Method for transferring thin film by using marangoni flow

Abstract

A method for transferring a thin film, according to the present invention, induces Marangoni flow by using an organic solvent having a surface tension lower than that of water, and thus enables a thin film to be safely transferred to a separator without damage and wrinkles. Therefore, the surface of the transferred nano-thin film exhibits a low root-mean-square roughness, and the performance of a lithium-sulfur (Li-S) battery comprising same can be significantly improved.

Description

Thin film transfer method using Marangoni flow

[0001] The present invention relates to a method for transferring a thin film using Marangoni flow.

[0002] One of the key strategies to improve the electrochemical performance of lithium-sulfur (Li-S) batteries is to install a functional interlayer on a commercial polypropylene (PP) separator to suppress the shuttle effect. This phenomenon occurs during the charge and discharge of the battery, which is caused by lithium polysulfide (Li2S). n , n ≥ 2) are dissolved in the electrolyte and generated while shuttled between the cathode (lithium metal) and the anode (sulfur).

[0003] It's crucial to install these functional interlayers thinly, as they increase the overall volume and weight of the battery and lengthen the lithium ion migration path, reducing energy density and capacity. However, the process of transferring the ultra-thin film to the PP separator presents a problem: the film is easily damaged.

[0004] Traditionally, water transfer printing has been used to transfer ultra-thin films onto PP separators. However, this method has failed to address the inherent mechanical strength of ultra-thin films, which can easily wrinkle and break. This compromises film quality during the transfer process and can lead to serious problems, including reduced battery performance.

[0005] Therefore, there is an urgent need to develop a simple and effective method for transferring ultra-thin films to separators without damage.

[0006] In order to solve the above problems, the present invention aims to provide a simple and effective method for transferring a thin film using Marangoni flow, which can transfer a large-area ultra-thin film to a separator without damage.

[0007] In order to achieve the above purpose, the inventors of the present invention have conducted continuous research to develop a simple and effective thin film transfer method, and have discovered that an ultra-thin film can be transferred to a separator without damage when using Marangoni flow, thereby completing the present invention.

[0008] The present invention provides a method for transferring a thin film using a Marangoni flow, comprising the steps of: (A) contacting a substrate on which a thin film has been formed with an organic solvent, and then laminating a polymer film in the presence of the organic solvent; and (B) immersing the substrate on which the polymer film has been laminated in water to transfer the thin film from the substrate to the polymer film.

[0009] According to one embodiment of the present invention, the organic solvent may have a lower surface tension than water.

[0010] According to one embodiment of the present invention, the surface tension of the organic solvent at 20°C may be 50 mN / m or less.

[0011] According to one embodiment of the present invention, the organic solvent is C 1-7 may contain alcohol.

[0012] According to one embodiment of the present invention, the substrate may be a glass substrate.

[0013] According to one embodiment of the present invention, a step of immersing the substrate (a') in water to form a water layer at least partially between the thin film and the substrate may be further performed prior to step (A).

[0014] According to one embodiment of the present invention, a step of forming a thin film by coating a thin film slurry composition on a substrate (a'') may be further performed prior to step (A).

[0015] According to one embodiment of the present invention, the thin film may include an ionomer, a conductive material, a conductive polymer, and an ionic liquid.

[0016] According to one embodiment of the present invention, the ionomer may include a fluorine-based ionomer.

[0017] According to one embodiment of the present invention, the conductive material may include a carbon-based conductive material.

[0018] According to one embodiment of the present invention, the conductive polymer may include at least one selected from the group consisting of polyethylenedioxythiophene: polystyrenesulfonic acid, polyacetylene, polypyrrole, polythiophene, polyaniline, poly(3-hexylthiophene), poly(3,4-ethylenedioxythiophene), poly(3-tetradecylthiophene), poly(2-methoxy-5-(2'-methylhexyloxy)-1,4-phenylenevinylene), polyphenylene vinylene, polyphenylene, and poly(methoxyphenylene vinylene).

[0019] According to one embodiment of the present invention, the ionic liquid is 1-ethyl-3-methylimidazolium boron tetrafluoride (EMIM-BF4), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), 1-ethyl-3-methylimidazolium tetracyanoborate (EMIM-TCB), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-TFSI), 1-ethyl-3-methylimidazolium sulfate (EMIM-SO4), 1-butyl-3-methylimidazolium boron tetrafluoride (BMIM-BF4), 1-decyl-3-methylimidazolium boron tetrafluoride (DMIM-BF4), 1-decyl-3-methylimidazolium It may include at least one selected from the group consisting of bis(trifluoromethylsulfonyl)imide (DMIM-TFSI).

[0020] According to one embodiment of the present invention, the thin film may have a thickness of 10 to 3000 nm.

[0021] According to one embodiment of the present invention, the polymer film may include a polyolefin-based polymer.

[0022] According to one embodiment of the present invention, the polymer film may have a thickness of 10 to 500 μm.

[0023] According to one embodiment of the present invention, the root mean square roughness (RMS) of the surface of the polymer film to which the thin film is transferred after step (B) may be 5 nm or less.

[0024] The method of transferring a thin film using Marangoni flow of the present invention uses an organic solvent with a lower surface tension than water to induce Marangoni flow, thereby safely and wrinkle-free transferring the thin film to a separator without damage. As a result, the transferred nano-thin film exhibits low surface roughness, significantly improving the performance of a lithium-sulfur (Li-S) battery containing the same.

[0025] Figure 1 is a process diagram briefly showing a method of transferring a thin film using a Marangoni flow according to one embodiment, and is performed in the order of (1)->(2)->(3)->(4).

[0026] FIG. 2 (a-1) is a scanning electron microscope (SEM) image of the surface of a polypropylene (PP) separator of Comparative Example 1, FIG. 2 (b-1) is an image analyzed by atomic force microscopy (AFM), FIG. 2 (a-2) is an image analyzed by scanning electron microscopy (SEM) of the surface of the thin film side of the 'polypropylene (PP) separator with a thin film transferred' manufactured according to Example 1, FIG. 2 (b-2) is an image analyzed by atomic force microscopy (AFM), and FIG. 2 (c) is an image of a polypropylene (PP) separator with a large-area thin film transferred manufactured according to Example 1.

[0027] Fig. 3 (a) is a scanning electron microscope (SEM) image analyzing a cross-section of a polypropylene (PP) separator (PCP) on which a thin film manufactured according to Example 1 is transferred, and Figs. 3 (b) and (c) are images analyzed using energy-dispersive X-ray spectroscopy (EDS) for F and C elements.

[0028] Fig. 4 (a) is an image of the surface of the PCP separator side of the anode according to Example 1 analyzed by SEM, Fig. 4 (b) is a surface SEM image of the anode according to Comparative Example 1, and Fig. 4 (c) is a cross-sectional SEM image of the anode according to Example 1.

[0029] FIG. 5 is a graph showing the rate capability results of batteries including positive electrodes with a sulfur loading amount of 3 mg / cm2 according to Examples 1 to 3 and Comparative Example 1, evaluated at 0.1 C, 0.2 C, 0.3 C, 0.4 C, 0.5 C, 0.6 C, 0.7 C, 0.8 C, 0.9 C, and 1.0 C.

[0030] FIG. 6 (a) is a graph showing the results of galvanostatic cycling performance evaluated at 0.5 C for batteries including positive electrodes with a sulfur loading amount of 3 mg / cm2 according to Examples 1 to 3 and Comparative Example 1, and FIG. 6 (b) is a graph showing the results of galvanostatic cycling performance evaluated at 1.0 C for batteries according to Examples 1 to 2 and Comparative Example 1.

[0031] Figure 7 is a graph showing the results of 0.1 mV / s, 0.2 mV / s, 0.5 mV / s, 0.7 mV / s, and 1.0 mV / s cyclic voltammetry of a battery containing a cathode having a sulfur loading amount of 2.25 mg / cm2 and a sulfur ratio per electrolyte / anode electrolyte (E / S) of 10. (a) is a graph of the results of Comparative Example 1, (b) is a graph of the results of Example 1, (c) is a graph of the results of Example 2, and (d) is a graph of the results of Example 3.

[0032] Figure 8 is a graph showing the Tafel slope by analyzing the cyclic voltammetry results for the batteries of Examples 1, 2, and Comparative Example 1.

[0033] Figure 9 is a graph showing the results of galvanostatic cycling under 0.1 C and lean electrolyte conditions of a battery according to Example 1.

[0034] Figure 10 is a graph showing the results of evaluating the electrochemical characteristics of a stainless-steel symmetric cell (a) and a full cell (b) of Example 1 and Comparative Example 1 using electrochemical impedance spectroscopy.

[0035] Figure 11 is a graph showing the change in shuttle current over time (10,000 seconds) for the batteries of Example 1 and Comparative Example 1.

[0036] Hereinafter, an embodiment of the present invention will be described in detail. In this context, unless otherwise defined, the technical and scientific terms used herein have the meanings commonly understood by those of ordinary skill in the art to which this invention pertains. In the following description, descriptions of well-known functions and configurations that may unnecessarily obscure the gist of the present invention will be omitted.

[0037] As used herein, the singular forms may be intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0038] In addition, units used in this specification without special mention are based on weight, and for example, units of % or ratio mean weight% or weight ratio, and weight% means the weight% that any one component of the entire composition occupies in the composition unless otherwise defined.

[0039] Additionally, the numerical ranges used herein include lower and upper limits and all values ​​within that range, increments logically derived from the shape and width of the defined range, all doubly defined values, and all possible combinations of upper and lower limits of numerical ranges defined in different shapes. Unless otherwise specifically defined in the specification of the present invention, values ​​outside the numerical range that may arise due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0040] The term "includes" as described in the present invention is an open-ended description having an equivalent meaning to expressions such as "comprises," "contains," "has," or "characterizes," and does not exclude additional elements, materials, or processes not listed.

[0041] Hereinafter, the present invention will be described in detail.

[0042] The present invention provides a method for transferring a thin film using a Marangoni flow, comprising the steps of: (A) contacting a substrate on which a thin film has been formed with an organic solvent, and then laminating a polymer film in the presence of the organic solvent; and (B) immersing the substrate on which the polymer film has been laminated in water to transfer the thin film from the substrate to the polymer film.

[0043] According to one embodiment of the present invention, a step of forming a thin film by coating a thin film slurry composition on a substrate (a'') prior to step (A) may be further performed. The coating method may use any commonly used or known liquid coating technology without limitation. In addition, the coated thin film slurry composition may be dried at an appropriate temperature, such as room temperature or 50°C to 150°C.

[0044] According to one embodiment of the present invention, the substrate may be a material having a higher surface tension than the thin film and / or polymer film, and specifically, may be a glass substrate. In this case, there is an advantage in that the thin film can be peeled from the substrate in step (a') described below, and the wrinkle-free thin film can be easily transferred to the polymer film without damage to the thin film in step (B).

[0045] According to one embodiment of the present invention, the thin film slurry composition may include a solvent, an ionomer, a conductive material, and a conductive polymer.

[0046] According to another embodiment of the present invention, the thin film slurry composition may include a solvent, an ionomer, a conductive material, a conductive polymer, and an ionic liquid.

[0047] According to another embodiment of the present invention, the step (a'') may be to form a first thin film by coating and drying a first thin film slurry composition including a solvent, an ionomer, a conductive material, and a conductive polymer, and then to form a second thin film by coating and drying a second thin film slurry composition including a solvent and an ionic liquid. At this time, the first thin film may include an ionomer, a conductive material, and a conductive polymer, and the second thin film may include an ionomer, a conductive material, a conductive polymer, and an ionic liquid. When forming a thin film by dividing the steps as described above, there is an advantage in that a nano-scale thin film can be formed, thereby realizing excellent ionic conductivity.

[0048] The above solvent may be used without limitation as long as it is a solvent in which the above-described ionomer, conductive material, conductive polymer or / and ionic liquid can be easily dispersed, and non-limiting examples thereof include water (distilled water) or alcohol such as IPA, and may be a hydrophilic solvent, but are not limited thereto.

[0049] According to one embodiment of the present invention, the ionomer may include a fluorinated ionomer. Non-limiting examples of the fluorinated ionomer include a perfluorosulfonic acid (PFSA) polymer or a perfluorocarboxylic acid (PFCA) polymer. Nafion (Dupont) can be used as the perfluorosulfonic acid polymer, and Flemion (Asahi Glass) can be used as the perfluorocarboxylic acid polymer.

[0050] The weight average molecular weight of the ionomer may be 100 g / mol to 100,000 g / mol, 200 g / mol to 10,000 g / mol, or 500 g / mol to 5,000 g / mol.

[0051] The ionic equivalent weight (EW) of the ionomer may be 100 to 50,000, 200 to 20,000, or 500 to 2,000.

[0052] According to one embodiment of the present invention, the ionomer may be included in an amount of 1 to 50 parts by weight, 5 to 30 parts by weight, or 10 to 20 parts by weight based on 100 parts by weight of the conductive polymer. Alternatively, the ionomer may be included in an amount of 0.1 to 30% by weight, 1 to 20% by weight, or 5 to 10% by weight based on the total weight of the composition. When the above range is satisfied, better coating properties may be achieved.

[0053] According to one embodiment of the present invention, the conductive material may include a carbon-based conductive material. Non-limiting examples of the carbon-based conductive material include carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; carbon fibers; and carbon nanotubes (CNTs) such as MWCNTs and SWCNTs.

[0054] According to one embodiment of the present invention, the conductive material may be included in an amount of 0.01 to 10 parts by weight, 0.05 to 5 parts by weight, or 0.1 to 2 parts by weight, based on 100 parts by weight of the conductive polymer. When the above range is satisfied, better coating properties and battery characteristics may be achieved.

[0055] According to one embodiment of the present invention, the conductive polymer may include at least one selected from the group consisting of polyethylenedioxythiophene: polystyrenesulfonic acid, polyacetylene, polypyrrole, polythiophene, polyaniline, poly(3-hexylthiophene), poly(3,4-ethylenedioxythiophene), poly(3-tetradecylthiophene), poly(2-methoxy-5-(2'-methylhexyloxy)-1,4-phenylenevinylene), polyphenylene vinylene, polyphenylene, and poly(methoxyphenylene vinylene).

[0056] According to one embodiment of the present invention, the conductive polymer may be included in an amount of 1 to 20 parts by weight, 2 to 15 parts by weight, 3 to 10 parts by weight, or 4 to 8 parts by weight based on 1 part by weight of the ionomer. Alternatively, the conductive polymer may be included in an amount of 5 to 80% by weight, 10 to 65% by weight, or 35 to 50% by weight based on the total weight of the composition. When the above range is satisfied, better coating properties and battery characteristics may be achieved.

[0057] According to one embodiment of the present invention, the ionic liquid means a salt in which cations and anions are imperfectly coordinated, at least one of the ions is organic, and at least one of the ions has a delocalized charge.

[0058] The ionic liquid may include one or more cations selected from the group consisting of quaternary ammonium, imidazolium, pyrazolium, oxazolium, thiazolium, triazolium, pyridinium, piperidinium, pyridazinium, pyrimidinium, pyridinium, pyrrolidinium, phosphonium, trialkyl sulfonium, pyrrole, and guanidinium.

[0059] The above ionic liquid is Cl - , Br - , I - , HSO4 - , NO3-, SO4 2- , CF3SO3 - , N(SO2CF3) 2- , CH3SO3 - , B(CN)4 - , C4F9SO3 - , PF6 - , N(CN)4 - , C(CN)4 - , BF4 - , Ac - , SCN - , HSO4 - , CH3SO4 - , C2H5SO4 - and C4H9SO4 -It may include one or more anions selected from the group consisting of:

[0060] The ionic liquid may have a molecular weight of 50 to 5,000 g / mol, 100 to 2,000 g / mol, or 200 to 500 g / mol.

[0061] Non-limiting examples of the above ionic liquids include 1-ethyl-3-methylimidazolium tetrafluoroborate (Emim-BF4), 1-ethyl-3-methylimidazolium trifluoromethane sulfonate (Emim-TFSA), 3-methyl-N-butyl-pyridinium tetrafluoroborate, 3-methyl-N-butyl-pyridinium trifluoromethane sulfonate, N-butyl-pyridinium tetrafluoroborate, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-2,3-dimethylimidazolium trifluoromethane sulfonate, 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-ethylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-methyl-3-propylimidazolium chloride, 1-methyl-3-hexylimidazolium chloride, 1-methyl-3-octyl imidazolium chloride, 1-methyl-3-decyl imidazolium chloride, 1-methyl-3-dodecyl imidazolium chloride, 1-methyl-3-hexadecylimidazolium chloride, 1-methyl-3-octadecyl imidazolium chloride, 1-ethylpyridinium bromide, 1-ethylpyridinium chloride, 1-butyl pyridinium chloride and 1-benzylpyridinium bromide, 1-butyl-3-methylimidazolium iodide, 1-butyl-3-methylimidazolium nitrate, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, 1-ethyl-3-methylimidazolium nitrate, 1-butyl pyridinium bromide, 1-butyl pyridinium Examples thereof include iodide, 1-butyl pyridinium nitrate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium trifluoroacetate, and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (Bmim-Tf2N).

[0062] Specifically, the ionic liquid is 1-ethyl-3-methylimidazolium boron tetrafluoride (EMIM-BF4), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), 1-ethyl-3-methylimidazolium tetracyanoborate (EMIM-TCB), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-TFSI), 1-ethyl-3-methylimidazolium sulfate (EMIM-SO4), 1-butyl-3-methylimidazolium boron tetrafluoride (BMIM-BF4), 1-decyl-3-methylimidazolium boron tetrafluoride (DMIM-BF4), 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (DMIM-TFSI). It may include one or more selected from the group consisting of:

[0063] According to one embodiment of the present invention, the thin film may be for a lithium-sulfur battery, and specifically, may be an intermediate layer interposed between separators of a lithium-sulfur battery to suppress the shuttle effect.

[0064] According to one embodiment of the present invention, the thin film may have a thickness of 10 to 3000 nm, 20 to 1000 nm, 30 to 500 nm, or 50 to 300 nm. Within the above range, the shuttle effect of a lithium-sulfur battery can be more effectively suppressed, thereby exhibiting excellent battery performance and lifespan characteristics.

[0065] According to one embodiment of the present invention, before step (A), a step (a') of immersing the substrate in water to form a water layer at least partially between the thin film and the substrate may be further performed. Specifically, step (a') may be, after step (a''), immersing the substrate on which the thin film is formed in water to induce a Marangoni flow between the thin film and the substrate to form a water layer. In particular, when a glass substrate is used, since the surface tension of the substrate is greater than the surface tension of the thin film, water flows between the thin film and the substrate to form a water layer, thereby separating the substrate and the thin film.

[0066] According to one embodiment of the present invention, step (A) is a step of contacting an organic solvent on a substrate on which a thin film has been formed, completely wetting the thin film with the organic solvent, and laminating a polymer film in the presence of the organic solvent without drying. The contacting method may be a method of wetting the thin film on the substrate using, without limitation, a means such as a dropper, spray, spoon, hose, or roller.

[0067] According to one embodiment of the present invention, the organic solvent may have a lower surface tension than water. Specifically, the surface tension of the organic solvent at 20°C may be 50 mN / m or less, 1 to 50 mN / m, 5 to 40 mN / m, or 10 to 30 mN / m.

[0068] According to one embodiment of the present invention, the organic solvent is C 1-10 Alcohol, C 1-7 Alcohol or C 1-3 It may contain alcohol. It may contain at least one selected from the group consisting of, but not limited to, methanol, ethanol, propanol, and IPA.

[0069] According to one embodiment of the present invention, the thin film may include an ionomer, a conductive material, a conductive polymer, and an ionic liquid, and a related description is omitted as it is the same as described above.

[0070] According to one embodiment of the present invention, the polymer film may use any material used for a separator of an electrochemical device without limitation, and specifically may include a polyolefin-based polymer, and the polymer film may be a polyolefin-based polymer separator. In addition, the polyolefin-based polymer may include at least one selected from the group consisting of polyethylene, polypropylene, polybutylene, and polypentene.

[0071] According to one embodiment of the present invention, the polymer film may have a thickness of, but is not limited to, 5 to 1000 μm, 10 to 500 μm, or 10 to 200 μm.

[0072] Additionally, a step of pressing the substrate on which the polymer film is laminated under a certain pressure can be further performed.

[0073] In the above step (A), when the polymer film is laminated, the thin film may have a stronger interaction with the polymer film, which is more hydrophobic than the substrate, and accordingly, the thin film in the presence of the organic solvent may maintain a state closer to the polymer film than to the substrate.

[0074] According to one embodiment of the present invention, as shown in FIG. 1, when a substrate including a thin film on which a polymer film is laminated in the presence of an organic solvent is immersed in water in step (B), the organic solvent of the thin film soaked in the organic solvent (having a lower surface tension than water) diffuses into the water, thereby having the effect of spreading the thin film without wrinkles, and at the same time, the organic solvent between the substrate and the thin film induces a Marangoni flow, thereby completely separating the substrate and the thin film. In other words, step (B) may be a method of separating a wrinkle-free thin film on a substrate by using the Marangoni flow of the organic solvent, and transferring it from the substrate to the polymer film.

[0075] According to one embodiment of the present invention, the root mean square roughness (RMS) of the surface of the polymer film to which the thin film is transferred after step (B) may be lower than that of the polymer film, and specifically may be 5 nm or less, 1 to 5 nm, or 2 to 4.5 nm.

[0076] A method for transferring a thin film using a Marangoni flow according to one embodiment of the present invention can be performed at room temperature, and the temperature can be easily controlled considering the characteristics of the organic solvent or the working efficiency.

[0077] The following examples will further illustrate the method for transferring a thin film using Marangoni flow according to the present invention. However, the following examples are merely a reference for further illustrating the present invention and are not intended to limit the present invention, which may be implemented in various forms. Furthermore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention pertains. Furthermore, the terminology used herein is solely for the purpose of effectively describing specific embodiments and is not intended to limit the present invention.

[0078] [Physical property evaluation method]

[0079] 1. Average molecular weight (Mw, Mn) [g / mol] and polydispersity index (PDI)

[0080] Molecular weight was measured using GPC as a PS standard.

[0081] 2. Surface roughness

[0082] The root mean square (RMS) roughness was measured using an atomic force microscope (AFM) analysis device.

[0083] 3. Galvanostatic Cycling Test

[0084] It was measured by constant current charge / discharge measurements with a multi-channel battery cycler system (Automatic Battery Cycler, WonATech) in the voltage range of 1.7 V - 2.8 V and current density of 40 - 4000 mA / g.

[0085] 4. Cyclic voltammetry (CV)

[0086] Cyclic voltammetry (CV) experiments were performed using a battery cycler system (Automatic Battery Cycler, WonATech) in the potential range of 1.7 V - 2.8 V (vs. Li / Li+) at several scan rates (0.1 mV / s, 0.2 mV / s, 0.5 mV / s, 0.7 mV / s, 1.0 mV / s).

[0087] 5. Electrochemical Impedance Spectroscopy (EIS)

[0088] Electrochemical impedance spectroscopy (EIS) measurements were performed with a WonATech ZIVE MP2 instrument with an amplitude of superimposed alternating current (AC) signals of 0.01 V in the frequency range of 100 kHz - 100 mHz.

[0089] [Manufacturing Example 1] Thin film slurry composition and manufacturing of thin film

[0090] 0.5 wt% of MWCNT as a conductive material was added to PEDOT:PSS (Poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate)), a conductive polymer, and mixed by tip sonication. Then, the prepared MWCNT / PEDOT:PSS mixture was mixed with PFSA (Aquivion), an ionomer. ® D72) was mixed in a weight ratio of 6:1. Then, distilled water (DI water) and the prepared PFSA / MWCNT / PEDOT:PSS mixture were mixed in a weight ratio of 1:1 to prepare a thin film slurry composition. In addition, EMIM TCB (Solarpur ® ) 30 mg was dissolved in 1 ml of IPA to prepare an EMIM TCB solution.

[0091] Next, the thin film slurry composition was applied onto a glass substrate at 80°C using a solution shearing technique and dried at 120°C for 10 minutes, and then an EMIM TCB solution was applied at 50°C and dried to finally form a thin film of about 90 nm.

[0092] [Manufacturing Example 2]

[0093] The same procedure as Manufacturing Example 1 was followed, except that the coating thickness was adjusted to form a thin film of approximately 750 nm.

[0094] [Manufacturing Example 3]

[0095] The same procedure as Manufacturing Example 1 was followed, except that the coating thickness was adjusted to form a thin film of approximately 1300 nm.

[0096] [Example 1]

[0097] As shown in Fig. 1, the thin film on the glass substrate according to the above Manufacturing Example 1 was completely immersed in water, and then the water was removed and dried. Then, ethanol was dropped onto the thin film using a dropper to wet all surfaces of the thin film with ethanol. A commercially available polypropylene (PP) separator (thickness: 25 μm) was laminated on the ethanol-wetted thin film, and then pressure was applied. At this time, hydrophobic interaction was induced between the ethanol-wetted thin film and the polypropylene (PP) separator. Then, the glass substrate on which the polypropylene (PP) separator and the thin film were laminated was immersed in water again, and it was confirmed that the thin film was transferred from the glass substrate to the polypropylene (PP) separator.

[0098] Finally, a polypropylene (PP) separator (PCP) to which a thin film manufactured according to Example 1 was transferred was obtained. The sample size was 9.5 cm x 7.5 cm. The surface of the polypropylene (PP) separator before transfer and the surface of the thin film side of the polypropylene (PP) separator to which the thin film manufactured according to Example 1 was transferred were analyzed using a scanning electron microscope (SEM) and an atomic force microscope (AFM), and the image of the actually manufactured separator of Example 1 is shown in FIG. 2.

[0099] In addition, the cross-section of the polypropylene (PP) separator (PCP) to which the thin film manufactured according to Example 1 was transferred was analyzed by scanning electron microscopy (SEM) and EDS, and is shown in Fig. 3.

[0100] [Example 2]

[0101] The same procedure as Example 1 was followed, except that a thin film on a glass substrate according to Manufacturing Example 2, rather than Manufacturing Example 1, was used.

[0102] [Example 3]

[0103] The same procedure as Example 1 was followed, except that a thin film on a glass substrate according to Manufacturing Example 3, not Manufacturing Example 1, was used.

[0104] [Comparative Example 1]

[0105] An untreated polypropylene (PP) membrane was prepared.

[0106] [Evaluation Example] Battery Performance Evaluation

[0107] In order to apply the polypropylene (PP) separator (hereinafter, PCP separator) to which the thin film manufactured according to Comparative Example 1 and Examples 1 to 3 was transferred to a lithium-sulfur (Li-S) battery, a battery was manufactured according to the method described below.

[0108] -Cathode manufacturing: Li metal chip - Purchased from the manufacturer (MTI Korea)

[0109] - Manufacture of anode layer: A cathode containing CNT, conductive material (Super P), and S was manufactured using a melt diffusion procedure. The manufactured CNT / S powder: Super P: LA132 binder was mixed in a weight ratio of 7:2:1, and then coated on an Al foil (current collector) using a bar coating process and dried to manufacture a cathode layer.

[0110] The PCP separator and the positive and negative electrodes were assembled to manufacture a battery, and specifically, the bottom cap, Li metal (negative electrode), gasket, the PCP separator of Comparative Example 1 and Examples 1 to 3 (so that the thin-film coated portion is in contact with the positive electrode), electrolyte injection, positive electrode layer, spacer, battery spring, and top cap were sequentially assembled, and then sealed using a coin cell battery manual sealer hydraulic cell pressing machine to manufacture a battery (full cell) according to one embodiment. In addition, a symmetric cell was manufactured using only stainless steel (SS) for both the positive and negative electrodes using the same method. The manufactured battery was evaluated for battery performance according to the above-described method. At this time, the battery manufactured using the PCP separator of Example 1 was indicated as PCP 90 nm, Example 2 as PCP 750 nm, Example 3 as PCP 1300 nm, and Comparative Example 1 as ref.

[0111] In Fig. 4 (a), an image of the surface of the PCP separator side of the anode according to Example 1 is shown by SEM analysis, and in Fig. 4 (c), an image of the surface of the anode according to Comparative Example 1 (ref) is shown by SEM analysis.

[0112] Figure 5 shows a graph showing the results of a rate capability test in which a full cell including a positive electrode with a sulfur loading of 3 mg / cm2 was evaluated at 0.1 C, 0.2 C, 0.3 C, 0.4 C, 0.5 C, 0.6 C, 0.7 C, 0.8 C, 0.9 C, and 1.0 C.

[0113] Figure 6 shows a graph showing the results of galvanostatic cycling of a full cell containing a positive electrode with a sulfur loading of 3 mg / cm2 at 0.5 C (a) and 1.0 C (b).

[0114] In addition, the results of 0.1 mV / s, 0.2 mV / s, 0.5 mV / s, 0.7 mV / s, and 1.0 mV / s cyclic voltammetry of a full cell containing a cathode having a sulfur loading amount of 2.25 mg / cm2 and a sulfur ratio per electrolyte / anode electrolyte (E / S) of 10 are shown in Fig. 7, and the overpotential values ​​are indicated. Comparative Example 1 confirmed an overpotential of 0.696 V, Example 1 confirmed an overpotential of 0.518 V, and Example 2 confirmed an overpotential of 0.675 V, and through this, it was confirmed that the cell of Example 1 showed a lower overpotential than Comparative Example 1, thereby showing significantly superior reaction kinetics.

[0115] In addition, the cyclic voltammetry results of the full cell were analyzed to obtain the Tafel slope, which is shown in Fig. 8. As seen in Fig. 8, Comparative Example 1 had a slope of 180.3 mV / dec. -1 , Example 1 is 131.4 mV / dec -1 and Example 2 is 175.5 mV / dec -1 The Tafel slope was measured. Through this, it was confirmed that Example 1 exhibited significantly superior battery performance as it exhibited a lower Tafel slope and overvoltage than Comparative Example 1.

[0116] The battery performance of a full cell including the PCP separator of Example 1, which showed the best effect, was evaluated under harsh conditions. A lithium-sulfur battery was manufactured including a cathode having a sulfur loading amount of 4.34 mg / cm2 and a low sulfur ratio per electrolyte / anode electrolyte (E / S) of 4.5, and the results of galvanostatic cycling at 0.1 C are shown in Fig. 9.

[0117] In addition, the symmetric cell (a) and full cell (b) of Example 1 and Comparative Example 1 were evaluated for their electrochemical characteristics by electrochemical impedance spectroscopy, and the resulting graph is shown in Fig. 10, and the σ (ionic conductivity), Rs (initial resistance), and R of each cell are shown in Table 1 below. ct (Charge Transfer Resistance) was recorded.

[0118] In addition, in order to confirm the shuttle effect suppression performance for the full cell of Example 1 and Comparative Example 1, the change in shuttle current according to time (10,000 seconds) was observed and shown in Fig. 11, and the shuttle current after 10,000 seconds was recorded in Table 1 below.

[0119] At this time, coin cells (Li radius (r) = 0.8 cm) were manufactured by injecting electrolyte from which LiNO3 was removed to measure the shuttle current, and were evaluated under the following measurement conditions using a battery cycler. In addition, the average value of the y-axis value (current per unit area (mA / ㎠)) in the obtained graph was obtained and recorded in Table 1 below.

[0120] - Measurement conditions: Precycling for 3 cycles at a 0.1 C rate, discharging to 2.38 V, and then holding the voltage for 15000 s to stabilize the current. The shuttle current was then measured at 2.38 V.

[0121] Symmetric cell Full cell Shuttle current R s [Ω]σ[mS / cm]R ct [Ω][mA / ㎠]Example 1 (PCP 90㎚)2.947.5519.20.025Comparative Example 1 (ref)8.792.5266.70.073

[0122] As shown in Table 1 above, the battery of Example 1 exhibited significantly higher ionic conductivity and lower charge transfer resistance than Comparative Example 1, and furthermore, it was confirmed that the shuttle current also showed a very low value. The battery including the separator of Example 1 effectively suppressed the shuttle effect even under conditions of high sulfur loading and lean electrolyte, and exhibited excellent ionic conductivity and improved lifespan characteristics even at high C-rate, thereby demonstrating excellent battery performance. Through this, it was confirmed that the thin film according to one embodiment was transferred to the separator over a large area without defects to sufficiently suppress the shuttle effect of a lithium-sulfur battery, and thus a lithium-sulfur battery including the same could implement excellent lifespan characteristics and battery performance.

[0123] As described above, the present invention has been described through specific matters and limited examples and comparative examples, but these are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and those skilled in the art to which the present invention pertains can make various modifications and variations based on this description.

[0124] Therefore, the idea of ​​the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the claims described below as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

Claims

1. (A) A step of contacting an organic solvent on a substrate on which a thin film has been formed, and then laminating a polymer film in the presence of the organic solvent; and (B) A method for transferring a thin film using Marangoni flow, comprising the step of immersing a substrate on which the polymer film is laminated in water to transfer the thin film from the substrate to the polymer film.

2. In paragraph 1, The above organic solvent is a thin film transfer method using Marangoni flow, which has a lower surface tension than water.

3. In paragraph 1, A method for transferring a thin film using Marangoni flow, wherein the surface tension of the organic solvent at 20°C is 50 mN / m or less.

4. In paragraph 1, The above organic solvent is C 1-7 A method for transferring a thin film using a Marangoni flow containing alcohol.

5. In paragraph 1, The above substrate is a thin film transfer method using Marangoni flow on a glass substrate.

6. In paragraph 1, A method for transferring a thin film using a Marangoni flow, further comprising the step of immersing the substrate in water (a') before the above step (A) to form a water layer at least partially between the thin film and the substrate.

7. In paragraph 1, A method for transferring a thin film using a Marangoni flow, further comprising: a step of forming a thin film by coating a thin film slurry composition on a substrate (a'') prior to the above step (A); 8. In paragraph 1, The above thin film is a method for transferring a thin film using a Marangoni flow including an ionomer, a conductive material, a conductive polymer, and an ionic liquid.

9. In paragraph 8, The above ionomer is a method for transferring a thin film using a Marangoni flow including a fluorine-based ionomer.

10. In paragraph 8, The above conductive material is a method for transferring a thin film using a Marangoni flow including a carbon-based conductive material.

11. In paragraph 8, A method for transferring a thin film using a Marangoni flow, wherein the conductive polymer comprises at least one selected from the group consisting of polyethylenedioxythiophene: polystyrenesulfonic acid, polyacetylene, polypyrrole, polythiophene, polyaniline, poly(3-hexylthiophene), poly(3,4-ethylenedioxythiophene), poly(3-tetradecylthiophene), poly(2-methoxy-5-(2'-methylhexyloxy)-1,4-phenylenevinylene), polyphenylene vinylene, polyphenylene, and poly(methoxyphenylene vinylene).

12. In paragraph 1, The above ionic liquids are 1-ethyl-3-methylimidazolium boron tetrafluoride (EMIM-BF4), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), 1-ethyl-3-methylimidazolium tetracyanoborate (EMIM-TCB), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-TFSI), 1-ethyl-3-methylimidazolium sulfate (EMIM-SO4), 1-butyl-3-methylimidazolium boron tetrafluoride (BMIM-BF4), 1-decyl-3-methylimidazolium boron tetrafluoride (DMIM-BF4), 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (DMIM-TFSI). A method for transferring a thin film using a Marangoni flow comprising at least one selected from the group consisting of:

13. In paragraph 1, The above thin film is a thin film transfer method using Marangoni flow having a thickness of 10 to 3000 nm.

14. In paragraph 1, The above polymer film is a thin film transfer method using Marangoni flow including a polyolefin polymer.

15. In paragraph 1, The above polymer film is a thin film transfer method using Marangoni flow with a thickness of 10 to 500㎛.

16. In paragraph 1, A method for transferring a thin film using Marangoni flow, wherein the root mean square roughness (RMS) of the surface of the polymer film to which the thin film is transferred after the above step (B) is 5 nm or less.

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