Method of preparing sulfur compound-based all-solide-state electrolyte

Abstract

A method for manufacturing a sulfide-based solid electrolyte according to embodiments involves mixing a solvent and a precursor in a reactor. An open vacuum atmosphere is formed in the reactor. The mixture inside the reactor is reacted under stirring or ultrasonic application conditions while maintaining the open vacuum atmosphere inside the reactor. A high-purity sulfide-based solid electrolyte can be manufactured with high efficiency.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a sulfide-based solid electrolyte. Background Technology

[0002] Lithium-ion batteries have been applied to small devices such as mobile phones and laptops, but recently, there is a trend of expanding to medium and large devices such as energy storage systems (ESS) and electric vehicles (EV). Since lithium-ion batteries use organic liquid electrolytes with added lithium salts, they carry the potential risk of electrolyte leakage as well as the resulting ignition and explosion.

[0003] Recently, research on all-solid-state batteries, which replace liquid electrolytes with solid electrolytes to overcome the limitations of lithium-ion batteries and improve battery stability, is being conducted. By utilizing solid electrolytes, all-solid-state batteries eliminate the risk of fire and explosion and possess high energy density, allowing them to be used in medium to large-scale devices such as electric vehicles and power storage systems, just like lithium-ion batteries.

[0004] Solid electrolytes are classified into oxide-based and sulfide-based types. In particular, sulfide-based solid electrolytes possess superior lithium ion conductivity compared to oxide-based solid electrolytes and offer the advantage of stability over a wide voltage range. Sulfide-based solid electrolytes are generally manufactured using either the melting method or the solid-state method. Specifically, the solid-state method consists of a process in which starting materials and balls are placed in a milling vessel, ground, and then heat-treated by applying high energy.

[0005] Conventional Korean Patent Publication No. 2019-0079135 discloses a method for manufacturing a sulfide-based solid electrolyte by mixing and grinding starting materials and then heat-treating the mixture. However, this solid-state method has problems such as difficulty in uniformly dispersing the starting materials, limitations in amorphization, and difficulty in scaling up the milling vessel, which makes large-scale synthesis difficult.

[0006] Recently, research on liquid-phase processes for synthesizing sulfide-based solid electrolytes using organic solvents has been conducted to address these issues; however, there are problems where the crystallinity of the obtained solid electrolytes decreases and ionic conductivity declines due to residual organic solvents during the liquid-phase process. Prior art literature

[0007] Korean Patent Publication No. 10-2019-0079135 The problem to be solved

[0008] One objective of the present invention is to provide a method for manufacturing a high-purity and high-efficiency sulfide-based solid electrolyte. means of solving the problem

[0009] One embodiment of the present invention discloses a method for manufacturing a sulfide-based solid electrolyte comprising the steps of: mixing a precursor and a solvent to form a mixture; reacting the mixture to produce a reactant; and heat-treating the reactant, wherein the heat treatment includes a first heat treatment step and a second heat treatment step performed at a higher temperature than the first heat treatment step, and in the first heat treatment step, the carbon in the reactant changes into amorphous carbon.

[0010] In this embodiment, the second heat treatment step can be performed in an inert gas atmosphere.

[0011] In the present embodiment, prior to the step of heat-treating the reactants, the method further includes a step of remixing the reactants, and the heat-treating step may heat-treat the remixed reactants.

[0012] In this embodiment, after drying the reactants, the dried reactants can be remixed.

[0013] In this embodiment, the remixing step may be performed by wet ball milling.

[0014] In this embodiment, after the step of heat-treating the reactant, a step of purifying the heat-treated reactant may be further included.

[0015] In this embodiment, the step of purifying the reactant may be performed by wet ball milling.

[0016] In this embodiment, after the step of purifying the reaction product, a step of drying the purified reaction product may be further included.

[0017] In this embodiment, the precursor may include an alkali metal sulfide, an alkali metal halide, and phosphorus pentasulfide.

[0018] In this embodiment, when forming the mixture, the alkali metal sulfide and the alkali metal halide are mixed in the solvent first, and the phosphorus pentasulfide can be additionally mixed second. Effects of the invention

[0019] According to the present invention, a high-purity sulfide-based solid electrolyte can be obtained. Brief explanation of the drawing

[0020] FIG. 1 is a schematic flowchart illustrating a method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention. FIG. 2 is a schematic flowchart illustrating a method for manufacturing a sulfide-based solid electrolyte according to another embodiment of the present invention. FIG. 3 is a schematic flowchart illustrating a method for manufacturing a sulfide-based solid electrolyte according to another embodiment of the present invention. Figure 4 is a figure showing the Raman spectroscopic results of a sulfide-based solid electrolyte according to the present invention. Figure 5 is a figure showing the X-ray diffraction (XRD) results of a sulfide-based solid electrolyte according to the present invention. Figures 6 and 7 illustrate the X-ray diffraction (XRD) and Raman spectroscopy results of a sulfide-based solid electrolyte according to the present invention. Figure 8 is a figure showing the results of electrochemical impedance analysis (EIS) of a sulfide-based solid electrolyte according to the present invention. Specific details for implementing the invention

[0021] The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete and to ensure that the spirit of the invention is sufficiently conveyed to a person skilled in the art.

[0022] In describing each drawing, similar reference numerals have been used for similar components. In the attached drawings, the dimensions of the structures are depicted enlarged from their actual size for clarity of the invention. Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the invention, the first component may be named the second component, and similarly, the second component may be named the first component. A singular expression includes a plural expression unless the context clearly indicates otherwise.

[0023] In this specification, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof. Furthermore, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only the case where it is "immediately above" the other part, but also the case where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "below" another part, this includes not only the case where it is "immediately below" the other part, but also the case where there is another part in between.

[0024] Unless otherwise specified, all numbers, values, and / or expressions used herein to represent amounts of ingredients, reaction conditions, polymer compositions, and formulations should be understood to be modified by the term “approximately” in all cases, as these numbers are essentially approximations reflecting the various uncertainties of measurement that occur in obtaining these values ​​among other things. Furthermore, where a numerical range is disclosed herein, such range is continuous and, unless otherwise indicated, includes all values ​​from the minimum value of such range up to the maximum value. Moreover, where such range refers to an integer, it includes all integers from the minimum value up to the maximum value, unless otherwise indicated.

[0025] FIG. 1 is a schematic flowchart illustrating a method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention.

[0026] Referring to FIG. 1, a method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention may include the steps of: mixing a precursor and a solvent in a reactor to form a mixture (S110); reacting the mixture to produce a reactant (S120); remixing the reactant (S130); and heat-treating the remixed reactant (S140).

[0027] The step (S110) of mixing the precursor and the solvent in the reactor can be performed by first introducing the solvent into the reactor and then introducing the precursor, by first introducing the precursor and then introducing the solvent, or by mixing the solvent and the precursor and introducing them into the reactor.

[0028] In some embodiments, the precursor may include an alkali metal sulfide (A2S; A is an alkali metal), an alkali metal halide (AX; X is a halogen), and phosphorus pentasulfide (P2S5).

[0029] Alkali metals may include lithium, sodium, potassium, or a combination thereof.

[0030] Halogens may include fluorine, chlorine, bromine, iodine, or combinations thereof.

[0031] In some embodiments, the alkali metal sulfide, alkali metal halide, and phosphorus pentasulfide may be mixed in a molar ratio of 4.5 to 5.5 : 1.5 to 2.5 : 0.5 to 1.5. For example, the alkali metal sulfide, alkali metal halide, and phosphorus pentasulfide may react stoichiometrically in a molar ratio of 5 : 2 : 1.

[0032] The above solvent may include a first solvent having low solubility for alkali metal sulfides and alkali metal halides. Additionally, the solvent may further include a second solvent that at least partially dissolves alkali metal sulfides and alkali metal halides.

[0033] The first solvent may include nitrile-based solvents, ether-based solvents, ester-based solvents, etc., and as the nitrile-based solvent, for example, acetonitrile may be included.

[0034] The second solvent above may include alcohol-based solvents, carboxylic acid-based solvents, ester-based solvents, ketone-based solvents, amine-based solvents, sulfoxide-based solvents, etc., and for example, acetic acid, acetylacetone, 2-aminoethanol, anisole, benzyl alcohol, 1-butanol, 2-butanol, 2-butanone, t-butyl alcohol, cyclohexanol, cyclohexanone, di-n-butyl phthalate, diethyl glycol, diglyme, dimethoxyethane, dimethylformamide, dimethyl phthalate, dimethyl sulfoxide, dioxane, ethanol, ether, ethyl acetate, ethyl acetoacetate, ethyl benzoate, ethylene glycol, glycerin, 1-heptanol, 1-hexanol, methanol, methyl acetate, methyl t-butyl ether, 1-octanol, 1-pentanol, It may include 2-pentanol, 3-pentanol, 2-pentanone, 3-pentanone, 1-propanol, tetrahydrofuran, etc.

[0035] Preferably, the second solvent may include acetone containing one oxygen atom, 2-aminoethanol, anisole, benzyl alcohol, 1-butanol, 2-butanol, i-butanol, 2-butanone, t-butyl alcohol, cyclohexanol, cyclohexanone, dimethylformamide, ethanol, ether, 1-heptanol, 1-hexanol, methanol, methyl t-butyl ether, 1-octanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-pentanone, 3-pentanone, 1-propanol, 2-propanol, tetrahydrofuran, etc.

[0036] The second solvent above can at least partially dissolve alkali metal sulfides and alkali metal halides, effectively promoting the reaction between alkali metal sulfides and alkali metal halides and phosphorus pentasulfide, thereby forming a high-purity sulfide-based solid electrolyte.

[0037] In some embodiments, when mixing the precursors, the alkali metal sulfide and the alkali metal halide are mixed first in a first solvent, and phosphorus pentasulfide can be additionally mixed secondarily.

[0038] In some embodiments, if the second solvent is further included, the second solvent may be mixed during the first mixing.

[0039] In some embodiments, the alkali metal sulfide and alkali metal halide may be pre-stirred in a first solvent during the first mixing. In this case, the alkali metal sulfide and alkali metal halide are dissolved in the first solvent, thereby reducing unreacted materials in the sulfide-based solid electrolyte synthesis reaction and increasing the purity of the synthesized product. For example, the pre-stirring may be performed at 500 rpm or more and may be performed for 0.5 to 10 hours, 0.5 to 5 hours, 0.5 to 3 hours, or 0.5 to 2 hours.

[0040] In some embodiments, the preliminary stirring may be performed at room temperature to 100°C. As the temperature of the preliminary stirring increases, the amount of impurities may decrease, and preferably, the preliminary stirring may be performed at a temperature that does not exceed the boiling point of the first solvent and / or the second solvent, for example, at 50 to 90°C or 50 to 85°C.

[0041] Next, the mixture is reacted to produce a reactant (S120).

[0042] The reaction product can be produced by wet ball milling. For example, the reaction product can be produced by table ball milling, vertical-ball milling, planetary milling, bead milling, etc.

[0043] As another example, the mixture inside the reactor can be reacted by stirring or ultrasonizing while maintaining an open vacuum state in which the gas pressure inside the reactor is maintained at -0.1 MPa or less, without the reactor being sealed. In this case, bubbles generated within the mixture by the stirring or ultrasonization may continue to be generated until the end of the reaction, and large bubbles may be formed. Mixing and contact between the reactants are promoted by the bubbles, which can increase the reaction rate.

[0044] As an optional example, the solvent used to form the mixture may be an oxygen-free organic solvent such as heptane, n-heptane, or toluene.

[0045] Once the reactants are formed, they are dried to remove the solvent. Drying can be performed by various methods such as vacuum drying, hot air drying, freeze-drying, and spray drying.

[0046] Next, the dried reaction mixture is remixed (S130).

[0047] By remixing, the reactants can be uniformly further mixed, residual solvent can be removed, and carbon, an impurity contained in the solvent, can be removed from the reactants.

[0048] For example, remixing can be achieved by wet ball milling. For example, it can be achieved by table ball milling, vertical-ball milling, planetary milling, bead milling, etc. As another example, remixing can be achieved by stirring, homogenizing, ultra-sonication, etc.

[0049] The solvent used for remixing may be the same as the solvent used to form the mixture. That is, the solvent used for remixing may include nitrile-based solvents, ether-based solvents, ester-based solvents, etc. As an optional example, the solvent used for remixing may be an oxygen-free organic solvent such as heptane, n-heptane, or toluene.

[0050] Such remixing can be performed for 10 minutes to 2 hours, and if necessary, it can be performed multiple times, and wet mixing and dry mixing can be repeated alternately.

[0051] In this way, by performing additional mixing after generating the reactants, it is possible to form a high-purity sulfide-based solid electrolyte by not only completely mixing different precursors with low energy but also effectively removing impurities such as carbon generated during wet synthesis.

[0052] Next, the remixed reactants are heat-treated (S140). The heat treatment can be performed for 1 to 24 hours at a temperature of 450°C or higher and 600°C or lower under an inert gas atmosphere such as CO, H2, N2, Ar, He, Ne, etc. Crystals of the reactants grow through the heat treatment.

[0053] FIG. 2 is a schematic flowchart illustrating a method for manufacturing a sulfide-based solid electrolyte according to another embodiment of the present invention.

[0054] Referring to FIG. 2, a method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention may include the step of mixing a precursor and a solvent in a reactor to form a mixture (S210), the step of reacting the mixture to produce a reactant (S220), the step of heat-treating the reactant first (S230), and the step of heat-treating the reactant second (S240).

[0055] The step of mixing the precursor and the solvent in the reactor (S210) and the step of reacting the mixture to produce a reactant (S220) are the same as described in FIG. 1, so they are not described again.

[0056] The precursor may include an alkali metal sulfide (A2S; A is an alkali metal), an alkali metal halide (AX; X is a halogen), and phosphorus pentasulfide (P2S5). The alkali metal may include lithium, sodium, potassium, or a combination thereof. The halogen may include fluorine, chlorine, bromine, iodine, or a combination thereof.

[0057] In some embodiments, the alkali metal sulfide, alkali metal halide, and phosphorus pentasulfide may be mixed in a molar ratio of 4.5 to 5.5 : 1.5 to 2.5 : 0.5 to 1.5. For example, the alkali metal sulfide, alkali metal halide, and phosphorus pentasulfide may react stoichiometrically in a molar ratio of 5 : 2 : 1.

[0058] The solvent may include a first solvent having low solubility for alkali metal sulfides and alkali metal halides. Additionally, the solvent may further include a second solvent that at least partially dissolves alkali metal sulfides and alkali metal halides, thereby effectively promoting the reaction between alkali metal sulfides and alkali metal halides and phosphorus pentasulfide to form a high-purity sulfide-based solid electrolyte.

[0059] The first solvent may include nitrile-based solvents, ether-based solvents, ester-based solvents, etc., and as the nitrile-based solvent, for example, acetonitrile may be included.

[0060] The second solvent above may include alcohol-based solvents, carboxylic acid-based solvents, ester-based solvents, ketone-based solvents, amine-based solvents, sulfoxide-based solvents, etc., and for example, acetic acid, acetylacetone, 2-aminoethanol, anisole, benzyl alcohol, 1-butanol, 2-butanol, 2-butanone, t-butyl alcohol, cyclohexanol, cyclohexanone, di-n-butyl phthalate, diethyl glycol, diglyme, dimethoxyethane, dimethylformamide, dimethyl phthalate, dimethyl sulfoxide, dioxane, ethanol, ether, ethyl acetate, ethyl acetoacetate, ethyl benzoate, ethylene glycol, glycerin, 1-heptanol, 1-hexanol, methanol, methyl acetate, methyl t-butyl ether, 1-octanol, 1-pentanol, It may include 2-pentanol, 3-pentanol, 2-pentanone, 3-pentanone, 1-propanol, tetrahydrofuran, etc. Preferably, the second solvent may include acetone containing one oxygen atom, 2-aminoethanol, anisole, benzyl alcohol, 1-butanol, 2-butanol, i-butanol, 2-butanone, t-butyl alcohol, cyclohexanol, cyclohexanone, dimethylformamide, ethanol, ether, 1-heptanol, 1-hexanol, methanol, methyl t-butyl ether, 1-octanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-pentanone, 3-pentanone, 1-propanol, 2-propanol, tetrahydrofuran, etc.

[0061] After producing a reaction product (S220) by reacting the mixture by means of wet ball milling, etc., heat treatment is performed, and as shown in FIG. 2, the heat treatment may include a first heat treatment step (S230) and a second heat treatment step (S240).

[0062] When reactants are formed by wet synthesis, residual solvent may remain even after drying. If a heat treatment process is carried out while residual solvent remains, elements such as carbon and nitrogen among the solvent components may participate in the reaction, potentially generating impurities. In particular, among the lithium (Li), phosphorus (P), sulfur (S), and halogen elements constituting sulfide-based solid electrolytes, the most stable phase at low temperatures is Li3PS4, which is synthesized around 200°C. Since this phase has lower ionic conductivity compared to crystalline azirodite-based solid electrolytes, it is treated as an impurity. Furthermore, if crystallization is carried out by heat treatment while impurities such as residual organic solvents are mixed in, the product may exhibit low purity, low crystallinity, as well as low ionic conductivity along with multiple impurity phases.

[0063] However, as in the present invention, if the heat treatment includes a first heat treatment step (S230) and a second heat treatment step (S240), additional impurities can be removed and a stable solid electrolyte crystal phase can be synthesized to induce high purity and high crystallinity.

[0064] More specifically, the first heat treatment step (S230) can further induce the volatilization of the solvent that may remain in the reactants, change the carbon among the elements of the remaining organic solvent into amorphous carbon with low electrical conductivity, and maintain the stoichiometric ratio between the precursors to induce the synthesis of structurally stable agarodite.

[0065] The first heat treatment step (S230) can be performed at a temperature of 100°C or higher where the solvent sufficiently volatilizes, and 450°C or lower where the amorphous carbon crystallizes.

[0066] The second heat treatment step (S240) can be performed at a temperature higher than the heat treatment temperature of the first heat treatment step (S230). The second heat treatment step (S240) can be performed for 1 hour to 24 hours at a temperature of 450°C or higher and 600°C or lower under an inert gas atmosphere such as CO, H2, N2, Ar, He, Ne, etc. Crystals of the reactant can grow through the second heat treatment.

[0067] Meanwhile, the embodiment described in FIG. 2 may further include a step of remixing the reactants included in FIG. 1 (S130 of FIG. 1), and as a result, impurities such as carbon generated during wet synthesis can be more effectively removed to form a high-purity sulfide-based solid electrolyte.

[0068] FIG. 3 is a schematic flowchart illustrating a method for manufacturing a sulfide-based solid electrolyte according to another embodiment of the present invention.

[0069] Referring to FIG. 3, a method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention may include the steps of: mixing a precursor and a solvent in a reactor to form a mixture (S310); reacting the mixture to produce a reaction product (S320); heat-treating the reaction product (S330); purifying the heat-treated reaction product (S340); and drying the purified reaction product (S350).

[0070] Below, the same content as explained in Figure 1 will not be repeated, and only the differences will be explained.

[0071] The precursor may include an alkali metal sulfide (A2S; A is an alkali metal), an alkali metal halide (AX; X is a halogen), and phosphorus pentasulfide (P2S5). The alkali metal may include lithium, sodium, potassium, or a combination thereof. The halogen may include fluorine, chlorine, bromine, iodine, or a combination thereof.

[0072] In some embodiments, the alkali metal sulfide, alkali metal halide, and phosphorus pentasulfide may be mixed in a molar ratio of 4.5 to 5.5 : 1.5 to 2.5 : 0.5 to 1.5. For example, the alkali metal sulfide, alkali metal halide, and phosphorus pentasulfide may react stoichiometrically in a molar ratio of 5 : 2 : 1.

[0073] The solvent may include a first solvent having low solubility for alkali metal sulfides and alkali metal halides. Additionally, the solvent may further include a second solvent that at least partially dissolves alkali metal sulfides and alkali metal halides, thereby effectively promoting the reaction between alkali metal sulfides and alkali metal halides and phosphorus pentasulfide to form a high-purity sulfide-based solid electrolyte.

[0074] The first solvent may include nitrile-based solvents, ether-based solvents, ester-based solvents, etc., and as the nitrile-based solvent, for example, acetonitrile may be included.

[0075] The second solvent above may include alcohol-based solvents, carboxylic acid-based solvents, ester-based solvents, ketone-based solvents, amine-based solvents, sulfoxide-based solvents, etc., and for example, acetic acid, acetylacetone, 2-aminoethanol, anisole, benzyl alcohol, 1-butanol, 2-butanol, 2-butanone, t-butyl alcohol, cyclohexanol, cyclohexanone, di-n-butyl phthalate, diethyl glycol, diglyme, dimethoxyethane, dimethylformamide, dimethyl phthalate, dimethyl sulfoxide, dioxane, ethanol, ether, ethyl acetate, ethyl acetoacetate, ethyl benzoate, ethylene glycol, glycerin, 1-heptanol, 1-hexanol, methanol, methyl acetate, methyl t-butyl ether, 1-octanol, 1-pentanol, It may include 2-pentanol, 3-pentanol, 2-pentanone, 3-pentanone, 1-propanol, tetrahydrofuran, etc. Preferably, the second solvent may include acetone containing one oxygen atom, 2-aminoethanol, anisole, benzyl alcohol, 1-butanol, 2-butanol, i-butanol, 2-butanone, t-butyl alcohol, cyclohexanol, cyclohexanone, dimethylformamide, ethanol, ether, 1-heptanol, 1-hexanol, methanol, methyl t-butyl ether, 1-octanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-pentanone, 3-pentanone, 1-propanol, 2-propanol, tetrahydrofuran, etc.

[0076] The steps of mixing the precursor and the solvent in the reactor (3210), reacting the mixture to produce a reactant (S320), and heat treatment (S330) are the same as described in FIG. 1, so they are not described again.

[0077] The step (S340) of purifying the heat-treated reactant can control the particle size of the reactant by further removing residual impurities of the reactant by physical force through additional mixing of the reactant and breaking the weak physical bonds of secondary and tertiary particles.

[0078] Heat-treated reactants may contain small amounts of impurities that are not completely removed, and particularly due to the heat treatment step, they may exhibit a wide particle size distribution depending on the crystallization mechanism. Additionally, since aggregation may occur due to surface energy when uniformly mixed, further purifying the heat-treated reactants resolves the aggregation, thereby enabling the production of a solid electrolyte with high purity and a uniform particle size distribution.

[0079] For example, the step of purifying the reactant (S340) can be performed by wet ball milling. For example, after mixing the reactant and the organic solvent, the reactant can be purified by ball milling. By removing impurities such as carbon on the surface of the reactant through ball milling and breaking weak bonds between particles, the particle size of the reactant can be controlled.

[0080] Ball milling can include various methods such as table ball milling, vertical-ball milling, planetary milling, and bead milling. In addition, mixing in the purification step may be achieved by stirring, homogenizing, ultra-sonication, etc.

[0081] Meanwhile, the purification step can be carried out in a wet or dry manner; in the case of the wet method, it includes a drying step, and in the case of the dry method, it does not include a drying step but may additionally include a dissolution step. The drying step may also be carried out by alternating between the dry and wet methods.

[0082] Next, the purified reaction product is dried (S350). The purified reaction product may be dried using a centrifuge. The purified reaction product is in a state where impurities have been removed and particle size controlled through a purification step, and it may be dried using centrifugation to prevent the particle size from increasing again due to surface energy during drying.

[0083] As an optional embodiment, in addition to the method described above, drying may be performed by including a general drying and subsequent release step, such as hot air drying, freeze-drying, or spray drying.

[0084] Meanwhile, the embodiment described in FIG. 3 may further include at least one of the step of remixing the reactants included in FIG. 1 (S130 of FIG. 1) and the first heat treatment step (S230 of FIG. 2) and the second heat treatment step (S240 of FIG. 2) included in FIG. 2, and as a result, impurities such as carbon generated during wet synthesis can be more effectively removed to form a high-purity sulfide-based solid electrolyte.

[0086] The present invention will be explained in more detail below through specific embodiments. The following embodiments are merely examples to aid in understanding the present invention and do not limit the scope of the present invention.

[0088] - Example: Preparation of Sulfide-based Solid Electrolyte -

[0089] The synthetic material for manufacturing sulfide-based solid electrolytes is Li 6-x PS 5-x Ha x (1≤x≤2), Li6PS5Cl was synthesized in the example where Ha is chloride and x is 1.

[0090] First, lithium sulfide (Li2S), lithium chloride (LiCl), and phosphorus pentasulfide (P2S5) were mixed in the solvent acetonitrile in a molar ratio of about 5:2:1 as precursors, and then ball milling was performed to form a mixture.

[0091] Next, the mixture was vacuum dried, and then wet ball milling was performed for 1 hour to produce the reaction product.

[0092] The generated reaction mixture was dried, and then remixed by wet ball milling.

[0093] Next, after drying the remixed reaction mixture, a first heat treatment was performed at 200°C for 5 hours to remove residual carbon, and a second heat treatment was performed at 550°C in an Ar atmosphere for 12 hours to grow crystals of the reaction mixture.

[0094] In addition, ball milling using acetonitrile as a solvent was performed for 2 hours, followed by centrifugation at 4000 RPM for 1 hour to remove the upper layer of the solution and purification process, and vacuum drying was performed for 12 hours to finally produce a sulfide-based solid electrolyte.

[0096] Comparative Example 1

[0097] Comparative Example 1 prepares a sulfide-based solid electrolyte in the same manner as the example, but differs in that the process of remixing the reactants after their formation is omitted.

[0098] FIG. 4 is a figure showing the Raman spectroscopic results of the Example and Comparative Example 1. (I) of FIG. 4 is the Raman spectroscopic result according to the Example, and (II) is the Raman spectroscopic result according to Example 1.

[0099] Referring to FIG. 4, in the case of Example (I) in which a remixing step was performed after the generation of the reactants, 470 cm when compared to Comparative Example 1 (II). -1 From the fact that the peaks show no significant difference, the PS4 3- It can be observed that while the bonding intensity is maintained, the overall area of ​​the peaks associated with carbon and impurities presumed to originate from the solvent is relatively reduced. Through this, it can be confirmed that remixing the reactants after their formation is effective in structurally stabilizing the sulfide-based solid electrolyte and removing impurities.

[0100] That is, according to the present invention, by additionally remixing the reactants, not only is complete mixing of the three precursors achieved at low energy, but impurities (such as carbon) generated during wet synthesis can also be effectively removed.

[0102] Comparative Example 2

[0103] Comparative Example 2 prepares a sulfide-based solid electrolyte in the same manner as the Example, but differs in that it undergoes a single heat treatment process compared to the Example.

[0104] FIG. 5 is a figure showing the X-ray diffraction (XRD) results of a sulfide-based solid electrolyte according to the present invention. (I) of FIG. 5 is the X-ray diffraction (XRD) result according to an example, and (III) is the X-ray diffraction (XRD) result according to Comparative Example 2.

[0105] Referring to FIG. 5, in the case of Comparative Example 2 (III), a large amount of Li3PS4, 16 (2θ / deg.) of impurity phase, along with Li2S, 29 (2θ / deg.), and LiCl, 32 (2θ / deg.) in stoichiometric ratios, is detected, whereas in the case of Example (I), which proceeded with a second heat treatment step after the first heat treatment step, it can be seen that Li3PS4 is hardly detected, and other impurities other than a small amount of Li2S are not detected.

[0106] That is, by performing heat treatment in stages divided into a first heat treatment stage and a second heat treatment stage, impurities can be additionally removed from the reactants, and a stable solid electrolyte crystal phase can be synthesized to induce high purity and high crystallinity.

[0108] Comparative Example 3

[0109] Comparative Example 3 prepares a sulfide-based solid electrolyte in the same way as the example, but differs in that it does not include purification and drying processes.

[0110] FIGS. 6 and 7 illustrate the X-ray diffraction (XRD) and Raman spectroscopy results of a sulfide-based solid electrolyte according to the present invention. In FIGS. 6 and 7, (I) is the X-ray diffraction (XRD) and Raman spectroscopy result according to an example, and (IV) is the X-ray diffraction (XRD) and Raman spectroscopy result according to Comparative Example 3.

[0111] First, as shown in FIG. 6, it can be seen that there is no significant difference in the X-ray diffraction (XRD) results between Example (I), which underwent purification and drying processes after heat treatment, and Comparative Example 3 (IV), which did not include purification and drying processes. In other words, even if purification and drying processes are performed after heat treatment, there is no significant difference in crystallinity, phase change, etc., so it can be seen that the purification and drying processes do not have a significant effect on the solid electrolyte.

[0112] In contrast, referring to FIG. 7, compared to Comparative Example 3 (IV), in the case of Example (I), a small amount of impurities remaining before purification, particularly carbon-related peak (1350–1580 cm⁻¹) -1 It shows a result where ) decreased sharply. On the other hand, PS4, the main bond of the sulfide solid electrolyte 3- peak(430cm -1 It can be seen that ) has no effect.

[0113] This means that a solid electrolyte with high purity and a uniform particle size distribution is manufactured by mixing the heat-treated reactants with an organic solvent, followed by a purification step involving ball milling and a drying step via centrifugation, thereby removing impurities such as carbon on the surface of the reactants and simultaneously resolving sample aggregation.

[0114] In addition, as a result of undergoing the purification and drying steps, as shown in Table 1 below, Example (I) has an average particle size (D) compared to Comparative Example 3 (IV). 50 It can be seen that the particle size distribution decreases.

[0115] D 50 Particle size distribution (Width) Example (I) 4.47 6.47 Comparative Example 3 (IV) 10.37 19.32

[0116] FIG. 8 is a figure illustrating the results of the electrochemical impedance analysis (EIS) of a sulfide-based solid electrolyte according to the present invention. FIG. 8 illustrates the electrochemical impedance (EIS) of a sulfide-based solid electrolyte according to an example.

[0117] Due to the characteristics of the battery, in order to maintain performance as an electrolyte, the electronic conductivity of the electrolyte itself must be minimized, and higher ionic conductivity is advantageous.

[0118] Referring to FIG. 8, it can be seen that the slope of the electrochemical impedance (EIS) according to the embodiment is 45° or greater, which is a result in low electronic conductivity and excellent ionic conductivity. Therefore, it can be seen that the sulfide-based solid electrolyte according to the present invention has excellent characteristics.

[0119] In addition, according to the present invention, a reactant is formed through wet milling including a solvent, but carbon can be effectively removed through a process of remixing the formed reactant, a first heat treatment, a second heat treatment, and a purification process, and the sulfide-based solid electrolyte having an argyrodite-type crystal structure can have a uniform particle size, and the particle size can be freely controlled through a purification process.

[0120] As such, the present invention has been described with reference to an embodiment illustrated in the drawings, but this is merely illustrative, and those skilled in the art will understand that various modifications and variations of the embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

Claim 1 A method for manufacturing a sulfide-based solid electrolyte comprising the steps of: mixing a precursor including an alkali metal sulfide, an alkali metal halide, and a phosphorus pentasulfide with a solvent to form a mixture; reacting the mixture to produce a reaction product; drying the reaction product; remixing the dried reaction product by wet ball milling; heat treating the remixed reaction product; purifying the heat-treated reaction product by wet ball milling; and drying the purified reaction product; wherein the alkali metal sulfide, the alkali metal halide, and the phosphorus pentasulfide are mixed in a molar ratio of 4.5 to 5.5 : 1.5 to 2.5 : 0.5 to 1.5, and the heat treatment includes a first heat treatment step and a second heat treatment step performed at a higher temperature than the first heat treatment step, wherein in the first heat treatment step, the carbon in the reaction product changes into amorphous carbon. Claim 2 A method for manufacturing a sulfide-based solid electrolyte according to claim 1, wherein the second heat treatment step is performed in an inert gas atmosphere. Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 delete Claim 10 A method for manufacturing a sulfide-based solid electrolyte according to claim 1, wherein, when forming the mixture, the alkali metal sulfide and the alkali metal halide are mixed first in the solvent, and the phosphorus pentasulfide is additionally mixed secondarily.

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