Porous polyetherimide / aramid nanofibril composite membrane and secondary battery comprising same

Abstract

Provided are: a porous polyetherimide / aramid nanofibril composite membrane; and a secondary battery comprising same. The composite membrane includes a polyaramid nanofibril framework defined by a plurality of irregular pores, and a plurality of polyetherimide particles positioned on the polyaramid nanofibril framework.

Description

Porous polyetherimide / aramid nanofibril composite membrane and secondary battery comprising the same

[0001] The present invention relates to a separator for a secondary battery, and more particularly, to a porous aramid nanofibril separator.

[0002] Secondary batteries are chemical batteries that utilize electrochemical reactions to continuously charge and discharge, enabling near-permanent use. They are categorized into lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and lithium secondary batteries. Among these, lithium secondary batteries dominate the secondary battery market due to their superior characteristics of high voltage and energy density compared to other types of batteries.

[0003] Lithium secondary batteries have been used in portable devices such as mobile phones and laptops due to their characteristics of high energy density and high output. In addition, interest in electric vehicles (EVs) has increased recently due to environmental issues. Compared to nickel-metal hydride batteries, they have no memory effect, making them convenient to use, and their high energy and high output characteristics allow for miniaturization, so research is actively being conducted as batteries for electric vehicles. In addition, the need for next-generation lithium batteries with high specific capacity and stable electrochemical properties even during high-speed charging and discharging is gradually increasing. Lithium metal theoretically has a very high specific capacity (3860 mAh / g) and low density (0.59 g / cm). 3 ), it is attracting attention as a negative electrode material for next-generation high-capacity batteries such as lithium-sulfur and lithium-air batteries due to its very low electrochemical potential (-3.04 V vs. the standard hydrogen electrode). It has a specific capacity more than 10 times that of the Li / C negative electrode currently used as a negative electrode, and has the advantage of being able to reduce the weight of the entire cell.

[0004] Lithium secondary batteries are composed of a cathode, an anode, an electrolyte, and a separator. Among these, the required characteristics of a lithium secondary battery separator are to electrically insulate the anode and anode by separating them, while also increasing lithium ion conductivity through high porosity. The polymer substrate commonly used for separators is mainly polyolefin (PO), which is advantageous for pore formation and has excellent chemical resistance, mechanical properties, and thermal properties. However, when existing polyolefin-based separators are used in secondary batteries that use metals such as lithium as the anode, dendrites form on the surface of the metal, such as lithium, with repeated charge and discharge. This causes deterioration of battery performance, such as low coulombic efficiency, and problems such as short circuits between electrodes that can cause fires are not resolved.

[0005] To address the above issues, various methods have been proposed, including changes in the materials and structures of electrodes, electrolytes, and interfaces. Among these, the development of new membranes capable of replacing existing olefin-based membranes is particularly crucial.

[0006] The problem to be solved by the present invention is to provide a separator that has excellent ionic conductivity and suppresses the formation of lithium dendrites generated in the solid-electrolyte-interface layer of the negative electrode, thereby increasing the lifespan and safety of the battery.

[0007] Another problem to be solved by the present invention is to provide a secondary battery including the separator.

[0008] The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0009] One aspect of the present invention provides a polyetherimide / aramid nanofibril composite porous membrane. The composite porous membrane comprises a polyaramid nanofibril framework defined by a plurality of irregular pores, and a plurality of polyetherimide particles positioned on the polyaramid nanofibril framework.

[0010] The above polyaramid nanofibril skeleton may have a diameter in the nanometer size. The above pores may have a diameter in the nanometer size.

[0011] The polyetherimide particles may be arranged separately from each other, or the polyetherimide particles may be combined on the surface of the polyaramide nanofibril skeleton to form a wavy polyetherimide sheath.

[0012] The above membrane may have a porosity of 80 to 99%.

[0013] Another aspect of the present invention provides a method for producing a polyetherimide / aramid nanofibril composite porous membrane. First, a polyetherimide / aramid nanoseed mixture (PEI / Aramid nanoseed mixture) is prepared. A polyetherimide / aramid nanoseed mixture layer is obtained using the polyetherimide / aramid nanoseed mixture. The polyetherimide / aramid nanoseed mixture layer is immersed in an alcohol-containing protic solvent to perform a first solvent exchange, thereby forming a polyetherimide / aramid nanofibril composite alcohol gel membrane by self-assembly. The polyetherimide / aramid nanofibril composite alcohol gel membrane is immersed in water to perform a second solvent exchange, specifically, exchanging the alcohol-containing protic solvent with water, thereby forming a polyetherimide / aramid nanofibril composite hydrogel membrane. A polyetherimide / aramid nanofibril composite hydrogel membrane is freeze-dried to form a polyetherimide / aramid nanofibril composite porous membrane.

[0014] The above polyetherimide / aramid nanoseed mixture can be prepared by mixing an aramid nanoseed dispersion and a polyetherimide solution. The aramid nanoseed dispersion can be obtained by stirring aramid microfibers in a first organic solvent containing a base. The polyetherimide solution can be obtained by solvating polyetherimide in a second organic solvent.

[0015] In the above polyetherimide / aramid nanoseed mixture, the aramid nanoseed and polyetherimide may be contained in an amount of 50 to 85 wt%, specifically 70 to 77 wt%, when the total weight of the aramid nanoseed and polyetherimide is 100.

[0016] Another aspect of the present invention provides a secondary battery. The secondary battery includes a positive electrode, a negative electrode, and a polyetherimide / aramid nanofibril composite porous membrane as a separator interposed between the positive electrode and the negative electrode.

[0017] According to the present invention, the polyetherimide / aramid nanofibril composite porous membrane can stably maintain its shape even at a high porosity of 90% or more due to the strong physical properties of the aramid nanofibril skeleton, and can improve the life characteristics by suppressing the formation of dendrites by having nanopores rather than micropores. In addition, since the polyetherimide on the surface has a high affinity for ions in the electrolyte, it can exhibit high ion conductivity and a high active ion transfer rate, and the particle-shaped or wave-shaped polyetherimide sheath can greatly improve the surface area, thereby helping the conduction of active ions in the electrolyte, thereby enabling high-speed charge / discharge.

[0018] The effects of the present invention are not limited to the technical problems mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

[0019] FIG. 1 is a schematic diagram illustrating a method for manufacturing a porous polyetherimide / aramid nanofibril composite membrane according to one embodiment of the present invention. FIG. 2 is a flow chart illustrating a method for manufacturing a porous polyetherimide / aramid nanofibril composite membrane according to one embodiment of the present invention.

[0020] FIG. 3 shows surface (a) and cross-sectional (b, c) field emission scanning electron microscope (FE-SEM) images of the ANF / PEI composite porous membrane manufactured according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, and the PEI membrane according to Comparative Example 2.

[0021] Figure 4 shows surface and cross-sectional field emission scanning electron microscope images of ANF / PEI composite porous membranes manufactured according to Manufacturing Examples 4 to 6.

[0022] Figure 5 is a high-magnification surface FE-SEM image of the ANF / PEI composite porous membrane according to Manufacturing Examples 1 to 3.

[0023] Figure 6 is a transmission electron microscope (TEM) image of an ANF / PEI composite porous membrane according to Manufacturing Example 3.

[0024] Figure 7 shows FE-SEM images of a commercialized polypropylene (Celgard 2400) membrane at (a) low magnification and (b) high magnification.

[0025] Figure 8 shows the results of surface porosity image color mapping of the ANF / PEI composite membrane manufactured according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, and the PEI membrane according to Comparative Example 2.

[0026] FIG. 9a is a graph showing N2 adsorption-desorption isotherms of ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, ANF membranes according to Comparative Example 1, PEI membranes according to Comparative Example 2, and Celgard 2400 (Comparative Example 3), and FIG. 9b is a graph showing pore size distributions of ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, ANF membranes according to Comparative Example 1, PEI membranes according to Comparative Example 2, and Celgard 2400 (Comparative Example 3).

[0027] Figure 10 is a graph showing the results of X-ray diffraction analysis of ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, an ANF film according to Comparative Example 1, and a PEI film according to Comparative Example 2.

[0028] FIG. 11a is an impedance graph of ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, an ANF film according to Comparative Example 1, a PEI film according to Comparative Example 2, and Celgard 2400 (Comparative Example 3), and FIG. 11b shows an enlarged impedance graph near the origin of FIG. 11a.

[0029] FIGS. 12a, 12b, and 12c are X-ray photoelectron spectroscopy (XPS) O 1s spectra for the ANF film according to Comparative Example 1, the PEI film according to Comparative Example 2, and the ANF / PEI composite film according to Preparation Example 3, respectively, showing O 1s spectra taken at 0 seconds. FIGS. 12d, 12e, and 12f are X-ray photoelectron spectroscopy (XPS) O 1s spectra for the ANF film according to Comparative Example 1, the PEI film according to Comparative Example 2, and the ANF / PEI composite film according to Preparation Example 3, respectively, showing O 1s spectra taken at 50 seconds.

[0030] Figure 13a is a photograph showing the results of an electrolyte wettability test of an ANF / PEI composite membrane (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, an ANF membrane according to Comparative Example 1, a PEI membrane according to Comparative Example 2, and Celgard 2400. Figure 13b is a graph showing the absorption height of the electrolyte absorbed over time in the electrolyte wettability test shown in Figure 13a.

[0031] Figures 14a, 14b, and 14c are graphs of Fourier transform infrared spectroscopy results of the C=O functional group, the C-O-C functional group, and the CN functional group of the PEI depending on the presence or absence of lithium salt in the electrolyte of the ANF / PEI composite films according to Manufacturing Examples 1 to 3 and the PEI film according to Comparative Example 2, respectively.

[0032] Figures 15a and 15b are graphs of Fourier transform infrared spectroscopy results of the C=O functional group and NH functional group of aramid according to the presence or absence of lithium salt in the electrolyte of the ANF / PEI composite films according to Manufacturing Examples 1 to 3 and the ANF film according to Comparative Example 2, respectively.

[0033] FIGS. 16a and 16b are Li 1s and F 1s XPS graphs of the ANF / PEI composite film according to Manufacturing Examples 1 to 3, the ANF film according to Comparative Example 1, the PEI film according to Comparative Example 2, and Celgard 2400 (Comparative Example 3), respectively.

[0034] Figure 17 is a graph showing the atomic ratio of Li and F obtained from the results of Figure 16 above.

[0035] Figure 18 shows a Li / Li symmetric cell using one of the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, the PEI membrane according to Comparative Example 2, and Celgard 2400 (Comparative Example 3) as a separator, at 1 mAh·cm. -2 Under the cycle capacity condition, the current density is 0.5 mA·cm -2 at 10 mA·cm-2 After increasing to 0.5 mA cm again -2 This is a graph showing the results of constant current cycling with reduced current.

[0036] FIG. 19a, FIG. 19b, FIG. 19c, and FIG. 19d are Li / Li symmetric cells using one of the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, the PEI membrane according to Comparative Example 2, and Celgard 2400 (Comparative Example 3) as a separator, respectively, at a current density of 0.5 mA cm. -2 and cycle capacity of 0.5 mAh cm -2 , current density 5 mA·cm -2 and cycle capacity of 0.5 mAh·cm -2 , current density 10 mA·cm -2 and cycle capacity of 1 mAh·cm -2 , current density 10 mA·cm -2 and cycle capacity of 10 mAh·cm -2 These are graphs showing the results of constant current cycling.

[0037] Figure 20 shows a Li / Li symmetric cell using any one of the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, the PEI membrane according to Comparative Example 2, and Celgard 2400 (Comparative Example 3) as a separator at a current density of 10 mA cm. -2 and cycle capacity 1 mAh·cm -2 The images, surface FE-SEM images, and cross-sectional FE-SEM images of the Li electrode surface obtained by disassembling the cell after 1500 cycles of constant current cycling under the conditions of .

[0038] Figure 21 shows a Li / Li symmetric cell using any one of the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, the PEI membrane according to Comparative Example 2, and Celgard 2400 (Comparative Example 3) as a separator at a current density of 10 mA cm. -2 and cycle capacity 1 mAh·cm -2 This is a graph showing the F atomic content ratio obtained by XPS analysis of the Li electrode surface (etching time 0 s) obtained by disassembling the cell after constant current cycling for 1500 cycles under the conditions of .

[0039] Figures 22a, 22b, and 22c show Li / Li symmetrical cells using one of the ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF film according to Comparative Example 1, the PEI film according to Comparative Example 2, and Celgard 2400 (Comparative Example 3) as a separator at a current density of 10 mA cm. -2 and cycle capacity 1 mAh·cm -2 These are impedance graphs obtained after operation for 5 cycles, 5 cycles, and 50 cycles under the conditions of .

[0040] FIG. 23 is a graph showing the charge / discharge results in a Li / LFP full cell using one of the ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF film according to Comparative Example 1, the PEI film according to Comparative Example 2, and Celgard 2400 as a separator, with the charge / discharge rate increased from 1C to 30C and then decreased to 1C.

[0041] FIG. 24 is a graph of discharge capacity and coulombic efficiency after 500 cycles at a charge / discharge rate of 10 C in a Li / LFP full cell using an ANF / PEI composite membrane (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, an ANF membrane according to Comparative Example 1, a PEI membrane according to Comparative Example 2, and any one of Celgard 2400 as a separator.

[0042] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. In describing the present invention, detailed descriptions of related known functions or configurations will be omitted if they are deemed to unnecessarily obscure the gist of the present invention. Furthermore, the terms used in this specification are intended to appropriately express preferred embodiments of the present invention and may vary depending on the user's intention or customary practices in the field to which the present invention pertains. Therefore, definitions of these terms should be based on the contents throughout this specification.

[0043] Identical reference numerals in each drawing represent identical elements.

[0044] Throughout the specification, when we say that an element is "on" another element, this includes not only cases where the element is in contact with the other element, but also cases where another element exists between the two elements.

[0045] Throughout the specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0046] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0047]

[0048] Porous polyetherimide / aramid nanofibril composite membrane

[0049] FIG. 1 is a schematic diagram illustrating a method for manufacturing a porous polyetherimide / aramid nanofibril composite membrane according to one embodiment of the present invention. FIG. 2 is a flow chart illustrating a method for manufacturing a porous polyetherimide / aramid nanofibril composite membrane according to one embodiment of the present invention.

[0050] Referring to FIGS. 1 and 2, first, an aramid nanoseed dispersion and a polyetherimide solution are prepared (S10). The aramid nanoseed dispersion is obtained by stirring aramid fibers in a first organic solvent containing a base, wherein the aramid fibers are split within the solvent to form nanoseeds, and the nanoseeds are dispersed within the solvent. The dispersion may be in a sol state.

[0051] The above aramid fiber refers to a high-tech fiber that is 5 to 10 times stronger than general fibers. While the strength of general polyester fiber is 3 to 4 g / d, the strength of aramid fiber is 20 to 27 g / d. In addition, aramid fiber, also called aromatic polyamide, is a high-performance heat-resistant material with a decomposition temperature of 400°C and can be used continuously at 160°C or higher, and the polymer itself has excellent heat resistance.

[0052] The above aramid fiber may have a weight average molecular weight of 1,000,000 to 5,000,000 g / mol, specifically 1,50,000 to 4,000,000 g / mol, and more specifically 2,000,000 to 4,000,000 g / mol.

[0053] The above aramid is a linear polymer in which more than 60% of the bonds connecting the benzene ring or naphthalene ring are amide bonds, and may include a high molecular weight, fully aromatic polyamide. In the case of aramids having a benzene ring, they are largely classified into meta-aramid and para-aramid depending on the substitution position of the amide bond. That is, they are classified into para-aramid fibers having a structure in which benzene rings are linearly connected via amide groups (CONH) and meta-aramid fibers in which they are not. Examples of meta-aramids include poly-metaphenylene isophthalamide and copolymers thereof, and examples of para-aramids include, but are not limited to, poly-paraphenylene terephthalamide and copolymers thereof, poly(paraphenylene)-copoly(3,4-diphenylene ether) terephthalamide, and the like.

[0054] The method for manufacturing aramid is not particularly limited, but generally includes a solution polymerization method through a condensation reaction between an aromatic diamine and an aromatic dicarboxylic acid or a dihalide of an aromatic dicarboxylic acid, a two-step interfacial polymerization method, etc., and aramid can be manufactured industrially by these methods. In addition, other components may be copolymerized with the aramid as long as the properties of the aramid are not impaired.

[0055] The above aramid fiber is an aramid microfiber having a diameter in the micrometer range, and the diameter may be 1 to 100 μm, specifically 5 to 20 μm, and more specifically 10 to 15 μm. In such aramid fiber, a plurality of polymer backbones form nanofibrils or nanofibrils having a diameter in the nanometer range, which are bonded by hydrogen bonds between amide groups, and these nanofibrils are further bonded by hydrogen bonds between amide groups to form microfibers in the micrometer range.

[0056] The aramid fibers can be dissolved in a ratio of 0.1 to 20 parts by weight relative to 100 parts by weight of the first organic solvent. Specifically, the aramid fibers can be dissolved in a ratio of 0.5 to 10 parts by weight, specifically 0.7 to 5 parts by weight, and more specifically 1 to 2 parts by weight relative to 100 parts by weight of the solvent. Within the above range, an appropriate viscosity can be exhibited, making it easy to form a film, and the manufactured film can exhibit appropriate strength and physical properties while having an appropriate thickness and pore size.

[0057] The first organic solvent may be an aprotic solvent such as, for example, dimethyl sulfoxide, N-methyl-2-pyrrolidone, dimethylformamide, dimethylsulfide, dimethylacetamide, or a mixture thereof. The base may be a strong base such as an alkali metal hydroxide, for example, KOH or NaOH. The base may be contained in an amount of 0.5 to 2 parts by weight relative to 100 parts by weight of the organic solvent, specifically, the aprotic solvent.

[0058] In the above dispersion, the amide groups of some polymer backbones included in the aramid fibers, i.e., aramid microfibers, are deprotonated by the strong base to form nitrogen anions (-CON - -) can be generated. As a result, the aramid microfibers can generate nitrogen anions (-CON - -) can be split in the solvent due to the strong electrostatic repulsion between them. In this process, not all amide groups of the polymer backbones are deprotonated, and hydrogen bonds between the amide groups of some polymer backbones can be maintained. In this way, the aramid microfibers can be converted into the nanoseeds in which some polymer backbones are aggregated by the remaining hydrogen bonds while being split by the electrostatic repulsion due to the deprotonation of some amide groups.

[0059] The above nanoseeds may be dispersed in the solvent and in a sol state, and if sufficiently dispersed, the nanoseeds may not be visible to the naked eye. Stirring may be used as described above to facilitate the dispersion.

[0060]

[0061] The above polyetherimide solution can be obtained by solvating polyetherimide in an organic solvent. To this end, polyetherimide can be placed in a second organic solvent and stirred. The stirring can be performed within a temperature range of 60°C to 80°C.

[0062] The polyetherimide is an amorphous, high-performance thermoplastic polymer with repeating imide and ether bonds within its backbone. It is characterized by high strength and rigidity at room and high temperatures, high long-term heat resistance, very stable dimensional and electrical properties, and a wide range of chemical resistance. Polyetherimide is characterized by excellent dimensional stability due to its amorphous structure and imide groups, low shrinkage, and highly isotropic mechanical properties, as well as a high glass transition temperature of 215°C, a continuous use temperature above 170°C, and high strength at high use temperatures.

[0063] In one specific example, the polyetherimide may be a polymer having a repeating unit represented by the following chemical formula 1.

[0064] [Chemical Formula 1]

[0065]

[0066] In the above chemical formula 1,

[0067] X may be one of the structures of the following chemical formulas 2a, 2b, and 2c,

[0068] [Chemical Formula 2a]

[0069]

[0070] [Chemical Formula 2b]

[0071]

[0072] [Chemical Formula 2c]

[0073]

[0074] Y may have a structure represented by the following chemical formula 3.

[0075] [Chemical Formula 3]

[0076]

[0077] In the above chemical formula 3, n can be 1 or 2.

[0078] The second organic solvent may be an aprotic solvent such as, for example, dimethyl sulfoxide, N-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfide, dimethylacetamide, or a mixture thereof. As an example, the second organic solvent may be a mixed solvent of dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP), and the DMSO and NMP may have a volume ratio of 1:1 to 1:5, for example, a volume ratio of 1:3.

[0079] The polyetherimide can be dissolved in a ratio of 1 to 30 parts by weight per 100 parts by weight of the second organic solvent. Specifically, the polyetherimide can be dissolved in a ratio of 10 to 26 parts by weight per 100 parts by weight of the second organic solvent. Within the above range, a viscosity suitable for application can be exhibited, the manufactured film can have an appropriate thickness, and also have an appropriate average pore size.

[0080]

[0081] After this, the prepared aramid nanoseed dispersion and the polyetherimide solution are mixed to prepare a polyetherimide / aramid nanoseed mixture (PEI / Aramid nanoseed mixture) (S20).

[0082] In the above polyetherimide / aramid nanoseed mixture, the aramid nanoseed and polyetherimide may be contained in an amount of 50 to 85 wt%, specifically 60 to 80 wt%, more specifically 65 to 78 wt% or 70 to 77 wt%, when the total weight of the aramid nanoseed and the polyetherimide is 100.

[0083]

[0084] After this, the polyetherimide / aramid nanoseed mixture can be applied onto a substrate to obtain a polyetherimide / aramid nanoseed mixture layer (S30).

[0085] The substrate used at this time may be glass, metal, semiconductor, or polymer substrate. The semiconductor substrate may be a silicon substrate, the metal substrate may be stainless steel, aluminum, or copper alloy, and the polymer substrate may be a PET substrate. Various methods may be used for the coating method, such as spin coating, blade coating, bar coating, dip coating, gravure coating, spray coating, roll coating, and die coating. The polyetherimide / aramid nanoseed mixed layer immediately after coating may have a thickness of tens to hundreds of micrometers, for example, 30 to 200 ㎛.

[0086]

[0087] The above polyetherimide / aramid nanoseed mixture layer can be immersed in an alcohol-containing protic solvent and subjected to a first solvent exchange to form a polyetherimide / aramid nanofibril composite film or a polyetherimide / aramid nanofibril composite alcohol gel film by self-assembly (S40).

[0088] The alcohol-containing protic solvent may be a solvent containing only alcohol or a mixed solvent of alcohol and water. In this case, the alcohol has a lower boiling point or freezing point than water, and may be, for example, methanol, ethanol, n-propanol, isopropyl alcohol, or a mixed solution thereof. Specifically, the alcohol may be ethanol. When the alcohol-containing protic solvent is a solvent containing only alcohol, the solvent may mean a solvent containing 99 to 100 wt% of alcohol, specifically, 99.3 to 100 wt% of alcohol, and the remainder containing water. In another example, when the alcohol-containing protic solvent is a mixed solvent of water and alcohol, the water and alcohol may have a volume ratio of 1:2 to 2:1, for example, 1:1. In this case, the freezing point of the mixed solvent may be about -40 degrees (℃).

[0089] The polyetherimide / aramid nanoseed mixture layer immediately after application may contain a mixed organic solvent (110) in which the first organic solvent and the second organic solvent are mixed during the preparation of the dispersion within the film. However, by immersing the polyetherimide / aramid nanoseed mixture layer in the alcohol-containing protic solvent, the organic solvent (110) may be replaced with the alcohol-containing protic solvent (120), thereby forming a polyetherimide / aramid nanofibril composite alcohol gel film (100).

[0090] Specifically, the alcohol-containing protic solvent converts the amide groups of the polymer backbones on the surface of the aramid nanoseeds in the mixed solution layer into amide anions (-CON --) is re-protonated to an amide group (-CONH-), and the original hydrogen bonds are restored between the re-protonated polymer backbones and the polymer backbones having the existing amide groups, thereby self-assembling to produce aramid nanofibers or aramid nanofibrils, which can be irregularly networked. At the same time, phase separation between the alcohol-containing protic solvent and the aramid nanofibrils (11) can be induced due to the difference in Hansen solubility parameter between the polyaramid and the alcohol-containing protic solvent. As a result, a nanofibril framework (11) defined by pores (10a) filled by an irregular number of alcohol-containing protic solvents (120) can be formed.

[0091] Meanwhile, the difference in the high Hansen solubility parameter of the polyetherimide and the alcohol-containing protic solvent, for example, ethanol, is 16.3 MPa. 1 / 2 Due to this, the phase transition in which polyetherimide aggregates occurs rapidly. In comparison, as an example of the alcohol-containing protic solvent, the pKa of ethanol is relatively high at 15.9, so the nanofibrillation of the aramid nanoseeds described above can proceed at a relatively slow rate.

[0092] Due to the high interfacial tension and negative spreading coefficient between the polyetherimide and the aramid, the aggregated (or phase-inverted) polyetherimide self-assembles into spherical particles (12) on the surface of the aramid nanofibril framework (11).

[0093] When the content of the polyetherimide is low, the polyetherimide particles (12) can sparsely self-assemble on the surface of the aramid nanofibril skeleton (11), and when the content of the polyetherimide is high, the polyetherimide particles (12) can combine on the surface of the aramid nanofibril skeleton (11) to form a wavy sheath. The polyetherimide particles (12) combine to form a wavy sheath when the total weight of the aramid nanoseeds (or aramid nanofibrils) and the polyetherimide is 100, and the content of the polyetherimide may be 68 to 87 wt%, specifically 70 to 80 wt%, and more specifically 72 to 78 wt%.

[0094]

[0095] After this, the polyetherimide / aramid nanofibril composite alcohol gel film (100) is immersed in water to perform a secondary solvent exchange, specifically, the alcohol-containing protic solvent (120) is exchanged with water, thereby forming a polyetherimide / aramid nanofibril composite hydrogel film (S50).

[0096] At this time, the water may be distilled water, or may also contain a solvent other than water. Specifically, the cavity (10a) may be filled with water.

[0097]

[0098] After this, the polyetherimide / aramid nanofibril composite hydrogel film can be freeze-dried to form a polyetherimide / aramid nanofibril composite porous film (S60).

[0099] The above freeze-drying is a process of rapidly sublimating water within a polyetherimide / aramid nanofibril composite hydrogel film under specific pressure conditions after lowering the temperature of a second solvent, specifically below the freezing point of water, so that the space (10a) previously filled with water can be filled with gas to aerogelize the polyetherimide / aramid nanofibril composite hydrogel film.

[0100] Thereafter, the polyetherimide / aramid nanofibril composite porous membrane can be pressed to reduce its thickness. The pressed membrane can have a thickness of about 10 to 70 μm, for example, about 15 to 30 μm. Since the membrane is porous, it can be easily compressed by applying pressure to reduce its thickness, for example, the thickness can be reduced to about 1 / 4. This pressing step can be performed during the secondary battery manufacturing process described below. Specifically, during the secondary battery manufacturing process, a positive electrode, the polyetherimide / aramid nanofibril composite porous membrane, and an anode are sequentially laminated to form a laminate, and then, in the process of pressing the laminate, the polyetherimide / aramid nanofibril composite porous membrane can be pressed to reduce its thickness.

[0101]

[0102] Polyetherimide / aramid nanofibril composite porous membrane

[0103] The polyetherimide / aramid nanofibril composite porous membrane formed through the manufacturing method of FIGS. 1 and 2 is a porous composite having a plurality of pores, and comprises a polyaramid nanofibril skeleton (11 in FIG. 1) defined by a plurality of irregular pores (10a in FIG. 1) and a plurality of polyetherimide particles (12) positioned on the polyaramid nanofibril skeleton.

[0104] The polyaramid nanofibril skeleton may be a bundle of polyaramid backbones in which a plurality of polyaramid backbones are bonded by hydrogen bonds. The polyaramid nanofibril skeleton may have a diameter in nanometer size, specifically about 10 to 100 nm, specifically about 20 to 50 nm.

[0105] The above polyetherimide particles (12) may be arranged separately from each other or may be combined on the surface of the polyaramide nanofibril skeleton to form a wavy polyetherimide sheath. Furthermore, the aramid nanofibril skeleton may not be exposed to the outside due to the polyetherimide sheath. The diameter of the polyetherimide particles (12) or the thickness of the polyetherimide sheath may be about 20 to 40 nm.

[0106] The affinity for ions in the electrolyte may be increased by the carbonyl group, ether group, etc. in the polyetherimide. In addition, the particle-shaped or wave-shaped polyetherimide sheath may induce an increase in surface area. When this composite porous membrane is used as a separator for a secondary battery, the increase in surface area may result in excellent wettability for the electrolyte. In addition, the size of the pores may be several to several hundred nm in nanometer size. Specifically, the pores may have a size of about 10 to 20 nm when measured by the Barrett-Joyner-Halenda method. In this way, since the composite porous membrane has nanometer-sized pores, compared to a case where the composite porous membrane has relatively large micrometer-sized pores, it can physically block dendrites that may be formed on an electrode in contact with the composite porous membrane, thereby preventing a short circuit of the battery, and thus the life characteristics of the battery can be greatly improved.

[0107] The porous composite membrane may have a surface roughness of 1 to 40 nm. In addition, the porous composite membrane may have a surface porosity of 1 to 30%, an overall porosity of 60 or 70 to 99%, specifically a porosity of 80 to 95%, an average pore diameter of 1 to 170 nm, and a thickness of 15 to 25 μm.

[0108]

[0109] secondary batteries

[0110] The secondary battery of the present invention can be manufactured using conventional methods known in the art. For example, it can be manufactured by inserting the aforementioned polyetherimide / aramid nanofibril composite porous membrane as a separator between the positive and negative electrodes and injecting an electrolyte. The polyetherimide / aramid nanofibril composite porous membrane can be easily compressed and its thickness reduced when pressure is applied, allowing it to be easily inserted into the battery during battery assembly.

[0111]

[0112] cathode

[0113] The above negative electrode may include at least one negative electrode active material layer selected from lithium metal, sodium metal, magnesium metal, or a lithium alloy. The lithium alloy may be an alloy composed of lithium and at least one metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn. When the negative electrode is made of sodium metal, the battery may be a sodium secondary battery, and when the negative electrode is made of magnesium metal, the battery may be a magnesium secondary battery. In the case of a sodium secondary battery or a magnesium secondary battery, the positive electrode active material and the electrolyte described below may be appropriately modified to include sodium or magnesium ions.

[0114] The above-described negative electrode may further include a negative electrode current collector under the negative electrode active material layer. The negative electrode current collector may generally be made to have a thickness of 3 to 500 μm. The negative electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. may be used. In addition, similar to the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine unevenness on the surface, and may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0115] In another embodiment, the negative electrode can be manufactured by mixing and stirring negative electrode active material particles with a solvent, a binder if necessary, a conductive agent, and a dispersant to prepare a slurry, applying (coating) the slurry to a negative electrode current collector, compressing the slurry, and then drying the slurry.

[0116] The above-mentioned negative electrode active material particles can be used without limitation as long as they are generally used in the art, and typically carbon materials can be used. Examples of usable carbon materials include both low-crystalline carbon and high-crystalline carbon. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes. The carbon material may have an average particle diameter that is typical of negative electrode active materials. For example, it may be 3 to 60 μm, but is not limited thereto.

[0117] The above-mentioned conductive material can be used without limitation as long as it is generally usable in the art, and for example, artificial graphite, natural graphite, carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, carbon fiber, metal fiber, aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, ruthenium, platinum, iridium, titanium oxide, polyaniline, polythiophene, polyacetylene, polypyrrole or mixtures thereof can be used.

[0118] The above binder can be used without limitation as long as it is generally used in the art, and for example, polyvinylidene fluoride (PVdF), copolymer of polyhexafluoropropylene-polyvinylidene fluoride (PVdF / HFP), poly(vinylacetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, polyvinylpyridine, alkylated polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), poly(ethyl acrylate), polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluorine rubber, ethylene-propylene-diene monomer (EPDM), sulfonated ethylene-propylene-diene monomer, carboxymethyl cellulose (CMC), regenerated cellulose, starch, hydroxypropyl cellulose, tetrafluoroethylene or mixtures thereof can be used. there is.

[0119]

[0120] anode

[0121] The above positive electrode can be manufactured by a conventional method known in the art, and may vary depending on the specific type of secondary battery.

[0122] Specifically, when the secondary battery is a lithium ion battery, the positive electrode may contain a positive electrode active material, a binder, and a conductive material. The positive electrode active material of the lithium ion battery may contain a lithium-transition metal oxide or a lithium-transition metal phosphate. The lithium-transition metal oxide may be a composite oxide of lithium and at least one transition metal selected from the group consisting of cobalt, manganese, nickel, and aluminum. The lithium-transition metal oxide may be, for example, Li(Ni 1-x-y Co x Mn y )O2(0≤x≤1, 0≤y≤1, 0≤x+y≤1), Li(Ni 1-x-y Co x Al y )O2(0≤x≤1, 0 <y≤1, 0<x+y≤1), 또는 Li(Ni 1-x-y Cox Mn y )2O4(0≤x≤1, 0≤y≤1, 0≤x+y≤1). The lithium-transition metal phosphate may be a complex phosphate of lithium and at least one transition metal selected from the group consisting of iron, cobalt, and nickel. The lithium-transition metal phosphate is, for example, Li(Ni 1-x-y Co x Fe y )PO4(0≤x≤1, 0≤y≤1, 0≤x+y≤1).

[0123] If the secondary battery is a lithium-sulfur battery, the positive electrode may contain a sulfur compound as a positive electrode active material and may further contain a binder and a conductive material. The sulfur compound may be solid sulfur (S8) and / or Li2S.

[0124] When the secondary battery is a lithium-air battery, the positive electrode may contain a carbon material, a catalyst for oxygen redox, or a combination thereof. The carbon material may include carbon black (super P, ketjen black, etc.), carbon nanotubes (CNT), graphite, graphene, porous carbon, or a combination thereof. The catalyst for oxygen redox may be a transition metal, a transition metal oxide, or a transition metal carbide. The transition metal may include ruthenium (Ru), palladium (Pd), iridium (Ir), cobalt (Co), nickel (Ni), iron (Fe), silver (Ag), manganese (Mn), platinum (Pt), gold (Au), nickel (Ni), copper (Cu), aluminum (Al), chromium (Cr), titanium (Ti), silicon (Si), molybdenum (Mo), tungsten (W), or a combination thereof. The above transition metal oxide may include ruthenium dioxide (RuO2), iridium dioxide (IrO2), tricobalt tetroxide (Co3O4), manganese dioxide (MnO2), cerium dioxide (CeO2), iron trioxide (Fe2O3), iron tetroxide (Fe3O4), nickel monoxide (NiO), copper oxide (CuO), a perovskite catalyst, or a combination thereof. The above transition metal carbide may include titanium carbide (TiC), silicon carbide (SiC), tungsten carbide (WC), molybdenum carbide (Mo2C) catalyst, or a combination thereof.

[0125] The positive electrode current collector is generally made with a thickness of 3 to 500 μm. The positive electrode current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the battery. Any metal with high conductivity, to which the slurry of the positive electrode active material can easily adhere, and which is non-reactive within the voltage range of the battery can be used. Non-limiting examples of the positive electrode current collector include foils made of aluminum, nickel, or a combination thereof.

[0126] The solvent for forming the above anode includes organic solvents such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, dimethyl acetamide, etc., or water, and these solvents can be used alone or in combination of two or more.

[0127] The amount of solvent used is sufficient to dissolve and disperse the electrode active material, binder, and conductive material, taking into account the coating thickness of the slurry and the manufacturing yield.

[0128] The above-mentioned challenger and binder are identical to those described in the description of the cathode and are therefore redundant, so their description is omitted.

[0129] The positive electrode may optionally contain a filler added to the mixture. The filler is optionally used as a component that suppresses the expansion of the positive electrode. Any fibrous material that does not induce chemical changes in the battery is not particularly limited. Examples of such materials include olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber.

[0130]

[0131] membrane

[0132] The polyetherimide / aramid nanofibril composite porous membrane described above can be used as a separator that insulates the electrodes between the anode and cathode.

[0133] The above polyetherimide / aramid nanofibril composite porous membrane can stably maintain its shape even at a high porosity of over 90% due to the strong physical properties of the aramid nanofibril skeleton, and can improve the life characteristics by suppressing the formation of dendrites by having nanopores rather than micropores. In addition, since the polyetherimide on the surface has a high affinity for ions in the electrolyte, it can exhibit high ion conductivity and a high active ion transfer rate, and the particle-shaped or wave-shaped polyetherimide sheath can greatly improve the surface area, helping the conduction of active ions in the electrolyte, and enabling high-speed charge / discharge.

[0134] The above polyetherimide / aramid nanofibril composite porous membrane can be compression-molded to have a thickness of about 5 to 30 μm, specifically, 10 to 25 μm.

[0135] The above separation membrane may be used alone using the polyetherimide / aramid nanofibril composite porous membrane, or may be used by laminating the polyetherimide / aramid nanofibril composite porous membrane on a porous polymer film made of a polyolefin polymer such as a conventional porous polymer film used as a separation membrane, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, but is not limited thereto.

[0136]

[0137] electrolyte

[0138] A battery can be manufactured by housing an electrode collector with the above-described structure in a pouch outer case and then injecting an electrolyte. However, this is not limited to this configuration, and the battery can be manufactured in various forms, such as a coin cell. Coin cells can be manufactured by applying an electrolyte.

[0139] The above electrolyte is a non-aqueous electrolyte containing a lithium salt, which may include a non-aqueous electrolyte and a lithium salt.

[0140] As the above non-aqueous electrolyte, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used. there is.

[0141] The above lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium 4-phenylborate, imide, etc. can be used.

[0142] In addition, for the purpose of improving charge-discharge characteristics, flame retardancy, etc., non-aqueous electrolytes may be added with, for example, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoroethylene may be further included to provide incombustibility, and carbon dioxide gas may be further included to improve high-temperature storage characteristics.

[0143]

[0144] battery module

[0145] The secondary battery according to the present invention can be used not only in a battery module used as a power source for a small device, but can also be used as a unit battery in a medium- to large-sized battery pack including a plurality of batteries. A battery module according to another embodiment of the present invention includes the aforementioned secondary battery as a unit battery, and a battery pack according to another embodiment of the present invention includes the battery module.

[0146] Examples of the above medium and large devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0147] The battery case used in the present invention may be one commonly used in the industry, and there is no limitation on the external shape according to the use of the battery. For example, it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0148]

[0149] Hereinafter, manufacturing examples and experimental examples are presented to aid in understanding the present invention. However, the following manufacturing examples and experimental examples are provided solely to aid in understanding the present invention, and the present invention is not limited to the following manufacturing examples and experimental examples.

[0150] <Manufacturing Examples 1 to 6: Manufacturing of ANF / PEI Porous Composite Membrane>

[0151] KOH (90 wt%, Sigma-Aldrich) was dried in a vacuum oven at 110°C for 2 h to completely remove residual moisture due to the hygroscopic nature of KOH. 1.25 g of aramid fiber (Kevlar fiber, DuPont), 100 mL of DMSO (Daejung Chemicals), and 1 g of KOH from which residual moisture had been removed were placed in a container at room temperature (27°C) and magnetically stirred for 2 weeks until a dark red solution was formed, thereby obtaining a 1.25 wt% aramid nanoseed dispersion. Poly(ether imide) (PEI) (a polymer of benzene-1,3-diamine and 5-[4-[2-[4-[(1,3-dioxo-2-benzofuran-5-yl)oxy]phenyl]propan-2-yl]phenoxy]-2-benzofuran-1,3-dione) (Sigma-Aldrich)) was dissolved in a 3:1 volume ratio NMP / DMSO solvent mixture at 80°C for 1 day to obtain a 15 wt% PEI solution. The aramid nanoseed dispersions and PEI solutions of different volume ratios shown in Table 1 were mixed to obtain mixed aramid nanoseed / PEI mixed solutions. 5 mL of each aramid nanoseed / PEI mixed solution was dropped onto a glass plate and bar-coated to a coating thickness of 180 μm. The coated glass plate was immediately immersed in ethanol for 30 min and then in deionized water for 30 min. As a result, the generated hydrogel was placed on a cooling bath filled with liquid nitrogen to form a frozen gel, and the frozen gel was freeze-dried to prevent the collapse of the porous structure. Prior to electrochemical testing, the generated sample was further dried at 120 °C for 2 days to completely remove residual moisture, thereby obtaining an aramid nanofibril (ANF) / PEI composite porous membrane.

[0152]

[0153] <Comparative Example 1: ANF membrane manufacturing>

[0154] An ANF membrane was manufactured by performing the same process as in Manufacturing Example 1, except that 5 mL of a 1.25 wt% aramid nanoseed dispersion without PEI solution was used instead of the aramid nanoseed / PEI mixed solution.

[0155]

[0156] <Comparative Example 1: PEI membrane manufacturing>

[0157] A PEI membrane was manufactured by performing the same process as in Manufacturing Example 1, except that 5 mL of a 15 wt% PEI solution without aramid nanoseed dispersion was used instead of the aramid nanoseed / PEI mixed solution.

[0158]

[0159] 1.25 wt% aramid nanoseed dispersion: 15 wt% PEI solution volume ratio ANF Wt% PEI Wt% ANF (Comparative Example 1) 1:0 1000 AP1 (Manufacturing Example 1) 8:1 4060 AP2 (Manufacturing Example 2) 6:1 3367 AP3 (Manufacturing Example 3) 4:1 2575 AP4 (Manufacturing Example 4) 2:1 1486 AP5 (Manufacturing Example 5) 1:1 892 AP6 (Manufacturing Example 6) 1:4 298 PEI (Comparative Example 2) 0:1 0100

[0160] FIG. 3 shows surface (a) and cross-sectional (b, c) field emission scanning electron microscope (FE-SEM) images of the ANF / PEI composite porous membranes manufactured according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, and the PEI membrane according to Comparative Example 2. FIG. 4 shows surface and cross-sectional field emission scanning electron microscope images of the ANF / PEI composite porous membranes manufactured according to Manufacturing Examples 4 to 6. FIG. 5 is a high-magnification surface FE-SEM image of the ANF / PEI composite porous membranes according to Manufacturing Examples 1 to 3. FIG. 6 is a transmission electron microscope (TEM) image of the ANF / PEI composite porous membrane according to Manufacturing Example 3. FIG. 7 is FE-SEM images taken at (a) low magnification and (b) high magnification of a commercialized polypropylene (Celgard 2400) membrane. Figure 8 shows the results of surface porosity image color mapping of the ANF / PEI composite membrane manufactured according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, and the PEI membrane according to Comparative Example 2.

[0161] Referring to FIGS. 3, 4, 5, 6, and 8, the ANF membrane according to Comparative Example 1 and the ANF / PEI composite porous membranes (AP1, AP2, AP3, AP4, AP5, and AP6) manufactured according to Manufacturing Examples 1 to 6 exhibited a porous structure with an aramid nanofibril (ANF) network defined by pores. PEI was attached to the aramid nanofibril (ANF) skeleton, and the shape of the PEI changed depending on the PEI content. Specifically, in the case of the ANF membrane without PEI, the surface of the nanofibrils was neat and smooth, whereas as the PEI content increased, it changed from separated PEI particles (AP1) to a wavy surface coating or sheath shape (AP3) formed by the merging of one layer of PEI particles. At this time, the diameter of the PEI particles was 32.7±7.4 nm. The ANF / PEI composite porous membranes (AP1, AP2, AP3) manufactured according to Manufacturing Examples 1 to 3 were found to have almost no micro-sized pores and mostly nano-sized pores or only nano-sized pores. This is because the micro-pores are randomly generated due to rapid phase inversion caused by the high Hansen solubility parameter (HSP) distance between PEI and ethanol, and for the same reason, an increase in surface porosity is observed when the PEI content increases from pure ANF to AP3.

[0162] As the PEI content increased further, more PEI particles were attached to the wavy surface coating formed by the merging of PEI particles in the first layer, and micro-sized pores also appeared (Fig. 4, AP4, AP5, and AP6).

[0163] During the solvent exchange process, the top surface of the sol-state film was immediately gelled upon exposure to moisture in the surrounding atmosphere, forming a layer with a relatively high density of nanofibrils. The ANF membrane according to Comparative Example 1 and the ANF / PEI composite porous membranes (AP1, AP2, AP3) manufactured according to Manufacturing Examples 1 to 3 gradually increased in surface porosity and pore size from 3.0% to 27.3% and from 27.7±6.0 nm to 141.6±28.6 nm, respectively. In addition, the nanofibril diameter gradually increased from 25.1±3.0 nm to 47.9±6.9 nm. The cross-sectional images of the ANF and AP samples show a highly porous structure with a higher porosity than the surface. This is primarily attributed to the unique nature of the two-step immersion process, which utilizes controlled reprotonation-mediated self-assembly of ANFs by sequential immersion in two protic solvents with different pHs. As the PEI content increased from pure ANF to pure PEI, the thickness of the membrane also increased from 46.9±2.0 to 62.3±0.8 μm.

[0164] Meanwhile, the PEI film according to Comparative Example 2 exhibited large micropores with a diameter of 3.7±0.5㎛ and a lower density.

[0165] Referring to Figure 7, the commercial membrane of Celgard 2400 exhibited anisotropic slit-shaped pores of several hundred nm.

[0166]

[0167] FIG. 9a is a graph showing N2 adsorption-desorption isotherms of ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, an ANF membrane according to Comparative Example 1, a PEI membrane according to Comparative Example 2, and Celgard 2400 (Comparative Example 3), and FIG. 9b is a graph showing the pore size distribution of ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, an ANF membrane according to Comparative Example 1, a PEI membrane according to Comparative Example 2, and Celgard 2400 (Comparative Example 3). This is the result of Brunauer-Emmett-Teller (BET) analysis to evaluate the mesoporous properties of membranes at the mesoscale of less than 50 nm.

[0168] Referring to FIGS. 9a and 9b, the ANF membrane according to Comparative Example 1 and the PEI / ANF composite porous membranes according to Preparation Examples 1 to 3 exhibited a very high porosity of ~95%, which was much higher than the porosity of the PEI membrane according to Comparative Example 2 and Celgard 2400. When the PEI content increased from pure ANF to AP3, the BET surface area and pore volume of the membranes gradually increased from 106.7 to 126.8 m2g-1 and from 0.277 to 0.445 cm3g-1, respectively. In contrast, the pore sizes of the AP samples were similar in the range of 12-13 nm. These results indicate that the addition of PEI contributed to the increase in areal and volumetric porosity at the mesoscale due to the undulating surface morphology of the PEI / ANF composite nanofibrils.

[0169]

[0170] Figure 10 is a graph showing the results of X-ray diffraction analysis of ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, an ANF film according to Comparative Example 1, and a PEI film according to Comparative Example 2. In this graph, the intensity of the XRD data was normalized to the maximum peak intensity of each graph for a clearer comparison between samples.

[0171] Referring to Figure 10, a broad amorphous diffraction pattern was observed in PEI due to its amorphous nature. ANF exhibited typical characteristic peaks of the (110), (200), and (004) planes for aramid nanofibers. When the PEI content increased from pure ANF to a ratio of AP3, the peak intensity associated with the (200) plane of ANFs, which is known to be oriented parallel to the ANF axis, decreased significantly. This result indicates that the molecular alignment of the aramid crystal domains is disrupted during the assembly process by the incorporation of PEI, which partially reprotonates the ANFs during the first immersion step.

[0172]

[0173] Figure 11a is an impedance graph of ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, an ANF film according to Comparative Example 1, a PEI film according to Comparative Example 2, and Celgard 2400 (Comparative Example 3), and Figure 11b shows an enlarged impedance graph near the origin of Figure 11a. The films were placed between a pair of stainless steel (SS) plates, and an electrolyte containing 1 M LiPF6 salt in a mixed solvent of EC:DEC:DMC (volume ratio of 1:1:1) was injected, and then the electrochemical impedance spectroscopy (EIS) measurement was used to investigate.

[0174] Referring to Figures 11a and 11b, when the PEI content increased from pure ANF to AP3, the bulk resistance (Rb) of the cell gradually decreased from 0.46 ± 0.01 to 0.37 ± 0.03 Ω. As a result, the ionic conductivity (σ) decreased from 1.61 ± 0.02 to 3.41 ± 0.24 mS cm. -1 The σ gradually increased and exceeded σ of Celgard 2400 by three times. This indicates that the highest ionic conductivity behavior was observed for AP3 among the tested membranes. This result is due to the very high bulk porosity of the AP sample and the Li of the surface PEI. + and PF6 -This may be due to its affinity for ions.

[0175]

[0176] FIGS. 12a, 12b, and 12c are X-ray photoelectron spectroscopy (XPS) O 1s spectra for the ANF film according to Comparative Example 1, the PEI film according to Comparative Example 2, and the ANF / PEI composite film according to Preparation Example 3, respectively, showing O 1s spectra taken at 0 seconds. FIGS. 12d, 12e, and 12f are X-ray photoelectron spectroscopy (XPS) O 1s spectra for the ANF film according to Comparative Example 1, the PEI film according to Comparative Example 2, and the ANF / PEI composite film according to Preparation Example 3, respectively, showing O 1s spectra taken at 50 seconds.

[0177] Referring to FIGS. 12a, 12b, 12c, 12d, 12e, and 12f, the XPS results of AP3 (Manufacturing Example 3) at an etching time of 0 s (surface) showed two distinct peaks with similar peak positions and intensities to the characteristic peaks of PEI (Comparative Example 2), whereas AP3 (Manufacturing Example 3) showed a decrease in intensity and a peak shift of the peak around 533 eV after etching for 50 s (5 nm etching), showing results similar to those of ANF (Comparative Example 1). From this, it can be seen that the rough outer surface of the ANF / PEI composite film of AP3 (Manufacturing Example 3) shows a PEI-rich composition, and the inner part has an ANF-rich composition.

[0178]

[0179] Figure 13a is a photograph showing the results of an electrolyte wettability test of an ANF / PEI composite membrane (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, an ANF membrane according to Comparative Example 1, a PEI membrane according to Comparative Example 2, and Celgard 2400. Figure 13b is a graph showing the absorption height of the electrolyte absorbed over time in the electrolyte wettability test shown in Figure 13a. At this time, a mixed solvent of EC:DEC:DMC (volume ratio of 1:1:1) was used as the electrolyte.

[0180] Referring to Figs. 13a and 13b, after immersing in the electrolyte for 80 minutes, most of the samples reached saturation values ​​in absorption heights. ANF (Comparative Example 1) and AP1 (Preparation Example 1) had similar absorption heights, but AP2 (Preparation Example 2) and AP3 (Preparation Example 3) samples had saturation values ​​in absorption heights that were 17% and 48% higher than those of ANF (Comparative Example 1) and AP1 (Preparation Example 1), respectively, due to the ether and carbonyl functional groups with high polarity resulting from the abundant PEI component on the surface.

[0181]

[0182] FIGS. 14a, 14b, and 14c are graphs of Fourier transform infrared spectroscopy results of the C=O functional group, the C-O-C functional group, and the C-N functional group of the PEI in the presence or absence of lithium salt in the electrolyte of the ANF / PEI composite membranes according to Manufacturing Examples 1 to 3 and the PEI membrane according to Comparative Example 2, respectively. FIGS. 15a and 15b are graphs of Fourier transform infrared spectroscopy results of the C=O functional group and the N-H functional group of the aramid in the ANF / PEI composite membranes according to Manufacturing Examples 1 to 3 and the ANF membrane according to Comparative Example 2, respectively, in the presence or absence of lithium salt in the electrolyte. This evaluation was performed in a wet state by immersing the samples in an electrolyte with or without LiPF6 salt in a mixed solvent of EC:DEC:DMC (volume ratio of 1:1:1).

[0183] Referring to Figures 14a, 14b, and 14c, a blue shift of the carbonyl (C=O) and ether (C-O-C) functional groups of PEI was observed in both the PEI membrane and the ANF / PEI composite membranes when LiPF6 was present in the electrolyte. This is due to Li + This can be attributed to the electrostatic interaction between the carbonyl (C=O) and oxygen, which has a relatively high electronegativity compared to carbon in the ether (C0C) of the ion and PEI. In addition, a blue shift of the CN functional group of the imide was also observed, which is similar to that of PF6. - It is due to electrostatic interaction with ions.

[0184] Referring to FIGS. 15a and 15b, it can be seen that the blue shift described with reference to FIGS. 14a, 14b, and 14c is also observed in the functional groups of ANF, but the degree of blue shift is significantly greater in the functional groups of PEI, as shown in FIGS. 14a, 14b, and 14c.

[0185] The results shown in Figures 14a, 14b, 14c, 15a, and 15b indicate that PEI has a higher Li content in the electrolyte than ANF in the ANF / PEI composite films. + and PF6 - This can be seen as meaning that it has a greater affinity for ions.

[0186]

[0187] Figures 16a and 16b are Li 1s and F 1s XPS graphs of the ANF / PEI composite films according to Manufacturing Examples 1 to 3, the ANF film according to Comparative Example 1, the PEI film according to Comparative Example 2, and Celgard 2400 (Comparative Example 3), respectively. Figure 17 is a graph showing the atomic ratio of Li and F obtained from the results of Figure 16. This evaluation was performed by immersing the samples in an electrolyte containing 1 M LiPF6 salt in a mixed solvent of EC:DEC:DMC (volume ratio of 1:1:1) for 30 minutes, washing them with the mixed solvent, and then drying them.

[0188] Referring to FIGS. 16a, 16b, and 17, as the PEI content was gradually increased from the pure ANF film according to Comparative Example 1 to Preparation Examples 1 to 3, a gradual increase in peak intensity was observed for both Li 1s and F 1s. Specifically, the atomic ratio of Li in the ANF / PEI composite film according to Preparation Example 3 increased from 1.13% to 3.52%, and the atomic ratio of F increased from 0.11% to 1.38%, respectively, compared to the pure ANF film according to Comparative Example 1. In particular, the ANF / PEI composite film according to Preparation Example 3 exhibited the highest atomic ratios for both Li and F. This result appears to be because the ANF / PEI composite film according to Preparation Example 3 has a larger surface area than the other samples due to the formation of an undulated PEI coating layer on the three-dimensionally interconnected ANF nanofibrillar framework.

[0189]

[0190] Manufacturing example of secondary battery (Li / Li symmetric cell)

[0191] CR2032 coin cells were assembled as lithium secondary batteries in an argon atmosphere glove box. Specifically, lithium foil was used for both the positive and negative electrodes, 100 μl of a solution containing 1 M LiPF6 salt dissolved in a mixed solvent of EC:DEC:DMC = 1:1:1 was used as the electrolyte, and any one of the membranes of Manufacturing Examples 1 to 6 and Comparative Examples 1 to 2 or the commercialized polypropylene membrane (Celgard 2400) of Comparative Example 3 was used as the separator.

[0192]

[0193] Manufacturing example of secondary battery (LFP / Li full cell)

[0194] An LFP slurry containing LiFePO4 (hereinafter referred to as LFP), carbon black, and PVDF in a mass ratio of 8:1:1 in NMP was stirred at 80°C for 24 h and then bar-coated on carbon-coated aluminum foil. The LFP-coated aluminum foil was completely dried at 120°C for 2 days in a vacuum oven to completely remove any residual NMP or moisture. The LFP electrode was then cut into disks with a diameter of 12 mm. The mass of the LFP electrode used in the rate performance and cycle performance tests was 6-7 mg cm -2 Secondary batteries were manufactured in the same manner as the Li / Li symmetric cell, except that the LFP electrode was placed as the positive electrode and lithium foil was placed as the negative electrode.

[0195] Figure 18 shows a Li / Li symmetric cell using one of the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, the PEI membrane according to Comparative Example 2, and Celgard 2400 (Comparative Example 3) as a separator, at 1 mAh·cm. -2 Under the cycle capacity condition, the current density is 0.5 mA·cm -2 at 10 mA·cm -2 After increasing to 0.5 mA cm again -2 This is a graph showing the results of constant current cycling with reduced current.

[0196] Referring to Figure 18, the current density is from 0.5 to 10 mA cm -2 When the current density increased to 0.5 mA cm, the overpotential of the polarized voltage profile increased gradually in a stepwise manner for all samples. -2 A relatively flat and stable voltage profile was observed with a slight decrease in overvoltage when the voltage was reduced to , which may be due to the formation of a stable SEI layer for the given test conditions.

[0197]

[0198] FIG. 19a, FIG. 19b, FIG. 19c, and FIG. 19d are Li / Li symmetric cells using one of the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, the PEI membrane according to Comparative Example 2, and Celgard 2400 (Comparative Example 3) as a separator, respectively, at a current density of 0.5 mA cm. -2 and cycle capacity of 0.5 mAh cm -2 , current density 5 mA·cm -2 and cycle capacity of 0.5 mAh·cm -2 , current density 10 mA·cm -2 and cycle capacity of 1 mAh·cm -2 , current density 10 mA·cm -2 and cycle capacity of 10 mAh·cm -2 These are graphs showing the results of constant current cycling.

[0199] Referring to Figures 19a, 19b, 19c, and 19d, low current density and capacity (0.5 mA cm) for Li / Li symmetric cells -2 , 0.5 mAh·cm -2 ) to high current density and capacity (10 mA·cm -2 , 10 mAh·cm -2 ) as a result of cycling, it was confirmed that when the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3 were used as a separator, it operated without an increase in overvoltage due to the formation of dendrites for up to 500 cycles under all current density and capacity conditions. On the other hand, in the case of Celgard 2400 (Comparative Example 3), it was confirmed that an increase in overvoltage due to the formation of dendrites and a low lifespan were shown in all experiments, and when the PEI membrane according to Comparative Example 2 was used as a separator, it was confirmed that as the current density and capacity increased, the number of cycles in which a short circuit occurred decreased, resulting in a decrease in the lifespan.

[0200]

[0201] Figure 20 shows a Li / Li symmetric cell using any one of the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, the PEI membrane according to Comparative Example 2, and Celgard 2400 (Comparative Example 3) as a separator at a current density of 10 mA cm. -2 and cycle capacity 1 mAh·cm -2 The images, surface FE-SEM images, and cross-sectional FE-SEM images of the Li electrode surface obtained by disassembling the cell after 1500 cycles of constant current cycling under the conditions of .

[0202] Referring to FIG. 20, when the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3 and the ANF membrane according to Comparative Example 1 were applied as separators, the Li electrodes had a thickness of about 302 μm without any noticeable features and also exhibited a metallic luster surface (a, b, c, d). Specifically, they were almost identical to fresh Li metal and exhibited a relatively flat surface with coalesced particles. This is presumed to be due to the layered merging of nucleated Li islands during deposition on the Li metal electrode. In contrast, the Li / Li symmetric cell applying Celgard 2400 as a separator failed after 119 cycles, and the obtained Li electrode exhibited a black surface composed of whiskers and tree-like dendrites with a significantly increased thickness of 642 μm (e). This morphology indicates the repetitive and continuous growth of Li dendrites with the formation of a new SEI layer after the new Li metal surface is exposed to the electrolyte by cracks in the SEI layer as the SEI layer becomes unstable with each cycle. The Li / Li symmetric cell applying the PEI film according to Comparative Example 2 as a separator failed after 870 cycles, and the resulting Li electrode exhibited a rough planar surface morphology with irregular protrusions and blunt tips of hundreds of nanometers to several micrometers (f), which is similar to the pore size of the PEI separator. It was assumed that this caused a hard short because the height change for the protruding part of the Li deposit was sufficient (>30 μm) to penetrate the separator.

[0203]

[0204] Figure 21 shows a Li / Li symmetric cell using any one of the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF membrane according to Comparative Example 1, the PEI membrane according to Comparative Example 2, and Celgard 2400 (Comparative Example 3) as a separator at a current density of 10 mA cm.-2 and cycle capacity 1 mAh·cm -2 This is a graph showing the F atomic content ratio obtained by XPS analysis of the Li electrode surface (etching time 0 s) obtained by disassembling the cell after constant current cycling for 1500 cycles under the conditions of .

[0205] Referring to Figure 21, the F atom ratio on the Li electrode surface gradually increased as the PEI content increased in the order of the ANF film according to Comparative Example 1, the ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, and the PEI film according to Comparative Example 2. This result indicates that, as previously discussed, PEI is a Li + and PF6 - This supports the idea that the electrostatic affinity for ions plays an important role in the formation of a stable SEI.

[0206]

[0207] Figures 22a, 22b, and 22c show Li / Li symmetrical cells using one of the ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF film according to Comparative Example 1, the PEI film according to Comparative Example 2, and Celgard 2400 (Comparative Example 3) as a separator at a current density of 10 mA cm. -2 and cycle capacity 1 mAh·cm -2 These are impedance graphs obtained after operation for 5 cycles, 5 cycles, and 50 cycles under the conditions of .

[0208] Referring to Figures 22a, 22b, and 22c, while Rb did not show any noticeable change, a significant decrease in Ri was observed, which may be attributed to the formation of a stable SEI layer during cycling. In the ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3 in which the PEI content increases in the ANF film according to Comparative Example 1, a decrease in Ri was observed after 5 cycles, and this trend became more evident after 50 cycles.

[0209] FIG. 23 is a graph showing the charge / discharge results in a Li / LFP full cell using one of the ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the ANF film according to Comparative Example 1, the PEI film according to Comparative Example 2, and Celgard 2400 as a separator, with the charge / discharge rate increased from 1C to 30C and then decreased to 1C.

[0210] Referring to Figure 23, the C-rate is 1C (1.2 mA·cm -2 ) at 30C (35.7mA·cm -2 ) and then decreased to 1C, the rate performance of the entire cell was tested, and the difference in capacity retention was 5C (6.0mA·cm -2 ) and this difference became more prominent as the charge / discharge rate increased. In addition, an increase in capacity retention was observed as the PEI content increased from the ANF film according to Comparative Example 1 to the ANF / PEI composite films (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3. This capacity retention was much higher than the capacity retention of 51.5% for Celgard 2400 (Comparative Example 3). Even at 30 C, the LFP / Li cell with the AP3 separator (Manufacturing Example 3) had a capacity of 38.3 mAh g, which is 28.1% of the initial specific capacity. -1 The LFP / Li cells showed excellent capacity retention at a specific capacity of 1C. After the charge / discharge rate was reduced again to 1C, most of the LFP / Li cells maintained their initial specific capacity.

[0211]

[0212] FIG. 24 is a graph of discharge capacity and coulombic efficiency after 500 cycles at a charge / discharge rate of 10 C in a Li / LFP full cell using an ANF / PEI composite membrane (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, an ANF membrane according to Comparative Example 1, a PEI membrane according to Comparative Example 2, and any one of Celgard 2400 as a separator.

[0213] Referring to FIG. 24, after 500 cycles, the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3 exhibited excellent capacity retention compared to the Celgard 2400 sample (Comparative Example 3). As the PEI content increased from the ANF membrane according to Comparative Example 1 to the ANF / PEI composite membranes (AP1, AP2, AP3) according to Manufacturing Examples 1 to 3, the capacity retention gradually increased. For example, the LFP / Li battery with the AP3 (Manufacturing Example 3) separator exhibited a capacity retention of 74.3% (from 90.7 to 67.4 mAh g -1 ) showed high capacity retention, while LFP / Li batteries with ANF (Comparative Example 1) and Celgard 2400 (Comparative Example 3) separators showed 36.9% (from 82.2 to 30.4 mAh·g), respectively. -1 ) and 38.9% (84.4 to 32.9 mAh·g -1 ) showed a reduced capacity retention rate. Considering that this result was achieved without electrolyte additives (e.g., fluoroethylene carbonate or vinylene carbonate), the cycling performance can be said to be comparable to the highest values ​​reported in the literature to date.

[0214] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. A polyaramide nanofibril skeleton defined by a plurality of irregular pores; and A polyetherimide / aramid nanofibril composite porous membrane comprising a plurality of polyetherimide particles positioned on the polyaramid nanofibril skeleton.

2. In paragraph 1, A polyetherimide / aramid nanofibril composite porous membrane having a polyaramide nanofibril skeleton having a diameter in the nanometer size.

3. In paragraph 1, The above-mentioned public is a polyetherimide / aramid nanofibril composite porous membrane having a diameter of nanometer size.

4. In paragraph 1, A polyetherimide / aramid nanofibril composite porous membrane in which the above polyetherimide particles are arranged separately from each other.

5. In paragraph 1, A polyetherimide / aramid nanofibril composite porous membrane, wherein the above polyetherimide particles are combined on the surface of the polyaramid nanofibril skeleton to form a wavy polyetherimide sheath.

6. In paragraph 1, The above membrane is a polyetherimide / aramid nanofibril composite porous membrane having a porosity of 60 to 99%.

7. Step of preparing a polyetherimide / aramid nanoseed mixture (PEI / Aramid nanoseed mixture); A step of obtaining a polyetherimide / aramid nanoseed mixture layer using the above polyetherimide / aramid nanoseed mixture; A step of immersing the polyetherimide / aramid nanoseed mixture layer in an alcohol-containing protic solvent and performing a first solvent exchange to form a polyetherimide / aramid nanofibril composite alcohol gel film by self-assembly; A step of immersing the polyetherimide / aramid nanofibril composite alcohol gel film in water and performing a second solvent exchange, specifically, exchanging the alcohol-containing protic solvent with water, to form a polyetherimide / aramid nanofibril composite hydrogel film; and A method for manufacturing a polyetherimide / aramid nanofibril composite porous membrane, comprising the step of forming a polyetherimide / aramid nanofibril composite porous membrane by freeze-drying the above polyetherimide / aramid nanofibril composite hydrogel membrane.

8. In paragraph 7, A method for producing a polyetherimide / aramid nanofibril composite porous membrane, wherein the above polyetherimide / aramid nanoseed mixture is produced by mixing an aramid nanoseed dispersion and a polyetherimide solution.

9. In paragraph 8, A method for producing a polyetherimide / aramid nanofibril composite porous membrane, wherein the above aramid nanoseed dispersion is obtained by stirring aramid microfibers in a first organic solvent containing a base.

10. In paragraph 8, A method for producing a polyetherimide / aramid nanofibril composite porous membrane, wherein the above polyetherimide solution is obtained by solvating polyetherimide in a second organic solvent.

11. In paragraph 7, A method for producing a polyetherimide / aramid nanofibril composite porous film, wherein the polyetherimide and the polyetherimide are contained in an amount of 50 to 85 wt% when the total weight of the aramid nanoseeds and the polyetherimide is 100 in the above polyetherimide / aramid nanoseed mixture.

12. In paragraph 7, A method for producing a polyetherimide / aramid nanofibril composite porous film, wherein the polyetherimide and the polyetherimide are contained in an amount of 70 to 77 wt% when the total weight of the aramid nanoseed and the polyetherimide is 100 in the above polyetherimide / aramid nanoseed mixture.

13. Bipolar; cathode; and A secondary battery comprising a polyetherimide / aramid nanofibril composite porous film according to any one of claims 1 to 6 as a separator interposed between the positive electrode and the negative electrode.

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