Positive electrode for all-solid-state secondary battery and all-solid-state secondary battery including same

Abstract

Disclosed are a positive electrode for an all-solid-state secondary battery and an all-solid-state secondary battery, the positive electrode including a positive electrode current collector, an adhesive binder layer including an adhesive polymer on the positive electrode current collector, and a positive electrode active material layer including a composite positive electrode active material and a cohesive binder on the adhesive binder layer, the composite positive electrode active material includes a Li2S-containing composite, and the all-solid-state secondary battery includes the positive electrode, a negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode.

Description

Technical Field

[0001] One or more embodiments relate to a positive electrode for an all-solid-state secondary battery and an all-solid-state secondary battery including the same. Background Technology

[0002] To meet recent industrial demands, extensive development has been undertaken to provide batteries with high energy density and safety. For example, lithium-ion batteries are used in various applications, including information devices, communication devices, and vehicles. Because vehicles are directly related to people's lives, safety is paramount.

[0003] In lithium-ion batteries that include liquid electrolytes, the risk of fire and / or explosion in the event of a short circuit may increase. All-solid-state secondary batteries using solid electrolytes instead of liquid electrolytes have been proposed. Solid electrolytes have a lower fire risk than liquid electrolytes.

[0004] By using a solid electrolyte instead of a liquid electrolyte, the risk of fire or explosion can be reduced in all-solid-state secondary batteries. All-solid-state secondary batteries offer improved safety. Summary of the Invention

[0005] Technical issues One or more embodiments include a positive electrode for an all-solid-state secondary battery with improved interlayer adhesion.

[0006] One or more embodiments include an all-solid-state secondary battery that has improved performance by including the positive electrode.

[0007] Solution to the problem According to one or more embodiments, The positive electrode for an all-solid-state secondary battery includes: a positive electrode current collector; an adhesive layer disposed on the positive electrode current collector and including an adhesive polymer; and a positive electrode active material layer disposed on the adhesive layer and including a composite positive electrode active material and an internal adhesive, wherein the composite positive electrode active material includes a Li2S-containing composite.

[0008] According to one or more embodiments, the all-solid-state secondary battery includes the above-described positive electrode, negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0009] Beneficial effects of the invention According to some aspects, by increasing the adhesion between the substrate and the electrode, the discharge capacity and rate characteristics are improved, and stable contact is achieved even after repeated contraction and expansion during cycling without detachment, thus providing an all-solid-state secondary battery with improved lifetime characteristics. Attached Figure Description

[0010] Figure 1This is a cross-sectional view of an all-solid-state secondary battery according to an embodiment.

[0011] Figure 2 This is a cross-sectional view of an all-solid-state secondary battery according to an embodiment.

[0012] Figure 3 This is a cross-sectional view of an all-solid-state secondary battery according to an embodiment.

[0013] Figure 4 This is a cross-sectional view of an all-solid-state secondary battery according to an embodiment.

[0014] Figure 5 This is a cross-sectional view of an all-solid-state secondary battery according to an embodiment.

[0015] List of reference numerals for key components 1 all-solid-state rechargeable battery; 10 positive electrodes 11 Positive current collector; 12 Positive active material layer 20 negative electrode; 21 negative electrode current collector 22 First negative electrode active material layer; 23 Thin film 24 Second negative electrode active material layer; 30 Electrolyte layer 40. Inactive components. Detailed Implementation

[0016] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. Furthermore, it will be understood that terms (such as those defined in common dictionaries) shall be interpreted as having a meaning consistent with their meaning in the context of the relevant field and shall not be interpreted in an idealized or overly formalized sense, unless expressly defined herein.

[0017] Exemplary embodiments will be described herein with reference to schematic cross-sectional views of preferred embodiments. Thus, variations in the illustrated shapes will be anticipated due to, for example, manufacturing techniques and / or tolerances. Therefore, the exemplary embodiments should not be construed as limited to the specific shapes of the areas shown herein, but rather include, for example, shape deviations caused by manufacturing processes. For example, areas shown or described as flat may generally have rough and / or non-linear characteristics. Furthermore, acute angles shown may be rounded (rounded). Therefore, the areas shown in the figures are schematic in nature, and their shapes are not intended to represent the actual shapes of areas of the device, nor are they intended to limit the scope of the claims.

[0018] However, the inventive concept can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. The same reference numerals in the drawings denote the same elements.

[0019] What will be understood is that when an element is referred to as being "on" another element, it can be directly on said other element, or there can be an intermediary element between them. Conversely, when an element is referred to as being "directly on" another element, there is no intermediary element between them.

[0020] Although the terms “first,” “second,” “third,” etc., may be used herein to describe various elements, components, regions, layers, and / or parts, these elements, components, regions, layers, and / or parts should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or part from another. Therefore, without departing from the teachings herein, the first element, first component, first region, first layer, or first part discussed below may be referred to as a second element, second component, second region, second layer, or second part.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the inventive concept. As used herein, unless otherwise stated, expressions used in the singular include the expression "at least one". "At least one" should not be construed as singular. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Terms such as "comprising" and / or "having" are intended to indicate the presence of features, areas, integers, processes, components, and / or elements disclosed in the specification, and are not intended to exclude the possibility that one or more other features, areas, integers, processes, components, and / or elements may be present or added.

[0022] Spatially relative terms such as “below,” “under,” “lower,” “above,” “upper,” or “upper” may be used herein to readily describe the relationship between one element or feature and another element(s) as shown in the accompanying drawings. It will be understood that, in addition to the orientations depicted in the drawings, the spatially relative terms are intended to cover different orientations of the device in use or operation. For example, if the device in the drawings is flipped, an element described as “below” other elements or features will be oriented “above” other elements or features. Thus, the exemplary term “below” can cover both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or in other orientations), and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0023] The term "group" can refer to the group of elements numbered 1 to 18 in the periodic table according to the classification system of the International Union of Pure and Applied Chemistry ("IUPAC").

[0024] In this disclosure, "particle size" or "particle diameter" refers to the average diameter of spherical particles or the average length of the major axis of non-spherical particles. Particle size can be measured using a particle size analyzer (PSA). "Particle size" or "particle diameter" is, for example, the average particle size. The "average particle size" is, for example, the median particle size (D50).

[0025] D50 can refer to the particle size corresponding to 50% of the particles in a cumulative distribution curve measured by laser diffraction, in which particles are accumulated in order of particle size from smallest to largest.

[0026] D90 can refer to the particle size corresponding to 90% of the particles in a cumulative distribution curve measured by laser diffraction, in which particles are accumulated in order of particle size from smallest to largest.

[0027] D10 can refer to the particle size corresponding to 10% of the particles in the cumulative distribution curve measured by laser diffraction, in which particles are accumulated in order of particle size from smallest to largest.

[0028] In this disclosure, the term "metal" includes metals and metalloids (such as silicon and germanium) that are in elemental or ionic states.

[0029] In this disclosure, the term "alloy" may refer to a combination of two or more metals.

[0030] In this disclosure, the term "electrode active material" can refer to a material used for an electrode that allows for lithiation and delithiation.

[0031] In this disclosure, the term "positive electrode active material" may refer to a material used for a positive electrode that allows for lithiation and delithiation.

[0032] In this disclosure, the term "negative electrode active material" may refer to a material used for a negative electrode that allows for lithiation and delithiation.

[0033] In this disclosure, the term "lithiation" and its variations refer to the process of introducing lithium into an electrode active material.

[0034] In this disclosure, the term "delithiation" and its variations refer to the process of removing lithium from the electrode active material.

[0035] In this disclosure, the term "charging" and its variations refer to the process of supplying electrochemical energy to a battery.

[0036] In this disclosure, the term "discharge" and its variations refer to the process of removing electrochemical energy from a battery.

[0037] In this disclosure, the terms "positive electrode" and "positive electrode" refer to an electrode that undergoes electrochemical reduction and lithiation during discharge.

[0038] In this disclosure, the terms "negative electrode" and "negative electrode" refer to an electrode that undergoes electrochemical oxidation and delithiation during discharge.

[0039] As used herein, the terms “thickness,” “length,” and “width” refer to, for example, average thickness, average length, and average width, respectively.

[0040] As used herein, the aspect ratio represents the ratio (L1 / L2) of the major axis length L1 (e.g., length) to the minor axis length L2 (e.g., diameter). Here, aspect ratio, major axis length, minor axis length, length, and diameter represent the average aspect ratio, average major axis length, average minor axis length, average length, and average diameter, respectively. The aspect ratio can be evaluated using a scanning electron microscope.

[0041] As used herein, the term "solid solution" is distinct from a mixture of two or more chemical substances and refers to a homogeneous crystalline phase containing two or more chemical substances.

[0042] As used herein, the term "two-dimensional carbon nanostructure" refers to a carbon nanostructure in which two dimensions are significantly larger than the third dimension. That is, a carbon nanostructure in which the region defined by the two dimensions is significantly larger than its thickness.

[0043] As used herein, the weight-average molecular weight of the polymer can be evaluated by gel permeation chromatography calibrated with polystyrene equivalents.

[0044] While specific embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently foreseen or may not be foreseen by the applicant or others skilled in the art. Therefore, the appended claims, both submitted and possibly modified, are intended to cover all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0045] The positive electrode for an all-solid-state secondary battery and the all-solid-state secondary battery including the positive electrode according to embodiments will be described in more detail below.

[0046] [positive electrode] The positive electrode for an all-solid-state secondary battery according to an embodiment includes: a positive electrode current collector; an adhesive layer disposed on the positive electrode current collector and including an adhesive polymer; and a positive electrode active material layer disposed on the adhesive layer and including a composite positive electrode active material and a cohesive adhesive, wherein the composite positive electrode active material includes a Li2S-containing composite.

[0047] In the positive electrode of an all-solid-state secondary battery using lithium sulfide as the positive electrode active material, it is desirable to improve the adhesion between the substrate and the electrode containing the lithium sulfide active material to prevent detachment from the substrate due to contraction and expansion during charging and discharging, and to improve electronic conductivity.

[0048] By forming an adhesive layer between the positive electrode active material layer and the substrate, and by using a positive electrode active material layer including a cohesive binder, this disclosure can provide a positive electrode with excellent electrochemical performance that does not detach from the surface of the substrate even after repeated contraction and expansion caused during charging and discharging, thereby improving the adhesion between the positive electrode active material layer including the Li2S-containing complex and the substrate and reducing the interfacial resistance between them.

[0049] The composite positive electrode active material, which is a Li2S-containing complex, may include a complex of Li2S and lithium salt, and the positive electrode active material layer may include the complex and a sulfide solid electrolyte.

[0050] The complex of Li2S and lithium salt can be Li2S-Li a X b (where 1≤a≤5 and 1≤b≤5), where X is I, Br, Cl, F, H, O, Se, Te, N, P, As, Sb, Al, B, OCl, PF6, BF4, SbF6, AsF6, ClO4, AlO2, AlCl4, NO3, CO3, BH4, SO4, BO3, PO4, NCl, NCl2, BN2 or any combination thereof.

[0051] In all-solid-state secondary batteries that use lithium sulfide as the positive electrode active material, lithium sulfide is an insulator with very low electrical and ionic conductivity. Therefore, it is desirable to combine lithium sulfide with materials that have high electrical and ionic conductivity. Lithium sulfide-containing positive electrode active materials may detach from the positive electrode current collector due to contraction and expansion during charge and discharge, and electronic conductivity may deteriorate; therefore, it is desirable to improve these properties.

[0052] Therefore, by using a Li2S-containing composite as the positive electrode active material, forming an adhesive layer including an adhesive polymer between the positive electrode current collector and the positive electrode active material layer, and using an internal cohesive binder included in the positive electrode active material layer, the positive electrode of this disclosure can further reduce the interfacial resistance between the positive electrode active material layer and the positive electrode current collector, and effectively prevent the degradation of the sulfide-based solid electrolyte included in the positive electrode active material layer during battery operation.

[0053] By forming an adhesive layer, the degradation of sulfide-based solid electrolytes in the positive electrode active material layer can be effectively prevented, the adhesion of the positive electrode can be increased, and the interfacial resistance between the positive electrode current collector and the positive electrode active material layer can be reduced.

[0054] The thickness of the adhesive layer according to the embodiment can be from about 5 nm to about 1 μm, from about 5 nm to about 800 nm, from about 5 nm to about 500 nm, from about 5 nm to about 400 nm, from about 5 nm to about 300 nm, from about 10 nm to about 300 nm, from about 10 nm to about 100 nm, or from about 10 nm to about 50 nm.

[0055] According to other embodiments, the thickness of the adhesive layer can be about 20 nm to about 1 μm, about 20 nm to about 800 nm, about 20 nm to about 500 nm, about 20 nm to about 300 nm, or about 20 nm to about 100 nm. If the thickness is within the above range, the interfacial resistance can be reduced, and the sulfide-based solid electrolyte contained in the positive electrode active material layer can be effectively protected.

[0056] The adhesive polymer constituting the adhesive layer may include, for example, at least one selected from polydopamine, cationic substituted polycarboxylic acids and their copolymers, poly(norepinephrine), poly(meth)acrylamide, polyvinyl alcohol, poly(2-hydroxyethyl(meth)acrylate), methyl methacrylate-co-(meth)acrylate copolymer, poly(meth)acrylate, poly(meth)acrylic acid and styrene-co-(meth)acrylate copolymer.

[0057] Cationic substituted polycarboxylic acids and their copolymers may include those selected from lithium-ion (Li) + Sodium ions (Na) + ), potassium ions (K) + ) and ammonium ions (NH4) + At least one cation selected from lithium polyacrylate (LiPAA) and lithium polymethacrylate (LiMAA). Polycarboxylic acids can refer to polymers prepared by polymerizing various types of monomers, including at least one monomer containing one or more carboxyl groups (-COOH), and having a weight-average molecular weight of 1,000 Da to 1,000,000 Da. Examples of polycarboxylic acids can be polyacrylic acid, polymethacrylic acid, and polymaleic acid. Cationic-substituted polycarboxylic acids are materials obtained by replacing the hydrogen atoms of a polycarboxylic acid with cations, and may include at least one selected from lithium polyacrylate (LiPAA) and lithium polymethacrylate.

[0058] A copolymer of cationicly substituted polycarboxylic acids is a copolymer comprising repeating units of monomers corresponding to the cationicly substituted polycarboxylic acids, and examples of copolymers may be lithium poly(acrylic acid-co-maleic acid), lithium poly(methyl vinyl ether-alternative-maleic acid), or lithium poly(butadiene-co-maleic acid).

[0059] At least one of the cationicly substituted polycarboxylic acids and their copolymers may have a glass transition temperature of 50°C or higher, for example, from about 50°C to about 200°C, or for example, from about 50°C to about 150°C. At least one of the cationicly substituted polycarboxylic acids and their copolymers may have a melting point of 100°C or higher, for example, from about 100°C to about 300°C, or for example, from about 100°C to about 200°C. If an interlayer is formed using a cationicly substituted polycarboxylic acid and its copolymer having such a glass transition temperature and melting point, the shape of the interlayer can be maintained at the battery operating temperature (e.g., from about 0°C to about 90°C). At least one of the cationicly substituted polycarboxylic acids and their copolymers may have a weight-average molecular weight of from about 1,000 Da to 1,000,000 Da and a degree of polymerization of from about 10 to about 1,500, for example, from about 14 to about 1,400.

[0060] Cationic substituted polycarboxylic acids can be, for example, lithium polyacrylate.

[0061] According to embodiments, the cohesive binder may be polytetrafluoroethylene, polyvinylidene fluoride (PVdF) resin, styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyethylene glycol (PEG), polypropylene glycol (PPG), toluene diisocyanate (TDI), polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, poly(ethylene-co-vinyl acetate) copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide, or combinations thereof. Based on 100 parts by weight of the positive electrode active material layer, the amount of the cohesive binder may be from about 0.5 parts by weight to about 10 parts by weight, from about 1 part by weight to about 10 parts by weight, from about 0.5 parts by weight to about 8 parts by weight, from about 0.5 parts by weight to about 5 parts by weight, from about 0.6 parts by weight to about 3 parts by weight, from about 0.7 parts by weight to about 2 parts by weight, or from about 0.8 parts by weight to about 1.5 parts by weight. Based on 100 parts by weight of the adhesive polymer of the adhesive layer, the amount of the cohesive binder may be from about 100 parts by weight to about 1000 parts by weight, from about 150 parts by weight to about 950 parts by weight, from about 200 parts by weight to about 900 parts by weight, from about 250 parts by weight to about 850 parts by weight, from about 300 parts by weight to about 800 parts by weight, from about 350 parts by weight to about 750 parts by weight, from about 400 parts by weight to about 700 parts by weight, or from about 450 parts by weight to about 650 parts by weight. If the amount of cohesive binder exceeds the above range, the amount of lithium sulfide complex in the positive electrode active material layer becomes relatively low, leading to a deterioration in capacity performance. If the amount of cohesive binder is less than the above range, the adhesion of the positive electrode active material layer may deteriorate.

[0062] The aforementioned positive electrode, including the adhesive binder layer, not only improves the adhesion between the current collector and the positive electrode active material layer, but also improves its stability and reliability against mechanical deformations such as bending, thereby enhancing battery performance. Therefore, in an all-solid-state secondary battery including a positive electrode containing lithium sulfide as the positive electrode active material, by forming the adhesive binder layer, it is possible to prevent the silicon active material from detaching from the current collector due to volume changes, and to prevent battery performance degradation due to increased interfacial resistance between the current collector and the positive electrode active material layer, thus providing a high-capacity solid-state secondary battery.

[0063] Li2S-containing complexes include, for example, complexes of Li2S and lithium salts.

[0064] The ductile Li₂S and lithium salt complex differs from conventional brittle oxide-based solid electrolytes (e.g., garnet-type oxide-based solid electrolytes). The lithium-ion conductive Li₂S and lithium salt complex differs from conventional lithium-free metal oxides (such as alumina) that do not have lithium-ion conductivity. The Li₂S and lithium salt complex is, for example, a product obtained by mechanically grinding Li₂S and lithium salt. Because the Li₂S and lithium salt complex is a product of the mechanochemical reaction of Li₂S and lithium salt, it differs from a simple mixture of Li₂S and lithium salt. In a simple mixture of Li₂S and lithium salt, a dense interface cannot be maintained between Li₂S and lithium salt, thus potentially providing high interfacial resistance and increasing the internal resistance of the solid electrolyte membrane.

[0065] The Li2S-lithium salt complex consists of Li2S-Li a X b(Where 1≤a≤5 and 1≤b≤5) represents X. X is I, Br, Cl, F, H, O, Se, Te, N, P, As, Sb, Al, B, OCl, PF6, BF4, SbF6, AsF6, ClO4, AlO2, AlCl4, NO3, CO3, BH4, SO4, BO3, PO4, NCl, NCl2, BN2, or any combination thereof. For example, a is 1, 2, 3, 4, or 5. For example, b is 1, 2, 3, 4, or 5. Lithium salts are, for example, compounds that do not contain sulfur (S). Lithium salts can be, for example, binary or ternary compounds. Lithium salts can be, for example, binary compounds composed of lithium and one element selected from groups 13 to 17 of the periodic table. Lithium salts can be, for example, ternary compounds composed of lithium and two elements selected from groups 13 to 17 of the periodic table. Binary compounds can include, for example, LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, or any combination thereof. By including such binary compounds, the composite can have further improved ionic conductivity. Because the solid electrolyte membrane includes such a composite, the internal resistance of the positive electrode can be further reduced. As a result, the cycle characteristics of the all-solid-state secondary battery including the positive electrode can be further improved. Ternary compounds can include, for example, Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2, or any combination thereof. By including such ternary compounds, the composite can have improved ionic conductivity. Because the positive electrode includes such a composite, the internal resistance of the positive electrode can be further reduced. As a result, the cycle characteristics of all-solid-state secondary batteries, including solid electrolyte membranes, can be further improved.

[0066] The complex can also include carbonaceous materials. The complex is a combination of Li₂S, lithium salts, and carbonaceous materials.

[0067] Carbonaceous materials can be, for example, any material comprising carbon atoms and commonly used in the art as a conductive material. Carbonaceous materials can be, for example, crystalline carbon, amorphous carbon, or any combination thereof. Carbonaceous materials can be, for example, calcined products of carbon precursors. Carbonaceous materials can be, for example, carbon nanostructures. Carbon nanostructures can be, for example, one-dimensional carbon nanostructures, two-dimensional carbon nanostructures, three-dimensional carbon nanostructures, or any combination thereof. Carbon nanostructures can be, for example, carbon nanotubes, carbon nanofibers, carbon nanoribbons, carbon nanorods, graphene, or any combination thereof. Carbonaceous materials can be, for example, porous or non-porous carbonaceous materials. Porous carbonaceous materials can include, for example, periodic and regular two-dimensional or three-dimensional pores. Porous carbonaceous materials can be, for example, carbon black (such as Ketjen black, acetylene black, superconducting acetylene black (Denka black), thermally cracked carbon black, and channel black), graphite, activated carbon, or any combination thereof. Carbonaceous materials can be, for example, in particulate, flake, or scaly form, but are not limited thereto, and any material commonly used in the art as a carbonaceous material can be used. Based on the total weight of the composite, the amount of carbon nanostructures contained in the composite of Li₂S, lithium salt, and carbonaceous material can be, for example, about 1 wt% to 20 wt%, about 5 wt% to 20 wt%, or about 10 wt% to 20 wt%. If the amount of carbonaceous material is excessively increased, the energy density of the dry cathode film and the all-solid-state secondary battery may decrease. If the amount of carbonaceous material is excessively reduced, the electronic conductivity of the composite of Li₂S, lithium salt, and carbonaceous material decreases, leading to an increase in the internal resistance of the dry cathode film. As a result, the cycle characteristics of the all-solid-state secondary battery may deteriorate.

[0068] Lithium salts and carbonaceous materials can each have a Mohs hardness higher than that of Li₂S. The Mohs hardness of Li₂S is, for example, 0.6 or less. The Mohs hardness of lithium salts can be 0.7 or greater, 0.8 or greater, 0.9 or greater, 1.0 or greater, 1.5 or greater, or 2.0 or greater. If the lithium salt has a Mohs hardness within the above range, Li₂S can be more easily pulverized during the grinding process, and a solid solution of Li₂S and the lithium salt can be formed more easily. For example, LiI can have a Mohs hardness of 2.0. Carbonaceous materials can have a Mohs hardness of 0.7 or greater, 0.8 or greater, 0.9 or greater, 1.0 or greater, 1.2 or greater, or 1.5 or greater. If the carbonaceous material has a Mohs hardness within the above range, Li₂S can be more easily pulverized during the grinding process, and a composite of Li₂S, lithium salt, and carbonaceous material can be formed more easily. Carbon nanofibers (CNFs) can have a Mohs hardness of 1.5.

[0069] Carbonaceous materials can include, for example, fibrous carbonaceous materials. Because the composite of Li₂S, lithium salt, and carbonaceous materials includes fibrous carbonaceous materials, the electronic conductivity of the composite can be further improved. Because the composite of Li₂S, lithium salt, and carbonaceous materials includes fibrous carbonaceous materials, electronic conduction from the surface to the interior of the composite can be facilitated. The dry cathode film including the composite of Li₂S, lithium salt, and carbonaceous materials can have reduced internal resistance, and the cycle characteristics of the all-solid-state secondary battery including the dry cathode film can be further improved.

[0070] The fibrous carbonaceous material can have an aspect ratio of, for example, 2 or greater, 3 or greater, 4 or greater, 5 or greater, 10 or greater, or 20 or greater. The fibrous carbonaceous material can have an aspect ratio of, for example, about 2 to about 30, about 3 to about 30, about 4 to about 30, about 5 to about 30, about 10 to about 30, or about 20 to about 30. The fibrous carbonaceous material can have an aspect ratio of, for example, about 2 to about 30, about 2 to about 20, about 2 to about 10, about 2 to about 8, about 2 to about 5, or about 2 to about 4. If the aspect ratio of the fibrous carbonaceous material is within the above ranges, the overall electronic conductivity of the composite of Li₂S, lithium salt, and carbonaceous material can be improved, and the local inhomogeneity of electronic conductivity can be further reduced in the composite of Li₂S, lithium salt, and carbonaceous material.

[0071] Fibrous carbonaceous materials can include, for example, carbon nanostructures. Carbon nanostructures can be, for example, carbon nanofibers (CNF), carbon nanotubes (CNT), carbon nanoribbons, carbon nanorods, or any combination thereof.

[0072] Carbon nanostructures can be primary carbon nanostructures formed by a single carbon nanostructure and secondary carbon nanostructures formed by multiple primary carbon nanostructures aggregated together.

[0073] Primary carbon nanostructures can have diameters of, for example, about 1 nm to about 200 nm, about 1 nm to about 150 nm, about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 30 nm, or about 1 nm to about 20 nm. Primary carbon nanostructures can have lengths of, for example, about 10 nm to about 2 μm, about 10 nm to about 1.5 μm, about 10 nm to about 1 μm, about 10 nm to about 500 nm, about 10 nm to about 400 nm, about 10 nm to about 300 nm, about 10 nm to about 200 nm, or about 10 nm to about 100 nm. The diameter and length of the primary carbon nanostructures can be measured by using images obtained through scanning electron microscopy (SEM) or transmission electron microscopy (TEM). In some embodiments, the diameter and / or length of the primary carbon nanostructures can be measured by laser diffraction.

[0074] Secondary carbon nanostructures are structures formed by the aggregation of primary carbon nanostructures, wholly or partially, in a bundle or rope-like manner. Secondary carbon nanostructures can include, for example, bundle-type carbon nanostructures, rope-type carbon nanostructures, or any combination thereof. Secondary carbon nanostructures can have diameters, for example, about 2 nm to about 200 nm, about 3 nm to about 150 nm, about 5 nm to about 100 nm, about 5 nm to about 50 nm, about 5 nm to about 30 nm, or about 5 nm to about 20 nm. Secondary carbon nanostructures can have lengths, for example, about 20 nm to about 2 μm, about 30 nm to about 1.5 μm, about 50 nm to about 1 μm, about 50 nm to about 500 nm, about 50 nm to about 400 nm, about 50 nm to about 300 nm, about 50 nm to about 200 nm, or about 50 nm to about 100 nm. The diameter and length of the secondary carbon nanostructures can be measured by using images obtained through SEM or optical microscopy. In some embodiments, the diameter and / or length of the secondary carbon nanostructures can be measured by laser diffraction. Secondary carbon nanostructures can be dispersed in solvents to transform them into primary carbon nanostructures, which can then be used to prepare composites of Li2S, lithium salts, and carbonaceous materials.

[0075] Complexes of Li₂S and lithium salts, or complexes of Li₂S, lithium salts, and carbonaceous materials, can include solid solutions of Li₂S and lithium salts. By including solid solutions of Li₂S and lithium salts, the complex can possess improved ionic conductivity. For example, compared to the ionic conductivity of Li₂S alone, the ionic conductivity of the solid solution of Li₂S and lithium salts can be increased because it includes lithium ions located within Li₂S microcrystals. As a result, the ionic conductivity of the complex can be improved, and the internal resistance of the complex can be reduced. Because the cathode includes such a complex, the internal resistance of the cathode can be further reduced. Consequently, the cycle characteristics of the all-solid-state secondary battery including the cathode can be further improved.

[0076] The size of Li2S crystallites obtained from the XRD spectra of Li2S and lithium salt composites or Li2S, lithium salt, and carbonaceous materials can be, for example, 20 nm or less, 15 nm or less, or 10 nm or less. The size of the Li2S crystallites obtained from the XRD spectra of the composites can be, for example, about 1 nm to about 20 nm, about 1 nm to about 15 nm, or about 3 nm to about 10 nm. As the size of the Li2S crystallites decreases, the contact area between Li2S and the lithium salt can be further increased. With the increase in the contact area between Li2S and the lithium salt, the ionic conductivity of the Li2S and lithium salt composite can be further increased. Because the cathode includes such a composite, the internal resistance of the cathode can be further reduced. As a result, the cycle characteristics of the all-solid-state secondary battery including the cathode can be further improved.

[0077] Due to the low ionic conductivity of Li₂S, composites containing lithium salts are formed to overcome these drawbacks. Compared to the ionic conductivity of Li₂S alone, composites of Li₂S and lithium salts, or composites of Li₂S, lithium salts, and carbonaceous materials, can provide improved ionic conductivity. Based on the total weight of the Li₂S and lithium salt composite, the amount of Li₂S in the composite can be from about 50 wt% to about 95 wt%, from about 50 wt% to about 90 wt%, from about 50 wt% to about 80 wt%, or from about 50 wt% to about 70 wt%. If the composite includes Li₂S within the above-mentioned range, a cathode with improved ionic conductivity and durability can be manufactured. Based on the total weight of the Li₂S and lithium salt composite, the amount of lithium salt in the Li₂S and lithium salt composite can be from about 5 wt% to about 50 wt%, from about 10 wt% to about 50 wt%, from about 20 wt% to about 50 wt%, or from about 30 wt% to about 50 wt%.

[0078] In the composite, the molar ratio of Li₂S to lithium salt can be, for example, about 50:50 to about 95:5, about 60:40 to about 95:5, about 60:40 to about 90:10, about 65:35 to about 90:10, about 65:35 to about 85:15, or about 70:30 to about 85:15. In the composite, the molar ratio of Li₂S to lithium salt can be, for example, about 50:50 to about 95:5, about 50:50 to about 90:10, about 50:50 to about 85:15, about 50:50 to about 80:20, about 50:50 to about 75:25, or about 50:50 to about 70:30. For example, in the composite, the amount of Li₂S can be greater than the amount of lithium salt, and in the composite, the molar ratio of Li₂S to lithium salt can be about 51:49 to about 95:5. If the molar ratio of Li₂S to lithium salt is within the above range, the cycle characteristics of lithium batteries including composite cathode active materials can be further improved. If the molar ratio of Li₂S is too high, the effect of lithium salt on increasing ionic conductivity will be negligible. If the molar ratio of Li₂S is too high, the energy density of all-solid-state secondary batteries including composite cathode active materials may decrease.

[0079] Lithium salts and carbonaceous materials can have a Mohs hardness greater than that of Li₂S. Li₂S can have a Mohs hardness of, for example, 0.6 or less. The Mohs hardness of lithium salts can be 0.7 or greater, 0.8 or greater, 0.9 or greater, 1.0 or greater, 1.5 or greater, or 2.0 or greater. If the Mohs hardness of lithium salts is within the above range, Li₂S can be more easily pulverized during the grinding process, and solid solutions of Li₂S and lithium salts can be formed more easily. The Mohs hardness of LiI can be, for example, 2.0. Carbonaceous materials can have a Mohs hardness of 0.7 or greater, 0.8 or greater, 0.9 or greater, 1.0 or greater, 1.2 or greater, or 1.5 or greater. If the Mohs hardness of carbonaceous materials is within the above range, Li₂S can be more easily pulverized during the grinding process, and composites of Li₂S, lithium salts, and carbonaceous materials can be formed more easily. Carbon nanofibers (CNFs) can have a Mohs hardness of, for example, 1.5.

[0080] In the composite of Li₂S, lithium salt, and carbonaceous materials, the amount of lithium salt can be approximately 1 wt% to approximately 40 wt%, approximately 5 wt% to approximately 35 wt%, approximately 10 wt% to approximately 35 wt%, approximately 15 wt% to approximately 35 wt%, approximately 20 wt% to approximately 35 wt%, or approximately 25 wt% to approximately 35 wt%, depending on the total weight of the composite. If the amount of lithium salt is too high, the energy density of the all-solid-state secondary battery may decrease. If the amount of lithium salt is too low, the ionic conductivity of the Li₂S, lithium salt, and carbonaceous material composite may deteriorate, leading to an increase in the internal resistance of the dry cathode film. As a result, the cycle characteristics of the all-solid-state secondary battery, including the dry cathode film, may deteriorate.

[0081] In a composite of Li₂S, lithium salt, and carbonaceous materials, the molar ratio of Li₂S to lithium salt can be, for example, about 50:50 to about 95:5, about 60:40 to about 95:5, about 60:40 to about 90:10, about 65:35 to about 90:10, about 65:35 to about 85:15, or about 70:30 to about 85:15. In another composite of Li₂S, lithium salt, and carbonaceous materials, the molar ratio of Li₂S to lithium salt can be, for example, about 50:50 to about 95:5, about 50:50 to about 90:10, about 50:50 to about 85:15, about 50:50 to about 80:20, about 50:50 to about 75:25, or about 50:50 to about 70:30. If the molar ratio of Li₂S to lithium salt is within the above ranges, the cycle characteristics of the all-solid-state secondary battery, including the dry cathode film, can be further improved. If the molar ratio of Li₂S is too high, the effect of lithium salt on increasing ionic conductivity will be negligible. If the molar ratio of Li₂S is too high, the energy density of all-solid-state secondary batteries, including composite cathode active materials, may decrease.

[0082] Complexes of Li₂S and lithium salts, or complexes of Li₂S, lithium salts, and carbonaceous materials, can exhibit, for example, a concentration of 1 × 10⁻⁶ at 25°C. -5 S / cm or greater, 2×10 -5 S / cm or greater, 4×10 -5 S / cm or greater, 6×10 -5 S / cm or greater, 8×10 -5 S / cm or greater or 1×10 -4 Ionic conductivity of S / cm or greater. Ionic conductivity can be measured by, for example, electrochemical impedance spectroscopy, DC polarization, etc. If the ionic conductivity of the Li₂S and lithium salt complex is within the above range, the internal resistance of the cathode including the Li₂S and lithium salt complex can be further reduced. The cycle characteristics of the all-solid-state secondary battery including the cathode can be improved.

[0083] The positive electrode active material layer may also include a solid electrolyte. The solid electrolyte may include sulfide solid electrolytes.

[0084] Based on the total weight of the Li₂S and lithium salt complex and the sulfide-based solid electrolyte, the amount of the sulfide-based solid electrolyte can be from about 0.1 wt% to about 20 wt%, from about 0.5 wt% to about 20 wt%, from about 0.5 wt% to about 15 wt%, from about 0.5 wt% to about 10 wt%, or from about 1 wt% to about 5 wt%. Based on the total weight of the cathode, the amount of the sulfide-based solid electrolyte can be, for example, from about 0.1 wt% to about 20 wt%, from about 0.5 wt% to about 20 wt%, from about 0.5 wt% to about 15 wt%, from about 0.5 wt% to about 10 wt%, or from about 1 wt% to about 5 wt%. If the cathode includes a sulfide-based solid electrolyte within the above range, the durability of the cathode can be further improved and its internal resistance can be further reduced. If the amount of the sulfide-based solid electrolyte is too low, its effect will be negligible. If the amount of the sulfide-based solid electrolyte is too high, the internal resistance of the cathode will increase.

[0085] The positive electrode active material layer may include, for example, particles of a Li₂S and lithium salt composite and particles of a sulfide-based solid electrolyte. The particle size of the Li₂S and lithium salt composite can be smaller than that of the sulfide-based solid electrolyte. The particle size of the Li₂S and lithium salt composite can be 90% or less, 80% or less, 60% or less, 40% or less, 20% or less, or 10% or less of the particle size of the sulfide-based solid electrolyte. The particles of the Li₂S and lithium salt composite can be arranged in pores between multiple particles of the sulfide-based solid electrolyte. Because the particles of the Li₂S and lithium salt composite are arranged in pores between multiple particles of the sulfide-based solid electrolyte, pinhole formation can be suppressed in the positive electrode, and the internal resistance of the positive electrode can be reduced. As a result, the durability of the positive electrode can be improved.

[0086] The particle size of sulfide-based solid electrolytes can be from about 1 μm to about 10 μm, from about 1 μm to about 8 μm, from about 1 μm to about 6 μm, from about 1 μm to about 5 μm, or from about 1 μm to about 3 μm. If the particle size of the sulfide-based solid electrolyte is within the above range, the durability of the cathode can be further improved. In this regard, the particle size of the sulfide-based solid electrolyte can be measured using laser diffraction or scanning electron microscopy (SEM). The particle size of the sulfide-based solid electrolyte is the arithmetic mean of the particle sizes of multiple particles measured from scanning electron microscope images using software. The particle size of the Li₂S-containing complex, which serves as the active material of the composite cathode, can be, for example, 10 μm or less, 8 μm or less, 5 μm or less, 2 μm or less, 1.5 μm or less, or 1 μm or less. The particle size of the complex can be, for example, from about 1 μm to about 10 μm, from about 2 μm to about 10 μm, from about 2 μm to 8 μm, or from about 3 μm to about 8 μm. The particle size of the composite can be, for example, about 0.1 μm to about 10 μm, about 0.1 μm to about 8 μm, about 0.1 μm to about 5 μm, about 0.1 μm to about 2 μm, about 0.1 μm to about 1.5 μm, or about 0.1 μm to about 1 μm. When the particle size of the composite is within the above range, volume change can be suppressed during charge and discharge, and degradation of the composite positive electrode active material including the composite can be suppressed during charge and discharge. Excessive increase in the particle size of the composite increases the volume change of the composite during charge and discharge, thereby promoting the degradation of the composite positive electrode active material including the composite. As a result, the cycle characteristics of the all-solid-state secondary battery including the composite positive electrode active material may deteriorate.

[0087] The particle size of Li2S included in the composite positive electrode active material (i.e., the particle size of Li2S included in the composite) can be, for example, 2 μm or less, 1.5 μm or less, or 1 μm or less. The particle size of Li2S can be, for example, about 0.1 μm to about 2 μm, about 0.1 μm to about 1.5 μm, or about 0.1 μm to about 1 μm. Because the particle size of the composite is within the above range, the particles can be more easily arranged in the pores between multiple sulfide-based solid electrolyte particles, which can suppress the formation of pinholes in the positive electrode and reduce the internal resistance of the positive electrode. As a result, the durability of the positive electrode can be improved.

[0088] In this regard, the particle size of the Li2S-containing complex can be measured using laser diffraction or scanning electron microscopy (SEM). The particle size of the Li2S-containing complex is the arithmetic mean of the particle sizes of multiple particles measured from scanning electron microscope images using software.

[0089] The particle size ratio of the sulfide-based solid electrolyte to the Li₂S-containing complex can be, for example, about 2:1 to about 200:1, about 2:1 to about 100:1, or about 2:1 to about 50:1. If the particle size ratio of the sulfide-based solid electrolyte to the Li₂S-containing complex is within the above range, defects in the cathode can be suppressed, thereby improving the durability of the cathode. If the particle size ratio of the sulfide-based solid electrolyte to the Li₂S-containing complex is too low, the porosity of the cathode may increase excessively, thereby reducing the durability of the cathode. If the particle size ratio of the sulfide-based solid electrolyte to the Li₂S-containing complex is too high, it may be difficult to uniformly disperse the Li₂S-containing complex in the cathode.

[0090] If a positive electrode comprising the aforementioned composite is used, lithium metal is not required as the negative electrode, thus enabling the use of a negative electrode-free all-solid-state secondary battery and providing an all-solid-state secondary battery with improved energy density. Because the composite of the positive electrode active material includes such a composition, the cycle characteristics of the all-solid-state secondary battery comprising the composite positive electrode active material can be improved. For example, the rate performance of the secondary battery comprising the composite positive electrode active material can be improved.

[0091] In the positive electrode active material layer, the solid electrolyte can be, for example, a sulfide-based solid electrolyte. The solid electrolyte included in the positive electrode can be the same as or different from the solid electrolyte included in the solid electrolyte layer. The average particle size D50 of the solid electrolyte included in the positive electrode active material layer can be smaller than the average particle size D50 of the solid electrolyte included in the electrolyte layer. For example, the average particle size D50 of the solid electrolyte included in the positive electrode active material layer can be 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 particle size D50 of the solid electrolyte included in the electrolyte layer. The average particle size D50 is, for example, the median particle size D50. The median particle size D50 is the particle size corresponding to 50% of the cumulative volume calculated from the smallest particle in a particle size distribution, for example, measured by laser diffraction.

[0092] Based on 100 parts by weight of the positive electrode active material layer, the amount of solid electrolyte may be about 10 parts by weight to about 60 parts by weight, about 10 parts by weight to about 50 parts by weight, about 20 parts by weight to about 50 parts by weight, or about 30 parts by weight to about 50 parts by weight.

[0093] [All-solid-state rechargeable battery] The all-solid-state secondary battery according to the embodiment may include a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive electrode includes the aforementioned positive electrode.

[0094] Reference Figures 1 to 5The all-solid-state secondary battery 1 may include a positive electrode 10, a negative electrode 20, and a solid electrolyte layer 30 disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10 may include a positive electrode according to an embodiment.

[0095] [positive electrode] [Positive electrode: Positive electrode active material] Reference Figures 1 to 5 The positive electrode 10 may include a positive electrode current collector 11, an adhesive layer 13 disposed on one or both sides of the positive electrode current collector 11, and a positive electrode active material layer 12 disposed on the adhesive layer 13. The positive electrode active material layer 12 may include a Li2S-containing complex as the positive electrode active material.

[0096] The positive electrode active material layer 12 may also include other positive electrode active materials that are different from the composite positive electrode active material described above.

[0097] Different positive electrode active materials may include, for example, Li2S-containing complexes. Li2S-containing complexes may include, for example: Li2S and carbon complexes; Li2S, carbon and solid electrolyte complexes; Li2S and solid electrolyte complexes; Li2S, lithium salt and carbon complexes; Li2S and metal carbide complexes; Li2S, carbon and metal carbide complexes; Li2S and metal nitride complexes; Li2S, carbon and metal nitride complexes; or any combination thereof.

[0098] The Li2S and carbon complex includes carbon. Carbon can be, for example, any material comprising carbon atoms and commonly used in the art as a conductive material. Carbon can be, for example, crystalline carbon, amorphous carbon, or any combination thereof. Carbon can be, for example, a calcined product of a carbon precursor. Carbon can be, for example, a carbon nanostructure. Carbon nanostructures can be, for example, one-dimensional carbon nanostructures, two-dimensional carbon nanostructures, three-dimensional carbon nanostructures, or any combination thereof. Carbon nanostructures can be, for example, carbon nanotubes, carbon nanofibers, carbon nanoribbons, carbon nanorods, graphene, graphene oxide (GO), reduced graphene oxide (rGO), graphene spheres (GB), or any combination thereof. Carbon can be, for example, porous carbon or non-porous carbon. Porous carbon can have, for example, periodic and regular two-dimensional or three-dimensional pores. Porous carbon can be, for example, carbon black (such as Ketjen black, acetylene black, Denka black, thermally cracked carbon black, and channel black), graphite, activated carbon, or any combination thereof. Carbon can be, for example, in particulate, sheet, or flake form, but is not limited thereto, and any material commonly used as carbon in the art can be used. The method for producing the Li2S and carbon complex can be dry, wet, or any combination thereof, but is not limited thereto. Any method commonly available in the art for producing the Li2S and carbon complex (such as grinding, heat treatment, and deposition) can also be used without limitation.

[0099] The complex of Li₂S, carbon, and solid electrolyte includes carbon and a solid electrolyte. For a description of carbon, refer to the above description of the complex of Li₂S and carbon. The solid electrolyte can be an amorphous solid electrolyte commonly used in the art as an ion-conducting material. The solid electrolyte can be, for example, an inorganic solid electrolyte. The solid electrolyte can be, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or any combination thereof. The solid electrolyte can be, for example, a sulfide solid electrolyte, an oxide solid electrolyte, or any combination thereof. Sulfide solid electrolytes can include, for example, Li, S, and P, and may also include halogen elements. Sulfide solid electrolytes can be selected from sulfide solid electrolytes used in solid electrolyte layers. Sulfide solid electrolytes can have, for example, a density of 1 × 10⁻⁶ at room temperature. -5 Ionic conductivity of S / cm or greater. Sulfide solid electrolytes may include, for example, at least one selected from the following: Li3PO4-Li2SO4, Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen atom), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (Where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Where p and q are positive numbers, and M is P, Si, Ge, B, Al, Ga, or In), Li 7-x PS 6-x Cl x (where 0≤x≤2), Li 7- x PS 6-x Br x (where 0 ≤ x ≤ 2) and Li 7-x PS 6-x I x(Where, 0 ≤ x ≤ 2). Sulfide solid electrolytes may be or include sulfide-germanium ore type solid electrolytes. Sulfide-germanium ore type solid electrolytes may be or include at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I. Sulfide-germanium ore type solid electrolytes may have a density of about 1.5 g / cc to about 2.0 g / cc. Sulfide solid electrolytes may be in particulate form, and the average particle size D50 of sulfide solid electrolytes in particulate form may be about 0.1 μm to about 1.9 μm. Oxide solid electrolytes include, for example, Li, O, and transition metal elements, and may optionally further include additional elements. Oxide solid electrolytes may, for example, have a density of 1 × 10⁻⁶ at room temperature. -5 Solid electrolytes with an ionic conductivity of S / cm or greater. Oxide-based solid electrolytes can be selected from those used in solid electrolyte layers. Solid electrolytes can be, for example, mixtures of sulfide-based solid electrolytes and lithium salts. For example, solid electrolytes may include mixtures of Li3PO4-Li2SO4 and binary lithium salts or mixtures of Li3PO4-Li2SO4 and ternary lithium salts.

[0100] Complexes of Li₂S and solid electrolytes include solid electrolytes. For a description of solid electrolytes, refer to the above description of complexes of Li₂S, carbon, and solid electrolytes.

[0101] Complexes of Li₂S, lithium salts, and carbon may include lithium salt compounds and carbon. For example, lithium salt compounds do not include sulfur (S) atoms. Lithium salt compounds may be binary compounds, for example, composed of lithium and an element selected from groups 13 to 17 of the periodic table. Binary compounds may include, for example, at least one selected from LiF, LiCl, LiBr, LiI, LiH, Li₂S, Li₂O, Li₂Se, Li₂Te, Li₃N, Li₃P, Li₃As, Li₃Sb, Li₃, and LiB₃. Lithium salt compounds may be ternary compounds, for example, composed of lithium and two elements selected from groups 13 to 17 of the periodic table. Ternary compounds may include, for example, at least one selected from Li₃OCl, LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiClO₄, LiAlO₂, LiAlCl₄, LiNO₃, Li₂CO₃, LiBH₄, Li₂SO₄, Li₃BO₃, Li₃PO₄, Li₄NCl, Li₅NCl₂, and Li₃BN₂. The lithium salt compound can be, for example, at least one lithium halide compound selected from LiF, LiCl, LiBr, and LiI. For the description of carbon, refer to the above description of Li₂S and carbon complexes.

[0102] Complexes of Li₂S and metal carbides can include metal carbides. Metal carbides can be, for example, two-dimensional metal carbides. Two-dimensional metal carbides are, for example, MXene. Two-dimensional metal carbides can be made from, for example, M... n+1 C n T x (Where M is a transition metal, T is an end group, T is O, OH and / or F, n = 1, 2 or 3, and x is the number of end groups) represents a two-dimensional metal carbide. Two-dimensional metal carbides can be, 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 any combination thereof. The surface of two-dimensional metal carbides can be capped with O, OH and / or F.

[0103] Complexes of Li₂S, carbon, and metal carbides may include both carbon and metal carbides. For a description of carbon, refer to the description of Li₂S and carbon complexes above. For a description of metal carbides, refer to the description of Li₂S and metal carbides above.

[0104] Complexes of Li₂S and metal nitrides can include metal nitrides. Metal nitrides can be, for example, two-dimensional metal nitrides. Two-dimensional metal nitrides can be formed from, for example, M... n+1 N n T x (Where M is a transition metal, T is an end group, T is O, OH and / or F, n = 1, 2 or 3, and x is the number of end groups) can be used to represent the surface of two-dimensional metal nitrides, which can be end-capped with O, OH and / or F.

[0105] Complexes of Li₂S, carbon, and metal nitrides may include carbon and metal nitrides. For a description of carbon, refer to the description of Li₂S and carbon complexes above. For a description of metal nitrides, refer to the description of Li₂S and metal nitride complexes above.

[0106] The size of the positive electrode active material can be, for example, about 0.1 μm to about 50 μm, about 0.5 μm to about 30 μm, about 0.5 μm to about 20 μm, or about 1 μm to about 10 μm. The size of Li2S can be, for example, about 1 nm to about 10 μm, about 10 nm to about 5 μm, about 10 nm to about 3 μm, or about 10 nm to about 1 μm. The size of the Li2S-containing complex can be, for example, about 0.1 μm to about 50 μm, about 0.5 μm to about 30 μm, about 0.5 μm to about 20 μm, or about 1 μm to about 10 μm.

[0107] The positive electrode active material layer 12 may also include, for example, sulfide compounds different from the aforementioned positive electrode active materials. Sulfide compounds may be, for example, compounds comprising metal elements other than Li and sulfur. Sulfide compounds may be, for example, compounds comprising metal elements belonging to groups 1 to 14 of the periodic table and having an atomic weight of 10 or greater and sulfur. Sulfide compounds may be, for example, FeS2, VS2, NaS, MnS, FeS, NiS, CuS, or any combination thereof. Because the positive electrode active material layer also includes sulfide compounds, the cycle characteristics of the all-solid-state secondary battery can be further improved. Based on the total weight of the positive electrode active material layer 12, the positive electrode active material layer 12 may include sulfide compounds in amounts of 10 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less.

[0108] The positive electrode active material can have a particulate shape, such as a spherical or ellipsoidal shape. The particle size of the positive electrode active material is not limited and can be within the range suitable for positive electrode active materials in conventional all-solid-state secondary batteries. Furthermore, the amount of positive electrode active material in the positive electrode 10 is not limited and can be within the range suitable for positive electrodes in conventional all-solid-state secondary batteries. Based on the total weight of the positive electrode active material layer 12, the amount of positive electrode active material included in the positive electrode active material layer 12 can be, for example, about 30 wt% to about 99 wt%, about 30 wt% to about 90 wt%, about 30 wt% to about 80 wt%, about 60 wt% to about 80 wt%, about 30 wt% to about 70 wt%, or about 30 wt% to about 50 wt%.

[0109] [Positive electrode: Conductive material] The positive electrode active material layer 12 may also include a conductive material. The conductive material may be, for example, a carbonaceous conductive material, a metallic conductive material, or any combination thereof. The carbonaceous conductive material may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof, but is not limited thereto, and any carbonaceous conductive material commonly available in the art may also be used. The metallic conductive material may be metal powder, metal fiber, or any combination thereof, but is not limited thereto, and any metallic conductive material commonly available in the art may also be used. Based on the total weight of the positive electrode active material layer 12, the amount of conductive material included 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%.

[0110] [Positive electrode: binder] The positive electrode active material layer 12 may include a binder. The binder may be styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene, but is not limited thereto; any binder commonly available in the art may be used. Based on the total weight of the positive electrode active material layer 12, the positive electrode active material layer 12 may include the binder in an amount, for example, from 1 wt% to 10 wt%. The binder may be omitted.

[0111] [Positive electrode: Other additives] In addition to the positive electrode active material, solid electrolyte, binder and conductive material, the positive electrode active material layer 12 may also include, for example, fillers, coating agents, dispersants and ion-conducting additives.

[0112] The fillers, coatings, dispersants, and ion-conducting additives included in the positive electrode active material layer 12 can be any known materials commonly used in electrodes of all-solid-state secondary batteries.

[0113] [Positive electrode: Positive current collector] The positive current collector 11 may be, for example, in the form of a plate or foil made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof. The positive current collector 11 may be omitted. The positive current collector 11 may have a thickness of, for example, about 1 μm to about 100 μm, about 1 μm to about 50 μm, about 5 μm to about 25 μm, or about 10 μm to about 20 μm.

[0114] The positive electrode current collector 11 may include, for example, a substrate film and a metal layer disposed on one or both sides of the substrate film. The substrate film may include, for example, a polymer. The polymer may 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 any combination thereof. The substrate film may be, for example, an insulator. Because the substrate film includes an insulating thermoplastic polymer, the substrate film can soften or liquefy in the event of a short circuit to stop the battery from operating, thereby 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, acting as an electrochemical fuse, can be cut off in the event of an overcurrent to prevent a short circuit. By controlling the thickness of the metal layer, the limiting current and the maximum current can be adjusted. The metal layer may be plated or deposited on the substrate film. As the thickness of the metal layer decreases, the limiting current and / or maximum current of the positive electrode current collector 11 decreases, thus improving the stability of the lithium battery in the event of a short circuit. Lead tabs can be added to the metal layer for external connections. The lead tabs can be welded to the metal layer or metal layer / substrate film stack structure via ultrasonic welding, laser welding, spot welding, etc. The metal layer can be electrically connected to the lead tabs when the substrate film and / or metal layer melts during welding. A metal sheet can also be added between the metal layer and the lead tabs for a stronger weld between them. The metal sheet can be a sheet of the same material as the metal layer. The metal sheet can be, for example, metal foil and metal mesh. The metal sheet can be, for example, Al foil, copper foil, and SUS foil. By placing the metal sheet on the metal layer and performing welding, the lead tabs can be welded to a metal sheet / metal layer stack structure or a metal sheet / metal layer / substrate film stack structure. When the substrate film, metal layer, and / or metal sheet melt during soldering, the metal layer or metal layer / metal sheet stack structure can be electrically connected to the lead patch. Metal sheets and / or lead patches can also be added to a portion of the metal layer. The substrate film can have a thickness of, for example, about 1 μm to about 50 μm, about 1.5 μm to about 50 μm, about 1.5 μm to about 40 μm, or about 1 μm to about 30 μm. When the thickness of the substrate film is within the above ranges, the weight of the electrode assembly can be reduced more effectively. The melting point of the substrate film can be, for example, about 100°C to about 300°C, about 100°C to about 250°C, or about 100°C to about 200°C. Because the substrate film has a melting point within the above ranges, the substrate film can melt during the soldering process to easily bond to the lead patch. To improve the adhesion between the substrate film and the metal layer, the substrate film can be subjected to surface treatments such as corona treatment.The thickness of the metal layer can be, for example, from about 0.01 μm to about 3 μm, from about 0.1 μm to about 3 μm, from about 0.1 μm to about 2 μm, or from about 0.1 μm to about 1 μm. When the thickness of the metal layer is within the above range, the stability of the electrode assembly can be achieved while maintaining its conductivity. The thickness of the metal sheet can be, for example, from about 2 μm to about 10 μm, from about 2 μm to about 7 μm, or from about 4 μm to about 6 μm. When the thickness of the metal sheet is within the above range, the metal layer can be more easily connected to the lead terminals. Because the positive electrode current collector 11 has the above structure, the weight of the positive electrode can be reduced, thereby increasing the energy density of the positive electrode and the lithium battery.

[0115] [Positive electrode: Inactive component] Reference Figure 4 and Figure 5 The positive electrode 10 may include a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on the side of the positive electrode current collector 11. An inactive component 40 may be disposed on one side surface of the positive electrode 10. (Refer to...) Figure 4 The inactive component 40 can be disposed on one side surface of each of the positive electrode active material layer 12 and the positive electrode current collector 11. (Refer to...) Figure 5 The inactive component 40 may be disposed on one side surface of the positive electrode active material layer 12 and located between the electrolyte layer 30 and the positive electrode current collector 30 facing the solid electrolyte layer 30. The inactive component 40 is not disposed on the side surface of the positive electrode current collector 11.

[0116] Because of the inactive component 40, crack formation in the electrolyte layer 30 is suppressed during the manufacturing and / or charge / discharge of the all-solid-state secondary battery 1, thereby improving the cycle characteristics of the all-solid-state secondary battery 1. In an all-solid-state secondary battery 1 excluding the inactive component 40, uneven pressure may be applied to the electrolyte layer 30 in contact with the positive electrode 10 during the manufacturing and / or charge / discharge of the all-solid-state secondary battery 1, leading to crack formation in the electrolyte layer 30 and lithium metal growth, thereby increasing the possibility of short circuits.

[0117] In the all-solid-state secondary battery 1, the thickness of the inactive component 40 can be greater than or the same as the thickness of the positive electrode active material layer 12. In some embodiments, the thickness of the inactive component 40 in the all-solid-state secondary battery 1 is substantially the same as the thickness of the positive electrode 10. If the thickness of the inactive component 40 is the same as the thickness of the positive electrode 10, a uniform pressure can be applied between the positive electrode 10 and the electrolyte layer 30, and the positive electrode 10 can be in sufficiently close contact with the electrolyte layer 30, thereby reducing the interfacial resistance between the positive electrode 10 and the electrolyte layer 30. In some embodiments, the electrolyte layer 30 can be sufficiently sintered during the pressing / manufacturing process of the all-solid-state secondary battery 1, thus reducing the internal resistance of the electrolyte layer 30 and the all-solid-state secondary battery 1 including it.

[0118] The inactive component 40 can be in contact with the electrolyte layer 30 while surrounding the side surface of the positive electrode 10. This contact effectively suppresses cracking caused by pressure differences in the electrolyte layer 30, which is not in contact with the positive electrode 10, during the pressing process. The inactive component 40 surrounding the side surface of the positive electrode 10 can be separated from the negative electrode 20, and more specifically, from the first negative electrode active material layer 22. This separation of the inactive component 40 from the electrolyte layer 30 and the negative electrode 20 reduces the possibility of short circuits caused by physical contact between the positive electrode 10 and the first negative electrode active material layer 22, or by lithium overcharging. For example, if the inactive component 40 is disposed on one side surface of the positive electrode active material layer 12 and one side surface of the positive electrode current collector 11, the possibility of short circuits caused by contact between the positive electrode current collector 11 and the negative electrode 20 can be suppressed more effectively.

[0119] Reference Figure 4 and Figure 5 The inactive member 40 extends from one side surface of the positive electrode 10 to the end of the electrolyte layer 30. By extending the inactive member 40 to the end of the electrolyte layer 30, cracks that occur at the end of the electrolyte layer 30 can be suppressed. The end of the electrolyte layer 30 is the outermost portion in contact with the side surface of the electrolyte layer 30. The inactive member 40 can extend to the outermost portion in contact with the side surface of the electrolyte layer 30. The inactive member 40 can be separated from the negative electrode 20, and more specifically, from the first negative electrode active material layer 22. The inactive member 40 can extend to the end of the electrolyte layer 30 but not in contact with the negative electrode 20. The inactive member 40 can fill the space between one side surface of the positive electrode 10 and the end of the electrolyte layer 30.

[0120] Reference Figure 4 and Figure 5The width of the inactive member 40 extending from one side surface of the positive electrode 10 to the end of the electrolyte layer 30 can be, for example, about 1% to about 30%, about 1% to about 25%, about 1% to about 20%, about 1% to about 15%, about 1% to about 10%, or about 1% to about 5% of the width of the positive electrode 10 between one side surface and the other side surface facing that side surface. If the width of the inactive member 40 is too large, the energy density of the all-solid-state secondary battery 1 may decrease. If the width of the inactive member 40 is too small, the effect of the inactive member 40 will be negligible.

[0121] The area of ​​the positive electrode 10 can be smaller than the area of ​​the electrolyte layer 30 in contact with the positive electrode 10. Inactive members 40 arranged around the side surface of the positive electrode 10 can compensate for the area difference between the positive electrode 10 and the electrolyte layer 30. The area of ​​the inactive members 40 can compensate for the difference between the area of ​​the positive electrode 10 and the area of ​​the electrolyte layer 30, thus effectively suppressing cracks in the electrolyte layer 30 caused by pressure differences during the pressing process. For example, the sum of the area of ​​the positive electrode 10 and the area of ​​the inactive members 40 can be the same as the area of ​​the electrolyte layer 30. The electrolyte layer 30 can be, for example, a solid electrolyte layer.

[0122] The area of ​​the positive electrode 10 may be, for example, less than 100%, 99% or less, 98% or less, 97% or less, 96% or less, or 95% or less of the area of ​​the electrolyte layer 30. The area of ​​the positive electrode 10 may be, for example, about 50% but less than 100%, about 50% to about 99%, about 55% to about 98%, about 60% to about 97%, about 70% to about 96%, about 80% to about 95%, or about 85% to about 95% of the area of ​​the electrolyte layer 30.

[0123] If the area of ​​the positive electrode 10 is equal to or greater than the area of ​​the electrolyte layer 30, the possibility of a short circuit caused by physical contact between the positive electrode 10 and the first negative electrode active material layer 22, or by overcharging of lithium, increases. The area of ​​the positive electrode 10 can, for example, be the same as the area of ​​the positive electrode active material layer 12. The area of ​​the positive electrode 10 can, for example, be the same as the area of ​​the positive electrode current collector 11.

[0124] The area of ​​the inactive component 40 may be, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the area of ​​the positive electrode 10. The area of ​​the inactive component 40 may be, for example, about 1% to about 50%, about 5% to about 40%, about 5% to about 30%, about 5% to about 20%, or about 5% to about 15% of the area of ​​the positive electrode 10.

[0125] The area of ​​the positive electrode 10 can be smaller than the area of ​​the negative electrode current collector 21. The area of ​​the positive electrode 10 can be, for example, less than 100%, 99% or less, 98% or less, 97% or less, 96% or less, or 95% or less of the area of ​​the negative electrode current collector 21. The area of ​​the positive electrode 10 can be, for example, 50% but less than 100%, about 50% to about 99%, about 55% to about 98%, about 60% to about 97%, about 70% to about 96%, about 80% to about 95%, or about 85% to about 95% of the area of ​​the negative electrode current collector 21. The area of ​​the negative electrode current collector 21 can, for example, be the same as the area of ​​the negative electrode 20. The area of ​​the negative electrode current collector 21 can, for example, be the same as the area of ​​the first negative electrode active material layer 22.

[0126] As used herein, “identical” area, length, width, thickness, and / or shape can include all cases having “substantially identical” area, length, width, thickness, and / or shape, except where the area, length, thickness, and / or shape has been intentionally modified. “Identical” area, length, width, and / or thickness can include, for example, a range of unintended differences in area, length, width, and / or thickness between objects being compared, less than 3%, less than 2%, less than 1%, less than 0.5%, or less than 0.1%.

[0127] The thickness of the inactive component 40 may, for example, be greater than the thickness of the first negative electrode active material layer 22. The thickness of the first negative electrode active material layer 22 may, for example, be 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the thickness of the inactive component 40. The thickness of the first negative electrode active material layer 22 may be approximately 1% to approximately 50%, approximately 1% to approximately 40%, approximately 1% to approximately 30%, approximately 1% to approximately 20%, or approximately 1% to approximately 10% of the thickness of the inactive component 40.

[0128] The inactive component 40 can be a gasket. By using a gasket as the inactive component 40, cracks that may occur in the electrolyte layer 30 due to pressure differences during the pressing process can be more effectively suppressed.

[0129] The inactive component 40 may have, for example, a single-layer structure. In some embodiments, although not shown in the figures, the inactive component 40 may have a multi-layer structure. In an inactive component 40 with a multi-layer structure, the individual layers may have different compositions. The inactive component 40 with a multi-layer structure may have, for example, a two-layer structure, a three-layer structure, a four-layer structure, or a five-layer structure. The inactive component 40 with a multi-layer structure may include, for example, at least one adhesive layer and at least one support layer. The adhesive layer can effectively prevent the separation of the positive electrode 10 from the electrolyte layer 30 due to volume changes of the positive electrode 10 during the charge and discharge process of the all-solid-state secondary battery 1, and provides adhesive strength between the support layer and other layers, thereby increasing the film strength of the inactive component 40. The support layer can provide support for the inactive component 40 to prevent uneven pressure applied to the electrolyte layer 30 during the pressing process or charge and discharge process, and to prevent deformation of the all-solid-state secondary battery 1.

[0130] The inactive component 40 can be, for example, a flame-retardant component. The flame-retardant inactive component provides flame retardancy, thus preventing thermal runaway and ignition of the all-solid-state secondary battery 1. As a result, the safety of the all-solid-state secondary battery 1 can be further improved. The flame-retardant inactive component can absorb moisture remaining in the all-solid-state secondary battery 1, thus preventing degradation of the all-solid-state secondary battery 1 and improving its lifespan characteristics.

[0131] The flame-retardant inactive component includes, for example, a matrix and a filler. The matrix may include, for example, a substrate and a reinforcing material. The matrix may include, for example, a fiber substrate and a fiber reinforcing material. By including a substrate, the matrix can be elastic. Therefore, the matrix effectively adapts to volume changes during the charging and discharging of the all-solid-state secondary battery 1 and can be arranged in various locations. The substrate included in the matrix may include, for example, a first fiber material. The substrate may include a first fiber material, thus effectively adapting to volume changes of the positive electrode 10 during the charging and discharging of the all-solid-state secondary battery 1 and suppressing deformation of the inactive component 40 caused by volume changes of the positive electrode 10. The first fiber material may be, for example, a material with an aspect ratio of 5 or greater, 20 or greater, or 50 or greater. The first fiber material may be, for example, a material with an aspect ratio of about 5 to about 1000, about 20 to about 1000, or about 50 to about 1000. The first fiber material may be, for example, an insulating material. Because the first fiber material may be an insulating material, short circuits between the positive electrode 10 and the negative electrode 20 caused by lithium dendrites or the like formed during the charging and discharging process of the all-solid-state secondary battery 1 can be effectively suppressed. The first fiber material may include, for example, at least one selected from pulp fibers, insulating polymer fibers, and ion-conducting polymer fibers. Because the matrix includes a reinforcing material, the strength of the matrix can be increased. Therefore, the matrix can prevent excessive volume changes during the 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 may include, for example, a second fiber material. Because the reinforcing material includes a second fiber material, the strength of the matrix can be increased more uniformly. The second fiber material may be, for example, a material with an aspect ratio of 3 or greater, 5 or greater, or 10 or greater. The second fiber material may be, for example, a material with an aspect ratio of about 3 to about 100, about 5 to about 100, or about 10 to about 100. The second fiber material may be, for example, a flame-retardant material. Because the second fiber material is a flame-retardant material, ignition caused during the charging and discharging process of the all-solid-state secondary battery 1 or due to thermal runaway caused by external impact can be effectively prevented. The second fiber material may be, for example, glass fiber, metal oxide fiber, or ceramic fiber.

[0132] In addition to the matrix, the flame-retardant inactive component may also include a filler. The filler may be located inside the matrix, on the surface of the matrix, or both inside and on the surface of the matrix. The filler may be, for example, an inorganic material. The filler included in the flame-retardant inactive component may be, for example, a hygroscopic agent. The filler may absorb moisture, for example, at temperatures below 100°C to remove residual moisture in the all-solid-state secondary battery 1, thereby preventing the degradation of the all-solid-state secondary battery 1. If the temperature of the all-solid-state secondary battery 1 exceeds 150°C during the charge-discharge process of the all-solid-state secondary battery 1 or due to thermal runaway caused by external impact, the filler may release the absorbed moisture, thereby effectively suppressing the ignition of the all-solid-state secondary battery 1. For example, the filler may be a flame retardant. The filler may be, for example, a hygroscopic metal hydroxide. The metal hydroxide included in the filler may be, for example, Mg(OH)2, Fe(OH)3, Sb(OH)3, Sn(OH)4, Ti(OH)3, Zr(OH)4, Al(OH)3, or any combination thereof. Based on 100 parts by weight of the flame-retardant inactive component 40, the amount of filler included in the flame-retardant inactive component may be, for example, about 10 parts by weight to about 80 parts by weight, about 20 parts by weight to about 80 parts by weight, about 30 parts by weight to about 80 parts by weight, about 40 parts by weight to about 80 parts by weight, about 50 parts by weight to about 80 parts by weight, about 60 parts by weight to about 80 parts by weight, or about 65 parts by weight to about 80 parts by weight.

[0133] The flame-retardant inactive component may also include, for example, an adhesive. The adhesive may include, for example, a curable polymer or a non-curable polymer. The curable polymer may be a polymer that cures by heat and / or pressure. The curable polymer may be, for example, a solid at room temperature. The flame-retardant inactive component 40 may include, for example, a hot-pressable curable polymer and / or its cured product. The hot-pressable curable polymer may be, for example, TSA-66 manufactured by Toray.

[0134] In addition to the substrate, reinforcing material, filler, and binder described above, the flame-retardant inactive component may also contain other materials. The flame-retardant inactive component may also include at least one material selected from, for example, paper, insulating polymers, ionically conductive polymers, insulating inorganic materials, oxide-based solid electrolytes, and sulfide-based solid electrolytes. The insulating polymer may be, for example, an olefin polymer, such as polypropylene (PP) and polyethylene (PE).

[0135] The density of the substrate or reinforcing material included in the flame-retardant inactive component may be, for example, about 10% to about 300%, about 10% to about 150%, about 10% to about 140%, about 10% to about 130%, or about 10% to about 120% of the density of the positive active material included in the positive active material layer 12.

[0136] The inactive component 40 may be a component that does not include an electrochemically active material (e.g., an electrode active material). The electrode active material may be a material that allows lithium insertion / extraction. Apart from the electrode active material, the inactive component 40 may be formed from any material commonly used in the art.

[0137] [negative electrode] [Negative electrode: Negative electrode active material] Reference Figures 1 to 5 The negative electrode 20 may include: a negative electrode current collector 21; and a first negative electrode active material layer 22 disposed on the negative electrode current collector 21.

[0138] The first negative electrode active material layer 22 may be, for example, a metal layer, and the metal layer may include lithium or a lithium alloy.

[0139] In some embodiments, the first negative electrode active material layer 22 may include, for example, a negative electrode active material and a binder.

[0140] The negative electrode active material included in the first negative electrode active material layer 22 can be, for example, a material for the negative electrode that allows the formation of alloys or compounds with lithium.

[0141] The negative electrode active material included in the first negative electrode active material layer 22 can, for example, be in particulate form. The particulate form of the negative electrode active material can have an average particle size of, 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 particulate form of the negative electrode active material can have an average particle size of, for example, about 10 nm to about 4 μm, about 10 nm to about 3 μm, about 10 nm to about 2 μm, about 10 nm to about 1 μm, about 10 nm to about 500 nm, about 10 nm to about 300 nm, or about 10 nm to about 100 nm. When the average particle size of the negative electrode active material is within the above ranges, reversible adsorption and / or desorption of lithium can occur more easily during charge and discharge. The average particle size of the negative electrode active material can be, for example, the median particle size D50 measured using a laser particle size analyzer.

[0142] The negative electrode active material included in the first negative electrode active material layer 22 may include at least one selected from, for example, carbonaceous negative electrode active materials and metallic or quasi-metallic negative electrode active materials.

[0143] Carbonaceous anode active materials may include, for example, amorphous carbon, crystalline carbon, porous carbon, or any combination thereof.

[0144] The carbonaceous negative electrode active material can be, for example, amorphous carbon. Amorphous carbon can be, for example, carbon black (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB), or graphene, but is not limited thereto; any carbon classified as amorphous carbon in the art can also be used. Amorphous carbon can be carbon that is non-crystalline or has very low crystallinity and is distinct from crystalline carbon or graphitic carbon.

[0145] The carbonaceous anode active material can be, for example, porous carbon. The pore volume in the porous carbon can be, for example, from about 0.1 cc / g to about 10.0 cc / g, from about 0.5 cc / g to about 5 cc / g, or from about 0.1 cc / g to about 1 cc / g. The porous carbon can have, for example, an average pore size from about 1 nm to about 50 nm, from about 1 nm to about 30 nm, or from about 1 nm to about 10 nm. The porous carbon can have, for example, an average pore size of about 100 nm. 2 / g to approximately 3000m 2 / g BET specific surface area.

[0146] Metallic or quasi-metallic anode active materials may include, but are not limited to, at least one selected from gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn), and any known metallic or quasi-metallic anode active material capable of forming an alloy or compound with lithium may also be used. For example, because nickel (Ni) does not form an alloy with lithium, Ni cannot be a metallic anode active material.

[0147] The first negative electrode active material layer 22 may include one type of negative electrode active material or a mixture of multiple different negative electrode active materials. For example, the first negative electrode active material layer 22 may include only amorphous carbon or include at least one selected from gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). In some embodiments, the first negative electrode active material layer 22 may include amorphous carbon and a mixture of at least one selected from 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., in the mixture may be a weight ratio, for example, about 99:1 to about 1:99, about 10:1 to about 1:2, about 5:1 to about 1:1, or about 4:1 to about 2:1. However, the mixing ratio is not limited to this, but is selected according to the desired characteristics of the all-solid-state secondary battery 1. Due to the composition of the negative electrode active material, the cycle characteristics of the all-solid-state secondary battery 1 can be further improved.

[0148] The negative electrode active material included in the first negative electrode active material layer 22 may include, for example, a mixture of first particles formed of amorphous carbon and second particles formed of a metal or a metalloid. The metal or metalloid may include, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). In some embodiments, the metalloid may be a semiconductor. Based on the total weight of the mixture, the amount of the second particles may be about 1 wt% to about 99 wt%, about 1 wt% to about 60 wt%, about 8 wt% to about 60 wt%, about 10 wt% to about 50 wt%, about 15 wt% to about 40 wt%, or about 20 wt% to about 30 wt%. Due to the amount of the second particles within the above range, the cycle characteristics of the all-solid-state secondary battery 1 can be further improved.

[0149] In some embodiments, the first negative electrode active material layer 22 may include a composite negative electrode active material. The composite negative electrode active material may include, for example, a carbonaceous carrier and a metal negative electrode active material supported on the carbonaceous carrier. Because the composite negative electrode active material has such a structure, localization of the metal negative electrode active material can be suppressed in the first negative electrode active material layer and a uniform distribution can be obtained. As a result, the cycle characteristics of the all-solid-state secondary battery 1 including the first negative electrode active material layer 22 can be further improved.

[0150] The metal negative electrode active material supported on the carbonaceous carrier may include, for example, a metal, a metal oxide, a composite of a metal and a metal oxide, or any combination thereof. The metal may include, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), tellurium (Te), and zinc (Zn). The metal oxide may 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, tellurium (Te) oxide, and zinc (Zn) oxide. The metal oxide may include, for example, Au x O y (where 0 < x ≤ 2 and 0 < y ≤ 3), Pt x O y (where 0 < x ≤ 1 and 0 < y ≤ 2), Pd x O y (where 0 < x ≤ 1 and 0 < y ≤ 1), Si x O y (where 0 < x ≤ 1 and 0 < y ≤ 2), Ag x O y (where 0 < x ≤ 2 and 0 < y ≤ 1), Al x O y(where 0 < x ≤ 2 and 0 < y ≤ 3), Bi x O y (where 0 < x ≤ 2 and 0 < y ≤ 3), Sn x O y (where 0 < x ≤ 1 and 0 < y ≤ 2), Te x O y (where 0 < x ≤ 1 and 0 < y ≤ 3), Zn x O y (where 0 < x ≤ 1 and 0 < y ≤ 1) or any combination thereof. The composite of the metal and the metal oxide may include, for example, Au and Au x O y (where 0 < x ≤ 2 and 0 < y ≤ 3), the composite of Pt and Pt x O y (where 0 < x ≤ 1 and 0 < y ≤ 2), the composite of Pd and Pd x O y (where 0 < x ≤ 1 and 0 < y ≤ 1), the composite of Si and Si x O y (where 0 < x ≤ 1 and 0 < y ≤ 2), the composite of Ag and Ag x O y (where 0 < x ≤ 1 and 0 < y ≤ 2), the composite of Al and Al x O y (where 0 < x ≤ 2 and 0 < y ≤ 3), the composite of Bi and Bi x O y (where 0 < x ≤ 2 and 0 < y ≤ 3), the composite of Sn and Sn x O y (where 0 < x ≤ 1 and 0 < y ≤ 2), the composite of Te and Te x O y (where 0 < x ≤ 1 and 0 < y ≤ 3), the composite of Zn and Zn x O y (where 0 < x ≤ 1 and 0 < y ≤ 1) or any combination thereof.

[0151] The carbonaceous carrier may be, for example, amorphous carbon. The amorphous carbon may be, for example, carbon black (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB), graphene, activated carbon, carbon nanofibers (CNF) or carbon nanotubes (CNT), but is not limited thereto, and any carbon classified as amorphous carbon in the art may also be used. The amorphous carbon may be carbon that does not have crystallinity or has very low crystallinity and is different from crystalline carbon or graphite-like carbon. The carbonaceous material may be, for example, a carbonaceous negative electrode active material.

[0152] Composite anode active materials can, for example, be in particulate form. Particulate composite anode active materials can have particle sizes, for example, from about 10 nm to about 4 μm, from about 10 nm to about 1 μm, from about 10 nm to about 500 nm, from about 10 nm to about 200 nm, or from about 10 nm to about 100 nm. Due to the average particle size of the composite anode active material within the above range, reversible adsorption and / or desorption of lithium can occur more easily during charge and discharge. Metal anode active materials supported on a support can, for example, be in particulate form. Metal anode active materials can have particle sizes, for example, from about 1 nm to about 200 nm, from about 1 nm to about 150 nm, from about 5 nm to about 100 nm, or from about 10 nm to about 50 nm. Carbonaceous supports can, for example, be in particulate form. Carbonaceous supports can have particle sizes, for example, from about 10 nm to about 2 μm, from about 10 nm to about 1 μm, from about 10 nm to about 500 nm, from about 10 nm to about 200 nm, or from about 10 nm to about 100 nm. Because the carbonaceous support has a particle size within the aforementioned range, it can be more uniformly arranged in the first negative electrode active material layer. The carbonaceous support can be, for example, nanoparticles with a particle size of 500 nm or smaller. The particle size of the composite negative electrode active material, the metal negative electrode active material, and the carbonaceous support can be, for example, the average particle size. The average particle size can be, for example, the median particle size D50 measured using a laser particle size analyzer. In some embodiments, the average particle size can be determined automatically, for example, using software or manually based on a manual from electron microscope images.

[0153] [Negative electrode: binder] The binder included in the first negative electrode active material layer 22 may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, or polymethyl methacrylate, but is not limited thereto; any binder commonly available in the art may also be used. The binder may be used alone or in combination of several different binders.

[0154] If the first negative electrode active material layer 22 includes a binder, it can be stabilized on the negative electrode current collector 21. Although the volume and / or relative position of the first negative electrode active material layer 22 may change, cracking can be suppressed in 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 include a binder, it may easily separate from the negative electrode current collector 21. If the first negative electrode active material layer 22 separates from the negative electrode current collector 21, the exposed area of ​​the negative electrode current collector 21 may come into contact with the electrolyte layer 30, thereby increasing the likelihood of a short circuit. The first negative electrode active material layer 22 can be prepared, for example, by applying a slurry in which the material constituting the first negative electrode active material layer 22 is dispersed to the negative electrode current collector 21 and drying the slurry. By adding a binder to the first negative electrode active material layer 22, the negative electrode active material can be stably dispersed in the slurry. For example, if the paste is applied to the negative electrode current collector 21 by screen printing, it is possible to suppress screen clogging (e.g., clogging by aggregates of negative electrode active material).

[0155] [Anode: Other additives] The first negative electrode active material layer 22 may also include additives used in conventional all-solid-state secondary batteries, such as fillers, coatings, dispersants, and ion-conducting agents.

[0156] [Negative electrode: Solid electrolyte] The first negative electrode active material layer 22 may further include a solid electrolyte. The solid electrolyte may be selected from those included in the electrolyte layer 30. The solid electrolyte included in the first negative electrode active material layer 22 can serve as a reaction site for initiating the formation of lithium metal in the first negative electrode active material layer 22, as a space for storing the formed lithium metal, or as a pathway for transporting lithium ions. The solid electrolyte may be omitted.

[0157] In the first negative electrode active material layer 22, for example, the amount of solid electrolyte can be higher in the region adjacent to the electrolyte layer 30 and lower in the region adjacent to the negative electrode current collector 21. In the first negative electrode active material layer 22, the solid electrolyte can have, for example, a concentration gradient, such that the concentration decreases from the region adjacent to the electrolyte layer 30 to the region adjacent to the negative electrode current collector 21.

[0158] [Negative Electrode: First Negative Electrode Active Material Layer] The ratio 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, B / A, can be from approximately 0.005 to approximately 0.45. The initial charge capacity of the positive electrode active material layer 12 can be relative to Li / Li +The initial charging capacity of the first negative electrode active material layer 22 can be determined by the first open-circuit voltage at the maximum charging voltage. This initial charging capacity can be determined relative to Li / Li + The voltage is determined by the second open-circuit voltage at 0.01V.

[0159] The maximum charging voltage can be determined by the type of positive electrode active material. The maximum charging voltage can be, for example, 1.5V, 2.0V, 2.5V, 3.0V, 3.5V, 4.0V, 4.2V, or 4.3V. For example, the maximum charging voltage of Li₂S or Li₂S-containing complexes relative to Li / Li + It can be 2.5V. For example, the maximum charging voltage of Li2S or Li2S-containing complexes relative to Li / Li + The voltage can be 3.0V. The ratio B / A of the initial charging capacity B of the first negative electrode active material layer 22 to the initial charging capacity A of the positive electrode active material layer can be, for example, about 0.01 to about 0.3, about 0.01 to about 0.2, or about 0.05 to about 0.1. The initial charging capacity (mAh) of the positive electrode active material layer 12 can be obtained by multiplying the specific charging 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. If various types of positive electrode active materials are used, the specific charging capacity × mass value of all positive electrode active materials can be calculated separately, and the sum of these values ​​can be regarded as the initial charging capacity of the positive electrode active material layer 12. The initial charging capacity of the first negative electrode active material layer 22 can be calculated in the same way. The initial charging capacity of the first negative electrode active material layer 22 can be obtained by multiplying the specific charging 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. If various types of negative electrode active materials are used, the specific charge capacity × mass value of each negative electrode active material can be calculated separately, and the sum of these values ​​can be considered as the initial charge capacity of the first negative electrode active material layer 22. The specific charge capacity of the positive and negative electrode active materials can be measured using a solid-state half-cell with lithium metal as the counter electrode. The initial charge capacity of the positive electrode active material layer 12 and the first negative electrode active material layer 22 can be measured using a solid-state half-cell at a constant current density (e.g., 0.1 mA / cm²). 2 Direct measurement is possible from the first open-circuit voltage (OCV) to the maximum charging voltage (e.g., 3.0V relative to Li / Li). + The positive electrode is measured using an operating voltage ranging from the second open-circuit voltage (OCV) to 0.01V. The negative electrode (e.g., lithium metal) can be measured using an operating voltage from the second open-circuit voltage (OCV) to 0.01V. For example, a solid-state half-cell including a positive electrode active material layer can be measured at 0.1mA / cm. 2 A constant current is applied from the first open-circuit voltage to 3.0V, and the solid half-cell, including the first negative electrode active material layer, can be charged at 0.1mA / cm.2 A constant current is applied to charge the circuit from the second open-circuit voltage to 0.01V. The current density during charging at a constant current can be, for example, 0.2 mA / cm². 2 or 0.5mA / cm 2 A solid-state half-cell, including a positive electrode active material layer, can be charged, for example, from a first open-circuit voltage to 2.5V, 2.0V, 3.5V, or 4.0V. The maximum charging voltage of the positive electrode active material can be determined by the maximum voltage of the battery that meets the safety conditions according to JISC 8712:2015 of the Japanese Standards Institute.

[0160] If the first negative electrode active material layer 22 has too low an initial charge capacity, its thickness may become too small. Therefore, lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 during repeated charge-discharge cycles will damage the first negative electrode active material layer 22, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery 1. If the first negative electrode active material layer 22 has too high a charge capacity, the energy density of the all-solid-state secondary battery 1 may decrease. Therefore, the internal resistance of the all-solid-state secondary battery 1 may increase due to the first negative electrode active material layer 22, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery 1.

[0161] The thickness of the first negative electrode active material layer 22 can be, 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 can be, for example, about 1% to about 50%, about 1% to about 40%, about 1% to about 30%, about 1% to about 20%, about 1% to about 10%, or about 1% to about 5% of the thickness of the positive electrode active material layer 12. The thickness of the first negative electrode active material layer 22 can be, for example, about 1 μm to about 20 μm, about 2 μm to about 15 μm, or about 3 μm to about 10 μm. If the first negative electrode active material layer 22 has too small a thickness, lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 will damage the first negative electrode active material layer 22, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery 1. If the first negative electrode active material layer 22 has too large a thickness, the energy density of the all-solid-state secondary battery 1 may decrease, and the internal resistance of the all-solid-state secondary battery 1 may increase due to the first negative electrode active material layer 22, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery 1. As the thickness of the first negative electrode active material layer 22 decreases, the initial charging capacity of the first negative electrode active material layer 22 can also decrease.

[0162] [Negative Electrode: Second Negative Electrode Active Material Layer] Reference Figure 3The all-solid-state secondary battery 1 may further include, for example, a second negative electrode active material layer 24 disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22 after charging. The second negative electrode active material layer 24 may be a metal layer comprising lithium or a lithium alloy. The metal layer may include lithium or a lithium alloy. Therefore, the second negative electrode active material layer 24, as a lithium-containing metal layer, can act as a lithium storage device. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, or a Li-Si alloy, but is not limited thereto; any lithium alloy commonly available in the art may also be used. The second negative electrode active material layer 24 may be formed from a single alloy, lithium, or a combination of various types of alloys. The second negative electrode active material layer 24 may be, for example, a plating layer. For example, the second negative electrode active material layer 24 may be plated between the first negative electrode active material layer 22 and the negative electrode current collector 21 during the charge and discharge process of the all-solid-state secondary battery 1.

[0163] The thickness of the second negative electrode active material layer 24 is not limited, but can be, for example, about 1 μm to about 500 μm, about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 1 μm to about 100 μm, or about 1 μm to about 50 μm. If the thickness of the second negative electrode active material layer 24 is too small, it may be difficult to obtain the function of the second negative electrode active material layer 24 as a lithium storage layer. If the thickness of the second negative electrode active material layer 24 is too large, the mass and volume of the all-solid-state secondary battery 1 will increase, and therefore the cycle characteristics of the all-solid-state secondary battery 1 may deteriorate.

[0164] In some embodiments, in the all-solid-state secondary battery 1, the second negative electrode active material layer 24 can be disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22 before assembling the all-solid-state secondary battery 1. If the second negative electrode active material layer 24 is disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22 before assembling the all-solid-state secondary battery 1, the second negative electrode active material layer 24, as a metal layer including lithium, can act as a lithium storage device. For example, a lithium foil can be disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22 before assembling the all-solid-state secondary battery 1.

[0165] If the second negative electrode active material layer 24 is plated during charging after the assembly of the all-solid-state secondary battery 1, the energy density of the all-solid-state secondary battery 1 can be increased because the second negative electrode active material layer 24 is not included during the assembly of the all-solid-state secondary battery 1. While charging the all-solid-state secondary battery 1, it is possible to charge beyond the charging capacity of the first negative electrode active material layer 22. For example, the first negative electrode active material layer 22 can be overcharged. During the initial charging, lithium can be adsorbed onto the first negative electrode active material layer 22. The negative electrode active material included in the first negative electrode active material layer 22 can form an alloy or compound with lithium ions that have migrated from the positive electrode 10. If the first negative electrode active material layer 22 is overcharged beyond its capacity, lithium can be plated onto the rear 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 a metal layer corresponding to the second negative electrode active material layer 24 can be formed by the plated lithium. The second negative electrode active material layer 24 can be a metal layer mainly composed of lithium (i.e., lithium metal). These results are achieved because the negative electrode active material included in the first negative electrode active material layer 22 comprises a material that forms an alloy or compound with lithium. During discharge, lithium in the first negative electrode active material layer 22 and the second negative electrode active material layer 24 (i.e., the metal layer) can be ionized to migrate in the direction toward the positive electrode 10. Therefore, lithium can be used as the negative electrode active material in the all-solid-state secondary battery 1. Because the second negative electrode active material layer 24 is coated with the first negative electrode active material layer 22, the first negative electrode active material layer 22 can be used as a protective layer for the second negative electrode active material layer 24 (i.e., the metal layer) to prevent the formation and growth of lithium dendrites. Therefore, short circuits and capacity reduction can be suppressed in the all-solid-state secondary battery 1, thereby improving the cycle characteristics of the all-solid-state secondary battery 1. If the second negative electrode active material layer 24 is set by charging after assembling the all-solid-state secondary battery 1, then the negative electrode 20 (i.e., the negative electrode current collector 21, the first negative electrode active material layer 22 and the region therebetween) can be a Li-free region that does not include lithium (Li) in the early state of charging or after the all-solid-state secondary battery 1 has been fully discharged.

[0166] [Negative electrode: Negative electrode current collector] The negative electrode current collector 21 can be formed of, for example, a material that does not react with lithium (i.e., a material that does not form alloys or compounds with lithium). The material constituting the negative electrode current collector 21 can be, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), but is not limited thereto, and any material commonly used as an electrode current collector in the art can also be used. The negative electrode current collector 21 can be formed of one metal selected from the above-mentioned metals, or an alloy or coating material of two or more metals. The negative electrode current collector 21 can be, for example, in the form of a plate or foil.

[0167] Reference Figure 2 The all-solid-state secondary battery 1 may further include a thin film 23 containing elements capable of forming an alloy with lithium, on one side of the negative electrode current collector 21. The thin film 23 may be disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22. The thin film 23 may include, for example, elements capable of forming an alloy with lithium. Examples of elements capable of forming an alloy with lithium include gold, silver, zinc, tin, indium, silicon, aluminum, and bismuth, but are not limited thereto, and any element known in the art capable of forming an alloy with lithium may also be used. The thin film 23 may be formed from any metal or an alloy of various types of metals. By disposing of the thin film 23 on one surface of the negative electrode current collector 21, the second negative electrode active material layer 24 deposited between the thin film 23 and the first negative electrode active material layer 22 can become flatter, thereby further improving the cycle characteristics of the all-solid-state secondary battery 1.

[0168] For example, the thin film 23 may have a thickness of about 1 nm to about 800 nm, about 10 nm to about 700 nm, about 50 nm to about 600 nm, or about 100 nm to about 500 nm. If the thickness of the thin film 23 is less than 1 nm, it may be difficult to obtain the functionality of the thin film 23. If the thickness of the thin film 23 is too large, lithium will be adsorbed in the thin film 23 and the amount of lithium plated in the negative electrode will be reduced, thus the energy density of the all-solid-state secondary battery 1 may be reduced and the cycle characteristics of the all-solid-state secondary battery 1 may be degraded. The thin film 23 may be formed on the negative electrode current collector 21 by, for example, vacuum deposition, sputtering, or plating. However, the method is not limited to this, and any method commonly used in the art to form the thin film 23 may be used.

[0169] Although not shown in the accompanying drawings, the negative electrode current collector 21 may include, for example, a substrate film and a metal layer disposed on one or both sides of the substrate film. The substrate film may include, for example, a polymer. The polymer may 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 any combination thereof. The polymer may be an insulating polymer. Because the substrate film includes an insulating thermoplastic polymer, the substrate film can soften or liquefy in the event of a short circuit to stop the operation of the battery, thereby 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 also include a metal sheet and / or lead terminals. For a detailed description of the substrate film, metal layer, metal sheet, and lead terminals of the negative electrode current collector 21, refer to the positive electrode current collector 11 described above. Because the negative electrode current collector 21 has the above structure, the weight of the negative electrode can be reduced, thereby increasing the energy density of the negative electrode and the lithium battery.

[0170] [Solid electrolyte layer] [Solid electrolyte layer: electrolyte] Reference Figures 1 to 5 , the solid electrolyte layer 30 can be disposed between the positive electrode 10 and the negative electrode 20 and includes a solid electrolyte separator. The solid electrolyte layer 30 can include, for example, a solid electrolyte, a gel electrolyte, or a combination thereof.

[0171] The solid electrolyte further included in the solid electrolyte layer 30 can include, for example, an oxide-based solid electrolyte, a polymer solid electrolyte, or any combination thereof.

[0172] The oxide-based solid electrolyte can be, for example, Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (where 0 < x < 2 and 0 ≤ y < 3), BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, where 0 ≤ x < 1 and 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 (where 0 < x < 2 and 0 < y < 3), Li x Al y Ti z (PO4)3 (where 0 < x < 2, 0 < y < 1, and 0 < z < 3), Li 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), Li x La y TiO3 (where 0 < x < 2 and 0 < y < 3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2, Li 3+ x La3M2O 12(where M = Te, Nb or Zr, and 0 ≤ x ≤ 10). The oxide-based solid electrolyte can be prepared, for example, by a sintering method or the like.

[0173] For example, the oxide-based solid electrolyte can be, for example, selected from Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2- a M a O 12 (M-doped LLZO, where M = Ga, W, Nb, Ta or Al, 0 < a < 2 and 0 ≤ x ≤ 10) garnet-type solid electrolyte.

[0174] The polymer solid electrolyte can include, for example, a mixture of a lithium salt and a polymer or a polymer having an ion-conductive functional group. The polymer solid electrolyte can be, for example, a polymer electrolyte that is in a solid state at 25 °C and 1 atm. The polymer solid electrolyte may not include a liquid. The polymer solid electrolyte contains a polymer. The polymer can be, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), poly(styrene-b-ethylene oxide) block copolymer (PS-PEO), poly(styrene-butadiene), poly(styrene-isoprene-styrene), poly(styrene-b-divinylbenzene) block copolymer, poly(styrene-ethylene oxide-styrene) block copolymer, polystyrene sulfonate (PSS), polyvinyl fluoride (PVF), poly(methyl methacrylate) (PMMA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), poly(ethylenedioxythiophene) (PEDOT), polypyrrole (PPY), polyacrylonitrile (PAN), polyaniline, polyacetylene, Nafion, Aquivion, Flemion, Gore, Aciplex, Morgane ADP, sulfonated poly(ether ether ketone) (SPEEK), sulfonated poly(arylene ether ketone ketone sulfone) (SPAEKKS), sulfonated poly(aryl ether ketone) (SPAEK), poly[bis(benzimidazole benzoisoquinolinone)] (SPBIBI), poly(styrene sulfonate) (PSS), lithium 9,10-diphenylanthracene-2-sulfonate (DPASLi + ) or any combination thereof, but not limited thereto, and any compound commonly used as a polymer electrolyte in the art can be used. The lithium salt can also be any lithium salt commonly used in the art. For example, the lithium salt can be LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1SO2)(C y F 2y+1 SO2 (where x and y are 1 to 20), LiCl, LiI, or any mixture thereof. The polymer included in the polymeric solid electrolyte can be, for example, a compound comprising 10 or more, 20 or more, 50 or more, or 100 or more repeating units. The polymer included in the polymeric solid electrolyte can have, for example, a weight-average molecular weight of 1000 Daltons (Da) or greater, 10,000 Da or greater, 100,000 Da or greater, or 1,000,000 Da or greater.

[0175] Gel electrolytes can be, for example, polymer gel electrolytes. Gel electrolytes can have a gel state without including polymers.

[0176] Polymer gel electrolytes may include, for example, a liquid electrolyte and a polymer, or an organic solvent and a polymer having ionicly conductive functional groups. A polymer gel electrolyte may be, for example, a polymer electrolyte in a gel state at 25°C and 1 atm. A polymer gel electrolyte may have, for example, a gel state without including a liquid. The liquid electrolyte used in a polymer gel electrolyte may be, for example, a mixture of ionic liquid, lithium salt, and organic solvent; a mixture of lithium salt and organic solvent; or a mixture of ionic liquid and organic solvent. The polymer used in a polymer gel electrolyte may be selected from polymers used in polymer solid electrolytes. The organic solvent may be selected from organic solvents used in liquid electrolytes. The lithium salt may be selected from lithium salts used in polymer solid electrolytes. Ionic liquids may refer to salts in a liquid state, as well as molten salts composed solely of ions at room temperature and with a melting point below room temperature. Ionic liquids may include, for example, at least one of the following compounds: a) at least one cation selected from ammonium, pyrrolidineonium, pyridinium, pyrimidineonium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, triazolium, and any mixture thereof; and b) at least one cation selected from BF4. - PF6 - AsF6 - SbF6 - AlCl4 - HSO4 - ClO4 - CH3SO3 - CF3CO2 - Cl - ,Br - I - SO4 - CF3SO3 - (FSO2)2N - (C2F2SO2)2N -(C2F2SO2)(CF2SO2)N - and (CF2SO2)2N - At least one anion is present. The polymer solid electrolyte can be impregnated with a liquid electrolyte in a secondary battery to form a polymer gel electrolyte. The polymer gel electrolyte may also include inorganic particles. The polymer included in the polymer gel electrolyte may be, for example, a compound comprising 10 or more, 20 or more, 50 or more, or 100 or more repeating units. The polymer included in the polymer gel electrolyte may have a weight-average molecular weight, for example, 500 Da or greater, 1000 Da or greater, 10,000 Da or greater, 100,000 Da or greater, or 1,000,000 Da or greater.

[0177] [Methods for manufacturing the positive electrode] The method for manufacturing a positive electrode according to an embodiment may include: providing an adhesive layer on a positive electrode current collector; providing a Li2S-containing composite; providing a sulfide-based solid electrolyte; mixing the Li2S-containing composite with the sulfide-based solid electrolyte to prepare a mixture; adding a cohesive binder to the mixture, mixing the mixture, and providing the mixture onto the adhesive layer to form a positive electrode active material layer.

[0178] The Li₂S and lithium salt complex can be prepared by mechanically grinding Li₂S and lithium salt. Grinding conditions are not limited, and any conditions that allow for the formation of the complex are feasible. The Li₂S and lithium salt complex is prepared by the following steps: Li₂S particles and lithium salt are added to a ball mill, and the mixture is stirred at a rate of about 100 rpm to about 1000 rpm for about 1 hour to about 20 hours. Stirring can be performed once or more.

[0179] The lithium salt can be, for example, LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2, or any combination thereof.

[0180] The composite of Li2S, lithium salt and carbonaceous material can be prepared, for example, by the following steps: mechanically grinding Li2S and lithium salt; and adding carbonaceous material to the grinding product, followed by grinding.

[0181] Sulfide-based solid electrolytes can be provided. Sulfide-based solid electrolytes can be as described above in the section on solid electrolyte membranes.

[0182] The Li2S-containing complex can be mixed with a sulfide-based solid electrolyte to prepare a mixture. The mixing ratio of the Li2S-containing complex to the sulfide-based solid electrolyte, by weight, can be, for example, about 50:50 to about 95:5, about 50:50 to about 90:10, about 50:50 to about 80:20, or about 50:50 to about 70:30.

[0183] The mixture may include a process solvent. By additionally including a process solvent, the mixture may have a slurry form. The solvent may be, for example, octyl acetate, but is not limited thereto, and any solvent commonly available in the art may be used. In some embodiments, the mixture may be prepared by a dry process excluding the process solvent.

[0184] Preparation of solid electrolytes.

[0185] An adhesive layer can be formed by using a composition comprising an adhesive for forming an adhesive layer.

[0186] The following describes a method for forming an adhesive layer that includes polydopamine as an adhesive binder.

[0187] According to some embodiments, compositions comprising dopamine, a solvent, and a buffer solution for forming a polydopamine layer can be prepared.

[0188] Dopamine can self-polymerize at a pH of about 8 to about 8.8 (e.g., about 8.5) to form polydopamine.

[0189] The composition used to form the polydopamine layer can have a pH of about 8.0 to about 8.8, for example, a pH of 8.5.

[0190] As a buffer solution, a buffer solution with a pH of about 8 to about 8.8 can be used, for example, a buffer solution including Tris-HCl and water (wherein the volume ratio of HCl to H2O is 3:1), ethylenediaminetetraacetic acid triborate (TBE), Tris-buffered saline (TBS) and phosphate-buffered saline (PBS) or combinations thereof.

[0191] As a solvent, materials that do not affect the pH of the composition, such as alcohols, can be used. Examples of alcohols may include ethanol, methanol, butanol, and isopropanol. Based on 100 parts by weight of dopamine, the amount of solvent can be from about 100 parts by weight to about 3000 parts by weight.

[0192] Drying can be carried out, for example, at a temperature range of about 20°C to about 25°C.

[0193] Coating can be performed by dipping, spraying, bar coating, die casting, comma coating, screen printing, etc. In some embodiments, an adhesive layer may also be formed on a separate substrate and then bonded to the positive electrode by pressing or lamination. Coating according to embodiments may refer to spraying.

[0194] According to other embodiments, a composition containing an adhesive binder can be prepared by dissolving a dopamine monomer, which is a polydopamine precursor, in an acid such as HCl. A positive current collector can be immersed in the composition. Subsequently, the positive current collector coated with the composition can be washed and dried to deposit the adhesive binder layer.

[0195] According to other embodiments, a composition for forming a polydopamine coating can be prepared by dispersing polydopamine in a distilled water buffer solution. The composition can be applied to a positive electrode current collector and dried to form a polydopamine coating, thereby distributing an intermediate layer on the surface of the positive electrode current collector. Coating can be performed by dip-coating, spraying, bar coating, die casting, comma coating, screen printing, etc.

[0196] Drying can be carried out, for example, at a temperature of about 30°C to about 90°C (e.g., 80°C).

[0197] In the following description, one or more exemplary embodiments of the inventive concept will be described in more detail with reference to the following examples and comparative examples. However, these examples are not intended to limit the purpose and scope of the one or more exemplary embodiments.

[0198] (Preparation of Li2S and lithium salt complex) Preparation Example 1: Li2S-LiI Complex Li₂S and LiI were mixed at a weight ratio of 30:20. The Li₂S-LiI composite was prepared by mechanically grinding the mixture using a ball mill. The grinding conditions were 25°C, 600 rpm, and 10 hours.

[0199] The size of the Li₂S-LiI composite is less than 1 μm. The size of the Li₂S-LiI composite was calculated from SEM images of the powder using software. The size of the Li₂S-LiI composite is the D50 average particle size.

[0200] Li₂S has a Mohs hardness of 0.6, and LiI has a Mohs hardness of 2.0. The Mohs hardness of the Li₂S-LiI composite is less than 2.

[0201] Preparation Example 2: Li2S-LiBr Complex The Li2S-LiBr complex was prepared in the same manner as in Preparation Example 1, except that LiBr was used instead of LiI.

[0202] Preparation Example 3: Li2S-LiCl Complex The Li2S-LiCl complex was prepared in the same manner as in Preparation Example 1, except that LiCl was used instead of LiI.

[0203] Comparative preparation example 1: Li2S-LiI-simple mixture A mixture of Li₂S and LiI in a weight ratio of 30:20 was used directly.

[0204] (Preparation of Li2S-LiI-CNF positive electrode active material) Preparation Example 4: Li₂S-LiI-CNF (50:30:20), two steps, 10 hours, 600 rpm, 28g (First step) Li₂S and LiI were mixed at a weight ratio of 50:30. The Li₂S-LiI composite was prepared by mechanically grinding the mixture using a ball mill. The grinding conditions were 25°C, 600 rpm, and 10 hours. The grinding energy applied to the sample during grinding was 28 G.

[0205] (Second step) Li₂S-LiI composite and carbon nanofibers (CNF) were mixed at a weight ratio of 80:20. The Li₂S-LiI-CNF composite was prepared by mechanically grinding the mixture using a ball mill. The grinding conditions were 25 °C, 600 rpm, and 10 hours. The grinding energy applied to the sample during grinding was 28 G. The Li₂S-LiI-CNF composite was used as the composite positive electrode active material.

[0206] Preparation Example 5: Li₂S-LiI-CNF, two steps, 8 hours, 600 rpm, 28g Except for changing the grinding time to 8 hours in the first and second steps, the Li2S-LiI-CNF complex was prepared in the same manner as in Preparation Example 4.

[0207] Preparation Example 6: Li₂S-LiI-CNF, two steps, 6 hours, 600 rpm, 28g Except for changing the grinding time to 6 hours in the first and second steps, the Li2S-LiI-CNF complex was prepared in the same manner as in Preparation Example 4.

[0208] Preparation Example 7: Li₂S-LiI-CNF, two steps, 4 hours, 600 rpm, 28g Except for changing the grinding time to 4 hours in the first and second steps, the Li2S-LiI-CNF complex was prepared in the same manner as in Preparation Example 4.

[0209] Comparative Preparation Example 2: A Simple Mixture of Li₂S, LiI, and CNF A mixture of Li₂S, LiI, and CNF in a weight ratio of 50:30:20 was used directly.

[0210] Comparative preparation example 3: Li₂S-LiI-CNF, two steps, 1 hour, 600 rpm, 28g Except for changing the grinding time to 1 hour in the first and second steps, the Li2S-LiI-CNF complex was prepared in the same manner as in Preparation Example 4.

[0211] Comparative preparation example 4: Li₂S-LiI-CNF, two steps, 20 hours, 600 rpm, 28g Except for changing the grinding time to 20 hours in the first and second steps, the Li2S-LiI-CNF complex was prepared in the same manner as in Preparation Example 4.

[0212] Comparative preparation example 5: Li₂S-LiI-CNF, 510 rpm, 10 hours, two steps, 20g (KR2017-0068448) (Tatsumisago)) (First step) Li₂S and LiI were mixed at a weight ratio of 30:20 to prepare a first mixture. The first mixture was then mechanically ground using a ball mill to prepare a Li₂S-LiI composite.

[0213] The grinding conditions were 25°C, 510 rpm, and 10 hours. The grinding energy applied to the sample during grinding was 20 G.

[0214] (Second step) A second mixture was prepared by mixing Li₂S-LiI composite and carbon nanofibers (CNF) at a weight ratio of 50:10. The second mixture was then mechanically milled using a ball mill to prepare the Li₂S-LiI-CNF composite.

[0215] The grinding conditions were 25°C, 510 rpm, and 10 hours. The grinding energy applied to the sample during grinding was 20 G. A Li₂S-LiI-CNF composite was used as the composite positive electrode active material.

[0216] Comparative preparation example 6: Li₂S-LiI-CNF, 10 hours, two steps, 10g The Li2S-LiI-CNF complex was prepared in the same manner as in Preparation Example 4, except that the grinding energy was changed to 10G by reducing the rotation speed in the first and second steps.

[0217] Comparative preparation example 7: Li₂S-LiI-CNF, 10 hours, two steps, 30g The Li2S-LiI-CNF complex was prepared in the same manner as in Preparation Example 4, except that the grinding energy was changed to 30G by increasing the rotation speed in the first and second steps.

[0218] Comparative Preparation Example 8: A Simple Mixture of Li₂S and CNF Li₂S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:30. This mixture was then used directly as the positive electrode active material.

[0219] Comparative preparation example 9: Li₂S-CNF, 600 rpm, 2 hours, one step, 20g Li₂S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:30. The Li₂S-CNF composite was prepared by mechanically milling the mixture using a ball mill. The milling conditions were 25°C, 600 rpm, and 2 hours. The milling energy applied to the sample during milling was 20 G. The Li₂S-CNF composite was used as the composite positive electrode active material.

[0220] Comparative preparation example 10: Li₂S-CNF, 600 rpm, 10 hours, one step, 20g Except for changing the grinding time to 10 hours, the Li2S-CNF complex was prepared in the same manner as in Comparative Preparation Example 9.

[0221] Comparative preparation example 11: Li₂S-CNF-LiI, 600 rpm, 10 hours, two steps, 20g (First step) Li₂S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:10. The Li₂S-CNF composite was prepared by mechanically milling the mixture using a ball mill. The milling conditions were 25 °C, 600 rpm, and 10 hours. The milling energy applied to the sample during milling was 20 G.

[0222] (Second step) The Li₂S-CNF composite and LiI were mixed at a weight ratio of 40:20. The mixture was mechanically milled using a ball mill to prepare the Li₂S-CNF-LiI composite. The milling conditions were 25°C, 600 rpm, and 10 hours. The milling energy applied to the sample during milling was 20 G. The Li₂S-CNF-LiI composite was used as the composite positive electrode active material.

[0223] Comparative preparation example 12: Li₂S-SE-CNF, 600 rpm, 10 hours, two steps, 20g (First step) Li₂S and Li₆PS₅Cl solid electrolyte (SE) were mixed at a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to prepare the Li₂S-SE composite. The milling conditions were 25°C, 600 rpm, and 10 hours. The milling energy applied to the sample during milling was 20 G.

[0224] (Second step) The Li₂S-SE composite and CNF were mixed at a weight ratio of 50:20. The Li₂S-SE-CNF composite was prepared by mechanically milling the mixture using a ball mill. The milling conditions were 25°C, 600 rpm, and 10 hours. The milling energy applied to the sample during milling was 20 G. The Li₂S-SE-CNF composite was used as the composite positive electrode active material.

[0225] Comparative preparation example 13: Li₂S-LiI-CNF, 600 rpm, 2 hours, one step, 20g Li₂S, LiI, and carbon nanofibers (CNF) were mixed in a weight ratio of 30:20:10. The mixture was mechanically milled using a ball mill to prepare the Li₂S-LiI-CNF composite. The milling conditions were 25°C, 600 rpm, and 2 hours. The milling energy applied to the sample during milling was 20 G. The Li₂S-LiI-CNF composite was used as the composite positive electrode active material.

[0226] (The manufacture of the positive electrode) Example 1: Al current collector / adhesive layer (polydopamine adhesive layer) / dry positive current collector containing Li2S-LiI-C and PTFE pole The composition forming the polydopamine layer was prepared by mixing 0.1 g of dopamine with 50 mL of a buffer solution with a pH of 8.5, and the viscosity and drying properties were improved by adding ethanol during the process without affecting the pH. The composition was applied to an Al foil serving as the positive electrode current collector by spraying via a nozzle and drying at about 25°C to form a polydopamine layer on the positive electrode current collector with a thickness of about 10 nm.

[0227] The Li₂S-LiI-CNF complex prepared in Preparation Example 4 was used as the positive electrode active material. Li₆PS₅Cl (D₅₀ = 3.0 μm, crystal) was prepared as a solid electrolyte, serving as a steric sulfide-germanium mineral-type crystal. PTFE was prepared as a binder.

[0228] The Li2S-LiI-CNF complex and the sulfide solid electrolyte were mixed in a mixer for 2 minutes to prepare a mixture.

[0229] PTFE, acting as a cohesive binder, is added to the mixture and mixed with it using a mixer for 20 seconds. The resulting cathode mixture powder is then kneaded and rolled to a thickness of approximately 100 μm to approximately 150 μm to prepare the cathode.

[0230] A cathode mixture was prepared by mixing a composite positive electrode active material, a solid electrolyte, and a cohesive binder (PTFE) in a weight ratio of 60:39:1.0. The cathode mixture was obtained by dry mixing using a ball mill. The amount of PTFE as the cohesive binder was 500 parts by weight, based on 10 parts by weight of polydopamine as the adhesive binder layer.

[0231] A positive electrode mixture was placed on an Al foil with an adhesive layer positioned thereon, and then pressed under a pressure of 200 MPa for 10 minutes to prepare a dry positive electrode. The positive electrode has a thickness of approximately 120 μm. The positive electrode active material layer has a thickness of approximately 100 μm, and the Al foil has a thickness of approximately 20 μm. The area of ​​the positive electrode active material layer is the same as the area of ​​the positive electrode current collector.

[0232] Example 2: Al current collector / adhesive layer (PAA adhesive layer) / dry cathode containing Li2S-LiI-C and PTFE The positive electrode is prepared in the same manner as in Example 1, except that an adhesive layer is formed by using lithium polyacrylate (Li-PAA) as described below.

[0233] First, an aqueous solution of lithium polyacrylate was prepared. 5 g of polyacrylic acid and 3.03 g of LiOH were mixed in 127.5 g of deionized water, and the mixture was stirred at room temperature (25°C) for 24 hours to prepare a solution containing 4 wt% lithium polyacrylate (weight average molecular weight: 450 × 10⁻⁶). 3 Aqueous solution of Da.

[0234] An aqueous solution of lithium polyacrylate was coated onto an Al foil and dried at 100°C to form an adhesive layer with a thickness of approximately 1 μm.

[0235] Example 3: Al current collector / adhesive layer (polydopamine layer) / dry cathode containing Li2S-LiI-C and PVDF The cathode was prepared in the same manner as in Example 1, except that PVDF was used instead of PTFE as the cohesive binder when preparing the cathode mixture.

[0236] Example 4: Al current collector / adhesive layer (PAA adhesive layer) / dry cathode containing Li2S-LiI-C and PVDF The cathode was prepared in the same manner as in Example 2, except that PVDF was used instead of PTFE as the cohesive binder when preparing the cathode mixture.

[0237] Example 5: Al current collector / adhesive layer (polydopamine adhesive layer) / dry positive current collector containing Li2S-LiI-C and PTFE pole Except that the weight ratio of composite positive electrode active material: solid electrolyte: cohesive binder (PTFE) is 60:37:3.0 when preparing the positive electrode mixture, the positive electrode is prepared in the same manner as in Example 1.

[0238] Comparative Example 1: Al current collector / dry cathode containing Li2S-LiI-C complex Besides using Al foil instead of setting it Adhesive layer In addition to the Al foil, the positive electrode is prepared in the same manner as in Example 1.

[0239] Comparative Example 2: Dry cathode with Al current collector / simple mixture containing Li2S, LiI and CNF The cathode was prepared in the same manner as in Example 1, except that a simple mixture of Li2S, LiI and CNF prepared in Comparative Preparation Example 2 was used instead of the Li2S-LiI-C complex prepared in Preparation Example 4.

[0240] Comparative Example 3: Al current collector / polydopamine layer / carbon coating / positive electrode containing Li2S-LiI-C The positive electrode is prepared in the same manner as in Example 1, except that a carbon coating is formed on the polydopamine layer according to the following process.

[0241] A composition for forming a carbon coating was prepared by dispersing multi-walled carbon nanotubes in a solution of N-methyl-2-pyrrolidone in which 10 wt% polyvinylidene fluoride was dissolved.

[0242] In the composition forming the carbon coating, the amount of multi-walled carbon nanotubes is 10 parts by weight, the amount of NMP is 80 parts by weight, and the amount of binder is 10 parts by weight. The composition is coated on the surface of a polydopamine layer and dried at 120°C for 4 hours to form a carbon coating with a thickness of about 100 nm on the polydopamine layer.

[0243] Reference Example 1: Positive current collector / polydopamine layer / positive active material layer The positive electrode is prepared in the same manner as in Example 1, except that an adhesive layer is formed on the Al foil and a positive active material layer is formed on the adhesive layer using a positive electrode mixture.

[0244] The composition forming the polydopamine layer was prepared by mixing 0.1 g of dopamine with 50 mL of a buffer solution with a pH of 8.5, and during the process, the composition was diluted with ethanol to improve viscosity and drying properties without affecting the pH. The composition was sprayed onto an Al foil via a nozzle and dried at about 25°C to form a polydopamine coating to a thickness of about 10 nm, thereby forming a positive electrode current collector / polydopamine layer / positive electrode active material layer stacked structure.

[0245] (Manufacturing of solid-state secondary batteries) Example 6: Al current collector / adhesive layer (polydopamine layer) / dry cathode containing Li2S-LiI-C and PTFE / / sulfur Solid electrolytes (SE) with chemical composition / / Ag-C coated SUS (The manufacture of the positive electrode) Use the positive electrode from Example 1.

[0246] (Manufacturing of the negative electrode) Prepare a 10 μm thick SUS foil as the negative electrode current collector. Prepare carbon black (CB) particles with a primary particle size of approximately 30 nm and silver (Ag) particles with an average particle size of approximately 60 nm as the negative electrode active materials.

[0247] A mixture of 4g of carbon black (CB) and silver (Ag) particles in a 3:1 weight ratio was added to a container, and 4g of an NMP solution including 7wt% PVDF binder (Kureha #9300) was added to prepare a mixed solution. NMP was gradually added to the mixed solution while stirring to prepare a slurry. The prepared slurry was applied to an SUS sheet using a bar coater and dried in air at 80°C for 10 minutes, followed by drying in a vacuum at 40°C for 10 hours to prepare a stacked structure. The prepared stacked structure was cold-rolled using a cold roll press to planarize the surface, thus preparing a negative electrode with a first negative electrode active material layer / negative electrode current collector structure. The thickness of the first negative electrode active material layer was approximately 15μm. The area of ​​the first negative electrode active material layer was the same as the area of ​​the negative electrode current collector.

[0248] (Manufacturing of solid electrolyte layer) A Li6PS5Cl solid electrolyte (D50 = 3.0 μm, crystal) was prepared as a sulforaphite-type crystal. 1.5 parts by weight of acrylic binder were added to 98.5 parts by weight of the solid electrolyte to prepare a mixture. Octyl acetate was added to the prepared mixture while stirring to prepare a slurry. The prepared slurry was applied to a 15 μm thick nonwoven fabric placed on a 75 μm thick PET substrate using a rod coater and dried in air at 80 °C for 10 minutes to obtain a stacked structure. The prepared stacked structure was dried in vacuum at 80 °C for 2 hours to prepare a solid electrolyte layer.

[0249] (Non-active component) A slurry prepared by mixing pulp fibers (cellulose fibers), glass fibers, aluminum hydroxide (Al(OH)3), acrylic binder and solvent is molded into a gasket form, and the solvent is removed from it to prepare a flame-retardant inactive component.

[0250] The weight ratio of pulp fiber (cellulose fiber), glass fiber, aluminum hydroxide (Al(OH)3), and acrylic binder is 20:8:70:2. The inactive component has a thickness of 120 μm.

[0251] Before arranging the manufactured flame-retardant inactive components on the solid electrolyte layer, they are heat-treated in a vacuum at 80°C for 5 hours to remove moisture and other substances from the flame-retardant inactive components.

[0252] (Manufacturing of all-solid-state secondary batteries) Reference Figure 4A solid electrolyte layer is disposed on the negative electrode, such that the first negative electrode active material layer is in contact with the solid electrolyte layer, and a positive electrode is disposed on the solid electrolyte layer. A gasket is arranged around the positive electrode to surround it and contact the solid electrolyte layer, thus fabricating a stacked structure. The gasket has a thickness of approximately 120 μm. A flame-retardant inactive component is used as the gasket. The gasket is positioned to contact the side surfaces of the positive electrode and the solid electrolyte layer. The positive electrode is located in the central region of the solid electrolyte layer, and the gasket is positioned to surround the positive electrode and extend to the end of the solid electrolyte layer. The area of ​​the positive electrode is approximately 90% of the area of ​​the solid electrolyte layer, and the gasket is positioned over the entire remaining 10% of the area of ​​the solid electrolyte layer where the positive electrode is not positioned.

[0253] The stacked structure was prepared by pressing at 85°C and 500 MPa for 30 minutes using a plate press. This pressing process sintered the solid electrolyte layer to improve battery characteristics. The sintered solid electrolyte layer had a thickness of approximately 45 μm. The Li6PS5Cl solid electrolyte, a type of silver sulfide germanite, contained within the sintered solid electrolyte layer, had a density of 1.6 g / cc. The area of ​​the solid electrolyte layer was the same as that of the negative electrode.

[0254] A pressed stacked structure is added to a bag and sealed to prepare an all-solid-state secondary battery. Portions of the positive and negative current collectors are extended to the outside of the sealed battery to serve as positive and negative terminals.

[0255] Examples 7 to 10 In addition to using the positive electrodes prepared in Examples 2 to 5 respectively, the all-solid-state secondary battery was prepared in the same manner as in Example 6.

[0256] Compare Examples 4 to 6 Except for using the positive electrodes prepared in Comparative Examples 1 to 3 respectively, all-solid-state secondary batteries were prepared in the same manner as in Example 6.

[0257] See Example 2 The all-solid-state secondary battery was prepared in the same manner as in Example 6, except that the positive electrode prepared in Reference Example 1 was used instead of the positive electrode prepared in Example 1.

[0258] Evaluation Example 1: XRD Analysis and SEM Analysis The bare Li₂S and pulverized Li₂S used in Preparation Example 1, as well as the Li₂S-LiI-C complex prepared in Preparation Example 4, were evaluated by measuring XRD spectra via CuKα radiation. The measurement results are shown in Table 1 below.

[0259] The size and lattice constant of the Li2S crystallites are derived from the first peak observed in the obtained XRD spectrum at a diffraction angle (2θ) corresponding to the crystal plane (111) at 27° ± 2.0°.

[0260] Except that the mixture of Li₂S and LiI in the first step of Preparation Example 4 was replaced with Li₂S, pulverized Li₂S was prepared by grinding under the same conditions. The second step was not performed.

[0261] The particle size (i.e., D50 diameter) of the composites was measured using a laser particle size analyzer (PSA), and the particle size of Li2S in the composites was measured using a scanning electron microscope to evaluate the bare Li2S and pulverized Li2S used in Preparation Example 1, as well as the Li2S-LiI-C composites prepared in Preparation Example 4. The measurement results are shown in Table 1 below.

[0262] Table 1

[0263] As shown in Table 1, the particle size and crystallite size of the Li2S-LiI-CNF composite are significantly reduced compared to Li2S. The Li2S-LiI-CNF composite comprises a Li2S-LiI solid solution, with Li2S crystallites having a size of less than 9.9 nm, and the composite has Li2S particle size of 2 μm or smaller.

[0264] Although not shown in Table 1, the Li₂S-LiI-CNF composite prepared in Example 4 has a larger lattice constant than that of bare Li₂S. It is believed that the increased lattice constant of the Li₂S-LiI-CNF composite compared to that of bare Li₂S is due to the LiI dissolved in the Li₂S crystal. Therefore, it is confirmed that the Li₂S-LiI-CNF composite forms a solid solution.

[0265] Although not shown in Table 1, the Li2S-LiI-CNF complex prepared in Example 4 has a particle size of approximately 5 μm.

[0266] Evaluation Example 2: XRD Analysis and SEM Analysis XRD spectra of the composite positive electrode active materials (i.e., the composites) prepared in Preparation Examples 4 to 7 and Comparative Preparation Examples 3 to 13 were obtained using CuKα radiation. The sizes of the Li₂S crystallites, calculated from the first peak observed at a diffraction angle (2θ) corresponding to the crystal plane (111) in the obtained XRD spectra, are shown in Table 2. The crystallite sizes were calculated using the Sherrer equation.

[0267] The particle size of Li₂S in the composite cathode active materials prepared in Preparation Examples 4 to 7 and Comparative Preparation Examples 3 to 13 was measured using SEM. The Li₂S particle size of the composite cathode active materials is the arithmetic mean or particle size of multiple particles measured using software from scanning electron microscope images. The measurement results are shown in Table 2 below.

[0268] Table 2

[0269] As shown in Table 2, the Li2S-LiI-CNF composites prepared in Examples 4 to 7 comprise a Li2S-LiI solid solution, the Li2S crystallites have a size of less than 9.9 nm, and the composites have a Li2S particle size of 2 μm or less.

[0270] In the Li2S-LiI-CNF composite of Comparative Preparation Example 3, the size of the Li2S crystallites was 9.9 nm or larger because the grinding energy was reduced during preparation.

[0271] In the Li2S-LiI-CNF composite of Comparative Preparation Example 4, because the grinding energy was increased during preparation, LiI separated as a separate phase, so no solid solution was formed and the size of Li2S crystallites increased.

[0272] In the Li2S-LiI-CNF complex of Comparative Preparation Example 6, no Li2S-LiI solid solution was formed because the grinding energy was excessively reduced during preparation.

[0273] In the Li2S-LiI-CNF complex of Comparative Preparation Example 7, the Li2S-LiI solid solution did not form properly due to the heat generated by the increased grinding energy during preparation.

[0274] In the first step of comparative preparation example 13, a Li2S-LiI-CNF complex was prepared. Therefore, the complex includes a Li2S-LiI solid solution, but the size of the Li2S crystallites is increased and the particle size of Li2S in the complex exceeds 2 μm.

[0275] No solid solution was formed in the simple mixture of Li2S and CNF in Comparative Preparation Example 8, and in the complexes of Comparative Preparation Example 9, Comparative Preparation Example 10, and Comparative Preparation Example 12.

[0276] In the Li2S-CNF-LiI complex of Comparative Preparation Example 11, because the Li2S-CNF complex was prepared in the first step and the Li2S-CNF-LiI complex was prepared in the second step, the Li2S-LiI solid solution was not properly formed.

[0277] Evaluation Example 3: Charge / Discharge Test The charge / discharge characteristics of the various all-solid-state secondary batteries prepared in Examples 6 to 10, Comparative Examples 4 to 6, and Reference Example 2 were evaluated by the following charge / discharge tests.

[0278] The all-solid-state secondary battery was tested by charging / discharging it in a constant temperature bath at 45°C.

[0279] The first cycle is performed by charging the battery at a constant current of 0.05C for 20 hours until the battery voltage reaches 2.8V. The battery is then discharged at a constant current of 0.05C for 20 hours until the battery voltage reaches 1.0V.

[0280] The second charge-discharge cycle was performed under the same conditions as the first cycle.

[0281] The discharge capacity of the second cycle was used as the standard capacity.

[0282] Perform a third cycle of 10 hours at a constant current of 0.1C until the battery voltage reaches 2.8V. Then, discharge the battery at a constant current of 0.1C for 10 hours until the battery voltage reaches 1.0V.

[0283] After the third cycle, the charge-discharge cycle was repeated under the same conditions as the third cycle until the 50th cycle. The measurement results are shown in Table 3 below.

[0284] The initial efficiency is represented by Equation 1 below, and the capacity retention rate is defined as shown in Equation 2 below.

[0285] Equation 1 Initial efficiency [%] = [Discharge capacity in the first cycle / Charge capacity in the first cycle] × 100 Equation 2 Capacity retention rate [%] = [Discharge capacity at 23rd cycle / Charge capacity at 3rd cycle] × 100 Table 3

[0286] As shown in Table 3, compared with the all-solid-state secondary batteries of Comparative Examples 4 to 6 using the positive electrodes of Comparative Examples 1 to 5 and the all-solid-state secondary battery of Reference Example 2, the all-solid-state secondary batteries of Examples 6 to 10 using the positive electrodes of Examples 1 to 5 exhibit improved lifetime characteristics. In the all-solid-state secondary batteries of Examples 8 and 10 including a polydopamine layer or the all-solid-state secondary battery of Example 9 including LiPAA, the discharge capacity is increased due to the improved adhesion between the positive electrode current collector and the positive electrode active material layer, and the capacity retention is increased due to the stable contact between the positive electrode current collector and the positive electrode active material layer, although the positive electrode active material does not detach during repeated charge and discharge cycles.

[0287] Although not shown in the accompanying drawings, it is confirmed that in the all-solid-state secondary batteries of Examples 6 to 10, a lithium metal layer serving as a second negative electrode active material layer is formed between the first negative electrode active material layer and the negative electrode current collector after initial charging. These results are confirmed by cross-sections of the all-solid-state secondary batteries obtained from SEM images. The SEM images showing the cross-section of the solid electrolyte layer also confirm that the Li2S-LiI-CNF complex is located in the pores between multiple particles of the sulfide-based solid electrolyte.

[0288] Evaluation Example 4: Evaluation of Magnification Characteristics The rate characteristics of the all-solid-state secondary batteries were evaluated according to Examples 6 to 10 and Comparative Examples 4 to 6. The all-solid-state secondary batteries were subjected to charge / discharge tests in a constant-temperature bath at 45°C.

[0289] The first cycle is performed by charging the battery at a constant current of 0.05C for 20 hours until the battery voltage reaches 2.8V. The battery is then discharged at a constant current of 0.05C for 20 hours until the battery voltage reaches 1.0V.

[0290] The second charge-discharge cycle was performed under the same conditions as the first cycle.

[0291] A third cycle was performed at a constant current of 0.1C for 10 hours until the battery voltage reached 2.8V. Subsequently, the battery was discharged at a constant current of 0.1C for 10 hours until the battery voltage reached 1.0V. A fourth cycle was performed under the same conditions as the third cycle.

[0292] After each charge / discharge cycle, the battery was allowed to rest for 10 minutes. Some results from the room temperature charge / discharge tests are shown in Table 4. The rate capability is defined as shown in Equation 3 below.

[0293] Equation 3 Rate capability [%] = [Discharge capacity in the 4th cycle / Discharge capacity in the 2nd cycle] × 100 Table 4

[0294] As shown in Table 4, the all-solid-state secondary batteries of Examples 6 to 10 have improved rate performance compared to the all-solid-state secondary batteries prepared in Comparative Examples 4 to 6 and Reference Example 2.

Claims

1. A positive electrode for an all-solid-state secondary battery, the positive electrode comprising: Positive current collector; An adhesive layer is disposed on the positive electrode current collector and includes an adhesive polymer; as well as A positive electrode active material layer is disposed on the adhesive layer and includes a composite positive electrode active material and a cohesive binder. The composite positive electrode active material includes a Li2S-containing complex.

2. The positive electrode according to claim 1, wherein, The adhesion polymer includes at least one selected from polydopamine, cationic substituted polycarboxylic acids, copolymers of cationic substituted polycarboxylic acids, polynorepinephrine, poly(meth)acrylamide, polyvinyl alcohol, poly(meth)acrylate, methyl methacrylate-co-(meth)acrylate, poly(meth)acrylate, poly(meth)acrylate, and styrene-(meth)acrylate copolymers.

3. The positive electrode according to claim 1, wherein, The thickness of the adhesive layer is 5 nm to 1 μm.

4. The positive electrode according to claim 1, wherein, The cohesive binder is a polyvinylidene fluoride (PVdF) resin, styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyethylene glycol (PEG), polypropylene glycol (PPG), toluene diisocyanate (TDI), polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, poly(ethylene-co-vinyl acetate) copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide, or a combination thereof.

5. The positive electrode according to claim 1, wherein, The Li2S-containing complex includes a complex of Li2S and a lithium salt, and The Li2S and lithium salt complex consists of Li2S-Li a X b This means that 1 ≤ a ≤ 5 and 1 ≤ b ≤ 5, and Wherein, X is I, Br, Cl, F, H, O, Se, Te, N, P, As, Sb, Al, B, OCl, PF6, BF4, SbF6, AsF6, ClO4, AlO2, AlCl4, NO3, CO3, BH4, SO4, BO3, PO4, NCl, NCl2, BN2, or a combination thereof.

6. The positive electrode according to claim 5, wherein, The Li2S-containing composite also includes carbonaceous materials. The carbonaceous material includes fibrous carbonaceous material. The fibrous carbonaceous material includes carbon nanostructures, wherein the carbon nanostructures include carbon nanofibers, carbon nanotubes, carbon nanoribbons, carbon nanorods, or combinations thereof, and Based on the total weight of the Li2S-containing composite, the amount of the carbonaceous material is from 1 wt% to 20 wt%.

7. The positive electrode according to claim 5, wherein, The lithium salt is a binary or ternary compound. The binary compound includes LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, or combinations thereof, and The ternary compounds include Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2, or combinations thereof.

8. The positive electrode according to claim 1, wherein, The Li2S-containing complex includes a solid solution of Li2S and a lithium salt. The Li₂S-containing complex has a particle size of 10 μm or smaller, and The size of the Li2S microcrystals obtained from the XRD spectrum of the Li2S-containing composite is 20 nm or smaller.

9. The positive electrode according to claim 1, wherein, Based on 100 parts by weight of the total weight of the positive electrode active material layer, the amount of the cohesive binder in the positive electrode active material layer is from 1 part by weight to 10 parts by weight, and based on 100 parts by weight of the adhesive polymer in the adhesive layer, the amount of the cohesive binder is from 100 parts by weight to 1000 parts by weight.

10. The positive electrode according to claim 1, wherein, In the Li2S-containing complex, the amount of Li2S is greater than the amount of lithium salt, and the molar ratio of Li2S to lithium salt in the Li2S-containing complex is from 51:49 to 95:

5.

11. The positive electrode according to claim 1, wherein, Based on the total weight of the positive electrode active material layer, the amount of the Li2S-containing composite is 60wt% to 80wt%.

12. The positive electrode according to claim 1, wherein, The positive electrode active material layer also includes a solid electrolyte, and The solid electrolyte includes sulfide solid electrolytes.

13. The positive electrode according to claim 9, wherein, The sulfide-based solid electrolyte is selected from one or more of the following: Li₂S-P₂S₅; Li₂S-P₂S₅-LiX, where X is a halogen atom; Li₂S-P₂S₅-Li₂O; Li₂S-P₂S₅-Li₂O-LiI; Li₂S-SiS₂; Li₂S-SiS₂-LiI; Li₂S-SiS₂-LiBr; Li₂S-SiS₂-LiCl; Li₂S-SiS₂-B₂S₃-LiI; Li₂S-SiS₂-P₂S₅-LiI; Li₂S-B₂S₃; Li₂S-P₂S₅-Z m S n Where m and n are positive numbers, and Z is Ge, Zn, or Ga; Li2S-GeS2; Li2S-SiS2-Li3PO4; Li2S-SiS2-Li p MO q Where p and q are positive numbers, and M is P, Si, Ge, B, Al, Ga, or In; Li 7-x PS 6-x Cl x Where 0 ≤ x ≤ 2; Li 7-x PS 6-x Br x Where 0 ≤ x ≤ 2; and Li 7-x PS 6-x I x Where 0 ≤ x ≤ 2, The sulfide-based solid electrolytes include silver-germanium sulfide-type solid electrolytes. The sulfide-germanium ore type solid electrolyte includes at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I. The sulfide-germanium ore type solid electrolyte has a density of 1.5 g / cc to 2.0 g / cc. The sulfide-based solid electrolyte is in particulate form, and The average particle size D50 of the sulfide-based solid electrolyte in particulate form is 0.1 μm to 1.9 μm.

14. An all-solid-state secondary battery, the all-solid-state secondary battery comprising: positive electrode; negative electrode; as well as A solid electrolyte layer is disposed between the positive electrode and the negative electrode. The positive electrode includes the positive electrode according to claim 1.

15. The all-solid-state secondary battery according to claim 14, wherein, The negative electrode includes a negative electrode current collector and a first negative electrode active material layer disposed on one side of the negative electrode current collector.

16. The all-solid-state secondary battery according to claim 15, wherein, The first negative electrode active material layer is a metal layer, wherein the metal layer comprises lithium or a lithium alloy, or The first negative electrode active material layer includes a negative electrode active material and a binder. The negative electrode active material is in the form of particles, and the average particle size of the negative electrode active material is 4 μm or smaller.

17. The all-solid-state secondary battery according to claim 16, wherein, The negative electrode active material includes at least one selected from carbonaceous negative electrode active materials and metallic or quasi-metallic negative electrode active materials. The carbonaceous negative electrode active material includes amorphous carbon, crystalline carbon, porous carbon, or combinations thereof. The metallic or quasi-metallic anode active material includes gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or combinations thereof. The negative electrode active material comprises a mixture of first particles formed of amorphous carbon and second particles formed of metal or quasi-metal, and Based on the total weight of the mixture, the amount of the second particle is from 1 wt% to 60 wt%.

18. The all-solid-state secondary battery according to claim 15, further comprising a second negative electrode active material layer, the second negative electrode active material layer being disposed at at least one of the following: between the negative electrode current collector and the first negative electrode active material layer; and between the negative electrode current collector and the solid electrolyte layer. in, The second negative electrode active material layer is a metal layer, and the metal layer comprises lithium or a lithium alloy.

19. The all-solid-state secondary battery according to claim 14, wherein, The solid electrolyte layer includes a solid electrolyte, a gel electrolyte, or a combination thereof. The solid electrolyte includes oxide solid electrolytes, polymer solid electrolytes, or combinations thereof, and The gel electrolyte includes a polymer gel electrolyte.

20. The all-solid-state secondary battery according to claim 14, wherein, The positive electrode includes a positive current collector, and the negative electrode includes a negative current collector. One of the positive electrode current collector and the negative electrode current collector includes a substrate film and a metal layer disposed on one or both sides of the substrate film. The substrate film comprises a polymer, and the polymer comprises polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or combinations thereof. The metal layer includes indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof.

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