ PS ４ It can also be used as a solid electrolyte raw material. Specifically, Li ３ PS ４ It is possible to prepare this by manufacturing it, and then use it as a raw material. In this case, the combination of solid electrolyte raw materials contained in the raw material is Li ３ PS ４ and the above lithium halogen combination, Li ３ PS ４ and the above halogen molecule combination, Li ３ PS ４A preferred combination is the lithium halide and halogen molecule described above.

[0065] The ratio of solid electrolyte raw materials used should be within the range of the atomic composition ratio (molar ratio) that the sulfide solid electrolyte of this embodiment may contain. For example, when lithium sulfide, phosphorus pentasulfide, and lithium halide are used as solid electrolyte raw materials, the mixing ratio (molar ratio) of these compounds is preferably 30-60:10-25:15-50, more preferably 45-55:10-15:30-50, even more preferably 45-50:11-14:35-45, and even more preferably 46-49:11-13:38-42. By using such a ratio of solid electrolyte raw materials, it is possible not only to improve the ionic conductivity of the sulfide solid electrolyte, but also to improve the structure c １ and c ２ It can efficiently promote the formation of the argyrodite-type crystal structure that it possesses, and structure c ２ This makes it easier to adjust the content ratio within a predetermined range, thereby efficiently and effectively improving the ionic conductivity and moldability of the resulting sulfide solid electrolyte in a balanced manner.

[0066] The raw material (solid electrolyte raw material) is preferably ground to an average particle size of 20 μm or less, more preferably 15 μm or less, and even more preferably 12 μm or less. In this specification, the average particle size is the particle size at which the accumulation of particles from the smallest particle size reaches 50% of the total when plotting a particle size distribution integration curve, and the volume distribution is the average particle size that can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer.

[0067] A grinder can be used to grind solid electrolyte raw materials. Examples of grinders include medium-type grinders such as container-driven grinders and medium-agitated grinders. Examples of container-driven grinders include agitated tanks, grinding tanks, or combinations thereof such as ball mills and bead mills. Examples of medium-agitated grinders include impact grinders such as cutter mills, hammer mills and pin mills; tower-type grinders such as tower mills; agitated tank-type grinders such as attritors, aquamizers and sand grinders; flow-tank type grinders such as visco mills and pearl mills; flow-pipe type grinders; annular-type grinders such as coball mills; continuous dynamic grinders; and various grinders such as single-shaft or multi-shaft kneaders. Pin mills are also preferred because they have a short processing time and allow for continuous grinding operations.

[0068] It is preferable to pre-mix the raw materials. Suitable mixers for pre-mixing include, for example, mechanical agitator mixers equipped with stirring blades in the reaction vessel to perform stirring (also referred to as stirring or agitation mixing). Examples of mechanical agitator mixers include high-speed agitator mixers and dual-arm mixers. Examples of high-speed agitator mixers include vertical-axis rotary mixers and horizontal-axis rotary mixers, and either type of mixer may be used. Other preferred mixers include, for example, container-rotating mixers and container-fixed mixers, as well as conical screw mixers such as the Nauta mixer and high-speed agitator mixers such as the FM mixer.

[0069] In this manufacturing method, it is preferable to heat-treat the material obtained by mixing and grinding the above-mentioned raw material in a solvent. As the solvent used during mixing and grinding, nonpolar solvents such as hydrocarbon solvents and polar solvents such as solvents containing heteroatoms are preferably used, and it is preferable to use a combination of nonpolar and polar solvents.

[0070] Examples of hydrocarbon solvents include saturated or unsaturated aliphatic hydrocarbons such as hexane, hexene, pentane, 2-ethylhexane, heptane, heptene, octane, decane, undecane, dodecane, and tridecane; saturated or unsaturated alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and cyclohexene; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, and tert-butylbenzene. Among these, aromatic hydrocarbon solvents are preferred, and toluene and xylene are more preferably used.

[0071] Furthermore, as solvents containing heteroatoms, polar solvents containing heteroatoms such as nitrogen atoms and oxygen atoms are also preferred, and it is preferable to use a solvent containing at least one atom selected from nitrogen atoms and oxygen atoms. Examples of such solvents include solvents containing oxygen atoms such as ether solvents, ester solvents, alcohol solvents, aldehyde solvents, and ketone solvents; and as solvents containing nitrogen atoms, solvents having groups containing nitrogen atoms such as amino groups, amide groups, nitro groups, and nitrile groups are preferred. Among these, ether solvents and nitrile solvents are preferably used.

[0072] Preferred ether solvents include ether compounds such as aliphatic ethers, alicyclic ethers, heterocyclic ethers, and aromatic ethers, with aliphatic ethers and alicyclic ethers being particularly preferred. Preferred aliphatic ethers include monoethers such as dimethyl ether, diethyl ether, diisopropyl ether, dibutyl ether, and tert-butyl methyl ether; diethers such as dimethoxymethane, dimethoxyethane, diethoxymethane, and diethoxyethane; and polyethers having three or more ether groups, such as diethylene glycol dimethyl ether (diglym) and triethylene oxide glycol dimethyl ether (trilym). Among these, monoethers are preferred.

[0073] Examples of alicyclic ethers include ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, dioxane, and dioxolane. Among the above aliphatic ethers and alicyclic ethers, diethyl ether and tetrahydrofuran are preferred.

[0074] Preferred nitrile solvents include aliphatic nitrile solvents such as acetonitrile, acrylonitrile, propionitrile, chloropropionitrile, isobutyronitrile, tert-butyronitrile, capronitrile, isocapronitrile, malononitrile, and fumanitrile; alicyclic nitrile solvents such as cyclohexylnitrile; and aromatic nitrile solvents such as benzonitrile and fluorobenzonitrile. Among these, aliphatic nitrile solvents are preferred, with propionitrile, isobutyronitrile, and isocapronitrile being more preferred.

[0075] When using a combination of a nonpolar solvent and a polar solvent, aromatic hydrocarbon solvents, particularly toluene and ethylbenzene, are preferred as the nonpolar solvent, and nitrile solvents, which have azeotropic properties with aromatic hydrocarbon solvents such as toluene and are easily removed together with aromatic hydrocarbon solvents such as toluene, are preferred as the polar solvent.

[0076] The content of the nonpolar solvent in the solvent is preferably 95% by mass or more. When a nonpolar solvent and a polar solvent are used in combination, the content of the polar solvent in the solvent is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, with an upper limit of preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0077] As for the equipment used for mixing and grinding the raw material components, the grinders exemplified as grinders that can be used for grinding the raw material components mentioned above are preferred, among which planetary ball mills, vibratory mills, rolling mills, and bead mills are preferred. As for the grinder, a grinder that circulates the slurry between the grinder (grinding mixer) that grinds the slurry and the temperature-holding tank (reaction vessel) can also be used. In addition, kneaders such as single-screw kneaders and multi-screw kneaders may be used.

[0078] When the above-mentioned raw material-containing material is mixed and ground, the raw material-containing material obtained by mixing and grinding forms a slurry with the solvent. Therefore, after mixing and grinding, the solvent contained in the slurry can be dried and removed. There are no particular restrictions on the drying method as long as the solvent can be removed. For example, it can usually be done by reduced-pressure drying (vacuum drying) using a vacuum pump or the like at around 5 to 100°C, preferably 10 to 85°C, more preferably 15 to 70°C, and even more preferably at room temperature (e.g., 23°C) (e.g., room temperature ± 5°C). The slurry may also be separated by filtration using a glass filter or the like, solid-liquid separation by decantation, or solid-liquid separation using a centrifuge or the like. Alternatively, solid-liquid separation may be performed first, followed by the drying described above. Furthermore, it is preferable to use the same solvent used during heat treatment as the solvent used during the mixing and grinding of the raw material-containing material. This is because drying of the solvent becomes unnecessary.

[0079] Heat treatment in a solvent is carried out using a pressure vessel or under reflux. Performing heat treatment in a solvent, that is, without removing the solvent, prevents aggregation of the treated materials and makes it possible to reduce the size of secondary particles of the sulfide solid electrolyte.

[0080] The solvent used during the heat treatment can be appropriately selected from the non-polar and polar solvents described above as the solvents used during the mixed grinding process. Therefore, the same solvent used during mixed grinding may be used, or a different solvent may be used. Using the same solvent is preferable because, as mentioned earlier, drying is unnecessary. Among the above solvents, aromatic hydrocarbon solvents are preferred.

[0081] The heating temperature in the heat treatment can be appropriately selected depending on the type of solid electrolyte raw material used, for example, preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and even more preferably 180°C or higher, with an upper limit of preferably 300°C or lower, more preferably 280°C or lower, even more preferably 270°C or lower, and even more preferably 260°C or lower. The heating time is preferably 10 minutes to 6 hours, more preferably 10 minutes to 3 hours, and even more preferably 30 minutes to 2 hours. By using the above conditions, PS ４ The structure is formed, making it easier for halogens to be incorporated into the crystal, and thus improving ionic conductivity. Furthermore, since the raw material mixture of fine crystals is heat-treated in a solvent, PS can be produced at relatively low temperatures. ４ It becomes easier to form a crystal structure containing the structure. As a result, structure c １ and c ２ The formation of can be efficiently promoted, and structure c ２ This makes it easier to adjust the content ratio within a predetermined range, thereby efficiently and effectively improving the ionic conductivity and moldability of the resulting sulfide solid electrolyte in a balanced manner.

[0082] When heat treatment is performed using a pressure vessel, if the heating temperature exceeds the boiling point of the solvent used, it is preferable to use an autoclave. When heat treatment is performed with reflux of the solvent, the method is not particularly limited, and for example, a condenser (e.g., a Dieblot condenser) that cools the vapor and returns it to the solvent can be used.

[0083] (Structure c １ and c ２ (Content ratio of) In the sulfide solid electrolyte of this embodiment, structure c １ and c ２ The structure c relative to the total content ２ The content ratio (hereinafter sometimes simply referred to as "content ratio") is greater than 33.7% and less than 65.0%. When the content ratio is within the above range, it is possible to improve ionic conductivity and moldability in a balanced manner. Here, structure c １ and c ２ Structure c relative to the total content ２The content ratio is as follows: diffraction peak P ０ The waveform was separated into two diffraction peaks P by fitting it with a Gaussian function. １ and diffraction peak P ２ Peak area (hereinafter referred to as "Area A") １ " and "Area A ２ It is also called "..." (and each has structure c １ and c ２ The content can be calculated using the following formula: Content ratio (%) = Area A ２ / (Area A １ +Area A ２ ) × 100

[0084] The content ratio calculated by the above formula is preferably 35.0% or more, more preferably 40.0% or more, and even more preferably 43.0% or more, with an upper limit of preferably 62.5% or less, more preferably 60.0% or less, and even more preferably 57.0% or less. When the content ratio is within the above range, it is possible to improve ionic conductivity and moldability in a well-balanced manner.

[0085] (Removal of solvent) This manufacturing method includes removing the solvent after performing heat treatment in the above solvent. The heat-treated product is obtained by removing the solvent from the slurry containing the solvent and the heat-treated product obtained by the above heat treatment.

[0086] As for the method of removing the solvent from the slurry, there are no particular restrictions as long as the solvent can be removed. For example, it can be dried using the same method as the drying method used to remove the solvent during the mixing and grinding process described above.

[0087] (Castration) This manufacturing method includes calcining the heat-treated product obtained by removing the solvent. This results in structure c １ and c ２ It can efficiently promote the formation of the argyrodite-type crystal structure that it possesses, and structure c ２This makes it easier to adjust the content ratio within a predetermined range, thereby efficiently and effectively improving the ionic conductivity and moldability of the resulting sulfide solid electrolyte. The heating temperature in the firing of the heat-treated product is preferably 300°C or higher, more preferably over 300°C, even more preferably 320°C or higher, even more preferably 350°C or higher, and particularly preferably 380°C or higher, with an upper limit of preferably 470°C or lower, more preferably 460°C or lower, even more preferably 450°C or lower, even more preferably 440°C or lower, and particularly preferably 430°C or lower. The heating time is preferably 1 minute to 6 hours, more preferably 1 minute to 2 hours, and even more preferably 5 minutes to 1 hour. If the heating temperature in firing is within the above range, structure c １ and c ２ This allows for efficient formation and enables a well-balanced improvement in ionic conductivity and moldability.

[0088] The firing process is preferably carried out in an inert gas atmosphere (e.g., nitrogen atmosphere, argon atmosphere) or a reduced-pressure atmosphere (especially in a vacuum). Furthermore, the firing process can be carried out using a firing furnace such as a stationary hearth kiln or a rotary kiln.

[0089] (Crushing) This manufacturing method preferably includes further crushing of the calcined material obtained by the above calcination. By crushing, the calcined material can be made into fine particles and adjusted to an average particle size suitable for the application. Also, by crushing, the structure c １ and c ２ The formation of can be efficiently promoted, and structure c ２ This makes it easier to adjust the content ratio within a predetermined range. In this way, by crushing the calcined material, not only can the particle size be adjusted, but the structure c of the resulting sulfide solid electrolyte can also be adjusted. １ and c ２ The formation of can be efficiently promoted, and structure c ２This makes it easier to adjust the content ratio within a predetermined range, thereby efficiently and effectively improving the ionic conductivity and moldability of the resulting sulfide solid electrolyte. Grinding is preferably carried out by wet grinding (also referred to as "wet micronization"). When wet grinding is performed, the material to be ground is preferably a fluid containing the above-mentioned calcined product and solvent.

[0090] When wet atomization is performed, suitable solvents include, for example, hydrocarbon solvents as exemplified above as nonpolar solvents, more preferably aromatic hydrocarbon solvents, and among these, toluene and xylene are more preferably used. When using a solvent, the amount of solvent used is adjusted so that the content of the calcined product in the fluid used for wet atomization is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, with an upper limit of preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0091] Furthermore, the fluid that is the target of wet atomization preferably contains a dispersant. Examples of preferred dispersants include nitrile solvents, ether solvents, and ester solvents. The nitrile solvent and ether solvent can be appropriately selected from the nitrile solvents and ether solvents exemplified as solvents used during the mixed grinding of the raw material-containing material.

[0092] Preferred ester solvents include, for example, aliphatic esters such as methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, methyl propionate, ethyl propionate, dimethyl oxalate, diethyl oxalate, dimethyl malonate, diethyl malonate, dimethyl succinate, and diethyl succinate; alicyclic esters such as methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, and dimethyl cyclohexanedicarboxylate; heterocyclic esters such as methyl pyridinecarboxylate, acetolactone, propiolactone, butyrolactone, and valerolactone; and aromatic esters such as methyl benzoate, ethyl benzoate, dimethyl phthalate, diethyl phthalate, butyl benzyl phthalate, dicyclohexyl phthalate, trimethyl trimellitate, and triethyl trimellitate.

[0093] When a dispersant is used, the amount of dispersant used is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, with an upper limit of preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, relative to the content of the calcined product contained in the above fluid.

[0094] The calcined material can be crushed using a crushing machine. The crushing machine can be appropriately selected from the examples of crushing machines that can be used for crushing the above raw materials, and container-driven crushing machines such as ball mills and bead mills are preferably used.

[0095] The grinding energy is preferably greater than 0.3 kWh / kg, more preferably 0.5 kWh / kg or more, and even more preferably 0.8 kWh / kg or more, with an upper limit of preferably 3.0 kWh / kg or less, more preferably 2.75 kWh / kg or less, and even more preferably 2.5 kWh / kg or less. When the grinding energy is within the above range, the average particle size can be efficiently adjusted, and the structure c １ and c ２ The formation of can be efficiently promoted, and structure c ２ Since the content ratio can be adjusted within a predetermined range, the ionic conductivity and moldability of the resulting sulfide solid electrolyte can be efficiently and effectively improved in a balanced manner.

[0096] (Applications) The sulfide solid electrolyte of this embodiment has high ionic conductivity and moldability. Therefore, it is suitable for use in electrode composites and in batteries, especially lithium-ion batteries, and particularly in all-solid-state batteries. The solid electrolyte of this embodiment may be used in the positive electrode layer, the negative electrode layer, or the electrolyte layer. Each layer can be manufactured by known methods.

[0097] [Electrode mixture] The electrode mixture of this embodiment is an electrode mixture comprising the sulfide solid electrolyte of this embodiment described above and an electrode active material.

[0098] As electrode active materials, positive electrode active materials and negative electrode active materials are selected depending on whether the electrode composite material is used as the positive electrode or the negative electrode. Conventional materials that have been used as such for the positive and negative electrode active materials can be used.

[0099] In electrode composite materials, the mixing ratio (mass ratio) of electrode active material and sulfide solid electrolyte is preferably 99.5:0.5 to 40:60, more preferably 99:1 to 50:50, and even more preferably 98:2 to 60:40, considering both improved battery performance and manufacturing efficiency.

[0100] The electrode composite material of this embodiment may also contain other components in addition to the sulfide solid electrolyte of this embodiment and the electrode active material described above, such as conductive materials like carbon-based materials, binders like thermoplastic elastomers and resins.

[0101] [Lithium-ion battery] The lithium-ion battery of this embodiment includes at least one of the sulfide solid electrolyte of this embodiment and the electrode composite material of this embodiment.

[0102] The lithium-ion battery of this embodiment is not particularly limited in its configuration as long as it contains either the sulfide solid electrolyte of this embodiment or the electrode mixture containing it, and for example, a different form of sulfide solid electrolyte or electrode mixture containing it may be used. Furthermore, the configuration of the lithium-ion battery may be that of a commonly used lithium-ion battery.

[0103] The lithium-ion battery of this embodiment preferably comprises, for example, a positive electrode layer, a negative electrode layer, an electrolyte layer, and a current collector. Preferably, the electrode composite material of this embodiment is used for the positive electrode layer and the negative electrode layer, and preferably, the sulfide solid electrolyte of this embodiment is used for the electrolyte layer. A lithium-ion battery in which a solid electrolyte is used as the electrolyte layer is also called an all-solid-state battery.

[0104] Furthermore, the above-mentioned battery preferably uses a current collector in addition to the positive electrode layer, electrolyte layer, and negative electrode layer, and known current collectors can be used. For example, a layer coated with Au or the like, which reacts with the above-mentioned solid electrolyte, can be used.

[0105] The present invention will now be specifically described with reference to examples, but the present invention is not limited in any way by these examples.

[0106] (Measurement by Powder X-ray Diffraction (XRD)) Powder X-ray diffraction (XRD) measurements were performed as follows. The samples obtained from the examples and comparative examples (powder) were packed into a groove with a diameter of 20 mm and a depth of 0.2 mm, and leveled with glass to prepare the samples. These samples were sealed with Kapton film for XRD and measured under the following conditions without exposure to air. Measurement device: D2 Phaser (Bruker Co., Ltd.) Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: Focused method Slit configuration: Solar slit 4°, divergent slit 1 mm, Kβ filter (Ni plate) used Detector: Semiconductor detector Measurement range: 2θ = 10⁻⁶⁰ deg Step width, scan speed: 0.05 deg, 0.05 deg / sec

[0107] (Structure c １ and c ２ (Measurement of crystallite size) Structure c １ and c ２ The crystallite size (L) was determined using Scherrer's formula (following the method of P. Scherrer et al.). Specifically, the results measured by the above (powder X-ray diffraction (XRD) measurement) were used to determine the diffraction peak at 2θ = 25.5 ± 0.5° (diffraction peak P ０For this, two Gaussian functions are fitted, and the diffraction peak P with the smallest peak intensity is found. １ Diffraction peak P has a peak shape and high peak intensity. ２ From the peak shapes, the crystallite size of each diffraction peak was calculated using Scherrer's formula below: Crystallite size (L) = Kλ / (β × cosθ) K: Scherrer's constant, 0.9 was used. λ: 1.5418 Å (Cu-Kα line) β: Calculated from β = w - B. w: The full width at half maximum of each diffraction peak after waveform separation of the diffraction peak with a peak top at 2θ = 25.5 ± 0.5° obtained by measurement into two diffraction peaks. B: Instrument constant (Powder X-ray diffraction (XRD) was measured for a standard material (silicon) using the same method as the powder X-ray diffraction (XRD) of the sulfide solid electrolyte described above, and B = 0.087° was obtained from the peak at 2θ = 28.5°.)

[0108] Furthermore, the above w (full width at half maximum obtained by measurement) was determined from the FWHW (full width at half maximum) obtained by peak fitting using the solver function in the following procedure, using diffraction peaks with a peak top at diffraction angle 2θ = 25.5 ± 0.5° obtained by powder X-ray diffraction (XRD) of sulfide solid electrolyte. First, the initial values ​​were set as follows: Background: The average value of the intensity at diffraction angles of peak top ± 1°. Structure c １ and c ２ The intensity of each is set to 2 / 3 and 1 / 3 of (maximum intensity of diffraction peak - background). Structure c １ and c ２ The full width at half maximum (FWHM) is set to 0.1° and 0.2°, respectively. Next, the Solver function of the spreadsheet software Excel (Microsoft Corporation) is used to determine "structure c １ The full width at half maximum of the diffraction peak < structure c ２ The constraint condition is set to be the "full width at half maximum of the diffraction peak", and the background and structure c １ and c ２ The peak intensity and FWHW (full width at half maximum) were used as variables, the solution method was set to GRG nonlinearity, and the analysis was performed to minimize the error between the fitting result and the measured value, and the solution was determined.

[0109] (Analysis of diffraction peaks with peak tops at diffraction angle 2θ = 25.5 ± 0.5°: Measurement of full width at half maximum and crystallite diameter) Using the results measured by the above (powder X-ray diffraction (XRD) measurement), the diffraction peak at 2θ = 25.5 ± 0.5° (diffraction peak P ０ The peak shape was determined using the Solver function of the spreadsheet software Excel (Microsoft Corporation) and fitted with a pseudo-Voigt function, and the resulting FWHW (full width at half maximum) was used to determine it.

[0110] (Analysis of diffraction peaks with peak tops at diffraction angle 2θ = 25.5 ± 0.5°: Determination of the proportion of the Lorentz function) The results measured by the above (measurement of powder X-ray diffraction (XRD)) were used for the measurement targets (powder) obtained in the examples and comparative examples. Diffraction peak at 2θ = 25.5 ± 0.5° (diffraction peak P ０ For this, the peak shape was fitted with a pseudo-Voigt function, and the proportion of the Lorentz function among the Gaussian function and Lorentz function convolved into the pseudo-Voigt function was calculated.

[0111] (Measurement of Ionic Conductivity) The ionic conductivity was measured as follows: For the objects obtained in the examples and comparative examples, a diameter of 10 mm (cross-sectional area S: 0.785 cm²) was measured. ２ A 0.3 g sample of the material to be measured was placed in a 3 cm high measuring cell and subjected to uniaxial compression molding at a molding pressure of 400 MPa using a uniaxial molding machine ("Single-Acting Cylinder MS2 (model number)", manufactured by Riken Kiki Co., Ltd.) to obtain a sample for measurement (thickness (L) 1-2 mm). 10 mg of conductive carbon powder was placed above and below the sample, and after pressure molding, electrode terminals were taken from the top and bottom, and measurements were taken at 25°C using the AC impedance method (frequency range: 1 MHz to 0.1 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. Near the right end of the arc observed in the high-frequency region, the real part Z' (Ω) at the point where -Z'' (Ω) is minimized was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following formula. Here, if it is not an arc, the intercept of the axis of the real part Z' (Ω) is taken as the bulk resistance R (Ω). R = ρ (L / S) σ = 1 / ρ

[0112] (Measurement of deformation rate) 0.15 g of the sample obtained in the examples and comparative examples was placed in a cylindrical jig with a diameter of 10 mm and a height of 3.5 cm, and a compression test was performed using a compression testing machine ("AGX-50kNVD (model number)", manufactured by Shimadzu Corporation) at a speed of 0.2 mm / min until the stress reached 550 MPa (the thickness of the sample after compression was approximately 1 mm). A stress-strain curve was prepared using the thickness of the sample at a stress of 100 MPa as the reference, and the gradient of stress against strain when the stress was between 400 and 550 MPa was defined as the deformation rate.

[0113] (Example 1) Lithium sulfide (manufactured by Idemitsu Kosan Co., Ltd.), phosphorus pentasulfide (manufactured by Thermophos Inc.), lithium chloride (manufactured by Honjo Chemical Co., Ltd.), and lithium bromide (manufactured by Honjo Chemical Co., Ltd.) were coarsely ground in a nitrogen atmosphere using a pin mill equipped with a quantitative feeder ("100UPZ (model number)", manufactured by Hosokawa Micron Corporation).

[0114] In a glove box under a nitrogen atmosphere, lithium sulfide, diphosphorus pentasulfide, lithium chloride, and lithium bromide, which are the raw materials for the solid electrolyte, were weighed in a molar ratio of 47.5:12.5:25.0:15.0, totaling 110 g. These were placed in a glass container and roughly mixed by shaking the container. The roughly mixed raw material-containing material was dispersed under a nitrogen atmosphere in a mixed solvent of 1140 mL of dehydrated toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 7 mL of dehydrated isobutyronitrile (manufactured by Kishida Chemical Co., Ltd.) to obtain a slurry (containing approximately 10% by mass of the raw material components). Next, the slurry was operated for 1 hour using a bead mill ("LMZ015 (model number)," manufactured by Ashizawa Finetech Co., Ltd.) to mix and grind the material, obtaining a slurry containing the ground raw materials.

[0115] Next, the slurry containing the pulverized raw materials was placed in an autoclave (capacity: 2000 mL, made of SUS316) equipped with a stirrer and a heating oil bath, and heat-treated at 200°C for 2 hours while stirring (rotation speed: 200 rpm). After heat treatment in the solvent, the slurry was transferred to a Schlenk bottle purged with nitrogen, and the solvent was removed by vacuum drying to obtain the heat-treated product.

[0116] The resulting heat-treated material was fired in an electric furnace (model number F-1404-A, manufactured by Tokyo Glass Machinery Co., Ltd.) inside a glove box under a nitrogen atmosphere. Specifically, while maintaining the temperature inside the electric furnace at 430°C, the door of the electric furnace was opened and 50g of the heat-treated material was quickly placed in a sagger (model number 999-60S, Al) ２ O ３ The sagger (manufactured by Tokyo Glass Machinery Co., Ltd.) was placed inside, the door was closed, and firing was carried out for 30 minutes. After that, the sagger was removed from the electric furnace, allowed to cool slowly, and then granulated using a sieve with a mesh size of 300 μm to obtain the powder.

[0117] The obtained powder, dehydrated toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., in an amount such that the powder content relative to the total amount of powder, dehydrated toluene, and dispersant was 10% by mass), and dispersant (dehydrated isobutyronitrile, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., in an amount of 20% by mass relative to the powder) were subjected to wet micronization. Specifically, a slurry containing the above powder, dehydrated toluene, and dispersant was operated using a bead mill ("LMZ015 (model number)", manufactured by Ashizawa Finetech Co., Ltd.) at a peripheral speed of 8 m / s, and wet micronization was carried out until the grinding energy was 2.2 kWh / kg. The obtained slurry was transferred to a Schlenk bottle purged with nitrogen, the solvent was removed by distillation, and it was vacuum dried at room temperature until dry, and then dried at 80°C for 1 hour to obtain the powder.

[0118] When the obtained powder was subjected to powder XRD diffraction measurements using the method described above, diffraction peaks originating from the argyrodite crystal structure were confirmed at 2θ = 25.5° and 29.9°, confirming that it is a sulfide solid electrolyte having an argyrodite crystal structure. The X-ray diffraction spectrum obtained from the powder XRD diffraction measurement is shown in Figure 1.

[0119] In the powder XRD diffraction measurement results, the diffraction peak P has its peak top at 2θ = 25.5°. ０ Regarding this, based on the above method, structure c １ and c ２ When the crystallite size was measured, structure c １ The crystallite size is 113 nm, and structure c ２The crystallite size is 24 nm, and from the area of ​​the diffraction peaks corresponding to these structures, structure c ２ The content ratio was confirmed to be 54.9%. Furthermore, the diffraction peak P measured by the above method was also found. ０ The full width at half maximum was 0.116°, and the ratio of the Lorentz function determined by the above method was 0.98.

[0120] When the ionic conductivity was measured using the method described above, it was confirmed to have a high ionic conductivity of 4.4 mS / cm. Furthermore, when the deformation rate was measured using the same method, it was found to be 2.90 GPa, confirming that it has excellent moldability.

[0121] (Examples 2-5 and Comparative Example 1) In Example 1, powder was obtained in the same manner as in Example 1, except that the grinding energy in wet pulverization was as shown in Table 1. When the obtained powder was measured by powder XRD diffraction using the method described above, diffraction peaks originating from the argyrodite crystal structure were confirmed at 2θ = 25.5° and 29.9° for all powders, thus confirming that it is a sulfide solid electrolyte having an argyrodite crystal structure. Furthermore, diffraction peak P measured by the method described above was also found. ０ The diffraction angle and full width at half maximum, and the structure c obtained by the above method １ and c ２ The crystallite size was measured, and the structure c ２ The results for the content ratio, ionic conductivity, deformation rate, and proportion of the Lorentz function are shown in Table 1.

[0122]

[0123] (Comparative Example 2) Powder was obtained in the same manner as in Example 1, except that the grinding energy in wet pulverization was as shown in Table 2. When the obtained powder was measured by powder XRD diffraction using the method described above, diffraction peaks originating from the argyrodite crystal structure were confirmed at 2θ = 25.5° and 29.9° for all powders, thus confirming that it is a sulfide solid electrolyte having an argyrodite crystal structure. Furthermore, diffraction peak P measured by the method described above was also found. ０The diffraction angle and full width at half maximum, and the structure c obtained by the above method １ and c ２ The crystallite size was measured, and the structure c ２ The results for the content ratio, ionic conductivity, and proportion of the Lorentz function are shown in Table 2.

[0124]

[0125] As shown in Table 1, the sulfide solid electrolyte of this embodiment has a diffraction peak (diffraction peak P) with a peak top at the diffraction angle 2θ = 25.5 ± 0.5°. ０ ) has a diffraction peak P ０ Based on this, the structure c whose crystallite size, as determined by Scherrer's formula, is 35 nm or larger. １ and structure c with a crystallite size of less than 35 nm ２ It has structure c ２ The content ratio was confirmed to be more than 33.7% but less than 65.0%. From the X-ray diffraction spectrum results, structure c １ and c ２ It was also confirmed that it has an argyrodite-type crystal structure. Furthermore, it was confirmed that the sulfide solid electrolyte of this embodiment, having the above configuration, not only has a high ionic conductivity of 4.4 to 5.7 mS / cm, but also a small deformation rate of 3.08 GPa or less, thus possessing excellent moldability.

[0126] On the other hand, the sulfide solid electrolyte obtained in Comparative Example 1 had a high ionic conductivity of 6.2 mS / cm, but a large deformation rate of 3.16 GPa, indicating poor moldability. It was confirmed that it is not possible to achieve both high ionic conductivity and excellent moldability.

[0127] Furthermore, the sulfide solid electrolyte obtained in Comparative Example 2 had an ionic conductivity of 2.2 mS / cm, which was found to be lower than that of Examples 1-5. This is because, as a result of applying a large grinding energy, the crystallite size was less than 35 nm, resulting in a structure c ２ This is thought to be because the content ratio of [the substance] exceeded 65.0%.

[0128] The sulfide solid electrolyte of this embodiment has an argyrodite-type crystal structure that exhibits high ionic conductivity and excellent moldability. Therefore, the sulfide solid electrolyte and electrode composite of this embodiment are suitably used in lithium-ion batteries, particularly in lithium-ion batteries used in information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, as well as in automotive applications, and especially in all-solid-state batteries.

Claims

1. In powder X-ray diffraction measurements using CuKα rays, a structure c has a diffraction peak with a peak top at a diffraction angle 2θ = 25.5 ± 0.5°, and the crystallite size determined using Scherrer's formula based on the said diffraction peak is 35 nm or larger. １ and structure c with a crystallite size of less than 35 nm ２ Includes the structure c １ and c ２ It has an argyrodite-type crystal structure, and the structure c １ and c ２ The structure c relative to the total content ２ A sulfide solid electrolyte having a content ratio of more than 33.7% but less than 65.0%.

2. The aforementioned structure c １ has a crystallite diameter of 50 nm or more and 500 nm or less, and the aforementioned structure c ２ has a crystallite diameter of 10 nm or more and 30 nm or less. The sulfide solid electrolyte according to claim 1.

3. The sulfide solid electrolyte according to claim 1 or 2, comprising a lithium atom, a phosphorus atom, and a sulfur atom as constituent atoms.

4. The sulfide solid electrolyte according to claim 3, further comprising a halogen atom.

5. A sulfide solid electrolyte according to any one of claims 1 to 4, wherein the ionic conductivity when molded at 400 MPa is 3.0 mS / cm or more.

6. An electrode mixture comprising a sulfide solid electrolyte according to any one of claims 1 to 5 and an electrode active material.

7. A lithium-ion battery comprising at least one of the sulfide solid electrolyte described in any one of claims 1 to 5 and the electrode composite material described in claim 6.

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