Sulfide-based glass-ceramic solid electrolyte

Abstract

The present invention relates to a sulfide-based glass-ceramic solid electrolyte including a lithium element (Li), a phosphorus element (P), a sulfur element (S), and a halogen element (Ha), and substituted with a first compound including an oxygen element (O).

Description

Sulfide-based glass ceramics solid electrolyte

[0001] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0134286 filed on October 2, 2024, and all contents disclosed in the literature of said Korean patent application are incorporated herein as part of the specification.

[0002] The present invention relates to a sulfide-based glass ceramic solid electrolyte.

[0003] With recent reports regarding the explosion risks of batteries using liquid electrolytes, the development of all-solid-state rechargeable batteries is actively underway. An all-solid-state rechargeable battery is a battery composed entirely of solid materials, specifically referring to a battery that uses a solid electrolyte. These batteries are safe as they eliminate the risk of explosions caused by electrolyte leakage, and they offer the advantage of being easy to manufacture in thin form.

[0004] However, solid electrolytes have lower ionic conductivity compared to liquid electrolytes, and they have problems such as reduced ionic conductivity performance due to resistance occurring at the interfaces between solid electrolyte particles or at the interfaces with other solid particles, such as the cathode active material within the battery.

[0005] Solid electrolytes are classified into oxide, polymer, and sulfide types. Research on sulfide solid electrolytes is actively underway because they possess relatively higher ionic conductivity and stability over a wide voltage range compared to oxide and polymer solid electrolytes. However, synthesizing sulfide crystalline solid electrolytes requires a heat treatment process at high temperatures for crystallization.

[0006] In particular, glass ceramic solid electrolytes can maintain glass properties at around 10% by increasing the number of nuclei (nucleation) through methods such as slowing down nucleation growth as much as possible and increasing defects, thereby generating a large amount of high ion-conducting phases, so that they can have high ion conductivity while simultaneously possessing the physical properties of glass.

[0007] However, when applying a general heat treatment method to heat-treat glass ceramic solid electrolytes, the synthesis temperature is relatively very low, but the time required for synthesis is significantly longer than that for crystalline solid electrolytes. Since the time required for synthesis is long, nucleation occurs during the heat treatment time rather than nucleation, so the mass production of glass ceramic solid electrolytes, which have excellent mechanical properties and a much wider variety of compositional combinations, is not improved, and there is a limitation that commercialization is difficult compared to crystalline solid electrolytes.

[0008] In addition, when sulfide-based glass-ceramics solid electrolytes are heat-treated at high temperatures above 300°C, sulfur volatilization occurs, causing a deficiency of sulfur within the structure, which can lead to problems such as structural instability and a decrease in ionic conductivity. Furthermore, the volatilized sulfur can be adsorbed onto the surroundings, causing contamination of equipment, and can also pose safety risks to workers due to strong odors.

[0009] The problem that the present invention aims to solve is to provide a sulfide-based glass ceramic solid electrolyte that not only improves atmospheric stability but also minimizes the reduction in ion conductivity.

[0010] According to one aspect of the present invention, a sulfide-based glass-ceramics solid electrolyte is provided, comprising a lithium element (Li), a phosphorus element (P), a sulfur element (S), and a halogen element (Ha), and substituted with a first compound comprising an oxygen element (O).

[0011] According to one embodiment of the present invention, the sulfide-based glass-ceramics solid electrolyte is prepared by a precursor comprising phosphorus sulfide and the first compound, wherein the content of the first compound relative to the total of the phosphorus sulfide and the first compound in the precursor is 5 to 30 mol%, thereby providing a sulfide-based glass-ceramics solid electrolyte.

[0012] According to one embodiment of the present invention, the first compound provides a sulfide-based glass-ceramics solid electrolyte comprising silica (SiO2), tin dioxide (SnO2), boron trioxide (B2O3), phosphate (P2O5) or phosphorus sulfide (P2S5).

[0013] According to one embodiment of the present invention, a sulfide-based glass-ceramics solid electrolyte is provided, further substituted with a second compound containing a fluorine element (F).

[0014] According to one embodiment of the present invention, the sulfide-based glass-ceramics solid electrolyte is prepared by a precursor comprising an alkali metal halide selected from one or more of lithium bromide (LiBr) and lithium iodide (LiI) and a second compound, wherein the content of the second compound relative to the total of the alkali metal halide selected from lithium bromide (LiBr) and lithium iodide (LiI) and the second compound in the precursor is 5 to 15 mol%.

[0015] According to one embodiment of the present invention, a sulfide-based glass-ceramics solid electrolyte is provided in which peaks exist at diffraction angles (2θ) of 20.0±0.2°, 23.5±0.2°, 28.7±0.2° and 29.3±0.2° in the X-ray diffraction (XRD) analysis graph of the sulfide-based glass-ceramics solid electrolyte.

[0016] According to one embodiment of the present invention, a sulfide-based glass-ceramics solid electrolyte is provided in which no peaks exist at diffraction angles (2θ) of 17.6±0.5°, 18.2±0.5°, and 25.9±0.5° in the X-ray diffraction (XRD) analysis graph of the sulfide-based glass-ceramics solid electrolyte.

[0017] According to one embodiment of the present invention, a sulfide-based glass-ceramics solid electrolyte is provided in which the peak corresponding to the diffraction angle (2θ) of 20.0±0.2° in the X-ray diffraction (XRD) analysis graph of the sulfide-based glass-ceramics solid electrolyte is the highest.

[0018] A sulfide-based glass ceramic solid electrolyte according to one embodiment of the present invention can not only improve atmospheric stability but also minimize the decrease in ion conductivity by expressing a high ion-conducting phase.

[0019] FIG. 1 is a flowchart illustrating an example of a method for manufacturing a sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention.

[0020] FIG. 2 is a flowchart showing another example of a method for manufacturing a sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention.

[0021] FIG. 3 is a flowchart showing another example of a method for manufacturing a sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention.

[0022] Figures 4 and 5 are graphs showing the XRD results of the intermediate product according to Evaluation Example 1.

[0023] Figure 6 is a graph showing the XRD results of the sulfide-based glass-ceramics solid electrolyte according to Evaluation Example 2.

[0024] Figures 7 and 8 are graphs showing the XRD results of the sulfide-based glass-ceramics solid electrolyte according to Evaluation Example 3.

[0025] The present invention is capable of various modifications and may have various embodiments; specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention, and the methods for achieving them, will become clear by referring to the embodiments described below in detail together with the drawings. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various forms.

[0026] In the following embodiments, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component.

[0027] In the following examples, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0028] In the following embodiments, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added.

[0029] In the following embodiments, when a part such as a film, region, or component is described as being on or above another part, it includes not only cases where it is directly on top of another part, but also cases where another film, region, or component is interposed in between.

[0030] In this specification, "substitution" may mean not only replacing some elements of a compound with new elements, but also that the substituted element becomes a component of the crystalline phase of the compound.

[0031] In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, so the present invention is not necessarily limited to what is illustrated.

[0032] 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 reference numerals.

[0033]

[0034] Sulfide-based glass ceramics solid electrolyte

[0035] A sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention may be substituted with a first compound comprising a lithium element (Li), a phosphorus element (P), a sulfur element (S), and a halogen element (Ha), and an oxygen element (O).

[0036] Sulfide-based glass-ceramics solid electrolytes can be manufactured using a network former that can produce glass on its own and a network modifier that can produce glass by mixing with the network former in a certain ratio. The network former is a component that forms the three-dimensional basic framework (network) of glass or amorphous material, and may be, for example, silica (SiO2), tin dioxide (SnO2), boron trioxide (B2O3), phosphate (P2O5), or phosphorus sulfide (P2S5), and preferably may be phosphate (P2O5). In addition, the network modifier is a component that breaks some bonds and modifies or relaxes the network within an already formed network structure, and may be an alkali metal oxide (e.g., Li2O, Na2O), an alkaline earth metal oxide (e.g., CaO, MgO), an alkali metal nitride (e.g., Li3N), an alkali metal sulfide (e.g., Li2S), or an alkali metal halide (e.g., LiF, NaCl, KBr, etc.), and preferably may be lithium fluoride (LiF).

[0037] In a sulfide-based glass-ceramic solid electrolyte according to one embodiment of the present invention, by introducing a first compound, which is a network former containing an oxygen element (O), to substitute the oxygen element (S) with the oxygen element (O), the bonding is strengthened by the oxygen element (O), and thus atmospheric stability can be improved. Furthermore, the sulfide-based glass-ceramic solid electrolyte of the present invention can achieve relatively high ionic conductivity by minimizing the reduction in ionic conductivity through satisfying a composition range sufficient to form a high ionic conductive phase.

[0038] The first compound containing the oxygen element (O) may include silica (SiO2), tin dioxide (SnO2), boron trioxide (B2O3), phosphate (P2O5) or phosphorus sulfide (P2S5), and preferably may include phosphate (P2O5).

[0039] A sulfide-based glass-ceramics solid electrolyte is prepared by a precursor comprising phosphorus sulfide and the first compound, wherein the content of the first compound relative to the total phosphorus sulfide and the first compound in the precursor may be 5 to 30 mol%.

[0040] Specifically, the lower limit of the content of the first substituted compound may be 5, 6, 7, 8, 9, or 10 mol%, and the upper limit of the content of the first substituted compound may be 30, 25, 20, or 15 mol%. If the content of the first substituted compound is below the above range, it means that the substitution of oxygen elements (O) is too small, so it is difficult to expect effects from PO bonds such as enhanced atmospheric stability. If the first substituted compound exceeds the above range, it means that the substitution of oxygen elements (O) is too large, so the number of strong PO bonds increases, hindering the movement of lithium ions and causing a sharp decrease in ionic conductivity. If the first substituted compound satisfies the above range, the movement of lithium ions is improved so that the decrease in ionic conductivity is not significant, thereby ensuring electrochemical stability, and atmospheric stability can be improved by partially generating PS bonds into PO bonds in advance.

[0041] A sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention may be further substituted with a second compound containing a fluorine element (F). By introducing a second compound, which is a network modifier containing a fluorine element (F), to substitute the fluorine element (F), thermodynamic stability is improved, thereby reducing the synthesis temperature of the sulfide-based glass-ceramics solid electrolyte, and fluoride ions (F - ) has strong bonding strength, which can reduce compressive density and widen the electrochemical stability window.

[0042] As a specific example, some of the iodine element (I) and bromine element (Br) can be replaced with the fluorine element (F). In this case, a second compound (e.g., LiF) which is a network modifier containing the fluorine element (F) can be used. Since lithium fluoride (LiF) has a wider oxidation / reduction potential range than other alkali metal halides such as LiBr and LiI, it can be partially used to form a sulfide-based solid electrolyte, thereby expanding the electrochemical stability range of the sulfide-based glass ceramic solid electrolyte.

[0043] A sulfide-based glass-ceramics solid electrolyte is prepared by a precursor comprising an alkali metal halide selected from one or more of lithium bromide (LiBr) and lithium iodide (LiI) and the second compound, wherein in the precursor, the content of the second compound relative to the total of the alkali metal halide selected from lithium bromide (LiBr) and lithium iodide (LiI) and the second compound may be 5 to 15 mol%. Specifically, the lower limit of the content of the substituted second compound may be 5, 6, 7, 8, 9, or 10 mol%, and the upper limit of the content of the substituted second compound may be 15, 14, 13, 12, or 11 mol%. If the content of the substituted second compound is below the above range, it implies that the substitution of the fluorine element (F) is too low, which may result in a high compressive density; if the content of the substituted second compound exceeds the above range, it implies that the substitution of the fluorine element (F) is too high, which may make vitrification difficult during the synthesis step of the sulfide-based glass-ceramics solid electrolyte and cause a sharp decrease in ionic conductivity. If the content of the substituted second compound satisfies the above range, the synthesis temperature can be reduced, and the fluoride ion (F - ) has strong bonding strength, which can reduce compressive density and widen the electrochemical stability window.

[0044] A sulfide-based glass-ceramic solid electrolyte according to one embodiment of the present invention has some mechanical powder characteristics of glass, so it has a lower elastic modulus than a sulfide-based crystalline solid electrolyte, resulting in excellent moldability and a relatively lower synthesis temperature. Additionally, although the sulfide-based glass-ceramic solid electrolyte has lower ionic conductivity than a crystalline solid electrolyte, the ionic conductivity can be improved if a high ionic conductivity phase is expressed.

[0045] In the sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention, peaks may exist at diffraction angles (2θ) of 20.0±0.2°, 23.5±0.2°, 28.7±0.2°, and 29.3±0.2° in the X-ray diffraction (XRD) analysis graph of the sulfide-based glass-ceramics solid electrolyte. Specifically, the peak corresponding to the diffraction angle (2θ) of 20.0±0.2° in the X-ray diffraction (XRD) analysis graph of the sulfide-based glass-ceramics solid electrolyte may be the highest. These peaks are high ion-conducting phases, indicating that the sulfide-based glass-ceramics solid electrolyte has high ion conductivity even though it is glass-ceramics.

[0046] In addition, in the X-ray diffraction (XRD) analysis graph of the sulfide-based glass-ceramic solid electrolyte according to one embodiment of the present invention, peaks may not exist at diffraction angles (2θ) of 17.6±0.5°, 18.2±0.5°, and 25.9±0.5°. These peaks are related to impurities and are low ionic conductive phases, so the absence of these peaks indicates that the sulfide-based glass-ceramic solid electrolyte has high ionic conductivity even though it is glass-ceramic.

[0047]

[0048] Method for manufacturing sulfide-based glass ceramic solid electrolyte

[0049] FIG. 1 is a flowchart showing one example of a method for manufacturing a sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention, FIG. 2 is a flowchart showing another example of a method for manufacturing a sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention, and FIG. 3 is a flowchart showing yet another example of a method for manufacturing a sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention.

[0050] Referring to FIG. 1, a method for manufacturing a sulfide-based glass-ceramics solid electrolyte may include the steps of: preparing a precursor solution by introducing a precursor containing an alkali metal sulfide, a phosphorus sulfide, a first compound containing an oxygen element (O), and an alkali metal halide into a solvent (S1); producing an intermediate product by first milling the precursor solution (S2); controlling the particle size of the intermediate product by second milling after adding a dispersant following the step (S2) (S3); drying the particle size-controlled intermediate product after the step (S3) (S4); and heat-treating the dried intermediate product (S5).

[0051] In the step (S1) of preparing a precursor solution, the precursor may include an alkali metal sulfide, a phosphorus sulfide, a first compound, and an alkali metal halide. The alkali metal sulfide is not particularly limited as long as it is used in the industry for the manufacture of sulfide-based solid electrolytes. For example, the alkali metal sulfide may be lithium sulfide (Li2S), sodium sulfide (Na2S), or potassium sulfide (K2S), and preferably lithium sulfide (Li2S).

[0052] Phosphorus sulfide is not particularly limited as long as it is used in the industry for the manufacture of sulfide-based solid electrolytes. For example, the phosphorus sulfide may be phosphorus pentasulfide (P2S5).

[0053] Lithium sulfide (Li2S)-phosphorus pentasulfide (P2S5)-based lithium secondary battery solid electrolytes have higher ionic conductivity compared to oxide-based solid electrolytes, and accordingly, the starting material needs to contain at least 60 mol% of lithium sulfide (Li2S). However, if the content of lithium sulfide (Li2S) is excessive, the amount of lithium sulfide (Li2S) remaining in the final glass ceramics increases, leading to increased reactivity with moisture and the active material interface, and lower 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 ceramics.

[0054] The first compound is not particularly limited as long as it is used in the industry for the manufacture of sulfide-based solid electrolytes. For example, the first compound may be silica (SiO2), tin dioxide (SnO2), boron trioxide (B2O3), phosphate (P2O5), or phosphorus sulfide (P2S5).

[0055] In the above precursor, the content of the first compound relative to the total of the phosphorus sulfide and the first compound may be 5 to 30 mol%.

[0056] Specifically, the lower limit of the content of the first substituted compound may be 5, 6, 7, 8, 9, or 10 mol%, and the upper limit of the content of the first substituted compound may be 30, 25, 20, or 15 mol%. If the content of the first substituted compound is below the above range, it means that the substitution of oxygen elements (O) is too small, so it is difficult to expect effects from PO bonds such as enhanced atmospheric stability. If the first substituted compound exceeds the above range, it means that the substitution of oxygen elements (O) is too large, so the number of strong PO bonds increases, hindering the movement of lithium ions and causing a sharp decrease in ionic conductivity. If the first substituted compound satisfies the above range, the movement of lithium ions is improved so that the decrease in ionic conductivity is not significant, thereby ensuring electrochemical stability, and atmospheric stability can be improved by partially generating PS bonds into PO bonds in advance.

[0057] Alkali metal halides are not particularly limited as long as they are used in the industry for the manufacture of sulfide-based solid electrolytes. For example, lithium bromide (LiBr) and lithium iodide (LiI) can be used together.

[0058] The precursor may further include a second compound containing a fluorine element (F). By introducing the second compound, which is a network modifier containing a fluorine element (F), to substitute the fluorine element (F), thermodynamic stability is improved, which can reduce the synthesis temperature of the sulfide-based glass-ceramics solid electrolyte, and fluoride ions (F - ) has strong bonding strength, which can reduce compressive density and widen the electrochemical stability window.

[0059] In the above precursor, the content of the second compound relative to the total of the alkali metal halide selected from lithium bromide (LiBr) and lithium iodide (LiI) and the second compound may be 5 to 15 mol%. Specifically, the lower limit of the content of the substituted second compound may be 5, 6, 7, 8, 9, or 10 mol%, and the upper limit of the content of the substituted second compound may be 15, 14, 13, 12, or 11 mol%. If the content of the substituted second compound is less than the above range, it means that the substitution of the fluorine element (F) is too small, so the compressive density may be high; and if the content of the substituted second compound exceeds the above range, it means that the substitution of the fluorine element (F) is too large, so vitrification is difficult during the synthesis step of the sulfide-based solid electrolyte, and the ionic conductivity may decrease rapidly. If the content of the substituted second compound satisfies the above range, the synthesis temperature can be reduced, and the fluoride ion (F - ) has strong bonding strength, which can reduce compressive density and widen the electrochemical stability window.

[0060] A precursor solution can be prepared by dissolving the above precursors in a nonpolar solvent. The solvent is not particularly limited as long as it is used in the industry for the manufacture of sulfide-based solid electrolytes. For example, the solvent may be one or more selected from the group consisting of heptane, hexane, cyclohexane, and toluene.

[0061] The first milling of step (S2) is a step for synthesizing an intermediate product, and the second milling of step (S3) may be a step for controlling the particle size of the intermediate product.

[0062] The first milling is a synthesis and grinding process that creates PS4 bonds with high energy. For example, the first milling can be performed for 24 hours at high energy of 350 to 400 RPM based on the Fritsch P5 mechanical milling machine, but is not limited to this method if the intermediate product is synthesized and ground.

[0063] The second milling is a process of controlling the particle size of an intermediate product by milling at low energy with a dispersant. For example, the second milling can be performed by adding a dispersant, which is a solvent, and then milling at low energy of 120 RPM for 12 hours, but this is not limited to methods that properly control the particle size.

[0064] The second milling process is performed using a single device, rather than separately recovering or drying the intermediate product formed from the first milling and then proceeding with the second milling. In other words, by performing the second milling immediately after the first milling is completed, a continuous particle size control process can be carried out, thereby optimizing the process steps.

[0065] A method for manufacturing a sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention allows intermediate product particles to be broken by a second milling to control particle size, and at the same time, by continuing the second milling without undergoing a drying step, the surface is maintained in a state where it is not exposed to the atmosphere by the solvent and amorphous particles are maintained evenly, thereby maintaining an atmosphere conducive to nucleation.

[0066] The first milling of step (S2) and the second milling of step (S3) can each be performed using balls by a planetary ball milling method, an attrition milling method, a SPEX milling method, a ball milling method, or a bead milling method. The intermediate product generated at this time may be a sulfide-based amorphous solid electrolyte.

[0067] Each of the first milling in step (S2) and the second milling in step (S3) can be performed for 5 to 40 hours. Specifically, the lower limit of the milling time may be 5 hours, 10 hours, 15 hours, or 20 hours, and the upper limit of the milling time may be 40 hours, 35 hours, 30 hours, or 25 hours. If the milling time is less than 5 hours, mixing is not properly performed, so an amorphous solid electrolyte with a constant composition cannot be produced, and if the milling time exceeds 40 hours, there is a risk of exceeding 170°C, which is the temperature at which the degree of crystallization increases locally; therefore, if the milling time satisfies the above range, a sulfide-based amorphous solid electrolyte satisfying a constant composition and uniformity can be produced.

[0068] The balls used during the first milling and second milling transfer impact energy to the precursor during the synthesis and particle size control of the intermediate product, and the mass and size of the balls may affect the synthesis and particle size control. For example, the balls may include one or more selected from the group consisting of glass, alumina, zirconia, and combinations thereof, and preferably, zirconia balls may be used.

[0069] In the first milling of step (S2) and the second milling of step (S3), milling can be performed by adjusting the mass ratio of the precursor to the ball to 1:10 to 1:20. If the mass ratio of the precursor to the ball exceeds the above range, it is difficult to mix the precursor, making it difficult to manufacture a sulfide-based amorphous solid electrolyte that satisfies uniformity. If the mass ratio of the precursor to the ball is below the above range, it may be difficult to grind the precursor. Therefore, when the mass ratio of the precursor to the ball satisfies the above range, sufficient mixing and grinding of the precursor can be achieved.

[0070] The diameter of the ball used in step (S2) may be 0.5 mm to 5 mm. The diameter (size) of the ball refers to the average particle size based on volume average. 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 ball falls outside the above range, sufficient energy is not transferred to the precursor, making synthesis difficult. Therefore, if the diameter (size) of the ball satisfies the above range, a large amount of energy is applied to the precursor, thereby reducing crystallinity and enabling the synthesis and grinding of the sulfide-based solid electrolyte.

[0071] The diameter of the ball used in step (S3) may be 0.1 mm to 1 mm. Specifically, the lower limit of the ball diameter may be 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, or 0.5 mm, and the upper limit of the ball diameter may be 1 mm, 0.9 mm, 0.8 mm, 0.7 mm, or 0.6 mm. If the diameter (size) of the ball exceeds the above range, the average particle size of the intermediate product may be formed too large, and if the diameter (size) of the ball is below the above range, energy is not sufficiently applied to the intermediate product, making it difficult for sufficient disintegration and grinding to occur. Therefore, if the diameter (size) of the ball satisfies the above range, a sulfide-based solid electrolyte having an appropriate particle size can be manufactured.

[0072] The average particle size controlled by step (S3) may be 0.1㎛ to 5㎛. The particle size can be controlled by adjusting the size of the zirconia ball used and the operating time. Specifically, the lower limit of the average particle size controlled by step (S3) may be 0.1㎛, 0.3㎛, 0.4㎛, 0.7㎛, 0.9㎛, or 1㎛, and the upper limit of the average particle size controlled by step (S3) may be 5㎛, 4.5㎛, 4㎛, 3.5㎛, 3㎛, ​​2.5㎛, 2㎛, or 1.5㎛.

[0073] If the average particle size controlled by step (S3) exceeds the above range, it may be difficult to achieve a state of maximum density in the battery manufacturing process and difficult to produce a uniform thickness. If the average particle size controlled by step (S3) is below the above range, it may be difficult to handle during the process and difficult to form a contact interface with the active material in the electrode layer due to the high specific surface area. Therefore, if the average particle size controlled by step (S3) satisfies the above range, the reduction in ion conductivity can be minimized by exhibiting a high ion-conducting phase even when the heat treatment temperature is lowered compared to a sulfide-based solid electrolyte that has not undergone a particle size control process.

[0074] The average particle size controlled by step (S3) can be measured by a statistical image analysis method using scanning electron microscope (SEM) analysis, but is not limited to this as long as the size can be measured.

[0075] A dispersant may be introduced during the particle size control step (S3). The dispersant is introduced during the second milling process and adsorbs to the particle surface during the second milling to prevent reactions with external substances or aggregation between particles, prevents unnecessary reactions caused by frictional heat between precursors, and contributes to fine particle formation. In this case, the grinding efficiency increases, and a uniform particle size distribution can be obtained. Additionally, since the dispersant is not introduced into the precursor solution from the beginning, it has the advantage of not interfering with the synthesis of the intermediate product. If the dispersant is introduced from the beginning, energy may not be sufficiently applied to the precursor, making it difficult to achieve sufficient synthesis, and because the particle size is not properly reduced, it may be difficult to proceed with particle size control simultaneously with the synthesis of the intermediate product.

[0076] The dispersant may be one or more selected from the group consisting of carbonate-based solvents, ether-based solvents, nitrile-based solvents, phosphate-based solvents, and sulfone-based solvents, but is not particularly limited as long as it is used in the industry for the manufacture of sulfide-based glass-ceramics solid electrolytes. For example, as an ether-based solvent, the dispersant may be one or more selected from the group consisting of dibutyl ether (DBE), diglyme, tetraglyme, dimethoxyethane (DME), and combinations thereof. The dispersant may be an aliphatic compound.

[0077] The mass ratio of the solvent and the dispersant may be 75:1 to 150:1. Specifically, the lower limit of the mass ratio of the solvent and the dispersant may be 75:1, 80:1, 85:1, 90:1, or 95:1, and the upper limit of the mass ratio of the solvent and the dispersant may be 150:1, 145:1, 140:1, 135:1, 130:1, or 125:1.

[0078] If the mass ratio of the solvent and the dispersant exceeds the above range, the concentration of the dispersant is too low, which causes energy to be dispersed and results in the material receiving too little energy during synthesis, potentially leading to a decrease in productivity.

[0079] If the mass ratio of the solvent and the dispersant is below the above range, the concentration of the dispersant is too high, so the frictional energy (shear force) by the ball is not properly applied and the frictional heat increases unnecessarily, making synthesis difficult and potentially causing the particle size to become unnecessarily large.

[0080] When the mass ratio of the solvent and the dispersant satisfies the above range, a uniform particle size distribution with an appropriate particle size distribution can be obtained.

[0081] Referring to FIG. 2, a method for manufacturing a sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention may further include a step (S2′) of drying an intermediate product before step (S3), and step (S2′) may be performed at 60°C to 100°C. In this case, it may be difficult to achieve a continuous particle size control process because the second milling cannot be performed immediately after the first milling is finished.

[0082] In addition, when undergoing the drying process (S2′), the surface of the intermediate product is dried, and the amorphous state is evenly dispersed on the particle surface. However, after drying, the glassy state is removed by the second milling step, resulting in uneven nucleation and localized energy concentration, which causes nucleation growth and may lower the expression of the high ion-conducting phase.

[0083] After step (S3), step (S4) of drying the particle size-controlled intermediate product may correspond to a solvent removal process that evaporates the solvent. The drying step may be carried out at 60°C to 100°C for a predetermined time. For example, it may be dried by a spray drying device in an inert atmosphere or by vacuum drying.

[0084] The step (S5) of heat-treating the dried intermediate product can be performed for 30 to 50 seconds. This includes the time required to raise the temperature from room temperature to the heat treatment temperature (T) and the time to maintain the temperature at the heat treatment temperature (T). If the temperature raising time and the maintenance time satisfy the above range, nucleation growth can be prevented to express an ion-conducting phase, thereby improving ion conductivity.

[0085] For example, the dried intermediate product can be heated to the heat treatment temperature (T) by performing a heat treatment at a heating rate of 6.6℃ / sec or higher.

[0086] Referring to FIG. 3, a method for manufacturing a sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention may further include a step (S6) of cooling a product obtained by heat treatment, and the cooling may proceed within 1 minute and be cooled to room temperature (25°C). Since the heat treatment equipment does not contain a refractory agent and includes a tube containing water, the sample can be removed and cooled immediately after the heat treatment step is finished. Accordingly, the overall process time can be shortened. At this time, the product may be a sulfide-based glass-ceramics solid electrolyte.

[0087] As described above, the sulfide-based solid electrolyte produced by the method for producing a sulfide-based solid electrolyte according to one embodiment of the present invention can control nucleation growth through thermal energy directly applied to the precursor, and thus can be effective for producing glass ceramics.

[0088] If the heat treatment step takes a long time, the manufactured sulfide-based solid electrolyte may lose its ionic conductivity and glass properties as crystal nuclei continue to grow during the heat treatment process. However, the sulfide-based solid electrolyte manufactured according to one embodiment of the present invention has a very short heat treatment time, which prevents the nucleation of the sulfide-based solid electrolyte and allows for the expression of a large amount of high ionic conductivity phase, thereby minimizing the reduction in ionic conductivity.

[0089] In addition, by significantly shortening the heat treatment time, sulfur volatilization can be minimized, allowing for the production of a structurally stable sulfide-based solid electrolyte. Furthermore, by directly transferring thermal energy to the mixture, heat loss to the surroundings is prevented, enabling appropriate control of the heat treatment temperature. Additionally, cooling occurs immediately upon stopping the transfer of thermal energy, allowing for rapid cooling to a low ambient temperature, thereby shortening the cooling time during the cooling stage.

[0090] Accordingly, the sulfide-based solid electrolyte prepared according to one embodiment of the present invention can be glass ceramics even if the heat treatment temperature is performed relatively low by carrying out a particle size control process before the heat treatment step.

[0091]

[0092] All-solid-state battery

[0093] The all-solid-state battery may include a negative electrode, a positive electrode, and a sulfide-based solid electrolyte layer disposed between the negative electrode and the positive electrode.

[0094] At this time, a sulfide-based solid electrolyte layer may be used as a sulfide-based glass-ceramics solid electrolyte layer according to one embodiment of the present invention.

[0095] The cathode may include a cathode current collector and a cathode active material layer formed on one side of the cathode current collector.

[0096] The negative electrode active material that may be included in the negative electrode active material layer may include one or more 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).

[0097] 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, as well as the bonding to the negative electrode current collector. The negative electrode binder may include, for example, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0098] A conductive material that may be included in the negative electrode active material layer can be used to further improve the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and may include, for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, copper, nickel, or silver powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, carbon nanotubes, etc.

[0099] The negative electrode current collector may be made of a material that is conductive and does not react with lithium without causing chemical changes in the battery, and may include various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric with fine irregularities formed on its surface. As an example, the negative electrode current collector may include one or more selected from the group consisting of copper (Cu), stainless steel (SS), titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni).

[0100] The positive electrode may include a positive current collector and a positive active material layer formed on one side of the positive current collector.

[0101] The positive active material that may be included in the positive active material layer may include one or more 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 to these, and any material used as a positive active material in the relevant technical field may be used.

[0102] A binder that may be included in the positive active material layer can improve the bonding between the positive active material and the conductive material, as well as the bonding to the positive current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0103] A conductive material that may be included in the positive electrode active material layer can be used to further enhance the conductivity of the positive electrode active material. Such conductive materials are not particularly limited as long as they are conductive without causing chemical changes in the battery, and examples include graphite such as natural graphite or synthetic graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, copper, nickel, or silver powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, carbon nanotubes, etc. may be used.

[0104] The positive current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc. Additionally, the positive current collector may form fine irregularities on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, nonwoven fabrics, etc.

[0105] The above all-solid-state battery can be manufactured by the steps of: manufacturing a sulfide-based glass-ceramics solid electrolyte according to one embodiment of the present invention; and manufacturing a cell by stacking a positive electrode, the solid electrolyte, and a negative electrode.

[0106]

[0107] Hereinafter, examples are presented to aid in understanding the present invention; however, the above examples are merely illustrative of the description and are not to be interpreted as limiting the scope of the present application to the examples described below. It is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the description, and that such variations and modifications fall within the scope of the appended claims.

[0108] Examples and Comparative Examples: Preparation of Solid Electrolytes

[0109] A total of 40g of precursors, mixed with lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), phosphorus pentoxide (P2O5), lithium bromide (LiBr), lithium iodide (LiI), and lithium fluoride (LiF) in the molar ratios shown in Table 1 below, were weighed and subjected to high-energy mechanical milling for 40 hours using a Fritsch P5 model with 400g of 1mm zirconia balls and 250cc of heptane, a nonpolar solvent.

[0110] Immediately after the first milling, without drying, a dispersant (dibutyl ether) was added to the container as is, and the second milling was performed for 12 hours at 120 rpm using a high-energy milling machine (Fritsch, P5 line) to produce an intermediate product with a particle size of 2 µm. At this time, the ratio of heptane solvent to dispersant (dibutyl ether) was 125:1.

[0111] After the intermediate product prepared after the second milling, vacuum drying was performed at 80°C to obtain the intermediate product, and then the zirconia balls were removed through a sieving machine to prepare the intermediate product.

[0112] Subsequently, the prepared intermediate was heated from room temperature to 220°C at a rate of 6.6°C per second, maintained at 220°C for 10 seconds in an inert atmosphere, and then cooled for 60 seconds to produce a sulfide-based glass-ceramics solid electrolyte. At this time, the total time required for heat treatment was 44 seconds, and the time required for cooling after heating was 60 seconds. That is, the total time required for heat treatment and cooling was 104 seconds.

[0113]

[0114] 6Li2S-(2-x)P2S5-xP2O5-(1-y)LiBr-(1-z)LiI-(y+z)LiFxyz Example 10.100 Example 20.200 Example 30.300 Example 40.10.050 Example 50.100.05 Comparative Example 000

[0115]

[0116] Evaluation Example 1: XRD measurement of intermediate products

[0117] To confirm the crystallinity of the dried intermediate products in Examples 1 to 5, XRD was measured at an angle of 10 to 40 degrees, and a PEEK dome holder was used for measurement considering the reactivity in the atmosphere. The XRD results are shown in Figures 4 and 5.

[0118] Figures 4 and 5 are graphs showing the XRD results of the intermediate product according to Evaluation Example 1.

[0119] Referring to FIG. 4, no peaks are observed in the XRD results of the dried intermediate products in Examples 1 to 3. Through this, it can be confirmed that even if P2S5 is substituted with P2O5 in the above amounts, no peaks for impurities such as raw materials, Li3PS4, Li3PO4, etc. are observed, and that amorphous (vitrification) is well achieved.

[0120] Referring to FIG. 5, no peaks are observed in the XRD results of the dried intermediate products in Examples 4 and 5. Through this, it can be confirmed that even if P2S5 is substituted with P2O5 in the above amounts and LiBr or LiI is substituted with LiF in the above amounts, no peaks for impurities such as raw materials, Li3PS4, Li3PO4, etc. are observed, and that amorphous (vitrification) is well achieved.

[0121]

[0122] Evaluation Example 2: XRD Measurement of Sulfide-Based Glass Ceramic Solid Electrolyte

[0123] To confirm the crystallinity of the sulfide-based glass-ceramics solid electrolytes prepared in Examples 1 and 5, XRD was measured at an angle of 10 to 40 degrees, and a PEEK dome holder was used for measurement considering the reactivity in the atmosphere. The XRD results are shown in Fig. 6.

[0124] Figure 6 is a graph showing the XRD results of the sulfide-based glass-ceramics solid electrolyte according to Evaluation Example 2.

[0125] Referring to FIG. 6, it can be confirmed that the sulfide-based glass-ceramics solid electrolyte prepared according to Examples 1 and 5 forms a highly ion-conducting phase, based on the observation of peaks at diffraction angles (2θ) of 20.0±0.2°, 23.5±0.2°, 28.7±0.2°, and 29.3±0.2° in the X-ray diffraction (XRD) analysis graph. Additionally, it can be confirmed that the most stable phase, lithium tetrasulfide (Li3PS4), is not formed, based on the observation that no peaks are observed at diffraction angles (2θ) of 17.6±0.5°, 18.2±0.5°, and 25.9±0.5° in the X-ray diffraction (XRD) analysis graph.

[0126]

[0127] Evaluation Example 3: XRD measurement of sulfide-based glass ceramic solid electrolyte

[0128] XRD was measured at an angle of 10 to 40 degrees to confirm the crystallinity of the sulfide-based glass-ceramics solid electrolytes prepared in Examples 1 and 5 according to the temperature range, and a PEEK dome holder was used for measurement considering the reactivity in the atmosphere. The XRD results are shown in Figures 7 and 8.

[0129] Figures 7 and 8 are graphs showing the XRD results of a sulfide-based glass-ceramics solid electrolyte prepared according to Evaluation Example 3.

[0130] Referring to FIG. 7, the sulfide-based glass-ceramics solid electrolyte according to Example 1 exhibited peaks of the high ionic conductivity phase (20.0±0.2°, 23.5±0.2°, 28.7±0.2°, and 29.3±0.2°) at a synthesis temperature of 250°C or higher as shown in FIG. 7; however, the sulfide-based glass-ceramics solid electrolyte according to Example 5 exhibited peaks of the high ionic conductivity phase (20.0±0.2°, 23.5±0.2°, 28.7±0.2°, and 29.3±0.2°) starting from 220°C or higher as shown in FIG. 8. Therefore, substituting the first and second compounds allows the synthesis temperature of the sulfide-based glass-ceramics solid electrolyte to be lowered, resulting in a stable solution even in low-temperature processes. Glass ceramics can be formed.

[0131]

[0132] Evaluation Example 4: Measurement of ionic conductivity, compressive density, and atmospheric stability evaluation

[0133] After confirming the crystallinity of the sulfide-based glass-ceramics solid electrolytes prepared according to Examples 1 to 5 and Comparative Examples, the specimens were molded at a pressure of 500 MPa in a pressurized cell in the form of a mold with a diameter of 13 mm and maintained at a temperature of 30°C for more than 3 hours. The lithium ion conductivity (mS / cm) was measured, and the thickness and weight were measured to determine the compressive density. The ion conductivity and compressive density are shown in Table 2 below.

[0134] In addition, to evaluate atmospheric stability, the specimen was left for 1 hour in a dew point environment of -30℃ and then recovered. The specimen was then measured using electrochemical impedance spectroscopy (EIS), and the results are shown in Table 2 below.

[0135]

[0136] Example 1 Example 5 Comparative Example Compressed Density 1.99 1.97 1.93 Ion Conductivity (Before Atmospheric Stability Evaluation) 4.30 4.21 6.02 Ion Conductivity (After Atmospheric Stability Evaluation) 3.98 3.91 2.50 Ion Conductivity Retention Rate 92.56% 92.87% 41.53%

[0137]

[0138] Referring to Table 2, the sulfide-based glass-ceramics solid electrolyte according to Example 1 has structural stability by substituting with a first compound containing an oxygen element (O), and since the ionic conductivity is maintained even after conducting an atmospheric stability evaluation, it can be confirmed that not only is atmospheric stability improved but the decrease in ionic conductivity is minimized.

[0139] In addition, the sulfide-based glass-ceramics solid electrolyte according to Example 5 maintains ionic conductivity even after an atmospheric stability evaluation is performed, even when additionally substituted with a second compound containing a fluorine element (F). Therefore, not only is atmospheric stability improved at low synthesis temperatures, but the decrease in ionic conductivity is minimized. Furthermore, by additionally substituting with a second compound containing a fluorine element (F), the compressive density of the sulfide-based glass-ceramics solid electrolyte can be reduced through strong bonding, thereby improving mechanical stability during the charge-discharge process.

[0140] In contrast, the sulfide-based glass-ceramics solid electrolyte according to the comparative example showed that when exposed to an atmosphere with a dew point of -30°C for 1 hour, the ionic conductivity decreased sharply to 2.5 mS / cm, exhibiting only 41.53% of the performance. This implies that high ionic conductivity solid electrolyte performance cannot be achieved unless a very restrictive atmosphere with a dew point of approximately -50°C is maintained during the secondary battery production process.

Claims

1. Contains lithium element (Li), phosphorus element (P), sulfur element (S), and halogen element (Ha), and A sulfide-based glass-ceramics solid electrolyte substituted with a first compound containing an oxygen element (O).

2. In Paragraph 1, The above sulfide-based glass-ceramics solid electrolyte is prepared by a precursor comprising phosphorus sulfide and the first compound, and A sulfide-based glass-ceramics solid electrolyte in which, in the above precursor, the content of the first compound relative to the total phosphorus sulfide and the first compound is 5 to 30 mol%.

3. In Paragraph 1, The first compound is a sulfide-based glass-ceramics solid electrolyte comprising silica (SiO2), tin dioxide (SnO2), boron trioxide (B2O3), phosphate (P2O5) or phosphorus sulfide (P2S5).

4. In Paragraph 1, A sulfide-based glass-ceramics solid electrolyte further substituted with a second compound containing a fluorine element (F).

5. In Paragraph 4, The above sulfide-based glass-ceramics solid electrolyte is prepared by a precursor comprising an alkali metal halide comprising one or more selected from lithium bromide (LiBr) and lithium iodide (LiI) and the second compound, and A sulfide-based glass-ceramics solid electrolyte, wherein, in the above precursor, the alkali metal halide selected from lithium bromide (LiBr) and lithium iodide (LiI) and the content of the second compound relative to the total of the second compound is 5 to 15 mol%.

6. In Paragraph 1, A sulfide-based glass-ceramics solid electrolyte having peaks at diffraction angles (2θ) of 20.0±0.2°, 23.5±0.2°, 28.7±0.2° and 29.3±0.2° in the X-ray diffraction (XRD) analysis graph of the above sulfide-based glass-ceramics solid electrolyte.

7. In Paragraph 6, A sulfide-based glass-ceramic solid electrolyte in which no peaks are present at diffraction angles (2θ) of 17.6±0.5°, 18.2±0.5°, and 25.9±0.5° in the X-ray diffraction (XRD) analysis graph of the above sulfide-based glass-ceramic solid electrolyte.

8. In Paragraph 6, A sulfide-based glass-ceramic solid electrolyte in which the peak corresponding to the diffraction angle (2θ) of 20.0±0.2° in the X-ray diffraction (XRD) analysis graph of the above sulfide-based glass-ceramic solid electrolyte is the highest.

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