All-solid-state secondary battery, and method for manufacturing same

Abstract

Proposed are an all-solid-state secondary battery and a method for manufacturing same, the all-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 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 electrode active material layer includes a composite positive electrode active material; the composite positive electrode active material includes a composite of (i) M2S, {ii) an alkali metal salt, (iii) an inorganic electronically conductive structure, and (iv) a fibrous carbon-based material having an aspect ratio of 2 or more or a two-dimensional carbon-based structure; M is an alkali metal; the alkali metal is Li or Na; the inorganic electronically conductive structure has an electronic conductivity of 10-3 S / cm or greater; the composite includes a solid solution of M2S and an alkali metal salt; and the two-dimensional carbon-based structure is graphene, graphene oxide, or a combination thereof.

Description

All-solid-state secondary battery and its manufacturing method

[0001] It relates to an all-solid-state secondary battery and a method for manufacturing the same.

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

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

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

[0005] One aspect is to provide an all-solid-state secondary battery having improved initial efficiency, high-rate characteristics and volumetric energy density by having an anode with an enhanced electronic conduction network.

[0006] Another aspect is to provide a method for manufacturing the above-described all-solid-state secondary battery.

[0007] According to the implementation example

[0008] It comprises an anode layer; a cathode layer; and a solid electrolyte layer disposed between the anode layer and the cathode layer,

[0009] The above 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, wherein the positive electrode active material layer includes a composite positive electrode active material, and the composite positive electrode active material includes a composite of i) M2S (M is Li or Na), 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, wherein M is an alkali metal, the alkali metal is Li or Na, and the electronic conductivity of the inorganic electronically conductive structure is 10 -3 S / cm or more,

[0010] An all-solid-state secondary battery is provided, wherein the complex comprises a solid solution of M2S and an alkali metal salt, and the two-dimensional carbon-based structure is graphene, graphene oxide, or a combination thereof.

[0011] The complex comprises 10 to 80 parts by weight of M2S, 1 to 40 parts by weight of alkali metal salt, and 1 to 20 parts by weight of inorganic electronically conductive structure, relative to 100 parts by weight of the complex.

[0012] The size of the above M2S is equal to or smaller than the size of the alkali metal salt,

[0013] The size of the above inorganic electronic conductive structure is the size of lithium sulfide and alkali metal salt.

[0014] Compared to the larger, the particle size gradually decreases in the order of the above-mentioned inorganic electronic conductive structure, alkali metal salt and M2S.

[0015] The above-mentioned positive electrode active material layer further includes a solid electrolyte, and the solid electrolyte includes a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof, and the content of the solid electrolyte is 10 to 60 parts by weight based on 100 parts by weight of the positive electrode active material layer.

[0016] The above negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer disposed on the negative electrode current collector.

[0017] According to another aspect, a method for manufacturing an all-solid-state secondary battery is provided, comprising: a step of first milling a composition including M2S, an alkali metal salt, and an inorganic electron-conductive structure; a step of adding and second milling a composition including a fibrous carbon-based material or a two-dimensional carbon-based structure having an aspect ratio of 2 or more to the first milled product to obtain a composite; a step of adding and mixing a binder to the composite to obtain a composition and manufacturing a positive electrode using the composition; a step of preparing an anode; and a step of arranging a solid electrolyte between the positive electrode and the negative electrode.

[0018] According to one aspect, it is possible to provide an all-solid-state secondary battery having improved initial efficiency and high-rate characteristics as well as improved volumetric energy density by providing an anode with an improved electronic conduction network using a composite using an inorganic electronically conductive structure.

[0019] Figure 1 is a schematic diagram showing the structure of a positive electrode active material layer according to an embodiment.

[0020] Figures 2 to 7 are cross-sectional views of an all-solid-state secondary battery according to an exemplary embodiment.

[0021] <Explanation of symbols for major parts of the drawing>

[0022] 1 All-solid-state secondary battery 10 Cathode

[0023] 11. Cathode current collector 12. Cathode active material layer

[0024] 20 Cathode 21 Cathode current collector

[0025] 22 First negative electrode active material layer 30 Electrolyte layer

[0026] 40 Inert Absences

[0027] Unless otherwise defined, all terms (including technical and scientific terms) used in this disclosure have the same meaning as commonly understood by those of ordinary skill in the art to which this disclosure pertains. Furthermore, terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning within the context of the relevant technology and this disclosure, and should not be interpreted in an idealized or overly formal sense.

[0028] Exemplary embodiments are described in this disclosure with reference to cross-sectional drawings that are schematic representations of idealized embodiments. As such, variations from the shapes depicted are to be expected, for example, as a result of manufacturing techniques and / or tolerances. Therefore, the embodiments described in this disclosure should not be construed as limited to the specific shapes of regions as depicted in this disclosure, but should encompass variations in shapes resulting from, for example, manufacturing. For example, regions depicted or described as flat may typically have rough and / or non-linear features. Moreover, angles depicted as sharp may be rounded. Therefore, the regions depicted in the drawings are schematic in nature, and their shapes are not intended to depict the precise shapes of the regions, nor are they intended to limit the scope of the claims.

[0029] This creative idea may be embodied in many different forms and should not be construed as limited to the embodiments described in this disclosure. These embodiments are provided so that this disclosure will be thorough and complete, and so that it will fully convey the scope of the creative idea to those skilled in the art. Like reference numerals in the drawings indicate like elements.

[0030] When a component is referred to as being "on" another component, it can be understood that it is either directly on top of the other component or that other components may be intervening between them. Conversely, when a component is referred to as being "directly on" another component, no intervening components are present.

[0031] Although terms such as "first," "second," "third," etc. may be used herein to describe various components, elements, regions, layers, and / or zones, these components, elements, regions, layers, and / or zones should not be limited by these terms. These terms are only used to distinguish one component, element, region, layer, or zone from another component, element, region, layer, or zone. Thus, a first component, element, region, layer, or zone described below may be referred to as a second component, element, region, layer, or zone without departing from the teachings of this disclosure.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms including "at least one," unless the content clearly dictates otherwise. "At least one" should not be construed as limiting to the singular. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items. The terms "comprises" and / or "comprising" as used in the detailed description specify the presence of stated features, regions, integers, steps, operations, components, and / or ingredients, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, components, ingredients, and / or groups thereof.

[0033] Spatially relative terms such as "below," "under," "lower," "above," "upper," and the like may be used herein to readily describe the relationship of one component or feature to another. It will be understood that spatially relative terms are intended to encompass different orientations of the device when in use or operation in addition to the orientations depicted in the drawings. For example, if the device in the drawings were turned over, a component described as "below" or "below" another component or feature would then be oriented "above" the other component or feature. Thus, the exemplary term "below" can encompass both the above and below orientations. The device may be arranged in other orientations (rotated 90 degrees or otherwise rotated), and the spatially relative terms used herein may be interpreted accordingly.

[0034] "Group" means a group in the periodic table of elements according to the International Union of Pure and Applied Chemistry ("IUPAC") Group 1-18 classification system.

[0035] In this disclosure, "particle diameter" refers to the average diameter when the particle is spherical, and refers to the average major axis length when the particle is non-spherical. The particle diameter can be measured using a particle size analyzer (PSA). The "particle diameter" is, for example, the average particle diameter. The "average particle diameter" is, for example, D50, the median particle diameter.

[0036] D50 is the size of the particle corresponding to 50% of the cumulative volume, calculated from the side of the particle with the smaller particle size in the size distribution of particles measured by, for example, laser diffraction.

[0037] D90 is the size of the particle corresponding to 90% of the cumulative volume, calculated from the side of the particle with the smaller particle size in the size distribution of particles measured by, for example, laser diffraction.

[0038] D10 is the size of the particle corresponding to 10% of the cumulative volume, calculated from the side of the particle having the smaller particle size in the size distribution of particles measured by, for example, laser diffraction.

[0039] In this disclosure, “metal” includes both metals and metalloids such as silicon and germanium, in their elemental or ionic states.

[0040] In this disclosure, “alloy” means a mixture of two or more metals.

[0041] In the present disclosure, “electrode active material” means an electrode material capable of undergoing lithiation and delithiation.

[0042] In the present disclosure, “positive electrode material” means a positive electrode material capable of undergoing lithiation and delithiation.

[0043] In the present disclosure, “negative electrode active material” means a negative electrode material capable of undergoing lithiation and delithiation.

[0044] In the present disclosure, “lithiation” and “lithiating” mean a process of adding lithium to an electrode active material.

[0045] In the present disclosure, “delithiation” and “delithiate” mean a process of removing lithium from an electrode active material.

[0046] In this disclosure, “charging” and “charging” mean a process of providing electrochemical energy to a battery.

[0047] In this disclosure, “discharging” and “discharging” mean the process of removing electrochemical energy from a battery.

[0048] In the present disclosure, “positive electrode” and “cathode” mean an electrode at which electrochemical reduction and lithiation occur during a discharge process.

[0049] In the present disclosure, “cathode” and “anode” mean electrodes where electrochemical oxidation and delithiation occur during a discharge process.

[0050] In this disclosure, “length” and “thickness” represent, for example, average length and average thickness. The length and thickness can be evaluated from scanning electron microscope images.

[0051] In the present disclosure, the aspect ratio represents the ratio (L1 / L2) of the major axis length L1 (e.g., length) and the minor axis length L2 (e.g., diameter). Here, the aspect ratio, major axis length, minor axis length, length, and diameter represent the average aspect ratio, average major axis length, average minor axis length, average length, and average diameter. The aspect ratio can be evaluated using a scanning electron microscope.

[0052] While specific implementations have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or unforeseen may occur to the applicant or those skilled in the art. Accordingly, the appended claims, as filed and as amended, are intended to encompass all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0053]

[0054] Hereinafter, composite cathode active materials and cathodes and all-solid-state secondary batteries including the composite cathode active materials according to exemplary embodiments will be described in more detail.

[0055] [Composite cathode active material]

[0056] According to an embodiment, a composite cathode active material includes a composite of 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, wherein M is an alkali metal, the alkali metal is Li or Na, and the electronic conductivity of the inorganic electronically conductive structure is 10 -3 The two-dimensional carbon-based structure is graphene, graphene oxide, or a combination thereof, wherein the complex comprises a solid solution of M2S and an alkali metal salt, and the two-dimensional carbon-based structure has a density of S / cm or more.

[0057] The carbon nanostructure may be at least one selected from a one-dimensional carbon nanostructure and a two-dimensional carbon nanostructure. In the present specification, a one-dimensional carbon nanostructure is a carbon nanostructure in which one dimension is significantly larger than the other two dimensions. In other words, a carbon nanostructure in which the length defined in one dimension is significantly larger than the other two dimensions. For example, the one-dimensional carbon nanostructure is at least one selected from a carbon nanotube, a carbon nanowire, a carbon nanofiber, a carbon nanobelt, a carbon nanorod, and a combination thereof.

[0058] As used herein, a "two-dimensional carbon nanostructure" is a carbon nanostructure in which two dimensions are significantly larger than one of the other dimensions. In other words, it is a carbon nanostructure in which the area defined by the two dimensions is significantly larger than the thickness.

[0059] The above fibrous carbon-based material is defined by its length and diameter, and the aspect ratio of the length and diameter is 2 or more, 3 or more, 5 or more, for example, 10 or more, and the length of the above fibrous carbon-based material is 1 to 50 μm and the diameter is 10 nm to 10 μm. In the present disclosure, the term “particle size” means the average circle diameter when the cross-section of the material is circular, and means the average major axis length when the cross-section of the material is non-circular.

[0060] The above fibrous carbon-based material includes, for example, carbon nanofibers.

[0061] The fibrous carbon-based material has the above-described length and diameter ranges, so that a conductive network within the anode can be formed relatively easily or suitably. The cross-section of the fibrous carbon-based material may include a polygonal shape such as a circle, triangle, or square.

[0062] Furthermore, utilizing the aforementioned composite can secure a more extended ion conduction path in the cathode active material layer. Therefore, during charging and discharging of an all-solid-state secondary battery, the interruption of the ion conduction path due to volume changes in the cathode active material in the cathode active material layer can be more effectively prevented. Consequently, the initial efficiency, discharge capacity, high-rate characteristics, and / or cycle life characteristics of the all-solid-state secondary battery can be improved.

[0063] Furthermore, utilizing the aforementioned composite can improve the uniformity of ion conduction paths within the positive electrode active material layer. Consequently, the pressure required for manufacturing an all-solid-state secondary battery can be reduced. In other words, an all-solid-state secondary battery with excellent ion conduction paths can be realized even under reduced pressure. Furthermore, the formation of local overvoltages within the positive electrode active material layer during the charge / discharge process of an all-solid-state secondary battery can be effectively prevented.

[0064] The carbon nanofibers described above can be controlled to increase conductivity and reduce side reactions between the positive electrode active material and the sulfide-based solid electrolyte by nitrogen and fluorine doping.

[0065] By using a composite containing the above-described fibrous carbon-based material, the brittle nature of the positive electrode can be complemented, enabling the manufacture of a positive electrode capable of thick film formation, thereby enabling the manufacture of an all-solid-state secondary battery with increased energy density. Furthermore, since the inclusion of the fibrous carbon-based material allows the volume change of the positive electrode active material during charge and discharge to be accommodated by dispersing it along the entire length, the volume change of the positive electrode active material can be accommodated more effectively than, for example, a carbon-based material in the form of spherical particles. Consequently, the disconnection between the positive electrode active material and the solid electrolyte due to the volume change of the positive electrode active material within the positive electrode active material layer can be suppressed, and the uniformity of the components within the positive electrode active material layer can be improved. Consequently, the cycle characteristics of the all-solid-state secondary battery can be improved.

[0066] In this specification, a thick film means a film having an anode loading level greater than 8 mg / cm2, for example, greater than or equal to 9 mg / cm2, greater than or equal to 10 mg / cm2, from 10 to 60 mg / cm2 or from 10 to 50 mg / cm2.

[0067] The above complex may not be in the form of a cluster, but rather may have a form in which the components of the complex are finely divided and uniformly dispersed.

[0068] The aspect ratio of the fibrous carbon-based material can be, for example, 2 or more, 3 or more, 4 or more, 5 or more, 10 or more, or 20 or more. The aspect ratio of the fibrous carbon-based material can be, for example, 2 to 30, 3 to 30, 4 to 30, 5 to 30, 10 to 30, or 20 to 30. The aspect ratio of the fibrous carbon-based material can be, for example, 2 to 30, 2 to 20, 2 to 10, 2 to 8, 2 to 5, or 2 to 4. By having the fibrous carbon-based material having an aspect ratio in this range, the overall electronic conductivity of the composite is improved, and local electronic conductivity imbalances within the composite can be further alleviated.

[0069] The fibrous carbon-based material may include, for example, a rod structure, a tube structure, a needle structure, a wire structure, or a combination thereof, but is not necessarily limited to these forms, and any fibrous structure that is used in the relevant technical field may be used. Since the fibrous carbon-based material has a rod structure, a tube structure, a needle structure, a wire structure, or the like, the ion conduction path is extended in an all-solid-state secondary battery including the fibrous carbon-based material, and the volume change of the positive electrode active material during charge and discharge of the all-solid-state secondary battery can be accommodated more effectively, and the ion conduction path in the all-solid-state secondary battery can be maintained despite the volume change of the positive electrode active material. As a result, deterioration of the all-solid-state secondary battery can be suppressed, and the cycle characteristics of the all-solid-state secondary battery can be improved.

[0070] The electronic conductivity of the above inorganic electronic conductive structure is 1×10 -3 S / cm or more, or 1×10 -2 It can be S / cm or more. The electronic conductivity can be measured using, for example, electrochemical impedance spectroscopy, direct current (DC) polarization method, etc. Since the composite containing such an inorganic electronic conductive structure has an electronic conductivity in this range, the internal resistance of the composite cathode active material containing the composite can be reduced. The initial efficiency, electrode energy density, and cycle life characteristics of the all-solid-state secondary battery containing the composite cathode active material can be improved.

[0071] Inorganic electronically conductive structures have small particle sizes and are uniformly dispersed throughout the composite, making them advantageous for forming conductive networks. Inorganic electronically conductive structures can have zero-dimensional, one-dimensional, two-dimensional, three-dimensional, or combinations thereof.

[0072] The zero-dimensional form can be a particle shape, the one-dimensional form can be a fiber shape, and the two-dimensional form can be a plate shape. When a composite using such an inorganic electron-conductive structure is used to manufacture a cathode and an all-solid-state secondary battery, the initial efficiency (specific capacity) is improved by reducing the side reaction characteristics with the solid electrolyte. Here, the side reaction refers to an increase in resistance due to the reaction between the hydroxyl group (H2O) present in the carbon layer of the CNF contained in the cathode and the solid electrolyte, and an increase in resistance due to the reaction of carbon with lithium polysulfide (Li2S4< Li2S6).

[0073] Increasing the content of inorganic electronically conductive structures in a composite increases electronic conductivity but may decrease ionic conductivity. Therefore, the domain size of two-dimensional carbon-based structures such as graphene is crucial. When graphene is used as a two-dimensional carbon-based structure, its domain size can be controlled by varying its thickness.

[0074] The length of the above-mentioned inorganic electron-conducting structure is 1 to 50 μm or 0.1 to 5 μm, and the thickness is 0.01 to 10 μm. By using a composite using a two-dimensional carbon nanostructure having such a length and thickness, an all-solid-state secondary battery with improved life characteristics can be manufactured by enhancing the electron-conducting network within the anode. In addition, the energy density within the electrode can be improved by reducing the conductive material content within the anode by strengthening the electron-conducting network. In addition, by reducing the conductive material content within the anode, the lithium sulfide content can be relatively increased, thereby improving the initial efficiency.

[0075] Any material that has a two-dimensional structure, a chalcogenide material, and electronic conductivity can be used as the inorganic electronic conductive structure.

[0076] The inorganic electronically conductive structure may have a zero-dimensional, one-dimensional, or two-dimensional structure form. A one-dimensional structure is, for example, in a fiber form, and a two-dimensional structure is, for example, in a plate-like form. Using an inorganic electronically conductive structure having a one-dimensional structure allows for the formation of a thick film as an anode, thereby producing an anode with improved electrode stability. Using an inorganic electronically conductive structure having a two-dimensional structure improves the effect of suppressing volume expansion of the anode.

[0077] The metal sulfide, for example a transition metal sulfide, may be 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 / or Cu4Mo6S8. For example, at least one metal sulfide can be selected from the group consisting of FeS2, CuS2, CoS2, Co3S4, NiS2, VS2, VS4, NbS2, NbS3, NbS4, NbS5, TaS2, TaS3, TaS4, TaS5, CrS3, MoS2, MoS3, MoS4, WS2, WS3, WS4, WS5. Such transition metal sulfides can have, for example, a two-dimensional plate-like form.

[0078] In another embodiment, the inorganic electronically conductive structure is, for example, VO2, ReO2, CrO2, ReO2, VO2, SnO2, TiO2, ZrO2, Al2O3, TeN, TiN, TiO, TiOx (0.75 <x<1.45), Ti n O 2n-1(4 <n<10), ReO3, CrO2, VO2 중에서 선택된 하나 이상의 금속 산화물, 또는 그 조합이다.

[0079] The inorganic electronically conductive structure may be, for example, alumina fibers, zirconia fibers, titania fibers, TeN fibers, SnO2 fibers, or a combination thereof. When having such a fiber shape, the inorganic electronically conductive material has a length of 0.1-5 um, a diameter of 0.01 um to 0.5 um, and an aspect ratio of 10 or more.

[0080] The content of the inorganic electronic conductive structure is 1 to 20 parts by weight, 1 to 18 parts by weight, or 1 to 15 parts by weight based on 100 parts by weight of the composite, and the content of the fibrous carbon-based material or the two-dimensional carbon-based structure is 1 to 40 parts by weight, 1 to 30 parts by weight, for example, 5 to 10 parts by weight based on 100 parts by weight of the composite.

[0081] According to one embodiment, the composite includes 30 to 80 parts by weight of M2S, 1 to 40 parts by weight of an alkali metal salt, 1 to 20 parts by weight of an inorganic electronically conductive structure, and 1 to 40 parts by weight of a fibrous carbon-based material or a two-dimensional carbon-based structure, relative to 100 parts by weight of the composite.

[0082] According to one embodiment, the size ratio (e.g., particle size or diameter) of the inorganic electronic conductive structure and LiI is, for example, 3:1 to 0.5:1, and the size ratio of the inorganic electronic conductive structure and Li2S is, for example, 2:1 to 0.5:1.

[0083] In this specification, the inorganic electronically conductive structure refers to an inorganic structure that has electronic conductivity and little ionic conductivity, and has a zero-dimensional, one-dimensional, two-dimensional, three-dimensional, or a combination thereof form. Here, the zero-dimensional form has a particle form, the one-dimensional form has a fiber form, and the two-dimensional form has a plate form.

[0084] In another embodiment, the size of the inorganic electron-conductive structure is larger than the size of the metallic lithium (e.g., lithium sulfide) and the alkali metal salt (LiI), and the particle size may gradually decrease in the order of the inorganic electron-conductive structure, the alkali metal salt (LiI), and M2S. The term “size” herein is, for example, an arithmetic mean value of the particle diameters of a plurality of particles measured using software from a scanning electron microscope image.

[0085] The size ratio of the inorganic electronic conductive structure and LiI is, for example, 3:1 to 1.5:1, and the size ratio of the inorganic electronic conductive structure and Li2S is, for example, 2:1 to 1.5:1.

[0086] When the inorganic electronic conductive structure has a two-dimensional plate shape, the length is 1 to 50 um, the thickness is 0.01 to 10 um, and the size of the M2S is 0.1 nm to 10 um.

[0087] The size of the above alkali metal salt (LiI) is 1 nm to 10 μm.

[0088] The above two-dimensional carbon-based structure has a plate-like shape, unlike one-dimensional carbon-based structures such as carbon nanofibers, and is, for example, graphene, graphene oxide, or a combination thereof.

[0089] Compared to one-dimensional carbon structures, two-dimensional carbon structures have a larger specific surface area and, thanks to the "house of cards" structural model and effect, can effectively encapsulate lithium sulfide, maintaining a robust network structure. Furthermore, when lithium sulfide expands during charge / discharge, the contact area with the cathode components is relatively large, ensuring robust connectivity.

[0090] Increasing the content of two-dimensional carbon structures, such as graphene, in a composite increases electronic conductivity but may decrease ionic conductivity. Therefore, the domain size of two-dimensional carbon structures, such as graphene, is crucial. When graphene is used as a two-dimensional carbon structure, its domain size can be controlled by varying its thickness.

[0091] The specific surface area of ​​the above two-dimensional carbon nanostructure is 1 to 50 m 2 / g, 1 to 30 m 2 / g, or 5 to 20 m 2 / g. And the thickness of the two-dimensional carbon nanostructure is 10 nm to 10 um, 100 nm to 8 um, 500 nm to 6 um, 1 to 5 um, or 1 to 3 um. By using a composite using a two-dimensional carbon nanostructure having such a specific surface area, diameter, and thickness, an all-solid-state secondary battery with improved life characteristics can be manufactured by improving the electronic conductivity network within the anode. In addition, the energy density within the electrode can be improved by reducing the content of the conductive material within the anode by strengthening the electronic conductivity network. In addition, by reducing the content of the conductive material within the anode, the content of lithium sulfide can be relatively increased, thereby improving the initial efficiency and / or energy density.

[0092] The thickness of the graphene according to an embodiment is 10 nm to 30 um, 100 nm to 30 um, or 1 to 3 um.

[0093] The above two-dimensional carbon-based structure includes a two-dimensional carbon-based structure doped with a dopant, wherein the dopant is an n-type (n-charge) dopant or a p-type (p-charge) dopant, and the dopant includes nitrogen (N), phosphorus (P), boron (B), sulfur (S), fluorine (F), chlorine (Cl), bromine (Br), germanium (Ge), gallium (Ga), or a combination thereof. By using the two-dimensional carbon-based structure doped in this way, the conductivity and side-reactivity characteristics can be controlled.

[0094] The dopant may include an n-type dopant, a p-type dopant, or a combination thereof. An n-type dopant is a dopant that introduces electrons into a carbon-based material by having more electrons than, for example, carbon. A p-type dopant is a dopant that introduces holes into a two-dimensional carbon-based structure by having fewer electrons than carbon. The carbon-based structure may include, for example, dopant-doped graphene. The doped graphene may include, for example, an n-type dopant, a p-type dopant, or a combination thereof. The dopant may include, for example, nitrogen (N), phosphorus (P), boron (B), sulfur (S), fluorine (F), chlorine (Cl), bromine (Br), germanium (Ge), gallium (Ga), or a combination thereof. Nitrogen (N) and phosphorus (P) are, for example, n-type dopants. Gallium (Ga) is, for example, a p-type dopant. The content of the dopant included in the doped carbon-based structure may be, for example, 3 at% or less or 1 at% or less. By doping the carbon-based structure with the dopant, the conductivity of the carbon-based material may be further increased.

[0095] The above M is an alkali metal. The alkali metal is Li or Na. M2S is, for example, Li2S and / or Na2S. The complex comprises a solid solution of M2S and an alkali metal salt.

[0096] By forming a complex of M2S with an alkali metal salt and an inorganic electronically conductive structure or a two-dimensional carbon-based structure, both the ionic conductivity and the electronic conductivity of M2S can be improved simultaneously. Since the complex includes an alkali metal salt, the ionic conductivity of the composite cathode active material can be improved, and the internal resistance of the cathode and the all-solid-state secondary battery including the composite cathode active material can be reduced. Since the complex includes a carbon-based material, the electronic conductivity of the composite cathode active material can be improved, and the internal resistance of the cathode and the all-solid-state secondary battery including the composite cathode active material can be reduced.

[0097] The composite includes M2S crystallites, and as the size of the M2S crystallites is reduced to 21 nm or less, the volume change of the M2S crystallites during charge and discharge can be alleviated. For example, as the size of the M2S crystallites is reduced, the volume change due to a single M2S crystallite is reduced, so the overall volume change of the composite during charge and discharge can be alleviated. For example, as the size of the M2S crystallites is reduced, the grain boundaries between a plurality of M2S crystallites can more easily accommodate the volume change of the M2S crystallites during charge and discharge, so the volume change of the composite during charge and discharge can be alleviated. The possibility of defects such as cracks occurring due to the volume change of the composite during charge and discharge can be reduced. When the composite cathode active material includes such a composite, the cycle characteristics of an all-solid-state secondary battery including the composite cathode active material can be improved. For example, the life characteristics of an all-solid-state secondary battery including such a composite cathode active material are improved.

[0098] The composite includes M2S crystallites, and as the size of the M2S crystallites is reduced to 21 nm or less, the contact area between the M2S crystallites and the alkali metal salt and / or the carbon-based material can be further increased. As the contact area between the M2S crystallites and the alkali metal salt and / or the carbon-based material increases, the ionic conductivity and / or battery conductivity of the composite can be further improved. When the composite cathode active material includes such a composite, the reversibility of the electrode reaction can be improved in an all-solid-state secondary battery including the composite cathode active material. As a result, the specific capacity of the composite cathode active material can be increased.

[0099] The ionic conductivity of the composite may increase when the composite includes a solid solution of M2S and an alkali metal salt. For example, since the solid solution of M2S and an alkali metal salt includes alkali metal ions arranged within the M2S crystallites, the ionic conductivity of the solid solution of M2S and an alkali metal salt may be improved compared to the ionic conductivity of M2S. Consequently, the ionic conductivity of the composite may be improved and the internal resistance of the composite may be reduced. When the composite cathode active material includes such a composite, the cycle characteristics of a secondary battery including the composite cathode active material may be improved. For example, the high-rate characteristics of a secondary battery including such a composite cathode active material may be improved.

[0100] Li2S-alkali metal salt-carbon framework composites are distinguished from simple mixtures of Li2S, alkali metal salts, and carbon frameworks. Simple mixtures of Li2S, alkali metal salts, and carbon frameworks fail to maintain a dense interface between the Li2S, alkali metal salt, and carbon frameworks, resulting in high interfacial resistance and consequently degrading the cycle life characteristics of all-solid-state secondary batteries.

[0101] The complex includes M2S. Since M2S has a high theoretical capacity, it can provide a secondary battery with a high energy density.

[0102] However, M2S has low ionic and / or electronic conductivity. To address or compensate for these shortcomings, M2S forms a composite with an alkali metal salt and a carbonaceous material. That is, M2S can have a high theoretical capacity, enabling the provision of secondary batteries with high energy densities. However, to overcome the shortcomings of M2S, such as low ionic and / or electronic conductivity, composites formed with M2S, an alkali metal salt, and a carbonaceous material can be utilized.

[0103] The content of M2S in the composite may be, for example, 10 to 80 wt%, 20 to 70 wt%, 30 to 60 wt%, or 40 to 60 wt% of the total weight of the composite. If the content of M2S is excessively increased, it may not be easy to improve the ionic conductivity and / or electronic conductivity of M2S. If the content of M2S is excessively low, the energy density of the secondary battery may be reduced.

[0104] The complex comprises an alkali metal salt. An alkali metal salt is, for example, a compound that does not contain sulfur (S). The alkali metal salt may be, for example, a binary compound or a ternary compound. The alkali metal salt may be, for example, a binary compound composed of an alkali metal and one element selected from Groups 13 to 17 of the Periodic Table of the Elements. The alkali metal salt may be, for example, a ternary compound composed of an alkali metal and two elements selected from Groups 13 to 17 of the Periodic Table of the Elements.

[0105] The alkali metal salt may be, for example, a lithium salt. The lithium salt binary compound may include, for example, LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, or a combination thereof. The lithium salt ternary compound may include, for example, Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2, or a combination thereof. The ionic conductivity of the complex may be further improved by including such a lithium salt in the complex. Such a lithium salt may more easily form a solid solution with Li2S, for example, in the complex.

[0106] The alkali metal salt may be, for example, a sodium salt. The sodium salt binary compound may include, for example, NaI, NaBr, NaCl, NaF, Na2O, Na2Se, Na3N, Na3P, Na3As, Na3Sb, Na3Al2, NaB3, or a combination thereof. The sodium salt ternary compound may include, for example, Na3OCl, NaBF4, NaPF6, NaAsF6, NaClO4, NaNO3, NaAlO2, NaAlCl4, NaNO3, Na2CO3, NaBH4, Na2SO4, Na3BO3, Na3PO4, Na4NCl, Na5NCl2, Na3BN2, or a combination thereof. The ionic conductivity of the complex may be further improved by including such a sodium salt in the complex. Such a sodium salt may more easily form a solid solution with Na2S, for example, in the complex.

[0107] The content of the alkali metal salt in the composite may be 1 to 40 wt%, 5 to 35 wt%, 10 to 35 wt%, 15 to 35 wt%, 20 to 35 wt%, or 25 to 35 wt% of the total weight of the composite. If the content of the alkali metal salt is excessively increased, the energy density of the all-solid-state secondary battery may decrease. If the content of the alkali metal salt is excessively low, the ionic conductivity of the composite may decrease, which may increase the internal resistance of the composite cathode active material. As a result, the cycle characteristics of the secondary battery may deteriorate.

[0108] The molar ratio of M2S and the alkali metal salt in the composite may be, for example, 50:50 to 95:5, 60:40 to 95:5, 60:40 to 90:10, 65:35 to 90:10, 65:35 to 85:15, or 70:30 to 85:15. The molar ratio of M2S and the alkali metal salt in the composite may be, for example, 50:50 to 95:5, 50:50 to 90:10, 50:50 to 85:15, 50:50 to 80:20, 50:50 to 75:25, or 50:50 to 70:30. When M2S and the alkali metal salt have a molar ratio in this range, the cycle characteristics of a secondary battery including the composite positive electrode active material can be further improved. If the molar ratio of M2S is excessively high, the ionic conductivity enhancement effect of the alkali metal salt may be minimal. If the molar ratio of M2S is excessively high, the energy density of the secondary battery containing the composite cathode active material may be reduced.

[0109] The molar ratio of Li2S and lithium salt in the composite may be, for example, 50:50 to 95:5, 60:40 to 95:5, 60:40 to 90:10, 65:35 to 90:10, 65:35 to 85:15, or 70:30 to 85:15. The molar ratio of Li2S and lithium salt in the composite may be, for example, 50:50 to 95:5, 50:50 to 90:10, 50:50 to 85:15, 50:50 to 80:20, 50:50 to 75:25, or 50:50 to 70:30. By having Li2S and lithium salt in this range of molar ratio, the cycle characteristics of an all-solid-state secondary battery including a composite cathode active material may be further improved. If the molar ratio of Li2S is excessively high, the ionic conductivity enhancement effect of lithium salts may be minimal. If the molar ratio of Li2S is excessively high, the energy density of all-solid-state secondary batteries containing composite cathode active materials may be reduced.

[0110] The molar ratio of Na2S and sodium salt in the complex is the same as that of Li2S and lithium salt described above, except that sodium salt is used instead of lithium salt.

[0111] The content of the fibrous carbon-based material or carbon-based structure included in the composite may be, for example, 1 to 20 wt%, 5 to 20 wt%, or 5 to 10 wt% of the total weight of the composite. If the content of the fibrous carbon-based material or carbon-based structure increases excessively, the energy density of the secondary battery may decrease. If the content of the fibrous carbon-based material or carbon-based structure decreases excessively, the electronic conductivity of the composite may decrease, which may increase the internal resistance of the composite positive electrode active material. As a result, the cycle characteristics of the all-solid-state secondary battery may deteriorate.

[0112] In the XRD spectrum of the above composite cathode active material, peaks appear at diffraction angles 2θ = 14.5±0.5, diffraction angle 2θ = 32.5±0.5°, and diffraction angle 2θ = 58.5±0.5° in relation to the crystal plane of molybdenum sulfide (MoS2).

[0113] The peak appearing at the diffraction angle 2θ = 14.5±0.5° is for the molybdenum sulfide (MoS2) (002) crystal plane, so the diffraction angle 2θ is, for example, 14.1°. And the peak appearing at the diffraction angle 2θ = 32.5±0.5° is for the molybdenum sulfide (MoS2) (100) crystal plane, so the diffraction angle 2θ is, for example, 32.9°. The peak appearing at the diffraction angle 2θ = 58.5±0.5° is for the molybdenum sulfide (MoS2) (110) crystal plane, so the diffraction angle 2θ is, for example, 58.8°.

[0114] In the X-ray diffraction spectrum (XRD) of the composite cathode active material, the first diffraction angle 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 may shift to a lower angle than the second diffraction angle of the fourth peak appearing at a diffraction angle 2θ = 14.5±0.5°, the fifth peak appearing at a diffraction angle 2θ = 32.5±0.5°, and the sixth peak appearing at a diffraction angle 2θ = 58.5±0.5° in the XRD spectrum of MoS2 used in the manufacture of the composite. The shift to a lower angle occurs more as the composite is formed during the milling process.

[0115] For example, the position of the first peak may shift to a lower angle compared to the position of the second peak. Additionally, the intensity of the first peak appearing at the diffraction angle 2θ = 14.5±0.5° is reduced compared to the intensity of the fourth peak appearing at the diffraction angle 2θ = 14.5±0.5° in the XRD spectrum of MoS2 used in the preparation of the composite.

[0116] In addition, crystal changes of the MoS2 material can be observed in the XRD during the milling process. The lithium sulfide-molybdenum sulfide (MoS2)-carbon material composite can have a reduced crystallite size compared to the lithium sulfide used in the manufacture of the composite. Since the lithium sulfide-molybdenum sulfide (MoS2)-carbon material composite has a reduced crystallite size, the volume change of the crystallite during charge and discharge is reduced, so the volume change of the composite including multiple crystallites can be alleviated during charge and discharge. The occurrence of defects such as cracks during charge and discharge of the composite cathode active material including such a composite can be suppressed. As a result, the cycle characteristics of the all-solid-state secondary battery including the composite cathode active material can be improved.

[0117] In the XRD spectrum of the composite, for example, the first lattice constant (d1) derived from the first peak corresponding to the (111) crystal plane of M2S at a diffraction angle 2θ = 27° ± 2.0° may be larger than the second lattice constant (d2) derived from the second peak corresponding to the (111) crystal plane of M2S at a diffraction angle 2θ = 27° ± 2.0° in the XRD spectrum of M2S used in the preparation of the composite. Since the M2S-alkali metal salt-carbon-based structure composite has a larger lattice constant (d) than the M2S used in the preparation of the composite, alkali metal ions can be more easily transferred within the M2S crystal structure of the composite. The ionic conductivity of the composite cathode active material including the composite can be further improved. The internal resistance of a secondary battery including the composite cathode active material can be reduced and the cycle characteristics can be improved. The difference between the first lattice constant (d1) and the second lattice constant (d2) may be 0.05 Å or more, 0.1 Å or more, 0.15 Å or more, 0.2 Å or more, or 0.25 Å or more. The size of the first lattice constant (d1) may be, for example, 5.78 Å or more, 5.80 Å or more, 5.82 Å or more, 5.85 Å or more, 5.90 Å or more, 5.95 Å or more, or 6.0 Å or more. Since the composite has such a size of the first lattice constant (d1), the ionic conductivity of the composite cathode active material including the composite can be further improved. The internal resistance of a secondary battery including the composite cathode active material can be reduced and the cycle characteristics can be improved.

[0118] In the XRD spectrum of the composite, for example, a first peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of M2S has a first diffraction angle, and in the XRD spectrum of M2S used in the preparation of the composite, a second peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of M2S has a second diffraction angle, and the first diffraction angle may be smaller than the second diffraction angle. For example, the position of the first peak may shift to a low angle compared to the position of the second peak. Therefore, the M2S-alkali metal salt-carbon-based material composite may have a reduced crystallite size compared to M2S used in the preparation of the composite. Since the M2S-alkali metal salt-carbon material composite has a reduced crystallite size, the volume change of the crystallites during charge and discharge is reduced, so the volume change of the composite containing multiple crystallites during charge and discharge can be alleviated. The occurrence of defects such as cracks during charge and discharge of the composite cathode active material containing such a composite can be suppressed. Consequently, the cycle characteristics of the secondary battery containing the composite cathode active material can be improved.

[0119] In the XRD spectrum of the composite, for example, a first peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of M2S has a first full width at half maximum (FWHM1), and in the XRD spectrum of M2S used in the production of the composite, a second peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of M2S has a second full width at half maximum (FWHM2), and the first full width at half maximum may be larger than the second full width. Accordingly, the M2S-alkali metal salt-carbon-based material composite may have an increased lattice strain compared to the M2S used in the production of the composite. For example, the M2S-alkali metal salt-two-dimensional carbon-based structure composite may have an increased lattice strain when M2S and an alkali metal salt form a solid solution. Since the M2S-alkali metal salt-two-dimensional carbon-based structure composite has an increased full width at half maximum (FWHM) compared to the M2S used in the composite preparation, the ionic conductivity of a composite cathode active material including the composite can be further improved. The internal resistance of an all-solid-state secondary battery including the composite cathode active material can be reduced and the cycle characteristics can be improved.

[0120] The particle size (particle diameter) of the composite cathode active material, i.e., the size of the composite particles, may be, for example, 10 ㎛ or less, 8 ㎛ or less, 5 ㎛ or less, 2 ㎛ or less, 1.5 ㎛ or less, or 1 ㎛ or less. The composite cathode active material may have the form of particles or composite particles. The size of the composite particles may be, for example, 1 to 10 ㎛, 2 to 10 ㎛, 2 to 8 ㎛, or 3 to 8 ㎛. The size of the composite particles may be, for example, 0.1 to 10 ㎛, 0.1 to 8 ㎛, 0.1 to 5 ㎛, 0.1 to 2 ㎛, 0.1 to 1.5 ㎛, or 0.1 to 1 ㎛. Since the composite particles have a size in this range, the volume change during charge and discharge is suppressed, and thus, deterioration of the composite cathode active material including the composite during charge and discharge can be suppressed. If the size of the composite particles increases excessively, the volume change of the composite during charge / discharge cycles may increase, accelerating the deterioration of the composite cathode active material containing the composite. Consequently, the cycle characteristics of the all-solid-state secondary battery containing such a composite cathode active material may deteriorate.

[0121] The size of the M2S particles included in the composite cathode active material, that is, the size of the M2S particles included in the composite, may be, for example, 2 ㎛ or less, 1.5 ㎛ or less, or 1 ㎛ or less. The size of the M2S particles may be, for example, 0.1 to 2 ㎛, 0.1 to 1.5 ㎛, or 0.1 to 1 ㎛ or less. Since the M2S particles have a size in this range, the volume change during charge and discharge is suppressed, and thus the deterioration of the composite cathode active material including the composite during charge and discharge can be suppressed. If the size of the M2S particles increases excessively, the volume change of the composite during charge and discharge may increase, which may accelerate the deterioration of the composite cathode active material including the composite. As a result, the cycle characteristics of a secondary battery including such a composite cathode active material may deteriorate.

[0122] Therefore, the cycle characteristics, such as life characteristics, of an all-solid-state secondary battery including a composite cathode active material can be improved. The size of the composite particles can be measured, for example, using laser diffraction, a scanning electron microscope, etc. The particle size of the composite particle is, for example, the arithmetic mean of the particle sizes of multiple particles measured using software from a scanning electron microscope image.

[0123] The composite can more easily conduct electrons from the surface to the interior of the composite by adding an alkali metal salt having ion conductivity and a carbon-based structure having electron conductivity to lithium sulfide particles. The internal resistance of the composite cathode active material including the composite can be reduced, and the cycle characteristics of an all-solid-state secondary battery including the composite cathode active material can be further improved.

[0124] In the present specification, the diameter and length of the carbon nanostructure can be measured from a scanning electron microscope (SEM) image or an optical microscope. Alternatively, the diameter and / or length of the carbon nanostructure can be measured by laser diffraction. The carbon nanostructure can be dispersed, for example, in a solvent or the like, to obtain a carbon nanostructure dispersion, and this dispersion can be used to prepare a composite. For example, the composite can include 10 to 80 parts by weight of M2S, 1 to 40 parts by weight of an alkali metal salt, and 1 to 20 parts by weight of a carbon-based structure, based on 100 parts by weight of the composite. The M2S content included in the composite can be, for example, 10 to 80 parts by weight, 20 to 70 parts by weight, 30 to 60 parts by weight, or 40 to 60 parts by weight of M2S, based on 100 parts by weight of the composite. The content of the alkali metal salt included in the composite may be, for example, 10 to 40 parts by weight, 15 to 40 parts by weight, 20 to 40 parts by weight, or 25 to 35 parts by weight of the alkali metal salt per 100 parts by weight of the composite. The content of the carbon-based material included in the composite may be, for example, 1 to 20 parts by weight, 5 to 20 parts by weight, or 5 to 15 parts by weight of the carbon-based material per 100 parts by weight of the composite. Since the composite has a composition of M2S, alkali metal salt, and carbon-based material in this range, a composite cathode active material including the composite can provide excellent ionic conductivity and / or electronic conductivity.

[0125] The ionic conductivity of the complex is, for example, 1×10 at 25°C. -5 S / cm or more, 2×10 -5 S / cm or more, 4×10 -5 S / cm or more, 6×10 -5 S / cm or more, 8×10 -5 S / cm or more or 1×10 -4It can be S / cm or more. The ionic conductivity can be measured using, for example, electrochemical impedance spectroscopy, DC polarization method, etc. Since the composite has an ionic conductivity in this range, the internal resistance of the composite cathode active material including the composite can be reduced. The cycle characteristics of the all-solid-state secondary battery including the composite cathode active material can be improved. The electronic conductivity of the composite can be, for example, 1×10 at 25°C. -5 S / cm or more, 2×10 -5 S / cm or more, 4×10 -5 S / cm or more, 6×10 -5 S / cm or more, 8×10 -5 S / cm or more or 1×10 -4 It can be S / cm or more. The electronic conductivity can be measured using, for example, electrochemical impedance spectroscopy, DC polarization method, etc. Since the composite has an electronic conductivity in this range, the internal resistance of the composite cathode active material including the composite can be reduced. The initial efficiency, electrode energy density, and cycle life characteristics of the all-solid-state secondary battery including the composite cathode active material can be improved.

[0126]

[0127] [anode]

[0128] [Cathode: Cathode active material]

[0129] Referring to FIGS. 2 to 7, the positive electrode (10) includes a positive electrode current collector (11); and a positive electrode active material layer (12) disposed on one or both sides of the positive electrode current collector (11). The positive electrode active material layer (12) includes a positive electrode active material.

[0130] The cathode active material layer (12) includes a composite cathode active material according to one embodiment. The cathode active material layer further includes a solid electrolyte. By including the composite cathode active material and the solid electrolyte, the cathode can have a further reduced internal resistance. Accordingly, the cycle characteristics of an all-solid-state secondary battery including the cathode can be further improved.

[0131] Figure 1 schematically illustrates the structure of a positive electrode active material layer according to an embodiment. In Figure 1, 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 a fibrous carbon material.

[0132] Referring to this, the positive electrode active material layer contains Li2S (1), LiI (2), and an inorganic electronically conductive structure (3). By containing CNF, which is a one-dimensional structure, a long path network effect is brought about, and by bringing about a house of cards effect of the inorganic electronically conductive structure, which is a two-dimensional structure, the electronic conductive network within the positive electrode is greatly improved. In addition, as shown in Fig. 1, the sizes of the inorganic electronically conductive structure (3), LiI (2), and Li2S (1) are 1≤2<3. When they have these sizes, the inorganic electronically conductive structure can well form a network that imparts electronic conductivity between lithium sulfide, which is an insulator. The sizes of the inorganic electronically conductive structure, LiI, and Li2S refer to average sizes.

[0133] Referring to FIGS. 2 to 7, the positive electrode (10) includes a positive electrode current collector (11); and a positive electrode active material layer (12) disposed on one or both sides of the positive electrode current collector (11). The positive electrode active material layer (12) includes the composite positive electrode active material and solid electrolyte described above.

[0134] The composite cathode active material may be included in an amount of 40 to 90 parts by weight, 40 to 80 parts by weight, 50 to 80 parts by weight, or 50 to 70 parts by weight, based on 100 parts by weight of the cathode active material layer (12). If the content of the composite cathode active material is excessively reduced, the energy density of the secondary battery is reduced. If the content of the composite cathode active material is excessively increased, the deterioration of the cathode may be accelerated due to the change in the volume of the cathode during charge and discharge. As a result, the cycle characteristics of the solid secondary battery (1) may be reduced.

[0135] The cathode active material layer (12) may additionally include other cathode active materials in addition to the composite cathode active material described above.

[0136] Other cathode active materials may include, for example, a Li2S-containing composite. The Li2S composite includes, for example, a composite of Li2S and a carbon-based material, a composite of Li2S and a carbon-based material and a solid electrolyte, a composite of Li2S and a solid electrolyte, a composite of Li2S and a lithium salt, a composite of Li2S and a metal carbide, a composite of Li2S and a carbon-based material and a metal carbide, a composite of Li2S and a metal nitride, a composite of Li2S and a carbon-based material and a metal nitride, or a combination thereof.

[0137] The composite of Li2S and a carbon-based material includes a carbon-based material. The carbon-based material refers to the carbon-based material of the composite cathode active material described above. The method for producing the composite of Li2S and a carbon-based material may be a dry method, a wet method, or a combination thereof, but is not limited thereto, and any method used in the art may be used. The method for producing the composite of Li2S and a carbon-based material includes, but is not limited to, milling, heat treatment, deposition, etc., and any method used in the art may be used.

[0138] A composite of Li2S, a carbon-based material, and a solid electrolyte includes a carbon-based material and a solid electrolyte. The carbon-based material refers to the composite of Li2S and a carbon-based material described above. The solid electrolyte can be, for example, any material used as an ion-conducting material in the relevant technical field. The solid electrolyte is, for example, an inorganic solid electrolyte. The solid electrolyte is, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte is, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. The sulfide-based solid electrolyte includes, for example, Li, S, and P, and may optionally further include a halogen element. The sulfide-based solid electrolyte can be selected from among the sulfide-based solid electrolytes used in the electrolyte layer. The sulfide-based solid electrolyte has, for example, a molecular weight of 1×10 at room temperature. -5 It can have an ionic conductivity of S / cm or more. The oxide-based solid electrolyte contains, for example, Li, O, and transition metal elements, and may optionally contain other elements. The oxide-based solid electrolyte has an ionic conductivity of, for example, 1×10 at room temperature. -5 It may be a solid electrolyte having an ionic conductivity of S / cm or more. The oxide-based solid electrolyte may be selected from among oxide-based solid electrolytes used in the electrolyte layer.

[0139] The composite of Li2S and a solid electrolyte includes a solid electrolyte. The solid electrolyte refers to the composite of Li2S, a carbon-based material, and a solid electrolyte described above.

[0140] The composite of Li2S and a lithium salt comprises Li2S and a lithium salt. The lithium salt refers to the lithium salt of the composite cathode active material described above. The lithium salt is particularly one or more lithium halide compounds selected from LiF, LiCl, LiBr, and LiI. The composite of Li2S and a lithium salt may be, for example, a composite of Li2 and a lithium halide. The composite of Li2 and a lithium salt may provide improved ionic conductivity by including a lithium halide compound. The composite of Li2S and a lithium salt is distinguished from a simple mixture of Li2S, a carbon-based material, and a lithium salt. A simple mixture of Li2S and a lithium salt may provide high interfacial resistance by failing to maintain a dense interface between Li2S and a lithium salt, which may result in reduced cycle life characteristics of an all-solid-state secondary battery.

[0141] The composite of Li2S and metal carbide includes metal carbide. The metal carbide is, for example, a two-dimensional metal carbide. The two-dimensional metal carbide is, for example, M n+1 C n T x (M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups) is expressed as 2D metal carbides, for example, Ti2CT x , (Ti 0.5 , Nb 0.5 )2CT x , Nb2CT x , V2CT x , Ti3C2T x , (V 0.5 , Cr 0.5 )3C2T x , Ti3CNT x , Ta4C3T x , Nb4C3T x or a combination thereof. The surface of the two-dimensional metal carbide is terminated with O, OH and / or F.

[0142] A composite of Li2S, a carbon-based material, and a metal carbide includes a carbon-based material and a metal carbide. The carbon-based material refers to the composite of Li2S and a carbon-based material described above. The metal carbide refers to the composite of Li2S and a metal carbide described above.

[0143] The complex of Li2S and metal nitride includes a metal nitride. The metal nitride is, for example, a two-dimensional metal nitride. The two-dimensional metal nitride is, for example, M n+1 N n T x (M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups) is expressed as The surface of the two-dimensional metal nitride is terminated with O, OH and / or F.

[0144] A composite of Li2S, a carbon-based material, and a metal nitride includes a carbon-based material and a metal nitride. The carbon-based material refers to the composite of Li2S and a carbon-based material described above. The metal carbide refers to the composite of Li2S and a metal nitride described above.

[0145] The cathode active material layer (12) may additionally include, for example, a sulfide-based compound that is distinct from the cathode active material described above. The sulfide-based compound may be, for example, a compound containing a metal element other than Li and the element sulfur. The sulfide-based compound may be, for example, a compound containing a metal element belonging to Groups 1 to 14 of the Periodic Table of Elements having an atomic weight of 10 or more and the element sulfur. The sulfide-based compound may be, for example, FeS2, VS2, NaS, MnS, FeS, NiS, CuS, or a combination thereof. By the cathode active material layer additionally including a sulfide-based compound, the cycle characteristics of the all-solid-state secondary battery may be further improved. The content of the sulfide-based compound included in the cathode active material layer (12) may be 10 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less of the total weight of the cathode active material layer (12).

[0146] [Anode: Solid electrolyte]

[0147] The positive electrode active material layer (12) may further include, for example, a solid electrolyte. The solid electrolyte may be, for example, 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 more details on the solid electrolyte, refer to the electrolyte layer (30) section.

[0148] The solid electrolyte included in the positive electrode active material layer (12) may have a smaller average D50 particle diameter than the solid electrolyte included in the electrolyte layer (30). Here, the solid electrolyte may have a particle form. For example, the average D50 particle diameter 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 of the average D50 particle diameter of the solid electrolyte included in the electrolyte layer (30). The average D50 particle diameter is, for example, a median particle diameter (D50). The median particle diameter (D50) is the size of particles corresponding to 50% of the cumulative volume, calculated from the side of particles having a small particle size in a size distribution of particles measured by, for example, a laser diffraction method.

[0149] The solid electrolyte may be included in an amount of 10 to 60 parts by weight, 10 to 50 parts by weight, 15 to 50 parts by weight, 20 to 50 parts by weight, 25 to 50 parts by weight, or 30 to 50 parts by weight, based on 100 parts by weight of the positive electrode active material layer (12). If the content of the solid electrolyte is excessively reduced, the internal resistance of the positive electrode may increase, thereby deteriorating the cycle characteristics of the secondary battery. If the content of the sulfide-based solid electrolyte is excessively increased, the energy density of the secondary battery (1) may be reduced.

[0150] [Polar: Challenger]

[0151] The cathode active material layer (12) may further include a conductive material. The conductive material may be, for example, a carbon-based conductive material, a metal-based conductive material, or a combination thereof. The carbon-based conductive material may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or a combination thereof, but is not limited thereto, and any material used as a carbon-based conductive material in the art may be used. The metal-based conductive material may be, for example, metal powder, metal fiber, or a combination thereof, but is not limited thereto, and any material used as a metal-based conductive material in the art may be used. The content of the conductive material included in the cathode active material layer (12) may be, for example, 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% of the total weight of the cathode active material layer (12).

[0152] The cathode active material layer (12) includes a carbon-based material, and the carbon-based material may be disposed only in the composite cathode active material. The cathode active material layer (12) may not additionally include a separate carbon-based material other than the composite cathode active material including the carbon-based material. Since the cathode active material layer does not include a separate carbon-based material, the energy density of the cathode and the secondary battery (1) can be improved and the manufacturing process can be simplified.

[0153] [Positive: Binder]

[0154] The positive electrode active material layer (12) may further include a binder. The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited thereto, and any binder used in the relevant technical field may be used. The binder content included in the positive electrode active material layer (12) may be, for example, 1 wt% to 10 wt% of the total weight of the positive electrode active material layer (12). The binder may be omitted.

[0155] [Positive: Other additives]

[0156] The cathode active material layer (12) may further include additives such as fillers, coating agents, dispersants, and ion conductive aids in addition to the cathode active material, solid electrolyte, binder, and conductive agent described above.

[0157] As fillers, coating agents, dispersants, ion conductivity aids, etc. that can be included in the positive electrode active material layer (12), known materials generally used in electrodes of all-solid-state secondary batteries can be used.

[0158] [Anode: Anode current collector]

[0159] The positive electrode collector (11) uses a plate or foil made of, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. The positive electrode collector (11) may be omitted. The thickness of the positive electrode collector (11) is, for example, 1 µm to 100 µm, 1 µm to 50 µm, 5 µm to 25 µm, or 10 µm to 20 µm.

[0160] The cathode current collector (11) may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The base film may be, for example, an insulator. Since the base film includes an insulating thermoplastic polymer, when a short circuit occurs, the base film softens or liquefies, thereby blocking battery operation and suppressing a rapid increase in current. The metal layer may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or an alloy thereof. The metal layer can act as an electrochemical fuse and be cut off in case of overcurrent to prevent a short circuit. The limit current and the maximum current can be controlled by adjusting the thickness of the metal layer. The metal layer can be plated or deposited on the base film. When the thickness of the metal layer is reduced, the limit current and / or the maximum current of the positive electrode current collector (11) decrease, so that the stability of the all-solid-state secondary battery in case of a short circuit can be improved. A lead tab can be added on the metal layer for connection to the outside. The lead tab can be welded to the metal layer or the metal layer / base film laminate by ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or the metal layer melt, so that the metal layer can be electrically connected to the lead tab. In order to make the welding of the metal layer and the lead tab more solid, a metal chip can be added between the metal layer and the lead tab.The metal piece may be a thin piece of the same material as the metal of the metal layer. The metal piece may be, for example, a metal foil, a metal mesh, etc. The metal piece may be, for example, aluminum foil, copper foil, SUS foil, etc. After the metal piece is placed on the metal layer, the lead tab may be welded to the metal piece / metal layer laminate or the metal piece / metal layer / base film laminate. During welding, the base film, the metal layer, and / or the metal piece may melt, so that the metal layer or the metal layer / metal piece laminate may be electrically connected to the lead tab. A metal chip and / or a lead tab may be added to a portion of the metal layer. The base film may have a thickness of, for example, 1 to 50 μm, 1.5 to 50 μm, 1.5 to 40 μm, or 1 to 30 μm. When the base film has a thickness in this range, the weight of the electrode assembly can be more effectively reduced. The melting point of the base film may be, for example, 100 to 300°C, 100 to 250°C or less, or 100 to 200°C. Since the base film has a melting point within this range, the base film can be melted and easily bonded to the lead tab during the welding process of the lead tab. To improve the adhesion between the base film and the metal layer, a surface treatment such as corona treatment may be performed on the base film. The thickness of the metal layer may be, for example, 0.01 to 3 μm, 0.1 to 3 μm, 0.1 to 2 μm, or 0.1 to μm. Since the metal layer has a thickness within this range, conductivity can be maintained while ensuring the stability of the electrode assembly. The thickness of the metal piece may be, for example, 2 to 10 μm, 2 to 7 μm, or 4 to 6 μm. Since the metal piece has a thickness within this range, the connection between the metal layer and the lead tab can be performed more easily. By having this structure, the positive electrode current collector (11) can reduce the weight of the positive electrode and consequently improve the energy density of the positive electrode and the all-solid-state secondary battery.

[0161] [Anode: Inert member]

[0162] Referring to FIGS. 5 and 6, the positive electrode (10) includes a positive electrode current collector (11) and a positive electrode active material layer (12) disposed on one side of the positive electrode current collector. An inactive member (40) is disposed on one side of the positive electrode (10). Referring to FIG. 5, the inactive member (40) is disposed on one side of the positive electrode active material layer (12) and the positive electrode current collector (11). Referring to FIG. 6, the inactive member (40) is disposed on one side of the positive electrode active material layer (12) and between the electrolyte layer (30) and the positive electrode current collector (11) facing the electrolyte layer (30). The inactive member (40) is not disposed on one side of the positive electrode current collector (11). The electrolyte layer (30) may be, for example, a solid electrolyte layer. The inactive member may be an elastic member.

[0163] By including an inert member (40), cracking of the electrolyte layer (30) is prevented during the manufacture and / or charging / discharging of the all-solid-state secondary battery (1), and as a result, the cycle characteristics of the all-solid-state secondary battery (2) are improved. In an all-solid-state secondary battery (1) that does not include an inert member (40), when the manufacture and / or charging / discharging of the all-solid-state secondary battery (1) is performed, uneven pressure is applied to the electrolyte layer (30) in contact with the positive electrode (10), which increases the possibility of cracking in the electrolyte layer (30), and thus, a short circuit may occur due to the growth of lithium metal through the crack.

[0164] In the all-solid-state secondary battery (1), the thickness of the inert member (40) is greater than or equal to the thickness of the positive electrode active material layer (12). Alternatively, in the all-solid-state secondary battery (1), the thickness of the inert member (40) is substantially equal to the thickness of the positive electrode (10). Since the thickness of the inert member (40) is equal to the thickness of the positive electrode (10), a uniform pressure is applied between the positive electrode (10) and the electrolyte layer (30), and the positive electrode (10) and the electrolyte layer (30) are sufficiently adhered to each other, so that the interfacial resistance between the positive electrode (10) and the electrolyte layer (30) can be reduced. In addition, since the electrolyte layer (30) is sufficiently sintered during the pressurized manufacturing process of the all-solid-state secondary battery (1), the internal resistance of the electrolyte layer (30) and the all-solid-state secondary battery (1) including the same is reduced.

[0165] The inert member (40) surrounds the side surface of the positive electrode (10) and is in contact with the electrolyte layer (30). By the inert member (40) surrounding the side surface of the positive electrode (10) and being in contact with the electrolyte layer (30), cracks in the electrolyte layer (30) that occur due to a pressure difference during the pressing process in the electrolyte layer (30) that does not come into contact with the positive electrode (20) can be effectively suppressed. The inert member (40) surrounds the side surface of the positive electrode (10) and is separated from the negative electrode (20), more specifically, the first negative electrode active material layer (22). The inert member (40) surrounds the side surface of the positive electrode (10), is in contact with the electrolyte layer (30), and is separated from the negative electrode (20). Therefore, the possibility of a short circuit occurring due to physical contact between the positive electrode (10) and the first negative electrode active material layer (22) or a short circuit occurring due to overcharging of lithium, etc., is suppressed. For example, by placing an inert member (40) on one side of the positive electrode active material layer (12) and simultaneously on one side of the positive electrode current collector (11), the possibility of a short circuit occurring due to contact between the positive electrode current collector (11) and the negative electrode (20) is more effectively suppressed.

[0166] Referring to FIGS. 6 and 7, the inert member (40) extends from one side of the positive electrode (30) to the end of the electrolyte layer (30). By extending the inert member (40) to the end of the electrolyte layer (30), cracks occurring at the end of the electrolyte layer (30) can be suppressed. The end of the electrolyte layer (30) is the outermost part that is in contact with the side of the electrolyte layer (30). The inert member (40) extends to the outermost part that is in contact with the side of the electrolyte layer (30). The inert member (40) is separated from the negative electrode (20), more specifically, from the first negative electrode active material layer (22). The inert member (40) extends to the end of the electrolyte layer (30), but does not contact the negative electrode (20). The inert member (40) fills a space extending from, for example, one side of the anode (30) to the end of the electrolyte layer (30).

[0167] Referring to FIGS. 5 and 6, the width of the inert member (40) extending from one side of the positive electrode (10) to the end of the electrolyte layer (30) is, for example, 1 to 30%, 1 to 25%, 1 to 20%, 1 to 15%, 1 to 10%, or 1 to 5% of the width between one side of the positive electrode (10) and the other side opposite to the one side. If the width of the inert member (40) is excessively large, the energy density of the all-solid-state secondary battery (1) is reduced. If the width of the inert member (40) is excessively small, the effect of arranging the inert member (40) is minimal.

[0168] The area of ​​the anode (10) is smaller than the area of ​​the electrolyte layer (30) in contact with the anode (10). An inert member (40) is arranged to surround the side of the anode (10) to compensate for the area difference between the anode (10) and the electrolyte layer (30). By compensating for the difference between the area of ​​the anode (10) and the area of ​​the electrolyte layer (30), cracks in the electrolyte layer (30) caused by the pressure difference during the pressing process are effectively suppressed. For example, the sum of the area of ​​the anode (10) and the area of ​​the inert member (40) is equal to the area of ​​the electrolyte layer (30). The electrolyte layer (30) may be, for example, a solid electrolyte layer.

[0169] The area of ​​the anode (10) is, for example, less than 100%, 99% or less, 98% or less, 97% or less, 96% or less, or 95% or less of the area of ​​the electrolyte layer (30). The area of ​​the anode (10) is, for example, 50% to less than 100%, 50% to 99%, 55% to 98%, 60% to 97%, 70% to 96%, 80% to 95%, or 85% to 95% of the area of ​​the electrolyte layer (30).

[0170] If the area of ​​the positive electrode (10) is equal to or larger than the area of ​​the electrolyte layer (30), the possibility of a short circuit occurring due to physical contact between the positive electrode (10) and the first negative electrode active material layer (22) or overcharging of lithium increases. The area of ​​the positive electrode (10) is, for example, equal to the area of ​​the positive electrode active material layer (12). The area of ​​the positive electrode (10) is, for example, equal to the area (11) of the positive electrode current collector.

[0171] The area of ​​the inert member (40) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the area of ​​the anode (10). The area of ​​the inert member (40) is, for example, 1% to 50%, 5% to 40%, 5% to 30%, 5% to 20%, or 5% to 15% of the area of ​​the anode (10).

[0172] The area (S1) of the positive electrode (10) is smaller than the area (S4) of the negative electrode current collector (21). The area (S1) of the positive electrode (10) is, for example, less than 100%, 99% or less, 98% or less, 97% or less, 96% or less, or 95% or less of the area (S4) of the negative electrode current collector (21). The area (S1) of the positive electrode (10) is, for example, 50% to less than 100%, 50% to 99%, 55% to 98%, 60% to 97%, 70% to 96%, 80% to 95%, or 85% to 95% of the area (S4) of the negative electrode current collector (21). The area (S4) of the negative electrode current collector (21) is, for example, the same as the area of ​​the negative electrode (20). The area (S4) of the negative electrode current collector (21) is, for example, the same as the area of ​​the first negative electrode active material layer (22).

[0173] As used herein, “same” area, length, width, thickness, and / or shape includes all instances of having “substantially the same” area, length, width, thickness, and / or shape, except where the area, length, width, thickness, and / or shape are intentionally different from each other. “Same” area, length, width, and / or thickness includes a range where the unintentional difference in the area, length, width, and / or thickness of the compared objects is, for example, less than 3%, less than 2%, less than 1%, less than 0.5%, or less than 0.1%.

[0174] The thickness of the inert member (40) is, for example, greater than the thickness of the first negative electrode active material layer (22). The thickness of the first negative electrode active material layer (22) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the thickness of the inert member (40). The thickness of the first negative electrode active material layer (22) is, for example, 1% to 50%, 1% to 40%, 1% to 30%, 1% to 20%, or 1% to 10% of the thickness of the inert member (40).

[0175] The inert member (40) may be a gasket. By using a gasket as the inert member (40), cracks in the electrolyte layer (30) caused by a pressure difference during the pressing process can be effectively suppressed.

[0176] The inert member (40) has, for example, a single-layer structure. Alternatively, although not shown in the drawing, the inert member (40) may have a multi-layer structure. In the inert member (40) having a multi-layer structure, each layer may have a different composition. The inert member having a multi-layer structure may have, for example, a two-layer structure, a three-layer structure, a four-layer structure, or a five-layer structure. The inert member (40) having a multi-layer structure may include, for example, one or more adhesive layers and one or more support layers. The adhesive layer effectively prevents, for example, a separation between the positive electrode (10) and the electrolyte layer (30) due to a change in the volume of the positive electrode (10) that occurs during the charge / discharge process of the all-solid-state secondary battery (10), and improves the film strength of the inert member (40) by providing a bonding force between the support layer and other layers. The support layer provides support to the inert member (40), prevents unevenness of pressure applied to the electrolyte layer (30) during the pressurization process or the charge / discharge process, and prevents deformation of the all-solid-state secondary battery (1) being manufactured.

[0177] The inert member (40) is, for example, a flame-retardant inert member. The flame-retardant inert member prevents thermal runaway and ignition of the all-solid-state secondary battery (1) by providing flame retardancy. Consequently, the safety of the all-solid-state secondary battery (1) is further improved. The flame-retardant inert member prevents deterioration of the all-solid-state secondary battery (1) by absorbing residual moisture within the all-solid-state secondary battery (1), thereby improving the lifespan characteristics of the all-solid-state secondary battery (1).

[0178] The flame-retardant inert member includes, for example, a matrix and a filler. The matrix includes, for example, a substrate and a reinforcing material. The matrix includes, for example, a fibrous substrate and a fibrous reinforcing material. Since the matrix includes the substrate, the matrix can have elasticity. Therefore, the matrix can effectively accommodate volume changes during charging and discharging of the all-solid-state secondary battery (1) and can be arranged at various positions. The substrate included in the matrix includes, for example, a first fibrous material. Since the substrate includes the first fibrous material, the volume changes of the positive electrode (30) occurring during the charging and discharging process of the all-solid-state secondary battery (1) can be effectively accommodated and deformation of the inert member (40) caused by the volume changes of the positive electrode (30) can be effectively suppressed. The first fibrous material is, for example, a material having an aspect ratio of 2 or more, 5 or more, 20 or more, or 50 or more. The first fibrous material is, for example, a material having an aspect ratio of 5 to 1000, 20 to 1000, or 50 to 1000. The first fibrous material is, for example, an insulating material. Since the first fibrous material is an insulating material, a short circuit between the positive electrode (30) and the negative electrode (20) caused by lithium dendrites, etc., generated during the charge and discharge process of the all-solid-state secondary battery (1) can be effectively prevented. The first fibrous material includes, for example, at least one selected from pulp fibers, insulating polymer fibers, and ion-conductive polymer fibers. The strength of the matrix is ​​improved by the inclusion of a reinforcing material in the matrix. Therefore, the matrix can prevent excessive volume change during charge and discharge of the all-solid-state secondary battery (1) and deformation of the all-solid-state secondary battery. The reinforcing material included in the matrix includes, for example, a second fibrous material. Since the reinforcing material includes the second fibrous material, the strength of the matrix can be increased more uniformly. The second fibrous material is, for example, a material having an aspect ratio of 2 or more, 3 or more, 5 or more, or 10 or more.The first fibrous material is, for example, a material having an aspect ratio of 2 to 100, 3 to 100, 5 to 100, or 10 to 100. The second fibrous material is, for example, a flame-retardant material. Since the second fibrous material is a flame-retardant material, ignition due to thermal runaway occurring during the charge / discharge process of the all-solid-state secondary battery (1) or due to external impact can be effectively suppressed. The second fibrous material is, for example, glass fiber, metal oxide fiber, ceramic fiber, etc.

[0179] The flame-retardant inert member includes a filler in addition to a matrix. The filler may be disposed within the matrix, on the surface of the matrix, or on both the interior and the surface. The filler is, for example, an inorganic material. The filler included in the flame-retardant inert member is, for example, a moisture getter. The filler removes moisture remaining in the all-solid-state secondary battery (1) by adsorbing moisture, for example, at a temperature below 100°C, thereby preventing deterioration of the all-solid-state secondary battery (1). In addition, when the temperature of the all-solid-state secondary battery (1) increases to 150°C or higher due to thermal runaway occurring during the charge / discharge process of the all-solid-state secondary battery (1) or an external impact, the filler releases the adsorbed moisture, thereby effectively suppressing ignition of the all-solid-state secondary battery (1). That is, the filler is, for example, a flame retardant. The filler is, for example, a metal hydroxide having moisture adsorption properties. The metal hydroxide contained in the filler is, for example, Mg(OH)2, Fe(OH)3, Sb(OH)3, Sn(OH)4, Ti(OH)3, Zr(OH)4, Al(OH)3, or a combination thereof. The content of the filler contained in the flame-retardant inert member is, for example, 10 to 80 parts by weight, 20 to 80 parts by weight, 30 to 80 parts by weight, 40 to 80 parts by weight, 50 to 80 parts by weight, 60 to 80 parts by weight, or 65 to 80 parts by weight, based on 100 parts by weight of the flame-retardant inert member (4).

[0180] The flame-retardant inert member may further comprise, for example, a binder. The binder may comprise, for example, a curable polymer or a non-curable polymer. A curable polymer is a polymer that cures by heat and / or pressure. A curable polymer is, for example, a solid at room temperature. The flame-retardant inert member (e.g., inert member (40)) comprises, for example, a thermo-pressure curable film and / or a cured product thereof. The thermo-pressure curable polymer is, for example, TSA-66 from Toray Industries.

[0181] The flame-retardant inert member may additionally include other materials in addition to the above-described substrate, reinforcing material, filler, and binder. The flame-retardant inert member may further include one or more selected from among paper, an insulating polymer, an ion-conducting polymer, an insulating inorganic material, an oxide-based solid electrolyte, and a sulfide-based solid electrolyte. The insulating polymer may be, for example, an olefin-based polymer such as polypropylene (PP) or polyethylene (PE).

[0182] The density of the substrate or reinforcing material included in the flame-retardant inert material may be, for example, 10% to 300%, 10% to 150%, 10% to 140%, 10% to 130%, or 10% to 120% of the density of the positive electrode active material included in the positive electrode active material layer (12).

[0183] The inert member (40) is a member that does not contain an electrochemically active material, for example, an electrode active material. The electrode active material is a material that absorbs / releases lithium. The inert member (40) is a member made of a material other than the electrode active material and used in the relevant technical field.

[0184] [All-solid-state secondary battery]

[0185] An all-solid-state secondary battery according to one embodiment includes the above-described 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 includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector.

[0186] The negative electrode layer includes a negative electrode current collector and a lithium host layer disposed on one surface of the negative electrode current collector, the lithium host layer includes a lithium host structure, the lithium host structure includes one or more lithium hosts, the lithium hosts include a carbon-based lithium host, a metal-based lithium host, a polymer-based lithium host, or a combination thereof, and includes a first inactive member disposed on one surface of the negative electrode layer.

[0187] A lithium precipitation layer may be formed inside and / or on the surface of the lithium host layer.

[0188] All-solid-state secondary batteries include lithium-containing sulfide-based cathode active materials as their cathode active materials. Therefore, the disruption of ion and / or electron transport pathways due to volume increase during initial discharge of non-lithium-containing sulfide-based cathode active materials, such as sulfur (S), is prevented. By preventing such disruption of ion and / or electron transport pathways, the cycle characteristics of all-solid-state secondary batteries are improved.

[0189] Since the all-solid-state secondary battery includes a lithium host layer in its anode layer, the lithium host layer acts as a support during the deposition of lithium metal in the anode layer, thereby suppressing the non-uniformity of lithium deposition. Furthermore, the formation and growth of lithium dendrites and / or isolated lithium (dead lithium) during the charge / discharge process of the all-solid-state secondary battery can be suppressed. Consequently, deterioration of the all-solid-state secondary battery is suppressed and cycle characteristics are improved.

[0190] By including a lithium host layer in the anode layer of an all-solid-state secondary battery, rapid volume changes in the anode layer during the charge / discharge process of the all-solid-state secondary battery can be suppressed. By suppressing rapid volume changes in the anode layer, deterioration of the all-solid-state secondary battery due to volume changes during the charge / discharge process of the all-solid-state secondary battery is suppressed, and cycle characteristics are improved.

[0191] Since the all-solid-state secondary battery includes a solid electrolyte layer, the migration of polysulfides generated during charging and discharging of the lithium-containing sulfide-based positive electrode active material to the negative electrode layer is blocked. Consequently, side reactions between polysulfides and the negative electrode active material are suppressed.

[0192] By arranging an inert material on one side of the cathode layer, short circuits between the lithium dendrites generated and grown during charging and discharging of the all-solid-state secondary battery and the anode and / or the lithium metal melting at high temperatures are more effectively suppressed. Consequently, short circuits in the all-solid-state secondary battery are prevented and the life characteristics are improved.

[0193] Referring to FIGS. 2 to 6, an all-solid-state secondary battery (1) includes a positive electrode layer (10); a negative electrode layer (20); and an electrolyte layer (30) disposed between the positive electrode layer (10) and the negative electrode layer (20). The negative electrode layer (20) includes a negative electrode current collector (21) and a first negative electrode active material layer (22) disposed on one surface of the negative electrode current collector.

[0194] [cathode]

[0195] [Cathode: Cathode active material]

[0196] Referring to FIGS. 3 to 6, the negative electrode (20) includes a first negative electrode active material layer (22). The first negative electrode active material layer (22) includes, for example, a negative electrode active material and a binder.

[0197] The negative electrode active material included in the first negative electrode active material layer (22) is, for example, a negative electrode material that can form an alloy or compound with lithium.

[0198] The negative electrode active material included in the first negative electrode active material layer (22) has, for example, a particle form. The average particle diameter of the negative electrode active material having a particle form is, for example, 4 ㎛ or less, 3 ㎛ or less, 2 ㎛ or less, 1 ㎛ or less, 500 nm or less, 300 nm or less, or 100 nm or less. The average particle diameter of the negative electrode active material having a particle form is, for example, 10 nm to 4 ㎛, 10 nm to 3 ㎛, 10 nm to 2 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 300 nm, or 10 nm to 100 nm. When the negative electrode active material has an average particle diameter in this range, reversible absorption and / or desorption of lithium can be facilitated during charge and discharge. The average particle size of the negative electrode active material is, for example, the median diameter (D50) measured using a laser particle size distribution meter.

[0199] The negative electrode active material included in the first negative electrode active material layer (22) includes, for example, at least one selected from among a carbon-based negative electrode active material and a metal or metalloid negative electrode active material.

[0200] Carbon-based negative electrode materials include, for example, amorphous carbon, crystalline carbon, porous carbon, or a combination thereof.

[0201] The carbon-based negative electrode material is, in particular, amorphous carbon. Amorphous carbon includes, but is not limited to, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), and graphene, and any material classified as amorphous carbon in the relevant technical field is acceptable. Amorphous carbon is carbon that has no crystallinity or very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon.

[0202] The carbon-based negative electrode active material may be, for example, porous carbon. The porous carbon has a pore volume of, for example, 0.1 cc / g to 10.0 cc / g, 0.5 cc / g to 5 cc / g, or 0.1 cc / g to 1 cc / g. The porous carbon has an average pore diameter of, for example, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 10 nm. The BET (Brunauer, Emmett, and Teller) specific surface area of ​​the porous carbon is, for example, 100 m 2 / g to 3,000 m 2 / g, 300 m 2 / g to 2,000 m 2 / g, or 500 m 2 / g to 1,000 m 2 / g is.

[0203] The metal or metalloid negative electrode active material includes, but is not limited to, one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn), and any metal or metalloid negative electrode active material that forms an alloy or compound with lithium in the relevant technical field may be used. For example, nickel (Ni) does not form an alloy with lithium and therefore is not a metal negative electrode active material.

[0204] The first negative electrode active material layer (22) includes a type of negative electrode active material among these negative electrode active materials, or includes a mixture of a plurality of different negative electrode active materials. For example, the first negative electrode active material layer (22) includes only amorphous carbon, or includes at least one selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the first negative electrode active material layer (22) includes a mixture of amorphous carbon and at least one selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The mixing ratio of the mixture of amorphous carbon and gold, etc., is a weight ratio, for example, 99:1 to 1:99, 10:1 to 1:2, 5:1 to 1:1, or 4:1 to 2:1, but is not necessarily limited to this range and is selected according to the required characteristics of the all-solid-state secondary battery (1). When the negative electrode active material has this composition, the cycle characteristics of the all-solid-state secondary battery (1) are further improved.

[0205] The negative electrode active material included in the first negative electrode active material layer (22) includes, for example, a mixture of first particles made of amorphous carbon and second particles made of a metal or a metalloid. The metal or metalloid includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the metalloid is a semiconductor. The content of the second particles is 1 to 99 wt%, 1 to 60 wt%, 8 to 60 wt%, 10 to 50 wt%, 15 to 40 wt%, or 20 to 30 wt% based on the total weight of the mixture. When the second particles have a content in this range, the cycle characteristics of, for example, an all-solid-state secondary battery (1) are further improved.

[0206] Alternatively, the first negative electrode active material layer (22) includes a composite negative electrode active material. The composite negative electrode active material may include, for example, a carbon-based support and a metal-based negative electrode active material supported on the carbon-based support. The composite negative electrode active material may have, for example, a structure in which silver (Ag) is supported on carbon particles. Since the composite negative electrode active material has such a structure, the uneven distribution of the metal-based negative electrode active material within the first negative electrode active material layer can be prevented and a uniform distribution can be obtained. As a result, the cycle characteristics of the all-solid-state secondary battery (1) including the first negative electrode active material layer (22) are further improved.

[0207] The metal-based negative electrode active material supported on the carbon-based support includes, for example, a metal, a metal oxide, a composite of a metal and a metal oxide, or a combination thereof. The metal includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), tellurium (Te), and zinc (Zn). The metal oxide includes, for example, gold (Au) oxide, platinum (Pt) oxide, palladium (Pd) oxide, silicon (Si) oxide, silver (Ag) oxide, aluminum (Al) oxide, bismuth (Bi) oxide, tin (Sn) oxide, tellurium (Te) oxide, and zinc (Zn) oxide. The metal oxide includes, for example, Au x O y (0 <x≤2, 0<y≤3), Pt x O y (0 <x≤1, 0<y≤2), Pd x O y (0 <x≤1, 0<y≤1), Si x 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 The y (0 <x≤1, 0<y≤3), Zn x The y (0 <x≤1, 0<y≤1) 또는 이들의 조합을 포함할 수 있다. 금속과 금속산화물의 복합체는 예를 들어 Au와 Au x The y (0 <x≤2, 0<y≤3)의 복합체, Pt와 Pt x The y (0 <x≤1, 0<y≤2)의 복합체, Pd와 Pd x The y (0 <x≤1, 0<y≤1)의 복합체, Si와 Si x The y (0 <x≤1, 0<y≤2)의 복합체, Ag 와 Ag x The y (0 <x≤2, 0<y≤1)의 복합체, Al과 Al x The y (0 <x≤2, 0<y≤3)의 복합체, Bi와 Bi x The y (0 <x≤2, 0<y≤3)의 복합체, Sn과 Sn x The y (0 <x≤1, 0<y≤2)의 복합체, Te과 Te x The y (0 <x≤1, 0<y≤3), Zn과 Zn x The y (0 <x≤1, 0<y≤1)의 복합체, 또는 이들의 조합을 포함할 수 있다.

[0208] The carbonaceous support is, for example, amorphous carbon. Amorphous carbon includes, but is not limited to, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), graphene, activated carbon, carbon nanofibers (CNF), carbon nanotubes (CNT), etc., and any material classified as amorphous carbon in the relevant technical field is possible. Amorphous carbon is carbon that has no crystallinity or very low crystallinity, and is distinguished from crystalline carbon or graphite carbon. Carbonaceous materials are, for example, carbonaceous negative electrode active materials.

[0209] The composite negative electrode active material may have, for example, a particle form. The particle size of the composite negative electrode active material having a particle form is, for example, 10 nm to 4 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. When the composite negative electrode active material has a particle size in this range, reversible absorption and / or desorption of lithium may be facilitated during charge and discharge. The metal-based negative electrode active material supported on the support may have, for example, a particle form. The particle size of the metal-based negative electrode active material may be, for example, 1 nm to 200 nm, 1 nm to 150 nm, 5 nm to 100 nm, or 10 nm to 50 nm. The carbon-based support may have, for example, a particle form. The particle size of the carbon-based support may be, for example, 10 nm to 2 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. By having a particle size in this range, the carbon-based support can be more uniformly arranged within the first negative electrode active material layer. The carbon-based support may be, for example, nanoparticles having a particle size of 500 nm or less. The particle sizes of the composite negative electrode active material, the particle sizes of the metal-based negative electrode active material, and the particle sizes of the carbon-based support are, for example, average particle sizes. The average particle size is, for example, the median diameter (D50) measured using a laser particle size distribution analyzer. Alternatively, the average particle size may be determined automatically using software, for example, from an electron microscope image, or manually by a manual method.

[0210] [Cathode: Binder]

[0211] The binder included in the first negative electrode active material layer (22) is, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc., but is not necessarily limited thereto and any binder used in the relevant technical field may be used. The binder may be composed of a single binder or a plurality of different binders.

[0212] Since the first negative electrode active material layer (22) includes a binder, the first negative electrode active material layer (22) is stabilized on the negative electrode current collector (21). In addition, cracking of the first negative electrode active material layer (22) is suppressed despite changes in the volume and / or relative position of the first negative electrode active material layer (22) during the charge and discharge process. For example, if the first negative electrode active material layer (22) does not include a binder, the first negative electrode active material layer (22) can be easily separated from the negative electrode current collector (21). As the first negative electrode active material layer (22) is separated from the negative electrode current collector (21), the possibility of a short circuit occurring increases as the negative electrode current collector (21) comes into contact with the electrolyte layer (30) at the exposed portion of the negative electrode current collector (21). The first negative electrode active material layer (22) is manufactured by, for example, applying a slurry in which the material constituting the first negative electrode active material layer (22) is dispersed onto the negative electrode current collector (21) and drying the slurry. By including a binder in the first negative electrode active material layer (22), stable dispersion of the negative electrode active material in the slurry is possible. For example, when applying the slurry onto the negative electrode current collector (21) by screen printing, it is possible to suppress clogging of the screen (for example, clogging by aggregates of the negative electrode active material).

[0213] [Cathode: Other additives]

[0214] The first negative electrode active material layer (22) may further include additives used in all-solid-state secondary batteries, such as fillers, coating agents, dispersants, and ion conductive aids.

[0215] [Cathode: Solid electrolyte]

[0216] The first negative electrode active material layer (22) may further include a solid electrolyte. The solid electrolyte may be, for example, a material selected from among the solid electrolytes included in the electrolyte layer (30). The solid electrolyte included in the first negative electrode active material layer (22) may act as a reaction site where lithium metal formation begins within the first negative electrode active material layer (22), a space where the formed lithium metal is stored, or a path for transferring lithium ions. The solid electrolyte may be omitted.

[0217] In the first negative electrode active material layer (22), the content of the solid electrolyte may be high, for example, in an area adjacent to the electrolyte layer (30), and low, for example, in an area adjacent to the negative electrode current collector (21). In the first negative electrode active material layer (22), the solid electrolyte may have a concentration gradient in which the concentration decreases, for example, from an area adjacent to the electrolyte layer (30) to an area adjacent to the negative electrode current collector (21).

[0218] [Cathode: First negative electrode active material layer]

[0219] The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer (22) and the initial charge capacity (A) of the positive electrode active material layer is 0.005 to 0.45. The initial charge capacity of the positive electrode active material layer (12) is the first open circuit voltage (1 st Li / Li from open circuit voltage) + The initial charge capacity of the first negative electrode active material layer (22) is determined at the maximum charging voltage. The initial charge capacity of the first negative electrode active material layer (22) is determined at the second open circuit voltage (2 nd Li / Li from open circuit voltage) + It is determined at 0.01 V.

[0220] The maximum charging voltage is determined by the type of cathode active material. The maximum charging voltage can be, for example, 1.5 V, 2.0 V, 2.5 V, 3.0 V, 3.5 V, 4.0 V, 4.2 V, or 4.3 V. For example, the maximum charging voltage of Li2S or Li2S composite is Li / Li + can be 2.5 V for Li2S or Li2S complex. For example, the maximum charging voltage of Li / Li + It can be 3.0 V for. The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer (22) and the initial charge capacity (A) of the positive electrode active material layer is, for example, 0.01 to 0.3, 0.01 to 0.2, or 0.05 to 0.1. The initial charge capacity (mAh) of the positive electrode active material layer (12) is obtained by multiplying the charge capacity density (charge specific capacity) (mAh / g) of the positive electrode active material by the mass (g) of the positive electrode active material in the positive electrode active material layer (12). When several types of positive electrode active materials are used, the charge capacity density × mass value is calculated for each positive electrode active material, and the sum of these values ​​is the initial charge capacity of the positive electrode active material layer (12). The initial charge capacity of the first negative electrode active material layer (22) is also calculated in the same way. The initial charge capacity of the first negative electrode active material layer (22) is obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the first negative electrode active material layer (22). When several types of negative electrode active materials are used, the charge capacity density × mass value is calculated for each negative electrode active material, and the sum of these values ​​is the initial charge capacity of the first negative electrode active material layer (22). The charge capacity density of each of the positive electrode active material and the negative electrode active material can be measured using a solid half-cell using lithium metal as a counter electrode. The initial charge capacity of each of the positive electrode active material layer (12) and the first negative electrode active material layer (22) is obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the first negative electrode active material layer (22). 2can be directly measured using a solid-state half-cell. For the positive electrode, the measurement is made from the first open circuit voltage (OCV) to the maximum charge voltage, e.g., 3.0 V (vs. Li / Li + ) can be performed for an operating voltage of up to 0.01 V for the cathode, for example, lithium metal, from the second open circuit voltage (OCV). For example, a solid-state half-cell having a cathode active material layer can measure a current of 0.1 mA / cm from the first open circuit voltage to 3.0 V. 2 The solid half-cell having the first negative active material layer is charged with a constant current of 0.1 mA / cm from the second open circuit voltage to 0.01 V. 2 It can be charged with a constant current. The current density during constant current charging is, for example, 0.2 mA / cm 2 , or 0.5 mA / cm 2 A solid-state battery having a positive electrode active material layer can be charged from a first open circuit voltage to, for example, 2.5 V, 2.0 V, 3.5 V, or 4.0 V. The maximum charge voltage of the positive electrode active material layer can be determined by the maximum voltage of the battery that satisfies the safety conditions according to JISC8712:2015 of the Japanese Standards Association.

[0221] If the initial charge capacity of the first negative electrode active material layer (22) is too small, the thickness of the first negative electrode active material layer (22) becomes very thin, so that lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) during repeated charge and discharge processes collapse the first negative electrode active material layer (22), making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the charge capacity of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases and the internal resistance of the all-solid-state secondary battery (1) due to the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1).

[0222] The thickness of the first negative electrode active material layer (22) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer (12). The thickness of the first negative electrode active material layer (22) is, for example, 1 to 50%, 1 to 40%, 1 to 30%, 1 to 20%, 1 to 10%, or 1 to 5% of the thickness of the positive electrode active material layer (12). The thickness of the first negative electrode active material layer (22) is, for example, 1 µm to 20 µm, 2 µm to 15 µm, or 3 µm to 10 µm. If the thickness of the first negative electrode active material layer (22) is too thin, lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) collapse the first negative electrode active material layer (22), making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the thickness of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases and the internal resistance of the all-solid-state secondary battery (1) due to the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the thickness of the first negative electrode active material layer (22) decreases, for example, the initial charge capacity of the first negative electrode active material layer (22) also decreases.

[0223] [Cathode: Second negative electrode active material layer]

[0224] Referring to FIG. 4, the all-solid-state secondary battery (1) further includes, after being charged, a second negative electrode active material layer (24) disposed, for example, between the negative electrode current collector (21) and the first negative electrode active material layer (22). The second negative electrode active material layer (24) is a metal layer containing lithium or a lithium alloy. The metal layer contains lithium or a lithium alloy. Therefore, since the second negative electrode active material layer (24) is a metal layer containing lithium, it functions as, for example, a lithium reservoir. The lithium alloy is, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, etc., but is not limited thereto, and any lithium alloy used in the art may be used. The second negative electrode active material layer (24) may be made of one of these alloys or lithium, or may be made of several types of alloys. The second negative electrode active material layer (24) is, for example, a plated layer. The second negative electrode active material layer (24) is deposited between the first negative electrode active material layer (22) and the negative electrode current collector (21), for example, during the charging process of an all-solid-state secondary battery (1).

[0225] The thickness of the second negative electrode active material layer (24) is not particularly limited, but is, for example, 1 ㎛ to 500 ㎛, 1 ㎛ to 200 ㎛, 1 ㎛ to 150 ㎛, 1 ㎛ to 100 ㎛, or 1 ㎛ to 50 ㎛. If the thickness of the second negative electrode active material layer (24) is too thin, it is difficult for the second negative electrode active material layer (24) to perform the role of a lithium reservoir. If the thickness of the second negative electrode active material layer (24) is too thick, the mass and volume of the all-solid-state secondary battery (1) may increase, and the cycle characteristics of the all-solid-state secondary battery (1) may rather deteriorate.

[0226] Alternatively, in the all-solid-state secondary battery (1), the second negative electrode active material layer (24) may be disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22), for example, before assembling the all-solid-state secondary battery (1). When the second negative electrode active material layer (24) is disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22) before assembling the all-solid-state secondary battery (1), the second negative electrode active material layer (24) acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil may be disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22) before assembling the all-solid-state secondary battery (1).

[0227] When the second negative electrode active material layer (24) is precipitated by charging after assembling the all-solid-state secondary battery (1), the energy density of the all-solid-state secondary battery (1) increases because the second negative electrode active material layer (24) is not included when assembling the all-solid-state secondary battery (1). When charging the all-solid-state secondary battery (1), the charging is performed in excess of the charging capacity of the first negative electrode active material layer (22). That is, the first negative electrode active material layer (22) is overcharged. At the initial stage of charging, lithium is absorbed into the first negative electrode active material layer (22). The negative electrode active material included in the first negative electrode active material layer (22) forms an alloy or compound with the lithium ions that have moved from the positive electrode (10). When charging exceeds the capacity of the first negative electrode active material layer (22), for example, lithium is deposited on the back surface of the first negative electrode active material layer (22), that is, between the negative electrode current collector (21) and the first negative electrode active material layer (22), and a metal layer corresponding to the second negative electrode active material layer (24) is formed by the deposited lithium. The second negative electrode active material layer (24) is a metal layer mainly composed of lithium (i.e., metallic lithium). This result is obtained, for example, by the negative electrode active material included in the first negative electrode active material layer (22) including a material that forms an alloy or compound with lithium. During discharge, lithium in the first negative electrode active material layer (22) and the second negative electrode active material layer (24), that is, the metal layer, is ionized and moves toward the positive electrode (10). Therefore, it is possible to use lithium as the negative electrode active material in an all-solid-state secondary battery (1). In addition, since the first negative electrode active material layer (22) covers the second negative electrode active material layer (24), it acts as a protective layer for the second negative electrode active material layer (24), i.e., the metal layer, and at the same time, it suppresses the precipitation and growth of lithium dendrites. Accordingly, it suppresses short circuits and capacity reduction of the all-solid-state secondary battery (1), and consequently improves the cycle characteristics of the all-solid-state secondary battery (1).In addition, when the second negative electrode active material layer (24) is placed by charging after assembling the all-solid-state secondary battery (1), the negative electrode (20), i.e., the negative electrode current collector (21) and the first negative electrode active material layer (22) and the region between them are Li-free regions that do not contain lithium (Li) in the initial state or the state after complete discharge of the all-solid-state secondary battery (1).

[0228] [Cathode: Negative current collector]

[0229] The negative electrode current collector (21) is composed of, for example, a material that does not react with lithium, i.e., does not form an alloy or a compound. The material constituting the negative electrode current collector (21) is, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), but is not necessarily limited thereto, and any material that can be used as an electrode current collector in the relevant technical field can be used. The negative electrode current collector (21) may be composed of one type of the above-described metal, or may be composed of an alloy or a coating material of two or more types of metals. The negative electrode current collector (21) is, for example, in the form of a plate or foil.

[0230] Referring to FIG. 3, the all-solid-state secondary battery (1) may further include a thin film (23) containing an element capable of forming an alloy with lithium on one surface of the negative electrode current collector (21). The thin film (23) is disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22). The thin film (23) contains, for example, an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium includes, but is not limited to, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and any element capable of forming an alloy with lithium in the art may be used. The thin film (23) may be composed of one of these metals or an alloy of several types of metals. In addition, a second negative electrode active material layer (24) may be deposited between the thin film (23) and the first negative electrode active material layer (22). By placing the thin film (23) on one surface of the negative electrode current collector (21), for example, the deposition shape of the second negative electrode active material layer (24) deposited between the thin film (23) and the first negative electrode active material layer (22) becomes flatter, and the cycle characteristics of the all-solid-state secondary battery (1) can be further improved.

[0231] The thickness of the thin film (23) is, for example, 1 nm to 800 nm, 10 nm to 700 nm, 50 nm to 600 nm, or 100 nm to 500 nm. If the thickness of the thin film (23) is less than 1 nm, it may be difficult for the function of the thin film (23) to be exerted. If the thickness of the thin film (23) is excessively thick, the thin film (23) itself absorbs lithium, which reduces the amount of lithium precipitated from the negative electrode, thereby lowering the energy density of the solid-state battery and deteriorating the cycle characteristics of the all-solid-state secondary battery (1). The thin film (23) may be disposed on the negative electrode current collector (21) by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like, but is not necessarily limited to these methods, and any method capable of forming the thin film (23) in the relevant technical field may be used.

[0232] Although not shown in the drawing, the negative electrode current collector (21) may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The polymer may be an insulating polymer. Since the base film includes an insulating thermoplastic polymer, when a short circuit occurs, the base film may soften or liquefy, thereby blocking battery operation and suppressing a rapid increase in current. The metal layer may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or an alloy thereof. The negative electrode current collector (21) may additionally include a metal piece and / or a lead tab. For more specific details regarding the base film, metal layer, metal chip, and lead tab of the negative electrode collector (21), refer to the positive electrode collector (11) described above. By having this structure, the negative electrode collector (21) can reduce the weight of the negative electrode, and consequently, improve the energy density of the negative electrode and the all-solid-state secondary battery.

[0233] [Electrolyte layer]

[0234] [Electrolyte layer: electrolyte]

[0235] Referring to FIGS. 1 to 6, the electrolyte layer (30) includes 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.

[0236] The solid electrolyte may include, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof.

[0237] The solid electrolyte is, for example, a sulfide-based solid electrolyte. The sulfide-based solid electrolyte is, for example, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li 7-x PS 6-x Cl x , 0 <x<2, Li 7-x PS 6-x Br x , 0 <x<2, 및 Li 7-x PS 6-x I x, 0 <x<2 중에서 선택된 하나 이상이다. 황화물계 고체전해질은 예를 들어 Li2S, P2S5등의 출발 원료를 용융 급냉법이나 기계적 밀링(mechanical milling) 법 등에 의해 처리하여 제작된다. 또한, 이러한 처리 후, 열처리를 수행할 수 있다. 고체전해질은 비정질이거나, 결정질이거나, 이들이 혼합된 상태일 수 있다. 또한, 고체전해질은 예를 들어 상술한 황화물계 고체 전해질 재료 중 적어도 구성 원소로서 황(S), 인(P) 및 리튬(Li)을 포함하는 것일 수 있다. 예를 들어, 고체전해질은 Li2S-P2S5을 포함하는 재료일 수 있다. 고체전해질을 형성하는 황화물계 고체 전해질 재료로 Li2S-P2S5를 포함하는 것을 이용하는 경우, Li2S와 P2S5의 혼합 몰비는, 예를 들어, Li2S : P2S5= 20 : 80 내지 90 : 10, 25 : 75 내지 90 : 10, 30 : 70 내지 70: 30, 40: 60 내지 60: 40 정도의 범위이다.

[0238] The sulfide-based solid electrolyte may include, for example, an argyrodite type solid electrolyte represented by the following chemical formula 1:

[0239] <Chemical Formula 1>

[0240] Li + 12-n-x A n+ X 2- 6-x Y - x

[0241] In the above formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta, X is S, Se or Te, Y is Cl, Br, I, F, CN, OCN, SCN or N3, and 1≤n≤5, 0≤x≤2. The sulfide-based solid electrolyte is, for example, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-xPS 6-x Br x , 0 <x<2 , 및 Li 7-x PS 6-x I x , 0 <x<2 중에서 선택된 하나 이상을 포함하는 아르지로다이트-타입(Argyrodite-type)의 화합물일 수 있다. 황화물계 고체전해질은 예를 들어 Li6PS5Cl, Li6PS5Br 및 Li6PS5I 중에서 선택된 하나 이상을 포함하는 아르지로다이트-타입(Argyrodite-type) 화합물일 수 있다.

[0242] The density of the argyrodite-type solid electrolyte may be 1.5 to 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 is reduced, and penetration of the electrolyte layer by Li can be effectively suppressed.

[0243] Oxide solid electrolytes include, for example, Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x<2, 0<y<1, 0<z<3), Li1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1 0≤y≤1), Li x La y TiO3(0 <x<2, 0<y<3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2, Li 3+x La3M2O 12 (M = Te, Nb, or Zr, 0≤x≤10), or a combination thereof. The oxide-based solid electrolyte is manufactured, for example, by a sintering method.

[0244] Oxide-based solid electrolytes include, for example, Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a M a O 12 (M doped LLZO, M=Ga, W, Nb, Ta, or Al, 0 <a<2, 0≤x≤10) 중에서 선택된 가넷계(Garnet-type) 고체전해질이다.

[0245] The polymer solid electrolyte may, for example, comprise a mixture of a lithium salt and a polymer, or a polymer having ion-conducting functional groups. The polymer solid electrolyte may, for example, be a polymer electrolyte that is solid at 25°C and 1 atm. The polymer solid electrolyte may, for example, not comprise a liquid.The polymer solid electrolyte comprises a polymer, and the polymer is, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene (PVDF-HFP), poly(styrene-b-ethylene oxide) block copolymer (PS-PEO), poly(styrene-butadiene), poly(styrene-isoprene-styrene), poly(styrene-b-divinylbenzene) block copolymer, poly(styrene-ethylene oxide-styrene) block copolymer, polystyrene sulfonate (PSS), polyvinyl fluoride (PVF), polymethyl methacrylate (PMMA, poly(methylmethacrylate), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polyethylenedioxythiophene (PEDOT), polypyrrole (PPY), polyacrylonitrile (PAN), polyaniline, Polyacetylene, Nafion, Aquivion, Flemion, Gore, Aciplex, Morgane ADP, sulfonated poly(ether ether ketone) (SPEEK), sulfonated poly(arylene ether ketone ketone sulfone) (SPAEKKS), sulfonated poly(aryl ether ketone) (SPAEK), poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI), poly(styrene sulfonate) (PSS), lithium 9,10-Diphenylanthracene-2-sulfonate (lithium 9,10-diphenylanthracene-2-sulfonate, DPASLi. +) or a combination thereof, but is not limited thereto, and any lithium salt that can be used in polymer electrolytes in the relevant technical field is possible. The lithium salt can be any lithium salt that can be used in the relevant technical field. The lithium salt is, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, Li(FSO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are each 1 to 20), LiCl, LiI or a mixture thereof, etc. The polymer included in the polymer solid electrolyte may be, for example, a compound including 10 or more, 20 or more, 50 or more, or 100 or more repeating units. The weight average molecular weight of the polymer included in the polymer solid electrolyte may be, for example, 1000 Dalton or more, 10,000 Dalton or more, 100,000 Dalton or more, or 1,000,000 Dalton or more.

[0246] A gel electrolyte is, for example, a polymer gel electrolyte. A gel electrolyte can have a gel state without containing a polymer, for example.

[0247] A polymer gel electrolyte may include, for example, a liquid electrolyte and a polymer, or an organic solvent and a polymer having an ion-conducting functional group. The polymer gel electrolyte may be, for example, a polymer electrolyte that is in a gel state at 25°C and 1 atm. The polymer gel electrolyte may, for example, have a gel state without containing a liquid. The liquid electrolyte used in the polymer gel electrolyte may be, for example, an ionic liquid, a mixture of a lithium salt and an organic solvent; a mixture of a lithium salt and an organic solvent; a mixture of an ionic liquid and an organic solvent; or a mixture of a lithium salt, an ionic liquid, and an organic solvent. The polymer used in the polymer gel electrolyte may be selected from among the polymers used in solid polymer electrolytes. The organic solvent may be selected from among the organic solvents used in liquid electrolytes. The lithium salt may be selected from among the lithium salts used in solid polymer electrolytes. An ionic liquid refers to a salt that has a melting point below room temperature, is composed solely of ions, and is liquid at room temperature or a molten salt at room temperature. The ionic liquid may include, for example, one or more cations selected from among a) ammonium compounds, pyrrolidinium compounds, pyridinium compounds, pyrimidinium compounds, imidazolium compounds, piperidinium compounds, pyrazolium compounds, oxazolium compounds, pyridazinium compounds, phosphonium compounds, sulfonium compounds, triazolium compounds, and mixtures thereof, and b) one or more anions selected from among BF4-, PF6-, AsF6-, SbF6-, AlCl4-, HSO4-, ClO4-, CH3SO3-, CF3CO2-, Cl-, Br-, I-, SO4-, CF3SO3-, (FSO2)2N-, (C2F5SO2)2N-, (C2F5SO2)(CF3SO2)N-, and (CF3SO2)2N-. A polymer solid electrolyte can form a polymer gel electrolyte, for example, by being impregnated into a liquid electrolyte in a secondary battery. The polymer gel electrolyte may further include inorganic particles. The polymer included in the polymer gel electrolyte may be, for example, a compound containing 10 or more, 20 or more, 50 or more, or 100 or more repeating units.The weight average molecular weight of the polymer included in the polymer gel electrolyte may be, for example, 500 Dalton or more, 1000 Dalton or more, 10,000 Dalton or more, 100,000 Dalton or more, or 1,000,000 Dalton or more.

[0248] [Electrolyte layer: binder]

[0249] The electrolyte layer (30) may include, for example, a binder. The binder included in the electrolyte layer (30) is not limited to, but may include, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., and any binder used in the relevant technical field may be used. The binder of the electrolyte layer (30) may be the same as or different from the binder included in the positive electrode active material layer (12) and the negative electrode active material layer (22). The binder may be omitted.

[0250] The content of the binder included in the electrolyte layer (30) is 0.1 to 10 wt%, 0.1 to 8 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 0.1 to 2 wt%, 0.1 to 1 wt%, 0.1 to 0.5 wt%, or 0.1 to 0.3 wt% based on the total weight of the electrolyte layer (30).

[0251] According to another embodiment, the content of the binder included in the electrolyte layer (30) is 0.5 wt% or less, or 0.1 wt% or less.

[0252] Referring to Fig. 7, the negative electrode layer (20) includes a negative electrode current collector (21) and a lithium host layer (22) disposed on one side of the negative electrode current collector (21). A first inactive member (42) is disposed on one side of the negative electrode layer (20).

[0253] The first inert member (42) is disposed on one side of the lithium host layer (22) and between the solid electrolyte layer (40) and the negative electrode current collector (21) facing the solid electrolyte layer (30). The first inert member (42) is not disposed on one side of the negative electrode current collector (21). The first inert member (42) is disposed on one side of the lithium host layer (22) and the negative electrode current collector (21). By including the first inert member (42), a short circuit between the lithium metal deposited on the lithium host layer (22) and the positive electrode layer (10) during charge and discharge of the all-solid-state secondary battery (1) is more effectively prevented, and as a result, the cycle characteristics of the all-solid-state secondary battery (2) are improved. By including the first inert member (42), cracking of the solid electrolyte layer (30) is prevented during the manufacture and / or charging and discharging of the all-solid-state secondary battery (1), and as a result, the cycle characteristics of the all-solid-state secondary battery (1) are improved. In the all-solid-state secondary battery (1) that does not include the first inert member (42), when the manufacture and / or charging and discharging of the all-solid-state secondary battery (1) is performed, uneven pressure is applied to the solid electrolyte layer (30) in contact with the negative electrode layer (20), which causes cracking of the solid electrolyte layer (30), and the possibility of a short circuit occurring due to the growth of lithium metal through the cracking increases.

[0254] Referring to FIGS. 3 to 6, in the all-solid-state secondary battery (1), the thickness (T2) of the first inactive member (42) is substantially the same as the thickness (T1) of the lithium host layer (22). Since the sum of the thickness (T2) of the first inactive member (42) and the thickness (T4) of the negative electrode current collector (21) is substantially the same as the thickness (T3) of the negative electrode layer (20), a uniform pressure is applied between the negative electrode layer (20) and the solid electrolyte layer (30), and the negative electrode layer (20) and the solid electrolyte layer (30) are sufficiently adhered to each other, thereby reducing the interfacial resistance between the negative electrode layer (20) and the solid electrolyte layer (30). In addition, since the solid electrolyte layer (30) is sufficiently sintered during the pressurized manufacturing process of the all-solid-state secondary battery (1), the internal resistance of the solid electrolyte layer (30) and the all-solid-state secondary battery (1) including the same is reduced.

[0255] The manufacturing method of an all-solid-state secondary battery according to an embodiment is as follows.

[0256] An all-solid-state secondary battery according to an embodiment is manufactured by comprising: a step of first milling a composition including M2S and an alkali metal salt; a step of second milling a composition obtained by adding an inorganic electron-conductive structure and a fibrous carbon-based material or a two-dimensional carbon-based structure having an aspect ratio of 2 or more to the product obtained by the first milling, thereby obtaining a composite; a step of manufacturing a positive electrode using a composition obtained by adding and mixing a binder into the composite; a step of preparing an anode; and a step of arranging an electrolyte between the positive electrode and the negative electrode.

[0257] A solid electrolyte may be added to the above composition.

[0258] The above solid electrolyte is a sulfide-based solid electrolyte. The size of the sulfide-based solid electrolyte is 0.1 nm to 10 um, for example, 100 nm to 3 um.

[0259] The above sulfide-based solid electrolyte is Li2S-P2S5, Li2S-P2S5-LiX, X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Brx , 0<x≤2, and Li 7-x PS 6-x I x , 0<x≤2, and at least one selected from the group consisting of: the sulfide-based solid electrolyte comprises an argyrodite-type solid electrolyte; and the argyrodite-type solid electrolyte comprises at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0260] The density of the above argyrodite-type solid electrolyte is 1.5 to 2.0 g / cc.

[0261] In the first milling and second milling above, the first milling process is performed at 100 to 1000 rpm, or 300 to 800 rpm, for 1 to 20 hours, or 5 to 10 hours, for example, for about 10 hours, so that the size of M2S becomes 100 nm or less.

[0262] During the first milling, the rpm and milling time are adjusted so that the size of M2S is less than 100 nm.

[0263] The secondary milling rpm and secondary milling time are adjusted to be smaller than those of the primary milling. The secondary milling time is performed for, for example, 1 to 7 hours or 2 to 5 hours.

[0264] In the step of obtaining the above complex, a carbon-based material may be further added to the composition. The carbon-based material may be carbon nanofibers, etc.

[0265] The present invention is explained in more detail through the following examples and comparative examples. However, the examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0266] (Manufacturing of composite cathode active materials)

[0267] In the following examples and comparative examples, % means weight %, and % of SE represents the content of the solid electrolyte when manufacturing the positive electrode mixture described below.

[0268] Example 1: 30% Li2S-20% LiI-3.25% CNF + 3.25% MoS2+ 42.5% SE

[0269] (Stage 1)

[0270] Li2S and LiI were mixed at a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 600 rpm, and 10 h in an inert atmosphere.

[0271] (Stage 2)

[0272] The Li2S-LiI composite was mixed with MoS2 and carbon nanofibers (CNF) at a weight ratio of 50:3.25:3.25. The mixture was mechanically milled using a ball mill. The milling conditions were an inert atmosphere, 25°C, and 60 rpm for 5 h. The Li2S-LiI-MoS2-CNF composite was used as a composite cathode active material.

[0273] The above MoS2 has a plate-like shape, and the plate-like MoS2 has a length (X direction) of about 30 um, a thickness (Z direction) of 5 um, and a width (Y direction) of about 15 um. The Mohs hardness of Li2S is 0.6, and the Mohs hardness of LiI is 2.0. In addition, 42.5% SE represents the content of the solid electrolyte in the positive electrode mixture described below. The same applies to the following examples and comparative examples.

[0274] Example 2: 30% Li2S- 20% LiI- 6.75% CNF + 0.75% MoS2+ 42.5% SE

[0275] In the second step, a Li2S-LiI-MoS2-CNF composite was manufactured in the same manner as in Example 1, except that the mixing weight ratio of the Li2S-LiI composite, MoS2, and carbon nanofiber (CNF) was changed to 50:0.75:6.75.

[0276] Example 3: 30% Li2S- 20% LiI- 0.75% CNF + 6.75% MoS2+ 42.5% SE

[0277] In the second step, a Li2S-LiI-MoS2-CNF composite was manufactured in the same manner as in Example 1, except that the mixing weight ratio of the Li2S-LiI composite, MoS2, and carbon nanofiber (CNF) was changed to 50:6.75:0.75.

[0278] Example 4: 30% Li2S- 20% LiI- 0.375% MoS2 supported CNF 7.5%+ 42.5% SE

[0279] (Stage 1)

[0280] Li2S and LiI were mixed at a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 600 rpm, and 10 h.

[0281] (Stage 2)

[0282] Li2S-LiI composite and MoS2-supported CNF were mixed at a weight ratio of 50:7.5. The MoS2 content in the MoS2-supported CNF was 0.375%.

[0283] MoS2-supported CNFs were prepared according to the method disclosed in Electrochimica Acta 254 (2017) 172-180 or Applied Surface Science 564 (2021) 150387. In the MoS2-supported CNFs, a chemical bond was formed between Mo of MoS2 and carbon of CNF.

[0284] The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI-TiO2 composite. The milling conditions were 25°C, 600 rpm for 5 h. The Li2S-LiI-MoS2-supported CNF composite was used as a composite cathode active material.

[0285] Example 5: 30% Li2S- 20% LiI- 3.25% graphene + 3.25% MoS2+ 42.5% SE

[0286] A composite was manufactured in the same manner as in Example 1, except that graphene was used instead of CNF.

[0287] As for graphene, the above graphene has a thickness of 20 nm and a specific surface area of ​​19 m 2 / g, Adeka graphene with a diameter of ~5um was purchased and used.

[0288] Comparative Example 1: Li2S-LiI-CNF, 510 rpm, 10 hr, 2 stages, 20G (KR 2017-0068448 (Tatsumi Sago)

[0289] (Stage 1)

[0290] A first mixture was prepared by mixing Li2S and LiI in a weight ratio of 30:20. The first mixture was mechanically milled using a ball mill to prepare a Li2S-LiI complex.

[0291] Milling conditions were 25 ℃, 510 rpm for 10 h. The milling energy applied to the sample during milling was 20 G.

[0292] (Stage 2)

[0293] A second mixture was prepared by mixing the Li2S-LiI complex and carbon nanofibers (CNF) at a weight ratio of 50:10. The second mixture was mechanically milled using a ball mill to produce a Li2S-LiI-CNF complex.

[0294] The milling conditions were 25°C, 510 rpm for 10 h. The milling energy applied to the sample during milling was 20 G. The Li2S-LiI-CNF composite was used as the composite cathode active material.

[0295] Reference Example 1: 30% Li2S - 20% LiI - 7.5% CNT + 42.5% SE

[0296] (Stage 1)

[0297] Li2S and LiI were mixed at a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 600 rpm, and 10 h in an inert atmosphere.

[0298] (Stage 2)

[0299] The Li2S-LiI composite and CNT were mixed at a weight ratio of 50:7.5. The mixture was mechanically milled using a ball mill. The milling conditions were an inert atmosphere, 25°C, and 60 rpm for 5 h. The Li2S-LiI-CNT composite was used as a composite cathode active material.

[0300] Comparative Example 2: 30% Li2S- 20% LiI+ (3.25% CNF+ 3.25% MoS2) simple mixture + 42.5% SE

[0301] A first mixture was prepared by mixing Li2S and LiI in a weight ratio of 30:20. The first mixture was mechanically milled using a ball mill to prepare a Li2S-LiI complex.

[0302] Milling conditions were 25 ℃, 600 rpm for 10 hours. The milling energy applied to the sample during milling was 20 G.

[0303] 3.25% CNF and 3.25% MoS2 were simply mixed in a mortar and pestle to the above Li2S-LiI composite.

[0304] Comparative Example 3: 30% Li2S- 20% LiI- 7.5% CNF + 42.5% SE

[0305] (Stage 1)

[0306] A first mixture was prepared by mixing Li2S and LiI in a weight ratio of 30:20. The first mixture was mechanically milled using a ball mill to prepare a Li2S-LiI complex.

[0307] Milling conditions were 25 ℃, 600 rpm for 10 hours. The milling energy applied to the sample during milling was 20 G.

[0308] (Stage 2)

[0309] A second mixture was prepared by mixing the Li2S-LiI complex and carbon nanofibers (CNF) at a weight ratio of 50:10. The second mixture was mechanically milled using a ball mill to produce a Li2S-LiI-CNF complex.

[0310] The milling conditions were 25°C, 600 rpm for 10 h. The milling energy applied to the sample during milling was 20 G. The Li2S-LiI-CNF composite was used as the composite cathode active material.

[0311] Comparative Example 4: Simple blend of 30% Li2S, 20% LiI, 3.25% CNF, 3.25% MoS2 + 43.5% SE

[0312] 30% Li2S, 20% LiI, 3.25% CNF, 3.25% MoS2 were simply mixed in a mortar and pestle.

[0313] (Manufacturing of positive and all-solid-state secondary batteries)

[0314] Example 6

[0315] (Polar electrode manufacturing)

[0316] The composite manufactured in Example 1 was prepared as a cathode active material. Li6PS5Cl (D50=3.0 μm, crystalline), which is an argyrodite-type crystal, was prepared as a solid electrolyte. PTFE was prepared as a binder. These materials were mixed in a weight ratio of composite cathode active material: solid electrolyte: binder = 58.7:42.5:1.2 to prepare a cathode mixture. The cathode mixture was obtained by dry mixing using a ball mill.

[0317] The positive electrode mixture was placed on one side of a positive electrode current collector made of aluminum foil coated on one side and plate pressed at a pressure of 200 MPa for 10 minutes to produce a positive electrode in the form of a sheet. The thickness of the positive electrode was approximately 120 μm and the loading level of the positive electrode mixture was approximately 8 mg / cm2. The thickness of the positive electrode active material layer was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm. The areas of the positive electrode active material layer and the positive electrode current collector were identical.

[0318] (Cathode manufacturing)

[0319] A 10 ㎛ thick SUS foil was prepared as a negative electrode current collector. Carbon black (CB) with a primary particle diameter of approximately 30 nm and silver (Ag) particles with an average particle diameter of approximately 60 nm were prepared as negative electrode active materials.

[0320] A mixed powder of 4 g of carbon black (CB) and silver (Ag) particles in a weight ratio of 3:1 was placed in a container, and 4 g of NMP (N-methylpyrrolidone) solution containing 7 wt% of PVDF binder (Kureha #9300) was added thereto to prepare a mixed solution. A slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution. The prepared slurry was applied to a SUS sheet using a bar coater, dried in air at 80°C for 10 minutes, and then vacuum-dried at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold roll pressed to flatten the surface, thereby preparing a negative electrode having a first negative electrode active material layer / negative electrode current collector structure. The thickness of the first negative electrode active material layer was approximately 15 μm. The areas of the first negative electrode active material layer and the negative electrode current collector were the same.

[0321] (Manufacturing of solid electrolyte layer)

[0322] Li6PS5Cl solid electrolyte in the form of argyrodite crystals (D 50 =3.0 um, crystalline), a mixture was prepared by adding 1.5 parts by weight of an acrylic binder to 98.5 parts by weight of the solid electrolyte. Octyl acetate was added to the prepared mixture and stirred to prepare a slurry. The prepared slurry was applied using a bar coater onto a 15 ㎛ thick nonwoven fabric placed on a 75 ㎛ thick PET substrate, and dried in air at 80 ℃ for 10 minutes to prepare a laminate. The prepared laminate was vacuum-dried at 80 ℃ for 2 hours to prepare a solid electrolyte layer.

[0323] (inert absence)

[0324] A flame-retardant inert member was manufactured by forming a slurry containing pulp fiber (cellulose fiber), glass fiber, aluminum hydroxide (Al(OH)3), an acrylic binder, and a solvent into a gasket shape and then removing the solvent.

[0325] The weight ratio of pulp fiber (cellulose fiber), glass fiber, aluminum hydroxide (Al(OH)3), and acrylic binder was 20:8:70:2. The thickness of the inert material was 120 ㎛.

[0326] Before placing the manufactured flame-retardant inert material on the solid electrolyte layer, moisture, etc. of the flame-retardant inert material was removed by vacuum heat treatment at 80°C for 5 hours.

[0327] (Manufacturing of all-solid-state secondary batteries)

[0328] Referring to Fig. 5, a solid electrolyte layer was placed on the negative electrode such that the first negative electrode active material layer was in contact with the solid electrolyte layer, and a positive electrode was placed on the solid electrolyte layer. A laminate was prepared by placing a gasket surrounding the positive electrode and in contact with the solid electrolyte layer. The thickness of the gasket was approximately 120 μm. The above-described flame-retardant inert material was used as the gasket. The gasket was placed so as to be in contact with the side surface of the positive electrode and the solid electrolyte layer. The positive electrode was placed at the center of the solid electrolyte layer, and the gasket was placed so as to surround the positive electrode and extend to the end of the solid electrolyte layer. The area of ​​the positive electrode was approximately 90% of the area of ​​the solid electrolyte layer, and the gasket was placed over the entire remaining 10% of the area of ​​the solid electrolyte layer where the positive electrode was not placed.

[0329] 85 prepared laminates oThe solid electrolyte layer was plate-pressed at 500 MPa for 30 min at C. This pressurization process sintered the solid electrolyte layer, thereby improving battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 ㎛. The density of the Li6PS5Cl solid electrolyte, which was an argyrodite-type crystal contained in the sintered solid electrolyte layer, was 1.6 g / cc. The area of ​​the solid electrolyte layer was the same as that of the negative electrode.

[0330] The pressurized laminate was placed in a pouch and vacuum-sealed to manufacture an all-solid-state secondary battery. Portions of the positive and negative current collectors were extended outside the sealed battery to serve as positive and negative terminals.

[0331] Examples 7 to 10

[0332] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Example 6, except that the composite positive electrode active material manufactured in Examples 2 to 5 was used instead of the composite positive electrode active material of Example 1.

[0333] Examples 11 to 15 (loading level of positive electrode composite is about 24 mg / cm2)

[0334] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Examples 6 to 10, except that the loading level of the positive electrode mixture was changed to approximately 24 mg / cm2 during the manufacture of the positive electrode.

[0335] Comparative Example 5: 30% Li2S - 20% LiI - 7.5% CNF + 42.5% SE (loading level of positive electrode composite is approximately 8 mg / cm2)

[0336] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Example 6, except that the composite positive electrode active material of Comparative Example 1 was used.

[0337] Comparative Example 6: 30% Li2S - 20% LiI - 7.5% CNF + 42.5% SE (loading level of the cathode composite is approximately 24 mg / cm2)

[0338] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Comparative Example 5, except that the loading level of the positive electrode mixture was changed to approximately 24 mg / cm2 during the manufacture of the positive electrode.

[0339] Comparative Example 7: Simple blend (loading level of positive electrode material is about 8 mg / cm2)

[0340] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Example 6, except that the composite positive electrode active material of Comparative Example 2 was used.

[0341] Comparative Example 8: Simple blend (loading level of positive electrode material is approximately 24 mg / cm2)

[0342] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Comparative Example 7, except that the loading level of the positive electrode mixture was changed to approximately 24 mg / cm2 during the manufacture of the positive electrode.

[0343] Reference Example 2: 30% Li2S - 20% LiI - 7.5% CNT + 42.5% SE (loading level of the cathode composite is approximately 8 mg / cm2)

[0344] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Example 6, except that the composite positive electrode active material of Reference Example 1 was used.

[0345] Reference Example 3: 30% Li2S - 20% LiI - 7.5% CNT + 42.5% SE (loading level of the cathode composite is approximately 24 mg / cm2)

[0346] A positive electrode and an all-solid-state secondary battery were manufactured in the same manner as in Reference Example 2, except that the loading level of the positive electrode mixture was changed to approximately 24 mg / cm2 during the manufacture of the positive electrode.

[0347] Evaluation Example 1: XRD Analysis and Scanning Electron Microscopy Analysis

[0348] XRD spectra were measured using Cu Kα radiation for the composite cathode active materials (i.e., composites) manufactured in Examples 1-5, Comparative Examples 1-4, and Reference Example 1. The Li2S crystallite sizes calculated from the first peak for the (111) crystal plane appearing at a diffraction angle of 2θ = 27° ± 2.0° in the measured XRD spectra are shown in Table 2 below. The crystallite sizes were calculated using the Sherrer Equation.

[0349] The Li2S particle size (D50 particle size) of the composite cathode active materials manufactured in Example 1-5, Comparative Example 1-2, and Reference Example 1 was measured using a laser particle size analyzer (PSA) and a scanning electron microscope. The Li2S particle size of the composite cathode active material is the arithmetic mean of the particle sizes of multiple Li2S particles measured using software from scanning electron microscope images. The measurement results are shown in Table 1 below.

[0350] Classification 1st stage milling 2nd stage milling Solid solution formation Li2S crystallite size [nm] Li2S particle size [㎛] Example 1 (30% Li2S-20% LiI- (3.25% CNF + 3.25% MoS2) + 42.5% SE) 600 rpm, 28 G, 10 hr 600 rpm, 28 G, 5 hr ○ Less than 9.81 Example 2 (30% Li2S-20% LiI- (6.75% CNF + 0.75% MoS2) + 42.5% SE 600 rpm, 28 G, 10 hr 600 rpm, 28 G, 5 hr ○ Less than 9.91 Example 3 (30% Li2S-20% LiI- (0.75% CNF + 6.75% MoS2) + 42.5% SE) 600 rpm, 28 G, 10 hr 600 rpm, 28 G, 5 hr ○9.81 Less than Example 4 (30% Li2S-20% LiI- (0.375% MoS2 supported CNF 7.5%) + 42.5% SE) 600 rpm, 28 G, 10 hr 600 rpm, 28 G, 5 hr ○9.91 Less than Example 5 (30% Li2S-20% LiI- (3.25% graphene + 3.25% MoS2) + 42.5% SE) 600 rpm, 28 G, 10 hr 600 rpm, 28 G, 5 hr ○9.91 Less than Comparative Example 1 (tatsumisago) (30% Li2S-20% LiI-10% CNF) 600 rpm, 28 G, 10 hr600 rpm, 28 G, 10 hr○9.81 Less than Comparative Example 2 (30% Li2S-20% LiI+(3.25% CNF+ 3.25% MoS2) simple mixture+42.5% SE)600 rpm, 28 G, 10 hr-○172 Comparative Example 3 (30% Li2S- 20% LiI- 7.5% CNF + 42.5% SE)600 rpm, 28 G, 10 hr600 rpm, 28 G, 10 hr○9.81 Less than Comparative Example 4 (30% Li2S+ 20% LiI+ (3.25% CNF+ 3.25% MoS2) simple mixture+42.5% SE)--X648 Reference Example 1 (30% Li2S- 20% LiI-(3.25% CNT+ 3.25% MoS2))600 rpm,28 G, 10 hr600 rpm,28 G, 5 hr○Less than 10.11.

[0351] In Table 1, SE represents the solid electrolyte used in the positive electrode mixture described below.

[0352] As shown in Table 1, the composites of Examples 1 to 5 included a Li2S-LiI solid solution, the size of the Li2S crystallites was less than 9.9 nm, and the Li2S particle size of the composites was 2 μm or less.

[0353] In contrast, as shown in Table 1, the simple mixture of Li2S, LiI, CNF, and MoS of Comparative Example 4 did not form a solid solution.

[0354] Evaluation Example 2: XRD Analysis

[0355] XRD spectra were measured using Cu Kα radiation for the complex of Example 1 and the simple mixture of Li2S, LiI, MoS2, and CNF of Comparative Example 4.

[0356] The complex of Example 1 moved at a low angle relative to the position compared to the mixture of Comparative Example 4.

[0357] The complex of Example 1 showed a pattern in which the 2θ=27°±2.0° peak shifted slightly to the left, indicating that a Li2S-LiI solid solution was formed, and the 2θ=27°±2.0° peak corresponds to the MoS2 crystal plane (111). In addition, the intensity of the MoS2 peak at 2θ=14.5±0.5°, i.e., 14.1°, was greatly reduced.

[0358] In contrast, in the case of Comparative Example 4, since a solid solution was not formed, the 2θ=27° peak remained as it was without shifting, and the MoS2 peak at 2θ=14.1° was observed without a decrease in intensity. In addition, in the case of Comparative Example 4, it was confirmed that there was no shift of the 2θ=27° ± 2.0° peak (no solid solution formed) or that the intensity of the 2θ=14.5±0.5° MoS2 peak, i.e., 14.1°, was not decreased.

[0359] As a result of the evaluation, it was found that the complex of Example 1 formed a solid solution, and compared to the simple mixture of Comparative Example 4, it was confirmed that there was a chemical bond between each component constituting the complex.

[0360] Evaluation Example 3: Charge / Discharge Test

[0361] The charge / discharge characteristics of the all-solid-state secondary batteries of Examples 6 to 15, Comparative Examples 5 to 7, and Reference Example 2 to 3, which employed the composite positive electrode active materials manufactured in Examples 1 to 5, Comparative Examples 1-2, and Reference Example 1, were evaluated by the following charge / discharge test.

[0362] Charge and discharge tests were performed by placing the solid secondary battery in a constant temperature bath at 45°C.

[0363] The first cycle involved charging for 12.5 hours at a constant current of 0.1 C until the battery voltage reached 2.5 V to 2.8 V. Subsequently, discharging was performed for 12.5 hours at a constant current of 0.1 C until the battery voltage reached 0.3 V.

[0364] The discharge capacity of the first cycle was taken as the standard capacity. The standard capacity is expressed as the specific capacity of Li2S in Table 1 below.

[0365] After the second cycle, charging and discharging were performed up to 150 cycles under the same conditions as the first cycle. The measurement results are shown in Tables 2 and 3 below. Table 2 below shows the results for a loading level of 8 mg / cm2, and Table 3 below shows the results for a loading level of 24 mg / cm2.

[0366] The initial efficiency is expressed by Equation 1 below.

[0367] <Formula 1>

[0368] Initial efficiency [%] = [1st cycle discharge capacity / 1st cycle charge capacity] × 100

[0369] The cycle count is the number of cycles required for the discharge capacity to decrease to 80% of the standard capacity after the second cycle. A higher cycle count is considered to indicate better life characteristics.

[0370] ClassificationCathode Active MaterialLoading LevelSpecific Capacity [mAh / g]Electrode Density (g / cm3)Electrode Capacity (mAh / g)Initial Efficiency [%]Lifespan (SOH80@)Example 6Example 1 (30% Li2S-20% LiI- 3.75% CNF + 3.75 % MoS2 + 42.5% SE) 8mg / cm2 1060 1.65 3188 3400Example 7Example 2 (30% Li2S-20% LiI- 6.75% CNF + 0.75 % MoS2 + 42.5% SE) 8mg / cm2 820 1.55 246 70 130Example 8Example 3 (30% Li2S-20% LiI- 0.75% CNF + 6.75 % MoS2 + 42.5% SE) SE)8mg / cm211001.733087630Example 9Example 4(30% Li2S-20% LiI- 0.375% MoS2 supported CNF 7.5%+ 42.5% SE)8mg / cm28101.624369110Example 10Example 5(30% Li2S-20% LiI- 3.75% graphene + 3.75% MoS2 + 42.5% SE)8mg / cm28701.6226175200Comparative Example 5Comparative Example 1 (Tatsumisago)30% Li2S-20% LiI-10% CNF + 42.5% SE8mg / cm28001.52408180Comparative Example 7Comparative Example 2(30% Li2S-20% LiI- 7.5% CNF + 42.5% SE) 8mg / cm2 700 1.482 106 510 Reference Example 2 Reference Example 1 (30% Li2S- 20% LiI - 7.5% CNT + 42.5% SE) 8mg / cm2 780 1.532 34575

[0371] As shown in Table 2, the all-solid-state secondary batteries of Examples 6 to 10 showed improved discharge capacity, initial efficiency, lifespan, and rate characteristics compared to the all-solid-state secondary batteries of Comparative Examples 5, 7, and Reference Example 2, which employed the composite positive electrode active materials of Comparative Examples 1, 2, and Reference Example 1.

[0372] ClassificationCathode Active MaterialLoading LevelSpecific Capacity [mAh / g]Electrode Density (g / cm3)Electrode Capacity (mAh / g)Initial Efficiency [%]Lifespan (SOH80@)Example 11Example 1 (30% Li2S- 20% LiI - 3.75% CNF + 3.75 % MoS2 + 42.5% SE)Thick Film)24mg / cm210101.6530383400Example 12Example 2 (30% Li2S- 20% LiI - 6.75% CNF + 0.75 % MoS2 + 42.5% SE)Thick Film)24mg / cm28001.552407190Example 13Example 3 (30% Li2S- 20% LiI - 0.75% CNF + 6.75 % MoS2 MoS2 + 42.5% SE) Thick film) 24mg / cm2 1050 1.731586580 Example 14 Example 4 (30% Li2S - 20% LiI - 5% MoS2 supported CNF 7.5% + 42.5% SE) Thick film) 24mg / cm2 790 1.62376780 Example 15 Example 5 (30% Li2S - 20% LiI - 3.75% graphene + 3.75% MoS2 + 42.5% SE) Thick film) 24mg / cm2 780 1.6223472150 Comparative Example 6 Comparative Example 1 (Tatsumisago) (30% Li2S - 20% LiI - 10% CNF + 42.5% SE) Thick film) 24mg / cm2 7501.52257965Comparative Example 8Comparative Example 2 (30% Li2S- 20% LiI - 7.5% CNF + 42.5% SE) Thick Film) 24mg / cm2 6501.48195648Reference Example 3Reference Example 1 (30% Li2S- 20% LiI - 7.5% CNT + 42.5% SE) Thick Film) 24mg / cm2 7401.53222522

[0373] As shown in Table 3, the all-solid-state secondary batteries of Examples 11 to 15 having a thick-film state positive electrode active material showed improved discharge capacity, initial efficiency, lifespan, and rate characteristics compared to the all-solid-state secondary batteries of Comparative Examples 6, 8, and Reference Example 3.

[0374] Evaluation Example 4: High-Rate Characteristic Evaluation

[0375] The high-rate characteristics of the all-solid-state secondary batteries of Examples 6 to 15, Comparative Examples 6-8, and Reference Example 2, which employed the composite positive electrode active materials manufactured in Examples 1 to 5, Comparative Examples 1-2, and Reference Example 1, were evaluated by the following charge-discharge test. The charge-discharge test was performed by placing the all-solid-state secondary batteries in a constant-temperature bath at 45°C.

[0376] Each solid-state secondary battery was charged at 45°C with a constant current of 0.1C until the battery voltage reached 4.2 V and a constant voltage of 4.2 V until the current value reached 0.1 C. Subsequently, the battery was discharged at a constant current of 0.1 C until the battery voltage reached 2.5 V.

[0377] Next, the battery was charged at a constant current of 0.1C until the battery voltage reached 4.2 V and a constant voltage of 4.2 V until the current value reached 0.1 C, and then discharged at a constant current of 0.33 C until the battery voltage reached 2.5 V.

[0378] The high-rate characteristics were evaluated according to Equation 3 before and after the above charging and discharging, and are shown in Table 4 below.

[0379] <Formula 3>

[0380] High rate characteristic (%) = (discharge capacity at 0.33C / discharge capacity at 0.1C) Х 100

[0381] Classification Cathode Active Material Loading Level High Rate Characteristics (0.33C / 0.1C) [%] [mAh / g] Example 6 Example 1 (30% Li2S - 20% LiI - 3.75% CNF + 3.75% MoS2 + 42.5% SE) 8mg / cm2 97 Example 7 Example 2 (30% Li2S - 20% LiI - 6.75% CNF + 0.75% MoS2 + 42.5% SE) 8mg / cm2 96 Example 8 Example 3 (30% Li2S - 20% LiI - 0.75% CNF + 6.75% MoS2 + 42.5% SE) 8mg / cm2 98 Example 9 Example 4 (30% Li2S - 20% LiI - 0.375% MoS2 Supported CNF 7.5% + 42.5% SE) 8mg / cm2 95 Example 10 Example 5 (30% Li2S - 20% LiI - 3.75% graphene + 3.75% MoS2 + 42.5% SE) 8mg / cm2 95 Example 11 Example 1 (30% Li2S - 20% LiI - 3.75% CNF + 3.75 % MoS2 + 42.5% SE) Thick film) 24mg / cm2 95 Example 12 Example 2 (30% Li2S - 20% LiI - 6.75% CNF + 0.75 % MoS2 + 42.5% SE) Thick film) 24mg / cm2 94 Example 13 Example 3 (30% Li2S - 20% LiI - 0.75% CNF + 6.75% MoS2 + 42.5% SE Thick film) 24mg / cm2 96Example 14Example 430% Li2S- 20% LiI - 5% MoS2 supported CNF 7.5% + 42.5% SE Thick film) 24mg / cm2 94Example 15Example 530% Li2S- 20% LiI - 3.75% graphene + 3.75% MoS2 + 42.5% SE Thick film) 24mg / cm2 94Comparative Example 5Comparative Example 1 (Tatsumisago) 30% Li2S- 20% LiI - 10% CNF + 42.5% SE 8mg / cm2 89Comparative Example 6Comparative Example 1 (Tatsumisago) (30% Li2S- 20% LiI - 10% CNF + 42.5% SE) Thick film) 24mg / cm285 Comparative Example 7 Comparative Example 2 (30% Li2S- 20% LiI - 7.5% CNF + 42.5% SE)8mg / cm284Comparative Example 8Comparative Example 2(30% Li2S- 20% LiI - 7.5% CNF + 42.5% SE)Thick Film) 24mg / cm281Reference Example 2Reference Example 1(30% Li2S- 20% LiI - 7.5% CNT + 42.5% SE)8mg / cm272Reference Example 3Reference Example 1(30% Li2S- 20% LiI - 7.5% CNT + 42.5% SE)Thick Film) 24mg / cm265.

[0382] As shown in Table 4, the all-solid-state secondary batteries of Examples 6 to 15 had improved high-rate characteristics compared to the all-solid-state secondary batteries of Comparative Examples 5 to 8 and Reference Examples 2 to 3.

Claims

1. Comprising an anode layer; a cathode layer; and a solid electrolyte layer disposed between the anode layer and the cathode layer, The above cathode layer comprises a cathode current collector; and a cathode active material layer disposed on one or both sides of the cathode current collector, The above cathode active material layer includes a composite cathode active material, The above composite bipolar active material is i)M 2 A composite comprising S and 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, wherein M is an alkali metal, and the alkali metal is Li or Na, The electronic conductivity of the above-mentioned inorganic electronic conductive structure is 10 -3 S / cm or more, The above complex is M 2 Containing a solid solution of S and an alkali metal salt, An all-solid-state secondary battery wherein the above two-dimensional carbon-based structure is graphene, graphene oxide, or a combination thereof.

2. In the first paragraph, the length of the fibrous carbon material is 1 to 50 ㎛ and the diameter is 10 nm to 10 ㎛, The above fibrous carbon material includes a rod structure, a tube structure, a needle structure, a wire structure or a combination thereof, The cross-section perpendicular to the longitudinal direction of the above fibrous carbon material has an irregular, circular or polygonal shape, An all-solid-state secondary battery, wherein the fibrous carbon-based material comprises carbon nanofibers.

3. In the first paragraph, the content of the inorganic electronic conductive structure in the complex is 1 to 20 parts by weight based on 100 parts by weight of the complex, The content of the above fibrous carbon material or two-dimensional carbon structure is 1 to 40 parts by weight based on 100 parts by weight of the composite, Above M 2 An all-solid-state secondary battery having a molar ratio of S and an alkali metal salt of 50:50 to 95:

5.

4. In paragraph 1, the M 2 The size of S is equal to or smaller than the size of the alkali metal salt, and the size of the inorganic electronic conductive structure is equal to or smaller than the size of lithium sulfide and the alkali metal salt. Compared to the large, above-mentioned inorganic electronic conductive structure, alkali metal salt and M 2 All-solid-state secondary battery with gradually decreasing particle size in S order.

5. In the first paragraph, the length of the inorganic electronic conductive structure is 1 to 50 um and the thickness is 0.01 to 10 um, and the M 2 The size of S is 0.1 nm to 10 um, The size of the above alkali metal salt is 1 nm to 10 um, An all-solid-state secondary battery, wherein the particle size of the above complex is 10 ㎛ or less.

6. In the first paragraph, the inorganic electronic conductive structure has a one-dimensional or two-dimensional structure form, The above inorganic electronic conductive structure comprises a transition metal sulfide, a metal sulfide containing at least one metal from Group 3 to Group 5, or a combination thereof, The above inorganic electronically conductive structure is titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, niobium, tantalum, molybdenum, tungsten or a combination thereof, The above inorganic electronic conductive structures are VO2, ReO2, CrO2, ReO2, VO2, SnO2, TiO2, ZrO2, Al2O3, TeN, TiN, TiO, TiOx (0.75 <x<1.45), Ti n O 2n-1 (4 <n<10), ReO3, CrO2, VO2 중에서 선택된 하나 이상의 금속 산화물, ZrS 2 , 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. In the first paragraph, in the X-ray diffraction spectrum (XRD) of the composite cathode active material, the first diffraction angle of the first peak appearing at a diffraction angle of 2θ = 14.5±0.5°, the second peak appearing at a diffraction angle of 2θ = 32.5±0.5°, and the third peak appearing at a diffraction angle of 2θ = 58.5±0.5° are, respectively, In the XRD spectrum of MoS2 used in the manufacture of the above complex, the second diffraction angle is smaller than that of the fourth peak appearing at a diffraction angle of 2θ = 14.5±0.5°, the fifth peak appearing at a diffraction angle of 2θ = 32.5±0.5°, and the sixth peak appearing at a diffraction angle of 2θ = 58.5±0.5°. An all-solid-state secondary battery, wherein the intensity of the first peak appearing at the diffraction angle 2θ= 14.5±0.5° is reduced compared to the intensity of the fourth peak appearing at the diffraction angle 2θ= 14.5±0.5° in the XRD spectrum of MoS2 used in the manufacture of the composite.

8. In the first paragraph, M in the XRD spectrum of the complex 2 The first lattice constant (d1) derived from the first peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of S is the M used in the preparation of the complex. 2 M in the XRD spectrum of S 2 It is larger than the second lattice constant (d2) derived from the second peak appearing at a diffraction angle of 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of S. An all-solid-state secondary battery having a first lattice constant (d1) size of 5.78 Å or greater.

9. An all-solid-state secondary battery having a structure in which, in the first paragraph, the composite cathode active material, iii) the inorganic electron-conductive structure, is supported on iv) a fibrous carbon-based material having an aspect ratio of 2 or more.

10. In the first paragraph, the positive electrode active material layer further includes a solid electrolyte, The above solid electrolyte includes a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof. An all-solid-state secondary battery, wherein the content of the solid electrolyte is 10 to 60 parts by weight based on 100 parts by weight of the cathode active material layer.

11. In the first paragraph, the alkali metal salt is a lithium salt or a sodium salt, The above alkali metal salt is a binary compound or a ternary compound, The above binary compounds are LiI, LiBr, LiCl, LiF, LiH, Li 2 O, Li 2 Se, Li 2 Te, Li 3 N, Li 3 P, Li 3 As, Li 3 Sb, Li 3 Al 2 , LiB 3 or a combination thereof, or NaI, NaBr, NaCl, NaF, Na 2 O, Na 2 Se, Na 3 N, Na 3 P, Na 3 As, Na 3 Sb, Na 3 Al 2 , NaB 3 or a combination thereof, The above ternary compound is Li 3 OCl, LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiNO 3 , Li 2 CO 3 , LiBH 4 , Li 2 SO 4 , Li 3 BO 3 , Li 3 PO 4 , Li 4 NCl, Li 5 NCl 2 , Li 3 BN 2 or a combination thereof, or Na 3 OCl, NaBF 4 , NaPF 6 , NaAsF 6 , NaClO 4 , NaNO 3 , NaAlO 2 , NaAlCl 4 , NaNO 3 , Na 2 CO 3 , NaBH 4 , Na 2 SO 4 , Na 3 BO 3 , Na 3 PO 4 , Na 4 NCl, Na 5 NCl 2 , Na 3 BN 2 An all-solid-state secondary battery comprising a combination thereof.

12. An all-solid-state secondary battery according to claim 1, wherein the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer disposed on the negative electrode current collector.

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

14. In the 11th paragraph, the negative electrode active material of the first negative electrode active material layer is an all-solid-state secondary battery including 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. In the first paragraph, the negative electrode layer includes a negative electrode current collector and a lithium host layer disposed on one surface of the negative electrode current collector, The above lithium host layer includes a lithium host structure, The above lithium host structure comprises one or more lithium hosts, wherein the lithium host comprises a carbon-based lithium host, a metal-based lithium host, a polymer-based lithium host, or a combination thereof, An all-solid-state secondary battery comprising a first inactive member disposed on one side of the cathode layer.

16. In the first paragraph, the negative electrode current collector is disposed between the negative electrode current collector and the first negative electrode active material layer. It further includes a second negative electrode active material layer, wherein the second negative electrode active material layer is a metal layer including lithium or a lithium alloy, An all-solid-state secondary battery, wherein the second negative electrode active material layer is a plated layer, and the thickness of the first negative electrode active material layer is greater than the thickness of the second negative electrode active material layer.

17. An all-solid-state secondary battery according to claim 1, further comprising an inert elastic member disposed on one surface of the positive electrode layer or the negative electrode layer, or not comprising the inert elastic member.

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

19. In the first paragraph, the negative electrode layer includes a negative electrode collector, At least one of the positive electrode current collector and the negative electrode current collector includes a base film and a metal layer disposed on one or both sides of the base film, The above base film comprises a polymer, and the polymer comprises polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI) or a combination thereof. An all-solid-state secondary battery, wherein the metal layer comprises indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. 20.M 2 A step of first milling a composition including S, an alkali metal salt, and an inorganic electronic conductive structure; A step of adding a composition including a fibrous carbon-based material or a two-dimensional carbon-based structure having an aspect ratio of 2 or more to a first milled product and performing second milling to obtain a composite; A step of adding and mixing a binder to the above complex to obtain a composition, and manufacturing a positive electrode using the composition; Step of preparing the cathode; and A method for manufacturing an all-solid-state secondary battery, comprising the step of placing a solid electrolyte between the positive electrode and the negative electrode.

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