solid electrolyte

Abstract

To provide a solid electrolyte that suppresses the generation of hydrogen sulfide while possessing high ionic conductivity. [Solution] A solid electrolyte having a composition represented by the following formula (A) and having an argyrodite-type crystal structure, wherein the lattice constant of the argyrodite-type crystal structure is 9.820 Å or less, and in powder X-ray diffraction measurements using CuKα rays, it has diffraction peaks at 2θ = 25.2 ± 0.5 deg and 29.7 ± 0.5 deg, and contains a Li3PO4 crystal structure. Li a P b S c O d X e ...(A) (In the formula, X is a halogen containing Cl and Br, a to e represent the composition ratio of each element, 4.8 ≤ a ≤ 5.3, b = 1, 3.8 ≤ c ≤ 4.4, 0)

Description

Technical Field

[0001] The present invention relates to a solid electrolyte and a method for manufacturing the same.

Background Art

[0002] Sulfide solid electrolytes are known to deteriorate due to moisture in the air. On the other hand, for example, in Patent Document 1, Li 7-a PS 6-a Ha a (where Ha represents a halogen. a satisfies 0.2 < a ≤ 1.8) and Li3PS4 are contained, and in the X-ray diffraction pattern obtained by measurement using the X-ray diffraction method (XRD), the ratio of the peak intensity appearing at a diffraction angle 2θ = where the peak intensity appearing at a diffraction angle 2θ = 26.0 to 28.8° derived from Li3PS4 is 0.04 to 0.3. Patent Document 2 discloses a sulfide solid electrolyte in which an alkaline compound is mixed with the solid electrolyte, and the ratio of the molar amount of the alkali metal contained in the alkaline compound to the molar amount of Li contained in the solid electrolyte is 1 / 1000 or more and 1 / 25 or less.

[0003] Further, Patent Documents 3 and 4 disclose sulfide-based solid electrolyte particles containing lithium, phosphorus, sulfur, and a halogen and having a cubic Argyrodite-type crystal structure, and sulfide-based solid electrolytes for lithium secondary batteries whose surfaces are coated with a compound having a non-Argyrodite-type crystal structure containing lithium, phosphorus, and sulfur.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] The solid electrolytes described in Patent Documents 1 to 4 fail to adequately achieve both suppression of hydrogen sulfide generation and ionic conductivity, and further improvements are needed. The object of the present invention is to provide a solid electrolyte that suppresses the generation of hydrogen sulfide and has high ionic conductivity, as well as a method for producing the same. [Means for solving the problem]

[0006] According to one embodiment of the present invention, a method for producing a solid electrolyte having an argyrodite-type crystal structure is provided, comprising a mixing step of mixing raw materials such that lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and halogen (X) satisfy the following formulas (11) to (14), and a heating step of heating the mixture obtained in the mixing step. 4.8 ≤ Li / P ≤ 5.3 ···(11) 3.8 ≤ S / P ≤ 4.4 ···(12) 0 <O / P≦0.8 ···(13) 1.0 <X / P≦2.0 ···(14) (Equation (11) is the molar ratio of Li to P, equation (12) is the molar ratio of S to P, equation (13) is the molar ratio of O to P, and equation (14) is the molar ratio of halogen (X) to P.)

[0007] Furthermore, according to one embodiment of the present invention, a solid electrolyte is provided having an argyrodite-type crystal structure containing lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and halogen (X), wherein the proportion of the Li3PO4 crystal structure in the total crystals of the solid electrolyte is 0.1% by mass or more and 3.0% by mass or less, and satisfies the following formulas (21) to (23). 4.8 ≤ Li / P ≤ 5.3 ···(21) 3.8 ≤ S / P ≤ 4.4 ···(22) 1.0 < X / P ≤ 2.0 ···(23) (Equation (21) is the molar ratio of Li to P, Equation (22) is the molar ratio of S to P, and Equation (23) is the molar ratio of halogen (X) to P.)

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a solid electrolyte having high ionic conductivity while suppressing the generation of hydrogen sulfide, and a method for producing the same.

Brief Description of the Drawings

[0009] [Figure 1] It is a schematic configuration diagram of a test apparatus for measuring the amount of hydrogen sulfide generated. [Figure 2] It is an X-ray diffraction (XRD) pattern of the solid electrolyte obtained in Example 1. [Figure 3] It is an XRD pattern of the solid electrolyte obtained in Example 2. [Figure 4] It is an XRD pattern of the solid electrolyte obtained in Example 3. [Figure 5] It is an XRD pattern of the solid electrolyte obtained in Example 4. [Figure 6] It is an XRD pattern of the solid electrolyte obtained in Comparative Example 1. [Figure 7] It is an XRD pattern of the solid electrolyte obtained in Comparative Example 2. [Figure 8] It is an XRD pattern of the solid electrolyte obtained in Comparative Example 3. [Figure 9] It is an XRD pattern of the solid electrolyte obtained in Comparative Example 4. [Figure 10] ​​​​​​​​​​ [First Embodiment] The method for producing a solid electrolyte according to an embodiment of the present invention includes the following mixing step and heating step, and produces a solid electrolyte having an argyrodite-type crystal structure. Mixing step: A step of mixing raw materials so that lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and halogen (X) satisfy the following formulas (11) to (14). 4.8 ≦ Li / P ≦ 5.3 ···(11) 3.8 ≦ S / P ≦ 4.4 ···(12) 0 < O / P ≦ 0.8 ···(13) 1.0 < X / P ≦ 2.0 ···(14) (Formula (11) is the molar ratio of Li to P, formula (12) is the molar ratio of S to P, formula (13) is the molar ratio of O to P, and formula (14) is the molar ratio of halogen (X) to P.) Heating step: A step of heating the mixture obtained in the mixing step.

[0011] [ [ In this embodiment, by adjusting the composition of the starting materials to formulas (11) to (14), unlike the conventional argyrodite-type crystal structure, the amount of sulfur ions (S 2- [ ) in the crystal decreases, and it is presumed that an argyrodite-type crystal structure in which halogen ions (Cl - [ , Br - [ , etc.) increase is formed. [ The argyrodite-type crystal structure has a PS4 3- [ structure as the main unit structure of the skeleton, and the sites around it are occupied by S surrounded by Li 2- [ and optionally halogen ions. A general argyrodite-type crystal structure is a crystal structure represented by the space group F-43M. Crystallographically, this crystal structure has 4a sites and 4d sites around the PS4 3- [ structure, and elements with a large ionic radius tend to occupy the 4a sites, while elements with a small ionic radius tend to occupy the 4d sites. [

[0012] [ [The unit cell of the argyrodite crystal structure has a total of eight 4a sites and 4d sites. The inventors of the present invention have identified S that occupies the sites in the argyrodite crystal structure. 2- However, assuming that this is the cause of hydrogen sulfide generation, S in the argyrodite crystal structure 2- We found that by relatively lowering the content of [the substance], the generation of hydrogen sulfide can be reduced. On the other hand, it was confirmed that simply reducing the amount of sulfur in the starting material causes some elements to form crystalline phases other than argyrodite crystals, such as β-Li3PS4, during the heating process, resulting in a significant decrease in ionic conductivity. As a result of the inventors' diligent efforts to solve this problem, they have surprisingly found that by using the compositions of formulas (11) to (14) above and including O in the starting material, the formation of crystalline phases other than argyrodite-type crystals such as β-Li3PS4 during the heating process is suppressed, and S in the crystal 2- We found that by increasing the amount of argyrodite-type crystal structure with a reduced amount of [unclear], it is possible to obtain a solid electrolyte with high ionic conductivity while sufficiently suppressing the generation of hydrogen sulfide.

[0013] In the mixing process, it is preferable that the above equations (11) to (14) satisfy the following equation. 4.85 ≤ Li / P ≤ 5.25 3.9 ≤ S / P ≤ 4.3 0.01 ≤ O / P ≤ 0.7 1.2 ≤ X / P ≤ 1.9 More preferably, in the mixing step, equations (11) to (14) satisfy the following equation. 4.9 ≤ Li / P ≤ 5.2 4.0 ≤ S / P ≤ 4.2 0.05 ≤ O / P ≤ 0.6 1.4 ≤ X / P ≤ 1.8

[0014] The raw materials used in this embodiment consist of two or more compounds and / or elemental elements combined in such a way that the solid electrolyte to be manufactured contains the essential elements in a predetermined molar ratio. Specifically, two or more compounds and elemental elements containing Li, P, S, O, and halogen (X) as a whole are used in combination.

[0015] Examples of lithium-containing raw materials include lithium compounds such as lithium sulfide (Li2S), lithium oxide (Li2O), lithium carbonate (Li2CO3), and lithium hydroxide (LiOH), as well as elemental lithium metal. Among these, lithium compounds are preferred from the viewpoint of ease of handling and reactivity, and Li2S is more preferred.

[0016] 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 from the viewpoint of ease of handling and reactivity, and diphosphorus pentasulfide (P2S5) is more preferred. Phosphorus compounds such as diphosphorus pentasulfide (P2S5) and elemental phosphorus can be used without particular limitation as long as they are industrially manufactured and sold.

[0017] Examples of raw materials containing halogen (X) include those of formula (M l -X m It is preferable to use at least one of a halogen compound and an elemental halogen represented by ). In the formula, 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. Li or P is preferred, and Li is more preferred. X is a halogen element selected from F, Cl, Br, and I. 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.

[0018] Specifically, halogen compounds include sodium halides such as NaI, NaF, NaCl, and NaBr; lithium halides such as LiF, LiCl, LiBr, and LiI; boron halides such as BCl3, BBr3, and BI3; aluminum halides such as AlF3, AlBr3, AlI3, and AlCl3; silicon halides such as SiF4, SiCl4, SiCl3, Si2Cl6, SiBr4, SiBrCl3, SiBr2Cl2, and SiI4; phosphorus halides such as PF3, PF5, PCl3, PCl5, POCl3, PBr3, POBr3, PI3, P2Cl4, and P2I4; and SF2, SF4, SF6, and S2F 10 Sulfur halides such as SCl2, S2Cl2, S2Br2; germanium halides such as GeF4, GeCl4, GeBr4, GeI4, GeF2, GeCl2, GeBr2, GeI2; arsenic halides such as AsF3, AsCl3, AsBr3, AsI3, AsF5; selenium halides such as SeF4, SeF6, SeCl2, SeCl4, Se2Br2, SeBr4; tin halides such as SnF4, SnCl4, SnBr4, SnI4, SnF2, SnCl2, SnBr2, SnI2; antimony halides such as SbF3, SbCl3, SbBr3, SbI3, SbF5, SbCl5; TeF4, Te2F 10 Examples include telluride halides such as TeF6, TeCl2, TeCl4, TeBr2, TeBr4, and TeI4; lead halides such as PbF4, PbCl4, PbF2, PbCl2, PbBr2, and PbI2; and bismuth halides such as BiF3, BiCl3, BiBr3, and BiI3.

[0019] Among these, lithium halides such as lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), and phosphorus halides such as phosphorus pentachloride (PCl5), phosphorus trichloride (PCl3), phosphorus pentabromide (PBr5), and phosphorus tribromide (PBr3) are preferred. Of these, lithium halides or PBr3 are preferred, lithium halides are more preferred from the viewpoint of ease of handling, and LiCl and LiBr are even more preferred from the viewpoint of further increasing ionic conductivity. The halogen compounds may be used individually from the above-mentioned compounds, or in combination of two or more compounds.

[0020] In this embodiment, compounds obtained by the reaction of the above raw materials may be used. For example, Li3PS4 may be synthesized from Li2S and P2S5, and Li3PS4, Li2O, and LiX may be used as raw materials. Note that Li3PS4 may be crystalline or amorphous, or a mixture of crystalline and amorphous.

[0021] In one embodiment, it is preferable to use one or more of Li2O and LiOH as raw materials. Furthermore, it is preferable to use Li2S, Li2O, P2S5, and LiX (where X is a halogen) as raw materials. For example, when using Li2S, Li2O, P2S5, and LiX as raw materials, the molar ratio of the input raw materials can be set to Li2S:Li2O:P2S5:LiX = 1.5~1.9:0.01~0.8:0.5:1.0~2.0.

[0022] In the mixing process, the raw materials mentioned above are mixed together. There are no particular limitations on the mixing method; any known method can be used. In this embodiment, the above raw materials may be subjected to mechanical stress and reacted simultaneously with mixing, or they may be pulverized simultaneously with mixing. Here, "applying mechanical stress" means applying mechanical shear force, impact force, etc. Means of applying mechanical stress include, for example, pulverizers such as planetary ball mills, vibratory mills, rolling mills, and bead mills, and kneaders such as single-screw kneaders and multi-screw kneaders. The mixing process may be carried out in the presence of a solvent (wet mixing) or without the use of a solvent (dry mixing).

[0023] In the case of dry mixing, the conditions for grinding and mixing are as follows: 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 carried out 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.

[0024] In one embodiment, wet mixing is preferred because it may be possible to suppress the formation of β-Li3PS4. Organic solvents can be used as solvents, preferably nonpolar solvents, polar solvents, or mixtures thereof. It is preferable that a nonpolar solvent, or a solvent mainly composed of a nonpolar solvent, be used, for example, that 95% or more by mass of the total organic solvent is a nonpolar solvent.

[0025] As a nonpolar solvent, hydrocarbon solvents are preferred. As a hydrocarbon solvent, saturated hydrocarbons, unsaturated hydrocarbons, or aromatic hydrocarbons can be used. Examples of saturated hydrocarbons include hexane, pentane, 2-ethylhexane, heptane, decane, tridecane, and cyclohexane. Examples of unsaturated hydrocarbons include hexene, heptene, and cyclohexene. Examples of aromatic hydrocarbons include toluene, xylene, ethylbenzene, decalin, and 1,2,3,4-tetrahydronaphthalene. Of these, toluene or xylene is preferred.

[0026] The hydrocarbon solvent is preferably dehydrated beforehand. Specifically, the water content is preferably 100 ppm by mass or less, and particularly preferably 30 ppm by mass or less.

[0027] In one embodiment, it is preferable that the organic solvent contains at least one of a nitrile compound and an ether compound. Examples of ether compounds include tetrahydrofuran and diethyl ether. As for nitrile compounds, R(CN) n A nitrile compound represented by the formula is preferred. In the formula, R is an alkyl group having 1 to 10 carbon atoms, or a group having an aromatic ring with 6 to 18 ring-forming carbon atoms. n is 1 or 2.

[0028] Examples include acetonitrile, propionitrile, 3-chloropropionitrile, benzonitrile, 4-fluorobenzonitrile, tertiary butyronitrile, isobutyronitrile, cyclohexylnitrile, capronitrile, isocapronitrile, malononitrile, and fumanitrile. Propionitrile, isocapronitrile, and isobutyronitrile are preferred. For example, nitrile compounds are preferable because they form an azeotrope with toluene, making them easy to remove from the treated material along with toluene during drying. The amount of nitrile compounds and ether compounds contained in the organic solvent is preferably 0.01 to 5% by mass, more preferably 0.1 to 3% by mass, and particularly preferably 0.3 to 1% by mass.

[0029] In wet mixing, it is preferable to use a bead mill. By mixing and grinding with a bead mill, the particle size of each raw material can be made smaller, which narrows the diffusion pathway of each element during the heating process. This makes it easier for each element to be used to form an argyrodite-type crystal structure, and as a result, the formation of other phases such as the Li3PS4 crystal structure is suppressed.

[0030] The mixture of raw materials obtained by removing the solvent from the processed material after wet mixing using a bead mill is mainly formed of fine crystals. By mixing and grinding the raw materials, the fineness of the raw materials progresses, and a mixture consisting of fine crystals of each raw material is obtained.

[0031] The raw material mixture may be calcined. In one embodiment, the raw material mixture is obtained by removing the solvent as described above and then calcining it to obtain a powdery calcined product. The heating temperature and time in calcination can be appropriately adjusted considering the composition of the calcined product, etc. For example, the heating temperature is preferably 150°C to 300°C, more preferably 160°C to 280°C, and particularly preferably 170°C to 250°C. The heating time is preferably 0.1 to 8 hours, more preferably 0.2 to 6 hours, and particularly preferably 0.25 to 4 hours.

[0032] There are no particular limitations on the heating equipment used for calcination. Examples include shear-type dryers such as FM mixers and Nauta mixers, stationary furnaces such as hearth kilns, and rotary furnaces such as rotary kilns. Drying may be performed before calcination, or drying and calcination may be performed simultaneously. There are no particular limitations on the atmosphere for calcination, but an inert gas atmosphere such as nitrogen or argon is preferred.

[0033] When calcining a mixture of raw materials in a solvent, the solvent used for calcination can be the non-polar solvent, polar solvent, or a mixture thereof as described above. Heating is performed on the slurry in which the mixture is dispersed in the solvent. The solvent used for calcination may be the same as the solvent used for mixing the raw materials, or a different solvent may be used. Using the same solvent is preferable because it eliminates the need for a solvent removal step.

[0034] The heating temperature and time during calcination can be adjusted as appropriate, taking into consideration the composition of the raw materials. For example, the heating temperature is preferably 150°C to 300°C, more preferably 160°C to 280°C, even more preferably 170°C to 270°C, and particularly preferably 180°C to 260°C. By using the above temperature range, a PS4 structure is formed, and halogens are more easily incorporated into the argyrodite-type crystal structure. Since the raw material mixture of fine crystals is calcined in a solution, it is possible to form crystals containing the PS4 structure at a relatively low temperature. The heating time is preferably 10 minutes to 6 hours, more preferably 10 minutes to 3 hours, and particularly preferably 30 minutes to 2 hours. There are no particular limitations on the heating device used for calcination, but if the heating temperature exceeds the boiling point of the solvent used, it is preferable to use an autoclave.

[0035] The solvent is removed from the slurry used for calcination, and the calcined material is recovered. The method of solvent removal is not particularly limited, but the solvent can be removed by distillation under atmospheric pressure or reduced pressure. Furthermore, filtration can be used in combination to increase productivity.

[0036] In the heating step, a solid electrolyte is obtained by heating the mixture or calcined material obtained in the mixing step. The heating temperature and time can be adjusted as appropriate, taking into consideration the composition of the mixture and calcined material. For example, the heating temperature is preferably 300°C to 470°C, more preferably above 300°C and 460°C or less, more preferably 320°C to 450°C, even more preferably 350°C to 440°C, and particularly preferably 380°C to 430°C. The heating time is preferably 1 to 360 minutes, more preferably 5 to 120 minutes, and particularly preferably 10 to 60 minutes. The atmosphere during heating is not particularly limited, but preferably it is under an inert gas atmosphere such as nitrogen or argon, rather than under a hydrogen sulfide gas stream. For the heating process, a firing furnace such as a stationary hearth kiln or a rotary kiln can be used. When heating calcined material, the non-polar solvent, polar solvent, or mixture thereof described above can be used as the solvent for heating. Heating is performed on a slurry in which the calcined material is dispersed in the solvent. The solvent used for heating may be the same as the solvent used for calcination, or a different solvent may be used. Using the same solvent is preferable because it eliminates the need for a step of replacing or removing the solvent before heating. Also, as with calcination, if the heating temperature exceeds the boiling point of the solvent used, it is preferable to use an autoclave.

[0037] The presence of an argyrodite-type crystal structure in the solid electrolyte obtained by the manufacturing method of this embodiment can be confirmed by powder X-ray diffraction measurements using CuKα rays, which show diffraction peaks at 2θ = 25.2 ± 0.5 deg and 29.7 ± 0.5 deg. The diffraction peaks at 2θ = 25.2 ± 0.5 degrees and 29.7 ± 0.5 degrees are peaks originating from the argyrodite crystal structure. Diffraction peaks of the argyrodite crystal structure may also appear at, for example, 2θ = 15.3±0.5deg, 17.7±0.5deg, 31.1±0.5deg, 44.9±0.5deg, and 47.7±0.5deg. Solid electrolytes may also have these peaks.

[0038] In this application, the position of the diffraction peak is determined as A±0.5deg or A±0.4deg, where A is the median value, but it is preferable that it be A±0.3deg. For example, in the case of the diffraction peak with 2θ = 25.2±0.5deg as described above, the median value A is 25.2deg, and it is preferable that it lies within the range of 2θ = 25.2±0.3deg. The same applies to the determination of the positions of all other diffraction peaks in this application.

[0039] The solid electrolyte may contain amorphous components as long as it has an X-ray diffraction pattern of the argyrodite-type crystal structure described above. The amorphous components exhibit a halo pattern in X-ray diffraction measurements, where the X-ray diffraction pattern shows virtually no peaks other than those originating from the raw materials. Furthermore, it may contain crystal structures other than the argyrodite-type crystal structure or raw materials.

[0040] [Second Embodiment] The solid electrolyte according to this embodiment has an argyrodite-type crystal structure containing lithium (Li), phosphorus (P), sulfur (S), oxygen (O), and halogen (X) as constituent elements, the proportion of the Li3PO4 crystal structure in the total crystals of the solid electrolyte is 0.1% by mass or more and 3.0% by mass or less, and satisfies the following formulas (21) to (23). 4.8 ≤ Li / P ≤ 5.3 ···(21) 3.8 ≤ S / P ≤ 4.4 ···(22) 1.0 <X / P≦2.0 ···(23) (Equation (21) is the molar ratio of Li to P, equation (22) is the molar ratio of S to P, and equation (23) is the molar ratio of halogen (X) to P.)

[0041] It is preferable that the above equations (21) to (23) satisfy the following equation. 4.85 ≤ Li / P ≤ 5.25 3.9 ≤ S / P ≤ 4.3 1.2 ≤ X / P ≤ 1.9 More preferably, the above equations (21) to (23) satisfy the following equation. 4.9 ≤ Li / P ≤ 5.2 4.0 ≤ S / P ≤ 4.2 1.4 ≤ X / P ≤ 1.8

[0042] The proportion of Li3PO4 crystal structures in the total crystals of the solid electrolyte is between 0.1% by mass and 3.0% by mass. Within this range, it is possible to suppress the generation of hydrogen sulfide while maintaining high ionic conductivity. The proportion of Li3PO4 crystal structure is preferably 0.3% by mass or more, and more preferably 0.5% by mass or more. Furthermore, the proportion of Li3PO4 crystal structure is preferably 2.0% by mass or less, more preferably 1.5% by mass or less, and more preferably 1.0% by mass or less.

[0043] In one embodiment, the proportion of argyrodite-type crystal structures in the total crystals of the solid electrolyte is 90% by mass or more. This makes it possible to achieve high ionic conductivity. The proportion of argyrodite-type crystal structures is preferably 93% by mass or more, more preferably 95% by mass or more, more preferably 96% by mass or more, and particularly preferably 97% by mass or more.

[0044] In one embodiment, the proportion of β-Li3PS4 crystal structures in the total crystals of the solid electrolyte is 5.0% by mass or less. Preferably, it is 4.0% by mass or less, and more preferably 3.0% by mass or less.

[0045] The proportions of argyrodite-type crystal structures, Li3PO4 crystal structures, and β-Li3PS4 crystal structures in the total crystals of the solid electrolyte were determined by synchrotron radiation analysis, as shown in the evaluation example.

[0046] The compositions of formulas (21) to (23) in this embodiment can be achieved by adjusting the blending of the raw materials. For example, the molar ratio of S can be lowered by reducing the amount of lithium sulfide (Li2S), and the molar ratio of Li and O can be adjusted by adding lithium oxide (Li2O). The solid electrolyte according to this embodiment can be obtained, for example, by the manufacturing method of the first embodiment described above.

[0047] In the solid electrolyte of this embodiment, examples of halogen (X) include F, Cl, Br, I, etc. The solid electrolyte may contain one type of halogen (X) or two or more types, but two types are more preferable. It is preferable that at least one of X is Cl or Br, and further, it is preferable that X contains Cl and Br.

[0048] In the solid electrolyte of one embodiment, in addition to the above Li, P, S, O and halogen (X), one or more elements selected from the group consisting of H, Si, Ge, Sn, Pb, B, Al, Ga, As, Sb and Bi can be contained to such an extent that the effects of the invention are not impaired.

[0049] In one embodiment, the solid electrolyte has a composition represented by the following formula (A). Li a P b S c O d X e ···(A) (In the formula, X is a halogen, a to e represent the composition ratios of the respective elements, and 4.8 ≦ a ≦ 5.3, b = 1, 3.8 ≦ c ≦ 4.4, 0 < d ≦ 0.8, 1 < e ≦ 2.0 are satisfied.)

[0050] X in the formula (A) may be one selected from the group consisting of F, Cl, Br and I, or may be two or more (x1, ···, x n :n is an integer of 2 or more and 4 or less). It is more preferable that X consists of two kinds (x1, x2). The molar ratio of each element is not particularly limited. X in the formula (A) is preferably Cl and Br. <00所作のコメントは、コメントの内容に基づいて翻訳されます。コメントの内容に基づいて翻訳されます。00298> In the present application, the molar ratio and composition of each element in the solid electrolyte can be measured by various methods known to those skilled in the art. However, except for special circumstances such as difficulty in analysis, it can be measured by ICP emission spectrometry. For example, in the case of the solid electrolyte described in the present application, the molar ratio and composition of elements other than oxygen can be measured by ICP emission spectrometry. The molar ratio of each element can be controlled by adjusting the content of each element in the raw material.

[0052] In one embodiment of the solid electrolyte, the lattice constant of the argyrodite crystal structure is preferably 9.820 Å or less, more preferably 9.815 Å or less, even more preferably 9.811 Å or less, and particularly preferably 9.810 Å or less, from the viewpoint of further suppressing hydrogen sulfide generation. If the lattice constant is within the above range, it is presumed that the sulfur elements in the 4a and 4d sites of the argyrodite crystal structure are sufficiently reduced and substituted with halogen elements with smaller ionic radii. The lattice constant can be measured by synchrotron radiation analysis as described in the examples.

[0053] In one embodiment of the solid electrolyte, from the viewpoint of further improving ionic conductivity, it is preferable that the ratio of the peak intensity of the diffraction peak originating from the Li3PS4 crystal structure to the diffraction peak at 2θ = 25.2 ± 0.5 deg originating from the argyrodite crystal structure is less than 0.04. This is because, compared to the argyrodite crystal structure, Li3PS4 has lower ionic conductivity, and therefore, the lower the content of the Li3PS4 crystal structure in the solid electrolyte, the more the decrease in ionic conductivity can be suppressed.

[0054] As previously mentioned, normally, reducing the amount of Li2S in the raw materials of a solid electrolyte to suppress hydrogen sulfide generation leads to a deficiency of the sulfur element necessary for forming an argyrodite-type crystal structure, making it easier for other crystalline phases such as Li3PS4 to form. However, the inventors have succeeded in reducing the amount of Li3PS4 produced and thus the sulfur element content of the argyrodite-type crystal structure itself by mixing the raw materials in a specific ratio, making it possible to achieve a higher level of both hydrogen sulfide generation suppression and ionic conductivity.

[0055] In this regard, in the invention described in Patent Document 1, the peak intensity ratio derived from Li3PS4 is increased by reducing Li2S, and it is considered that the sulfur element is not reduced from the argyrodite crystal structure itself as in one embodiment of the present invention, but rather the reduced element is converted into another crystal structure such as Li3PS4 instead of the argyrodite crystal structure.

[0056] Furthermore, by reducing the sulfur element content to reduce the amount of hydrogen sulfide generated, while maintaining the argyrodite crystal structure and exhibiting high ionic conductivity by ensuring the presence of oxygen during the heating process. In Patent Document 2, Li2O is added after the argyrodite crystal structure is formed by heating, and oxygen is not present during the heating process that forms the argyrodite crystal structure, as in the first embodiment. Therefore, it is difficult to achieve high ionic conductivity while reducing the amount of hydrogen sulfide generated, as in the first embodiment.

[0057] The solid electrolyte of the present invention can be used in lithium-ion batteries and the like. Specifically, it can be used in the solid electrolyte layer, positive electrode, negative electrode, etc., of a battery. In one embodiment, the electrode for the lithium-ion battery may contain known active materials, conductive additives, etc., in addition to the solid electrolyte. A binder may also be included. A lithium-ion battery according to one embodiment includes the solid electrolyte of the present invention. In one embodiment, the lithium-ion battery is an all-solid-state battery. In one embodiment, the all-solid-state battery includes a laminate comprising a positive electrode current collector, a positive electrode, an electrolyte layer, a negative electrode, and a negative electrode current collector in that order. In the lithium-ion battery, it is preferable that one or more components selected from the group consisting of a positive electrode, an electrolyte layer, and a negative electrode contain the solid electrolyte of the present invention. [Examples]

[0058] The present invention will be described in more detail below with reference to examples. The evaluation method is as follows:

[0059] (1) Amount of hydrogen sulfide (H2S) generated by solid electrolytes A schematic diagram of the test apparatus is shown in Figure 1. Test apparatus 1 mainly consists of a flask 10 for humidifying nitrogen, a static mixer 20 for mixing humidified nitrogen and unhumidified nitrogen, a dew point meter 30 (VAISALA M170 / DMT152) for measuring the moisture content of the mixed nitrogen, a double reaction tube 40 for placing the sample to be measured, a dew point meter 50 for measuring the moisture content of the nitrogen discharged from the double reaction tube 40, and a hydrogen sulfide meter 60 (AMI Model 3000RS) for measuring the hydrogen sulfide concentration contained in the discharged nitrogen. These components are connected by tubes (not shown). The temperature of the flask 10 is set to 10°C by a cooling tank 11. Furthermore, 6mm diameter Teflon® tubing was used to connect each component. In this diagram, the tubes are not shown, and instead, the flow of nitrogen is indicated by arrows.

[0060] The evaluation procedure was as follows: Approximately 1 g of powdered sample 41 was weighed into a nitrogen glow box with a dew point of -80°C, and placed inside the reaction tube 40, sandwiched between quartz wool 42, and then sealed. The inside of the reaction tube 40 was maintained at room temperature (approximately 25°C).

[0061] Nitrogen was supplied into apparatus 1 from a nitrogen source (not shown) at 0.02 MPa. The supplied nitrogen passed through a bifurcated pipe BP, and a portion was supplied to flask 10 for humidification. The remainder was supplied directly to the static mixer 20 as unhumidified nitrogen. The amount of nitrogen supplied to flask 10 was adjusted by a needle valve V.

[0062] The dew point is controlled by adjusting the flow rates of unhumidified nitrogen and humidified nitrogen using a flow meter FM with a needle valve. Specifically, the flow rate of unhumidified nitrogen was 800 mL / min and the flow rate of humidified nitrogen was 10-30 mL / min, both were supplied to a static mixer 20 for mixing, and the dew point of the mixed gas (a mixture of unhumidified nitrogen and humidified nitrogen) was confirmed using a dew point meter 30.

[0063] After adjusting the dew point to -30°C, the three-way stopcock 43 was rotated to allow the mixed gas to flow through the reaction tube 40 for 2 hours. The amount of hydrogen sulfide contained in the mixed gas that passed through sample 41 was measured with a hydrogen sulfide meter 60, and the amount of hydrogen sulfide generated per gram of solid electrolyte (cc / g) was calculated. The amount of hydrogen sulfide was recorded at 15-second intervals. For reference, the dew point of the mixed gas after exposure was also measured with a dew point meter 50. After measurement, the gas was passed through an alkali trap 70 to remove hydrogen sulfide from the nitrogen.

[0064] (2) Measurement of ionic conductivity of solid electrolytes The sample was filled into a tablet molding machine and molded under a pressure of 22 MPa. 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 thick). The ionic conductivity of this molded body was measured by AC impedance measurement. The conductivity values ​​used were those obtained at 25°C.

[0065] (3) X-ray diffraction (XRD) measurement The powder of the argyrodite-type solid electrolyte prepared in each example was uniformly packed into a 20 mm diameter, 0.2 mm deep groove using glass to create a sample. This sample was measured using an XRD Kapton film to prevent exposure to air. The 2θ position of the diffraction peak was determined by Le Bail analysis using the XRD analysis program RIETAN-FP. The following measurements were performed using the D2 PHASER powder X-ray diffraction analyzer from BRUKER Corporation. The powder X-ray diffraction analyzer was installed in a room where the temperature was controlled to 25°C. Tube voltage: 30kV Tube current: 10mA X-ray wavelength: Cu-Kα ray (1.5418Å) Optical system: Concentration method Slit configuration: Solar slit 4°, divergence slit 1mm, Kβ filter (Ni plate) used Detector: Semiconductor detector Measurement range: 2θ = 10 - 60 degrees Step size, scan speed: 0.05deg, 0.05deg / sec To confirm the existence of a crystal structure based on the measurement results, the peak positions were analyzed using the XRD analysis program RIETAN-FP. The baseline was corrected using an 11th-order orthogonal polynomial, and the peak positions were determined.

[0066] (4)ICP measurement The powder of the solid electrolyte 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, and then diluted as appropriate to prepare the measurement solution. This 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.

[0067] Manufacturing Example 1 [Production of lithium sulfide (Li2S)] The production and purification of Li2S was carried out as follows. Toluene (manufactured by Sumitomo Corporation) was dehydrated as a non-water-soluble medium, and 303.8 kg of the dehydrated toluene, with a moisture content of 100 ppm measured using a Karl Fischer moisture meter, was added to a 500 L stainless steel reaction vessel under a nitrogen atmosphere. Subsequently, 33.8 kg of anhydrous lithium aqueous oxide (manufactured by Honjo Chemical Co., Ltd.) was added, and the mixture was stirred at 131 rpm with a twin-star stirring blade while maintaining a temperature of 95°C. The slurry was heated to 104°C while hydrogen sulfide (manufactured by Sumitomo Seika Co., Ltd.) was injected at a supply rate of 100 L / min. Azeotropic gas of water and toluene was continuously discharged from the reaction vessel. This azeotropic gas was dehydrated by condensation in an external condenser. During this process, the same amount of toluene as was distilled out was continuously supplied to maintain a constant reaction solution level. The water content in the condensate gradually decreased, and no water distillation was observed 24 hours after the introduction of hydrogen sulfide. During the reaction, the solid was dispersed and stirred in toluene, and no water separated from the toluene. After this, the hydrogen sulfide was replaced with nitrogen and the mixture was circulated at 100 L / min for 1 hour. The obtained solids were filtered and dried to obtain Li2S, a white powder.

[0068] Example 1 As starting materials, Li2S, P2S5, LiBr (manufactured by Honjo Chemical Co., Ltd.), LiCl (manufactured by Honjo Chemical Co., Ltd.), and Li2O (manufactured by Fujifilm Wako Pure Chemical Corporation) from Production Example 1 were used. The starting materials were roughly ground using a pin mill and mixed so that the molar ratio (Li2S:P2S5:LiCl:LiBr:Li2O) was 1.65:0.5:1.0:0.6:0.05. Specifically, 0.402g of Li2S, 0.589g of P2S5, 0.225g of LiCl, 0.276g of LiBr, and 0.008g of Li2O were mixed. The mixture and 30g of 10mm diameter zirconia balls were placed in a 45mL zirconia pot of a planetary ball mill (Fritsch, model P-7) and completely sealed. The pot was kept under a nitrogen atmosphere. The mixture was processed in the planetary ball mill at 150rpm for 10 minutes (premixing). Subsequently, it was processed at 370rpm for 15 hours (mechanical milling) to obtain a powder of the raw material mixture. Approximately 1.5 g of the raw material mixture was packed into a Tammann tube (PT2, manufactured by Tokyo Glass Equipment Co., Ltd.) in a glove box under an Ar atmosphere, and then placed in an electric furnace and heated. Specifically, the temperature was raised from room temperature to 380°C in 1 hour, then raised to 430°C in 30 minutes, and held at 430°C for 2 hours. After that, it was removed from the electric furnace and allowed to cool to obtain a solid electrolyte.

[0069] Table 1 shows the molar ratio of the raw materials, the molar ratio of each element, the amount of hydrogen sulfide generated by the obtained solid electrolyte, and the ionic conductivity. The XRD pattern of the solid electrolyte is shown in Figure 2. Diffraction peaks of the argyrodite crystal structure were observed at 2θ = 15.6deg, 18.1deg, 25.6deg, 30.1deg, 31.5deg, and 45.1deg.

[0070] Examples 2-4, Comparative Examples 1-5 Solid electrolytes were prepared and evaluated in the same manner as in Example 1, except that the molar ratio of the starting materials was changed as shown in Table 1. The results are shown in Table 1. The XRD patterns of the solid electrolytes obtained in Examples 2-4 and Comparative Examples 1-5 are shown in Figures 3-10, respectively. In Example 2, diffraction peaks of the argyrodite crystal structure were observed at 2θ = 15.6deg, 18.1deg, 25.6deg, 30.1deg, 31.5deg, and 45.1deg. Diffraction peaks originating from Li3PO4 were also observed in the solid electrolyte of Example 2. In Example 3, diffraction peaks of the argyrodite crystal structure were observed at 2θ = 15.7deg, 18.1deg, 25.6deg, 30.1deg, 31.5deg, and 45.1deg. In Example 4, diffraction peaks of the argyrodite crystal structure were observed at 2θ = 15.7deg, 18.1deg, 25.7deg, 30.2deg, 31.6deg, and 45.1deg. Table 2 shows the results of determining the composition of the solid electrolyte by ICP measurement for Examples 2 and 4 and Comparative Examples 1, 2, and 5.

[0071] [Table 1]

[0072] [Table 2]

[0073] Example 5 The same Li2S, P2S5, LiCl, and LiBr as in Example 1, along with LiOH (liquid hydroxide monohydrate manufactured by Honjo Chemical Co., Ltd., dried to obtain lithium hydroxide), were used as starting materials. The starting materials were roughly ground using a pin mill and mixed so that the molar ratio (Li2S:P2S5:LiCl:LiBr:LiOH) was 1.6:0.5:1.0:0.6:0.2. Specifically, 0.3884g of Li2S, 0.5871g of P2S5, 0.224g of LiCl, 0.2753g of LiBr, and 0.0253g of LiOH were mixed. In the following steps, similar to Example 1, the raw material mixture was processed using a planetary ball mill, and the mixture was heat-treated to obtain a solid electrolyte. The evaluation results are shown in Table 3. The XRD pattern of the solid electrolyte is shown in Figure 11. Diffraction peaks of the argyrodite crystal structure were observed at 2θ = 15.6deg, 18.0deg, 25.6deg, 30.1deg, 31.5deg, and 45.0deg.

[0074] [Table 3]

[0075] In Table 1, Comparative Examples 1-3 show that the molar ratio of sulfur in the solid electrolyte was changed by varying the amount of Li2S added. Comparative Example 1 belongs to the category of solid electrolytes with high ionic conductivity among those having an argyrodite crystal structure. Although it exhibits excellent ionic conductivity, it is evident that it generates a large amount of hydrogen sulfide. In Examples 1-4 and Comparative Examples 4 and 5, the amount of Li2S added was reduced while Li2O was added. As a result, even though the amount of sulfur in the solid electrolyte (molar ratio of 4.1) was the same as in Comparative Example 2, Example 2 showed sufficiently high ionic conductivity and significantly reduced hydrogen sulfide generation. A similar trend can be observed in Example 4 and Comparative Example 3. On the other hand, in Comparative Examples 4 and 5, where Li2O was further added, the amount of hydrogen sulfide generated increased. Therefore, it was confirmed that adding a predetermined amount of Li2O is effective when reducing the sulfur content in the solid electrolyte by reducing the amount of Li2S used. Furthermore, in Example 5, where LiOH was added instead of Li2O, the same effect as in Example 2 was obtained, confirming that either raw material can be used.

[0076] Evaluation example Synchrotron radiation analysis was performed on Examples 2 and 4 and Comparative Examples 1, 4, and 5 to analyze the lattice constant of the argyrodite crystal structure and the proportion of argyrodite crystal structures, Li3PO4 crystal structures, and β-Li3PS4 crystal structures in the total crystals of the solid electrolyte. Specifically, measurements were performed under the following conditions. The solid electrolyte powders prepared in Examples 2 and 4, and Comparative Examples 1, 4, and 5 were loaded into 0.3 mmΦ capillaries in a glove box, and the capillary tips were sealed with a curable resin to prepare samples for synchrotron radiation analysis.

[0077] Measurements were performed using the powder diffraction beamline "BL19B2" at SPring-8 under the following conditions. During the measurement, nitrogen gas at 100K was blown onto the sample for 1 minute using a nitrogen gas blowing type sample cooling device manufactured by Rigaku Corporation, and the measurement was performed while maintaining this condition. X-ray energy: 25 keV Optical system: transmission method Detector: 1D solid-state Si detector MYTHEN (12-unit) Detector threshold: 19 keV Measurement range: 2θ = 4 - 60 degrees Step size: 0.005deg Exposure time: 30 seconds x 2 times

[0078] The measurement data was corrected to 0.005° intervals using a script specifically for BL19B2, and then analyzed using that corrected data. For the analysis of peak positions to confirm the crystal structure, the Rigaku XRD analysis program PDXL2 (Version 2.7.3.0) was used, and the peaks were obtained by PDXL automatic profiling. For the analysis to determine the lattice constants and abundances of the crystal structure, the Rigaku XRD analysis program PDXL2 (Version 2.7.3.0) was used, and the lattice constants and abundances of the crystal structure were determined using Rietveld analysis with the following function. Peak shape: Split-type pseudo-Voigt function Background: β-spline function Peak shift: Device function (Δ2θ = Z + Dcosθ + Tsin2θ)

[0079] In the analysis of the lattice constant, the X-ray energy value was corrected before the analysis. Specifically, CeO2 was measured under the above measurement conditions, but with the temperature changed to 300K and the exposure time to 20 seconds. The measurement results were then subjected to Rietveld analysis under the above analysis conditions, and the X-ray energy value was corrected so that the lattice constant was 5.41165 Å. Furthermore, in the analysis of peak shapes, the same profile function used for the argyrodite crystal structure was applied to crystals other than the argyrodite crystal structure for analysis. Furthermore, in the Rietveld analysis, a Rwp value of 10% or less was used as an indicator of the validity of the results. The results are shown in Table 4.

[0080] [Table 4]

[0081] Table 4 shows that the lattice constants of Examples 2 and 4 are smaller than those of the comparative example. This is because, within the argyrodite crystal structure of the examples, sulfur ions (S) with large ionic radii are present. 2- It can be inferred that the lattice constant became smaller because the ) was missing, and instead, a halogen ion with a small ionic radius occupied one or more of the 4a or 4d sites.

[0082] 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. All references made in this specification and to the application on which the priority claim of this application under the Paris Convention rest with respect to this specification.

Claims

1. A solid electrolyte having a composition represented by the following formula (A) and having an argyrodite-type crystal structure, The lattice constant of the argyrodite-type crystal structure is 9.820 Å or less. In powder X-ray diffraction measurements using CuKα rays, diffraction peaks were observed at 2θ = 25.2 ± 0.5 deg and 29.7 ± 0.5 deg. Li ３ PO ４ A solid electrolyte containing a crystalline structure. Li ａ P ｂ S ｃ O ｄ X ｅ ・・・(A) (In the formula, X is a halogen containing Cl and Br, a to e represent the composition ratio of each element, satisfying 4.8 ≤ a ≤ 5.3, b = 1, 3.8 ≤ c ≤ 4.4, 0 < d ≤ 0.8, and 1 < e ≤ 2.0.)

2. The proportion of β-Li ３ PS ４ in all crystals in the solid electrolyte is 5.0% by mass or less, and the solid electrolyte according to claim 1.

3. The solid electrolyte according to claim 1 or 2, wherein the lattice constant of the argyrodite-type crystal structure is 9.811 Å or less.

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