Solid electrolyte, electrode mixture including same, solid electrolyte layer, and solid battery

Abstract

The present invention addresses the problem of further suppressing the production of hydrogen sulfide while keeping the ion conductivity of a solid electrolyte high. A solid electrolyte according to the present invention includes lithium (Li), phosphorous (P), sulfur (S), a halogen (X), and nitrogen (N). The nitrogen (N) is observed at the surface of the solid electrolyte by X-ray photoelectron spectroscopy. Ideally, the value of a semiquantitative value for the nitrogen (N) relative to the total of semiquantitative values for the lithium (Li), the phosphorous (P), the sulfur (S), and the halogen (X) at a sputtering time of 0 min as measured by x-ray photoelectron spectroscopy is at least 0.003.

Description

Solid electrolyte, electrode mixture containing the same, solid electrolyte layer, and solid battery

[0001] The present invention relates to a solid electrolyte. The present invention also relates to an electrode mixture containing the solid electrolyte, a solid electrolyte layer, and a solid-state battery.

[0002] In recent years, secondary batteries have been attracting attention as an effort to prevent global warming by reducing carbon dioxide emissions. Among these, solid-state batteries using sulfide solid electrolytes have attracted attention. Solid-state batteries using sulfide solid electrolytes have the advantage of simplifying safety devices and achieving excellent manufacturing costs and productivity because they do not use flammable organic solvents. Furthermore, this type of solid electrolyte is advantageous from the perspective of improving safety and durability, since ionic species other than lithium ions do not migrate within the electrolyte, preventing side reactions due to the migration of anions.

[0003] One type of solid electrolyte known is a sulfide solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X). Because sulfide solid electrolytes contain sulfur, there is a possibility that the sulfur may react with moisture to generate hydrogen sulfide under certain circumstances. Therefore, the present applicant previously proposed a solid electrolyte in which the surface of a compound containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X) and having a cubic argyrodite-type crystal structure is coated with a compound containing lithium, phosphorus, and sulfur and having a non-argyrodite-type crystal structure (see Patent Document 1). This solid electrolyte has the advantages of suppressing hydrogen sulfide generation while ensuring a predetermined lithium ion conductivity.

[0004] US2019 / 312304A1

[0005] The present inventors have conducted extensive research to further improve the performance of solid-state batteries and have found that it is necessary to further suppress the generation of hydrogen sulfide while maintaining a high level of ionic conductivity of the solid electrolyte.

[0006] The present invention provides a solid electrolyte containing lithium (Li), phosphorus (P), sulfur (S), a halogen (X), and nitrogen (N), wherein the presence of nitrogen (N) is observed on the surface of the solid electrolyte by X-ray photoelectron spectroscopy.

[0007] The present invention also provides a method for producing a solid electrolyte, which comprises mixing core particles containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X) with ammonium halide particles to obtain a mixture, and heating the mixture to form a layer in which nitrogen (N) is concentrated on the surface of the core particles.

[0008] FIG. 1 is an X-ray diffraction chart of the solid electrolytes obtained in the examples and comparative examples.

[0009] The present invention will be described below based on preferred embodiments. The present invention relates to a solid electrolyte. The solid electrolyte of the present invention preferably has lithium ion conductivity. The solid electrolyte of the present invention preferably contains lithium (Li), phosphorus (P), sulfur (S), and a halogen (X). Examples of the halogen (X) include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The halogen (X) may be one of these elements or a combination of two or more. In particular, the halogen (X) is preferably a combination of chlorine (Cl) and bromine (Br). The solid electrolyte of the present invention preferably further contains nitrogen (N) in addition to the above elements. That is, the sulfide solid electrolyte preferably contains Li, P, S, X, and N.

[0010] As described above, the solid electrolyte of the present invention preferably contains N element, and N element is preferably concentrated on the surface of the solid electrolyte particles and in the vicinity thereof. By having N element in such a state, the solid electrolyte of the present invention is capable of suppressing the generation of hydrogen sulfide.

[0011] As described above, the solid electrolyte of the present invention can suppress the generation of hydrogen sulfide by containing elemental nitrogen. While the reason for this is unclear, the inventors speculate as follows: It is speculated that some of the P-S bonds on the particle surface of the solid electrolyte are replaced with P-N bonds, resulting in a decrease in the sulfur content on the surface, thereby suppressing the generation of hydrogen sulfide. In addition, it is speculated that when the solid electrolyte comes into contact with water, the reaction between P-N bonds and water occurs preferentially over the reaction between P-S bonds and water, thereby effectively suppressing the generation of hydrogen sulfide. It is also speculated that the preferential presence of P-N bonds on the surface can suppress the generation of hydrogen sulfide while maintaining high ionic conductivity.

[0012] In the solid electrolyte of the present invention, the presence of N element on the surface of the solid electrolyte particles can be confirmed by X-ray photoelectron spectroscopy (hereinafter also referred to as "XPS"). XPS can provide information on the surface layer of the object to be measured, down to a few nanometers. When the solid electrolyte particles of the present invention are measured by XPS, a peak attributable to N element is observed in the binding energy range of, for example, 396 eV to 404 eV.

[0013] The abundance of N atoms on the surface of the solid electrolyte particles of the present invention can be evaluated by the semi-quantitative value of N relative to the sum of the semi-quantitative values ​​of Li, P, S, and X elements at a sputtering time of 0 min measured by XPS (hereinafter also referred to as the "nitrogen abundance ratio"). In the solid electrolyte particles of the present invention, it is preferable that the nitrogen abundance ratio is 0.003 or more from the viewpoint of effectively suppressing the generation of hydrogen sulfide. To further enhance this advantage, the nitrogen abundance ratio is preferably 0.005 or more, and even more preferably 0.007 or more. From the viewpoint of maintaining ionic conductivity, the upper limit of the nitrogen abundance ratio is preferably 0.05 or less, more preferably 0.02 or less, and even more preferably 0.01 or less.

[0014] From the viewpoint of suppressing the generation of hydrogen sulfide while maintaining ionic conductivity, it is preferable that the N element is concentrated on the surface of the solid electrolyte particles and in the vicinity thereof, as described above. The degree of concentration of the N element can be determined by the ratio of the semi-quantitative value of the N element to the sum of the semi-quantitative values ​​of the Li element, the P element, the S element, and the X element at a sputtering time of 0 min measured by XPS, expressed as E １ The value of the semi-quantitative value of the N element relative to the sum of the semi-quantitative values ​​of the Li element, the P element, the S element, and the X element at a sputtering time of 10.5 minutes measured by XPS is E ２ When this is done, E ２ / E １ (hereinafter, this value will also be referred to as "nitrogen enrichment rate"). In the present invention, a nitrogen enrichment rate of 0.2 or less is preferred from the viewpoint of maintaining ionic conductivity while effectively suppressing the generation of hydrogen sulfide. To make this advantage even more pronounced, the nitrogen enrichment rate is preferably 0.1 or less, and more preferably 0. The reason why a sputtering time of 10.5 minutes was adopted in defining the nitrogen enrichment rate is that this is a sufficient time for the measurement results to saturate and for the composition in the central region of the solid electrolyte particles to be observed.

[0015] The method for setting the nitrogen abundance ratio and nitrogen enrichment rate in the solid electrolyte as described above will be described later.

[0016] From the viewpoint of further suppressing the generation of hydrogen sulfide from the solid electrolyte, it is also preferable that the solid electrolyte of the present invention has lithium halide enriched on the particle surface and in the vicinity thereof. The degree of enrichment of lithium halide can be evaluated by the sum of the semi-quantitative values ​​of Li and X elements relative to the semi-quantitative value of P element at a sputtering time of 0 min measured by XPS (hereinafter, this ratio is also referred to as the "LiX abundance ratio"). In the present invention, from the viewpoint of effectively suppressing the generation of hydrogen sulfide, it is preferable that the LiX abundance ratio is 7.7 or more. From the viewpoint of further enhancing this advantage, the LiX abundance ratio is more preferably 7.9 or more, even more preferably 8.4 or more, and even more preferably 9.5 or more. From the viewpoint of maintaining ionic conductivity, the upper limit of the LiX abundance ratio is preferably 20.0 or less, and even more preferably 10.0 or less. A method for setting the LiX abundance ratio in the solid electrolyte as described above will be described later.

[0017] From the viewpoint of further suppressing the generation of hydrogen sulfide from the solid electrolyte, it is also preferable that the amount of S element present at and near the particle surface is small in the solid electrolyte of the present invention. The amount of S element present can be evaluated by the difference between the semi-quantitative value of Li element and S element relative to the semi-quantitative value of P element at a sputtering time of 0 min measured by XPS (hereinafter, this ratio is also referred to as the "sulfur abundance ratio"). In the present invention, from the viewpoint of effectively suppressing the generation of hydrogen sulfide, it is preferable that the sulfur abundance ratio is 1.9 or more. From the viewpoint of further enhancing this advantage, the sulfur abundance ratio is preferably 2.4 or more, and more preferably 2.9 or more. The upper limit of the sulfur abundance ratio is preferably 5.0 or less, and more preferably 3.2 or less, from the viewpoint of maintaining ionic conductivity. A method for setting the sulfur abundance ratio in the solid electrolyte as described above will be described later.

[0018] The detailed methods for measuring the nitrogen abundance ratio, nitrogen enrichment rate, LiX abundance ratio, and sulfur abundance ratio will be explained in the examples described later.

[0019] The solid electrolyte of the present invention is preferably a crystalline substance. In particular, the solid electrolyte of the present invention preferably contains a crystal structure having a crystal phase of an argyrodite-type crystal structure. The argyrodite-type crystal structure has the chemical formula: Ag ８ GeS ６ This is a crystalline structure possessed by a group of compounds derived from minerals represented by the formula: Whether or not a sulfide solid electrolyte has a crystalline phase with an argyrodite-type crystalline structure can be confirmed by measurement using X-ray diffraction (hereinafter also referred to as "XRD"). For example, in a diffraction pattern measured by XRD, a crystalline phase with an argyrodite-type crystalline structure exhibits characteristic diffraction peaks at 2θ = 25.5° ± 1.0°, 30.0° ± 1.0°, and 30.9° ± 1.0°. Furthermore, depending on the elemental species constituting the sulfide solid electrolyte, in addition to the above diffraction peaks, characteristic diffraction peaks may be observed 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 the above-mentioned diffraction peaks may be, for example, ± 0.7°, ± 0.5°, or ± 0.3°. To identify the diffraction peaks derived from the argyrodite-type crystal structure, data from PDF No. 00-034-0688, for example, is used. When obtaining the X-ray diffraction pattern, Cu-Kα is used as the radiation source. Hereinafter, when X-ray diffraction patterns are referred to in this specification, Cu-Kα is used as the radiation source.

[0020] In the solid electrolyte of the present invention, from the viewpoint of suppressing the generation of hydrogen sulfide, it is preferable that at least two diffraction peaks are observed in the range of 2θ = 28° to 30° in an X-ray diffraction pattern measured by an XRD device. In particular, in the solid electrolyte of the present invention, one of the two diffraction peaks, Peak A, is preferably observed in the range of 2θ = 28.0° to 29.3°, and Peak B is preferably observed in the range of 2θ = 29.3° to 30.3°. Peak A is preferably observed in the range of 2θ = 28.0° to 29.3°, particularly in the range of 28.6° to 29.2°. Peak B is preferably observed in the range of 2θ = 29.3° to 30.3°, particularly in the range of 2θ = 29.4° to 30.1°.

[0021] In addition, the peak intensity of peak A is I Ａ and the peak intensity of peak B is I Ｂ When I Ａ I against Ｂ The value of I Ｂ / I Ａ From the viewpoint of effectively suppressing the generation of hydrogen sulfide, it is preferable that I is 11.0 or less. Ｂ / I Ａ The value of I is preferably 10.0 or less, and more preferably 9.0 or less. Ｂ / I Ａ The value of is preferably 0.5 or more, more preferably 3.0 or more, and even more preferably 7.0 or more.

[0022] It is preferable that either one of the above-mentioned peaks A and B is a diffraction peak derived from the argyrodite-type crystal structure. The other peak is preferably a diffraction peak derived from lithium halide. In particular, it is preferable that diffraction peak A observed on the low-angle side is a diffraction peak derived from lithium halide, and diffraction peak B observed on the high-angle side is a diffraction peak derived from the argyrodite-type crystal structure.

[0023] The solid electrolyte of the present invention is preferably an aggregate of particles. In this case, from the viewpoint of suppressing an increase in resistance due to an increase in surface area and from the viewpoint of facilitating mixing with an active material, the volume cumulative particle size D at 50% cumulative volume as determined by a laser diffraction / scattering particle size distribution measurement method is preferably 0.01. ５０ From the viewpoint of suppressing adhesion, aggregation, and particle size growth due to heating, the volume cumulative particle size D ５０ is preferably 100 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and particularly preferably 3 μm or less.

[0024] The solid electrolyte of the present invention has lithium ion conductivity in a solid state. The solid electrolyte preferably has a lithium ion conductivity of 0.1 mS / cm or more at room temperature, i.e., 25°C, more preferably 0.5 mS / cm or more, and particularly preferably 1.5 mS / cm or more, and particularly preferably 2.5 mS / cm or more. The lithium ion conductivity can be measured using the method described in the Examples below.

[0025] Next, a preferred method for producing the solid electrolyte of the present invention will be described. This production method is roughly divided into the following steps A and B. [Step A] Core particles containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X) are mixed with ammonium halide particles to obtain a mixture. [Step B] The mixture is heated to form a layer of concentrated nitrogen (N) on the surface of the core particles. Each step will be described below.

[0026] [Step A] In this step, core particles are prepared. The core particles are the base material of the solid electrolyte of the present invention and constitute the majority of the solid electrolyte of the present invention. The core particles can be preferably produced by a solid-state reaction in which a raw material composition is heated and sintered. The raw material composition is a mixture of raw material powders containing the above-mentioned elements that constitute the core particles. The raw material composition contains one or more compounds containing at least one of Li, P, S, and X.

[0027] The raw material powder may be, for example, a compound containing an Li element, a compound containing an S element, a compound containing a P element, or a compound containing an X element.

[0028] The raw material powder may contain at least two or more elements selected from Li, P, S, and X in one compound. For example, the raw material powder may be a compound containing Li and X, a compound containing P and S, a compound containing Li and S, a compound containing P and X, or a compound containing S and X. An example of the compound containing Li and X is lithium halide. An example of the compound containing P and S is diphosphorus trisulfide (P ２ S ３ ) and diphosphorus pentasulfide (P ２ S ５ As a compound containing Li and S, for example, lithium sulfide (Li ２ As a compound containing P element and X element, for example, PX ３ and P ２ X ５ Examples of compounds containing S and X elements include SX ２ , SX ４ , SX ６ , S ２ X １０ Sulfur halides such as the following can be used.

[0029] The raw material powders are preferably subjected to a pulverization process before being mixed to adjust the particle size to a predetermined size. For pulverization, a media agitation mill such as a ball mill or a bead mill can be used.

[0030] After the grinding of the raw material powders is completed, the raw material powders are mixed to obtain a raw material composition. The raw material powders are preferably mixed in a ratio that will result in the composition of the elements in the target solid electrolyte. The raw material powders are also preferably mixed using a media stirring mill.

[0031] Next, the raw material composition is subjected to a calcination process to cause a solid-state reaction and obtain a crystalline calcined product. The calcination atmosphere can be, for example, an inert gas atmosphere such as an argon atmosphere or a nitrogen atmosphere, or a hydrogen sulfide atmosphere. From the viewpoint of adjusting the ratio of sulfur element contained in the core particles, it is preferable to use an inert gas atmosphere.

[0032] From the viewpoint of ensuring that a solid-phase reaction of the raw material composition occurs, the firing temperature is, for example, preferably 200° C. or higher, more preferably 300° C. or higher, even more preferably 350° C. or higher, and even more preferably 400° C. or higher. On the other hand, in consideration of industrial producibility and economic efficiency, the firing temperature is, for example, preferably 700° C. or lower, more preferably 600° C. or lower, and even more preferably 550° C. or lower.

[0033] The firing time is not critical, and may be any time that allows a fired product of the desired composition to be obtained. Specifically, the firing time is preferably long enough for the solid-phase reaction of the raw material composition to occur sufficiently. The firing time may be, for example, 30 minutes or more, 2 hours or more, or 3 hours or more. On the other hand, the firing time may be, for example, 10 hours or less, or 5 hours or less.

[0034] After firing, the fired product is crushed or pulverized as necessary, and further classified as necessary to adjust the particle size to a predetermined particle size. In particular, the volume cumulative particle size D at 50% cumulative volume by a laser diffraction / scattering particle size distribution measurement method is ５０ It is preferable to adjust the particle size of the fired product so that the particle size is 0.5 μm or more and 0.9 μm or less, particularly 0.65 μm or more and 0.75 μm or less. This allows the desired core particles to be obtained.

[0035] The core particles thus prepared are mixed with ammonium halide particles. Either dry or wet mixing may be used for the mixing. From the viewpoint of obtaining a solid electrolyte with high lithium ion conductivity, dry mixing is advantageous. For dry mixing, a media-agitating mill such as a ball mill or a bead mill may be used.

[0036] From the viewpoint of successfully obtaining a solid electrolyte in which hydrogen sulfide generation is suppressed, the mixing ratio of the core particles and the ammonium halide particles is preferably 1.0 mass% or more, more preferably 2.0 mass% or more, and even more preferably 3.0 mass% or more, relative to the total amount of the core particles and the ammonium halide particles. Also, the ratio of the ammonium halide particles relative to the total amount of the core particles and the ammonium halide particles is preferably 20.0 mass% or less, more preferably 10.0 mass% or less, and even more preferably 5.0 mass% or less.

[0037] Examples of the ammonium halide to be mixed with the core particles include ammonium fluoride, ammonium chloride, ammonium bromide, and ammonium iodide. These ammonium halides can be used alone or in combination of two or more.

[0038] It is preferable that the particle size of the ammonium halide is controlled in order to successfully produce the desired solid electrolyte. Specifically, the volume cumulative particle size D at 50% by volume of the cumulative volume of the core particles measured by a laser diffraction / scattering particle size distribution measurement method is ５０ D Ｃ and the volume cumulative particle size D at 50% by volume of the cumulative volume of ammonium halide particles measured by a laser diffraction / scattering particle size distribution measurement method. ５０ D Ａ When this is done, D Ｃ / D Ａ The value of D is preferably 0.002 or more, more preferably 0.01 or more, and even more preferably 0.03 or more. Ｃ / D Ａ The value of is preferably 1.5 or less, more preferably 0.15 or less, and even more preferably 0.07 or less. By adjusting the particle size of the core particle and the particle size of the ammonium halide in this manner, solid electrolyte particles in which N element is concentrated on and near the surface can be successfully produced.

[0039] Particle size D of ammonium halide particles ＡThe value 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.

[0040] [Step B] In this step, the mixture of core particles and ammonium halide particles obtained in step A is subjected to a calcination process. The calcination process causes the S element in the core particles to react with the H element in the ammonium halide, resulting in the S element being released as hydrogen sulfide. This reduces the amount of S element on the surface and near the surface of the resulting solid electrolyte particles. This suppresses the generation of hydrogen sulfide from the solid electrolyte. Furthermore, as a result of the reaction between the S element in the core particles and the H element in the ammonium halide, a coating of a compound containing N element is formed on the surface of the core particles. This also suppresses the generation of hydrogen sulfide from the solid electrolyte. Furthermore, as a result of the reaction between the S element in the core particles and the H element in the ammonium halide, lithium halide is formed on the surface of the core particles. This also suppresses the generation of hydrogen sulfide from the solid electrolyte. This mechanism of action allows the generation of hydrogen sulfide to be suppressed more effectively than ever before while maintaining a high level of ionic conductivity of the solid electrolyte.

[0041] The firing temperature in this step is preferably 120° C. or higher, particularly 150° C. or higher, and especially 190° C. or higher, from the viewpoint of successfully removing the S element from the surface of the core particle and successfully forming a layer where the N element and lithium halide are concentrated on the surface of the core particle. Furthermore, the firing temperature is preferably 300° C. or lower, particularly 250° C. or lower, and especially 210° C. or lower, from the viewpoint of not impairing the lithium ion conductivity of the core particle.

[0042] The firing time is not critical as long as a solid electrolyte having a desired composition is obtained. Specifically, provided that the firing temperature is within the above-mentioned range, the firing time may be, for example, 1 hour or more, 2 hours or more, or 4 hours or more. On the other hand, the firing time may be, for example, 20 hours or less, 10 hours or less, or 6 hours or less.

[0043] The firing atmosphere is preferably an inert gas atmosphere such as nitrogen gas or a rare gas such as argon gas or helium gas.

[0044] After firing, the fired product may be crushed or pulverized as necessary, and may further be classified as necessary, to obtain the desired solid electrolyte powder.

[0045] The solid electrolyte thus obtained 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 for constituting a lithium battery, such as a solid electrolyte layer, a positive electrode layer, or a negative electrode layer.

[0046] Specifically, the solid electrolyte of the present invention can be used in a 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. In other words, the solid electrolyte can be used in so-called solid-state batteries. More specifically, it can be used in lithium solid-state batteries. The lithium solid-state battery may be a primary battery or a secondary battery. There is no particular limitation on the shape of the battery, and shapes such as a laminated type, a cylindrical type, and a prismatic type can be adopted. The term "solid-state battery" includes not only solid-state batteries that do not contain any liquid or gel-like substance as an electrolyte, but also batteries that contain, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of a liquid or gel-like substance as an electrolyte.

[0047] When the solid electrolyte layer contains the solid electrolyte of the present invention, the solid electrolyte layer can be produced, for example, by dropping a slurry consisting of the solid electrolyte, a binder, and a solvent onto a substrate and scraping it off with a doctor blade or the like, by contacting the substrate with the slurry and then cutting it with an air knife, or by forming a coating film by screen printing or the like and then heating and drying to remove the solvent. Alternatively, the solid electrolyte can be produced by compacting a powdered solid electrolyte by pressing or the like and then appropriately processing it. The thickness of the solid electrolyte layer is typically preferably 5 μm to 300 μm, and more preferably 10 μm to 100 μm, in order to balance short-circuit prevention and volumetric capacity density.

[0048] The solid electrolyte of the present invention can also be used together with an active material to form an electrode mixture. The proportion of the solid electrolyte in the electrode mixture is typically 10% by mass or more and 50% by mass or less. The electrode mixture may contain other materials such as a conductive material as needed. An electrode mixture, a binder, and a solvent are mixed to form a paste, which is then applied to a current collector such as aluminum foil and dried to form electrodes such as a positive electrode and a negative electrode.

[0049] The cathode material constituting the cathode layer can be any cathode material used as a cathode active material in lithium-ion batteries. For example, lithium-containing cathode active materials, specifically spinel-type lithium transition metal oxides and lithium metal oxides with layered structures, can be used. The use of a high-voltage cathode material as the cathode material can improve energy density. In addition to the cathode active material, the cathode material may contain a conductive material or other materials.

[0050] As the negative electrode material constituting the negative electrode layer, a negative electrode material used as a negative electrode active material in a lithium ion battery can be appropriately used. Since the solid electrolyte of the present invention is electrochemically stable, it can be used at a potential of lithium metal or a lower potential comparable to that of lithium metal (about 0.1 V vs. Li ＋ Carbonaceous materials such as graphite, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon), which are materials that are charged and discharged using a lithium-ion battery (Li / Li), can be used as the negative electrode material. This can significantly improve the energy density of solid-state batteries. Silicon or tin, which are promising high-capacity materials, can also be used as the active material. The negative electrode material may also contain a conductive material or other materials in addition to the negative electrode active material.

[0051] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0052] [Example 1] [Step A] Lithium sulfide (Li ２ S) powder, diphosphorus pentasulfide (P ２ S ５ ) powder, lithium chloride (LiCl) powder, and lithium bromide (LiBr) powder were mixed with Li ５．４ P.S.４．４ Br ０．８ Cl ０．８ The raw material composition was then weighed and mixed to obtain a raw material composition. The raw material composition was fired at 500°C for 4 hours to obtain a fired product. The firing was carried out using a tubular electric furnace. Nitrogen gas with a purity of 100% was circulated through the electric furnace during firing. The fired product was then pulverized to obtain a powder of core particles (D ５０ The obtained core particle powder and ammonium chloride powder (D ５０ The powder mixture was dry-mixed with ammonium chloride (particle size: 250 μm) in a mortar until homogeneous. The proportion of ammonium chloride in the mixed powder was 10% by mass.

[0053] [Step B] The mixed powder was fired in a nitrogen atmosphere at 200° C. for 5 hours. The fired product was crushed in a mortar and the particle size was adjusted using a sieve with 53 μm openings to obtain the desired solid electrolyte powder.

[0054] [Example 2] D as ammonium chloride powder ５０ The solid electrolyte powder was obtained in the same manner as in Example 1 except for the above.

[0055] [Example 3] D as ammonium chloride powder ５０ The solid electrolyte powder was obtained in the same manner as in Example 1 except for the above.

[0056] [Example 4] D as ammonium chloride powder ５０ The core particle powder and the ammonium chloride powder were mixed for 1 hour using a dry particle compounding device NOB-MINI (manufactured by Hosokawa Micron Corporation). The rotor rotation speed was 6000 rpm. A solid electrolyte powder was obtained in the same manner as in Example 1, except for the above.

[0057] Comparative Example 1 In step B of Example 1, ammonium chloride powder was not used. Except for this, a solid electrolyte powder was obtained in the same manner as in Example 1. This solid electrolyte was obtained through the firing step in step B of Example 1.

[0058] Comparative Example 2 The core particles used in Example 1 were used as the solid electrolyte in this comparative example. This solid electrolyte did not undergo the firing step B in Example 1.

[0059] [Evaluation] The solid electrolytes obtained in the examples and comparative examples were evaluated for particle size D by the following method. ５０ and D ９５ The volume cumulative particle size (volume cumulative particle size at 95% cumulative volume) was measured using a laser diffraction / scattering particle size distribution measurement method. The nitrogen abundance ratio, nitrogen enrichment rate, LiX abundance ratio, and sulfur abundance ratio were also measured using the following methods. XRD measurements were also performed using the following methods. The XRD measurement results are shown in Figure 1. Furthermore, the lithium ion conductivity and hydrogen sulfide generation amount were measured using the following methods. The results are shown in Table 1 below.

[0060] [Particle size D ５０ and D ９５ Using an automatic sample feeder for a laser diffraction particle size distribution measurement device ("Microtorac SDC" manufactured by Nikkiso Co., Ltd.), the flow rate of the measurement sample containing the solid electrolyte was set to 50%, and the measurement sample containing the solid electrolyte was irradiated with 30 W ultrasonic waves for 60 seconds. Thereafter, the particle size distribution was measured using a laser diffraction particle size distribution measurement device "MT3000II" manufactured by Nikkiso Co., Ltd., and the particle sizes at which the cumulative volumes were 50% and 95% by volume were determined from the obtained volume-based particle size distribution chart, and these values ​​were respectively designated as D ５０ and D ９５ It was decided.

[0061] [Nitrogen Abundance Ratio, Nitrogen Enrichment Rate, LiX Abundance Ratio, and Sulfur Abundance Ratio] The surface of the sulfide solid electrolyte was measured using a VersaProbe III XPS device manufactured by ULVAC-PHI, Inc. The conditions used for the measurement were as follows: Excitation X-ray: Monochrome AlKα ray (1486.7 eV) Output: 50 W X-ray diameter: 200 μm Pass energy: 26 eV Photoelectron escape angle: 45° (Ar ion etching conditions) Acceleration voltage: 4 kV Sputtering area: 2 mm × 2 mm Sputtering rate: SiO ２ The peak intensity reading and quantitative value calculation were performed using data analysis software (ULVAC-PHI, Inc.'s "MultiPak Ver. 9.9"). Shirley was used as the background mode. Charge correction was performed by setting the binding energy of the hydrocarbon (C-H) peak in the C1s spectrum to 284.8 eV.

[0062] [XRD Measurement] Measurements were performed using a Malvern Panalytical tabletop X-ray diffractometer "Aeris" without exposure to air. The measurement conditions were as follows: - Radiation source: CuKα - Tube voltage: 40 kV - Tube current: 15 mA - Measurement method: Focusing method (reflection method) - Detector: One-dimensional semiconductor detector - Incident Soller slit: Soller slit 0.02 rad - Longitudinal limiting slit: 20 mm - Receiving Soller slit: 0.02 rad - Incident slit: 1 / 2° - Receiving slit: Open - Measurement range: 2θ = 10 to 105° - Step width: 0.01° - Scan speed: 1.67° / min. The background intensity obtained from the Kapton film in the non-exposed holder was subtracted before analyzing the measurement results.

[0063] [Lithium ion conductivity] The solid electrolyte was measured in a glove box purged with sufficiently dried Ar gas (dew point -60°C or lower) to obtain a lithium ion conductivity of about 6 t / cm. ２The pellets were subjected to uniaxial pressure molding under a load of 1000 kJ / cm2 and approximately 0.5 to 8 mm thick to prepare samples for measuring lithium ion conductivity. The lithium ion conductivity of the samples was measured using a Solartron 1255B impedance measuring device manufactured by Toyo Corporation. The measurements were performed by the AC impedance method at a temperature of 25°C and a frequency of 0.1 Hz to 1 MHz.

[0064] [Amount of Hydrogen Sulfide Generated] The amount of hydrogen sulfide generated from the solid electrolyte was measured using a detector tube. 2 mg of solid electrolyte was weighed into a metal container in a glove box purged with thoroughly dried Ar gas (dew point -60°C or less), and then placed in a sealed laminated film bag. A 1000 ml glass separable flask was placed in a thermo-hygrostat chamber maintained at room temperature (25°C) and a dew point of -30°C adjusted by mixing dry air and atmospheric air. The flask was then maintained until the interior of the flask was identical to the environment inside the thermo-hygrostat chamber. Next, the sealed bag containing the solid electrolyte was opened in the thermo-hygrostat chamber, and the solid electrolyte was quickly placed in the separable flask. The separable flask was then sealed. The amount of hydrogen sulfide generated from immediately after sealing until 30 minutes had elapsed was measured using a gas detector (Gastec No. 4LL) 30 minutes later.

[0065]

[0066] As is clear from the results shown in Table 1, the solid electrolytes obtained in each Example suppressed the generation of hydrogen sulfide while maintaining a high level of conductivity. Furthermore, as is clear from the results shown in Figure 1, the solid electrolytes obtained in each Example exhibited two diffraction peaks in the range of 2θ = 28° to 30° by XRD measurement. Of the two diffraction peaks, the one observed on the lower angle side is thought to be derived from lithium chloride, and the one observed on the higher angle side is thought to be derived from an argyrodite-type crystal structure.

[0067] As described above in detail, the present invention provides a solid electrolyte that can further suppress the generation of hydrogen sulfide compared to conventional solid electrolytes while maintaining a high level of ionic conductivity.

Claims

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

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

3. The value of the semi-quantitative value of nitrogen (N) element relative to the sum of the semi-quantitative values ​​of lithium (Li), phosphorus (P), sulfur (S), and halogen (X) elements at a sputtering time of 0 min measured by X-ray photoelectron spectroscopy is E １ The value of the semi-quantitative value of nitrogen (N) element relative to the sum of the semi-quantitative values ​​of lithium (Li), phosphorus (P), sulfur (S) and halogen (X) elements measured by X-ray photoelectron spectroscopy at a sputtering time of 10.5 minutes is defined as E ２ When this is done, E ２ / E １ The solid electrolyte according to claim 1 or 2, wherein the value of is 0.2 or less.

4. A solid electrolyte according to claim 1 or 2, in which the ratio of the sum of the semi-quantitative values ​​of lithium (Li) and halogen (X) to the semi-quantitative value of phosphorus (P) at a sputtering time of 0 min measured by X-ray photoelectron spectroscopy is 7.7 or more.

5. The solid electrolyte according to claim 1 or 2, which contains a crystalline phase having an argyrodite-type crystal structure.

6. A solid electrolyte according to claim 1 or 2, in which the ratio of the difference between the semi-quantitative values ​​of lithium (Li) and sulfur (S) to the semi-quantitative value of phosphorus (P) at a sputtering time of 0 min measured by X-ray photoelectron spectroscopy is 1.9 or more.

7. The solid electrolyte according to claim 1 or 2, wherein at least two diffraction peaks are observed in the range of 2θ=28° to 30° in an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα radiation.

8. An electrode mixture comprising the solid electrolyte according to claim 1 and an active material.

9. A solid electrolyte layer containing the solid electrolyte according to 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 producing a solid electrolyte, comprising: mixing core particles containing lithium (Li), phosphorus (P), sulfur (S), and a halogen (X) with ammonium halide particles to obtain a mixture; and heating the mixture to form a layer of concentrated nitrogen (N) on the surface of the core particles.

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