Method for producing sulfide-based solid electrolytes

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] This invention relates to a method for producing sulfide-based solid electrolytes. [Background technology]

[0002] Lithium-ion batteries have been used in small devices such as mobile phones and laptops, but recently their use has been expanded to medium and large devices such as energy storage systems (ESS) and electric vehicles (EVs). Because lithium-ion batteries utilize an organic liquid electrolyte to which lithium salts are added, they pose a potential risk of not only electrolyte leakage but also ignition and explosion caused by such leakage.

[0003] In recent years, research has been progressing on all-solid-state batteries, which replace the liquid electrolyte with a solid electrolyte to overcome the limitations of lithium-ion batteries and improve battery stability. All-solid-state batteries, by using a solid electrolyte, do not pose a risk of fire or explosion, have a high energy density, and, like lithium-ion batteries, can be used in medium to large-scale equipment such as electric vehicles and power storage systems.

[0004] Solid electrolytes are classified into oxide-based and sulfide-based types. In particular, sulfide-based solid electrolytes have superior lithium-ion conductivity compared to oxide-based solid electrolytes and offer the advantage of stable operation over a wide voltage range. Sulfide-based solid electrolytes are generally manufactured by melting or solid-phase methods. The solid-phase method, in particular, involves placing the starting material and balls in a milling vessel, grinding them, and then applying high energy for heat treatment.

[0005] Conventionally, Korean Published Patent No. 2019-0079135 discloses a method for producing a sulfide-based solid electrolyte by mixing and grinding starting materials and then heat-treating them. However, such solid-phase methods have problems such as difficulty in uniformly dispersing the starting materials, limitations in amorphousness, difficulty in scaling up the milling vessel, and difficulty in large-scale synthesis.

[0006] In recent years, research has been progressing on liquid-phase processes that use organic solvents to synthesize sulfide-based solid electrolytes in order to solve these problems. However, there is a problem that the crystallinity of the solid electrolyte obtained in the liquid-phase process is reduced due to residual organic solvents, and the ionic conductivity decreases. [Overview of the project] [Problems that the invention aims to solve]

[0007] One objective of the present invention is to provide a method for producing highly pure and highly efficient sulfide-based solid electrolytes. [Means for solving the problem]

[0008] One embodiment of the present invention discloses a method for producing 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 comprises a primary heat treatment step and a secondary heat treatment step performed at a higher temperature than the primary heat treatment step, and in the primary heat treatment step, the carbon in the reactant is converted to amorphous carbon. [Effects of the Invention]

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

[0010] [Figure 1] This is a schematic flowchart illustrating a method for producing a sulfide-based solid electrolyte according to one embodiment of the present invention. [Figure 2] This is a schematic flowchart illustrating a method for producing a sulfide-based solid electrolyte according to another embodiment of the present invention. [Figure 3] This is a schematic flowchart illustrating a method for producing a sulfide-based solid electrolyte according to another embodiment of the present invention. [Figure 4] This figure shows the Raman spectroscopy results of the sulfide-based solid electrolyte according to the present invention. [Figure 5]This figure shows the results of X-ray diffraction analysis (XRD) of the sulfide-based solid electrolyte according to the present invention. [Figure 6] This figure shows the results of X-ray diffraction analysis (XRD) and Raman spectroscopy of the sulfide-based solid electrolyte according to the present invention. [Figure 7] This figure shows the results of X-ray diffraction analysis (XRD) and Raman spectroscopy of the sulfide-based solid electrolyte according to the present invention. [Figure 8] This figure shows the electrochemical impedance spectroscopy (EIS) results of the sulfide-based solid electrolyte according to the present invention. [Modes for carrying out the invention]

[0011] One embodiment of the present invention discloses a method for producing 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 comprises a primary heat treatment step and a secondary heat treatment step performed at a higher temperature than the primary heat treatment step, and in the primary heat treatment step, the carbon in the reactant is converted to amorphous carbon.

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

[0013] In this embodiment, the step of remixing the reactants is further included before the step of heat-treating the reactants, and the heat-treating step allows the remixed reactants to be heat-treated.

[0014] In this embodiment, the reactants can be dried and then remixed.

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

[0016] In this embodiment, after the step of heat-treating the reactant, a step of purifying the heat-treated reactant can be further included.

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

[0018] In this embodiment, after the step of purifying the reactant, a step of drying the purified reactant can be further included.

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

[0020] In this embodiment, when forming the mixture, the alkali metal sulfide and the alkali metal halide can be primarily mixed in the solvent, and then phosphorus pentasulfide can be further secondarily mixed.

[0021] The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments related to 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 so that the disclosed content is thorough and complete, and so that the idea of the present invention can be fully conveyed to those of ordinary skill in the art.

[0022] In describing each drawing, the same reference numerals were used for the same components. In the accompanying drawings, the dimensions of the structures are shown enlarged for clarity of the invention. Terms such as "first," "second," etc., can be used to describe various components, but such components should not be limited by such terms. The 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 plural expressions unless the context clearly indicates otherwise.

[0023] In this specification, terms such as “includes” or “have” are intended to specify the presence of features, figures, steps, actions, components, parts, or combinations thereof as described herein, and should be understood not to preemptively exclude the possibility of the presence or addition of one or more other features, figures, steps, actions, components, parts, or combinations thereof. Furthermore, when a part such as a layer, membrane, region, or plate is said to be “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 part such as a layer, membrane, region, or plate is said to be “below” another part, this includes not only when it is “directly below” the other part, but also when there is another part in between.

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

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

[0026] Referring to Figure 1, a method for producing 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 of mixing the precursor and solvent in the reactor (S110) can be carried out by first adding the solvent to the reactor and then adding the precursor, or by first adding the precursor and then adding the solvent, or by mixing the solvent and precursor and then adding them to the reactor.

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

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

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

[0031] In some embodiments, the alkali metal sulfides, alkali metal halides, 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 sulfides, alkali metal halides, and phosphorus pentasulfide can be reacted in a stoichiometric molar ratio of 5:1:2.

[0032] The solvent may include a first solvent in which alkali metal sulfides and alkali metal halides have low solubility. 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 a nitrile solvent, an ether solvent, an ester solvent, and the nitrile 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, etc., 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, acetate acetate, 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, etc.

[0035] Preferably, the second solvent may include acetone containing one oxygen element, 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.

[0036] The second solvent at least partially dissolves the alkali metal sulfide and alkali metal halide, effectively promoting the reaction between the alkali metal sulfide and alkali metal halide 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 alkali metal halide can be primary-mixed in a first solvent, and then phosphorus pentasulfide can be further secondary-mixed.

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

[0039] In some embodiments, the alkali metal sulfide and alkali metal halide can be pre-stirred in the first solvent during the primary mixing. In this case, the alkali metal sulfide and alkali metal halide dissolve in the first solvent, reducing unreacted material in the sulfide-based solid electrolyte synthesis reaction and increasing the purity of the synthesized product. For example, the pre-stirring can be carried out at 500 rpm or higher 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 initial stirring can be performed at room temperature to 100°C. As the temperature of the initial stirring increases, the amount of impurities can decrease, and preferably, the initial stirring can 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 reactants can be produced by wet ball milling. For example, the reactants can be formed using table ball milling, vertical ball milling, planetary ball milling, or bead milling.

[0043] As another example, the reactor can be reacted by maintaining an open vacuum state, keeping the gas pressure inside the reactor below -0.1 MPa, even if the reactor is not sealed, and stirring or using ultrasound to move the mixture inside the reactor. In this case, bubbles generated in the mixture by the stirring or application of ultrasound can be continuously generated until the end of the reaction, forming bulky bubbles. These bubbles can promote mixing and contact between the reactants and increase the reaction rate.

[0044] In any embodiment, 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 done by various methods, including vacuum drying, hot air drying, freeze-drying, and spray drying.

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

[0047] Remixing allows for more uniform mixing of the reactants, removal of residual solvent, and removal of carbon, an impurity contained in the solvent, from the reactants.

[0048] In one example, remixing can be carried out by wet ball milling. For example, this can be done by table ball milling, vertical ball milling, planetary ball milling, or bead milling. In another example, remixing may be carried out by stirring, homogenizing, or ultra-sonication.

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

[0050] This type of remixing can be carried out for 10 minutes to 2 hours, and can be done multiple times as needed, with alternating wet and dry mixing procedures.

[0051] Thus, by performing additional mixing after generating the reactants, it is possible to achieve complete mixing of different precursors at low energy, as well as 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 carried out at a temperature of 450°C to 600°C for 1 to 24 hours under an inert gas atmosphere such as CO, H2, N2, Ar, He, or Ne. The heat treatment causes crystals of the reactants to grow.

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

[0054] Referring to Figure 2, a method for producing 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 (S210); reacting the mixture to produce a reactant (S220); performing a primary heat treatment on the reactant (S230); and performing a secondary heat treatment on the reactant (S240).

[0055] The steps of mixing the precursor and solvent in the reactor (S210) and reacting the mixture to produce the reactant (S220) are the same as those described in Figure 1, so they will not be explained again.

[0056] 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). 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 sulfides, alkali metal halides, 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 sulfides, alkali metal halides, and phosphorus pentasulfide can be reacted in a stoichiometric molar ratio of 5:1:2.

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

[0059] The first solvent may include a nitrile solvent, an ether solvent, an ester solvent, and the nitrile 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, etc., 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, acetate acetate, 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, etc. Preferably, the second solvent may include acetone containing one oxygen element, 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.

[0061] After reacting the mixture using wet ball milling or the like to produce reactants (S220), heat treatment is performed. As shown in Figure 2, the heat treatment may include a primary heat treatment step (S230) and a secondary 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 with residual solvent present, elements such as carbon and nitrogen, which make up the solvent, may participate in the reaction, potentially generating impurities. In particular, among the elements lithium (Li), phosphorus (P), sulfur (S), and halogen (Halogen) that constitute sulfide-based solid electrolytes, the most stable phase at low temperatures is Li3PS4, which is synthesized at around 200°C. This phase has lower ionic conductivity compared to crystalline argyrodite-based solid electrolytes and is therefore treated as an impurity. Furthermore, if crystallization is carried out by heat treatment with impurities such as residual organic solvents present, it can result in low purity, low crystallinity, and low ionic conductivity along with numerous impurity phases.

[0063] However, as in the present invention, by including a primary heat treatment step (S230) and a secondary heat treatment step (S240), impurities can be further removed, a stable solid electrolyte crystalline phase can be synthesized, and a high purity and high crystallinity can be achieved.

[0064] More specifically, the primary heat treatment step (S230) further induces the volatilization of any solvent remaining in the reactants, converting carbon in the residual organic solvent into amorphous carbon with low electrical conductivity, thereby maintaining the stoichiometric ratio between precursors and inducing the synthesis of a structurally stable argyrodite.

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

[0066] The secondary heat treatment step (S240) can be performed at a higher temperature than the primary heat treatment step (S230). The secondary heat treatment step (S240) can be performed at a temperature of 450°C to 600°C for 1 to 24 hours under an inert gas atmosphere such as CO, H2, N2, Ar, He, or Ne. The secondary heat treatment can promote the growth of crystals in the reactants.

[0067] On the other hand, the embodiment described in Figure 2 may further include a step of remixing the reactants included in Figure 1 (S130 in Figure 1), which allows for more effective removal of impurities such as carbon generated during wet synthesis, thereby forming a high-purity sulfide-based solid electrolyte.

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

[0069] Referring to Figure 3, a method for producing 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 reactant (S320); heat-treating the reactant (S330); purifying the heat-treated reactant (S340); and drying the purified reactant (S350).

[0070] In the following sections, we will not repeat the same information as explained in Figure 1, but will only explain the differences.

[0071] 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). 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 sulfides, alkali metal halides, 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 sulfides, alkali metal halides, and phosphorus pentasulfide can be reacted in a stoichiometric molar ratio of 5:1:2.

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

[0074] The first solvent may include a nitrile solvent, an ether solvent, an ester solvent, and the nitrile 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, etc., 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, acetate acetate, 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, etc. Preferably, the second solvent may include acetone containing one oxygen element, 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.

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

[0077] The step of purifying the heat-treated reactants (S340) allows for further removal of residual impurities from the reactants by physical force and control of the particle size of the reactants by further mixing the reactants and breaking the weak physical bonds between secondary and tertiary particles.

[0078] Heat-treated reactants may contain small amounts of impurities that have not been completely removed, and in particular, after the heat treatment step, they may have a wide particle size distribution due to the crystallization mechanism. Furthermore, if uniformly mixed, aggregation may occur due to surface energy. Therefore, by further purifying the heat-treated reactants, it is possible to eliminate aggregation and produce a solid electrolyte with high purity and a uniform particle size distribution.

[0079] For example, the step of purifying the reactants (S340) can be carried out by wet ball milling. For instance, after mixing the reactants with an organic solvent, the reactants can be purified by ball milling. Ball milling removes impurities such as carbon from the surface of the reactants and breaks weak bonds between particles, thereby controlling the particle size of the reactants.

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

[0081] On the other hand, the purification step can be carried out wet or dry. If it is carried out wet, it includes a drying step, while if it is carried out dry, it does not include a drying step but may include an additional elimination step. The drying step can also be carried out by alternating between dry and wet drying.

[0082] Next, the purified reaction product is dried (S350). The purified reaction product may be dried using a centrifuge. The purified reaction product, having had impurities removed and its particle size adjusted through the purification step, can be dried using centrifugation 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 may be carried out by including a thawing step after a common drying method such as hot air drying, freeze drying, or spray drying.

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

[0085] The present invention will be described in more detail below through specific embodiments. The following embodiments are merely illustrative to aid in understanding the present invention, and the scope of the present invention is not limited thereto.

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

[0087] The synthetic materials used in the production of sulfide-based solid electrolytes are Li 7-x PS 6-x Ha x (1 ≤ x ≤ 2), and in the embodiment, Li6PS5Cl was synthesized with Ha being chloride and x being 1.

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

[0089] Next, the mixture was vacuum-dried, and then wet ball milling was performed for 1 hour to generate the reaction product.

[0090] After drying the resulting reactants, they were remixed by wet ball milling.

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

[0092] Furthermore, after ball milling with acetonitrile as the solvent for 2 hours, the upper layer of the solution was removed by centrifugation at 4000 RPM for 1 hour to perform a purification step, and the drying step involved vacuum drying for 12 hours to finally produce a sulfide-based solid electrolyte.

[0093] Comparative Example 1

[0094] Comparative Example 1 produced a sulfide-based solid electrolyte in the same manner as the embodiment, but differed in that it omitted the step of remixing the reactants after their formation.

[0095] Figure 4 shows the Raman spectroscopy results for the embodiment and Comparative Example 1. Figure 4(I) shows the Raman spectroscopy results for the embodiment, and (II) shows the Raman spectroscopy results for Comparative Example 1.

[0096] Referring to Figure 4, in the case of Embodiment (I), in which a remixing step was performed after the formation of the reactants, the result was 470 cm² compared to Comparative Example 1 (II). -1 Since the peaks are not significantly different, PS4 3-While the bonding intensity was maintained, the total area of ​​peaks related to carbon, an impurity presumed to originate from the solvent, was relatively reduced. This confirms that remixing the reactants after their formation is effective in structurally stabilizing the sulfide-based solid electrolyte and removing impurities.

[0097] In other words, 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) that are generated during wet synthesis.

[0098] Comparative Example 2

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

[0100] Figure 5 shows the results of X-ray diffraction analysis (XRD) of the sulfide-based solid electrolyte according to the present invention. Figure 5(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 Figure 5, in Comparative Example 2(III), along with the impurity phase Li3PS4 at 16 (2θ / deg.), large amounts of Li2S at 27 (2θ / deg.), LiCl at 29 (2θ / deg.), and LiCl at 32 (2θ / deg.) are detected in accordance with stoichiometric ratios. In contrast, in Embodiment (I), where the secondary heat treatment step is carried out after the primary heat treatment step, not only is Li3PS4 hardly detected, but no other impurities are detected except for a small amount of Li2S.

[0102] In other words, by performing heat treatment in two separate steps, a primary heat treatment step and a secondary heat treatment step, impurities can be further removed from the reactants, a stable solid electrolyte crystalline phase can be synthesized, and a high purity and high crystallinity can be achieved.

[0103] Comparative Example 3

[0104] Comparative Example 3 produced a sulfide-based solid electrolyte in the same manner as in the embodiment, but had a difference in that it did not include the purification and drying processes.

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

[0106] First, as shown in Fig. 6, it can be seen that there is no significant difference in the X-ray diffraction analysis (XRD) results between Embodiment (I) that has undergone the purification and drying processes after heat treatment and Comparative Example 3 (IV) that does not include the purification and drying processes. That is, even after undergoing the purification and drying processes after heat treatment, there is no significant difference in crystallinity, phase change, etc., indicating that the purification and drying processes do not have a significant impact on the solid electrolyte.

[0107] In contrast, referring to Fig. 7, in the case of Embodiment (I) compared to Comparative Example 3 (IV), a small amount of impurities remaining before purification, particularly peaks related to carbon (1350~1580 cm -1 ) show a result of a sharp decrease. On the other hand, it can be seen that there is no influence on the peak (430 cm 3- ) of PS4 -1 , which is the main bond of the sulfide solid electrolyte.

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

[0109] Also, as a result of undergoing the purification step and the drying step, as shown in Table 1 below, Embodiment (I) has a smaller average particle size (D 50) This shows that the particle size distribution becomes smaller.

[0110] [Table 1]

[0111] Figure 8 shows the electrochemical impedance spectroscopy (EIS) results of a sulfide-based solid electrolyte according to the present invention. Figure 8 shows the electrochemical impedance (EIS) of a sulfide-based solid electrolyte according to an embodiment. Due to the characteristics of batteries, in order to maintain the performance as an electrolyte, the electronic conductivity of the electrolyte itself must be kept to a minimum, and a higher ionic conductivity is advantageous.

[0112] Referring to Figure 8, it can be seen that the slope of the electrochemical impedance (EIS) in the embodiment is 45° or more, which indicates 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 properties.

[0113] Furthermore, according to the present invention, although the reactants are formed by wet milling containing a solvent, carbon can be effectively removed through the steps of remixing the formed reactants, primary heat treatment, secondary heat treatment, and purification, 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 adjusted through the 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 with ordinary skill in the art will understand that various modifications and variations of embodiments are possible therefrom. Therefore, the true scope of technical protection of the present invention should be determined by the technical idea of ​​the appended claims.

Claims

1. A step of mixing a precursor containing an alkali metal sulfide, an alkali metal halide, and phosphorus pentasulfide with a solvent to form a mixture, The steps include: reacting the mixture to produce a reactant, The step includes heat-treating the reactant, The heat treatment includes a primary heat treatment step and a secondary heat treatment step performed at a higher temperature than the primary heat treatment step. A method for producing a sulfide-based solid electrolyte, wherein the primary heat treatment step is performed at a temperature of 100°C to 450°C such that the residual solvent is converted into amorphous carbon.

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

3. Before the step of heat-treating the reactants, The process further includes the step of remixing the reaction product, The method for producing a sulfide-based solid electrolyte according to claim 1, wherein the heat treatment step involves heat-treating the remixed reactants.

4. The method for producing a sulfide-based solid electrolyte according to claim 3, wherein the remixing step involves drying the reactants and then remixing the dried reactants.

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, A method for producing a sulfide-based solid electrolyte according to claim 1, further comprising the 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 reaction product is performed by wet ball milling.

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

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