Positive electrode active material for lithium-sulfur battery, positive electrode comprising same, and manufacturing method therefor

Abstract

The present invention relates to a positive electrode active material. The positive electrode active material may include lithium sulfide, an ion-conductive salt, and a carbon-based material. More specifically, the lithium sulfide may include at least one of Li2Sn (1≤n≤8, where n is an integer), and the ion-conductive salt may include a lithium salt. The positive electrode active material may have a single-particle form in which the lithium sulfide, the ion-conductive salt, and the carbon-based material are composited.

Description

Anode active material for lithium-sulfur batteries, a cathode including the same, and a method for manufacturing the same.

[0001] This is about lithium-sulfur batteries.

[0002]

[0003] Lithium-sulfur batteries are batteries that use sulfur-based materials as the cathode active material. Sulfur, the main material, is abundant in resources and has a low weight per atom. Technological development is underway for lithium-sulfur batteries, which theoretically possess a higher energy density compared to lithium-ion batteries, which have a relatively low energy density relative to their weight.

[0004] In a lithium-sulfur battery, when discharged, lithium releases electrons and is oxidized as it ionizes into lithium cations, while the sulfur-based material, which is the positive electrode active material, is reduced as it accepts electrons. Meanwhile, the sulfur-based material is converted into a sulfur anion form through a reduction reaction.

[0005] Lithium cations generated by the oxidation reaction of lithium are transferred to the anode through the electrolyte, and sulfur-based compounds combine with sulfur anions generated by the reduction reaction to form salts. Before discharge, sulfur has a cyclic S8 structure, and through the reduction reaction, lithium polysulfide (Li2S) is formed. x The battery is driven through a shuttle mechanism that converts to , 1≤x≤8).

[0006]

[0007] The problem that the present invention aims to solve is to provide a lithium-sulfur battery with high energy density using a positive electrode active material having a single particle form.

[0008] Another problem that the present invention aims to solve is to provide a method for manufacturing a positive electrode active material that produces particles of a uniform shape through a wet manufacturing method.

[0009]

[0010] A positive electrode active material according to the concept of the present invention may include lithium sulfide, an ion-conducting salt, and a carbon-based material. The lithium sulfide is Li2Sn It includes at least one of (1≤n≤8, where n is an integer), and the ion-conducting salt may include a lithium salt. The positive electrode active material may have a single particle form in which the lithium sulfide, the ion-conducting salt, and the carbon-based material are combined.

[0011] A positive electrode according to the concept of the present invention may include the positive electrode active material; and a solid electrolyte.

[0012] A method for manufacturing an anode active material according to the concept of the present invention may include: preparing a precursor mixed solution; spray-drying the precursor mixed solution to obtain a composite powder; and heat-treating the composite powder. The precursor mixed solution may include lithium sulfate, an ion-conducting salt, and a carbon-based material.

[0013]

[0014] According to one aspect, the performance of a lithium-sulfur battery can be improved by increasing the composite density and energy density of the electrode.

[0015] According to another aspect, the uniformity of active material manufacturing can be improved by controlling particle size, shape, etc.

[0016]

[0017] FIG. 1 is a plan view of a lithium-sulfur battery according to embodiments of the present invention.

[0018] Figure 2 is a cross-sectional view along the line A-A' of Figure 1.

[0019] Figure 3 is a cross-sectional view of the positive active material layer of one embodiment.

[0020] Figure 4 illustrates a positive active material of one embodiment.

[0021] FIGS. 5a to 5f are SEM images of a positive electrode active material according to embodiments of the present invention.

[0022] FIG. 6 is an enlarged view of the M region of FIG. 2, and is a cross-sectional view of the positive active material layer of one embodiment.

[0023] FIG. 7 is a cross-sectional view of a lithium-sulfur battery according to one embodiment of the present invention.

[0024] FIG. 8 is a cross-sectional view of a lithium-sulfur battery according to one embodiment of the present invention.

[0025] FIG. 9 is a cross-sectional view of a lithium-sulfur battery according to one embodiment of the present invention.

[0026] FIGS. 10 to 12 illustrate a method for manufacturing a positive electrode active material according to an embodiment of the present invention.

[0027]

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] In this specification, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state.

[0034] In this specification, “alloy” means a mixture of two or more metals.

[0035] In this specification, “electrode active material” refers to an electrode material capable of undergoing lithiation and delithiation.

[0036] In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0037] In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0038] In this specification, “lithiation” and “to lithiate” refer to the process of adding lithium to an electrode active material.

[0039] In this specification, “delithiation” and “to delithiate” refer to the process of removing lithium from an electrode active material.

[0040] In this specification, “charge” and “to charge” refer to the process of providing electrochemical energy to a battery.

[0041] In this specification, “discharge” and “discharge” refer to the process of removing electrochemical energy from a battery.

[0042] In this specification, “anode” and “cathode” refer to electrodes where electrochemical reduction and lithiation occur during the discharge process.

[0043] In this specification, “negative electrode” and “anode” refer to electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0044] In this specification, “lithium-sulfur battery” may be used interchangeably with “lithium-sulfur all-solid-state battery” or “all-solid-state battery.”

[0045]

[0046] lithium sulfur battery (10)

[0047] FIG. 1 is a plan view of a lithium-sulfur battery according to embodiments of the present invention. FIG. 2 is a cross-sectional view along line A-A' of FIG. 1. FIG. 3 is intended to explain a positive electrode active material layer of one embodiment of the present invention.

[0048] Referring to FIGS. 1 and 2, a lithium-sulfur battery (10) according to the present invention 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). However, not limited thereto, the lithium-sulfur battery (10) 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).

[0049] positive electrode (100)

[0050] An anode layer (100) according to one embodiment of the present invention may include an anode current collector (110) and an anode active material layer (120) disposed on the anode current collector (110). The anode active material layer (120) may include an anode active material, a solid electrolyte, a conductive material, and a binder.

[0051] The positive current collector (110) may provide a reference surface on which the positive active material layer (120) is disposed. The positive current collector (110) 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), lithium (Li), or an alloy thereof. The positive current collector (110) may include a plate or a foil. In another embodiment of the present invention, the positive current collector (110) may be omitted. 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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 all-solid-state battery (10) can be improved.

[0059] Referring to FIG. 3, the positive active material layer (120) according to embodiments of the present invention may include a positive active material (CAC), a solid electrolyte (SEP), and a binder (BID). The positive active material (CAC) within the positive active material layer may reversibly absorb and release lithium ions. The positive active material (CAC) may include a plurality of particles. The positive active material according to the present invention may include a sulfide-based positive active material. The sulfide-based positive active material may include a sulfur-based compound. The sulfide-based positive active material may include, for example, nickel sulfide, copper sulfide, lithium sulfide, lithium polysulfide, a lithium sulfide-containing composite, or a combination thereof.

[0060] According to an embodiment of the present invention, the positive electrode active material (CAC) may comprise a lithium sulfide, an ion-conducting salt, and a carbon-based material. By including the above materials, the positive electrode active material (CAC) can be used as an electrochemical energy source by possessing ion conductivity and electron conductivity while reversibly absorbing / releasing lithium ions. For example, the positive electrode active material may be a composite of a lithium sulfide, an ion-conducting salt, and a carbon-based material.

[0061] Lithium sulfide is Li2S n It may include at least one of (1 ≤ n ≤ 8, where n is an integer). By including lithium sulfide in the positive electrode active material, capacity can be improved. Lithium sulfide can serve as the lithium source for the lithium-sulfur battery. Through the continuous oxidation / reduction reaction of lithium sulfide, lithium ions can move between the positive and negative electrodes, while electrons simultaneously move through an external circuit to generate current. In a lithium-sulfur battery using a sulfide-based material as the positive electrode, since lithium sulfide can act as a lithium source, the provision of a lithium source at the negative electrode can be omitted. That is, by including a lithium-containing sulfide in the positive electrode, a negative electrode structure can be introduced in which lithium is omitted at the negative electrode. Consequently, the energy density of the lithium-sulfur battery can be improved.

[0062] Ionic conductive salts can improve the ionic conductivity of the cathode active material (CAC). In the case of the aforementioned lithium sulfide, since its ionic conductivity is very low in itself, the ionic conductivity of the cathode active material (CAC) can be improved by including ionic conductive salts.

[0063] The ion-conducting salt may include a lithium salt. The lithium salt may include a lithium halide, which is a compound of lithium and a halogen element. In one embodiment, the lithium salt may include LiF, LiCl, LiBr, LiI, or a combination thereof. By including a lithium salt in the ion-conducting salt, the ion conductivity of the cathode active material can be improved.

[0064] The ion-conducting salt may further include a metal halide. The metal halide may include a compound of a metal and a halogen element. The metal of the metal halide may include at least one selected from the group consisting of aluminum (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn). For example, the metal halide may include AlI3, AgI, SnI4, etc. The metal halide may include a lithium-affinity metal to improve the ion conductivity of the cathode active material. The metal halide may maintain the overall shape of the cathode active material and reduce interfacial resistance.

[0065] Carbon-based materials are materials containing carbon atoms and may include, without limitation, materials used as conductive materials in the relevant technical field. For example, carbon-based materials may include crystalline carbon, amorphous carbon, or a combination thereof. Carbon-based materials may include a calcined product of a carbon precursor. In one embodiment, the carbon-based precursor may include at least one selected from the group consisting of sucrose, glucose, RF (Resorcinol-Formaldehyde) resin, PVA (Polyvinyl alcohol), pitch, chitosan, carbon black, carbon nanofiber, carbon nanotube, graphite, etc. By including a carbon-based material in the positive electrode active material, the electronic conductivity can be improved and the cycle characteristics of the battery can be improved.

[0066] The content of lithium sulfide in the cathode active material (CAC) may be 50 wt% to 95 wt%, 50 wt% to 90 wt%, 50 wt% to 80 wt%, or 50 wt% to 70 wt% of the total weight of the cathode active material (CAC). By including lithium sulfide within the above range, a high-capacity cathode active material can be provided.

[0067] The content of the ion-conducting salt in the positive electrode active material (CAC) may be 10 wt% to 50 wt%, 20 wt% to 40 wt%, 10 wt% to 30 wt%, or 20 wt% to 30 wt% of the total weight of the positive electrode active material (CAC). By including the ion-conducting salt within the above range, excellent ion conductivity and ductility can be achieved.

[0068] The ion-conducting salt may include a lithium salt and a metal halide. If the ion-conducting salt further includes a metal halide, the weight ratio of the lithium salt to the metal halide may be 1:27 to 3:1, 1:3 to 3:1, or about 1:1. Alternatively, the molar ratio of the lithium salt to the metal halide may be 1:9 to 9:1, 1:3 to 3:1, or about 1:1.

[0069] The content of carbon-based material in the positive electrode active material (CAC) may be 1 wt% to 20 wt%, 1 wt% to 10 wt%, 5 wt% to 10 wt%, 5 wt% to 20 wt%, 10 wt% to 20 wt%, or 10 wt% to 15 wt% with respect to the total weight of the positive electrode active material (CAC). By including carbon-based material within the above range, the electron conductivity of the positive electrode active material (CAC) can be improved.

[0070] Hereinafter, a positive electrode active material according to an embodiment of the present invention will be described in more detail. Referring to FIG. 4, the positive electrode active material (CAC) may have a single particle (SP) form. In this specification, a single particle (SP) may mean a particle existing independently. More specifically, a single particle (SP) may mean that materials forming a composite exist as a single particle without being separated. That is, it may mean that multiple materials form a composite but exist as a single particle. In one embodiment, the positive electrode active material (CAC) may include a single particle (SP) in which lithium sulfide (LPS), an ion-conducting salt (ICS), and a carbon-based material (CMA) are composited.

[0071] In one embodiment, referring to FIG. 4, the positive electrode active material (CAC) may comprise a solid solution of lithium sulfide (LPS), an ion-conducting salt (ICS), and a carbonaceous material (CMA). Specifically, the positive electrode active material (CAC) may be in the form of a single particle (SP) in which three particles of lithium sulfide (LPS), an ion-conducting salt (ICS), and a carbonaceous material (CMA) exist as a single phase.

[0072] Ionic conductivity can be enhanced as the cathode active material comprises a solid solution of lithium sulfide (LPS), an ion-conducting salt (ICS), and a carbon-based material (CMA). For example, the ionic conductivity of a single particle can be enhanced compared to the ionic conductivity of the lithium sulfide itself by containing lithium ions disposed within the lithium sulfide crystallites of the single particle existing as a solid solution.

[0073] Compared to simply mixing lithium sulfide (LPS) and the like within the positive active material layer (120) to form an amorphous powder, by including a single particle (SP) existing as a solid solution of a single phase, a positive active material (CAC) with improved performance can be provided. For example, the single particle forms a more stable and uniform structure, thereby maintaining physical and chemical changes during the charging and discharging of the battery more consistently. In addition, since the single particle (SP) exists as a single phase, ion and electron transport pathways can be formed more smoothly. As a result, both the electrochemical and mechanical properties of the positive active material (CAC) can be improved.

[0074] Referring to FIGS. 5a to 5f, the positive active material may include spherical single particles (SP). The single particles (SP) may be in the shape of a perfect sphere or an elliptical sphere. The single particles (SP) may generally have a spherical shape, but may have a non-smooth shape including irregular protrusions or depressions on parts of their surface. Additionally, as shown in FIGS. 5c to 5f, the positive active material may be a spherical particle overall, but may include voids in some internal regions.

[0075] In one embodiment, the sphericity of a single particle (SP) may be 0.7 to 1.0. Sphericity may be an evaluation of the degree to which the shape of the particle is close to an ideal sphere. For example, sphericity can be measured by analyzing 2D or 3D images captured by a scanning electron microscope (SEM). In this case, sphericity can be calculated using the following Equation 1.

[0076] <Equation 1>

[0077] Sphericity = 4πA / P 2 (A is the cross-sectional area of ​​the particle, P is the perimeter of the particle)

[0078] The average particle size of the cathode active material (CAC) may be 1 μm to 15 μm. That is, the average particle size of the single particle (SP) may be 1 μm to 15 μm. In one embodiment, the average particle size may refer to the diameter (D50) of a particle whose cumulative volume is 50 volume% in the particle size distribution measured by a particle size analyzer.

[0079] The Span value analyzed by a particle size analyzer of the cathode active material (CAC) may be 2.0 to 5.0, 2.0 to 4.0, or 2.5 to 3.7. The Span value may be calculated using the following Equation 2.

[0080] <Equation 2>

[0081] Span = (D 90 -D 10 ) / D 50

[0082] In the above Equation 2, D n represents the size of the particles corresponding to the top n% in the particle size distribution. That is, D n represents the particle size when n% of the total particles are less than or equal to that size.

[0083] By including the single particle (SP) as described above in the positive electrode active material (CAC), the particle uniformity of the positive electrode is increased and the composite density is increased, thereby improving energy density. The increased composite density of the positive electrode active material layer provides a stable electrode plate shape, which can improve lifespan characteristics.

[0084] In addition, the uniform particle distribution within the anode improves the density of the composite material and the adhesion to the electrode plate, and consequently, the content of other additives such as binders or conductive materials can be minimized. As described above, by providing an anode active material with a uniform and consistent form, the electrochemical stability and process stability of the battery can be improved.

[0085] Referring to FIG. 6, the positive active material layer of one embodiment may include a first particle (CAC1) of large size and a second particle (CAC2) of small size. The average particle size of the first particle (CAC1) may be larger than the average particle size of the second particle (CAC2). The average particle size of the first particle (CAC1) may be 8 μm to 15 μm, 8 μm to 12 μm, or 6 μm to 15 μm. The average particle size of the second particle (CAC2) may be 1 μm to 6 μm, or 1 μm to 3 μm.

[0086] In one embodiment, the mixing weight ratio of the first and second particles (CAC1, CAC2) may be 5:5 to 8:2, or 7:3 to 8:2. By including particles with different average particle sizes, the composite density of the positive active material layer can be further improved. For example, the composite density of the positive active material layer may be 1.5 g / cc to 2.0 g / cc, or 1.7 g / cc to 2.0 g / cc.

[0087] Referring again to FIG. 3, the positive active material layer (120) may further include a solid electrolyte (SEP) in addition to the positive active material (CAC). The solid electrolyte (SEP) in the positive active material layer may be the same as or different from the solid electrolyte in the solid electrolyte layer (300) to be described later.

[0088] The solid electrolyte (SEP) 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 (SEP) in the positive 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 of the solid electrolyte in the solid electrolyte layer (300).

[0089] In one embodiment, the content of the positive active material (CAC) in the positive active material layer (120) may be 10% to 99% by weight, 40% to 90% by weight, 50% to 90% by weight, or 60% to 90% 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 positive active material (CAC) in the positive electrode (100), and may mean a ratio calculated based on the weight excluding the positive current collector (110) in the positive electrode (100).

[0090] Among the components within the positive active material layer (120), the positive active material (CAC) may have the largest content. The content of the solid electrolyte (SEP) within the positive active material layer (120) may be 10% to 70% by weight, 10% to 60% by weight, or 10% to 40% 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 solid electrolyte (SEP) within the positive electrode (100), and may mean a ratio calculated based on the weight excluding the positive current collector (110) within the positive electrode (100).

[0091] The solid electrolyte (SEP) may be, for example, a sulfide-based solid electrolyte. Sulfide-based solid electrolytes are, for example, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn, or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q, p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x , 0≤x≤2, and one or more selected from. Sulfide-based solid electrolytes are produced by processing starting materials, such as Li2S or P2S5, by methods such as melt quenching or mechanical milling. 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 comprising Li2S-P2S5 to form a solid electrolyte, the molar ratio of Li2S and P2S5 is, for example, in the range of Li2S : P2S5 = 20 : 80 to 90 : 10, 25 : 75 to 90 : 10, 30 : 70 to 70 : 30, and 40 : 60 to 60 : 40.

[0092] Sulfide-based solid electrolytes may include, for example, an argyrodite-type solid electrolyte represented by the following chemical formula 1:

[0093] <Chemical Formula 1>

[0094] Li + 12-n-x A n+ X 2- 6-x Y - x

[0095] 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, for example, one or more selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0096] Alternatively, sulfide-based solid electrolytes are Li 7-c 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 may be candium (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.

[0097] The density of the argyrodite-type solid electrolyte may be 1.5 to 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or higher, the internal resistance of the lithium-sulfur battery is reduced, and penetration of the solid electrolyte layer by Li can be effectively suppressed.

[0098] The positive active material layer (120) may further include a conductive material. The conductive material may be, for example, a carbon-based material, a metal-based material, or a combination thereof. 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, and may mean a ratio calculated based on the weight excluding the positive current collector in the positive.

[0099] Metallic materials may be metal powders, metal fibers, or combinations thereof, but are not limited to these; any metallic material used as a conductive material in the relevant technical field is acceptable.

[0100] The conductive material is a material containing carbon atoms and may include, without limitation, materials used as conductive materials in the relevant technical field. For example, the conductive material may include crystalline carbon, amorphous carbon, or a combination thereof.

[0101] The conductive material may include carbon nanostructures. The conductive material may include, for example, porous carbon or non-porous carbon. Porous carbon may include, 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 within the conductive material may be, for example, particle form, sheet form, fibrous form, etc., but is not limited thereto, and any form used as carbon in the relevant technical field may be possible.

[0102] In one embodiment, the conductive material may include a fibrous carbon-based material. By including a fibrous carbon-based material in the conductive material, the electron conductivity of the positive active material layer (120) can be further improved. By including a fibrous carbon-based material in the conductive material, electron conduction from the surface to the interior of the positive active material layer (120) can be performed more easily. The internal resistance of the positive active material layer (120) is reduced by the conductive material, and the cycle characteristics of the secondary battery can be further improved.

[0103] The aspect ratio of the fibrous carbon-based material may be, for example, 2 or more, 3 or more, 4 or more, 5 or more, 10 or more, or 20 or more. The aspect ratio of the fibrous carbon-based material may be, for example, 2 to 30, 3 to 30, 4 to 30, 5 to 30, 10 to 30, or 20 to 30. The aspect ratio of the fibrous carbon-based material may be, for example, 2 to 30, 2 to 20, 2 to 10, 2 to 8, 2 to 5, or 2 to 4. By having the aspect ratio of the fibrous carbon-based material within this range, the overall electron conductivity of the positive active material layer (120) is improved, and the local imbalance of electron conductivity within the positive active material layer (120) can be further alleviated.

[0104] Fibrous carbon-based materials may include, for example, carbon nanostructures. Carbon nanostructures may include, for example, carbon nanofibers (CNF), carbon nanotubes (CNT), carbon nanobelts, carbon nanorods, or combinations thereof. Carbon nanostructures may form a primary carbon nanostructure composed of a single carbon nanostructure and a secondary carbon nanostructure formed by the aggregation of multiple carbon nanostructures.

[0105] The diameter of the primary carbon nanostructure may be, for example, 1 nm to 200 nm, 1 nm to 150 nm, 1 nm to 100 nm, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 20 nm. The length of the primary carbon nanostructure may be, for example, 10 nm to 2 µm, 10 nm to 1.5 µm, 10 nm to 1 µm, 10 nm to 500 nm, 10 nm to 400 nm, 10 nm to 300 nm, 10 nm to 200 nm, or 10 nm to 100 nm. The diameter and length of the primary carbon nanostructure may be measured from scanning electron microscope (SEM) or transmission electron microscope (TEM) images. Alternatively, the diameter and / or length of the primary carbon nanostructure may be measured by laser diffraction.

[0106] The secondary carbon nanostructure may be a structure formed by assembling primary carbon nanostructures, for example, to form a bundle or rope type, either wholly or partially. The secondary carbon nanostructure may include, for example, bundle-type carbon nanostructures, rope-type carbon nanostructures, or a combination thereof. The diameter of the secondary carbon nanostructure may be, for example, 2 nm to 200 nm, 3 nm to 150 nm, 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 30 nm, or 5 nm to 20 nm. The length of the secondary carbon nanotube structure may be, for example, 20 nm to 2 µm, 30 nm to 1.5 µm, 50 nm to 1 µm, 50 nm to 500 nm, 50 nm to 400 nm, 50 nm to 300 nm, 50 nm to 200 nm, or 50 nm to 100 nm or more. The diameter and length of the secondary carbon nanostructure may be measured from scanning electron microscope (SEM) images or optical microscopes. Alternatively, the diameter and / or length of the secondary carbon nanostructure may be measured by laser diffraction.

[0107] The positive active material layer (120) may further include a binder (BID). The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyethylene, etc., but is not limited to these and may be any binder used in the relevant technical field. The content of the binder (BID) 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 (BID) may be omitted. This may be used in the same sense as the content of the binder in the positive, and may mean a ratio calculated based on the weight excluding the positive current collector in the positive.

[0108] The positive active material layer (120) may further include additives such as a coating agent, a dispersant, and an ion conductivity aid in addition to the positive active material (CAC) and solid electrolyte (SEP) described above. Known materials generally used in electrodes of all-solid-state batteries or lithium-sulfur batteries may be used as coating agents, dispersants, and ion conductivity aids that may be included in the positive active material layer (120).

[0109] cathode (200)

[0110] The negative electrode layer (200) may include a negative electrode current collector (210) and a negative electrode coating layer (220) on the negative electrode current collector (210). The negative electrode current collector (210) may provide a reference surface on which the negative electrode 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.

[0111] 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.

[0112] 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 battery (10) can be improved.

[0113] The negative electrode coating layer (220) can be configured to allow lithium metal to grow between the lithium-sulfur battery (10) and the negative electrode current collector (210) during charging. The negative electrode coating layer (220) can serve as a protective layer for the lithium metal and simultaneously suppress the precipitation and growth of lithium dendrites.

[0114] The cathode coating layer (220) may include metal and carbon. For example, the cathode coating layer (220) may include at least one metal selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The cathode coating layer (220) may include at least one carbon selected from the group consisting of carbon black, acetylene black, furnace black, ketjen black, and graphene. In one embodiment, the cathode coating layer (220) may include a mixture of carbon black and silver (Ag).

[0115] The cathode coating layer (220) may further include other additives in addition to metal and carbon. The cathode coating layer (220) may further include at least one additive selected from the group consisting of, for example, binders, fillers, coating agents, dispersants, and ion-conducting aids.

[0116] The negative electrode coating layer (220) may have a smaller thickness compared to the positive electrode active material layer (120). The thickness of the negative electrode 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 electrode active material layer (120). The thickness of the negative electrode coating layer (220) may be, for example, 1 µm to 20 µm, 2 µm to 10 µm, or 3 µm to 7 µm. If the thickness of the negative electrode coating layer (220) is excessively thin, lithium dendrites formed between the negative electrode coating layer (220) and the negative electrode current collector (210) may cause the negative electrode coating layer (220) to collapse, thereby degrading the cycle characteristics of the all-solid-state battery (10). If the thickness of the negative electrode coating layer (220) increases excessively, the energy density of the all-solid-state battery (10) decreases, and the internal resistance of the all-solid-state battery (10) due to the negative electrode coating layer (220) increases, which may degrade the cycle characteristics of the cell.

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

[0118] solid electrolyte layer (300)

[0119] A solid electrolyte layer (300) may be provided between the positive electrode layer (100) and the negative electrode layer (200). The solid electrolyte layer (300) may include a sulfide-based solid electrolyte with excellent lithium ion conductivity characteristics. The solid electrolyte in the solid electrolyte layer (300) may be the same as or different from any one of the materials included in the solid electrolyte (SEP, see FIG. 3) in the aforementioned positive electrode active material layer (120).

[0120] The solid electrolyte layer (300) may include a first solid electrolyte layer (310) and a second solid electrolyte layer (320). The first solid electrolyte layer (310) may be adjacent to the anode layer (100), and the second solid electrolyte layer (320) may be adjacent to the cathode layer (200).

[0121] Referring to FIG. 2, the first solid electrolyte layer (310) may include a first solid electrolyte. The first solid electrolyte may have a particle shape such as a sphere or an ellipsoid. The first solid electrolyte may include a sulfide-based solid electrolyte. The first solid electrolyte may be amorphous, crystalline, or a mixture thereof. Additionally, 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. 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 may be, for example, in the range of Li2S : P2S5 = 50 : 50 to 90 : 10.

[0122] In one embodiment, the first solid electrolyte is 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 an argyrodite-type compound comprising one or more selected from (0≤x≤2). The first solid electrolyte may include an argyrodite-type compound comprising one or more selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0123] In another embodiment, the first solid electrolyte is Li 7-c M a PS 6-c X c It may include an argyrodite-type compound comprising. Here, X may be Cl, Br, or a combination thereof. M may be Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof. a and c may each be a real number between 0 and 2.

[0124] 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 first solid electrolyte is, for example, 15 GPa to 35 GPa.

[0125] The second solid electrolyte layer (320) may include a second solid electrolyte. The second solid electrolyte may have a particle shape such as a sphere or an ellipsoid. The second solid electrolyte may include a sulfide-based solid electrolyte. The description of the second solid electrolyte may be the same or similar as that described above for the first solid electrolyte. In one embodiment, the second solid electrolyte may have substantially the same composition as the first solid electrolyte. In another embodiment, the second solid electrolyte may have a composition similar to that of the first solid electrolyte.

[0126] The second solid electrolyte can come into direct contact with the negative electrode coating layer (220). By doing so, the second solid electrolyte can suppress lithium dendrites formed between the negative electrode coating layer (220) and the negative electrode current collector (210). The second solid electrolyte can effectively suppress negative side reactions. This can improve the cell performance of the lithium-sulfur battery (10) according to the present invention.

[0127] Each of the first and second solid electrolyte layers (310, 320) may further include a binder. The binder 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 in the solid electrolyte layer (300) may be the same as or different from the binder in the positive active material layer (120) or the binder in the negative coating layer (220).

[0128] The content of the binder in the solid electrolyte layer (300) may be 0.1 to 10 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 0.1 to 1 wt%, 0 to 0.5 wt%, or 0 to 0.1 wt% with respect to the total weight of the solid electrolyte layer (300).

[0129] In another embodiment of the present invention, the solid electrolyte layer (300) may be provided as a single layer structure rather than a double layer structure of the first solid electrolyte layer (310) and the second solid electrolyte layer (320).

[0130] Referring again to FIGS. 1 and FIGS. 2, the anode layer (100) and the first solid electrolyte layer (310) can form an anode composite layer (CSH). The cathode layer (200) and the second solid electrolyte layer (320) can form a cathode composite layer (ASH). An anode composite layer (CSH) can be laminated on the cathode composite layer (ASH).

[0131] The area of ​​the cathode composite layer (ASH) and the area of ​​the anode composite layer (CSH) may differ from each other. Specifically, the area of ​​the cathode composite layer (ASH) may be larger than the area of ​​the anode composite layer (CSH). The anode composite layer (CSH) may completely overlap within the cathode composite layer (ASH).

[0132] In one embodiment of the present invention, the first solid electrolyte layer (310) may have substantially the same area as the anode layer (100). The second solid electrolyte layer (320) may have substantially the same area as the cathode layer (200).

[0133] Specifically, the positive electrode composite layer (CSH) may have a first width (WI1) in a first direction (D1). The negative electrode composite layer (ASH) may have a second width (WI2) in a first direction (D1). The first width (WI1) may be smaller than the second width (WI2). The positive electrode composite layer (CSH) may have a third width (WI3) in a second direction (D2). The negative electrode composite layer (ASH) may have a fourth width (WI4) in a second direction (D2). The third width (WI3) may be smaller than the fourth width (WI4).

[0134] A lithium-sulfur battery (10) according to the present embodiment can be manufactured by forming a negative electrode composite layer (ASH) on a first carrier film and forming a positive electrode composite layer (CSH) on a second carrier film, and then laminating the negative electrode composite layer (ASH) and the positive electrode composite layer (CSH).

[0135] In one embodiment, as shown in FIG. 2, the positive active material layer (120) in a discharged state may have a first thickness (TK1). The lithium sulfur battery (10) may have a first height (HE1) in a third direction (D3). The first height (HE1) may be the sum of the thickness of the positive composite layer (CSH) and the thickness of the negative composite layer (ASH).

[0136] In the embodiments described below, detailed descriptions of technical features that overlap with those previously described with reference to FIGS. 1 to 3 are omitted, and the differences are described in detail.

[0137] FIG. 7 is a cross-sectional view along line A-A' of FIG. 1, illustrating a lithium-sulfur battery according to another embodiment of the present invention. Referring to FIG. 7, in one embodiment, a lithium-sulfur battery (10) in a charged state may further include a lithium metal layer (230) provided between a negative electrode current collector (210) and a negative electrode coating layer (220). The negative electrode layer (200) according to the present embodiment may include a negative electrode current collector (210), a negative electrode coating layer (220), and a lithium metal layer (230) between them.

[0138] 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 negative electrode coating layer (220) and the negative electrode current collector (210) during the charging process of the lithium-sulfur battery (10), for example.

[0139] The lithium metal layer (230) may have a third thickness (TK3). The third thickness (TK3) is not particularly limited, but may be, for example, 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 third thickness (TK3) 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 third thickness (TK3) of the lithium metal layer (230) is excessively thick, the mass and volume of the lithium-sulfur battery (10) increase, and the cycle characteristics of the lithium-sulfur battery (10) may actually deteriorate.

[0140] In another embodiment of the present invention, 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 negative electrode coating layer (220) before assembly of the lithium-sulfur battery (10). When the lithium metal layer (230) is placed between the negative electrode current collector (210) and the negative electrode coating layer (220) before assembly of the lithium-sulfur battery (10), 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 negative electrode coating layer (220) before assembly of the lithium-sulfur battery (10).

[0141] When a lithium metal layer (230) is deposited by charging after the assembly of the lithium-sulfur battery (10), the energy density of the lithium-sulfur battery (10) can be increased because the lithium metal layer (230) is not included during the assembly of the lithium-sulfur battery (10). When charging the lithium-sulfur battery (10), it can be charged beyond the charging capacity of the negative electrode coating layer (220). That is, the negative electrode coating layer (220) is overcharged. At the beginning of charging, lithium can be absorbed in the negative electrode coating layer (220). When charging beyond the capacity of the negative electrode coating layer (220), lithium can be deposited, for example, between the negative electrode coating layer (220) and the negative electrode current collector (210). A lithium metal layer (230) can be formed by the deposited lithium.

[0142] 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 battery (10). In addition, since the negative electrode coating layer (220) covers the lithium metal layer (230), the negative electrode coating layer (220) can protect the lithium metal layer (230) and simultaneously suppress the precipitation growth of lithium dendrites. Therefore, the negative electrode coating layer (220) can suppress short circuits and capacity degradation of the lithium-sulfur battery (10) and improve the cycle characteristics of the lithium-sulfur battery (10).

[0143] When a lithium metal layer (230) is formed by charging after assembly of the lithium-sulfur battery (10), the negative electrode layer (200), that is, the negative electrode current collector (210) and the negative electrode 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 battery (10).

[0144] The positive active material layer (120) from which lithium ions are released by charging the lithium-sulfur battery (10) may have a second thickness (TK2). The second thickness (TK2) of the positive active material layer (120) may be smaller than the first thickness (TK1) of FIG. 2.

[0145] In one embodiment of the present invention, the difference between the first thickness (TK1) and the second thickness (TK2) may be substantially the same or similar to the third thickness (TK3) of the lithium metal layer (230). For example, the third thickness (TK3) may be 1.0 to 1.5 times, or 1.0 to 1.2 times, the difference between the first thickness (TK1) and the second thickness (TK2). According to the present invention, the thickness of the positive active material layer (120) may be reduced by the same amount as the thickness of the lithium metal layer (230) formed by charging the lithium-sulfur battery (10).

[0146] Although not illustrated, the lithium-sulfur battery (10) may operate (i.e., charge and / or discharge) while being pressurized by a pressurizing jig. In one embodiment, the lithium-sulfur battery (10) may be pressurized to 0.8 MPa to 2 MPa. For example, the lithium-sulfur battery (10) may have an internal pressure of about 1 MPa when discharged, and the lithium-sulfur battery (10) may have an internal pressure of about 1.5 MPa when charged. The ratio of the internal pressure of the lithium-sulfur battery (10) in the charged state of FIG. 7 to the internal pressure of the lithium-sulfur battery (10) in the discharged state of FIG. 2 may be 1.0 to 2.0, or 1.2 to 1.8.

[0147] The height (or thickness or volume) of the lithium-sulfur battery (10) may change according to charging and discharging under the aforementioned pressurized state. In the lithium-sulfur battery (10) according to the present embodiment, the thickness of the positive active material layer (120) may decrease in correspondence with the lithium metal layer (230) formed by charging. Accordingly, the second height (HE2) of the charged lithium-sulfur battery (10) shown in FIG. 7 may be similar to the first height (HE1) of the discharged lithium-sulfur battery (10) shown in FIG. 2. For example, the second height (HE2) may be 1 to 1.5 times, or 1 to 1.2 times, the first height (HE1).

[0148] FIG. 8 is a cross-sectional view along line A-A' of FIG. 1, intended to illustrate a lithium-sulfur battery according to another embodiment of the present invention. Referring to FIG. 8, the lithium-sulfur battery (10) according to the present embodiment may further include a gasket (GSK). The gasket (GSK) may be provided to surround the positive electrode composite layer (CSH). The gasket (GSK) may fill the step difference on the side of the lithium-sulfur battery (10) caused by the difference in area between the negative electrode composite layer (ASH) and the positive electrode composite layer (CSH). The gasket (GSK) may surround the four sides of the positive electrode composite layer (CSH). For example, the thickness of the gasket (GSK) may be substantially the same as the thickness of the positive electrode composite layer (CSH).

[0149] The upper surface of the second solid electrolyte layer (320) may include a first region in contact with the first solid electrolyte layer (310) and a second region in contact with the gasket (GSK). The second region may be a peripheral region of the upper surface of the second solid electrolyte layer (320). The second region may surround the first region.

[0150] The gasket (GSK) can prevent cracking of the solid electrolyte layer (300) during the manufacture of the lithium-sulfur battery (10) and / or during the charging and discharging of the lithium-sulfur battery (10). This can improve the cycle characteristics of the lithium-sulfur battery (10). If the lithium-sulfur battery (10) does not include the gasket (GSK), uneven pressure is applied to the negative electrode composite layer (ASH) in contact with the positive electrode composite layer (CSH), causing cracking in the solid electrolyte layer (300), and the likelihood of a short circuit occurring due to the growth of lithium metal through this may increase.

[0151] The thickness of the gasket (GSK) may be greater than the thickness of the positive composite layer (CSH) or substantially equal to the thickness of the positive composite layer (CSH). Since the thickness of the gasket (GSK) is equal to the thickness of the positive composite layer (CSH), a uniform pressure is applied between the positive composite layer (CSH) and the negative composite layer (ASH), and the positive composite layer (CSH) and the negative composite layer (ASH) are sufficiently in contact, thereby reducing the interfacial resistance between the first solid electrolyte layer (310) and the second solid electrolyte layer (320). Additionally, the internal resistance of the solid electrolyte layer (300) may be reduced as the solid electrolyte layer (300) is sufficiently sintered during the pressurized manufacturing process of the lithium-sulfur battery (10).

[0152] The gasket (GSK) may have a single-layer structure, for example. Alternatively, although not shown in the drawings, the gasket (GSK) may have a multi-layer structure. In a gasket (GSK) having a multi-layer structure, each layer may have a different composition. A gasket (GSK) having a multi-layer structure may have, for example, a two-layer structure, a three-layer structure, a four-layer structure, or a five-layer structure. A gasket (GSK) having a multi-layer structure may include, for example, one or more adhesive layers and one or more support layers.

[0153] The gasket (GSK) may include, for example, a flame-retardant inert member. By providing flame retardancy, the flame-retardant inert member can prevent thermal runaway and the possibility of ignition of the lithium-sulfur battery (10). Consequently, the gasket (GSK) can further enhance the safety of the lithium-sulfur battery (10). By absorbing residual moisture within the lithium-sulfur battery (10), the flame-retardant inert member prevents the deterioration of the lithium-sulfur battery (10), thereby improving the lifespan characteristics of the lithium-sulfur battery (10).

[0154] FIG. 9 is a cross-sectional view along line A-A' of FIG. 1, illustrating a lithium-sulfur battery according to another embodiment of the present invention. Referring to FIG. 9, the positive electrode layer (100) may further include a coating layer (CTL) provided between the positive electrode current collector (110) and the positive electrode active material layer (120). The coating layer (CTL) may be placed directly on, for example, one or both sides of the positive electrode current collector (110). The coating layer (CTL) may be coated on one or both sides of the positive electrode current collector (110). No other layer may be placed between the positive electrode current collector (110) and the coating layer (CTL).

[0155] By placing the 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 coating layer (CTL) between the positive current collector (110) and the positive active material layer (120), side reactions between the filler (FIL), solid electrolyte (SEP), or positive active material (CAC) and the positive current collector (110) can be more effectively suppressed. For example, the coating layer (CTL) can prevent corrosion of the sulfide-based positive active material (e.g., Li2S) by the positive current collector (110). Consequently, the coating layer (CTL) can suppress the degradation of the lithium-sulfur battery (10) during the charging and discharging process and improve cycle characteristics.

[0156] The thickness of the 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 positive current collector (110). The thickness of the 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 coating layer (CTL) have a thickness within this range, the bonding strength between the positive current collector (110) and the positive active material layer (120) is further improved, and the increase in interfacial resistance can be suppressed. The thickness of the coating layer (CTL) can be measured, for example, from a scanning electron microscope (SEM) image of a cross- section of the coating layer (CTL).

[0157] The coating layer (CTL) may include, for example, a carbon-based conductive material. The carbon-based conductive material included in the coating layer (CTL) may be selected from among the carbon-based conductive materials used in the positive active material layer (120). The coating layer (CTL) may include the same carbon-based conductive material as the carbon-based conductive material used in the positive active material layer (120). By including the carbon-based conductive material, the coating layer (CTL) may be, for example, a conductive layer.

[0158] The coating layer (CTL) may additionally include, for example, a binder. By additionally including a binder in the 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 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.

[0159] The binder included in the coating layer (CTL) may be selected from among the binders used in the positive active material layer (120). The coating layer (CTL) may include the same binder as the binder used in the positive active material layer (120). The binder included in the coating layer (CTL) is, for example, a fluorine-based binder. The fluorine-based binder included in the coating layer (CTL) is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a combination thereof. The coating layer (CTL) may be, for example, a binding layer containing a binder. The coating layer (CTL) may be, for example, a conductive layer containing a binder and a carbon-based conductive material.

[0160] The coating layer (CTL) can be disposed on the positive current collector (110) in a dry or wet manner, for example. The coating layer (CTL) can be disposed on the positive current collector (110) in a dry manner by deposition, for example, CVD, PVD, etc. The coating layer (CTL) can be disposed on the positive current collector (110) in a wet manner by, for example, spin coating, dip coating, etc. The coating layer (CTL) can be disposed on the positive current collector (110) by, for example, depositing a carbon-based conductive material onto a substrate by deposition. The dry-coated coating layer (CTL) may be made of a carbon-based conductive material and may not contain a binder. The coating layer (CTL) can be disposed on the positive 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 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.

[0161] The negative electrode layer (200) may further include a thin film (TFL) provided between the negative electrode current collector (210) and the negative electrode coating layer (220). The thin film (TFL) may be provided on one side of the negative electrode current collector (210) to form an alloy with lithium.

[0162] 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.

[0163] By placing the thin film (TFL) on one side of the negative current collector (210), the deposition pattern of the lithium metal layer (230, see FIG. 4) deposited between, for example, the thin film (TFL) and the negative coating layer (220) is further flattened, and the cycle characteristics of the all-solid-state battery (10) can be further improved.

[0164] 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 all-solid-state battery (10) and may lower the cycle characteristics of the all-solid-state battery (10). 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 a thin film in the relevant technical field may be possible.

[0165]

[0166] Manufacturing of lithium-sulfur batteries

[0167] A method for manufacturing a lithium-sulfur battery according to an embodiment of the present invention may include manufacturing a positive electrode, manufacturing a negative electrode, placing a solid electrolyte layer between the positive electrode and the negative electrode, and assembling the battery.

[0168] Excluding general aspects regarding the manufacture of all-solid-state batteries including a solid electrolyte layer, the following description focuses on the method for manufacturing a positive electrode active material according to an embodiment of the present invention.

[0169] Method for manufacturing positive electrode active material

[0170] A method for manufacturing a positive electrode active material according to an embodiment of the present invention provides a method for manufacturing a sulfide-based positive electrode active material through a wet spray process. Specifically, the method for manufacturing a positive electrode active material may include preparing a precursor mixed solution; spray-drying the precursor mixed solution to obtain a composite powder; and heat-treating the composite powder.

[0171] FIG. 10 illustrates the preparation of a precursor mixed solution. Referring to FIG. 10, the precursor mixed solution (PRC) may contain materials constituting the cathode active material in a solvent (SLV). The precursor mixed solution (PRC) may be prepared by mixing lithium sulfate (LSF), an ion-conducting additive (ICM), and a carbon-based additive (CBM) in a solvent (SLV). For example, water, ethanol, etc. may be used as the solvent (SLV).

[0172] The ion-conducting additive (ICM) may include a lithium salt. The lithium salt may include, for example, a lithium halide, which is a compound of lithium and a halogen element. In one embodiment, the lithium salt may include LiI, LiCl, LiBr, LiI, or a combination thereof.

[0173] The ion-conducting additive (ICM) may further include a metal halide. The metal halide may include a compound of a metal and a halogen element. In this case, the metal of the metal halide may include at least one selected from the group consisting of aluminum (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn). For example, the metal halide may include AlI3, AgI, SnI4, etc.

[0174] The carbon-based additive may include at least one selected from the group consisting of sucrose, glucose, RF (Resorcinol-Formaldehyde), PVA (Polyvinylalchol), pitch, chitosan, carbon black, carbon nanofiber (CNF), carbon nanotube (CNT), graphite, etc. By controlling the type of carbon-based additive in the mixed solution, the degree of particle uniformity and particle size of the cathode active material being manufactured can be controlled.

[0175] For example, sucrose possesses high solubility and low viscosity, making it possible to form relatively uniform particles during spray drying. Consequently, it is possible to provide an anode active material in which carbon-based materials are uniformly mixed within a single particle. As another example, pitch is a high-molecular-weight carbon material with very high viscosity, which can be advantageous for manufacturing large particles during spray drying. Pitch may exist in an amorphous structure after spray drying and can be crystallized through a subsequent heat treatment step.

[0176] Preparing a precursor mixed solution may include controlling the concentration of the mixed solution. In this case, the concentration of the mixed solution may refer to the concentration of solids within the mixed solution. More specifically, the concentration of solids within the mixed solution may be controlled within the range of 2% to 50% by weight, 2% to 30% by weight, 10% to 30% by weight, or 2% to 20% by weight. In this case, the concentration of solids may refer to a value calculated as a percentage of the weight of the solid material remaining after the solvent evaporates, relative to the total weight of the mixed solution (i.e., the spray liquid).

[0177] As the concentration of solids in the mixed solution increases, the average particle size of the final product (e.g., positive electrode active material) may increase. In other words, the particle size of the positive electrode active material can be controlled by controlling the concentration of solids in the precursor mixed solution. However, if the solid content is greater than 20%, it becomes difficult to control the average particle size of the positive electrode active material, and the variation in particle size may increase.

[0178] FIG. 11 illustrates obtaining a composite powder by spray-drying a precursor mixture solution. Referring to FIG. 11, a composite powder (CPD) can be obtained by performing spray drying (SPR) on a prepared precursor mixture solution (PRC). Spray drying (SPR) can be performed using commonly used spray drying equipment. For example, spray drying can be performed using at least one selected from an ultrasonic spray drying device, an air nozzle spray drying device, an ultrasonic nozzle spray drying device, a filter expansion droplet generator, and an electrostatic spray drying device.

[0179] Single particles composed of lithium sulfide, ion-conducting salts, and carbon-based materials can be formed through spray drying (SPR). Additionally, spray drying can form cathode active materials into single particles of a desired size by controlling the carrier gas flow rate and velocity, residence time in the reactor, temperature, spray speed, and spray pressure.

[0180] Spray drying (SPR) may include controlling the spray rate. The spray rate refers to the speed at which the liquid is sprayed through the spray drying (SPR) and can be defined as the amount of liquid sprayed per unit time (mL / min). The spray rate can be controlled within a range of 5 mL / min to 100 mL / min. If the spray rate is 5 mL / min or less, productivity may be significantly reduced due to the generation of non-uniform particles and increased drying time. In contrast, if the spray rate is 100 mL / min or more, the droplets may not be sufficiently dried, and problems may arise where particles aggregate in an undried state, generating uneven particles. By controlling the spray rate within the above range, it becomes possible to generate uniform particles, and processability may be increased. In this case, as the spray rate increases, the average particle size of the manufactured cathode active material may increase.

[0181] Spray drying (SPR) may involve controlling the spray pressure. Spray pressure refers to the pressure inside the nozzle when a liquid is sprayed through the nozzle. In other words, it refers to the intensity of the liquid spray. The higher the spray pressure, the smaller the size of the sprayed droplets may be. The higher the spray pressure, the smaller the average particle size of the cathode active material produced through the spray drying process may be. The spray pressure may be in the range of 20 kPa to 300 kPa. If the spray pressure is excessively high, the spray liquid may decompose into fine particles, forming excessively small particles. Consequently, it may be impossible to form single particles because the particles do not aggregate during the drying process. Furthermore, if the spray pressure is too low, the formation of non-uniform droplets prevents effective drying, and the quality of the final product may deteriorate.

[0182] Spray drying (SPR) can be performed at a first temperature (T1). For example, the first temperature (T1) can be controlled within a range of 40°C to 250°C, greater than 50°C and less than or equal to 230°C, or 100°C to 200°C. The higher the drying temperature, the faster the droplets convert into a solid, making it difficult to form large particles. That is, as the first temperature (T1) decreases, the average particle size of the final product produced may increase. For example, by lowering the first temperature (T1), a positive electrode active material with a large average particle size can be produced.

[0183] FIG. 12 illustrates the heat treatment of a composite powder. Referring to FIG. 12, the composite powder (CPD) obtained by the spray drying (SPR) described above can be heat-treated (CAL) at a second temperature (T2). The heat treatment (CAL) may involve calcining the composite powder.

[0184] The heat treatment (CAL) may be performed under a reducing atmosphere. For example, it may be performed using a hydrogen (H2) / argon (Ar) mixed gas, a hydrogen (H2) / nitrogen (N2) mixed gas, an argon gas (Ar), or a nitrogen gas (N2). The second temperature (T2) may be 300 °C to 800 °C, 300 °C to 600 °C, or 400 °C to 700 °C. The heat treatment (CAL) may be performed for 2 to 8 hours.

[0185] The composite powder (CPD) can be transformed into a final product (PRD) through a heat treatment process. Additional heat treatment steps can partially alter the crystallinity and properties of the particles. For example, particles existing in an amorphous state after spray drying can be converted into a crystalline state. Furthermore, the uniformity of the particles can be improved by removing residual solvent from the spray drying process. Through the heat treatment process, carbon-based additives can be carbonized and converted into carbon fibers. This can improve the electronic conductivity of the cathode active material. The particles can also be sintered through the heat treatment process, which can increase mechanical strength. Consequently, a single-particle cathode active material (CAC) with a stable structure and high ionic and electronic conductivity can be manufactured.

[0186] As described above, by including a spray drying process of a wet mixed solution, the size and uniformity of the cathode active material (CAC) can be easily controlled. In the case of sulfide-based cathode active materials, it is very important to form a composite with conductive materials due to the low ionic conductivity of lithium sulfide itself. When composites are formed through a general grinding process, amorphous particles are produced, and it is more difficult to form a uniform solid solution, resulting in a problem of reduced performance of the cathode active material. Furthermore, due to the amorphous shape and small size, there are limitations in achieving high capacity through high electrode density.

[0187] By manufacturing a positive electrode active material in the form of a single particle, the density of the positive electrode composite of a lithium-sulfur battery can be improved, and the uniformity of the electrode plate can be enhanced. Consequently, the performance of a lithium-sulfur battery can be improved through the method for manufacturing an active material according to an embodiment of the present invention.

[0188]

[0189] The present invention will be explained in more detail below through examples. However, these examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0190] [Manufacture of positive electrode active material]

[0191] (Example)

[0192] Step 1: Preparation of precursor solution

[0193] A precursor solution was prepared by mixing lithium sulfate, an ion-conducting additive, and a carbon-based additive in water (H2O). LiI was used as the ion-conducting additive, and precursor solutions were prepared by varying the type of carbon-based additive and / or the concentration of the solid content.

[0194] 1. A precursor solution was prepared by mixing Li2SO4: LiI: resorcinol in a weight ratio of 6: 1.25: 6 and dissolving it in water, and then adding 1 ml of a 38% ammonium hydroxide aqueous solution and 1.5 ml of a 30% formalin solution per 100 ml of water. The precursor solutions of Preparation Examples 1-1 to 1-4 were prepared by adjusting the concentration of the solid content to 10% to 30% by weight.

[0195] 2. The precursor solutions of Preparation Examples 2-1 to 2-2 were prepared by dissolving Li2SO4:LiI:PVA in water at a ratio of 6:1.25:6 and adjusting the concentration of the solid content to 10% to 30%.

[0196] 3. The precursor solutions of Preparation Examples 3-1 to 3-2 were prepared by dissolving Li2SO4:LiI:Sucrose in water in a ratio of 6:1.25:6 and adjusting the concentration of the solid content to 10% to 30% by weight.

[0197] 4. The precursor solutions of Preparation Examples 4-1 to 4-2 were prepared by mixing with water in a ratio of Li2SO4:LiI:Pitch = 6:4:2 and adjusting the concentration of the solid content to 10% to 30% by weight.

[0198] 5. A precursor solution of Preparation Example 5-1 was prepared by mixing Li2SO4:LiI:CNF in water in a ratio of 6:4:2 to a solid content concentration of 30%.

[0199] 6. After mixing with water in a ratio of Li2SO4:LiI:CB = 6:4:2, the precursor solution of Preparation Example 6-1 was prepared so that the solid content concentration was 30%.

[0200] When the solid content concentration was 10%, small particle sizes were formed, and when the solid content concentration was 30%, larger particles were formed.

[0201] Phase 2: Spraying Process

[0202] The prepared precursor solution was fed into a spray dryer (B”U”CHI Mini Spray Dryer S-200) and dried. Specifically, the precursor solution was fed into the spray dryer at an inlet temperature of 180°C and an outlet temperature of 100°C, with a solution injection rate of 10 ml / min, a spray gas velocity of 1800 L / h, and a drying gas velocity of 35 m / h. 2 A composite powder was obtained by drying at / h. The particle size was controlled through spray rate control.

[0203] Step 3: Heat Treatment Process

[0204] A cathode active material was prepared by heat-treating the manufactured composite powder. The manufactured composite powder was placed in a zirconium crucible and heat-treated in an Ar atmosphere for about 2 hours. The heat treatment temperature was controlled in the range of 400 to 700°C, and the results are shown in the table below.

[0205]

[0206] (Comparative Example)

[0207] The cathode active material of the comparative example was prepared using a dry ball milling process instead of the wet process of the example. Specifically, Li2S as a sulfur compound and LiI as an ion-conducting material were mixed in a weight ratio of approximately 30:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C at 600 rpm for 10 hours.

[0208] The Li2S-LiI composite and carbon nanofiber (CNF) were mixed in a weight ratio of approximately 50:10. The mixture was mechanically milled using a ball mill to prepare Li2S-LiI-CNF. The milling conditions were 25°C at 510 rpm for 10 hours.

[0209] The lithium-sulfur carbon composite prepared as described above was used as the positive electrode active material.

[0210] The cathode active materials prepared according to the examples and comparative examples below are summarized and shown in Table 1.

[0211] Synthesis Method Carbon Source Heat Treatment Temperature (°C) Solid Content Concentration (%) Spray Rate (ml / min) Shape / Size (D50) Preparation Example 1-1 Spray dry RF 700°C 10% 10ml / min Single particle / 4.8 μm Preparation Example 1-2 Spray dry RF 700°C 30% 10ml / min Single particle / 8.4 μm Preparation Example 1-3 Spray dry RF 700°C 10% 50ml / min Single particle / 6.2 μm Preparation Example 1-4 Spray dry RF 700°C 30% 50ml / min Single particle / 11.0 μm Preparation Example 2-1 Spray dry PVA 400°C 10% 10ml / min Single particle / 3.6 μm Preparation Example 2-2 Spray dry PVA 400°C 30% 10ml / min Single particle / 7.6 μm Preparation Example 3-1 Spray dry Sucrose 600℃ 10% 10ml / min single particle / 3.3 μm Preparation Example 3-2 Spray dry Sucrose 600℃ 30% 10ml / min single particle / 6.9 μm Preparation Example 4-1 Spray dry Pitch 500℃ 10% 10ml / min single particle / 5.2 μm Preparation Example 4-2 Spray dry Pitch 500℃ 30% 10ml / min single particle / 9.3 μm Preparation Example 5-1 Spray dry CNF 500℃ 30% 10ml / min single particle / 6.2 μm Preparation Example 6-1 Spray dry CB 500℃ 30% 10ml / min single particle / 7.5 μm Comparative Example 1-1 Ball mill CNF amorphous / 7.1 μm

[0212] Referring to Table 1, the shape and size of the cathode active material particles produced through the wet manufacturing method of the present invention can be seen. Specifically, it can be seen that the shape and size of the cathode active material can be easily controlled through factors such as the type of carbon-based additive, the concentration of solids, and the spraying speed.

[0213] Unlike the comparative example, by manufacturing a single-particle cathode active material and easily controlling its size and shape, the performance of the battery can be easily improved, such as by increasing the density of the cathode composite.

[0214]

[0215] Evaluation Example 1: Analysis of Cathode Active Material

[0216] FIGS. 5a to 5f are SEM images of a positive electrode active material according to an embodiment of the present invention. Referring to these figures, it can be confirmed that the positive electrode active material according to the embodiments of the present invention is a single particle having an overall spherical shape.

[0217] The particle size distribution of the cathode active material was analyzed using a particle size analyzer. Specifically, the Span value was calculated and analyzed.

[0218] The crystal structure of the cathode active material was analyzed using X-ray diffraction (XRD). Specifically, the size and lattice constant of the Li2S crystallites were derived from the first peak corresponding to the (111) crystal plane appearing at a diffraction angle 2θ = 27° ± 2.0° in the XRD spectrum.

[0219] The analysis results of the cathode active material are shown in Table 2 below.

[0220] Ionic conductivity mS / cm Electronic conductivity mS / cm Span rate (%) Li2S Crystalline particle size (nm) Lattice constant (Å) Preparation Example 1-17.0 X 10⁻⁶ -3 9.13.112.25.76 Manufacturing Example 2-16.8 X 10 -3 7.53.613.25.76 Manufacturing Example 3-16.6 X 10 -315.22.712.15.75 Manufacturing Example 4-15.3 X 10 -3 9.62.912.65.76 Manufacturing Example 5-16.7 X 10 -3 12.13.112.55.76 Manufacturing Example 6-13.6 X 10 -3 5.6 3.3 1 3.5 5.76 Comparative Example 1-1 3.2 X 10 -3 5.44.114.35.75Bare Li2S2.1 -10 ---

[0221] Referring to Table 2, it can be seen that the Li2S crystallite size in the cathode active material according to the embodiments of the present invention is 12.1 nm to 13.5 nm, which is lower than that of the comparative example. It can also be seen that the ionic conductivity and electrical conductivity are higher than those of the comparative example. In addition, the lattice constant value is equal to or greater than that of the comparative example, which is determined to be because the cathode active material forms a solid solution of lithium sulfide, an ionic conductive salt, and a carbon-based material.

[0222] Furthermore, considering the range of the calculated span values, it can be seen that the particle size distribution of the positive electrode active material is uniform. This implies that the method for manufacturing the positive electrode active material of the present invention facilitates the control of particle shape and size compared to the generally used ball mill solid-state method. Consequently, it is possible to manufacture uniform electrodes that are easy to synthesize in large quantities.

[0223]

[0224] [Manufacturing of Lithium-Sulfur Batteries]

[0225] Manufacturing of anodes

[0226] Anodes were prepared in the same manner, except that the anode active materials prepared according to the above preparation examples and comparative examples were used, respectively. An azirodite-based solid electrolyte (Li6PS5Cl, D50 = 3.0 μm) was prepared as the solid electrolyte. PTFE was prepared as the binder. The specific composition of the anodes is shown in Table 3 below.

[0227] The positive electrode active material and the solid electrolyte were placed in a mixer and mixed for about 2 minutes. A binder was added to the mixed powder and mixed with a mixer for about 20 seconds. The mixed powder was further mixed using a kneader and then passed through calender rolls to produce a membrane-shaped positive electrode active material layer. During the additional mixing and calendering process using the kneader, the binder was fiberized.

[0228] An anode was manufactured by placing a prepared anode active material layer on an anode current collector made of carbon-coated aluminum foil.

[0229] Preparation of a solid electrolyte layer

[0230] A mixture was prepared by adding an acrylic binder to a solid electrolyte, Li6PS5Cl, which is an argyrodite-type crystal. The solid electrolyte and the binder were mixed in an amount of 98.5 parts by weight and 1.5 parts by weight, respectively. A slurry was prepared by stirring while adding octyl acetate to the prepared mixture. The prepared slurry was applied using a bar coater onto a 15 μm thick nonwoven fabric placed on a 75 μm thick PET substrate, and a laminate was prepared by drying in air at 80°C for 10 minutes. After vacuum drying the prepared laminate at 80°C for 2 hours, the solid electrolyte layer was separated from the PET substrate to produce a solid electrolyte layer.

[0231] Manufacturing of the cathode

[0232] A SUS foil with a thickness of about 10 μm was prepared as a cathode current collector. As cathode coating materials, carbon black (CB) with a primary particle size of about 30 nm and silver (Ag) particles with an average particle size of about 60 nm were prepared.

[0233] 4 g of a mixed powder, prepared by mixing carbon black (CB) and silver particles 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 was prepared by stirring the mixed solution while gradually adding NMP to it. The prepared slurry was applied to a SUS sheet using a bar coater, dried in air at 80°C for 10 minutes, and then vacuum dried at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold-roll-pressed to flatten the surface to manufacture a cathode having a cathode coating layer / cathode current collector structure. The thickness of the cathode coating layer was approximately 15 μm. The surface areas of the cathode coating layer and the cathode current collector were the same.

[0234] Battery assembly

[0235] A solid electrolyte layer was positioned so that the cathode coating layer and the solid electrolyte layer were in contact, and an anode was placed on the solid electrolyte layer. The prepared laminate was subjected to plate pressing at approximately 85°C and a pressure of 500 MPa for 30 minutes. This pressing treatment sintered the solid electrolyte layer, thereby improving battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 μm.

[0236] Lithium-sulfur batteries containing positive electrode active materials according to the examples and comparative examples are summarized in Table 3 below.

[0237] Cathode active material (wt%) Solid electrolyte (wt%) Binder (wt%) Composition density (g / cc) Example 1 Preparation Example 1-1 80 wt% 19 wt% 1 wt% 1.62 Example 2 Preparation Example 2-1 80 wt% 19 wt% 1 wt% 1.72 Example 3 Preparation Example 3-1 80 wt% 19 wt% 1 wt% 1.74 Example 4 Preparation Example 4-1 80 wt% 19 wt% 1 wt% 1.69 Example 5 Preparation Example 1-2 70 wt% Preparation Example 3-1 10 wt% 19 wt% 1 wt% 1.79 Example 6 Preparation Example 1-2 60 wt% Preparation Example 3-1 20 wt% 19 wt% 1 wt% 1.82 Example 7 Preparation Example 1-2 50 wt% Preparation Example 3-1 30 wt% 19 wt% 1 wt% 1.84 Comparative Example 1 Comparative Example 1-1 80 wt% 19 wt% 1 wt% 1.58 Comparative Example 2 Comparative Example 1-1 70 wt% 29 wt% 1 wt% 1.56

[0238] Referring to Table 2, it can be seen that the electrode composite density of the lithium-sulfur battery according to the embodiments of the present invention is significantly higher than that of the comparative examples. This means that by controlling the size and shape of the positive electrode active material, a positive electrode with a uniform and stable structure can be manufactured. In addition, it can be seen that the composite density is higher in the case of Examples 5 to 7, which are manufactured to include positive electrode active material particles of different sizes.

[0239] The specific degree of performance improvement of the lithium-sulfur battery can be confirmed through the evaluation examples described below.

[0240]

[0241] Evaluation Example 2: Battery Performance Evaluation

[0242] The performance of the lithium-sulfur battery manufactured according to the embodiments and comparative examples of the present invention was evaluated. The first cycle involved charging at a constant current of 0.05 C for 20 hours until the battery voltage reached 2.8 V. Subsequently, discharging was performed at a current of 0.05 C for 20 hours until the battery voltage reached 1.0 V.

[0243] The second cycle involved charging at a constant current of 0.1 C for 10 hours until the battery voltage reached 2.8 V. Subsequently, discharging was performed at a constant current of 0.1 C for 10 hours until the battery voltage reached 1.0 V.

[0244] For the second cycle discharge capacity, the specific capacity based on Li2S and the specific capacity based on the entire electrode were measured, respectively.

[0245] After the second cycle, charging and discharging were performed for up to 20 cycles under the same conditions as the second cycle. The capacity retention rate was evaluated as shown in Equation 1 below.

[0246] <Mathematical Formula 1>

[0247] Capacity Retention Rate[%] = [20th Cycle Discharge Capacity / 1st Cycle Discharge Capacity] × 100

[0248] The measurement results of the charge / discharge characteristics of the lithium-sulfur battery are shown in Table 4 below.

[0249] 2nd Cycle (0.1 C) Discharge Capacity [mAh / g, Li2S] 2nd Cycle (0.1 C) Discharge Capacity [mAh / g, Electrode] Rate Characteristic (%) (0.1C / 0.05C Discharge Capacity) Capacity Retention Rate [%] (Capacity retention rate after 20 cycles at 0.1C) Example 18 2241196.994 Example 28 2641397.693 Example 38 2541397.494 Example 48 2141196.989 Example 58 334179892 Example 68 3741998.293 Example 78 3541897.894 Comparative Example 18 1040596.482 Comparative Example 28 6938194.285

[0250] Referring to the results in Table 4, it can be seen that the performance of the lithium-sulfur battery according to the embodiments of the present invention is further improved.

[0251] Specifically, by referring to the results regarding the specific capacity (mAh / g, Li2S) based on Li2S and the discharge capacity results for the electrodes, it can be seen that the discharge capacity of the lithium-sulfur battery according to the embodiments is higher than that of the comparative examples. This means that the discharge capacity relative to the mass of Li2S, which acts as a lithium source within the cathode active material, is high. This indicates that the single-particle composite synthesized by the method of the present invention is effective for the movement of lithium ions because its ionic and electronic conductivity are uniform compared to the composite of the comparative example. Consequently, it can be seen that the energy density is improved relative to the same mass. Furthermore, looking at the results regarding rate characteristics and capacity retention rate, it can be seen that the characteristics of the lithium-sulfur battery according to the embodiments have been improved.

[0252] By introducing a single-particle cathode active material, a cathode active material layer with a structure that is more stable, uniform, and dense compared to an amorphous one can be provided. As a result, a lithium-sulfur battery with overall improved rate characteristics, life characteristics, and energy density can be provided.

Claims

1. A positive active material comprising lithium sulfide, an ion-conducting salt, and a carbon-based material: The above lithium sulfide is Li2S n Includes at least one of (1≤n≤8, n is an integer), and The above ion-conducting salt includes a lithium salt, and The above positive active material has a single particle form in which the lithium sulfide, the ion-conducting salt, and the carbon-based material are combined.

2. In Paragraph 1, The above single particle comprises a solid solution of the lithium sulfide, the ion-conducting salt, and the carbon-based material. Positive active material.

3. In Paragraph 1, The sphericity of the above single particle is 0.7 to 1.0, Positive active material.

4. In Paragraph 1, The above lithium salt comprises LiF, LiCl, LiBr, LiI, or a combination thereof. Positive active material.

5. In Paragraph 1, The above ion-conducting salt further comprises a metal halide, and The metal of the above metal halide comprises at least one selected from the group consisting of aluminum (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn). Positive active material.

6. In Paragraph 5, The above lithium salt is LiI, and the above metal halide is AlI3, Positive active material.

7. In Paragraph 1, The average particle size of the above single particles is 1 μm to 15 μm, Positive active material.

8. In Paragraph 1, The span value of the single particle measured by a particle size analyzer is 2.5 to 3.7, Positive active material.

9. Anode active material according to paragraph 1; and Anode containing a solid electrolyte.

10. In Paragraph 9, The above positive active material includes a first particle and a second particle, and The average particle size of the first particle is larger than the average particle size of the second particle. anode.

11. In Paragraph 10, The average particle size of the first particle is 8 μm to 15 μm, and The average particle size of the second particle is 1 μm to 6 μm, anode.

12. In Paragraph 10, The mixing weight ratio of the first and second particles within the anode is 5:5 to 8:2, anode.

13. In Paragraph 9, The above solid electrolyte is Li 7-c M a PS 6-c X c It is an argyrodite-type sulfide-based solid electrolyte represented by (0≤a≤2, 0≤c≤2), and The above X is F, Br, Cl, or a combination thereof, and The above M is candium (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, anode.

14. Preparation of a precursor mixture solution; Obtaining a composite powder by spray-drying the above precursor mixture solution; and The above composite powder includes heat-treating, A method for manufacturing a positive electrode active material, wherein the above-mentioned precursor mixed solution comprises lithium sulfate, an ion-conducting additive, and a carbon-based additive.

15. In Paragraph 14, Preparing the above precursor mixed solution comprises adjusting the concentration of the mixed solution to a range of 2% by weight to 50% by weight. Method for manufacturing positive electrode active material.

16. In Paragraph 14, The above spray drying includes adjusting the spray pressure to a range of 20 kPa to 300 kPa, Method for manufacturing positive electrode active material.

17. In Paragraph 14, The above spray drying includes controlling the spray rate to a range of 5 mL / min to 100 mL / min, Method for manufacturing positive electrode active material.

18. In Paragraph 14, The above spray drying is performed at a temperature of 40 ℃ to 250 ℃, Method for manufacturing positive electrode active material.

19. In Paragraph 14, The above heat treatment is performed at a temperature of 300 ℃ to 800 ℃, and Performed in a reducing atmosphere composed of hydrogen (H2) and argon (Ar) gases, Method for manufacturing positive electrode active material.

20. In Paragraph 14, The above carbon-based additive is at least one selected from the group consisting of sucrose, glucose, RF (Resorcinol-Formaldehyde), PVA (Polyvinylalchol), pitch, chitosan, carbon black, carbon nanofiber (CNF), carbon nanotube (CNT), and graphite. Method for manufacturing positive electrode active material.

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