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

Abstract

The objective is to provide a sulfide-based solid electrolyte with improved lithium-ion conductivity, a method for manufacturing a sulfide-based solid electrolyte, and an all-solid-state battery containing a sulfide-based solid electrolyte. [Solution] This disclosure relates to a sulfide-based solid electrolyte which is a glass ceramic, wherein the sulfide-based solid electrolyte includes a thio-LISICON Region II type crystalline phase, and the sulfide-based solid electrolyte has the chemical formula (100-z)[{0.75+y / 75+6.25x / 75}Li2S-{0.25-12.5(x / 2) / 75}P2S5-{12.5x / 75}SiS2]-zLiHa, wherein in the chemical formula, Ha is one or more elements selected from halogen elements,

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. Patent Document 4 reports a sulfide-based solid electrolyte, which is a glass ceramic containing a thiolysicon region II type crystalline phase, in which the ionic conductivity is improved by adding a slightly excess amount of Li2S.

[0005] However, further improvements are needed regarding the lithium-ion conductivity and stability of sulfide-based solid electrolytes with respect to lithium metal anodes. [Prior art documents] [Patent Documents]

[0006] Japanese Patent Document 1 Japanese Unexamined Patent Application Publication No. 2015-011898 Japanese Patent Document 2 Japanese Unexamined Patent Application Publication No. 2017-100907 Japanese Patent Document 3 International Publication No. 2019 / 098245 Japanese Patent Document 4 Japanese Unexamined Patent Application Publication No. 2024-118804 Summary of the Invention Problems to be Solved by the Invention

[0007] The present disclosure aims to provide a sulfide-based solid electrolyte with improved lithium ion conductivity, a method for manufacturing the sulfide-based solid electrolyte, and an all-solid-state battery including the sulfide-based solid electrolyte.

[0008] Also, the present disclosure aims to provide a sulfide-based solid electrolyte with improved stability against a lithium metal negative electrode, a method for manufacturing the sulfide-based solid electrolyte, and an all-solid-state battery including the sulfide-based solid electrolyte.

[0009] However, the problems to be solved by the present disclosure are not limited to the above problems, and other problems will be clearly understood by those skilled in the art from the description of the invention below. Means for Solving the Problems

[0010] To achieve the above object, the present disclosure provides a sulfide-based solid electrolyte that is glass ceramics, wherein the sulfide-based solid electrolyte contains a crystal phase of the Thio-LISICON Region II type, the sulfide-based solid electrolyte has (100-z)[{0.75 + y / 75 + 6.25x / 75}Li2S - {0.25 - 12.5(x / 2) / 75}P2S5 - {12.5x / 75}SiS2] - zLiHa a chemical formula represented by In the above chemical formula, Ha is one or more elements selected from halogen elements, A sulfide-based solid electrolyte satisfying 0 < x < 0.75, 0 < y < 2.25, and 15 ≤ z ≤ 30 is provided.

[0011] In one embodiment, x may satisfy 0.005 ≤ x ≤ 0.025.

[0012] In one embodiment, y may satisfy 0.2 < y < 0.4.

[0013] In one embodiment, z may satisfy 23 ≤ z ≤ 27.

[0014] In one embodiment, Ha may include Br.

[0015] In one embodiment, 0.50° ≤ W ≤ 0.55° may be satisfied. Here, W is the full width at half maximum of the peak detected at 20.3 ± 0.4° in XRD measurement.

[0016] In one embodiment, the ratio of the number of moles of Si to the total number of moles of Si and P may be more than 0% and less than 25%.

[0017] The present disclosure is a method for manufacturing a sulfide-based solid electrolyte according to any one of the above embodiments, Mixing a lithium source, a phosphorus source, a silicon source, a sulfur source, and a halogen source to obtain a mixture, Firing the mixture at a temperature of 150°C to 250°C, A method including the above steps is provided.

[0018] The present disclosure is A all-solid-state battery including a positive electrode, a negative electrode, and a solid electrolyte layer, The all-solid-state battery provided, in which the solid electrolyte layer includes the sulfide-based solid electrolyte according to any one of the above embodiments.

[0019] In one embodiment, the negative electrode includes a negative electrode active material layer, The negative electrode active material layer includes lithium metal, lithium alloy, or a combination thereof.

[0020] In one embodiment, the negative electrode includes a negative electrode current collector. During initial charging, the negative electrode current collector does not contain negative electrode active material. During charging, lithium ions are supplied from the positive electrode active material layer, and a lithium metal layer, acting as the negative electrode active material, is formed on the negative electrode current collector. [Effects of the Invention]

[0021] 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.

[0022] Furthermore, this disclosure can provide a sulfide-based solid electrolyte with improved stability to a lithium metal anode, a method for producing a sulfide-based solid electrolyte, and an all-solid-state battery containing a sulfide-based solid electrolyte.

[0023] However, the effects achieved through this disclosure are not limited to those described above, and other technical effects will be clearly understood by those skilled in the art from the description of the invention below. [Brief explanation of the drawing]

[0024] [Figure 1] The X-ray diffraction (XRD) patterns of the sulfide solid electrolytes in Examples 1-5 and Comparative Example 1 are shown. [Figure 2] The X-ray diffraction (XRD) patterns of the sulfide solid electrolytes in Examples 6-9 and Comparative Example 2 are shown. [Figure 3] This graph shows the lithium ion conductivity as a function of the sulfide-based solid electrolyte composition in each example and comparative example. [Modes for carrying out the invention]

[0025] The following provides a more detailed explanation of this disclosure.

[0026] 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.

[0027] [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 may comprise 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 such as a solid electrolyte layer. 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.

[0028] <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.

[0029] 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.

[0030] 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.

[0031] In this disclosure, the sulfide-based solid electrolyte includes a thiolysicon region II type crystalline phase. The sulfide-based solid electrolyte includes Li3PS4 crystalline phase, Li4P2S6 crystalline phase, Li7PS6 crystalline phase and Li7P3S 11 Other crystalline phases, such as a crystalline phase, may be further included. Since the thiolysicon 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.

[0032] 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. In XRD measurements, peaks for thiolysicon region type II crystalline phase are observed at 2θ = 20.3±0.4°, 23.5±0.5°, and 29.6±0.5° in the XRD patterns. Furthermore, the crystallite size contained in the crystalline phase can be evaluated from the full width at half maximum of the XRD pattern.

[0033] Sulfide-based solid electrolytes may contain impurity phases. Examples of impurity phases include crystalline or amorphous phases such as Li2S phase, P2S5 phase, SiS2 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 a small amount or not at all. For example, such impurity phases may be contained at a content within the error range of the measuring device.

[0034] In the present disclosure, the sulfide-based solid electrolyte has a chemical formula represented by (100 - z)[{0.75 + y / 75 + 6.25x / 75}Li2S - {0.25 - 12.5(x / 2) / 75}P2S5 - {12.5x / 75}SiS2] - zLiHa. In the above chemical formula, Ha is one or more elements selected from halogen elements, and 0 < x < 0.75, 0 < y < 2.25, and 15 ≤ z ≤ 30 are satisfied.

[0035] 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 base composition of Li2S(75%) - P2S5(25%) where the molar ratio of Li2S to P2S5 is 3:1, that is, 0.75Li2S - 0.25P2S5. The present inventor has reported that the ion conductivity is improved by adding an excessive amount of Li2S to the above base composition (Patent Document 4). If the coefficient of the excessively added Li2S is y, the above base composition is represented as follows. {0.75 + y / 75}Li2S - {0.25}P2S5

[0036] In the present disclosure, it was confirmed that by substituting a part of P with Si, the ionic conductivity is further improved. When the coefficient of the Si substitution amount is x, the composition is expressed as follows. On the other hand, by including Si in the sulfide-based solid electrolyte, it is possible to achieve the stabilization of the crystal structure, the suppression of lattice strain and defects, the improvement of the chemical stability at grain boundaries, and the improvement of the stability in high-temperature processes, thereby suppressing the deterioration of electrochemical properties during long-term driving. {0.75 + y / 75 + 6.25x / 75}Li2S - {0.25 - 12.5(x / 2) / 75}P2S5 - {12.5x / 75}SiS2 By substituting P with Si, the amount of Si increases and the amount of P decreases. Also, P can be in the form of a trivalent anion PS4 3- and Si can be in the form of a tetravalent anion SiS4 4- so Li increases to maintain the charge of the sulfide-based solid electrolyte neutral after Si substitution.

[0037] By setting the coefficient of the halogen addition amount as z, the chemical formula of the sulfide-based solid electrolyte of the present disclosure is derived. (100 - z)[{0.75 + y / 75 + 6.25x / 75}Li2S - {0.25 - 12.5(x / 2) / 75}P2S5 - {12.5x / 75}SiS2] - zLiHa The sulfide-based solid electrolyte of the present disclosure represented by such a chemical formula can have high lithium ion conductivity and excellent stability against lithium metal.

[0038] In the above chemical formula, x indicates the amount of P substituted with Si. x satisfies 0 < x < 0.75. x may satisfy 0.001 ≤ x ≤ 0.3. Preferably, x may satisfy 0.002 ≤ x ≤ 0.05. More preferably, x may satisfy 0.005 ≤ x ≤ 0.025. Even more preferably, x may satisfy 0.006 ≤ x ≤ 0.02. When x satisfies the above range, a part of P (PS4 3- ) in the sulfide solid electrolyte is Si (SiS4 4-) is replaced so that the sulfide solid electrolyte can have an electronic state and / or a crystal structure suitable for lithium ion conduction and can have excellent stability against lithium metal. When x = 0, no change in the electronic state and / or crystal structure occurs due to the substitution of Si, and the effect of improving the lithium ion conductivity cannot be obtained. When x ≥ 0.75, excess Si can have an adverse effect on the lithium ion conductivity, and a thiolysicon region II-type crystal phase may not be formed, and the sulfide-based solid electrolyte may become unstable against lithium metal.

[0039] 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. Therefore, the sulfide-based solid electrolyte can have a high lithium ion conductivity and can have excellent stability against lithium metal. When y = 0, the effect of suppressing the formation of unwanted skeletal structures such as P2S6 4- 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 and the excellent stability against lithium metal cannot be obtained.

[0040] In the above chemical formula, z represents the content of lithium halide (LiHa) in the sulfide-based solid electrolyte. z satisfies 15 ≤ z ≤ 30. Preferably, z may satisfy 23 ≤ z ≤ 27. More preferably, z may satisfy 24 ≤ z ≤ 26. Even more preferably, z = 25 may be satisfied. When z satisfies the above range, lithium halide can suppress the influence of unwanted skeletal structures such as P2S6 4- Therefore, the sulfide-based solid electrolyte can have a high lithium ion conductivity and can have excellent stability against lithium metal.

[0041] In the above chemical formula, halogen (Ha) is one or more elements selected from halogen elements. Halogen (Ha) may include chlorine (Cl), bromine (Br), iodine (I), or two or more of these. Preferably, halogen (Ha) may include bromine (Br), iodine (I), or two or more of these. More preferably, halogen (Ha) may include bromine (Br). When sulfur (S) in a sulfide-based solid electrolyte is a divalent anion, it has a stronger attraction to lithium ions compared to a monovalent halogen and can significantly inhibit the movement of lithium ions. In particular, by including bromine (Br) as the halogen, the sulfur (S) occupancy rate at a specific site in the sulfide-based solid electrolyte decreases, the halogen occupancy rate at that site increases, and the lithium ion mobility around the bromine (Br) site can become more active. As a result, lithium ion conductivity can be improved. In addition, 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 reduce lithium ion conductivity, thereby further improving the lithium ion conductivity of sulfide-based solid electrolytes, and can also have excellent stability relative to lithium metal.

[0042] PS4, which constitutes a sulfide-based solid electrolyte. 3- (tetrahedron), P2S7 4- (A dimer unit formed by connecting two PS4 tetrahedra) 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.

[0043] In the sulfide-based solid electrolyte of this disclosure, P(PS4) 3- ) part of Si(SiS4 4- ) can be substituted with PS4, a trivalent anion in sulfide-based solid electrolytes. 3- SiS4 is a tetravalent anion. 4- By substituting with , it is possible to adjust the electronic state and / or crystal structure to one suitable for lithium ion conduction. In sulfide-based solid electrolytes, there is a concern that group 14 elements such as Si may be reduced and precipitated at the lithium metal anode during charging of all-solid-state batteries. However, by limiting the amount of Si substitution to a certain range, a sulfide solid electrolyte that is stable with respect to lithium metal and has improved lithium ion conductivity can be obtained.

[0044] The lithium-ion conductivity of sulfide-based solid electrolytes (also referred to herein as "ionic conductivity" or "ionic conductivity") refers to the lithium-ion conductivity at room temperature (25°C, 298K) and atmospheric pressure (1 atm), unless otherwise specified. When sulfide-based solid electrolytes are used in all-solid-state batteries, 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 electrolytes of this disclosure may be 4.8 mS / cm or higher, preferably 5.5 mS / cm or higher, more preferably 6.6 mS / cm or higher, and even more preferably 7.0 mS / cm or higher.

[0045] The thiolysicone region II type crystalline phase contained in sulfide-based solid electrolytes can be evaluated by XRD measurement. As shown in Figures 1 and 2, the thiolysicone region II type crystalline phase exhibits main peaks at 2θ = 20.3 ± 0.4°, 23.5 ± 0.5°, and 29.6 ± 0.5°. The peak observed at 2θ = 29.6 ± 0.5° has the highest peak intensity, but it overlaps with peaks originating from multiple crystal structures other than the thiolysicone region II type crystalline phase, making it unsuitable for evaluating the thiolysicone region II type crystalline phase. Therefore, in this disclosure, sulfide-based solid electrolytes containing the thiolysicone region II type crystalline phase are evaluated based on the peak observed at 2θ = 20.3 ± 0.4°, which has the second highest peak intensity.

[0046] The full width at half maximum (FWHM) W of the peak observed at 2θ = 20.3 ± 0.4° may satisfy 0.40° ≤ W ≤ 0.90°. Preferably, the FWHM W may satisfy 0.45° ≤ W ≤ 0.70°, more preferably 0.50° ≤ W ≤ 0.55°, and even more preferably 0.52° ≤ W ≤ 0.55°. When the FWHM W satisfies the above range, the crystallite size of the thiolysicon region II type crystalline phase contained in the sulfide-based solid electrolyte is large, which may lead to an improvement in ionic conductivity. When the FWHM W is 0.40° or greater, the crystallite size of the thiolysicon region II type crystalline phase does not become excessively large, which may make it easier to maintain the glass-ceramic structure of the sulfide-based solid electrolyte. When the FWHM W is 0.90° or less, the crystallite size of the thiolysicon region II type crystalline phase is large, which may lead to an improvement in ionic conductivity.

[0047] The sulfide-based solid electrolyte of this disclosure is P(PS4) 3- ) part of Si(SiS4 4-) is substituted with ). The ratio of moles of Si to the total number of moles of Si and P, i.e., Si / (Si+P), can be greater than 0% and less than 25%. Preferably, Si / (Si+P) is greater than 0% and 10% or less, more preferably greater than 0% and 2% or less, even more preferably greater than 0.1% and 1% or less, and most preferably greater than 0.2% and 0.5% or less. When the above ratio of moles satisfies the above range, the sulfide solid electrolyte can have an electronic state and / or crystal structure suitable for lithium ion conduction. When the above ratio of moles is 0, no change in the electronic state and / or crystal structure due to Si substitution occurs, and the effect of improving lithium ion conductivity is not obtained. When the above ratio of moles is less than 25%, the excess Si does not adversely affect lithium ion conductivity, a thiolithicon region II type crystal phase is formed, and the sulfide-based solid electrolyte can become stable with respect to lithium metal.

[0048] 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 silicon 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.

[0049] The lithium source, phosphorus source, silicon source, sulfur source, and halogen source may be compounds such as sulfides, oxides, and nitrides. Lithium sulfide (Li2S) can be used as the lithium source, diphosphorus pentasulfide (P2S5) as the phosphorus source, silicon disulfide (SiS2) as the silicon 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, silicon source, and halogen source may also serve as the sulfur source.

[0050] The step of obtaining the above mixture involves mixing and grinding raw materials such as a lithium source, a phosphorus source, a silicon 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.

[0051] 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 can be determined to be optimal according to the composition of the glass ceramics, for example, the firing temperature is 150°C to 250°C. Preferably, it may be 170°C to 230°C, more preferably 180°C to 220°C, and even more preferably 190°C to 205°C. When the firing temperature is within the above range, the formation of a thiolysicon region II type crystalline phase is promoted, and a sulfide-based solid electrolyte that is glass ceramic is obtained. Since the thiolysicon 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. If the firing temperature is not within the above range, a thiolysicon region II type crystalline structure is not formed, the effect of improving lithium ion conductivity is not obtained, and it is unstable with respect to lithium metal.

[0052] [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.

[0053] <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 of the solid electrolyte layer can be appropriately adjusted within the above range, taking into consideration lithium-ion conductivity, physical strength, energy density of the battery to which it is applied, etc. 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 2 It may have a tensile strength of 15 vol% or less, or about 10 vol% or less. For example, the porosity can be evaluated by immersion in water. Thus, the solid electrolyte layer according to this disclosure can have high mechanical strength despite being a thin film.

[0054] <Positive and negative electrodes> In this disclosure, the positive electrode and the negative electrode 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 including a plurality of electrode active material particles and a solid electrolyte. The electrodes may further include one or more conductive materials and binder resins as needed. The electrodes may also further include a variety of additives for the purpose of complementing or improving the physicochemical properties of the electrodes.

[0055] In this disclosure, any negative electrode active material that can be used as a negative electrode active material for lithium-ion secondary batteries can be used. For example, the negative electrode active material may be carbon such as non-graphitizable carbon or graphite carbon; Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2(0≦x≦1), Sn x Me 1-x 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 therefrom can be used. In a specific embodiment, the negative electrode active material can include a carbon-based material and / or Si.

[0056] The negative electrode includes a negative electrode active material layer, and the negative electrode active material layer can include lithium metal, a lithium alloy, or a combination thereof.

[0057] The negative electrode can be one in which a negative electrode active material layer is formed on at least one surface of a negative electrode current collector. Also, the negative electrode can be a free-standing negative electrode in which the negative electrode active material layer itself is self-supporting without a negative electrode current collector.

[0058] The negative electrode current collector is not particularly limited as long as it supports the negative electrode active material layer, does not induce a chemical change in the battery, and has high electrical conductivity. For example, copper; stainless steel; aluminum; nickel; titanium; palladium; fired carbon; those obtained by surface treatment of copper or stainless steel with carbon, nickel, silver, etc.; aluminum-cadmium alloy, etc. can be used.

[0059] The negative electrode current collector can also form fine irregularities on its surface to enhance the bonding force with the negative electrode active material, and can be realized in various forms such as a film, sheet, foil, mesh, net, porous body, foam, non-woven fabric body, etc.

[0060] The lithium alloy may be, for example, an alloy of lithium with sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), tin (Sn), or a mixture thereof.

[0061] The negative electrode active material may be provided in the form of a thin film or a powder.

[0062] The negative electrode active material may be a lithium metal, specifically a lithium metal thin film or lithium metal powder.

[0063] The negative electrode may include a negative electrode current collector, and during initial charging, the negative electrode current collector does not contain negative electrode active material. During charging, lithium ions are supplied from the positive electrode active material layer, and a lithium metal layer as negative electrode active material is formed on the negative electrode current collector. The negative electrode may be free of negative electrode active material before the initial lithium metal deposition (initial charging) is performed.

[0064] During charging, lithium ions are supplied from the positive electrode active material contained in the positive electrode active material layer, and a lithium metal layer can be formed on the negative electrode current collector as the negative electrode active material. Specifically, when an all-solid-state battery having an anode-free battery structure is charged by applying a voltage above a certain level, lithium ions are detached from the positive electrode active material in the positive electrode, and the detached lithium ions move through the solid electrolyte layer to the negative electrode current collector side, forming a lithium metal layer consisting purely of lithium on the negative electrode current collector, thus forming the negative electrode. This formation of a lithium metal layer by charging has the advantage of being able to form a thin film layer and being very easy to adjust the interface properties, compared to conventional negative electrodes where a lithium metal layer is sputtered onto the negative electrode current collector or where lithium foil and the negative electrode current collector are laminated.

[0065] In particular, because the anode-free battery structure prevents any exposure of lithium metal to the atmosphere during the battery assembly process, it is possible to fundamentally solve problems such as the formation of an oxide film on the surface due to the high reactivity of lithium itself, and the resulting reduction in the lifespan of lithium secondary batteries. The formed lithium metal layer can form a uniform, continuous, or discontinuous layer on the negative electrode current collector. For example, if the negative electrode current collector is in foil form, it may have a continuous thin film form, and if the negative electrode current collector has a three-dimensional porous structure, the lithium metal layer may be formed discontinuously. That is, a discontinuous layer means that within a specific region, there are regions where the lithium metal layer is present and regions where it is not, but the regions where the lithium metal layer is absent are distributed in an island-like manner, isolated, discontinuous, or separated from the regions where the lithium compound is present, which means that the regions where the lithium metal layer is present are distributed without continuity.

[0066] In one embodiment, the lithium metal layer formed through such charging and discharging functions as a negative electrode and may have a thickness of at least 50 nm and 100 μm, preferably 1 μm to 50 μm. If the thickness is below the lower limit of the above range, the battery's charging and discharging efficiency decreases sharply. Conversely, if it exceeds the upper limit of the above range, while the lifespan characteristics may be stable, there is a problem of a low energy density in the battery.

[0067] In one embodiment, the lithium metal layer is manufactured as an anode-free battery without lithium metal during battery assembly. Compared to conventional lithium secondary batteries assembled using lithium foil, this can prevent the formation of an oxide layer on the lithium metal layer during the assembly process, either completely or almost completely. This prevents the degradation of battery life caused by the oxide layer.

[0068] In one embodiment, the charging range for forming the lithium metal layer can be charged once at 0.01 - 0.2C within a voltage range of 4.5V to 2.5V. If the charging is performed below the above range, it becomes difficult to form the lithium metal layer. Conversely, if it exceeds the above range, after battery damage and over-discharge occur, charging and discharging cannot be properly performed.

[0069] 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 positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), 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 - 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 - 0.3) Ni-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 - 0.1) or lithium manganese composite oxide represented by Li2Mn3AO8 (A = Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x O4 spinel structure 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 Li is substituted with an alkaline earth metal ion; disulfide compounds; Fe2(MoO4)3, etc. can be included, but are not limited thereto.

[0070] In this disclosure, the current collector can be any electrical conductive current collector known in the field of secondary batteries, such as a metal plate, which can be appropriately used according to the polarity of the electrode.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] Example 1 Using lithium sulfide (Li2S, Mitsuwa Chemical), phosphorus pentasulfide (P2S5, Aldrich), silicon disulfide (SiS2, Mitsuwa Chemical), lithium bromide (LiBr, Aldrich), and lithium iodide (LiI, Aldrich) as raw materials, 11.045+X Si x P 3-x S 12.023 Br 1.2 I 0.8 A mixed powder was obtained by weighing and mixing in a mortar and pestle in an Ar gas-flowing glove box so that the design composition was x=0.01. 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 milling was performed at 500 rpm for 20 hours. After that, the pot was opened in the glove box and the powder was recovered. This powder was placed in a carbon crucible, sealed, and then calcined at 195°C for 3 hours while flowing Ar gas. The calcined powder was recovered to obtain a solid electrolyte.

[0077] The above design composition corresponds to x=0.01, y=0.28, and z=25 in the chemical formula (100-z)[{0.75+y / 75+6.25x / 75}Li2S-{0.25-12.5(x / 2) / 75}P2S5-{12.5x / 75}SiS2]-zLiHa.

[0078] Example 2 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount of Si substitution x was set to 0.0225.

[0079] Example 3 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount of Si substitution x was set to 0.03.

[0080] Example 4 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount of Si substitution x was set to 0.045.

[0081] Example 5 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount of Si substitution x was set to 0.06.

[0082] Example 6 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount of Si substitution x was set to 0.075.

[0083] Example 7 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount of Si substitution x was set to 0.15.

[0084] Example 8 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount of Si substitution x was set to 0.225.

[0085] Example 9 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount of Si substitution x was set to 0.3.

[0086] 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 Si was added, i.e., the substitution amount x was set to 0.

[0087] Comparative Example 2 As shown in Table 1, a solid electrolyte was obtained in the same manner as in Example 1, except that the amount of Si substitution x was set to 0.75.

[0088] [Table 1]

[0089] [evaluation] The following evaluations were performed using the obtained solid electrolyte.

[0090] (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.

[0091] (Measurement of lithium-ion conductivity) A predetermined amount of solid electrolyte was placed in a Machor tube, and the Machor tube and pellet molding jig (upper and lower press pins) were combined and press-molded at 5 MPa using a single-screw press to obtain a solid electrolyte pellet. Subsequently, a predetermined amount of gold powder was placed on both sides of the pellet, and then press-molded 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.

[0092] (Stability evaluation for lithium metal) To evaluate the stability of solid electrolytes relative to lithium metal, all-solid-state batteries were fabricated and charge-discharge tests were performed. As the solid electrolyte layer, the solid electrolyte of Comparative Example 2 (x=0.75), which had the highest Si substitution amount x, was used. 80 mg of solid electrolyte was placed in a molding jig and press-molded at 6 MPa for 1 minute to obtain a solid electrolyte pellet. 17 mg of positive electrode mixture was placed on one side of the solid electrolyte pellet, and a SUS press pin from the molding jig was pressed against it to form a positive electrode layer. A SUS foil was placed on top of the positive electrode layer and press-molded at 30 MPa for 1 minute. A Li-SUS foil was placed on the side of the solid electrolyte pellet opposite the positive electrode layer and press-molded at 2 MPa for 30 seconds. Subsequently, a Macol tube cell was fabricated by combining SUS press pins. This was installed in a battery cell, and a torque of 2.0 N·m was applied to obtain an all-solid-state battery. Using the fabricated all-solid-state batteries, charge-discharge tests were conducted with a voltage range of 4.25V-3.0V, charging conditions of CC(0.05C)-CV(0.01C), and discharging conditions of CC(0.05C). Initial charge-discharge efficiency was determined from the charge-discharge curves, and the stability of the solid electrolyte relative to lithium metal was evaluated.

[0093] [Evaluation Results] (crystalline phase) The XRD patterns obtained by XRD measurement are shown in Figures 1 and 2. As shown in Figures 1 and 2, peaks originating from thiolysicon region II were observed in all samples at 2θ = 20.3±0.4°, 23.5±0.5°, and 29.4±0.5°, confirming that a sulfide-based solid electrolyte, which is a glass ceramic, was obtained. Other peaks observed in the XRD patterns may originate from crystalline phases other than the thiolysicon region II type crystalline phase, as well as from raw materials such as Li2S, P2S5, SiS2, LiBr, and LiI.

[0094] The peak observed at 2θ = 29.4 ± 0.5°, which had the highest peak intensity, was difficult to analyze due to the overlap of multiple peaks. Therefore, the peak observed at 2θ = 20.3 ± 0.4°, which had the second highest peak intensity, was used to evaluate the effect on the ionic conductivity of sulfide-based solid electrolytes.

[0095] (Lithium-ion conductivity) Table 1 shows the measurement results of lithium ion conductivity (also called lithium ion conductivity). Figure 3 shows the composition dependence of lithium ion conductivity. The horizontal axis of Figure 3 represents the design composition Li 11.045+X Si x P 3-x S 12.023 Br 1.2 I 0.8 The amount of Si substitution x in the given expression is shown, and the vertical axis represents lithium-ion conductivity.

[0096] As shown in Table 1, in Comparative Example 1, where not a portion of P was substituted with Si, the ionic conductivity was 6.5 mS / cm. In Examples 1 to 9, where a portion of P was substituted with Si, the ionic conductivity ranged from 4.8 mS / cm to 7.3 mS / cm. In particular, Example 1, where the Si substitution amount x was 0.01, had an ionic conductivity of 7.3 mS / cm, and Example 2, where the Si substitution amount x was 0.0225, had an ionic conductivity of 6.6 mS / cm, showing improved ionic conductivity compared to Comparative Example 1. It was confirmed that adjusting the amount of Si added to the sulfide-based solid electrolyte improved ionic conductivity. In Comparative Example 2, where Si was excessively substituted, the ionic conductivity was 4.1 mS / cm. It is thought that the excess Si adversely affected the lithium ion conductivity.

[0097] As can be seen from Figure 3, in Examples 5 to 8, the ionic conductivity improved as the amount of Si substitution x increased. Although further verification is needed, this suggests that even in compositions with a relatively large amount of Si substitution x, such as in Example 8, a sulfide-based solid electrolyte with a crystal structure suitable for lithium ion conduction can be obtained by adjusting conditions such as the firing temperature.

[0098] Table 1 shows the measurement results of the full width at half maximum (FWHM) W of the peak observed at 2θ = 20.3 ± 0.4°. A smaller FWHM W tends to indicate higher ionic conductivity. This suggests that in sulfide-based solid electrolytes, such as glass ceramics, larger crystallite sizes of thiolysicon region II type materials result in higher ionic conductivity. It is thought that the small amount of Si added to the sulfide-based solid electrolyte increased the crystallite size of thiolysicon region II type materials, thereby improving ionic conductivity.

[0099] (Changes in lithium-ion conductivity due to changes in firing temperature) The procedure was the same as in Example 8, except that the firing was performed at a firing temperature of 200°C for 3 hours.

[0100] Using lithium sulfide (Li2S, Mitsuwa Chemical), phosphorus pentasulfide (P2S5, Aldrich), silicon disulfide (SiS2, Mitsuwa Chemical), lithium bromide (LiBr, Aldrich), and lithium iodide (LiI, Aldrich) as raw materials, 11.045+X Si x P 3-x S 12.023 Br 1.2 I 0.8 A mixed powder was obtained by weighing and mixing in a mortar and pestle in an Ar gas-flowing glove box so that x = 0.01 according to the design composition. 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 milling was performed at 500 rpm for 20 hours. After that, the pot was opened in the 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.

[0101] The above design composition corresponds to x=0.225, y=0.28, and z=25 in the chemical formula (100-z)[{0.75+y / 75+6.25x / 75}Li2S-{0.25-12.5(x / 2) / 75}P2S5-{12.5x / 75}SiS2]-zLiHa. As a result, the ionic conductivity was measured at 7.2 mS / cm, which is an increase from the ionic conductivity of 6.3 mS / cm in Example 8. This confirms that the ionic conductivity can be further improved by suitably adjusting the firing temperature. Furthermore, it was confirmed that the ionic conductivity can be further improved compared to the comparative example without Si by adjusting the amount of Si substitution x and the firing temperature.

[0102] (Stability against lithium metal) The initial efficiency of the all-solid-state battery using the solid electrolyte of Comparative Example 2 (x=0.75), which had the highest Si substitution amount x, as the solid electrolyte layer was a high 91.2%. When the Si substitution amount x is excessive, it is unstable with respect to Li and easily reduced. Even when the solid electrolyte of Comparative Example 2, which is considered to be the most unstable, was used as the solid electrolyte layer, the solid electrolyte layer was stable with respect to lithium metal and showed a relatively high initial efficiency. Therefore, it is considered highly likely that the solid electrolytes of Examples 1 to 9, which have a lower Si substitution amount x than Comparative Example 2, will also show high stability with respect to lithium metal.

[0103] The inventors have found that by using 0.75Li2S-0.25P2S5 as the base composition and adding an excess amount of Li2S to a sulfide-based solid electrolyte, and further substituting a portion of the P with Si, they have obtained a sulfide-based solid electrolyte that is a glass ceramic with improved ionic conductivity and high stability against lithium metal.

[0104] 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. The aforementioned sulfide-based solid electrolyte is (100-z)〔{0.75+y / 75+6.25x / 75}Li ２ S-{0.25-12.5(x / 2) / 75}P ２ S ５ -{12.5x / 75}SiS ２ 〕-zLiHa It has the chemical formula represented by, In the above chemical formula, Ha is one or more elements selected from halogen elements, A sulfide-based solid electrolyte satisfying 0 < x < 0.75, 0 < y < 2.25, and 15 ≤ z ≤ 30.

2. The sulfide-based solid electrolyte according to claim 1, wherein x satisfies 0.005 ≤ x ≤ 0.

025.

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

4.

4. The sulfide-based solid electrolyte according to claim 3, wherein z satisfies 23 ≤ z ≤ 27.

5. The sulfide-based solid electrolyte according to claim 4, wherein the Ha contains Br.

6. A sulfide-based solid electrolyte according to claim 1, satisfying 0.50° ≤ W ≤ 0.55°: W is the full width at half maximum of the peak detected at 20.3 ± 0.4° in the XRD measurement.

7. The sulfide-based solid electrolyte according to claim 1, wherein the ratio of moles of Si to the total number of moles of Si and P is greater than 0% and less than 25%.

8. A method for producing a sulfide-based solid electrolyte according to claim 1, A step of mixing a lithium source, a phosphorus source, a silicon 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...

9. 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.

10. The aforementioned negative electrode includes a negative electrode active material layer, The all-solid-state battery according to claim 9, wherein the negative electrode active material layer includes lithium metal, a lithium alloy, or a combination thereof.

11. The aforementioned negative electrode includes a negative electrode current collector. During initial charging, the negative electrode current collector does not contain negative electrode active material. The all-solid-state battery according to claim 9, wherein lithium ions are supplied from the positive electrode active material layer by charging, and a lithium metal layer as a negative electrode active material is formed on the negative electrode current collector.

Images