Method for producing sulfide solid electrolytes

Abstract

To provide a novel method for producing a sulfide solid electrolyte having higher ionic conductivity.SOLUTION: A method for producing a sulfide solid electrolyte containing Argyrodite-type crystal includes: a process of pulverizing and mixing a raw material containing lithium, phosphorus, sulfur, chlorine and bromine with a pulverizer to fabricate an intermediate; and a process of performing heat treatment to the intermediate at 350 to 480°C, where a molar ratio c(Cl / P) of the chlorine to phosphorus and a molar ratio d(Br / P) of the bromine to phosphorus in the raw material satisfy the following formula (1). 1.2<c+d<1.9...(1)SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a method for producing a sulfide solid electrolyte. [Background technology]

[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 their power sources has become increasingly important. Among these batteries, lithium-ion batteries are attracting attention due to their high energy density.

[0003] Currently available lithium-ion batteries use electrolytes containing flammable organic solvents, requiring the installation of safety devices to suppress temperature rise during short circuits and improvements in structure and materials to prevent short circuits. In contrast, lithium-ion batteries that use a solid electrolyte, making the battery entirely solid, do not use flammable organic solvents within the battery. This allows for simplification of safety devices and is considered to offer advantages in terms of manufacturing costs and productivity.

[0004] 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. Patent documents 1-5 and non-patent documents 1-3 disclose argyrodite type crystal structures containing one type of halogen. Furthermore, non-patent documents 4 and 5 disclose Li6PS5Cl 1-x Br x Solid electrolytes with the following composition have been reported, and an argyrodite-type crystal structure containing two halogens has been disclosed. Some argyrodite-type crystal structures exhibit high lithium ion conductivity. However, further improvement in ionic conductivity is needed. In addition, sulfide-based solid electrolytes generally have the problem of potentially reacting with moisture in the atmosphere to generate hydrogen sulfide. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Special Publication No. 2010-540396 [Patent Document 2] International release WO2015 / 011937 [Patent Document 3] International release WO2015 / 012042 [Patent Document 4] Japanese Patent Publication No. 2016-24874 [Patent Document 5] International release WO2016 / 104702 [Non-patent literature]

[0006] [Non-Patent Document 1] Angew.chem Vol.47(2008),No.4,P.755-758 [Non-Patent Document 2] Phys.Status.Solidi Vol.208(2011),No.8,P.1804-1807 [Non-Patent Document 3] Solid State Ionics Vol.221(2012)P.1-5 [Non-Patent Document 4] Abstracts of the 82nd Annual Meeting of the Electrochemical Society (2015), 2H08 [Non-Patent Document 5] Proceedings of the 94th Annual Meeting of the Chemical Society of Japan, 2014, II, p. 474, 1 H2-50 [Overview of the project] [Problems that the invention aims to solve]

[0007] One of the objectives of the present invention is to provide a novel sulfide solid electrolyte having higher ionic conductivity. Another objective of the present invention is to provide a novel sulfide solid electrolyte that suppresses the generation of hydrogen sulfide through reaction with moisture in the atmosphere. [Means for solving the problem]

[0008] According to one embodiment of the present invention, a novel sulfide solid electrolyte is provided, comprising lithium, phosphorus, sulfur, chlorine, and bromine, wherein in powder X-ray diffraction using CuKα rays, diffraction peak A is observed at 2θ = 25.2 ± 0.5 deg and diffraction peak B is observed at 2θ = 29.7 ± 0.5 deg, and diffraction peaks A and B satisfy the following formula (A), and the molar ratio of chlorine to phosphorus c (Cl / P) and the molar ratio of bromine to phosphorus d (Br / P) satisfy the following formula (1). 1.2 <c+d<1.9···(1) 0.845 A / S B <1.200···(A) (In the formula, S A This indicates the area of ​​diffraction peak A, and S B (This indicates the area of ​​diffraction peak B.) Furthermore, according to one embodiment of the present invention, an electrode mixture containing the above-mentioned sulfide solid electrolyte and an active material is provided. Furthermore, according to one embodiment of the present invention, a lithium-ion battery is provided which includes at least one of the above-mentioned sulfide solid electrolyte and the above-mentioned electrode composite material. [Effects of the Invention]

[0009] According to one embodiment of the present invention, a sulfide solid electrolyte with high ionic conductivity can be provided. Furthermore, according to one embodiment of the present invention, it is possible to provide a sulfide solid electrolyte that suppresses the amount of hydrogen sulfide generated by reaction with moisture in the atmosphere. [Brief explanation of the drawing]

[0010] [Figure 1] This is a plan view of an example of a multi-screw kneader used in the production of sulfide solid electrolytes, broken at the center of the rotating shaft. [Figure 2] This is a plan view of a portion of a rotating shaft where paddles are installed, in an example of a multi-screw kneader used for the manufacture of sulfide solid electrolytes, with the view perpendicular to the rotating shaft. [Figure 3] This is the X-ray diffraction pattern of the sulfide solid electrolyte obtained in Example 1.​ [Figure 4] This is the X-ray diffraction pattern of the sulfide solid electrolyte obtained in Comparative Example 2. [Figure 5] This is an explanatory diagram of the apparatus used for evaluating the amount of hydrogen sulfide generated from the sulfide solid electrolyte. [Figure 6] This is the result of the structural analysis by synchrotron radiation of the sulfide solid electrolyte obtained in Example 1.

Mode for Carrying Out the Invention

[0011] The sulfide solid electrolyte according to one embodiment of the present invention contains lithium (Li), phosphorus (P), sulfur (S), chlorine (Cl), and bromine (Br) as constituent elements. In powder X-ray diffraction using CuKα radiation, it has a diffraction peak A at 2θ = 25.2 ± 0.5 deg and a diffraction peak B at 29.7 ± 0.5 deg, and the diffraction peaks A and B satisfy the following formula (A). 0.845 < S A / S B <1.200 ··· (A) (In the formula, S A represents the area of diffraction peak A, and S B represents the area of diffraction peak B.)

[0012] Diffraction peaks A and B are peaks derived from an argyrodite-type crystal structure. In addition to diffraction peaks A and B, diffraction peaks of the argyrodite-type crystal structure may also appear, for example, at 2θ = 15.3 ± 0.5 deg, 17.7 ± 0.5 deg, 31.1 ± 0.5 deg, 44.9 ± 0.5 deg, or 47.7 ± 0.5 deg. The sulfide solid electrolyte of this embodiment may have these peaks.

[0013] In this application, the position of the diffraction peak is determined as A ± 0.5 degrees, where A is the median value, but it is preferable that it be A ± 0.3 degrees. For example, in the case of the diffraction peak with 2θ = 25.2 ± 0.5 degrees as described above, the median value A is 25.2 degrees, and it is preferable that it lies within the range of 2θ = 25.2 ± 0.3 degrees. The same applies to the determination of the positions of all other diffraction peaks in this application.

[0014] The sulfide solid electrolyte of this embodiment satisfies formula (A) above, thereby achieving higher ionic conductivity than conventional solid electrolytes containing argyrodite-type crystal structures. Formula (A) above represents the area ratio of diffraction peaks (S A / S B This means that the diffraction peak area ratio (S) is larger than that of conventional solid electrolytes containing argyrodite-type crystal structures. A / S B The ratio is preferably 0.850 or more and 1.150 or less, and more preferably 0.860 or more and 1.100 or less.

[0015] Area ratio (S A / S B A large area ratio (S) is thought to mean that the proportion of halogens (total of Cl and Br) occupying sites in the argyrodite crystal structure is high. In particular, it is estimated that the site occupancy rate of Br has increased compared to the conventional technology. Generally, sulfide solid electrolytes contain a mixture of various crystalline and amorphous components. Some of the Cl and Br added as constituent elements of the sulfide solid electrolyte form an argyrodite crystal structure, while the other Cl and Br form crystalline structures other than the argyrodite crystal structure and amorphous components. It is also possible that they are contained in the residual raw material. In this embodiment, by increasing the proportion of halogens occupying sites in the argyrodite crystal structure, in particular the site occupancy rate of Br, compared to the conventional technology, the area ratio (S) is increased. A / S B This study found that the ratio () becomes larger, and the ionic conductivity of the sulfide solid electrolyte increases.

[0016] The argyrodite crystal structure is used in PS43- The structure has a skeletal structure as its main unit, with surrounding sites occupied by S surrounded by Li and halogens (Cl, Br). The area ratio of the X-ray diffraction peaks of a crystal structure can be calculated from the elemental coordinates of that crystal structure (see XRD Diffraction Handbook, 3rd Edition, Rigaku Denki Co., Ltd., 2000, pp. 14-15). A typical argyrodite crystal structure is represented by space group F-43M and is the crystal structure shown as No. 216 in the database of International Tables for Crystallography Volume G: Definition and exchange of crystallographic data (ISBN: 978-1-4020-3138-0). The crystal structure shown as No. 216 includes PS4 3- 4a and 4d sites exist around the periphery of the structure; elements with a large ionic radius tend to occupy the 4a site, while elements with a small ionic radius tend to occupy the 4d site.

[0017] The unit cell of an argyrodite crystal structure has a total of eight 4a and 4d sites. The area ratio of the X-ray diffraction peaks was calculated for two cases: Case 1, where four Cl atoms and four S atoms are arranged in these sites, and Case 2, where four Cl atoms, two Br atoms, and two S atoms are arranged in these sites. The results showed that in Case 2, the area of ​​diffraction peak A (diffraction peak at 2θ=25deg) was larger than in Case 1, while the area of ​​diffraction peak B (diffraction peak at 2θ=30deg) changed less. From the above calculation results, it was found that the area ratio (S) changes when Br occupies a site. A / S B It is thought that ) will become larger.

[0018] Generally, the area ratio and intensity ratio of X-ray diffraction peaks are proportional to the number of electrons in an element (see "Guide to X-ray Crystal Analysis," Shokabo (1983)). Cl and S have roughly the same number of electrons, while Br has more electrons, so it is thought that the site occupancy of Br was high in the crystal diffraction plane corresponding to diffraction peak A. Furthermore, considering the size of the ionic radius, it can be estimated that the occupancy was particularly high at the 4a site.

[0019] An increase in the amount of halogens occupying sites in an argyrodite crystal structure means a relative decrease in the amount of sulfur (S) occupying sites in the argyrodite crystal structure. Halogens with a valency of -1 have a weaker attraction to lithium than sulfur (S) with a valency of -2. Also, they attract fewer Li atoms. Therefore, the density of Li around the sites decreases, and Li becomes more mobile, which is thought to increase the ionic conductivity of the argyrodite crystal structure.

[0020] Furthermore, when only Cl is present as the halogen, the occupancy rate of S at the 4a sites becomes high. By using Br, which has an ionic radius equivalent to S, together with Cl, the Br occupancy rate at the 4a sites increases, and as a result, the overall halogen occupancy rate improves. Also, even if Cl occupies some of the 4a sites, the Cl at the 4a sites is unstable and may be desorbed during the heat treatment process. Therefore, it is considered preferable not only to increase the halogen occupancy rate, but also for halogens with appropriate ionic radii to occupy appropriate sites. In this embodiment, it is presumed that the ionic conductivity is high because two types of halogens (Cl and Br) occupy large amounts and appropriately at sites in the argyrodite crystal structure.

[0021] Furthermore, this embodiment is characterized in that the molar ratio c (Cl / P) of chlorine to phosphorus and the molar ratio d (Br / P) of bromine to phosphorus satisfy the following formula (1). 1.2 <c+d<1.9···(1) c+d is the molar ratio of chlorine and bromine to phosphorus. By setting it within the above range, the effect of improving the ionic conductivity of the sulfide solid electrolyte is enhanced. c+d is preferably 1.4 to 1.8, and more preferably 1.5 to 1.7.

[0022] In the sulfide solid electrolyte according to one embodiment of the present invention, the molar ratio d (Br / P) of bromine to phosphorus is preferably 0.15 or more and 1.6 or less. The molar ratio d is more preferably 0.2 or more and 1.2 or less, and more preferably 0.4 or more and 1.0 or less.

[0023] Furthermore, it is preferable that the molar ratio of chlorine to phosphorus c (Cl / P) and the molar ratio of bromine to phosphorus d (Br / P) satisfy the following formula (2). 0.08 <d / (c+d)<0.8···(2) d / (c+d) is more preferably 0.15 or more and 0.6 or less, and even more preferably 0.2 or more and 0.5 or less.

[0024] It is preferable that the molar ratio a (Li / P) of lithium to phosphorus, the molar ratio b (S / P) of sulfur to phosphorus, the molar ratio c (Cl / P) of chlorine to phosphorus, and the molar ratio d (Br / P) of bromine to phosphorus satisfy the following formulas (3) to (5). 5.0 ≤ a ≤ 7.5 ···(3) 6.5 ≤ a + c + d ≤ 7.5 ···(4) 0.5 ≤ ab ≤ 1.5 ···(5) (In the equation, b>0, c>0, and d>0 are satisfied.) By satisfying the above equations (3) to (5), an argyrodite-type crystal structure is more likely to be formed.

[0025] In equation (3) above, it is preferable that 5.0 ≤ a ≤ 6.8, and more preferably that 5.2 ≤ a ≤ 6.6. In equation (4) above, it is preferable that 6.6 ≤ a + c + d ≤ 7.4, and more preferably that 6.7 ≤ a + c + d ≤ 7.3. In the above equation (5), it is preferable that 0.6 ≤ ab ≤ 1.3, and more preferably that 0.7 ≤ ab ≤ 1.3.

[0026] The sulfide solid electrolyte according to this embodiment may contain, in addition to Li, P, S, Cl, and Br, Si, Ge, Sn, Pb, B, Al, Ga, As, Sb, Bi, O, Se, Te, etc., to the extent that it does not impair the effects of the present invention. Alternatively, it may consist substantially of only Li, P, S, Cl, and Br. Consisting substantially of only Li, P, S, Cl, and Br means that the sulfide solid electrolyte, excluding unavoidable impurities, consists only of Li, P, S, Cl, and Br as constituent elements.

[0027] The molar ratios and compositions of each element mentioned above refer to those in the resulting sulfide solid electrolyte, not the molar ratios and compositions of the raw materials used in the manufacturing process. The molar ratios of each element can be controlled, for example, by adjusting the content of each element in the raw materials.

[0028] In this application, the molar ratios and compositions of each element in the sulfide solid electrolyte shall be those measured by ICP emission spectrometry, except in special circumstances such as difficulty in analysis. The measurement method for ICP emission spectrometry is described in the examples.

[0029] In the sulfide solid electrolyte according to one embodiment of the present invention, it is preferable that the diffraction peak of lithium halide is not present in powder X-ray diffraction using CuKα rays, or if present, that the following formula (B) is satisfied. 0 C / I A <0.08···(B) (In the formula, I C represents the intensity of the diffraction peak of lithium halide, and I A (This represents the intensity of the diffraction peak at 2θ = 25.2 ± 0.5 degrees.)

[0030] ​Equation (B) above indicates that the amount of lithium halide is relatively small compared to the argyrodite crystal structure. The presence of lithium halide indicates that there are halogens in the sulfide solid electrolyte that do not occupy sites in the argyrodite crystal structure. Intensity I of the diffraction peak of lithium halide C If the lithium halide is LiCl, then the intensity of the diffraction peak appearing in the range 34.0deg ≤ 2θ ≤ 35.5deg shall be used. However, if there are two or more diffraction peaks in this range, then the intensity of the diffraction peak appearing at the highest angle shall be used. If it is LiBr, then I C This refers to the intensity of the diffraction peak appearing in the range 32.5deg ≤ 2θ ≤ 33.9deg. However, if there are two or more diffraction peaks in this range, the intensity of the diffraction peak appearing at the lowest angle is used. The reason for this definition is that when a novel crystal structure containing halogens, as described later, exists, diffraction peaks appear at 14.4±0.5deg and 33.8±0.5deg. Here, if a diffraction peak is observed at 14.4±0.5deg, but only one diffraction peak is observed in the range 32.5deg ≤ 2θ ≤ 35.5deg, these diffraction peaks are considered to originate from the novel crystal structure containing halogens, as described later. In this case, the diffraction peak of lithium halide is considered not to have appeared. Note that if diffraction peaks of LiCl and LiBr are observed, I C This is the sum of the intensities of these diffraction peaks. Equation (B) is 0 C / I A It is more preferable that it be <0.07, 0 C / I A It is even more preferable that it be <0.06.

[0031] Furthermore, in the sulfide solid electrolyte according to one embodiment of the present invention, it is preferable that the diffraction peaks at 2θ = 14.4 ± 0.5 deg and 33.8 ± 0.5 deg are not present in powder X-ray diffraction using CuKα rays, or if present, the following formula (C) is satisfied. 0 D / I​​​A <0.09···(C) (In the formula, I D This represents the intensity of the diffraction peak at 2θ = 14.4 ± 0.5 degrees, and I A (This represents the intensity of the diffraction peak at 2θ = 25.2 ± 0.5 degrees.)

[0032] Crystals exhibiting diffraction peaks at 2θ = 14.4 ± 0.5 degrees and 33.8 ± 0.5 degrees are novel, but are presumed to contain halogens in part. Equation (C) above indicates that this novel crystal structure is relatively less common than the argyrodite-type crystal structure. The presence of this novel crystal structure indicates that, among the total halogens in the sulfide solid electrolyte, there are halogens that do not occupy sites in the argyrodite-type crystal structure. Equation (C) is 0 D / I A It is more preferable that it be <0.06, and furthermore, 0 C / I D It is preferable that the value be <0.05.

[0033] In the sulfide solid electrolyte according to one embodiment of the present invention, it is preferable that the lattice constant of the argyrodite-type crystal structure is 9.800 Å or more and 9.920 Å or less. A small lattice constant in an argyrodite crystal structure is thought to indicate a high amount of chlorine and bromine contained in that crystal structure. It is believed that when the lattice constant is less than 9.800 Å, bromine is less likely to be incorporated into the crystal structure.

[0034] The lattice constants of the argyrodite crystal structure are calculated by performing a full pattern fitting (WPF) analysis using crystal structure analysis software, based on the XRD pattern obtained from X-ray diffraction (XRD) measurements. Details of the measurement are shown in the examples.

[0035] In the sulfide solid electrolyte according to one embodiment of the present invention, 31 ​​In P-NMR measurements, it is preferable that the material has peaks in each of the following regions: 81.5–82.5 ppm (hereinafter referred to as the first region), 83.2–84.7 ppm (hereinafter referred to as the second region), 85.2–86.7 ppm (hereinafter referred to as the third region), and 87.2–89.4 ppm (hereinafter referred to as the fourth region), and that the ratio of the sum of the areas of the peaks in 81.5–82.5 ppm and 83.2–84.7 ppm to the total area of ​​all peaks in 78–92 ppm is 60% or more. A high ratio of the sum of the areas of the first and second peaks is presumed to indicate a large sum of chlorine and bromine incorporated into the argyrodite-type crystal structure. As a result, the ionic conductivity of the solid electrolyte is increased. The peak in the first region is called the first peak (P1), the peak in the second region is called the second peak (P2), the peak in the third region is called the third peak (P3), and the peak in the fourth region is called the fourth peak (P4). The presence of a peak in a region means that there is a peak with a peak top within the region, or that a peak exists in this region when separated by the nonlinear least squares method.

[0036] In the azirodite crystal structure (Li6PS5Cl) where the halogen is chlorine, PS4 is present in the crystal. 3- The difference in the distribution of free chlorine (Cl) and free sulfur (S) around the structure determines the solid 31 It has been reported that multiple phosphorus resonance lines with different chemical shifts are observed overlapping in the P-NMR spectrum (Non-Patent Literature 1). Based on these findings, the present inventors have developed a solid form of azirodite crystal with different ratios of free halogen and free sulfur. 31 P-NMR spectra were examined. As a result, the NMR signals observed in the 78-92 ppm region were found to be from four types of PS4 with different distributions of surrounding free sulfur and free halogens. 3- We found that the structure could be separated into peaks. Furthermore, we found that when the area ratio of the peak on the high-field side (the sum of the first and second peaks mentioned above) was high, the ionic conductivity of the solid electrolyte was high. The first and second peaks mentioned above are associated with PS4, where most of the surrounding free elements are Cl and Br. 3-It is presumed to be due to the structure. On the other hand, the third and fourth peaks are PS4, where most of the surrounding free elements are sulfur. 3- It is presumed to be due to its structure.

[0037] A sulfide solid electrolyte according to one embodiment of the present invention can be produced, for example, by a manufacturing method comprising the steps of producing an intermediate by applying mechanical stress to a mixture of raw materials and causing a reaction, and heat-treating the intermediate to crystallize it.

[0038] The raw materials used consist of two or more compounds or combinations of elements that, as a whole, contain the elements essential to the sulfide solid electrolyte being manufactured: lithium, phosphorus, sulfur, chlorine, and bromine.

[0039] Examples of lithium-containing raw materials include lithium compounds such as lithium sulfide (Li2S), lithium oxide (Li2O), and lithium carbonate (Li2CO3), as well as elemental lithium metal. Among these, lithium compounds are preferred, and lithium sulfide is more preferred. The lithium sulfide described above can be used without particular limitations, but high-purity lithium sulfide is preferred. Lithium sulfide can be produced, for example, by the methods described in Japanese Patent Publication No. 7-330312, Japanese Patent Publication No. 9-283156, Japanese Patent Publication No. 2010-163356, and Japanese Patent Publication No. 2011-84438. Specifically, lithium sulfide can be synthesized by reacting lithium hydroxide and hydrogen sulfide in a hydrocarbon-based organic solvent at 70°C to 300°C to produce lithium hydrosulfide, and then desulfurizing this reaction solution (Japanese Patent Publication No. 2010-163356). Furthermore, lithium sulfide can be synthesized by reacting lithium hydroxide and hydrogen sulfide in an aqueous solvent at 10°C to 100°C to produce lithium hydrosulfide, and then desulfurizing this reaction solution (Japanese Patent Publication No. 2011-84438).

[0040] Examples of phosphorus-containing raw materials include phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5), phosphorus compounds such as sodium phosphate (Na3PO4), and elemental phosphorus. Among these, phosphorus sulfides are preferred, and diphosphorus pentasulfide (P2S5) is more preferred. The phosphorus compounds and elemental phosphorus can be used without particular limitation as long as they are industrially manufactured and sold.

[0041] The raw materials containing chlorine and / or bromine preferably include, for example, a halogen compound represented by the following formula (6). M l -X m ...(6)

[0042] In formula (6), M represents sodium (Na), lithium (Li), boron (B), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), germanium (Ge), arsenic (As), selenium (Se), tin (Sn), antimony (Sb), tellurium (Te), lead (Pb), bismuth (Bi), or any of these elements bonded to oxygen or sulfur. Lithium (Li) or phosphorus (P) is preferred, and lithium (Li) is more preferred. X is either chlorine (Cl) or bromine (Br). Furthermore, l is an integer of 1 or 2, and m is an integer from 1 to 10. When m is an integer from 2 to 10, that is, when there are multiple X values, X may be the same or different. For example, in SiBrCl3, which will be discussed later, m is 4, and X consists of two different elements, Br and Cl.

[0043] Examples of halogen compounds represented by the above formula (6) include NaCl, NaBr, LiCl, LiBr, BCl3, BBr3, AlBr3, AlCl3, SiCl4, SiCl3, Si2Cl6, SiBr4, SiBrCl3, SiBr2Cl2, PCl3, PCl5, POCl3, PBr3, POBr3, P2Cl4, SCl2, S2Cl2, S2Br2, GeCl4, GeBr4, GeCl2, GeBr2, AsCl3, AsBr3, SeCl2, SeCl4, Se2Br2, SeBr4, SnCl4, SnBr4, SnCl2, SnBr2, SbCl3, SbBr3, SbCl5, TeCl2, TeCl4, TeBr2, TeBr4, PbCl4, PbCl2, PbBr2, BiCl3, BiBr3, etc.

[0044] Among these, lithium chloride (LiCl), lithium bromide (LiBr), phosphorus pentachloride (PCl5), phosphorus trichloride (PCl3), phosphorus pentabromide (PBr5), or phosphorus tribromide (PBr3) are preferred. Of these, LiCl, LiBr, or PBr3 are preferred, with LiCl and LiBr being more preferred. The halogen compound may be one of the above compounds used alone, or two or more compounds may be used in combination. In other words, at least one of the above compounds can be used.

[0045] In one embodiment of the present invention, the raw materials include a lithium compound, a phosphorus compound, and a halogen compound, wherein at least one of the lithium compound and the phosphorus compound preferably contains a sulfur element, more preferably a combination of Li2S, phosphorus sulfide, LiCl, and LiBr, and even more preferably a combination of Li2S, P2S5, LiCl, and LiBr. For example, when using Li2S, P2S5, LiCl, and LiBr as raw materials for a sulfide solid electrolyte, the molar ratio of the input materials can be set to Li2S:P2S5:Total of LiCl and LiBr = 30-60:10-25:15-50.

[0046] In one embodiment of the present invention, the above raw materials are reacted by applying mechanical stress to obtain an intermediate. Here, "applying mechanical stress" means applying mechanical shear force, impact force, etc. Means of applying mechanical stress include, for example, a pulverizer such as a planetary ball mill, a vibratory mill, or a rolling mill, or a kneader. In the prior art (for example, Patent Document 2), the raw material powder is pulverized and mixed to an extent that maintains its crystallinity. In contrast, in this embodiment, it is preferable to apply mechanical stress to the raw material to cause a reaction and form an intermediate containing glass components. That is, the raw material powder is pulverized and mixed with stronger mechanical stress than in the prior art until at least a portion of it can no longer maintain its crystallinity. This generates the PS4 structure, which is the basic framework of the argyrodite crystal structure, at the intermediate stage, and allows for high dispersion of halogens. It is presumed that the highly dispersed halogens in the intermediate are efficiently introduced into the sites in the argyrodite crystal structure by heat treatment. As a result, it is presumed that the sulfide solid electrolyte of this embodiment exhibits high ionic conductivity. Furthermore, the presence of a glass (amorphous) component in the intermediate can be confirmed by the presence of a broad peak (halo pattern) caused by the amorphous component in XRD measurements.

[0047] For grinding and mixing conditions, for example, if a planetary ball mill is used as the grinder, the rotation speed should be set to tens to hundreds of revolutions per minute, and the processing should be done for 0.5 to 100 hours. More specifically, in the case of the planetary ball mill used in the embodiment of this application (manufactured by Fritsch: model number P-7), the rotation speed of the planetary ball mill is preferably 350 rpm to 400 rpm, and more preferably 360 rpm to 380 rpm. If zirconia balls are used as the grinding media, their diameter is preferably 0.2 to 20 mm.

[0048] The intermediate prepared by grinding and mixing is heat-treated. The heat treatment temperature is preferably 350-480°C, more preferably 360-460°C, and even more preferably 380-450°C. Lowering the heat treatment temperature slightly compared to conventional methods tends to increase the amount of halogens contained in the argyrodite crystal structure. This is presumed to be because at higher heat treatment temperatures, halogens are more likely to detach from sites in the argyrodite crystal structure. The atmosphere for heat treatment is not particularly limited, but it is preferably an inert gas atmosphere such as nitrogen or argon, rather than a hydrogen sulfide stream. By suppressing the substitution of free halogens in the crystal structure with sulfur, the amount of halogens in the crystal structure can be increased, and as a result, it is presumed that the ionic conductivity of the resulting sulfide solid electrolyte will improve.

[0049] When a kneader is used as a means of applying the above-mentioned mechanical stress, the kneader is not particularly limited, but a multi-shaft kneader equipped with two or more shafts is preferred from the viewpoint of ease of manufacture.

[0050] A multi-screw mixer can be, for example, equipped with a casing and two or more rotating shafts arranged to penetrate the casing longitudinally and having paddles (screws) along the axial direction, with a raw material supply port at one end of the casing in the longitudinal direction and a discharge port at the other end, and as long as two or more rotational movements interact with each other to generate mechanical stress, there are no particular restrictions on other configurations. By rotating the two or more rotating shafts equipped with paddles of such a multi-screw mixer, two or more rotational movements can interact with each other to generate mechanical stress, and it is possible to apply this mechanical stress to the raw material moving along the rotating shafts from the supply port to the discharge port and cause it to react.

[0051] A preferred example of a multi-screw mixer that can be used in one embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a plan view of the multi-screw mixer broken at the center of the rotating shaft, and Figure 2 is a plan view of the portion of the rotating shaft where the paddles are provided, broken perpendicular to the rotating shaft. The multi-screw kneader shown in Figure 1 is a twin-screw kneader equipped with a casing 1 having a feed port 2 at one end and a discharge port 3 at the other end, and two rotating shafts 4a and 4b that penetrate the longitudinal direction of the casing 1. Paddles 5a and 5b are provided on the rotating shafts 4a and 4b, respectively. Raw materials enter the casing 1 from the feed port 2, react with mechanical stress applied to the paddles 5a and 5b, and the resulting reaction product is discharged from the discharge port 3.

[0052] There are no particular restrictions on the number of rotating shafts 4, as long as there are two or more. Considering versatility, it is preferable to have 2 to 4 shafts, and more preferably 2 shafts. Furthermore, it is preferable that the rotating shafts 4 are parallel shafts that are parallel to each other. The paddle 5 is mounted on the rotating shaft for kneading the raw materials and is also called a screw. Its cross-sectional shape is not particularly limited and can be a roughly triangular shape with each side of an equilateral triangle uniformly convex in the shape of a circular arc, as shown in Figure 2, as well as a circle, ellipse, roughly quadrilateral, etc. It may also be a shape based on these shapes with a notch in part.

[0053] When multiple paddles are provided, each paddle may be mounted on the axis of rotation at a different angle, as shown in Figure 2. Furthermore, to achieve a greater mixing effect, interlocking paddles can be selected. The paddle rotation speed is not particularly limited, but is preferably 40-300 rpm, more preferably 40-250 rpm, and even more preferably 40-200 rpm.

[0054] The multi-screw kneader may be equipped with a screw 6 on the supply port 2 side, as shown in Figure 1, in order to ensure that raw materials are supplied into the kneader without interruption, and may also be equipped with a reverse screw 7 on the discharge port 3 side, as shown in Figure 1, in order to prevent the reaction product obtained via the paddle 5 from accumulating inside the casing. Commercially available kneaders can also be used as multi-screw mixers. Examples of commercially available multi-screw mixers include the KRC Kneader (manufactured by Kurimoto Iron Works Co., Ltd.).

[0055] The mixing time for the raw materials varies depending on the types and composition ratios of the elements constituting the sulfide solid electrolyte to be obtained, as well as the reaction temperature. It can be adjusted as appropriate, preferably 5 minutes to 50 hours, more preferably 10 minutes to 15 hours, and even more preferably 1 to 12 hours. The mixing temperature of the raw materials varies depending on the type and composition ratio of elements constituting the sulfide solid electrolyte to be obtained, as well as the reaction time. It should be adjusted as appropriate, preferably 0°C or higher, more preferably 25°C or higher, even more preferably 100°C or higher, and most preferably 250°C or higher. The higher the temperature, the easier it is to precipitate the argyrodite-type crystal structure at the mixing stage. It is thought that the argyrodite-type crystal structure precipitates more easily at temperatures of 350°C or higher. The upper limit of the mixing temperature should be such that the resulting argyrodite-type crystal structure does not decompose, i.e., it should be below 500°C.

[0056] The intermediate discharged from the multi-screw kneader may be supplied again from the feed port to further advance the reaction, depending on the progress of the reaction. The progress of the reaction can be determined by the increase or decrease in the peaks of the resulting intermediate that originate from the raw materials.

[0057] A sulfide solid electrolyte is obtained by heat-treating the intermediate obtained by kneading. The heat treatment temperature is preferably 350 to 480°C, more preferably 360 to 460°C, and even more preferably 380 to 450°C. The atmosphere for heat treatment is not particularly limited, but it is preferably an inert gas atmosphere such as nitrogen or argon, rather than a hydrogen sulfide gas stream.

[0058] The sulfide solid electrolyte of the present invention can be used in solid electrolyte layers, positive electrodes, negative electrodes, etc., of lithium-ion secondary batteries and the like.

[0059] [Electrode composite material] An electrode composite material according to one embodiment of the present invention comprises the sulfide solid electrolyte of the present invention described above and an active material, or is manufactured using the sulfide solid electrolyte of the present invention. When a negative electrode active material is used as the active material, it becomes a negative electrode composite material. On the other hand, when a positive electrode active material is used, it becomes a positive electrode composite material.

[0060] ·Negative electrode composite material A negative electrode composite material can be obtained by blending a negative electrode active material with the sulfide solid electrolyte of the present invention. For example, carbon materials, metallic materials, etc., can be used as the negative electrode active material. Composites consisting of two or more of these materials can also be used. Furthermore, negative electrode active materials to be developed in the future can also be used. Furthermore, it is preferable that the negative electrode active material has electronic conductivity. Examples of carbon materials include graphite (e.g., artificial graphite), graphite carbon fibers, resin-fired carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fibers, vapor-grown carbon fibers, natural graphite, and non-graphitizable carbon. Examples of metallic materials include elemental metals, alloys, and metallic compounds. Examples of elemental metals include metallic silicon, metallic tin, metallic lithium, metallic indium, and metallic aluminum. Examples of alloys include alloys containing at least one of silicon, tin, lithium, indium, and aluminum. Examples of metallic compounds include metal oxides. Examples of metal oxides include silicon oxide, tin oxide, and aluminum oxide.

[0061] The preferred mixing ratio of the negative electrode active material to the solid electrolyte is negative electrode active material:solid electrolyte = 95% by weight:5% by weight to 5% by weight:95% by weight, more preferably 90% by weight:10% by weight to 10% by weight:90% by weight, and even more preferably 85% by weight:15% by weight to 15% by weight:85% by weight. If the amount of negative electrode active material in the negative electrode composite is too low, the electrical capacitance will be low. Also, if the negative electrode active material has electronic conductivity and does not contain a conductive additive, or contains only a small amount of a conductive additive, the electronic conductivity (electron conduction path) within the negative electrode may decrease, potentially leading to a lower rate characteristic or a decrease in the utilization rate of the negative electrode active material, resulting in a decrease in electrical capacitance. On the other hand, if the amount of negative electrode active material in the negative electrode composite is too high, the ionic conductivity (ionic conduction path) within the negative electrode may decrease, potentially leading to a lower rate characteristic or a decrease in the utilization rate of the negative electrode active material, resulting in a decrease in electrical capacitance.

[0062] The negative electrode composite material may further contain a conductive additive. If the electron conductivity of the negative electrode active material is low, it is preferable to add a conductive additive. The conductive additive only needs to be conductive, and its electron conductivity is preferably 1 × 10⁻⁶. 3 S / cm or more, more preferably 1 × 10 5 It is S / cm or higher. Specific examples of conductive additives include, preferably, carbon materials, substances containing at least one element selected from the group consisting of nickel, copper, aluminum, indium, silver, cobalt, magnesium, lithium, chromium, gold, ruthenium, platinum, beryllium, iridium, molybdenum, niobium, osnium, rhodium, tungsten, and zinc, and more preferably elemental carbon or carbon materials other than elemental carbon with high conductivity; and elemental metals, mixtures, or compounds containing nickel, copper, silver, cobalt, magnesium, lithium, ruthenium, gold, platinum, niobium, osnium, or rhodium. Specific examples of carbon materials include carbon blacks such as Ketjenblack, acetylene black, Denka black, thermal black, and channel black; graphite, carbon fiber, and activated carbon. These can be used individually or in combination of two or more. Among these, acetylene black, Denka black, and Ketjenblack, which have high electronic conductivity, are preferred.

[0063] When the negative electrode composite material contains a conductive additive, the content of the conductive additive in the composite material is preferably 1 to 40% by mass, more preferably 2 to 20% by mass. If the content of the conductive additive is too low, the electronic conductivity of the negative electrode may decrease, potentially resulting in poor rate characteristics, and the utilization rate of the negative electrode active material may decrease, potentially leading to a decrease in capacitance. On the other hand, if the content of the conductive additive is too high, the amount of negative electrode active material and / or solid electrolyte will decrease. It is presumed that a decrease in the amount of negative electrode active material will lead to a decrease in capacitance. Furthermore, if the amount of solid electrolyte decreases, the ionic conductivity of the negative electrode may decrease, potentially resulting in poor rate characteristics, and the utilization rate of the negative electrode active material may decrease, potentially leading to a decrease in capacitance.

[0064] A binder may also be included to ensure that the negative electrode active material and the solid electrolyte are tightly bonded to each other. As binders, fluororesins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and fluororubber, or thermoplastic resins such as polypropylene and polyethylene, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, and natural butyl rubber (NBR) can be used individually or as a mixture of two or more. Water-based binders such as cellulose-based or aqueous dispersions of styrene-butadiene rubber (SBR) can also be used.

[0065] The negative electrode composite material can be manufactured by mixing a solid electrolyte, a negative electrode active material, and any conductive additive and / or binder. The mixing method is not particularly limited, but for example, dry mixing using a mortar and pestle, ball mill, bead mill, jet mill, planetary ball mill, vibrating ball mill, sand mill, or cutter mill can be applied, and wet mixing can be applied after dispersing the raw materials in an organic solvent and mixing using a mortar and pestle, ball mill, bead mill, planetary ball mill, vibrating ball mill, sand mill, or film mix, and then removing the solvent. Of these, wet mixing is preferred in order to avoid destroying the negative electrode active material particles.

[0066] • Cathode composite material A positive electrode composite material can be obtained by blending a positive electrode active material with the solid electrolyte of the present invention. The positive electrode active material is a material that allows for the insertion and removal of lithium ions, and materials known as positive electrode active materials in the battery field can be used. Furthermore, positive electrode active materials to be developed in the future can also be used.

[0067] Examples of positive electrode active materials include metal oxides and sulfides. Sulfides include metallic sulfides and nonmetallic sulfides. Metal oxides include, for example, transition metal oxides. Specifically, V2O5, V6O 13 , LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a Co b Mnc )O2 (where 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), LiNi 1-Y Co Y O2, LiCo 1-Y Mn Y O2, LiNi 1-Y Mn Y O2 (where 0 ≤ Y < 1), Li(Ni a Co b Mn c )O4 (0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-Z Ni Z O4, LiMn 2-Z Co Z O4 (where 0 < Z < 2), LiCoPO4, LiFePO4, CuO, Li(Ni a Co b Al c )O2 (where 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), etc. can be mentioned. As metal sulfides, titanium sulfide (TiS2), molybdenum sulfide (MoS2), iron sulfide (FeS, FeS2), copper sulfide (CuS), nickel sulfide (Ni3S2), etc. can be mentioned. In addition, as metal oxides, bismuth oxide (Bi2O3), bismuth lead oxide (Bi2Pb2O5), etc. can be mentioned. As non-metal sulfides, organic disulfide compounds, carbon sulfide compounds, etc. can be mentioned. In addition to the above, niobium selenide (NbSe3), metallic indium, sulfur can also be used as the positive electrode active material.

[0068] The positive electrode composite material may further contain a conductive aid. The conductive aid is the same as that of the negative electrode composite material. <0000​​​​​​​A lithium-ion battery according to one embodiment of the present invention comprises at least one of the sulfide solid electrolytes and electrode composites of the present invention described above, or is manufactured using at least one of the sulfide solid electrolytes and electrode composites of the present invention. The structure of a lithium-ion battery is not particularly limited, but generally it has a structure in which a negative electrode layer, an electrolyte layer, and a positive electrode layer are stacked in that order. The following describes each layer of the lithium-ion battery.

[0071] (1) Negative electrode layer The negative electrode layer is preferably a layer manufactured from the negative electrode composite material of the present invention. Alternatively, the negative electrode layer is preferably a layer containing the negative electrode composite material of the present invention. The thickness of the negative electrode layer is preferably 100 nm to 5 mm, more preferably 1 μm to 3 mm, and even more preferably 5 μm to 1 mm. The negative electrode layer can be manufactured by known methods, such as coating methods and electrostatic methods (electrostatic spraying method, electrostatic screening method, etc.).

[0072] (2) Electrolyte layer The electrolyte layer is a layer containing a solid electrolyte or a layer manufactured from a solid electrolyte. The solid electrolyte is not particularly limited, but is preferably the sulfide solid electrolyte of the present invention. The electrolyte layer may consist only of a solid electrolyte, or it may further contain a binder. The same binder used in the negative electrode composite of the present invention can be used as the binder.

[0073] The thickness of the electrolyte layer is preferably 0.001 mm or more and 1 mm or less. The solid electrolyte in the electrolyte layer may be fused. Fusion means that some of the solid electrolyte particles dissolve, and the dissolved portion becomes integrated with other solid electrolyte particles. The electrolyte layer may also be a plate-like body of solid electrolyte, and this includes cases where some or all of the solid electrolyte particles have dissolved to form a plate-like body. The electrolyte layer can be manufactured by known methods, such as coating methods and electrostatic methods (electrostatic spraying method, electrostatic screening method, etc.).

[0074] (3) Positive electrode layer The positive electrode layer is a layer containing a positive electrode active material, and is preferably a layer containing the positive electrode composite material of the present invention or a layer manufactured from the positive electrode composite material of the present invention. The thickness of the positive electrode layer is preferably 0.01 mm or more and 10 mm or less. The positive electrode layer can be manufactured by known methods, such as coating methods and electrostatic methods (electrostatic spraying method, electrostatic screening method, etc.).

[0075] (4) Current collector The lithium-ion battery of this embodiment preferably further comprises current collectors. For example, the negative electrode current collector is provided on the side of the negative electrode layer opposite to the electrolyte layer, and the positive electrode current collector is provided on the side of the positive electrode layer opposite to the electrolyte layer. As a current collector, plate-shaped or foil-shaped materials made of copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, indium, lithium, or alloys thereof can be used.

[0076] The lithium-ion battery of this embodiment can be manufactured by bonding and joining the above-mentioned components. Methods of joining include stacking the components and applying pressure to bond them together, or applying pressure by passing them between two rolls (roll to roll). Alternatively, the bonding surface may be bonded via an active material having ion conductivity or an adhesive material that does not inhibit ion conductivity. In bonding, heat fusion may be used as long as the crystal structure of the solid electrolyte does not change. Furthermore, the lithium-ion battery of this embodiment can also be manufactured by sequentially forming the above-mentioned components. It can be manufactured by known methods, for example, by coating methods, electrostatic methods (electrostatic spraying method, electrostatic screening method, etc.). [Examples]

[0077] The present invention will be described in more detail below with reference to examples. The evaluation method is as follows: (1) Ionic conductivity measurement and electronic conductivity measurement The sulfide solid electrolyte produced in each example was filled into a tablet molding machine, and a pressure of 407 MPa (press display value 22 MPa) was applied using a mini press to form a molded body. Carbon was placed on both sides of the molded body as electrodes, and pressure was applied again using the tablet molding machine to produce a molded body for measurement (approximately 10 mm in diameter and 0.1-0.2 cm in thickness). The ionic conductivity of this molded body was measured by AC impedance measurement. The ionic conductivity values ​​used were those obtained at 25°C. In this example, the ionic conductivity measurement method used was for an ionic conductivity of 1.0 × 10⁻⁶. -6 If the ionic conductivity was less than S / cm, it was determined that measurement was impossible because accurate measurement of ionic conductivity was not possible. Furthermore, the electron conductivity of this molded body was measured by DC electrical measurement. The electron conductivity values ​​used were those obtained at 25°C. Note that the electron conductivity when a voltage of 5V was applied was 1.0 × 10⁻⁶. -6 If the value was less than S / cm, the electronic conductivity was considered unmeasurable.

[0078] (2) X-ray diffraction (XRD) measurement From the sulfide solid electrolyte powder produced in each example, circular pellets with a diameter of 10 mm and a height of 0.1 to 0.3 cm were formed to serve as samples. These samples were measured without exposure to air using an airtight XRD holder. The 2θ position of the diffraction peak was determined using the centroid method with the XRD analysis program JADE. The following measurements were performed using Rigaku Corporation's SmartLab powder X-ray diffraction analyzer. Tube voltage: 45kV Tube current: 200mA X-ray wavelength: Cu-Kα ray (1.5418Å) Optical system: Parallel beam method Slit configuration: Solar slit 5°, incident slit 1mm, light-receiving slit 1mm Detector: Scintillation counter Measurement range: 2θ = 10 - 60 degrees Step size, scan speed: 0.02deg, 1deg / min

[0079] To confirm the existence of a crystal structure based on the measurement results, the peak positions were analyzed using the XRD analysis program JADE. A baseline was drawn using a cubic approximation to determine the peak positions.

[0080] The intensity and area of ​​the diffraction peaks at 2θ = 25.2 ± 0.5 deg (diffraction peak A) and 2θ = 29.7 ± 0.5 deg (diffraction peak B) were analyzed using the following procedure, and the area ratio was calculated. In the XRD pattern, the position of the maximum peak at 2θ = 23 to 27 degrees is determined, and the intensity (height) of that peak top is defined as the intensity I of the diffraction peak. A The area S of diffraction peak A is calculated by integrating the 41 measured intensity points located at ±0.4 degrees from the maximum peak position. A Similarly, the maximum peak position at 2θ = 28 to 32 degrees was determined, and the area S of the diffraction peak B was calculated by integrating the measured intensities of 41 points located ±0.4 degrees from that maximum peak position. B S A and S B From, the area ratio (S A / S B ) was calculated. Intensity I of the diffraction peak of lithium halide C When lithium halide is LiCl, the peak at 2θ = 34.0~35.5deg is identified, and the intensity of the peak top is taken as the intensity of the diffraction peak I. C This was done. If there are two or more peaks in the range, the intensity of the peak identified at the highest angle is used. In the case of LiBr, the peak at 2θ = 32.5 to 33.9 degrees is identified, and the intensity of the peak top is used as the intensity of the diffraction peak I. C This was done. Furthermore, if there are two or more peaks within the specified range, the intensity of the peak identified at the lowest angle is used. Furthermore, the peaks located at 2θ = 14.0 to 15.0 degrees were identified, and the intensity of the peak top was defined as the intensity of the diffraction peak I. D That's what I decided.

[0081] (3)ICP measurement The sulfide solid electrolyte powder prepared in each example was weighed and collected in a vial under an argon atmosphere. KOH alkaline aqueous solution was added to the vial, and the sample was dissolved while taking care to collect sulfur. The solution was then diluted as needed to prepare the measurement solution. This solution was measured using a Paschenrunge-type ICP-OES instrument (SPECTRO ARCOS, SPECTRO Corporation) to determine its composition. Calibration curve solutions were prepared using 1000 mg / L standard solutions for ICP measurement for Li, P, and S, and 1000 mg / L standard solutions for ion chromatography for Cl and Br. Two measurement solutions were prepared for each sample, and five measurements were taken with each solution. The average value was then calculated. The composition was determined by the average of the measurements from these two solutions.

[0082] (4) Lattice constants of argyrodite crystal structures XRD was measured under the same conditions as in (2) above. The obtained XRD patterns were subjected to full pattern fitting (WPF) analysis using JADE ver6, a crystal structure analysis software from MDI Corporation, to identify each crystal component contained in the XRD pattern and calculate the lattice constant of each component.

[0083] • Background removal of XRD patterns The XRD pattern after measurement contains scattered light from the instrument and signals from the airtight holder at low angles. To remove these signals, a baseline that attenuates from the low angles was calculated using a three-dimensional approximation, matching the XRD pattern.

[0084] Identification of peak components For each component contained in the sample, peak components were identified by superimposing patterns calculated from structural information in the Inorganic Crystal Structure Database (ICSD) onto the XRD patterns. Table 1 shows the structural information used.

[0085] [Table 1]

[0086] ·WPF analysis The main parameter settings for WPF analysis are shown below. X-ray wavelength: Cukα ray (λ=1.54184Å) Fitting parameters: Peak shape was approximated as a symmetrical peak. The temperature factor was excluded from the fitting. If crystals such as Li2S remain as fine peaks, the fitting may not converge. In such cases, structures other than argyrodite crystals and lithium halide crystals were excluded from the fitting, the full width at half maximum and intensity were manually entered, and the fitting was performed to calculate the lattice constant of the argyrodite crystal. Regarding the lattice constant, we confirmed that the peak positions of the crystal structure being evaluated closely matched the fitting results. For the area ratio, an R value of 10% or less was used as an indicator of the validity of the results. The R value, which is an indicator of the accuracy of the fitting, may be high if there are many unknown peaks or if amorphous peaks remain.

[0087] (5)Solid 31 P-NMR measurement Approximately 60 mg of the powder sample was packed into an NMR sample tube, and the solid sample was analyzed using the following apparatus and conditions. 31 P-NMR spectra were obtained. Equipment: ECZ400R unit (manufactured by JEOL Ltd.) Observed nuclei: 31 P Observation frequency: 161.944MHz Measurement temperature: room temperature Pulse sequence: Single pulse (using a 90° pulse) 90° pulse width: 3.8μ Waiting time after FID measurement until the next pulse is applied: 300s Magic angle rotation speed: 12kHz Total number of times: 16 Measurement range: 250 ppm to -150 ppm solid 31 In the measurement of the P-NMR spectrum, the chemical shift was obtained using (NH4)2HPO4 (chemical shift 1.33 ppm) as an external reference.

[0088] Solid 31 The NMR signals in the range of 78 to 92 ppm in the P-NMR spectrum were separated into Gaussian functions or Pseudo-Voigt functions (linear sum of Gaussian function and Lorentz function) by the non-linear least squares method. In addition to the peaks due to the argyrodite-type crystal structure containing chlorine and bromine in the above range, a peak due to Li7PS6 at 88.5 to 90.5 ppm and a peak due to the β-phase of Li3PS4 at 86 to 87.6 ppm may be observed overlapping. Therefore, when these two peaks are not observed and when they are observed, waveform separation was performed by different methods.

[0089] (5-1) When peaks due to β-phase of Li7PS6 and Li3PS4 are not observed The NMR signals in the range of 78 to 92 ppm were separated into four Gaussian functions or Pseudo-Voigt functions (linear sum of Gaussian function and Lorentz function) with the positions and full width at half maximum ranges shown in Table 2 by the non-linear least squares method. The areas S1 to S4 of each of the obtained peaks A to C and their total S all (=S1 + S2 + S3 + S4) were used to calculate the area ratio (%) of each peak.

[0090]

Table 2

[0091] (5-2) When peaks due to β-phase of Li7PS6 or Li3PS4 are observed As shown in Table 3, in addition to the four peaks due to the argyrodite-type crystal structure containing chlorine, using the peaks due to Li7PS6 (peak I) or Li3PS4 (peak II), the NMR signals in the range of 78 to 92 ppm were separated using the non-linear least squares method, and the areas S1 to S4 of the obtained peaks A to C, the areas b1 and b2 of peaks I and II, and their total S <00​​​​​​​

[0093] Manufacturing Example 1 (Production of lithium sulfide (Li2S)) 200 g of anhydrous LiOH (manufactured by Honjo Chemical Co., Ltd.), dried under inert gas, was placed in a 500 mL separable flask equipped with a stirrer. The flask was heated under a nitrogen stream and the internal temperature was maintained at 200 °C. The nitrogen gas was switched to hydrogen sulfide gas (manufactured by Sumitomo Seika), and the flow rate was set to 500 mL / min to react the anhydrous LiOH with hydrogen sulfide. The water generated by the reaction was condensed and recovered using a condenser. After 6 hours of reaction, 144 mL of water was recovered. The reaction was continued for another 3 hours, but no further water was observed. The product powder was recovered, and its purity and XRD were measured. The results showed a purity of 98.5%, and a peak pattern for Li2S was confirmed by XRD.

[0094] Example 1 In Production Example 1, Li2S (purity 98.5%), phosphorus pentasulfide (P2S5: Thermophos, purity 99.9% or higher), lithium chloride (LiCl: Sigma-Aldrich, purity 99%), and lithium bromide (LiBr: Sigma-Aldrich, purity 99%) were used as starting materials (the purity of each starting material was the same in all subsequent examples). The materials were mixed so that the molar ratio of Li2S, P2S5, LiCl, and LiBr (Li2S:P2S5:LiCl:LiBr) was 1.9:0.5:1.0:0.6. Specifically, 0.447g, 0.569g, 0.217g, and 0.267g of lithium sulfide were mixed to form the raw material mixture.

[0095] The raw material mixture and 30g of 10mm diameter zirconia balls were placed in a zirconia pot (45mL) of a planetary ball mill (Fritsch, model P-7) and completely sealed. The pot was kept under an argon atmosphere. The mixture was processed in the planetary ball mill at a rotation speed of 370rpm for 15 hours (mechanical milling) to obtain a glassy powder (intermediate).

[0096] Approximately 1.5 g of the above intermediate powder was packed into a Tammann tube (PT2, manufactured by Tokyo Glass Equipment Co., Ltd.) in a glove box under an Ar atmosphere. The opening of the Tammann tube was sealed with quartz wool, and the container was further sealed with a SUS airtight container to prevent air from entering. The airtight container was then placed in an electric furnace (FUW243PA, manufactured by Advantech Co., Ltd.) and heat-treated. Specifically, the temperature was raised from room temperature to 430°C at a rate of 2.5°C / min (reaching 430°C in approximately 3 hours), and then maintained at 430°C for 8 hours. After that, it was slowly cooled to obtain a sulfide solid electrolyte.

[0097] The ionic conductivity (σ) of the sulfide solid electrolyte was 13.0 mS / cm. Figure 3 shows the XRD pattern of the sulfide solid electrolyte. Peaks originating from the argyrodite crystal structure were observed at 2θ = 15.5, 17.9, 25.4, 29.9, 31.3, 44.9, 47.8, 52.4, and 59.1 degrees. ICP analysis was performed on the sulfide solid electrolyte to measure the molar ratio of each element. The results showed that the molar ratio a (Li / P) was 5.35, the molar ratio b (S / P) was 4.33, the molar ratio c (Cl / P) was 1.102, and the molar ratio d (Br / P) was 0.62. The raw material composition and manufacturing conditions are shown in Table 4. The molar ratios of each element in the raw materials and the sulfide solid electrolyte are shown in Table 5. The area, area ratio, and ionic conductivity σ of diffraction peaks A and B in the XRD pattern of the sulfide solid electrolyte are shown in Table 6. The intensity and intensity ratio of the diffraction peaks in the XRD pattern of the sulfide solid electrolyte are shown in Table 7. The lattice constant and 31 Table 8 shows the area ratios of the P-NMR peaks. [Table 4]

[0098] [Table 5] *X is the sum of Cl and Br.

[0099] [Table 6] In the table, S A is the area of diffraction peak A (2θ = 25.2 ± 0.5 deg), and S B is the area of diffraction peak B (29.7 ± 0.5 deg).

[0100]

Table 7

[0101]

Table 8

[0102] Comparative Example 1 The same raw materials as in Example 1 were placed in a Schlenk flask and mixed by hand shaking. The obtained raw material mixture was heat-treated at 430 °C for 8 hours in the same manner as in Example 1 to obtain a sulfide solid electrolyte. The sulfide solid electrolyte was evaluated in the same manner as in Example 1. The results are shown in Tables 5 to 8. In Comparative Example 1, since the raw material mixing before heat treatment was insufficient, the halogen did not disperse even after heat treatment, and as a result, it is presumed that the introduction of halogen into the sites in the argyrodite-type crystal structure was insufficient.

[0103] Example 2 In Example 2, a two-roll kneader was used instead of the planetary ball mill of Example 1 for the preparation of the intermediate. The kneading using the two-roll kneader was specifically carried out as follows. A feeder (microfeeder, manufactured by Aisin Nanotechnologies Corporation) and a twin-screw compound extruder (KRC kneader, paddle diameter φ8mm, manufactured by Kurimoto Iron Works Co., Ltd.) were installed in a glove box. A mixture of 3.76g of LiCl, 4.63g of LiBr, 7.75g of Li2S, and 9.87g of P2S5 was supplied at a constant speed from the supply section via the feeder, and kneading was performed at a rotation speed of 150 rpm and a temperature of 250°C (measured with a thermometer on the outer surface of the twin-screw compound extruder casing). After approximately 120 minutes, the powder was discharged from the kneader outlet. The discharged powder was returned to the supply section and kneaded again, and this operation was repeated 5 times. The total reaction time was approximately 10 hours. The obtained intermediate was heat-treated at 430°C for 8 hours in the same manner as in Example 1 to obtain a sulfide solid electrolyte. The obtained sulfide solid electrolyte was evaluated in the same manner as in Example 1. The results are shown in Tables 5-8. The twin-screw compounding extruder used to mix the raw materials is a device that achieves a very high degree of mixing, so it is thought that the constituent elements were highly dispersed in the intermediate. As a result, it can be presumed that the ionic conductivity improved.

[0104] Examples 3-7, Comparative Examples 2-4 A sulfide solid electrolyte was prepared and evaluated in the same manner as in Example 1, except that the raw material composition was changed as shown in Table 4. The results are shown in Tables 5 to 8. In Comparative Example 2, it is thought that the halogens occupying sites in the crystal structure detached due to the high heat treatment temperature. Cl located at the 4a site and Br located at the 4d site are more likely to detach from their sites. Figure 4 shows the XRD patterns of the sulfide solid electrolyte prepared in Comparative Example 2. The presence of lithium halide crystals and novel crystals exhibiting diffraction peaks at 2θ = 14.4 ± 0.5 deg and 33.8 ± 0.5 deg suggests that these crystals were formed by the detachment of some of the Cl and Br that occupied sites in the argyrodite-type crystal structure. Furthermore, XRD measurements of the sulfide solid electrolytes obtained in each example revealed peaks originating from the argyrodite crystal structure.

[0105] Examples 8-12, Comparative Example 5 Except for changes to the raw material composition and manufacturing conditions as shown in Table 9, sulfide solid electrolytes were prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 10-12. In addition, XRD measurements of the sulfide solid electrolytes obtained in each example revealed peaks originating from the argyrodite crystal structure.

[0106] [Table 9]

[0107] [Table 10] *X is the sum of Cl and Br.

[0108] [Table 11] In the table, S A This is the area of ​​diffraction peak A (2θ = 25.2 ± 0.5 deg), and S B This represents the area of ​​diffraction peak B (29.7 ± 0.5 deg).

[0109] [Table 12]

[0110] Example 13 The intermediate was prepared in the same manner as in Example 1, except that the raw material composition and preparation conditions were changed as shown in Table 9. In a glove box under an Ar atmosphere, approximately 1.5 g of the intermediate powder was packed into a glass tube with a sealing function, and the tip of the glass tube was sealed with a special jig to prevent air from entering. The glass tube was then placed in an electric furnace. The special jig was inserted into a fitting inside the electric furnace and connected to a gas flow pipe, and heat treatment was carried out while hydrogen sulfide was flowed at 0.5 L / min. Specifically, the temperature was raised from room temperature to 500°C at a rate of 3°C / min and held at 500°C for 4 hours. After that, it was slowly cooled to obtain a sulfide solid electrolyte. The obtained sulfide solid electrolyte was evaluated in the same manner as in Example 1. The results are shown in Tables 10-12. The sulfide solid electrolyte obtained in Example 13 also had an electronic conductivity of 10. -6 The concentration was less than S / cm. Furthermore, XRD measurements revealed peaks originating from an argyrodite crystal structure.

[0111] Example 14 Similar to Example 2, the intermediate was prepared by kneading using a twin-screw kneader. Specifically, the intermediate was obtained in the same manner as in Example 2, except that a mixture of 1.447 g of LiCl, 1.779 g of LiBr, 2.980 g of Li2S, and 3.794 g of P2S5 was supplied at a constant speed from the supply section via a feeder. The obtained intermediate was heat-treated at 430°C for 4 hours to obtain a sulfide solid electrolyte.

[0112] The evaluation results of the obtained sulfide solid electrolytes are shown in Tables 10-12. The sulfide solid electrolyte obtained in Example 14 has an electronic conductivity of 10. -6 The concentration was less than S / cm. Furthermore, XRD measurements revealed peaks originating from an argyrodite crystal structure.

[0113] Example 15 Except for changing the preparation conditions as shown in Table 9, sulfide solid electrolytes were prepared and evaluated in the same manner as in Example 14. The results are shown in Tables 10-12. The sulfide solid electrolyte obtained in Example 15 has an electronic conductivity of 10. -6 The concentration was less than S / cm. Furthermore, XRD measurements revealed peaks originating from an argyrodite crystal structure.

[0114] [Hydrogen sulfide generation amount from sulfide solid electrolytes] The amount of hydrogen sulfide generated by the sulfide solid electrolytes produced in Example 10 and Comparative Example 4 was evaluated using the apparatus shown in Figure 5. This apparatus consists of a flask 1 for humidifying the air, a flask 2 equipped with a thermometer / hygrometer 6 for measuring the temperature and humidity of the humidified air, a Schlenk bottle 3 for introducing the sample 4, and a hydrogen sulfide meter 7 for measuring the hydrogen sulfide concentration in the air, all connected in this order via tubing. The evaluation procedure is as follows. Approximately 0.1 g of the powdered sample, prepared by thoroughly grinding the sample in a mortar and pestle in a nitrogen glow box with a dew point of -80°C, was weighed and placed inside a 100 ml Schlenk vial 3, which was then sealed (numbered 4 in Figure 5). Next, air was introduced into flask 1 at a rate of 500 mL / min. The air flow rate was measured using a flow meter 5. The air in flask 1 was humidified by passing it through water. Subsequently, the humidified air was introduced into flask 2, and the temperature and humidity of the air were measured. Immediately after the start of flow, the air temperature was 25°C and the humidity was 80-90%. After that, the humidified air was circulated through Schlenk vial 3 and brought into contact with the sample 4. The humidified air circulated through Schlenk vial 3 was passed through a hydrogen sulfide analyzer 7 (AMI Model 3000RS) to measure the amount of hydrogen sulfide contained in the humidified air. The measurement time was from immediately after the air flow until 1 hour after flow. The amount of hydrogen sulfide was recorded at 15-second intervals. The amount of hydrogen sulfide generated per gram of sample (mg / g) was calculated from the total amount of hydrogen sulfide observed over two hours. As a result, the amount was 26 mg / g for the sulfide solid electrolyte in Example 10 and 64 mg / g for the sulfide solid electrolyte in Comparative Example 4.

[0115] [Lithium-ion battery] Lithium-ion batteries were manufactured using the sulfide solid electrolytes obtained in Example 13 and Comparative Example 1, respectively, and their rate characteristics were evaluated.

[0116] (A) Manufacturing of lithium-ion batteries 50 mg of the sulfide solid electrolyte obtained in Example 13 or Comparative Example 1 was placed into a stainless steel mold with a diameter of 10 mm, leveled, and the electrolyte layer thickness was made uniform. Then, a pressure of 185 MPa was applied from the top surface of the electrolyte layer using a hydraulic press to form the mixture. Li4Ti5O is used as the positive electrode active material. 12 Coat Limited 0.8 Co 0.15 Al 0.05 O2 and the sulfide solid electrolyte obtained in Example 13 or Comparative Example 1 were mixed in a weight ratio of 70:30 to form the positive electrode material. 15 mg of the positive electrode material was placed on the top surface of the electrolyte layer and leveled to ensure that the thickness of the positive electrode layer was uniform. Then, a pressure of 407 MPa was applied from the top surface of the positive electrode layer using a hydraulic press to form the material. The negative electrode material was prepared by mixing graphite powder, which is the negative electrode active material, and the sulfide solid electrolyte obtained in Example 13 or Comparative Example 1 in a weight ratio of 60:40. 12 mg of the negative electrode material was placed on the side of the electrolyte layer opposite the positive electrode layer and leveled to ensure that the thickness of the negative electrode layer was uniform. Then, a pressure of 555 MPa was applied from the top surface of the negative electrode layer using a hydraulic press to press-molde it, thereby producing lithium-ion batteries with a three-layer structure consisting of a positive electrode, a solid electrolyte layer, and a negative electrode.

[0117] (B) Rate characteristic test The lithium-ion batteries manufactured in (A) above were left to stand in a constant temperature bath set to 25°C for 12 hours and then evaluated. In the first cycle, they were charged to 4.2V at 0.1C (0.189mA) and discharged to 3.1V at 0.1C (0.189mA). From the second to the tenth cycle, they were charged to 4.2V at 0.5C (0.945mA) and discharged to 3.1V at 0.5C (0.945mA). The capacity at the tenth cycle was measured. Using the same sample, a separately manufactured battery was used, and the capacity at the tenth cycle was measured when it was charged and discharged from the first to the tenth cycle at 0.1C. The ratio of the capacity when charged and discharged at 0.5C to the capacity when charged and discharged at 0.1C was used as the evaluation value for the rate characteristic. The rate characteristic of the lithium-ion battery using sulfide solid electrolyte in Example 13 was 73%. The lithium-ion battery using sulfide solid electrolyte in Comparative Example 1 was 50%.

[0118] [Example of evaluation] Structural analysis using synchrotron radiation and neutrons was performed on the sulfide solid electrolyte obtained in Example 1. Specifically, synchrotron X-ray diffraction was performed at BL19B2 of SPring-8. Samples sealed in glass capillaries were measured. After correcting the measurement data using a CeO2 standard sample, Rietveld analysis was performed based on the structural model of the argyrodite crystal. Neutron diffraction was measured at BL20 of J-PARC. In neutron diffraction, the occupancy rate of each site, distinguishing between S and Cl at the 4a and 4d sites, can be calculated by Rietveld structural analysis. The occupancy rate, i.e., abundance ratio, of the 4a and 4d sites was calculated from a structural model that satisfied both the synchrotron X-ray diffraction and neutron diffraction data. Figure 6 shows the results of structural analysis using synchrotron radiation. The small difference between the measured data and the analyzed data confirms the high consistency of the fitting. From the analysis results, it can be confirmed that, regarding the site selectivity of halogens, chlorine (Cl) tends to occupy the 4d site, while bromine (Br) tends to occupy the 4a site.

[0119] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will find it easy to make many modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and effects of the present invention. Accordingly, many of these modifications fall within the scope of the present invention. The entire contents of the Japanese application specification, which forms the basis for the Paris Convention priority of this application, are incorporated herein by reference.

Claims

1. A process of producing an intermediate by crushing and mixing raw materials containing lithium, phosphorus, sulfur, chlorine, and bromine in a pulverizer, The process includes a step of heat-treating the intermediate at 350 to 480°C. A method for producing a sulfide solid electrolyte, comprising an argyrodite-type crystal in which the molar ratio c (Cl / P) of chlorine to phosphorus and the molar ratio d (Br / P) of bromine to phosphorus satisfy the following formula (1). 1.2<c+d≦1.7...(1)

2. The manufacturing method according to Claim 1, wherein the molar ratio d (Br / P) of bromine to phosphorus in the raw material is 0.15 or more and 1.6 or less.

3. The manufacturing method according to claim 1 or 2, wherein the molar ratio c (Cl / P) of chlorine to phosphorus and the molar ratio d (Br / P) of bromine to phosphorus of the raw material satisfy the following formula (2). 0.08<d / (c+d)<0.8...(2)

4. The manufacturing method according to any one of Claims 1 to 3, wherein the molar ratio a of lithium to phosphorus (Li / P), the molar ratio b of sulfur to phosphorus (S / P), the molar ratio c of chlorine to phosphorus (Cl / P), and the molar ratio d of bromine to phosphorus (Br / P) of the raw materials satisfy the following formulas (3) to (5). 5.0 ≤ a ≤ 7.5 ... (3) 6.5≦a+c+d≦7.5...(4) 0.5 ≤ a - b ≤ 1.5 ... (5) (The equation satisfies b > 0, c > 0, and d > 0.)

5. The manufacturing method according to any one of claims 1 to 4, wherein c + d in formula (1) is 1.4 or more and 1.7 or less.

6. The manufacturing method according to any one of claims 1 to 5, wherein the temperature of the heat treatment is 360 to 460°C.

7. The manufacturing method according to any one of claims 1 to 6, wherein the atmosphere for the heat treatment is an inert gas atmosphere.

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