All-solid-state secondary battery and method for manufacturing all-solid-state secondary battery

Abstract

The invention provides an all-solid-state secondary battery and a method for manufacturing the all-solid-state secondary battery. The all-solid-state secondary battery comprises a positive electrode layer; a negative electrode layer; and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, in which: the positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on one surface or both surfaces of the positive electrode current collector; the positive active material layer comprises a composite positive active material; the composite positive electrode active material includes a composite of the following: (i) M2S; (ii) an alkali metal salt; (iii) an inorganic electronically conductive structure; and (iv) a fibrous carbon-based material or a two-dimensional carbon-based structure having an aspect ratio of 2 or more; m is alkali metal; the alkali metal is Li or Na; the inorganic electron conductive structure has an electron conductivity of 10 <-3 > S / cm or greater; the compound comprises a solid solution of M2S and alkali metal salt; and the two-dimensional carbon-based structure is graphene, graphene oxide, or a combination thereof.

Description

Technical Field

[0001] One or more embodiments relate to all-solid-state secondary batteries and methods for preparing all-solid-state secondary batteries. Background Technology

[0002] Recently, due to industrial demands, batteries with high energy density and safety are being actively developed. For example, lithium batteries are used for various purposes in information devices, communication devices, and vehicles. Specifically, automotive safety is receiving great attention because it directly affects human life.

[0003] Lithium-ion batteries using liquid electrolytes are more prone to catching fire and / or exploding due to short circuits. Solid-state secondary batteries using solid electrolytes instead of liquid electrolytes have been proposed. Compared to liquid electrolytes, solid electrolytes are less likely to cause fires.

[0004] Therefore, by using a solid electrolyte instead of a liquid electrolyte, all-solid-state secondary batteries can reduce the risk of fire or explosion. Solid-state secondary batteries offer improved safety. Summary of the Invention

[0005] Technical issues One or more embodiments include an all-solid-state secondary battery with improved initial efficiency, high rate performance and volumetric energy density by including a positive electrode with an improved electronic conductivity network.

[0006] One or more embodiments include a method for preparing a solid-state secondary battery.

[0007] Technical solution According to one or more embodiments, the all-solid-state secondary battery includes: A positive electrode layer, a negative electrode layer, and a solid electrolyte layer are disposed between the positive electrode layer and the negative electrode layer. The positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on one or both sides of the positive electrode current collector. The positive electrode active material layer includes a composite positive electrode active material, which comprises the following composites: i) M₂S; ii) an alkali metal salt; iii) an inorganic electronically conductive structure; and iv) a two-dimensional carbonaceous structure or a fibrous carbonaceous material with an aspect ratio of 2 or greater, wherein M is an alkali metal, the alkali metal is Li or Na, and the inorganic electronically conductive structure has an aspect ratio of 10. -3 S / cm or greater electronic conductivity The complex includes a solid solution of M2S and an alkali metal salt, and the two-dimensional carbonaceous structure is graphene, graphene oxide, or a combination thereof.

[0008] The composite may include about 10 to about 80 parts by weight of M2S, about 1 to about 40 parts by weight of an alkali metal salt, and about 1 to about 20 parts by weight of an inorganic electronically conductive structure, relative to 100 parts by weight.

[0009] The size of M2S can be equal to or smaller than that of alkali metal salts, and The size of inorganic electronically conductive structures can be larger than that of lithium sulfide and alkali metal salts, and the particle size can gradually decrease in the following order: inorganic electronically conductive structures > alkali metal salts > M2S.

[0010] The positive electrode active material layer may also include a solid electrolyte, which may include sulfide solid electrolytes, oxide solid electrolytes, polymer solid electrolytes or combinations thereof, wherein the amount of solid electrolyte may be from about 10 parts by weight to about 60 parts by weight relative to 100 parts by weight of the positive electrode active material layer.

[0011] The negative electrode layer may include a negative electrode current collector and a first negative electrode active material layer disposed on the negative electrode current collector.

[0012] According to one or more embodiments, a method for preparing an all-solid-state secondary battery includes the following steps: first grinding a composition comprising M2S, an alkali metal salt, and an inorganic electronically conductive structure; obtaining a composite by adding a composition comprising a fibrous carbonaceous material or a two-dimensional carbonaceous structure to the product of the first grinding and performing a second grinding; preparing a composition by adding a binder to the composite and then mixing them, and preparing a positive electrode by using the composition; preparing a negative electrode; and disposing an electrolyte between the positive and negative electrodes, thereby preparing the all-solid-state secondary battery described above.

[0013] Beneficial effects of the invention According to one aspect, by using a composite material employing an inorganic electronic conductive structure, a solid-state secondary battery with improved volumetric energy density, improved initial efficiency, and high-rate performance can be provided by including a positive electrode with an improved electronic conductive network. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of the positive electrode active material layer according to an embodiment.

[0015] Figures 2 to 7 All are cross-sectional views of the all-solid-state secondary battery according to the embodiments.

[0016] List of reference numerals for key components 1 All-solid-state secondary battery 10 positive electrode 11 Positive current collector 12 Positive active material layer 20 negative electrode 21 negative electrode current collector 22 First negative electrode active material layer 30 Electrolyte layer 40. Inactive components. Detailed Implementation

[0017] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will also be understood that terms (such as those defined in common dictionaries) shall be interpreted as having the same meaning as they have in the context of the specification and in the relevant field, and shall not be interpreted in an idealized or overly formal sense, unless expressly defined herein.

[0018] The embodiments are described herein with reference to schematic cross-sectional views as idealized embodiments. Thus, variations in the illustrated shapes will be anticipated, for example, due to manufacturing techniques and / or tolerances. Therefore, the embodiments described herein should not be construed as limited to the specific shapes of the areas shown herein, but will include shape deviations, for example, due to manufacturing processes. For example, areas shown or described as flat may generally have rough and / or non-linear characteristics. Furthermore, corners shown as sharp may be rounded. Therefore, the areas shown in the figures are schematic in nature, and their shapes are not intended to illustrate the precise shapes of the areas, nor are they intended to limit the scope of the given claims.

[0019] However, these inventive concepts can be implemented in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concepts to those skilled in the art. In the accompanying drawings, the same reference numerals always refer to the same elements.

[0020] It will also be understood that when an element is referred to as "on" or "above" another element, the element may be directly on the other element, or an intermediary element may be present. Conversely, when an element is referred to as "directly on" or "directly above" another element, no intermediary element is present.

[0021] It will be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. For example, without departing from the teachings of this disclosure, a first element, first component, first region, first layer, or first portion may be referred to as a second element, second component, second region, second layer, or second portion.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the inventive concept. As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” are also intended to include the plural forms that also include “at least one.” The term “at least one” should not be construed as limited to the singular form. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. It will also be understood that when the terms “comprising” or “including” and / or variations thereof are used in this specification, it indicates the presence of the stated features, regions, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and / or groups thereof.

[0023] Furthermore, spatial relative terms such as “below,” “bottom,” or “below,” and “above,” “top,” or “above” may be used herein to facilitate the description of the relationship between one element or feature and another. It will be understood that, in addition to the orientations depicted in the figures, the spatial relative terms are intended to cover different orientations of the device when it is used or operated. For example, if the device in one of the figures is flipped, the element described as being “below” or “bottom” of another element will subsequently be oriented to be “above” or “top” of said other element. Thus, the example term “below” can therefore cover both “below” and “above” orientations. The device may be placed in other orientations (it may be rotated 90 degrees or in different orientations), and the spatial relative terms used herein may be interpreted accordingly.

[0024] "Group" refers to a group in the periodic table of elements according to the group numbering system of the International Union of Pure and Applied Chemistry ("IUPAC"), from group 1 to group 18.

[0025] As used herein, the term "particle size" refers to the average particle size if the particles are spherical, and to the average major axis length if the particles are non-spherical. Particle size can be measured using a particle size analyzer (PSA). As used herein, the term "particle size" refers, for example, the average particle size. As used herein, the term "average particle size" refers, for example, the median particle size (D50).

[0026] D50 can refer to the particle size corresponding to 50% of the cumulative volume, calculated from the side of the particle with the smallest particle size in a particle size distribution such as that measured by laser diffraction.

[0027] D90 can refer to the particle size corresponding to 90% of the cumulative volume, calculated from the side of the particle with the smallest particle size in a particle size distribution measured by laser diffraction.

[0028] D10 can refer to the particle size corresponding to 10 cumulative volume % calculated from the side of the particle with the smallest particle size in a particle size distribution such as that measured by laser diffraction.

[0029] As used herein, the term "metal" refers to both metals and metalloids that are in elemental or ionic form (such as silicon and germanium).

[0030] As used herein, the term "alloy" means a mixture of two or more metals.

[0031] As used herein, the term "electrode active material" refers to an electrode material capable of undergoing lithiation and delithiation.

[0032] As used herein, the term "positive electrode active material" refers to a positive electrode material capable of undergoing lithiation and delithiation.

[0033] As used herein, the term "negative electrode active material" refers to a negative electrode material capable of undergoing lithiation and delithiation.

[0034] As used herein, the term "lithiation" and its variations refer to the process of adding lithium to an electrode active material.

[0035] As used herein, the term “delithiation” and its variations refer to the process of removing lithium from the electrode active material.

[0036] As used herein, the term “charging” and its variations refer to the process by which a battery provides electrochemical energy.

[0037] As used herein, the term "discharge" and its variations refer to the process of removing electrochemical energy from a battery.

[0038] As used herein, the terms "positive electrode" and "positive electrode" refer to the electrode that undergoes electrochemical reduction and lithiation during the discharge process.

[0039] As used herein, the terms "negative electrode" and "negative electrode" refer to the electrode that undergoes electrochemical oxidation and delithiation during the discharge process.

[0040] As used herein, the terms “length” and “thickness” refer, for example, average length and average thickness. Length and thickness can be evaluated using scanning electron microscope images.

[0041] As used herein, the aspect ratio represents the ratio (L1 / L2) of the major axis length L1 (e.g., length) to the minor axis length L2 (e.g., diameter). Here, aspect ratio, major axis length, minor axis length, length, and diameter represent the average aspect ratio, average major axis length, average minor axis length, average length, and average diameter. The aspect ratio can be evaluated using a scanning electron microscope.

[0042] While specific examples are described herein, the applicant or a person skilled in the art will realize that alternatives, modifications, variations, improvements, and substantial equivalents (including those not currently foreseen or understood) may exist for the examples disclosed herein. Therefore, the appended claims, as filed and possibly amended, are intended to cover all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0043] The composite positive electrode active material, the positive electrode including the composite positive electrode active material, and the all-solid-state secondary battery according to the embodiments will be described in more detail below.

[0044] [Composite positive electrode active material] The composite positive electrode active material according to the embodiments may include the following composites: i) M2S; ii) alkali metal salt; iii) inorganic electronically conductive structure; and iv) two-dimensional carbonaceous structure or fibrous carbonaceous material having an aspect ratio of 2 or greater, wherein M is an alkali metal, the alkali metal is Li or Na, and the inorganic electronically conductive structure has an aspect ratio of 10. -3 The composite has an electronic conductivity of S / cm or greater, and comprises a solid solution of M2S and an alkali metal salt, and the two-dimensional carbonaceous structure is graphene, graphene oxide, or a combination thereof.

[0045] Carbon nanostructures can be at least one selected from one-dimensional carbon nanostructures and two-dimensional carbon nanostructures. As used herein, a one-dimensional carbon nanostructure is a carbon nanostructure with one dimension significantly larger than the other two dimensions. That is, a one-dimensional carbon nanostructure is a carbon nanostructure whose length defined by one dimension is significantly greater than the length defined by the other two dimensions. For example, a one-dimensional carbon nanostructure can be at least one selected from carbon nanotubes, carbon nanowires, carbon nanofibers, carbon nanoribbons, carbon nanorods, or combinations thereof.

[0046] As used herein, the term "two-dimensional carbon nanostructure" refers to a carbon nanostructure in which two dimensions are significantly larger than the other dimensions. In other words, a two-dimensional carbon nanostructure is a carbon nanostructure whose area, defined by two dimensions, is significantly larger than its thickness.

[0047] The fibrous carbonaceous material can be defined by its length and diameter, and the aspect ratio of its length to its diameter can be 2 or greater, 3 or greater, 5 or greater, for example, 10 or greater. Furthermore, the fibrous carbonaceous material can have a length of about 1 μm to about 50 μm and a diameter of about 10 nm to about 10 μm. As used herein, the term "particle size" refers to the average diameter of a circle when the cross-section of the material is circular, and to the average length of its major axis when the cross-section of the material is non-circular.

[0048] For example, fibrous carbonaceous materials can include carbon nanofibers.

[0049] Because fibrous carbonaceous materials have lengths and diameters within the above ranges, a conductive network can be easily formed inside the positive electrode. The cross-section of the fibrous carbonaceous material can include polygonal shapes, such as circles, triangles, and rectangles.

[0050] In some embodiments, the use of this composite can ensure further elongation of ion conduction pathways within the positive electrode active material layer. When the solid-state secondary battery is charged and discharged, the disruption of ion conduction pathways due to volume changes in the positive electrode active material within the positive electrode active material layer can be more effectively suppressed. Therefore, all-solid-state secondary batteries can exhibit improved initial efficiency, discharge capacity, high-rate performance, and / or lifetime characteristics.

[0051] Furthermore, the use of this composite can improve the uniformity of ion conduction pathways in the positive electrode active material layer. In some embodiments, the pressure required during the manufacture of all-solid-state secondary batteries can be reduced. In some embodiments, even under reduced pressure, all-solid-state secondary batteries with excellent ion conduction pathways can be achieved. In some embodiments, the formation of localized overvoltages within the positive electrode active material layer during the charging and discharging processes of the all-solid-state secondary battery can be effectively prevented.

[0052] By controlling the aforementioned carbon nanofibers, the conductivity of the carbon nanofibers is increased and the side reactions between the positive electrode active material and the sulfide solid electrolyte are reduced through doping with nitrogen, fluorine, etc.

[0053] Using a composite containing the aforementioned fibrous carbonaceous material allows for the fabrication of a thick-film cathode by mitigating its brittleness. Therefore, an all-solid-state secondary battery with increased energy density can be fabricated. Furthermore, because it includes fibrous carbonaceous material, the volume change of the cathode active material during charging and discharging can be accommodated throughout the entire length of the fibrous carbonaceous material. Thus, for example, compared to carbonaceous materials in the form of spherical particles, the volume change of the cathode active material can be accommodated more effectively. Therefore, the disconnection between the cathode active material and the solid electrolyte due to volume changes within the cathode active material layer can be suppressed, and the uniformity of the constituent components within the cathode active material layer can be improved. Therefore, the cycle performance of the all-solid-state secondary battery can be improved.

[0054] As used herein, the term "thick film" refers to a film with a thickness greater than 8 mg / cm³. 2 (For example, 9 mg / cm) 2 Or larger, 10 mg / cm 2 Or larger, approximately 10 mg / cm³ 2 Approximately 60 mg / cm 2 or approximately 10 mg / cm³ 2 Approximately 50 mg / cm2 The membrane with positive electrode loading level.

[0055] Complexes may not have a cluster form, but rather a state in which the constituent components of the complex are uniformly distributed fine particles.

[0056] For example, fibrous carbonaceous materials can have an aspect ratio of 2 or greater, 3 or greater, 4 or greater, 5 or greater, 10 or greater, or 20 or greater. For example, fibrous carbonaceous materials can have an aspect ratio of 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. For example, fibrous carbonaceous materials can have an aspect ratio of 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. Using fibrous carbonaceous materials with aspect ratios within the above ranges can improve the overall electronic conductivity of the composite and further reduce the local irregularities in electronic conductivity within the composite.

[0057] Fibrous carbonaceous materials can have, for example, rod-like, tubular, needle-like, linear, or combinations thereof structures. However, fibrous carbonaceous materials are not limited to the aforementioned forms and can be any carbonaceous material with a fibrous structure available in the art. Because fibrous carbonaceous materials have rod-like, tubular, needle-like, or linear structures, ion conduction paths can be lengthened within all-solid-state secondary batteries incorporating fibrous carbonaceous materials, and the volume changes of the positive electrode active material during charging and discharging can be accommodated more effectively. Furthermore, even with such volume changes of the positive electrode active material, the ion conduction paths within the all-solid-state secondary battery can be maintained. Therefore, degradation of the all-solid-state secondary battery can be suppressed, and its cycle performance can be improved.

[0058] Inorganic electronic conductivity structures can have 1×10 -3 S / cm or greater or 1×10 -2 Electronic conductivity of S / cm or greater. Electronic conductivity can be measured, for example, using electrochemical impedance spectroscopy, DC polarization methods, etc. Because composites containing inorganic electronically conductive structures have electronic conductivity in the above range, composite positive electrode active materials including these composites can have reduced internal resistance. All-solid-state secondary batteries including composite positive electrode active materials can have improved initial efficiency, electrode energy density, and lifetime characteristics.

[0059] Because inorganic electronically conductive structures have small particle sizes and are uniformly dispersed in the composite, they can be advantageous for the formation of conductive networks. Inorganic electronically conductive structures can have zero-dimensional, one-dimensional, two-dimensional, three-dimensional, or combinations thereof.

[0060] Examples of zero-dimensional structures can include particulate forms, examples of one-dimensional structures can include fibrous forms, and examples of two-dimensional structures can include plate forms. If a composite using the aforementioned inorganic electron-conductive structure is used to prepare a positive electrode and an all-solid-state secondary battery, an improvement in initial efficiency (specific capacity) can be achieved due to a reduction in side reactions with the solid electrolyte. Side reactions include, for example, reactions between the solid electrolyte and hydroxyl groups (H2O) in the carbon layer of CNF included in the positive electrode that lead to an increase in resistance, and reactions between carbon and polysulfide lithium (Li2S4 < Li2S6).

[0061] Increasing the amount of the inorganic electron-conductive structure in the composite can cause an increase in electron conductivity but also a decrease in ionic conductivity. Therefore, the domain size of a two-dimensional carbonaceous structure (e.g., graphene) can become important. If graphene is used as the two-dimensional carbonaceous structure, the thickness of the graphene can be used to control the domain size of the graphene.

[0062] The inorganic electron-conductive structure can have a length of about 1 μm to about 50 μm and a thickness of about 0.01 μm to about 10 μm. By using a composite using a two-dimensional carbon nanostructure having a length and thickness within the above ranges, it is possible to prepare an all-solid-state secondary battery that exhibits improved lifetime characteristics by improving the electron-conductive network inside the positive electrode. In some embodiments, strengthening the electron-conductive network can reduce the amount of conductive material in the positive electrode, thereby improving the energy density in the electrode. In addition, since the amount of lithium sulfide relatively increases as the amount of conductive material in the positive electrode decreases, the initial efficiency can be improved.

[0063] The inorganic electron-conductive structure can be any material having a two-dimensional structure, having a chalcogenide material, and having electron conductivity.

[0064] The inorganic electron-conductive structure can have the form of a zero-dimensional structure, the form of a one-dimensional structure, or the form of a two-dimensional structure. For example, the one-dimensional structure can be in the form of a fiber, and for example, the two-dimensional structure can have the form of a plate. By using an inorganic electron-conductive structure having a one-dimensional structure, the positive electrode can be formed into a thick film and a positive electrode having improved electrode stability, and using an inorganic electron-conductive structure having a two-dimensional structure can improve the effect of suppressing volume expansion of the positive electrode.

[0065] Metal sulfides (e.g., transition metal sulfides) can be selected from among ZrS2, FeS, FeS2, CuS, Cu2S, CuS2, Cu9S8, Cu7S4, CoS, CoS2, Co3S4, Co9S8, NiS, NiS2, Ni9S8, Ni3S2, VS, VS2, V2S3, V2S5, VS4, NbS2, NbS3, NbS4, NbS5, NB2S3, Nb2S5, TaS2, TaS3, TaS4, TaS5, Ta2S3, Ta2S5, Cr2S3, CrS3, MoS2, MoS3, MoS4, WS2, WS3, WS4, WS5, MnS, Mn2S3, TiS2, NiNb3S6, Cu2MoS4, and / or Cu4Mo6S8. For example, at least one metal sulfide can be selected from among FeS2, CuS2, CoS2, Co3S4, NiS2, VS2, VS4, NbS2, NbS3, NbS4, NbS5, TaS2, TaS3, TaS4, TaS5, CrS3, MoS2, MoS3, MoS4, WS2, WS3, WS4, and WS5. These transition metal sulfides can have, for example, a plate form in two-dimensional form.

[0066] According to some embodiments, the inorganic electronic conductive structure can be, for example, one or more metal oxides selected from among VO2, ReO2, CrO2, ReO2, VO2, SnO2, TiO2, ZrO2, Al2O3, TeN, TiN, TiO x (0.75 < x < 1.45), Ti n O 2n-1 (4 < n < 10), ReO3, CrO2, and VO2, or a combination thereof.

[0067] For example, the inorganic electronic conductive structure can be alumina fibers, zirconia fibers, titanium dioxide fibers, TeN fibers, SnO2 fibers, or a combination thereof. If the inorganic electronic conductive structure has such a fibrous form, the inorganic electronic conductive structure can have a length of about 0.1 μm to about 5 μm, a diameter of about 0.01 μm to about 0.5 μm, and an aspect ratio of 10 or greater.

[0068] With respect to 100 parts by weight of the composite, the amount of the inorganic electronic conductive structure can be about 1 part by weight to about 20 parts by weight, about 1 part by weight to about 18 parts by weight, or about 1 part by weight to about 15 parts by weight. With respect to 100 parts by weight of the composite, the amount of the fibrous carbonaceous material or two-dimensional carbonaceous structure can be about 1 part by weight to about 40 parts by weight, about 1 part by weight to about 30 parts by weight (e.g., about 5 parts by weight to about 10 parts by weight).

[0069] In some embodiments, relative to 100 parts by weight of the composite, it may include about 30 parts by weight to about 80 parts by weight of M2S, about 1 part by weight to about 40 parts by weight of an alkali metal salt, about 1 part by weight to about 20 parts by weight of an inorganic electronically conductive structure, and about 1 part by weight to about 40 parts by weight of a fibrous carbonaceous material or a two-dimensional carbonaceous structure.

[0070] In some embodiments, the size ratio of the inorganic electronically conductive structure to LiI can be, for example, from about 3:1 to about 0.5:1, and the size ratio of the inorganic electronically conductive structure to Li2S can be, for example, from about 2:1 to about 0.5:1.

[0071] In this specification, the term "inorganic electronically conductive structure" refers to an inorganic structure having electronic conductivity and negligible ionic conductivity, and refers to a material having zero-dimensional, one-dimensional, two-dimensional, or three-dimensional form or any combination thereof. As used herein, "zero-dimensional" refers to a particulate form; "one-dimensional" refers to a fibrous form; and "two-dimensional" refers to a plate-like form.

[0072] In some embodiments, the size of the inorganic electronically conductive structure can be larger than that of lithium sulfide and alkali metal salt (LiI), and the particle size can decrease gradually in the following order: inorganic electronically conductive structure > alkali metal salt (LiI) > M2S. The size can be the arithmetic mean of the particle sizes of multiple particles measured from scanning electron microscope images using software.

[0073] The size ratio of the inorganic electronically conductive structure to LiI can be, for example, from about 3:1 to about 1.5:1, and the size ratio of the inorganic electronically conductive structure to Li2S can be, for example, from about 2:1 to about 1.5:1.

[0074] If the inorganic electronic conductive structure has the form of a two-dimensional plate, the inorganic electronic conductive structure can have a length of about 1 μm to about 50 μm and a thickness of about 0.01 μm to about 10 μm, and the M2S can have a size of about 0.1 nm to about 10 μm.

[0075] The size of alkali metal salts (LiI) can be from about 1 nm to about 10 μm.

[0076] Unlike one-dimensional carbon structures (such as carbon nanofibers), two-dimensional carbon structures have a plate-like structure and can include, for example, graphene, graphene oxide, or combinations thereof.

[0077] Compared to one-dimensional carbonaceous structures, two-dimensional carbonaceous structures have a larger specific surface area, and due to the house-of-cards effect, this helps to successfully maintain the network structure by thoroughly surrounding lithium sulfide. Furthermore, even with the volume expansion of lithium sulfide during charging and discharging, the contact surface with the positive electrode component can be large, and the connection can be well maintained.

[0078] Increasing the amount of two-dimensional carbonaceous structures (e.g., graphene) in a composite can increase its electronic conductivity but may decrease its ionic conductivity. Therefore, the domain size of the two-dimensional carbonaceous structure (e.g., graphene) can become important. If graphene is used as the two-dimensional carbonaceous structure, the domain size can be controlled by the thickness of the graphene.

[0079] The specific surface area of ​​two-dimensional carbon nanostructures can be approximately 1 m². 2 / g to approximately 50m 2 / g, approximately 1m 2 / g to approximately 30m 2 / g, or approximately 5m 2 / g to approximately 20m 2 / g. Furthermore, the two-dimensional carbon nanostructures can have thicknesses of about 10 nm to about 10 μm, about 100 nm to about 8 μm, about 500 nm to about 6 μm, about 1 μm to about 5 μm, or about 1 μm to 3 μm. By using composites utilizing two-dimensional carbon nanostructures having specific surface area, diameter, and thickness within the above ranges, it is possible to fabricate all-solid-state secondary batteries exhibiting improved lifetime characteristics by improving the electronic conductivity network within the cathode. In some embodiments, strengthening the electronic conductivity network can reduce the amount of conductive material in the cathode, thereby improving the energy density in the electrode. Furthermore, since the amount of lithium sulfide relatively increases as the amount of conductive material in the cathode decreases, the initial efficiency can be improved.

[0080] In one or more embodiments, the graphene may have a thickness of about 10 nm to about 30 μm, about 100 nm to about 30 μm, or about 1 μm to about 3 μm.

[0081] Two-dimensional carbon structures can include doped two-dimensional carbon structures, wherein the dopant can be an n-type dopant or a p-type dopant, and the dopant can include nitrogen (N), phosphorus (P), boron (B), sulfur (S), fluorine (F), chlorine (Cl), bromine (Br), germanium (Ge), gallium (Ga), or combinations thereof. Using such doped two-dimensional carbon structures allows for control over electrical conductivity and side reaction properties.

[0082] Dopants can include n-type dopants, p-type dopants, or combinations thereof. An n-type dopant can be, for example, a dopant having more electrons than carbon, thus introducing electrons into the two-dimensional carbonaceous material. A p-type dopant can be a dopant having fewer electrons than carbon, thus introducing holes into the two-dimensional carbonaceous structure. The carbonaceous structure can include, for example, doped graphene. Doped graphene can include n-type dopants, p-type dopants, or combinations thereof. Dopants can include, for example, nitrogen (N), phosphorus (P), boron (B), sulfur (S), fluorine (F), chlorine (Cl), bromine (Br), germanium (Ge), gallium (Ga), or combinations thereof. For example, nitrogen (N) and phosphorus (P) are n-type dopants. For example, gallium (Ga) is a p-type dopant. The dopant content in the doped carbonaceous structure can be, for example, 3 at% or less, or 1 at% or less. Because the carbonaceous structure is doped with dopants, it can have further increased electrical conductivity.

[0083] M can be an alkali metal. The alkali metal can be Li or Na. M₂S can be, for example, Li₂S or Na₂S. The complex can include a solid solution of M₂S and an alkali metal salt.

[0084] Because M2S forms complexes with alkali metal salts and inorganic electronically conductive structures or two-dimensional carbonaceous structures, the ionic and electronic conductivity of M2S can be improved. Because the complex includes alkali metal salts, the ionic conductivity of the composite positive electrode active material can be improved, and the internal resistance of the positive electrode and the all-solid-state secondary battery incorporating the composite positive electrode active material can be reduced. Because the complex includes carbonaceous materials, the electronic conductivity of the composite positive electrode active material can be improved, and the internal resistance of the positive electrode and the solid-state secondary battery incorporating the composite positive electrode active material can be reduced.

[0085] The composite includes M2S microcrystals, and because the size of the M2S microcrystals is reduced to 21 nm or less, the volume change of the M2S microcrystals during charging and discharging can be mitigated. For example, since the reduction in the size of the M2S microcrystals means that the volume change caused by a single M2S microcrystal is also reduced, the overall volume change of the composite during charging and discharging can be mitigated. For example, since the grain boundaries between multiple M2S microcrystals can more easily accommodate the volume change of the M2S microcrystals during charging and discharging as the size of the M2S microcrystals decreases, the volume change of the composite during charging and discharging can be mitigated. Furthermore, the likelihood of defects (i.e., cracks) caused by the volume change of the composite during charging and discharging can be reduced. Using a composite positive electrode active material including the above composite, a secondary battery including the composite positive electrode active material can have improved cycle performance. For example, a lithium battery including the composite positive electrode active material can have improved lifespan characteristics.

[0086] The composite includes M2S microcrystals, and because the size of the M2S microcrystals is reduced to 21 nm or less, the contact surface between the M2S microcrystals and the alkali metal salt and / or carbonaceous material can be further increased. This increased contact surface between the M2S microcrystals and the alkali metal salt and / or carbonaceous material can lead to a further increase in the ionic and / or electronic conductivity of the composite. If the composite positive electrode active material includes such a composite, the reversibility of the electrode reaction can be improved in a secondary battery including the composite positive electrode active material. This can lead to an increase in the specific capacity of the composite positive electrode active material.

[0087] Since the composite includes a solid solution of M2S and an alkali metal salt, the ionic conductivity of the composite can be increased. For example, because the solid solution of M2S and the alkali metal salt includes alkali metal ions disposed within the M2S microcrystals, the solid solution of M2S and the alkali metal salt can have improved ionic conductivity compared to that of M2S itself. Therefore, the ionic conductivity of the composite can be improved, and the internal resistance of the composite can be reduced. Using a composite positive electrode active material including the above composite, a secondary battery including the composite positive electrode active material can have improved cycle performance. For example, a lithium battery including the composite positive electrode active material can have improved high-rate performance.

[0088] Complexes of Li₂S, alkali metal salts, and carbonaceous structures can be distinguished from simple mixtures of Li₂S, alkali metal salts, and carbonaceous structures. Because simple mixtures of Li₂S, alkali metal salts, and carbonaceous structures cannot maintain a dense interface between them, they may provide high interfacial resistance and thus potentially lead to deterioration of the lifetime characteristics of solid-state secondary batteries.

[0089] The composite can include M2S. Due to the high theoretical capacity of M2S, it can provide a secondary battery with high energy density.

[0090] However, M2S exhibits low ionic and / or electronic conductivity, and to address this drawback, M2S is combined with alkali metal salts and carbonaceous materials to form composites. That is, M2S can possess a high theoretical capacity, thus enabling the provision of secondary batteries with high energy density. However, to overcome the disadvantages of low ionic and / or electronic conductivity such as that of M2S, composites formed from M2S, alkali metal salts, and carbonaceous materials can be used.

[0091] For example, the amount of M2S in the composite may be about 10 wt% to about 80 wt%, about 20 wt% to about 70 wt%, about 30 wt% to about 60 wt%, or about 40 wt% to about 60 wt% relative to the total weight of the composite. If the amount of M2S is excessively increased, it may be difficult to improve the ionic conductivity and / or electronic conductivity of M2S. If the amount of M2S is too low, the energy density of the secondary battery may deteriorate.

[0092] The complex may include an alkali metal salt. An alkali metal salt may be, for example, a compound that does not contain sulfur (S). An alkali metal salt may be, for example, a binary or ternary compound. For example, an alkali metal salt may be a binary compound consisting of an alkali metal and one element selected from groups 13 to 17 of the periodic table. For example, an alkali metal salt may be a ternary compound consisting of an alkali metal and two elements selected from groups 13 to 17 of the periodic table.

[0093] Alkali metal salts can be, for example, lithium salts. Examples of binary lithium salt compounds include LiI, LiBr, LiCl, LiF, LiH, Li₂O, Li₂Se, Li₂Te, Li₃N, Li₃P, Li₃As, Li₃Sb, Li₃Al₂, LiB₃, or combinations thereof. Examples of ternary lithium salt compounds include Li₃OCl, LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiClO₄, LiAlO₂, LiAlCl₄, LiNO₃, Li₂CO₃, LiBH₄, Li₂SO₄, Li₃BO₃, Li₃PO₄, Li₄NCl, Li₅NCl₂, Li₃BN₂, or combinations thereof. Using complexes including lithium salts, the complexes can possess further improved ionic conductivity. For example, lithium salts can more readily form solid solutions with Li₂S within the complex.

[0094] Alkali metal salts can be, for example, sodium salts. Examples of binary sodium salt compounds include NaI, NaBr, NaCl, NaF, Na₂O, Na₂Se, Na₃N, Na₃P, Na₃As, Na₃Sb, Na₃Al₂, NaB₃, or combinations thereof. Examples of ternary sodium salt compounds include Na₃OCl, NaBF₄, NaPF₆, NaAsF₆, NaClO₄, NaNO₃, NaAlO₂, NaAlCl₄, NaNO₃, Na₂CO₃, NaBH₄, Na₂SO₄, Na₃BO₃, Na₃PO₄, Na₄NCl, Na₅NCl₂, Na₃BN₂, or combinations thereof. Using complexes comprising sodium salts, the complexes can possess further improved ionic conductivity. For example, sodium salts can more readily form solid solutions with Na₂S within the complex.

[0095] In the composite, the amount of alkali metal salt relative to the total weight of the composite can be from about 1 wt% to about 40 wt%, from about 5 wt% to about 35 wt%, from about 10 wt% to about 35 wt%, from about 15 wt% to about 35 wt%, from about 20 wt% to about 35 wt%, or from about 25 wt% to about 35 wt%. If the amount of alkali metal salt is excessively increased, the energy density of the all-solid-state secondary battery may deteriorate. If the amount of alkali metal salt is too low, the ionic conductivity of the composite decreases, which may increase the internal resistance of the composite positive electrode active material. Therefore, the cycle performance of the all-solid-state secondary battery may deteriorate.

[0096] In the composite, the molar ratio of M2S to the alkali metal salt can be, for example, about 50:50 to about 95:5, about 60:40 to about 95:5, about 60:40 to about 90:10, about 65:35 to about 90:10, about 65:35 to about 85:15, or about 70:30 to about 85:15. Alternatively, the molar ratio of M2S to the alkali metal salt in the composite can be, for example, about 50:50 to about 95:5, about 50:50 to about 90:10, about 50:50 to about 85:15, about 50:50 to about 80:20, about 50:50 to about 75:25, or about 50:50 to about 70:30. Utilizing molar ratios of M2S to the alkali metal salt within the above ranges can further improve the cycle performance of all-solid-state secondary batteries including composite positive electrode active materials. If the molar fraction of M2S is too high, the effect of alkali metal salts on improving ionic conductivity becomes negligible. However, if the molar fraction of M2S is too high, the energy density of all-solid-state secondary batteries, including composite cathode active materials, may degrade.

[0097] In the composite, the molar ratio of Li₂S to lithium salt can be, for example, about 50:50 to about 95:5, about 60:40 to about 95:5, about 60:40 to about 90:10, about 65:35 to about 90:10, about 65:35 to about 85:15, or about 70:30 to about 85:15. Alternatively, the molar ratio of Li₂S to lithium salt can be, for example, about 50:50 to about 95:5, about 50:50 to about 90:10, about 50:50 to about 85:15, about 50:50 to about 80:20, about 50:50 to about 75:25, or about 50:50 to about 70:30. Using molar ratios of Li₂S to lithium salt within the above ranges, the cycle performance of all-solid-state secondary batteries, including composite cathode active materials, can be further improved. If the molar fraction of Li₂S is too high, the effect of the lithium salt on improving ionic conductivity is negligible. If the molar fraction of Li2S is too high, the energy density of all-solid-state secondary batteries, including composite cathode active materials, may degrade.

[0098] Except for using sodium salt instead of lithium salt, the molar ratio of Na2S to sodium salt in the complex can be the same as the molar ratio of Li2S to lithium salt mentioned above.

[0099] For example, the amount of fibrous carbonaceous material or carbonaceous structure included in the composite may be about 1 wt% to about 20 wt%, about 5 wt% to about 20 wt%, or about 5 wt% to about 10 wt%, relative to the total weight of the composite. If the amount of fibrous carbonaceous material or carbonaceous structure is excessively increased, the energy density of the secondary battery may deteriorate. If the amount of fibrous carbonaceous material or carbonaceous structure is excessively reduced, the electronic conductivity of the composite decreases, which may increase the internal resistance of the composite positive electrode active material. Therefore, the cycle performance of the all-solid-state secondary battery may deteriorate.

[0100] In the XRD spectrum of the composite positive electrode active material, peaks related to the crystal plane of molybdenum sulfide (MoS2) appear at diffraction angles of 2θ = 14.5 ± 0.5°, 2θ = 32.5 ± 0.5°, and 2θ = 58.5 ± 0.5°.

[0101] The peak appearing at a diffraction angle 2θ = 14.5 ± 0.5° relates to the (002) crystal plane of molybdenum sulfide (MoS2), and the diffraction angle 2θ can be, for example, 14.1°. Furthermore, the peak appearing at a diffraction angle 2θ = 32.5 ± 0.5° relates to the (100) crystal plane of molybdenum sulfide (MoS2), and the diffraction angle 2θ can be, for example, 32.9°. The peak appearing at a diffraction angle 2θ = 58.5 ± 0.5° relates to the (110) crystal plane of molybdenum sulfide (MoS2), and the diffraction angle 2θ can be, for example, 58.8°.

[0102] In the X-ray diffraction (XRD) spectrum of the composite positive electrode active material, if the composite shows a first peak at a diffraction angle of 2θ = 14.5 ± 0.5°, a second peak at a diffraction angle of 2θ = 32.5 ± 0.5°, and a third peak at a diffraction angle of 2θ = 58.5 ± 0.5°, and the XRD spectrum of MoS2 used to prepare the aforementioned composite shows a fourth peak at a diffraction angle of 2θ = 14.5 ± 0.5°, a fifth peak at a diffraction angle of 2θ = 32.5 ± 0.5°, and a sixth peak at a diffraction angle of 2θ = 58.5 ± 0.5°, then the first diffraction angle of each of the first, second, and third peaks can be shifted to an angle lower than the second diffraction angle of each of the fourth, fifth, and sixth peaks. This shift to a lower angle can occur when the composite is formed during the milling process.

[0103] For example, the position of the first peak may have shifted to a lower angle than the position of the second peak. Furthermore, in the XRD spectrum of MoS2 used to prepare the composite, the intensity of the first peak appearing at a diffraction angle of 2θ = 14.5 ± 0.5° may be reduced compared to the intensity of the fourth peak appearing at a diffraction angle of 2θ = 14.5 ± 0.5°.

[0104] In some embodiments, crystal changes in the MoS2 material can be observed in XRD during the milling process. The lithium sulfide-molybdenum sulfide (MoS2)-carbon composite can have a smaller crystallite size than the lithium sulfide used in preparing the composite. Because the lithium sulfide-molybdenum sulfide (MoS2)-carbon composite has a smaller crystallite size, the volume change of the crystallites during charging and discharging is reduced; therefore, composites comprising multiple crystallites can exhibit reduced volume changes during charging and discharging. Defects (such as crack formation) in the composite cathode active material comprising the composite can be suppressed during charging and discharging. Therefore, all-solid-state secondary batteries comprising composite cathode active materials can have improved cycle performance.

[0105] For example, the first lattice constant (d1) derived from the first peak corresponding to the (111) crystal plane of M2S at a diffraction angle of 2θ = 27° ± 2.0° in the XRD spectrum of the composite can be greater than the second lattice constant (d2) derived from the second peak corresponding to the (111) crystal plane of M2S at a diffraction angle of 2θ = 27° ± 2.0° in the XRD spectrum of the M2S used to prepare the aforementioned composite. Because the M2S-alkali metal salt-carbon structure composite has a larger lattice constant (d) than the M2S used to prepare the composite, alkali metal ions can be more easily transported within the M2S crystal structure of the composite. The composite positive electrode active material including the composite can have further improved ionic conductivity. The secondary battery including the composite positive electrode active material can have reduced internal resistance and improved cycle performance. The difference between the first lattice constant (d1) and the second lattice constant (d2) can be 0.05 Å or greater, 0.1 Å or greater, 0.15 Å or greater, 0.2 Å or greater, or 0.25 Å or greater. For example, the magnitude of the first lattice constant (d1) can be 5.78 Å or greater, 5.80 Å or greater, 5.82 Å or greater, 5.85 Å or greater, 5.90 Å or greater, 5.95 Å or greater, or 6.0 Å or greater. Using a composite material having a first lattice constant (d1) within the above range, the composite positive electrode active material including the composite material can have further improved ionic conductivity. Secondary batteries including the composite positive electrode active material can have reduced internal resistance and improved cycle performance.

[0106] For example, if the first peak appearing at a diffraction angle of 2θ = 27° ± 2.0° corresponding to the (111) plane of M2S in the XRD spectrum of the composite can have a first diffraction angle, and the second peak appearing at a diffraction angle of 2θ = 27° ± 2.0° corresponding to the (111) plane of M2S in the XRD spectrum of the M2S used to prepare the aforementioned composite can have a second diffraction angle, then the first diffraction angle can be smaller than the second diffraction angle. For example, the position of the first peak can have been shifted to a lower angle than the position of the second peak. Then, the M2S-alkali metal salt-carbon material composite can have a smaller crystallite size than the M2S used in preparing the composite. Because the M2S-alkali metal salt-carbon material composite has a smaller crystallite size, the volume change of the crystallite during charging and discharging is reduced, and therefore, the composite comprising multiple crystallites can exhibit a reduced volume change during charging and discharging. Defects (such as crack formation) in the composite positive electrode active material including the composite during charging and discharging can be suppressed. Therefore, all-solid-state secondary batteries, including composite positive electrode active materials, can have improved cycle performance.

[0107] For example, in the XRD spectrum of the composite, the first peak corresponding to the (111) crystal plane of M2S at a diffraction angle of 2θ = 27° ± 2.0° can have a first full width at half maximum (FWHM1), and in the XRD spectrum of the M2S used to prepare the aforementioned composite, the second peak corresponding to the (111) crystal plane of M2S at a diffraction angle of 2θ = 27° ± 2.0° can have a second full width at half maximum (FWHM2), wherein FWHM1 can be greater than FWHM2. Then, the M2S-alkali metal salt-carbonaceous material composite can have a higher lattice strain than the M2S used in preparing the composite. For example, when M2S and the alkali metal salt form a solid solution, the M2S-alkali metal salt-carbonaceous structure composite can have an increased lattice strain. Because the M2S-alkali metal salt-carbonaceous structure composite has a higher FWHM than the M2S used in preparing the composite, the composite positive electrode active material including the composite can have further improved ionic conductivity. All-solid-state secondary batteries, including composite positive electrode active materials, can have reduced internal resistance and improved cycle performance.

[0108] The particle size (e.g., the size of the composite positive electrode active material) can be, for example, 10 μm or less, 8 μm or less, 5 μm or less, 2 μm or less, 1.5 μm or less, or 1 μm or less. The particle size of the composite can be, for example, in the range of about 1 μm to about 10 μm, in the range of about 2 μm to about 8 μm, or in the range of about 3 μm to about 8 μm. The size of the composite particles can be, for example, in the range of about 0.1 μm to about 10 μm, about 0.1 μm to about 8 μm, about 0.1 μm to about 5 μm, about 0.1 μm to about 2 μm, about 0.1 μm to about 1.5 μm, or about 0.1 μm to about 1 μm. By using composite particles having sizes within the above ranges, volume changes during charging and discharging are suppressed, and therefore, the degradation of the composite positive electrode active material including the composite during charging and discharging can be suppressed. If the size of the composite particles increases excessively, the volume change of the composite during charging and discharging increases, which can accelerate the degradation of the composite positive electrode active material including the composite. Therefore, all-solid-state secondary batteries including composite positive electrode active materials can have improved cycle performance.

[0109] Therefore, all-solid-state secondary batteries incorporating composite positive electrode active materials can exhibit improved cycle performance (e.g., improved lifetime characteristics). For example, the size of the composite particles (e.g., the particle size of the composite) can be measured using laser diffraction, scanning electron microscopy, etc. For instance, the particle size of the composite can be the arithmetic mean of the particle sizes of multiple particles measured from scanning electron microscope images using software.

[0110] Because the composite contains ionicly conductive alkali metal salts and electronically conductive carbonaceous structures in addition to lithium sulfide ions, it can facilitate electron conduction from the surface of the composite to its interior. This reduces the internal resistance of the composite cathode active material and further improves the cycle performance of the all-solid-state secondary battery.

[0111] The diameter and length of carbon nanostructures can be measured from SEM images or optical microscope images. In other embodiments, the diameter and / or length of carbon nanostructures can be measured by laser diffraction methods. For example, carbon nanostructures can be dispersed in solvents or the like to prepare dispersions of carbon nanostructures. These dispersions are used to prepare composites.

[0112] For example, relative to 100 parts by weight of the composite, it may include about 10 parts by weight to about 80 parts by weight of M2S, about 1 part by weight to about 40 parts by weight of an alkali metal salt, and about 1 part by weight to about 20 parts by weight of a carbonaceous structure. For example, relative to 100 parts by weight of the composite, the amount of M2S included in the composite may be about 10 parts by weight to about 80 parts by weight, about 20 parts by weight to about 70 parts by weight, about 30 parts by weight to about 60 parts by weight, or about 40 parts by weight to about 60 parts by weight. For example, relative to 100 parts by weight of the composite, the amount of alkali metal salt included in the composite may be about 10 parts by weight to about 40 parts by weight, about 15 parts by weight to about 40 parts by weight, about 20 parts by weight to about 40 parts by weight, or about 25 parts by weight to about 35 parts by weight. For example, relative to 100 parts by weight of the composite, the amount of carbonaceous material included in the composite may be about 1 part by weight to about 20 parts by weight, about 5 parts by weight to about 20 parts by weight, or about 5 parts by weight to about 15 parts by weight. Composites containing M2S, alkali metal salts, and carbonaceous materials within the above ranges, including composite positive electrode active materials, can provide excellent ionic and / or electronic conductivity.

[0113] For example, the composite can have a 1×10⁻⁶ ion content at 25°C. -5 S / cm or greater, 2×10 -5 S / cm or greater, 4×10 - 5 S / cm or greater, 6×10 -5 S / cm or greater, 8×10 -5 S / cm or greater, or 1×10 -4 Ionic conductivity of S / cm or greater. Ionic conductivity can be measured, for example, using electrochemical impedance spectroscopy, DC polarization methods, etc. Using composites with ionic conductivity in the above range, composite positive electrode active materials containing the composites can exhibit reduced internal resistance. All-solid-state secondary batteries including composite positive electrode active materials can exhibit improved cycle performance. For example, the composite can exhibit 1×10⁻⁶ ions / cm or greater at 25°C. -5 S / cm or greater, 2×10 -5 S / cm or greater, 4×10 -5 S / cm or greater, 6×10 -5 S / cm or greater, 8×10 -5 S / cm or greater, or 1×10 -4Electronic conductivity of S / cm or greater. Electronic conductivity can be measured, for example, using electrochemical impedance spectroscopy, DC polarization methods, etc. Using composites with electronic conductivity in the above range, composite cathode active materials containing these composites can exhibit reduced internal resistance. All-solid-state secondary batteries incorporating composite cathode active materials can exhibit improved initial efficiency, electrode energy density, and lifetime characteristics.

[0114] [positive electrode] [Positive electrode: Positive electrode active material] Reference Figures 2 to 7 The positive electrode 10 may include a positive electrode current collector 11; and a positive electrode active material layer 12, disposed on one or both sides of the positive electrode current collector 11. The positive electrode active material layer 12 may include a positive electrode active material.

[0115] The positive electrode active material layer 12 may include a composite positive electrode active material according to the embodiment. The positive electrode active material layer may also include a solid electrolyte. Because the positive electrode includes a composite positive electrode active material and a solid electrolyte, the internal resistance can be further reduced. Therefore, the cycle performance of the all-solid-state secondary battery with the positive electrode can be further improved.

[0116] Figure 1 The structure of the positive electrode active material layer according to an embodiment is schematically shown. Figure 1 In this study, Li₂S is used as an example of M₂S, LiI is used as an example of an alkali metal salt, and carbon nanofibers (CNF) are used as fibrous carbonaceous materials.

[0117] Referring to the foregoing, the positive electrode active material layer comprises Li₂S (1), LiI (2), and an inorganic electronic conductive structure (3). The CNF, as a one-dimensional structure, can induce long-path network effects, and the inorganic electronic conductive structure, as a two-dimensional structure, brings about the house-of-cards effect, thus significantly improving the electronic conductive network inside the positive electrode. Figure 1 As shown, the sizes of the inorganic electronically conductive structure (3), LiI (2), and Li2S (1) are 1 ≤ 2 < 3. If the aforementioned components have this order of sizes, the inorganic electronically conductive structure can easily form a network that imparts electronic conductivity between lithium sulfides, which are insulators. The sizes of the inorganic electronically conductive structure, LiI, and Li2S refer to their respective average sizes.

[0118] Reference Figures 2 to 7 The positive electrode 10 may include a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on one or both sides of the positive electrode current collector 11. The positive electrode active material layer 12 may include a composite positive electrode active material and a solid electrolyte.

[0119] Relative to 100 parts by weight of the positive electrode active material layer 12, the positive electrode active material layer 12 may include approximately 40 parts by weight to approximately 90 parts by weight, approximately 40 parts by weight to approximately 80 parts by weight, approximately 50 parts by weight to approximately 80 parts by weight, or approximately 50 parts by weight to approximately 70 parts by weight of a composite positive electrode active material. If the amount of the composite positive electrode active material is excessively reduced, the energy density of the all-solid-state secondary battery may deteriorate. If the amount of the composite positive electrode active material is excessively increased, it may accelerate the degradation of the positive electrode caused by volume changes during charging and discharging. Therefore, the cycle performance of the all-solid-state secondary battery 1 may deteriorate.

[0120] In addition to the above-mentioned composite positive electrode active material, the positive electrode active material layer 12 may also include other known positive electrode active materials.

[0121] Other positive electrode active materials may include, for example, Li2S-containing complexes. Examples of Li2S complexes may include: complexes of Li2S and carbonaceous materials; complexes of Li2S, carbonaceous materials, and solid electrolytes; complexes of Li2S and solid electrolytes; complexes of Li2S and lithium salts; complexes of Li2S and metal carbides; complexes of Li2S, carbonaceous materials, and metal carbides; complexes of Li2S and metal nitrides; complexes of Li2S, carbonaceous materials, and metal nitrides; or combinations thereof.

[0122] The Li2S and carbonaceous material composite may include the carbonaceous material. For details on the carbonaceous material, refer to the section on carbonaceous materials in the composite cathode active material. The method for preparing the Li2S and carbonaceous material composite may be a dry method, a wet method, or a combination thereof; however, the method is not limited to these and may be any method available in the art. For example, the method for preparing the Li2S and carbonaceous material composite may be grinding, heat treatment, deposition, etc.; however, the method is not limited to these and may be any method available in the art.

[0123] The composite of Li₂S, carbonaceous materials, and solid electrolytes may include both carbonaceous materials and solid electrolytes. For details on carbonaceous materials, refer to the above description of composites of Li₂S and carbonaceous materials. The solid electrolyte can be, for example, any material that can be used as an ion-conducting material in the art. The solid electrolyte can be, for example, an inorganic solid electrolyte. The solid electrolyte can be, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte can be, for example, a sulfide solid electrolyte, an oxide solid electrolyte, or a combination thereof. Sulfide solid electrolytes may contain, for example, Li, S, and P, and optionally, halogen elements. Sulfide solid electrolytes may be selected from sulfide solid electrolytes used in the electrolyte layer. For example, a sulfide solid electrolyte may have a density of 1 × 10⁻⁶ at room temperature. -5Oxide solid electrolytes can contain, for example, Li, O, and transition metals, and optionally other elements. For example, oxide solid electrolytes can have an ionic conductivity of 1 × 10⁻⁶ S / cm or greater at room temperature. -5 Solid electrolytes with an ionic conductivity of S / cm or greater. Oxide solid electrolytes can be selected from oxide solid electrolytes used in the electrolyte layer.

[0124] Complexes of Li₂S and solid electrolytes may include solid electrolytes. For details on solid electrolytes, refer to the section on complexes of Li₂S, carbonaceous materials, and solid electrolytes.

[0125] Li₂S and lithium salt complexes may include both Li₂S and lithium salts. For details on lithium salts, refer to the section on lithium salts in composite cathode active materials described above. The lithium salt may be at least one lithium halide compound selected from LiF, LiCl, LiBr, and LiI. For example, a Li₂S and lithium salt complex may be a Li₂S-lithium halide complex. Because the Li₂S and lithium halide complex includes a lithium halide compound, it can provide further improved ionic conductivity. Li₂S and lithium salt complexes can be distinguished from simple mixtures of Li₂S and lithium salts. Because simple mixtures of Li₂S and lithium salts cannot maintain a dense interface between Li₂S and lithium salts, they may provide high interfacial resistance and lead to deterioration of the lifespan characteristics of solid-state secondary batteries.

[0126] Complexes of Li₂S and metal carbides may include metal carbides. The metal carbides may be, for example, two-dimensional metal carbides. Two-dimensional metal carbides may be composed of, for example, M… n+1 C n T x (M is a transition metal, T is an end group, T is O, OH and / or F, n = 1, 2 or 3, x is the number of end groups) Two-dimensional metal carbides can be, for example, Ti2CT. x 、(Ti 0.5 , Nb 0.5 )2CT x Nb2CT x V2CT x Ti3C2T x 、(V 0.5 Cr 0.5 3C2T x Ti3CNT x Ta4C3T x Nb4C3T x Or a combination thereof. The surface of two-dimensional metal carbides can be capped by O, OH and / or F.

[0127] Complexes of Li₂S, carbonaceous materials, and metal carbides may include both carbonaceous materials and metal carbides. For details on carbonaceous materials, refer to the section on complexes of Li₂S and carbonaceous materials. For details on metal carbides, refer to the section on complexes of Li₂S and metal carbides.

[0128] Complexes of Li₂S and metal nitrides can include metal nitrides. Metal nitrides can be, for example, two-dimensional metal nitrides. Two-dimensional metal nitrides can be formed from, for example, M... n+1 N n T x (M is a transition metal, T is an end group, T is O, OH and / or F, n=1, 2 or 3, and x is the number of end groups) represents the two-dimensional metal nitride. The surface of the two-dimensional metal nitride can be capped by O, OH and / or F.

[0129] Complexes of Li₂S, carbonaceous materials, and metal nitrides may include both carbonaceous materials and metal nitrides. For details regarding carbonaceous materials, refer to the section on complexes of Li₂S and carbonaceous materials. For details regarding metal nitrides, refer to the section on complexes of Li₂S and metal nitrides.

[0130] The positive electrode active material layer 12 may also include, for example, sulfide compounds distinct from the aforementioned positive electrode active material. Sulfide compounds may be, for example, compounds comprising sulfur and metallic elements other than Li. Sulfide compounds may be, for example, compounds containing sulfur and metallic elements belonging to groups 1 to 14 of the periodic table with an atomic weight of 10 or greater. Sulfide compounds may be, for example, FeS2, VS2, NaS, MnS, FeS, NiS, CuS, or combinations thereof. Since the positive electrode active material layer also includes sulfide compounds, the cycle performance of the all-solid-state secondary battery can be further improved. The amount of such sulfide compounds included in the positive electrode active material layer 12 relative to the total weight of the positive electrode active material layer 12 may be 10 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less.

[0131] [Positive electrode: Solid electrolyte] The positive electrode active material layer 12 may also include, for example, a solid electrolyte. For example, the solid electrolyte may be a sulfide-based solid electrolyte. The solid electrolyte included in the positive electrode 10 may be the same as or different from the solid electrolyte included in the electrolyte layer 30. For details regarding the solid electrolyte, refer to the description of the electrolyte layer 30.

[0132] The solid electrolyte included in the positive electrode active material layer 12 may have a smaller median particle size (D50) than that of the solid electrolyte included in the electrolyte layer 30. For example, the median particle size (D50) of the solid electrolyte included in the positive electrode active material layer 12 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 relative to the median particle size (D50) of the solid electrolyte included in the electrolyte layer 30. The average particle size may be, for example, the median particle size (D50). The median particle size (D50) may refer to the particle size corresponding to a cumulative volume of 50 vol%, counted from the smallest particle size in the particle size distribution measured by laser diffraction.

[0133] Relative to 100 parts by weight of the positive electrode active material layer 12, a solid electrolyte may be included in amounts of approximately 10 parts by weight to approximately 60 parts by weight, approximately 10 parts by weight to approximately 50 parts by weight, approximately 20 parts by weight to approximately 50 parts by weight, or approximately 30 parts by weight to approximately 50 parts by weight. If the amount of solid electrolyte is excessively reduced, the internal resistance of the positive electrode increases, leading to a deterioration in the cycle performance of the secondary battery. If the amount of sulfide-based solid electrolyte is excessively increased, the energy density of the all-solid-state secondary battery 1 may decrease.

[0134] [Positive electrode: Conductive material] The positive electrode active material layer 12 may also include a conductive material. The conductive material may be, for example, a carbonaceous conductive material, a metallic conductive material, or a combination thereof. Examples of carbonaceous conductive materials may include graphite, carbon black, acetylene black, Ketjen black, carbon fibers, and combinations thereof. However, carbonaceous conductive materials are not limited to the foregoing examples and may be any material available in the art as a carbonaceous conductive material. Metallic conductive materials may be metal powder, metal fibers, or combinations thereof, but are not limited thereto, and may be any metallic conductive material available in the art. For example, the amount of conductive material included in the positive electrode active material layer 12 may be from about 1 wt% to about 30 wt%, from about 1 wt% to about 20 wt%, or from about 1 wt% to about 10 wt% relative to the total weight of the positive electrode active material layer 12.

[0135] The positive electrode active material layer may include carbonaceous materials, and the carbonaceous materials may be disposed solely in the composite positive electrode active material. Apart from the composite positive electrode active material containing carbonaceous materials, the positive electrode active material layer 12 may not contain any additional carbonaceous materials. Because the positive electrode active material layer does not contain any additional carbonaceous materials, the positive electrode and the secondary battery 1 can have improved energy density, and their manufacturing process can be simplified.

[0136] [Positive electrode: binder] The positive electrode active material layer 12 may also include a binder. The binder may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to the foregoing examples; any material used as a binder in the art may be used. The amount of binder included in the positive electrode active material layer 12 relative to the total weight of the positive electrode active material layer 12 may be, for example, from about 1 wt% to about 10 wt%. The binder may be omitted.

[0137] [Positive electrode: Other additives] In addition to the positive electrode active material, solid electrolyte, binder and conductive material mentioned above, the positive electrode active material layer 12 may also include, for example, additives (such as fillers, coating agents, dispersants and ionic conductive agents).

[0138] For the fillers, coatings, dispersants, and ion-conducting additives that may be included in the positive electrode active material layer 12, known materials commonly used in electrodes in all-solid-state secondary batteries can be used.

[0139] [Positive electrode: Positive current collector] For example, the positive current collector 11 can be a plate, foil, or the like formed of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof. The positive current collector 11 can be omitted. The positive current collector 11 can have a thickness of, for example, about 1 μm to about 100 μm, about 1 μm to about 50 μm, about 5 μm to about 25 μm, or about 10 μm to about 20 μm.

[0140] For example, the positive current collector 11 may include a substrate film and a metal layer disposed on one or both sides of the substrate film. The substrate film may include, for example, a polymer. For example, the polymer may be a thermoplastic polymer. For example, the polymer may include polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or combinations thereof. For example, the substrate film may be an insulator. Because the substrate film includes an insulating thermoplastic polymer, in the event of a short circuit, the substrate film softens or liquefies, hindering the operation of the battery and thus preventing a rapid increase in current. For example, the metal layer may include indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or alloys thereof. In the event of an overcurrent, the metal layer may disconnect, thereby acting as an electrochemical fuse to provide protection against short circuits. The limiting current and the maximum current can be controlled by controlling the thickness of the metal layer. The metal layer may be plated or deposited on the substrate film. Because the thickness of the metal layer is reduced, the limiting current and / or maximum current of the positive electrode current collector 11 is reduced, thus improving the stability of the lithium battery during short circuits. Lead tabs can be added to the metal layer for external connection. The lead tabs can be welded to the metal layer or metal layer / substrate film laminate by ultrasonic welding, laser welding, spot welding, etc. When the substrate film and / or metal layer melts during welding, the metal layer can be electrically connected to the lead tabs. For stronger welding between the metal layer and the lead tabs, a metal sheet can be added between the metal layer and the lead tabs. The metal sheet can be a thin sheet of the same material as the metal layer. For example, the metal sheet can be a metal foil, metal mesh, etc. For example, the metal sheet can be aluminum foil, copper foil, SUS foil, etc. By placing the metal sheet on the metal layer and then welding the metal layer to the lead tabs, the lead tabs can be welded to the metal sheet / metal layer laminate or the metal sheet / metal layer / substrate film laminate. When the substrate film, metal layer, and / or metal sheet melt during soldering, the metal layer or metal layer / metal sheet laminate can be electrically connected to the lead patch. Metal sheets and / or lead patches can be further added to a portion of the metal layer. For example, the substrate film can have a thickness of about 1 μm to about 50 μm, about 1.5 μm to about 50 μm, about 1.5 μm to about 40 μm, or about 1 μm to about 30 μm. Using a substrate film with a thickness within the above ranges allows for a more effective reduction in the weight of the electrode assembly. For example, the substrate film can have a melting point of about 100°C to about 300°C, about 100°C to about 250°C or lower, or about 100°C to about 200°C. Because the substrate film has a melting point within the above ranges, it can easily melt and bond to the lead patch during soldering. To improve the adhesion between the substrate film and the metal layer, the substrate film can be surface-treated (e.g., corona treatment).For example, the metal layer can have a thickness of about 0.01 μm to about 3 μm, about 0.1 μm to about 3 μm, about 0.1 μm to about 2 μm, or about 0.1 μm to about 1 μm. Using a metal layer with a thickness within the above range, the electrode assembly can provide stability while maintaining conductivity. For example, the metal sheet can have a thickness of about 2 μm to about 10 μm, about 2 μm to about 7 μm, or about 4 μm to about 6 μm. Using a metal sheet with a thickness within the above range, the metal layer and lead terminals can be more easily connected. Because the positive current collector 11 has the above structure, the weight of the positive electrode can be reduced, thus improving the energy density of the positive electrode and the lithium battery.

[0141] [Positive electrode: Inactive component] Reference Figure 5 and Figure 6 The positive electrode 10 may include a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on one surface of the positive electrode current collector 11. Inactive components 40 may be disposed on the side surface of the positive electrode 10. (See reference...) Figure 5 The inactive component 40 can be disposed on the side surfaces of the positive electrode current collector 11 and the positive electrode active material layer 12. (Refer to...) Figure 6 The inactive component 40 may be disposed on the side surface of the positive electrode active material layer 12 and between the electrolyte layer 30 and the positive electrode current collector 11 opposite to the electrolyte layer 30. The inactive component 40 may not be disposed on the side surface of the positive electrode current collector 11. For example, the electrolyte layer 30 may be a solid electrolyte layer.

[0142] By including the inactive component 40, the cracking of the solid electrolyte layer 30 can be prevented during the manufacture and / or charging and discharging of the all-solid-state secondary battery 1, thus improving the cycle performance of the all-solid-state secondary battery 1. In an all-solid-state secondary battery 1 without the inactive component 40, cracks may form in the electrolyte layer 30 due to uneven pressure applied to the electrolyte layer 30 in contact with the positive electrode 10 during the manufacture and / or charging and discharging of the all-solid-state secondary battery 1, and the possibility of short circuits may increase due to the resulting lithium metal growth.

[0143] In the all-solid-state secondary battery 1, the thickness of the inactive component 40 can be greater than or equal to the thickness of the positive electrode active material layer 12. In other embodiments, the thickness of the inactive component 40 in the all-solid-state secondary battery 1 can be substantially the same as the thickness of the positive electrode 10. Because the thickness of the inactive component 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 because the positive electrode 10 and the electrolyte layer 30 are sufficiently in contact with each other, the interfacial resistance between the positive electrode 10 and the electrolyte layer 30 can be reduced. Furthermore, because the electrolyte layer 30 is sufficiently sintered during the pressing manufacturing process of the all-solid-state secondary battery 1, the electrolyte layer 30 and the all-solid-state secondary battery 1 including the electrolyte layer 30 can have reduced internal resistance.

[0144] The inactive component 40 can contact the electrolyte layer 30 while surrounding the side surface of the positive electrode 10. Since the inactive component 40 is in contact with the electrolyte layer 30 while surrounding the side surface of the positive electrode 10, the electrolyte layer 30, which is not in contact with the positive electrode 10, can be effectively prevented from cracking due to pressure differences during the pressing process. The inactive component 40 can be separated from the negative electrode 20, and more specifically, from the first negative electrode active material layer 22, while surrounding the side surface of the positive electrode 10. The inactive component 40 can be in contact with the electrolyte layer 30 while surrounding the side surface of the positive electrode 10, and can be separated from the negative electrode 20. This reduces the risk of short circuits caused by physical contact between the positive electrode 10 and the first negative electrode active material layer 22, or by lithium overcharging. For example, because the inactive component 40 is simultaneously disposed on the side surface of the positive electrode active material layer and the side surface of the positive electrode current collector 11, the risk of short circuits caused by contact between the positive electrode current collector 11 and the negative electrode 20 can be effectively suppressed.

[0145] Reference Figure 5 and Figure 6 The inactive member 40 can extend from the side surface of the positive electrode 10 to the end of the electrolyte layer 30. Because the inactive member 40 extends to the end of the electrolyte layer 30, crack formation at the end of the electrolyte layer 30 can be suppressed. The end of the electrolyte layer 30 can be the outermost portion continuous with the side surface of the electrolyte layer 30. The inactive member 40 can extend to the outermost portion continuous with the side surface of the electrolyte layer 30. The inactive member 40 can be separated from the negative electrode 20, and more specifically, from the first negative electrode active material layer 22. The inactive member 40 can extend to the end of the electrolyte layer 30, but may not contact the negative electrode 20. For example, the inactive member 40 can fill the space extending from the side surface of the positive electrode 10 to the end of the electrolyte layer 30.

[0146] Reference Figure 5 and Figure 6The width of the inactive member 40 extending from the side surface of the positive electrode 10 to the end of the electrolyte layer 30 can be, for example, about 1% to about 30%, about 1% to about 25%, about 1% to about 20%, about 1% to about 20%, about 1% to about 15%, about 1% to about 10%, or about 1% to about 5% of the width between one side surface of the positive electrode 10 and the other side surface opposite to said one side surface. If the width of the inactive member 40 is too large, the energy density of the all-solid-state secondary battery 1 may decrease. If the width of the inactive member 40 is too small, the effect of placing the inactive member 40 may be negligible.

[0147] The surface area of ​​the positive electrode 10 can be smaller than the surface area of ​​the electrolyte layer 30 in contact with the positive electrode 10. The inactive component 40 compensates for the surface area difference between the positive electrode 10 and the electrolyte layer 30 by surrounding the side surface of the positive electrode 10. Because the surface area of ​​the inactive component 40 compensates for the difference between the surface areas of the positive electrode 10 and the electrolyte layer 30, the rupture of the electrolyte layer 30 caused by the pressure difference during the pressing process can be effectively suppressed. For example, the sum of the surface areas of the positive electrode 10 and the inactive component 40 can be equal to the surface area of ​​the electrolyte layer 30. For example, the electrolyte layer 30 can be a solid electrolyte layer.

[0148] For example, the surface area of ​​the positive electrode 10 may be less than 100%, less than 99%, less than 98%, less than 97%, less than 96%, or less than 95% of the surface area of ​​the electrolyte layer 30. For example, the surface area of ​​the positive electrode 10 may be about 50% to less than 100%, about 50% to about 99%, about 55% to about 98%, about 60% to about 97%, about 70% to about 96%, about 80% to about 95%, or about 85% to about 95% of the surface area of ​​the electrolyte layer 30.

[0149] If the surface area of ​​the positive electrode 10 is equal to or greater than the surface area of ​​the electrolyte layer 30, the possibility of a short circuit due to physical contact between the positive electrode 10 and the first negative electrode active material layer 22, or due to lithium overcharging, increases. For example, the surface area of ​​the positive electrode 10 may be equal to the surface area of ​​the positive electrode active material layer 12. For example, the surface area of ​​the positive electrode 10 may be equal to the surface area of ​​the positive electrode current collector 11.

[0150] For example, the surface area of ​​the inactive component 40 may be 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less relative to the surface area of ​​the positive electrode 10. For example, the surface area of ​​the inactive component 40 may be about 1% to about 50%, about 5% to about 40%, about 5% to about 30%, about 5% to about 20%, or about 5% to about 15% relative to the surface area of ​​the positive electrode 10.

[0151] The surface area S1 of the positive electrode 10 is smaller than the surface area S4 of the negative electrode current collector 21. For example, the surface area S1 of the positive electrode 10 may be less than 100%, 99%, 98%, 97%, 96%, or 95% of the surface area S4 of the negative electrode current collector 21. For example, the surface area S1 of the positive electrode 10 may be less than 50% to 100%, about 50% to about 99%, about 55% to about 98%, about 60% to about 97%, about 70% to about 96%, about 80% to about 95%, or about 85% to about 95% of the surface area S4 of the negative electrode current collector 21. For example, the surface area S4 of the negative electrode current collector 21 may be equal to the surface area of ​​the negative electrode 20. For example, the surface area S4 of the negative electrode current collector 21 may be equal to the surface area of ​​the first negative electrode active material layer 22.

[0152] As used herein, unless otherwise indicated, "equivalent" and / or "identical" area, length, width, thickness, and / or shape or form may include "substantially equivalent" and "substantially identical" area, length, width, thickness, and / or shape or form. For example, "equivalent" and / or "identical" area, length, width, thickness, and / or shape or form may include unintended differences in area, length, width, thickness, and / or shape or form within the range of less than 3%, less than 2%, less than 1%, less than 0.5%, or less than 0.1%.

[0153] For example, the thickness of the inactive component 40 may be greater than the thickness of the first negative electrode active material layer 22. For example, the thickness of the first negative electrode active material layer 22 may be 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less relative to the thickness of the inactive component 40. For example, the thickness of the first negative electrode active material layer 22 may be about 1% to about 50%, about 1% to about 40%, about 1% to about 30%, about 1% to about 20%, or about 1% to about 10% relative to the thickness of the inactive component 40.

[0154] The inactive component 40 can be, for example, a gasket. Using a gasket as the inactive component 40 can effectively suppress the formation of cracks in the electrolyte layer 30 due to pressure differences during the pressing process.

[0155] For example, the inactive component 40 may have a single-layer structure. In other embodiments, although not shown in the figures, the inactive component 40 may have a multi-layer structure. In an inactive component 40 with a multi-layer structure, the individual layers may have different configurations. The inactive component 40 with a multi-layer structure may have, for example, a two-layer structure, a three-layer structure, a four-layer structure, or a five-layer structure. The inactive component 40 with a multi-layer structure may include, for example, one or more adhesive layers and one or more support layers. For example, the adhesive layer can effectively prevent separation between the positive electrode 10 and the electrolyte layer 30 due to volume changes that occur during the charging and discharging of the positive electrode 10, and can improve the film strength of the inactive component 40 by providing adhesion between the support layer and other layers. The support layer can provide support for the inactive component 40, prevent uneven pressure applied to the electrolyte layer 30 during the pressing process or charging and discharging process, and prevent shape deformation of the manufactured all-solid-state secondary battery 1.

[0156] The inactive component 40 may have, for example, a flame-retardant inactive component. The flame retardancy provided by the flame-retardant inactive component can reduce the risk of thermal runaway and explosion of the all-solid-state secondary battery 1. Therefore, the safety of the all-solid-state secondary battery 1 can be further improved. Since the flame-retardant inactive component absorbs residual moisture inside the all-solid-state secondary battery 1, it can prevent the degradation of the all-solid-state secondary battery 1, thereby improving the lifespan characteristics of the all-solid-state secondary battery 1.

[0157] The flame-retardant inactive component may include, for example, a matrix and a filler. For example, the matrix may include a substrate and a reinforcing material. For example, the matrix may include a fiber substrate and a fiber reinforcing material. Because the matrix includes a substrate, the matrix can be elastic. The matrix can be placed in various locations and effectively accommodates volume changes in the all-solid-state secondary battery 1 during charging and discharging. The substrate included in the matrix may include, for example, a first fiber material. Because the substrate includes a first fiber material, it can effectively accommodate volume changes in the positive electrode 10 during charging and discharging of the all-solid-state secondary battery 1, and can effectively suppress deformation of the inactive component 40 caused by volume changes in the positive electrode 10. For example, the first fiber material may be a material with an aspect ratio of 2 or greater, 5 or greater, 20 or greater, or 50 or greater. For example, the first fiber material may be a material with an aspect ratio of about 5 to about 1,000, about 20 to about 1,000, or about 50 to about 1,000. For example, the first fiber material may be an insulating material. Because the first fibrous material is an insulating material, it can effectively prevent short circuits that may occur between the positive electrode 10 and the negative electrode 20 due to lithium dendrites or the like during charging and discharging of the all-solid-state secondary battery 1. Examples of the first fibrous material may include at least one selected from pulp fibers, insulating polymer fibers, and ion-conducting polymer fibers. Since the matrix includes a reinforcing material, the strength of the matrix can be improved. The matrix can be used to prevent the all-solid-state secondary battery 1 from undergoing excessive volume changes during charging and discharging and to protect the all-solid-state secondary battery 1 from deformation. The reinforcing material included in the matrix may include, for example, a second fibrous material. Since the reinforcing material includes a second fibrous material, a more uniform increase in the strength of the matrix can be achieved. For example, the second fibrous material may be a material with an aspect ratio of 2 or greater, 3 or greater, 5 or greater, or 10 or greater. For example, the first fibrous material may be a material with an aspect ratio of about 2 to about 100, about 3 to about 100, about 5 to about 100, or about 10 to about 100. For example, the second fibrous material may be a flame-retardant material. Because the second fibrous material is a flame-retardant material, it can effectively suppress fires caused by thermal runaway during charging and discharging of the all-solid-state secondary battery 1 or by external impacts. For example, the second fibrous material can be glass fiber, metal oxide fiber, ceramic fiber, etc.

[0158] In addition to the matrix, the flame-retardant inactive component may also include a filler. The filler may be disposed within the matrix, on the surface of the matrix, or both. Examples of fillers may include inorganic materials. The filler included in the flame-retardant inactive component may be, for example, a hygroscopic agent. For example, the filler can remove residual moisture from the all-solid-state secondary battery 1 by adsorbing water vapor at temperatures below 100ºC, thereby preventing the degradation of the all-solid-state secondary battery 1. Furthermore, if the temperature of the all-solid-state secondary battery 1 rises to 150°C or higher due to thermal runaway caused by external impact, or during charging and discharging of the all-solid-state secondary battery 1, the filler can release the adsorbed moisture to effectively prevent the all-solid-state secondary battery 1 from igniting. For example, the filler may be a flame retardant. For example, the filler may be a hygroscopic metal hydroxide. The metal hydroxide included in the filler may be, for example, Mg(OH)2, Fe(OH)3, Sb(OH)3, Sn(OH)4, Ti(OH)3, Zr(OH)4, Al(OH)3, or combinations thereof. The amount of filler included in the flame-retardant inactive component 4 relative to 100 parts by weight may be, for example, about 10 parts by weight to about 80 parts by weight, about 20 parts by weight to about 80 parts by weight, about 30 parts by weight to about 80 parts by weight, about 40 parts by weight to about 80 parts by weight, about 50 parts by weight to about 80 parts by weight, about 60 parts by weight to about 80 parts by weight, or about 65 parts by weight to about 80 parts by weight.

[0159] The flame-retardant inactive component may include, for example, an adhesive. The adhesive may include, for example, a curable polymer or a non-curable polymer. The curable polymer may be a polymer that cures by heat and / or pressure. For example, the curable polymer may be solid at room temperature. The flame-retardant inactive component 40 may include, for example, a thermosetting curable film and / or its cured product. The thermosetting curable film may be, for example, Toray's TSA-66.

[0160] In addition to the substrate, reinforcing material, filler, and binder described above, the flame-retardant inactive component may also include other materials. For example, the flame-retardant inactive component may also include at least one selected from paper, insulating polymer, ion-conducting polymer, insulating inorganic material, oxide solid electrolyte, and sulfide solid electrolyte. The insulating polymer may be an olefin polymer (such as polypropylene (PP), polyethylene (PE), etc.).

[0161] The substrate or reinforcing material included in the flame-retardant inactive component may have a density relative to, for example, about 10% to about 300%, about 10% to about 150%, about 10% to about 140%, about 10% to about 130%, or about 10% to about 120% of the density of the positive active material included in the positive active material layer 12.

[0162] The inactive component 40 may be a component that does not contain any electrochemically active material (i.e., electrode active material). The electrode active material may be a material that adsorbs / desorbs lithium. The inactive component 40 may be a component made of a material that is not an electrode active material available in the art.

[0163] Solid-state rechargeable batteries A solid-state secondary battery according to one or more embodiments may include: a positive electrode layer; a negative electrode layer; and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The negative electrode layer may include a negative electrode current collector and a first negative electrode active material layer disposed on one side of the negative electrode current collector.

[0164] The negative electrode layer may include a negative electrode current collector and a lithium host layer disposed on one side of the negative electrode current collector. The lithium host layer may include a lithium host structure, which may include one or more lithium hosts. The lithium host may include a carbon-based lithium host, a metal-based lithium host, a polymer-based lithium host, or a combination thereof. The negative electrode layer may include a first inactive component disposed on the side surface of the negative electrode layer.

[0165] A lithium plating layer can be formed inside and / or on the surface of the lithium host layer.

[0166] All-solid-state secondary batteries may include lithium-containing sulfide-based positive electrode active materials as positive electrode active materials. In some embodiments, blockage of ion and / or electron transport paths due to volume expansion of lithium-free sulfide-based positive electrode active materials (e.g., sulfur (S)) during initial discharge can be prevented. By preventing such blockage of ion and / or electron transport paths, the cycle performance of all-solid-state secondary batteries can be improved.

[0167] Because all-solid-state secondary batteries include a lithium host layer on top of the negative electrode layer, the lithium host acts as a carrier while lithium metal is deposited onto the negative electrode layer, thus reducing or suppressing unevenness in lithium deposition. During the charging and discharging of the solid-state secondary battery, the formation and growth of lithium dendrites and / or dead lithium can be reduced or suppressed. Therefore, degradation of the all-solid-state secondary battery can be prevented, and its cycle performance can be improved.

[0168] Because all-solid-state secondary batteries include a lithium host layer on top of the negative electrode layer, the drastic volume changes of the negative electrode layer during charging and discharging can be reduced or suppressed. Since these drastic volume changes of the negative electrode layer are reduced or suppressed, the degradation of the all-solid-state secondary battery due to volume changes during charging and discharging can be reduced or suppressed, and the cycle performance of the all-solid-state secondary battery can be improved.

[0169] In all-solid-state secondary batteries, including a solid electrolyte layer can prevent the migration of polysulfides to the negative electrode layer during charging and discharging of lithium-containing sulfide-based positive electrode active materials. Therefore, side reactions between polysulfides and the negative electrode active material can be suppressed.

[0170] Because the first inactive component is disposed on the side surface of the negative electrode layer, the formation and growth of lithium dendrites and / or short circuits between the positive electrode and the lithium metal molten at high temperatures can be more effectively suppressed during the charging and discharging of the solid-state secondary battery. Therefore, short circuits in the all-solid-state secondary battery can be prevented, and the lifetime characteristics of the all-solid-state secondary battery can be improved.

[0171] Reference Figures 2 to 6 The all-solid-state secondary battery 1 may include: a positive electrode 10; a negative electrode 20; and an electrolyte layer 30 disposed between the positive electrode 10 and the negative electrode 20. The negative electrode 20 may include a negative electrode current collector 21 and a first negative electrode active material layer 22 disposed on one side of the negative electrode current collector 21.

[0172] [negative electrode] [Negative electrode: Negative electrode active material] Reference Figures 3 to 6 The negative electrode 20 may include a first negative electrode active material layer 22. The first negative electrode active material layer 22 may include, for example, a negative electrode active material and a binder.

[0173] The negative electrode active material included in the first negative electrode active material layer 22 can be, for example, a negative electrode material that can form an alloy or compound with lithium.

[0174] The negative electrode active material included in the first negative electrode active material layer 22 can be, for example, in particulate form. The negative electrode active material in particulate form can have, for example, an average particle size of 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, 500 nm or less, 300 nm or less, or 100 nm or less. For example, the negative electrode active material in particulate form can have an average particle size of about 10 nm to about 4 μm, about 10 nm to about 3 μm, about 10 nm to about 2 μm, about 10 nm to about 1 μm, about 10 nm to about 500 nm, about 10 nm to about 300 nm, or about 10 nm to about 100 nm. Negative electrode active materials having an average particle size within the above range can promote reversible adsorption and / or desorption of lithium during charging / discharging. The average particle size of the negative electrode active material can be, for example, the median particle size (D50) measured by a laser-type particle size analyzer.

[0175] The negative electrode active material included in the first negative electrode active material layer 22 may include at least one selected from, for example, carbonaceous negative electrode active materials and metallic or quasi-metallic negative electrode active materials.

[0176] Carbonaceous anode active materials may include, for example, amorphous carbon, crystalline carbon, porous carbon, or combinations thereof.

[0177] Carbonaceous anode active materials can be, for example, amorphous carbon. Examples of amorphous carbon may include carbon black (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB), graphene, etc.; however, carbonaceous anode active materials are not limited to the foregoing examples and can be any material classified as amorphous carbon in the art. Amorphous carbon is carbon that does not have a crystalline structure or has extremely low crystallinity, thus distinguishing it from crystalline carbon or graphitic carbon.

[0178] The carbonaceous anode active material can be, for example, porous carbon. For example, the pores included in the porous carbon can have a pore volume of about 0.1 cc / g to about 10.0 cc / g, about 0.5 cc / g to about 5 cc / g, or about 0.1 cc / g to about 1 cc / g. For example, the pores included in the porous carbon can have an average pore size of about 1 nm to about 50 nm, about 1 nm to about 30 nm, or about 1 nm to about 10 nm. The BET specific surface area of ​​the porous carbon can be, for example, about 100 m². 2 / g to approximately 3,000m 2 / g.

[0179] Metallic or quasi-metallic anode active materials may include at least one selected from gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn), but are not necessarily limited to the aforementioned materials. Metallic or quasi-metallic anode active materials may be any metallic or quasi-metallic anode active material available in the art that can form alloys or compounds with lithium. For example, nickel (Ni) does not form alloys with lithium and is therefore not considered a metallic anode active material.

[0180] Among the above-mentioned negative electrode active materials, the first negative electrode active material layer 22 may include a single negative electrode active material, or may include a mixture of multiple different types of negative electrode active materials. For example, the first negative electrode active material layer 22 may include only amorphous carbon, or may include one or more of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). In some embodiments, the first negative electrode active material layer 22 may include amorphous carbon and a mixture of at least one of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). In such a mixture, the mixing ratio of amorphous carbon to the metal described herein (such as gold (Au)) can be from about 99:1 to about 1:99, from about 10:1 to about 1:2, from about 5:1 to about 1:1, or from about 4:1 to about 2:1 by weight, but is not limited thereto, and can be selected according to the desired characteristics of the all-solid-state secondary battery 1. Since the negative electrode active material has the above composition, the cycle performance of the all-solid-state secondary battery 1 can be further improved.

[0181] The negative electrode active material included in the first negative electrode active material layer 22 may include, for example, a mixture of first particles made of amorphous carbon and second particles made of metal or metalloid. Examples of metal or metalloid may include gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), etc. In some embodiments, the metalloid may be a semiconductor. The content of the second particles may be from about 1 wt% to about 99 wt%, from about 1 wt% to about 60 wt%, from about 8 wt% to about 60 wt%, from about 10 wt% to about 50 wt%, from about 15 wt% to about 40 wt%, or from about 20 wt% to about 30 wt% relative to the total weight of the mixture. When the amount of the second particles is within the above ranges, the cycle performance of the all-solid-state secondary battery 1 can be further improved.

[0182] In some embodiments, the first negative electrode active material layer 22 may include a composite negative electrode active material. For example, the composite negative electrode active material may include a carbonaceous support and a metal-based negative electrode active material supported on the carbonaceous support. For example, the composite negative electrode active material may have a structure in which silver (Ag) is supported on carbon particles. By using a composite negative electrode active material with the above structure, uneven distribution of the metal-based negative electrode active material within the first negative electrode active material layer can be prevented, thereby producing a uniform distribution. Therefore, the cycle performance of the all-solid-state secondary battery 1 including the first negative electrode active material layer 22 can be further improved.

[0183] Examples of metal-based negative electrode active materials supported on carbonaceous carriers may include metals, metal oxides, metal-metal oxide composites, or combinations thereof. Metals may include, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), tellurium (Te), zinc (Zn), etc. Examples of metal oxides may include gold (Au) oxide, platinum (Pt) oxide, palladium (Pd) oxide, silicon (Si) oxide, silver (Ag) oxide, aluminum (Al) oxide, bismuth (Bi) oxide, tin (Sn) oxide, tellurium (Te) oxide, zinc (Zn) oxide, etc. For example, metal oxides may include Au x O y (0 < x ≤ 2, 0 < y ≤ 3), Pt x O y (0 < x ≤ 1, 0 < y ≤ 2), Pd x O y (0 < x ≤ 1, 0 < y ≤ 1), Si x O y (0 < x ≤ 1, 0 < y ≤ 2), Ag x O y (0 < x ≤ 2, 0 < y ≤ 1), Al x O y (0 < x ≤ 2, 0 < y ≤ 3), Bi x O y (0 < x ≤ 2, 0 < y ≤ 3), Sn x O y (0 < x ≤ 1, 0 < y ≤ 2), Te x O y (0 < x ≤ 1, 0 < y ≤ 3), Zn x O y (0 < x ≤ 1, 0 < y ≤ 1) or combinations thereof. Examples of metal-metal oxide composites may include composites of Au and Au x O y (0 < x ≤ 2, 0 < y ≤ 3), composites of Pt and Pt x O y (0 < x ≤ 1, 0 < y ≤ 2), composites of Pd and Pd x O y (0 < x ≤ 1, 0 < y ≤ 1), composites of Si and Si x O y (0 < x ≤ 1, 0 < y ≤ 2), composites of Ag and Ag x O y (0 < x ≤ 2, 0 < y ≤ 1), composites of Al and Al x O y (0 < x ≤ 2, 0 < y ≤ 3), composites of Bi and Bix O y complexes of (0 < x ≤ 2, 0 < y ≤ 3), Sn, and Sn x O y complexes of (0 < x ≤ 1, 0 < y ≤ 2), Te, and Te x O y complexes of (0 < x ≤ 1, 0 < y ≤ 3), Zn, and Zn x O y complexes of (0 < x ≤ 1, 0 < y ≤ 1) or combinations thereof.

[0184] The carbonaceous carrier can be, for example, amorphous carbon. Examples of amorphous carbon can include carbon black (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB), graphene, activated carbon, carbon nanofibers (CNF), carbon nanotubes (CNT), etc. However, amorphous carbon is not limited to the foregoing examples and can be any material classified as amorphous carbon in the art. Amorphous carbon is carbon that does not have a crystal structure or has a very low crystallinity, and thus can be distinguished from crystalline carbon or graphite carbon. The carbonaceous material can be, for example, a carbonaceous negative electrode active material.

[0185] The composite negative electrode active material can have, for example, a particulate form. The particle size of the composite negative electrode active material having a particulate form can be, for example, about 10 nm to about 4 μm, about 10 nm to about 1 μm, about 10 nm to about 500 nm, about 10 nm to about 200 nm, or about 10 nm to about 100 nm. If the composite negative electrode active material has a particle size within the above range, the reversible adsorption and / or desorption of lithium during charging and discharging can be further promoted. The metal-based negative electrode active material loaded on the carrier can have, for example, a particulate form. For example, the metal-based negative electrode active material can have a particle size of about 1 nm to about 200 nm, about 1 nm to about 150 nm, about 5 nm to about 100 nm, or about 10 nm to about 50 nm. For example, the carbonaceous carrier can have a particulate form. For example, the carbonaceous carrier can have a particle size of about 10 nm to about 2 μm, about 10 nm to about 1 μm, about 10 nm to about 500 nm, about 10 nm to about 200 nm, or about 10 nm to about 100 nm. By using a carbonaceous carrier having a particle size within the above range, a more uniform distribution within the first negative electrode active material layer can be achieved. For example, the carbonaceous carrier can be nanoparticles with a particle size of 500 nm or less. The particle size of the composite negative electrode active material, the particle size of the metal-based negative electrode active material, and the particle size of the carbonaceous carrier can be, for example, the average particle size. The average particle size can be, for example, the median particle size (D50) measured by a laser-type particle size distribution analyzer. In some embodiments, the average particle size can be automatically determined from an electron microscope image using software or manually determined using a manual.

[0186] [Negative electrode: Binder] The binder included in the first negative electrode active material layer 22 can be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc. However, the binder is not limited to the foregoing examples and can be any material that can be used as a binder in the art. The binder can consist of a single type of binder or multiple types of binders.

[0187] Since the first negative electrode active material layer 22 may include a binder, it can be stabilized on the negative electrode current collector 21. Furthermore, despite volume changes and / or displacements of the first negative electrode active material layer 22 during charging and discharging processes, crack formation in the first negative electrode active material layer 22 can be suppressed. For example, if the first negative electrode active material layer 22 does not contain any binder, it may easily delaminate from the negative electrode current collector 21. In areas where the negative electrode current collector 21 is exposed due to delamination of the first negative electrode active material layer 22 from the negative electrode current collector 21, the negative electrode current collector 21 may come into contact with the electrolyte layer 30, thus increasing the possibility of a short circuit. For example, the first negative electrode active material layer 22 can be prepared by coating the negative electrode current collector 21 with a slurry in which the material forming the first negative electrode active material layer 22 is dispersed and then drying it. By including a binder in the first negative electrode active material layer 22, stable dispersion of the negative electrode active material within the slurry can be achieved. For example, if the paste is coated onto the negative electrode current collector 21 by screen printing, it is possible to prevent screen clogging (e.g., clogging by aggregates of negative electrode active material).

[0188] [Negative electrode: Other additives] The first negative electrode active material layer 22 may also include other additives (such as fillers, coatings, dispersants, ion-conducting agents, etc.) used in conventional solid-state secondary batteries.

[0189] [Negative electrode: Solid electrolyte] The first negative electrode active material layer 22 may also include a solid electrolyte. The solid electrolyte may be, for example, a material selected from solid electrolytes included in the electrolyte layer 30. The solid electrolyte included in the first negative electrode active material layer 22 may serve as a reaction site for the initiation of lithium metal formation, as a space for storing the formed lithium metal, or as a pathway for the transfer of lithium ions within the first negative electrode active material layer 22. The solid electrolyte may be omitted.

[0190] For example, in the first negative electrode active material layer 22, the concentration of the solid electrolyte can be high in the region adjacent to the electrolyte layer 30 and low in the region adjacent to the negative electrode current collector 21. For example, the solid electrolyte in the first negative electrode active material layer 22 can have a concentration gradient that gradually decreases from the region adjacent to the electrolyte layer 30 to the region adjacent to the negative electrode current collector 21.

[0191] [Negative Electrode: First Negative Electrode Active Material Layer] The ratio (B / A) of the initial charging capacity (B) of the first negative electrode active material layer 22 to the initial charging capacity (A) of the positive electrode active material layer can be from about 0.005 to about 0.45. The initial charging capacity of the positive electrode active material layer 12 can be increased by charging from the first open-circuit voltage to a value relative to Li / Li + The initial charge capacity of the first negative electrode active material layer 22 can be determined by discharging from the second open-circuit voltage to a value relative to Li / Li. + The value is measured at 0.01V.

[0192] The maximum charging voltage can be determined by the type of positive electrode active material. The maximum charging voltage can be, for example, 1.5V, 2.0V, 2.5V, 3.0V, 3.5V, 4.0V, 4.2V, or 4.3V. For example, the maximum charging voltage of Li₂S or Li₂S complexes relative to Li / Li + It can be 2.5V. For example, the maximum charging voltage of Li2S or Li2S complexes relative to Li / Li +The voltage can be 3.0V. The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer 22 to the initial charge capacity (A) of the positive electrode active material layer can be, for example, about 0.01 to about 0.3, about 0.01 to about 0.2, or about 0.05 to about 0.1. The initial charge capacity (mAh) of the positive electrode active material layer 12 can be obtained by multiplying the specific charge capacity (mAh / g) of the positive electrode active material layer 12 by the mass (g) of the positive electrode active material in the positive electrode active material layer 12. If multiple types of positive electrode active materials are used, the product of specific charge capacity × mass can be calculated for each positive electrode active material, and the sum of these products can be defined as 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 can also be calculated in the same way. The initial charge capacity of the first negative electrode active material layer 22 can be obtained by multiplying the specific charge capacity (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the first negative electrode active material layer 22. If multiple types of negative electrode active materials are used, the product of charge specific capacity × mass can be calculated for each negative electrode active material, and the sum of these products can be defined as the initial charge capacity of the first negative electrode active material layer 22. The charge specific capacity of each of the positive and negative electrode active materials can be measured using a solid-state half-cell utilizing lithium metal as the 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 can be measured using a solid-state half-cell at a constant current density (e.g., 0.1 mA / cm²). 2 Direct measurement is possible under these conditions. For the positive electrode, measurements can be taken from the first open-circuit voltage (OCV) to the maximum charging voltage (e.g., 3.0V relative to Li / Li). + The operating voltage is measured. For the negative electrode, this measurement can be performed relative to the negative electrode (e.g., lithium metal) from a second OCV to 0.01V. For example, a solid half-cell with a positive electrode active material layer can be measured at 0.1mA / cm. 2 A solid half-cell with a constant current from the first OCV to 3.0V can be charged at 0.1mA / cm. 2 A constant current discharges from the second OCV to 0.01V. For example, the current density during constant current charging can be 0.2mA / cm². 2 or 0.5mA / cm 2 A solid-state half-cell with a positive electrode active material layer can be charged from the first OCV to, for example, 2.5V, 2.0V, 3.5V, or 4.0V. The maximum charging voltage of the positive electrode active material layer can be determined based on the maximum voltage of a single cell that meets the safety conditions described in JISC 8712:2015 of the Japanese Standards Institute.

[0193] 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 extremely small. Therefore, lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 during repeated charge / discharge processes may cause the first negative electrode active material layer 22 to collapse, making it difficult to improve the cycle performance of the all-solid-state secondary battery 1. If the charge capacity of the first negative electrode active material layer 22 is too large, the energy density of the all-solid-state secondary battery 1 may decrease, and the internal resistance of the all-solid-state secondary battery 1 caused by the first negative electrode active material layer 22 may increase, making it difficult to achieve improved cycle performance of the all-solid-state secondary battery 1.

[0194] For example, the first negative electrode active material layer 22 may have a thickness of 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less relative to the thickness of the positive electrode active material layer 12. For example, the first negative electrode active material layer 22 may have a thickness of about 1% to about 50%, about 1% to about 40%, about 1% to about 30%, about 1% to about 20%, about 1% to about 10%, or about 1% to about 5% relative to the thickness of the positive electrode active material layer 12. For example, the first negative electrode active material layer 22 may have a thickness of about 1 μm to about 20 μm, about 2 μm to about 15 μm, or about 3 μm to about 10 μm. If the first negative electrode active material layer 22 is too thin, lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 may cause the first negative electrode active material layer 22 to collapse, thus making it difficult to achieve improved cycle performance of the all-solid-state secondary battery 1. If the first negative electrode active material layer 22 is too thick, the energy density of the all-solid-state secondary battery 1 may decrease, and the internal resistance of the all-solid-state secondary battery 1 caused by the first negative electrode active material layer 22 may increase, thus making it difficult to achieve improved cycle performance of the all-solid-state secondary battery 1. If the thickness of the first negative electrode active material layer 22 is reduced, for example, the initial charging capacity of the first negative electrode active material layer 22 may also decrease.

[0195] [Negative electrode: Second negative electrode active material layer] Reference Figure 4The all-solid-state secondary battery 1 may further include, for example, a second negative electrode active material layer 24 disposed between the negative electrode current collector 21 and the first negative electrode active material layer 22 after charging. The second negative electrode active material layer 24 may be a metal layer comprising lithium or a lithium alloy. The metal layer may include lithium or a lithium alloy. Thus, the second negative electrode active material layer 24, as a lithium-containing metal layer, can be used, for example, as a lithium storage device. The lithium alloy may include, for example, Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, Li-Si alloy, etc., but is not limited thereto, and may be any material that can be used as a lithium alloy in the art. The second negative electrode active material layer 24 may be composed of one of such alloys or lithium, or may be composed of various types of such alloys. The second negative electrode active material layer 24 may be, for example, a plating. For example, the second negative electrode active material layer 24 may be plated between the first negative electrode active material layer 22 and the negative electrode current collector 21 during the charging process of the all-solid-state secondary battery 1.

[0196] The second negative electrode active material layer 24 is not limited to any specific thickness, but can have a thickness of, for example, about 1 μm to about 500 μm, about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 1 μm to about 100 μm, or about 1 μm to about 50 μm. If the thickness of the second negative electrode active material layer 24 is too small, it may not be able to adequately function as a lithium storage device. If the thickness of the second negative electrode active material layer 24 is too large, the mass and volume of the all-solid-state secondary battery 1 increase, and therefore, the cycle performance of the all-solid-state secondary battery 1 may be more prone to degradation.

[0197] In some embodiments, 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. If the second negative electrode active material layer 24 is positioned 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 is a lithium-containing metal layer and thus acts as a lithium storage device. For example, a lithium foil may be positioned 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.

[0198] If the second negative electrode active material layer 24 is deposited by charging after assembling the all-solid-state secondary battery 1, then the second negative electrode active material layer 24 is not included during the assembly of the all-solid-state secondary battery 1. Therefore, the all-solid-state secondary battery 1 can have an increased energy density. If the all-solid-state secondary battery 1 is charged, it can be charged beyond the charging capacity of the first negative electrode active material layer 22. In some embodiments, the first negative electrode active material layer 22 can be overcharged. At the start of charging, lithium can be 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 can form an alloy or compound with lithium ions moving from the positive electrode 10. If charging exceeds the capacity of the first negative electrode active material layer 22, lithium can be deposited, for example, on the back side of the first negative electrode active material layer 22 (e.g., between the negative electrode current collector 21 and the first negative electrode active material layer 22), and then a metal layer corresponding to the second negative electrode active material layer 24 can be formed by the deposited lithium. The second negative electrode active material layer 24 can be a metal layer mainly composed of lithium (i.e., metallic lithium). This result can be attributed to the fact that the negative electrode active material included in the first negative electrode active material layer 22 comprises a material that forms an alloy or compound with lithium. During discharge, lithium in the first negative electrode active material layer 22 and the second negative electrode active material layer 24 (e.g., a metal layer) is ionized and migrates toward the positive electrode 10. Therefore, lithium can be used as the negative electrode active material in the all-solid-state secondary battery 1. Because the first negative electrode active material layer 22 is coated on the second negative electrode active material layer 24, the first negative electrode active material layer 22 can serve as a protective layer for the second negative electrode active material layer 24 (e.g., a metal layer), while suppressing the precipitation and growth of lithium dendrites. Therefore, short circuits and capacity decay in the all-solid-state secondary battery 1 can be suppressed, thus improving the cycle performance of the all-solid-state secondary battery 1. Furthermore, if the second negative electrode active material layer 24 is set by charging after assembling the all-solid-state secondary battery 1, then when the all-solid-state secondary battery 1 is in the initial state or fully discharged state, the negative electrode 20 (e.g., the negative electrode current collector 21, the first negative electrode active material layer 22 and the area therebetween) is a Li-free region without Li.

[0199] [Negative electrode: Negative electrode current collector] The negative electrode current collector 21 can be formed of a material that does not react with lithium (e.g., does not form an alloy or compound with lithium). Examples of materials forming the negative electrode current collector 21 may include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), etc. However, the material forming the negative electrode current collector 21 is not limited to the aforementioned materials, but can be any material that can be used as an electrode current collector in the art. The negative electrode current collector 21 can be formed of one of the aforementioned metals, an alloy of two or more of them, or a covering material. The negative electrode current collector 21 can be, for example, plate-shaped or foil-shaped.

[0200] Reference Figure 3 The all-solid-state secondary battery 1 may also include a thin film 23 containing elements capable of forming an alloy with lithium on one side of the negative electrode current collector 21. Figure 3 Thin film 23 may be located between negative electrode current collector 21 and first negative electrode active material layer 22. Thin film 23 may include, for example, elements capable of forming alloys with lithium. Examples of elements capable of forming alloys with lithium may include, but are not limited to, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and any element available in the art capable of forming alloys with lithium may be used. Thin film 23 may be composed of one of the aforementioned metals, or may be composed of an alloy of different types of metals. Since thin film 23 is disposed on negative electrode current collector 21, the deposition form of second negative electrode active material layer 24 deposited between thin film 23 and first negative electrode active material layer 22 can be further planarized, and the cycle performance of all-solid-state secondary battery 1 can be further improved.

[0201] The thickness of the thin film 23 can be, for example, about 1 nm to about 800 nm, about 10 nm to about 700 nm, about 50 nm to about 600 nm, or about 100 nm to about 500 nm. If the thickness of the thin film 23 is less than 1 nm, it may be difficult to achieve the functions attributable to the thin film 23. If the thickness of the thin film 23 is too large, it causes the thin film 23 to adsorb lithium itself, thereby reducing the amount of lithium deposited at the negative electrode. Therefore, the solid-state battery may have a reduced energy density, and the cycle performance of the all-solid-state secondary battery 1 may deteriorate. The thin film 23 can be formed on the negative electrode current collector 21 by methods such as vacuum deposition, sputtering, and coating. However, it is not limited to the foregoing methods, and any method available in the art capable of forming the thin film 23 can be used.

[0202] Although not shown in the accompanying drawings, the negative electrode current collector 21 may include, for example, a substrate film and a metal layer disposed on one or both sides of the substrate film. The substrate film may include, for example, a polymer. For example, the polymer may be a thermoplastic polymer. For example, the polymer may include polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or combinations thereof. The polymer may be an insulating polymer. Because the substrate film includes an insulating thermoplastic polymer, in the event of a short circuit, the substrate film may soften or liquefy, thereby preventing battery operation to suppress a rapid increase in current. In one or more embodiments, the metal layer may include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or alloys thereof. The negative electrode current collector 21 may also include a metal sheet and / or lead terminals. For details regarding the substrate film, metal layer, metal sheet, and lead terminals of the negative electrode current collector 21, refer to the positive electrode current collector 11 described above. By utilizing the negative electrode current collector 21 with such a structure, the weight of the electrode can be reduced, thereby improving the energy density of the all-solid-state secondary battery.

[0203] [Electrolyte layer] [Electrolyte layer: Electrolyte] Reference Figures 1 to 6 The electrolyte layer 30 may include an electrolyte disposed between the positive electrode 10 and the negative electrode 20. The electrolyte may include, for example, a solid electrolyte, a gel electrolyte, or a combination thereof.

[0204] Examples of solid electrolytes may include sulfide solid electrolytes, oxide solid electrolytes, polymer solid electrolytes, or combinations thereof.

[0205] Solid electrolytes can be, for example, sulfide-based solid electrolytes. Sulfide-based solid electrolytes can be, for example, selected from at least one of the following: Li₂S-P₂S₅; Li₂S-P₂S₅-LiX, where X is a halogen element; Li₂S-P₂S₅-Li₂O; Li₂S-P₂S₅-Li₂O-LiI; Li₂S-SiS₂; Li₂S-SiS₂-LiI; Li₂S-SiS₂-LiBr; Li₂S-SiS₂-LiCl; Li₂S-SiS₂-B₂S₃-LiI; Li₂S-SiS₂-P₂S₅-LiI; Li₂S-B₂S₃; Li₂S-P₂S₅-Z m S n Where m and n are both positive numbers, and Z is Ge, Zn, or Ga; Li2S-GeS2; Li2S-SiS2-Li3PO4; Li2S-SiS2-Li p MO qWhere p and q are both positive numbers, and M is P, Si, Ge, B, Al, Ga, or In; Li 7-x PS 6-x Cl x Where 0 ≤ x ≤ 2; Li 7-x PS 6-x Br x Where 0 ≤ x ≤ 2; and Li 7-x PS 6-x I x Where 0 ≤ x ≤ 2. Sulfide solid electrolytes can be prepared by treating starting materials such as Li₂S and P₂S₅ by methods such as melt quenching, mechanical grinding, etc. After such treatment, heat treatment can be performed. Sulfide solid electrolytes can be amorphous or crystalline, or a mixture of amorphous and crystalline states. In some embodiments, among the sulfide solid electrolyte materials described herein, the solid electrolyte can be a material containing at least sulfur (S), phosphorus (P), and lithium (Li) as its constituent elements. For example, the solid electrolyte can be a material comprising Li₂S-P₂S₅. If the sulfide solid electrolyte material used to form the solid electrolyte comprises Li₂S-P₂S₅, the mixing molar ratio of Li₂S:P₂S₅ can be in the range of, for example, about 20:80 to about 90:10, about 25:75 to about 90:10, about 30:70 to about 70:30, or about 40:60 to about 60:40.

[0206] For example, sulfide solid electrolytes may include sulfogermanium ore-type solid electrolytes represented by Formula 1: Formula 1 Li + 12-n-x A n+ X 2- 6-x Y - x In Equation 1, A can be P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; X can be S, Se, or Te; Y can be Cl, Br, I, F, CN, OCN, SCN, or N3, and can satisfy 1 ≤ n ≤ 5 and 0 ≤ x ≤ 2. For example, sulfide solid electrolytes can be selected from Li... 7-x PS 6-x Cl x (where 0≤x≤2), Li 7-x PS 6-x Br x (where 0 ≤ x ≤ 2) and Li 7-x PS 6-x I xOne or more argyrodite-type compounds in (where 0 ≤ x ≤ 2). For example, the sulfide-based solid electrolyte can be an argyrodite-type compound including at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0207] The argyrodite-type solid electrolyte can have a density of about 1.5 g / cc to about 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or more, the internal resistance of the all-solid-state secondary battery can be reduced, and Li penetration into the electrolyte layer can be more effectively suppressed.

[0208] For example, the oxide-based all-solid electrolyte can be Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 < x < 2 and 0 < y < 3), BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT) (0 ≤ x < 1 and 0 ≤ y < 1), Pb(Mg 1 / 3 Nb 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 and 0 < y < 3), Li x Al y Ti z (PO4)3 (0 < x < 2, 0 < y < 1, and 0 < z < 3), Li 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 (0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), Li x La y TiO3 (0 < x < 2 and 0 < y < 3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O - Al2O3 - SiO2 - P2O5 - TiO2 - GeO2, Li 3+x La3M2O 12(M = Te, Nb or Zr, and 0 ≤ x ≤ 10) or a combination thereof. For example, an oxide-based solid electrolyte is manufactured by a sintering method or the like.

[0209] For example, the oxide-based solid electrolyte may be selected from Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a M a O 12 (M-doped LLZO, M = Ga, W, Nb, Ta or Al, 0 < a < 2 and 0 ≤ x ≤ 10) garnet-type solid electrolyte.

[0210] For example, the polymer solid electrolyte may include a mixture of a lithium salt and a polymer, or include a polymer having an ion-conductive functional group. For example, the polymer solid electrolyte may be a polymer electrolyte in a solid state at 25 °C and 1 atm. For example, the polymer solid electrolyte may not contain a liquid. The polymer solid electrolyte may include a polymer, and the polymer may be, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), poly(styrene-b-ethylene oxide) block copolymer (PS-PEO), poly(styrene-butadiene), poly(styrene-isoprene-styrene), poly(styrene-b-divinylbenzene) block copolymer, poly(styrene-ethylene oxide-styrene) block copolymer, polystyrene sulfonate (PSS), polyvinyl fluoride (PVF), poly(methyl methacrylate) (PMMA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), 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(benzimidazolebenzoisoquinolinone)] (SPBIBI), poly(styrene sulfonate) (PSS), 9,10-diphenylanthracene-2-sulfonic acid lithium (DPASLi + ) or a combination thereof. However, the polymer is not limited to the foregoing examples and may be any material used for polymer electrolytes in the art. The lithium salt may be any lithium salt available in the art. The lithium salt may be, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F2x+1 SO2)(C y F 2y+1 SO2 (where x and y are integers from 1 to 20), LiCl, LiI, or mixtures thereof. For example, the polymer included in the polymeric solid electrolyte can be a compound containing 10 or more repeating units, 20 or more repeating units, 50 or more repeating units, or 100 or more repeating units. For example, the polymer included in the polymeric solid electrolyte can have a weight-average molecular weight of 1,000 Daltons or greater, 10,000 Daltons or greater, 100,000 Daltons or greater, or 1,000,000 Daltons or greater.

[0211] For example, a gel electrolyte can be a polymeric gel electrolyte. For example, a gel electrolyte can have a gel state and not contain a liquid.

[0212] For example, a polymeric gel electrolyte may include a liquid electrolyte and a polymer, or an organic solvent and a polymer having ionicly conductive functional groups. For example, a polymeric gel electrolyte may be a polymeric electrolyte in a gel state at 25°C and 1 atm. For example, a polymeric gel electrolyte may have a gel state without containing a liquid. The liquid electrolyte used in a polymeric gel electrolyte may be, for example, a mixture of an ionic liquid, 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 a polymeric gel electrolyte may be selected from polymers used in solid polymeric electrolytes. The organic solvent may be selected from organic solvents used in liquid electrolytes. The lithium salt may be selected from lithium salts used in solid polymeric electrolytes. An ionic liquid may refer to a room-temperature molten salt composed solely of ions and having a melting point at room temperature or lower, or a salt that is liquid at room temperature. For example, the ionic liquid can be selected from at least one of the following compounds: a) at least one cation selected from ammonium, pyrrolidineonium, pyridinium, pyrimidineonium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazineonium, phosphonium, sulfonium, triazolium, and mixtures thereof; and b) a cation selected from BF4. - PF6 - AsF6 - SbF6 - AlCl4 - HSO4 - ClO4 - CH3SO3 - CF3CO2 - Cl - ,Br - I - SO4 2- CF3SO3 -(FSO2)2N - (C2F5SO2)2N - (C2F5SO2)(CF3SO2)N - and (CF3SO2)2N - At least one anion in the electrolyte. For example, a polymeric solid electrolyte can be formed by impregnating it in a liquid electrolyte in a secondary battery to form a polymeric gel electrolyte. The polymeric gel electrolyte may also include inorganic particles. For example, the polymer included in the polymeric gel electrolyte may be a compound comprising 10 or more repeating units, 20 or more repeating units, 50 or more repeating units, or 100 or more repeating units. For example, the polymer included in the polymeric gel electrolyte may have a weight-average molecular weight of 500 Daltons or greater, 1,000 Daltons or greater, 10,000 Daltons or greater, 100,000 Daltons or greater, or 1,000,000 Daltons or greater.

[0213] [Electrolyte layer: binder] The solid electrolyte layer 30 may also include, for example, a binder. Examples of binders included in the electrolyte layer 30 may include styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc. However, the binder is not limited to the foregoing examples and may be any binder available in the art. The binder in the electrolyte layer 30 may be the same as or different from the binders included in the positive electrode active material layer 12 and the first negative electrode active material layer 22. The binder may be omitted.

[0214] The amount of binder included in the electrolyte layer 30 may be from about 0 wt% to about 10 wt%, from about 0 wt% to about 5 wt%, from about 0 wt% to about 3 wt%, from about 0 wt% to about 1 wt%, from about 0 wt% to about 0.5 wt%, or from about 0 wt% to about 0.1 wt% relative to the total weight of the electrolyte layer 30.

[0215] Reference Figure 7 The negative electrode 20 may include a negative electrode current collector 21 and a lithium host layer 22 disposed on one surface of the negative electrode current collector 21. A first inactive component 42 may be disposed on a side surface of the negative electrode 20.

[0216] The first inactive component 42 may be disposed on the side surface of the lithium host layer 22, and between the solid electrolyte layer 30 and the negative electrode current collector 21 opposite to the solid electrolyte layer 30. Alternatively, the first inactive component 42 may not be disposed on the side surface of the negative electrode current collector 21. (Refer to...) Figure 7The first inactive component 42 can be disposed on the side surface of each of the negative electrode current collector 21 and the lithium body layer 22. By including the first inactive component 42, short circuits between the positive electrode 10 and the lithium metal plated on the lithium body layer 22 during charging and discharging of the all-solid-state secondary battery 1 can be prevented more effectively, thereby improving the cycle performance of the all-solid-state secondary battery 1. Because the inclusion of the first inactive component 42 prevents the solid electrolyte layer 30 from cracking during the manufacturing and / or charging and discharging of the all-solid-state secondary battery 1, the cycle performance of the all-solid-state secondary battery 1 can be improved. In an all-solid-state secondary battery 1 without the first inactive component 42, cracks may form in the solid electrolyte layer 30 that is in contact with the negative electrode 20 due to uneven pressure applied during the manufacturing and / or charging and discharging of the all-solid-state secondary battery 1, leading to the growth of lithium metal, and thus increasing the possibility of a short circuit.

[0217] Reference Figure 3 and Figure 7 In the all-solid-state secondary battery 1, the thickness T2 of the first inactive component 42 can be substantially the same as the thickness T1 of the lithium host layer 22. Since the sum of the thickness T2 of the first inactive component 42 and the thickness T4 of the negative electrode current collector 21 is substantially the same as the thickness T3 of the negative electrode 20, a uniform pressure is applied between the negative electrode 20 and the solid electrolyte layer 30. Furthermore, because the negative electrode 20 and the solid electrolyte layer 30 are sufficiently in contact with each other, the interfacial resistance between the negative electrode 20 and the solid electrolyte layer 30 can be reduced. Moreover, since the solid electrolyte layer 30 is sufficiently sintered during the pressing manufacturing process of the all-solid-state secondary battery 1, the solid electrolyte layer 30 and the all-solid-state secondary battery 1 including the solid electrolyte layer 30 can have reduced internal resistance.

[0218] The method for preparing an all-solid-state secondary battery according to the embodiments is described in detail below.

[0219] The all-solid-state secondary battery according to the embodiment can be prepared by the following steps: first grinding a composition comprising M2S and an alkali metal salt; obtaining a composite by second grinding the composition obtained by adding an inorganic electronically conductive structure and a two-dimensional carbonaceous structure or a fibrous carbonaceous material having an aspect ratio of 2 or greater to the product obtained by the first grinding; preparing a composition by adding a binder to the composite and then mixing them, and preparing a positive electrode by using the composition; preparing a negative electrode; and placing an electrolyte between the positive and negative electrodes.

[0220] Solid electrolytes can be added to the composition.

[0221] Solid electrolytes can be sulfide-based solid electrolytes. Sulfide-based solid electrolytes can have a size of about 0.1 nm to about 10 μm (e.g., about 100 nm to about 3 μm).

[0222] Sulfide solid electrolytes can be selected from at least one of the following: Li₂S-P₂S₅; Li₂S-P₂S₅-LiX, where X is a halogen element; Li₂S-P₂S₅-Li₂O; Li₂S-P₂S₅-Li₂O-LiI; Li₂S-SiS₂; Li₂S-SiS₂-LiI; Li₂S-SiS₂-LiBr; Li₂S-SiS₂-LiCl; Li₂S-SiS₂-B₂S₃-LiI; Li₂S-SiS₂-P₂S₅-LiI; Li₂S-B₂S₃; Li₂S-P₂S₅-Z m S n Where m and n are both positive numbers, and Z is Ge, Zn, or Ga; Li2S-GeS2; Li2S-SiS2-Li3PO4; Li2S-SiS2-Li p MO q Where p and q are both positive numbers, and M is P, Si, Ge, B, Al, Ga, or In; Li 7-x PS 6-x Cl x Where 0 ≤ x ≤ 2; Li 7- x PS 6-x Br x Where 0 ≤ x ≤ 2; and Li 7-x PS 6-x I x Where 0 ≤ x ≤ 2. In some embodiments, the sulfide solid electrolyte may include a sulfide-germanium ore type solid electrolyte. In some embodiments, the sulfide-germanium ore type solid electrolyte may include at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0223] In some embodiments, the sulfide-germanium ore type solid electrolyte may have a density of about 1.5 g / cc to about 2.0 g / cc.

[0224] During the first and second grinding processes, the first grinding process may be carried out at a rate of about 100 rpm to about 1,000 rpm or about 300 rpm to about 800 rpm for a duration of about 1 hour to about 20 hours or about 5 hours to about 10 hours (e.g., about 10 hours) until the size of the M2S becomes 100 nm or smaller.

[0225] The grinding duration of the first grinding can be controlled to reduce the size of the M2S to 100 nm or smaller, and the grinding rate (in rpm) and grinding duration of the second grinding can be controlled to be less than those of the first grinding. The second grinding can be carried out for a duration of, for example, from about 1 hour to about 7 hours or from about 2 hours to about 5 hours.

[0226] When obtaining the composite, carbonaceous materials can be further added to the composition. These carbonaceous materials can include carbon nanofibers, etc.

[0227] The inventive concept will be described in more detail through the following examples and comparative examples. However, it will be understood that the examples provided are for illustrative purposes only and are not to be construed as limiting the scope of the inventive concept.

[0228] (Preparation of composite positive electrode active material) In the following examples and comparisons, % means wt%, and % in SE means the content of solid electrolyte used in the preparation of the cathode mixture.

[0229] Example 1: 30%Li₂S - 20%LiI - 3.25%CNF + 3.25%MoS₂ + 42.5%SE (Step 1) Li₂S and LiI were mixed at a weight ratio of 30:20. The resulting mixture was mechanically milled using a ball mill to prepare the Li₂S-LiI composite. The milling conditions were 25°C and 600 rpm for 10 hours under an inert atmosphere.

[0230] (Step 2) The Li₂S-LiI composite, MoS₂, and carbon nanofibers (CNF) were mixed at a weight ratio of 50:3.25:3.25. The mixture was mechanically ground using a ball mill. The grinding conditions were inert atmosphere, 25°C, and 60 rpm for 5 hours. The Li₂S-LiI-MoS₂-CNF composite was used as the composite positive electrode active material.

[0231] MoS2 exists in plate form, and the plate-shaped MoS2 has a length of approximately 30 μm (X direction), a thickness of 5 μm (Z direction), and a width of approximately 15 μm (Y direction). Li2S has a Mohs hardness of 0.6, and LiI has a Mohs hardness of 2.0. Furthermore, 42.5% SE indicates the amount of solid electrolyte used to prepare the cathode mixture described below. This applies to the examples and comparative examples below.

[0232] Example 2: 30%Li₂S - 20%LiI - 6.75%CNF + 0.75%MoS₂ + 42.5%SE Except for changing the mixing weight ratio of Li2S-LiI composite, MoS2 and carbon nanofibers (CNF) in step 2 to 50:0.75:6.75, the Li2S-LiI-MoS2-CNF composite was prepared according to the same process as in Example 1-1.

[0233] Example 3: 30%Li₂S - 20%LiI - 0.75%CNF + 6.75%MoS₂ + 42.5%SE Except for changing the mixing weight ratio of Li2S-LiI composite, MoS2 and carbon nanofibers (CNF) in step 2 to 50:6.75:0.75, the Li2S-LiI-MoS2-CNF composite was prepared according to the same process as in Example 1.

[0234] Example 4: 30% Li₂S - 20% LiI - 7.5% (0.375% MoS₂-loaded CNF) + 42.5% SE (Step 1) Li₂S and LiI were mixed at a weight ratio of 30:20. The resulting mixture was mechanically milled using a ball mill to prepare the Li₂S-LiI composite. The milling conditions were 25°C and 600 rpm for 10 hours.

[0235] (Step 2) The Li₂S-LiI composite and MoS₂-loaded CNF were mixed at a weight ratio of 50:7.5. The MoS₂ content in the MoS₂-loaded CNF was 0.375%.

[0236] MoS2-supported CNFs were prepared by methods disclosed in Electrochimica Acta 254 (2017) 172-180 or Applied Surface Science 564 (2021) 150387. In MoS2-supported CNFs, chemical bonds are formed between Mo in MoS2 and carbon in CNF.

[0237] The mixture obtained was mechanically ground using a ball mill to prepare the Li₂S-LiI-TiO₂ composite. The grinding conditions were 25°C and 600 rpm for 5 hours. A Li₂S-LiI-MoS₂-supported CNF composite was used as the composite positive electrode active material.

[0238] Example 5: 30%Li₂S - 20%LiI - 3.25%Graphene + 3.25%MoS₂ + 42.5%SE Except that graphene was used instead of CNF, the composite was prepared using the same process as in Example 1.

[0239] For graphene, a thickness of 20 nm and a specific surface area of ​​19 m² were used, purchased from Adeka Corp. 2 / g of graphene with a diameter of approximately 5μm.

[0240] Comparative Example 1: Li2S-LiI-CNF, 510rpm, 10 hours, 2 steps, 20g (KR 2017-0068448 (Tatsumisago)) (Step 1) A first mixture was prepared by mixing Li₂S and LiI at a weight ratio of 30:20. The first mixture was then mechanically ground using a ball mill to produce a Li₂S-LiI composite.

[0241] The grinding conditions were 25°C and 510 rpm for 10 hours. The grinding energy applied to the sample during grinding was 20 G.

[0242] (Step 2) A second mixture was prepared by mixing the Li₂S-LiI composite and carbon nanofibers (CNF) at a weight ratio of 50:10. The second mixture was mechanically milled using a ball mill to produce the Li₂S-LiI-CNF composite.

[0243] The grinding conditions were 25°C and 510 rpm for 10 hours. The grinding energy applied to the sample during grinding was 20 G. A Li₂S-LiI-CNF composite was used as the composite positive electrode active material.

[0244] Reference Example 1: 30%Li₂S - 20%LiI - 7.5%CNT + 42.5%SE (Step 1) Li₂S and LiI were mixed at a weight ratio of 30:20. The resulting mixture was mechanically milled using a ball mill to prepare the Li₂S-LiI composite. The milling conditions were 25°C and 600 rpm for 10 hours under an inert atmosphere.

[0245] (Step 2) The Li₂S-LiI composite and CNTs were mixed at a weight ratio of 50:7.5. The mixture was mechanically ground using a ball mill. The grinding conditions were inert atmosphere, 25°C, 60 rpm for 5 hours. The Li₂S-LiI-CNT composite was used as the composite positive electrode active material.

[0246] Comparative Example 2: A simple mixture of 30% Li₂S - 20% LiI + (3.25% CNF + 3.25% MoS₂) + 42.5% SE A first mixture was prepared by mixing Li₂S and LiI at a weight ratio of 30:20. The first mixture was then mechanically ground using a ball mill to produce a Li₂S-LiI composite.

[0247] The grinding conditions were 25°C and 600 rpm for 10 hours. The grinding energy applied to the sample during grinding was 20 G.

[0248] The Li2S-LiI complex was simply mixed with 3.25% CNF and 3.25% MoS2 in a mortar.

[0249] Comparison Example 3: 30%Li₂S - 20%LiI - 7.5%CNF + 42.5%SE (Step 1) A first mixture was prepared by mixing Li₂S and LiI at a weight ratio of 30:20. The first mixture was then mechanically ground using a ball mill to produce a Li₂S-LiI composite.

[0250] The grinding conditions were 25°C and 600 rpm for 10 hours. The grinding energy applied to the sample during grinding was 20 G.

[0251] (Step 2) A second mixture was prepared by mixing the Li₂S-LiI composite and carbon nanofibers (CNF) at a weight ratio of 50:10. The second mixture was mechanically milled using a ball mill to produce the Li₂S-LiI-CNF composite.

[0252] The grinding conditions were 25°C and 600 rpm for 10 hours. The grinding energy applied to the sample during grinding was 20 G. A Li₂S-LiI-CNF composite was used as the composite positive electrode active material.

[0253] Comparative Example 4: 30% Li₂S-20% LiI-(3.25% CNF+3.25% MoS₂) simple blend + 43.5% SE Simply mix 30% Li₂S, 20% LiI, 3.25% CNF and 3.25% MoS₂ in a mortar.

[0254] (Preparation of cathode and solid-state secondary battery) Example 6 (Preparation of the positive electrode) The composite prepared in Example 1 was used as the positive electrode active material. Li6PS5Cl crystals (D50 = 3.0 μm, crystals) of the argyrogermanium sulfide type were prepared as the solid electrolyte. PTFE was prepared as the binder. These materials were mixed at a weight ratio of composite positive electrode active material: solid electrolyte: binder = 58.7:42.5:1.2 to prepare a positive electrode mixture. The positive electrode mixture was obtained by dry mixing using a ball mill.

[0255] The positive electrode mixture was placed on one side of a positive electrode current collector made of aluminum foil coated with carbon on one side, and pressed at a pressure of 200 MPa for 10 minutes to produce a sheet-like positive electrode. The thickness of the positive electrode was approximately 120 μm, and the loading level of the positive electrode mixture was approximately 8 mg / cm³. 2 The thickness of the positive electrode active material layer is approximately 100 μm, and the thickness of the carbon-coated aluminum foil is approximately 20 μm. The positive electrode active material layer and the positive electrode current collector have the same surface area.

[0256] (Preparation of the negative electrode) As the negative electrode current collector, a 10 μm thick SUS sheet is prepared. As the negative electrode active material, carbon black (CB) with a primary particle size of about 30 nm and silver (Ag) particles with an average particle size of about 60 nm are prepared.

[0257] In a container containing 4 grams of a mixed powder of CB and Ag particles in a weight ratio of 3:1, 4 grams of an NMP solution containing 7 wt% PVDF binder (#9300, KUREHA) was added to prepare a mixed solution. The mixed solution was stirred while NMP was slowly added to it to create a slurry. The prepared slurry was coated onto an SUS sheet using a bar coater and dried in the open air at 80°C for 10 minutes, followed by vacuum drying at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold-rolled to planarize its surface to prepare a negative electrode with a first negative electrode active material layer / negative electrode current collector structure. The thickness of the negative electrode active material layer was approximately 15 μm. The first negative electrode active material layer and the negative electrode current collector had the same surface area.

[0258] (Preparation of solid electrolyte layer) In the sulfide-germanium ore type crystal Li6PS5Cl solid electrolyte (D 50In a mixture of 3.0 μm (crystals), 1.5 parts by weight of polyacrylic acid binder were added relative to 98.5 parts by weight of solid electrolyte to prepare a mixture. The prepared mixture was stirred while octyl acetate was added to prepare a slurry. The prepared slurry was coated onto a 15 μm thick nonwoven fabric placed on a 75 μm thick PET substrate using a bar coater and then air-dried at 80°C for 10 minutes to prepare a laminate. The prepared laminate was then vacuum-dried at 80°C for 2 hours to produce the solid electrolyte layer.

[0259] (Non-active component) A slurry obtained by mixing cellulose fibers, glass fibers, aluminum hydroxide (Al(OH)3), polyacrylic acid binder and solvent is formed into a gasket, and then the solvent is removed from it to manufacture a flame-retardant inactive component.

[0260] The weight ratio of pulp fiber (cellulose fiber): glass fiber: aluminum hydroxide (Al(OH)3): polyacrylic acid binder is 20:8:70:2. The thickness of the inactive component is 120μm.

[0261] Before placing the manufactured flame-retardant inactive component on the solid electrolyte layer, the flame-retardant inactive component is heat-treated in a vacuum at 80°C for 5 hours to remove moisture and other substances.

[0262] (Preparation of solid-state secondary batteries) like Figure 5 As shown, a solid electrolyte layer is disposed on a negative electrode layer, such that a first negative electrode active material layer is in contact with the solid electrolyte layer, and a positive electrode is disposed on the solid electrolyte layer. A gasket may be disposed around the positive electrode, thus fabricating a laminate. The gasket thickness is approximately 120 μm. A flame-retardant inactive component is used as the gasket. The gasket is configured such that it contacts the side surface of the positive electrode and the solid electrolyte layer. The positive electrode is disposed in the central portion of the solid electrolyte layer, and the gasket is positioned to extend to the end portion of the solid electrolyte layer, surrounding the positive electrode. The surface area of ​​the positive electrode is approximately 90% of the surface area of ​​the solid electrolyte layer, and the gasket is disposed in the remaining 10% of the surface area of ​​the solid electrolyte layer in which the positive electrode is not disposed.

[0263] The prepared laminate was pressed at 85°C under a pressure of 500 MPa for 30 minutes. This pressing process sintersects the solid electrolyte layer and improves battery performance. The thickness of the sintered solid electrolyte layer is approximately 45 μm. The density of the Li6PS5Cl solid electrolyte, a type of silver sulfide germanite, contained in the sintered solid electrolyte layer, is 1.6 g / cc. The surface area of ​​the solid electrolyte layer is the same as that of the negative electrode.

[0264] The pressed laminate is placed in a bag and vacuum-sealed to manufacture a solid-state secondary battery. A portion of the positive current collector and a portion of the negative current collector extend out of the sealed battery and serve as the positive and negative terminals, respectively.

[0265] Examples 7 to 10 Except that the composite positive electrode active material prepared in Examples 2 to 5 is used instead of the composite positive electrode active material prepared in Example 1, the positive electrode and the all-solid-state secondary battery are prepared according to the same process as in Example 6.

[0266] Examples 11 to 15 (the loading level of the cathode mixture is approximately 24 mg / cm³) 2 ) In addition to changing the loading level of the cathode mixture used to prepare the cathode to approximately 24 mg / cm³ 2 In addition, the positive electrode and the all-solid-state secondary battery were prepared using the same process as in Examples 6 to 10.

[0267] Comparative Example 5: 30%Li₂S - 20%LiI - 7.5%CNF + 42.5%SE (the loading level of the cathode mixture is approximately 8 mg / cm²) 2 ) Except for using the composite positive electrode active material of Comparative Example 1, the positive electrode and the all-solid-state secondary battery were prepared according to the same process as in Example 6.

[0268] Comparative Example 6: 30%Li₂S - 20%LiI - 7.5%CNF + 42.5%SE (the loading level of the cathode mixture is approximately 24 mg / cm²) 2 ) In addition to changing the loading level of the cathode mixture used to prepare the cathode to approximately 24 mg / cm³ 2 In addition, the cathode and all-solid-state secondary battery were prepared using the same process as in Comparative Example 5.

[0269] Comparative Example 7: Simple blend (positive electrode mixture loading level of approximately 8 mg / cm³) 2 ) Except for using the composite positive electrode active material of Comparative Example 2, the positive electrode and all-solid-state secondary battery were prepared according to the same process as in Example 6.

[0270] Comparative Example 8: Simple blend (positive electrode mixture loading level of approximately 24 mg / cm³) 2 ) In addition to changing the loading level of the cathode mixture used to prepare the cathode to approximately 24 mg / cm³ 2 In addition, the cathode and all-solid-state secondary battery were prepared using the same process as in Comparative Example 7.

[0271] Reference Example 2: 30%Li₂S - 20%LiI - 7.5%CNT + 42.5%SE (the loading level of the cathode mixture is approximately 8 mg / cm³) 2 ) Except for using the composite positive electrode active material of Reference Example 1, the positive electrode and the all-solid-state secondary battery are prepared according to the same process as in Example 6.

[0272] Reference Example 3: 30%Li₂S - 20%LiI - 7.5%CNT + 42.5%SE (the loading level of the cathode mixture is approximately 24 mg / cm²). 2 ) In addition to changing the loading level of the cathode mixture used to prepare the cathode to approximately 24 mg / cm³ 2 In addition, the positive electrode and the all-solid-state secondary battery are prepared according to the same process as in Reference Example 2.

[0273] Evaluation Example 1: XRD and Scanning Electron Microscopy Analysis For the composite positive electrode active materials (i.e., composites) prepared in Examples 1 to 5, Comparative Examples 1 to 4, and Reference Example 1, XRD spectra were measured using CuKα radiation. Based on the measured XRD spectra, the Li₂S crystallite size calculated from the first peak corresponding to the (111) plane appearing at a diffraction angle of 2θ = 27° ± 2.0° is shown in Table 2. Crystal sizes were measured using the Sherrer equation.

[0274] The particle size (D50) of each Li₂S in the composite positive electrode active materials prepared in Examples 1 to 5, Comparative Examples 1 and 2, and Reference Example 1 was measured using a particle size analyzer (PSA) and a laser-based scanning electron microscope. The Li₂S particle size of the composite positive electrode active material is the arithmetic mean of the particle sizes of multiple Li₂S particles measured using software in the scanning electron microscope images. The measurement results are shown in Table 1 below.

[0275] [Table 1]

[0276] In Table 1, SE represents the solid electrolyte used to prepare the above-mentioned positive electrode mixture.

[0277] As shown in Table 1, the composites of Examples 1 to 5 were found to include Li2S-LiI solid solutions, with Li2S crystallites smaller than 9.9 nm in size and Li2S particles of 2 μm or smaller in the composites.

[0278] As shown in Table 1, it was found that the simple mixture of Li2S, LiI, CNF and MoS2 in Comparative Example 4 failed to form a solid solution.

[0279] Evaluation Example 2: XRD Analysis For the complex in Example 1 and the simple mixture of Li2S, LiI, MoS2 and CNF in Comparative Example 4, XRD spectra were measured using CuKα radiation.

[0280] Compared to the position of the mixture in Comparative Example 4, the position of the complex in Example 1 has shifted to a lower angle.

[0281] The composite in Example 1 shows a slight left shift of the peak at 2θ = 27° ± 2.0°, indicating the formation of a Li2S-LiI solid solution, where the peak at 2θ = 27° ± 2.0° corresponds to the MoS2(111) crystal plane. The MoS2 peak at 2θ = 14.5 ± 0.5° (e.g., 14.1°) shows a drastically reduced intensity.

[0282] In Comparative Example 4, since no solid solution was formed, the peak at 2θ = 27° ± 2.0° did not shift, and a MoS2 peak at 2θ = 14.1° with no decrease in intensity was observed. Furthermore, this confirms that Comparative Example 4 exhibited no peak shift at 2θ = 27° ± 2.0° (no solid solution formed), and that the intensity of the MoS2 peak at 2θ = 14.5 ± 0.5° (e.g., 14.1°) did not decrease.

[0283] The evaluation results show that the complex in Example 1 has formed a solid solution, and compared with the simple mixture in Comparative Example 4, it shows that there are chemical bonds between the components that form the complex.

[0284] Evaluation Example 3: Cyclic Test The following cycle tests were conducted to evaluate the cycle performance of solid-state secondary batteries using composite positive electrode active materials prepared in Examples 6 to 15, Comparative Examples 5 to 7, and Reference Examples 2 and 3, respectively.

[0285] Cyclic tests were conducted while the all-solid-state secondary battery was placed in a constant temperature bath at 45°C.

[0286] In the first cycle, each battery is charged at a constant current of 0.1C for 12.5 hours until the battery voltage reaches 2.5V to 2.8V. Then, the battery is discharged at a constant current of 0.1C for 12.5 hours until the battery voltage reaches 0.3V.

[0287] The discharge capacity of the first cycle was used as the standard capacity. The standard capacity is expressed as the specific capacity of Li₂S in Table 1.

[0288] After the second cycle, charging and discharging were performed under the same conditions as the first cycle until 150 cycles were completed. The measurement results are shown in Tables 2 and 3. Table 2 pertains to a load level of 8 mg / cm³. 2 In the examples, Table 3 relates to a loading level of 24 mg / cm³. 2 Examples of implementations.

[0289] The initial efficiency is represented by Equation 2 below.

[0290] Equation 1 Initial efficiency [%] = [Discharge capacity in the first cycle / Charge capacity in the first cycle] × 100 Cycle count refers to the number of cycles required for the discharge capacity to drop to 80% of its standard capacity after the second cycle. A higher cycle count indicates a battery with better lifespan characteristics.

[0291] [Table 2]

[0292] As shown in Table 2, compared with the solid-state secondary batteries of Comparative Examples 5 and 7 and Reference Example 2, which respectively adopted the composite positive electrode active materials of Comparative Example 1, Comparative Example 2 and Reference Example 1, the solid-state secondary batteries of Examples 6 to 10 showed improvements in discharge capacity, initial efficiency, lifetime and high-rate performance.

[0293] [Table 3]

[0294] As shown in Table 3, compared with the solid-state secondary batteries of Comparative Example 6, Comparative Example 8 and Reference Example 3, the solid-state secondary batteries of Examples 11 to 15, which all have a thick film state of positive electrode active material, showed improvements in discharge capacity, initial efficiency, lifetime and high-rate performance.

[0295] Evaluation Example 4: Evaluation of High-Rate Performance The following cycling tests were conducted to evaluate the high-rate performance of solid-state secondary batteries using composite positive electrode active materials prepared in Examples 6 to 15, Comparative Examples 6 to 8, and Reference Example 2, respectively. The cycling tests were performed while the all-solid-state secondary batteries were placed in a thermostatic bath at 45°C.

[0296] Each all-solid-state secondary battery was charged at 45°C with a constant current of 0.1C until the battery voltage reached 4.2V, and then charged at a constant voltage of 4.2V until the current value was 0.1C. Subsequently, the battery was discharged at a constant current of 0.1C until the battery voltage reached 2.5V.

[0297] Subsequently, each battery is charged at a constant current of 0.1C and a constant voltage of 4.2V until the battery voltage reaches 4.2V, and then discharged at a constant current of 0.33C until the battery voltage reaches 2.5V.

[0298] After the above charging and discharging, the high-rate performance of the battery was evaluated according to Equation 3, and some of the results are shown in Table 4.

[0299] Equation 3 High-rate performance (%) = (Discharge capacity at 0.33C / Discharge capacity at 0.1C) × 100 [Table 4]

[0300] As shown in Table 4, it was found that the solid-state secondary batteries of Examples 6 to 15 have improved high-rate performance compared with the solid-state secondary batteries of Comparative Examples 5 to 8 and Reference Examples 2 and 3.

Claims

1. A solid-state secondary battery comprising: a positive electrode layer; a negative electrode layer; and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer comprises: a positive electrode current collector; and a positive electrode active material layer disposed on one side or both sides of the positive electrode current collector, wherein the positive electrode active material layer comprises a composite positive electrode active material, wherein the composite positive electrode active material comprises a composite of: i) M 2 S; ii) an alkali metal salt; iii) an inorganic electron conductive structure; and iv) a two-dimensional carbonaceous structure or a fibrous carbonaceous material having an aspect ratio of 2 or more, wherein M is an alkali metal, and the alkali metal is Li or Na, wherein the composite comprises a solid solution of the M 2 S and the alkali metal salt, and wherein the two-dimensional carbonaceous structure is graphene, graphene oxide, or a combination thereof. 2.The solid-state secondary battery according to claim 1, wherein the fibrous carbonaceous material has a length of 1 μm to 50 μm and a diameter of 10 nm to 10 μm, wherein the fibrous carbonaceous material has a rod-like structure, a tube-like structure, a needle-like structure, a wire-like structure, or a combination thereof, wherein a cross section of the fibrous carbonaceous material perpendicular to a length direction thereof has an irregular shape, a circular shape, or a polygonal shape, and wherein the fibrous carbonaceous material comprises carbon nanofibers. 3.The solid-state secondary battery according to claim 1, wherein a content of the inorganic electron conductive structure in the composite is 1 part by weight to 20 parts by weight with respect to 100 parts by weight of the composite, and wherein a content of the fibrous carbonaceous material or the two-dimensional carbonaceous structure is 1 part by weight to 40 parts by weight with respect to 100 parts by weight of the composite, wherein a molar ratio of the M 2 S to the alkali metal salt is 50:50 to 95:

5. 4.The solid-state secondary battery according to claim 1, wherein a size of the M 2 S is equal to or smaller than a size of the alkali metal salt, and a size of the inorganic electron conductive structure is larger than sizes of lithium sulfide and the alkali metal salt, and wherein particle sizes are gradually decreased in the following order: the inorganic electron conductive structure, the alkali metal salt, and the M 2 S. 5.The solid-state secondary battery according to claim 1, wherein the inorganic electron conductive structure has a length of 1 μm to 50 μm and a thickness of 0.01 μm to 10 μm, and the M 2 S has a size of 0.1 nm to 10 μm, wherein the alkali metal salt has a size of 1 nm to 10 μm, and wherein a composite of the M 2 S, the alkali metal salt, the inorganic electron conductive structure, and the fibrous carbonaceous material has a particle size of 10 μm or less. 6.The solid-state secondary battery according to claim 1, wherein the inorganic electron conductive structure has a one-dimensional structure form or a two-dimensional structure form, wherein the inorganic electron conductive structure comprises a transition metal sulfide, a metal sulfide comprising at least one metal in Groups 3 to 5 of the periodic table, or a combination thereof. ​ wherein the inorganic electron conductive structure has an electronic conductivity of 10 -3 S / cm or more, ​ ​ ​ wherein ​ ​ ​ ​ ​ wherein ​ ​ ​ ​ wherein, ​ ​ wherein ​ ​ ​ ​ wherein ​ ​ wherein the inorganic electron conductive structure includes titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, niobium, tantalum, molybdenum, tungsten, or a combination thereof, and The inorganic electronic conductive structure is at least one metal selected from the group consisting of VO2, ReO2, CrO2, ReO2, VO2, SnO2, TiO2, ZrO2, Al2O3, TeN, TiN, TiO, TiO x (0.75 < x < 1.45), Ti n O 2n-1 (4 < n < 10), ReO3, CrO2, and VO2; at least one metal material selected from the group consisting of ZrS2, FeS, FeS2, CuS, Cu2S, CuS2, Cu9S8, Cu7S4, CoS, CoS2, Co3S4, Co9S8, NiS, NiS2, Ni9S8, Ni3S2, VS, VS2, V2S3, V2S5, VS4, NbS2, NbS3, NbS4, NbS5, Nb2S3, Nb2S5, TaS2, TaS3, TaS4, TaS5, Ta2S3, Ta2S5, Cr2S3, CrS3, MoS2, MoS3, MoS4, WS2, WS3, WS4, WS5, MnS, Mn2S3, TiS2, NiNb3S6, Cu2MoS4, and Cu4Mo6S8; or a combination thereof.

7. The all-solid-state secondary battery according to claim 1, wherein each of the first peak appearing at a diffraction angle 2θ = 14.5 ± 0.5°, the second peak appearing at a diffraction angle 2θ = 32.5 ± 0.5°, and the third peak appearing at a diffraction angle 2θ = 58.5 ± 0.5° of the composite on an X-ray diffraction (XRD) spectrum of the composite positive electrode active material is smaller than a second diffraction angle of each of a fourth peak appearing at a diffraction angle 2θ = 14.5 ± 0.5°, a fifth peak appearing at a diffraction angle 2θ = 32.5 ± 0.5°, and a sixth peak appearing at a diffraction angle 2θ = 58.5 ± 0.5° on an XRD spectrum of the MoS2 used for producing the composite, wherein the first peak appearing at a diffraction angle 2θ = 14.5 ± 0.5° on the XRD spectrum of the MoS2 used for producing the composite has a reduced intensity with respect to an intensity of the fourth peak appearing at a diffraction angle 2θ = 14.5 ± 0.5°.

8. The all-solid-state secondary battery according to claim 1, wherein a first lattice constant d1 derived from a first peak corresponding to a (111) crystal plane of M2S appearing at a diffraction angle 2θ = 27° ± 2.0° on an XRD spectrum of the composite is larger than a second lattice constant d2 derived from a second peak corresponding to the (111) crystal plane of M2S appearing at a diffraction angle 2θ = 27° ± 2.0° on an XRD spectrum of the M2S used for producing the composite, and wherein the first lattice constant d1 has a size of 5.78 Å or more.

9. The all-solid-state secondary battery according to claim 1, wherein the composite positive electrode active material has a structure in which the iii) inorganic electron conductive structure is supported on the iv) fibrous carbonaceous material having an aspect ratio of 2 or more.

10. The all-solid-state secondary battery according to claim 1, wherein the positive electrode active material layer further includes a solid electrolyte, and wherein the solid electrolyte includes a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof, wherein the content of the solid electrolyte is 10 parts by weight to 60 parts by weight with respect to 100 parts by weight of the positive electrode active material layer.

11. The all-solid-state secondary battery according to claim 1, wherein the alkali metal salt is a lithium salt or a sodium salt, and the alkali metal salt is a binary compound or a ternary compound, wherein the binary compound includes LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, or a combination thereof; or NaI, NaBr, NaCl, NaF, Na2O, Na2Se, Na3N, Na3P, Na3As, Na3Sb, Na3Al2, NaB3, or a combination thereof, and 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; or Na3OCl, NaBF4, NaPF6, NaAsF6, NaClO4, NaNO3, NaAlO2, NaAlCl4, NaNO3, Na2CO3, NaBH4, Na2SO4, Na3BO3, Na3PO4, Na4NCl, Na5NCl2, Na3BN2, or a combination thereof.

12. The all-solid-state secondary battery of claim 1, wherein, the negative electrode layer comprises a negative electrode current collector and a first negative electrode active material layer disposed on the negative electrode current collector.

13. The all-solid-state secondary battery of claim 12, wherein, the negative electrode active material of the first negative electrode active material layer comprises at least one of a carbon-based negative electrode active material and a metal-based negative electrode active material, wherein the carbon-based negative electrode active material comprises amorphous carbon, crystalline carbon, porous carbon, or a combination thereof, and the metal-based negative electrode active material comprises gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof.

14. The all-solid-state secondary battery of claim 11, wherein, the negative electrode active material of the first negative electrode active material layer comprises a mixture of a metal-based negative electrode active material and a carbon-based material, a metal-based negative electrode active material supported on a carbon-based material, or a combination thereof.

15. The all-solid-state secondary battery of claim 1, wherein the negative electrode layer comprises a negative electrode current collector and a lithium host layer disposed on one side of the negative electrode current collector, wherein the lithium host layer comprises a lithium host structure, wherein the lithium host structure comprises at least one lithium host comprising a carbon-based lithium host, a metal-based lithium host, a polymer-based lithium host, or a combination thereof, and wherein the all-solid-state secondary battery further comprises a first inactive member disposed on the negative electrode layer.

16. The all-solid-state secondary battery of claim 1, The all-solid-state secondary battery further includes a second negative electrode active material layer provided between the negative electrode current collector and the first negative electrode active material layer, wherein the second negative electrode active material layer is a metal layer comprising lithium or a lithium alloy, wherein the second negative electrode active material layer is a plated layer, and a thickness of the first negative electrode active material layer is greater than a thickness of the second negative electrode active material layer.

17. The all-solid-state secondary battery of claim 1, the all-solid-state secondary battery further comprises an inactive elastic member disposed on one side of the positive electrode layer or the negative electrode layer, or does not comprise the inactive elastic member.

18. The all-solid-state secondary battery of claim 1, wherein the electrolyte layer comprises a solid electrolyte, a gel electrolyte, or a combination thereof, wherein the solid electrolyte comprises a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof, and wherein the gel electrolyte comprises a polymer gel electrolyte.

19. The all-solid-state secondary battery of claim 1, wherein, the negative electrode layer comprises a negative electrode current collector, wherein at least one of the positive electrode current collector and the negative electrode current collector comprises a base film and a metal layer disposed on one side or both sides of the base film, wherein the base film comprises a polymer, wherein the polymer comprises polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof, and 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.

20. A method of preparing a solid-state secondary battery, the method comprising the steps of: performing first grinding on a composition comprising M2S, an alkali metal salt, and an inorganic electron conductive structure; obtaining a composite by adding a composition comprising a fibrous carbonaceous material or a two-dimensional carbonaceous structure having an aspect ratio of 2 or more to a product of the first grinding and performing second grinding; preparing a composition by adding a binder to the composite and then mixing them, and preparing a positive electrode by using the composition; preparing a negative electrode; and disposing a solid electrolyte between the positive electrode and the negative electrode, thereby preparing the all-solid-state secondary battery of claim 1.

Images