Solid sulfide electrolyte, method for producing the same, electrode composite and lithium-ion battery

Abstract

To provide: a solid sulfide electrolyte having high ionic conductivity and excellent shutdown performance; an electrode composite using the solid sulfide electrolyte; a battery using the solid sulfide electrolyte; and a method for producing the solid sulfide electrolyte.SOLUTION: A solid sulfide electrolyte has an argillodite-type crystal structure containing a complex anion, a lithium atom, a sulfur atom, and a phosphorus atom, wherein an angle to be shifted to a lower angle of a diffraction peak 2θSE, measured by an X-ray diffraction measurement method using a specified CuKα beam, is 0.001° or more. An electrode composite and a battery using the solid sulfide electrolyte, and a method for producing the electrolyte are also provided.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a sulfide solid electrolyte, a method for producing the same, an electrode mixture, and a lithium ion battery. [Background technology]

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become increasingly important. Traditionally, lithium-ion batteries used for such applications have used electrolytes containing flammable organic solvents. When a short circuit occurs inside a lithium-ion battery using an electrolyte, the resulting Joule heat can cause the battery to overheat. This heat can cause the lithium-ion battery to go into thermal runaway, potentially resulting in the electrolyte catching fire. For this reason, lithium-ion batteries using an electrolyte are equipped with a shutdown function that dissolves the separator and stops further discharge reactions when thermal runaway occurs.

[0003] By making lithium-ion batteries fully solid-state, flammable organic solvents are no longer necessary inside the battery, which simplifies safety devices and is highly productive, so batteries in which the electrolyte solution is replaced with a solid electrolyte layer are being developed. However, although thermal runaway can still occur in such lithium-ion batteries, because lithium-ion batteries do not require separators, a different countermeasure to thermal runaway is required compared to lithium-ion batteries that use electrolyte solutions. As the solid electrolyte layer, the use of sulfide solid electrolytes with high lithium ion conductivity (hereinafter simply referred to as ionic conductivity) has been considered. In particular, sulfide solid electrolytes containing an argyrodite crystal structure, which are excellent in ionic conductivity, are desired.

[0004] As a solid electrolyte material having shutdown performance, a solid electrolyte material containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, with the content of each of these atoms being within a specific range, has been disclosed (see, for example, Patent Document 1). Furthermore, sulfide solid electrolytes containing anions consisting of two or more atoms (hereinafter referred to as composite anions) are known (see, for example, Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-87525 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-27554 [Patent Document 3] US2021 / 0296690 publication Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a sulfide solid electrolyte having high ionic conductivity and excellent shutdown performance, an electrode composite using the sulfide solid electrolyte, a battery using the sulfide solid electrolyte, and a method for producing the sulfide solid electrolyte. [Means for solving the problem]

[0007] The sulfide solid electrolyte according to the present invention is A sulfide solid electrolyte having an argyrodite-type crystal structure containing a composite anion, lithium atoms, sulfur atoms, and phosphorus atoms, wherein the diffraction peak 2θ measured by the X-ray diffraction measurement method using the CuKα ray described below is SE The sulfide solid electrolyte has a low-angle shift angle of 0.001° or more. (X-ray diffraction measurement method) A mixture of Li7PS6, which is a standard substance, and the sulfide solid electrolyte (the mixture ratio is Li7PS6:sulfide solid electrolyte=10 parts by mass:90 parts by mass) is used as a measurement sample, and X-ray diffraction measurement is performed on the measurement sample using CuKα radiation. The diffraction peak corresponding to the diffraction peak appearing at 2θ=30.0° due to the Li7PS6 crystal structure of the sulfide solid electrolyte is calculated as 2θ=30.0°. SE The standard material Li7PS6 has a 2θ of 30.0° and the 2θ SE The difference between these is the angle to be shifted to the lower angle side.

[0008] The method for producing a sulfide solid electrolyte according to the present invention is a method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure, which method includes mixing a raw material containing a lithium atom, a sulfur atom, and a phosphorus atom, a salt of a composite anion, and a solvent, removing the solvent, and heating. The electrode mixture according to the present invention is an electrode mixture containing the sulfide solid electrolyte and an electrode active material. The lithium ion battery according to the present invention is a lithium ion battery including at least one of the sulfide solid electrolyte and the electrode mixture. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a sulfide solid electrolyte having high ionic conductivity and excellent shutdown performance, an electrode composite using the sulfide solid electrolyte, a battery using the sulfide solid electrolyte, and a method for producing the sulfide solid electrolyte. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 4 is a conceptual diagram illustrating a method for calculating a shift angle. [Figure 2] FIG. 1 is a flow diagram illustrating a preferred embodiment of a method for producing a sulfide solid electrolyte according to the present embodiment. [Figure 3] 1 shows XRD patterns of sulfide solid electrolytes produced in Examples 1 to 7 and Comparative Example 1. [Figure 4]1 is an enlarged view of the XRD patterns of the sulfide solid electrolytes produced in Examples 1 to 7 and Comparative Example 1 around 2θ=30.0°. [Figure 5] 10 is a CV curve used to evaluate the irreversible capacity of the lithium ion battery produced in Example 14. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of a range of values ​​expressed as "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values.

[0012] (Findings gained by the inventors to arrive at the present invention) As a result of extensive research aimed at solving the above problems, the present inventors have discovered the following and have completed the present invention. The solid electrolyte described in Patent Document 1 is one in which the content ratio of lithium ions, sulfur ions, phosphorus ions, and halogen ions contained in the solid electrolyte has been investigated, but the ionic conductivity is not high and the shutdown performance is not sufficient.

[0013] Patent Documents 2 and 3 discuss the introduction of composite anions into solid electrolytes, but do not evaluate the shutdown performance because they do not aim to achieve shutdown performance using composite anions. Furthermore, the solid electrolyte described in Patent Document 2 contains a thiolisicone-like crystal phase, and therefore differs from the sulfide solid electrolyte of the present embodiment, which contains an argyrodite-type crystal structure. Patent Document 3 shows the results of X-ray diffraction measurements of the solid electrolyte using CuKα radiation in Figures 3a to 3c. However, these do not show peaks corresponding to 2θ = 18.0°, 30.0°, and 31.4°, which are characteristic of the argyrodite-type crystal structure. Therefore, the solid electrolyte described in Patent Document 3 is considered to have a structure different from the argyrodite-type crystal structure of the present invention. Furthermore, the method described in the examples of Patent Document 3 is considered to be unable to produce a solid electrolyte having an argyrodite-type crystal structure, based on the content ratio of lithium ions, sulfur ions, phosphorus ions, and halogen ions in the solid electrolyte, which is assumed from the raw materials used. From the above, it is assumed that the solid electrolyte described in Patent Document 3 is not a sulfide solid electrolyte having an argyrodite-type crystal structure.

[0014] In sulfide solid electrolytes containing the Li7PS6 crystal structure, a diffraction peak due to the argyrodite-type crystal structure appears at 2θ=30.0°. The inventors have discovered that when a sulfide solid electrolyte contains a composite anion, the peak corresponding to the diffraction peak at 2θ=30.0° of a sulfide solid electrolyte containing the Li7PS6 crystal structure is shifted to a lower angle while maintaining the argyrodite-type crystal structure. The inventors have discovered that a sulfide solid electrolyte shifted to a lower angle in this manner suppresses the decrease in ionic conductivity and has excellent shutdown performance. As will be described later, the Li7PS6 crystal structure is known to have diffraction peaks other than those at 2θ=30.0°. However, focusing on the peak that appears at 2θ=30.0° and shifting this to the lower angle side, it was discovered that a sulfide solid electrolyte can achieve both high ionic conductivity and excellent shutdown performance, a phenomenon that had not previously been recognized.

[0015] In this specification, "shutdown performance" means the ability of a lithium-ion battery to stop thermal runaway by causing the sulfide solid electrolyte to degrade due to the heat generated, thereby interrupting the chain of abnormal reactions in the lithium-ion battery and suppressing further heat generation, thereby stopping the thermal runaway. A lithium-ion battery having shutdown performance is preferable because it allows the safe use of electronic devices and the like equipped with the battery. Although the reason why the inclusion of the composite anion results in the development of shutdown performance is unclear, it is thought that the composite anion decomposes due to heat, and the resulting decomposition products of the composite anion disrupt the crystalline structure that provides ionic conductivity, thereby restricting the movement of lithium ions in the sulfide solid electrolyte and suppressing thermal runaway. The temperature at which the composite anion decomposes to develop shutdown performance can be evaluated as the decomposition onset temperature, which will be described later.

[0016] The sulfide solid electrolytes according to the first to fifth aspects of this embodiment, the methods for producing the sulfide solid electrolytes according to the sixth to tenth aspects, the electrode composites according to the eleventh and twelfth aspects, and the lithium ion battery according to the thirteenth aspect will be described below.

[0017] The sulfide solid electrolyte according to the first aspect of the present embodiment is A sulfide solid electrolyte having an argyrodite-type crystal structure containing a composite anion, lithium atoms, sulfur atoms, and phosphorus atoms, wherein the diffraction peak 2θ measured by the X-ray diffraction measurement method using the CuKα ray described below is SE The sulfide solid electrolyte has a low-angle shift angle of 0.001° or more. (X-ray diffraction measurement method) A mixture of Li7PS6, which is a standard substance, and the sulfide solid electrolyte (the mixture ratio is Li7PS6:sulfide solid electrolyte=10 parts by mass:90 parts by mass) is used as a measurement sample, and X-ray diffraction measurement is performed on the measurement sample using CuKα radiation. The diffraction peak corresponding to the diffraction peak appearing at 2θ=30.0° due to the Li7PS6 crystal structure of the sulfide solid electrolyte is calculated as 2θ=30.0°. SEThe standard material Li7PS6 has a 2θ of 30.0° and the 2θ SE The difference between these is the angle to be shifted to the lower angle side. A Li7PS6 crystal structure that does not contain a composite anion is an argyrodite-type crystal structure, but the sulfide solid electrolyte of this embodiment contains an argyrodite-type crystal structure, but by containing a composite anion, the diffraction peak at 2θ = 30.0° attributable to the argyrodite-type crystal structure of the Li7PS6 crystal structure is shifted to a lower angle. A sulfide solid electrolyte having a peak shifted to a lower angle as described above has high ionic conductivity and excellent shutdown performance. The sulfide solid electrolyte will be described later.

[0018] In this specification, the term "shift to a lower angle" refers to the shift of the diffraction peak at 2θ=30.0° of the Li7PS6 crystal structure not containing the composite anion (the diffraction peak at 2θ=30.0° of the Li7PS6 standard material) to a lower angle due to the sulfide solid electrolyte containing the composite anion described below. SE ) is 0.001° or greater. The diffraction angle 2θ depends on the lattice spacing d of the material, and according to the Bragg equation, as 2θ decreases, d increases. A shift in 2θ to a lower angle means that although the argyrodite-type crystal structure is maintained, the crystal structure of the argyrodite-type crystal structure has changed, and d has increased due to the complex anions that make up the crystal structure.

[0019] In other words, the sulfide solid electrolyte of this embodiment can be said to be a sulfide solid electrolyte containing a specific atom, in which the diffraction peak corresponding to the diffraction peak appearing at 2θ=30.0° of the standard substance Li7PS6 is shifted to a lower angle side due to the inclusion of a composite anion. When a sulfide solid electrolyte contains halogen atoms in its crystal structure, the diffraction peak that appears at 2θ=30.0° of the Li7PS6 crystal structure shifts to a higher angle. Therefore, the "shift to a lower angle" when a sulfide solid electrolyte that does not contain a composite anion contains halogen atoms means that the diffraction peak shifts to a lower angle due to the inclusion of a composite anion, compared to the diffraction peak corresponding to 2θ=30.0° of the Li7PS6 crystal structure of a sulfide solid electrolyte that contains halogen atoms but does not contain a composite anion.

[0020] FIG. 3 shows the XRD pattern of this embodiment. A conceptual diagram illustrating a method for calculating the shift angle, enlarging the area around 2θ=30.0°, is shown in FIG. 1. XRD pattern 1 of a sulfide solid electrolyte (Li7PS6 crystal structure) that does not contain a composite anion and XRD pattern 2 of a sulfide solid electrolyte of this embodiment that contains a composite anion, are shown. The absolute value of the difference between diffraction peak 4, which appears at 2θ=30.0° in the Li7PS6 crystal structure and is due to the argyrodite-type crystal structure, and diffraction peak 5, which corresponds to the diffraction peak of the sulfide solid electrolyte of this embodiment that contains a composite anion, is the shift angle 6 (the "angle shifted to a lower angle" described above, also referred to as the "shift angle" hereinafter, in degrees). Diffraction peak 5 appears at a lower angle than diffraction peak 4. Due to the inclusion of a composite anion, diffraction peak 5 is shifted to a lower angle than diffraction peak 4. In other words, the diffraction peak of the sulfide solid electrolyte containing the composite anion, which corresponds to the diffraction peak at 2θ = 30.0° due to the argyrodite-type crystal structure of the Li7PS6 crystal structure of the sulfide solid electrolyte containing no composite anion, is shifted to a lower angle. Since XRD patterns are measurements that may contain errors, the influence of errors can be reduced by calculating the shift angle using XRD pattern 3 of the sulfide solid electrolyte containing the composite anion and containing Li7PS6 as an internal standard. The peaks in XRD pattern 3 can be identified by referring to XRD patterns 1 and 2. This allows the peak position of the diffraction peak at 2θ = 30.0° that corresponds to the diffraction peak due to the Li7PS6 crystal structure to be determined. When the sulfide solid electrolyte contains halogen atoms in its crystal structure, the shift angle is defined based on the diffraction peak that appears at 2θ=30.0° and corresponds to the diffraction peak attributable to the Li7PS6 crystal structure. The XRD pattern using CuKα radiation can be obtained, for example, by the method described in the Examples.

[0021] As used herein, the term "comprising a composite anion" means that the sulfide solid electrolyte contains a composite anion, which will be described later. "Comprising" means that the composite anion is incorporated into the argyrodite-type crystal structure as a component constituting the crystal structure. As used herein, the term "composite anion" means an anion containing multiple types of atoms.

[0022] When the sulfide solid electrolyte contains lithium atoms, sulfur atoms, and phosphorus atoms, the sulfide solid electrolyte has ionic conductivity due to the lithium atoms, and the ionic conductivity is preferably high.

[0023] The sulfide solid electrolyte according to the second aspect of the present embodiment is the same as that according to the first aspect, The sulfide solid electrolyte further contains halogen atoms. By including halogen atoms, the sulfide solid electrolyte preferably includes a stable argyrodite-type crystal structure.

[0024] The sulfide solid electrolyte according to the third aspect of the present embodiment is, in the first or second aspect, The sulfide solid electrolyte has an angle shifted to the lower angle side of 0.001° or more and 1.0° or less. The angle of this shift to the lower angle side, i.e., the shift angle, depends on the type and content of the composite anion in the sulfide solid electrolyte. As described above, the shift angle is 0.001° or more, and the upper limit is 1.0° or less (a shift angle of 0.001° or more and 1.0° or less), which is preferable because it exhibits excellent shutdown performance.

[0025] The sulfide solid electrolyte according to the fourth aspect of the present embodiment is any one of the first to third aspects, The sulfide solid electrolyte has a content of the composite anion of 0.20 mol or less per 1.0 mol of lithium atoms contained in the sulfide solid electrolyte. This range is preferable because the sulfide solid electrolyte exhibits high ionic conductivity.

[0026] The sulfide solid electrolyte according to a fifth aspect of the present embodiment is any one of the first to fourth aspects, The composite anion is NO3 - , SO4 2- , CO3 2- , CO 2- and BF4 - The sulfide solid electrolyte is at least one selected from the following: The composite anion having the above structure or a combination thereof is preferable because, when used as a component of a lithium ion battery, even if the lithium ion battery experiences thermal runaway, the composite anion is decomposed by the generated heat, thereby stopping the thermal runaway and exhibiting excellent shutdown performance. Furthermore, composite anions having these structures are preferable because they are less susceptible to decomposition due to heating during the production of a sulfide solid electrolyte, as described below.

[0027] A method for producing a sulfide solid electrolyte according to a sixth aspect of the present embodiment includes: A method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure, the method comprising mixing a raw material containing lithium atoms, sulfur atoms, and phosphorus atoms, a salt of a composite anion, and a solvent, removing the solvent, and heating. The sulfide solid electrolyte according to the first to fifth aspects can be produced by the method for producing a sulfide solid electrolyte according to the sixth aspect of the present embodiment. According to the above-described production method, by using a salt of a composite anion together with the raw material ingredients in the conventional production process of a sulfide solid electrolyte, it is possible to produce a sulfide solid electrolyte containing the composite anion in its crystal structure.

[0028] A method for producing a sulfide solid electrolyte according to a seventh aspect of the present embodiment is the same as the method for producing a sulfide solid electrolyte according to the sixth aspect, The composite anion is NO3 - , SO4 2- , CO3 2- , CO 2- and BF4 - The present invention provides a method for producing at least one sulfide solid electrolyte selected from the following: When the composite anion has the above structure, the sulfide solid electrolyte according to the fifth aspect can be easily obtained, which is preferable.

[0029] The method for producing a sulfide solid electrolyte according to an eighth aspect of the present embodiment is the same as the method for producing a sulfide solid electrolyte according to the sixth or seventh aspect, The method for producing a sulfide solid electrolyte is one in which the solvent contains a complexing agent that forms a complex with the raw material ingredients. By including a complexing agent, which will be described later, a complex containing the complexing agent is formed, and through this complex, PS4 3- This is preferable because the units can be selectively synthesized and the amount of energy required for their production can be reduced. The solvent preferably contains a complexing agent that forms a complex with the raw material ingredients, and a solvent that dissolves all or part of the raw material ingredients, such as lithium halide, that are used as needed. This is preferable because all or part of the raw material ingredients and the salt of the composite anion are dissolved, and the reaction rate is increased. In addition, when a complex is used, high temperatures are not required in the production process, and PS4 3- Then, if necessary, the solvent described below is distilled off and the complexing agent described below is removed, whereby a sulfide solid electrolyte having an argyrodite phase can be produced. The use of a complexing agent in this manner eliminates the need for high-temperature heating during the production process, which would decompose the composite anion, and is therefore preferred because it can suppress decomposition of the composite anion and allows the sulfide solid electrolyte to exhibit excellent shutdown performance.

[0030] A ninth aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to any one of the sixth to eighth aspects, In the method for producing a sulfide solid electrolyte, the solubility of the salt of the composite anion in the solvent is 10 g / L or more. When the solubility of the salt of the composite anion in the solvent is within the above range, the salt of the composite anion dissolves in the solvent when the raw material ingredients, the salt of the composite anion, and the solvent are mixed, and the salt of the composite anion is easily incorporated into the sulfide solid electrolyte, which is preferable. Dissolving the salt of the composite anion in the solvent is preferable because a sufficient amount of the composite anion is incorporated into the sulfide solid electrolyte in a short period of time.

[0031] A tenth aspect of the present embodiment relates to a method for producing a sulfide solid electrolyte according to any one of the sixth to ninth aspects, In this method for producing a sulfide solid electrolyte, the solvent removal and the heating are carried out at 250°C or less. It is preferable to carry out the solvent removal and the heating at 250° C. or less, since this can suppress decomposition of the composite anion and allows the sulfide solid electrolyte to exhibit excellent shutdown performance.

[0032] The electrode mixture according to an eleventh aspect of this embodiment is An electrode composite comprising the sulfide solid electrolyte according to any one of the first to fifth aspects and an electrode active material. The sulfide solid electrolyte according to the first to fifth aspects is a sulfide solid electrolyte having high ionic conductivity and excellent shutdown performance, and an electrode mixture using this has excellent shutdown performance and is preferable because it results in excellent battery characteristics.

[0033] An electrode mixture according to a twelfth aspect of the present embodiment is the electrode mixture according to the eleventh aspect, An electrode composite includes the sulfide solid electrolyte according to any one of the first to fifth aspects, at least one sulfide solid electrolyte different from the sulfide solid electrolyte, and an electrode active material. In addition to the sulfide solid electrolytes according to the first to fifth aspects, at least one sulfide solid electrolyte different from the sulfide solid electrolytes is contained, which further improves ionic conductivity, and thus a lithium ion battery using this has excellent battery characteristics, which is preferable.

[0034] A lithium ion battery according to a thirteenth aspect of the present embodiment comprises: A lithium ion battery comprising at least one of the sulfide solid electrolyte according to the first to fifth aspects and the electrode mixture according to the eleventh or twelfth aspect. The sulfide solid electrolyte and the electrode mixture have excellent properties as described above, and therefore an electrode mixture using them has excellent shutdown performance and excellent battery properties, which is preferable.

[0035] Hereinafter, the sulfide solid electrolyte, the method for producing the sulfide solid electrolyte, the electrode mixture, and the lithium ion battery of this embodiment will be described in more detail based on the above-mentioned embodiments.

[0036] [Sulfide solid electrolyte containing argyrodite-type crystal structure] The sulfide solid electrolyte having an argyrodite-type crystal structure in this embodiment is required to have a diffraction peak in which the diffraction peak appearing at 2θ=30.0° corresponding to the diffraction peak attributable to the Li7PS6 crystal structure is shifted to a lower angle in X-ray diffraction measurement using CuKα rays, and to be a sulfide solid electrolyte having an argyrodite-type crystal structure composed of a composite anion, lithium atoms, sulfur atoms, and phosphorus atoms. The shift to the low angle side is as described above.

[0037] The sulfide solid electrolyte having an argyrodite-type crystal structure is a crystalline sulfide solid electrolyte, and in an X-ray diffraction pattern, peaks derived from the solid electrolyte are observed. It is a material that does not require the presence or absence of peaks derived from the raw materials (raw material inclusions) of the sulfide solid electrolyte. That is, it contains a crystal structure derived from the argyrodite-type crystal structure, and a portion of the crystal structure may be derived from the solid electrolyte, or the entire crystal structure may be derived from the solid electrolyte. Furthermore, as long as the sulfide solid electrolyte having an argyrodite-type crystal structure has the X-ray diffraction pattern described above, it may also contain an amorphous sulfide solid electrolyte (also referred to as a "glass component") as part of the crystal structure. Therefore, sulfide solid electrolytes having an argyrodite-type crystal structure include so-called glass ceramics obtained by heating an amorphous solid electrolyte (glass component) above its crystallization temperature.

[0038] In this specification, the amorphous sulfide solid electrolyte (glass component) refers to a solid electrolyte whose X-ray diffraction pattern is a halo pattern in which no peaks other than those derived from the material are observed in X-ray diffraction measurement, and it does not matter whether or not there are peaks derived from the raw materials (raw material contents) of the solid electrolyte.

[0039] In this specification, the term "solid electrolyte" refers to an electrolyte that remains solid at 25°C under a nitrogen atmosphere. The "sulfide solid electrolyte" of this embodiment must contain lithium atoms, sulfur atoms, and phosphorus atoms, and preferably further contains halogen atoms. By containing lithium atoms, the sulfide solid electrolyte becomes a solid electrolyte with ionic conductivity due to lithium ions.

[0040] <Mixed anions> The sulfide solid electrolyte having an argyrodite-type crystal structure in this embodiment must contain a composite anion. The composite anion is an anion containing multiple types of atoms, as described above. The atoms contained in the composite anion are preferably two or more atoms selected from sulfur atoms, oxygen atoms, nitrogen atoms, carbon atoms, boron atoms, hydrogen atoms, halogen atoms, and phosphorus atoms. However, composite anions containing only phosphorus atoms and sulfur atoms are excluded.

[0041] The complex anion is NO3 - , SO4 2- , CO3 2- , CO 2- and BF4 - It is more preferable that the compound is at least one selected from the following: To achieve both high ionic conductivity and excellent shutdown performance, NO3 - , SO4 2- and BF4 - More preferably, at least one selected from NO3 - and BF4 - At least one selected from the group consisting of NO3 - is particularly preferred.

[0042] The composite anion having the above structure is preferable because it decomposes due to heat generation during thermal runaway, providing excellent shutdown performance, and the sulfide solid electrolyte containing the composite anion exhibits high ionic conductivity. Furthermore, these structures suppress decomposition due to heating, which is performed as needed during the production of the sulfide solid electrolyte, and the produced sulfide solid electrolyte is preferable because it has high ionic conductivity and excellent shutdown performance.

[0043] If the content of the composite anion is 0.20 mol or less per 1.0 mol of lithium atoms contained in the sulfide solid electrolyte, the sulfide solid electrolyte will exhibit high ionic conductivity, which is preferable. The upper limit of the content of the composite anion is more preferably 0.18 mol or less, even more preferably 0.16 mol or less, even more preferably 0.14 mol or less, and particularly preferably 0.13 mol or less, in order to obtain high ionic conductivity.

[0044] The lower limit of the content of the composite anion is preferably 0.0010 mol or more, more preferably 0.0040 mol or more, even more preferably 0.0080 mol or more, still more preferably 0.0120 mol or more, and particularly preferably 0.0140 mol or more, in order to obtain excellent shutdown performance. The content of the composite anion can be determined, for example, by the method described in the Examples.

[0045] <Sulfide solid electrolyte> The sulfide solid electrolyte of this embodiment is required to have an argyrodite-type crystal structure composed of a composite anion, lithium atoms, sulfur atoms, and phosphorus atoms. From the viewpoint of obtaining higher ionic conductivity, it is preferable that the argyrodite-type crystal structure is contained as the main crystal. In this specification, "contains as the main crystal" means that the proportion of the target crystal structure in the crystal structure is 80% or more, preferably 90% or more, and more preferably 95% or more.

[0046] More specifically, the sulfide solid electrolyte of this embodiment is Li 7-xi PS 6-xi XI xi (wherein XI represents a monovalent composite anion, and xi is greater than 0 and less than or equal to 1.8) or Li7PS 6-xii XII xii(wherein XII represents a divalent composite anion, and xii is greater than 0 and not greater than 1.8). In these composition formulae, XI and XII may represent one type of composite anion, or two or more types of composite anions. Also, the composition may contain both XI and XII, in which case XI and XII are included so that the sum of xi and xii is not greater than 1.8.

[0047] In the above formula, XI represents a monovalent composite anion. In order to achieve both high ionic conductivity and excellent shutdown performance, NO3 - or BF4 - is more preferred, and NO3 - is even more preferred. XII represents a divalent complex anion, but in order to achieve both high ionic conductivity and excellent shutdown performance, SO4 2- , CO3 2- or CO 2- is preferred, and SO4 2- or CO3 2- is more preferred, and SO4 2- is more preferred.

[0048] In the above formula, xi corresponds to the content of monovalent composite anions in the sulfide solid electrolyte, and in order to achieve both high ionic conductivity and excellent shutdown performance, these values ​​are each independently preferably 0.01 or more and 1.40 or less, more preferably 0.05 or more and 1.20 or less, and even more preferably 0.10 or more and 1.00 or less. xii corresponds to the content of divalent composite anions in the sulfide solid electrolyte, and in order to achieve both high ionic conductivity and excellent shutdown performance, these are each independently preferably 0.01 or more and 1.40 or less, more preferably 0.05 or more and 1.20 or less, and even more preferably 0.10 or more and 1.00 or less.

[0049] <Argyrodite-type crystal structure and its diffraction peaks> Diffraction peaks of the argyrodite-based crystal structure of the Li7PS6 crystal structure appear, for example, near 2θ=15.3°, 17.7°, 30.0°, 31.1°, 44.9°, and 47.7°. The sulfide solid electrolyte of this embodiment also contains an argyrodite-type crystal structure and therefore has diffraction peaks corresponding to these, but the diffraction peak corresponding to 2θ=30.0° is shifted to a lower angle. In this specification, the peak position may vary within a range of 0.5°. Although the peak position of the diffraction peak may vary in this manner, by measuring a mixture containing a reference material and a sulfide solid electrolyte using the X-ray diffraction measurement method described above, the diffraction peak of the reference material Li7PS6 appearing at 2θ=30.0° and the peak of the Li7PS6 crystal structure of the sulfide solid electrolyte will vary in the same manner. Therefore, even if the peak position varies within the above range, the shift angle will not vary within a range of 0.5°.

[0050] The sulfide solid electrolyte of this embodiment has high ionic conductivity and excellent shutdown performance because the diffraction peak shifted to the low-angle side is shifted to the low-angle side by 0.001° or more. From the viewpoint of achieving even better shutdown performance, the lower limit of the shift angle is more preferably 0.002° or more, more preferably 0.005° or more, and even more preferably 0.010° ​​or more. In order to increase ionic conductivity, the upper limit of the shift angle is preferably 1.0° or less, more preferably 0.5° or less, even more preferably 0.2° or less, and even more preferably 0.15° or less.

[0051] The specific method for measuring the shift angle is the X-ray diffraction measurement method described above. A more detailed method will be described in the Examples section, but the shift angle can be determined by adding an internal standard (Li7PS6) to the measurement sample and performing XRD measurement. The shift angle can be determined by reading the 2θ of the diffraction peak due to the argyrodite-type crystal structure of the internal standard (Li7PS6) that appears at 2θ = 30.0° and the corresponding diffraction peak of the sulfide solid electrolyte containing the composite anion, and then calculating the difference between the two.

[0052] From the viewpoint of obtaining higher ionic conductivity, the sulfide solid electrolyte of this embodiment preferably does not contain crystalline Li3PS4 (β-Li3PS4). Whether or not a sulfide solid electrolyte contains crystalline Li3PS4 (β-Li3PS4) can be confirmed by the presence or absence of diffraction peaks at 2θ = 17.5° and 26.1° seen in crystalline Li3PS4. In this specification, a sulfide solid electrolyte is considered to contain crystalline Li3PS4 (β-Li3PS4) if it does not contain such diffraction peaks, or if it does contain such peaks, the peaks are extremely small compared to the diffraction peaks of the argyrodite-type crystal structure.

[0053] The shape of the sulfide solid electrolyte of this embodiment is not particularly limited, but may be, for example, particulate. The average particle diameter (D 50 ) is preferably 0.01 μm or more, more preferably 0.03 μm or more, even more preferably 50 μm or less, still more preferably 0.05 μm or more, and even more preferably 0.1 μm or more, since this determines the particle size of the solid electrolyte to be produced, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 10 μm or less, and even more preferably 3 μm or less, since a decrease in ionic conductivity can be suppressed.

[0054] (Other properties of sulfide solid electrolytes) The ionic conductivity of the sulfide solid electrolyte of this embodiment is typically 1.00 × 10 -5S / cm or more, and furthermore, 0.80×10 -4 S / cm or more, 1.00×10 -4 S / cm or more, 1.05×10 -4 S / cm or more, 1.08×10 -4 The upper limit is not particularly limited, and a higher value is preferable.

[0055] The upper limit of the decomposition start temperature of the composite anion contained in the sulfide solid electrolyte of this embodiment is preferably 230° C. or lower, more preferably 210° C. or lower, even more preferably 200° C. or lower, and even more preferably 190° C. or lower, in order to exhibit shutdown performance during thermal runaway. In order to suppress decomposition during normal use and improve the battery characteristics of the lithium ion battery, the lower limit is preferably 160° C. or higher, more preferably 170° C. or higher, even more preferably 175° C. or higher, and even more preferably 180° C. or higher.

[0056] (Amorphous sulfide solid electrolyte) The amorphous sulfide solid electrolyte contains lithium atoms, sulfur atoms, and phosphorus atoms, and preferably further contains halogen atoms. Typical examples include solid electrolytes composed of lithium sulfide and phosphorus sulfide, more preferably lithium halide, such as LiS-P2S5, LiS-P2S5-LiI, LiS-P2S5-LiCl, LiS-P2S5-LiBr, and LiS-P2S5-LiI-LiBr; and solid electrolytes containing other atoms such as oxygen atoms and silicon atoms, such as LiS-P2S5-Li2O-LiI and LiS-SiS2-P2S5-LiI. From the viewpoint of obtaining higher ionic conductivity, preferred examples of solid electrolytes include Li2S-P2S5, which is composed of lithium sulfide and phosphorus sulfide, and solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, and Li2S-P2S5-LiI-LiBr. The types of atoms constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0057] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D 50 ) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 to 200 μm.

[0058] [Method for producing sulfide solid electrolyte] The method for producing the sulfide solid electrolyte of this embodiment includes the steps of: The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure includes mixing a raw material containing lithium atoms, sulfur atoms, and phosphorus atoms, a salt of a composite anion, and a solvent, removing the solvent, and heating. According to the method for producing a sulfide solid electrolyte of the present embodiment, a sulfide solid electrolyte including the argyrodite-type crystal structure can be produced.

[0059] <Raw material content> The raw material contents of this embodiment must contain lithium atoms, sulfur atoms, and phosphorus atoms, but one or more compounds containing at least one atom selected from lithium atoms, sulfur atoms, and phosphorus atoms may be used. That is, in this embodiment, the Li7PS6 can be used as the raw material content, or two or more compounds containing at least one atom of lithium, sulfur, and phosphorus atoms, and optionally halogen atoms, can also be used as the raw material content. As described above, the sulfide solid electrolyte in this embodiment contains lithium, sulfur, and phosphorus atoms and a composite anion, and therefore raw materials for which two or more compounds are used contain alkali metal atoms, sulfur, and phosphorus atoms, and optionally halogen atoms.

[0060] Compounds that can be used as raw materials contain at least one atom of an alkali metal atom, a sulfur atom, a phosphorus atom, and, if necessary, a halogen atom. More specifically, alkali metal sulfides such as lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; alkali metal halides such as lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide, and sodium halides such as sodium iodide, sodium fluoride, sodium chloride, and sodium bromide; phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5); various phosphorus fluorides (PF3, PF5), various phosphorus chlorides (PCl3, PC Representative examples of the starting material include phosphorus halides such as thiophosphoryl fluoride (PSF3), thiophosphoryl chloride (PSCl3), thiophosphoryl bromide (PSBr3), thiophosphoryl iodide (PSI3), thiophosphoryl fluoride dichloride (PSCl2F), and thiophosphoryl fluoride dibromide (PSBr2F); and starting materials composed of at least two atoms selected from the above four types of atoms, such as fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2), with bromine (Br2) and iodine (I2) being preferred.

[0061] Examples of compounds that can be used as raw materials other than those mentioned above include compounds that contain at least one atom selected from the above four types of atoms and also contain atoms other than the four types of atoms, more specifically lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; metal sulfides such as silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, tin sulfide (SnS, SnS), aluminum sulfide, and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; metal halides such as aluminum halides, silicon halides, germanium halides, arsenic halides, selenium halides, tin halides, antimony halides, tellurium halides, and bismuth halides; and phosphorus oxyhalides such as phosphorus oxychloride (POCl3) and phosphorus oxybromide (POBr3).

[0062] In this embodiment, from the viewpoint of more easily obtaining a sulfide solid electrolyte having high ionic conductivity, a lithium atom is more preferred, and among halogen atoms, a chlorine atom, a bromine atom, and an iodine atom are preferred, with a bromine atom and an iodine atom being more preferred. These atoms may be used alone or in combination. From the same viewpoint, preferred compounds that can be used as raw materials include, among the above, alkali metal sulfides such as lithium sulfide and sodium sulfide; phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5); elemental halogens such as fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2); and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; among alkali metal sulfides, lithium sulfide is preferred; among phosphorus sulfides, diphosphorus pentasulfide is preferred; among elemental halogens, chlorine (Cl2), bromine (Br2), and iodine (I2) are preferred, with bromine (Br2) and iodine (I2) being more preferred; and among lithium halides, lithium chloride, lithium bromide, and lithium iodide are preferred, with lithium bromide and lithium iodide being more preferred.

[0063] Preferred examples of combinations of compounds that can be used as raw materials include a combination of lithium sulfide and diphosphorus pentasulfide, and when a compound containing a halogen atom is used, a combination of lithium sulfide, diphosphorus pentasulfide, and a lithium halide, and a combination of lithium sulfide, diphosphorus pentasulfide, and an elemental halogen. Preferred lithium halides include lithium bromide, lithium iodide, and lithium chloride, and preferred elemental halogens are bromine and iodine. In this embodiment, the alkali metal sulfides, alkali metal halides, halogen elements, and other compounds may be used alone or in combination of two or more of the above-mentioned examples.

[0064] In the present embodiment, when lithium sulfide is used as the compound containing an alkali metal, the lithium sulfide is preferably in the form of particles. The average particle size of lithium sulfide particles (D 50) is preferably 10 μm or more and 2000 μm or less, more preferably 30 μm or more and 1500 μm or less, and even more preferably 50 μm or more and 1000 μm or less. 50 ) is the particle size at which 50% of the total particle size is obtained by accumulating the particle size distribution curve from the smallest particle size, and the volume distribution is the average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution analyzer. Furthermore, among the above-mentioned examples of raw materials, solid raw materials preferably have an average particle size similar to that of the lithium sulfide particles, i.e., within the same range as that of the lithium sulfide particles.

[0065] When lithium sulfide and diphosphorus pentasulfide are used as the raw material ingredients, the ratio of lithium sulfide to the total of lithium sulfide and diphosphorus pentasulfide is preferably 60 mol% or more, more preferably 65 mol% or more, and even more preferably 68 mol% or more, in order to obtain high ionic conductivity and excellent shutdown performance, and furthermore, to obtain higher chemical stability, and the upper limit is preferably 80 mol% or less, more preferably 78 mol% or less, and even more preferably 76 mol% or less.

[0066] <Salts of mixed anions> The salt of the composite anion of this embodiment is preferably a salt of the composite anion and a cation described below. The composite anion is as described above. The cation may be an organic cation such as an ammonium ion or a pyrimidinium ion, but is preferably a metal ion because it can suppress a decrease in ionic conductivity and shutdown performance even if it remains in the produced sulfide solid electrolyte. It is preferably a metal ion corresponding to a metal atom contained in the raw material inclusion, and is particularly preferably a lithium ion.

[0067] More specifically, salts of complex anions include LiNO3, Li2SO4, Li2CO3, LiBF4, NaNO3, Na2SO4, Na2CO3, NaBF4, KNO3, K2SO4, K2CO3, KBF4, AgNO3, Ag2SO4, Ag2CO3, AgBF4, Pb(NO3)2, PbSO4, PbCO3, Pb(BF4)2, Sr(NO3)2, SrSO4, SrCO3, Sr(BF4)2, Ba(NO3)2, BaSO4, BaCO3, Ba(BF 4)2, NH4NO3, (NH4)2SO4, (NH4)2CO3 or NH4BF4 are preferred, LiNO3, Li2SO4, Li2CO3, LiBF4, NaNO3, Na2SO4, Na2CO3, NaBF4, KNO3, K2SO4, K2CO3 or KBF4 are more preferred, LiNO3, Li2SO4, Li2CO3 or LiBF4 are even more preferred, LiNO3, Li2SO4 or Li2BF4 are even more preferred, and LiNO3 is particularly preferred. These are preferably used alone or in combination, and are preferably used alone from the viewpoint of ease of the production process.

[0068] <Solvent> The solvent in this embodiment is preferably one or a mixture of two or more selected from a complexing agent that forms a complex with the raw material ingredients, a solvent that dissolves a salt of the composite anion, a solvent that dissolves lithium halide used as needed, and other solvents. As the solvent in this embodiment, various solvents broadly called organic solvents can be used.

[0069] These solvents are not clearly distinguished from one another, and the complexing agent may function as a solvent for dissolving the salt of the composite anion and / or a solvent for dissolving the lithium halide used as needed, or the solvent for dissolving the salt of the composite anion may function as a solvent for dissolving the lithium halide used as needed.

[0070] Two or more of these solvents may be used, but one solvent for dissolving the lithium halide and / or the salt of the composite anion and one complexing agent may simultaneously exhibit their respective effects. When two or more solvents are used in combination as the solvent, the solvent may be one that relatively exhibits the function as a complexing agent more strongly, one that relatively exhibits the function as a solvent for dissolving the salt of the composite anion more strongly, or one that relatively exhibits the function as a solvent for dissolving the lithium halide more strongly.

[0071] When the raw material contains lithium halide, the complexing agent may function as a solvent that dissolves lithium halide, or a solvent that dissolves a salt of a composite anion may function as a solvent that dissolves lithium halide. As the other solvent, a solvent in which the raw material ingredients and the salt of the composite anion have low solubility is preferred. The solvent of this embodiment preferably contains a complexing agent that forms a complex with the raw material ingredients, and this complexing agent may also function as a solvent that dissolves the salt of the composite anion.

[0072] When a solvent is used, the amount of solvent used is preferably 100 mL or more, more preferably 200 mL or more, even more preferably 250 mL or more, and even more preferably 300 mL or more per 1 kg of the total amount of the raw materials, and the upper limit is preferably 3000 mL or less, more preferably 2500 mL or less, even more preferably 2000 mL or less, and even more preferably 1550 mL or less. When the amount of solvent used is within the above range, the raw materials can be reacted efficiently.

[0073] The solvent varies depending on the type of solute, i.e., the raw material inclusion and the composite anion, but the solubility of the salt of the composite anion in the solvent at 25°C is preferably 10 g / L or more. A completely dissolved composite anion is preferred because it can be uniformly incorporated into the raw material inclusion in a short time. Depending on the amount of solvent used, the composite anion may not be completely dissolved, resulting in a slurry state. However, since the dissolved composite anion is incorporated into the sulfide solid electrolyte, the composite anion present as a solid is subsequently dissolved and incorporated into the sulfide solid electrolyte, and therefore the composite anion does not need to be completely dissolved.

[0074] The solubility of the salt of the composite anion in the solvent is preferably 13 g / L or more, more preferably 15 g / L or more. There is no particular upper limit, but in commonly used solvents, the solubility is often 30 g / L or less. In this specification, the solubility is defined as the saturation amount (g) of a salt of a complex anion per 1 L of a solvent.

[0075] (complexing agent) It is preferable that the solvent contains a complexing agent that forms a complex with the raw material ingredients, since this allows the sulfide solid electrolyte to be produced at a low temperature and prevents the composite anion from decomposing during the production. Furthermore, by using a complex compound as the raw material compound, the compound is mixed with a salt of the composite anion, and the mixed anion is uniformly incorporated into the sulfide solid electrolyte. The uniform presence of the mixed anion in the sulfide solid electrolyte allows the sulfide solid electrolyte as a whole to exhibit shutdown performance, which is preferable because even if thermal runaway or the like occurs, the chain reaction can be quickly broken.

[0076] The complexing agent is preferably a solvent containing an atom other than carbon or hydrogen, such as a heteroatom such as a nitrogen atom, oxygen atom, sulfur atom, or halogen atom. Preferred examples of the complexing agent include ether solvents, ester solvents, alcohol solvents, aldehyde solvents, and ketone solvents containing an oxygen atom as a heteroatom.

[0077] Preferred examples of the ether solvent include aliphatic ethers such as dimethyl ether, diethyl ether, tert-butyl methyl ether, dimethoxymethane, dimethoxyethane, diethylene glycol dimethyl ether (diglyme), triethylene oxide glycol dimethyl ether (triglyme), diethylene glycol, and triethylene glycol; alicyclic ethers such as ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, and dioxane; heterocyclic ethers such as furan, benzofuran, and benzopyran; and aromatic ethers such as methyl phenyl ether (anisole), ethyl phenyl ether, dibenzyl ether, and diphenyl ether.

[0078] Preferred examples of the ester solvent include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, and isopropyl acetate; aliphatic esters such as methyl propionate, ethyl propionate, dimethyl oxalate, diethyl oxalate, dimethyl malonate, diethyl malonate, dimethyl succinate, and diethyl succinate; alicyclic esters such as methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, and dimethyl cyclohexanedicarboxylate; heterocyclic esters such as methyl pyridinecarboxylate, methyl pyrimidinecarboxylate, acetolactone, propiolactone, butyrolactone, and valerolactone; and aromatic esters such as methyl benzoate, ethyl benzoate, dimethyl phthalate, diethyl phthalate, butyl benzyl phthalate, dicyclohexyl phthalate, trimethyl trimellitate, and triethyl trimellitate.

[0079] Preferred examples of the solvent include alcohol solvents such as ethanol and butanol; aldehyde solvents such as formaldehyde, acetaldehyde and dimethylformamide; and ketone solvents such as acetone and methyl ethyl ketone. These alcohol-based solvents, aldehyde-based solvents, and ketone-based solvents function as complexing agents, but are also preferred as solvents for dissolving lithium halide, which is used as needed. Therefore, when used in combination with an ester solvent as a complexing agent, the PS4 complexed by the ester solvent can be easily dissolved. 3- However, an alcohol-based solvent is preferred because it smoothly forms an argyrodite phase with the lithium halide dissolved in the alcohol-based solvent, etc. The alcohol-based solvent is also preferred as a solvent for dissolving the salt of the composite anion, as will be described in detail later. The alcohol-based solvent is also useful as a solvent for dissolving the salt of the composite anion described below, and serves as both a solvent for dissolving lithium halide and a solvent for dissolving the salt of the composite anion.

[0080] Examples of solvents containing a nitrogen atom as a heteroatom include solvents having a group containing a nitrogen atom, such as an amino group, an amide group, a nitro group, or a nitrile group. Preferred examples of solvents having an amino group include aliphatic amines such as ethylenediamine, diaminopropane, dimethylethylenediamine, diethylethylenediamine, dimethyldiaminopropane, tetramethyldiaminomethane, tetramethylethylenediamine (TMEDA), and tetramethyldiaminopropane (TMPDA); alicyclic amines such as cyclopropanediamine, cyclohexanediamine, and bisaminomethylcyclohexane; heterocyclic amines such as isophoronediamine, piperazine, dipiperidylpropane, and dimethylpiperazine; and aromatic amines such as phenyldiamine, tolylenediamine, naphthalenediamine, methylphenylenediamine, dimethylnaphthalenediamine, dimethylphenylenediamine, tetramethylphenylenediamine, and tetramethylnaphthalenediamine. Preferred examples of the solvent include nitrogen atom-containing solvents such as dimethylformamide, acetonitrile, acrylonitrile, and nitrobenzene.

[0081] Preferred examples of the solvent containing a halogen atom as a hetero atom include dichloromethane, chlorobenzene, trifluoromethylbenzene, chlorobenzene, chlorotoluene, and bromobenzene. Preferred examples of the solvent containing a sulfur atom include dimethyl sulfoxide and carbon disulfide.

[0082] When a complexing agent is used, the amount of the complexing agent used is preferably 100 mL or more, more preferably 200 mL or more, even more preferably 250 mL or more, and even more preferably 300 mL or more per 1 kg of the total amount of the raw materials, and the upper limit is preferably 3000 mL or less, more preferably 2500 mL or less, even more preferably 2000 mL or less, and even more preferably 1550 mL or less. When the amount of the solvent used is within the above range, the raw materials can be reacted efficiently.

[0083] (Solvent that dissolves salts of complex anions) It is preferable that the solvent contains a solvent that dissolves the salt of the composite anion, because the dissolved composite anion is easily incorporated into the raw material mixture when mixing the raw material ingredients with the salt of the composite anion, thereby shortening the mixing processing time.Furthermore, dissolving the composite anion is preferable because it allows the composite anion to be uniformly incorporated into the sulfide solid electrolyte, resulting in a sulfide solid electrolyte with excellent shutdown performance. As the solvent for dissolving the salt of the composite anion, those listed as complexing agents can be preferably used, but protic polar solvents such as alcohol-based solvents and sulfinyl-based solvents such as dimethyl sulfoxide are more preferred, and alcohol-based solvents are even more preferred.

[0084] The solvent for dissolving the salt of the complex anion varies depending on the type of the solute complex anion, but the solubility of the salt of the complex anion in the solvent for dissolving the salt of the complex anion at 25°C is preferably 10 g / L or more. Complete dissolution of the complex anion is preferable because it allows the complex anion to be incorporated uniformly and in a short time into the raw material inclusions. Depending on the amount of solvent used for dissolving the salt of the complex anion, the complex anion may not be completely dissolved, resulting in a slurry state. However, since once the dissolved complex anion is incorporated into the sulfide solid electrolyte, further complex anions present as solids will sequentially dissolve and be incorporated into the sulfide solid electrolyte, the complex anion does not need to be completely dissolved.

[0085] The solubility of the mixed anion salt in a solvent that dissolves the mixed anion salt is preferably 13 g / L or more, more preferably 15 g / L or more. There is no particular upper limit, but in commonly used solvents, the solubility is often 30 g / L or less.

[0086] The alcohol solvent may be a primary alcohol, a secondary alcohol, or a tertiary alcohol, or may be a monohydric alcohol, a dihydric alcohol, or a trihydric alcohol. In order to improve the solubility of the composite anion, a monohydric primary alcohol is preferred. The alcohol solvent has a smaller number of carbon atoms and a more linear alkyl chain, which increases its ability to dissolve salts of composite anions, and therefore preferably has 5 or less carbon atoms, more preferably 4 or less, even more preferably 3 or less, and even more preferably 2 or less. More specifically, methanol, ethanol, 1-propyl alcohol, n-butyl alcohol, isobutyl alcohol, 1-pentanol, or 2-pentanol is preferred, methanol, ethanol, 1-propyl alcohol, or n-butyl alcohol is more preferred, methanol, ethanol, or 1-propyl alcohol is more preferred, and ethanol is even more preferred.

[0087] When a solvent for dissolving the salt of the composite anion is used, the amount of the solvent for dissolving the salt of the composite anion is preferably 100 mL or more, more preferably 200 mL or more, even more preferably 250 mL or more, and even more preferably 300 mL or more per 1 kg of the total amount of the raw materials, and the upper limit is preferably 3000 mL or less, more preferably 2500 mL or less, even more preferably 2000 mL or less, and even more preferably 1550 mL or less. When the amount of the solvent is within the above range, the raw materials can be reacted efficiently.

[0088] (Other solvents) The use of the other solvent is preferable because it can reduce the amount of solvent used to dissolve the raw material ingredients such as lithium halide, the complexing agent, and the salt of the composite anion. When mixing the raw material ingredients, the salt of the composite anion, and the complexing agent, the use of the other solvent is preferable because the complexing agent is dissolved in the other solvent and is uniformly mixed with the raw material ingredients.

[0089] When using other solvents, the amount of the other solvents used is preferably 100 mL or more, more preferably 200 mL or more, even more preferably 250 mL or more, and even more preferably 300 mL or more per 1 kg of the total amount of raw material ingredients. In order to maintain the solubility of raw material ingredients such as lithium halide and salts of composite anions, the upper limit is preferably 3000 mL or less, more preferably 2500 mL or less, even more preferably 2000 mL or less, and even more preferably 1550 mL or less.

[0090] The other solvents vary depending on the types of raw material components such as lithium halide and the composite anion as solutes, but the solubility of the raw material components such as lithium halide and the salt of the composite anion in the other solvents is preferably 2 g / L or less at 25° C. There is no particular lower limit.

[0091] As the other solvent, hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents are preferred.

[0092] Examples of aliphatic hydrocarbons include hexane, pentane, 2-ethylhexane, heptane, octane, decane, undecane, dodecane, and tridecane. Examples of alicyclic hydrocarbons include cyclohexane and methylcyclohexane. Examples of aromatic hydrocarbon solvents include benzene, toluene, xylene, mesitylene, ethylbenzene, tert-butylbenzene, trifluoromethylbenzene, and nitrobenzene.

[0093] <Mixing> In this embodiment, it is necessary to mix the raw material ingredients, the salt of the composite anion, and the solvent. The mixing can be carried out using a stirrer, mixer, grinder, etc. The raw materials can be mixed using a stirrer, and the raw materials are ground using a grinder, but they are also mixed at the same time. In other words, the raw material contents, the salt of the composite anion, and the solvent can be mixed by stirring, mixing, grinding, or a combination of these processes.

[0094] Examples of the stirrer or mixer include a mechanical stirring mixer that is equipped with stirring blades in a reaction vessel and can stir (also referred to as mixing by stirring or stirring mixing). Examples of the mechanical stirring mixer include a high-speed stirring mixer and a double-arm mixer. Examples of the high-speed stirring mixer include a vertical-axis rotary mixer and a horizontal-axis rotary mixer, and either type of mixer may be used.

[0095] Examples of the shape of the stirring blade used in the mechanical stirring mixer include blade type, arm type, anchor type, paddle type, full zone type, ribbon type, multi-stage blade type, double arm type, shovel type, double blade type, flat blade type, C-type blade type, etc., and from the viewpoint of promoting the reaction of the raw materials more efficiently, the shovel type, flat blade type, C-type blade type, anchor type, paddle type, full zone type, etc. are preferred, with the anchor type, paddle type, and full zone type being more preferred.

[0096] When a mechanically agitated mixer is used, the rotation speed of the agitator blades can be adjusted appropriately depending on the volume of the fluid in the reaction tank, the temperature, the shape of the agitator blades, etc., and is not particularly limited. However, it is usually set to about 5 rpm or more and 400 rpm or less. From the viewpoint of more efficiently promoting the reaction of the raw materials, the rotation speed is preferably 10 rpm or more and 300 rpm or less, more preferably 15 rpm or more and 250 rpm or less, and even more preferably 20 rpm or more and 200 rpm or less.

[0097] The temperature conditions when mixing is performed using a mixer are not particularly limited, and any temperature may be used as long as decomposition of the composite anion does not occur or is suppressed, and is, for example, usually −30 to 120° C., preferably −10 to 100° C., more preferably 0 to 80° C., and even more preferably 10 to 60° C. The mixing time is usually 0.1 to 500 hours, and from the viewpoint of making the raw materials more uniformly dispersed and promoting the reaction, it is preferably 1 to 450 hours, more preferably 10 to 425 hours, even more preferably 20 to 400 hours, and even more preferably 40 to 375 hours.

[0098] The method of mixing with pulverization using a pulverizer has been conventionally adopted as a solid-phase method (mechanical milling method). As the pulverizer, for example, a media-type pulverizer using pulverization media can be used. Media-type mills are broadly classified into vessel-driven mills and media-agitation mills. Examples of vessel-driven mills include agitation tanks, grinding tanks, and combinations thereof, such as ball mills and bead mills. Examples of media-agitation mills include impact mills such as cutter mills, hammer mills, and pin mills; tower mills and other tower-type mills; agitation tank mills such as attritors, aquamizers, and sand grinders; flow-tank mills such as Viscomill and pearl mills; flow-tube mills; annular mills such as Coball mills; continuous dynamic mills; and single- or multi-shaft kneaders. Among these, considering the ease of adjusting the particle size of the resulting sulfide, the ball mills and bead mills exemplified as vessel-driven mills are preferred, and planetary mills are particularly preferred.

[0099] These pulverizers can be appropriately selected depending on the desired scale, etc. For relatively small scales, container-driven pulverizers such as ball mills and bead mills can be used, while for large scales or mass production, other types of pulverizers may be used.

[0100] Furthermore, as will be described later, when the materials are in a liquid state involving a liquid such as a solvent or in a slurry state during mixing, it is preferable to use a wet mill that can handle wet milling. Representative examples of wet mills include wet bead mills, wet ball mills, and wet vibration mills, with wet bead mills using beads as milling media being preferred because they allow for flexible adjustment of milling conditions and are suitable for smaller particle sizes. Alternatively, dry mills such as dry media mills (e.g., dry bead mills, dry ball mills, and dry vibration mills) and dry non-media mills (e.g., jet mills) can also be used.

[0101] Furthermore, when the material to be mixed is in a liquid or slurry state, a flow-through mill that can be operated to circulate as needed can also be used. Specifically, a mill that circulates the material between a mill (milling mixer) that pulverizes the slurry and a temperature holding tank (reaction vessel) can be used.

[0102] The size of the beads or balls used in the ball mill or bead mill may be appropriately selected depending on the desired particle size, processing amount, etc. For example, the diameter of the beads is usually 0.05 mm or more, preferably 0.1 mm or more, more preferably 0.3 mm or more, with the upper limit being usually 5.0 mm or less, preferably 3.0 mm or less, more preferably 2.0 mm or less. The diameter of the balls is usually 2.0 mm or more, preferably 2.5 mm or more, more preferably 3.0 mm or more, with the upper limit being usually 20.0 mm or less, preferably 15.0 mm or less, more preferably 10.0 mm or less. Examples of materials include metals such as stainless steel, chrome steel, and tungsten carbide; ceramics such as zirconia and silicon nitride; and minerals such as agate.

[0103] Furthermore, when a ball mill or bead mill is used, the rotation speed varies depending on the scale of the treatment and cannot be generalized, but is usually 10 rpm or more, preferably 20 rpm or more, and more preferably 50 rpm or more, with the upper limit being usually 1,000 rpm or less, preferably 900 rpm or less, more preferably 800 rpm or less, and even more preferably 700 rpm or less. The grinding time in this case varies depending on the scale of the treatment and cannot be generalized, but is usually 0.5 hours or more, preferably 1 hour or more, more preferably 5 hours or more, and even more preferably 10 hours or more, with the upper limit being usually 100 hours or less, preferably 72 hours or less, more preferably 48 hours or less, and even more preferably 36 hours or less.

[0104] By selecting the size and material of the media (beads, balls) used, the rotor rotation speed, time, etc., it is possible to perform mixing, stirring, pulverization, or a combination of these processes, and it is possible to adjust the particle size, etc. of the resulting sulfide.

[0105] As the crusher, a machine capable of crushing an object using ultrasonic waves, such as a machine called an ultrasonic crusher, ultrasonic homogenizer, or probe ultrasonic crusher, can be used. In this case, various conditions such as the frequency of the ultrasonic waves may be appropriately selected depending on the average particle size of the desired sulfide solid electrolyte, and the frequency may be, for example, about 1 kHz or more and 100 kHz or less, and from the viewpoint of more efficiently pulverizing the sulfide solid electrolyte, the frequency is preferably 3 kHz or more and 50 kHz or less, more preferably 5 kHz or more and 40 kHz or less, and even more preferably 10 kHz or more and 30 kHz or less. The output of the ultrasonic crusher is usually about 500 to 16,000W, preferably 600 to 10,000W, more preferably 750 to 5,000W, and even more preferably 900 to 1,500W.

[0106] <Removing the solvent> After mixing using a solvent, it is necessary to remove the solvent from the fluid (usually a slurry) obtained by mixing. By removing the solvent, a powdered sulfide solid electrolyte complex is obtained. Making it into a powder is preferable because it improves workability. The solvent removed by removing the solvent is intended to remove the solvent present as a liquid, and may include removing the complexing agent that forms a complex.

[0107] The solvent can be removed from the fluid obtained by mixing at a temperature that depends on the type of solvent. Alternatively, the solvent can be evaporated by drying under reduced pressure (vacuum drying) using a vacuum pump or the like at typically 5 to 100°C, preferably 10 to 85°C, more preferably 15 to 70°C, and even more preferably at about room temperature (23°C) (for example, about room temperature ±5°C).

[0108] The solvent may be removed by filtering the fluid using a glass filter or the like, by solid-liquid separation by decantation, or by solid-liquid separation using a centrifuge or the like. Specifically, solid-liquid separation can be easily performed by decantation, in which the fluid is transferred to a container, the sulfide is precipitated, and then the supernatant solvent is removed, or by filtration using, for example, a glass filter with a pore size of about 10 to 200 μm, preferably 20 to 150 μm. The solvent may be removed by a combination of the above methods.

[0109] <Heating> The method for producing the sulfide solid electrolyte of this embodiment requires heating. The heating includes at least one of heating for removing the complexing agent from the complex (removal of the complexing agent) and heating for obtaining a crystalline sulfide solid electrolyte (crystallization). The removal of the complexing agent and the crystallization may be carried out independently, or may be carried out simultaneously in a single heating. In the method for producing the sulfide solid electrolyte of this embodiment, the solvent removal and heating are preferably carried out at 250° C. or less.

[0110] In the method for producing a sulfide solid electrolyte of this embodiment, the steps in which the temperature becomes highest are removing the solvent and heating. Therefore, by specifying the upper limit of the temperatures for removing the solvent and heating, it is possible to suppress decomposition of the composite anion in the sulfide solid electrolyte during production of the sulfide solid electrolyte, which is preferable. The upper limit is more preferably 210° C. or less, even more preferably 180° C. or less, and even more preferably 160° C. or less. The lower limit is not particularly limited, but is preferably 20° C. or more, and more preferably 50° C. or more.

[0111] (Removal of complexing agent) When a complexing agent is used as a solvent, a complex is produced by mixing a raw material containing lithium atoms, sulfur atoms, and phosphorus atoms, a salt of a composite anion, and a solvent. Heating the resulting complexing agent to obtain an (amorphous or crystalline) sulfide solid electrolyte is preferred because it provides a sulfide solid electrolyte with high ionic conductivity. When heating is performed for the purpose of removing the complexing agent, it is preferably performed after the mixing, and more preferably after removing the solvent. When heating for removing the complexing agent and heating for crystallization are both performed,

[0112] By including a step of heating the complexed product, the complexing agent in the complexed product is removed, and a decomplexed product containing lithium atoms, sulfur atoms, phosphorus atoms, a composite anion, and, if necessary, a halogen atom is obtained. Here, the removal of the complexing agent in the complexed product is supported by the fact that the results of X-ray diffraction patterns, gas chromatography analysis, etc. show that the complexing agent forms a cocrystal of the complexed product, and also by the fact that the solid electrolyte obtained by removing the complexing agent by heating the complexed product has the same X-ray diffraction pattern as a solid electrolyte obtained by a conventional method without using a complexing agent.

[0113] In this embodiment, the sulfide solid electrolyte is obtained by heating the complex to remove the complexing agent from the complex. The less complexing agent in the sulfide solid electrolyte, the better, but the sulfide solid electrolyte may contain a complexing agent to the extent that it does not impair the performance of the sulfide solid electrolyte. The content of the complexing agent in the sulfide solid electrolyte is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. The lower limit is not particularly limited.

[0114] Specifically, when the complex is subjected to differential thermal analysis (DTA) at a temperature increase rate of 10°C / min using a differential thermal analyzer (DTA), the heating temperature is preferably set to 5°C or lower, more preferably 10°C or lower, and even more preferably 20°C or lower, starting from the temperature at the top of the exothermic peak observed at the lowest temperature. The lower limit is not particularly limited, but may be set to about 40°C or higher (the temperature at the top of the exothermic peak observed at the lowest temperature). By setting the temperature range as described above, the sulfide solid electrolyte can be obtained more efficiently and reliably. The heating temperature for obtaining a sulfide solid electrolyte cannot be generally defined because it varies depending on the structure of the sulfide solid electrolyte to be obtained. However, it is generally preferably 250°C or lower, more preferably 180°C or lower, and even more preferably 160°C or lower. There is no particular lower limit, but the temperature is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 110°C or higher.

[0115] The heating time is not particularly limited as long as the desired sulfide solid electrolyte is obtained, but is preferably, for example, 1 minute or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, and even more preferably 1 hour or more. The upper limit of the heating time is not particularly limited, but is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and even more preferably 3 hours or less.

[0116] Furthermore, heating is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in a vacuum), as this can prevent deterioration (e.g., oxidation) of the sulfide solid electrolyte. The heating method is not particularly limited, and examples thereof include methods using a hot plate, a vacuum heating device, an argon gas atmosphere furnace, and a calcination furnace. Furthermore, industrially, a horizontal dryer or a horizontal vibration fluidized dryer having a heating means and a feeding mechanism can also be used, and the method may be selected depending on the amount of heat to be processed.

[0117] (crystallization) In this embodiment, the amorphous sulfide solid electrolyte may be crystallized to form a crystalline sulfide solid electrolyte as needed. Crystallization is preferable because it increases ionic conductivity. Crystallization is also preferable to further grow the crystals of the crystalline sulfide solid electrolyte.

[0118] Crystallization is preferably carried out either after said mixing, after removal of the solvent or after removal of the complexing agent. When an amorphous sulfide solid electrolyte is heated (crystallized) to obtain a crystalline sulfide solid electrolyte, the heating temperature can be determined depending on the structure of the crystalline sulfide solid electrolyte, and is preferably higher than the heating temperature required to obtain a sulfide solid electrolyte by removing the complexing agent. Specifically, the amorphous sulfide solid electrolyte or the amorphous sulfide solid electrolyte is subjected to differential thermal analysis (DTA) using a differential thermal analyzer (DTA) at a temperature increase rate of 10 ° C. / min. The temperature is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, and even more preferably 20 ° C. or higher, starting from the peak top temperature of the exothermic peak observed at the lowest temperature. The upper limit is 40 ° C. or lower, more preferably 30 ° C. or lower, and even more preferably 20 ° C. or lower. By using such a temperature range, a crystalline sulfide solid electrolyte can be obtained more efficiently and reliably. The heating temperature for obtaining a crystalline sulfide solid electrolyte cannot be generally defined because it varies depending on the structure of the crystalline sulfide solid electrolyte to be obtained. However, it is generally preferably 130°C or higher, more preferably 135°C or higher, and even more preferably 140°C or higher. In order to suppress decomposition of the composite anion, the upper limit is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 210°C or lower.

[0119] The heating time is not particularly limited as long as the desired sulfide solid electrolyte is obtained, but is preferably, for example, 1 minute or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, and even more preferably 1 hour or more. The upper limit of the heating time is not particularly limited, but is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and even more preferably 3 hours or less.

[0120] (to crush) This embodiment preferably includes pulverizing the complex or sulfide solid electrolyte as needed. By pulverizing the complex or sulfide solid electrolyte, a sulfide solid electrolyte with a small particle size can be obtained, which is preferable because it allows the formation of a uniform and thin separator layer and improves contact with the positive electrode active material. The pulverization is preferably carried out using the pulverizer described in the mixing section. It is also preferable to carry out the crystallization again after pulverization, since this can increase the ionic conductivity.

[0121] The average particle size (D 50 ) is determined appropriately as desired, but is usually 0.01 μm or more and 50 μm or less, preferably 0.03 μm or more and 5 μm or less, and more preferably 0.05 μm or more and 3 μm or less. By setting the average particle size in this range, it is possible to meet the demand for a sulfide solid electrolyte having a small average particle size of 3 μm or less.

[0122] The pulverization time is not particularly limited as long as it is a time that allows the sulfide solid electrolyte to have a desired average particle size, and is usually from 0.1 hours to 100 hours. From the viewpoint of efficiently achieving a desired particle size, the pulverization time is preferably from 0.3 hours to 72 hours, more preferably from 0.5 hours to 48 hours, and even more preferably from 1 hour to 24 hours.

[0123] In this specification, the average particle size (D 50 ) is a value measured by a laser diffraction particle size distribution measurement method, and can be measured, for example, by the method described in the Examples.

[0124] (Applications of sulfide solid electrolytes) The sulfide solid electrolyte of this embodiment has high ionic conductivity and excellent shutdown performance, and is suitable for use in electrode mixtures for lithium ion batteries and lithium ion batteries. The sulfide solid electrolyte of this embodiment may be used in the positive electrode layer, the negative electrode layer, or the electrolyte layer.

[0125] The lithium ion battery preferably includes a current collector in addition to the positive electrode layer, electrolyte layer, and negative electrode layer, and a known current collector can be used. For example, a layer of a material that reacts with the sulfide solid electrolyte, such as Au, Pt, Al, Ti, or Cu, coated with Au or the like can be used.

[0126] [Electrode composite material] The electrode mixture of this embodiment is required to contain the sulfide solid electrolyte and an electrode active material described below. Furthermore, by including at least one sulfide solid electrolyte different from the sulfide solid electrolyte of this embodiment, the ionic conductivity is further improved and the excellent shutdown performance of the sulfide solid electrolyte of this embodiment is exhibited, which is preferable.

[0127] When a sulfide solid electrolyte different from the sulfide solid electrolyte of this embodiment is used together with the sulfide solid electrolyte of this embodiment, the content of the sulfide solid electrolyte of this embodiment based on the total amount of the sulfide solid electrolyte is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, in order to exhibit excellent shutdown performance. The upper limit is not particularly limited, and is preferably substantially 100% by mass.

[0128] (electrode active material) As the electrode active material, a positive electrode active material or a negative electrode active material is adopted depending on whether the electrode mixture is used for the positive electrode or the negative electrode.

[0129] The positive electrode active material can be any material that can promote a battery chemical reaction involving the movement of lithium ions due to atoms that are used to exhibit ionic conductivity, preferably lithium atoms, in relation to the negative electrode active material. Examples of such positive electrode active materials that can insert and extract lithium ions include oxide-based positive electrode active materials and sulfide-based positive electrode active materials.

[0130] Preferred examples of oxide-based positive electrode active materials include lithium-containing transition metal composite oxides such as LMO (lithium manganese oxide), LCO (lithium cobalt oxide), NMC (lithium nickel manganese cobalt oxide), NCA (lithium nickel cobalt aluminate), LNCO (lithium nickel cobalt oxide), and olivine-type compounds (LiMeNPO4, Me=Fe, Co, Ni, Mn). Examples of sulfide-based positive electrode active materials include sulfur (S), titanium sulfide (TiS2), molybdenum sulfide (MoS2), iron sulfide (FeS, FeS2), copper sulfide (CuS), and nickel sulfide (Ni3S2). In addition to the above positive electrode active materials, niobium selenide (NbSe3) and the like can also be used. The positive electrode active material can be used alone or in combination of two or more kinds.

[0131] The negative electrode active material can be any material that can promote a battery chemical reaction involving the movement of lithium ions originating from lithium atoms, such as an atom that is used as an atom to exhibit ionic conductivity, preferably a metal that can form an alloy with lithium atoms, an oxide thereof, an alloy of the metal with lithium atoms, etc. As such a negative electrode active material capable of inserting and extracting lithium ions, any material known in the field of batteries as a negative electrode active material can be used without any limitation. Examples of such negative electrode active materials include metallic lithium, metallic indium, metallic aluminum, metallic silicon, metallic tin, and other metallic lithium or metals capable of forming alloys with metallic lithium, oxides of these metals, and alloys of these metals with metallic lithium.

[0132] The electrode active material used in this embodiment may have a coating layer on its surface. The material for forming the coating layer is an ion conductor such as an atom that exhibits ionic conductivity in the sulfide solid electrolyte, preferably a nitride or oxide of lithium atoms, or a composite thereof. Specifically, lithium nitride (Li3N), Li4GeO4, and the like, which have a main structure, for example, Li 4-2x Zn x Conductors with a lithiated crystal structure such as GeO4, and those with a Li3PO4-type framework structure such as Li 4-x Ge 1-x P x Conductors with thiolicon-type crystal structures such as S4, La 2 / 3-x Li 3xExamples include conductors having a perovskite crystal structure such as TiO3, and conductors having a NASICON crystal structure such as LiTi2(PO4)3. Also, Li y Ti 3-y O4(0 <y<3)、Li4Ti5O 12 Examples include lithium titanates such as (LTO), lithium metal oxides of metals belonging to Group 5 of the periodic table such as LiNbO3 and LiTaO3, and oxide-based conductors such as Li2O-B2O3-P2O5, Li2O-B2O3-ZnO, and Li2O-Al2O3-SiO2-P2O5-TiO2.

[0133] An electrode active material having a coating layer can be obtained, for example, by applying a solution containing various atoms constituting the material that forms the coating layer to the surface of the electrode active material, and then firing the electrode active material after application at a temperature preferably between 200°C and 400°C. Here, the solution containing various atoms may be a solution containing alkoxides of various metals such as lithium ethoxide, titanium isopropoxide, niobium isopropoxide, tantalum isopropoxide, etc. In this case, the solvent may be an alcoholic solvent such as ethanol or butanol, an aliphatic hydrocarbon solvent such as hexane, heptane or octane, or an aromatic hydrocarbon solvent such as benzene, toluene or xylene. The above-mentioned attachment may be carried out by immersion, spray coating or the like.

[0134] From the viewpoint of improving production efficiency and battery performance, the firing temperature is preferably 200°C or higher and 400°C or lower, more preferably 250°C or higher and 390°C or lower, and the firing time is usually about 1 minute to 10 hours, preferably 10 minutes to 4 hours.

[0135] The coverage of the coating layer is preferably 90% or more, more preferably 95% or more, and even more preferably 100% of the surface area of ​​the electrode active material, i.e., the entire surface is covered. The thickness of the coating layer is preferably 1 nm or more, more preferably 2 nm or more, and the upper limit is preferably 30 nm or less, more preferably 25 nm or less. The thickness of the coating layer can be measured by cross-sectional observation using a transmission electron microscope (TEM), and the coverage rate can be calculated from the thickness of the coating layer, elemental analysis values, and BET specific surface area.

[0136] (Other ingredients) The electrode mixture of this embodiment may contain other components such as a conductive material, a binder, etc. in addition to the sulfide solid electrolyte and electrode active material. That is, the method for producing an electrode mixture of this embodiment may use other components such as a conductive material, a binder, etc. in addition to the sulfide solid electrolyte and electrode active material. The other components such as a conductive material, a binder, etc. may be added to and mixed with the sulfide solid electrolyte and the electrode active material when mixing the sulfide solid electrolyte and the electrode active material. Examples of the conductive material, from the viewpoint of improving battery performance by improving electronic conductivity, include carbon-based materials such as artificial graphite, graphite carbon fiber, resin-baked carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads, furfuryl alcohol resin-baked carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and non-graphitizable carbon.

[0137] By using a binder, the strength of the positive and negative electrodes when they are fabricated is improved. The binder is not particularly limited as long as it can impart functions such as binding property and flexibility, and examples thereof include fluorine-based polymers such as polytetrafluoroethylene and polyvinylidene fluoride, thermoplastic elastomers such as butylene rubber and styrene-butadiene rubber, and various resins such as acrylic resin, acrylic polyol resin, polyvinyl acetal resin, polyvinyl butyral resin, and silicone resin.

[0138] In order to improve battery performance and take production efficiency into consideration, the compounding ratio (mass ratio) of the electrode active material to the sulfide solid electrolyte in the electrode mixture is preferably 99.5:0.5 to 40:60, more preferably 99:1 to 50:50, and even more preferably 98:2 to 60:40.

[0139] When a conductive material is contained, the content of the conductive material in the electrode mixture is not particularly limited, but in consideration of improving battery performance and production efficiency, the content is preferably 0.5 mass% or more, more preferably 1 mass% or more, and even more preferably 1.5 mass% or more, and the upper limit is preferably 10 mass% or less, preferably 8 mass% or less, and even more preferably 5 mass% or less. Furthermore, when a binder is contained, the content of the binder in the electrode mixture is not particularly limited, but in consideration of improving battery performance and production efficiency, the content is preferably 1 mass % or more, more preferably 3 mass % or more, and even more preferably 5 mass % or more, with the upper limit being preferably 20 mass % or less, preferably 15 mass % or less, and even more preferably 10 mass % or less.

[0140] [Lithium-ion battery] The lithium ion battery of this embodiment is required to include at least one selected from the sulfide solid electrolyte of this embodiment and the electrode mixture.

[0141] The lithium ion battery of the present embodiment is not particularly limited in its configuration as long as it includes the sulfide solid electrolyte of the present embodiment, an electrode composite containing the sulfide solid electrolyte, or another form of sulfide solid electrolyte or an electrode composite containing the sulfide solid electrolyte, and may have the configuration of a commonly used lithium ion battery.

[0142] The lithium ion battery of this embodiment preferably includes, for example, a positive electrode layer, a negative electrode layer, an electrolyte layer, and a current collector. The positive electrode layer and the negative electrode layer preferably use the electrode mixture of this embodiment, and the electrolyte layer preferably uses the sulfide solid electrolyte of this embodiment.

[0143] The current collector may be a known material, for example, a layer of Au or the like coated with a material that reacts with the solid electrolyte, such as Au, Pt, Al, Ti, or Cu. [Example]

[0144] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples in any way. (1) Measurement method (1-1) X-ray diffraction (XRD) measurement (XRD pattern) The obtained crystalline sulfide solid electrolyte was measured by XRD measurement. The following measurement sample was filled into a groove with a diameter of 20 mm and a depth of 0.2 mm, and the groove was leveled with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured without exposing it to air. The powder X-ray diffraction measurement was carried out using a MAC Science M03xrf under the following conditions.

[0145] Tube voltage: 40kV Tube current: 40mA X-ray wavelength: Cu-Kα ray (1.5418Å) Optical system: Concentration method Slit configuration: Soller slit 0.5° (both incident and receiving sides), divergence slit 0.3 mm, monochromator used) Detector: Semiconductor detector Measurement range: 2θ=10-60deg Step width, integration time: 0.05 deg, 10 seconds / deg Measurement sample: sulfide solid electrolyte produced in each example

[0146] The shift angle was measured using the measurement sample described below and calculated from the peak position of the diffraction peak at 2θ = 30.0° of Li7PS6 used as the internal standard and the corresponding peak position of the diffraction peak for each example. The peak position of the diffraction peak at 2θ = 30.0° due to the Li7PS6 crystal structure and the peak position of the corresponding diffraction peak can be confirmed from the XRD pattern of the sulfide solid electrolyte produced in each example alone, so the peaks in the XRD pattern can be assigned using this value as a reference. This method reduces errors in the shift angle. Measurement sample: 90 parts by mass of the sulfide solid electrolyte powder produced in each example was mixed with 10 parts by mass of Li7PS6 produced as an internal standard by the method described in the production of Li7PS6 described below, and the mixture was stirred uniformly.

[0147] (1-2) Observation of decomposition of complex anions (TG-DTA measurement, decomposition onset temperature) The sulfide solid electrolytes produced in each example were measured using a simultaneous differential thermal and thermogravimetric analyzer (TG-DTA, Mettler Toledo, model: TGA / DSC1). The temperature was raised from room temperature at a rate of 10°C / min. When weight loss was confirmed in the TG curve and heat generation was observed in the DTA curve, it was determined that decomposition of the composite anion had occurred. The temperature at which heat generation of 5% from the baseline was observed in the DTA curve was defined as the temperature (°C) at which decomposition began. Table 1 shows the decomposition starting temperature (decomposition starting temperature (° C.)) of each sulfide solid electrolyte.

[0148] (1-3) Measurement of ionic conductivity The ionic conductivity of the sulfide solid electrolyte produced in each example was measured as follows. From the sulfide solid electrolyte, a 10 mm diameter (cross-sectional area S: 0.785 cm 2) and a height (L) of 0.1 to 0.3 cm were molded into circular pellets to serve as samples. Electrode terminals were attached to the top and bottom of the samples, and measurements were made at 25°C using the AC impedance method (frequency range: 1 MHz to 100 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high-frequency region was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following equation: R=ρ(L / S) σ=1 / ρ

[0149] (1-4) Battery characteristics (CV measurement (evaluation of irreversible capacity) To evaluate the irreversible capacity, the following CV measurement cell was used. A total of 100 mg of the sulfide solid electrolyte obtained in the examples and granular Denka Black (particle size: 35 nm, manufactured by Denka Co., Ltd.) (sulfide solid electrolyte: Denka Black (mass ratio) = 85:15) were mixed in a mortar for 10 minutes to obtain powder (1) for measurement. 100 mg of electrolyte for the separator layer was added to a 10 mm diameter battery cell, and the cell was pressurized in a stainless steel mold at 10 MPa / cm 2 After pressing three times while rotating by 120° at a pressure of 20 MPa / cm, 50 mg of powder (1) was added. 2 Then, the powder (1) was pressed three times with a pressure of 20 MPa / cm from the opposite side of the powder (1). 2 The press was performed three times, rotating the press by 120° each time.

[0150] The electrolyte for the separator was synthesized under the following conditions. A 1-L reactor equipped with an impeller was charged with 20.5 g of L2S, 33.1 g of P2S5, 10.0 g of LiI, and 6.5 g of LiBr under a nitrogen atmosphere. After rotating the impeller, 630 g of toluene was added, and the resulting slurry was stirred for 10 minutes. The reactor was connected to a recirculating bead mill ("Star Mill LMZ015" (product name), manufactured by Ashizawa Finetech Co., Ltd., zirconia bead material: zirconia, bead diameter: 0.5 mm, bead amount: 456 g), and milling was performed for 45 hours (pump flow rate: 650 mL / min, bead mill peripheral speed: 12 m / s, mill jacket temperature: 45 °C). The obtained slurry was dried under vacuum at room temperature (25°C) and then heated (80°C) to obtain a white powder of amorphous sulfide solid electrolyte. The obtained white powder was further heated under vacuum at 195°C for 2 hours to obtain a white powder of crystalline sulfide solid electrolyte. In the XRD spectrum of the crystalline sulfide solid electrolyte, crystallization peaks were detected at 2θ = 20.2° and 23.6°, confirming that the crystalline sulfide solid electrolyte had a thiolithium region II crystal structure. The average particle size (D 50 ) was 4.5 μm and the ionic conductivity was 5.0 mS / cm.

[0151] An InLi foil (having a layered structure, " / " indicates the space between each layer. In: 10mmφ×0.1mm / Li: 9mmφ×0.08mm / SUS: 10mmφ×0.1mm) was placed on the opposite side of the electrolyte measurement powder (1) for the separator layer, and a pressure of 6 MPa / cm was applied. 2 The cell was fixed with four screws with an insulator between them to prevent a short circuit between the powder (1) and the InLi foil, and the screws were fixed with a torque of 8 N m to obtain the measurement cell.

[0152] The obtained measurement cell was connected to a measuring device ("VSP-3 (model number)", manufactured by Biologic), and a CV curve was obtained under the following conditions. Measurement temperature: 25℃ Sweep speed: 0.1mV / s Potential measurement range: Open circuit voltage (+2.7V) → +5.0V → +2.7V Number of cycles: 5

[0153] (2) Manufacturing of Li7PS6 Lithium sulfide (Li2S) and 2.70 g of diphosphorus pentasulfide (P2S5) were mixed in a mortar and pestle for 5 minutes in a nitrogen glove box with a dew point of -80 °C. The entire amount of the resulting mixture was added to a 300 mL reaction vessel together with 76 g of ethyl propionate as a complexing agent and a stirrer, and mixed for 10 minutes, after which it was subjected to ultrasonic irradiation (31 kHz, 1000 W) for 1 hour. Further, 76 g of ethanol was added, and the mixture was heated to 90° C. with stirring, and the ethyl propionate and ethanol present as liquid were distilled off. After distilling off the liquid, the temperature was raised to 120°C, and then heated at 120°C for 1 hour to remove ethyl propionate from the complex. The whole amount of the obtained powder was further heated at 120°C for 3 hours to obtain crystallized Li7PS6.

[0154] (Examples 1 to 7 and Comparative Example 1) In the production of (2) Li7PS6, Li2S and P2S5 are used together with Li 7-x PS 6-x (NO3) x The sulfide solid electrolytes of Examples 1 to 7 were produced in the same manner as in (2) Production of Li7PS6, except that LiNO3 was further added so that x had the value shown in Table 1. The Li7PS6 produced in the above (2) Production of Li7PS6 was designated as Comparative Example 1. The XRD measurement results of the obtained sulfide solid electrolytes of each example are shown in Figure 3, and an enlarged view of the vicinity of 2θ=30.0° is shown in Figure 4. From these, it was confirmed that all of Examples 1 to 7 and Comparative Example 1 contained an argyrodite-type crystal structure.

[0155] The shift angles and ionic conductivities of the obtained sulfide solid electrolytes of Examples 1 to 7 and Comparative Example 1 are shown in Table 1. It was confirmed that the diffraction peaks of the sulfide solid electrolytes obtained in Examples 1 to 7 were shifted to lower angles due to the inclusion of an organic group. It was confirmed that the shift angle of the sulfide solid electrolytes of Examples 1 to 7 increased as x increased, and it was also confirmed that the ionic conductivity tended to increase accordingly. These sulfide solid electrolytes were found to exhibit high ionic conductivity, and it was confirmed that they can be used as materials for lithium-ion batteries. Furthermore, the sulfide solid electrolytes of Examples 1 to 7 were confirmed to have excellent shutdown performance, as decomposition of the composite anion was observed.

[0156] [Table 1]

[0157] (Examples 8 to 14) Using the sulfide solid electrolytes obtained in Examples 1 to 7, lithium ion batteries were produced by the method described in (1-4) Battery Characteristics above (Examples 8 to 14). As a representative example, the CV curve at the fifth cycle of the lithium ion battery (Example 14) produced using the sulfide solid electrolyte obtained in Example 7 is shown in Figure 5. The lithium ion batteries of Examples 8 to 13 also showed similar CV curves, confirming that these lithium ion batteries of the present embodiment are suitable for practical use in terms of irreversible capacity. [Industrial Applicability]

[0158] The sulfide solid electrolyte of this embodiment has high ionic conductivity and excellent shutdown performance, and is suitable for use in batteries, particularly batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones. Furthermore, according to the method for producing a sulfide solid electrolyte of this embodiment, the sulfide solid electrolyte can be easily produced.

Claims

1. A sulfide solid electrolyte having an argyrodite-type crystal structure containing a composite anion, a lithium atom, a sulfur atom, and a phosphorus atom, wherein the diffraction peak 2θ measured by the X-ray diffraction measurement method using the CuKα ray described below ＳＥ a sulfide solid electrolyte in which the angle shifted to the lower angle side is 0.001° or more. (X-ray diffraction measurement method) Standard substance Li ７ P.S. ６ and the sulfide solid electrolyte (the mixing ratio is ７ P.S. ６ : the sulfide solid electrolyte = 10 parts by mass: 90 parts by mass. The measurement sample was subjected to X-ray diffraction measurement using CuKα rays, and the Li contained in the sulfide solid electrolyte was ７ P.S. ６ The diffraction peak corresponding to the diffraction peak appearing at 2θ = 30.0° due to the crystal structure is called 2θ ＳＥ The standard substance Li ７ P.S. ６ 2θ=30.0° and the above 2θ ＳＥ The difference between these is the angle to be shifted to the lower angle side.

2. The sulfide solid electrolyte according to claim 1 , wherein the sulfide solid electrolyte further contains a halogen atom.

3. The sulfide solid electrolyte according to claim 1 or 2, wherein the angle shifted to the lower angle side is 0.001° or more and 1.0° or less.

4. The sulfide solid electrolyte according to claim 1 or 2, wherein the content of the composite anion is 0.20 mol or less per 1.0 mol of lithium atoms contained in the sulfide solid electrolyte.

5. The composite anion is NO ３ － , S.O. ４ ２－ , CO ３ ２－ , CO ２－ and B.F. ４ － The sulfide solid electrolyte according to claim 1 or 2, which is at least one selected from the group consisting of:

6. mixing a raw material containing a lithium atom, a sulfur atom, and a phosphorus atom, a salt of a composite anion, and a solvent; removing the solvent; Heating, A method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure, comprising:

7. The composite anion is NO ３ － , S.O. ４ ２－ , CO ３ ２－ , CO ２－ and B.F. ４ － The method for producing a sulfide solid electrolyte according to claim 6, wherein the sulfide solid electrolyte is at least one selected from the group consisting of:

8. The method for producing a sulfide solid electrolyte according to claim 6 or 7, wherein the solvent contains a complexing agent that forms a complex with the raw material ingredients.

9. The method for producing a sulfide solid electrolyte according to claim 6 or 7, wherein the solubility of the salt of the composite anion in the solvent is 10 g / L or more.

10. The method for producing a sulfide solid electrolyte according to claim 6 or 7, wherein the removing of the solvent and the heating are carried out at 250°C or less.

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

12. The electrode mixture according to claim 11, further comprising at least one sulfide solid electrolyte different from the sulfide solid electrolyte.

13. A lithium ion battery comprising at least one of the sulfide solid electrolyte according to claim 1 or 2 and the electrode mixture according to claim 11 or 12.

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