Separator for lithium-sulfur batteries and lithium-sulfur batteries containing the same

Abstract

The lithium-sulfur battery according to the present invention can achieve a high discharge capacity of sulfur (S) even with a small amount of positive electrode material. The lithium-sulfur battery according to the present invention can reduce the process cost for manufacturing the positive electrode by manufacturing the positive electrode by a dry manufacturing method in which a positive electrode active material powder is compressed into a predetermined shape without a manufacturing process of a slurry for the electrode active material layer. The lithium-sulfur battery according to the present invention can eliminate the variation in reaction of the positive electrode manufactured by the dry manufacturing method by using a multi-layer separator.

Description

[Technical Field]

[0001] The present invention relates to a separator for lithium-sulfur batteries and a lithium-sulfur battery comprising the separator and having a high energy density.

[0002] This application claims priority based on Korean Patent Application No. 10-2022-0022383 filed on 21 February 2022 and Korean Patent Application No. 10-2022-0183787 filed on 23 December 2022, and all content disclosed in the specifications and drawings of said applications is incorporated into this application. [Background technology]

[0003] As the application range of lithium-ion batteries expands beyond portable electronic devices to include electric vehicles (EVs) and electric storage systems (ESS), demand for high-capacity, high-energy-density, and long-life lithium-ion batteries is growing.

[0004] Among the many types of lithium secondary batteries, lithium-sulfur batteries are battery systems that use sulfur-based materials containing sulfur-sulfur (SS) bonds as the positive electrode active material, and use lithium metal, carbon-based materials that can intercalate / deintercalate lithium ions, or silicon or tin that form an alloy with lithium as the negative electrode.

[0005] In lithium-sulfur batteries, sulfur, the main material of the positive electrode active material, has advantages in that it is easy to supply and demand due to its low atomic weight and abundant resources, is inexpensive, non-toxic, and environmentally friendly.

[0006] Furthermore, lithium-sulfur batteries undergo a conversion reaction between lithium ions and sulfur at the positive electrode (S8 + 16Li + +16e -Lithium-sulfur batteries (8Li2S) have a theoretical specific capacity of 1,675 mAh / g, and when lithium metal is used as the negative electrode, they exhibit a theoretical energy density of 2,600 Wh / kg. Research is progressing on the theoretical energy density of lithium-sulfur batteries, which are being studied in relation to other battery systems (Ni-MH batteries: 450 Wh / kg, Li-FeS batteries: 480 Wh / kg, Li-MnO2 batteries: 1,000 Wh / kg, Na-S batteries: 800 Wh / kg) and lithium-ion batteries (250 Wh / kg). Among the secondary batteries developed so far, lithium-sulfur batteries are attracting attention due to their high capacity, environmental friendliness, and low cost.

[0007] Specifically, in the case of lithium-sulfur batteries, when lithium metal is used as the negative electrode active material, the theoretical specific capacity is very high at 3,860 mAh / g, and the standard hydrogen electrode (SHE) is also very low at -3.045 V. As a result, high-capacity, high-energy-density batteries can be realized, and various research and development efforts are being undertaken as next-generation battery systems.

[0008] However, lithium metal, the negative electrode active material, is highly chemically and electrochemically reactive and readily reacts with the electrolyte, causing a protective film to form on the negative electrode surface. This passivation layer creates local differences in current density, leading to the formation of lithium dendrites (thorn-like dendritic crystals) on the surface of the lithium metal. Furthermore, these lithium dendrites not only increase the physical and chemical instability of lithium secondary batteries by causing internal short circuits and dead lithium, but also reduce the battery's capacity and cycle life.

[0009] Therefore, during discharge, a lithium-sulfur battery undergoes a reduction reaction at the positive electrode where sulfur accepts electrons, and an oxidation reaction at the negative electrode where lithium is ionized.

[0010] In lithium-sulfur batteries, lithium polysulfide (Li2Sx, x=2~8) is generated at the positive electrode during discharge. Some of this lithium polysulfide dissolves in the electrolyte, causing side reactions within the battery and leading to further accelerated battery degradation. Additionally, shuttle reactions may occur during charging, significantly reducing charge-discharge efficiency. Furthermore, as mentioned above, the lithium metal used in the negative electrode continuously reacts with the electrolyte, promoting the decomposition of lithium salts and electrolyte additives.

[0011] As mentioned earlier, the formation of polysulfides reduces the battery's lifespan characteristics.

[0012] Recently, SSE (sparingly solvating electrolyte) systems have been proposed to prevent polysulfide release, and 1500m 2 It has been found that by using high-specific-surface-area carbon materials with a BET specific-surface-area of ​​1 / g or more, it is possible to achieve more than 90% of the theoretical capacity. However, improvements in the lifespan and output characteristics of lithium-sulfur batteries are still necessary.

[0013] In this regard, in order to realize a battery system with a high energy density of 400 Wh / kg or 600 Wh / L or more, 4.0 mAh / cm² is required. 2 Therefore, the development of a functional lithium-sulfur battery is necessary.

[0014] Lithium-sulfur batteries may be manufactured using a dry process for the positive electrode material, which may lead to variations in the reactivity of the positive electrode material.

[0015] In a lithium-sulfur battery, which consists of a positive electrode, a positive electrode active material, a negative electrode, a negative electrode-active material, a separator interposed between the positive and negative electrodes, and an electrolyte, the separator is designed to enable the battery to operate at a high energy density, thereby improving its lifespan characteristics as it approaches the theoretical capacity of sulfur (S). [Overview of the project]

Problems to be Solved by the Invention

[0016] The present invention is incorporated into the development of a separator for a lithium-sulfur battery that overcomes the drawbacks of the prior art. In particular, a separator for a lithium-sulfur battery having a high energy density of 400 Wh / kg and 600 Wh / L or more is provided so that the lithium-sulfur battery is driven to approach the theoretical capacity of sulfur (S) as much as possible, and the object is to improve the life characteristics of the lithium-sulfur battery.

[0017] Another object is to provide a lithium-sulfur battery including the separator. Furthermore, it is still another object of the present invention to provide a lithium-sulfur battery in which, particularly during the driving of the battery, the variation in the reactivity of the positive electrode active material is reduced.

Means for Solving the Problems

[0018] The present invention relates to a separator for a lithium-sulfur battery. A first aspect of the present invention is a separator for a lithium-sulfur battery, wherein the separator includes a first layer having a porosity of 50 vol% or more, the first layer is disposed on one surface of the separator, and the layer thickness of the first layer is 50% or more based on 100% of the thickness of the separator.

[0019] A second aspect of the present invention is the separator for a lithium-sulfur battery according to the first aspect, wherein the first layer has a porosity of 80 vol% or less.

[0020] A third aspect of the present invention is the separator for a lithium-sulfur battery according to the first aspect or the second aspect, wherein the separator includes a second layer having a porosity of 25 vol% or more and less than 50 vol%, and the second layer is disposed on the other surface, which is the opposite surface of one surface of the separator.

[0021] A fourth aspect of the present invention is a separator for a lithium-sulfur battery according to the third aspect, wherein the separator is composed of a first layer and a second layer, and the first layer and the second layer are stacked in this order.

[0022] A fifth aspect of the present invention is a separator for a lithium sulfur battery according to any one of the first to fourth aspects, wherein the first layer is a monolayer or a multilayer including two or more unit layers, and if it includes two or more unit layers, each unit layer has a porosity of 50 vol% or more and 80 vol% or less.

[0023] A sixth aspect of the present invention is a separator for a lithium-sulfur battery according to the fifth aspect, wherein, when the first layer is a multilayer, the unit layers are arranged such that the porosity increases toward one surface with respect to the thickness direction of the separator.

[0024] A seventh aspect of the present invention is a separator for a lithium sulfur battery according to any one of the first to fifth aspects, wherein the second layer is a monolayer or a multilayer including two or more unit layers, and if the second layer includes two or more unit layers, each unit layer has a porosity of less than 50 vol% and 25 vol% or more.

[0025] An eighth aspect of the present invention is a separator for a lithium-sulfur battery according to the seventh aspect, wherein, when the second layer is a multilayer, the unit layers are arranged such that the porosity decreases toward the other surface with respect to the thickness direction of the separator.

[0026] A ninth aspect of the present invention is a separator for a lithium-sulfur battery according to any one of the first to eighth aspects, wherein the thickness of the separator is 20 μm to 500 μm.

[0027] A tenth aspect of the present invention is a separator for a lithium-sulfur battery according to any one of the first to ninth aspects, wherein the first layer comprises one or more selected from a porous polymer film, a porous nonwoven fabric containing a polymer material, glass fiber, and carbon paper.

[0028] An eleventh aspect of the present invention is a separator for a lithium-sulfur battery according to any one of the third to tenth aspects, wherein the second layer comprises a porous polymer film, a porous nonwoven fabric containing a polymer material, or both.

[0029] A twelfth aspect of the present invention relates to a lithium-sulfur battery. The lithium-sulfur battery according to the present invention includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode, a negative electrode and a separator interposed between the negative electrode and the positive electrode, the positive electrode including a positive electrode active material layer, the positive electrode active material layer including a sulfur-based material including sulfur and / or a sulfur compound, the separator being as described in any one of the first to tenth aspects, the first layer of the separator facing the positive electrode active material layer.

[0030] A thirteenth aspect of the present invention is a lithium-sulfur battery according to the twelfth aspect, wherein the electrolyte comprises a lithium salt and an organic solvent, and the organic solvent comprises a first organic solvent containing a fluorine-based ether compound and a second organic solvent containing a glyme-based compound.

[0031] A fourteenth aspect of the present invention is a lithium-sulfur battery according to the twelfth or thirteenth aspect of the present invention, wherein the sulfur-based material containing sulfur and / or a sulfur compound is included in the positive electrode active material layer in the form of a sulfur-carbon composite, and the sulfur-based material is present in an amount of 60 wt% or more relative to 100 wt% of the positive electrode active material layer.

[0032] A fifteenth aspect of the present invention is a lithium-sulfur battery according to the fourteenth aspect, wherein the sulfur-carbon composite contains sulfur and carbon in a weight ratio of 60:40 to 80:20.

[0033] A sixteenth aspect of the present invention is a lithium sulfur battery according to any one of the twelve to fifteenth aspects, wherein the positive electrode includes a current collector and a positive electrode active material layer disposed on at least one surface of the current collector, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material is present in an amount of 99 wt% or more relative to 100 wt% of the positive electrode active material layer, the positive electrode active material contains an amount of 90 wt% or more of a sulfur-carbon composite relative to 100 wt% of the positive electrode active material, and the sulfur-carbon composite includes a sulfur-based material containing sulfur and / or a sulfur compound.

[0034] A 17th aspect of the present invention is a lithium-sulfur battery according to any one of the 12th to 16th aspects, wherein the negative electrode comprises a lithium metal and / or a lithium alloy as a negative electrode active material, and the lithium alloy is an alloy of lithium and another metal.

[0035] An eighteenth aspect of the present invention is a lithium sulfur battery according to any one of the twelveth to seventeenth aspects, wherein the first and second organic solvents are present in an amount of 90 vol% or more relative to 100 vol% of the total organic solvent.

[0036] A 19th aspect of the present invention is a lithium sulfur battery according to any one of the 12th to 18th aspects, wherein the first organic solvent comprises one or more of the following: 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), bis(fluoromethyl) ether, 2-fluoromethyl ether, bis(2,2,2-trifluoroethyl) ether, propyl 1,1,2,2-tetrafluoroethyl ether, isopropyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl isobutyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,2'H,3H-decafluorodipropyl ether, and 1H,1H,2'H-perfluorodipropyl ether.

[0037] A 20th aspect of the present invention is a lithium sulfur battery according to any one of the 12th to 19th aspects, wherein the second organic solvent is fluorine-free and contains one or more of dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, and polyethylene glycol methyl ethyl ether.

[0038] A 21st aspect of the present invention is a lithium-sulfur battery according to any one of the 12th to 20th aspects, wherein the electrolyte comprises lithium-bis(trifluoromethanesulfonyl)imide, dimethoxyethane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. [Effects of the Invention]

[0039] Lithium-sulfur batteries to which the separator according to the present invention is applied can achieve high energy densities of 400 Wh / kg and 600 Wh / L or more, and can operate to approach the theoretical capacity of sulfur. Therefore, a high discharge capacity of sulfur (S) can be achieved even with a small amount of positive electrode material. In addition, the life characteristics of lithium-sulfur batteries can be improved, and in particular, when a positive electrode manufactured by a dry manufacturing method in which positive electrode active material powder is pressed into a predetermined shape is applied, variations in the reactivity of the positive electrode are reduced, resulting in improved high capacity and life characteristics of lithium-sulfur batteries.

[0040] The best results of the present invention are achieved by the specific embodiments and combinations thereof described below. [Brief explanation of the drawing]

[0041] [Figure 1] This graph shows the cyclic voltammetry evaluation results for the lithium-sulfur battery of Example 1. [Figure 2] This graph shows the cyclic voltammetry evaluation results for the lithium-sulfur battery of Example 2. [Figure 3] This graph shows the cyclic voltammetry evaluation results for the lithium-sulfur battery of Example 3. [Figure 4] This graph shows the cyclic voltammetry evaluation results for the lithium-sulfur battery of Example 4. [Figure 5] This graph shows the cyclic voltammetry evaluation results for the lithium-sulfur battery of Comparative Example 1. [Figure 6] This graph shows the cyclic voltammetry evaluation results for the lithium-sulfur battery in Comparative Example 2. [Figure 7] This graph shows the cyclic voltammetry evaluation results for the lithium-sulfur battery in Comparative Example 3. [Figure 8] This graph shows the cyclic voltammetry evaluation results for the lithium-sulfur battery of Comparative Example 4. [Modes for carrying out the invention]

[0042] The present invention will be described in more detail below.

[0043] The terms and words used in this specification and in the claims are not to be interpreted in their usual or dictionary sense, but rather in a sense and concept that corresponds to the technical idea of ​​the present invention, in accordance with the principle that the inventor himself can appropriately define the concept of a term in order to best describe the invention.

[0044] The terms used herein are used solely to describe specific embodiments and are not intended to limit the invention. Terms such as “comprise” or “have” used herein should be understood as intended to indicate the presence of features, figures, stages, operations, components, parts, or combinations thereof as explicitly stated in the specification, and should not be understood as preemptively excluding the possibility of the presence or addition of one or more other features, figures, stages, operations, components, parts, or combinations thereof unless specifically pointed out herein or clearly inconsistent with the context. The term “comprise” explicitly includes the meaning of “consists of” or “composed of,” although this is not necessarily limited thereto.

[0045] Furthermore, terms and phrases used throughout this specification, such as "about" and "substantially," are used to mean, in or near the numerical value of the manufacturing and material tolerances presented in the sense of the terms mentioned, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that mention precise or absolute numerical values ​​in order to aid in understanding the invention.

[0046] Throughout this specification, the phrase "A and / or B" means "A or B or both."

[0047] In the present invention, the "specific surface area" is measured by the BET method. Specifically, it can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using BELSORP-mini II manufactured by BEL Japan, Inc.

[0048] As used herein, the term "polysulfide" encompasses both "polysulfide ion (Sx 2- , x = 2 - 8)" and "lithium polysulfide (Li2S x or LiS x - , x = 2 - 8)".

[0049] As used herein, the term "composite" means a substance in which two or more materials are combined to form physically and chemically different phases while exhibiting a more effective function.

[0050] As used herein, the term "porosity" means the ratio of the volume occupied by pores to the total volume in a certain structure, and vol% is used as its unit, and it can be used interchangeably with terms such as void fraction and porosity.

[0051] In the present invention, the measurement of the porosity is not limited to any specific method. In one embodiment of the present invention, the porosity can be measured using a pore size distribution measuring device (Porosimetry analyzer) such as BELSORP (BET equipment) manufactured by BEL JAPAN, Inc. using an adsorbing gas such as nitrogen.

[0052] In the present invention, "particle size (D 50 )" means the particle diameter based on the 50% criterion of the volume cumulative particle size distribution of the particles. The particle size (D 50The particle size can be measured using the laser diffraction method. For example, particles can be dispersed in a dispersion medium, then placed in a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiated with ultrasound at approximately 28 kHz at an output of 60 W, and after obtaining a volume-cumulative particle size distribution graph, the particle size corresponding to 50% of the volume-cumulative amount can be determined.

[0053] Furthermore, the size and thickness of each component shown in the figures are arbitrarily indicated for ease of explanation, and therefore the present invention is not necessarily limited to the items shown in the figures. In the figures, the thickness is shown enlarged to clearly show various layers and regions. In addition, in the figures, the thickness of some layers and regions is shown exaggerated for ease of explanation.

[0054] The present invention relates to a separator for a lithium-sulfur battery, wherein the separator comprises a first layer and a second layer stacked on top of each other, and the first layer has a porosity of 50 vol% or more. The present invention also relates to a lithium-sulfur battery, wherein the lithium-sulfur battery comprises an electrode assembly comprising a positive electrode (or cathode) containing a positive electrode active material layer, a negative electrode (or anode) containing a negative electrode active material layer, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the separator is according to the present invention, the second layer faces the negative electrode active material layer, and the first layer faces the positive electrode active material layer.

[0055] Next, the separator for lithium-sulfur batteries and the lithium-sulfur battery according to the present invention will be described in more detail.

[0056] Separator The separator may have a structure in which a plurality of porous films are stacked. In the present invention, the separator may include a first layer and a second layer, and in the lithium sulfur battery according to the present invention, the first layer is arranged to face the positive electrode active material layer during the manufacture of the electrode assembly. The positive electrode active material layer may have the constituent features described below. In the present invention, the porosity of the first layer may be greater than that of the second layer. The porosity of the first layer may be 50 vol% or more. On the other hand, the porosity of the second layer may be less than 50 vol%.

[0057] In one embodiment of the present invention, the thickness of the separator may be 20 μm to 500 μm.

[0058] First porous separator layer The first porous separator layer is positioned on one of the two surfaces of the separator and faces the positive electrode active material layer. In this specification, the "first porous separator layer" may be abbreviated as the "first layer". As will be described later, in the lithium sulfur battery according to the present invention, the positive electrode active material layer may contain no binder or only a very small amount of binder, and may be manufactured by a powder bonding method. In the case of a positive electrode manufactured by such a method, there is a risk of charging variations occurring during charging.

[0059] Thus, from the perspective of preventing charging variations in the compressed powder-like positive electrode, it is preferable that the first layer of the separator has a porosity of 50 vol% or more. Preferably, the porosity is between 50 vol% and 80 vol%. If the porosity of the first layer is less than 50 vol%, the effect of improving charging variations will be minimal, and for this reason, the battery may not operate properly. On the other hand, if the porosity exceeds 80 vol%, there is a concern that the physical strength of the separator will decrease and it will be more prone to losing its shape.

[0060] In one embodiment of the present invention, the thickness of the first layer may be 50% or more of the total thickness of the separator. Specifically, the thickness of the first layer may be 20 μm to 500 μm, 20 μm to 400 μm, or 25 μm to 350 μm. Preferably, it may be 40 μm to 400 μm. If the thickness of the first layer is less than 50% of the total thickness of the separator, or if it is thin, such as less than 20 μm, the effect of improving the charging variation of the positive electrode will be minimal, and for this reason, the battery may not be able to operate normally. On the other hand, if the thickness is excessively thick, exceeding 500 μm, the energy density of the battery will decrease when the battery is applied, which is undesirable.

[0061] On the other hand, the first layer may be nonconductive or conductive. In the present invention, the first layer satisfies the above-described constituent characteristics and may include, for example, one or more selected from the group consisting of a porous membrane containing a polymer material such as a porous polymer film or nonwoven fabric, glass fibers, and carbon paper. In one embodiment of the present invention, the polymer film may be a film formed from a polymer of polyolefin polymers such as polyethylene, polypropylene, polybutylene, and polypentene, either individually or as a mixture thereof. Examples of polyethylene may be polymer materials such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene.

[0062] In one embodiment of the present invention, the polymer film may be manufactured by a dry manufacturing method in which a polymer resin is melted and extruded, and then micropores are formed using a stretching process, or by a wet manufacturing method in which a pore-forming agent such as paraffin is mixed with the polymer resin to form a film, and then micropores are formed by dissolving the pore-forming agent.

[0063] The nonwoven fabric contains a polymer material, and examples of the polymer material include polyphenylene oxide, polyimide, polyamide, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyphenylene sulfide, polyacetal, polyethersulfone, polyetherether ketone, and polyester, and may contain one of these or a mixture of two or more selected from these.

[0064] In one specific embodiment of the present invention, the first layer may be a monolayer. Alternatively, the first layer may have a multilayer configuration including two or more unit layers. If the separator includes two or more unit layers, it is preferable that each of the unit layers independently has a porosity of 50 vol% or more and 80 vol% or less.

[0065] Furthermore, each unit layer may include one or more materials selected from the group consisting of porous membranes containing polymer materials such as porous polymer films or nonwoven fabrics, glass fibers, and carbon paper. For explanations of these materials, please refer to the content described above.

[0066] In one embodiment, if the first layer is a multilayer, the unit layers may be arranged such that the porosity increases toward one surface with respect to the thickness direction of the separator, and the unit layer having the highest porosity may be positioned to face the positive electrode.

[0067] Second porous separator layer The separator according to the present invention may have a second porous separator layer disposed on the other surface, which is the opposite surface to the first surface. The second layer has a porosity of 25 vol% or more and less than 50 vol%, and is positioned to face the negative electrode during the manufacture of the electrode assembly. In this specification, the "second porous separator layer" may be abbreviated as the "second layer".

[0068] The second layer is not particularly limited as long as it is an insulating material used in electrochemical elements. Such a second layer electrically separates the negative electrode and the positive electrode and provides a pathway for lithium ions to move. Any material that is commonly used as a separator in lithium secondary batteries can be used without any particular limitations.

[0069] In one embodiment of the present invention, the second layer may include a porous polymer film.

[0070] In one embodiment of the present invention, the polymer film is a film formed from polyolefin polymers such as polyethylene, polypropylene, polybutylene, and polypentene, either individually or as a mixture thereof. The polyethylene can be of various types, such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.

[0071] The polymer film may be manufactured by a dry manufacturing method in which a polymer resin is melted and extruded, and then micropores are formed using a stretching process, or by a wet manufacturing method in which a pore-forming agent such as paraffin is mixed with the polymer resin to form a film, and then micropores are formed by dissolving the pore-forming agent.

[0072] Furthermore, the second layer may be a porous nonwoven fabric, such as a nonwoven fabric containing high-melting-point glass fibers or polymer materials. Examples of the polymer materials include polyolefin polymers such as polyethylene and polypropylene, polyethylene terephthalate, polyphenylene oxide, polyimide, polyamide, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyphenylene sulfide, polyacetal, polyether sulfone, polyetherether ketone, and polyester, and may contain one of these or a mixture of two or more selected from these. Alternatively, a coated porous sheet containing ceramic components or polymeric substances may be used as the second layer to ensure heat resistance or mechanical strength.

[0073] In one embodiment of the present invention, the second layer may be a monolayer. Alternatively, the second layer may be a multilayer comprising two or more unit layers, and if the second layer comprises two or more unit layers, it is preferable that each unit layer has a porosity of less than 50 vol% and 25 vol% or more. In a more specific embodiment, if the second layer is a multilayer, the unit layers may be arranged such that the porosity decreases toward the other surface with respect to the thickness direction of the separator.

[0074] In the present invention, the unit layer included in the second layer may be one or more of the porous polymer film and porous polymer nonwoven fabric described above, and please refer to the above description for details.

[0075] In one specific embodiment of the present invention, the second layer has a porosity of 25 vol or more and less than 50 vol%, or 35 vol% or more and less than 50 vol%, in terms of insulating properties, resistive properties, and ionic conductivity.

[0076] On the other hand, in one specific embodiment of the present invention, the separator is composed of the first layer and the second layer, and the first layer and the second layer are stacked in this order. Here, the first layer may be a single layer or may have a multi-layer configuration. Alternatively, the second layer may be a single layer or may have a multi-layer configuration. In one specific embodiment, both the first and second layers may be single layers.

[0077] The second layer may have a thickness of 5 μm to 30 μm, 5 μm to 25 μm, 10 μm to 25 μm, 10 μm to 20 μm, or 15 μm to 20 μm.

[0078] The second layer may have a porosity of 25 vol% or more and less than 50 vol%, 30 vol% or more and less than 50 vol%, 35 vol% or more and less than 50 vol%, or 40 vol% or more and less than 50 vol%.

[0079] In one embodiment of the present invention, each layer constituting the separator may be bonded together as a result of a lamination process. Alternatively, without lamination, or even if a lamination process is performed, the layers may simply be stacked together without bonding. On the other hand, even if the layers are simply stacked, the stacked structure of the separator can be stably maintained by external shape-fixing elements such as a battery case. The lamination process may mean, for example, a pressing process that adheres or bonds the electrodes and the separator after lamination. In one embodiment, the pressing process may be performed by a hot pressing method.

[0080] Lithium-ion rechargeable battery Next, each component of the lithium-sulfur battery according to the present invention will be described in more detail.

[0081] positive electrode The positive electrode according to the present invention includes a current collector and a positive electrode active material layer disposed on at least one surface of the current collector.

[0082] Current collector The current collector can be any material used in the relevant art, as long as it is electrically conductive and used as a current collector component. For example, the positive electrode current collector can be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and minute irregularities may be formed on the surface of the positive electrode current collector to enhance the adhesion of the positive electrode active material. The positive electrode current collector can be made of a wide variety of materials, such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0083] Cathode active material layer The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer may or may not contain a conductive material, as necessary. The conductive material is a component different from the carbon material in the sulfur-carbon composite described later, and means a component separate from the positive electrode active material which is a sulfur-carbon composite. For example, containing a conductive material means that a separate conductive material component may be included, separate from the carbon material contained in the sulfur-carbon composite. To give another example, even if the positive electrode active material layer does not contain a conductive material, the carbon material of the sulfur-carbon composite is included as a component of the positive electrode active material.

[0084] The positive electrode active material may be present in 100 wt% of the positive electrode active material layer at a concentration of 60 wt% or more, or 70 wt% or more, or 80 wt% or more. For example, the positive electrode active material may be present in 90 wt% or more, or 99 wt% or more, relative to 100 wt% of the positive electrode active material layer.

[0085] The positive electrode active material layer has a loading capacity of 4.0 mAh / cm² based on the area of ​​the electrode active material layer. 2 It is preferable that the above conditions are met. Furthermore, it is preferable that the positive electrode active material layer has a porosity of 60 vol% or less. Such loading amounts and porosity ranges are advantageous for the lithium sulfur battery according to the present invention to achieve high energy densities of 400 Wh / kg and 600 Wh / L or more.

[0086] On the other hand, in one embodiment of the present invention, the positive electrode active material layer may consist only of the positive electrode active material. That is, the positive electrode active material layer may not contain other materials in addition to the positive electrode active material, such as binder material and conductive material. If it contains components other than the positive electrode active material, it is preferable that the amount of these components in the positive electrode active material layer be controlled to less than 1 wt%, less than 0.1 wt%, or less than 0.05 wt%. In one specific embodiment of the present invention, the positive electrode active material layer consists only of the positive electrode active material.

[0087] On the other hand, in the present invention, the positive electrode active material layer is manufactured by a dry manufacturing method. In this specification, "dry manufacturing method" means that when forming the positive electrode active material layer, the "method of producing a fluid slurry by putting electrode material into a solvent" is not applied, and the powdered positive electrode active material is compressed or otherwise pressed to form a certain shape. In one embodiment of the present invention, the positive electrode active material layer can be formed by coating a powdered electrode material containing the positive electrode active material onto the surface of a current collector, compressing it to form a layered structure, and then joining it with the current collector. Alternatively, the electrode can be manufactured by first pressing the powdered electrode material containing the positive electrode active material alone to form an electrode film, and then joining the electrode film and the current collector by pressure. On the other hand, in one embodiment of the present invention, the electrode material may consist only of the positive electrode active material.

[0088] According to one aspect of the present invention, electrodes can be manufactured by supplying prepared electrode material to a roll-type pressing device using a supply device such as a screw feeder. In this case, by sending the current collector to a molding device such as a compression roller at the same time as supplying the electrode material, an electrode active material layer can be directly formed on the current collector. Alternatively, a method can be applied in which the electrode material is scattered on the current collector, uniformly leveled with a blade or the like to adjust the thickness, and then molded using a pressing device.

[0089] On the other hand, in one embodiment of the present invention, the powdered electrode material containing the positive electrode active material may be heat-treated at a temperature of 100°C or higher for a predetermined period of time before being applied to the current collector. The heat treatment time is not limited to any specific time, but may take about 10 minutes to 1 hour.

[0090] positive electrode active material The positive electrode active material according to the present invention comprises a sulfur-based material (e.g., sulfur and / or sulfur compounds), the sulfur-based material may be included in the form of a sulfur-carbon composite.

[0091] In this specification, the term "sulfur-based material" refers collectively to any material containing sulfur and / or sulfur compounds, and any material containing the element sulfur.

[0092] In the present invention, the sulfur-based material may be present in an amount of 60 wt% or more relative to 100 wt% of the positive electrode active material layer.

[0093] In one embodiment of the present invention, the positive electrode active material may contain 80 wt% or more, preferably 90 wt% or more, of a sulfur-carbon composite with respect to 100 wt% of the positive electrode active material layer, and more preferably, the positive electrode active material may consist solely of a sulfur-carbon composite.

[0094] Lithium-sulfur batteries are attracting attention as a next-generation rechargeable battery because, among various types of rechargeable batteries, they not only possess high discharge capacity and theoretical energy density, but also have the advantage of being environmentally friendly, as sulfur, used as the positive electrode active material, is abundant in reserve and inexpensive, thus reducing the manufacturing cost of the batteries.

[0095] In lithium-sulfur batteries, sulfur, the positive electrode active material, is an insulator. Therefore, to compensate for its low electrical conductivity, sulfur-carbon composites, which combine sulfur with a conductive carbon material, are commonly used.

[0096] The sulfur-carbon composite comprises a porous carbon material and sulfur, with the sulfur supported in the pores of the porous carbon material.

[0097] In one embodiment of the present invention, the sulfur-carbon composite may contain sulfur and carbon in a weight ratio of 60:40 to 80:20. In the sulfur-carbon composite, if the carbon content exceeds 40 wt%, there is a risk of reduced adhesive strength. On the other hand, if the carbon content is less than 20 wt%, it is difficult to compensate for the low electrical conductivity of sulfur.

[0098] The carbon material has a porous structure containing numerous pores of varying sizes on its surface and interior, and acts as a support that provides a framework to which sulfur can be uniformly and stably immobilized, compensating for the low electrical conductivity of sulfur and enabling the electrochemical reaction to proceed smoothly. In particular, in a sulfur-carbon composite, the carbon material that acts as a sulfur support has a large pore volume, a wide BET specific surface area, and an appropriate particle size (D 50 When this is present, the sulfur load capacity is high, the irreversible capacity is low, and the energy density can be increased to improve the utilization rate of sulfur during electrochemical reactions.

[0099] In the sulfur-carbon composite of the present invention, the carbon material used as the sulfur carrier can generally be produced by carbonizing a wide variety of carbon material precursors.

[0100] On the other hand, in one embodiment of the present invention, the pores of the carbon material may have a diameter in the range of 0.5 nm to 10 nm, based on the longest diameter. The carbon material can be used without limitation as long as it is a material that can be normally used as the positive electrode of a lithium sulfur battery, such as spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk-shaped.

[0101] The carbon material may be any porous and conductive carbon-based material commonly used in the industry. For example, it may include one or more selected from the group consisting of graphite, graphene, graphene oxide (rGO), carbon blacks such as Denka Black, acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Thermal Black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); graphite such as natural graphite, artificial graphite, and expanded graphite; carbon nanoribbons; and carbon nanobelts, carbon nanorods, and activated carbon.

[0102] The aforementioned sulfur-based material, for example, sulfur and / or sulfur compounds, does not have electrical conductivity on its own and is therefore used in combination with the carbon material described above. In one embodiment of the present invention, the sulfur-based material is inorganic sulfur (S8), Li2S n Disulfide compounds such as (n≧1), 2,5-dimercapto-1,3,4-thiadiazole and 1,3,5-trithiocyanuric acid, as well as organosulfur compounds and carbon-sulfur polymers ((C2S x ) n It may be one or more selected from the group consisting of x = 2.5 to 50, n ≥ 2. Preferably, it may contain inorganic sulfur (S8).

[0103] In the sulfur-carbon composite according to the present invention, the sulfur-based material is located on at least one of the surfaces of the pores of the carbon material, either internally or externally, and can be present in a region of less than 100%, preferably 1 to 95%, and more preferably 60 to 90%, of the entire internal and external surface of the carbon material. When the sulfur and / or sulfur compound is within this range on the surface of the carbon material, it is most effective in terms of the electron transfer (exchange) area and the wettability of the electrolyte. Specifically, since the sulfur-based material is thinly and uniformly impregnated into the surface of the carbon material within this range, the electron transfer contact area can be increased during the charge and discharge process. If the sulfur-based material is located in a region of 100% of the entire surface of the carbon material, the carbon material will be completely covered by sulfur, reducing the wettability of the electrolyte and resulting in poor contact with the conductive material contained in the electrode, preventing electron transfer and, as a result, being unable to participate in the reaction.

[0104] On the other hand, in one embodiment of the present invention, the sulfur-carbon composite may be formed by simply mixing a sulfur-based material such as sulfur and / or sulfur compounds with a carbon material, or it may have a core-shell structure in the form of a coating or support. The core-shell structure in the form of a coating is in which either the sulfur-based material, which is sulfur and / or sulfur compounds, or the carbon material is coated with another substance. For example, the surface of the carbon material may be encased in the sulfur-based material, or vice versa. The support form may be in which the sulfur-based material is filled inside the carbon material, particularly in the internal pores. The form of the sulfur-carbon composite can be any form as long as it satisfies the content ratio of the sulfur-based compound to the carbon material presented above, and is not particularly limited in the present invention.

[0105] On the other hand, in one embodiment of the present invention, the sulfur-carbon composite has a particle size (D) that ensures appropriate strength and reactivity. 50 The particle size (D 50 If the particle size (D) is less than 20 μm, there is a risk that the strength will decrease, 50If the particle size exceeds 80 μm excessively, there is a risk of decreased reactivity.

[0106] Furthermore, in one embodiment of the present invention, the sulfur-carbon composite is obtained by the following manufacturing method.

[0107] The method for producing the sulfur-carbon composite according to the present invention is not particularly limited and is commonly known in the art, and can be produced by a composite method comprising the steps of (S1) mixing a carbon material with a sulfur-based material, namely sulfur and / or a sulfur compound, and (S2) compounding the materials.

[0108] The mixing in step (S1) is for the purpose of increasing the degree of mixing between the sulfur-based material and the carbon material, and can be carried out using a stirring device commonly used in this industry. At this time, the mixing time and rate can also be selectively adjusted according to the content and conditions of the raw materials.

[0109] The compounding method in step (S2) is not particularly limited in the present invention, and methods commonly used in the industry can be used. For example, methods commonly used in the industry, such as dry compounding or wet compounding such as spray coating, can be used. For example, a method can be used in which the mixture of the sulfur-based material and the carbon material obtained after mixing is ball-milled and then left in an oven at 120°C to 160°C for 20 minutes to 1 hour so that the molten sulfur can be uniformly coated on the internal and external surfaces of the carbon material.

[0110] The sulfur-carbon composite produced using the aforementioned manufacturing method has a high specific surface area and a high amount of sulfur-based material supported, resulting in a structure that improves sulfur utilization. This not only improves the electrochemical reactivity of sulfur but also enhances the accessibility and contactability of the electrolyte, thereby improving the capacity and lifespan characteristics of lithium-sulfur batteries.

[0111] Other cathode materials In one embodiment of the present invention, the positive electrode active material may consist solely of the sulfur-carbon composite. In addition to the sulfur-carbon composite, it may further contain one or more additives selected from transition metal elements, group IIIA elements, group IVA elements, sulfur compounds of these elements, and alloys of these elements with sulfur.

[0112] In one specific embodiment of the present invention, the positive electrode active material layer may contain a lithium transition metal composite oxide represented by the following chemical formula 1. [Chemical formula 1] Li a Ni b Co c M 1 d M 2 e O2 In the above chemical formula 1, M 1 This can be Mn, Al, or a combination thereof, preferably Mn or Mn and Al.

[0113] Said M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2 While elements are not essential, when present in appropriate amounts, they can play a role in promoting particle growth during firing or improving the stability of the crystal structure.

[0114] negative electrode The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector. In one embodiment of the present invention, the negative electrode active material layer may include one or more selected from lithium metal and lithium alloy as the negative electrode active material. The lithium alloy is an alloy of lithium with a dissimilar metal, and the dissimilar metal may include one or more selected from Al and Mg. According to one specific embodiment of the present invention, the negative electrode active material layer may be formed in the form of a thin film on the surface of the negative electrode current collector. The formation method may be a method that involves preparing a lithium metal thin film having a predetermined thickness, laminating the thin film and the current collector, and depositing lithium metal onto the surface of the current collector. A wide variety of deposition methods can be used for the deposition, such as electron beam deposition, organometallic vapor deposition, reactive sputtering, high-frequency sputtering, and magnetron sputtering, and the invention is not limited to these. Since each of the vapor deposition methods described above is a known method, a detailed explanation thereof is omitted in this specification.

[0115] As the negative electrode current collector, materials commonly used in the art can be used, such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys. The negative electrode current collector can usually have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, minute irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, a wide variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics can be used.

[0116] The conductive material is used to impart conductivity to the negative electrode and can be used without particular limitations as long as it does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used. The conductive material is usually included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, relative to the total weight of the negative electrode active material layer.

[0117] electrolyte In the present invention, the electrolyte may include an organic solvent and a lithium salt.

[0118] Organic solvents The aforementioned organic solvent acts as a medium through which ions participating in the electrochemical reaction of the battery can move.

[0119] In the present invention, the organic solvent comprises a first organic solvent containing a fluorinated ether compound and a second organic solvent containing a glyme compound. The first and second organic solvents may be present in a proportion of 90 vol% or more, preferably 95 vol% or more, and more preferably 99 vol% or more, based on 100 vol% of the total organic solvent. In one embodiment of the present invention, the organic solvent may consist only of the first and second organic solvents.

[0120] The aforementioned organic solvent is preferable because it allows for the utilization of 80% or more of the theoretical capacity of sulfur, which is 1675 mAh / g, used as a component of the positive electrode active material. It is also preferable because it enables the achievement of high voltage and high capacity of 2.0 V or higher and 1300 mAh / g or higher discharge capacity under room temperature conditions for the aforementioned positive electrode.

[0121] Specifically, the first organic solvent is a fluorine-based ether compound, and by having an inhibitory effect on the dissolution and decomposition of polysulfide, it improves the Coulombic efficiency (CE) of the battery and ultimately plays a role in improving the battery's lifespan. More specifically, the first solvent containing the fluorine-based ether compound has exceptional structural stability compared to ordinary organic solvents containing alkeins due to fluorine substitution, and therefore has very high stability. As a result, when this is used as the electrolyte in a lithium-sulfur battery, the stability of the electrolyte can be dramatically improved, thereby improving the lifespan performance of the lithium-sulfur battery. The fluorine-based ether compound may include, for example, one or more selected from the group consisting of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), bis(fluoromethyl) ether, 2-fluoromethyl ether, bis(2,2,2-trifluoroethyl) ether, propyl 1,1,2,2-tetrafluoroethyl ether, isopropyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl isobutyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,2'H,3H-decafluorodipropyl ether, and 1H,1H,2'H-perfluorodipropyl ether.

[0122] On the other hand, the second solvent is an electrolyte solvent containing a glyme compound (but not containing fluorine), which not only dissolves the lithium salt to give the electrolyte lithium ion conductivity, but also plays a role in eluting sulfur, which is the positive electrode active material, to facilitate the electrochemical reaction with lithium. Specific examples of the glyme compound include one or more selected from the group consisting of dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, and polyethylene glycol methyl ethyl ether. On the other hand, in one embodiment of the present invention, it is preferable that the second solvent contains dimethoxyethane.

[0123] In the present invention, the first and second solvents are not particularly limited, but may have a volume ratio of 1:99 to 99:1. In one specific embodiment of the present invention, it is preferable that the organic solvent contains a first solvent containing a fluorine-based ether compound in a higher content ratio than the second solvent containing a glyme-based compound. When the first solvent containing the fluorine-based ether compound is contained in a higher content ratio than the second solvent containing a glyme-based compound, it is advantageous in that it suppresses the formation of polysulfides, enables the realization of a battery capacity close to the theoretical capacity of sulfur, and suppresses the decrease in battery capacity associated with battery use. For this reason, it is preferable to set the first solvent containing the fluorine-based ether compound to be contained in a higher content ratio than the second solvent containing a glyme-based compound.

[0124] In one embodiment of the present invention, preferably, the first solvent comprises 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), and the second solvent may comprise dimethoxyethane.

[0125] On the other hand, in one embodiment of the present invention, in addition to the first and second organic solvents, a further third organic solvent may be further included as needed. Such third organic solvents are not particularly limited and include, for example, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; and R-CN (where R is C2-C2). 20 Nitriles such as linear, branched, or cyclic hydrocarbon groups (which may contain double-bonded aromatic rings or ether bonds); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used.

[0126] Lithium salt The lithium salts mentioned above are compounds capable of providing lithium ions in the electrolyte. Examples of such lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3CO2, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiCH3SO3, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiC4BO8, LiCl, LiBr, and LiB 10 Cl 10 LiI or LiB(C2O4)2 can be used. In the present invention, in order to increase the potential for utilizing sulfur and to realize high-capacity and high-voltage batteries, it is preferable that the lithium salt includes Li-TFSI. More preferably, the lithium salt may contain LiN(CF3SO2)2(Li-TFSI) in an amount of 80 wt% or more, or 90 wt% or more, or 100% based on 100 wt% of the total lithium salt.

[0127] The concentration of the lithium salt is in the range of 0.1 to 2.0 M, preferably 0.5 to 1 M, and more preferably 0.5 to 0.75 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and effective lithium ion movement. If the lithium salt concentration is below this range, it may become difficult to secure ionic conductivity suitable for battery operation, and if it exceeds this range, the viscosity of the electrolyte may increase, reducing the mobility of lithium ions, or the decomposition reaction of the lithium salt itself may increase, potentially degrading the battery performance.

[0128] In one specific embodiment of the present invention, in an electrolyte comprising a first solvent, a second solvent, and a lithium salt, the molar ratio of the lithium salt, the second solvent, and the first solvent may be 1:0.5 to 3:4.1 to 15. Furthermore, in one embodiment of the present invention, the molar ratio of the lithium salt, the second solvent, and the first solvent may be 1:2:4 to 13, 1:3:3 to 10, or 1:4:5 to 10. Thus, the electrolyte contained in the lithium sulfur battery of the present invention may contain a first solvent containing a fluorine-based ether compound in a higher content ratio than the second solvent containing a glyme-based compound.

[0129] Other additives The electrolyte may further contain additives in addition to the electrolyte components, with the aim of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity. For example, the additives may be, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, either alone or in combination. The additives may be included in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, relative to the total weight of the electrolyte.

[0130] In the present invention, the electrode assembly includes a negative electrode, a positive electrode, and a separator interposed between the negative and positive electrodes. For example, the assembly may be stacked with the separator interposed between the negative and positive electrodes to form a stacked or stack / folding structure, or it may be wound up to form a jelly-roll type structure. In addition, when a jelly-roll structure is formed, an additional separator may be placed on the outside to prevent the negative and positive electrodes from touching each other.

[0131] A further aspect of the present invention relates to an electrochemical element including the electrode assembly. The electrochemical element comprises the electrode assembly and an electrolyte housed together in a battery case, and the battery case can be any type commonly used in the art, such as a pouch type or a metal can type, without any particular limitations.

[0132] The shape of the lithium-sulfur battery is not particularly limited and can take on a wide variety of shapes, such as cylindrical, stacked, or coin-shaped.

[0133] Furthermore, the present invention provides a battery module that includes the lithium-sulfur battery as a unit cell. The battery module can be used as a power source for medium- and large-sized devices that require high-temperature stability, long cycle characteristics, and high capacity characteristics.

[0134] Examples of the aforementioned medium- and large-sized devices include, but are not limited to, power tools powered by battery-powered motors; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0135] The following are preferred embodiments to further the understanding of the present invention. However, the following embodiments are merely illustrative of the present invention, and it will be obvious to those skilled in the art that a wide variety of changes and modifications can be made within the scope of the present invention and the technical concept, and that such variations and modifications will naturally fall within the scope of the claims.

[0136] Manufacturing example [Production of sulfur-carbon composites] Carbon nanotubes (CNTs, with an average of 6 walls) and sulfur were uniformly mixed, pulverized by ball milling, and then left in an oven at 155°C for 30 minutes to produce a sulfur-carbon composite. The sulfur content in 100 wt% of the sulfur-carbon composite was 75 wt%. The CNTs had a specific surface area of ​​approximately 3000 m². 2 The stomata volume is approximately 1.9 cm³ / g. 3 The concentration was / g. Furthermore, the pore size of the CNTs was approximately 0.5 to 0.75 nm.

[0137] [Manufacturing of positive electrodes] The sulfur-carbon composite obtained in the above manufacturing example was heat-treated at 155°C for 35 minutes. The heat-treated sulfur-carbon composite was applied to a prepared aluminum thin film (thickness 10 μm) and then pressed to produce a positive electrode. The produced positive electrode had a capacitance of 3 mAh / cm². 2 The porosity was 60 vol%.

[0138] [Battery manufacturing] Along with the positive electrode, a lithium metal thin film with a thickness of 35 μm was used as the negative electrode.

[0139] The electrolyte was prepared by mixing LiN(CF3SO2)2 (concentration: 0.65M), dimethoxyethane (second solvent), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) (first solvent) in a molar ratio of 1:2:9 at room temperature (20°C to 25°C).

[0140] Specifically, the manufactured positive electrode and negative electrode were positioned facing each other, a separator was interposed between them, and then the manufactured electrolyte was injected to produce a lithium-sulfur battery. In the battery, the first layer of the separator faced the positive electrode active material layer of the positive electrode, and the second layer faced the negative electrode active material of the negative electrode. In the battery, the positive electrode and negative electrode each consisted of seven plates. The separators used in each example and comparative example are described in Examples 1 to 4 and Comparative Examples 1 to 4 below, and are summarized in Tables 1 and 2 below.

[0141] Example 1 A porous polyethylene film (20 μm thick, 46 vol%) was prepared as the second layer, and a nonwoven fabric made of polyethylene terephthalate (30 μm thick, 50 vol%) was prepared as the first layer. These were then joined together to create a separator.

[0142] Example 2 A porous polyethylene film (20 μm thick, 46 vol%) was prepared as the second layer, and a nonwoven polyethylene terephthalate fabric (90 μm thick, 60 vol%) was prepared as the first layer. These were then joined together to create a separator.

[0143] Example 3 A porous polyethylene film (20 μm thick, 46 vol%) was prepared as the second layer, and carbon paper (120 μm thick, 75 vol%) was prepared as the first layer. These were then joined together to create a separator.

[0144] Example 4 A porous polyethylene film (20 μm thick, 46 vol%) was prepared as the second layer, and glass fiber (300 μm thick, 50 vol%) was prepared as the first layer. These were then joined together to create a separator.

[0145] Comparative Example 1 Only a porous polyethylene film (20 μm thick, 46 vol%) was prepared as the separator.

[0146] Comparative Example 2 Only a nonwoven fabric made of polyethylene terephthalate (thickness 90 μm, porosity 60 vol%) was prepared as the separator.

[0147] Comparative Example 3 Only glass fibers (300 μm thick, 75 vol%) were used as the separator.

[0148] Comparative Example 4 A porous polyethylene film (20 μm thick, 46 vol%) was prepared as the second layer, and a porous polyethylene film (20 μm thick, 46 vol%) was prepared as the first layer. These were then joined together to create a separator.

[0149] [Table 1]

[0150] [Table 2]

[0151] [evaluation] The lithium-sulfur battery according to the present invention showed a trend in cyclic voltammetry that was substantially the same as that of a battery using conventional electrodes, and the battery operated smoothly. Figures 1 to 4 show the results of Examples 1 to 4 in order. From this, it was confirmed that a battery with high energy density can be manufactured. On the other hand, comparative example batteries that did not use a double-layer separator, or that used a double-layer separator but did not have the constitutive features of the present invention, were unable to operate. Figures 5 to 8 show the results of Comparative Examples 1 to 4 in order.

[0152] Method for measuring particle size Using a particle size distribution analyzer (model: Bluewave, manufacturer: Microtrac), the dry method was used to determine the particle size distribution. 50 The corresponding particle size was measured. When the carbon material was formed into secondary particles by aggregation, the primary particle size was observed and measured using an electron scanning microscope (model: SEM, manufacturer: JEOL Ltd.).

[0153] Method for measuring porosity The film thickness of each porous membrane in the separator was measured using TESA μ-hite equipment.

[0154] Method of measuring cyclic voltammetry Cyclic voltammetry was performed under conditions of a scanning speed of 0.5 mV / s and 3 cycles in the voltage range of 0.5 V to 4.0 V.

[0155] The features disclosed in the above-mentioned description and in the dependent claims can be important elements in realizing the aspects of disclosure made in the independent claims in a wide variety of forms, either individually or in any combination thereof.

Claims

1. A separator for lithium-sulfur batteries having a high energy density of 400 Wh / kg or more, The separator includes a first layer having a porosity of 50 vol% or more. The first layer is placed on one surface of the separator, The thickness of the first layer is 50% or more compared to the thickness of the separator (100%). The separator includes a second layer having a porosity of 25 vol% or more and less than 50 vol%, and the second layer is disposed on the other surface of the separator which is the opposite surface to the one surface. The thickness of the first layer is 40 μm to 400 μm, and the thickness of the second layer is 5 μm to 20 μm. The second layer comprises a porous polymer film, and is a separator for a lithium-sulfur battery.

2. The separator for a lithium-sulfur battery according to claim 1, wherein the first layer has a porosity of 80 vol% or less.

3. The separator for a lithium-sulfur battery according to claim 1, wherein the separator is composed of the first layer and the second layer, and the first layer and the second layer are stacked in this order.

4. The separator for a lithium sulfur battery according to claim 1, wherein the first layer is a monolayer or a multilayer comprising two or more unit layers, and if comprising two or more unit layers, each unit layer has a porosity of 50 vol% or more and 80 vol% or less.

5. The separator for a lithium-sulfur battery according to claim 4, wherein, when the first layer is a multilayer, the unit layers are arranged such that the porosity increases toward one surface with respect to the thickness direction of the separator.

6. The separator for a lithium sulfur battery according to claim 1, wherein the second layer is a monolayer or a multilayer comprising two or more unit layers, and if the second layer comprises two or more unit layers, each unit layer has a porosity of less than 50 vol% and 25 vol% or more.

7. The separator for a lithium-sulfur battery according to claim 6, wherein, if the second layer is a multilayer, the unit layers are arranged such that the porosity decreases toward the other surface with respect to the thickness direction of the separator.

8. The separator for a lithium-sulfur battery according to claim 1, wherein the thickness of the separator is 45 μm to 420 μm.

9. The separator for a lithium-sulfur battery according to claim 1, wherein the first layer comprises one or more selected from a porous polymer film, a porous nonwoven fabric containing a polymer material, glass fiber, and carbon paper.

10. The separator for a lithium-sulfur battery according to claim 1, wherein the second layer further comprises a porous nonwoven fabric containing a polymer material.

11. Includes an electrode assembly and an electrolyte, The electrode assembly includes a positive electrode, a negative electrode, and a separator interposed between the negative electrode and the positive electrode. The positive electrode includes a positive electrode active material layer, the positive electrode active material layer includes a sulfur-based material containing sulfur and / or a sulfur compound, and the separator is as described in any one of claims 1 to 10. A lithium sulfur battery in which the first layer of the separator faces the positive electrode active material layer.

12. The lithium sulfur battery according to claim 11, wherein the electrolyte comprises a lithium salt and an organic solvent, and the organic solvent comprises a first organic solvent containing a fluorine-based ether compound and a second organic solvent containing a glyme-based compound.

13. The lithium sulfur battery according to claim 11, wherein the sulfur-based material containing sulfur and / or a sulfur compound is included in the positive electrode active material layer in the form of a sulfur-carbon composite, and the sulfur-based material is present in an amount of 60 wt% or more relative to 100 wt% of the positive electrode active material layer.

14. The lithium sulfur battery according to claim 13, wherein the sulfur-carbon composite contains sulfur and carbon in a weight ratio of 60:40 to 80:

20.

15. The lithium sulfur battery according to claim 11, wherein the positive electrode includes a current collector and a positive electrode active material layer disposed on at least one surface of the current collector, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material is present in an amount of 99 wt% or more relative to 100 wt% of the positive electrode active material layer, the positive electrode active material contains an amount of 90 wt% or more of a sulfur-carbon composite relative to 100 wt% of the positive electrode active material layer, and the sulfur-carbon composite includes a sulfur-based material containing sulfur and / or a sulfur compound.

16. The lithium sulfur battery according to claim 11, wherein the negative electrode includes a lithium metal and / or a lithium alloy as a negative electrode active material, and the lithium alloy is an alloy of lithium and another metal.

17. The lithium sulfur battery according to claim 12, wherein the first and second organic solvents are present in an amount of 90 vol% or more relative to 100 vol% of the total organic solvent.

18. The lithium sulfur battery according to claim 12, wherein the first organic solvent comprises one or more of the following: 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), bis(fluoromethyl) ether, 2-fluoromethyl ether, bis(2,2,2-trifluoroethyl) ether, propyl 1,1,2,2-tetrafluoroethyl ether, isopropyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl isobutyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,2'H,3H-decafluorodipropyl ether, and 1H,1H,2'H-perfluorodipropyl ether.

19. The lithium sulfur battery according to claim 12, wherein the second organic solvent is fluorine-free and contains one or more of the following: dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, and polyethylene glycol methyl ethyl ether.

20. The lithium sulfur battery according to claim 12, wherein the electrolyte comprises lithium-bis(trifluoromethanesulfonyl)imide, dimethoxyethane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

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