KR20170120279A - Preaparation method of nitrogen doped carbon-silicon complex and nitrogen doped carbon silicon complex prepared by the same - Google Patents

Abstract

The present invention relates to a process for the production of nitrogen-doped carbon-silicon composites and the nitrogen-doped carbon-silicon composites produced thereby.
According to the method for producing a nitrogen-doped carbon-silicon composite of the present invention, since the composite is formed through the eutectic mixture state, the carbon-silicon composite in which silicon is uniformly dispersed in the nitrogen-doped graphite carbon continuous phase can be produced. In addition, the nitrogen-doped carbon-silicon composite thus prepared has excellent electrical conductivity, strength, and capacity retention, and thus can be used as a negative electrode active material of a lithium secondary battery.

Description

TECHNICAL FIELD The present invention relates to a method for producing a nitrogen-doped carbon-silicon composite, and a nitrogen-doped carbon-silicon composite produced by the method. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a process for the production of nitrogen-doped carbon-silicon composites and the nitrogen-doped carbon-silicon composites produced thereby.

With the rapid development of the electronics, communications and computer industries, applications of energy storage technologies are expanding to camcorders, mobile phones, notebook PCs, and even electric vehicles. Accordingly, development of a small secondary battery which is light and long-lasting and has high reliability and high performance is underway, and a lithium secondary battery is attracting attention as a battery satisfying such a demand.

Graphite, which is widely used as an anode material of lithium secondary batteries, has a low electrochemical reduction potential of about 0.1 V and is very stable in charging and discharging processes, which is advantageous in producing high efficiency lithium secondary batteries. However, the theoretical capacity of graphite is limited to about 372 mAh / g, which limits its application to future large and medium-sized cells requiring high capacity.

On the other hand, silicon, which is attracting much attention as a next-generation high-capacity cathode material, has an electrochemical reduction potential of about 0.4 V and theoretically has a high capacity of about 4200 mAh / g. Silicon, however, has low electrical conductivity and involves a large volume change of about 400% when inserting and desorbing lithium ions. Problems such as breakage of the negative electrode active material caused by such volume change, loss of contact with the current collector, deterioration of cell performance due to unstable SEI (Solid Electrolyte Interface) layer are fatal disadvantages in commercialization of the silicon anode material.

In order to solve such problems, studies have been actively made on carbon-silicon composites coated with carbon material such as graphite on silicon particles. Such a carbon-silicon composite has the advantage of forming a stable SEI layer by blocking the contact between the silicon particles and the electrolyte and increasing the electric conductivity. However, the conventional carbon - silicon composites have a low mechanical strength and are broken in the electrode manufacturing process, which limits the performance of the composite itself.

Accordingly, it is necessary to develop a new negative electrode active material which can replace the conventional negative electrode active material, can realize a high capacity, and has high strength.

Korean Patent Laid-Open Publication No. 2014-0107926, a method for producing a silicon-based anode active material containing a nitrogen-doped carbon coating, and a lithium secondary battery comprising the same

The present inventors have studied a method for producing a nitrogen-doped graphitic carbon-silicon composite having improved strength compared to the existing carbon by mixing a silicon-based active material, a carbon precursor, and a nitrogen precursor, followed by heat treatment. The obtained nitrogen-doped carbon-silicon composite exhibited excellent strength and cell characteristics, thereby completing the present invention.

Accordingly, it is an object of the present invention to provide a method for producing a nitrogen-doped carbon-silicon composite.

It is also an object of the present invention to provide a nitrogen-doped carbon-silicon composite produced by the above process.

Still another object of the present invention is to provide an electrode comprising the nitrogen-doped carbon-silicon composite as an active material, and a lithium secondary battery including the electrode.

In order to accomplish the above object, the present invention provides a method for manufacturing a semiconductor device, comprising: mixing a silicon-based active material and a carbon precursor with urea or cyanuric acid; And

Heat treating the resulting mixture;

Silicon-carbon composite, wherein the nitrogen-doped carbon-

The present invention also provides a nitrogen-doped carbon-silicon composite produced by the above production method, an electrode including the carbon-silicon composite as an active material, and a lithium secondary battery including the electrode as a cathode.

According to the method for producing a nitrogen-doped carbon-silicon composite of the present invention, since the composite is formed through the eutectic mixture state, the carbon-silicon composite in which silicon is uniformly dispersed in the nitrogen-doped graphite carbon continuous phase can be produced. In addition, the nitrogen-doped carbon-silicon composite thus prepared has excellent electrical conductivity, strength, and capacity retention, and thus can be used as a negative electrode active material of a lithium secondary battery.

1 is a scanning electron microscope (SEM) photograph of the composite prepared in Example 1. Fig.
2 is a scanning electron microscope (SEM) photograph of the composite of Example 1 after the rolling process.
3 is a graph showing the battery performance evaluation results of a battery including a negative electrode made of the composite of Examples 1 and 2 and Comparative Example 1. Fig.
4 is a graph showing the battery performance evaluation results of a battery including a negative electrode made of the composite of Example 3 and Comparative Example 2. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Method for producing nitrogen-doped carbon-silicon composite

The present invention relates to a method for producing a silicon-based active material, comprising the steps of: mixing a silicon-based active material and a carbon precursor with urea or cyanuric acid; And

Heat treating the resulting mixture;

Silicon-carbon composite, wherein the nitrogen-doped carbon-

The nitrogen-doped carbon-silicon composite produced by the present invention has a structure in which a silicon-based active material is impregnated in a graphitic nitrogen-doped carbon continuous phase having a graphite structure.

The nitrogen-doped carbon is produced by mixing and heat-treating the carbon precursor and the nitrogen precursor, and the nitrogen precursor is urea or cyanuric acid. According to the present invention, a carbon precursor, a nitrogen precursor and a silicon-based active material are mixed and heat-treated to prepare a nitrogen-doped carbon-silicon composite through an eutectic mixture. In other words, nitrogen doping occurs in the carbon precursor and a complex is formed, so that the silicon is uniformly distributed in the nitrogen-doped carbon continuous phase, so that an electrically conductive path can be effectively generated in the non-conductive silicon and a structure similar to graphite And thus the strength compared to the conventional carbon increases. Therefore, the degradation of the electrode can be improved.

The silicon-based active material of the nitrogen-doped carbon-silicon composite produced by the present invention is not particularly limited in the present invention, but specifically includes Si, SiO _x (0 <x <2) It can be more than a species. When a carbon-silicon composite is used as the silicon-based active material, the carbon-silicon composite may have a core-shell structure coated with a nitrogen-doped carbon layer.

At this time, the content of the carbon precursor is limited in consideration of the content of the silicon-based active material and the carbon in the finally obtained composite. That is, when the composite according to the present invention is used as an electrode active material, the nitrogen-doped carbon present in the composite should have durability so that the volume of the silicon is not entirely changed, and the electrical conductivity must be sufficiently increased. Preferably, the silicon-based active material: carbon precursor is used in a weight ratio of 1: 0.1 to 1:20, more preferably in a weight ratio of 1: 1 to 1:10. If the amount is less than the above range, it is difficult to achieve uniform performance of the carbon coating on the silicon surface. If the above range is exceeded, the content of silicon in the composite decreases to reduce the capacity and irreversible due to carbon, It is appropriately adjusted within the above range.

The carbon precursor of the nitrogen-doped carbon-silicon composite produced by the present invention has a molecular weight of not less than 1000 g / mol and contains at least two groups selected from the group consisting of hydroxyl groups, ester groups, ether groups and carboxyl groups in the molecular structure Functional group. When the molecular weight of the carbon precursor is 1000 g / mol or more, the yield after carbonization is high. Non-limiting examples of such carbon precursors include lignin, tannic acid, and carboxymethylcellulose. The carbon precursor may be nitrogen-doped by reacting with a nitrogen precursor, urea or cyanuric acid, by containing at least two functional groups in the hydroxyl group, the ester group, the ether group and the carboxyl group.

In the present invention, the silicon-based active material and the carbon precursor may be mixed with a nitrogen precursor after forming secondary particles. Secondary particle means a particle in a physically distinguishable state in which primary particles, which are minimum unit particles, are gathered. The method for forming secondary particles is not particularly limited in the present invention, and a commonly used method can be used. These secondary particles have a smaller specific surface area than the primary particles, and can evenly mix with the nitrogen precursor during the reaction, thereby enabling more uniform nitrogen doping. Further, since the particles are less entangled than in the case of using a primary particle to form a composite, and the phenomenon of sticking to the reaction vessel is less than that in the case of using a primary particle, the resulting composite can be easily recovered.

The nitrogen-doped carbon-silicon composite according to the present invention may further include a conductive material for improving conductivity. The conductive material is not particularly limited in the present invention, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Graphene; Conductive fibers such as carbon fiber and metal fiber such as carbon nanotube (CNT) and carbon nanofiber (CNF); Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And polyphenylene derivatives. Such a conductive material may be added to a mixture of the silicon-based active material, the carbon precursor and the nitrogen precursor before the heat treatment, or may be included in the secondary particles.

The nitrogen precursor of the nitrogen-doped carbon-silicon composite produced by the present invention is urea or cyanuric acid. In the present invention, the nitrogen precursor acts as a reactant and as a solvent (molten solvent). Since the nitrogen precursor is used in an excessive molar amount as compared with the mixture of the silicon-based active material and the carbon precursor, the nitrogen-doped carbon-silicon composite can be easily produced. The urea or cyanuric acid may be contained in the same amount to 10 times the mass of the total mass of the silicon-based active material and the carbon precursor, and preferably the same amount to 3 times the mass.

The carbon content-to-carbon (N / C) ratio of the nitrogen-doped carbon-silicon composite produced by the present invention is 0.01 to 0.6, preferably 0.01 to 0.3. This can be controlled by the ratio of the carbon precursor and the nitrogen precursor used in the preparation of the composite. If the nitrogen content is less than the above range, it is difficult to form a structure similar to graphite when nitrogen-doped carbon is formed. If the nitrogen-doped carbon content exceeds the above range, the carbon conductivity may be deteriorated.

In the method of manufacturing a nitrogen-doped carbon-silicon composite according to the present invention, the heat treatment step may be performed in three successive steps. Preferably, the first heat treatment is performed at a temperature of 120 ° C to 200 ° C for the first heat treatment, 200 ° C to 700 ° C for the second heat treatment, and 700 ° C to 1000 ° C for the third heat treatment. The heat treatment time for each step is not particularly limited in the present invention, but is preferably 1 to 20 hours.

In the first heat treatment process, the mixture of the silicon-based active material, the carbon precursor, and the nitrogen precursor is liquefied and becomes a eutectic mixture state. Although the melting point of the carbon precursor used in the present invention is 200 ° C or higher and pyrolysis occurs at such a high temperature, since the melting point of the mixture is lowered in the presence of urea or cyanuric acid which is a nitrogen precursor, A mixture is formed. During this first heat treatment process, a first reaction occurs in which the carbon precursor is doped with nitrogen.

When the eutectic mixture is subjected to the second heat treatment, the nitrogen-doped carbon precursors form a ring structure with each other. Finally, a dehydrogenation reaction takes place in the third heat treatment step, and the conjugated graphite carbon is formed. -Silicon &lt; / RTI &gt;

According to the method for producing a nitrogen-doped carbon-silicon composite of the present invention, a complex is formed in the eutectic mixture state, so that a composite in which the silicon-based active material is uniformly distributed in the nitrogen-doped carbon continuous phase can be produced. In this nitrogen-doped carbon-silicon composite, the nitrogen-doped carbon has a conjugation structure, which can provide an effective electrically conductive path to the non-conductive silicon, and has a structure similar to that of graphite. As a result, the composite is not broken at the time of manufacturing the electrode, so that the performance as originally designed can be realized, and the life characteristics of the battery can be improved because the whole volume is not broken even by the volume expansion due to silicon.

Lithium secondary battery

The lithium secondary battery according to the present invention uses a nitrogen-doped carbon-silicon composite, which comprises an anode and a cathode, a separator interposed therebetween and an electrolyte, and which is produced according to the present invention as a negative electrode active material.

The nitrogen-doped carbon-silicon composite produced according to the present invention is excellent in strength and can not be fractured during the production of electrodes, so that it is possible to realize the original performance of the composite. It can alleviate capacity degradation due to the volume expansion of silicon, And capacity retention rate.

The configurations of the positive electrode, negative electrode, separator, and electrolyte of the lithium secondary battery are not particularly limited in the present invention, and are well known in the art.

The positive electrode includes a positive electrode active material formed on the positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, carbon, nickel , Titanium, silver, or the like may be used. At this time, the cathode current collector may use various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric having fine irregularities formed on the surface so as to increase the adhesive force with the cathode active material.

As the cathode active material constituting the electrode layer, all of the cathode active materials available in the art can be used. As specific examples of such a cathode active material, lithium metal; Lithium cobalt-based oxides such as LiCoO ₂ ; Li _{1 + x} Mn _{2 - x} O ₄ (where x is 0 to 0.33), lithium manganese-based oxides such as LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide such as Li ₂ CuO ₂ ; Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; LiNi _{1 - x} M _x O ₂ wherein M is Co, Mn, Al, Cu, Fe, Mg, B, or Ga and x is 0.01 to 0.3; LiMn _{2 - x} MxO ₂ (where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 to 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni , Cu Or Zn); Nickel-manganese-lithium complex represented by Li (Ni _a Co _b Mn _c ) O ₂ (where 0 <a <1, 0 <b <1, 0 <c < Cobalt oxide; Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Sulfur or disulfide compounds; _{LiFePO 4, LiMnPO 4, LiCoPO 4} , LiNiPO 4 , such as phosphate; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

At this time, the electrode layer may further include a binder resin, a conductive material, a filler, and other additives in addition to the cathode active material.

The binder resin is used for bonding between the electrode active material and the conductive material and bonding to the current collector. Non-limiting examples of such binder resins include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymethacrylic acid (PMA), polymethylmethacrylate (PMMA) (PAM), polymethacrylamide, polyacrylonitrile (PAN), polymethacrylonitrile, polyimide (PI), alginic acid, alginate, chitosan, carboxymethylcellulose Propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), polyvinylpyrrolidone, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ), Fluorine rubber, various copolymers thereof, and the like.

The conductive material is used to further improve the conductivity of the electrode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives and the like can be used.

The negative electrode includes a negative electrode active material formed on the negative electrode collector, and the negative electrode active material uses the nitrogen-doped carbon-silicon composite prepared according to the present invention. Also, a mixed electrode in which the nitrogen-doped carbon-silicon composite produced according to the present invention is mixed with graphite and the capacity per weight is adjusted may be used.

The negative electrode current collector may be specifically selected from the group consisting of copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium or silver, and an aluminum-cadmium alloy may be used as the alloy. In addition, fired carbon, a nonconductive polymer surface-treated with a conductive material, or a conductive polymer may be used.

The negative electrode may further include a binder resin, a conductive material, a filler, and other additives as described above with reference to the positive electrode.

The separator may be made of a porous substrate. The porous substrate may be any porous substrate commonly used in an electrochemical device. For example, the porous substrate may be a polyolefin porous film or a nonwoven fabric. no.

The separator may be formed of a material selected from the group consisting of polyethylene, polypropylene, polybutylene, polypentene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, A porous substrate made of any one selected from the group consisting of polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalate, or a mixture of two or more thereof.

The electrolyte solution of the lithium secondary battery is a non-aqueous electrolyte solution containing a lithium salt and is composed of a lithium salt and a solvent. Non-aqueous organic solvents, organic solid electrolytes, and inorganic solid electrolytes are used as the solvent.

The lithium salt may be dissolved in the nonaqueous electrolyte solution. For example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiSCN, LiC ₄ BO ₈ , LiCF ₃ CO ₂ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiC ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, and lithium tetraphenylborate.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, -Dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, 4-methyl- The organic solvent may be selected from the group consisting of diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, Dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer including a secondary dissociation group, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

Further, the non-aqueous liquid electrolyte may further contain other additives for the purpose of improving the charge-discharge characteristics, flame retardancy, and the like. Examples of the additive include pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, (N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, trichloroaluminum, fluoroethylene carbonate (FEC), propenesultone (PRS), vinylene carbonate VC), and the like.

The lithium secondary battery according to the present invention can be laminated, stacked, and folded in addition to winding, which is a general process. The battery case may have a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Changes and modifications may fall within the scope of the appended claims.

Example 1: Preparation of nitrogen-doped carbon-silicon composite

4 g of tannic acid and 2.8 g of silicone were dispersed in 300 ml of water using a homogenizer, and the dispersed mixture was spray-dried to prepare tannic acid-silicon secondary particles.

Two grams of urea (10 g) was mixed evenly in a mortar with respect to the total amount (5 g) of the secondary particles prepared as described above. The mixture was then added to an alumina boat and heated at 170 ° C for 1 hour, 500 ° C for 3 hours, and 800 ° C for 3 hours under an argon atmosphere to produce a nitrogen-doped carbon-silicon composite. At this time, the temperature raising rate was set at 10 占 폚 / min.

Example 2: Preparation of a nitrogen-doped carbon-silicon composite containing CNTs

10 g of silicon was added to 1000 ml of water in which 0.5 g of CNT had been dispersed and stirred, then 0.5 g of tannic acid was added. The mixed solution was spray-dried to prepare tannic acid-CNT-silicone secondary particles.

4 g of the secondary particles prepared above and 10 g of urea were evenly mixed in a mortar. Then, the mixture was added to an alumina boat and heated at 170 ° C for 1 hour, 500 ° C for 3 hours and 800 ° C for 3 hours under an argon atmosphere to prepare a nitrogen-doped carbon-silicon composite (at a heating rate of 10 ° C / min) .

Example 3: Preparation of a nitrogen-doped carbon-silicon composite containing CNTs

4 g of the composite prepared in Comparative Example 2, 2 g of tannic acid and 2 g of urea were mixed and heated at 170 ° C. for 1 hour, 500 ° C. for 3 hours and 800 ° C. for 3 hours under nitrogen atmosphere, (Temperature raising rate of 10 ° C / min).

Comparative Example 1: Preparation of carbon-silicon composite

3.4 g of tannic acid and 4 g of silicon were mixed by induction mixing and then heated at 170 DEG C for 1 hour, 500 DEG C for 3 hours and 800 DEG C for 3 hours under an argon atmosphere to prepare a carbon-silicon composite (heating rate of 10 DEG C / min ).

Comparative Example 2: Preparation of carbon-silicon composite including CNT

10 g of silicon was added to 1000 ml of water in which 0.5 g of CNT had been dispersed and stirred, then 0.5 g of tannic acid was added. The mixed solution was spray-dried and then heated at 170 ° C for 1 hour, 500 ° C for 3 hours and 800 ° C for 3 hours under an argon atmosphere to prepare a carbon-silicon composite (at a heating rate of 10 ° C / min).

Experimental Example 1: Structural analysis of nitrogen-doped carbon

The following experiment was conducted to confirm the structural characteristics of the nitrogen-doped carbon prepared according to the present invention.

Lignin was used as a carbon precursor and the mixture was heated at 170 ° C for 1 hour, at 500 ° C for 3 hours, and at a temperature of 150 ° C under an argon atmosphere. The lignin was mixed with lignin, lignin: urea = 1: Raman spectroscopic analysis was performed on the material carbonized by heating at 800 DEG C for 3 hours.

sample D / G ratio (D / G ratio) Lignin 0.93 Lignin: urea = 1: 0.7 1.04 Lignin: urea = 1: 2 1.1

From Table 1, it can be seen that the higher the ratio of urea in the mixture, the higher the D / G ratio value. From the above results, it can be seen that the nitrogen-doped carbon produced according to the present invention has the character of graphitic carbon, and the higher the proportion of urea as the nitrogen precursor, It can be confirmed that graphite is higher.

Experimental Example  2: Preparation of electrode

The composites prepared in the above Examples and Comparative Examples were used as negative active materials to prepare negative electrodes. The anode active material, the conductive material, and the binder were mixed at a weight ratio of 80:10:10, and N-methyl-2-pyrrolidone (NMP) was used as the binder. (NMP) to prepare a slurry. The slurry was coated on one side of a copper foil having a thickness of 20 μm, rolled and dried to prepare a negative electrode for a lithium secondary battery.

FIG. 2 is a scanning electron microscope (SEM) photograph of a carbon-silicon composite coated with nitrogen dispersed in an active material layer after a negative electrode is produced from the composite of Example 1. FIG. 2, it can be seen that the composite structure remains spherical without being broken even after rolling.

Experimental Example 3: Preparation of battery and evaluation of cell performance

(1) Manufacture of batteries

A coin type half cell including the negative electrode prepared in Experimental Example 1 was prepared. Lithium metal was used as an anode and polyethylene having a thickness of 20 μm was used as a separator. LiPF ₆ 1.0 M as a lithium salt in a solvent of diethyl carbonate (DEC): fluoroethylene carbonate (FEC) = 7: 3, vinylene carbonate (VC) of 3% by weight was used.

(2) Evaluation of battery performance

The initial capacity was measured by charging and discharging the coin-type half-cells manufactured in (1) at 25 ° C under the condition of 0.1 ° C, and an additional 0.1 C charging and discharging was performed once, followed by 50 cycles at a rate of 0.5C.

FIG. 3 shows the normalized capacity retention according to the number of cycles of a battery including the composite prepared in Examples 1 and 2 and Comparative Example 1 as a negative electrode active material. The normalized capacity according to the number of cycles of the battery including the composite prepared in Example 3 and Comparative Example 2 as a negative electrode active material is shown in FIG.

Referring to FIG. 3, the carbon-silicon composite electrode of Comparative Example 1 showed a capacity retention rate of 60% after 50 cycles, while the nitrogen-coated carbon-silicon composite of Example 1 showed 82%, CNT of Example 2 The further nitrogen-coated carbon-silicon composites show an improved capacity retention of 88%.

Referring to FIG. 4, when the nitrogen-doped carbon-silicon composite of the present invention is applied to a generally manufactured carbon-silicon composite (Comparative Example 2) to coat nitrogen-doped carbon (Example 3) The capacity retention ratio after 50 cycles is improved. From this, it is possible to improve the capacity retention ratio by increasing the strength of the composite by merely introducing the nitrogen-doped carbon coating by applying the nitrogen-doped carbon-silicon composite manufacturing method according to the present invention to the existing carbon-silicon composite can confirm.

According to the method for producing a nitrogen-doped carbon-silicon composite according to the present invention, a nitrogen-doped carbon-silicon composite in which silicon is dispersed in a graphite nitrogen-doped carbon continuous phase having excellent electrical conductivity and strength can be obtained. The thus prepared nitrogen-doped carbon-silicon composite can be used as a negative electrode active material of a lithium secondary battery and exhibits excellent battery performance.

Claims (13)

Mixing the silicon-based active material and the carbon precursor with urea or cyanuric acid; And
Heat treating the resulting mixture;
Wherein the nitrogen-doped carbon-silicon composite is a mixture of carbon and silicon. The method according to claim 1,
Wherein the silicon-based active material is at least one selected from the group consisting of Si, SiO _x (0 < x < 2) and carbon composites thereof. The method according to claim 1,
Wherein the carbon precursor is a compound having a molecular weight of 1000 g / mol or more and containing at least two functional groups selected from the group consisting of a hydroxyl group, an ester group, an ether group, and a carboxyl group in a molecular structure Carbon composite. The method according to claim 1,
Wherein the carbon precursor is at least one selected from the group consisting of lignin, tannic acid, and carboxymethyl cellulose. The method according to claim 1,
Wherein the silicon-based active material: carbon precursor is used in a weight ratio of 1: 0.1 to 1:20. The method according to claim 1,
Wherein the urea or cyanuric acid is contained in the same amount to 10 times the mass of the silicon-based active material and the total carbon precursor mass. The method according to claim 1,
Wherein the mixture further comprises a conductive material. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; 8. The method of claim 7,
Wherein the conductive material is any one selected from the group consisting of graphite, carbon black, graphene, conductive fiber, metal powder, conductive whisker, conductive metal oxide, polyphenylene derivative, and combinations thereof. Silicon composite. The method according to claim 1,
The heat treatment step is performed in three successive steps,
The first heat treatment is performed at 120 ° C or more and less than 200 ° C;
The second heat treatment is performed at a temperature of 200 DEG C or more and less than 700 DEG C;
Wherein the third heat treatment is performed at a temperature of 700 ° C to 1000 ° C. A nitrogen-doped carbon-silicon composite produced by the process according to any one of claims 1 to 9. 11. The method of claim 10,
Characterized in that the nitrogen content (N / C ratio) of the nitrogen-doped carbon to carbon is 0.01 to 0.6. Active material; Conductive material; And an electrode for a lithium secondary battery comprising a binder,
Wherein the active material comprises the nitrogen-doped carbon-silicon composite of claim 10. anode; cathode; A separator interposed between the anode and the cathode; And a lithium secondary battery comprising an electrolyte,
Wherein the negative electrode is the electrode of claim 12.

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