Negative electrode and lithium-sulfur battery comprising same

Abstract

The present invention relates to a negative electrode and a battery comprising same. Specifically, the present invention relates to a negative electrode for a lithium-sulfur battery, the negative electrode comprising a negative electrode current collector, a first coating layer disposed on the negative electrode current collector, and a second coating layer disposed on the first coating layer, wherein: the first coating layer comprises a first metal and a first carbon-based material; the second coating layer comprises a second metal and a second carbon-based material; each of the first and second metals is a lithiophilic metal capable of alloying with lithium; a mass ratio of the first metal and the first carbon-based material is 1:10 to 1:2.5; and a mass ratio of the second metal to the second carbon-based material is 1:2 to 1:1.

Description

Negative electrode and lithium-sulfur battery including the same

[0001] The present invention relates to a cathode and a lithium-sulfur battery comprising the same.

[0002] Recently, driven by industrial demands, the development of batteries with high energy density and safety is actively underway. For example, lithium-ion batteries are being commercialized not only in the fields of information and communication devices but also in the automotive sector. In the automotive sector, safety is considered particularly important because it is directly related to human life.

[0003] Recently, all-solid-state batteries in which liquid electrolytes are replaced with solid electrolytes have been proposed. By not using flammable organic dispersion media, all-solid-state batteries can significantly reduce the likelihood of fire or explosion in the event of a short circuit. Therefore, these all-solid-state batteries can offer significantly higher safety compared to lithium-ion batteries that use liquid electrolytes.

[0004] The problem that the present invention aims to solve is to provide a cathode with improved conductivity.

[0005] Another problem that the present invention aims to solve is to provide a lithium-sulfur battery comprising the above-mentioned cathode.

[0006] A negative electrode for a lithium-sulfur battery according to the concept of the present invention comprises a negative electrode current collector, a first coating layer disposed on the negative electrode current collector, and a second coating layer disposed on the first coating layer, wherein the first coating layer comprises a first metal and a first carbon-based material, and the second coating layer comprises a second metal and a second carbon-based material, and each of the first and second metals is a lithium-affinity metal capable of forming an alloy with lithium, and the mass ratio of the first metal and the first carbon-based material may be 1:10 to 1:2.5, and the mass ratio of the second metal and the second carbon-based material may be 1:2 to 1:1.

[0007] A lithium-sulfur battery according to another concept of the present invention comprises: a positive electrode; a negative electrode including a negative electrode current collector, a first coating layer disposed on the negative electrode current collector, and a second coating layer disposed on the first coating layer; and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the first coating layer comprises a first metal and a first carbon-based material, and the second coating layer comprises a second metal and a second carbon-based material, and each of the first and second metals is a lithium-affinity metal capable of forming an alloy with lithium, and the mass ratio of the first metal and the first carbon-based material may be 1:10 to 1:2.5, and the mass ratio of the second metal and the second carbon-based material may be 1:2 to 1:1.

[0008] The cathode according to the present invention can have reduced interfacial resistance and improved conductivity. In addition, a lithium-sulfur battery including the cathode can have improved lifespan characteristics.

[0009] FIGS. 1 to 3 are cross-sectional views of a lithium-sulfur battery according to an exemplary embodiment of the present invention.

[0010] FIG. 4 is a cross-sectional view of a cathode according to an exemplary embodiment of the present invention.

[0011] FIG. 5 is an enlarged view of the M region of FIG. 4, and is a schematic diagram exemplarily showing the cross-sections of the first coating layer and the second coating layer.

[0012] FIGS. 6 and 7 are cross-sectional views of a lithium-sulfur battery according to an exemplary embodiment of the present invention.

[0013] FIG. 8 is an enlarged view of the N region of FIG. 7, and is a schematic diagram of a cross-section including a first coating layer, a second coating layer, and a lithium metal layer.

[0014] Figure 9 is a schematic diagram showing the coating layer and lithium metal layer of a comparative example.

[0015] In order to fully understand the structure and effects of the present invention, preferred embodiments of the present invention are described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various modifications can be made. The description of these embodiments is provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention.

[0016] In this specification, when a component is described as being on another component, it means that it may be formed directly on the other component or that a third component may be interposed between them. Additionally, in the drawings, the thicknesses of the components are exaggerated for the effective description of the technical content. Throughout the specification, parts indicated by the same reference numeral represent the same components.

[0017] The embodiments described herein will be described with reference to cross-sectional and / or plan views, which are exemplary illustrations of the invention. In the drawings, the thicknesses of films and regions are exaggerated for effective description of the technical content. Accordingly, the regions illustrated in the drawings are schematic in nature, and the shapes of the regions illustrated in the drawings are intended to illustrate specific forms of regions of the device and are not intended to limit the scope of the invention. Although terms such as first, second, third, etc., have been used to describe various components in the various embodiments of this specification, these components should not be limited by such terms. These terms are used merely to distinguish one component from another. The embodiments described and illustrated herein also include their complementary embodiments.

[0018] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, 'comprises' and / or 'comprising' do not exclude the presence or addition of one or more other components to the mentioned components.

[0019] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0020] Unless otherwise defined in this specification, the particle size may be the average particle size. Additionally, the particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. The average particle size (D50) may be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) value may be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Alternatively, it may be measured using a laser diffraction method. When measuring by laser diffraction, more specifically, after dispersing the particles to be measured in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasound of about 28 kHz at an output of 60 W, and then the average particle size (D50) at 50% of the particle size distribution in the measuring device can be calculated.

[0021] In this specification, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state.

[0022] In this specification, “alloy” means a mixture of two or more metals.

[0023] In this specification, “electrode active material” refers to an electrode material capable of undergoing lithiation and delithiation.

[0024] In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0025] In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0026] In this specification, “lithiation” and “to lithiate” refer to the process of adding lithium to an electrode active material.

[0027] In this specification, “delithiation” and “to delithiate” refer to the process of removing lithium from an electrode active material.

[0028] In this specification, “charge” and “to charge” refer to the process of providing electrochemical energy to a battery.

[0029] In this specification, “discharge” and “discharge” refer to the process of removing electrochemical energy from a battery.

[0030] In this specification, “anode” and “cathode” refer to electrodes where electrochemical reduction and lithiation occur during the discharge process.

[0031] In this specification, “negative electrode” and “anode” refer to electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0032] lithium-sulfur all-solid-state battery (1000)

[0033] FIGS. 1 and FIGS. 2 are cross-sectional views of a lithium-sulfur battery according to an exemplary embodiment of the present invention.

[0034] Referring to FIG. 1, a lithium-sulfur all-solid-state battery (1000) according to one embodiment may include a positive electrode layer (100), a negative electrode layer (200) facing the positive electrode layer (100), and a solid electrolyte layer (300) disposed between the positive electrode layer (100) and the negative electrode layer (200). The positive electrode layer (100) may include a positive electrode current collector (110) and a positive electrode active material layer (120). The negative electrode layer (200) may include a negative electrode current collector (210) and a coating layer (220). However, not limited thereto, the lithium-sulfur all-solid-state battery (1000) may further include an additional functional layer, such as an adhesion enhancing layer, disposed between the positive electrode layer (100) and the solid electrolyte layer (300) or between the negative electrode layer (200) and the solid electrolyte layer (300).

[0035] Referring to FIG. 2, a coating layer (220) of a lithium-sulfur all-solid-state battery (1000) according to one embodiment may include a first coating layer (221) and a second coating layer (222).

[0036]

[0037] anode layer (100)

[0038] The positive layer (100) of one embodiment includes a positive current collector (110) and a positive active material layer (120) disposed on the positive current collector (110).

[0039] The positive current collector (110) can provide a reference surface on which the positive active material layer (120) is placed. The positive current collector (110) may include, for example, a plate or foil comprising 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.

[0040] The thickness of the positive current collector (110) may be, for example, 1 μm to 100 μm, 1 μm to 50 μm, 5 μm to 25 μm, or 10 μm to 20 μm.

[0041] Meanwhile, unlike as illustrated in FIG. 1, the positive current collector (110) may be omitted in one embodiment of the present invention. Although not illustrated, a carbon layer with a thickness of 0.1 μm to 4 μm may be further disposed between the positive current collector (110) and the positive active material layer (120) to increase the bonding strength between the positive current collector (110) and the positive active material layer (120).

[0042] The positive current collector (110) 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.

[0043] The base film may be, for example, an insulator. Since the base film contains an insulating thermoplastic polymer, the base film may soften or liquefy upon the occurrence of a short circuit, thereby interrupting battery operation and suppressing a sudden increase in current.

[0044] The metal layer may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or alloys thereof. The metal layer may act as an electrochemical fuse and cut off in the event of an overcurrent to perform a short-circuit prevention function. The limit current and maximum current can be controlled by adjusting the thickness of the metal layer. The metal layer may be plated or deposited on a base film. As the thickness of the metal layer decreases, the limit current and / or maximum current of the positive current collector (110) decreases, thereby improving the stability of the lithium battery in the event of a short circuit.

[0045] A lead tab may be added to the metal layer for external connection. The lead tab may be welded to the metal layer or the metal layer / base film laminate by ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or metal layer melt, allowing the metal layer to be electrically connected to the lead tab.

[0046] To make the weld between the metal layer and the lead tab more robust, a metal chip may be added between the metal layer and the lead tab. The metal chip may be a thin sheet of the same material as the metal of the metal layer. The metal chip may be, for example, metal foil, metal mesh, etc. The metal chip may be, for example, aluminum foil, copper foil, SUS foil, etc. The lead tab may be welded to a metal chip / metal layer laminate or a metal chip / metal layer / base film laminate by placing the metal chip on the metal layer and then welding it to the lead tab. During welding, as the base film, metal layer, and / or metal chip melt, the metal layer or the metal layer / metal chip laminate may be electrically connected to the lead tab. A metal chip and / or lead tab may be added to a portion of the metal layer.

[0047] The thickness of the base film may be, for example, 1 to 50 μm, 1.5 to 50 μm, 1.5 to 40 μm, or 1 to 30 μm. By having the base film within this thickness range, the weight of the electrode assembly can be reduced more effectively. The melting point of the base film may be, for example, 100 to 300 °C, 100 to 250 °C or lower, or 100 to 200 °C. By having the base film within this melting point range, the base film can melt during the welding process of the lead tab and be easily bonded to the lead tab. Surface treatments, such as corona treatment, may be performed on the base film to improve the adhesion between the base film and the metal layer.

[0048] 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. By having the metal layer within this range of thickness, the stability of the electrode assembly can be ensured while maintaining conductivity. The thickness of the metal piece may be, for example, 2 to 10 μm, 2 to 7 μm, or 4 to 6 μm. By having the metal piece within this range of thickness, the connection between the metal layer and the lead tab can be performed more easily. Since the positive current collector (110) has a laminated structure of the base film and the metal layer described above, the weight of the positive layer (100) can be reduced, and consequently, the energy density of the lithium-sulfur all-solid-state battery (1000) can be improved.

[0049]

[0050] The positive active material layer (120) may include a positive active material and a solid electrolyte.

[0051] The cathode active material may include a lithium-containing sulfide-based cathode active material. The lithium-containing sulfide-based cathode active material is, for example, an electrode material to which lithium is added to a sulfur-based cathode active material. The sulfur-based cathode active material includes, for example, a sulfur-based material, a composite containing a sulfur-based material, or a combination thereof. The sulfur-based material is, for example, inorganic sulfur, Li2S n (n>1), it may be a disulfide compound, an organic sulfur compound, a carbon-sulfur polymer, or a combination thereof. The sulfur-based material-containing composite may be inorganic sulfur, Li2S n(n>1), it may be a composite containing a disulfide compound, an organic sulfur compound, a carbon-sulfur polymer, or a combination thereof. The sulfur-based material-containing composite may include, for example, a composite of a sulfur-based material and carbon, a composite of a sulfur-based material, carbon and a solid electrolyte, a composite of a sulfur-based material and a solid electrolyte, a composite of a sulfur-based material and a metal carbide, a composite of a sulfur-based material, carbon and a metal carbide, a composite of a sulfur-based material and a metal nitride, a composite of a sulfur-based material, carbon and a metal nitride, or a combination thereof. Since the lithium-containing sulfide-based cathode active material provides a higher discharge capacity per unit weight compared to the oxide-based cathode active material, the energy density per unit weight of an all-solid-state secondary battery containing the lithium-containing sulfide-based cathode active material can be improved.

[0052] The lithium-containing sulfide-based cathode active material includes, for example, Li2S, Li2S-containing composites, or combinations thereof. By including Li2S, Li2S-containing composites, or combinations thereof with high capacity as the lithium-containing sulfide-based cathode active material, the use of lithium metal can be omitted during the manufacture of all-solid-state secondary batteries. Since lithium metal possesses high reactivity and great ductility, it can reduce mass producibility during battery manufacturing. Therefore, the mass producibility of all-solid-state secondary batteries can be improved. Since lithium metal is omitted from the anode layer, the volume of the anode layer is reduced, thereby improving the energy density per unit volume of the all-solid-state secondary battery and enabling the construction of an all-solid-state secondary battery with a simpler structure.

[0053] Lithium-containing sulfide-based cathode active materials (e.g., Li2S) undergo delithiation during initial charging, for example, causing a decrease in volume, and then increase again through lithiation during subsequent discharge. Therefore, since the volume of the lithium-containing sulfide-based cathode active material changes while maintaining the ion and / or electron transport pathways provided by conductive materials placed around the material, the likelihood of the ion and / or electron transport pathways being severed is low. In contrast, sulfur-based cathode active materials (e.g., S) undergo lithiation during initial discharge, for example, causing a increase in volume, and then decrease again through delithiation during subsequent charging. Consequently, the initial ion and / or electron transport pathways provided by conductive materials placed around the sulfur-based cathode active material may collapse due to the initial volume increase of the sulfur-based cathode active material, thus increasing the likelihood of the ion and / or electron transport pathways being severed.

[0054] The particle size of the lithium-containing sulfide-based cathode active material may be, for example, 1 nm to 50 µm, 10 nm to 50 µm, 50 nm to 40 µm, 100 nm to 30 µm, 500 nm to 30 µm, or 1 µm to 20 µm. By having the lithium-containing sulfide-based cathode active material have a particle size within this range, the cycle characteristics of an all-solid-state secondary battery containing the lithium sulfide-based cathode active material can be further improved. The Li2S-containing composite is, for example, a composite of Li2S and a conductive material. The conductive material is, for example, an ion-conducting material, an electron-conducting material, or a combination thereof.

[0055] The electronic conductivity of an electronically conductive material is, for example, 1.0 × 10⁻⁶ 3 S / m, 1.0×10 4 S / m, or 1.0×10⁻⁶ 5It is S / m or greater. The form of the electronically conductive material is, for example, particulate electronically conductive material, plate-shaped electronically conductive material, rod-shaped electronically conductive material, or a combination thereof, but is not necessarily limited to these. The electronically conductive material may be, for example, carbon, metal powder, metal compound, etc. When carbon is included as the electronically conductive material, since carbon has high electronic conductivity and is lightweight, it is possible to realize an all-solid-state secondary battery having a high energy density per unit mass. The electronically conductive material may have pores. By having pores in the electronically conductive material, Li2S can be contained within the pores, which can increase the contact area between Li2S and the electronically conductive material and increase the specific surface area of ​​Li2S. The pore capacity is, for example, 0.1 cc / g to 20.0 cc / g, 0.5 cc / g to 10 cc / g, or 0.5 cc / g to 5 cc / g. The average pore diameter is, for example, 1 nm to 100 nm, 1 nm to 50 nm, or 1 nm to 20 nm. The BET specific surface area of ​​the electron-conducting material having pores is 200 m² when the average pore diameter is 15 nm or less. 2 / g to 4500 m 2 / g, and if the average pore diameter is greater than 15 nm, 100 m 2 / g to 2500 m 2 It is / g. BET specific surface area, pore diameter, pore capacity, and average pore diameter can be obtained, for example, using the nitrogen adsorption method.

[0056] The ionic conductivity of an ion-conducting material is, for example, 1.0 × 10⁻⁶ -5 S / m, 1.0×10 -4 S / m, or 1.0×10⁻⁶ -3It is greater than S / m. The ion-conducting material may have pores. By having pores, Li2S can be contained within the pores, thereby increasing the contact area between Li2S and the ion-conducting material and increasing the specific surface area of ​​Li2S. The form of the ion-conducting material may be, for example, particulate ion-conducting material, plate-shaped electron-conducting material, rod-shaped electron-conducting material, or a combination thereof, but is not necessarily limited to these. The ion-conducting material may be, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, etc. When a sulfide-based solid electrolyte is included as the ion-conducting material, since the sulfide-based solid electrolyte has high ion conductivity and can be molded into various shapes, it is possible to realize an all-solid-state secondary battery with a large capacity.

[0057] Li2S-containing complexes include, for example, a complex of Li2S and carbon, a complex of Li2S, carbon and a solid electrolyte, a complex of Li2S and a solid electrolyte, a complex of Li2S and a metal carbide, a complex of Li2S, carbon and a metal carbide, a complex of Li2S and a metal nitride, a complex of Li2S, carbon and a metal nitride, or a combination thereof.

[0058] The composite of Li2S and carbon contains carbon. Carbon may be any material containing carbon atoms, for example, used as a conductive material in the art. Carbon may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. Carbon may be, for example, a calcined product of a carbon precursor. Carbon may be, for example, a carbon nanostructure. Carbon nanostructures may be, for example, one-dimensional carbon nanostructures, two-dimensional carbon nanostructures, three-dimensional carbon nanostructures, or a combination thereof. Carbon nanostructures may be, for example, carbon nanotubes, carbon nanofibers, carbon nanobelts, carbon nanorods, graphene, or a combination thereof. Carbon may be, for example, porous carbon or non-porous carbon. Porous carbon may contain, for example, periodic and regular two-dimensional or three-dimensional pores. Porous carbon may be, for example, carbon black such as Ketjen black, acetylene black, Denka black, thermal black, channel black; graphite, activated carbon, or a combination thereof. The form of carbon may be, for example, in the form of particles, sheets, flakes, etc., but is not limited to these; any form used as carbon in the relevant technical field is possible. The method of manufacturing the Li2S and carbon composite may be a dry method, a wet method, or a combination thereof, but is not limited to these; and the method of manufacturing the Li2S and carbon composite in the relevant technical field may be, for example, milling, heat treatment, deposition, etc., but is not necessarily limited to these; any method used in the relevant technical field is possible.

[0059] The composite of Li2S, carbon, and solid electrolyte comprises carbon and a solid electrolyte. Carbon refers to the composite of Li2S and carbon described above. The solid electrolyte may be any material used as an ion-conducting material in the art, for example. The solid electrolyte is, for example, an inorganic solid electrolyte. The solid electrolyte is, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte is, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a lithium salt compound, or a combination thereof. The sulfide-based solid electrolyte comprises, for example, Li, S, and P, and may optionally further comprise a halogen element. The sulfide-based solid electrolyte may be selected from among sulfide-based solid electrolytes used in the solid electrolyte layer. The sulfide-based solid electrolyte is, for example, 1 × 10⁻⁶ at room temperature. -5 It can have an ionic conductivity of S / cm or greater. Oxide-based solid electrolytes include, for example, Li, O, and transition metal elements, and may optionally include other elements. Oxide-based solid electrolytes, for example, 1×10⁻⁶ at room temperature -5It may be a solid electrolyte having an ionic conductivity of S / cm or higher. The oxide-based solid electrolyte may be selected from the oxide-based solid electrolytes used in the solid electrolyte layer. The solid electrolyte comprises, for example, a lithium salt compound, and the lithium salt compound is, for example, an inorganic compound. The solid electrolyte comprises, for example, a lithium salt compound, and the lithium salt compound does not contain, for example, sulfur (S) atoms. The solid electrolyte comprises, for example, a lithium salt compound, and the lithium salt compound may be a binary compound composed of, for example, lithium and one element selected from Groups 13 to 17 of the periodic table. The binary compound may comprise, for example, one or more selected from LiF, LiCl, LiBr, LiI, LiH, Li2S, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, and LiB3. The lithium salt compound used as a solid electrolyte may be, for example, a ternary compound composed of lithium and two elements selected from groups 13 to 17 of the periodic table. The ternary compound comprises, for example, one or more selected from Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, and Li3BN2. The lithium salt compound is, in particular, one or more lithium halide compounds selected from LiF, LiCl, LiBr, and LiI.

[0060] The complex of Li2S and a solid electrolyte includes a solid electrolyte. The solid electrolyte refers to the complex of Li2S, carbon, and a solid electrolyte described above.

[0061] The complex of Li2S and metal carbide contains 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 xIt is expressed as (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). Two-dimensional metal carbides are, for example, Ti2CT x , (Ti 0.5 , Nb 0.5 )2CT x , Nb2CT x , V2CT x , Ti3C2T x , (V 0.5 , Cr 0.5 )3C2T x , Ti3CNT x , Ta4C3T x , Nb4C3T x Or a combination of these. The surface of a two-dimensional metal carbide is terminated by O, OH and / or F.

[0062] The complex of Li2S, carbon, and metal carbide includes carbon and metal carbide. Carbon refers to the complex of Li2S and carbon described above. Metal carbide refers to the complex of Li2S and metal carbide described above.

[0063] The complex of Li2S and metal nitride contains the metal nitride. The metal nitride is, for example, a two-dimensional metal nitride. The two-dimensional metal nitride is, for example, M n+1 N n T x It is expressed as (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). The surface of a two-dimensional metal nitride is terminated by O, OH and / or F.

[0064] The complex of Li2S, carbon, and metal nitride includes carbon and metal nitride. Carbon refers to the complex of Li2S and carbon described above. Metal carbide refers to the complex of Li2S and metal nitride described above.

[0065] A lithium-containing sulfide-based cathode active material may include a composite of a sulfide-based material, a carbon-based conductive material, and a metal halide salt.

[0066] Sulfide-based materials may contain elemental sulfur (S). Sulfur is attracting attention as a next-generation cathode material due to its high theoretical capacity (1,672 mAh / g), its abundance on Earth, and its relatively low cost. In one embodiment, the elemental sulfur (S) is S8 and Li2S n It may exist in a form including at least one of (1 ≤ n ≤ 8, where n is an integer). That is, the sulfide-based material according to one embodiment is S8, Li2S n It may include (1 ≤ n ≤ 8, where n is an integer) or a combination thereof. A sulfide-based material undergoes a continuous oxidation / reduction reaction of sulfur and / or lithium sulfide. For example, the reaction process of lithium polysulfide and lithium sulfide by the continuous reduction reaction of sulfur in the sulfide-based material can be expressed as S8→Li2S8→Li2S6→Li2S4→Li2S2→Li2S, etc. In this process, lithium ions move between the anode and cathode, and at the same time, electrons move through an external circuit, which can generate an electric current. A sulfide-based material according to one embodiment may include Li2S. For example, the reaction process of lithium polysulfide and lithium sulfide by the continuous oxidation reaction of Li2S in the sulfide-based material can be expressed as Li2S→Li2S2→Li2S4→Li2S6→Li2S8→S8, etc. In this process, lithium ions move between the anode and cathode, and at the same time, electrons move through an external circuit, which can store energy.

[0067] The content of the sulfide-based material included in the composite may be, for example, 20 to 80 wt%, 30 to 70 wt%, 35 to 65 wt%, or 40 to 70 wt% of the total weight of the positive active material layer. If the content of the sulfide-based material increases excessively, the electronic conductivity of the composite decreases, which may increase the internal resistance of the positive active material. If the content of the sulfide-based material decreases excessively, the energy density of the secondary battery may decrease.

[0068] Carbon-based conductive materials are materials containing carbon atoms, and any material used as a conductive material in the relevant technical field is acceptable. Carbon-based conductive materials may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. Carbon-based conductive materials may be, for example, a sintered product of a carbon precursor. Carbon-based conductive materials may be, for example, carbon nanostructures. Carbon nanostructures may be, for example, one-dimensional carbon nanostructures, two-dimensional carbon nanostructures, three-dimensional carbon nanostructures, or a combination thereof. Carbon-based conductive materials may include, for example, carbon nanotubes (CNT), carbon nanofibers (CNF), carbon nanobelts, carbon nanorods, graphene, or a combination thereof. Carbon-based conductive materials may be, for example, porous carbon-based materials or non-porous carbon-based materials. Porous carbon-based materials may include, for example, periodic and regular two-dimensional or three-dimensional pores. Porous carbon-based materials may be, for example, carbon black such as Ketjen black, acetylene black, Denka black, thermal black, and channel black; graphite, activated carbon, or a combination thereof. The form of the carbon-based conductive material may be, for example, particle form, sheet form, flake form, etc., but is not limited to these; any form used as a carbon-based conductive material in the relevant technical field is possible.

[0069] The content of the carbon-based conductive material included in the composite may be, for example, 1 to 20 wt%, 1 to 15 wt%, or 5 to 10 wt% of the total weight of the positive electrode active material layer. If the content of the carbon-based conductive material increases excessively, the energy density of the secondary battery may decrease. If the content of the carbon-based conductive material decreases excessively, the electronic conductivity of the composite decreases, and the internal resistance of the positive electrode active material may increase.

[0070] The content ratio of the sulfide-based material and the carbon-based conductive material included in the composite may be 1:1 to 50:1, 1:1 to 25:1, 2:1 to 25:1, 3:1 to 25:1, 3:1 to 20:1, or 4:1 to 10:1 by weight. By satisfying the content ratio of the sulfide-based material and the carbon-based conductive material within the above ranges, the electronic conductivity of the composite can be improved, and the specific capacity of the positive active material can be improved, thereby improving the energy density of the secondary battery.

[0071] Metal halide salts may include alkali metal salts and boron group metal salts. That is, a composite according to another embodiment may be a composite of a sulfide-based material, an alkali metal salt, a boron group metal salt, and a carbon-based conductive material. The ionic conductivity of the composite may be further enhanced by including such alkali metal salts. By including such boron group metal salts, the composite may easily accommodate volume changes of the anode active material, thereby suppressing the occurrence of cracks within the anode active material.

[0072] The content ratio of the alkali metal salt and boron group metal salt included in the metal halide salt may be 1:1 to 1:10, 1:1 to 1:5, or 1:2 to 1:4 by weight. The content ratio of the alkali metal salt and boron group metal salt included in the metal halide salt may be 5:1 to 1:5, 3:1 to 1:3, or 2:1 to 1:2 by molar ratio. By satisfying the content ratio of the alkali metal salt and boron group metal salt within the above ranges, the ionic conductivity of the composite can be improved, and the occurrence of cracks inside the anode active material can be suppressed by easily accommodating volume changes of the anode active material.

[0073] The alkali metal salt may be a binary compound composed of, for example, an alkali metal and one element selected from Group 17 of the periodic table. The alkali metal salt may be, for example, a lithium salt. The alkali metal salt may include, for example, LiF, LiCl, LiBr, LiI, or a combination thereof. Such alkali metal salts can form a complex with a sulfide-based material to improve the ionic conductivity of the positive electrode active material.

[0074] Boron group metal salts may be binary compounds composed, for example, of a boron group metal and one element selected from Group 17 of the periodic table. Boron group metal salts may include, for example, AlF3, AlCl3, AlBr3, AlI3, GaF3, GaCl3, GaBr3, GaI3, InF3, InCl3, lnBr3, lnI3, TlF3, TlCl3, TlBr3, TlI3, or combinations thereof. These boron group metal salts can form complexes with sulfide-based materials to maintain a constant overall shape of the cathode active material and lower interfacial resistance.

[0075] The content ratio of the sulfide-based material and the metal halide salt included in the composite may be 1:1 to 100:1, 2:1 to 50:1, 3:1 to 25:1, 3:1 to 20:1, or 4:1 to 10:1 by weight. By satisfying the content ratio of the sulfide-based material and the metal halide salt within the above ranges, the ionic conductivity of the composite can be improved, and the specific capacity of the positive electrode active material can be improved, thereby improving the energy density of the secondary battery.

[0076] The content of the metal halide salt included in the composite may be, for example, 0 to 30 wt%, 0 to 20 wt%, or 0 to 10 wt% of the total weight of the anode active material layer. The content of the metal halide salt included in the composite may be, for example, 1 to 30 wt%, 1 to 20 wt%, or 1 to 10 wt% of the total weight of the composite. The content of the metal halide salt included in the composite may be, for example, 3 to 30 wt%, 3 to 20 wt%, or 5 to 10 wt% of the total weight of the composite. If the content of the metal halide salt increases excessively, the energy density may decrease.

[0077] Lithium-containing sulfide-based cathode active materials include, for example, Li2S-LiF-AlF3-CNT, Li2S-LiF-AlCl3-CNT, Li2S-LiF-AlBr3-CNT, Li2S-LiF-AlI3-CNT, Li2S-LiF-GaF3-CNT, Li2S-LiF-GaCl3-CNT, Li2S-LiF-GaBr3-CNT, Li2S-LiF-GaI3-CNT, Li2S-LiF-InF3-CNT, Li2S-LiF-InCl3-CNT, Li2S-LiF-InBr3-CNT, Li2S-LiF-InI3-CNT, Li2S-LiF-TlF3-CNT, Li2S-LiF-TlCl3-CNT, Li2S-LiF-TlBr3-CNT, Li2S-LiF-TlI3-CNT, It may include Li2S-LiF-AlF3-CNF, Li2S-LiF-AlCl3-CNF, Li2S-LiF-AlBr3-CNF, Li2S-LiF-AlI3-CNF, Li2S-LiF-GaF3-CNF, Li2S-LiF-GaCl3-CNF, Li2S-LiF-GaBr3-CNF, Li2S-LiF-GaI3-CNF, Li2S-LiF-InF3-CNF, Li2S-LiF-InCl3-CNF, Li2S-LiF-InBr3-CNF, Li2S-LiF-InI3-CNF, Li2S-LiF-TlF3-CNF, Li2S-LiF-TlCl3-CNF, Li2S-LiF-TlBr3-CNF, Li2S-LiF-TlI3-CNF, or a combination thereof.

[0078] The content of the sulfide-based positive active material included in the positive active material layer (120) may be, for example, 5 wt% to 95 wt%, 10 wt% to 90 wt%, 15 wt% to 90 wt%, 20 wt% to 90 wt%, or 30 wt% to 80 wt% of the total weight of the positive active material layer (120).

[0079] The positive active material layer (120) may additionally include, for example, a sulfide-based compound distinct from Li2S. The sulfide-based compound may be, for example, a compound containing a metal element other than Li and a sulfur element. The sulfide-based compound may be, for example, a compound containing a metal element belonging to Group 1 to Group 14 of the periodic table with an atomic weight of 10 or more and a sulfur element. The sulfide-based compound may be, for example, FeS2, VS2, NaS, MnS, FeS, NiS, CuS, or a combination thereof. By additionally including a sulfide-based compound in the positive active material layer (120), the cycle characteristics of the all-solid-state secondary battery may be further improved. The content of the sulfide-based compound distinct from Li2S included in the positive active material layer (120) 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 positive active material layer (120).

[0080]

[0081] The positive active material layer (120) may include a solid electrolyte. The solid electrolyte may be any material used as an ion-conducting material in the art, for example. The solid electrolyte may be, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof.

[0082] The solid electrolyte in the positive active material layer (120) may have an average particle size (D50) smaller than that of the solid electrolyte in the solid electrolyte layer (300). For example, the average particle size of the solid electrolyte in the positive active material layer (120) may be 100% or less, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 20% or less of the average particle size of the solid electrolyte in the solid electrolyte layer (300).

[0083] The solid electrolyte may include a sulfide-based solid electrolyte with excellent lithium ion conductivity characteristics. Sulfide-based solid electrolytes include, for example, Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (m, n are positive numbers, uppercase “Z” is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are positive numbers, uppercase “M” is one of P, Si, Ge, B, Al, Ga, In), Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), and Li 7-x PS 6-x I x It may include at least one selected from (0≤x≤2).

[0084] Sulfide-based solid electrolytes may include, for example, an argyrodite-type solid electrolyte represented by the following chemical formula 1:

[0085] <Chemical Formula 1>

[0086] Li + 12-n-x A n+ X 2- 6-x Y - x

[0087] 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. Sulfide-based solid electrolytes are, for example, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x It may be an argyrodite-type compound containing one or more selected from 0≤x≤2. The sulfide-based solid electrolyte may be an argyrodite-type compound containing one or more selected from, for example, Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0088] Sulfide-based solid electrolytes are, for example, Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), and Li 7-x PS 6-x I x It may be an argyrodite-type compound comprising one or more selected from (0≤x≤2). In particular, the sulfide-based solid electrolyte may be an argyrodite-type compound comprising one or more selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0089] Alternatively, sulfide-based solid electrolytes are Li 7-a M a PS 6-c X cIt may be an argyrodite-type compound containing (0≤a≤2, (0≤c≤2)). Here, X may be F, Br, Cl, or a combination thereof. M can be scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), or a combination thereof. there is.

[0090] The density of the azyrodite-type solid electrolyte may be 1.5 g / cc to 2.0 g / cc. By having a density of 1.5 g / cc or higher for the azyrodite-type solid electrolyte, the internal resistance of the all-solid-state battery is reduced, and defects such as penetration and short circuit of the solid electrolyte film due to lithium dendrite formation can be prevented. The elastic modulus of the solid electrolyte may be, for example, 15 GPa to 35 GPa.

[0091] The solid electrolyte in the positive active material layer (120) may be the same as or different from the solid electrolyte in the solid electrolyte layer (300).

[0092] The solid electrolyte included in the positive electrode active material layer (120) may have the same average particle size (D50) as the solid electrolyte included in the solid electrolyte layer (300). The solid electrolyte included in the positive electrode active material layer (120) may have a smaller average particle size (D50) compared to the solid electrolyte included in the solid electrolyte layer (300). For example, the average particle size (D50) of the solid electrolyte included in the positive electrode active material layer (120) 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 particle size (D50) of the solid electrolyte included in the solid electrolyte layer (300). Meanwhile, the average particle size (D50) may be the median diameter measured using a laser particle size distribution meter.

[0093] The content of the solid electrolyte in the positive active material layer may be, for example, 1% to 40% by weight of the total weight of the positive active material layer.

[0094]

[0095] The positive active material layer (120) may further include a conductive material. The conductive material may provide conductivity without causing chemical changes in the lithium-sulfur all-solid-state battery (1000), thereby increasing the conductivity of the positive active material and the solid electrolyte. The conductive material may include any material used as a conductive material in the relevant technical field without limitation. The conductive material may be, for example, a carbon-based material, a metal-based material, or a combination thereof. The metal-based material may be a metal powder, a metal fiber, or a combination thereof, but is not limited to these, and any metal-based material used as a conductive material in the relevant technical field is possible. The carbon-based material may include crystalline carbon, amorphous carbon, or a combination thereof. The carbon-based material may include, for example, one or more selected from graphite, carbon black, acetylene black, carbon nanotubes (CNT), carbon nanofibers (CNF), carbon nanobelts, carbon nanorods, and graphene. The internal resistance of the positive active material layer (120) may be reduced by the conductive material, and the cycle characteristics of the secondary battery may be further improved.

[0096] The content of the conductive material in the positive active material layer (120) may be, for example, 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight of the total weight of the positive active material layer (120). This may be used in the same sense as the content of the conductive material in the positive electrode, and may mean a ratio calculated based on the weight excluding the positive current collector in the positive electrode.

[0097]

[0098] The positive active material layer (120) may further include a binder. The binder may include a material for bonding the positive active material and conductive material contained in the positive active material layer (120) and for improving the bonding strength with the positive current collector (110). The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyethylene, etc., but is not limited to these, and any material used as a binder in the relevant technical field may be possible. The content of the binder in the positive active material layer (120) may be, for example, 0.1% to 10% by weight, 0.5% to 5% by weight, or 0.5% to 2% by weight of the total weight of the positive active material layer (120). The binder may be omitted. This can be used interchangeably with the binder content within the anode, and may refer to a ratio calculated based on the weight excluding the anode current collector within the anode.

[0099]

[0100] The positive active material layer (120) may further include additives such as fillers, coating agents, dispersants, and ion conductivity aids in addition to the positive active material, solid electrolyte, conductive material, and binder described above. Known materials generally used in electrodes of all-solid-state secondary batteries may be used as fillers, coating agents, dispersants, and ion conductivity aids that may be included in the positive active material layer (120).

[0101]

[0102] FIG. 3 is a cross-sectional view of a lithium-sulfur battery according to an exemplary embodiment of the present invention. Referring to FIG. 3, the positive layer (100) may further include a positive coating layer (CTL) provided between a positive current collector (110) and a positive active material layer (120). The positive coating layer (CTL) may be disposed directly, for example, on one or both sides of the positive current collector (110). The positive coating layer (CTL) may be coated on one or both sides of the positive current collector (110). No other layer may be disposed between the positive current collector (110) and the positive coating layer (CTL).

[0103] By placing the positive coating layer (CTL) directly on one or both sides of the positive current collector (110), the bonding strength between the positive current collector (110) and the positive active material layer (120) can be further improved. By placing the positive coating layer (CTL) between the positive current collector (110) and the positive active material layer (120), side reactions between the solid electrolyte or positive active material and the positive current collector (110) can be more effectively suppressed. For example, the positive coating layer (CTL) can prevent corrosion of the sulfide-based positive active material (e.g., Li2S) by the positive current collector (110). Consequently, the positive coating layer (CTL) can suppress the degradation of the lithium-sulfur all-solid-state battery (1000) during the charging and discharging process and improve cycle characteristics.

[0104] The thickness of the anode coating layer (CTL) is, for example, 0.01 to 20%, 0.1 to 20%, 0.5 to 20%, 1 to 20%, 1 to 15%, 1 to 10%, 2 to 8%, or 3 to 7% of the thickness of the anode current collector (110). The thickness of the anode coating layer (CTL) may be, for example, 10 nm to 5 µm, 50 nm to 5 µm, 200 nm to 4 µm, 500 nm to 3 µm, 500 nm to 2 µm, 500 nm to 1.5 µm, or 700 nm to 1.3 µm. By having the anode coating layer (CTL) have a thickness within this range, the bonding strength between the anode current collector (110) and the anode active material layer (120) is further improved, and the increase in interfacial resistance can be suppressed. The thickness of the anode coating layer (CTL) can be measured, for example, from a scanning electron microscope (SEM) image of a cross-section of the anode coating layer (CTL).

[0105] The anode coating layer (CTL) may include, for example, a carbon-based conductive material. The carbon-based conductive material included in the anode coating layer (CTL) may be selected from the conductive materials described above. The anode coating layer (CTL) may include a carbon-based conductive material identical to the conductive material (30) used in the anode active material layer (120) or the carbon-based conductive material (CA) of the first anode active material (11). By including a carbon-based conductive material, the anode coating layer (CTL) may be, for example, a conductive layer.

[0106] The positive coating layer (CTL) may additionally include, for example, a binder. By additionally including a binder in the positive coating layer (CTL), the bonding strength between the positive current collector (110) and the positive active material layer (120) can be further improved. The binder included in the positive coating layer (CTL) is, for example, a conductive binder or a non-conductive binder. The conductive binder is, for example, an ion-conducting binder and / or an electron-conducting binder. A binder having both ion conductivity and electron conductivity may belong to both an ion-conducting binder and an electron-conducting binder.

[0107] The binder included in the anode coating layer (CTL) may be selected from among the binders used in the anode active material layer (120). The anode coating layer (CTL) may include the same binder as the binder used in the anode active material layer (120). The binder included in the anode coating layer (CTL) is, for example, a fluorine-based binder. The fluorine-based binder included in the anode coating layer (CTL) is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a combination thereof. The anode coating layer (CTL) may be, for example, a binding layer containing a binder. The anode coating layer (CTL) may be, for example, a conductive layer containing a binder and a carbon-based conductive material.

[0108] The anode coating layer (CTL) can be disposed on the anode current collector (110) in a dry or wet manner, for example. The anode coating layer (CTL) can be disposed on the anode current collector (110) in a dry manner by deposition, for example, CVD, PVD, etc. The anode coating layer (CTL) can be disposed on the anode current collector (110) in a wet manner, for example, by spin coating, dip coating, etc. The anode coating layer (CTL) can be disposed on the anode current collector (110) by, for example, depositing a carbon-based conductive material onto a substrate by deposition. The dry-coated anode coating layer (CTL) may be made of a carbon-based conductive material and may not contain a binder. The anode coating layer (CTL) can be disposed on the anode current collector (110) by, for example, coating a composition comprising a carbon-based conductive material, a binder, and a solvent onto the surface of the electrode current collector and drying it. The anode coating layer (CTL) may have a single-layer structure or a multi-layer structure including multiple layers. The multi-story structure can be a 2-story structure, a 3-story structure, a 4-story structure, etc.

[0109]

[0110] solid electrolyte layer (300)

[0111] The solid electrolyte layer (300) is disposed between the positive electrode layer (100) and the negative electrode layer (200) and may include a sulfide-based solid electrolyte with excellent lithium ion conductivity characteristics. The solid electrolyte included in the solid electrolyte layer (300) may be the same as or different from any one of the materials that may be included in the solid electrolyte included in the aforementioned positive electrode active material layer (120).

[0112] In one embodiment, the solid electrolyte layer (300) may include a sulfide-based solid electrolyte. The sulfide-based solid electrolyte may be manufactured by processing starting materials, such as Li2S or P2S5, by a melt quenching method or a mechanical milling method. Additionally, heat treatment may be performed after such processing. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. Furthermore, the solid electrolyte may include sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the sulfide-based solid electrolyte materials described above. For example, the solid electrolyte may be a material containing Li2S-P2S5. When using a sulfide-based solid electrolyte material containing Li2S-P2S5 to form the solid electrolyte, the molar ratio of Li2S and P2S5 is, for example, in the range of Li2S : P2S5 = 50 : 50 to 90 : 10.

[0113] Sulfide-based solid electrolytes are, for example, Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), and Li 7-x PS 6-x I x It may be an argyrodite-type compound comprising one or more selected from (0≤x≤2). In particular, the sulfide-based solid electrolyte may be an argyrodite-type compound comprising one or more selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0114] Alternatively, sulfide-based solid electrolytes are Li 7-a M a PS 6-c X cIt may be an argyrodite-type compound containing (0≤a≤2, (0≤c≤2)). Here, X may be F, Br, Cl, or a combination thereof. M can be scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), or a combination thereof. there is.

[0115] The density of the azyrodite-type solid electrolyte may be 1.5 g / cc to 2.0 g / cc. Since the azyrodite-type solid electrolyte has a density of 1.5 g / cc or higher, the internal resistance of the all-solid-state battery is reduced, and defects such as penetration and short circuit of the solid electrolyte film due to lithium dendrite formation can be prevented. The elastic modulus of the solid electrolyte is, for example, 15 GPa to 35 GPa.

[0116] The solid electrolyte layer (300) may further include a binder. The binder included in the solid electrolyte layer (300) is, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these. The binder of the solid electrolyte layer (300) may be the same as or different from the binder included in the positive electrode active material layer (120) or the binder included in the coating layer (220).

[0117] Meanwhile, although not shown, a carbon layer may be further included to improve adhesion between the coating layer (220) and the solid electrolyte layer (300).

[0118]

[0119] cathode layer (200)

[0120] Referring to FIG. 1, a lithium-sulfur all-solid-state battery (1000) according to one embodiment may include a negative electrode layer (200) comprising a negative electrode current collector (210) and a coating layer (220) disposed on the negative electrode current collector (210).

[0121] The negative electrode layer (200) may include a negative electrode current collector (210) and a coating layer (220) on the negative electrode current collector (210). The negative electrode current collector (210) may provide a reference surface on which the coating layer (220) is placed. The negative electrode current collector (210) may include, for example, a material that does not react with lithium, that is, does not form any alloys or compounds with lithium. For example, the negative electrode current collector (210) may include at least one metal selected from the group consisting of copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni). The thickness of the negative electrode current collector (210) may be 1 μm to 20 μm, more specifically 5 μm to 15 μm, and more specifically 7 μm to 10 μm.

[0122] The negative current collector (210) may be composed of one of the metals described above, or may include an alloy of two or more metals or a coating material. The negative current collector (210) may, for example, have a plate-like or foil-like shape. Meanwhile, in one embodiment, the negative current collector (210) may be omitted.

[0123] Although not illustrated, a negative current collector (210) according to one embodiment may include 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. By including an insulating thermoplastic polymer in the base film, the base film may soften or liquefy upon a short circuit, thereby blocking battery operation and suppressing a sudden 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 current collector (210) 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 current collector (210), refer to the positive electrode current collector (110) described above. By having the negative electrode current collector (210) have this structure, the weight of the negative electrode layer (200) can be reduced, and consequently, the energy density of the lithium-sulfur all-solid-state battery (1000) can be improved.

[0124]

[0125] FIG. 4 is a perspective view of a cathode according to one embodiment of the present invention.

[0126] Referring to FIG. 4, the cathode layer (200) may include a cathode current collector (210) and a coating layer (220). The coating layer (220) may include a first coating layer (221) disposed on the cathode current collector and a second coating layer (222) disposed on the first coating layer (221).

[0127] FIG. 5 is an enlarged view of the M region of FIG. 4, a schematic diagram showing the cross-section of the first coating layer (221) and the second coating layer (222).

[0128] Referring to FIG. 5, the first coating layer (221) may include a first carbon-based material (CP1) and a first metal (MP1), and the second coating layer (222) may include a second carbon-based material (CP1) and a second metal (MP2).

[0129] Referring to FIGS. 4 and 5, the coating layer (220) can be configured to allow lithium metal to grow between the lithium-sulfur all-solid-state battery (1000) and the negative current collector (210) during charging. The coating layer (220) can serve as a protective layer for the lithium metal and simultaneously suppress the precipitation and growth of lithium dendrites.

[0130] In this specification, “coating layer (220)” may mean including both the first coating layer (221) and the second coating layer (222).

[0131] The coating layer (220) may include metal and carbon. The first coating layer (221) may include a first carbon-based material (CP1) and a first metal (MP1), and the second coating layer (222) may include a second carbon-based material (CP2) and a second metal (MP2).

[0132] In one embodiment, the first carbon-based material (CP1) and the second carbon-based material (CP2) may each have a particle shape. The average particle size (D50) of the first carbon-based material (CP1) and the second carbon-based material (CP2) may be 10 nm to 1 µm. For example, the average particle size (D50) of the first carbon-based material (CP1) and the second carbon-based material (CP2) may be 10 nm or more, 20 nm or more, or 30 nm or more. For example, the average particle size (D50) of the first carbon-based material (CP1) and the second carbon-based material (CP2) may be 1 µm or less, 100 nm or less, 70 nm or less, or 50 nm or less.

[0133] If the average particle size (D50) of each of the first carbon-based material (CP1) and the second carbon-based material (CP2) satisfies the range described above, the volume change of the battery during charging and discharging can be minimized, and a lithium-sulfur all-solid-state battery with a long lifespan can be provided.

[0134] Each of the first carbon-based material (CP1) and the second carbon-based material (CP2) may have a porous structure. For example, the BET specific surface area of ​​each of the first carbon-based material (CP1) and the second carbon-based material (CP2) is 5 m² 2 / g to 1000m 2 / g, or 30m 2 / g to 100m 2 It can be / g. For example, the BET specific surface area of ​​a carbonaceous material (CCM) is 5m² 2 / g or more, 10m 2 / g or more, 20m 2 / g or more, 30m 2 / g or more, 40m 2 / g or more, 50m 2 / g or more, 60m 2 / g or more, 100m 2 / g or more, 200m 2 / g or more, 300m 2 / g or more, or 400m 2 It can be greater than / g. For example, the BET specific surface area of ​​a carbonaceous material (CCM) is 1000 m² 2 / g or less, 900m 2 / g or less, 800m 2 / g or less, 700m 2 / g or less, 600m 2 / g or less, 500m 2 / g or less, 400m 2 / g or less, 300m 2 / g or less, 200m 2 / g or less, 100m 2 / g or less, 90m 2 / g or less, 80m 2 / g or less, or 70m 2 It may be less than / g.

[0135] If the BET specific surface area of ​​each of the first carbon-based material (CP1) and the second carbon-based material (CP2) satisfies the range described above, the volume change of the battery during charging and discharging can be minimized, and a lithium-sulfur all-solid-state battery with a long lifespan can be provided.

[0136] The first carbon-based material (CP1) and the second carbon-based material (CP2) may be different or identical. For example, each of the first carbon-based material (CP1) and the second carbon-based material (CP2) may include carbon black, acetylene black, furnace black, ketjen black, graphene, and combinations thereof.

[0137] The first metal (MP1) and the second metal (MP2) may be different or the same. Each of the first metal (MP1) and the second metal (MP2) may include at least one of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof.

[0138] The average particle size of each of the first metal (MP1) and the second metal (MP2) may be 5 nm to 300 nm. For example, the average particle size (PTS) of each of the first metal (MP1) and the second metal (MP2) may be 5 nm or more, or 10 nm or more. For example, the average particle size of each of the first metal (MP1) and the second metal (MP2) may be 300 nm or less, 200 nm or less, or 100 nm or less. If the average particle size of the first metal (MP1) and the second metal (MP2) satisfies the range described above, lithium ions can easily move toward the negative electrode current collector (210) during charging and discharging of the lithium-sulfur all-solid-state battery.

[0139] According to embodiments of the present invention, the average particle size of each of the first metal (MP1) and the second metal (MP2) may be relatively small. The average particle size of the first metal (MP1) and the second metal (MP2) may refer to the average size of the metal particles (MP1, MP2) present in the coating layer (220). The average particle size may be defined as the average length of the major axis and minor axis measured by randomly selecting 100 metal particles in the coating layer (220) in an electron microscope image. This average particle size may be calculated as a geometric average or an arithmetic average.

[0140] In one embodiment, the first coating layer (221) and the second coating layer (222) may comprise a mixture of carbon black and silver (Ag).

[0141] The mass ratio of the first carbon-based material (CP1) and the first metal (MP1) in the first coating layer (221) may be, for example, 1:10 to 1:2.5, 1:8 to 1:2.5, or 1:5 to 1:2.25.

[0142] The mass ratio of the second carbon-based material (CP2) and the second metal (MP2) in the second coating layer (222) may be, for example, 1:2 to 1:1, or 1:1.75 to 1:1.25.

[0143] The content of the first metal (MP1) in the first coating layer (221) may be less than the content of the second metal (MP2) in the second coating layer (222). That is, the metal content in the second coating layer (222), which is closer to the solid electrolyte layer (300), may be greater than that in the first coating layer (221), which is the coating layer in contact with the negative current collector (210).

[0144] If the metal content is high in the second coating layer (222) that the lithium ions moving from the anode come into contact with first, the diffusion rate of lithium ions in the cathode can be improved and uniform lithium electrodeposition can be induced. In addition, by reducing the interfacial resistance, the overvoltage generated during lithium deposition can be reduced.

[0145] In addition, since the metal content in the first coating layer (221) is lower than that in the second coating layer (222), it is possible to offset the disadvantages that may occur when the metal content is excessive. The disadvantages that may occur when the metal content in the coating layer (220) is excessive include the fact that the structure of the electrode becomes unstable due to a large change in volume during charging and discharging, or that the weight of the electrode increases.

[0146] The coating layer (220) may have a smaller thickness compared to the positive active material layer (120). The thickness of the coating layer (220) may be, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive active material layer (120). In this case, the thickness of the coating layer (220) may refer to the sum of the thickness of the first coating layer (TK1) and the thickness of the second coating layer (TK2).

[0147] The total thickness of the coating layer (220) may be, for example, 1 µm to 25 µm, or 5 µm to 20 µm, or 5 µm to 15 µm. If the thickness of the coating layer (220) is excessively thin, lithium dendrites formed between the coating layer (220) and the negative electrode current collector (210) may cause the coating layer (220) to collapse, thereby degrading the cycle characteristics of the lithium-sulfur all-solid-state battery (1000). If the thickness of the coating layer (220) is excessively increased, the energy density of the lithium-sulfur all-solid-state battery (1000) decreases, and the internal resistance of the lithium-sulfur all-solid-state battery (1000) caused by the coating layer (220) increases, which may degrade the cycle characteristics of the cell. The total thickness of the coating layer (220) may refer to the sum of the thickness of the first coating layer (TK1) and the thickness of the second coating layer (TK2).

[0148] The thickness of the first coating layer (TK1) and the thickness of the second coating layer (TK2) may be the same. The thickness of the first coating layer (TK1) may be thicker than the thickness of the second coating layer (TK2).

[0149] The thickness of the first coating layer (TK1) may be, for example, 1 μm to 15 μm, or 1 μm to 10 μm. The thickness of the second coating layer (TK2) may be, for example, 1 μm to 10 μm, or 1 μm to 8 μm.

[0150] If the thickness of the first coating layer (TK1) and the thickness of the second coating layer (TK2) fall outside the above range, or if the thickness of the second coating layer (TK2) is greater than the thickness of the first coating layer (TK1), it may cause structural defects due to volume expansion. Additionally, the weight of the battery may increase as the second coating layer (222), which has a high metal content, is thicker. If the thickness of the second coating layer (TK2) is greater than the thickness of the first coating layer (TK1), the rate characteristics may decrease.

[0151] The coating layer (220) may further include a binder. Each of the first coating layer (221) and the second coating layer (222) may further include a binder. The binder may include a water-based binder, an organic-based binder, or a combination thereof. The binder may include, for example, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer comprising ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or a combination thereof. The binder is not limited thereto as long as it is readily selectable by a person skilled in the art.

[0152] The coating layer (220) may further include other additives in addition to those described above. The coating layer (220) may further include, for example, at least one additive selected from the group consisting of fillers, coating agents, dispersants, and ion-conducting aids.

[0153] The fillers, coating agents, dispersants, ion-conducting aids, etc. that may be included in the coating layer (220) may include known materials generally used by those skilled in the art.

[0154] Meanwhile, although not shown, a carbon layer may be further included to improve adhesion between the coating layer (220) and the solid electrolyte layer (300).

[0155] The first coating layer (221) and the second coating layer (222) can be verified through methods such as cross-sectional analysis using a scanning electron microscope (SEM). Specifically, the metal content within the first coating layer (221) and the second coating layer (222) can be verified by comparing them. Through cross-sectional analysis, the first coating layer (221), the second coating layer (222), and the boundary between them can be defined.

[0156] A region within the coating layer (220) in which the metal content is smaller than a predetermined content can be defined as the first coating layer (221). A region within the coating layer (220) in which the metal content is larger than a predetermined content can be defined as the second coating layer (222). For example, a region in which the mass ratio of carbon-based material to metal is greater than 2.2 can be defined as the first coating layer (221). A region in which the mass ratio of carbon-based material to metal is less than 2.2 can be defined as the second coating layer (222).

[0157] However, if the battery undergoes charging and discharging after manufacturing, the metal within the coating layer (220) may move toward the current collector. Since the metal content within the coating layer (220) may change after charging and discharging compared to the initial state of the battery, it may not be easy to distinguish between the first coating layer (221) and the second coating layer (222). In a battery that has undergone a certain number of cycles or more after manufacturing, the first coating layer (221) and the second coating layer (222) can be identified through another method described later.

[0158]

[0159] FIGS. 6 and 7 are cross-sectional views of a lithium-sulfur all-solid-state battery (1000) according to another embodiment of the present invention.

[0160] Referring to FIGS. 6 and 7, the lithium-sulfur all-solid-state battery (1000) may further include a lithium metal layer (230) disposed between a negative electrode current collector (210) and a coating layer (220) upon charging. The lithium metal layer (230) may include lithium or a lithium alloy. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, etc., but is not limited to these, and any alloy used as a lithium alloy in the relevant technical field may be possible.

[0161] The lithium metal layer (230) may include metal particles (MP1, MP2) that were present on the first coating layer (221) and the second coating layer (222). Within the coating layer (220), the metal particles (MP1, MP2) may diffuse toward the negative current collector (210) during the charging / discharging process of the battery. Additionally, if the metal particles (MP1, MP2) remain irreversibly on the negative current collector (210) after diffusing due to charging / discharging, a pore may be formed in the space where the original metal particles (MP1, MP2) were located.

[0162] Therefore, before battery operation, the first coating layer (221) and the second coating layer (222) can be distinguished by their metal content, but once the lithium metal layer (230) is formed, it may not be easy to distinguish the first coating layer (221) and the second coating layer (222) by their metal content due to the movement of metal particles.

[0163] That is, in the battery after operation, only the content of metal particles (MP1, MP2) of the first coating layer (221) and the second coating layer (222) should be measured; in addition to the metal particles (MP1, MP2), the pores formed in the space where the metal particles were located must also be taken into account so that the actual metal content of the battery before operation can be inferred. FIG. 8 is an enlarged view of the N region of FIG. 7 and is a schematic diagram showing the metal distribution within the battery after charging and discharging. Specifically, FIG. 8 is a schematic diagram showing the results of a post-use analysis of the coating layer (220) within the cell after 10 charge / discharge cycles following the formation process.

[0164] Referring to FIG. 8, if the first metal (MP1) in the first coating layer (221) irreversibly diffuses toward the negative current collector (210) or exists in the form of a lithium alloy in the lithium metal layer (230), a first pore (POR1) may be formed at the original location of the first metal (MP1). Likewise, in the second coating layer (222), a second pore (POR2) ​​may be formed at the location where the second metal (MP1) was.

[0165] That is, the presence of the first metal (MP1) prior to operation can be indirectly confirmed from the first pore (POR1) formed in the first coating layer (221) after the operation of the all-solid-state battery (1000). The presence of the second metal (MP2) prior to operation can be indirectly confirmed from the second pore (POR2) ​​formed in the second coating layer (222) after the operation of the all-solid-state battery (1000).

[0166] FIG. 9 is a schematic diagram of Comparative Example 1 or 2 having a coating layer (220) formed as a single layer. Specifically, it is a schematic diagram showing a cross-section of a battery having a coating layer (220) formed as a single layer after undergoing 10 or more charge / discharge cycles after the formation process.

[0167] Referring to FIG. 9, a battery having a single-layer coating layer (220) may also form pores (POR3) by irreversibly moving metal particles (MP3) through charging and discharging. The appearance of the pores formed in a battery having a single-layer coating layer (220) as in FIG. 9 and in a battery according to the present invention as in FIG. 8 may differ. That is, when the total metal content of the entire coating layer is the same, the appearance of the pores formed may differ when the coating layer is manufactured as a single layer compared to when the coating layer is manufactured by dividing it into a first coating layer (221) with a low metal content and a second coating layer (222) with a high metal content.

[0168] When inferring the existing metal content from the first pore (POR1) and the second pore (POR2), the number of pores or the pore area may be used. For example, the pore area can be analyzed using a program such as Image J. However, it is not limited to methods that can be appropriately selected by a person skilled in the art. In addition, this analysis can be statistically calculated by taking multiple scanning electron microscope (SEM) images.

[0169]

[0170] lithium metal layer (230)

[0171] Referring to FIGS. 6 and 7, a lithium-sulfur all-solid-state battery (1000) according to one embodiment may further include a lithium metal layer (230) disposed between a negative electrode current collector (210) and a coating layer (220) upon charging. The thickness of the lithium metal layer (230) may be further increased upon charging of the unit cell (CEL).

[0172] The lithium metal layer (230) may include lithium or a lithium alloy. Since the lithium metal layer (230) is a metal layer containing lithium, it may function as, for example, a lithium reservoir. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, but is not limited to these; any alloy used as a lithium alloy in the relevant technical field may be possible. The lithium metal layer (230) may be composed of one of these alloys or lithium, or may be composed of various types of alloys. The lithium metal layer (230) may be, for example, a plated layer. The lithium metal layer (230) may be deposited between the coating layer (220) and the negative current collector (210) during the charging process of the lithium-sulfur all-solid-state battery (1000), for example.

[0173] The thickness of the lithium metal layer (230) is not particularly limited, but, for example, it may be 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the thickness of the lithium metal layer (230) is excessively thin, it may be difficult for the lithium metal layer (230) to perform the role of a lithium reservoir. If the thickness of the lithium metal layer (230) is excessively thick, the mass and volume of the lithium-sulfur all-solid-state battery (1000) increase, and the cycle characteristics of the lithium-sulfur all-solid-state battery (1000) may actually deteriorate.

[0174] In another embodiment, a lithium metal layer (230) within the negative electrode layer (200) may be provided, for example, between the negative electrode current collector (210) and the coating layer (220) before assembly of the lithium-sulfur all-solid-state battery (1000). When the lithium metal layer (230) is placed between the negative electrode current collector (210) and the coating layer (220) before assembly of the lithium-sulfur all-solid-state battery (1000), the lithium metal layer (230) acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil may be placed between the negative electrode current collector (210) and the coating layer (220) before assembly of the lithium-sulfur all-solid-state battery (1000).

[0175] When a lithium metal layer (230) is deposited by charging after assembly of the lithium-sulfur all-solid-state battery (1000), the energy density of the lithium-sulfur all-solid-state battery (1000) can be increased because the lithium metal layer (230) is not included during assembly of the lithium-sulfur all-solid-state battery (1000). When charging the lithium-sulfur all-solid-state battery (1000), it can be charged beyond the charging capacity of the coating layer (220). That is, the coating layer (220) is overcharged. At the beginning of charging, lithium can be absorbed in the coating layer (220). When charging beyond the capacity of the coating layer (220), lithium can be deposited, for example, between the coating layer (220) and the negative electrode current collector (210). A lithium metal layer (230) can be formed by the deposited lithium.

[0176] The lithium metal layer (230) can be composed mainly of lithium (i.e., metallic lithium). During discharge, the lithium in the lithium metal layer (230) can be ionized and move to the positive electrode layer (100). In other words, lithium can be used as a negative electrode active material in the lithium-sulfur all-solid-state battery (1000). In addition, since the coating layer (220) covers the lithium metal layer (230), the coating layer (220) can protect the lithium metal layer (230) and simultaneously suppress the precipitation growth of lithium dendrites. Therefore, the coating layer (220) can suppress short circuits and capacity degradation of the lithium-sulfur all-solid-state battery (1000) and improve the cycle characteristics of the lithium-sulfur all-solid-state battery (1000).

[0177] When a lithium metal layer (230) is formed by charging after assembly of a lithium-sulfur all-solid-state battery (1000), the negative electrode layer (200), that is, the negative electrode current collector (210) and the coating layer (220) and the region between them may be a Li-free region that does not contain lithium (Li) in the initial state or after complete discharge of the lithium-sulfur all-solid-state battery (1000).

[0178]

[0179] FIG. 3 is a cross-sectional view of a lithium-sulfur battery according to an exemplary embodiment of the present invention. Referring to FIG. 3, the negative electrode layer (200) may further include a thin film (TFL) provided between the negative electrode current collector (210) and the coating layer (220). The thin film (TFL) may be provided on one surface of the negative electrode current collector (210) to form an alloy with lithium.

[0180] The thin film (TFL) may include, for example, an element capable of forming an alloy with lithium. Elements capable of forming an alloy with lithium include, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., but are not necessarily limited to these, and any element capable of forming an alloy with lithium in the relevant technical field is possible. The thin film (TFL) may be composed of one of these metals or may be composed of an alloy of various types of metals.

[0181] By placing the thin film (TFL) on one side of the negative electrode current collector (210), the deposition pattern of the lithium metal layer (230) deposited between, for example, the thin film (TFL) and the coating layer (220) is further flattened, and the cycle characteristics of the lithium-sulfur all-solid-state battery (1000) can be further improved.

[0182] The thickness of the thin film (TFL) may be, 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 (TFL) is less than 1 nm, it may be difficult to perform the function provided by the thin film (TFL). If the thickness of the thin film (TFL) is excessively thick, the thin film (TFL) itself absorbs lithium, and the amount of lithium precipitated in the negative electrode layer (200) decreases, which lowers the energy density of the lithium-sulfur all-solid-state battery (1000) and may lower the cycle characteristics of the lithium-sulfur all-solid-state battery (1000). The thin film (TFL) may be formed on the negative electrode current collector (210) by, for example, vacuum deposition, sputtering, plating, etc., but is not necessarily limited to these methods, and any method capable of forming the thin film (TFL) in the relevant technical field may be possible.

[0183]

[0184] The present invention will be explained in more detail below through examples. However, these examples are intended to illustrate the invention and the scope of the invention is not limited to these examples.

[0185]

[0186] Example 1: First coating layer (metal:carbon=1:3) - Second coating layer (metal:carbon=2:3) / same thickness. A SUS foil with a thickness of 10 μm was prepared as a cathode current collector. Carbon black (CB) with a primary particle size of about 30 nm and silver (Ag) particles with an average particle diameter of about 60 nm were prepared.

[0187] 4 g of a mixed powder of carbon black (CB) and silver (Ag) particles mixed in a weight ratio of 3:1 was placed in a container, and 4 g of an NMP solution containing 7 wt% of a PVDF binder (Kureha # 9300) was added to prepare a mixed solution. A slurry for preparing a first coating layer was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution.

[0188] A slurry for manufacturing a second coating layer was prepared in the same manner as above by changing the weight ratio of carbon black (CB) and silver (Ag) particles to 3:2.

[0189] The slurry for manufacturing the first coating layer 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. The slurry for manufacturing the second coating layer was applied thereon, and the same drying process was repeated. A laminate in which the slurry for manufacturing the first coating layer and the slurry for manufacturing the second coating layer were laminated on a current collector was cold-roll-pressed to flatten the surface, thereby manufacturing a cathode having a structure of a second coating layer / first coating layer / cathode current collector.

[0190] The thickness of the first coating layer and the second coating layer was the same, and the total thickness of the coating layer was about 10 μm. The area of ​​the first coating layer and the second coating layer and the cathode current collector was the same.

[0191] Example 2: 1st coating layer (metal:carbon=1:4) - 2nd coating layer (metal:carbon=2:3) / Same thickness

[0192] A cathode was prepared in the same manner as in Example 1, except that carbon black (CB) and silver (Ag) particles were mixed in a mass ratio of 4:1 in a slurry for preparing the first coating layer.

[0193] Example 3: 1st coating layer (metal:carbon=1:3) - 2nd coating layer (metal:carbon=2:3) / 1st coating layer : 2nd coating layer thickness = 3:2

[0194] A cathode was prepared in the same manner as in Example 1, except that the thickness of the first coating layer was 6 μm and the thickness of the second coating layer was 4 μm.

[0195] Comparative Example 1: Coating layer (Metal:Carbon=2:3) / Same thickness

[0196] A single-layer coating layer was prepared using only the slurry for preparing the second coating layer of Example 1. The cathode was prepared in the same manner as in Example 1. The thickness of the coating layer was approximately 10 μm.

[0197] Comparative Example 2: Coating layer (Metal:Carbon=1:3) / Same thickness

[0198] A single-layer coating layer was prepared using only the slurry for preparing the first coating layer of Example 1. The cathode was prepared in the same manner as in Example 1. The thickness of the coating layer was approximately 10 μm.

[0199] Comparative Example 3: 1st coating layer (metal:carbon=2:3) - 2nd coating layer (metal:carbon=1:3) / Same thickness

[0200] In Example 1, the positions of the first coating layer and the second coating layer were changed. Otherwise, the cathode was prepared in the same manner as in Example 1. The total thickness of the coating layer was approximately 10 μm.

[0201] Comparative Example 4: 1st coating layer (metal:carbon=1:3) - 2nd coating layer (metal:carbon=2:1) ​​ / Same thickness

[0202] A cathode was prepared in the same manner as in Example 1, except that carbon black (CB) and silver (Ag) particles were mixed in a mass ratio of 1:2 in a slurry for preparing the second coating layer.

[0203] However, in the case of Comparative Example 4, it was confirmed that the formation of the second coating layer was not easy due to the aggregation of metal particles in the second coating layer. Accordingly, Comparative Example 4 was excluded from the following evaluation examples.

[0204] Table 1 below summarizes the coating layer compositions of the above examples and comparative examples.

[0205] Coating layer Thickness of 1st coating layer : Thickness of 2nd coating layer 1st coating layer (Metal : Carbon) 2nd coating layer (Metal : Carbon) Example 1 1:32:31:1 Example 2 1:42:31:1 Example 3 1:32:33:2 Comparative Example 12:31:1 Comparative Example 21:31:1 Comparative Example 32:31:31:1 Comparative Example 4 1:32:11:1

[0206] Evaluation Example 1 - Measurement of overvoltage due to lithium electrodeposition

[0207] Except for Comparative Example 4, in which the coating layer formation was not easy, the overvoltage due to lithium electrodeposition was measured for the cathodes of Examples 1 to 3 and Comparative Examples 1 to 3.

[0208] First, a uniaxial pressurized cell (half cell) comprising the cathodes of Examples 1 to 3 and Comparative Examples 1 to 3, a lithium metal counter electrode with a thickness of about 100 μm, and a Li6PS5Cl solid electrolyte which is an argyrodite-type crystal was prepared as a torque cell structure. Specifically, 150 mg of Li6PS5Cl solid electrolyte was placed in a 13 mm PEEK mold and pressurized at 300 MPa for 30 seconds to form a pellet, and the aforementioned cathode and lithium metal counter electrode were placed on each side of the pellet and pressurized at 300 MPa for 2 minutes to prepare the cell.

[0209] After connecting the cell manufactured above to an ammeter, the cell was charged at room temperature, and the initial potential due to charging was measured. The overpotential due to lithium electrodeposition refers to the value obtained by subtracting the thermodynamic equilibrium potential value from the measured initial potential value, and this is shown in Table 2 below.

[0210] Overvoltage (mV) due to lithium electrodeposition Example 113.6 Example 214.0 Example 314.2 Comparative Example 119.2 Comparative Example 222.8 Comparative Example 320.7

[0211] Looking at Table 2, it can be seen that the lithium electrodeposition overvoltage of the examples is lower than that of the comparative examples. This is believed to be because the diffusion or rearrangement rate of lithium during initial charging in a cathode with a structure similar to that of the examples increases, thereby increasing the diffusion creep rate of lithium within the cathode.

[0212] Evaluation Example 2 - High Rate Characteristic Evaluation

[0213] High-rate characteristics were evaluated for cells containing the cathodes of Examples 1 to 3 and Comparative Examples 1 to 3, excluding Comparative Example 4, in which the formation of the coating layer was not easy. The specific manufacturing method of the cell is as follows.

[0214] (Manufacturing of the anode layer)

[0215] A metal halide salt mixture was prepared by mixing LiI powder and AlI3 powder in a mass ratio of 10:30. A Li2S-LiI-AlI3 composite was prepared by mixing Li2S and the prepared metal halide salt powder in a mass ratio of 40:20 and then performing ball milling. The milling conditions were 25°C and 600 rpm for 10 hours. The milling energy applied to the sample during milling was 28 G. The composite and CNF were mixed in a weight ratio of 60:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI-AlI3-CNF composite. The milling conditions were 25°C and 600 rpm for 10 hours. The milling energy applied to the sample during milling was 28 G. The Li2S-LiI-AlI3-CNF composite was used as the cathode active material. Li6PS5Cl, an argyrodite-type crystal (D50=3.0 μm, crystalline), was prepared as a solid electrolyte. PTFE was prepared as a binder. These materials were mixed in a weight ratio of positive active material : solid electrolyte : binder = 70 : 30 : 1.2 to prepare a positive composite. The positive composite was obtained by dry mixing using a ball mill.

[0216] An anode was manufactured by placing the anode composite on one side of an anode current collector made of aluminum foil coated with carbon on one side and performing a plate press at a pressure of 200 MPa for 10 minutes. The thickness of the anode was approximately 120 μm. The thickness of the anode active material layer was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm. The area of ​​the anode active material layer and the anode current collector were the same.

[0217] (Preparation of solid electrolyte layer)

[0218] An acrylic binder (SX-A334, Zeon Co., Ltd.) was added to octyl acetate to prepare a 4 wt% binder solution. The prepared acrylic binder solution was added to a Li6PS5Cl solid electrolyte (D50=3 μm, crystalline), which is an argyrodite-type crystal, and mixed using a Thinky mixer to prepare a slurry. The slurry contained 1.5 parts by weight of the acrylic binder per 98.5 parts by weight of the solid electrolyte. The prepared slurry was applied onto a nonwoven fabric using a bar coater and dried in a convection oven at 80°C for 10 minutes to obtain a laminate. The obtained laminate was vacuum dried at 70°C for 2 hours.

[0219] (Manufacturing of all-solid-state batteries)

[0220] A laminate was prepared by placing a solid electrolyte layer between the anode layer and the cathode layer. An all-solid-state secondary battery was manufactured by isotactic-pressing the prepared laminate at 80°C at a pressure of 500 MPa for 30 minutes. This pressurization process sinters the solid electrolyte layer, thereby improving battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 μm.

[0221] (evaluation)

[0222] Cells manufactured by the above method were evaluated in the range of 1.0 to 2.8 V under conditions of 45 ℃. Discharge rate characteristics were evaluated through a process of 0.05 C charge / discharge, 0.05 C charge followed by 0.5 C discharge after one formation at 0.05 C. Rate characteristics (%) were calculated and expressed as 0.5 C discharge capacity / 0.05 C discharge capacity. Since the anodes were manufactured under identical conditions, the initial capacity is the same. Therefore, high rate characteristics were confirmed by measuring the discharge capacity under the 0.5 C condition.

[0223] 0.5 C Discharge Rate (%) Example 185.7 Example 284.8 Example 384.2 Comparative Example 180.1 Comparative Example 277.2 Comparative Example 378.9

[0224] The results are as shown in Table 3 above. It can be confirmed that the discharge rate characteristics of Examples 1 to 3 are relatively superior. On the other hand, Comparative Examples 1 to 3 have lower discharge rate characteristics compared to the Examples, which is attributed to the application of an Ag / C double layer with a controlled Ag ratio in the Examples, which improves the conductivity of lithium ions and relatively reduces the interfacial resistance.

[0225] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

Claims

1. A negative current collector, a first coating layer disposed on the negative current collector, and a second coating layer disposed on the first coating layer, wherein The first coating layer comprises a first metal and a first carbon-based material, and The second coating layer comprises a second metal and a second carbon-based material, and Each of the first and second metals is a lithium-affinity metal capable of forming an alloy with lithium, and The mass ratio of the first metal and the first carbon-based material is 1:10 to 1:2.5, and The mass ratio of the second metal and the second carbon-based material is 1:2 to 1:1, Negative electrode for lithium-sulfur battery.

2. In Paragraph 1, Each of the first metal and the second metal comprises at least one of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof. Negative electrode for lithium-sulfur battery.

3. In Paragraph 1, Each of the above-mentioned first carbon-based material and second carbon-based material comprises carbon black, acetylene black, furnace black, Kettjen black, graphene, or a combination thereof. Negative electrode for lithium-sulfur battery.

4. In Paragraph 1, Each of the first coating layer and the second coating layer further comprises a binder, Negative electrode for lithium-sulfur battery.

5. In Paragraph 4, The above binder comprises a water-based binder, an organic binder, or a combination thereof. Negative electrode for lithium-sulfur battery.

6. In Paragraph 4, The above binder comprises polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer comprising ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or a combination thereof. Negative electrode for lithium-sulfur battery.

7. In Paragraph 1, The thickness of the first coating layer is the same as the thickness of the second coating layer. Negative electrode for lithium-sulfur battery.

8. In Paragraph 1, The thickness of the first coating layer is thicker than the thickness of the second coating layer. Negative electrode for lithium-sulfur battery.

9. In Paragraph 1, The thickness of the first coating layer is 1 μm to 15 μm, and The thickness of the second coating layer is 1 μm to 10 μm, Negative electrode for lithium-sulfur battery.

10. Anode; A cathode comprising a cathode current collector, a first coating layer disposed on the cathode current collector, and a second coating layer disposed on the first coating layer; and A solid electrolyte layer disposed between the anode and the cathode, wherein The first coating layer comprises a first metal and a first carbon-based material, and The second coating layer comprises a second metal and a second carbon-based material, and Each of the first and second metals is a lithium-affinity metal capable of forming an alloy with lithium, and The mass ratio of the first metal and the first carbon-based material is 1:10 to 1:2.5, and The mass ratio of the second metal and the second carbon-based material is 1:2 to 1:1, Lithium-sulfur battery.

11. In Paragraph 10, Each of the first metal and the second metal comprises at least one of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof. Lithium-sulfur battery.

12. In Paragraph 10, Each of the above-mentioned first carbon-based material and second carbon-based material comprises carbon black, acetylene black, furnace black, Kettjen black, graphene, or a combination thereof. Lithium-sulfur battery.

13. In Paragraph 10, The thickness of the first coating layer is the same as the thickness of the second coating layer. Lithium-sulfur battery.

14. In Paragraph 10, The thickness of the first coating layer is thicker than the thickness of the second coating layer. Lithium-sulfur battery.

15. In Paragraph 10, The thickness of the first coating layer is 1 μm to 15 μm, and The thickness of the second coating layer is 1 μm to 10 μm, Lithium-sulfur battery.

16. In Paragraph 10, The region between the negative current collector of the above-mentioned negative electrode and the first coating layer is a Li-free region that does not contain lithium (Li). Lithium-sulfur battery.

17. In Paragraph 10, The above-mentioned negative current collector comprises at least one of copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or a combination thereof. Lithium-sulfur battery.

18. In Paragraph 10, The thickness of the above-mentioned cathode current collector is 1 μm to 20 μm, Lithium-sulfur battery.

19. In Paragraph 10, The above solid electrolyte layer is Li + 12-n-x A n+ X 2- 6-x Y - x It comprises an argyrodite-type sulfide-based solid electrolyte represented by (1≤n≤5, 0≤x≤2), and The above A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, Ta, or a combination thereof, and The above X is S, Se, Te, or a combination thereof, and The above Y is Cl, Br, I, F, CN, OCN, SCN, N3, or a combination thereof, Lithium-sulfur battery.

20. In Paragraph 10, Each of the first metal and the second metal comprises at least one of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof. Lithium-sulfur battery.

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