Positive electrode for all-solid secondary battery and all-solid secondary battery comprising same

Abstract

Disclosed is a positive electrode for an all-solid secondary battery, the positive electrode comprising: a positive electrode current collector; a carbon coating layer on the positive electrode current collector; and a positive electrode active material layer on the carbon coating layer and containing composite positive electrode active material and a solid electrolyte, the composite positive electrode active material comprising a Li2S-containing composite. In addition, disclosed is an all-solid secondary battery comprising: said positive electrode; a negative electrode; and a solid electrolyte layer disposed between the positive and negative electrodes.

Description

Cathode for all-solid-state secondary battery and all-solid-state secondary battery containing the same

[0001] The present invention relates to a positive electrode for an all-solid-state secondary battery and an all-solid-state secondary battery including the same.

[0002] Recent industrial demands have led to the active development of batteries with high energy density and safety. Lithium batteries, for example, are used in a variety of applications, including information technology, communications devices, and automobiles. Because automobiles are life-threatening, safety is also crucial.

[0003] Lithium batteries using liquid electrolytes may have an increased risk of fire and / or explosion in the event of a short circuit. All-solid-state secondary batteries using solid electrolytes instead of liquid electrolytes are being proposed. Solid electrolytes are less likely to catch fire than liquid electrolytes.

[0004] All-solid-state secondary batteries can reduce the risk of fire or explosion by using solid electrolytes instead of liquid electrolytes. Solid-state batteries can also offer improved safety.

[0005] One aspect is to provide a positive electrode for an all-solid-state secondary battery, which includes a Li2S-containing composite and a carbon coating layer between a positive electrode current collector and a positive electrode active material layer, thereby reducing volume change during charge and discharge.

[0006] Another aspect is to provide an all-solid-state secondary battery with improved performance, including the above-mentioned positive electrode.

[0007] According to the implementation example

[0008] positive current collector;

[0009] a carbon coating layer positioned on the positive electrode collector; and

[0010] A positive electrode for an all-solid-state secondary battery is provided, which includes a positive electrode active material layer positioned on the carbon coating layer and containing a composite positive electrode active material and a solid electrolyte, wherein the composite positive electrode active material includes a Li2S-containing composite.

[0011] An intermediate layer containing an adhesive polymer is further included between the carbon coating layer and the positive electrode active material layer.

[0012] The above positive electrode active material layer may further include at least one selected from a binder and a conductive material.

[0013] According to another embodiment, an all-solid-state secondary battery is provided, which includes the above-described positive electrode; a negative electrode; and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0014] According to one aspect, it is possible to provide an all-solid-state secondary battery having improved cycle characteristics by suppressing side reactions of a sulfide-based solid electrolyte, preventing deterioration, and reducing interfacial electronic resistance.

[0015] Figures 1 to 5 are cross-sectional views of an all-solid-state secondary battery according to an exemplary embodiment.

[0016] <Explanation of symbols>

[0017] 1 All-solid-state secondary battery 10 Cathode

[0018] 11. Cathode current collector 12. Cathode active material layer

[0019] 13: Middle layer 20 cathode

[0020] 21 Negative current collector 22 First negative electrode active material layer

[0021] 23 Thin film 24 Second negative electrode active material layer

[0022] 30 electrolyte layer 40 inert member

[0023] Unless otherwise defined, all terms (including technical and scientific terms) used in this disclosure have the same meaning as commonly understood by those of ordinary skill in the art to which this disclosure pertains. Furthermore, terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning within the context of the relevant technology and this disclosure, and should not be interpreted in an idealized or overly formal sense.

[0024] Exemplary embodiments are described in this disclosure with reference to cross-sectional drawings that are schematic representations of idealized embodiments. As such, variations from the shapes depicted are to be expected, for example, as a result of manufacturing techniques and / or tolerances. Therefore, the embodiments described in this disclosure should not be construed as limited to the specific shapes of regions as depicted in this disclosure, but should encompass variations in shapes resulting from, for example, manufacturing. For example, regions depicted or described as flat may typically have rough and / or non-linear features. Moreover, angles depicted as sharp may be rounded. Therefore, the regions depicted in the drawings are schematic in nature, and their shapes are not intended to depict the precise shapes of the regions, nor are they intended to limit the scope of the claims.

[0025] This creative idea may be embodied in many different forms and should not be construed as limited to the embodiments described in this disclosure. These embodiments are provided so that this disclosure will be thorough and complete, and so that it will fully convey the scope of the creative idea to those skilled in the art. Like reference numerals in the drawings indicate like elements.

[0026] When a component is referred to as being "on" another component, it can be understood that it is either directly on top of the other component or that other components may be intervening between them. Conversely, when a component is referred to as being "directly on" another component, no intervening components are present.

[0027] Although terms such as "first," "second," "third," etc. may be used herein to describe various components, elements, regions, layers, and / or zones, these components, elements, regions, layers, and / or zones should not be limited by these terms. These terms are only used to distinguish one component, element, region, layer, or zone from another component, element, region, layer, or zone. Thus, a first component, element, region, layer, or zone described below may be referred to as a second component, element, region, layer, or zone without departing from the teachings of this disclosure.

[0028] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms including "at least one," unless the content clearly dictates otherwise. "At least one" should not be construed as limiting to the singular. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items. The terms "comprises" and / or "comprising" as used in the detailed description specify the presence of stated features, regions, integers, steps, operations, components, and / or ingredients, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, components, ingredients, and / or groups thereof.

[0029] Spatially relative terms such as "below," "under," "lower," "above," "upper," and the like may be used herein to readily describe the relationship of one component or feature to another. It will be understood that spatially relative terms are intended to encompass different orientations of the device when in use or operation in addition to the orientations depicted in the drawings. For example, if the device in the drawings were turned over, a component described as "below" or "below" another component or feature would then be oriented "above" the other component or feature. Thus, the exemplary term "below" can encompass both the above and below orientations. The device may be arranged in other orientations (rotated 90 degrees or otherwise rotated), and the spatially relative terms used herein may be interpreted accordingly.

[0030] "Group" means a group in the periodic table of elements according to the International Union of Pure and Applied Chemistry ("IUPAC") Group 1-18 classification system.

[0031] In the present disclosure, "particle size" or "particle diameter" refers to the average diameter when the particles are spherical, and refers to the average major axis length when the particles are non-spherical. The particle diameter or particle size can be measured using a particle size analyzer (PSA). The "particle size" or "particle diameter" refers to, for example, the average particle diameter. The "average particle diameter" refers to, for example, the median particle diameter, D50.

[0032] D50 is the size of the particle corresponding to 50% of the cumulative volume, calculated from the particle side with a smaller particle size in the particle size distribution measured by laser diffraction.

[0033] D90 is the size of the particle corresponding to 90% of the cumulative volume, calculated from the particle side with a smaller particle size in the particle size distribution measured by laser diffraction.

[0034] D10 is the size of the particle corresponding to 10% of the cumulative volume, calculated from the particle side with a small particle size in the particle size distribution measured by laser diffraction.

[0035] In this disclosure, “metal” includes both metals and metalloids such as silicon and germanium, in their elemental or ionic states.

[0036] In this disclosure, “alloy” means a mixture of two or more metals.

[0037] In the present disclosure, "electrode active material" means an electrode material capable of undergoing lithiation and delithiation, "positive electrode active material" means a positive electrode material capable of undergoing lithiation and delithiation, and "negative electrode active material" means a negative electrode material capable of undergoing lithiation and delithiation.

[0038] In the present disclosure, “lithiation” and “lithiate” mean a process of adding lithium to an electrode active material, and “delithiation” and “delithiate” mean a process of removing lithium from an electrode active material.

[0039] In the present disclosure, “charging” and “charging” mean a process of providing electrochemical energy to a battery, and “discharging” and “discharging” mean a process of removing electrochemical energy from a battery.

[0040] In the present disclosure, “positive electrode” and “cathode” mean an electrode where electrochemical reduction and lithiation occur during a discharge process, and “negative electrode” and “anode” mean an electrode where electrochemical oxidation and delithiation occur during a discharge process.

[0041] In this disclosure, “thickness,” “length,” and “width” mean average thickness, average length, and average width, respectively. The average thickness, average length, and average width can be evaluated using a scanning electron microscope, etc.

[0042] In the present disclosure, the aspect ratio represents the ratio (L1 / L2) of the major axis length L1 (e.g., length) and the minor axis length L2 (e.g., diameter). Here, the 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. The aspect ratio can be evaluated using a scanning electron microscope.

[0043] In this specification, a solid solution is different from a mixture of two or more chemical species and refers to a homogeneous crystal phase containing two or more chemical species.

[0044] As used herein, a "two-dimensional carbon nanostructure" is a carbon nanostructure in which two dimensions are significantly larger than one of the other dimensions. In other words, it is a carbon nanostructure in which the area defined by the two dimensions is significantly larger than the thickness.

[0045] Additionally, any numerical range recited herein is intended to include all sub-ranges of the same numerical precision contained within the recited range. For example, a range of "1.0 to 10.0" is intended to include all sub-ranges between the recited minimum value of 1.0 and the recited maximum value of 10.0, i.e., those having a minimum value greater than or equal to 1.0 and a maximum value less than or equal to 10.0, e.g., 2.4 to 7.6. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations recited herein, and any minimum numerical limitation recited herein is intended to include all upper numerical limitations recited herein. Accordingly, Applicants reserve the right to amend this specification, including claims, to explicitly recite all sub-ranges contained within the ranges expressly recited herein.

[0046] In the present disclosure, the weight average molecular weight of the polymer can be evaluated using polystyrene-converted gel permeation chromatography.

[0047] While specific implementations have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or unforeseen may occur to the applicant or those skilled in the art. Accordingly, the appended claims, as filed and as amended, are intended to encompass all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0048] Hereinafter, a positive electrode, an all-solid-state secondary battery including the positive electrode, and a method for manufacturing the all-solid-state secondary battery according to exemplary embodiments are described in more detail.

[0049] [anode]

[0050] A cathode according to an embodiment includes a cathode current collector; a carbon coating layer positioned on the cathode current collector; and a cathode active material layer positioned on the carbon coating layer and containing a composite cathode active material and a solid electrolyte, wherein the composite cathode active material includes a Li2S-containing complex.

[0051] The above Li2S-containing complex includes a composite of Li2S and a lithium salt, which is Li2S-Li a X b It is expressed as (1≤a≤5, 1≤b≤5).

[0052] The above 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.

[0053] In all-solid-state secondary batteries using lithium sulfide as the cathode active material, lithium sulfide is an insulator with virtually no electrical or ionic conductivity. Therefore, composites with materials with high electrical and ionic conductivity are required. Furthermore, during charge and discharge, shrinkage and expansion of lithium sulfide-containing materials can cause the cathode active material to detach from the cathode current collector, degrading electronic conductivity. Therefore, improvements are needed.

[0054] Accordingly, the positive electrode of the present disclosure forms a carbon coating layer between the positive electrode current collector and the positive electrode active material layer containing the Li2S-containing complex. By forming the carbon coating layer in this way, the interfacial area between the positive electrode current collector and the positive electrode active material layer can be expanded, thereby improving adhesive strength and reducing the electronic resistance at the interface.

[0055] According to one embodiment, an intermediate layer containing an adhesive polymer may be further included between the carbon coating layer and the positive electrode active material layer. The carbon coating layer, which is a conductive particle layer, may cause a side reaction at the interface with the sulfide-based solid electrolyte particles present in the positive electrode active material layer during battery operation. However, as described above, if the intermediate layer is formed between the carbon coating layer and the positive electrode active material layer, the problem of deterioration of the sulfide-based solid electrolyte can be suppressed. The carbon coating layer, which is a conductive particle layer, can effectively suppress the problem of deterioration of the sulfide-based solid electrolyte by causing a side reaction at the interface with the sulfide-based solid electrolyte particles present in the positive electrode active material layer during battery operation.

[0056] In addition, by suppressing the side reaction between the conductive particles of the carbon coating layer and the sulfide-based solid electrolyte of the positive electrode active material layer, the deterioration of the sulfide-based solid electrolyte can be prevented, and further, the contact area between the positive electrode active material layer and the intermediate layer can be maximized and the adhesive strength can be increased, thereby further reducing the interfacial electronic resistance. The positive electrode current collector, carbon coating layer, and intermediate layer can be said to be a type of substrate for the positive electrode plate, and can be said to be a positive electrode substrate capable of preventing deterioration of the sulfide-based solid electrolyte. Such a positive electrode substrate has high adhesive strength with the positive electrode active material layer, low interfacial resistance, and can effectively suppress the problem of deterioration of the sulfide-based solid electrolyte during battery operation.

[0057] The above positive electrode suppresses the interfacial side reaction between the conductive material and the sulfide-based solid electrolyte, thereby preventing deterioration of the sulfide-based solid electrolyte, and increases the adhesion between the current collector substrate and the positive electrode active material layer and maximizes the contact area, thereby reducing the interfacial electronic resistance. The thickness of the carbon coating layer is, for example, 1 um or less, 1 nm to 1 um, 5 nm to 1 um, 5 nm to 800 nm, 5 nm to 700 nm, 5 nm to 600 nm, 8 nm to 550 nm, 10 nm to 500 nm, 10 nm to 450 nm, 10 nm to 400 nm, 10 nm to 350 nm, 10 nm to 300 nm, 10 nm to 200 nm, 10 nm to 150 nm, 10 nm to 100 nm, 20 nm to 100 nm, 20 nm to 80 nm, or 20 nm to 50 nm, in which case the adhesion between the positive electrode substrate and the positive electrode active material layer can be increased and the electrochemical characteristics of the positive electrode can be improved.

[0058] The carbon coating layer includes a carbon material, which may include, for example, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, porous carbon, or a combination thereof.

[0059] The intermediate layer may cover the carbon coating layer in the form of a continuous film. The intermediate layer is formed to have a thickness of several to several tens of nanometers, and can effectively prevent deterioration of the sulfide-based solid electrolyte without adversely affecting the battery, and can improve the adhesion of the positive electrode and reduce the interfacial resistance. The thickness of the intermediate layer may be, for example, 1 nm to 1 um, 1 nm to 800 nm, 1 nm to 500 nm, 1 nm to 400 nm, 3 nm to 400 nm, 5 nm to 300 nm, 8 nm to 300 nm, 10 nm to 300 nm, 10 nm to 200 nm, 10 nm to 100 nm, 10 nm to 80 nm, or 10 nm to 50 nm. The intermediate layer is formed in the above-described thickness range, and can effectively protect the solid electrolyte while reducing the interfacial resistance. The above intermediate layer not only prevents side reactions between the sulfide-based solid electrolyte and the conductive material, but also has high adhesive strength, thereby improving the adhesion between the substrate and the positive electrode active material layer and reducing the interfacial electrical resistance.

[0060] According to another embodiment, the thickness of the intermediate layer may be, for example, 20 nm to 1 um, 20 nm to 800 nm, 20 nm to 500 nm, 20 nm to 300 nm, or 20 nm to 100 nm. When the intermediate layer is formed in the above-described thickness range, the solid electrolyte can be effectively protected while lowering the interfacial resistance.

[0061] The adhesive polymer constituting the intermediate layer is, for example, at least one selected from polydopamine, a cationically substituted polycarboxylic acid, a cationically substituted polycarboxylic acid copolymer, poly(norepinephrin), poly(meth)acrylamide, polyvinyl alcohol, poly(2-hydroxymethyl(meth)acrylate), poly(methyl(meth)acrylate-co-(meth)acrylic acid), polymethyl(meth)acrylate, poly((meth)acrylic acid), and poly(styrene-co-(meth)acrylic acid).

[0062] The above cation-substituted polycarboxylic acid and its copolymer have one or more cations selected from, for example, lithium ions (Li+), sodium ions (Na+), potassium ions (K+), and ammonium ions (NH4+). Polycarboxylic acid means a polymer formed by polymerization of one or more types of monomers having one or more carboxyl groups (-COOH), and has a weight average molecular weight of 1,000 to 1,000,000. Examples of such polycarboxylic acids include polyacrylic acid, polymethacrylic acid, and polymaleic acid. The cation-substituted polycarboxylic acid is a substance in which hydrogen of the polycarboxylic acid is replaced with a cation, and includes, for example, one or more selected from lithium polyacrylate (LiPAA) and lithium polymethacrylate.

[0063] A cation-substituted polycarboxylic acid copolymer is a copolymer containing monomer repeating units corresponding to a cation-substituted polycarboxylic acid, examples of which include poly(acrylic acid-co-maleic acid) lithium salt, poly(methylvinyl ether-alt-maleic acid) lithium salt, or poly(butadiene-co-maleic acid) lithium salt.

[0064] At least one selected from the cation-substituted polycarboxylic acid and copolymer thereof has a glass transition temperature of 50°C or higher, for example, 50 to 200°C, 50 to 180°C, and specifically, 50 to 150°C. And at least one selected from the cation-substituted polycarboxylic acid and copolymer thereof has a melting point of 100°C or higher, for example, 100 to 300°C, 100 to 250°C, and specifically, 100 to 200°C. When an intermediate layer is formed using a cation-substituted polycarboxylic acid and copolymer thereof having such a glass transition temperature and melting point, the intermediate layer can maintain its shape at a battery operating temperature (for example, 0 to 90°C). At least one selected from the above cation-substituted polycarboxylic acid and copolymers thereof has a weight average molecular weight of 1,000 to 1,000,000, and a degree of polymerization of 10 to 1500, 12 to 1500, for example, 14 to 1400.

[0065] An example of a cation-substituted polycarboxylic acid is lithium polyacrylate (Li-PAA).

[0066] The above-described positive electrode has an intermediate layer, which not only improves the adhesive strength between the current collector and the positive electrode active material layer, but also enhances stability and reliability against mechanical deformation such as bending, thereby improving the battery performance of the all-solid-state secondary battery. Therefore, in an all-solid-state secondary battery using a positive electrode containing lithium sulfide as the positive electrode active material, the phenomenon of the positive electrode active material being detached from the surface of the positive electrode collector due to changes in the volume of the positive electrode active material is prevented, and an adhesive binder layer is formed to reduce the interfacial resistance between the current collector and the positive electrode active material layer, thereby enabling the implementation of an all-solid-state secondary battery having a high capacity.

[0067] Li2S-containing complexes include, for example, complexes of Li2S and lithium salts.

[0068] The composite of Li2S and a lithium salt is ductile, and thus can be distinguished from brittle oxide-based solid electrolytes, such as garnet-structured oxide-based solid electrolytes. The composite of Li2S and a lithium salt is lithium-ion conductive, and thus can be distinguished from conventional lithium-free metal oxides, such as alumina, which do not have lithium-ion conductivity. The composite of Li2S and a lithium salt is, for example, the result of mechanical milling of Li2S and a lithium salt. The composite of Li2S and a lithium salt is, for example, the result of a mechanochemical reaction of Li2S and a lithium salt, and thus can be distinguished from a simple mixture of Li2S and a lithium salt. A simple mixture of Li2S and a lithium salt can provide high interfacial resistance by failing to maintain a dense interface between Li2S and a lithium salt, which can result in an increase in the internal resistance of the positive electrode.

[0069] The complex of Li2S and lithium salt is Li2S-Li a X b It is expressed as (1≤a≤5, 1≤b≤5).

[0070] 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. a is, for example, 1, 2, 3, 4 or 5, and b is, for example, 1, 2, 3, 4 or 5.

[0071] A lithium salt is, for example, a compound that does not contain sulfur (S). The lithium salt may be, for example, a binary compound or a ternary compound. The lithium salt may be, for example, a binary compound composed of lithium and one element selected from Groups 13 to 17 of the periodic table of elements. The lithium salt may be, for example, a ternary compound composed of lithium and two elements selected from Groups 13 to 17 of the periodic table of elements. The binary compound may include, for example, LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, or a combination thereof. The ionic conductivity of the composite may be further improved by including such binary compounds. The internal resistance of the positive electrode may be further reduced by including a composite of Li2S and a lithium salt in the positive electrode active material layer. As a result, the cycle characteristics of an all-solid-state secondary battery including such a positive electrode can be further improved. The ternary compound can include, for example, Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2, or a combination thereof. When the composite includes such a ternary compound, the ionic conductivity of the composite can be further improved. When the positive electrode includes such a complex, the internal resistance of the positive electrode can be further reduced. As a result, the cycle characteristics of an all-solid-state secondary battery including such a positive electrode active material layer can be further improved.

[0072] The Li2S-containing composite may further include a carbon-based material. The Li2S-containing composite is, for example, a composite of Li2S, a lithium salt, and a carbon-based material.

[0073] The carbon-based material may be any material containing carbon atoms that is used as a conductive material in the relevant technical field. The carbon-based material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The carbon-based material may be, for example, a sintered product of a carbon precursor. The carbon-based material may be, for example, a carbon nanostructure. The carbon nanostructure may be, for example, a one-dimensional carbon nanostructure, a two-dimensional carbon nanostructure, a three-dimensional carbon nanostructure, or a combination thereof. The carbon nanostructure may be, for example, a carbon nanotube, a carbon nanofiber, a carbon nanobelt, a carbon nanorod, graphene, or a combination thereof. The carbon-based material may be, for example, a porous carbon-based material or a non-porous carbon-based material. The porous carbon-based material may include, for example, periodic and regular two-dimensional or three-dimensional pores. The porous carbon-based material may be, for example, carbon black such as Ketjen Black, acetylene black, Denka Black, thermal black, channel black, etc.; It can be graphite, activated carbon, or a combination thereof. The form of the carbon-based material is not limited to, for example, particle form, sheet form, flake form, etc., and any carbon-based material used in the relevant technical field is possible. The content of the carbon-based material included in the composite of Li2S, lithium salt, and carbon-based material can be, for example, 1 to 20 wt%, 5 to 20 wt%, or 10 to 20 wt% of the total weight of the composite of Li2S, lithium salt, and carbon-based material. If the content of the carbon-based material increases excessively beyond the above range, the energy density of the all-solid-state secondary battery may decrease. If the content of the carbon-based material decreases excessively beyond the above range, the electronic conductivity of the composite of Li2S, lithium salt, and carbon-based material may decrease, which may increase the internal resistance of the positive electrode active material layer. As a result, the cycle characteristics of the all-solid-state secondary battery may deteriorate.

[0074] The Mohs hardness of the lithium salt and the carbon-based material may be greater than that of Li2S. The Mohs hardness of Li2S is, for example, about 0.6 or less. The Mohs hardness of the lithium salt may be about 0.7 or more, about 0.8 or more, about 0.9 or more, about 1.0 or more, about 1.5 or more, or about 2.0 or more. When the lithium salt has a Mohs hardness in this range, the pulverization of Li2S can be performed more easily during the milling process, and a solid solution of Li2S and the lithium salt can be formed more easily. The Mohs hardness of LiI is, for example, about 2.0. The Mohs hardness of the carbon-based material may be about 0.7 or more, about 0.8 or more, about 0.9 or more, about 1.0 or more, about 1.2 or more, or about 1.5 or more. Since the carbon-based material has a Mohs hardness in this range, the grinding of Li2S can be performed more easily during the milling process, and a composite of Li2S, a lithium salt, and a carbon-based material can be formed more easily. The modal hardness of carbon nanofibers (CNF) is, for example, 1.5.

[0075] The carbon-based material may include, for example, a fibrous carbon-based material. When a composite of Li2S, a lithium salt, and a carbon-based material includes the fibrous carbon-based material, the electronic conductivity of the composite of Li2S, a lithium salt, and a carbon-based material can be further improved, and electronic conduction can be more easily performed from the surface to the inside of the composite of Li2S, a lithium salt, and a carbon-based material. The internal resistance of a positive electrode active material layer including a composite of Li2S, a lithium salt, and a carbon-based material can be reduced, and the cycle characteristics of an all-solid-state secondary battery including the positive electrode active material layer can be further improved.

[0076] The aspect ratio of the fibrous carbon-based material can be, for example, about 2 or greater, about 3 or greater, about 4 or greater, about 5 or greater, about 10 or greater, or about 20 or greater. The aspect ratio of the fibrous carbon-based material can be, 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 aspect ratio of the fibrous carbon-based material can be, 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. By having an aspect ratio of the fibrous carbon-based material in this range, the overall electronic conductivity of the composite of Li2S, lithium salt, and carbon-based material is improved, and the local electronic conductivity imbalance within the composite of Li2S, lithium salt, and carbon-based material can be further alleviated.

[0077] The fibrous carbon-based material may include, for example, carbon nanostructures. The carbon nanostructures may include, for example, carbon nanofibers (CNFs), carbon nanotubes (CNTs), carbon nanobelts, carbon nanorods, or combinations thereof.

[0078] The carbon nanostructure can form a primary carbon nanostructure composed of a single carbon nanostructure and a secondary carbon nanostructure composed of a plurality of carbon nanostructures aggregated together.

[0079] The diameter of the primary carbon nanostructure can be, for example, 1 nm to 200 nm, 1 nm to 150 nm, 1 nm to 100 nm, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 20 nm. The length of the primary carbon nanostructure can be, for example, 10 nm to 2 μm, 10 nm to 1.5 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 400 nm, 10 nm to 300 nm, 10 nm to 200 nm, or 10 nm to 100 nm. The diameter and length of the primary carbon nanostructure can be measured from scanning electron microscope (SEM) or transmission electron microscope (TEM) images. Here, the diameter and length represent an average diameter and an average length, respectively. Alternatively, the diameter and / or length of the primary carbon nanostructures can be measured by laser diffraction.

[0080] Secondary carbon nanostructures are, for example, structures formed by assembling primary carbon nanostructures in whole or in part to form bundles or bundle-type structures. The secondary carbon nanostructures may include, for example, bundle-type carbon nanostructures, rope-type carbon nanostructures, or combinations thereof. The diameter of the secondary carbon nanostructures may be, for example, 2 nm to 200 nm, 3 nm to 150 nm, 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 30 nm, or 5 nm to 20 nm. The length of the secondary carbon nanotube structure can be, for example, 20 nm to 2 ㎛, 30 nm to 1.5 ㎛, 50 nm to 1 ㎛, 50 nm to 500 nm, 50 nm to 400 nm, 50 nm to 300 nm, 50 nm to 200 nm, or 50 nm to 100 nm. Here, the diameter and length represent an average diameter and an average length, respectively. The diameter and length of the secondary carbon nanostructure can be measured from a scanning electron microscope (SEM) image or an optical microscope. Alternatively, the diameter and / or length of the secondary carbon nanostructure can be measured by laser diffraction. The secondary carbon nanostructure can be converted into a primary carbon nanostructure, for example, by dispersing it in a solvent or the like, and then used to prepare a composite of Li2S, a lithium salt, and a carbon-based material.

[0081] A composite of Li2S and a lithium salt or a composite of Li2S, a lithium salt, and a carbon-based material may include, for example, a solid solution of Li2S and a lithium salt. The ionic conductivity of the composite may increase due to the inclusion of the solid solution of Li2S and a lithium salt. For example, since the solid solution of Li2S and a lithium salt includes lithium ions arranged within Li2S crystallites, the ionic conductivity of the solid solution of Li2S and a lithium salt may be improved compared to the ionic conductivity of Li2S. Consequently, the ionic conductivity of the composite may be improved and the internal resistance of the composite may be reduced. By including such a composite in the positive electrode, the internal resistance of the positive electrode may be further reduced. Consequently, the cycle characteristics of an all-solid-state secondary battery including such a positive electrode may be further improved.

[0082] The size of Li2S crystallites obtained from the XRD spectrum of a complex of Li2S and a lithium salt or a complex of Li2S, a lithium salt, and a carbon-based material may be, for example, 20 nm or less, 15 nm or less, or 10 nm or less. The size of Li2S crystallites obtained from the XRD spectrum of the complex may be, for example, 1 to 20 nm, 1 to 15 nm, or 3 to 10 nm. As the size of Li2S crystallites decreases, the contact area between Li2S and a lithium salt may further increase. As the contact area between Li2S and a lithium salt further increases, the ionic conductivity of the complex of Li2S and a lithium salt may further increase. The internal resistance of the positive electrode may further decrease when the positive electrode includes such a complex. As a result, the cycle characteristics of an all-solid-state secondary battery including such a positive electrode may further improve.

[0083] Since Li2S has low ionic conductivity, a complex with a lithium salt is formed to overcome this drawback. A complex of Li2S and a lithium salt or a composite of Li2S and a lithium salt and a carbon-based material can provide improved ionic conductivity compared to Li2S alone. The content of Li2S in the complex may be 50 to 95 wt%, 50 to 90 wt%, 50 to 80 wt%, or 50 to 70 wt% of the total weight of the complex of Li2S and a lithium salt. By having the complex with a Li2S content in this range, a cathode with improved ionic conductivity and durability can be manufactured. The content of the lithium salt in the complex of Li2S and a lithium salt may be 5 to 50 wt%, 10 to 50 wt%, 20 to 50 wt%, or 30 to 50 wt% of the total weight of the complex of Li2S and a lithium salt.

[0084] The molar ratio of Li2S and lithium salt in the composite may be, for example, 50:50 to 95:5, 60:40 to 95:5, 60:40 to 90:10, 65:35 to 90:10, 65:35 to 85:15, or 70:30 to 85:15. The molar ratio of Li2S and lithium salt in the composite may be, for example, 50:50 to 95:5, 50:50 to 90:10, 50:50 to 85:15, 50:50 to 80:20, 50:50 to 75:25, or 50:50 to 70:30. By having Li2S and lithium salt in this range of molar ratio, the cycle characteristics of a lithium battery including the composite cathode active material can be further improved. If the molar ratio of Li2S is excessively high, the improvement in ionic conductivity by lithium salts may be minimal. If the molar ratio of Li2S is excessively high, the energy density of all-solid-state secondary batteries containing composite cathode active materials may be reduced.

[0085] In the composite of Li2S, a lithium salt, and a carbon-based material, the content of the lithium salt may be, for example, 1 to 40 wt%, 5 to 35 wt%, 10 to 35 wt%, 15 to 35 wt%, 20 to 35 wt%, or 25 to 35 wt% of the total weight of the composite of Li2S, a lithium salt, and a carbon-based material. If the content of the lithium salt is excessively increased, the energy density of the all-solid-state secondary battery may decrease. If the content of the lithium salt is excessively low, the ionic conductivity of the composite of Li2S, a lithium salt, and a carbon-based material may decrease, thereby increasing the internal resistance of the positive electrode. As a result, the cycle characteristics of the all-solid-state secondary battery including the positive electrode may deteriorate.

[0086] In the composite of Li2S, a lithium salt, and a carbon-based material, the molar ratio of Li2S and a lithium salt may be, for example, 50:50 to 95:5, 60:40 to 95:5, 60:40 to 90:10, 65:35 to 90:10, 65:35 to 85:15, or 70:30 to 85:15. In the composite of Li2S, a lithium salt, and a carbon-based material, the molar ratio of Li2S and a lithium salt may be, for example, 50:50 to 95:5, 50:50 to 90:10, 50:50 to 85:15, 50:50 to 80:20, 50:50 to 75:25, or 50:50 to 70:30. By maintaining the molar ratio of Li2S and lithium salt within this range, the cycle characteristics of an all-solid-state secondary battery including a positive electrode can be further improved. If the molar ratio of Li2S is excessively high, the ionic conductivity enhancement effect of the lithium salt may be minimal. If the molar ratio of Li2S is excessively high, the energy density of an all-solid-state secondary battery including a composite positive electrode active material may be reduced.

[0087] The ionic conductivity of a complex of Li2S and a lithium salt or a complex of Li2S, a lithium salt and a carbon-based material is, for example, 1×10 at 25°C. -5 S / cm or more, 2×10 -5 S / cm or more, 4×10 -5S / cm or more, 6×10 -5 S / cm or more, 8×10 -5 S / cm or more or 1×10 -4 It can be S / cm or more. The ionic conductivity can be measured using, for example, electrochemical impedance spectroscopy, direct current polarization method, etc. Since the complex of Li2S and lithium salt has an ionic conductivity in this range, the internal resistance of the positive electrode including the complex of Li2S and lithium salt can be further reduced. The cycle characteristics of an all-solid-state secondary battery including the positive electrode can be improved.

[0088] The Li2S-containing composite may further comprise a solid electrolyte. The solid electrolyte may comprise a sulfide-based solid electrolyte.

[0089] The content of the complex of Li2S and a lithium salt may be, for example, 0.1 to 20 wt%, 0.5 to 20 wt%, 0.5 to 15 wt%, 0.5 to 10 wt% or 1 to 5 wt% of the total weight of the complex of Li2S and a lithium salt and the sulfide-based solid electrolyte. The content of the complex of Li2S and a lithium salt may be, for example, 0.1 to 20 wt%, 0.5 to 20 wt%, 0.5 to 15 wt%, 0.5 to 10 wt% or 1 to 5 wt% of the total weight of the positive electrode. When the positive electrode has the content of the complex of Li2S and a lithium salt in this range, the durability of the positive electrode can be further improved and the internal resistance can be further reduced. If the content of the complex of Li2S and a lithium salt is too low, the effect may be minimal. If the content of the complex of Li2S and lithium salt increases excessively, the internal resistance of the positive electrode may increase.

[0090] The cathode active material layer may include, for example, composite particles of Li2S and a lithium salt and sulfide-based solid electrolyte particles. The size of the composite particles of Li2S and a lithium salt may be smaller than, for example, the size of the sulfide-based solid electrolyte particles. The size of the composite particles of Li2S and a lithium salt may be, for example, 90% or less, 80% or less, 60% or less, 40% or less, 20% or less, or 10% or less of the size of the sulfide-based solid electrolyte particles. The composite particles of Li2S and a lithium salt may be arranged in pores between a plurality of sulfide-based solid electrolytes, for example. By arranging the composite particles of Li2S and a lithium salt in the pores between a plurality of sulfide-based solid electrolytes, pinhole formation within the cathode can be suppressed, and the internal resistance of the cathode can be reduced. As a result, the durability of the cathode can be improved.

[0091] The size of the sulfide-based solid electrolyte particles may be, for example, 1 to 10 μm, 1 to 8 μm, 1 to 6 μm, 1 to 5 μm, or 1 to 3 μm. When the sulfide-based solid electrolyte particles have a size in this range, the durability of the positive electrode can be further improved. The size of the sulfide-based solid electrolyte particles can be measured using, for example, laser diffraction, scanning electron microscopy, etc. The size of the sulfide-based solid electrolyte particles is, for example, an arithmetic mean of the particle sizes of multiple particles measured using software from a scanning electron microscope image.

[0092] The particle size of the composite of Li2S and a lithium salt or the composite of Li2S and a lithium salt and a carbon-based material may 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 size of the composite particles may be, for example, 1 to 10 μm, 2 to 10 μm, 2 to 8 μm, or 3 to 8 μm. The size of the composite particles may be, for example, 0.1 to 10 μm, 0.1 to 8 μm, 0.1 to 5 μm, 0.1 to 2 μm, 0.1 to 1.5 μm, or 0.1 to 1 μm or less. When the composite particles have a size in this range, they can be more easily arranged in the gaps between the plurality of sulfide-based solid electrolytes, pinhole formation within the positive electrode can be suppressed, and the internal resistance of the positive electrode can be reduced. As a result, the durability of the positive electrode can be improved. The size of the composite particles can be measured, for example, using laser diffraction, scanning electron microscopy, etc. The size of the composite is, for example, the arithmetic mean of the particle sizes of multiple particles measured using software from scanning electron microscopy images.

[0093] The size of the composite particles containing Li2S, which is a composite cathode active material, may 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 size of the composite particles may be, for example, 1 to 10 μm, 2 to 10 μm, 2 to 8 μm, or 3 to 8 μm. The size of the composite particles may be, for example, 0.1 to 10 μm, 0.1 to 8 μm, 0.1 to 5 μm, 0.1 to 2 μm, 0.1 to 1.5 μm, or 0.1 to 1 μm.

[0094] The size of the Li2S particles included in the composite cathode active material, i.e., the size of the Li2S particles included in the composite, may be, for example, 2 ㎛ or less, 1.5 ㎛ or less, or 1 ㎛ or less. The size of the Li2S particles may be, for example, 0.1 to 2 ㎛, 0.1 to 1.5 ㎛, or 0.1 to 1 ㎛ or less. Since the Li2S particles have a size in this range, the volume change during charge and discharge is suppressed, and thus the deterioration of the composite cathode active material including the composite during charge and discharge can be suppressed. If the size of the Li2S particles increases excessively, the volume change of the composite during charge and discharge may increase, and thus the deterioration of the composite cathode active material including the composite may be accelerated. As a result, the cycle characteristics of an all-solid-state secondary battery including such a composite cathode active material may deteriorate.

[0095] The size of the Li2S-containing composite particles can be measured using, for example, laser diffraction, scanning electron microscopy, etc. The size of the Li2S-containing composite is, for example, the arithmetic mean of the particle sizes of multiple particles measured using software from scanning electron microscopy images.

[0096] The ratio of the size of the sulfide-based solid electrolyte particles to the size of the composite particles of Li2S and lithium salt may be, for example, 2:1 to 200:1, 2:1 to 180:1, 2:1 to 150:1, 2:1 to 120:1, 2:1 to 100:1, 2:1 to 80:1, or 2:1 to 50:1. When the ratio of the size of the sulfide-based solid electrolyte particles to the size of the composite particles of Li2S and lithium salt is within this range, the formation of defects in the positive electrode can be suppressed, thereby further improving the durability of the positive electrode. If the ratio of the size of the sulfide-based solid electrolyte particles to the size of the composite particles of Li2S and lithium salt is excessively small, the porosity of the positive electrode may increase excessively, thereby reducing the durability of the positive electrode. If the ratio of the size of the sulfide-based solid electrolyte particles to the size of the composite particles of Li2S and lithium salt is too large, uniform dispersion of the composite particles of Li2S and lithium salt within the cathode may be difficult.

[0097] By using a positive electrode containing the above-described composite, a lithium metal negative electrode can be eliminated, enabling the use of a non-anode all-solid-state secondary battery, thereby providing an all-solid-state secondary battery with improved energy density. Here, the non-anode all-solid-state secondary battery does not include a lithium metal negative electrode. In addition, since the composite positive electrode active material includes such a composite, the cycle characteristics of the all-solid-state secondary battery including the composite positive electrode active material can be improved. For example, the rate characteristics of the all-solid-state secondary battery including such a composite positive electrode active material can be improved.

[0098] In the positive electrode active material layer, the solid electrolyte may be, for example, a sulfide-based solid electrolyte. The solid electrolyte included in the positive electrode may be the same as or different from the solid electrolyte included in the electrolyte layer. The solid electrolyte included in the positive electrode active material layer may have a smaller average D50 particle size than the solid electrolyte included in the electrolyte layer. For example, the average D50 particle size of the solid electrolyte included in the positive electrode active material layer may 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 D50 particle size of the solid electrolyte included in the electrolyte layer. The average D50 particle size is, for example, the median particle diameter (D50). The median particle diameter (D50) is the size of particles corresponding to 50% of the cumulative volume, calculated from the side of particles having a smaller particle size in a size distribution of particles measured by, for example, laser diffraction.

[0099] The solid electrolyte may be included in an amount of 10 to 60 parts by weight, 10 to 50 parts by weight, 20 to 50 parts by weight, or 30 to 50 parts by weight, per 100 parts by weight of the cathode active material layer.

[0100] [All-solid-state secondary battery]

[0101] An all-solid-state secondary battery according to one embodiment includes a positive electrode; a negative electrode; and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive electrode may include the positive electrode according to one embodiment.

[0102] Referring to FIGS. 1 to 5, an all-solid-state secondary battery (1) includes 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) includes a positive electrode according to one embodiment.

[0103] [anode]

[0104] [Cathode: Cathode active material]

[0105] Referring to FIGS. 1 to 5, the positive electrode (10) includes a positive electrode current collector (11); a carbon coating layer (13) disposed on one or both sides of the positive electrode current collector (11) and a positive electrode active material layer (12) disposed thereon. The positive electrode active material layer (12) includes a Li2S-containing composite as the positive electrode active material. Although not shown in the drawings, an intermediate layer may be additionally disposed between the carbon coating layer (13) and the positive electrode active material layer (12) disposed thereon.

[0106] The Li2S-containing complex includes, for example, a complex of Li2S and carbon, a complex of Li2S and carbon and a solid electrolyte, a complex of Li2S and a solid electrolyte, a complex of Li2S and a lithium salt and carbon, a complex of Li2S and a metal carbide, a complex of Li2S and carbon and a metal carbide, a complex of Li2S and a metal nitride, a complex of Li2S and carbon and a metal nitride, or a combination thereof.

[0107] In the Li2S-containing composite, carbon can be any material containing carbon atoms that is used as a conductive material in the art. The carbon can be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The carbon can be, for example, a sintered product of a carbon precursor. The carbon can be, for example, a carbon nanostructure. The carbon nanostructure can be, for example, a one-dimensional carbon nanostructure, a two-dimensional carbon nanostructure, a three-dimensional carbon nanostructure, or a combination thereof. The carbon nanostructure can be, for example, a carbon nanotube, a carbon nanofiber, a carbon nanobelt, a carbon nanorod, graphene, graphene oxide (GO), reduced graphene oxide (rGO), graphene balls (GB), or a combination thereof. The carbon can be, for example, porous carbon or non-porous carbon.

[0108] The method for producing a complex of Li2S and carbon may be, but is not limited to, a dry method, a wet method, or a combination thereof, and in the relevant technical field, the method for producing a complex of Li2S and carbon may be, for example, milling, heat treatment, deposition, etc., but is not necessarily limited to these, and any method used in the relevant technical field may be used.

[0109] The composite of Li2S, carbon, and a solid electrolyte comprises carbon and a solid electrolyte. Carbon refers to the composite of Li2S and carbon described above. The solid electrolyte can be any material used as an ion-conducting material in the relevant technical field, for example. The solid electrolyte is, for example, an inorganic solid electrolyte. The solid electrolyte is, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte is, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. The sulfide-based solid electrolyte comprises, for example, Li, S, and P, and may optionally further comprise a halogen element. The sulfide-based solid electrolyte can be selected from among the sulfide-based solid electrolytes used in the solid electrolyte layer. The sulfide-based solid electrolyte has, for example, a density of 1×10 -5 It can have an ionic conductivity of S / cm or more. Sulfide-based solid electrolytes include, for example, Li3PO4-Li2SO4, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q, p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x , may include one or more selected from 0≤x≤2. The oxide-based solid electrolyte includes, for example, Li, O, and a transition metal element, and may optionally further include other elements. The oxide-based solid electrolyte may include, for example, 1×10 at room temperature. -5 It may be a solid electrolyte having an ionic conductivity of S / cm or more. The oxide-based solid electrolyte may be selected from oxide-based solid electrolytes used in the solid electrolyte layer. The solid electrolyte may be, for example, a mixture of a sulfide-based solid electrolyte and a lithium salt. For example, it may be a mixture of Li3PO4-Li2SO4 and a binary lithium salt, or a mixture of Li3PO4-Li2SO4 and a ternary lithium salt.

[0110] The composite of Li2S and a solid electrolyte includes a solid electrolyte. The solid electrolyte refers to the composite of Li2S, carbon, and a solid electrolyte described above.

[0111] A complex of Li2S and a lithium salt and carbon comprises a lithium salt compound and carbon. The lithium salt compound does not contain, for example, a sulfur (S) atom. The lithium salt compound can be, for example, a binary compound composed of lithium and one element selected from Groups 13 to 17 of the Periodic Table of Elements. The binary compound can include, for example, one or more selected from LiF, LiCl, LiBr, LiI, LiH, Li2S, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, LiI3, and LiB3. The lithium salt compound can be, for example, a ternary compound composed of lithium and two elements selected from Groups 13 to 17 of the Periodic Table of Elements. The ternary compound includes, for example, one or more selected from Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, and Li3BN2. The lithium salt compound is particularly one or more lithium halide compounds selected from LiF, LiCl, LiBr, and LiI. Carbon refers to the complex of Li2S and carbon described above.

[0112] The composite of Li2S and metal carbide includes metal carbide. The metal carbide is, for example, a two-dimensional metal carbide. The two-dimensional metal carbide is, for example, MXene. The two-dimensional metal carbide is, for example, M n+1 C n T x (M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups) is expressed as 2D metal carbides, for example, Ti2CT x , (Ti 0.5 , Nb 0.5 )2CT x , Nb2CT x , V2CT x, Ti3C2T x , (V 0.5 , Cr 0.5 )3C2T x , Ti3CNT x , Ta4C3T x , Nb4C3T x or a combination thereof. The surface of the two-dimensional metal carbide is terminated with O, OH and / or F.

[0113] The complex of Li2S, carbon, and metal carbide includes carbon and metal carbide. Carbon refers to the complex of Li2S and carbon described above. Metal carbide refers to the complex of Li2S and metal carbide described above.

[0114] The complex of Li2S and metal nitride includes a metal nitride. The metal nitride is, for example, a two-dimensional metal nitride. The two-dimensional metal nitride is, for example, M n+1 N n T x (M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups) is expressed as The surface of the two-dimensional metal nitride is terminated with O, OH and / or F.

[0115] A complex of Li2S, carbon, and a metal nitride includes carbon and a metal nitride. Carbon refers to the complex of Li2S and carbon described above. Metal carbide refers to the complex of Li2S and a metal nitride described above.

[0116] The size of the cathode active material can be, for example, 0.1 to 50 μm, 0.5 to 30 μm, 0.5 to 20 μm, or 1 to 10 μm. The size of Li2S can be, for example, 1 nm to 10 μm, 10 nm to 5 μm, 10 nm to 3 μm, or 10 nm to 1 μm. The size of the Li2S-containing composite can be, for example, 0.1 to 50 μm, 0.5 to 30 μm, 0.5 to 20 μm, or 1 to 10 μm.

[0117] The cathode active material layer (12) may additionally include, for example, a sulfide-based compound that is distinct from the cathode active material described above. The sulfide-based compound may be, for example, a compound containing a metal element other than Li and the element sulfur. The sulfide-based compound may be, for example, a compound containing a metal element belonging to Groups 1 to 14 of the Periodic Table of Elements having an atomic weight of 10 or more and the element sulfur. The sulfide-based compound may be, for example, FeS2, VS2, NaS, MnS, FeS, NiS, CuS, or a combination thereof. By the cathode active material layer additionally including a sulfide-based compound, the cycle characteristics of the all-solid-state secondary battery may be further improved. The content of the sulfide-based compound included in the cathode active material layer (12) may be 10 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less of the total weight of the cathode active material layer (12).

[0118] The shape of the positive electrode active material is, for example, a particle shape such as a sphere or an ellipse. The particle size of the positive electrode active material is not limited and is within a range applicable to positive electrode active materials of a conventional all-solid-state secondary battery. The content of the positive electrode active material of the positive electrode layer (10) is also not limited and is within a range applicable to positive electrode layers of a conventional all-solid-state secondary battery. The content of the positive electrode active material included in the positive electrode active material layer (12) may be, for example, 30 wt% to 99 wt%, 30 wt% to 90 wt%, 30 wt% to 80 wt%, 30 wt% to 70 wt%, or 30 wt% to 50 wt% of the total weight of the positive electrode active material layer (12).

[0119] [Polar: Challenger]

[0120] The cathode active material layer (12) may further include a conductive material. The conductive material may be, for example, a carbon-based conductive material, a metal-based conductive material, or a combination thereof. The carbon-based conductive material may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or a combination thereof, but is not limited thereto, and any material used as a carbon-based conductive material in the art may be used. The metal-based conductive material may be, for example, metal powder, metal fiber, or a combination thereof, but is not limited thereto, and any material used as a metal-based conductive material in the art may be used. The content of the conductive material included in the cathode active material layer (12) may be, for example, 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% of the total weight of the cathode active material layer (12).

[0121] [Positive: Binder]

[0122] The positive electrode active material layer (12) may further include a binder. The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited thereto, and any binder used in the relevant technical field may be used. The binder content included in the positive electrode active material layer (12) may be, for example, 1 wt% to 10 wt% of the total weight of the positive electrode active material layer (12). The binder may be omitted.

[0123] [Positive: Other additives]

[0124] The cathode active material layer (12) may further include additives such as fillers, coating agents, dispersants, and ion conductive aids in addition to the cathode active material, solid electrolyte, binder, and conductive agent described above.

[0125] As fillers, coating agents, dispersants, ion conductivity aids, etc. that the positive electrode active material layer (12) may include, known materials generally used in electrodes of all-solid-state secondary batteries may be used.

[0126] [Anode: Anode current collector]

[0127] The positive electrode collector (11) uses a plate or foil made of, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. The positive electrode collector (11) may be omitted. The thickness of the positive electrode collector (11) is, for example, 1 µm to 100 µm, 1 µm to 50 µm, 5 µm to 25 µm, or 10 µm to 20 µm.

[0128] The cathode current collector (11) may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The base film may be, for example, an insulator. Since the base film includes an insulating thermoplastic polymer, when a short circuit occurs, the base film softens or liquefies, thereby blocking battery operation and suppressing a rapid increase in current. The metal layer may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or an alloy thereof. The metal layer can act as an electrochemical fuse and be cut off in case of overcurrent to prevent a short circuit. The limit current and the maximum current can be controlled by adjusting the thickness of the metal layer. The metal layer can be plated or deposited on the base film. As the thickness of the metal layer decreases, the limit current and / or the maximum current of the positive electrode current collector (11) decreases, thereby improving the stability of the lithium battery in case of a short circuit. A lead tab can be added on the metal layer for connection to the outside. The lead tab can be welded to the metal layer or the metal layer / base film laminate by ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or the metal layer melt, so that the metal layer can be electrically connected to the lead tab. In order to strengthen the welding of the metal layer and the lead tab, a metal chip can be added between the metal layer and the lead tab.The metal piece may be a thin piece of the same material as the metal of the metal layer. The metal piece may be, for example, a metal foil, a metal mesh, etc. The metal piece may be, for example, aluminum foil, copper foil, SUS (stainless steel) foil, etc. After the metal piece is placed on the metal layer, the lead tab may be welded to the metal piece / metal layer laminate or the metal piece / metal layer / base film laminate. During welding, the base film, the metal layer, and / or the metal piece may melt, so that the metal layer or the metal layer / metal piece laminate may be electrically connected to the lead tab. A metal chip and / or a lead tab may be added to a portion of the metal layer. The base film may have a thickness of, for example, 1 to 50 μm, 1.5 to 50 μm, 1.5 to 40 μm, or 1 to 30 μm. When the base film has a thickness in this range, the weight of the electrode assembly can be more effectively reduced. The melting point of the base film may be, for example, 100 to 300°C, 100 to 250°C or less, or 100 to 200°C. Since the base film has a melting point within this range, the base film can be melted and easily bonded to the lead tab during the welding process of the lead tab. To improve the adhesion between the base film and the metal layer, a surface treatment such as corona treatment may be performed on the base film. The thickness of the metal layer may be, for example, 0.01 to 3 μm, 0.1 to 3 μm, 0.1 to 2 μm, or 0.1 to μm. Since the metal layer has a thickness within this range, conductivity can be maintained while ensuring the stability of the electrode assembly. The thickness of the metal piece may be, for example, 2 to 10 μm, 2 to 7 μm, or 4 to 6 μm. Since the metal piece has a thickness within this range, the connection between the metal layer and the lead tab can be performed more easily. By having this structure, the positive electrode collector (11) can reduce the weight of the positive electrode and consequently improve the energy density of the positive electrode and lithium battery.

[0129] [Anode: Inert member]

[0130] Referring to FIGS. 4 and 5, the positive electrode (10) includes a positive electrode current collector (11), a carbon coating layer (13) disposed on one surface of the positive electrode current collector, and a positive electrode active material layer (12) disposed thereon. An intermediate layer (not shown) may be further disposed between the carbon coating layer (13) and the positive electrode active material layer (12) disposed thereon.

[0131] An inactive member (40) is disposed on one side of the positive electrode (10). Referring to FIG. 4, the inactive member (40) is disposed on one side of the positive electrode active material layer (12) and the positive electrode current collector (11). Referring to FIG. 5, the inactive member (40) is disposed on one side of the positive electrode active material layer (12) and is disposed between the solid electrolyte layer (30) and the positive electrode current collector (11) facing the solid electrolyte layer (30). The inactive member (40) is not disposed on one side of the positive electrode current collector (11).

[0132] By including an inert member (40), cracking of the electrolyte layer (30) is prevented during the manufacture and / or charging / discharging of the all-solid-state secondary battery (1), and as a result, the cycle characteristics of the all-solid-state secondary battery (2) are improved. In an all-solid-state secondary battery (1) that does not include an inert member (40), when the manufacture and / or charging / discharging of the all-solid-state secondary battery (1) is performed, uneven pressure is applied to the electrolyte layer (30) in contact with the positive electrode (10), which increases the possibility of cracking in the electrolyte layer (30), and thus, a short circuit may occur due to the growth of lithium metal through the crack.

[0133] In the all-solid-state secondary battery (1), the thickness of the inert member (40) is greater than or equal to the thickness of the positive electrode active material layer (12). Alternatively, in the all-solid-state secondary battery (1), the thickness of the inert member (40) is substantially equal to the thickness of the positive electrode (10). Since the thickness of the inert member (40) is equal to the thickness of the positive electrode (10), a uniform pressure is applied between the positive electrode (10) and the electrolyte layer (30), and the positive electrode (10) and the electrolyte layer (30) are sufficiently adhered to each other, so that the interfacial resistance between the positive electrode (10) and the electrolyte layer (30) can be reduced. In addition, since the electrolyte layer (30) is sufficiently sintered during the pressurized manufacturing process of the all-solid-state secondary battery (1), the internal resistance of the electrolyte layer (30) and the all-solid-state secondary battery (1) including the same is reduced.

[0134] The inert member (40) surrounds the side surface of the positive electrode (10) and is in contact with the electrolyte layer (30). By the inert member (40) surrounding the side surface of the positive electrode (10) and being in contact with the electrolyte layer (30), cracks in the electrolyte layer (30) that occur due to a pressure difference during the pressing process in the electrolyte layer (30) that does not come into contact with the positive electrode (20) can be effectively suppressed. The inert member (40) surrounds the side surface of the positive electrode (10) and is separated from the negative electrode (20), more specifically, the first negative electrode active material layer (22). The inert member (40) surrounds the side surface of the positive electrode (10), is in contact with the electrolyte layer (30), and is separated from the negative electrode (20). Therefore, the possibility of a short circuit occurring due to physical contact between the positive electrode (10) and the first negative electrode active material layer (22) or a short circuit occurring due to overcharging of lithium, etc., is suppressed. For example, by placing an inert member (40) on one side of the positive electrode active material layer (12) and simultaneously on one side of the positive electrode current collector (11), the possibility of a short circuit occurring due to contact between the positive electrode current collector (11) and the negative electrode (20) is more effectively suppressed.

[0135] Referring to FIGS. 4 and 5, the inert member (40) extends from one side of the positive electrode (30) to the end of the electrolyte layer (30). By extending the inert member (40) to the end of the electrolyte layer (30), cracks occurring at the end of the electrolyte layer (30) can be suppressed. The end of the electrolyte layer (30) is the outermost part that is in contact with the side of the electrolyte layer (30). The inert member (40) extends to the outermost part that is in contact with the side of the electrolyte layer (30). The inert member (40) is separated from the negative electrode (20), more specifically, from the first negative electrode active material layer (22). The inert member (40) extends to the end of the electrolyte layer (30), but does not contact the negative electrode (20). The inert member (40) fills a space extending from, for example, one side of the anode (30) to the end of the electrolyte layer (30).

[0136] Referring to FIGS. 4 and 5, the width of the inert member (40) extending from one side of the positive electrode (10) to the end of the electrolyte layer (30) is, for example, 1 to 30%, 1 to 25%, 1 to 20%, 1 to 15%, 1 to 10%, or 1 to 5% of the width between one side of the positive electrode (10) and the other side opposite to the one side. If the width of the inert member (40) is excessively large, the energy density of the all-solid-state secondary battery (1) is reduced. If the width of the inert member (40) is excessively small, the effect of arranging the inert member (40) is minimal.

[0137] The area of ​​the anode (10) is smaller than the area of ​​the electrolyte layer (30) in contact with the anode (10). An inert member (40) is arranged to surround the side of the anode (10) to compensate for the area difference between the anode (10) and the electrolyte layer (30). By compensating for the difference between the area of ​​the anode (10) and the area of ​​the electrolyte layer (30), cracks in the electrolyte layer (30) caused by the pressure difference during the pressing process are effectively suppressed. For example, the sum of the area of ​​the anode (10) and the area of ​​the inert member (40) is equal to the area of ​​the electrolyte layer (30). The electrolyte layer (30) may be, for example, a solid electrolyte layer.

[0138] The area of ​​the anode (10) is, 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 anode (10) is, for example, 50% to less than 100%, 50% to 99%, 55% to 98%, 60% to 97%, 70% to 96%, 80% to 95%, or 85% to 95% of the area of ​​the electrolyte layer (30).

[0139] If the area of ​​the positive electrode (10) is equal to or larger than the area of ​​the electrolyte layer (30), the possibility of a short circuit occurring due to physical contact between the positive electrode (10) and the first negative electrode active material layer (22) or overcharging of lithium increases. The area of ​​the positive electrode (10) is, for example, equal to the area of ​​the positive electrode active material layer (12). The area of ​​the positive electrode (10) is, for example, equal to the area (11) of the positive electrode current collector.

[0140] The area of ​​the inert member (40) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the area of ​​the anode (10). The area of ​​the inert member (40) is, for example, 1% to 50%, 5% to 40%, 5% to 30%, 5% to 20%, or 5% to 15% of the area of ​​the anode (10).

[0141] The area (S1) of the positive electrode (10) is smaller than the area (S4) of the negative electrode current collector (21). The area (S1) of the positive electrode (10) is, for example, less than 100%, 99% or less, 98% or less, 97% or less, 96% or less, or 95% or less of the area (S4) of the negative electrode current collector (21). The area (S1) of the positive electrode (10) is, for example, 50% to less than 100%, 50% to 99%, 55% to 98%, 60% to 97%, 70% to 96%, 80% to 95%, or 85% to 95% of the area (S4) of the negative electrode current collector (21). The area (S4) of the negative electrode current collector (21) is, for example, the same as the area of ​​the negative electrode (20). The area (S4) of the negative electrode current collector (21) is, for example, the same as the area of ​​the first negative electrode active material layer (22).

[0142] As used herein, “same” area, length, width, thickness, and / or shape includes all instances of having “substantially the same” area, length, width, thickness, and / or shape, except where the area, length, width, thickness, and / or shape are intentionally different from each other. “Same” area, length, width, and / or thickness includes a range where the unintentional difference in the area, length, width, and / or thickness of the compared objects is, for example, less than 3%, less than 2%, less than 1%, less than 0.5%, or less than 0.1%.

[0143] The thickness of the inert member (40) is, for example, greater than the thickness of the first negative electrode active material layer (22). The thickness of the first negative electrode active material layer (22) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the thickness of the inert member (40). The thickness of the first negative electrode active material layer (22) is, for example, 1% to 50%, 1% to 40%, 1% to 30%, 1% to 20%, or 1% to 10% of the thickness of the inert member (40).

[0144] The inert member (40) may be a gasket. By using a gasket as the inert member (40), cracks in the electrolyte layer (30) caused by a pressure difference during the pressing process can be effectively suppressed.

[0145] The inert member (40) has, for example, a single-layer structure. Alternatively, although not shown in the drawing, the inert member (40) may have a multi-layer structure. In the inert member (40) having a multi-layer structure, each layer may have a different composition. The inert member having 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 inert member (40) having a multi-layer structure may include, for example, one or more adhesive layers and one or more support layers. The adhesive layer effectively prevents, for example, a separation between the positive electrode (10) and the electrolyte layer (30) due to a change in the volume of the positive electrode (10) that occurs during the charge / discharge process of the all-solid-state secondary battery (10), and improves the film strength of the inert member (40) by providing a bonding force between the support layer and other layers. The support layer provides support to the inert member (40), prevents unevenness of pressure applied to the electrolyte layer (30) during the pressurization process or the charge / discharge process, and prevents deformation of the all-solid-state secondary battery (1) being manufactured.

[0146] The inert member (40) is, for example, a flame-retardant inert member. The flame-retardant inert member prevents thermal runaway and ignition of the all-solid-state secondary battery (1) by providing flame retardancy. Consequently, the safety of the all-solid-state secondary battery (1) is further improved. The flame-retardant inert member prevents deterioration of the all-solid-state secondary battery (1) by absorbing residual moisture within the all-solid-state secondary battery (1), thereby improving the lifespan characteristics of the all-solid-state secondary battery (1).

[0147] The flame-retardant inert member includes, for example, a methacrylic and a filler. The methacrylic includes, for example, a substrate and a reinforcing material. The methacrylic includes, for example, a fibrous substrate and a fibrous reinforcing material. Since the methacrylic includes the substrate, the methacrylic can have elasticity. Therefore, the methacrylic can effectively accommodate volume changes during charge and discharge of the all-solid-state secondary battery (1) and can be arranged at various positions. The substrate included in the methacrylic includes, for example, a first fibrous material. Since the substrate includes the first fibrous material, the volume changes of the positive electrode (30) occurring during charge and discharge of the all-solid-state secondary battery (1) can be effectively accommodated and deformation of the inert member (40) caused by the volume changes of the positive electrode (30) can be effectively suppressed. The first fibrous material is, for example, a material having an aspect ratio of 5 or more, 20 or more, or 50 or more. The first fibrous material is, for example, a material having an aspect ratio of 5 to 1000, 20 to 1000, or 50 to 1000. The first fibrous material is, for example, an insulating material. Since the first fibrous material is an insulating material, a short circuit between the positive electrode (30) and the negative electrode (20) caused by lithium dendrites, etc., generated during the charge and discharge process of the all-solid-state secondary battery (1) can be effectively prevented. The first fibrous material includes, for example, at least one selected from pulp fibers, insulating polymer fibers, and ion-conductive polymer fibers. The strength of the methacrylic is improved by the inclusion of a reinforcing material in the methacrylic. Therefore, the methacrylic can prevent excessive volume change during charge and discharge of the all-solid-state secondary battery (1) and deformation of the all-solid-state secondary battery. The reinforcing material included in the methacrylic includes, for example, a second fibrous material. Since the reinforcing material includes the second fibrous material, the strength of the methacrylic can be increased more uniformly. The second fibrous material is, for example, a material having an aspect ratio of 3 or more, 5 or more, or 10 or more.The first fibrous material is, for example, a material having an aspect ratio of 3 to 100, 5 to 100, or 10 to 100. The second fibrous material is, for example, a flame-retardant material. Since the second fibrous material is a flame-retardant material, ignition due to thermal runaway occurring during the charge / discharge process of the all-solid-state secondary battery (1) or due to external impact can be effectively suppressed. The second fibrous material is, for example, glass fiber, metal oxide fiber, ceramic fiber, etc.

[0148] The flame-retardant inert member includes a filler in addition to the metatrix. The filler may be disposed within the metatrix, on the surface of the metatrix, or on both the interior and the surface. The filler is, for example, an inorganic material. The filler included in the flame-retardant inert member is, for example, a moisture getter. The filler removes moisture remaining in the all-solid-state secondary battery (1) by adsorbing moisture, for example, at a temperature below 100°C, thereby preventing deterioration of the all-solid-state secondary battery (1). In addition, when the temperature of the all-solid-state secondary battery (1) increases to 150°C or higher due to thermal runaway occurring during the charge / discharge process of the all-solid-state secondary battery (1) or an external impact, the filler releases the adsorbed moisture, thereby effectively suppressing ignition of the all-solid-state secondary battery (1). That is, the filler is, for example, a flame retardant. The filler is, for example, a metal hydroxide having moisture adsorption properties. The metal hydroxide contained in the filler is, for example, Mg(OH)2, Fe(OH)3, Sb(OH)3, Sn(OH)4, TI(OH)3, Zr(OH)4, Al(OH)3, or a combination thereof. The content of the filler contained in the flame-retardant inert member is, for example, 10 to 80 parts by weight, 20 to 80 parts by weight, 30 to 80 parts by weight, 40 to 80 parts by weight, 50 to 80 parts by weight, 60 to 80 parts by weight, or 65 to 80 parts by weight, based on 100 parts by weight of the flame-retardant inert member (4).

[0149] The flame-retardant inert member may further comprise, for example, a binder. The binder may comprise, for example, a curable polymer or a non-curable polymer. A curable polymer is a polymer that cures by heat and / or pressure. A curable polymer is, for example, a solid at room temperature. The flame-retardant inert member (40) comprises, for example, a heat-pressure curable film and / or a cured product thereof. The heat-pressure curable polymer is, for example, TSA-66 from Toray.

[0150] The flame-retardant inert member may additionally include other materials in addition to the above-described substrate, reinforcing material, filler, and binder. The flame-retardant inert member may further include one or more selected from among paper, an insulating polymer, an ion-conducting polymer, an insulating inorganic material, an oxide-based solid electrolyte, and a sulfide-based solid electrolyte. The insulating polymer may be, for example, an olefin-based polymer such as polypropylene (PP) or polyethylene (PE).

[0151] The density of the substrate or the density of the reinforcing material included in the flame-retardant inert member may be, for example, 10% to 300%, 10% to 150%, 10% to 140%, 10% to 130%, or 10% to 120% of the density of the positive electrode active material included in the positive electrode active material layer (12).

[0152] The inert member (40) is a member that does not contain an electrochemically active material, for example, an electrode active material. The electrode active material is a material that absorbs / releases lithium. The inert member (40) is a member made of a material other than the electrode active material and used in the relevant technical field.

[0153] [cathode]

[0154] [Cathode: Cathode active material]

[0155] Referring to FIGS. 1 to 5, the negative electrode (20) includes a negative electrode current collector (21) and a first negative electrode active material layer (22) disposed on one surface of the negative electrode current collector (21).

[0156] The first negative electrode active material layer (22) is, for example, a metal layer, and the metal layer may include lithium or a lithium alloy.

[0157] Alternatively, the first negative electrode active material layer (22) may include, for example, a negative electrode active material and a binder.

[0158] The negative electrode active material included in the first negative electrode active material layer (22) is, for example, a negative electrode material that can form an alloy or compound with lithium.

[0159] The negative electrode active material included in the first negative electrode active material layer (22) has, for example, a particle form. The average particle diameter of the negative electrode active material having a particle form is, for example, 4 ㎛ or less, 3 ㎛ or less, 2 ㎛ or less, 1 ㎛ or less, 500 nm or less, 300 nm or less, or 100 nm or less. The average particle diameter of the negative electrode active material having a particle form is, for example, 10 nm to 4 ㎛, 10 nm to 3 ㎛, 10 nm to 2 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 300 nm, or 10 nm to 100 nm. When the negative electrode active material has an average particle diameter in this range, reversible absorption and / or desorption of lithium can be facilitated during charge and discharge. The average particle size of the negative electrode active material is, for example, the median diameter (D50) measured using a laser particle size distribution meter.

[0160] The negative electrode active material included in the first negative electrode active material layer (22) includes, for example, at least one selected from among a carbon-based negative electrode active material and a metal or semi-metal negative electrode active material.

[0161] Carbon-based negative electrode materials include, for example, amorphous carbon, crystalline carbon, porous carbon, or a combination thereof.

[0162] The carbon-based negative electrode material is, in particular, amorphous carbon. Amorphous carbon includes, but is not limited to, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), and graphene, and any material classified as amorphous carbon in the relevant technical field is acceptable. Amorphous carbon is carbon that has no crystallinity or very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon.

[0163] The carbon-based negative electrode active material may be, for example, porous carbon. The porous carbon has a pore volume of, for example, 0.1 cc / g to 10.0 cc / g, 0.5 cc / g to 5 cc / g, or 0.1 cc / g to 1 cc / g. The porous carbon has an average pore diameter of, for example, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 10 nm. The porous carbon has a BET surface area of, for example, 100 m 2 / g to 3000 m 2 / g is.

[0164] The metal or metalloid negative electrode active material includes, but is not limited to, one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn), and any metal or metalloid negative electrode active material that forms an alloy or compound with lithium in the relevant technical field may be used. For example, nickel (Ni) does not form an alloy with lithium and therefore is not a metal negative electrode active material.

[0165] The first negative electrode active material layer (22) includes a type of negative electrode active material among these negative electrode active materials, or includes a mixture of a plurality of different negative electrode active materials. For example, the first negative electrode active material layer (22) includes only amorphous carbon, or includes at least one selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the first negative electrode active material layer (22) includes a mixture of amorphous carbon and at least one selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The mixing ratio of the mixture of amorphous carbon and gold, etc., is a weight ratio, for example, 99:1 to 1:99, 10:1 to 1:2, 5:1 to 1:1, or 4:1 to 2:1, but is not necessarily limited to this range and is selected according to the required characteristics of the all-solid-state secondary battery (1). When the negative electrode active material has this composition, the cycle characteristics of the all-solid-state secondary battery (1) are further improved.

[0166] The negative electrode active material included in the first negative electrode active material layer (22) includes, for example, a mixture of first particles made of amorphous carbon and second particles made of a metal or a metalloid. The metal or metalloid includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the metalloid is a semiconductor. The content of the second particles is 1 to 99 wt%, 1 to 60 wt%, 8 to 60 wt%, 10 to 50 wt%, 15 to 40 wt%, or 20 to 30 wt% based on the total weight of the mixture. When the second particles have a content in this range, the cycle characteristics of, for example, an all-solid-state secondary battery (1) are further improved.

[0167] Alternatively, the first negative electrode active material layer (22) includes a composite negative electrode active material. The composite negative electrode active material may include, for example, a carbon-based support and a metal-based negative electrode active material supported on the carbon-based support. Since the composite negative electrode active material has such a structure, the metal-based negative electrode active material can be prevented from being localized within the first negative electrode active material layer and a uniform distribution can be achieved. As a result, the cycle characteristics of the all-solid-state secondary battery (1) including the first negative electrode active material layer (22) are further improved.

[0168] The metal-based negative electrode active material supported on the carbon-based support includes, for example, a metal, a metal oxide, a composite of a metal and a metal oxide, or a combination thereof. The metal includes, 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 includes, for example, Au. x O y (0 <x≤2, 0<y≤3), Pt x O y (0 <x≤1, 0<y≤2), Pd x O y(0 <x≤1, 0<y≤1), Si x The y (0 <x≤1, 0<y≤2), Ag x The y (0 <x≤2, 0<y≤1), Al x The y (0 <x≤2, 0<y≤3), Bi x The y (0 <x≤2, 0<y≤3), Sn x The y (0 <x≤1, 0<y≤2), Te x The y (0 <x≤1, 0<y≤3), Zn x The y (0 <x≤1, 0<y≤1) 또는 이들의 조합을 포함할 수 있다. 금속과 금속산화물의 복합체는 예를 들어 Au와 Au x The y (0 <x≤2, 0<y≤3)의 복합체, Pt와 Pt x The y (0 <x≤1, 0<y≤2)의 복합체, Pd와 Pd x The y (0 <x≤1, 0<y≤1)의 복합체, Si와 Si x The y (0 <x≤1, 0<y≤2)의 복합체, Ag 와 Ag x The y (0 <x≤1, 0<y≤2)의 복합체, Al과 Al x The y (0 <x≤2, 0<y≤3)의 복합체, Bi와 Bi x The y (0 <x≤2, 0<y≤3)의 복합체, Sn과 Sn x The y (0 <x≤1, 0<y≤2)의 복합체, Te과 Te x The y (0 <x≤1, 0<y≤3), Zn과 Zn x The y (0 <x≤1, 0<y≤1)의 복합체, 또는 이들의 조합을 포함할 수 있다.

[0169] The carbonaceous support is, for example, amorphous carbon. Amorphous carbon includes, but is not limited to, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), graphene, activated carbon, carbon nanofibers (CNF), carbon nanotubes (CNT), etc., and any material classified as amorphous carbon in the relevant technical field is possible. Amorphous carbon is carbon that has no crystallinity or very low crystallinity, and is distinguished from crystalline carbon or graphite carbon. Carbonaceous materials are, for example, carbonaceous negative electrode active materials.

[0170] The composite negative electrode active material may have, for example, a particle form. The particle size of the composite negative electrode active material having a particle form is, for example, 10 nm to 4 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. When the composite negative electrode active material has a particle size in this range, reversible absorption and / or desorption of lithium may be facilitated during charge and discharge. The metal-based negative electrode active material supported on the support may have, for example, a particle form. The particle size of the metal-based negative electrode active material may be, for example, 1 nm to 200 nm, 1 nm to 150 nm, 5 nm to 100 nm, or 10 nm to 50 nm. The carbon-based support may have, for example, a particle form. The particle size of the carbon-based support may be, for example, 10 nm to 2 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. By having a particle size in this range, the carbon-based support can be more uniformly arranged within the first negative electrode active material layer. The carbon-based support may be, for example, nanoparticles having a particle size of 500 nm or less. The particle sizes of the composite negative electrode active material, the particle sizes of the metal-based negative electrode active material, and the particle sizes of the carbon-based support are, for example, average particle sizes. The average particle size is, for example, the median diameter (D50) measured using a laser particle size distribution analyzer. Alternatively, the average particle size may be determined automatically using software, for example, from an electron microscope image, or manually by a manual method.

[0171] [Cathode: Binder]

[0172] The binder included in the first negative electrode active material layer (22) is, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc., but is not necessarily limited thereto and any binder used in the relevant technical field may be used. The binder may be composed of a single binder or a plurality of different binders.

[0173] Since the first negative electrode active material layer (22) includes a binder, the first negative electrode active material layer (22) is stabilized on the negative electrode current collector (21). In addition, cracking of the first negative electrode active material layer (22) is suppressed despite changes in the volume and / or relative position of the first negative electrode active material layer (22) during the charge and discharge process. For example, if the first negative electrode active material layer (22) does not include a binder, the first negative electrode active material layer (22) can be easily separated from the negative electrode current collector (21). As the first negative electrode active material layer (22) is separated from the negative electrode current collector (21), the possibility of a short circuit occurring increases as the negative electrode current collector (21) comes into contact with the electrolyte layer (30) at the exposed portion of the negative electrode current collector (21). The first negative electrode active material layer (22) is manufactured by, for example, applying a slurry in which the material constituting the first negative electrode active material layer (22) is dispersed onto the negative electrode current collector (21) and drying the slurry. By including a binder in the first negative electrode active material layer (22), stable dispersion of the negative electrode active material in the slurry is possible. For example, when applying the slurry onto the negative electrode current collector (21) by screen printing, it is possible to suppress clogging of the screen (for example, clogging by aggregates of the negative electrode active material).

[0174] [Cathode: Other additives]

[0175] The first negative electrode active material layer (22) may further include additives used in a conventional all-solid-state secondary battery (1), such as fillers, coating agents, dispersants, and ion conductive aids.

[0176] [Cathode: Solid electrolyte]

[0177] The first negative electrode active material layer (22) may further include a solid electrolyte. The solid electrolyte may be, for example, a material selected from among the solid electrolytes included in the electrolyte layer (30). The solid electrolyte included in the first negative electrode active material layer (22) may act as a reaction site where lithium metal formation begins within the first negative electrode active material layer (22), a space where the formed lithium metal is stored, or a path for transferring lithium ions. The solid electrolyte may be omitted.

[0178] In the first negative electrode active material layer (22), the content of the solid electrolyte may be high, for example, in an area adjacent to the electrolyte layer (30), and low, for example, in an area adjacent to the negative electrode current collector (21). In the first negative electrode active material layer (22), the solid electrolyte may have a concentration gradient in which the concentration decreases, for example, from an area adjacent to the electrolyte layer (30) to an area adjacent to the negative electrode current collector (21).

[0179] [Cathode: First negative electrode active material layer]

[0180] The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer (22) and the initial charge capacity (A) of the positive electrode active material layer is 0.005 to 0.45. The initial charge capacity of the positive electrode active material layer (12) is the first open circuit voltage (1 st Li / Li from open circuit voltage) + The initial charge capacity of the first negative electrode active material layer (22) is determined at the maximum charging voltage. The initial charge capacity of the first negative electrode active material layer (22) is determined at the second open circuit voltage (2 nd Li / Li from open circuit voltage) + It is determined at 0.01 V.

[0181] The maximum charge voltage is determined by the type of cathode active material. The maximum charge voltage can be, for example, 1.5 V, 2.0 V, 2.5 V, 3.0 V, 3.5 V, 4.0 V, 4.2 V, or 4.3 V. For example, the maximum charge voltage of Li2S or Li2S-containing composite is Li / Li + can be 2.5 V for Li2S or Li2S containing composites. For example, the maximum charging voltage of Li / Li + It can be 3.0 V for. The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer (22) and the initial charge capacity (A) of the positive electrode active material layer is, for example, 0.01 to 0.3, 0.01 to 0.2, or 0.05 to 0.1. The initial charge capacity (mAh) of the positive electrode active material layer (12) is obtained by multiplying the charge capacity density (charge specific capacity) (mAh / g) of the positive electrode active material by the mass (g) of the positive electrode active material in the positive electrode active material layer (12). When several types of positive electrode active materials are used, the charge capacity density × mass value is calculated for each positive electrode active material, and the sum of these values ​​is the initial charge capacity of the positive electrode active material layer (12). The initial charge capacity of the first negative electrode active material layer (22) is also calculated in the same way. The initial charge capacity of the first negative electrode active material layer (22) is obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the first negative electrode active material layer (22). When several types of negative electrode active materials are used, the charge capacity density Х mass value is calculated for each negative electrode active material, and the sum of these values ​​is the initial charge capacity of the first negative electrode active material layer (22). The charge capacity density of each of the positive electrode active material and the negative electrode active material can be measured using a solid half-cell using lithium metal as a counter electrode. The initial charge capacity of each of the positive electrode active material layer (12) and the first negative electrode active material layer (22) is obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass value of the negative electrode active material in the first negative electrode active material layer (22). 2can be directly measured using a solid-state half-cell. For the positive electrode, the measurement is made from the first open circuit voltage (OCV) to the maximum charge voltage, e.g., 3.0 V (vs. Li / Li + ) can be performed for an operating voltage of up to 0.01 V for the cathode, for example, lithium metal, from the second open circuit voltage (OCV). For example, a solid-state half-cell having a cathode active material layer can measure a current of 0.1 mA / cm from the first open circuit voltage to 3.0 V. 2 The solid half-cell having the first negative active material layer is charged with a constant current of 0.1 mA / cm from the second open circuit voltage to 0.01 V. 2 It can be charged with a constant current. The current density during constant current charging is, for example, 0.2 mA / cm 2 , or 0.5 mA / cm 2 A solid-state battery having a positive electrode active material layer can be charged from a first open circuit voltage to, for example, 2.5 V, 2.0 V, 3.5 V, or 4.0 V. The maximum charge voltage of the positive electrode active material layer can be determined by the maximum voltage of the battery that satisfies the safety conditions according to JISC8712:2015 of the Japanese Standards Association.

[0182] If the initial charge capacity of the first negative electrode active material layer (22) is too small, the thickness of the first negative electrode active material layer (22) becomes very thin, so that lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) during repeated charge and discharge processes collapse 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 charge capacity of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases and the internal resistance of the all-solid-state secondary battery (1) due to the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1).

[0183] The thickness of the first negative electrode active material layer (22) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer (12). The thickness of the first negative electrode active material layer (22) is, for example, 1 to 50%, 1 to 40%, 1 to 30%, 1 to 20%, 1 to 10%, or 1 to 5% of the thickness of the positive electrode active material layer (12). The thickness of the first negative electrode active material layer (22) is, for example, 1 µm to 20 µm, 2 µm to 15 µm, or 3 µm to 10 µm. If the thickness of the first negative electrode active material layer (22) is too thin, lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) collapse the first negative electrode active material layer (22), making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the thickness of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases and the internal resistance of the all-solid-state secondary battery (1) due to the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the thickness of the first negative electrode active material layer (22) decreases, for example, the initial charge capacity of the first negative electrode active material layer (22) also decreases.

[0184] [Cathode: Second negative electrode active material layer]

[0185] Referring to FIG. 3, the all-solid-state secondary battery (1) further includes, after being charged, a second negative electrode active material layer (24) disposed, for example, between the negative electrode current collector (21) and the first negative electrode active material layer (22). The second negative electrode active material layer (24) is a metal layer containing lithium or a lithium alloy. The metal layer contains lithium or a lithium alloy. Therefore, since the second negative electrode active material layer (24) is a metal layer containing lithium, it functions as, for example, a lithium reservoir. The lithium alloy is, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, etc., but is not limited thereto, and any lithium alloy used in the art may be used. The second negative electrode active material layer (24) may be made of one of these alloys or lithium, or may be made of several types of alloys. The second negative electrode active material layer (24) is, for example, a plated layer. The second negative electrode active material layer (24) is deposited between the first negative electrode active material layer (22) and the negative electrode current collector (21), for example, during the charging process of an all-solid-state secondary battery (1).

[0186] The thickness of the second negative electrode active material layer (24) is not limited, but is, for example, 1 ㎛ to 500 ㎛, 1 ㎛ to 200 ㎛, 1 ㎛ to 150 ㎛, 1 ㎛ to 100 ㎛, or 1 ㎛ to 50 ㎛. If the thickness of the second negative electrode active material layer (24) is too thin, it is difficult for the second negative electrode active material layer (24) to perform the role of a lithium reservoir. If the thickness of the second negative electrode active material layer (24) is too thick, the mass and volume of the all-solid-state secondary battery (1) may increase, and the cycle characteristics of the all-solid-state secondary battery (1) may rather deteriorate.

[0187] Alternatively, in the all-solid-state secondary battery (1), the second negative electrode active material layer (24) may be disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22), for example, before assembling the all-solid-state secondary battery (1). When 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) acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil may 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).

[0188] When the second negative electrode active material layer (24) is precipitated by charging after assembling the all-solid-state secondary battery (1), the energy density of the all-solid-state secondary battery (1) increases because the second negative electrode active material layer (24) is not included when assembling the all-solid-state secondary battery (1). When charging the all-solid-state secondary battery (1), the charging is performed in excess of the charging capacity of the first negative electrode active material layer (22). That is, the first negative electrode active material layer (22) is overcharged. At the initial stage of charging, lithium is absorbed into the first negative electrode active material layer (22). The negative electrode active material included in the first negative electrode active material layer (22) forms an alloy or compound with the lithium ions that have moved from the positive electrode (10). When charging exceeds the capacity of the first negative electrode active material layer (22), for example, lithium is deposited on the back surface of the first negative electrode active material layer (22), that is, 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) is formed by the deposited lithium. The second negative electrode active material layer (24) is a metal layer mainly composed of lithium (i.e., metallic lithium). This result is obtained, for example, by the negative electrode active material included in the first negative electrode active material layer (22) including 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), that is, the metal layer, is ionized and moves toward the positive electrode (10). Therefore, it is possible to use lithium as the negative electrode active material in an all-solid-state secondary battery (1). In addition, since the first negative electrode active material layer (22) covers the second negative electrode active material layer (24), it acts as a protective layer for the second negative electrode active material layer (24), i.e., the metal layer, and at the same time, it suppresses the precipitation and growth of lithium dendrites. Accordingly, it suppresses short circuits and capacity reduction of the all-solid-state secondary battery (1), and consequently improves the cycle characteristics of the all-solid-state secondary battery (1).In addition, when the second negative electrode active material layer (24) is disposed by charging after assembling the all-solid-state secondary battery (1), the negative electrode (20), i.e., the negative electrode current collector (21) and the first negative electrode active material layer (22) and the region between them are Li-free regions that do not contain lithium (Li) in the initial state or the state after complete discharge of the all-solid-state secondary battery (1).

[0189] [Cathode: Negative current collector]

[0190] The negative electrode current collector (21) is composed of, for example, a material that does not react with lithium, i.e., does not form an alloy or a compound. The material constituting the negative electrode current collector (21) is, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), but is not necessarily limited thereto, and any material that can be used as an electrode current collector in the relevant technical field can be used. The negative electrode current collector (21) may be composed of one type of the above-described metal, or may be composed of an alloy or a coating material of two or more types of metals. The negative electrode current collector (21) is, for example, in the form of a plate or foil.

[0191] Referring to FIG. 2, the all-solid-state secondary battery (1) may further include a thin film (23) containing an element capable of forming an alloy with lithium on one surface of the negative electrode collector (21). The thin film (23) is disposed between the negative electrode collector (21) and the first negative electrode active material layer (22). The thin film (23) contains, for example, an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium includes, but is not limited to, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and any element capable of forming an alloy with lithium in the art may be used. The thin film (23) is composed of one of these metals or an alloy of several types of metals. By placing the thin film (23) on one surface of the negative electrode current collector (21), for example, the deposition shape of the second negative electrode active material layer (24) deposited between the thin film (23) and the first negative electrode active material layer (22) becomes flatter, and the cycle characteristics of the all-solid-state secondary battery (1) can be further improved.

[0192] The thickness of the thin film (23) is, for example, 1 nm to 800 nm, 10 nm to 700 nm, 50 nm to 600 nm, or 100 nm to 500 nm. If the thickness of the thin film (23) is less than 1 nm, it may be difficult for the function of the thin film (23) to be exerted. If the thickness of the thin film (23) is excessively thick, the thin film (23) itself absorbs lithium, which reduces the amount of lithium precipitated from the negative electrode, thereby lowering the energy density of the solid-state battery and deteriorating the cycle characteristics of the all-solid-state secondary battery (1). The thin film (23) may be disposed on the negative electrode current collector (21) by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like, but is not necessarily limited to these methods, and any method capable of forming the thin film (23) in the relevant technical field may be used.

[0193] Although not shown in the drawing, the negative electrode current collector (21) may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The polymer may be an insulating polymer. Since the base film includes an insulating thermoplastic polymer, when a short circuit occurs, the base film may soften or liquefy, thereby blocking battery operation and suppressing a rapid increase in current. The metal layer may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or an alloy thereof. The negative electrode current collector (21) may additionally include a metal piece and / or a lead tab. For more specific details regarding the base film, metal layer, metal chip, and lead tab of the negative electrode collector (21), refer to the positive electrode collector (11) described above. By having this structure, the negative electrode collector (21) can reduce the weight of the negative electrode, and consequently, improve the energy density of the negative electrode and lithium battery.

[0194] [Solid electrolyte layer]

[0195] [Solid electrolyte layer: electrolyte]

[0196] Referring to FIGS. 1 to 5, a solid electrolyte layer (30) is disposed between the positive electrode (10) and the negative electrode (20). The solid electrolyte layer (30) may further include, for example, a solid electrolyte, a gel electrolyte, or a combination thereof.

[0197] The solid electrolyte contained in the solid electrolyte layer is a sulfide-based solid electrolyte.

[0198] The solid electrolyte additionally included in the solid electrolyte layer (30) may include, for example, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof.

[0199] Oxide solid electrolytes include, for example, Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x<2, 0<y<1, 0<z<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1 0≤y≤1), Li x La y TiO3(0 <x<2, 0<y<3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2, Li 3+x La3M2O 12 (M = Te, Nb, or Zr, 0≤x≤10), or a combination thereof. The oxide-based solid electrolyte is manufactured, for example, by a sintering method.

[0200] Oxide-based solid electrolytes include, for example, Li7La3Zr2O12 (LLZO) and Li 3+x La3Zr 2-a M a O 12 (M doped LLZO, M=Ga, W, Nb, Ta, or Al, 0 <a<2, 0≤x≤10) 중에서 선택된 가넷계(Garnet-type) 고체전해질이다.

[0201] The polymer solid electrolyte may, for example, comprise a mixture of a lithium salt and a polymer, or a polymer having ion-conducting functional groups. The polymer solid electrolyte may be, for example, a polymer electrolyte that is solid at 25°C and 1 atm. The polymer solid electrolyte may not, for example, comprise a liquid.The polymer solid electrolyte comprises a polymer, and the polymer is, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), 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), polymethyl methacrylate (PMMA, poly(methylmethacrylate), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polyethylenedioxythiophene (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(benzimidazobenzisoquinolinones)] (SPBIBI), poly(styrene sulfonate) (PSS), lithium 9,10-Diphenylanthracene-2-sulfonate (lithium 9,10-diphenylanthracene-2-sulfonate, DPASLi. +) or a combination thereof, but is not limited thereto, and any lithium salt that can be used in polymer electrolytes in the relevant technical field is possible. The lithium salt can be any lithium salt that can be used in the relevant technical field. The lithium salt is, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are each 1 to 20), LiCl, LiI or a mixture thereof, etc. The polymer included in the polymer solid electrolyte may be, for example, a compound including 10 or more, 20 or more, 50 or more or 100 or more repeating units. The weight average molecular weight of the polymer included in the polymer solid electrolyte may be, for example, 1000 Dalton or more, 10,000 Dalton or more, 100,000 Dalton or more or 1,000,000 Dalton or more.

[0202] A gel electrolyte is, for example, a polymer gel electrolyte. A gel electrolyte can have a gel state without containing a polymer, for example.

[0203] A polymer gel electrolyte may include, for example, a liquid electrolyte and a polymer, or an organic solvent and a polymer having an ion-conducting functional group. The polymer gel electrolyte may be, for example, a polymer electrolyte that is in a gel state at 25°C and 1 atm. The polymer gel electrolyte may, for example, have a gel state without containing a liquid. The liquid electrolyte used in the polymer gel electrolyte may be, for example, an ionic liquid, a mixture of a lithium salt and an organic solvent; a mixture of a lithium salt and an organic solvent; a mixture of an ionic liquid and an organic solvent; or a mixture of a lithium salt, an ionic liquid, and an organic solvent. The polymer used in the polymer gel electrolyte may be selected from among the polymers used in solid polymer electrolytes. The organic solvent may be selected from among the organic solvents used in liquid electrolytes. The lithium salt may be selected from among the lithium salts used in solid polymer electrolytes. An ionic liquid refers to a salt that has a melting point below room temperature, is composed solely of ions, and is liquid at room temperature or a molten salt at room temperature. The ionic liquid may include, for example, one or more cations selected from among a) ammonium compounds, pyrrolidinium compounds, pyridinium compounds, pyrimidinium compounds, imidazolium compounds, piperidinium compounds, pyrazolium compounds, oxazolium compounds, pyridazinium compounds, phosphonium compounds, sulfonium compounds, triazolium compounds, and mixtures thereof, and b) one or more anions selected from among BF4-, PF6-, AsF6-, SbF6-, AlCl4-, HSO4-, ClO4-, CH3SO3-, CF3CO2-, Cl-, Br-, I-, SO4-, CF3SO3-, (FSO2)2N-, (C2F5SO2)2N-, (C2F5SO2)(CF3SO2)N-, and (CF3SO2)2N-. A polymer solid electrolyte can form a polymer gel electrolyte, for example, by being impregnated into a liquid electrolyte in a secondary battery. The polymer gel electrolyte may further include inorganic particles. The polymer included in the polymer gel electrolyte may be, for example, a compound containing 10 or more, 20 or more, 50 or more, or 100 or more repeating units.The weight average molecular weight of the polymer included in the polymer gel electrolyte may be, for example, 500 Dalton or more, 1000 Dalton or more, 10,000 Dalton or more, 100,000 Dalton or more, or 1,000,000 Dalton or more.

[0204] [Cathode manufacturing method]

[0205] To manufacture the positive electrode, a carbon coating layer is first formed on the positive electrode current collector.

[0206] Next, an intermediate layer containing an adhesive polymer is further formed on top of the carbon coating layer. The intermediate layer improves the adhesion between the carbon coating layer disposed on the positive electrode current collector and the positive electrode active material layer.

[0207] Separately, the present invention includes a step of providing a Li2S-containing complex; a step of providing a sulfide-based solid electrolyte; a step of preparing a mixture by mixing the Li2S-containing complex and the sulfide-based solid electrolyte; and a step of preparing a positive electrode by coating and drying the mixture on the carbon coating layer.

[0208] As a Li2S-containing complex, a complex of Li2S and a lithium salt or a complex of Li2S, a lithium salt and a carbon-based material can be provided.

[0209] A complex of Li2S and a lithium salt can be prepared, for example, by mechanically milling Li2S and a lithium salt. The milling conditions are not limited, and any conditions that can form a complex of Li2S and a lithium salt can be used. A complex of Li2S and a lithium salt can be prepared by placing Li2S particles and a lithium salt in a ball mill and stirring at a speed of 100 to 1,000 rpm for 1 to 20 hours. The stirring can be performed more than once.

[0210] As lithium salts, 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 combinations thereof can be used.

[0211] A composite of Li2S, a lithium salt, and a carbon-based material can be manufactured, for example, through a step of mechanically milling Li2S and a lithium salt; a step of adding a carbon-based material to the milled product, and milling the same.

[0212] A sulfide-based solid electrolyte is provided. A mixture is prepared by mixing a Li2S-lithium salt complex and the sulfide-based solid electrolyte.

[0213] The mixing ratio of the Li2S-containing complex and the sulfide-based solid electrolyte may be, for example, a weight ratio of 50:50 to 95:5, 50:50 to 90:10, 50:50 to 80:20, or 50:50 to 70:30.

[0214] The mixture may additionally include a process solvent. By additionally including a process solvent, the mixture may take the form of a slurry. The solvent may be, for example, octyl acetate, but is not limited thereto, and any solvent used in the art may be used. Alternatively, the mixture may be prepared dry without including a process solvent.

[0215] The above intermediate layer is formed using an intermediate layer forming composition containing an adhesive polymer.

[0216] The method for forming the intermediate layer using polydopamine as an example of the adhesive polymer is as follows.

[0217] According to one embodiment, a composition for forming a polydopamine layer containing dopamine, a solvent, and a buffer solution is prepared. Dopamine is converted into polydopamine through a self-polymerization reaction at a pH of about 8 to 8.8, for example, about 8.5.

[0218] The pH of the composition for forming the above polydopamine layer is 8.0 to 8.8, for example, about 8.5.

[0219] A buffer solution is a solution with a pH of about 8 to 8.8, and examples of buffer solutions that can be used include a buffer solution containing Tris-HCl and water (the volume ratio of HCl and H2O is 3:1), Tris borate ethylene diamine tetra-acetic acid (TBE), Tris-buffered saline (TBS), and phosphate-buffered saline (PBS).

[0220] The solvent used herein is a substance that does not affect the pH of the composition, such as an alcohol-based compound. Examples of alcohol-based compounds include ethanol, methanol, butanol, and isopropanol. The solvent content is, for example, in the range of 100 to 3,000 parts by weight based on 100 parts by weight of dopamine.

[0221] The above drying is carried out, for example, in the range of 20 to 25°C.

[0222] The above coating may be applied by dipping, spray coating, bar coating, die casting, comma coating, screen printing, etc. In addition, it is also possible to form the coating on a separate substrate and then bond it to the anode by pressing or lamination. The coating according to one embodiment refers to the spray coating method.

[0223] In another embodiment, a dopamine monomer, a polydopamine precursor, is dissolved in an acid such as HCl to prepare a composition containing an adhesive polymer. A positive electrode current collector having a carbon coating layer is immersed in the composition. The resulting composition-coated electrode is then washed and dried to form an intermediate layer on the surface of the carbon coating layer.

[0224] According to another embodiment, a polydopamine coating layer composition is prepared in which polydopamine is dispersed in a distilled water buffer solution. This is coated on the carbon coating layer of the positive electrode current collector on which the carbon coating layer is formed, and dried to form a polydopamine coating layer, thereby forming an intermediate layer on the surface of the positive electrode current collector. The coating may be performed by dipping, spray coating, bar coating, die casting, comma coating, screen printing, or the like.

[0225] The above drying is carried out at, for example, 30 to 90°C, for example, 80°C.

[0226] The present invention is explained in more detail through the following examples and comparative examples. However, the examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0227] (Manufacture of a complex of Li2S and lithium salt)

[0228] Manufacturing Example 1: Li2S-LiI complex

[0229] Li2S and LiI were mixed at a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 600 rpm, and 10 h.

[0230] The size of the Li2S-LiI complex was less than 1 μm. The size of the Li2S-LiI complex was calculated by software from scanning electron microscope images of the Li2S-LiI complex powder. The size of the Li2S-LiI complex is the average particle diameter of D50.

[0231] The Mohs hardness of Li2S was 0.6, and that of LiI was 2.0. The Mohs hardness of the Li2S-LiI composite was less than 2.

[0232] Manufacturing Example 2: Li2S-LiBr complex

[0233] A Li2S-LiBr complex was prepared in the same manner as in Preparation Example 1, except that LiBr was used instead of LiI.

[0234] Manufacturing Example 3: Li2S-LiCl complex

[0235] A Li2S-LiCl complex was prepared in the same manner as in Preparation Example 1, except that LiCl was used instead of LiI.

[0236] Comparative Manufacturing Example 1: Simple mixture of Li2S and LiI

[0237] A mixture of Li2S and LiI with a weight ratio of 30:20 was used as is.

[0238] (Manufacture of Li2S-LiI-CNF cathode active material)

[0239] Manufacturing Example 4: Li2S-LiI-CNF (50:30:20)

[0240] (Stage 1)

[0241] Li2S and LiI were mixed in a weight ratio of 50:30. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was approximately 28 G.

[0242] (Stage 2)

[0243] Li2S-LiI composite and carbon nanofiber (CNF) were mixed at a weight ratio of 80:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI-CNF composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 28 G. The Li2S-LiI-CNF composite was used as a composite cathode active material.

[0244] Manufacturing Example 5: Li2S-LiI-CNF, 2 steps, 8 hr, 600 rpm, 28G

[0245] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 4, except that the milling time in the first and second steps was changed to about 8 hours.

[0246] Manufacturing Example 6: Li2S-LiI-CNF, 2 steps, 6 hr, 600 rpm, 28G

[0247] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 4, except that the milling time in the first and second steps was changed to about 6 hours.

[0248] Manufacturing Example 7: Li2S-LiI-CNF, 2 steps, 4 hr, 600 rpm, 28G

[0249] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 4, except that the milling time in the first and second steps was changed to about 4 hours.

[0250] Comparative Manufacturing Example 2: Simple mixture of Li2S, LiI, and CNF

[0251] A mixture of Li2S, LiI, and CNF in a weight ratio of 50:30:20 was used as is.

[0252] Comparative Manufacturing Example 3: Li2S-LiI-CNF, 2 steps, 1 hr, 600 rpm, 28G

[0253] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 4, except that the milling time in the first and second steps was changed to 1 hour.

[0254] Comparative Manufacturing Example 4: Li2S-LiI-CNF, 2 steps, 20 hr, 600 rpm, 28G

[0255] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 4, except that the milling time in the first and second steps was changed to 20 hours.

[0256] Comparative Manufacturing Example 5: Li2S-LiI-CNF, 510 rpm, 10 hr, 2 stages, 20G (KR 2017-0068448 (Tatsumi Sago), (1st stage)

[0257] A first mixture was prepared by mixing Li2S and LiI in a weight ratio of 30:20. The first mixture was mechanically milled using a ball mill to prepare a Li2S-LiI complex.

[0258] Milling conditions were 25°C, 510 rpm for 10 hours. The milling energy applied to the sample during milling was 20 G.

[0259] (Stage 2)

[0260] A second mixture was prepared by mixing the Li2S-LiI complex and carbon nanofibers (CNF) at a weight ratio of 50:10. The second mixture was mechanically milled using a ball mill to produce a Li2S-LiI-CNF complex.

[0261] The milling conditions were 25°C, 510 rpm, and 10 h. The milling energy applied to the sample during milling was 20 G. The Li2S-LiI-CNF composite was used as the composite cathode active material.

[0262] Comparative Manufacturing Example 6: Li2S-LiI-CNF, 10 hr, 2 steps, 10 G

[0263] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 4, except that the rotation speed was reduced in the first and second steps and the milling energy was changed to 10 G.

[0264] Comparative Manufacturing Example 7: Li2S-LiI-CNF, 10 hr, 2 steps, 30 G

[0265] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 4, except that the rotation speed was increased in the first and second steps and the milling energy was changed to 30 G.

[0266] Comparative Manufacturing Example 8: Simple mixture of Li2S and CNF

[0267] Li2S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:30. The mixture was used as a cathode active material.

[0268] Comparative Manufacturing Example 9: Li2S-CNF, 600 rpm, 2 hr, 1 step, 20 G

[0269] Li2S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:30. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 600 rpm for 2 h. The milling energy applied to the sample during milling was 20 G. The Li2S-CNF composite was used as a composite cathode active material.

[0270] Comparative Manufacturing Example 10: Li2S-CNF, 600 rpm, 10 hr, 1 step, 20 G

[0271] A Li2S-CNF composite was manufactured using the same method as in Comparative Manufacturing Example 7, except that the milling time was changed to 10 hours.

[0272] Comparative Manufacturing Example 11: Li2S-CNF-LiI, 600 rpm, 10 hr, 2 steps, 20G

[0273] (Stage 1)

[0274] Li2S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-CNF composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 20 G.

[0275] (Stage 2)

[0276] 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 a Li2S-CNF-LiI composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 20 G. The Li2S-LiI-CNF composite was used as a composite cathode active material.

[0277] Comparative Manufacturing Example 12: Li2S-SE-CNF, 600 rpm, 10 hr, 2 steps, 20G

[0278] (Stage 1)

[0279] 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 a Li2S-SE composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 20 G.

[0280] (Stage 2)

[0281] Li2S-SE composite and CNF were mixed at a weight ratio of 50:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-SE-CNF composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 20 G. The Li2S-SE-CNF composite was used as a composite cathode active material.

[0282] Comparative Manufacturing Example 13: Li2S-LiI-CNF, 600 rpm, 2 hr, 1 step, 20 G

[0283] 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 a Li2S-LiI-CNF composite. The milling conditions were 25°C, 600 rpm, and 2 h. The milling energy applied to the sample during milling was 20 G. The Li2S-LiI-CNF composite was used as a composite cathode active material.

[0284] (Manufacturing of positive electrode)

[0285] Example 1: Al current collector / Carbon / Li2S-LiI-C containing dry cathode

[0286] N-methyl-2-pyrrolidone containing 10 wt% polyvinylidene fluoride binder dissolved therein

[0287] A carbon coating layer composition was prepared by dispersing multi-walled carbon nanotubes in a solution. In the carbon coating layer composition, the content of multi-walled carbon nanotubes was 10 parts by weight, the content of NMP (e.g., N-Methylpyrrolidone or 1-methyl-2-pyrrolidinone) was 80 parts by weight, and the content of the binder was 10 parts by weight. This was applied to the surface of a 17 ㎛ thick aluminum foil current collector, which is a positive electrode current collector, and dried at a temperature of 120°C for 4 hours, thereby forming a carbon coating layer with a thickness of about 100 nm on the positive electrode current collector.

[0288] The Li2S-LiI-CNF composite manufactured in Manufacturing Example 4 was prepared as a cathode active material. Li6PS5Cl, an argyrodite-type crystal (D50=3.0 μm, crystalline), was prepared as a solid electrolyte. PTFE was prepared as a binder.

[0289] The Li2S-LiI-CNF composite and the solid electrolyte were placed in a mixer and mixed for 2 minutes. Polytetrafluoroethylene (PTFE) was added to the mixed resultant and mixed in a mixer for 20 seconds. The obtained positive electrode composite powder was kneaded and then rolled out with a roller to a thickness of 100 to 150 μm to manufacture a positive electrode. Mixing the composite and solid electrolyte first, and then adding and mixing PTFE, allows for better mixing of the composite and solid electrolyte.

[0290] The above composite cathode active material: solid electrolyte: binder was mixed in a weight ratio of 60:39:1.0 to prepare a cathode mixture. The cathode mixture was obtained by dry mixing using a ball mill.

[0291] The positive electrode was manufactured by placing the positive electrode active material on an aluminum foil having a carbon coating layer and plate pressing at a pressure of 200 MPa for 10 minutes. The thickness of the positive electrode was approximately 120 μm. The thickness of the positive electrode active material layer was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm. The areas of the positive electrode active material layer and the positive electrode current collector were the same.

[0292] Example 2: Dry cathode containing Al current collector / Carbon / polydopamine / Li2S-LiI-C

[0293] A positive electrode was manufactured in the same manner as in Example 1, except that an intermediate layer was formed on top of the carbon coating layer of Example 1 as follows and a positive electrode active material layer using a positive electrode mixture was formed on top of the intermediate layer.

[0294] A composition for forming a polydopamine layer was prepared by mixing 0.1 g of dopamine with 50 ml of a buffer solution having a pH of 8.5, and diluting the mixture with ethanol to improve viscosity and drying characteristics without affecting the pH during the process. The composition was spray-coated on the surface of the carbon coating layer through a nozzle, and dried at about 25°C to form a polydopamine layer as an intermediate layer with a thickness of about 10 nm on the carbon coating layer.

[0295] Example 3: Dry cathode containing Al current collector / Carbon / polydopamine / Li2S-LiI-C

[0296] A positive electrode was manufactured in the same manner as in Example 1, except that the weight ratio of composite positive electrode active material: solid electrolyte: binder was changed to 70:29:1.0 when manufacturing the positive electrode mixture.

[0297] Example 4: Dry cathode containing Al current collector / Carbon / polydopamine / Li2S-LiI-C

[0298] A positive electrode was manufactured in the same manner as in Example 2, except that the weight ratio of composite positive electrode active material: solid electrolyte: binder was changed to 70:29:1.0 when manufacturing the positive electrode mixture.

[0299] Example 5: Dry cathode containing Al current collector / Carbon / Li-PAA / Li2S-LiI-C composite

[0300] A positive electrode was manufactured in the same manner as in Example 1, except that lithium polyacrylate (Li-PAA) was used instead of polydopamine when forming the intermediate layer.

[0301] Comparative Example 1: Dry cathode containing Al current collector / Li2S-LiI-C composite

[0302] An anode was manufactured in the same manner as in Example 1, except that aluminum foil was used instead of the aluminum foil having a carbon coating layer.

[0303] Comparative Example 2: Dry cathode containing a simple mixture of Al current collector / Li2S and LiI and CNF

[0304] A positive electrode was manufactured in the same manner as in Example 1, except that a simple mixture of Li2S, LiI, and CNF prepared in Comparative Manufacturing Example 2 was used instead of the Li2S-LiI-C complex manufactured in Manufacturing Example 4.

[0305] Comparative Example 3: Al current collector / polydopamine layer / carbon coating layer / Li2S-LiI-C containing cathode

[0306] In Example 2, an anode was manufactured in the same manner as in Example 1, except that the stacking order of the intermediate layer and the carbon coating layer was reversed.

[0307] The positive electrode manufactured according to Comparative Example 3 had a polydopamine layer positioned between the current collector and the carbon coating layer, making it difficult to suppress the side reaction of the sulfide-based solid electrolyte between the carbon coating layer and the positive electrode active material layer.

[0308] Reference Example 1: Positive electrode current collector / polydopamine layer / positive electrode active material layer / SE / Ag / C negative electrode layer

[0309] A positive electrode was manufactured in the same manner as in Example 1, except that an intermediate layer was formed on top of aluminum foil as follows and a positive electrode active material layer using a positive electrode mixture was formed on top of the intermediate layer.

[0310] A composition for forming a polydopamine layer was prepared by mixing 0.1 g of dopamine with 50 ml of a buffer solution having a pH of 8.5, and diluting the mixture with ethanol to improve viscosity and drying characteristics without affecting the pH during the process. The composition was spray-coated on the surface of aluminum foil through a nozzle, and dried at about 25°C to form a polydopamine layer with a thickness of about 10 nm, thereby forming a structure in which a positive electrode collector / polydopamine layer / positive electrode active material layer are laminated.

[0311] (Manufacturing of all-solid-state secondary batteries)

[0312] Example 6: Al current collector / Carbon / Li2S-LiI-C containing dry cathode / sulfide-based solid electrolyte (SE) / Ag-C coated SUS

[0313] (Polar electrode manufacturing)

[0314] The positive electrode of Example 1 was used.

[0315] (Cathode manufacturing)

[0316] A 10 ㎛ thick SUS foil was prepared as a negative electrode collector. Carbon black (CB) with a primary particle diameter of approximately 30 nm and silver (Ag) particles with an average particle diameter of approximately 60 nm were prepared as negative electrode active materials.

[0317] A mixed powder of 4 g of carbon black (CB) and silver (Ag) particles in a weight ratio of 3:1 was placed in a container, and 4 g of an NMP solution containing 7 wt% of PVDF binder (Kureha #9300) was added thereto to prepare a mixed solution. A slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution. The prepared slurry was applied to a SUS sheet using a bar coater, dried in air at 80°C for 10 minutes, and then vacuum-dried at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold roll pressed to flatten the surface, thereby preparing a negative electrode having a first negative electrode active material layer / negative electrode current collector structure. The thickness of the first negative electrode active material layer was approximately 15 μm. The areas of the first negative electrode active material layer and the negative electrode current collector were the same.

[0318] (Manufacturing of solid electrolyte layer)

[0319] Li6PS5Cl solid electrolyte in the form of argyrodite crystals (D 50=3.0 ㎛, crystalline), and 1.5 parts by weight of an acrylic binder was added to 98.5 parts by weight of the solid electrolyte to prepare a mixture. Octyl acetate was added to the prepared mixture and stirred to prepare a slurry. The prepared slurry was applied using a bar coater on a 15 ㎛ thick nonwoven fabric placed on a 75 ㎛ thick PET substrate, and dried in air at 80°C for 10 minutes to prepare a laminate. The prepared laminate was vacuum-dried at 80°C for 2 hours to prepare a solid electrolyte layer.

[0320] (inert absence)

[0321] A flame-retardant inert member was manufactured by forming a slurry containing pulp fiber (cellulose fiber), glass fiber, aluminum hydroxide (Al(OH)3), an acrylic binder, and a solvent into a gasket shape and then removing the solvent.

[0322] The weight ratio of pulp fiber (cellulose fiber), glass fiber, aluminum hydroxide (Al(OH)3), and acrylic binder was 20:8:70:2. The thickness of the inert material was 120 ㎛.

[0323] Before placing the manufactured flame-retardant inert material on the solid electrolyte layer, moisture, etc. of the flame-retardant inert material was removed by vacuum heat treatment at 80°C for 5 hours.

[0324] (Manufacturing of all-solid-state secondary batteries)

[0325] Referring to Fig. 4, a solid electrolyte layer was placed on the negative electrode such that the first negative electrode active material layer was in contact with the solid electrolyte layer, and a positive electrode was placed on the solid electrolyte layer. A laminate was prepared by placing a gasket surrounding the positive electrode and in contact with the solid electrolyte layer. The thickness of the gasket was approximately 120 ㎛. The above-described flame-retardant inert material was used as the gasket. The gasket was placed so as to be in contact with the side surface of the positive electrode and the solid electrolyte layer. The positive electrode was placed at the center of the solid electrolyte layer, and the gasket was placed so as to surround the positive electrode and extend to the end of the solid electrolyte layer. The area of ​​the positive electrode was approximately 90% of the area of ​​the solid electrolyte layer, and the gasket was placed on the entire remaining 10% of the area of ​​the solid electrolyte layer where the positive electrode was not placed.

[0326] 85 prepared laminates o The solid electrolyte layer was plate-pressed at 500 MPa for 30 min at C. This pressurization process sintered the solid electrolyte layer, thereby improving battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 ㎛. The density of the Li6PS5Cl solid electrolyte, which was an argyrodite-type crystal contained in the sintered solid electrolyte layer, was 1.6 g / cc. The area of ​​the solid electrolyte layer was the same as that of the negative electrode.

[0327] The pressurized laminate was placed in a pouch and vacuum-sealed to manufacture an all-solid-state secondary battery. Portions of the positive and negative current collectors were extended outside the sealed battery to serve as positive and negative terminals.

[0328] Examples 7 to 10

[0329] An all-solid-state secondary battery was manufactured in the same manner as in Example 6, except that the positive electrodes manufactured in Examples 2 to 5 were used.

[0330] Comparative examples 4 to 6:

[0331] An all-solid-state secondary battery was manufactured in the same manner as Example 6, except that the positive electrodes manufactured in Comparative Examples 1 to 3 were used.

[0332] Reference Example 2

[0333] An all-solid-state secondary battery was manufactured in the same manner as Example 6, except that the positive electrode manufactured in Reference Example 1 was used.

[0334] Evaluation Example 1: XRD Analysis and Scanning Electron Microscopy Analysis

[0335] XRD spectra were measured using Cu Kα radiation for the raw material (bare) Li2S used in Manufacturing Example 1, the pulverized Li2S, and the Li2S-LiI-C composite manufactured in Manufacturing Example 4. The measurement results are shown in Table 1 below.

[0336] The Li2S crystallite size and lattice constant were derived from the first peak for the (111) crystal plane appearing at a diffraction angle of 2θ= 27° ± 2.0° in the XRD spectrum.

[0337] Crushed Li2S was prepared by milling under the same conditions as in Manufacturing Example 4, except that the 50:30:20 weight ratio mixture of Li2S, LiI, and CNF was changed to 100 parts by weight of Li2S.

[0338] The particle size (i.e., D50 particle diameter) of the composites was measured using a laser-based particle size analyzer (PSA) for the raw material (bare) Li2S used in Manufacturing Example 1, the pulverized Li2S, and the Li2S-LiI-CNF composite manufactured in Manufacturing Example 4, and the Li2S particle size of the composites was measured using a scanning electron microscope. The measurement results are shown in Table 1 below.

[0339] Li2S crystallite size [nm]Li2S particle size [㎛]bare Li2S658milled Li2S15-Li2S-LiI-C compositeless than10less than1

[0340] As shown in Table 1, the particle size and crystallite size of the Li2S-LiI-CNF composite were significantly reduced compared to Li2S. The Li2S-LiI-CNF composite contained a Li2S-LiI solid solution, the size of the Li2S crystallites was less than 9.9 nm, and the Li2S particle size of the composite was about 2 μm or less.

[0341] Although not shown in Table 1, the lattice constant of the Li2S-LiI-CNF composite of Preparation Example 1 was larger than that of bare Li2S. The increase in the lattice constant of the Li2S-LiI-CNF composite compared to that of bare Li2S was thought to be due to the dissolution of LiI within the Li2S crystal. Therefore, it was confirmed that the Li2S-LiI-CNF composite formed a solid solution.

[0342] Although not shown in Table 1, the particle size of the Li2S-LiI-CNF composite of Manufacturing Example 1 was approximately 5 μm.

[0343] Evaluation Example 2: XRD Analysis and Scanning Electron Microscopy Analysis

[0344] XRD spectra were measured using Cu Kα radiation for the composite cathode active materials (i.e., composites) manufactured in Manufacturing Examples 4 to 7 and Comparative Manufacturing Examples 3 to 13. The Li2S crystallite sizes calculated from the first peak for the (111) crystal plane appearing at a diffraction angle of 2θ = 27° ± 2.0° in the measured XRD spectra are shown in Table 2 below. The crystallite sizes were calculated using the Sherrer Equation.

[0345] The Li2S particle sizes of the composite cathode active materials manufactured in Manufacturing Examples 4 to 7 and Comparative Manufacturing Examples 3 to 13 were measured using a scanning electron microscope. The Li2S particle size of the composite cathode active material is the arithmetic mean of the particle sizes of multiple Li2S particles measured using software from scanning electron microscope images. The measurement results are shown in Table 2 below.

[0346] Classification 1st stage milling 2nd stage milling Solid solution formation Li2S crystallite size [nm] Li2S particle size [㎛] Manufacturing example 4 (28 G, 10 hr) (Li2S-LiI-CNF complex) 600 rpm, 28 G, 10 hr 600 rpm, 28 G, 10 hr ○ Less than 9.81 Manufacturing example 5 (28 G, 8 hr) (Li2S-LiI-CNF complex) 600 rpm, 28 G, 8 hr 600 rpm, 28 G, 8 hr ○ Less than 7.21 Manufacturing example 6 (28 G, 6 hr) (Li2S-LiI-CNF complex) 600 rpm, 28 G, 6 hr 600 rpm, 28 G, 6 hr ○ Less than 8.21 Manufacturing example 7 (28 G, 4 hr)(Li2S-LiI-CNF complex)600 rpm, 28 G, 4 hr600 rpm, 28 G, 4 hr○9.51 Less than Comparative Manufacturing Example 3 (28 G, 1 hr)(Li2S-LiI-CNF complex)600 rpm, 28 G, 1 hr600 rpm, 28 G, 1 hr○20.11 Less than Comparative Manufacturing Example 4 (28 G, 20 hr)(Li2S-LiI-CNF complex)600 rpm, 28 G, 20 hr600 rpm, 28 G, 20 hr△11.81 Less than Comparative Manufacturing Example 5 (Li2S-LiI-CNF complex)510 rpm, 20 G, 10 hr510 rpm, 20 G, 10 hr○9.91 Less than Comparative Manufacturing Example 6 (7 G, 10 hr)(Li2S-LiI-CNF complex)300 rpm, 7 G, 10 hr300 rpm, 7 G, 10 hr×27.23Comparative Manufacturing Example 7(38 G, 10 hr)(Li2S-LiI-CNF complex)700 rpm, 38 G, 10 hr700 rpm, 38 G, 10 hr△15.62Comparative Manufacturing Example 8(0 G)(Li2S+ CNF simple mixture)--×66.678Comparative Manufacturing Example 9(28 G, 1 hr)(Li2S-CNF complex)600 rpm, 20 G, 2 hr-×24.073Comparative Manufacturing Example 10(28 G, 10 hr)(Li2S-CNF complex)600 rpm, 20 G, 10 hr-×9.Less than 891 Comparative Manufacturing Example 11 (28 G, 10 hr) (Li2S-CNF-LiI complex) 600 rpm, 28 G, 10 hr 600 rpm, 28 G, 10 hr × 15.22 Comparative Manufacturing Example 12 (28 G, 10 hr) (Li2S-SE-CNF complex) 600 rpm, 28 G, 10 hr 600 rpm, 28 G, 10 hr × 8.91 Less than Comparative Manufacturing Example 13 (28 G, 2 hr) (Li2S-LiI-CNF complex) 600 rpm, 20 G, 2 hr - ○223.

[0347] As shown in Table 2, the Li2S-LiI-CNF composites of Preparation Examples 4 to 7 included a Li2S-LiI solid solution, the size of the Li2S crystallites was less than 9.9 nm, and the Li2S particle size of the composite was 2 μm or less.

[0348] In the Li2S-LiI-CNF composite of Comparative Manufacturing Example 3, the size of the Li2S crystallites was 9.9 nm or more due to the reduction in milling energy during manufacturing.

[0349] In the Li2S-LiI-CNF composite of Comparative Manufacturing Example 4, as the milling energy increased during manufacturing, LiI was phase separated into a separate phase, a solid solution was not formed, and the size of the Li2S crystallites also increased.

[0350] The Li2S-LiI-CNF composite of Comparative Manufacturing Example 6 failed to form a Li2S-LiI solid solution because the milling energy was excessively reduced during manufacturing.

[0351] In the Li2S-LiI-CNF composite of Comparative Manufacturing Example 7, a Li2S-LiI solid solution was not properly formed due to heat generation caused by increased milling energy during manufacturing.

[0352] The Li2S-LiI-CNF composite of Comparative Manufacturing Example 13 was manufactured in the first step, so it included a Li2S-LiI solid solution, but the Li2S crystallite size increased, and the Li2S particle size of the composite exceeded 2 μm.

[0353] The simple mixture of Li2S and CNF of Comparative Manufacturing Example 8 and the complexes of Comparative Manufacturing Examples 9, 10, and 12 did not form a solid solution.

[0354] In the Li2S-CNF-LiI complex of Comparative Manufacturing Example 11, a Li2S-LiI solid solution was not properly formed because the Li2S-CNF complex was manufactured in the first step and then the Li2S-CNF-LiI complex was manufactured in the second step.

[0355] Evaluation Example 3: Charge / Discharge Test

[0356] The charge / discharge characteristics of the all-solid-state secondary batteries manufactured in Examples 6 to 10, Comparative Examples 4 to 6, and Reference Example 2 were evaluated by the following charge / discharge test.

[0357] Charge and discharge tests were performed by placing the solid secondary battery in a constant temperature bath at 45°C.

[0358] The first cycle involved charging for 20 hours at a constant current of 0.05 C until the battery voltage reached 2.8 V. Subsequently, discharging was performed for 20 hours at a constant current of 0.05 C until the battery voltage reached 1.0 V.

[0359] Charge and discharge tests were performed by placing the solid secondary battery in a constant temperature bath at 45°C.

[0360] The second cycle was charged and discharged under the same conditions as the first cycle.

[0361] The second cycle discharge capacity was set as the standard capacity.

[0362] The third cycle involved charging for 10 hours at a constant current of 0.1 C until the battery voltage reached 2.8 V. Subsequently, discharging was performed for 10 hours at a constant current of 0.1 C until the battery voltage reached 1.0 V. Afterwards, charging and discharging were performed for up to 23 cycles under the same conditions as the third cycle. The measurement results are shown in Table 3 below.

[0363] The initial efficiency is expressed by Equation 1 below, and the capacity retention rate is expressed by Equation 2 below.

[0364] <Formula 1>

[0365] Initial efficiency [%] = [1st cycle discharge capacity / 1st cycle charge capacity] × 100

[0366] <Formula 2>

[0367] Capacity retention rate (%) = [23rd cycle discharge capacity / 3rd cycle discharge capacity] × 100

[0368] Classification 0.05C Discharge capacity (mAh) Initial efficiency (%) Capacity retention rate (%) (20 times) Example 6 (Al current collector / Carbon / Li2S-LiI-C containing dry cathode) (Weight ratio of composite cathode active material: solid electrolyte: binder = 60:39:1.0) 96175.8 86.5 Example 7 (Al current collector / Carbon / polydopamine layer / Li2S-LiI-C containing dry cathode) (Weight ratio of composite cathode active material: solid electrolyte: binder = 60:39:1.0) 97282.68 8.9 Example 8 (Al current collector / Carbon / Li2S-LiI-C containing dry cathode) (Weight ratio of composite cathode active material: solid electrolyte: binder = 70:29:1.0) 96879.2 85.2 Example 9 (Al current collector / Carbon / Polydopamine layer / Li2S-LiI-C containing dry cathode) (Weight ratio of composite cathode active material:solid electrolyte:binder = 70:29:1.0) 97784.8 87.7 Example 10 (Al current collector / Carbon / Li-PAA / Li2S-LiI-C composite containing dry cathode) 97982.289.1 Comparative Example 4 (Al current collector / Li2S-LiI-C composite containing dry cathode) 70972.659.1 Comparative Example 5 (Al current collector / Li2S and LiI and simple mixture of CNF containing dry cathode) 32256.479.2 Comparative Example 6 (Al current collector / Polydopamine layer / Carbon coating layer / Li2S-LiI-C Containing positive electrode) 86880.281.2 Reference example 2 (positive electrode current collector / polydopamine layer / positive electrode active material layer) 57673.270.2

[0369] As shown in Table 3, the all-solid-state secondary batteries of Examples 6 to 10 employing the positive electrodes of Examples 1 to 5 showed improved life characteristics compared to the all-solid-state secondary batteries of Comparative Examples 4 to 6 employing the positive electrodes of Comparative Examples 1 to 3 and the all-solid-state secondary battery of Reference Example 2. The all-solid-state secondary batteries of Examples 7 to 9 having an intermediate layer containing polydopamine and the all-solid-state secondary battery of Example 10 having an intermediate layer containing lithium polyacrylate improved discharge capacity due to improved adhesion between the positive electrode current collector and the positive electrode active material layer, and even when charge and discharge were repeated during the cycle, stable contact between the positive electrode current collector and the positive electrode active material layer was achieved without delamination of the positive electrode active material, thereby improving capacity retention.

[0370] Although not shown in the drawing, it was confirmed that a lithium metal layer, which is a second negative electrode active material layer, was formed between the first negative electrode active material layer and the negative electrode current collector after the initial charge in the all-solid-state secondary batteries of Examples 6 to 10. This was confirmed through a cross-sectional scanning electron microscope image of the all-solid-state secondary battery. In addition, it was confirmed in a scanning electron microscope image of a cross-section of the solid electrolyte layer that a Li2S-LiI-CNF complex was arranged in the gaps between a plurality of sulfide-based solid electrolyte particles.

[0371] Evaluation Example 4: Rate-limiting characteristic evaluation

[0372] The rate characteristics of the all-solid-state secondary batteries of Examples 6 to 10 employing the positive electrodes manufactured in Examples 1 to 5 and the all-solid-state secondary batteries of Comparative Examples 4 to 6 employing the positive electrodes manufactured in Comparative Examples 1 to 3 were evaluated by the following charge-discharge test. The charge-discharge test was performed by placing the all-solid-state secondary batteries in a constant temperature bath at 45°C.

[0373] The lithium batteries manufactured in Examples 6 to 10 and Comparative Examples 4 to 6 were charged at a constant current of 0.05 C rate at 45°C until the voltage reached 2.8 V (vs. Li). Subsequently, they were discharged at a constant current of 0.05 C rate until the voltage reached 1.0 V (vs. Li) (formation cycle).

[0374] The lithium battery that had undergone the Mars cycle was charged at a constant current of 0.05 C rate at 45°C until the voltage reached 2.8 V (vs. Li). Subsequently, it was discharged at a constant current of 0.05 C rate until the voltage reached 1.0 V (vs. Li) (first cycle).

[0375] The lithium battery that had undergone the first cycle was charged at a constant current of 0.05 C rate at 45°C until the voltage reached 2.8 V (vs. Li). Subsequently, the battery was discharged at a constant current of 0.05 C rate until the voltage reached 1.0 V (vs. Li) (second cycle).

[0376] The lithium battery that had undergone the second cycle was charged at a constant current of 0.1 C rate at 45°C until the voltage reached 2.8 V (vs. Li). Subsequently, it was discharged at a constant current of 0.1 C rate until the voltage reached 1.0 V (vs. Li) (third cycle).

[0377] The lithium battery that had undergone the third cycle was charged at a constant current of 0.1 C rate at 45°C until the voltage reached 2.8 V (vs. Li). Subsequently, it was discharged at a constant current of 0.1 C rate until the voltage reached 1.0 V (vs. Li) (4th cycle).

[0378] In all charge / discharge cycles, a 10-minute pause was provided after each charge / discharge cycle. Some of the results of the room-temperature charge / discharge experiments are shown in Table 4 below. The rate characteristics are defined by Equation 3 below.

[0379] <Formula 1>

[0380] Rate characteristic [%] = [Discharge capacity in the 4th cycle / Discharge capacity in the 1st cycle] Х 100

[0381] Classification Rate characteristics (0.1C / 0.05C)(%)Example 6 (Al current collector / Carbon / Li2S-LiI-C containing dry cathode)(composite cathode active material: solid electrolyte: binder = 60:39:1.0 weight ratio) 98.2Example 7 (Al current collector / Carbon / polydopamine layer / Li2S-LiI-C containing dry cathode)(composite cathode active material: solid electrolyte: binder = 60:39:1.0 weight ratio) 97.8Example 8 (Al current collector / Carbon / Li2S-LiI-C containing dry cathode)(composite cathode active material: solid electrolyte: binder = 70:29:1.0 weight ratio) 96.8Example 9 (Al current collector / Carbon / polydopamine layer / Li2S-LiI-C Dry positive electrode) (composite positive electrode active material: solid electrolyte: binder = 70:29:1.0 weight ratio) 96.2 Example 10 (Al current collector / Carbon / Li-PAA / Li2S-LiI-C composite containing dry positive electrode) 97.6 Comparative example 4 (Al current collector / Li2S-LiI-C composite containing dry positive electrode) 80.5 Comparative example 5 (Al current collector / Li2S and LiI and CNF simple mixture containing dry positive electrode) 56.3 Comparative example 6 (Al current collector / polydopamine layer / carbon coating layer / Li2S-LiI-C containing positive electrode) 93.2 Reference example 2 (positive electrode collector / polydopamine layer / positive electrode active material layer) 84.2

[0382] As shown in Table 4, the all-solid-state secondary batteries of Examples 6 to 10 had improved rate characteristics compared to the all-solid-state secondary batteries manufactured in Comparative Examples 4 to 6 and Reference Example 2.

Claims

1. Bipolar collector; a carbon coating layer positioned on the positive electrode collector; and It comprises a positive electrode active material layer located on the carbon coating layer and containing a composite positive electrode active material and a solid electrolyte, The above composite cathode active material is a cathode for an all-solid-state secondary battery, comprising a Li2S-containing composite.

2. A positive electrode for an all-solid-state secondary battery, wherein the carbon coating layer has a thickness of 1 μm or less in the first paragraph.

3. In the first paragraph, the carbon coating layer is made of natural graphite, artificial graphite, carbon black, An all-solid-state secondary battery cathode comprising acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, porous carbon, or a combination thereof.

4. A positive electrode for an all-solid-state secondary battery, further comprising an intermediate layer containing an adhesive polymer between the carbon coating layer and the positive electrode active material layer in the first paragraph.

5. In the fourth paragraph, the adhesive polymer is at least one selected from polydopamine, a cation-substituted polycarboxylic acid, a cation-substituted polycarboxylic acid copolymer, polynorepinephrine, poly(meth)acrylamide, polyvinyl alcohol, polyhydroxyethyl(meth)acrylate, poly(methyl(meth)acrylate-co-(meth)acrylic acid), polymethyl(meth)acrylate, poly(meth)acrylic acid), and styrene-(meth)acrylic acid copolymer.

6. A positive electrode for an all-solid-state secondary battery, wherein the thickness of the intermediate layer in the fourth paragraph is 5 nm to 1 ㎛.

7. In the first paragraph, the Li2S-containing complex includes a composite of Li2S and a lithium salt; The above complex of Li2S and lithium salt is Li2S-Li a X b It is expressed as (1≤a≤5, 1≤b≤5), A positive electrode for an all-solid-state secondary battery, 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.

8. In the 7th paragraph, the Li2S-containing composite further includes a carbon-based material, The above carbon-based material includes a fibrous carbon-based material, The above fibrous carbon material includes a carbon nanostructure, The above carbon nanostructure includes carbon nanofibers, carbon nanotubes, carbon nanobelts, carbon nanorods, or a combination thereof, A positive electrode for an all-solid-state secondary battery, wherein the content of the carbon-based material is 1 to 20 wt% of the total weight of the Li2S-containing composite.

9. In paragraph 7, the lithium salt is a binary compound or a ternary compound, The above binary compound comprises LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3 or a combination thereof, A cathode for an all-solid-state secondary battery, wherein the ternary compound comprises Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2 or a combination thereof.

10. In the first paragraph, the Li2S-containing complex includes a solid solution of Li2S and a lithium salt, The size of the above Li2S-containing composite particles is 10 μm or less, A positive electrode for an all-solid-state secondary battery, wherein the size of Li2S crystallites obtained from the XRD spectrum of the above Li2S-containing complex is 20 nm or less.

11. A positive electrode for an all-solid-state secondary battery, wherein the Li2S content in the Li2S-containing complex is higher than the lithium salt content, and the molar ratio of the Li2S and the lithium salt in the complex is 51:49 to 95:

5.

12. A positive electrode for an all-solid-state secondary battery, wherein the content of the Li2S-containing complex in the first paragraph is 60 to 80 wt% of the total weight of the positive electrode active material layer.

13. In the first paragraph, the solid electrolyte is a sulfide-based solid electrolyte, The above sulfide-based solid electrolyte is Li2S-P2S5, Li2S-P2S5-LiX, X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x , at least one selected from 0≤x≤2, The above sulfide-based solid electrolyte includes an argyrodite-type solid electrolyte, An all-solid-state secondary battery positive electrode, wherein the argyrodite-type solid electrolyte comprises at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I, the density of the argyrodite-type solid electrolyte is 1.5 to 2.0 g / cc, the sulfide-based solid electrolyte is in the form of particles, and the average particle diameter (D50) of the particles is 0.1 ㎛ to 1.9 ㎛.

14. A positive electrode; a negative electrode; and a solid electrolyte layer disposed between the positive electrode and the negative electrode, An all-solid-state secondary battery, wherein the positive electrode comprises a positive electrode according to any one of claims 1 to 13.

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

16. In paragraph 15, the first negative electrode active material layer is a metal layer, The above metal layer contains lithium or a lithium alloy, or An all-solid-state secondary battery, wherein the first negative electrode active material layer includes a negative electrode active material and a binder, the negative electrode active material has a particle form, and the average particle diameter of the negative electrode active material is 4 ㎛ or less.

17. In paragraph 16, the negative electrode active material includes at least one selected from a carbon-based negative electrode active material and a metal or metalloid negative electrode active material, The above carbon-based negative electrode active material includes amorphous carbon, crystalline carbon, porous carbon, or a combination thereof. The above metal or metalloid negative electrode active material includes gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof. The above negative active material comprises a mixture of first particles made of amorphous carbon and second particles made of a metal or a metalloid, An all-solid-state secondary battery, wherein the content of the second particles is 1 to 60 wt% based on the total weight of the mixture.

18. In the 15th paragraph, a second negative electrode active material layer is further included, which is disposed 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. An all-solid-state secondary battery, wherein the second negative electrode active material layer is a metal layer, and the metal layer includes lithium or a lithium alloy.

19. In the 14th paragraph, the solid electrolyte layer further includes a solid electrolyte, a gel electrolyte, or a combination thereof, The above solid electrolyte includes a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof, An all-solid-state secondary battery, wherein the gel electrolyte comprises a polymer gel electrolyte.

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

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