Energy storage device cathode nanocomposite comprising nanobleneded assembly, preparation method therefor, and cathode and energy storage device which comprise same

Abstract

The present invention relates to an energy storage device cathode nanocomposite, a preparation method therefor, and a cathode and an energy storage device which comprise same, the nanocomposite comprising an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with a carboxyl group are nanoblended.

Description

Nanocomposite for energy storage device cathode comprising nanoblending assembly, method for producing same, and cathode and energy storage device comprising same

[0001] The present invention relates to a nanocomposite for an energy storage device cathode comprising a nanoblending assembly, a method for producing the same, and an anode and an energy storage device comprising the same.

[0002] To meet the rapidly increasing demands for a variety of modern portable and wearable electronic devices, energy storage devices such as lithium-ion batteries (LIBs) require smaller and lighter electrodes, higher energy / power densities, and longer operating stability. To achieve these goals, much research has focused on enhancing capacity and rate performance, primarily through the synthesis of novel electrode materials and / or rational design of electrode structures. Recently, areal performance indicators, such as areal capacity, have been recognized as another important factor reflecting the actual performance level of electrodes. As a promising approach to improving such areal performance, highly porous and conductive fibril-based fabrics with a large specific surface area have attracted attention as three-dimensional current collectors for electrodes capable of achieving high active material loading capacities. Specifically, a mixed slurry of electrode components, typically consisting of powdered active materials (e.g., metal oxides), conductive carbon additives (e.g., carbon black (CB) and carbon nanotubes (CNTs)), and polymeric binders, has been deposited on fibrillated current collectors (FCCs) using conventional coating methods such as dip coating, doctor blade coating, printing, and vacuum filtration. Although these approaches have contributed to improving the areal performance of electrodes to some extent, significant challenges still remain to be addressed to further enhance energy storage performance.

[0003] Previously reported studies have not deeply considered the complementary interfacial interactions between slurry components and the uniformity of the blend components on the overall electrode performance. For example, when preparing metal oxide nanoparticle (MO NP)-based slurries, hydrophobic carbon additives (e.g., CB or CNTs) are mechanically mixed with the active MO NPs with the aid of a polymer binder. However, undesirable interfacial interactions between the MO NPs and the carbon additive, between the MO NPs and the polymer binder, and between adjacent MO NPs lead to agglomeration and separated phases. Furthermore, slurry-coated electrodes inevitably experience non-uniform migration of the components during solvent evaporation (i.e., low-density carbon additives float to the top surface, while high-density MO NPs sink to the bottom). This phenomenon leads to a non-uniform distribution of conductive components among the MO NPs, which hinders the formation of efficient charge transfer pathways within the electrode. Moreover, weakly adsorbed components are highly susceptible to volume expansion of MO NPs during the charge / discharge process in LIBs, resulting in structural defects and rapid capacity decay of the electrode. While these defects can be mitigated using polymer binders, insulating / inert polymer binders act as contact resistance, reducing the energy efficiency of the electrode. Furthermore, when porous FCCs are utilized as three-dimensional current collectors, conventional coating methods have many difficulties in uniformly depositing highly concentrated and viscous slurries across the entire area from the exterior to the interior of the FCC. In this case, agglomeration / segregation of electrode components due to undesirable interfacial interactions can block the numerous pores of the porous FCC.

[0004] In particular, when using MO NPs with high capacity but low electrical conductivity, agglomeration due to non-uniform mixing significantly inhibits electron transport and ion diffusion, leading to a decrease in the active surface area and an increase in the overall resistance of the electrode. Although the introduction of one-dimensional carbon nanotubes (CNTs) as a carbon additive can form a nanoporous and conductive network structure for easy charge transfer, the bulky size and low tap density of the CNTs increase the thickness of the electrode, significantly reducing the volumetric performance. An alternative to improving the packing density (or volumetric performance) of the electrode is to use carbon nanoclusters (CNs) composed of nano-sized CBs instead of bulky CNTs. However, hydrophobic CNs tend to easily aggregate, resulting in high contact resistance at the interface between adjacent MO NPs without CNs. Despite these important issues, the influence of the physical size and interfacial interactions of carbon additives on the energy storage performance has been overlooked over the past several decades and has been less studied than that of other components of MO NP-based electrodes.

[0005] Therefore, beyond the simple introduction of conductive components, the effective spatial distribution / arrangement of the components based on favorable interfacial interactions should be considered to maximize the large active surface area and high energy capacity of nano-sized MO NPs and improve the overall performance level of the electrode. In other words, exploring direct nanoblending assemblies of high-capacity MO NPs and conductive CNs, while still enabling uniform coating and robust interfacial interactions without the use of polymer binders, can support the successful development of high-performance energy storage electrodes.

[0006] The present invention is intended to provide a nanocomposite for an energy storage device cathode, which is characterized by including an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with carboxyl groups are nanoblended, and is applied to a high-performance energy storage device and an electrode.

[0007] However, the technical problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0008] The present invention provides a nanocomposite for an energy storage device cathode comprising an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with carboxyl groups are nanoblended.

[0009] The above nanocomposite for the energy storage device cathode may be in a binder-free form.

[0010] The above transition metal oxide nanoparticles may be one or more nanoparticles selected from the group consisting of iron oxide, manganese oxide, titanium oxide, and ruthenium oxide.

[0011] The above surface-modified carbon black may have hydrophilic properties.

[0012] The above surface-modified carbon black can be manufactured by treating carbon black with an acid solution.

[0013] The above nanoblended assembly may be formed through coordination bonding between the surface of the transition metal oxide nanoparticles and the carboxyl group of the modified carbon black.

[0014] In one embodiment of the present invention, a method for producing a nanocomposite for an energy storage device anode is provided, comprising the steps of: (a) producing carbon black surface-modified with a carboxyl group; and (b) performing a reaction to substitute an organic ligand on the surface of a transition metal oxide nanoparticle with the surface-modified carbon black, thereby producing an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with a carboxyl group are nanoblended.

[0015] In another embodiment of the present invention, an energy storage device negative electrode is provided, comprising: a negative electrode current collector; and a nanocomposite for negative electrode coated on the negative electrode current collector.

[0016] The above negative electrode current collector may be based on a conductive fabric support surface-modified with an amine group.

[0017] In another embodiment of the present invention, an energy storage device including the cathode is provided.

[0018] The nanocomposite for an energy storage device cathode according to the present invention is characterized by including an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with carboxyl groups are nanoblended, so that uniform distribution of carbon black surface-modified with carboxyl groups can be induced within the assembly without a polymer binder, thereby effectively reducing contact resistance between adjacent transition metal oxide nanoparticles.

[0019] The nanocomposite for an energy storage device cathode according to the present invention can be usefully applied to high-performance energy storage devices and electrodes such as lithium-ion batteries and pseudocapacitors.

[0020] Figure 1 illustrates a schematic diagram of a CCN-mediated nanoblending assembly based on coordination bonding induced by a ligand substitution reaction for the fabrication of binder-free Fe3O4NP-based energy storage electrodes.

[0021] In Fig. 2, (a) HR-TEM images of OA-Fe3O4NP (left) and CCN (right) are shown. The two insets show the highly ordered crystal structure of OA-Fe3O4NP with a lattice spacing (d) of 2.53 Å attributable to the (311) phase and the paracrystal structure of CCN with a particle size of ∼7 nm, respectively. (b) Photographs of hydrophobic CN (left) and surface-modified hydrophilic CCN (right) in ethanol are shown. (c) (Fe3O4NP / CCN) nFTIR spectra and schematic diagrams of the layered self-assembly process of the composites are shown according to the number of bilayers (n). (d) Images of sessile water droplets are shown at n = 2.5 (top left) with the outermost OA-Fe3O4NP layer and at n = 3.0 (top right) with the outermost CCN layer. (Fe3O4NP / CCN) according to the number of bilayers. n The change in contact angle (θ) of the composite (bottom) is shown. (e) Cross-sectional FE-SEM and EDS elemental mapping images at n = 20, along with the number of bilayers (Fe3O4NP / CCN). n The change in film thickness of the composite is shown. (f) Under an external voltage range of ±1.5 V (Fe3O4NP / CCN). 20 This graph shows the current density (log J) - electric field (log E) of the complex.

[0022] In Fig. 3, during the initial 5 cycles (Fe3O4NP / CCN) 20 -(a) CV curve of LIB electrode (0.1 mV s -1 ) and (b) GCD curves (at a scan rate of 0.1 A g -1 (c) at a current density of 0.1 A g -1 In the 5th cycle of GCD measurement at a current density of (Fe3O4NP / CCN) 20 -The differential capacitance graph of the LIB electrode is shown. (d) The initial 5 activation cycles (0.1 A g -1 ) after 0.1 to 2.0 A g -1 (Fe3O4NP / CCN) at different current densities in the range 20 -The rate performance of the LIB electrode is shown. (e) 1.0 A g -1 (Fe3O4NP / CCN) for 3000 GCD cycles at a current density of 20 -The long-term operating stability of the LIB electrode is shown. In this case, the specific capacity is the total mass including Fe3O4NP and CCN of the electrode (~0.11 mg cm-2 ) was calculated based on.

[0023] In Fig. 4, (a) (Fe3O4NP / CCN) 20 - Low-magnification planar (left), high-magnification planar (middle), and cross-sectional (right) FE-SEM images of (b) slurry-FCC electrodes. (c) (Fe3O4NP / CCN) 20 - CV curve of the 5th cycle between FCC and slurry-FCC electrodes at a scan rate of 0.1 mV s -1 (d) compared to the initial 5 activation cycles (0.1 A g -1 ) after 0.1 to 2.0 A g -1 At current density varying from (Fe3O4NP / CCN) 20 -Comparison of speed performance between FCC and slurry-FCC. (e) (Fe3O4NP / CCN) 20 -Comparison of Nyquist plots between FCC and slurry-FCC electrodes. The inset shows the equivalent circuit of the electrode. (f) 1.0 A g -1 (Fe3O4NP / CCN) for 300 GCD cycles at a current density of 20 -Comparison of long-term operating stability between FCC and slurry-FCC electrodes. In this case, (Fe3O4NP / CCN) 20 -Total mass of FCC and slurry-FCC electrodes is ~6.2 mg cm -2 was adjusted to the same extent.

[0024] Herein, we fabricated binder-free MO NP electrodes with a uniformly distributed structure, favorable interfacial interactions, and remarkably high energy storage performance by utilizing nanoblending assembly mediated by interface-modified CN. In this invention, carboxyl (COOH) groups were introduced onto the surface of hydrophobic CN, and then COOH-functionalized CN (CCN) was used as a conductive linker that could directly and firmly connect all interfaces between adjacent MO NPs. Specifically, oleic acid (OA) and oleylamine (OAm) ligand-stabilized Fe3O4NPs (denoted as OA-Fe3O4NP) were sequentially layered-assembled with CCN through coordination bonds (i.e., multidentate bonds) induced by ligand substitution reactions between the COOH groups of CCN and the Fe3O4NP surface (Fig. 1). Based on the formation of efficient charge transfer pathways, the CCN-mediated Fe3O4NP electrode exhibited high capacity, excellent rate performance, and long-term operating stability in LIB systems. In particular, the inventors confirmed that the CCN-mediated nanoblending assembly could uniformly and densely introduce electrode components into the entire area of ​​the three-dimensional porous FCC without clogging of the agglomerated phase and pores. As a result, the fabricated fabric-type LIB electrode exhibited a high capacity of ~5.67 mAh cm -2 It showed significantly improved area performance, which was superior to that of conventional slurry-coated electrodes.

[0025]

[0026] Effective spatial distribution / arrangement of active and conductive components within metal oxide nanoparticle (MO NP)-based electrodes can have a critical impact on the performance of lithium-ion batteries. Herein, we demonstrate that a nanoblending structure based on favorable interfacial interactions between high-capacity MO NPs and interfacially modified carbon nanoclusters (CNs) can significantly enhance the performance and charge transfer kinetics of binder-free energy storage electrodes. In the present invention, carboxyl group (COOH)-functionalized CN (CCN) can be sequentially assembled with MO NPs using coordination bonds induced by an in situ ligand substitution reaction between the COOH groups and the NP surface. This nanoblending assembly can induce a uniform distribution of conductive CCN within a dense MO NP array without the presence of insulating organics (i.e., polymeric binders and stabilizing ligands) and without aggregation / segregation of the components, thereby effectively reducing the contact resistance between adjacent MO NPs. These CCN-mediated MO NP electrodes can exhibit significantly higher capacity and superior charge transfer behavior compared to conventional slurry-coated electrodes in lithium-ion batteries. The present invention provides a comprehensive understanding of charge transfer according to the interfacial structure between electrode components, and further provides a foundation for developing high-performance energy storage electrodes.

[0027]

[0028] Hereinafter, the present invention will be described in detail.

[0029]

[0030] Nanocomposites for energy storage device cathodes

[0031]

[0032] The present invention provides a nanocomposite for an energy storage device cathode comprising an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with carboxyl groups are nanoblended.

[0033]

[0034] The nanocomposite for an energy storage device anode according to the present invention comprises a nanoblending assembly, which may be in a binder-free form, i.e., substantially free of a polymer binder. The nanocomposite for an energy storage device anode can induce a uniform distribution of carbon black surface-modified with carboxyl groups within the assembly without a polymer binder, thereby effectively reducing the contact resistance between adjacent transition metal oxide nanoparticles.

[0035]

[0036] First, the nanoblending assembly according to the present invention includes transition metal oxide nanoparticles as a negative electrode active material.

[0037] The above transition metal oxide nanoparticles refer to a state after a ligand substitution reaction, and may be a state in which the organic ligand (native ligand) is removed. Meanwhile, in a state before the ligand substitution reaction, the nanoparticles may be in a state in which they are bound to an organic ligand in a solution. Specifically, the organic ligand may have a relatively large volume and low affinity (i.e., adsorption energy), and the organic ligand may be oleic acid, oleylamine, etc., wherein oleic acid corresponds to a monodentate / bidentate ligand, and oleylamine corresponds to a monodentate ligand.

[0038] Specifically, the transition metal oxide nanoparticles may be one or more nanoparticles selected from the group consisting of iron oxide, manganese oxide, titanium oxide, and ruthenium oxide, and are preferably one or more nanoparticles selected from the group consisting of Fe3O4, MnO2, TiO2, and RuO2, and are more preferably Fe3O4 nanoparticles, but are not limited thereto. In addition, the particle size of the transition metal oxide nanoparticles may be 1 nm to 500 nm, and is preferably 5 nm to 100 nm, but is not limited thereto.

[0039]

[0040] Next, the nanoblending assembly according to the present invention comprises carbon black surface-modified with carboxyl groups as a conductive material. The surface-modified carbon black can function as a conductive linker. However, if carbon nanotubes are used instead of carbon black, their large volume increases the thickness of the nanocomposite, which is unfavorable for the performance of energy storage devices and electrodes.

[0041] Carbon black prior to the surface modification is hydrophobic, but upon surface modification with a carboxyl group, the surface-modified carbon black may have hydrophilic properties.

[0042] Specifically, the surface-modified carbon black can be produced by treating carbon black with an acid solution. The acid solution can be a mixture of sulfuric acid and nitric acid, preferably a mixture in which the volume ratio of sulfuric acid and nitric acid is 1:1 to 5:1. The surface treatment can be performed at 50°C to 90°C for 1 to 5 hours, followed by cooling to room temperature and complete removal of any residual acid. This allows hydrophobic carbon black to be made hydrophilic.

[0043]

[0044] Finally, the nanoblended assembly according to the present invention may be achieved through coordination bonding between the surface of the transition metal oxide nanoparticles and the carboxyl groups of the modified carbon black. That is, instead of the organic ligand, the carbon black surface-modified with the carboxyl groups, which are multidentate ligands, may be coordinately bonded to the surface of the transition metal nanoparticles.

[0045] Accordingly, the transition metal oxide nanoparticles and the carbon black surface-modified with carboxyl groups can form a single double layer, and then repeatedly immersed to form a nanoblended assembly through layer-by-layer self-assembly. The number of layers of the double layer may be about 1 to about 50 layers, and is preferably about 10 to about 30 layers, but is not limited thereto, and the capacity may increase as the number of layers of the double layer increases. Accordingly, the thickness of the nanoblended assembly (film) may be about 20 nm to about 1,000 nm, and is preferably about 200 nm to about 600 nm, but is not limited thereto.

[0046]

[0047] Method for manufacturing nanocomposites for energy storage device cathodes

[0048]

[0049] The present invention provides a method for producing a nanocomposite for an energy storage device anode, comprising the steps of: (a) producing carbon black surface-modified with a carboxyl group; and (b) producing an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with a carboxyl group are nanoblended by performing a reaction of replacing organic ligands on the surface of transition metal oxide nanoparticles with the surface-modified carbon black.

[0050]

[0051] First, the method for manufacturing a nanocomposite for an energy storage device cathode according to the present invention includes a step [step (a)] of manufacturing carbon black surface-modified with carboxyl groups. Here, since the "carbon black surface-modified with carboxyl groups" has been described above, a redundant description will be omitted.

[0052] The carbon black surface-modified with the above-described carboxyl group can be produced by treating carbon black with an acid solution. The acid solution may be a mixture of sulfuric acid and nitric acid, preferably a mixture in which the volume ratio of sulfuric acid and nitric acid is 1:1 to 5:1. The surface treatment can be performed at 50°C to 90°C for 1 to 5 hours, followed by cooling to room temperature and complete removal of any residual acid. This allows hydrophobic carbon black to be made hydrophilic.

[0053]

[0054] Next, the method for manufacturing a nanocomposite for an energy storage device cathode according to the present invention includes a step [step (b)] of manufacturing an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with carboxyl groups are nanoblended by performing a reaction of replacing organic ligands on the surface of transition metal oxide nanoparticles with the surface-modified carbon black. Here, since the "assembly in which transition metal oxide nanoparticles and carbon black surface-modified with carboxyl groups are nanoblended" has been described above, a redundant description will be omitted.

[0055] The reaction of replacing the organic ligand on the surface of the transition metal oxide nanoparticle by the surface-modified carbon black can be performed by immersing the negative electrode current collector, on which the surface-modified carbon black is adsorbed on the outermost surface, in a solution containing the transition metal oxide nanoparticle. The solution containing the transition metal oxide nanoparticle is a solution containing an organic ligand (native ligand) on the surface of the transition metal nanoparticle, and the organic ligand may have a relatively large volume and low affinity (i.e., adsorption energy). Specifically, the organic ligand may be oleic acid, oleylamine, or the like, wherein oleic acid corresponds to a monodentate / bidentate ligand, and oleylamine corresponds to a monodentate ligand.

[0056] The above immersion can be performed for about 1 minute to about 20 minutes, thereby performing a ligand substitution reaction. That is, carbon black surface-modified with a carboxyl group, which is a multidentate ligand, can be coordinately bonded to the surface of the transition metal oxide nanoparticles instead of the organic ligand.

[0057] Therefore, the above transition metal oxide nanoparticles and the carbon black surface-modified with the carboxyl group can form a double layer and then form a nanoblended assembly through layered self-assembly by repeating immersion.

[0058]

[0059] Cathode and energy storage devices

[0060]

[0061] The present invention provides an energy storage device negative electrode comprising a negative electrode current collector; and a nanocomposite for negative electrode coated on the negative electrode current collector.

[0062] In addition, the present invention provides an energy storage device including the cathode.

[0063]

[0064] An energy storage device according to the present invention comprises the negative electrode, characterized in that the negative electrode comprises a negative electrode current collector; and the negative electrode nanocomposite coated on the negative electrode current collector. Here, since the "negative electrode nanocomposite" has been described above, a redundant description will be omitted.

[0065]

[0066] The energy storage device is a device that stores produced electric energy and allows it to be used when power is needed, and includes lithium-ion batteries (LIBs) and pseudocapacitors. These devices require electrodes that are smaller and lighter than existing devices, and need to have high energy / power density, long-term operating stability, and improved area performance (capacity). In addition, the energy storage device is configured to include a separator, a positive electrode and a negative electrode positioned with the separator between them, and an electrolyte in contact with the positive electrode and the negative electrode. The negative electrode current collector and the negative electrode nanocomposite described below can be applied to the negative electrode.

[0067] The above negative electrode current collector may be made of a known conductive material such as a Ni or Cu plate, and is preferably based on a conductive fabric support to have both flexible properties and conductivity, but is not limited thereto.

[0068] Specifically, the conductive fabric support is an insulating fabric support that has been made conductive, and may be made by coating a conductive coating material on the insulating fabric support, or by carbonizing the insulating fabric support through heat treatment and then performing electroplating to provide conductivity. At this time, the insulating fabric support is a fabric support in which a plurality of fibers are interwoven and have a plurality of pores created by the intersecting fibers. These fibers are long, thin, and softly bendable linear objects, and may include both natural fibers and synthetic fibers. Therefore, the insulating fabric support has flexible properties by weaving natural fibers or synthetic fibers alone, or by blending and weaving these fibers. For example, the fibers may be one or more selected from the group consisting of cotton, polyester, nylon, and acrylic fibers, but are not limited thereto.

[0069] Meanwhile, the negative electrode current collector can be surface-modified with an amine group. For example, the negative electrode current collector can be surface-modified with a hydroxyl group first, and then immersed in a polyethyleneimine (PEI) solution or the like, thereby finally surface-modifying the negative electrode current collector with an amine group. At this time, the amine group can form a hydrogen bond with a carboxyl group present on the surface of the carbon black.

[0070]

[0071] As reviewed above, the nanocomposite for an energy storage device cathode according to the present invention is characterized by including an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with carboxyl groups are nanoblended, so that uniform distribution of carbon black surface-modified with carboxyl groups can be induced within the assembly without a polymer binder, thereby effectively reducing contact resistance between adjacent transition metal oxide nanoparticles.

[0072] The nanocomposite for an energy storage device cathode according to the present invention can be usefully applied to high-performance energy storage devices and electrodes such as lithium-ion batteries and pseudocapacitors.

[0073]

[0074] Hereinafter, preferred examples are presented to aid in understanding the present invention. However, the following examples are provided solely to facilitate a better understanding of the present invention, and the scope of the present invention is not limited by the following examples.

[0075]

[0076] [Example]

[0077] ingredient

[0078] Iron(III) acetylacetonate (Fe(acac)3, 97%), 1,2-hexadecanediol (90%), oleic acid (OA, 90%), oleylamine (OAm, 70%), benzyl ether (98%), polyethyleneimine (PEI, branched, M w ~800), polyacrylic acid (PAA, M v~450,000), Fe3O4 nanopowder (particle size: 50–100 nm, 97%), and fluoroethylene carbonate (FEC, 99%) were purchased from Sigma-Aldrich. Organic solvents (ethanol and toluene), sulfuric acid (H2SO4, 98%), and nitric acid (HNO3, 60%) were purchased from Daejung Chemical (Korea). Carbon nanoclusters (CN) were purchased from MTI Korea (Korea). Lithium hexafluorophosphate (LiPF6, 1.0 mol L) dissolved in a solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7. -1 ) organic electrolytes were purchased from Dongwha Electrolyte (Korea). All chemical reagents were used as received without further purification.

[0079] Synthesis of OA-Fe3O4 NPs

[0080] Monodispersed OA-Fe3O4NPs with an average diameter of ~7 nm in toluene were synthesized using a previously reported protocol. Fe(acac)3 (2 mmol), 1,2-hexadecanediol (10 mmol), OA (6 mmol), OAm (6 mmol), and benzyl ether (20 mL) were added to a three-necked flask with vigorous stirring under an inert gas flow. The reaction mixture was then heated at 200 °C for 2 h and sequentially at 300 °C for 1 h. After the reaction was completed, the heating mantle was removed, the flask was cooled to room temperature, and an excess of ethanol was added to precipitate the OA-Fe3O4NPs, which were then centrifuged (8000 rpm, 10 min). The separated OA-Fe3O4NPs were dissolved in toluene containing OA (0.05 mL) and OAm (0.05 mL). Additional centrifugation (8000 rpm, 10 min) was performed several times with excess ethanol to collect pure OA-Fe3O4NPs, which were re-dissolved in toluene for further use.

[0081] Synthesis of CCN

[0082] COOH-functionalized CN (CCN) was prepared by acid treatment of hydrophobic CN. Briefly, CN (0.5 g) was added to a single-necked flask with stirring in a mixture of H2SO4 (30 mL) and HNO3 (10 mL) under atmospheric conditions and surface treated at 70°C for 3 h. After the reaction was completed and the flask was cooled to room temperature, the product was slowly purified using triple-distilled water, followed by centrifugation (10,000 rpm, 10 min) and vacuum filtration to completely remove any residual acid. The vacuum-filtered CCN film was completely dried in a vacuum oven and dissolved in ethanol for further use.

[0083] Layered self-assembly of (Fe3O4 NP / CCN)n composite

[0084] First, all experimental procedures for layered self-assembly were performed in a fume hood for safety. The concentrations of OA-Fe3O4NP dissolved in toluene and CCN dissolved in ethanol were 10 and 2 mg mL, respectively. -1 The flat substrates (including Si wafers, SiO2 / Si wafers, gold-sputtered Si wafers, quartz glass, QCM electrodes, and Ni plates) were surface-treated using a UV-ozone treatment unit for 30 min, and the porous FCC was used without further surface treatment. These surface-treated substrates were treated with an amine (NH2)-functionalized PEI solution (2 mg mL in ethanol). -1 ) for 30 minutes to form a solid lower layer, then washed with pure ethanol to remove weakly adsorbed substances, and dried to remove residual solvent. Subsequently, the PEI-coated substrate was immersed in the OA-Fe3O4NP solution (washed with toluene and dried) and the CCN solution (washed and dried) for 10 minutes each to form (Fe3O4NP / CCN). n A single bilayer of the complex was created. This experimental procedure was repeated until the desired number of bilayers (n) was obtained.

[0085] Fabrication of slurry-FCC electrodes

[0086] Active Fe3O4 nanopowder, conductive CN, COOH-functionalized PAA binder in a weight ratio of 8:1:1, 50 mg mL in ethanol -1 A slurry was prepared by mechanically dispersing the solution at a concentration of . Next, the slurry was layered on the FCC through a dip coating method and dried in a vacuum oven at 120°C for 8 hours to prepare an electrode.

[0087] Lithium-ion battery (LIB) measurement

[0088] To evaluate the electrochemical properties of LIB electrodes using Ni plate or porous FCC as current collector, half cells were assembled in an argon-filled glove box (O2<0.1 ppm, H2O<0.1 ppm) using Li foil as counter / reference electrode, Celgard separator, and CR2032-type coin cells. LiPF6 (1.0 mol L) dissolved in a mixture of EC / DMC (3:7, v / v) with FEC additive (10 wt%) was used. -1 ) solution was used as an organic electrolyte. Electrochemical measurements were performed at room temperature in the range of 0.01 to 3.0 V (vs. Li + / Li) was performed in the voltage range, and the impedance was 10 with an amplitude of 0.01 mV. 5 It was measured in the frequency range of 0.01 Hz.

[0089]

[0090] Example 1: Preparation of CCN-mediated Fe3O4 NP electrode

[0091] To fabricate high-performance energy storage electrodes with high capacity and excellent rate performance, we first synthesized OA-Fe3O4NPs with a diameter of ~7 nm dispersed in toluene and CCN (in this case, CCN is composed of bundles of ~20 nm-sized CB) dispersed in ethanol, which were confirmed by high-resolution transmission electron microscopy (HR-TEM) analysis (Fig. 2(a)-(b)). When CCN was spin-coated on a SiO2 / Si wafer with a thickness of ~420 nm, the electrical conductivity and sheet resistance of the formed CCN film were ~1.97 S cm, respectively. -1 and ~1.21 × 10 4 W sq -1 was measured. From these results, it was found that the surface-modified CCN could effectively function as a conductive component in the electrode. In addition, the hydrophilic COOH group on the CCN surface enabled CCN to have good dispersion stability in ethanol (Fig. 2(b)).

[0092] A notable feature of CCN is that it can be sequentially assembled with OA-Fe3O4NP through an in situ ligand substitution reaction between the COOH group of CCN and bulky organic ligands (i.e., OA and OAm) bound to the NP surface. To better understand this ligand substitution reaction, (Fe3O4NP / CCN) n The FTIR spectra of the complexes were analyzed according to the number of bilayers (n) (Fig. 2(c)). In this case, OA-Fe3O4NP showed a peak at 3000–2800 cm -1In the wavenumber range of , a strong CH stretching peak due to the long alkyl chain of the native OA / OAm ligand was observed. On the other hand, in the case of CCN with COOH groups without alkyl chains, no absorption peak was detected in the same range. Therefore, the effective substitution reaction of the native ligand by the COOH group of CCN on the surface of Fe3O4NP could be clearly confirmed by the anticorrelated changes in the CH stretching peaks during the alternating stacking of OA-Fe3O4NP and CCN.

[0093] In particular, when CCN is assembled with OA-Fe3O4NP, the neutral COOH group on the CCN surface can form a strong bond with one or two O atoms and Fe atoms on the NP surface, forming an anionic carboxyl ion (COO - ) was converted to COOH groups. That is, CCN with multiple COOH groups acted as a multidentate ligand with higher affinity (i.e., adsorption energy) for the surface of Fe3O4NP than the native monodentate / bidentate OA and monodentate OAm ligands, effectively removing bulky organic ligands. This phenomenon demonstrated that CCN could directly connect all interfaces between adjacent Fe3O4NPs based on the coordination bonds induced by the ligand substitution reaction without using a polymer binder.

[0094] These ligand substitution reactions have different layer numbers (Fe3O4NP / CCN) nThis could be further confirmed by measuring the water contact angle of the composite (Fig. 2(d)). When the OA-Fe3O4NP layer was deposited on the substrate, the contact angle was measured to be 89 ± 5°, indicating a hydrophobic surface characteristic due to the native ligand remaining on the top surface of the Fe3O4NP. However, when a hydrophilic CCN layer was additionally deposited on the substrate coated with the OA-Fe3O4NP layer, the contact angle decreased significantly to 19 ± 2°. This large change in the contact angle was periodically observed as the outermost layer was changed from OA-Fe3O4NP to CCN or vice versa, which meant that the hydrophobic native ligand on the NP surface was effectively removed by the hydrophilic CCN during the assembly process.

[0095] (Fe3O4NP / CCN) n The overall film thickness of the composite increased linearly from ~99 (n = 5) to 425 nm (n = 20), showing a uniform distribution of CCN within the Fe3O4NP array, as observed by field-emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) elemental mapping (Fig. 2(e)). The formed (Fe3O4NP / CCN) n The composite has a uniform nanoblended structure and is similar to the previously reported slurry-coated FeO x -Higher than the base electrode by ~2.68 g cm -3 showed a mass density of . These results demonstrated that the present CCN-mediated nanoblending assembly can produce electrode structures that are very uniformly and densely filled with NPs with precisely controlled introduction amount (or film thickness).

[0096] In addition, the present inventors verified the role of CCN as a conductive linker (Fe3O4NP / CCN) 20 The electrical properties of the composite were investigated (Fig. 2(f)). In this case, the CCN-mediated Fe3O4NP thin film showed a conduction mechanism relationship between the current density (J) and the electric field (E) (J ∝Eα ) with ohmic conduction behavior at much higher current levels (~10 -1 mA) and it exhibited insulating properties (α is ~0.01 and ~10 -8 This contrasted sharply with the OA-Fe3O4NP films, which exhibited a current level of 10 mA. This remarkable improvement in the electrical properties of the CCN-mediated Fe3O4NP films was attributed to the formation of uniform nanoblend / interconnected structures by conductive CCN during the layer-by-layer self-assembly process and the effective removal of insulating native ligands, which significantly reduced the contact resistance occurring at the interface between adjacent Fe3O4NPs.

[0097]

[0098] Example 2: LIB electrode using CCN-mediated Fe3O4 NP assembly

[0099] Based on the successful formation of the CCB-mediated Fe3O4NP electrode, the electrochemical properties were investigated to confirm the applicability of the electrode as a LIB cathode. (Fe3O4NP / CCN) laminated on a Ni plate 20 Composite ((Fe3O4NP / CCN) 20 Coin-type half-cells were assembled using Li foil as a counter / reference electrode and LiB electrode (denoted as -LIB electrode). First, the Li storage behavior of the electrodes was examined at 0.1 mV s -1 At a scan rate of 0.01 to 3.0 V (vs. Li + / Li) was analyzed by cyclic voltammetry (CV) scans in the voltage range (Fig. 3(a)). In the first reductive sweep, weak reduction peaks at ~1.60 and 1.01 V were attributed to the following reaction [Fe3O4+ xLi + + xe →Li x As described in (Fe3O4), max x = 2], Li x Irreversible Li into crystalline Fe3O4 to form (Fe3O4) +was attributed to the insertion. Afterwards, a strong reduction peak at ~0.64 V was observed in Li x Fe in (Fe3O4) 0 / Conversion reaction to Li2O mixture [Li x (Fe3O4) + (8-x)Li + + (8-x)e →3Fe 0 + 4Li2O] as well as the formation of an inorganic solid electrolyte interface (SEI) layer due to irreversible electrolyte decomposition. In sequential oxidative sweeps, Fe 0 In Fe 2+ and Fe 3+ Two broad oxidation peaks associated with the reconversion reaction were observed at ~1.60 and 1.86 V, respectively. From the second CV cycle onwards, both the reduction and oxidation peaks shifted slightly to higher voltage values, indicating an improved redox behavior due to the reduced polarization caused by the formation of Fe3O4 nanoparticles with smaller sizes than the original NPs during the activation process. The subsequent CV curves gradually overlapped well with each other, suggesting a reversible and stable Li storage behavior of the electrode.

[0100] 0.1 A g -1 (Fe3O4NP / CCN) at a current density of 20 The galvanostatic charge-discharge (GCD) curve of the LIB electrode also showed a conversion reaction-based electrochemical behavior consistent with the CV results (Fig. 3(b)). The total mass of the complex (~0.11 mg cm -2 ), the first discharge cycle yielded a relatively low coulombic efficiency of ~76.7% and a specific capacity of ~1,655 mAh g -1The specific capacity was calculated. This irreversible capacity loss in the initial cycle was caused by the inevitable formation of an inorganic SEI layer and electrolyte decomposition, as commonly observed in nanostructured metal oxide-based LIB cathodes with large active surface areas. In the fifth cycle, the discharge capacity was approximately ~1,205 mAh g at a Coulombic efficiency of ~96.5%. -1 The capacity decreased and the capacity value remained almost constant in the subsequent cycles. Interestingly, the obtained capacity value is higher than the theoretical capacity of Fe3O4 (~924 mAh g -1 ) was far exceeded, which could be explained by (1) partial capacity contribution of CCN and (2) additional storage capacity by electrolyte-derived surface layer in low voltage range. For a deeper understanding of electrolyte-derived surface layer, differential capacity vs. voltage curve of electrode was plotted at 0.1 A g -1 The voltage range is from the 5th GCD cycle at a current density of (I) Fe3O4 lattice. In this case, the voltage range is (I) Li into the Fe3O4 lattice. + It can be divided into three regions: (I) insertion (3.00-1.25 V), (II) conversion reaction of Fe3O4 nanoparticles (1.25-0.75 V), and (III) electrolyte-derived surface layer (0.75-0.01 V). As confirmed in the voltage range indicated by region (III), the capacity due to the electrolyte-derived surface layer accounted for a significant portion of the total capacity, which clearly supported the existence of additional capacity in the low voltage range.

[0101] Next, 0.1 A g -1 By measuring the specific capacity while gradually increasing the current density after 5 initial activation cycles in (Fe3O4NP / CCN) 20 -The rate performance of the LIB electrode was evaluated (Fig. 3(d)). The current density was 0.1 to 2.0 A g -1 As the charge increases, the average specific capacity is ~1,205 to 610 mAh g -1, which corresponds to a capacity retention of ~50.7%. The current density was again 0.1 A g -1 When the specific capacity was reduced to , the specific capacity recovered to ~98.0% of the initial capacity, indicating excellent reversibility of the electrode. These excellent capacitance values ​​and rate performance could be explained by the fact that the uniformly distributed CCN networks within the dense Fe3O4NP array provide well-interconnected charge transfer paths, enabling efficient Li storage behavior despite high electrode density.

[0102] Since metal oxide-based LIB cathodes inevitably undergo a significant volume expansion of the active material (approximately ~100% for Fe3O4) during the Li storage process, long-term operating stability must be considered to ensure successful application in LIBs. Therefore, (Fe3O4NP / CCN) 20 -The cycling performance of the LIB electrode is 1.0 A g -1 The GCD cycles were investigated at a current density of 3000 (Fig. 3(e)). The initial discharge capacity was ~792 mAh g -1 was measured at ~690 mAh g after 60 cycles. -1 Then, after 500 cycles, it decreased to ~800 mAh g -1 The gradual capacity increase (i.e., negative fading) with these cycles could be attributed to the pseudocapacitance behavior and / or activation process of the polymer gel-like layer formed on the electrode surface. Consequently, the electrode retained ~81.6% (~646 mAh g) of its initial capacity with a high Coulombic efficiency of ~99.0% even after 3000 cycles. -1 ) was maintained. This excellent operating stability signified the excellent structural integrity of the electrode through the robust interfacial interaction between CCN and Fe3O4, which could effectively protect against repeated volume changes of the active Fe3O4.

[0103]

[0104] Example 3: FCC-based LIB electrode using CCN-mediated Fe3O4 NP assembly

[0105] Thin film type (Fe3O4NP / CCN) n Although composites can achieve excellent properties in terms of specific / volumetric capacity, rate performance, and operating stability in LIBs, their low areal performance level due to the low introduction amount of active materials has limited their practical use. Although (Fe3O4NP / CCN) n Although the introduction of the composite could be further increased by increasing the number of double layers, the thicker electrode layers would inevitably increase the charge transfer length, which could adversely affect the overall energy efficiency. To address this critical issue, the inventors used a three-dimensional porous FCC with a large specific surface area instead of a nonporous planar collector. Due to the structural advantages of the porous FCC (Fe3O4NP / CCN) n The introduction amount of the complex was increased by about 54 times compared to when using a planar collector with the same number of double layers.

[0106] In particular, the present CCN-mediated nanoblending assembly was able to effectively introduce electrode components into all accessible areas from the outside to the inside of the porous FCC. The high introduction amount of the composite (~6.2 mg cm -2), the Fe3O4NP array was uniformly and densely coated on the entire surface of the porous structure without noticeable NP agglomeration and pore blockage, as confirmed in the FE-SEM image (Fig. 4(a)). Meanwhile, we also prepared a comparative sample using dip coating of a slurry obtained by mechanically mixing commercial Fe3O4 nanopowder, CN, and COOH-functionalized polymer binder (polyacrylic acid; PAA). In this case, the slurry-coated FCC showed an inhomogeneous fibril structure with agglomerated phase and blocked pores due to the high viscosity of the slurry and unfavorable interfacial interactions between the electrode components (Fig. 4(b)). In particular, the agglomerated phase and blocked pores of Fe3O4NP with low conductivity can significantly limit charge transfer within the electrode and full utilization of the large surface area of ​​FCC, so slurry-coated FCC (denoted as slurry-FCC) is (Fe3O4NP / CCN). 20 FCC coated with composite ((Fe3O4NP / CCN) 20 -FCC) is predicted to show overall inferior energy storage performance.

[0107] To determine the effect of porous FCC and electrode layer uniformity on energy storage performance, (Fe3O4NP / CCN) 20 -FCC and slurry-FCC electrodes were introduced at the same dose (~6.2 mg cm -2 ) and their electrochemical properties were investigated. (Fe3O4NP / CCN) 20 -FCC electrode is 0.1 mV s -1 In the fifth CV scan at a scan rate of , a higher current response was observed compared to the slurry-FCC electrode (Fig. 4(c)). In this case, the area charge density estimated from the integrated CV area was (Fe3O4NP / CCN) 20 -In the case of FCC electrode (Fe3O4NP / CCN) 20-It was approximately 48 times higher than that of the LIB flat electrode, and simultaneously exhibited distinct oxidation / reduction peaks corresponding to the conversion reaction of Fe3O4. These results clearly demonstrate that the porous FCC significantly improves the areal performance of the electrode by enabling high introduction of Fe3O4NP without compromising the charge transfer behavior.

[0108] To further confirm the advantages of porous FCC, the present inventors (Fe3O4NP / CCN) 20 -The GCD curves of the FCC and slurry-FCC electrodes were investigated according to the current density (Fig. 4(d)). In this case, all GCD measurements were performed at 0.1 A g -1 After five initial activation cycles, (Fe3O4NP / CCN) 20 -FCC electrode is 0.1 A g -1 ~5.67 mAh cm -2 It delivered a maximum average area capacity of 2.0 A g -1 ~42.0% of initial capacity (~2.38 mAh cm -2 ) was maintained. On the other hand, the slurry-FCC electrode was maintained at 0.1 A g -1 ~3.04 mAh cm -2 It showed an output area capacity of 2.0 A g -1 At ~28.6% (~0.87 mAh cm -2 ) showed capacity retention. In addition, the current density was 0.1 A g at 2.0 -1 When returned to the slurry-FCC electrode, it recovered only ~80.1% of its original capacity and showed continuous capacity decay, which was lower than that of the (Fe3O4NP / CCB) electrode, which recovered ~90.5% of its original capacity. 20 -This contrasted sharply with the FCC electrode. This significant difference in performance levels was further confirmed by electrochemical impedance spectroscopy (EIS). (Fe3O4NP / CCB) 20- The FCC electrode exhibited a significantly lower charge transfer resistance (~44 W) compared to the slurry-FCC electrode (charge transfer resistance: ~346 W) (Fig. 4(e)), indicating excellent charge transfer behavior at the electrode / electrolyte interface. In addition, (Fe3O4NP / CCB) 20 -FCC electrode is 1.0 A g -1 Even after 300 GCD cycles at a current density of ~99.7% Coulombic efficiency and ~82.5% (~2.93 mAh cm -2 ) showed a capacity retention of ~61.3% (~1.14 mAh cm) of the initial capacity, but the slurry-FCC electrode retained ~61.3% (~1.14 mAh cm) of the initial capacity. -2 ) was maintained (Fig. 4(f)). Consequently, the CCN-mediated nanoblending assembly was quite useful in inducing efficient spatial distribution / arrangement of electrode components and utilizing the large surface area of ​​the porous FCC.

[0109]

[0110] The foregoing description of the present invention is for illustrative purposes only. Those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. A nanocomposite for an energy storage device cathode comprising an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with carboxyl groups are nanoblended.

2. In paragraph 1, A nanocomposite for an energy storage device cathode, characterized in that the nanocomposite for an energy storage device cathode is in a binder-free form.

3. In paragraph 1, A nanocomposite for an energy storage device cathode, characterized in that the above transition metal oxide nanoparticles are at least one nanoparticle selected from the group consisting of iron oxide, manganese oxide, titanium oxide, and ruthenium oxide.

4. In paragraph 1, A nanocomposite for an energy storage device cathode, characterized in that the surface-modified carbon black has hydrophilicity.

5. In paragraph 1, A nanocomposite for an energy storage device cathode, characterized in that the surface-modified carbon black is manufactured by treating carbon black with an acid solution.

6. In paragraph 1, A nanocomposite for an energy storage device cathode, characterized in that the nanoblended assembly is formed through coordination bonding between the surface of the transition metal oxide nanoparticles and the carboxyl group of the modified carbon black. 7.(a) a step of producing carbon black surface-modified with carboxyl groups; and (b) A method for producing a nanocomposite for an energy storage device negative electrode, comprising the step of producing an assembly in which transition metal oxide nanoparticles and carbon black surface-modified with carboxyl groups are nanoblended by performing a reaction of replacing organic ligands on the surface of transition metal oxide nanoparticles with the surface-modified carbon black.

8. Negative current collector; and An energy storage device negative electrode comprising a nanocomposite for negative electrode according to any one of claims 1 to 6 coated on the negative electrode current collector.

9. In paragraph 8, An energy storage device negative electrode, characterized in that the negative current collector is based on a conductive fabric support surface-modified with an amine group.

10. An energy storage device comprising a cathode according to Article 8.

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