Water-based binder for lithium secondary battery, and lithium secondary battery including same

Abstract

The present invention relates to a binder that can be used in a lithium secondary battery, particularly a lithium-sulfur battery, and is prepared by RAFT polymerization, comprises a polyalkyl methacrylate-derived block and a polyacrylic acid-derived block with a thiocarbonyl thio functional group at the center thereof, and comprises an aliphatic functional group at the end thereof. Therefore, electrical conductivity and elution of lithium polysulfide in an electrode using the binder are suppressed.

Description

Aqueous binder for lithium secondary batteries and lithium secondary batteries containing the same

[0001] The present invention relates to an aqueous binder that can be used in the electrode of a lithium secondary battery. In particular, the present invention relates to an aqueous binder that can be used in the positive electrode of a lithium-sulfur battery using lithium metal as the negative electrode, and to a lithium secondary battery comprising the same.

[0002] This application claims priority to Korean Patent Application No. 2024-0116057, filed with the Korean Intellectual Property Office on August 28, 2024, the entire disclosure of which is incorporated herein by reference.

[0003] As the scope of application of lithium secondary batteries expands beyond portable electronic devices to include electric vehicles (EVs) and electric storage systems (ESS), the demand for lithium secondary batteries with high capacity, high energy density, and long lifespan is increasing.

[0004] Among various lithium secondary batteries, lithium-sulfur batteries are battery systems that use sulfur-based materials containing sulfur-sulfur bonds as positive electrode active materials, and lithium metal, carbon-based materials that allow lithium ion insertion / deinsertion, or silicon or tin that form alloys with lithium as negative electrode active materials. Sulfur, the main ingredient of the positive electrode active material in lithium-sulfur batteries, has the advantages of low atomic weight, abundant resources, easy supply, low cost, non-toxicity, and environmental friendliness.

[0005] In addition, lithium-sulfur batteries have a conversion reaction between lithium ions and sulfur (S8+16Li) at the cathode. + +16e - -> The theoretical specific capacity from 8Li2S reaches 1,675 mAh / g, and when lithium metal is used as the negative electrode, it shows a theoretical energy density of 2,600 Wh / kg. This is a very high figure compared to the theoretical energy density of other battery systems currently being studied (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), and therefore, it is attracting attention as a high-capacity, eco-friendly, and low-cost lithium secondary battery among the secondary batteries being developed so far.

[0006] When a lithium-sulfur battery is discharged, sulfur accepts electrons at the positive electrode and a reduction reaction occurs, and lithium polysulfide (Li2S) is formed at the positive electrode. x , x=2~8) are generated, and some of them are easily dissolved in the electrolyte, causing side reactions within the battery, accelerating battery deterioration and causing a shuttle reaction during the charging process, which significantly reduces charge / discharge efficiency. As a result, lithium-sulfur batteries currently under development have specific capacities that are far below the theoretical specific capacity. Therefore, there is a need to develop a lithium-sulfur battery with a high specific capacity at the level of the theoretical specific capacity.

[0007] In particular, there is a need to develop a technology to suppress the decrease in energy density caused by the shuttle effect that causes loss of positive electrode active material as described above.

[0008] The present invention aims to solve the above-described problems and provide a lithium-sulfur battery having a high specific capacity at the theoretical specific capacity level.

[0009] In addition, the present invention seeks to provide a lithium-sulfur battery with high energy density.

[0010] To achieve the above purpose,

[0011] According to one aspect of the present invention, a binder for a lithium secondary battery according to the following embodiments is provided.

[0012] A binder for a lithium secondary battery according to the first embodiment,

[0013] A thiocarbonyl thio functional group represented by the following formula 1,

[0014] A first polyalkyl methacrylate-derived block covalently bonded to one terminal of the above thiocarbonyl thio functional group,

[0015] A second polyalkyl methacrylate-derived block covalently bonded to the other terminal of the thiocarbonyl thio functional group,

[0016] A first polyacrylic acid derived block covalently bonded to one end of the first polyalkyl methacrylate derived block, and

[0017] A second polyacrylic acid derived block covalently bonded to one end of the second polyalkyl methacrylate derived block,

[0018] The terminal organic functional group includes an aliphatic functional group.

[0019] [Formula 1]

[0020]

[0021] According to the second embodiment, in the first embodiment,

[0022] At least one carboxyl group (-COOH) in the first polyacrylic acid-derived block and the second polyacrylic acid-derived block is lithium-substituted (-COO - Li + ) may include.

[0023] According to the third embodiment, in the first embodiment or the second embodiment,

[0024] The first polyacrylic acid-derived block and the second polyacrylic acid-derived block may independently contain 50 to 1500 acrylic acid repeating structures.

[0025] According to the fourth embodiment, in any one of the first to third embodiments,

[0026] The first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may independently contain 50 to 1500 alkyl methacrylate repeating structures.

[0027] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0028] The alkyl included in at least one of the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may include at least one of a polyethylene glycol repeating unit, a polypropylene glycol repeating unit, and a polyethylene-polypropylene glycol repeating unit.

[0029] According to the sixth embodiment, in any one of the first to fifth embodiments,

[0030] The above alkyl may contain 1 to 30 polyethylene glycol repeat units.

[0031] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0032] The terminal organic functional group is a lithium-substituted carbonyl group (-COO - Li + ) may be included.

[0033] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0034] The pH of the aqueous dispersion in which the above lithium secondary battery binder is dispersed in water may be in the range of 6.2 to 7.8.

[0035]

[0036] According to another embodiment of the present invention, a method for manufacturing an electrode for a lithium secondary battery is provided.

[0037] The method for manufacturing an electrode for a lithium secondary battery according to the 9th embodiment is as follows:

[0038] It may include applying and drying a slurry in which a binder, a sulfur-based compound, and a conductive carbon material according to any one of the first to eighth embodiments are mixed in an aqueous solvent onto at least one surface of a current collector to obtain an electrode.

[0039] According to the tenth embodiment, in the ninth embodiment,

[0040] It may include obtaining the binder through a polymerization reaction of a RAFT initiator containing an aliphatic functional group and a thiocarbonyl thio functional group, an alkyl methacrylate and acrylic acid.

[0041] According to the eleventh embodiment, in the ninth or tenth embodiment,

[0042] Before the above polymerization reaction,

[0043] The method may further include a step of preparing the RAFT initiator as a mixture of carbon disulfide (CS2), trihalomethane, and tetraalkylene ammonium bisulfate.

[0044] According to the 12th embodiment, in any one of the 9th to 11th embodiments,

[0045] The above RAFT initiator may include S,S'-bis(R,R'-dimethyl-R''-acetic acid)-trithiocarbonate (BDAAT).

[0046] According to the 13th embodiment, in any one of the 9th to 12th embodiments,

[0047] Comprising heat treating a mixture of the above sulfur compound and a conductive carbon material to obtain a sulfur-carbon composite,

[0048] The slurry may be obtained by mixing the sulfur-carbon complex and the binder in the aqueous solvent.

[0049] According to the 14th embodiment, in any one of the 9th to 13th embodiments,

[0050] The electrode obtained above includes the current collector and an active material layer provided on at least one surface of the current collector,

[0051] The above active material layer may have a thickness of 250 μm or more.

[0052]

[0053] According to another embodiment of the present invention, an electrode for a lithium secondary battery according to the following embodiments is provided.

[0054] The electrode for a lithium secondary battery according to the 15th embodiment is:

[0055] It may include a binder, a sulfur compound, and a conductive carbon material according to any one of the first to eighth embodiments.

[0056]

[0057] According to another embodiment of the present invention, a lithium secondary battery according to the following embodiments is provided.

[0058] A lithium secondary battery according to the 16th embodiment,

[0059] It may include an electrode according to the 15th embodiment.

[0060] A binder according to one aspect of the present invention has a functional group capable of forming a hydrogen bond at the terminal and includes a block having high elasticity and ion conductivity in the main chain. Therefore, the binder according to one aspect of the present invention can exhibit a beneficial effect in suppressing volume expansion when used in an electrode of a lithium secondary battery due to its high elasticity characteristics. Furthermore, when the binder is used in the positive electrode of a lithium-sulfur battery, it has the advantage of suppressing the shuttle effect caused by the elution of lithium polysulfide from the positive electrode.

[0061] In particular, the ion conductivity of the binder is dramatically improved by the block having high elasticity and ion conductivity included in the main chain compared to the conventional PAA (poly acrylic acid) binder, thereby demonstrating the advantage of being able to manufacture a binder suitable for an aqueous binder process and an electrode through an aqueous process using the same.

[0062] Accordingly, it is possible to provide a lithium secondary battery, particularly a lithium-sulfur battery, which exhibits improved electrochemical performance compared to electrodes using conventional aqueous binders such as PAA.

[0063] Figure 1 shows 1H NMR of an intermediate product during the synthetic process of Example 1 in the present specification.

[0064] Figure 2 shows 1H NMR of Example 1 in the present specification.

[0065] Figure 3 shows the FT-IR spectra of Examples 1 and 2 in the present specification.

[0066] Figure 4 shows 1H NMR of an intermediate product during the synthetic process of Example 3 in the present specification.

[0067] Figure 5 shows 1H NMR of Example 3 in the present specification.

[0068] Figure 6 shows the FT-IR spectra of Examples 3 and 4 in the present specification.

[0069] FIG. 7 is an SEM image of the surface of an anode manufactured to the indicated thickness using PAA binder, binders of Example 1 and Example 2 according to an experimental example in the present specification.

[0070] Figure 8 is a graph showing the results of measuring discharge capacity according to charge and discharge cycles according to an experimental example in this specification.

[0071] Figure 9 is a graph showing the results of measuring discharge capacity according to charge and discharge cycles according to an experimental example in this specification.

[0072] Hereinafter, the present invention will be described in more detail.

[0073] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0074] The terminology used in the present invention is only 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. It should be understood that the terms "comprise" or "have" in the present invention are intended to specify 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.

[0075] The term "composite" used in this specification refers to a material in which two or more materials are combined to form physically and chemically different phases and exhibit more effective functions.

[0076] The term "(poly)sulfide" as used herein means "(poly)sulfide ion (S x 2- , 1≤x - ≤8)" and "lithium (poly)sulfide (Li2S) x or Li2S x - It is a concept that includes all of "1≤x ≤8".

[0077] The term "polysulfide" as used herein means "polysulfide ion (S x 2- , 1 <x - ≤8)" and "lithium polysulfide (Li2S) x or Li2S x - 1 <x ≤8)"를 모두 포함하는 개념이다.

[0078] Lithium-sulfur batteries have a problem in that lithium polysulfide, which is formed by the reduction reaction of sulfur (S8) at the positive electrode during charging and discharging, is eluted from the positive electrode into the electrolyte, and as a result, the capacity of the battery does not represent the theoretical capacity.

[0079] According to one aspect of the present invention, a lithium-sulfur battery having improved electrochemical performance by suppressing the dissolution of lithium polysulfide from the cathode and enhancing the electrical conductivity of the electrode, an electrode therefor, and a binder usable therefor are provided. Furthermore, a binder usable not only in lithium-sulfur batteries but also in other types of lithium secondary batteries and, furthermore, in electrochemical devices is provided.

[0080]

[0081] A binder for a lithium secondary battery according to one aspect of the present invention comprises a thiocarbonyl thio functional group represented by the following formula 1:

[0082] A first polyalkyl methacrylate-derived block covalently bonded to one terminal of the above thiocarbonyl thio functional group,

[0083] A second polyalkyl methacrylate-derived block covalently bonded to the other terminal of the thiocarbonyl thio functional group,

[0084] A first polyacrylic acid derived block covalently bonded to one end of the first polyalkyl methacrylate derived block, and

[0085] It includes a second polyacrylic acid derived block covalently bonded to one end of the second polyalkyl methacrylate derived block.

[0086] [Formula 1]

[0087]

[0088] Specifically, the terminal organic functional group of the binder includes an aliphatic functional group.

[0089] In one embodiment of the present invention, the organic functional group at the terminal end of the binder is bonded to the terminal end of each of the first polyacrylic acid-derived block and the second polyacrylic acid-derived block, and may preferably be composed only of an aliphatic functional group.

[0090] In one embodiment of the present invention, the structure of the binder may be expressed, for example, by the following chemical formula 1, but the present invention is not limited thereto.

[0091] [Chemical Formula 1]

[0092]

[0093] In the above chemical formula 1,

[0094] R1 and R2 are each independently Li + , H, C1 to C 50 Alkyl group of, -(C2H4O)oM5 (o=integer from 1 to 20, M5=Li + , H or direct bond) and -(C3H6O)pM6 (p = integer from 1 to 20, M6 = Li + , H or direct bond) is selected from at least one of the following,

[0095] M1 and M2 are each independently Li+ and H are selected from among

[0096] A and B are each independently an aliphatic functional group,

[0097] n1 and n2 are each independently integers from 50 to 1500,

[0098] m1 and m2 are each independently an integer between 50 and 1500.

[0099]

[0100] In one embodiment of the present invention, the first polyacrylic acid-derived block and the second polyacrylic acid-derived block may each include a repeating unit of -(C2H3C(O)OQ)- (wherein, Q=M1 or M2), as shown in the chemical formula 1.

[0101] In one embodiment of the present invention, at least one carboxyl group (-COOQ) in the first polyacrylic acid-derived block and the second polyacrylic acid-derived block is lithium-substituted (-COO - Li + ) may include.

[0102] In another embodiment of the present invention, all carboxyl groups in the first polyacrylic acid-derived block and the second polyacrylic acid-derived block are substituted with lithium to form -COO - Li + It may have the structure of .

[0103] Since the carboxyl group in the first polyacrylic acid-derived block and the second polyacrylic acid-derived block has a lithium-substituted structure, when included in an electrode, it can exhibit the effect of suppressing the phenomenon of lithium polysulfide being eluted from the electrode through hydrogen bonding, but the mechanism of the present invention is not limited thereto.

[0104] In one embodiment of the present invention, the first polyacrylic acid-derived block and the second polyacrylic acid-derived block may independently contain 50 to 1500 acrylic acid repeating structures. For example, in the chemical formula 1, n1 and n2 may each independently be an integer of 50 to 1500, 100 to 1300, 100 to 150, 200 to 1300, 300 to 1300, 500 to 1300, 1000 to 1200, or 1050 to 1150, or 1100, but the present invention is not limited thereto.

[0105] In one embodiment of the present invention, the binder includes a first polyalkyl methacrylate-derived block between the thiocarbonyl thio functional group and the first polyacrylic acid-derived block, and includes a second polyalkyl methacrylate-derived block between the thiocarbonyl thio functional group and the second polyacrylic acid-derived block. The first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may each be included between the thiocarbonyl thio functional group and the polyacrylic acid-derived block, thereby playing a role in improving elasticity and / or ionic conductivity of the binder, but the mechanism of the present invention is not limited thereto.

[0106] In one embodiment of the present invention, the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may independently contain 50 to 1500, for example, 100 to 1500, alkyl methacrylate repeating structures. For example, in the above chemical formula 1, m1 and m2 may each independently be an integer of 50 to 1500, an integer of 100 to 1500, an integer of 200 to 1300, an integer of 200 to 300, an integer of 500 to 1300, an integer of 800 to 1200, an integer of 1000 to 1200, an integer of 1000 to 1100, an integer of 1050 to 1150, or an integer of 1100, but the present invention is not limited thereto.

[0107] In one embodiment of the present invention, the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may each include a repeating unit of -(C2H3C(O)OW)- (wherein, W=R1 or R2), as shown in the chemical formula 1.

[0108] In one embodiment of the present invention, the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block are each independently Li as structures of R1 and R2 depending on the type of monomer used to prepare them. + , H, C1 to C 50 Alkyl group of, -(C2H4O)oM5 (o=integer from 1 to 20, M5=Li +, H or direct bond) and -(C3H6O)pM6 (p = integer from 1 to 20, M6 = Li + , It may include one or more structures selected from among H or direct bonds.

[0109] In another embodiment of the present invention, R1 and R2 in the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block are independently -(C2H4O)oM5 (o=integer from 1 to 20, M5=Li) + , H or direct bond) and -(C3H6O)pM6 (p = integer from 1 to 20, M6 = Li + , H or a direct bond) may include a structure. The structure of -(C2H4O)o- is a repeating unit of polyethylene glycol (PEG), and the structure of -(C3H6O)p- is a repeating unit of polypropylene glycol (PPG), and the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may independently include a PEG, PPG or polyethylene-polypropylene glycol (PEPPG) structure in the structure. All of the PEG, PPG and PEPPG structures include an -OH structure at the terminal, thereby increasing the terminal -OH content of the binder, and thereby have the advantage of dramatically improving the ionic conductivity and elasticity of the binder, but the mechanism of the present invention is not limited thereto.

[0110] In one embodiment of the present invention, at least one of the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may include at least one of a polyethylene glycol repeating unit, a polypropylene glycol repeating unit, and a polyethylene-polypropylene glycol repeating unit.

[0111] In one embodiment of the present invention, when at least one of the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block includes at least one of the polyethylene glycol repeating unit, the polypropylene glycol repeating unit, and the polyethylene-polypropylene glycol repeating unit, the number of these repeating units may be, for example, 1 to 30, specifically 1 to 25, or 1 to 20, but the present invention is not limited thereto.

[0112] In one embodiment of the present invention, the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block may each include polyethylene glycol repeating units as R1 and R2 in the above chemical formula 1. At this time, the polyethylene glycol repeating units may be included in an amount of 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 present invention is not limited thereto.

[0113] In one embodiment of the present invention, at least a portion of the terminal hydroxyl groups (-OH) of the polyethylene glycol group, polypropylene glycol group or polyethylene-polypropylene glycol group in the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block are substituted with lithium to form -O - Li + It may have the structure of .

[0114] In another embodiment of the present invention, the terminal hydroxyl group (-OH) of the polyethylene glycol group, polypropylene glycol group or polyethylene-polypropylene glycol group in the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block is all substituted with lithium to form -O - Li + It may have the structure of .

[0115] In one embodiment of the present invention, the binder may include an aliphatic functional group as the terminal organic functional group. Specifically, in the chemical formula 1, structures A and B may include aliphatic functional groups. More specifically, in the chemical formula 1, structures A and B may be composed solely of aliphatic functional groups.

[0116] In one embodiment of the present invention, the structure A and the structure B are each a polyacrylic acid-derived structure, and can be represented by, for example, the following chemical formulas 2 and 3.

[0117] [Chemical Formula 2]

[0118]

[0119] [Chemical Formula 3]

[0120]

[0121] In the above chemical formula 2 and chemical formula 3,

[0122] M3 and M4 are each independently Li + and H are selected.

[0123] In one embodiment of the present invention, when the structure B and the structure B in the binder have the structures of the chemical formula 2 and chemical formula 3, respectively, the M3 and M4 are lithiated to form Li + It could be.

[0124] According to one embodiment of the present invention, the binder has a lithium-substituted carboxyl group (-COO) at the terminal. - Li + ) can achieve excellent adsorption properties for lithium polysulfide, and thereby have an excellent effect of suppressing the shuttle effect in which lithium polysulfide is eluted from the electrode into the electrolyte, but the mechanism of the present invention is not limited thereto.

[0125] In one embodiment of the present invention, the binder may preferably exhibit a pH of 8 or lower in an aqueous dispersion state due to a carboxyl functional group included in the structure. More preferably, at least a portion of the carboxyl groups in the binder are in a lithium-substituted form (-COO - Li + ), the binder may exhibit, in an aqueous dispersion state, a pH of, for example, 6 or more and 8 or less, more preferably 6.0 or more and 8.0 or less.

[0126] In one embodiment of the present invention, the pH of the aqueous dispersion in which the binder is dispersed in water may be, for example, in the range of 6.2 to 7.8, specifically 6.3 to 7.7, 6.4 to 7.6, or 6.5 to 7.4.

[0127] In this specification, the pH of the aqueous dispersion of the binder can be measured by a known method for measuring the pH of an aqueous dispersion of the binder, and the measurement method is not particularly limited. For example, the pH may be measured at room temperature (23°C) for a dispersion in which the binder is dispersed in an amount of 5 wt%. In addition, the pH of the aqueous dispersion may be measured using a known pH measuring device, for example, an Orion Star A121 device from ThermoFisher Scientific, but the measurement method is not limited thereto.

[0128] Considering that the pH of the aqueous dispersion of a general PAA binder is 6.0 or lower, for example, in the range of pH 4.5 to 6.0, the binder according to one embodiment of the present invention has an advantage in terms of stability when used in the manufacture of an electrode of a lithium secondary battery, but the present invention is not limited thereto.

[0129] In one embodiment of the present invention, the binder may be included such that the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block have a symmetrical or asymmetrical structure based on the thiocarbonyl thio functional group. In terms of ease of synthesis of the binder, the binder may have a structure in which the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block have a symmetrical structure based on the thiocarbonyl thio functional group, but the present invention is not limited thereto.

[0130] In one embodiment of the present invention, the binder may be included such that the first polyacrylic acid-derived block and the second polyacrylic acid-derived block have a symmetrical or asymmetrical structure based on the thiocarbonyl thio functional group. In terms of ease of synthesis of the binder, the binder may have a structure such that the first polyacrylic acid-derived block and the second polyacrylic acid-derived block have a symmetrical structure based on the thiocarbonyl thio functional group, but the present invention is not limited thereto.

[0131] In one embodiment of the present invention, the binder may be included such that the structure A and the structure B have a symmetrical or asymmetrical structure based on the thiocarbonyl thio functional group. In terms of ease of synthesis of the binder, the binder may have a structure in which the structure A and the structure B have a symmetrical structure based on the thiocarbonyl thio functional group, but the present invention is not limited thereto.

[0132] In one embodiment of the present invention, the binder may include a compound having a structure represented by the following chemical formula 4.

[0133] [Chemical Formula 4]

[0134]

[0135] In the above chemical formula 4,

[0136] n1 and n2 are each independently integers from 50 to 1500,

[0137] m1 and m2 are each independently an integer between 50 and 1500.

[0138] In one embodiment of the present invention, the viscosity of the binder is not particularly limited as long as it is a viscosity suitable for use in an electrode for a lithium secondary battery. However, for example, it may be preferable that the binder have a molecular weight such that the viscosity at 23°C is 3,000 cP or more based on an aqueous solution containing 3 wt% of the binder. Here, the viscosity represents a standard measured by an intrinsic viscosity measurement method using a Bath, Kinematic viscosity (J-BV08) viscometer.

[0139] In one embodiment of the present invention, the weight average molecular weight (Mw) of the binder may be, for example, 7,000 g / mol to 1,000,000 g / mol. Specifically, the weight average molecular weight of the binder may be 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 present invention is not limited thereto.

[0140] In one embodiment of the present invention, the weight average molecular weight of the binder can be measured according to a known method for measuring the weight average molecular weight of a polymer, and is not particularly limited. For example, the weight average molecular weight of the binder 1 H NMR, 13 It can be measured using analytical methods such as C NMR, Mass spectroscopy, FT-IR, and HPLC.

[0141] In one embodiment of the present invention, the weight average molecular weight of the binder can be measured by the following method, but the measurement method is not limited thereto.

[0142] In one embodiment of the present invention, the weight average molecular weight (Mw) is calculated using gel permeation chromatography (GPC, PL GPC220, Agilent Technologies) for 1 g of binder solution under the following conditions.

[0143] Column: PLmixed B Х 2,

[0144] Solvent: DMF / 0.05 M LiBr (0.45㎛ Filtered),

[0145] Flow rate: 1.0 ㎖ / min,

[0146] Sample concentration: 4.0 mg / ml,

[0147] Injection volume: 100 ㎕,

[0148] Column temperature: 65℃

[0149] Detector: Waters RI Detector, Standard: PS)

[0150]

[0151] Hereinafter, a method for manufacturing the binder according to one embodiment of the present invention will be described. However, a binder having the above-described structure can be manufactured by other organic synthesis methods, and the method for manufacturing the binder is not limited thereto.

[0152] According to one embodiment of the present invention, the binder may be manufactured through a RAFT polymerization (Reversible Addition-Fragmentation chain transfer polymerization) reaction.

[0153] In one embodiment of the present invention, the method for producing the binder by RAFT polymerization may largely include the following two processes.

[0154] The first process is the process of preparing a RAFT initiator.

[0155] The second process is a process of performing a polymerization reaction between polymerization raw materials using a prepared RAFT initiator.

[0156] In one embodiment of the present invention, the RAFT initiator can be prepared by obtaining a commercially available RAFT reagent or by directly manufacturing it, and there is no particular limitation on the preparation method.

[0157] In one embodiment of the present invention, the organic functional group included in the RAFT initiator may be included as a terminal functional group of the binder, and as described above, the terminal organic functional group of the binder includes an aliphatic functional group. Accordingly, preferably, the RAFT initiator may include an aliphatic functional group, and more specifically, the RAFT initiator may be prepared as one composed solely of an aliphatic functional group.

[0158] In one embodiment of the present invention, the RAFT initiator may include an aliphatic functional group and a thiocarbonyl thio functional group.

[0159] According to one embodiment of the present invention, the RAFT initiator may be prepared using a mixture of carbon disulfide (CS2), trihalomethane, and tetraalkylene ammonium bisulfate.

[0160] For example, a RAFT initiator can be obtained by adding carbon disulfide (CS2) and trihalomethane to an organic solvent such as acetone, adding tetraalkylene ammonium bisulfate as a phase transfer catalyst (PTC), mixing, adding NaOH, and performing acid work-up with HCl.

[0161] According to one embodiment of the present invention, trichloromethane can be used as the trihalomethane.

[0162] According to one embodiment of the present invention, tetrabutyl ammonium bisulfate can be used as the tetraalkylene ammonium bisulfate.

[0163] According to one embodiment of the present invention, S,S'-bis(R,R'-dimethyl-R''-acetic acid)-trithiocarbonate (BDAAT) can be used as a RAFT initiator.

[0164] In one embodiment of the present invention, the binder can be obtained by dissolving the RAFT initiator prepared above and a polymerization raw material of a predetermined equivalent amount in an organic solvent and then thermally polymerizing.

[0165] In one embodiment of the present invention, the second process can be performed as a one-step reaction to simultaneously form a polyalkyl methacrylate-derived block and a polyacrylic acid-derived block in the RAFT initiator.

[0166] In another embodiment of the present invention, the second process may be performed as a two-step reaction to sequentially form a polyalkyl methacrylate-derived block and a polyacrylic acid-derived block in the RAFT initiator.

[0167] For example, in one embodiment of the present invention, the second process may be performed by sequentially forming a polyacrylic acid-derived block in a RAFT initiator, and forming a polyalkyl methacrylate. To this end, first, the RAFT initiator prepared above and a predetermined amount of an acrylic acid-based monomer may be dissolved in an organic solvent, followed by thermal polymerization to obtain a precursor including a polyacrylic acid-derived block bound to the RAFT initiator. Next, the precursor and a predetermined amount of an alkyl methacrylate-based monomer may be dissolved in an organic solvent, followed by thermal polymerization to obtain the binder.

[0168] In one embodiment of the present invention, the method for manufacturing the binder may further include a step of performing lithiation of the manufactured binder. For example, the binder may include a plurality of carboxyl groups at the terminals, and in this case, the binder may be brought into contact with a LiOH aqueous solution to lithiate the carboxyl groups, thereby obtaining a lithiated binder.

[0169] For example, a binder represented by the following chemical formula 4 can be manufactured according to the following method, but the method for manufacturing the binder is not limited thereto.

[0170] First, BDAAT prepared above is prepared as a RAFT initiator.

[0171] Dissolve 0.25 mmol of prepared BDAAT in 20 ml of 1,4-dioxane together with 400 equivalents of acrylic acid (AA) and 4,4'-azobis(4-cyanovaleic acid) (V-501), and react at 75°C for 18 hours to obtain an intermediate product (PAA 400 ) is obtained. The obtained intermediate product (PAA 400 ) 0.8 g of poly(ethylene glycol) methyl ether acrylate (PM) (Mn=480) was dissolved in 30 ml of distilled water together with V-501, and reacted at 75°C for 18 hours to obtain the intermediate product P(AA 400 -b-PM400 ) is obtained. The obtained P(AA 400 -b-PM 400 ) reacted with 4 equivalents of 10 wt% LiOH aqueous solution relative to the number of carboxyl groups (-COOH) at room temperature overnight to obtain P(AA) 400 -b-PM 400 )-Li is obtained.

[0172] [Chemical Formula 4]

[0173]

[0174] According to another aspect of the present invention, a method for manufacturing an electrode for a lithium secondary battery using the above-described binder can be provided.

[0175] The method for manufacturing the above lithium secondary battery electrode may include a step of applying and drying a slurry containing the binder and active material mixed in an appropriate solvent onto at least one surface of a current collector. Optionally, the slurry may further include a conductive material.

[0176] According to one aspect of the present invention, the binder may be particularly effective in suppressing the dissolution of lithium polysulfide within the positive electrode of a lithium-sulfur battery. Accordingly, the binder may be used in the manufacture of the positive electrode of a lithium-sulfur battery, and the method for manufacturing the electrode of the lithium secondary battery may be a method for manufacturing the positive electrode of a lithium-sulfur battery.

[0177] A method for manufacturing a lithium secondary battery according to one aspect of the present invention may include applying and drying a slurry in which the binder, sulfur-based compound, and conductive carbon material are mixed in an aqueous solvent onto at least one surface of a current collector to obtain an electrode.

[0178] The above binder cites what has been described above about the binder.

[0179] In one embodiment of the present invention, the binder may have excellent properties of dissolving in an aqueous solvent, specifically, water, by having terminal functional groups lithiated. Accordingly, a method of manufacturing an electrode using the binder has the advantage of being able to use an aqueous solvent, specifically, water. In this case, the water may be distilled water or deionized water. However, the present invention is not necessarily limited thereto, and if necessary, a lower alcohol that is easily mixed with water may be used. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol, and butanol, and preferably, these may be mixed with water and used. The content of the solvent in the slurry may be contained at a level that has a concentration that facilitates coating, and the specific content varies depending on the coating method and device.

[0180] The method for applying the slurry is not particularly limited in the present invention, and examples thereof include methods such as doctor blade, die casting, comma coating, and screen printing. In addition, the slurry may be applied onto the current collector by molding it on a separate substrate and then pressing or lamination.

[0181] After the above application, a drying process for solvent removal can be performed. The drying process is performed at a temperature and time that can sufficiently remove the solvent, and the conditions may vary depending on the type of solvent and are therefore not particularly limited to the present invention. Examples include drying using warm air, hot air, low-humidity air, vacuum drying, and drying using irradiation with (far) infrared rays and electron beams. The drying speed is usually adjusted to remove the solvent as quickly as possible within a speed range that does not cause cracks in the active material layer due to stress concentration or cause the active material layer to peel off from the current collector.

[0182] Additionally, in one embodiment of the present invention, the density of the active material within the electrode can be increased by further including a step of pressing the electrode after drying. Examples of pressing methods include mold pressing and roll pressing.

[0183] In one embodiment of the present invention, the porosity of the electrode manufactured by the composition and manufacturing method described above, specifically, the positive electrode active material layer including a sulfur-based compound, may be 50 to 80% by volume, specifically, 60 to 75% by volume. If the porosity of the positive electrode is less than 50% by volume, the filling degree of the positive electrode slurry composition including the positive electrode active material, the conductive agent, and the binder becomes excessively high, so that sufficient electrolyte capable of exhibiting ionic and / or electrical conductivity cannot be maintained between the positive electrode active materials, which may result in a deterioration in the output characteristics or cycle characteristics of the battery, and a serious decrease in the overvoltage and discharge capacity of the battery. On the other hand, if the porosity of the positive electrode exceeds 80% by volume and has excessively high porosity, the physical and electrical connection with the current collector is lowered, which may result in a problem of reduced adhesive strength and difficulty in reaction. In addition, the increased porosity may be filled with electrolyte, which may result in a problem of a lower energy density of the battery, so the porosity is appropriately controlled within the above range.

[0184] In one embodiment of the present invention, the sulfur-based compound may be used without particular limitation as long as it is a material that can be used as a positive electrode active material of a lithium-sulfur battery, including a disulfide (SS) structure. The sulfur-based compound may include, for example, all sulfur-containing compounds that can be formed through a reduction reaction of inorganic sulfur (S8) or an oxidation reaction of lithium sulfide (Li2S). Specifically, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 1 < x ≤ 8), disulfide compounds, carbon-sulfur polymer ((C2S) y ) n, y = 2.5 to 50, n≥2) or may include two or more of these.

[0185] In one embodiment of the present invention, it may be preferable that the sulfur compound includes inorganic sulfur (S8).

[0186] In one embodiment of the present invention, the sulfur-based compound may be utilized in the form of a sulfur-carbon composite supported on a conductive porous carbon material. Specifically, the sulfur-carbon composite may include a porous carbon material and a sulfur-based compound supported on at least one of the inner and outer surfaces of the pores of the porous carbon material. In the case of sulfur acting as a positive electrode active material, it may be preferable to use it in a composite with a conductive material such as a carbon material because sulfur alone does not have electrical conductivity. Therefore, the conductive carbon material for supporting the sulfur-based compound is preferably a porous material.

[0187] In one embodiment of the present invention, the porous carbon material is used to support a sulfur-based compound as a positive electrode active material, and to provide a framework in which the sulfur-based compound can be uniformly and stably fixed, while improving the conductivity of the positive electrode. Any porous carbon material can be used without particular limitation in its type.

[0188] The above porous carbon material can generally be manufactured by carbonizing precursors of various carbon materials. The porous carbon material includes pores that are not regular therein, and the average diameter of the pores ranges from 1 to 200 nm, and the porosity can range from 10 to 90 volume% of the total volume of the porous carbon material. If the average diameter of the pores is less than the above range, the pore size is only at the molecular level, making sulfur impregnation impossible. Conversely, if it exceeds the above range, the mechanical strength of the porous carbon material is weakened, making it undesirable for application to the electrode manufacturing process.

[0189] In one embodiment of the present invention, the 'average pore diameter' can be measured according to a method known in the art for measuring the pore diameter of a porous material, and the measuring method is not particularly limited. For example, the pore diameter can be measured according to a scanning electron microscope (SEM), a field emission electron microscope (laser diffraction method), a laser diffraction method, or the BET (Brunauer-Emmett-Teller) method. The measurement using the laser diffraction method can be, for example, using a commercially available laser diffraction particle size measuring device (for example, Microtrac MT 3000). In addition, the measurement according to the BET method can be, for example, using an analyzer of the BELSORP series of BEL Japan, but is not limited thereto.

[0190] In one embodiment of the present invention, the 'porosity' refers to the ratio of the volume occupied by pores to the total volume of a structure, and uses % as its unit, and can be used interchangeably with terms such as porosity and porosity. In the present invention, the measurement of the porosity is not particularly limited, and according to one embodiment of the present invention, for example, it can be measured according to the BET method using nitrogen gas or the mercury penetration method (Hg porosimeter) and ASTM D2873.

[0191] The shape of the above porous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tubular or bulk-shaped, and may be used without limitation as long as it is a shape commonly used in lithium-sulfur batteries.

[0192] The porous carbon material may be any material commonly used in the art that has a porous structure or a high specific surface area. For example, the porous carbon material may be at least one selected from the group consisting of graphite; graphene; carbon black such as Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); and graphite and activated carbon such as natural graphite, artificial graphite, and expanded graphite, but is not limited thereto. Preferably, the porous carbon material may be a carbon nanotube.

[0193] In one embodiment of the present invention, the porous carbon material may include carbon black, and the sulfur-carbon complex may include a complex of the sulfur compound and the carbon black.

[0194] In one embodiment of the present invention, the method for producing the sulfur-carbon composite is not particularly limited to the present invention, and any method commonly used in the art may be used. For example, a method may be used in which the sulfur-based compound is mixed with the porous carbon material, followed by heat treatment to inject the molten sulfur-based compound into the porous carbon material. However, the present invention is not limited thereto.

[0195] In one embodiment of the present invention, the weight ratio of the sulfur compound and the porous carbon material in the sulfur-carbon composite may be, for example, 5:5 to 9:1, 6:4 to 9:2, or 6:4 to 7:3, but the present invention is not limited thereto. When the weight ratio is in the above-described range, it may be preferable in terms of the electron transfer area of ​​the sulfur-carbon composite and the wettability of the positive electrode with the electrolytic cell, and for example, the available surface area in the sulfur-carbon composite increases, which may be preferable in suppressing the elution of sulfur from the positive electrode, but the present invention is not limited thereto.

[0196] In one embodiment of the present invention, the method for manufacturing the electrode for a lithium secondary battery may further include heat-treating a mixture of the sulfur-based compound and the conductive carbon material to obtain a sulfur-carbon composite, and accordingly, the slurry for forming the electrode may be obtained by mixing the sulfur-carbon composite and the binder in the aqueous solvent.

[0197] In one embodiment of the present invention, the current collector supports the positive electrode active material, and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. can be used. The positive electrode current collector can form fine irregularities on its surface to strengthen the bonding strength with the positive electrode active material, and can use various forms such as a film, sheet, foil, mesh, net, porous body, foam, non-woven fabric, etc.

[0198] In one embodiment of the present invention, the electrode may further include a transition metal element, a Group ⅢA element, a Group ⅣA element, or a mixture of two or more thereof, in addition to a sulfur-based compound as an active material, as long as the purpose of the present invention is not impaired. The transition metal element 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, and the Group ⅢA element may include Al, Ga, In, Ti, and the Group ⅣA element may include Ge, Sn, Pb, and the like.

[0199] In one embodiment of the present invention, the sulfur-carbon complex may be 50 wt% or more based on the total weight of the electrode. Specifically, the sulfur-carbon complex may be, for example, 70 wt% or more, or 80 wt% or more, based on the total weight of the electrode active material layer. Specifically, the sulfur-carbon complex may be included in an amount of 80 wt% to 100 wt% or 80 wt% to 90 wt% based on the total weight of the electrode active material layer. If the content of the sulfur-carbon complex is less than the above range, the relative content of auxiliary materials such as a conductive material and a binder increases and the content of the sulfur-carbon complex decreases, making it difficult to implement a high-capacity, high-energy-density battery. Conversely, if it exceeds the above range, the content of the conductive material or binder described below is relatively insufficient, which causes a problem in that the physical properties of the electrode deteriorate.

[0200] In one embodiment of the present invention, the electrode active material layer may further include a conductive material in addition to the conductive carbon material for complexing the sulfur-carbon composite. The conductive material is a material that electrically connects the electrolyte and the electrode active material and serves as a path for electrons to move from a current collector to the electrode active material. Any conductive material that is physically distinct from the carbon contained in the sulfur-carbon composite and is a component of the electrode may be used without limitation.

[0201] In one embodiment of the present invention, the conductive material may be, for example, carbon black such as Super-P, Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon black; carbon derivatives such as carbon nanotubes or fullerene; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorocarbon, aluminum, and nickel powder; or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole, which may be used alone or in combination.

[0202] In one embodiment of the present invention, the content of the conductive material may be 1 to 15 wt% or 5 to 10 wt% based on the total weight of the positive electrode active material.

[0203] In one embodiment of the present invention, the binder may further include, in addition to the above-described binder, a conventional binder that can be used in an electrode active material layer, as long as it does not impede the purpose of the present invention. For example, the binder may include a fluororesin binder including polyvinylidene fluoride (PVdF), a polyvinylidene fluoride polymer containing at least one vinylidene fluoride as a repeating unit, polytetrafluoroethylene (PTFE), or a mixture of two or more thereof; a rubber binder including styrene butadiene rubber (SBR), acrylonitrile-butidiene rubber, or styrene-isoprene rubber; an acrylic binder; a cellulose binder including carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; a polyalcohol binder; It may further include one, two or more kinds of mixtures or copolymers selected from the group consisting of polyolefin binders including polyethylene and polypropylene; polyimide binders; polyester binders; and silane binders.

[0204] In one embodiment of the present invention, the content of the binder may be 1 to 15 wt% or 5 to 10 wt% based on the total weight of the positive electrode active material layer. By using the content of the binder within the above-described range, not only is the bonding strength between the current collector and the electrode active material layer excellent, but it can also exhibit a beneficial effect in terms of suppressing lithium polysulfide eluted from the electrode, but the present invention is not limited thereto.

[0205] In one embodiment of the present invention, the electrode manufactured above includes a current collector and an electrode active material layer formed on at least one surface of the current collector.

[0206] At this time, according to one embodiment of the present invention, the thickness of the electrode active material layer may 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 is within the above-described range, it may be preferable in terms of the capacity relative to the weight of the electrode, but the present invention is not limited thereto.

[0207] In the present specification, the thickness of the electrode active material layer may be measured during the process of applying the slurry during the manufacture of the electrode active material layer, or may be measured on the dried final electrode. When measuring the thickness of the electrode active material layer on the dried final electrode, a known thickness measuring device may be used. The thickness measuring device may be, for example, a thickness measuring device manufactured by Mitutoyo Corporation. Alternatively, the thickness of the entire electrode may be measured through an electron microscope photograph of the electrode cross-section, and the thickness of the electrode active material layer may be measured by excluding the thickness of the current collector.

[0208]

[0209] According to another aspect of the present invention, a lithium secondary battery including the electrode is provided.

[0210] In one embodiment of the present invention, the lithium secondary battery may include the electrode as a positive electrode and the negative electrode as a counter electrode.

[0211] In one embodiment of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer applied to one or both surfaces of the negative electrode current collector. Alternatively, the negative electrode may be a lithium metal plate.

[0212] The above negative electrode current collector is for supporting the negative electrode active material layer, and the description regarding the above current collector is used.

[0213] In one embodiment of the present invention, the negative electrode active material layer may include a conductive material, a binder, etc. in addition to the negative electrode active material. The negative electrode active material may be lithium (Li +) can be reversibly intercalated or deintercalated, a material that can react with lithium ions to form a reversibly lithium-containing compound, lithium metal or a lithium alloy. The lithium ions (Li + ) can be reversibly inserted or de-inserted, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The lithium ion (Li + ) can be, for example, tin oxide, titanium nitrate or silicon. The lithium alloy can be, for example, an alloy of a metal selected from the group consisting of lithium (Li) and 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). The conductive material can be as described above, and the binder can include a binder according to one aspect of the present invention, a conventional binder or a mixture thereof, and is not particularly limited thereto.

[0214] In one embodiment of the present invention, the lithium secondary battery may be a lithium-sulfur battery, and in this case, the negative electrode active material may be lithium metal, and specifically, may be in the form of a lithium metal thin film or lithium metal powder. According to one embodiment of the present invention, the negative electrode may not have a current collector and may be composed of a lithium metal or lithium alloy thin film.

[0215] The above lithium secondary battery includes an electrolyte in addition to a positive electrode and a negative electrode, and may further include a separator as needed.

[0216] In one embodiment of the present invention, the electrolyte may include a lithium salt.

[0217] The above lithium salt can be used without particular limitation as long as it can be used in the lithium secondary battery, specifically, a lithium-sulfur battery. For example, the above lithium salt can be 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, lithium lower aliphatic carboxylate, lithium 4-phenylborate, lithium imide, or two or more thereof.

[0218] In one embodiment of the present invention, the electrolyte may further include a non-aqueous solvent in addition to a lithium salt, or may be included in the form of a solid electrolyte layer formed on at least one surface of the electrode without a solvent.

[0219] In one embodiment of the present invention, the lithium secondary battery may include a separator as needed, and the separator separates or insulates the positive electrode and the negative electrode from each other and enables lithium ion transport between the positive electrode and the negative electrode. The separator may be made of a porous non-conductive or insulating material, and any material commonly used as a separator in a lithium secondary battery may be used without special limitation. The separator may be an independent member such as a film, or may be a coating layer added to the positive electrode and / or the negative electrode.

[0220] In one embodiment of the present invention, the lithium secondary battery may have various shapes, for example, a coin shape, a square shape, a pouch shape, or a cylindrical shape, but is not limited thereto.

[0221]

[0222] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0223]

[0224] [Binder Manufacturing]

[0225] Manufacturing example 1.

[0226] - Synthesis of S,S-bis(R,R'-dimethyl-R'-acetic acid)-trithiocarbonate (BDAAT)

[0227]

[0228] BDAAT was synthesized as a RAFT initiator according to the following method.

[0229] The title BDAAT was prepared by mixing CS2, chloroform, acetone, and tetrabutyl ammonium hydrogensulfate as a phase transfer catalyst (PTC), adding NaOH, and performing acid work-up with hydrochloric acid.

[0230]

[0231] Example 1

[0232] - P(AA 400 -b-PM 400 ) Synthesis of binders

[0233]

[0234]

[0235] 400 equivalents of acrylic acid (AA, acrylic acid) relative to 0.25 mmol of BDAAT of the above manufacturing example 1 were dissolved in 20 ml of 1,4-dioxane together with 1 wt% of V-501 (4,4'-Azobis(4-cyanovaleric acid)) relative to the total 100 wt% of BDAAT and acrylic acid, and reacted at 75°C for 18 h to obtain PAA as an intermediate product. 400 Got it.

[0236] 0.8 g PA 400 400 equivalents of poly(ethylene glycol) methyl ether acrylate (PM) (M n =480) was dissolved in 30 ml of distilled water together with V-501 and reacted at 75 ℃ for 18 h to obtain P(AA) as the binder of Example 1. 400 -b-PM 400 ) was obtained.

[0237] PAA 400 As a result of synthesis, the 1H NMR spectrum is shown in Figure 1, and P(AA 400 -b-PM 400 ) as a result of synthesis, the 1H NMR spectrum is shown in Figure 2.

[0238]

[0239] Example 2

[0240] - P(AA 400 -b-PM 400 )-Synthesis of Li binder

[0241]

[0242] P(AA) obtained in Example 1 400 -b-PM 400 ) was reacted with 4 equivalents of 10 wt% LiOH aqueous solution relative to the number of -COOH functional groups at room temperature overnight to obtain P(AA) as the binder of Example 2. 400 -b-PM 400 )-Li was obtained.

[0243] P(AA 400 -b-PM 400 )-Li synthesis results, the TFT-IR spectrum is shown in Fig. 3.

[0244]

[0245] Example 3

[0246] - P(AA 200 -b-PM 600 ) Synthesis of binders

[0247]

[0248] PAA was prepared as an intermediate product in the same manner as Example 1, except that 200 equivalents of acrylic acid (AA) were used compared to 0.25 mmol of BDAAT in the above Preparation Example 1. 200 was synthesized.

[0249] 0.8 g of PAA 200 P(AA) as a binder of Example 3 was prepared in the same manner as in Example 1, except that 600 equivalents of poly(ethylene glycol) methyl ether acrylate (PM) were used. 200 -b-PM 600 ) was obtained.

[0250] PAA 200 As a result of synthesis, the 1H NMR spectrum is shown in Fig. 4, and P(AA 200 -b-PM 600 ) as a result of synthesis, the 1H NMR spectrum is shown in Figure 5.

[0251]

[0252] Example 4

[0253] - P(AA 200 -b-PM 600 )-Synthesis of Li binder

[0254]

[0255]

[0256] P(AA) obtained in Example 3 200 -b-PM 600) was reacted with 4 equivalents of 10 wt% LiOH aqueous solution relative to the number of -COOH functional groups at room temperature overnight to obtain P(AA) as the binder of Example 4. 200 -b-PM 600 )-Li was obtained.

[0257] P(AA 200 -b-PM 600 )-Li synthesis results, the TFT-IR spectrum is shown in Fig. 6.

[0258]

[0259] Comparative Example 1

[0260] - P(AA 400 -b-PM 400 ) Synthesis of (b-type) binder

[0261]

[0262]

[0263] The RAFT polymerization reaction was initiated using DBTTC (dibenzyl trithiocarbonate) containing an aromatic functional group at the terminal as a RAFT initiator.

[0264] Dissolve 400 equivalents of acrylic acid (AA) relative to 0.25 mmol DBTTC (dibenzyl trithiocarbonate) in 20 ml of 1,4-dioxane together with V-501 (4,4'-Azobis(4-cyanovaleric acid)) and react at 75°C for 18 h to obtain PAA. 400 Got it.

[0265] 0.8 g PAA 400 400 equivalents of poly(ethylene glycol) methyl ether acrylate (PM)(M n =480) was dissolved in 30 ml of DMF with AIBN and reacted at 75 ℃ for 18 h to obtain P(AA 400 -b-PM 400 ) (b-type) was obtained.

[0266]

[0267] [Making of positive electrodes]

[0268] Comparative Example 2

[0269] 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).

[0270] The manufactured KB / S, polyacrylic acid (PAA) binder, and conductive agent (Super P) were mixed in a weight ratio of 80:10:10, and 3 wt% of PVA dispersant was added, and then mixed in a thinky mixer in the water phase to prepare a cathode slurry.

[0271] The prepared positive electrode slurry was coated on aluminum foil with a doctor blade to a thickness of 200 μm, and then dried at 50°C for 14 h to obtain a positive electrode.

[0272]

[0273] Comparative Example 3

[0274] As a binder, the binder (P(AA) manufactured in the above comparative example 1 400 -b-PM 400 ) (b-type)) was used, and the positive electrode was obtained in the same manner as in Comparative Example 2, except that the positive electrode slurry was coated at 350 μm.

[0275]

[0276] Example 5

[0277] As a binder, the binder (P(AA) manufactured in the above Example 1 400 -b-PM 400 )) was used, and the positive electrode was obtained in the same manner as in Comparative Example 2, except that the positive electrode slurry was coated at 350 μm.

[0278]

[0279] Example 6

[0280] As a binder, the binder (P(AA) manufactured in the above Example 2 400 -b-PM 400)-Li) and coated the cathode slurry to 350 μm, and the cathode was obtained in the same manner as in Comparative Example 2.

[0281]

[0282] Example 7

[0283] As a binder, the binder (P(AA) manufactured in the above Example 3 200 -b-PM 600 )) was used, and the positive electrode was obtained in the same manner as in Comparative Example 2, except that the positive electrode slurry was coated at 350 μm.

[0284]

[0285] Example 8

[0286] As a binder, the binder (P(AA) manufactured in the above Example 4 200 -b-PM 600 )-Li) and coated the cathode slurry to 350 μm, and the cathode was obtained in the same manner as in Comparative Example 2.

[0287]

[0288] [Manufacturing of Coin-Type Lithium Secondary Batteries]

[0289] As the positive electrode, each of the positive electrodes manufactured in Comparative Example 2, Comparative Example 3, and Examples 5 to 8 was used, and as the negative electrode, lithium metal having a thickness of 100 μm was prepared.

[0290] An electrode assembly was prepared by positioning the positive and negative electrodes so that they face each other and interposing a polypropylene separator having a thickness of 25 ㎛ and a porosity of 41 vol% between them.

[0291] The prepared electrode assembly was placed in a coin-shaped case and 50 ㎕ / mg of an electrolyte solution containing 1 M lithium salt (LiTFSI) dissolved in a mixed solvent of dioxolane and dimethoxyethane (DME) 1:1 (v / v) was added. s Coin-type batteries were manufactured by injecting with an El / S ratio of .

[0292]

[0293] [Observation of the surface of the anode]

[0294] Figure 7 shows the results of observing the surface of the anode using SEM images after manufacturing the anode using different binders.

[0295] Figure 7 shows, from the left, an SEM image of a positive electrode manufactured using the same method as Comparative Example 2 in which a positive electrode was manufactured using PAA, but after coating the positive electrode slurry to a thickness of 150 μm and drying it, an SEM image (center) of a positive electrode manufactured using the same method as Example 1, but after coating the positive electrode slurry to a thickness of 200 μm and drying it, and an SEM image (right) of a positive electrode manufactured using the same method as Example 2, but after coating the positive electrode slurry to a thickness of 200 μm and drying it.

[0296] As shown in Fig. 7, even though the anode including the binder of Examples 1 and 2 was formed thicker, the phenomenon of the binder being unevenly clumped was observed only on the surface of the anode formed thinner using PAA.

[0297] Through this, it was inferred that by using a binder according to one embodiment of the present invention, the distribution uniformity of the binder within the anode can be improved, thereby further improving the electrical performance of the anode.

[0298] In particular, the PAA used in Comparative Example 2 contains -COOH in all monomers, so that hydrogen bonds occur between them every time to form a dimer, whereas in the case of Examples 1 and 2, which are block copolymer binders of polyacrylic acid and polyalkyl methacrylate, -COOH is included in the polyalkyl methacrylate block, and a larger number of -COOH atoms are included that can interact with lithium polysulfide, and it is inferred that this effect is caused by the excellent adsorption ability of polyethylene glycol itself to lithium polysulfide.

[0299]

[0300] [Physical Properties Evaluation of Coin-Type Lithium Secondary Batteries]

[0301] Each of the coin-type lithium secondary batteries manufactured above was discharged once at room temperature (25°C) at a 0.1 C rate in the range of 2.5 V to 1.8 V, then charged and discharged twice at a 0.1 C rate in the range of 1.8 V to 2.5 V, then charged and discharged three times at a 0.2 C rate in the range of 1.8 V to 2.5 V, and then the charge and discharge cycles were repeated at a 0.5 C rate.

[0302] After 134 cycles at a 0.5C rate, the discharge capacity graphs of the batteries using the positive electrodes of Comparative Example 2, Comparative Example 3, Example 5, and Example 6, respectively, and after 29 cycles, the discharge capacity graphs of the batteries using the positive electrodes of Comparative Example 2, Example 7, and Example 8, respectively, are shown in Fig. 8 (134 cycles) and Fig. 9 (29 cycles), respectively.

[0303] Tables 1 and 2 below show the results of measuring the capacity retention rate compared to the initial capacity (0.5 C rate 1 cycle) after 134 cycles or 29 cycles, respectively.

[0304] Binder type sulfur loading (mg / cm) 2 )Cycle progress number (times)Capacity maintenance rate (%) (@ 0.5C rate)Comparative example 2PAA1.5013434.86Example 5P(AA 400 -b-PM 400 )58.72 Example 6P(AA 400 -b-PM 400 )-Li51.46

[0305] Binder type sulfur loading (mg / cm) 2 )Cycle progress number (times)Capacity maintenance rate (%) (@ 0.5C rate)Comparative example 2PAA3.17292.62Example 7P(AA 200 -b-PM 600 )63.11 Example 8P(AA 200 -b-PM 600 )-Li23.67

[0306] According to FIG. 8, FIG. 9, Table 1 and Table 2, it was confirmed that not only did the discharge capacity of the battery increase by using the binder according to one embodiment of the present invention, but the capacity retention rate was also excellent.

[0307] Specifically, according to FIG. 8, it was confirmed that a positive electrode using a binder containing an aromatic functional group at the terminal, although manufactured by a RAFT polymerization reaction, had a poor effect due to a decrease in initial capacity. In addition, referring to FIGS. 8 and 9, it was confirmed that when PAA was used as a positive electrode binder, the battery capacity was poor, whereas when the binders of Examples 7 and 8 according to one embodiment of the present invention were used, the battery capacity was dramatically improved. This was inferred to be due to the suppression of lithium polysulfide dissolution and the improvement of electrical conductivity by the binder.

[0308]

[0309] [Calculating the number of monomers in the binder]

[0310]

[0311] The above Example 1 (P(AA) 400 -b-PM 400 )) and Example 3 (P(AA 200 -b-PM 600 )) In order to measure the number average molecular weight and weight average molecular weight of the binder manufactured in, methylation was performed by reacting at room temperature (25°C) for 72 hours using TMS CHN2 (Trimethylsilyl diazomethane) under MeOH / THR reaction conditions.

[0312] The number-average molecular weight (Mn) of the binder of Example 1, measured using THF-GPC, was 2472 g / mol, and the weight-average molecular weight (Mw) was 2486 g / mol (PDI = 1.005). In addition, the molecular weight (Mn) of the binder of Example 3, measured using the same method, was 21,000 g / mol, and the weight-average molecular weight (Mw) was 27,000 g / mol (PDI = 1.3).

[0313] Considering that the conversion rate of the above Example 1 was 12.1% and the conversion rate of Example 3 was 6.6%, when the conversion rate of 100% is secured based on Example 1, a theoretical weight average molecular weight of 221,106.39 g / mol is obtained. Based on this, and based on the above-described experiments, in order to obtain a binder with a weight average molecular weight of 300,000 g / mol for controlling the viscosity of the binder in the positive electrode slurry, it was calculated that it may be more preferable to use 1,000 to 1,100 units of each of the acrylic acid monomer and the poly(ethylene glycol) methyl ether acrylate monomer and achieve a conversion rate of 50% or more.

Claims

1. A thiocarbonyl thio functional group represented by the following formula 1, A first polyalkyl methacrylate-derived block covalently bonded to one terminal of the above thiocarbonyl thio functional group, A second polyalkyl methacrylate-derived block covalently bonded to the other terminal of the thiocarbonyl thio functional group, A first polyacrylic acid derived block covalently bonded to one end of the first polyalkyl methacrylate derived block, and A second polyacrylic acid derived block covalently bonded to one end of the second polyalkyl methacrylate derived block, A binder for a lithium secondary battery, wherein the terminal organic functional group includes an aliphatic functional group. [Formula 1] 2. In claim 1, At least one carboxyl group (-COOH) in the first polyacrylic acid-derived block and the second polyacrylic acid-derived block is lithium-substituted (-COO - Li + ) Binder for lithium secondary batteries.

3. In claim 1, A binder for a lithium secondary battery, wherein the first polyacrylic acid-derived block and the second polyacrylic acid-derived block independently contain 50 to 1500 acrylic acid repeating structures.

4. In claim 1, A binder for a lithium secondary battery, wherein the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block independently contain 50 to 1500 alkyl methacrylate repeating structures.

5. In claim 1, A binder for a lithium secondary battery, wherein the alkyl included in at least one of the first polyalkyl methacrylate-derived block and the second polyalkyl methacrylate-derived block includes at least one of a polyethylene glycol repeating unit, a polypropylene glycol repeating unit, and a polyethylene-polypropylene glycol repeating unit.

6. In claim 5, A binder for a lithium secondary battery, wherein the alkyl group comprises 1 to 30 polyethylene glycol repeating units.

7. In claim 1, The terminal organic functional group is a lithium-substituted carbonyl group (-COO - Li + ) for a lithium secondary battery.

8. In claim 1, A binder for a lithium secondary battery, wherein the pH of the aqueous dispersion in which the binder for a lithium secondary battery is dispersed in water is in the range of 6.2 to 7.

8.

9. A method for manufacturing an electrode for a lithium secondary battery, comprising applying and drying a slurry in which a binder, a sulfur-based compound, and a conductive carbon material according to any one of claims 1 to 8 are mixed in an aqueous solvent onto at least one surface of a current collector to obtain an electrode.

10. In claim 9, A method for producing an electrode for a lithium secondary battery, comprising obtaining the binder through a polymerization reaction of a RAFT initiator containing an aliphatic functional group and a thiocarbonyl thio functional group, an alkyl methacrylate and acrylic acid.

11. In claim 10, Before the above polymerization reaction, A method for manufacturing an electrode for a lithium secondary battery, further comprising a step of preparing the RAFT initiator as a mixture of carbon disulfide (CS2), trihalomethane, and tetraalkylene ammonium bisulfate.

12. In claim 10, A method for manufacturing an electrode for a lithium secondary battery, wherein the RAFT initiator comprises S,S'-bis(R,R'-dimethyl-R''-acetic acid)-trithiocarbonate, BDAAT.

13. In claim 9, Comprising heat treating a mixture of the above sulfur compound and a conductive carbon material to obtain a sulfur-carbon composite, A method for manufacturing an electrode for a lithium secondary battery, comprising mixing the sulfur-carbon complex and the binder in the aqueous solvent to obtain the slurry.

14. In claim 9, The electrode obtained above includes the current collector and an active material layer provided on at least one surface of the current collector, A method for manufacturing an electrode for a lithium secondary battery, wherein the active material layer has a thickness of 250 ㎛ or more.

15. An electrode for a lithium secondary battery, comprising a binder, a sulfur-based compound, and a conductive carbon material according to any one of claims 1 to 8.

16. A lithium secondary battery comprising an electrode according to claim 15.

Images