Sulfide-based solid electrolyte, method for producing a sulfide-based solid electrolyte, and all-solid-state battery containing a sulfide-based solid electrolyte

Abstract

To provide a sulfide-based solid electrolyte having improved lithium ionic conductivity, a method for preparing the sulfide-based solid electrolyte, and a solid-state battery comprising the sulfide-based solid electrolyte.SOLUTION: The present disclosure provides a sulfide-based solid electrolyte that is a glass ceramic, the sulfide-based solid electrolyte comprising a thio-LISICON Region II-type crystalline phase, and having a chemical formula presented by (100-x){(0.75+y / (100-x))Li2S-0.25 P2S5}-xLiHa, where Ha is one or more elements selected from halogen elements, and 15≤x≤30 and 0<y<2.25 are satisfied.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to a sulfide-based solid electrolyte, a method for producing a sulfide-based solid electrolyte, and an all-solid-state battery containing a sulfide-based solid electrolyte. [Background technology]

[0002] To improve safety, extend lifespan, and increase energy density, the development of all-solid-state batteries is progressing, in which the electrolyte of lithium-ion batteries is replaced with a solid electrolyte. Among the many solid electrolytes, Li 10 GeP2S 12 Sulfide-based solid electrolytes, such as those mentioned above, have advantages such as high lithium-ion conductivity similar to that of liquid electrolytes, and are soft, making it easy to achieve adhesion with active materials. Therefore, the practical application of all-solid-state batteries using sulfide-based solid electrolytes is expected.

[0003] Lithium metal is attracting attention as a negative electrode material for all-solid-state batteries because its low weight per unit volume and large theoretical capacity allow for a high mass energy density (Wh / kg). However, Li 10 GeP2S 12 Sulfide-based solid electrolytes, such as those mentioned above, have a problem in that they have low stability with respect to lithium metal, making them difficult to use with lithium metal anodes.

[0004] To address this problem, Patent Documents 1 to 3 report sulfide-based solid electrolytes, which are glass ceramics that are stable with respect to lithium metal.

[0005] However, conventional technology does not include P2S6 contained in sulfide-based solid electrolytes. 4- Undesirable skeletal structures, such as those mentioned above, can lead to a problem where the lithium-ion conductivity of sulfide-based solid electrolytes decreases. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-011898 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-100907 [Patent Document 3] International Publication No. 2019 / 098245 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] An object of the present disclosure is to provide a sulfide-based solid electrolyte having improved lithium ion conductivity, a method for producing a sulfide-based solid electrolyte, and a all-solid-state battery including the sulfide-based solid electrolyte. [Means for Solving the Problems]

[0008] To achieve the above object, the present disclosure provides a sulfide-based solid electrolyte that is glass ceramics, the sulfide-based solid electrolyte includes a thio-lithium superionic conductor region II (Thio-LISICON Region II) type crystal phase, has a chemical formula represented by (100-x){(0.75+y / (100-x))Li2S-0.25P2S5}-xLiHa, in the chemical formula, Ha is one or more elements selected from halogen elements, and satisfies 15≦x≦30 and 0<y<2.25, and provides a sulfide-based solid electrolyte.

[0009] In one embodiment, x may satisfy 23≦x≦27.

[0010] In one embodiment, y may satisfy 0.2<y<0.4.

[0011] In one embodiment, Ha may include Br.

[0012] In one embodiment, I1 / I2<0.06 may be satisfied. Here, I1 is 380 to 400 cm in Raman spectroscopy measurement -1I2 is the intensity of the peak detected, and in Raman spectroscopy measurements, I2 is 415-425 cm⁻¹. -1 This is the intensity of the peak detected.

[0013] This disclosure relates to a method for producing a sulfide-based solid electrolyte as described in any one of the above embodiments, A step of mixing a lithium source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture, The process involves firing the mixture at a temperature of 150°C to 250°C, This provides a method that includes [something].

[0014] This disclosure is, An all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer, The present invention provides an all-solid-state battery in which the solid electrolyte layer includes a sulfide-based solid electrolyte described in any one of the above embodiments. [Effects of the Invention]

[0015] This disclosure provides a sulfide-based solid electrolyte with improved lithium-ion conductivity, a method for producing a sulfide-based solid electrolyte, and an all-solid-state battery containing a sulfide-based solid electrolyte. [Brief explanation of the drawing]

[0016] [Figure 1] The X-ray diffraction (XRD) patterns of the examples and comparative examples are shown. [Figure 2] This graph shows the lithium ion conductivity as a function of sulfide-based solid electrolyte composition. [Figure 3] The Raman spectra of Example 2, Comparative Example 1, and Comparative Example 2 are shown. [Modes for carrying out the invention]

[0017] The following provides a more detailed explanation of this disclosure.

[0018] Terms and words used in this specification and in the claims should not be interpreted restrictively in their usual or dictionary sense, but rather in a sense and concept consistent with the technical idea of ​​this disclosure, in accordance with the principle that inventors can appropriately define the concepts of terms in order to best describe their invention.

[0019] [Solid electrolyte for all-solid-state batteries] The solid electrolyte for all-solid-state batteries disclosed herein may comprise one or more of sulfide-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes. Preferably, the solid electrolyte for all-solid-state batteries disclosed herein is a sulfide-based solid electrolyte. The solid electrolyte for all-solid-state batteries may be mixed with a positive electrode mixture and used as a positive electrode material, mixed with a negative electrode mixture and used as a negative electrode material, or used as a separator. Depending on the application, the solid electrolyte for all-solid-state batteries may further comprise additives such as lithium salts, conductive materials, and binder resins.

[0020] <Sulfide solid electrolyte> The sulfide-based solid electrolyte is not particularly limited as long as it contains sulfur (S), and known sulfide-based solid electrolytes can be used. The sulfide-based solid electrolyte may be amorphous, glass, or glass ceramic.

[0021] In this disclosure, the sulfide-based solid electrolyte is a glass ceramic. Because the sulfide-based solid electrolyte, being a glass ceramic, has high stability with respect to lithium metal, it enables the use of lithium metal, which has a high mass energy density, as the negative electrode material. Glass ceramic is a type of glass in which fine crystals are deposited internally by heat treatment; it is also called crystallized glass. Because the sulfide-based solid electrolyte, being a glass ceramic, has fine crystals internally, it promotes the conduction of lithium ions and can have high lithium ion conductivity.

[0022] Non-restrictive examples of sulfide-based solid electrolytes include Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS, and may contain one or more of these. However, it is not limited to these examples.

[0023] In this disclosure, the sulfide-based solid electrolyte includes a thio-LISICON Region II type crystalline phase. The sulfide-based solid electrolyte includes a Li3PS4 crystalline phase, a Li4P2S6 crystalline phase, a Li7PS6 crystalline phase, and a Li7P3S 11 Other crystalline phases, such as a crystalline phase, may be further included. Since the thio-LISICON Region II type crystalline phase can have high lithium-ion conductivity, a sulfide-based solid electrolyte containing this crystalline phase can also have high lithium-ion conductivity.

[0024] The proportion of crystalline phase (also referred to as "crystal structure" in this specification) contained in sulfide-based solid electrolytes can be quantitatively or semi-quantitatively evaluated from XRD patterns. One method is to evaluate the proportion of crystalline phase by comparing the peak intensities of the XRD patterns. Peak intensities can be evaluated based on height or area. Thio-LISICON Region II type crystalline phases are observed as peaks at 2θ = 20.3±0.5°, 23.5±0.5°, and 29.6±0.5° in XRD patterns obtained by XRD measurements.

[0025] Sulfide-based solid electrolytes may contain impurity phases. Examples of impurity phases include crystalline or amorphous phases such as Li2S phase, P2S5 phase, LiI phase, LiBr phase, and Li3PS4 phase. Since such impurity phases can reduce the lithium ion conductivity of sulfide-based solid electrolytes, it is preferable that they are contained in small amounts or not at all.

[0026] In the present disclosure, the sulfide-based solid electrolyte has a chemical formula represented by (100 - x){(0.75 + y / (100 - x))Li2S - 0.25P2S5} - xLiHa. In the above chemical formula, Ha is one or more elements selected from halogen elements, and 15 ≤ x ≤ 30, 0 < y < 2.25 are satisfied. As sulfide-based solid electrolytes, compositions such as Li2S(67%) - P2S5(33%), Li2S(70%) - P2S5(30%), and Li2S(75%) - P2S5(25%) in molar ratio are known. The sulfide-based solid electrolyte of the present disclosure has a designed composition in which an excess amount of Li2S and lithium halide (LiHa) are added based on Li2S(75%) - P2S5(25%) where the molar ratio of Li2S to P2S5 is 3:1. A sulfide-based solid electrolyte having such a designed composition can have high lithium ion conductivity.

[0027] In the above chemical formula, x indicates the content of lithium halide (LiHa) in the sulfide-based solid electrolyte. x satisfies 15 ≤ x ≤ 30. Preferably, x may satisfy 23 ≤ x ≤ 27. More preferably, x may satisfy 24 ≤ x ≤ 26. Even more preferably, x = 25 may be satisfied. When x satisfies the above range, the lithium halide can suppress the influence of unwanted skeletal structures such as P2S6 4- etc., so the sulfide-based solid electrolyte can have high lithium ion conductivity.

[0028] In the above chemical formula, y represents an excess amount of Li2S. y satisfies 0 < y < 2.25. y may satisfy 0.14 < y < 0.56. Preferably, y may satisfy 0.2 < y < 0.4. More preferably, y may satisfy 0.25 ≤ y ≤ 0.35. Even more preferably, y may satisfy 0.26 ≤ y ≤ 0.30. When y satisfies the above range, due to the excess amount of Li2S, the formation of unwanted skeletal structures such as P2S6 4- is suppressed, so the sulfide-based solid electrolyte can have a high lithium ion conductivity. When y = 0, the effect of suppressing the formation of unwanted skeletal structures cannot be obtained. When y ≥ 2.25, too much Li2S promotes the formation of unwanted skeletal structures, so the effect of improving the lithium ion conductivity cannot be obtained.

[0029] In the above chemical formula, halogen (Ha) is one or more elements selected from halogen elements. Halogen (Ha) may include chlorine (Cl), bromine (Br), and iodine (I). Preferably, halogen (Ha) may include bromine (Br). When sulfur (S) in the sulfide-based solid electrolyte is a divalent anion, it has a stronger ability to attract lithium ions than monovalent halogen and can greatly inhibit the movement of lithium ions. In particular, by including bromine (Br) as the halogen, the sulfur (S) occupancy at specific sites in the sulfide-based solid electrolyte decreases, the halogen occupancy at these sites increases, and the lithium ion mobility around the bromine (Br) sites can become active. As a result, the lithium ion conductivity can be improved. Also, bromine (Br) can combine with Li in the sulfide-based solid electrolyte to form lithium bromide (LiBr), which is a water-absorbing substance. Lithium bromide (LiBr) can adsorb moisture that can lower the lithium ion conductivity and further improve the lithium ion conductivity of the sulfide-based solid electrolyte.

[0030] PS4 that constitutes the sulfide-based solid electrolyte 3- (tetrahedron), P2S7 4- (dimer unit in which two PS4 tetrahedrons are connected) and P2S6 4-Skeletal structures such as those with a missing sulfur atom from the dimer unit can be quantitatively or semi-quantitatively evaluated from Raman spectra. P2S6 4- The skeletal structure is 380-400cm -1 It is detected by [method], and its peak intensity is represented by I1. PS4 3- The skeletal structure is 415-425 cm. -1 It is detected, and its peak intensity is represented by I2. In this disclosure, peak intensity is evaluated based on height. By evaluating the peak intensity ratio I1 / I2, P2S6 4- The proportion of the skeletal structure can be quantitatively evaluated. P2S6 4- The skeletal structure is known to lack sulfur atoms, which can reduce lithium-ion conductivity.

[0031] Preferably, the sulfide-based solid electrolyte according to this disclosure may satisfy a peak intensity ratio I1 / I2 < 0.06. More preferably, the peak intensity ratio I1 / I2 ≤ 0.03, even more preferably, the peak intensity ratio I1 / I2 ≤ 0.01, and most preferably, I1 / I2 = 0. When the peak intensity ratio I1 / I2 satisfies the above range, the sulfide-based solid electrolyte can reduce lithium ion conductivity P2S6 4- It contains almost no skeletal structure, and as a result, it can have high lithium-ion conductivity.

[0032] The lithium-ion conductivity of a sulfide-based solid electrolyte (also referred to herein as "ionic conductivity") refers to the lithium-ion conductivity at room temperature (25°C, 298K) and atmospheric pressure (1 atm), unless otherwise specified. When a sulfide-based solid electrolyte is used in an all-solid-state battery, it is practically desirable for the lithium-ion conductivity to be 4 mS / cm or higher. The lithium-ion conductivity of the sulfide-based solid electrolyte of this disclosure is 2.4 mS / cm or higher, preferably 2.9 mS / cm or higher, more preferably 4 mS / cm or higher, even more preferably 5 mS / cm or higher, and most preferably 5.5 mS / cm or higher.

[0033] The sulfide-based solid electrolytes of this disclosure can be obtained by a manufacturing method comprising the steps of: mixing a lithium source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture; and calcining the mixture at a temperature of 150°C to 250°C. The steps of obtaining the mixture and calcining may be carried out under an inert gas atmosphere such as argon gas and nitrogen gas.

[0034] The lithium source, phosphorus source, sulfur source, and halogen source may be compounds such as sulfides, oxides, or nitrides. Lithium sulfide (Li2S) can be used as the lithium source, diphosphorus pentasulfide (P2S5) as the phosphorus source, and lithium halides (LiHa) such as lithium bromide (LiBr) and lithium iodide (LiI) as the halogen source. Sulfur can also be supplied from other elemental sources. In other words, one or more of the lithium source, phosphorus source, and halogen source may also serve as the sulfur source.

[0035] The step of obtaining the above mixture involves mixing and grinding raw materials such as a lithium source, a phosphorus source, a sulfur source, and a halogen source, and then amorphous and vitrifying them. The step of obtaining the mixture may be carried out using a mechanical milling apparatus known in the art. Examples of mechanical milling apparatuses include ball mills, bead mills, stirring tanks, and grinding tanks. Conditions such as the rotation speed, time, and number of rotations of the mechanical milling apparatus can be appropriately set by those skilled in the art to amorphous and vitrify the raw materials.

[0036] The above firing step is a step in which at least a portion of the amorphous and vitrified mixture is crystallized to form glass ceramics. The firing temperature is 150°C to 250°C. Preferably, it is 170°C to 230°C, and more preferably, 180°C to 220°C. When the firing temperature is within the above range, the formation of a thio-LISICON Region II type crystalline phase is promoted, and a sulfide-based solid electrolyte that is a glass ceramic is obtained. Since the thio-LISICON Region II type crystalline phase has high lithium ion conductivity, a sulfide-based solid electrolyte containing this crystalline phase can have high lithium ion conductivity.

[0037] [All-solid battery] The electrolyte for all-solid-state batteries disclosed herein can be used in all-solid-state batteries including a positive electrode, a negative electrode, and a solid electrolyte layer. The solid electrolyte for all-solid-state batteries can be used together with the active material in the electrode active material layer of the positive electrode and the negative electrode. The solid electrolyte for all-solid-state batteries can be used as a material for the solid electrolyte layer. The average particle size of the electrolyte for all-solid-state batteries can be controlled depending on the application. By controlling the average particle size of the electrolyte for all-solid-state batteries, the lithium-ion conductivity can be improved.

[0038] <Solid electrolyte layer> In this disclosure, the solid electrolyte layer may have a thickness of about 50 μm or less, preferably about 15 μm to 50 μm. The thickness can be appropriate within the above range, taking into consideration lithium-ion conductivity, physical strength, and the energy density of the battery to which it is applied. For example, in terms of lithium-ion conductivity and energy density, the thickness may be 10 μm or more, 20 μm or more, or 30 μm or more. On the other hand, in terms of physical strength, the thickness may be 50 μm or less, 45 μm or less, or 40 μm or less. Furthermore, the solid electrolyte layer has a thickness range and a load capacity of about 100 kgf / cm². 2 ~Approx. 2,000kgf / cm 2It may have a tensile strength. Further, the solid electrolyte layer may have a porosity of 15 vol% or less, or about 10 vol% or less. For example, the porosity can be evaluated by the water immersion method. Thus, the solid electrolyte layer according to the present disclosure can have high mechanical strength despite being a thin film.

[0039] <Positive electrode and negative electrode> In the present disclosure, the positive electrode and the negative electrode each include a current collector and an electrode active material layer formed on at least one surface of the current collector. The electrode active material layer includes a plurality of electrode active material particles and a solid electrolyte. Further, the electrode can further include one or more of a conductive material and a binder resin as needed. Further, the electrode can further include various additives for the purpose of complementing or improving the physicochemical properties of the electrode.

[0040] In the present disclosure, any material can be used as the negative electrode active material as long as it can be used as the negative electrode active material of a lithium ion secondary battery. For example, the negative electrode active material includes carbon such as graphitizable carbon and graphite carbon; Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x [[ID=1十八]]Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), etc. metal composite oxides; lithium metal; lithium alloy; silicon metal; silicon-based alloy; indium metal; indium alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxides; lithium titanium oxides, etc. One or more selected from the above can be used. In a specific embodiment, the negative electrode active material can include a carbon-based material and / or Si.

[0041] In the case of the positive electrode, the electrode active material can be used without limitation as long as it can be used as the positive electrode active material of a lithium-ion secondary battery. For example, the electrode active material can be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; the chemical formula Li 1+x Mn 2-x O4 (x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; the chemical formula LiNi 1-x A x O2 (A = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3) nickel-site type lithium nickel oxide represented by; the chemical formula LiMn 2-x A x O2 (A = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or lithium manganese composite oxide represented by Li2Mn3AO8 (A = Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x O4 spinel-structured lithium manganese composite oxide represented by; Li(Ni a Co b Mn c )O2 (a, b, c are atomic fractions of independent elements, 0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1).) NCM-based composite oxide represented by; LiMn2O4 in which a part of the chemical formula of Li is substituted with an alkaline earth metal ion; disulfide compounds; Fe2(MoO^4)3, etc. can be included, but are not limited thereto.

[0042] In the present disclosure, the current collector can be an electrically conductive current collector known in the secondary battery field such as a metal plate, and can be appropriately used according to the polarity of the electrode.

[0043] In this disclosure, the conductive material is usually added in an amount of 1% to 30% by weight based on the total weight of the mixture containing the electrode active material. Such conductive materials are not particularly limited as long as they do not induce chemical changes in the battery and are conductive, and may include, for example, one or more mixtures of conductive materials selected from graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0044] In this disclosure, the binder resin is not particularly limited as long as it is a component that assists in the bonding of the active material to the conductive material and to the current collector, and examples include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers. The binder resin can usually be included in an amount of 1 to 30% by weight, or 1 to 10% by weight, based on 100% by weight of the electrode active material layer.

[0045] In this disclosure, the electrode active material layer may contain one or more additives as needed, such as oxidation stabilizers, reduction stabilizers, flame retardants, heat stabilizers, and anti-fogging agents.

[0046] This disclosure provides a secondary battery having the structure described above. This disclosure also provides a battery module including a secondary battery as a unit battery, a battery pack including a battery module, and a device including a battery pack as a power source. Specific examples of the device include, but are not limited to, power tools driven by electric motors; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power systems.

[0047] The present disclosure will be described in more detail below with reference to examples, but these examples are for illustrative purposes only and do not limit the scope of the present disclosure.

[0048] Example 1 Using lithium sulfide (Li2S, Mitsuwa Chemical), phosphorus pentasulfide (P2S5, Aldrich), lithium bromide (LiBr, Aldrich), and lithium iodide (LiI, Aldrich) as raw materials, the materials were weighed and mixed in a mortar and pestle in an Ar gas-flow glove box to obtain a mixed powder, with the design composition (56.25+y)Li2S-18.75P2S5-15LiBr-10LiI such that the excess amount of Li2S added was y=0.14. This mixed powder was placed in a ZrO2 pot along with ZrO2 balls and sealed to obtain a sealed pot. This sealed pot was placed in a planetary ball mill apparatus and ball milled at 500 rpm for 20 hours. After that, the pot was opened in a glove box and the powder was recovered. This powder was placed in a carbon crucible, sealed, and then calcined at 200°C for 3 hours while flowing Ar gas. The calcined powder was recovered to obtain a solid electrolyte.

[0049] Example 2 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the excess amount of Li2S added, y, was set to 0.28.

[0050] Example 3 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the excess amount of Li2S added, y, was set to 0.56.

[0051] Example 4 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the excess amount of Li2S added, y, was set to 1.22.

[0052] Example 5 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the excess amount of Li2S added, y, was set to 1.69.

[0053] Comparative Example 1 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that no excess Li2S was added, i.e., the excess amount y was set to 0.

[0054] Comparative Example 2 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the excess amount of Li2S added, y, was set to 2.25.

[0055] [Table 1]

[0056] [evaluation] The following evaluations were performed using the obtained solid electrolyte.

[0057] (XRD measurement) A predetermined amount of solid electrolyte was placed in a sealed holder within an Ar gas-flow glove box, and XRD measurements were performed.

[0058] (Measurement of lithium-ion conductivity) A predetermined amount of solid electrolyte was placed inside a Machor tube, and the Machor tube and pellet molding jig (upper and lower press pins) were combined and press-formed at 5 MPa using a single-screw press. Subsequently, a predetermined amount of gold powder was placed on both sides of the pellet, and then press-formed at 7.5 MPa using a single-screw press to obtain a Machor tube cell. The obtained Machor tube cell was placed in an electrochemical measurement jig cell, and pressurized to 5.0 N·m using a torque wrench to obtain a lithium ion conductivity measurement cell. The obtained lithium ion conductivity measurement cell was connected to an impedance measuring device, and the resistance value of the solid electrolyte pellet was measured at room temperature (298 K) and atmospheric pressure (1 atm) to derive the lithium ion conductivity [mS / cm] of the solid electrolyte.

[0059] (Raman spectroscopy measurement) A predetermined amount of solid electrolyte was placed in a sealed holder, and Raman spectroscopy measurements were performed (using a LambdaVision MicroRAM with a laser excitation wavelength of 532 nm). (380-400 cm⁻¹) -1 P2S6 detected 4- Presence or absence of peak and intensity I1, and 415-425cm -1 PS4 detected 3- The peak intensity I2 was measured, and the peak intensity ratio I1 / I2 was evaluated. Peak intensity was based on the height of the peak.

[0060] [Evaluation Results] (crystalline phase) The XRD patterns obtained by XRD measurement are shown in Figure 1. As shown in Figure 1, in all of Examples 1 to 5 and Comparative Examples 1 and 2, peaks originating from the Thio-LISICON Region II type crystalline phase were observed at 2θ = 20.3±0.5°, 23.5±0.5°, and 29.6±0.5°, confirming that sulfide-based solid electrolytes, which are glass ceramics, were obtained. Other peaks observed in the XRD patterns may originate from crystalline phases other than the Thio-LISICON Region II type crystalline phase, as well as from raw materials such as Li2S, P2S5, LiBr, and LiI.

[0061] (Lithium-ion conductivity) Table 1 shows the measurement results of lithium ion conductivity. Figure 2 shows the composition dependence of lithium ion conductivity. In Figure 2, the horizontal axis represents the amount of excess Li2S added (y) in the design composition (56.25+y)Li2S-18.75P2S5-15LiBr-10LiI, and the vertical axis represents the lithium ion conductivity. As shown in Table 1, the lithium ion conductivity in Examples 1 to 5 ranged from 2.6 mS / cm to 5.5 mS / cm. On the other hand, in Comparative Example 1, where no excess Li2S was added, the conductivity was 2.3 mS / cm, and in Comparative Example 2, where the excess amount of Li2S added (y) was 2.25, the conductivity was 0.9 mS / cm. By adding a specific amount of excess Li2S, it was possible to increase the lithium ion conductivity. In particular, in Example 2, where the excess amount of Li2S added (y) = 0.28, the lithium ion conductivity was the highest at 5.5 mS / cm. It was found that slightly increasing the molar ratio of Li2S to P2S5 from 3 improved the lithium ion conductivity of the solid electrolyte.

[0062] (Raman spectrum) The Raman spectra of Example 2 and Comparative Examples 1 and 2 are shown in Figure 3. For all samples, the range was 415–425 cm⁻¹. -1 PS4 3- A peak was detected. On the other hand, 380-400 cm -1 P2S6 in 4- Peaks were detected in Comparative Examples 1 and 2, but not in Example 2, which exhibited high lithium-ion conductivity. Although not shown in the figures, in Examples 1 and 3 to 5, the range was 380-400 cm⁻¹. -1 P2S6 in 4- A peak was detected.

[0063] P2S6 obtained from Raman spectroscopy 4- Peak intensity I1 and PS4 3- Table 1 shows the peak intensity ratio I1 / I2 with respect to peak intensity I2. Example 2, which shows high lithium-ion conductivity, is P2S6. 4-Since no peak was detected, the peak intensity ratio I1 / I2 was virtually zero (NA). In Examples 1 and 3 to 5 and Comparative Example 2, where Li2S was added in excess, the peak intensity ratio I1 / I2 was 0.06 to 0.1, while in Comparative Example 1, where Li2S was not added in excess, the peak intensity ratio I1 / I2 was 0.08. In Example 2, where the excess amount y = 0.28, the lithium ion conductivity was significantly improved. Although not bound by theory, the sulfur supplied from the excess amount of Li2S may have contributed to the formation of P2S6 4- It is thought that the deficiency of sulfur, which is presumed to be a factor in the formation of the skeletal structure, was resolved, resulting in improved lithium-ion conductivity.

[0064] Although this disclosure has been described above with reference to limited embodiments and drawings, it is understood that this disclosure is not limited thereto and that various modifications and variations are possible within the equivalent scope of the technical concept and the appended claims by persons with ordinary skill in the art to which this disclosure pertains.

Claims

1. A sulfide-based solid electrolyte that is a glass ceramic, The aforementioned sulfide-based solid electrolyte contains a thio-LISICON Region II type crystalline phase. (100-x) {(0.75+y / (100-x))Li ２ S-0.25P ２ S ５ It has the chemical formula represented by}-xLiHa, A sulfide-based solid electrolyte in the chemical formula described above, wherein Ha is one or more elements selected from halogen elements, and satisfies 23 ≤ x ≤ 27 and 0 < y < 2.

25.

2. The sulfide-based solid electrolyte according to claim 1, wherein y satisfies 0.2 < y < 0.

4.

3. The sulfide-based solid electrolyte according to claim 2, wherein the Ha contains Br.

4. I １ / I ２ A sulfide-based solid electrolyte according to claim 1 that satisfies <0.06: I １ In Raman spectroscopy measurements, the range is 380–400 cm⁻¹. －１ This is the intensity of the peak detected, I ２ is the intensity of the peak detected at 415 - 425 cm －１ in Raman spectroscopy measurement.

5. A method for producing a sulfide-based solid electrolyte according to claim 1, A step of mixing a lithium source, a phosphorus source, a sulfur source, and a halogen source to obtain a mixture, The process involves firing the mixture at a temperature of 150°C to 250°C, Methods that include...

6. An all-solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer, An all-solid-state battery wherein the solid electrolyte layer contains the sulfide-based solid electrolyte described in claim 1.

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