Composition for coating secondary battery separator, secondary battery separator using same, and secondary battery

Abstract

The present invention relates to a composition for coating a secondary battery separator, a secondary battery separator using same, and a secondary battery, the composition being capable of suppressing the formation of metal dendrites in a secondary battery, particularly a sodium secondary battery, and thus improving the durability of the battery.

Description

Composition for coating a secondary battery separator, secondary battery separator and secondary battery using the same

[0001] The present invention relates to a composition for coating a secondary battery separator, and a secondary battery separator and a secondary battery using the same, and more particularly, to a composition for coating a secondary battery separator, which can suppress the formation of metal dendrites by coating a secondary battery separator with a bottle brush-like polymer, thereby improving the durability of the battery, and a secondary battery separator and a secondary battery using the same.

[0002] This application is based on the research results obtained from the research project "Development of a multifunctional bottle brush-type polymer membrane for suppressing dendritic metal growth in high-capacity sodium metal batteries" (Project ID: 1711194653, Project No.: 00209631, Research period: 2024.03.01 ~ 2025.02.28) supported by the National Research Foundation of Korea.

[0003]

[0004] Driven by global demands for carbon neutrality, the use of medium- to large-sized secondary batteries, such as those used in electric vehicles and energy storage systems, is increasing. Lithium-ion batteries, which currently account for a significant portion of the secondary battery market, typically use graphite, a layered structure, as their anode. However, graphite has limited lithium-ion storage capacity, so efforts are ongoing to apply lithium metal, which has a very high theoretical capacity, as the anode.

[0005] Separators for secondary batteries physically separate the positive and negative electrodes, preventing short circuits. They also function as ion transport pathways, allowing electrolyte ions to move through the pores within the separator. Therefore, they must possess both excellent mechanical strength and high ionic conductivity. Currently, most separators for lithium-ion batteries use polyolefins, such as polyethylene and polypropylene, as their raw materials, and these polymers are subjected to dry or wet stretching processes to form pores.

[0006] However, lithium metal reserves are very small and are predicted to be depleted around 2040. In addition, the unit price is very high. Therefore, the demand for next-generation secondary battery systems with high capacity / high energy density that overcome the performance limitations of existing lithium-ion batteries is rapidly increasing, and the related market size is growing very significantly. Sodium metal is being proposed as the next-generation to replace lithium metal, but sodium metal batteries have the disadvantage of not having an optimized separator material. Specifically, there was an attempt to directly use polyolefin polymers for lithium-ion batteries for sodium batteries, but polyolefin-based separators have poor wettability with sodium electrolyte and their pores are too small to smoothly conduct sodium ions. Glass fiber (GF) membranes have been adopted as separators for sodium-ion batteries due to their excellent affinity for sodium electrolytes and high ionic conductivity. However, when sodium metal is used as the cathode, the pores of the glass fiber membrane are too large and non-uniform, which cannot suppress the sodium dendrites that are generated during charge and discharge, causing a problem of short circuits. In addition, during this process, an uneven organic-inorganic composite film is formed on the surface of the sodium anode, reducing the lifespan and capacity of the battery.

[0007] Therefore, since an optimized separator material has not yet been secured for sodium metal batteries, it is expected that entry into the relevant market will be very easy once technological maturity is confirmed. In addition, there is no research that systematically reveals the mechanism by which sodium dendrite metal growth is inhibited due to the structure and functionality of the polymer included in the composition coating the separator, so development of original technology is necessary.

[0008]

[0009] The technical problem to be achieved by the present invention is to provide a secondary battery separator coating composition capable of preventing the formation of metal dendrites by chelating metal ions using a brush-like polymer, a method for manufacturing the same, a secondary battery separator using the same, and a secondary battery including the same.

[0010] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the description below.

[0011]

[0012] One embodiment of the present invention provides a secondary battery separator coating composition comprising a copolymer including a first block represented by the following chemical formula 1 and a second block represented by the following chemical formula 2:

[0013] [Chemical Formula 1]

[0014]

[0015] [Chemical Formula 2]

[0016]

[0017] In the above chemical formula 1, repeating units M1 and M2 are each independently selected from the following chemical formula 3,

[0018] [Chemical Formula 3]

[0019]

[0020] In the above chemical formulas 1 to 3,

[0021] R1 is each independently hydrogen or a methyl group, A is an oxygen atom or a methylene group (-CH2-),

[0022] When the above A is an oxygen atom, R2 is each independently hydrogen or a methyl group,

[0023] When the above 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,

[0024] 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; a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms,

[0025] m and n are integers from 5 to 100, respectively,

[0026] x, y and z are integers from 1 to 100, respectively,

[0027] a is an integer from 0 to 10,

[0028] q is an integer from 0 to 5.

[0029] Another embodiment of the present invention provides a secondary battery separator comprising a fiber substrate and a coating layer positioned on at least one surface of the fiber substrate, wherein the coating layer is formed from a secondary battery separator coating composition according to an embodiment of the present invention.

[0030] Another embodiment of the present invention provides a secondary battery including a secondary battery separator according to an embodiment of the present invention.

[0031]

[0032] A secondary battery separator coating composition according to one embodiment of the present invention can form a coating layer capable of preventing the formation of metal dendrites by chelating metal cations.

[0033] According to one embodiment of the present invention, a secondary battery separator capable of preventing the formation of metal dendrites can be provided.

[0034] According to one embodiment of the present invention, a secondary battery capable of preventing the formation of metal dendrites can be provided.

[0035] The effects of the present invention are not limited to the effects described above, and effects not mentioned will be clearly understood by those skilled in the art from the present specification and the attached drawings.

[0036]

[0037] Figure 1 is a drawing briefly showing a process of coating a secondary battery separator coating composition of the present invention on a glass fiber separator.

[0038] Figure 2 shows 1H-NMR spectra for compounds of chemical formula 1-1-1(a), chemical formula 2-1-1(b), and chemical formula 3-1(c) synthesized in Example 1.

[0039] Figure 3 shows DSC thermograms for compounds of chemical formula 1-1-1 (PPG), chemical formula 2-1-1 (PSt), and chemical formula 3-1 (BBP) synthesized in Example 1 and a composition mixed with NaTFSI (NaBBP).

[0040] Figure 4 is a photograph taken by SEM of a conventional glass fiber separator and a glass fiber separator coated with a composition manufactured in Example 1 of the present invention.

[0041] Figure 5 is a graph showing the porosity and pore diameter measured by the mercury porosimetry for a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention.

[0042] Figure 6 is a graph showing the weight of the coating layer measured by thermogravimetric analysis for a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention.

[0043] Figure 7 is a graph analyzing FT-IR 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.

[0044] Figure 8 is a graph analyzing the ionic 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.

[0045] Figure 9 is a capacity-voltage curve graph 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.

[0046] Figure 10 shows SEM images of the surface (a, c) and cross-section (b, d) of the Na metal electrode after one cycle of operation of a Na / Cu coin cell manufactured by introducing a conventional glass fiber separator (a, b) and a glass fiber separator coated with the composition of Example 1 (c, d).

[0047] Figure 11 is a graph analyzing the coulombic 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, during operation for 0 to 100 cycles.

[0048] Figure 12 is a graph analyzing the voltage according to operation for 0 to 500 hours of a Na / Na 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.

[0049] Figure 13 is a photograph of the Na metal surface taken using an SEM after operating a Na / Na 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.

[0050] FIG. 14 is a graph analyzing the discharge capacity and coulombic efficiency for 0 to 1500 hours of operation for 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.

[0051]

[0052] Throughout this 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 specifically stated.

[0053] Throughout this specification, when it is said 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.

[0054] Throughout this specification, the unit “parts by weight” may mean the weight ratio between each component.

[0055] Throughout this specification, “(meth)acrylate” is used to refer to both acrylate and methacrylate.

[0056] Throughout this specification, “A and / or B” means “A and B, or A or B.”

[0057] Throughout the present specification, the term “monomer unit” may mean a form in which a monomer is reacted within a polymer, and specifically may mean 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.

[0058] Throughout the present 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 having a concentration of 1 wt% of the compound is prepared by adding tetrahydrofuran (THF) and the compound to a 1 ml glass bottle, and a standard sample (polystyrene) and the sample are filtered through a filter (pore size: 0.45 μm), and then injected into a GPC injector. The elution time of the sample sample is compared with the calibration curve of the standard sample, thereby obtaining the molecular weight and molecular weight distribution of the compound. At this time, Infinity II 1260 (Agilient) can be used as the measuring device, and the flow rate can be set to 1.00 mL / min and the column temperature to 40.0 °C.

[0059] Throughout the specification of this application, “glass transition temperature (Tg)” can be measured using differential scanning calorimetry (DSC), and specifically, using DSC (Differential Scanning Calorimeter, DSC-STAR3, METTLER TOLEDO), the sample is heated at a heating rate of 5 ℃ / min in a temperature range of -60 ℃ to 150 ℃, and the experiment is performed twice (cycles) in the above section. The midpoint of the DSC curve created as a point where there is a heat change is measured to obtain the glass transition temperature.

[0060] Throughout this specification, metal salt may mean a state in which metal ions are chelated.

[0061] Hereinafter, the present invention will be described in more detail.

[0062] Composition for coating secondary battery separator

[0063] One embodiment of the present invention provides a secondary battery separator coating composition comprising a copolymer including a first block represented by the following chemical formula 1 and a second block represented by the following chemical formula 2:

[0064] [Chemical Formula 1]

[0065]

[0066] [Chemical Formula 2]

[0067]

[0068] In the above chemical formula 1, repeating units M1 and M2 are each independently selected from the following chemical formula 3,

[0069] [Chemical Formula 3]

[0070]

[0071] In the above chemical formulas 1 to 3,

[0072] R1 is each independently hydrogen or methyl group,

[0073] A is an oxygen atom or a methylene group (-CH2-),

[0074] When the above A is an oxygen atom, R2 is each independently hydrogen or a methyl group,

[0075] When the above 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,

[0076] 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; a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms,

[0077] m and n are integers from 5 to 100, respectively,

[0078] x, y and z are integers from 1 to 100, respectively,

[0079] a is an integer from 0 to 10,

[0080] q is an integer from 0 to 5.

[0081] Specifically, the copolymer is a block copolymer having a backbone polymerized with a cyclic olefin monomer such as norbornene, and including a first block including the repeating units M1 and M2 and a second block containing polystyrene in a side chain.

[0082] According to one embodiment of the present invention, the copolymer can cause microphase separation, so that the mechanical strength of a separation membrane including a coating layer formed using the composition can be improved.

[0083] A secondary battery separator coating composition according to one embodiment of the present invention comprises the copolymer, thereby forming an inter-electrode metal cation, particularly an alkali metal cation, for example, Na, in a secondary battery, particularly a sodium secondary battery. + The flux of the metal (Na) can be controlled, thereby enabling uniform deposition of the metal (Na) and suppressing the growth of dendrites. More specifically, the unshared electron pair of the oxygen atom or nitrogen atom included in the repeating units M1 and M2 forms a coordination bond with the metal cation through dipole-dipole interaction, thereby enabling doping of the metal cation, thereby forming a complex similar to a crown ether.

[0084] 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 of m:n, in a secondary battery including a separator in which a coating layer is formed using the composition, an alkali metal cation, for example, Na + It can control the flux and suppress the growth of dendrites, thereby improving the durability and efficiency of the battery.

[0085] 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.

[0086] According to one embodiment of the present invention, q in the chemical formula 2 may be 0. When q is 0, the phenyl group of the polystyrene repeating unit included in the chemical formula 2 is not substituted.

[0087] According to one embodiment of the present invention, the number average molecular weight (M) of the copolymer n ) 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.

[0088] Preferably, the first block may be represented by the following chemical formula 4.

[0089] [Chemical Formula 4]

[0090]

[0091] In the above chemical formula 4,

[0092] R1 is each independently hydrogen or methyl group,

[0093] m is an integer between 5 and 100,

[0094] x and y are integers from 1 to 100, respectively,

[0095] a1 is an integer from 3 to 10, and a2 is an integer from 0 to 10.

[0096] When the first block is represented by the chemical formula 4, the dendrite growth inhibition effect of the secondary battery separator coating composition can be further improved, and the durability of the separator including the coating layer formed using the composition can be improved. Specifically, a metal cation can be doped to the oxygen of the ethylene glycol repeating unit included in the chemical formula 4, and the glycidyl group can be crosslinked with a hydroxyl group present on the surface of the fiber substrate, thereby improving the durability of the separator.

[0097] According to one embodiment of the present invention, in the chemical formula 4, x may be 10 to 30, and y may be 1 to 10.

[0098] 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.

[0099] Preferably, the cation of the metal salt may be a cation of at least one alkali metal selected from lithium, sodium and potassium. More preferably, the cation of the metal salt is Na+ It could be.

[0100] According to one embodiment of the present invention, the anion of the metal salt may be at least one selected from TFSI (bis(trifluoromethylsulfonyl)amide anion), PF6, ClO4, BF4, and AsF6.

[0101] According to one embodiment of the present invention, the cation of the metal salt may form a coordination bond with the unshared electron pair of the oxygen atom or nitrogen atom included in the repeating units M1 and M2. By forming the coordination bond, the cation of the metal salt may be doped into the first block, and by being doped, an alkali metal cation, for example, Na, may be used in a secondary battery using a separator in which a coating layer is formed using the composition. + It can control the flux and suppress the growth of dendrites, thereby improving the durability and efficiency of the battery.

[0102] According to one embodiment of the present invention, the molar ratio of the cation of the metal salt to the total molar number 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.

[0103] According to one embodiment of the present invention, when the first block is represented by the chemical formula 4, the molar ratio of the cation of the metal salt to the total molar number 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.

[0104] According to one embodiment of the present invention, the secondary battery separator coating composition may further include a solvent as needed. The solvent may be an organic solvent, and for example, tetrahydrofuran (THF) may be used as the solvent.

[0105] Method for producing a copolymer of the present invention

[0106] 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.

[0107] According to one embodiment of the present invention, the first block can be obtained by a step of reacting a compound of the following chemical formula 1A with a compound of the following chemical formula 1B and / or a compound of the following chemical formula 1C to synthesize a macromonomer of the following chemical formula 1-1; and a step of polymerizing the macromonomer represented by the following chemical formula 1-1 in the presence of a catalyst.

[0108] According to one embodiment of the present invention, the second block can be obtained by a step of reacting a compound of the following chemical formula 1A and a compound of the following chemical formula 1D to synthesize a macromonomer of the following chemical formula 2-1; and a step of polymerizing the macromonomer represented by the following chemical formula 2-1 in the presence of a catalyst.

[0109] 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.

[0110] [Chemical Formula 1A]

[0111]

[0112] [Chemical Formula 1B]

[0113]

[0114] [Chemical Formula 1C]

[0115]

[0116] [Chemical Formula 1-1]

[0117]

[0118] [Chemical Formula 1D]

[0119]

[0120] [Chemical Formula 2-1]

[0121]

[0122] In the above chemical formulas, X is a fluorine group, a chlorine group, a bromine group or an iodine group, R1 is independently 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; A substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, x, y and z are each an integer of 1 to 100, a1 is an integer of 3 to 10, a2 is an integer of 0 to 10, and q is an integer of 0 to 5.

[0123] According to one embodiment of the present invention, in the step of polymerizing the macromonomer of the chemical formula 1-1 and the macromonomer of the chemical 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.

[0124] According to one embodiment of the present invention, in the step of polymerizing the macromonomer of the chemical formula 1-1 and the macromonomer of the chemical formula 2-1 in the presence of a catalyst, the catalyst is a Grubbs Catalyst ® ) may be included.

[0125] According to one embodiment of the present invention, after polymerizing the macromonomer of Chemical Formula 1-1 and the macromonomer of Chemical 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 as described above.

[0126] Secondary battery separator and secondary battery including the same

[0127] Another embodiment of the present invention provides a secondary battery separator comprising a fiber substrate and a coating layer positioned on at least one surface of the fiber substrate, wherein the coating layer is formed from a secondary battery separator coating composition according to an embodiment of the present invention.

[0128] 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 of the porosity and median pore diameter of the secondary battery separator, a uniform porous structure is provided, thereby improving the efficiency of a secondary battery including the same.

[0129] 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.

[0130] According to one embodiment of the present invention, the thickness of the coating layer may be 200 to 300 ㎛.

[0131] According to one embodiment of the present invention, the fiber substrate can be used without any particular limitation 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.

[0132] Another embodiment of the present invention provides a secondary battery including a secondary battery separator according to an embodiment of the present invention.

[0133] A secondary battery according to one embodiment of the present invention may be a sodium secondary battery.

[0134]

[0135] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention is not limited to the examples described below. The examples in this specification are provided to more fully explain the present invention to those of ordinary skill in the art.

[0136] All reagents and materials, unless otherwise stated, were purchased from Sigma Aldrich and used as received.

[0137] Example 1

[0138] (1) Synthesis of PPG (poly(PEGMA-co-GMA)) macromonomer

[0139]

[0140] A solution containing 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) was subjected to three freeze-pump-thaw cycles to remove oxygen in the solution. As a ligand for ATRP polymerization, 0.31 g of PMDETA (N, N, N`, N``, N`-pentamethyldiethylenetriamine) was additionally added to the solution, and oxygen in the solution was removed through three more freeze-pump-thaw cycles. The solution was stirred at 70°C for 10 minutes, diluted in chloroform solvent, and passed through a basic alumina column (Sigma-Aldrich) to remove the CuBr catalyst. Afterwards, unreacted substances were removed by precipitation in hexane solvent, and dried to obtain a PPG (poly(PEGMA-co-GMA)) macromonomer compound represented by the chemical formula 1-1-1.

[0141] (2) Synthesis of PSt (polystyrene) macromonomer

[0142]

[0143] A solution containing 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 in 5 mL of dimethylformamide (DMF) was subjected to three freeze-pump-thaw cycles to remove oxygen in the solution. As a ligand for ATRP polymerization, 0.083 g of PMDETA (N, N, N`, N``, N`-pentamethyldiethylenetriamine) was additionally added to the solution, and oxygen in the solution was removed through three more freeze-pump-thaw cycles. The solution was stirred at 90°C for 3.5 hours, diluted in chloroform solvent, and passed through a basic alumina column to remove the CuBr catalyst. Afterwards, unreacted substances were removed by precipitation in hexane solvent, and dried to obtain a PSt (polystyrene) macromonomer compound represented by the chemical formula 2-1-1.

[0144] (3) Brush-type polymer (BBP) polymerization

[0145]

[0146]

[0147] 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, followed by stirring at 30°C for 2 hours to perform a polymerization reaction.

[0148] Then, 0.67 mL of a solution containing the compound represented by the chemical formula 2-1-1 obtained above at a concentration of 0.05 M was added, and the mixture was stirred for 2 more hours to perform a polymerization reaction. To terminate the reaction, 0.1 mL of ethyl vinyl ether was added, and the mixture was purified by precipitation in diethyl ether three times to obtain a brush-shaped polymer compound represented by the chemical formula 3-1.

[0149] A composition for coating a secondary battery separator was obtained by dissolving 0.080 g of the compound of the above-mentioned chemical formula 3-1 and 0.036 g of sodium trifluoromethanesulfonimide (NaTFSI) in 1.0 mL of anhydrous tetrahydrofuran (THF).

[0150] A glass fiber separator (Whatman, thickness: 260 μm) was immersed in the secondary battery separator coating composition for 2 hours. Thereafter, the glass fiber separator was taken out, dried for 3 hours, and then heat-treated at 120°C for 15 hours to initiate a cross-linking reaction between the glycidyl moiety contained in the chemical formula 3-1 and the hydroxyl groups on the surface of the glass fiber. As a result, it was confirmed that a 260 μm coating layer was formed on the separator.

[0151] Figure 1 is a drawing briefly showing a process of coating a secondary battery separator coating composition of the present invention on a glass fiber separator.

[0152] Experimental Example 1: Physical property analysis of synthesized compounds

[0153] The compounds of chemical formula 1-1-1, chemical formula 2-1-1, and chemical formula 3-1 synthesized in Example 1 were analyzed for their properties as follows.

[0154] Specifically, 1H-NMR spectra were obtained at room temperature using an AscendTM 400 spectrometer (400 MHz) using CDCl3 and tetramethylsilane (TMS) as a standard (Sigma-Aldrich). Number-average molecular weight and polydispersity (D) 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.

[0155] Figure 2 shows the compounds of chemical formula 1-1-1(a), chemical formula 2-1-1(b), and chemical formula 3-1(c) synthesized in Example 1. 1 H-NMR spectra are shown. The number average molecular weights (M) of the compounds of chemical formulas 1-1-1, 2-1-1, and 3-1 synthesized in Example 1 are shown in Table 1 below. n ), dispersion (D), 1 Fraction of PPG blocks calculated from H-NMR spectra (f PPG ), number average degree of polymerization (N sc ) and the number-average degree of polymerization of the backbone (N bb ) was shown.

[0156]

[0157] Compound M n (kDa)Df PPG N sc N bb Chemical Formula 1-1-15.951.12-18.1-Chemical Formula 2-1-15.701.11-51.3-Chemical Formula 3-13221.720.82-54.5

[0158]

[0159] Referring to Table 1 above, the PSt macromonomer represented by Chemical Formula 2-1-1 maintained its number-average molecular weight at approximately 5 kDa, which is significantly lower than the entanglement molecular weight (Me) of polystyrene of 17 kDa, thereby maximizing the mobility of polyethylene oxide (PEO) chains in the copolymer represented by Chemical Formula 3-1. The unentangled and highly mobile PEO chains can effectively control the flux of metal cations such as Na+ between the electrolyte and electrode by promoting dipole-dipole interactions with metal cations.

[0160] Experimental Example 1-2: Confirmation of Phase Separation of Synthesized Compounds

[0161] In order to confirm whether there is a characteristic microphase separation induced by self-assembly in the copolymer represented by Chemical Formula 3-1 synthesized in Example 1, the glass transition temperature was measured for the compounds of Chemical Formula 1-1-1 (PPG), Chemical Formula 2-1-1 (PSt), and Chemical Formula 3-1 synthesized in Example 1 (BBP) and the composition mixed with NaTFSI (NaBBP). The glass transition temperature was measured in a nitrogen atmosphere (cooling rate: 1°C min). -1 , heating rate: 10°C min -1 ) was measured by differential scanning calorimetry (DSC) using a TA Instruments DSC25.

[0162] Figure 3 shows DSC thermograms for compounds of chemical formula 1-1-1 (PPG), chemical formula 2-1-1 (PSt), and chemical formula 3-1 (BBP) synthesized in Example 1 and a composition mixed with NaTFSI (NaBBP).

[0163] Referring to FIG. 3, in the copolymer (BBP) represented by Chemical Formula 3-1 synthesized in Example 1, there are two Tg derived from the PPG block (-48.1°C) and the PSt block (81.3°C), respectively, which suggests that microphase separation occurred in the BBP. In addition, the fact that the two Tg values ​​observed in the BBP are not significantly different from the Tg values ​​of Chemical Formula 1-1-1 (PPG) and Chemical Formula 2-1-1 (PSt), respectively, indicates that chain mobility within each separated microphase is maintained. In addition, 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.

[0164] Experimental Example 2-1: Membrane-SEM

[0165] Figure 4 is a photograph taken by SEM of a conventional glass fiber separator and a glass fiber separator coated with a composition manufactured in Example 1 of the present invention. The scanning electron microscope (SEM) used for the measurement was a Regulus 8230-Oxford EDS (Hitachi Inc., Tokyo, Japan), and the measurement was performed at an acceleration voltage of 10 kV.

[0166] Referring to Fig. 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.

[0167] Experimental Example 2-2: Membrane Porosity and Pore Size Measurement

[0168] Figure 5 is a graph showing the porosity and pore diameter measured by mercury porosimetry 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 porosimetry was performed using an AutoPore IV 9500 mercury (Hg) intrusion porosimeter (Micromeritics, USA).

[0169] Referring to FIG. 5, the porosity of the conventional glass fiber separator was about 90% and the average pore diameter was about 3.0 ㎛, while 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 ㎛, confirming that the porosity and average pore diameter were reduced. In particular, the median pore diameter decreased from about 5.5 ㎛ to 3 ㎛ before and after coating, showing a large decrease compared to the average pore diameter and porosity. This suggests that the coating composition of the present invention can mainly fill pores of relatively large sizes to provide a uniform distribution of pore sizes and a uniform porous structure.

[0170] Experimental Example 2-3: Weight Measurement of the Membrane-Coating Layer

[0171] Figure 6 is a graph showing the weight of the coating layer measured by thermogravimetric analysis of a conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention. Specifically, the thermogravimetric analysis was performed in a nitrogen atmosphere (heating rate: 10 ℃ min). -1 ) was performed using a TA Instruments TGA55.

[0172] Referring to FIG. 6, it was confirmed that the weight of the coating layer was 36 parts by weight with respect to 100 parts by weight of the total weight of the separator in the glass fiber separator coated with the composition of Example 1 of the present invention.

[0173] Experimental Example 2-4: Membrane-FT-IR Measurement

[0174] FT-IR is 400 to 4000 cm -1 8 cm in wavelength range -1 Transmittance was measured at each wavelength in absorption mode using a Nicolet 6700 spectrophotometer with a resolution of .

[0175] Figure 7 is a graph analyzing FT-IR 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.

[0176] Referring to FIG. 7, the peak corresponding to the composition of Example 1 of the present invention was 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.

[0177] Experimental Example 3-1: Ionic Conductivity and Electrolyte Absorption of the Separator

[0178] 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 potentiostat (Biologic, France) at 30°C with an amplitude of 10 mV over 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.

[0179] [Formula 1]

[0180] σ= (1 / R) × (d / A)

[0181] In the above equation 1, R represents the resistance obtained from the impedance spectrum, d represents the thickness of the separator, and A represents the area of ​​the electrode.

[0182] A 1 M hexafluorophosphate (NaPF6) solution (ethylene carbonate:propylene carbonate:diethyl carbonate (EC):propylene carbonate:diethyl carbonate) 1:1:1 vol% solution (Welcos) containing 2 wt% fluoroethylene carbonate (FEC) was used as the electrolyte. 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.

[0183] [Formula 2]

[0184] Electrolyte absorption (%) = (W wet -W dry ) / W dry × 100

[0185] In the above equation 2, W dry and W wet means the weight before and after immersion in the electrolyte, respectively. Before analysis, the conventional glass fiber separator wetted with the electrolyte and the glass fiber separator coated with the composition of Example 1 of the present invention were prepared by immersing in 1 M NaPF6 (Welcos) of EC:PC:DEC (1:1:1 vol%) containing 2 wt% FEC for 24 hours in an argon-filled glove box (O2<0.1 ppm, H2O<0.1 ppm).

[0186] 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.

[0187] Referring to FIG. 8, the glass fiber separator coated with the composition of Example 1 of the present invention did not show a significant change in ionic conductivity, electrolyte absorption, and thickness compared to the conventional glass fiber separator, and in particular, the glass fiber coated with the composition of Example 1 had a conductivity of 4.1 mS·cm at 30°C. -1 The ionic conductivity of uncoated glass fiber (5.2 mS cm) was shown. -1 ) is at a similar level.

[0188] These results indicate that the electrochemical properties of the glass fiber separator are not significantly deteriorated even when coated with the composition of the present invention.

[0189] Experimental Example 3-2: Evaluation of Na Electrodeposition Behavior in a Na / Cu Cell

[0190] 0.5 mAh / cm 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. 2 The first cycle was driven under conditions of current density and temperature of 30 ℃. All coin cell components were assembled in an argon-filled glove box (O2<0.1 ppm, H2O<0.1 ppm).

[0191] Galvanostatic cycling tests on coin cells were performed at a current density of 0.5 mA cm at 30°C. -2 , total capacity 0.5mAh cm -2 The measurements were performed on a WBCS-3000 battery cycling system (WonATech Co., Korea). Electrochemical impedance spectroscopy (EIS) was performed on a VMP3 multichannel potentiostat (Biologic, France) in the frequency range of 0.1–100 MHz with an amplitude of 10 mV at 30°C.

[0192] Figure 9 is a capacity-voltage curve graph 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.

[0193] Referring to FIG. 9, it was confirmed that the coin cell manufactured using the glass fiber separator coated with the composition of Example 1 exhibited a significantly higher capacity per unit area compared to the coin cell using the conventional glass fiber separator.

[0194] Figure 10 shows SEM images of the surface (a, c) and cross-section (b, d) of the Na metal electrode after one cycle of operation of a Na / Cu coin cell manufactured by introducing a conventional glass fiber separator (a, b) and a glass fiber separator coated with the composition of Example 1 (c, d).

[0195] Referring to FIG. 10, it can be seen that Na was deposited on the surface of the Na metal electrode of a coin cell manufactured using a conventional glass fiber separator in a very irregular shape in the first cycle (a), and many pinholes and cracks were formed in the cross-section (b), whereas in the Na metal electrode of a coin cell manufactured using a glass fiber separator coated with the composition of Example 1, it was confirmed that Na was deposited very smoothly and uniformly on both the electrode surface (c) and the cross-section (d), and no dendrites were formed.

[0196] Figure 11 is a graph analyzing the coulombic 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, during operation for 0 to 100 cycles.

[0197] Referring to Fig. 11, a secondary battery manufactured using a glass fiber separator coated with the composition of the present invention maintained a coulombic efficiency of up to 100%, whereas a secondary battery manufactured using a conventional glass fiber separator showed a behavior in which the coulombic efficiency rapidly decreased after 40 cycles. Since each coin cell differs only in the presence or absence of a coating on the separator, it can be seen that a secondary battery manufactured using a coated glass fiber separator induces more stable Na electrodeposition characteristics.

[0198]

[0199] Experimental Example 3-3: Evaluation of Na Electrodeposition Behavior in a Na / Na Symmetric Cell

[0200] 0.5 mA / cm 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. 2 Under current density and temperature conditions of 30℃, one cycle of sodium deposition for 1 hour and desorption for 1 hour was considered one cycle, and the operation was conducted for a total of 300 hours. All coin cell components were assembled in an argon-filled glove box (O2<0.1 ppm, H2O<0.1 ppm). In the case of a Na / Na symmetric cell, since both sides are Na metal, the cycle of removing Na from one side and depositing it on the other side was continuously repeated, and the point in time when a short circuit of the secondary battery occurred due to Na metal dendrites was analyzed.

[0201] Figure 12 is a graph analyzing the voltage according to operation for 0 to 500 hours of a Na / Na 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.

[0202] 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 piercing the separator, 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 deposits were formed, but a short circuit did not occur for 500 hours, indicating that durability was improved by coating with the composition of the present invention.

[0203] Figure 13 is a photograph of the surface of the Na metal electrode taken by SEM after operating a Na / Na 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 for 320 hours and 500 hours, respectively. The scanning electron microscope (SEM) used for the measurement was a Regulus 8230-Oxford EDS (Hitachi Inc., Tokyo, Japan), and the measurement was performed at an acceleration voltage of 10 kV.

[0204] Referring to Fig. 13, in the case of a Na / Na secondary battery manufactured using a conventional glass fiber separator, many Na deposits with very irregular shapes were formed on the Na metal surface 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 was deposited evenly, showing a smooth surface.

[0205] Experimental Example 3-4: Evaluation of Na Electrodeposition Behavior in a Na / PBA Cell

[0206] A conventional glass fiber separator and a glass fiber separator coated with the composition of Example 1 of the present invention were introduced between a Na metal electrode and a PBA electrode to manufacture a Na / PBA coin cell. All coin cell components were assembled in an argon-filled glove box (O2<0.1 ppm, H2O<0.1 ppm). Prussian blue analog (PBA, Na 2-x Fe[Fe(CN)6]) was synthesized through a well-known precipitation method.

[0207] For Na / PBA cells, voltages from 2.0 to 4.0 V and current density at 10 C (1.2 A·g -1 ) was operated for 1500 cycles, with one cycle being Na deposition for 1 hour and desorption for 1 hour.

[0208] FIG. 14 is a graph analyzing the discharge capacity and coulombic efficiency of a Na / PBA 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, when operated for 0 to 1500 hours.

[0209] 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 was 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.

[0210] Although the present invention has been described above through 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 idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. A composition for coating a secondary battery separator comprising a copolymer including 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, 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 methyl group, A is an oxygen atom or a methylene group (-CH2-), When the above A is an oxygen atom, R2 is each independently hydrogen or a methyl group, When the above 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, 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; a substituted or unsubstituted alkoxy group having 1 to 20 carbon atoms, m and n are integers from 5 to 100, respectively, x, y and z are integers from 1 to 100, respectively, a is an integer from 0 to 10, q is an integer from 0 to 5.

2. In paragraph 1, A composition for coating a secondary battery separator, wherein the molar ratio m:n of the first block and the second block is 70:30 to 90:

10.

3. In paragraph 1, A secondary battery separator coating composition, wherein m is an integer from 30 to 70 and n is an integer from 5 to 15.

4. In paragraph 1, A composition for coating a secondary battery separator, wherein q is 0 in the above chemical formula 2.

5. In paragraph 1, The above first block is a secondary battery separator coating composition represented by the following chemical formula 4: [Chemical Formula 4] In the above chemical formula 4, R1 is each independently hydrogen or methyl group, m is an integer between 5 and 100, x and y are integers from 1 to 100, respectively, a1 is an integer from 3 to 10, and a2 is an integer from 0 to 10.

6. In paragraph 5, A composition for coating a secondary battery separator, wherein in the above chemical formula 4, x is 10 to 30 and y is 1 to 10.

7. In any one of paragraphs 1 to 6, The composition for coating the secondary battery separator further comprises a metal salt, A composition for coating a secondary battery separator, wherein the cation of the metal salt is a cation of at least one metal 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.

8. In paragraph 7, A composition for coating a secondary battery separator, wherein the anion of the metal salt is at least one selected from TFSI (bis(trifluoromethylsulfonyl)amide anion), PF6, ClO4, BF4, and AsF6.

9. In paragraph 7, A secondary battery separator coating composition wherein the cation of the metal salt forms a coordination bond with the unshared electron pair of the oxygen atom or nitrogen atom included in the repeating units M1 and M2.

10. In paragraph 7, A composition for coating a secondary battery separator, wherein the molar ratio of the cation of the metal salt to the total molar number of oxygen atoms and nitrogen atoms included in the first block is 0.01 to 0.

7.

11. A secondary battery separator comprising a fiber substrate and a coating layer positioned on at least one surface of the fiber substrate, A secondary battery separator, wherein the coating layer is formed from a secondary battery separator coating composition according to claim 1.

12. In paragraph 11, A secondary battery separator having a porosity of 60 to 90%.

13. In paragraph 11, A secondary battery separator having a median pore diameter of 2.0 to 4.0 μm.

14. In paragraph 11, A secondary battery separator, wherein the coating layer is included in an amount of 20 to 50 parts by weight relative to 100 parts by weight of the secondary battery separator.

15. In paragraph 11, A secondary battery separator having a thickness of the coating layer of 200 to 300 ㎛.

16. In paragraph 11, A secondary battery separator wherein the above fiber substrate includes glass fiber.

17. A secondary battery comprising a secondary battery separator according to Article 11.

18. In paragraph 17, The secondary battery above is a sodium secondary battery.

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