Graphene network battery

Abstract

The present invention relates to a graphene network battery, the graphene network battery comprising a positive electrode current collector, a positive electrode mixture, a separator, a negative electrode mixture and a negative electrode current collector, wherein the negative electrode mixture comprises a negative electrode material layer formed on the upper part of the negative electrode current collector and comprising a silicon negative electrode active material and a binder, and a structure-stabilized graphene layer formed on at least one surface of the negative electrode material layer.

Description

Technical Field

[0001] This invention relates to a graphene network battery. Background Technology

[0002] Lithium-ion rechargeable batteries are devices that store and utilize energy through the repeated insertion and extraction of lithium ions and the charging and discharging process. They have become an important power source in various applications, from portable electronic devices to large equipment such as electric vehicles. As mentioned above, lithium-ion rechargeable batteries have the advantages of miniaturization and weight reduction, as well as providing high capacity, high energy density, safety, and long lifespan. Therefore, it is important to develop technologies to further improve their performance.

[0003] The performance of lithium-ion batteries depends on components such as the negative electrode, positive electrode, separator, and electrolyte, with the negative electrode playing a crucial role in determining battery capacity. Currently, carbon-based materials are mainly used as negative electrode active materials, but research continues on novel high-capacity negative electrode active materials to achieve performance exceeding the theoretical capacity (372 mAh / g). In particular, silicon, with a theoretical capacity as high as 4200 mAh / g, is attracting significant attention as a potential next-generation negative electrode active material that could replace current carbon-based materials.

[0004] However, silicon negative electrode active materials undergo volume changes of approximately 300% or even higher during charge and discharge, leading to pulverization of the active material and electrical isolation from the current collector. This electrical isolation significantly reduces the battery's capacity retention rate and is a major factor hindering the commercial application of silicon negative electrode active materials. To address this issue, techniques such as coating a carbon layer on silicon or preparing composites have been proposed, but these techniques have not yet reached a practical commercialization level.

[0005] Currently, commercially available lithium-ion rechargeable batteries incorporate small amounts (less than 5%) of materials, such as silicon oxide (SiOx) or silicon-carbon composites (Si / C), into their negative electrode plates to achieve an energy density of approximately 300 Wh / kg. However, to meet the high energy density requirements of large devices such as electric vehicles, new designs and technologies are needed to improve the capacity and stability of silicon negative electrode active materials. In particular, innovative methods are required to address issues such as initial efficiency degradation, volume changes, and electrical delamination in silicon negative electrode active materials.

[0006] Graphene, as a novel material for solving these problems, is attracting attention. Graphene is the thinnest known material and exhibits excellent physical properties such as current density, strength, thermal conductivity, and electron mobility. However, its strong self-adhesiveness makes it difficult to disperse in polymers or solvents. Summary of the Invention

[0007] Technical issues

[0008] The purpose of this invention is to provide a graphene network battery that effectively controls the volume change (shrinkage-expansion) of the silicon negative electrode active material by introducing a structurally stabilized graphene layer on the negative electrode side, and improves the battery's capacity retention and extends its charge-discharge life by preventing the silicon negative electrode material layer from delaminating.

[0009] Another objective of this invention is to reduce energy consumption and greenhouse gas emissions generated during typical recycling processes by applying a newly proposed low-temperature heat treatment technology, thereby achieving both economic benefits and environmental sustainability.

[0010] Meanwhile, other objectives not specified in this invention will be further considered within the scope readily apparent from the following detailed description and its effects.

[0011] Solution to the problem

[0012] To achieve the above objectives, the following solutions are proposed.

[0013] According to an embodiment of the present invention, a graphene network battery includes: a positive electrode current collector, a positive electrode mixture, a separator, a negative electrode mixture, and a negative electrode current collector, wherein the negative electrode mixture includes a negative electrode material layer formed on the upper part of the negative electrode current collector and comprising a silicon negative electrode active material and a binder; and a structure-stabilized graphene layer formed on at least one surface of the negative electrode material layer.

[0014] In one embodiment, the structurally stabilized graphene layer may be characterized by being formed on the uppermost part of the negative electrode material layer.

[0015] In an embodiment, the structurally stabilized graphene layer may be characterized by having a thickness of 50 nm to 3000 nm.

[0016] In an embodiment, the structurally stabilized graphene layer may be characterized as being located between the negative electrode material layer and the current collector.

[0017] In an embodiment, the structurally stabilized graphene layer may be characterized by having a thickness of 10 nm to 500 nm.

[0018] In an embodiment, the negative electrode material layer and the structurally stabilized graphene layer may be characterized by being stacked alternately.

[0019] In embodiments, the adhesive may be characterized by being selected from at least one of the following groups: styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and graphene-based mixed adhesives.

[0020] In an embodiment, when the adhesive is a graphene-mixed adhesive, the graphene-mixed adhesive may be characterized by comprising functionalized graphene having functional groups, and a polymer adhesive bonded to the functionalized graphene by the functional groups.

[0021] In an embodiment, the silicon negative electrode material may be characterized by selecting at least one from the group consisting of silicon, silicon compounds, and graphene-silicon hybrid negative electrode active materials.

[0022] In an embodiment, when the silicon negative electrode material is a graphene-silicon hybrid negative electrode active material, the graphene-silicon hybrid negative electrode active material may be characterized by including a graphene coating layer formed by self-adsorbing functionalized graphene with functional groups onto the surface of silicon or a silicon compound.

[0023] Beneficial effects

[0024] The graphene network battery of the present invention has a three-dimensional structure in which a structurally stabilized graphene layer and a silicon negative electrode layer are stacked on each other. The structurally stabilized graphene layer effectively controls the volume change (shrinkage-expansion) of the silicon negative electrode active material, preventing the silicon negative electrode material layer from delaminating due to the volume change of the silicon negative electrode material, thereby improving the battery's capacity retention rate and extending its charge-discharge life.

[0025] Furthermore, the graphene network battery according to an embodiment of the present invention includes a silicon negative electrode material layer, which includes at least one of a silicon-graphene hybrid negative electrode active material (functionalized graphene self-adsorbed thereon) and a binder (functionalized graphene bonded thereto by functional groups), thereby forming a three-dimensional graphene network between the structurally stabilized graphene layer and the silicon negative electrode material layer, and thus more effectively controlling the volume change (shrinkage-expansion) of the silicon negative electrode active material.

[0026] Furthermore, although not explicitly stated herein, it should be understood that the effects and temporary effects of the technical features of the present invention described in the following specification are all processed in accordance with the description in the present invention specification. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a graphene network battery according to an embodiment of the present invention.

[0028] Figure 2 This is a diagram used to describe the self-adsorption of functionalized graphene in graphene-silicon hybrid negative electrode active materials.

[0029] Figure 3 This is a diagram used to illustrate the functional groups formed on functionalized graphene according to the present invention.

[0030] Figure 4This is a diagram illustrating the structure of a graphene-based hybrid adhesive.

[0031] Figure 6 The FT-IR spectral analysis results of the graphene hybrid binder are shown.

[0032] Figure 7 The Raman spectral analysis results of the graphene hybrid binder are shown.

[0033] Figure 8 This diagram is used to describe the structure in which negative electrode material layers and structurally stabilized graphene layers are alternately formed in multiple layers.

[0034] Figure 9 This is a flowchart of a method for manufacturing graphene network batteries.

[0035] Figure 10 This is a schematic diagram illustrating the process of forming a structurally stable graphene layer through electrophoretic deposition.

[0036] Figure 11 Scanning electron microscope (SEM) images of the current collector layer, the structure-stabilized graphene layer (bottom), the Si / G negative electrode material layer, and the structure-stabilized graphene layer (top) are shown.

[0037] The accompanying drawings are merely examples to illustrate the technical concept of the present invention, and the scope of the present invention is not limited thereto. Detailed Implementation

[0038] The structure and effects of the present invention will now be described with reference to the accompanying drawings and various embodiments thereof. In describing the present invention, detailed descriptions of known functions will be omitted if it is believed that such detailed descriptions might unnecessarily obscure the essential points of the invention that are obvious to those skilled in the art.

[0039] Figure 1 This is a schematic diagram of a graphene network battery according to an embodiment of the present invention.

[0040] like Figure 1 As shown, the graphene network battery according to an embodiment of the present invention includes a positive electrode current collector, a positive electrode mixture, a separator, a negative electrode mixture, and a negative electrode current collector.

[0041] The graphene network battery according to an embodiment of the present invention is characterized by a negative electrode.

[0042] A negative electrode mixture 20 is formed on one surface of the negative electrode current collector 10. The negative electrode mixture 20 includes: a negative electrode material layer comprising a silicon negative electrode active material 21, a binder 22 and a conductive material 23; and a structure-stabilized graphene layer 24 formed on at least one surface of the negative electrode material layer.

[0043] Each component will be described in more detail below.

[0044] Silicon negative electrode active material

[0045] As the silicon negative electrode active material 2, at least one of the group consisting of silicon, silicon compounds, and graphene-silicon hybrid negative electrode active materials can be selected. The silicon compound can be at least one of silicon oxide, silicon nitride, and silicon-carbon composites. Graphene-silicon hybrid negative electrode active materials refer to materials in which functionalized graphene self-adsorbs its functional groups onto silicon or silicon compounds, such as… Figure 2 As shown. Figure 3 As shown, the functionalized graphene 1 of the present invention refers to a material in which functional groups are formed on graphene, and the functional groups can vary depending on the application of the functionalized graphene.

[0046] The reason why the functionalized graphene of the present invention can self-adsorb onto silicon or silicon compounds is that there is an interaction between the functionalized graphene and the silicon or silicon compound, such as electrostatic bonding, hydrogen bonding, and / or covalent bonding. For example, the functionalized graphene has a positive charge and therefore can electrostatically bond to the surface of silicon or silicon compounds that have a negative charge. In this case, the surface of the silicon or silicon compound may have a negative charge, or it may be made negatively charged through surface treatment of the sol-gel system or pH control. In particular, silicon oxide has a negative charge due to the presence of oxygen groups on its surface.

[0047] The functional groups of the functionalized graphene used in the graphene-silicon hybrid negative electrode active material can be amino (-NH2) or amide (-NHCO-). The zeta potential of this functionalized graphene is 40 mV or higher, preferably 50 mV or higher. As described above, if the zeta potential is 40 mV or higher, preferably 50 mV or higher, the functionalized graphene exhibits good dispersibility with the solvents used in the preparation of the graphene-silicon hybrid negative electrode active material and can self-adsorb onto the surface of silicon or silicon compounds via electrostatic bonding. For silicon oxide, in addition to electrostatic bonding, the functionalized graphene also adsorbs onto the surface of silicon or silicon compounds via hydrogen (H2) groups of the amino (-NH2) or amide (-NHCO-) ​​functional groups of the functionalized graphene of the present invention. + ) and oxygen (O) on the surface of silicon oxide - Hydrogen bonds are formed and further covalent bonds are formed through dehydration reactions, which can then strongly self-adsorb onto silicon oxide.

[0048] However, in order for the functionalized graphene of this invention to self-adsorb onto silicon or silicon compounds, the amount of functional groups bonded to the graphene must be controlled. Typically, graphene oxide is known to have an interlayer spacing of about 0.85 nm to about 1.25 nm, the specific value depending on the degree of oxidation; however, the functionalized graphene of this invention has an interlayer spacing of about 3.558 nm. (XRD 2θ 25°) to approximately 4.790 Interlayer spacing of (18.5°). If the interlayer spacing is less than approximately 3.558... This means that there is a lack or absence of functional groups capable of physicochemical bonding to achieve mixing; if the interlayer spacing is greater than approximately 4.790... If this is done, the physical properties of graphene will be impaired.

[0049] In graphene-silicon hybrid negative electrode active materials, the content of functionalized graphene is from 0.02 wt% to 5 wt% relative to silicon or silicon compounds. If the content of functionalized graphene relative to silicon or silicon compounds is less than 0.02 wt%, the functionalized graphene network is insufficient and the thickness is inadequate, leading to low initial efficiency and capacity retention of the graphene-silicon hybrid negative electrode active material. If the content of functionalized graphene relative to silicon or silicon compounds is greater than 5 wt%, the excessively formed graphene network and overly thick graphene coating layer will hinder the lithium-ion transport path, resulting in a decrease in charging capacity. Therefore, the content of functionalized graphene in the graphene-silicon hybrid negative electrode active material is preferably from 0.02 wt% to 5 wt% relative to silicon or silicon compounds, and in this case, the thickness of the functionalized graphene coating layer is from 1 nm to 5 nm.

[0050] In addition, graphene-silicon hybrid negative electrode active materials are prepared by mixing functionalized graphene colloids with silicon or silicon compound dispersions.

[0051] Functionalized graphene colloids are prepared using the following method. First, an aqueous solution of graphene oxide is prepared. The preparation of the aqueous solution of graphene oxide can be achieved by exfoliation of graphene oxide prepared using the Hummers method and modified methods, or commercially available graphene oxide. Then, functional groups are introduced onto the graphene oxide. Additives for forming functional groups are added to the aqueous solution of graphene oxide, stirred, and then ultrasonically dispersed to introduce functional groups into the graphene oxide, forming functionalized graphene. Specifically, about 50 to about 150 parts by weight of additives are added to about 100 parts by weight of the aqueous solution of graphene oxide, and stirred at about 90°C to about 120°C for about 12 hours to about 36 hours to form functionalized graphene. The functional groups to be introduced can be determined by the additives.

[0052] As an additive for forming amino or amide groups, organic monomers or polymers capable of forming amino or amide groups can be used. For example, additives selected from ethylenediamine, triethylamine, paraphenylenediamine, orthophenylenediamine, mesophenylenediamine, 3,3',4,4'-tetraaminobiphenyl, and 3,3',4,4'-tetraaminoterphenyl can be used. An organic monomer or polymer of at least one of the following groups: aaminoterphenyl, benzidine, 1,5-diaminonaphthalene, (E)-4,4'-(diazene-1,2-diyl)dianiline, ethylenediamine, 1,6-diaminohexane, 1,8-diaminooactne, and 4,4-oxidianiline.

[0053] Deionized water and ethanol can be mixed and used as solvents for the prepared functionalized graphene colloids; for example, 70 vol% to 90 vol% of deionized water and 10 vol% to 30 vol% of ethanol can be mixed and used. The content of the functionalized graphene included can be from 1 wt% to 3 wt%.

[0054] Because the functionalized graphene of this invention possesses the property of self-adsorption onto the surface of silicon or silicon compounds, a graphene-silicon hybrid negative electrode active material can be prepared simply by mixing a silicon or silicon compound dispersion with the prepared functionalized graphene colloid. Specifically, this step is characterized by the absence of dispersing agents or bonding agents that facilitate the bonding of silicon or silicon compounds. Next, the coprecipitate formed according to the graphene-silicon hybrid negative electrode active material dispersion is centrifuged and filtered, and the separated graphene-silicon hybrid negative electrode active material is washed with ethanol, then separated and dried. Finally, heat treatment can be performed at 150°C to 600°C under a nitrogen atmosphere to ultimately prepare the graphene-silicon hybrid negative electrode active material.

[0055] Table 1 below shows the results of the performance of graphene-silicon hybrid negative electrode active materials specified according to the heat treatment temperature.

[0056] [Table 1]

[0057]

[0058] Referring to Table 1, when the heat treatment temperature of the graphene-silicon hybrid negative electrode active material is below 80℃, there is a problem that the functionalized graphene cannot fully adhere, resulting in incomplete bonding. When the heat treatment temperature of the graphene-silicon hybrid negative electrode active material is above 150℃, the conductivity increases with the reduction of functional groups; however, if the heat treatment temperature is above 700℃, the silicon grain size increases, and byproducts such as SiC and SiN are generated. Therefore, the heat treatment temperature of the graphene-silicon hybrid negative electrode active material should be above 80℃ and below 700℃, preferably between 150℃ and 600℃.

[0059] adhesives

[0060] The adhesive 22 may be at least one selected from the group consisting of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and graphene mixed adhesives.

[0061] For graphene-based adhesives, such as Figure 4 As shown, the functionalized graphene 1 is bonded to polymer binders 222 and 223 via functional group 221 of the functionalized graphene 1. The functionalized graphene 1 bonded to the polymer binder has at least one functional group. For example, the functional group formed on the functionalized graphene bonded to the polymer binder may be at least one selected from the group consisting of silyl, amide, azide, anhydride, urea, urethane, amino, alkylene, epoxy, and mercapto groups.

[0062] The polymeric adhesive used in the graphene hybrid adhesive 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).

[0063] Table 2 below summarizes the types of polymer adhesives that can be bonded based on the functional groups of functionalized graphene.

[0064] [Table 2]

[0065]

[0066] Furthermore, to prevent the silicon negative electrode active material from delaminating from the current collector due to expansion and contraction during charging and discharging, the polymer adhesive should possess high adhesion and elasticity. Therefore, the graphene-based hybrid adhesive used in this invention may include a first polymer adhesive 222 for improving adhesion and a second polymer adhesive 223 for improving elasticity. For example, polyacrylic acid may be included as the first polymer adhesive, and polyurethane or styrene-butadiene rubber may be included as the second polymer adhesive.

[0067] For reference, the graphene coating layer formed by functionalized graphene in the graphene-silicon hybrid negative electrode active material has different functions and different positions than the functionalized graphene in the graphene hybrid binder.

[0068] The method for preparing functionalized graphene colloids is the same as that described in the description of graphene-silicon hybrid negative electrode active materials. However, the functional groups of the functionalized graphene used in the graphene hybrid binder can be different.

[0069] As an additive for forming silyl groups, organosilane compounds capable of forming silyl groups can be used, such as those derived from triethoxysilane, tetraethoxysilane, aminopropyltriethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, octadecyltrimethoxysilane, (3-methacryloxy)propyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropylmethyldimethoxysilane. The group consisting of methyldiethoxysilane and 3-glycidoxypropyltriethoxysilane, and the group consisting of 3-isocyanatepropyltriethoxysilane and 3-(trimethoxysilyl)propylsuccinic anhydride.As additives, organic monomers or polymers capable of forming amino or amide groups can be used. For example, those derived from ethylenediamine, triethylamine, paraphenylenediamine, orthophenylenediamine, mesophenylenediamine, 3,3',4,4'-tetraaminobiphenyl, and 3,3',4,4'-tetraaminoterphenyl can be used. Choose any one from the group consisting of minoterphenyl, benzidine, 1,5-diaminonaphthalene, (E)-4,4'-(diazene-1,2-diyl)dianiline, ethylenediamine, 1,6-diaminohexane, 1,8-diaminooactne, and 4,4-oxidianiline.

[0070] As additives for forming amino or amide groups, organic monomers or polymers capable of forming amino or amide groups can be used. For example, additives derived from ethylenediamine, triethylamine, paraphenylenediamine, orthophenylenediamine, mesophenylenediamine, 3,3',4,4'-tetraaminobiphenyl, and 3,3',4,4'-tetraaminoterphenyl can be used. Choose any one from the group consisting of tetraaminobiphenyl, benzidine, 1,5-diaminonaphthalene, (E)-4,4'-(diazene-1,2-diyl)dianiline, ethylenediamine, 1,6-diaminohexane, 1,8-diaminooactne, and 4,4-oxidianiline.

[0071] As an additive for forming an anhydride functional group, an organic monomer or polymer capable of forming an anhydride functional group can be used, for example, any one selected from the group consisting of maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, pyromellitic anhydride, naphthalic anhydride and trimellitic anhydride.

[0072] As an additive capable of forming an azide group, an organic monomer or polymer can be used, for example, any one selected from the group consisting of sodium azide, methyl azidoacetate, phenylazide, 2-azidoethanol, azidoacetic acid, and 2-azidoethylamine.

[0073] As an additive capable of forming urea or urethane groups, an organic monomer or polymer may be used, 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.

[0074] 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 may be used.

[0075] As an additive capable of forming epoxy groups, epoxy organic monomers or polymers can be used, 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.

[0076] As an additive capable of forming a thiol group, an organic monomer or polymer can be used, for example, any one selected from the group consisting of 2-mercaptoethanol, 1-thioglycerol, 3-mercaptopropanesulfonic acid, D-pentaerythritoltetra(3-mercaptopropionate), 4-mercaptophenol, Methyl 3-mercaptopropionate, 6-thioguanine, 1-hexanethiol, ethanethiol, and benzylmercaptan.

[0077] As a reference, the amount of functional groups introduced into functionalized graphene can be determined by adjusting the amount of additives, stirring temperature, and stirring time.

[0078] The functionalized graphene used in the graphene hybrid binder has an absolute zeta potential of 40 mV or greater, preferably 50 mV or greater. If the zeta potential is 40 mV or greater, preferably 50 mV or greater, the functionalized graphene exhibits good dispersibility with the solvents used in the preparation of the functionalized graphene colloid.

[0079] A graphene hybrid binder was prepared by adding polymer binder monomers to a functionalized graphene colloid. The addition of the polymer binder monomers was carried out in two steps. First, the functionalized graphene colloid was diluted 15 to 25 times with deionized water and then stirred. Next, less than 50 wt% of the polymer binder monomers to be added was added, and the mixture was reacted at 35°C to 45°C for 30 to 90 minutes. Then, the remaining polymer binder monomers were added. If the polymer binder monomers were not added in stages as described above, the functionalized graphene and the polymer binder monomers would not mix sufficiently. After the second addition of the polymer binder monomers, polymerization was carried out to attach the polymer binder monomers to the functional groups of the functionalized graphene. After the second introduction of the polymer binder monomers, the temperature was raised to 50°C to 70°C, and the polymerization reaction was carried out for 8 to 12 hours. In this step, the functional groups of the functionalized graphene molecularly bonded to the polymer binder. After the polymerization reaction was completed, the unreacted material was washed and homogenized to prepare the graphene hybrid binder (GHPB).

[0080] Furthermore, unlike the methods described above for preparing graphene hybrid binders, which use polymer binder monomers, polymer binders can be directly bonded to functionalized graphene. The method for directly bonding polymer binders to functionalized graphene includes: preparing a functionalized graphene colloid; adding a polymer binder to the functionalized graphene colloid; polymerizing the polymer binder onto the functional groups of the functionalized graphene; removing unreacted substances after the reaction is complete; and then performing solvent replacement and homogenization.

[0081] Since the preparation of functionalized graphene colloids is the same as the production method described above, its description is omitted here.

[0082] After preparing the functionalized graphene colloid, a polymer binder is added. The addition of the polymer binder is carried out in two steps. First, the functionalized graphene colloid is diluted. Specifically, the functionalized graphene colloid is diluted 15 to 25 times with deionized water and stirred. Then, 20 to 40 wt% of the total polymer binder is added, stirred at room temperature for 20 to 40 minutes, and then homogenized ultrasonically for 20 to 40 minutes. Afterward, the remaining polymer binder is added. If the polymer binder is not added in the above steps, the functionalized graphene and the polymer binder will not mix sufficiently. After the second addition of the polymer binder, the polymer binder is bonded to the functionalized graphene functional groups. After the second introduction of the polymer binder, the temperature is raised to 50°C to 70°C, and a polymerization reaction is carried out for 8 to 12 hours. In this step, the functional groups of the functionalized graphene and the polymer binder undergo molecular bonding. After the polymerization reaction is complete, the unreacted material is washed and homogenized to prepare the graphene hybrid binder (GHPB).

[0083] Figure 6 The FT-IR spectral analysis results of the graphene hybrid adhesive used in this invention are shown.

[0084] 1 wt% of silane-functionalized graphene was dispersed in a mixed solvent of deionized water and ethanol at a mass ratio of 8:2, and homogenized by ultrasonication for at least 30 minutes to prepare a graphene colloid. Then, 20 wt% of a polymer binder (PAA or PA / PU) was added, and the mixture was stirred at room temperature for 30 minutes, followed by ultrasonic homogenization for 30 minutes. The remaining polymer binder was then added. After all the polymer binder was added, the temperature was raised to 60°C, and the polymerization reaction was carried out for 10 hours. After the reaction, the mixture was centrifuged three times at 2000 rpm for 30 minutes each time. Unreacted material was then washed and vacuum filtered, and finally, the solvent was added. Subsequently, homogenization was performed for 30 minutes using ultrasound or a high-speed homogenizer to prepare a graphene hybrid binder (GHPB), and the prepared graphene hybrid binder was analyzed by FT-IR spectroscopy.

[0085] exist Figure 6 Among them, GHPB-1 (G Mixed PAA) is a sample with a functionalized graphene content of 0.01 wt%, a PAA polymer binder, and a simple mixture of functionalized graphene and polymer binder. GHPB-1 (G Mixed PAA) is a sample with a functionalized graphene content of 0.01 wt%, a PAA polymer binder, and functionalized graphene and polymer binder bonded together through functional groups. GHPB-2 (G Mixed PAA-PUD) is a sample with a functionalized graphene content of 0.03 wt%, a PAA and PU polymer binder, and functionalized graphene and polymer binder bonded together through functional groups. (Reference) Figure 6In the FT-IR spectra of samples containing a simple mixture of functionalized graphene and polymer binder, the characteristic peaks of functionalized graphene and PAA appeared mixed. Conversely, in the FT-IR spectra of GHPB-1 (G mixed PAA) and GHPB-2 (G mixed PAA-PUD), the characteristic peaks of the polymer binder (PAA, PU) were clearly observed, while the 1650 cm⁻¹ peak was clearly visible. -1 The characteristic peaks of the nearby functionalized graphene were weakened. This is because the functionalized graphene bonded to the polymer binder.

[0086] To more accurately confirm the bonding between functionalized graphene and the polymer binder, Raman spectroscopy analysis was performed. Figure 7 Raman spectral analysis results of the graphene hybrid binder are shown. Because unreacted substances are removed during the preparation of the graphene hybrid binder, if the functionalized graphene is not bonded to the graphene hybrid binder, the characteristic peaks of functionalized graphene will not be observed in the Raman spectral analysis results. However, as... Figure 7 As shown, the D peak (1350 cm⁻¹) that was not detected in Raman spectroscopy analysis can be confirmed to have been detected. -1 ) and G peak (1580 cm) -1 Therefore, combining Figure 6 The results and Figure 7 The results show that the graphene hybrid binder enables functionalized graphene and polymer binder to bond molecularly with each other through the functional groups of functionalized graphene.

[0087] Next, finished samples coated with GHPB-1 (G-mixed PAA) and finished samples coated with GHPB-2 (G-mixed PAA-PUD) were coated onto the negative electrode current collector (copper current collector) and subjected to cross-cutting tests. As a comparative example, cross-cutting tests were performed after the PAA was coated onto the negative electrode current collector.

[0088] The cross-cut test is a method for evaluating the adhesion of a coating. Multiple lines are drawn at regular intervals on the coating surface to form a grid pattern. Adhesive tape is then applied and removed to confirm the coating's adhesion. The state of the coating and the grid pattern after removing the tape are observed, and the adhesion is categorized into different levels. Test results are classified as follows: 5B is the highest adhesion level, indicating no coating has peeled off the grid pattern after the test; 4B indicates less than 5% of the coating has peeled off the grid pattern; 3B indicates 5% to 15% of the coating has peeled off the grid pattern; 2B indicates 15% to 35% of the coating has peeled off the grid pattern; 1B indicates 35% to 65% of the coating has peeled off the grid pattern; and 0B is the lowest adhesion level, indicating that more than 65% of the coating has peeled off the grid pattern.

[0089] PAA adhesive is known to have superior spot adhesion compared to SBR and CMC, which are widely used as adhesives for negative electrode materials. PAA adhesive also achieved a cross-cutting test result of 3B. In contrast, both graphene-modified adhesive samples achieved a cross-cutting test result of 5B, indicating that the coating did not peel off at all.

[0090] Table 3 also lists the effect of functionalized graphene content in the graphene hybrid adhesive on performance. PAA was used as the polymer adhesive, and each polymer adhesive was coated onto the copper current collector, followed by tape and cut tests. In the tape test, after 10 repeated applications of the tape, if the coating did not peel off, it was marked as satisfactory. (Excellent); if the coating peels off once, it is marked as... (Good); if the coating peels off 2 to 3 times, it is marked as bad. (Medium); all other cases are marked as X (Poor).

[0091] [Table 3]

[0092]

[0093] As shown in Table 3, it was confirmed that when the content of functionalized graphene in the graphene-based adhesive of the present invention is from 0.01 wt% to 0.5 wt%, excellent 5B grade tape test and scratch test results were observed, indicating excellent adhesion. However, if the content of functionalized graphene exceeds 0.5 wt%, the internal cohesive force of the functionalized graphene is greater than its adhesion to the adherend, resulting in decreased adhesion. Therefore, the content of functionalized graphene in the graphene-based adhesive of the present invention can be from 0.01 wt% to 0.5 wt%, preferably from 0.01 wt% to 0.3 wt%.

[0094] To analyze the impact of graphene-based hybrid binders on battery performance, two negative electrode active materials were prepared: one was a silicon-based negative electrode active material (particle size: 7 μm to 10 μm), and the other was a graphene-silicon hybrid negative electrode active material (particle size: 7 μm to 10 μm) coated with a functionalized graphene coating onto silicon metal via self-adsorption. The silicon metal particles with the functionalized graphene coating were prepared as follows: Functionalized graphene colloids (positively charged due to functionalization) and silicon particles with a central particle size of 7 μm to 10 μm were spontaneously adsorbed by ultrasonic dispersion in ethanol solvent for 10 minutes. The particles were then centrifuged or vacuum filtered, dried at 80 °C, and finally heat-treated at 300 °C in a nitrogen atmosphere to obtain the final product. The functionalized graphene content in the silicon metal particles with the functionalized graphene coating was 2 wt%. The preparation of silicon metal particles with functionalized graphene coating can be found in Korean Patent Publication No. 10-2023-0099837.

[0095] To evaluate the performance of the secondary battery, a negative electrode was fabricated by using prepared silicon metal particles or silicon metal particles with a functionalized graphene coating as the negative electrode active material.

[0096] Comparative Example 1 consists of 8 μm silicon metal particles, artificial graphite (Si:artificial graphite = 1:1), conductive agent (Super P Black), and polymer binder (SBR:CMC = 7:3) in a weight ratio of 40:40:10:10.

[0097] Example 1 consists of 8 μm silicon metal particles (Si), artificial graphite (Si:artificial graphite = 1:1), conductive material (Super P Black), and graphene hybrid binder (GHPB) in a weight ratio of 40:40:10:10. In this case, SBR and CMC bonded by functional groups are used as the graphene hybrid binder, and the content of functionalized graphene in the graphene hybrid binder is 0.05 wt%, and SBR and CMC are included in a weight ratio of 7:3.

[0098] Comparative Example 2 and Examples 2 to 4 were prepared by increasing the weight of the negative electrode active material (Si: artificial graphite = 1:1) by reducing the amount of graphene mixed binder.

[0099] Example 5 consists of an 8 μm graphene-silicon hybrid negative electrode active material (Si / G), artificial graphite (Si / G: artificial graphite = 1:1), a conductive material (Super P Black), and a graphene hybrid binder (GHPB) in a weight ratio of 40:40:10:10. In this case, SBR and CMC bonded by functional groups can be used as the graphene hybrid binder, wherein the content of functionalized graphene in the graphene hybrid binder is 0.05 wt%, and SBR and CMC are included in a weight ratio of 7:3.

[0100] Examples 6 to 9 were prepared by increasing the weight of the graphene-silicon hybrid negative electrode active material (Si: artificial graphite = 1:1) by reducing the amount of graphene-mixed binder.

[0101] Comparative Example 3 is the same as Comparative Example 1, except that the silicon metal particles are replaced with a graphene-silicon hybrid negative electrode active material (Si / G: artificial graphite = 1:1).

[0102] In addition, the content of functionalized graphene in the graphene-silicon hybrid negative electrode active material used in Comparative Examples 3 and Examples 5 to 9 is 2 wt%.

[0103] First, evaluate the properties of the half-cell.

[0104] The negative electrode is prepared as follows: The binder solution is diluted with deionized water, and the negative electrode active material and conductive material are added. The mixture is stirred in a homogenizer for 1 hour to prepare a slurry. The prepared slurry is coated onto a copper current collector with a thickness of approximately 15 μm to a thickness of approximately 75 μm. It is then dried at approximately 90°C for approximately 2 hours, extruded, and dried in a vacuum oven at approximately 120°C for approximately 4 hours to completely remove the solvent, thereby preparing the electrode.

[0105] A button half-cell (CR2032) was prepared using lithium metal foil as the positive electrode, polyethylene separator, electrolyte, and a pre-prepared negative electrode. In this case, the electrolyte was prepared and used by mixing a 1.2 M LiPF6 solution with a mixed solution of ethylene carbonate (EC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) at a weight ratio of 3:7 (EC / DEC / FEC = 2 / 6 / 2 (volume ratio)).

[0106] The performance of half-cells and full cells was evaluated using the IEC 62620 standard as follows: At room temperature (25±5℃), the cells were charged at a constant current rate of 0.1 C to 0.01 V, then charged at a constant voltage rate of 0.01 V (with a cutoff current of 0.01 C), and finally discharged at a constant current rate of 0.1 C to 1.5 V. The discharge capacity and initial charge-discharge efficiency under these conditions were calculated. Lifetime was evaluated at room temperature (25±5℃) by charging at a constant current rate of 0.1 C to 0.005 V, then charging at a constant voltage rate of 0.005 V (with a cutoff current of 0.005 C), and finally discharging at a constant current rate of 0.1 C to 1.5 V. This charge-discharge cycle was repeated 50 times to evaluate the charge-discharge performance.

[0107] In addition, the full battery underwent 500 charge-discharge cycle performance evaluations to compare its lifespan performance.

[0108] When manufacturing a full cell, the negative electrode is manufactured using the same method as for a half cell. The positive electrode is manufactured by adding NCM622 active material with a center particle size of 8 μm and conductive material (Super P Black) to a PVdF binder solution dissolved in NMP solvent, and then stirring using a homogenizer for 1 hour to prepare a slurry. In this case, the positive electrode material consists of NCM622, conductive material, and PVdF binder in a weight ratio of 80:10:10.

[0109] The prepared positive electrode slurry was coated onto an aluminum current collector with a thickness of about 20 μm to a thickness of about 75 μm, dried at about 120°C for about 2 hours, then extruded and dried in a vacuum oven at about 120°C for about 4 hours to completely remove the solvent, thereby preparing the positive electrode.

[0110] Full cells were assembled under the same conditions as those used to manufacture half cells, with the manufactured positive electrode used instead of lithium metal foil, and their lifetime performance was evaluated after 500 repeated charge-discharge cycles.

[0111] The performance of half-cell and full-cell batteries will be evaluated below. Initial efficiency and lifetime are calculated as follows.

[0112] Initial efficiency (%) = (First cycle discharge capacity / First cycle charge capacity) × 100

[0113] Lifespan (%) = (Discharge capacity in the nth cycle / Discharge capacity in the first cycle) × 100

[0114] Table 4 shows the results of performance evaluation of half-cells containing silicon metal particles as negative electrode active materials (Si: artificial graphite = 1:1).

[0115] [Table 4]

[0116]

[0117] In Comparative Example 1, the capacity gradually decreased starting from the 10th charge-discharge cycle, and by the 50th cycle, most of the silicon metal particles were destroyed, resulting in a significant decrease in capacity retention.

[0118] In Comparative Example 2, the initial discharge capacity was higher than that of Comparative Example 1 due to the reduction in binder, but the capacity decrease was also greater than that of Comparative Example 1. This is because the higher content of silicon metal particles resulted in a greater effect of volume expansion and contraction during charging and discharging.

[0119] It was confirmed that Examples 1 to 4 (wherein the graphene-based adhesive of the present invention is used as the adhesive) exhibited significantly higher capacity retention after 10 charge-discharge cycles than the comparative examples. In particular, Examples 1 to 3 maintained an extremely high capacity retention of approximately 75% even after 50 charge-discharge cycles. However, Example 4 (wherein the adhesive content is significantly reduced) showed a capacity decrease to 60.1% after 50 charge-discharge cycles. This is because the reduced adhesive content leads to decreased adhesion, which in turn causes current collector delamination due to the expansion and contraction behavior of silicon metal particles during charge and discharge; furthermore, the increased formation of the SEI layer results in irreversible capacity loss, ultimately leading to capacity loss.

[0120] Therefore, if the negative electrode material contains silicon metal particles, the content of graphene hybrid binder can be 7 wt% to 10 wt% of the total weight of the negative electrode material.

[0121] Table 5 shows the evaluation results of half-cells containing silicon metal particles (with functionalized graphene as a coating layer) as negative electrode active materials.

[0122] [Table 5]

[0123]

[0124]

[0125]

[0126] Comparing Examples 1 to 3 with Examples 5 to 7, if silicon metal particles with functionalized graphene coatings are used as negative electrode active materials, it can be seen that the initial efficiency of Examples 5 to 7 is higher than that of Examples 1 to 3, and the capacity retention is also significantly higher after 50 charge-discharge cycles.

[0127] In Examples 5 to 7, the functionalized graphene coating layer, which self-bonds to the silicon metal particles, primarily controls the expansion and contraction behavior of the silicon metal particles during charging and discharging, while the graphene-based adhesive, with its excellent adhesion and elasticity, secondarily controls the expansion and contraction behavior of the silicon metal particles during charging and discharging.

[0128] In particular, when silicon metal particles with functionalized graphene coatings are used as negative electrode active materials, excellent capacity retention is observed even when the content of graphene mixed binder is 6 wt% (Example 8).

[0129] However, in Example 9, the binder content was significantly reduced, and the capacity dropped to 89.5% after 50 charge-discharge cycles. This is because the reduced binder content led to decreased adhesion, which in turn caused current collector delamination due to the expansion and contraction behavior of silicon metal particles during charge and discharge; in addition, the thickening of the SEI layer led to irreversible capacity loss, ultimately resulting in capacity loss.

[0130] Furthermore, in Comparative Example 3, using a mixture of SBR and SMC instead of the graphene-based adhesive of the present invention as the binder, the capacity retention after 50 charge-discharge cycles was lower than that of Examples 5 to 8, but still reached 94.3%. This is because the functionalized graphene coating applied to the silicon metal particles effectively controlled the expansion and contraction behavior of the silicon metal particles during charge and discharge. However, as described later, the capacity retention of Comparative Example 3 decreased significantly after 100 charge-discharge cycles.

[0131] Table 6 shows the performance evaluation results of the full cell using silicon metal particles coated with functionalized graphene as the negative electrode active material. High-speed charge-discharge performance is expressed as discharge capacity at 2C rate / discharge capacity at 0.2C rate. (C: current rate)

[0132] [Table 6]

[0133]

[0134]

[0135] During the full-cell evaluation, Comparative Example 4 exhibited a rapid decline in performance due to the shrinkage and expansion of the silicone.

[0136] By introducing GHPB, Example 10 exhibits improved high-speed charge-discharge performance due to increased lifetime and electrical connectivity, but capacity retention is only below 70% at the 100th charge-discharge cycle.

[0137] In Examples 11 to 14, using silicon metal particles coated with functionalized graphene as the negative electrode active material and a graphene-based adhesive as the binder, it can be seen that even after 500 charge-discharge cycles, the capacity retention rate can still reach over 80%. Furthermore, due to the interaction between the functionalized graphene coating with silicon metal particles and the functionalized graphene contained in the graphene-based adhesive, its high-speed charge-discharge performance is also excellent, with a capacity retention rate exceeding 80%.

[0138] In other words, the lifespan is improved due to the control of the shrinkage-expansion of silicon metal particles with functionalized graphene coating and the enhanced adhesion between graphene-based adhesive and current collector; and the high-speed charge-discharge performance is significantly improved because a network is formed between silicon metal particles with functionalized graphene coating, graphene-based adhesive, and current collector through graphene.

[0139] In summary, if silicon metal particles with functionalized graphene coatings are used as the negative electrode active material, the content of graphene mixed binder can be 5 wt% to 10 wt%, preferably 6 wt% to 10 wt%, based on the total weight of the negative electrode material.

[0140] conductive materials

[0141] As conductive additive 23, at least one selected from the group consisting of carbon black and carbon nanotubes can be used.

[0142] Graphene layers with stabilized structure

[0143] like Figure 1 As shown, the structure-stabilized graphene layer 24 is characterized in that at least one layer is inserted into the negative electrode material layer. For example, the structure-stabilized graphene layer 24 can be formed to cover the uppermost surface of the negative electrode material layer, or it can be sandwiched between the negative electrode material layer and the current collector 10. The negative electrode material layer can also be sandwiched between the structure-stabilized graphene layers 24. Alternatively, as... Figure 8As shown, the negative electrode material layer and the structurally stabilized graphene layer 24 can be formed in multiple alternating layers. That is, the structurally stabilized graphene layer 24 can also be placed in the middle of the negative electrode material layer.

[0144] Figure 9 This is a schematic flowchart of a method for manufacturing a graphene network battery according to an embodiment of the present invention, the method including a process of forming a structurally stabilized graphene layer.

[0145] First, a functionalized graphene colloid is prepared. This functionalized graphene colloid can be prepared using the preparation method of functionalized graphene described in the above-mentioned silicon negative electrode active material or binder, and its zeta potential can be above +40 mV, preferably above +50 mV.

[0146] Next, a structurally stabilized graphene layer is formed on the current collector. Alternatively, a negative electrode material layer can be formed first on the current collector, followed by a structurally stabilized graphene layer. Alternatively, a structurally stabilized graphene layer can be formed first on the current collector, followed by a negative electrode material layer, and finally another structurally stabilized graphene layer formed on the negative electrode material layer. Furthermore, multiple layers can be formed by repeatedly forming negative electrode material layers and structurally stabilized graphene layers.

[0147] When forming a structurally stabilized graphene layer on the current collector, casting or electrophoretic deposition (EPD) can be used. The thickness of the structurally stabilized graphene layer formed on the current collector can range from 10 nm to 500 nm. To ensure electrical connectivity with the current collector and to form a graphene network, the structurally stabilized graphene layer formed on the current collector should be thin and uniform.

[0148] Electrophoretic deposition (EPD) can be used to form a structurally stabilized graphene layer on the negative electrode material layer. The thickness of the structurally stabilized graphene layer formed on the current collector can range from 50 nm to 3000 nm. The structurally stabilized graphene layer formed on the current collector is used to control the shrinkage-expansion of the silicon negative electrode active material and to form a graphene network.

[0149] The structure-stabilized graphene layer formed by casting or electrophoretic deposition can be dried.

[0150] Figure 10 This diagram illustrates the process of forming a structurally stable graphene layer through electrophoretic deposition.

[0151] like Figure 10As shown, a negative electrode current collector (a negative electrode current collector having a negative electrode material layer) is connected to the (-) terminal, and a counter electrode (e.g., SUS) is connected to the (+) terminal. The negative electrode current collector (a negative electrode current collector having a negative electrode material layer) and the counter electrode are immersed in diluted graphene colloid, and a voltage is applied. The functionalized graphene of the present invention carries a positive charge of +40 mV or higher, and therefore migrates to the negative electrode current collector (a negative electrode current collector having a negative electrode material layer) connected to the (-) terminal and is electrodeposited. Subsequently, a structurally stabilized graphene layer is formed by drying.

[0152] Figure 11 Scanning electron microscope (SEM) images of the current collector layer, the structure-stabilized graphene layer (bottom), the Si / G negative electrode material layer, and the structure-stabilized graphene layer (top) are shown.

[0153] A structurally stable graphene layer (bottom) was formed by electrophoretically depositing 0.05 wt.% functionalized graphene at a voltage of 20 V for 30 seconds; a structurally stable graphene layer (top) was formed by electrophoretically depositing 0.05 wt.% functionalized graphene at a voltage of 25 V for 60 seconds.

[0154] First, by comparing the current current collector layer with the structurally stabilized graphene layer (bottom), the unique wrinkled and folded shapes and edges of the graphene sheet can be seen.

[0155] Next, by comparing the structurally stabilized graphene layer (bottom) and the Si / G negative electrode material layer, it can be seen that the structurally stabilized graphene layer (bottom) is invisible due to the presence of the Si / G negative electrode material layer.

[0156] Finally, comparing the Si / G negative electrode material layer and the structurally stabilized graphene layer (capping layer), it can be seen that even after the formation of the structurally stabilized graphene layer, the roughness of the Si / G negative electrode material layer is still visible, as are the unique wrinkles and folds of the graphene sheet and its edges.

[0157] The negative electrode material layer can be formed by mixing negative electrode active materials, conductive materials and binders to prepare a negative electrode slurry, and then coating the slurry onto a current collector or a structurally stabilized graphene layer.

[0158] After the formation of the structurally stabilized graphene layer and the negative electrode material layer on the current collector, extrusion and drying are performed, and the battery is assembled. After battery assembly, electrolyte is injected, and then the battery is sealed. Known methods can be used from the formation of the structurally stabilized graphene layer and the negative electrode material layer on the current collector to the completion of battery assembly.

[0159] The physical properties and battery performance of the graphene layers stabilized by the structure were evaluated.

[0160] First, functionalized graphene colloids with a zeta potential above +40 mV and a concentration of 0.5 wt.% were prepared. The functionalized graphene was dispersed in a solvent of 50% ethanol and 50% IPA and homogenized by ultrasound for at least 30 minutes.

[0161] In some examples or comparative examples, 0.5 wt.% functionalized graphene colloid was cast onto a copper current collector with a thickness of 17 μm (wet film thickness 30 μm, rate 30 mm / s) and then dried at 60 °C for 1 hour to form a structurally stabilized graphene layer on the current collector.

[0162] In other examples or comparative examples, a graphene layer was formed on a copper current collector using electrophoretic deposition. A 0.5 wt.% functionalized graphene colloid was diluted 10-fold to obtain a 0.05 wt.% graphene colloid. The negative electrode current collector was connected to the (-) terminal, and the counter electrode (SUS) was connected to the (+) terminal. The negative electrode current collector and the counter electrode were immersed in the diluted graphene colloid, and electrophoretic deposition was performed for 1 minute with a voltage of 20 V applied. The mixture was then dried at 60 °C for 4 hours to form a structurally stable graphene layer on the current collector.

[0163] A negative electrode slurry is prepared by mixing the negative electrode active material, binder, and conductive material in a weight ratio of 80:10:10. According to examples or comparative examples, the negative electrode active material may be artificial graphite, silicon metal (Si), or a graphene-silicon hybrid negative electrode active material (Si / G); the binder may be an SBR-CMC (7:3) hybrid binder, a PAA binder, or a graphene hybrid binder (GHPB); and the conductive material may be carbon black or Super p Black.

[0164] The prepared slurry is coated onto a current collector or onto a structure-stabilized graphene layer formed on the current collector and dried to prepare the negative electrode of the example or comparative example.

[0165] A slurry prepared by mixing lithium oxide (LCO, NCM, NCMA, NCA, LMO or LFP), conductive material, PVDF binder and NMP solvent is coated onto the positive electrode current collector to prepare the positive electrode.

[0166] Polyethylene separators are used as separators.

[0167] The manufactured negative electrode, positive electrode, and separator are used to manufacture negative electrode half-cells or full cells, and their performance is evaluated.

[0168] First, the adhesion of the negative electrode material of the comparative and example to the current collector was evaluated using tape test and scribing test, and the results are shown in Table 7 below.

[0169] [Table 7]

[0170]

[0171] The cross-cut test is a method for evaluating the adhesion of a coating. Multiple lines are drawn at regular intervals on the coating surface to form a grid pattern. Adhesive tape is then applied and removed to confirm the coating's adhesion. The state of the coating and the grid pattern after removing the tape are observed, and the adhesion is categorized into different levels. Test results are classified as follows: 5B is the highest adhesion level, indicating no coating has peeled off the grid pattern after the test; 4B indicates less than 5% of the coating has peeled off the grid pattern; 3B indicates 5% to 15% of the coating has peeled off the grid pattern; 2B indicates 15% to 35% of the coating has peeled off the grid pattern; 1B indicates 35% to 65% of the coating has peeled off the grid pattern; and 0B is the lowest adhesion level, indicating that more than 65% of the coating has peeled off the grid pattern.

[0172] If the coating does not peel off after repeatedly applying and removing the tape 10 times, mark it as such. (Excellent); if the coating peels off once, it is marked as... (Good); if the coating peels off 2 to 3 times, it is marked as bad. (Medium); the rest are marked as X (Poor).

[0173] like Figure 4 As shown, when the structurally stabilized graphene layer is introduced into the negative electrode material layer, both the tape test and cross-section test results show excellent results. This indicates that the interlayer adhesion is significantly improved due to the introduction of the structurally stabilized graphene layer.

[0174] Next, we will evaluate the performance of the graphene network battery.

[0175] Comparative Examples 5 and 7 used negative electrode materials composed of 0.7 μm silicon particles, conductive material (Super PBlack), and binder (SBR:CMC = 7:3) in a weight ratio of 80:10:10.

[0176] Comparative Examples 6 and 8, as well as Examples 16 and 41, used negative electrode materials with the same composition as Comparative Examples 5 and 7, and used PAA with a molecular weight of 1,000,000 g / mol as a binder.

[0177] Examples 17 to 40, 42 and 43 employ a graphene-silicon hybrid negative electrode active material (Si / G) as the negative electrode material, wherein the Si / G contains 2.0 wt% functionalized graphene (relative to 0.7 μm silicon particles). Example 17 employs a binder composed of a 7:3 mixture of SBR and CMC, with the remainder consisting of a graphene hybrid binder (GHPB).

[0178] The negative electrode materials of Comparative Examples 5 to 8 and Examples 16 to 43 were prepared by further diluting the binder solution in deionized water, adding the negative electrode active material and the conductive material, and stirring the mixture for 1 hour using a homogenizer to prepare a negative electrode slurry.

[0179] The following describes the preparation of a structurally stabilized graphene layer (bottom) on the negative electrode current collector.

[0180] In Example 17, 0.5 wt% functionalized graphene colloid was coated onto a copper current collector with a thickness of 17 μm (wet film thickness 30 μm, rate 30 mm / s), and then dried at 60 °C for 1 hour to form a structurally stabilized graphene layer (bottom) on the current collector.

[0181] In Examples 19, 20, 21, 22 and 42, 0.1 wt% functionalized graphene colloid was coated under the same conditions, wherein structurally stabilized graphene layers (bottoms) of 5 nm, 10 nm, 20 nm and 40 nm were formed by varying the number of coatings.

[0182] In Examples 23 to 40 and 43, electrophoretic deposition was performed using 0.05 wt% functionalized graphene colloid. A copper current collector with a thickness of 17 μm was connected to the (+) end, and a counter electrode made of SUS material was connected to the (-) end. A voltage of 10 V to 30 V was applied for 10 seconds to 5 minutes. This formed structurally stabilized graphene layers (bottoms) of various thicknesses, which were then dried at 60 °C for 4 hours.

[0183] Subsequently, the prepared negative electrode slurry was coated onto a structurally stabilized graphene layer (substrate) to a thickness of 30 μm, dried at 90 °C for 2 hours, and then extruded. It was then dried in a vacuum oven at 120 °C for 4 hours to form the negative electrode material layer. In the comparative example and the example without a structurally stabilized graphene layer (substrate), the negative electrode slurry was coated onto a copper current collector with a thickness of 17 μm in the same manner and dried to form the negative electrode material layer.

[0184] In the example of a negative electrode material layer comprising a structurally stabilized graphene layer (capping layer), the negative electrode material layer is first formed, and then the structurally stabilized graphene layer (capping layer) is formed by an electrophoretic deposition process. Finally, it is dried at 60°C for 4 hours to finally prepare the negative electrode.

[0185] A coin cell (CR2032) was prepared using the prepared electrode as the negative electrode, lithium metal foil as the positive electrode, a polyethylene separator, and an electrolyte containing 1.2 M LiPF6 with an EC / DEC / FEC ratio of 2 / 6 / 2 (v / v). Charge-discharge cycles were performed at 0.24 mA (1 C / 20) over a voltage range of 0.2 V to 1.5 V; or by charging to 0.001 V with a constant current of 130 mA / g, followed by a constant voltage charge to 65 mA / g. Discharge was performed at a constant current of 130 mA / g to 1.5 V, and this process was repeated 100 times to evaluate charge-discharge performance. For the full cell, performance was evaluated after 500 charge-discharge cycles to compare its lifetime.

[0186] When manufacturing a full cell, the negative electrode is manufactured using the same method as a half cell. The positive electrode is manufactured by adding NCM622 active material with a central particle size of 8 μm and conductive material (Super P Black) to a PVdF binder solution dissolved in NMP solvent, and then stirring using a homogenizer for 1 hour to prepare a slurry. The positive electrode material consists of NCM622: conductive material: PVdF binder in a weight ratio of 80:10:10.

[0187] The prepared positive electrode paste was coated onto an aluminum current collector with a thickness of 20 μm to a thickness of 65 μm, dried at 120 °C for 2 hours, and then extruded. Finally, it was dried in a vacuum oven at 120 °C for 4 hours to completely remove the solvent.

[0188] The assembly conditions for the full cell were the same as for the half cell, except that a pre-prepared positive electrode was used instead of lithium metal foil. Lifetime performance was evaluated after 500 charge-discharge cycles, with lifetime (%) calculated as: (capacity at the nth cycle / capacity at the first cycle × 100). The evaluation results for high-speed charge-discharge performance were expressed as the discharge capacity at 2C divided by the discharge capacity at 0.2C.

[0189] Table 8 below shows the evaluation results of the half-cell properties of the example and comparative examples.

[0190] [Table 8]

[0191]

[0192] The initial discharge capacity of Comparative Example 6 and Examples 16 to 17 is approximately twice that of Examples 1 to 15 because artificial graphite was not mixed in as the negative electrode active material.

[0193] Comparative Example 5 had a lower initial discharge capacity and exhibited a rapid performance decline during lifetime evaluation due to the expansion and contraction of the silicon negative electrode material from the start of charge and discharge.

[0194] Comparative Example 6 exhibited normal initial discharge capacity due to the use of PAA adhesive with excellent adhesion. However, during the lifetime evaluation, the silicon negative electrode material delaminated with the current collector due to the expansion and contraction of the silicon negative electrode material from the start of charging and discharging, resulting in rapid performance degradation.

[0195] Example 16 exhibited normal initial discharge capacity and demonstrated excellent performance during the first 10 charge-discharge cycles in the lifetime evaluation, but its performance declined at the 50th charge-discharge cycle. This indicates that partial delamination occurred between the negative electrode active material and the current collector.

[0196] Furthermore, in Examples 17 and 18, the upper and lower surfaces of the negative electrode material layer were coated with structurally stabilized graphene layers, exhibiting excellent initial discharge capacity and excellent capacity retention after 50 charge-discharge cycles. This indicates that the structurally stabilized graphene layers on the upper and lower surfaces of the negative electrode material layer can effectively control the expansion and contraction of the silicon negative electrode material during charge and discharge.

[0197] Table 9 below shows the results of evaluating half-cell performance for each condition for the structurally stabilized graphene layer (bottom).

[0198] [Table 9]

[0199]

[0200]

[0201] Table 9 shows the results of evaluating the initial discharge capacity, high-rate performance, and lifetime performance based on the thickness of the structurally stabilized graphene layer (bottom). When the thickness of the graphene bottom layer is 5 nm, the formation of the graphene network is insufficient, resulting in a capacity retention of 81.4% at the 100th charge-discharge cycle. Although this is not absolutely bad, the decrease in capacity retention is greater than in other examples.

[0202] On the other hand, when the thickness of the structure-stabilized graphene layer (bottom) is too thick, reaching more than 600 nm, the electrical path between the current collector and the active material is restricted, resulting in a decrease in high-rate performance.

[0203] Considering the above, the thickness of the structure-stabilized graphene layer (bottom) can be from 10 nm to 500 nm, preferably from 10 nm to 100 nm.

[0204] Table 10 below shows the results of evaluating half-cell performance for each condition for the structurally stabilized graphene layer (cap).

[0205] [Table 10]

[0206]

[0207]

[0208] Table 10 shows the evaluation results of initial discharge capacity, high-rate performance, and cycle life performance based on the thickness of the structurally stabilized graphene layer (cap). When the thickness of the structurally stabilized graphene layer (cap) is 40 nm, the graphene cannot adequately control the shrinkage and expansion of the silicon negative electrode material, resulting in a capacity retention of 78.4% after 100 charge-discharge cycles. While not absolutely bad, the decrease in capacity retention is indeed greater than in other examples.

[0209] On the other hand, when the thickness of the structure-stabilized graphene layer (capping layer) is too thick, reaching more than 4000 nm, the movement path of lithium ions between the electrolyte and the active material is restricted, thus resulting in a decrease in initial discharge capacity, a decrease in high-rate performance, and a reduction in lifetime performance.

[0210] Considering the above, the thickness of the structurally stabilized graphene layer (cap) can be from 50 nm to 3000 nm, preferably from 50 nm to 500 nm.

[0211] Table 11 below shows the results of evaluating the full-cell performance of graphene network batteries.

[0212] [Table 11]

[0213]

[0214] Comparative Examples 7 and 8 exhibited a rapid decline in performance during the full-cell evaluation due to the expansion and contraction of the silicon negative electrode material.

[0215] Compared to the comparative examples, Example 41 exhibits relatively better lifetime performance, but its capacity continues to decrease as charge and discharge continue. This indicates that during long-life evaluation, the silicon negative electrode material gradually delaminates from the current collector, resulting in a greater decrease in its capacity retention compared to other examples.

[0216] Furthermore, in Examples 42 and 43, the application of structurally stabilized graphene layers (bottom and top) also demonstrated excellent capacity retention after up to 500 charge-discharge cycles during full-cell evaluation. This indicates that the structurally stabilized graphene layers (bottom and top) can effectively control the contraction-expansion of the silicon negative electrode material during charge-discharge processes.

[0217] Considering the above, it can be seen that the three-dimensional graphene network negative electrode structure (which introduces a structurally stabilized graphene layer into the negative electrode material) exhibits significant performance in improving stability and lifetime during charge-discharge cycles.

[0218] The scope of protection of this invention is not limited to the description and representation of the embodiments explicitly described above. Furthermore, it should be reiterated that even if significant changes or substitutions occur in the technical field to which this invention pertains, the scope of protection of this invention shall not be limited thereto.

[0219] This patent application was prepared and filed with the support of the following Korean National Research and Development Program.

[0220] Project ID: 20014475

[0221] Ministry: Department of Trade, Industry and Energy Research

[0222] Management Agency: Korea Institute for Industrial Technology Evaluation

[0223] Research Project Title: Technology Development of Nano-Integrated Innovative Products

[0224] Research Project Title: Development of Anti-fog Headlight Technology Based on Nanocomposite Materials with a Water Generation Area of ​​Less Than or Equal to 10%

[0225] Contribution rate: 1 / 4

[0226] Lead organization: Best Graphene Co., Ltd.

[0227] Study period: April 1, 2021 to December 31, 2025 (4 years and 9 months in total)

[0228] Project ID: RS-2023-00303772

[0229] Ministry: Ministry of Small and Medium Enterprises and Entrepreneurship

[0230] Research Management Organization: Technology Information Promotion Organization for Small and Medium Enterprises

[0231] Research Project Title: Technological Innovation Development (R&D) for Small and Medium-sized Enterprises

[0232] Research Title: Application Research of Functionalized Graphene Hybrid Silicon Technology in the Commercialization of High-Capacity Silicon Hybrid Negative Electrode Materials

[0233] Contribution rate: 1 / 4

[0234] Lead organization: Best Graphene Co., Ltd.

[0235] Study period: October 20, 2023 to October 19, 2026 (36 months in total)

[0236] Project ID: RS-2024-00419914

[0237] Ministry: Ministry of Trade, Industry and Energy

[0238] Research Management Institution: Korea Institute of Industrial Technology Planning and Evaluation

[0239] Research Project Title: Electronic Component Technology Development

[0240] Research Task Title: Development of High-Capacity MLCC Electric Vehicle Product Technology Based on Graphene-BaTiO3 Composite Media

[0241] Contribution rate: 1 / 4

[0242] Lead organization: Best Graphene Co., Ltd.

[0243] Study period: April 1, 2024 to December 31, 2027 (3 years and 9 months in total)

[0244] Project ID: RS-2024-00431451

[0245] Ministry: Ministry of Trade, Industry and Energy

[0246] Research Management Institution: Korea Institute of Industrial Technology Planning and Evaluation

[0247] Research Project Title: Materials and Components Technology Development Project

[0248] Research Task Title: Development of High-Durability, High-Stability Conductive Microfiber Composite Material Technology

[0249] Contribution rate: 1 / 4

[0250] Lead organization: Best Graphene Co., Ltd.

[0251] Study period: July 1, 2024 to December 31, 2027 (3 years and 6 months in total).

Claims

1. A graphene network battery, the graphene network battery comprising: A positive electrode current collector, a positive electrode mixture, a separator, a negative electrode mixture, and a negative electrode current collector, wherein the negative electrode mixture comprises: a negative electrode material layer formed on the upper part of the negative electrode current collector and comprising a silicon negative electrode active material and a binder; and a structure-stabilized graphene layer formed on at least one surface of the negative electrode material layer.

2. The graphene network battery of claim 1, wherein, The structurally stabilized graphene layer is formed on the uppermost part of the negative electrode material layer.

3. The graphene network battery of claim 2, wherein, The structure-stabilized graphene layer has a thickness of 50 nm to 3000 nm.

4. The graphene network battery according to claim 1, wherein, The structure-stabilized graphene layer is sandwiched between the negative electrode material layer and the current collector.

5. The graphene network battery according to claim 4, wherein, The structure-stabilized graphene layer has a thickness of 10 nm to 500 nm.

6. The graphene network battery according to claim 1, wherein, The negative electrode material layer and the structure-stabilized graphene layer are stacked alternately.

7. The graphene network battery according to claim 1, wherein, The adhesive is selected from at least one of the group consisting of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and graphene mixed adhesives.

8. The graphene network battery according to claim 7, wherein, When the adhesive is a graphene hybrid adhesive, the graphene hybrid adhesive includes functionalized graphene having functional groups and a polymer adhesive bonded to the functionalized graphene through functional groups.

9. The graphene network battery according to claim 1, wherein, The silicon negative electrode material is selected from at least one material chosen from the group consisting of silicon, silicon compounds, and graphene-silicon hybrid negative electrode active materials.

10. The graphene network battery according to claim 1, wherein, When the silicon negative electrode material is a graphene-silicon hybrid negative electrode active material, the graphene-silicon hybrid negative electrode active material includes a graphene coating layer formed by self-adsorption of functionalized graphene with functional groups onto the surface of silicon or a silicon compound.

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