KR20140130578A - Negative electrode active material for lithum-ion secondary battery using composite of nanofiber and graphene, and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium-ion secondary battery and to a manufacturing method thereof, and specifically, to a negative electrode active material for a lithium-ion secondary battery using a composite of carbon nano-fiber including a metal nano-fiber or metal nano-particles and graphene bonded thereto, and to a manufacturing method thereof. The present invention provides a negative electrode active material for a lithium-ion secondary battery, which comprises a nano-fiber and a graphene bonding layer bonded to at least a part of the surface of the nano-fiber, wherein the nano-fiber is a nano-fiber consisting of at least one between a metal or an alloy thereof, or a carbon nano-fiber including at least one type of nano-particles between a metal or an alloy thereof. According to the present invention, a negative electrode active material is composed by using a metal nano-fiber consisting of a metal or an alloy thereof, or a carbon nano-fiber including nano-particles of a metal or an alloy thereof, and a graphene bonding layer bonded thereto so as to have a structure capable of suppressing the change in the diameter of the nano-fiber due to the insertion/taking-out reaction of lithium ions. Furthermore, the negative electrode active material for a lithium-ion secondary battery uses a one-dimensional nano-fiber, not a multicrystalline structure, thereby having a high electric conductivity and being stably operated as the expansion of the nano-fiber is suppressed. Moreover, the negative electrode active material for a lithium-ion secondary battery minimizes the growth of SEI film produced on the surface of the nano-fiber, thereby effectively suppressing the increase of charge transfer resistance due to the SEI film.

Description

TECHNICAL FIELD The present invention relates to a negative electrode active material for a lithium-ion secondary battery using a composite of nanofibers and graphene, and a method for manufacturing the negative active material for a lithium-

The present invention relates to a negative electrode active material for a lithium ion secondary battery and a method of manufacturing the same. More specifically, the present invention relates to a negative electrode active material for a lithium-ion secondary battery using a composite of carbon nanofibers comprising metal nanofibers or metal nanoparticles and graphene bound thereto An active material and a method of manufacturing the same.

Recently, due to the depletion of fossil fuels and the demand for reduction of greenhouse gases such as carbon dioxide due to global warming, a smart grid including electric vehicles and the use of renewable energy and energy storage functions has attracted great attention. In this regard, The secondary battery is attracting attention as an energy storage means.

However, for smooth and efficient use of electric vehicles and smart grids, energy density, power density, and long life characteristics are required to be at least twice that of conventional lithium ion secondary batteries. For example, in the case of electric vehicles, The driving distance and power density at the moment are closely related to acceleration performance. In order to improve these characteristics, a method of using a high-capacity lithium-alloy-based metal material such as a silicon-based alloy or a tin-based alloy having a theoretical capacity value higher than 372 mAh / g of conventional graphite, . However, the lithium-alloy-based metal materials such as the silicon-based alloys and the tin-based alloys, which are attracting attention as high-capacity anode active materials, are liable to be excessively increased to three times or more the volume of the electrode material while lithium ions form metal alloys of Li4.4Si and Li4.4Sn Which may lead to volume expansion, which may lead to problems such as collapse of the electrode material, reduction in capacity, and shortening of battery life.

In order to overcome such problems, researches have been actively conducted on nano-structured electrode materials capable of buffering the stress caused by bulk expansion as much as possible. When the electrode active material used in a battery is made into a nanometer size, it is possible to reduce the relative movement distance of the lithium ion, so that it is easy to obtain a high output. Further, the high surface area of the nanomaterial makes contact with more electrolyte, Allows you to expect chemical reactions. In particular, when the electrode active material is composed of one-dimensional nanofibers among various nanostructures, wide pores between the nanofibers provide space for expansion of the electrode active material, and easily transmit electrons in the direction of the long fiber axis At the same time, it has a structure that enables short lithium ion diffusion to the cylindrical surface, and has been attracting attention as a cathode material. However, even if a negative electrode active material is composed of nanofibers, the problem of volume expansion of a conventional negative electrode active material can not be fundamentally solved. Also, since the negative electrode active material is composed of a nanostructure, resistance increases due to polycrystallinity of the nanostructure, There arises a problem that the metal material that can be used as the material is limited to a material having a higher electrical conductivity. In addition, as the lithium ion enters and leaves, there arises a problem of an increase in charge transfer resistance (CTR) due to the formation of a solid electrolyte interphase (SEI) film growing in a cylindrical shape on the surface of the nanofiber electrode, .

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide a structure capable of suppressing a diameter change of nanofibers due to lithium ion insertion / elimination or alloying / dealloying reaction , Has a high electrical conductivity, has a stable structure even when the volume of the nanofiber is changed during high-speed charging and discharging, minimizes the growth of the SEI film on the surface of the nanofiber, and can effectively suppress the increase of the charge transfer resistance And an anode active material for a lithium-ion secondary battery, and a process for producing the same.

According to an aspect of the present invention, there is provided a negative active material for a lithium-ion secondary battery, comprising: a nanofiber; And a graphene binding layer bonded to at least a part of the surface of the nanofiber, wherein the nanofiber is a nanofiber composed of at least one of a metal or an alloy thereof, or a nanoparticle of at least one of a metal or an alloy thereof Carbon nanofibers.

Here, the graphene binding layer may be a single layer which is in close contact with the cylindrical surface of the nanofiber, or a multiple layer of graphene binding layer which additionally surrounds them.

Wherein the graphene binder layer has a charge opposite to the charge of the first functional group and the graphene binder layer has a function of binding the first functional group and the second functional group, To the nanofibers.

Here, the graphene binding layer may include a second functional group having a charge opposite to that of the first functional group.

Here, the graphene binder layer may be composed of a single layer or a mixture of two or more of graphene oxide or reduced graphene oxide having a laminated structure.

Here, the diameter of the nanofibers may be in the range of 30 nm to 5 mu m.

Here, the metal may be composed of one or more of a metalloid, a post-transition metal, a transition metal, and an alkali metal.

The metal may be at least one selected from the group consisting of silicon, germanium, aluminum, antimony, tin, titanium, vanadium, chromium, cobalt, , One or more of nickel (Ni), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), lithium (Li) and sodium (Na).

Here, when the nanofiber is a carbon nanofiber, the nanoparticle may have a diameter ranging from 1 nm to 1 μm.

According to another aspect of the present invention, there is provided a method for manufacturing an anode active material for a lithium-ion secondary battery, comprising the steps of: (a) preparing a solution in which at least one of a metal and an alloy thereof is contained in the form of nanoparticles or metal salts, ; (B) electrospinning the solution to form a polymer fiber including one or more of the nanoparticles or the metal salt; (C) heat-treating the polymer fibers to form nanofibers including the metal or the alloy thereof; And (d) binding graphene to the nanofibers.

Here, the nanofiber may be a carbon nanofiber including the metal or alloy nanoparticles.

Here, the nanofiber may be a nanofiber composed of the metal or the alloy.

Following the step (c), (c1) a step of attaching a functional group having a charge to the nanofibers may be further included.

The functional group may be a carbonyl group, a carboxyl group, a hydroxyl group, a nitrile group, a silyl group, a cyano group, an amino group, an alkyl group, an alkoxy group or an ester group or a mixture of two or more thereof.

In the step (a), when the metal salt is included in the solution, the metal salt may be mixed with the polymer and dissolved in the solution.

Here, the metal salt may be one or a mixture of two or more of an organic acid salt, a halogen salt, an inorganic acid salt, an alkoxy salt, a sulfide salt or an amide salt.

The metal salt may be at least one selected from the group consisting of an acetate salt, a chloride salt, an acetylacetonate salt, a nitrate salt, a methoxide salt, an ethoxide salt, a butoxide salt, an isopropoxide salt, a sulfide salt, an oxytriisopropoxide salt, Hexanoate salt, cetyl ethylhexanoate salt, butanoate salt, ethylamide salt or amide salt, or a mixture of two or more thereof.

In the step (a), the metal may be at least one selected from the group consisting of Si, Ge, Al, Sb, Sn, Ti, A mixture of one or more of Cr, Co, Ni, Mn, Fe, Zn, Cu, Li, .

The polymer may be at least one selected from the group consisting of polyvinyl acetate (PVAc), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polymethylmethacrylate (PMMA), polyacrylic acid (PC), polyphenylene isophthalamide (PMIA), polyethylamine (PEI), polyethylene terephthalate (PET), polytrimethylene tetra phthalate (PTT), polybutylene Polytetrafluoroethylene (PBT), polysulfone (PSF), polyetheretherketone (PEEK), polystyrene (PS), polyvinylidene fluoride (PVDF), polyurethane, polyvinyl butyral- vinyl butyral resin, PVB, polyvinyl ester (PVE), polyferrocenyldimethylsilane (PFDMS), polyimide, poly-pyrrole-2,5-diyl (p-nitrobenylidene) Methylene (POM), polyethyleneimine (PEI), polyacrylamines (PAM) (PEG), polylactides (PLLA / PDLA), polycaprolactone (PCL), polyglycolic acid (PGA), poly-beta-hydroxyalkanoates Polybutylene succinate (PBS), polyether urethane urea (PEUU), polyvinyl chloride (PVC), chitin, dextran, DNA, collagen, gelatin, lecithin, fibroin SF), jane (CASP), or gluten, or a mixture of two or more thereof.

In the step (a), if the solution contains a metal salt, the ratio of the metal salt to the solution may range from 0.5 wt% to 90 wt%.

In the step (a), when the metal salt is contained in the solution, the weight ratio of the metal salt and the polymer may be in the range of 5: 1 to 1: 5.

In the step (a), when the metal salt is contained in the solution, the solvent of the solution may be one in which the metal salt and the polymer are soluble.

The solvent may be selected from the group consisting of dimethylformamide (DMF), dimethylacetamide (DMAc), acetone, tetrahydrofuran, water, acetic acid, hexafluoroisopropanol, methanol, ethanol, propanol, chloroform, dichloro And may be one or a mixture of two or more of methane, tetrahydrofuran, formic acid, acetic acid, trifluoroacetic acid, isopropanol or toluene.

Here, in the step (b), the solution may be spun at a rate of 5 μl to 100 μl per minute using a metal needle having an anode voltage of 5 kV to 20 kV applied thereto.

Here, the step (c) may be performed through heat treatment in a reducing atmosphere.

Here, the heat treatment may be performed at a temperature of 150 ° C to 1500 ° C and an inert atmosphere.

In the heat treatment, the polymer and the metal salt may be deoxidized by mixing hydrogen with an inert gas.

Here, the step (c) may include: (c1) drying the solvent in a vacuum or air atmosphere at a temperature of 100 ° C to 110 ° C to evaporate the solvent; Stabilizing the polymer at a temperature of 150 ° C to 400 ° C (c2); (C3) deoxidizing the polymer and the metal salt at a temperature of 400 ° C to 700 ° C and a reducing atmosphere containing an inert gas or hydrogen.

If the nanofiber is a carbon nanofiber, the step (c3) may be followed by (c4) carbonizing the polymer in an inert gas at 500 ° C to 1500 ° C.

Here, the step (d) may be performed using graphen having a charge.

Here, the graphen having the charge may be one of graphene oxide or graphene with charged functional groups, or a mixture thereof.

Here, when the graphene oxide is graphene oxide, the graphene oxide may be formed by oxidizing graphene in a strongly acidic solution.

When the graphene is a graphene with charged functional groups attached thereto, the functional group may be substituted with at least one of a carbonyl group, a carboxyl group, a hydroxyl group, a nitrile group, a silyl group, a cyano group, an amino group, an alkyl group, an alkoxy group and an ester group Or more.

According to the present invention, by constructing the negative electrode active material by using the metal nanofiber composed of the metal or the alloy or the carbon nanofiber including the nanoparticles of the metal or the alloy and the graphene binder layer bound thereto, Which has a structure capable of suppressing the diameter change of the nanofibers due to desorption or alloying / dealloying reaction and has a high electrical conductivity by using the one-dimensional nanofiber which is not a polycrystalline structure, Discloses an anode active material for a lithium-ion secondary battery and a method for manufacturing the same, which can stably operate by suppressing expansion and minimize the growth of an SEI film formed on the surface of a nanofiber, thereby effectively suppressing an increase in charge transfer resistance .

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1 is a view illustrating a structure of a carbon nanofiber anode active material according to an embodiment of the present invention, in which graphene oxide is bound and metal nanoparticles are incorporated. FIG.
FIG. 2 is a view illustrating a process for manufacturing a carbon nanofiber anode active material in which graphene oxide is bound and metal nanoparticles are incorporated according to an embodiment of the present invention. FIG.
FIG. 3 is a scanning electron microscope (SEM) photograph of a metal nanofiber prepared by removing carbon by heat treatment using a polymer which is not suitable for carbonization according to an embodiment of the present invention.
4 is a scanning electron microscope (SEM) photograph of a carbon nanofiber including metal nanoparticles produced by crystal growth of a metal salt in a nanofiber using a polymer suitable for carbonization according to an embodiment of the present invention.
5 is a scanning electron microscope (SEM) photograph of carbon nanofibers containing silicon nanoparticles prepared using polymer and silicon nanoparticles suitable for carbonization according to an embodiment of the present invention.
6 is a transmission electron microscope (TEM) photograph of a carbon nanofiber including silicon nanoparticles prepared according to an embodiment of the present invention.
7 is a scanning electron microscope (SEM) image of carbon nanofibers containing silicon nanoparticles bound with graphene oxide prepared using 2 ml of graphene oxide according to an embodiment of the present invention.
8 is a scanning electron microscope (SEM) image of carbon nanofibers containing silicon nanoparticles bound with graphene oxide prepared using 4 ml of graphene oxide according to an embodiment of the present invention.
9 is a transmission electron microscope (TEM) image of carbon nanofibers containing silicon nanoparticles bound with graphene oxide prepared using 2 ml of graphene oxide according to an embodiment of the present invention.
FIG. 10 is a transmission electron microscope (TEM) photograph of a carbon nanofiber including graphene oxide-bound silicon nanoparticles prepared using 4 ml of graphene oxide according to an embodiment of the present invention. FIG.
11 is a Raman spectroscopy graph of a complex of carbon nanofibers and graphene oxide bound with functional groups and silicon nanoparticles prepared according to an embodiment of the present invention.
FIG. 12 is a graph showing the results of a comparison between a carbon nanofiber anode active material having graphene oxide-bound carbon nanofibers prepared according to an embodiment of the present invention and a carbon nano-fiber negative active material containing silicon nanoparticles prepared as a comparative example Charge / discharge capacity characteristics graph.
13 is a graph of voltage characteristics of a carbon nanofiber electrode active material containing silicon nanoparticles prepared as a comparative example of the present invention.
14 is a graph of voltage characteristics of a carbon nanofiber electrode active material containing silicon nanoparticles bound with graphene oxide prepared according to an embodiment of the present invention.
15 is a graph showing changes in SEI film resistance and CTR characteristics according to graphene oxide binding for one embodiment and comparative example of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments will be described in detail below with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terms first, second, etc. may be used to describe various components, but the components are not limited by the terms, and the terms are used only for the purpose of distinguishing one component from another Is used.

In the prior art, the resistance of the negative active material of the lithium-ion secondary battery is increased due to the structure of the nanostructure of the polycrystalline lithium-ion secondary battery, and the volume of the negative active material expands and shrinks due to the insertion / The shape of the metal nanofiber 110 or the metal or its alloy made of the one-dimensional metal or its alloy is increased by focusing on the fact that the SEI film is grown on the surface and the charge transfer resistance (CTR) The negative electrode active material 100 is composed of the carbon nanofibers 110 including the nanoparticles 120 of the alloy and the graphene binding layer 130 bonded to the carbon nanofibers 110 so that lithium ions are inserted / removed or alloying / alloying / dealloying reaction of the nanofibers 110. The use of the nanofibers 110 having a one-dimensional shape, which is not a polycrystalline structure, An anode active material for a lithium secondary battery having a property that the expansion of the nanofibers 110 is suppressed to operate stably and the growth of the SEI film on the surface of the nanofibers 110 is minimized, (100) and a manufacturing method thereof.

FIG. 1 illustrates a structure of a carbon nanofiber 110 anode active material 100, to which an oxide graphene 130 is bound according to an embodiment of the present invention and includes metal nanoparticles 120. The negative electrode active material 100 may include a nanofiber 110 and a graphene binding layer 130 bonded to at least a part of the surface of the nanofiber 110. The nanofiber 110 may be a metal or a metal Or may be a carbon nanofiber 110 including nanoparticles 120 of a metal or an alloy thereof. The diameter of the nanofibers 110 may be selected within a range of 30 nm to 5 mu m. Here, the graphene used in the graphene binding layer 130 includes pure graphene, oxidized graphene, and reduced oxidized graphene.

At least one of a metalloid, a transition metal, a transition metal, and an alkali metal may be used as the metal composing the nanofibers 110 or included in the carbon nanofibers 110. For example, at least one of silicon (Si), germanium (Ge), aluminum (Al), antimony (Sb), tin (Sn), titanium (Ti), vanadium (V), chromium (Cr), cobalt It is possible to use nickel (Ni), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), lithium (Li), sodium (Na) As used herein, the term " metalloid " includes silicon, germanium and the like as an element having intermediate properties between metal and nonmetal. The nanoparticles 120 included in the carbon nanofiber 110 may have a diameter ranging from 1 nm to 1 μm. More specifically, when the nanofiber 110 is formed, The diameter of the nanoparticles 120 is in the range of 1 nm to 200 nm, and in the case of using the metal nanoparticles 120, the diameter of the nanoparticles 120 is in the range of 30 nm to 1 μm. Within the above range, the nanoparticles 120 of the metal or its alloy contained in the carbon nanofibers 110 can undergo a charging / discharging cycle without significant deformation of the nanoparticles 120 even when lithium ions are inserted and desorbed.

FIG. 3 is a cross-sectional view of a metal nanofiber 110 made of nickel according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of a carbon nanofiber 110 having metal nanoparticles 120 according to an embodiment of the present invention. And FIG. 5 is a scanning electron microphotograph of carbon nanofibers 110 containing silicon nanoparticles 120 according to an embodiment of the present invention. 4, tin cobalt nanoparticles 120 contained in the carbon nanofibers 110 can be clearly identified, and FIG. 5 shows a case where the nanoparticles 120 are added in the form of silicon nanoparticles 120 Giving.

The graphene binding layer 130 may be composed of a single layer or a graphene oxide having a stacked structure, a reduced graphene oxide, or a mixture thereof. In order to effectively suppress the volume expansion of the nanofibers 110 due to the insertion of the lithium ions, the graphene binding layer 130 may be formed of one layer which closely contacts the cylindrical surface of the nanofibers 110, It is preferable to bind in the form of multiple ply.

The carbon nanofibers 110 and the graphene binder layer 130 react with lithium ions during charging and discharging to have a smaller capacity than the single carbon based negative active material (graphite, 372 mAh / g), but can contribute to the total negative electrode capacity have. Specifically, the metal and its alloy-based negative active material M undergoes an alloy reaction of M + xLi ⁺ + xe ↔ Li _x M ( _x ≤4.4) since the discharge reaction involved in the insertion (intercalation) reactions 6C ⁺ Li + ↔ LiC ₆ to contribute to the negative electrode capacity, metals, but ever than the control of the alloy-based negative electrode active material, a carbon nano fiber 110 and the graphene binder layer (130) also contributes to the total cathode capacity.

Further, in order to strongly bond the graphene binder layer 130 to the nanofibers 110, a charge-generating functional group 210 may be additionally included. In this case, a first functional group 210 having a charge is attached to the nanofiber 110, and the graphene binding layer 130 has a charge opposite to that of the first functional group 210, Can be strongly adhered to each other. A second functional group having a charge opposite to that of the first functional group 210 may be attached to the graphene binding layer 130 in order to charge the graphene binding layer 130, And a method of causing the pin itself to have a negative charge. When the charged functional group 210 is charged in the solution, the graphene binding layer 130 is attached to the nanofibers 110 through a wet process.

Since the nanofiber anode active material 100 having the structure as described above has a structure in which the cylindrical surface of the nanofiber 110 is surrounded by the graphene 130 in various directions, The nanofibers 110 which are tightly bound to the metal nanoparticles 110 suppress the volume expansion of the negative electrode active material 100 due to the insertion of lithium ions during the charging reaction and prevent the metal and its alloy nanoparticles 120 or portions of the negative electrode active material 100 The structural change of the negative electrode active material 100 can be minimized by preventing the debris from coming off, and the non-uniform growth of the SEI film is suppressed, thereby lowering the increase of the charge transfer resistance (CTR). The negative electrode active material 100 has a high electrical conductivity according to the characteristics of the nanofiber 110 and the graphene binder layer 130 and is superior in terms of continuous high speed as compared with the negative electrode active material 100 composed of the nanofiber 110 alone. It is possible to provide a high capacitance value even in charging and discharging.

In addition, the negative electrode active material 100 may have a one-dimensional structure in the form of fiber or wire. The void spaces between the nanofibers 110 prevent the structural collapse due to the volume expansion of the negative electrode active material 100 during the insertion-desorption reaction of lithium ions, so that the negative electrode active material 100 can stably maintain its structure for a long period of time, . ≪ / RTI >

FIG. 2 illustrates a process for fabricating a carbon nanofiber 110 anode active material 100 in which oxide graphene 130 is bound and metal nanoparticles 120 are bound according to an embodiment of the present invention.

A method of manufacturing a nanofiber 110 anode active material 100 in which graphene 130 is bound and nanoparticles 120 are bound to each other according to an embodiment of the present invention includes the steps of (a) Preparing a solution which is contained in the form of nanoparticles 120 or a metal salt and in which a polymer precursor or a polymer is dissolved; (b) electrospinning the solution to form a polymeric fiber including one or more of the nanoparticles 120 or the metal salt; (c) reducing the polymer nanofibers through heat treatment or the like to produce carbon nanofibers (110) containing nanoparticles (120) of a metal or an alloy thereof or mixture nanoparticles (120) thereof; And (d) binding the graphene 130 to the nanofibers 110.

According to one embodiment of the present invention, as shown in FIG. 2, the tannonano fibers 110 having the silicon nanoparticles 120 embedded therein through the steps (a), (b) and (c) (FIG. 2 (a)). In step (d), an amino functional group 210 having a positive charge is attached to the surface of the carbon nanofiber 110 The carbon nanofibers 110 attached with the amino functional group 130 and the graphene oxide having a negative electric charge are stirred in an aqueous solution to bind the graphene 130 and the carbon nanotubes 120 containing the silicon nanoparticles 120 Thereby forming the fiber 110 anode active material 100 (Fig. 2 (c)).

The detailed description of the series of manufacturing steps described above is as follows.

First, the step (a) of preparing a solution in which at least one of a metal or an alloy thereof is contained in the form of nanoparticles 120 or a metal salt and in which a polymer precursor or a polymer is dissolved is prepared.

A metal such as aluminum (Al), antimony (Sb), or tin (Sn), a metal such as titanium (Ti), vanadium A transition metal such as lithium (V), chromium (Cr), cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), zinc (Zn) Na). Among them, at least one of them may be contained in the form of metal salt or metal nanoparticles 120.

The metal salt may be a salt that is mixed with a specific polymer and dissolved in the solution. For example, an organic acid salt, a halogen salt, an inorganic acid salt, an alkoxy salt, a sulfide salt, an amide salt, or the like may be used. Specifically, there may be mentioned, for example, acetates, chlorides, acetylacetonates, nitrates, methoxides, ethoxides, butoxides, isopropoxide, sulfides, oxytriisopropoxide, (ethyl or cetylethyl) hexanoate, , Ethyl amide, and amide salt may be used. The content of the metal salt may be selected within a range of 0.5 wt% to 90 wt%, preferably 1 wt% to 30 wt%, and more preferably 1.5 wt% to 20 wt% in the total spinning solution. have. When the ratio of the metal salt is too low, when the nanofiber 110 is the metal nanofiber 110, the metal nanofiber 110 may not be formed but may be broken into nanofibers. In the case of the metal nanoparticles 120, the metal nanoparticles 120 used as the active material occupy only a very small specific gravity with respect to the total weight, resulting in a problem that the capacity of the negative electrode becomes low. On the other hand, when the ratio of the metal salt is too high, when the metal nanofiber 110 is to be formed, the metal salt may not dissolve in the electrospinning solution and may be solidified. Further, since the ion concentration is high, And the metal nanoparticles 120 embedded in the carbon nanofibers 110 may be formed on the surface of the carbon nanofibers 110 or on the outside, There is a problem that the metal can not be embedded in the graphene binding layer 130 and the effect of the graphene binding layer 130, which is characterized by the improvement of the electrical conductivity and the relaxation of the volume change of the metal nanoparticles 110, . As a result of the experiment, it was confirmed that the cathode performance can be maximized when the metal salt is contained in the electrospinning solution in the above range.

In addition, the weight ratio of the metal salt and the polymer may be determined within a range of 5: 1 to 1: 5. The diameter of the metal nanofibers 110 or the size and density of the metal nanoparticles 120 included in the carbon nanofibers 110 may be optimized as the negative electrode active material 100 in the above range.

If the polymer used for the carbonization is a polymer suitable for carbonization, the nanofibers 110 have a shape of the metal particles 120 embedded in the carbon nanofibers 110 through heat treatment in a reducing atmosphere after electrospinning, If the polymer used is a polymer which is not suitable for carbonization, it will have a shape of metal nanofibers 110 containing a small amount or a small amount of carbon through heat treatment in a reducing atmosphere after electrospinning.

The solvent of the solution is not particularly limited as long as the polymer and the metal salt are soluble. Examples of the solvent include dimethylformamide (DMF), dimethylacetamide (DMAc), acetone, tetrahydrofuran, water, (Such as hydrochloric acid, hydrobromic acid, acetic acid, hexafluoroisopropanol, methanol, ethanol, propanol, chloroform, dichloromethane, tetrahydrofuran, formic acid, acetic acid, trifluoroacetic acid, isopropanol, Or a mixture of two or more of them may be used.

Next, the step (b) of irradiating the solution with the nanoparticles 120 or the polymer fibers containing one or more of the metal salts is carried out.

In the electrospinning, the solution prepared in the step (a) is radiated through a metal needles having an electric field, and collected on a grounded metal plate to form a polymer nanofiber including a metal salt.

The apparatus used in the electrospinning is a metering pump capable of injecting the spinning liquid at a constant speed, a metal pipe or metal needle connected thereto, and a DC power supply for applying a voltage between the metal needle and the grounding plate . One or more metal tubes or metal needles may be used, and a cylindrical drum-type electrospinning device may also be used.

In the electrospinning, the spinning solution prepared in the step (a) is spun to a metal needle having a positive voltage of 5 to 20 kV at a flow rate of 5 to 100 μl / min. In this case, the solution is attracted to the grounded metal plate due to the electric attraction force. At this time, the solution formed on the metal needle tip in the form of a droplet having a small area is momentarily attracted to the current collecting plate to increase the surface area. The polymer nanofibers containing the metal salts elongated in the form of fibers are collected on the collecting plate.

Next, the step (c) of reducing the polymer nanofibers through heat treatment or the like to produce carbon nanofibers 110 containing nanoparticles 120 of a metal or an alloy thereof or mixture nanoparticles 120 thereof .

 In step (c), the polymer nanofibers formed in step (b) may be subjected to heat treatment in one or more stages to finally form the carbon nanofibers 110 or the metal nanofibers 110 containing the metal nanoparticles 120, .

The heat treatment may be conducted in a series of processes in an inert atmosphere at a temperature range of 150 ° C to 1500 ° C. In this temperature range, nanofiber carbonization may occur depending on the kind of polymer used, nucleation of the metal and crystal growth may occur easily. The heat treatment in the inert atmosphere may be conducted in an argon (Ar) or nitrogen (N ₂ ) gas atmosphere. In addition, a certain amount of hydrogen (H ₂ ) may be injected during the heat treatment to induce deoxidation of the polymer and the metal salt to make a non-oxidized metal state crystal.

The heat treatment step may be performed through a series of steps including the following steps. First, as a preprocessing step, the electrospun polymer fibers are subjected to a stabilization treatment in an atmosphere at 150 ° C to 400 ° C followed by evaporation of the solvent through drying at 100 ° C in a vacuum or atmospheric air, The polymer is transformed into a form suitable for carbonization through a cycle-azeotropic reaction.

After the pretreatment, the polymer fibers are subjected to a deoxidation step in a reducing atmosphere at 400 ° C to 700 ° C inert or partially containing hydrogen. In this step, the oxygen contained in the polymer and the metal salt can be reduced with hydrogen to prevent oxidation of the metal. At this time, if a polymer not suitable for carbonization is used in the step (a), the polymer is decomposed into hydrocarbon gas or carbon dioxide in this step, so that the nanofiber 110 made of metal can be produced.

On the other hand, when the polymer is a polymer suitable for carbonization, the electrospun polymer fiber undergoes a carbonization process in an inert atmosphere at 500 ° C to 1500 ° C. At this time, the polymer inside the polymer fiber is converted into semi-crystallized carbon through the carbonization process. At this time, the crystallinity of the carbon is proportional to the carbonization temperature and may greatly affect the strength, electrical conductivity and cathode performance of the carbon nanofiber 110.

Therefore, carbon nanofibers 110 or metal nanofibers 110 suitable for use as active materials are not produced because heat treatment is performed at a temperature of 400 ° C or lower in the process after the pretreatment, since carbonization and metal crystallization do not occur. In the step (c), either one or both of heat treatment in an inert atmosphere or chemical heat treatment can be used.

Next, a step (d) of binding the graphene 130 to the nanofibers 110 is performed. As the graphene 130, graphene directly synthesized through conventional graphene or Hummer's method can be used. As a method of binding the graphene 130 to the nanofibers 110, a solution in which the graphene 130 is dispersed is subjected to vacuum filtration, chemical vapor deposition, air spraying, electrostatic spraying, dip coating, And the like can be used in combination.

The graphene 130 and the nanofibers 110 may have a charge opposite to that of the graphene 130, and then the graphene 130 and the nanofibers 110 may be strongly adhered to each other. The graphene 130 may be given a charge by oxidation or by attaching the functional group 210 to the graphene 130.

A method of imparting charge to the graphene 130 through oxidation is described first. First, by using a graphene oxide dispersion solution which can be produced by the Hummer method in the graphene production step, the oxidized graphene 130 can be easily prepared without a separate oxidation process. Alternatively, the graphene 130 or the common graphene generated through a physical or chemical extrapolate reaction to graphite may be oxidized in the strongly acidic solution to form the oxidized graphene 130. Since the graphene oxide 130 is negatively charged in the solution, it can easily bind to the nanofiber 110 with the positively charged functional group 210 attached thereto.

Next, a method of attaching the functional group 210 will be described. A functional group 210 may be attached to the graphene 130 so as to be positively or negatively charged in the solution. The functional group 210 may include a carbonyl group, a carboxyl group, a hydroxyl group, a nitrile group, a silyl group, , An alkoxy group, an ester group and the like can be used. As in the case of the graphene 130, a carbonyl group, a carboxyl group, a hydroxyl group, a nitrile group, a silyl group, a cyanide group, a cyanide group, and a cyanide group may be added to the nanofiber 110 by attaching a functional group 210, Group, an amino group, an alkyl group, an alkoxy group, an ester group, and the like. The graphene 130 having the charged functional group 210 attached thereto and the nanofibers 110 having the functional group 210 having the opposite electrical charge can be strongly adhered by stirring in solution.

Hereinafter, embodiments and comparative examples according to the present invention will be described in detail.

EXAMPLE Preparation of carbon nanofiber 110 anode active material 100 with graphene 130 bound and silicon nanoparticles 120

(A) Preparation of spinning liquid for making polymer nanofibers

Silicone nanoparticles 120 (50 nm, Sigma-Aldrich Co., Ltd., USA) were used as the metal, and polyacrylonitrile (PAN, Mw = 150,000, Sigma-Aldrich Co., USA) was used as the polymer. , 0.3 g of silicon nanoparticles (120) was dissolved in 3 g of N, N dimethylformamide (99.8%, Sigma-Aldrich Co., USA) DMF, 1 g of PAN was mixed with 6 g of DMF, and the mixture was stirred at 80 ° C for 6 hours. Then, the two solutions were combined to prepare a spinning solution.

(B) Polymer nanofibers including silicone nanoparticles 120 through electrospinning

The electrospinning was carried out using a metal needle of 21G at a rate of 15 l / min under a voltage of 15 kV. The spacing between the metal needles and the ground plane was fixed at 15 cm and electrospinning was carried out for 6 hours. Thus, polymer nanofibers containing silicon nanoparticles 120 were prepared.

(C) Heat treatment step for the polymer nanofibers

The polymer nanofibers were stabilized in air at 260 ° C for 1 hour and then heat-treated in a nitrogen atmosphere at 700 ° C for 5 hours. Finally, the carbon nanofibers 110 containing the silicon nanoparticles 120 were finally produced. 5 is a scanning electron microscope (SEM) photograph of the carbon nanofibers 110 containing the silicon nanoparticles 120. FIG. Silicon nanoparticles 120 having a diameter of 50 nm are included in the carbon nanofibers 110 and on the surface of the carbon nanofibers 110 having a diameter of about 150 to 300 nm. 6 is a transmission electron microscope (TEM) photograph of the carbon nanofibers 110. FIG. Referring to these photographs, the shape of the silicon nanoparticles 120 contained in the carbon nanofibers 110 and the carbon film surrounding them can be confirmed. This carbon film partially contributes to reducing the volume change of the silicon nanoparticles 120 during charging and discharging, and in addition, the carbon nanofibers 110 themselves also function as an active material.

(D) attaching the amino functional group 210 to the carbon nanofibers 110

0.2 g of the carbon nanofibers 110 containing the silicon nanoparticles 120 manufactured through the above-described procedure was collected and a part of the carbon nanofibers 110 was broken using a ball-mill. Through this process, the length of the carbon nanofibers 110 is reduced, and the adhesion of the graphene 130 is facilitated. The carbon nanofibers 110 were dispersed in 20 ml of a toluene solution by sonication for 30 minutes. Thereafter, 30 ml of toluene was further added, and 1 ml of 3-aminopropyltriethoxysilane (APS) was introduced. The mixture was refluxed in a nitrogen atmosphere at 110 ° C for 24 hours to form an amino functional group 210) was attached. Then, the carbon nanofibers 110 to which the functional groups 210 were attached were thoroughly washed and dried at 80 ° C for 12 hours.

(E) binding of the grafted oxide 130 to the carbon nanofibers 110 to which the amino functional group 210 is attached,

The carbon nanofibers 110 to which 33 mg of the amino functional group 210 is attached are dispersed in 80 ml of DI water. Thereafter, 2 ml or 4 ml of an aqueous solution of oxidized graphene (2 mg / ml, Sigma-Aldrich) was slowly added thereto while stirring well for 1 hour. Thereafter, 1 ml of hydrazine monohydrate is added and refluxed for 12 hours to chemically reduce the oxidized graphene 130.

The carbon nanofibers 110 bonded with the chemically reduced graphene grains 130 are thoroughly washed with ultrapure water and then centrifuged to obtain black powder. FIGS. 7 and 8 are SEM micrographs of the carbon nanofibers 110 having the reduced oxide graphenes 130 bound thereto and containing the silicon nanoparticles 120 manufactured through the above-described processes. 7 shows a case where oxidized graphene 130 reduced to the outside of carbon nanofibers 110 containing silicon nanoparticles 120 is bound using 2 ml of aqueous solution of oxidized graphene 130, It is confirmed that the oxidized graphene 130 is closely adhered to the surface of the carbon nanofibers 110. 8, when the concentration of the aqueous solution of the oxidized graphene 130 is higher than that shown in FIG. 8, not only the reduced oxidized graphene 130 adheres closely to the curved surface of the carbon nanofibers 110, It can also be seen that they are stretched over the fibers 110 as well. This can be confirmed by the transmission electron microscope photographs of FIGS. 9 and 10. In FIG. 9, it can be seen that the reduced graphene 130 is closely adhered to the surface of the carbon nanofibers 110, In FIG. 10 corresponding to a case where the concentration of the fin 130 solution is doubled, it can be seen that another graphene layer 130 is stretched over the various carbon nanofibers 110. Therefore, when the concentration of the graphene 130 solution is low, the oxidized graphene 130 is preferentially bound to the surface of the carbon nanofibers 110 to which the functional group 210 is attached. If the concentration of the graphene 130 solution is high, It can be seen that the fins 130 are piled up into a plurality of layers over several carbon nanofibers 110.

11 is a Raman spectroscopic data obtained after the functional group 210 and the graphene 130 are attached to the carbon nanofibers 110 containing the silicon nanoparticles 120. FIG. It can be seen that the silicon-specific peak generated at around 510 nm shifted by -6 cm ^-1 due to the surface energy change of the carbon nanofiber 110 after the amino functional group 210 was attached. The peak value is returned to the original position through reduction treatment after attaching the oxidation graphene 130. Further, in the case of the sample to which the graphene 130 is attached, it is possible to observe the G-band and the 2D-band, which are characteristic Raman lines of the graphene 130.

[Comparative Example 1] Production of carbon nanofibers 110 containing silicon nanoparticles 120

The nanofibers 110 were manufactured using the same electrospinning apparatus as the above embodiment except that the carbon nanofibers 110 having the silicon nanoparticles 120 not subjected to the graphene- ).

[Comparative Example 2] Production of metal nanofibers 110 from which carbon was removed

The nanofibers 110 were prepared using the same electrospinning apparatus as in the above example except that 2 g of nickel (II) acetate and 2 g of polyvinylpyrrolidone, which were not suitable for carbonization, were used as comparative examples. 1,300,000 MW) was dissolved in DMF solution, electrospinned, and then subjected to reduction heat treatment to prepare nickel nanofibers (110). At this time, unlike the embodiment and the comparative example 1, the carbon inside the nickel nanofibers 110 is not carbonized in the nanofiber form, but is vaporized and removed from the nanofibers upon heat treatment. As a result, metal nanofibers 110 crystallized in the form of fibers are produced. 3 is a scanning electron micrograph of the metal nanofibers 110 formed as described above.

[Comparative Example 3] Preparation of carbon nanofibers (110) containing metal nanoparticles (120) formed through nucleation and crystal growth in a heat treatment step

The nanofibers were produced using the same electrospinning apparatus as in the above example except that tin (IV) acetate salt and 0.003 mol of cobalt (II) acetate salt were used in place of silicon nanoparticles (120) Carbon nanofibers 110 were prepared. 4 is a scanning electron microscope (SEM) image of the carbon nanofibers 110 including the tin cobalt alloy nanoparticles 120 formed as described above.

Test Example A negative electrode of a secondary battery using a carbon nanofiber 110 (Comparative Example 1) containing silicon nanoparticles 120 and a negative electrode active material 100 (Example) having a graphene 130 attached thereto Character rating

The graphene 130 was attached to the carbon nanofibers 110 containing the silicon nanoparticles 120 and the carbon nanofibers 110 containing the silicon nanoparticles 120 described in Comparative Example 1 A negative electrode characteristic of a secondary battery using an anode active material (100) was compared and evaluated.

The carbon nanofibers 110 and the silicon nano-particles 110, both of which were grafted with the graphene 130 produced in Examples and Comparative Example 1 and containing the silicon nanoparticles 120, (Li-PAA) binder at a weight ratio of 15 wt%, and Super-P carbon particles at a weight ratio of 75 wt% to 10 wt% of the carbon nanofibers 110 containing the particles 120, % By weight, thinly applied on a copper foil in the form of a slurry, and dried in a vacuum atmosphere to prepare respective electrode plates. At this time, the Li-PAA binder was prepared by mixing and neutralizing 25 wt% aqueous solution of polyacrylic acid with lithium hydroxide monohydrate (10 wt%) at a molar ratio of 1: 1.

The secondary battery including the electrode was assembled into a coin cell (CR2032-type coin cell) in a glove box formed in an argon atmosphere. A solution of 1.2 mol of LiPF ₆ dissolved in ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3: 7 was used as the electrolyte of the coin cell. At this time, 7 wt% of fluoroethylene carbonate (FEC) was added to the electrolyte as an electrolyte improving agent. A metal lithium plate (Foote Mineral Co.) having a purity of 99.99% was used as a counter electrode of the working electrode. A polypropylene film (Celgard Inc.) was used as a separator between the two electrodes, and the capacity was measured within a voltage range of 0.05 to 2.5 V under a constant current using a Marco 4000 model as a charge / discharge test apparatus.

12 shows the capacitance characteristics obtained after 100 cycles of charge and discharge for Comparative Example 1 and Example. At this time, the charging / discharging current was fixed at a relatively high value of 400 mA / g in order to apply a constant load to the negative electrode active material 100. 13 and 14 show the first, second and fifty charge / discharge curves of Comparative Example 1 and Example, respectively. The initial discharge capacity value of Comparative Example 1 was 1726 mAh / g, which was very high. However, due to the rapid charge / discharge rate, the volume of the silicon nanoparticles 120 was changed, The discharge capacity value in the cycle dropped to 700 mAh / g, which is significantly reduced to about 100 mAh / g when the charge / discharge was continued up to 50 cycles. On the other hand, in the case of the embodiment in which the carbon nanofibers 110 containing the silicon nanoparticles 120 were well wrapped with the graphene 130, the discharge capacity was partially reduced in the second cycle from the initial 1058 mAh / g to 780 mAh / It can be confirmed that the capacity value is maintained well without large loss of 747 mAh / g up to 50 cycles.

FIG. 15 shows changes in characteristics of SEI film resistance and charge transfer resistance (CTR) according to graphene binding according to an embodiment and a comparative example of the present invention. In FIG. 15 (c), the measured values of the SEI film resistance and the charge transfer resistance with respect to the impedance of the comparative example 1 and the example are displayed and compared with the calculated value, which shows that they are in good agreement . 15 (a) and 15 (b), R _E represents a series resistance, R _SEI represents an SEI film resistance, R _CT represents a charge transfer resistance, and R _P represents a phase change resistance. 15 (b), the SEI membrane resistance value (46.46?) Of the nanofiber 110 surrounded by the graphene 130 of the embodiment is about 30 % ≪ / RTI > In addition, in the case of the charge transfer resistance, the charge transfer resistance of the nanofiber 110 of Comparative Example 1 in which the graphene 130 is not attached is 133.4?, Whereas in the embodiment where the graphene 130 is attached, The resistance is only 15.7?, Which is 8 times higher than the resistance. This is because the graphene 130 having excellent electrical conductivity is closely attached to the cylindrical surface of the one-dimensional nanofiber 110, thereby promoting the reduction of the resistance of the SEI film grown on the surface of the nanofiber 110, And reduces the charge transfer resistance caused by diffusion into the inside.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments described in the present invention are not intended to limit the technical spirit of the present invention but to illustrate the present invention. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents thereof should be construed as being included in the scope of the present invention.

100: anode active material
110: metal or carbon nanofiber
120: metal or alloy nanoparticles
130: graphene binding layer
210: functional group

Claims (33)

Nanofiber; And
And a graphene binder layer which is bonded to at least a part of the surface of the nanofiber,
The nano-
A nanofiber composed of at least one of a metal and an alloy thereof,
The negative electrode active material for a lithium-ion secondary battery according to claim 1, wherein the negative electrode active material is a carbon nanofiber including at least one of nanoparticles of a metal or an alloy thereof. The method according to claim 1,
Wherein the graphene binding layer comprises:
And a plurality of layers of a graphene binder layer which completely surrounds the cylindrical surface of the nanofiber and completely surrounds the nanofiber, or further folds them again. The negative active material for a lithium-ion secondary battery according to claim 1, The method according to claim 1,
Further comprising a first functional group having a charge attached to the nanofiber,
Wherein the graphene binding layer has a charge opposite to that of the first functional group,
Wherein the graphene binding layer is bound to the nanofiber through bonding with the first functional group. The method of claim 3,
Wherein the graphene binding layer comprises a second functional group having a charge opposite to the charge of the first functional group. The method according to claim 1 or 3,
Wherein the graphene binding layer is composed of one or a mixture of two or more of graphene oxide or reduced graphene oxide having a single layer or a laminated structure. Negative electrode active material for secondary battery. The method according to claim 1 or 3,
Wherein the nanofiber has a diameter in a range of 30 nm to 5 mu m. The method according to claim 1 or 3,
The negative electrode active material for a lithium-ion secondary battery according to claim 1, wherein the metal is one or more of a metalloid, a transition metal, a transition metal, and an alkali metal. 8. The method of claim 7,
The metal may be at least one selected from the group consisting of Si, Ge, Al, Sb, Sn, Ti, V, Cr, Wherein the lithium secondary battery is made of one or more of Ni, Mn, Fe, Zn, Cu, Li and Na. Negative active material. The method according to claim 1 or 3,
When the nanofiber is a carbon nanofiber,
Wherein the nanoparticles have a diameter ranging from 1 nm to 1 占 퐉. (a) preparing a solution in which at least one of a metal or an alloy thereof is contained in the form of nanoparticles or a metal salt and in which a polymer is dissolved;
(b) electrospinning the solution to form a polymeric fiber including one or more of the nanoparticles or the metal salt;
(c) heat-treating the polymer fibers to form nanofibers including the metal or the alloy thereof; And
and (d) binding the graphene to the nanofibers. 11. The method of claim 10,
Wherein the nanofibers are carbon nanofibers containing the metal or alloy nanoparticles. ≪ RTI ID = 0.0 > 11. < / RTI > 11. The method of claim 10,
Wherein the nanofiber is a nanofiber composed of the metal or the alloy. ≪ RTI ID = 0.0 > 21. < / RTI > 13. The method according to claim 11 or 12,
Following step (c) above,
(c1) attaching a functional group having charge to the nanofibers to the negative electrode active material for lithium ion secondary batteries. 14. The method of claim 13,
Wherein the functional group is at least one of a carbonyl group, a carboxyl group, a hydroxyl group, a nitrile group, a silyl group, a cyano group, an amino group, an alkyl group, an alkoxy group, and an ester group or a mixture of two or more thereof. 11. The method of claim 10,
In the step (a)
When the solution contains a metal salt,
Wherein the metal salt is a salt that is mixed with the polymer and is soluble in the solution. 16. The method of claim 15,
Wherein the metal salt is at least one of an organic acid salt, a halogen salt, an inorganic acid salt, an alkoxy salt, a sulfide salt, or an amide salt or a mixture of two or more thereof. 17. The method of claim 16,
The metal salt may be selected from the group consisting of an acetate salt, a chloride salt, an acetylacetonate salt, a nitrate salt, a methoxide salt, an ethoxide salt, a butoxide salt, an isopropoxide salt, a sulfide salt, an oxytriisopropoxide salt, Wherein one or a mixture of two or more selected from the group consisting of cetyl ethylhexanoate salt, butanoate salt, ethylamide salt and amide salt is used as a solvent for the negative electrode active material for a lithium-ion secondary battery. 11. The method of claim 10,
In the step (a)
The metal may be at least one selected from the group consisting of Si, Ge, Al, Sb, Sn, Ti, V, Cr, Characterized in that the negative electrode is a mixture of one or more of Ni, Mn, Fe, Zn, Cu, Li, or Na. A method for manufacturing an active material. 11. The method of claim 10,
The polymer may be selected from the group consisting of polyvinyl acetate (PVAc), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polymethylmethacrylate (PMMA), polyacrylic acid (PAA), polycarbonate PC), polyphenylene isophthalamide (PMIA), polyethylamine (PEI), polyethylene terephthalate (PET), polytrimethylene tetraphthalate (PTT), polybutylene terephthalate Polybutylene terephthalate (PBT), polysulfone (PSF), polyetheretherketone (PEEK), polystyrene (PS), polyvinylidene fluoride (PVDF), polyurethane, polyvinyl butyral resin, PVB), polyvinyl ester (PVE), polyferrocenyldimethylsilane (PFDMS), polyimide, poly-pyrrole-2,5-diyl (p-nitrobenylidene), PPy), polyoxymethylene POM), polyethyleneimine (PEI), polyacrylamine (PAM), polyethyl (PEG), polylactides (PLLA / PDLA), polycaprolactone (PCL), polyglycolic acid (PGA), poly- beta -hydroxyalkanoates (PHA) Polybutylene succinate (PBS), polyether urethane urea (PEUU), polyvinyl chloride (PVC), chitin, dextran, DNA, collagen, gelatin, lecithin, fibroin (SF) , Jane (CASP), or gluten, or a mixture of two or more thereof. 11. The method of claim 10,
In the step (a)
When the solution contains a metal salt,
Wherein the ratio of the metal salt to the solution is in the range of 0.5 wt% to 90 wt%. 11. The method of claim 10,
In the step (a)
When the solution contains a metal salt,
Wherein the weight ratio of the metal salt to the polymer is in the range of 5: 1 to 1: 5. 11. The method of claim 10,
In the step (a)
When the solution contains a metal salt,
Wherein the solvent of the solution is soluble in the metal salt and the polymer. 23. The method of claim 22,
The solvent is selected from the group consisting of dimethylformamide (DMF), dimethylacetamide (DMAc), acetone, tetrahydrofuran, water, acetic acid, hexafluoroisopropanol, methanol, ethanol, propanol, chloroform, dichloromethane, Wherein the negative electrode active material is one or a mixture of two or more selected from the group consisting of tetrahydrofuran, formic acid, acetic acid, trifluoroacetic acid, isopropanol, and toluene. 11. The method of claim 10,
In the step (b)
Wherein said solution is spun at a rate of 5 占 퐇 to 100 占 퐇 per minute using a metal needle having an anode voltage of 5 kV to 20 kV. 11. The method of claim 10,
The step (c)
Wherein the negative electrode active material is formed by heat treatment in a reducing atmosphere. 26. The method of claim 25,
Wherein the heat treatment is performed at a temperature of 150 ° C to 1500 ° C and in an inert atmosphere. 26. The method of claim 25,
Wherein the polymer and the metal salt are deoxidized by mixing hydrogen with an inert gas in the heat treatment. ≪ RTI ID = 0.0 > 8. < / RTI > 11. The method of claim 10,
The step (c)
(c1) drying the solution in a vacuum or at a temperature of 100 ° C to 110 ° C to evaporate the solvent;
(c2) stabilizing the polymer at a temperature of from 150 ° C to 400 ° C;
(c3) deoxidizing the polymer and the metal salt at a temperature of 400 ° C to 700 ° C and in a reducing atmosphere containing an inert gas or hydrogen. The method for producing a negative electrode active material for a lithium-ion secondary battery according to claim 1, 29. The method of claim 28,
When the nanofiber is a carbon nanofiber,
Following the step (c3)
(c4) carbonizing the polymer in an inert gas at 500 [deg.] C to 1500 [deg.] C. 14. The method of claim 13,
The step (d)
Wherein the negative electrode active material is a graphite negative electrode active material. 31. The method of claim 30,
Wherein the graphen having the charge is one of graphene oxide or graphene having a charged functional group attached thereto or a mixture thereof. 32. The method of claim 31,
When the graphene is graphene oxide,
Wherein the graphene oxide is formed by oxidizing graphene in a strongly acidic solution. ≪ RTI ID = 0.0 > 8. < / RTI > 32. The method of claim 31,
If the graphene is graphene with charged functional groups,
Wherein the functional group is at least one of a carbonyl group, a carboxyl group, a hydroxyl group, a nitrile group, a silyl group, a cyano group, an amino group, an alkyl group, an alkoxy group, and an ester group or a mixture of two or more thereof.

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