Separator coating material, comprising conductive metal-organic framework, for secondary battery, and lithium-sulfur secondary battery comprising same

Abstract

The present application relates to a separator coating material, comprising a conductive metal-organic framework, for a lithium-sulfur secondary battery, and a separator and a lithium-sulfur secondary battery comprising same. The lithium-sulfur secondary battery of the present application has excellent battery performance and lifespan characteristics by preventing a shuttle phenomenon of a polysulfide through the lithium polysulfide adsorption ability of the separator for a secondary battery.

Description

Separator coating material for secondary batteries including conductive metal-organic frameworks and lithium-sulfur secondary batteries including the same

[0001] The present invention relates to a separator coating material for a lithium-sulfur secondary battery including a conductive metal-organic framework, a separator including the same, and a lithium-sulfur secondary battery.

[0002] Recently, the miniaturization and lightweighting of electronic products, electronic devices, and communication devices is rapidly progressing. With the growing need for electric vehicles due to environmental concerns, demand for improved performance of secondary batteries, which power these products, is also increasing. Among these, lithium secondary batteries are attracting considerable attention as high-performance batteries due to their high energy density and high standard electrode potential.

[0003] In particular, the lithium-sulfur (Li-S) battery is a secondary battery that uses a sulfur-based material with a sulfur-sulfur bond as a positive electrode active material and lithium metal as an negative electrode active material. Sulfur, the main ingredient of the positive electrode active material, has the advantages of being abundant, non-toxic, and having a low weight per atom. In addition, the theoretical discharge capacity and theoretical energy density of the lithium-sulfur battery are 1,675 mAh / g-sulfur and 2,600 Wh / kg, respectively, which are much higher than the theoretical energy densities of other batteries currently being studied (Ni-MH battery: 450 Wh / kg; Li-FeS battery: 480 Wh / kg; Li-MnO2 battery: 1,000 Wh / kg; and Na-S battery: 800 Wh / kg), making it the most promising battery among the batteries being developed to date.

[0004] During the discharge reaction of a lithium-sulfur battery, an oxidation reaction of lithium occurs at the anode, and a reduction reaction of sulfur occurs at the cathode. The lithium-sulfur battery generates lithium polysulfide (Li2S) during discharge. x, x is 2 to 8) are generated, which dissolve in the electrolyte and diffuse to the cathode, causing various side reactions and reducing the capacity of sulfur participating in the electrochemical reaction. In addition, during the charging process, the lithium polysulfide causes a shuttle reaction, which significantly reduces the charge / discharge efficiency.

[0005] To address this issue, methods of adding sulfur-absorbing additives have been proposed. However, this leads to additional battery side effects due to degradation. Therefore, methods such as adding metal chalcogenides or alumina to delay the outflow of the positive electrode active material, i.e., sulfur, or coating the surface with oxycarbonate have been proposed. However, these methods not only result in sulfur loss or complication during the processing, but also limit the amount of sulfur that can be added. Therefore, the lithium polysulfide problem must be resolved as a top priority for the commercialization of lithium-sulfur batteries.

[0006] [Prior Art Literature]

[0007] [Non-patent literature]

[0008] AF Hofmann, DN Fronczek, WG Bessler, Mechanistic modeling of polysulfide shuttle and capacity loss in lithium-sulfur batteries, Journal of Power Sources, 259 (2014) 300-310.

[0009] The present invention relates to a separator coating material for a lithium-sulfur secondary battery including a conductive metal-organic framework, a separator including the same, and a lithium-sulfur secondary battery.

[0010] However, the problems that the present invention seeks to solve are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0011] The first aspect of the present invention provides a separator coating material for a lithium-sulfur secondary battery, comprising: a metal-organic framework including a transition metal and a linker; a carbon conductive material; and a binder.

[0012] The second aspect of the present invention provides a separator for a lithium-sulfur secondary battery, including a separator coating material and a substrate for a lithium-sulfur secondary battery according to the first aspect.

[0013] The third aspect of the present invention provides a lithium-sulfur secondary battery comprising a separator for a lithium-sulfur secondary battery, including a separator coating material and substrate for a lithium-sulfur secondary battery according to the first aspect; a cathode comprising sulfur; an anode comprising lithium; and an electrolyte.

[0014] A separator coating material for a lithium-sulfur secondary battery, comprising a metal-organic framework according to embodiments of the present disclosure; a carbon conductive material; and a binder, can provide catalytic properties, improved lithium polysulfide (LiPS) adsorption capacity, and improved electrolyte wettability when used in a lithium-sulfur secondary battery due to the high surface area and conductivity of the metal-organic framework. In addition, due to the synergistic effect of the metal-organic framework and the carbon conductive material, there is an additional advantage in that the carbon conductive material improves the electrical conductivity of the metal-organic framework and the carbon conductive material physically inhibits the dissolution of lithium polysulfide.

[0015] The lithium-sulfur secondary battery according to the embodiments of the present invention has excellent battery performance and lifespan characteristics due to the prevention of the shuttle phenomenon of polysulfide due to the lithium polysulfide adsorption ability of the secondary battery separator. Specifically, the lithium-sulfur secondary battery has a current density of 335 mA g -1 About 1151 mAh g at a rate of (0.2 C) -1 It exhibits high specific capacity, 335 mA g even after 100 cycles. -1 About 813 mAh g at a rate of (0.2 C) -1It exhibits excellent discharge capacity, which can maintain approximately 70% of the initial capacity.

[0016] FIG. 1 a and b are schematic diagrams illustrating, in one embodiment of the present invention, (a) a method for suppressing polysulfide dissolution in a lithium-sulfur secondary battery using a Ni3(2,3,6,7,10,11-hexahydroxytriphenylene)2(Ni-HHTP)@SP coated separator, and (b) a process for synthesizing a Ni-HHTP metal-organic framework (MOF).

[0017] FIGS. 2A and 2B show, in one embodiment of the present invention, the results of a polysulfide adsorption test, namely (a) a digital image of the Li2S6 adsorption test and (b) a UV-vis absorption spectrum of the polysulfide solution for each corresponding sample.

[0018] FIGS. 3A to 3H illustrate the results of characterization of Ni-HHTP and Ni-HHTP@SP membranes in one embodiment of the present invention, including (a) low-magnification and (b) high-magnification SEM images of the Ni-HHTP membrane, (c) low-magnification and (d) high-magnification SEM images of the Ni-HHTP@SP membrane, (e) cross-sectional SEM image of the Ni-HHTP@SP membrane, and element mapping images corresponding to (f) oxygen, (g) carbon, and (h) nickel of the Ni-HHTP@SP membrane.

[0019] Figures 4a to 4i show the electrochemical performance of various separators in one embodiment of the present invention, including (a) CV profiles of Li2S6 symmetric cells according to various types of separators, (b) Nyquist plots, and (c) 0.1 mV s -1 CV curves of lithium-sulfur batteries using different separators at scan rates of 0.1 to 0.4 mV s for batteries with (d) PE, (e) Ni-HHTP, and (f) Ni-HHTP@SP separators. -1CV curves at scan rates of ; Peak current (I) on the x-axis for PE, Ni-HHTP, and Ni-HHTP@SP in (g) the anodic oxidation process (O1), (h) the first cathodic reduction process (R1), and (h) the second cathodic reduction process (R2). p ) and the square root of the scan speed on the y-axis (ν 0.5 ) CV plots, (i) Li ion diffusion coefficients of Ni-HHTP, Ni-HHTP@SP, and PE separators.

[0020] Figures 5a to 5c show the electrochemical performance of various membranes in one embodiment of the present invention, (a) 0.2 C (335 mA g -1 ), (a) Cycling performance of Li-S cells using different types of separators, (b) Discharge / charge voltage profiles in the third cycle of cells using PE, Ni-HHTP, and Ni-HHTP@SP, (c) 0.1 C(167 mA g -1 ) to 2 C(3344 mA g -1 ) shows the speed performance of PE, Ni-HHTP, and Ni-HHTP@SP at the C-speed.

[0021] Hereinafter, with reference to the attached drawings, implementation examples and embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. However, the present invention may be implemented in various different forms and is not limited to the implementation examples and embodiments described herein. In addition, in the drawings, parts irrelevant to the description have been omitted to clearly explain the present invention, and similar parts have been designated with similar drawing reference numerals throughout the specification.

[0022] Throughout this specification, when a part is said to be "connected" to another part, this includes not only cases where it is "directly connected" but also cases where it is "electrically connected" with another element in between.

[0023] Throughout this specification, when it is said that an element is "on" another element, this includes not only cases where the element is in contact with the other element, but also cases where another element exists between the two elements.

[0024] Throughout this specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0025] The terms "about," "substantially," and the like used in this specification are used in a meaning that is at or close to the numerical value when manufacturing and material tolerances inherent in the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which exact or absolute values ​​are mentioned to aid understanding of the present application.

[0026] The terms “step of ~” or “step of ~” as used throughout this specification do not mean “step for ~.”

[0027] Throughout this specification, the term "combination(s) thereof" included in the expressions in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expressions in the Makushi format, and means including one or more selected from the group consisting of said components.

[0028] Throughout this specification, references to “A and / or B” mean “A or B, or A and B.”

[0029] Below, the implementation examples of the present invention are described in detail, but the present invention may not be limited thereto.

[0030] The first aspect of the present invention provides a separator coating material for a lithium-sulfur secondary battery, comprising: a metal-organic framework including a transition metal and a linker; a carbon conductive material; and a binder.

[0031] In one embodiment of the present invention, the transition metal may be one or more selected from Ni, Mg, Fe, Sc, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Ta, Ir, Pt, Au and Co.

[0032] In one embodiment of the present invention, the linker includes at least one selected from 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP), 2,3,6,7,10,11-hexaiminotriphenylene (HITP), 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine (H6TDPAT), benzene-1,3,5-tricarboxylic acid (BTC), pyromellitic acid, terephthalic acid linkers, and imidazole linkers. May include, but may not be limited to.

[0033] In one embodiment of the present invention, the terephthalic acid linker may include, but is not limited to, terephthalic acid, 2-aminoterephthalic acid, 2-sulfoterephthalate, 2,5-(dianilino)terephthalic acid, 2-hydroxyethylterephthalic acid, 2-(6-carboxypyridin-3-yl)terephthalic acid, 2-(2-carboxyphenoxy)terephthalic acid, or 2,5-dihydroxyterephthalic acid. there is.

[0034] In one embodiment of the present invention, the imidazole-based linker may include, but is not limited to, 2-methylimidazole, 2-ethylimidazole, 2-chloroimidazole, 4-bromoimidazole, 2-iodoimidazole, 4-iodoimidazole, 2-nitroimidazole, 2-chloromethylbenzimidazole, methylbenzimidazole, 2-aminobenzimidazole, 5-nitrobenzimidazole, or benzimidazole.

[0035] In one embodiment of the present invention, the metal-organic framework may include Ni3(2,3,6,7,10,11-hexahydroxytriphenylene)2 (Ni3(2,3,6,7,10,11-hexahydroxytriphenylene)2; Ni3(HHTP)2).

[0036] In one embodiment of the present invention, the separator coating material for a lithium-sulfur secondary battery can provide catalytic properties, improved lithium polysulfide (LiPS) adsorption capacity, and improved electrolyte wettability due to the high surface area and conductivity of the metal-organic framework when used in a lithium-sulfur secondary battery.

[0037] In one embodiment of the present invention, the carbon conductive material may include at least one selected from carbon black, graphite, carbon nanofibers (CNF), carbon nanotubes (CNT), carbon nanowires (CNW), carbon nanoribbons, and graphene, but may not be limited thereto.

[0038] In one embodiment of the present invention, the carbon black may include, but may not be limited to, Super P.

[0039] In one embodiment of the present invention, the separator coating material for a lithium-sulfur secondary battery includes the metal-organic framework and the carbon conductive material, so that the carbon conductive material can improve the electrical conductivity of the metal-organic framework, and the carbon conductive material can physically suppress the dissolution of lithium polysulfide.

[0040] In one embodiment of the present invention, the binder may include one or more selected from polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyamideimide (PAI), polydioctylfluorenecofluorenecomethylbenzoic ester (PFFOMB), polyethylenedioxythiophene:poly(styrenesulfonate) (PEDOT:PSS), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), poly(tetrafluoroethylene) (PTFE), polyacrylonitrile (PAN), polyaniline (PANI), and polyacrylic acid (PAA), but may not be limited thereto.

[0041] In one embodiment of the present invention, the weight ratio of the metal-organic framework and the carbon conductive material may be about 1:0.01 to about 1:1, but may not be limited thereto.

[0042] In one embodiment of the present invention, the weight ratio of the metal-organic framework and the carbon conductive material is about 1:0.01 to about 1:1, about 1:0.01 to about 1:0.7, about 1:0.01 to about 1:0.5, about 1:0.01 to about 1:0.3, about 1:0.01 to about 1:0.2, about 1:0.01 to about 1:0.15, about 1:0.01 to about 1:0.125, about 1:0.05 to about 1:1, about 1:0.05 to about 1:0.7, about 1:0.05 to about 1:0.5, about 1:0.05 to about 1:0.3, about 1:0.05 to about 1:0.2, about 1:0.05 to about 1:0.15, about 1:0.05 to about 1:0.125, about 1:0.07 to about 1:1, about 1:0.07 to about 1:0.7, about 1:0.07 to about 1:0.5, about 1:0.07 to about 1:0.3, about 1:0.07 to about 1:0.2, about 1:0.07 to about 1:0.15, about 1:0.07 to about 1:0.125, about 1:0.09 to about 1:1, about 1:0.09 to about 1:0.7, about 1:0.09 to about 1:0.5, about 1:0.09 to about 1:0.3, about 1:0.09 to about 1:0.2, about 1:0.09 to about 1:0.15, about 1:0.09 to about 1:0.125, about 1:0.1 to about 1:1, about 1:0.1 to about 1:0.7, about 1:0.1 to about 1:0.5, about 1:0.1 to about 1:0.3, about 1:0.1 to about 1:0.2, about 1:0.1 to about 1:0.15, or about 1:0.1 to about 1:0.125.

[0043] In one embodiment of the present invention, the weight ratio of the metal-organic framework and the binder may be about 1:0.01 to about 1:1, but may not be limited thereto.

[0044] In one embodiment of the present invention, the weight ratio of the metal organic framework and the binder is about 1:0.01 to about 1:1, about 1:0.01 to about 1:0.7, about 1:0.01 to about 1:0.5, about 1:0.01 to about 1:0.3, about 1:0.01 to about 1:0.2, about 1:0.01 to about 1:0.15, about 1:0.01 to about 1:0.125, about 1:0.05 to about 1:1, about 1:0.05 to about 1:0.7, about 1:0.05 to about 1:0.5, about 1:0.05 to about 1:0.3, about 1:0.05 to about 1:0.2, about 1:0.05 to about 1:0.15, about 1:0.05 to about 1:0.125, about 1:0.07 to about 1:1, about 1:0.07 to about 1:0.7, about 1:0.07 to about 1:0.5, about 1:0.07 to about 1:0.3, about 1:0.07 to about 1:0.2, about 1:0.07 to about 1:0.15, about 1:0.07 to about 1:0.125, about 1:0.09 to about 1:1, about 1:0.09 to about 1:0.7, about 1:0.09 to about 1:0.5, about 1:0.09 to about 1:0.3, about 1:0.09 to about 1:0.2, about 1:0.09 to about 1:0.15, about 1:0.09 to about 1:0.125, about 1:0.1 to about 1:1, about 1:0.1 to about 1:0.7, about 1:0.1 to about 1:0.5, about 1:0.1 to about 1:0.3, about 1:0.1 to about 1:0.2, about 1:0.1 to about 1:0.15, or about 1:0.1 to about 1:0.125.

[0045] In one embodiment of the present invention, the separator coating material for a lithium-sulfur secondary battery may include Ni3(2,3,6,7,10,11-hexahydroxytriphenylene)2, carbon black, and PVDF.

[0046] In one embodiment of the present invention, when the separator coating material for a lithium-sulfur secondary battery includes Ni3(2,3,6,7,10,11-hexahydroxytriphenylene)2, carbon black, and PVDF, the weight ratio of Ni3(2,3,6,7,10,11-hexahydroxytriphenylene)2, carbon black, and PVDF may be about 1:0.125:0.125.

[0047] In one embodiment of the present invention, the thickness of the separator coating material for the lithium-sulfur secondary battery may be about 10 μm to about 30 μm, but may not be limited thereto.

[0048] In one embodiment of the present invention, the thickness of the separator coating material for the lithium-sulfur secondary battery may be from about 10 μm to about 30 μm, from about 10 μm to about 25 μm, from about 10 μm to about 20 μm, or from about 10 μm to about 15 μm, but may not be limited thereto.

[0049] The second aspect of the present invention provides a separator for a lithium-sulfur secondary battery, including a separator coating material and a substrate for a lithium-sulfur secondary battery according to the first aspect.

[0050] Detailed explanations of parts that overlap with the first aspect of the present application have been omitted, but the contents described in the first aspect of the present application may be equally applied even if the explanation is omitted in the second aspect of the present application.

[0051] In one embodiment of the present invention, the substrate may be used without limitation as long as it is a substrate commonly used as a separator substrate for a secondary battery in the relevant industry, and may be, for example, a polymer substrate.

[0052] In one embodiment of the present invention, the polymer substrate may include one or more selected from polyolefin including polyethylene or polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylenenaphthalene, but may not be limited thereto.

[0053] In one embodiment of the present invention, the loading amount of the separator coating material for lithium-sulfur secondary batteries is about 0.2 mg / cm 2 About 2 mg / cm 2 It may be, but may not be limited to,

[0054] In one embodiment of the present invention, the loading amount of the separator coating material for lithium-sulfur secondary batteries is about 0.2 mg / cm 2 About 2 mg / cm 2 , about 0.2 mg / cm 2 About 1.5 mg / cm 2 , about 0.2 mg / cm 2 About 1 mg / cm 2 , about 0.2 mg / cm 2 About 0.9 mg / cm 2 , about 0.2 mg / cm 2 About 0.8 mg / cm 2 , about 0.2 mg / cm 2 About 0.7 mg / cm 2 , about 0.5 mg / cm 2 About 2 mg / cm 2 , about 0.5 mg / cm 2 About 1.5 mg / cm 2 , about 0.5 mg / cm 2 About 1 mg / cm 2 , about 0.5 mg / cm 2 About 0.9 mg / cm 2 , about 0.5 mg / cm 2About 0.8 mg / cm 2 , about 0.5 mg / cm 2 About 0.7 mg / cm 2 It could be.

[0055] In one embodiment of the present invention, the separator coating material for the lithium-sulfur secondary battery may be coated on one side or both sides of the substrate.

[0056] In one embodiment of the present invention, the thermal stability of the substrate can be improved by forming the separator coating material for the lithium-sulfur secondary battery on a portion or the entire surface of the substrate.

[0057] The third aspect of the present invention provides a lithium-sulfur secondary battery comprising a separator for a lithium-sulfur secondary battery, including a separator coating material and substrate for a lithium-sulfur secondary battery according to the first aspect; a cathode comprising sulfur; an anode comprising lithium; and an electrolyte.

[0058] Detailed descriptions of overlapping parts with the first and second aspects of the present application have been omitted, but the contents described for the first and second aspects of the present application may be equally applied even if the description is omitted in the third aspect of the present application.

[0059] In one embodiment of the present invention, the sulfur content ratio of the cathode may be about 10 wt% or more, but may not be limited thereto.

[0060] In one embodiment of the present invention, the cathode may include, but is not limited to, one or more selected from sulfur, sulfur-carbon complex, and sulfur-selenium complex.

[0061] In one embodiment of the present invention, the electrolyte may include an organic solvent electrolyte and a lithium salt. Any organic solvent electrolyte and lithium salt commonly used in the industry may be used without limitation. For example, the organic solvent may be N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, It may include tetrahydrofuran derivatives, ethers, or methyl propionate, ethyl propionate, and the lithium salt is LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, LiC(CF3SO2)3, (CF3SO2)2NLi, or (FSO2)2NLi.

[0062] In one embodiment of the present invention, the lithium-sulfur secondary battery has the characteristics of excellent battery performance and lifespan characteristics, as the shuttle phenomenon of polysulfide is prevented due to the lithium polysulfide adsorption ability of the secondary battery separator. Specifically, the lithium-sulfur secondary battery has a current density of 335 mA g -1 About 1151 mAh g at a rate of (0.2 C) -1 It exhibits high specific capacity, 335 mA g even after 100 cycles. -1About 813 mAh g at a rate of (0.2C) -1 It exhibits excellent discharge capacity, which can maintain approximately 70% of the initial capacity.

[0063] Hereinafter, the present invention will be described in more detail using examples. However, the following examples are provided only to help understand the present invention, and the contents of the present invention are not limited to the following examples.

[0064] [Example]

[0065] 1. Materials and Methods

[0066] 1.1 Prepare materials

[0067] All commercial chemicals used in the experiment were unpurified. These chemicals were nickel(II) acetate tetrahydrate (Ni(OCOCH3) 2·4H2O, 98%, Sigma-Aldrich), 2,3,6,7,10,11-Hexahydroxytriphenylene Hydrate (HHTP, >95%, TCI-chemicals), N-methyl pyrrolidone (NMP, ≥99%, Sigma-Aldrich), dimethoxy ethane (DME, Sigma-Aldrich), 1,3-dioxolane (DOL, Sigma-Aldrich), acetone (CH3COCH3, Sigma-Aldrich), lithium sulfide (Li2S, Sigma-Aldrich), Super P carbon black (SP), sulfur (S, Sigma-Aldrich), ketjen black (KB, SCI Materials Hub) and polyvinylidene fluoride (PVDF, Sigma-Aldrich).

[0068] Synthesis of Ni-HHTP

[0069] Ni3(HHTP)2 was synthesized based on a slightly modified method by the Hmadeh group. Figure 1b shows the structure of a 2,3,6,7,10,11-Hexahydroxytriphenylene (HHTP) organic linker and Ni(OAc) 2· A synthetic method for producing Ni-HHTP using a 4H2O metal node is presented. 7 mg of HHTP and Ni(OAc) 2·10 mg of 4H2O(Ni) was dissolved in a vial containing 4 mL of deionized water. The mixture was then heated in an isothermal oven at 85°C for 12 h. The reaction solution was allowed to cool naturally to room temperature to allow crystals to precipitate. The resulting Ni-HHTP powder was washed with water and acetone to remove any remaining impurities. Finally, the Ni-HHTP powder was dried in a vacuum oven at 85°C for 24 h to remove any residual water and acetone.

[0070] Fabrication of Ni-HHTP@SP modified membrane

[0071] The basic separator used in the present invention is a PE membrane with a thickness of 9 μm. To disperse Ni-HHTP (8 mg), Super P (1 mg), and PVDF (1 mg), 17 mL of NMP was added. Then, the mixture was sonicated for 1 hour to disperse uniformly. The solution was filtered through a PE membrane using a vacuum filtration method, so that powder was accumulated on the membrane to prepare Ni-HHTP and Ni-HHTP@SP coated membranes. The membranes with the coated layer were dried in a vacuum oven at 80°C for 12 hours to remove NMP. All coated membranes had a molecular weight of 0.7 mg cm -2 The loading amount was fixed. The same procedure was followed when coating the membrane with Ni-HHTP and SP.

[0072] 1.2 Material Characterization

[0073] The crystal structure of the powder is Cu K at a wavelength of 1.54 Å. αThe membrane properties were investigated by X-ray diffraction (XRD) analysis using a MiniFlex600 instrument utilizing radiation. The morphology and elemental mapping of the membrane were evaluated by scanning electron microscopy (SEM) using a JSM-7800F instrument. Nitrogen adsorption-desorption isotherms were obtained at a temperature of 77 K using a Brunauer-Emmett-Teller (BET) measuring instrument (Quantachrome, FL-33426). Thermogravimetric analysis (TGA) was performed using a METTLER TOLEDO TGA3+ thermogravimetric analyzer. The contact angle of the sample was measured using a contact angle meter (Kruss, DSA 25). LiPS adsorption tests were performed using a UV-Vis spectrometer (Agilent, Cary 300).

[0074] Preparation of Li2S6 / Li2S8 solution

[0075] Lithium sulfide (Li2S) and sulfur (S) were combined in a molar ratio of 1:5 to prepare a Li2S6 solution. A solvent mixture was prepared by mixing equal volumes of dimethoxyethane (DME) and 1,3-dioxolane (DOL) in a suitable vessel. The Li2S and S mixture was slowly added to the DME / DOL solvent mixture and stirred thoroughly, and the mixture was stirred continuously for 48 h while maintaining the temperature at 60°C. This extended stirring time was necessary to complete the synthesis and promote the formation of Li2S6. After the synthesis was completed, the solution was cooled to room temperature. A similar approach was used to prepare the Li2S8 solution, using lithium sulfide (Li2S) and sulfur (S) in a molar ratio of 1:8.

[0076] Cathode manufacturing

[0077] For the active materials of S and ketjen black (S@KB), S and KB were mixed in a mass ratio of 7:3 and infiltrated at 155°C for 8 hours. TGA analysis confirmed that the sulfur content of KB was 70%. The cathode was composed of the active material S@KB, the conductive material Super P, and the binder PVDF, and the mass ratio of S@KB:Super P:PVDF was 8:1:1. A certain amount of NMP was added and mixed well using a Thinky mixer to form a uniformly distributed slurry. Then, the slurry was coated on an aluminum (Al) foil to obtain about 1.3 mg cm -2 The sulfur content above was achieved. The coated electrode was dried overnight in a vacuum oven at 80°C. Ultimately, prior to cell assembly, the electrode was punched to obtain circular pieces with a diameter of 12 mm.

[0078] 1.3 Electrochemical testing

[0079] Electrochemical measurements were performed using a coin cell configuration, specifically a CR2032 type assembled inside an Ar glove box. The negative electrode was made of lithium metal, and the prepared electrode was used as the positive electrode. The electrolyte consisted of a solution containing 1 M LiTFSI and 0.4 M LiNO3 in a 1:1 volume ratio of dimethoxy ethane (DME) and 1,3-dioxolane (DOL). Room-temperature cycling performance and cyclic voltammetry (CV) experiments were performed using a battery tester (wonatech, WBCS3000L). Cycling tests and rate performance measurements were performed within a voltage range of 1.7 V to 2.6 V, and CV scans were performed at 0.1 mV s -1 was performed at 1.5 V to 2.8 V with a scan rate of 0.1 mV s -1 within 0.4 mV s -1) the voltage range used is 1.5 V to 3 V. Li + The diffusion coefficient of ions can be described using the Randles-Sevcik equation (Eq. 1 below) in the voltage range of -0.8 V to 0.8 V.

[0080] [Formula 1]

[0081] Randles-Sevcik equation: I p = 268600×e 1.5 ×A×D 0.5 ×v 0.5 ×C Li

[0082] In Equation 1, I p is the peak current, e is the number of electrons participating in the reaction (e=2 for LSB), A is the electrode area, v is the scan rate, C Li represents the lithium ion concentration in the electrolyte.

[0083] Electrochemical impedance spectroscopy (EIS) was performed using a biological SP-150e impedance analyzer with an AC voltage amplitude of 10 mV over a frequency range of 10 mHz to 100 kHz.

[0084] 2. Results and Discussion

[0085] 2.1. Material Characterization Results

[0086] MOFs possess high surface areas and tunable chemical properties through various combinations of metal ions and organic ligands. However, three-dimensional MOFs still have limited electrical conductivity, making them difficult to apply to LSB. Ni-HHTP is a conductive Ni3(2,3,6,7,10,11-hexahydroxytriphentlene)2 (Ni3(2,3,6,7,10,11-hexahydroxytriphentlene)2) MOF and acts as an efficient redox mediator to accelerate the conversion reaction rate of sulfur (S) species. It is characterized by metal nodes containing nickel (Ni) centers and π-conjugated organic linkers, hexahydroxytriphentlene, providing electrical conductivity and exhibiting strong affinity for LiPS. Therefore, by utilizing the unique properties of Ni-HHTP, we aimed to apply it to suppress LiPS dissolution, a critical drawback in LSB operation, by coating it on the membrane surface (Fig. 1a).

[0087] As shown in Fig. 1b, Ni-HHTP was synthesized hydrothermally using nickel acetate and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP). The resulting 2D layer consists of a structure composed of hexagonal pores, and individual units are alternately stacked through π-π interactions and hydrogen bonds to form 1D channels. The morphology and structure of the synthesized Ni-HHTP were characterized using SEM and XRD. The Ni-HHTP exhibited a nanorod shape, and the XRD pattern showed a unique peak corresponding to the (100) plane perpendicular to the Ni-HHTP at approximately 4.6°, and a peak indicating the presence of the (002) plane formed through π-stacking interactions at 27°. Additional characterization of Ni-HHTP, including nitrogen adsorption-desorption isotherm and pore size distribution, was performed by BET analysis. Ni-HHTP has a pore size of about 106.75 m2 g -1 surface area, pore size ranging from 16.7 Å to 20 Å, and 0.492 cc g -1 The type I adsorption isotherm with a pore volume of was shown, confirming the micro-porous structure.

[0088] To evaluate the interaction between Ni-HHTP and LiPS, an adsorption test was performed by adding 20 mg of Ni-HHTP powder to a 2 mM Li2S6 solution (Fig. 2a). For comparison, the same experimental conditions were applied to Co-HHTP and SP. The original Li2S6 solution was yellow. The color change after 12 h of adding each powder to the yellow Li2S6 solution was observed to determine the degree of adsorption of each substance. Ni-HHTP produced the most transparent solution, whereas SP showed a color similar to the original Li2S6 solution. This indicates that Ni-HHTP has the ability to adsorb polar Li2S6 and nitrogen, whereas SP, as a nonpolar substance, has limitations in adsorbing polar LiPS. In addition, UV-visible analysis was performed on the upper solution obtained from the adsorption test (Fig. 2b). S6 of Li2S6 2- When paper was present, all samples exhibited broad absorbances in the 250 nm to 350 nm range. However, the solution containing Ni-HHTP powder exhibited the lowest absorbance, consistent with the color difference of the solutions. This highlights the strong interaction between Ni-HHTP and LiPS, indicating its potential to suppress the shuttle effect.

[0089] To prevent self-discharge within the cell, a functional separator was fabricated by coating a Ni-HHTP@SP composite on one side of a PE separator using a vacuum filtration method. The stability, dimensional stability, and thermal shrinkage properties of the coating layer of the synthesized separator were evaluated. The coating layer remained intact even after immersion in electrolyte for 6 hours and bending, demonstrating resilience. In addition, the Ni-HHTP and Ni-HHTP@SP coated separators exhibited higher thermal stability than the bare PE separator, which melts at 120°C.

[0090] To optimize the coating thickness, functional membranes were fabricated with different mass ratios of Ni-HHTP, SP, and PVDF. 0.7 mg cm -2 The Ni-HHTP coated with a loading of 0.7 mg cm showed the highest discharge capacity even after 18 cycles and exhibited bulk resistance similar to that of the PE membrane. Considering these comprehensive results, -2 It can be confirmed that the loading amount is suitable for maintaining excellent performance. In the present invention, a small amount of Super P was added to complement the moderate electrical conductivity of Ni-HHTP and to suppress the physical dissolution of LiPS in LSB. The interaction between LiPS and Ni-HHTP effectively suppressed dissolution, while the moderate electrical conductivity of Ni-HHTP enhanced the reaction kinetics. To verify the effect of Ni-HHTP and Super P, samples containing Ni-HHTP and a mixture of Ni-HHTP and Super P were compared. As a result, it was confirmed that even a small amount of Super P improved electrical conductivity and effectively suppressed LiPS dissolution, showing a synergistic effect with Ni-HHTP.

[0091] The top-view SEM images and EDS mapping results in Figs. 3a to 3h confirm the uniform and dense distribution of the coating layer. In addition, the cross-sectional SEM image in Fig. 3e shows a 14 μm-thick coating layer on the 9 μm-thick PE separator. In addition, the Ni-HHTP-coated separator not only improved the electrolyte wettability but also enhanced the affinity for LiPS, as shown in the contact angle measurement. While the contact angle of the PE separator was 63.4 degrees, the contact angle of the Ni-HHTP-coated separator was significantly reduced to 23.2 degrees due to the polar coating layer. In addition to the improved electrical conductivity, this polar coating layer is expected to improve both the wetting behavior and ionic conductivity of the modified Ni-HHTP@SP functional separator. In addition, the diffusion capacity of the coated functional separator was evaluated by placing 10 mM Li2S6 on the left side of the H-cell and placing a pure DME / DOL solution on the right side. The color change of the solution was used to predict the diffusion rate, indicating that LiPS diffusion was inhibited in the Ni-HHTP and Ni-HHTP@SP coated membranes compared to PE due to the effective impedance of LiPS permeation. Ni-HHTP@SP effectively mitigates short-term leaching compared to Ni-HHTP due to the additional physical barrier role of Super P.

[0092] Electrochemical properties

[0093] To investigate the effect of Ni-HHTP on the redox kinetics and improved conversion reaction of LiPS, cyclic voltammetry (CV) tests were performed in symmetric cells with and without Li2S6 in the voltage range of -0.8 V to 0.8 V. As shown in Fig. 4a, in the absence of Li2S6, no current was observed, confirming the involvement of dissolved LiPS as a reactive species. When the electrolyte containing Li2S6 was used, the symmetric cell exhibited redox peak currents, indicating that the adsorption and conversion processes of LiPS were occurring smoothly. Ni-HHTP promoted efficient charge transfer through the Ni node and accelerated the multivalent sulfur redox reaction. However, the weaker peak intensity of Ni-HHTP compared to Ni-HHTP@SP may be due to the lower electrical conductivity of Ni-HHTP compared to SP, which affects the extent of the redox reaction.

[0094] This effect is also clearly evident in the electrochemical performance. The EIS results of LSB are shown in Fig. 4b, where the semicircle in the high-frequency region represents the charge transfer resistance, and the diagonal line in the low-frequency region represents the Li content in the electrode. + The diffusion of ions is shown. The size of the semicircle indicates that the Rct value is lower when using Ni-HHTP@SP and Ni-HHTP separators, which means the improvement of electrical conductivity due to Ni-HHTP and SP. In addition, CV measurements were performed to evaluate the reversibility of the cells (Fig. 4c). In this process, all cells showed two reduction peaks occurring at about 2.28 V and 2.02 V, which are indicative of the long-chain LiPS (Li2S) of cyclic S8. n, 4 < n < 8) and the subsequent conversion of long-chain LiPS to solid short-chain lithium sulfides (Li2S2 / Li2S). Similarly, in the anodic scan process, two overlapping oxidation peaks around 2.35 V indicate that the short-chain lithium sulfides were oxidized again to elemental S8. The CV results showed two reduction peaks and one oxidation peak, which are typical for the redox reaction of Li-S in LSB. For the cells using Ni-HHTP and Ni-HHTP@SP coated separators, the redox potentials were higher and the peak intensities were also greater than those of the cell using PE separator. This demonstrates the positive effect of Ni-HHTP in reducing the polarization and accelerating the reaction kinetics.

[0095] LiPS released during the charging and discharging process is deposited on the surface of the separator and the top surface of the cathode to form an insulating layer. This layer is Li + It limits the life of LSB by hindering the diffusion of ions and increasing the electrical resistance. Therefore, to elucidate this phenomenon, the Li of LSB was investigated using PE, Ni-HHTP, and Ni-HHTP@SP separators. + The ion diffusion coefficient was characterized.

[0096] Therefore, the high slope can be used as an indicator of improved kinetics during the charge-discharge process of the Li-S reaction. As shown in Fig. 4g and h, the slopes (R1, R2) of the reduction peaks increased by 109% and 113% for Ni-HHTP@SP, and 128% and 134%, respectively, compared to Ni-HHTP and PE. The significantly improved performance of Ni-HHTP and Ni-HHTP@SP cells compared to PE cells is attributed to the fast electron and Li transport in the separator. +It shows that there is a close correlation with the mobility of ions (i in Fig. 4). Therefore, the Ni-HHTP@SP coated separator effectively interacts with LiPS and acquires the ability to accelerate the redox kinetics of LiPS.

[0097] In Fig. 5a, 0.2 C current density (335 mA g -1 ) to compare the cycling performance between PE, Ni-HHTP, and Ni-HHTP@SP coated separators. Ni-HHTP (682 mAh g -1 ) and Ni-HHTP@SP (813 mAh g -1 ) LSB using coated separator is a bare PE separator (450 mAh g -1 ) and it can be confirmed that it maintains excellent electrochemical performance even after 100 cycles.

[0098] To understand the cause of these differences, Fig. 5b shows the voltage profiles of half-cells using different coated separators during the third cycle at a rate of 0.2 C. In the voltage profile of LSB, two plateaus are observed during the discharge process. The first plateau is the peak of the Li2S x (x=4 to 8), and the second plateau represents the reduction of long-chain LiPS to Li2S2 / Li2S. The first plateau is related to the formation of soluble LiPS, which indicates the LiPS capture ability of the coated membrane.

[0099] When using Ni-HHTP and Ni-HHTP@SP coated separators, the first plateau is noticeably enhanced compared to the PE separator, indicating that Ni-HHTP effectively adsorbs LiPS. In addition, the second plateau is attributed to the enhanced capacity due to the strong electrical conductivity of SP. Therefore, the capacity enhancement of batteries using Ni-HHTP and Ni-HHTP@SP coated separators is expected to be related to the increased electrolyte adsorption capacity and the suppression of LiPS release. However, in the case of cells using Ni-HHTP@SP, the enhanced capacity due to the enhanced electrical conductivity of Super P leads to a rapid capacity drop due to the weak polarity, which is then stabilized by the effect of Ni-HHTP.

[0100] In addition, Fig. 5c analyzes the rate capacity of the cell using the coated separator. The cell using the Ni-HHTP@SP separator has a rate capacity of 1337 mAh g at 0.1 C, 0.2 C, 0.3 C, 0.5 C, 1 C, and 2 C, respectively. -1 , 1107 mAh g -1 , 965 mAh g -1 , 791 mAh g -1 , 634 mAh g -1 , and 520 mAh g -1 The capacity was proven to be 1675 mA g -1 Even at a high 1 C rate, the cell using Ni-HHTP@SP separator showed a capacity of 634 mAh g -1 While maintaining high capacities, cells using Ni-HHTP and PE separators showed significantly reduced capacity degradation above 2 C rates.

[0101] 3. Conclusion

[0102] A functional membrane was designed by coating a composite composed of a conductive 2D nickel hexahydroxytriphenylene (Ni-HHTP) metal-organic framework (MOF) and a small amount of Super P on a commonly used polyethylene (PE) membrane. The Ni-HHTP MOF has a high surface area and a 0.26 S cm -1 6 × 10 -3 S cm -1 It provides an intermediate electrical conductivity in the range of . This provides catalytic properties and enhances the adsorption of LiPS as well as improves the wettability of the electrolyte. In addition, the addition of Super P complements the intermediate electrical conductivity of Ni-HHTP and helps to physically inhibit the dissolution of LiPS. The strong interaction between the dissolved LiPS and Ni-HHTP in the electrolyte inhibits the dissolution, and the intermediate electrical conductivity of Ni-HHTP improves the reaction kinetics. To confirm the effects of Ni-HHTP and Super P in LSB, the inventors compared samples using only Ni-HHTP and a mixture of Ni-HHTP and Super P. As a result, it was confirmed that even at a small amount of addition, Super P exhibited excellent electrical conductivity and acted as a physical barrier, demonstrating a synergistic effect with Ni-HHTP. As a result, the LSB with the Ni-HHTP@SP coated membrane showed an electrical conductivity of 335 mA g -1 About 1151 mAh g at (0.2 C) -1 It exhibits high specific capacity, maintaining 70% of the initial capacity even after 100 cycles and 635 mAh g at 2 C. -1 It was demonstrated that LSB provides high discharge capacity. These results highlight the practical applicability of LSB through a simple membrane surface design using conductive 2D MOF.

[0103] In summary, we have introduced a novel approach to enhance the performance of LSBs by designing a functional separator. By coating a conductive 2D Ni-HHTP MOF containing Super P onto a standard polyethylene (PE) separator, we effectively addressed the LiPS shuttle phenomenon. This hybrid Ni-HHTP@SP separator significantly enhances battery performance by improving LiPS adsorption and electrolyte wettability. Cells with the Ni-HHTP@SP separator exhibit enhanced specific capacity, excellent capacity retention, and superior redox kinetics.

[0104] The above description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single entity may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined manner.

[0105] The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. A metal-organic framework comprising a transition metal and a linker; carbon conductive material; and bookbinder A separator coating material for a lithium-sulfur secondary battery, comprising:

2. In paragraph 1, A separator coating material for a lithium-sulfur secondary battery, wherein the transition metal comprises at least one selected from Ni, Mg, Fe, Sc, Ti, V, Cr, Mn, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Ta, Ir, Pt, Au and Co.

3. In paragraph 1, The above linker comprises at least one selected from 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP), 2,3,6,7,10,11-hexaiminotriphenylene (HITP), 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine (H6TDPAT), benzene-1,3,5-tricarboxylic acid (BTC), pyromellitic acid, terephthalic acid linkers, and imidazole linkers, lithium-sulfur. Separator coating material for secondary batteries.

4. In paragraph 1, A separator coating material for a lithium-sulfur secondary battery, wherein the metal-organic framework comprises Ni3(2,3,6,7,10,11-hexahydroxytriphenylene)2.

5. In paragraph 1, A separator coating material for a lithium-sulfur secondary battery, wherein the carbon conductive material comprises at least one selected from carbon black, graphite, carbon nanofiber (CNF), carbon nanotube (CNT), carbon nanowire (CNW), carbon nanoribbon, and graphene.

6. In paragraph 1, A separator coating material for a lithium-sulfur secondary battery, wherein the binder comprises at least one selected from polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyamideimide (PAI), polydioctylfluorenecofluorenecomethylbenzoic ester (PFFOMB), polyethylenedioxythiophene:poly(styrenesulfonate) (PEDOT:PSS), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), poly(tetrafluoroethylene) (PTFE), polyacrylonitrile (PAN), polyaniline (PANI), and polyacrylic acid (PAA).

7. In paragraph 1, A separator coating material for a lithium-sulfur secondary battery, wherein the weight ratio of the metal-organic framework and the carbon conductive material is 1:0.01 to 1:

1.

8. In paragraph 1, A separator coating material for a lithium-sulfur secondary battery, wherein the weight ratio of the metal organic framework and the binder is 1:0.01 to 1:

1.

9. In paragraph 1, The above lithium-sulfur secondary battery separator coating material comprises Ni3(2,3,6,7,10,11-hexahydroxytriphenylene)2, carbon black, and PVDF.

10. In paragraph 1, A separator coating material for a lithium-sulfur secondary battery, wherein the thickness of the separator coating material for a lithium-sulfur secondary battery is 10 μm to 30 μm.

11. A separator for a lithium-sulfur secondary battery, comprising a separator coating material and substrate for a lithium-sulfur secondary battery according to Article 1.

12. In paragraph 11, The loading amount of the above lithium-sulfur secondary battery separator coating material is 0.2 mg / cm 2 2 mg / cm 2 A separator for lithium-sulfur secondary batteries.

13. In paragraph 11, A separator for a lithium-sulfur secondary battery, wherein the above-mentioned separator coating material for a lithium-sulfur secondary battery is coated on one side or both sides of the above-mentioned substrate.

14. A lithium-sulfur secondary battery comprising a separator coating material and substrate for a lithium-sulfur secondary battery according to Article 1; a cathode comprising sulfur; an anode comprising lithium; and an electrolyte.

15. In paragraph 14, A lithium-sulfur secondary battery, wherein the sulfur content of the cathode is 10 wt% or more.

16. In paragraph 14, A lithium-sulfur secondary battery, wherein the cathode comprises at least one selected from a sulfur-carbon complex and a sulfur-selenium complex.

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