Method for producing sulfide-based solid electrolyte

Abstract

In the method for producing a sulfide-based solid electrolyte according to the embodiment, a solvent and a precursor are mixed in a reactor. An open-type vacuum atmosphere is formed in the reactor. While maintaining the open-type vacuum atmosphere in the reactor, the mixture in the reactor is reacted under stirring or ultrasonic application conditions. A sulfide-based solid electrolyte with high purity can be produced with high efficiency.

Description

[Technical field]

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

[0002] Lithium secondary batteries have been used in small devices such as mobile phones and laptops, but recently they have been expanded to medium and large devices such as energy storage systems (ESS) and electric vehicles (EV). Lithium secondary batteries use an organic liquid electrolyte with added lithium salt, which means there is a risk of electrolyte leakage as well as the potential risk of fire and explosion.

[0003] In recent years, research has been conducted into all-solid-state batteries, which overcome the limitations of such lithium secondary batteries and replace liquid electrolytes with solid electrolytes to improve battery stability. All-solid-state batteries, which use solid electrolytes, are free of the risk of fire or explosion, have high energy density, and can be used in medium- to large-sized devices such as electric vehicles and power storage systems, just like lithium secondary batteries.

[0004] Solid electrolytes are divided into oxide-based and sulfide-based. In particular, sulfide-based solid electrolytes have superior lithium ion conductivity and are stable over a wide voltage range compared to oxide-based solid electrolytes. Sulfide-based solid electrolytes are generally manufactured by a melting method or a solid-state method. In particular, the solid-state method involves putting starting materials and balls into a milling vessel, grinding them, and then providing high energy to perform a heat treatment.

[0005] Previously, Korean Patent Publication No. 2019-0079135 disclosed a method for manufacturing a sulfide-based solid electrolyte by mixing and grinding starting materials and heat-treating the mixture. However, this solid-phase method has problems such as difficulty in uniformly dispersing the starting materials, limitations in amorphization, and difficulty in enlarging the milling vessel, making it difficult to mass-produce the electrolyte.

[0006] In recent years, in order to solve these problems, research has been conducted into a liquid phase process in which a sulfide-based solid electrolyte is synthesized using an organic solvent. However, there is a problem that the crystallinity of the solid electrolyte obtained in the liquid phase process is reduced due to residual organic solvent, etc., and the ionic conductivity is reduced. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a method for producing a high-purity and high-efficiency sulfide-based solid electrolyte. [Means for solving the problem]

[0008] One embodiment of the present invention discloses a method for producing a sulfide-based solid electrolyte, the method including 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, the heat treatment including a first heat-treatment step and a second heat-treatment step performed at a temperature higher than that of the first heat-treatment step, and in the first heat-treatment step, carbon in the reactant is converted to amorphous carbon. Effect of the Invention

[0009] According to the present invention, a high-purity sulfide-based solid electrolyte can be obtained. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic flow chart illustrating a method for producing a sulfide-based solid electrolyte according to an embodiment of the present invention. [Diagram 2] 4 is a schematic flow chart illustrating a method for producing a sulfide-based solid electrolyte according to another embodiment of the present invention. [Diagram 3] 4 is a schematic flow chart illustrating a method for producing a sulfide-based solid electrolyte according to another embodiment of the present invention. [Figure 4] FIG. 2 is a diagram showing the results of Raman spectroscopy of the sulfide-based solid electrolyte according to the present invention. [Diagram 5]FIG. 2 is a diagram showing the results of X-ray diffraction analysis (XRD) of the sulfide-based solid electrolyte according to the present invention. [Figure 6] FIG. 2 is a diagram showing the results of X-ray diffraction analysis (XRD) and Raman spectroscopy of the sulfide-based solid electrolyte according to the present invention. [Figure 7] FIG. 2 is a diagram showing the results of X-ray diffraction analysis (XRD) and Raman spectroscopy of the sulfide-based solid electrolyte according to the present invention. [Figure 8] FIG. 2 shows electrochemical impedance spectroscopy (EIS) results of a sulfide-based solid electrolyte according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] One embodiment of the present invention discloses a method for producing a sulfide-based solid electrolyte, the method including 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, the heat treatment including a first heat-treatment step and a second heat-treatment step performed at a temperature higher than that of the first heat-treatment step, and in the first heat-treatment step, carbon in the reactant is converted to amorphous carbon.

[0012] In this embodiment, the second heat treatment step may be performed in an inert gas atmosphere.

[0013] In this embodiment, the method may further include a step of remixing the reactants before the step of heat-treating the reactants, and the step of heat-treating may include heat-treating the remixed reactants.

[0014] In this embodiment, after the reactants are dried, the dried reactants can be remixed.

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

[0016] In this embodiment, the method may further include purifying the heat-treated reactant after the step of heat-treating the reactant.

[0017] In this embodiment, the step of purifying the reactants may be performed by wet ball milling.

[0018] In this embodiment, the method may further include, after the step of purifying the reactants, drying the purified reactants.

[0019] In this embodiment, the precursors may include an alkali metal sulfide, an alkali metal halide, and phosphorus pentasulfide.

[0020] In the present embodiment, when the mixture is formed, the alkali metal sulfide and the alkali metal halide may be primarily mixed in the solvent, and the phosphorus pentasulfide may be secondarily mixed therein.

[0021] The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments in conjunction 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 in this specification are provided so that the disclosed content is thorough and complete, and so that the idea of ​​the present invention can be fully conveyed to those skilled in the art.

[0022] While describing each drawing, the same reference numerals are used for the same components. In the accompanying drawings, the dimensions of the structures are shown exaggerated for clarity of the present invention. Terms such as first, second, etc. can be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing a certain component from another component. For example, the first component can be named the second component, and the second component can be named the first component, without departing from the scope of the present invention. A singular expression includes a plural expression unless the context clearly indicates otherwise.

[0023] In this specification, the terms "comprise" or "have" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described herein, and should be understood not to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. In addition, when a layer, film, region, plate, or other part is described as being "on" another part, this includes not only when it is "directly on" the other part, but also when there is another part in between. Conversely, when a layer, film, region, plate, or other part is described as being "under" the other part, this includes not only when it is "directly under" the other part, but also when there is another part in between.

[0024] Unless otherwise indicated, all numbers, values ​​and / or expressions expressing amounts of ingredients, reaction conditions, polymer compositions and formulations used herein are approximations reflecting various uncertainties of measurement that occur in obtaining these values ​​among other things that are inherently different, and therefore should be understood to be modified in all cases by the term "about". Also, when a range of values ​​is disclosed herein, the range is continuous and includes all values ​​from the minimum value to said maximum value, including the maximum value, unless otherwise indicated. Furthermore, when such a range refers to integers, it includes all integers from the minimum value to said maximum value, including the maximum value, unless otherwise indicated.

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

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

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

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

[0029] The alkali metal may include lithium, sodium, potassium or a combination thereof.

[0030] The halogen may include fluorine, chlorine, bromine, iodine, or a combination thereof.

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

[0032] The solvent may include a first solvent in which the alkali metal sulfide and the alkali metal halide have low solubility, and may further include a second solvent in which the alkali metal sulfide and the alkali metal halide at least partially dissolve.

[0033] The first solvent may include a nitrile-based solvent, an ether-based solvent, an ester-based solvent, or the like, and the nitrile-based solvent may include, for example, acetonitrile.

[0034] The second solvent may include alcohol-based solvents, carboxylic acid-based solvents, ester-based solvents, ketone-based solvents, amine-based solvents, sulfoxide-based solvents, and the like, and may include, 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, 2-pentanol, 3-pentanol, 2-pentanone, 3-pentanone, 1-propanol, tetrahydrofuran, and the like.

[0035] Preferably, the second solvent may include acetone, 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, and the like, each of which contains one oxygen element.

[0036] The second solvent can at least partially dissolve the alkali metal sulfide and the alkali metal halide, and effectively promote the reaction of the alkali metal sulfide and the alkali metal halide with phosphorus pentasulfide to form a high-purity sulfide-based solid electrolyte.

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

[0038] In some embodiments, when 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 the alkali metal halide may be pre-mixed in the first solvent during the primary mixing. In this case, the alkali metal sulfide and the alkali metal halide are dissolved in the first solvent, the amount of unreacted material in the sulfide-based solid electrolyte synthesis reaction is reduced, and the purity of the synthesis product may be increased. For example, the pre-mixing may be performed at 500 rpm or more 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 pre-stirring can be performed at room temperature to 100° C. As the temperature of the pre-stirring increases, the amount of impurities can be reduced, and preferably, the pre-stirring can be performed at a temperature not exceeding 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] The mixture is then reacted to produce a reactant (S120).

[0042] The reactants can be formed by wet ball milling, for example, table ball milling, vertical-ball milling, planetary milling, bead milling, etc.

[0043] As another example, the reactor may be kept in an open vacuum state with the gas pressure inside the reactor maintained at -0.1 MPa or less without being sealed, and the mixture inside the reactor may be stirred or ultrasonicated to react with the mixture. In this case, bubbles generated in the mixture by the stirring or ultrasonic application may be continuously generated until the end of the reaction, forming bulky bubbles. The bubbles may promote mixing and contact between the reactants, thereby increasing the reaction rate.

[0044] In any embodiment, the solvent used in forming the mixture can be an oxygen-free organic solvent such as heptane, n-heptane, toluene, and the like.

[0045] Once the reactant has been formed, it is dried to remove the solvent, which can be done by a variety of methods such as vacuum drying, hot air drying, freeze drying, spray drying, etc.

[0046] The dried reactants are then remixed (S130).

[0047] Remixing further mixes the reactants uniformly, removes residual solvent, and removes carbon contained in the solvent as an impurity from the reactants.

[0048] In one example, remixing can be accomplished by wet ball milling, such as by table ball milling, vertical-ball milling, planetary milling, bead milling, etc. In another example, remixing can be accomplished by stirring, homogenizing, ultra-sonication, etc.

[0049] The solvent used for remixing may be the same as the solvent used for forming the mixture. That is, the solvent used for remixing may include nitrile-based solvents, ether-based solvents, ester-based solvents, etc. In any embodiment, the solvent used for remixing may be an organic solvent that does not contain oxygen, such as heptane, n-heptane, or toluene.

[0050] Such remixing can be carried out for 10 minutes to 2 hours, and can be carried out multiple times as necessary. Wet mixing and dry mixing can also be alternately repeated.

[0051] In this way, by performing additional mixing after generating the reactants, it is possible to completely mix different precursors with low energy, as well as to effectively remove impurities such as carbon generated during wet synthesis, thereby forming a high-purity sulfide-based solid electrolyte.

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

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

[0054] Referring to FIG. 2, a method for producing a sulfide-based solid electrolyte according to an embodiment of the present invention may include a step of mixing a precursor and a solvent in a reactor to form a mixture (S210), a step of reacting the mixture to produce a reactant (S220), a step of first heat-treating the reactant (S230), and a step of second heat-treating the reactant (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 those described in FIG. 1, and therefore will not be described repeatedly.

[0056] The precursors may include alkali metal sulfides (AS; A is an alkali metal), alkali metal halides (AX; X is a halogen), and phosphorus pentasulfide (P2S5). The alkali metals may include lithium, sodium, potassium, or combinations thereof. The halogens may include fluorine, chlorine, bromine, iodine, or combinations thereof.

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

[0058] The solvent may include a first solvent in which the alkali metal sulfide and the alkali metal halide have low solubility, and the solvent may further include a second solvent in which the alkali metal sulfide and the alkali metal halide at least partially dissolve, thereby effectively promoting the reaction of the alkali metal sulfide and the alkali metal halide with phosphorus pentasulfide to form a high-purity sulfide-based solid electrolyte.

[0059] The first solvent may include a nitrile-based solvent, an ether-based solvent, an ester-based solvent, or the like, and the nitrile-based solvent may include, for example, acetonitrile.

[0060] The second solvent may include alcohol-based solvents, carboxylic acid-based solvents, ester-based solvents, ketone-based solvents, amine-based solvents, sulfoxide-based solvents, and the like, and may include, 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, 2-pentanol, 3-pentanol, 2-pentanone, 3-pentanone, 1-propanol, tetrahydrofuran, and the like. Preferably, the second solvent may include acetone, 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, and the like, each of which contains one oxygen element.

[0061] After the mixture is reacted to produce a reactant (S220) by wet ball milling or the like, a heat treatment is performed. 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 the solvent is dried. If the heat treatment process is performed with residual solvent remaining, carbon and nitrogen, among the elements that make up the solvent, may participate in the reaction and generate impurities. In particular, among the elements that make up the sulfide-based solid electrolyte, lithium (Li), phosphorus (P), sulfur (S), and halogen, the most stable phase at low temperatures is Li3PS4, which is synthesized at around 200°C, and this phase has a lower ionic conductivity than the crystalline structure of the argyrodite-based solid electrolyte, so it is treated as an impurity. In addition, if crystallization is performed by heat treatment in a state where impurities such as residual organic solvents are mixed, it may have low purity, low crystallinity, and low ionic conductivity along with many impurity phases.

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

[0064] More specifically, the first heat treatment step (S230) further induces the volatilization of the solvent that may remain in the reactants, converts the carbon among the elements of the residual organic solvent into amorphous carbon with low electrical conductivity, and maintains the stoichiometric ratio between the precursors, thereby inducing the synthesis of a structurally stable argyrodite.

[0065] The first heat treatment step (S230) can be performed at a temperature of 100° C. or more at which the solvent is sufficiently volatilized and 450° C. or less at which the amorphous carbon is crystallized.

[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 in an inert gas atmosphere such as CO, H2, N2, Ar, He, Ne, etc. at a temperature of 450°C to 600°C for 1 hour to 24 hours. The second heat treatment can grow crystals of the reactant.

[0067] Meanwhile, the embodiment described in FIG. 2 may further include a step of remixing the reactants included in FIG. 1 (S130 in FIG. 1), so that 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 flow chart illustrating a method for producing a sulfide-based solid electrolyte according to another embodiment of the present invention.

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

[0070] In the following, the same contents as those explained in FIG. 1 will not be explained repeatedly, but only the differences will be explained.

[0071] The precursors may include alkali metal sulfides (AS; A is an alkali metal), alkali metal halides (AX; X is a halogen), and phosphorus pentasulfide (P2S5). The alkali metals may include lithium, sodium, potassium, or combinations thereof. The halogens may include fluorine, chlorine, bromine, iodine, or combinations thereof.

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

[0073] The solvent may include a first solvent in which the alkali metal sulfide and the alkali metal halide have low solubility, and the solvent may further include a second solvent in which the alkali metal sulfide and the alkali metal halide at least partially dissolve, thereby effectively promoting the reaction of the alkali metal sulfide and the alkali metal halide with phosphorus pentasulfide to form a high-purity sulfide-based solid electrolyte.

[0074] The first solvent may include a nitrile-based solvent, an ether-based solvent, an ester-based solvent, or the like, and the nitrile-based solvent may include, for example, acetonitrile.

[0075] The second solvent may include alcohol-based solvents, carboxylic acid-based solvents, ester-based solvents, ketone-based solvents, amine-based solvents, sulfoxide-based solvents, and the like, and may include, 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, 2-pentanol, 3-pentanol, 2-pentanone, 3-pentanone, 1-propanol, tetrahydrofuran, and the like. Preferably, the second solvent may include acetone, 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, and the like, each of which contains one oxygen element.

[0076] The step of mixing the precursor and the solvent in the reactor (S310), the step of reacting the mixture to produce a reactant (S320), and the heat treatment step (S330) are the same as those described in FIG. 1, and therefore will not be described repeatedly.

[0077] The step of purifying the heat-treated reactants (S340) further mixes the reactants to further remove residual impurities in the reactants using physical forces, and finally controls the particle size of the reactants by breaking weak physical bonds between secondary and tertiary particles.

[0078] The heat-treated reactants may have a small amount of impurities that are not completely removed, and may have a wide particle size distribution due to a crystallization mechanism, especially after the heat treatment step. Also, since agglomeration may occur due to surface energy when mixed uniformly, the heat-treated reactants may be further refined to eliminate the agglomeration of the reactants and produce a solid electrolyte with high purity and uniform particle size distribution.

[0079] In one example, the step of purifying the reactants (S340) can be performed by wet ball milling. For example, the reactants can be mixed with an organic solvent and then ball milled to purify the reactants. Ball milling can remove impurities such as carbon on the surface of the reactants and can control the particle size of the reactants by breaking weak bonds between the particles.

[0080] Ball milling can include various methods such as table ball milling, vertical-ball milling, planetary milling, bead milling, etc. Additionally, mixing in the refining step may be accomplished by stirring, homogenizing, ultra-sonication, etc.

[0081] On the other hand, the purification step can be performed in a wet or dry manner, and in the case of the wet method, a drying step can be included, and in the case of the dry method, a decomposition step can be included instead of the drying step. The drying step can also be performed by repeatedly alternating between the dry method and the wet method.

[0082] Then, the purified reactant is dried (S350). The purified reactant may be dried using a centrifuge. The purified reactant, which has been subjected to the purification step to remove impurities and adjust the particle size, may be dried using a centrifuge to prevent the particle size from becoming larger again due to surface energy during drying.

[0083] In any embodiment, in addition to the methods described above, drying can be accomplished by conventional post-drying methods such as hot air drying, freeze drying, spray drying, and the like, including a dehydration step.

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

[0085] The present invention will be described in more detail with reference to the following specific embodiments. The following embodiments are merely examples for the purpose of aiding understanding of the present invention, and are not intended to limit the scope of the present invention.

[0086] Embodiment: Production of sulfide-based solid electrolyte

[0087] The synthesis of sulfide-based solid electrolytes is Li 7-x P.S. 6-x Ha x Li6PS5Cl, where (1≦x≦2) and in the embodiment, Ha is chloride and x is 1, was synthesized.

[0088] First, lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and lithium chloride (LiCl) were mixed as precursors in acetonitrile, and then ball milling was performed to form a mixture.

[0089] The mixture was then vacuum dried and then wet ball milled for 1 hour to produce the reaction product.

[0090] The resulting reactants were dried and then remixed by wet ball milling.

[0091] Next, the remixed reactants were dried and then subjected to a primary heat treatment at 200°C for 5 hours to remove residual carbon, and a secondary heat treatment was performed at 550°C for 12 hours in an Ar atmosphere to grow crystals of the reactants.

[0092] In addition, ball milling was performed for 2 hours using acetonitrile as a solvent, followed by centrifuging at 4000 RPM for 1 hour to remove the upper layer of the solution, followed by a purification step of drying in vacuum for 12 hours to finally produce a sulfide-based solid electrolyte.

[0093] Comparative Example 1

[0094] In Comparative Example 1, a sulfide-based solid electrolyte was produced by a method similar to that of the embodiment, but the difference was that the step of remixing the reactants after their production was omitted.

[0095] 4 is a diagram showing the results of Raman spectroscopy for the embodiment and Comparative Example 1. Fig. 4(I) shows the results of Raman spectroscopy for the embodiment, and (II) shows the results of Raman spectroscopy for Comparative Example 1.

[0096] Referring to FIG. 4, in the case of embodiment (I) in which the remixing step was performed after the reaction product was generated, the reaction mixture was 470 cm compared to Comparative Example 1 (II). -1 Since there is no significant difference in the peaks of PS4 3-It can be seen that the bonding intensity is maintained, while the total area of ​​the peaks related to carbon, an impurity presumed to be generated from the solvent, is relatively reduced. This confirms that remixing the reactants after their generation stabilizes the structure of the sulfide-based solid electrolyte and is effective in removing impurities.

[0097] That is, according to the present invention, by further remixing the reactants, it is possible to not only completely mix the three precursors with low energy, but also to effectively remove impurities (such as carbon) generated during wet synthesis.

[0098] Comparative Example 2

[0099] In Comparative Example 2, a sulfide-based solid electrolyte was produced by the same method as in the embodiment, but was different from the embodiment in that it underwent a single heat treatment process.

[0100] 5 is a diagram showing the results of X-ray diffraction analysis (XRD) of the sulfide-based solid electrolyte according to the present invention, in which (I) shows the results of X-ray diffraction analysis (XRD) according to the embodiment, and (III) shows the results of X-ray diffraction analysis (XRD) according to Comparative Example 2.

[0101] Referring to FIG. 5, in the case of Comparative Example 2 (III), along with the impurity phase Li3PS4 of 16 (2θ / deg.), large amounts of Li2S of 27 (2θ / deg.), LiCl of 29 (2θ / deg.), and 32 (2θ / deg.) were detected in accordance with the stoichiometric ratio, whereas in the case of embodiment (I) in which the second heat treatment step was carried out after the first heat treatment step, not only was Li3PS4 almost not detected, but other impurities were not detected except for a small amount of Li2S.

[0102] That is, by performing the heat treatment in a first heat treatment step and a second heat treatment step, impurities can be further removed from the reactants, and a stable solid electrolyte crystalline phase can be synthesized, leading to high purity and high crystallinity.

[0103] Comparative Example 3

[0104] In Comparative Example 3, a sulfide-based solid electrolyte was produced by a method similar to that of the embodiment, but the difference is that the purification and drying processes were not included.

[0105] 6 and 7 are diagrams showing the results of X-ray diffraction analysis (XRD) and Raman spectroscopy of the sulfide-based solid electrolyte according to the present invention. In Fig. 6 and Fig. 7, (I) shows the results of X-ray diffraction analysis (XRD) and Raman spectroscopy according to the embodiment, and (IV) shows the results of X-ray diffraction analysis (XRD) and Raman spectroscopy according to Comparative Example 3.

[0106] First, as shown in Figure 6, there is no significant difference in the X-ray diffraction analysis (XRD) results between the embodiment (I) that underwent purification and drying processes after the heat treatment and the comparative example 3 (IV) that did not include the purification and drying processes. That is, even if the purification and drying processes are performed after the heat treatment, there is no significant difference in the crystallinity, phase change, etc., and therefore it can be seen that the purification and drying processes do not have a significant effect on the solid electrolyte.

[0107] In contrast, referring to FIG. 7, in the case of embodiment (I), compared to comparative example 3 (IV), the small amount of impurities remaining before purification, particularly the peaks related to carbon (1350 to 1580 cm -1 ) rapidly decreased. On the other hand, the main bond in the sulfide solid electrolyte, PS4 3- Peak (430cm -1 ) has no effect.

[0108] This means that the heat-treated reactants are mixed with an organic solvent, and then a purification step of ball milling and a drying step of centrifugation are performed to remove impurities such as carbon on the surface of the reactants, and at the same time, the agglomeration of the sample is eliminated, thereby producing a solid electrolyte with high purity and uniform particle size distribution.

[0109] In addition, as a result of the purification step and the drying step, as shown in Table 1 below, the embodiment (I) had a smaller average particle size (D 50) and the particle size distribution becomes smaller.

[0110] [Table 1]

[0111] Fig. 8 is a diagram showing the results of electrochemical impedance spectroscopy (EIS) of the sulfide-based solid electrolyte according to the present invention. Fig. 8 shows the electrochemical impedance (EIS) of the sulfide-based solid electrolyte according to the embodiment. In terms of the characteristics of the battery, in order to maintain the performance as an electrolyte, the electronic conductivity of the electrolyte itself needs to be minimized, and the higher the ionic conductivity, the more advantageous it is.

[0112] 8, it can be seen that the slope of the electrochemical impedance (EIS) according to the embodiment is 45° or more, which means that the electronic conductivity is small and the ionic conductivity is excellent. Therefore, it can be seen that the sulfide-based solid electrolyte according to the present invention has excellent properties.

[0113] In addition, according to the present invention, a reactant is formed by wet milling containing a solvent, and carbon can be effectively removed through a step of remixing the formed reactant, a first heat treatment, a second heat treatment, and a purification step. The sulfide-based solid electrolyte having an Argyrodite-type crystal structure can have a uniform particle size, and the particle size can be freely adjusted through a purification step.

[0114] Thus, the present invention has been described with reference to one embodiment shown in the drawings, but this is merely illustrative, and those skilled in the art will appreciate that various modifications and variations of the embodiment are possible. Therefore, the true technical scope of the present invention should be determined by the technical ideas of the appended claims.

Claims

1. mixing a precursor and a solvent to form a mixture; reacting the mixture to form a reactant; and heat treating the reactants; The heat treatment includes a first heat treatment step and a second heat treatment step performed at a temperature higher than that of the first heat treatment step, In the first heat treatment step, carbon in the reactant is converted into amorphous carbon.

2. The method for producing a sulfide-based solid electrolyte according to claim 1 , wherein the second heat treatment step is performed in an inert gas atmosphere.

3. Prior to the step of heat treating the reactants, further comprising the step of remixing the reactants; The method for producing a sulfide-based solid electrolyte according to claim 1 , wherein the heat-treating step heat-treats the remixed reactants.

4. The method for producing a sulfide-based solid electrolyte according to claim 3 , wherein the reactants are dried and then remixed.

5. The method for producing a sulfide-based solid electrolyte according to claim 4 , wherein the remixing step is performed by wet ball milling.

6. After the step of heat treating the reactants, The method for producing a sulfide-based solid electrolyte according to claim 1 , further comprising a step of purifying the heat-treated reactant.

7. The method for producing a sulfide-based solid electrolyte according to claim 6 , wherein the step of purifying the reactants is performed by wet ball milling.

8. The method for producing a sulfide-based solid electrolyte according to claim 7 , further comprising, after the step of purifying the reactant, a step of drying the purified reactant.

9. The method for producing a sulfide-based solid electrolyte according to claim 1 , wherein the precursor comprises an alkali metal sulfide, an alkali metal halide, and phosphorus pentasulfide.

10. Upon forming the mixture, The method for producing a sulfide-based solid electrolyte according to claim 9 , wherein the alkali metal sulfide and the alkali metal halide are primarily mixed in the solvent, and the phosphorus pentasulfide is further secondarily mixed therein.

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