WO2015156446A1 - Graphene-metal nanoparticle composite, carbon nanofiber composite containing composite, and secondary battery containing carbon nanoparticle composite - Google Patents

Graphene-metal nanoparticle composite, carbon nanofiber composite containing composite, and secondary battery containing carbon nanoparticle composite Download PDF

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WO2015156446A1
WO2015156446A1 PCT/KR2014/005507 KR2014005507W WO2015156446A1 WO 2015156446 A1 WO2015156446 A1 WO 2015156446A1 KR 2014005507 W KR2014005507 W KR 2014005507W WO 2015156446 A1 WO2015156446 A1 WO 2015156446A1
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composite
graphene
carbon nanofiber
carbon
metal
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French (fr)
Korean (ko)
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양갑승
김보혜
김소연
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전남대학교산학협력단
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
    • B82B1/00—Nanostructures formed by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a carbon nanofiber composite, and more particularly, to a graphene-metal nanoparticle composite, a carbon nanofiber composite including the composite, and a secondary battery including the carbon nanoparticle composite.
  • lithium metal is used as a negative electrode active material of a lithium secondary battery.
  • carbon-based negative electrode active materials are used instead of lithium metal.
  • graphite graphite
  • the carbon-based negative electrode active material such as graphite has a limited upper limit of about 372 mAh / g. Insufficient negative electrode materials are available.
  • the development of electric vehicles is urgently required due to the depletion of fossil fuels.However, when the existing lithium secondary battery is applied, it is difficult to operate a long distance of more than 200km by a single charge. It is also not suitable for long-term energy storage systems for storing power generated by sources.
  • metal-based anode materials especially silicon (Si) -based anode materials
  • Si silicon
  • the silicon anode material has a problem that a large volume change of more than 300% occurs by causing a change in crystal structure when absorbing and storing lithium.
  • Graphite which is currently used as a cathode material, has a volume expansion rate of about 1.2 times due to lithium charging, whereas, in case of silicon, when lithium is absorbed and stored in the maximum amount, it is converted to Li 4.4 Si and is about 4.12 times larger than the volume of silicon before volume expansion. Because of the expansion, the volume of the electrode collapses due to the volume expansion, and thus the coulombic efficiency becomes low, making it difficult to continue using.
  • the lithium ion battery can be improved during the intercalation / desorption process of lithium.
  • the negative electrode active material for a silicon-based lithium secondary battery hybridized with carbon nanofibers prepared by vapor-growing carbon-coated silicon nanoparticles or carbon nanofibers is pyrolysis method, chemical / thermal vapor deposition (CVD / TVD) method, and chemicals using gel. Synthesis and hydrothermal carbonization methods are used, and these methods require high temperature reaction conditions, require expensive precursors, and have difficulty in commercialization because they are difficult to mass produce.
  • nanostructured electrodes are expected to significantly improve the energy density and velocity characteristics, and the relaxation and speed of volume change due to the insertion / extraction of lithium ions. If the anode or cathode materials have high specific surface area, the solid-state diffusion path is reduced and the interface between anode-membrane-cathode is greatly increased. Therefore, the three-dimensional structure of the nanostructured material will enable high-rate discharge characteristics and high-output lithium-ion batteries. do.
  • nanostructured materials as electrode material by electrospinning not only provides excellent electron conductivity and reduces the diffusion path in the electrode, but also a lot of Li + It is possible to alleviate the stress generated in the lithium secondary battery with high output and high energy density is expected.
  • electrospinning is the only method that can produce hundreds of nanometers to tens of nanofibers using a polymer solution.
  • Carbon nanofibers manufactured using these electrospinning techniques have high electrical conductivity, high specific surface area, metal, Since carbon nanofibers containing metal oxides, porous materials, carbon nanotubes, and the like are easily manufactured, very high electrochemical activity can be expected when manufacturing secondary battery electrode materials.
  • Carbon nanofiber composites and activated carbon nanofiber composites prepared from the composite components of the present invention are excellent in specific surface area and electrical conductivity relative to volume, and constituent fibers form a network. It can be used as an electrode material for electric double layer supercapacitor, electromagnetic wave shielding material, high conductivity material, catalyst support and composite material reinforcement material.
  • the metal nanoparticles are prevented from growing too large or aggregated to prevent them from becoming large particles, and the metal nanoparticles are uniformly dispersed in the carbon nanofibers, and the volume change is alleviated, thereby improving the electrical contactability.
  • a negative electrode active material capable of securing cycle characteristics.
  • the present inventors have completed the present invention by focusing on the fact that a large number of studies have been made to surround the metal nanoparticles with a graphene sheet to prevent the metal nanoparticles from agglomerating into large particles.
  • Another object of the present invention is to provide a carbon nanofiber composite having a graphene-metal nanoparticle composite (G / M composite) evenly dispersed in a carbon nanofiber matrix and a method of manufacturing the same.
  • Another object of the present invention is to include a carbon nanofiber composite containing a G / M composite as an electrode active material, so that the metal nanoparticles are not exposed to the outside of the carbon nanofibers to buffer the volume change of the metal nanoparticles due to charging and discharging
  • an electrode capable of inducing an effective electrochemical reaction by reducing the specific resistance of the electrode surface by preventing the aggregation of metal nanoparticles.
  • Still another object of the present invention is to provide a secondary battery having excellent charge and discharge characteristics, high capacity, and excellent volume stability by applying an electrode including a carbon nanofiber composite having a G / M composite evenly dispersed therein as an electrode active material.
  • the object of the present invention is not limited to the above-mentioned object, and even if not explicitly stated, the object of the invention that can be recognized by those skilled in the art can be naturally included from the description of the detailed description below. .
  • the present invention is a metal nanoparticle; It provides a graphene-metal nanoparticle composite comprising a; and a graphene sheet formed by surrounding the metal nanoparticles.
  • the metal nanoparticles are selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au.
  • the metal nanoparticles are modified to have a -NH 2 group.
  • the metal nanoparticles and the graphene sheet are coupled by electrostatic attraction.
  • the graphene-metal nanoparticle composite has a size of 50nm or less.
  • the present invention carbon nanofibers; It provides a carbon nanofiber composite comprising a; and graphene-metal nanoparticle composite constituting a portion of the carbon nanofiber.
  • the graphene-metal nanoparticle composite is a metal nanoparticle; And a graphene sheet formed by wrapping the metal nanoparticles.
  • the metal nanoparticles are selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au.
  • the metal nanoparticles are modified to have a -NH 2 group.
  • the metal nanoparticles and the graphene sheet are coupled by electrostatic attraction.
  • the carbon nanofiber composite has a diameter of 100 to 300 nm, a specific surface area of 300 m 2 / g or less, and an average pore diameter of 1 to 2 nm.
  • the graphene-metal nanoparticle composite is located uniformly dispersed in the carbon nanofibers.
  • the graphene-metal nanoparticle composite can be pulverized to form a powder in a state maintained.
  • the graphene-metal nanoparticle composite has a size of 50nm or less.
  • the present invention comprises the steps of preparing a spinning solution comprising any one of the above-described graphene-metal nanoparticle composite and carbon fiber precursor; Electrospinning the spinning solution to obtain precursor spinning fibers; Oxidatively stabilizing the precursor spun fiber to obtain a flame resistant fiber; And carbonizing the flame resistant fiber to obtain a carbon nanofiber composite.
  • the spinning solution is contained within 30 parts by weight of the graphene-metal nanoparticle composite per 100 parts by weight of the carbon nanofiber precursor and the graphene-metal nanoparticle composite.
  • the carbon nanofiber precursor and graphene-metal nanoparticle composite are included in a weight ratio of 4: 1 to 20: 1.
  • the concentration of the graphene-metal nanoparticle composite contained in the spinning solution to control one or more of the size and distribution of the graphene-metal nanoparticle composite contained in the carbon nanofiber composite.
  • the present invention provides an electrode comprising any one of the carbon nanofiber composites described above as an electrode active material.
  • the carbon nanofiber composite is in powder form.
  • the present invention provides a secondary battery comprising the electrode described above.
  • the secondary battery does not separate the electrode active material contained in the electrode even after 100 cycles of charge and discharge.
  • the secondary battery maintains a discharge capacity of 600 mAh / g even after 100 cycles of charge and discharge.
  • the present invention has the following excellent effects.
  • the graphene-metal nanoparticle composite of the present invention it is possible to prevent the metal nanoparticles from growing too large or aggregated to become large particles.
  • the electrode of the present invention includes a carbon nanofiber composite containing a G / M composite as an electrode active material, so that the metal nanoparticles are not exposed to the outside of the carbon nanofibers to buffer the volume change of the metal nanoparticles due to charging and discharging.
  • the specific resistance of the electrode surface can be reduced to induce an effective electrochemical reaction.
  • the secondary battery of the present invention can secure excellent charge and discharge characteristics, high capacity, excellent volume stability and the like by applying an electrode including a carbon nanofiber composite evenly dispersed G / M complex as an electrode active material.
  • FIG. 1 is a manufacturing process diagram showing an embodiment of manufacturing graphene oxide (GO) using the Hammers method (Hummers method) to produce a G / M complex according to an embodiment of the present invention.
  • FIG. 2 is a manufacturing process diagram showing an embodiment of manufacturing Amino-functionalized silicon nanoparticles to prepare a G / M complex according to an embodiment of the present invention.
  • Figure 3 is a schematic diagram of manufacturing a silicon composite (G / Si) surrounded by graphene (G) of one embodiment of the G / M complex according to an embodiment of the present invention.
  • FIG. 4 is a manufacturing process diagram of the G / Si composite shown in FIG.
  • FIG 5 (a) is a scanning microscope picture of the graphene oxide (GO) prepared according to Figure 1
  • (b) is a transmission microscope picture of graphene oxide (GO).
  • FIG 6 (a) is a scanning microscope picture of the G / Si composite prepared according to Figure 4, (b) is a high magnification scanning microscope picture of the G / Si complex, d is a transmission microscope picture of the G / Si complex, (d) is a high magnification transmission micrograph of a G / Si composite.
  • FIG. 7 is a schematic view and web pictures of carbon nanofiber composite (GSP) manufacturing process including graphene-silicon nanoparticles according to another embodiment of the present invention ((a) precursor radiation fiber, (b) flame-resistant fiber, (c) ) Carbonized fiber].
  • GSP carbon nanofiber composite
  • GSP carbon nanofiber composite
  • FIG. 8 is a scanning micrograph according to graphene-silicon nanoparticle composite content in a carbon nanofiber composite (GSP) including graphene-silicon nanoparticles according to another embodiment of the present invention [(a) 5 wt% G / Si containing, (b) containing 10 wt% G / Si, (c) containing 20 wt% G / Si, (d) containing 20 wt% Si].
  • (A) to (c) is a transmission micrograph according to the graphene-silicon nanoparticle composite content in the carbon nanofiber composite (GSP) including the graphene-silicon nanoparticles according to another embodiment of the present invention [(a) 10-GSP, (b) 20-GSP, (c) 20-SP], and (d) are 10-GSP Limited Field Electron Diffraction (SAED).
  • GSP carbon nanofiber composite
  • SAED 10-GSP Limited Field Electron Diffraction
  • (a) is an X-ray diffraction pattern (XRD) graph of GSP, G / Si, and GO
  • (b) is a Raman spectrum graph of GSP, G / Si, and GO.
  • (a) is a charge and discharge result graph of CNF
  • (b) is a charge and discharge result graph of 5-GSP
  • (c) is a charge and discharge result graph of 10-GSP
  • (d) is a 20-GSP. The charge and discharge results of the graph.
  • FIG. 12 shows a differential capacity curve of 20-GSP, and (b) shows a Nyquist plot of GSP and CNF.
  • (a) is a 50 cycle characteristic result graph of 20-GSP, 10-GSP, 5-GSP, and CNF
  • (b) is a 50 cycle characteristic result graph of 20-SP.
  • FIG 16 (a) is a top-view scanning micrograph before charge and discharge of grinded 20-GSP according to another embodiment of the present invention, (b) is a top-view scanning microscope picture after 100 cycles of charge and discharge, ( c) is a top-view scanning micrograph before charge and discharge of silicon nanoparticles, and (d) is a top-view scan micrograph of silicon nanoparticles after 100 cycles of charge and discharge.
  • the metal nanoparticles are not exposed to the outside of the carbon nanofibers, thereby buffering the volume change of the metal nanoparticles due to charging and discharging as well as the metal.
  • This is because it is possible to provide an electrode and a secondary battery having excellent charge / discharge characteristics, high capacity, and excellent volume stability by preventing the aggregation of nanoparticles, thereby reducing the resistivity of the electrode surface to induce an effective electrochemical reaction.
  • the G / M complex of the present invention is a metal nanoparticle; And a graphene sheet formed by surrounding the metal nanoparticles. This structure prevents the agglomeration and particle growth of the metal nanoparticles and can uniformly disperse the metal nanoparticles in the carbon nanofiber matrix.
  • the metal nanoparticles may be one or more selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au, the silicon (Si) -based negative electrode material
  • the theoretical capacity is about 4,200 mAh / g, which is the most promising material because it is 10 times larger than graphite material, but the silicon anode material causes a large change in crystal structure when absorbing and storing lithium, resulting in a large volume change of more than 300%.
  • Si silicon
  • the G / M complex of the present invention was conceived that the graphene oxide is negatively charged and the metal nanoparticles are positively charged. As a result of the experiment, the metal nanoparticles and the graphene oxide sheet are strongly bound by electrostatic attraction to oxidize the metal nanoparticles. It was confirmed that the G / M composite formed by wrapping with the graphene sheet was kept fairly stable.
  • the metal nanoparticles may be modified to have -NH 2 groups.
  • the size of the metal nanoparticles can be controlled as desired.
  • the G / M composite may have a size of 50 nm or less so as to be uniformly dispersed in the carbon nanofiber composite. It can be formed to have.
  • the G / M complex of the present invention can be prepared as follows.
  • the graphene oxide sheet may be formed by any known method, and in the present invention, a carboxyl group (COOH) or a hydroxyl group (OH) group is introduced into graphite by using the Hummers method (negative charge).
  • Graphene oxide sheet (GO) having a compound was synthesized (Chem. Mater. 1999, 11 (3), 771-778).
  • the graphene oxide sheet may have a structure of 20 layers or less, more preferably, a single layer structure or a 10 layer structure.
  • the silicon nanoparticles can enhance the positive charge by a known method, for example, can be modified to amino-funtionalized silicon, which is a silicon nanoparticle having -NH 2 groups using APS.
  • APS Angew. Chem. Int. Ed. 2010, 49, 8408-8411.
  • modified Amino-funtionalized silicon has a positive charge, it is possible to prepare a G / Si composite in which GO is strongly bound through GO and electrostatic attraction and reduced by GO.
  • the G / M composite of the present invention is electrically conductive when the carbon nanofiber composite in which the G / M composite is uniformly dispersed as an electrode is formed by complexing graphene having excellent thermal conductivity, mechanical strength and electrical properties with metal nanoparticles. It can have excellent and excellent mechanical properties.
  • Carbon nanofiber composite of the present invention is carbon nanofibers; And a graphene-metal nanoparticle composite constituting a part of the carbon nanofibers.
  • the graphene-metal nanoparticle composite has the same characteristics as described above and thus goes to the description above.
  • the carbon nanofiber composite including the G / M composite has a diameter of 100 to 300 nm, a specific surface area of 300 m 2 / g or less, and an average pore diameter of 1 to 2 nm.
  • the carbon nanofiber composite of the present invention can be pulverized to form a powder form in a state in which the G / M composite is maintained, so that the carbon nanofiber composite may be used as it is, that is, as a web, but can be used by pulverizing into a powder form You can increase your chances.
  • the inclusion of the G / M complex in the carbon nanofiber matrix exhibits a certain synergistic effect, but when the G / M complex is uniformly dispersed and positioned, it showed better characteristics.
  • Carbon nanofiber composite manufacturing method of the present invention comprises the steps of preparing a spinning solution comprising a G / M complex and a carbon fiber precursor; Electrospinning the spinning solution to obtain precursor spinning fibers; Oxidative stabilizing the precursor spun fiber to obtain a flame resistant fiber; And carbonizing the flame resistant fiber to obtain a carbon nanofiber composite.
  • the spinning solution contains the graphene-metal nanoparticle composite within 30 parts by weight per 100 parts by weight of the carbon nanofiber precursor and the graphene-metal nanoparticle composite.
  • the spinning solution content ratio of the G / M composite is experimentally determined as the content ratio of electrospinning well. In other words, if the concentration is higher than the upper limit, it is difficult to spin due to the influence of the spinning solution viscosity and the fibers are not formed well.
  • the carbon nanofiber precursor and the graphene-metal nanoparticle composite may be included in a weight ratio of 4: 1 to 20: 1.
  • the polymer for carbon nanofiber precursor is polyacrylonitrile (PAN, polyacrylonitrile), polyvinyl alcohol (PVA, polyvinylachol), polyimide (PI, polyimide), polybenzimidazole (PBI, polybenzimidazol), phenol resin (phenol resin), epoxy resin, polyethylene (PE, polyethylene), polypropylene (PP, polypropylene), polyvinylchloride (PVC, polyvinylchloride), polystyrene (PS, polystyrene), polyaniline (PA, polyanaline), Polymethyl methacrylate (PMMA, polymethylmethacrylate), polyvinylidene chloride (PVDC, polyvinylidence chloride), polyvinylidene fluoride (PVDF, povinylidene fluoride) and various pitch (pitch) and the like can be used.
  • PAN polyacrylonitrile
  • PVA polyvinyl alcohol
  • PI polyimide
  • PBI polybenzimidazole
  • the type of the polymer for carbon nanofiber precursor for the production of the spinning solution can be used by selecting a suitable solvent that can dissolve the polymer. That is, the solvent in which the carbon fiber precursor is dissolved in the spinning solution is not limited so long as it can disperse all the prepared carbon fiber precursor and the G / M composite.
  • the solvent in which the carbon fiber precursor is dissolved in the spinning solution is not limited so long as it can disperse all the prepared carbon fiber precursor and the G / M composite.
  • at least one of dimethyformamide (DMF), dimethysulfoxide (DMSO) and tetrahydrofuran (THF) was used.
  • Polyacrylonitrile (PAN, molecular weight 160,000) was used as the carbon nanofiber precursor, and a modified acrylic containing 5-15% copolymer as well as 100% homopolymer can be used.
  • As the composition of the copolymer itaconic acid or methylacrylate may be used as the copolymer.
  • Oxidation stabilization may be carried out by supplying compressed air at a flow rate of 5-20 mL per minute using a hot air circulating fan and maintaining at 200-300 ° C. for 30 minutes or more at a temperature increase rate of 1 ° C. per minute.
  • the carbonization may be performed by maintaining the temperature in an inert gas atmosphere for 30 minutes to 2 hours after heating up to 750 to 850 ° C. at a rate of 5 ° C. per minute.
  • At least one of the size and distribution of the graphene-metal nanoparticle composites included in the carbon nanofiber composites by controlling the concentration of the graphene-metal nanoparticle composites contained in the spinning solution during the manufacture of the carbon nanofiber composites of the present invention. Can be controlled. That is, graphene forms a G / M complex surrounding the metal nanoparticles in order to prevent the metal nanoparticles from growing too large or aggregated to become large particles and exposed to the outside of the carbon nanofibers, and the G / M complex contained in the spinning solution. This is because the carbon nanofiber composite having the metal nanoparticles controlled to the desired size can be uniformly distributed in the carbon nanofiber matrix by controlling the concentration of.
  • the electrode of the present invention includes the above-described carbon nanofiber composite as an electrode active material.
  • the carbon nanofiber composite used in the electrode of the present invention includes a G / M composite, for example, the electrode of the present invention may be used as a negative electrode in a secondary battery.
  • the carbon nanofiber composite may be used as the web state prepared by electrospinning, or may be used after being pulverized into a powder form.
  • the secondary battery of the present invention includes an electrode including a carbon nanofiber composite as an electrode active material.
  • the electrode active material contained in the electrode is not separated from the substrate even after 100 cycles of charge and discharge, and the discharge capacity is maintained at 600 mAh / g even after 100 cycles of charge and discharge.
  • This characteristic is due to the structure of the carbon nanofiber composite used as the electrode active material, since the metal nanoparticles dispersed in the carbon nanofiber matrix are in the form of a G / M composite, the graphene surrounding the metal nanoparticles suppresses the volume expansion of the metal nanoparticles. It is expected to act as a support.
  • the silicon nanoparticles were modified with amino-funtionalized silicon having -NH 2 groups using APS.
  • the modified nanoparticles were positively charged.
  • the Amino-funtionalized silicon nanoparticles have a positive charge and GO has a negative charge, the Amino-funtionalized silicon nanoparticles are strongly bound through electrostatic attraction.
  • amino-funtionalized silicon nanoparticles with positive charges can prevent agglomeration and large growth due to repulsion between positive charges.
  • Example 1 The GO obtained in Example 1 was observed with an electron microscope, and the photograph is shown in FIG. 5 as a result.
  • SEM (FIG. 5A) and TEM (FIG. 5B) photographs show that GO synthesized by the Hammers method is composed of thin layers of GO with graphite peeled off, and the number of GO layers is about 1-10. .
  • the surface of GO has been reported to be negatively charged and easy to disperse in polar solvents.
  • the G / Si composite obtained in Example 3 was observed with an electron microscope, and the photograph is shown in FIG. 6 as a result.
  • the SEM (FIGS. 6A and B) photos show that the silicon nanoparticles are covered with graphene sheets
  • the TEM (FIGS. 6C and d) photos show that about 3 nm of thin, pliable and corrugated graphene is formed of the silicon nanoparticles. It can be seen from the edge that the graphene layer surrounds the silicon nanoparticles well. In addition, it was confirmed that the graphene layer is well connected to the separated particles without agglomeration of the adjacent silicon nanoparticles through the TEM (Fig. 6c and d) photograph.
  • the carbon nanofiber precursor was prepared by preparing a PAN pure polymer and a G / Si composite, dissolving the PAN and G / Si composites in DMF prepared as a solvent, and dispersing the same by dispersing using ultrasonic waves as follows.
  • G / Si composite (20 wt%: 0.60 g) was added to the polymer solution, and then ultrasonically dispersed for 2 hours to increase the dispersion of silicon. It was dissolved for 4 hours at °C to prepare a spinning solution (G / Si / PAN solution).
  • the homogenized spinning solution (G / Si / PAN solution) was electrospun using an electrospinner. At this time, the spinning condition was put into the 30 ml syringe attached to a 0.5 mm needle and the fiber precursor solution was electrospun by applying a voltage of 20 kV. In this case, the distance between the needle and the current collector was maintained at 15 cm, and the dissolution rate of the fiber precursor solution was 3 ml / h. When the fibers were accumulated in the current collector, the nonwoven fabric was removed to separate the precursor spinning fiber.
  • the precursor spinning fiber (G / Si / PAN-based spinning fiber) obtained by electrospinning was supplied at a flow rate of 5-20 mL per minute using a hot air circulation fan at 200-300 ° C. at a temperature rising rate of 1 ° C. per minute. Stabilized by maintaining for 1 hour to obtain a G / Si / PAN-based flame resistant fiber.
  • GSP G / Si / PAN-based Carbon Nanofiber Composite
  • G / Si / PAN-based carbon nanofiber composite (20-GSP) was prepared by carbonizing the G / Si / PAN-based flame resistant fiber obtained through stabilization at 800 ° C. under an inert gas (N 2 , Ar gas) atmosphere. It was.
  • a G / Si / PAN-based carbon nanofiber composite (10-GSP) was prepared in the same manner as in Example 1 except that 10 wt% (0.30 g) of G / Si composite was used as the spinning solution.
  • a G / Si / PAN-based carbon nanofiber composite (5-GSP) was prepared in the same manner as in Example 1 except that 5 wt% (0.15 g) of G / Si composite was used as the spinning solution.
  • a Si / PAN-based carbon nanofiber composite (20-SP) having a silicon content of 20 wt% of Comparative Example was prepared in the same manner as in Example 1 except that Si was used instead of the G / Si composite when preparing the spinning solution.
  • Comparative Example carbon nanofibers were obtained in the same manner as in Example 1 except that the G / Si composite was not used in the preparation of the spinning solution.
  • the average diameter range of the obtained carbon nanofiber composite was 250-350 nm, and 5-GSP having a low concentration of the G / Si composite had a smooth surface without generating particles or beads, whereas the concentration of the G / Si composite was It can be seen that as is increased, clusters are present in the middle segment of the fiber and the number of clusters increases.
  • the energy dispersive X-ray spectroscopy (EDX) of the 10-GSP surface revealed that the C, O, and Si elements were present in an atomic ratio of 78.83%, 6.18%, and 15.96%, respectively.
  • high magnification SEM images show that 20-GSP has clusters in the fiber, while 20-SP shows that the clustered nanoparticles of the nanoparticles aggregated are exposed on the surface of the carbon fiber. there was.
  • FIGS. 9A and 9C From (a), (b), and (c) of FIGS. 9A and 9C, in which TEM images of 10-GSP, 20-GSP, and 20-SP are shown, nanoparticles having a size of 50 nm or less are well dispersed in a carbon nanofiber matrix.
  • 20-SP has cluster clusters on the surface of carbon nanofibers.
  • the superlattice diffraction points in the form of (110), (220), and (311) appear in the diffraction pattern of the limited field electron diffraction (SAED) (FIG. 9d) of the nanoparticles present in the 10-GSP to know the internal structure of the material. Through this, the crystalline diffraction pattern of the silicon nanoparticles was confirmed.
  • SAED limited field electron diffraction
  • graphite exhibits a 2 ⁇ value at 26.5 kV, which is known as a representative crystal peak observed in the extra structure (002) of graphite.
  • functional groups such as carboxyl groups or hydroxyl groups containing oxygen are bound between the graphite layers in the (001) plane. It can be seen that the result of inducing phase shift by increasing graphite interlayer distance (Polymer, 2011, 35 (6), 565-573.).
  • 20-GSP, 10-GSP and 5-GSP which are the G / Si / PAN carbon nanofiber composites obtained in Examples 2 to 4, were cut to prepare a negative electrode material, and the prepared negative electrode and LiPF 6 1: 1 vol% Coin cells composed of ethylene carbonate (EC) / dimethyl carbonate (DMC) liquid electrolyte were prepared to prepare secondary batteries 1 to 3 (20-GSP, 10-GSP, 5-GSP).
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • a coin cell was prepared in the same manner as in Example 5, except that SP-20 obtained in Comparative Example 1 was used as a negative electrode, to prepare Comparative Example Secondary Battery 1 (SP-20).
  • a coin cell was prepared in the same manner as in Example 5 except that the CNF nonwoven fabric obtained in Comparative Example 2 was used as a negative electrode, to prepare Comparative Example Secondary Battery 2 (CNP).
  • CNP Comparative Example Secondary Battery 2
  • the secondary batteries obtained in Examples 5 to 7 were charged and discharged using a WBCS3000L charging / discharging device manufactured by Won-A tech, and the charge and discharge capacity and cycle characteristics of the lithium secondary batteries manufactured as negative electrodes were investigated. 11 is shown. Charging and discharging was performed at a voltage range of 0.02 to 1.50 V at a current of 100 mA / g.
  • the electrolyte is decomposed to form a coating SEI (Solid Electrolyte Interface or Solid Electrolyte Inter-phase) on the electrode surface.
  • SEI Solid Electrolyte Interface or Solid Electrolyte Inter-phase
  • electrolyte decomposition due to electron transfer between the electrode and the electrolyte is suppressed, and only insertion and removal of lithium ions can be selectively performed.
  • Li x Si is formed in which Si crystals are crystallized due to the reaction of silicon and lithium by electrochemical reaction, and the reaction peak of Li x Si appears at a low voltage of 0.1 V.
  • Example 6 In order to determine the interfacial properties of 10-GSP, 20-GSP, and CNF obtained in Example 5, Example 6, and Comparative Example 4, analysis was performed by electrochemical impedance spectroscopy (EIS), and the results are shown in FIG. It is shown in (b). Impedance measurement was performed using Jahner Electrik IM6e, and the frequency range was tested by applying 100 kHz-10 mHz and AC signal 10 mV mV.
  • EIS electrochemical impedance spectroscopy
  • Figure 12 (b) is a Nyquist plot showing the characteristics of the carbon nanofiber composite electrode in the imaginary term and real term impedance according to the frequency. According to the frequency of the AC potential, a straight line with a constant slope appears in the high frequency region where the semicircle is low. At this time, the semicircle is controlled by the reaction rate due to charge transfer, but the straight portion is controlled by the diffusion of the reactants. (The Korean Institute of Electrical and Electronic Material Engineers, 2011, 24 (4), 333-339).
  • the small R f value in the 20-GSP electrode is also related to the formation of the SEI film.
  • the film formed by the solvent decomposition reaction acts as a protective film on the electrode surface, so that the smooth insertion / reinsertion of lithium ions into the electrode is achieved without large resistance. It can be seen that it shows excellent discharge capacity.
  • 20-GSP shows a large slope of the straight line, which shows that the diffusion rate of lithium ions is fast because the solid state diffusion resistance due to diffusion of lithium ions into the bulk cathode is low due to the electrical conductivity of graphene. .
  • 20-SP shows the highest cathode initial capacity, but after 50 charge / discharge cycles, GSP electrodes showed better cycle characteristics than Comparative Example 3.
  • the carbon nanofiber composite 20-SP prepared by mixing only silicon and polyacrylonitrile without graphene is exposed to the surface of the carbon nanofibers because the particles become larger due to the attraction between the silicon.
  • the cycle characteristics were reduced due to the volume expansion of silicon. This shows that due to the miscibility between PAN and silicon nanoparticles, agglomeration of metals occurs, which makes it difficult to uniformly disperse the silicon nanoparticles.
  • 10-GSP and 20-GSP which are samples prepared by adding a G / Si composite, exhibit stable capacity reduction because the graphene encloses the silicon, thereby suppressing the agglomeration of silicon particles into larger particles. Dispersed evenly within the nanofibers, it not only buffers the large volume change of silicon nanoparticles due to the charging and discharging of the existing lithium ion battery, but also reduces the resistivity of the electrode surface of the lithium ion battery, thereby making it an effective electrochemical reaction during battery charging and discharging. This can be induced.
  • graphene plays a role in buffering the agglomeration of silicon particles in 10-GSP and 20-GSP electrodes, so that silicon is dispersed in the CNF matrix, so that electrochemically active sites are increased and carbon nanofibers maintain electrical conductivity. As such, the electrochemical properties are expected to be very excellent.
  • FIG. 14 is a photograph of the electron scanning microscope results of 5-GSP, 10-GSP, and 20-GSP after 50 cycles of charging and discharging. Therefore, it can be seen from FIG.
  • the G / Si / PAN-based carbon nanofiber composite obtained in Examples 2 to 4 is used as an electrode in a fibrous web state as in Examples 5 to 7 as compared with the conventional case using a particulate form, electrons move by themselves. This is very fast and does not require an active material, a binder and a conductive agent, other solvents, auxiliary facilities, etc., and has the advantage of eliminating the process of preparing and coating a slurry. In addition, the expected effect is expected to be very large as a cathode material to replace the graphite in the future because of its easy handling.
  • 20-GSP of the web form obtained in Example 2 was ground to prepare a powder.
  • Super-P was used as the conductive material and polyacrylic acid was used as the binder.
  • the composition of the electrode was mixed at 80 wt% of the negative electrode active material, 10 wt% of the conductive material, and 10 wt% of the binder.
  • a coin cell consisting of the prepared negative electrode and LiPF 6 1: 1 vol% ethylene carbonate (EC) / dimethyl carbonate (DMC) liquid electrolyte was prepared to prepare a secondary battery 4 (grinded 20-GSP).
  • a coin cell was prepared in the same manner as in Example 8 except that silicon nanoparticles were used as a negative electrode active material, thereby preparing Comparative Example Secondary Batteries 3 (Si NPs).
  • the grinded 20-GSP prepared in Example 8 and Si NPs prepared in Comparative Example 5 were charged and discharged using a WBCS3000L charge / discharge device of Won-A tech. Charging and discharging were performed at a voltage range of 0.005 to 2.0 V at a current of 100 mA / g. As a result of charge and discharge of the lithium secondary batteries according to Example 8 and Comparative Example 5, cycle characteristics and coulombic efficiencies are shown in FIG. 15.
  • the initial capacity of the silicon nanoparticles shows a very high high capacity close to 4000 mA / g, but the crystalline silicon nanoparticles shows a rapid decrease in capacity as the cycle increases. This seems to be a phenomenon caused by rapid volume expansion because lithium does not reversibly move due to the affinity between the two materials in the silicon.
  • grinded 20-GSP maintains higher capacity than silicon nanoparticles even after 100 charge / discharge results, and also shows better cycle characteristics and Klong efficiency.
  • 20-GSP not only prevents graphene from agglomeration of silicon, but also disperses it evenly in carbon nanofibers, and also inhibits volume expansion by buffering carbon nanofibers acting as a matrix. As the cycle increases, the capacity decreases more stably than silicon nanoparticles.
  • the surface photograph of the grinded 20-GSP obtained before charging and discharging shows a clean and uniform surface
  • the surface photograph of silicon nanoparticles shows a relatively uniform surface although there are some cracks on the surface. Can be.
  • the silicon nanoparticles are cracked as the volume increased during the alloying process with lithium decreases when recharged, compared to grinded 20-GSP. You can see that they form a surface.
  • 20-GSP showed no cracks or the active material falling from the current collector through 100 SEM images before and after 100 cycles, and the substrate under the active material was not exposed. It can be explained that it exhibits excellent cycle characteristics compared to nanoparticles.
  • the lithium ion battery manufactured using the carbon nanofiber composite including the G / M composite of the present invention can expect excellent charge / discharge characteristics, high capacity, and excellent volume stability.
  • the carbon nanofiber composite including the G / M composite of the present invention is used only in a lithium ion battery, the cell performance is improved even when used as an electrode active material in an energy storage device including other types of secondary batteries. It can be expected that long term driving performance can be improved as well.

Abstract

The present invention relates to a carbon nanofiber composite, and more particularly, to a graphene-metal nanoparticle composite, a carbon nanofiber composite containing the composite, and a secondary battery containing the carbon nanoparticle composite.

Description

그래핀-금속나노입자복합체, 상기 복합체를 포함하는 탄소나노섬유복합체 및 상기 탄소나노입자복합체를 포함하는 이차전지Graphene-metal nanoparticle composite, carbon nanofiber composite including the composite, and secondary battery comprising the carbon nanoparticle composite
본 발명은 탄소나노섬유복합체에 대한 것으로, 보다 구체적으로는 그래핀-금속나노입자복합체, 상기 복합체를 포함하는 탄소나노섬유복합체 및 상기 탄소나노입자복합체를 포함하는 이차전지에 관한 것이다.The present invention relates to a carbon nanofiber composite, and more particularly, to a graphene-metal nanoparticle composite, a carbon nanofiber composite including the composite, and a secondary battery including the carbon nanoparticle composite.
21세기는 반도체 산업의 비약적인 발전으로 노트북 컴퓨터, 휴대폰, DMB폰, 휴대형 통신장치등 소형 전기전자기구들이 단순한 정보수신에서 쌍방향 통신을 기본으로 하는 멀티미디어 기능이 보편화되는 새로운 통신 패러다임의 정보통신시대가 도래하고 있다. 이러한 다기능 전기전자기구들의 요구에 부응하기 위해 고용량, 고출력 이차전지가 전지재료를 중심으로 연구 개발되고 있다.The 21st century is a breakthrough in the semiconductor industry, and a new communication paradigm has emerged, in which small electric and electronic devices such as notebook computers, mobile phones, DMB phones, portable communication devices, etc. are becoming more popular. Doing. In order to meet the demands of such multifunctional electric and electronic devices, high capacity, high output secondary batteries have been researched and developed mainly on battery materials.
종래 리튬이차전지의 음극활물질로는 리튬 금속을 사용하였으나 현재에는 리튬 금속 대신 탄소계 음극활물질이 많이 사용되고 있다. 탄소계 음극활물질로는 결정질계 탄소 중 흑연(그래파이트)이 대표적으로 사용되고 있는데 흑연과 같은 탄소계 음극활물질은 이론용량의 상한이 약 372 mAh/g로 제한되어 있어, 고용량을 요구하는 모바일 디지털융합기기에 부응하는 음극소재로는 미흡하다. 특히, 자동차 분야에서는 화석연료 고갈에 따라 전기자동차의 개발이 시급하게 요구되고 있으나, 기존 리튬이차전지를 적용할 경우, 일회 충전으로 200㎞ 이상의 장거리 운행이 곤란하며, 기존 리튬이차전지는 신재생에너지원에 의해 발전된 전력을 저장하기 위한 장주기 에너지 저장시스템에도 적합하지 않은 실정이다.Conventionally, lithium metal is used as a negative electrode active material of a lithium secondary battery. Currently, carbon-based negative electrode active materials are used instead of lithium metal. As the carbon-based negative electrode active material, graphite (graphite) in crystalline carbon is typically used. The carbon-based negative electrode active material such as graphite has a limited upper limit of about 372 mAh / g. Insufficient negative electrode materials are available. In particular, in the automobile field, the development of electric vehicles is urgently required due to the depletion of fossil fuels.However, when the existing lithium secondary battery is applied, it is difficult to operate a long distance of more than 200km by a single charge. It is also not suitable for long-term energy storage systems for storing power generated by sources.
따라서 최근에 상용 흑연전극을 대체하기 위한 새로운 고용량 소재들이 많이 등장하고 있는데 그 중에서 금속계 음극소재 특히 실리콘(Si)계 음극소재가 이론적인 용량이 약 4,200 mAh/g으로 흑연소재에 비해 10배 이상 크기 때문에 가장 유망한 소재로 대두되고 있다. 그러나 실리콘 음극소재는 리튬을 흡수 저장 할 때에 결정구조의 변화를 야기 시켜 300% 이상의 큰 부피변화가 발생하는 문제점이 있다. 현재 음극재료로 사용되고 있는 흑연은 리튬 충전에 의한 부피 팽창율이 약 1.2배 정도인데 반해, 실리콘의 경우 리튬을 최대량 흡수저장하면, Li4.4Si로 전환되어 부피 팽창 전 실리콘의 부피에 비해 약 4.12배까지 팽창하기 때문에 이 부피 팽창 때문에 전극의 구조가 붕괴되어 쿨롱효율이 낮아져 계속사용이 어렵게 된다. Recently, many new high-capacity materials have been introduced to replace commercial graphite electrodes. Among them, metal-based anode materials, especially silicon (Si) -based anode materials, have a theoretical capacity of about 4,200 mAh / g, which is more than 10 times larger than graphite materials. Therefore, it is emerging as the most promising material. However, the silicon anode material has a problem that a large volume change of more than 300% occurs by causing a change in crystal structure when absorbing and storing lithium. Graphite, which is currently used as a cathode material, has a volume expansion rate of about 1.2 times due to lithium charging, whereas, in case of silicon, when lithium is absorbed and stored in the maximum amount, it is converted to Li 4.4 Si and is about 4.12 times larger than the volume of silicon before volume expansion. Because of the expansion, the volume of the electrode collapses due to the volume expansion, and thus the coulombic efficiency becomes low, making it difficult to continue using.
실리콘 전극의 상술한 문제점을 해결하기 위하여 많은 연구가 진행되고 있으며, 그 중 하나가 실리콘 나노입자를 탄소 매트릭스에 분산시켜 탄소 매트릭스가 실리콘의 기계적 스트레스를 완화하고, 전극의 구조적 완전성(structural integrity)을 유지시킴으로써, 리튬의 층간 삽입/탈리 과정동안 리튬이온전지의 가역성 (cyclability)의 향상을 유도하는 것이다. In order to solve the above-described problems of the silicon electrode, a lot of research is being conducted, one of which is to disperse the silicon nanoparticles in the carbon matrix so that the carbon matrix to relieve the mechanical stress of the silicon, and the structural integrity of the electrode In this case, the lithium ion battery can be improved during the intercalation / desorption process of lithium.
그러나 탄소가 코팅된 실리콘 나노입자 또는 탄소 나노 섬유를 기상 성장시켜 제조된 탄소 나노 섬유를 혼성화시킨 실리콘계 리튬 이차전지용 음극 활물질은 pyrolysis법, chemical/thermal vapor deposition(CVD/TVD)법, gel을 이용한 화학적 합성법, 및 hydrothermal carbonization법 등을 사용하는데, 이들 방법들은 고온의 반응조건이 필요하거나, 고가의 전구체를 필요로 하며, 대량생산이 어렵기 때문에 상용화에 대한 문제점이 있다.However, the negative electrode active material for a silicon-based lithium secondary battery hybridized with carbon nanofibers prepared by vapor-growing carbon-coated silicon nanoparticles or carbon nanofibers is pyrolysis method, chemical / thermal vapor deposition (CVD / TVD) method, and chemicals using gel. Synthesis and hydrothermal carbonization methods are used, and these methods require high temperature reaction conditions, require expensive precursors, and have difficulty in commercialization because they are difficult to mass produce.
최근 나노구조 전극은 에너지 밀도와 속도 특성 그리고 리튬이온의 삽입/이탈 에 의한 부피 변화의 완화 및 속도를 크게 향상시킬 수 있을 것으로 기대되므로 이들에 대한 관심이 집중되고 있다. 양극이나 음극 소재들이 높은 비표면적을 지니고 있으면 고상 확산경로가 감소되고 양극-분리막-음극의 계면이 크게 증대되므로 나노구조재료의 3차원 구조화로 고율방전특성과 고출력 리튬이온전지의 구현이 가능할 것으로 예측된다.Recently, nanostructured electrodes are expected to significantly improve the energy density and velocity characteristics, and the relaxation and speed of volume change due to the insertion / extraction of lithium ions. If the anode or cathode materials have high specific surface area, the solid-state diffusion path is reduced and the interface between anode-membrane-cathode is greatly increased. Therefore, the three-dimensional structure of the nanostructured material will enable high-rate discharge characteristics and high-output lithium-ion batteries. do.
기존 전극기술의 한계성을 극복하기 위하여 전기방사법을 이용하여 나노구조재료들을 전극재료로 활용하면 전극에서 우수한 전자전도도를 제공하고 확산경로를 감소시킬 수 있을 뿐만이 아니라, 다량의 Li+이 삽입과 이탈과정에서 발생하는 스트레스를 완화시킬 수 있어 고출력 및 고에너지 밀도를 지닌 리튬이차전지가 기대된다. 또한 전기방사기법은 고분자용액을 이용하여 수백 나노에서 수십 나노의 섬유를 제조할 수 있는 유일한 방법으로써 이러한 전기방사기법을 이용하여 제조된 탄소나노섬유는 전기전도도가 매우 높고 비표면적이 높으며, 금속, 금속산화물, 다공성물질, 카본나노튜브 등을 함유하는 탄소나노섬유의 제조가 용이하기 때문에 이차전지전극물질의 제조 시 매우 높은 전기화학적 활성을 기대할 수 있다.In order to overcome the limitations of the existing electrode technology, the use of nanostructured materials as electrode material by electrospinning not only provides excellent electron conductivity and reduces the diffusion path in the electrode, but also a lot of Li + It is possible to alleviate the stress generated in the lithium secondary battery with high output and high energy density is expected. In addition, electrospinning is the only method that can produce hundreds of nanometers to tens of nanofibers using a polymer solution. Carbon nanofibers manufactured using these electrospinning techniques have high electrical conductivity, high specific surface area, metal, Since carbon nanofibers containing metal oxides, porous materials, carbon nanotubes, and the like are easily manufactured, very high electrochemical activity can be expected when manufacturing secondary battery electrode materials.
이 제조공정은 간단하고 기본적으로 일반적인 탄소섬유 제조과정과 유사하여 저가 양산이 가능한 기술이다. 본 발명에서의 복합적인 성분으로부터 제조된 탄소나노섬유 복합체 및 활성탄소나노섬유 복합체는 체적대비 비표면적, 전기전도성이 우수하고, 구성 섬유들이 네트워크를 형성하고 있어 전극 제조시 바인더 없이 2차 전지용 전극소재로 사용될 수 있으며 더 나아가 전기이중층 슈퍼캐퍼시터용 전극재료, 전자파 차폐재, 고전도성 재료, 촉매 지지체 및 복합재료용 보강소재 등으로 매우 유용하다.This manufacturing process is simple and basically similar to general carbon fiber manufacturing process, and it is a technology that can be mass produced at low cost. Carbon nanofiber composites and activated carbon nanofiber composites prepared from the composite components of the present invention are excellent in specific surface area and electrical conductivity relative to volume, and constituent fibers form a network. It can be used as an electrode material for electric double layer supercapacitor, electromagnetic wave shielding material, high conductivity material, catalyst support and composite material reinforcement material.
그러나 현재 주로 사용되고 있는 방법인 탄소전구체 폴리아크릴로나이트릴(PAN)에 금속 또는 금속전구체를 혼합하여 방사 하였을 때 금속 또는 금속산화물 상태로 고르게 분산시키기 어렵고, 금속입자가 응집되는 현상을 보여 탄소나노섬유 표면에 노출이 되면 금속의 부피팽창에 의해 금속 입자 표면 균열에 의한 계속적 계면 발생, 전지의 충방전 효율 감소, 지속적 전해액 분해 반응 및 이에 따른 전해액의 사용량 증가, 계면 발생과 입자간 전도도 감소에 의한 전지 저항 증가 및 전지 수명 감소 등의 문제점이 발생할 수 있다.However, carbon nanofibers are difficult to be dispersed evenly in the metal or metal oxide state when the metal precursor is mixed with the carbon precursor polyacrylonitrile (PAN), which is currently used, and is dispersed. When exposed to the surface, due to the volume expansion of the metal, continuous interface generation due to the surface crack of the metal particles, reduction of charge and discharge efficiency of the battery, continuous electrolyte decomposition reaction and the increase of the amount of use of the electrolyte solution, battery generation due to the interface generation and particle conductivity Problems such as increased resistance and reduced battery life may occur.
따라서 금속 나노입자가 너무 크게 성장하는 것을 억제하거나 응집하여 큰 입자가 되는 것을 방지하고, 탄소나노섬유 내에 금속나노입자가 균일하게 분산함과 동시에 부피의 변화를 완화하여 전기적 접촉성을 개선함으로써 고용량 및 사이클 특성을 확보할 수 있는 음극활물질에 대한 개발 필요성이 대두되고 있는 실정이다.Therefore, the metal nanoparticles are prevented from growing too large or aggregated to prevent them from becoming large particles, and the metal nanoparticles are uniformly dispersed in the carbon nanofibers, and the volume change is alleviated, thereby improving the electrical contactability. There is a need for development of a negative electrode active material capable of securing cycle characteristics.
본 발명자들은 다수의 연구 결과 금속나노입자를 그래핀시트로 둘러싸게 되면 금속나노입자가 응집하여 큰 입자가 되는 것을 방지할 수 있는 것에 착안하여 본 발명을 완성하였다.The present inventors have completed the present invention by focusing on the fact that a large number of studies have been made to surround the metal nanoparticles with a graphene sheet to prevent the metal nanoparticles from agglomerating into large particles.
따라서, 본 발명의 목적은 금속나노입자가 너무 크게 성장하거나 응집하여 큰 입자가 되는 것을 방지할 수 있는 구조를 갖는 그래핀-금속나노입자복합체를 제공하는 것이다.Accordingly, it is an object of the present invention to provide a graphene-metal nanoparticle composite having a structure capable of preventing metal nanoparticles from growing or agglomerating too large and becoming large particles.
본 발명의 다른 목적은 그래핀-금속나노입자복합체(G/M복합체)가 탄소나노섬유 매트릭스 내에 고르게 분산된 탄소나노섬유복합체 및 그 제조방법을 제공하는 것이다.Another object of the present invention is to provide a carbon nanofiber composite having a graphene-metal nanoparticle composite (G / M composite) evenly dispersed in a carbon nanofiber matrix and a method of manufacturing the same.
본 발명의 또 다른 목적은 G/M복합체가 포함된 탄소나노섬유복합체를 전극 활물질로 포함함으로써 금속나노입자가 탄소나노섬유 외부로 노출되지 않으므로 충전 및 방전에 따른 금속나노입자의 부피변화를 완충시켜줄 뿐만 아니라 금속나노입자의 응집현상을 방지함으로써 전극표면의 비저항을 감소시켜 효과적인 전기화학반응을 유도할 수 있는 전극을 제공하는 것이다.Another object of the present invention is to include a carbon nanofiber composite containing a G / M composite as an electrode active material, so that the metal nanoparticles are not exposed to the outside of the carbon nanofibers to buffer the volume change of the metal nanoparticles due to charging and discharging In addition, it is to provide an electrode capable of inducing an effective electrochemical reaction by reducing the specific resistance of the electrode surface by preventing the aggregation of metal nanoparticles.
본 발명의 또 다른 목적은 G/M복합체가 고르게 분산된 탄소나노섬유복합체를 전극활물질로 포함하는 전극을 적용함으로써 우수한 충방전 특성, 고용량, 우수한 부피 안정성 등이 확보된 이차전지를 제공하는 것이다.Still another object of the present invention is to provide a secondary battery having excellent charge and discharge characteristics, high capacity, and excellent volume stability by applying an electrode including a carbon nanofiber composite having a G / M composite evenly dispersed therein as an electrode active material.
본 발명의 목적은 이상에서 언급한 목적으로 제한되지 않으며, 명시적으로 언급되지 않았더라도 후술되는 발명의 상세한 설명의 기재로부터 통상의 지식을 가진 자가 인식할 수 있는 발명의 목적 역시 당연히 포함될 수 있을 것이다.The object of the present invention is not limited to the above-mentioned object, and even if not explicitly stated, the object of the invention that can be recognized by those skilled in the art can be naturally included from the description of the detailed description below. .
상술된 본 발명의 목적을 달성하기 위해, 먼저 본 발명은 금속나노입자; 및 상기 금속나노입자를 감싸서 형성된 그래핀시트;을 포함하는 그래핀-금속나노입자복합체를 제공한다.In order to achieve the object of the present invention described above, first the present invention is a metal nanoparticle; It provides a graphene-metal nanoparticle composite comprising a; and a graphene sheet formed by surrounding the metal nanoparticles.
바람직한 실시예에 있어서, 상기 금속나노입자는 Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au 로 구성된 그룹에서 선택된다. In a preferred embodiment, the metal nanoparticles are selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au.
바람직한 실시예에 있어서, 상기 금속나노입자는 -NH2기를 갖도록 개질된다.In a preferred embodiment, the metal nanoparticles are modified to have a -NH 2 group.
바람직한 실시예에 있어서, 상기 금속나노입자와 상기 그래핀시트는 정전기적 인력으로 결합된다.In a preferred embodiment, the metal nanoparticles and the graphene sheet are coupled by electrostatic attraction.
바람직한 실시예에 있어서, 상기 그래핀-금속나노입자복합체는 50nm이하의 크기를 갖는다. In a preferred embodiment, the graphene-metal nanoparticle composite has a size of 50nm or less.
또한, 본 발명은 탄소나노섬유; 및 상기 탄소나소섬유의 일부를 구성하는 그래핀-금속나노입자복합체;를 포함하는 탄소나노섬유복합체를 제공한다.In addition, the present invention carbon nanofibers; It provides a carbon nanofiber composite comprising a; and graphene-metal nanoparticle composite constituting a portion of the carbon nanofiber.
바람직한 실시예에 있어서, 상기 그래핀-금속나노입자복합체는 금속나노입자; 및 상기 금속나노입자를 감싸서 형성된 그래핀시트;을 포함한다. In a preferred embodiment, the graphene-metal nanoparticle composite is a metal nanoparticle; And a graphene sheet formed by wrapping the metal nanoparticles.
바람직한 실시예에 있어서, 상기 금속나노입자는 Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au 로 구성된 그룹에서 선택된다. In a preferred embodiment, the metal nanoparticles are selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au.
바람직한 실시예에 있어서, 상기 금속나노입자는 -NH2기를 갖도록 개질된다. In a preferred embodiment, the metal nanoparticles are modified to have a -NH 2 group.
바람직한 실시예에 있어서, 상기 금속나노입자와 상기 그래핀시트는 정전기적 인력으로 결합된다. In a preferred embodiment, the metal nanoparticles and the graphene sheet are coupled by electrostatic attraction.
바람직한 실시예에 있어서, 상기 탄소나노섬유복합체는 직경이 100 ~ 300 nm이고, 비표면적은 300 m2/g 이하이며, 평균 세공직경은 1 ~ 2 nm이다. In a preferred embodiment, the carbon nanofiber composite has a diameter of 100 to 300 nm, a specific surface area of 300 m 2 / g or less, and an average pore diameter of 1 to 2 nm.
바람직한 실시예에 있어서, 상기 그래핀-금속나노입자복합체는 상기 탄소나노섬유 내에 균일하게 분산되어 위치한다. In a preferred embodiment, the graphene-metal nanoparticle composite is located uniformly dispersed in the carbon nanofibers.
바람직한 실시예에 있어서, 상기 그래핀-금속나노입자복합체가 유지된 상태로 분말상을 이루도록 분쇄될 수 있다.In a preferred embodiment, the graphene-metal nanoparticle composite can be pulverized to form a powder in a state maintained.
바람직한 실시예에 있어서, 상기 그래핀-금속나노입자복합체는 50nm이하의 크기를 갖는다. In a preferred embodiment, the graphene-metal nanoparticle composite has a size of 50nm or less.
또한, 본 발명은 상술된 어느 하나의 그래핀-금속나노입자복합체 및 탄소섬유전구체를 포함하는 방사용액을 준비하는 단계; 상기 방사용액을 전기방사하여 전구체방사섬유를 얻는 단계; 상기 전구체방사섬유를 산화안정화하여 내염화섬유를 얻는 단계; 및 상기 내염화섬유를 탄화하여 탄소나노섬유복합체를 얻는 단계;를 포함하는 탄소나노섬유복합체 제조방법을 제공한다.In addition, the present invention comprises the steps of preparing a spinning solution comprising any one of the above-described graphene-metal nanoparticle composite and carbon fiber precursor; Electrospinning the spinning solution to obtain precursor spinning fibers; Oxidatively stabilizing the precursor spun fiber to obtain a flame resistant fiber; And carbonizing the flame resistant fiber to obtain a carbon nanofiber composite.
바람직한 실시예에 있어서, 상기 방사용액은 상기 탄소나노섬유전구체 및 그래핀-금속나노입자복합체의 총함량 100 중량부 당 그래핀-금속나노입자복합체는 30중량부 이내로 포함된다. In a preferred embodiment, the spinning solution is contained within 30 parts by weight of the graphene-metal nanoparticle composite per 100 parts by weight of the carbon nanofiber precursor and the graphene-metal nanoparticle composite.
바람직한 실시예에 있어서, 상기 탄소나노섬유전구체 및 그래핀-금속나노입자복합체는 4:1 내지 20:1의 중량비로 포함된다. In a preferred embodiment, the carbon nanofiber precursor and graphene-metal nanoparticle composite are included in a weight ratio of 4: 1 to 20: 1.
바람직한 실시예에 있어서, 상기 방사용액에 포함되는 그래핀-금속나노입자복합체의 농도를 제어하여 상기 탄소나노섬유복합체에 포함되는 그래핀-금속나노입자복합체의 크기 및 분포도 중 하나 이상을 제어한다. In a preferred embodiment, by controlling the concentration of the graphene-metal nanoparticle composite contained in the spinning solution to control one or more of the size and distribution of the graphene-metal nanoparticle composite contained in the carbon nanofiber composite.
또한, 본 발명은 상술된 어느 하나의 탄소나노섬유복합체를 전극활물질로 포함하는 전극을 제공한다.In addition, the present invention provides an electrode comprising any one of the carbon nanofiber composites described above as an electrode active material.
바람직한 실시예에 있어서, 상기 탄소나노섬유복합체는 분말 상이다. In a preferred embodiment, the carbon nanofiber composite is in powder form.
또한 본 발명은 상술된 전극을 포함하는 이차전지를 제공한다.In another aspect, the present invention provides a secondary battery comprising the electrode described above.
바람직한 실시예에 있어서, 상기 이차전지는 충방전 100사이클이 경과되어도 상기 전극에 포함된 전극활물질이 기판과 분리되지 않는다. In a preferred embodiment, the secondary battery does not separate the electrode active material contained in the electrode even after 100 cycles of charge and discharge.
바람직한 실시예에 있어서, 상기 이차전지는 충방전 100사이클이 경과되어도 방전용량이 600 mAh/g을 유지한다. In a preferred embodiment, the secondary battery maintains a discharge capacity of 600 mAh / g even after 100 cycles of charge and discharge.
본 발명은 다음과 같은 우수한 효과를 갖는다.The present invention has the following excellent effects.
먼저, 본 발명의 그래핀-금속나노입자복합체에 의하면 금속나노입자가 너무 크게 성장하거나 응집하여 큰 입자가 되는 것을 방지할 수 있다. First, according to the graphene-metal nanoparticle composite of the present invention, it is possible to prevent the metal nanoparticles from growing too large or aggregated to become large particles.
또한, 본 발명에 의하면 그래핀-금속나노입자복합체(G/M복합체)가 탄소나노섬유 매트릭스 내에 고르게 분산된 탄소나노섬유복합체 및 그 제조방법을 제공할 T수 있다. In addition, according to the present invention, it is possible to provide a carbon nanofiber composite having a graphene-metal nanoparticle composite (G / M composite) evenly dispersed in a carbon nanofiber matrix and a manufacturing method thereof.
또한, 본 발명의 전극은 G/M복합체가 포함된 탄소나노섬유복합체를 전극 활물질로 포함함으로써 금속나노입자가 탄소나노섬유 외부로 노출되지 않으므로 충전 및 방전에 따른 금속나노입자의 부피변화를 완충시켜줄 뿐만 아니라 금속나노입자의 응집현상을 방지함으로써 전극표면의 비저항을 감소시켜 효과적인 전기화학반응을 유도할 수 있다.In addition, the electrode of the present invention includes a carbon nanofiber composite containing a G / M composite as an electrode active material, so that the metal nanoparticles are not exposed to the outside of the carbon nanofibers to buffer the volume change of the metal nanoparticles due to charging and discharging In addition, by preventing agglomeration of metal nanoparticles, the specific resistance of the electrode surface can be reduced to induce an effective electrochemical reaction.
또한, 본 발명의 이차전지는 G/M복합체가 고르게 분산된 탄소나노섬유복합체를 전극활물질로 포함하는 전극을 적용함으로써 우수한 충방전 특성, 고용량, 우수한 부피 안정성 등이 확보될 수 있다.In addition, the secondary battery of the present invention can secure excellent charge and discharge characteristics, high capacity, excellent volume stability and the like by applying an electrode including a carbon nanofiber composite evenly dispersed G / M complex as an electrode active material.
본 발명의 이러한 기술적 효과들은 이상에서 언급한 범위만으로 제한되지 않으며, 명시적으로 언급되지 않았더라도 후술되는 발명의 실시를 위한 구체적 내용의 기재로부터 통상의 지식을 가진 자가 인식할 수 있는 발명의 효과 역시 당연히 포함된다.These technical effects of the present invention are not limited to the above-mentioned range, and even if not explicitly stated, the effects of the invention that can be recognized by those skilled in the art from the description of the specific contents for the implementation of the following invention are also mentioned. Of course included.
도 1은 본 발명의 일 실시예에 따른 G/M복합체를 제조하기 위해 하머즈 법 (Hummers method)을 이용한 산화 그래핀 (GO)을 제조하는 일 구현예를 도시한 제조공정도이다.1 is a manufacturing process diagram showing an embodiment of manufacturing graphene oxide (GO) using the Hammers method (Hummers method) to produce a G / M complex according to an embodiment of the present invention.
도 2는 본 발명의 일 실시예에 따른 G/M복합체를 제조하기 위해 Amino-functionalized silicon 나노입자를 제조하는 일 구현예를 도시한 제조공정도이다.2 is a manufacturing process diagram showing an embodiment of manufacturing Amino-functionalized silicon nanoparticles to prepare a G / M complex according to an embodiment of the present invention.
도 3은 본 발명의 일 실시예에 따른 G/M복합체 중 일 구현예인 그래핀(G)으로 둘러싸인 실리콘 복합체 (G/Si)를 제조하는 모식도이다.Figure 3 is a schematic diagram of manufacturing a silicon composite (G / Si) surrounded by graphene (G) of one embodiment of the G / M complex according to an embodiment of the present invention.
도 4는 도 3에 도시된 G/Si 복합체의 제조공정도이다.4 is a manufacturing process diagram of the G / Si composite shown in FIG.
도 5중 (a)는 도 1에 따라 제조된 산화그래핀 (GO)의 주사현미경 사진이고, (b)는 산화 그래핀 (GO)의 투과현미경 사진이다. In Figure 5 (a) is a scanning microscope picture of the graphene oxide (GO) prepared according to Figure 1, (b) is a transmission microscope picture of graphene oxide (GO).
도 6중 (a)는 도 4에 따라 제조된 G/Si 복합체의 주사현미경 사진이고, (b)는 G/Si 복합체의 고배율 주사현미경 사진이며, ㄹ는 G/Si 복합체의 투과현미경 사진이고, (d)는 G/Si 복합체의 고배율 투과현미경 사진이다. In Figure 6 (a) is a scanning microscope picture of the G / Si composite prepared according to Figure 4, (b) is a high magnification scanning microscope picture of the G / Si complex, d is a transmission microscope picture of the G / Si complex, (d) is a high magnification transmission micrograph of a G / Si composite.
도 7은 본 발명의 다른 실시예에 따른 그래핀-실리콘 나노입자를 포함하는 탄소나노섬유복합체(GSP) 제조공정 모식도 및 웹 사진[(a) 전구체방사섬유, (b) 내염화섬유, (c) 탄화섬유] 이다. Figure 7 is a schematic view and web pictures of carbon nanofiber composite (GSP) manufacturing process including graphene-silicon nanoparticles according to another embodiment of the present invention ((a) precursor radiation fiber, (b) flame-resistant fiber, (c) ) Carbonized fiber].
도 8은 본 발명의 다른 실시예에 따른 그래핀-실리콘 나노입자를 포함하는 탄소나노섬유복합체(GSP)에서 그래핀-실리콘나노입자복합체 함량에 따른 주사현미경사진이다[(a) 5 wt% G/Si 함유, (b) 10 wt% G/Si 함유,(c) 20 wt% G/Si 함유, (d) 20 wt% Si 함유]. 8 is a scanning micrograph according to graphene-silicon nanoparticle composite content in a carbon nanofiber composite (GSP) including graphene-silicon nanoparticles according to another embodiment of the present invention [(a) 5 wt% G / Si containing, (b) containing 10 wt% G / Si, (c) containing 20 wt% G / Si, (d) containing 20 wt% Si].
도 9 중 (a) 내지 (c)는 본 발명의 다른 실시예에 따른 그래핀-실리콘 나노입자를 포함하는 탄소나노섬유복합체(GSP)에서 그래핀-실리콘나노입자복합체 함량에 따른 투과현미경사진이며[(a)10-GSP, (b)20-GSP, (c) 20-SP], (d)는 10-GSP의 제한시야 전자회절법 (SAED)이다.(A) to (c) is a transmission micrograph according to the graphene-silicon nanoparticle composite content in the carbon nanofiber composite (GSP) including the graphene-silicon nanoparticles according to another embodiment of the present invention [(a) 10-GSP, (b) 20-GSP, (c) 20-SP], and (d) are 10-GSP Limited Field Electron Diffraction (SAED).
도 10 중 (a)는 본 발명에서 얻어진 GSP, G/Si, GO의 X선 회절 패턴 (XRD) 그래프이고, (b)는 GSP, G/Si, GO의 Raman spectrum 그래프이다.In FIG. 10, (a) is an X-ray diffraction pattern (XRD) graph of GSP, G / Si, and GO, and (b) is a Raman spectrum graph of GSP, G / Si, and GO.
도 11 중 (a)는 CNF의 충방전 결과그래프이고, (b)는 5-GSP의 충방전 결과그래프이며, (c)는 10-GSP의 충방전 결과그래프이고, (d)는 20-GSP의 충방전 결과그래프이다.In FIG. 11, (a) is a charge and discharge result graph of CNF, (b) is a charge and discharge result graph of 5-GSP, (c) is a charge and discharge result graph of 10-GSP, and (d) is a 20-GSP. The charge and discharge results of the graph.
도 12 중 (a)는 20-GSP의 미분용량곡선(Differential Capacity Curve)이고, (b)는 GSP와 CNF의 Nyquist plot이다.In FIG. 12, (a) shows a differential capacity curve of 20-GSP, and (b) shows a Nyquist plot of GSP and CNF.
도 13 중 (a)는 20-GSP, 10-GSP, 5-GSP, CNF의 50 사이클 특성 결과그래프이고, (b)는 20-SP의 50 사이클 특성 결과그래프이다.In FIG. 13, (a) is a 50 cycle characteristic result graph of 20-GSP, 10-GSP, 5-GSP, and CNF, and (b) is a 50 cycle characteristic result graph of 20-SP.
도 14는 50 사이클 후 5-GSP, 10-GSP, 20-GSP의 주사현미경 사진이다.14 is a scanning micrograph of 5-GSP, 10-GSP, 20-GSP after 50 cycles.
도 15는 20-GSP와 Si NPs의 100 사이클 특성과 쿨롱효율특성 결과이다.15 shows the results of 100 cycles and Coulomb efficiency of 20-GSP and Si NPs.
도 16 중 (a)는 본 발명의 또 다른 실시예에 따른 grinded 20-GSP의 충방전 전 top-view 주사현미경 사진이고, (b)는 100 사이클 충방전 후 top-view 주사현미경 사진이며, (c)는 실리콘 나노입자의 충방전 전 top-view 주사현미경 사진이고, (d)는 100 사이클 충방전 후 실리콘 나노입자의 top-view 주사현미경 사진이다.In Figure 16 (a) is a top-view scanning micrograph before charge and discharge of grinded 20-GSP according to another embodiment of the present invention, (b) is a top-view scanning microscope picture after 100 cycles of charge and discharge, ( c) is a top-view scanning micrograph before charge and discharge of silicon nanoparticles, and (d) is a top-view scan micrograph of silicon nanoparticles after 100 cycles of charge and discharge.
본 발명에서 사용되는 용어는 본 발명에서의 기능을 고려하면서 가능한 현재 널리 사용되는 일반적인 용어들을 선택하였으나, 이는 당 분야에 종사하는 기술자의 의도 또는 판례, 새로운 기술의 출현 등에 따라 달라질 수 있다. 또한, 특정한 경우는 출원인이 임의로 선정한 용어도 있으며, 이 경우 해당되는 발명의 설명 부분에서 상세히 그 의미를 기재할 것이다. 따라서 본 발명에서 사용되는 용어는 단순한 용어의 명칭이 아닌, 그 용어가 갖는 통상의 의미와 본 발명의 명세서 전반에 걸쳐 기재된 내용을 토대로 해석되어야 한다.The terms used in the present invention have been selected as widely used general terms as possible in consideration of the functions in the present invention, but this may vary according to the intention or precedent of the person skilled in the art, the emergence of new technologies and the like. In addition, in certain cases, there is also a term arbitrarily selected by the applicant, in which case the meaning will be described in detail in the description of the invention. Therefore, the terms used in the present invention should not be interpreted based on the general meaning of the term but the contents described throughout the specification of the present invention, rather than simply the name of the term.
이하, 첨부한 도면 및 바람직한 실시예들을 참조하여 본 발명의 기술적 구성을 상세하게 설명한다.Hereinafter, with reference to the accompanying drawings and preferred embodiments will be described in detail the technical configuration of the present invention.
그러나, 본 발명은 여기서 설명되는 실시예에 한정되지 않고 다른 형태로 구체화 될 수도 있다. 명세서 전체에 걸쳐 본 발명을 설명하기 위해 사용되는 동일한 참조번호는 동일한 구성요소를 나타낸다.However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Like reference numerals used to describe the present invention throughout the specification denote like elements.
본 발명의 기술적 특징은 금속나노입자가 너무 크게 성장하거나 응집하여 큰 입자가 되는 것을 방지할 수 있는 구조를 갖는 그래핀-금속나노입자복합체(G/M복합체) 및 상기 G/M복합체가 탄소나노섬유 매트릭스 내에 고르게 분산된 탄소나노섬유복합체를 개발한 것에 있다. Technical features of the present invention is a graphene-metal nanoparticle composite (G / M composite) having a structure that can prevent the metal nanoparticles grow or aggregate too large to become large particles are carbon nano It is to develop a carbon nanofiber composite evenly dispersed in the fiber matrix.
즉, G/M복합체가 포함된 탄소나노섬유복합체를 전극 활물질로 포함하게 되면, 금속나노입자가 탄소나노섬유 외부로 노출되지 않으므로 충전 및 방전에 따른 금속나노입자의 부피변화를 완충시켜줄 뿐만 아니라 금속나노입자의 응집현상을 방지함으로써 전극표면의 비저항을 감소시켜 효과적인 전기화학반응을 유도할 수 있어 우수한 충방전 특성, 고용량, 우수한 부피 안정성 등이 확보된 전극 및 이차전지를 제공할 수 있기 때문이다. In other words, when the carbon nanofiber composite including the G / M composite is included as an electrode active material, the metal nanoparticles are not exposed to the outside of the carbon nanofibers, thereby buffering the volume change of the metal nanoparticles due to charging and discharging as well as the metal. This is because it is possible to provide an electrode and a secondary battery having excellent charge / discharge characteristics, high capacity, and excellent volume stability by preventing the aggregation of nanoparticles, thereby reducing the resistivity of the electrode surface to induce an effective electrochemical reaction.
따라서, 본 발명의 G/M복합체는 금속나노입자; 및 상기 금속나노입자를 감싸서 형성된 그래핀시트;를 포함하는 구조를 갖는다. 이러한 구조를 통해 금속나노입자의 응집과 입자성장을 막고 금속나노입자를 탄소나노섬유 매트릭스내에 균일하게 분산시킬 수 있다. Therefore, the G / M complex of the present invention is a metal nanoparticle; And a graphene sheet formed by surrounding the metal nanoparticles. This structure prevents the agglomeration and particle growth of the metal nanoparticles and can uniformly disperse the metal nanoparticles in the carbon nanofiber matrix.
여기서, 금속나노입자는 Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au 로 구성된 그룹에서 선택되는 하나 이상일 수 있는데, 실리콘(Si)계 음극소재가 이론적인 용량이 약 4,200 mAh/g으로 흑연소재에 비해 10배 이상 크기 때문에 가장 유망한 소재이지만 실리콘 음극소재는 리튬을 흡수 저장 할 때에 결정구조의 변화를 매우 크게 야기 시켜 300% 이상의 큰 부피변화가 발생하는 문제점을 갖는 소재인 것을 고려하여 구체적 실시예에서는 금속나노입자로 Si를 선정하여 사용하였다. Here, the metal nanoparticles may be one or more selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au, the silicon (Si) -based negative electrode material The theoretical capacity is about 4,200 mAh / g, which is the most promising material because it is 10 times larger than graphite material, but the silicon anode material causes a large change in crystal structure when absorbing and storing lithium, resulting in a large volume change of more than 300%. In consideration of being a material having a problem that in the specific embodiment was used to select Si as the metal nanoparticles.
본 발명의 G/M복합체는 산화그래핀이 음전하를 띠고 금속나노입자가 양전하를 띠는데 착안된 것으로, 실험결과 금속나노입자와 산화그래핀시트가 정전기적 인력으로 강하게 결합되어 금속나노입자를 산화그래핀시트로 감싸서 형성된 G/M복합체가 상당히 안정적으로 유지되는 것을 확인하였다. The G / M complex of the present invention was conceived that the graphene oxide is negatively charged and the metal nanoparticles are positively charged. As a result of the experiment, the metal nanoparticles and the graphene oxide sheet are strongly bound by electrostatic attraction to oxidize the metal nanoparticles. It was confirmed that the G / M composite formed by wrapping with the graphene sheet was kept fairly stable.
이러한 정전기적 결합력을 강화하기 위해 금속나노입자를 -NH2기를 갖도록 개질하여 사용할 수 있을 것이다. In order to enhance the electrostatic bonding force, the metal nanoparticles may be modified to have -NH 2 groups.
본 발명의 G/M복합체는 금속나노입자를 산화그래핀으로 감싸게 되므로 금속나노입자의 크기를 원하는 대로 제어할 수 있는데, 예를 들어 탄소나노섬유복합체에 균일하게 분산될 수 있도록 50nm이하의 크기를 갖도록 형성할 수 있다. Since the G / M composite of the present invention wraps the metal nanoparticles with graphene oxide, the size of the metal nanoparticles can be controlled as desired. For example, the G / M composite may have a size of 50 nm or less so as to be uniformly dispersed in the carbon nanofiber composite. It can be formed to have.
한편, 본 발명의 G/M복합체는 다음과 같이 제조할 수 있다.On the other hand, the G / M complex of the present invention can be prepared as follows.
먼저, 산화그래핀시트는 공지된 모든 방법으로 형성할 수 있는데, 본 발명에서는 허머즈 방법 (Hummers method)을 이용해 카르복실기 (COOH)나 하이드록시기 (OH)기를 그라파이트에 도입하여 negative charge (음전하)를 갖는 산화그래핀시트(GO)를 합성하였다 (Chem. Mater. 1999, 11(3), 771-778). 이 때 산화그래핀시트는 20층 이하의 구조일 수 있는데, 보다 적합하게는 단층구조 내지 10층 구조이내일 수 있다.First, the graphene oxide sheet may be formed by any known method, and in the present invention, a carboxyl group (COOH) or a hydroxyl group (OH) group is introduced into graphite by using the Hummers method (negative charge). Graphene oxide sheet (GO) having a compound was synthesized (Chem. Mater. 1999, 11 (3), 771-778). In this case, the graphene oxide sheet may have a structure of 20 layers or less, more preferably, a single layer structure or a 10 layer structure.
금속나노입자로 실리콘(Si)을 사용하는 경우, 실리콘나노입자는 공지된 방법으로 양전하를 강화할 수 있는데 예를 들어 APS를 이용해 -NH2기를 갖는 실리콘 나노입자인 amino-funtionalized silicon으로 개질할 수 있다(Angew. Chem. Int. Ed. 2010, 49, 8408-8411). In the case of using silicon (Si) as the metal nanoparticles, the silicon nanoparticles can enhance the positive charge by a known method, for example, can be modified to amino-funtionalized silicon, which is a silicon nanoparticle having -NH 2 groups using APS. Angew. Chem. Int. Ed. 2010, 49, 8408-8411.
개질된 Amino-funtionalized silicon은 양전하(positive charge)를 갖기 때문에 GO와 정전기적 인력을 통해 강하게 결합되고 환원반응에 의해 GO가 환원된 G/Si 복합체를 제조할 수 있다. Since modified Amino-funtionalized silicon has a positive charge, it is possible to prepare a G / Si composite in which GO is strongly bound through GO and electrostatic attraction and reduced by GO.
이와 같이 본 발명의 G/M복합체는 열전도성, 기계적 강도 및 전기적특성이 우수한 그래핀을 금속나노입자와 복합화 함으로써 G/M복합체가 균일하게 분산된 탄소나노섬유복합체를 전극으로 사용하게 되면 전기 전도성이 우수하고 우수한 역학적 특성을 가질 수 있다. As described above, the G / M composite of the present invention is electrically conductive when the carbon nanofiber composite in which the G / M composite is uniformly dispersed as an electrode is formed by complexing graphene having excellent thermal conductivity, mechanical strength and electrical properties with metal nanoparticles. It can have excellent and excellent mechanical properties.
본 발명의 탄소나노섬유복합체는 탄소나노섬유; 및 상기 탄소나소섬유의 일부를 구성하는 그래핀-금속나노입자복합체;를 포함하는 구조를 갖는다. 여기서, 그래핀-금속나노입자복합체는 상술된 바와 동일한 특성을 가지므로 상술된 설명으로 가름한다. Carbon nanofiber composite of the present invention is carbon nanofibers; And a graphene-metal nanoparticle composite constituting a part of the carbon nanofibers. Here, the graphene-metal nanoparticle composite has the same characteristics as described above and thus goes to the description above.
G/M복합체를 포함하는 탄소나노섬유복합체는 직경이 100 ~ 300 nm이고, 비표면적은 300 m2/g 이하이며, 평균 세공직경은 1 ~ 2 nm인 특성을 가지고 있다. The carbon nanofiber composite including the G / M composite has a diameter of 100 to 300 nm, a specific surface area of 300 m 2 / g or less, and an average pore diameter of 1 to 2 nm.
한편, 본 발명의 탄소나노섬유복합체는 G/M복합체가 유지된 상태로 분말상을 이루도록 분쇄될 수 있어 탄소나노섬유복합체를 제조된 상태 그대로 즉 웹으로 사용할 수도 있지만 분말상으로 분쇄하여 사용이 가능하므로 적용가능성을 높일 수 있다. On the other hand, the carbon nanofiber composite of the present invention can be pulverized to form a powder form in a state in which the G / M composite is maintained, so that the carbon nanofiber composite may be used as it is, that is, as a web, but can be used by pulverizing into a powder form You can increase your chances.
또한, 탄소나노섬유 매트릭스 내에 G/M복합체를 포함하기만 하면 일정한 상승효과를 나타내지만, G/M복합체가 균일하게 분산되어 위치하게 되면 보다 우수한 특성을 나타내었다. In addition, the inclusion of the G / M complex in the carbon nanofiber matrix exhibits a certain synergistic effect, but when the G / M complex is uniformly dispersed and positioned, it showed better characteristics.
본 발명의 탄소나노섬유복합체 제조방법은 G/M복합체 및 탄소섬유전구체를 포함하는 방사용액을 준비하는 단계; 방사용액을 전기방사하여 전구체방사섬유를 얻는 단계; 전구체방사섬유를 산화안정화하여 내염화섬유를 얻는 단계; 및 내염화섬유를 탄화하여 탄소나노섬유복합체를 얻는 단계;를 포함한다. Carbon nanofiber composite manufacturing method of the present invention comprises the steps of preparing a spinning solution comprising a G / M complex and a carbon fiber precursor; Electrospinning the spinning solution to obtain precursor spinning fibers; Oxidative stabilizing the precursor spun fiber to obtain a flame resistant fiber; And carbonizing the flame resistant fiber to obtain a carbon nanofiber composite.
여기서, 방사용액은 탄소나노섬유전구체 및 그래핀-금속나노입자복합체의 총함량 100 중량부 당 그래핀-금속나노입자복합체가 30중량부 이내로 포함된다. 이러한 G/M 복합체의 방사 용액 함량비는 전기방사가 잘 이루어지는 함량비로서 실험적으로 결정된 것이다. 즉 농도가 상한보다 높아지면 방사 용액 점도의 영향으로 인해 방사가 어렵고 섬유가 잘 형성되지 않기 때문이다. 특히, 탄소나노섬유전구체 및 그래핀-금속나노입자복합체는 4:1 내지 20:1의 중량비로 포함될 수 있다. Here, the spinning solution contains the graphene-metal nanoparticle composite within 30 parts by weight per 100 parts by weight of the carbon nanofiber precursor and the graphene-metal nanoparticle composite. The spinning solution content ratio of the G / M composite is experimentally determined as the content ratio of electrospinning well. In other words, if the concentration is higher than the upper limit, it is difficult to spin due to the influence of the spinning solution viscosity and the fibers are not formed well. In particular, the carbon nanofiber precursor and the graphene-metal nanoparticle composite may be included in a weight ratio of 4: 1 to 20: 1.
한편, 탄소나노섬유 전구체용 고분자는 폴리아크릴로나이트릴(PAN, polyacrylonitrile), 폴리비닐알콜(PVA, polyvinylachol), 폴리이미드(PI, polyimide), 폴리벤질이미다졸(PBI, polybenzimidazol), 페놀 수지(phenol resin), 에폭시 수지(epoxy resin), 폴리에칠렌(PE, polyethylene), 폴리프로필렌(PP, polypropylene), 폴리비닐클로라이드(PVC, polyvinylchloride), 폴리스타이렌(PS, polystyrene), 폴리아닐린(PA, polyanaline), 폴리메칠메타클레이트(PMMA, polymethylmethacrylate), 폴리비닐리덴클로라이드(PVDC, polyvinylidence chloride), 폴리비닐리덴 플루오라이드(PVDF, povinylidene fluoride) 및 각종 피치(pitch) 등이 사용될 수 있다.On the other hand, the polymer for carbon nanofiber precursor is polyacrylonitrile (PAN, polyacrylonitrile), polyvinyl alcohol (PVA, polyvinylachol), polyimide (PI, polyimide), polybenzimidazole (PBI, polybenzimidazol), phenol resin (phenol resin), epoxy resin, polyethylene (PE, polyethylene), polypropylene (PP, polypropylene), polyvinylchloride (PVC, polyvinylchloride), polystyrene (PS, polystyrene), polyaniline (PA, polyanaline), Polymethyl methacrylate (PMMA, polymethylmethacrylate), polyvinylidene chloride (PVDC, polyvinylidence chloride), polyvinylidene fluoride (PVDF, povinylidene fluoride) and various pitch (pitch) and the like can be used.
또한 방사용액의 제조에는 탄소나노섬유 전구체용 고분자의 종류에 따라 해당 고분자를 용해할 수 있는 적절한 용매를 선택하여 사용할 수 있다. 즉 방사용액에서 탄소섬유전구체가 용해되는 용매는 준비된 탄소섬유전구체, G/M 복합체를 모두 분산시킬 수 있기만 하면 제한되지는 않기 때문이다. 하지만 본 발명의 실시예에서는 dimethyformamide(DMF), dimethysulfoxide(DMSO), tetrahydrofuran(THF) 중 어느 하나 이상이 사용되었다. 탄소나노섬유 전구체로는 폴리아크릴나이트릴 (PAN, 분자량=160,000)이 사용되었는데, 100% 순중합체 (homopolymer) 뿐 아니라 5-15%의 공중합체 (copolymer)를 함유한 개질된 아크릴을 사용할 수 있다. 공중합체의 조성으로는 이타콘산 (itaconic acid)나 메틸아크릴레이트 (methylacrylate, MA)등을 공중합 물질로 사용할 수 있다. In addition, according to the type of the polymer for carbon nanofiber precursor for the production of the spinning solution can be used by selecting a suitable solvent that can dissolve the polymer. That is, the solvent in which the carbon fiber precursor is dissolved in the spinning solution is not limited so long as it can disperse all the prepared carbon fiber precursor and the G / M composite. However, in the embodiment of the present invention, at least one of dimethyformamide (DMF), dimethysulfoxide (DMSO) and tetrahydrofuran (THF) was used. Polyacrylonitrile (PAN, molecular weight = 160,000) was used as the carbon nanofiber precursor, and a modified acrylic containing 5-15% copolymer as well as 100% homopolymer can be used. . As the composition of the copolymer, itaconic acid or methylacrylate may be used as the copolymer.
산화안정화는 전구체방사섬유를 열풍순환爐를 사용하여 압축공기를 분당 5~20 mL의 유속으로 공급하고, 분당 1 ℃의 승온 속도로 200~300 ℃에서 30분 이상 유지하여 수행될 수 있다.  Oxidation stabilization may be carried out by supplying compressed air at a flow rate of 5-20 mL per minute using a hot air circulating fan and maintaining at 200-300 ° C. for 30 minutes or more at a temperature increase rate of 1 ° C. per minute.
내염화섬유를 탄화하고자 하는 경우, 탄화는 분당 5 ℃의 승온 속도로 750 ~ 850 ℃까지 승온 한 후 불활성 기체 분위기에서 30분 내지 2시간 유지하여 수행될 수 있다. When carbonizing the flame resistant fiber, the carbonization may be performed by maintaining the temperature in an inert gas atmosphere for 30 minutes to 2 hours after heating up to 750 to 850 ° C. at a rate of 5 ° C. per minute.
특히, 본 발명의 탄소나노섬유복합체 제조시 방사용액에 포함되는 그래핀-금속나노입자복합체의 농도를 제어하여 탄소나노섬유복합체에 포함되는 그래핀-금속나노입자복합체의 크기 및 분포도 중 하나 이상을 제어할 수 있다. 즉 금속나노입자가 너무 크게 성장하거나 응집하여 큰 입자가 됨으로써 탄소나노섬유 외부에 노출되는 것을 막기 위하여 그래핀이 금속나노입자를 둘러싼 G/M 복합체를 형성하고, 방사용액에 포함되는 G/M 복합체의 농도를 제어하여 원하는 크기로 제어된 금속나노입자가 탄소나노섬유 매트릭스 내에 고르게 분포하는 탄소나노섬유복합체를 제조할 수 있기 때문이다.In particular, at least one of the size and distribution of the graphene-metal nanoparticle composites included in the carbon nanofiber composites by controlling the concentration of the graphene-metal nanoparticle composites contained in the spinning solution during the manufacture of the carbon nanofiber composites of the present invention. Can be controlled. That is, graphene forms a G / M complex surrounding the metal nanoparticles in order to prevent the metal nanoparticles from growing too large or aggregated to become large particles and exposed to the outside of the carbon nanofibers, and the G / M complex contained in the spinning solution. This is because the carbon nanofiber composite having the metal nanoparticles controlled to the desired size can be uniformly distributed in the carbon nanofiber matrix by controlling the concentration of.
본 발명의 전극은 상술된 탄소나노섬유복합체를 전극활물질로 포함한다. 특히 본 발명의 전극에 사용된 탄소나노섬유복합체가 G/M복합체를 포함하고 있으므로 예를 들어 본 발명의 전극은 이차전지에서 음극으로 사용될 수 있다. 이 때 탄소나노섬유복합체는 전기방사되어 제조된 웹 상태 그대로 사용될 수도 있고, 분말 상으로 분쇄되어 사용될 수도 있다. The electrode of the present invention includes the above-described carbon nanofiber composite as an electrode active material. In particular, since the carbon nanofiber composite used in the electrode of the present invention includes a G / M composite, for example, the electrode of the present invention may be used as a negative electrode in a secondary battery. At this time, the carbon nanofiber composite may be used as the web state prepared by electrospinning, or may be used after being pulverized into a powder form.
본 발명의 이차전지는 탄소나노섬유복합체를 전극활물질로 포함하는 전극을 포함한다. 본 발명의 이차전지는 충방전 100사이클이 경과되어도 전극에 포함된 전극활물질이 기판과 분리되지 않을 뿐만 아니라, 충방전 100사이클이 경과되어도 방전용량이 600 mAh/g을 유지한다. 이러한 특성은 전극활물질로 사용된 탄소나노섬유복합체의 구조상 탄소나노섬유 매트릭스 내에 분산된 금속나노입자가 G/M복합체 형태이므로 금속나노입자를 둘러싸고 있는 그래핀이 금속나노입자의 부피 팽창을 억제하면서도 동시에 지지체로 작용하기 때문인 것으로 예측된다.The secondary battery of the present invention includes an electrode including a carbon nanofiber composite as an electrode active material. In the secondary battery of the present invention, the electrode active material contained in the electrode is not separated from the substrate even after 100 cycles of charge and discharge, and the discharge capacity is maintained at 600 mAh / g even after 100 cycles of charge and discharge. This characteristic is due to the structure of the carbon nanofiber composite used as the electrode active material, since the metal nanoparticles dispersed in the carbon nanofiber matrix are in the form of a G / M composite, the graphene surrounding the metal nanoparticles suppresses the volume expansion of the metal nanoparticles. It is expected to act as a support.
실시예 1Example 1
1. GO 합성1. GO Synthesis
도 1에 도시된 바와 같은 순서로 H2SO4와 KMnO4를 이용한 하머즈 방법 (Hummers method)을 통해 그라파이트에 카르복실기 (COOH)나 하이드록시기 (OH)기가 도입된 산화그래핀시트(GO)를 합성하였다(Chem. Mater. 1999, 11(3), 771-778). 이 때 합성된 GO는 후술하는 바와 같이 대체적으로 1 내지 10층구조를 가지고 있었다. H 2 SO 4 and in the order as shown in FIG. Using KMnO 4 Graphene oxide sheets (GO) having a carboxyl group (COOH) or a hydroxyl group (OH) group introduced into graphite were synthesized by the Hammers method (Chem. Mater. 1999, 11 (3), 771-778). ). GO synthesized at this time had a 1 to 10 layer structure as described below.
2. Amino-funtionalized silicon 나노입자 합성2. Synthesis of Amino-funtionalized silicon nanoparticles
도 2에 도시된 바와 같은 순서로 실리콘 나노입자는 APS를 이용해 -NH2기를 갖는 amino-funtionalized silicon으로 개질하였다. 개질된 나노입자는 양전하를 띠고 있었다.In the order as shown in FIG. 2, the silicon nanoparticles were modified with amino-funtionalized silicon having -NH 2 groups using APS. The modified nanoparticles were positively charged.
3. G/Si 복합체 제조3. G / Si Composite Manufacturing
도 3에 도시된 바와 같이, Amino-funtionalized silicon 나노입자는 양전하를 갖고, GO는 음전하를 갖기 때문에 정전기적 인력을 통해 강하게 결합하게 된다. 또한 양전하를 갖는 amino-funtionalized silicon 나노입자들은 양전하들끼리의 반발력에 의해 응집되고 크게 성장하는 것을 막아 줄 수 있다. As shown in FIG. 3, since the Amino-funtionalized silicon nanoparticles have a positive charge and GO has a negative charge, the Amino-funtionalized silicon nanoparticles are strongly bound through electrostatic attraction. In addition, amino-funtionalized silicon nanoparticles with positive charges can prevent agglomeration and large growth due to repulsion between positive charges.
도 4에 도시된 바와 같은 순서로 GO가 둘러싼 실리콘 복합체에 환원제인 hydrazine을 이용해 GO를 환원함으로써 G/Si 복합체를 제조하였다. 제조된 G/Si 복합체는 40nm 크기였다. In the order as shown in Figure 4 by reducing the GO by using a hydrazine as a reducing agent in the silicon composite surrounded by GO G / Si composites were prepared. The prepared G / Si composite was 40 nm in size.
실험예 1Experimental Example 1
실시예 1에서 얻어진 GO를 전자현미경으로 관찰하고 그 결과 사진을 도 5에 도시하였다. SEM(도 5a)과 TEM (도 5b) 사진을 통해 하머즈 방법에 의해 합성된 GO는 그라파이트가 박리되어 얇은 층의 GO들로 구성되어 있고, GO의 층수는 1~10개 정도임을 알 수 있다. 일반적으로 GO의 단층면에는 카르복실기와 하이드록시기가 존재하므로 GO 표면은 음전하를 띠고 극성용매에서 분산이 용이함이 보고되어 있다.The GO obtained in Example 1 was observed with an electron microscope, and the photograph is shown in FIG. 5 as a result. SEM (FIG. 5A) and TEM (FIG. 5B) photographs show that GO synthesized by the Hammers method is composed of thin layers of GO with graphite peeled off, and the number of GO layers is about 1-10. . In general, since the carboxyl group and the hydroxyl group exist on the monolayer of GO, the surface of GO has been reported to be negatively charged and easy to disperse in polar solvents.
실험예 2Experimental Example 2
실시예 3에서 얻어진 G/Si 복합체를 전자현미경으로 관찰하고 그 결과 사진을 도 6에 도시하였다. SEM (도 6a와 b) 사진에서 실리콘 나노입자들이 그래핀 시트로 피복되어 있음을 볼 수 있고, TEM (도 6c와 d) 사진을 통해 약 3 nm의 얇고 유연하며 주름진 그래핀이 실리콘 나노입자의 가장자리(edge)에서 발견됨을 통해 그래핀층이 실리콘 나노입자들을 잘 둘러싸고 있음을 알 수 있다. 또한 그래핀층이 근접한 실리콘 나노입자들을 뭉치게 하지 않고 분리된 입자들끼리 잘 연결하고 있음을 TEM (도 6c와 d) 사진을 통해 확인하였다.The G / Si composite obtained in Example 3 was observed with an electron microscope, and the photograph is shown in FIG. 6 as a result. The SEM (FIGS. 6A and B) photos show that the silicon nanoparticles are covered with graphene sheets, and the TEM (FIGS. 6C and d) photos show that about 3 nm of thin, pliable and corrugated graphene is formed of the silicon nanoparticles. It can be seen from the edge that the graphene layer surrounds the silicon nanoparticles well. In addition, it was confirmed that the graphene layer is well connected to the separated particles without agglomeration of the adjacent silicon nanoparticles through the TEM (Fig. 6c and d) photograph.
실시예 2Example 2
1. 방사용액 제조1. Preparation of spinning solution
탄소나노섬유 전구체로는 PAN 순중합체와, G/Si 복합체를 준비하여, 용매로 준비된 DMF에 PAN, G/Si 복합체를 용해시켜 다음과 같이 초음파을 이용한 분산방법으로 분산시켜 방사용액을 제조하였다.The carbon nanofiber precursor was prepared by preparing a PAN pure polymer and a G / Si composite, dissolving the PAN and G / Si composites in DMF prepared as a solvent, and dispersing the same by dispersing using ultrasonic waves as follows.
PAN 3.00 g을 DMF에 용해하여 고분자용액을 제조한 후, G/Si 복합체 (20 wt% : 0.60 g)을 상기 고분자용액에 첨가한 후 실리콘의 분산도를 높이기 위해 2시간 동안 초음파 분산하고, 70℃에서 4시간 동안 용해하여 방사용액 (G/Si/PAN 용액)을 제조하였다. After dissolving 3.00 g of PAN in DMF to prepare a polymer solution, G / Si composite (20 wt%: 0.60 g) was added to the polymer solution, and then ultrasonically dispersed for 2 hours to increase the dispersion of silicon. It was dissolved for 4 hours at ℃ to prepare a spinning solution (G / Si / PAN solution).
2. 전구체방사섬유제조2. Precursor spinning fiber manufacturing
상기 균질화된 방사용액 (G/Si/PAN 용액)을 전기방사기를 이용하여 전기방사하였다. 이때 방사조건은 0.5 ㎜의 주사바늘이 부착된 30 ㎖ 실린지에 상기 섬유전구체 용액을 넣고 20 ㎸의 전압을 가하여 전기방사 하였다. 이때 주사바늘과 집전체간의 거리는 15 ㎝로 유지하고 섬유전구체 용액의 용출속도는 3 ㎖/h로 하며, 집전체에서 섬유가 집적되면 부직포를 떼어내어 분리함으로서 전구체 방사섬유를 제조하였다.The homogenized spinning solution (G / Si / PAN solution) was electrospun using an electrospinner. At this time, the spinning condition was put into the 30 ml syringe attached to a 0.5 mm needle and the fiber precursor solution was electrospun by applying a voltage of 20 kV. In this case, the distance between the needle and the current collector was maintained at 15 cm, and the dissolution rate of the fiber precursor solution was 3 ml / h. When the fibers were accumulated in the current collector, the nonwoven fabric was removed to separate the precursor spinning fiber.
3. 내염화섬유제조3. Manufacture of flame resistant fiber
전기방사하여 얻은 전구체 방사섬유(G/Si/PAN계 방사 섬유)를 열풍순환爐를 사용하여 압축공기를 분당 5~20 mL의 유속으로 공급하고, 분당 1 ℃의 승온 속도로 200~300 ℃에서 1시간 유지하여 안정화하여 G/Si/PAN계 내염화섬유를 얻었다.  The precursor spinning fiber (G / Si / PAN-based spinning fiber) obtained by electrospinning was supplied at a flow rate of 5-20 mL per minute using a hot air circulation fan at 200-300 ° C. at a temperature rising rate of 1 ° C. per minute. Stabilized by maintaining for 1 hour to obtain a G / Si / PAN-based flame resistant fiber.
4. G/Si/PAN계 탄소나노섬유복합체 (GSP) 제조4. Manufacture of G / Si / PAN-based Carbon Nanofiber Composite (GSP)
안정화과정을 거쳐 얻어진 G/Si/PAN계 내염화섬유를 비활성 기체 (N2, Ar 기체) 분위기하의 800 ℃의 온도에서 탄화하여 G/Si/PAN계 탄소나노섬유복합체 (20-GSP)를 제조하였다.G / Si / PAN-based carbon nanofiber composite (20-GSP) was prepared by carbonizing the G / Si / PAN-based flame resistant fiber obtained through stabilization at 800 ° C. under an inert gas (N 2 , Ar gas) atmosphere. It was.
실시예 3Example 3
방사용액에 G/Si 복합체를 10 wt%( 0.30 g) 사용한 것을 제외하면 실시예1과 동일한 방법을 수행하여 G/Si/PAN계 탄소나노섬유복합체(10-GSP)를 제조하였다.A G / Si / PAN-based carbon nanofiber composite (10-GSP) was prepared in the same manner as in Example 1 except that 10 wt% (0.30 g) of G / Si composite was used as the spinning solution.
실시예 4Example 4
방사용액에 G/Si 복합체를 5 wt%(0.15 g)사용한 것을 제외하면 실시예1과 동일한 방법을 수행하여 G/Si/PAN계 탄소나노섬유복합체(5-GSP)를 제조하였다.A G / Si / PAN-based carbon nanofiber composite (5-GSP) was prepared in the same manner as in Example 1 except that 5 wt% (0.15 g) of G / Si composite was used as the spinning solution.
비교예 1Comparative Example 1
방사용액 제조시 G/Si 복합체 대신 Si를 사용한 것을 제외하면 실시예 1과 동일한 방법으로 비교예 실리콘 함량 20wt%를 갖는 Si/PAN계 탄소나노섬유복합체 (20-SP)를 제조하였다. A Si / PAN-based carbon nanofiber composite (20-SP) having a silicon content of 20 wt% of Comparative Example was prepared in the same manner as in Example 1 except that Si was used instead of the G / Si composite when preparing the spinning solution.
비교예 2Comparative Example 2
방사용액 제조시 G/Si 복합체를 사용하지 않은 것을 제외하면, 실시예 1과 동일한 방법으로 비교예 탄소나노섬유 (CNF)를 얻었다.Comparative Example carbon nanofibers (CNF) were obtained in the same manner as in Example 1 except that the G / Si composite was not used in the preparation of the spinning solution.
실험예 3Experimental Example 3
실시예 2 내지 4에서 G/Si/PAN계 탄소나노섬유복합체를 제조하는 과정에서 얻어진 전구체방사섬유, 내염화섬유 및 탄화섬유의 웹을 관찰하여 각각의 웹사진을 도 7에 도시하였다.The webs of the precursor spun fiber, the flame resistant fiber, and the carbonized fiber obtained in the process of manufacturing the G / Si / PAN-based carbon nanofiber composites in Examples 2 to 4 were observed, and the respective web photographs are shown in FIG. 7.
도 7에 도시된 바와 같이 전구체방사섬유가 도시된 (a)는 회색, 내염화섬유가 도시된 (b)는 갈색, 탄화섬유가 도시된 (c)는 검은색을 나타내었음을 알 수 있다.As shown in Figure 7, it can be seen that (a) is shown the precursor radiation fiber, gray (b) is shown the flame resistant fiber is brown, (c) is shown the carbonized fiber is black.
실험예 4Experimental Example 4
실시예 2 내지 4에서 얻어진 G/Si 복합체가 포함된 탄소나노섬유복합체인 20-GSP, 10-GSP, 5-GSP, 그리고 비교예 1 에서 얻어진 20-SP를 SEM으로 관찰하고 그 결과 사진을 도 8에 도시하였다. 20-GSP, 10-GSP, 5-GSP, and 20-SP obtained in Comparative Example 1, which are carbon nanofiber composites containing the G / Si composites obtained in Examples 2 to 4, were observed by SEM, and the photographs are shown in FIG. 8 is shown.
도 8로부터, 얻어진 탄소나노섬유복합체의 평균 직경범위는 250-350 nm 였고, G/Si 복합체의 농도가 낮은 5-GSP는 입자나 비드의 생성 없이 매끄러운 표면을 갖는 반면, G/Si 복합체의 농도가 증가할수록 클러스터 (cluster)가 섬유 중간 마디에 존재하고 클러스터의 수가 증가함을 볼 수 있다. 10-GSP 표면의 에너지 분산형 X-선 분광기 (EDX)로 분석한 결과 C, O, Si 원소가 각각 78.83%, 6.18%, 15.96%의 원자비로 존재함을 확인하였다. 특히 고배율 SEM사진 (도8c와 d)에서 20-GSP는 클러스터 (cluster)가 섬유 내에 있는 반면, 20-SP는 나노입자들이 뭉쳐 덩어리 된 포도송이 나노입자들이 탄소섬유 표면에 노출되어짐을 관찰 할 수 있었다.From Fig. 8, the average diameter range of the obtained carbon nanofiber composite was 250-350 nm, and 5-GSP having a low concentration of the G / Si composite had a smooth surface without generating particles or beads, whereas the concentration of the G / Si composite was It can be seen that as is increased, clusters are present in the middle segment of the fiber and the number of clusters increases. The energy dispersive X-ray spectroscopy (EDX) of the 10-GSP surface revealed that the C, O, and Si elements were present in an atomic ratio of 78.83%, 6.18%, and 15.96%, respectively. In particular, high magnification SEM images (Figs. 8c and d) show that 20-GSP has clusters in the fiber, while 20-SP shows that the clustered nanoparticles of the nanoparticles aggregated are exposed on the surface of the carbon fiber. there was.
실험예 5Experimental Example 5
실시예 2 및 3에서 얻어진 G/Si 복합체가 포함된 탄소나노섬유복합체인 20-GSP, 10-GSP, 그리고 비교예 1 에서 얻어진 20-SP를 TEM으로 관찰하고 그 결과 사진을 도 9에 도시하였다. 20-GSP, 10-GSP, and 20-SP obtained in Comparative Example 1, which are carbon nanofiber composites containing the G / Si composites obtained in Examples 2 and 3, were observed by TEM, and the photographs are shown in FIG. 9. .
10-GSP, 20-GSP, 20-SP의 TEM 사진이 도시된 도 9의 (a),(b),(c)로부터, 50 nm 이하의 크기를 갖는 나노입자들이 탄소나노섬유 matrix 내에 잘 분산되어 있는 반면, 20-SP는 클러스터 덩어리들이 탄소나노섬유 표면에 존재하고 있다. 물질 내부구조를 알기위해 10-GSP에 존재하는 나노 입자의 제한시야 전자회절법 (SAED) (도 9d)에 의한 회절패턴에는 (110), (220), (311) 형태의 초격자 회절점이 나타나고 있으며 이를 통해 실리콘 나노입자의 결정성 회절패턴을 확인하였다. From (a), (b), and (c) of FIGS. 9A and 9C, in which TEM images of 10-GSP, 20-GSP, and 20-SP are shown, nanoparticles having a size of 50 nm or less are well dispersed in a carbon nanofiber matrix. In contrast, 20-SP has cluster clusters on the surface of carbon nanofibers. The superlattice diffraction points in the form of (110), (220), and (311) appear in the diffraction pattern of the limited field electron diffraction (SAED) (FIG. 9d) of the nanoparticles present in the 10-GSP to know the internal structure of the material. Through this, the crystalline diffraction pattern of the silicon nanoparticles was confirmed.
실험예 6Experimental Example 6
Si 결정도를 알아보기 위해 5-GSP, 10-GSP, 20-GSP, G/Si, GO의 X선 회절분석을 하고, 그 결과를 도 10중 (a)에 나타내었으며, GSP, G/Si, GO의 Raman spectrum을 관찰하고 그 결과를 도 10 중 (b)에 나타내었다.X-ray diffraction analysis of 5-GSP, 10-GSP, 20-GSP, G / Si, GO to determine the Si crystallinity, the results are shown in (a) of Figure 10, GSP, G / Si, Raman spectrum of GO was observed and the results are shown in (b) of FIG.
일반적으로 그라파이트는 2θ값이 26.5ㅀ에서 나타나고 이는 흑연의 증간구조 (002) 면에서 관찰되는 대표적인 결정피크로 알려져 있다. 하머즈 법으로 처리된 GO는 2θ=26.5o 위치에서 결정피크가 사라지고 2θ=12o 부근에서 새로운 결정피크가 생성된 것을 확인할 수 있었다. 이는 이미 보고된 바와 같이 그라파이트의 흑연구조가 팽창 또는 박리가 진행되어 2θ=26.5o 위치의 결정성 영역이 사라지고 (001) 면에서 흑연 층간에 산소를 포함하는 카르복실기나 하이드록시기와 같은 관능기가 결합되어 흑연 층간거리를 증가시켜 상변이를 유도한 결과임을 알 수 있다 (Polymer, 2011, 35(6), 565-573.). 실리콘이 복합화된 G/Si 뿐 아니라 실리콘계 탄소나노섬유 복합체 모두 2θ = 23°를 중심으로 결정성이 낮은 탄소를 나타내는 폭이 넓은 피크와 더불어 Si 2θ = 28, 48, 57°에서 각각 (110), (220), (311) 면을 갖는 실리콘 나노입자의 결정성 피크들을 관찰하였다.In general, graphite exhibits a 2θ value at 26.5 kV, which is known as a representative crystal peak observed in the extra structure (002) of graphite. In the GO treated by the Hammers method, the crystal peak disappeared at 2θ = 26.5 o and a new crystal peak was generated near 2θ = 12 o . This is because the graphite structure of graphite expands or peels off as it is reported, and the crystalline region at 2θ = 26.5 o disappears, and functional groups such as carboxyl groups or hydroxyl groups containing oxygen are bound between the graphite layers in the (001) plane. It can be seen that the result of inducing phase shift by increasing graphite interlayer distance (Polymer, 2011, 35 (6), 565-573.). Silicon-based carbon nanofiber composites as well as G / Si composited with silicon have broad peaks representing low crystalline carbon centered at 2θ = 23 ° and Si 2θ = 28, 48, and 57 °, respectively (110), Crystalline peaks of silicon nanoparticles having (220) and (311) planes were observed.
라만 스펙트럼을 분석한 결과 도 10의 (b)에 도시된 바와 같이 1360cm-1 과 1580cm-1 에서 각각 탄소의 D-band 와 G-band가 관찰되었고, 498cm-1 에서 나타나는 강한 피크는 나노사이즈의 결정질 Si의 E2g모드에 의한 것이고, 300cm-1 근처에서 face-centered cubic(fcc)다이아몬드 구조타입을 갖는 결정질 Si의 피크가 5-GSP, 10-GSP, 20-GSP, G/Si에서 모두 확인되었다.Analysis of the Raman spectrum as shown in FIG. 10 (b) were each D-band and G-band of carbon observed at 1360cm -1 and 1580cm -1, a strong peak appears at 498cm -1 is the nano-sized The peaks of crystalline Si with the face-centered cubic (fcc) diamond structure type near 300cm -1 were observed at 5-GSP, 10-GSP, 20-GSP, and G / Si due to the E2g mode of crystalline Si. .
실시예 5 내지 7Examples 5-7
실시예 2 내지 4에서 얻어진 G/Si/PAN계 탄소나노섬유복합체인 20-GSP, 10-GSP, 5-GSP를 절단하여 이를 음극재로 제조하고, 제조된 음극 및 LiPF6 1:1 vol %의 ethylene carbonate (EC)/dimethyl carbonate (DMC) 액체전해질로 구성되는 코인셀을 제조하여 이차전지1 내지 3(20-GSP, 10-GSP, 5-GSP)을 준비하였다.20-GSP, 10-GSP and 5-GSP, which are the G / Si / PAN carbon nanofiber composites obtained in Examples 2 to 4, were cut to prepare a negative electrode material, and the prepared negative electrode and LiPF 6 1: 1 vol% Coin cells composed of ethylene carbonate (EC) / dimethyl carbonate (DMC) liquid electrolyte were prepared to prepare secondary batteries 1 to 3 (20-GSP, 10-GSP, 5-GSP).
비교예 3Comparative Example 3
음극으로 비교예 1에서 얻어진 SP-20을 사용한 것을 제외하면 실시예5와 동일한 방법으로 코인셀을 제조하여 비교예이차전지1(SP-20)를 준비하였다.A coin cell was prepared in the same manner as in Example 5, except that SP-20 obtained in Comparative Example 1 was used as a negative electrode, to prepare Comparative Example Secondary Battery 1 (SP-20).
비교예 4Comparative Example 4
음극으로 비교예 2에서 얻어진 CNF부직포를 사용한 것을 제외하면 실시예5와 동일한 방법으로 코인셀을 제조하여 비교예이차전지2(CNP)를 준비하였다.A coin cell was prepared in the same manner as in Example 5 except that the CNF nonwoven fabric obtained in Comparative Example 2 was used as a negative electrode, to prepare Comparative Example Secondary Battery 2 (CNP).
실험예 7Experimental Example 7
실시예 5 내지 7에서 얻어진 이차전지에 대해 Won-A tech사의 WBCS3000L 충방전 기기를 사용하여 충방전 실험을 실시하여 제조된 리튬이차전지의 음극으로써 충방전용량 및 사이클 특성을 조사하고, 그 결과를 도 11에 나타내었다. 충방전은 100 mA/g의 전류로 0.02 내지 1.50 V의 전압범위에서 수행하였다.The secondary batteries obtained in Examples 5 to 7 were charged and discharged using a WBCS3000L charging / discharging device manufactured by Won-A tech, and the charge and discharge capacity and cycle characteristics of the lithium secondary batteries manufactured as negative electrodes were investigated. 11 is shown. Charging and discharging was performed at a voltage range of 0.02 to 1.50 V at a current of 100 mA / g.
도 11에서 보듯이, 실시예 5 내지 7에서 얻어진 이차전지의 20-GSP, 10-GSP, 5-GSP의 경우 626 mAh/g, 778 mAh/g, 923 mAh/g의 음극 초기용량을 나타낸 반면, 비교예 3에서 얻어진 비교예이차전지 CNF는 767 mAh/g의 음극 초기용량을 나타내고 있다. 또한 첫번째 충방전 후 초기 쿨롱효율은 CNF는 44%, 5-GSP는 48%, 10-GSP는 57%, 20-GSP는 61%를 보여주고 있다. 따라서 G/Si의 농도가 높은 20-GSP의 초기 용량과 첫번째 충방전 후 초기 쿨롱효율이 높음을 알 수 있다.As shown in FIG. 11, in the case of 20-GSP, 10-GSP, and 5-GSP of the secondary batteries obtained in Examples 5 to 7, the initial capacities of the cathodes of 626 mAh / g, 778 mAh / g, and 923 mAh / g are shown. And Comparative Example Secondary Battery CNF obtained in Comparative Example 3 exhibit a negative electrode initial capacity of 767 mAh / g. The initial coulombic efficiency after the first charge and discharge shows 44% for CNF, 48% for 5-GSP, 57% for 10-GSP, and 61% for 20-GSP. Therefore, it can be seen that the initial capacity of 20-GSP having a high G / Si concentration and the initial coulombic efficiency after the first charge / discharge are high.
실험예 8Experimental Example 8
실시예5에서 얻어진 20-GSP의 미분용량곡선(Differential Capacity Curve)을 관찰하고 그 결과를 도 12 (a)에 나타내었다. The differential capacity curve of 20-GSP obtained in Example 5 was observed and the results are shown in FIG. 12 (a).
도 12 중 (a)로부터 첫 번째 방전동안 0.64 V 근처에서 리튬 이온이 흑연에 삽입되기에 앞서 전해질이 분해되어 전극 표면에 피막 SEI (Solid Electrolyte Interface 또는 Solid Electrolyte Inter-phase)가 형성되고, 이 SEI를 통해 전극과 전해질 사이에서의 전자 이동에 의한 전해질 분해가 억제되어 선택적으로 리튬 이온의 삽입ㅇ탈리만 가능하게 된다. 첫 번째 사이클로부터 전기화학반응에 의해 실리콘과 리튬의 반응으로 인해 Si 결정이 비결정화 되어지는 LixSi사 생성되는데 특히 낮은 전압인 0.1 V에서 LixSi의 반응피크가 나타남을 알 수 있다. 두 번째 사이클부터 방전동안 3개의 환원피크 0.3, 0.24 and 0.08V와 충전반응 동안 0.29 and 0.45V에서 두개의 산화피크가 관찰되었고, 이는 비결정 Si의 리튬화/탈리튬화 반응 (lithiation/delithiation)을 나타내고 있다.Before the lithium ion is inserted into the graphite near 0.64 V during the first discharge from (a) of FIG. 12, the electrolyte is decomposed to form a coating SEI (Solid Electrolyte Interface or Solid Electrolyte Inter-phase) on the electrode surface. Through this, electrolyte decomposition due to electron transfer between the electrode and the electrolyte is suppressed, and only insertion and removal of lithium ions can be selectively performed. It can be seen from the first cycle that Li x Si is formed in which Si crystals are crystallized due to the reaction of silicon and lithium by electrochemical reaction, and the reaction peak of Li x Si appears at a low voltage of 0.1 V. From the second cycle, two oxidation peaks were observed at 0.3, 0.24 and 0.08V during the reduction and 0.29 and 0.45V during the charge reaction, which was responsible for the lithiation / delithiation of amorphous Si. It is shown.
실험예 9Experimental Example 9
실시예 5, 실시예 6 및 비교예4에서 얻어진 10-GSP, 20-GSP, CNF의 계면 특성을 알아보기 위해 전기화학 임피던스 분광학 (electrochemical impedance spectroscopy, EIS)으로 분석하고, 그 결과를 도 12 중 (b)에 나타내었다. 임피던스 측정은 Jahner Electrik IM6e를 사용하였고, 주파수 영역은 100 kHz - 10 mHz, 교류신호 10 mV mV 를 인가하여 실험하였다. In order to determine the interfacial properties of 10-GSP, 20-GSP, and CNF obtained in Example 5, Example 6, and Comparative Example 4, analysis was performed by electrochemical impedance spectroscopy (EIS), and the results are shown in FIG. It is shown in (b). Impedance measurement was performed using Jahner Electrik IM6e, and the frequency range was tested by applying 100 kHz-10 mHz and AC signal 10 mV mV.
도 12 (b)는 탄소나노섬유 복합체 전극의 특성을 주파수에 따라 허수항과 실수항 임피던스로 도시한 Nyquist plot이다. 교류전위의 주파수에 따라 고주파영역에는 반원이 낮은 주파수 영역에서는 일정한 기울기를 갖는 직선이 나타난다. 이때 반원은 전하전이에 의한 반응속도의 지배를 받지만 직선 부분은 반응물질의 확산에 의하여 지배를 받는다. (전기전자재료학회논문지, 2011, 24(4), 333-339). 고주파에서 반원의 시작 부분과 끝부분의 값의 차를 전하이동저항 (charge transfer resistance, R f )라고 하는데, CNF, 5-GSP, 10-GSP, 20-GSP 전극에서 Rf값이 각각 70.26 Ω, 56.98 Ω,48.02 Ω, 42.96 Ω 순서로 감소하였다. 이는 G/Si 복합체의 농도가 증가할수록 Rf값이 감소함을 알 수 있는데, Si을 둘러싼 그래핀의 밀도가 높을수록 실리콘 입자들이 잘 분리되어 CNR matric 내에 잘 분산되므로 반응 면적이 넓어져 리튬이온이 삽입/탈삽입 되는 동안 전극에서 전해질로, 또는 전해질에서 전극으로 전자가 이동할 경우 극복해야 하는 저항성이 줄어들기 때문으로 생각된다. 또한 20-GSP 전극에서 작은 Rf값은 SEI 필름의 형성과도 관계가 있는데 용매 분해 반응으로 인하여 형성된 피막이 전극표면에 보호막 역할을 해주어 전극 속으로 리튬이온의 원활한 삽입/탈삽입이 큰 저항 없이 이루어지기 때문에 우수한 방전 용량을 나타냄을 알 수 있다. 저주파에서 20-GSP는 직선의 기울기가 크게 나타나는데 이는 리튬 이온의 벌크 음극으로의 확산에 의한 고체상태 확산 저항이 그래핀의 전기전도도로 인해 낮기 때문에 리튬이온의 확산 이동 속도가 빠르다는 것을 알 수 있다.Figure 12 (b) is a Nyquist plot showing the characteristics of the carbon nanofiber composite electrode in the imaginary term and real term impedance according to the frequency. According to the frequency of the AC potential, a straight line with a constant slope appears in the high frequency region where the semicircle is low. At this time, the semicircle is controlled by the reaction rate due to charge transfer, but the straight portion is controlled by the diffusion of the reactants. (The Korean Institute of Electrical and Electronic Material Engineers, 2011, 24 (4), 333-339). In that the difference between the value of the start of the class and the end portion of the high-frequency charge transfer resistance (charge transfer resistance, R f) , CNF, 5-GSP, 10-GSP, each of the R f values in the 20-GSP electrode 70.26 Ω , 56.98 Ω, 48.02 Ω, and 42.96 Ω. It can be seen that the R f value decreases as the concentration of the G / Si composite increases. The higher the density of graphene surrounding Si, the more the silicon particles are separated and dispersed well in the CNR matric. It is thought that the resistance to overcome when electrons move from the electrode to the electrolyte or from the electrolyte to the electrode during this insertion / reinsertion is reduced. In addition, the small R f value in the 20-GSP electrode is also related to the formation of the SEI film. The film formed by the solvent decomposition reaction acts as a protective film on the electrode surface, so that the smooth insertion / reinsertion of lithium ions into the electrode is achieved without large resistance. It can be seen that it shows excellent discharge capacity. At low frequencies, 20-GSP shows a large slope of the straight line, which shows that the diffusion rate of lithium ions is fast because the solid state diffusion resistance due to diffusion of lithium ions into the bulk cathode is low due to the electrical conductivity of graphene. .
실험예 10Experimental Example 10
실시예 5 내지 7에서 얻어진 20-GSP, 10-GSP, 5-GSP 및 비교예3 및 4에서 얻어진 SP-20, CNF의 사이클 특성을 조사하고 그 결과를 도 13 및 도 14에 나타내었다. Cycle characteristics of 20-GSP, 10-GSP, 5-GSP and SP-20 and CNF obtained in Comparative Examples 3 and 4 were investigated and the results are shown in FIGS. 13 and 14.
도 13에서 알 수 있듯이 20-SP가 가장 높은 음극초기용량을 나타내지만 50회 충방전 후에는 GSP 전극들이 비교예 3보다 좋은 사이클 특성을 보이고 있다. 특히 20-GSP와 10-GSP 전극은 이론용량 372 mAh/g을 갖는 그라파이트보다 더 높은 용량을 유지하고 싸이클이 증가할수록 안정적인 용량감소를 보이고 있다   As can be seen in FIG. 13, 20-SP shows the highest cathode initial capacity, but after 50 charge / discharge cycles, GSP electrodes showed better cycle characteristics than Comparative Example 3. FIG. In particular, 20-GSP and 10-GSP electrodes maintain higher capacity than graphite with theoretical capacity of 372 mAh / g and show stable capacity decrease with increasing cycles.
이러한 결과로부터, 그래핀 없이 실리콘과 폴리아크릴로니트릴만 혼합하여 제조한 탄소나노섬유복합체 20-SP은 실리콘간의 인력이 작용하여 뭉쳐져서 입자가 커지므로 탄소나노 섬유 표면에 노출되어 리튬이차전지음극으로 사용하는 경우 초기 방전용량은 크지만 실리콘의 부피팽창으로 인해 사이클 특성이 떨어지는 것을 확인할 수 있었다. 이는 PAN과 실리콘 나노입자간의 혼화성이 떨어져 금속의 뭉침현상이 발생하기 때문에, 실리콘 나노입자 상태로 고르게 분산하는데 어려운 문제점을 지니는 것을 보여준다. From these results, the carbon nanofiber composite 20-SP prepared by mixing only silicon and polyacrylonitrile without graphene is exposed to the surface of the carbon nanofibers because the particles become larger due to the attraction between the silicon. When used as the initial discharge capacity is large, but the cycle characteristics were reduced due to the volume expansion of silicon. This shows that due to the miscibility between PAN and silicon nanoparticles, agglomeration of metals occurs, which makes it difficult to uniformly disperse the silicon nanoparticles.
반면, G/Si 복합체를 첨가하여 제조한 시료인 10-GSP와 20-GSP가 안정적인 용량감소를 나타내는 이유는 그래핀이 실리콘을 둘러쌈으로써 실리콘 입자들이 응집하여 보다 큰 입자가 되는 것을 억제함으로써 탄소나노 섬유 내에 고루 분산되어 기존의 리튬이온전지의 충전 및 방전에 따른 실리콘 나노입자의 큰 부피변화를 완충시켜줄 뿐만 아니라, 리튬이온전지 전극 표면의 비저항을 감소시켜 전지의 충전 및 방전 시 효과적인 전기화학반응을 유도할 수 있기 때문이다. 따라서 10-GSP와 20-GSP 전극에서 그래핀은 실리콘 입자의 뭉침현상을 완충(buffering)해 주는 역할을 함으로써 실리콘이 CNF matrix 내에 분산되어 전기화학적 활성 사이트가 증가하고 탄소나노섬유가 전기전도도를 유지 시키기 때문에 이와 같이 전기화학적 특성이 매우 우수한 것으로 예측된다. On the other hand, 10-GSP and 20-GSP, which are samples prepared by adding a G / Si composite, exhibit stable capacity reduction because the graphene encloses the silicon, thereby suppressing the agglomeration of silicon particles into larger particles. Dispersed evenly within the nanofibers, it not only buffers the large volume change of silicon nanoparticles due to the charging and discharging of the existing lithium ion battery, but also reduces the resistivity of the electrode surface of the lithium ion battery, thereby making it an effective electrochemical reaction during battery charging and discharging. This can be induced. Therefore, graphene plays a role in buffering the agglomeration of silicon particles in 10-GSP and 20-GSP electrodes, so that silicon is dispersed in the CNF matrix, so that electrochemically active sites are increased and carbon nanofibers maintain electrical conductivity. As such, the electrochemical properties are expected to be very excellent.
도 14는 충방전 50 싸이클 후 5-GSP, 10-GSP, 20-GSP의 전자주사현미경 결과 사진이므로, 도 14로부터 충방전 후에도 섬유의 모양이 잘 유지 되고 있음을 확인할 수 있다. 14 is a photograph of the electron scanning microscope results of 5-GSP, 10-GSP, and 20-GSP after 50 cycles of charging and discharging. Therefore, it can be seen from FIG.
따라서 입자상을 사용하는 기존의 경우와 비교하여 실시예 2 내지 4에서 얻어진 G/Si/PAN계 탄소나노섬유복합체를 실시예 5 내지 7과 같이 섬유웹 상태로 전극으로 사용하게 되면 그 자체로 전자 이동이 매우 빠르며, 활물질, 바인더 및 도전제, 기타 용매, 부대시설 등이 필요하지 않고, 슬러리를 제조하여 코팅하는 공정이 없어도 되는 장점을 지니고 있다. 또한 취급이 용이하기 때문에 추후 그라파이트를 대체하는 음극물질로 기대효과가 매우 클 것으로 예측된다.Therefore, when the G / Si / PAN-based carbon nanofiber composite obtained in Examples 2 to 4 is used as an electrode in a fibrous web state as in Examples 5 to 7 as compared with the conventional case using a particulate form, electrons move by themselves. This is very fast and does not require an active material, a binder and a conductive agent, other solvents, auxiliary facilities, etc., and has the advantage of eliminating the process of preparing and coating a slurry. In addition, the expected effect is expected to be very large as a cathode material to replace the graphite in the future because of its easy handling.
실시예 8Example 8
실시예 2에서 얻어진 웹형태의 20-GSP을 grinding 하여 파우더로 제조하였다. 전극을 제조하기 위해 도전재로는 Super-P, 바인더로는 polyacrylic acid를 사용하였다. 전극의 조성은 각각 음극 활물질 80 wt%, 도전재 10 wt%, 바인더 10 wt%의 비율로 넣어 혼합하였다. 상기 제조된 음극 및 LiPF6 1:1 vol %의 ethylene carbonate (EC)/dimethyl carbonate (DMC) 액체전해질로 구성되는 코인셀을 제조하여 이차전지4(grinded 20-GSP)를 준비하였다.20-GSP of the web form obtained in Example 2 was ground to prepare a powder. To prepare the electrode, Super-P was used as the conductive material and polyacrylic acid was used as the binder. The composition of the electrode was mixed at 80 wt% of the negative electrode active material, 10 wt% of the conductive material, and 10 wt% of the binder. A coin cell consisting of the prepared negative electrode and LiPF 6 1: 1 vol% ethylene carbonate (EC) / dimethyl carbonate (DMC) liquid electrolyte was prepared to prepare a secondary battery 4 (grinded 20-GSP).
비교예 5Comparative Example 5
음극활물질로 실리콘나노입자를 사용한 것을 제외하면 실시예8과 동일한 방법으로 코인셀을 제조하여 비교예이차전지3(Si NPs)을 준비하였다.A coin cell was prepared in the same manner as in Example 8 except that silicon nanoparticles were used as a negative electrode active material, thereby preparing Comparative Example Secondary Batteries 3 (Si NPs).
실험예 11Experimental Example 11
실시예 8에서 제조된 grinded 20-GSP와 비교예5에서 제조된 Si NPs를 대상으로 Won-A tech사의 WBCS3000L 충방전 기기를 사용하여 충방전 실험을 하였다. 충방전은 100 mA/g의 전류로 0.005 ~ 2.0 V의 전압범위에서 수행하였다. 실시예 8 및 비교예 5에 따른 리튬이차전지의 충방전 결과, 사이클 특성 및 쿨롱효율을 각각 도 15에 나타내었다.The grinded 20-GSP prepared in Example 8 and Si NPs prepared in Comparative Example 5 were charged and discharged using a WBCS3000L charge / discharge device of Won-A tech. Charging and discharging were performed at a voltage range of 0.005 to 2.0 V at a current of 100 mA / g. As a result of charge and discharge of the lithium secondary batteries according to Example 8 and Comparative Example 5, cycle characteristics and coulombic efficiencies are shown in FIG. 15.
도 15에서 알 수 있듯이, 실리콘 나노입자(Si NPs)의 초기용량은 4000 mA/g에 가까운 매우 높은 고용량을 보이지만 싸이클이 증가할수록 결정성 실리콘나노입자는 급격한 용량감소를 보이고 있다. 이는 리튬이 실리콘내부에서 두 물질간의 친화력에 의해 리튬이 가역적으로 이동하지 않고 남음으로써 급격한 부피팽창에 의해 나타난 현상으로 보인다. As can be seen in Figure 15, the initial capacity of the silicon nanoparticles (Si NPs) shows a very high high capacity close to 4000 mA / g, but the crystalline silicon nanoparticles shows a rapid decrease in capacity as the cycle increases. This seems to be a phenomenon caused by rapid volume expansion because lithium does not reversibly move due to the affinity between the two materials in the silicon.
그러나 grinded 20-GSP는 100회 충방전 결과에도 실리콘 나노입자보다 더 높은 용량을 유지하고 있고 사이클 특성 및 클롱 효율 또한 더욱 우수함을 알 수 있다. 20-GSP는 그래핀이 실리콘의 뭉침 현상을 방지하는 역할을 하여 탄소나노섬유 내에 고루 분산되게 할 뿐만 아니라, matrix로 작용하는 탄소나노섬유가 실리콘 활물질 사이에서 완충작용으로 부피팽창을 억제하며 실리콘의 지지역할을 하여 싸이클이 증가할수록 실리콘 나노입자 보다 안정적인 용량감소를 보이고 있다.However, grinded 20-GSP maintains higher capacity than silicon nanoparticles even after 100 charge / discharge results, and also shows better cycle characteristics and Klong efficiency. 20-GSP not only prevents graphene from agglomeration of silicon, but also disperses it evenly in carbon nanofibers, and also inhibits volume expansion by buffering carbon nanofibers acting as a matrix. As the cycle increases, the capacity decreases more stably than silicon nanoparticles.
실험예 12Experimental Example 12
충방전 100 싸이클 전후의 grinded 20-GSP과 실리콘 나노입자(Si NPs)를 주사현미경으로 관찰하고, top-view 전자주사현미경 사진을 도 16에 나타내었다. The grinded 20-GSP and silicon nanoparticles (Si NPs) before and after 100 cycles of charge and discharge were observed under a scanning microscope, and top-view electron scanning micrographs are shown in FIG. 16.
충방전 전에 얻은 grinded 20-GSP의 표면 사진(도 16a)은 깨끗하고 균일한 표면을 보이며, 실리콘 나노입자의 표면 사진(도 16c)도 표면에 약간의 크랙이 존재 하긴 하지만 비교적 균일한 표면을 볼 수 있다. 그러나 도 16d에서 볼 수 있듯이 100 싸이클 후 실리콘 나노입자는 grinded 20-GSP에 비해 리튬과 합금반응 과정에서 증가했던 부피가 다시 충전할 때 줄어들면서 크랙이 발생하고, 그 결과 약 50 μm 내외의 작은 조각들이 표면을 이루고 있음을 볼 수 있다.The surface photograph of the grinded 20-GSP obtained before charging and discharging (FIG. 16A) shows a clean and uniform surface, and the surface photograph of silicon nanoparticles (FIG. 16C) shows a relatively uniform surface although there are some cracks on the surface. Can be. However, as can be seen in FIG. 16d, after 100 cycles, the silicon nanoparticles are cracked as the volume increased during the alloying process with lithium decreases when recharged, compared to grinded 20-GSP. You can see that they form a surface.
Grinded 20-GSP과 실리콘 나노입자의 단면 SEM 결과 (도 16 b와 d)를 보면, 20-GSP의 활물질 두께는 충방전 전 11.5 μm에서 100 싸이클 후 21.0 μm으로 팽창함을 관찰 하였다. 실리콘 나노 입자의 경우, 활물질 두께는 충방전 전 41 μm 이지만, 100 싸이클 후 전극과 집전체의 분리로 인해 단면의 사진을 관찰 할 수가 없는데 이는 크랙에 의해 갈라진 실리콘 활물질과 구리 집전체 사이에 전기적 접촉이 나쁨을 시사하며 따라서 충방전이 진행됨에 따라 전극의 저항 증가와 지속적인 용량의 감소를 설명할 수 있다.  In cross-sectional SEM results of Grinded 20-GSP and silicon nanoparticles (FIG. 16b and d), it was observed that the active material thickness of 20-GSP expanded from 11.5 μm before charge and discharge to 21.0 μm after 100 cycles. In the case of silicon nanoparticles, the thickness of the active material is 41 μm before charging and discharging, but after 100 cycles, the photo of the cross section cannot be observed due to the separation of the electrode and the current collector. This implies that this is bad, and thus the increase in the resistance of the electrode and the continuous decrease in capacity can be explained as the charge and discharge proceed.
따라서 100 싸이클 전후의 SEM 사진을 통해 20-GSP은 크랙이 생성되거나 활물질이 집전체에서 떨어지는 현상도 볼 수 없고, 활물질 아래의 기판도 드러나지 않았는데 이처럼 충방전 후에도 활물질이 기판에 잘 붙어 있을 수 있어서 실리콘 나노입자에 비해 우수한 사이클 특성을 보인다고 설명될 수 있다.Therefore, 20-GSP showed no cracks or the active material falling from the current collector through 100 SEM images before and after 100 cycles, and the substrate under the active material was not exposed. It can be explained that it exhibits excellent cycle characteristics compared to nanoparticles.
상술된 실험결과들로부터 본 발명의 G/M 복합체를 포함하는 탄소나노섬유 복합체를 사용하여 제조된 리튬이온전지는 우수한 충방전 특성, 고용량, 우수한 부피 안정성을 기대할 수 있음을 알 수 있다.From the above experimental results, it can be seen that the lithium ion battery manufactured using the carbon nanofiber composite including the G / M composite of the present invention can expect excellent charge / discharge characteristics, high capacity, and excellent volume stability.
또한, 본 발명의 G/M 복합체를 포함하는 탄소나노섬유 복합체가 리튬이온전지에 사용된 경우만을 예시하였으나, 다른 종류의 이차전지를 포함한 에너지저장장치에 전극활물질로 사용되는 경우에도 셀 성능을 향상시킬 뿐만 아니라 장기 운전 성능 역시 향상될 수 있음이 예측될 수 있다. In addition, although the carbon nanofiber composite including the G / M composite of the present invention is used only in a lithium ion battery, the cell performance is improved even when used as an electrode active material in an energy storage device including other types of secondary batteries. It can be expected that long term driving performance can be improved as well.
본 발명은 이상에서 살펴본 바와 같이 바람직한 실시 예를 들어 도시하고 설명하였으나, 상기한 실시 예에 한정되지 아니하며 본 발명의 정신을 벗어나지 않는 범위 내에서 당해 발명이 속하는 기술분야에서 통상의 지식을 가진 자에 의해 다양한 변경과 수정이 가능할 것이다.Although the present invention has been shown and described with reference to preferred embodiments as described above, it is not limited to the above-described embodiments and those skilled in the art without departing from the spirit of the present invention. Various changes and modifications will be possible.

Claims (23)

  1. 금속나노입자; 및Metal nanoparticles; And
    상기 금속나노입자를 감싸서 형성된 그래핀시트;을 포함하는 그래핀-금속나노입자복합체.Graphene-metal nanoparticle composite comprising a; graphene sheet formed by surrounding the metal nanoparticles.
  2. 제 1 항에 있어서,The method of claim 1,
    상기 금속나노입자는 Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au 로 구성된 그룹에서 선택되는 것을 특징으로 하는 그래핀-금속나노입자복합체. The metal nanoparticles are graphene-metal nanoparticles composite, characterized in that selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au.
  3. 제 1 항에 있어서,The method of claim 1,
    상기 금속나노입자는 -NH2기를 갖도록 개질된 것을 특징으로 하는 그래핀-금속나노입자복합체.Graphene-metal nanoparticles composite, characterized in that the metal nanoparticles are modified to have a -NH 2 group.
  4. 제 1 항에 있어서,The method of claim 1,
    상기 금속나노입자와 상기 그래핀시트는 정전기적 인력으로 결합된 것을 특징으로 하는 그래핀-금속나노입자복합체.The metal nanoparticles and the graphene sheet is a graphene-metal nanoparticles composite, characterized in that coupled by electrostatic attraction.
  5. 제 1 항에 있어서,The method of claim 1,
    상기 그래핀-금속나노입자복합체는 50nm이하의 크기를 갖는 것을 특징으로 하는 그래핀-금속나노입자복합체.The graphene-metal nanoparticle composite is a graphene-metal nanoparticle composite, having a size of 50nm or less.
  6. 탄소나노섬유; 및Carbon nano fiber; And
    상기 탄소나소섬유의 일부를 구성하는 그래핀-금속나노입자복합체;를 포함하는 탄소나노섬유복합체.Carbon nanofiber composite comprising a; graphene-metal nanoparticle composite constituting part of the carbon nanofiber.
  7. 제 6 항에 있어서,The method of claim 6,
    상기 그래핀-금속나노입자복합체는 금속나노입자; 및 상기 금속나노입자를 감싸서 형성된 그래핀시트;을 포함하는 것을 특징으로 하는 탄소나노섬유복합체.The graphene-metal nanoparticle composite includes metal nanoparticles; And a graphene sheet formed by wrapping the metal nanoparticles.
  8. 제 7 항에 있어서,The method of claim 7, wherein
    상기 금속나노입자는 Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au 로 구성된 그룹에서 선택되는 것을 특징으로 하는 탄소나노섬유복합체. The metal nanoparticles are selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag, Au.
  9. 제 7 항에 있어서,The method of claim 7, wherein
    상기 금속나노입자는 -NH2기를 갖도록 개질된 것을 특징으로 하는 탄소나노섬유복합체.The carbon nanofiber composite is characterized in that the metal nano-particles are modified to have a -NH 2 group.
  10. 제 7 항에 있어서,The method of claim 7, wherein
    상기 금속나노입자와 상기 그래핀시트는 정전기적 인력으로 결합된 것을 특징으로 하는 탄소나노섬유복합체.The metal nanoparticles and the graphene sheet is carbon nanofiber composite, characterized in that coupled by electrostatic attraction.
  11. 제 6 항에 있어서,The method of claim 6,
    상기 탄소나노섬유복합체는 직경이 100 ~ 300 nm이고, 비표면적은 300 m2/g 이하이며, 평균 세공직경은 1 ~ 2 nm인 것을 특징으로 하는 탄소나노섬유복합체. The carbon nanofiber composite has a diameter of 100 to 300 nm, a specific surface area of 300 m 2 / g or less, and an average pore diameter of 1 to 2 nm.
  12. 제 6 항에 있어서,The method of claim 6,
    상기 그래핀-금속나노입자복합체는 상기 탄소나노섬유 내에 균일하게 분산되어 위치하는 것을 특징으로 하는 탄소나노섬유복합체.The graphene-metal nanoparticle composite is a carbon nanofiber composite, characterized in that it is uniformly dispersed in the carbon nanofiber.
  13. 제 6 항에 있어서,The method of claim 6,
    상기 그래핀-금속나노입자복합체가 유지된 상태로 분말상을 이루도록 분쇄될 수 있는 것을 특징으로 하는 탄소나노섬유복합체.Carbon nano-fiber composite, characterized in that the graphene-metal nanoparticle composite can be pulverized to form a powder form in a maintained state.
  14. 제 6 항에 있어서,The method of claim 6,
    상기 그래핀-금속나노입자복합체는 50nm이하의 크기를 갖는 것을 특징으로 하는 탄소나노섬유복합체.The graphene-metal nanoparticle composite is a carbon nanofiber composite, characterized in that having a size of less than 50nm.
  15. 제 1 항 내지 제 5 항 중 어느 한 항의 그래핀-금속나노입자복합체 및 탄소섬유전구체를 포함하는 방사용액을 준비하는 단계;Preparing a spinning solution comprising the graphene-metal nanoparticle complex of any one of claims 1 to 5 and a carbon fiber precursor;
    상기 방사용액을 전기방사하여 전구체방사섬유를 얻는 단계;Electrospinning the spinning solution to obtain precursor spinning fibers;
    상기 전구체방사섬유를 산화안정화하여 내염화섬유를 얻는 단계; 및Oxidatively stabilizing the precursor spun fiber to obtain a flame resistant fiber; And
    상기 내염화섬유를 탄화하여 탄소나노섬유복합체를 얻는 단계;를 포함하는 탄소나노섬유복합체 제조방법.Carbonizing the flame resistant fiber to obtain a carbon nanofiber composite; carbon nanofiber composite manufacturing method comprising a.
  16. 제 15 항에 있어서, The method of claim 15,
    상기 방사용액은 상기 탄소나노섬유전구체 및 그래핀-금속나노입자복합체의 총함량 100 중량부 당 그래핀-금속나노입자복합체는 30중량부 이내로 포함되는 것을 특징으로 하는 탄소나노섬유복합체 제조방법. The spinning solution is a carbon nanofiber composite manufacturing method, characterized in that the graphene-metal nanoparticle composite per 100 parts by weight of the total carbon nanofiber precursor and graphene-metal nanoparticle composite is contained within 30 parts by weight.
  17. 제 16 항에 있어서,The method of claim 16,
    상기 탄소나노섬유전구체 및 그래핀-금속나노입자복합체는 4:1 내지 20:1의 중량비로 포함되는 것을 특징으로 하는 탄소나노섬유복합체 제조방법. The carbon nanofiber precursor and graphene-metal nanoparticle composite is a carbon nanofiber composite manufacturing method, characterized in that it comprises a weight ratio of 4: 1 to 20: 1.
  18. 제 15 항에 있어서, The method of claim 15,
    상기 방사용액에 포함되는 그래핀-금속나노입자복합체의 농도를 제어하여 상기 탄소나노섬유복합체에 포함되는 그래핀-금속나노입자복합체의 크기 및 분포도 중 하나 이상을 제어하는 것을 특징으로 하는 탄소나노섬유복합체 제조방법.By controlling the concentration of the graphene-metal nanoparticle composite contained in the spinning solution, carbon nanofibers, characterized in that to control at least one of the size and distribution of the graphene-metal nanoparticle composite contained in the carbon nanofiber composite Composite manufacturing method.
  19. 제 6 항 내지 제 14 항 중 어느 한 항의 탄소나노섬유복합체를 전극활물질로 포함하는 전극.An electrode comprising the carbon nanofiber composite according to any one of claims 6 to 14 as an electrode active material.
  20. 제 19 항에 있어서,The method of claim 19,
    상기 탄소나노섬유복합체는 분말 상인 것을 특징으로 하는 전극.The carbon nanofiber composite is an electrode, characterized in that the powder phase.
  21. 제 19 항의 전극을 포함하는 이차전지.A secondary battery comprising the electrode of claim 19.
  22. 제 21 항에 있어서,The method of claim 21,
    상기 이차전지는 충방전 100사이클이 경과되어도 상기 전극에 포함된 전극활물질이 기판과 분리되지 않는 것을 특징으로 하는 이차전지.The secondary battery is a secondary battery, characterized in that the electrode active material contained in the electrode is not separated from the substrate even after 100 cycles of charge and discharge.
  23. 제 21 항에 있어서,The method of claim 21,
    상기 이차전지는 충방전 100사이클이 경과되어도 방전용량이 600 mAh/g을 유지하는 것을 특징으로 하는 이차전지.The secondary battery is characterized in that the discharge capacity maintains 600 mAh / g even after 100 cycles of charge and discharge.
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