KR101594836B1 - Graphene-metal nano particle complex, carbon nanofiber composites comprising the complex, and rechargeable battery comprising th composites - Google Patents

Abstract

 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 comprising the carbon nanofiber composite.

Description

TECHNICAL FIELD [0001] The present invention relates to a carbon nanofiber composite including a graphene-metal nanoparticle composite, a carbon nanofiber composite including the composite, and a carbon nanoparticle composite,

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 comprising the carbon nanofiber composite.

In the 21st century, the rapid development of the semiconductor industry has led to the era of information communication, which is a new communication paradigm in which compact electronic devices such as notebook computers, mobile phones, DMB phones, and portable communication devices merely receive information from two- . In order to meet the demands of these multifunctional electric and electronic devices, high capacity and high power secondary batteries are being researched and developed mainly on battery materials.

Conventionally, lithium metal is used as an anode active material of a lithium secondary battery, but carbon based anode active material is used instead of lithium metal. As the carbonaceous anode active material, graphite (graphite) is typically used as a crystalline carbon. Since the upper limit of the theoretical capacity of the carbonaceous anode active material such as graphite is limited to about 372 mAh / g, a mobile digital fusion device Is not sufficient as an anode material to meet the requirements of the present invention. In particular, in the field of automobiles, development of electric vehicles is urgently required due to depletion of fossil fuels. However, when the existing lithium secondary battery is applied, it is difficult to operate the lithium secondary battery over a long distance by a single charge. It is not suitable for a long-term energy storage system for storing electric power generated by a circle.

Recently, new high-capacity materials have been introduced to replace commercial graphite electrodes. Among them, metallic anode materials, especially silicon anode materials, have a theoretical capacity of about 4,200 mAh / g, Therefore, it is emerging as the most promising material. However, the silicon negative electrode material causes a crystal structure change when lithium is absorbed and stored, resulting in a large volume change of 300% or more. In the case of graphite, which is currently used as an anode material, the bulk expansion rate by lithium charging is about 1.2 times. In the case of silicon, when maximum amount of lithium is absorbed and stored, it is converted to Li _4.4 Si and is about 4.12 times larger than the volume of silicon before volume expansion. The volume expansion causes the structure of the electrode to collapse and the Coulomb efficiency to be lowered, making it difficult to continue use.

Many researches have been conducted to solve the above-mentioned problems of the silicon electrode. One of them is to disperse the silicon nanoparticles in the carbon matrix so that the carbon matrix relaxes the mechanical stress of the silicon, and the structural integrity of the electrode Thereby inducing an improvement in the cyclability of the lithium ion battery during intercalation / deintercalation of lithium.

However, the anode active material for a silicon-based lithium secondary battery hybridized with carbon nanofibers prepared by vapor-growing silicon nanoparticles or carbon nanofibers coated with carbon can be produced by pyrolysis, chemical / thermal vapor deposition (CVD / TVD) Synthetic methods, and hydrothermal carbonization. These methods require high-temperature reaction conditions, require expensive precursors, and are difficult to mass-produce, resulting in problems in commercialization.

Recently, nanostructured electrodes have been attracting much attention because they are expected to improve the energy density and speed characteristics, and the relaxation and speed of volume change due to lithium ion intercalation / deintercalation. If the anode and cathode materials have a high specific surface area, the solid-phase diffusion path is reduced and the interface between the anode-separator-cathode is greatly increased. Therefore, the three-dimensional structure of the nanostructured material is expected to realize a high rate discharge characteristic and a high output lithium- do.

Not only be when utilizing nanostructured material using the electrospinning process as an electrode material to excellent electronic conductivity in the electrode and can reduce the diffusion path, in order to overcome the limitation of conventional electrode technology, a large amount of Li ⁺ is inserted into and leaving the process The lithium secondary battery having high output and high energy density can be expected. Electrospinning is the only way to fabricate fibers from hundreds of nanometers to tens of nanometers by using a polymer solution. Carbon nanofibers produced using this electrospinning technique have high electrical conductivity, high specific surface area, Since the production of carbon nanofibers containing metal oxide, porous material, carbon nanotubes and the like is easy, a very high electrochemical activity can be expected in the production of a secondary battery electrode material.

This manufacturing process is simple and basically similar to a general carbon fiber manufacturing process, and is a low cost mass production technology. The carbon nanofiber composite and the activated carbon nanofiber composite prepared from the composite component of the present invention have excellent specific surface area and electrical conductivity as compared with the volume, and the constituent fibers form a network. Therefore, And is further useful as an electrode material for an electric double layer super capacitor, an electromagnetic wave shielding material, a highly conductive material, a catalyst support, and a reinforcing material for a composite material.

However, when a metal or metal precursor is mixed with a carbon precursor polyacrylonitrile (PAN), which is mainly used at present, it is difficult to uniformly disperse into a metal or metal oxide state, When the surface is exposed, the surface expansion of the metal due to the volume expansion of the metal causes continuous interfacial cracking, reduction of the charging / discharging efficiency of the battery, continual electrolytic decomposition reaction and accordingly increase in the amount of electrolyte used, Problems such as increase in resistance and reduction in battery life may occur.

Therefore, it is possible to prevent the metal nanoparticles from growing too large or to prevent the metal nanoparticles from becoming large particles by aggregation and to uniformly disperse the metal nanoparticles in the carbon nanofiber, There is a growing need for development of an anode active material capable of ensuring cycle characteristics.

The inventors of the present invention have completed the present invention by focusing on the fact that metal nanoparticles can be prevented from becoming large particles when the metal nanoparticles are surrounded by a graphene sheet.

Accordingly, an object of the present invention is to provide a graphene-metal nano-particle composite having a structure capable of preventing metal nanoparticles from becoming too large or coagulated to become large particles.

Another object of the present invention is to provide a carbon nanofiber composite in which a graphene-metal nanoparticle composite (G / M composite) is uniformly dispersed in a carbon nanofiber matrix and a method of manufacturing the same.

It is a further object of the present invention to provide a carbon nanofiber composite containing a G / M composite as an electrode active material, thereby preventing the metal nanoparticles from being exposed to the outside of the carbon nanofibers, thereby buffering the volume change of the metal nanoparticles due to charging and discharging In addition, it is an object of the present invention to provide an electrode capable of inducing an effective electrochemical reaction by reducing the specific resistance of the electrode surface by preventing agglomeration of the metal nanoparticles.

Another object of the present invention is to provide a secondary battery having excellent charge / discharge characteristics, high capacity, and excellent volume stability by applying an electrode including a carbon nanofiber composite in which the G / M composite is uniformly dispersed as an electrode active material.

The object of the present invention is not limited to the above-mentioned objects, and although not explicitly mentioned, the object of the invention which can be recognized by a person skilled in the art from the description of the detailed description of the invention .

In order to accomplish the objects of the present invention, first, the present invention provides a metal nanoparticle; And a graphene sheet formed by wrapping the metal nanoparticles.

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,

In a preferred embodiment, the metal nanoparticles are modified to have -NH ₂ groups.

In a preferred embodiment, the metal nanoparticles and the graphene sheet are bonded with electrostatic attraction.

In a preferred embodiment, the graphene-metal nanoparticle composite has a size of 50 nm or less.

The present invention also relates to carbon nanofibers; And a graphene-metal nanoparticle composite constituting a part of the carbon nanofibers.

In a preferred embodiment, the graphene-metal nanoparticle composite comprises metal nanoparticles; And a graphene sheet formed by wrapping the metal nanoparticles.

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,

In a preferred embodiment, the metal nanoparticles are modified to have -NH ₂ groups.

In a preferred embodiment, the metal nanoparticles and the graphene sheet are bonded with electrostatic attraction.

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.

In a preferred embodiment, the graphene-metal nanoparticle composite is uniformly dispersed in the carbon nanofibers.

In a preferred embodiment, the graphene-metal nanoparticle composite may be pulverized to form a powder in a state of being held.

In a preferred embodiment, the graphene-metal nanoparticle composite has a size of 50 nm or less.

The present invention also provides a method of preparing a spinning solution, comprising: preparing a spinning solution containing any of the graphene-metal nanoparticle composites and a carbon fiber precursor as described above; Electrospinning the spinning solution to obtain precursor spinning fibers; Oxidizing and stabilizing the precursor-emitting fibers to obtain chlorinated fibers; And carbonizing the chlorinated fibers to obtain a carbon nanofiber composite material.

In a preferred embodiment, the spinning solution contains the graphene-metal nanoparticle composite in an amount of 30 parts by weight or less per 100 parts by weight of the total content of the carbon nanofibre precursor and the graphene-metal nanoparticle composite.

In a preferred embodiment, the carbon nanofibre precursor and the graphene-metal nanoparticle complex are included in a weight ratio of 4: 1 to 20: 1.

In a preferred embodiment, the concentration of the graphene-metal nanoparticle composite contained in the spinning solution is controlled to control at least one of size and distribution of the graphene-metal nanoparticle composite contained in the carbon nanofiber composite.

The present invention also provides an electrode comprising any one of the carbon nanofiber composites described above as an electrode active material.

In a preferred embodiment, the carbon nanofiber composite is in powder form.

The present invention also provides a secondary battery comprising the above-described electrode.

In a preferred embodiment, the electrode active material contained in the secondary battery is not separated from the substrate even after 100 cycles of charging and discharging have elapsed.

In a preferred embodiment, the secondary battery maintains a discharge capacity of 600 mAh / g even after 100 cycles of charge and discharge have elapsed.

The present invention has the following excellent effects.

First, according to the graphene-metal nanoparticle composite of the present invention, it is possible to prevent the metal nanoparticles from becoming too large or becoming agglomerated into large particles.

Further, according to the present invention, a carbon nanofiber composite in which a graphene-metal nanoparticle composite (G / M composite) is uniformly dispersed in a carbon nanofiber matrix can be provided, and a method of manufacturing the same.

In addition, according to the electrode of the present invention, since the metal nanoparticles are not exposed to the outside of the carbon nanofiber by including the carbon nanofiber composite containing the G / M composite as an electrode active material, the volume change of the metal nanoparticles due to charging and discharging It is possible to prevent the aggregation phenomenon of the metal nanoparticles as well as to reduce the specific resistance of the electrode surface, thereby inducing an effective electrochemical reaction.

In addition, the secondary battery of the present invention can secure excellent charge / discharge characteristics, high capacity, and excellent volume stability by applying an electrode including a carbon nanofiber composite material in which the G / M composite is uniformly dispersed as an electrode active material.

These technical advantages of the present invention are not limited to the above-mentioned technical scope, and even if not explicitly mentioned, the effect of the invention which can be recognized by a person skilled in the art from the description of the concrete contents for carrying out the invention Of course.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a manufacturing process diagram illustrating an embodiment of manufacturing an oxidized graphene (GO) using the Hummers method to produce a G / M composite according to an embodiment of the present invention.
FIG. 2 is a manufacturing process diagram illustrating one embodiment of manufacturing an amino-functionalized silicon nanoparticle to produce a G / M composite according to an embodiment of the present invention.
FIG. 3 is a schematic diagram for preparing a silicon composite (G / Si) surrounded by graphene (G), which is an embodiment of the G / M composite according to an embodiment of the present invention.
4 is a view showing a manufacturing process of the G / Si composite shown in FIG.
FIG. 5A is a scanning electron micrograph of the oxidized graphene GO prepared according to FIG. 1, and FIG. 5B is a transmission microscope photograph of the oxidized graphene GO.
FIG. 6 (a) is a scanning electron micrograph of the G / Si composite prepared according to FIG. 4, (b) is a high magnification scanning micrograph of the G / Si composite, (d) is a high magnification transmission micrograph of the G / Si composite.
FIG. 7 is a schematic view of a manufacturing process of a carbon nanofiber composite (GSP) containing graphene-silicon nanoparticles according to another embodiment of the present invention and a web photograph [(a) precursor spinning fiber, (b) ) Carbon fiber].
8 is a scanning electron micrograph of a graphene-silicon nanocomposite composite in a carbon nanofiber composite (GSP) containing graphene-silicon nanoparticles according to another embodiment of the present invention [(a) 5 wt% G / Si containing (b) 10 wt% G / Si containing (c) 20 wt% G / Si containing (d) 20 wt% Si.
9 (a) to 9 (c) are transmission electron micrographs of carbon nanofiber composite (GSP) containing graphene-silicon nanoparticle complex according to another embodiment of the present invention, 20-SPSP, (d) is the SAEA of 10-GSP limited field-of-view electron diffraction (SAED).
10 (a) is an X-ray diffraction pattern (XRD) graph of GSP, G / Si and GO obtained in the present invention, and (b) is a Raman spectrum graph of GSP, G / Si and GO.
FIG. 11 (a) is a graph of charge / discharge of CNF, FIG. 11 (b) is a graph of charging / discharging of 5-GSP, Fig.
12 (a) is a differential capacity curve of 20-GSP, and (b) is a Nyquist plot of GSP and CNF.
13 (a) is a 50-cycle characteristic graph of 20-GSP, 10-GSP, 5-GSP and CNF, and FIG.
14 is a scanning micrograph of 5-GSP, 10-GSP and 20-GSP after 50 cycles.
15 shows the results of 100 cycle characteristics and Coulomb efficiency characteristics of 20-GSP and Si NPs.
16 (a) is a top-view scanning micrograph of a grinded 20-GSP before charge / discharge according to another embodiment of the present invention, (b) is a top-view scanning microscope photograph after 100 cycles of charging and discharging, (c) is a top-view scanning micrograph of silicon nanoparticles before and after charging and discharging, and (d) is a top-view scanning micrograph of silicon nanoparticles after 100 cycles of charge and discharge.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Also, in certain cases, there may be a term selected arbitrarily by the applicant, in which case the meaning thereof will be described in detail in the description of the corresponding invention. Accordingly, the terms used in the present invention should not be construed to be mere terms, but should be interpreted based on the ordinary meanings of the terms and contents described throughout the specification of the present invention.

Hereinafter, the technical structure of the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.

However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Like reference numerals used to describe the present invention throughout the specification denote like elements.

The technical feature of the present invention is that a graphene-metal nano-particle composite (G / M composite) having a structure that prevents metal nanoparticles from becoming too large or agglomerated to become large particles and a G / And a carbon nanofiber composite material dispersed evenly in a fiber matrix.

That is, when the carbon nanofiber composite containing 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 change in volume of the metal nanoparticles due to charging and discharging, 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 because it is possible to induce an effective electrochemical reaction by reducing the resistivity of the electrode surface by preventing agglomeration of nanoparticles.

Thus, the G / M composite of the present invention can be a metal nanoparticle; And a graphene sheet formed by wrapping the metal nanoparticles. With this structure, it is possible to prevent aggregation and particle growth of the metal nanoparticles and uniformly disperse the metal nanoparticles in the carbon nanofiber matrix.

The metal nanoparticles may be at least one selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag and Au. The theoretical capacity is about 4,200 mAh / g, which is the most promising material because it is more than 10 times larger than the graphite material. However, the silicon cathode material causes a large change in crystal structure when absorbing and storing lithium, In the concrete examples, Si was selected as the metal nanoparticles and used.

In the G / M composite of the present invention, the graphene oxide is negatively charged and the metal nanoparticles are positively charged. As a result, the metal nanoparticles and the oxidized graphene sheet are strongly bonded to each other by electrostatic attraction to oxidize the metal nanoparticles It was confirmed that the G / M composite formed by being wrapped in the graphene sheet stays fairly stable.

In order to enhance the electrostatic bonding force, the metal nanoparticles may be modified to have -NH ₂ groups.

Since the G / M composite of the present invention encapsulates the metal nanoparticles with the oxidized graphene, the size of the metal nanoparticles can be controlled as desired. For example, the size of the G / M composite is 50 nm or less so as to be uniformly dispersed in the carbon nanofiber composite Respectively.

Meanwhile, the G / M composite of the present invention can be prepared as follows.

In the present invention, a carboxyl group (COOH) or a hydroxyl group (OH) group is introduced into graphite using a Hummers method to form a negative charge (negative charge) (GO) having an average particle size of 10 nm was synthesized (Chem. Mater. 1999, 11 (3), 771-778). At this time, the oxidized graphene sheet may have a structure of 20 layers or less, more preferably a single layer structure to a 10 layer structure.

When silicon (Si) is used as the metal nanoparticles, the silicon nanoparticles can be enriched in positive charge by a known method, for example by APS, and can be modified with amino-funtionalized silicon, which is a silicon nanoparticle having -NH ₂ groups (Angew Chem. Int. Ed., 2010, 49, 8408-8411).

Since the modified aminofunctionalized silicon has a positive charge, a G / Si complex can be produced in which GO is strongly bonded through electrostatic attraction and GO is reduced by a reduction reaction.

As described above, when the G / M composite of the present invention is made by compositing the graphene having excellent thermal conductivity, mechanical strength and electrical characteristics with the metal nanoparticles, if the carbon nanofiber composite material in which the G / M composite is uniformly dispersed is used as an electrode, Can have excellent and excellent mechanical properties.

The carbon nanofiber composite according to the present invention comprises 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 those described above, and therefore, the above-described explanation is not repeated.

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.

On the other hand, the carbon nanofiber composite according to the present invention can be pulverized to form a powder state in a state in which the G / M composite is held, so that the carbon nanofiber composite can be used as it is in the form of a web. However, The possibility can be increased.

In addition, if the G / M composite is included in the carbon nanofiber matrix, the G / M composite exhibits a certain synergistic effect. However, when the G / M composite is uniformly dispersed,

The method for preparing a carbon nanofiber composite according to the present invention comprises the steps of: preparing a spinning solution containing a G / M composite and a carbon fiber precursor; Electrospinning the spinning solution to obtain precursor spinning fibers; Oxidizing and stabilizing the precursor-emitting fibers to obtain chlorinated fibers; And carbonizing the chlorinated fibers to obtain a carbon nanofiber composite.

Herein, the spinning solution contains the graphene-metal nanoparticle complex in an amount of 30 parts by weight or less per 100 parts by weight of the total content of the carbon nanofibre precursor and the graphene-metal nano-particle composite. The ratio of the spinning solution content of the G / M composite was determined experimentally as the content ratio of the electrospinning. That is, when the concentration is higher than the upper limit, spinning is difficult due to the influence of spinning solution viscosity and fibers are not formed well. In particular, the carbon nanofiber precursor and the graphene-metal nanoparticle complex may be included in a weight ratio of 4: 1 to 20: 1.

On the other hand, the polymer for the carbon nanofiber precursor includes polyacrylonitrile (PAN), polyvinyllachol (PVA), polyimide (PI), polybenzimidazole (PBI) phenol resin, epoxy resin, polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polystyrene (PS), polystyrene (PA) Polymethylmethacrylate (PMMA), polyvinylidene chloride (PVDC), polyvinylidene fluoride (PVDF), and various pitches may be used.

In preparing the spinning solution, an appropriate solvent capable of dissolving the polymer may be selected depending on the kind of the polymer for the carbon nanofiber precursor. That is, the solvent in which the carbon fiber precursor is dissolved in the spinning solution is not limited as long as it can disperse all of the prepared carbon fiber precursor and 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 it is possible to use a modified acrylic containing 5% to 15% copolymer as well as 100% pure homopolymer . As the composition of the copolymer, itaconic acid or methylacrylate (MA) may be used as a copolymer.

  Oxidation stabilization can be performed by supplying compressed air at a flow rate of 5 to 20 mL per minute using a hot air circulating furnace and maintaining the temperature at 200 to 300 DEG C for 30 minutes or more at a rate of 1 DEG C per minute.

When the chlorinated fibers are to be carbonized, the carbonization can be carried out by raising the temperature to 750 to 850 ° C at a heating rate of 5 ° C per minute and then maintaining it in an inert gas atmosphere for 30 minutes to 2 hours.

Particularly, when controlling the concentration of the graphene-metal nanoparticle composite contained in the spinning solution in the production of the carbon nanofiber composite of the present invention, at least one of the size and distribution of the graphene-metal nanoparticle composite included in the carbon nanofiber composite Can be controlled. That is, in order to prevent the metal nanoparticles from growing too much or aggregating to become large particles, the graphene forms a G / M composite surrounding the metal nanoparticles and prevents the G / M composite contained in the spinning solution The carbon nano fiber composite in which the metal nanoparticles controlled in the desired size are uniformly distributed in the carbon nanofiber matrix can be manufactured.

The electrode of the present invention comprises 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, the electrode of the present invention can be used as a negative electrode in a secondary battery. At this time, the carbon nanofiber composite material may be used in the form of a web prepared by electrospinning, or it may be used as a powder.

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 is because the metal nanoparticles dispersed in the carbon nanofiber matrix in the structure of the carbon nanofiber composite used as the electrode active material are in the form of the G / M composite, so that graphene surrounding the metal nanoparticles suppresses the volume expansion of the metal nanoparticles Because it acts as a support.

Example 1

1. GO synthesis

H ₂ SO _{4 in the} order as shown in FIG. 1 Using KMnO ₄ 1999, 11 (3), 771-778 (1999), which is a method of synthesizing an oxidized graphene sheet (GO) having a carboxyl group (COOH) or a hydroxyl group (OH) group introduced into graphite through the Hummers method ). At this time, the synthesized GO had a generally 1 to 10 layer structure as described below.

2. Amino-funtionalized silicon nanoparticle synthesis

The silicon nanoparticles were modified to amino-funtionalized silicon having -NH ₂ groups by APS in the order shown in FIG. The modified nanoparticles were positively charged.

3. G / Si composite manufacturing

As shown in FIG. 3, the aminofunctionalized silicon nanoparticles have a positive charge, and the GO has a negative charge, so that they are strongly coupled through an electrostatic attractive force. Also, amino-funtionalized silicon nanoparticles with positive charge can be prevented from aggregating and growing by repulsion between positive charges.

4, the GO is reduced by using a reducing agent, hydrazine, in the silicon composite surrounded by the GO G / Si composite. The prepared G / Si composite was 40 nm in size.

Experimental Example 1

The GO obtained in Example 1 was observed with an electron microscope, and a photograph thereof was shown in Fig. The GO prepared by the Hamers method through the SEM (FIG. 5A) and TEM (FIG. 5B) photographs is composed of GO layers with graphite being peeled off, and the number of GO layers is about 1 to 10 . It has been reported that the GO surface is negatively charged and easily dispersed in a polar solvent because the carboxyl group and the hydroxy group exist in the GO layer in general.

Experimental Example 2

The G / Si composite obtained in Example 3 was observed with an electron microscope, and a photograph thereof is shown in Fig. 6 (a) and 6 (b) show that the silicon nanoparticles are covered with a graphene sheet, and a thin, flexible, wrinkled graphene of about 3 nm through the TEM (Figs. 6c and d) It can be seen that the graphene layer closely surrounds the silicon nanoparticles through the discovery at the edge. 6 (c) and 6 (d) that the graphene layer closely connects the separated particles without causing adjacent silicon nanoparticles to aggregate.

Example 2

1. Production of spinning solution

PAN nanoparticle precursors and PAN / G / Si composites were prepared by dissolving PAN and G / Si complexes in DMF prepared as solvents and dispersed by ultrasonic dispersion method as follows.

The polymer solution was prepared by dissolving 3.00 g of PAN in DMF. Then, a G / Si composite (20 wt%: 0.60 g) was added to the polymer solution and ultrasonically dispersed for 2 hours in order to increase the degree of dispersion of silicon. Deg.] C for 4 hours to prepare a spinning solution (G / Si / PAN solution).

2. Manufacture of precursor yarn fibers

The homogenized spinning solution (G / Si / PAN solution) was electrospun using an electrospinning machine. At this time, the spinning conditions were such that the fiber precursor solution was put into a 30 ml syringe having a 0.5 mm needle, and a voltage of 20 kV was applied to radiate it. At this time, the distance between the injection needle and the collector was maintained at 15 ㎝, and the elution speed of the fiber precursor solution was 3 ㎖ / h. When the fibers were accumulated in the current collector, the nonwoven fabric was separated and separated to prepare the precursor spinning fiber.

3. Manufacture of chlorinated fibers

 The precursor radiation fibers (G / Si / PAN spinning fibers) obtained by electrospinning were supplied with compressed air at a flow rate of 5 to 20 mL per minute using a hot air circulating furnace and heated at a rate of 1 ° C. per minute at a temperature of 200 to 300 ° C. And then stabilized for 1 hour to obtain chlorinated fibers in the G / Si / PAN system.

4. Manufacture of G / Si / PAN based carbon nanofiber composite (GSP)

G / Si / PAN-based carbon nanofiber composite (20-GSP) was produced by carbonizing G / Si / PAN-based chlorinated fibers obtained through stabilization process at 800 ° C under an inert gas (N ₂ , Respectively.

Example 3

G / Si / PAN type 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 in the spinning solution.

Example 4

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 in the spinning solution.

Comparative Example 1

A Si / PAN 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 in producing the spinning solution.

Comparative Example 2

Comparative carbon nanofibers (CNF) were obtained in the same manner as in Example 1, except that the G / Si composite was not used in producing the spinning solution.

Experimental Example 3

FIG. 7 shows webs of the precursor spinning fibers, chlorinated fibers and carbon fibers obtained in the process of producing the G / Si / PAN based carbon nanofiber composites in Examples 2 to 4, respectively.

As shown in FIG. 7, it can be seen that the precursor radiation fibers are shown in gray (a), the chlorinated fibers (b) are shown in brown, and the carbonized fibers (c) are shown in black.

Experimental Example 4

20-GSP, 10-GSP and 5-GSP, which are the carbon nanofiber composites containing the G / Si complexes obtained in Examples 2 to 4, and 20-SP obtained in Comparative Example 1 were observed by SEM. 8.

8, the average diameter range of the obtained carbon nanofiber composites was 250-350 nm, and 5-GSP having a low concentration of G / Si composite had a smooth surface without generation of particles or beads, while the concentration of G / Si composite The number of clusters increases as the number of clusters increases. As a result of analyzing the energy dispersive X-ray spectroscopy (EDX) of the 10-GSP surface, it was confirmed that C, O and Si elements exist at atomic ratios of 78.83%, 6.18% and 15.96%, respectively. Especially in the high magnification SEM photographs (Fig. 8c and d), 20-GSP shows that the cluster is in the fiber while 20-SP shows that the grapevine nanoparticles are clumped and clumped on the carbon fiber surface there was.

Experimental Example 5

20-GSP and 10-GSP, which are carbon nanofiber composites containing the G / Si composite obtained in Examples 2 and 3, and 20-SP obtained in Comparative Example 1 were observed with TEM, and the results are shown in FIG. .

9 (a), 9 (b) and 9 (c) showing TEM photographs of 10-GSP, 20-GSP and 20-SP, nanoparticles having a size of 50 nm or less are well dispersed in the carbon nanofiber matrix While 20-SP cluster clusters are on the surface of carbon nanofibers. In order to know the internal structure of the material, superlattice diffraction peaks of (110), (220), and (311) were observed in the diffraction pattern by the limited field electron diffraction (SAED) Which confirmed the crystalline diffraction pattern of the silicon nanoparticles.

Experimental Example 6

The results of X-ray diffraction analysis of 5-GSP, 10-GSP, 20-GSP, G / Si and GO are shown in FIG. 10 (a) The Raman spectrum of GO was observed and the results are shown in FIG. 10 (b).

Generally, graphite appears at a 2θ value of 26.5 °, which is known as a typical crystal peak observed in the interstitial structure (002) plane of graphite. The GO treated by the Hamers method showed that the crystal peak disappears at 2θ = 26.5 ^° and a new crystal peak is generated at 2θ = 12 ^° . This is because as already reported, the graphite structure of the graphite expands or peels and the crystalline region at 2? = 26.5 ^o disappears, and a functional group such as a carboxyl group or a hydroxy group containing oxygen is interposed between graphite layers on the (001) plane And the phase transition is induced by increasing the distance between graphite layers (Polymer, 2011, 35 (6), 565-573.). In addition to the G / Si complexed with silicon, as well as the silicon-based carbon nanofiber composite, both of the (110) and (200) peaks at Si 2θ = 28, 48 and 57 °, (220) and (311) planes of the silicon nanocrystals were observed.

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 peak of crystalline Si having a face-centered cubic (fcc) diamond structure type near 300 cm ^-1 was confirmed in 5-GSP, 10-GSP, 20-GSP and G / Si by the E2g mode of crystalline Si .

Examples 5 to 7

Example 2 20-GSP G / Si / PAN-based carbon nanofiber composite material obtained in to 4, 10-GSP, by cutting a 5-GSP and manufacture them as a negative electrode material, the prepared cathode, and LiPF ₆ 1: 1 vol% (20-GSP, 10-GSP, and 5-GSP) were prepared by preparing a coin cell consisting of ethylene carbonate (EC) / dimethyl carbonate (DMC) liquid electrolyte.

Comparative Example 3

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 a comparative secondary battery 1 (SP-20).

Comparative Example 4

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 a comparative secondary battery 2 (CNP).

Experimental Example 7

The secondary batteries obtained in Examples 5 to 7 were subjected to a charge-discharge test using a WBCS3000L charge / discharge device of Won-A tech Co., Ltd. The charge / discharge capacity and cycle characteristics of the lithium secondary batteries were examined. 11. The charge / discharge was performed in a voltage range of 0.02 to 1.50 V with a current of 100 mA / g.

As shown in FIG. 11, the cathode initial capacities of the secondary batteries obtained in Examples 5 to 7 were 626 mAh / g, 778 mAh / g and 923 mAh / g for 20-GSP, 10-GSP and 5-GSP , And the comparative secondary cell CNF obtained in Comparative Example 3 exhibits a negative electrode initial capacity of 767 mAh / g. The initial Coulomb efficiency after the first charge / 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 with a high concentration of G / Si and the initial coulombic efficiency after the first charge and discharge are high.

Experimental Example 8

The differential capacity curve of 20-GSP obtained in Example 5 was observed and the results are shown in Fig. 12 (a).

12 (a), the electrolyte is decomposed to form a solid electrolyte interface (SEI) or solid electrolyte inter-phase on the electrode surface before lithium ions are inserted into the graphite at about 0.64 V during the first discharge, The decomposition of the electrolyte due to the movement of the electrons between the electrode and the electrolyte is suppressed through the through hole and the insertion of the lithium ion can be selectively performed. From the first cycle, it can be seen that Li _x Si is produced by the reaction of silicon and lithium by the electrochemical reaction and the Si crystal is amorphized. Especially, the reaction peak of Li _x Si appears at the low voltage of 0.1 V. During the discharge from the second cycle, two oxidation peaks at 0.3, 0.24 and 0.08 V and 0.29 and 0.45 V during the charge reaction were observed, indicating the lithiation / delithiation of amorphous Si Respectively.

Experimental Example 9

The interfacial characteristics of 10-GSP, 20-GSP and CNF obtained in Examples 5 and 6 and Comparative Example 4 were analyzed by electrochemical impedance spectroscopy (EIS) (b). Impedance measurement was performed using Jahner Electrik IM6e, and the frequency range was 100 kHz - 10 mHz, and the AC signal was 10 mV mV.

FIG. 12 (b) is a Nyquist plot showing the characteristics of the carbon nanofiber composite electrode as an imaginary term and a real term impedance according to the frequency. Depending on the frequency of the AC potential, a straight line appears in the high frequency region with a constant slope in the low frequency region of the semicircle. In this case, the semicircle is subject to the reaction rate by the charge transfer, but the straight portion is dominated by the diffusion of the reactant. (Journal of 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, respectively. It can be seen that as the concentration of G / Si complex increases, the R _f value decreases. The higher the density of graphene surrounding Si, the better the silicon particles are separated and well dispersed in the CNR matrix, It is believed that the resistance to be overcome when the electrons move from the electrode to the electrolyte or from the electrolyte to the electrode during the insertion / removal is reduced. In addition, the small R _f value at the 20-GSP electrode is related to the formation of the SEI film. The film formed due to the solvent decomposition reaction acts as a protective film on the electrode surface, so that the smooth insertion / It is understood that the discharge capacity is excellent. At low frequencies, 20-GSP shows a large linear slope, indicating that the diffusion velocity 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 the graphene .

Experimental Example 10

Cycle characteristics of 20-GSP, 10-GSP and 5-GSP obtained in Examples 5 to 7 and SP-20 and CNF obtained in Comparative Examples 3 and 4 were examined, and the results are shown in FIGS.

  As can be seen from FIG. 13, 20-SP shows the highest initial capacity of the negative electrode. However, after 50 cycles of charging / discharging, the GSP electrodes show better cycle characteristics than Comparative Example 3. In particular, the 20-GSP and 10-GSP electrodes maintain a higher capacity than the graphite with a theoretical capacity of 372 mAh / g and exhibit stable capacity reduction as the cycle increases

From these results, the carbon nanofiber composite 20-SP prepared by mixing only silicon and polyacrylonitrile without graphene is exposed to the surface of carbon nanofibers because of the attraction of silicon grains, , The initial discharge capacity was large, but the cycle characteristics were deteriorated due to the volume expansion of the silicon. This shows that there is a difficulty in evenly dispersing into the state of silicon nanoparticles because the mixing of PAN and silicon nanoparticles is disadvantageous due to the metal aggregation.

On the other hand, 10-GSP and 20-GSP, which are prepared by adding G / Si composite, show stable capacity reduction because graphene encapsulates the silicon to inhibit the silicon particles from aggregating into larger particles, It disperses uniformly in the nanofiber to buffer the large volume change of the silicon nanoparticles due to the charging and discharging of the conventional lithium ion battery. In addition, it reduces the specific resistance of the surface of the lithium ion battery electrode, . ≪ / RTI > Therefore, in 10-GSP and 20-GSP electrodes, graphene buffers the aggregation of silicon particles, so that silicon is dispersed in the CNF matrix to increase electrochemically active sites and carbon nanofibers maintain electrical conductivity The electrochemical characteristics are expected to be very excellent.

FIG. 14 is a scanning electron micrograph of 5-GSP, 10-GSP and 20-GSP after 50 cycles of charging and discharging, so that it can be seen from FIG. 14 that the shape of the fibers is well maintained even after charging and discharging.

Therefore, when the G / Si / PAN based carbon nanofiber composite obtained in Examples 2 to 4 is used as an electrode in the state of fiber web as in Examples 5 to 7 as compared with the conventional case using the particulate phase, Is very fast and does not require an active material, a binder, a conductive agent, other solvent, or an auxiliary facility, and does not require a process of manufacturing and coating slurry. Since it is easy to handle, it is expected that the anticipated effect will be very high as a negative electrode material which replaces graphite in the future.

Example 8

20-GSP in the form of a web obtained in Example 2 was grinded to prepare a powder. Super-P was used as the conductive material and polyacrylic acid was used as the binder in order to manufacture the electrode. The compositions of the electrodes were mixed at a ratio of 80 wt% of the anode active material, 10 wt% of the conductive material, and 10 wt% of the binder, respectively. A coin cell consisting of the prepared negative electrode and a 1: 1 vol.% Ethylene carbonate (EC) / dimethyl carbonate (DMC) liquid electrolyte of LiPF ₆ was prepared to prepare a grinded 20-GSP.

Comparative Example 5

A coin cell was prepared in the same manner as in Example 8 except that silicon nanoparticles were used as the negative electrode active material, and a comparative secondary battery 3 (Si NPs) was prepared.

Experimental Example 11

The grinded 20-GSP prepared in Example 8 and the Si NPs prepared in Comparative Example 5 were subjected to a charge-discharge test using Won-A tech WBCS3000L charge / discharge device. The charge and discharge was carried out in a voltage range of 0.005 to 2.0 V with a current of 100 mA / g. The charging and discharging cycle characteristics and the coulombic efficiency of the lithium secondary battery according to Example 8 and Comparative Example 5 are shown in Fig.

As can be seen in FIG. 15, the initial capacity of the silicon nanoparticles (Si NPs) is very high, close to 4000 mA / g, but the crystalline silicon nanoparticles show a drastic decrease in capacity as the cycle increases. This seems to be caused by the rapid expansion of the volume of lithium due to the absence of reversible migration of lithium due to the affinity between the two materials inside the silicon.

However, the grinded 20-GSP maintains a higher capacity than the silicon nanoparticles even after 100 cycles of charging / discharging, and the cycle characteristics and the clone efficiency are also superior. 20-GSP prevents graphene from aggregating in the carbon nanofibers, and the carbon nanofibers acting as a matrix suppress the volume expansion of the silicon active material by buffering action, As the support increases, the capacity decreases more steadily than the silicon nanoparticles.

Experimental Example 12

The grinded 20-GSP and silicon nanoparticles (Si NPs) before and after 100 cycles of charging and discharging were observed with a scanning microscope and a top-view scanning electron microscope photograph is shown in FIG.

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 the silicon nanoparticles (FIG. 16C) shows a relatively uniform surface . However, as shown in FIG. 16 (d), after 100 cycles, the silicon nanoparticles were reduced in volume when the volume of lithium and alloy reaction increased during the recharging process compared with the grinded 20-GSP, resulting in cracks. As a result, Can be seen to form the surface.

  The cross-sectional SEM results of Grinded 20-GSP and silicon nanoparticles (Figs. 16 b and d) show that the active material thickness of 20-GSP swells from 11.5 μm before charging / discharging to 21.0 μm after 100 cycles. In the case of silicon nanoparticles, the active material thickness is 41 μm before charging and discharging. However, after 100 cycles, it is impossible to observe the cross-sectional photograph due to the separation of the electrode and the current collector. This is because the electrical contact between the silicon active material cracked by the crack and the copper current collector This indicates that the resistance of the electrode increases and the capacity decreases continuously as the charge / discharge progresses.

Therefore, the SEM image of about 100 cycles shows that the 20-GSP does not exhibit cracking or fall off the active material from the current collector, and the substrate under the active material is not exposed. Even after charging and discharging, the active material may stick to the substrate, It can be explained that it exhibits excellent cycle characteristics as compared with the nanoparticles.

From the above-described experimental results, it can be seen that the lithium ion battery manufactured using the carbon nanofiber composite material including the G / M composite of the present invention can be expected to have excellent charge / discharge characteristics, high capacity, and excellent volume stability.

In addition, although the carbon nanofiber composite including the G / M composite of the present invention is used for a lithium ion battery, the cell performance is improved even when the carbon nanofiber composite is used as an electrode active material in an energy storage device including other kinds of secondary batteries. It can be predicted that the long-term operation performance can be improved as well.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, Various changes and modifications will be possible.

Claims (23)

Metal nanoparticles; And
And a graphene sheet formed by wrapping the metal nanoparticles so as to prevent agglomeration of the metal nanoparticles so that the graphene-metal nanoparticle composite has a size of 50 nm or less.
The method according to claim 1,
Wherein the metal nanoparticles are selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag and Au. .
The method according to claim 1,
Wherein the metal nanoparticles are modified to have -NH ₂ groups.
The method according to claim 1,
Wherein the metal nanoparticles and the graphene sheet are bonded with electrostatic attraction.
delete Carbon nanofibers; And
And a graphene-metal nanoparticle composite constituting a part of the carbon nanofibers,
The graphene-metal nanoparticle composite may include metal nanoparticles; And a graphene sheet formed by wrapping the metal nanoparticles so as to prevent agglomeration of the metal nanoparticles, thereby having a size of 50 nm or less.
delete The method according to claim 6,
Wherein the metal nanoparticles are selected from the group consisting of Si, Sn, Ge, Al, Pb, Zn, Co, Cu, Ti, Ni, Li, Ag and Au.
The method according to claim 6,
Wherein the metal nanoparticles are modified to have -NH ₂ groups.
The method according to claim 6,
Wherein the metal nanoparticles and the graphene sheet are bonded together by an electrostatic attractive force.
The method according to claim 6,
Wherein 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 method according to claim 6,
Wherein the graphene-metal nanoparticle composite is uniformly dispersed in the carbon nanofibers.
The method according to claim 6,
Wherein the graphene-metal nanoparticle composite is pulverized so as to be in a powder state while the graphene-metal nanoparticle composite is held.
delete Preparing a spinning solution comprising a carbon fiber precursor and the graphene-metal nanoparticle complex of any one of claims 1 to 4;
Electrospinning the spinning solution to obtain precursor spinning fibers;
Oxidizing and stabilizing the precursor-emitting fibers to obtain chlorinated fibers; And
And carbonizing the chlorinated fibers to obtain a carbon nanofiber composite material,
Wherein the spinning solution comprises the carbon nanofibre precursor and the graphene-metal nanoparticle complex in a weight ratio of 4: 1 to 20: 1.
delete delete 16. The method of claim 15,
Wherein the concentration of the graphene-metal nanoparticle composite contained in the spinning solution is controlled to control at least one of size and distribution of the graphene-metal nanoparticle composite contained in the carbon nanofiber composite. A method for producing a carbon nanofiber composite material.
An electrode comprising the carbon nanofiber composite according to any one of claims 6 to 13 as an electrode active material.
20. The method of claim 19,
Wherein the carbon nanofiber composite is in powder form.
20. A secondary battery comprising the electrode of claim 19.
22. The method of claim 21,
Wherein the electrode active material contained in the secondary battery is not separated from the substrate even after 100 cycles of charging and discharging have elapsed.
22. The method of claim 21,
Wherein the secondary battery maintains a discharge capacity of 600 mAh / g even after 100 cycles of charge and discharge have elapsed.

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