Solid electrolyte, and electrode mixture, solid electrolyte layer, and solid-state battery comprising the same

Abstract

The present application has an object to further suppress generation of hydrogen sulfide compared with the past while maintaining ion conductivity of a solid electrolyte at a high level. The solid electrolyte contains lithium (Li) element, phosphorus (P) element, sulfur (S) element, halogen (X) element, and nitrogen (N) element. The presence of nitrogen (N) element is observed on the surface of the aforementioned solid electrolyte by X-ray photoelectron spectroscopy. The semi-quantitative value of nitrogen (N) element at a sputtering time of 0 minutes measured by X-ray photoelectron spectroscopy is suitably 0.003 or more relative to the sum of semi-quantitative values of lithium (Li) element, phosphorus (P) element, sulfur (S) element, and halogen (X) element.

Description

Technical Field

[0001] This invention relates to solid electrolytes. Furthermore, this invention relates to electrode mixtures comprising solid electrolytes, solid electrolyte layers, and solid-state batteries. Background Technology

[0002] In recent years, secondary batteries have garnered attention as a countermeasure to prevent global warming by reducing carbon dioxide emissions. Among these, solid-state batteries using sulfide solid electrolytes have attracted particular interest. Solid-state batteries using sulfide solid electrolytes offer advantages such as simplified safety devices and superior manufacturing costs and productivity because they do not use flammable organic solvents. Furthermore, since ions other than lithium ions do not move within the electrolyte, side reactions caused by anion movement do not occur, which is beneficial from the perspective of improving safety and durability.

[0003] As a type of solid electrolyte, sulfide solid electrolytes containing lithium (Li), phosphorus (P), sulfur (S), and halogen (X) are known. Since sulfide solid electrolytes contain sulfur, sulfur may react with moisture to produce hydrogen sulfide, depending on the environment. Therefore, the applicant previously proposed a solid electrolyte in which the surface of a compound containing lithium (Li), phosphorus (P), sulfur (S), and halogen (X) with a cubic crystal structure of sulfide-germanium sulfide is coated with a compound containing lithium, phosphorus, and sulfur with a non-sulfide-germanium sulfide crystal structure (see Patent Document 1). According to this solid electrolyte, it has the advantages of suppressing the generation of hydrogen sulfide and ensuring the specified lithium-ion conductivity.

[0004] Existing technical documents

[0005] Patent documents

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

[0007] The problem the invention aims to solve

[0008] The inventors conducted in-depth research to further improve the performance of solid-state batteries and discovered the following issue: it is necessary to further suppress the generation of hydrogen sulfide while maintaining the high ionic conductivity of the solid electrolyte.

[0009] Solution for solving the problem

[0010] This invention provides a solid electrolyte comprising lithium (Li), phosphorus (P), sulfur (S), halogen (X), and nitrogen (N).

[0011] The presence of nitrogen (N) was observed on the surface of the aforementioned solid electrolyte using X-ray photoelectron spectroscopy.

[0012] In addition, the present invention provides a method for manufacturing a solid electrolyte, wherein,

[0013] A mixture is obtained by mixing core particles containing lithium (Li), phosphorus (P), sulfur (S) and halogen (X) elements with ammonium halide particles.

[0014] The aforementioned mixture is heated to form a nitrogen (N) enriched layer on the surface of the aforementioned core particles. Attached Figure Description

[0015] Figure 1 These are X-ray diffraction patterns of the solid electrolytes obtained in the examples and comparative examples. Detailed Implementation

[0016] The present invention will now be described based on its preferred embodiments.

[0017] This invention relates to solid electrolytes. Preferably, the solid electrolyte of this invention has lithium-ion conductivity.

[0018] The solid electrolyte of the present invention preferably contains lithium (Li), phosphorus (P), sulfur (S), and a halogen (X). Examples of halogen (X) include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The halogen (X) can be one of these elements, or a combination of two or more. A particularly preferred combination of chlorine (Cl) and bromine (Br) is the halogen (X).

[0019] The solid electrolyte of the present invention preferably contains nitrogen (N) in addition to the elements mentioned above. That is, the sulfide solid electrolyte preferably contains Li, P, S, X, and N.

[0020] The solid electrolyte of the present invention preferably contains nitrogen (N) as described above, but N is preferably enriched on and near the surface of the solid electrolyte particles. By presenting N in this manner, the generation of hydrogen sulfide in the solid electrolyte of the present invention is suppressed.

[0021] The solid electrolyte of the present invention, by including nitrogen element as described above, is able to suppress the generation of hydrogen sulfide. The reason for this is not yet clear, but the inventors speculate as follows.

[0022] It can be inferred that some of the PS bonds on the surface of solid electrolyte particles are replaced by PN bonds, resulting in a reduction in the sulfur content on the surface, which in turn suppresses the production of hydrogen sulfide. Furthermore, it can be inferred that when the solid electrolyte comes into contact with water, the reaction between PN bonds and water occurs preferentially over the reaction between PS bonds and water, thus effectively suppressing the production of hydrogen sulfide. Additionally, it can be inferred that by preferentially placing PN bonds on the surface, the production of hydrogen sulfide can be suppressed while maintaining high ion conductivity.

[0023] In the solid electrolyte of the present invention, the presence of nitrogen (N) on the particle surface of the solid electrolyte can be confirmed by X-ray photoelectron spectroscopy (hereinafter also referred to as "XPS"). According to XPS, information about a few nanometers of the surface layer of the object being measured can be obtained. When measuring the particles of the solid electrolyte of the present invention by XPS, peaks originating from nitrogen (N) are observed in a binding energy range, for example, 396 eV or higher and 404 eV or lower.

[0024] The amount of nitrogen atoms present on the surface of the solid electrolyte particles of the present invention can be evaluated based on the value of the semi-quantitative value of nitrogen at a sputtering time of 0 minutes, as measured by XPS, relative to the sum of the semi-quantitative values ​​of Li, P, S, and X (hereinafter also referred to as the "nitrogen presence ratio"). In the particles of the solid electrolyte of the present invention, from the viewpoint of effectively suppressing hydrogen sulfide generation, a nitrogen presence ratio of 0.003 or higher is preferred. From the viewpoint of making this advantage even more significant, a nitrogen presence ratio of 0.005 or higher is preferred, and more preferably 0.007 or higher.

[0025] From the viewpoint of maintaining ionic conductivity, the upper limit of the nitrogen presence ratio is preferably 0.05 or less, more preferably 0.02 or less, and even more preferably 0.01 or less.

[0026] From the viewpoint of suppressing hydrogen sulfide generation and maintaining ionic conductivity, in the solid electrolyte of the present invention, as described above, nitrogen (N) is preferably enriched on and near the particle surface of the solid electrolyte. Regarding the degree of N enrichment, E1 is defined as the semi-quantitative value of N measured by XPS at a sputtering time of 0 minutes relative to the sum of the semi-quantitative values ​​of Li, P, S, and X elements, and E2 is defined as the semi-quantitative value of N measured by XPS at a sputtering time of 10.5 minutes relative to the sum of the semi-quantitative values ​​of Li, P, S, and X elements. The value of E2 / E1 (hereinafter also referred to as "nitrogen enrichment rate") can be used for evaluation. In the present invention, from the viewpoint of effectively suppressing hydrogen sulfide generation and maintaining ionic conductivity, a nitrogen enrichment rate of 0.2 or less is preferred. From the viewpoint of making this advantage even more significant, a nitrogen enrichment rate of 0.1 or less is preferred, and more preferably 0.

[0027] The reason for using a sputtering time of 10.5 minutes in the definition of nitrogen enrichment rate is that it is the time required for the measurement results to reach saturation, which is sufficient to observe the composition in the central region of the solid electrolyte particles.

[0028] The method for setting the nitrogen content ratio and nitrogen enrichment rate in the solid electrolyte as described above will be described later.

[0029] From the viewpoint of further suppressing the generation of hydrogen sulfide from the solid electrolyte, in the solid electrolyte of the present invention, it is also preferable that lithium halides are enriched on and near the surface of the particles. The degree of enrichment of lithium halides can be evaluated based on the sum of the semi-quantitative values ​​of Li and X elements at a sputtering time of 0 minutes, as measured by XPS, relative to the semi-quantitative value of P element (hereinafter also referred to as the "LiX presence ratio"). In the present invention, from the viewpoint of effectively suppressing the generation of hydrogen sulfide, a LiX presence ratio of 7.7 or higher is preferred. From the viewpoint of making this advantage more significant, a LiX presence ratio of 7.9 or higher is further preferred, more preferably 8.4 or higher, and even more preferably 9.5 or higher.

[0030] Regarding the upper limit of the LiX presence ratio, from the viewpoint of maintaining ionic conductivity, the LiX presence ratio is preferably 20.0 or less, and more preferably 10.0 or less.

[0031] The method for setting the LiX content in the solid electrolyte as described above will be described later.

[0032] From the viewpoint of further suppressing the generation of hydrogen sulfide from the solid electrolyte, it is also preferable that the amount of sulfur (S) present on and near the particle surface is low in the solid electrolyte of the present invention. The amount of sulfur present can be evaluated based on the difference between the semi-quantitative values ​​of Li and S elements at a sputtering time of 0 minutes, measured by XPS, relative to the semi-quantitative value of P (hereinafter also referred to as the "sulfur presence ratio"). In the present invention, from the viewpoint of effectively suppressing the generation of hydrogen sulfide, a sulfur presence ratio of 1.9 or higher is preferred. From the viewpoint of making this advantage more significant, a sulfur presence ratio of 2.4 or higher is preferred, and more preferably 2.9 or higher.

[0033] From the viewpoint of maintaining ionic conductivity, the upper limit of the sulfur content is preferably 5.0 or less, and more preferably 3.2 or less.

[0034] The method for setting the sulfur content in the solid electrolyte as described above will be described later.

[0035] The detailed methods for determining the nitrogen presence ratio, nitrogen enrichment rate, LiX presence ratio, and sulfur presence ratio are described in the examples described later.

[0036] The solid electrolyte of the present invention is preferably a crystalline substance. Particularly preferred is a solid electrolyte comprising a crystal phase having a sulforaphite-germanium-type crystal structure. A sulforaphite-germanium-type crystal structure refers to a crystal structure possessed by compounds derived from minerals with the chemical formula Ag8GeS6. Whether a sulfide solid electrolyte possesses a sulforaphite-germanium-type crystal phase can be confirmed by X-ray diffraction (hereinafter also referred to as "XRD") or similar methods. For example, in the diffraction pattern obtained by XRD, the sulforaphite-germanium-type crystal phase exhibits characteristic diffraction peaks at positions of 2θ = 25.5° ± 1.0°, 30.0° ± 1.0°, and 30.9° ± 1.0°. In addition to the aforementioned diffraction peaks, depending on the elemental composition of the sulfide solid electrolyte, characteristic diffraction peaks also appear at 2θ = 15.3°±1.0°, 18.0°±1.0°, 44.3°±1.0°, 47.2°±1.0°, 51.7°±1.0°, 58.3°±1.0°, 60.7°±1.0°, 61.5°±1.0°, 70.4°±1.0°, and 72.6°±1.0°. The range of each of these diffraction peaks can be, for example, ±0.7°, ±0.5°, or ±0.3°. For the identification of diffraction peaks originating from argillium sulfide-germanium-type crystal structures, data from PDF number 00-034-0688 are used, for example.

[0037] When obtaining the aforementioned X-ray diffraction pattern, Cu-Kα was used as the X-ray source. Hereafter, in all cases where X-ray diffraction patterns are mentioned in this specification, Cu-Kα will be used as the X-ray source.

[0038] From the viewpoint of suppressing hydrogen sulfide generation, the solid electrolyte of the present invention preferably exhibits at least two diffraction peaks in the X-ray diffraction pattern measured by an XRD apparatus within the range of 2θ = 28° to 30°. In particular, the solid electrolyte of the present invention preferably exhibits peak A, which is one of the aforementioned two diffraction peaks, within the range of 2θ = 28.0° or higher and 29.3° or lower, and preferably peak B is observed within the range of 2θ = 29.3° or higher and 30.3° or lower.

[0039] Regarding peak A, it is preferably observed in the range of 2θ = 28.0° or higher and 29.3° or lower, and particularly preferably in the range of 28.6° or higher and 29.2° or lower.

[0040] Regarding peak B, it is preferred to be observed in the range of 2θ = 29.3° or higher and 30.3° or lower, and particularly preferred to be observed in the range of 29.4° or higher and 30.1° or lower.

[0041] Additionally, when the peak intensity of peak A is set to I... ASet the peak intensity of peak B to I. B From the perspective of effectively suppressing hydrogen sulfide production, I is preferred. B Compared to I A The value of I B / I A Below 11.0. From the perspective of making this advantage more significant, I B / I A The value is preferably 10.0 or less, and more preferably 9.0 or less.

[0042] From the perspective of maintaining ionic conductivity, I B / I A The value is preferably 0.5 or higher, more preferably 3.0 or higher, and even more preferably 7.0 or higher.

[0043] Either peak A or peak B is preferably a diffraction peak originating from a sterigmasite-type crystal structure. The other peak is preferably a diffraction peak originating from lithium halide. It is particularly preferred that diffraction peak A observed at a low angle is a diffraction peak originating from lithium halide, and that diffraction peak B observed at a high angle is a diffraction peak originating from a sterigmasite-type crystal structure.

[0044] The solid electrolyte of the present invention is preferably an aggregate of particles. In this case, from the viewpoints of suppressing the increase in resistance caused by the increase in surface area and facilitating mixing with active materials, the volumetric cumulative particle size D is determined based on a cumulative volume of 50% by laser diffraction scattering particle size distribution method. 50 Preferably, the particle size is 0.1 μm or more, more preferably 0.4 μm or more, and even more preferably 0.6 μm or more. Furthermore, from the viewpoint of suppressing adhesion, aggregation, and particle size growth caused by heating, the volumetric cumulative particle size D... 50 Preferably, it is 100 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and particularly preferably 3 μm or less.

[0045] The solid electrolyte of the present invention exhibits lithium-ion conductivity in a solid state. Preferably, the solid electrolyte has a lithium-ion conductivity of 0.1 mS / cm or higher at room temperature, i.e., 25°C, more preferably 0.5 mS / cm or higher, and more preferably 1.5 mS / cm or higher, particularly 2.5 mS / cm or higher. The lithium-ion conductivity can be measured using the methods described in the examples below.

[0046] Next, a preferred method for manufacturing the solid electrolyte of the present invention will be described.

[0047] This manufacturing method is roughly divided into the following steps A and B.

[0048] [Process A]

[0049] A mixture is obtained by mixing core particles containing lithium (Li), phosphorus (P), sulfur (S) and halogen (X) elements with ammonium halide particles.

[0050] [Process B]

[0051] The aforementioned mixture is heated to form a nitrogen (N) enriched layer on the surface of the aforementioned core particles.

[0052] The following is a description of each process.

[0053] [Process A]

[0054] In this process, core particles are prepared. Core particles are the base material of the solid electrolyte of this invention and constitute the majority of the solid electrolyte of this invention.

[0055] The core particles can be suitably manufactured by a solid-state reaction involving heating and sintering of the raw material composition. The aforementioned raw material composition is a mixture of raw material powders comprising the elements constituting the core particles described above. The raw material composition comprises one or more compounds containing at least one element selected from Li, P, S, and X.

[0056] The aforementioned raw material powder may be, for example, a compound containing Li, a compound containing S, a compound containing P, or a compound containing X.

[0057] In the aforementioned raw material powder, a compound may contain at least two or more elements selected from Li, P, S, and X. For example, as the aforementioned raw material powder, compounds containing Li and X, compounds containing P and S, compounds containing Li and S, compounds containing P and X, and compounds containing S and X may be used.

[0058] Lithium halides can be used as compounds containing both Li and X elements.

[0059] Phosphorus sulfides, such as phosphorus trisulfide (P2S3) and phosphorus pentasulfide (P2S5), can be used as compounds containing P and S elements.

[0060] As a compound containing both Li and S elements, lithium sulfide (Li2S) can be used, for example.

[0061] Phosphorus halides such as PX3 and P2X5 can be used as compounds containing both phosphorus (P) and phosphorus (X) elements.

[0062] As compounds containing both sulfur (S) and x (X) elements, for example, SX2, SX4, SX6, and S2X can be used. 10 Isohalated sulfur.

[0063] The aforementioned raw material powders are preferably fed into a grinding process and adjusted to a specified particle size before being mixed. Media-stirred mills, such as ball mills or bead mills, can be used in the grinding process.

[0064] After the aforementioned raw material powders are pulverized, the raw material powders are mixed to obtain a raw material composition. The raw material powders are preferably mixed in proportions that form the elemental composition of the target solid electrolyte. A media stirring mill is also preferably used in the mixing of the raw material powders.

[0065] Next, the raw material composition is fed into a firing process to undergo a solid-state reaction, resulting in a crystalline fired product. The firing atmosphere can be an inert gas atmosphere, such as argon or nitrogen, or a hydrogen sulfide atmosphere. From the viewpoint of adjusting the proportion of sulfur in the core particles, an inert gas atmosphere is preferred.

[0066] From the viewpoint of reliably generating a solid-state reaction of the raw material composition, the firing temperature is preferably, for example, 200°C or higher, more preferably 300°C or higher, even more preferably 350°C or higher, and still more preferably 400°C or higher. On the other hand, considering industrial production feasibility and economic efficiency, the firing temperature is preferably, for example, 700°C or lower, more preferably 600°C or lower, and even more preferably 550°C or lower.

[0067] The firing time is not a critical time; it is simply the time required to obtain a fired product with the desired composition. Specifically, a firing time that allows sufficient solid-state reaction of the raw material composition to occur is preferred. The firing time can be, for example, 30 minutes or more, 2 hours or more, or 3 hours or more. On the other hand, the firing time can be, for example, 10 hours or less, or 5 hours or less.

[0068] After firing, the fired material is crushed or pulverized as needed, and then graded to adjust to a specified particle size. A particularly preferred method is to use a volumetric cumulative particle size D at a cumulative volume of 50% based on a laser diffraction scattering particle size distribution determination method. 50 The particle size of the sintered material is adjusted to be 0.5 μm or larger and 0.9 μm or smaller, particularly 0.65 μm or larger and 0.75 μm or smaller. This yields the target core particles.

[0069] The prepared core particles are mixed with ammonium halide particles. Either dry or wet mixing can be used. From the viewpoint of obtaining a solid electrolyte with high lithium-ion conductivity, dry mixing is advantageous. Media stirring mills, such as ball mills or bead mills, can be used for dry mixing.

[0070] From the viewpoint of successfully obtaining a solid electrolyte in which hydrogen sulfide generation is suppressed, regarding the mixing ratio of core particles and ammonium halide particles, the proportion of ammonium halide particles relative to the total amount of both is preferably set to 1.0% by mass or more, more preferably 2.0% by mass or more, and even more preferably 3.0% by mass or more. Furthermore, the proportion of ammonium halide particles relative to the total amount of both is preferably set to 20.0% by mass or less, more preferably 10.0% by mass or less, and even more preferably 5.0% by mass or less.

[0071] Examples of ammonium halides that can be mixed with the core particles include ammonium fluoride, ammonium chloride, ammonium bromide, and ammonium iodide. These ammonium halides can be used alone, or two or more can be used in combination.

[0072] From the perspective of successfully manufacturing the target solid electrolyte, it is preferable to control the particle size of ammonium halide. Specifically, the volumetric cumulative particle size D, determined by laser diffraction scattering particle size distribution method, is used when the cumulative volume of the core particles is 50% by volume. 50 Let's call it D C The cumulative particle size D of ammonium halide particles when the cumulative volume of the particles is 50% (volume %) was determined by laser diffraction scattering particle size distribution method. 50 Let's call it D A At that time, D C / D A The value of is preferably set to 0.002 or higher, more preferably 0.01 or higher, and even more preferably 0.03 or higher. Additionally, D C / D A The value of is preferably set to 1.5 or less, more preferably to 0.15 or less, and even more preferably to 0.07 or less. By adjusting the particle size of the core particles and the particle size of the ammonium halide in this way, it is possible to successfully manufacture particles of a solid electrolyte enriched with N elements on and around the surface.

[0073] The particle size D of ammonium halide A The value of the micrometer itself is preferably 0.3 μm or more and 500 μm or less, more preferably 10 μm or more and 300 μm or less, and even more preferably 10 μm or more and 30 μm or less.

[0074] [Process B]

[0075] In this process, a mixture of core particles obtained in step A and ammonium halide particles is fed into a calcination process. During calcination, the sulfur (S) in the core particles reacts with the hydrogen (H) in the ammonium halide, and the S is released as hydrogen sulfide. Therefore, the amount of S on and near the surface of the resulting solid electrolyte particles is reduced. This suppresses the formation of hydrogen sulfide in the solid electrolyte.

[0076] Furthermore, the sulfur (S) in the core particles reacts with the hydrogen (H) in the ammonium halide, resulting in a coating of nitrogen-containing compounds on the surface of the core particles. This also helps to suppress the production of hydrogen sulfide in the solid electrolyte.

[0077] Furthermore, the sulfur (S) in the core particles reacts with the hydrogen (H) in the ammonium halide, resulting in the formation of lithium halide on the surface of the core particles. This also helps to suppress the formation of hydrogen sulfide in the solid electrolyte.

[0078] Through this mechanism of action, the generation of hydrogen sulfide can be further suppressed compared to the past while maintaining the high ionic conductivity of the solid electrolyte.

[0079] From the viewpoint of enabling the sulfur element to detach smoothly from the surface of the core particle and to form a layer enriched with nitrogen and lithium halide on the surface of the core particle, the firing temperature in this process is preferably set to 120°C or higher, particularly preferably 150°C or higher, and especially preferably 190°C or higher.

[0080] Furthermore, from the viewpoint of not impairing the lithium-ion conductivity of the core particles, the firing temperature is preferably set to 300°C or below, particularly preferably 250°C or below, and especially preferably 210°C or below.

[0081] The firing time is not a critical time; it is simply the time required to obtain a solid electrolyte with the target composition. Specifically, with the firing temperature within the aforementioned range as a condition, the firing time can be, for example, more than 1 hour, more than 2 hours, or more than 4 hours. On the other hand, the firing time can be, for example, less than 20 hours, less than 10 hours, or less than 6 hours.

[0082] The firing atmosphere is preferably set as a non-reactive gas atmosphere such as nitrogen, argon and helium.

[0083] After firing, the fired material can be crushed or pulverized as needed, and then graded accordingly. This yields the powder of the target solid electrolyte.

[0084] The solid electrolyte obtained in this way can be used alone or in combination with other solid electrolytes. For example, the solid electrolyte of the present invention can be used as a material constituting a lithium battery, such as a material constituting a solid electrolyte layer, a positive electrode layer, or a negative electrode layer.

[0085] Specifically, the solid electrolyte of the present invention can be used in batteries having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive and negative electrode layers. That is, the solid electrolyte can be used in so-called solid-state batteries. More specifically, it can be used in lithium solid-state batteries.

[0086] Lithium solid-state batteries can be primary or secondary batteries. There are no particular restrictions on the shape of the battery; for example, they can be laminated, cylindrical, or prismatic. The term "solid-state battery" includes not only those batteries that completely do not contain liquid or gel-like substances as electrolytes, but also those containing, for example, less than 50% by mass, less than 30% by mass, or less than 10% by mass of liquid or gel-like substances as electrolytes.

[0087] When the solid electrolyte layer contains the solid electrolyte of the present invention, the solid electrolyte layer can be manufactured, for example, by methods such as: dripping a slurry containing a solid electrolyte, a binder, and a solvent onto a substrate and then grinding it with a scraper or the like; cutting it with an air knife after the substrate has come into contact with the slurry; or forming a coating film by screen printing or the like, and then removing the solvent by heating and drying. Alternatively, it can be manufactured by pressing the powdered solid electrolyte into a pressed powder and then processing it appropriately.

[0088] To balance the prevention of short circuits and volumetric capacity density, the thickness of the solid electrolyte layer is typically 5 μm or more and 300 μm or less, and more preferably 10 μm or more and 100 μm or less.

[0089] The solid electrolyte of the present invention can also be used with active materials to form an electrode mixture. Typically, the proportion of solid electrolyte in the electrode mixture is 10% by mass or more and 50% by mass or less. The electrode mixture may also contain other materials such as conductive materials as needed.

[0090] Electrode mixtures, binders, and solvents are mixed to form a paste, which is then applied to current collectors such as aluminum foil and dried to produce positive and negative electrodes.

[0091] As the cathode material constituting the cathode layer, cathode materials used as cathode active materials in lithium-ion batteries can be appropriately used. Examples include lithium-containing cathode active materials, specifically spinel-type lithium transition metal oxides and lithium metal oxides with layered structures. By using high-voltage cathode materials, energy density can be increased. In addition to the cathode active material, the cathode material may also contain conductive materials, or other materials.

[0092] As the negative electrode material constituting the negative electrode layer, a negative electrode material used as the negative electrode active material in lithium-ion batteries can be appropriately used. The solid electrolyte of this invention is electrochemically stable, therefore lithium metal can be used, or at a low potential comparable to lithium metal (approximately 0.1V vs. Li). +Materials that are charged and discharged under Li (Li) conditions, namely carbon-based materials such as graphite, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon), can be used as anode materials. This significantly improves the energy density of solid-state batteries. Alternatively, silicon or tin, which are expected to be high-capacity materials, can be used as active materials. Regarding anode materials, in addition to the active material, conductive materials or other materials may also be included.

[0093] Example

[0094] The present invention will now be described in more detail through embodiments. However, the scope of the present invention is not limited to these embodiments.

[0095] [Example 1]

[0096] [Process A]

[0097] To become Li 5.4 PS 4.4 Br 0.8 Cl 0.8 The composition was prepared by weighing and mixing lithium sulfide (Li₂S) powder, phosphorus pentasulfide (P₂S₅) powder, lithium chloride (LiCl) powder, and lithium bromide (LiBr) powder to obtain a raw material composition. The raw material composition was calcined at 500°C for 4 hours to obtain a calcined product. Calcination was carried out using a tubular electric furnace. During calcination, 100% pure nitrogen gas was circulated within the furnace. The obtained calcined product was pulverized to obtain core particle powder (D). 50 =0.7μm).

[0098] The obtained core particle powder was mixed with ammonium chloride powder (D) using a mortar. 50 Dry mix (particles with a diameter of 250 μm) until homogeneous. The proportion of ammonium chloride in the mixed powder is set at 10% by mass.

[0099] [Process B]

[0100] Under a nitrogen atmosphere, the mixed powder was calcined at 200°C for 5 hours. The resulting calcined product was crushed in a mortar and the particle size was adjusted using a 53 μm sieve to obtain the powder of the target solid electrolyte.

[0101] [Example 2]

[0102] As ammonium chloride powder, D is used 50 The powder has a particle size of 20 μm. Furthermore, the proportion of ammonium chloride in the mixture of the core particle powder and the ammonium chloride powder is set to 4% by mass. Otherwise, a solid electrolyte powder is obtained in the same manner as in Example 1.

[0103] [Example 3]

[0104] As ammonium chloride powder, D is used50 The powder has a particle size of 20 μm. Furthermore, the proportion of ammonium chloride in the mixture of the core particle powder and the ammonium chloride powder is set to 10% by mass. Otherwise, a solid electrolyte powder is obtained in the same manner as in Example 1.

[0105] [Example 4]

[0106] As ammonium chloride powder, D is used 50 The powder has a particle size of 20 μm. Furthermore, the proportion of ammonium chloride in the mixture of core particle powder and ammonium chloride powder was set to 4% by mass. Using a dry particle recombining apparatus NOB-MINI (manufactured by Hosokawa Micron Group), the core particle powder and ammonium chloride powder were mixed for 1 hour. The rotor speed was set to 6000 rpm. Otherwise, a solid electrolyte powder was obtained in the same manner as in Example 1.

[0107] [Comparative Example 1]

[0108] In step B of Example 1, ammonium chloride powder is not used. Otherwise, a solid electrolyte powder is obtained in the same manner as in Example 1. This solid electrolyte is obtained by the calcination process of step B in Example 1.

[0109] [Comparative Example 2]

[0110] The core particles used in Example 1 were used as the solid electrolyte in this comparative example. This solid electrolyte was not subjected to the firing process of step B in Example 1.

[0111] [evaluate]

[0112] For the solid electrolytes obtained in the examples and comparative examples, the particle size D was determined by the following method. 50 and D 95 (The cumulative particle size at 95% volume percentage based on laser diffraction scattering particle size distribution determination). Additionally, the nitrogen presence ratio, nitrogen enrichment rate, LiX presence ratio, and sulfur presence ratio were determined using the following methods. Furthermore, XRD measurements were performed using the following methods. The XRD results are shown below. Figure 1 Furthermore, the lithium-ion conductivity and hydrogen sulfide production were determined using the following methods. The results are shown in Table 1 below.

[0113] Particle size D 50 and D 95 ]

[0114] Using an automatic sample feeder (Microtorac SDC, manufactured by Nikkiso Co., Ltd.) for laser diffraction particle size distribution measurement, the flow rate of the sample containing solid electrolyte was set to 50%, and the sample was irradiated with 30W ultrasound for 60 seconds. Then, the particle size distribution was measured using a Nikkiso Co., Ltd. laser diffraction particle size distribution measuring machine (MT3000II). The particle sizes at 50% and 95% of the cumulative volume were determined from the obtained volume-based particle size distribution graph, and these values ​​were taken as D. 50 and D 95 .

[0115] [Nitrogen presence ratio, nitrogen enrichment rate, LiX presence ratio, and sulfur presence ratio]

[0116] The surface of sulfide solid electrolytes was measured using an XPS apparatus VersaProbe III manufactured by ULVAC-PHI, Inc. The conditions used in the measurement are described below.

[0117] • Excitation X-rays: Monochromatic AlKα rays (1486.7 eV)

[0118] Power: 50W

[0119] X-ray diameter: 200 μm

[0120] • Energy: 26eV

[0121] • Photoelectron escape angle: 45°

[0122] (Ar ion etching conditions)

[0123] Accelerating voltage: 4kV

[0124] Sputtering area: 2mm × 2mm

[0125] • Sputtering rate: 9.9 nm / min (converted to SiO2)

[0126] In addition, peak intensity readings and quantitative calculations were performed using data analysis software ("MultiPak Ver 9.9" manufactured by ULVAC-PHI, Inc.). It should be noted that the background mode used was Shirley. Charge correction was performed by setting the binding energy of the hydrocarbon (CH) peak in the C1s spectrum to 284.8 eV.

[0127] [XRD Measurement]

[0128] Measurements were performed using the Malvern Panalytical Aeris benchtop X-ray diffractometer, under non-atmospheric exposure conditions. The measurement conditions are described below.

[0129] • Radiation source: CuKα

[0130] • Tube voltage: 40kV

[0131] Tube current: 15mA

[0132] • Measurement method: Concentration method (reflectance method)

[0133] • Detector: One-dimensional semiconductor detector

[0134] • Incident Soler slit: The Soler slit is 0.02 rad.

[0135] • Length-limiting slit: 20mm

[0136] • Light receiving Soler slit: 0.02 rad

[0137] • Entrance slit: 1 / 2°

[0138] • Light receiving slit: Open

[0139] • Measurement range: 2θ = 10~105°

[0140] • Step width: 0.01°

[0141] • Scanning speed: 1.67° / minute

[0142] The results were analyzed after subtracting the background intensity obtained from the Kapton film of the non-exposed retainer.

[0143] [Lithium-ion conductivity]

[0144] In a glove box purged with thoroughly dried Ar gas (dew point below -60°C), an application of approximately 6 t / cm was applied to the solid electrolyte. 2 The lithium-ion conductivity of the samples was determined by uniaxial compression molding under a load, producing granules with a diameter of 10 mm and a thickness of approximately 0.5 mm to 8 mm. The lithium-ion conductivity of the samples was measured using a Solartron 1255B impedance measuring device from TOYO Corporation. Measurements were performed by AC impedance method at a temperature of 25°C and a frequency of 0.1 Hz to 1 MHz.

[0145] [Hydrogen sulfide production]

[0146] A detection tube is used to determine the amount of hydrogen sulfide produced by a solid electrolyte.

[0147] In a glove box purged with thoroughly dried Ar gas (dew point below -60°C), weigh 2 mg of solid electrolyte into each metal container, place it into a laminated film bag, and seal it.

[0148] A 1000 ml glass detachable flask was placed in a constant temperature and humidity bath with a dew point of -30°C, adjusted by mixing dry air with atmospheric pressure, and maintained at room temperature (25°C). The environment inside the detachable flask was kept identical to that inside the constant temperature and humidity bath. Next, a sealed bag containing solid electrolyte was opened in the constant temperature and humidity bath, and the solid electrolyte was quickly prepared in the detachable flask. The detachable flask was then sealed again. The hydrogen sulfide generated from the moment of sealing until 30 minutes later was measured using a gas detector (GASTEC CORPORATION No. 4LL).

[0149] [Table 1]

[0150]

[0151] As can be clearly seen from the results shown in Table 1, the solid electrolytes obtained in each embodiment maintain a high level of conductivity and suppress the generation of hydrogen sulfide.

[0152] In addition, by Figure 1 The results clearly show that the solid electrolytes obtained in each embodiment exhibited two diffraction peaks in the range of 2θ = 28° to 30° as determined by XRD. It can be assumed that the diffraction peak observed at the lower angle originates from lithium chloride, while the diffraction peak observed at the higher angle originates from a steric argillacene-type crystal structure.

[0153] Industrial availability

[0154] As detailed above, according to the present invention, a solid electrolyte is provided that can further suppress the generation of hydrogen sulfide compared with the past while maintaining the ionic conductivity of the solid electrolyte at a high level.

Claims

1. A solid electrolyte comprising lithium (Li), phosphorus (P), sulfur (S), halogen (X), and nitrogen (N). The presence of nitrogen (N) was observed on the surface of the solid electrolyte by X-ray photoelectron spectroscopy.

2. The solid electrolyte according to claim 1, wherein, The semi-quantitative value of nitrogen (N) at a sputtering time of 0 minutes, measured by X-ray photoelectron spectroscopy, is greater than 0.003 relative to the sum of the semi-quantitative values ​​of lithium (Li), phosphorus (P), sulfur (S), and halogen (X).

3. The solid electrolyte according to claim 1 or 2, wherein, The semi-quantitative value of nitrogen (N) at a sputtering time of 0 minutes, measured by X-ray photoelectron spectroscopy, is defined as E1 relative to the sum of the semi-quantitative values ​​of lithium (Li), phosphorus (P), sulfur (S), and halogen (X). When E2 is defined as the semi-quantitative value of nitrogen (N) at a sputtering time of 10.5 minutes, measured by X-ray photoelectron spectroscopy, relative to the sum of the semi-quantitative values ​​of lithium (Li), phosphorus (P), sulfur (S), and halogen (X),... The value of E2 / E1 is below 0.

2.

4. The solid electrolyte according to claim 1 or 2, wherein, The ratio of the sum of the semi-quantitative values ​​of lithium (Li) and halogen (X) elements to the semi-quantitative value of phosphorus (P) at a sputtering time of 0 minutes, as measured by X-ray photoelectron spectroscopy, is greater than 7.

7.

5. The solid electrolyte according to claim 1 or 2, comprising a crystal phase having a sulforaphite-germanium type crystal structure.

6. The solid electrolyte according to claim 1 or 2, wherein, The ratio of the difference between the semi-quantitative values ​​of lithium (Li) and sulfur (S) at a sputtering time of 0 minutes, as measured by X-ray photoelectron spectroscopy, to the semi-quantitative value of phosphorus (P) is greater than 1.

9.

7. The solid electrolyte according to claim 1 or 2, wherein, In the X-ray diffraction pattern obtained by using an X-ray diffraction apparatus with CuKα rays, at least two diffraction peaks were observed in the range of 2θ = 28° to 30°.

8. An electrode mixture comprising the solid electrolyte and active substance as described in claim 1.

9. A solid electrolyte layer comprising the solid electrolyte of claim 1.

10. A solid-state battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer, the solid-state battery containing the solid electrolyte of claim 1.

11. A method for manufacturing a solid electrolyte, wherein, A mixture is obtained by mixing core particles containing lithium (Li), phosphorus (P), sulfur (S) and halogen (X) elements with ammonium halide particles. The mixture is heated to form a nitrogen (N) enriched layer on the surface of the core particles.

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