Cylindrical lithium-sulfur battery and its manufacturing method

Abstract

The lithium-sulfur battery according to the present invention may have a structure in which a jelly-roll-type electrode assembly constituting the battery is covered with a polymer film having heat shrinkability, and the polymer film is shrunk during an activation process to compress the electrode assembly from the outside to the inside. As a result, the battery is operated with the electrode assembly appropriately compressed, thereby maximizing electrochemical performance.

Description

[Technical Field]

[0001] The present invention relates to a lithium-sulfur battery suitable for cylindrical lithium-sulfur batteries and a method for manufacturing the same.

[0002] This application claims priority based on Korean Patent Application No. 2022-0177194 filed with the Korean Intellectual Property Office on December 16, 2022, and the entire contents disclosed in the specification of that application are incorporated herein by reference. [Background technology]

[0003] As the application areas of secondary batteries expand to electric vehicles (EVs) and energy storage systems (ESSs), lithium-ion batteries (LIBs), which have a relatively low weight energy storage density (~250Wh / kg), have limitations in their application to such products. In contrast, lithium-sulfur secondary batteries, which have a theoretically high weight energy storage density (~2,600Wh / kg), are attracting attention as a next-generation secondary battery technology.

[0004] A lithium-sulfur secondary battery is a battery system that uses a sulfur-based material with a sulfur-sulfur bond as the positive electrode active material and lithium metal as the negative electrode active material.Such lithium-sulfur secondary batteries have the advantage that sulfur, the main material of the positive electrode active material, is abundant worldwide, is non-toxic, and has a low weight per atom.

[0005] During discharge, lithium-sulfur secondary batteries undergo oxidation as the negative electrode active material, lithium, releases electrons and becomes ionized, while the positive electrode active material, sulfur-based materials, receive electrons and become reduced. The lithium oxidation reaction involves lithium metal releasing electrons to transform into lithium cations. The sulfur reduction reaction involves sulfur-sulfur bonds receiving two electrons to transform into sulfur anions. The lithium cations produced by the lithium oxidation reaction are transported to the positive electrode via the electrolyte and combine with the sulfur anions produced by the sulfur reduction reaction to form a salt. Specifically, sulfur, which has a cyclic S8 structure before discharge, is converted into lithium polysulfides (Li2Sx, x = 8, 6, 4, 2) through reduction. When these lithium polysulfides are completely reduced, lithium sulfide (Li2S) is ultimately produced.

[0006] In order for a lithium-sulfur battery to operate and exhibit appropriate electrochemical performance, an appropriate level of pressure must be applied to the electrode assembly during operation. If the lithium-sulfur battery has a pouch-type housing, pressure applied from outside the housing can be transmitted to the electrode assembly. However, if a lithium-sulfur battery is designed to be cylindrical and a cylindrical metal can is used as the battery housing, pressure cannot be applied to the electrode assembly during battery operation, making it difficult to operate the battery normally. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in light of the background of the prior art as described above, and has an object to provide a system for applying pressure to a cylindrical lithium-sulfur battery while it is in operation.

[0008] Specifically, the present invention aims to provide a lithium-sulfur battery having a structure in which pressure can be applied to an electrode assembly while the lithium-sulfur battery is in operation, in which a jelly roll assembly is housed in a cylindrical case, and a method for manufacturing the same.

[0009] The present invention aims to provide a lithium-sulfur battery, particularly a cylindrical lithium-sulfur battery, with improved battery performance, and a method for manufacturing the same.

[0010] The technical problems that the present invention aims to solve are not limited to the problems described above, and other problems not mentioned will be clearly understood by those skilled in the art from the detailed description of the invention described below. [Means for solving the problem]

[0011] According to one aspect of the present invention, there is provided a lithium-sulfur battery having the following features:

[0012] The lithium-sulfur battery according to the first aspect comprises: The battery includes a jelly-roll type electrode assembly having a structure in which a negative electrode, a positive electrode, and a separator (separation membrane) are wound together, a polymer film layer covering all or at least a portion of the outer surface of the electrode assembly, a case containing the electrode assembly covered with the polymer film layer, and an electrolyte, and the positive electrode includes a sulfur-based compound as an active material.

[0013] According to the second aspect, in the first aspect, The polymeric film layer may include at least one heat-shrinkable polymer.

[0014] According to the third aspect, in the first or second aspect, The polymer film layer may include at least one heat-shrinkable polymer having a shrinkage starting temperature of 40°C to 80°C.

[0015] According to a fourth aspect, in any one of the first to third aspects, The polymer film layer is a first polymer film in direct contact with an outer surface of the electrode assembly; a second polymeric film covering all or at least a portion of the outer surface of the first polymeric film.

[0016] According to the fifth aspect, in any one of the first to fourth aspects, The shrinkage starting temperature of the first polymer film is 50°C to 200°C, and the shrinkage starting temperature of the second polymer film is 40°C to 80°C, or The first polymer film may have a shrinkage starting temperature of 40°C to 80°C, and the second polymer film may have a shrinkage starting temperature of 50°C to 200°C.

[0017] According to the sixth aspect, in any one of the first to fifth aspects, the electrode assembly is pressed from the outside to the inside by the polymer film layer, The pressure applied to the electrode assembly when the lithium-sulfur battery is in a charged state may be greater than or equal to the pressure applied to the electrode assembly when the lithium-sulfur battery is in a discharged state.

[0018] According to the seventh aspect, in any one of the first to sixth aspects, The case may be cylindrical.

[0019] According to the eighth aspect, in any one of the first to seventh aspects, The polymer film layer may further include heat-absorbing inorganic particles.

[0020] According to another aspect of the present invention, there is provided a method for producing a lithium-sulfur battery having the following features.

[0021] A method for manufacturing a lithium-sulfur battery according to a ninth embodiment includes: (S1) obtaining a jelly-roll type electrode assembly in which a negative electrode, a positive electrode, and a separator are wound together; (S2) forming a polymer film layer covering all or at least a portion of the outer surface of the electrode assembly; (S3) housing the electrode assembly coated with the polymer film layer together with an electrolyte in a case, and then performing an activation process; The activation step includes (S4) a step of thermally shrinking the polymer film layer in a discharged state of the battery, The positive electrode contains a sulfur-based compound as an active material.

[0022] According to the tenth aspect, in the ninth aspect, The discharged state may be a state of charge (SOC) of less than 1%.

[0023] According to the eleventh aspect, in the ninth or tenth aspect, The activation step includes a step of discharging the battery at least once, and may include a step of heat-shrinking the polymer film layer after the first discharge and before charging the battery once.

[0024] According to the twelfth aspect, in any one of the ninth to eleventh aspects, the polymer film layer includes a first polymer film that directly contacts the outer surface of the electrode assembly, and a second film that covers all or at least a portion of the outer surface of the first film; Step S4 may involve heat shrinking the first polymer film and the second polymer film at different temperature ranges.

[0025] According to the thirteenth aspect, in any one of the ninth to twelfth aspects, Step S4 may be performed at a temperature range equal to or lower than the decomposition temperature of the electrolyte.

[0026] According to the 14th aspect, in any one of the 9th to 13th aspects, The case may be cylindrical. [Effects of the Invention]

[0027] In a lithium-sulfur battery according to one aspect of the present invention, the electrode assembly can be pressurized during operation of the battery by thermal shrinkage of the polymer film layer covering the electrode assembly.

[0028] In particular, the electrode assembly pressurized by the polymer film that has shrunk in a discharged state can achieve the effect of being pressurized at a higher pressure when the lithium-sulfur battery is charged.

[0029] As a result, the lithium-sulfur battery according to one aspect of the present invention can exhibit excellent performance.

[0030] Furthermore, by covering the electrode assembly with a polymer film having high temperature shrinkage properties, it is possible to prevent and block contact between the electrode assembly and air, thereby achieving the effect of improving the fire safety of the lithium-sulfur battery.

[0031] According to a method for manufacturing a lithium-sulfur battery in another aspect of the present invention, it is possible to provide a lithium-sulfur battery having a structure that allows the battery to be pressurized during operation.

[0032] In addition to this, the present invention can have various other effects, which will be explained in the respective embodiments, and explanations of effects that can be easily inferred by those skilled in the art will be omitted.

[0033] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention to be given later, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to only the matters depicted in these drawings. [Brief explanation of the drawings]

[0034] [Figure 1]1 is a diagram illustrating the steps of a method for manufacturing an electrode assembly according to an embodiment of the present invention. First, a jelly-roll-type electrode assembly for manufacturing a lithium-sulfur battery is manufactured. Next, the exterior of the electrode assembly is coated with a heat-shrinkable polymer film to form a polymer film layer, and then the electrode assembly is housed in a case together with an electrolyte. The battery is then discharged through an activation process, and heat is supplied from an external heat source in the discharged state to induce contraction of the polymer film. Then, when the battery is charged, the electrode assembly is subjected to a higher pressure than in the discharged state, resulting in a lithium-sulfur battery. [Figure 2] 1 is a graph showing the results of examining the deterioration of a lithium-sulfur battery containing a conjugated heterocyclic compound as a non-aqueous solvent in the electrolyte when exposed to 80° C. It was found that the reference battery, which was charged and discharged at room temperature, gradually deteriorated with repeated charge-discharge cycles, while the battery of Comparative Example 1, which was exposed to heat at 80° C., rapidly deteriorated with repeated charge-discharge cycles. [Figure 3] 1 is a graph showing the results of evaluation of charge-discharge characteristics of a lithium-sulfur battery with and without pressure applied during charge-discharge. DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in the specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as having meanings and concepts corresponding to the technical ideas of the present invention, in accordance with the principle that the inventors themselves can appropriately define the concepts of terms in order to best describe the invention.

[0036] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can be substituted therefor at the time of this application.

[0037] In addition, the accompanying drawings are not drawn to scale, and the dimensions of some components may be exaggerated to aid in understanding the invention. In addition, the same components may be designated by the same reference numerals in different embodiments.

[0038] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0039] In this specification, terms indicating directions such as up, down, left, right, front, back, inside, and outside are used merely for the convenience of explanation, and it will be obvious to those skilled in the art of the present invention that they may differ depending on the position of a reference object, the position of an observer, etc.

[0040] Furthermore, throughout this specification, when a part is described as "including" or "having" certain elements, this does not mean that other elements are excluded, but that other elements may also be included, unless otherwise specified.

[0041] The present invention relates to a lithium-sulfur battery and a method for manufacturing the same.

[0042] In this specification, the lithium-sulfur battery is a general term for batteries that contain a sulfur-based compound as a positive electrode active material and use a lithium material as a negative electrode active material.

[0043] In one embodiment of the present invention, the sulfur-based compound is not particularly limited as long as it can be used as a positive electrode active material for a lithium-sulfur battery. For example, the sulfur-based compound can be inorganic sulfur (S), LiS, etc. n (n≧1), disulfide compounds, organic sulfur compounds, carbon-sulfur polymers (C2S x ) n , x=an integer of 2.5 to 50, and n≧2), or a mixture of two or more thereof.

[0044] In one embodiment of the present invention, the positive electrode may include inorganic sulfur (S8) as a positive electrode active material.

[0045] A lithium-sulfur battery according to an embodiment of the present invention has a structure in which a jelly-roll type electrode assembly is housed in a case together with an electrolyte.

[0046] The jelly roll type electrode assembly is a general term for an electrode assembly having a structure in which a negative electrode, a positive electrode, and a separator are wound together.

[0047] Specifically, the jelly-roll type electrode assembly may refer to a structure in which a separator is interposed between a current collector and a long sheet-shaped positive electrode and a negative electrode, each having an electrode active material applied to the surface of the current collector, and a separator is further laminated on one surface of the positive electrode and / or the negative electrode, and the assembly is then wound into a jelly-roll shape.

[0048] In an embodiment of the present invention, the jelly-roll type electrode assembly may have a structure in which a stack of separator / negative electrode / separator / positive electrode or negative electrode / separator / positive electrode / separator is wound in one direction around a winding shaft, but is not limited thereto.

[0049] The jelly roll-type electrode assembly has a central void formed at the center of the winding, with the top and bottom ends open in the longitudinal direction of the electrode assembly. This void is created by removing the mandrel used when winding the sheet-like electrode assembly. In one embodiment of the present invention, a cylindrical metal center pin can be inserted into the central void to support the jelly roll structure.

[0050] The battery case may have an upper opening sealed by a cap assembly.

[0051] According to one aspect of the present invention, the electrode assembly has a structure in which all or at least a portion of an outer surface is covered with a polymer film layer.

[0052] In one embodiment of the present invention, the polymeric film layer may comprise at least one heat-shrinkable polymer.

[0053] The heat-shrinkable polymer is a polymer that has the property of shrinking or expanding with a change in temperature, and is a general term for polymers that have the property of shrinking when the temperature rises and reaches a shrinkage starting temperature.

[0054] Specifically, the heat-shrinkable polymer has the property of shrinking when exposed to an external heat source. During the production of a polymer film, heat is applied, the film is drawn, stretched, and then cooled. When the film is reheated, the stretched film returns to its original position. That is, during the production of the polymer film, residual stress is generated by stretching, and when a certain amount of heat or more is applied while the residual stress is present, the film shrinks and the residual stress is relieved.

[0055] The polymer film layer is a polymer film having these properties. As described below, during the activation process of a lithium-sulfur battery, when the electrode assembly is discharged and its volume is relatively small, the polymer film layer is heated by an external heat source and shrinks, adhering to the surface of the electrode assembly, and a predetermined pressure is applied to the inside of the electrode assembly due to the contraction force of the shrinkable polymer film. Meanwhile, the volume of the battery increases during charging, but the once-shrunk polymer film layer maintains its contracted state, so that when the volume of the battery increases (i.e., when charging), the amount of pressure applied to the inside of the electrode assembly by the polymer film layer may increase.

[0056] In one embodiment of the present invention, the polymer film may be manufactured in a tubular shape and applied so that the polymer film layer wraps around the side of the electrode assembly.

[0057] In one embodiment of the present invention, the heat-shrinkable polymer contained in the polymer film layer may have a heat-shrink operating temperature of 55°C to 120°C.

[0058] Meanwhile, in the method for manufacturing the lithium-sulfur battery, as described below, the electrode assembly coated with the polymer film layer is housed in a case together with an electrolyte, and then the polymer film layer is shrunk. Therefore, it is preferable that the heat-shrinkable polymer has a shrinkage initiation temperature that is equal to or lower than the temperature at which the electrolyte decomposes.

[0059] For example, according to one embodiment of the present invention, the lithium-sulfur battery may include a conjugated heterocyclic compound as a non-aqueous solvent in the electrolyte, and the conjugated heterocyclic compound may include a substance that begins to decompose when exposed to a temperature of 80°C or higher.

[0060] FIG. 2 is a graph showing the results of a comparative evaluation of the charge-discharge characteristics of a lithium-sulfur battery (Comparative Example 1) that was manufactured and then exposed to heat at 80°C after containing a conjugated heterocyclic compound, such as 2-methylfuran, as a non-aqueous solvent in the electrolyte, compared with the charge-discharge characteristics of a lithium-sulfur battery (reference) that was not exposed to heat.

[0061] Referring to FIG. 2, it has been confirmed that a battery having battery components that decompose when exposed to heat rapidly deteriorates when exposed to high temperatures.

[0062] In this case, it may be preferable that the heat-shrinkable polymer used in the polymer film layer has a shrinkage initiation temperature of, for example, 80° C. or less.

[0063] In one embodiment of the present invention, the heat-shrinkable polymer used in the polymer film layer may include one having a shrinkage initiation temperature of, for example, 40°C to 80°C. Specifically, the polymer film layer may include a heat-shrinkable polymer having a shrinkage initiation temperature of 50°C to 70°C. For example, the polymer film layer may include a heat-shrinkable polymer having a shrinkage initiation temperature of 60°C to 65°C.

[0064] In this specification, the term "shrinkage initiation temperature of a heat-shrinkable polymer" refers to the first temperature at which a shrinkage stress having the same value as the initial load is obtained when a graph of shrinkage stress as a function of temperature is plotted by fixing a polymer film at room temperature (23°C to 25°C) under a predetermined initial load and then measuring the stress when the polymer film is shrunk while applying heat at a predetermined heating rate.

[0065] In this case, in measuring the shrinkage starting temperature, the predetermined temperature rise rate may be, for example, 2.5° C. / second.

[0066] FIG. 3 shows the results of evaluating the charge-discharge characteristics of a jelly-roll-type electrode assembly that includes a positive electrode using a sulfur-based compound containing a sulfur (S)-sulfur (S) bond as the positive electrode active material and a negative electrode using lithium metal, with a polyethylene separator interposed between them and then wound around one end of the electrode assembly. The electrode assembly was then loaded into a case together with an electrolyte and charged and discharged while applying pressure to the electrode assembly using a jig (Example 1) and without applying pressure (Comparative Example 2).

[0067] Referring to FIG. 3, it was confirmed that in Comparative Example 2, in which no pressure was applied during charging and discharging, the rate of battery deterioration accelerated with repeated charge and discharge cycles, whereas in Example 1, in which pressure was applied during charging and discharging, the life characteristics were improved.

[0068] In one embodiment of the present invention, the electrode assembly may be preferably pressurized by the polymer film layer at a pressure equal to or greater than atmospheric pressure, more preferably at a pressure of 1.5 atm to 3 atm, and more preferably at a pressure of 1.5 atm to 2.5 atm.

[0069] In one embodiment of the present invention, it may be preferable that the pressure applied to the electrode assembly by the polymer film layer in a discharge state (DOD (depot of discharge) 100%) is 2 atm.

[0070] In one embodiment of the present invention, the heat-shrinkable polymer may include at least one selected from polyethylene, polyolefin-based polymers, polyester-based polymers, polyvinylidene fluoride, polyethylene terephthalate, polyester, polyvinyl chloride (PVC), and fluoroelastics.

[0071] In one embodiment of the present invention, the polymer film layer may be composed of a single polymer film. As described above, the polymer film covering all or at least a portion of the outer surface of the electrode assembly may contain a heat-shrinkable polymer, thereby exerting the effect of applying pressure to the electrode assembly.

[0072] In another embodiment of the present invention, the polymer film layer may further include at least one layer of polymer film for blocking air from the electrode assembly, in addition to at least one layer of polymer film for applying pressure to the electrode assembly.

[0073] When the polymer film layer includes two or more polymer films, they may be named in the order of proximity to the outer surface of the electrode assembly, such as the first polymer film, the second polymer film, ... the nth polymer film.

[0074] In one embodiment of the present invention, the polymer film layer may include a first polymer film that directly contacts the outer surface of the electrode assembly, and a second polymer film that covers all or at least a portion of the outer surface of the first polymer film.

[0075] When the polymer film layer includes two or more polymer films, the at least two polymer films may have the same shrinkage initiation temperature, or may have different shrinkage initiation temperatures depending on their roles.

[0076] In one embodiment of the present invention, when the polymer film layer further includes a polymer film having a shrinkage onset temperature of 50°C to 200°C, for example, 80°C to 180°C, 100°C to 150°C, specifically 130°C to 150°C, in addition to the polymer film having a shrinkage onset temperature of 40°C to 80°C, when the lithium-sulfur battery is exposed to high temperatures, the shrinkage of the additional polymer film blocks contact between the electrode assembly and air, thereby significantly reducing the risk of fire in the lithium-sulfur battery, but the present invention is not limited thereto.

[0077] In one embodiment of the present invention, when the polymer film layer includes at least two polymer films, the shrinkage starting temperature of the first polymer film may be 50°C to 200°C, and the shrinkage starting temperature of the second polymer film may be 40°C to 80°C.

[0078] In another embodiment of the present invention, when the polymer film layer includes at least two polymer films, the shrinkage starting temperature of the first polymer film may be 40°C to 80°C, and the shrinkage starting temperature of the second polymer film may be 50°C to 200°C.

[0079] In one embodiment of the present invention, the electrode assembly has all or at least a portion of its outer surface covered with a polymer film having the above-described properties, thereby receiving pressure from the outside to the inside.

[0080] In this case, it is preferable that the polymer film covers the electrode assembly so that the pressure applied to the electrode assembly when the lithium-sulfur battery is in a charged state is greater than or equal to the pressure applied to the electrode assembly when the lithium-sulfur battery is in a discharged state (see FIG. 1).

[0081] In an embodiment of the present invention, it may be more preferable that the polymer film covers the electrode assembly such that the pressure applied to the electrode assembly when the lithium-sulfur battery is in a charged state is greater than the pressure applied to the electrode assembly when the lithium-sulfur battery is in a discharged state.

[0082] In one embodiment of the present invention, the battery case may be cylindrical. When the electrode assembly is an electrode assembly coated with the above-described polymer film layer, it can be used in pouch-type and prismatic batteries, but even when applied to cylindrical batteries that cannot be pressurized using conventional methods, it can exert a pressurizing effect on the electrode assembly.

[0083] In one embodiment of the present invention, the polymer film may be made of only a heat-shrinkable polymer, but may further contain heat-absorbing inorganic particles.

[0084] In one embodiment of the present invention, the heat-absorbing inorganic particles may be any inorganic particles known in the art to have heat-absorbing properties. Non-limiting examples of the heat-absorbing inorganic particles include one or more compounds selected from the group consisting of antimony-containing compounds, aluminum hydroxide (Al(OH)), magnesium hydroxide (Mg(OH)), guanidine-based compounds, boron-containing compounds, and zinc stannate compounds. The antimony-containing compound may be, for example, antimony trioxide (SbO), antimony tetroxide (SbO), antimony pentoxide (SbO), or a mixture of two or more of these. The guanidine-based compound may be guanidine nitride, guanidine sulfamate, guanidine phosphate, guanylurea phosphate, or a mixture of two or more of these. The boron-containing compound may be HBO, HBO, or a mixture of these. The zinc stannate compound may be Zn2SnO4, ZnSnO3, ZnSn(OH)6, or a mixture of two or more of these.

[0085] In one embodiment of the present invention, the positive electrode may have a positive electrode active material layer formed on at least one surface of a positive electrode current collector, the positive electrode having a positive electrode tab attached thereto. The positive electrode tab may be attached to a blank portion of the positive electrode current collector where the positive electrode active material is not applied by ultrasonic welding or other methods. However, the present invention is not limited to this positive electrode tab attachment method, and various tab attachment techniques known at the time of filing of the present invention may be employed in the present invention.

[0086] Meanwhile, the positive electrode current collector may be a thin metal plate having excellent conductivity, such as aluminum (Al) foil, and the positive electrode tab may be made of aluminum (Al), for example.

[0087] In one embodiment of the present invention, the negative electrode may be a free-standing lithium metal or lithium alloy. Alternatively, the negative electrode may be a free-standing lithium metal or lithium alloy with a support attached to at least one surface thereof. Alternatively, the negative electrode may be formed by coating at least one surface of a negative electrode current collector with a negative electrode active material. A negative electrode tab may be attached to the negative electrode. Similar to the positive electrode tab, the negative electrode tab may be attached to a non-coated portion of the negative electrode current collector where no negative electrode active material is coated, and various attachment methods, such as ultrasonic welding, may be used. The negative electrode current collector may be a conductive metal sheet, for example, copper (Cu) or nickel (Ni) foil, and the negative electrode tab may be made of nickel (Ni), for example.

[0088] In one embodiment of the present invention, the separator can be any material that insulates the positive and negative electrodes of a jelly-roll electrode assembly and allows active material ions to be exchanged between them. Specifically, the separator can be a porous polymer film, such as a porous film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate of two or more layers thereof. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Separators coated with a coating layer containing a heat-resistant polymer material, such as a ceramic component or an engineering plastic, can also be used to ensure heat resistance or mechanical strength.

[0089] In one embodiment of the present invention, the sulfur-based compound as the positive electrode active material may be included in the form of a sulfur-carbon composite composite with a carbon material. Preferably, the positive electrode active material contains 80 wt% or more of the sulfur-carbon composite relative to 100 wt% of the positive electrode active material, and 70 wt% or more of the sulfur-based material relative to 100 wt% of the sulfur-carbon composite.

[0090] In one embodiment of the present invention, the sulfur-carbon composite may be a composite of simply mixed sulfur and a carbon material, or may be a core-shell structured coating or support. The core-shell structured coating form is a coating of either sulfur or a carbon material with the other material. For example, the surface of the carbon material may be coated with sulfur, or vice versa. The carbon material may have a porous structure with pores inside and on its surface, and in particular, the internal pores may be filled with sulfur.

[0091] The carbon material has a porous structure containing a large number of non-uniform pores on the surface and inside, and serves as a carrier providing a framework for uniformly and stably immobilizing sulfur, thereby compensating for the low electrical conductivity of sulfur and enabling the electrochemical reaction to proceed smoothly. The carbon material may be any porous and conductive carbon-based material commonly used in the art, such as graphite, graphene, carbon black (e.g., denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black), carbon nanotubes (CNTs) (e.g., single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), carbon fibers (e.g., graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs)), graphite (e.g., natural graphite, artificial graphite, and expanded graphite), carbon nanoribbons, carbon nanobelts, carbon nanorods, and activated carbon.

[0092] In one embodiment of the present invention, the sulfur-carbon composite can be prepared by a composite method including the steps of mixing a carbon material and sulfur to form a mixture and then composite the mixture.

[0093] The mixing for preparing the sulfur-carbon composite can be performed using a stirrer commonly used in the art to enhance the degree of mixing between sulfur and carbon materials. The mixing time and speed can also be selectively adjusted depending on the contents and conditions of the raw materials.

[0094] The composite method for preparing the sulfur-carbon composite is not particularly limited in the present invention, and may be a method commonly used in the art. For example, methods commonly used in the art, such as dry composite or wet composite, such as spray coating, may be used. For example, a method may be used in which the mixture of sulfur and carbon material obtained after mixing is heat-treated so that the molten sulfur is uniformly coated on the inner and outer surfaces of the carbon material. Meanwhile, in one embodiment of the present invention, a process of pulverizing the mixture of sulfur and carbon material using a ball mill or the like may be performed before the heat treatment. In one embodiment of the present invention, the heat treatment is performed at a temperature of 120°C to 160°C for about 20 minutes to 24 hours, and a heating device such as an oven may be used.

[0095] The sulfur-carbon composite prepared by the above-described method has a high specific surface area, a high sulfur loading, and a structure that improves sulfur utilization. This not only improves the electrochemical reactivity of sulfur but also improves the accessibility and contactability of the electrolyte, thereby improving the capacity and life characteristics of lithium-sulfur batteries.

[0096] With respect to the configurations, materials, manufacturing methods, etc. of the positive electrode, negative electrode, and separator, other than those described in this specification, content that is widely known to those skilled in the art can be adopted in the present invention, and detailed description of these content will be omitted in this specification.

[0097] Meanwhile, the electrode assembly coated with the polymer film layer as described above is housed in a battery case and filled with an electrolyte, so that it can operate as a lithium secondary battery.

[0098] In one embodiment of the present invention, the electrolyte may be any electrolyte that can be used in a cylindrical lithium-sulfur battery, such as a solid electrolyte membrane, or a non-aqueous solvent and a lithium salt.

[0099] In one embodiment of the present invention, when the electrolyte has a composition including a non-aqueous solvent and a lithium salt, the non-aqueous solvent may preferably include a chain ether compound and a conjugated heterocyclic compound.

[0100] In one embodiment of the present invention, the conjugated heterocyclic compound is a general term for compounds that have a structure in which p orbitals of three or more adjacent atoms constituting the compound can overlap with other p orbitals of adjacent atoms connected by a σ bond, and that contain atoms other than carbon as ring atoms in the structure.

[0101] In one embodiment of the present invention, the non-aqueous solvent contains a conjugated heterocyclic compound. This allows the ring-opening polymerization reaction of the heterocyclic compound to form a polymer protective film (solid electrolyte interface, SEI) on the surface of the lithium-based metal (negative electrode) during the initial discharge step of the battery, thereby suppressing the formation of lithium dendrites. Furthermore, the decomposition of the electrolyte on the surface of the lithium-based metal and the associated side reactions can be reduced, thereby improving the life characteristics of the lithium-sulfur battery. Furthermore, the conjugated structure of the non-aqueous solvent makes it difficult for salt to dissolve due to the delocalization of lone pair electrons of the heteroatom, typically the sulfur atom, thereby reducing the amount of polysulfide leaching from the electrolyte.

[0102] In one embodiment of the present invention, the conjugated heterocyclic compound may be a 4- to 15-membered, preferably 4- to 7-membered, more preferably 5- to 6-membered heterocyclic compound. Furthermore, such a conjugated heterocyclic compound may be a heterocyclic compound substituted or unsubstituted with one or more groups selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen group, a nitro group (-NO), an amine group (-NH), and a sulfonyl group (-SO). Furthermore, the conjugated heterocyclic compound may be a polycyclic compound of a heterocyclic compound and one or more of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms.

[0103] When the conjugated heterocyclic compound is substituted with an alkyl group having 1 to 4 carbon atoms, the radicals are stabilized and side reactions with the electrolyte are suppressed, which is preferable. When the conjugated heterocyclic compound is substituted with a halogen group or a nitro group, a functional protective film can be formed on the surface of the lithium-based metal, which is preferable. In this case, the formed functional protective film is a compact protective film and is stable, which has the advantages of enabling uniform deposition of the lithium-based metal and suppressing side reactions between the polysulfide and the lithium-based metal.

[0104] In one embodiment of the present invention, the conjugated heterocyclic compound may include at least one of a conjugated cyclic ether compound and a thiophene-based compound.

[0105] In one embodiment of the present invention, the conjugated cyclic ether compound may include, for example, a furan-based compound and a pyran-based compound. More specifically, the conjugated cyclic ether compound may include, but is not limited to, furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, or a mixture of two or more selected from the above.

[0106] In one embodiment of the present invention, the thiophene-based compound may include, but is not limited to, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, 2,5-dimethylthiophene, or a mixture of two or more thereof.

[0107] As described above, in one embodiment of the present invention, the non-aqueous solvent preferably has a decomposition temperature higher than the shrinkage initiation temperature of the polymer film.

[0108] In one embodiment of the present invention, the non-aqueous solvent may be a mixture of 2-methylfuran and 1,2-dimethoxyethane, for example, a mixture having a volume ratio of 5:5 to 2:8.

[0109] In the present invention, the lithium salt is a compound 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, etc., can be used. In the present invention, from the viewpoint of increasing the possibility of utilizing sulfur and realizing a battery with a high capacity and a high voltage, the lithium salt preferably includes Li-TFSI. More preferably, the lithium salt may include LiN(CF3SO2)2 (Li-TFSI) in a content of 80 wt% or more, 90 wt% or more, or 100% based on 100 wt% of the total lithium salt.

[0110] 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 concentration of the lithium salt is in this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively. If the concentration of the lithium salt is below this range, it may be difficult to ensure ionic conductivity suitable for battery operation. If the concentration of the lithium salt is above this range, the viscosity of the electrolyte may increase, reducing lithium ion mobility or increasing the decomposition reaction of the lithium salt itself, which may result in reduced battery performance.

[0111] Next, the method for manufacturing a lithium-sulfur battery according to the present invention will be described in detail with reference to FIG.

[0112] According to FIG. 1, a method for manufacturing a lithium-sulfur battery according to one embodiment of the present invention includes the steps of (a) manufacturing a jelly roll for a lithium-sulfur battery, (b) coating the jelly roll with a shrinkable polymer film layer, and (c) inserting the electrode assembly into a cylindrical can, injecting an electrolyte, and sealing the can. Then, (d) as the battery formation progresses and reaches a discharged state, (e) applying an external heat source to shrink the polymer film layer. Then, (f) as the battery is charged, the electrode assembly expands in volume, but the pressure applied to the electrode assembly increases due to the shrinkage of the polymer film layer.

[0113] In FIG. 1, the magnitude of pressure applied to the electrode assembly in a discharged state and the magnitude of pressure applied to the electrode assembly in a charged state are indicated by the lengths of the arrows.

[0114] Another aspect of the present invention provides a method for manufacturing a lithium-sulfur battery, comprising: (S1) obtaining a jelly-roll type electrode assembly in which a negative electrode, a positive electrode, and a separator are wound together; (S2) forming a polymer film layer covering all or at least a portion of the outer surface of the electrode assembly; (S3) The electrode assembly coated with the polymer film layer is housed in a case together with an electrolyte, and then an activation process is performed.

[0115] In this case, the activation step includes (S4) a step of thermally shrinking the polymer film layer in a discharged state of the battery.

[0116] As described above, the positive electrode contains a sulfur-based compound as an active material.

[0117] (S1) In one embodiment of the present invention, a jelly roll type electrode assembly can be obtained according to a conventional method for obtaining a jelly roll type electrode assembly.

[0118] For example, a jelly roll-type electrode assembly can be manufactured by first winding one end of a separator (separation membrane) a predetermined number of times around a core, and then winding the positive and negative electrodes together. This is an example of an embodiment of winding an electrode assembly into a jelly roll shape, but the present invention is not limited thereto. Then, the core is removed from the center of the wound jelly roll-type electrode assembly. In one embodiment of the present invention, a center pin of an appropriate shape can be inserted at the position where the core was removed. In another embodiment, the core can be used as the center pin.

[0119] (S2) Next, a polymer film layer is formed to cover all or at least a portion of the outer surface of the electrode assembly.

[0120] That is, the polymer film layer is formed by covering all or part of the outer surface of the electrode assembly with the polymer film.

[0121] The coating may be applied to all or at least a portion of the exterior of the electrode assembly.

[0122] In one embodiment of the present invention, the polymer film may be in a sheet shape and configured to wrap around the side surface of the electrode assembly.

[0123] In another embodiment of the present invention, the polymer film may be prepared in the shape of a cylindrical tube, and configured to wrap around the side of the electrode assembly.

[0124] (S3) Next, the jelly-roll type electrode assembly coated with the polymer film layer is placed in a battery case, and an electrolyte may be injected into the case before, after, or simultaneously with placing the electrode assembly in the battery case.

[0125] In one embodiment of the present invention, the method may further include welding the jelly roll structure to a lower end of the battery case after the electrode assembly is housed in the battery case. The opening of the battery case may be sealed with a cap assembly (not shown). Preferably, an electrolyte is injected into the case before sealing the battery, allowing the electrode assembly to be impregnated with the electrolyte.

[0126] After the electrode assembly and the electrolyte are housed in a case, a battery activation process is carried out.

[0127] The lithium-sulfur battery is assembled with the positive electrode in a charged state immediately after assembly, so the activation process is performed from the first discharge.

[0128] (S4) The activation process includes a step of heat-shrinking the polymer film layer in a discharged state of the battery.

[0129] As described above, the shrinkage causes the polymer film layer to adhere closely to the electrode assembly, and the adhesion force may apply pressure to the inside of the battery.

[0130] The activation step renders the battery electrochemically active and includes discharging the battery one or more times, specifically, it may include discharging the battery one or more times and charging the battery one or more times.

[0131] In one embodiment of the present invention, the activation process includes an aging step to allow the injected electrolyte to diffuse uniformly within the battery, a charging step of the battery, and a discharging step of the battery, and one or more of these steps may be further performed.

[0132] Meanwhile, the shrinking step of the shrinkable polymer film is preferably performed when the volume of the jelly roll structure is at its minimum during the activation process. Generally, the volume of a lithium-sulfur battery increases when it is charged and decreases when it is discharged. Therefore, the shrinking step may be performed when the volume of the electrode assembly is at its minimum, i.e., in a discharged state.

[0133] In one embodiment of the present invention, the heat shrinking step of the polymer film layer is preferably performed when the lithium-sulfur battery is in a discharged state, for example, when the state of charge (SOC) is less than 1%.

[0134] In one embodiment of the present invention, the activation process includes a step of discharging the battery at least once, and may include a step of heat-shrinking the polymer film layer after the first discharge and before charging the battery once.

[0135] As described above, in one embodiment of the present invention, the polymer film layer may include a first polymer film that directly contacts the outer surface of the electrode assembly, and a second polymer film that covers all or at least a portion of the outer surface of the first polymer film.

[0136] In this case, if the first polymer film and the second polymer film have different shrinkage start temperatures, step S4 may be performed to heat-shrink the first polymer film and the second polymer film in different temperature ranges.

[0137] In one embodiment of the present invention, the activation process includes a step of applying a heat source to shrink the polymer films, and in this case, the step of shrinking the first polymer film and the step of shrinking the second polymer film may be performed sequentially or simultaneously.

[0138] In another embodiment of the present invention, when the lithium-sulfur battery includes polymer film layers in which the first polymer film has a shrinkage start temperature of 40° C. to 80° C. and the second polymer film has a shrinkage start temperature of 50° C. to 200° C., the activation process may include a step of shrinking only the first polymer film, but not a step of shrinking the second polymer film. This may achieve an effect of improving the fire safety of the lithium-sulfur battery by compressing the electrode assembly through the first polymer film and blocking contact between the electrode assembly and air through the second polymer film in the event of a fire.

[0139] As described above, in one embodiment of the present invention, step S4 is preferably performed in a temperature range equal to or lower than the decomposition temperature of the electrolyte.

[0140] For example, step S4 may include applying a temperature of 55°C to 120°C to the lithium-sulfur battery in a discharged state, for example, applying a temperature of 40°C to 80°C, 50°C to 70°C, or 60°C to 65°C to shrink the polymer film.

[0141] As described above, once the polymer film has shrunk, it maintains its shrunk state. Therefore, even if the electrode assembly expands and increases in volume due to charging, the shrunk polymer film maintains its shape, thereby maintaining the pressure of the electrode assembly. Preferably, the pressure applied to the electrode assembly when the lithium-sulfur battery is charged is greater than or equal to the pressure applied in the discharged state, and more preferably, greater than the pressure applied in the discharged state.

[0142] According to yet another aspect of the present invention, there is provided a battery module including the lithium-sulfur battery as a unit cell.

[0143] The battery module can be used as a power source for medium to large devices that require high temperature stability, long cycle characteristics, and high capacity characteristics.

[0144] Examples of the medium- to 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.

Claims

1. a jelly-roll type electrode assembly having a structure in which a negative electrode, a positive electrode, and a separator are wound together; a polymer film layer covering all or at least a portion of the outer surface of the electrode assembly; a case for accommodating the electrode assembly covered with the polymer film layer; Electrolytes, Including, The positive electrode of the lithium-sulfur battery contains a sulfur-based compound as an active material.

2. 10. The lithium-sulfur battery of claim 1, wherein the polymeric film layer comprises at least one heat-shrinkable polymer.

3. 2. The lithium-sulfur battery of claim 1, wherein the polymer film layer comprises at least one heat-shrinkable polymer having a shrinkage start temperature of 40°C to 80°C.

4. The polymer film layer is a first polymer film directly contacting an outer surface of the electrode assembly; a second polymer film covering all or at least a portion of the exterior surface of the first polymer film.

5. The shrinkage starting temperature of the first polymer film is 50°C to 200°C, and the shrinkage starting temperature of the second polymer film is 40°C to 80°C, or 5. The lithium-sulfur battery according to claim 4, wherein the first polymer film has a shrinkage start temperature of 40 to 80°C, and the second polymer film has a shrinkage start temperature of 50 to 200°C.

6. the electrode assembly is pressed from the outside to the inside by the polymer film layer, 6. The lithium-sulfur battery according to claim 1, wherein a pressure applied to the electrode assembly when the lithium-sulfur battery is in a charged state is greater than or equal to a pressure applied to the electrode assembly when the lithium-sulfur battery is in a discharged state.

7. 10. The lithium-sulfur battery of claim 1, wherein the case is cylindrical.

8. 10. The lithium-sulfur battery of claim 1, wherein the polymer film layer further comprises heat-absorbing inorganic particles.

9. (S1) obtaining a jelly-roll type electrode assembly in which a negative electrode, a positive electrode, and a separator are wound together; (S2) forming a polymer film layer covering all or at least a portion of the outer surface of the electrode assembly; (S3) placing the electrode assembly coated with the polymer film layer in a case together with an electrolyte, and then performing an activation process; Including, The activation step includes (S4) a step of thermally shrinking the polymer film layer in a discharged state of the battery, The method for producing a lithium-sulfur battery, wherein the positive electrode contains a sulfur-based compound as an active material.

10. The method for manufacturing a lithium-sulfur battery according to claim 9, wherein the discharged state is a state of charge (SOC) of less than 1%.

11. 10. The method for manufacturing a lithium-sulfur battery according to claim 9, wherein the activation step includes a step of performing at least one discharge, and a step of heat-shrinking the polymer film layer after the first discharge and before performing one charge.

12. the polymer film layer includes a first polymer film that directly contacts the outer surface of the electrode assembly, and a second polymer film that covers all or at least a portion of the outer surface of the first polymer film; 12. The method of claim 9, wherein step S4 comprises heat-shrinking the first polymer film and the second polymer film at different temperature ranges.

13. The method for manufacturing a lithium-sulfur battery according to claim 9, wherein step S4 is performed at a temperature range equal to or lower than the decomposition temperature of the electrolyte.

14. The method for manufacturing a lithium-sulfur battery according to claim 9, wherein the case is cylindrical.

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