Sulfide solid electrolyte production method

Abstract

A production method according to the present invention produces a sulfide solid electrolyte by using a starting material composition including elemental lithium (Li), elemental phosphorus (P), and elemental sulfur (S). The starting material composition contains one or more sulfur-containing components that include elemental sulfur (S), and one or more sulfur-free components that do not include elemental sulfur (S). If D1 is defined as the volume cumulative particle size D50 of one or more of the sulfur-containing components at a cumulative volume of 50 vol% as measured by a laser diffraction / scattering particle size distribution measurement method, and D2 is defined as the volume cumulative particle size D50 of one or more of the sulfur-free components at a cumulative volume of 50 vol% as measured by the laser diffraction / scattering particle size distribution measurement method, D1 equals 5.0×D2 or less. One or more of the sulfur-containing components have a volume cumulative particle size D50 of 50 μm or less.

Description

Method for producing sulfide solid electrolyte

[0001] The present invention relates to a method for producing a sulfide solid electrolyte.

[0002] In recent years, CO ２ Secondary batteries have been attracting attention as an approach to preventing global warming by reducing CO2 emissions. Among these, solid-state batteries using solid electrolytes are expected to be put into practical use as they combine safety and durability.

[0003] In order to realize solid-state batteries, the development of solid electrolytes has been vigorously pursued. For example, Patent Document 1 proposes a method for producing a sulfide solid electrolyte by mixing raw materials that have been pre-pulverized to have a volume-based average particle size of 20 μm or less, and then performing heat treatment. The document also describes that the method described in this document allows the production of a sulfide solid electrolyte in a shorter time than conventional methods.

[0004] Patent Document 2 proposes a method for producing a solid electrolyte by synthesizing a complex using lithium sulfide having an average particle size of 0.1 μm to 300 μm and heating the complex. The document also describes that the method described in the document makes it possible to produce a solid electrolyte with high ionic conductivity.

[0005] JP 2018-206611 A

[0006] A solid electrolyte is required to have ionic conductivity comparable to that of an electrolytic solution. However, the methods described in Patent Documents 1 and 2 do not easily produce a solid electrolyte with ionic conductivity high enough to obtain a solid-state battery that can exhibit sufficient performance for practical use. Therefore, an object of the present invention is to provide a method for easily producing a solid electrolyte with high ionic conductivity.

[0007] The present invention provides a method for producing a sulfide solid electrolyte using a raw material composition containing lithium (Li), phosphorus (P), and sulfur (S), wherein the raw material composition contains at least one sulfur-containing component that is a component containing sulfur (S), and at least one sulfur-free component that is a component that does not contain sulfur (S), and wherein at least one of the sulfur-containing components has a volume-cumulative particle size D at 50% by volume of a cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method. ５０ D １ and a volume cumulative particle size D of at least one of the sulfur-free components at a cumulative volume of 50% by volume measured by a laser diffraction / scattering particle size distribution measurement method. ５０ D ２ When this is done, D １ is 5.0 x D ２ At least one of the sulfur-containing components has a volume cumulative particle size D ５０ The above-mentioned problems have been solved by providing a method for producing a sulfide solid electrolyte in which the particle size is 50 μm or less.

[0008] The present invention will be described below based on preferred embodiments. The present invention relates to a method for producing a solid electrolyte. The solid electrolyte that is the target of the production method of the present invention preferably contains at least lithium (Li), phosphorus (P), and sulfur (S). That is, the solid electrolyte that is the target of the production method of the present invention is a sulfide solid electrolyte.

[0009] The sulfide solid electrolyte, which is the target of the manufacturing method of the present invention, may contain other elements in addition to the elements Li, P, and S. Examples of other elements include various halogen elements such as chlorine (Cl), bromine (Br), and iodine (I), iron (Fe), zinc (Zn), germanium (Ge), lead (Pb), carbon (C), nitrogen (N), and oxygen (O).

[0010] The manufacturing method of the present invention uses a raw material composition containing Li, P, and S elements. Specifically, the manufacturing method of the present invention can be broadly divided into the following steps (1) to (4). Step (1): A step of preparing a sulfur-containing component and a sulfur-free component. Step (2): A step of mixing the sulfur-containing component and the sulfur-free component to prepare a raw material composition. Step (3): A step of calcining the raw material composition to obtain a calcined product. Step (4): A step of pulverizing the calcined product. Steps (1), (2), (3), and (4) are performed in this order. After completion of step (4), a step of sieving the pulverized calcined product may be performed, if necessary. Furthermore, additional steps may be performed, if necessary, between steps (1) and (2), between steps (2) and (3), and / or between steps (3) and (4). Each of steps (1) to (4) is described below.

[0011] <Step (1)> In this step, a sulfur-containing component is prepared. Also in this step, a sulfur-free component is prepared. The sulfur-containing component is made of a substance containing S element. However, the sulfur-containing component may contain other elements in addition to S element. Examples of other elements include one or a combination of two or more of Li element; P element; Fe element; Zn element; Ge element; Pb element; O element, etc. Therefore, the sulfur-containing component can be an S element source, Li element source, P element source, Fe element source, Zn element source, Ge element source, Pb element source, O element source, etc. in the raw material composition prepared in step (2) described below. Depending on the type of the target sulfide solid electrolyte, the sulfur-containing component may be one type or two or more types. As the sulfur-containing component, for example, lithium sulfide (Li ２ S), diphosphorus pentasulfide (P ２ S ５ ), iron(II) sulfide (FeS), iron(III) sulfide (Fe ２ S ３ ), zinc sulfide (ZnS), germanium sulfide (GeS), lead sulfide (PbS) and lithium sulfate (Li ２ SO ４ ) and the like can be used. ２ S can be used as a source of S element and a source of Li element.２ S ５ can be used as a source of S and P elements. ２ S ３ can be used as a source of S and Fe elements. ZnS can be used as a source of S and Zn elements. GeS can be used as a source of S and Ge elements. PbS can be used as a source of S and Pb elements. Li ２ SO ４ can be used as a source of Li, S and O elements.

[0012] The sulfur-free component is composed of a substance that does not contain S element. The sulfur-free component is composed of a compound containing elements other than S element. Examples of the other elements include Li element; various halogen elements such as Cl element, Br element, and I element; C element; O element; P element; Fe element; N element; hydrogen (H) element; and combinations of two or more of these. Therefore, the sulfur-free component can be a Li element source, a Cl element source, a Br element source, an I element source, a C element source, an O element source, a P element source, an Fe element source, an N element source, an H element source, and the like in the raw material composition prepared in step (2) described below. Depending on the type of the target sulfide solid electrolyte, the sulfur-free component may be one type or two or more types. Examples of the sulfur-free component include lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), lithium carbonate (Li ２ CO ３ ), yellow phosphorus (P ４ ), red phosphorus (P), and phosphates. Examples of phosphates include lithium phosphate (Li ３ P.O. ４ ), iron(III) phosphate (FePO ４ ) and ammonium hydrogen phosphate (NH ４ ) ２ HPO ４ Among these, LiCl can be used as a Li element source and a Cl element source. LiBr can be used as a Li element source and a Br element source. LiI can be used as a Li element source and an I element source. Li ２ CO ３can be used as a source of Li, C and O elements. ４ and P can be used as a source of P element. ３ P.O. ４ can be used as a source of Li, P and O elements. ４ can be used as a source of Fe, P and O elements. (NH ４ ) ２ HPO ４ can be used as an N element source, an H element source, a P element source and an O element source.

[0013] The manufacturing method of the present invention is a method for producing a sulfide solid electrolyte using a sulfur-containing component and a sulfur-free component as starting materials. One of its features is that the particle size of the sulfur-containing component and the particle size of the non-sulfur-containing component are in a predetermined relationship. Sulfide solid electrolytes are required to have high ionic conductivity in order to improve the performance of solid-state batteries. However, as described in Patent Documents 1 and 2, for example, simply adjusting the particle size of one starting material has not been sufficient to produce a solid electrolyte with sufficiently high ionic conductivity. The present inventors conducted extensive research to address this issue and unexpectedly found that a sulfide solid electrolyte with high ionic conductivity can be produced by using starting materials for the sulfur-containing component and the non-sulfur-containing component, in which the particle sizes of both components are in a predetermined relationship. Furthermore, the manufacturing method of the present invention does not require, for example, designing the composition of the sulfide solid electrolyte or using additives to enhance ionic conductivity. Therefore, the manufacturing method of the present invention also has the advantage of being able to more easily produce a solid electrolyte with high ionic conductivity than conventional manufacturing methods.

[0014] Specifically, in the production method of the present invention, the volume cumulative particle size D at 50% cumulative volume of at least one of the sulfur-containing components is measured by a laser diffraction / scattering particle size distribution measurement method. ５０ (Hereinafter, simply referred to as "volume cumulative particle size D ５０ ") is also called D １and the volume cumulative particle size D of at least one of the sulfur-free components at 50% cumulative volume by a laser diffraction / scattering particle size distribution measurement method. ５０ D ２ When this is done, D １ is 5.0 x D ２ It is preferable that the sulfide solid electrolyte has a high ionic conductivity. In order to make this advantage more remarkable, it is preferable that the sulfide solid electrolyte has a high ionic conductivity. １ and at least one of the sulfur-free components D ２ That is, D １ For example, 4.0×D ２ More preferably, it is 2.5×D or less. ２ More preferably, it is 1.0 x D or less. ２ From the viewpoint of making the above-mentioned advantages even more remarkable, it is even more preferable that D ２ The coefficient of is preferably close to 1.0. ２ The coefficient of is, for example, preferably 0.020 or more, more preferably 0.025 or more, and even more preferably 0.030 or more. ２ When the coefficient of is within the above range, the desired effect is sufficiently achieved.

[0015] D １ and D ２ Although it is not entirely clear why such a relationship makes it possible to produce a sulfide solid electrolyte with high ionic conductivity, the present inventors believe that the reason may be as follows. However, the scope of the present invention is not limited to such a theory. １ but at least one of the sulfur-free components D ２ It is believed that this is because, when the value of β is equal to or less than a predetermined value, a Li-P-S skeletal structure is easily formed when a solid-state reaction occurs in step (3) described below, and the non-sulfur-containing components are efficiently substituted, thereby increasing the crystallization rate of the argyrodite-type crystal structure.

[0016] D １ and D ２In order to achieve the above relationship, it is preferable to use a combination of a sulfur-containing component and a sulfur-free component having a predetermined particle size, to adjust the particle size by grinding the sulfur-containing component and the sulfur-free component, or to synthesize and use a sulfur-containing component having a predetermined particle size and a sulfur-free component having a predetermined particle size. １ and D ２ are the volume cumulative particle diameters D of the sulfur-containing components, respectively. ５０ and the volume cumulative particle size D of the sulfur-free component ５０ This is what I mean.

[0017] When the sulfur-containing component and the sulfur-free component are each one or more kinds, the volume cumulative particle size D of one sulfur-containing component is ５０ or the volume cumulative particle size D of any one sulfur-containing component selected from two or more sulfur-containing components ５０ D １ and the volume cumulative particle size D of one sulfur-free component ５０ or the volume cumulative particle size D of any one sulfur-free component selected from two or more sulfur-free components ５０ D ２ When this is done, D １ ≦5.0×D ２ In this embodiment, for example, D １ ≦4.0×D ２ It is more preferable that the relationship of D １ ≦2.5×D ２ It is preferable that the relationship of １ ≦1.0×D ２ However, when the sulfur-containing component and the sulfur-free component are both of the same type, the above relationship does not apply.

[0018] When the sulfur-containing component and the sulfur-free component are each one or two or more types, the above-mentioned D １ and D ２ However, when the sulfur-containing component and the sulfur-free component are both of the same type, the above relationship does not apply.

[0019] When the sulfur-containing component and the sulfur-free component are each one or more kinds, the above-mentioned D is satisfied in all combinations of one arbitrarily selected sulfur-containing component and one arbitrarily selected sulfur-free component. １ and D ２ However, when the sulfur-containing component and the sulfur-free component are both of the same type, the above relationship does not apply.

[0020] The pulverization may be carried out by a dry method or a wet method. Various pulverization devices can be used for the pulverization. Examples of pulverization devices that can be used include a ball mill, a bead mill, a paint shaker, an airflow pulverizer, a homogenizer, a rod mill, a vibration ball mill, a planetary mill, and a disk mill. Alternatively, the pulverization can be carried out in a mortar.

[0021] The sulfur-containing component has a volume cumulative particle size D ５０ is preferably equal to or less than a predetermined value. This facilitates the formation of a Li-P-S skeletal structure when a solid-state reaction occurs in step (3) described below, and also increases the crystallization rate of the argyrodite-type crystal structure by efficiently substituting non-sulfur-containing components. As a result, the present inventors believe that a sulfide solid electrolyte with high ionic conductivity can be easily produced. Specifically, at least one of the sulfur-containing components has a volume cumulative particle size D ５０ The volume cumulative particle diameter D of the sulfur-containing component is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. ５０ On the other hand, the volume cumulative particle diameter D ５０ may be, for example, 1.0 μm or more, 2.0 μm or more, or 3.0 μm or more. ５０ It is preferable that the volume cumulative particle diameter D of all the sulfur-containing components is within the above range. ５０ is preferably within the above range, because this allows the ionic conductivity of the sulfide solid electrolyte to be further increased.

[0022] Volume cumulative particle size D of sulfur-containing component ５０ Independently, the volume cumulative particle size D of the sulfur-free component ５０ is also preferably equal to or less than a predetermined value. This facilitates the formation of a Li-P-S skeletal structure when a solid-state reaction occurs in step (3) described below, and also increases the crystallization rate of the argyrodite-type crystal structure by efficiently substituting the sulfur-free components. As a result, the present inventors believe that a sulfide solid electrolyte with high ionic conductivity can be easily produced. Specifically, at least one of the sulfur-free components has a volume cumulative particle size D ５０ The volume cumulative particle size D of the sulfur-free component is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. ５０ On the other hand, the volume cumulative particle diameter D ５０ may be, for example, 1.0 μm or more, 2.0 μm or more, or 3.0 μm or more. In addition, at least one of the sulfur-free components may have a volume cumulative particle size D ５０ It is preferable that the volume cumulative particle diameter D of all the sulfur-free components is within the above range. ５０ is particularly preferably within the above range, because this allows the ionic conductivity of the sulfide solid electrolyte to be further increased.

[0023] In the manufacturing method of the present invention, the sulfur-containing component and the sulfur-free component have a volume cumulative particle size D ５０ From the viewpoint of increasing the ionic conductivity of the sulfide solid electrolyte, the volume cumulative particle diameter D ５０ It is particularly preferred that the volume cumulative particle diameter D of the sulfur-containing component and the sulfur-free component is 50 μm or less. ５０ On the other hand, the volume cumulative particle diameter D ５０ may be, for example, 1.0 μm or more, 2.0 μm or more, or 3.0 μm or more.

[0024] The sulfur-containing and non-sulfur-containing components are divided into two groups by their volume cumulative particle size D ５０ is preferably a predetermined value or less, and among the respective components, the volume cumulative particle diameter D ５０ Specifically, when there are two or more sulfur-containing components and two or more sulfur-free components, the volume cumulative particle diameter D ５０ The volume cumulative particle size D of the sulfur-containing component is the smallest ５０ D １ｍｉｎ and the volume cumulative particle size D ５０ The volume cumulative particle size D of the sulfur-containing component having the largest ５０ D １ｍａｘ When this is the case, １ｍａｘ The D １ｍｉｎ The value of (D １ｍｉｎ / D １ｍａｘ ) is, for example, preferably 0.010 or more, more preferably 0.040 or more, even more preferably 0.15 or more, and even more preferably 0.30 or more. １ｍｉｎ / D １ｍａｘ may be, for example, less than 1.0, may be 0.90 or less, or may be 0.80 or less. １ｍｉｎ / D １ｍａｘ When the amount of sulfur in the solid-state reaction mixture is within the above range, a Li-P-S skeletal structure is easily formed when a solid-state reaction occurs in step (3) described below, and the non-sulfur-containing components are efficiently substituted, resulting in a high crystallization rate of the argyrodite-type crystal structure. As a result, the inventors believe that a sulfide solid electrolyte with high ionic conductivity can be easily produced.

[0025] Regarding the sulfur-free components, specifically, among the sulfur-free components, the volume cumulative particle size D ５０ The volume cumulative particle size D of the sulfur-free component is the smallest ５０ D ２ｍｉｎ and among the sulfur-free components, the volume cumulative particle size D ５０ The volume cumulative particle size D of the sulfur-free component having the largest ５０ D ２ｍａｘ When this is the case, ２ｍａｘ The D ２ｍｉｎ The value of (D ２ｍｉｎ / D２ｍａｘ ) is preferably 0.010 or more, more preferably 0.10 or more, and even more preferably 0.30 or more. ２ｍｉｎ / D ２ｍａｘ may be, for example, less than 1.0, may be 0.90 or less, or may be 0.70 or less. ２ｍｉｎ / D ２ｍａｘ The inventors believe that by keeping the content of sulfur-free components within the above range, the crystallization rate of the argyrodite-type crystal structure is increased by efficiently substituting sulfur-free components with the desired composition, and as a result, a sulfide solid electrolyte with high ionic conductivity can be easily produced.

[0026] In the manufacturing method of the present invention, for all of the sulfur-containing components and sulfur-free components, their volume cumulative particle diameters D ５０ Specifically, it is preferable that the volume cumulative particle diameter D ５０ The volume cumulative particle size D of the component having the smallest ５０ D ５０ｍｉｎ The volume cumulative particle size D ５０ The volume cumulative particle size D of the component having the largest ５０ D ５０ｍａｘ When this is the case, ５０ｍａｘ The D ５０ｍｉｎ The value of (D ５０ｍｉｎ / D ５０ｍａｘ ) is, for example, preferably 0.010 or more, more preferably 0.020 or more, even more preferably 0.10 or more, and even more preferably 0.30 or more. ５０ｍｉｎ / D ５０ｍａｘ may be, for example, less than 1.0, may be 0.80 or less, or may be 0.60 or less. ５０ｍｉｎ / D ５０ｍａｘ When the ratio is within the above range, a Li-P-S skeletal structure is easily formed when a solid-state reaction occurs in step (3) described below, and the non-sulfur-containing components are efficiently substituted, resulting in a high crystallization rate of the argyrodite-type crystal structure. As a result, the inventors believe that a sulfide solid electrolyte with high ionic conductivity can be easily produced.

[0027] D １ｍｉｎ / D １ｍａｘ , D ２ｍｉｎ / D ２ｍａｘ and D ５０ｍｉｎ / D ５０ｍａｘ In order to achieve the above range, for example, a sulfur-containing component and a sulfur-free component having a predetermined particle size may be used in combination, or the particle sizes of the sulfur-containing component and the sulfur-free component may be adjusted by pulverization and then combined, or a sulfur-containing component having a predetermined particle size and a sulfur-free component having a predetermined particle size may be synthesized and combined.

[0028] <Step (2)> Once the sulfur-containing component and the sulfur-free component are prepared, they are mixed to prepare a raw material composition. This raw material composition contains at least one sulfur-containing component and at least one non-sulfur-containing component. The amounts of the sulfur-containing component and the sulfur-free component used can be appropriately set so as to obtain the composition of the sulfide solid electrolyte, which is the target of the production method of the present invention. For mixing, a known mixing device can be used. For example, a mixing device such as a ball mill, a bead mill, or a paint shaker can be used. These devices may be of the rotation type, or of the rotation type and revolution type.

[0029] The mixing of the sulfur-containing component and the sulfur-free component may be performed by a dry method or a wet method. Examples of liquid media that can be used in wet mixing include various organic solvents. Specific examples include linear saturated aliphatic hydrocarbons such as hexane, heptane, and decane; cyclic saturated aliphatic hydrocarbons such as cyclohexane; and aromatic hydrocarbons such as benzene and toluene. In the production method of the present invention, dry mixing can be adopted from the viewpoint of omitting the post-treatment drying step. It is preferable that the mixing of the sulfur-containing component and the sulfur-free component is performed under conditions that do not cause pulverization of the sulfur-containing component and the sulfur-free component before mixing, i.e., under conditions that do not substantially change the particle size of the sulfur-containing component and the sulfur-free component before and after mixing. This is because a sulfide solid electrolyte with high ionic conductivity is easily obtained.

[0030] <Step (3)> In this step, the raw material composition prepared in step (2) is fired to obtain a fired product. This fired product is the desired sulfide solid electrolyte. The firing is carried out by drying the raw material composition as needed, then crushing and classifying it, and then firing it in an inert gas atmosphere or hydrogen sulfide (H ２ It is preferable to perform the calcination under a gas flow of S. By setting the calcination temperature at 350°C or higher, sulfur deficiency can be suppressed. Furthermore, by setting the calcination temperature at 350°C or higher, it is possible to suppress the unreacted sulfur-containing component and sulfur-free component from remaining in the solid electrolyte, and to suppress a decrease in ion conductivity.

[0031] When hydrogen sulfide gas is used as the firing atmosphere, the sulfur partial pressure of the atmosphere can be increased by the sulfur gas generated by decomposition of hydrogen sulfide during firing. As a result, even if the firing temperature is set high, sulfur deficiency is unlikely to occur in the resulting solid electrolyte, and the development of electronic conductivity can be suppressed. Specific firing temperatures are, for example, preferably 350°C or higher, and more preferably 450°C or higher. Meanwhile, the firing temperature is, for example, preferably 650°C or lower, more preferably 600°C or lower, and even more preferably 500°C or lower.

[0032] When an inert gas is used as the firing atmosphere, setting the firing temperature high tends to cause sulfur deficiency in the resulting solid electrolyte. From this viewpoint, the firing temperature is preferably, for example, 350°C or higher, and more preferably 400°C or higher. On the other hand, the firing temperature is preferably, for example, 600°C or lower, and more preferably 550°C or lower.

[0033] Regardless of the firing atmosphere, the firing time is preferably, for example, 1 hour or more, more preferably 2 hours or more, and even more preferably 3 hours or more. On the other hand, the firing time is, for example, preferably 10 hours or less, more preferably 8 hours or less, and even more preferably 6 hours or less. From the viewpoint of eliminating unreacted phases due to uneven heating, the temperature rise rate during firing is, for example, preferably 250°C / h or less, more preferably 200°C / h or less, and even more preferably 150°C / h or less. On the other hand, the temperature rise rate is, for example, preferably 50°C / h or more, and even more preferably 80°C / h or more. By keeping the temperature rise rate within the above range, firing efficiency can be maintained.

[0034] The thus obtained fired product, i.e., the sulfide solid electrolyte, can be, for example, Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ -LiX (where "X" represents one or more halogen elements), Li ２ S-P ２ S ５ -P ２ O ５ , Li ２ S-Li ３ P.O. ４ -P ２ S ５ , Li ３ P.S. ４ , Li ４ P ２ S ６ , Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S ４ , Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ , Li ７－ｘ P.S. ６－ｘ X ｘ(where "X" represents one or more halogen elements, and 0.2<x<2.0 or 0.2<x<1.8). Among these sulfide solid electrolytes, it is preferable to produce a solid electrolyte containing a crystalline phase having an argyrodite-type crystal structure, from the viewpoint of particularly high lithium ion conductivity.

[0035] <Step (4)> In this step, the fired product obtained in step (3) is pulverized. This allows a solid-state battery to be more easily obtained using the fired product after pulverization (i.e., sulfide solid electrolyte). The pulverization may be performed in a dry or wet manner. Dry pulverization and wet pulverization can be performed by the methods described above. From the viewpoint of improving packing properties and increasing lithium ion conductivity, dry pulverization is preferred.

[0036] After pulverization, the pulverized product may be classified as needed, for example, by passing it through a 20 μm sieve.

[0037] The sulfide solid electrolyte thus obtained has lithium ion conductivity in a solid state. The lithium ion conductivity of the solid electrolyte is preferably 2.0 mS / cm or more, more preferably 2.2 mS / cm or more, and even more preferably 2.4 mS / cm or more, at room temperature, i.e., 25°C. The lithium ion conductivity can be measured using the method described in the examples below.

[0038] The sulfide solid electrolyte produced by the method of the present invention can be used as a material for constituting a solid electrolyte layer, a positive electrode layer, or a negative electrode layer. Specifically, the sulfide solid electrolyte produced by the method of the present invention can be used in a battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer. That is, the sulfide solid electrolyte produced by the method of the present invention can be used in so-called solid-state batteries. More specifically, it can be used in lithium solid-state batteries. The lithium solid-state battery may be a primary battery or a secondary battery. The shape of the battery is not particularly limited, and shapes such as a laminated type, a cylindrical type, and a prismatic type can be adopted. The term "solid-state battery" includes not only solid-state batteries that do not contain any liquid or gel-like substance as an electrolyte, but also batteries that contain, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of a liquid or gel-like substance as an electrolyte.

[0039] When the solid electrolyte layer contains a sulfide solid electrolyte produced by the method of the present invention, the solid electrolyte layer can be produced, for example, by dropping a slurry consisting of the sulfide solid electrolyte, a binder, and a solvent onto a substrate and scraping it off with a doctor blade or the like, by contacting the substrate with the slurry and then cutting it with an air knife, or by forming a coating film by screen printing or the like and then removing the solvent by heating and drying. Alternatively, the solid electrolyte layer can be produced by compacting a powdered sulfide solid electrolyte by pressing or the like and then appropriately processing it. The thickness of the solid electrolyte layer is typically preferably 5 μm to 300 μm, and more preferably 10 μm to 100 μm, in order to balance short-circuit prevention and volumetric capacity density.

[0040] The sulfide solid electrolyte produced by the method of the present invention may be used together with an active material to form an electrode mixture. The proportion of the sulfide solid electrolyte in the electrode mixture is typically 10% by mass or more and 50% by mass or less. The electrode mixture may contain other materials such as a conductive additive or a binder as needed. A paste is prepared by mixing the electrode mixture with a solvent, and the paste is applied to a current collector such as aluminum foil and dried to form a positive electrode layer and a negative electrode layer.

[0041] The cathode material constituting the cathode layer can be any cathode material used as a cathode active material in lithium-ion batteries. For example, lithium-containing cathode active materials, specifically spinel-type lithium transition metal oxides and lithium metal oxides with layered structures, can be used. The use of a high-voltage cathode material as the cathode material can improve energy density. In addition to the cathode active material, the cathode material may contain a conductive material or other materials.

[0042] As the negative electrode material constituting the negative electrode layer, a negative electrode material used as a negative electrode active material in a lithium ion battery can be appropriately used. Since the sulfide solid electrolyte produced by the method of the present invention is electrochemically stable, it can be used at a potential of lithium metal or a lower potential comparable to that of lithium metal (about 0.1 V vs. Li ＋ Carbonaceous materials such as graphite, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon), which are charged and discharged using a lithium-ion battery (Li / Li), can be used as the negative electrode material. This can significantly improve the energy density of solid-state batteries. Silicon or tin, which are promising high-capacity materials, can also be used as the active material.

[0043] Although the present invention has been described above based on the preferred embodiments, the present invention is not limited to the above embodiments.

[0044]

[0023] In relation to the above-described embodiment, the following method for producing a sulfide solid electrolyte is further disclosed: [1] A method for producing a sulfide solid electrolyte using a raw material composition containing lithium (Li), phosphorus (P), and sulfur (S), wherein the raw material composition contains at least one sulfur-containing component that is a component containing sulfur (S), and at least one sulfur-free component that is a component that does not contain sulfur (S), and at least one of the sulfur-containing components has a volume-cumulative particle size D at 50% of the cumulative volume by a laser diffraction / scattering particle size distribution measurement method. ５０ D １ and a volume cumulative particle size D of at least one of the sulfur-free components at a cumulative volume of 50% by volume measured by a laser diffraction / scattering particle size distribution measurement method. ５０ D ２ When this is done, D １is 5.0 x D ２ At least one of the sulfur-containing components has a volume cumulative particle size D ５０ The method for producing a sulfide solid electrolyte, wherein the particle size is 50 μm or less.

[0045] [2] The sulfur-containing component and the sulfur-free component have a volume cumulative particle size D ５０ [3] The method according to [1], wherein the volume cumulative particle diameter D of the sulfur-containing component is independently 50 μm or less. ５０ The volume cumulative particle size D of the sulfur-containing component is the smallest ５０ D １ｍｉｎ and the volume cumulative particle size D ５０ The volume cumulative particle size D of the sulfur-containing component having the largest ５０ D １ｍａｘ When this is the case, １ｍａｘ The D １ｍｉｎ [4] The method according to [1] or [2], wherein the ratio of the volume cumulative particle diameter D ５０ The volume cumulative particle size D of the sulfur-free component is the smallest ５０ D ２ｍｉｎ and among the sulfur-free components, the volume cumulative particle size D ５０ The volume cumulative particle size D of the sulfur-free component having the largest ５０ D ２ｍａｘ When this is the case, ２ｍａｘ The D ２ｍｉｎ [5] The method according to any one of [1] to [3], wherein the ratio of the volume cumulative particle diameter D ５０ The volume cumulative particle size D of the component having the smallest ５０ D ５０ｍｉｎ The volume cumulative particle size D ５０ The volume cumulative particle size D of the component having the largest ５０ D ５０ｍａｘ When this is the case, ５０ｍａｘ The D ５０ｍｉｎ[6] The manufacturing method according to any one of [1] to [4], wherein the ratio of is 0.010 or more. [6] The manufacturing method according to any one of [1] to [5], wherein the raw material composition is fired to obtain a fired product. [7] The manufacturing method according to [6], wherein the fired product is pulverized. [8] The manufacturing method according to [6] or [7], wherein the fired product contains a crystalline phase having an argyrodite-type crystal structure.

[0046] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0047] [Example 1] (1) Step: Li as a sulfur-containing component ２ S powder and P ２ S ５ As sulfur-free components, LiCl powder and LiBr powder were prepared. The volume-cumulative particle diameters D ５０ is as shown in Table 1. ２ Volume cumulative particle size D of S ５０ In Table 1, Li ２ Volume cumulative particle size D of S powder ５０ When is set to 1, P ２ S ５ The relative values ​​for LiBr powder, LiCl powder and LiBr powder are given.

[0048] (2) Process Composition formula Li ５．４ P.S. ４．４ Cl ０．８ Br ０．８ After each powder was weighed after pulverization, the powders were dry-mixed using a ball mill to prepare a raw material composition so that a sulfide solid electrolyte of the formula (I) was obtained.

[0049] Step (3) The raw material composition was fired to obtain a fired product comprising a sulfide solid electrolyte. The firing was carried out using a tubular electric furnace. Nitrogen gas with a purity of 100% was circulated through the electric furnace during firing. The firing temperature was set to 500°C. As a result of XRD measurement, it was confirmed that the fired product contained a crystalline phase having an argyrodite-type crystal structure.

[0050] Step (4): The fired product was pulverized using a mortar and pestle and passed through a 20 μm sieve to obtain the desired sulfide solid electrolyte.

[0051] [Examples 2 to 5 and Comparative Examples 1 and 2] In Example 1, the volume cumulative particle diameter D shown in Table 1 ５０ In Examples 2 and 3, the target sulfide solid electrolyte was obtained in the same manner as in Example 1, except that the powder having the following structure was used: ２ Volume cumulative particle size D of S ５０ In Examples 4 and 5, the size of the Li particles after pulverization was 10 μm or more and 20 μm or less. ２ Volume cumulative particle size D of S ５０ In Comparative Examples 1 and 2, the size of the Li particles after pulverization was 2 μm or more and 5 μm or less. ２ Volume cumulative particle size D of S ５０ was greater than 50 μm.

[0052] [Evaluation] In the examples and comparative examples, the volume cumulative particle diameter D of each powder used in preparing the raw material composition was ５０ The volume cumulative particle size D of the sulfur-containing component was measured by the following method. １ The volume cumulative particle size D of the sulfur-free component ２ The values ​​obtained by dividing by are shown in Table 2. Furthermore, the lithium ion conductivity of the sulfide solid electrolytes obtained in the examples and comparative examples was measured by the following method.

[0053] [Volume cumulative particle size D ５０ Measurement of the particle size distribution of the sulfide solid electrolyte by the laser diffraction scattering particle size distribution measurement method was carried out according to the following procedure. Using an automatic sample feeder for a laser diffraction particle size distribution measurement device (Microtrac SDC manufactured by Microtrac-Bell Corporation), the flow rate of the measurement sample containing the sulfide solid electrolyte was set to 50%, and the measurement sample was irradiated with 30 W ultrasonic waves for 60 seconds. Thereafter, the particle size distribution was measured using a laser diffraction particle size distribution measurement device "MT3300EXII" manufactured by Microtrac-Bell Corporation, and the particle size at which the cumulative volume was 50% by volume was determined from the obtained volume-based particle size distribution chart. The volume-cumulative particle size D ５０ The volume cumulative particle diameter D ５０When measuring, the organic solvent was passed through a 60 μm filter, the solvent refractive index was 1.50, the particle permeability condition was "permeable", the particle refractive index was 1.59, the shape was "non-spherical", the measurement range was 0.133 μm to 704.0 μm, the measurement time was 10 seconds, and the measurement was carried out twice, and the average of the obtained measured values ​​was taken as the volume cumulative particle diameter D ５０ The measurement sample containing the sulfide solid electrolyte was prepared as follows. First, 0.3 g of the sulfide solid electrolyte and 5.7 g of a dispersant-containing liquid (mass ratio of toluene to dispersant (SN Dispersant 9228 manufactured by San Nopco Ltd.) = 19:1) were mixed by hand to prepare a slurry containing the sulfide solid electrolyte. Next, 6 ml of the slurry containing the sulfide solid electrolyte was poured into an organic solvent (toluene) to prepare a measurement sample containing the sulfide solid electrolyte.

[0054] [Lithium ion conductivity] The sulfide solid electrolyte powders obtained in the examples and comparative examples were subjected to a lithium ion conductivity test at about 6 t / cm in a glove box purged with sufficiently dried Ar gas (dew point -60°C or lower). ２ The pellets were uniaxially pressed under a load of 1000 kJ / cm2 to prepare samples for measuring lithium ion conductivity. The lithium ion conductivity was measured using a Solartron 1255B electrochemical measurement system (1280C) and an impedance / gain-phase analyzer (SI1260) manufactured by Solartron Analytical. The measurement conditions were an AC impedance method at a temperature of 25°C, a frequency of 100 Hz to 1 MHz, and an amplitude of 100 mV.

[0055]

[0056]

[0057] As is clear from the results shown in Tables 1 and 2, Examples 1 to 5 have higher lithium ion conductivity than Comparative Examples 1 and 2. Generally, the volume cumulative particle diameter D of the sulfide solid electrolyte ５０ The larger the particle size, the higher the lithium ion conductivity. ５０Even in the examples having the above structure, the lithium ion conductivity was high, and therefore it is clear that the production method of the present invention can provide a sulfide solid electrolyte having high lithium ion conductivity.

[0058] According to the method of the present invention, a sulfide solid electrolyte having high ionic conductivity can be easily produced.

Claims

1. A method for producing a sulfide solid electrolyte using a raw material composition containing lithium (Li), phosphorus (P) and sulfur (S), wherein the raw material composition contains at least one sulfur-containing component that is a component that contains sulfur (S) element, and at least one sulfur-free component that is a component that does not contain sulfur (S), and at least one of the sulfur-containing components has a volume cumulative particle size D at 50% cumulative volume measured by a laser diffraction / scattering particle size distribution measurement method. ５０ D １ and a volume cumulative particle size D at 50% cumulative volume of at least one of the sulfur-free components measured by a laser diffraction / scattering particle size distribution measurement method. ５０ D ２ When this is done, D １ is 5.0 x D ２ At least one of the sulfur-containing components has a volume cumulative particle size D ５０ The method for producing a sulfide solid electrolyte, 2. The sulfur-containing component and the sulfur-free component are each formed by mixing the sulfur-containing component and the sulfur-free component with each other by their volume-cumulative particle size D ５０ The method according to claim 1 , wherein each of the first and second insulating layers is independently 50 μm or less.

3. Among the sulfur-containing components, the volume cumulative particle size D ５０ The volume cumulative particle size D of the sulfur-containing component is the smallest ５０ D １ｍｉｎ The volume cumulative particle size D ５０ The volume cumulative particle size D of the sulfur-containing component having the largest ５０ D １ｍａｘ When the D １ｍａｘ The D １ｍｉｎ The method according to claim 1 , wherein the ratio is 0.010 or more.

4. Among the sulfur-free components, the volume cumulative particle size D ５０ The volume cumulative particle size D of the sulfur-free component having the smallest ５０ D ２ｍｉｎ Among the sulfur-free components, the volume cumulative particle size D ５０ The volume cumulative particle size D of the sulfur-free component having the largest ５０ D ２ｍａｘ When the D ２ｍａｘ The D ２ｍｉｎ The method according to claim 1 , wherein the ratio is 0.010 or more.

5. The volume cumulative particle size D of the sulfur-containing component and the sulfur-free component ５０ The volume cumulative particle size D of the component having the smallest ５０ D ５０ｍｉｎ The volume cumulative particle size D ５０ The volume cumulative particle size D of the component having the largest ５０ D ５０ｍａｘ When the D ５０ｍａｘ The D ５０ｍｉｎ The method according to claim 1 , wherein the ratio is 0.010 or more.

6. The method according to claim 1, further comprising calcining the raw material composition to obtain a calcined product.

7. The method according to claim 6, wherein the fired product is pulverized.

8. The method according to claim 6 or 7, wherein the fired product contains a crystalline phase having an argyrodite-type crystal structure.

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