KR102309681B1 - Separator for lithium-sulfur battery and method for manufacturing same - Google Patents

Abstract

A separator for a lithium-sulfur battery comprising a porous membrane, wherein at least a portion of the porous membrane is coated with polyimide, a separator for a lithium-sulfur battery is disclosed.
The separator for a lithium-sulfur battery provided in one aspect of the present invention has the effect of improving the life and capacity of the battery by controlling the shuttling phenomenon in the lithium-sulfur battery.

Description

Separator for lithium-sulfur battery and method for manufacturing same

The present invention relates to a lithium-sulfur separator and a method for manufacturing the same.

As interest in energy storage technology increases, the field of application expands to the energy of mobile phones, tablets, laptops and camcorders, and even electric vehicles (EVs) and hybrid electric vehicles (HEVs), Research and development of chemical devices is gradually increasing. Electrochemical devices are the field receiving the most attention in this aspect, and among them, the development of secondary batteries such as lithium-sulfur batteries capable of charging/discharging is the focus of interest, and recently, capacity density in developing such batteries And in order to improve the specific energy, it leads to R&D for the design of new electrodes and batteries.

Such an electrochemical device, among them, a lithium-sulfur (Li-S) battery, has a high energy density and is spotlighted as a next-generation secondary battery that can replace a lithium-ion battery. In such a lithium-sulfur battery, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur during discharge. At this time, sulfur is converted from a ring structure S8 to a linear structure lithium polysulfide (Li ₂ S ₂ , Li ₂ S ₄ , Li _{2 ).} S ₆ , Li ₂ S ₈ ) is formed, and this lithium-sulfur battery is characterized by exhibiting a step-by-step discharge voltage until _{polysulfide (PS) is completely reduced to Li 2 S.}

However, the lithium-sulfur battery has a large problem in that capacity is reduced due to polysulfide (PS) shuttling on the positive electrode side. That is, the long-chain polysulfide (Li ₂ S ₆ , Li ₂ S ₈ ) has high solubility in the organic electrolyte, so unwanted movement (PS shuttling) may occur through the electrolyte toward the negative electrode. A decrease in capacity due to irreversible loss of the positive electrode active material and a decrease in battery life due to deposition of sulfur particles on the lithium surface occur. In order to solve this problem, various studies such as adding a PS adsorption material to the positive electrode composite or modifying an existing separator made of PE or the like have been conducted recently, but a clear solution is not presented.

It is an object of the present invention to provide a separator for a lithium-sulfur battery capable of controlling a shuttling phenomenon in a lithium-sulfur battery.

In order to achieve the above object, in one aspect of the present invention

A separator for lithium-sulfur batteries comprising a porous membrane,

At least a portion of the porous membrane is provided with a lithium-sulfur battery separator, characterized in that coated with polyimide.

In addition, in another aspect of the present invention

contacting at least a portion of the porous membrane with a polyimide precursor solution;

A lithium-sulfur battery separator manufacturing method comprising a.

In addition, in another aspect of the present invention

anode;

cathode; and

a separator positioned between the anode and the cathode;

A lithium-sulfur battery comprising:

The separator is provided with a lithium-sulfur battery including a porous membrane at least a part of which is coated with polyimide.

Furthermore, in another aspect of the present invention

preparing a separation membrane by contacting at least a portion of the porous membrane with a polyimide precursor solution;

A lithium-sulfur battery manufacturing method comprising a.

The separator for a lithium-sulfur battery provided in one aspect of the present invention has the effect of improving the life and capacity of the battery by controlling the shuttling phenomenon in the lithium-sulfur battery.

1a and 1b show a surface SEM image of a glass fiber used in an embodiment of the present invention,
Figure 1c shows a surface SEM image of polypropylene used in an experimental example of the present invention,
Figure 1d shows a photograph according to the change in the polyimide content in the glass fiber according to an experimental example of the present invention,
Figure 1e shows a schematic diagram, a manufacturing process, and a molecular structure of a polyimide-coated glass fiber manufactured according to an embodiment of the present invention;
1f to 1l show SEM images of glass fibers according to the polyimide content according to an experimental example of the present invention. FIGS. 1f and 1g are the surface and cross-section of PI-GF-0.5, and FIG. 1h is an NMP solvent. The surface of PI-GF-3 coated using
1m shows the FT-IR spectra of glass fiber and PI-GF-0.5 according to an experimental example of the present invention;
Figure 1n shows the results of TGA analysis of glass fibers and PI-GF-0.5 according to an experimental example of the present invention;
_{Figure 2 shows the absorption test results of polyimide powder in Li 2} S ₆ solution according to an experimental example of the present invention, Figure 2a is a photographic image of the supernatant at the initial mixing, Figure 2b is the supernatant after 10 hours of mixing A photographic image, Figure 2c shows the UV-vis spectra of the supernatant, Figure 2d shows self-discharge at an open circuit voltage, and Figure 2e shows the potential decreasing rate corresponding thereto,
Figure 3a is a graph comparing the electrochemical performance according to the type of separator at ^{2 mgS/cm 2} and 0.3 C according to an experimental example of the present invention;
3b to 3d show the charge/discharge profile according to the type of separator, according to an experimental example of the present invention, FIG. 3b is polypropylene, FIG. 3c is glass fiber, FIG. 3d is PI-GF-0.3, FIG. 3e is PI-GF-0.5, Figure 3f is shown for PI-GF-1.0,
Figure 4 shows lithium stripping / plating performance according to the type of separator according to an experimental example of the present invention, Figure 4a is cycle stability for 1700 hours (500 cycles) at a constant current density of 0.35 mA, Figure 4b is 0.35 mA / cm2 speed characteristic for a current density of from up to 2.8 mA / cm ^2, Fig. 4c is a second glass fiber, and the speed characteristics of the PI-GF-0.5 in mgS / cm ^2, Figure 4d is a PI-GF- corresponding thereto It shows a charge/discharge profile of 0.5,
5a shows an EIS Nyquist plot in an Al/separator-electrolyte/Al symmetric cell according to an experimental example of the present invention;
Figure 5b shows the ionic conductivity according to the presence or absence of a _{1 M Li 2} S ₆ solution with respect to the polyimide content, according to an experimental example of the present invention;
Figure 5c shows an EIS Nyquist plot of a lithium-sulfur battery comprising a glass fiber, PI-GF-0.5, and PI-GF-1.0 separator according to an experimental example of the present invention;
6a to 6c show a photographic image of a separator after cycling, according to an experimental example of the present invention, FIG. 6a is glass fiber, FIG. 6b is PI-GF-0.5, FIG. will,
6d to 6f are SEM images of the separation membrane after cycling, according to an experimental example of the present invention. FIG. 6d is glass fiber, FIG. 6e is PI-GF-0.5, and FIG. will,
Figure 6g shows the TGA analysis results before and after cycling of PI-GF-0.5 according to an experimental example of the present invention;
6h to 6j show EDS mapping of the separator according to an experimental example of the present invention, FIG. 6h shows glass fiber, FIG. 6i shows PI-GF-0.5, and FIG. 6j shows PI-GF-1.0,
6k to 6m show the results of EDS mapping analysis of the separator according to an experimental example of the present invention, FIG. 6k is glass fiber, FIG. 6l is PI-GF-0.5, and FIG. will,
Figure 6n shows the EDS elemental analysis result of the separation membrane according to an experimental example of the present invention.
7 shows an image of coating glass fibers using an aqueous polyamic acid solution according to an embodiment of the present invention;
8 shows an image of coating glass fibers using an organic polyamic acid solution according to a comparative example of the present invention;
9 shows an image of coating glass fibers treated with oxygen plasma using an organic polyamic acid solution according to another embodiment of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is those well known and commonly used in the art.

In one aspect of the invention

A separator for lithium-sulfur batteries comprising a porous membrane,

At least a portion of the porous membrane is provided with a lithium-sulfur battery separator, characterized in that coated with polyimide.

Hereinafter, the separator for a lithium-sulfur battery provided in one aspect and another aspect of the present invention will be described in detail for each configuration.

First, the lithium-sulfur battery separator includes a porous membrane.

The porous membrane may be at least one selected from the group consisting of a polyolefin-based porous membrane, a ceramic-based porous membrane, and an organic compound-based porous membrane.

For example, the polyolefin-based porous membrane may be a porous membrane such as polypropylene or polyethylene.

For example, the ceramic-based porous membrane may be a porous membrane using glass fiber, montmorillonite (MMT), or the like.

For example, organic compound-based porous membranes include cellulose, Nafion, polyvinylidene fluoride (PVDF), Poly(phthalazinone ether sulfone ketone) (PPESK), polyaryletherketone (PAEK), polylactic acid ( It may be a porous membrane using poly(lactic acid), PLA), or the like.

In one embodiment, the porous membrane may be a porous membrane including glass fibers. In the case of a porous membrane including glass fibers, there is an advantage that the shape and pore formation are easy, and there is also an advantage that the temperature stability is excellent at 550 °C.

Therefore, it may be preferable to select a glass fiber as a porous membrane for the construction of a battery having high temperature stability. In addition, since the surface of the glass fiber porous membrane has polarity, it may be preferable to use the glass fiber porous membrane in that a certain level of polysulfide adsorption is possible by itself.

At least a portion of the glass fibers may be coated with polyimide, and at least a portion of one surface of the porous membrane including the glass fibers may be coated with polyimide.

The polyimide may be included in 0.5 wt% to 15 wt% in the separator. Preferably 1 wt% to 8 wt% may be included, more preferably 1.5 wt% to 6 wt% may be included, and even more preferably 2 wt% to 5 wt% may be included.

When polyimide is contained in less than 0.5 wt% in the separator, there is a problem that the shuttling effect may not be sufficiently controlled. There is a problem that performance degradation may occur.

In another aspect of the present invention

contacting at least a portion of the porous membrane with a polyimide precursor solution;

A lithium-sulfur battery separator manufacturing method comprising a.

Hereinafter, a method for manufacturing a separator for a lithium-sulfur battery provided in another aspect of the present invention will be described in detail.

First, the method for manufacturing a separator for a lithium-sulfur battery provided in another aspect of the present invention includes contacting at least a portion of a porous membrane with a polyimide precursor solution.

The polyimide precursor solution may be an aqueous polyamic acid solution.

The concentration of the polyamic acid in the aqueous polyamic acid solution may be 0.1 wt% to 5.0 wt%. Preferably it may be 0.1 wt% to 1.5 wt%, more preferably 0.2 wt% to 1.2 wt%, and more preferably 0.4 wt% to 0.8 wt%.

By controlling the concentration of the polyamic acid, the amount of polyimide to be finally coated on the porous membrane can be adjusted. Therefore, when the concentration of the polyamic acid is less than 0.1 wt%, there is a problem that the polyimide is coated with a small amount and the shuttling effect may not be sufficiently controlled. If the concentration of the polyamic acid exceeds 5.0 wt%, the viscosity becomes too high There is a problem in that the coating is limited because the porous membrane is not well impregnated, that is, the porous membrane is not well wetted.

The polyamic acid aqueous solution may further include a water-soluble agent.

The water-soluble agent may be an amine-based water-soluble agent or an imidazole-based water-soluble agent.

The amine-based water-soluble agent includes, but is not limited to, 2-Dimethylaminoethanol (DMEA), N,N-Diethylethanolamine (DEEA), 3-Dimethylaminopropanol, Diethanolamine (DEA), 3-Diethylamino-1-propanol, N-Methyldiethanolamine (MDEA) , Triethanol amine (TEOA), Diethanolisopropylamine, Diethanolisopropanolamine (DEIPA), N,N-Dimethylisopropanolamine, 1-[Ethyl(2-hydroxyethyl)amino)]-2-propanol, Triisopropanolamine, N-(2-hydroxyethyl)-N-( 2-hydroxypropyl)methylamine, 3-[2-hydroxyethyl(methyl)amino]propane-1,2-diol, 3-[ethyl(2-hydroxyethyl)amino]propane-1,2-diol, 2-(Diethylamino)propanol , 1- [methyl (propyl) amino] propan-2-ol, N,N-Diethyl-2-hydroxypropylamine, 1- (ethylmethylamino) -2-propanol, 2- (Dimethylamino) -2-methyl-1-propanol ( DMAMP-80), 3-Dimethylamino-1-propanol, 4-Dimethylamino-1-butanol, 1-(dimethylamino)-2-methyl-2-propanol, 1-(Dipropylamino)-2-propanol, 2-(Butylmethylamino) ethanol, 2-(Dipropylamino)ethanol, 2-[Methyl(2-methylpropyl)amino]ethanol, 2-[sec-Butyl(methyl)amino]ethanol, 2-(Isopropylpropylamino)Ethanol, 1-[(2-Hydroxyethy) l)propylamino]-2-propanol, 1-[Butyl(methyl)amino]propan-2-ol, N-Propyl Diethanolamine, Ethylamine, Diethylamine, Propylamine, Dipropylamine, Butylamine, Pentylamine, Hexylamine, Cyclohexylamine, N-ethyl-N -methyl-2-propanamine, Diethylisopropylamine, N,N-diisopropylamine (DIPA), N-ethyl-N-methyl-1,2-ethanediamine, N,N-dimethylhexylamine, or N,N-dimethylethylamine.

The imidazole-based water-soluble agent includes, but is not limited to, 1,2-Dimethylimidazole, Imidazole, 2-methylimidazole, 1-Methylimidazole, 2-Ethylimidazole, 4(5)-Methylimidazole, 2-Ethyl-4-methylimidazole, 2,2′ midazole), Benzimidazole, 1-Benzyl-2-methylimidazole, 2-Methyl-1-pyrroline, Pyrazole, 2-ethyl-4-ethyl imidazole, 2-methyl-4-ethyl imidazole, 1-methyl-4-ethyl imidazole, 1-methylpyrrolidine, 5-methylbenzimidazole, Isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, 4-n-propylpyridine, or 2-Ethyl-4-methy-1H -limidazole-1-propanenitrile.

In an embodiment of the present invention, the polyamic acid aqueous solution comprises: polymerizing the polyamic acid in an organic solvent; preparing polyamic acid particles; and mixing the polyamic acid particles and the water-soluble agent with water.

The polyamic acid may be formed by polymerizing a diamine monomer and a dianhydride monomer.

The diamine monomer may be, but is not limited to, ODA, mTB, pPDA, mPDA, or a mixture thereof.

The dianhydride monomer may be, but is not limited to, PMDA, BPDA, BTDA, ODPA, or a mixture thereof.

The organic solvent may be a polar aprotic solvent, and may be, for example, NMP, DMF and DMAc.

Through this, a polyamic acid varnish may be formed.

The preparing of the polyamic acid particles may include precipitating the polymerized polyamic acid in an organic solvent and drying the same.

In the step of precipitating the polyamic acid, any solvent having poor solubility with the polyamic acid may be used as the precipitating agent. For example, it may be a protic solvent or an aprotic solvent. The protic solvent may include, but is not limited to, water, methanol, ethanol, isopropyl alcohol, or mixtures thereof, and the aprotic solvent includes, but is not limited to, acetone, TMF, methyl ethyl keton (MEK), acetonitrile (MeCN) or a mixture thereof.

The drying step may be performed at a vacuum temperature of 20°C to 60°C for 6 hours or more.

Thereafter, an aqueous polyamic acid solution can be obtained by mixing the polyamic acid particles and a water-soluble agent with water.

Polyamic acid is generally well soluble in organic solvents and has limited solubility in water, but in the above step, solubility in water can be improved by forming a polyamic acid salt with a water-soluble agent in the polyamic acid. As such, when the polyimide is coated using the aqueous polyamic acid solution, the polyimide may be coated more uniformly than when the organic solvent is used, and aggregation may occur when the polyimide is coated with the organic solvent.

In addition, the polyimide precursor solution may be an organic solution of polyamic acid.

The polyamic acid organic solution may be in a form in which polyamic acid is dissolved in an organic solvent such as NMP, DMF, DMAc, THF, and Toluene.

When the polyamic acid organic solution is used, the porous membrane may be surface-treated.

Various surface treatment methods may be used without limitation, and for example, may be surface-treated with plasma, and more specifically, may be surface-treated with oxygen plasma.

When the porous membrane is surface-treated in this way, even if it is coated using an organic solvent, aggregation does not occur and uniform coating may be possible.

The contacting in the step of contacting at least a portion of the porous membrane with the polyimide precursor solution may be performed by various methods such as, for example, dipping, spraying, rolling, meyer bar coating, blade coating, etc. However, it is not limited to a specific method.

In addition, the method for manufacturing a separator for a lithium-sulfur battery provided in another aspect of the present invention may further include heat-treating the porous membrane in contact with the polyimide precursor solution.

The heat treatment may be performed at 200 °C to 500 °C, preferably at 250 °C to 450 °C, more preferably at 300 °C to 400 °C.

The heat treatment may be performed in a convection oven or a vacuum oven, and may be performed while slowly increasing the temperature.

The heat treatment may be performed for 10 minutes to 300 minutes, preferably 50 minutes to 250 minutes, more preferably 100 minutes to 200 minutes.

By thermally imidizing the polyimide precursor on the porous membrane through the heat treatment, polyimide may be formed in at least a portion of the porous membrane.

The lithium-sulfur battery separator manufacturing method has the advantage that it can be manufactured by a very simple method since it can be prepared only by contacting the porous membrane with a polyimide precursor solution.

In another aspect of the present invention

anode;

cathode; and

a separator positioned between the anode and the cathode;

A lithium-sulfur battery comprising:

The separator is provided with a lithium-sulfur battery including a porous membrane at least a part of which is coated with polyimide.

Hereinafter, a lithium-sulfur battery provided in another aspect of the present invention will be described in detail for each configuration.

First, the lithium-sulfur battery provided in another aspect of the present invention includes a positive electrode.

In one embodiment, the positive electrode layer is prepared by preparing a positive electrode composition including a positive electrode active material, a conductive material, and a binder, and then directly coating and drying a slurry prepared by diluting it in a predetermined solvent (dispersion medium) on the positive electrode current collector and drying the positive electrode composition. can form. Alternatively, after casting the slurry on a separate support, a film obtained by peeling from the support may be laminated on a positive electrode current collector to prepare a positive electrode layer. In addition, the positive electrode may be manufactured in various ways using methods well known to those skilled in the art.

The conducting material serves as a path through which electrons move from the positive electrode current collector to the positive electrode active material, and not only provides electronic conductivity, but also electrically connects the electrolyte and the positive electrode active material to lithium ions (Li ⁺ ) in the electrolyte. It serves as a pathway to move to and react with this sulfur at the same time. Therefore, if the amount of the conductive material is not sufficient or does not perform its role properly, the non-reactive portion of the sulfur in the electrode increases, which eventually leads to a decrease in capacity. In addition, since it adversely affects the high-rate discharge characteristics and the charge/discharge cycle life, it is necessary to add an appropriate conductive material. The content of the conductive material is preferably added appropriately within the range of 001 to 30% by weight based on the total weight of the positive electrode composition.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, graphite; carbon black such as Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black and Summer Black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used. Specific examples of commercially available conductive materials include acetylene black-based Chevron Chemical Company or Denka Singapore Private Limited, Gulf Oil Company products, Ketjenblack, EC-based Armac Company (Armak Company) product, Vulcan XC-72 Cabot Company (Cabot Company) product, Super-P (Product of Timcal Corporation), etc. can be used.

The binder is for well adhering the positive electrode active material to the current collector, it must be well soluble in a solvent, and must not only form a conductive network between the positive electrode active material and the conductive material, but also have adequate impregnation property of the electrolyte. The binder may be any binder known in the art, and specifically, a fluororesin-based binder including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); a rubber-based binder including a styrene-butadiene rubber, an acrylonitrile-butydiene rubber, and a styrene-isoprene rubber; Cellulose binders including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders; Polyolefin-based binders including polyethylene and polypropylene; Polyimide-based binders, polyester-based binders, silane-based binders; may be a mixture or copolymer of one or more selected from the group consisting of, but is not limited thereto.

The content of the binder may be 0.5 to 30% by weight based on the total weight of the positive electrode composition, but is not limited thereto. If the content of the binder resin is less than 0.5% by weight, the physical properties of the positive electrode may be lowered, and the positive electrode active material and the conductive material may fall off, and if it exceeds 30% by weight, the ratio of the active material and the conductive material in the positive electrode is relatively reduced The battery capacity may be reduced, and the efficiency may be lowered by acting as a resistive element.

Next, a slurry obtained by diluting a positive electrode composition including a positive electrode active material, a conductive material, and a binder in a solvent is applied on the positive electrode current collector. The positive electrode composition including the above-described positive electrode active material, conductive material, and binder may be mixed with a predetermined solvent to prepare a slurry. In this case, the solvent should be easy to dry and can dissolve the binder well, but it is most preferable that the positive active material and the conductive material can be maintained in a dispersed state without dissolving. When the solvent dissolves the positive electrode active material, the sulfur in the slurry has a high specific gravity (D = 2.07), so sulfur sinks in the slurry, causing sulfur to collect on the current collector during coating, causing problems in the conductive network, leading to problems in battery operation. There is this. The solvent (dispersion medium) may be water or an organic solvent, and the organic solvent may be at least one selected from the group consisting of dimethylformamide, isopropyl alcohol or acetonitrile, methanol, ethanol, and tetrahydrofuran.

Subsequently, there is no particular limitation on a method of applying the positive electrode composition in the slurry state, for example, doctor blade coating, dip coating, gravure coating, slit die coating. coating), spin coating, comma coating, bar coating, reverse roll coating, screen coating, cap coating, etc. can be manufactured. The positive electrode composition that has been subjected to such a coating process is then dried through evaporation of the solvent (dispersion medium), the density of the coating film, and the adhesion between the coating film and the current collector. At this time, the drying is carried out according to a conventional method, it is not particularly limited.

Next, a lithium-sulfur battery provided in another aspect of the present invention includes a negative electrode.

As the negative electrode, any material capable of occluding and releasing lithium ions may be used, and for example, a metal material such as lithium metal or a lithium alloy, and a carbon material such as low crystalline carbon or high crystalline carbon may be exemplified. Soft carbon and hard carbon are representative of low crystalline carbon, and natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch-based carbon fiber as high crystalline carbon. (Mesophase pitch based carbon fiber), carbon microspheres (Meso-carbon microbeads), liquid crystal pitches (Mesophase pitches), and high-temperature calcined carbon such as petroleum and coal tar pitch derived cokes (Petroleum or coal tar pitch derived cokes) are representative. In addition, alloys containing silicon or _{oxides such as Li 4} Ti ₅ O ₁₂ are well-known cathodes.

In this case, the negative electrode may include a binder, and the binder includes polyvinylidenefluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), and polyacrylonitrile. (Polyacrylonitrile), polymethylmethacrylate, styrene-butadiene rubber (SBR), etc., various types of binder polymers may be used.

The negative electrode may optionally further include a negative electrode current collector for supporting the negative electrode active layer including the negative electrode active material and the binder. The negative electrode current collector may be specifically selected from the group consisting of copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium or silver, and an aluminum-cadmium alloy may be used as the alloy. In addition, calcined carbon, a non-conductive polymer surface-treated with a conductive agent, or a conductive polymer may be used.

The binder serves as a paste of the negative active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, and a buffering effect against expansion and contraction of the active material. Specifically, the binder is the same as described above for the binder of the positive electrode. In addition, the negative electrode may be a lithium metal or a lithium alloy. As a non-limiting example, the negative electrode may be a thin film of lithium metal, and lithium and one selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al and Sn. It may be an alloy with the above metals.

Next, the lithium-sulfur battery provided in another aspect of the present invention includes a separator between the positive electrode and the negative electrode.

The separation membrane may be a porous membrane at least partially coated with polyimide.

The porous membrane may be at least one selected from the group consisting of a polyolefin-based porous membrane, a ceramic-based porous membrane, and an organic compound-based porous membrane.

For example, the polyolefin-based porous membrane may be a porous membrane such as polypropylene or polyethylene.

For example, the ceramic-based porous membrane may be a porous membrane using glass fiber, montmorillonite (MMT), or the like.

For example, organic compound-based porous membranes include cellulose, Nafion, polyvinylidene fluoride (PVDF), Poly(phthalazinone ether sulfone ketone) (PPESK), polyaryletherketone (PAEK), polylactic acid ( It may be a porous membrane using poly(lactic acid), PLA).

In one embodiment, the porous membrane may be a porous membrane including glass fibers. The porous membrane may be a separator for a lithium-sulfur battery, characterized in that at least a portion of the glass fiber is coated with polyimide, or a separator for a lithium-sulfur battery, characterized in that at least a portion of the porous membrane is coated with polyimide have.

The polyimide may be included in 0.5 wt% to 15 wt% in the separator. Preferably 1 wt% to 8 wt% may be included, more preferably 1.5 wt% to 6 wt% may be included, and more preferably 2 wt% to 5 wt% may be included.

When polyimide is contained in less than 0.5 wt% in the separator, there is a problem that the shuttling effect may not be sufficiently controlled. There is a problem that performance degradation may occur.

In addition, the lithium-sulfur battery provided in another aspect of the present invention may further include an electrolyte between the positive electrode and the negative electrode.

The electrolyte includes a solvent and a lithium salt, and may further include additives, if necessary. As the solvent, a conventional non-aqueous solvent serving as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Examples of the non-aqueous solvent include carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, and aprotic solvents.

More specific examples, as the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) ), ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC), and the ester solvent is methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl There are propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone and caprolactone, and the ether-based solvent is di ethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, diglyme, triglyme, tetraglyme, tetrahydrofuran, 2-methyltetrahydrofuran and polyethylene glycol dimethyl ether and the like. In addition, the ketone-based solvent includes cyclohexanone, and the alcohol-based solvent includes ethyl alcohol and isopropyl alcohol, and the aprotic solvent includes nitriles such as acetonitrile, and ami such as dimethylformamide. Drew, dioxolanes such as 1,3-dioxolane (DOL), and sulfolane. The above non-aqueous solvents can be used alone or in mixture of two or more, and when two or more are mixed, the mixing ratio can be appropriately adjusted according to the performance of the intended battery, and 1,3-dioxolane and dimethoxyethane A solvent mixed in a volume ratio of 1:1 may be exemplified.

In addition, the lithium-sulfur battery provided in another aspect of the present invention may further include a porous substrate between the positive electrode and the negative electrode.

The porous substrate may be any one selected from the group consisting of carbon, metal, and polymer.

The porous substrate made of carbon may be any one selected from the group consisting of carbon paper, carbon cloth, carbon felt, and combinations thereof.

Preferably, the porous substrate may be a carbon cloth. The carbon cloth is a current collector, a conductive material for the positive electrode, and a sulfur carrier, and the carbon cloth can perform the roles of these three positive electrode components, and the carbon cloth electrode can be used as a flexible electrode in a lithium-sulfur secondary battery.

The porous substrate made of the metal may be at least one selected from the group of metals such as aluminum. The porous aluminum has a low density and is preferable in that it is light when carrying an electrolyte. In order to increase the porosity of the porous aluminum, it is preferable to use the aluminum in the form of an aluminum mesh, and the aluminum mesh can be prepared by, for example, pouring aluminum into a porous polyurethane foam to harden it and then burning the polyurethane.

The porous substrate made of the polymer can be any polymer film having porosity, and commercially available polytetrafluoroethylene membrane, polypropylene membrane, polyethylene membrane, polyimide membrane, polysulfone membrane, Any one porous polymer substrate selected from the group consisting of a polyethersulfone film and a polyvinylidene fluoride film may be used.

In addition, the porous substrate made of the polymer may be a porous substrate made of a conductive polymer, and the conductive polymer may be made of at least one selected from conductive polymers of polyaniline, polythiophene, polyacetylene, and polypyrrole. As the porous substrate made of the conductive polymer, it is preferable to use a non-woven fabric obtained by spinning fibers, or a foam obtained by mixing a foaming agent and heating it to foam.

The form of the porous substrate is not particularly limited as long as it forms a three-dimensional structure such as mesh, foam, fabric, paper, or sheet. However, for the convenience of manufacturing, it is more preferable to laminate fibers to form a nonwoven fabric, or to use a foaming agent to form a foam.

In another aspect of the invention

preparing a separation membrane by contacting at least a portion of the porous membrane with a polyimide precursor solution;

A lithium-sulfur battery manufacturing method comprising a.

With respect to the lithium-sulfur battery manufacturing method, the above-described method for manufacturing a separator for a lithium-sulfur battery and a lithium-sulfur battery have already been described, and both are applicable and will not be repeated below.

Hereinafter, the present invention will be described in more detail through Examples and Experimental Examples. The scope of the present invention is not limited to specific embodiments, and should be construed by the appended claims. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

<Example 1> Polyimide coating using aqueous polyamic acid solution

Pyromellitic dianhydride (PMDA) and m-tolidine (m-TB) were purchased from Sunlight Chem (China) and dried in a vacuum oven at 60° C. for 24 hours before use. N-methyl-2-pyrrolidone (NMP, 99.8%) and dimethylethanolamine (DMEA, 99.5%) were purchased from Sigma-Aldrich (KOREA) and used as such without further purification. Glass microfiber (GF/C grade) membrane (Whatman™, pore size: 1.2 μm, thickness: 260 μm) was also used as is.

PAA, a precursor solution of polyimide (PI), was synthesized using PMDA and m-TB. First, m-TB (21.229 g, 0.1 mol) was dissolved in NMP (387.369 g) at 0 °C under a nitrogen atmosphere. After complete dissolution, PMDA (21.812 g, 0.1 mol) was added gradually. A viscous and yellow PAA solution with a solids content of ˜10 wt % was obtained after stirring for 24 h. To obtain PAA powder, the PAA solution was poured into deionized water, ground using a blender, filtered, and dried overnight at 40°C in a vacuum oven. Then, an aqueous solution of PAA was prepared by adding DMEA as a solubilizer to water in an amount twice that of the repeating unit. PI-GF was prepared by simply immersing the GF membrane in PAA aqueous solution as it was prepared. The dipped GF membrane was dried in a convection oven at 50° C. for 1 hour and then heated in a vacuum oven at 350° C. for 2 hours for thermal imidization.

The blank electrolyte was prepared in a 1:1 (v/v) mixture of 1,3-dioxolane (DOL, Sigma-Aldrich, 99.8%) and 1,2-dimethoxyethane (DME, Sigma-Aldrich, 99.5%) in 1 wt. 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, Sigma-Aldric, 99.95%) containing % lithium nitrate (LiNO _{3 , Sigma-Aldrich 99.99%).} To prepare the catholyte (1M Li ₂ S ₆ ), elemental sulfur (Sigma-Aldrich, ≥99.5%) and Li ₂ S (Alfa-Aesar, 99.9%) as a sulfur source were mixed in a blank electrolyte and heated to 50° C. overnight. heated.

Lithium-sulfur battery (LSB) cells were _{assembled using CR2032 coin cells in an Ar-charged glove box (O 2} and H ₂ O concentrations less than 0.1 ppm). The cathode solution was immersed in commercial carbon fiber (CC, CH900-20, Kuractive, Kuraray Chemical Co., Ltd., Tokyo, Japan, 21 mg), and a blank electrolyte (100 μl) was added to prepare a total amount of 200 μl of the electrolyte. did. Then, a PI-GF (or GF) separator with a diameter of 19 mm and a Li metal anode with a diameter of 10 mm and a thickness of 0.75 mm were sequentially placed on top of the CC cathode.

<Example 2> Polyimide coating using organic polyamic acid solution

Polyimide was coated in the same manner as in Example 1, but an organic solution in which 3% of polyamic acid was dissolved in an NMP solution, not an aqueous polyamic acid solution, was used, and the oxygen plasma-treated glass fiber was coated therewith.

<Comparative Example 1>

Prepared in the same manner as in Example 2, but coated with glass fibers without surface treatment.

<Experimental Example 1> Confirmation of polyimide formation on glass fiber

In the following experimental examples, thermogravimetric analysis (TGA-50) was performed under nitrogen with a heating rate (CDFC) of 10 °C/min in a temperature range of 25 °C and 900 °C, and Fourier transform infrared (FT-IR) spectra were recorded with a JACSO FT-IR 4100 spectrometer. In addition, cycle stability was evaluated in the potential range between ^{1.8 V vs Li/Li +} and 2.6 V vs Li/Li ⁺ using a WBCS 3000 multi-channel cycler (WonATech, Seoul, Korea), and electrochemical impedance spectroscopy (EIS) ) was measured from 250 kHz to 0.05 Hz by a VSP (Bio-Logic, Seyssinet-Pariset, France) potentiostat.

The GF membrane consists essentially of borosilicate microfibers with a thickness ranging from 120 nm to 1900 nm (Figs. 1a, 1b). Random array stacking with a thickness of 260 μm forms an open porous structure with a pore size of about 1.2 μm, which is about 28 times that of a typical battery separator based on polypropylene (PP) (0.043 μm), that is, Celgard 2400. bigger

In addition to its high thermal stability, such as 550 °C (vs. ~90 °C for Celgard 2400), which is much higher than the thermal imidization temperature of PI, GF provides much higher electrolyte permeability than Celgard membranes, thus reducing the effect of surface functional groups, i.e. PI, on the internal It can be an ideal separator (or substrate) model for investigating polysulfide shuttles without interfering with physical trapping in the pore structure.

PI contrasts with PP in that it has high thermal stability (>500° C.) and wettability to electrolyte solvents. PI is introduced into the GFs by simple immersion in PAA aqueous solution and thermal curing as shown in Figure 1e. After the PAA loaded on GF was completely converted to PI by heating at 350° C. for 2 hours, pale yellow PI-GF that can be confirmed to be formed of PI can be obtained ( FIG. 1D ). By immersing GFs in PAA aqueous solutions at different concentrations (0.3, 0.5 and 1.0 wt%), the amount of PI in the GFs and the depth of color can be gradually changed. Hereinafter, depending on the concentration, these separators are referred to as PI-GF-x (x = 0.3, 0.5 and 1.0).

In order to form a uniform PI thin film on the hydrophilic surface of GF, water was used instead of an organic solvent as a solvent for PAA to improve wettability and coating properties through hydrogen bonding. In general, PAA is well soluble in polar aprotic organic solvents such as NMP, DMF and DMAc, while it has limited solubility in water. Dissolution in water can be promoted by reaction with water solubilizers that are alcohol amines or tertiary amines such as dimethylethanolamine (DMEA) and trimethylamine. These amine compounds form a salt complex with PAA through an acid-amine reaction, which substantially increases solubility in water. It was found that the surface of GF was actually wetted by PAA aqueous solution faster than organic PAA solution of NMP. Thereby, as shown in the SEM image, the PI coating formed from the aqueous solution is homogeneous and smooth, and the PI coating from the NMP solution is highly self-agglomerated (Fig. 1h). The surface morphology of GF has little effect before and after PI formation (PI-GF-0.5), which means that the very thin PI coating layer does not affect the chemical structure of silica and is attached to the GF surface due to the strong surface affinity of PAA with GF. This means that it is formed uniformly. This can be applied to ˜3 wt % PAA solution ( FIGS. 1F , 1G and 1I-1 ).

Formation of PI in GF can be confirmed through FT-IR. In the FT-IR spectrum of PI-GF-0.5, the weak absorption bands of the imide ring composed of carbonyl carbon bonded to nitrogen are 725 (modified), 1363 (CN) and 1722 (C=O, sym.) cm ⁻¹ appears anew (Fig. 1m). The conversion of PAA to PI is found to be successful as the characteristic broadband disappears in the range of ^{3000 to 4000 cm −1} meaning the NH and OH bonds of PAA. The remaining strong bands at 450, 787 and 1013 cm ⁻¹ are attributed to the bending oscillations of silica embedded in borosilicate microfibers, symmetric stretching oscillations, and asymmetric stretching oscillations of Si—O—Si. The content of PI in PI-GF-x was evaluated by heating PI-GF-x samples in a muffle furnace to 550° C. under air for 4 hours. As expected, the mass loss increases as x increases from 0.3 to 1.0. That is, the PI-GF-0.3 to 1.0 samples showed a mass loss of 2.6, 4.0, and 6.7 wt%, respectively, corresponding to the PI content of PI-GF-x (Fig. 1n inset table). This means that the PI loading on GF can be simply fine-tuned with initial concentrations of aqueous PAA solutions ranging from 0.3 to 1 wt%. The actual content of PI may be lower by about 1 wt% than the value obtained after pyrolysis in a muffle furnace. That is, borosilicate fibers also contribute to a mass loss of ~1 wt% as a result of removal of surface hydroxyl groups (Fig. 1n). In addition, since PI-GF shows a mass loss of less than 1 wt%, it guarantees thermal stability up to 300 °C, and PI-GF-0.5 shows a rapid mass loss around 400 °C as a result of pyrolysis of PI, and continuous mass up to 700 °C loss (Fig. 1n).

<Experimental Example 2> Evaluation of polysulfide adsorption capacity of polyimide-coated glass fibers

Prior to electrochemical characterization of PI-GF-x samples in LSB cells, adsorption of polysulfide by PI powder to confirm whether PI-GF-x provides sufficient heterogeneous adsorption sites (or PI content) for polysulfide. ability was evaluated first. PI powders (50, 100, and 150 mg) prepared under the same conditions except for using GF were _{stirred vigorously with 25 mM Li 2} S ₆ solution (1.6 mL) in an Ar-filled glove box for 12 hours to equilibrate was mixed until reached. The photographic image of the resulting supernatant shows that the dark brown catholyte gradually becomes colorless with increasing amount of PI powder and finally turns into a clear solution at 150 mg (Figs. 2a and 2b). _{Similarly, the absorption at 350 and 450 nm, corresponding to S 6} ^2- dissolved in DOL:DME (1:1, v/v), decreases substantially with increasing PI powder in the UV-Vis spectrum of the supernatant. (Fig. 2c). In this result, the adsorption capacity of the PI powder for Li ₂ S ₆ is estimated to be about _{0.4 μmol Li 2 S 6 / mg} PI. Assuming that the sulfur utilization efficiency is 70% at a sulfur loading of 2 mgS/cm ² area and the remaining 30% is completely dissolved in the electrolyte, more than 12 mg of PI, which is more than 10 times greater than the PI content of PI-GF-1, is required. . This means that all PI-GF-x samples show a significant lack of surface adsorption, but the thin PI coating on the GFs is very likely to expose more carbonyl groups with high affinity to polysulfides as hetero-adsorption sites due to the nanostructure. high. Indeed, it can be seen that the self-discharge of the LSB cell at open circuit voltage (OCV) is much reduced in the PI-GF-x sample when compared with the Celgard 2400 (Figs. 2d and 2e). From the stable OCV values of GF alone, it can be seen that the surface silanol groups of borosilicate microfibers are effective for polysulfide adsorption and self-discharge prevention, which is consistent with the previous report that polysulfide is efficiently captured in porous silica. . However, the exception is that the PI-GF-1.0 sample exhibits somewhat poorer self-discharge protection than other samples containing pure GF. As will be discussed later, PI content greater than 1 mg in PI-GF interferes with ion transport, especially in the presence of polysulfides.

<Experimental Example 3> Performance evaluation of lithium-sulfur batteries

Microporous carbon fibers (CC) with a small pore size of 1.2 nm, a high surface area of ^{1630 m 2 /g and a high pore volume of 0.87 cm 3} /g could be a suitable sulfur support material for the high performance of flexible LSBs. LSB cells produced without the use of additional conductive additives, polymeric binders and porous support materials were ^{1100 corresponding to an areal sulfur loading of 2 mg/cm 2} and 6 mg/cm ² and sulfur utilization efficiencies of 66% and 33% at 0.3 C. and a specific capacity of 548 mAh/g. In particular, the capacity loss of 0.137 and 0.129% per cycle is negligible over 100 cycles due to the efficient physical entrapment of polysulfide in micropores of ~1.2 nm. When ~34% of polysulfide is permanently present in the catholyte, this is made possible in part by _{a sacrificial LiNO 3 additive that can passivate the surface of the Li metal anode.} The problem is that the _{protective SEI layer based on LiSO x} is transient and continuously decomposes over the cycle, eventually leading to cell performance degradation. If it is important to minimize the detrimental effects of polysulfide shuttling on Li metal anodes, additional trapping options for polysulfides are indispensable to avoid the same fate of LSB cells.

To investigate the effect of PI-GF-x on the electrochemical performance of CC, constant current cycling using potential limiting (GCPL) and electrochemical impedance spectroscopy (EIS) was performed with 1.8 V vs Li/Li ⁺ and 2.6 V vs Li/Li + ^It was performed at a sulfur loading per area of 2 mgS/cm ² and a current density per area of ^{1.0 mA/cm 2 corresponding to 0.3 C in the potential range between +.} Using 1M Li ₂ S ₆ catholyte as the sulfur source, the E/S ratio was set to ~60, and the electrolyte is considered a dilute solution under these conditions. The low concentration gradient makes it difficult for PI-GF-x to drive the surface adsorption of polysulfide to equilibrium. Harsh conditions are used to exaggerate polysulfide shuttling in LSB cells as the dilute electrolyte induces more polysulfide dissolution from the cathode. These cells were placed in OCV for 12 h to induce a self-discharge response prior to GCPL testing, and then charged to the upper potential first to electrochemically infiltrate sulfur into CC. To avoid confusion unless otherwise noted, the first charge curve has been removed from the GCPL profile.

3A shows a graph of dose versus number of cycles of PI-GF-x samples. PI-GF-0.5 outperformed other samples including GF in terms of dose generation and cycle stability. PI-GF-0.5 produces a maximum capacity of 1328 mAh/g, corresponding to a sulfur utilization efficiency of 79.5%, with a high coulombic efficiency of 99.12% and a marginal capacity loss of 0.099%/cycle for 120 cycles, while the other samples have 10 % produces slightly lower capacity, and rapid cell degradation occurs at 60-70 cycles. The CC cathode combined with PI-GF-0.5 still works in the same way as Celgard 2400 or GF, as expected (Fig. 3b). The GCPL profile of PI-GF-0.5 was 2.3 during discharge corresponding to the reduction reaction of polysulfide/lithium sulfide _{with high sulfur (Li 2} S _x , 4≤x≤8) and low sulfur (Li ₂ S _{x , 1≤x), respectively.} Two typical plateaus are shown at V vs Li/Li ⁺ and 2.0 V vs Li/Li ⁺ potentials, followed by a charge profile with a gradual slope towards the upper potential due to subsequent oxidation reactions of lithium sulfide and polysulfide to elemental sulfur. see. For PI-GF-0.5, the capacity ratio of low-polysulfide (700-800 mAh/g) and high-polysulfide (500 mAh/g) is maintained at -1.45, which is much lower than the theoretical value. This can be attributed to the microporous CC, which is efficient in the reaction of soluble high-polysulfide causing shuttling, but poor in reaction of insoluble low-polysulfide causing pore clogging. PI-GF-0.5 can mainly contribute to the improvement in the reaction of high-polysulfide by delaying polysulfide shuttling to keep the high-polysulfide close to the reaction site of CC, which is why PI-GF-0.5 is charged with It shows no shuttling during operation, and the charging profile drops or fluctuates without reaching the upper potential. Furthermore, PI is an electrochemically active material for lithium ions in the potential range between ^{1.9 V vs Li/Li +} and 2.3 V vs Li/Li ⁺ which is well encompassed at the lower and upper potentials of GCPL measurements. However, it is impossible to accurately measure the mass of PI participating in the electrochemical reaction, and it is rare that such a reaction occurs consistently over a long distance without close contact with the current collector.

To improve the electrochemical performance of LSB cells, PI-GF-0.5 was analyzed in more detail. Polar polymers containing oxygen or nitrogen atoms in polymer separators such as polyacrylonitrile and poly(methyl methacrylate) promote lithium-ion transport and distribution, and thus, due to high affinity in carbonate-based electrolytes, lithium metal anodes can improve the performance of This was assumed to be the same for the PI of the ether-based electrolyte. The pyridine nitrogen atom of PI, acting as a lithium affinity site, can modulate the cationic pathway and their nucleation. It is also expected to reduce the overpotential required for lithium plating/stripping.

In lithium plating/stripping using a 1M LiTFSI solution dissolved in DOL:DME (1:1, v/v), superior cycle safety and speed characteristics of PI-GF-0.5 compared to GF were confirmed. During the cycle stability test of 1700 hours (500 cycles) at a constant current density of 0.35 mA/cm ² , the overpotential remains low at the level of 5 mV, except for the initial fluctuation of PI-GF-0.5 during conditioning (Fig. 4a). In the subsequent speed characteristic test, ^{as the current density increased from 0.35 mA/cm 2} to 2.8 mA/cm ² , the overvoltage increased only slightly to about 0.3 mV ^{and remained stable even at 2.8 mA/cm 2} ( FIG. 4b ).

Despite the superior performance of the lithium metal anode, the PI-GF-0.5-based LSB cell exhibits slightly lower rate characteristics than the GF-based cell. This means that polysulfide adsorption affects lithium-ion transport through PI-GF-0.5 (Figs. 4c and d). To clarify the effect of polysulfide adsorption on the ionic conductivity of PI-GF-0.5, EIS measurements were performed using an Al/membrane-electrolyte/Al symmetric cell. The ionic conductivity (σ) was calculated as in Equation 1 below.

[Equation 1]

σ = d / (R _b A)

where d is the thickness of the separator, R _b is the intersection of the Z-axis and the Nyquist plot at the highest frequency, representing the bulk electrolyte resistance, and A is the contact area between the electrode and the separator. In the absence of polysulfide, the ionic conductivity of the PI-GF-x sample gradually increased with increasing PI content, becoming 1.36 times higher than that of GF, which is in good agreement with the results of the lithium plating/stripping reaction (Figs. 5a, 5b). ). Conversely, the ionic conductivity decreases with the PI content in the presence of polysulfides. The effect is particularly evident in the case of x = 1 (PI-GF-1), where large amounts of polysulfide-affinity PI substantially reduce the ionic conductivity enabling the adsorption of polysulfide, leading to abrupt LSB cell performance degradation. Able to know. At a sulfur loading per area of 2 mgS/cm ² , the same can be interpreted for the initial bulk cell resistance of the PI-GF-x-based LSB (Fig. 5c). For example, the bulk resistance and charge transfer resistance are noticeably increased due to the high loading of polysulfide on the surface of PI-GF-1.

Photographic and SEM images of the circulating electrode and separator can roughly evaluate/quantify and visualize the surface adsorption mode of polysulfide. LSB cells with GF, PI-GF-0.5 and PI-GF-1 were ^{dissociated after charge/discharge cycles at a sulfur loading per area of 2 mgS/cm 2} , and changes in surface morphology, texture and color were observed. Judging from the color change of the cycled separator sample, polysulfide shuttling is evident in the LSB cell even at this low per-area sulfur loading (Figs. 6a-6c). In the utilization efficiency of the GCPL experiment, it was assumed that about 20 to 30% of the total sulfur added was dissolved in the electrolyte solution. GF and PI-GF-x are changed to yellow and green by polysulfide, respectively. In the photographic image of PI-GF-x, it can be seen that the higher the PI content, the darker the green color. Similarly, it can be seen from the SEM images that the formation of particles and thin coating layers in PI-GF-x is more important with increasing PI content. The particles fill the voids between the GF fibers. In addition, a thin coating layer of polysulfide is created on the edge and completely covers the space by cohesive force. This could be the reason why the ionic conductivity of PI-GF-1 based LSB cells is greatly reduced.

The TGA results of cycled PI-GF-0.5 show that the weight loss of about 7% and 12% is concentrated at about 100°C and 450°C, respectively. The latter is mainly due to the adsorbed polysulfide in PI-GF-0.5. Given that the sublimation of elemental sulfur mainly occurs at < 300 °C, the high evaporation temperature means that polysulfide binds strongly to PI-GF-0.5. EDS mapping and quantification results show that sulfur is actually well distributed in the membrane samples after DME washing. PI-GF-0.5 contains about 10% less sulfur than GF, which indicates that the thin polysulfide layer created between the fibers can prevent the polysulfide from penetrating deeply into PI-GF-0.5. it means.

<Experimental Example 4> Evaluation of polyimide coating using an organic solvent

The polyimide coating state of Examples 1 and 2 was evaluated and shown in FIGS. 7 to 9 . 7 is a case in which coating is performed using an aqueous polyamic acid solution as in Example 1, FIG. 8 is a case in which a polyamic acid dissolved in an NMP solution is coated on pure glass fiber as in Comparative Example 1, FIG. 9 is as in Example 2 It is an image showing the case where the polyamic acid dissolved in the NMP solution was coated on the glass fiber surface-treated with oxygen plasma.

As described above, in Comparative Example 1, when the polyamic acid organic solution was used, it was confirmed that the polyimide was agglomerated and uniform coating did not occur. Even if the mixed acid organic solution is used, it can be confirmed that a uniform coating is possible as in Example 1.

Claims (12)

A separator for lithium-sulfur batteries comprising a porous membrane,
At least a portion of the porous membrane is coated with polyimide,
The polyimide is contained in 0.5 wt% to 15 wt% of the separator,
Separator for lithium-sulfur batteries.
According to claim 1,
The porous membrane is a lithium-sulfur battery separator, characterized in that at least one selected from the group consisting of a polyolefin-based porous membrane, a ceramic-based porous membrane, and an organic compound-based porous membrane.
delete contacting at least a portion of the porous membrane with a polyimide precursor solution;
The method for manufacturing a separator for a lithium-sulfur battery of claim 1 comprising a.
5. The method of claim 4,
The polyimide precursor solution is a lithium-sulfur battery separator manufacturing method, characterized in that the polyamic acid aqueous solution.
6. The method of claim 5,
The polyamic acid aqueous solution is a lithium-sulfur battery separator manufacturing method, characterized in that it contains a water-soluble agent.
5. The method of claim 4,
The polyimide precursor solution is a lithium-sulfur battery separator manufacturing method, characterized in that the polyamic acid organic solution.
8. The method of claim 7,
The porous membrane is a lithium-sulfur battery separator manufacturing method, characterized in that the surface treatment with plasma.
anode;
cathode; and
The separator of claim 1 positioned between the anode and the cathode;
A lithium-sulfur battery comprising a.
10. The method of claim 9,
The lithium-sulfur battery further comprises a porous substrate between the positive electrode and the negative electrode.
11. The method of claim 10,
The porous substrate is a lithium-sulfur battery, characterized in that the carbon cloth (carbon cloth).
Preparing the separation membrane of claim 1 by contacting at least a portion of the porous membrane with a polyimide precursor solution;
A lithium-sulfur battery manufacturing method comprising a.

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