Polymer electrolyte membrane for lithium secondary battery, comprising copolymer containing poly(ethylene glycol) double-grafted onto poly(arylene ether sulfone), method for manufacturing same, and lithium secondary battery comprising same

Abstract

One embodiment of the present invention provides a polymer electrolyte membrane for a lithium secondary battery. An embodiment according to the present invention provides a polymer electrolyte membrane comprising a compound additive in addition to a graft copolymer, and a lithium secondary battery comprising same has high ion conductivity and electrochemical performance, facilitates lithium ion movement even in a wide temperature range, and exhibits excellent properties, electrochemical stability, surface stability, and battery performance.

Description

Polymer electrolyte membrane for lithium secondary batteries comprising a copolymer in which poly(ethylene glycol) is doubly grafted onto poly(arylene ether sulfone), a method for producing the same, and a lithium secondary battery comprising the same

[0001] The present invention relates to an electrolyte for a lithium secondary battery, and more particularly, to an electrolyte membrane for a lithium secondary battery having excellent electrochemical properties by applying a highly conductive co-solvent to a copolymer in which poly(ethylene glycol) is doubly grafted onto poly(arylene ether sulfone).

[0002] Recently, lithium secondary batteries (LIBs) have become one of the most promising energy storage and conversion devices due to their long operating cycle, high energy density, and ability to meet environmental constraints, and have been widely applied in fields such as portable electronic devices, wearable devices, and electric vehicles. However, LIBs exhibit significant capacity loss (approximately 60% loss at -40°C compared to room temperature) and significant polarization effects (ohmic polarization, concentration polarization, and electrochemical polarization) in some special low-temperature regions (polar regions, high-altitude regions, outer space, and regions with harsh winters) and high-temperature regions (desert regions, equatorial countries), making their use difficult.

[0003] In particular, in low-temperature environments, lithium secondary batteries experience increased electrolyte viscosity and decreased internal ion diffusion rates, leading to decreased ionic conductivity. Furthermore, freezing and crystallization of the electrolyte severely impede ion transport, resulting in significant capacity degradation. One approach to addressing these issues is the development of a solid polymer electrolyte membrane that incorporates a cosolvent with a low freezing point and high ionic conductivity.

[0004] The present invention provides an electrolyte membrane having excellent thermal, mechanical, and electrochemical performance over a wide temperature range by applying a highly conductive co-solvent to a copolymer in which PEG is double grafted onto PAES as a method for solving the problems of the prior art described above.

[0005] The technical problems to be solved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0006] In order to achieve the above technical task, one embodiment of the present invention provides a polymer electrolyte membrane for a lithium secondary battery.

[0007] According to one embodiment of the present invention, a polymer electrolyte membrane for a lithium secondary battery comprises a graft copolymer in which poly(ethylene glycol) is doubly grafted onto poly(arylene ether sulfone), represented by the following chemical formula 1; and a compound additive, wherein the compound additive comprises an ionic liquid; ethylene carbonate; and ethyl propionate.

[0008] [Chemical Formula 1]

[0009]

[0010] In the above chemical formula 1, n is an integer from 45 to 90, and k is an integer from 50 to 70.

[0011] In an embodiment of the present invention, the graft copolymer is a polymer electrolyte membrane for a lithium secondary battery, characterized in that it is synthesized by an esterification reaction of a compound represented by the following chemical formula 2 and a compound represented by the following chemical formula 3:

[0012] [Chemical Formula 2]

[0013]

[0014] In the above chemical formula 2, n is an integer from 45 to 90.

[0015] [Chemical Formula 3]

[0016]

[0017] In the above chemical formula 3, k is an integer from 50 to 70.

[0018] In an embodiment of the present invention, the ionic liquid is at least one selected from among N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR14-TFSI), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI), 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPP-TFSI), 1-methyl-1-butylpiperidinium bis(trifluoromethylsulfonyl)imide (MBP-TFSI), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI-TFSI). It may be a polymer electrolyte membrane for a lithium secondary battery characterized by including:

[0019] In an embodiment of the present invention, the polymer electrolyte membrane for a lithium secondary battery may be characterized in that the compound additive is contained in an amount of 30 to 80 wt% relative to the total weight of the polymer electrolyte membrane.

[0020] Another embodiment of the present invention for achieving the above technical task provides a lithium secondary battery including the polymer electrolyte membrane for the secondary battery.

[0021] Another embodiment of the present invention for achieving the above technical task provides a method for manufacturing a polymer electrolyte membrane for a secondary battery.

[0022] A method for manufacturing a polymer electrolyte membrane for a lithium secondary battery according to one embodiment of the present invention comprises the steps of: mixing a solution containing a graft copolymer represented by the following chemical formula 1, a cosolvent, and a solvent; applying the solution onto a substrate; and heat-treating the applied solution; wherein the cosolvent comprises an ionic liquid, ethylene carbonate, and ethyl propionate.

[0023] [Chemical Formula 1]

[0024]

[0025] In the above chemical formula 1, n is an integer from 45 to 90, and k is an integer from 50 to 70.

[0026] In an embodiment of the present invention, the ionic liquid is at least one selected from among N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR14-TFSI), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI), 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPP-TFSI), 1-methyl-1-butylpiperidinium bis(trifluoromethylsulfonyl)imide (MBP-TFSI), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI-TFSI). It may be a method for manufacturing a polymer electrolyte membrane for a lithium secondary battery characterized by including:

[0027] In the embodiment of the present invention, the method for manufacturing a polymer electrolyte membrane for a lithium secondary battery may be characterized in that the co-solvent is included in the solution at 30 to 80 wt%.

[0028] In an embodiment of the present invention, the solvent of the mixed solution may be a method for manufacturing a polymer electrolyte membrane for a lithium secondary battery, characterized in that it includes tetrahydrofuran (THF).

[0029] In an embodiment of the present invention, a method for manufacturing a polymer electrolyte membrane for a lithium secondary battery may further include a step of ultrasonically treating the solution after the mixing step.

[0030] Another embodiment of the present invention for achieving the above technical task provides a polymer electrolyte membrane for a lithium secondary battery manufactured by the above manufacturing method.

[0031] According to an embodiment of the present invention, as a means of solving the problems of existing lithium secondary batteries, a polymer electrolyte membrane including a compound additive in a graft copolymer is provided, and a lithium secondary battery including the same has high ionic conductivity and electrochemical performance, facilitates lithium ion movement even in a wide temperature range, and has excellent physical properties, electrochemical stability, surface stability, and battery performance.

[0032] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the detailed description of the present invention or the composition of the invention described in the claims.

[0033] Figure 1 is a flow chart schematically illustrating a method for manufacturing an electrolyte membrane for a lithium secondary battery according to one embodiment of the present invention.

[0034] Figure 2 is a drawing showing the NMR spectrum of the manufactured PAGES-g-2PEG.

[0035] Figure 3 is a drawing showing the FTIR spectrum of the manufactured PAGES-g-2PEG.

[0036] Figure 4 is a diagram showing the ionic conductivity of PAES-g-2PEG and PAES-g-2PEG containing various types of cosolvents.

[0037] Figure 5 is a diagram showing the lithium ion transport capacity of PAES-g-2PEG and PAES-g-2PEG containing various types of cosolvents.

[0038] Figure 6 is a diagram showing the UTM curve of PAES-g-2PEG and PAES-g-2PEG containing various types of cosolvents.

[0039] Figure 7 is a diagram showing the membrane flexibility of PAES-g-2PEG and PAES-g-2PEG containing various types of cosolvents.

[0040] Figure 8 is a diagram showing the membrane flexibility of PAES-g-2PEG containing IL-EC-EP co-solvent at various temperatures.

[0041] Figure 9 is a diagram showing LSV curves at various temperatures of PAES-g-2PEG containing IL co-solvent.

[0042] Figure 10 is a diagram showing LSV curves of PAES-g-2PEG containing IL-EC co-solvent at various temperatures.

[0043] Figure 11 is a diagram showing LSV curves at various temperatures of PAES-g-2PEG containing IL-EC-DMC co-solvent.

[0044] Figure 12 is a diagram showing LSV curves at various temperatures of PAES-g-2PEG containing IL-EC-EP co-solvent.

[0045] Figure 13 shows the plating / stripping voltage-time profiles of PAES-g-2PEG membranes in a lithium symmetric cell with and without EC plasticizer at 2.0 mA / cm.

[0046] Figure 14 is a diagram showing the charge / discharge profile of PAES-g-2PEG containing IL-EC-EP co-solvent.

[0047] Figure 15 is a diagram showing the rate performance of PAES-g-2PEG containing IL-EC-EP co-solvent.

[0048] Figure 16 is a diagram showing the performance of a Li / SEM / S cell comprising a PAES-g-2PEG membrane containing 70% IL, with or without an EC plasticizer of PAES-g-2PEG containing IL-EC-EP co-solvent.

[0049] Hereinafter, the present invention will be described with reference to the attached drawings. However, the present invention can be implemented in various different forms and is therefore not limited to the embodiments described herein. In the drawings, irrelevant parts have been omitted for clarity of description, and similar parts have been designated with similar reference numerals throughout the specification.

[0050] Throughout the specification, when a part is said to be "connected (connected, contacted, or coupled)" to another part, this includes not only cases where it is "directly connected," but also cases where it is "indirectly connected" with another part in between. Furthermore, when a part is said to "include" a component, this does not exclude other components, but rather implies that it may include other components, unless otherwise specifically stated.

[0051] The terminology used herein is merely used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, it should be understood that the terms "comprises" or "has" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0052] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0053]

[0054] A polymer electrolyte membrane for a lithium secondary battery according to one embodiment of the present invention is described.

[0055] A polymer electrolyte membrane for a lithium secondary battery according to one embodiment of the present invention comprises a graft copolymer represented by the following chemical formula 1, which is a copolymer in which poly(ethylene glycol) is doubly grafted onto poly(arylene ether sulfone), and a compound additive, wherein the compound additive comprises an ionic liquid and ethylene carbonate.

[0056] [Chemical Formula 1]

[0057]

[0058] In chemical formula 1, n is an integer from 45 to 90, and k is an integer from 50 to 70.

[0059] The copolymer represented by the above chemical formula 1 (hereinafter referred to as PAES-g-2PEG) has a structure in which a poly(ethylene glycol) (PEG) segment containing a flexible ether group that enables smooth transport of lithium ions is doubly grafted onto poly(arylene ether sulfone) (PAES) having excellent mechanical properties and thermal / chemical stability, and thus has high lithium ion conductivity while exhibiting high thermal stability and mechanical strength, and can be utilized as an effective polymer electrolyte membrane material for lithium secondary batteries.

[0060] At this time, the graft copolymer can be synthesized by esterifying a compound represented by the following chemical formula 2 and a compound represented by the following chemical formula 3.

[0061] [Chemical Formula 2]

[0062]

[0063] In the above chemical formula 2, n is an integer from 45 to 90.

[0064] [Chemical Formula 3]

[0065]

[0066] In the above chemical formula 3, k is an integer from 50 to 70.

[0067] The compound represented by the above chemical formula 2 has a structure in which poly(arylene ether sulfone) (PAES) is the main chain and a double carboxyl group is introduced into the side chain. A compound having this structure (hereinafter referred to as PAES-2COOH) can be synthesized by an esterification reaction between PAES and maleic acid (Maleicacid).

[0068] At this time, in order to increase the esterification reactivity, it is preferable to carry out the reaction in the presence of 4-dimethylaminopyridine (DMAP) and N,N'-dicyclohexylcarbodiimide (DCC).

[0069] Additionally, the above reaction can be performed at a temperature of 60 to 100°C in a DMF solvent, but is not limited thereto.

[0070] The compound represented by the above chemical formula 3 (hereinafter referred to as PEG-OH) has a structure including a hydroxyl group at the terminal of poly(ethylene glycol) (PEG) containing an ether group.

[0071] Therefore, the PAEG-2COOH and PEG-OH of the present invention can synthesize a copolymer through an esterification reaction due to the presence of a carboxyl group and a hydroxyl group.

[0072] At this time, in order to increase the esterification reactivity, it is preferable to carry out the reaction in the presence of 4-dimethylaminopyridine (DMAP) and N,N'-dicyclohexylcarbodiimide (DCC).

[0073] Additionally, the above reaction can be performed at a temperature of 60 to 100°C in a DMF solvent, but is not limited thereto.

[0074] Meanwhile, a polymer electrolyte membrane for a lithium secondary battery according to one embodiment of the present invention further includes an additional compound additive in addition to the graft copolymer (PAES-g-2PEG) represented by the above chemical formula 1.

[0075] At this time, the compound additive includes an ionic liquid (hereinafter referred to as IL), ethylene carbonate (hereinafter referred to as EC), and ethyl propionate (hereinafter referred to as EP).

[0076] At this time, the compound additive may be included in the polymer electrolyte membrane at 30 to 80 wt%.

[0077] First, in the presence of the ionic liquid, the graft copolymer of the present invention undergoes phase separation of PAES and PEG, forming a larger conductive domain, thereby facilitating the movement of lithium ions.

[0078] A graft copolymer (PAES-g-2PEG), which is one component of the present invention, includes a PEG segment that has high chemical compatibility with an ionic liquid and forms a conductive channel that contributes to the movement of lithium ions, and a PAES main chain that maintains mechanical stability even under high concentration ionic liquid conditions as a non-conductive domain.

[0079] Specifically, PAES, a polymer with low compatibility with ionic liquids, has excellent thermal, mechanical, and chemical stability due to the rigid phenyl group in the main chain and is used as a non-conductive domain, and PEG is a flexible polymer with excellent compatibility with ionic liquids and facilitates the movement of lithium ions.

[0080] Meanwhile, the graft copolymer (PAES-g-2PEG) forms a large, irregularly shaped conductive domain (a phase with a lot of PEG) in the presence of an ionic liquid, which allows for easy phase separation, and the polymer electrolyte membrane of the present invention can have a reduced interfacial resistance between the electrode and the electrolyte membrane surface, and facilitate lithium ion movement due to the large conductive domain, thereby greatly improving ion conductivity.

[0081] In addition, the lithium ion yield increases as the Coulomb repulsion between the anion and ether group of the ionic liquid increases.

[0082] In addition, ionic liquids enhance stability in polymer electrolyte membranes for lithium secondary batteries due to their wide electrochemical window, and they also play a role in mitigating the evaporation and flammability of organic solvents due to their high boiling point (>300°C), fire resistance, and non-volatility over a wide temperature range.

[0083] At this time, the ionic liquid refers to a substance that exists in a liquid state without forming a crystal due to the asymmetry in the sizes of cations and anions.

[0084] The ionic liquid used in the present invention is not particularly limited, but may be any one selected from among N-methyl-N-butylpyridinium bis(trifluoromethylsulfonyl)imide (PYR14-TFSI), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI), 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPP-TFSI), 1-methyl-1-butylpiperidinium bis(trifluoromethylsulfonyl)imide (MBP-TFSI), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI-TFSI). It is desirable to include more than one.

[0085] As described above, the polymer electrolyte membrane of the present invention can secure excellent mechanical properties because it includes a copolymer based on a PAES main chain exhibiting high mechanical strength and thermal properties.

[0086] In addition, in the polymer electrolyte membrane of the present invention, the PAES main chain and PEG segment of the graft copolymer undergo phase separation in the presence of an ionic liquid, thereby forming a larger conductive domain, thereby facilitating the movement of lithium ions.

[0087] In particular, since the graft copolymer of the present invention has a structure in which PEG is doubly grafted onto the PAES main chain, the amount of PEG segments increases compared to when one PEG segment is grafted, thereby improving the interaction between the ether group present in the flexible PEG segment and lithium ions, thereby obtaining higher lithium ion conductivity.

[0088] Meanwhile, the present invention adopts ethylene carbonate as one component of the compound additive.

[0089] Conventional lithium secondary batteries have had problems, such as significant capacity loss and polarization effects in particularly low-temperature or high-temperature regions, making their use difficult. Furthermore, electrolyte conduction increases in low-temperature environments, and internal ion diffusion rates decrease, resulting in decreased ionic conductivity. The present invention aims to address these issues by introducing a compound additive with a low freezing point and high ionic conductivity.

[0090] Ethylene carbonate, a material with a high dielectric constant (ε = 89), promotes the dissociation of lithium salts and limits ion aggregation, thereby generating a large amount of mobile lithium ions and accelerating the ion conduction characteristics within lithium secondary batteries. In addition, ethylene carbonate plasticizes PEG together with IL, enhancing the movement of mobile segments and preventing ion aggregation. Therefore, lithium ions can easily move through coordination interactions between the ether functional groups of mobile PEG segments even at low temperatures with the help of the ion complex [Li-(EC)5)].

[0091] In addition, the shielding effect of EC is enhanced at high temperatures, facilitating lithium ion transport, and thus, a polymer electrolyte membrane including EC can help transport lithium ions over a wide temperature range.

[0092] According to one example, when the polymer electrolyte membrane for the lithium secondary battery includes an ionic liquid and ethylene carbonate, the ionic liquid and ethylene carbonate may be contained in an amount of 30 to 80 wt% based on the total weight of the polymer electrolyte membrane. In addition, the volume % of the ionic liquid and ethylene carbonate may be 1:0.5 to 2.

[0093] Additionally, the compound additive further includes ethyl propionate (EP).

[0094] The above ethyl propionate, a characteristic component of the present invention, has a low freezing point (-73°C) and low viscosity (0.493 mPa / s), which not only effectively prevents freezing of EC and IL in low-temperature environments but also ensures high mobility of PEG segments. By further including ethyl propionate in the compound additive, it can contribute to maintaining the stability of the fluid PEG segments at both low and high temperatures. Therefore, lithium ion mobility of the PEG domains is facilitated over a wide temperature range.

[0095] According to one example, the ionic liquid, ethylene carbonate, and ethyl propionate of the polymer electrolyte membrane for the lithium secondary battery may be contained in an amount of 30 to 80 wt% based on the total weight of the polymer electrolyte membrane. In addition, the volume % of the ionic liquid, ethylene carbonate, and ethyl propionate may be 1:0.3 to 0.8:0.3 to 0.8.

[0096] For example, a polymer electrolyte membrane comprising IL-EC-EP in PAES-g-2PEG according to one embodiment of the present invention exhibited a high lithium ion mobility of about 0.309 to 0.853 in the temperature range of -40°C to 90°C, and high ionic conductivities of 0.197, 0.757, and 6.0 mS / cm at -40°C, 30°C, and 90°C, respectively, and exhibited high flexibility without mechanical damage in the temperature range of -40°C to 90°C, with a tensile strength of 1.0 MPa and an elongation at break of 80%. In addition, the PAES-g-2PEG polymer electrolyte membrane comprising IL-EC-EP exhibited electrochemical stability windows of 6.0, 5.2, and 4.5 V at -40, 30, and 90°C, respectively, and exhibited high stability without overpotential as a result of a 1000-hour cycling test.

[0097] The polymer electrolyte membrane for the lithium secondary battery may be in the form of a solid electrolyte membrane, and may be formed by casting a solution containing the above-described compound additive as a cosolvent. The manufacturing method will be described later.

[0098]

[0099] Next, a method for manufacturing a polymer electrolyte membrane for a lithium secondary battery according to one embodiment of the present invention will be described.

[0100] Another embodiment of the present invention for achieving the above technical task provides a method for manufacturing a polymer electrolyte membrane for a lithium secondary battery.

[0101] Figure 1 is a flow chart schematically illustrating a method for manufacturing a polymer electrolyte membrane for a lithium secondary battery according to one embodiment of the present invention.

[0102] A method for manufacturing a polymer electrolyte membrane for a lithium secondary battery according to one embodiment of the present invention is characterized by including a step (S100) of mixing a solution including a graft copolymer represented by the following chemical formula 1, an ionic liquid, a cosolvent including ethylene carbonate and ethyl propionate, and a solvent, as shown in FIG. 1; a step (S200) of applying the solution onto a substrate; and a step (S300) of heat-treating the applied solution.

[0103] [Chemical Formula 1]

[0104]

[0105] In the above chemical formula 1, n is an integer from 45 to 90, and k is an integer from 50 to 70.

[0106] First, a step (S100) of mixing a solution including a graft copolymer represented by the above chemical formula 1; a cosolvent including an ionic liquid and ethylene carbonate; and a solvent can be performed.

[0107] Specifically, the step (S100) is to mix the above-described graft copolymer, cosolvent, and solvent, and it is preferable that the cosolvent in the mixed solution is contained in an amount of 30 to 80 wt%.

[0108] As an example, the solvent may be, but is not limited to, tetrahydrofuran (THF).

[0109] According to an example, the mixing may be performed by stirring at room temperature for 10 to 14 hours, and may further include a step (S110) of performing additional ultrasonic treatment on the solution after mixing.

[0110] At this time, the cosolvent is positioned in the PEG domain of the graft copolymer, as described in the secondary battery polymer electrolyte membrane described above, to impart the properties of each compound included in the cosolvent. As described above, the cosolvent includes an ionic liquid and ethylene carbonate, and may further include ethyl propionate or dimethyl carbonate, and preferably may further include ethyl propionate.

[0111] In one example, the co-solvent may be contained in an amount of 30 to 80 wt% relative to the total weight of the polymer electrolyte membrane. In addition, the volume % of the ionic liquid, ethylene carbonate, and ethyl propionate may be 1:0.3 to 0.8:0.3 to 0.8.

[0112] Next, a step (S200) of applying the solution onto a substrate is performed. In one embodiment, the mixed solution may be applied onto a Teflon substrate, and an electrolyte film of a certain thickness may be formed using a doctor blade.

[0113] Afterwards, a step (S300) of heat treating the applied solution is performed.

[0114] According to one example, the applied solution is dried at room temperature for 1 to 3 hours, and then dried at a temperature of 50 to 70°C to completely remove the solvent, thereby manufacturing a polymer electrolyte membrane for a lithium secondary battery.

[0115] A lithium secondary battery including a polymer electrolyte membrane for a lithium secondary battery manufactured according to the above-described method has the characteristics of high ionic conductivity and electrochemical performance, easy lithium ion movement even over a wide temperature range, and excellent physical properties, electrochemical stability, surface stability, and battery performance.

[0116] Hereinafter, the present invention will be described in more detail through manufacturing examples, comparative examples, and experimental examples. However, the present invention is not limited to the following manufacturing examples and experimental examples.

[0117]

[0118] Manufacturing Example 1: Synthesis of PAES-g-2PEG

[0119] First, HPV (5.72 g, 0.02 mol) and FPS (5.08 g, 0.02 mol) were dissolved in a solvent containing DMSO (80 g) and toluene (70 g) in a 500 mL three-necked flask and reacted at 170°C for 24 hours to produce PAES.

[0120] Dried PAES (5.0 g), DCC (4.64 g), DMAP (0.1374 g), and maleic acid (2.01 g) were dissolved in 65 mL of DMF solvent and reacted at 80°C for 48 hours under a nitrogen gas environment to prepare PAES-2COOH.

[0121] The solution was precipitated in IPA, washed with water, and then PAES-2COOH was dried in a vacuum oven at 80 °C for 24 h. PAES-2COOH (3.025 g), PEG (30 g), DMAP (0.046 g), and DCC (5.106 g) were dissolved in 65 mL DMF solvent and stirred at 80 °C for 2 h under a nitrogen gas atmosphere to obtain PAES-2PEG.

[0122] This esterification reaction was carried out at 95°C for 48 hours to obtain a high yield, and the solution was precipitated in 100 mL of ether, impurities were removed with distilled water, and then dried in a vacuum oven at 60°C for 24 hours to obtain PAES-2PEG.

[0123]

[0124] Manufacturing Example 2: IL-EC-EP co-solvent synthesis

[0125] Ionic liquid (IL) was prepared by uniformly dissolving 1-methylpyrrolidine (PYR, 10.0 g) and 1-iodobutane (IB, 19.0 g) in a mixed solvent of THF (10 mL) and ethyl acetate (25 mL) at room temperature for 24 h. IL (PYR-TFSI) was obtained through an ion exchange reaction between dried PYR (9.5 g) and LiTFSI (10 g) in DI (9 g). Next, IL, EC, and EC were mixed in a ratio of 4 / 3 / 3 (volume ratio, v / v / v) to prepare a cosolvent.

[0126]

[0127] Manufacturing Example 3: Manufacturing of electrolyte membrane

[0128] PAES-2PEG (0.2 g) was dissolved in 6 mL of THF solvent, and the solution was stirred evenly. IL-EC-EP co-solvent was dissolved in 1 mL of THF. The solution was stirred at room temperature for 12 h, and then ultrasonicated for 15 min to thoroughly mix the co-solvent and PAES-2PEG. The solution was then applied to a Teflon substrate, dried at room temperature for 2 h, and then dried again at 60 °C to completely remove the THF solvent.

[0129]

[0130] Experimental Example 1: Confirmation of PAGES-g-2PEG synthesis

[0131] Figure 2 is a drawing showing the NMR spectrum of the manufactured PAGES-g-2PEG.

[0132] Figure 3 is a drawing showing the FTIR spectrum of the manufactured PAGES-g-2PEG.

[0133] 1The synthesis of PAES-g-2PEG copolymer was confirmed through H-NMR spectrum. In Fig. 2, peaks at 7.94 ppm, 7.14 ppm, and 7.02 ppm were confirmed from the aromatic functional groups of the PAES main chain, and new peaks at 3.52 ppm and 3.27 ppm were confirmed from the CH2 and CH3 of the grafted side chain PEG.

[0134] Also, in the above figure 3, 1650 cm -1 Esterification between PAES-2COOH and PEG was also confirmed by the vibration occurring in , where C=O appears in the ester group.

[0135]

[0136] Experimental Example 2: Analysis of PAGES-g-2PEG lithium ion transfer number

[0137] Figure 4 is a diagram showing the ionic conductivity of PAES-g-2PEG and PAES-g-2PEG containing various types of cosolvents.

[0138] The ionic conductivity of the PAES-g-2PEG membrane containing various types of co-solvents was determined by the bulk resistance of the Nyquist diagram as shown in Fig. 4, and the ionic conductivity was measured over various temperature ranges.

[0139] Addition of a cosolvent to the electrolyte membrane increases the ionic conductivity when the temperature increases from -40°C to 90°C, because lithium ions become more easily coordinated with the ether groups (-O-) of the mobile PEG segments as the temperature increases.

[0140] In particular, the PAES-g-2PEG membrane using IL-EC-EP showed higher ionic conductivity than the commercial membrane. This suggests that good phase separation of the electrolyte membrane is important for lithium ion transport.

[0141] Specifically, the ionic conductivities of the PAES-g-2PEG membrane using IL-EC-EP were 0.197, 0.757, and 6.0 mS / cm at -40, 30, and 90 °C, respectively, which were higher than the ionic conductivities of the membranes using other co-solvents such as IL-EC and IL-EC-DMC.

[0142] This is because EP, which has low viscosity (0.493 mPa / s), high dielectric constant, high boiling point (99.5 °C), and low freezing point (-73 °C), was used as the IL-EC-EP co-solvent, and the presence of EP contributes to maintaining the fluid PEG segments stable at low and high temperatures. Therefore, lithium ion transport in the PEG domains is facilitated over a wide temperature range.

[0143] Figure 5 is a diagram showing the lithium ion transport capacity of PAES-g-2PEG and PAES-g-2PEG containing various types of cosolvents.

[0144] Lithium ion transport number significantly affects the output of the battery due to the concentration polarization caused by the unwanted migration of TFSI anions as lithium ions move within the electrolyte membrane. Figure 5 shows the lithium ion transport number of PAES-g-2PEG membranes using various types of solvents over a wide temperature range. The PAES-g-2PEG membrane using IL-EC-EP showed the highest lithium ion transport number of 0.309 to 0.853 over the temperature range of -40 °C to 90 °C. At low temperatures, the presence of EP with a low freezing point played a significant role in preventing the freezing state of IL and EC due to their high miscibility.

[0145] IL and EC plasticize PEG, enhancing the mobility of the mobile segments and preventing ion aggregation. Therefore, lithium ions can easily move between the ether functional groups of the mobile PEG segments even at low temperatures with the help of the ionic complex [Li-(EC)5)] through coordination interactions. In addition, it was confirmed that the plasticizing effect of IL-EC-EP and the shielding effect of EC were enhanced at high temperatures, facilitating lithium ion transport. This demonstrated that the self-assembled PAES-g-2PEG membrane using IL-EC-EP is advantageous for lithium ion transport over a wide temperature range.

[0146]

[0147] Experimental Example 3: Mechanical Property Analysis

[0148] Figure 6 is a diagram showing the UTM curve of PAES-g-2PEG and PAES-g-2PEG containing various types of cosolvents.

[0149] Figure 6 shows the tensile strength and elongation at break of PAES-g-2PEG membranes containing 70 wt % of the co-solvent at room temperature, respectively. There is no significant difference in the tensile strength and elongation at break of all PAES-g-2PEG membranes prepared using different co-solvents. The PAES-g-2PEG membrane containing IL-EC-EP exhibits a tensile strength of 1.0 MPa and an elongation at break of 80%.

[0150] Figure 7 is a diagram showing the membrane flexibility of PAES-g-2PEG and PAES-g-2PEG containing various types of cosolvents.

[0151] Figure 8 is a diagram showing the membrane flexibility of PAES-g-2PEG containing IL-EC-EP co-solvent at various temperatures.

[0152] In addition, the flexibility of all manufactured PAES-g-2PEG membranes was investigated through a torsion test. As shown in FIG. 7, the manufactured membrane maintained a solid state with excellent flexibility without mechanical damage even when repeatedly wound around a narrow cylindrical glass rod with a diameter of 5.0 mm due to the presence of rigid PAES domains, and as shown in FIG. 8, the PAES-g-2PEG membrane including IL-EC-EP exhibited high flexibility without mechanical damage even in a wide temperature range of -40°C to 90°C.

[0153]

[0154] Experimental Example 4: Electrochemical Characteristics Analysis

[0155] Figure 9 is a diagram showing LSV curves at various temperatures of PAES-g-2PEG containing IL co-solvent.

[0156] Figure 10 is a diagram showing LSV curves of PAES-g-2PEG containing IL-EC co-solvent at various temperatures.

[0157] Figure 11 is a diagram showing LSV curves at various temperatures of PAES-g-2PEG containing IL-EC-DMC co-solvent.

[0158] Figure 12 is a diagram showing LSV curves at various temperatures of PAES-g-2PEG containing IL-EC-EP co-solvent.

[0159] As shown in the above Figures 9 to 12, it can be seen that the electrochemical stability window of all manufactured PAES-g-2PEG membranes increases as the temperature decreases because the oxidation kinetics is low at low temperatures.

[0160] In particular, the PAES-g-2PEG membrane containing the IL-EC-EP co-solvent (Fig. 12) exhibited electrochemical stability windows of 6.0, 5.2, and 4.5 V at -40, 30, and 90°C, respectively.

[0161]

[0162] Experimental Example 5: Interface Stability Analysis

[0163] Figure 13 shows the plating / stripping voltage-time profiles of PAES-g-2PEG membranes in a lithium symmetric cell with and without EC plasticizer at 2.0 mA / cm.

[0164] As shown in the above Figure 13, the cell assembled with the PAES-g-2PEG membrane including IL-EC-EP delivered a low overpotential (~0.25 V at the initial stage) and was stable without a significant change in the overpotential (0.27 V) even after 1000 h of cycling at room temperature.

[0165] Cells assembled with PAES-g-2PEG membranes containing IL-EC-EP operated well for 1,000 h during stripping and plating without short-circuiting at various temperatures. The results indicate that PAES-g-2PEG membranes containing IL-EC-EP exhibit high interfacial stability, enabling high lithium transport over a wide temperature range, effectively suppressing lithium dendrite growth.

[0166]

[0167] Experimental Example 6: Cell Battery Performance Analysis

[0168] Figure 14 is a diagram showing the charge / discharge profile of PAES-g-2PEG containing IL-EC-EP co-solvent.

[0169] Figure 15 is a diagram showing the rate performance of PAES-g-2PEG containing IL-EC-EP co-solvent.

[0170] Figure 16 is a diagram showing the performance of a Li / SEM / S cell comprising a PAES-g-2PEG membrane containing 70% IL, with or without an EC plasticizer of PAES-g-2PEG containing IL-EC-EP co-solvent.

[0171] As shown in FIG. 14, the cell assembled with the PAES-g-2PEG membrane containing IL-EC-EP shows a high discharge capacity (999.2 mAh / g) at 0.2 C-rate with a Coulombic efficiency of 99.23% at room temperature.

[0172] In addition, as shown in the above Figure 15, it showed high speed performance of 92.93%, 93.21%, and 94.81% at temperatures of -40, 30, and 90 ℃, respectively.

[0173] For long-term tests, cells assembled with PAES-g-2PEG membranes including IL-EC-EP exhibited excellent cycling stability with a Coulombic efficiency of more than 99% after 200 cycles, along with capacity retentions of 70, 95, and 96% at -40, 30, and 90 °C, respectively.

[0174] Therefore, when the polymer electrolyte membrane according to the embodiment of the present invention is used in a lithium secondary battery, there is an effect of increasing the performance of the lithium secondary battery.

[0175] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single entity may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined manner.

[0176] The scope of the present invention is indicated by the claims described below, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. A graft copolymer in which poly(ethylene glycol) is doubly grafted onto poly(arylene ether sulfone), represented by the following chemical formula 1; and Contains compound additives, The above compound additive is, ionic liquid; ethylene carbonate; and ethyl propionate; Polymer electrolyte membrane for lithium secondary batteries characterized by including: [Chemical Formula 1] In the above chemical formula 1, n is an integer from 45 to 90, and k is an integer from 50 to 70.

2. In paragraph 1, The above graft copolymer is, A polymer electrolyte membrane for a lithium secondary battery characterized by being synthesized by an esterification reaction of a compound represented by the following chemical formula 2 and a compound represented by the following chemical formula 3: [Chemical Formula 2] In the above chemical formula 2, n is an integer from 45 to 90. [Chemical Formula 3] In the above chemical formula 3, k is an integer from 50 to 70.

3. In paragraph 1, The above ionic liquid is characterized in that it includes at least one selected from N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR14-TFSI), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI), 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPP-TFSI), 1-methyl-1-butylpiperidinium bis(trifluoromethylsulfonyl)imide (MBP-TFSI), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI-TFSI). Polymer electrolyte membrane for secondary batteries.

4. In paragraph 1, A polymer electrolyte membrane for a lithium secondary battery, characterized in that the compound additive is contained in an amount of 30 to 80 wt% relative to the total weight of the polymer electrolyte membrane.

5. A lithium secondary battery comprising the polymer electrolyte membrane for a lithium secondary battery of paragraph 1.

6. A step of mixing a solution containing a graft copolymer represented by the following chemical formula 1, a cosolvent, and a solvent; A step of applying the above solution onto a substrate; and a step of heat treating the applied solution; The above common solvent is, A method for manufacturing a polymer electrolyte membrane for a lithium secondary battery, characterized in that it comprises an ionic liquid, ethylene carbonate, and ethyl propionate: [Chemical Formula 1] In the above chemical formula 1, n is an integer from 45 to 90, and k is an integer from 50 to 70.

7. In paragraph 6, The above ionic liquid is characterized in that it includes at least one selected from N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR14-TFSI), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI), 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPP-TFSI), 1-methyl-1-butylpiperidinium bis(trifluoromethylsulfonyl)imide (MBP-TFSI), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI-TFSI). Method for manufacturing a polymer electrolyte membrane for secondary batteries.

8. In paragraph 6, A method for manufacturing a polymer electrolyte membrane for a lithium secondary battery, characterized in that the co-solvent is contained in the solution at 30 to 80 wt%.

9. In paragraph 6, A method for manufacturing a polymer electrolyte membrane for a lithium secondary battery, characterized in that the solvent of the above mixed solution includes tetrahydrofuran (THF).

10. In paragraph 6, A method for manufacturing a polymer electrolyte membrane for a lithium secondary battery, characterized in that it further comprises a step of ultrasonic treating the solution after the above mixing step.

11. A polymer electrolyte membrane for a lithium secondary battery manufactured by the manufacturing method of Article 6.

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