All-solid-state secondary batteries

Abstract

The all-solid-state secondary battery comprises a positive electrode layer; a negative electrode layer; and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer comprises a positive electrode current collector and a positive electrode active material layer disposed on one or more surfaces of the positive electrode current collector, and one or more of the positive electrode active material layer and the solid electrolyte layer comprises a first two-dimensional sulfide-based solid electrolyte, and the negative electrode layer comprises a negative electrode current collector and a first negative electrode active material layer disposed on one or more surfaces of the negative electrode current collector, and the initial charge capacity (B) of the first negative electrode active material layer is less than approximately 50% of the initial charge capacity (A) of the positive electrode active material layer.

Description

[Technical Field]

[0001] This invention relates to an all-solid-state secondary battery. [Background technology]

[0002] Recently, there has been active development of batteries that offer increased energy density and stability. Lithium batteries are used in information equipment, communication equipment, and automobiles. Since automobiles are critical to human life, stability is crucial.

[0003] Lithium batteries containing liquid electrolytes contain flammable organic solvents. Lithium batteries containing liquid electrolytes have a high risk of overheating and fire in the event of a short circuit.

[0004] Solid electrolytes have a reduced risk of overheating and fire during short circuits compared to liquid electrolytes. Lithium batteries containing solid electrolytes may offer improved safety compared to lithium batteries containing liquid electrolytes. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] A lithium battery includes a positive electrode active material layer, which may contain a conductive material to improve charge-discharge characteristics. The conductive material is, for example, a carbon-based conductive material. Carbon-based conductive materials have high electronic conductivity but low ionic conductivity. A solid electrolyte may be used to improve the ionic conductivity of the positive electrode active material layer. Conventional solid electrolytes have particle morphologies with an aspect ratio of less than 2. Conventional solid electrolyte particles with an aspect ratio of less than 2 have difficulty forming long-distance ion conduction pathways. In lithium batteries containing conventional solid electrolyte particles with an aspect ratio of less than 2, there is a higher likelihood of ion conduction pathway disruption occurring during charging and discharging. A lithium battery includes, for example, a sulfide-based positive electrode active material, which undergoes significant volume changes during charging and discharging. During charging and discharging of a lithium battery, conventional solid electrolyte particles with an aspect ratio of less than 2 have difficulty suppressing ion conduction pathway disruption and increased internal resistance due to volume changes in the sulfide-based positive electrode active material. Therefore, a method is required to suppress the disruption of ion conduction paths in the positive electrode active material layer due to volume changes in the positive electrode active material during charging and discharging of lithium batteries, thereby suppressing the increase in the internal resistance of the lithium battery.

[0006] Lithium batteries containing solid electrolytes may have relatively increased interfacial resistance and decreased ionic conductivity compared to lithium batteries containing liquid electrolytes. Therefore, lithium batteries containing solid electrolytes have relatively lower efficiency and power output characteristics compared to lithium batteries containing liquid electrolytes. Consequently, there is a need for methods to improve the efficiency and power output characteristics of lithium batteries containing solid electrolytes by reducing interfacial resistance and increasing ionic conductivity.

[0007] A lithium battery contains a solid electrolyte layer, which, for example, contains solid electrolyte particles with an aspect ratio of less than 2. Because the solid electrolyte layer contains solid electrolyte particles with an aspect ratio of less than 2, the length of the interfacial paths between the solid electrolyte particles formed in the thickness direction of the solid electrolyte layer is similar to the thickness of the solid electrolyte layer. Therefore, the paths for lithium dendrites deposited during the charging and discharging process of the lithium battery to pass through the solid electrolyte layer are shortened, potentially increasing the likelihood of a short circuit in the lithium battery due to lithium dendrites. Thus, a method is needed to more effectively suppress lithium dendrite growth and thus more effectively prevent short circuits in lithium batteries.

[0008] One embodiment is to provide a new all-solid-state secondary battery. [Means for solving the problem]

[0009] Based on one example, The positive electrode layer; the negative electrode layer; and the solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, The positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on one or more surfaces (e.g., one surface or both surfaces) of the positive electrode current collector. One or more of the positive electrode active material layer and the solid electrolyte layer include a first two-dimensional sulfide-based solid electrolyte, The negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer disposed on one or more surfaces (e.g., one surface or both surfaces) of the negative electrode current collector. A solid-state secondary battery is provided in which the initial charge capacity (B) of the first negative electrode active material layer is less than 50% of the initial charge capacity (A) of the positive electrode active material layer.

[0010] Based on another concrete example, The positive electrode layer; the negative electrode layer; and the solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, The positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on one or more surfaces (e.g., one surface or both surfaces) of the positive electrode current collector. One or more of the positive electrode active material layer and the solid electrolyte layer include a first two-dimensional sulfide-based solid electrolyte, A solid-state secondary battery is provided, comprising a negative electrode layer and a first negative electrode active material layer disposed on one or more surfaces (e.g., one surface or both surfaces) of the negative electrode current collector.

[0011] Based on another concrete example, The positive electrode layer; the negative electrode layer; and the solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, The positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on one or both sides of the positive electrode current collector. An all-solid-state secondary battery is provided, wherein one or more of the positive electrode active material layer and the solid electrolyte layer include a first two-dimensional sulfide-based solid electrolyte. [Effects of the Invention]

[0012] In one respect, a new all-solid-state secondary battery structure can provide an all-solid-state secondary battery in which short circuits are suppressed and cycle characteristics are improved. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram of a two-dimensional sulfide-based solid electrolyte, illustrating an exemplary embodiment. [Figure 2] This is a schematic diagram of a two-dimensional sulfide-based solid electrolyte with a core / shell structure, illustrating an exemplary embodiment. [Figure 3] This is a cross-sectional view of a two-dimensional sulfide-based solid electrolyte with a core / shell structure, illustrating an exemplary embodiment. [Figure 4] This is a cross-sectional view of a two-dimensional sulfide-based solid electrolyte with a core / intermediate / shell structure, illustrating an exemplary embodiment. [Figure 5A] This is a cross-sectional view of a positive electrode active material layer containing a two-dimensional sulfide-based solid electrolyte, illustrating an exemplary embodiment. [Figure 5B] This is a cross-sectional view of a positive electrode active material layer containing a two-dimensional sulfide-based solid electrolyte, illustrating an exemplary embodiment. [Figure 5C] This is a cross-sectional view of a positive electrode active material layer containing a two-dimensional sulfide-based solid electrolyte, illustrating an exemplary embodiment. [Figure 6] This is a cross-sectional view of a solid electrolyte layer containing a two-dimensional sulfide-based solid electrolyte, illustrating an exemplary embodiment. [Figure 7] This is a cross-sectional view of a solid electrolyte layer containing an irregularly shaped sulfide-based solid electrolyte, illustrating an exemplary embodiment. [Figure 8] This is a schematic diagram of a solid electrolyte layer containing a two-dimensional sulfide-based solid electrolyte, illustrating an exemplary embodiment. [Figure 9] This is a schematic diagram of a solid electrolyte layer containing an irregularly shaped sulfide-based solid electrolyte, illustrating an exemplary embodiment. [Figure 10] This is a cross-sectional view of an all-solid-state secondary battery, illustrating one exemplary example. [Figure 11] This is a cross-sectional view of an exemplary example of a bi-cell all-solid-state secondary battery. [Figure 12] This is a cross-sectional view of an all-solid-state secondary battery, illustrating one exemplary example. [Figure 13] This is a cross-sectional view of an all-solid-state secondary battery, illustrating one exemplary example. [Figure 14] This is a cross-sectional view of an exemplary example of a bi-cell all-solid-state secondary battery. [Modes for carrying out the invention]

[0014] Various embodiments are illustrated in the accompanying drawings. However, this inventive idea can be embodied in many other forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided so as to make this disclosure thorough and complete, and will fully convey the scope of this inventive idea to those who have ordinary skill in the art. The same reference numerals in the drawings refer to the same components.

[0015] When one component is said to be "on top of" another, it can be understood that it may also be directly above the other component, or that other components may be interposed between them. In contrast, when one component is said to be "directly above" another, there is no component interposed between them.

[0016] Terms such as “First,” “Second,” and “Third” may be used herein to describe a variety of components, elements, regions, layers, and / or areas, but these components, elements, regions, layers, and / or areas should not be limited by these terms. These terms are used solely to distinguish one component, element, region, layer, or area from other elements, elements, regions, layers, or areas. Thus, the first component, element, region, layer, or area described below may also refer to the second component, element, region, layer, or area without exception as taught herein.

[0017] The terms used herein are for illustrative purposes only and are not intended to limit the present invention. The singular forms used herein include plural forms, including “at least one,” unless otherwise explicitly indicated. “At least one” should not be construed as limiting to the singular. As used herein, the terms “and / or” include all any combination of one or more of the listed items. “Including” and / or “Including” as used in the detailed description identify the presence of the expressed features, regions, integers, stages, operations, components, and / or ingredients, and do not exclude the presence or addition of one or more other features, regions, integers, stages, operations, components, ingredients, and / or groups thereof.

[0018] Spatially relative terms such as “down,” “underside,” “bottom,” “up,” “top,” and “upper” may be used to easily describe the relationship between one component or feature and other components or features. Spatially relative terms will be understood to be intended to include different orientations of the device when used or operated in the direction illustrated in the drawings. For example, if the device in the drawings is inverted, a component described as “down” or “below” another component or feature will be oriented “up” the other component or feature. Thus, the exemplary term “down” may encompass both up and down directions. The device may be positioned in other directions (rotated by 90° or in other directions), and the spatially relative terms used herein may be interpreted accordingly.

[0019] Unless otherwise specifically defined, all terms used herein (including technical and scientific terms) have the same meaning as those generally understood by a person of ordinary skill in the art to which this disclosure pertains. Furthermore, it will be understood that terms as defined in commonly used dictionaries should be interpreted to have a meaning consistent with the meaning in the context of the relevant technology and the content of this disclosure, and should not be interpreted in an idealized or overly formal sense.

[0020] Exemplary embodiments are described herein with reference to cross-sectional views, which are schematic diagrams of idealized embodiments. Thus, deformation from the illustrated shape should be expected as a result of, for example, manufacturing techniques and / or tolerances. Accordingly, the embodiments described herein should not be construed as being limited to specific shapes of regions as illustrated herein, and should include, for example, deviations of shape caused by manufacturing. For example, a region illustrated or described as flattened may typically be rough and / or have nonlinear features. Furthermore, sharply illustrated corners may be rounded. Accordingly, the regions illustrated in the drawings are essentially schematic, and their shapes are not intended to illustrate the exact shape of the region and are not intended to limit the scope of the claims.

[0021] "Group" refers to a group of elements in the periodic table according to the International Union of Pure and Applied Chemistry (IUPAC) classification system of groups 1-18.

[0022] In this specification, "aspect ratio" can be measured, for example, from scanning electron microscope (SEM), transmission electron microscope (TEM), or atomic microscope (AFM) images.

[0023] In this specification, the "morphology," "structure," "length," "surface area," and / or "thickness" of a two-dimensional sulfide-based solid electrolyte may be measured, for example, from scanning electron microscope (SEM), transmission electron microscope (TEM), or atomic microscope (AFM) images.

[0024] In this specification, the "thickness" and / or "diameter" of the core and shell of the positive electrode active material may be measured, for example, from scanning electron microscope (SEM), transmission electron microscope (TEM), or atomic microscope (AFM) images.

[0025] In this specification, "particle size" refers to the average diameter if the particle is spherical, and to the average major axis length if the particle is non-spherical. Particle size can be measured using a particle size analyzer (PSA). "Particle size" is, for example, the average particle size. "Average particle size" is, for example, the median particle size, D50.

[0026] D50 is the particle size that corresponds to the 50% cumulative volume, calculated from the smallest particle size in the particle size distribution measured by laser diffraction.

[0027] D90 is the particle size that corresponds to the 90% cumulative volume, calculated from the smallest particle size in the particle size distribution measured by laser diffraction.

[0028] D10 is the particle size that corresponds to the 10% cumulative volume, calculated from the smallest particle size in the particle size distribution measured by laser diffraction.

[0029] In this invention, "metal" includes both metals and metalloids such as silicon and germanium, in either an elemental or ionic state.

[0030] In this invention, "alloy" means a mixture of two or more metals.

[0031] In this invention, "electrode active material" means an electrode material that can be lithium-treated and delithiated.

[0032] In this invention, "positive electrode active material" means a positive electrode material that can be lithium-ionized and delithiated.

[0033] In this invention, "negative electrode active material" means a negative electrode material that can be lithium-treated and delithiated.

[0034] In this invention, "lithification" and "lithification" refer to the process of adding lithium to the electrode active material.

[0035] In this invention, "desitization" and "to delithiate" refer to the process of removing lithium from the electrode active material.

[0036] In this invention, "charging" and "to charge" refer to the process of providing electrochemical energy to a battery.

[0037] In this invention, "discharge" and "to discharge" refer to the process of removing electrochemical energy from a battery.

[0038] In this invention, "positive electrode" and "cathode" refer to electrodes in which electrochemical reduction and lithiumization occur during the discharge process.

[0039] In this invention, "negative electrode" and "anode" refer to electrodes in which electrochemical oxidation and delithiation occur during the discharge process.

[0040] While specific examples have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or foreseeable may arise for the applicant or those skilled in the art. Accordingly, the claims of the application and any modifications thereof are intended to include all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0041] The following provides a more detailed explanation of all-solid-state rechargeable batteries using illustrative examples.

[0042] [All-solid-state secondary battery] An all-solid-state secondary battery according to one embodiment includes a positive electrode layer; a negative electrode layer; and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on one or both sides of the positive electrode current collector, one or more of the positive electrode active material layer and the solid electrolyte layer include a first two-dimensional sulfide-based solid electrolyte, and the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer disposed on one side of the negative electrode current collector, wherein the initial charge capacity (B) of the first negative electrode active material layer is less than 50% of the initial charge capacity (A) of the positive electrode active material layer.

[0043] In all-solid-state secondary batteries, the inclusion of a positive electrode active material layer, and the positive electrode active material layer containing a first-dimensional two-dimensional sulfide-based solid electrolyte, allows for a more extended ion conduction pathway in the positive electrode active material layer. Therefore, during charging and discharging of the all-solid-state secondary battery, the interruption of the ion conduction pathway due to volume changes in the positive electrode active material layer can be more effectively prevented. As a result, the initial efficiency, discharge capacity, high-rate characteristics, and / or life characteristics of the all-solid-state secondary battery can be improved.

[0044] In all-solid-state secondary batteries, the inclusion of a positive electrode active material layer, and the inclusion of a first-dimensional two-dimensional sulfide-based solid electrolyte in the positive electrode active material layer, can improve the uniformity of ion conduction pathways within the positive electrode active material layer. Consequently, the pressure required during the manufacture of all-solid-state secondary batteries can be reduced. That is, all-solid-state secondary batteries with excellent ion conduction pathways can be realized even at reduced pressure. Furthermore, the formation of localized overvoltages within the positive electrode active material layer during the charge-discharge process of all-solid-state secondary batteries can be effectively prevented.

[0045] By including a positive electrode active material layer in an all-solid-state secondary battery, and by including a first two-dimensional sulfide-based solid electrolyte with a reduced specific surface area in the positive electrode active material layer, moisture stability is increased, side reactions between the positive electrode active material and the sulfide-based solid electrolyte are reduced, and the interfacial resistance of the positive electrode active material layer is reduced, which can suppress the decrease in ionic conductivity. Therefore, the efficiency and power characteristics of the all-solid-state secondary battery can be improved.

[0046] By including a positive electrode active material layer in the all-solid-state secondary battery, and by including a first two-dimensional sulfide-based solid electrolyte in the positive electrode active material layer, the volume changes of the positive electrode active material during charging and discharging can be accommodated more effectively. The two-dimensional sulfide-based solid electrolyte can be arranged around the positive electrode active material in the positive electrode active material layer. Since the two-dimensional sulfide-based solid electrolyte can accommodate the volume changes of the positive electrode active material during charging and discharging by distributing them across the entire area, it can accommodate the volume changes of the positive electrode active material more effectively than, for example, a sulfide-based solid electrolyte in the form of spherical particles. As a result, discontinuity between the positive electrode active material and the solid electrolyte due to the volume changes of the positive electrode active material is suppressed within the positive electrode active material layer, and the uniformity of the constituent components within the positive electrode active material layer is improved. As a result, the cycle characteristics of the all-solid-state secondary battery can be improved.

[0047] In an all-solid-state secondary battery, the inclusion of a solid electrolyte layer, and the inclusion of a first two-dimensional sulfide-based solid electrolyte in the solid electrolyte layer, can further effectively suppress the growth of lithium dendrites in the thickness direction of the solid electrolyte layer. Therefore, the occurrence of short circuits and other problems caused by lithium dendrite growth during charging and discharging of the all-solid-state secondary battery can be further effectively suppressed. As a result, the lifespan characteristics of the all-solid-state secondary battery can be improved.

[0048] By including a solid electrolyte layer in the all-solid-state secondary battery, and by including a first two-dimensional sulfide-based solid electrolyte having an increased surface area in the solid electrolyte layer, the possibility of pinhole formation on the surface of the solid electrolyte layer during manufacturing can be reduced. Therefore, the growth of lithium dendrites originating from these pinholes can be more effectively suppressed during charging and discharging of the all-solid-state secondary battery. As a result, the lifespan characteristics of the all-solid-state secondary battery can be improved.

[0049] Referring to Figures 1 to 13, the all-solid-state secondary battery 1 includes a positive electrode layer 10, a negative electrode layer 20, and a solid electrolyte layer 30 disposed between the positive electrode layer 10 and the negative electrode layer 20. The positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on one or both sides of the positive electrode current collector. The positive electrode active material layer 12, the solid electrolyte layer 30, or a combination thereof, includes a first two-dimensional sulfide-based solid electrolyte 100. The negative electrode layer 20 includes a negative electrode current collector 21 and a first negative electrode active material layer 22 disposed on one side of the negative electrode current collector. The initial charge capacity (B) of the first negative electrode active material layer 22 is less than 50% of the initial charge capacity (A) of the positive electrode active material layer 12.

[0050] [Positive electrode layer] [Positive electrode layer: solid electrolyte] The positive electrode active material layer 12 contains a first two-dimensional sulfide-based solid electrolyte.

[0051] Referring to Figures 1 to 4, the first two-dimensional sulfide-based solid electrolyte 100 is defined by its length L and thickness T. The length L of the first two-dimensional sulfide-based solid electrolyte 100 is the maximum distance between the two ends of the first two-dimensional solid electrolyte 100 in a direction perpendicular to the thickness direction (y direction) of the first two-dimensional sulfide-based solid electrolyte 100. The thickness T of the first two-dimensional sulfide-based solid electrolyte 100 is the maximum distance between the two ends of the first two-dimensional solid electrolyte 100 in the thickness direction (y direction) of the first two-dimensional sulfide-based solid electrolyte 100. In other embodiments, the first two-dimensional sulfide-based solid electrolyte 100 includes a first surface S1, a second surface S2 opposite to the first surface S1, and side surfaces S3a, S3b, S3c, S3d connecting the first surface S1 and the second surface S2, and is defined by the area of ​​the first surface S1 or the second surface S1 and the heights of the side surfaces S3a, S3b, S3c, S3d. The area of ​​the first surface S1 or the second surface S2 is, for example, the product of the maximum and minimum distances between the two ends of the perimeter of the first surface S1 or the second surface S2. The heights of the side surfaces S3a, S3b, S3c, S3d are the maximum distances between the first surface S1 and the second surface S2. In other embodiments, the area of ​​the first surface or the second surface is the integral value of the area read in a scanning electron microscope plane view image of the first two-dimensional sulfide-based solid electrolyte 100 in the thickness direction (y direction). The side height is the maximum height read from the longitudinal (x or z direction) scanning electron microscope side view image of the first two-dimensional sulfide-based solid electrolyte 100.

[0052] The aspect ratio of the length L to the thickness T of the first two-dimensional sulfide-based solid electrolyte 100 is, for example, 3 or more, 4 or more, 5 or more, 10 or more, or 20 or more. The aspect ratio of the length L to the thickness T of the first two-dimensional sulfide-based solid electrolyte 100 is, for example, 3 to 500, 3 to 400, 4 to 300, 5 to 200, or 10 to 200. By having such a range for the aspect ratio of the first two-dimensional sulfide-based solid electrolyte 100, the ion conduction pathways in the lithium battery containing the first two-dimensional sulfide-based solid electrolyte 100 are extended, more effectively accommodating the volume change of the positive electrode active material during charging and discharging of the lithium battery, and maintaining the ion conduction pathways in the lithium battery despite the volume change of the positive electrode active material. As a result, degradation of the lithium battery can be suppressed and the cycle characteristics of the lithium battery can be improved.

[0053] The length L of the first two-dimensional sulfide-based solid electrolyte 100 can be, for example, 0.1 to 50 μm, 0.5 to 50 μm, 1 to 50 μm, 1 to 30 μm, 1 to 20 μm, or 1 to 10 μm. The thickness T of the first two-dimensional sulfide-based solid electrolyte 100 can be, for example, 10 nm to 30 μm, 10 nm to 20 μm, 10 nm to 10 μm, 10 nm to 5 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 300 nm, or 10 nm to 100 nm. By having such a range for the length and / or thickness of the first two-dimensional sulfide-based solid electrolyte 100, the ion conduction path is extended within the lithium battery containing the first two-dimensional sulfide-based solid electrolyte 100, more effectively accommodating the volume change of the positive electrode active material during charging and discharging of the lithium battery, and maintaining the ion conduction path within the lithium battery despite the volume change of the positive electrode active material. As a result, the degradation of lithium batteries can be suppressed, and the cycle characteristics of lithium batteries can be improved.

[0054] The first two-dimensional sulfide-based solid electrolyte 100 may include, for example, a plate structure, a flake structure, or a combination thereof, but is not necessarily limited to such forms. Any two-dimensional structure that is used in the art can be used. By having a plate structure, flake structure, etc., the ion conduction path is extended within the lithium battery containing the first two-dimensional sulfide-based solid electrolyte 100, which can more effectively accommodate the volume change of the positive electrode active material during charging and discharging of the lithium battery, and can maintain the ion conduction path within the lithium battery despite the volume change of the positive electrode active material. As a result, degradation of the lithium battery can be suppressed and the cycle characteristics of the lithium battery can be improved.

[0055] The surfaces S1 and S2 of the first two-dimensional sulfide-based solid electrolyte 100 may have, for example, irregular, circular, or polygonal shapes. The shapes of the surfaces S1 and S2 of the first two-dimensional sulfide-based solid electrolyte 100 are determined, for example, by a plane view of the first two-dimensional sulfide-based solid electrolyte 100 in the thickness direction (y direction). Polygonal shapes include, for example, triangular, quadrilateral, pentagonal, hexagonal, heptagonal, octagonal, nonagonal, or decagonal shapes, but are not necessarily limited thereto; any polygonal shape that is used in the art is acceptable.

[0056] Referring to Figures 2 to 4, the first two-dimensional sulfide-based solid electrolyte 100 may have a core 110 / shell 120 structure, for example, including a core 110 and a shell 120 disposed on the core 110. The core 110 / shell 120 structure of the first two-dimensional sulfide-based solid electrolyte 100 allows ion conduction paths to extend within the lithium battery containing the first two-dimensional sulfide-based solid electrolyte 100, more effectively accommodating volume changes of the positive electrode active material during charging and discharging of the lithium battery, and maintaining ion conduction paths within the lithium battery despite volume changes of the positive electrode active material. As a result, degradation of the lithium battery can be suppressed, and the cycle characteristics of the lithium battery can be improved. In contrast, a simple mixture of core 110 material and shell 120 material can cause aggregation of the core 110 material and / or shell 120 material, thus failing to provide extended ion conduction pathways within the lithium battery. This can more effectively accommodate volume changes of the positive electrode active material during charging and discharging of the lithium battery, potentially disrupting ion conduction pathways within the lithium battery due to volume changes in the positive electrode active material. As a result, lithium battery degradation can increase, and the cycle characteristics of the lithium battery can deteriorate. Therefore, a first two-dimensional sulfide-based solid electrolyte 100 having a core 110 / shell 120 structure is distinguished from a simple mixture of core 110 material and shell 120 material as a composite in which the core 110 is coated by the shell 120.

[0057] The core 110 may include, for example, carbon-based materials, polymer materials, metal-containing inorganic materials, sulfide-based solid electrolytes, oxide-based solid electrolytes, or combinations thereof. Any material capable of forming a two-dimensional structure can be used for the core 110.

[0058] Carbon-based materials may include, but are not limited to, artificial graphite, natural graphite, carbon black (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB), graphene, graphene oxide, reduced graphene oxide, carbon nanobelt, and carbon nanosheet. Any carbon-based material with a two-dimensional structure used in the relevant art is acceptable.

[0059] Polymer materials include, for example, poly-2-vinylpyridine, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, polychlorotrifluoroethylene, perfluoroalkoxy copolymer, fluorinated cyclic ether, polyethylene oxide diacrylate, polyethylene oxide dimethacrylate, polypropylene oxide diacrylate, polypropylene oxide dimethacrylate, polymethylene oxide diacrylate, polymethylene oxide dimethacrylate, polyalkyldiol diacrylate, polyalkyldiol dimethacrylate, polydivinylbenzene, polyether, polycarbonate, polyamide, polyester, polyvinyl chloride, polyimide, polycarboxylic acid, polysulfonic acid, polyvinyl alcohol, polysulfone, polystyrene, polyethylene, polypropylene, poly(p-phenylene), polyacetylene, poly(p-phenylenevinylene), polyaniline, polypyrrole, polythiophene, poly(2,5-ethylenevinylene), polyacene, and poly(naphthalene-2,6-diyl), polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, poly(vinyl acetate), poly(vinylbutyral-co-vinyl alcohol-co-vinyl acetate), poly(methyl methacrylate-co-ethyl acrylate), polyacrylonitrile, polyvinyl chloride-co-vinyl acetate, poly(1-vinylpyrrolidone-co-vinyl acetate), polyvinylpyrrolidone, polyacrylate, polymethacrylate, polyurethane, polyvinyl ether, acrylonitrile-butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene-styrene rubber The polymer material may be obtained from one or more acrylate monomers selected from the group consisting of sulfonated styrene / ethylene-butylene triblock copolymer, ethoxylated neopentyl glycol diacrylate, ethoxylated bisphenol A diacrylate, ethoxylated aliphatic urethane acrylate, ethoxylated alkylphenol acrylate, and alkyl acrylate, or one or more selected from polyvinyl alcohol, polyimide, epoxy resin, and acrylic resin, or a combination thereof, but is not necessarily limited to these; any polymer capable of forming a two-dimensional structure in the art may be used. The polymer material may further contain lithium salts. The polymer material may have a two-dimensional structure.

[0060] Metal-containing inorganic materials include, but are not limited to, SiO2, TiO2, Al2O3, AlN, SiC, BaTiO3, MOF (Metal Organic Framework), POSS (Polyhedral Oligomeric Silsesquioxanes), Li2CO3, Li3PO4, Li3N, Li3S4, Li2O, montmorillonite, or combinations thereof; any metal-containing inorganic material capable of forming a two-dimensional structure in the art is usable. Metal-containing inorganic materials may have a two-dimensional structure. Metal-containing inorganic materials may have a two-dimensional nanostructure.

[0061] Sulfide-based solid electrolytes include, 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, 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, M is one of P, Si, Ge, B, Al, GaIn, Li 7-x PS 6-x Cl x , 0 ≤ x ≤ 2, Li 7-x PS 6-x Br x , 0 ≤ x ≤ 2, and Li 7-x PS 6-x I x , selected from one or more of 0 ≤ x ≤ 2. Sulfide-based solid electrolytes are produced, for example, by treating starting materials such as Li2S and P2S5 by methods such as melt quenching or mechanical milling. Further, heat treatment can be performed after such treatment. Sulfide-based solid electrolytes are either amorphous, crystalline, or in a mixed state thereof. Also, sulfide-based solid electrolytes contain, for example, at least sulfur (S), phosphorus (P), and lithium (Li) as constituent elements among the aforementioned sulfide-based solid electrolyte materials. For example, sulfide-based solid electrolytes are also materials containing Li2S-P2S5. When utilizing the inclusion of Li2S-P2S5 in sulfide-based solid electrolyte materials, the mixing molar ratio of Li2S and P2S5 is, for example, in the range of about Li2S:P2S5 = 50:50 to 90:10. Sulfide-based solid electrolytes are Li 7-x PS 6-x Cl x , 0 ≤ x ≤ 2, Li 7-x PS 6-x Br x , 0 ≤ x ≤ 2, and Li 7-x PS6-x I x It is also an argyrodite-type compound containing one or more elements selected from 0 ≤ x ≤ 2. Sulfide-based solid electrolytes may contain one or more elements selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I. Sulfide-based solid electrolytes may have a two-dimensional structure.

[0062] Oxide-based solid electrolytes include, for example, Li 1+x+y Al x Ti 2-x Si y P 3-y O 12( 0 <x<2、0≦y<3)、BaTiO3、Pb(Zr,Ti)O3(PZT)、Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≦x<1, 0≦y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2、0<y<3)、Li x Al y Ti z (PO4)3(0 <x<2、0<y<1、0<z<3)、Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≦x≦1 0≦y≦1), Li x La y TiO3(0 <x<2、0<y<3)、Li2O、LiOH、Li2CO3、LiAlO2、Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2、Li 3+x La3M2O 12(M = Te, Nb, or Zr, 0 ≦ x ≦ 10), or a combination thereof. The oxide-based solid electrolyte is produced, for example, by a sintering method or the like. The oxide-based solid electrolyte is, for example, Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a M a O 12 (M doped LLZO, M = Ga, W, Nb, Ta, or Al, 0 < a < 2, 0 ≦ x ≦ 10) is a garnet-type solid electrolyte selected therefrom. The oxide-based solid electrolyte may have a two-dimensional structure.

[0063] The core 110 can be used as a template for the first two-dimensional sulfide-based solid electrolyte 100. The core 110 can have an excellent elastic modulus. The elastic modulus of the core 110 is, for example, 1 MPa or more, 10 MPa or more, or 100 MPa or more. The elastic modulus of the core 110 is, for example, 1 MPa to 1 GPa, 10 MPa to 1 GPa, or 100 MPa to 1 GPa. When the core 110 has an elastic modulus within such a range, the mechanical properties of the first two-dimensional sulfide-based solid electrolyte 100 can be further improved.

[0064] The shell 120 can include, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, and a coating material. The coating material can be disposed on a part or all of the core 110. The coating material can impart, for example, water resistance and adhesion to the core 110.

[0065] The sulfide-based solid electrolyte and the oxide-based solid electrolyte can be selected from among the solid electrolytes included in the core 110.

[0066] The coating material is not particularly limited and can be any material that provides the first two-dimensional sulfide-based solid electrolyte 100 with the physical properties necessary for a lithium battery, such as water resistance and bonding strength. The coating material is, for example, a sulfide-based solid electrolyte that is substantially free of crosslinked sulfur and Li2S. The coating material is, for example, a composition containing only Li2S and compounds containing group 14-15 elements of the periodic table, such as P, Si, and Ge. In a composition containing only Li2S and P2S5, the Li2S content is 70%-85%. In a composition containing only Li2S and P2S5, the Li2S content is 50%-80%. In a composition containing only Li2S and GeS2, the Li2S content is 50%-80%. In the aforementioned compositions, no crosslinked sulfur peak is observed in the Raman spectrum and no Li2S peak is observed in the XRD spectrum. The sulfide-based solid electrolyte having the aforementioned mole fractions can reduce the amount of hydrogen sulfide generated. The sulfide-based solid electrolyte does not contain cross-linked sulfur and does not contain Li2S, which can reduce the amount of hydrogen sulfide generated. The sulfide-based solid electrolyte is also a sulfide glass.

[0067] The coating material is also a sulfide-based solid electrolyte containing, for example, crystallized glass having a composition of yLi2S-(100-x-y)P2S5.xP2O5 (0<x<25 and 67<y<80). Such crystallized glass has an ortho composition, thus having improved stability against water and the amount of hydrogen sulfide generated can be reduced. Ortho generally refers to the oxo acid obtained by hydrating the same oxide with the highest degree of hydration. In the Li2S-P2S5-based sulfide solid electrolyte, the crystal composition with the most Li2S added to P2S5, that is, Li3PS4 corresponds to the ortho composition. Since the molar fraction of Li2S is 75% in 75Li2S-25 P2S5, it has an ortho composition and substantially does not contain crosslinked sulfur. Crosslinked sulfur is, for example, the sulfur that crosslinks two phosphorus atoms in S3P-S-PS3 formed by the reaction of Li2S and P2S5. Such crosslinked sulfur is likely to react with water and generate hydrogen sulfide easily. The fact that the sulfide-based solid electrolyte substantially does not contain crosslinked sulfur can be confirmed, for example, by measuring the Raman spectrum. In the Raman spectrum, the peak of S3P-S-PS3 is usually at 402 cm -1 as shown. In the Raman spectrum of the sulfide-based solid electrolyte, the peak at 402 cm -1 is not detected at all. In the Raman spectrum of the sulfide-based solid electrolyte, the peak (417 cm 3- ) indicating PS4 -1 can be confirmed.

[0068] The coating material may include, for example, a binder. The binder may be, but is not limited to, polyethylene (PE), polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, or combinations thereof. Any binder that can be used in the art is acceptable.

[0069] One or more of the core 110 and shell 120 may contain a sulfide-based solid electrolyte. By including one or more of the core 110 and shell 120 a sulfide-based solid electrolyte, excellent ionic conductivity and mechanical properties can be provided simultaneously.

[0070] The core 110 may, for example, include a two-dimensional nanostructure. By including a two-dimensional nanostructure in the core 110, the shell 120 placed on the core 110 can easily have a two-dimensional structure.

[0071] Two-dimensional nanostructures may include, but are not limited to, graphene, graphene oxide, reduced graphene oxide, carbon nanobelts, carbon nanosheets, carbon nanoplates, carbon nanoflakes, SiO2, TiO2, Al2O3, AlN, SiC, BaTiO3, or combinations thereof; any two-dimensional nanostructure used in the art is acceptable.

[0072] By including such a two-dimensional nanostructure as a core 110, the first two-dimensional sulfide-based solid electrolyte 100 extends the ion conduction pathway within the lithium battery containing the first two-dimensional sulfide-based solid electrolyte 100, more effectively accommodating the volume change of the positive electrode active material during charging and discharging of the lithium battery, and maintaining the ion conduction pathway within the lithium battery despite the volume change of the positive electrode active material. As a result, degradation of the lithium battery can be further suppressed, and the cycle characteristics of the lithium battery can be further improved.

[0073] Referring to Figures 2 to 4, the ratio of the first thickness T1 of the core 110 to the first thickness T2 of the shell 120 can be, for example, 1:0.01 to 1:1000, 1:0.1 to 1:100, 1:0.1 to 1:10, 1:0.5 to 1:5, 1:1 to 1:4, 1:1 to 1:3, or 1:1 to 1:2.

[0074] The ratio of the first length L1 of the core 110 to the second length L2 of the shell 120 is also 1:1 to 1:10, 1:1.01:1:5, 1.01:1:2, 1:1.03 to 1:1.5, 1:1.05 to 1:1.3, and 1:1.05 to 1:1.1.

[0075] The first two-dimensional sulfide-based solid electrolyte 100, by having a core 110 and a shell 120 with a ratio of thickness and / or length within such a range, extends the ion conduction pathway within the lithium battery containing the first two-dimensional sulfide-based solid electrolyte 100, more effectively accommodating the volume change of the positive electrode active material during charging and discharging of the lithium battery, and maintaining the ion conduction pathway within the lithium battery despite the volume change of the positive electrode active material. As a result, degradation of the lithium battery can be further suppressed, and the cycle characteristics of the lithium battery can be further improved.

[0076] Although not shown in the drawings, the core 110 may have a multilayer structure. Having a multilayer structure allows for even greater versatility in controlling the shape, physical properties, and other characteristics of the core 110. The core 110 may, for example, have a two-layer, three-layer, or four-layer structure. Each layer of the multilayer core 110 may contain materials that are equal to or different from each other.

[0077] Although not shown in the drawings, the shell 120 may have a multilayer structure. Having a multilayer structure allows for more diverse control over the shell's form, physical properties, etc. The shell 120 may, for example, have a two-layer, three-layer, or four-layer structure. Each layer of the multilayer shell 120 may contain materials that are equal to or different from each other.

[0078] Referring to Figure 4, an intermediate layer 130 may be further included between the core 110 and the shell 120. The inclusion of the intermediate layer 130 in the first two-dimensional sulfide-based solid electrolyte 100 can improve the bonding strength between the core 110 and the shell 120, thereby improving the structural stability of the core 110 and the shell 120. The intermediate layer 130 is optional.

[0079] The intermediate layer 130 may have a third thickness T3 and a third length L3. The third length L3 of the intermediate layer 130 is, for example, greater than the first length L1 of the core 110 and less than the second length L2 of the shell 120. The third length L3 of the intermediate layer 130 is, for example, 101% to 150%, 101% to 120%, or 101% to 110% of the first length L1 of the core 110. The third thickness T3 of the intermediate layer 130 is, for example, 1% to 50%, 1% to 20%, or 1% to 10% of the first thickness T1 of the core 110. The material of the intermediate layer 130 may be selected from the material used for the core 110 and the material used for the shell 120. The material of the intermediate layer is, for example, a polymer.

[0080] Referring to Figure 5A, the positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12, the positive electrode active material layer 12 includes a first region 12A adjacent to the positive electrode current collector 11 and a second region 12B adjacent to the solid electrolyte layer 30, for example, the first two-dimensional sulfide-based solid electrolyte 100 is disposed in the first region 12A and the first two-dimensional sulfide-based solid electrolyte 100 is free in the second region 12B. The thickness of the first region 12A is 50% or less, 40% or less, 30% or less, or 20% or less of the total thickness of the positive electrode active material layer 12. The first two-dimensional sulfide-based solid electrolyte 100 can be uniformly distributed within the first region 12A, for example. In other embodiments, the first two-dimensional sulfide-based solid electrolyte 100 can have a concentration gradient that decreases within the first region 12A in the direction from the positive electrode current collector 11 towards the solid electrolyte layer 30. The first two-dimensional sulfide-based solid electrolyte 100 is placed in the first region 12A, and the second region 12B is free, allowing for the formation of longer-distance ion conduction paths in the first region 12A with an increased separation distance from the positive electrode layer. This facilitates the conduction of lithium ions into the positive electrode active material layer 12. Consequently, the increase in internal resistance during charging and discharging of the lithium battery is suppressed, and the cycle characteristics of the lithium battery can be further improved.

[0081] Referring to Figure 5B, the positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12, the positive electrode active material layer 12 includes a first region 12A adjacent to the positive electrode current collector 11 and a second region 12B adjacent to the solid electrolyte layer 30, for example, the first two-dimensional sulfide-based solid electrolyte 100 is disposed in the second region 12B and the first two-dimensional sulfide-based solid electrolyte 100 is free in the first region 12A. The thickness of the second region 12B is 50% or less, 40% or less, 30% or less, or 20% or less of the total thickness of the positive electrode active material layer 12. The first two-dimensional sulfide-based solid electrolyte 100 may be uniformly distributed within the second region 12B, for example. In other embodiments, the first two-dimensional sulfide-based solid electrolyte 100 may have a concentration gradient that decreases within the second region 12B toward the positive electrode current collector 11, for example. By placing the first two-dimensional sulfide-based solid electrolyte 100 in the second region 12B adjacent to the solid electrolyte layer 30, the interfacial resistance between the electrolyte layer 30 and the positive electrode active material layer 12 is further effectively reduced, and lithium ions can be more easily conducted from the solid electrolyte layer 30 into the interior of the positive electrode active material layer 12. Therefore, the increase in internal resistance during charging and discharging of the lithium battery is suppressed, and the cycle characteristics of the lithium battery can be further improved.

[0082] Referring to Figure 5C, the positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode active material layer 12 includes a first region 12A adjacent to the positive electrode current collector and a second region 12B adjacent to the solid electrolyte layer 30. For example, the first two-dimensional sulfide-based solid electrolyte 100 can be placed in the first region 12A and the second region 12B. By simultaneously placing the first two-dimensional sulfide-based solid electrolyte 100 in the first region 12A and the second region 12B, the overall ionic conductivity of the positive electrode active material layer 12 can be improved.

[0083] Referring to Figures 5A to 5C and Figures 10 to 13, the content of the first two-dimensional sulfide-based solid electrolyte 100 is, for example, 1-50 wt%, 1-40 wt%, 5-40 wt%, 10-40 wt%, 15-40 wt%, 20-40 wt%, and 25-40 wt% of the total weight of the positive electrode active material layer 12. The content of the first two-dimensional sulfide-based solid electrolyte 100 is, for example, 1-30 wt%, 1-25 wt%, 1-20 wt%, 1-10 wt%, or 1-5 wt% of the total weight of the positive electrode active material layer 12. By having a first two-dimensional sulfide-based solid electrolyte 100 content within such a range, the ion conduction pathways within the positive electrode active material layer 12 containing the first two-dimensional sulfide-based solid electrolyte 100 are extended, more effectively accommodating the volume change of the positive electrode active material during charging and discharging of the lithium battery, and maintaining the ion conduction pathways within the lithium battery despite the volume change of the positive electrode active material. As a result, degradation of the lithium battery can be further suppressed, and the cycle characteristics of the lithium battery can be further improved. If the content of the first two-dimensional sulfide-based solid electrolyte 100 is excessively high, the filling between the first two-dimensional sulfide-based solid electrolyte 100 within the positive electrode active material layer 12 may be insufficient, and the interfacial resistance may increase.

[0084] The positive electrode active material layer 12 may further contain an amorphous sulfide-based solid electrolyte distinct from the first two-dimensional sulfide-based solid electrolyte 100. The aspect ratio of the amorphous sulfide-based solid electrolyte is less than 2, 1.5 or less, or 1.3 or less. The particle size of the amorphous sulfide-based solid electrolyte is, for example, 0.1-50 μm, 0.1-50 μm, 0.1-30 μm, 0.1-20 μm, 0.1-10 μm, 0.1-5 μm, or 0.1-3 μm. The weight ratio of the first two-dimensional sulfide-based solid electrolyte 100 to the amorphous sulfide-based solid electrolyte is, for example, 1:99~99:1, 5:95~95:5, 10:90~90:10, 20:80~80:20, or 30:70~70:30. The weight ratio of the first two-dimensional sulfide-based solid electrolyte 100 to the amorphous sulfide-based solid electrolyte is, for example, 1:99~50:50, 3:97~40:60, 5:95~30:70, 5:95~25:75, or 5:95~20:80. By having the first two-dimensional sulfide-based solid electrolyte 100 and the amorphous sulfide-based solid electrolyte in such a weight ratio range, the degradation of the lithium battery can be further suppressed and the cycle characteristics of the lithium battery can be further improved.

[0085] The size of the solid electrolyte contained in the positive electrode active material layer 12 is smaller than the size of the solid electrolyte contained in the solid electrolyte layer 30. For example, the average D50 particle size of the solid electrolyte contained in the positive electrode active material layer 12 is 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 20% or less of the average D50 particle size of the solid electrolyte contained in the solid electrolyte layer 30. The average D50 particle size is, for example, the median particle size (D50). The median particle size (D50) is, for example, the particle size corresponding to the 50% cumulative volume calculated from the particle size side with the smallest particle size in the particle size distribution measured by laser diffraction. The particle size of the sulfide-based solid electrolyte can be measured using, for example, a laser diffraction method or a dynamic light scattering method measuring device. The particle size is measured, for example, using a laser scattering particle size analyzer (e.g., HORIBA LA-920), and is the median particle size (D50) value when 50% of the particles are accumulated from the smallest particle side in terms of volume. In other embodiments, the particle size of sulfide-based solid electrolytes may be measured from scanning electron microscope (SEM) images or optical microscopes.

[0086] [Cathode layer: Cathode active material] Referring to Figures 10 to 14, the positive electrode active material layer 12 includes, for example, a positive electrode active material.

[0087] The positive electrode active material contained in the positive electrode active material layer 12 is a positive electrode active material capable of reversibly absorbing and desorbing lithium ions. The positive electrode active material includes, for example, an oxide-based positive electrode active material, a sulfide-based positive electrode active material, or a combination thereof.

[0088] Oxide-based cathode active materials include, for example, lithium transition metal oxides, metal oxides, or combinations thereof. Lithium transition metal oxides include, for example, lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium manganate, lithium iron phosphate, or combinations thereof. Lithium oxides include, for example, iron oxide, vanadium oxide, or combinations thereof.

[0089] Sulfide-based cathode active materials include, for example, nickel sulfide, copper sulfide, Li2S, Li2S-containing composites, or combinations thereof.

[0090] The oxide-based cathode active material may be one or more composite oxides of a metal selected from, for example, cobalt, manganese, nickel, and combinations thereof, and lithium. aA 1-b B’ b D2 (where in the above formula, 0.90 ≤ a ≤ 1 and 0 ≤ b ≤ 0.5); Li a E 1-b B’ b O 2-c D c (where 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 (where in the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B’ c D α (where in the above formula, 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 (where in the above formula, 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 O2 (where in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Mn b B’ c D α (where in the above formula, 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 (where in the above formula, 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 O2 (where in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Nib E c G d O2(In the above formula, 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 G e O2(In the above formula, 0.90≦a≦1, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1);Li a NiG b O2 (In the above formula, 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (In the above formula, 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (In the above formula, 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (In the above formula, 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) This may include compounds represented by any one of the chemical formulas Fe2(PO4)3(0≦f≦2);LiFePO4.

[0091] In the chemical formulas representing the aforementioned compounds, A is Ni, Co, Mn, or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, 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; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof. It is also possible to use compounds with a coating layer attached to the surface of the aforementioned compounds, and it is also possible to use mixtures of the aforementioned compounds and compounds with a coating layer attached. The coating layer added to the surface of the aforementioned compound includes, for example, a coating element compound of an oxide, hydroxide, oxyhydroxy, oxycarbonate, or hydroxycarbonate of the coating element. The compound forming such a 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 positive electrode active material. The coating method is, for example, spray coating or immersion method. The specific coating method is well understood by those skilled in the art, so a detailed explanation is omitted.

[0092] The oxide-based cathode active material may include, for example, lithium transition metal oxides represented by the following chemical formulas 1 to 8: <Chemical formula 1> Li a Ni x Co y M z O 2-b A b In the aforementioned chemical formula 1, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.8 ≤ x < 1, 0 ≤ y ≤ 0.3, 0 < z ≤ 0.3, and x + y + z = 1, M is manganese (Mn), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B) or a combination thereof, A is F, S, Cl, Br or a combination thereof, <Chemical Formula 2> LiNi x Co y Mn z O2 <Chemical Formula 3> LiNi x Co y Al z O2 In the Chemical Formulas 2 and 3, 0.8 ≤ x ≤ 0.95, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2 and x + y + z = 1, <Chemical Formula 4> LiNi x Co y Mn z Al w O2 In the Chemical Formula 4, 0.8 ≤ x ≤ 0.95, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, 0 < w ≤ 0.2, and x + y + z + w = 1, <Chemical Formula 5> Li a Co x M y O 2-b A b In the Chemical Formula 5, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.9 ≤ x ≤ 1, 0 ≤ y ≤ 0.1, and x + y = 1, M is manganese (Mn), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B) or a combination thereof, A is F, S, Cl, Br or a combination thereof, <Chemical Formula 6> Li a Ni x Mn y M’ z O 2-b A b In the Chemical Formula 6, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0 < x ≤ 0.3, 0.5 ≤ y < 1, 0 < z ≤ 0.3, and x + y + z = 1, M’ is cobalt (Co), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B) or a combination thereof, A is F, S, Cl, Br or a combination thereof, <Chemical Formula 7> Li a M1 x M2 y PO 4-b X b In the Chemical Formula 7, 0.90 ≤ a ≤ 1.1, 0 ≤ x ≤ 0.9, 0 ≤ y ≤ 0.5, 0.9 < x + y < 1.1, 0 ≤ b ≤ 2, M1 is chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr) or a combination thereof, M2 is magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), zinc (Zn), boron (B), niobium (Nb), gallium (Ga), indium (In), molybdenum (Mo), tungsten (W), aluminum (Al), silicon (Si), chromium (Cr), vanadium (V), scandium (Sc), yttrium (Y) or a combination thereof, and X is O, F, S, P or a combination thereof. <Chemical Formula 8> Li a M3 zPO4 In the aforementioned chemical formula 8, 0.90 ≤ a ≤ 1.1 and 0.9 ≤ z ≤ 1.1. M3 is chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), or a combination thereof.

[0093] The oxide-based positive electrode active material is also covered by a coating layer. Any coating layer known to be used for positive electrode active materials in all-solid-state secondary batteries can be used. For example, the coating layer may be Li2O-ZrO2(LZO).

[0094] The size of the oxide-based cathode active material is, for example, 0.1–30 μm, 0.5–20 μm, or 1–15 μm. The oxide-based cathode active material is, for example, single-crystal grains or polycrystalline grains.

[0095] Sulfide-based cathode active materials may include, for example, Li2S-containing composites. Li2S-containing composites include, for example, composites of Li2S and carbon, composites of Li2S, carbon and solid electrolyte, composites of Li2S and solid electrolyte, composites of Li2S and lithium salt, composites of Li2S, lithium salt and carbon, composites of Li2S and metal carbide, composites of Li2S, carbon and metal carbide, composites of Li2S and metal nitride, composites of Li2S, carbon and metal nitride, or combinations thereof.

[0096] The Li2S-carbon composite contains carbon. The carbon can be any material containing carbon atoms that is used as a conductive material in the art. The carbon can be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The carbon can also be, for example, a calcined carbon precursor. The carbon can also be, for example, a carbon nanostructure. The carbon nanostructure can be, for example, a one-dimensional carbon nanostructure, a two-dimensional carbon nanostructure, a three-dimensional carbon nanostructure, or a combination thereof. The carbon nanostructure can also be, for example, a carbon nanotube, a carbon nanofiber, a carbon nanobelt, a carbon nanorod, graphene, graphene oxide (GO), reduced graphene oxide (rGO), graphene balls (GB), or a combination thereof. The carbon can be, for example, porous carbon or non-porous carbon. Porous carbon can, for example, contain periodic and regular two-dimensional or three-dimensional pores. Porous carbon includes, for example, carbon blacks such as Ketjenblack, acetylene black, Denka black, thermal black, and channel black; graphite, activated carbon, or combinations thereof. The form of carbon can be, for example, particulate, sheet, or flake, but is not limited to these; any form used as carbon in the art is acceptable. The method for producing the Li2S-carbon composite can be, for example, a dry method, a wet method, or a combination thereof; and the method for producing the Li2S-carbon composite in the art can be, for example, milling, heat treatment, or vapor deposition, but is not necessarily limited to these; any method used in the art is acceptable.

[0097] The Li2S-carbon-solid electrolyte composite comprises carbon and a solid electrolyte. The carbon refers to the Li2S-carbon composite described above. The solid electrolyte can be, for example, an amorphous solid electrolyte, any of which is used as an ion-conducting material in the art. The solid electrolyte is, for example, an inorganic solid electrolyte. The solid electrolyte is, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte is, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. A sulfide-based solid electrolyte may contain, for example, Li, S, and P, and may further selectively contain halogen elements. The sulfide-based solid electrolyte may be selected from among the sulfide-based solid electrolytes used in the solid electrolyte layer. A sulfide-based solid electrolyte may, for example, have a capacitance of 1 × 10⁻¹⁶ at room temperature. -5 Sulfide-based solid electrolytes can have an ionic conductivity of S / cm or higher. Examples include Li3PO4-Li2SO4, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen, 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, and Li2S-P2S5-Z. m S n m and n are positive numbers, Z is one of Ge, Zn, or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q p and q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li 7-x PS 6-x Cl x , 0≦x≦2, Li 7-x PS 6-x Br x , 0≦x≦2, and Li 7-x PS 6-x I x It may contain one or more elements selected from 0 ≤ x ≤ 2. Oxide-based solid electrolytes include, for example, Li, O, and transition metal elements, and may further selectively contain other elements. Oxide-based solid electrolytes have a capacitance of, for example, 1 × 10⁻¹⁶ at room temperature. -5The solid electrolyte has an ionic conductivity of S / cm or higher. Oxide-based solid electrolytes can be selected from among oxide-based solid electrolytes used in the solid electrolyte layer. The solid electrolyte can also be, for example, a mixture of a sulfide-based solid electrolyte and a lithium salt. For example, it can be a mixture of Li3PO4-Li2SO4 and a two-component lithium salt, or a mixture of Li3PO4-Li2SO4 and a three-component lithium salt.

[0098] The Li2S-solid electrolyte complex includes a solid electrolyte. The solid electrolyte refers to the Li2S-carbon-solid electrolyte complex described above.

[0099] The Li2S and lithium salt complex includes lithium salt compounds. Lithium salt compounds do not contain, for example, sulfur (S) atoms. Lithium salt compounds are also binary compounds consisting of, for example, lithium and one element selected from Group 13 to Group 17 of the periodic table. Binary compounds may include, for example, one or more selected from LiF, LiCl, LiBr, LiI, LiH, Li2S, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, LiI3, and LiB3. Lithium salt compounds are also ternary compounds consisting of, for example, lithium and two elements selected from Group 13 to Group 17 of the periodic table. The ternary compound includes, for example, one or more selected from Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, and Li3BN2. The lithium salt compound is one or more lithium halide compounds selected in particular from LiF, LiCl, LiBr, and LiI. The Li2S-solid electrolyte complex includes a solid electrolyte. The solid electrolyte refers to the solid electrolyte used in the Li2S-carbon-solid electrolyte complex described above. The Li2S-solid electrolyte composite includes, for example, a composite of Li2S and one or more lithium salts selected from LiF, LiCl, LiBr, LiI, LiH, Li2S, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, LiI3, and LiB3.

[0100] The Li2S-lithium salt-carbon complex contains a lithium salt compound and carbon. The carbon refers to the Li2S-carbon complex described above.

[0101] The Li2S-metal carbide composite contains metal carbide. The metal carbide is, for example, a two-dimensional metal carbide. A two-dimensional metal carbide is, for example, maxine (MXene). A two-dimensional metal carbide is, for example, M n+1 C n T x It is expressed as (where M is the transition metal, T is the terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups). Two-dimensional metal carbides are, for example, Ti2CT. x , (Ti 0.5 Nb 0.5 )2CT x Nb2CT x V2CT x Ti3C2T x , (V 0.5 , Cr 0.5 )3C2T x , Ti3CNT x Ta4C3T x Nb4C3T x Or a combination thereof. The surface of a two-dimensional metal carbide is terminated with O, OH and / or F.

[0102] The Li2S-carbon-metal carbide composite contains carbon and metal carbide. Carbon refers to the Li2S-carbon composite described above. Metal carbide refers to the Li2S-metal carbide composite described above.

[0103] The Li2S-metal nitride composite contains the metal nitride. The metal nitride is, for example, a two-dimensional metal nitride. The two-dimensional metal nitride is, for example, M n+1 N n T xIt is expressed as (where M is the transition metal, T is the terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups). The surface of the two-dimensional metallic nitride is terminated with O, OH and / or F.

[0104] The Li2S-carbon-metal nitride composite includes carbon and metal nitride. Carbon refers to the Li2S-carbon composite described above. Metal carbide refers to the Li2S-metal nitride composite described above.

[0105] The Li2S-containing composite may further include, for example, a second-dimensional sulfide-based solid electrolyte (not shown). The Li2S-containing composite is also a composite of Li2S and a second-dimensional sulfide-based solid electrolyte, or a composite of Li2S, a second-dimensional sulfide-based solid electrolyte, and the aforementioned carbon, solid electrolyte, lithium salt, metal carbide, or metal nitride.

[0106] The Li2S-containing composite further includes a second two-dimensional sulfide-based solid electrolyte, which can further suppress the degradation of the lithium battery and further improve the cycle characteristics of the lithium battery. The size of the second two-dimensional sulfide-based solid electrolyte is smaller than the size of the first two-dimensional sulfide-based solid electrolyte 100. The length and / or thickness of the second two-dimensional sulfide-based solid electrolyte is 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less, respectively, of the length and / or thickness of the first two-dimensional sulfide-based solid electrolyte 100. The length and / or thickness of the second two-dimensional sulfide-based solid electrolyte is also 0.1-50%, 0.5-40%, 1-30%, 1-20%, or 1-10%, respectively, of the length and / or thickness of the first two-dimensional sulfide-based solid electrolyte 100. The second two-dimensional sulfide-based solid electrolyte may have the same morphology as the first two-dimensional sulfide-based solid electrolyte 100, but in an even smaller size. The second two-dimensional sulfide-based solid electrolyte, having such reduced length and / or thickness, can be easily distributed within the Li2S-containing composite. The reduced length and / or thickness of the second two-dimensional sulfide-based solid electrolyte can further suppress the degradation of the lithium battery and further improve its cycle characteristics.

[0107] The size of the sulfide-based cathode active material can be, for example, 0.1-50 μm, 0.5-30 μm, 0.5-20 μm, or 1-10 μm. The size of Li2S can be, for example, 1 nm-10 μm, 10 nm-5 μm, 10 nm-3 μm, or 10 nm-1 μm. The size of the Li2S-containing composite can be, for example, 0.1-50 μm, 0.5-30 μm, 0.5-20 μm, or 1-10 μm.

[0108] The positive electrode active material is also a composite positive electrode active material that includes, for example, a core that intercepts / releases lithium and a shell disposed on the core.

[0109] The composite cathode active material includes, for example, a core that intercalates / releases lithium; and a shell disposed along the surface of the core, wherein the shell has a chemical formula M a ObOne or more first metal oxides represented by (0 < a ≤ 3, 0 < b < 4, and if a is 1, 2, or 3, b is not an integer); and graphene, wherein the first metal oxide is disposed within a graphene matrix, and M is one or more metals selected from Groups 2 to 13, Group 15, and Group 16 of the periodic table. The core for lithium insertion / extraction includes, for example, the aforementioned Li2S-containing composite, and the Li2S-containing composite includes, for example, a composite of Li2S and carbon, a composite of Li2S, carbon, and a solid electrolyte, a composite of Li2S and a solid electrolyte, a composite of Li2S and a lithium salt, a composite of Li2S, a lithium salt, and carbon, a composite of Li2S and a metal carbide, a composite of Li2S, carbon, and a metal carbide, a composite of Li2S and a metal nitride, a composite of Li2S, carbon, and a metal nitride, or a combination thereof. The core for lithium insertion / extraction may include, for example, a lithium transition metal oxide represented by Chemical Formulas 1 to 8. The core for lithium insertion / extraction may include, for example, a lithium transition metal oxide having a Ni content of 80 mol% or more. A shell containing, for example, the first metal oxide and graphene is disposed on the core for lithium insertion / extraction. Conventional graphene is difficult to uniformly coat on the core due to aggregation. In contrast, the composite cathode active material uses a composite containing a plurality of first metal oxides disposed in a graphene matrix, thereby preventing the aggregation of graphene and disposing a uniform shell on the core. Therefore, by effectively blocking the contact between the core and the electrolyte, side reactions due to the contact between the core and the electrolyte are prevented. The shell containing graphene has flexibility, so by easily accommodating the volume change of the composite cathode active material during charge and discharge, the generation of cracks inside the composite cathode active material is suppressed. Since graphene has high conductivity, the interfacial resistance between the composite cathode active material and the electrolyte is reduced. Therefore, despite the introduction of the shell containing graphene, the internal resistance of the lithium battery is maintained or decreased. Also, since the first metal oxide has voltage resistance, it can prevent the deterioration of the Li2S-containing composite or lithium transition metal oxide contained in the core during charge and discharge at high voltage.As a result, the cycle characteristics and high-temperature stability of the lithium battery containing the composite cathode active material are improved. The shell may include, for example, one type of first metal oxide, or two or more different first metal oxides. The metal contained in the first metal oxide is, for example, one or more selected from among Al, Nb, Mg, Sc, Ti, Zr, V, W, Mn, Fe, Co, Pd, Cu, Ag, Zn, Sb, and Se. The first metal oxide is, for example, Al2O. z (0 < z < 3), NbO x (0 < x < 2.5), MgO x (0 < x < 1), Sc2O z (0 < z < 3), TiO y (0 < y < 2), ZrO y (0 < y < 2), V2O z (0 < z < 3), WO y (0 < y < 2), MnO y (0 < y < 2), Fe2O z (0 < z < 3), Co3O w (0 < w < 4), PdO x (0 < x < 1), CuO x (0 < x < 1), AgO x (0 < x < 1), ZnO x (0 < x < 1), Sb2O z (0 < z < 3), and SeO y (0 < y < 2) and is one or more selected therefrom. By arranging such a first metal oxide in the graphene matrix, the uniformity of the shell disposed on the core is improved, and the voltage resistance of the composite cathode active material is further improved. For example, the shell contains Al2Ox (0 < x < 3) as the first metal oxide. The shell has the chemical formula M a O cIt may further contain one or more second metal oxides represented by (0 < a ≤ 3, 0 < c ≤ 4, and if a is 1, 2, or 3, c is an integer). The M is one or more metals selected from Groups 2 to 13, Group 15, and Group 16 of the periodic table. For example, the second metal oxide contains the same metal as the first metal oxide, and c / a, which is the ratio of c to a of the second metal oxide, has a value even larger than b / a, which is the ratio of b to a of the first metal oxide. For example, c / a > b / a. The second metal oxide is selected from, for example, Al2O3, NbO, NbO2, Nb2O5, MgO, Sc2O3, TiO2, ZrO2, V2O3, WO2, MnO2, Fe2O3, Co3O4, PdO, CuO, AgO, ZnO, Sb2O3, and SeO2. The first metal oxide is a reduction product of the second metal oxide. By reducing part or all of the second metal oxide, the first metal oxide is obtained. Therefore, the first metal oxide has a lower oxygen content and a higher metal oxidation number than the second metal oxide. For example, the shell contains Al2Ox (0 < x < 3) as the first metal oxide and Al2O3 as the second metal oxide. The thickness of the shell is, for example, 1 nm to 5 μm, 1 nm to 1 μm, 1 nm to 500 nm, 1 nm to 200 nm, 1 nm to 100 nm, 1 nm to 90 nm, 1 nm to 80 nm, 1 nm to 70 nm, 1 nm to 60 nm, 1 nm to 50 nm, 1 nm to 40 nm, 1 nm to 30 nm, 1 nm to 20 nm, or 1 nm to 10 nm. By having such a thickness range for the shell, an increase in the internal resistance of the lithium battery containing the composite cathode active material is suppressed. The average particle size of one or more selected from the first metal oxide and the second metal oxide contained in the composite is also 1 nm to 1 μm, 1 nm to 500 nm, 1 nm to 200 nm, 1 nm to 100 nm, 1 nm to 70 nm, 1 nm to 50 nm, 1 nm to 30 nm, 3 nm to 30 nm, 3 nm to 25 nm, 5 nm to 25 nm, 5 nm to 20 nm, or 7 nm to 20 nm. By having such a nano-scale particle size for the first metal oxide and / or the second metal oxide, it can be more uniformly distributed in the graphene matrix of the composite. Therefore, such a composite can be uniformly coated on the core without aggregation to form a shell.Furthermore, the first metal oxide and / or the second metal oxide can be more uniformly distributed on the core by having a particle size within such a range. Therefore, the uniform distribution of the first metal oxide and / or the second metal oxide on the core can more effectively exhibit dielectric strength. The average particle size of the first and second metal oxides can be measured, for example, using a laser diffraction or dynamic light scattering measuring device. In other embodiments, the particle size of the first and second metal oxides can be measured using a scanning electron microscope and a transmission electron microscope.

[0110] The shape of the positive electrode active material is, for example, a perfect sphere, an ellipsoid, or some other particle shape. The particle size of the positive electrode active material is not particularly limited and is within the range applicable to the positive electrode active material of conventional all-solid-state secondary batteries. The content of the positive electrode active material in the positive electrode layer 10 is also not particularly limited and is within the range applicable to the positive electrode layer of conventional all-solid-state secondary batteries. The content of the positive electrode active material contained in the positive electrode active material layer 12 is, for example, 10 wt% to 99 wt%, 10 wt% to 90 wt%, 10 wt% to 80 wt%, 10 wt% to 70 wt%, or 10 wt% to 50 wt% of the total weight of the positive electrode active material layer 12.

[0111] [Positive electrode layer: conductive material] The positive electrode active material layer 12 may further contain a conductive material. The conductive material may be, for example, a carbon-based conductive material, a metallic conductive material, or a combination thereof. The carbon-based conductive material may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or a combination thereof, but is not limited to these; any material used as a carbon-based conductive material in the art may be used. The metallic conductive material may be, for example, metal powder, metal fiber, or a combination thereof; any material used as a metallic conductive material in the art may be used. The conductive material content in the positive electrode active material layer 12 may be, for example, 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% of the total weight of the positive electrode active material layer 12.

[0112] [Positive electrode layer: Binder] The positive electrode active material layer 12 may further contain a binder. The binder may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these; any binder that can be used in the art is acceptable. The binder content of the positive electrode active material layer 12 may be, for example, 1 wt% to 10 wt% of the total weight of the positive electrode active material layer 12. The binder is optional.

[0113] [Positive electrode layer: Other additives] In addition to the aforementioned positive electrode active material, solid electrolyte, binder, and conductive material, the positive electrode active material layer 12 may further contain additives such as fillers, coating agents, dispersants, and ion conductivity enhancers.

[0114] The positive electrode active material layer 12 may contain fillers, coatings, dispersants, ion conductivity enhancers, etc., and other known materials generally used in electrodes for all-solid-state secondary batteries can be used.

[0115] [Positive electrode layer: Positive electrode current collector] The positive electrode current collector 11 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 an alloy thereof. The positive electrode current collector 11 is optional. The thickness of the positive electrode current collector 11 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.

[0116] The positive electrode current collector 11 may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may also be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The base film may also be, for example, an insulator. By including an insulating thermoplastic polymer in the base film, the base film may soften or liquefy when a short circuit occurs, interrupting battery operation and suppressing a rapid increase in current. The metal layer may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or alloys thereof. The metal layer can act as an electrochemical fuse, disconnecting in the event of overcurrent to prevent short circuits. The limit current and maximum current can be adjusted by adjusting the thickness of the metal layer. The metal layer is plated or deposited onto the base film. Reducing the thickness of the metal layer reduces the limit current and / or maximum current of the positive electrode current collector 11, thereby improving the stability of the lithium battery during short circuits. Lead tabs can be added to the metal layer for external connection. The lead tabs can be welded to the metal layer or the metal layer / base film laminate by ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or metal layer may melt while the metal layer is electrically connected to the lead tab. To further strengthen the weld between the metal layer and the lead tab, a metal chip can be added between the metal layer and the lead tab. The metal chip is also a thin piece of the same material as the metal layer. Metal pieces can also be, for example, metal foil or metal mesh. Examples of metal pieces include aluminum foil, copper foil, and SUS foil.After placing a metal chip on a metal layer, the lead tab can be welded to a metal chip / metal layer laminate or a metal chip / metal layer / base film laminate by welding the lead tab to it. During welding, the base film, metal layer, and / or metal chip may melt, while the metal layer or metal layer / metal chip laminate is electrically connected to the lead tab. A metal chip and / or lead tab may be added to a portion of the metal layer. The thickness of the base film can be, for example, 1-50 μm, 1.5-50 μm, 1.5-40 μm, or 1-30 μm. Having the base film in such a thickness range can further effectively reduce the weight of the electrode assembly. The melting point of the base film can be, for example, 100-300°C, 100-250°C or less, or 100-200°C. Having the base film in such a melting point range allows the base film to melt during the process of welding the lead tab and easily bond to the lead tab. To improve the adhesion between the base film and the metal layer, a surface treatment such as corona treatment may be performed on the base film. The thickness of the metal layer can be, for example, 0.01-3 μm, 0.1-3 μm, 0.1-2 μm, or 0.1 μm. Having the metal layer in such a thickness range can ensure the stability of the electrode assembly while maintaining conductivity. The thickness of the metal piece can also be, for example, 2-10 μm, 2-7 μm, or 4-6 μm. Having the metal piece in such a thickness range can further facilitate the connection between the metal layer and the lead tab. Having such a structure in the positive electrode current collector 11 can reduce the weight of the positive electrode, and as a result, improve the energy density of the positive electrode and the lithium battery.

[0117] [Positive electrode layer: Inert material] Referring to Figures 12 to 14, the positive electrode 10 includes a positive electrode current collector 11, a positive electrode active material layer 12 disposed on one surface of the positive electrode current collector, and further includes inactive members 40, 40a, and 40b disposed on one side surface of the positive electrode layer 10.

[0118] The inclusion of the inert member 40 prevents cracking of the solid electrolyte layer 30 during the manufacturing of the all-solid-state secondary battery 1 and / or during charging and discharging, thereby improving the cycle characteristics of the all-solid-state secondary battery 2. In an all-solid-state secondary battery 1 that does not include the inert member 40, uneven pressure is applied to the solid electrolyte layer 30 that is in contact with the positive electrode 10 during the manufacturing of the all-solid-state secondary battery 1 and / or during charging and discharging, causing cracks to occur in the solid electrolyte layer 30, and the growth of lithium metal through these cracks increases the likelihood of short circuits.

[0119] The inert member 40 is positioned along the side surface of the positive electrode layer 10, surrounding the positive electrode layer. The inert member 40 surrounds, for example, part or all of the side surface of the positive electrode 10 and is in contact with the solid electrolyte layer 30. By surrounding the side surface of the positive electrode 10 and being in contact with the solid electrolyte layer 30, the inert member 40 can effectively suppress cracks in the solid electrolyte layer 30 that occur due to the pressure difference during the pressurization process in the solid electrolyte layer 30 that is not in contact with the positive electrode 20. The inert member 40 surrounds the side surface of the positive electrode 10 and is separated from the negative electrode 20, and more specifically, from the first negative electrode active material layer 22. The inert member 40 surrounds the side surface of the positive electrode 10, is in contact with the solid electrolyte layer 30, and is separated from the negative electrode 20. Therefore, physical contact between the positive electrode 10 and the first negative electrode active material layer 22 prevents short circuits from occurring, or the possibility of short circuits occurring due to lithium overcharging, etc., is suppressed. Referring to Figure 3, the inert member 40 is placed on one side surface of the positive electrode active material layer 12, and simultaneously on one side surface of the positive electrode current collector 11, thereby more effectively suppressing the possibility of a short circuit occurring due to contact between the positive electrode current collector 11 and the negative electrode 20. In another embodiment, referring to Figure 4, the inert member 40 is placed on one side surface of the positive electrode active material layer 12 and between the solid electrolyte layer 40 and the positive electrode current collector 11 facing the solid electrolyte layer 40. The inert member 40 is not placed on one side surface of the positive electrode current collector 11. By placing the inert member 40 between the positive electrode current collector 11 and the solid electrolyte layer 30, a short circuit due to contact between the positive electrode current collector 11 and the negative electrode 20 can be effectively prevented.

[0120] Although not shown in the drawings, some or all of the inert members 40, 40a, and 40b may be positioned away from the sides of the positive electrode layer 10. By positioning some or all of the inert members 40, 40a, and 40b away from the sides of the positive electrode layer 10, the manufacturing process of the all-solid-state secondary battery 1 can be further simplified and the manufacturing speed of the all-solid-state secondary battery 1 can be increased. By positioning some or all of the inert members 40, 40a, and 40b away from the sides of the positive electrode layer 10, the volume change of the positive electrode layer 10 in the lateral direction during charging and discharging can be more effectively accommodated, thereby further improving the life characteristics of the all-solid-state secondary battery 1. The distances between the inert members 40, 40a, and 40b and the sides of the positive electrode layer 10 are, independently of each other, for example, 0.1 μm to 10 mm, 1 μm to 1 mm, 1 μm to 500 μm, 1 μm to 100 μm, 1 μm to 50 μm, or 1 μm to 10 μm.

[0121] The inert member 40 may further include a positioning unit (not shown) configured to determine the position of the inert member 40 on the solid electrolyte layer 30. The inert member 40 including the positioning unit can facilitate the determination of the position of the inert member 40 on the solid electrolyte layer 30. As a result, the manufacturing speed of the all-solid-state secondary battery 1 can be increased and the ease of manufacturing can be improved.

[0122] Referring to Figures 13 and 14, the inert member 40 extends from one side of the positive electrode 30 to the end of the solid electrolyte layer 30. By extending the inert member 40 to the end of the solid electrolyte layer 30, cracks that occur at the end of the solid electrolyte layer 30 can be suppressed. The end of the solid electrolyte layer 30 is the outermost part that is in contact with the side of the solid electrolyte layer 30. The inert member 40 extends to the outermost part that is in contact with the side of the solid electrolyte layer 30. The inert member 40 is separated from the negative electrode layer 20, and more specifically, from the first negative electrode active material layer 22. The inert member 40 extends to the end of the solid electrolyte layer 30, but does not come into contact with the negative electrode layer 20. The inert member 40 fills, for example, the space that extends from one side of the positive electrode layer 30 to the end of the solid electrolyte layer 30.

[0123] The inert member 40 is, for example, a gasket. By using a gasket as the inert member 40, cracks in the solid electrolyte layer 30 caused by the pressure difference during the pressing process can be effectively suppressed.

[0124] The inert member 40 has, for example, a single-layer structure. In other embodiments, the inert member 40 may have a multilayer structure. In an inert member 40 having a multilayer structure, each layer may have a different composition from the others. An inert member having a multilayer structure may have, for example, a two-layer, three-layer, four-layer, or five-layer structure. An inert member having a multilayer structure may include, for example, one or more adhesive layers and one or more support layers. The adhesive layer effectively prevents separation between the positive electrode layer 10 and the solid electrolyte layer 30 due to volume changes in the positive electrode layer 10 that occur during the charging and discharging process of the all-solid-state secondary battery 10, and improves the film strength of the inert member 40 by providing bonding force between the support layer and the other layers. The support layer provides support force to the inert member 40, prevents non-uniformity of the pressure applied to the solid electrolyte layer 30 during the pressurizing process or charging and discharging process, and prevents deformation of the shape of the manufactured all-solid-state secondary battery 1.

[0125] Referring to Figure 14, the all-solid-state secondary battery 1 includes a positive electrode 10, a negative electrode 20, and solid electrolyte layers 30, 30a, and 30b disposed between them. The positive electrode layer 10 includes a positive electrode current collector 11 and a first positive electrode active material layer 12a and a second positive electrode active material layer 12b, respectively, disposed on both sides of the positive electrode current collector 11. The solid electrolyte layer 30 includes a first solid electrolyte layer 30a in contact with the first positive electrode active material layer 12a and a second solid electrolyte layer 30b in contact with the second positive electrode active material layer 12b. The negative electrode layer 20 includes a first negative electrode layer 20a in contact with the first solid electrolyte layer 30a and a second negative electrode layer 20b in contact with the second solid electrolyte layer 30b. An inert member 40 is disposed between the first solid electrolyte layer 30a and the second solid electrolyte layer 30b, which face each other, surrounding the sides of the positive electrode layer 10. The inert member 40 includes, for example, a first inert member 50a that contacts the first solid electrolyte layer 30a and a second inert member 40b that contacts the second solid electrolyte layer 30b. Thus, the all-solid-state secondary battery 1 has a bi-cell structure. Because the all-solid-state secondary battery 1 has such a bi-cell structure, the solid electrolyte layer 30 and the negative electrode layer 20 are arranged symmetrically facing each other with the positive electrode layer 10 at the center, so that structural deformation due to pressure applied during the manufacture of the all-solid-state secondary battery 1 is more effectively suppressed. Thus, cracks in the solid electrolyte layer 30 are suppressed during the manufacturing process and / or charge / discharge process of the all-solid-state secondary battery 1, preventing short circuits in the all-solid-state secondary battery 1, and as a result, the cycle characteristics of the all-solid-state secondary battery 1 are further improved. In addition, since only one positive electrode current collector 11 is used for multiple positive electrode active material layers 12a, 12b, the energy density of the all-solid-state secondary battery 1 is increased.

[0126] Referring to Figures 12 to 14, the inert member 40 is, for example, a flame-retardant inert member. By providing flame retardancy, the flame-retardant inert member can prevent thermal runaway and ignition of the all-solid-state secondary battery 1. As a result, the stability of the all-solid-state secondary battery 1 is further improved. By configuring the flame-retardant inert member to absorb residual moisture in the all-solid-state secondary battery 1, deterioration of the all-solid-state secondary battery 1 is prevented, and the lifespan characteristics of the all-solid-state secondary battery 1 are improved.

[0127] The flame-retardant inert member includes, for example, a matrix and a filler. The matrix includes, for example, a base material and a reinforcing material. The matrix includes, for example, a fibrous base material and a fibrous reinforcing material. The matrix may have elasticity because it includes a base material. Therefore, the matrix can effectively accommodate the volume change during charging and discharging of the all-solid-state secondary battery 1 and be positioned in various locations. The base material containing the matrix includes, for example, a first fibrous material. The base material including the first fibrous material can effectively accommodate the volume change of the positive electrode layer 30 that occurs during the charging and discharging process of the all-solid-state secondary battery 1, and can effectively suppress the deformation of the first inert member 40 due to the volume change of the positive electrode layer 30. The first fibrous material is, for example, a material with an aspect ratio of 5 or more, 20 or more, or 50 or more. The first fibrous material is, for example, a material with an aspect ratio of 5 to 1000, 20 to 1000, or 50 to 1000. The first fibrous material is, for example, an insulating material. The first fibrous material, being an insulating material, can effectively prevent short circuits between the positive electrode layer 30 and the negative electrode layer 20 caused by lithium dendrites and the like that generated during the charging and discharging process of the all-solid-state secondary battery 1. The first fibrous material includes, for example, one or more selected from pulp fibers, insulating polymer fibers, and ion-conducting polymer fibers. The inclusion of a reinforcing material in the matrix improves the strength of the matrix. Therefore, the matrix can prevent excessive volume changes during charging and discharging of the all-solid-state secondary battery 1 and prevent deformation of the all-solid-state secondary battery. The reinforcing material included in the matrix includes, for example, a second fibrous material. The inclusion of a second fibrous material in the reinforcing material can further uniformly increase the strength of the matrix. The second fibrous material is, for example, a material with an aspect ratio of 3 or more, 5 or more, or 10 or more. The first fibrous material is, for example, a material with an aspect ratio of 3 to 100, 5 to 100, or 10 to 100. The second fibrous material is, for example, a flame-retardant material. The second fibrous material can effectively suppress ignition caused by thermal runaway that occurs during the charging and discharging process or external impact of the all-solid-state secondary battery 1 due to its flame-retardant properties. The second fibrous material is, for example, glass fiber, metal oxide fiber, or ceramic fiber.

[0128] The flame-retardant inert member contains a filler outside the matrix. The filler may be located inside the matrix, on the matrix surface, or both inside and on the surface. The filler is, for example, an inorganic material. The filler included in the flame-retardant inert member is, for example, a moisture getter, a flame retardant, or a lithium immobilizer. The moisture getter prevents the degradation of the solid-state secondary battery 1 by removing residual moisture from the solid-state secondary battery 1 by adsorbing moisture at temperatures below 100°C. Furthermore, if the temperature of the solid-state secondary battery 1 rises above 150°C due to thermal runaway occurring during the charging / discharging process or external shock, the moisture getter can release the adsorbed moisture and effectively suppress ignition of the solid-state secondary battery 1. The moisture getter is, for example, a metal hydroxide with moisture-adsorbing properties. The metal hydroxides contained in the fillers are, for example, Mg(OH)2, Fe(OH)3, Sb(OH)3, Sn(OH)4, Ti(OH)3, Zr(OH)4, Al(OH)3, or combinations thereof. The flame retardant contains, for example, one or more selected from zinc borate, calcium molybdate zinc complex, MoO3, (NH4)2Mo2O7, Sb2O3, and Sb3O5. The lithium immobilizer is, for example, a compound that reacts with liquid lithium at a temperature of 180°C or higher, which is the melting point of lithium, to immobilize the lithium. The lithium immobilizer can, for example, react with liquid lithium to convert the lithium into other insoluble compounds. The lithium immobilizer is, for example, a metal oxide that is reactive with liquid lithium. The metal oxides contained in the fillers are, for example, TiO2, ZrO2, HfO2, ThO2, or combinations thereof. Metal oxides, for example, react with liquid lithium to produce Li2O and metal. The reaction equation is, for example, 4Li + MO2 -> M + 2Li2O. The reaction of liquid lithium with metal oxides to produce lithium oxide solidifies the liquid lithium. This can suppress leakage of molten liquid lithium to the positive electrode. Therefore, the stability of all-solid-state secondary batteries can be improved.

[0129] The filler content of the flame-retardant inert member is, for example, 1 to 80 parts by weight, 5 to 80 parts by weight, 10 to 80 parts by weight, 20 to 80 parts by weight, 30 to 80 parts by weight, 40 to 80 parts by weight, 50 to 80 parts by weight, 60 to 80 parts by weight, or 65 to 80 parts by weight per 100 parts by weight of the flame-retardant inert member 4.

[0130] The flame-retardant inert member may further include, for example, a binder. The binder may include, for example, a curable polymer or a non-curable polymer. A curable polymer is a polymer that is cured by heat and / or pressure. A curable polymer is, for example, a solid at room temperature. The flame-retardant inert member includes, for example, a heat- and pressure-curable film and / or its cured product. An example of a heat- and pressure-curable polymer is Toray's TSA-66.

[0131] The flame-retardant inert member may further include other materials in addition to the base material, reinforcing material, filler, and binder described above. The flame-retardant inert member may further include, for example, one or more selected from paper, insulating polymers, ion-conducting polymers, insulating inorganic materials, oxide-based solid electrolytes, and sulfide-based solid electrolytes. The insulating polymer may also be an olefin-based polymer such as polypropylene (PP) or polyethylene (PE).

[0132] The density of the base material or reinforcing material contained in the flame-retardant inert member is, for example, 10% to 300%, 10% to 150%, 10% to 140%, 10% to 130%, or 10% to 120% of the density of the positive electrode active material contained in the lithium host layer 22.

[0133] The inert member 40 is a member that does not contain an electrochemically active substance, such as an electrode active material. An electrode active material is a substance that intercalates / releases lithium. The inert member 40 is a member made of a substance other than an electrode active material that is used in the art.

[0134] [Solid electrolyte layer] [Solid electrolyte layer: solid electrolyte] Referring to Figures 6 to 14, the solid electrolyte layer 30 includes a solid electrolyte disposed between the positive electrode layer 10 and the negative electrode layer 20.

[0135] Referring to Figures 6 and 8, the solid electrolyte layer 30 may include, for example, a first two-dimensional sulfide-based solid electrolyte 100 arranged along one direction. By aligning the first two-dimensional sulfide-based solid electrolyte 100 along one direction, the density of the solid electrolyte layer 30 can be further increased. As a result, the energy density of the lithium battery can be further increased.

[0136] The direction in which the first two-dimensional sulfide-based solid electrolyte 100 is aligned is, for example, a direction distinct from the thickness direction (y-direction) of the solid electrolyte layer 30. The angle between the direction in which the first two-dimensional sulfide-based solid electrolyte 100 is aligned and the thickness direction of the solid electrolyte layer 30 is, for example, 10-170°, 20-160°, 30-150°, 14-135°, 60-120°, or 75-105°.

[0137] The first two-dimensional sulfide-based solid electrolyte 100 can be aligned, for example, in a direction substantially perpendicular to the thickness direction of the solid electrolyte layer (the z-direction or the x-direction). That is, the first two-dimensional sulfide-based solid electrolyte 100 can be aligned such that its first surface S1 and / or second surface S2 are positioned parallel to the surface of the solid electrolyte layer 30.

[0138] By including a first two-dimensional sulfide-based solid electrolyte aligned along a direction distinct from the thickness direction of the solid electrolyte layer 30, the growth of lithium dendrites in the thickness direction of the solid electrolyte layer 30 can be suppressed, thereby preventing short circuits and other problems. As a result, degradation of the all-solid-state secondary battery can be suppressed, and its lifespan characteristics can be improved.

[0139] The direction in which the first two-dimensional sulfide-based solid electrolyte 100 is stacked is, for example, similar to the thickness direction of the solid electrolyte layer 30. The angle between the direction in which the first two-dimensional sulfide-based solid electrolyte 100 is stacked and the thickness direction of the solid electrolyte layer 30 is, for example, -30 to 30° or -20 to 20°. That is, the first two-dimensional sulfide-based solid electrolyte 100 can be stacked in the thickness direction of the solid electrolyte layer 30 such that the first surface S1 and / or second surface S2 of the first two-dimensional sulfide-based solid electrolyte 100 are arranged in a direction parallel to the surface of the solid electrolyte layer 30.

[0140] The first two-dimensional sulfide-based solid electrolyte 100 can be stacked, for example, in the thickness direction of the solid electrolyte layer 30. The solid electrolyte layer 30 may contain a first two-dimensional sulfide-based solid electrolyte laminate 200. The solid electrolyte layer 30 may contain multiple first two-dimensional sulfide-based solid electrolyte laminates 200. The number of first two-dimensional sulfide-based solid electrolytes 100 contained in one first two-dimensional sulfide-based solid electrolyte laminate 200 is 2 or more, 5 or more, 10 or more, 50 or more, 100 or more, or 200 or more. The number of first two-dimensional sulfide-based solid electrolytes 100 contained in one first two-dimensional sulfide-based solid electrolyte laminate 200 is 2 to 1000, 5 to 1000, 10 to 1000, 50 to 1000, 100 to 1000, or 200 to 1000. By including a first two-dimensional sulfide-based solid electrolyte 100 that is stacked along a direction similar to the thickness direction of the solid electrolyte layer 30, the growth of lithium dendrites in the thickness direction of the solid electrolyte layer 30 can be suppressed, thereby preventing short circuits and other problems. As a result, the degradation of the all-solid-state secondary battery can be suppressed, and its lifespan characteristics can be improved.

[0141] The content of the first two-dimensional sulfide-based solid electrolyte 100 is, for example, 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or 95 wt% or more of the total weight of the solid electrolyte layer 30. The content of the first two-dimensional sulfide-based solid electrolyte 100 is, for example, 50-100 wt%, 60-100 wt%, 70-100 wt%, 80-100 wt%, 90-99.99 wt%, or 95-99 wt% of the total weight of the solid electrolyte layer 30. By including such a high content of the first two-dimensional sulfide-based solid electrolyte 100 in the solid electrolyte layer 30, the possibility of pinhole P (pinhole) formation on the surface of the solid electrolyte layer 30 during manufacturing can be further reduced. Therefore, the growth of lithium dendrites originating from the pinholes can be more effectively suppressed during charging and discharging of the all-solid-state secondary battery. As a result, the lifespan characteristics of all-solid-state rechargeable batteries can be further improved.

[0142] In contrast, as shown in Figures 7 and 9, in a solid electrolyte layer 30 containing an amorphous sulfide-based solid electrolyte 100A with an aspect ratio of less than 2, lithium dendrites can easily grow in the thickness direction of the solid electrolyte layer 30 because the grain boundaries between the amorphous sulfide-based solid electrolyte 100A particles are connected in the thickness direction of the solid electrolyte layer 30. Furthermore, since pinholes P (pinholes) can easily form between the amorphous sulfide-based solid electrolyte 100A particles on the surface of the solid electrolyte layer 30, lithium dendrites can grow even more easily through such pinholes. As a result, the possibility of short circuits in lithium batteries containing such solid electrolyte layers 30 increases, and the cycle characteristics deteriorate.

[0143] The first two-dimensional sulfide-based solid electrolyte 100 may be selected from among the sulfide-based solid electrolytes contained in the positive electrode active material layer 12. In other embodiments, the solid electrolyte layer 30 may include an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof.

[0144] The oxide-based solid electrolyte can be selected from among the oxide-based solid electrolytes used in the positive electrode active material layer 12.

[0145] Polymeric solid electrolytes may include, for example, dry polymeric electrolytes, gel polymeric electrolytes, or combinations thereof.

[0146] A dry polymer electrolyte is, for example, an electrolyte that is a mixture of a lithium salt and a polymer. A dry polymer electrolyte is, for example, a polymer electrolyte that does not contain a liquid electrolyte. The polymers contained in a dry polymer electrolyte may be, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), poly(styrene-β-ethylene oxide) block copolymer (PS-PEO), poly(styrene-butadiene), poly(styrene-isoprene-styrene), poly(styrene-β-divinylbenzene) block copolymer, poly(styrene-ethylene oxide-styrene) block copolymer, or combinations thereof. Any lithium salt used for lithium salts in the art may be used. For example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(x and y are 1-20), LiCl, LiI, or mixtures thereof, etc.

[0147] A gel polymer electrolyte is an electrolyte containing a liquid electrolyte and a polymer. The liquid electrolyte is, for example, a mixture of a lithium salt and an organic solvent. The polymer contained in the gel polymer electrolyte can be selected from among the polymers contained in dry polymer electrolytes. The lithium salt can be selected from among the lithium salts used in dry polymer electrolytes.

[0148] The solid electrolyte layer 30 is also impermeable to lithium polysulfide. Therefore, it can block side reactions between lithium polysulfide, which is generated during the charging and discharging of the sulfide-based positive electrode active material, and the negative electrode layer. Consequently, the cycle characteristics of the all-solid-state secondary battery 1, which includes the solid electrolyte layer 30, can be improved.

[0149] [Solid electrolyte layer: binder] The solid electrolyte layer 30 may, for example, contain a binder. Examples of binders included in the solid electrolyte layer 30 include styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene, but are not limited to these; any binder usable in the relevant art is acceptable. The binder in the solid electrolyte layer 30 may be the same as, or different from, the binder in the positive electrode active material layer 12 and the negative electrode active material layer 22. The binder is optional.

[0150] The binder content of the solid electrolyte layer 30 is 0.1-10 wt%, 0.1-5 wt%, 0.1-3 wt%, 0.1-1 wt%, 0-0.5 wt%, or 0-0.1 wt% relative to the total weight of the solid electrolyte layer 30.

[0151] [Negative electrode layer] [Negative electrode layer: negative electrode active material] Referring to Figures 10-14, the negative electrode layer 20 includes a first negative electrode active material layer 22. The first negative electrode active material layer 22 includes, for example, a negative electrode active material and a binder.

[0152] The negative electrode active material contained in the first negative electrode active layer 22 is, for example, a negative electrode material that forms an alloy or compound with lithium.

[0153] The negative electrode active material contained in the first negative electrode active material layer 22 has, for example, a particle form. The average particle size of the negative electrode active material having a particle form is, for example, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, 500 nm or less, 300 nm or less, or 100 nm or less. The average particle size of the negative electrode active material having a particle form is, for example, 10 nm to 4 μm, 10 nm to 3 μm, 10 nm to 2 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 300 nm, or 10 nm to 100 nm. Having an average particle size in such a range of negative electrode active material makes reversible absorption and / or desorbing of lithium during charging and discharging even easier. The average particle size of the negative electrode active material is, for example, the median diameter (D50) measured using a laser particle size analyzer.

[0154] The negative electrode active material contained in the first negative electrode active material layer 22 includes, for example, one or more selected from carbon-based negative electrode active materials and metal or semimetallic negative electrode active materials.

[0155] Carbon-based negative electrode active materials include, for example, amorphous carbon, crystalline carbon, porous carbon, or combinations thereof.

[0156] Carbon-based negative electrode active materials are particularly amorphous carbon. Amorphous carbons include, for example, carbon black (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB), and graphene, but are not necessarily limited to these; any material classified as amorphous carbon in the context of the relevant technology can be used. Amorphous carbon is carbon that does not have crystallinity or has very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon.

[0157] Carbon-based negative electrode active materials include, for example, porous carbon. The pore volume of porous carbon is, for example, 0.1 cc / g to 10.0 cc / g, 0.5 cc / g to 5 cc / g, or 0.1 cc / g to 1 cc / g. The average pore diameter of porous carbon is, for example, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 10 nm. The BET specific surface area of ​​porous carbon is, for example, 100 m². 2 / g~3000m 2 It is / g.

[0158] The metallic or metalloid anode active material includes, but is not limited to, one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Any metallic or metalloid anode active material that forms an alloy or compound with lithium in the art is acceptable. For example, nickel (Ni) does not form an alloy with lithium and is therefore not a metallic anode active material.

[0159] The first negative electrode active material layer 22 contains one type of negative electrode active material or a mixture of several different negative electrode active materials. For example, the first negative electrode active material layer 22 contains only amorphous carbon or one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). In other embodiments, the first negative electrode active material layer 22 contains a mixture of amorphous carbon and one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The mixing ratio of amorphous carbon and gold, etc., is, by weight, for example, 99:1 to 1:99, 10:1 to 1:2, 5:1 to 1:1, or 4:1 to 2:1, but is not necessarily limited to such ranges and is selected according to the required characteristics of the all-solid-state secondary battery 1. Having such a composition in the negative electrode active material further improves the cycle characteristics of the all-solid-state secondary battery 1.

[0160] The negative electrode active material contained in the first negative electrode active material layer 22 includes, for example, a mixture of first particles made of amorphous carbon and second particles made of a metal or metalloid. The metal or metalloid includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). In other embodiments, the metalloid is a semiconductor. The content of the second particles is 1 to 99% by weight, 1 to 60% by weight, 8 to 60% by weight, 10 to 50% by weight, 15 to 40% by weight, or 20 to 30% by weight based on the total weight of the mixture. Having the second particles in such a range of content further improves the cycle characteristics of, for example, the all-solid-state secondary battery 1.

[0161] In other embodiments, the first negative electrode active material layer 22 includes a composite negative electrode active material. The composite negative electrode active material may include, for example, a carbon-based support and a metallic negative electrode active material supported on the carbon-based support. Having such a structure in the composite negative electrode active material prevents uneven distribution of the metallic negative electrode active material within the first negative electrode active material layer, resulting in a uniform distribution. As a result, the cycle characteristics of the all-solid-state secondary battery 1 including the first negative electrode active material layer 22 are further improved.

[0162] The metallic anode active material supported on a carbon-based support includes, for example, metals, metal oxides, composites of metals and metal oxides, or combinations thereof. Metals include, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Metal oxides include, for example, gold (Au) oxide, platinum (Pt) oxide, palladium (Pd) oxide, silicon (Si) oxide, silver (Ag) oxide, aluminum (Al) oxide, bismuth (Bi) oxide, tin (Sn) oxide, and zinc (Zn) oxide. Metal oxides include, for example, Au x O y (0 <x≦2、0<y≦3)、Pt x O y (0 <x≦1、0<y≦2)、Pd x O y(0 < x ≤ 1, 0 < y ≤ 1), Si x O y (0 < x ≤ 1, 0 < y ≤ 2), Ag x O y (0 < x ≤ 2, 0 < y ≤ 1), Al x O y (0 < x ≤ 2, 0 < y ≤ 3), Bi x O y (0 < x ≤ 2, 0 < y ≤ 3), Sn x O y (0 < x ≤ 1, 0 < y ≤ 2), Zn x O y (0 < x ≤ 1, 0 < y ≤ 1), or may include combinations thereof. The composite of metal and metal oxide is, for example, a composite of Au and Au x O y (0 < x ≤ 2, 0 < y ≤ 3), a composite of Pt and Pt x O y (0 < x ≤ 1, 0 < y ≤ 2), a composite of Pd and Pd x O y (0 < x ≤ 1, 0 < y ≤ 1), a composite of Si and Si x O y (0 < x ≤ 1, 0 < y ≤ 2), a composite of Ag and Ag x O y (0 < x ≤ 2, 0 < y ≤ 1), a composite of Al and Al x O y (0 < x ≤ 2, 0 < y ≤ 3), a composite of Bi and Bi x O y (0 < x ≤ 2, 0 < y ≤ 3), a composite of Sn and Sn x O y (0 < x ≤ 1, 0 < y ≤ 2), a composite of Zn and Zn x O y (0 < x ≤ 1, 0 < y ≤ 1), or may include combinations thereof.

[0163] Carbon-based supports include, for example, amorphous carbon. Amorphous carbon includes, for example, carbon black (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB), graphene, activated carbon, carbon nanofibers (CNF), and carbon nanotubes (CNT), but is not limited to these; any material classified as amorphous carbon in the relevant art can be used. Amorphous carbon is carbon that does not have crystallinity or has very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon. Carbon paper is a material such as a carbon-based negative electrode active material.

[0164] The composite anode active material may, for example, have a particulate form. The particle size of the composite anode active material having a particulate form is, for example, 10 nm to 4 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. Having a particle size in such a range for the composite anode active material makes the reversible absorption and / or desorbing of lithium during charging and discharging even easier. The metallic anode active material supported on a support may, for example, have a particulate form. The particle size of the metallic anode active material may, for example, be 1 nm to 200 nm, 1 nm to 150 nm, 5 nm to 100 nm, or 10 nm to 50 nm. The carbon-based support may, for example, have a particulate form. The particle size of the carbon-based support is, for example, 10 nm to 2 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. Having such a particle size range allows the carbon-based support to be more uniformly distributed within the first anode active material layer. The carbon-based support is also, for example, nanoparticles with a particle size of 500 nm or less. The particle size of the composite anode active material, the particle size of the metallic anode active material, and the particle size of the carbon-based support are, for example, average particle sizes. The average particle size is, for example, the median diameter (D50) measured using a laser particle size analyzer. In other embodiments, the average particle size may be automatically determined using software from, for example, electron microscope images, or passively determined manually.

[0165] [Negative electrode layer: Binder] The binder contained in the first negative electrode active material layer 22 is, 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 that can be used in the art is acceptable. The binder may consist of one or more different binders.

[0166] The inclusion of a binder in the first negative electrode active material layer 22 stabilizes the first negative electrode active material layer 22 on the negative electrode current collector 21. Furthermore, cracking of the first negative electrode active material layer 22 is suppressed despite volume changes and / or relative positional changes of the first negative electrode active material layer 22 during the charge-discharge process. For example, if the first negative electrode active material layer 22 does not contain a binder, the first negative electrode active material layer 22 can easily separate from the negative electrode current collector 21. The detachment of the first negative electrode active material layer 22 from the negative electrode current collector 21 increases the likelihood of a short circuit occurring due to the exposed portion of the negative electrode current collector 21 coming into contact with the solid electrolyte layer 30. The first negative electrode active material layer 22 is manufactured, for example, by coating a slurry in which the materials constituting the first negative electrode active material layer 22 are dispersed onto the negative electrode current collector 21 and drying it. By incorporating a binder into the first negative electrode active material layer 22, stable dispersion of the negative electrode active material in the slurry is possible. For example, when the slurry is applied onto the negative electrode current collector 21 by screen printing, screen clogging (e.g., clogging due to aggregates of the negative electrode active material) can be suppressed.

[0167] [Negative electrode layer: Other additives] The first negative electrode active material layer 22 may further contain additives used in conventional all-solid-state secondary batteries 1, such as fillers, coating agents, dispersants, and ion conductivity enhancers.

[0168] [Negative electrode layer: solid electrolyte] The first negative electrode active material layer 22 may further contain a solid electrolyte. The solid electrolyte is, for example, a material selected from among the solid electrolytes contained in the solid electrolyte layer 30. The solid electrolyte contained in the first negative electrode active material layer 22 may act as a reaction site where the formation of lithium metal is initiated within the first negative electrode active material layer 22, as a space where the formed lithium metal is stored, or as a pathway for the transfer of lithium ions. The solid electrolyte is optional.

[0169] In the first negative electrode active material layer 22, the content of the solid electrolyte is, for example, high in the region adjacent to the solid electrolyte layer 30 and low in the region adjacent to the negative electrode current collector 21. In the first negative electrode active material layer 22, the solid electrolyte may have a concentration gradient in which the concentration decreases from the region adjacent to the solid electrolyte layer 30 to the region adjacent to the negative electrode current collector 21.

[0170] [Negative electrode layer: First negative electrode active material layer] The initial charge capacity (B) of the first negative electrode active material layer is less than 50%, 45% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the initial charge capacity (A) of the positive electrode active material layer. For example, the ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer 22 to the initial charge capacity (A) of the positive electrode active material layer is 0.005 to 0.45. The initial charge capacity of the positive electrode active material layer 12 is determined from the first open circuit voltage (1 st open circuit voltage) to the maximum charging voltage with respect to Li / Li+. The initial charge capacity of the first negative electrode active material layer 22 is determined at 0.01 V with respect to Li / Li+ from the second open circuit voltage (2 nd open circuit voltage).

[0171] The maximum charging voltage is determined by the type of the positive electrode active material. The maximum charging voltage is, for example, 1.5 V, 2.0 V, 2.5 V, 2.8 V, 3.0 V, 3.5 V, 4.0 V, 4.2 V, or 4.3 V. For example, the maximum charging voltage of Li2S or a Li2S composite is also 2.5 V with respect to Li / Li + For example, the maximum charging voltage of Li 2 S or a Li2S composite is 3.0 V with respect to Li / Li + The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer 22 to the initial charge capacity (A) of the positive electrode active material layer is, for example, 0.001 to less than 0.5, 0.01 to 0.45, 0.01 to 0.4, 0.01 to 0.3, 0.01 to 0.2, or 0.05 to 0.1.

[0172] The initial charge capacity (mAh) of the positive electrode active material layer 12 is obtained by multiplying the charge specific capacity (mAh / g) of the positive electrode active material by the mass (g) of the positive electrode active material in the positive electrode active material layer 12. When various positive electrode active materials are used, the charge specific capacity × mass value is calculated for each positive electrode active material, and the sum of these values ​​is the initial charge capacity of the positive electrode active material layer 12. The initial charge capacity of the first negative electrode active material layer 22 is calculated in a similar manner. The initial charge capacity of the first negative electrode active material layer 22 is obtained by multiplying the charge specific capacity (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the first negative electrode active material layer 22. When various negative electrode active materials are used, the charge specific capacity × mass value is calculated for each negative electrode active material, and the sum of these values ​​is the initial charge capacity of the first negative electrode active material layer 22. The charge specific capacity densities of the positive electrode active material and the negative electrode active material can be measured using an all-solid-state half-cell with lithium metal as the relative electrode. The initial charge capacity of the positive electrode active material layer 12 and the first negative electrode active material layer 22 is constant at a current density of, for example, 0.1 mA / cm². 2 This can be directly measured using an all-solid-state half-cell. With respect to the positive electrode, the measurement is taken from the first open-circuit voltage (OCV) to the maximum charging voltage, for example, 3.0V (vs. Li / Li + The measurement can be performed for operating voltages up to 3.0V. For the negative electrode, the measurement can be performed for operating voltages from the second open-circuit voltage (OCV) up to 0.01V for the negative electrode, for example, lithium metal. For example, an all-solid-state half-cell with a positive electrode active material layer can be measured from the first open-circuit voltage up to 3.0V at a rate of 0.1mA / cm². 2 When charged with a constant current, the all-solid-state half-cell having a first negative electrode active material layer draws 0.1 mA / cm² from the second open-circuit voltage up to 0.01 V. 2 It can be charged with a constant current. The current density during constant current charging is, for example, 0.2 mA / cm². 2 , or 0.5 mA / cm 2It is also the case. The all-solid-state half-cell having the positive electrode active material layer can be charged, for example, from the first open-circuit voltage to 2.5 V, 2.0 V, 3.5 V, or 4.0 V. The maximum charging voltage of the positive electrode active material layer can be determined by the maximum voltage of the battery that satisfies the safety conditions according to JIS C8712:2015 of the Japanese Standards Association.

[0173] If the initial charging capacity of the first negative electrode active material layer 22 is excessively small, the thickness of the first negative electrode active material layer 22 becomes very thin, so that lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 in the repeated charge-discharge process collapse the first negative electrode active material layer 22 and it is difficult to improve the cycle characteristics of the all-solid-state secondary battery 1. If the charging capacity of the first negative electrode active material layer 22 increases excessively, the energy density of the all-solid-state secondary battery 1 decreases, and the internal resistance of the all-solid-state secondary battery 1 due to the first negative electrode active material layer 22 increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery 1.

[0174] The thickness of the first negative electrode active material layer 22 is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer 12. The thickness of the first negative electrode active material layer 22 is, for example, 1 to 50%, 1 to 40%, 1 to 30%, 1 to 20%, 1 to 10%, or 1 to 5% of the thickness of the positive electrode active material layer 12. The thickness of the first negative electrode active material layer 22 is, for example, 1 μm to 20 μm, 2 μm to 15 μm, or 3 μm to 10 μm. If the thickness of the first negative electrode active material layer 22 is excessively thin, lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 collapse the first negative electrode active material layer 22 and it is difficult to improve the cycle characteristics of the all-solid-state secondary battery 1. If the thickness of the first negative electrode active material layer 22 increases excessively, the energy density of the all-solid-state secondary battery 1 decreases, and the internal resistance of the all-solid-state secondary battery 1 due to the first negative electrode active material layer 22 increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery 1. If the thickness of the first negative electrode active material layer 22 decreases, for example, the initial charging capacity of the first negative electrode active material layer 22 also decreases.

[0175] [Negative electrode layer: Second negative electrode active material layer] Although not shown in the drawings, the all-solid-state secondary battery 1 further includes a second negative electrode active material layer, which is placed between, for example, the negative electrode current collector 21 and the first negative electrode active material layer 22 after charging. The second negative electrode active material layer is a metallic layer containing lithium or a lithium alloy. The metallic layer contains lithium or a lithium alloy. Therefore, since the second negative electrode active material layer is a metallic layer containing lithium, it acts, for example, as a lithium reservoir. Examples of lithium alloys include, but are not limited to, Li-Al alloys, Li-Sn alloys, Li-In alloys, Li-Ag alloys, Li-Au alloys, Li-Zn alloys, Li-Ge alloys, and Li-Si alloys; any alloy used as a lithium alloy in the art can be used. The second negative electrode active material layer may consist of one of such alloys or lithium, or of various types of alloys. The second negative electrode active material layer is, for example, a plated layer. The second negative electrode active material layer is deposited, for example, between the first negative electrode active material layer 22 and the negative electrode current collector 21 during the charging process of the all-solid-state secondary battery 1.

[0176] The thickness of the second negative electrode active material layer is not particularly limited, but for example, it can be 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the thickness of the second negative electrode active material layer is excessively thin, it will be difficult for the second negative electrode active material layer to perform its role as a lithium reservoir. If the thickness of the second negative electrode active material layer is excessively thick, the mass and volume of the all-solid-state secondary battery 1 will increase, which may actually degrade the cycle characteristics of the all-solid-state secondary battery 1.

[0177] In other embodiments, the second negative electrode active material layer in the all-solid-state secondary battery 1 may be placed, for example, between the negative electrode current collector 21 and the first negative electrode active material layer 22 before the assembly of the all-solid-state secondary battery 1. When the second negative electrode active material layer 23 is placed between the negative electrode current collector 21 and the first negative electrode active material layer 22 before the assembly of the all-solid-state secondary battery 1, the second negative electrode active material layer acts as a lithium reservoir because it is a lithium-containing metal layer. For example, lithium foil may be placed between the negative electrode current collector 21 and the first negative electrode active material layer 22 before the assembly of the all-solid-state secondary battery 1.

[0178] If the second negative electrode active material layer is deposited by charging after the assembly of the all-solid-state secondary battery 1, the energy density of the all-solid-state secondary battery 1 increases because the second negative electrode active material layer is not included during the assembly of the all-solid-state secondary battery 1. When the all-solid-state secondary battery 1 is charged, it is charged beyond the charging capacity of the first negative electrode active material layer 22. That is, the first negative electrode active material layer 22 is overcharged. In the initial stages of charging, lithium is absorbed into the first negative electrode active material layer 22. The negative electrode active material contained in the first negative electrode active material layer 22 forms an alloy or compound with lithium ions that have moved from the positive electrode layer 10. If the capacity of the first negative electrode active material layer 22 is exceeded during charging, for example, lithium is deposited on the back surface of the first negative electrode active material layer 22, i.e., between the negative electrode current collector 21 and the first negative electrode active material layer 22, and the deposited lithium forms a metal layer corresponding to the second negative electrode active material layer. The second negative electrode active material layer is a metal layer mainly composed of lithium (i.e., metallic lithium). Such results can be obtained, for example, by including a substance in the first negative electrode active material layer 22 that forms an alloy or compound with lithium. During discharge, the lithium in the first negative electrode active material layer 22 and the second negative electrode active material layer, i.e., the metal layer, is ionized and moves toward the positive electrode layer 10. Therefore, lithium can be used as the negative electrode active material in the all-solid-state secondary battery 1. Furthermore, since the first negative electrode active material layer 22 covers the second negative electrode active material layer, it acts as a protective layer for the second negative electrode active material layer, i.e., the metal layer, and also suppresses the deposition and growth of lithium dendrites. Therefore, short circuits and capacity degradation of the all-solid-state secondary battery 1 are suppressed, and as a result, the cycle characteristics of the all-solid-state secondary battery 1 are improved. Furthermore, when the second negative electrode active material layer is positioned by charging after the assembly of the all-solid-state secondary battery 1, the negative electrode layer 20, that is, the negative electrode current collector 21, the first negative electrode active material layer 22, and the region between them, are lithium (Li)-free regions that do not contain lithium (Li) in the initial state or after complete discharge of the all-solid-state secondary battery 1.

[0179] [Negative electrode layer: negative electrode current collector] The negative electrode current collector 21 is composed of a material that does not react with lithium, i.e., does not form any alloys or compounds. The materials that make up the negative electrode current collector 21 include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), but are not necessarily limited to these; any material that can be used as an electrode current collector in the art can be used. The negative electrode current collector 21 may be composed of one of the aforementioned metals, or of an alloy or coating material of two or more metals. The negative electrode current collector 21 may be in the form of a plate or foil, for example.

[0180] The all-solid-state secondary battery 1 may further include, for example, a thin film containing an element that forms an alloy with lithium on one surface of the negative electrode current collector 21, although this is not shown in the drawings. The thin film is placed between the negative electrode current collector 21 and the first negative electrode active material layer 22. The thin film contains, for example, an element that forms an alloy with lithium. The elements that form an alloy with lithium include, for example, gold, silver, zinc, tin, indium, silicon, aluminum, and bismuth, but are not necessarily limited to these; any element that forms an alloy with lithium in the art can be used. The thin film is composed of one of these metals or an alloy of various types of metals. By placing the thin film on one surface of the negative electrode current collector 21, for example, the deposition morphology of the second negative electrode active material layer deposited between the thin film 24 and the first negative electrode active material layer 22 can be further flattened, and the cycle characteristics of the all-solid-state secondary battery 1 can be further improved.

[0181] The thickness of the thin film is, for example, 1 nm to 800 nm, 10 nm to 700 nm, 50 nm to 600 nm, or 100 nm to 500 nm. If the thickness of the thin film is less than 1 nm, the function of the thin film is difficult to achieve. If the thickness of the thin film is excessively thick, the thin film itself may absorb lithium, reducing the amount of lithium deposited at the negative electrode, which can lower the energy density of the all-solid-state battery and degrade the cycle characteristics of the all-solid-state secondary battery 1. The thin film can be placed on the negative electrode current collector 21 by methods such as vacuum deposition, sputtering, or plating, but is not necessarily limited to such methods; any method capable of forming a thin film in the relevant art can be used.

[0182] Although not shown in the drawings, the negative electrode current collector 21 may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may also be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The polymer may also be an insulating polymer. By including an insulating thermoplastic polymer in the base film, the base film may soften or liquefy when a short circuit occurs, interrupting battery operation and suppressing a rapid increase in current. The metal layer may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or alloys thereof. The negative electrode current collector 21 may further include metal pieces and / or lead tabs. For more specific details regarding the base film, metal layer, metal chip, and lead tab of the negative electrode current collector 21, please refer to the positive electrode current collector 11 described above. The negative electrode current collector 21 having such a structure can reduce the weight of the negative electrode, thereby improving the energy density of the negative electrode and the lithium battery.

[0183] The present invention will be explained in more detail through the following examples and comparative examples. However, the examples are for illustrative purposes only and do not limit the scope of the present invention to them alone.

[0184] (Two-dimensional sulfide solid electrolyte) Production example 1: First two-dimensional sulfide solid electrolyte A rGO (reduced graphene oxide)-Li6PS5Cl composite was prepared as the first two-dimensional solid electrolyte. The rGO-Li6PS5Cl composite was fabricated by the method disclosed in Materials Today Energy 23 (2022) 100913, except that the weight ratio of rGO to Li6PS5Cl was changed to 1:60. The rGO-Li6PS5Cl composite consisted of an rGO core coated with a Li6PS5Cl shell, which is an argyrodite-type crystalline material. The rGO-Li6PS5Cl composite had a flake morphology with a thickness of approximately 1 μm, a length of approximately 3 μm, and an aspect ratio of 3. The plane view of the rGO-Li6PS5Cl composite showed a polygonal morphology. The thickness and length of the rGO-Li6PS5Cl composite are average values ​​calculated from multiple composite particles read from scanning electron microscope images.

[0185] (All-solid-state secondary battery) Example 1: Mono-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI composite), flake solid electrolyte:particulate solid electrolyte = 10:40 weight ratio, first two-dimensional solid electrolyte (Negative electrode layer manufacturing) A 10 μm thick SUS foil was prepared as the negative electrode current collector. In addition, carbon black (CB) with a primary particle size of approximately 30 nm and silver (Ag) particles with an average particle size of approximately 60 nm were prepared as the negative electrode active material.

[0186] A mixed powder of carbon black (CB) and silver (Ag) particles in a 3:1 weight ratio was placed in a container, and 4 g of NMP solution containing 7 wt% PVDF binder (Kureha Corporation #9300) was added to prepare a mixed solution. NMP (N-methyl-2-pyrrolidone) was gradually added to the prepared mixed solution while stirring to produce a slurry. The prepared slurry was applied to a SUS sheet using a bar coater and dried in air at 80°C for 10 minutes to prepare a laminate. The prepared laminate was vacuum dried at 40°C for 10 hours. The dried laminate was cold roll pressed to flatten the surface of the first negative electrode active material layer of the laminate and to produce a negative electrode layer. The thickness of the first negative electrode active material layer was approximately 15 μm. The area of ​​the first negative electrode active material layer and the negative electrode current collector were the same. The initial charge capacity of the negative electrode layer (i.e., the first negative electrode active material layer) was measured using the half-cell described above.

[0187] (Positive electrode layer manufacturing) A Li2S-C-LiI composite was prepared as the positive electrode active material. The Li2S-C-LiI composite was manufactured by the method disclosed in Nano Lett. 2016, 16, 7, 4521-4527, except that Li6PS5Cl was replaced with LiI. An rGO (reduced graphene oxide)-Li6PS5Cl composite, manufactured in Manufacturing Example 1, was prepared as the first two-dimensional solid electrolyte. Li6PS5Cl (D50 = 3.0 μm, crystalline), an argyrodite-type crystalline solid electrolyte, was prepared. Ketjen black was prepared as the conductive agent. The aspect ratio of the irregular particulate solid electrolyte was less than 2.

[0188] Such materials were mixed by weight in the ratio of positive electrode active material:first two-dimensional solid electrolyte:amorphous particulate solid electrolyte:conductive agent = 40:10:40:10 to prepare a positive electrode mixture. The positive electrode mixture was obtained by dry mixing using a ball mill. The positive electrode mixture obtained by ball milling formed an ionic conductive and conductive network.

[0189] The positive electrode mixture was placed on one surface of a carbon-coated aluminum foil positive electrode current collector, and the positive electrode layer was manufactured by plate pressing at a pressure of 200 MPa for 10 minutes. The thickness of the positive electrode layer was approximately 120 μm. The thickness of the positive electrode active material layer was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm. The area of ​​the positive electrode active material layer and the positive electrode current collector were the same. The initial charge capacity of the positive electrode layer (i.e., the positive electrode active material layer) was measured using the aforementioned half-cell. The ratio (B / A) of the initial charge capacity of the first negative electrode active material layer (B) to the initial charge capacity of the positive electrode active material layer (A) was less than 0.5. The initial charge capacity of the positive electrode active material layer was measured at the first open-circuit voltage (1 st open circuit voltage) to 2.8 V vs. Li / Li + This was determined by the charging up to 2. The initial charge capacity of the first negative electrode active material layer is determined by the second open circuit voltage (2 nd open circuit voltage) to 0.01 V vs. Li / Li + This was determined by the charging time. In addition, in Examples 2-10 and 12, the ratio (B / A) was less than 0.5.

[0190] (Manufacturing of solid electrolyte layer) To a Li6PS5Cl solid electrolyte (D50 = 3.0 μm, crystalline) which is an argyrodite-type crystal, 1.5 parts by weight of an acrylic binder was added to 98.5 parts by weight of the solid electrolyte to prepare a mixture. While stirring, octyl acetate was added to the prepared mixture to produce a slurry. The produced slurry was coated onto a non-woven fabric with a thickness of 15 μm placed on a PET substrate with a thickness of 75 μm using a bar coater, and dried at a temperature of 80 °C in air for 10 minutes to obtain a laminate. The obtained laminate was vacuum dried at 80 °C for 2 hours. A solid electrolyte layer was produced by the above steps.

[0191] (Flame-retardant inert member) A slurry obtained by mixing cellulose fiber, glass fiber, aluminum hydroxide (Al(OH)3), an acrylic binder and a solvent was formed into a gasket shape, and then the solvent was removed to produce a flame-retardant inert member.

[0192] The weight ratio of cellulose fiber, glass fiber, aluminum hydroxide (Al(OH)3), and the acrylic binder was 20:8:70:2. The thickness of the inert member was 120 μm.

[0193] Before placing the produced flame-retardant inert member on the solid electrolyte layer, it was vacuum heat-treated at 80 °C for 5 hours to remove moisture and the like of the flame-retardant inert member.

[0194] (Manufacture of all-solid-state secondary battery) Referring to FIG. 1, a solid electrolyte layer was disposed on a negative electrode layer such that a first negative electrode active material layer was in contact with the solid electrolyte layer. A flame-retardant inert member was disposed on the solid electrolyte layer by thermal pressing to prepare a negative electrode layer / solid electrolyte layer / inert member laminate.

[0195] An electrode assembly (electrode assembly) was prepared by placing the inert member on one surface of the positive electrode layer so as to face the positive electrode active material layer. The inert member was positioned around the positive electrode layer, surrounding its sides and in contact with the solid electrolyte layer. The inert member was used as a gasket. The positive electrode layer was placed on the center of the solid electrolyte layer, with the gasket surrounding the positive electrode layer and extending to the end of the solid electrolyte layer. The area of ​​the positive electrode layer was approximately 90% of the solid electrolyte layer area, and the gasket was placed over the remaining 10% of the solid electrolyte layer where the positive electrode layer was not located.

[0196] The prepared negative electrode layer / solid electrolyte layer / positive electrode layer electrode assembly was subjected to plate press processing. Such press processing sinters the solid electrolyte layer, improving the battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 μm. The sintered electrode assembly was placed in a pouch and sealed to prepare the sealed electrode assembly. Parts of the positive electrode current collector and negative electrode current collector protruded from the outside of the sealed electrode assembly and were used as the positive electrode layer terminals and negative electrode layer terminals.

[0197] An electrode assembly was placed between two pressure plates (not shown), the two pressure plates were screwed together, and a constant pressure was applied to both sides of the electrode assembly to manufacture an all-solid-state secondary battery.

[0198] Example 2: Mono-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI composite), flake solid electrolyte:particulate solid electrolyte = 5:45 weight ratio (including first two-dimensional solid electrolyte) An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of flake solid electrolyte to particulate solid electrolyte was changed to 5:45.

[0199] Example 3: Mono-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI composite), flake solid electrolyte:particulate solid electrolyte = 20:20 weight ratio (including first two-dimensional solid electrolyte) An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of flake solid electrolyte to particulate solid electrolyte was changed to 20:20.

[0200] Example 4: Mono-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI composite), flake solid electrolyte:particulate solid electrolyte = 30:20 weight ratio (including first two-dimensional solid electrolyte) An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of flake solid electrolyte to particulate solid electrolyte was changed to 30:20.

[0201] Example 5: Mono-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI composite), flake solid electrolyte:particulate solid electrolyte = 40:10 by weight ratio (including first two-dimensional solid electrolyte) An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of flake solid electrolyte to particulate solid electrolyte was changed to 40:10.

[0202] Example 6: Mono-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI-2D solid electrolyte composite), flake solid electrolyte:particulate solid electrolyte=10:40 weight ratio, first and second two-dimensional solid electrolytes An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that a Li2S-C-LiI-2D solid electrolyte composite was used instead of a Li2S-C-LiI composite as the positive electrode active material.

[0203] The Li2S-C-LiI-2D solid electrolyte complex was prepared by the following method.

[0204] A Li2S-C-LiI composite was prepared in the same manner as in Example 1. A 4:1 weight ratio mixture of the Li2S-C-LiF composite and the rGO (reduced graphene oxide)-Li6PS5Cl composite prepared in Production Example 1 was mixed slowly using a mixer. Then, the mixture was compounded again using the mixer at a rotation speed of approximately 100 to 2000 rpm for approximately 0.1 to 20 hours to prepare a Li2S-C-LiI-2D solid electrolyte composite.

[0205] Example 7: Mono-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI-2D solid electrolyte composite), flake solid electrolyte: particulate solid electrolyte = 0:50 weight ratio, second two-dimensional solid electrolyte An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the Li2S-CNF composite used in Example 6 was used as the positive electrode active material, the weight ratio of flake solid electrolyte to particulate solid electrolyte in the positive electrode mixture was changed to 0:50, and the plate solid electrolyte was not used.

[0206] Example 8: Mono-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI composite), flake solid electrolyte:particulate solid electrolyte = 10:40 weight ratio, 2-layer positive electrode active material layer (flake solid electrolyte placed at the top) A first cathode mixture was prepared using the same method as in Example 1.

[0207] The second cathode mixture was prepared in the same manner as in Example 1, except that the weight ratio of flake solid electrolyte to particulate solid electrolyte was changed to 0:50 and the flake solid electrolyte was not used.

[0208] An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that a first positive electrode mixture (containing flake solid electrolyte) and a second positive electrode mixture (flake solid electrolyte component) were sequentially arranged on a positive electrode current collector to produce the positive electrode layer.

[0209] The positive electrode active material layer consisted of a first positive electrode active material layer derived from the first positive electrode mixture and a second positive electrode active material layer derived from the second positive electrode mixture, each with a thickness of 50 μm.

[0210] The first positive electrode active material layer adjacent to the positive electrode current collector contained a plate solid electrolyte, while the second positive electrode active material layer adjacent to the solid electrolyte layer was free of flake solid electrolyte.

[0211] Example 9: Mono-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI composite), flake solid electrolyte:particulate solid electrolyte = 10:40 weight ratio, 2-layer positive electrode active material layer (flake solid electrolyte placed at the lower end) An all-solid-state secondary battery was manufactured in the same manner as in Example 8, except that the positions of the first positive electrode active material layer and the second positive electrode active material layer were reversed, the second positive electrode active material layer was placed adjacent to the positive electrode current collector, and the first positive electrode active material layer was placed adjacent to the solid electrolyte layer. The second positive electrode active material layer adjacent to the positive electrode current collector contained flake solid electrolyte, while the first positive electrode active material layer adjacent to the solid electrolyte layer was free of flake solid electrolyte.

[0212] Example 10: Mono-cell all-solid-state secondary battery, oxide-based cathode active material (NCA), flake solid electrolyte:particulate solid electrolyte = 10:40 by weight ratio (Positive electrode layer manufacturing) LiNi coated with Li2O-ZrO2(LZO) is used as the positive electrode active material. 0.8 Co 0.15 Mn 0.05O2(NCM) was prepared. The LZO-coated cathode active material was manufactured by the method described in Korean Published Patent No. 10-2016-0064942. As the first two-dimensional solid electrolyte, an rGO (reduced graphene oxide)-Li6PS5Cl composite manufactured in Manufacturing Example 1 was prepared. Li6PS5Cl, an argyrodite-type crystalline solid electrolyte with an irregular shape and particulate form (D50 = 0.5 μm, crystalline), was prepared. A polytetrafluoroethylene (PTFE) binder was prepared. Carbon nanofibers (CNF) were prepared as the conductive agent. Such materials were mixed with xylene solvent in a weight ratio of positive electrode active material:first two-dimensional solid electrolyte:atypical particulate solid electrolyte:conductive agent:binder = 84:2:9.5:3:1.5 to form a slurry into a sheet, which was then vacuum-dried at 40°C for 8 hours to produce a positive electrode sheet. The manufactured positive electrode sheet was placed on the carbon layer of a positive electrode current collector made of aluminum foil coated with a carbon layer on one side, and the positive electrode layer was manufactured by heated roll pressing at 85°C. The total thickness of the positive electrode layer was approximately 120 μm. The thickness of the positive electrode active material layer was approximately 95 μm, and the thickness of the carbon-coated aluminum foil was approximately 25 μm.

[0213] (All-solid-state secondary battery manufacturing) An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode layer described above was used.

[0214] Example 11: Mono-cell all-solid-state secondary battery, oxide-based cathode active material (NCA), flake solid electrolyte:particulate solid electrolyte = 10:40 weight ratio, first two-dimensional solid electrolyte, solid electrolyte layer is a first two-dimensional solid electrolyte laminate. (Positive electrode layer manufacturing) LiNi coated with Li2O-ZrO2 (LZO) as the positive electrode active material. 0.8 Co 0.15 Mn 0.05O2(NCM) was prepared. The LZO-coated cathode active material was manufactured by the method disclosed in Korean Published Patent No. 10-2016-0064942. Li6PS5Cl, an argyrodite-type crystalline solid (D50=0.5μm, crystalline), was prepared as the solid electrolyte. A polytetrafluoroethylene (PTFE) binder was prepared as the binder. Carbon nanofibers (CNF) were prepared as the conductive agent. Such materials were mixed with xylene solvent in a weight ratio of cathode active material:first two-dimensional solid electrolyte:amorphous particulate solid electrolyte:conductive agent:binder = 84:11.5:3:1.5. The slurry was formed into a sheet and then vacuum-dried at 40°C for 8 hours to produce a cathode sheet. A positive electrode sheet was manufactured by placing a positive electrode sheet on the carbon layer of a positive electrode current collector made of aluminum foil coated with a carbon layer on one side, and then manufacturing the positive electrode layer using a heated roll press at 85°C. The total thickness of the positive electrode layer was approximately 120 μm. The thickness of the positive electrode active material layer was approximately 95 μm, and the thickness of the carbon-coated aluminum foil was approximately 25 μm. The initial charge capacity of the positive electrode layer (i.e., the positive electrode active material layer) was measured using the aforementioned half-cell. The ratio (B / A) of the initial charge capacity of the first negative electrode active material layer (B) to the initial charge capacity of the positive electrode active material layer (A) was less than 0.5. The initial charge capacity of the positive electrode active material layer was measured using the first open-circuit voltage (1 st open circuit voltage) to 4.25 V vs. Li / Li + This was determined by the charging up to 2. The initial charge capacity of the first negative electrode active material layer is determined by the second open circuit voltage (2 nd open circuit voltage) to 0.01 V vs. Li / Li + This was determined by the charging time.

[0215] (Manufacturing of solid electrolyte layer) As the first two-dimensional solid electrolyte, a mixture was prepared by adding 1.5 parts by weight of an acrylic binder to 98.5 parts by weight of the rGO (reduced graphene oxide)-Li6PS5Cl composite manufactured in Manufacturing Example 1. Octyl acetate was added to the prepared mixture while stirring to produce a slurry. The prepared slurry was applied using a bar coater onto a 15 μm thick nonwoven fabric placed on a 75 μm thick PET substrate, and dried in air at 80°C for 10 minutes to obtain a laminate. The obtained laminate was vacuum dried at 80°C for 2 hours. The solid electrolyte layer was manufactured by the above steps.

[0216] (All-solid-state secondary battery manufacturing) An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode layer and solid electrolyte layer described above were used.

[0217] Comparative example 1: Mono-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI composite), flake solid electrolyte: particulate solid electrolyte = 0:50 weight ratio An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of flake solid electrolyte to particulate solid electrolyte was changed to 0:50 and the flake solid electrolyte was not used.

[0218] Comparative Example 2: Mono-cell all-solid-state secondary battery, oxide-based cathode active material (NCA), flake solid electrolyte:particulate solid electrolyte = 0:50 by weight ratio An all-solid-state secondary battery was manufactured in the same manner as in Example 10, except that the weight ratio of flake solid electrolyte to particulate solid electrolyte was changed to 0:50 and the flake solid electrolyte was not used.

[0219] Comparative Example 3: A mono-cell all-solid-state secondary battery was used. Instead of a sulfide-based cathode active material (Li2S-C-LiI composite) and a flake solid electrolyte (a composite of rGO and Li6PS5Cl), a simple mixture of rGO and Li6PS5Cl was used.

[0220] An all-solid-state secondary battery was used in the same manner as in Example 1, except that a 1:60 weight-ratio mixture of rGO and Li6PS5Cl was used instead of a flake solid electrolyte (a composite of rGO and Li6PS5Cl).

[0221] Comparative Example 4: A mono-cell all-solid-state secondary battery was used, with an oxide-based cathode active material (NCA) and a simple mixture of rGO and Li6PS5Cl instead of a flake solid electrolyte (a composite of rGO and Li6PS5Cl).

[0222] An all-solid-state secondary battery was used in the same manner as in Example 10, except that a 1:60 weight-ratio mixture of rGO and Li6PS5Cl was used instead of a flake solid electrolyte (a composite of rGO and Li6PS5Cl).

[0223] Reference example 1: Sulfide-based positive electrode active material, no inert materials used (free) An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that flame-retardant inert materials (i.e., gaskets) were not used during the manufacturing of the all-solid-state secondary battery.

[0224] Reference example 2: Oxide-based positive electrode active material, no inert materials used (free) An all-solid-state secondary battery was manufactured in the same manner as in Example 10, except that flame-retardant inert materials (i.e., gaskets) were not used during the manufacturing of the all-solid-state secondary battery.

[0225] Example 12: One bi-cell all-solid-state secondary battery, sulfide-based positive electrode active material (Li2S-C-LiI composite), flake solid electrolyte:particulate solid electrolyte = 10:40 by weight ratio, first two-dimensional solid electrolyte (Manufacturing of bi-cell all-solid-state rechargeable batteries) The positive electrode layer was prepared in the same manner as in Example 1, except that the positive electrode active material layer was arranged on both sides of the positive electrode current collector.

[0226] The total thickness of the positive electrode layer was approximately 220 μm. The thickness of the positive electrode active material layer was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm.

[0227] Two negative electrode layers, solid electrolyte layers, and flame-retardant inert members were prepared using the same method as in Example 1.

[0228] Referring to Figure 3, a solid electrolyte layer was arranged on the negative electrode layer such that the first negative electrode active material layer was in contact with the solid electrolyte layer, and a positive electrode layer was placed on the solid electrolyte layer. The positive electrode layer had a structure in which positive electrode active material layers were arranged on both sides of the positive electrode current collector. A gasket was placed around the positive electrode layer, surrounding it and in contact with the solid electrolyte layer. The thickness of the gasket was approximately 220 μm. The gasket could be, for example, two 110 μm thick gaskets stacked together, or a single 220 μm thick gasket. The flame-retardant inert material was used as the gasket.

[0229] The gasket was positioned so as to be in contact with the sides of the positive electrode layer and the solid electrolyte layer. The positive electrode layer was positioned in the center of the solid electrolyte layer, with the gasket surrounding the positive electrode layer and extending to the end of the solid electrolyte layer. The area of ​​the positive electrode layer was approximately 90% of the area of ​​the solid electrolyte layer, and the gasket was positioned over the remaining 10% of the solid electrolyte layer where the positive electrode layer was not located. The solid electrolyte layer was placed on the positive electrode layer and gasket, and the negative electrode layer was placed on the solid electrolyte layer to prepare the laminate.

[0230] The prepared laminate was subjected to plate press treatment at 85°C. Such press treatment sinters the solid electrolyte layer, improving the battery characteristics. The thickness of one sintered solid electrolyte layer was approximately 45 μm. The area of ​​the solid electrolyte layer was the same as the area of ​​the negative electrode layer. The pressurized laminate was placed in a pouch and vacuum-sealed to manufacture an all-solid-state secondary battery. Parts of the positive electrode current collector and negative electrode current collector were extended to the outside of the sealed battery and used as the positive electrode layer terminals and negative electrode layer terminals.

[0231] Evaluation Example 1: High-Temperature Life Characteristics Test The charge-discharge characteristics of the all-solid-state secondary batteries manufactured in Examples 1 to 9, Example 12, Comparative Example 1, Comparative Example 3, and Reference Example 1 were evaluated by the following charge-discharge tests. The charge-discharge tests were performed by placing the all-solid-state secondary batteries in a constant temperature bath at 45°C.

[0232] The first cycle operates at 0.6mA / cm² until the battery voltage reaches 2.5V to 2.8V. 2 The battery was charged with a constant current of 0.6mA / cm² for 12.5 hours. Then, the current was increased until the battery voltage reached 0.5V. 2 Discharge was performed for 12.5 hours at a constant current.

[0233] The charge-discharge characteristics of the all-solid-state secondary batteries manufactured in Examples 10 and 11, Comparative Example 2, Comparative Example 4, and Reference Example 2 were evaluated by the following charge-discharge tests. The charge-discharge tests were performed by placing the all-solid-state secondary batteries in a constant temperature bath at 45°C.

[0234] The first cycle operates at 0.6mA / cm² until the battery voltage reaches 3.9V to 4.25V. 2 The battery was charged at a constant current of 0.6mA / cm² for 12.5 hours. Then, the battery voltage was increased to 2.5V. 2 Discharge was performed for 12.5 hours at a constant current.

[0235] The discharge capacity of the first cycle was used as the standard capacity. After the second cycle, charging and discharging were performed under the same conditions as the first cycle up to 150 cycles. The measurement results are shown in Table 2 below.

[0236] A device was considered to have superior lifespan characteristics if the number of cycles required for the discharge capacity to decrease to 95% of the standard capacity after the second cycle increased.

[0237] In Reference Example 1 and Reference Example 2, the all-solid-state secondary batteries experienced short circuits before the completion of the first cycle, making it impossible to measure their life characteristics.

[0238] [Table 1]

[0239] As shown in Table 1, the all-solid-state secondary batteries containing sulfide-based positive electrode active materials in Examples 1 to 9 and Example 12 showed improved lifespan characteristics compared to the all-solid-state secondary batteries in Comparative Examples 1 and 3.

[0240] The lithium batteries of Examples 1 to 9 were found to have improved lifespan characteristics by including a flake solid electrolyte, which provides increased ion conduction pathways and more effectively accommodates the volume change of the positive electrode active material during charging and discharging.

[0241] In the all-solid-state secondary batteries of Examples 1 to 5, the lifespan characteristics changed depending on the weight ratio of flake solid electrolyte to particulate solid electrolyte.

[0242] The all-solid-state secondary battery containing the flake solid electrolyte in Example 1 showed improved lifespan characteristics compared to the all-solid-state secondary battery in Comparative Example 3, which contained a simple mixture of graphene and solid electrolyte. It was determined that the simple mixture of graphene and solid electrolyte degrades the performance of the all-solid-state secondary battery due to increased side reactions caused by heterogeneous mixing.

[0243] The all-solid-state secondary batteries containing oxide-based cathode active materials in Examples 10 and 11 showed improved lifespan characteristics compared to the all-solid-state secondary batteries in Comparative Examples 2 and 4.

[0244] The all-solid-state secondary battery of Example 10 was found to have improved lifespan characteristics by having an increased ion conduction pathway due to the placement of a flake solid electrolyte in the positive electrode active material layer, and by more effectively accommodating the volume change of the positive electrode active material during charging and discharging.

[0245] In the all-solid-state secondary battery of Example 11, the arrangement of flake solid electrolyte in the solid electrolyte layer reduced the formation of pinholes on the surface of the solid electrolyte layer, thereby suppressing cracks in the solid electrolyte layer and resulting short circuits, and thus improving the lifespan characteristics.

[0246] The all-solid-state secondary battery containing the flake solid electrolyte in Example 10 showed improved lifetime characteristics compared to the all-solid-state secondary battery in Comparative Example 4, which contained a simple mixture of graphene and solid electrolyte. It was determined that the simple mixture of graphene and solid electrolyte degrades the performance of the all-solid-state secondary battery due to increased side reactions caused by heterogeneous mixing.

[0247] The all-solid-state secondary battery of Example 12 was found to have improved lifespan characteristics compared to the all-solid-state secondary batteries of Examples 1 to 5, which have a monocell structure, by effectively mitigating volume changes during charging and discharging due to its bicell structure in which the components are symmetrically arranged.

[0248] In the all-solid-state secondary batteries of Examples 1 to 12, after the first charging cycle was completed, SEM images of the cross-sections of these batteries were measured to confirm that a lithium metal deposition layer corresponding to the second negative electrode active material layer had formed between the solid electrolyte layer and the negative electrode current collector.

[0249] As mentioned above, the all-solid-state secondary battery according to this embodiment can be applied to various portable devices, vehicles, and the like.

[0250] Although an exemplary embodiment has been described in detail above based on the attached drawings, this original idea is not limited to such an example. It is self-evident to any person with ordinary skill in the art to which this original idea belongs that various modifications or alterations can be derived within the scope of the technical idea described in the claims, and it goes without saying that these also fall within the technical scope of this original idea. [Industrial applicability]

[0251] In one respect, a new all-solid-state secondary battery structure can provide an all-solid-state secondary battery in which short circuits are suppressed and cycle characteristics are improved. [Explanation of symbols]

[0252] 1 All-solid-state secondary battery 10 Positive electrode layer 11 Positive electrode current collector 12 Cathode active material layer 20 Negative electrode layer 21 Negative electrode current collector 22 First negative electrode active material layer 30 Solid electrolyte layer 40 Inert member 100 1st 2D sulfide solid electrolyte 110, 120 cores 130 Middle Class 200 First two-dimensional sulfide-based solid electrolyte laminate

Claims

1. The positive electrode layer; the negative electrode layer; and the solid electrolyte layer between the positive electrode layer and the negative electrode layer, The positive electrode layer includes a positive electrode current collector and a positive electrode active material layer on one or more surfaces of the positive electrode current collector. One or more of the positive electrode active material layer and the solid electrolyte layer include a first two-dimensional sulfide-based solid electrolyte, The negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer on one surface of the negative electrode current collector. An all-solid-state secondary battery in which the initial charge capacity (B) of the first negative electrode active material layer is less than approximately 50% of the initial charge capacity (A) of the positive electrode active material layer.

2. The first two-dimensional sulfide-based solid electrolyte is defined by its length and thickness, The aspect ratio of the length to the thickness is approximately 3 or more. The length of the first two-dimensional sulfide-based solid electrolyte is approximately 1 to 50 μm, and the thickness is approximately 10 nm to 30 μm. The all-solid-state secondary battery according to claim 1, wherein the first two-dimensional sulfide-based solid electrolyte includes a plate structure, a flake structure, or a combination thereof.

3. The surface of the first two-dimensional sulfide-based solid electrolyte has an irregular, circular, or polygonal shape. The all-solid-state secondary battery according to claim 1, wherein the polygonal shape includes a triangular, square, pentagonal, hexagonal, heptagonal, octagonal, nonagonal, or decagonal shape.

4. The first two-dimensional sulfide-based solid electrolyte includes a core and a shell on the core, The core comprises a carbon-based material, a polymer, a metal-containing inorganic material, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. The shell comprises a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a coating material, or a combination thereof. One or more of the core and shell contain a sulfide-based solid electrolyte, The core includes a two-dimensional nanostructure, The aforementioned two-dimensional nanostructures include graphene, graphene oxide, reduced graphene oxide, carbon nanobelts, carbon nanosheets, carbon nanoplates, carbon nanoflakes, and SiO2. ２ , TiO ２ Al ２ O ３ , AlN, SiC, BaTiO ３ The all-solid-state secondary battery according to claim 1, including or a combination thereof.

5. The ratio of the first thickness of the core to the second thickness of the shell is 1:0.01 to 1:1000. The all-solid-state secondary battery according to claim 4, wherein the ratio of the first length of the core to the second length of the shell is 1:1 to 1:

100.

6. The positive electrode active material layer includes a first region adjacent to the positive electrode current collector and a second region adjacent to the solid electrolyte layer. In the first region, a first two-dimensional sulfide-based solid electrolyte is present, and in the second region, the first two-dimensional sulfide-based solid electrolyte is free. Either the first two-dimensional sulfide-based solid electrolyte is present in the second region and the first two-dimensional sulfide-based solid electrolyte is free in the first region, or The all-solid-state secondary battery according to claim 1, wherein the first two-dimensional sulfide-based solid electrolyte is present in the first region and the second region.

7. The content of the first two-dimensional sulfide-based solid electrolyte is 1 to 50 wt% of the total weight of the positive electrode active material layer. The positive electrode active material layer further comprises an amorphous sulfide-based solid electrolyte that is distinguishable from the first two-dimensional sulfide-based solid electrolyte, The all-solid-state secondary battery according to claim 1, wherein the weight ratio of the first two-dimensional sulfide-based solid electrolyte to the amorphous sulfide-based solid electrolyte is 1:99 to 99:

1.

8. The positive electrode active material layer contains a positive electrode active material, The positive electrode active material includes an oxide-based positive electrode active material, a sulfide-based positive electrode active material, or a combination thereof. The oxide-based positive electrode active material includes a lithium transition metal oxide, a metal oxide, or a combination thereof. The lithium transition metal oxide includes lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium manganate, lithium iron phosphate, or a combination thereof, and the lithium oxide includes iron oxide, vanadium oxide, or a combination thereof. The aforementioned sulfide-based positive electrode active material is nickel sulfide, copper sulfide, Li ２ S, Li ２ The all-solid-state secondary battery according to claim 1, comprising a sulfur-containing composite or a combination thereof.

9. The above-mentioned Li ２ The S-containing composite is a composite of Li ２ S and carbon, Li ２ A composite of S, carbon and a solid electrolyte, Li ２ A composite of S and a solid electrolyte, Li ２ A composite of S and a lithium salt, Li ２ A composite of S, a lithium salt and carbon, Li ２ A composite of S and a metal carbide, Li ２ A composite of S, carbon and a metal carbide, Li ２ A composite of S and a metal nitride, Li ２ The all-solid-state secondary battery according to claim 8, comprising a composite of S, carbon and a metal nitride or a combination thereof.

10. The Li ２ The S-containing complex further contains a second-dimensional sulfide-based solid electrolyte, The all-solid-state secondary battery according to claim 8, wherein the size of the second two-dimensional sulfide-based solid electrolyte is smaller than the size of the first two-dimensional sulfide-based solid electrolyte.

11. The positive electrode active material layer further comprises one or more selected from a conductive material and a binder. The all-solid-state secondary battery according to claim 1, wherein the conductive material includes a carbon-based conductive material.

12. The positive electrode layer further includes an inactive member on one side surface, The inert member surrounds the positive electrode layer along the side surface of the positive electrode layer, The all-solid-state secondary battery according to claim 1, wherein the inert member includes a positioning portion configured to determine the position of the inert member on the solid electrolyte layer.

13. The all-solid-state secondary battery according to claim 1, comprising a first two-dimensional sulfide-based solid electrolyte in which the solid electrolyte layer is arranged along one direction.

14. The first two-dimensional sulfide-based solid electrolyte is aligned substantially perpendicular to the thickness direction of the solid electrolyte layer, The first two-dimensional sulfide-based solid electrolyte is stacked in the thickness direction of the solid electrolyte layer, The all-solid-state secondary battery according to claim 13, wherein the content of the first two-dimensional sulfide-based solid electrolyte is about 50 wt% or more of the total weight of the solid electrolyte layer.

15. The first negative electrode active material layer comprises a negative electrode active material and a binder. The all-solid-state secondary battery according to claim 1, wherein the negative electrode active material has a particle form, and the average particle size of the negative electrode active material is about 4 μm or less.

16. The anode active material comprises one or more selected from carbon-based anode active materials and metal-based anode active materials. The carbon-based negative electrode active material includes amorphous carbon, crystalline carbon, porous carbon, or a combination thereof. The all-solid-state secondary battery according to claim 15, wherein the metallic negative electrode active material includes gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof.

17. The negative electrode active material comprises a mixture of first particles containing amorphous carbon and second particles containing metal. The all-solid-state secondary battery according to claim 15, wherein the content of the second particles is about 8 to 60% by weight based on the total weight of the mixture.

18. The negative electrode active material includes a carbon-based support and a metallic negative electrode active material supported on the carbon-based support. The aforementioned metallic negative electrode active material includes a metal, a metal oxide, a composite of a metal and a metal oxide, or a combination thereof. The metallic anode active material has a particle form, and the particle size of the metallic anode active material is about 1 nm to 200 nm. The all-solid-state secondary battery according to claim 15, wherein the carbon-based support has a particle form and the particle size of the carbon-based support is about 10 nm to 2 μm.

19. The material further includes a second negative electrode active material layer between the solid electrolyte layer and the negative electrode current collector, The second negative electrode active material layer is one or more of the following: between the first negative electrode active material layer and the first protective layer, and between the first negative electrode active material layer and the solid electrolyte layer. The all-solid-state secondary battery according to claim 1, wherein the second negative electrode active material layer is a metal layer containing lithium metal or a lithium alloy.

20. One or more of the positive electrode current collector and the negative electrode current collector include a base film and one or more metal layers on one surface of the base film. The base film comprises a polymer, and the polymer comprises polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The all-solid-state secondary battery according to claim 1, wherein the metal layer comprises indium (In), copper (Cu), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.

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