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

Abstract

The present invention relates to a positive electrode active material for a lithium-sulfur battery and a manufacturing method therefor, the positive electrode active material for a lithium-sulfur battery comprising a composite of a sulfur-based substance, a metal halide salt, and a carbon-based material doped with a transition metal.

Description

Cathode active material for lithium-sulfur batteries and method for manufacturing the same

[0001] The present invention relates to a positive electrode active material for a lithium-sulfur battery and a method for manufacturing the same.

[0002] Lithium-ion batteries are used in various fields due to their long lifespan, low self-discharge rate, and safety. However, because lithium-ion batteries utilize metal oxides such as lithium cobalt oxide (LCO) and lithium nickel cobalt aluminum oxide (NCA) as cathode materials, they are expensive and have limitations in improving energy density. Consequently, there is growing interest in batteries that can enhance energy density while ensuring stability and price competitiveness.

[0003] The problem that the present invention aims to solve is to provide a positive electrode active material for a lithium-sulfur battery capable of improving rate characteristics such as energy density and cycle life, and a method for manufacturing the same.

[0004] Another problem to be solved by the present invention is to provide a lithium-sulfur battery with reduced cell resistance and improved lifespan characteristics.

[0005] A positive electrode active material for a lithium-sulfur battery according to one embodiment of the present invention comprises a composite of a sulfur-based material, a metal halide salt, and a carbon-based material doped with a transition metal.

[0006] A method for manufacturing a positive electrode active material for a lithium-sulfur battery according to another embodiment of the present invention comprises the steps of: manufacturing a carbon-based material doped with a transition metal; first milling a mixture of a sulfur-based material and a metal halide salt; and second milling a mixture of the first milling product and the carbon-based material doped with a transition metal.

[0007] A lithium-sulfur battery according to another embodiment of the present invention comprises a positive electrode including the positive active material; a negative electrode; and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0008] A positive electrode active material for a lithium-sulfur battery according to one embodiment of the present invention comprises a composite of a sulfur-based material, a metal halide salt, and a carbon-based material doped with a transition metal, thereby having excellent ionic conductivity and electronic conductivity.

[0009] In addition, a lithium-sulfur battery according to another embodiment of the present invention includes a positive electrode comprising a positive electrode active material for the lithium-sulfur battery, thereby having excellent current density and energy density characteristics, and excellent cycle characteristics such as no overvoltage or capacity degradation due to repeated charging and discharging.

[0010] FIG. 1 is a cross-sectional view of a lithium-sulfur battery according to one embodiment of the present invention.

[0011] Figures 2 and 3 are schematic diagrams illustrating the ion conduction pathway of lithium ions.

[0012] Figure 4 is a scanning electron microscope (SEM) image of a transition metal-doped carbon-based material (Example 1) according to one embodiment of the present invention.

[0013] FIG. 5 is a transmission electron microscope (TEM) image of a transition metal-doped carbon-based material (Example 1) according to one embodiment of the present invention.

[0014] Figure 6 shows the results of elemental analysis through EDX mapping (Energy Dispersive X-ray spectroscopy mapping) of a transition metal-doped carbon-based material (Example 1) according to one embodiment of the present invention.

[0015] Figure 7 shows the results of X-ray diffraction analysis of a doped carbon-based material and a carbon-based material not doped with transition metals.

[0016] Figure 8 shows the discharge curves in the first cycle (0.05C) of Example 1 and Comparative Example 1.

[0017] Figure 9 shows the discharge curves at the second cycle (0.05C) of Example 1 and Comparative Example 1.

[0018] FIG. 10 shows the discharge curves at the third cycle (0.1C) of Example 1 and Comparative Example 1.

[0019] FIG. 11 is a schematic cross-sectional view showing an enlarged view of area A of FIG. 1.

[0020] FIG. 12 is a schematic cross-sectional view showing an enlarged view of area B of FIG. 4.

[0021] FIG. 13 shows a schematic flowchart of a method for manufacturing a positive electrode active material for a lithium-sulfur battery according to one embodiment of the present invention.

[0022] FIG. 14 is a schematic diagram of the steps for manufacturing a carbon-based material doped with a transition metal according to one embodiment of the present invention.

[0023] FIGS. 15 and 16 are cross-sectional views of a lithium-sulfur battery according to another embodiment of the present invention.

[0024] [Explanation of the symbol]

[0025] 1: Lithium-sulfur battery

[0026] 100: Anode 110: Anode current collector

[0027] 120: Positive active material layer 121: Positive active material

[0028] 122: Sulfide-based solid electrolyte 123: Ionic conductive complex

[0029] 121a: Sulfur series substances 121b: First metal halide salts

[0030] 121c: Secondary metal halide salts 121d: Carbonaceous substances

[0031] 200: Cathode 210: Cathode current collector

[0032] 220: Coating layer 230: Lithium metal layer

[0033] 300: Solid electrolyte layer

[0034] 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.

[0035] 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.

[0036] The embodiments described herein will be explained with reference to cross-sectional and / or plan views, which are exemplary illustrations of the invention. In the drawings, the thicknesses of the films and regions are exaggerated for effective explanation 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.

[0037] In the various embodiments of this specification, terms such as first, second, primary, secondary, etc., have been used to describe various components, but 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.

[0038] All numbers and expressions indicating the amounts of components, reaction conditions, etc. described in this specification should be understood as being modified by the term "about" in all cases unless otherwise specified.

[0039] 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.

[0040] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0041] 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.

[0042] In this specification, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state, and “alloy” means a mixture of two or more metals.

[0043] In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation, and “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0044] In this specification, “lithiation” and “to lithiate” refer to the process of adding lithium to an electrode active material, and “delithiation” and “to delithiate” refer to the process of removing lithium from an electrode active material.

[0045] In this specification, “charge” and “to charge” refer to the process of providing electrochemical energy to a battery, and “discharge” and “to discharge” refer to the process of removing electrochemical energy from a battery.

[0046] In this specification, “anode” refers to an electrode where electrochemical reduction and lithiation occur during the discharge process, and “cathode” refers to an electrode where electrochemical oxidation and delithiation occur during the discharge process.

[0047] In this specification, “ionic conductivity” refers to the ability of ions to move within a material, meaning the degree to which ions, such as lithium ions, can move smoothly between electrodes, and “electronic conductivity” refers to the ability of electrons to move within a material, meaning the degree to which electrons can move smoothly between electrodes.

[0048] Lithium-sulfur batteries are batteries that use sulfur-based materials as the cathode active material. Sulfur is non-toxic and abundant, offering excellent price competitiveness. Furthermore, compared to lithium-ion batteries that use metallic materials such as nickel and cobalt as cathode materials, lithium-sulfur batteries utilize the lighter sulfur, resulting in a higher energy density relative to weight. Consequently, it is easy to achieve characteristics of both lightness and high capacity.

[0049] Unlike lithium-ion batteries, which generate electrical energy through the redox reaction of electrons separated from lithium ions, lithium-sulfur batteries generate energy through the stepwise conversion of sulfur. Specifically, sulfur, which has a structure consisting of eight atoms in a ring form, undergoes a continuous reduction reaction during discharge and is converted into lithium polysulfide, which has a linear structure, and finally converted into lithium sulfide, thereby generating electrical energy.

[0050] Lithium-sulfur batteries offer the advantage of easily ensuring high capacity and stability; however, sulfur, the main component of the cathode active material, is an insulator and thus exhibits low ionic and electronic conductivity. Furthermore, problems arise where volume changes occur during charging and discharging, or polysulfides—intermediates of the reduction reaction—leach out, degrading the battery's capacity and lifespan. Consequently, research is ongoing to improve the performance and lifespan characteristics of lithium-sulfur batteries.

[0051] Meanwhile, currently commercialized lithium-ion batteries utilize liquid electrolytes and polymer separators. While the liquid electrolyte can penetrate the pores between the anode and cathode to function as a conduction pathway for lithium ions, it poses risks such as fire and explosion due to continuous charging, discharging, or degradation. Additionally, polymer separators are susceptible to damage due to their weak mechanical properties and can cause short circuits by allowing physical contact between the anode and cathode.

[0052] Consequently, there is growing interest in solid electrolytes that can replace liquid electrolytes and polymer separators while ensuring high stability and energy density. Solid electrolytes can be classified into sulfide-based, oxide-based, and polymer-based types. Sulfide-based solid electrolytes exhibit excellent ionic conductivity but suffer from low atmospheric and electrochemical stability. Oxide-based solid electrolytes offer relatively good ionic conductivity and electrochemical stability but have the problem of high interfacial resistance. Polymer-based solid electrolytes have low interfacial resistance due to their excellent flexibility but also suffer from very low ionic conductivity. Therefore, research is continuing on all-solid-state batteries that can ensure stability while maintaining excellent performance, such as ionic conductivity.

[0053] FIG. 1 is a cross-sectional view of a lithium-sulfur battery according to an embodiment of the present invention. Referring to FIG. 1, a lithium-sulfur battery (1) according to an embodiment of the present invention may include a positive electrode (100), a negative electrode (200), and a solid electrolyte layer (300) disposed between the positive electrode (100) and the negative electrode (200). More specifically, a lithium-sulfur battery (1) according to an embodiment of the present invention may have a structure in which a negative electrode (200), a solid electrolyte layer (300), a positive active material layer (120), and a positive current collector (110) are stacked in order. However, not limited thereto, the lithium-sulfur battery (1) may further include an additional functional layer, such as an adhesion enhancing layer, between the positive electrode (100) and the solid electrolyte layer (300), or between the negative electrode (200) and the solid electrolyte layer (300).

[0054]

[0055] Cathode active material for lithium-sulfur batteries

[0056] A positive electrode active material for a lithium-sulfur battery according to one embodiment of the present invention comprises a composite of a sulfur-based material, a metal halide salt, and a carbon-based material doped with a transition metal. More specifically, the positive electrode active material according to one embodiment of the present invention may be a composite of a sulfur-based material, a metal halide salt, and a carbon-based material doped with a transition metal.

[0057] FIGS. 2 and FIGS. 3 are schematic diagrams illustrating the ion conduction pathways of lithium ions. Specifically, FIGS. 2 and FIGS. 3 illustrate, respectively, enlarged schematic diagrams of a positive electrode active material layer including a positive electrode active material (CAC) and a solid electrolyte (SEP), showing the ion conduction pathway (R1) and the blocked ion conduction pathway (R2) of lithium ions.

[0058] Referring to FIGS. 2 and 3, the solid electrolyte (SEP) can form an ion conduction path (R1) to move lithium ions. However, if there is insufficient solid electrolyte within the positive active material layer or if the solid electrolyte is isolated by the positive active material (CAC), the movement of lithium ions may not proceed smoothly due to the blocked ion conduction path (R2). Additionally, if the ion conductivity of the positive active material is low, ion contact between the positive active materials may not proceed smoothly. As such, if the movement or contact of lithium ions does not proceed smoothly, there is a problem that the ion conductivity of the positive active material layer may be reduced and the energy density may be lowered.

[0059] A positive electrode active material for a lithium-sulfur battery according to one embodiment of the present invention comprises a composite of a sulfur-based material, a metal halide salt, and a carbon-based material doped with a transition metal, thereby having excellent ionic conductivity and electronic conductivity. More specifically, since the positive electrode active material for a lithium-sulfur battery comprises the composite, it has excellent ionic conductivity and electronic conductivity, so ionic contact between positive electrode active materials is smooth, and even if the solid electrolyte is isolated by the positive electrode active material, an ion transport path (R1) of lithium ions can be smoothly formed, thereby improving rate characteristics such as energy density and cycle life of a lithium-sulfur battery containing the same.

[0060] FIG. 11 is a schematic cross-sectional view illustrating an enlarged view of area A of FIG. 1. Specifically, a positive active material layer according to one embodiment of the present invention may include a positive active material (121) and a sulfide-based solid electrolyte (122). Referring to FIG. 11, an ion conduction path (R1') through which lithium ions move to the sulfide-based solid electrolyte (122) and an ion conduction path (R2”) through which lithium ions move to the sulfide-based solid electrolyte (122) and the positive active material (121) may be formed in the positive active material layer according to one embodiment of the present invention.

[0061] FIG. 12 is a schematic cross-sectional view showing an enlarged view of region B of FIG. 11. FIG. 5 is an enlarged view of the region corresponding to region B of FIG. 11 to explain in more detail a positive electrode active material, specifically a composite of a sulfur-based material, a metal halide salt, and a transition metal-doped carbon-based material within the positive electrode active material. A positive electrode active material according to one embodiment of the present invention may include a composite of a sulfur-based material (121a), a first metal halide salt (121b), a second metal halide salt (121c), and a transition metal-doped carbon-based material (121d).

[0062] The above-mentioned positive active material may have a particle form. For example, the above-mentioned positive active material may be a composite of the sulfur-based material, a metal halide salt, and a carbon-based material doped with a transition metal, and the composite of the sulfur-based material, the metal halide salt, and the carbon-based material doped with a transition metal may have a particle form.

[0063] For example, the particle size of the positive active material may be 8 μm or less. For example, the average particle size (D50) of the positive active material or the composite may be 7 μm or less or 6 μm or less, and may be 1 μm or more, 2 μm or more, 3 μm or more, or 4 μm or more.

[0064] By satisfying the above range for the particle size of the positive electrode active material, more specifically the particle size of the composite, volume change during charging and discharging can be suppressed, thereby effectively preventing degradation and improving lifespan characteristics. If the particle size of the composite falls outside the above range, volume change of the composite during charging and discharging increases, which may accelerate degradation and consequently degrade the cycle characteristics and lifespan characteristics of the battery.

[0065] The above particle size may be the average particle size (D50) measured using laser diffraction, scanning electron microscopy, etc. For example, the particle size of the above composite may be the arithmetic mean of the particle sizes of a plurality of particles measured using software in a scanning electron microscopy image.

[0066] The above-mentioned positive electrode active material can have excellent electrical conductivity by comprising a complex of a sulfur-based material, a metal halide salt, and a transition metal-doped carbon-based material. The electrical conductivity of the above-mentioned positive electrode active material is 1.0 × 10⁻⁶ at 45°C. -3 S / cm to 1.0 × 10 -1 It may be S / cm. For example, the electrical conductivity of the positive active material or the composite is 1.5 × 10⁻⁶ -3 S / cm or greater, 3.0 × 10-3 S / cm or greater, 5.0 × 10 -3 S / cm or more or 7.0 × 10 -3 It may be greater than S / cm, and 5.0 × 10 -2 S / cm or less, 2.0 × 10 -2 S / cm or less or 1.0 × 10 -2 It may be less than S / cm. The above electrical conductivity may be measured using the DC polarization method.

[0067] In addition, the content of the positive active material may be 40% to 80% by weight with respect to the total weight of the positive active material layer. For example, the content of the positive active material in the positive active material layer may be 45% to 80% by weight, 50% to 80% by weight, or 60% to 75% by weight with respect to the total weight of the positive active material layer. By satisfying the above ranges for the content of the positive active material, the rate characteristics of the battery containing it can be improved.

[0068] The content of the composite of the sulfur-based material, metal halide salt, and transition metal-doped carbon-based material may be 40% to 90% by weight with respect to the total weight of the positive electrode active material layer. For example, the content of the composite of the sulfur-based material, metal halide salt, and transition metal-doped carbon-based material within the positive electrode active material layer may be 50% to 85% by weight or 60% to 80% by weight with respect to the total weight of the positive electrode active material layer. By satisfying the above ranges for the content of the composite of the sulfur-based material, metal halide salt, and transition metal-doped carbon-based material, the capacity characteristics of the battery containing the same can be improved.

[0069]

[0070] sulfur-based substances

[0071] According to one embodiment of the present invention, the sulfur-based material (121a) is S8 and Li2S nIt may include at least one of (1 ≤ n ≤ 8, where n is an integer). Specifically, the positive active material of the present invention may include elemental sulfur (S), and the elemental sulfur may exist in the form of a sulfur-based material including at least one of S8 and Li2Sn (1 ≤ n ≤ 8, where n is an integer). For example, the content of the elemental sulfur in the positive active material layer may be 10% to 80% by weight, 10% to 65% by weight, or 15% to 60% by weight with respect to the total weight of the positive active material layer.

[0072] Sulfur is attracting attention as a next-generation cathode material because it has a high theoretical capacity (1,672 mAh / g), is abundant on Earth, and is relatively inexpensive. Since sulfur has relatively low ionic conductivity, the cathode active material may include a solid electrolyte, a binder, a conductive material, etc., so that a smooth ionic conduction path for lithium ions can be formed.

[0073] The above sulfur-based material may undergo a continuous oxidation / reduction reaction of sulfur and / or lithium sulfide. For example, the above sulfur-based material (121a) may undergo S through a continuous reduction reaction of sulfur. 8-> It can be converted from Li2S8 to Li2S6 to Li2S4 to Li2S2 to Li2S. During this process, lithium ions move between the anode and cathode, and simultaneously, electrons move through an external circuit to generate an electric current.

[0074] The content of the sulfur-based material may be 10% to 80% by weight with respect to the total weight of the composite. For example, the content of the sulfur-based material may be 15% to 80% by weight, 20% to 70% by weight, 25% to 70% by weight, or 40% to 70% by weight with respect to the total weight of the composite.

[0075]

[0076] metal halide salts

[0077] According to one embodiment of the present invention, the metal halide salt may include two different types of metal halide salts. Specifically, the metal halide salt may include a first metal halide salt (121b) containing an alkali metal and a second metal halide salt (121c) containing a boron group metal (see FIG. 12). Since the metal halide salt includes two different types of metal halide salts, a composite, more specifically a solid solution, can be formed, thereby improving ion conductivity while maintaining the overall shape, reducing interfacial resistance, and effectively suppressing the leaching of lithium polysulfide, which can improve the capacity and cycle characteristics of the battery.

[0078] The above solid solution is (1-xy)Li2S n It may include -xAX-yBX3 or (1-xy)S8-xAX-yBX3. The x and the y are each 0.01 ≤ x ≤ 0.3 and 0.01 ≤ y ≤ 0.3, and the n is an integer 1 ≤ n ≤ 8, the A is an alkali metal, the B is a boron group metal, and the X is a halogen element.

[0079] The first metal halide salt may be a binary compound composed of an alkali metal and one element selected from Group 17 of the periodic table. Specifically, the first metal halide salt may be a lithium salt. For example, the first metal halide salt may include LiF, LiCl, LiBr, LiI, or a combination thereof.

[0080] The above first metal halide salt can improve the ion conductivity of the positive electrode active material by more easily forming a composite, more specifically a solid solution, with the above sulfur-based material.

[0081] The content of the first metal halide salt may be 2.5% to 15% by weight with respect to the total weight of the composite. For example, the content of the first metal halide salt may be 2.5% to 10% by weight, 3.3% to 6.6% by weight, 5% to 12.5% ​​by weight, or 6% to 10% by weight with respect to the total weight of the composite.

[0082] The weight ratio of the sulfur-based material and the first metal halide salt may be 30:1 to 1:1. For example, the weight ratio of the sulfur-based material and the first metal halide salt may be 20:1 to 2:1 or 10:1 to 3:1.

[0083] In addition, the second metal halide salt may be a binary compound composed of a boron group metal and one element selected from Group 17 of the periodic table. For example, the second metal halide salt may include AlF3, AlCl3, AlBr3, AlI3, GaF3, GaCl3, GaBr3, GaI3, InF3, InCl3, lnBr3, lnI3, TiF3, TiCl3, TiBr3, TiI3, or a combination thereof.

[0084] The second metal halide salt can more easily form a composite, more specifically a solid solution, with the sulfur-based material and the first metal halide salt, thereby suppressing the leaching of lithium polysulfide and improving the capacity and cycle characteristics of the battery.

[0085] In addition, the second metal halide salt can lower interfacial resistance while maintaining the overall shape of the composite. Specifically, the sulfur-based material undergoes oxidation / reduction to produce S8 and Li2S nEven if the shape is deformed between (1 ≤ n ≤ 8, where n is an integer), the shape deformation of the composite and / or the positive active material can be minimized by the second metal halide salt, thereby easily maintaining the overall shape and thus improving cycle characteristics.

[0086] The content of the second metal halide salt may be 7.5% to 45% by weight with respect to the total weight of the composite. For example, the content of the second metal halide salt may be 7.5% to 30% by weight, 10% to 20% by weight, 15% to 37.5% by weight, or 20% to 31% by weight with respect to the total weight of the composite.

[0087] The weight ratio of the sulfur-based material and the second metal halide salt may be 10:1 to 1:1. For example, the weight ratio of the sulfur-based material and the second metal halide salt may be 5:1 to 1:1 or 5:1 to 2:1.

[0088] In addition, the weight ratio of the first metal halide salt and the second metal halide salt may be 1:1 to 1:20. For example, the weight ratio of the first metal halide and the second metal halide salt may be 3:1 to 1:9, 1:1 to 1:9, or 1:2 to 1:9. By satisfying the above ranges for the weight ratio of the first and second metal halide salts, the effect of improving ion conductivity and capacitance characteristics can be maximized.

[0089] The content of the metal halide salt may be 10% to 60% by weight with respect to the total weight of the composite. For example, the total content of the metal halide salt may be 10% to 40% by weight, 15% to 30% by weight, 20% to 50% by weight, or 25% to 45% by weight with respect to the total weight of the composite.

[0090]

[0091] Transition metal-doped carbon-based materials

[0092] The transition metal-doped carbon-based material (121d) can form a complex with the sulfur-based material (121a) and the metal halide salt (121b and 121c). The complex of the sulfur-based material, the metal halide salt, and the transition metal-doped carbon-based material is distinguished from a simple mixture of the sulfur-based material, the metal halide salt, and the transition metal-doped carbon-based material. A simple mixture of the sulfur-based material, the metal halide salt, and the transition metal-doped carbon-based material may have high interfacial resistance because it fails to maintain a dense interface between the sulfur-based material, the metal halide salt, and the transition metal-doped carbon-based material, which can degrade the lifespan characteristics of the battery.

[0093] FIG. 4 is a scanning electron microscope (SEM) image of a transition metal-doped carbon-based material (Example 1) according to one embodiment of the present invention, FIG. 5 is a transmission electron microscope (TEM) image of a transition metal-doped carbon-based material (Example 1) according to one embodiment of the present invention, and FIG. 6 shows the results of elemental analysis through EDX mapping (Energy Dispersive X-ray spectroscopy mapping) of a transition metal-doped carbon-based material (Example 1) according to one embodiment of the present invention.

[0094] A carbon-based material doped with a transition metal according to one embodiment of the present invention may be manufactured using an electrospinning method. Referring to FIGS. 4 to 6, it can be confirmed that the carbon-based material according to one embodiment of the present invention does not exhibit crystalline convex shapes on its surface and that the transition metal Fe is doped with a uniform thickness. Since the carbon-based material doped with a transition metal according to one embodiment of the present invention is manufactured using an electrospinning method, the doped material is well dispersed with a uniform thickness, thereby exhibiting excellent properties. A method for manufacturing a carbon-based material doped with a transition metal using an electrospinning method will be described in detail below.

[0095] The content of the transition metal doped into the carbon-based material may be 5 ppm to 200 ppm. For example, the content of the transition metal doped into the carbon-based material may be 5 ppm to 180 ppm, 5 ppm to 160 ppm, 10 ppm to 130 ppm, or 10 ppm to 100 ppm. By satisfying the above range for the doping amount of the transition metal, the dispersibility of the doped transition metal can be improved. For example, if the doping amount of the transition metal exceeds the above range, aggregation of the transition metal may occur, which may reduce the uniformity of the doping thickness or dispersibility.

[0096] The above transition metal may include iron (Fe), titanium (Ti), zinc (Zn), vanadium (V), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), molybdenum (Mo), palladium (Pd), silver (Ag), cadmium (Cd), tungsten (W), iridium (Ir), gallium (Ga), indium (In), or a combination thereof. When the above transition metal includes iron (Fe), it may be advantageous in that it can increase the electrochemically active sites of carbon to promote the insertion and release of lithium ions, but it is not limited thereto.

[0097] The above-mentioned carbon-based material is a material containing carbon atoms and is not particularly limited as long as it is used as a conductive material in the relevant technical field. Furthermore, the form of the above-mentioned carbon-based material may be in the form of particles, sheets, flakes, etc., but is not limited thereto. For example, the carbon-based material may include crystalline carbon, amorphous carbon, or a combination thereof, and may also include a calcined product of a carbon precursor.

[0098] In addition, the carbon-based material may be a carbon nanostructure and may include a one-dimensional carbon nanostructure, a two-dimensional carbon nanostructure, a three-dimensional carbon nanostructure, or a combination thereof. For example, the carbon nanostructure may include carbon nanotubes (CNT), carbon nanofibers (CNF), carbon nanobelts, carbon nanorods, graphene, or a combination thereof.

[0099] In addition, the carbon-based material may be a porous carbon-based material or a non-porous carbon-based material and may include periodic and regular two-dimensional or three-dimensional pores. For example, the carbon-based material may include carbon black such as Ketjen black, acetylene black, Denka black, thermal black, channel black, graphite, activated carbon, or a combination thereof.

[0100] In addition, the carbon-based material may include a fibrous carbon-based material. If the carbon-based material is a fibrous carbon-based material, electron conduction from the surface to the interior of the composite containing it can be performed more easily, thereby further improving electron conductivity. As a result, the internal resistance of the positive electrode active material containing the composite can be reduced, and the cycle characteristics of the battery containing it can be further improved.

[0101] The aspect ratio of the fibrous carbon-based material may be 2 or more, 3 or more, 4 or more, 5 or more, 10 or more, or 20 or more, and may be 2 to 30, 2 to 20, 2 to 10, 2 to 8, 2 to 5, 2 to 4, 3 to 30, 4 to 30, 5 to 30, 10 to 30, or 20 to 30. By satisfying the above ranges for the aspect ratio of the fibrous carbon-based material, the effect of enhancing the electronic conductivity of the composite containing it can be maximized, while also mitigating the imbalance of local electronic conductivity within the composite.

[0102] The diameter of the fibrous carbon-based material may be 0.01 μm to 10 μm, 0.05 μm to 10 μm, or 0.1 μm to 5 μm, and the length may be 1 μm to 50 μm or 1 μm to 20 μm. The diameter and length of the fibrous carbon-based material may be measured from scanning electron microscope (SEM) or transmission electron microscope (TEM) images, or may be measured by laser diffraction.

[0103] Additionally, the fibrous carbon-based material may include carbon nanostructures. For example, the carbon nanostructures may include carbon nanofibers (CNF), carbon nanotubes (CNT), carbon nanobelts, carbon nanorods, or a combination thereof. The 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.

[0104] For example, the primary carbon nanostructure may have a diameter of 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, and a length of 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.

[0105] Additionally, the secondary carbon nanostructure may be a structure formed by assembling primary carbon nanostructures to form a bundle or rope type, either wholly or partially. For example, the secondary carbon nanostructure may include a bundle-type carbon nanostructure, a rope-type carbon nanostructure, or a combination thereof.

[0106] For example, the secondary carbon nanostructure may have a diameter of 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, and a length of 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.

[0107] The diameter and length of the above primary and secondary carbon nanostructures may be measured from scanning electron microscope (SEM) or transmission electron microscope (TEM) images, or may be measured by laser diffraction.

[0108] Specifically, the carbon-based material may include carbon nanofibers (CNF), graphene, carbon nanotubes (CNT), carbon black, acetylene black, activated carbon, graphite, or a combination thereof.

[0109] As a specific example, the carbon-based material may be a carbon nanofiber. By using a carbon nanofiber as the carbon-based material, the effect of improving rate characteristics due to transition metal doping can be maximized.

[0110] The carbon nanofiber may have a length of 1 μm to 50 μm. For example, the length of the carbon nanofiber may be 1 μm to 40 μm, 1.5 μm to 35 μm, 2 μm to 25 μm, or 3 μm to 20 μm.

[0111] The carbon nanofiber may have a diameter of 0.01 μm to 10 μm. For example, the diameter of the carbon nanofiber may be 0.02 μm to 8 μm, 0.05 μm to 10 μm, or 0.1 μm to 5 μm.

[0112] The carbon nanofiber may have an aspect ratio of 2 to 30. For example, the aspect ratio of the carbon nanofiber may be 2 to 25, 3 to 20, 4 to 15, 5 to 10, 5 to 30, 10 to 30, or 20 to 30.

[0113] In addition, the transition metal-doped carbon-based material may have peaks at diffraction angles (2θ) of 25±0.2° and 43±0.2° in X-ray powder diffraction (XRD). More specifically, the transition metal-doped carbon-based material may have peaks at diffraction angles (2θ) of 25±0.2° and 43±0.2° in X-ray powder diffraction (XRD) by including carbonized carbon.

[0114] Figure 7 shows the results of X-ray diffraction analysis of doped carbon-based materials and carbon-based materials not doped with transition metals. Specifically, 1.8 g of polyvinylpyrrolidone (PVP) was dissolved in 8.2 g of water at room temperature and stirred for 24 hours; then, 5 mM, 10 mM, 20 mM, 30 mM, 40 mM, and 50 mM of FeCl3·6H2O were added, respectively, and stirred for 24 hours to prepare mixed solutions of transition metal precursors and carbon precursors. Depending on the content of FeCl3·6H2O, they were designated as Fe@CNF-5, Fe@CNF-10, Fe@CNF-20, Fe@CNF-30, Fe@CNF-40, and Fe@CNF-50 (see Figure 7).

[0115] Subsequently, the above-mentioned mixed solution was placed in a disposable syringe, and an electrospinning process was performed for 12 hours using a stainless steel nozzle to form a pre-carbon-based material. At this time, the electrospinning process conditions were 22 kV, 0.0004 mm / s, and 15 cm. Afterward, the pre-carbon-based material was left overnight in an oven at 60°C, and then carbonized through heat treatment to produce iron (Fe)-doped carbon nanofibers (FeCNF). At this time, the heat treatment was performed sequentially by stabilizing the material by leaving it in a furnace at 150°C for 24 hours, raising the temperature to 220°C for pre-oxidation, and then carbonizing it at a temperature of 900°C for 2 hours under an inert gas (Ar2).

[0116] X-ray diffraction analysis results were obtained for the iron (Fe)-doped carbon nanofiber (FeCNF) and the transition metal-undoped CNF prepared above using an XRD-7000 (manufacturer: Shimadzu). Specifically, the diffracted wavelength was measured by colliding the above carbon-based material with Cu Kα radiation at 40 mA and 40 kV at a diffraction angle (2θ) of 10° to 80° and a scan speed of 2° / min. At this time, the diffraction angle (2θ) at which the peak of the diffracted wavelength appears was confirmed.

[0117] Referring to FIG. 7, iron (Fe)-doped carbon nanofibers (FeCNF) have peaks at diffraction angles (2θ) of about 25° and 43°, whereas the CNF of Comparative Example 1 did not show a peak.

[0118] In addition, the above transition metal-doped carbon-based material has an electrical conductivity of 1.0 × 10⁻⁶ 4 S / cm to 1.0 × 10 6 It can be S / cm. For example, the electrical conductivity of the above transition metal-doped carbon-based material is 3.0 × 10⁻⁶ 4 S / cm or greater, 5.0 × 10 4 S / cm or more or 7.0 × 10 4 It may be greater than S / cm, and 9.0 × 10 5 S / cm or less, 5.0 × 10 5 S / cm or less or 1.0 × 10 5 It may be less than S / cm.

[0119] The above transition metal-doped carbon-based material may have a specific surface area of ​​3 m² / g to 30 m² / g. For example, the specific surface area of ​​the above transition metal-doped carbon-based material may be 5 m² / g to 25 m² / g, 7 m² / g to 20 m² / g, or 9 m² / g to 15 m² / g.

[0120] The content of the transition metal-doped carbon-based material may be 1% to 30% by weight with respect to the total weight of the composite. For example, the content of the transition metal-doped carbon-based material may be 1% to 25% by weight, 5% to 20% by weight, or 10% to 20% by weight with respect to the total weight of the composite. By satisfying the above range for the content of the carbon-based material, the cycle characteristics of the battery containing it can be further improved. Specifically, if the content of the transition metal-doped carbon-based material is below the above range, the electronic conductivity of the composite containing it may be too low, which may increase the internal resistance of the positive electrode active material, and if the content of the transition metal-doped carbon-based material exceeds the above range, the energy density of the battery containing it may decrease.

[0121]

[0122] Method for manufacturing a positive electrode active material for a lithium-sulfur battery

[0123] A method for manufacturing a positive electrode active material for a lithium-sulfur battery according to another embodiment of the present invention comprises the steps of: manufacturing a carbon-based material doped with a transition metal; first milling a mixture of a sulfur-based material and a metal halide salt; and second milling a mixture of the first milling product and the carbon-based material doped with a transition metal.

[0124] FIG. 13 shows a schematic flowchart of a method (S100) for manufacturing a positive electrode active material for a lithium-sulfur battery according to one embodiment of the present invention. With reference to FIG. 13, the method for manufacturing a positive electrode active material for a lithium-sulfur battery will be described in detail below.

[0125] First, a transition metal-doped carbon-based material is prepared. The transition metal-doped carbon-based material will be described in detail below.

[0126] Subsequently, the mixture is mixed with a sulfur-based material and a metal halide salt, and the mixture is milled once. The description of the sulfur-based material and the metal halide salt is as described above.

[0127] The sulfur-based material, the first metal halide salt, and the second metal halide salt can be mixed in a weight ratio of 40:1 to 15:10 to 30. For example, the mixing weight ratio of the sulfur-based material, the first metal halide salt, and the second metal halide salt may be 40:2 to 10:10 to 25 or 40:3 to 10:10 to 20.

[0128] The above primary milling may refer to a grinding process as mechanical milling. For example, the above primary milling may be performed by a ball mill or a bead mill. Additionally, the above primary milling may be performed at 25°C and may be performed for 1 hour to 15 hours, 2 hours to 12 hours, or 5 hours to 10 hours at 100 rpm to 1,500 rpm, 150 rpm to 1,000 rpm, or 250 rpm to 800 rpm. At this time, the energy of the primary milling may be 10 G to 60 G, 10 G to 45 G, or 15 G to 40 G.

[0129] Subsequently, the primary milling product, that is, the complex of the sulfur-based material-first metal halide salt-second metal halide salt obtained by the primary milling, can be mixed with the transition metal-doped carbon-based material in a weight ratio of 1:1 to 15:1. For example, the mixing weight ratio of the primary milling product and the carbon-based material may be 2:1 to 12:1, 3:1 to 10:1, or 4:1 to 10:1.

[0130] The above secondary milling may refer to a grinding process as mechanical milling. For example, the above secondary milling may be performed by a ball mill or a bead mill. Additionally, the above secondary milling may be performed at 25°C and may be performed for 1 hour to 15 hours, 2 hours to 12 hours, or 5 hours to 10 hours at 100 rpm to 1,500 rpm, 150 rpm to 1,000 rpm, or 250 rpm to 800 rpm. At this time, the energy of the secondary milling may be 10 G to 60 G, 10 G to 45 G, or 15 G to 40 G. Furthermore, the process conditions of the above primary milling and the above secondary milling may be the same or different.

[0131] FIG. 14 schematically illustrates the steps for manufacturing a transition metal-doped carbon-based material according to one embodiment of the present invention. With reference to FIG. 14, a method for manufacturing a transition metal-doped carbon-based material will be described in detail below.

[0132] The description of the above transition metals and carbon-based materials is as previously stated.

[0133] The step of manufacturing the above transition metal-doped carbon-based material may include: a step of preparing a mixed solution of a transition metal precursor and a carbon precursor; a step of forming a pre-carbon-based material by electrospinning the mixed solution; and a step of carbonizing the pre-carbon-based material by heat treatment.

[0134] First, a mixed solution of a transition metal precursor (TM-precursor) and a carbon precursor (C-precursor) can be prepared (see FIG. 13 (a) and FIG. 14 (a)).

[0135] The above transition metal precursor may be derived from an aqueous solution containing a transition metal as described above, and the above carbon precursor may be derived from polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), cellulose, polyvinyl alcohol (PVA), polycaprolactone (PCL), phenolic resin, or a combination thereof, but is not limited thereto.

[0136] Subsequently, the above mixed solution can be electrospun to form a pre-carbon-based material (pre-CBM) (see FIG. 13 (b) and FIG. 14 (b)).

[0137] Specifically, a carbon-based material doped with a transition metal according to one embodiment of the present invention may be manufactured using an electrospinning method. As a specific example, a pre-carbon-based material in the form of a porous membrane can be manufactured by electrospinning the above-mentioned mixed solution. Using an electrospinning method has an advantageous effect in that the amount of transition metal doping can be easily controlled.

[0138] Afterwards, the above-mentioned pre-carbonized material can be heat-treated to carbonize it (see FIG. 13 (c) and FIG. 14 (c)).

[0139] Specifically, the heat treatment step may include a step of stabilizing at 120°C to 180°C; a step of pre-oxidizing at 200°C or higher; and a step of carbonizing at 800°C or higher.

[0140] As a specific example, the above-mentioned pre-carbon-based material can be left overnight in an oven at 40°C to 80°C, 45°C to 75°C, or 50°C to 70°C, and then carbonized through heat treatment to produce a transition metal-doped carbon-based material (121d).

[0141] For example, the stabilization step may be performed by leaving it at 125°C to 160°C or 140°C to 180°C for 12 to 48 hours or 20 to 30 hours, the pre-oxidation step may be performed at 210°C or higher or 220°C or higher, and the carbonization step may be performed under an inert gas at 850°C or higher, 900°C or higher, or 950°C or higher for 1 hour or more, 2 hours or more, or 3 hours or more.

[0142]

[0143] lithium-sulfur battery

[0144] A lithium-sulfur battery according to another embodiment of the present invention comprises a positive electrode including the positive active material; a negative electrode; and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0145] More specifically, a lithium-sulfur battery according to another embodiment of the present invention comprises a cathode containing a cathode active material for a lithium-sulfur battery having the characteristics described above, thereby having excellent current density and energy density characteristics, and excellent cycle characteristics such as no overvoltage or capacity degradation due to repeated charging and discharging. The lithium-sulfur battery may be a lithium-sulfur all-solid-state battery.

[0146] FIG. 15 is a cross-sectional view of a lithium-sulfur battery according to another embodiment of the present invention. Referring to FIG. 15, a lithium-sulfur battery (1) according to one embodiment of the present invention may include a positive electrode (100) composed of a positive electrode current collector (110) and a positive electrode active material layer (120), a negative electrode (200) composed of a negative electrode current collector (210) and a coating layer (220), and a solid electrolyte layer (300) disposed between the positive electrode (100) and the negative electrode (200). More specifically, a lithium-sulfur battery (1) according to one embodiment of the present invention may have a structure in which a negative electrode current collector (210), a coating layer (220), a solid electrolyte layer (300), a positive electrode active material layer (120), and a positive electrode current collector (110) are stacked in order.

[0147]

[0148] anode

[0149] A lithium-sulfur battery (1) according to another embodiment of the present invention includes a positive electrode (100) comprising the positive electrode active material. More specifically, the positive electrode (100) may include a positive electrode active material layer (120) comprising the positive electrode active material. The description of the positive electrode active material is as described above.

[0150] The anode (100) may include an anode current collector (110). The anode (100) may include an anode current collector (110) and an anode active material layer (120) disposed on at least one surface of the anode current collector (110). More specifically, the anode may include an anode current collector (110) and an anode active material layer (120) on one or both surfaces of the anode current collector (110). The anode (100) may include an anode active material layer (120) comprising an anode current collector (110) and the anode active material disposed on at least one surface thereof (see FIG. 1 and 15).

[0151] <Blocked Household>

[0152] The positive current collector (110) can provide a reference surface on which a positive active material layer is disposed. For example, the positive current collector (110) may include a plate or foil comprising indium (In), copper (Cu), magnesium (Mg), stainless steel (SUS), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. As a specific example, the positive current collector (110) may be an aluminum foil.

[0153] The thickness of the anode 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.

[0154] According to another embodiment of the present invention, the anode (100) may further include a carbon layer between the anode current collector (110) and the anode active material layer (120). For example, the carbon layer may include amorphous carbon, crystalline carbon, etc., and may have a thickness of 0.1 μm to 4 μm. By including the carbon layer, the bonding strength between the anode current collector and the anode active material layer can be further improved.

[0155] <Anode Active Material Layer>

[0156] FIG. 11 is a schematic cross-sectional view showing an enlarged view of area A of FIG. 1. Referring to FIG. 11, a positive active material layer (120) according to one embodiment of the present invention may include a positive active material (121) and a sulfide-based solid electrolyte (122).

[0157] The description of the positive active material (121) above is as described above.

[0158] The above sulfide-based solid electrolyte (122) can provide an ion transfer pathway within the above positive active material layer (120). The positive active material layer (120) according to one embodiment of the present invention may have a further reduced internal resistance by including the above-described positive active material (121) and the above sulfide-based solid electrolyte (122), thereby further improving the cycle characteristics of the battery including it.

[0159] The above sulfide-based solid electrolyte (122) may have a particle form and may be dispersed among the positive active materials (121) (see FIG. 11).

[0160] The above sulfide-based solid electrolyte (122) may include a complex of Li2S and a solid electrolyte, and may be, for example, an inorganic solid electrolyte. Additionally, the above sulfide-based solid electrolyte (122) may include Li, S and / or P, and may optionally include a halogen element.

[0161] For example, the above sulfide-based solid electrolyte is 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 and n are positive, Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive, respectively, M is one of P, Si, Ge, B, Al, Ga, or In), Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), and Li 7-x PS 6-x I x It may include one or more selected from (0≤x≤2).

[0162] The above sulfide-based solid electrolyte is Li 7-a-c M a PS 6-c X c It may include argyrodite-type compounds represented by (0≤a≤2, 0≤c≤2).

[0163] The above X may be F, Br, Cl, I, 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), It may be antimony (Sb), bismuth (Bi), or a combination thereof.

[0164] The density of the above azirodite-type solid electrolyte may be 1.5 g / cc to 2.0 g / cc. By satisfying the above range for the density of the azirodite-type solid electrolyte, the internal resistance of the battery containing it can be reduced, and defects such as penetration or short-circuiting of the solid electrolyte film due to lithium dendrite formation can be prevented. In addition, the elastic modulus of the above azirodite-type solid electrolyte may be 15 GPa to 35 GPa or 15 GPa to 30 GPa.

[0165] In addition, the above sulfide-based solid electrolyte is 1 × 10⁻⁶ at room temperature -5 It can have an ionic conductivity of S / cm or greater. For example, the ionic conductivity of the sulfide-based solid electrolyte is 1.5 × 10⁻⁶ at room temperature. -5 S / cm or more, 2 × 10 -5 S / cm or more, 4 × 10 -5 S / cm or more, 6 × 10 -5 S / cm or more, 8 × 10 -5 S / cm or more or 1 × 10 -4 It may be greater than S / cm.

[0166] According to another embodiment of the present invention, the positive electrode active material layer may further include a solid electrolyte in addition to the sulfide-based solid electrolyte. Specifically, the positive electrode active material layer may include, in addition to the aforementioned sulfide-based solid electrolyte, a sulfide-based solid electrolyte and / or an oxide-based solid electrolyte different therefrom.

[0167] For example, the above positive active material layer is 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 It may include one or more sulfide-based solid electrolytes selected from , 0 ≤ x ≤ 2, and Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 < x <2, 0 ≤ y <3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Tiy O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x<2, 0<y<1, 0<z<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1 0≤y≤1), Li x La y TiO3(0 <x<2, 0<y<3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2, Li 3+x La3M2O 12 (M=Te, Nb, or Zr, 0≤x≤10), Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a M a O 12 (M-doped LLZO, M=Ga, W, Nb, Ta, or Al, 0 <a<2, 0≤x≤10) 중에서 선택된 가넷계(Garnet-type) 고체 전해질을 더 포함할 수 있으나, 이에 한정되는 것은 아니다. 구체적인 일례로, 상기 고체 전해질은 Li6PS5Cl을 포함할 수 있다.

[0168] In addition, the solid electrolyte in the positive active material layer (120) may be the same as or different from the solid electrolyte in the solid electrolyte layer (300).

[0169] The solid electrolyte in the positive active material layer (120) may have an average particle size (D50) smaller than that of the solid electrolyte in the solid electrolyte layer (300). For example, the average particle size (D50) of the solid electrolyte 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 compared to the average particle size (D50) of the solid electrolyte in the solid electrolyte layer (300).

[0170] The content of the sulfide-based solid electrolyte may be 10% to 40% by weight with respect to the total weight of the positive electrode active material layer. For example, the content of the sulfide-based solid electrolyte in the positive electrode active material layer may be 15% to 40% by weight, 20% to 40% by weight, or 20% to 35% by weight with respect to the total weight of the positive electrode active material layer. By satisfying the above range for the content of the sulfide-based solid electrolyte, the capacity characteristics of the battery containing it can be further improved.

[0171] The weight ratio of the positive active material and the sulfide-based solid electrolyte in the positive active material layer may be 40:60 to 90:10, 50:50 to 85:15, or 60:40 to 80:20. By satisfying the above ranges for the weight ratio of the positive active material and the sulfide-based solid electrolyte, the cycle characteristics of the battery can be maintained at a certain level or higher while securing excellent capacity characteristics.

[0172] According to another embodiment of the present invention, the positive active material layer may further include a binder, a conductive material, etc.

[0173] The above positive active material layer may include a binder comprising one or more selected from styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxylated nitrile-butadiene rubber (XNBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, and polyethylene. By further including such a binder, the positive active material layer can more effectively repair the contact detachment and weakened network between the components resulting from repeated charging and discharging. In other words, since the bonding strength between solid particles within the positive active material layer can be maintained more easily, the effect of improving the battery life can be maximized.

[0174] The content of the binder may be 0.5% to 5% by weight, 0.5% to 4% by weight, 0.5% to 3.5% by weight, or 0.5% to 2% by weight based on the total weight of the positive electrode active material layer.

[0175] The conductive material described above is conductive without causing chemical changes and can improve the electrical conductivity of the anode active material and the sulfide-based solid electrolyte. The conductive material may include a carbon-based material. For example, the conductive material may include one or more selected from graphite, carbon black, acetylene black, carbon nanofibers, and carbon nanotubes.

[0176] The content of the conductive material may be 0.5% to 5% by weight, 0.5% to 4% by weight, 0.5% to 3.5% by weight, or 0.5% to 2% by weight based on the total weight of the positive electrode active material layer.

[0177] According to another embodiment of the present invention, the positive active material layer may further include additives such as a filler, a coating agent, a dispersant, and an ion conductivity aid. Known materials generally used in electrodes of all-solid-state batteries may be used as the filler, coating agent, dispersant, ion conductivity aid, etc., and are not particularly limited.

[0178] For example, the filler may include organic fillers and / or inorganic fillers, and the filler may have an elastic modulus of 1 MPa to 2,000 MPa, 1 MPa to 500 MPa, or 5 MPa to 100 MPa, and an average particle size of 0.01 μm to 10 μm, 0.05 μm to 5 μm, or 0.1 μm to 5 μm. The elastic modulus of the filler may be measured using a tensile testing machine on a sample obtained by molding the organic filler at 150°C to 200°C for 10 minutes using a vacuum pressure press. The average particle size of the filler may be measured using a laser scattering particle size distribution analyzer.

[0179]

[0180] cathode

[0181] A lithium-sulfur battery (1) according to another embodiment of the present invention includes a negative electrode (200).

[0182] Additionally, the cathode (200) may include a cathode current collector (210) and a coating layer (220). The cathode current collector may provide a reference surface on which the coating layer is placed (see FIG. 15).

[0183] The above-mentioned negative electrode current collector (210) may include a material that does not react with lithium, that is, does not form an alloy or compound with lithium. For example, the above-mentioned negative electrode current collector (210) may include at least one metal selected from the group consisting of copper (Cu), stainless steel (SUS), titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni). The above-mentioned negative electrode current collector (210) may be composed of one of the metals described above, or may include an alloy or coating material of two or more metals.

[0184] Additionally, the negative current collector (210) may be in the form of a plate or a foil, and the thickness of the negative current collector may be 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0185] According to another embodiment of the present invention, the lithium-sulfur battery may not include a negative electrode current collector. That is, the negative electrode current collector may be omitted.

[0186] The coating layer (220) can be configured to allow lithium metal to grow between the solid electrolyte layer (300) and the negative current collector (210). The coating layer (220) can serve as a protective layer for the lithium metal and simultaneously suppress the precipitation and growth of lithium dendrites.

[0187] The coating layer (220) may be a single-layer structure or a multi-layer structure including multiple layers. For example, the coating layer may be a single layer or a structure of two, three, or four layers.

[0188] The coating layer (220) may include a metal-carbon composite. More specifically, the coating layer (220) may include a composite of metal particles and a carbon-based material.

[0189] The metal-carbon composite may have a particle form, and the average particle size of the metal-carbon composite may be 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, or 900 nm or less, or 10 nm to 4 μm, 10 nm to 3 μm, 10 nm to 2 μm, 10 nm to 1 μm, or 10 nm to 900 nm. By satisfying the above ranges for the average particle size of the metal-carbon composite, reversible absorption and / or desorption of lithium during charging and discharging may be more facilitated.

[0190] The average particle size of the above metal-carbon composite is the median diameter (D50) measured using a laser particle size distribution meter.

[0191] The metal particles in the metal-carbon composite may comprise at least one metal or metalloid 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). Additionally, the carbon-based material in the metal-carbon composite may comprise at least one selected from the group consisting of carbon black, acetylene black, furnace black, Kettjen black, and graphene. As a specific example, the carbon-based material in the metal-carbon composite may be amorphous carbon. The amorphous carbon may be carbon that does not have crystallinity or has very low crystallinity.

[0192] The weight ratio of the metal particles and the carbon-based material in the coating layer (220) may be 10:1 to 1:2. For example, the mixing ratio of the metal particles and the carbon-based material may be 5:1 to 1:1 or 4:1 to 2:1.

[0193] In addition, the content of the metal particles may be 8% to 60% by weight, 10% to 50% by weight, 15% to 40% by weight, or 20% to 30% by weight with respect to the total weight of the metal-carbon composite. By satisfying the above ranges for the content of the metal particles, the cycle characteristics of the battery can be further improved.

[0194] According to another embodiment of the present invention, the coating layer (220) may further include other additives in addition to the metal-carbon composite. For example, the coating layer (220) may further include at least one additive selected from the group consisting of binders, fillers, coating agents, dispersants, and ion-conducting aids.

[0195] Additionally, the thickness of the coating layer (220) may be smaller than the thickness of the positive active material layer. For example, the thickness of the coating layer (220) may be 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive active material layer, and may be 1 μm to 20 μm, 2 μm to 10 μm, or 3 μm to 7 μm. By satisfying the above range, the cycle characteristics of the battery can be further improved. If the thickness of the coating layer (220) exceeds the above range, the energy density of the battery containing it may decrease, and the internal resistance may increase, thereby degrading the cycle characteristics.

[0196] According to another embodiment of the present invention, the cathode may further include a thin film between the cathode current collector and the coating layer. The thin film may be disposed on one surface of the cathode current collector and may form an alloy with lithium.

[0197] The thin film may include elements capable of forming an alloy with lithium. For example, the thin film may include gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., capable of forming an alloy with lithium, but is not limited thereto; any element capable of forming an alloy with lithium in the relevant technical field is possible. The thin film may be composed of one of these metals, or may be composed of an alloy of various types of metals.

[0198] By including the above thin film, the precipitation pattern of the lithium metal layer precipitated between the thin film and the coating layer can be further flattened, and the cycle characteristics of the battery can be further improved.

[0199] For example, the thickness of the thin film may be 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 is less than the above range, it may be difficult to perform the function of the thin film, and if it exceeds the above range, the thin film may absorb lithium, and the amount of lithium precipitated at the negative electrode may decrease, so the energy density and cycle characteristics of the battery may be degraded.

[0200] The above thin film may be formed by vacuum deposition, sputtering, plating, etc., but is not limited thereto.

[0201] According to another embodiment of the present invention, the cathode may further include a carbon layer between the cathode current collector and the solid electrolyte layer. The description of the carbon layer is as described above.

[0202] According to another embodiment of the present invention, the cathode may include a cathode active material layer corresponding to the coating layer.

[0203] The negative electrode active material in the above negative electrode active material layer may include a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0204] A material capable of reversibly intercalating / deintercalating the above lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0205] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0206] As a material capable of doping and undoping the above lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The above Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), a Si-Q alloy (wherein Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The above Sn-based negative electrode active material may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0207] The silicon-carbon composite may be a composite of silicon and amorphous carbon. As a specific example, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include a secondary particle (core) assembled from silicon primary particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particle. The amorphous carbon may also be located between the silicon primary particles, for example, the silicon primary particles may be coated with the amorphous carbon. Additionally, the secondary particles may be dispersed within an amorphous carbon matrix.

[0208] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0209] The above Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0210] In addition, the content of the cathode active material in the cathode active material layer may be 90% to 99% by weight with respect to the total weight of the cathode active material layer. For example, the content of the cathode active material may be 93% to 99% by weight or 96% to 98.5% by weight with respect to the total weight of the cathode active material layer.

[0211] As a specific example, the above-mentioned negative electrode active material may include at least one of graphite and Si composites.

[0212] When the above-mentioned cathode active material includes a Si composite and graphite together, the Si composite and graphite may be included in the form of a mixture, in which case the weight ratio of the Si composite and graphite may be 1:99 to 50:50. For example, the weight ratio of the Si composite and graphite may be 3:97 to 20:80 or 5:95 to 20:80.

[0213] The above Si composite may include a core containing Si-based particles and an amorphous carbon coating layer, for example, the Si-based particles may be a Si-C composite, SiO x It may include one or more of (0 < x ≤ 2) and Si alloys. For example, the Si-C composite may include a core containing Si particles and crystalline carbon and an amorphous carbon coating layer located on the surface of the core.

[0214] The above crystalline carbon may include, for example, graphite, and more specifically, may include natural graphite, artificial graphite, or a mixture thereof.

[0215] The above-mentioned cathode may include a binder. The cathode binder can effectively bond the cathode active material particles to each other and can serve to effectively bond the cathode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof may be used.

[0216] The above-mentioned non-aqueous binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or a combination thereof.

[0217] The above-mentioned water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0218] When a water-based binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As the cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. The alkali metal salt may include Na, K, or Li.

[0219] The above dry binder is a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0220] In addition, the content of the binder may be 0.5% to 5% by weight with respect to the total weight of the cathode. For example, the content of the cathode binder may be 0.5% to 3.5% by weight or 0.5% to 2% by weight based on the total weight of the cathode.

[0221] The above-mentioned cathode may include a conductive material. The description of the conductive material is as previously stated.

[0222]

[0223] solid electrolyte layer

[0224] A lithium-sulfur battery according to another embodiment of the present invention includes a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0225] The above solid electrolyte layer (300) may include a solid electrolyte.

[0226] The above solid electrolyte may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. As a specific example, the solid electrolyte included in the solid electrolyte layer (300) may be the same as or different from the solid electrolyte included in the positive electrode active material layer (110).

[0227] The description of the above solid electrolyte is as previously stated.

[0228] FIG. 16 is a cross-sectional view of a lithium-sulfur battery according to another embodiment of the present invention. Referring to FIG. 16, a lithium-sulfur battery (1) according to one embodiment of the present invention may include a positive electrode (100) composed of a positive electrode current collector (110) and a positive electrode active material layer (120), a negative electrode (200) composed of a negative electrode current collector (210), a coating layer (220), and a lithium metal layer (230) disposed between the negative electrode current collector (210) and the coating layer (220), and a solid electrolyte layer (300) disposed between the positive electrode (100) and the negative electrode (200). More specifically, a lithium-sulfur battery (1) according to one embodiment of the present invention may have a structure in which a negative electrode current collector (210), a lithium metal layer (230), a coating layer (220), a solid electrolyte layer (300), a positive electrode active material layer (120), and a positive electrode current collector (110) are stacked in order.

[0229] The lithium metal layer (230) may include lithium or a lithium alloy. The lithium metal layer is a metal layer containing lithium and can function as a lithium reservoir. For example, the lithium alloy may be a Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, Li-Si alloy, etc., but is not limited thereto. The lithium alloy may be composed of one of the metals described above or may include an alloy of two or more metals.

[0230] In addition, the lithium metal layer may be a plated layer formed by precipitation between the coating layer and the negative electrode current collector during the charging process.

[0231] For example, the thickness of the lithium metal layer may be 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. By satisfying the above range, the cycle characteristics of the battery containing the lithium metal layer can be improved without degrading the performance. If the thickness of the lithium metal layer is less than the above range, it cannot sufficiently perform the role of a lithium reservoir, and if it exceeds the above range, the mass and volume of the battery may increase, leading to a decrease in performance and a decrease in cycle characteristics.

[0232] According to another embodiment of the present invention, the lithium metal layer may be provided between the negative electrode current collector and the coating layer before assembly of the battery. As a specific example, the lithium metal layer (230) may be disposed as a lithium foil between the negative electrode current collector (210) and the coating layer (220) before assembly of the battery.

[0233] According to another embodiment of the present invention, the lithium metal layer may be formed by precipitation through charging after the assembly of the battery. In this case, since the lithium metal layer is not included during the assembly of the battery, the energy density of the battery may be increased, and charging may be performed beyond the charging capacity of the coating layer. That is, the coating layer may be overcharged. Specifically, lithium may be absorbed in the coating layer during the initial stage of charging, but when charged beyond the capacity of the coating layer, lithium may be precipitated between the coating layer and the negative electrode current collector to form a lithium metal layer.

[0234] Since the above lithium metal layer can be composed mainly of lithium, the lithium in the lithium metal layer can be ionized and move to the positive electrode during discharge. That is, the lithium in the lithium metal layer can be used as a negative electrode active material.

[0235] In addition, since the coating layer can be disposed on the lithium metal layer, the coating layer can cover and protect the lithium metal layer and suppress the precipitation growth of lithium dendrites. Therefore, short circuits and capacity degradation of the battery can be suppressed, and the cycle characteristics of the battery can be improved.

[0236] When a lithium metal layer is formed by charging after assembly of the battery, the negative current collector, the coating layer, 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 battery.

[0237] Examples and comparative examples of the present invention are described below. However, the following examples are merely one example of the present invention, and the present invention is not limited to the following examples.

[0238]

[0239] [Example]

[0240] Manufacturing of lithium-sulfur batteries

[0241] Example 1

[0242] (1) Preparation of carbon-based materials doped with transition metals

[0243] 1.8 g of polyvinylpyrrolidone (PVP) was dissolved in 8.2 g of water at room temperature and stirred for 24 hours, then 5 mM of FeCl3·6H2O was added and stirred for 24 hours to prepare a mixed solution of a transition metal precursor and a carbon precursor.

[0244] Subsequently, the above mixed solution was placed in a disposable syringe, and an electrospinning process was performed for 12 hours using a stainless steel nozzle to form a preliminary carbon-based material. At this time, the electrospinning process conditions were 22 kV, 0.0004 mm / s, and 15 cm.

[0245] Subsequently, the above-mentioned pre-carbon-based material was left overnight in an oven at 60°C, and then carbonized through heat treatment to produce iron (Fe)-doped carbon nanofibers (FeCNF). At this time, the heat treatment was performed sequentially by stabilizing the material by leaving it in a furnace at 150°C for 24 hours, then raising the temperature to 220°C for pre-oxidation, and finally carbonizing it at a temperature of 900°C for 2 hours under an inert gas (Ar2).

[0246] (2) Preparation of positive electrode active material

[0247] Li2S, LiI, and AlI3 were mixed in a weight ratio of 40:5:15. The mixture was mechanically milled using a ball mill to produce a Li2S-LiI-AlI3 composite. At this time, the first milling was performed at 25°C and 450 rpm for 10 hours, and the milling energy applied to the sample during the first milling was 20 G.

[0248] Subsequently, the prepared Li2S-LiI-AlI3 composite and the FeCNF prepared in step (1) were mixed in a weight ratio of 6:1. The mixture was mechanically milled a second time using a ball mill to produce a Li2S-LiI-AlI3-FeCNF composite. At this time, the second milling was performed at 25°C and 450 rpm for 10 hours, and the milling energy applied to the sample during the second milling was 20 G.

[0249] (3) Preparation of the anode

[0250] Li6PS5Cl (D50 = 1.0 μm, crystalline), which is an argyrodite-type crystal, was prepared as a sulfide-based solid electrolyte. An anode slurry was prepared by mixing the anode active material prepared in step (2) and the sulfide-based solid electrolyte in a weight ratio of 70:30. The anode slurry was applied onto an Al foil with a thickness of 15 μm, dried at 100°C, and then pressed to produce an anode with an anode active material layer formed thereon.

[0251] (4) Preparation of the cathode

[0252] A stainless steel (SUS) foil with a thickness of 10 μm was prepared as a cathode current collector. As a metal-carbon composite, carbon black (CB) with a primary particle size of about 30 nm and silver (Ag) particles with an average particle diameter of about 60 nm were prepared.

[0253] 4 g of a mixed powder, prepared by mixing the carbon black (CB) and silver (Ag) particles in a weight ratio of 3:1, was placed in a container, and 4 g of a methylpyrrolidone (NMP) solution containing 7 wt% of a polyvinylidene fluoride (PVDF) binder (Kureha # 9300) was added to prepare a mixed solution. A slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution. The prepared slurry was applied to a SUS foil using a bar coater, dried at 80°C in air for 10 minutes, and then vacuum dried at 40°C for 10 hours to produce a laminate. The surface of the manufactured laminate was flattened by cold roll pressing to produce a cathode having a coating layer / cathode current collector structure. At this time, the thickness of the coating layer was approximately 15 μm, and the surface area of ​​the coating layer and the cathode current collector were the same.

[0254] (5) Preparation of a solid electrolyte layer

[0255] 98.5 parts by weight of Li6PS5Cl solid electrolyte, which is an argyrodite-type crystal, and 1.5 parts by weight of an acrylic binder were mixed. Octyl acetate was added to the mixture while stirring to prepare a slurry. The prepared slurry was applied using a bar coater onto a 15 μm thick nonwoven fabric placed on a 75 μm thick PET substrate, dried at 80°C in air for 10 minutes, and then vacuum dried at 40°C for 2 hours to prepare a solid electrolyte layer.

[0256] (6) Manufacture of lithium-sulfur batteries

[0257] A laminate was prepared by placing a solid electrolyte layer prepared in step (5) on the coating layer of the cathode prepared in step (4), and placing a positive electrode such that the positive active material layer of the positive electrode prepared in step (3) contacts the solid electrolyte layer (see FIG. 15). The laminate was subjected to plate press treatment at 85°C for 30 minutes at a pressure of 500 MPa. By this press treatment, the solid electrolyte layer is sintered, which can improve battery characteristics, and the thickness of the sintered solid electrolyte layer was approximately 45 μm. In addition, the density of the Li6PS5Cl solid electrolyte, which is an argyrodite-type crystal contained in the sintered solid electrolyte layer, was 1.6 g / cc, and the area of ​​the solid electrolyte layer was the same as the area of ​​the cathode.

[0258] Subsequently, a lithium-sulfur battery was manufactured by placing the pressurized laminate into a pouch and vacuum sealing it. Parts of the positive and negative current collectors were extended outside the sealed battery to serve as the positive and negative terminals.

[0259]

[0260] Comparative Example 1

[0261] A lithium-sulfur battery was manufactured in the same manner as in Example 1, except that an iron-undoped CNF was used instead of the FeCNF manufactured in step (1).

[0262]

[0263] [Evaluation Example]

[0264] Evaluation Example 1: Evaluation of Electrical Characteristics

[0265] For the transition metal-doped carbon-based material prepared in Example 1 above and the positive active material containing it, and the CNF of Comparative Example 1 above and the positive active material containing it, the ionic conductivity and electrical conductivity were measured using the DC polarization method.

[0266] Specifically, an ion-blocking cell was fabricated as follows, and electrical conductivity was measured using the DC polarization method. A lower mold made of SUS material was placed inside a PEEK insulator with an inner diameter of 13 pi, and after inserting a SUS foil (thickness: 10 µm, size: 13 pi), 160 mg of the sample was placed, and uniaxial pressure was applied at 440 MPa for 1 minute and 30 seconds. After the uniaxial pressure was completed, a SUS foil (thickness: 10 µm, size: 13 pi) was inserted, followed by the upper mold made of SUS material, and uniaxial pressure was applied at 300 MPa for 30 seconds. Subsequently, the electrical conductivity was measured by tightening with a torque value of 4 Nm.

[0267] In addition, an electron-blocking cell was fabricated as described below, and ion conductivity was measured using the DC polarization method. A lower mold made of SUS material was placed inside a PEEK insulator with an inner diameter of 13 pi, and SUS foil (thickness: 10 µm, size: 13 pi), Li foil (thickness: 20 µm, size: 13 pi), and In foil (thickness: 50 µm, size: 13 pi) were added in sequence. Subsequently, 150 mg of solid electrolyte (Li6PS5Cl (D50 = 1.0 µm, crystalline)) was added, and uniaxial pressurization was performed at 300 MPa for 30 seconds. Afterward, 160 mg of the sample was added, and uniaxial pressurization was performed at 440 MPa for 1 minute and 30 seconds. Subsequently, 150 mg of solid electrolyte (Li6PS5Cl (D50 = 1.0 µm, crystalline)) was added, and uniaxial pressurization was performed at 300 MPa for 30 seconds. Afterward, After inserting In foil (thickness: 50 µm, size: 13 pi), Li foil (thickness: 20 µm, size: 13 pi), and SUS foil (thickness: 10 µm, size: 13 pi) in sequence, an upper mold made of SUS material was inserted, and uniaxial pressing was performed at 300 MPa for 30 seconds. Subsequently, electrical conductivity was measured by tightening with a torque value of 4 Nm.

[0268] At this time, the electrical conductivity and ion conductivity were measured by placing the cell in a 45°C chamber for 3 hours to achieve internal temperature equilibrium, then applying a constant voltage of 0.02V, 0.05V, and 0.1V respectively, leaving it for 30 minutes to obtain the stabilized current value, and then calculating the average value, which is shown in Table 1 below.

[0269]

[0270] Classification Carbon-based material Anode active material Electrical conductivity (S / cm) Electrical conductivity (S / cm) Ionic conductivity (S / cm) Example 19.94 × 10 41.35 × 10 -2 7.01 × 10 -6 Comparative Example 18.13 × 10 4 1.09 × 10 -2 6.44 × 10 -6

[0271]

[0272] Referring to Table 1 above, the positive electrode active material of Example 1 included a carbon-based material doped with a transition metal, and thus had superior ionic conductivity and electrical conductivity compared to the positive electrode active material of Comparative Example 1.

[0273]

[0274] Evaluation Example 2: Evaluation of Charge / Discharge Characteristics

[0275] Charge and discharge characteristics were evaluated by performing charge and discharge on the lithium-sulfur batteries prepared in Example 1 and Comparative Example 1 above.

[0276] Specifically, the lithium-sulfur battery was placed in a constant temperature bath at 45°C and charged and discharged in CC mode. At this time, the charging start voltage was 1.76V for Example 1 and 1.74V for Comparative Example 1. The first and second cycles were charged to a battery voltage of 2.8V at 0.05C and discharged to 0.3V at 0.05C, and the third cycle was charged to a battery voltage of 2.8V at 0.1C and discharged to 0.3V at 0.1C. At this time, the charging capacity (mAh / g) and discharge capacity (mAh / g) of the first to third cycles were measured, respectively. In addition, the charging efficiency (%) was calculated according to the following Equation A, and the discharge capacity ratio (%) according to the rate was calculated according to the following Equation B to evaluate the rate characteristics.

[0277] [Equation A]

[0278] Charging efficiency = (Discharging capacity / Charging capacity) × 100

[0279] [Equation B]

[0280] Discharge capacity ratio = (0.1C discharge capacity(3 rd Discharge capacity) / 0.05C Discharge capacity(2nd Discharge capacity)) × 100

[0281]

[0282] Classification Example 1 Comparative Example 1 1st Cycle Charge Capacity (mAh / g) 976947 Discharge Capacity (mAh / g) 965936 Charging Efficiency 98.9% 98.8% 2nd Cycle Charge Capacity (mAh / g) 923860 Discharge Capacity (mAh / g) 877822 Charging Efficiency 95.0% 95.6% 3rd Cycle Discharge Capacity (mAh / g) 836734 Capacity Retention Rate (%) 95.3% 89.3%

[0283]

[0284] Referring to Table 2 above, the lithium-sulfur battery of Example 1 did not exhibit overvoltage or capacity degradation due to repeated charging and discharging compared to Comparative Example 1, and also had excellent capacity characteristics and a discharge capacity ratio according to rate.

[0285] FIG. 8 shows the discharge curves of Example 1 and Comparative Example 1 at the first cycle and 0.05 C, FIG. 9 shows the discharge curves of Example 1 and Comparative Example 1 at the second cycle and 0.05 C, and FIG. 10 shows the discharge curves of Example 1 and Comparative Example 1 at the third cycle and 0.05 C.

[0286] As shown in FIGS. 8 to 10, the lithium-sulfur battery of Example 1 did not exhibit overvoltage or capacity degradation due to repeated charging and discharging, whereas the lithium-sulfur battery of Comparative Example 1 showed a decrease in capacity characteristics as the number of charge-discharge cycles increased.

[0287] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

Claims

A positive electrode active material for a lithium-sulfur battery comprising a composite of a sulfur-based material, a metal halide salt, and a transition metal-doped carbon-based material. In Article 1, A positive electrode active material for a lithium-sulfur battery, wherein the content of the transition metal doped into the carbon-based material is 5 ppm to 200 ppm. In Article 1, A positive electrode active material for a lithium-sulfur battery, wherein the above transition metal comprises iron (Fe), titanium (Ti), zinc (Zn), vanadium (V), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), molybdenum (Mo), palladium (Pd), silver (Ag), cadmium (Cd), tungsten (W), iridium (Ir), gallium (Ga), indium (In), or a combination thereof. In Article 1, The above carbon-based material is a positive electrode active material for a lithium-sulfur battery comprising carbon nanofibers (CNF), graphene, carbon nanotubes (CNT), carbon black, acetylene black, activated carbon, graphite, or a combination thereof. In Article 4, The above carbon nanofibers are, The length is 1 μm to 50 μm, and The diameter is 0.01 μm to 10 μm, and A positive electrode active material for a lithium-sulfur battery having an aspect ratio of 2 to 30. In Article 1, The above transition metal-doped carbon-based material is a positive electrode active material for a lithium-sulfur battery having peaks at diffraction angles (2θ) of 25±0.2° and 43±0.2° in X-ray powder diffraction (XRD). In Article 1, The above transition metal-doped carbon-based material has an electrical conductivity of 1.0 × 10⁻⁶ 4 S / cm to 1.0 × 10 6 A positive electrode active material for a lithium-sulfur battery having S / cm and a specific surface area of ​​3 m² / g to 30 m² / g. In Article 1, A positive electrode active material for a lithium-sulfur battery, wherein the content of the carbon-based material doped with the transition metal is 1% to 30% by weight based on the total weight of the composite. In Article 1, The above sulfur-based materials are S8 and Li2S n A positive electrode active material for a lithium-sulfur battery comprising at least one of (1 ≤ n ≤ 8, where n is an integer). In Article 1, A positive electrode active material for a lithium-sulfur battery, wherein the content of the sulfur-based material is 10% to 80% by weight based on the total weight of the composite. In Article 1, The above metal halide salt comprises a first metal halide salt comprising an alkali metal and a second metal halide salt comprising a boron group metal, and is a positive electrode active material for a lithium-sulfur battery. In Article 11, The first metal halide salt comprises LiF, LiCl, LiBr, LiI, or a combination thereof, and The above second metal halide salt comprises AlF3, AlCl3, AlBr3, AlI3, GaF3, GaCl3, GaBr3, GaI3, InF3, InCl3, lnBr3, lnI3, TiF3, TiCl3, TiBr3, TiI3, or a combination thereof, a positive electrode active material for a lithium-sulfur battery. In Article 1, A positive electrode active material for a lithium-sulfur battery, wherein the content of the metal halide salt is 10% to 60% by weight based on the total weight of the composite. In Article 11, A positive electrode active material for a lithium-sulfur battery, wherein the content of the first metal halide salt is 2.5% to 15% by weight based on the total weight of the composite, and the content of the second metal halide salt is 7.5% to 45% by weight based on the total weight of the composite. In Article 11, A positive electrode active material for a lithium-sulfur battery, wherein the weight ratio of the first metal halide salt to the second metal halide salt is 1:1 to 1:

20. In Article 1, The above positive active material is, The average particle size is 8 μm or less, and Electrical conductivity is 1.0 × 10 -3 S / cm to 1.0 × 10 -1 A positive electrode active material for lithium-sulfur batteries with S / cm. A step of manufacturing a carbon-based material doped with a transition metal; A step of primary milling a mixture of a sulfur-based material and a metal halide salt; and A method for manufacturing a positive electrode active material for a lithium-sulfur battery, comprising the step of secondarily milling a mixture of the first milling product and the transition metal-doped carbon-based material. In Article 17, The step of manufacturing the above-mentioned transition metal-doped carbon-based material is: A step of preparing a mixed solution of a transition metal precursor and a carbon precursor; A step of forming a preliminary carbon-based material by electrospinning the above mixed solution; and A method for manufacturing a positive electrode active material for a lithium-sulfur battery, comprising the step of heat-treating and carbonizing the above-mentioned pre-carbon-based material. In Article 18, The above heat treatment step is, A step of stabilizing at 120℃ to 180℃; A step of pre-oxidizing at 200℃ or higher; and A method for manufacturing a positive electrode active material for a lithium-sulfur battery, comprising a step of carbonizing at 800℃ or higher. Anode comprising the positive active material of claim 1; cathode; and A lithium-sulfur battery comprising a solid electrolyte layer disposed between the anode and the cathode.

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