Composite binder for silicon electrode of lithium secondary battery, manufacturing method therefor, and silicon electrode of lithium secondary battery using same

Abstract

The present invention relates to a composite binder for a silicon electrode of a lithium secondary battery, wherein the composite binder comprises: a polymer composite including a polymer and a furan group bonded to the polymer; and a carbon material bearing a carbon-carbon double bond, and is formed by combining the polymer composite and the carbon material through a chemical reaction by heat.

Description

Composite binder for silicon electrode of lithium secondary battery and method for manufacturing same, and silicon electrode of lithium secondary battery using same

[0001] The present invention relates to a composite binder for a silicon electrode of a lithium secondary battery and a method for manufacturing the same. The present invention also relates to a lithium secondary battery comprising such a composite binder.

[0002] Lithium secondary battery electrodes incorporate conductive materials like carbon black to enhance conductivity. Existing techniques for improving the dispersibility of conductive materials include using dispersants like surfactants and modifying carbon black to add functional groups.

[0003] Among the technologies for improving the dispersibility of carbon black using existing dispersants, sufficient dispersibility could not be obtained when a small amount of dispersant was added, and when a large amount of dispersant was added, there was a problem of reduced electrical conductivity and a relatively small content of active material in the electrode, which lowered the energy density of the electrode.

[0004] In the case of technology to improve dispersibility by modifying existing carbon black, a representative method is to introduce functional groups through acid treatment, but this has the problem of causing defects on the surface of carbon black, resulting in a deterioration in electrical conductivity.

[0005] Korean Patent No. 10-1799923 (published on March 24, 2016) discloses a secondary battery electrode active material slurry comprising a dispersant comprising one compound or a mixture of one or more compounds selected from the group consisting of five or more isocyanate compounds and polyfunctional tertiary polyamine compounds to improve the dispersibility of the conductive material. However, the prior art still has problems associated with the addition of a dispersant to disperse the conductive material.

[0006] The technical problem that the present application seeks to solve is to provide a composite binder for a silicon electrode of a lithium secondary battery and a method for manufacturing the same.

[0007] Another technical problem that the present application seeks to solve is to provide a silicon electrode for a lithium secondary battery using the same.

[0008] To solve the above technical problem, the present invention provides a composite binder for a silicon electrode of a lithium secondary battery, a method for manufacturing the same, and a silicon electrode of a lithium secondary battery including the same.

[0009] In one embodiment of the present invention, the present invention may include a composite binder for a silicon electrode of a lithium secondary battery, which comprises a polymer composite including a polymer and a furan group bonded to the polymer; and a carbon material including a carbon-carbon pi (Π) bond; and wherein the polymer composite and the carbon material are formed by combining through a chemical reaction caused by heat.

[0010] In one embodiment, the heat-induced chemical reaction may comprise a Diels-Alder reaction performed at a temperature range of 70°C to 90°C.

[0011] In one embodiment, the polymer is a water-soluble polymer having a number average molecular weight of 30,000 to 500,000, and may include at least one of poly(acrylic acid) (PAA), sodium carboxymethyl cellulose (CMC), chitosan, poly(vinyl alcohol) and guar gum.

[0012] In one embodiment, the polymer composite may be represented by chemical formula 1.

[0013] [Chemical Formula 1]

[0014]

[0015] Here, n is between 5000 and 6300, and m is between 500 and 700.

[0016] In one embodiment, the carbon material may include at least one of graphene, reduced graphene, carbon nanotubes, and derivatives thereof.

[0017] In one embodiment, the polymer complex may be bonded to 30% to 85% of the polymer repeating units with the furan group.

[0018] In one embodiment, the weight ratio (wt%) of the polymer composite and the carbon material may be 9:1 to 7:3.

[0019] In one embodiment, the composite binder suppresses volume expansion of the negative electrode active material, and the volume of the electrode including the negative electrode active material may increase by 40% to 56% after 300 cycles compared to the initial volume.

[0020] In one embodiment, the polymer composite comprises: 1 When analyzed by H NMR, it may have peak values ​​at 7.3 ppm to 7.5 ppm, 6.35 ppm to 6.45 ppm, and 6.28 ppm to 6.35 ppm.

[0021] In one embodiment, the polymer in the polymer complex is PAA (Poly(acrylic acid)), and when the polymer complex is analyzed by 1H NMR, the peak ratio of 7.3 ppm to 7.5 ppm and the integral ratio of 2.10 ppm to 2.22 ppm may be 10:1 to 11:1.

[0022] In one embodiment, the Raman spectrum results at 1300 cm -1 1700 cm inland -1 In the Raman shift I before and after the polymer composite and carbon material are chemically bonded by heat D / I G The value before chemical bonding:after chemical bonding may be 0.017:0.04 to 1.08:1.16.

[0023] In one embodiment, a method for producing a composite binder for a silicon electrode of a lithium secondary battery may be provided, including the steps of: dissolving a polymer in ultrapure water to produce a polymer aqueous solution; adding a solution containing furan to the polymer aqueous solution, stirring the solution, and drying the solution to obtain a polymer composite; and heating the dried polymer composite and carbon material in ultrapure water while stirring to produce a composite binder.

[0024] In one embodiment, the pH of the step of preparing the polymer aqueous solution may be 5 to 6.

[0025] In one embodiment, the heating temperature in the step of manufacturing the composite binder may be 70°C to 90°C.

[0026] In one embodiment, the polymer is a water-soluble polymer and may include at least one of poly(acrylic acid) (PAA), sodium carboxymethyl cellulose (CMC), chitosan, poly(vinyl alcohol) and guar gum.

[0027] In one embodiment, the carbon material may include at least one of graphene, reduced graphene, carbon nanotubes, and derivatives thereof.

[0028] In one embodiment of the present invention, the present invention may include a silicon electrode for a lithium secondary battery, including a composite binder for a silicon electrode of a lithium secondary battery having at least one of the above-described characteristics; a negative electrode active material including silicon; and a conductive material.

[0029] In one embodiment, the negative electrode active material, composite binder, and conductive material may be included in a weight ratio of 70:15:15 to 95:5:0.

[0030] In one embodiment, the conductive material may include at least one of super P, carbon nanotubes, carbon black, graphene, and graphite.

[0031] According to the present invention, a composite binder for a silicon electrode of a lithium secondary battery, which suppresses expansion of a silicon active material and uniformly disperses a conductive material, a method for producing the same, and a silicon electrode of a lithium secondary battery using the same can be provided.

[0032] In addition, according to the present invention, the conductive material can be effectively dispersed without adding a separate dispersant, and the lifespan and performance of the electrode can be improved.

[0033] Figure 1 schematically illustrates the effect of an FPAA-AHNSrGo composite binder according to one embodiment of the present invention within an electrode.

[0034] Figure 2 schematically illustrates the effect of an FCMC-SWCNT composite binder according to one embodiment of the present invention within an electrode.

[0035] Figure 3 schematically illustrates a synthesis process of an FPAA-AHNSrGo composite binder according to one embodiment of the present invention.

[0036] Figure 4 schematically illustrates a synthesis process of an FCMC-SWCNT composite binder according to one embodiment of the present invention.

[0037] Figure 5 is a diagram of PAA, FPAA and furfurylamine according to one embodiment of the present invention. 1 This is the result of H NMR analysis.

[0038] Figure 6 is a diagram of an FPAA according to one embodiment of the present invention. 1 This is the result of H NMR analysis.

[0039] Figure 7 is a diagram of CMC, FCMC and furfurylamine according to one embodiment of the present invention. 1 This is the result of H NMR analysis.

[0040] FIGS. 8 and 9 are the results of elemental analysis performed to determine how much of the carboxymethyl group was substituted with a furan group during the synthesis of FCMC according to one embodiment of the present invention.

[0041] Figure 10 shows the XPS analysis results of GO and AHNS-rGO according to one embodiment of the present invention.

[0042] Figure 11 shows the XPS analysis results of AHNSrGO, FPAA, FPAA / AHNSrGO (before heating) and FPAA / AHNSrGO (after heating) according to one embodiment of the present invention.

[0043] Figure 12 shows the Raman analysis results of GO, AHNSrGO, and FPAA-AHNSrGO according to one embodiment of the present invention.

[0044] Figure 13 shows the results of Raman analysis of FCMC-SWCNTs according to one embodiment of the present invention.

[0045] FIG. 14 shows SEM images of PAA, PAA-rGO, and FPAA-rGO binders to determine the degree of dispersion of rGO due to a crosslinking reaction with a binder according to one embodiment of the present invention.

[0046] FIG. 15 is an image of the electrode surface taken using SEM and EDS after manufacturing the electrode using PAA, PAA-rGO, and FPAA-rGO binders according to one embodiment of the present invention.

[0047] Figure 16 is a graph comparing the specific capacity according to the current rate of an electrode using a PAA or FPAA-rGO binder according to one embodiment of the present invention.

[0048] Figures 17 and 18 are graphs comparing the specific capacity according to the content of the conductive material in an electrode using a PAA or FPAA-rGO binder according to one embodiment of the present invention.

[0049] FIG. 19 is a graph comparing the specific capacities of electrodes in a full cell including a negative electrode using a PAA or FPAA-rGO binder and a positive electrode including NCM811 according to one embodiment of the present invention when the binder and conductive material are different.

[0050] FIG. 20 shows the volume change in a full cell including a negative electrode using a PAA or FPAA-rGO binder and a positive electrode including NCM811 according to one embodiment of the present invention.

[0051] Figure 21 compares the specific capacities of electrodes when using a CMC-SWCNT or FCMC-SWCNT (DS=0.82) binder according to one embodiment of the present invention.

[0052] Fig. 22 is a graph comparing the specific capacity of an FCMC-SWCNT electrode according to the degree of substitution of FCMC in an electrode using an FCMC-SWCNT composite binder according to one embodiment of the present invention.

[0053] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, the technical concept of the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosure is thorough and complete and to sufficiently convey the spirit of the present invention to those skilled in the art.

[0054] In this specification, when a component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component may be interposed between them. In addition, in the drawings, the thicknesses of films and regions are exaggerated for the purpose of effectively explaining the technical contents.

[0055] Also, although terms such as first, second, and third have been used to describe various components in various embodiments of this specification, these components should not be limited by these terms. These terms are only used to distinguish one component from another. Thus, what is referred to as a first component in one embodiment may be referred to as a second component in another embodiment. Each embodiment described and illustrated herein also includes its complementary embodiments. Also, the term "and / or" has been used herein to mean including at least one of the components listed before and after.

[0056] In the specification, singular expressions include plural expressions unless the context clearly dictates otherwise. Furthermore, terms such as "comprises" or "has" are intended to specify the presence of a feature, number, step, component, or combination thereof described in the specification, but should not be construed as excluding the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0057] In addition, when describing the present invention below, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

[0058] The present invention discloses a technology relating to a composite binder for a silicon electrode of a lithium secondary battery. According to one embodiment of the present invention, the composite binder may be in the form of a polymer composite in which a furan group is bonded to a water-soluble polymer, and a carbon material is bonded to it. The furan group may bond to the carbon material through a Diels-Alder reaction to form a composite binder. The composite binder has both hydrophilic and hydrophobic portions, and thus, as a binder, it may stabilize the volume expansion of an anode active material and uniformly disperse a conductive material. In addition, the composite binder may disperse the conductive material through pi-pi interactions with the conductive material due to the pi bonds of the carbon material. In addition, since the composite binder includes a carbon material, the carbon material may function as a conductive material even in the absence of the conductive material.

[0059] The present invention provides a composite binder for a silicon electrode of a lithium secondary battery, a method for manufacturing the same, and a silicon electrode of a lithium secondary battery including the same. Fig. 1 schematically shows the effect of an FPAA-AHNSrGo composite binder, which is an example of the present invention, in an electrode in comparison with a PAA binder. In addition, Fig. 2 schematically shows the effect of an FCMC-SWCNT composite binder, which is another example of the present invention, in an electrode in comparison with a general binder. It can be confirmed from Figs. 1 and 2 that the composite binder according to an example of the present invention acts as a binder for a silicon active material and uniformly disperses a conductive material by including a carbon material. In Figs. 1 and 2, the carbon material (AHNSrGO or SWCNT) included in the composite binder can disperse the conductive material through a π-π interaction with the conductive material.

[0060] In one embodiment of the present invention, the present invention may include a composite binder for a silicon electrode of a lithium secondary battery, which comprises a polymer composite including a polymer and a furan group bonded to the polymer; and a carbon material including a carbon-carbon pi (Π) bond; and wherein the polymer composite and the carbon material are formed by combining through a chemical reaction caused by heat.

[0061] The chemical reaction induced by heat may include a Diels-Alder reaction performed at a temperature range of 70°C to 90°C. The furan group included in the polymer complex may bond with the carbon material through the Diels-Alder reaction. The Diels-Alder reaction refers to a heat-induced cycloaddition reaction between the HOMO (Highest Occupied Molecular Orbital) of a diene and the LUMO (Lowest Unoccupied Molecular Orbital) of a dienophile. Therefore, by applying heat, the composite binder may be formed due to a chemical reaction between the polymer complex and the carbon material.

[0062] The polymer may be a water-soluble polymer having a number average molecular weight of 30,000 to 500,000. Or preferably, the polymer may be a water-soluble polymer having a number average molecular weight of 30,000 to 50,000. Or preferably, the polymer may be a water-soluble polymer having a number average molecular weight of 400,000 to 500,000. The polymer may be a polymer containing at least one of a carboxyl group (COOH) or a hydroxyl group (OH), and may include, but is not limited to, at least one of poly(acrylic acid) (PAA), sodium carboxymethyl cellulose (CMC), chitosan, poly(vinyl alcohol), and guar gum. The water-soluble property of the polymer may function as a binder that suppresses expansion of the silicon anode. The polymer may preferably be one capable of binding the furan group as a functional group.

[0063] The furan group may be formed by reacting a compound having a functional group capable of bonding to the polymer with the polymer. For example, the furan group may be formed by bonding at least one of furfurylamine, 1-(Furan-2-yl)ethanamine, 3-(Furan-2-yl)propan-1-amine, and furan-2-amine to the polymer, but is not limited thereto. In this case, the compound having a functional group capable of bonding to the polymer has an amino group, and the amino group can react with the polymer.

[0064] Therefore, the polymer complex may be formed, for example, by a chemical reaction between furfurylamine and PAA, and the polymer complex may be represented by chemical formula 1.

[0065] [Chemical Formula 1]

[0066]

[0067] Here, n is between 5000 and 6300, and m is between 500 and 700.

[0068] The above chemical formula 1 may be formed by a chemical reaction of chemical formulas 2 and 3.

[0069] [Chemical Formula 2]

[0070]

[0071] Here, x is between 5500 and 7000.

[0072] [Chemical Formula 3]

[0073]

[0074] The chemical reaction in which chemical formula 3 is formed by the above chemical formulas 1 and 2 can be expressed as chemical formula 4.

[0075] [Chemical Formula 4]

[0076] (C3H4O2) x + C5H7NO → (C3H4O2) n -ran-(C7H7NO2) m

[0077] Here, x is between 5500 and 7000, n is between 5000 and 6300, and m is between 500 and 700.

[0078] In chemical formula 4 (C3H4O2) n -ran-(C7H7NO2) m is the chemical formula 1, (C3H4O2) x is chemical formula 2, and C5H7NO may be chemical formula 3.

[0079] The polymer composite may have furan groups bonded to 30% to 85% of the polymer repeating units. The ratio of the furan groups bonded may affect the ratio of the carbon material bonded to the furan groups, and the ratio of the carbon material bonded may affect the effectiveness of the polymer composite. If the furan groups bond less than 30%, the effect of dispersing the conductive material in the electrode may be reduced, and electrical conductivity may be reduced. In addition, if the furan groups bond more than 80%, the performance as a binder may be reduced.

[0080] The carbon material may include at least one of graphene, reduced graphene, carbon nanotubes, and derivatives thereof. The carbon material may include a carbon-carbon pi (Π) bond so as to be capable of undergoing a Diels-Alder reaction with a furan group of the polymer composite. The carbon material may be dispersed and bonded to the polymer composite through the Diels-Alder reaction. The carbon material may be a hydrophobic portion of the composite binder and may disperse a conductive material having hydrophobic properties without agglomeration. The weight ratio (wt%) of the polymer composite and the carbon material in the composite binder may be 9:1 to 7:3. When the carbon material is combined in an amount of less than 1 wt%, the effect of dispersing the conductive material in the electrode may be reduced, and electrical conductivity may be reduced. In addition, when the carbon material is combined in an amount exceeding 3 wt%, the performance as a binder may be reduced.

[0081] The more uniformly the conductive material is dispersed in the electrode of a lithium secondary battery, the higher the electrical conductivity can be. However, since the binder or negative electrode active material has water-soluble characteristics, the conductive material may aggregate or exist only in a portion. Therefore, in order to improve the performance of the battery, it is important for the conductive material to be uniformly dispersed, and the carbon material, which has hydrophobic properties like the conductive material, can uniformly disperse the conductive material. In addition, since the carbon material has a pi (Π) bond, the conductive material can be dispersed through the pi (Π) bond and pi-pi interaction of the conductive material. Through such interactions, an efficient conductive network can be formed within the electrode even with a small amount of the conductive material.

[0082] In addition, the carbon material itself has conductivity and can function as a conductive material. The composite binder can perform the functions of a binder and a conductive material even in the absence of a conductive material in a silicon electrode.

[0083] The composite binder can control the volume expansion of the negative electrode active material. The negative electrode active material may be, for example, silicon, and a silicon negative electrode has a disadvantage in that its volume expands / shrinks during charge / discharge, thereby reducing the performance and lifespan of the battery. The composite binder can compensate for this disadvantage by controlling the expansion of the negative electrode active material. For example, the composite binder can suppress the volume expansion of the negative electrode active material, and the volume of an electrode including the negative electrode active material can increase by 40% to 56% after 300 cycles compared to the initial volume.

[0084] In addition, the above polymer complex is formed by bonding of furan groups. 1 The polymer complex may have a specific peak value during H NMR analysis. 1When H NMR analysis is performed, it may have peak values ​​at 7.3 ppm to 7.5 ppm, 6.35 ppm to 6.45 ppm, and 6.28 ppm to 6.35 ppm. In addition, when the polymer in the polymer complex is PAA, the polymer complex 1 In H NMR analysis, the peak at 7.3 ppm to 7.5 ppm and the integral ratio at 2.10 ppm to 2.22 ppm may be 10:1 to 11:1.

[0085] In addition, the above composite binder can have a specific ratio in the Raman spectrum result due to the bonding of the polymer composite and the carbon material. Raman spectrum result 1300cm -1 1700 cm inland -1 In the Raman shift I before and after the polymer composite and carbon material are chemically bonded by heat D / I G The values ​​may be 0.017:0.04 to 1.08:1.16 before chemical bonding:after chemical bonding.

[0086] In addition, in one embodiment of the present invention, the composite binder can be manufactured by a method for manufacturing a composite binder for a silicon electrode of a lithium secondary battery, including the steps of: dissolving a polymer in ultrapure water to prepare a polymer aqueous solution; adding a solution containing furan to the polymer aqueous solution, stirring the solution, and drying the solution to obtain a polymer composite; and heating the dried polymer composite and carbon material in ultrapure water while stirring to prepare a composite binder.

[0087] Before adding the furan-containing solution to the polymer aqueous solution, the polymer aqueous solution may be set to a state suitable for the furan group to react with the polymer. The furan-containing solution may refer to a solution containing the furan group. The polymer aqueous solution may have an appropriate pH and reagent. This may be a state in which the carboxyl group of the polymer and the amino group of the furan group can bond. For example, in the step of preparing the polymer aqueous solution, the pH may be adjusted to 5.0 to 6.0. In addition, in the step of adding the furan-containing solution to the polymer aqueous solution, EDC ((1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride)) and NHS (N-hydroxysuccinimide) may be added.

[0088] In the step of manufacturing the above composite binder, the heating temperature may be 70°C to 90°C. This may be a temperature at which the polymer and the furan group can undergo a Diels-Alder reaction.

[0089] The polymer contained in the polymer aqueous solution is a water-soluble polymer and may include at least one of PAA (Poly(acrylic acid)) and CMC (Sodium Carboxymethyl Cellulose). The water-soluble property of the polymer may function as a binder that alleviates expansion and contraction of a silicon negative electrode. The polymer may preferably be one capable of binding the furan group as a functional group. For example, the polymer may include a carboxyl group. The furan group may have a functional group capable of binding to the polymer. For example, the furan group may be formed by binding furfurylamine to the polymer. In this case, the amino group of furfurylamine may react with the polymer.

[0090] The carbon material may include at least one of graphene, reduced graphene, carbon nanotubes, and derivatives thereof. The carbon material may include a carbon-carbon pi (Π) bond so as to be capable of undergoing a Diels-Alder reaction with a furan group of the polymer composite. The carbon material may be uniformly bonded to the polymer composite through the Diels-Alder reaction. The carbon material may be a hydrophobic portion of the composite binder and may uniformly disperse a conductive material having hydrophobic properties.

[0091] In addition, in one embodiment of the present invention, the present invention may include a silicon electrode for a lithium secondary battery, including a composite binder for a silicon electrode of a lithium secondary battery having at least one of the above-described characteristics; a negative electrode active material including silicon; and a conductive material.

[0092] The above negative electrode active material, composite binder, and conductive agent may be included in a weight ratio of 70:15:15 to 95:5:0. Here, when the conductive agent is 0, it may mean that no conductive agent is added, and it may mean that the composite binder also performs the function of a conductive agent.

[0093] The above-mentioned challenge material may include at least one of super P, carbon nanotubes, carbon black, graphene, and graphite.

[0094] Therefore, the composite binder according to one embodiment of the present invention can suppress aggregation between conductive materials and improve dispersibility by inducing non-covalent bonds between the carbon material and the conductive material. In addition, the carbon material included in the composite binder has conductivity in itself, so it can function as a conductive material even in the absence or near absence of the conductive material. This method disperses the conductive material within the electrode through the highly conductive carbon material without modifying the conductive material, thereby enabling even electrical connection between active materials using a small amount of conductive material without reducing conductivity. In addition, this method can produce a high-energy density silicon-based electrode with a high active material content without the problem of deterioration of electrical conductivity.

[0095]

[0096] Hereinafter, examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the scope of the present invention is not limited by the following examples.

[0097]

[0098] In the examples, comparative examples and drawings related thereto, AHNSrGO or AHNS-rGO represents the same as rGO.

[0099]

[0100] [Example]

[0101]

[0102] 1. Example 1

[0103] (1) Preparation of FPAA-AHNS-rGO composite binder

[0104] Figure 3 schematically illustrates the process of synthesizing FPAA-AHNSrGO.

[0105] 1) FPAA manufacturing

[0106] 1 g of poly(acrylic acid) (PAA) was dissolved in DI water (100 mL) and the pH was adjusted to 5.5–5.7 with 1 M NaOH. After adjusting the pH, organic catalysts EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide) and NHS (N-hydroxysuccinimide) were added and stirred for 30 minutes. 266 mg (1.38 mmol) of EDC and 159.8 mg (1.38 mmol) of NHS were added. Furfurylamine (0.24 mL, 0.1 equiv.) was added to the stirred solution and stirred at room temperature for 24 hours to react. The reacted solution was dialyzed against DI water and dried to obtain a white crystalline solid.

[0107] 2) AHNS-rGO synthesis

[0108] A 5 mg / ml aqueous dispersion of GO (Angstron Materials) was diluted with deionized water to prepare a 2 mg / ml GO dispersion. 6-amino-4-hydroxy-2-naphthalenesulfonic acid (AHNS, TCI) was dissolved in deionized water to prepare a 20 wt% AHNS aqueous solution. 6 mg of ammonia solution (Sigma Aldrich) was added to 5 ml of the AHNS aqueous solution. 100 ml of the prepared GO aqueous dispersion (2 mg / ml) was slowly added to the alkaline AHNS solution. The mixed solution was stirred and heated at 70°C for 24 h to functionalize the surface of GO with AHNS. After functionalization, 2 ml of hydrazine monohydrate (Sigma Aldrich) was added. The mixture was heated at 100°C for 20 h to reduce the AHNS-functionalized GO. Afterwards, the mixture was washed with deionized water, filtered, and the residue was dried in a vacuum oven at 25°C. The dried AHNS-rGO was redispersed in anhydrous ethanol to prepare AHNS-functionalized reduced graphene oxide (AHNS-rGO) dispersed in ethanol. Although the carboxyl and hydroxyl groups on the GO surface were removed during the reduction process, AHNS-rGO was well dispersed in water and ethanol due to the hydrophilic group (-SO3H) of AHNS.

[0109] 3) Manufacturing of FPAA-AHNSrGO

[0110] FPAA and AHNS-rGO were stirred in DI water at a weight ratio of 8:2 at 80°C for 24 h.

[0111]

[0112] 2. Examples 2-1, 2-2

[0113] Half cells were manufactured using the composite binder manufactured in Example 1. Two types of half cells were manufactured by varying the weight ratio of SiO:FPAA-AHNSrGO:carbon black. The electrolyte was 1M LiPF6 (EC:DEC:FEC:VC=44.5:44.5:10:1 v / v), and the cut-off voltage of the cell was 0.01 V / 1 V vs. Li / Li. + It was.

[0114] Classification drawing SiO:FPAA-AHNSrGO:Carbon black (wt%) Example 2-15wt%80:15:5 Example 2-215wt%70:15:15

[0115]

[0116] 3. Example 3: A full cell was manufactured using the half-cell manufactured in Example 2-1 as the negative electrode. In the full cell, the positive electrode was manufactured using NCM811:PVDF:SuperP in a weight ratio of 8:1:1, and an NP ratio of 1.2.

[0117]

[0118] 4. Examples 4-1 and 4-2

[0119] (1) Preparation of FCMC-SWCNT composite binder

[0120] Figure 4 schematically illustrates the process for synthesizing a FCMC-SWCNT composite binder. To pendant a furfurylamine group to CMC, the pH was adjusted with HCl, and then amide bonding was performed using an organic catalyst (EDC / NHS, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide / N-hydroxysuccinimide).

[0121] 1) FCMC manufacturing

[0122] FCMC (Furfurylamine-functionalized CMC) was prepared by varying the degree of substitution (DS) of furfurylamine in CMC, as in Example 4-1 (DS=0.82) and Example 4-2 (DS=0.32).

[0123] First, Example 4-1 (DS=0.82) was prepared as follows. 1 g of carboxymethyl cellulose (Carboxymethyl cellulose) was dissolved in DI water (100 mL), and the pH was adjusted to 5.5–5.7 using 0.5 M HCl. EDC (195 mg, 1.19 mmol) and NHS (137.8 mg, 1.19 mmol) were added to the pH-adjusted solution, and the mixture was stirred for 30 minutes. Furfurylamine (0.207 mL, 1 equiv.) was added, and the mixture was stirred at room temperature for 24 hours to obtain a polymer solution. This polymer solution was dialyzed against DI water, and then dried to obtain a white crystalline solid.

[0124] Example 4-2 (DS=0.32) was prepared as follows. 1 g of carboxymethyl cellulose (Carboxymethyl cellulose) was dissolved in DI water (100 mL), and the pH was adjusted to 5.5–5.7 using 0.5 M HCl. EDC (62.1 mg, 0.379 mmol) and NHS (43.9 mg, 0.379 mmol) were added to the pH-adjusted solution, and the mixture was stirred for 30 minutes. Furfurylamine (0.066 mL, 0.32 equiv.) was added, and the mixture was stirred at room temperature for 24 hours to obtain a polymer solution. This polymer solution was dialyzed against DI water, and then dried to obtain a white crystalline solid.

[0125] 2) Manufacturing of FCMC-SWCNTs

[0126] FCMC and SWCNT were dispersed in DI water at a weight ratio of 20:1 using tip sonication at 80°C for 40 minutes, while simultaneously binding SWCNT to FCMC.

[0127] Example of displaying the substitution diagram for the division 4-10.82DS=0.82 Example of displaying the substitution diagram for the division 4-20.32DS=0.32

[0128]

[0129] 5. Examples 5-1, 5-2

[0130] Half cells were manufactured using the composite binders prepared in Examples 4-1 and 4-2. The half cells were manufactured with a weight ratio of Si / C:FCMC:SBR:SWCNTs of 94.75:2.5:2.5:0.25. The electrolyte used was 1 M LiPF6 (EC:DEC:FEC:VC=44.5:44.5:10:1 v / v), and the cut-off voltage was 0.005 V / 1.5 V vs. Li / Li. + And, Crate was 1C.

[0131] Composite binder Example 5-1 Example 4-1 Example 5-2 Example 4-2

[0132]

[0133] 6. Example 6

[0134] A full cell was manufactured using the half-cell manufactured in Example 5-1 as the negative electrode. In the full cell, the positive electrode was manufactured with NCM811:PVDF:Super P in a weight ratio of 80:10:10.

[0135]

[0136] [Comparative example]

[0137] A comparative example was prepared for comparison with the composite binder and electrode according to the above example.

[0138] 1. Comparative Example 1

[0139] As comparative examples, PAA binder (Comparative Example 1-1) and PAA-rGO binder (Comparative Example 1-2) were manufactured.

[0140]

[0141] 2. Comparative Example 2

[0142] As a comparative example, in Example 2, the binder was changed to PAA binder, and an electrode with 5 wt% carbon black added (Comparative Example 2-1) and an electrode with 15 wt% carbon black added (Comparative Example 2-2) were manufactured.

[0143]

[0144] [Experimental Example]

[0145]

[0146] 1. 1 H NMR and elemental analysis results

[0147] PAA, FPAA and furfurylamine respectively 1 The results of H NMR analysis are shown in Figures 5 and 6. In Figure 5, 1 Through H NMR analysis, it can be confirmed that the peaks at 7.17 ppm, 6.13 ppm, 5.95 ppm, and 3.62 ppm in furfurylamine shift to peaks at 7.42 ppm, 6.4 ppm, 6.33 ppm, and 4.02 ppm in FPAA. This confirms that FPAA is synthesized through an amide bond between the NH2 group of furfurylamine and the COOH group of PAA. In addition, the peaks of FPAA 1 In the H NMR analysis results (Fig. 6), it can be confirmed that some of the COOH groups of PAA were substituted with furfurylamine through the integral ratio of the hydrogen peak of methylidene at 2.16 ppm (right side of Fig. 6) and the hydrogen peak of furan at 7.42 ppm (left side of Fig. 6).

[0148] Figure 7 shows the chemical compositions of CMC, FCMC and furfurylamine. 1This is the result of H NMR analysis. In Fig. 7, it can be confirmed that the peaks at 7.17 ppm, 6.13 ppm, 5.95 ppm, and 3.62 ppm of furfurylamine shift to peaks at 7.42 ppm, 6.4 ppm, 6.33 ppm, and 4.02 ppm in FCMC. This confirms that FCMC is synthesized through an amide bond between the NH2 group of furfurylamine and the COOH group of CMC.

[0149] Figures 8 and 9 show the results of elemental analysis performed to determine the extent to which carboxymethyl groups were substituted with furan groups during the synthesis of FCMC. Figure 8 shows the result of elemental analysis when the degree of substitution (DS) is 0.82, and Figure 9 shows the result of elemental analysis when the degree of substitution is 0.32. The mass of the furan group and the carboxymethyl group were calculated based on (a) the furan group and (b) the carboxymethyl group on the right side of Figure 8. In Figures 8 and 9, the mass percentages of nitrogen in the elemental analysis results of FCMC were approximately 4.03% and 1.82%, respectively. Using this, the mass percentages of the furan group were 86.07% and 38.87%, respectively. Since the mass percentage of the carboxymethyl group is 100 minus the mass percentage of the furan group, when the mass percentage of the carboxymethyl group is obtained using this method, it was calculated as 13.93% for Fig. 8 and 61.13% for Fig. 9. The molecular weights of the furan group and the carboxymethyl group are 299 and 220, respectively, and when the mass percentages thereof are divided by their respective molecular weights, the ratio of (a) the furan group and (b) the carboxymethyl group can be determined. In Fig. 8, (a) furan group: (b) carboxymethyl group = 4.55:1, and in Fig. 9, (a) furan group: (b) carboxymethyl group = 1:2.14. Therefore, it was found that Fig. 8 had a degree of substitution of FCMC of 0.82, and Fig. 9 had a degree of substitution of FCMC of 0.32.

[0150]

[0151] 2. XPS (X-ray photoelectron spectroscopy) and Raman analysis results

[0152] XPS analysis was performed on the FPAA-AHNSrGO composite binder and is shown in Figs. 10 and 11. In Fig. 10, it can be confirmed that the peaks of OC=O, C=O, and C-O of GO (Graphene Oxide) (left side of Fig. 10) decreased in AHSNrGO (right side of Fig. 10), indicating that GO was successfully reduced. In addition, the CN peak increased in AHNSrGO in the right graph of Fig. 10, confirming that AHNS groups were successfully bound to the surface of GO. Fig. 11 shows the XPS analysis results for AHNSrGO, FPAA, FPAA / AHNSrGO (before heating), and FPAA / AHNSrGO (after heating). FPAA / AHNSrGO (before heating) is a simple blend of FPAA and AHNSrGO, and FPAA / AHNSrGO (after heating) is the result of analyzing the sediment harvested by centrifugation after heating FPAA and AHNSrGO to induce the Diels-Alder reaction. As shown in Fig. 11, unlike FPAA / AHNSrGO (before heating), the result of FPAA / AHNSrGO (after heating) confirms the presence of an oxygen functional group in the C1s peak, confirming that FPAA and AHNSrGO are covalently bonded.

[0153] Figure 12 shows the Raman analysis results of GO, AHNSrGO, and FPAA-AHNSrGO. In Figure 12, it can be seen that the D peak increased as the Diels-Alder reaction changed the sp2 bond to the sp3 bond. This allows I D / I G It can be confirmed that the ratio increases from 1.08 to 1.16 and that a cyclization reaction occurs due to the Diels-Alder reaction.

[0154] Figure 13 shows the Raman analysis results of SWCNTs and FCMC-SWCNTs. In Figure 13, the D peak increases in FCMC-SWCNTs compared to SWCNTs due to the Diels-Alder reaction, and I D / I G We can see that the rain increased from 0.017 to 0.04.

[0155]

[0156] 3. SEM (scanning electron microscope) and EDS (energy dispersive spectrometer) analysis results

[0157] Figure 14 shows SEM images of PAA, PAA-rGO, and FPAA-rGO binders to determine the degree of dispersion of rGO due to crosslinking with a binder. FPAA with a furan group crosslinks the furan group to a water-soluble binder (PAA) through a Diels-Alder reaction, thereby suppressing aggregation of rGO and ensuring uniform dispersion.

[0158] Figure 15 is an image of the electrode surface taken using SEM and EDS after manufacturing the electrode using the binder of Figure 14. Unlike other electrodes, the surface of the FPAA-rGO electrode shows a form in which carbon black (conductive material) is evenly dispersed through highly dispersed rGO, thereby suppressing aggregation. This is the result of rGO uniformly bonded to the FPAA-rGO composite binder inducing pi-pi interaction with carbon black, thereby inducing dispersion of the carbon black.

[0159] In addition, as a result of observing the morphology of carbon and silicon through EDS in Fig. 15, it can be confirmed that FPAA-rGO has suppressed aggregation of carbon and silicon, and the carbon conductive material is evenly dispersed within the electrode.

[0160]

[0161] 4. Observation results of specific capacity of electrodes

[0162] Figure 16 compares the specific capacity according to the current rate of electrodes using PAA binder and FPAA-rGO binder. Figure 16 is a rate performance graph according to the type of binder, and it can be confirmed that the FPAA-rGO composite binder has a superior lifespan at high charge / discharge rates. This is a result of the improved electrical conductivity due to the uniform dispersion of the conductive agent (carbon black).

[0163] Figure 17 compares the specific capacities of electrodes using PAA and FPAA-rGO as binders. Figure 17 is a graph comparing the specific capacities when the carbon black content in the electrode is 15 wt%, and it can be confirmed that the FPAA-rGO composite binder has a superior capacity. This is because the FPAA-rGO composite binder provides a continuously uniform conductive path, thereby alleviating the problem of accelerated loss of electrical contact between the active material and the conductive material due to volume changes in the silicon-based electrode during charge and discharge. In this case, it can be confirmed that the performance and lifespan of the electrode are improved.

[0164] Figure 18 shows the results of comparing the specific capacities of electrodes under the conditions of Figure 17 by reducing the content of the conductive agent (carbon black 5 wt%). Figure 18 confirms that the FPAA-rGO composite binder has superior cycle life. This confirms that even when using a small amount of the conductive agent, FPAA-rGO can efficiently secure the conductivity of the active material because it uniformly disperses the conductive agent.

[0165] Figure 19 is a graph comparing the specific capacities of full-cell electrodes manufactured using positive electrodes including NCM811 and with different binders and conductive agents. In Figure 19, PAA or FPAA-rGO was used as the binder, and 5 wt% or 15 wt% of carbon black was added as the conductive agent. In the case of the FPAA-rGO composite binder, when the conductive agent was reduced from 15 wt% to 5 wt%, the specific capacity decreased by 7.5% after 300 cycles, and in the case of the PAA binder, when the conductive agent was reduced from 15 wt% to 5 wt%, the specific capacity decreased by 12.7% after 300 cycles. This confirms that the capacity loss rate due to the decrease in conductive agent content is also smaller in the FPAA-rGO composite binder in the full cell.

[0166] Fig. 20 shows the volume expansion of the electrode after 300 cycles of the full-cell electrode of Fig. 19, to which 15 wt% of the conductive material was added. The upper photo of Fig. 20 shows the initial volume and the volume after 300 cycles when PAA binder was used, in order from the left, and the lower photo shows the initial volume and the volume after 300 cycles when FPAA-rGO binder was used. In Fig. 20, in the case of PAA binder, the volume of the electrode expanded (181%) from 11.4 μm to 32.0 μm, whereas in the case of FPAA-rGO binder, the volume of the electrode expanded (55.3%) from 11.4 μm to 17.7 μm, confirming that the volume expansion of the silicon electrode was alleviated.

[0167] Figure 21 compares the specific capacities of electrodes using CMC-SWCNT and FCMC-SWCNT (DS=0.82) as binders. SWCNTs were included at 0.25 wt% in each electrode. As shown in Figure 21, it can be confirmed that the FCMC-SWCNT composite binder has a superior capacity even as the number of cycles increases. This is because the FCMC-SWCNT composite binder provides a continuously uniform conductive path, thereby alleviating the problem of accelerated loss of electrical contact between the active material and the conductive material due to volume changes in the silicon-based electrode during charge and discharge. In this case, it can be confirmed that the performance and lifespan of the electrode are improved.

[0168] Figure 22 is a graph comparing the specific capacity of FCMC-SWCNT electrodes according to the degree of FCMC substitution in the FCMC-SWCNT composite binder. Figure 22 demonstrates that a higher degree of FCMC substitution in the FCMC binder results in better capacity. This is because the more furan groups present, the more cross-linking occurs with the SWCNTs within the composite binder, further enhancing the dispersion of the SWCNTs used as the conductive agent. This demonstrates that the composite binder ensures uniform dispersion of the conductive agent, thereby enhancing electrode performance.

[0169]

[0170] Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering its technical spirit or essential characteristics. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims

1. A polymer composite comprising a polymer and a furan group bonded to the polymer; and A carbon material comprising a carbon-carbon pi (Π) bond; The polymer composite and carbon material are formed by combining through a chemical reaction caused by heat. Composite binder for silicon electrodes of lithium secondary batteries.

2. In paragraph 1, The chemical reaction by the above heat is a Diels-Alder reaction that is performed in a temperature range of 70℃ to 90℃. Composite binder for silicon electrodes of lithium secondary batteries.

3. In paragraph 1, The above polymer is a water-soluble polymer having a number average molecular weight of 30,000 to 500,000, Containing at least one of PAA (Poly(acrylic acid)), CMC (Sodium Carboxymethyl Cellulose), Chitosan, Poly(vinyl alcohol) and Guar Gum. Composite binder for silicon electrodes of lithium secondary batteries.

4. In paragraph 1, The above polymer complex is represented by chemical formula 1. Composite binder for silicon electrode of lithium secondary battery: [Chemical Formula 1] Here, n is between 5000 and 6300, and m is between 500 and 700.

5. In paragraph 1, The above carbon material comprises at least one of graphene, reduced graphene, carbon nanotubes and derivatives thereof. Composite binder for silicon electrodes of lithium secondary batteries.

6. In paragraph 1, The polymer complex has the furan group bonded to 30% to 85% of the polymer repeating units. Composite binder for silicon electrodes of lithium secondary batteries.

7. In paragraph 1, The weight ratio (wt%) of the above polymer composite and carbon material is 9:1 to 7:

3. Composite binder for silicon electrodes of lithium secondary batteries.

8. In paragraph 1, The above composite binder controls the volume expansion of the negative electrode active material, After 300 cycles, the electrode volume expands by 40% to 56% compared to the initial volume. Composite binder for silicon electrodes of lithium secondary batteries.

9. In paragraph 1, The above polymer composite 1 In H NMR analysis, it has peak values ​​at 7.3 ppm to 7.5 ppm, 6.35 ppm to 6.45 ppm, and 6.28 ppm to 6.35 ppm. Composite binder for silicon electrodes of lithium secondary batteries.

10. In paragraph 1, In the above polymer complex, the polymer is PAA (Poly(acrylic acid)), Of the above polymer composites 1 In H NMR analysis, the peaks at 7.3 ppm to 7.5 ppm and the integral ratios at 2.10 ppm to 2.22 ppm are 10:1 to 11:

1. Composite binder for silicon electrodes of lithium secondary batteries.

11. In paragraph 1, Raman spectrum results 1300cm -1 Within 1700 cm -1 In the Raman shift I before and after the polymer composite and carbon material are chemically bonded by heat D / I G The ratio of values ​​before chemical bonding:after chemical bonding is 0.017:0.04 to 1.08:1.16, Composite binder for silicon electrodes of lithium secondary batteries.

12. A step of preparing a polymer aqueous solution by dissolving the polymer in ultrapure water; A step of adding a solution containing furan to the polymer aqueous solution, stirring, and drying to obtain a polymer complex; and A step of manufacturing a composite binder by heating the dried polymer composite and carbon material while stirring in ultrapure water; A method for manufacturing a composite binder for a silicon electrode of a lithium secondary battery.

13. In paragraph 12, The pH of the step of preparing the above polymer aqueous solution is 5 to 6. A method for manufacturing a composite binder for a silicon electrode of a lithium secondary battery.

14. In paragraph 12, In the step of manufacturing the above composite binder, the heating temperature is 70℃ to 90℃. A method for manufacturing a composite binder for a silicon electrode of a lithium secondary battery.

15. In paragraph 12, The polymer is a water-soluble polymer and comprises at least one of PAA (Poly(acrylic acid) and CMC (Sodium Carboxymethyl Cellulose), Chitosan, Poly(vinyl alcohol) and Guar Gum. A method for manufacturing a composite binder for a silicon electrode of a lithium secondary battery.

16. In paragraph 12, The above carbon material comprises at least one of graphene, reduced graphene, carbon nanotubes and derivatives thereof. A method for manufacturing a composite binder for a silicon electrode of a lithium secondary battery.

17. A composite binder for a silicon electrode of a lithium secondary battery according to any one of claims 1 and 11; A negative electrode active material comprising silicon; and Including a challenge, Silicon electrode for secondary batteries.

18. In paragraph 17, The above negative active material, composite binder and conductive material are included in a weight ratio of 70:15:15 to 95:5:

0. Silicon electrode for secondary batteries.

19. In Article 17, The above challenge material comprises at least one of super P, carbon nanotube, carbon black, graphene and graphite. Silicon electrode for secondary batteries.

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