Graphene network battery

Abstract

The present invention relates to a graphene network battery comprising: a positive electrode current collector; a positive electrode composite; a separator; a negative electrode composite; and a negative electrode current collector, wherein the negative electrode composite includes: a negative electrode material layer formed on the negative electrode current collector and including a silicon negative electrode active material and a binder; and a structural-stabilizing graphene layer formed on at least one surface of the negative electrode material layer.

Description

Graphene network battery

[0001] The present invention relates to a graphene network battery.

[0002] Lithium-ion batteries are devices that store and utilize energy through charging and discharging processes involving the repeated insertion and extraction of lithium ions. They have established themselves as essential power sources in various application fields, ranging from portable electronic devices to medium- and large-scale devices such as electric vehicles. As these batteries enable miniaturization and lightweight design while offering high capacity, high energy density, stability, and a long lifespan, the development of technologies with further enhanced performance is essential.

[0003] The performance of a lithium-ion battery depends on its components, such as the anode, cathode, separator, and electrolyte, and among these, the anode plays a key role in determining battery capacity. Currently, carbon-based materials are mainly used as anode active materials, but research on new high-capacity anode active materials is continuously being conducted to achieve performance exceeding the theoretical capacity (372 mAh / g). In particular, silicon is a material with a theoretical capacity of 4,200 mAh / g and is attracting attention as a next-generation anode active material to replace existing carbon-based anode active materials.

[0004] However, silicon anode active materials undergo a volume change of more than 300% during the charge and discharge process, which leads to pulverization of the anode active material and electrical separation from the current collector. This electrical separation drastically reduces the battery's capacity retention rate, acting as a major factor that makes the commercialization of silicon anode active materials difficult. To address this, technologies such as coating silicon with a carbon layer or fabricating it in a composite form have been proposed, but they have not yet reached a level where they can be practically commercialized.

[0005] Currently, commercial lithium-ion batteries achieve an energy density of approximately 300 Wh / kg by adding a small amount (less than 5%) of materials such as silicon oxide (SiOx) or silicon-carbon composites (Si / C) to the negative electrode plates. However, to meet the high energy density required for large devices such as electric vehicles, new designs and technological developments are needed to improve the capacity and stability of silicon negative electrode active materials. In particular, innovative approaches are required to address issues such as the initial efficiency degradation, volume change, and electrical delamination of silicon negative electrode active materials.

[0006] Graphene is attracting attention as a new material to solve these problems. As the thinnest material currently in existence, graphene possesses excellent physical properties such as current density, strength, thermal conductivity, and electron mobility; however, it has limitations in that its strong self-cohesion makes it difficult to disperse within polymers or solvents.

[0007] One objective of the present invention is to provide a graphene network battery capable of effectively controlling the volume change (shrinkage-expansion) of the silicon anode active material and preventing delamination of the silicon anode layer by introducing a structure-stabilized graphene layer on the cathode side, thereby increasing the capacity retention rate of the battery and extending the charge-discharge life.

[0008] Another objective of the present invention is to reduce energy consumption and greenhouse gas emissions generated in existing recycling processes by applying a newly proposed low-temperature heat treatment technology, and to simultaneously achieve economic efficiency and environmental sustainability.

[0009] Meanwhile, other unspecified objects of the present invention will be further considered to the extent that they can be easily inferred from the following detailed description and effects.

[0010] To solve the problem described above, the following solution is proposed.

[0011] A graphene network battery according to one embodiment of the present invention comprises a positive current collector, a positive composite, a separator, a negative composite, and a negative current collector, wherein the negative composite is formed on the upper portion of the negative current collector and comprises a negative electrode material layer comprising a silicon negative electrode active material and a binder; and a structure-stabilizing graphene layer formed on at least one surface of the negative electrode material layer.

[0012] In one embodiment, the structure-stabilizing graphene layer may be characterized by being formed on the uppermost portion of the cathode layer.

[0013] In one embodiment, the thickness of the structure-stabilizing graphene layer may be 50 to 3,000 nm.

[0014] In one embodiment, the structure-stabilizing graphene layer may be characterized as being interposed between the cathode layer and the current collector.

[0015] In one embodiment, the thickness of the structure-stabilizing graphene layer may be 10 to 500 nm.

[0016] In one embodiment, the cathode material layer and the structure-stabilizing graphene layer may be stacked alternately.

[0017] In one embodiment, the binder may be characterized as being at least one selected from the group consisting of styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PAA), and graphene hybrid binder.

[0018] In one embodiment, when the binder is a graphene hybrid binder, the graphene hybrid binder may be characterized by comprising: functionalized graphene having functional groups formed thereon; and a polymer binder bonded to the functionalized graphene by the functional groups.

[0019] In one embodiment, the silicon anode material may be characterized as being at least one selected from the group consisting of silicon, silicon compounds, and graphene-silicon hybrid anode active materials.

[0020] In one embodiment, when the silicon anode material is a graphene-silicon hybrid anode active material, the graphene-silicon hybrid anode active material may be characterized by comprising a graphene coating layer formed by self-adsorption of functionalized graphene having functional groups on the surface of silicon or a silicon compound.

[0021] A graphene network battery according to one embodiment of the present invention has a three-dimensional structure in which a structure-stabilized graphene layer and a silicon anode layer are stacked together, and the structure-stabilized graphene layer effectively controls the volume change (shrinkage-expansion) of the silicon anode active material and prevents delamination of the silicon anode layer due to the volume change of the silicon anode material, thereby increasing the capacity retention rate of the battery and extending the charge-discharge life.

[0022] In addition, a graphene network battery according to one embodiment of the present invention comprises at least one of a silicon-graphene hybrid negative electrode active material in which functionalized graphene is self-adsorbed or a binder in which functionalized graphene is bonded by functional groups, thereby forming a three-dimensional graphene network between a structure-stabilized graphene layer and a silicon negative electrode layer, and thereby more effectively controlling the volume change (shrinkage-expansion) of the silicon negative electrode active material.

[0023] Meanwhile, it should be added that even if an effect is not explicitly mentioned here, the effects described in the following specification and the provisional effects expected by the technical features of the present invention are treated as described in the specification of the present invention.

[0024] FIG. 1 is a schematic diagram of a graphene network battery according to one embodiment of the present invention.

[0025] Figure 2 is a diagram illustrating the self-adsorption of functionalized graphene in a graphene-silicon hybrid cathode active material.

[0026] Figure 3 is a diagram illustrating the functional groups formed on the functionalized graphene of the present invention.

[0027] Figure 4 is a diagram showing the structure of a graphene hybrid binder.

[0028] Figure 6 shows the FT-IR spectrum analysis results of the graphene hybrid binder.

[0029] Figure 7 shows the results of the Raman spectrum analysis of the graphene hybrid binder.

[0030] Figure 8 is a diagram illustrating a structure formed in multiple layers by alternating cathode layers and structure-stabilizing graphene layers.

[0031] Figure 9 is a flowchart according to the manufacturing method of a graphene network battery.

[0032] Figure 10 is a diagram illustrating the process of forming a structure-stabilized graphene layer through an electrophoretic electrodeposition process.

[0033] Figure 11 is a Scanning Electron Microscope (SEM) image of the current collector layer, the structure-stabilized graphene layer (Bottom), the Si / G cathode layer, and the structure-stabilized graphene layer (Cover).

[0034] It should be noted that the attached drawings are provided as examples for reference to help understand the technical concept of the present invention, and the scope of the rights of the present invention is not limited by them.

[0035] Hereinafter, with reference to the drawings, we will examine the configuration of the present invention as guided by various embodiments thereof and the effects derived therefrom. In describing the present invention, detailed descriptions of related known functions are omitted if they are deemed obvious to a person skilled in the art and could unnecessarily obscure the essence of the invention.

[0036] FIG. 1 is a schematic diagram of a graphene network battery according to one embodiment of the present invention.

[0037] As shown in FIG. 1, a graphene network battery according to one embodiment of the present invention comprises a positive current collector, a positive composite, a separator, a negative composite, and a negative current collector.

[0038] The negative electrode side of a graphene network battery according to one embodiment of the present invention is characterized.

[0039] A cathode composite (20) is formed on one side of a cathode current collector (10). The cathode composite (20) comprises a cathode layer composed of a silicon cathode active material (21), a binder (22), and a conductive material (23), and a structure-stabilizing graphene layer (24) formed on at least one side of the cathode layer.

[0040] Below, we will examine each component in more detail.

[0041]

[0042] silicon negative electrode active material

[0043] As a silicon negative electrode active material (2), at least one selected from the group consisting of silicon, silicon compounds, and graphene-silicon hybrid negative electrode active materials may be used. As a silicon compound, at least one of silicon oxide, silicon nitride, and silicon carbon composite may be used. A graphene-silicon hybrid negative electrode active material means that functionalized graphene is self-adsorbed onto silicon or a silicon compound by the functional groups of the functionalized graphene, as shown in FIG. 2. The functionalized graphene (1) referred to in the present invention means that functional groups are formed on graphene, as shown in FIG. 3, and the functional groups may vary depending on the target to which the functionalized graphene is applied.

[0044] The reason the functionalized graphene of the present invention self-adsorbs to silicon or silicon compounds is that the functionalized graphene interacts with silicon or silicon compounds through electrostatic bonding, hydrogen bonding, and / or covalent bonding. For example, since functionalized graphene has a (+) charge, it electrostatically bonds to the surface of silicon or silicon compounds that have a (-) charge. In this case, the surface of the silicon or silicon compound may have a (-) charge, or surface treatment or pH adjustment of the sol-gel system may be performed to make it have a (-) charge. In particular, in the case of silicon oxide, it acquires a (-) charge due to oxygen groups on the surface.

[0045] The functional groups of the functionalized graphene used in the graphene-silicon hybrid anode active material may be amine groups (-NH2) or amide groups (-NHCO-). The zeta potential of the functionalized graphene is 40 mV or higher, preferably 50 mV or higher. When the zeta potential is 40 mV or higher, preferably 50 mV or higher, the functionalized graphene exhibits high dispersibility in the solvent used during the process of manufacturing the graphene-silicon hybrid anode active material and self-adsorbs onto the surface of silicon or silicon compounds through electrostatic bonding. In the case of silicon oxide, in addition to electrostatic bonding, the hydrogen (H) of the amine group (-NH2) or amide group (-NHCO-), which is the functional group of the functionalized graphene of the present invention + ) and oxygen (O on the silicon oxide surface - It forms hydrogen bonds with ) and further forms covalent bonds through dehydration reactions, allowing for even stronger self-adsorption.

[0046] However, in order for the functionalized graphene of the present invention to self-adsorb onto silicon or silicon compounds, it is necessary to control the amount of functional groups bonded to the graphene. Generally, oxidized graphene is known to have an interplanar distance of 0.85 to 1.25 nm depending on the degree of oxidation, but the functionalized graphene of the present invention has an interplanar distance of 3.558 (XRD 2θ degree 25˚) to 4.790 Å (18.5˚). If the interplanar distance is less than 3.558 Å, it means that there is a lack or absence of functional groups capable of forming physicochemical bonds to achieve hybridization, and if the interplanar distance exceeds 4.790 Å, there is a problem of deterioration in the physical properties of the graphene.

[0047] The content of functionalized graphene in the graphene-silicon hybrid anode active material may be 0.02 to 5 wt% relative to silicon or a silicon compound. If the content of functionalized graphene relative to silicon or a silicon compound is less than 0.02 wt%, there is a problem that the initial efficiency and capacity retention rate of the manufactured graphene-silicon hybrid anode active material are low because the functionalized graphene network is insufficient and does not form a sufficient thickness. If the content of functionalized graphene relative to silicon or a silicon compound exceeds 5 wt%, the formation of an excessive graphene network and a graphene coating layer thickness greater than necessary blocks the path of lithium ions, resulting in a decrease in charge capacity. Therefore, it is preferable that the content of functionalized graphene in the graphene-silicon hybrid anode active material be 0.02 to 5 wt% relative to silicon or a silicon compound, and the thickness of the coating layer by the functionalized graphene is 1 to 5 nm.

[0048] Meanwhile, the fabrication of the graphene-silicon hybrid cathode active material is carried out by mixing functionalized graphene colloid with a silicon or silicon compound dispersion.

[0049] Functionalized graphene colloid is prepared by the following method. An aqueous solution of graphene oxide is prepared. The aqueous solution of graphene oxide can be prepared by producing graphite oxide using the Hummers and Improved Methods or by performing an exfoliation process using commercially available graphite oxide. Next, functional groups are imparted to the graphene oxide. An additive for forming functional groups is added to the aqueous solution of graphene oxide, stirred, and then ultrasonically dispersed to impart functional groups to the graphene oxide, thereby forming functionalized graphene. Specifically, 50 to 150 parts by weight of the additive are added to 100 parts by weight of the aqueous solution of graphene oxide, and the mixture is stirred at 90 to 120°C for 12 to 36 hours to form functionalized graphene. The functional groups to be imparted to the graphene can be determined by the additive.

[0050] As an additive for forming an amine or amide group, organic monomers or polymers capable of forming an amine or amide group may 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 may be used.

[0051] Deionized water and ethanol can be mixed and used as the solvent for the manufactured functionalized graphene colloid; for example, 70 to 90 vol% of deionized water and 10 to 30 vol% of ethanol can be mixed and used. The content of functionalized graphene included therein can be 1 to 3 wt%.

[0052] Since the functionalized graphene of the present invention has the property of self-adsorbing onto the surface of silicon or silicon compounds, a graphene-silicon hybrid negative electrode active material is produced simply by mixing a silicon or silicon compound dispersion with the prepared functionalized graphene colloid. In particular, this step is characterized by not using a dispersion aid or a binding aid that can help silicon or silicon compounds bind to each other. Next, the co-precipitate resulting from the formation of 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, separated, and dried. Then, the graphene-silicon hybrid negative electrode active material can be finally completed by heat treatment at 150 to 600 °C in a nitrogen atmosphere.

[0053] Table 1 below shows the results of characterizing the graphene-silicon hybrid anode active material according to the heat treatment temperature.

[0054]

[0055] G content relative to Si (wt.%) Final heat treatment temperature (°C, N₂) Graphene bonding strength evaluation Powder resistivity (Ω·m) Si Crystal Size (nm) Detection of SiC, SiN (XRD) 0--10 12 Abnormal 3.5 Not Detected 380 Partial Detachment 8.5 × 10 4 3.5 Not Detected 3150 No Detachment 9.7 × 10 2 3.5 Undetected 3300 No Delay 7.2 × 10 1 3.6 Not Detected 3600 No Delay 4.5 × 10 0 3.7 Undetected 3700 No Delay 1.3 × 10 0 10.2 Detected 3900 No Delay 6.3 × 10 -2 25.6 detection

[0056] Referring to Table 1, when the heat treatment temperature of the graphene-silicon hybrid anode active material is 80 degrees or lower, there is a problem of insufficient bonding strength because the functionalized graphene is not fully adhered. When the heat treatment temperature of the graphene-silicon hybrid anode active material is 150 degrees or higher, the electrical conductivity is improved as the functional groups are reduced, but when the heat treatment temperature is 700 degrees or higher, there is a problem of silicon crystal size growth and the formation of by-products such as SiC and SiN. Therefore, the heat treatment temperature of the graphene-silicon hybrid anode active material can be performed at a temperature greater than 80 degrees and less than 700 degrees, preferably between 150 and 600 degrees.

[0057]

[0058] bookbinder

[0059] The binder (22) may be at least one selected from the group consisting of styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PAA), and graphene hybrid binder.

[0060] In the case of a graphene hybrid binder, as shown in FIG. 4, the functionalized graphene (1) and the polymer binder (222, 223) are bonded by the functional group (221) of the functionalized graphene (1). The functionalized graphene (1) bonded to the polymer binder has at least one functional group formed thereon. 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 a silane group, an amide group, an azide group, an hydride group, a urea group, a urethane group, an amine group, an alkylene group, an epoxide group, and a mercapto group.

[0061] The polymer binder used in the graphene hybrid binder 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 carboxymethylcellulose (CMC).

[0062] Table 2 below summarizes the types of polymer binders that can be bonded according to the functional groups of functionalized graphene.

[0063]

[0064] No. Functional Group Polymer Binder 1 Silane PAA, PI, PEI, PU 2 Amide, Amine PAA, PI, PEI, PU 3 Anhydride, Azide PAA, SBR, CMC 4 Urea, Urethane PAA, PEI, PEI 5 Alkylene PAA, PEI, SBR, CMC 6 Epoxide, Mercapto PAA, PEI, SBR, CMC

[0065] Meanwhile, in order to prevent delamination from the current collector caused by expansion and contraction during the charging and discharging process of the silicon negative electrode active material, the adhesive strength and elasticity of the polymer binder must be high together. To this end, the graphene hybrid binder used in the present invention may include a first polymer binder (222) to improve adhesive strength and a second polymer binder (223) to improve elasticity. For example, the first polymer binder may include polyacrylic acid, and the second polymer may include urethane or styrene butadiene rubber.

[0066] For reference, the graphene coating layer formed by functionalized graphene in the aforementioned graphene-silicon hybrid anode active material and the functionalized graphene in the graphene hybrid binder differ in their formation location and role.

[0067] The method for preparing functionalized graphene colloids is the same as the method introduced when explaining graphene-silicon hybrid anode active materials. However, the functional groups of the functionalized graphene used in graphene hybrid binders may differ.

[0068] As an additive for forming a silane group, an organic silane compound capable of forming a silane group may 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-isocyanate propyltriethoxysilane and 3-(Trimethoxysilyl)propylsuccinic anhydride may be used.As additives, organic monomers or polymers capable of forming amine or amide groups may 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 may be used.

[0069] As an additive for forming an amine or amide group, organic monomers or polymers capable of forming an amine or amide group may 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 may be used.

[0070] As an additive for forming an anhydride (anhydrous) functional group, an organic monomer or polymer capable of forming an anhydride functional group may 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 may be used.

[0071] Organic monomers or polymers can be used as additives 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.

[0072] Organic monomers or polymers may be used as additives capable of forming urea groups or urethane groups, and, for example, any one selected from the group consisting of isocyanate, polyol, ethoxysilane, polyethylene glycol, tolylene diisocyanate, methylene diphenyl diisocyanate, polytetramethylene ether glycol, and poly-caprolactone may be used.

[0073] 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.

[0074] As an additive capable of forming an epoxide group, an epoxidized organic monomer or polymer may 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 may be used.

[0075] Organic monomers or polymers can be used as additives capable of forming a mercapto group, 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.

[0076] For reference, the amount of functional groups introduced into functionalized graphene can be determined by adjusting the amount of additive, stirring temperature, and stirring time.

[0077] The zeta potential of the functionalized graphene used in the graphene hybrid binder has an absolute value of 40 mV or higher, preferably 50 mV or higher. When the zeta potential is 40 mV or higher, preferably 50 mV or higher, the functionalized graphene has high dispersibility in the solvent used in the process of preparing the functionalized graphene colloid.

[0078] A polymer binder monomer is added to the functionalized graphene colloid prepared to manufacture a graphene hybrid binder. The step of adding the polymer binder monomer to the functionalized graphene colloid is performed in two stages. First, the functionalized graphene colloid is diluted. That is, the functionalized graphene colloid is diluted 15 to 25 times in deionized water and then 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 divided manner, the functionalized graphene and the polymer binder monomer will not mix well. 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 raised to 50 to 70°C, and the polymerization reaction is carried out for 8 to 12 hours. At this stage, the functional groups of the functionalized graphene and the polymer binder are molecularly bonded. After the polymerization reaction is completed, the unreacted material is washed and homogenized to produce a graphene hybrid binder (GHPB).

[0079] Meanwhile, unlike the method for manufacturing the graphene hybrid binder described above which uses a polymer binder monomer, it is also possible to directly bind a polymer binder to functionalized graphene. The method of directly binding a polymer binder to functionalized graphene includes the steps of preparing a functionalized graphene colloid, adding a polymer binder to the functionalized graphene colloid, binding the polymer binder to the functional groups of the functionalized graphene, and removing unreacted material after the reaction is finished, and replacing the solvent and homogenizing.

[0080] The step of preparing the functionalized graphene colloid is the same as the manufacturing method described above, so it is omitted here.

[0081] 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 to the functionalized graphene colloid is performed in two stages. First, the functionalized graphene colloid is diluted. That is, the functionalized graphene colloid is diluted 15 to 25 times in deionized water and then stirred. Next, only 20 to 40 wt% of the total mass of the polymer binder to be added is added in the first stage, stirred at room temperature for 20 to 40 minutes, and then homogenized by ultrasound for 20 to 40 minutes. Then, the remaining polymer binder is added in the second stage. If the polymer binder is not added in stages in this manner, the functionalized graphene and the polymer binder will not mix well. After the second addition of the polymer binder, the step of binding the polymer binder to the functional groups of the functionalized graphene is performed. After the second addition of the polymer binder, the temperature is raised to 50 to 70 ℃, and the polymerization reaction is carried out for 8 to 12 hours. At this stage, the functional groups of the functionalized graphene and the polymer binder are molecularly bonded. After the polymerization reaction is completed, the unreacted material is washed and homogenized to produce a graphene hybrid binder (GHPB).

[0082] Figure 6 is the result of the FT-IR spectrum analysis of the graphene hybrid binder used in the present invention.

[0083] A graphene colloid was prepared by dispersing 1 wt% of functionalized graphene containing silane groups in a solvent mixture of deionized water and ethanol in an 8:2 mass ratio, and the mixture was dispersed and homogenized using ultrasound for at least 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 then homogenized using ultrasound for 30 minutes before the remaining polymer binder was added. After the addition of the total amount of polymer binder, the temperature was raised to 60 ℃, and the polymerization reaction was carried out for 10 hours. After the reaction was completed, centrifugation was performed three times at 2000 rpm for 30 minutes; after washing for unreacted materials and passing through a vacuum filter, the solvent was added. Subsequently, a graphene hybrid binder (GHPB) was prepared by homogenizing using ultrasound or a high-speed homogenizer for 30 minutes, and FT-IR spectral analysis was performed on the prepared graphene hybrid binder.

[0084] 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 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 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 polymer binder are bonded by functional groups. Referring to Fig. 6, in the FT-IR spectrum of the sample in which the functionalized graphene and polymer binder are simply mixed, the FT-IR characteristic peaks of functionalized graphene and PAA appear mixed. In contrast, in the FT-IR spectra of GHPB-1 (G hybrid PAA) completion and GHPB-2 (G hybrid PAA-PUD) completion, characteristic peaks of the polymer binders (PAA, PU) appear clearly, and the 1650 cm⁻¹ of functionalized graphene -1 It can be observed that the characteristic peak in the vicinity has decreased. This is a result of the combination of functionalized graphene and a polymer binder.

[0085] Raman spectrum analysis was performed to more accurately confirm whether functionalized graphene is bound to the polymer binder. Figure 7 shows the results of the Raman spectrum analysis of the graphene hybrid binder. Since unreacted materials were removed during the preparation of the graphene hybrid binder, if functionalized graphene is not bound to the graphene hybrid binder, the characteristic peak of functionalized graphene would not be visible in the Raman spectrum analysis results. However, as shown in Figure 7, the D peak (1350 cm⁻¹), which is not measured in the Raman spectrum analysis, -1 ) and G peak (1580 cm⁻¹) -1It can be confirmed that ) is measured. Therefore, by combining the results of Fig. 6 and Fig. 7, it can be seen that the graphene hybrid binder is molecularly bonded between the functionalized graphene and the polymer binder through the functional groups of the functionalized graphene.

[0086] 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 onto the cathode current collector (copper current collector). As a comparative example, a cross-cut test was performed after coating PAA onto the cathode current collector.

[0087] The cross-cut test is a method used to evaluate the adhesion of a coating. A grid pattern is created by drawing multiple lines at regular intervals on the coated surface, and then tape is applied and removed to check how well the coating adheres. The adhesion is classified into grades by observing the condition of the coating on the removed tape and the grid pattern. The test results can be categorized into the following grades: 5B is the highest adhesion grade, meaning that the coating does not peel off at all from the grid pattern after the test. 4B indicates that less than 5% of the coating on the grid pattern has peeled off. 3B shows a coating loss in the range of 5–15% of the grid pattern. 2B indicates that 15–35% of the coating has peeled off from the grid pattern. 1B indicates that 35–65% of the coating has peeled off from the grid pattern. 0B is the lowest adhesion grade, meaning that more than 65% of the coating has peeled off.

[0088] The cross-cut test result of the PAA binder, known to have superior adhesion compared to SBR and CMC which are widely used as cathode binders, was 3B. In contrast, the cross-cut test result of both samples of the graphene hybrid binder was 5B, indicating that the coating did not peel off at all.

[0089] Meanwhile, the effect of the content of functionalized graphene in the graphene hybrid binder is shown in Table 3 below. PAA was used as the polymer binder, and tape tests and cross-cut tests were performed after coating each polymer binder onto a copper current collector. For the tape test, the coating was removed 10 times after attaching the tape; if it did not peel off, it was marked as ◎ (Excellent); if it peeled off once, it was marked as ○ (Good); if it peeled off 2 to 3 times, it was marked as △ (Medium); otherwise, it was marked as X (Poor).

[0090]

[0091] 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

[0092] As shown in Table 3, when the content of functionalized graphene in the graphene hybrid binder of the present invention is 0.01 to 0.5 wt%, it was confirmed that it has excellent adhesion, showing excellent tape test results and 5B cross-cut test results. However, if the content of functionalized graphene exceeds 0.5 wt%, the internal cohesive force of the functionalized graphene becomes greater than the adhesion force to the substrate, resulting in a decrease in adhesion. Therefore, the content of functionalized graphene in the graphene hybrid binder of the present invention may be 0.01 to 0.5 wt%, and preferably 0.01 to 0.3 wt%.

[0093] To analyze the effect of a graphene hybrid binder on the characteristics of a battery, a negative electrode active material in the form of silicon metal (particle size: 7 to 10 μm) and a graphene-silicon hybrid negative electrode active material having a functionalized graphene coating layer self-adsorbed and coated on the silicon metal (particle size: 7 to 10 μm) were prepared. Silicon metal particles having a functionalized graphene coating layer were prepared by spontaneously adsorbing silicon particles with a central particle size of 7 to 10 μm by ultrasonically dispersing functionalized graphene colloids, which have a positive charge through functionalization, in an ethanol solvent for 10 minutes. Subsequently, after centrifugation or vacuum filtration, the mixture was dried at 80 °C and heat-treated at 300 °C in a nitrogen atmosphere to complete the final process. The content of functionalized graphene contained in the silicon metal particles having a functionalized graphene coating layer is 2 wt%. For the preparation of silicon metal particles having a functionalized graphene coating layer, reference may be made to the contents disclosed in Korean Published Patent No. 10-2023-0099837.

[0094] To evaluate the performance of a secondary battery, a negative electrode was manufactured using silicon metal particles prepared for the purpose of evaluating the performance of a secondary battery or silicon metal particles having a functionalized graphene coating layer as the negative electrode active material.

[0095] Comparative Example 1 consists of 8 μm silicon metal particles, artificial graphite (Si : artificial graphite = 1:1), a conductive material (super p black), and a polymer binder (SBR:CMC = 7:3) in a weight ratio of 40:40:10:10.

[0096] Example 1 consists of 8 μm silicon metal particles (Si), artificial graphite (Si : 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, the graphene hybrid binder used was one in which SBR and CMC were bonded by functional groups, the content of functionalized graphene in the graphene hybrid binder was 0.05 wt%, and SBR and CMC were included in a weight ratio of 7:3.

[0097] 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 an amount equal to the decrease in the graphene hybrid binder.

[0098] 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, the graphene hybrid binder may be one in which SBR and CMC are bonded by functional groups, 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.

[0099] Examples 6 to 9 were prepared by increasing the weight of the graphene-silicon hybrid negative electrode active material (Si / G : artificial graphite = 1:1) by an amount equal to the decrease in the graphene hybrid binder.

[0100] Comparative Example 3 is identical to Comparative Example 1, except that a graphene-silicon hybrid negative electrode active material (Si / G : artificial graphite = 1:1) was used instead of silicon metal particles.

[0101] Meanwhile, the content of functionalized graphene in the graphene-silicon hybrid negative electrode active material used in Comparative Example 3 and Examples 5 to 9 was 2 wt%.

[0102] First, the characteristics of the half cell were evaluated.

[0103] The cathode was prepared as follows. A binder solution was further diluted in deionized water, the cathode active material and conductive material were added, and a slurry was prepared by stirring with a homomixer for 1 hour. The prepared slurry was coated to a thickness of 75 µm onto a 15 µm thick copper current collector, dried at 90°C for 2 hours, and then pressed. The solvent was completely removed by drying in a vacuum oven at 120°C for 4 hours to complete the process.

[0104] A coin half cell (CR2032) was manufactured using a lithium metal foil, a polyethylene separator, and a cathode prepared using an electrolyte as the positive electrode. At this time, the electrolyte used was a mixture of 1.2 M LiPF6 and a mixture of 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.

[0105] The characteristics of half cells and full cells were evaluated as follows, applying the IEC 62620 standard. At room temperature (25±5℃), rectified charging was performed to 0.01V with a 0.1C-rate current, followed by constant voltage charging from 0.01V (termination current was 0.01C-rate), and constant current discharge was performed to 1.5V with a 0.1C-rate current. Under the above conditions, the discharge amount and initial charge / discharge efficiency were calculated. For the life evaluation, rectified charging was performed to 0.005V with a 0.1C-rate current at room temperature (25±5℃), followed by constant voltage charging from 0.005V (termination current was 0.005C-rate), and constant current discharge was performed to 1.5V with a 0.1C-rate current. This was repeated 50 times to evaluate the charge / discharge characteristics.

[0106] Meanwhile, for the full cell, the lifespan characteristics were compared by evaluating the characteristics of 500 repeated charge and discharge cycles.

[0107] When fabricating the full cell, the cathode was prepared in the same manner as the half cell, and the anode was prepared by adding an 8 μm center particle size NCM622 active material and a conductive material (super p black) to a PVdF binder solution dissolved in NMP solvent and stirring with a homomixer for 1 hour to prepare a slurry. At this time, the anode material consists of NCM622, conductive material, and PVdF binder in a weight ratio of 80:10:10.

[0108] The manufactured anode slurry was coated to a thickness of 75 μm onto a 20 μm thick aluminum current collector, dried at 120°C for 2 hours, and then compressed. The anode was completed by drying in a vacuum oven at 120°C for 4 hours to completely remove the solvent.

[0109] Full cell assembly is identical to the half cell fabrication conditions, but uses a fabricated anode instead of lithium metal foil, and lifespan characteristics were compared through 500 repeated charge-discharge evaluations.

[0110] The characteristics of the half cell and full cell were evaluated below. The initial efficiency and lifetime were calculated as follows.

[0111]

[0112] Initial efficiency (%) = (Discharge capacity per cycle / Charge capacity per cycle) x 100

[0113] Lifespan (%) = (n-cycle discharge capacity / 1-cycle discharge capacity) x 100

[0114]

[0115] Table 4 shows the results of evaluating the characteristics of a half cell containing silicon metal particles as the negative electrode active material (Si : artificial graphite = 1:1).

[0116]

[0117] No. Binder Binder Content (wt%) Initial Discharge Capacity (mAh / g) Capacity Retention Rate (10 Cycles) (%) Capacity Retention Rate (50 Cycles) (%) Comparative Example 1 SBR+CMC 10169 1.478 27.5 Comparative Example 2 SBR+CMC 8173 3.56 2.12 3.5 Example 1 GHPB 10169 8.88 7.57 5.2 Example 2 GHPB 8174 2.38 7.77 5.1 Example 3 GHPB 7176 3.78 7.47 5.0 Example 4 GHPB 6178 1.78 2.56 0.1

[0118] In Comparative Example 1, a gradual decrease in capacity occurred starting from 10 charge-discharge cycles, and at the 50th cycle, most of the silicon metal particles were destroyed, resulting in a very low capacity retention rate.

[0119] In Comparative Example 2, the initial discharge capacity was higher than in Comparative Example 1 due to the reduction in binder, but the decrease in capacity was greater than in Comparative Example 1. This is because, due to the higher content of silicon metal particles, it was more affected by volume expansion and contraction during charging and discharging.

[0120] It was confirmed that Examples 1 to 4, which include the graphene hybrid binder of the present invention as a binder, showed a very high capacity retention rate at the 10th charge-discharge cycle compared to the comparative example. In particular, Examples 1 to 3 showed a very high capacity retention rate of 75% even at the 50th charge-discharge cycle. However, in Example 4, where the binder content was significantly reduced, a decrease in capacity of 60.1% was observed at the 50th charge-discharge cycle. This is because the adhesion decreased with the decrease in binder content, causing detachment from the current collector due to the expansion and contraction behavior of the silicon metal particles during charge-discharge; furthermore, the capacity decreased because irreversible capacity occurred as the SEI layer formation increased.

[0121] Therefore, when silicon metal particles are included as the cathode active material, the content of the graphene hybrid binder may be 7 to 10 wt% of the total weight of the cathode material.

[0122] Table 5 shows the results of evaluating the characteristics of a half cell containing silicon metal particles having functionalized graphene as a coating layer as a negative electrode active material.

[0123]

[0124] No. Cathode Active Material Type Binder Type Binder Content (wt%) Initial Discharge Capacity (mAh / g) Initial Efficiency (%) Capacity Retention Rate (50 Cycles) (%) Comparative Example 1 Si : Artificial Graphite = 1:1 SBR+CMC 10169 1.48 9.22 7.5 Comparative Example 2 Si : Artificial Graphite = 1:1 SBR+CMC 8173 3.58 9.32 3.5 Example 1 Si : Artificial Graphite = 1:1 GHPB 10169 8.89 0.27 5.2 Example 2 Si : Artificial Graphite = 1:1 GHPB 8174 2.39 0.57 5.1 Example 3 Si : Artificial Graphite = 1:1 GHPB 7176 3.79 0.17 5.0 Example 5 Si / G : Artificial Graphite = 1:1GHPB101672.092.996.3 Example 6 Si / G : Artificial Graphite = 1:1GHPB81725.293.196.1 Example 7 Si / G : Artificial Graphite = 1:1GHPB71736.493.096.2 Example 8 Si / G : Artificial Graphite = 1:1GHPB61757.692.196.0 Example 9 Si / G : Artificial Graphite = 1:1GHPB51779.787.189.5 Comparative Example 3 Si / G : Artificial Graphite = 1:1SBR+CMC101669.391.194.3

[0125] When comparing Examples 1 to 3 with Examples 5 to 7, it can be seen that when silicon metal particles having functionalized graphene as a coating layer are included as the negative electrode active material, Examples 5 to 7 have a higher initial efficiency than Examples 1 to 3, and the capacity retention rate after 50 charge-discharge cycles is significantly higher.

[0126] This is because in the case of Examples 5 to 7, the silicon metal particles have a functionalized graphene coating layer that is self-bonded to the silicon metal particles on the surface, so the functionalized graphene coating layer primarily controls the expansion and contraction behavior of the silicon metal particles during charging and discharging, and the graphene hybrid binder secondarily controls the expansion and contraction behavior of the silicon metal particles during charging and discharging due to excellent adhesion and excellent elasticity.

[0127] In particular, when silicon metal particles having functionalized graphene as a coating layer were included as the negative electrode active material, an excellent capacity retention rate was observed even when the graphene hybrid binder content was 6 wt% (Example 8).

[0128] However, in Example 9, where the binder content was significantly reduced, a decrease in capacity of 89.5% was observed at the time of 50 charge-discharge cycles. This is because the adhesive strength decreased with the decrease in binder content, causing detachment from the current collector due to the expansion and contraction behavior of the silicon metal particles during charge-discharge, and furthermore, the capacity decreased because irreversible capacity occurred as the SEI layer formation increased.

[0129] Meanwhile, in the case of Comparative Example 3, a mixture of SBR and SMC was used as the binder instead of the graphene hybrid binder of the present invention. It can be seen that the capacity retention rate after 50 charge-discharge cycles was 94.3%, which is lower than that of Examples 5 to 8 but still satisfactory. This is because the functionalized graphene coating layer coating the silicon metal particles efficiently controls the expansion and contraction behavior of the silicon metal particles during charge-discharge cycles. However, as will be seen later, the capacity retention rate of Comparative Example 3 eventually decreases significantly after 100 charge-discharge cycles.

[0130] Table 6 shows the results of evaluating the characteristics of a full cell containing silicon metal particles with a functionalized graphene coating layer as the negative electrode active material. Fast charge / discharge characteristics were expressed as the discharge capacity under 2C conditions divided by the discharge capacity under 0.2C conditions. (C: current rate)

[0131]

[0132] No. Cathode Active Material Type Binder Type Binder Content Capacity Retention Rate (50 cycles) (%) Capacity Retention Rate (100 cycles) (%) Capacity Retention Rate (300 cycles) (%) Capacity Retention Rate (500 cycles) (%) Fast Charge / Discharge Characteristics (%) Comparative Example 4 Si : Artificial Graphite = 1:1 SBR+CMC 102 6.8 10.8 Intermediate Intermediate 31 Example 10 Si : Artificial Graphite = 1:1 GHPB 107 5.4 6 5.7 6 3.1 57.8 53 Example 11 Si / G : Artificial Graphite = 1:1 GHPB 109 6.2 95.1 93.1 90.5 82 Example 12 Si / G : Artificial Graphite = 1:1 GHPB 89 6.3 95.2 92.9 90.6 83 Example 13 Si / G : Artificial Graphite = 1:1 GHPB 796.295.293.290.484 Example 14 Si / G : Artificial Graphite = 1:1 GHPB 695.894.192.790.184 Example 15 Si / G : Artificial Graphite = 1:1 GHPB 587.685.180.171.281 Comparative Example 3 Si / G : Artificial Graphite = 1:1 SBR+CMC 1093.152.135.6 Middle 72

[0133] Comparative Example 4 showed rapid performance degradation due to silicon shrinkage and expansion during full-cell evaluation.

[0134] Example 10 showed improved lifespan and increased high-speed charge / discharge characteristics due to increased electrical connections through the introduction of GHPB, but the capacity retention rate at the time of 100 charge / discharge cycles was 70% or less.

[0135] In the case of Examples 11 to 14, which include silicon metal particles having a functionalized graphene coating layer as the negative electrode active material and use a graphene hybrid binder as the binder, it can be seen that the capacity retention rate is high at over 80% even after 500 charge-discharge cycles. In addition, due to the interaction between the functionalized graphene coating layer coating the silicon metal particles and the functionalized graphene contained in the graphene hybrid binder, the fast charge-discharge characteristics were also excellent at over 80%.

[0136] In other words, the lifespan was improved by controlling the shrinkage and expansion of silicon metal particles with a functionalized graphene coating layer and strengthening the bonding force with the current collector by the graphene hybrid binder, and the high-speed charge / discharge characteristics were significantly enhanced due to the formation of a graphene network between the silicon metal particles with the functionalized graphene coating layer, the graphene hybrid binder, and the current collector.

[0137] 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 binder may be 5 to 10 wt% with respect to the total weight of the negative electrode material, and preferably 6 to 10 wt%.

[0138]

[0139] Challenge

[0140] As a conductive material (23), at least one selected from the group consisting of carbon black and carbon nanotubes can be used.

[0141]

[0142] Structurally stabilized graphene layer

[0143] As shown in FIG. 1, the structure-stabilizing graphene layer (24) is characterized by being inserted into the cathode composite material at least once. For example, the structure-stabilizing graphene layer (24) may be formed to cover the uppermost surface of the cathode material layer or may be interposed between the cathode material layer and the current collector (10). It is also possible for the cathode material layer to be interposed between the structure-stabilizing graphene layers (24). Alternatively, as shown in FIG. 8, it is possible for the cathode material layer and the structure-stabilizing graphene layer (24) to be formed in a multilayer manner with alternating layers. That is, it is also possible for the structure-stabilizing graphene layer (24) to be placed in the middle of the cathode material layer.

[0144] FIG. 9 is a schematic flowchart of a method for manufacturing a graphene network battery according to one embodiment of the present invention, which includes a process of forming a structure-stabilized graphene layer.

[0145] First, a functionalized graphene colloid is prepared. The functionalized graphene colloid can be prepared by the method for manufacturing functionalized graphene described in the silicon negative electrode active material or binder described above, and can have a positive charge with a zeta potential of +40 mV or higher, preferably +50 mV or higher.

[0146] Next, a structure-stabilized graphene layer is formed on the current collector. However, it is also possible to form a structure-stabilized graphene layer on top of a cathode layer formed on the current collector. Alternatively, it is possible to form a structure-stabilized graphene layer on the current collector, form a cathode layer on top of it, and then form another structure-stabilized graphene layer on top of it. Furthermore, it is possible to form a multilayer structure by repeating the process of forming the cathode layer and the structure-stabilized graphene layer.

[0147] When forming a structure-stabilized graphene layer on a current collector, casting or electrophoretic deposition (EPD) can be used. The thickness of the structure-stabilized graphene layer formed on the current collector can be 10 to 500 nm. The structure-stabilized graphene layer formed on the current collector is formed thinly and uniformly to ensure electrical connectivity with the current collector and to form a graphene network.

[0148] Electrophoretic deposition (EPD) can be used to form a structure-stabilized graphene layer on the cathode layer. The thickness of the structure-stabilized graphene layer formed on the current collector can be 50 to 3,000 nm. The structure-stabilized graphene layer formed on the cathode layer is intended to control the shrinkage and expansion of the silicon cathode active material and to form a graphene network.

[0149] After creating a structure-stabilized graphene layer through casting or electrophoretic electrodeposition, drying can be performed.

[0150] Figure 10 is intended to explain the process of forming a structure-stabilized graphene layer through electrophoretic electrodeposition.

[0151] As shown in FIG. 10, a negative current collector (a negative current collector with a negative layer formed thereon) is connected to the (-) electrode, and a counter electrode (e.g., SUS) is connected to the (+) electrode. The negative current collector (a negative current collector with a negative layer formed thereon) and the counter electrode are immersed in diluted graphene colloid, and a voltage is applied. Since the functionalized graphene of the present invention has a positive charge of +40mV or more, it moves to the negative current collector (a negative current collector with a negative layer formed thereon) connected to the (-) electrode and is electrodeposited. Subsequently, a structure-stabilized graphene layer is formed by performing drying.

[0152] Figure 11 is a Scanning Electron Microscope (SEM) image of the current collector layer, the structure-stabilized graphene layer (Bottom), the Si / G cathode layer, and the structure-stabilized graphene layer (Cover).

[0153] The structure-stabilized graphene layer (Bottom) is formed by electrophoretic deposition of functionalized graphene at a concentration of 0.05 wt.% at 20 V for 30 seconds, and the structure-stabilized graphene layer (Cover) is formed by electrophoretic deposition of functionalized graphene at a concentration of 0.05 wt.% at 25 V for 60 seconds.

[0154] First, comparing the current collector layer and the structurally stabilized graphene layer (Bottom), it can be seen that the inherent crumpled and folded shapes and edges of the graphene sheet are visible.

[0155] Next, comparing the structurally stabilized graphene layer (Bottom) and the Si / G anode layer, it can be seen that the structurally stabilized graphene layer (Bottom) is obscured by the Si / G anode layer.

[0156] Finally, when comparing the Si / G cathode layer and the structure-stabilized graphene layer (Cover), it can be seen that the roughness of the Si / G cathode layer remains unchanged even after the structure-stabilized graphene layer (Cover) is formed, and the inherent crumpled and folded shapes and edges of the graphene sheet are also visible.

[0157] The cathode layer can be formed by mixing a cathode active material, a conductive material, and a binder to prepare a cathode slurry, and then casting it onto a current collector or a structure-stabilized graphene layer.

[0158] Once the formation of the structure-stabilized graphene layer and the cathode layer on the current collector is complete, compression and drying are performed, and the cell is assembled. After assembling the cell, the electrolyte is introduced, and the cell is sealed. From the time the formation of the structure-stabilized graphene layer and the cathode layer on the current collector is completed until the stage of completing the battery, known methods may be used.

[0159] The physical properties and battery performance based on the structurally stabilized graphene layer were evaluated.

[0160] First, a functionalized graphene colloid was prepared having a positive charge with a zeta potential of +40mV or higher and a concentration of 0.5 wt.%. The functionalized graphene was dispersed and homogenized by ultrasound for more than 30 minutes using a solvent of 50% ethanol and 50% IPA (isopropyl alcohol).

[0161] In some examples or comparative examples, a structure-stabilized graphene layer was formed on a copper current collector with a thickness of 17 μm by coating with 0.5 wt.% functionalized graphene colloid via casting (wet film thickness 30 μm, speed 30 mm / s) and then drying at 60°C for 1 hour.

[0162] In other examples or comparative examples, a graphene layer was formed on a copper current collector by electrophoretic electrodeposition. A 0.05 wt.% graphene colloid was prepared by diluting the prepared 0.5 wt.% functionalized graphene colloid tenfold. A negative current collector was connected to the (-) electrode, and a counter electrode (SUS) was connected to the (+) electrode. The negative current collector and the counter electrode were immersed in the diluted graphene colloid, and the electrophoretic electrodeposition process was carried out by applying 20V for 1 minute. A structure-stabilized graphene layer was formed on the current collector by drying at 60°C for 4 hours.

[0163] A cathode slurry is prepared by mixing a cathode active material, a binder, and a conductive material in a weight ratio of 80:10:10. Depending on the example or comparative example, the cathode active material may be artificial graphite, silicon metal (Si), or a graphene-silicon hybrid cathode active material (Si / G); the binder may be an SBR-CMC (7:3) mixed 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 applied to a current collector or a structure-stabilized graphene layer formed on the current collector and dried to produce the cathode of the example or comparative example.

[0165] The cathode material was prepared by coating a slurry mixed with lithium oxide (LCO, NCM, NCMA, NCA, LMO, LFP), a conductive material, a PVDF binder, and an NMP solvent onto a cathode current collector.

[0166] A polyethylene membrane was used as the separator.

[0167] Using the prepared cathode, anode, and separator, a cathode half-cell or full-cell was fabricated and its performance evaluated.

[0168] First, the adhesion strength of the cathode materials of the comparative example and the example to the current collector was tested through tape tests and cross-cut tests, and the results are shown in Table 7 below.

[0169]

[0170] Cathode Material Composition (Cathode Active Material - Conductive Material - Binder) Tape Test Cross-cut Test Synthetic Graphite-Carbon Black-SBR, CMC Binder ○3B Silicon Metal-Carbon Black-SBR, CMC Binder X1B Silicon Metal-Carbon Black-PAA Binder △2B Silicon Metal-Carbon Black-GHPB Binder ○3BSi / G-Carbon Black-GHPB Binder ◎4BSi / G-Carbon Black-SBR, CMC Binder + Formation of structurally stabilized graphene layers on the upper and lower surfaces of the cathode layer ◎5BSi / G-Carbon Black-GHPB Binder + Formation of structurally stabilized graphene layers on the upper and lower surfaces of the cathode layer ◎5B

[0171] The cross-cut test is a method used to evaluate the adhesion of a coating. A grid pattern is created by drawing multiple lines at regular intervals on the coated surface, and then tape is applied and removed to check how well the coating adheres. The adhesion is classified into grades by observing the condition of the coating on the removed tape and the grid pattern. The test results can be categorized into the following grades: 5B is the highest adhesion grade, meaning that the coating does not peel off at all from the grid pattern after the test. 4B indicates that less than 5% of the coating on the grid pattern has peeled off. 3B shows a coating loss in the range of 5–15% of the grid pattern. 2B indicates that 15–35% of the coating has peeled off from the grid pattern. 1B indicates that 35–65% of the coating has peeled off from the grid pattern. 0B is the lowest adhesion grade, meaning that more than 65% of the coating has peeled off.

[0172] For the tape test, the coating was removed 10 times after attaching the tape, and if it did not peel off, it was marked as ◎ (Excellent); if it peeled off once, it was marked as ○ (Good); if it peeled off 2 to 3 times, it was marked as △ (Medium); otherwise, it was marked as X (Poor).

[0173] Referring to Table 4, when a structure-stabilized graphene layer is introduced into the cathode layer, excellent results are shown in both the tape test and the cross-cut test, indicating that the interlayer adhesion is significantly improved with the introduction of the structure-stabilized graphene layer.

[0174] Next, the performance of the graphene network battery was evaluated.

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

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

[0177] The cathode materials of Examples 17–40, 42, and 43 utilized a graphene-silicon hybrid cathode active material (Si / G), and the Si / G used had a functionalized graphene content of 2.0 wt% relative to 0.7 μm silicon particles. Example 17 used a binder composed of a 7:3 mixture of SBR and CMC, while the remainder was constructed using a graphene hybrid binder (GHPB).

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

[0179] A structure-stabilized graphene layer (Bottom) on the cathode current collector was fabricated as follows.

[0180] Example 17 involved coating a copper current collector with a thickness of 17 μm with 0.5 wt% functionalized graphene colloid (wet film thickness 30 μm, speed 30 mm / s) and drying at 60°C for 1 hour to form a structure-stabilized graphene layer (Bottom) on the current collector.

[0181] Examples 19, 20, 21, 22, and 42: 0.1 wt% functionalized graphene colloid was coated under the same conditions, but with different coating cycles to form structurally stabilized graphene layers (Bottom) of 5 nm, 10 nm, 20 nm, and 40 nm.

[0182] Examples 23 to 40 and 43 were performed using an electrophoretic electrodeposition process with 0.05 wt% functionalized graphene colloid. A copper current collector with a thickness of 17 μm was connected to the (-) electrode and a counter electrode made of SUS material was connected to the (+) electrode, and a voltage of 10 to 30 V was applied for 10 seconds to 5 minutes. Through this, a structure-stabilized graphene layer (Bottom) of varying thickness was formed, and the layers were dried at 60°C for 4 hours.

[0183] Subsequently, the prepared cathode material slurry was coated to a thickness of 30 μm on the structure-stabilized graphene layer (Bottom), dried at 90°C for 2 hours, and then compressed. The cathode material layer was formed by drying in a vacuum oven at 120°C for 4 hours. For comparative examples and examples without a structure-stabilized graphene layer (Bottom), the cathode material slurry was applied to a copper current collector with a thickness of 17 μm in the same manner and dried to complete the cathode material layer.

[0184] In the case of an example including a structure-stabilized graphene layer (Cover) on a cathode layer, a structure-stabilized graphene layer (Cover) was formed by performing an electrophoretic electrodeposition process after forming the cathode layer. The cathode was finally completed by drying at 60°C for 4 hours.

[0185] A coin half cell (CR2032) was fabricated using the manufactured electrode as the negative electrode, a lithium metal foil, a polyethylene separator as the positive electrode, and an electrolyte containing 1.2 M LiPF6 with EC / DEC / FEC=2 / 6 / 2 (v / v). Charging and discharging were performed at a current of 0.24 mA (1C / 20) in a voltage range of 0.2 to 1.5 V, or by charging with a constant current of 130 mA / g to 0.001 V, followed by charging with a constant voltage of 65 mA / g. Discharging was performed at a constant current of 130 mA / g to 1.5 V, and this process was repeated 100 times to evaluate the charge-discharge characteristics. For the full cell, the life characteristics were compared by evaluating the charge-discharge characteristics over 500 repeated cycles.

[0186] When fabricating the full cell, the cathode was fabricated in the same way as the half cell, and for the anode, an NCM622 active material with a center particle size of 8 μm and a conductive material (Super P Black) were added to a PVdF binder solution dissolved in NMP solvent and stirred with a homomixer for 1 hour to prepare a slurry. The anode material was composed of NCM622:conductive material:PVdF binder in a weight ratio of 80:10:10.

[0187] The prepared anode slurry was coated to a thickness of 65 μm onto a 20 μm thick aluminum current collector, dried at 120°C for 2 hours, and then compressed. The product was completed by drying in a vacuum oven at 120°C for 4 hours to completely remove the solvent.

[0188] Full cell assembly was carried out under the same conditions as the half cell, but a fabricated cathode was used instead of lithium metal foil. Life characteristics were compared through 500 repeated charge-discharge evaluations, and the life (%) was calculated as (n-cycle discharge capacity / 1-cycle discharge capacity) × 100. The fast charge-discharge evaluation was expressed as the discharge capacity under 2C conditions divided by the discharge capacity under 0.2C conditions.

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

[0190]

[0191] No. Graphene Layer (Bottom) Cathode Layer Graphene Layer (Cover) Initial Discharge Capacity (mAh / g) Capacity Retention Rate (10 Cycles) (%) Capacity Retention Rate (50 Cycles) (%) Comparative Example 5 None Silicon Metal-Carbon Black-SBR, CMC Binder None 160 521.5 5.5 Comparative Example 6 None Silicon Metal-Carbon Black-PAA Binder None 3250 35.1 8.7 Example 16 None Silicon Metal-Carbon Black-PAA Binder EPD (25V, 60s) 332 59 57 5.4 Example 17 Casting Si / G-Carbon Black-SBR, CMC Binder EPD (25V, 60s) 335 69 8.5 97.8 Example 18 EPD (20V, 30s) Si / G-Carbon Black-GHPB Binder EPD(25V, 60s)335298.798.1

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

[0193] Comparative Example 5 had a low initial discharge capacity, and during the life evaluation process, rapid performance degradation occurred due to the shrinkage and expansion of the silicon anode material from the beginning of the charge-discharge cycle.

[0194] Comparative Example 6 applied a PAA binder with excellent adhesion, so the initial discharge capacity was normal, but during the life evaluation process, detachment from the current collector due to the shrinkage and expansion of the silicon anode material occurred from the beginning of the charge-discharge, causing a rapid decline in performance.

[0195] Example 16 showed normal initial discharge capacity and excellent performance up to 10 charge-discharge cycles during the life evaluation process, but performance degradation was observed at the 50th charge-discharge cycle. This suggests that some negative electrode active material was detached from the current collector.

[0196] Meanwhile, Examples 17 and 18, in which a structure-stabilized graphene layer was applied to the upper and lower surfaces of the cathode layer, showed excellent initial discharge capacity and capacity retention rate at the time of 50 charge-discharge cycles. This means that the structure-stabilized graphene layer on the upper and lower surfaces of the cathode layer effectively controls the shrinkage and expansion of the silicon cathode during charge-discharge.

[0197] Table 9 below shows the results of evaluating the half-cell characteristics of the structure-stabilized graphene layer (Bottom) under different conditions.

[0198]

[0199] Example Graphene layer (Bottom) Cathode layer Graphene layer (cover) Initial discharge capacity (mAh / g) Rate characteristic (2C) (%) Capacity retention rate (100 cycles) (%) 19 Casting (5 nm) Si / G - Carbon Black - GHPB Binder EPD (25V, 60s) (150 nm) 330 580.5 81.4 20 Casting (10 nm) 331 082.1 95.8 21 Casting (20 nm) 331 881.9 95.7 22 Casting (40 nm) 332 081.8 95.3 23 EPD (50 nm) 331 982.3 95.6 24 EPD (100 nm) 332 381.5 96.0 25 EPD (200 nm) 332 878.6 96.1 26 EPD (500 nm)331575.795.127EPD(600 nm)33016596.028EPD(1000 nm)32856194.929EPD(2000 nm)32105594.1

[0200] Table 9 shows the results of evaluating the initial discharge capacity, high-rate characteristics, and lifespan characteristics according to the thickness of the structurally stabilized graphene layer (Bottom). When the thickness of the graphene Bottom Layer is 5 nm, the graphene network formation is insufficient, and the capacity retention rate at 100 charge-discharge cycles is 81.4%. Although this cannot be evaluated as absolutely bad, it was found that the drop in capacity retention rate was significant compared to other examples.

[0201] On the other hand, when the thickness of the structurally stabilized graphene layer (Bottom) is excessively thick (more than 600 nm), the electrical path between the current collector and the active material is restricted, and a phenomenon was observed in which high-rate performance deteriorates.

[0202] Considering these circumstances, the thickness of the structure-stabilized graphene layer (Bottom) may be 10 to 500 nm, and preferably 10 to 100 nm.

[0203] Table 10 below shows the results of evaluating the half-cell characteristics of the structure-stabilized graphene layer (Cover) under different conditions.

[0204]

[0205] Example No. Graphene Layer (Bottom) Cathode Layer Graphene Layer (Cover) Initial Discharge Capacity (mAh / g) Rate Characteristic (2C) (%) Capacity Retention Rate (100 Cycles) (%) 30 EPD (150 nm) Si / G-Carbon Black-GHPB Binder EPD (40 nm) 330 780.5 78.4 31 EPD (50 nm) 331 782.2 95.7 32 EPD (100 nm) 331 582.8 95.0 33 EPD (200 nm) 332 181.9 95.2 34 EPD (300 nm) 331 882.0 95.5 35 EPD (500 nm) 332 281.8 95.9 36 EPD (800 nm) 332 578.6 96.0 37 EPD (1000 nm)329875.795.538EPD(2000 nm)32957992.139EPD(3000 nm)32107891.140EPD(4000 nm)29084377.5

[0206] Table 10 shows the results of evaluating the initial discharge capacity, high-rate characteristics, and lifespan characteristics according to the thickness of the structure-stabilized graphene layer (Cover). When the thickness of the structure-stabilized graphene layer (Cover) is 40 nm, the graphene does not sufficiently control the shrinkage and expansion of the silicon anode material, resulting in a capacity retention rate of 78.4% at 100 charge-discharge cycles. While this cannot be evaluated as absolutely bad, it was confirmed that the drop in capacity retention rate was significant compared to other examples.

[0207] On the other hand, when the thickness of the structure-stabilized graphene layer (Cover) is excessively thick, exceeding 4000 nm, the movement path of Li cations between the electrolyte and the active material is restricted, resulting in a decrease in initial discharge capacity, a decrease in high-rate performance, and a reduction in lifespan performance.

[0208] Considering these circumstances, the thickness of the structure-stabilized graphene layer (Cover) may be 50 to 3000 nm, and preferably 50 to 500 nm.

[0209] Table 11 below shows the results of evaluating the full cell characteristics of the graphene network battery.

[0210]

[0211] No. Graphene Layer (Bottom) Cathode Layer Graphene Layer (Cover) Capacity Retention Rate (50 cycles) (%) Capacity Retention Rate (100 cycles) (%) Capacity Retention Rate (500 cycles) (%) Comparative Example 7 None Silicon Metal-Carbon Black-SBR, CMC Binder None 5.3 Discontinued Discontinued Comparative Example 8 None Silicon Metal-Carbon Black-PAA Binder None 9.5 Discontinued Discontinued Example 41 None Silicon Metal-Carbon Black-PAA Binder EPD (150 nm) 75.46 8.9 Discontinued Example 42 Casting (20 nm) Si / G-Carbon Black-GHPB Binder EPD (150 nm) 97.99 7.29 2.8 Example 43 EPD (50 nm) Si / G-Carbon Black-GHPB Binder EPD (150 nm)98.297.693.1

[0212] Comparative Examples 7 and 8 experienced a rapid decline in performance due to the shrinkage and expansion of the silicon anode material during the full-cell evaluation process.

[0213] Example 41 exhibited relatively superior lifespan characteristics compared to the comparative example, but a continuous decrease in capacity was observed as charging and discharging progressed. This suggests that the silicon anode material is gradually detaching from the current collector during the long-life evaluation process, and the drop in capacity retention rate was found to be greater compared to other examples.

[0214] Meanwhile, Examples 42 and 43, which applied a structure-stabilized graphene layer (Bottom, Cover), showed a very excellent capacity retention rate up to 500 charge-discharge cycles during the full-cell evaluation process. These results indicate that the structure-stabilized graphene layer (Bottom, Cover) effectively controls the shrinkage and expansion of the silicon anode material during charge-discharge.

[0215] Considering all these circumstances, it can be seen that the 3D graphene network cathode electrode structure, which incorporates a structure-stabilized graphene layer into the cathode material, demonstrates remarkable performance in terms of stability and lifespan improvement during the charging and discharging process.

[0216] The scope of protection of the present invention is not limited to the description and expression of the embodiments explicitly described above. Furthermore, it is added once again that the scope of protection of the present invention cannot be limited by obvious changes or substitutions in the technical field to which the present invention belongs.

[0217] This patent document was prepared and filed under the support of the following national research and development project of the Republic of Korea.

[0218]

[0219] Project ID: 20014475

[0220] Ministry Name: Ministry of Trade, Industry and Energy

[0221] Research Management Agency: Korea Institute of Industrial Technology Planning and Evaluation

[0222] Research Project Name: Technology Development for Innovative Nano-Convergence Products

[0223] Research Project Title: Development of Nanocomposite Material-Based Anti-Fog Headlamp Technology with Moisture Generation Area of ​​10% or Less

[0224] Contribution rate: 1 / 4

[0225] Organizer: Best Graphene Co., Ltd.

[0226] Research Period: April 1, 2021 – December 31, 2025 (Total 4 years and 9 months)

[0227]

[0228] Project ID: RS-2023-00303772

[0229] Ministry Name: Ministry of SMEs and Startups

[0230] Specialized Research Management Agency: Korea Technology Information Promotion Agency for SMEs

[0231] Research Project Name: SME Technology Innovation Development (R&D)

[0232] Research Project Title: Development of Functionalized Graphene Hybrid Silicon Technology for the Commercialization of High-Capacity Silicon Composite Anode Materials

[0233] Contribution rate: 1 / 4

[0234] Organizer: Best Graphene Co., Ltd.

[0235] Research Period: October 20, 2023 – October 19, 2026 (Total 36 months)

[0236]

[0237] Project ID: RS-2024-00419914

[0238] Ministry Name: Ministry of Trade, Industry and Energy

[0239] Research Management Agency: Korea Institute of Industrial Technology Planning and Evaluation

[0240] Research Project Name: Electronic Components Industry Technology Development

[0241] Research Project Title: Development of Commercialization Technology for High-Capacity MLCCs for Electric Vehicles Based on Graphene-BaTiO3 Composite Dielectrics

[0242] Contribution rate: 1 / 4

[0243] Organizer: Best Graphene Co., Ltd.

[0244] Research Period: April 1, 2024 – December 31, 2027 (Total 3 years and 9 months)

[0245]

[0246] Project ID: RS-2024-00431451

[0247] Ministry Name: Ministry of Trade, Industry and Energy

[0248] Research Management Agency: Korea Institute of Industrial Technology Planning and Evaluation

[0249] Research Project Name: Materials and Components Technology Development Project

[0250] Research Project Title: Development of High-Durability and High-Stability Conductive Microfiber Composite Material Technology

[0251] Contribution rate: 1 / 4

[0252] Organizer: Best Graphene Co., Ltd.

[0253] Research Period: July 1, 2024 – December 31, 2027 (Total 3 years and 6 months)

Claims

1. A graphene network battery comprising a positive electrode current collector, a positive electrode composite, a separator, a negative electrode composite, and a negative electrode current collector, The above cathode composite is, A cathode material layer formed on the upper portion of the above-mentioned cathode current collector and comprising a silicon cathode active material and a binder; and A graphene network battery comprising a structure-stabilizing graphene layer formed on at least one surface of the above-mentioned cathode layer.

2. In Paragraph 1, The above-described structurally stabilized graphene layer is a graphene network battery formed on the uppermost part of the above-described cathode layer.

3. In Paragraph 2, A graphene network battery characterized by the thickness of the structure-stabilized graphene layer being 50 to 3,000 nm.

4. In Paragraph 1, The above-described structure-stabilized graphene layer is a graphene network battery interposed between the above-described negative electrode layer and the above-described current collector.

5. In Paragraph 4, A graphene network battery characterized by the thickness of the structure-stabilized graphene layer being 10 to 500 nm.

6. In Paragraph 1, A graphene network battery in which the above-mentioned cathode layer and the above-mentioned structurally stabilized graphene layer are alternately stacked.

7. In Paragraph 1, The above binder is at least one selected from the group consisting of styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PAA), and graphene hybrid binder, for a graphene network battery.

8. In Paragraph 7, A graphene network battery comprising, where the binder is a graphene hybrid binder, the graphene hybrid binder having functionalized graphene with formed functional groups; and a polymer binder bonded to the functionalized graphene by the functional groups.

9. In Paragraph 1, The above silicon anode material is at least one selected from the group consisting of silicon, silicon compounds, and graphene-silicon hybrid anode active materials, in a graphene network battery.

10. In Paragraph 1, A graphene network battery in which, when the silicon anode material is a graphene-silicon hybrid anode active material, the graphene-silicon hybrid anode active material comprises a graphene coating layer formed by self-adsorption of functionalized graphene having functional groups on the surface of silicon or a silicon compound.

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