Polymer and aramid nanofibril composite membrane, manufacturing method thereof, and secondary battery comprising same

Abstract

The present invention relates to a polymer and aramid nanofibril composite membrane, a manufacturing method thereof, and a secondary battery comprising same. According to an embodiment of the present invention, it is possible to provide a membrane composed of a polymer and aramid nanofibril composite having a maximum porosity of about 98% by sequentially performing phase separation of the polymer, nanofibrillization of aramid nanoseeds, and pore generation by polymer swelling.

Description

Polymer and aramid nanofiber composite membrane, method for producing the same, and secondary battery comprising the same

[0001] The present invention relates to a polymer and aramid nanofiber composite membrane, a method for manufacturing the same, and a secondary battery comprising the same. More specifically, the polymer and aramid nanofiber composite membrane can be used as a separator for secondary batteries due to its ultraporous structure, and the secondary battery can secure high energy density and stable long-term operation.

[0002] Separators are a key material, accounting for approximately 20% of the manufacturing cost of secondary batteries. Currently commercialized separators are made of polyolefin, which, due to its inherent properties, suffer from low porosity and electrolyte wettability, as well as poor thermal stability. To develop next-generation batteries with high energy density, it is essential to improve these low porosity and wettability.

[0003] Furthermore, commercially available separators currently face significant challenges, including dendrite growth and thermal runaway, which can lead to membrane damage and short circuits. Controlling porosity and pore size during membrane manufacturing is a challenging process. Separators with surface pores exceeding several micrometers also present problems such as self-discharge, short circuits, and dendrite formation. Therefore, there is a need to manufacture high-capacity secondary battery separators that can effectively prevent membrane damage and short circuits.

[0004] One object of the present invention is to provide a polymer and aramid nanofiber composite membrane capable of simultaneously implementing the advantages of aramid nanofibers and polymers.

[0005] Another object of the present invention is to solve the problem of lithium dendrites forming on the surface of a negative electrode when using a conventional lithium metal battery separator by manufacturing a separator having a high porosity and nanopores and a high affinity for lithium salts and electrolytes.

[0006] A polymer and aramid nanofiber composite membrane according to the present invention comprises a polymer containing a polar functional group and an aramid nanofiber frame surrounding the polymer, wherein the polymer surrounds macropores.

[0007] In one embodiment, the polymer including the polar functional group may be any one selected from the group consisting of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyimide (PI), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), poly-N-isopropylacrylamide (PNIPAM), and polyethylene oxide (PEO).

[0008] In one embodiment, the polymer and aramid nanofiber composite membrane may have a porosity of 95.2% to 97.8%.

[0009] In one embodiment, the macropores may have a diameter of 140 nm to 700 nm.

[0010] The method for producing a polymer and aramid nanofiber composite membrane according to the present invention comprises the steps of mixing a polymer suspension and an aramid nanoseed suspension and applying the mixture onto a substrate to form a polymer and aramid nanoseed suspension membrane, immersing the polymer and aramid nanoseed suspension membrane in a protic solvent to produce a polymer and aramid nanofiber protic solvent gel, immersing the polymer and aramid nanofiber protic solvent gel in water to produce a polymer and aramid nanofiber hydrogel, and drying the polymer and aramid nanofiber hydrogel.

[0011] In one embodiment, the polymer comprises a polar functional group and may be any one selected from the group consisting of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyimide (PI), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), poly-N-isopropylacrylamide (PNIPAM), and polyethylene oxide (PEO).

[0012] In one embodiment, the protic solvent may be any one selected from alcohol, acid, ammonia and water.

[0013] In one embodiment, the polymer and aramid nanofiber protic solvent gel may be immersed in water, causing the polymer to swell and the aramid nanofiber frame to expand.

[0014] In one embodiment, freeze-drying may be performed in the step of drying the polymer and aramid nanofiber hydrogel.

[0015] In one embodiment, in the polymer and aramid nanofiber composite membrane, the polymer includes macropores, and the porosity of the macropores may be 95.2% to 97.8%.

[0016] In one embodiment, in the polymer and aramid nanofiber composite membrane, the polymer comprises macropores, and the pores may have a diameter of 140 nm to 700 nm.

[0017] A secondary battery according to the present invention includes a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is a polymer and aramid nanofiber composite membrane according to the present invention.

[0018] In one embodiment, the wettability of the electrolyte to the separator can be controlled due to the polar functional groups of the polymer.

[0019] In one embodiment, the anode includes a metal salt, and the polar functional group of the polymer can combine with an anion constituting the metal salt to form a solid electrolyte interphase (SEI) layer.

[0020] According to the present invention, the aramid composite membrane can be utilized as a separator in a lithium metal battery in which lithium metal is used as an anode, including a lithium-sulfur battery and a lithium-air battery, and a metal anode battery in which a metal such as sodium or magnesium is used as an anode.

[0021] According to the present invention, in a polymer and aramid nanofiber composite membrane, the aramid nanofibers can stably maintain the shape of the membrane even in a state of ultra-porous porosity of about 98% due to a three-dimensional (3D) nanostructure formed by self-assembly, and the polymer applied to the surface of the composite membrane exhibits high affinity for electrolytes and lithium salt anions because it has highly polar hydroxyl groups.

[0022] According to the present invention, the polymer and aramid nanofiber composite membrane has a high lithium ion transfer rate (Li) due to high ionic conductivity and ionic affinity resulting from the ultraporous structure. + The transference number (Tn) is high. Therefore, when a battery is manufactured with a positive electrode containing a lithium salt, a high energy density can be achieved even if a thin lithium negative electrode with a small capacity is used, and stable operation is possible by suppressing the formation of lithium dendrites even under conditions where a small amount of electrolyte is used.

[0023] FIG. 1 is a schematic diagram showing a method for manufacturing an aramid nanofiber composite membrane according to one embodiment of the present invention.

[0024] Figure 2a shows photographs of an aramid nanoseed suspension in ethanol over time. Figure 2b shows photographs of an aramid nanofiber ethanol gel in distilled water (DI) over time. Figure 2c shows photographs of a polyvinyl alcohol suspension in ethanol over time. Figure 2d shows photographs of a polyvinyl alcohol ethanol gel in distilled water (DI) over time.

[0025] Figure 3a is an image of Comparative Examples 1 to 3, Manufacturing Examples 1 and 2 taken with a surface field emission scanning electron microscope (FE-SEM). Figure 3b is an image of Comparative Examples 1 to 3, Manufacturing Examples 1 and 2 taken with a surface field emission scanning electron microscope (FE-SEM) at high magnification. Figure 3c is a result of color mapping the surface porosity images of Comparative Examples 1 to 3, Manufacturing Examples 1 and 2.

[0026] Figure 4a is a cross-sectional field emission scanning electron microscope (FE-SEM) image of Comparative Examples 1 to 3, Manufacturing Examples 1 and 2. Figure 4b is a cross-sectional field emission scanning electron microscope (FE-SEM) image of Comparative Examples 1 to 3, Manufacturing Examples 1 and 2 taken at high magnification.

[0027] Figure 5 is a surface field emission scanning electron microscope (FE-SEM) image of Comparative Example 5.

[0028] Figure 6a is a graph showing the N2 adsorption-desorption isotherms of Comparative Examples 1, 3, 4, Manufacturing Examples 1, and 2. Figure 6b is a graph showing the pore size distribution of Comparative Examples 1, 3, 4, Manufacturing Examples 1, and 2.

[0029] Fig. 7a is an impedance graph of stainless / stainless cells manufactured using Comparative Examples 1, 3, 2, Manufacturing Examples 1, and 2. Fig. 7b is an impedance graph enlarged near the origin of the graph in Fig. 7a. Fig. 7c is an Arrhenius graph of ionic conductivity of stainless / stainless cells manufactured using Comparative Examples 1, 3, 2, Manufacturing Examples 1, and 2.

[0030] Figure 8a is an image showing the results of a wettability test for a carbonate electrolyte with a ratio of EC:DEC:DMC = 1:1:1 for Comparative Examples 1, 3, 2, Manufacturing Examples 1, and 2. Figure 8b is a graph showing the absorption height of the electrolyte absorbed over time in the electrolyte wettability test of Figure 8a.

[0031] FIG. 9a is a graph showing the results of Fourier transform infrared spectroscopy of the NH functional group of aramid and the OH functional group of polyvinyl alcohol depending on the presence or absence of LiPF6 salt in the EC:DEC:DMC = 1:1:1 electrolyte for Comparative Examples 1 and 3, Manufacturing Examples 1 and 2. FIG. 9b is a graph showing the results of Fourier transform infrared spectroscopy of the CO functional group of polyvinyl alcohol depending on the presence or absence of LiPF6 salt in the EC:DEC:DMC = 1:1:1 electrolyte for Comparative Examples 1 and 3, Manufacturing Examples 1 and 2. FIG. 9c is a graph showing the results of Fourier transform infrared spectroscopy of the C=O functional group of aramid depending on the presence or absence of LiPF6 salt in the EC:DEC:DMC = 1:1:1 electrolyte for Comparative Examples 1 and 3, Manufacturing Examples 1 and 2.

[0032] Figures 10a and 10b are X-ray photoelectron spectroscopy (XPS) spectra of Comparative Examples 1, 3, 4, Manufacturing Examples 1, and 2. Figure 10c is a graph showing the atomic ratio according to the change in the content of PVA.

[0033] Figure 11a is a graph showing the results of thermogravimetric analysis of Comparative Examples 1, 3, 4, Manufacturing Examples 1, and 2. Figure 11b is an image showing the results of heat treatment tests performed at 25°C, 125°C, and 175°C for Comparative Examples 1, 3, 4, Manufacturing Examples 1, and 2.

[0034] Figure 12 is a graph showing the results of measuring the Coulombic efficiency of a lithium / copper half-cell manufactured using any one of Comparative Example 1, Comparative Example 3, Comparative Example 4, Manufacturing Example 1, and Manufacturing Example 2 as a separator, adding 7.5 wt% of FEC as an additive, and using an EC:DEC:DMC = 1:1:1 electrolyte containing 1 M LiPF6 dissolved therein.

[0035] Figure 13a shows the capacity of a lithium symmetric cell using any one of Comparative Example 1, Comparative Example 3, Comparative Example 4, Manufacturing Example 1, and Manufacturing Example 2 as a separator when using a carbonate electrolyte of EC:DEC:DMC = 1:1:1 with 1M LiPF6 dissolved therein, at 1 mAh cm -2 Under the specific capacity conditions, the current density is 0.5 mA cm -2 From 10 mA cm -2 After increasing to 0.5 mA cm again -2 When reduced to, the constant current cycling results are shown. Figure 13b shows the current density of 10 mA cm when using a carbonate electrolyte of EC:DEC:DMC = 1:1:1 with 1 M LiPF6 dissolved in it in a lithium symmetric cell using any one of Comparative Example 1, Comparative Example 3, Comparative Example 4, Manufacturing Example 1, and Manufacturing Example 2 as a separator. -2 and specific capacity 1mAh cm -2 The results of constant current cycling under these conditions.

[0036] Figures 14a to 14e show the current density after cycling of 10 mA cm in lithium symmetrical cells manufactured by applying any one of Comparative Example 1, Manufacturing Example 1, Manufacturing Example 2, Comparative Example 3, and Comparative Example 4 as a separator, respectively.-2 and specific capacity 1 mAh cm -2 The photographs, surface scanning electron microscope images, and cross-sectional scanning electron microscope images of the Li electrode surface obtained by disassembling the cell after constant current cycling for 1500 cycles under the conditions of . Figure 14f is a graph showing the ratio of fluorine components present on the Li electrode surface.

[0037] Figure 15 shows a LFP / Li full cell manufactured using a carbonate electrolyte of EC:DEC:DMC = 1:1:1 containing 1M LiPF6 dissolved with 7.5 wt% FEC as an additive, using any one of Comparative Example 1, Manufacturing Example 1, Manufacturing Example 2, Comparative Example 3, and Comparative Example 4 as a separator, and having a cathode loading of 8 to 10 mg cm. -2 , this is a graph measuring the discharge capacity and coulombic efficiency (CE) under the conditions of a charge / discharge rate of 1C and a cathode / anode capacity ratio of 2.03.

[0038] Figure 16 shows an NCM / Li full cell manufactured using a carbonate electrolyte of EC:DEC:DMC = 1:1:1 containing 1M LiPF6 dissolved with 7.5 wt% FEC as an additive, using one of Manufacturing Example 2 and Comparative Example 4 as a separator, with a cathode loading of 18 mg cm. -2 , charge / discharge rate 1C, negative / positive electrode capacity ratio 0.96, electrolyte / positive electrode capacity ratio 4 g Ah -1 This is a graph measuring the discharge capacity and coulombic efficiency under the conditions.

[0039] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings and the contents described in the attached drawings, but the present invention is not limited or restricted by the embodiments.

[0040] The terminology used herein is for the purpose of describing embodiments only and is not intended to limit the present invention. In this specification, the singular also includes the plural unless the context clearly dictates otherwise. As used herein, the terms "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components, steps, operations, and / or elements.

[0041] The terms “embodiment,” “example,” “aspect,” “example,” and the like as used herein are not to be construed as implying that any aspect or design described is better or advantageous over other aspects or designs.

[0042] Also, the term 'or' means 'inclusive or' rather than 'exclusive or'. That is, unless stated otherwise or clear from context, the expression 'x utilizes a or b' means any one of the natural inclusive permutations.

[0043] Additionally, as used in this specification and claims, the singular forms “a” or “an” should generally be construed to mean “one or more” unless otherwise indicated or clear from the context to be in the singular form.

[0044] Additionally, when a part such as a film, layer, area, or component request is said to be "on top" or "over" another part, this includes not only cases where it is directly on top of the other part, but also cases where there are other films, layers, areas, components, etc. intervening therebetween.

[0045]

[0046] The present invention relates to a two-step solvent exchange process that improves upon the phase inversion technique using a protic solvent for a suspension of nanoseeds used to manufacture conventional aramid porous films and aramid composite films. More specifically, the process integrates polymer phase separation, aramid nanoseed nanofiberization, and polymer swelling to induce coordinated self-assembly. This allows for the production of a polymer and aramid nanofiber composite membrane with a maximum porosity of approximately 98%.

[0047]

[0048] The polymer and aramid nanofiber composite membrane according to the present invention comprises a polymer having polar functional groups and an aramid nanofiber frame surrounding the polymer, wherein the polymer surrounds macropores. The aramid nanofiber frame means that the aramid nanofibers are arranged in a three-dimensional (3D) lattice shape.

[0049] When aramid nanofibers are formed from aramid nanoseeds, mesopores (2 to 50 nm) and macropores (> 50 nm) are basically formed due to the lattice structure of the aramid nanofibers. The method for producing a polymer and aramid nanofiber composite membrane according to the present invention is characterized by the formation of additional macropores larger in size than existing macropores due to the swelling process of the polymer.

[0050]

[0051] In one embodiment, the polymer and aramid nanofiber composite membrane may have a porosity of 95.2% to 97.8%. The porosity refers to the porosity of the total pores, including mesopores and macropores.

[0052]

[0053] In some embodiments, the macropores may have a diameter of from 140 nm to 700 nm.

[0054]

[0055] The method for manufacturing a polymer and aramid nanofiber composite membrane (400) according to the present invention includes the steps of mixing a polymer suspension and an aramid nanoseed suspension and applying the mixture onto a substrate to form a polymer and aramid nanoseed suspension membrane (100), immersing the polymer and aramid nanoseed suspension membrane (100) in a protic solvent to produce a polymer and aramid nanofiber protic solvent gel (200), immersing the polymer and aramid nanofiber protic solvent gel (200) in water to produce a polymer and aramid nanofiber hydrogel (300), and drying the polymer and aramid nanofiber hydrogel (300). Hereinafter, the four steps will be described in detail.

[0056]

[0057] 1. Step of forming a polymer suspension and aramid nanoseed suspension film (layer)

[0058] Aramid nanoseeds (130) are added to an organic solvent containing a base and stirred to prepare an aramid nanoseed suspension. A polymer (110) is added to an organic solvent and stirred with heat to prepare a polymer solution.

[0059] A suspension of aramid nanoseed suspension and a polymer solution is mixed and applied onto a substrate to prepare a polymer suspension and an aramid nanoseed suspension film. At this time, the suspension film is in a sol phase.

[0060]

[0061] 2. Step for producing a polymer and aramid nanofiber protic solvent gel

[0062] A polymer and aramid nanofiber protic solvent gel is prepared by immersing a polymer and aramid nanoseed suspension membrane in a protic solvent through a first solvent exchange. The polymer and aramid nanoseed suspension membrane is prepared by sequentially performing phase separation of the polymer, nanofiberization of the aramid nanoseeds, and self-assembly of the phase-separated polymer (210) and the aramid nanofibers in a protic solvent to produce a polymer and aramid nanofiber protic solvent gel. When the polymer dissolved in the polymer and aramid nanoseed suspension membrane is immersed in a protic solvent, the protic solvent is a non-solvent that does not react with the polymer, so the polymer undergoes phase separation in the protic solvent to form polymer aggregates.

[0063] The peptide bond (-CONH-) of the aramid nanoseed is a deprotonated peptide bond (-CON) that has its hydrogen ion removed by the strong base added when preparing the aramid nanoseed suspension. - -) exist in the form of . When the aramid nanoseeds come into contact with a protic solvent, they are reprotonated into a peptide bond (-CONH-) by protons. In addition, as in the phase separation process of polyvinyl alcohol described above, since the protic solvent is a non-solvent that does not react with the reprotonated aramid nanoseeds, the reprotonated aramid nanoseeds undergo phase separation in the protic solvent, forming nanofiber aggregates and the aramid nanoseeds becoming fibers.

[0064]

[0065] Thereafter, the aramid nanoseeds become aramid nanofibers, and the polymer aggregates self-assemble into the aramid nanofibers using the aramid nanofibers as a frame to form a polymer and aramid nanofiber protic solvent gel. The polymer and aramid nanofiber protic solvent gel has a structure including a polymer (420) that surrounds macropores (410) and an aramid nanofiber frame (230) that surrounds the polymer. The protic gel forms a three-dimensional cross-linked structure by hydrogen bonds, van der Waals forces, etc., and means a state in which a significant amount of protic solvent is contained without being dissolved.

[0066]

[0067] 3. Step for manufacturing polymer and aramid nanofiber hydrogels

[0068] When a polymer and aramid nanofiber protic solvent gel is immersed in water and a secondary solvent exchange (replacing the protic solvent with water) is performed, a polymer and aramid nanofiber hydrogel is created. At this time, the polymer absorbs moisture and swells, and the aramid nanofiber frame surrounding the polymer with increased size is pushed out and also expands, increasing the size of the macropores surrounded by the polymer and increasing the porosity. As the aramid nanofiber frame expands, the thickness (thickness) of the aramid nanofibers that make up it decreases. The hydrogel forms a three-dimensional cross-linked structure through hydrogen bonds, van der Waals forces, etc., and means a state in which it contains a significant amount of water without being dissolved. In addition, the self-assembled polymer and aramid nanofiber protic solvent gel or hydrogel is a form in which the polymer and the aramid nanofibers are combined or attached.

[0069]

[0070] 4. Drying step of polymer and aramid nanofiber hydrogel

[0071] The swollen polymer and aramid nanofiber hydrogel can be freeze-dried. Drying the swollen polymer and aramid nanofiber hydrogel removes both the protic solvent and water, inducing pore formation and ultimately producing an ultraporous polymer and aramid nanofiber composite membrane.

[0072] Freeze-drying is a process that freezes water and sublimates it without passing through the liquid phase. Freeze-drying prevents the collapse of the porous structure of the dried sample, compared to oven-drying or room-temperature drying. Furthermore, rather than directly immersing the expanded polymer and aramid nanofiber hydrogel in liquid nitrogen or freezing it in a freezing chamber, it is preferable to attach the hydrogel manufactured on a silicon substrate and then freeze-dry it in a liquid nitrogen bath.

[0073]

[0074] A secondary battery according to the present invention includes a cathode, an anode, an electrolyte, and a separator disposed between the cathode and the anode, wherein the separator is a polymer and aramid nanofiber composite membrane according to the present invention. Due to the increased porosity of the macropores on the surface of the composite membrane, the manufactured composite membrane exhibits low resistance and high ionic conductivity. In addition, by introducing highly polar hydroxyl groups (-OH) contained in the polymer to the surface of the aramid nanofibers, the composite membrane exhibits high electrolyte wettability and high anion affinity when manufacturing a battery using the high-polarity composite membrane as a separator. Electrolyte wettability for the separator refers to the affinity between the separator and the electrolyte. At this time, the electrolyte is manufactured using a combination of highly polar solvents, and since the polymer also has high polarity, the composite membrane has high affinity for the electrolyte. If the electrolyte wettability of the separator in the battery is high, the operating performance of the battery is not reduced even if a small amount of electrolyte is used, and the use of a small amount of electrolyte ultimately effectively reduces the weight of the entire cell, which helps achieve high energy density.

[0075] In addition, the composite membrane exhibits a high lithium ion transfer rate due to its excellent ion affinity, and when a battery is manufactured by including a fluorine-containing lithium salt, it induces the formation of a highly stable fluorine-based SEI layer at the interface between the negative electrode and the electrolyte after charge and discharge cycles. Due to the synergistic effect of the rapid and uniform lithium ion distribution at the interface due to the high ionic conductivity, the high lithium ion transfer rate, and the stable SEI layer formation, the formation of lithium dendrites generated in the SEI layer of the negative electrode can be effectively suppressed, and even under conditions of low negative electrode / positive electrode capacity ratio and lean electrolyte, which are essential for achieving high energy density, it enables stable operation of the battery, and thus it can be usefully used as a separator for next-generation batteries with high energy density. In addition, although the above effect was described based on a lithium secondary battery, the above effect is also applicable to various metal secondary batteries such as a sodium secondary battery and a magnesium secondary battery.

[0076]

[0077] FIG. 1 is a schematic diagram showing a method for manufacturing an aramid nanofiber composite membrane according to one embodiment of the present invention. Referring to FIG. 1, when a polyvinyl alcohol (PVA) / aramid nanoseed suspension is immersed in ethanol, which is a non-solvent (a solvent incompatible with polymers) and a protic solvent, phase separation of the polyvinyl alcohol and nanofiberization of the aramid nanoseeds occur sequentially. When the polyvinyl alcohol / aramid nanofiber ethanol gel thus produced is immersed in water, swelling of the polyvinyl alcohol causes the polyvinyl alcohol / aramid nanofiber hydrogel to expand. Thereafter, when the swollen polyvinyl alcohol / aramid nanofiber hydrogel is freeze-dried, an ultraporous polyvinyl alcohol / aramid nanofiber composite membrane can be obtained.

[0078]

[0079] The polymer containing a polar functional group may be any one selected from the group consisting of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyimide (PI), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), poly-N-isopropylacrylamide (PNIPAM), and polyethylene oxide (PEO). The above polymers are capable of swelling in water.

[0080] Preferably, the polymer may be any one selected from polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyimide (PI), and polyvinylidene fluoride (PVDF). These polymers are not only swellable in water, but are also polar polymers that easily bond to aramid nanofibers.

[0081] More preferably, the polymer may be polyvinyl alcohol (PVA). Among the above polymers, polyvinyl alcohol (PVA) contains the highest concentration of highly polar functional groups, which makes it most susceptible to swelling and forming additional pores during a solvent exchange process using a protic solvent and water.

[0082]

[0083] High molecular weight polymers, such as polyvinyl alcohol (Mw = 145,000), are large in size, whereas aramid nanofiber frames have nano-sized pores. Therefore, if the aramid nanoseeds are fibrillated first and then polyvinyl alcohol is added, the polyvinyl alcohol diffuses and blocks the pores of the aramid nanofibers, preventing further diffusion of polyvinyl alcohol into the pores. This causes swelling to occur only on the surface of the aramid nanofibers where the polyvinyl alcohol exists, making it difficult to form a homogeneous nanoporous structure. Therefore, it is essential for the polymer phase separation to proceed faster before the fibrillation of the aramid nanoseeds to form a homogeneous nanoporous structure and for the polyvinyl alcohol to be complexed with the aramid nanofibers at the molecular scale.

[0084]

[0085] Phase separation of the polymer and nanofiberization of aramid nanoseeds occur at different rates. To confirm this, separate tests were conducted on pure polyvinyl alcohol and aramid nanoseeds.

[0086] Figure 2a shows photographs of a suspension of aramid nanoseeds suspended in ethanol over time. The nanofiberization of the aramid nanoseeds by the protic solvent ethanol is confirmed by the color change. As the nanoseeds transition from a nanofiber state to a nanofiber state, light scattering decreases, gradually fading the color.

[0087] Figure 2b shows photographs of an aramid nanofiber (ANF) ethanol gel immersed in distilled water (DI) over time. No changes were observed in the aramid nanofiber ethanol gel over time in the distilled water.

[0088] Figure 2c shows photographs of a polyvinyl alcohol (PVA) suspension in ethanol over time. Initially, the PVA suspension was not visible to the naked eye, but over time, phase separation occurred and was visible to the naked eye.

[0089] Figure 2d is a photograph of a polyvinyl alcohol (PVA) ethanol gel immersed in distilled water (DI) over time. When immersed in distilled water, the PVA ethanol gel transforms into a PVA hydrogel over time. During this process, the ethanol constituting the PVA ethanol gel is exchanged with distilled water, causing swelling, which increases the size of the PVA gel.

[0090] Referring to Figures 2a and 2c, it can be seen that the phase separation of polyvinyl alcohol (PVA) (Figure 2c) progresses faster than the fiberization of aramid (Figure 2a). This prevents the pores of the aramid nanofibers from becoming clogged, and allows for the formation of a uniform composite membrane.

[0091]

[0092] The protic solvent is a non-solvent that does not react with the polymer and the aramid nanoseeds. In one embodiment, the protic solvent may be any one selected from alcohol, acid, ammonia, and water. The alcohol may be any one selected from methanol, ethanol, propanol, and butanol. The acid may be any one selected from acetic acid, hydrochloric acid, and hydrofluoric acid. Preferably, the protic solvent may be ethanol.

[0093] Ethanol is H + It has a relatively high pKa of 15.9 with almost no ions. Such weakly protic solvents can form deprotonated peptide bonds (-CON) of aramid nanoseeds. - -) can be slowly reprotonated to the peptide bond (-CONH-), which can induce the formation of a loose aramid nanofiber network. The less dense aramid nanofibers enable the formation of larger diameter pores.

[0094]

[0095] Hereinafter, the present invention will be described in more detail through examples. These examples are intended to explain the present invention more specifically, but the scope of the present invention is not limited by these examples.

[0096]

[0097] [Comparative Example 1] Aramid nanofiber membrane (ANF)

[0098] An aramid nanoseed suspension dispersed in dimethyl sulfoxide (DMSO) was cast onto a glass substrate to form a liquid aramid nanoseed suspension film. The substrate onto which the aramid nanoseed suspension film was cast was immersed in a 95 v / v% ethanol solution in a water bath at room temperature for 30 minutes to produce a homogeneous aramid nanofiber ethanol gel. The substrate with the aramid nanofiber ethanol gel attached was then immersed in water in a separate water bath at room temperature for 30 minutes to produce an aramid nanofiber hydrogel. The aramid nanofiber hydrogel was then separated from the glass substrate, attached to a silicon wafer, and freeze-dried at -75°C for 8 hours to produce an aramid nanofiber film containing 100 v / v% aramid nanofiber (ANF).

[0099]

[0100] [Comparative Example 2] Polyvinyl alcohol membrane (PVA)

[0101] A polyvinyl alcohol solution dissolved in dimethyl sulfoxide (DMSO) was cast onto a glass substrate to form a liquid aramid nanoseed suspension film. The substrate onto which the polyvinyl alcohol suspension film was cast was immersed in a 95 v / v% ethanol solution in a water bath at room temperature for 30 minutes to produce a homogeneous polyvinyl alcohol ethanol gel. The substrate with the polyvinyl alcohol ethanol gel attached was then immersed in water in a separate water bath at room temperature for 30 minutes to produce a polyvinyl alcohol hydrogel. The polyvinyl alcohol hydrogel was then separated from the glass substrate, attached to a silicon wafer, and freeze-dried at -75°C for 8 hours to produce a polyvinyl alcohol film containing 100 v / v% polyvinyl alcohol (PVA).

[0102]

[0103] [Comparative Example 3] Polyvinyl alcohol / aramid nanofiber composite membrane (APV14)

[0104] A polyvinyl alcohol suspension dispersed in dimethyl sulfoxide (DMSO) at a concentration of 1.25 w / w% and an aramid nanoseed suspension dispersed in dimethyl sulfoxide (DMSO) at a concentration of 5 w / w% were uniformly mixed in a volume ratio of 20:80, and then casted onto a glass substrate to form a polyvinyl alcohol / aramid nanoseed suspension film. The substrate on which the polyvinyl alcohol / aramid nanoseed suspension film was cast was immersed in a 95 v / v% ethanol solution in a water bath at room temperature for 30 minutes to produce a homogeneous polyvinyl alcohol / aramid nanofiber ethanol gel. The substrate with the polyvinyl alcohol / aramid nanofiber ethanol gel attached was then immersed in water in a separate water bath at room temperature for 30 minutes to produce a polyvinyl alcohol / aramid nanofiber hydrogel. Afterwards, the substrate with the polyvinyl alcohol / aramid nanofiber hydrogel attached was freeze-dried at -75°C for 8 hours to produce a polyvinyl alcohol / aramid nanofiber composite membrane containing 14 v / v% of aramid nanofiber (ANF) and 86 v / v% of polyvinyl alcohol (PVA).

[0105]

[0106] [Comparative Example 4] Celgard 2400

[0107] I purchased a microporous membrane (product name: Celgard 2400) from Welcos.

[0108]

[0109] [Manufacturing Example 1] Polyvinyl alcohol / aramid nanofiber composite membrane (APV72)

[0110] A polyvinyl alcohol / aramid nanofiber composite membrane containing 72 v / v% of aramid nanofibers (ANF) and 28 v / v% of polyvinyl alcohol (PVA) was obtained by manufacturing it using the same manufacturing method as Comparative Example 3, except that the aramid nanoseed suspension and the polyvinyl alcohol suspension were mixed in a volume ratio of 20:1.

[0111]

[0112] [Manufacturing Example 2] Polyvinyl alcohol / aramid nanofiber composite membrane (APV26)

[0113] A polyvinyl alcohol / aramid nanofiber composite membrane containing 26 v / v% of aramid nanofibers (ANF) and 74 v / v% of polyvinyl alcohol (PVA) was obtained by manufacturing it using the same manufacturing method as Comparative Example 3, except that the aramid nanoseed suspension and the polyvinyl alcohol suspension were mixed in a volume ratio of 20:20.

[0114]

[0115] The polyvinyl alcohol (PVA) content was increased in the following order: Comparative Example 4 (Celgard 2400) / Comparative Example 1 (ANF), Manufacturing Example 1 (APV72), Manufacturing Example 2 (APV26), Comparative Example 3 (APV14), and Comparative Example 2 (PVA).

[0116]

[0117] [Experimental Example 1] Measurement of porosity according to changes in PVA content

[0118] Fig. 3a is an image of Comparative Examples 1 to 3, Manufacturing Examples 1 and 2 taken with a surface field emission scanning electron microscope (FE-SEM). Fig. 3b is an image of Comparative Examples 1 to 3, Manufacturing Examples 1 and 2 taken with a surface field emission scanning electron microscope (FE-SEM) at high magnification. Fig. 3c is a result of color mapping of the surface porosity images of Comparative Examples 1 to 3, Manufacturing Examples 1 and 2. In this case, the surface porosity refers to the porosity including both mesopores and macropores. Referring to Fig. 3c, it can be confirmed that the surface porosity (SP) sequentially increases from 3.0% to 58.8% as the polyvinyl alcohol content increases.

[0119] Table 1 below shows the results of calculating the interfacial tension and spreading coefficient of polyvinyl alcohol (PVA) and aramid nanofibers (ANF) in ethanol. Referring to Table 1, it can be confirmed that PVA and aramid nanofibers have relatively low interfacial tension and positive spreading coefficient in ethanol.

[0120] γ ANF-PVA [mN m -1 ]S ANF-PVA [mN m -1 ]ANF2.85.7PVA2.8-ethanol--

[0121]

[0122] Relatively low interfacial tension (2.8 mN m) between polyvinyl alcohol and aramid nanofibers -1 ) and positive spreading coefficient (5.7 mN m -1 ) so that polyvinyl alcohol exists in a state of being evenly spread on the surface of the aramid nanofibers. Referring to Fig. 3b, it can be confirmed in Manufacturing Examples 1 and 2 that as the polyvinyl alcohol content in the aramid nanofiber composite membrane increases, a polyvinyl alcohol interconnected layer is created between the aramid nanofibers, and it can be confirmed that the diameter of the aramid nanofibers constituting the aramid nanofiber frame expanded by polyvinyl alcohol increases from 22.0 nm (ANF) to 46.0 nm (APV14).

[0123]

[0124] Table 2 below shows the porosity calculated from the density of Comparative Examples 1, 3, 4, Manufacturing Examples 1, and 2. Referring to Table 2, by introducing aramid nanostructures and forming pores by swelling of polyvinyl alcohol, the ratio of macropores in the aramid nanofiber composite membrane can be increased from 95.1% to 97.9% by increasing the polyvinyl alcohol content without creating micro-sized pores.

[0125] Porosity [%] ANF (Comparative Example 1) 95.1±1.0 2400 (Comparative Example 4) 37.0±1.5 APV72 (Manufacturing Example 1) 95.9±1.5 APV26 (Manufacturing Example 2) 97.4±0.7 APV14 (Comparative Example 3) 97.9±1.3

[0126]

[0127]

[0128] [Experimental Example 2] Measurement of pore size according to changes in PVA content

[0129] Fig. 4a is a cross-sectional field emission scanning electron microscope (FE-SEM) image of Comparative Examples 1 to 3, and Manufacturing Examples 1 and 2. Fig. 4b is a cross-sectional field emission scanning electron microscope (FE-SEM) image of Comparative Examples 1 to 3, and Manufacturing Examples 1 and 2 taken at high magnification. Referring to Figs. 4a and 4b, an increase in the size of macropores according to an increase in the polyvinyl alcohol content can also be confirmed in the cross-sectional images of the composite membrane. As the PVA content increased in Comparative Example 1 (ANF), Manufacturing Example 1 (APV72), Manufacturing Example 2 (APV26), and Comparative Example 3 (APV14), the diameters of the macropores tended to increase to 134.8 nm, 140.2 nm, 194.1 nm, and 710.0 nm, respectively.

[0130] Also, referring to Fig. 4a, it can be confirmed that the thickness of the composite film increases as the polyvinyl alcohol content increases, as swelling progresses further. In addition, the photo inserted in Fig. 4a was taken by positioning the composite film on the upper part of the Hanyang University mark image, and it can be confirmed that the transparency of the composite film gradually decreases, so that the mark appears increasingly blurry. This is because the degree of swelling increases as the polyvinyl alcohol content increases, which increases the porosity and pore diameter, and the light scattering phenomenon increases due to the additional pores created, which reduces the transparency of the composite film.

[0131]

[0132] Fig. 5 is a surface field emission scanning electron microscope (FE-SEM) image of Comparative Example 5. Referring to Fig. 5, it can be confirmed that Comparative Example 2 exhibits a smaller pore size and porosity than Examples 1 and 2.

[0133]

[0134] Fig. 6a is a graph showing the N2 adsorption-desorption isotherms of Comparative Examples 1, 3, 4, Manufacturing Examples 1, and 2. Fig. 6b is a graph showing the pore size distribution of Comparative Examples 1, 3, 4, Manufacturing Examples 1, and 2. Referring to Figs. 6a and 6b, as the polyvinyl alcohol content increases, the swelling of the polyvinyl alcohol also increases, so that pores larger than the meso size (50 nm) are formed, and as a result, the surface area for N2 adsorption-desorption is 141.04 m 2 g -1 86.63 m from (APV72) 2 g -1 (APV14) and the pore volume was reduced to 0.389 cm 3 g -1 0.228 cm in 3 g -1 You can see that it decreases.

[0135]

[0136] Table 3 below summarizes the BET measurement results of Figures 6a and 6b. Referring to Table 3, the surface area, volume, and size of the mesopores showed a tendency to decrease with increasing polyvinyl alcohol content after a slight increase in APV72.

[0137]

[0138] Pore ​​surface area (BET surface area) [m 2 g -1 ]Pore volume [cm 3 g -1]Pore size [nm]ANF (Comparative Example 1) 106.70 0.277 9.92 400 (Comparative Example 4) 46.10 0.39 228.2 APV72 (Manufacturing Example 1) 141.0 40.38 910.0 APV26 (Manufacturing Example 2) 121.65 0.319 9.3 APV14 (Comparative Example 3) 86.63 0.22 89.5

[0139]

[0140] [Experimental Example 3] Measurement of battery impedance according to changes in PVA content

[0141] Fig. 7a is an impedance graph of stainless steel / stainless steel cells manufactured using Comparative Examples 1, 3, and 2, Manufacturing Examples 1 and 2. Fig. 7b is an impedance graph enlarged near the origin of the graph in Fig. 7a. Fig. 7c is an Arrhenius graph of ionic conductivity of stainless steel / stainless steel cells manufactured using Comparative Examples 1, 3, and 2, Manufacturing Examples 1 and 2. Referring to Figs. 7a to 7c, as the content of polyvinyl alcohol increases, the ratio of macropores, surface porosity, and pore size increase, resulting in a decrease in bulk resistance and a decrease in activation energy. Bulk resistance is a value obtained from a portion in contact with the x-axis at a high frequency, and means the resistance (resistance of the electrolyte and separator in the electrochemical cell) that impedes the movement of ions within the electrolyte. When measuring EIS (Electrochemical Impedance Spectroscopy), only the bulk resistance can be observed when only a stainless steel cell is used, and the bulk resistance refers only to the resistance of the electrolyte and separator of the manufactured cell.

[0142]

[0143] [Experimental Example 4] Analysis of electrolyte wettability according to changes in PVA content

[0144] Table 4 summarizes the results of the stainless steel symmetrical cells of Figs. 7a to 7c. Referring to Table 4, the bulk resistance (R) increases with increasing polyvinyl alcohol content. b ), decrease in ionic conductivity (σ), increase in activation energy (E a ) can be confirmed to have a decreasing trend. Lithium ion transfer rate (t Li + ) can be confirmed to have an increasing tendency as the polyvinyl alcohol content increases, except for APV14 (Comparative Example 3) in which polyvinyl alcohol is added in excess.

[0145] R b [Ω]σ[mS cm -1 ]E a [kJ mol -1 ]t Li + Thickness [μm] ANF (Comparative Example 1) 0.46±0.01 1.61±0.02 14.96 0.63 14.42 400 (Comparative Example 4) 1.27±0.10 0.98±0.08 11.50 0.30 25.0 APV72 (Manufacturing Example 1) 0.41±0.03 1.76±0.12 13.93 0.66 14.4 APV26 (Manufacturing Example 2) 0.36±0.02 2.43±0.13 10.60 0.78 17.3 APV14 (Comparative Example 3) 0.38±0.01 2.73±0.10 11.46 0.70 20.7

[0146]

[0147] Fig. 8a is an image showing the results of a wettability test for a carbonate electrolyte with a ratio of EC:DEC:DMC = 1:1:1 for Comparative Examples 1, 3, 2, Manufacturing Examples 1, and 2. Fig. 8b is a graph showing the absorption height of the electrolyte absorbed over time in the electrolyte wettability test of Fig. 8a. Referring to Figs. 8a and 8b, it can be confirmed that the electrolyte absorption height increases as the polyvinyl alcohol content increases due to the introduction of polyvinyl alcohol, which has many hydroxyl groups, which are polar functional groups.

[0148]

[0149] [Experimental Example 5] Analysis of the behavior of PVA functional groups according to changes in PVA content.

[0150] FIG. 9a is a graph showing the results of Fourier transform infrared spectroscopy of the NH functional group of aramid and the OH functional group of polyvinyl alcohol depending on the presence or absence of LiPF6 salt in the EC:DEC:DMC = 1:1:1 electrolyte for Comparative Examples 1 and 3, Manufacturing Examples 1 and 2. FIG. 9b is a graph showing the results of Fourier transform infrared spectroscopy of the CO functional group of polyvinyl alcohol depending on the presence or absence of LiPF6 salt in the EC:DEC:DMC = 1:1:1 electrolyte for Comparative Examples 1 and 3, Manufacturing Examples 1 and 2. FIG. 9c is a graph showing the results of Fourier transform infrared spectroscopy of the C=O functional group of aramid depending on the presence or absence of LiPF6 salt in the EC:DEC:DMC = 1:1:1 electrolyte for Comparative Examples 1 and 3, Manufacturing Examples 1 and 2. In the drawing, "w / o LiPF6" means "without LiPF6", and "w LiPF6" means "with LiPF6". Referring to FIGS. 9a to 9c, it can be confirmed that a blue shift occurs in the positions of functional groups depending on the presence or absence of LiPF6 salt. This tendency is due to the highly polar OH functional group and CO functional group among the functional groups of polyvinyl alcohol, the NH functional group of aramid, and the PF6 - This is more prominent due to the ion-dipole interaction with the ions. Referring to Fig. 9b, in the case of Comparative Example 3, a stronger blue shift is observed due to the free CO functional group possessed by the excess PVA. Referring to Fig. 9c, in the case of the C=O functional group of the aramid, the degree of blue shift decreases as the PVA content increases, and it can be confirmed that no shift occurs in the cases of Preparation Example 2 and Comparative Example 3. This is because the interaction at the ANF-PVA interface is abundantly formed, so that the free C=O functional group that can interact with lithium ions decreases.

[0151]

[0152] [Experimental Example 6] Analysis of F and Li atomic ratios according to changes in PVA content

[0153] Figures 10a and 10b are X-ray photoelectron spectroscopy (XPS) spectra of Comparative Examples 1, 3, 4, Manufacturing Examples 1, and 2. Figure 10c is a graph showing the atomic ratio according to the change in the content of PVA. Referring to Figures 10a and 10c, as the content of polyvinyl alcohol containing a highly polar functional group increases, the polar functional group and lithium salt ion (PF6) in particular increases. - ) due to the high affinity between the two, it can be confirmed that the intensity of the F 1s peak on the surface increases. At this time, the hydrogen atoms of the polar functional groups, OH functional group and NH functional group, are electron-rich PF6. - It has high affinity because it can act as an electron acceptor for ions, and has polar functional groups and PF6 - Ion-dipole interactions are formed between ions. As a result, the mechanical strength increases as the content of polyvinyl alcohol increases, resulting in LiF, Li, an F-based SEI layer that is effective in suppressing lithium dendrite formation. x PO y F z Li x PF y It can induce the formation of back. Referring to Figures 10b and 10c, since the interaction of the ANF-PVA interface is formed abundantly and the free C=O functional group is reduced, Li + It can be confirmed that the interaction with ions tends to decrease in the order of Comparative Example 1, Manufacturing Example 1, and Manufacturing Example 2. However, in the case of Comparative Example 3, since there are many CO functional groups, Li + The interaction with ions increases rapidly. Therefore, in a battery using an ANF / PVA composite membrane as a separator, PF6 - The affinity with ions contributes to improving the lithium ion transfer rate.

[0154]

[0155] [Experimental Example 7] Analysis of thermal stability according to changes in PVA content

[0156] Fig. 11a is a graph showing the results of thermogravimetric analysis of Comparative Examples 1, 3, and 4, Manufacturing Examples 1, and 2. Fig. 11b is an image showing the results of heat treatment tests performed at 25°C, 125°C, and 175°C for Comparative Examples 1, 3, and 4, Manufacturing Examples 1, and 2. Referring to Figs. 11a and 11b, it can be confirmed that the Manufacturing Examples exhibit high thermal stability and dimensional stability, except for APV14 (Comparative Example 3), which contains an excessive amount of polyvinyl alcohol, due to the high thermal stability and high temperature dimensional stability of aramid nanofibers.

[0157]

[0158] [Experimental Example 8] Analysis of battery behavior according to changes in PVA content

[0159] Fig. 12 is a graph showing the results of measuring the Coulombic efficiency of a lithium / copper half-cell fabricated using an EC:DEC:DMC = 1:1:1 electrolyte containing 1 M LiPF6 dissolved therein, and applying any one of Comparative Example 1, Comparative Example 3, Comparative Example 4, Manufacturing Example 1, and Manufacturing Example 2 as a separator, adding 7.5 wt% FEC as an additive. Referring to Fig. 12, it can be confirmed that the battery exhibits stable behavior up to about 244 cycles even when copper, which exhibits lithium non-affinity (lithiophobic), is used as a current collector due to the effective dendrite formation suppression effect by the high ion conductivity and ion transfer rate of Manufacturing Example 2.

[0160]

[0161] Figure 13a shows the capacity of a lithium symmetric cell using any one of Comparative Example 1, Comparative Example 3, Comparative Example 4, Manufacturing Example 1, and Manufacturing Example 2 as a separator when using a carbonate electrolyte of EC:DEC:DMC = 1:1:1 with 1M LiPF6 dissolved therein, at 1 mAh cm -2 Under the specific capacity conditions, the current density is 0.5 mA cm -2 From 10 mA cm -2 After increasing to 0.5 mA cm again -2 When reduced to, the constant current cycling results are shown. Figure 13b shows the current density of 10 mA cm when using a carbonate electrolyte of EC:DEC:DMC = 1:1:1 with 1 M LiPF6 dissolved in it in a lithium symmetric cell using any one of Comparative Example 1, Comparative Example 3, Comparative Example 4, Manufacturing Example 1, and Manufacturing Example 2 as a separator. -2 and specific capacity 1mAh cm -2 These are the results of constant current cycling under the conditions. Referring to FIGS. 13a and 13b, it can be confirmed that Comparative Examples 3 and 4 showed unstable cycling results, high overvoltage, and short lifespan characteristics due to the formation of lithium dendrites due to the large pore size of the aramid nanofibers, whereas the batteries manufactured using Comparative Example 1, Manufacturing Examples 1, and Manufacturing Example 2 showed stable cycling behavior, low overvoltage, and long lifespan.

[0162]

[0163] Figures 14a to 14e show the current density after cycling of 10 mA cm in lithium symmetrical cells manufactured by applying any one of Comparative Example 1, Manufacturing Example 1, Manufacturing Example 2, Comparative Example 3, and Comparative Example 4 as a separator, respectively. -2 and specific capacity 1 mAh cm -2These are photographs, surface scanning electron microscope images, and cross-sectional scanning electron microscope images of the Li electrode surface obtained by disassembling the cell after constant current cycling for 1500 cycles under the conditions of . Fig. 14f is a graph showing the ratio of fluorine components present on the surface of the Li electrode. Referring to Figs. 14a to 14e, in the photographs and scanning electron microscope images of the cell electrodes manufactured by Comparative Example 1, Manufacturing Example 1, and Manufacturing Example 2, it can be confirmed that the Li electrode has a relatively smooth surface due to the stable cycling behavior of the battery, and the thickness of the Li electrode slightly increases. In addition, referring to Fig. 14f, as the ratio of polyvinyl alcohol increases, the atomic ratio of F increases, and through this, due to the high ion affinity of polyvinyl alcohol, an F-based SEI layer with a high fluorine ratio, LiF, Li x PO y F z Li x PF y It can be expected that the back will be formed. This type of SEI is Li + It facilitates the diffusion of ions and has high mechanical strength, effectively inhibiting the formation of lithium dendrites.

[0164]

[0165] Figure 15 shows a LFP / Li full cell manufactured using a carbonate electrolyte of EC:DEC:DMC = 1:1:1 containing 1M LiPF6 dissolved with 7.5 wt% FEC as an additive, using any one of Comparative Example 1, Manufacturing Example 1, Manufacturing Example 2, Comparative Example 3, and Comparative Example 4 as a separator, and having a cathode loading of 8 to 10 mg cm. -2, a graph measuring the discharge capacity and coulombic efficiency (CE) under conditions of a charge / discharge rate of 1C and a cathode / anode capacity ratio of 2.03. Referring to Fig. 15, it can be confirmed that stable behavior occurs up to 172 cycles even under conditions of a low cathode / anode capacity ratio (i.e., use of a thin lithium cathode) due to the excellent lithium dendrite formation suppression ability of the aramid nanofiber composite membrane.

[0166]

[0167] Figure 16 shows an NCM / Li full cell manufactured using a carbonate electrolyte of EC:DEC:DMC = 1:1:1 containing 1M LiPF6 dissolved with 7.5 wt% FEC as an additive, using one of Manufacturing Example 2 and Comparative Example 4 as a separator, with a cathode loading of 18 mg cm. -2 , charge / discharge rate 1C, negative / positive electrode capacity ratio 0.96, electrolyte / positive electrode capacity ratio 4 g Ah -1 This is a graph measuring the discharge capacity and coulombic efficiency under the conditions. Referring to Fig. 16, it can be confirmed that the aramid nanofiber composite membrane behaves stably even under conditions of low cathode / anode capacity ratio and low electrolyte / anode capacity ratio, which are essential conditions for operating a high energy density battery, due to its excellent lithium dendrite formation inhibition ability and high electrolyte affinity.

[0168]

[0169] Table 5 shows the energy density of the battery (manufactured using Manufacturing Example 2) tested under the conditions of low cathode / anode capacity ratio and low electrolyte / anode capacity ratio of Fig. 16, and the measured values ​​for energy density calculation. Referring to Table 5, in the case of the NCM / Li full cell manufactured using the aramid nanofiber composite membrane of Manufacturing Example 2, the energy density of the currently commercialized lithium-ion battery is approximately 250 Wh kg. -1 350.7 Wh kg, approximately 40% higher than the previous year -1 It was confirmed that it exhibits excellent energy density.

[0170] APV26 NCM / Li cell Cathode mass [mg] 22.1 Membrane mass [mg] 0.20 20 μm Li mass [mg] 1.01 Electrolyte mass [mg] 14.6 Total mass [mg] 37.9 Energy [mWh] 13.3 Energy density [Wh kg -1 ]350.7

[0171]

[0172] Although the present invention has been described with reference to limited embodiments and drawings, it is not limited to the above-described embodiments, and those skilled in the art will appreciate that various modifications and variations may be made based on this disclosure. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the following claims but also by equivalents thereof.

Claims

1. A polymer containing a polar functional group; and Aramid nanofiber frame wrapping the above polymer Including, A polymer and aramid nanofiber composite membrane characterized in that the polymer surrounds macropores.

2. In paragraph 1, A polymer and aramid nanofiber composite membrane characterized in that the polymer containing the polar functional group is any one selected from the group consisting of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyimide (PI), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), poly-N-isopropylacrylamide (PNIPAM), and polyethylene oxide (PEO).

3. In paragraph 1, A polymer and aramid nanofiber composite membrane characterized in that the polymer and aramid nanofiber composite membrane has a porosity of 95.2% to 97.8%.

4. In paragraph 1, A polymer and aramid nanofiber composite membrane characterized in that the above macropores have a diameter of 140 nm to 700 nm.

5. A step of mixing a polymer suspension and an aramid nanoseed suspension and applying the mixture onto a substrate to form a polymer and aramid nanoseed suspension film; A step of immersing the above polymer and aramid nanoseed suspension film in a protic solvent to produce a polymer and aramid nanofiber protic solvent gel; A step of preparing a polymer and aramid nanofiber hydrogel by immersing the polymer and aramid nanofiber protic solvent gel in water; and A step of drying the above polymer and aramid nanofiber hydrogel A method for producing a polymer and aramid nanofiber composite membrane comprising:

6. In paragraph 5, A method for producing a polymer and aramid nanofiber composite membrane, characterized in that the polymer contains a polar functional group and is selected from the group consisting of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyimide (PI), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), poly-N-isopropylacrylamide (PNIPAM), and polyethylene oxide (PEO).

7. In paragraph 5, A method for producing a polymer and aramid nanofiber composite membrane, characterized in that the protic solvent is any one selected from alcohol, acid, ammonia, and water.

8. In paragraph 5, A method for producing a polymer and aramid nanofiber composite membrane, characterized in that the polymer swells and the aramid nanofiber frame expands in the step of immersing the polymer and aramid nanofiber protic solvent gel in water.

9. In paragraph 5, A method for producing a polymer and aramid nanofiber composite membrane, characterized in that freeze-drying is performed in the step of drying the polymer and aramid nanofiber hydrogel.

10. In paragraph 5, In the above polymer and aramid nanofiber composite membrane, the polymer contains macropores, A method for producing a polymer and aramid nanofiber composite membrane, characterized in that the porosity of the above macropores is 95.2% to 97.8%.

11. In paragraph 5, In the above polymer and aramid nanofiber composite membrane, the polymer contains macropores, A method for producing a polymer and aramid nanofiber composite membrane, wherein the pores have a diameter of 140 nm to 700 nm.

12. Bipolar; cathode; electrolyte; and including a separator disposed between the anode and the cathode, A secondary battery characterized in that the above separator is a polymer and aramid nanofiber composite membrane according to claim 1.

13. In paragraph 11, A secondary battery characterized in that the wettability of the electrolyte to the separator is controlled due to the polar functional group of the polymer.

14. In paragraph 11, The above anode contains a metal salt, A secondary battery characterized in that the polar functional group of the polymer combines with anions constituting the metal salt to form a SEI (Solid Electrolyte Interphase) layer.

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