Sulfide-based solid electrolyte, method for preparing the same, and all-solid-state battery including the same

Abstract

This disclosure provides a sulfide-based solid electrolyte, a method for preparing the same, and an all-solid-state battery including the same. According to one embodiment of the sulfide-based solid electrolyte of this disclosure, the content of at least one element A selected from the group consisting of Group 1 and Group 2 elements excluding Li is from 0.1 mol% to 5 mol% during inductively coupled plasma (ICP) spectroscopy analysis. According to this disclosure, the moisture stability of the sulfide-based solid electrolyte can be improved.

Description

Technical Field

[0001] This disclosure relates to a sulfide-based solid electrolyte, a method for preparing the same, and an all-solid-state battery including the same. Background Technology

[0002] Recently, there has been ongoing development of all-solid-state batteries, including solid-state electrolytes. These all-solid-state batteries use solid-state electrolytes instead of existing liquid electrolytes, thus offering superior safety in the context of explosions / fires and potentially increasing energy density. Solid-state electrolytes suitable for use in such batteries primarily include polymer-based solid-state electrolytes, oxide-based solid-state electrolytes, and sulfide-based solid-state electrolytes.

[0003] Sulfide-based solid electrolytes, with their relatively high ionic conductivity, have attracted attention as electrolytes with great commercial potential. Therefore, there is an urgent need to develop a technology to improve the performance of sulfide-based solid electrolytes. Summary of the Invention

[0004] Technical issues

[0005] According to one aspect of this disclosure, a sulfide-based solid electrolyte with improved moisture stability is provided.

[0006] According to another aspect of this disclosure, a sulfide-based solid electrolyte with improved ionic conductivity is provided.

[0007] According to another aspect of this disclosure, sulfide-based solid electrolytes can be prepared using low-cost raw materials.

[0008] According to another aspect of this disclosure, a method for preparing a sulfide-based solid electrolyte that is easy to synthesize on a large scale is provided.

[0009] Technical solution

[0010] According to one embodiment of the sulfide-based solid electrolyte, during inductively coupled plasma (ICP) spectroscopy analysis, the content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements other than Li is 0.1 mol% to 5 mol%.

[0011] In some implementations, the sulfide-based solid electrolyte can be represented by the following chemical formula 1.

[0012] [Chemical Formula 1]

[0013] Li a PS b (M1) c (M2) d A x B y

[0014] In the chemical formula 1, 1 ≤ a ≤ 6, 1 ≤ b ≤ 5, 0 ≤ c ≤ 3, 0 ≤ d ≤ 3, 0 < x ≤ 1, 0 < y ≤ 2, Li is lithium, P is phosphorus, S is sulfur, M1 is a Group 17 element, M2 is a Group 17 element different from M1, A is at least one selected from the group consisting of Group 1 elements other than Li and Group 2 elements, and B is at least one selected from the group consisting of Group 17 elements, NO3 - and BF4 - and at least one selected from the group consisting of BF4.

[0015] In some embodiments, the element A may correspond to A in the compound represented by the following chemical formula 2.

[0016] [Chemical formula 2]

[0017] AB y

[0018] In the chemical formula 2, A is at least one selected from the group consisting of Group 1 elements other than Li and Group 2 elements, B is at least one selected from the group consisting of Group 17 elements, NO3 - and BF4 - and at least one selected from the group consisting of BF4, and y is 1 or 2.

[0019] In some embodiments, for the sulfide-based solid electrolyte, when performing scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS), the binding energy of the peak representing the element A may be different from the binding energies of the peaks representing phosphorus (P) and sulfur (S).

[0020] In some embodiments, for the sulfide-based solid electrolyte, when performing SEM-EDS analysis using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS), the region representing the element A in the EDS mapping image may include a region different from the regions representing phosphorus (P) and sulfur (S).

[0021] A method for preparing a sulfide-based solid electrolyte according to one embodiment may include: a step of preparing a first solution by mixing a sulfur compound represented by Chemical Formula 3 and a lithium compound represented by Chemical Formula 4 with a first solvent; a step of obtaining a first mixture comprising lithium sulfide (Li2S) and a compound represented by Chemical Formula 2 from the first solution; a step of preparing a second solution by mixing the first mixture with i) phosphorus pentasulfide (P2S5), a first lithium halide and a second solvent, or with ii) phosphorus pentasulfide (P2S5), a first lithium halide, a second lithium halide and a second solvent; and a step of obtaining a second mixture from the second solution and then heat-treating it to obtain a sulfide-based solid electrolyte, wherein the sulfide-based solid electrolyte, when analyzed by inductively coupled plasma spectroscopy (ICP), has an element A content corresponding to A in the compound represented by Chemical Formula 2 of 0.1 to 5 mol.

[0022] [Chemical Formula 2]

[0023] AB y

[0024] In the chemical formula 2, A is selected from at least one element from the group consisting of Group 1 elements (excluding Li) and Group 2 elements, and B is selected from Group 17 elements and NO3. - and BF4 - At least one of the groups, where y is 1 or 2.

[0025] [Chemical Formula 3]

[0026] A x S

[0027] In the chemical formula 3, A is at least one selected from the group consisting of Group 1 elements other than Li and Group 2 elements, S is sulfur, and x is 1 or 2.

[0028] [Chemical Formula 4]

[0029] LiB

[0030] In the aforementioned chemical formula 4, Li represents lithium, and B is selected from Group 17 elements, NO3. - and BF4 - At least one of the groups.

[0031] In some implementations, the sulfide-based solid electrolyte can be represented by the following chemical formula 1.

[0032] [Chemical Formula 1]

[0033] Li a PS b (M1) c (M2) d Ax B y

[0034] In the chemical formula 1, 1 ≤ a ≤ 6, 1 ≤ b ≤ 5, 0 ≤ c ≤ 3, 0 ≤ d ≤ 3, 0 < x ≤ 1, 0 < y ≤ 2, Li is lithium, P is phosphorus, S is sulfur, M1 is a Group 17 element, M2 is a Group 17 element different from M1, A is at least one selected from the group consisting of Group 1 elements and Group 2 elements other than Li, and B is at least one selected from the group consisting of Group 17 elements, NO3 - and BF4 - and at least one selected from the group consisting of BF4

[0035] In some embodiments, the method for preparing the sulfide-based solid electrolyte may further include a step of removing a part of the compound represented by the chemical formula 2 before the step of obtaining the first mixture from the first solution.

[0036] In some embodiments, the step of removing a part of the compound represented by the chemical formula 2 may be performed by cooling the first solution to 15°C to 25°C.

[0037] In some embodiments, the first solvent may include at least one selected from the group consisting of alcohol solvents, tetrahydrofuran solvents, and phosphoramide solvents.

[0038] In some embodiments, the second solvent may include at least one selected from the group consisting of alcohol solvents, tetrahydrofuran solvents, cyanide solvents, and phosphoramide solvents.

[0039] In some embodiments, the heat treatment of the second mixture may be performed at a temperature of 250°C to 650°C.

[0040] The all-solid-state battery according to one embodiment includes a sulfide-based solid electrolyte according to any one of the above embodiments.

[0041] Effects of the Invention

[0042] According to one embodiment of the present disclosure, the moisture stability of the sulfide-based solid electrolyte can be improved.

[0043] According to another embodiment of the present disclosure, the ionic conductivity of the sulfide-based solid electrolyte can be enhanced.

[0044] According to still another embodiment of the present disclosure, the sulfide-based solid electrolyte can be prepared with excellent economy.

[0045] According to still another embodiment of the present disclosure, large-scale synthesis can be easily performed when preparing the sulfide-based solid electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A graph showing the results of impedance analysis of the sulfide-based solid electrolyte of the example before and after exposure to air;

[0047] Figure 2 A graph showing the results of impedance analysis of the sulfide-based solid electrolyte of the comparative example before and after exposure to air;

[0048] Figure 3a A graph showing the results of peak analysis of the individual components based on binding energy using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) of the sulfide-based solid electrolyte of the example;

[0049] Figures 3b to 3d The sulfide-based solid electrolytes of the examples were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to determine elemental A (…). Figure 3b ),phosphorus( Figure 3c ) and sulfur ( Figure 3d A graph showing the results;

[0050] Figure 4a A graph showing the results of peak analysis of the individual components based on binding energy using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) of the sulfide-based solid electrolyte of the comparative example;

[0051] Figure 4b and Figure 4c The analysis of phosphorus (P) in the sulfide-based solid electrolyte, which is shown as a comparative example, was performed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Figure 4b ) and sulfur ( Figure 4c The result is shown in the figure. Detailed Implementation

[0052] The technology disclosed in this specification and its implementation examples will now be described in detail with reference to the accompanying drawings. However, the implementation of the technology can be modified in many other ways, and its scope is not limited to the implementation examples described below. Furthermore, the technology disclosed in this specification can be applied not only to the configuration of the implementation examples described below, but can also be configured by selectively combining all or part of the various implementation examples, allowing for various modifications.

[0053] As mentioned above, there is a need to develop a technique to improve the performance of sulfide-based solid electrolytes. According to one implementation example, ionic conductivity and / or moisture stability can be improved by doping the sulfide-based solid electrolyte with a different element. Example, a portion of the phosphorus (P) or sulfur (S) in Li6PS5Cl, a sulfide-based solid electrolyte with a sulfide-germanium sulfide structure, can be replaced with another element.

[0054] According to an implementation example of the present disclosure, a sulfide-based solid electrolyte with improved properties such as moisture stability can be prepared by replacing lithium (Li) in the sulfide-based solid electrolyte with a foreign element. According to the said implementation example, a sulfide-based solid electrolyte with improved properties can be easily synthesized in large quantities, and the economy of the manufacturing process can also be excellent. The following will refer to Figures 1 to 4c specifically describe the implementation examples of the technology disclosed in the present disclosure.

[0055] Sulfide-based solid electrolytes

[0056] In the sulfide-based solid electrolyte according to an implementation example, when analyzed by inductively coupled plasma spectroscopy (ICP), the content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements other than Li is 0.1 mol% to 5 mol%. The sulfide-based solid electrolyte can have excellent moisture stability by replacing (or doping) part of lithium (Li) with a foreign element.

[0057] In some implementation examples, the sulfide-based solid electrolyte can be represented by the following Chemical Formula 1.

[0058] [Chemical Formula 1]

[0059] Li a PS b (M1) c (M2) d A x B y

[0060] In Chemical Formula 1, 1 ≤ a ≤ 6, 1 ≤ b ≤ 5, 0 ≤ c ≤ 3, 0 ≤ d ≤ 3, 0 < x ≤ 1, 0 < y ≤ 2, Li is lithium, P is phosphorus, S is sulfur, M1 is a Group 17 element, M2 is a Group 17 element different from M1, A is at least one selected from the group consisting of Group 1 elements and Group 2 elements other than Li, and B is at least one selected from the group consisting of Group 17 elements, NO3 - and BF4 - The element A can correspond to A in Chemical Formula 1.

[0061] In some implementation examples, the element A can correspond to A in the compound represented by the following Chemical Formula 2.

[0062] [Chemical Formula 2]

[0063] AB y

[0064] In Chemical Formula 2, A is at least one selected from the group consisting of Group 1 elements and Group 2 elements other than Li, and B is at least one selected from the group consisting of Group 17 elements, NO3- and BF4 - At least one of the groups, where y is 1 or 2.

[0065] The compound represented by chemical formula 2 can be generated in the process of preparing lithium sulfide (Li2S) by reacting a sulfur compound represented by chemical formula 3 and a lithium compound represented by chemical formula 4.

[0066] [Chemical Formula 3]

[0067] A x S

[0068] In the chemical formula 3, A is at least one selected from the group consisting of Group 1 elements other than Li and Group 2 elements, S is sulfur, and x is 1 or 2.

[0069] [Chemical Formula 4]

[0070] LiB

[0071] In the aforementioned chemical formula 4, Li represents lithium, and B is selected from Group 17 elements, NO3. - and BF4 - At least one of the groups.

[0072] In some implementations, the sulfide-based solid electrolyte represented by Formula 1 can be a sodium (Na) doped sulfide-based solid electrolyte in which some lithium (Li) is replaced by sodium (Na). Specifically, the compound represented by Formula 2 can be sodium chloride (NaCl). When sodium (Na) is doped into the sulfide-based solid electrolyte represented by Formula 1, the electrolyte can exhibit excellent water stability and ionic conductivity.

[0073] In some implementations, the compound represented by chemical formula 3 may be sodium sulfide (Na2S), and the compound represented by chemical formula 4 may be lithium chloride (LiCl).

[0074] In the inductively coupled plasma (ICP) analysis of the sulfide-based solid electrolyte, the content of at least one element A selected from the group consisting of Group 1 and Group 2 elements excluding Li is from 0.1 mol% to 5 mol%. According to the ICP analysis, the content of cations contained in the analyte can be quantitatively measured. The ICP analysis equipment is not particularly limited. For example, the ICP analysis can be performed using an Agilent 5800.

[0075] In some implementations, when the sulfide-based solid electrolyte is analyzed by inductively coupled plasma spectroscopy (ICP), the content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements other than Li can be less than 3 mol% or less than 1.5 mol%, and can be more than 0.5 mol%, more than 1 mol%, or more than 1.4 mol%.

[0076] In some implementations, for the sulfide-based solid electrolyte, when performing SEM-EDS analysis using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), the binding energy of the peak representing element A may be different from the binding energies of the peaks representing phosphorus (P) and sulfur (S).

[0077] The peaks representing phosphorus (P) and sulfur (S) may correspond to the peaks of phosphorus (P) and sulfur (S) contained in the sulfide-based solid electrolyte represented by chemical formula 1, and the peaks representing element A may correspond to the peaks of element A contained in the compound represented by chemical formula 2.

[0078] like Figure 3a As shown, in some implementations, for the sulfide-based solid electrolyte, SEM-EDS analysis indicates that the peaks of phosphorus (P) and sulfur (S) in Formula 1 are different from and can be clearly distinguished from the peaks corresponding to A in Formula 2.

[0079] In some implementations, in the chemical formula 1, the peak representing sulfur (S) can appear at binding energies of 0.1 to 0.2 keV (exemplarily 0.15 keV) and 2.3 to 2.4 keV (exemplarily 2.31 keV) during SEM-EDS analysis, and the peak representing phosphorus (P) can appear at binding energies of 2.1 to 2.2 keV (exemplarily 2.013 keV) during SEM-EDS analysis.

[0080] In some implementations, the peak corresponding to A in Formula 2 can appear at a binding energy of 1.0 to 1.1 keV during SEM-EDS analysis.

[0081] In some implementations, for the sulfide-based solid electrolyte, when performing SEM-EDS analysis using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), the region representing element A in the EDS mapping image may include a region different from the region representing phosphorus (P) and sulfur (S). Examplely, the region representing phosphorus (P) and sulfur (S) may correspond to the region representing the sulfide-based solid electrolyte shown in Formula 1. Additionally, the region representing element A may correspond to the region representing the compound shown in Formula 2.

[0082] The distinction between regions representing each component in the EDS mapping image can be performed by quantizing the points of each component detected in the EDS mapping image and storing the images of the regions where the target component was detected.

[0083] like Figures 3b to 3d As shown, in some implementations, for the sulfide-based solid electrolyte, during SEM-EDS analysis, the region in the EDS mapping image corresponding to A in Formula 2 may include a region that is distinctly different from the regions representing phosphorus (P) and sulfur (S) in Formula 1.

[0084] The SEM-EDS analysis equipment and conditions are not particularly limited. For example, the SEM-EDS analysis can be performed using a Bruker FlatQuad with an EDS device linked to the SEM, under conditions of a 5kV accelerating voltage, a 130kcps pulse throughput, and a 15mm working distance.

[0085] The sulfide-based solid electrolyte according to any of the above implementation examples can be prepared by the method described below.

[0086] Preparation method of sulfide-based solid electrolyte

[0087] A method for preparing a sulfide-based solid electrolyte according to one embodiment includes: a step of preparing a first solution by mixing a sulfur compound represented by Chemical Formula 3 and a lithium compound represented by Chemical Formula 4 with a first solvent; a step of obtaining a first mixture from the first solution comprising lithium sulfide (Li2S) and a compound represented by Chemical Formula 2; a step of preparing a second solution by mixing the first mixture with i) phosphorus pentasulfide (P2S5), a first lithium halide and a second solvent, or with ii) phosphorus pentasulfide (P2S5), a first lithium halide, a second lithium halide and a second solvent; and a step of obtaining a second mixture from the second solution and then heat-treating it to obtain a sulfide-based solid electrolyte, wherein the sulfide-based solid electrolyte, when analyzed by inductively coupled plasma spectroscopy (ICP), has an element A content corresponding to A in the compound represented by Chemical Formula 2 of 0.1 mol% to 5 mol%.

[0088] [Chemical Formula 2]

[0089] AB y

[0090] In the chemical formula 2, A is selected from at least one element from the group consisting of Group 1 elements (excluding Li) and Group 2 elements, and B is selected from Group 17 elements and NO3. - and BF4 - At least one of the groups, where y is 1 or 2.

[0091] [Chemical Formula 3]

[0092] A x S

[0093] In the chemical formula 3, A is at least one selected from the group consisting of Group 1 elements other than Li and Group 2 elements, S is sulfur, and x is 1 or 2.

[0094] [Chemical Formula 4]

[0095] LiB

[0096] In the aforementioned chemical formula 4, Li represents lithium, and B is selected from Group 17 elements, NO3. - and BF4 - At least one of the groups.

[0097] The method for preparing the sulfide-based solid electrolyte can utilize inexpensive raw materials to produce it economically. Furthermore, the method employs a liquid-phase synthesis reaction, thus facilitating large-scale synthesis. Each step of the method for preparing the sulfide-based solid electrolyte is described in detail below.

[0098] <First Solution Preparation Steps>

[0099] The first solution preparation step may be performed by reacting a sulfur compound (A) represented by the chemical formula 3. x The first solution may contain lithium sulfide (Li₂S) synthesized by reacting a compound (LiB) represented by chemical formula 3 and chemical formula 4 with a lithium compound (LiB) represented by chemical formula 2. y The sulfur compound represented by the chemical formula 3 (A) x Lithium (S) and the lithium compound (LiB) represented by the chemical formula 4 can be prepared in a molar ratio of 1:2 for the synthesis of lithium sulfide (Li2S).

[0100] In some implementations, the first solution preparation step can be performed at a temperature above room temperature. For example, the first solution preparation step can be performed at a temperature above 25°C, or at a temperature below the boiling point of the solvent (for example, below 70°C).

[0101] In some implementations, the method for preparing the sulfide-based solid electrolyte may further include a step of removing a portion of the compound represented by Chemical Formula 2 before obtaining the first mixture from the first solution. The compound represented by Chemical Formula 2 can be a compound used for doping the sulfide-based solid electrolyte with a different element; however, excessive amounts of this compound can actually degrade the performance of the sulfide-based solid electrolyte. Therefore, by removing a portion of the compound represented by Chemical Formula 2 before obtaining the first mixture from the first solution, a sulfide-based solid electrolyte with excellent performance can be prepared.

[0102] In some implementations, the step of removing a portion of the compound represented by Formula 2 can be performed by cooling the first solution to 15°C to 25°C. Lowering the temperature of the first solution to below room temperature (25°C) can reduce the solubility of the compound represented by Formula 2 contained in the first solution, causing it to precipitate. If the temperature of the first solution exceeds 25°C, the compound represented by Formula 2 may not precipitate well. Conversely, if the temperature of the first solution is below 15°C, the solubility of lithium sulfide (Li₂S) also decreases, thus the amount of lithium sulfide (Li₂S) obtained may be reduced, and excessive precipitation of the compound represented by Formula 2 may prevent the doping of the sulfide-based solid electrolyte.

[0103] In some implementations, the first solvent may be a polar solvent. Example, the first solvent may include at least one selected from the group consisting of alcohol solvents, tetrahydrofuran solvents, and phosphoramide solvents.

[0104] The alcohol solvent is not particularly limited, and can be any alcohol compound containing a hydroxyl group (-OH). For example, the alcohol solvent may be methanol, ethanol, isopropanol, etc.

[0105] The tetrahydrofuran solvent is not particularly limited, as long as it is a compound having a pentagonal heterocycle with four carbon atoms and an oxygen atom connected by a single bond. Examplely, the tetrahydrofuran solvent can be one or more compounds selected from tetrahydrofuran; and compounds in which at least one functional group is bonded at the second or third carbon position of the tetrahydrofuran. Examplely, the compound in which at least one functional group is bonded at the second or third carbon position of the tetrahydrofuran can be 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2-(isocyanomethyl)tetrahydrofuran, 3-(aminomethyl)tetrahydrofuran, etc.

[0106] The phosphoramide solvent is not particularly limited, and can be any compound having a structure in which a phosphorus atom is connected to an oxygen atom by a double bond and then to an oxygen or nitrogen atom by three single bonds. Examples of phosphoramide solvents include phosphoramide, diethyl phosphoramidate, and hexamethyl phosphoramide.

[0107] In some implementations, the concentration of the first solution can be from 0.1 to 0.5 M. When the concentration of the first solution is below 0.1 M, the amount of solvent used increases, which can lead to an increase in the process unit price. When the concentration of the first solution is above 0.5 M, the yield of the sulfide-based solid electrolyte can decrease.

[0108] <Steps for obtaining the first mixture>

[0109] The first mixture obtaining step refers to the step of obtaining a first mixture containing lithium sulfide (Li₂S) and a compound represented by the chemical formula 2 from the first solution prepared as described above. Substances precipitated in the first solution can be removed by filtration. Filtration of the first solution can be carried out in an inert gas environment such as argon (Ar).

[0110] In some implementations, the method for preparing the sulfide-based solid electrolyte further includes a step of removing a portion of the compound represented by chemical formula 2 before obtaining the first mixture from the first solution. In this case, a portion of the compound represented by chemical formula 2 can be removed by filtration after precipitation in the first solution through a cooling process.

[0111] The first mixture can be obtained by drying the first solution after filtration to remove the first solvent. The first solution after filtration contains the first mixture, and when the first solvent is removed by drying, a high-purity first mixture can be obtained.

[0112] The drying process of the first solution can be carried out at a temperature above the boiling point of the first solvent used, that is, at a temperature at which the first solvent can be removed. In some implementations, the drying process of the first solution can be carried out in a vacuum or in an inert gas environment such as argon (Ar) at a temperature above 70°C, or at a temperature below 900°C.

[0113] <Second Solution Preparation Steps>

[0114] The second solution preparation step can be a step of preparing a second mixture for preparing a sulfide-based solid electrolyte and a second solution containing the same from the first mixture obtained as described above. Specifically, the second solution preparation step can be a step of mixing the first mixture with i) phosphorus pentasulfide (P2S5), a first lithium halide and a second solvent, or with ii) phosphorus pentasulfide (P2S5), a first lithium halide, a second lithium halide and a second solvent.

[0115] The first lithium halide refers to lithium halide represented by the chemical formula LiM1, where M1 is a group 17 element, meaning it is the same as M1 in chemical formula 1.

[0116] The second lithium halide refers to a lithium halide represented by the chemical formula LiM2 that is different from the first lithium halide. M2 is a group 17 element that is different from M1, and means the same as M2 in chemical formula 1.

[0117] In some implementations, the content of the first mixture contained in the second solution may be from 34% to 44% by weight.

[0118] In some implementations, the content of phosphorus pentasulfide (P2S5) in the second solution can be from 41% to 42% by weight.

[0119] In some implementations, where the second solution preparation step involves mixing the first mixture with phosphorus pentasulfide (P2S5), a first lithium halide, and a second solvent, the content of the first lithium halide in the second solution can be from 15% to 24% by weight.

[0120] In some implementations, where the second solution preparation step involves mixing the first mixture with phosphorus pentasulfide (P2S5), a first lithium halide, a second lithium halide, and a second solvent, the total content of the first and second lithium halides in the second solution can be from 22% to 28% by weight. The weight ratio of the first and second lithium halides in the second solution can be from 0.18 to 22.

[0121] In some implementations, the second solvent may be a polar solvent. Example, the second solvent may include at least one selected from the group consisting of alcohol-based solvents, tetrahydrofuran-based solvents, cyanide-based solvents, and phosphoramide-based solvents.

[0122] The cyanide-based solvent is not particularly limited, as long as it is a cyanide containing a cyano group (C≡N). Examples include benzoyl cyanide, 4-methylbenzylcyanide, allyl cyanide, and acetonitrile.

[0123] The detailed descriptions of the alcohol-based solvents, tetrahydrofuran-based solvents, and phosphoramide-based solvents are repeated from the above descriptions, and therefore are omitted.

[0124] <Steps for obtaining sulfide-based solid electrolytes>

[0125] The step of obtaining the sulfide-based solid electrolyte refers to obtaining a second mixture from the second solution prepared as described above, and subjecting it to heat treatment to obtain the sulfide-based solid electrolyte represented by the chemical formula 1.

[0126] The second mixture can be obtained by removing the second solvent by drying the second solution prepared above. The second solution contains the second mixture, and a high-purity second mixture can be obtained by removing the second solvent through a drying process.

[0127] The second mixture may be i) a mixture of the first mixture, phosphorus pentasulfide (P2S5) and the first lithium halide, or ii) a mixture of the first mixture, phosphorus pentasulfide (P2S5), the first lithium halide and the second lithium halide.

[0128] The drying process of the second solution can be carried out at a temperature above the boiling point of the second solvent used, that is, at a temperature at which the second solvent can be removed. In some implementations, the drying process of the second solution can be carried out under vacuum at a temperature above 70°C, or at a temperature below 200°C.

[0129] Heat treatment of the second mixture obtained from the second solution can form a sulfide-based solid electrolyte represented by the chemical formula 1. In some implementations, the heat treatment of the second mixture can be performed at a temperature of 250°C to 650°C. Exemplarily, the heat treatment of the second mixture can be performed at a temperature above 350°C or 450°C, or at a temperature below 600°C or 550°C. The heat treatment of the second mixture can be performed in an inert gas environment such as argon (Ar).

[0130] All-solid-state batteries

[0131] An all-solid-state battery according to one embodiment includes a sulfide-based solid electrolyte according to any of the above embodiments. Example, the all-solid-state battery may include a sulfide-based solid electrolyte according to any of the above embodiments located between the negative and positive electrodes.

[0132] The structure and composition of the positive and negative electrodes are not particularly limited. Example, the positive and negative electrodes may each include an electrode current collector and an electrode mixture layer located on at least one side of the electrode current collector.

[0133] The composition of the electrode current collector is not particularly limited. Example, the electrode current collector may be a plate or foil composed of one or more of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), and their alloys. Furthermore, the thickness of the electrode current collector is not particularly limited. Example, the thickness of the negative electrode current collector may be from 0.1 μm to 50 μm.

[0134] The electrode mixture layer may contain either a positive or negative active material. The positive and negative active materials are not particularly limited and may contain compounds capable of reversibly inserting and deintercalating lithium ions.

[0135] The positive electrode active material is not particularly limited. Example, the positive electrode active material may comprise a lithium nickel metal oxide. The lithium nickel metal oxide may also comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0136] In some implementations, the positive electrode active material or the lithium nickel metal oxide may contain a layered structure or a crystal structure represented by the following chemical formula 5.

[0137] [Chemical Formula 5]

[0138] Li x Ni a Mb O 2+z

[0139] In the chemical formula 5, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.

[0140] The chemical structure represented by Formula 5 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material, and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn can be provided together with Ni as the main active element of the positive electrode active material. It should be understood that Formula 5 is provided to represent the bonding relationships of the main active element and includes the introduction and substitution of additional elements.

[0141] In some implementations, auxiliary elements may also be included, which are added to the main active element to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure to form bonds, and it should be understood that this also includes the chemical structures represented by Formula 5.

[0142] Examplely, the auxiliary element may include at least one selected from Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may also function similarly to Al, acting as an auxiliary active element that, together with Co or Mn, contributes to the capacity / output activity of the positive electrode active material.

[0143] By way of example, the positive electrode active material or the lithium nickel metal oxide may contain a layered structure or a crystal structure represented by the following chemical formula 5-1.

[0144] [Chemical Formula 5-1]

[0145] Li x Ni a M1 b1 M2 b2 O 2+z

[0146] In chemical formula 5-1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 5-1, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1.

[0147] The positive electrode active material may further include a coating element or a doping element. For example, an element substantially the same as or similar to the above-described auxiliary element may be used as the coating element or the doping element. Exemplarily, a single one of the above elements or a combination of two or more thereof may be used as the coating element or the doping element.

[0148] The coating element or the doping element may be present on the surface of the lithium nickel metal oxide particles, or may be included in the bonding structure represented by Chemical Formula 5 or Chemical Formula 5-1 through penetration of the surface of the lithium nickel metal oxide particles.

[0149] The positive electrode active material may include a lithium nickel cobalt manganese (NCM) - based lithium oxide. In this case, an NCM - based lithium oxide with an increased nickel content may be used.

[0150] The content of Ni in the NCM - based lithium oxide (for example, the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0151] In some implementations, the positive electrode active material may also include a lithium cobalt oxide - based active material, a lithium manganese oxide - based active material, a lithium nickel oxide - based active material, or a lithium iron phosphate (LFP) - based active material (for example, LiFePO4).

[0152] In some implementations, the positive electrode active material may include a manganese - rich (Mn - ric) - based active material having a chemical structure or crystal structure represented by Chemical Formula 6, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide) - based active material, or a cobalt - less - based active material.

[0153] [Chemical Formula 6]

[0154] p[Li2MnO3]·(1 - p)[Li q JO2]

[0155] In Chemical Formula 6, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0156] The negative electrode active material is not particularly limited. Exemplarily, the negative electrode active material may be one or more selected from the group consisting of carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon-containing materials, and tin-containing materials.

[0157] Exemplarily, the crystalline carbon may be graphite-based carbon, such as natural graphite, artificial graphite, graphitized coke, graphitized mesocarbon microbeads (MCMB), and graphitized mesophase pitch-based carbon fibers (MPCF).

[0158] Exemplarily, the amorphous carbon may be hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), or mesophase pitch-based carbon fibers (MPCF).

[0159] Exemplarily, the elements contained in the lithium metal may be aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0160] The silicon-containing material is not particularly limited as long as it contains silicon, and it may be an active material capable of alloying with lithium (Li). Exemplarily, the silicon-containing material may be one or more selected from the group consisting of silicon (Si), silicon oxide (SiOx; 0 < x < 2), metal-doped silicon oxide (SiOx; 0 < x < 2), carbon-coated silicon oxide (SiOx; 0 < x < 2), silicon-carbon composite materials (Si-C), and silicon alloys.

[0161] The electrode binder layer may further contain a binder. The binder is not particularly limited. Exemplarily, the positive electrode binder layer may contain one or two or more of polyvinylidene fluoride, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile-based polymethyl methacrylate, etc. as the binder.

[0162] In addition, the negative electrode binder layer may contain any one selected from rubber-based binders such as styrene-butadiene rubber (SBR), fluororubber, ethylene-propylene rubber, butadiene rubber, isoprene rubber, and silane rubber; cellulose-based binders such as carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts; and combinations thereof.

[0163] The electrode mixture layer may also contain a conductive material. The conductive material is not particularly limited. Example, the conductive material may include graphite such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, carbon fiber, and carbon nanotubes (CNTs); metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or one or more conductive polymers such as polyphenylene derivatives.

[0164] Example

[0165] 1. Preparation of sulfide-based solid electrolytes

[0166] 1) Example

[0167] Sodium sulfide (Na₂S) and lithium chloride (LiCl) were weighed in a 1:2 molar ratio to prepare a sulfur compound and a lithium compound, respectively. The sodium sulfide (Na₂S) and lithium chloride (LiCl) were mixed with ethanol as a first solvent at a temperature above 25°C (55°C) to prepare a first solution with a concentration of 0.3M. After stirring the first solution with a magnetic stirrer, the precipitated material in the first solution was filtered under an argon (Ar) atmosphere. Under these conditions, the temperature of the first solution was between 15°C and 25°C. Subsequently, the first solution was dried at a temperature above 70°C to remove the first solvent and recover the first mixture containing lithium sulfide (Li₂S) and sodium chloride (NaCl).

[0168] A second solution was prepared by mixing the recovered first mixture with phosphorus pentasulfide (P2S5) and lithium chloride (LiCl) with acetonitrile as a second solvent. In this case, the first mixture, phosphorus pentasulfide (P2S5), and lithium chloride (LiCl) were added in proportions of 42.7 wt%, 41.4 wt%, and 15.9 wt%, respectively, and the second solvent was added to achieve a solution concentration of 1 L (100 g / L) relative to 100 g of the raw material mixture.

[0169] After stirring the second solution with a magnetic stirrer, the second solution was dried at a temperature above 70°C to remove the second solvent, thereby obtaining a second mixture. Subsequently, the second mixture was heat-treated at 550°C under an argon (Ar) atmosphere to obtain a sodium-doped sulfide-based solid electrolyte.

[0170] 2) Comparative examples

[0171] Except for cooling the first solution to 0°C to maximize the precipitation of sodium chloride (NaCl) before filtering the precipitate in the first solution under argon (Ar) atmosphere, a sulfide-based solid electrolyte was obtained by the same method as described in the embodiment.

[0172] 2. Evaluation of sulfide-based solid electrolytes

[0173] 1) Inductively Coupled Plasma Spectroscopy (ICP) Analysis

[0174] A certain amount of sulfide-based solid electrolyte was weighed in a quantity that would not pose a safety hazard to workers due to the hydrogen sulfide generated by the sulfide-based solid electrolyte. This amount of sulfide-based solid electrolyte from the examples and comparative examples was then dissolved in triple-distilled water free of any ions and allowed to react fully before analysis by ICP. In this case, the reaction of the sulfide-based solid electrolyte in distilled water was carried out as follows.

[0175] 1. After thoroughly mixing 20 mg of sample with 15 mL of distilled water, remove any suspended matter using a 0.45 μm syringe filter.

[0176] 2. After adding 5 drops of nitric acid, mix well.

[0177] Then, in order to determine the concentration of element A, ICP analysis was performed using an inductively coupled plasma (ICP) spectrometer, and the results are shown in Table 1 below. In this case, the ICP analysis was performed using an Agilent 700s under the conditions described below.

[0178] - RF Power (W): 1200

[0179] - Coolant gas (L / min): 15

[0180] - Auxiliary gas (L / min): 1.5

[0181] - Carrier gas (L / min): 0.75

[0182] 2) SEM-EDS analysis

[0183] To prevent contact with air, the sulfide-based solid electrolyte samples of the examples and comparative examples used for SEM-EDS analysis were prepared into a powder state inside a glove box. SEM-EDS analysis of the sulfide-based solid electrolytes of the examples and comparative examples was then performed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results are as follows: Figures 3a to 4cAs shown. In this case, the SEM-EDS analysis was performed using a Bruker FlatQuad with an EDS device linked to the SEM, under conditions of 5kV accelerating voltage, 130kcps pulse throughput, and 15mm working distance.

[0184] 3) Assess ionic conductivity and moisture stability

[0185] (1) Ionic conductivity

[0186] For the sulfide-based solid electrolytes prepared in the examples and comparative examples, AC impedance analysis was performed at room temperature to confirm the lithium-ion conductivity. The results are shown in Table 1 below. Specifically, 100 mg of solid electrolyte was placed in a mold and subjected to a pressure of 370 MPa to prepare particles. The granular solid electrolyte was then placed in a lithium-ion conductivity measuring fixture. The fixture was then placed in a constant temperature and humidity chamber and left at room temperature for 3 hours. An AC potential of 100 mV was then applied, and a frequency sweep was performed from 1000 Hz to 1 MHz. The obtained impedance was used as a reference to measure the ionic conductivity.

[0187] (2) Moisture stability

[0188] The moisture stability was evaluated by measuring the decrease in ionic conductivity of the prepared sulfide-based solid electrolytes from the examples and comparative examples after exposure to air. Specifically, 100 mg of the solid electrolyte was exposed to air with a dew point of -40°C at room temperature (23 ± 5°C) for 1 hour, and the ionic conductivity of the solid electrolyte was measured according to the method described above. Then, the measured ionic conductivity value was compared with the ionic conductivity value before exposure to air to calculate the reduction rate, and the results are shown in Table 1 below.

[0189] Table 1

[0190]

[0191] Refer to Table 1. Figure 1 and Figure 2 It can be confirmed that, compared with the sulfide-based solid electrolyte of the example, which did not detect element A during ICP analysis, the sulfide-based solid electrolyte of the comparative example not only had relatively lower ionic conductivity values ​​before and after exposure to air, but also a relatively greater rate of decrease in ionic conductivity before and after exposure to air.

[0192] On the other hand, reference Figure 3aIn the sulfide-based solid electrolyte of the examples, a peak with a binding energy different from that representing phosphorus (P) and sulfur (S) can be clearly identified, namely, the peak representing element A. Additionally, refer to... Figures 3b to 3d It can be confirmed that the region representing element A in the EDS mapping image of the sulfide-based solid electrolyte of the embodiment ( Figure 3b This includes regions representing phosphorus (P) and sulfur (S). Figure 3c and Figure 3d Different regions.

[0193] Conversely, refer to Figure 4a It can be confirmed that in the sulfide-based solid electrolyte of the comparative example, only peaks representing phosphorus (P) and sulfur (S) were detected, while no peak representing element A was detected. Additionally, see reference... Figure 4b and Figure 4c It can be confirmed that, for the sulfide-based solid electrolyte of the comparative example, regions representing phosphorus (P) and sulfur (S) were identified in the EDS mapping image, respectively. Figure 4b and Figure 4c However, the region representing element A was not identified.

Claims

1. A sulfide-based solid electrolyte, wherein, during inductively coupled plasma spectroscopy analysis, the content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements excluding Li is 0.1 mol% to 5 mol%.

2. The sulfide-based solid electrolyte according to claim 1, wherein, The sulfide-based solid electrolyte is represented by the following chemical formula 1. [Chemical Formula 1] The a PS b (M1) c (M2) d A x B y In the chemical formula 1, 1 ≤ a ≤ 6, 1 ≤ b ≤ 5, 0 ≤ c ≤ 3, 0 ≤ d ≤ 3, 0 < x ≤ 1, 0 < y ≤ 2, Li is lithium, P is phosphorus, S is sulfur, M1 is a Group 17 element, M2 is a Group 17 element different from M1, A is at least one selected from the group consisting of Group 1 elements other than Li and Group 2 elements, and B is at least one selected from the group consisting of Group 17 elements, NO3 - and BF4 - and the group consisting of.

3. The sulfide-based solid electrolyte according to claim 1, wherein, The element A corresponds to A in the compound represented by the following chemical formula 2. [Chemical Formula 2] AB y In the chemical formula 2, A is selected from at least one element from the group consisting of Group 1 elements (excluding Li) and Group 2 elements, and B is selected from Group 17 elements and NO3. - and BF4 - At least one of the groups, where y is 1 or 2.

4. The sulfide-based solid electrolyte according to claim 1, wherein, When performing scanning electron microscopy-energy dispersive X-ray spectroscopy analysis using scanning electron microscopy and energy dispersive X-ray spectroscopy, the binding energy of the peak representing element A is different from that of the peaks representing phosphorus (P) and sulfur (S).

5. The sulfide-based solid electrolyte according to claim 1, wherein, When performing scanning electron microscopy-energy dispersive X-ray spectroscopy analysis using scanning electron microscopy and energy dispersive X-ray spectroscopy, the region representing element A in the energy dispersive X-ray spectroscopy map includes a different region than the regions representing phosphorus (P) and sulfur (S).

6. A method for preparing a sulfide-based solid electrolyte, wherein, include: The step of preparing a first solution by mixing a sulfur compound represented by the following chemical formula 3 and a lithium compound represented by the following chemical formula 4 with a first solvent; The step of obtaining a first mixture comprising lithium sulfide (Li2S) and a compound represented by the following chemical formula 2 from the first solution; The step of preparing the second solution by mixing the first mixture with i) phosphorus pentasulfide (P2S5), lithium first halide and second solvent, or with ii) phosphorus pentasulfide (P2S5), lithium first halide, lithium second halide and second solvent; as well as The step of obtaining a second mixture from the second solution and then subjecting it to heat treatment to obtain a sulfide-based solid electrolyte. During inductively coupled plasma spectroscopy analysis, the sulfide-based solid electrolyte, corresponding to the content of element A in the compound represented by the following chemical formula 2, is 0.1 mol% to 5 mol%. [Chemical Formula 2] AB y In the chemical formula 2, A is selected from at least one element from the group consisting of Group 1 elements (excluding Li) and Group 2 elements, and B is selected from Group 17 elements and NO3. - and BF4 - At least one of the groups, where y is 1 or 2. [Chemical Formula 3] A x S In the chemical formula 3, A is at least one selected from the group consisting of elements from Group 1 and Group 2 other than Li, S is sulfur, and x is 1 or 2. [Chemical Formula 4] LiB In the aforementioned chemical formula 4, Li represents lithium, and B is selected from Group 17 elements, NO3. - and BF4 - At least one of the groups.

7. The method for preparing a sulfide-based solid electrolyte according to claim 6, wherein, The sulfide-based solid electrolyte is represented by the following chemical formula 1. [Chemical Formula 1] The a PS b (M1) c (M2) d A x B y In the chemical formula 1, 1 ≤ a ≤ 6, 1 ≤ b ≤ 5, 0 ≤ c ≤ 3, 0 ≤ d ≤ 3, 0 < x ≤ 1, 0 < y ≤ 2, Li is lithium, P is phosphorus, S is sulfur, M1 is a Group 17 element, M2 is a Group 17 element different from M1, A is at least one selected from the group consisting of Group 1 elements and Group 2 elements other than Li, and B is at least one selected from the group consisting of Group 17 elements, NO3 - and BF4 - and is selected from the group consisting of.

8. The method for preparing a sulfide-based solid electrolyte according to claim 6, wherein, Prior to the step of obtaining the first mixture from the first solution, the method further includes a step of removing a portion of the compound represented by the chemical formula 2.

9. The method for preparing a sulfide-based solid electrolyte according to claim 8, wherein, The step of removing a portion of the compound represented by the chemical formula 2 is carried out by cooling the first solution to 15°C to 25°C.

10. The method for preparing a sulfide-based solid electrolyte according to claim 6, wherein, The first solvent includes at least one selected from the group consisting of alcohol solvents, tetrahydrofuran solvents, and phosphoramide solvents.

11. The method for preparing a sulfide-based solid electrolyte according to claim 6, wherein, The second solvent includes at least one selected from the group consisting of alcohol solvents, tetrahydrofuran solvents, cyanide solvents and phosphoramide solvents.

12. The method for preparing a sulfide-based solid electrolyte according to claim 6, wherein, The heat treatment of the second mixture was carried out at a temperature of 250°C to 650°C.

13. An all-solid-state battery comprising a sulfide-based solid electrolyte according to any one of claims 1 to 5.

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