Sulfide solid electrolyte, electrode binder using the same, solid electrolyte layer, and solid-state battery

Abstract

The sulfide solid electrolyte of the present invention contains the following compound: the compound contains a crystalline phase having a thiogermanate-type crystal structure and is represented by Li a PS b X c (X is at least one halogen element. a represents a number of 3.0 or more and 6.0 or less. b represents a number of 3.5 or more and 4.8 or less. c represents a number of 0.1 or more and 3.0 or less). When the amount of lithium quantified by the peak of 1s of Li measured by X-ray photoelectron spectroscopy is denoted as A Li , the amount of phosphorus quantified by the peak of 2p of P is denoted as A P , the amount of sulfur quantified by the peak of 2p of S is denoted as A S , the amount of halogen quantified by the peak of the halogen is denoted as A X , the value of A Li / (A Li +A P +A S +A X ) with respect to the specific surface area (m 2 g ‑1 ) is 3.40 (m ‑2 g) or more.

Description

Technical Field

[0001] The present invention relates to a sulfide solid electrolyte, an electrode mixture using the same, a solid electrolyte layer, and a solid-state battery. Background Art

[0002] In recent years, solid electrolytes have attracted much attention as alternatives to electrolytes used in various liquid-based batteries. A solid-state battery using such a solid electrolyte is expected to be put into practical use as a battery having higher safety and higher energy density than a liquid-based battery using a flammable organic solvent.

[0003] As prior art related to solid electrolytes, for example, the technique described in Patent Document 1 is known. This document describes a sulfide solid electrolyte in which the surface of a compound containing lithium, phosphorus, sulfur, and a halogen and having a thiogermanate crystal structure is covered with a compound containing lithium, phosphorus, and sulfur and having a non-thiogermanate crystal structure. In this document, by controlling the surface of the sulfide solid electrolyte, generation of hydrogen sulfide from the solid electrolyte is suppressed, or the lithium ion conductivity of the solid electrolyte is ensured.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: US2019 / 312304A1 Summary of the Invention

[0007] However, the technique described in Patent Document 1 mainly aims to solve the problem of suppressing the generation of hydrogen sulfide, and further improvement in lithium ion conductivity is required. Therefore, an object of the present invention is to provide a solid electrolyte having high lithium ion conductivity.

[0008] The present invention provides a sulfide solid electrolyte containing the following compound: the compound contains a crystalline phase having a thiogermanate crystal structure and is represented by Li a PS b X c (X is at least one halogen element. a represents a number of 3.0 or more and 6.0 or less. b represents a number of 3.5 or more and 4.8 or less. c represents a number of 0.1 or more and 3.0 or less),

[0009] When the amount of lithium (atomic %) quantified by the peak of 1s of Li measured by X-ray photoelectron spectroscopy (XPS) is denoted as A Li 、the amount of phosphorus (atomic %) quantified by the peak of 2p of P is denoted as A P 、the amount of sulfur (atomic %) quantified by the peak of 2p of S is denoted as A S 、the amount of halogen (atomic %) quantified by the peak of the halogen is denoted as A X 、ALi / (A Li +A P +A S +A X ) with respect to the specific surface area (m 2 g -1 ) is 3.40 (m -2 g) or more. Detailed implementation manners

[0010] Hereinafter, the present invention will be described according to its preferred implementation manners. The sulfide solid electrolyte (hereinafter also simply referred to as "solid electrolyte") of the present invention contains Li a PS b X c (X is at least one halogen element. a represents a number of 3.0 or more and 6.0 or less. b represents a number of 3.5 or more and 4.8 or less. c represents a number of 0.1 or more and 3.0 or less.) The compound shown. This compound is solid at room temperature (25 °C) and has lithium ion conductivity. In the following description, for convenience, this compound will also be referred to as "Compound A".

[0011] Compound A in the present invention is a crystalline material containing a crystalline phase having a thiogermanate crystal structure. In particular, Compound A may contain a glass component, that is, an amorphous component. That Compound A "contains a crystalline phase having a thiogermanate crystal structure" means that as long as Compound A contains at least a crystalline phase having a thiogermanate crystal structure, it may also contain a crystalline phase different from the crystalline phase having a thiogermanate crystal structure (also referred to as "heterophase"). Of course, the heterophase may not be contained. As the compound constituting the heterophase, for example, Li3PS4 can be cited.

[0012] In Compound A, the proportion of the crystalline phase having a thiogermanate crystal structure with respect to all the crystalline phases constituting Compound A can be, for example, 10% by mass or more, 20% by mass or more, or 50% by mass or more. Among them, Compound A preferably contains a crystalline phase having a thiogermanate crystal structure as the main phase.

[0013] Here, the "main phase" means: the phase with the largest proportion with respect to the total amount of all the crystalline phases constituting the solid electrolyte of the present invention. Therefore, the content ratio of Compound A with respect to all the crystalline phases constituting the solid electrolyte of the present invention is, for example, preferably 60% by mass or more, and among them, more preferably 70% by mass or more, 80% by mass or more, 90% by mass or more.

[0014] On the other hand, the "heterophase" means: the phase with a proportion smaller than the above-mentioned main phase with respect to the total amount of all the crystalline phases constituting the solid electrolyte of the present invention.

[0015] It should be noted that the proportion of the crystalline phase can be determined, for example, by calculating the content measured using X-ray diffraction.

[0016] The crystalline phase having a argyrodite-type crystal structure means: a crystalline phase possessed by a compound group derived from the mineral represented by the chemical formula Ag8GeS6. From the viewpoint of improving lithium ion conductivity, the aforementioned compound having a argyrodite-type crystal structure preferably has a crystal structure belonging to the cubic crystal system.

[0017] Whether the solid electrolyte of the present invention contains a compound having a argyrodite-type crystal structure can be confirmed, for example, by XRD measurement. That is, in the X-ray diffraction pattern measured by an X-ray diffractometer using CuKα1 radiation, the crystalline phase of the argyrodite-type crystal structure has characteristic peaks at 2θ = 15.34° ± 1.00°, 17.74° ± 1.00°, 25.19° ± 1.00°, 29.62° ± 1.00°, 30.97° ± 1.00°, 44.37° ± 1.00°, 47.22° ± 1.00°, 51.70° ± 1.00°. Further, for example, it also has characteristic peaks at 2θ = 54.26° ± 1.00°, 58.35° ± 1.00°, 60.72° ± 1.00°, 61.50° ± 1.00°, 70.46° ± 1.00°, 72.61° ± 1.00°. It should be noted that the "peak" in this specification refers to the apex of the peak. In addition, the aforementioned peaks preferably exist independently of each other without overlapping with other peaks.

[0018] In the solid electrolyte of the present invention, the crystalline phase of the argyrodite-type crystal structure constituting compound A preferably becomes the main phase with respect to all the crystalline phases. The solid electrolyte of the present invention may be composed only of compound A, or may further contain a substance having a phase different from the crystalline phase of the argyrodite-type crystal structure within the range not impairing the effects of the present invention. Examples of such a heterogeneous substance include lithium halide.

[0019] The solid electrolyte of the present invention contains compound A as described above. And, the solid electrolyte of the present invention preferably controls the surface state of the particles of the solid electrolyte. Specifically, the particles of the solid electrolyte of the present invention preferably control the proportion of lithium element present on the particle surface to a high value, whereby the lithium ion conductivity of the solid electrolyte of the present invention is improved. The reason for this is considered by the present inventors as follows.

[0020] The solid electrolyte of the present invention conducts lithium ions in a state where the particles of the solid electrolyte are in contact with each other. Regarding one of the resistance factors during lithium ion conduction, the contact resistance between particles, i.e., the grain boundary resistance, is known. The inventors of the present invention conducted in-depth research on means for reducing the grain boundary resistance, and as a result, it was found that by having a large amount of lithium element present on the surface of the particles of the solid electrolyte, the lithium ion conduction between particles proceeds smoothly. As a result, in the solid electrolyte according to the present invention, the grain boundary resistance at the contact interface between the particles is reduced, and the lithium ion conductivity is improved.

[0021] From the viewpoint of making the above advantageous effects more remarkable, in the solid electrolyte of the present invention, A Li / (A Li +A P +A S +A X ) evaluates the amount of lithium element on the surface of the particles of the solid electrolyte with respect to the specific surface area A (m 2 g -1 ) value. The definitions of A Li , A P , A S and A X are as described below.

[0022] A Li is the amount of lithium (atomic %) quantified by the peak of 1s of Li (lithium atom) measured by X-ray photoelectron spectroscopy (hereinafter also referred to as "XPS").

[0023] A P is the amount of phosphorus (atomic %) quantified by the peak of 2p of P (phosphorus atom) measured by XPS.

[0024] A S is the amount of sulfur (atomic %) quantified by the peak of 2p of S (sulfur atom) measured by XPS.

[0025] A X is the amount of halogen (atomic %) quantified by the peak of the halogen. The electron orbit of the halogen is determined according to the specific type of the halogen. For example, when the halogen is fluorine, the 1s electron orbit is used. When the halogen is chlorine, the 2p electron orbit is used. When the halogen is bromine, the 3p electron orbit is used. When the halogen is iodine, the 3d electron orbit is used.

[0026] In the present invention, the value of A Li / (A Li +A P +A S +A X ) with respect to the specific surface area A (m 2 g -1 ), that is, {A Li / (A Li +AP +A S +A X ) / A is preferably 3.40 (m -2 g) or more, more preferably 3.43 (m -2 g) or more, and still more preferably 3.45 (m -2 g) or more. In the following description, {A Li / (A Li +A P +A S +A X )} / A is also referred to as the "lithium occupancy rate". If the lithium occupancy rate on the surface of the solid electrolyte particles is above this value, the grain boundary resistance at the contact interface between the particles decreases, and the lithium ion conductivity increases. The higher the value of the lithium occupancy rate, the more preferable it is. The lithium occupancy rate achievable with the current state of the art is about 3.63 (m -2 g). Since the lithium occupancy rate is high, the lithium ion conductivity of the solid electrolyte becomes sufficiently high.

[0027] The lithium occupancy rate on the surface of the solid electrolyte of the present invention can be determined by XPS as described above. The specific method will be described in detail in the following examples.

[0028] Regarding the value of the specific surface area A used for calculating the lithium occupancy rate, it is preferably 5.0 m 2 g -1 or more, more preferably 8.0 m 2 g -1 or more, and still more preferably 10.0 m 2 g -1 or more. In addition, the value of the specific surface area A is preferably 13.1 m 2 g -1 or less, more preferably 13.0 m 2 g -1 or less, and still more preferably 12.9 m 2 g -1 or less. The specific method for the specific surface area A will be described in detail in the following examples.

[0029] The solid electrolyte of the present invention shows a high value of preferably 4.8 mS / cm or more, more preferably 4.9 mS / cm or more, and still more preferably 5.0 mS / cm or more for the lithium ion conductivity at room temperature (25°C) by controlling the lithium occupancy rate on its surface. The lithium ion conductivity of the solid electrolyte can be measured by the method described in the following examples.

[0030] The compound A contained in the solid electrolyte of the present invention is represented by Li a PS b X c as described above. Here, "the compound A is represented by Lia PS b X c means: including a substance fed in such a way that compound A becomes Li a PS b X c In this compositional formula, a representing the molar ratio of lithium (Li) element is preferably a number of 3.0 or more and 6.0 or less, more preferably a number of 3.2 or more and 5.8 or less, and further preferably a number of 3.4 or more and 5.4 or less. It should be noted that a can be less than 5.4.

[0031] In addition, in the above compositional formula, b representing the molar ratio of sulfur (S) element is preferably a number of 3.5 or more and 4.8 or less, more preferably a number of 3.8 or more and 4.6 or less, and further preferably a number of 4.0 or more and 4.4 or less. It should be noted that b can be less than 4.4.

[0032] Furthermore, in the above compositional formula, c is preferably a number of 0.1 or more and 3.0 or less, more preferably a number of 0.2 or more and 2.5 or less, and further preferably a number of 0.4 or more and 2.0 or less. The lithium ion conductivity of compound A within this range is sufficiently increased. In the above compositional formula, X represents at least one halogen element. When X is one kind, examples of compound A include Li a PS b F c 、Li a PS b Cl c 、Li a PS b Br c and Li a PS b I c etc. When X is two kinds, compound A is represented by Li a PS b X 1 y X 2 z X and X 1 and X 2 represent different halogen elements. In addition, y and z represent numbers that satisfy c = y + z and are greater than 0. As a combination of X 1 and X 2 for example, combinations such as Cl and Br, Cl and I, and Br and I can be cited. When X is three kinds, compound A is represented by Li a PS b X 1 y X 2 z X3 v is represented by X 1 , X 2 and X 3 represent different halogen elements. In addition, y, z, and v represent numbers that satisfy c = y + z + v and are greater than 0. As X 1 and X 2 and X 3 combinations, for example, a combination of Cl, Br, and I can be cited. In the solid electrolyte of the present invention, sometimes only one of the above-mentioned compound A is included, or sometimes two or more of the compound A are included.

[0033] In the present invention, the compound A obtained in such a way that the feed amount becomes Li a PS b X c may contain elements other than lithium (Li) element, phosphorus (P) element, sulfur (S) element, and halogen (X) element. For example, there is a possibility that a part of the lithium (Li) element is replaced with other alkali metal elements, or a part of the phosphorus (P) element is replaced with other nitrogen group elements, or a part of the sulfur (S) element is replaced with other chalcogen elements.

[0034] In the solid electrolyte of the present invention, in addition to containing the compound A, impurities may be contained, for example. From the viewpoint of having a low impact on performance, for example, the content of impurities can be made less than 5 mol%, preferably less than 3 mol%, and particularly preferably less than 1 mol%.

[0035] The solid electrolyte of the present invention contains powder in the form of an aggregate of particles. The particle size of the solid electrolyte of the present invention is represented by the volume-based cumulative particle size D when the cumulative volume based on the laser diffraction scattering particle size distribution measurement method is 50% by volume. For example, it is preferably 1.0 μm or less, more preferably 0.95 μm or less, and particularly preferably 0.90 μm or less. On the other hand, the aforementioned volume-based cumulative particle size D 50 is preferably 0.40 μm or more, more preferably 0.45 μm or more, and particularly preferably 0.50 μm or more, for example. By making the volume-based cumulative particle size D 50 of the solid electrolyte of the present invention have the aforementioned upper limit, the specific surface area of the solid electrolyte becomes larger, and the amount of lithium element present on the particle surface increases. Thus, the lithium ion conductivity of the solid electrolyte can be sufficiently improved. On this basis, when the solid electrolyte of the present invention is used in combination with other solid electrolytes, there is also an advantage that the solid electrolyte of the present invention easily enters the gaps of the other solid electrolytes. Due to this, the contact points and contact area between the solid electrolytes become larger, and an improvement in lithium ion conductivity can be achieved efficiently. On the other hand, by making the volume-based cumulative particle size D 50 of the solid electrolyte of the present invention have the aforementioned lower limit, the following advantages can be obtained: 50Having the aforementioned lower limit, it is possible to suppress an increase in the total surface area of the powder of the solid electrolyte, and it is possible to suppress the occurrence of adverse conditions such as an increase in resistance and difficulty in mixing with the active material.

[0036] The solid electrolyte of the present invention is preferably manufactured by the following method. As raw materials, a lithium source compound, a phosphorus source compound, a sulfur source compound, and a halogen source compound are used. As the lithium source compound, for example, lithium sulfide (Li2S) can be used. As the phosphorus source compound, for example, diphosphorus pentasulfide (P2S5) can be used. As the sulfur source compound, when the lithium source compound and / or the phosphorus source compound is a sulfide, the sulfide can be used as the sulfur source compound. As the halogen source compound, lithium halide (LiX) can be used. These raw materials are mixed so that the molar ratios of lithium element, phosphorus element, sulfur element, and halogen group element reach a specified molar ratio. And, by calcining the mixed raw materials in an inert atmosphere or in an atmosphere containing hydrogen sulfide gas, it is possible to obtain a compound A having a thioargentite-type crystal structure and represented by Li a PS b X c The atmosphere containing hydrogen sulfide gas can be 100% hydrogen sulfide gas, or it can also be a mixed gas of hydrogen sulfide gas and an inert gas such as argon. The calcination temperature is preferably, for example, 350°C or higher and 550°C or lower. The holding time at this temperature is preferably, for example, 0.5 hours or longer and 20 hours or shorter.

[0037] A solid electrolyte containing compound A is obtained by the above method. By controlling the particle size of the solid electrolyte, the lithium presence rate on the surface of the particles can be increased. As a result of the research by the present inventors, it has been clarified that in order to control the lithium presence rate on the surface of the particles of the solid electrolyte, it is advantageous to perform a specified pulverization treatment on the solid electrolyte.

[0038] The pulverization treatment can be carried out wet or dry. In the pulverization treatment, various media mills can be used. As the media mill, a ball mill, a bead mill, a paint stirrer, a homogenizer, etc. can be used. As the dispersion medium used in the media mill, various ceramic balls and beads such as alumina and zirconia can be used. The diameter of the dispersion medium can be set, for example, to 0.1 mm or more and 50 mm or less.

[0039] When the pulverization treatment is carried out wet, from the viewpoint of being able to suppress the generation of hydrogen sulfide caused by the reaction of the solid electrolyte with water, it is preferable to use an organic solvent as the dispersion medium. As the organic solvent, for example, aromatic organic solvents such as toluene, xylene, benzene, and solvent naphtha can be cited; aliphatic organic solvents such as heptane, decane, n-hexane, cyclohexane, and mineral spirits can be cited. These organic solvents can be used alone or in combination of two or more.

[0040] Mix the aforementioned organic solvent with the solid electrolyte to form a slurry, and subject the slurry to wet grinding. From the perspective of smoothly obtaining a solid electrolyte with high lithium ion conductivity, it is preferable to set the concentration of the solid electrolyte contained in the slurry, for example, to be 5% by mass or more and 50% by mass or less. In wet grinding using a media mill, regarding the ratio of the dispersion medium to the slurry, from the perspective of easily obtaining a solid electrolyte with high lithium ion conductivity, it is preferable to use a dispersion medium that is 5 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of the slurry. From the perspective of easily obtaining a solid electrolyte with high lithium ion conductivity, it is preferable that the dispersion time based on the media mill is generally set to be 0.5 hours or more and 60 hours or less.

[0041] When performing wet grinding, from the perspective of increasing the ratio of lithium element on the particle surface of the solid electrolyte and enhancing the lithium ion conductivity of the solid electrolyte, it is preferable that the volume-based particle size D of the solid electrolyte after wet grinding 50 is adjusted to be preferably 1.5 μm or less, more preferably 1.0 μm or less, and further preferably 0.8 μm or less.

[0042] The solid electrolyte of the present invention obtained by such operations can be used, for example, as a material for constituting a solid electrolyte layer, a material contained in an electrode mixture containing an active material. Specifically, it can be used as a positive electrode mixture for constituting a positive electrode layer containing a positive electrode active material or a negative electrode mixture for constituting a negative electrode layer containing a negative electrode active material. Therefore, the solid electrolyte of the present invention can be used in a battery having a solid electrolyte layer, a so-called solid-state battery. More specifically, it can be used in a lithium solid-state battery. The lithium solid-state battery can be a primary battery or a secondary battery, and preferably, it is used in a lithium secondary battery. A "solid-state battery" means that in addition to including a solid-state battery that completely does not contain a liquid substance or a gel-like substance as an electrolyte, it also includes, for example, a mode in which 50% by mass or less, 30% by mass or less, or 10% by mass or less of a liquid substance or a gel-like substance is contained as an electrolyte.

[0043] The solid electrolyte layer in the solid-state battery can be manufactured by the following methods, etc.: for example, a method of dropping a slurry containing the solid electrolyte, a binder, and a solvent of the present invention onto a substrate and scraping it with a squeegee, etc.; a method of cutting with a doctor blade after bringing the substrate into contact with the slurry; a method of forming a coating film by screen printing, etc., and then removing the solvent through heating and drying. Alternatively, it can also be manufactured by pressing and molding the powder of the solid electrolyte of the present invention and then appropriately processing it. In the solid electrolyte layer, in addition to containing the solid electrolyte of the present invention, other solid electrolytes can also be contained. The thickness of the solid electrolyte layer in the present invention is typically preferably 5 μm or more and 300 μm or less, more preferably 10 μm or more and 100 μm or less.

[0044] The solid-state battery preferably has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer, and the solid electrolyte layer contains the solid electrolyte of the present invention. As the shape of the solid-state battery, for example, a laminated type, a cylindrical type, a square type, etc. can be cited.

[0045] The positive electrode mixture in the solid-state battery containing the solid electrolyte of the present invention contains a positive electrode active material. As the positive electrode active material, for example, a material used as the positive electrode active material of a lithium secondary battery can be appropriately used. As the positive electrode active material, for example, spinel-type lithium transition metal compounds, lithium metal oxides having a layered structure, etc. can be cited. In addition to the positive electrode active material, the positive electrode mixture may also contain other materials such as a conductive assistant.

[0046] The negative electrode mixture in the solid-state battery containing the solid electrolyte of the present invention contains a negative electrode active material. As the negative electrode active material, for example, a negative electrode mixture used as the negative electrode active material of a lithium secondary battery can be appropriately used. As the negative electrode active material, for example, carbon materials such as lithium metal, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon), lithium titanate, titanium niobium composite oxides, silicon, silicon compounds, tin, and tin compounds can be cited. In addition to the negative electrode active material, the negative electrode mixture may also contain other materials such as a conductive assistant.

[0047] Examples

[0048] Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the present invention is not limited to these examples.

[0049] 〔Example 1〕

[0050] Weigh Li2S powder, P2S5 powder, LiCl powder, and LiBr powder in such a composition that it becomes Li 5.4 PS 4.4 Cl 0.8 Br 0.8 Use a ball mill to crush and mix these powders to obtain a mixed powder. Roast the mixed powder to obtain a roasted product containing a lithium-ion conductive sulfide. The roasting is carried out using a tubular electric furnace. During the roasting, hydrogen sulfide gas with a purity of 100% is circulated into the electric furnace at 1.0 L / min. The roasting temperature is set to 450 °C, and roasting is carried out for 4 hours. As a result of XRD measurement, it can be confirmed that the roasted product has a crystalline phase of a thiogermanate-type crystal structure and a crystalline phase of LiCl 0.5 Br 0.5 .

[0051] After roughly crushing the calcined product with a mortar and pestle, it was further crushed using a hammer crusher. The crushed product was mixed with a solvent to form a slurry with a concentration of 12% by mass. This slurry was fed into a bead mill device (zirconia beads with a diameter of 0.3 mm) for wet grinding. Toluene was used as the solvent for the slurry. With respect to 100 parts by mass of the slurry, 15 parts by mass of beads were used, and wet grinding was carried out for 3 hours. After wet grinding, the slurry was subjected to solid-liquid separation, and the solid component was dried. The dried calcined product was screened through a sieve with a mesh size of 53 μm to obtain the target solid electrolyte.

[0052] [Examples 2 and 3, and Comparative Example 1]

[0053] The calcination temperature and slurry concentration in Example 1 were changed to the values shown in Table 1 below. Otherwise, the same operations as in Example 1 were carried out to obtain a solid electrolyte.

[0054] [Comparative Example 2]

[0055] In Example 1, the calcined product was manufactured in such a composition as Li 5.4 PS 4.4 Cl 1.6 Br 0.0 In addition, the calcination temperature and slurry concentration in Example 1 were changed to the values shown in Table 1 below. Otherwise, the same operations as in Example 1 were carried out to obtain a solid electrolyte.

[0056] [Comparative Example 3]

[0057] In Example 1, the calcined product was manufactured in such a composition as Li 5.8 PS 4.8 Cl 1.2 Br 0.0 In addition, the calcination temperature and slurry concentration in Example 1 were changed to the values shown in Table 1 below. Otherwise, the same operations as in Example 1 were carried out to obtain a solid electrolyte.

[0058] [Evaluation 1]

[0059] For the solid electrolytes obtained in the examples and comparative examples, the volume-based particle size D 50 was measured using the following method. Their results are shown in Table 1 below.

[0060] [Measurement of D 50

[0061] Using an automatic sample feeder for a laser diffraction particle size distribution measuring device (“Microtrac SDC” manufactured by Microtrac-Bell Corporation), a sample (powder) was put into an organic solvent. After irradiating with ultrasonic waves of 30 W for 60 seconds multiple times at a flow rate of 50%, the particle size distribution was measured using a laser diffraction particle size distribution measuring machine “MT3000II” manufactured by Microtrac-Bell Corporation. D was measured from the obtained volume-based particle size distribution spectrum. 50 It should be noted that toluene was used as the organic water-soluble solvent.

[0062] 〔Evaluation 2〕

[0063] For the solid electrolytes obtained in the examples and comparative examples, the lithium existence rate at the surface of the solid electrolyte was measured by the following method. The results are shown in Table 1 below.

[0064] Using Versa Probe III manufactured by ULVAC-PHI, the surface of the particles of the solid electrolyte was analyzed. The conditions used in the measurement are as follows.

[0065] Excitation X-ray: Monochromatic Al ray (1486.7 eV)

[0066] Output power: 50 W

[0067] Acceleration voltage: 15 kV

[0068] X-ray irradiation diameter: 200 μmφ

[0069] Measurement area: 1000 μm × 1000 μm

[0070] Take-off Angle: 45°

[0071] Pass energy: 26.0 eV

[0072] Energy step: 0.1 eV

[0073] Using data analysis software (“MULTIPAK Ver9.0” manufactured by ULVAC-PHI), the XPS data was analyzed. The background mode used was Iterated Shirley. As follows, the orbit used for calculation was determined for each element.

[0074] Li: 1s

[0075] P: 2s

[0076] S: 2s

[0077] Cl: 2p

[0078] Br: 3p

[0079] More specifically, for the solid electrolyte, XPS is used to analyze the surface of the solid electrolyte under the aforementioned conditions, and the peak area is obtained from the resulting X-ray photoelectron spectroscopy spectrum. For all the above elements, the atomic composition percentage is calculated.

[0080] 〔Evaluation 3〕

[0081] For the solid electrolytes obtained in the examples and comparative examples, the specific surface area A is measured. Specifically, using a pretreatment device “BELPREP-vacII” manufactured by Microtrac-Bell, the sample (powder) is heated at 120 °C for 1 hour in a vacuum. Thereafter, using a specific surface area measuring device “BELSORP-miniII” manufactured by Microtrac-Bell, the specific surface area A is calculated by the BET (Brunauer-Emmett-Teller) method from the nitrogen adsorption amount at liquid nitrogen temperature (77 K). The measurement results are shown in Table 1 below.

[0082] 〔Evaluation 4〕

[0083] For the solid electrolytes obtained in the examples and comparative examples, the lithium ion conductivity is measured by the following method. The results are shown in Table 1 below.

[0084] The solid electrolyte is uniaxially press-molded in a glove box replaced with sufficiently dried Ar gas (dew point of -60 °C or lower). Further, it is molded at 200 MPa using a cold isostatic pressing device to produce pellets with a diameter of 10 mm and a thickness of about 4 mm to 5 mm. After applying a carbon paste as an electrode to both upper and lower surfaces of the pellets, heat treatment is performed at 180 °C for 30 minutes to produce a sample for measuring ion conductivity. Using Solartron 1255B of TOYO CORPORATION, the lithium ion conductivity of the sample is measured. The measurement is performed by the AC impedance method under the conditions of a temperature of 25 °C and a frequency of 0.1 Hz to 1 MHz.

[0085] [Table 1]

[0086]

[0087] It is clearly understood from the results shown in Table 1 that the lithium ion conductivity of the solid electrolytes obtained in each example is higher than that of the solid electrolytes of the comparative examples.

[0088] Industrial Applicability

[0089] According to the present invention, a sulfide solid electrolyte having a high lithium ion conductivity can be provided.

Claims

1. A sulfide solid electrolyte containing the following compounds: The compound contains a crystalline phase having a argyrodite-type crystal structure and is represented by Li a PS b X c , wherein X is at least one halogen element, a represents a number of 3.0 or more and 6.0 or less, b represents a number of 3.5 or more and 4.8 or less, c represents a number of 0.1 or more and 3.0 or less, Let the amount of lithium (atomic %) quantified by the peak of 1s of Li determined by X-ray photoelectron spectroscopy (XPS) be denoted as A Li Let the amount of phosphorus (atomic %) quantified by the peak of 2p of P be denoted as A P Let the amount of sulfur (atomic %) quantified by the peak of 2p of S be denoted as A S Let the amount of halogen (atomic %) quantified by the peak of halogen be denoted as A X When A Li / (A Li +A P +A S +A X ) is relative to the specific surface area (m 2 g -1 ) of the sulfide solid electrolyte, the value is 3.40% / m 2 g -1 or more.

2. The sulfide solid electrolyte according to claim 1, wherein, The specific surface area is 13.1 m 2 g -1 or less.

3. The sulfide solid electrolyte according to claim 1 or 2, having a lithium ion conductivity of 4.8 mS / cm or more at 25°C.

4. The sulfide solid electrolyte according to claim 1 or 2, having a D50 of 1.0 μm or less.

5. An electrode mixture containing the sulfide solid electrolyte according to any one of claims 1 to 4 and an active material.

6. A solid electrolyte layer containing the sulfide solid electrolyte according to any one of claims 1 to 4.

7. A solid-state battery containing the sulfide solid electrolyte according to any one of claims 1 to 4.

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