Graphene hybrid polymer binder composite, method for manufacturing graphene hybrid polymer binder composite, and graphene network battery comprising graphene hybrid polymer binder composite

Abstract

The present invention relates to a graphene hybrid polymer binder composite comprising: functionalized graphene having a functional group; and a polymer binder bonded to the functionalized graphene by the functional group.

Description

Graphene hybrid polymer binder composite, method for producing graphene hybrid polymer binder composite, graphene network battery including graphene hybrid polymer binder composite

[0001] The present invention relates to a graphene hybrid polymer binder composite, a method for producing a graphene hybrid polymer binder composite, and a graphene network battery comprising the graphene hybrid polymer binder composite.

[0002] Efforts to achieve carbon neutrality are actively underway worldwide as a key strategy to combat global warming and climate change. Carbon neutrality aims to minimize greenhouse gas emissions and promote sustainable energy use.

[0003] Batteries play a crucial role in achieving carbon neutrality. The proliferation of electric vehicles, high-performance mobile devices, and the emergence of new technologies like drones are driving the demand for higher-performance batteries.

[0004] The most widely used battery today is the lithium secondary battery. Lithium secondary batteries are based on the principle that lithium ions move from the cathode to the anode during discharge, and then move back from the anode to the cathode during charging.

[0005] Lithium secondary batteries consist of a cathode, anode, electrolyte, and a separator. To increase the energy density of lithium secondary batteries, active research has been conducted on technologies such as increasing the capacity of cathode and anode active materials, increasing the density of electrode plates, thinning the separator, and increasing the charge / discharge voltage. However, recent progress in improving the energy density of lithium secondary batteries has reached its limits, prompting the development of new anode materials.

[0006] Graphite has been primarily used as an anode material in lithium secondary batteries. Graphite has a stable crystal structure and a theoretical capacity of 372 mAh / g. However, with the growing demand for high-capacity batteries, silicon is attracting attention as a new anode material to replace graphite.

[0007] Silicon's theoretical capacity is significantly higher than that of graphite, at 4,200 mAh / g. This high theoretical capacity is due to the fact that each silicon atom can contain up to 4.4 lithium atoms, forming an alloy. However, silicon experiences a volume expansion of approximately 300 to 400% when absorbing lithium, resulting in pulverization of the negative active material. Furthermore, silicon suffers from capacity loss due to the formation of an excessive solid electrolyte interphase (SEI) layer during charge and discharge.

[0008] Attempts have been made to utilize graphene to address these issues. However, its self-cohesion, low dispersibility, and poor silicon adsorption have hindered commercialization.

[0009] Previously, a method for coating non-bonding graphene on the surface of silicon or silicon compounds using spray drying has been proposed. Coating graphene on the surface of silicon or silicon compounds using spray drying relies on van der Waals bonding, and while the formation of a graphene coating layer is favorable, the bonding strength is insufficient, resulting in a significantly poor control of the formation of a reaction layer during secondary battery charge and discharge or the shrinkage-expansion behavior of silicon.

[0010] Accordingly, the inventor of the present invention has solved this problem through functionalized graphene that self-adsorbs to silicon or silicon compounds in Republic of Korea Publication No. 10-2023-0099837 (prior patent).

[0011] However, the problem of expansion and contraction of silicon during charge and discharge is not limited to the micronization of the negative electrode active material itself. In other words, even if the micronization problem is solved by forming a graphene coating layer on silicon or a silicon compound as in the prior patent, there is still the problem of the negative electrode active material being detached from the current collector due to the expansion and contraction of the negative electrode active material containing silicon during charge and discharge. If the negative electrode active material is detached from the current collector, the capacity retention rate of the battery is bound to decrease significantly. For the commercialization of lithium secondary batteries, the capacity retention should be at least 80% even after 500 or more charge and discharge cycles, but this is not the case.

[0012] To solve the problem of the negative electrode active material, including silicon, being detached from the current collector due to expansion and contraction during charge and discharge, the binder must be improved.

[0013] Above all, in order to increase the theoretical capacity, a new polymer binder is needed that maintains the capacity by 80% or more, preferably 90% or more, even after 500 charge / discharge cycles with a small amount of binder.

[0014] One object of the present invention is to propose a novel binder having both excellent adhesiveness and high elasticity so as to prevent detachment of a negative electrode active material from a current collector in response to volume expansion of a negative electrode active material including silicon during charging and discharging.

[0015] In addition, another object of the present invention is to propose a lithium secondary battery having excellent initial discharge capacity and high capacity retention rate even after 500 charge / discharge cycles.

[0016] Meanwhile, other unspecified purposes of the present invention will be additionally considered within the scope that can be easily inferred from the detailed description and effects thereof below.

[0017]

[0018] To achieve the purpose proposed above, the following solutions are proposed.

[0019] A graphene hybrid polymer binder composite according to one embodiment of the present invention comprises: functionalized graphene having a functional group formed thereon; and a polymer binder bonded to the functionalized graphene by the functional group.

[0020] In one embodiment, the functional group may be characterized by at least one selected from the group consisting of a silane group, an amide group, an azide group, an anhydride, a urea group, a urethane group, an amine group, an alkylene group, an epoxide group, and a mercapto group.

[0021] In one embodiment, the polymer binder may be characterized by being at least one selected from the group consisting of polyacrylic acid (PAA), polyimide (PI), polyetherimide (PEI), polyurethane / polyurea (PU), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC).

[0022] In one embodiment, the polymer binder may be characterized by including a first polymer binder for improving adhesion to a negative electrode active material including silicon and a current collector, and a second polymer binder for improving elasticity.

[0023] In one embodiment, the content of the functionalized graphene may be characterized as being 0.01 to 0.5 wt%.

[0024] In one embodiment, the content of the functionalized graphene may be characterized as being 0.01 to 0.3 wt%.

[0025] A method for manufacturing a graphene hybrid polymer binder composite according to another embodiment of the present invention comprises the steps of: (a) preparing a functionalized graphene colloid having a functional group formed thereon; (b) adding a polymer binder or a polymer binder monomer to the colloid; (c) forming a polymer binder bonded to a functional group of the functionalized graphene by combining the polymer binder with a functional group of the functionalized graphene or polymerizing the polymer binder monomer; and (d) removing unreacted substances.

[0026] In another embodiment, in the step (b), in the case of the polymer binder, a part of the total mass of the polymer binder to be added is added to the colloid, stirred and homogenized, and then the remainder is added to the colloid; in the case of the polymer binder monomer, a part of the total mass of the polymer binder monomer to be added is added to the colloid, reacted, and then the remainder is added to the colloid.

[0027] In another embodiment, the functionalized graphene may be characterized by an absolute value of zeta potential of 40 mV or more.

[0028] According to another embodiment of the present invention, a graphene network battery includes a positive electrode, a negative electrode, and a binder interposed between the positive electrode and the negative electrode, wherein the negative electrode includes a current collector; and an negative electrode material formed on the current collector and including a negative electrode active material conductive material including silicon and a binder; wherein the binder may include functionalized graphene having a functional group formed thereon; and a polymer binder bonded to the functionalized graphene by the functional group.

[0029] In another embodiment, the content of the graphene hybrid polymer binder composite may be characterized as being 6 to 10 wt% with respect to the total weight of the negative electrode material.

[0030] In another embodiment, the negative active material may be characterized by including silicon metal particles having a functionalized graphene coating layer on the surface.

[0031] In one embodiment of the present invention, a graphene hybrid polymer binder composite is formed by bonding functionalized graphene and a polymer binder through functional groups formed on the functionalized graphene, thereby improving the adhesive strength and physical performance of the polymer binder.

[0032] Therefore, when a graphene hybrid polymer binder composite according to one embodiment of the present invention is applied to a negative electrode material of a lithium secondary battery, the phenomenon of the negative electrode active material including silicon being detached from the current collector due to expansion and contraction behavior during charge and discharge can be prevented, and the capacity retention rate is maintained at 80% or more, and preferably 90% or more, even after 500 charge and discharge cycles.

[0033] Meanwhile, even if the effect is not explicitly mentioned herein, it is added that the effect and its provisional effect described in the following specification expected by the technical features of the present invention are treated as described in the specification of the present invention.

[0034] Figure 1 is a schematic diagram of a cathode structure to which a graphene hybrid polymer binder composite according to one embodiment of the present invention is applied.

[0035] FIG. 2 is a schematic flow chart of a first method for manufacturing a graphene hybrid polymer binder composite according to one embodiment of the present invention.

[0036] Figure 3 shows the results of zeta potential measurements of functionalized graphene, oxidized graphene, and non-oxidized graphene used in the present invention.

[0037] Figure 4 is a schematic flow chart of a second manufacturing method of a graphene hybrid polymer binder composite according to one embodiment of the present invention.

[0038] FIG. 5 is a photograph showing each process of a second manufacturing method of a graphene hybrid polymer binder composite according to one embodiment of the present invention.

[0039] Figure 6 is a result of FT-IR spectrum analysis of a graphene hybrid polymer binder composite according to one embodiment of the present invention.

[0040] Figure 7 is a Raman spectrum analysis result of a graphene hybrid polymer binder composite according to one embodiment of the present invention.

[0041] Figure 8 shows the results of a cross-cut test to confirm the adhesive performance of a graphene hybrid polymer binder composite according to one embodiment of the present invention.

[0042] It is to be understood that the attached drawings are provided for reference only to help understand the technical concept of the present invention, and the scope of the present invention is not limited thereby.

[0043] Hereinafter, with reference to the drawings, the configuration of the present invention, guided by various embodiments thereof, and the effects resulting from such configurations will be examined. In describing the present invention, detailed descriptions of related, well-known functions that are obvious to those skilled in the art and that may unnecessarily obscure the gist of the present invention will be omitted.

[0044] Figure 1 is a schematic diagram of a cathode structure to which a graphene hybrid polymer binder composite according to one embodiment of the present invention is applied.

[0045] A graphene hybrid polymer binder composite (10) according to one embodiment of the present invention comprises functionalized graphene (11) and a polymer binder (13, 14) bonded by a functional group (12) of the functionalized graphene (11).

[0046] Functionalized graphene (11) means that at least one type of functional group (12) is formed. The functional group (12) formed on the functionalized graphene (11) may be at least one selected from the group consisting of a silane group, an amide group, an azide group, an anhydride, a urea group, a urethane group, an amine group, an alkylene group, an epoxide group, and a mercapto group.

[0047] The polymer binder (13, 14) may be at least one selected from the group consisting of polyacrylic acid (PAA), polyimide (PI), polyetherimide (PEI), polyurethane / polyurea (PU), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC). In particular, the graphene hybrid polymer binder composite (10) of the present invention may include a first polymer binder (13) and a second polymer binder (14). The first polymer binder (13) is intended to improve the adhesive strength between the negative electrode active material (1) containing silicon and the current collector (4), and the second polymer binder (14) is intended to provide elasticity to the binder to prevent the negative electrode active material (1) containing silicon from being detached from the current collector (4) due to expansion and contraction behavior during charging and discharging.

[0048] Table 1 below summarizes the types of polymer binders that can be combined with functionalized graphene according to its functional group.

[0049]

[0050] Sequential functional group polymer binder 1SilanePAA, PI, PEI, PU 2Amide, AminePAA, PI, PEI, PU 3Anhydride, AzidePAA, SBR, CMC 4Urea, UrethanePAA, PEI, PEI 5AlkylenePAA, PEI, SBR, CMC 6Epoxide, MercaptoPAA, PEI, SBR, CMC

[0051]

[0052] The functionalized graphene (11) included in the graphene hybrid polymer binder composite (10) is bonded to the polymer binder (13, 14) through a functional group (12), and thus has the effect of increasing the adhesive strength and elasticity of the polymer binder (10) in addition to the effect of providing a conductive path like the conductive material (3).

[0053] Meanwhile, in order to prevent the negative electrode active material including silicon from detaching from the current collector due to expansion and contraction during the charge and discharge process, the adhesive strength and elasticity of the polymer binder must both be high. To this end, the polymer binder (13, 14) may include a first polymer binder (13) for improving adhesive strength and a second polymer binder (14) for improving elasticity. For example, the first polymer binder may include polyacrylic acid, and the second polymer may include urethane or styrene butadiene rubber.

[0054] According to one embodiment of the present invention, a negative electrode structure to which a graphene hybrid polymer binder composite is applied may further include, in addition to the graphene hybrid polymer binder composite (10), a negative electrode active material (1) containing silicon and a conductive material (3). In addition, a graphene coating layer (2) may be formed on the surface of the negative electrode active material (1) containing silicon. At this time, the graphene coating layer (2) formed on the surface of the negative electrode active material (1) has a different position and role from that of the functionalized graphene (11) of the graphene hybrid polymer binder composite (10).

[0055] The negative active material (1) containing silicon may be at least one of silicon metal such as silicon metal particles, silicon metal nanoparticles, etc., silicon compounds such as silicon oxide, silicon-carbon composite, etc., and silicon alloys.

[0056] The conductive material (3) may be at least one of carbon black (e.g., Super P Black, acetylene black, etc.), graphene, carbon nanotubes, and conductive polymers (polypyrrole, polyaniline, etc.). The positions and roles of the graphene and the functionalized graphene (11) of the graphene hybrid polymer binder composite (10) included in the conductive material (3) are different.

[0057] When the negative electrode material described above is applied to a lithium secondary battery, high capacity due to silicon contained in the negative electrode active material and improved capacity retention due to the graphene hybrid polymer binder composite can be achieved simultaneously.

[0058] FIG. 2 is a schematic flow chart of a first method for manufacturing a graphene hybrid polymer binder composite according to one embodiment of the present invention.

[0059] Referring to FIG. 2, a first method for manufacturing a graphene hybrid polymer binder composite according to one embodiment of the present invention includes a step of manufacturing a functionalized graphene colloid, a step of adding a polymer binder monomer to the functionalized graphene colloid, a step of polymerizing the polymer binder monomer to a functional group of the functionalized graphene, and a step of removing unreacted materials after the reaction is completed, and a step of replacing and homogenizing a solvent.

[0060] The steps for preparing functionalized graphene colloid are performed as follows.

[0061] Prepare a graphene oxide solution. The graphene oxide solution can be prepared by producing graphite oxide using the Hummers and Improved Methods, or by performing an exfoliation process using commercially available graphite oxide.

[0062] Next, functional groups are imparted to the graphene oxide. An additive for forming functional groups is added to the graphene oxide aqueous solution, stirred, and then dispersed ultrasonically to impart functional groups to the graphene oxide, forming functionalized graphene. Specifically, 50 to 150 parts by weight of the additive is added to 100 parts by weight of the graphene oxide aqueous solution, and the mixture is stirred at 90 to 120°C for 12 to 36 hours to form functionalized graphene.

[0063] The functional groups to be imparted to graphene can be determined by additives.

[0064] As an additive for forming a silane group, an organic silane compound capable of forming a silane group can be used, for example, triethoxysilane, tetraethoxysilane, aminopropyltriethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, octadecyltrimethoxysilane, (3-methacryloxy)propyltrimethoxysilane, 3-Glycidoxypropyl Methyldimethoxysilane, 3-Glycidoxypropyl Trimethoxysilane, 3-Glycidoxypropyl methyldiethoxysilane, 3-Glycidoxypropyl triethoxysilane, Any one selected from the group consisting of 3-Isocyanatepropyltriethoxysilane, 3-(Trimethoxysilyl)propylsuccinic anhydride can be used."As the additive, an organic monomer or polymer capable of forming an amine group or an amide group can be used, for example, ethylenediamine, triethylamine, paraphenylenediamine, o-phenylenediamine, mesophenylenediamine, 3,3',4,4'-tetraaminobiphenyl, 3,3',4,4'-tetraaminoterphenyl, benzidine, 1,5-diaminonaphthalene, (E)-4,4'-(diazene-1,2-diyl)dianiline, ethylenediamine, Any one selected from the group consisting of 1,6-diaminohexane, 1,8-diaminooctane, and 4,4-oxidianiline can be used.

[0065] As an additive for forming an amine group or an amide group, an organic monomer or polymer capable of forming an amine group or an amide group can be used, for example, ethylenediamine, triethylamine, paraphenylenediamine, o-phenylenediamine, mesophenylenediamine, 3,3',4,4'-tetraaminobiphenyl, 3,3',4,4'-tetraaminoterphenyl, benzidine, 1,5-diaminonaphthalene, (E)-4,4'-(diazene-1,2-diyl)dianiline, Any one selected from the group consisting of ethylenediamine, 1,6-diaminohexane, 1,8-diaminooctane, and 4,4-oxidianiline can be used.

[0066] As an additive for forming an anhydride functional group, an organic monomer or polymer capable of forming an anhydride functional group can be used, and for example, any one selected from the group consisting of maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, pyromellitic anhydride, naphthalic anhydride, and trimellitic anhydride can be used.

[0067] An organic monomer or polymer can be used as an additive capable of forming an azide group, and for example, any one selected from the group consisting of sodium azide, methyl azidoacetate, phenyl azide, 2-azidoethanol, azidoacetic acid, and 2-azidoethylamine can be used.

[0068] As an additive capable of forming a urea group or urethane group, an organic monomer or polymer may be used, and for example, any one selected from the group consisting of isocyanate, polyol, ethoxysilane, polyethylene glycol, toluene diisocyanate, methylene diphenyl diisocyanate, polytetramethylene ether glycol, and polycaprolactone may be used.

[0069] Any one selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, and 1,8-octanediol can be used.

[0070] As an additive capable of forming an epoxide group, an epoxidized organic monomer or polymer may be used, and for example, any one selected from the group consisting of epoxidized alkylene oxide, glycidyl methacrylate, styrenized epoxide, glycidyl amine, bisphenol A epoxy, epoxidized novolac, and epoxidized polyethylene oxide may be used.

[0071] As an additive capable of forming a mercapto group, an organic monomer or polymer may be used, and for example, any one selected from the group consisting of 2-mercaptoethanol, 1-thioglycerol, 3-mercaptopropanesulfonic acid, D-pentaerythritol tetra(3-mercaptopropionate), 4-mercaptophenol, methyl 3-mercaptopropionate, 6-thioguanine, 1-hexanethiol, ethanethiol, and benzylmercaptan may be used.

[0072] Once stirring is complete, a large-capacity circulating ultrasonic dispersion system produces 1 ton of functionalized graphene colloid per hour. The amount of functional group introduced can be determined by adjusting the amount of additive, stirring temperature, and stirring time. More specifically, the ratio of additive to graphene oxide, the timing and rate of additive addition at the beginning of the reaction, and the stirring speed and time are crucial.

[0073] Meanwhile, Fig. 3 shows the results of measuring the zeta potential of the functionalized graphene, oxidized graphene, and non-oxidized graphene used in the present invention. As shown in Fig. 3, the zeta potential of the functionalized graphene of the present invention has an absolute value of 40 mV or more, preferably 50 mV or more. When the zeta potential is 40 mV or more, preferably 50 mV or more, the functionalized graphene has high dispersibility in the solvent used in the process of manufacturing the functionalized graphene colloid. In other words, the low dispersibility problem of the conventional graphene is solved (see the functionalized graphene colloid mixing in Fig. 5).

[0074] A mixture of deionized water and ethanol can be used as a solvent for the manufactured functionalized graphene colloid. For example, a mixture of 70 to 90 vol% deionized water and 10 to 30 vol% ethanol can be used. The content of functionalized graphene contained therein can be 1 to 3 wt%.

[0075] Next, a step of adding a polymer binder monomer to the functionalized graphene colloid is performed. The step of adding a polymer binder monomer to the functionalized graphene colloid is performed in two steps. First, the functionalized graphene colloid is diluted. That is, the functionalized graphene colloid is diluted 15 to 25 times in deionized water and stirred. Next, less than 50 wt% of the total mass of the polymer binder monomer to be added is added in the first step and reacted at 35 to 45 °C for 30 to 90 minutes. Then, the remaining polymer binder monomer is added in the second step. If the polymer binder monomer is not added in this manner, the functionalized graphene and the polymer binder monomer will not mix well.

[0076] After the second addition of the polymer binder monomer, a step of polymerizing the polymer binder monomer onto the functional groups of the functionalized graphene is performed. After the second addition of the polymer binder monomer, the temperature is increased to 50 to 70°C, and the polymerization reaction is performed for 8 to 12 hours. During this step, the functional groups of the functionalized graphene and the polymer binder are molecularly bonded.

[0077] After the polymerization reaction was completed, the unreacted material was washed and homogenized to produce a graphene hybrid polymer binder composite (GHPB).

[0078] Meanwhile, unlike the first manufacturing method that uses a polymer binder monomer, the polymer binder can be directly bonded to functionalized graphene.

[0079] FIG. 4 is a schematic flow chart of a second method for manufacturing a graphene hybrid polymer binder composite according to an embodiment of the present invention, and FIG. 5 is a photograph showing each process of the second method for manufacturing a graphene hybrid polymer binder composite according to an embodiment of the present invention.

[0080] Referring to FIGS. 4 and 5, a second method for manufacturing a graphene hybrid polymer binder composite according to one embodiment of the present invention includes a step of manufacturing a functionalized graphene colloid, a step of adding a polymer binder to the functionalized graphene colloid, a step of bonding the polymer binder to a functional group of the functionalized graphene, and a step of removing unreacted materials after the reaction is completed, and a step of replacing and homogenizing a solvent.

[0081] The steps for manufacturing functionalized graphene colloids are the same as in the first manufacturing method, so their description is omitted here.

[0082] Once the functionalized graphene colloid is prepared, the next step is to add a polymer binder to the functionalized graphene colloid. The step of adding the polymer binder monomer to the functionalized graphene colloid is performed in two steps. First, the functionalized graphene colloid is diluted. That is, the functionalized graphene colloid is diluted 15 to 25 times in deionized water and stirred. Next, only 20 to 40 wt% of the total mass of the polymer binder monomer to be added is added in the first step, stirred at room temperature for 20 to 40 minutes, and then homogenized using ultrasound for 20 to 40 minutes. The remaining polymer binder is then added in the second step. If the polymer binder is not added in this manner, the functionalized graphene and the polymer binder will not mix well.

[0083] After the secondary addition of the polymer binder, a step is performed to bind the polymer binder to the functional groups of the functionalized graphene. Following the secondary addition of the polymer binder monomer, the temperature is increased to 50 to 70°C, and a polymerization reaction is performed for 8 to 12 hours. During this step, the functional groups of the functionalized graphene and the polymer binder are molecularly bonded.

[0084] After the polymerization reaction was completed, the unreacted material was washed and homogenized to produce a graphene hybrid polymer binder composite (GHPB).

[0085]

[0086] Experimental Example 1: Analysis of Graphene Hybrid Polymer Binder Composites

[0087] Graphene colloids were prepared by dispersing 1 wt% of functionalized graphene having silane groups in a solvent containing deionized water and ethanol in a mass ratio of 8:2, and the dispersion was homogenized and dispersed by ultrasonication for more than 30 minutes. Next, 20 wt% of the total amount of polymer binder (PAA or PA / PU) was added, stirred at room temperature for 30 minutes, and homogenized by ultrasonication for 30 minutes before adding the remaining polymer binder. After the addition of the entire amount of polymer binder, the temperature was increased to 60 °C, and the polymerization reaction was performed for 10 hours. After completion of the reaction, centrifugation was performed three times at 2000 rpm for 30 minutes, and after washing the unreacted matter and filtering under reduced pressure, the solvent was added. After that, the mixture was homogenized for 30 minutes using ultrasonication or a high-speed homogenizer to prepare a graphene hybrid polymer binder composite (GHPB).

[0088] Figure 6 is a result of FT-IR spectrum analysis of a graphene hybrid polymer binder composite according to one embodiment of the present invention.

[0089] In Fig. 6, GHPB-1 (G hybrid PAA) is a sample in which the functionalized graphene content is 0.01 wt%, the polymer binder is PAA, and the functionalized graphene and the polymer binder are simply mixed. GHPB-1 (G hybrid PAA) completion is a sample in which the functionalized graphene content is 0.01 wt%, the polymer binder is PAA, and the functionalized graphene and the polymer binder are bonded by functional groups. GHPB-2 (G hybrid PAA-PUD) completion is a sample in which the functionalized graphene content is 0.03 wt%, the polymer binders are PAA and PU, and the functionalized graphene and the polymer binder are bonded by functional groups.

[0090] Referring to Fig. 6, in the FT-IR spectrum of a sample in which functionalized graphene and a polymer binder are simply mixed, the FT-IR characteristic peaks of functionalized graphene and the characteristic peaks of PAA appear mixed together.

[0091] In contrast, the FT-IR spectra of GHPB-1 (G hybrid PAA) completion and GHPB-2 (G hybrid PAA-PUD) completion clearly show the characteristic peaks of polymer binders (PAA, PU), and the peaks of functionalized graphene at 1650 cm -1 It can be seen that the characteristic peaks in the vicinity have decreased. This is a result of the combination of functionalized graphene and polymer binder.

[0092] To more accurately determine whether functionalized graphene is bound to a polymer binder, Raman spectrum analysis was performed. Figure 7 shows the results of Raman spectrum analysis of a graphene hybrid polymer binder composite according to an embodiment of the present invention.

[0093] Since unreacted materials were removed during the process of manufacturing the graphene hybrid polymer binder composite, the characteristic peaks of functionalized graphene would not be confirmed in the Raman spectrum analysis results if functionalized graphene was not bound to the polymer binder.

[0094] However, as seen in Fig. 7, the D peak (1350 cm) is not measured in the Raman spectrum analysis. -1 ) and G peak (1580 cm -1 ) can be confirmed to be measured.

[0095] Therefore, by synthesizing the results of FIG. 6 and FIG. 7, it can be seen that in the graphene hybrid polymer binder composite according to one embodiment of the present invention, the functionalized graphene and the polymer binder are molecularly bonded by the functional group of the functionalized graphene.

[0096] Next, a cross-cut test was performed after coating the GHPB-1 (G hybrid PAA) completion sample and the GHPB-2 (G hybrid PAA-PUD) completion sample on a copper current collector. As a comparative example, a cross-cut test was performed after coating PAA on a copper current collector.

[0097] The cross-cut test is a method for evaluating the adhesion of a coating. A grid pattern is created by drawing several lines at regular intervals on a coated surface. Tape is then applied and removed to determine how well the coating adheres. Adhesion is graded by observing the removed tape and the coating on the grid pattern. The test results can be divided into the following grades: 5B is the highest adhesion grade, indicating no coating peeling off from the grid pattern after the test. 4B indicates less than 5% of the coating peeled off from the grid pattern. 3B indicates coating loss in the range of 5-15% of the grid pattern. 2B indicates 15-35% of the coating peeled off from the grid pattern. 1B indicates 35-65% of the coating peeled off from the grid pattern. 0B is the lowest adhesion grade, indicating more than 65% of the coating peeled off.

[0098] Figure 8 shows the results of a cross-cut test to confirm the adhesive performance of a graphene hybrid polymer binder composite according to one embodiment of the present invention.

[0099] As can be seen in Fig. 8, the cross-cut test result of PAA binder, which is known to have better point adhesion than SBR and CMC, which are widely used as negative electrode binders, was 3B.

[0100] In comparison, in the case of the graphene hybrid polymer binder composite of the present invention, it can be seen that the cross-cut test result for both samples was 5B, indicating that the coating was not peeled off at all.

[0101] Meanwhile, the effect of the content of functionalized graphene in the graphene hybrid polymer binder composite is shown in Table 2 below. PAA was used as the polymer binder, and after coating each polymer binder on a copper current collector, a tape test and a cross-cut test were performed. In the tape test, the tape was attached and removed 10 times. If the coating was not peeled off, it was marked as ◎ (excellent), if it was peeled off once, it was marked as ○ (good), if it was peeled off 2 to 3 times, it was marked as △ (medium), and otherwise, it was marked as X (poor).

[0102]

[0103] Polymer Binder Tape TestCross-cut TestSBRX0B or less70% SBR+ 30% CMC△1BPAA○3BGHPB (0.01wt% Graphene / Binder)◎5BGHPB (0.03wt% Graphene / Binder)◎5BGHPB (0.05wt% Graphene / Binder)◎5BGHPB (0.1wt% Graphene / Binder)◎5BGHPB (0.3wt% Graphene / Binder)◎5BGHPB (0.5wt% Graphene / Binder)○4BGHPB (0.6% Graphene / Binder)△2B

[0104]

[0105] As shown in Table 2, the graphene hybrid polymer binder composite of the present invention, when the content of functionalized graphene is 0.01 to 0.5 wt%, exhibits excellent tape test results and 5B cross-cut test results, confirming excellent adhesive strength. However, when the content of functionalized graphene exceeds 0.5 wt%, the internal cohesion of the functionalized graphene becomes greater than the adhesive strength to the adherend, resulting in a decrease in adhesive strength.

[0106] Therefore, the content of functionalized graphene in the graphene hybrid polymer binder composite of the present invention may be 0.01 to 0.5 wt%, and preferably 0.01 to 0.3 wt%.

[0107]

[0108] Experimental Example 2: Characterization of a Battery Containing a Negative Electrode Material Using a Graphene Hybrid Polymer Binder Composite

[0109] To analyze the characteristics of the battery, we prepared anode active materials consisting of silicon metal (particle size: 7 to 10 μm) and a functionalized graphene coating layer spontaneously coated on the silicon metal (particle size: 7 to 10 μm). The silicon metal particles with a functionalized graphene coating layer were prepared by spontaneously adsorbing functionalized graphene colloids with positive charges due to functionalization and silicon particles with a center particle size of 7 to 10 μm in an ethanol solvent for 10 minutes through ultrasonic dispersion. The resulting particles were then centrifuged or filtered under reduced pressure, dried at 80°C, and heat-treated at 300°C in a nitrogen atmosphere to complete the process. The content of functionalized graphene in the silicon metal particles with a functionalized graphene coating layer is 2 wt%. The preparation of the silicon metal particles with a functionalized graphene coating layer can be referred to the contents disclosed in Korean Patent Publication No. 10-2023-0099837.

[0110] To evaluate the performance of a secondary battery, a negative electrode was manufactured using silicon metal particles or silicon metal particles having a functionalized graphene coating layer as a negative electrode active material.

[0111] Comparative Example 1 is composed of 8 um silicon metal particles, artificial graphite (Si: artificial graphite = 1:1), a conductive agent (super p black), and a polymer binder (SBR:CMC=7:3) in a weight ratio of 40:40:10:10.

[0112] Example 1 is composed of 8 μm silicon metal particles (Si), artificial graphite (Si: artificial graphite = 1:1), a conductive material (super p black), and a graphene hybrid polymer binder composite (GHPB) in a weight ratio of 40:40:10:10. At this time, the graphene hybrid polymer binder composite can utilize SBR and CMC bonded by functional groups, and the content of functionalized graphene in the graphene hybrid polymer binder composite is 0.05 wt%, and SBR and CMC are included in a weight ratio of 7:3.

[0113] Comparative Example 2 and Examples 2 to 4 were manufactured by increasing the weight of the negative active material (Si: artificial graphite = 1:1) by the amount of the graphene hybrid polymer binder composite reduced.

[0114] Example 5 is composed of silicon metal particles (Si / G) having a functionalized graphene coating layer of 8 μm, artificial graphite (Si / G: artificial graphite = 1:1), a conductive material (super p black), and a graphene hybrid polymer binder composite (GHPB) at a weight ratio of 40:40:10:10. At this time, the graphene hybrid polymer binder composite can utilize SBR and CMC bonded by functional groups, and the content of functionalized graphene in the graphene hybrid polymer binder composite is 0.05 wt%, and SBR and CMC are included at a weight ratio of 7:3.

[0115] Examples 6 to 9 were produced by increasing the weight of the negative active material (Si / G: artificial graphite = 1:1) by the amount of the graphene hybrid polymer binder composite reduced.

[0116] Comparative Example 3 is the same as Comparative Example 1, except that silicon metal particles having a functionalized graphene coating layer are used instead of silicon metal particles.

[0117] Meanwhile, the content of functionalized graphene in the silicon metal particles having a functionalized graphene coating layer used in Comparative Example 3 and Examples 5 to 9 was 2 wt%.

[0118] First, the characteristics of the half-cell were evaluated.

[0119] The cathode material was prepared as follows. The binder solution was further diluted in deionized water, and the cathode active material and conductive material were added. The solution was stirred for 1 hour using a homogenizer to prepare a slurry. The prepared slurry was coated to a thickness of 75 μm on a 15 μm-thick copper current collector, dried at 90°C for 2 hours, pressed, and dried in a vacuum oven at 120°C for 4 hours to completely remove the solvent.

[0120] A coin half-cell (CR2032) was manufactured using the manufactured negative electrode material as the negative electrode and lithium metal foil, polyethylene separator, and electrolyte as the positive electrode. At this time, the electrolyte was a mixture of 1.2 M LiPF6 and ethylene carbonate (EC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) (EC / DEC / FEC=2 / 6 / 2 (volume ratio) in a weight ratio of 3:7).

[0121] The characteristics of half-cells and full-cells were evaluated as follows by applying the IEC 62620 standard. At room temperature (25±5℃), constant-current charging was performed to 0.01 V with a current of 0.1 C-rate, followed by constant-voltage charging at 0.01 V (end current is 0.01 C-rate), and constant-current discharge to 1.5 V with a current of 0.1 C-rate. Discharge amount calculation and initial charge / discharge efficiency calculation were performed under the above conditions. The life evaluation was performed by constant-current charging to 0.005 V with a current of 0.1 C-rate at room temperature (25±5℃), followed by constant-voltage charging at 0.005 V (end current is 0.005 C-rate), and constant-current discharge to 1.5 V with a current of 0.1 C-rate. This was repeated 50 times to evaluate the charge / discharge characteristics.

[0122] Meanwhile, for full cells, the life characteristics were compared by evaluating the charge-discharge characteristics 500 times.

[0123] When manufacturing a full cell, the negative electrode material was manufactured in the same manner as the half cell, and the positive electrode material was prepared by dissolving the NCM622 active material with a center particle diameter of 8 um and the conductive material (super p black) in a PVdF binder solution in NMP solvent and stirring for 1 hour using a homomixer to prepare a slurry. At this time, the positive electrode material is composed of NCM622, the conductive material, and the PVdF binder in a weight ratio of 80:10:10.

[0124] The manufactured positive electrode slurry was coated to a thickness of 75 μm on a 20 μm thick aluminum collector, dried at 120°C for 2 hours, pressed, and dried in a vacuum oven at 120°C for 4 hours to completely remove the solvent, completing the positive electrode.

[0125] Full cell assembly was performed under the same conditions as half-cell manufacturing, using a manufactured positive electrode instead of lithium metal foil, and the life characteristics were compared through 500 cycles of charge-discharge evaluation.

[0126] Below, the characteristics of half-cells and full-cells were evaluated. The initial efficiency and lifespan were calculated as follows.

[0127]

[0128] Initial efficiency (%) = (1-time discharge capacity / 1-time charge capacity) x 100

[0129] Lifespan (%) = (n discharge capacity / 1 discharge capacity) x 100

[0130]

[0131] Table 3 shows the results of evaluating the characteristics of a half-cell containing silicon metal particles as a negative electrode active material.

[0132]

[0133] Sequence Binder content (wt%) Initial discharge capacity (mAh / g) Capacity retention (10 times) (%) Capacity retention (50 times) (%) Comparative example 1 SBR+CMC 10 169 1.478 27.5 Comparative example 2 SBR+CMC 8 173 3.56 2.12 3.5 Example 1 GHPB 10 169 8.88 7.57 5.2 Example 2 GHPB 8 174 2.38 7.77 5.1 Example 3 GHPB 7 176 3.78 7.47 5.0 Example 4 GHPB 6 178 1.78 2.56 0.1

[0134]

[0135] In Comparative Example 1, a gradual decline in capacity was observed from the 10th charge / discharge cycle, and at the 50th cycle, most of the silicon metal particles were destroyed, resulting in a very low capacity retention rate.

[0136] Comparative Example 2 showed a higher initial discharge capacity than Comparative Example 1 due to binder reduction, but the decrease in capacity was greater than that of Comparative Example 1. This is because the content of silicon metal particles was higher, and thus the effect of volume expansion and contraction during charge and discharge was greater.

[0137] It was confirmed that Examples 1 to 4, which included the graphene hybrid polymer binder composite of the present invention as a binder, had a very high capacity retention rate at 10 charge / discharge cycles compared to the comparative examples. In particular, Examples 1 to 3 showed a very high capacity retention rate of around 75% even at 50 charge / discharge cycles. However, in Example 4, where the binder content was greatly reduced, a capacity decrease of 60.1% was observed at 50 charge / discharge cycles. This is because the adhesive strength decreased as the binder content decreased, resulting in detachment from the current collector due to the expansion and contraction behavior of the silicon metal particles during charge / discharge, and further, the irreversible capacity occurred as the SEI layer formation increased, resulting in a decrease in capacity.

[0138] Therefore, when the negative electrode material includes silicon metal particles, the content of the graphene hybrid polymer binder composite can be 7 to 10 wt% with respect to the total weight of the negative electrode material.

[0139]

[0140] Table 4 shows the results of evaluating the characteristics of a half-cell containing silicon metal particles with functionalized graphene as a coating layer as a negative electrode active material.

[0141]

[0142] Sequence Anode material type Binder type Binder content (wt%) Initial discharge capacity (mAh / g) Initial efficiency (%) Capacity retention (50 times) (%) Comparative example 1 Si Metal SBR + CMC 10 16 9 1.4 8 9.2 2 7.5 Comparative example 2 Si Metal SBR + CMC 8 17 3 3.5 8 9.3 2 3.5 Example 1 Si Metal GHPB 10 16 9 8.8 9 0.2 7 5.2 Example 2 Si Metal GHPB 8 17 4 2.3 9 0.5 7 5.1 Example 3 Si Metal GHPB 7 17 6 ​​3.7 9 0.1 7 5.0 Example 5 Si / GGHPB 10 16 7 2.0 9 2.9 9 6.3 Example 6 Si / GGHPB 8 17 2 5.2 9 3.1 9 6.1 Example 7Si / GGHPB71736.493.096.2Example 8Si / GGHPB61757.692.196.0Example 9Si / GGHPB51779.787.189.5Comparative example 3Si / GSBR+CMC101669.391.194.3

[0143]

[0144] Comparing Examples 1 to 3 and Examples 5 to 7, it can be seen that when silicon metal particles having functionalized graphene as a coating layer are included as a negative electrode active material, Examples 5 to 7 have higher initial efficiency than Examples 1 to 3, and the capacity retention rate after 50 charge / discharge cycles is significantly higher.

[0145] In the case of Examples 5 to 7, since the silicon metal particles have a functionalized graphene coating layer self-bonded to the silicon metal particles on the surface, the functionalized graphene coating layer primarily controls the expansion and contraction behavior of the silicon metal particles during charge and discharge, and the graphene hybrid polymer binder composite secondarily controls the expansion and contraction behavior of the silicon metal particles during charge and discharge with excellent adhesiveness and elasticity.

[0146] In particular, when silicon metal particles having functionalized graphene as a coating layer were included as a negative electrode active material, excellent capacity retention was observed even when the content of the graphene hybrid polymer binder composite was 6 wt% (Example 8).

[0147] However, in Example 9, where the binder content was significantly reduced, a capacity decrease of 89.5% was observed at the 50th charge / discharge cycle. This is because the adhesive strength decreased as the binder content decreased, which resulted in detachment from the current collector due to the expansion and contraction behavior of the silicon metal particles during charge / discharge, and further, the irreversible capacity occurred as the SEI layer formation increased, which resulted in a decrease in capacity.

[0148] Meanwhile, in the case of Comparative Example 3, a mixture of SBR and SMC was used as a binder instead of the graphene hybrid polymer binder composite of the present invention. Although the capacity retention rate after 50 charge / discharge cycles was lower than Examples 5 to 8, it was found to be good at 94.3%. This is because the functionalized graphene coating layer coating the silicon metal particles effectively controls the expansion and contraction behavior of the silicon metal particles during charge / discharge. However, as seen later, the capacity retention rate of Comparative Example 3 is significantly reduced after 100 charge / discharge cycles.

[0149] Table 5 presents the results of evaluating the characteristics of a full cell containing silicon metal particles coated with functionalized graphene as the negative active material. The high-speed charge / discharge characteristics are expressed as the discharge capacity at 2C / discharge capacity at 0.2C (C: current rate).

[0150]

[0151] Sequence Anode material type Binder type Binder content Capacity retention rate (50 times) (%) Capacity retention rate (100 times) (%) Capacity retention rate (300 times) (%) Capacity retention rate (500 times) (%) High-speed charge / discharge characteristics (%) Comparative example 4Si Metal SBR+CMC 1026.810.8 Discontinued Discontinued 31 Example 10Si Metal GHPB 1075.465.763.157.853 Example 11Si / GGHPB 1096.295.193.190.582 Example 12Si / GGHPB 896.395.292.990.683 Example 13Si / GGHPB 796.295.293.290.484 Example 14Si / GGHPB695.894.192.790.184 Example 15Si / GGHPB587.685.180.171.281 Comparative Example 3Si / GSBR+CMC1093.152.135.6 Interrupted 72

[0152]

[0153] Comparative Example 4 showed rapid performance degradation due to silicone shrinkage and expansion during full cell evaluation.

[0154] Example 10 showed that the introduction of GHPB resulted in an improvement in the lifespan and high-speed charge / discharge characteristics due to increased electrical connection, but the capacity retention rate at 100 charge / discharge cycles was less than 70%.

[0155] In Examples 11 to 14, which included silicon metal particles having a functionalized graphene coating layer as a negative active material and used a graphene hybrid polymer binder composite as a binder, it was found that the capacity retention rate was high at over 80% even after 500 charge / discharge cycles. In addition, the high-speed charge / discharge characteristics were also excellent at over 80% due to the interaction between the functionalized graphene coating layer coating the silicon metal particles and the functionalized graphene included in the graphene hybrid polymer binder composite.

[0156] That is, the lifespan was improved by the shrinkage-expansion control effect of the silicon metal particles with the functionalized graphene coating layer and the strengthening of the bonding force with the current collector by the graphene hybrid polymer binder composite, and the high-speed charge-discharge characteristics were very excellent due to the network formation by graphene between the silicon metal particles with the functionalized graphene coating layer - the graphene hybrid polymer binder composite - the current collector.

[0157] In conclusion, when silicon metal particles having a functionalized graphene coating layer are included as a negative electrode active material, the content of the graphene hybrid polymer binder composite may be 5 to 10 wt%, and preferably 6 to 10 wt%, based on the total weight of the negative electrode material.

[0158] A battery with an improved lifespan due to the network formed by the graphene contained in the cathode material can be called a graphene network battery. In particular, a graphene network battery not only has an improved lifespan but also has excellent high-speed charge / discharge characteristics.

[0159] The graphene hybrid polymer binder composite according to one embodiment of the present invention described above can be used in lithium secondary batteries. It may also be used to secure other materials that exhibit expansion and contraction behavior, such as silicon anode materials.

[0160] The scope of protection of the present invention is not limited to the description and expression of the embodiments explicitly described above. Furthermore, it should be noted that the scope of protection of the present invention may not be limited by obvious modifications or substitutions within the technical field to which the present invention pertains.

Claims

1. Functionalized graphene with functional groups formed; and A graphene hybrid polymer binder composite comprising the functionalized graphene and a polymer binder bonded by the functional group.

2. In paragraph 1, A graphene hybrid polymer binder composite, wherein the functional group is at least one selected from the group consisting of a silane group, an amide group, an azide group, an anhydride, a urea group, a urethane group, an amine group, an alkylene group, an epoxide group, and a mercapto group.

3. In paragraph 1, The above polymer binder is a graphene hybrid polymer binder composite, wherein at least one polymer binder is selected from the group consisting of polyacrylic acid (PAA: Poly Acrylic Acid), polyimide (PI: Poly Imide), polyether imide (PEI: Poly Ether Imide), polyurethane / polyurea (PU: Poly Urethane, Poly Urea), styrene-butadiene rubber (SBR: Styrene-Butadiene Rubber), and carboxymethyl cellulose (CMC: Carboxymethyl Cellulose).

4. In paragraph 1, The above polymer binder is a graphene hybrid polymer binder composite including a first polymer binder for improving adhesion to a negative electrode active material including silicon and a current collector, and a second polymer binder for improving elasticity.

5. In paragraph 1, A graphene hybrid polymer binder composite having a content of the functionalized graphene of 0.01 to 0.5 wt%.

6. In paragraph 1, A graphene hybrid polymer binder composite having a content of the functionalized graphene of 0.01 to 0.3 wt%. 7.(a) A step of preparing a functionalized graphene colloid having a functional group formed; (b) a step of adding a polymer binder or a polymer binder monomer to the colloid; (c) a step of combining the functional group of the polymer binder and the functionalized graphene or polymerizing the polymer binder monomer to form a polymer binder combined with the functional group of the functionalized graphene; and (d) a step of removing unreacted substances; a method for producing a graphene hybrid polymer binder composite.

8. In paragraph 7, In step (b) above In the case of the above polymer binder, a portion of the total mass of the polymer binder to be added is added to the colloid, stirred and homogenized, and then the remainder is added to the colloid. A method for producing a graphene hybrid polymer binder composite, comprising adding a portion of the total mass of the polymer binder monomer to be added to the colloid, reacting the portion, and then adding the remainder to the colloid.

9. In paragraph 7, The above functionalized graphene is a method for producing a graphene hybrid polymer binder composite having an absolute value of zeta potential of 40 mV or more.

10. Containing a positive electrode, a negative electrode, and a binder interposed between the positive electrode and the negative electrode, The above negative electrode comprises a current collector; and a negative electrode material formed on the current collector and comprising a negative electrode active material conductive material including silicon and a binder; A graphene network battery, which is a graphene hybrid polymer binder composite comprising: the binder is functionalized graphene having a functional group formed thereon; and a polymer binder bonded to the functionalized graphene by the functional group.

11. In paragraph 10, A graphene network battery, wherein the content of the graphene hybrid polymer binder composite is 6 to 10 wt% based on the total weight of the negative electrode material.

12. In paragraph 10, A graphene network battery wherein the negative active material is a polymer binder composite including silicon metal particles having a functionalized graphene coating layer on the surface.

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