Method for producing sulfide solid electrolyte

Abstract

This production method is a method for producing a sulfide solid electrolyte using a starting material composition containing a lithium (Li) element, a phosphorus (P) element, and a sulfur (S) element. The raw material composition contains at least one sulfur-containing component that contains a sulfur (S) element, and at least one sulfur-free component that does not contain a sulfur (S) element. D1 is 5.0 * D2 or less, where D1 is the volume cumulative particle diameter D50 at a cumulative volume of 50 vol% as determined by a laser diffraction scattering particle size distribution measurement method for at least one of the sulfur-containing components, and D2 is the volume cumulative particle diameter D50 at a cumulative volume of 50 vol% as determined by a laser diffraction scattering particle size distribution measurement method for at least one of the sulfur-free components. The volume cumulative particle diameter (D50) of at least one of the sulfur-containing components is 50 [mu] m or less.

Description

Technical Field

[0001] This invention relates to a method for manufacturing sulfide solid electrolytes. Background Technology

[0002] In recent years, secondary batteries have attracted attention as a countermeasure to prevent global warming by reducing CO2. Among them, solid-state batteries, which use solid electrolytes, are expected to be put into practical use as batteries that combine safety and durability.

[0003] To realize solid-state batteries, the development of solid electrolytes is actively underway. For example, Patent Document 1 proposes a method for manufacturing a sulfide solid electrolyte by mixing raw materials that have been pre-crushed to a volumetric average particle size of less than 20 μm and then subjecting them to heat treatment. This document describes that, according to the method described herein, a sulfide solid electrolyte can be manufactured in a shorter time than previously possible.

[0004] Patent Document 2 discloses a method for manufacturing a solid electrolyte by synthesizing a complex using lithium sulfide with an average particle size of 0.1 μm or more and 300 μm or less, and then heating the complex. This document describes a method for manufacturing a solid electrolyte with high ionic conductivity.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-206611

[0008] Patent Document 2: US2022 / 0336848 A1 Summary of the Invention

[0009] Solid electrolytes are required to have ionic conductivity comparable to that of liquid electrolytes. However, the methods described in Patent Documents 1 and 2 make it difficult to manufacture solid electrolytes with ionic conductivity high enough to produce solid-state batteries with sufficient performance for practical use.

[0010] Therefore, the objective of this invention is to provide a method for easily manufacturing solid electrolytes with high ionic conductivity.

[0011] The present invention solves the above-mentioned problems by providing a method for manufacturing a sulfide solid electrolyte, wherein the method uses a raw material composition comprising lithium (Li), phosphorus (P), and sulfur (S) to manufacture the sulfide solid electrolyte.

[0012] The above-mentioned raw material composition contains at least one component containing sulfur (S), i.e., a sulfur-containing component, and at least one component that does not contain sulfur (S), i.e., a sulfur-free component.

[0013] The cumulative volumetric particle size D at 50% of the cumulative volume of at least one of the sulfur-containing components described above, determined by laser diffraction scattering particle size distribution method. 50 Let D1 be the cumulative volumetric particle size D at 50% capacity of at least one of the above sulfur-free components, determined by laser diffraction scattering particle size distribution method. 50 When D2 is set, D1 is less than or equal to 5.0 × D2.

[0014] The cumulative volumetric particle size D of at least one of the above sulfur-containing components 50 It is below 50μm. Detailed Implementation

[0015] The present invention will now be described based on its preferred embodiments. The present invention relates to a method for manufacturing a solid electrolyte. The solid electrolyte, as the object of the manufacturing method of the present invention, preferably contains at least lithium (Li), phosphorus (P), and sulfur (S). That is, the solid electrolyte, as the object of the manufacturing method of the present invention, is a sulfide solid electrolyte.

[0016] In addition to Li, P, and S, the sulfide solid electrolyte that is the object of the manufacturing method of the present invention may also contain other elements. 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).

[0017] 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 is generally divided into the following steps (1) to (4).

[0018] (1) Process: The process of preparing sulfur-containing and sulfur-free components.

[0019] (2) Process: The process of preparing a raw material composition by mixing the sulfur-containing component and the sulfur-free component mentioned above.

[0020] (3) Process: The process of calcining the above raw material composition to obtain the calcined product.

[0021] (4) Process: The process of crushing the above-mentioned calcined material.

[0022] (1) Steps, (2) Steps, (3) Steps and (4) are performed in sequence. After step (4) is completed, a sieving process can be performed on the pulverized calcined material as needed. In addition, additional processes can be performed between steps (1) and (2), between steps (2) and (3), and / or between steps (3) and (4) as needed.

[0023] The following describes the processes (1) to (4) respectively.

[0024] <(1) Process>

[0025] In this process, sulfur-containing components are prepared. Additionally, in this process, sulfur-free components are prepared.

[0026] The sulfur-containing component is formed from substances containing the element S. However, the sulfur-containing component may contain other elements besides S. Examples of other elements include, for example, one or more combinations of the following: Li; P; Fe; Zn; Ge; Pb; and O. Therefore, the sulfur-containing component in the raw material composition prepared in step (2) described later can be a source of S, Li, P, Fe, Zn, Ge, Pb, and O elements.

[0027] Depending on the type of the target sulfide solid electrolyte, the sulfur-containing component can be one or more.

[0028] As sulfur-containing components, lithium sulfide (Li₂S), phosphorus pentasulfide (P₂S₅), iron(II) sulfide (FeS), iron(III) sulfide (Fe₂S₃), zinc sulfide (ZnS), germanium sulfide (GeS), lead sulfide (PbS), and lithium sulfate (Li₂SO₄) can be used. Among these, Li₂S can be used as both a sulfur (S) and lithium (Li) source. P₂S₅ can be used as both a sulfur (S) and phosphorus (P) source. FeS and Fe₂S₃ can be used as both sulfur (S) and iron (Fe) sources. ZnS can be used as both a sulfur (S) and zinc (Zn) source. GeS can be used as both a sulfur (S) and zinc (Ge) source. PbS can be used as both a sulfur (S) and phosphorus (Pb) source. Li₂SO₄ can be used as a lithium (Li), sulfur (S), and oxygen (O) source.

[0029] The sulfur-free component is formed from a substance that does not contain sulfur (S). The sulfur-free component is formed from a compound containing elements other than sulfur (S). Examples of these other elements include: Li; various halogen elements such as Cl, Br, and I; C; O; P; Fe; N; and one or more combinations of hydrogen (H). Therefore, the sulfur-free component in the raw material composition prepared in step (2) described later can be a source of Li, Cl, Br, I, C, O, P, Fe, N, and H elements.

[0030] Depending on the type of the target sulfide solid electrolyte, the sulfur-free component can be one type, or it can be two or more types.

[0031] Examples of sulfur-free components include: lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), lithium carbonate (Li₂CO₃), yellow phosphorus (P₄), red phosphorus (P), and phosphates. Examples of phosphates include: lithium phosphate (Li₃PO₄), iron(III) phosphate (FePO₄), and ammonium hydrogen phosphate (NH₄)₂HPO₄. LiCl can be used as a source of both Li and Cl elements. LiBr can be used as a source of both Li and Br elements. LiI can be used as a source of both Li and I elements. Li₂CO₃ can be used as a source of Li, C, and O elements. P₄ and P can be used as sources of P elements. Li₃PO₄ can be used as a source of both Li, P, and O elements. FePO₄ can be used as a source of both Fe, P, and O elements. (NH₄)₂HPO₄ can be used as a source of N, H, P, and O elements.

[0032] The manufacturing method of the present invention is a method for manufacturing sulfide solid electrolytes using sulfur-containing components and sulfur-free components as starting materials. One of its features is that the particle size of the sulfur-containing components and the particle size of the sulfur-free components are in a specified relationship.

[0033] To improve the performance of solid-state batteries, high ionic conductivity of sulfide solid electrolytes is desirable. However, as described in Patent Documents 1 and 2, it is difficult to manufacture solid electrolytes with sufficiently high ionic conductivity simply by adjusting the particle size of a single starting material.

[0034] Regarding this improvement, the inventors conducted in-depth research and unexpectedly discovered that by using a predetermined relationship between the particle size of the sulfur-containing component and the particle size of the sulfur-free component in the starting material of the sulfide solid electrolyte, it is possible to manufacture a sulfide solid electrolyte with high ionic conductivity. Furthermore, the manufacturing method of the present invention does not require designing, for example, the composition of the sulfide solid electrolyte as the object of the manufacturing method and / or using additives to improve ionic conductivity. Therefore, the manufacturing method according to the present invention also has the advantage of being able to easily manufacture a solid electrolyte with high ionic conductivity compared to conventional manufacturing methods.

[0035] Specifically, in the manufacturing method of the present invention, the cumulative volumetric particle size D at 50% capacity of at least one of the sulfur-containing components is determined by laser diffraction scattering particle size distribution method. 50 (Hereinafter referred to as "cumulative particle size D") 50 Let D1 be the cumulative volumetric particle size D at 50% capacity, based on a laser diffraction scattering particle size distribution method, which does not contain at least one of the sulfur components. 50 When D2 is specified, D1 is preferably 5.0 × D2 or less. This allows for the easy manufacture of sulfide solid electrolytes with high ionic conductivity. From the viewpoint of further emphasizing this advantage, regarding D1 for at least one sulfur-containing component and D2 for at least one sulfur-free component, D1 is, for example, further preferably 4.0 × D2 or less, more preferably 2.5 × D2 or less, and even more preferably 1.0 × D2 or less. From the viewpoint of further emphasizing the above advantages, the coefficient of D2 is preferably close to 1.0. The coefficient of D2 is, for example, preferably 0.020 or more, more preferably 0.025 or more, and even more preferably 0.030 or more. By keeping the coefficient of D2 within the above range, the desired effect can be fully realized.

[0036] The reason why a sulfide solid electrolyte with high ionic conductivity can be manufactured by placing D1 and D2 in such a relationship is not entirely clear, but the inventors believe it may be based on the following reasons. However, the scope of the present invention is not limited to this theory. The reason is that by making the D1 of at least one of the sulfur-containing components below a predetermined value relative to the D2 of at least one of the sulfur-free components, a Li-PS framework structure is easily formed during the solid-phase reaction in step (3) described later, and the sulfur-free components are effectively replaced, thereby increasing the crystallinity of the sulfide-germanium ore-type crystal structure.

[0037] To make D1 and D2 have the above relationship, it is suitable to: combine sulfur-containing components and sulfur-free components with a specified particle size, or adjust the particle size by pulverizing the sulfur-containing components and sulfur-free components separately, or synthesize sulfur-containing components and sulfur-free components with a specified particle size and use them together.

[0038] When there is one sulfur-containing component and one sulfur-free component, D1 and D2 are the volumetric cumulative particle sizes of the sulfur-containing component, respectively. 50 and the cumulative particle size D of the sulfur-free component 50 .

[0039] When there are one or more sulfur-containing and sulfur-free components, the volumetric cumulative particle size D of one sulfur-containing component is calculated. 50 Or the volumetric cumulative particle size D selected from any one of two or more sulfur-containing components. 50 Let D1 be the volumetric cumulative particle size D of a sulfur-free material. 50 Or the cumulative volumetric particle size D selected from any one of two or more sulfur-free components. 50 When D2 is defined as D1, the relationship D1 ≤ 5.0 × D2 is satisfied. In this embodiment, it is more preferable, for example, to satisfy the relationship D1 ≤ 4.0 × D2, wherein it is more preferably satisfied, D1 ≤ 2.5 × D2, and even more preferably satisfied, D1 ≤ 1.0 × D2. However, the above relationship does not apply when both the sulfur-containing component and the sulfur-free component are of the same type.

[0040] When there are one or more sulfur-containing and sulfur-free components, the combination of sulfur-containing and sulfur-free components may also be an example, which does not satisfy the above relationships D1 and D2. However, when there is only one sulfur-containing and one sulfur-free component, the above relationships do not apply.

[0041] When there are one or more sulfur-containing and sulfur-free components, all combinations of any chosen sulfur-containing and sulfur-free components can satisfy the relationships D1 and D2 described above. However, when there is only one sulfur-containing and one sulfur-free component, the above relationships do not apply.

[0042] Grinding can be carried out dry or wet. Various grinding devices can be used. Examples of grinding devices include ball mills, bead mills, paint mixers, air jet mills, homogenizers, rod mills, vibratory ball mills, planetary mills, and disc mills. Alternatively, grinding can be done using a mortar and pestle.

[0043] The preferred sulfur-containing component has a volumetric cumulative particle size D. 50 The value is below the specified value. Therefore, when a solid-phase reaction occurs in step (3) described later, a Li-PS framework structure is easily formed, and the sulfur-free components are effectively replaced, thereby increasing the crystallinity of the sulfide-germanium ore-type crystal structure. As a result, the inventors believe that it is possible to easily manufacture sulfide solid electrolytes with high ionic conductivity.

[0044] Specifically, the volumetric cumulative particle size D of at least one of the sulfur-containing components 50 Preferably, it is 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. The volumetric cumulative particle size D of the sulfur-containing component... 50 Smaller is preferred. On the other hand, the volumetric cumulative particle size D 50 For example, it can be 1.0μm or larger, 2.0μm or larger, or 3.0μm or larger.

[0045] Furthermore, this is because: at least one of the sulfur-containing components has a preferred volumetric cumulative particle size D 50 Within the above range, the preferred total volumetric cumulative particle size D of the sulfur-containing components is... 50 Within the aforementioned range, this allows for further improvement in the ionic conductivity of sulfide solid electrolytes.

[0046] The volumetric cumulative particle size D of sulfur-containing components 50 Independently, the volumetric cumulative particle size D without sulfur components 50 Preferably, the value is below a specified value. Therefore, when a solid-phase reaction occurs in step (3) described later, a Li-PS framework structure is easily formed, and the sulfur-free components are effectively replaced, resulting in a higher crystallinity of the sulfide-germanium ore-type crystal structure. As a result, the inventors believe that it is possible to easily manufacture sulfide solid electrolytes with high ionic conductivity.

[0047] Specifically, the volumetric cumulative particle size D of the component that does not contain at least one of the sulfur components is... 50 Preferably, it is 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. The volumetric cumulative particle size D without sulfur components. 50 Smaller is preferred. On the other hand, the volumetric cumulative particle size D 50 For example, it can be 1.0μm or larger, 2.0μm or larger, or 3.0μm or larger.

[0048] Furthermore, this is because: at least one preferred volumetric cumulative particle size D of the sulfur-free components is not present. 50 Within the above range, the total volumetric cumulative particle size D that is particularly preferred is free of sulfur components. 50 Within the aforementioned range, this allows for further improvement in the ionic conductivity of sulfide solid electrolytes.

[0049] In the manufacturing method of the present invention, the cumulative volumetric particle size D of the sulfur-containing component and the sulfur-free component is... 50 Each particle size is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. From the viewpoint of improving the ionic conductivity of sulfide solid electrolytes, the cumulative volumetric particle size D of both sulfur-containing and sulfur-free components is particularly preferred. 50The particle size is below 50 μm. The cumulative volumetric particle size D of the sulfur-containing and sulfur-free components is... 50 Smaller is preferred. On the other hand, the volumetric cumulative particle size D 50 For example, it can be 1.0μm or larger, 2.0μm or larger, or 3.0μm or larger.

[0050] Cumulative particle size D of sulfur-containing and sulfur-free components 50 Preferably, the volumetric cumulative particle size D is below a specified value among various components. 50 It is also preferable to be in a specified relationship. Specifically, when there are two or more sulfur-containing and sulfur-free components, the volume-cumulative particle size D of the sulfur-containing component is... 50 The smallest volumetric cumulative particle size D of this sulfur-containing component 50 Let's call it D 1min The volumetric cumulative particle size D of the sulfur-containing component 50 The largest cumulative particle size D of this sulfur-containing component 50 Let's call it D 1max At that time, the D 1min Relative to D 1max The value of D 1min / D 1max For example, it is preferably 0.010 or higher, more preferably 0.040 or higher, even more preferably 0.15 or higher, and still more preferably 0.30 or higher. On the other hand, D 1min / D 1max For example, it can be less than 1.0, below 0.90, or below 0.80. By making D... 1min / D 1max Within the aforementioned range, a Li-PS framework structure is readily formed during the solid-phase reaction in step (3) described later, and the sulfur-free components are effectively replaced, thereby increasing the crystallinity of the sulfide-germanium ore-type crystal structure. As a result, the inventors believe that it is possible to easily manufacture sulfide solid electrolytes with high ionic conductivity.

[0051] Regarding the sulfur-free component, specifically, the volumetric cumulative particle size D of the sulfur-free component... 50 The smallest volumetric cumulative particle size D of the sulfur-free component 50 Let's call it D 2min The cumulative particle size D of the sulfur-free component 50 The largest cumulative particle size D of the sulfur-free component 50 Let's call it D 2max At that time, the D 2min Relative to D 2max The value of D 2min / D 2maxThe value is preferably 0.010 or higher, more preferably 0.10 or higher, and even more preferably 0.30 or higher. On the other hand, D... 2min / D 2max For example, it can be less than 1.0, below 0.90, or below 0.70. By making D... 2min / D 2max Within the aforementioned range, the sulfur-free components are effectively replaced with the desired composition, thereby increasing the crystallinity of the silver sulfide-germanium ore-type crystal structure. As a result, the inventors believe that it is possible to readily manufacture sulfide solid electrolytes with high ionic conductivity.

[0052] In the manufacturing method of the present invention, it is also preferable to have a cumulative volumetric particle size D of both sulfur-containing and sulfur-free components. 50 The relationship is defined. Specifically, the volumetric cumulative particle size D of the sulfur-containing and sulfur-free components is... 50 The smallest volumetric cumulative particle size D of this component 50 Let's call it D 50min The cumulative particle size D of the sulfur-containing component and the sulfur-free component. 50 The largest cumulative particle size D of this component 50 Let's call it D 50max At that time, the D 50min Relative to D 50max The value of D 50min / D 50max For example, it is 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. On the other hand, D 50min / D 50max For example, it can be less than 1.0, below 0.80, or below 0.60. By making D... 50min / D 50max Within the aforementioned range, a Li-PS framework structure is readily formed during the solid-phase reaction in step (3) described later, and the sulfur-free components are effectively replaced, thereby increasing the crystallinity of the sulfide-germanium ore-type crystal structure. As a result, the inventors believe that it is possible to easily manufacture sulfide solid electrolytes with high ionic conductivity.

[0053] In order to make D 1min / D 1max D 2min / D 2max and D 50min / D 50maxWithin the aforementioned range, for example, sulfur-containing and sulfur-free components with a specified particle size can be used in combination, or components obtained by adjusting the particle size of sulfur-containing and sulfur-free components separately through pulverization can be combined, or sulfur-containing and sulfur-free components with a specified particle size can be synthesized and used in combination.

[0054] <(2) Process>

[0055] After preparing the sulfur-containing and sulfur-free components, they are mixed to prepare a raw material composition. This raw material composition contains at least one sulfur-containing component and at least one sulfur-free component. The amounts of the sulfur-containing and sulfur-free components used can be appropriately set in a manner that constitutes the composition of the sulfide solid electrolyte, which is the object of the manufacturing method of this invention. Mixing can be performed using known mixing equipment. For example, a ball mill, bead mill, or paint mixer can be used. These devices can be rotary, or a combination of rotary and revolving types.

[0056] The mixing of sulfur-containing and sulfur-free components can be carried out in a dry manner or in a wet manner. Various organic solvents can be used as the liquid medium for wet mixing. Specifically, examples include: chain saturated aliphatic hydrocarbons such as hexane, heptane, and decane; cyclic saturated aliphatic hydrocarbons such as cyclohexane; and aromatic hydrocarbons such as benzene and toluene.

[0057] From the viewpoint that the drying process after processing can be omitted, dry mixing can be used in the manufacturing method of the present invention.

[0058] It should be noted that the mixing of sulfur-containing and sulfur-free components is preferably carried out under conditions where the sulfur-containing and sulfur-free components are pulverized before mixing, that is, under conditions where their particle size does not substantially change before and after mixing. This is because it is easy to obtain a sulfide solid electrolyte with high ionic conductivity.

[0059] <(3) Process>

[0060] In this process, the raw material composition prepared in process (2) is calcined to obtain a calcined product. The calcined product is the target sulfide solid electrolyte. Calcination is preferably carried out by drying the raw material composition as needed, followed by crushing and grading, and under an inactive gas atmosphere or with hydrogen sulfide (H2S) gas flowing through it. By preferably setting the calcination temperature to 350°C or higher, sulfur loss can be suppressed. In addition, by setting the calcination temperature to 350°C or higher, unreacted sulfur-containing and sulfur-free components remaining in the solid electrolyte can be suppressed, thereby suppressing the decrease in ionic conductivity.

[0061] When hydrogen sulfide gas is used as the calcination atmosphere, the sulfur gas generated by the decomposition of hydrogen sulfide during calcination can increase the sulfur partial pressure of the atmosphere. Therefore, even if the calcination temperature is set high, the resulting solid electrolyte is less prone to sulfur defects, thus suppressing the manifestation of electronic conductivity. Specifically, the calcination temperature is preferably 350°C or higher, more preferably 450°C or higher. On the other hand, the aforementioned calcination temperature is preferably 650°C or lower, more preferably 600°C or lower, and even more preferably 500°C or lower.

[0062] When using an inactive gas as the calcination atmosphere, if the calcination temperature is set too high, the resulting solid electrolyte tends to be prone to sulfur defects. From this perspective, a calcination temperature of 350°C or higher is preferred, and more preferably 400°C or higher. On the other hand, a calcination temperature of 600°C or lower is preferred, and more preferably 550°C or lower.

[0063] Regardless of the calcination atmosphere, the calcination time is preferably 1 hour or more, more preferably 2 hours or more, and even more preferably 3 hours or more. On the other hand, the calcination time is preferably 10 hours or less, more preferably 8 hours or less, and even more preferably 6 hours or less.

[0064] From the viewpoint of eliminating unreacted phases caused by uneven heating, the heating rate during calcination is 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 heating rate is preferably 50°C / h or more, more preferably 80°C / h or more. By keeping the heating rate within the above range, calcination efficiency can be maintained.

[0065] Examples of calcined products, i.e., sulfide solid electrolytes, obtained in this way include: Li₂S-P₂S₅, Li₂S-P₂S₅-LiX (where "X" represents one or more halogen elements), Li₂S-P₂S₅-P₂O₅, Li₂S-Li₃PO₄-P₂S₅, Li₃PS₄, Li₄P₂S₆, Li₂S₅, and Li₂S₅. 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, Li7P3S 11 Li 3.25 P 0.95 S4, Li 7-x PS 6-x X x("X" represents one or more halogen elements, 0.2 < x < 2.0 or 0.2 < x < 1.8, etc.) Among these sulfide solid electrolytes, from the viewpoint of particularly high lithium-ion conductivity, it is preferable to manufacture solid electrolytes containing crystal phases with a sulfide-germanium-type crystal structure.

[0066] <(4) Process>

[0067] In this process, the calcined material obtained in process (3) is pulverized. As a result, a solid-state battery can be obtained more easily using the pulverized calcined material (i.e., sulfide solid electrolyte). Pulverization can be carried out in a dry manner or in a wet manner. Both dry and wet pulverization can be carried out by the methods described above. From the viewpoint of improving fillability and lithium-ion conductivity, dry pulverization is preferred.

[0068] After pulverization, the resulting pulverized material can be classified as needed. Classification can be performed, for example, through a 20 μm sieve.

[0069] The resulting sulfide solid electrolyte exhibits lithium-ion conductivity in its solid state. The lithium-ion conductivity of the solid electrolyte is preferably 2.0 mS / cm or higher at room temperature, i.e., 25°C, more preferably 2.2 mS / cm or higher, and even more preferably 2.4 mS / cm or higher. The lithium-ion conductivity can be measured using the methods described in the examples below.

[0070] The sulfide solid electrolyte manufactured by the method of the present invention can be used as a material constituting a solid electrolyte layer, a positive electrode layer, or a negative electrode layer. Specifically, the sulfide solid electrolyte manufactured by the method of the present invention can be used in batteries having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive and negative electrode layers. That is, the sulfide solid electrolyte manufactured 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. Lithium solid-state batteries can be primary or secondary batteries. The shape of the battery is not particularly limited; for example, it can be laminated, cylindrical, or prismatic. "Solid-state battery" includes not only solid-state batteries that do not contain any liquid or gel-like substances as electrolytes, but also those containing, for example, 50% by mass or less, 30% by mass or less, or 10% by mass or less of liquid or gel-like substances as electrolytes.

[0071] When the solid electrolyte layer contains a sulfide solid electrolyte manufactured by the method of the present invention, the solid electrolyte layer can be manufactured, for example, by: dripping a slurry formed of sulfide solid electrolyte, binder, and solvent onto a substrate and smoothing it with a scraper or the like; cutting the substrate with an air knife after it comes into contact with the slurry; forming a coating film by screen printing or the like, and then removing the solvent by heating and drying, etc. Alternatively, it can be manufactured by pressing or the like to form a pressed powder of powdered sulfide solid electrolyte and then performing appropriate processing.

[0072] From the perspective of balancing short-circuit prevention and volumetric capacity density, the thickness of the solid electrolyte layer is typically preferred to be 5 μm or more and 300 μm or less, and more preferably 10 μm or more and 100 μm or less.

[0073] The sulfide solid electrolyte produced by the method of the present invention can also 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 also contain other materials such as conductive additives and binders, as needed. By mixing the electrode mixture with a solvent to prepare a paste, coating it onto a current collector such as aluminum foil, and allowing it to dry, a positive electrode layer and a negative electrode layer can be formed.

[0074] As the cathode material constituting the cathode layer, cathode materials used as cathode active materials in lithium-ion batteries can be appropriately used. Examples include lithium-containing cathode active materials, specifically spinel-type lithium transition metal oxides and lithium metal oxides with layered structures. By using high-voltage cathode materials, energy density can be increased. In addition to cathode active materials, cathode materials may also contain conductive materials, or other materials.

[0075] As the negative electrode material constituting the negative electrode layer, a negative electrode material used as the negative electrode active material in lithium-ion batteries can be appropriately used. The sulfide solid electrolyte manufactured by the method of this invention is electrochemically stable, therefore lithium metal can be used, or at a low potential comparable to lithium metal (approximately 0.1V relative to Li). + Materials used in solid-state batteries for charging and discharging (S / Li) include carbon-based materials such as graphite, artificial graphite, natural graphite, and hard carbon (difficult-to-graphite carbon). This significantly improves the energy density of solid-state batteries. Alternatively, silicon or tin, which are expected to be high-capacity materials, can be used as active materials.

[0076] The present invention has been described above based on its preferred embodiments, but the present invention is not limited to the above embodiments.

[0077] Regarding the above embodiments, the following method for manufacturing sulfide solid electrolytes is further disclosed.

[0078] [1] A method for manufacturing a sulfide solid electrolyte, which uses a raw material composition containing lithium (Li), phosphorus (P) and sulfur (S) to manufacture the sulfide solid electrolyte.

[0079] The above-mentioned raw material composition contains at least one component containing sulfur (S), i.e., a sulfur-containing component, and contains at least one component that does not contain sulfur (S), i.e., a sulfur-free component.

[0080] The cumulative volumetric particle size D at 50% of the cumulative volume of at least one of the sulfur-containing components described above, determined by laser diffraction scattering particle size distribution method. 50 Let D1 be the cumulative volumetric particle size D at 50% capacity of at least one of the above sulfur-free components, determined by laser diffraction scattering particle size distribution method. 50 When D2 is set, D1 is less than or equal to 5.0 × D2.

[0081] The cumulative volumetric particle size D of at least one of the above sulfur-containing components 50 It is below 50μm.

[0082] [2] According to the manufacturing method described in [1], wherein the cumulative volumetric particle size D of the sulfur-containing component and the sulfur-free component is... 50 Each is independently below 50μm.

[0083] [3] According to the manufacturing method described in [1] or [2], wherein the volume-cumulative particle size D of the sulfur-containing component is... 50 The smallest volumetric cumulative particle size D of this sulfur-containing component 50 Let's call it D 1min The volumetric cumulative particle size D of the sulfur-containing component 50 The largest cumulative particle size D of this sulfur-containing component 50 Let's call it D 1max At that time, the D 1min Relative to D 1max The ratio is above 0.010.

[0084] [4] The manufacturing method according to any one of [1] to [3], wherein the volumetric cumulative particle size D of the sulfur-free component is... 50 The smallest volumetric cumulative particle size D of the sulfur-free component 50 Let's call it D 2min The cumulative particle size D of the sulfur-free component 50 The largest cumulative particle size D of the sulfur-free component 50 Let's call it D 2max At that time, the D 2min Relative to D 2maxThe ratio is above 0.010.

[0085] [5] The manufacturing method according to any one of [1] to [4], wherein the volume cumulative particle size D of the sulfur-containing component and the sulfur-free component is... 50 The smallest volumetric cumulative particle size D of this component 50 Let's call it D 50min The cumulative particle size D of the sulfur-containing component and the sulfur-free component. 50 The largest cumulative particle size D of this component 50 Let's call it D 50max At that time, the D 50min Relative to D 50max The ratio is above 0.010.

[0086] [6] The manufacturing method according to any one of [1] to [5], wherein the above-mentioned raw material composition is calcined to obtain a calcined product.

[0087] [7] The manufacturing method according to [6], wherein the above-mentioned calcined material is pulverized.

[0088] [8] The manufacturing method according to [6] or [7], wherein the calcined product contains a crystal phase having a sulfogermanium-type crystal structure.

[0089] Example

[0090] The present invention will now be described in more detail through examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" refers to "mass %".

[0091] [Example 1]

[0092] (1) Process

[0093] As sulfur-containing components, Li₂S powder and P₂S₅ powder were prepared. As sulfur-free components, LiCl powder and LiBr powder were prepared. The volumetric cumulative particle size D of these powders was determined. 50 As shown in Table 1, the volumetric cumulative particle size D of Li₂S is... 50 The particle size is between 2 μm and 5 μm. It should be noted that Table 1 records the volumetric cumulative particle size D of the Li₂S powder. 50 The relative values ​​of P2S5 powder, LiCl powder, and LiBr powder when set to 1.

[0094] (2) Process

[0095] To obtain the composition formula Li 5.4 PS 4.4 Cl 0.8 Br 0.8After weighing and pulverizing each powder using the method of sulfide solid electrolyte, the powders are dry-mixed using a ball mill to prepare the raw material composition.

[0096] (3) Process

[0097] The raw material composition was calcined to obtain a calcined product formed from a sulfide solid electrolyte. Calcination was carried out using a tubular electric furnace. During calcination, 100% pure nitrogen gas was circulated within the furnace. The calcination temperature was set to 500°C. XRD analysis confirmed that the calcined product contained a crystalline phase with a sulfide-germanium-type crystal structure.

[0098] (4) Process

[0099] The calcined material was pulverized using a mortar and pestle and passed through a 20 μm sieve. This yielded the target sulfide solid electrolyte.

[0100] [Examples 2-5 and Comparative Examples 1 and 2]

[0101] In Example 1, a particle size D with the volumetric cumulative size shown in Table 1 was used. 50 The powder, except that, yielded the target sulfide solid electrolyte in the same manner as in Example 1.

[0102] In Examples 2 and 3, the volumetric cumulative particle size D of the pulverized Li₂S was... 50 It is between 10μm and 20μm.

[0103] In Examples 4 and 5, the volumetric cumulative particle size D of the pulverized Li2S was... 50 It is between 2μm and 5μm.

[0104] In Comparative Examples 1 and 2, the volumetric cumulative particle size D of the pulverized Li₂S was... 50 More than 50μm.

[0105] [evaluate]

[0106] In the examples and comparative examples, the volumetric cumulative particle size D of each powder used in the preparation of the raw material composition is... 50 The following method was used to determine the value. In addition, the value obtained by dividing the cumulative volumetric particle size D1 of the sulfur-containing component by the cumulative volumetric particle size D2 of the sulfur-free component is shown in Table 2.

[0107] In addition, the lithium-ion conductivity of the sulfide solid electrolytes obtained in the examples and comparative examples was determined by the following method.

[0108] [cumulative particle size D] 50 ]

[0109] The particle size distribution of sulfide solid electrolytes based on laser diffraction scattering particle size distribution determination was determined according to the following steps. Using an automatic sample feeder (Microtrac SDC, manufactured by Microtrac BEL Co., Ltd.) for laser diffraction particle size distribution determination, the flow rate of the sample containing the sulfide solid electrolyte was set to 50%, and the sample was irradiated with 30W ultrasound for 60 seconds. Subsequently, the particle size distribution was measured using a Microtrac BEL Co., Ltd. laser diffraction particle size distribution determination machine (MT3300EXII). Based on the obtained volume-based particle size distribution diagram, the particle size at which the cumulative volume reaches 50% was determined and recorded as the cumulative volume particle size D. 50 It should be noted that the volumetric cumulative particle size D was measured. 50 The organic solvent was passed through a 60 μm filter. The solvent refractive index was set to 1.50, the particle permeability condition was set to "permeable," the particle refractive index was set to 1.59, the shape was set to "non-spherical," the measurement range was set to 0.133 μm to 704.0 μm, and the measurement time was set to 10 seconds. Two measurements were performed, and the average value of the obtained measurements was taken as the volumetric cumulative particle size D. 50 .

[0110] The sample for determining the sulfide solid electrolyte was prepared as follows. First, a slurry containing the sulfide solid electrolyte was prepared by manually mixing 0.3 g of the sulfide solid electrolyte and 5.7 g of liquid containing a dispersant (mass ratio of toluene to dispersant (SAN NOPCO Corporation's SNDISPERSANT 9228)) = 19:1. Next, 6 ml of the slurry containing the sulfide solid electrolyte was added to an organic solvent (toluene) to prepare the sample for determining the sulfide solid electrolyte.

[0111] [Lithium-ion conductivity]

[0112] The powder of the sulfide solid electrolyte obtained in the examples and comparative examples was applied at approximately 6 t / cm in a glove box purged with thoroughly dried Ar gas (dew point below -60°C). 2 The lithium-ion conductivity was measured by uniaxial compression molding under a load, producing granules with a diameter of 10 mm and a thickness of approximately 1 mm to 8 mm. 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. Measurement conditions were set as follows: temperature 25°C, frequency 100 Hz to 1 MHz, and amplitude 100 mV using AC impedance method.

[0113] [Table 1]

[0114]

[0115] [Table 2]

[0116]

[0117] The results shown in Tables 1 and 2 clearly demonstrate that Examples 1-5 exhibit higher lithium-ion conductivity compared to Comparative Examples 1 and 2. Typically, the volumetric cumulative particle size D of sulfide solid electrolytes... 50 The larger the particle size, the higher the lithium-ion conductivity, but even with a smaller cumulative particle size D than Comparative Examples 1 and 2, the lithium-ion conductivity remains relatively high. 50 In the embodiments described, the lithium-ion conductivity is also high. Therefore, it can be seen that a sulfide solid electrolyte with high lithium-ion conductivity can be obtained by the manufacturing method of the present invention.

[0118] Industrial availability

[0119] According to the method of the present invention, sulfide solid electrolytes with high ionic conductivity can be easily manufactured.

Claims

1. A method for manufacturing a sulfide solid electrolyte, comprising using a raw material composition containing lithium (Li), phosphorus (P), and sulfur (S) to manufacture the sulfide solid electrolyte. The raw material composition contains at least one component containing sulfur (S), i.e., a sulfur-containing component, and at least one component that does not contain sulfur (S), i.e., a sulfur-free component. The cumulative volumetric particle size D at 50% of the cumulative volume of at least one of the sulfur-containing components, determined by laser diffraction scattering particle size distribution method. 50 Let D1 be the cumulative volumetric particle size D at 50% capacity of at least one of the sulfur-free components, determined by laser diffraction scattering particle size distribution method. 50 When D2 is set, D1 is less than or equal to 5.0 × D2. The cumulative particle size D of at least one of the sulfur-containing components 50 It is below 50μm.

2. The manufacturing method according to claim 1, wherein, The cumulative particle size D of the sulfur-containing component and the sulfur-free component 50 Each is independently below 50μm.

3. The manufacturing method according to claim 1, wherein, The volumetric cumulative particle size D of the sulfur-containing component 50 The smallest volumetric cumulative particle size D of this sulfur-containing component 50 Let's call it D 1min The volumetric cumulative particle size D of the sulfur-containing component 50 The largest cumulative particle size D of this sulfur-containing component 50 Let's call it D 1max At that time, the D 1min Relative to D 1max The ratio is 0.010 or higher.

4. The manufacturing method according to claim 1, wherein, The volumetric cumulative particle size D of the sulfur-free component 50 The smallest volumetric cumulative particle size D of the sulfur-free component 50 Let's call it D 2min The cumulative particle size D of the sulfur-free component 50 The largest cumulative particle size D of the sulfur-free component 50 Let's call it D 2max At that time, the D 2min Relative to D 2max The ratio is 0.010 or higher.

5. The manufacturing method according to claim 1, wherein, The cumulative particle size D of the sulfur-containing component and the sulfur-free component is calculated. 50 The smallest volumetric cumulative particle size D of this component 50 Let's call it D 50min The cumulative particle size D of the sulfur-containing component and the sulfur-free component. 50 The largest cumulative particle size D of this component 50 Let's call it D 50max At that time, the D 50min Relative to D 50max The ratio is 0.010 or higher.

6. The manufacturing method according to claim 1, wherein, The raw material composition is calcined to obtain a calcined product.

7. The manufacturing method according to claim 6, wherein, The calcined material is pulverized.

8. The manufacturing method according to claim 6 or 7, wherein, The calcined product contains a crystal phase with a sulfogermanium-type crystal structure.

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