Water-based binder for lithium secondary battery and lithium secondary battery comprising the same

Abstract

This invention relates to an adhesive that can be used in lithium secondary batteries, particularly lithium-sulfur batteries, wherein the adhesive is manufactured via a reversible addition-fragmentation chain transfer (RAFT) polymerization reaction and has a structure comprising polymethyl methacrylate-derived blocks and polyacrylic acid-derived blocks centered on a thiocarbonyl sulfur functional group, and an aliphatic functional group at the outermost end. Therefore, it has the effect of improving the conductivity of the electrode using the adhesive and suppressing the dissolution of lithium polysulfides.

Description

Technical Field

[0001] This invention relates to an aqueous binder for use in lithium secondary battery electrodes. More particularly, this invention relates to an aqueous binder for use in the positive electrode of a lithium-sulfur battery using a lithium metal negative electrode, and a lithium secondary battery comprising the same.

[0002] This application is based on and claims priority to Korean Patent Application No. 2024-0116057, filed in Korea on August 28, 2024, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] Because lithium-ion batteries are used in a wide range of applications, including not only portable electronic devices, but also electric vehicles (EVs) and energy storage systems (ESS), there is an increasing demand for lithium-ion batteries with higher capacity, higher energy density and longer lifespan.

[0004] In lithium-ion secondary batteries, lithium-sulfur batteries are battery systems that use sulfur-based materials containing sulfur-sulfur bonds as the positive electrode active material and lithium metal, carbon-based materials in which lithium ions intercalate / deintercalate, or silicon or tin alloyed with lithium as the negative electrode active material. In lithium-sulfur batteries, sulfur, as the main component of the positive electrode active material, has a low atomic weight, is abundant and readily available globally, and is inexpensive, low in toxicity, and environmentally friendly.

[0005] Furthermore, in lithium-sulfur batteries, the conversion reaction between lithium ions and sulfur in the cathode (S₈ + 16Li) is based on... + +16e - The theoretical specific capacity of →8Li₂S is 1,675 mAh / g, and the theoretical energy density is 2,600 Wh / kg when lithium metal is used as the anode. Because this value is higher than the theoretical energy density of other battery systems currently under investigation (Ni-MH battery: 450 Wh / kg, Li-FeS battery: 480 Wh / kg, Li-MnO₂ battery: 1,000 Wh / kg, Na-S battery: 800 Wh / kg) and lithium-ion batteries (250 Wh / kg), lithium-sulfur batteries are attracting attention as a high-capacity, environmentally friendly, and low-cost lithium-ion secondary battery among those developed to date.

[0006] During the discharge of a lithium-sulfur battery, sulfur undergoes a reduction reaction as it accepts electrons at the positive electrode, resulting in the formation of lithium polysulfides (Li₂S₂) at the positive electrode. x(x=2~8), and some lithium polysulfides readily dissolve in the electrolyte, causing side reactions in the battery. This leads to accelerated battery degradation, and during charging, shuttle reactions occur, resulting in a significant decrease in charge / discharge efficiency. Therefore, the specific capacity of currently developed lithium-sulfur batteries is far lower than their theoretical specific capacity. Thus, there is a need to develop lithium-sulfur batteries with specific capacities as high as the theoretical level.

[0007] In particular, technologies need to be developed to suppress the decrease in energy density caused by the loss of positive electrode active material due to the shuttle effect. Summary of the Invention

[0008] Technical issues

[0009] The present invention aims to solve the above problems, and therefore aims to provide a lithium-sulfur battery with a specific capacity as high as the theoretical specific capacity level.

[0010] The present invention also aims to provide a lithium-sulfur battery with high energy density.

[0011] Technical solution

[0012] To achieve the above objectives, according to one aspect of the present invention, an adhesive is provided for a lithium secondary battery according to the following embodiments.

[0013] The adhesive for lithium secondary batteries according to the first embodiment comprises: The thiocarbonyl sulfur functional group represented by Equation 1 below; The first polymethyl methacrylate-derived block is covalently bonded to one end of the thiocarbonyl sulfur functional group; A second polymethyl methacrylate-derived block covalently bonded to the other end of the thiocarbonyl sulfur functional group; A first polyacrylic acid-derived block covalently bonded to one end of a first polymethyl methacrylate-derived block; and A second polyacrylic acid-derived block covalently bonded to one end of a second polymethyl methacrylate-derived block. The outermost terminal organic functional groups include aliphatic functional groups. [Formula 1]

[0014] According to the second implementation plan, in the first implementation plan... At least one carboxyl group (-COOH) in the first polyacrylic acid-derived block and the second polyacrylic acid-derived block may include a lithium-substituted carboxyl group (-COO). - Li + ).

[0015] According to the third implementation scheme, in the first or second implementation scheme... The first polyacrylic acid-derived block and the second polyacrylic acid-derived block can each independently contain 50 to 1500 repeating acrylic acid structures.

[0016] According to the fourth implementation plan, in any of the first to third implementation plans, The first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block can each independently contain 50 to 1500 repeating alkyl methacrylate structures.

[0017] According to the fifth implementation plan, in any one of the first to fourth implementation plans, The alkyl group contained in at least one of the first polymethyl methacrylate-derived block or the second polymethyl methacrylate-derived block may contain at least one of polyethylene glycol repeating units, polypropylene glycol repeating units, or polyethylene glycol-polypropylene glycol repeating units.

[0018] According to the sixth implementation plan, in any one of the first to fifth implementation plans, The alkyl group may contain 1 to 30 repeating polyethylene glycol units.

[0019] According to the seventh implementation plan, in any one of the first to sixth implementation plans, The outermost terminal organic functional group may include a lithium-substituted carboxyl group (-COO). - Li + ).

[0020] According to the eighth implementation plan, in any one of the first to seventh implementation plans, The pH of the dispersion of the binder for lithium secondary batteries in water can be in the range of 6.2 to 7.8.

[0021] According to another embodiment of the present invention, a method for manufacturing an electrode for a lithium secondary battery is provided.

[0022] The method for manufacturing electrodes for lithium secondary batteries according to the ninth embodiment may include: A slurry is applied to at least one surface of a current collector and dried to obtain an electrode. The slurry comprises a mixture of a binder, a sulfur compound, and a conductive carbon material in an aqueous solvent according to any one of the first to eighth embodiments.

[0023] According to the tenth implementation plan, in the ninth implementation plan, The method may include obtaining an adhesive through the polymerization reaction of a reversible addition-fragmentation chain transfer (RAFT) initiator containing aliphatic and thiocarbonyl functional groups, an alkyl methacrylate, and acrylic acid.

[0024] According to the eleventh implementation plan, in the ninth or tenth implementation plan, Before the polymerization reaction, The method may also include preparing a RAFT initiator as a mixture of carbon disulfide (CS2), trihalomethane, and tetraalkylammonium bisulfate.

[0025] According to the twelfth implementation plan, in any one of the ninth to eleventh implementation plans, RAFT initiators may include S,S'-bis(R,R'-dimethyl-R''-acetic acid)-trithiocarbonate (BDAAT).

[0026] According to the thirteenth implementation plan, in any one of the ninth to twelfth implementation plans, The method may include heat-treating a mixture of sulfur compounds and conductive carbon materials to obtain a sulfur-carbon composite, and A slurry can be obtained by mixing a sulfur-carbon composite with a binder in an aqueous solvent.

[0027] According to the fourteenth implementation plan, in any one of the ninth to thirteenth implementation plans, The obtained electrode may include a current collector and an active material layer present on at least one surface of the current collector, and The thickness of the active material layer can be 250 μm or more.

[0028] According to yet another embodiment of the present invention, an electrode for a lithium secondary battery is provided according to the following embodiment.

[0029] The electrode for a lithium secondary battery according to the fifteenth embodiment may include: The adhesive, sulfur compound, and conductive carbon material according to any one of the first to eighth embodiments.

[0030] According to yet another embodiment of the present invention, a lithium secondary battery is provided according to the following embodiment.

[0031] The lithium secondary battery according to the sixteenth embodiment may include: Electrode according to the fifteenth embodiment.

[0032] Beneficial effects

[0033] The adhesive according to one aspect of the invention comprises blocks in the main chain that have functional groups capable of hydrogen bonding at their ends and exhibit high elasticity and ionic conductivity. Therefore, the adhesive according to one aspect of the invention, due to its high elasticity, can have a beneficial effect on suppressing volume expansion when used in the electrodes of lithium secondary batteries. Furthermore, when the adhesive is used in the positive electrode of lithium-sulfur batteries, it has the advantage of suppressing the shuttle effect of lithium polysulfides dissolved from the positive electrode.

[0034] In particular, compared with existing polyacrylic acid (PAA) adhesives, the ionic conductivity of the adhesive can be significantly improved by including highly elastic and ionicly conductive blocks in the main chain. Therefore, it is possible to manufacture an adhesive suitable for water-based adhesive processes, and electrodes can be manufactured through water-based processes by using this adhesive.

[0035] Therefore, compared with electrodes using existing aqueous binders such as PAA, there are advantages in providing lithium secondary batteries, especially lithium-sulfur batteries, with improved electrochemical performance. Attached Figure Description

[0036] Figure 1 The 1H nuclear magnetic resonance (NMR) of the intermediate product during the synthesis process of Example 1 in this specification is shown.

[0037] Figure 2 The 1H NMR of Example 1 in this specification is shown.

[0038] Figure 3 The Fourier transform infrared (FT-IR) spectra of Examples 1 and 2 in this specification are shown.

[0039] Figure 4 The 1H NMR of the intermediate product during the synthesis process of Example 3 in this specification is shown.

[0040] Figure 5 The 1H NMR of Example 3 in this specification is shown.

[0041] Figure 6 The FT-IR spectra of Examples 3 and 4 in this specification are shown.

[0042] Figure 7 The images are scanning electron microscope (SEM) images of the surface of a positive electrode with the indicated thickness, manufactured using PAA adhesive, the adhesive of Example 1, and the adhesive of Example 2 according to the experimental examples in this specification.

[0043] Figure 8 It is a graph showing the measurement results of the change in discharge capacity with charge-discharge cycles according to the experimental examples in this specification.

[0044] Figure 9 It is a graph showing the measurement results of the change in discharge capacity with charge-discharge cycles according to the experimental examples in this specification. Detailed Implementation

[0045] The present invention will be described in more detail below.

[0046] The terms or words used in the specification and the appended claims should not be construed as limited to the general and dictionary meanings, but should be interpreted based on the principle that allows the inventor to appropriately define the terms for the best explanation, according to the meanings and concepts corresponding to the technical aspects of the present invention.

[0047] As used herein, the terms are used to describe embodiments of the present invention but are not intended to be limiting. Unless the context clearly dictates otherwise, the singular forms include the plural forms. It should be understood that when used in this specification, the terms "comprising", "including" and "having" specifically denote the presence of the stated features, numbers, steps, operations, elements, components or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components or combinations thereof.

[0048] As used herein, the term "complex" refers to a combination of two or more materials, thus having physically and chemically distinct phases and being more effective in function.

[0049] As used herein, the term "(poly)sulfide" includes "(poly)sulfide ions (S x 2- , 1 ≤ x - ≤ 8)" and "(poly)lithium sulfide (Li2S x or Li2S x - , 1 ≤ x ≤ 8)".

[0050] As used herein, the term "polysulfide" includes "polysulfide ions (S x 2- , 1 < x - ≤ 8)" and "polylithium sulfide (Li2S x or Li2S x - , 1 < x ≤ 8)".

[0051] In a lithium-sulfur battery, during charge and discharge, polysulfide generated by the reduction reaction of sulfur (S8) dissolves from the positive electrode into the electrolyte, resulting in a battery capacity lower than the theoretical capacity.

[0052] According to one aspect of the present invention, there is provided a lithium-sulfur battery, an electrode for a lithium-sulfur battery, and an adhesive for use in a lithium-sulfur battery, the lithium-sulfur battery having improved electrochemical performance by suppressing the dissolution of polysulfide from the positive electrode and improving the conductivity of the electrode. In addition, there is provided an adhesive for use in any other type of lithium secondary battery and an electrochemical device.

[0053] The adhesive for a lithium secondary battery according to one aspect of the present invention comprises: A thiocarbonylthio functional group represented by the following formula 1; The first polymethyl methacrylate-derived block is covalently bonded to one end of the thiocarbonyl sulfur functional group; A second polymethyl methacrylate-derived block covalently bonded to the other end of the thiocarbonyl sulfur functional group; A first polyacrylic acid-derived block covalently bonded to one end of a first polymethyl methacrylate-derived block; and A second polyacrylic acid-derived block covalently bonded to one end of a second polymethyl methacrylate-derived block.

[0054] [Formula 1]

[0055] Specifically, the organic functional groups at the outermost end of the adhesive include aliphatic functional groups.

[0056] In one embodiment of the invention, the organic functional group at the outermost end of the adhesive can be bonded to the outermost ends of the first polyacrylic acid-derived block and the second polyacrylic acid-derived block, and preferably, can be composed of aliphatic functional groups.

[0057] In one embodiment of the invention, the structure of the adhesive may be represented by, for example, the following chemical formula 1, but the invention is not limited thereto.

[0058] [Chemical Formula 1]

[0059] In the above chemical formula 1, R1 and R2 are each independently selected from Li + H, C1-C 50 Alkyl group, -(C2H4O)oM5 (o = integers from 1 to 20, M5 = Li + H or direct bond) and -(C3H6O)pM6 (p = integers from 1 to 20, M6 = Li + At least one of (H or direct bond), M1 and M2 are each independently selected from Li + and H, A and B are each independently aliphatic functional groups. n1 and n2 are each independent integers between 50 and 1500. m1 and m2 are each independent integers from 50 to 1500.

[0060] In one embodiment of the invention, the first polyacrylic acid-derived block and the second polyacrylic acid-derived block may each contain a repeating unit as shown in the above chemical formula 1 -(C2H3C(O)OQ)- (where Q=M1 or M2).

[0061] In one embodiment of the invention, at least one carboxyl group (-COOQ) in the first polyacrylic acid-derived block and the second polyacrylic acid-derived block may comprise a lithium-substituted carboxyl group (-COO). - Li + ).

[0062] In another embodiment of the invention, when the carboxyl groups in the first polyacrylic acid-derived block and the second polyacrylic acid-derived block are completely replaced by lithium, it can have -COO. - Li + The structure.

[0063] Because the carboxyl groups in the first polyacrylic acid-derived block and the second polyacrylic acid-derived block have lithium-substituted structures, when they are included in the electrode, there may be an effect of inhibiting the dissolution of lithium polysulfides from the electrode through hydrogen bonding, but the mechanism of the present invention is not limited thereto.

[0064] In one embodiment of the invention, the first polyacrylic acid-derived block and the second polyacrylic acid-derived block may each independently comprise 50 to 1500 repeating acrylic acid structures. For example, in the above chemical formula 1, n1 and n2 may each independently be an integer of 50 to 1500, 100 to 1300, 100 to 1500, 200 to 1300, 300 to 1300, 500 to 1300, 1000 to 1200, or 1050 to 1150, or 1100, but the invention is not limited thereto.

[0065] In one embodiment of the invention, the adhesive comprises a first polymethyl methacrylate-derived block between a thiocarbonyl sulfide functional group and a first polyacrylic acid-derived block, and a second polymethyl methacrylate-derived block between a thiocarbonyl sulfide functional group and a second polyacrylic acid-derived block. Because the first and second polymethyl methacrylate-derived blocks are each comprised between a thiocarbonyl sulfide functional group and a polyacrylic acid-derived block, they can improve the elasticity and / or ionic conductivity of the adhesive, but the mechanism of the invention is not limited thereto.

[0066] In one embodiment of the invention, the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may each independently comprise 50 to 1500 repeating alkyl methacrylate structures, and may comprise, for example, 100 to 1500 repeating alkyl methacrylate structures. For example, in the above chemical formula 1, m1 and m2 may each independently be an integer of 50 to 1500, 100 to 1500, 200 to 1300, 300 to 1300, 500 to 1300, 800 to 1200, 1000 to 1200, 1000 to 1100, 1050 to 1150, or 1100, but the invention is not limited thereto.

[0067] In one embodiment of the invention, the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may each contain a repeating unit as shown in Formula 1 above -(C2H3C(O)OW)- (where W=R1 or R2).

[0068] In one embodiment of the invention, the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may each independently contain components selected from Li, depending on the type of monomer used to manufacture them. + H, C1-C 50 Alkyl group, -(C2H4O)oM5 (o = integers from 1 to 20, M5 = Li + H or direct bond) and -(C3H6O)pM6 (p = integers from 1 to 20, M6 = Li + At least one of the following structures (H or direct bond) is used as the structure of R1 and R2.

[0069] In another embodiment of the invention, in the first polymethyl methacrylate-derived block and the second polymethyl methacrylate-derived block, R1 and R2 may each independently contain -(C2H4O)oM5 (o = an integer from 1 to 20, M5 = Li). + H or direct bond) and -(C3H6O)pM6 (p = integers from 1 to 20, M6 = Li +The structure consists of H or direct bonds. The -(C2H4O)o- structure is a repeating unit of polyethylene glycol (PEG), and the -(C3H6O)p- structure is a repeating unit of polypropylene glycol (PPG). The first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block can each independently contain PEG, PPG, or polyethylene glycol-polypropylene glycol (PEGPPG) within the structure. Because all PEG, PPG, and PEGPPG structures have a -OH structure at the end, there is an advantage in increasing the concentration of terminal -OH in the adhesive, thereby significantly improving the ionic conductivity and elasticity of the adhesive, but the mechanism of the present invention is not limited thereto.

[0070] In one embodiment of the invention, at least one of the first polyalkyl methacrylate-derived block or the second polyalkyl methacrylate-derived block may contain at least one of polyethylene glycol repeating units, polypropylene glycol repeating units, or polyethylene glycol-polypropylene glycol repeating units.

[0071] In one embodiment of the invention, when at least one of the first polyalkyl methacrylate-derived block or the second polyalkyl methacrylate-derived block comprises at least one of polyethylene glycol repeating unit, polypropylene glycol repeating unit or polyethylene glycol-polypropylene glycol repeating unit, the number of repeating units may be, for example, 1 to 30, specifically 1 to 25 or 1 to 20, but the invention is not limited thereto.

[0072] In one embodiment of the invention, the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may each contain polyethylene glycol repeating units as R1 and R2 in the above-described chemical formula 1. In this case, the number of polyethylene glycol repeating units may be 1 to 30, specifically 1 to 25 or 1 to 20, for example 5 to 15, 5 to 10, 6 to 9 or 9, but the invention is not limited thereto.

[0073] In one embodiment of the invention, in the first polymethyl methacrylate-derived block and the second polymethyl methacrylate-derived block, at least a portion of the terminal hydroxyl groups (-OH) of the polyethylene glycol group, polypropylene glycol group, or polyethylene glycol-polypropylene glycol group can be replaced with lithium to obtain -O-Li. + The structure.

[0074] In another embodiment of the invention, in the first polymethyl methacrylate-derived block and the second polymethyl methacrylate-derived block, the terminal hydroxyl groups (-OH) of the polyethylene glycol groups, polypropylene glycol groups, or polyethylene glycol-polypropylene glycol groups can be completely replaced by lithium to obtain -O-Li. + The structure.

[0075] In one embodiment of the invention, the adhesive may include an aliphatic functional group as an organic functional group at its outermost end. Specifically, in the above chemical formula 1, structures A and B may contain aliphatic functional groups. More specifically, in the above chemical formula 1, structures A and B may be composed of aliphatic functional groups.

[0076] In one embodiment of the invention, structures A and B can be structures derived from polyacrylic acid, and can be represented, for example, by the following chemical formulas 2 and 3, respectively.

[0077] [Chemical Formula 2]

[0078] [Chemical Formula 3]

[0079] In the above chemical formulas 2 and 3, M3 and M4 were each independently selected from Li + And H.

[0080] In one embodiment of the present invention, when structure A and structure B in the adhesive have structures of chemical formula 2 and chemical formula 3, respectively, M3 and M4 can be lithiumized to form Li. + .

[0081] According to one embodiment of the invention, the adhesive can be modified by lithium-substituted carboxyl groups (-COO) at the ends. - Li + The present invention can improve the adsorption of lithium polysulfides, thereby suppressing the shuttle effect of lithium polysulfides dissolved from the electrode into the electrolyte, but the mechanism of the present invention is not limited thereto.

[0082] In one embodiment of the invention, the adhesive preferably exhibits a pH below 8 when dispersed in water due to the carboxyl functional groups included in its structure. More preferably, because at least a portion of the carboxyl groups in the adhesive are lithium-substituted (-COO) - Li + The presence of this component allows the adhesive, when dispersed in water, to exhibit, for example, a pH greater than 6 and less than 8, more preferably a pH greater than 6.0 and less than 8.0.

[0083] In one embodiment of the invention, the pH of the dispersion of the adhesive in water may be, for example, in the range of 6.2 to 7.8, specifically in the range of 6.3 to 7.7, 6.4 to 7.6, or 6.5 to 7.4.

[0084] In this specification, the pH of the adhesive dispersion in water can be measured by any known method for measuring the pH of the adhesive dispersion in water, and the measurement method is not limited to any particular method. For example, pH can be measured at room temperature (23°C) in a 5% by weight adhesive dispersion. Furthermore, the pH of aqueous dispersions can be measured using a known pH meter such as the ThermoFisher Scientific Orion Star A121, but the measurement method is not limited to this.

[0085] When considering that the pH of the PAA adhesive dispersion in water is below 6.0, for example in the range of 4.5 to 6.0, the adhesive according to one embodiment of the invention may be more advantageous in terms of stability in the manufacture of electrodes for lithium secondary batteries, but the invention is not limited thereto.

[0086] In one embodiment of the invention, the adhesive may comprise a first polyalkyl methacrylate-derived block and a second polyalkyl methacrylate-derived block that are symmetrical or asymmetrical with respect to the thiocarbonyl sulfur functional group. Regarding ease of adhesive synthesis, the adhesive may have a symmetrical structure of the first and second polyalkyl methacrylate-derived blocks with respect to the thiocarbonyl sulfur functional group, but the invention is not limited thereto.

[0087] In one embodiment of the invention, the adhesive may comprise a first polyacrylic acid-derived block and a second polyacrylic acid-derived block that are symmetrical or asymmetrical with respect to the thiocarbonyl sulfur functional group. Regarding ease of adhesive synthesis, the adhesive may have a symmetrical structure of the first and second polyacrylic acid-derived blocks with respect to the thiocarbonyl sulfur functional group, but the invention is not limited thereto.

[0088] In one embodiment of the invention, the adhesive may comprise structures A and B that are symmetrical or asymmetrical with respect to the thiocarbonylsulfonium functional group. Regarding ease of synthesizing the adhesive, the adhesive may have structures A and B that are symmetrical with respect to the thiocarbonylsulfonium functional group, but the invention is not limited thereto.

[0089] In one embodiment of the invention, the adhesive may comprise a compound having the structure of the following chemical formula 4.

[0090] [Chemical Formula 4]

[0091] In the above chemical formula 4, n1 and n2 are each independent integers between 50 and 1500. m1 and m2 are each independent integers from 50 to 1500.

[0092] In one embodiment of the invention, the viscosity of the adhesive is not limited to a specific range and can be within a suitable range for use in electrodes for lithium secondary batteries, but for example, based on a solution of 3% by weight of the adhesive in water, the adhesive may preferably have a molecular weight of 3000 cP or higher at 23°C. Here, viscosity refers to the standard viscosity measured using the intrinsic viscosity measurement method with Bath, Kinematicviscosity (J-BV08).

[0093] In one embodiment of the invention, the weight-average molecular weight (Mw) of the adhesive can be, for example, from 7,000 g / mol to 1,000,000 g / mol. Specifically, the weight-average molecular weight of the adhesive can be from 10,000 g / mol to 900,000 g / mol, 50,000 g / mol to 800,000 g / mol, 100,000 g / mol to 500,000 g / mol, 200,000 g / mol to 400,000 g / mol, 250,000 g / mol to 350,000 g / mol, or 250,000 g / mol to 300,000 g / mol, specifically 300,000 g / mol, but the invention is not limited thereto.

[0094] In one embodiment of the invention, the weight-average molecular weight of the adhesive can be measured by any known method for measuring the weight-average molecular weight of the polymer, and the measurement method is not limited to a specific method. For example, the weight-average molecular weight of the adhesive can be used. 1 HNMR, 13 C NMR, mass spectrometry, FT-IR or HPLC analysis are used for measurement.

[0095] In one embodiment of the present invention, the weight-average molecular weight of the adhesive can be measured by the following method, but the measurement method is not limited thereto.

[0096] In one embodiment of the invention, the weight-average molecular weight (Mw) of 1 g of adhesive solution is calculated using gel permeation chromatography (GPC, PL GPC220, Agilent Technologies) under the following conditions.

[0097] Column: PL hybrid B×2, Solvent: DMF / 0.05 M LiBr (filtered at 0.45 μm) Flow rate: 1.0 ml / min Sample concentration: 4.0 mg / ml Injection volume: 100 μl Column temperature: 65℃ Detector: Waters RI detector, Standard: PS The following will describe a method for manufacturing an adhesive according to one embodiment of the present invention. However, the adhesive having the above-described structure can be manufactured by any other organic synthesis method, and the method for manufacturing the adhesive is not limited thereto.

[0098] According to one embodiment of the invention, the adhesive can be manufactured by a reversible addition-fragmentation chain transfer polymerization (RAFT polymerization) reaction.

[0099] In one embodiment of the present invention, the method for manufacturing an adhesive by RAFT polymerization may mainly include the following two steps: Prepare RAFT initiators; and The polymerization reaction between the polymer raw materials was carried out using the prepared RAFT initiator.

[0100] In one embodiment of the present invention, the RAFT initiator can be prepared by obtaining commercially available RAFT reagents or by direct preparation, and the preparation method is not limited to a specific method.

[0101] In one embodiment of the invention, the organic functional groups contained in the RAFT initiator can be included as terminal functional groups of the adhesive, and as described above, the organic functional groups at the outermost ends of the adhesive include aliphatic functional groups. Therefore, preferably, the RAFT initiator can contain aliphatic functional groups, and more specifically, a RAFT initiator composed of aliphatic functional groups can be prepared.

[0102] In one embodiment of the present invention, the RAFT initiator may contain an aliphatic functional group and a thiocarbonyl thiofunctional group.

[0103] According to one embodiment of the invention, the RAFT initiator can be prepared using a mixture of carbon disulfide (CS2), trihalomethane, and tetraalkylammonium bisulfate.

[0104] For example, RAFT initiators can be obtained by adding carbon disulfide (CS2) and trihalomethanes to an organic solvent such as acetone, adding tetraalkylammonium bisulfate as a phase transfer catalyst (PTC) and mixing them together, followed by the addition of NaOH, and finally acid treatment with HCl.

[0105] According to one embodiment of the present invention, trihalomethanes may include trichloromethane.

[0106] According to one embodiment of the present invention, tetraalkylammonium bisulfate may include tetrabutylammonium bisulfate.

[0107] According to one embodiment of the present invention, the RAFT initiator may include S,S'-bis(R,R'-dimethyl-R''-acetic acid)-trithiocarbonate (BDAAT).

[0108] In one embodiment of the invention, the adhesive can be obtained by dissolving a prepared RAFT initiator and a predetermined amount of polymerizing raw materials in an organic solvent, followed by thermal polymerization.

[0109] In one embodiment of the invention, the second step can be carried out using a RAFT initiator to simultaneously form polymethyl methacrylate-derived blocks and polyacrylic acid-derived blocks in a one-step reaction.

[0110] In another embodiment of the invention, the second step can be carried out using a RAFT initiator to sequentially form polymethyl methacrylate-derived blocks and polyacrylic acid-derived blocks through a two-step reaction.

[0111] For example, in one embodiment of the invention, the second step may include sequentially forming polyacrylic acid-derived blocks on a RAFT initiator and forming polyalkyl methacrylate. To this end, firstly, the prepared RAFT initiator and a predetermined equivalent of an acrylic monomer can be dissolved in an organic solvent, followed by thermal polymerization to obtain a precursor comprising polyacrylic acid-derived blocks bound to the RAFT initiator. Subsequently, the precursor and a predetermined equivalent of an alkyl methacrylate monomer can be dissolved in an organic solvent, followed by thermal polymerization to obtain an adhesive.

[0112] In one embodiment of the invention, the method of manufacturing the adhesive may further include a step of lithiation of the resulting adhesive. For example, the adhesive may contain a plurality of carboxyl groups at the ends, and in this case, for lithiation of the carboxyl groups, the lithilated adhesive may be obtained by contacting the adhesive with an aqueous LiOH solution.

[0113] For example, an adhesive represented by the following chemical formula 4 can be manufactured by the following methods, but the methods for manufacturing adhesives are not limited to this.

[0114] First, prepare the BDAAT as a RAFT initiator.

[0115] 0.25 mmol of prepared BDAAT was dissolved together with 400 equivalents of acrylic acid (AA) and 4,4'-azobis(4-cyanopentanoic acid) (V-501) in 20 ml of 1,4-dioxane, and reacted at 75 °C for 18 hours to obtain the intermediate product (PAA). 400 ). 0.8 g of the intermediate product (PAA) was obtained. 400) was dissolved in 30 ml of distilled water along with 400 equivalents of poly(ethylene glycol) methyl ether acrylate (PM) (Mn=480) and V-501, and reacted at 75°C for 18 hours to obtain the intermediate product P(AA). 400 -b-PM 400 At room temperature, relative to the obtained P(AA) 400 -b-PM 400 After reacting P(AA) with 4 equivalents of 10% by weight LiOH aqueous solution overnight, P(AA) was obtained. 400 -b-PM 400 )-Li.

[0116] [Chemical Formula 4]

[0117] According to another aspect of the present invention, a method for manufacturing an electrode for a lithium secondary battery using the above-described adhesive can be provided.

[0118] A method for manufacturing electrodes for lithium secondary batteries may include the following steps: coating a slurry containing a mixture of binder and active material in a suitable solvent onto at least one surface of a current collector; and drying the slurry. Optionally, the slurry may also contain a conductive material.

[0119] According to one aspect of the invention, the binder can be particularly efficient in suppressing the dissolution of lithium polysulfides within the positive electrode of a lithium-sulfur battery. Therefore, the binder can be used to manufacture the positive electrode of a lithium-sulfur battery, and the method for manufacturing a lithium secondary battery electrode can be the same as the method for manufacturing a lithium-sulfur battery positive electrode.

[0120] A method for manufacturing a lithium secondary battery according to one aspect of the present invention may include: coating a slurry containing a mixture of a binder, a sulfur compound and a conductive carbon material in an aqueous solvent onto at least one surface of a current collector; and drying the slurry to obtain an electrode.

[0121] For details on the adhesive, please refer to the adhesive description above.

[0122] In one embodiment of the invention, the binder can be readily dissolved in an aqueous solvent (specifically, water) through lithiation of the terminal functional groups. Therefore, the method of fabricating electrodes using the binder can have the advantage of using an aqueous solvent (specifically, water). In this case, the water may include distilled water or deionized water. However, the invention is not necessarily limited thereto, and if necessary, lower alcohols that are readily miscible with water can be used. Lower alcohols may include, for example, methanol, ethanol, propanol, isopropanol, and butanol, and preferably, they are miscible with water. The amount of solvent in the slurry can be at an optimal concentration for easy coating and can vary depending on the coating method and apparatus.

[0123] The method of coating the slurry is not limited to the specific method in the present invention, and may include, for example, blade coating, die casting, comma coating or screen printing. In addition, the slurry can be coated onto the current collector by forming on a substrate and pressing or laminating.

[0124] After coating, a drying process can be carried out to remove the solvent. The drying process can be carried out at a temperature and for a time sufficient to remove the solvent. The conditions can vary according to the type of solvent and are not particularly limited to the present invention. For example, the drying method can include: warm air drying, hot air drying or low humidity air drying; vacuum drying; or drying using radiation such as (far) infrared rays or electron beams. Generally, the drying speed is adjusted to remove the solvent as quickly as possible within a speed range, thereby preventing cracks in the active material layer or separation of the active material layer from the current collector due to stress accumulation.

[0125] In addition, in one embodiment of the present invention, after drying, the method may further include a step of pressing the electrode to increase the density of the active material within the electrode. The pressing method can include, for example, die pressing or roll pressing.

[0126] In one embodiment of the present invention, the porosity of the electrode manufactured by the above composition and manufacturing method, specifically the porosity of the positive electrode active material layer containing a sulfur-based compound, can be 50 to 80% by volume, specifically 60 to 75% by volume. When the porosity of the positive electrode is less than 50% by volume, the filling degree of the positive electrode slurry composition containing the positive electrode active material, the conductive material and the binder is too high, so that it is impossible to retain a sufficient amount of electrolyte to ensure ion conduction and / or electrical conduction between the positive electrode active materials, which reduces the output characteristics or cycle characteristics of the battery and exacerbates the decrease in the overvoltage and discharge capacity of the battery. On the contrary, when the positive electrode has an excessively high porosity of more than 80% by volume, it results in a reduction in the physical and electrical connection with the current collector, thus resulting in low adhesion strength and poor reaction, and the increased porosity is filled with electrolyte, which can lead to a decrease in the energy density of the battery. Therefore, the porosity is appropriately adjusted to the above range.

[0127] In one embodiment of the present invention, the sulfur-based compound is not limited to a specific sulfur-based compound, and may include any material containing a disulfide (SS) structure that can be used as a positive electrode active material of a lithium-sulfur battery. The sulfur-based compound can include, for example, any sulfur-containing compound that can be formed by the reduction reaction of inorganic sulfur (S8) or the oxidation reaction of lithium sulfide (Li2S). Specifically, the sulfur-based compound can include inorganic sulfur (S8), lithium sulfide (Li2S), polysulfide (Li2S x , 1 < x ≤ 8), disulfide compounds, carbon-sulfur polymers ((C₂S y )) n , y = 2.5 to 50, n ≥ 2) or more than two of them.

[0128] In one embodiment of the invention, the sulfur compound may preferably include inorganic sulfur (S8).

[0129] In one embodiment of the invention, sulfur compounds can be used in the form of a sulfur-carbon composite supported on a conductive porous carbon material. Specifically, the sulfur-carbon composite may comprise the porous carbon material and a sulfur compound supported on at least one of the pores of the porous carbon material or on the outer surface of the porous carbon material. Because sulfur used as a positive electrode active material is not conductive, sulfur can preferably be combined with a conductive material such as carbon to form a composite. Therefore, for loading sulfur compounds, the conductive carbon material preferably comprises a porous material.

[0130] In one embodiment of the present invention, the porous carbon material can be loaded with sulfur compounds as positive electrode active materials, providing a uniform and stable framework for maintaining the sulfur compounds and improving the conductivity of the positive electrode, and is not limited to a specific type and can include any type of porous carbon material.

[0131] Porous carbon materials are typically manufactured through the carbonization of various carbon precursors. These materials can contain irregularly shaped pores. The average pore size can range from 1 to 200 nm. The porosity can range from 10 to 90% by volume of the total volume of the porous carbon material. When the average pore size is smaller than these ranges, the pore size is at the molecular level, making sulfur impregnation impossible. Conversely, when the average pore size is larger than these ranges, the mechanical strength of the porous carbon material decreases, making it undesirable for use in electrode manufacturing processes.

[0132] In one embodiment of the invention, the "average pore size" can be measured by any known method for measuring the pore size of porous materials, and the measurement method is not limited to a specific method. For example, the pore size can be measured using scanning electron microscopy (SEM), field emission scanning electron microscopy, laser diffraction, or the Brunauer-Emmett-Teller (BET) method. Measurements using laser diffraction can, for example, use a commercially available laser diffractometer (e.g., Microtrac MT 3000). Furthermore, measurements using the BET method can, for example, use the BELSORP series analyzer from BEL Corporation of Japan, but are not limited to this.

[0133] In one embodiment of the present invention, "porosity" refers to the ratio of the volume occupied by pores in a structure to its total volume, and its unit is %. Porosity can be used interchangeably with void ratio, void fraction, etc. In the present invention, the measurement of porosity is not limited to a specific method, and according to one embodiment of the present invention, porosity can be measured according to, for example, the BET method using nitrogen, the Hg porosity determination method, or ASTM D2873.

[0134] The porous carbon material can be spherical, rod-shaped, needle-shaped, sheet-like, tubular, or block-shaped. The shape is not limited to a specific shape and can include any shape commonly used in lithium-sulfur batteries.

[0135] Porous carbon materials can include any type of commonly used carbon material having a porous structure or high specific surface area. For example, porous carbon materials can include at least one selected from: graphite; graphene; carbon black such as tandoor black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), or activated carbon fibers (ACFs); and graphite such as natural graphite, artificial graphite, or expanded graphite; and activated carbon, but are not limited thereto. Preferably, porous carbon materials can include carbon nanotubes.

[0136] In one embodiment of the invention, the porous carbon material may include carbon black, and the sulfur-carbon composite may include a composite of sulfur compounds and carbon black.

[0137] In one embodiment of the invention, the method for manufacturing the sulfur-carbon composite is not limited to the specific method described in this invention, and may include any method commonly used in the art. For example, the sulfur-carbon composite can be manufactured by mixing a sulfur compound with a porous carbon material, subjecting it to heat treatment, and incorporating the molten sulfur compound into the porous carbon material, but the invention is not limited thereto.

[0138] In one embodiment of the invention, the weight ratio of sulfur compounds to porous carbon material in the sulfur-carbon composite can be, for example, 5:5 to 9:1, 6:4 to 9:2, or 6:4 to 7:3, but the invention is not limited thereto. When the weight ratio falls within the above range, it is desirable in terms of the electron transfer area of ​​the sulfur-carbon composite and the electrolyte wetting of the cathode, and for example, the increased usable surface in the sulfur-carbon composite is desirable in terms of suppressing sulfur dissolution from the cathode, but the invention is not limited thereto.

[0139] In one embodiment of the invention, the method of manufacturing an electrode for a lithium secondary battery may further include heat-treating a mixture of a sulfur compound and a conductive carbon material to obtain a sulfur-carbon composite. Accordingly, the slurry for forming the electrode can be obtained by mixing the sulfur-carbon composite and a binder in an aqueous solvent.

[0140] In one embodiment of the invention, the current collector supports a positive electrode active material, not limited to a specific type, and may include any material with high conductivity that does not cause chemical changes in the battery. For example, the current collector may include: copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon; copper or stainless steel with a surface treated with carbon, nickel, or silver; or an aluminum-cadmium alloy. The positive electrode current collector may have a finely textured surface to improve the bonding strength with the positive electrode active material, and may be presented in a variety of different forms such as membranes, sheets, foils, sieves, meshes, porous bodies, foams, or nonwoven fabrics.

[0141] In one embodiment of the present invention, without departing from the purpose of the invention, the electrode may, in addition to sulfur compounds, comprise transition metal elements, Group IIIA elements, Group IVA elements, or mixtures of two or more thereof as active materials. Transition metal elements may include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Pt, Au, or Hg; Group IIIA elements may include Al, Ga, In, or Ti; and Group IVA elements may include Ge, Sn, or Pb.

[0142] In one embodiment of the invention, the content of the sulfur-carbon composite can be 50% by weight or more, based on the total weight of the electrode. Specifically, the content of the sulfur-carbon composite can be, for example, 70% by weight or more, or 80% by weight or more, based on the total weight of the electrode active material layer. Specifically, the content of the sulfur-carbon composite can be 80% to 100% by weight or 80% to 90% by weight, based on the total weight of the electrode active material layer. When the amount of the sulfur-carbon composite is below the above range, the relative amount of auxiliary materials such as conductive materials or binders increases, while the amount of the sulfur-carbon composite decreases, making it difficult to achieve a battery with high capacity and high energy density. Conversely, when the amount of the sulfur-carbon composite is greater than the above range, the amount of conductive materials or binders, as described below, is relatively insufficient, leading to a decrease in the physical properties of the electrode.

[0143] In one embodiment of the invention, in addition to the conductive carbon material used to prepare the sulfur-carbon composite, the electrode active material layer may also comprise a conductive material. The conductive material serves as a pathway for electrons to move from the current collector to the electrode active material by electrically connecting the electrolyte to the electrode active material, and is physically different from the carbon contained in the sulfur-carbon composite. The conductive material is not limited to a specific type and may include any type of material that is conductive.

[0144] In one embodiment of the invention, the conductive material may include, for example, substances used alone or in combination, such as: carbon black materials such as Super-P, Danka Black, acetylene black, Ketjen Black, channel black, furnace black, lamp black, thermal cracking black, or carbon black; carbon derivatives such as carbon nanotubes or fullerenes; conductive fibers such as carbon fibers or metal fibers; fluorocarbons; metal powders such as aluminum powder or nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0145] In one embodiment of the present invention, the amount of conductive material may be 1 to 15% by weight or 5 to 10% by weight, based on the total weight of the positive electrode active material layer.

[0146] In one embodiment of the invention, in addition to the adhesives described above, the adhesive may also include any commonly used adhesives that can be used in the electrode active material layer without departing from the purpose of the invention. For example, the adhesive may also include any of the following: fluoropolymer adhesives, including polyvinylidene fluoride (PVdF), polyvinylidene fluoride polymers containing at least one repeating unit of PVdF, polytetrafluoroethylene (PTFE), or mixtures of two or more thereof; rubber adhesives, including styrene-butadiene rubber (SBR), nitrile rubber, or styrene-isoprene rubber; acrylic adhesives; cellulose adhesives, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol adhesives; polyolefin adhesives, including polyethylene or polypropylene; polyimide adhesives; polyester adhesives; and silane adhesives, or mixtures or copolymers of two or more thereof.

[0147] In one embodiment of the present invention, the amount of adhesive may be 1 to 15% by weight or 5 to 10% by weight, based on the total weight of the positive electrode active material layer. When the amount of adhesive falls within the above range, the bonding strength between the current collector and the electrode active material layer can be improved, and it can have a beneficial effect on inhibiting the dissolution of lithium polysulfides from the electrode, but the present invention is not limited thereto.

[0148] In one embodiment of the invention, the electrode manufactured as described above comprises a current collector and an electrode active material layer present on at least one surface of the current collector.

[0149] In this case, according to one embodiment of the present invention, the thickness of the electrode active material layer can be 100 μm or more, specifically 200 μm or more, for example 250 μm or more. When the thickness of the electrode active material layer falls within the above range, the capacity of the electrode relative to its weight can be desirable, but the present invention is not limited thereto.

[0150] In this specification, the thickness of the electrode active material layer can be measured during the coating process of the slurry during the preparation of the electrode active material layer, or it can be measured in the final dried electrode. The thickness of the electrode active material layer in the final dried electrode can be measured using a known thickness measuring instrument. Such an instrument could be, for example, a Mitutoyo thickness gauge. Alternatively, the thickness of the electrode can be measured using a cross-sectional electron microscope image of the electrode, and the thickness of the electrode active material layer can be calculated by subtracting the thickness of the current collector from the thickness of the electrode.

[0151] According to another aspect of the present invention, a lithium secondary battery comprising the above-described electrodes is provided.

[0152] In one embodiment of the present invention, a lithium secondary battery may include an electrode as a positive electrode and a negative electrode as a counter electrode.

[0153] In one embodiment of the invention, the negative electrode may comprise a negative electrode current collector and a layer of negative electrode active material coated on one or both surfaces of the negative electrode current collector. Alternatively, the negative electrode may be a lithium metal plate.

[0154] The negative electrode current collector supports the negative electrode active material layer, and for details about the negative electrode current collector, please refer to the description of the current collector mentioned above.

[0155] In one embodiment of the present invention, the negative electrode active material layer may comprise a negative electrode active material, and may also comprise a conductive material or a binder. The negative electrode active material may include: materials capable of reversibly inserting or de-intercalating lithium ions (Li... + Materials capable of reversibly inserting or deintercalating lithium ions (Li₂) include lithium metals and lithium alloys, materials that react with lithium ions to reversibly form lithium-containing compounds, and lithium metal or lithium alloys. + The materials can include, for example, crystalline carbon, amorphous carbon, or mixtures thereof. (The last part, "with lithium ions (Li...)," appears to be a fragment and doesn't translate directly. It's best left as is.) + Materials that can reversibly form lithium-containing compounds through a reaction may include, for example, tin oxide, titanium nitrate, or silicon. Lithium alloys may include, for example, alloys of lithium (Li) with metals selected from: sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn). For details regarding conductive materials, refer to the foregoing description, and the adhesive is not limited to a specific adhesive and may include adhesives according to one aspect of the invention, existing adhesives, or mixtures thereof.

[0156] In one embodiment of the invention, the lithium secondary battery can be a lithium-sulfur battery, and in this case, the negative electrode active material can be lithium metal, specifically, in the form of lithium metal foil or lithium metal powder. According to one embodiment of the invention, the negative electrode can contain only lithium metal or lithium alloy foil, without a current collector.

[0157] In addition to the positive and negative electrodes, lithium secondary batteries may also contain an electrolyte, and may also contain a separator if needed.

[0158] In one embodiment of the invention, the electrolyte may comprise a lithium salt.

[0159] Lithium salts are not limited to a specific type and can include any lithium salt that can be used in lithium secondary batteries, specifically lithium-sulfur batteries. For example, lithium salts can include: LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiC4BO8, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, (C2F5SO2)2NLi, (SO2F)2NLi, (CF3SO2)3CLi, lithium chloroborane, lower aliphatic carboxylic acids, lithium tetraphenylborate, lithium imide, or two or more thereof.

[0160] In one embodiment of the invention, in addition to the lithium salt, the electrolyte may also contain a non-aqueous solvent. Alternatively, the electrolyte may be contained in the form of a solid electrolyte layer present on at least one surface of the electrode without the need for a solvent.

[0161] In one embodiment of the invention, the lithium secondary battery may include a separator as needed, and the separator may separate or insulate the positive and negative electrodes, allowing lithium ions to transport between the positive and negative electrodes. The separator may be made of a porous, non-conductive or insulating material and may include any separator material commonly used in lithium secondary batteries. The separator may be a self-standing component such as a membrane, or a coating added to the positive and / or negative electrodes.

[0162] In one embodiment of the invention, the lithium secondary battery can have a variety of different shapes, and can be, for example, coin-shaped, prism-shaped, pouch-shaped or cylindrical, but is not limited thereto.

[0163] The following embodiments are presented to aid in understanding the invention, but these embodiments are provided for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and variations can be made within the scope and technical aspects of the invention, and it should be understood that such changes and variations fall within the scope of the appended claims.

[0164] [Preparation of Adhesives]

[0165] Preparation Example 1

[0166] Synthesis of S,S-bis(R,R'-dimethyl-R'-acetic acid)-trithiocarbonate (BDAAT)

[0167] BDAAT, as a RAFT initiator, is synthesized by the following method.

[0168] The above-mentioned BDAAT was prepared by mixing CS2, chloroform, acetone and tetrabutylammonium bisulfate as a phase transfer catalyst (PTC), then adding NaOH, and finally acid treatment with hydrochloric acid.

[0169] Example 1

[0170] P(AA 400 -b-PM 400 Synthesis of adhesives

[0171] Based on a total of 100 wt% BDAAT and acrylic acid, acrylic acid (AA) in an amount of 400 equivalents relative to the 0.25 mmol BDAAT in Preparation Example 1 was dissolved together with 1 wt% V-501 (4,4'-azobis(4-cyanopentanoic acid)) in 20 ml of 1,4-dioxane, and reacted at 75°C for 18 hours to obtain PAA. 400 As an intermediate product.

[0172] Relative to 0.8 g of PAA 400 400 equivalents of poly(ethylene glycol) methyl ether acrylate (PM) (M n =480) was dissolved together with V-501 in 30 ml of distilled water, and reacted at 75°C for 18 hours to obtain P(AA) 400 -b-PM 400 As the adhesive of Example 1.

[0173] Figure 1 Shown as PAA 400 The 1H NMR spectrum of the synthesis results, and

[0174] Figure 2 It shows that as P(AA) 400 -b-PM 400 The 1H NMR spectrum of the synthesis results.

[0175] Example 2

[0176] P(AA400 -b-PM 400 Synthesis of )-Li adhesives

[0177] Compared with P(AA) obtained in Example 1 400 -b-PM 400 P(AA) was obtained by reacting a 10% by weight aqueous solution of LiOH with 4 equivalents of -COOH functional groups at room temperature overnight. 400 -b-PM 400 )-Li was used as the adhesive in Example 2.

[0178] Figure 3 It shows that as P(AA) 400 -b-PM 400 TFT-IR spectra of the synthesis results of )-Li.

[0179] Example 3

[0180] P(AA 200 -b-PM 600 Synthesis of adhesives

[0181] PAA was synthesized according to the same method as in Example 1, except that acrylic acid (AA) was used in an amount of 200 equivalents relative to the 0.25 mmol BDAAT used in Preparation Example 1. 200 As an intermediate product.

[0182] In addition to using PAA relative to 0.8 g 200 In addition to 600 equivalents of poly(ethylene glycol) methyl ether acrylate (PM), P(AA) was obtained according to the same method as in Example 1. 200 -b-PM 600 As the adhesive in Example 3.

[0183] Figure 4 Shown as PAA 200 The 1H NMR spectrum of the synthesis results, and

[0184] Figure 5 It shows that as P(AA) 200 -b-PM 600 The 1H NMR spectrum of the synthesis results.

[0185] Example 4

[0186] P(AA 200 -b-PM 600 Synthesis of )-Li adhesives

[0187] Compared with P(AA) obtained in Example 3 200 -b-PM 600 P(AA) was obtained by reacting a 10% by weight aqueous solution of LiOH with 4 equivalents of -COOH functional groups at room temperature overnight. 200 -b-PM 600 )-Li was used as the adhesive in Example 4.

[0188] Figure 6 It shows that as P(AA) 200 -b-PM 600 TFT-IR spectra of the synthesis results of )-Li.

[0189] Comparative Example 1

[0190] P(AA 400 -b-PM 400 Synthesis of (Type B) adhesive

[0191] The RAFT polymerization reaction is initiated using dibenzyl trithiocarbonate (DBTTC), which contains aromatic functional groups at its outermost end, as the RAFT initiator.

[0192] Acrylic acid (AA) in an amount of 400 equivalents relative to 0.25 mmol DBTTC (dibenzyl trithiocarbonate) was dissolved together with V-501 (4,4'-azobis(4-cyanopentanoic acid)) in 20 ml of 1,4-dioxane and reacted at 75 °C for 18 hours to obtain PAA. 400 .

[0193] Relative to 0.8 g of PAA 400 400 equivalents of poly(ethylene glycol) methyl ether acrylate (PM)(M) n =480) was dissolved together with AIBN in 30 ml of DMF and reacted at 75°C for 18 hours to obtain P(AA) 400 -b-PM 400 (Type b).

[0194] [Preparation of the positive electrode]

[0195] Comparative Example 2

[0196] Sulfur (S8) and Ketjen black (KB) were mixed in a weight ratio of 7:3, ground in a mortar, and heat-treated at 155°C for 30 minutes to produce a sulfur-carbon composite (KB / S).

[0197] The obtained KB / S, polyacrylic acid (PAA) binder and conductive material (Super P) were mixed in a weight ratio of 80:10:10, 3% PVA dispersant was added, and the mixture was mixed in water using a Thinky mixer to prepare the positive electrode slurry.

[0198] The prepared positive electrode slurry was coated onto aluminum foil to a thickness of 200 μm using a doctor blade and dried at 50°C for 14 hours to obtain the positive electrode.

[0199] Comparative Example 3

[0200] In addition to using the adhesive (P(AA) prepared in Comparative Example 1) 400 -b-PM 400 (Type b) was used as a binder and the positive electrode slurry was coated up to 350 μm. The positive electrode was obtained by the same method as Comparative Example 2.

[0201] Example 5

[0202] In addition to using the adhesive (P(AA) prepared in Example 1) 400 -b-PM 400 The positive electrode was obtained by using the same method as Comparative Example 2, where the positive electrode slurry was coated up to 350 μm as a binder.

[0203] Example 6

[0204] In addition to using the adhesive (P(AA) prepared in Example 2) 400 -b-PM 400 Using Li as a binder and coating the positive electrode slurry up to 350 μm, a positive electrode was obtained by the same method as Comparative Example 2.

[0205] Example 7

[0206] In addition to using the adhesive (P(AA) prepared in Example 3) 200 -b-PM 600 The positive electrode was obtained by using the same method as Comparative Example 2, where the positive electrode slurry was coated up to 350 μm as a binder.

[0207] Example 8

[0208] In addition to using the adhesive (P(AA) prepared in Example 4) 200 -b-PM 600 Using Li as a binder and coating the positive electrode slurry up to 350 μm, a positive electrode was obtained by the same method as Comparative Example 2.

[0209] [Preparation of coin-type lithium secondary batteries]

[0210] As the positive electrode, the positive electrodes of each of Comparative Examples 2, 3 and 5 to 8 were used, and as the negative electrode, a 100 μm thick lithium metal was prepared.

[0211] The positive and negative electrodes are placed on opposite sides with a polypropylene separator in between to prepare the electrode assembly. In this case, the separator has a thickness of 25 μm and a porosity of 41% by volume.

[0212] Place the prepared electrode assembly into the coin-shaped shell and administer at 50 μl / mg s An El / S ratio is injected into the electrolyte to manufacture a coin cell, and in this case, the electrolyte contains a 1 M lithium salt (LiTFSI) dissolved in a solvent containing a 1:1 (volume / volume) mixture of dioxolane and dimethoxyethane (DME).

[0213] [Surface observation of the positive electrode]

[0214] Figure 7 The surface observations of SEM images of positive electrodes prepared using different adhesives are shown.

[0215] exist Figure 7 In the images, the left-hand SEM image shows a positive electrode manufactured using the same method as the positive electrode manufactured using PAA in Comparative Example 2, wherein the positive electrode was manufactured by coating a positive electrode slurry to a thickness of 150 μm and then drying it. The middle SEM image shows a positive electrode manufactured using the same method as in Example 1, wherein the positive electrode was manufactured by coating a positive electrode slurry to a thickness of 200 μm and then drying it. The right-hand SEM image shows a positive electrode manufactured using the same method as in Example 2, wherein the positive electrode was manufactured by coating a positive electrode slurry to a thickness of 200 μm and then drying it.

[0216] like Figure 7 As shown, the positive electrode containing the adhesives of Examples 1 and 2 is thicker, but adhesive agglomeration was only observed on the surface of the thinner positive electrode formed using PAA.

[0217] Therefore, it is inferred that using an adhesive according to an embodiment of the present invention can improve the uniformity of adhesive distribution within the positive electrode, thereby further improving the electrical performance of the positive electrode.

[0218] In particular, the PAA used in Comparative Example 2 contains -COOH in all monomers, and each -COOH forms a dimer through hydrogen bonding; while in the cases of the block copolymer adhesives of polyacrylic acid and polyalkyl methacrylate in Examples 1 and 2, their effect is attributed to the greater number of -COOH located near the polyethylene glycol blocks contained in the polyalkyl methacrylate blocks and interacting with lithium polysulfides, and the strong adsorption capacity of polyethylene glycol for lithium polysulfides.

[0219] [Performance Evaluation of Coin-Type Lithium-ion Secondary Batteries]

[0220] Each prepared coin-shaped lithium secondary battery was discharged once at room temperature (25°C) in the range of 2.5 V to 1.8 V at a rate of 0.1C, then charged and discharged twice in the range of 1.8 V to 2.5 V at a rate of 0.1C, then charged and discharged three times in the range of 1.8 V to 2.5 V at a rate of 0.2C, and then the charge and discharge cycle was repeated at a rate of 0.5C.

[0221] Figure 8 (134 cycles) shows the discharge capacity graph of each battery using the positive electrodes of Comparative Example 2, Comparative Example 3, Example 5, and Example 6 after 134 cycles at a 0.5C rate. Figure 9 (29 cycles) shows the discharge capacity of each battery using the positive electrode of Comparative Example 2, Example 7 and Example 8 after 29 cycles.

[0222] Tables 1 and 2 below show the measurements of capacity retention relative to the initial capacity (0.5C rate, 1 cycle) after 134 cycles or 29 cycles, respectively.

[0223] [Table 1]

[0224] [Table 2]

[0225] according to Figure 8 and 9 Tables 1 and 2 confirm that the use of an adhesive according to an embodiment of the invention improves the battery's discharge capacity and achieves a high capacity retention rate.

[0226] Specifically, according to Figure 8 It was confirmed that cathodes manufactured via RAFT polymerization, but using binders containing aromatic functional groups at the outermost ends, exhibited poor performance due to a decrease in initial capacity. Furthermore, reference... Figure 8 and 9 It was confirmed that using PAA as the positive electrode binder reduced battery capacity, while using the binders of Examples 7 and 8 according to an embodiment of the present invention significantly improved battery capacity. This is presumably attributed to the binder inhibiting the dissolution of lithium polysulfides and improving conductivity.

[0227] [Calculation of the number of monomers in the adhesive]

[0228] To measure Example 1 (P(AA) 400-b-PM 400 )) and Example 3 (P(AA) 200 -b-PM 600 Each of the number-average molecular weight and weight-average molecular weight of the adhesive prepared in the process was methylated by reacting it with trimethylsilyldiazomethane (TMS CHN2) at room temperature (25°C) for 72 hours under MeOH / THR reaction conditions.

[0229] When measured using THF-GPC, the number-average molecular weight (Mn) of the methylated adhesive of Example 1 was 2472 g / mol, and the weight-average molecular weight (Mw) was 2486 g / mol (PDI = 1.005). Furthermore, when measured using the same method, the molecular weight (Mn) of the adhesive of Example 3 was 21,000 g / mol, and the weight-average molecular weight (Mw) was 27,000 g / mol (PDI = 1.3).

[0230] Considering that the conversion rate of Example 1 was 12.1% and that of Example 3 was 6.6%, a theoretical weight-average molecular weight of 221,106.39 g / mol was obtained when the conversion rate of Example 1 was 100%. Therefore, based on the above experiments, in order to obtain a binder with a weight-average molecular weight of 300,000 g / mol to control the viscosity of the binder in the cathode slurry, calculations show that it is more desirable to use 1,000 to 1,100 acrylic acid monomers and 1,000 to 1,100 poly(ethylene glycol) methyl ether acrylate monomers, achieving a conversion rate of over 50%.

Claims

1. An adhesive for lithium secondary batteries, the adhesive comprising: The thiocarbonyl sulfur functional group represented by Equation 1 below; A first polymethyl methacrylate-derived block covalently bonded to one end of the thiocarbonyl sulfur functional group; A second polymethyl methacrylate-derived block covalently bonded to the other end of the thiocarbonyl sulfur functional group; A first polyacrylic acid-derived block covalently bonded to one end of the first polymethyl methacrylate-derived block; and A second polyacrylic acid-derived block covalently bonded to one end of the second polymethyl methacrylate-derived block. The outermost terminal organic functional groups include aliphatic functional groups. [Formula 1] 。 2. The adhesive for lithium secondary batteries according to claim 1, At least one carboxyl group (-COOH) in the first polyacrylic acid-derived block and the second polyacrylic acid-derived block includes a lithium-substituted carboxyl group (-COO). - Li + ).

3. The adhesive for lithium secondary batteries according to claim 1, The first polyacrylic acid-derived block and the second polyacrylic acid-derived block each independently contain 50 to 1500 repeating acrylic acid structures.

4. The adhesive for lithium secondary batteries according to claim 1, The first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block each independently contain 50 to 1500 repeating alkyl methacrylate structures.

5. The adhesive for lithium secondary batteries according to claim 1, The alkyl group contained in at least one of the first polymethyl methacrylate-derived block or the second polymethyl methacrylate-derived block comprises at least one of polyethylene glycol repeating units, polypropylene glycol repeating units, or polyethylene glycol-polypropylene glycol repeating units.

6. The adhesive for lithium secondary batteries according to claim 5, The alkyl group comprises 1 to 30 repeating polyethylene glycol units.

7. The adhesive for lithium secondary batteries according to claim 1, The organic functional group at the outermost end includes a lithium-substituted carboxyl group (-COO). - Li + ).

8. The adhesive for lithium secondary batteries according to claim 1, The pH of the dispersion of the binder for the lithium secondary battery in water is in the range of 6.2 to 7.

8.

9. A method for manufacturing an electrode for a lithium secondary battery, the method comprising: The slurry is applied to at least one surface of the current collector and the slurry is dried to obtain the electrode. The slurry comprises a mixture of the binder, sulfur compound, and conductive carbon material as described in any one of claims 1 to 8 in an aqueous solvent.

10. The method for manufacturing an electrode for a lithium secondary battery according to claim 9, The method includes: The adhesive is obtained by polymerization of a reversible addition-fragmentation chain transfer (RAFT) initiator containing aliphatic and thiocarbonyl functional groups, an alkyl methacrylate, and acrylic acid.

11. The method for manufacturing an electrode for a lithium secondary battery according to claim 10, wherein prior to the polymerization reaction, the method further comprises: The RAFT initiator is prepared as a mixture of carbon disulfide (CS2), trihalomethane, and tetraalkylammonium bisulfate.

12. The method for manufacturing an electrode for a lithium secondary battery according to claim 10, The RAFT initiator mentioned above includes S,S'-bis(R,R'-dimethyl-R''-acetic acid)-trithiocarbonate (BDAAT).

13. The method for manufacturing electrodes for lithium secondary batteries according to claim 9, The method includes heat-treating a mixture of the sulfur compound and the conductive carbon material to obtain a sulfur-carbon composite, and The slurry is obtained by mixing the sulfur-carbon composite with the binder in the aqueous solvent.

14. The method for manufacturing an electrode for a lithium secondary battery according to claim 9, The obtained electrode comprises the current collector and an active material layer present on at least one surface of the current collector, and The thickness of the active material layer is 250 μm or more.

15. An electrode for a lithium secondary battery, the electrode comprising: The adhesive according to any one of claims 1 to 8; sulfur compounds; and Conductive carbon materials.

16. A lithium secondary battery comprising the electrode of claim 15.

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