Coating composition for secondary battery separator, secondary battery separator and secondary battery using the same

Abstract

The present invention relates to a composition for coating a secondary battery separator that can suppress the formation of metal dendrites in a secondary battery, particularly a sodium secondary battery, and thereby improve the durability of the battery, a secondary battery separator using the same, and a secondary battery.

Description

Technology Field

[0001] The present invention relates to a composition for coating a secondary battery separator, a secondary battery separator using the same, and a secondary battery. Specifically, it relates to a composition for coating a secondary battery separator that can suppress the formation of metal dendrites and thereby improve the durability of the battery by coating the secondary battery separator with a bottle-shaped polymer, a secondary battery separator using the same, and a secondary battery. Background Technology

[0002] In response to global demands for carbon neutrality, the use of medium- and large-sized rechargeable batteries, such as those in electric vehicles and energy storage systems, is increasing. Lithium-ion batteries, which currently account for a large share of the rechargeable battery market, generally use graphite with a layered structure as the anode. However, because graphite has a limited capacity for storing lithium ions, continuous attempts are being made to apply lithium metal, which has a very high theoretical capacity, as the anode.

[0003] Separators for secondary batteries serve to physically separate the contact between the positive and negative electrodes to prevent short circuits, while simultaneously acting as ion transport channels that move ions from the electrolyte through the pores within the separator. Therefore, they must have excellent mechanical strength and high ion conductivity. Currently, most separators for lithium-ion batteries use polyolefin-based polyethylene and polypropylene as the base material, and pores are formed by processing the polymers through a dry or wet stretching process.

[0004] However, as lithium metal has very limited crustal reserves and is predicted to be depleted around 2040, coupled with its very high unit cost, there is a surging demand for next-generation rechargeable battery systems capable of overcoming the performance limitations of existing lithium-ion batteries. Consequently, the size of the related market is growing significantly. While sodium metal is being proposed as a next-generation alternative to lithium metal, sodium metal batteries suffer from the disadvantage of lacking optimized separator materials. Specifically, although there have been attempts to directly apply polyolefin polymers used in lithium-ion batteries to sodium batteries, polyolefin-based separators exhibit poor wettability with sodium electrolytes and have pores that are too small to conduct sodium ions efficiently. Glass fiber (GF) membranes have been adopted as separators for sodium-ion batteries due to their excellent affinity for sodium electrolytes and high ion conductivity; however, when sodium metal is used as the anode, the pores of the glass fiber membrane are too large and non-uniform, which prevents the suppression of sodium dendrites generated during charging and discharging, leading to short circuits. In addition, during this process, an uneven organic-inorganic composite film was formed on the surface of the sodium anode, resulting in a decrease in the battery's lifespan and capacity.

[0005] Therefore, in the case of sodium metal batteries, since optimized separator materials have not been secured to date, entry into the relevant market is expected to be very easy once technological maturity is confirmed. Furthermore, as there is a complete lack of research systematically elucidating the mechanism by which the structure and functionality of polymers included in the separator coating composition inhibit sodium dendrite metal growth, the development of core technologies is currently necessary. The problem to be solved

[0006] The technical problem that the present invention aims to solve is to provide a composition for coating a secondary battery separator capable of preventing the formation of metal dendrites by chelating metal ions with a bottle-type polymer, a method for manufacturing the same, a secondary battery separator using the same, and a secondary battery including the same.

[0007] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0008] One embodiment of the present invention provides a composition for coating a secondary battery separator comprising a copolymer comprising a first block represented by the following chemical formula 1 and a second block represented by the following chemical formula 2:

[0009] [Chemical Formula 1]

[0010]

[0011] [Chemical Formula 2]

[0012]

[0013] In the above Chemical Formula 1, the repeating units M1 and M2 are each independently selected from the following Chemical Formula 3, and

[0014] [Chemical Formula 3]

[0015]

[0016] In the above chemical formulas 1 to 3,

[0017] R1 is independently hydrogen or a methyl group, and A is an oxygen atom or a methylene group (-CH2-), and

[0018] If A is an oxygen atom, R2 is independently a hydrogen or methyl group, respectively, and

[0019] Where A is a methylene group, R2 is independently a glycidyl group, a carboxylic acid group, a substituted or unsubstituted amine group, a substituted or unsubstituted ester group having 2 to 20 carbon atoms; and a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms.

[0020] R3 is each independently a halogen group, a hydroxyl group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, a substituted or unsubstituted ester group having 2 to 20 carbon atoms; and a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms.

[0021] m and n are integers from 5 to 100, respectively, and

[0022] x, y, and z are each integers from 1 to 100, and

[0023] a is an integer from 0 to 10, and

[0024] q is an integer from 0 to 5.

[0025] Another embodiment of the present invention provides a secondary battery separator comprising a fiber substrate and a coating layer located on at least one surface of the fiber substrate, wherein the coating layer is formed from a composition for coating a secondary battery separator according to one embodiment of the present invention.

[0026] Another embodiment of the present invention provides a secondary battery comprising a secondary battery separator according to one embodiment of the present invention. Effects of the invention

[0027] According to one embodiment of the present invention, a composition for coating a secondary battery separator can form a coating layer that prevents the formation of metal dendrites by chelating metal cations.

[0028] According to one embodiment of the present invention, a secondary battery separator capable of preventing the formation of metal dendrites can be provided.

[0029] According to one embodiment of the present invention, a secondary battery capable of preventing the formation of metal dendrites can be provided.

[0030] The effects of the present invention are not limited to those described above, and unmentioned effects will be clearly understood by those skilled in the art from the present specification and the accompanying drawings. Brief explanation of the drawing

[0031] FIG. 1 is a diagram briefly illustrating the process of coating a glass fiber separator with the composition for coating a secondary battery separator of the present invention. FIG. 2 is for the compounds of Formula 1-1-1(a), Formula 2-1-1(b), and Formula 3-1(c) synthesized in Example 1 1 Shows the H-NMR spectrum. Figure 3 is a DSC thermogram of the compounds of formula 1-1-1 (PPG), formula 2-1-1 (PSt), and formula 3-1 (BBP) synthesized in Example 1, and the composition (NaBBP) mixed with NaTFSI. Figure 4 is an SEM image of a conventional glass fiber separator and a glass fiber separator coated with the composition prepared in Example 1 of the present invention. Figure 5 is a graph showing the porosity and pore diameter measured by the mercury pore method for a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention. Figure 6 is a graph showing the weight of the coating layer by measuring the conventional glass fiber separator and the glass fiber separator coated with the composition of Example 1 of the present invention by thermogravimetric analysis. Figure 7 is a graph showing the FT-IR analysis of a conventional glass fiber separator, a glass fiber separator coated with the composition of Example 1 of the present invention, and the composition of Example 1 of the present invention. Figure 8 is a graph analyzing the ion conductivity, electrolyte absorption, and thickness of a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention. FIG. 9 is a graph of the capacity-voltage curve of a Na / Cu coin cell manufactured by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention, respectively. FIG. 10 is an SEM image of the surface (a, c) and cross-section (b, d) of a Na metal electrode after one cycle of operation of a Na / Cu coin cell prepared by introducing a conventional glass fiber separator (a, b) and a glass fiber separator (c, d) coated with the composition of Example 1, respectively. FIG. 11 is a graph analyzing the Coulomb efficiency of Na / Cu coin cells manufactured by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention, respectively, and driving them for 0 to 100 cycles. FIG. 12 is a graph analyzing the voltage of Na / Na coin cells manufactured by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention, respectively, and operating them for 0 to 500 hours. Figure 13 is a photograph of the Na metal surface taken with an SEM after operating a Na / Na coin cell prepared by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention, respectively. FIG. 14 is a graph analyzing the discharge capacity and Coulomb efficiency of Na / PBA coin cells manufactured by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention, respectively, during operation for 0 to 1500 hours. Specific details for implementing the invention

[0032] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0033] Throughout this specification, when a component is described as being located "on" another component, this includes not only cases where a component is in contact with another component, but also cases where another component exists between the two components.

[0034] Throughout the entire specification, the unit "parts by weight" may refer to the ratio of weight between each component.

[0035] Throughout this specification, "(meth)acrylate" is used to refer collectively to acrylates and methacrylates.

[0036] Throughout this specification, "A and / or B" means "A and B, or A or B".

[0037] Throughout this specification, the term "monomer unit" may refer to a form in which a monomer is reacted within a polymer, and specifically, may refer to a form in which the monomer undergoes a polymerization reaction to form the backbone of the polymer, for example, a main chain or a side chain.

[0038] Throughout this specification, the “weight-average molecular weight” and “number-average molecular weight” of a compound can be calculated using the molecular weight and molecular weight distribution of the compound. Specifically, a sample with a compound concentration of 1 wt% is prepared by placing tetrahydrofuran (THF) and the compound in a 1 ml glass vial. After filtering the standard sample (polystyrene) and the sample through a filter (pore size 0.45 μm), the sample is injected into a GPC injector, and the molecular weight and molecular weight distribution of the compound can be obtained by comparing the elution time of the sample with the calibration curve of the standard sample. At this time, an Infinity II 1260 (Agilient) can be used as the measuring instrument, and the flow rate can be set to 1.00 mL / min and the column temperature to 40.0 °C.

[0039] Throughout the entire specification, the “glass transition temperature (Tg)” can be measured using Differential Scanning Analysis (DSC). Specifically, using a Differential Scanning Calorimeter (DSC-STAR3, METTLER TOLEDO), the sample is heated at a rate of 5 ℃ / min within a temperature range of -60 ℃ to 150 ℃, and two cycles of the experiment are conducted in the above range. The glass transition temperature can then be obtained by measuring the midpoint of the DSC curve created at the point where the amount of heat change is present.

[0040] Throughout this specification, metal salt may refer to a state in which metal ions are chelated.

[0041] The present invention will be described in more detail below.

[0042] Composition for coating secondary battery separators

[0043] One embodiment of the present invention provides a composition for coating a secondary battery separator comprising a copolymer comprising a first block represented by the following chemical formula 1 and a second block represented by the following chemical formula 2:

[0044] [Chemical Formula 1]

[0045]

[0046] [Chemical Formula 2]

[0047]

[0048] In the above Chemical Formula 1, the repeating units M1 and M2 are each independently selected from the following Chemical Formula 3, and

[0049] [Chemical Formula 3]

[0050]

[0051] In the above chemical formulas 1 to 3,

[0052] R1 is independently a hydrogen or a methyl group, and

[0053] A is an oxygen atom or a methylene group (-CH2-), and

[0054] If A is an oxygen atom, R2 is independently a hydrogen or methyl group, respectively, and

[0055] Where A is a methylene group, R2 is independently a glycidyl group, a carboxylic acid group, a substituted or unsubstituted amine group, a substituted or unsubstituted ester group having 2 to 20 carbon atoms; and a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms.

[0056] R3 is each independently a halogen group, a hydroxyl group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, a substituted or unsubstituted ester group having 2 to 20 carbon atoms; and a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms.

[0057] m and n are integers from 5 to 100, respectively, and

[0058] x, y, and z are each integers from 1 to 100, and

[0059] a is an integer from 0 to 10, and

[0060] q is an integer from 0 to 5.

[0061] Specifically, the copolymer is a block copolymer having a backbone polymerized from cyclic olefin monomers such as norbornene, and comprising a first block containing repeating units M1 and M2 and a second block containing polystyrene in its side chain.

[0062] According to one embodiment of the present invention, microphase separation may occur in the copolymer, thereby improving the mechanical strength of a separation membrane comprising a coating layer formed using the composition.

[0063] A composition for coating a secondary battery separator according to one embodiment of the present invention comprises the copolymer, thereby allowing metal cations between electrodes, particularly alkali metal cations, e.g., Na₂⁻, in a secondary battery, particularly a sodium secondary battery. + The flux can be controlled, thereby enabling uniform electrodeposition of metal (Na) and suppressing the growth of dendrites. More specifically, the non-covalent electron pairs of oxygen or nitrogen atoms included in the repeating units M1 and M2 form coordinate bonds with metal cations through dipole-dipole interactions, thereby enabling doping of metal cations and forming complexes similar to crown ethers.

[0064] According to one embodiment of the present invention, the molar ratio m:n of the first block and the second block may be 70:30 to 90:10. More specifically, the ratio of m:n may be 70:30 to 85:15, 70:30 to 82:18, 75:25 to 90:10, 75:25 to 85:15, 75:25 to 82:18, 80:20 to 90:10, 80:20 to 85:15, or 80:20 to 82:18. By satisfying the above-described range, an alkali metal cation, e.g. Na, in a secondary battery comprising a separator having a coating layer formed using the composition + The flux can be controlled, and the growth of dendrites can be suppressed to improve the durability and efficiency of the battery.

[0065] According to one embodiment of the present invention, m may be an integer from 30 to 70, and n may be an integer from 5 to 15.

[0066] According to one embodiment of the present invention, q in Formula 2 may be 0. When q is 0, the phenyl group of the polystyrene repeating unit included in Formula 2 is not substituted.

[0067] According to one embodiment of the present invention, the number average molecular weight (M) of the copolymer n The number average molecular weight of the copolymer may be 100 kDa to 10,000 kDa. More specifically, the number average molecular weight of the copolymer may be 100 kDa to 5,000 kDa, 100 kDa to 3,000 kDa, 100 kDa to 1,000 kDa, 100 kDa to 500 kDa, 200 kDa to 3,000 kDa, 200 kDa to 2,000 kDa, 200 kDa to 1,000 kDa, 200 kDa to 500 kDa, or 200 kDa to 400 kDa.

[0068] Preferably, the first block may be represented by the following chemical formula 4.

[0069] [Chemical Formula 4]

[0070]

[0071] In the above chemical formula 4,

[0072] R1 is independently a hydrogen or a methyl group, and

[0073] m is an integer from 5 to 100, and

[0074] x and y are integers from 1 to 100, respectively, and

[0075] a1 is an integer from 3 to 10, and a2 is an integer from 0 to 10.

[0076] When the first block is represented by the above chemical formula 4, the dendrite growth inhibition effect of the composition for coating a secondary battery separator can be further enhanced, and the durability of the separator including the coating layer formed using the same can be improved. Specifically, a metal cation can be doped into the oxygen of the ethylene glycol repeating unit included in the above chemical formula 4, and the glycidyl group can be cross-linked with the hydroxyl group present on the surface of the fiber substrate, thereby improving the durability of the separator.

[0077] According to one embodiment of the present invention, in the above formula 4, x may be 10 to 30 and y may be 1 to 10.

[0078] A composition for coating a secondary battery separator according to one embodiment of the present invention may further include a metal salt. The cation of the metal salt may be a cation of one or more metals selected from lithium, sodium, magnesium, potassium, calcium, aluminum, manganese, iron, cobalt, nickel, copper, gallium, indium, niobium, zirconium, strontium, yttrium, tungsten, hafnium, tantalum, rhenium, molybdenum, and ruthenium.

[0079] Preferably, the cation of the metal salt may be a cation of one or more alkali metals selected from lithium, sodium, and potassium. More preferably, the cation of the metal salt is Na + It could be.

[0080] According to one embodiment of the present invention, the anion of the metal salt may be one or more selected from TFSI (bis(trifluoromethylsulfonyl)amide anion), PF6, ClO4, BF4, and AsF6.

[0081] According to one embodiment of the present invention, the cation of the metal salt may form a coordinate bond with a lone pair of electrons of an oxygen atom or a nitrogen atom included in the repeating units M1 and M2. By forming the coordinate bond, the cation of the metal salt may be doped into the first block, and by being doped, an alkali metal cation, e.g. Na₂, in a secondary battery using a separator that forms a coating layer using the composition, may be doped. + The flux can be controlled, and the growth of dendrites can be suppressed to improve the durability and efficiency of the battery.

[0082] According to one embodiment of the present invention, the molar ratio of the cation of the metal salt to the total moles of oxygen atoms and nitrogen atoms included in the first block may be 0.01 to 0.7, 0.1 to 0.7, 0.1 to 0.5, or 0.1 to 0.3.

[0083] According to one embodiment of the present invention, when the first block is represented by the formula 4, the molar ratio of the cation of the metal salt to the total mole of ethylene oxide repeating units included in the first block may be 0.01 to 0.7, 0.1 to 0.7, 0.1 to 0.5, or 0.1 to 0.3.

[0084] According to one embodiment of the present invention, the composition for coating a secondary battery separator may further include a solvent as needed. The solvent may be an organic solvent, and for example, tetrahydrofuran (THF) may be used as a solvent.

[0085] Method for manufacturing the copolymer of the present invention

[0086] A copolymer comprising a first block represented by the above chemical formula 1 and a second block represented by the above chemical formula 2 can be obtained by synthesizing the first block and the second block respectively and then polymerizing them.

[0087] According to one embodiment of the present invention, the first block may be obtained by the steps of: synthesizing a macromonomer of Formula 1-1 by reacting a compound of Formula 1A with a compound of Formula 1B and / or a compound of Formula 1C; and polymerizing the macromonomer represented by Formula 1-1 in the presence of a catalyst.

[0088] According to one embodiment of the present invention, the second block can be obtained by the steps of: synthesizing a macromonomer of Formula 2-1 by reacting a compound of Formula 1A with a compound of Formula 1D; and polymerizing the macromonomer represented by Formula 2-1 in the presence of a catalyst.

[0089] According to one embodiment of the present invention, the first block and the second block can be polymerized in the presence of a catalyst to form a block copolymer.

[0090] [Chemical Formula 1A]

[0091]

[0092] [Chemical Formula 1B]

[0093]

[0094] [Chemical Formula 1C]

[0095]

[0096] [Chemical Formula 1-1]

[0097]

[0098] [Chemical Formula 1D]

[0099]

[0100] [Chemical Formula 2-1]

[0101]

[0102] In the above chemical formulas, X is a fluorine group, a chlorine group, a bromine group, or an iodine group; R1 is independently a hydrogen or a methyl group; R2 is independently a glycidyl group, a carboxylic acid group, a substituted or unsubstituted amine group, a substituted or unsubstituted ester group having 2 to 20 carbon atoms; a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms; and R3 is independently a halogen group, a hydroxyl group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, a substituted or unsubstituted ester group having 2 to 20 carbon atoms; It is a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, and x, y, and z are each integers from 1 to 100, a1 is an integer from 3 to 10, a2 is an integer from 0 to 10, and q is an integer from 0 to 5.

[0103] According to one embodiment of the present invention, in the step of polymerizing the macromonomer of Formula 1-1 and the macromonomer of Formula 2-1 in the presence of a catalyst, the reaction temperature may be 10°C to 60°C and the reaction time may be 1 hour to 10 hours.

[0104] According to one embodiment of the present invention, in the step of polymerizing the macromonomer of Formula 1-1 and the macromonomer of Formula 2-1 in the presence of a catalyst, the catalyst is a Grubbs catalyst. ® It may include ).

[0105] According to one embodiment of the present invention, after polymerizing the macromonomer of Formula 1-1 and the macromonomer of Formula 2-1 in the presence of a catalyst and synthesizing a copolymer, a step of adding a metal salt may be further performed. The metal salt may be described in reference to the foregoing.

[0106] Secondary battery separator and secondary battery including the same

[0107] Another embodiment of the present invention provides a secondary battery separator comprising a fiber substrate and a coating layer located on at least one surface of the fiber substrate, wherein the coating layer is formed from a composition for coating a secondary battery separator according to one embodiment of the present invention.

[0108] According to one embodiment of the present invention, the porosity of the secondary battery separator may be 60 to 90%, and the median pore diameter may be 2.0 to 4.0 μm. By satisfying the above-described ranges for the porosity and median pore diameter of the secondary battery separator, a uniform porous structure is provided, and the efficiency of the secondary battery including the same can be improved.

[0109] According to one embodiment of the present invention, the coating layer may be included in an amount of 20 to 50 parts by weight relative to 100 parts by weight of the secondary battery separator.

[0110] According to one embodiment of the present invention, the thickness of the coating layer may be 200 to 300 μm.

[0111] According to one embodiment of the present invention, the fiber substrate may be used without special limitations as long as it is used in the field of secondary battery separators, and may include, for example, electrospun polymer fibers, glass fibers, cellulose fibers, or carbon fibers.

[0112] Another embodiment of the present invention provides a secondary battery comprising a secondary battery separator according to one embodiment of the present invention.

[0113] A secondary battery according to one embodiment of the present invention may be a sodium secondary battery.

[0114] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain the present invention to those with average knowledge in the art.

[0115] All reagents and materials not otherwise mentioned below were purchased from Sigma Aldrich and used as is.

[0116] Example 1

[0117] (1) Synthesis of PPG (poly(PEGMA-co-GMA)) macromonomer

[0118]

[0119] Oxygen in the solution was removed by performing a freeze-pump-thaw cycle 3 times on a solution prepared by dissolving 0.32 g of N-(2-bromopropanoylethyl)-exo,cis-2,3-dicarboximide (NI-Br), 5.0 g of poly(ethylene glycol) methyl ether methacrylate (PEGMA), 0.16 g of glycidyl methacrylate (GMA), and 0.13 g of CuBr as a catalyst in 10 mL of dimethylformamide (DMF). 0.31 g of PMDETA (N, N, N`, N``, N`-pentamethyldiethylenetriamine) was additionally added to the solution as a ligand for ATRP polymerization, and oxygen in the solution was removed through three freeze-pump-thaw cycles. The solution was stirred at 70 °C for 10 minutes, then diluted with chloroform solvent and passed through a basic alumina column (Sigma-Aldrich) to remove the CuBr catalyst. Subsequently, the solution was precipitated in hexane solvent to remove unreacted materials and dried to obtain the PPG (poly(PEGMA-co-GMA)) macromonomer compound represented by chemical formula 1-1-1.

[0120] (2) Synthesis of PSt (polystyrene) macromonomers

[0121]

[0122] Oxygen in the solution was removed by performing a freeze-pump-thaw cycle 3 times on a solution in which 0.086 g (0.24 mmol) of N-(2-bromopropanoylethyl)-exo,cis-2,3-dicarboximide (NI-Br), 5.0 g (48 mmol) of styrene, and 0.034 g (0.24 mmol) of CuBr as a catalyst were dissolved in 5 mL of dimethylformamide (DMF). 0.083 g of PMDETA (N, N, N`, N``, N`-pentamethyldiethylenetriamine) was additionally added to the solution as a ligand for ATRP polymerization, and oxygen in the solution was removed through three freeze-pump-thaw cycles. The solution was stirred at 90 °C for 3.5 hours, then diluted with chloroform solvent and passed through a basic alumina column to remove the CuBr catalyst. Subsequently, the unreacted materials were removed by precipitation in hexane solvent, and the solution was dried to obtain the PSt (polystyrene) macromonomer compound represented by Chemical Formula 2-1-1.

[0123] (3) Bottle brush polymer (BBP) polymerization

[0124]

[0125] 1.0 g of the compound represented by the chemical formula 1-1-1 obtained above was dissolved in 4.2 mL of methylene chloride, and Grubbs Catalyst® 3rd Generation (G3, M300, Sigma Aldrich) was added and the polymerization reaction was carried out by stirring at 30 ℃ for 2 hours.

[0126] Then, 0.67 mL of a solution containing the compound represented by Chemical Formula 2-1-1 obtained earlier at a concentration of 0.05 M was added, and the polymerization reaction was carried out by stirring for another 2 hours. To terminate the reaction, 0.1 mL of ethyl vinyl ether was added, and the mixture was purified by precipitating it three times in diethyl ether to obtain a bottle brush-shaped polymer compound represented by Chemical Formula 3-1.

[0127] A composition for coating a secondary battery separator was obtained by dissolving 0.080 g of the compound of chemical formula 3-1 obtained above and 0.036 g of sodium trifluoromethanesulfonimide (NaTFSI) in 1.0 mL of anhydrous tetrahydrofuran (THF).

[0128] A glass fiber separator (Whatman, thickness: 260) to the above composition for coating a secondary battery separator μ m) was immersed for 2 hours. Afterward, the glass fiber separator was removed, dried for 3 hours, and then heat-treated at 120°C for 15 hours to facilitate a cross-linking reaction between the glycidyl moiety contained in Chemical Formula 3-1 and the hydroxyl groups on the surface of the glass fiber. As a result, it was confirmed that a coating layer of 260 μm was formed on the separator.

[0129] FIG. 1 is a diagram briefly illustrating the process of coating a glass fiber separator with the composition for coating a secondary battery separator of the present invention.

[0130] Experimental Example 1: Analysis of Physical Properties of the Synthesized Compound

[0131] The compounds of Formula 1-1-1, Formula 2-1-1, and Formula 3-1 synthesized in Example 1 above were analyzed for their characteristics as follows.

[0132] Specifically, 1H-NMR spectra were obtained at room temperature using an Ascend™ 400 spectrometer (400 MHz) with CDCl3 and a tetramethylsilane (TMS) reference (Sigma-Aldrich) as solvents. Number average molecular weight and dispersion (Ð) were measured by size-exclusive chromatography (SEC) using an Ultimate 3000 HPLC system (Thermo Fisher Scientific Inc., USA). HPLC-grade THF (JT Baker®) was used as the solvent.

[0133] FIG. 2 is for the compounds of Formula 1-1-1(a), Formula 2-1-1(b), and Formula 3-1(c) synthesized in Example 1 1 H-NMR spectra are shown. Table 1 below shows the number average molecular weights (M) of the compounds of Formula 1-1-1, Formula 2-1-1, and Formula 3-1 synthesized in Example 1. n ), dispersion(Ð), 1 Fraction of PPG blocks calculated from H-NMR spectrum (f PPG ), number average degree of polymerization (N sc ) and number average degree of polymerization (N of backbone) bb It represented ).

[0134] compound M n (kDa) Ð f PPG N sc N bb Chemical formula 1-1-1 5.95 1.12 - 18.1 - Chemical formula 2-1-1 5.70 1.11 - 51.3 - Chemical formula 3-1 322 1.72 0.82 - 54.5

[0135] Referring to Table 1 above, the number average molecular weight of the PSt macromonomer represented by Chemical Formula 2-1-1 was maintained at approximately 5 kDa, which is significantly lower than the entanglement molecular weight (Me) of polystyrene, which is 17 kDa. This allows for the maximization of the mobility of the polyethylene oxide (PEO) chains in the copolymer represented by Chemical Formula 3-1. The unentangled and highly mobile PEO chains promote dipole-dipole interactions with metal cations, thereby effectively controlling the flux of metal cations such as Na+ between the electrolyte and the electrode.

[0136] Experimental Example 1-2: Confirmation of Phase Separation of Synthesized Compound

[0137] To determine whether characteristic microphase separation induced by self-assembly exists in the copolymer represented by Formula 3-1 synthesized in Example 1, the glass transition temperatures were measured for Formula 1-1-1 (PPG), Formula 2-1-1 (PSt), the compound of Formula 3-1 (BBP), and the composition mixed with NaTFSI (NaBBP), respectively, synthesized in Example 1. The glass transition temperatures were measured in a nitrogen atmosphere (cooling rate: 1°C min -1 , heating rate: 10°C min -1 It was measured using differential scanning calorimetry (DSC) with a TA Instruments DSC25.

[0138] Figure 3 is a DSC thermogram of the compounds of formula 1-1-1 (PPG), formula 2-1-1 (PSt), and formula 3-1 (BBP) synthesized in Example 1, and the composition (NaBBP) mixed with NaTFSI.

[0139] Referring to Fig. 3, in the copolymer represented by Formula 3-1 (BBP) synthesized in Example 1, two Tg values ​​derived from the PPG block (-48.1°C) and the PSt block (81.3°C), respectively, exist, suggesting that microphase separation occurred in the BBP. Furthermore, the fact that the two Tg values ​​observed in the BBP do not differ significantly from the Tg values ​​of Formula 1-1-1 (PPG) and Formula 2-1-1 (PSt), respectively, indicates that chain mobility within each separated microphase is maintained. Additionally, in the composition mixed with NaTFSI, the Tg value corresponding to the PPG block increased significantly from -48.1°C to 16.7°C, whereas the Tg value corresponding to the PSt block showed a much less pronounced increase from -81.3°C to 94.7°C. This indicates that Na + This suggests that the doping is mainly present in the domain of the PPG block.

[0140] Experimental Example 2-1: Membrane-SEM

[0141] Figure 4 is a SEM image of a conventional glass fiber separator and a glass fiber separator coated with the composition prepared in Example 1 of the present invention. The scanning electron microscope (SEM) used for measurement was a Regulus 8230-Oxford EDS (Hitachi Inc., Tokyo, Japan), and the measurement was performed at an acceleration voltage of 10 kV.

[0142] Referring to Figure 4, it was confirmed that the pore size of the coated glass fiber separator was reduced compared to the pore size of the conventional glass fiber separator. This is because the thickness of the single fibers of the glass fiber increased as the composition of the present invention was coated.

[0143] Experimental Example 2-2: Measurement of Membrane Porosity and Pore Size

[0144] FIG. 5 is a graph showing the porosity and pore diameter measured by the mercury pore method for a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention. Specifically, the mercury pore method used an AutoPore IV 9500 mercury (Hg) intrusion porosity meter (Micromeritics, USA).

[0145] Referring to Fig. 5, compared to the porosity of a conventional glass fiber separator and the average pore diameter of about 3.0 μm, the porosity of the glass fiber separator coated with the composition of Example 1 was about 85% and the average pore diameter was about 2.75 μm, confirming that the porosity and average pore diameter were reduced. In particular, the median pore diameter decreased from about 5.5 μm to 3 μm before and after coating, showing a significantly larger decrease compared to the average pore diameter and porosity. This suggests that the coating composition of the present invention can provide a uniform distribution of pore size and a uniform porous structure by mainly filling relatively large pores.

[0146] Experimental Example 2-3: Measurement of the weight of the separator-coating layer

[0147] FIG. 6 is a graph analyzing the weight of the coating layer by measuring a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention using thermogravimetric analysis. Specifically, thermogravimetric analysis was performed under a nitrogen atmosphere (heating rate: 10 ℃ min -1 It was performed using TA Instruments TGA55 under ).

[0148] Referring to FIG. 6, it was confirmed that in a glass fiber separator coated with the composition of Example 1 of the present invention, the weight of the coating layer is 36 parts by weight relative to the total weight of the separator, which is 100 parts by weight.

[0149] Experimental Example 2-4: Membrane-FT-IR Measurement

[0150] FT-IR is 400 to 4000 cm⁻¹ -1 8 cm in the wavelength range -1 Transmittance was measured for each wavelength in the absorption mode of the Nicolet 6700 spectrophotometer with the resolution of .

[0151] Figure 7 is a graph showing the FT-IR analysis of a conventional glass fiber separator, a glass fiber separator coated with the composition of Example 1 of the present invention, and the composition of Example 1 of the present invention.

[0152] Referring to Fig. 7, the peak corresponding to the composition of Example 1 of the present invention is also observed in the glass fiber separator coated with the composition of Example 1 of the present invention, so it was confirmed that the composition of the present invention was well coated on the glass fiber separator.

[0153] Experimental Example 3-1: Ionic Conductivity of Separator and Electrolyte Absorption

[0154] The ionic conductivity of a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention was measured by AC impedance spectroscopy using a VMP3 multi-channel potentiometer (Biologic, France) at 30°C with an amplitude of 10 mV and a frequency range of 10 Hz to 1 MHz. Each separator was prepared by sandwiching it between two stainless steel electrodes of a 2032 coin cell. The ionic conductivity (σ) was calculated by the following Equation 1.

[0155] [Equation 1]

[0156] σ = (1 / R ) × ( d / A )

[0157] In Equation 1 above, R represents the resistance obtained from the impedance spectrum, d represents the thickness of the separator, and A represents the area of ​​the electrode.

[0158] As the electrolyte, a 1 M hexafluorophosphate (NaPF6) ethylene carbonate:propylene carbonate:diethyl carbonate (DEC) 1:1:1 vol% solution (Welcos) containing 2 wt% fluoroethylene carbonate (FEC) was used. The electrolyte absorption was measured by measuring the weight change before and after immersion in the electrolyte for 24 hours. The resulting electrolyte absorption was calculated by Equation 2 below.

[0159] [Equation 2]

[0160] Electrolyte absorption (%) = ( W wet W dry ) / W dry × 100

[0161] In the above Equation 2 W dry and W wet represents the weight before and after immersion in the electrolyte, respectively. Prior to analysis, a conventional glass fiber separator wetted with the electrolyte and a glass fiber separator coated with the composition of Example 1 of the present invention were prepared by immersing for 24 hours in 1 M NaPF6 (Welcos) containing 2 wt% FEC in EC:PC:DEC (1:1:1 vol%) in an argon-filled glove box (O2 < 0.1 ppm, H2O < 0.1 ppm).

[0162] Figure 8 is a graph analyzing the ionic conductivity, electrolyte uptake, and thickness of a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention.

[0163] Referring to FIG. 8, the glass fiber separator coated with the composition of Example 1 of the present invention did not show significant changes in ion conductivity, electrolyte absorption, and thickness compared to a conventional glass fiber separator, and in particular, the glass fiber coated with the composition of Example 1 showed 4.1 mS·cm at 30°C. -1 It showed the ionic conductivity of uncoated glass fiber (5.2 mScm). -1 It is at a similar level to ).

[0164] These results indicate that the electrochemical properties of the glass fiber separator are not significantly degraded even when coated with the composition of the present invention.

[0165] Experimental Example 3-2: Evaluation of Na Electrodeposition Behavior in Na / Cu Cells

[0166] For Na / Cu coin cells manufactured by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention between a Na metal electrode and a Cu metal electrode, 0.5 mAh / cm 2The first cycle was run under conditions of a current density and a temperature of 30°C. All coin cell components were assembled in a glove box filled with argon (O2 <0.1 ppm, H2O <0.1 ppm).

[0167] The galvanostatic cycling test for the coin cell was performed at a current density of 0.5 mA cm at 30°C. -2 , total capacity 0.5mAh cm -2 It was performed on a WBCS-3000 battery cycle system (WonATech Co., Korea). Electrochemical impedance spectroscopy (EIS) was performed on a VMP3 multi-channel potentiostat (Biologic, France) at 30°C with an amplitude of 10 mV in a frequency range of 0.1 to 100 MHz.

[0168] FIG. 9 is a graph of the capacity-voltage curve of a Na / Cu coin cell manufactured by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention, respectively.

[0169] Referring to Fig. 9, it was confirmed that a coin cell manufactured using a glass fiber separator coated with the composition of Example 1 exhibits a significantly higher capacity per unit area compared to a coin cell using a conventional glass fiber separator.

[0170] FIG. 10 is an SEM image of the surface (a, c) and cross-section (b, d) of a Na metal electrode after one cycle of operation of a Na / Cu coin cell prepared by introducing a conventional glass fiber separator (a, b) and a glass fiber separator (c, d) coated with the composition of Example 1, respectively.

[0171] Referring to FIG. 10, it can be seen that on the surface of the Na metal electrode of a coin cell manufactured using a conventional glass fiber separator, Na was electrodeposited in a very irregular shape in the first cycle (a) and many pinholes and cracks occurred in the cross-section (b), whereas on the Na metal electrode of a coin cell manufactured using a glass fiber separator coated with the composition of Example 1, Na was electrodeposited very smoothly and uniformly on both the electrode surface (c) and the cross-section (d) and no dendrites occurred.

[0172] FIG. 11 is a graph analyzing the Coulomb efficiency of Na / Cu coin cells manufactured by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention, respectively, and driving them for 0 to 100 cycles.

[0173] Referring to Fig. 11, a secondary battery manufactured using a glass fiber separator coated with the composition of the present invention maintained a Coulomb efficiency of 100%, whereas a secondary battery manufactured using a conventional glass fiber separator showed a behavior in which the Coulomb efficiency decreased rapidly after 40 cycles. Since each coin cell differs only in whether or not the separator is coated, it can be seen that the secondary battery manufactured using the coated glass fiber separator induces more stable Na electrodeposition characteristics.

[0175] Experimental Example 3-3: Evaluation of Na Electrodeposition Behavior in Na / Na Symmetric Cells

[0176] For Na / Na coin cells manufactured by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention between two Na metal electrodes, 0.5 mA / cm 2The system was operated for a total of 300 hours under current density and a temperature of 30°C, with one cycle consisting of electrodepositing Na for 1 hour and depositing it for 1 hour. All coin cell components were assembled in a glove box filled with argon (O2 < 0.1 ppm, H2O < 0.1 ppm). In the case of the Na / Na symmetric cell, since both sides were Na metal, the cycle of detaching Na from one side and electrodepositing it on the other side was continuously repeated, and the point at which a short circuit occurred in the secondary battery due to Na metal dendrites was analyzed.

[0177] FIG. 12 is a graph analyzing the voltage of Na / Na coin cells manufactured by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention, respectively, and operating them for 0 to 500 hours.

[0178] Referring to Fig. 12, in the case of a Na / Na coin cell manufactured using a conventional glass fiber separator, the voltage increased rapidly after 300 hours of operation, which can be seen as a result of dendrites penetrating the separator and causing a short circuit. On the other hand, in the case of a Na / Na coin cell manufactured using a glass fiber separator coated with the composition of the present invention, the voltage increased gradually and thick Na electrodepositories were formed, but no short circuit occurred for 500 hours, indicating that durability was improved by coating with the composition of the present invention.

[0179] Figure 13 is a SEM image of the surface of a Na metal electrode after operating Na / Na coin cells, prepared by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention, for 320 hours and 500 hours, respectively. The scanning electron microscope (SEM) used for measurement was Regulus 8230-Oxford EDS (Hitachi Inc., Tokyo, Japan), and the measurement was performed at an acceleration voltage of 10 kV.

[0180] Referring to Fig. 13, in the case of a Na / Na secondary battery manufactured using a conventional glass fiber separator, many Na electrodeposits of very irregular shape were formed on the surface of the Na metal after 320 hours, whereas in the case of a Na / Na cell manufactured using a glass fiber separator coated with the composition of the present invention, it was confirmed that the Na metal showed a smooth surface and was evenly electrodeposited.

[0181] Experimental Example 3-4: Evaluation of Na Electrodeposition Behavior in Na / PBA Cell

[0182] A Na / PBA coin cell was prepared by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention between a Na metal electrode and a PBA electrode. All components of the coin cell were assembled in a glove box filled with argon (O2 < 0.1 ppm, H2O < 0.1 ppm). Prussian blue analog (PBA, Na 2-x Fe[Fe(CN)6]) was synthesized through the widely known precipitation method.

[0183] For a Na / PBA cell, a voltage of 2.0 to 4.0 V and a current density of 10 C (1.2 A g -1 Under the conditions, electrodepositing Na for 1 hour and desorbing it for 1 hour was defined as 1 cycle, and the process was run up to 1500 cycles.

[0184] FIG. 14 is a graph analyzing the discharge capacity and Coulomb efficiency of Na / PBA coin cells manufactured by introducing a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention, respectively, and operating them for 0 to 1500 hours.

[0185] Referring to Fig. 14, in the case of a Na / PBA coin cell manufactured using a conventional glass fiber separator, the capacity dropped sharply after 600 cycles and the operation of the cell stopped, but in the case of a Na / PBA coin cell manufactured using a glass fiber separator coated with the composition of the present invention, it was confirmed that it exhibited very stable charge / discharge behavior and capacity retention rate for 1500 cycles.

[0186] Although the present invention has been described above by limited embodiments, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs.

Claims

Claim 1 Composition for coating a secondary battery separator comprising a copolymer comprising a first block represented by the following Chemical Formula 1 and a second block represented by the following Chemical Formula 2: [Chemical Formula 1] [Chemical Formula 2] In the above Chemical Formula 1, the repeating units M1 and M2 are each independently selected from the following Chemical Formula 3, [Chemical Formula 3] In the above chemical formulas 1 to 3, R1 is each independently hydrogen or a methyl group, and A is an oxygen atom or a methylene group (-CH2-); where A is an oxygen atom, R2 is each independently hydrogen or a methyl group; where A is a methylene group, R2 is each independently a glycidyl group, a carboxylic acid group, a substituted or unsubstituted amine group, a substituted or unsubstituted ester group having 2 to 20 carbon atoms; a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms; and R3 is each independently a halogen group, a hydroxyl group, a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, a substituted or unsubstituted ester group having 2 to 20 carbon atoms; It is a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, m and n are each integers from 5 to 100, x, y and z are each integers from 1 to 100, a is an integer from 0 to 10, and q is an integer from 0 to 5. Claim 2 A composition for coating a secondary battery separator according to claim 1, wherein the molar ratio m:n of the first block and the second block is 70:30 to 90:

10. Claim 3 A composition for coating a secondary battery separator according to claim 1, wherein m is an integer from 30 to 70 and n is an integer from 5 to 15. Claim 4 A composition for coating a secondary battery separator according to claim 1, wherein q in the above chemical formula 2 is 0. Claim 5 A composition for coating a secondary battery separator according to claim 1, wherein the first block is represented by the following chemical formula 4: [Chemical Formula 4] In the above chemical formula 4, R1 is independently hydrogen or a methyl group, m is an integer from 5 to 100, x and y are integers from 1 to 100, a1 is an integer from 3 to 10, and a2 is an integer from 0 to 10. Claim 6 A composition for coating a secondary battery separator according to claim 5, wherein in the above chemical formula 4, x is 10 to 30 and y is 1 to 10. Claim 7 A composition for coating a secondary battery separator according to any one of claims 1 to 6, wherein the composition for coating a secondary battery separator further comprises a metal salt, and the cation of the metal salt is a cation of one or more metals selected from lithium, sodium, magnesium, potassium, calcium, aluminum, manganese, iron, cobalt, nickel, copper, gallium, indium, niobium, zirconium, strontium, yttrium, tungsten, hafnium, tantalum, rhenium, molybdenum, and ruthenium. Claim 8 A composition for coating a secondary battery separator according to claim 7, wherein the anion of the metal salt is one or more selected from TFSI (bis(trifluoromethylsulfonyl)amide anion), PF6, ClO4, BF4, and AsF6. Claim 9 A composition for coating a secondary battery separator according to claim 7, wherein the cation of the metal salt forms a coordinate bond with a non-covalent electron pair of an oxygen atom or a nitrogen atom included in the repeating units M1 and M2. Claim 10 A composition for coating a secondary battery separator according to claim 7, wherein the molar ratio of the cation of the metal salt to the total moles of oxygen atoms and nitrogen atoms included in the first block is 0.01 to 0.

7. Claim 11 A secondary battery separator comprising a fiber substrate and a coating layer located on at least one surface of the fiber substrate, wherein the coating layer is formed from a composition for coating a secondary battery separator according to claim 1. Claim 12 In claim 11, the secondary battery separator has a porosity of 60 to 90%. Claim 13 A secondary battery separator according to claim 11, wherein the median pore diameter of the secondary battery separator is 2.0 to 4.0 μm. Claim 14 In claim 11, the secondary battery separator is a coating layer comprising 20 to 50 parts by weight per 100 parts by weight of the secondary battery separator. Claim 15 A secondary battery separator according to claim 11, wherein the thickness of the coating layer is 200 to 300 μm. Claim 16 In claim 11, the fiber substrate comprises a glass fiber, forming a secondary battery separator. Claim 17 A secondary battery comprising a secondary battery separator according to paragraph 11. Claim 18 In paragraph 17, the above secondary battery is a secondary battery that is a sodium secondary battery.

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