Solid electrolyte, manufacturing method thereof, and solid electrolyte sheet including same

Abstract

The present invention relates to a solid electrolyte comprising: a lithium ion conductive sulfide-based compound core; and a first coating layer positioned on the surface of the sulfide-based compound core and containing carbon (C), wherein the first coating layer has a carbon concentration gradient in which the carbon concentration gradually decreases from the outermost surface of the first coating layer toward the center of the core, and the difference between the carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary between the first coating layer and the core is 18 to 43 atomic %.

Description

Solid electrolyte, method for manufacturing the same, and solid electrolyte sheet including the same

[0001] The present invention claims priority to Korean Patent Application No. 10-2024-0180620, filed on December 6, 2024, and the contents of the said priority patent are all included in this specification.

[0002] The present invention relates to a solid electrolyte, a method for manufacturing the same, and a solid electrolyte sheet comprising the same.

[0003] As research on the safety issues and energy density of high-capacity batteries gains attention, all-solid-state batteries are emerging as next-generation batteries. The aforementioned all-solid-state battery ensures safety by replacing the liquid electrolyte, which is prone to explosions, with a solid electrolyte. Since it does not use flammable solvents within the battery, it completely eliminates the risk of ignition or explosion caused by reactions such as the decomposition of conventional electrolytes.

[0004] In addition, since lithium metal or lithium alloys can be used as the cathode material, the energy density relative to the mass and volume of the battery can be improved. Inorganic solid electrolytes are generally used as the solid electrolytes in the above-mentioned all-solid-state batteries, and various studies are currently underway regarding sulfide-based solid electrolytes having a composition such as Li6PS5Cl, which has an argyrodite structure, among the above-mentioned all-solid-state batteries.

[0005] For the practical application of all-solid-state batteries, large-area batteries must be fabricated; to achieve this, it is essential to sheet the cathode, separator, and anode, just as in conventional lithium-ion batteries. In particular, the separator in an all-solid-state battery consists of a solid electrolyte and a binder, and its properties (ionic conductivity, electrochemical stability, and chemical stability) vary depending on the manufacturing method and the selected solid electrolyte material.

[0006] In particular, the solid electrolyte layer used as a separator in all-solid-state batteries prevents contact between the anode and cathode during charging and discharging, can suppress lithium dendrites, and must facilitate the movement of lithium ions in a thin thickness to maximize battery energy density.

[0007] However, generally, the numerous voids existing between multiple solid electrolyte particles within the solid electrolyte layer cause lithium dendrite growth within the battery, leading to a short circuit or degradation of the battery's rate characteristics.

[0008] Furthermore, self-standing solid electrolyte sheets are required for the convenience of battery fabrication, and securing mechanical rigidity is crucial for manufacturing such self-standing sheets.

[0009]

[0010] Accordingly, one objective of the present invention is to provide a solid electrolyte that can prevent battery short circuits caused by lithium dendrite growth by reducing internal voids when applied as a solid electrolyte layer (or solid electrolyte sheet) and can improve mechanical strength, a method for manufacturing the same, and a solid electrolyte sheet including the same.

[0011]

[0012] One embodiment of the present invention provides a solid electrolyte comprising: a lithium ion-conducting sulfide-based compound core; and a first coating layer containing carbon (C) located on the surface of the sulfide-based compound core, wherein the first coating layer has a carbon concentration gradient in which the carbon concentration gradually decreases from the outermost surface of the first coating layer toward the center of the core, and the difference between the carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary between the first coating layer and the core is 18 to 43 atomic %).

[0013] The concentration of carbon at the outermost surface of the first coating layer may be 28 to 65 atomic%.

[0014] The concentration of carbon at a depth of 10 nm from the outermost surface of the first coating layer toward the center of the core may be 17 to 33 atomic%.

[0015] The concentration of carbon at the boundary with the core of the first coating layer may be 9.5 to 20 atomic%.

[0016] The first coating layer may have an average thickness of 7.5 to 22 nm.

[0017] The above solid electrolyte may further include a carbon-containing second coating layer present at the grain boundary of the sulfide-based compound core.

[0018] The content of carbon contained in the second coating layer relative to the total carbon in the solid electrolyte may be 0.2 to 1 weight%.

[0019] The above sulfide-based compound may have an argyrodite-based crystal structure.

[0020] The above sulfide-based compound can be represented by the following chemical formula 1.

[0021] [Chemical Formula 1]

[0022] Li x1 P y1 S z1 D w1 M1 a1 M2 a2

[0023] In the above chemical formula 1, D is a halogen element such as F, Cl, Br, I, or a combination thereof, M1 is B, Al, Si, Ga, Ge, In, Sn, or a combination thereof, M2 is O, N, As, Se, Sb, Te, or a combination thereof, and 4≤x1≤8, 0.5≤y1≤1.5, 3≤z1≤7, 0≤a1≤2, 0≤a2≤2.

[0024] The above solid electrolyte may have an average particle size (D50) of 1.5 to 4.5 μm.

[0025]

[0026] Another embodiment of the present invention provides a method for manufacturing a solid electrolyte comprising the steps of: preparing a lithium ion-conducting sulfide-based compound; mixing a carbon raw material and a solvent to form a coating solution; and adding the sulfide-based compound to the coating solution, followed by drying and coating heat treatment, wherein the amount of the carbon raw material added is 0.15 to 0.45 weight% based on the total weight of the sulfide-based compound, and the coating heat treatment temperature is 40 to 100°C.

[0027] The above carbon raw material may be a binding polymer compound.

[0028] The concentration of the carbon raw material in the coating solution may be 0.1 to 2 weight%.

[0029] The above carbon raw material may have a molecular weight of 400,000 to 600,000 g / mol.

[0030] The above carbon raw material may be nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), styrene-butadiene-styrene copolymer (SBS), acrylic resin, styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile (PAN), polymethyl methacrylate, or a combination thereof.

[0031]

[0032] Another embodiment of the present invention provides a solid electrolyte sheet comprising the aforementioned solid electrolyte and binder.

[0033] The above solid electrolyte sheet may be a self-standing film.

[0034]

[0035] Another embodiment of the present invention provides an all-solid-state battery comprising: an anode layer; a cathode layer; and a solid electrolyte layer located between the anode layer and the cathode layer and containing the aforementioned solid electrolyte.

[0036]

[0037] In one embodiment of the present invention, the solid electrolyte includes a carbon coating layer having a carbon concentration gradient on the surface of a lithium ion conductive compound, thereby reducing internal voids when applied to a solid electrolyte layer (or solid electrolyte sheet), which can prevent battery short circuits caused by lithium dendrite growth and improve the mechanical strength of the solid electrolyte layer (or solid electrolyte sheet).

[0038] In addition, in one embodiment of the present invention, the solid electrolyte includes a carbon coating layer having a carbon concentration gradient on the surface of a lithium ion-conducting compound, thereby improving capacity and lifespan characteristics when applied to an all-solid-state battery.

[0039]

[0040] FIG. 1 is a conceptual diagram of a solid electrolyte according to one embodiment of the present invention.

[0041] Figure 2 is a conceptual diagram of a conventional solid electrolyte.

[0042] Figures 3 and 4 are XPS analysis graphs of the solid electrolyte prepared according to Example 1.

[0043] Figures 5 and 6 are XPS analysis graphs of a solid electrolyte prepared according to Comparative Example 1.

[0044] Figure 7 is a conceptual diagram showing the method for evaluating the bending strength of a solid electrolyte sheet according to Experimental Example 2.

[0045] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0046] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0047] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0048] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0049] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0050] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0051] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0052]

[0053] 1. Solid electrolyte

[0054] A solid electrolyte according to one embodiment of the present invention comprises a lithium ion-conducting sulfide-based compound core; and a first coating layer containing carbon (C) located on the surface of the sulfide-based compound core.

[0055] The above lithium ion-conducting sulfide-based compound is not particularly limited as long as it is a sulfide-based compound having lithium ion conductivity.

[0056] The above sulfide compounds are, for example, Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n(where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (where p and q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In), Li3PS4, Li7P3S 11 , Li 7-x PS 6-x Cl x (where 0≤x≤2), Li 7-x PS 6-x Br x (where 0≤x≤2), and Li 7-x PS 6-x I x (However, it may be one or more selected from 0≤x≤2).

[0057] More specifically, the above sulfide-based compound may have an argyrodite-based crystal structure. Sulfide-based compounds with an argyrodite-based crystal structure may have particularly excellent ionic conductivity.

[0058] Whether a solid electrolyte has an azirodite-based crystal structure can be confirmed, for example, by XRD measurement. That is, in the X-ray diffraction pattern measured by an X-ray diffraction device (XRD) using CuKα1 rays, the crystal phase of the azirodite-based crystal structure has characteristic peaks at 2θ=15.34°±1.00°, 17.74°±1.00°, 25.19°±1.00°, 29.62°±1.00°, 30.97°±1.00°, 44.37°±1.00°, 47.22°±1.00°, and 51.70°±1.00°. In addition, for example, it has characteristic peaks at 2θ=54.26°±1.00°, 58.35°±1.00°, 60.72°±1.00°, 61.50°±1.00°, 70.46°±1.00°, and 72.61°±1.00°. Meanwhile, the fact that the solid electrolyte does not contain a crystal phase of an azirodite-based crystal structure can be confirmed by not having a characteristic peak of the crystal phase of the azirodite-based crystal structure described above.

[0059] The statement that a solid electrolyte has an azirodite-based crystal structure means that the solid electrolyte has at least a crystal phase of an azirodite-based crystal structure. In the present invention, it is preferable that the solid electrolyte has a crystal phase of an azirodite-based crystal structure as a main phase. At this time, "main phase" refers to the phase that has the largest proportion relative to the total amount of all crystal phases constituting the solid electrolyte. Accordingly, the content ratio of the crystal phase of an azirodite-based crystal structure contained in the solid electrolyte is preferably, for example, 60 mass% or more relative to the total crystal phases constituting the solid electrolyte, and among them, it is more preferable to have 70 mass% or more, 80 mass% or more, or 90 mass% or more. In addition, the ratio of the crystal phase can be confirmed, for example, by XRD.

[0060] The sulfide-based solid electrolyte with the azirodite-based crystal structure described above includes, for example, Li, P, S, and halogen elements, and may further include other doping elements as needed. As other doping elements are further included in the azirodite-based crystal structure, the moisture stability of the solid electrolyte may be improved, or electrochemical characteristics such as the capacity of the battery may be more preferably realized.

[0061] For example, the sulfide compound with the above-mentioned azirodite crystal structure can be represented by the following chemical formula 1.

[0062] [Chemical Formula 1]

[0063] Li x1 P y1 S z1 D w1 M1 a1 M2 a2

[0064] In the above chemical formula 1, D is a halogen element such as F, Cl, Br, I, or a combination thereof, M1 is B, Al, Si, Ga, Ge, In, Sn, or a combination thereof, M2 is O, N, As, Se, Sb, Te, or a combination thereof, and 4≤x1≤8, 0.5≤y1≤1.5, 3≤z1≤7, 0≤a1≤2, 0≤a2≤2.

[0065] However, recently, for the convenience of manufacturing all-solid-state batteries, the solid electrolyte layer used in all-solid-state batteries is required to be a solid electrolyte sheet in the form of a self-standing film. At this time, even if the binding between solid electrolyte particles within the solid electrolyte sheet is maximized using a binder, numerous voids occur, which induces the growth of lithium dendrites within the battery, causing a problem of short circuits or degradation of rate characteristics. In addition, even if a binder is used to fabricate the solid electrolyte sheet, there was a problem with insufficient mechanical strength.

[0066] Accordingly, the inventors conducted research on a solid electrolyte capable of preventing battery short circuits and improving the mechanical strength of a solid electrolyte sheet by minimizing voids within the sheet when applied to the sheet. As a result, they discovered that this problem could be solved by forming a carbon coating layer with a concentration gradient on the surface of a lithium-ion conductive compound, thereby completing the present invention. Furthermore, the inventors additionally discovered that the capacity and lifespan characteristics of the all-solid-state battery can also be comprehensively improved when the said coating layer is applied.

[0067]

[0068] Specifically, a solid electrolyte according to one embodiment of the present invention is located on the surface of a lithium ion-conducting sulfide-based compound core and includes a first coating layer containing carbon (C).

[0069] In this regard, FIG. 1 is a conceptual diagram of a solid electrolyte according to one embodiment of the present invention, and FIG. 2 is a conceptual diagram of a conventional solid electrolyte.

[0070] Referring to FIGS. 1 and 2, the solid electrolyte according to the present invention further includes a carbon-containing coating layer on the surface of the core, thereby improving the density between a plurality of solid electrolyte particles, so that internal voids can be reduced when applied to a solid electrolyte sheet (or solid electrolyte layer). Accordingly, battery short circuits are prevented, and the bonding strength between solid electrolytes is improved, so that the mechanical strength of the solid electrolyte sheet (or solid electrolyte layer) can be improved.

[0071] At this time, the first coating layer has a carbon concentration gradient in which the carbon concentration gradually decreases from the outermost surface of the first coating layer to the center of the core.

[0072] In particular, the difference between the carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary with the core of the first coating layer may be 18 to 43 atomic %), and more specifically, 20 to 40 atomic %). When the degree of the carbon concentration gradient of the first coating layer satisfies the above range, the mechanical strength improvement of the solid electrolyte sheet and the effect of preventing battery short circuits can be more preferably realized. More specifically, if the degree of the concentration gradient is too small, the effect of improving mechanical strength and the effect of suppressing battery short circuits may be negligible. If the degree of the concentration gradient is too large, the effect of suppressing battery short circuits may be negligible, and the ionic conductivity of the solid electrolyte sheet may deteriorate. Furthermore, when the degree of the carbon concentration gradient satisfies the above range, the capacity and lifespan characteristics of the all-solid-state battery may be improved.

[0073] In addition, the carbon concentration on the outermost surface of the first coating layer may be 28 to 65 atomic%, and more specifically, 30 to 60 atomic%. When the carbon concentration on the outermost surface of the first coating layer satisfies the above range, the mechanical strength improvement of the solid electrolyte sheet and the effect of preventing battery short circuits can be more preferably realized. More specifically, if the carbon concentration on the outermost surface of the first coating layer is too low, the effect of improving mechanical strength and the effect of suppressing battery short circuits may be negligible. If the carbon concentration on the outermost surface of the first coating layer is too high, the effect of suppressing battery short circuits may be negligible, and the ionic conductivity of the solid electrolyte sheet may deteriorate. Furthermore, when the carbon concentration on the outermost surface of the first coating layer satisfies the above range, the capacity and lifespan characteristics of the all-solid-state battery may be improved.

[0074] In addition, the carbon concentration at a depth of 10 nm from the outermost surface of the first coating layer toward the center of the core may be 17 to 33 atomic%, and more specifically, 17.5 to 30 atomic%. When the carbon concentration at a depth of 10 nm from the outermost surface of the first coating layer toward the center of the core satisfies the above range, the mechanical strength improvement of the solid electrolyte sheet and the battery short-circuit prevention effect can be more preferably realized. More specifically, if the carbon concentration at a depth of 10 nm from the outermost surface of the first coating layer toward the center of the core is too low, the mechanical strength improvement effect and the battery short-circuit suppression effect may be negligible. If the carbon concentration at a depth of 10 nm from the outermost surface of the first coating layer toward the center of the core is too high, the battery short-circuit suppression effect may be negligible, and the ionic conductivity of the solid electrolyte sheet may deteriorate. Furthermore, when the carbon concentration at a depth of 10 nm from the outermost surface of the first coating layer toward the center of the core satisfies the above range, the capacity and lifespan characteristics of the all-solid-state battery may be improved.

[0075] In addition, the carbon concentration at the boundary with the core of the first coating layer may be 9.5 to 20 atomic%, and more specifically, 9.8 to 19 atomic%. When the carbon concentration at the boundary with the core of the first coating layer satisfies the above range, the mechanical strength improvement and battery short-circuit prevention effects of the solid electrolyte sheet can be more preferably realized. More specifically, if the carbon concentration at the boundary with the core of the first coating layer is too low, the mechanical strength improvement effect and battery short-circuit suppression effect may be negligible. If the carbon concentration at the boundary with the core of the first coating layer is too high, the battery short-circuit suppression effect may be negligible, and the ionic conductivity of the solid electrolyte sheet may deteriorate. Furthermore, when the carbon concentration at the boundary with the core of the first coating layer satisfies the above range, the capacity and lifespan characteristics of the all-solid-state battery may be improved.

[0076] Meanwhile, the carbon concentration at the outermost surface of the first coating layer, the carbon concentration at a depth of 10 nm from the outermost surface of the first coating layer toward the center of the core, and the carbon concentration at the boundary with the core of the first coating layer can be measured through the analysis of carbon concentration at different depths according to etching using XPS (X-ray photoelectron spectroscopy) analysis on solid electrolyte powder particles.

[0077] In addition, the first coating layer may have an average thickness of 7.5 to 22 nm, and more specifically, 7.8 to 20 nm. When the average thickness of the first coating layer satisfies the above range, the mechanical strength improvement of the solid electrolyte sheet and the effect of preventing battery short circuits can be more preferably realized. More specifically, if the average thickness of the first coating layer is too small, the effect of improving mechanical strength and the effect of suppressing battery short circuits may be negligible. If the average thickness of the first coating layer is too large, the effect of suppressing battery short circuits may be negligible, and the ionic conductivity of the solid electrolyte sheet may deteriorate. Furthermore, when the average thickness of the first coating layer satisfies the above range, the capacity and lifespan characteristics of the all-solid-state battery may be improved.

[0078] Meanwhile, the average thickness of the first coating layer can be measured by the following method. First, the thickness of the first coating layer for a single solid electrolyte particle can be obtained by observing a TEM (Transmission Electron Microscope) image of a cross-section of the solid electrolyte particle milled by FIB (Focused Ion Beam) and calculating the average thickness for any 20 points in the coating layer. Additionally, the average thickness of the first coating layer can be obtained by calculating the coating layer thickness for any 30 solid electrolyte particles within the solid electrolyte powder using the same method as above and then calculating the average.

[0079] In addition, the solid electrolyte according to the present invention may further include a second carbon-containing coating layer present at the grain boundary of the sulfide-based compound core. Since the carbon-containing coating layer is present not only on the surface of the solid electrolyte but also at the grain boundary within the core, the coating layer has adhesive properties, thereby reducing pores and cracks that mainly occur within the grain boundary, lowering the porosity within the solid electrolyte layer, and thereby increasing ion conductivity or suppressing dendrites. Furthermore, when manufacturing an all-solid-state battery, high pressure (e.g., 500 MPa) is applied, or high pressure is applied during operation; in this process, cracks may occur from the grain boundary of the solid electrolyte. At this time, since the sulfide-based solid electrolyte is a material with strong brittle characteristics and is difficult to recover after cracking occurs, the cracked grain boundary can be re-adhered through the carbon coating layer with elastic properties to increase density and increase ion conductivity.

[0080] The content of carbon contained in the second coating layer relative to the total carbon in the solid electrolyte may be 0.2 to 1 weight percent. When the content of carbon contained in the second coating layer satisfies the above range, the content of carbon occupied by the first coating layer and the second coating layer in the total coating layer is optimized, so that the mechanical strength improvement and battery short-circuit prevention effects of the aforementioned solid electrolyte sheet can be more preferably realized.

[0081] In addition, the solid electrolyte may have an average particle size (D50) of 1.5 to 4.5 μm. When the average particle size (D50) of the solid electrolyte satisfies the above range, the bonding force between solid electrolytes and lithium ion mobility are controlled optimally, so that the ion conductivity and mechanical strength of the solid electrolyte sheet (or solid electrolyte layer) can be more preferably realized. In addition, the average particle size (D50) of the solid electrolyte also affects the coating layer formation yield, so when the average particle size (D50) of the solid electrolyte satisfies the above range, the effects of preventing short circuits and improving mechanical strength due to the coating can be more preferably realized.

[0082] In this specification, the average particle size (D50) may be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D50) may be measured, for example, using a laser diffraction method.

[0083] Meanwhile, the first or second coating layer may be derived from a binding carbon-containing polymer compound. Accordingly, the effect of improving the density between solid electrolytes due to the formation of the coating layer is better realized, and the effect of improving the mechanical strength of the sheet (or solid electrolyte layer) can be more preferably realized. This will be explained in more detail in the manufacturing method described later.

[0084]

[0085] 2. Method for manufacturing solid electrolyte

[0086] Another embodiment of the present invention provides a method for manufacturing a solid electrolyte comprising the steps of: preparing a lithium ion-conducting sulfide-based compound; mixing a carbon raw material and a solvent to form a coating solution; and adding the sulfide-based compound to the coating solution, followed by drying and coating heat treatment, wherein the amount of the carbon raw material added is 0.15 to 0.45 weight% based on the total weight of the sulfide-based compound, and the coating heat treatment temperature is 40 to 100°C.

[0087] Hereinafter, a method for manufacturing a solid electrolyte according to another embodiment of the present invention will be described in detail step by step.

[0088]

[0089] First, prepare a lithium ion-conducting sulfide-based compound.

[0090] The above lithium ion conductive sulfide-based compound can be prepared by purchasing a commercially available lithium ion conductive sulfide-based compound, or it can be manufactured according to a general method for manufacturing lithium ion conductive sulfide-based compounds in the industry.

[0091] More specifically, the above lithium ion conductive sulfide-based compound may be an argyrodite-based crystal structure compound. The technical significance thereof is the same as previously described.

[0092] The above lithium ion conductive sulfide-based compound can be manufactured by, for example, a step of mixing a lithium raw material, a phosphorus raw material, and a halogen element raw material to form a mixture; and a step of heat-treating the mixture.

[0093] The above lithium raw material may be, for example, Li2S, Li2S2, or a combination thereof, but is not necessarily limited thereto.

[0094] The above-mentioned phosphorus raw material may be, for example, P2S5, P2O5, or a combination thereof, but is not necessarily limited thereto.

[0095] The above-mentioned halogen element raw material may be, for example, LiF, LiCl, LiBr, LiI, or a combination thereof, but is not necessarily limited thereto. More specifically, the above-mentioned halogen element raw material may be LiCl.

[0096] The above mixing can be performed by mechanical mixing or chemical mixing.

[0097] The above mechanical mixing can be performed by methods such as a planetary mill, paint shaker, ball mill, bead mill, homogenizer, hammer mill, turbo mill, disc mill, planetary mill, mechanofusion, etc.

[0098] The above chemical mixing can be performed, for example, by melt quenching.

[0099] The above mixing can be performed for 4 to 12 hours, specifically for 6 to 10 hours, and more specifically for 7 to 9 hours. If the mixing time is too short, the mixing may be insufficient, and the synthesis of the solid electrolyte may not occur well in the heat treatment process described later. If the mixing time is too long, the mixing may be fully completed after a certain period, and even if the mixing is continued further, the mixing state will remain the same, which may cause problems in terms of process efficiency.

[0100] The above mixing can be performed at a rotational speed of 100 to 500 rpm, specifically at 150 to 450 rpm, and more specifically at 200 to 400 rpm. If the rotational speed is too slow, the balls may not penetrate into the powder, resulting in less overall mixing of the powder particles or lower energy, which may lead to insufficient atomization of the powder particles. On the other hand, if the rotational speed is too fast, the powder particles may become concentrated in one area, resulting in less even mixing.

[0101] Of course, if a doping element is to be introduced into a sulfide-based lithium ion conductive compound, additional doping raw materials may be mixed when forming the above mixture.

[0102] Next, optionally as needed, after the step of forming the mixture, the method may further include a step of compressing the mixture to form pellets.

[0103] At this time, the compression can be performed at a pressure of 100 to 500 MPa, specifically 150 to 450 MPa, and more specifically 200 to 400 MPa. If the pressure is too low, a problem may arise where interfacial resistance increases due to insufficient binding between powder particles. On the other hand, if the pressure is too high, the binding between powder particles is already established, so the binding state does not change even if additional pressure is applied, which may cause problems in terms of process efficiency. Therefore, forming pellets at an appropriate pressure is desirable in terms of productivity.

[0104] Next, the above mixture is heat-treated to form a sulfide-based lithium ion conductive compound.

[0105] At this time, the heat treatment can be performed at a temperature of 400 to 700°C, and more specifically at 500 to 600°C. If the heat treatment temperature is too low, the synthesis of the solid electrolyte with an azirodite crystal structure may not occur sufficiently, or it may be synthesized into an amorphous crystal structure, which may result in a decrease in the ionic conductivity of the solid electrolyte. If the heat treatment temperature is too high, the elements constituting the solid electrolyte may vaporize, causing the solid electrolyte to be lost, or impurity phases may be generated, which may result in a decrease in the ionic conductivity of the solid electrolyte.

[0106] In addition, the heat treatment can be performed for 2 to 8 hours, and more specifically, for 3 to 5 hours. If the heat treatment time is too short, the synthesis of the solid electrolyte with an azirodite crystal structure may not occur sufficiently, or it may be synthesized into an amorphous crystal structure, which may result in a decrease in the ionic conductivity of the solid electrolyte. If the heat treatment time is too long, the elements constituting the solid electrolyte may vaporize, causing the solid electrolyte to be lost, or impurity phases may be generated, which may result in a decrease in the ionic conductivity of the solid electrolyte.

[0107] In addition, the heat treatment may be performed in an inert gas atmosphere. Since the heat treatment is performed in an inert gas atmosphere, there may be an advantage in that contact with atmospheric moisture can be blocked. The inert gas atmosphere may be, for example, an Ar, N2, H2, or He atmosphere, and more specifically, an Ar atmosphere.

[0108] Next, the sulfide-based lithium ion conductive compound can be ground to control the average particle size (D50), and finally, a final solid electrolyte powder with an average particle size (D50) of 1.5 to 4.5 μm can be obtained.

[0109] At this time, the grinding method is not particularly limited, and, for example, a dry grinding or wet grinding method may be used.

[0110]

[0111] Next, a coating solution is formed by mixing carbon raw materials and a solvent.

[0112] The above carbon raw material may be a binding polymer compound. Accordingly, the coating layer itself becomes binding, thereby further enhancing the binding force between solid electrolytes and improving the density between solid electrolytes, which allows for a better realization of the effect of reducing internal voids. Consequently, the effect of improving the mechanical strength of the solid electrolyte sheet (or solid electrolyte layer) due to the coating can be realized more preferably.

[0113] The above carbon raw material may be, for example, nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), styrene-butadiene-styrene copolymer (SBS), acrylic resin, styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile (PAN), polymethyl methacrylate, or a combination thereof, but is not necessarily limited thereto.

[0114] At this time, the amount of carbon raw material added may be 0.15 to 0.45 weight% based on the total weight of the sulfide-based compound, and more specifically, 0.18 to 0.42 weight%. When the amount of carbon raw material added satisfies the above range, carbon is coated in an appropriate amount, and the various physical properties of the solid electrolyte, such as the difference between the carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary with the core of the first coating layer, can be more precisely controlled within the range according to the present invention. As a result, the effect of improving the mechanical strength of the solid electrolyte sheet and preventing battery short circuits can be more preferably realized, and the capacity and lifespan characteristics of the all-solid-state battery can be realized more excellently.

[0115] In addition, the concentration of the carbon raw material in the coating solution may be 0.1 to 2 weight%, and more specifically, 0.1 to 1 weight% or 0.1 to 0.4 weight%. When the concentration of the carbon raw material in the coating solution satisfies the above range, carbon is coated with an appropriate coating yield, and the various physical properties of the solid electrolyte, such as the difference between the carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary with the core of the first coating layer, can be more precisely controlled within the range according to the present invention. As a result, the effect of improving the mechanical strength of the solid electrolyte sheet and preventing battery short circuits can be more preferably realized, and the capacity and lifespan characteristics of the all-solid-state battery can be realized more excellently.

[0116] In addition, the carbon raw material may have a molecular weight of 400,000 to 600,000 g / mol. The molecular weight of the carbon raw material affects the coating yield during the subsequent coating heat treatment reaction. When the molecular weight satisfies the above range, carbon is coated with an appropriate coating yield, and the various physical properties of the solid electrolyte, such as the difference between the carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary with the core of the first coating layer, can be more precisely controlled within the range according to the present invention. As a result, the mechanical strength of the solid electrolyte sheet and the effect of preventing battery short circuits can be more preferably realized, and the capacity and lifespan characteristics of the all-solid-state battery can be realized more excellently.

[0117]

[0118] Next, the sulfide-based compound is added to the coating solution, followed by drying and coating heat treatment.

[0119] Through the above input and drying process, the entire surface of the solid electrolyte is coated with a coating solution to evenly coat the coating raw material, and at the same time, the solvent can be removed.

[0120] At this time, the coating heat treatment temperature may be 40 to 100°C. When the coating heat treatment temperature satisfies the above range, carbon is coated with an appropriate coating yield, and the various physical properties of the solid electrolyte, such as the difference in carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary with the core of the first coating layer, can be more precisely controlled within the range according to the present invention. As a result, the mechanical strength of the solid electrolyte sheet and the effect of preventing battery short circuits can be more preferably realized, and the capacity and lifespan characteristics of the all-solid-state battery can be realized more excellently.

[0121]

[0122] 3. Solid electrolyte sheet

[0123] Another embodiment of the present invention provides a solid electrolyte sheet comprising the aforementioned solid electrolyte and binder.

[0124] The above solid electrolyte sheet may be a self-standing film as its mechanical strength is sufficiently improved by including the solid electrolyte according to the present invention.

[0125] The remaining components of the solid electrolyte sheet may be selected from configurations common in the industry.

[0126] In other words, any binder commonly used in the industry may be used without restriction.

[0127] In addition, the solid electrolyte sheet may optionally include additional supports to further maximize mechanical strength as needed.

[0128] The support can serve as a framework to increase the mechanical rigidity of the solid electrolyte sheet.

[0129] The above support may comprise, for example, a fibrous polymer resin composed of polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyvinylidene fluoride (PVDF), Teflon (PTFE), or a combination thereof, but is not necessarily limited thereto.

[0130]

[0131] 4. All-solid-state battery

[0132] Another embodiment of the present invention provides an all-solid-state battery comprising: an anode layer; a cathode layer; and a solid electrolyte layer located between the anode layer and the cathode layer and containing the aforementioned solid electrolyte.

[0133] The above solid electrolyte layer may be directly caused by the aforementioned solid electrolyte sheet.

[0134] More specifically, the anode layer may include an anode current collector and an anode active material layer disposed on the anode current collector.

[0135] The above positive active material layer may include, for example, a positive active material and a solid electrolyte. The solid electrolyte included in the positive active material layer may be the same as or different from the solid electrolyte included in the solid electrolyte sheet.

[0136] The cathode active material is a material capable of reversibly absorbing and desorbing lithium ions. The cathode active material may be, for example, 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 manganate, and lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide, but is not necessarily limited to these; any material used as a cathode active material in the relevant technical field is acceptable. The cathode active material may be a single material or a mixture of two or more materials.

[0137] The above lithium transition metal oxide is, for example, Li a A 1-b B b D2(wherein 0.90 ≤ a ≤ 1, and 0 ≤ b ≤ 0.5); Li a E 1-b B b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE 2-b B b O 4-c D c (In the above equation, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B c D α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Co b B c O 2-α F α(In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b B c O 2-α F2(wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c D α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mn b B c O 2-α F α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c O 2-α F2(wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c G d O2(wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d GeO2(wherein the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2(in the above equation, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a CoGb O2(in the above equation, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a MnG b O2(in the above equation, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4(wherein 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f)Fe2(PO4)3(0 ≤ f ≤ 2); a compound represented by any one of the chemical formulas of LiFePO4. In such a compound, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof. A compound having a coating layer added to the surface of such a compound may also be used, and a mixture of the compound described above and a compound having a coating layer added may also be used. The coating layer applied to the surface of such a compound comprises, for example, a coating element compound of an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of a coating element. The compound forming this coating layer is amorphous or crystalline. The coating elements included in the coating layer are Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The method for forming the coating layer is selected within a range that does not adversely affect the physical properties of the cathode active material. The coating method is, for example, spray coating or immersion. Since specific coating methods are well understood by those skilled in the art, a detailed explanation will be omitted.

[0138] The positive electrode active material layer may include, for example, a solid electrolyte. The solid electrolyte included in the positive electrode layer may be the same as or different from the solid electrolyte included in the solid electrolyte layer.

[0139] The positive active material layer may include, for example, a binder. The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these, and any binder used in the relevant technical field is acceptable.

[0140] The positive active material layer may include, for example, a conductive material. The conductive material may include, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, etc., but is not limited to these, and any material used as a conductive material in the relevant technical field is acceptable.

[0141] The positive active material layer may further include additives such as fillers, coating agents, dispersants, and ion conductivity aids in addition to the positive active material, solid electrolyte, binder, and conductive material described above, for example.

[0142] As fillers, coating agents, dispersants, ion conductivity aids, etc. that may be included in the positive electrode active material layer, known materials generally used in electrodes of all-solid-state secondary batteries can be used.

[0143] The positive current collector may be a plate or foil made of, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof. The thickness of the positive current collector may be, for example, 1 µm to 100 µm, 1 µm to 50 µm, 5 µm to 25 µm, or 10 µm to 20 µm.

[0144]

[0145] More specifically, the above cathode layer may include a cathode current collector and a cathode active material layer disposed on the cathode current collector.

[0146] The above cathode active material layer may include, for example, a cathode active material and a binder.

[0147] The above-mentioned negative electrode active material may include, for example, a carbon-based negative electrode active material, a metal / metallic negative electrode active material, or a combination thereof.

[0148] The above carbon-based cathode active material may be amorphous carbon. The above amorphous carbon may be, for example, carbon black (CB), acetylene black (AB), furnace black (FB), Kettjen black (KB), graphene, etc., but is not necessarily limited to these, and any carbon classified as amorphous carbon in the relevant technical field is possible. Amorphous carbon is carbon that does not have crystallinity or has very low crystallinity and is distinguished from crystalline carbon or graphite-based carbon.

[0149] The metal / metallic anode active material comprises one or more selected from the group consisting of lithium (Li), gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn), but is not necessarily limited to these, and any metal anode active material or metallic anode active material that forms an alloy or compound with lithium in the relevant technical field is acceptable.

[0150] The binder included in the negative electrode active material layer may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc., but is not necessarily limited to these, and any binder used in the relevant technical field is acceptable. The binder may be composed of a single binder or a plurality of different binders.

[0151] The cathode active material layer is stabilized on the cathode current collector by including a binder. In addition, cracking of the cathode active material layer is suppressed despite volume changes and / or relative positional changes of the cathode active material layer during the charging and discharging process.

[0152] The negative electrode active material layer may further include additives used in conventional all-solid-state batteries, such as fillers, coating agents, dispersants, ion conductivity aids, etc.

[0153] The all-solid-state battery may further include a second negative electrode active material layer disposed between the negative electrode current collector and the negative electrode active material layer upon charging. The second negative electrode active material layer may be deposited between the negative electrode current collector and the negative electrode current collector during the charging process, or may be further disposed on the negative electrode active material layer during electrode assembly. This second negative electrode active material layer may be a metal layer comprising lithium or a lithium alloy. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, but is not limited thereto; any alloy used as a lithium alloy in the relevant technical field is acceptable. The second negative electrode active material layer may be composed of one of these alloys and / or lithium, or may be composed of various types of alloys and / or lithium.

[0154] The negative electrode current collector may be composed of, for example, a material that does not react with lithium, that is, does not form either an alloy or a compound. The negative electrode current collector may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), but is not necessarily limited to these; any material used as an electrode current collector in the relevant technical field is acceptable. The negative electrode current collector may be composed of one of the metals described above, or may be composed of an alloy or coating material of two or more metals. The negative electrode current collector may be, for example, in the form of a plate or a foil.

[0155]

[0156] The embodiments of the present invention will be described in more detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited by the following examples.

[0157]

[0158] Example 1

[0159] (1) Preparation of solid electrolyte

[0160] (Preparation of lithium ion-conducting sulfide-based compound) Li6PS5Cl was synthesized by a dry method. Specifically, Li2S, P2S5, and LiCl were weighed according to the composition and mixed at 300 rpm for 8 hours using a high-viscosity mill (Planetary Mill). Then, pellets were prepared at 300 MPa, and the Li6PS5Cl azirodite-based sulfide-based compound was synthesized by heat treatment at 550°C in an argon (Ar) atmosphere. Subsequently, the synthesized sulfide-based compound was pulverized by ball milling to obtain an average particle size (D50) of 3 μm.

[0161] (Formation of coating solution) Hydrogenated nitrile butadiene rubber (H-NBR) with a molecular weight of 500,000 g / mol was added to an isobutyl-isobutylate solvent to form a coating solution as a carbon raw material. At this time, the concentration of H-NBR in the coating solution was set to 0.2 wt%. In addition, the amount of H-NBR added was set to 0.2 wt% based on the total weight of the prepared Li6PS5Cl compound.

[0162] After (coating), the prepared Li6PS5Cl was added to the coating solution to impregnate the surface of the sulfide-based compound with the coating solution, and after mixing for 10 minutes in an acoustic mixer (Resodyn mixer, Pharama), the powder was obtained by drying in a vacuum evaporator, and then a coating layer was formed by heat-treating the coating in an oven at 50°C under a vacuum atmosphere for 12 hours.

[0163] Accordingly, a solid electrolyte with a carbon coating layer was finally manufactured.

[0164] (2) Manufacturing of solid electrolyte sheets

[0165] A solid electrolyte composition (slurry) was formed by mixing the solid electrolyte prepared above with a xylene solvent in which 2 wt% of H-NBR binder was dissolved. At this time, the content of the H-NBR binder was set to 2 wt% based on the total weight of the solid electrolyte and the H-NBR binder.

[0166] Subsequently, the above solid electrolyte composition (slurry) was applied onto a PET (polyethylene terephthalate) substrate using a blade coating method.

[0167] Afterwards, the above-described coated solid electrolyte composition (slurry) was dried at 50°C and peeled off from the PET substrate to produce a self-standing solid electrolyte sheet.

[0168] (3) Manufacturing of solid-state batteries

[0169] The solid electrolyte sheet manufactured above is 0.785 cm 2 After stamping out the material to an area of ​​[size] and placing it into a compaction cell, a composite electrode was loaded on top. The composite electrode was prepared by mixing an anode slurry of anode active material (NCM811):solid electrolyte (Li6PS5Cl):conductor (Denka Black) in a weight ratio of 70:29:1, and then [loading] 0.785 cm 2 It was fabricated with a loading of 20.0 mg over an area and densified at 300 MPa. Subsequently, it was bonded at 50 MPa using an In-Li counter electrode as the cathode and the cell was connected at the same pressure.

[0170]

[0171] Example 2

[0172] A solid electrolyte, a solid electrolyte sheet, and an all-solid-state battery were prepared by carrying out the same procedure as in Example 1, except that in the coating solution formation step, the amount of H-NBR added to the coating solution was 0.3% by weight based on the total weight of the prepared Li6PS5Cl compound.

[0173]

[0174] Example 3

[0175] A solid electrolyte, a solid electrolyte sheet, and an all-solid-state battery were prepared by carrying out the same procedure as in Example 1, except that in the coating solution formation step, the amount of H-NBR added to the coating solution was 0.4 wt% based on the total weight of the prepared Li6PS5Cl compound.

[0176]

[0177] Comparative Example 1

[0178] After preparing the Li6PS5Cl compound, a solid electrolyte, a solid electrolyte sheet, and an all-solid-state battery were prepared in the same manner as in Example 1, except that a coating solution formation and coating step were not performed and no separate coating treatment was performed.

[0179]

[0180] Comparative Example 2

[0181] A solid electrolyte, a solid electrolyte sheet, and an all-solid-state battery were prepared by carrying out the same procedure as in Example 1, except that in the coating solution formation step, the amount of H-NBR added to the coating solution was 0.1 wt% based on the total weight of the prepared Li6PS5Cl compound.

[0182]

[0183] Comparative Example 3

[0184] A solid electrolyte, a solid electrolyte sheet, and an all-solid-state battery were prepared by carrying out the same procedure as in Example 1, except that in the coating solution formation step, the amount of H-NBR added to the coating solution was 0.5 wt% based on the total weight of the prepared Li6PS5Cl compound.

[0185]

[0186] Table 1 below summarizes the process conditions of the examples and comparative examples.

[0187] Coating Process Conditions Carbon Raw Material Amount of Carbon Raw Material Input (Based on Total Weight of Sulfide Compounds, Weight%) Concentration of Carbon Raw Material in Coating Solution (Weight%) Comparative Example 1 --- Comparative Example 2 H-NBR (Molecular Weight 500,000 g / mol) 0.1 0.2 Example 1 H-NBR (Molecular Weight 500,000 g / mol) 0.2 0.2 Example 2 H-NBR (Molecular Weight 500,000 g / mol) 0.3 0.2 Example 3 H-NBR (Molecular Weight 500,000 g / mol) 0.4 0.2 Comparative Example 3 H-NBR (Molecular Weight 500,000 g / mol) 0.5 0.2

[0188] Tables 2 and 3 below summarize the solid electrolyte properties, solid electrolyte sheet properties, and all-solid-state battery performance evaluations according to Experimental Examples 1 to 3 described below.

[0189] Carbon concentration (atomic%) at 0 nm (outermost surface) of solid electrolyte Carbon concentration (atomic%) at 10 nm Carbon concentration (atomic%) at the boundary between the first coating layer and the substrate (core) Difference in carbon concentration (atomic%) at the boundary between the outermost surface of the first coating layer and the core Average thickness (nm) of the first coating layer Comparative Example 133302 Comparative Example 227169167 Example 1321810228 Example 24322143312 Example 35227183417 Comparative Example 36835224624

[0190] Solid Electrolyte Sheet All-Solid State Battery Performance Bending Strength (MPa) Ionic Conductivity (mS / cm) Short Circuit Detection Initial Discharge Capacity (mAh / g) Capacity Retention Rate (100 Cycles, %) Comparative Example 1 21.3 Short Circuit 8622 Comparative Example 2 61.2 Short Circuit 9643 Example 1 71.1 Drive 18678 Example 2 81 Drive 19292 Example 3 120.7 Drive 17684 Comparative Example 3 150.4 Overvoltage 14564

[0191] Experimental Example 1: Evaluation of Solid Electrolyte Properties

[0192] (1) Evaluation of carbon concentration in the first coating layer

[0193] The concentration of carbon at the outermost surface of the first coating layer, the concentration of carbon at a depth of 10 nm from the outermost surface of the first coating layer toward the center of the core, and the concentration of carbon at the boundary with the core of the first coating layer can be measured through the analysis of carbon concentration at different depths according to etching using XPS (X-ray photoelectron spectroscopy) analysis on solid electrolyte powder particles.

[0194] In this regard, Figures 3 and 4 are XPS analysis graphs of the solid electrolyte prepared according to Example 1.

[0195] Figures 5 and 6 are XPS analysis graphs of a solid electrolyte prepared according to Comparative Example 1.

[0196] (Meanwhile, the first coating layer refers to a coating layer located on the surface of the Li6PS5Cl core (base material).)

[0197] The measurement equipment and conditions for XPS analysis are as follows.

[0198] - Measuring equipment: Nexsa G2 (Thermo Fisher)

[0199] - Resolution: 0.59 eV / Ag3d5 (at pass energy 30 and spot size 10 µm)

[0200] - X-ray: Monochromatic Al_12kV, 10mA

[0201] - Spot size: 400um

[0202] 1) Step size : Survey scan : 1 eV interval

[0203] narrow scan: 0.1 eV interval

[0204] 2) Pass energy: survey scan: 200ev

[0205] Narrow scan: 50eV

[0206]

[0207] (2) Evaluation of the average thickness of the first coating layer

[0208] The average thickness of the first coating layer was measured by the following method. First, the thickness of the first coating layer for a single solid electrolyte particle was determined by observing a TEM (Transmission Electron Microscope) image of the cross-section of the solid electrolyte particle milled by FIB (Focused Ion Beam) and calculating the average thickness for 20 arbitrary points within the coating layer. Additionally, the average thickness of the first coating layer was determined by calculating the coating layer thickness for 30 arbitrary solid electrolyte particles within the solid electrolyte powder using the same method as above and then calculating the average.

[0209]

[0210] Experimental Example 2: Evaluation of Physical Properties of Solid Electrolyte Sheets

[0211] (1) Mechanical strength (bending strength)

[0212] The bending strength of the solid electrolyte sheet was measured in a dry room atmosphere with moisture removed using a universal testing machine (UTM), model Zwick Roell Z2.5 TS, Instron 2810 SERIES MICRO 3-POINT BEND FIXTURE (2810-411). Specifically, referring to Fig. 7, the bottom of the solid electrolyte sheet sample was supported by two fulcrums, and a pointed pressure part descended from the top to apply force to the center of the sample, measuring the force (F) until the sample broke. At this time, the solid electrolyte sheet sample size, the descending speed of the pressure part (measurement speed), and the distance between fulcrums (L) were determined as follows.

[0213] Sample size: 10mm (length) x 5mm (width)

[0214] Measurement speed: 1.2mm / min

[0215] Distance between fulcrums(L):3mm

[0216] (2) Ionic conductivity

[0217] After connecting the cell with a pressure of 70 MPa using SUS as the working electrode with the manufactured solid electrolyte sheet, the impedance was measured by applying a voltage of 10 mV at 30°C.

[0218]

[0219] Experimental Example 3: Evaluation of Electrochemical Characteristics of All-Solid State Battery

[0220] (1) Evaluate whether the battery is short-circuited

[0221] When evaluating charge and discharge after cell fabrication, the phenomenon where the voltage does not rise during a single charge was determined to assess whether the battery was short-circuited.

[0222] (2) Evaluation of initial discharge capacity

[0223] After fabricating the all-solid-state battery, it was aged at 25°C for 12 hours, and then a charge-discharge test was conducted at 30°C. To evaluate the initial capacity, the reference capacity was set to 200 mAh / g, and the battery was charged to 4.25V with a constant current of 0.1C. Then, the voltage was switched to a constant voltage, and charging continued until the terminal current reached 0.05C. After a 10-minute rest time following charging, the battery was discharged with a reference capacity of 200 mAh / g and a constant current of 0.1C until it reached 2.5V.

[0224] (3) Life characteristic evaluation (30℃, 100 cycles)

[0225] After fabricating the all-solid-state battery, it was charged to 4.25V at 30°C with a constant current of 0.5C, then switched to a constant voltage and charged until the termination current reached 0.05C. After a 10-minute rest time following charging, it was discharged at a constant current of 1.0C until it reached 2.5V. 100 charge-discharge cycles were performed under these conditions, and the capacity retention rate of the 100th cycle was calculated relative to the first cycle.

[0226]

[0227] Referring to Tables 1 to 3, in the case of Examples 1 to 3, where the input amount of carbon raw material as a coating raw material and the coating solution concentration were appropriately controlled, it was confirmed that the various physical properties, including the difference in carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary with the core of the first coating layer, were appropriately realized within the range according to the present invention. As a result, it was confirmed that the mechanical strength of the solid electrolyte sheet was improved, the battery operated normally without short circuits, and the ion conductivity was also found to be satisfactory. Furthermore, it was confirmed that the capacity and lifespan characteristics of the all-solid-state battery were excellently realized.

[0228] In the case of Comparative Example 1, as a result of not applying a coating, there was no tendency of a carbon concentration gradient within the first coating layer, and as a result, it was confirmed that the mechanical strength of the solid electrolyte sheet was significantly degraded compared to the example, a short circuit occurred in the battery, and the capacity and lifespan characteristics were significantly degraded.

[0229] In the case of Comparative Example 2, as a result of the input amount of carbon raw material being too small, it was confirmed that various physical properties, including the difference in carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary with the core of the first coating layer (i.e., the degree of concentration gradient), were obtained at too small. Consequently, the mechanical strength of the solid electrolyte sheet deteriorated, and a short circuit occurred in the battery. Furthermore, the capacity and lifespan characteristics of the battery deteriorated significantly compared to the example.

[0230] In the case of Comparative Example 3, as a result of the excessive amount of carbon raw material input, it was confirmed that various physical properties, including the difference in carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary with the core of the first coating layer (i.e., the degree of concentration gradient), were obtained too significantly. Consequently, it was confirmed that the ionic conductivity of the solid electrolyte sheet deteriorated too much, and an overvoltage occurred during battery operation. Furthermore, the capacity and lifespan characteristics of the battery deteriorated significantly compared to the examples.

[0231]

[0232] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0233] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

1. A lithium ion conductive sulfide-based compound core; and Located on the surface of the above-mentioned sulfide-based compound core, it comprises a first coating layer containing carbon (C), The first coating layer has a carbon concentration gradient in which the carbon concentration gradually decreases from the outermost surface of the first coating layer toward the center of the core, A solid electrolyte in which the difference between the carbon concentration (atomic %) at the outermost surface of the first coating layer and the carbon concentration (atomic %) at the boundary with the core of the first coating layer is 18 to 43 atomic %).

2. In Paragraph 1, A solid electrolyte having a carbon concentration of 28 to 65 atomic% at the outermost surface of the first coating layer.

3. In Paragraph 1, A solid electrolyte having a carbon concentration of 17 to 33 atomic% at a depth of 10 nm from the outermost surface of the first coating layer toward the center of the core.

4. In Paragraph 1, A solid electrolyte having a carbon concentration of 9.5 to 20 atomic% at the boundary with the core of the first coating layer.

5. In Paragraph 1, The first coating layer is a solid electrolyte having an average thickness of 7.5 to 22 nm.

6. In Paragraph 1, A solid electrolyte further comprising a carbon-containing second coating layer present at the grain boundary of the above-mentioned sulfide-based compound core.

7. In Paragraph 6, A solid electrolyte having a carbon content of the second coating layer relative to the total carbon in the solid electrolyte of 0.2 to 1 weight%.

8. In Paragraph 1, The above sulfide-based compound is a solid electrolyte having an argyrodite-based crystal structure.

9. In Paragraph 1, The above sulfide-based compound is a solid electrolyte represented by the following chemical formula 1: [Chemical Formula 1] The x1 P y1 S z1 D w1 M1 a1 M2 a2 In the above chemical formula 1, D is a halogen element such as F, Cl, Br, I, or a combination thereof, M1 is B, Al, Si, Ga, Ge, In, Sn, or a combination thereof, M2 is O, N, As, Se, Sb, Te, or a combination thereof, and 4≤x1≤8, 0.5≤y1≤1.5, 3≤z1≤7, 0≤a1≤2, 0≤a2≤2.

10. In Paragraph 1, The above solid electrolyte is a solid electrolyte having an average particle size (D50) of 1.5 to 4.5 μm.

11. Step of preparing a lithium ion-conducting sulfide-based compound; A step of forming a coating solution by mixing a carbon raw material and a solvent; and The method includes the step of adding the sulfide-based compound to the coating solution, followed by drying and coating heat treatment. The input amount of the above carbon raw material is 0.15 to 0.45 weight% based on the total weight of the sulfide-based compound, and A method for manufacturing a solid electrolyte in which the coating heat treatment temperature is 40 to 100℃.

12. In Paragraph 11, The above carbon raw material is a method for manufacturing a solid electrolyte which is a binding polymer compound.

13. In Paragraph 11, A method for manufacturing a solid electrolyte in which the concentration of carbon raw material in the coating solution is 0.1 to 2 weight%.

14. In Paragraph 11, The above carbon raw material is a method for manufacturing a solid electrolyte having a molecular weight of 400,000 to 600,000 g / mol.

15. In Paragraph 11, A method for manufacturing a solid electrolyte in which the above-mentioned carbon raw material is nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), styrene-butadiene-styrene copolymer (SBS), acrylic resin, styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile (PAN), polymethyl methacrylate, or a combination thereof.

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