Method for manufacturing sulfide-based solid electrolyte

Abstract

The present invention relates to a method for manufacturing a sulfide-based solid electrolyte, comprising the steps of: preparing a precursor solution by adding a precursor containing an alkali metal sulfide, a phosphorus sulfide, and a halogen compound to a solvent (S1); milling the precursor solution to manufacture an intermediate product (S2); drying the intermediate product (S3); thermally treating the dried intermediate product (S4); and cooling the product obtained by the thermal treatment (S5), wherein the step of thermally treating the dried intermediate product (S4) comprises raising temperature from room temperature to a thermal treatment temperature according to formula 1 below, and then maintaining the temperature for a holding time of 10 seconds to 20 seconds. [Formula 1] Tg + 80°C ≤ T ≤ Tg + 150°C wherein Tg is the glass transition temperature of the dried intermediate product.

Description

Method for manufacturing sulfide-based solid electrolyte

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

[0002] Recent reports of explosion risks in batteries using liquid electrolytes have led to active development of all-solid-state secondary batteries. All-solid-state secondary batteries are composed entirely of solid materials, specifically those using solid electrolytes. These all-solid-state secondary batteries are safe, eliminating the risk of explosion due to electrolyte leakage, and offer the advantage of being easy to manufacture in thinner sizes.

[0003] However, solid electrolytes have lower ionic conductivity than liquid electrolytes, and have problems such as resistance occurring at the interface between solid electrolyte particles or resistance occurring at the interface with other solid particles, such as positive electrode active materials in the battery, which reduces ionic conductivity.

[0004] Among solid electrolytes, active research is being conducted on sulfide-based solid electrolytes, which boast relatively high ionic conductivity. However, synthesizing sulfide-based solid electrolytes requires a high-temperature heat treatment process for crystallization.

[0005] In particular, the glass-ceramic solid electrolyte can maintain glass properties at around 10% by increasing the number of nuclei (nucleation) by slowing down nuclei growth as much as possible and increasing defects, thereby generating a large number of high-ionic conductivity phases, and simultaneously having the physical properties of glass.

[0006] However, when applying a general heat treatment method to heat treat a glass-ceramic (glass crystal) solid electrolyte, the synthesis temperature is relatively very low, but the time required for synthesis is significantly longer than that of a crystalline solid electrolyte. Since the time required for synthesis is long, nuclei grow during the heat treatment time rather than generate nuclei, so the mass production of glass-ceramic solid electrolytes with excellent mechanical properties and a much wider range of compositional combinations is not improved, and there is a limitation in that commercialization is difficult compared to crystalline solid electrolytes.

[0007] Furthermore, heat treatment of sulfide-based solid electrolytes at temperatures exceeding 300°C can lead to sulfur volatilization, which can lead to structural instability and reduced ionic conductivity. Furthermore, the volatilized sulfur can adsorb to surroundings, contaminating equipment and posing a safety risk to workers due to its strong odor.

[0008] To solve these problems, methods such as using hydrogen sulfide gas (H2S) or heat treating by raising the temperature around the sulfide-based solid electrolyte material are being used. However, hydrogen sulfide gas (H2S) is very dangerous, difficult to control its flow rate, and is a corrosive gas, making it very difficult to handle. In addition, hydrogen sulfide gas (H2S) has the problem of unstable supply and high cost. In addition, the existing heat treatment method of heat treating by raising the ambient temperature requires heat treatment for a long time at a temperature higher than the actual heat treatment temperature in order to sufficiently transfer heat to the material. In addition, when synthesizing a glass ceramic-based solid electrolyte in which the material becomes amorphous, there is a problem that it is not easy to exhibit high ionic conductivity because the temperature is not sufficiently transferred even after heat treatment for a long time.

[0009] The problem to be solved by the present invention is to provide a method for manufacturing a sulfide-based solid electrolyte by directly transferring heat energy to a precursor of the sulfide-based solid electrolyte to rapidly increase the temperature, thereby exhibiting a high ionic conductivity phase, and thereby minimizing the decrease in ionic conductivity.

[0010] Another problem that the present invention seeks to solve is minimizing the volatilization of sulfur by directly and rapidly transferring strong thermal energy to the precursor of a sulfide-based solid electrolyte.

[0011] According to one aspect of the present invention, a method for producing a sulfide-based solid electrolyte is provided, comprising: a step (S1) of preparing a precursor solution by introducing a precursor containing an alkali metal sulfide, a phosphorus sulfide, and a halogen compound into a solvent; a step (S2) of preparing an intermediate product by milling the precursor solution; a step (S3) of drying the intermediate product; a step (S4) of heat-treating the dried intermediate product; and a step (S5) of cooling the product obtained by the heat treatment, wherein the step (S4) of heat-treating the dried intermediate product is performed by heating from room temperature to a heat treatment temperature according to the following equation 1 and then holding the temperature for 10 to 20 seconds.

[0012] [Formula 1]

[0013] T g + 80℃ ≤ T ≤ T g + 150℃

[0014] The above T g is the glass transition temperature of the above dried intermediate product.

[0015] According to one embodiment of the present invention, a method for producing a sulfide-based solid electrolyte is provided, wherein the alkali metal sulfide includes lithium sulfide (Li2S), sodium sulfide (Na2S), or potassium sulfide (K2S).

[0016] According to one embodiment of the present invention, a method for producing a sulfide-based solid electrolyte is provided, wherein the halogen compound includes at least one material selected from the group consisting of lithium bromide (LiBr), lithium chloride (LiCl), lithium iodide (LiI), and lithium fluoride (LiF).

[0017] According to one embodiment of the present invention, a method for producing a sulfide-based solid electrolyte is provided, wherein the solvent is at least one selected from the group consisting of heptane, hexane, cyclohexane, and toluene.

[0018] According to one embodiment of the present invention, a method for producing a sulfide-based solid electrolyte is provided, wherein the step (S2) of producing an intermediate product by milling the precursor solution can be performed for 5 to 40 hours.

[0019] According to one embodiment of the present invention, the step (S2) of milling the precursor solution to produce an intermediate product provides a method for producing a sulfide-based solid electrolyte, which can be performed using balls in a planetary ball mill method, an attrition mill method, a SPEX mill method, a ball milling method, or a bead mill method.

[0020] According to one embodiment of the present invention, the step (S2) of milling the precursor solution to produce an intermediate product provides a method for producing a sulfide-based solid electrolyte by milling while adjusting the mass ratio of the precursor and the ball to 1:10 to 1:20.

[0021] According to one embodiment of the present invention, a method for manufacturing a sulfide-based solid electrolyte is provided, wherein the diameter of the ball is 0.5 mm to 5 mm.

[0022] According to one embodiment of the present invention, a method for manufacturing a sulfide-based solid electrolyte is provided in which the step (S3) of drying the intermediate product is performed at 60°C to 100°C.

[0023] According to one embodiment of the present invention, a method for manufacturing a sulfide-based solid electrolyte is provided, in which the step (S4) of heat-treating the dried intermediate product is performed for 30 to 50 seconds.

[0024] According to one embodiment of the present invention, a method for manufacturing a sulfide-based solid electrolyte is provided, in which the step (S5) of cooling the product obtained by the heat treatment is performed within 1 minute.

[0025] According to one embodiment of the present invention, a method for manufacturing a sulfide-based solid electrolyte having a glass-ceramic structure is provided.

[0026] A method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention can exhibit a high ionic conductivity phase by rapidly increasing the temperature by directly transferring heat energy to a precursor, thereby minimizing a decrease in ionic conductivity and volatilization of sulfur.

[0027] In addition, the method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention can shorten the process time by quickly cooling by the surrounding low temperature after directly transferring heat to the precursor and then stopping the energy transfer, and can prevent heat loss by directly transferring heat and appropriately control the heat treatment temperature, and can easily control the particle size because it does not have a large effect on the particle size of the precursor.

[0028] Figure 1 is a flowchart showing a method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention.

[0029] Figure 2 is a graph showing the DSC results of an intermediate product according to a manufacturing example.

[0030] Figure 3 is a graph showing the XRD results of an intermediate product according to a manufacturing example and a sulfide-based solid electrolyte manufactured according to Comparative Example 1.

[0031] Figure 4 is a graph showing the XRD results of an intermediate product according to a manufacturing example and a sulfide-based solid electrolyte manufactured according to Comparative Example 2.

[0032] FIG. 5 is a graph showing XRD of a sulfide-based solid electrolyte manufactured according to Examples 1 and 2 according to one embodiment of the present invention.

[0033] FIG. 6 is a graph showing the XRD of a sulfide-based solid electrolyte manufactured according to Example 3 according to one embodiment of the present invention.

[0034] The present invention is capable of various modifications and embodiments. Specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention, as well as the methods for achieving them, will become clearer with reference to the embodiments described in detail below, along with the drawings. However, the present invention is not limited to the embodiments disclosed below and can be implemented in various forms.

[0035] In the examples below, the terms first, second, etc. are not used in a limiting sense, but are used for the purpose of distinguishing one component from another.

[0036] In the examples below, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0037] In the examples below, terms such as “include” or “have” mean that a feature or component described in the specification is present, and do not preclude the possibility that one or more other features or components may be added.

[0038] In the following examples, when a part such as a film, region, component, etc. is said to be on or above another part, it includes not only a case where it is directly on top of the other part, but also a case where another film, region, component, etc. is interposed in between.

[0039] For convenience of explanation, the sizes of components in the drawings may be exaggerated or reduced. For example, the sizes and thicknesses of each component shown in the drawings are arbitrarily indicated for convenience of explanation, and thus the present invention is not necessarily limited to what is shown.

[0040] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings, and when describing with reference to the drawings, identical or corresponding components will be given the same drawing reference numerals.

[0041]

[0042] Method for manufacturing sulfide-based solid electrolyte

[0043] Figure 1 is a flowchart showing a method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention.

[0044] Referring to FIG. 1, a method for manufacturing a sulfide-based solid electrolyte may include a step (S1) of preparing a precursor solution by introducing a precursor including an alkali metal sulfide, a phosphorus sulfide, and a halogen compound into a solvent, a step (S2) of manufacturing an intermediate product by milling the precursor solution, a step (S3) of drying the intermediate product, a step (S4) of heat-treating the dried intermediate product, and a step (S5) of cooling the product obtained by the heat treatment.

[0045] In the step (S1) of preparing a precursor solution, the precursor may include an alkali metal sulfide, a phosphorus sulfide, or a halide. The alkali metal sulfide is not particularly limited as long as it is used in the art for producing a sulfide-based solid electrolyte. For example, the alkali metal sulfide may be lithium sulfide (Li2S), sodium sulfide (Na2S), or potassium sulfide (K2S), and preferably lithium sulfide (Li2S).

[0046] The phosphosulfide is not particularly limited as long as it is used in the manufacture of sulfide-based solid electrolytes in the art. For example, the phosphosulfide may be diphosphorus pentasulfide (P2S5).

[0047] The halogen compound is not particularly limited as long as it is used in the art for manufacturing a sulfide-based solid electrolyte. For example, it may include one or more substances selected from the group consisting of lithium bromide (LiBr), lithium chloride (LiCl), lithium iodide (LiI), and lithium fluoride (LiF). Alternatively, the halogen compound may include two substances, for example, lithium bromide (LiBr) and lithium iodide (LiI) may be used together.

[0048] If the alkali metal sulfide is lithium sulfide (Li2S), the phosphorus sulfide is diphosphorus pentasulfide (P2S5), and the halogen compound is lithium bromide (LiBr) and lithium iodide (LiI), there is no particular limitation as long as the amounts are those used in the manufacture of sulfide-based solid electrolytes in the art. For example, the molar ratio of lithium sulfide (Li2S): diphosphorus pentasulfide (P2S5): lithium bromide (LiBr): lithium iodide (LiI) may be 6:2:1:1. The lithium sulfide (Li2S)-phosphorus pentasulfide (P2S5)-based lithium secondary battery solid electrolyte has higher ionic conductivity than the oxide-based solid electrolyte, and therefore, the content of lithium sulfide (Li2S) needs to be about 60 mol% or more in the starting material. However, when the content of lithium sulfide (Li2S) is excessive, the amount of lithium sulfide (Li2S) remaining in the final glass-ceramic increases, which increases moisture reactivity and reactivity with the active material interface, and lowers electrochemical stability. Therefore, the above-described mixing ratio may be the optimal ratio for improving ionic conductivity while reducing the content of lithium sulfide (Li2S) remaining in the final glass-ceramic.

[0049] The solvent can be a nonpolar solvent that dissolves the precursors to prepare a precursor solution. The solvent is not particularly limited as long as it is used in the art for manufacturing sulfide-based solid electrolytes. For example, the solvent may be one or more selected from the group consisting of heptane, hexane, cyclohexane, and toluene.

[0050] The step (S2) of milling the precursor solution to produce an intermediate product can be performed using balls, such as a planetary ball mill method, an attrition mill method, a SPEX mill method, a ball milling method, or a bead mill method. For example, it can be performed using any known ball milling device used for high-energy ball milling.

[0051] Milling can form an intermediate by mixing and grinding precursors. The intermediate can be a sulfide-based amorphous solid electrolyte.

[0052] The step (S2) of milling the precursor solution to produce an intermediate product can be performed for 5 to 40 hours. Specifically, the lower limit of the milling time can be 5 hours, 10 hours, 15 hours, or 20 hours, and the upper limit of the milling time can be 40 hours, 35 hours, 30 hours, or 25 hours. If the milling time is less than 5 hours, mixing is not performed properly, making it impossible to produce an amorphous solid electrolyte with a consistent composition. If the milling time exceeds 40 hours, there is a concern that the temperature at which crystallinity locally increases may exceed 170°C. Therefore, if the milling time satisfies the above range, an amorphous solid electrolyte with a consistent composition and uniformity can be produced.

[0053] The balls used in milling assist in dispersion by transmitting impact energy to the precursor during mixing and crushing of the precursor, and the mass and size of the balls may affect the mixing and crushing. For example, the balls may include at least one selected from the group consisting of glass, alumina, zirconia, and combinations thereof, and zirconia balls are preferably used.

[0054] In the step (S2) of manufacturing an intermediate product by milling a precursor solution, the milling can be performed by adjusting the mass ratio of the precursor and the balls to 1:10 to 1:20. If the mass ratio of the precursor and the balls exceeds the above range, it is difficult to mix the precursors, making it difficult to manufacture a sulfide-based amorphous solid electrolyte that satisfies uniformity. If the mass ratio of the precursor and the balls is less than the above range, it may be difficult to grind the precursor. Therefore, if the mass ratio of the precursor and the balls satisfies the above range, mixing and grinding of the precursor can be sufficiently achieved.

[0055] The diameter (size) of the balls used in milling may be 0.5 mm to 5 mm. The diameter (size) of the balls refers to the average particle size based on the volume average, and specifically, the lower limit of the ball diameter may be 0.5 mm, 0.8 mm, 1 mm, 1.5 mm, 2 mm, or 2.5 mm, and the upper limit of the ball diameter may be 5 mm, 4.5 mm, 4 mm, 3.5 mm, or 3 mm. If the diameter (size) of the balls exceeds the above range, the average particle size of the sulfide-based solid electrolyte may be formed to be too large, and if the diameter (size) of the balls is less than the above range, sufficient energy is not transferred to the precursor, making it difficult to synthesize. Therefore, if the diameter (size) of the balls satisfies the above range, a sulfide-based solid electrolyte having an appropriate particle size can be synthesized and milled.

[0056] The step (S3) of drying the intermediate product may correspond to a solvent removal process that evaporates the solvent after the step (S2) of milling the precursor solution to produce the intermediate product. The drying step may be performed at a temperature of 60°C to 100°C for a predetermined period of time. For example, drying may be performed using a spray dryer in an inert atmosphere or vacuum drying.

[0057] Figure 2 is a graph showing the DSC results of an intermediate product according to a manufacturing example.

[0058] Referring to Figure 2, the glass transition temperature (T) of the dried intermediate product g ) is about 170℃, and the first crystallization temperature (T c1 ) is about 180℃, and the secondary crystallization temperature (T c2 ) can be confirmed to be about 250℃. That is, even if the intermediate product is dried at a temperature in the above range, the glass transition temperature (T g ) is formed below, the dried intermediate product may be a sulfide-based amorphous solid electrolyte.

[0059] The step (S4) of heat-treating the dried intermediate product is a step of heat-treating a sulfide-based amorphous solid electrolyte to produce a solid electrolyte that is crystallized into a glass crystal, and can be performed by raising the temperature from room temperature to a heat-treatment temperature according to Equation 1 below and then holding the temperature for 10 to 20 seconds. When heat-treating is performed for 10 to 20 seconds at a heat-treatment temperature (T) according to Equation 1 below, volatilization of sulfur can be prevented due to the short heat-treatment time, and ionic conductivity can be maximized by inducing more nucleation than nucleus growth.

[0060] [Formula 1]

[0061] T g + 80℃ ≤ T ≤ T g + 150℃

[0062] The above T g is the glass transition temperature of the above dried intermediate product.

[0063] The above heat treatment temperature (T) is the glass transition temperature (T) of the dried intermediate product. g ) can be determined based on T . Specifically, the lower limit of the heat treatment temperature (T ) is T g + 80℃, T g + 85℃, T g + 90℃, T g + 95℃ or T g + 100℃, and the upper limit of the heat treatment temperature (T) is T g + 150℃, T g + 145℃, T g + 140℃, T g + 135℃ or T g + It can be 130℃.

[0064] It can be confirmed from FIGS. 5 and 6 that when the heat treatment temperature (T) satisfies the above range and the heating time (10 to 20 seconds) is satisfied, the most stable phase, lithium tetrasulfide (Li3PS4), is not generated. Therefore, the method for manufacturing a sulfide-based solid electrolyte according to the present invention can significantly improve the ionic conductivity of a sulfide-based solid electrolyte by preventing the generation of lithium tetrasulfide (Li3PS4), which is the most stable phase.

[0065] Heat treatment temperature (T) is T g + If it is less than 80℃, it is difficult to provide sufficient energy for nucleation of intermediate products with only the above heating time (10 to 20 seconds), and the heat treatment temperature (T) is lower than the glassification temperature (T g ) is less than , the crystallization of the solid electrolyte does not occur properly, and only an amorphous solid electrolyte exists. Since a certain degree of crystallinity is not present, ionic conductivity is not properly displayed.

[0066] Also, the heat treatment temperature (T) is T g + When the temperature exceeds 150℃, the degree of crystallinity may increase, but the ionic conductivity may decrease as the most stable phase, lithium tetrasulfide (Li3PS4), is formed by nuclei growth rather than nucleation.

[0067] The step (S4) of heat-treating the dried intermediate product can be performed for 30 to 50 seconds. Specifically, the lower limit of the heat-treatment time can be 30 seconds, 32 seconds, 34 seconds, 36 seconds, 38 seconds, or 40 seconds, and the upper limit of the heat-treatment time can be 50 seconds, 49 seconds, 48 ​​seconds, 47 seconds, 46 seconds, or 45 seconds. This includes the time required to increase the temperature from room temperature to the heat-treatment temperature (T) and the time required to maintain the temperature at the heat-treatment temperature (T). When the temperature-elevation time and the maintaining time satisfy the above range, nuclei growth can be prevented, an ion-conducting phase can be developed, and ion conductivity can be improved.

[0068] For example, the dried intermediate product can be heated to the heat treatment temperature (T) by performing heat treatment at a heating rate of 6.6°C / second or higher.

[0069] In the cooling step (S5) of the product obtained through heat treatment, cooling is carried out within 1 minute, so that it can be cooled to room temperature (25℃). Since the RTA equipment does not contain a refractory and includes a tube containing water, the sample can be taken out and cooled immediately after the heat treatment step is completed. Accordingly, the overall process time can be shortened and the decrease in ionic conductivity can be minimized. If the cooling time exceeds the above range, there is a concern that the ionic conductivity may be reduced due to partial nucleus growth occurring as the thermal energy is evenly distributed throughout the sample during the cooling time. In this case, the product may be a sulfide-based solid electrolyte having a glass-ceramic structure.

[0070] As described above, the sulfide-based solid electrolyte manufactured using the method for manufacturing a sulfide-based solid electrolyte according to an embodiment of the present invention can be applied to an all-solid-state battery and used as an electrolyte of the all-solid-state battery.

[0071]

[0072] solid electrolyte

[0073] A sulfide-based solid electrolyte manufactured according to one embodiment of the present invention may have a glass-ceramic structure. The method for manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention enables the control of nuclear growth through thermal energy directly applied to the precursor, thereby being effective in producing glass crystals.

[0074] If the heat treatment step takes a long time, the manufactured sulfide-based solid electrolyte has crystal nuclei that continue to grow during the heat treatment process, thereby reducing ionic conductivity. However, the sulfide-based solid electrolyte manufactured according to one embodiment of the present invention has a very short heat treatment time, thereby preventing nuclei from growing in the sulfide-based solid electrolyte and allowing a high ionic conductivity phase to be expressed in large quantities, thereby minimizing the reduction in ionic conductivity.

[0075] In addition, by significantly shortening the heat treatment time, the volatilization of sulfur can be minimized, so that a structurally stable sulfide-based solid electrolyte can be manufactured, and by directly transferring heat energy to the mixture, heat loss to the surroundings can be prevented, so that the heat treatment temperature can be appropriately controlled, and by stopping the transfer of heat energy, cooling is performed immediately, so that rapid cooling to a low temperature of the surroundings is possible, so that the cooling time of the cooling step can be shortened.

[0076]

[0077] All-solid-state battery

[0078] A method for manufacturing an all-solid-state battery may include a step of manufacturing a sulfide-based solid electrolyte according to one embodiment of the present invention; and a step of manufacturing a cell by laminating a positive electrode, the solid electrolyte, and a negative electrode.

[0079] For example, according to the above manufacturing method, an all-solid-state battery may include a cathode, an anode, and a sulfide-based solid electrolyte layer disposed between the cathode and the anode.

[0080] At this time, the sulfide-based solid electrolyte layer may be a sulfide-based solid electrolyte manufactured using a sulfide-based solid electrolyte manufacturing method according to one embodiment of the present invention.

[0081] The negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on one surface of the negative electrode current collector.

[0082] The negative electrode active material that may be included in the negative electrode active material layer may include at least one selected from the group consisting of lithium (Li), amorphous carbon, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn).

[0083] A binder that may be included in the negative electrode active material layer can improve the bonding between the negative electrode active material and the conductive material and the bonding to the negative electrode current collector. Examples of the negative electrode binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluoroelastomer, and various copolymers thereof.

[0084] A conductive material that can be included in the negative electrode active material layer can be used to further improve the conductivity of the negative electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, aluminum, copper, nickel, and silver powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, carbon nanotubes, and the like.

[0085] The negative electrode current collector may be made of a material that is conductive and does not react with lithium without causing a chemical change in the battery, and may include various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc. having fine irregularities formed on the surface. For example, the negative electrode current collector may include at least one selected from the group consisting of copper (Cu), stainless steel (SS), titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni).

[0086] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on one surface of the positive electrode current collector.

[0087] The cathode active material that can be included in the cathode active material layer may include at least one selected from lithium transition metal oxides such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganese oxide, lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide, but is not necessarily limited thereto, and any cathode active material used in the relevant technical field may be used.

[0088] A binder that can be included in the positive electrode active material layer can improve the bonding between the positive electrode active material and the conductive material, as well as the bonding to the positive electrode current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluoroelastomer, and various copolymers thereof.

[0089] A conductive material that can be included in the positive electrode active material layer can be used to further improve the conductivity of the positive electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, aluminum, copper, nickel, and silver powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, and carbon nanotubes.

[0090] The positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector may form fine irregularities on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0091] Hereinafter, examples are presented to help understand the present invention, but the examples are only illustrative of the present disclosure, and the scope of the present application is not construed as being limited to the examples described below, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0092] Manufacturing example: Manufacturing of intermediate products

[0093] A total of 40 g of precursors consisting of lithium sulfide (Li2S), diphosphorus pentasulfide (P2S5), lithium bromide (LiBr), and lithium iodide (LiI) mixed in a ratio of 6:2:1:1 was weighed and subjected to high-energy milling (mechanical milling) for 40 hours using a Fritsch P5 model along with 500 g of 3 mm zirconia balls and 250 cc of heptane, a non-polar solvent.

[0094] The intermediate product manufactured after milling was obtained by vacuum drying at 80°C, and then the zirconia balls were removed through a sieving machine to prepare the intermediate product.

[0095]

[0096] Example 1: Preparation of solid electrolyte

[0097] The intermediate product prepared according to the above manufacturing example was subjected to overshooting heat treatment up to 250°C in an RTA device. The heating rate in the RTA device was 6.6°C per second and maintained in an inert atmosphere for 10 seconds, resulting in a total heat treatment time of 49 seconds. The cooling time after heating was 60 seconds. In other words, the total time required for heat treatment and cooling was 109 seconds.

[0098]

[0099] Example 2: Preparation of solid electrolyte

[0100] A sulfide-based solid electrolyte was manufactured in the same manner as Example 1, except that the intermediate product prepared according to the above manufacturing example was subjected to overshooting heat treatment at a temperature of 270°C in an RTA device.

[0101]

[0102] Example 3: Preparation of solid electrolyte

[0103] A sulfide-based solid electrolyte was manufactured in the same manner as Example 1, except that the intermediate product prepared according to the above manufacturing example was subjected to overshooting heat treatment at a temperature of 300°C in an RTA device.

[0104]

[0105] Comparative Example 1

[0106] The intermediate product prepared according to the above manufacturing example was subjected to vitrification at a temperature (T) in a general tube furnace. g ) was heat treated up to 170℃. The heating rate was 5℃ per minute and maintained in an inert atmosphere for 12 hours, so the total time required for heat treatment was 749 minutes. The time required for cooling after heating was 1 hour. In other words, the total time required for heat treatment and cooling was 749 minutes.

[0107]

[0108] Comparative Example 2

[0109] The intermediate product prepared according to the above manufacturing example was subjected to vitrification at a temperature (T) in an RTA device. g ) was heat treated up to 170℃. The heating rate was 6.6℃ per second and maintained in an inert atmosphere for 10 seconds, so the total time required for heat treatment was 32 seconds. The time required for cooling after heating was 1 minute. In other words, the total time required for heat treatment and cooling was 92 seconds.

[0110]

[0111] Evaluation Example 1: DCS

[0112] In order to confirm the glass transition temperature (Tg) and crystallization temperature (Tc) of the intermediate product manufactured according to the above manufacturing example, DSC was measured and analyzed to determine the glass transition temperature (Tg) and crystallization temperature (Tc). The DSC results of the intermediate product are shown in Fig. 2.

[0113] Referring to Figure 2, it can be confirmed that the glass transition temperature (Tg) of the dried intermediate product is about 170°C, the primary crystallization temperature (Tc1) is about 180°C, and the secondary crystallization temperature (Tc2) is about 250°C.

[0114]

[0115] Evaluation Example 2: XRD

[0116] In order to confirm the crystallinity of the sulfide-based solid electrolytes manufactured according to Example 1, Comparative Example 1, and Comparative Example 2, XRD was measured at an angle of 10 to 40 degrees, and a dome holder made of PEEK material was used for the measurement considering the reactivity in the air. The XRD results are shown in FIGS. 3 to 6.

[0117] Fig. 3 is a graph showing the XRD results of an intermediate product according to a manufacturing example and a sulfide-based solid electrolyte manufactured according to Comparative Example 1. Fig. 4 is a graph showing the XRD results of an intermediate product according to a manufacturing example and a sulfide-based solid electrolyte manufactured according to Comparative Example 2. Fig. 5 is a graph showing the XRD of a sulfide-based solid electrolyte manufactured according to Examples 1 and 2 according to an embodiment of the present invention. Fig. 6 is a graph showing the XRD of a sulfide-based solid electrolyte manufactured according to Example 3 according to an embodiment of the present invention.

[0118] Referring to Figures 3 and 4, the intermediate product according to the manufacturing example and the sulfide-based solid electrolyte manufactured according to Comparative Examples 1 and 2 do not have peaks observed in the XRD results. This is because the first crystallization temperature (T c1 ) It can be confirmed that a glassy crystalline solid electrolyte is not formed because nuclei are not generated due to heat treatment at a temperature lower than 180℃ for an insufficient time.

[0119] Referring to FIGS. 5 and 6, it can be confirmed that the sulfide-based solid electrolytes manufactured according to Examples 1 to 3 exhibit high ionic conductivity phases at around 20°C, 23.5°C, 28.6°C, and 29.3°C based on XRD results, while the most stable phase, lithium tetrasulfide (Li3PS4), is not formed. This is because, through overshooting, a method for promoting nucleation, strong energy is briefly irradiated, and crystal nuclei are instantaneously formed at high temperatures of 250°C, 270°C, and 300°C, and nuclei are maintained from growing through a short heat treatment time and cooling time.

[0120] Whether a high ionic conductivity phase was formed in the sulfide-based solid electrolytes manufactured according to Examples 1 to 3 and Comparative Examples 1 and 2 is shown in Table 1 below.

[0121]

[0122] Evaluation Example 3: Ionic Conductivity and Compressed Density

[0123] After confirming the crystallinity of the sulfide-based solid electrolytes manufactured according to Examples 1 to 3 and Comparative Examples 1 and 2, they were pressurized at 6.6 tons in a mold-shaped pressurized cell with a diameter of 13 mm, and then maintained at a temperature of 30°C for more than 3 hours in an oven, and then the lithium ion conductivity was measured, and the thickness and weight were measured to determine the compressed density. The ion conductivity and compressed density are shown in Table 1 below.

[0124]

[0125] Presence or absence of high ionic conductivity Ionic conductivity (mS / cm) Compressed density (g / cc) Example 104.871.98 Example 205.621.97 Example 306.781.95 Comparative example 1X--Comparative example 2X--

[0126]

[0127] According to Table 1 above, it can be confirmed that the sulfide-based solid electrolytes manufactured according to Examples 1 to 3 exhibit improved ionic conductivity by inducing nucleation without generating lithium tetrasulfide (Li3PS4), which is the most stable phase, by heat treatment at a heat treatment temperature of 250°C to 320°C, thereby exhibiting a high ionic conductivity phase.

[0128] In addition, the sulfide-based solid electrolytes manufactured according to Examples 1 to 3 have high compression densities, which can be interpreted as meaning that a large amount of glass (amorphous) structure remains. Since glass (amorphous) has excellent formability, the higher the compression density in the same material, the better the formability. Therefore, the sulfide-based solid electrolyte manufactured according to one embodiment of the present invention can be advantageously applied to all-solid-state batteries.

[0129] However, in the case of the sulfide-based solid electrolytes manufactured according to Comparative Examples 1 and 2, a high ionic conductivity phase was not developed.

Claims

1. A step (S1) of preparing a precursor solution by introducing a precursor containing alkali metal sulfide, phosphorus sulfide, and halogen compound into a solvent; A step (S2) of manufacturing an intermediate product by milling the above precursor solution; Step of drying the above intermediate product (S3); A step (S4) of heat-treating the above dried intermediate product; and A step (S5) of cooling the product obtained through the above heat treatment is included; The step (S4) of heat-treating the above-mentioned dried intermediate product is a method for manufacturing a sulfide-based solid electrolyte, which comprises heating the product from room temperature to a heat treatment temperature according to the following formula 1 and then holding the temperature for 10 to 20 seconds: [Formula 1] T g + 80℃ ≤ T ≤ T g + 150℃ The above T g is the glass transition temperature of the above dried intermediate product.

2. In paragraph 1, A method for producing a sulfide-based solid electrolyte, wherein the alkali metal sulfide comprises lithium sulfide (Li2S), sodium sulfide (Na2S), or potassium sulfide (K2S).

3. In paragraph 1, A method for producing a sulfide-based solid electrolyte, wherein the above halogen compound comprises at least one substance selected from the group consisting of lithium bromide (LiBr), lithium chloride (LiCl), lithium iodide (LiI), and lithium fluoride (LiF).

4. In paragraph 1, A method for producing a sulfide-based solid electrolyte, wherein the solvent is at least one selected from the group consisting of heptane, hexane, cyclohexane, and toluene.

5. In paragraph 1, A method for producing a sulfide-based solid electrolyte, wherein the step (S2) of producing an intermediate product by milling the precursor solution can be performed for 5 to 40 hours.

6. In paragraph 1, A method for producing a sulfide-based solid electrolyte, wherein the step (S2) of producing an intermediate product by milling the precursor solution may be performed using a ball using a planetary ball mill method, an attrition mill method, a SPEX mill method, a ball mill method, or a bead mill method.

7. In paragraph 6, A method for manufacturing a sulfide-based solid electrolyte, wherein the step (S2) of manufacturing an intermediate product by milling the precursor solution is performed by adjusting the mass ratio of the precursor and the ball to 1:10 to 1:

20.

8. In paragraph 6, A method for manufacturing a sulfide-based solid electrolyte, wherein the diameter of the ball is 0.5 mm to 5 mm.

9. In paragraph 1, A method for manufacturing a sulfide-based solid electrolyte, wherein the step (S3) of drying the intermediate product is performed at 60°C to 100°C.

10. In paragraph 1, A method for manufacturing a sulfide-based solid electrolyte, wherein the step (S4) of heat-treating the above-mentioned dried intermediate product is performed for 30 to 50 seconds.

11. In paragraph 1, A method for manufacturing a sulfide-based solid electrolyte, wherein the step (S5) of cooling the product obtained through the above heat treatment is performed within 1 minute.

12. In paragraph 1, The above sulfide-based solid electrolyte is a method for manufacturing a sulfide-based solid electrolyte having a glass-ceramic structure.

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