Method for manufacturing sulfide-based solid electrolyte having core-shell structure, and solid electrolyte manufactured thereby

Abstract

The present invention relates to a method for manufacturing a sulfide-based solid electrolyte having a core-shell structure, and to a solid electrolyte manufactured thereby. More specifically, disclosed are a method for manufacturing a sulfide-based solid electrolyte having a core-shell structure, and to a solid electrolyte manufactured thereby, the method comprising the steps of: (1) introducing a sulfide-based first solid electrolyte, lithium metal, and a transfer catalyst into a polar aprotic solvent and allowing same to react to prepare a first dispersion solution in which the first solid electrolyte and lithium ion (Li+) transfer catalyst radicals are dispersed; (2) introducing sulfur (S) element and an M-S compound (wherein M is at least one selected from B, Al, Ga, In, Si, Ge, Sn, As, Sb, and Bi) into the first dispersion solution and allowing same to react to prepare a second dispersion solution in which first solid electrolyte particles, each having a second solid electrolyte comprising a Li-M-S compound bonded to a surface thereof, are dispersed; and (3) recovering a powder from the second dispersion solution and heat-treating the recovered powder to prepare a sulfide-based solid electrolyte having a core-shell structure in which a second solid electrolyte is bonded to the surface of first solid electrolyte particles.

Description

Method for manufacturing a core-shell structured sulfide-based solid electrolyte and a solid electrolyte manufactured thereby

[0001] The present invention relates to a method for manufacturing a core-shell structured sulfide-based solid electrolyte and a solid electrolyte manufactured thereby. Specifically, the invention relates to a method for manufacturing a core-shell structured sulfide-based solid electrolyte in which a second solid electrolyte shell, which is a Li-MS compound, is bonded to a first solid electrolyte core using a co-precipitation synthesis method.

[0002] All-solid-state lithium-ion batteries (ASSLB) use a solid electrolyte and are batteries with superior energy density and improved safety compared to lithium-ion batteries. ASSLBs, which use a thermally stable solid electrolyte (SE) instead of the liquid organic electrolyte of LIBs, have the advantage of reducing the risk of explosion and fire.

[0003] Sulfide-based solid electrolytes (SSEs) are receiving significant attention because they enable the realization of high-rate or high-loading electrodes due to their high lithium ion conductivity and high lithium transition number at room temperature, and LGPS type (e.g., Li 10 GeP2S 12 Solid electrolytes having a crystal structure of ) or azirodite (e.g., Li6PS5Cl) have recently attracted commercial attention. However, the above-mentioned sulfide-based solid electrolytes have poor moisture stability. Water molecules in the atmosphere decompose the bonds of bridging sulfur within the sulfide-based solid electrolytes or non-bonding sulfur. 2- It reacts with to produce hydrogen sulfide (H2S) and lowers crystallinity, thereby reducing lithium ion conductivity.

[0004] H2O + S 2- → H2S + O 2-

[0005] In particular, Li6PS5Cl, the basic composition of azirodite, exhibits rapid degradation upon exposure to atmosphere or moisture due to moisture instability. While atmospheric stability is improved through methods such as oxygen doping or surface oxidation, this process presents a problem of significantly reduced ionic conductivity. Consequently, there are attempts to increase the proportion of halogen elements to enhance the moisture stability of Li6PS5Cl. However, increasing the proportion of halogen elements leads to non-bonding S 2- Although reducing it can improve moisture stability and lithium-ion conductivity, it is not a fundamental solution because it cannot prevent atmospheric water molecules from breaking down the bonds of cross-linked sulfur bonded to P.

[0006] Meanwhile, lithium-ion conductive sulfide-based solid electrolytes can be manufactured by dry or wet synthesis methods, but wet synthesis is more preferable for mass production. In this regard, the inventors previously utilized a co-precipitation method for the mass production of alkali metal ion conductive chalcogenide-based solid electrolytes. This method allows for the easy recovery of precursors and solvent reuse by terminating the reaction in a single-pot process within a single solvent, and enables the synthesis of solid electrolytes with ion conductivity equivalent to that of conventional synthesis methods. Examining the process of synthesizing Li6PS5Cl using this method, the alkali metal lithium undergoes intermediate stages (polysulfide, polythiophosphate) through a transfer catalyst to dissolve sulfur (S8) and phosphorus pentoxide (P2S5), ultimately leading to the co-precipitation of all precursors in the form of Li2S or Li3PS4. A characteristic feature of this process is that the dissolved LiCl is also co-precipitated. Li, referred to as thio-LISICON x In the case of MS4 (x=3~5, M=B, Al, Ga, In, Si, Ge, Sn, P, As, Sb, Sb), dissolution and co-precipitation of the raw materials are also possible using this co-precipitation method.

[0007] Accordingly, the inventors [address] the weak PS bonds or non-bonding S of the first solid electrolyte with high ion conductivity. 2- A coating layer is formed to prevent cracking due to moisture, and a core-shell structured solid electrolyte is synthesized in which a second solid electrolyte layer is coated on a first solid electrolyte core using a co-precipitation method, thereby completing the present invention.

[0008] Accordingly, the present invention has as its technical problem to provide a method for manufacturing a sulfide-based solid electrolyte with a core-shell structure.

[0009] In addition, the present invention has another technical problem to solve by providing a core-shell structured sulfide-based solid electrolyte manufactured by the above method.

[0010] In addition, the present invention has another technical problem to solve by providing an all-solid-state battery comprising a core-shell structured sulfide-based solid electrolyte manufactured by the above method.

[0011] In order to solve the above technical problem, the present invention,

[0012] (1) By introducing a sulfide-based first solid electrolyte, lithium metal, and a transfer catalyst into a polar aprotic solvent and reacting them, the first solid electrolyte and lithium ions (Li + ) A step of preparing a first dispersion solution in which transfer catalyst radicals are dispersed;

[0013] (2) A step of preparing a second dispersion solution in which a first solid electrolyte particle, which is a Li-MS compound, is dispersed on the surface by adding a sulfur (S) element and an MS compound (wherein M is one or more selected from B, Al, Ga, In, Si, Ge, Sn, As, Sb, and Bi) to the first dispersion solution and reacting them; and

[0014] (3) A step of recovering powder from the second dispersion solution and heat-treating to produce a core-shell structured sulfide-based solid electrolyte in which the second solid electrolyte is bonded to the surface of the first solid electrolyte particles; the present invention provides a method for producing a core-shell structured sulfide-based solid electrolyte, characterized by including the step of: (3) recovering powder from the second dispersion solution and heat-treating to produce a core-shell structured sulfide-based solid electrolyte in which the second solid electrolyte is bonded to the surface of the first solid electrolyte particles.

[0015] In the present invention, the first solid electrolyte is characterized by being one or more selected from the group consisting of LGPS-based solid electrolytes, LPSX(X=Cl, Br, I)-based solid electrolytes, and LPS-based solid electrolytes.

[0016] The Li-MS compound, which is the second solid electrolyte mentioned above, has low ionic conductivity but relatively high stability against moisture or atmosphere. m MS n (wherein M is one or more elements selected from B, Al, Ga, In, Si, Ge, Sn, As, Sb and Bi, and 1≤m≤8, 1≤n≤7) is the characteristic.

[0017] In addition, the present invention is characterized in that the heat treatment is performed at 200 to 500°C.

[0018] In addition, the present invention is characterized in that, among the sulfide-based solid electrolyte having a first solid electrolyte core-second solid electrolyte shell structure, the second solid electrolyte is included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the first solid electrolyte.

[0019] In addition, the present invention is characterized in that the ionic conductivity of the core-shell structured sulfide-based solid electrolyte is at least 1 mS / cm.

[0020] In addition, in the present invention, the transfer catalyst comprises naphthalene, acenaphthylene, acenaphthene, diphenyl, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo(k)fluoranthene, benzo(b)fluoranthene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene, dibenz(a,h)anthracene, and It is characterized by being one or more polycyclic aromatic hydrocarbons (PAHs) selected from the group consisting of benzo(g,h,i)perylene.

[0021] In addition, in the present invention, the polar aprotic solvent is characterized by being one or more selected from the group consisting of aliphatic mono-ether, aliphatic di-ether, cyclic ether, poly ether, ACN (acetonitrile), DMF (dimethylformamide), EA (ethyl acetate), DMC (dimethyl carbonate), and EP (ethyl propionate).

[0022] In addition, to solve the other technical problems mentioned above, the present invention provides a core-shell structured sulfide-based solid electrolyte characterized by being manufactured by the method described above.

[0023] In addition, to solve the above-mentioned other technical problem, the present invention provides an all-solid-state battery comprising the solid electrolyte manufactured above.

[0024] According to the present invention described above, a thio-lysicone sulfide-based solid electrolyte with excellent atmospheric and moisture stability is coated onto a sulfide-based solid electrolyte core with high ion conductivity using a co-precipitation method, and a core-shell structured sulfide-based solid electrolyte can be manufactured by controlling a heat treatment process. According to the present invention, a shell is formed on a sulfide-based solid electrolyte core with high ion conductivity, and by using a thio-lysicone solid electrolyte that does not contain phosphorus, the effect of improving atmospheric and moisture stability is achieved.

[0025] FIG. 1 schematically illustrates the structure of a core-shell structured sulfide-based solid electrolyte manufactured according to the present invention (10: first solid electrolyte, 20: second solid electrolyte)

[0026] Figure 2 is a flowchart illustrating the manufacturing process of a core-shell structured sulfide-based solid electrolyte according to the present invention.

[0027] FIG. 3 shows the manufacturing process of a core-shell structured sulfide-based solid electrolyte using a co-precipitation method according to the present invention and the manufactured solid electrolyte particles.

[0028] [Correction pursuant to Rule 91 14.05.2025] FIG. 4 shows the synthesis and analysis results of Li4SiS4 according to one embodiment of the present invention, FIG. 4a shows the synthesis method of Li4SiS4, and FIG. 4b shows the XRD analysis results of Li4SiS4.

[0029] Figure 5a shows the mass fraction of Li4SiS4 according to temperature in accordance with one embodiment of the present invention, Figure 5b shows the measurement results of the ionic conductivity of Li4SiS4 synthesized at different heat treatment temperatures during synthesis, and Figures 5c and 5d show the SEM analysis and EDS analysis results of Li4SiS4 synthesized at different heat treatment temperatures during synthesis.

[0030] Figure 6a shows the XRD analysis results of Li4SiS4@Li6PS5Cl synthesized at different heat treatment temperatures according to one embodiment of the present invention, and Figure 6b shows the SEM-EDS analysis results.

[0031] FIG. 7a shows the results of measuring the lithium ion conductivity of Li4SiS4@Li6PS5Cl synthesized at different heat treatment temperatures according to one embodiment of the present invention, FIG. 7b shows the results of measuring the current over time, and FIG. 7c shows the results of measuring the ion conductivity according to the measurement temperature.

[0032] [Correction pursuant to Rule 91 14.05.2025] FIG. 8a shows the ionic conductivity of Li4SiS4@Li6PS5Cl synthesized with different Li4SiS4 contents according to one embodiment of the present invention, and FIG. 8b shows the results of measuring hydrogen sulfide emission.

[0033] [Correction pursuant to Rule 91 14.05.2025] FIG. 9a shows the XRD measurement results of Li4SiS4@Li6PS5Cl synthesized with different Li4SiS4 content and heat treatment temperature according to one embodiment of the present invention, and FIG. 9b shows the XPS analysis results.

[0034] [Correction pursuant to Rule 91 14.05.2025][Deleted]

[0035] The present invention will be described in detail below.

[0036] Throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0037] FIG. 1 schematically illustrates the structure of a core-shell structured sulfide-based solid electrolyte manufactured according to the present invention. The sulfide-based solid electrolyte according to the present invention is a sulfide-based solid electrolyte for an all-solid-state battery and comprises a core (10) and a shell (20). The core (10) is a sulfide-based solid electrolyte with high ion conductivity but requiring improved atmospheric and moisture stability, and the shell (20) is a thioricicon-type sulfide-based solid electrolyte with low ion conductivity but high atmospheric and moisture stability.

[0038] FIG. 2 is a flowchart illustrating the manufacturing process of a core-shell structured sulfide-based solid electrolyte according to the present invention, and FIG. 3 is a schematic representation of the manufacturing process according to one embodiment of the present invention. The solid electrolyte of the present invention is manufactured by a reaction in which a second solid electrolyte is coated on the surface of a first solid electrolyte using a co-precipitation method. That is, by reacting a lithium, MS compound with a sulfur element, a core-shell structured solid electrolyte can be manufactured in which a Li-MS compound is bonded as a second solid electrolyte to the surface of a first solid electrolyte.

[0039] Accordingly, in one embodiment, the present invention comprises (1) introducing a sulfide-based first solid electrolyte, lithium metal, and a transfer catalyst into a polar aprotic solvent and reacting them, thereby producing a first solid electrolyte and lithium ions (Li + The present invention provides a method for manufacturing a core-shell structured sulfide-based solid electrolyte, comprising: (1) a step of preparing a first dispersion solution in which a transfer catalyst radical is dispersed; (2) a step of preparing a second dispersion solution in which a first solid electrolyte particle, which is a Li-MS compound, is dispersed on the surface by introducing a sulfur (S) element and an MS compound (wherein M is one or more selected from B, Al, Ga, In, Si, Ge, Sn, As, Sb, and Bi) into the first dispersion solution and reacting them; and (3) a step of recovering powder from the second dispersion solution and heat-treating it to manufacture a core-shell structured sulfide-based solid electrolyte in which the second solid electrolyte is bonded on the surface of the first solid electrolyte particle.

[0040] The following steps are explained in detail.

[0041] First, step (1) involves introducing a sulfide-based first solid electrolyte, lithium metal, and a transfer catalyst into a polar aprotic solvent and reacting them, thereby producing a first solid electrolyte and lithium ions (Li + ) This is a step of preparing a first dispersion solution in which transfer catalyst radicals are dispersed.

[0042] That is, when lithium metal and a transfer catalyst are introduced into a polar aprotic solvent and reacted, the lithium metal is ionized by the transfer catalyst to form a lithium ion-transfer catalyst radical solution in which ions and electrons combine with the transfer catalyst, and a first solid electrolyte is introduced into this solution to form a first solid electrolyte-lithium ion (Li + A first dispersion solution in which radicals are dispersed is prepared.

[0043] The first solid electrolyte is a sulfide-based solid electrolyte, preferably one or more selected from the group consisting of LGPS-based solid electrolytes, LPSX(X=Cl, Br, I)-based solid electrolytes, and LPS-based solid electrolytes.

[0044] At this time, the solvent is preferably a polar aprotic solvent of the ether series that accelerates the action of the transfer catalyst, and one or more selected from the group consisting of aliphatic mono-ether, aliphatic di-ether, cyclic ether, and poly ether may be used. In addition, polar aprotic solvents including ACN (acetonitrile), DMF (dimethylformamide), EA (ethyl acetate), DMC (dimethyl carbonate), and EP (ethyl propionate) capable of forming a solid electrolyte precursor may be used.

[0045] Aliphatic monoethers may be one or more of dimethyl ether, diethyl ether, methyl ethyl ether, methyl normal propyl ether, and methyl isopropyl. Aliphatic diethers may be one or more of methylal and glycol dimethyl ether. An example of a cyclic ether may be tetrahydrofuran (THF). Polyethers may be one or more of glycol formal, methyl glycerol formal, dimethylene pentaerythrite, and glycerol mono-formal methyl ether.

[0046] A transfer catalyst is a catalyst capable of transferring ions and electrons by ionizing lithium metal, and mediates the transfer of electrons. In the present invention, lithium metal ions and electrons are transferred from lithium metal to form a lithium ion-transfer catalyst radical. At this time, the transfer catalyst may be a polycyclic aromatic hydrocarbon (PAH). Polycyclic aromatic hydrocarbons include naphthalene, acenaphthylene, acenaphthene, diphenyl, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo(k)fluoranthene, benzo(b)fluoranthene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene, dibenz(a,h)anthracene, and One or more selected from the group consisting of benzo(g,h,i)perylene may be used. Among them, naphthalene is an aromatic hydrocarbon consisting of two benzene rings, and since it has the most stable structure among polycyclic aromatic hydrocarbons because it has a strong carbon-hydrogen bond energy and is not easily oxidized, it is desirable to use naphthalene as a transfer catalyst.

[0047] Next, step (2) is a step of preparing a second dispersion solution in which a first solid electrolyte particle, in which a second solid electrolyte, which is a Li-MS compound, is dispersed on the surface, by adding a sulfur (S) element and an MS compound (wherein M is one or more selected from B, Al, Ga, In, Si, Ge, Sn, As, Sb, and Bi) to the first dispersion solution and reacting them with the radical. That is, the lithium ion-transfer catalyst radical reacts with sulfur to form a polysulfide, and then reacts with the MS compound to completely dissolve the sulfur and the MS compound, after which it is bonded to and coated on the surface of the first solid electrolyte in the form of a Li-MS compound. In this way, a second dispersion solution in which a core-shell structured solid electrolyte is dispersed is prepared.

[0048] At this time, the second solid electrolyte, which is a Li-MS compound forming the shell, is Li m MS n (However, M is one or more elements selected from Al, Si, Ge, Sn, Sb, In, and Bi, and 1≤m≤8, 1≤n≤7). For example, it may be Li4SnS4, Li4SiS4, Li4GeS4, LiAlS2, Li3SbS4, Li3SbS3, LiInS2, Li3BiS3, Li5BiS4, LiBiS2, or a combination thereof. This second solid electrolyte is a thiorisicon (thio-lithium superionic conductor) material, which has low ionic conductivity but cross-linked sulfur or non-bonding S 2- It does not contain [unclear text], which can increase atmospheric and moisture stability. Therefore, the sulfide-based solid electrolyte in the core can improve atmospheric and moisture stability by preventing the weak PS bonds from breaking.

[0049] In addition, in the present invention, among the sulfide-based solid electrolyte having a first solid electrolyte core-second solid electrolyte shell structure, the second solid electrolyte is included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the first solid electrolyte. More preferably, it is included in an amount of 1 to 5 parts by weight. When the content of the second solid electrolyte is within the above range, a sulfide-based solid electrolyte for an all-solid-state battery can be obtained that exhibits high stability even after exposure to air and moisture and has high lithium ion conductivity.

[0050] Next, step (3) is to recover powder from the second dispersion solution and heat treat it to produce a core-shell structured sulfide-based solid electrolyte in which the second solid electrolyte is bonded to the surface of the first solid electrolyte particles.

[0051] Since the second dispersion solution has solid electrolyte particles with a core-shell structure in which the second solid electrolyte is bonded to the surface of the first solid electrolyte, it can be separated and recovered as powder by one or more methods including natural sedimentation, centrifugation, spraying, filtering, and hydrocyclone. At this time, after recovering the powder, the remaining solvent can be recovered and reintroduced into step (1) for reuse.

[0052] Subsequently, the recovered powder is heat-treated to produce a first solid electrolyte and a second solid electrolyte with a core-shell structure. This is a process of crystallizing the recovered powder by heat treatment, and since the size can be maintained even after heat treatment, an additional grinding process is not required. Preferably, the heat treatment is carried out at 200 to 500°C.

[0053] Specifically, the heat treatment involves a process of first heating the recovered powder at room temperature to 200°C or vacuum drying to remove residual solvent or transfer catalyst, followed by second heating at 200°C in a vacuum or inert gas atmosphere to crystallize the first solid electrolyte core degraded by solvent exposure and the second solid electrolyte coated on the surface.

[0054] During the first heating, vacuum conditions are created to prevent contact with oxygen or moisture, and the prepared solid electrolyte powder is heat-treated by heating at room temperature to 200°C or vacuum drying to remove residual solvent and transfer catalyst. If heat treatment is performed below room temperature, it takes a long time to completely remove the transfer catalyst that may remain in the powder itself. If heat treatment is performed above 200°C, although the time required to remove residual solvent and transfer catalyst can be shortened, not only may the elements constituting the solid electrolyte evaporate, but it also does not produce a more excellent effect on the subsequent crystallization of the core-shell structured solid electrolyte compared to the case where heat treatment is performed at a lower temperature. Therefore, for an efficient process, it is desirable to perform heat treatment through first heating at room temperature to 200°C. In the case of THF solvent, for the efficient removal of residual solvent and residual transfer catalyst and for the subsequent crystallization of the solid electrolyte, it is desirable to perform first heat treatment under a vacuum of 60 to 120°C. Accordingly, no impurities derived from the transfer catalyst remain in the final obtained core-shell structured solid electrolyte.

[0055] When performing the second heating, an inert gas environment or vacuum conditions are created to block contact with oxygen or moisture, just as in the first heating, and the solid electrolyte powder that has undergone the first heat treatment is heated at 200 to 500°C according to the crystallization characteristics according to the composition. More preferably, 300 to 500°C is preferred. If the second heat treatment is performed at a temperature below 200°C, the crystallization of the manufactured core-shell structured solid electrolyte is not sufficiently achieved, and if the second heat treatment is performed at a temperature exceeding 500°C, coarsening of the manufactured core-shell structured solid electrolyte powder may occur, which is undesirable.

[0056] At this time, the second solid electrolyte, which is crystallized by the heat treatment to form a shell, may have a glassy structure. Since the crystal structure varies depending on the heat treatment temperature, a glassy shell is formed by heat treatment at 200 to 500°C. In addition, the thickness of the shell may be, for example, 10 nm to 1 µm. When the thickness of the shell is within the above range, a sulfide-based solid electrolyte for an all-solid-state battery can be obtained that has high stability even after exposure to air and moisture.

[0057] As such, according to the present invention, a core-shell structured sulfide-based solid electrolyte can be manufactured using co-precipitation. At this time, the ionic conductivity of the manufactured core-shell structured sulfide-based solid electrolyte is at least 1 mS / cm. Accordingly, the sulfide-based solid electrolyte has high stability against atmosphere and moisture and excellent ionic conductivity, thereby improving the cycle characteristics of an all-solid-state secondary battery containing it.

[0058] Accordingly, in another aspect, the present invention relates to a core-shell structured sulfide-based solid electrolyte characterized by being manufactured by the above method, and to an all-solid-state battery comprising the same.

[0059] Preferably, the all-solid-state battery comprises a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive and negative electrodes, wherein the solid electrolyte and the solid electrolyte layer in the positive and negative electrodes are characterized by comprising a core-shell structured solid electrolyte manufactured by the method described above. Since the core-shell structured solid electrolyte can improve stability against air, moisture, and solvents during the mixing, electrode plate, and assembly processes for manufacturing such an all-solid-state battery, the performance of the finally manufactured all-solid-state battery can also be improved compared to cases using conventional solid electrolytes.

[0060] The embodiments of the present invention will be described in more detail below. However, the following embodiments are provided merely to aid in understanding the present invention and do not limit the scope of the present invention.

[0061] <Example 1> Synthesis of Glassy Li4SiS4 (g-Li4SiS4)

[0062] The g-Li4SiS4 solid electrolyte was synthesized using Li metal (≥99%, Aldrich), S powder (≥99%, Aldrich), and SiS2 (in-house manufactured). A stoichiometric mixture of Si (99%, Sigma-Aldrich) and S (99.98%, Sigma-Aldrich) powders underwent a solid-gas phase reaction. This mixture was placed in a sealed, homemade Al2O3 crucible (7 cm²) under an argon environment. 3 It was placed in ) and heated to 800°C at a rate of 10°C / min for 10 hours, then cooled to room temperature.

[0063] The g-Li4SiS4 solid electrolyte was prepared using a Li2S-free one-pot method. Stoichiometric amounts of the precursor were mixed with tetrahydrofuran (THF, anhydrous, ≥ 99%, inhibitor-free, Aldrich) and corresponding amounts of naphthalene (NAP, 99%, Aldrich). The resulting mixture was stirred at 500 RPM at room temperature (RT) until no lithium metal was observed, thereby completing the reaction. Subsequently, the precipitate was filtered and recovered, and dried on a vacuum hot plate at 120°C for 6 hours to completely remove THF. The dried powder was then ground in an agate mortar for 15 minutes and subsequently heat-treated. All processes, except for stirring, were carried out in an argon-filled glove box with O2 < 0.1 ppm and H2O < 0.1 ppm.

[0064] <Example 2> Synthesis of core-shell structured g-Li4SiS4@Li6PS5Cl.

[0065] To manufacture core-shell g-Li4SiS4@Li6PS5Cl powder, commercial Li6PS5Cl(σ i =2.44 mScm -1 , c-Li6PS5Cl) was purchased from a domestic supplier in Korea.

[0066] First, lithium metal and NAP powder were placed in THF solvent and stirred at room temperature until all the lithium was dissolved. Second, c-Li6PS5Cl was added to the lithium solution and stirred at room temperature until homogenized and lithiated c-Li6PS5Cl was formed. Third, S and SiS2 were added to the mixture and stirred for 12 hours. Finally, the precipitate was filtered and collected, and dried under vacuum at 120°C for 6 hours to completely remove the solvent.

[0067] <Experimental Example>

[0068] Material property analysis

[0069] Powder XRD patterns were collected, and the structure and crystal phase were analyzed via X-ray diffraction (XRD) (Philips / PANalytical, X-pert PRO MPD) using Cu Kα radiation (wavelength, λ=0.15406 nm). Measurements were performed at a step size of 0.026 for 8 min -1 It was performed at a scanning speed of .

[0070] Morphological characteristics were determined using a field emission scanning electron microscope (FE-SEM, Hitachi FE-SEM S4800) and SEM-coupled energy dispersive spectroscopy (EDS).

[0071] The electronic states of the elements were analyzed by X-ray photoelectron spectroscopy (XPS, Kα+XPS System, Thermo Scientific, Loughborough, UK). XPS was performed using a monochromatic Al Kα light source (h₀=1486.6 eV) and a spot size of 400 μm.

[0072] Chemical stability test.

[0073] A chemical stability test was performed to measure the H2S generation of SSE powder in a humid environment. SSE samples were placed in a sealed desiccator with a relative humidity of 10%. 0.5 g of SSE powder was dispersed in a Petri dish, and H2S generation was measured using an H2S sensor (Cosmos, XS-2200). The operating temperature was 25°C, and the entire experiment was conducted in a dry room with a dew point of -60.5°C.

[0074] Electrochemical property analysis.

[0075] Ionic conductivity (σ) of SSE powder i) was measured using electrochemical impedance spectroscopy (EIS). An In|SSE|In (In: Indium foil) symmetric cell was assembled using a commercial press cell jig (TLP1109-S, TERALEADER, Korea). The powder was pelletized at 300 MPa (*?*=10 mm) for 2 minutes. The density of the SSE pellets is approximately 82–85% of the theoretical density. EIS analysis was performed in the frequency range of 1 MHz to 1 Hz. The electronic conductivity (σ) of the SSE powder e ) was measured by chronoamperometry (CA) for 1,800 seconds at a voltage of 1.0 V. The activation energy (Ea) of SSE was evaluated using EIS in a temperature range of 25–60°C and was calculated according to the Arrhenius equation.

[0076]

[0077] (where σ is ionic conductivity, T is temperature (K), A is exponential factor, Ea is activation energy, and kB is Boltzmann constant)

[0078] The analysis results are shown in Figures 4 to 10.

[0079] First, Figure 4a shows the synthesis method of Li4SiS4 according to Example 1, and Figure 4b shows the XRD analysis results according to the heat treatment temperature during the synthesis of Li4SiS4. As the heat treatment temperature increased, the peaks became more distinct, peaks similar to Li4SiS4 were observed starting from 300°C, and the most distinct peaks were confirmed at 500°C. Through this, it can be confirmed that the degree of crystallinity can be increased by controlling the heat treatment temperature from 300°C to 500°C during the synthesis of Li4SiS4.

[0080] In addition, Figure 5a shows the mass fraction according to the heat treatment temperature during the synthesis of Li4SiS4 according to Example 1, and it can be seen that there is a mass reduction due to the evaporation of residual solvent and residual transfer catalyst, stable drying conditions at around 150 to 200°C, and a small amount of sulfur loss at temperatures exceeding 200°C.

[0081] Figure 5b shows the results of measuring the ionic conductivity of Li4SiS4 synthesized at different heat treatment temperatures during synthesis. The best ionic conductivity was observed when heat-treated at 300°C, while at 500°C, the ionic conductivity was similar to that at 200°C. Since the ionic conductivity of Li4SiS4 is 1 / 100th that of the azirodite solid electrolyte, it can be seen that the coating layer must be applied with a thickness that is as thin as possible while still providing atmospheric and moisture stability.

[0082] Figures 5c and 5d show the SEM and EDS analysis results of Li4SiS4 synthesized at different heat treatment temperatures during synthesis. It can be seen that in the absence of the first solid electrolyte to be coated, Li4SiS4 undergoes growth reaching tens of µm at a very rapid rate following homogeneous nucleation, and that the surface changes from amorphous to crystalline depending on the heat treatment temperature.

[0083] From the above results, it can be confirmed that nucleation must be rapidly induced during the synthesis of Li4SiS4, and that it is appropriate to control the heat treatment to between 200°C and 500°C. In addition, EDS results indicate that sulfur is lost during the heat treatment process at high temperatures, so the heat treatment time must also be appropriately controlled.

[0084] Figure 6a shows the XRD analysis results when the heat treatment temperature was different during the synthesis of Li4SiS4@Li6PS5Cl of Example 2. When compared with the XRD results of the Li6PS5Cl raw material, Li6PS5Cl-THF coated with Li4SiS4, and the subsequent heat treatment, it shows that the crystal structure of the raw material is minimally damaged during the coating process and the azirodite structure of the raw material is well maintained even after Li4SiS4 crystallization.

[0085] Figure 6b shows the results of SEM-EDS analysis, which confirms that Si is uniformly spread on the surface of the solid electrolyte, indicating that Li4SiS4 is coated on the surface of Li6PS5Cl with an azirodite structure.

[0086] From the above results, it can be confirmed that the present invention can produce Li4SiS4@Li6PS5Cl with a core-shell structure by coating Li4SiS4 on the surface of Li6PS5Cl by a co-precipitation method and crystallizing it through heat treatment.

[0087] Figure 7a shows the EIS analysis results for measuring the lithium ion conductivity of Li4SiS4@Li6PS5Cl prepared at different heat treatment temperatures according to Example 2, Figure 7b shows the ion conductivity results according to temperature, and Figure 7c shows a comparison of the room temperature ion conductivity when Li4SiS4 is coated at 5%. It was confirmed that compared to the original Li6PS5Cl material, the ion conductivity decreased at 300°C and 500°C after drying (Li6PS5Cl-THF), but when the heat treatment temperature was 400°C, it was found to be high at a level similar to that of the original Li6PS5Cl material. In particular, from Fig. 7c, when Li4SiS4 was coated at 5%, it showed an ionic conductivity of 2.42 mS / cm, which is almost similar to Li6PS5Cl when the heat treatment temperature was 400℃, and when heat treated at 300 and 500℃, it was 1.7 and 1.5 mS / cm, respectively, confirming that it has an ionic conductivity of at least 1 mS / cm.

[0088] Figure 8a shows the results of measuring the hydrogen sulfide emission of Li4SiS4@Li6PS5Cl synthesized with different Li4SiS4 contents in Example 2, and Figure 8b shows the results of measuring the weight change. Referring to Figure 8a, compared to the emission of 43.2 ppm from uncoated Li6PS5Cl, it was significantly reduced to 28.1 ppm when coated with 5% Li4SiS4, and further reduced to 25.8 ppm when the content was increased to 10%, confirming that the stability against moisture was enhanced by the Li4SiS4 coating. Referring to Figure 8b, it was shown that the weight change of the solid electrolyte decreased as the amount of Li4SiS4 coating increased, which also implies that the stability against moisture was improved.

[0089] From these results, it can be confirmed that forming a Li4SiS4 shell coating layer on a Li6PS5Cl core improves stability in the atmosphere, preventing the generation of hydrogen sulfide and enhancing moisture stability.

[0090] In addition, Figure 9a shows the XRD measurement results before and after the moisture stability test of Li4SiS4@Li6PS5Cl synthesized according to Example 2, but with different Li4SiS4 content and heat treatment temperatures. Referring to this, it can be confirmed that the synthesized Li4SiS4@Li6PS5Cl exhibits the same peak as Li6PS5Cl, and also exhibits the same peak after the moisture stability test. That is, it can be confirmed that the solid electrolyte particles are stably maintained in the atmosphere due to crystallization by coating and heat treatment of Li4SiS4. In addition, Figure 9b shows the XPS analysis results. In the Li6PS5Cl sample, the intensity of the O 1s peak decreased before and after the moisture stability test, whereas no significant change was observed in the O 1s peak before and after the moisture stability test of the 5% Li4SiS4@Li6PS5Cl sample, which means that almost no reaction with moisture occurred in the atmosphere.

[0091] From the results of the above-described examples and test examples, it can be confirmed that a core-shell structured sulfide-based solid electrolyte can be manufactured by coating a thio-ricicone sulfide-based solid electrolyte core with an azirodite-type sulfide-based solid electrolyte core using a coprecipitation method and controlling the heat treatment process. Accordingly, according to the present invention, atmospheric and moisture stability can be improved by forming a shell on a sulfide-based solid electrolyte core and using a thio-ricicone solid electrolyte that does not contain phosphorus.

[0092] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not to limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments. The scope of protection of the present invention shall be interpreted by the claims, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

1. (1) By introducing a sulfide-based first solid electrolyte, lithium metal, and a transfer catalyst into a polar aprotic solvent and reacting them, the first solid electrolyte and lithium ions (Li + ) A step of preparing a first dispersion solution in which transfer catalyst radicals are dispersed; (2) A step of preparing a second dispersion solution in which a first solid electrolyte particle, which is a Li-MS compound, is dispersed on the surface by adding a sulfur (S) element and an MS compound (wherein M is one or more selected from B, Al, Ga, In, Si, Ge, Sn, As, Sb, and Bi) to the first dispersion solution and reacting them; and (3) A step of recovering powder from the second dispersion solution and heat-treating to produce a core-shell structured sulfide-based solid electrolyte in which the second solid electrolyte is bonded to the surface of the first solid electrolyte particles; characterized by a method for producing a core-shell structured sulfide-based solid electrolyte.

2. In Paragraph 1, A method for manufacturing a core-shell structured sulfide-based solid electrolyte, characterized in that the first solid electrolyte is one or more selected from the group consisting of LGPS-based solid electrolytes, LPSX(X=Cl, Br, I)-based solid electrolytes, and LPS-based solid electrolytes.

3. In Paragraph 1, The above Li-MS compound is Li m MS n A method for manufacturing a core-shell structured sulfide-based solid electrolyte, characterized in that (wherein M is one or more elements selected from B, Al, Ga, In, Si, Ge, Sn, As, Sb, and Bi, and 1≤m≤8, 1≤n≤7).

4. In Paragraph 1, A method for manufacturing a core-shell structured sulfide-based solid electrolyte, characterized in that the above heat treatment is performed at 200 to 500°C.

5. In Paragraph 1, A method for manufacturing a core-shell structured sulfide-based solid electrolyte, characterized in that, among the sulfide-based solid electrolyte having a first solid electrolyte core-second solid electrolyte shell structure, the second solid electrolyte is included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the first solid electrolyte.

6. In Paragraph 1, A method for manufacturing a core-shell structured sulfide-based solid electrolyte, characterized in that the ionic conductivity of the core-shell structured sulfide-based solid electrolyte is at least 1 mS / cm.

7. In Paragraph 1, The above transfer catalyst is naphthalene, acenaphthylene, acenaphthene, diphenyl, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo(k)fluoranthene, benzo(b)fluoranthene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene, dibenz(a,h)anthracene, and A method for manufacturing a core-shell structured sulfide-based solid electrolyte, characterized by being one or more polycyclic aromatic hydrocarbons (PAHs) selected from the group consisting of benzo(g,h,i)perylene.

8. In Paragraph 1, A method for manufacturing a core-shell structured sulfide-based solid electrolyte, characterized in that the polar aprotic solvent is one or more selected from the group consisting of aliphatic mono-ether, aliphatic di-ether, cyclic ether, poly ether, ACN (acetonitrile), DMF (dimethylformamide), EA (ethyl acetate), DMC (dimethyl carbonate), and EP (ethyl propionate).

9. A core-shell structured sulfide-based solid electrolyte characterized by being manufactured by the method of any one of claims 1 to 8.

10. An all-solid-state battery characterized by including a solid electrolyte according to claim 9.

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