KR101261989B1 - Method of Producing Negative Electrode Materials of Lithium Seconary Battery Having Metal-Carbon Core-Shell Structures - Google Patents

Abstract

The present invention relates to a method for producing a negative electrode material for a lithium battery, and more particularly, to supply a solution of a mixture of acrylonitrile-based copolymer, metal or metal oxide or metal sulfide, solvent or a mixture in a molten state at a constant flow rate Adding a core / shell composite is added, and heat treatment to carbonize.
Therefore, the manufacturing process of the present invention is simpler than the conventional invention, and is suitable for mass production of nano-cathode materials, and adopts a core and a shell containing the same monomer acrylonitrile-based copolymer to minimize heterogeneity and thus uniform radioactivity. Maximization is possible.
In addition, it has excellent thermal stability and can maintain stable behavior even when pulverizing due to the volume change of metal / metal oxide / metal sulfide materials.The size and wall thickness of tube life are controlled by adjusting the electrospinning parameters (flow rate, core and shell concentration). Can be adjusted.

Description

Method of Producing Negative Electrode Materials of Lithium Seconary Battery Having Metal-Carbon Core-Shell Structures

The present invention relates to a method for producing a negative electrode material for a lithium secondary battery having a metal-carbon core shell structure.

With the spread of portable electric and electronic devices, development of a new secondary battery, such as a nickel-metal hydride battery or a lithium secondary battery, is actively under way. The lithium secondary battery is a battery using carbon such as graphite as a negative electrode active material, an oxide containing lithium as a positive electrode active material, and a non-aqueous solvent as an electrolyte. Since lithium is a highly ionized metal, development of a battery with high energy density can be achieved because high voltage can be generated.

Lithium transition metal oxides containing lithium are mainly used as the positive electrode active material used therein, and more than 90% of layered lithium transition metal oxides such as cobalt, nickel, and ternary systems in which cobalt, nickel, and manganese coexist are used have.

As the spread of portable small electric electronic devices has spread, there has been a demand for dramatic improvements in performance such as battery capacity and lifespan. Capacity improvement is expected by developing anode based on sulfide, metal based on Si or Sn, etc. However, in the case of sulfide emerging as cathode material, it is difficult to control the route of sulfur movement by substitution, and silicon as anode material In the case of tin and tin, the crystal structure changes as the lithium-ion enters and exits, and the capacity is improved due to the problem of breaking the electrical contact between the negative electrode materials due to the volume expansion caused by the lithium-ion. On the other hand, conventional carbon materials such as graphite have a low storage capacity of lithium-ions, but there is no deterioration in life characteristics due to volume change. Therefore, in the case of negative electrode materials, there are many attempts to combine carbon materials with metal / metal oxides. Has been done. However, in general, the use of methods such as vapor deposition improves the capacity and life characteristics, but the process is complicated and expensive, and when the carbon precursor and the metal / metal oxide nanoparticles are mixed by the conventional electrospinning process, etc. , But the process is simplified, but the life characteristics are not improved due to the aggregation of nanoparticles.

The Si / C composite fiber was prepared by the L.Ji team using single nozzle electrospinning and the same study invented a number of metals or metal oxides (L. Ji et al. Electrochemistry communications 11 (2009) 1146-1149). . It used polyacrylonitrile which can be carbonized as a matrix, and used silicon powder as a filler. However, general nanoparticles, such as silicon powder, are difficult to disperse through a single nozzle because of dispersion problems, and due to the nature of the electrospinning process, materials with high conductivity tend to be attracted to the surface. There is a problem in that the effect of carbon complexation for the purpose of stabilization by binding in the matrix is inferior.

Tin core / carbon shell structures were also fabricated using coaxial electrospinning from the Y. Yu group (Y. Yu et al. Angew. Chem. Int. Ed. 48 (2009) 6485-6489). The technique was made by using a carbonizable polyacrylonitrile, the core was prepared using a mineral oil as a carrier of tin, and then removed with octane. However, mineral oil, which is a substance used as a core solution, is too difficult to control the viscosity, and unlike the polymer solution, it is difficult to transfer the shear force imparted by the shell solution, and requires an additional process of removing it with octane, and carbon shell after carbonization. Uniformity is disadvantageous for massification and commercialization.

The J.Cho team fabricated a silicon core / carbon shell structure using the tube shape as a template (J. Cho et al. Nano letters 8 (2008) 3688-3691). The technique is based on an SBA tube as a template and manufactured through a complex process that includes impregnation, etching and heat treatment. However, this has a disadvantage in that the manufacturing process is not easy due to the complexity of the process, and the mass and commercialization are difficult as the electrochemical properties are continuously reduced. As a conventional patent, the Republic of Korea Patent Registration 10-09180500000, the Republic of Korea Patent Publication 10-2007-0109118, the Republic of Korea Patent Publication 10-2007-0102881, each of the negative electrode active material including a lithium secondary battery, a metal nanocrystal composite containing a negative electrode active material for a lithium secondary battery In addition, there are patents related to the negative electrode active paper and the manufacturing method thereof, but the existing patents are patents of the negative electrode material itself, there is a heterogeneity because it is not the core and shell containing the same monomer, and due to the volume change of the metal / metal oxide active material There is a problem that the grinding is not stable.

The present inventors have found that there is a problem in making a core using existing PMMA or mineral oil, and styrene acrylonitrile (Styrene-acrylonitrile, SAN) using styrene and acrylonitrile as a unit of a suitable core material. ) Can be used as a carrier and core of metal, metal oxides or metal sulfides to minimize heterogeneity between the two solutions that may appear during electrospinning, and have good thermal stability, forming the core's structure, which eventually thermally decomposes, We developed a system that is uniform and easily adjustable in size through control.

In order to overcome the problems of core-shell structure formation, uniformity, and complex process problems of the prior art, the present inventors have completed the formation of a core / shell structure in a simple process, and have a metal, metal oxide, or metal structure. The sulfide nanoparticles were wrapped in a uniform thickness of a carbon shell to prepare a lithium ion battery material having mechanical superiority.

The present invention is suitable for mass production of nano-cathode materials through the simplification of the process and has a long aspect ratio compared to the production by neutralization, and the core and the shell containing the same monomer can be adopted to minimize heterogeneity to maximize uniform radioactivity. By utilizing SAN, which has excellent thermal stability, it helps to form carbon nanotube structure in stabilization process, so that stable behavior can be maintained even when pulverization due to volume change of metal / metal oxide / metal sulfide material. And the shell concentration) to control the size and wall thickness of the tube life.

Accordingly, an object of the present invention is to expand the system to produce a lithium ion battery negative electrode material having a core / shell structure which is a combination of a shell of carbon and a core which is a metal, metal oxide or metal sulfide nanoparticle.

Other objects and advantages of the present invention will become more apparent from the following detailed description of the invention, claims and drawings.

According to one aspect of the invention, the invention provides (i) 20-45% by weight of acrylonitrile copolymer as the material of the core, and acrylonitrile copolymer 10-40 which is not the same as the material of the core as the material of the shell. Supplying a solution or mixture in a molten state of a mixture of wt%, metal or metal oxide or metal sulfide 1-35 wt%, and solvent 30-65 wt%;

(ii) applying a voltage to the mixture to form a core / shell composite

(iii) a method for producing a negative electrode material for a lithium battery, comprising the step of carbonizing and graphitizing the core / shell composite at 700-3000 ° C.

According to another aspect of the present invention, the present invention provides a negative electrode material for a lithium battery produced by the above method.

According to still another aspect of the present invention, the present invention provides a lithium battery comprising a negative electrode material for a lithium battery produced by the above method.

Features and advantages of the present invention are as follows.

(i) The present invention relates to a method for producing a negative electrode material for a lithium battery, and more particularly to a solution or a mixture of a mixture of acrylonitrile-based copolymers, metal or metal oxides or metal sulfides, solvents or molten state at a constant flow rate Supplying and applying a voltage to form a core / shell composite, and heat treating and carbonizing.

(ii) The present invention has a simpler process compared to the conventional invention, and is suitable for mass production of nano-cathode materials.

(iii) The core and the shell containing the same monomer acrylonitrile-based copolymer is adopted to minimize heterogeneity and maximize uniform radioactivity.

(vi) The thermal stability is excellent, and stable behavior can be maintained even by grinding due to the volume change of the metal / metal oxide or metal sulfide material.

(v) It is possible to control the size of the tube holes and the wall thickness by adjusting the electrospinning parameters (flow rate, core and shell concentration).

1 is a diagram showing a mixture of two solutions and a coaxial nozzle structure for producing a nanofiber having a core / shell structure.
Figure 2 is a diagram showing the overall overview of the heat treatment process of the present invention. The x-axis is time, the y-axis shows the temperature of each step, and the gas conditions to be performed step by step are described below.
3 is a view showing the core / shell structure formation and the PAN microstructure change by the process of the cyclization reaction and carbonization process of polyacrylonitrile according to the heat treatment process.
4 is a micrograph showing the structure of silicon / carbon composite nanofibers (left panel) and silicon oxide / carbon composite nanofibers (right panel).
FIG. 5 is a view to confirm that the electrochemical behavior of the silicon core / carbon shell composite nanofibers is improved when using the composite nanofibers as a secondary battery negative electrode material, to confirm that the electrochemical behavior is more stable than the single nozzle. It was. The x-axis is the capacity in mAh / g, the y-axis is the voltage in V.
FIG. 6 shows the stability of electrochemical behavior compared to a single nozzle when used as a secondary battery anode material through the use of composite nanofibers, and shows the behavior of capacity and voltage when a single nozzle is used. The x-axis is the capacity in mAh / g, the y-axis is the voltage in V.
7 is a graph showing that the microstructure grows and deforms into a graphite structure as the carbonization temperature increases from the egg structure to 800, 1000, and 1200 ° C. in order.
8 is a graph showing that the initial irreversible capacity due to the egg bed structure decreases as the carbonization temperature increases, and the numerical value at 800 ° C. is graphed.
9 is a graph showing that the initial irreversible capacity decreases due to the warm layer structure as the carbonization temperature is increased.
10 is a graph showing that the initial irreversible capacity decreases due to the egg layer structure as the carbonization temperature increases, and the numerical value at 1200 ° C. is graphed.
FIG. 11 is a graph for confirming the behavior of capacity and voltage according to temperature conditions during carbonization, and is a graph showing numerical values when carbonized at 800 ° C. FIG.
12 is a graph showing the values of carbonization at 1000 ° C. for confirming the behavior of capacity and voltage according to temperature conditions during carbonization.
13 is a graph for confirming the behavior of the capacity and voltage according to the temperature conditions during the carbonization process, a graph showing the value when carbonized at 1200 ℃.

Hereinafter, the present invention will be described in more detail.

(I) 20-45% by weight of acrylonitrile copolymer as the material of the core, 10-40% by weight of acrylonitrile copolymer which is not the same as the material of the core as the material of the shell, metal or metal oxide Supplying a solution of a mixture of 1-35 wt% metal sulfide and 30-65 wt% solvent or a mixture in a molten state;

(ii) applying a voltage to the mixture to form a core / shell composite;

(iii) a method for producing a negative electrode material for a lithium battery, comprising the step of carbonizing and graphitizing the core / shell composite at 700-3000 ° C.

In the present invention, a material required to form the core and the shell structure uses two or more different acrylonitrile-based copolymers. Acrylonitrile copolymers include styrene acrylonitrile (SAN), polyacrylonitrile (PAN), acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA) or acrylonitrile butyrate Diene (NBR) and the like, but is not necessarily limited thereto.

More preferably, the acrylonitrile-based copolymer uses styrene acrylonitrile (SAN) and polyacrylonitrile (PAN), and SAN is used as the core material and PAN is used as the shell material. More preferably, styrene acrylonitrile is 20-45 weight% and polyacrylonitrile (PAN) 10-40 weight% as a mixing ratio. Most preferably, 25-35% by weight of styreneacrylonitrile and 5-40% by weight of polyacrylonitrile.

SAN and PAN both contain acrylonitrile, the same carbon monomer. Since the SAN contains styrene, the cohesion of the copolymer is weak and has a property of thermal decomposition at 400 ℃ or more.

The mixture includes an acrylonitrile-based copolymer and a metal or metal oxide or metal sulfide. Metals include silicon (Si), tin (Sn), germanium (Ge), antimony (Sb), titanium (Ti), indium (In), copper (Cu), zirconium (Zr), cobalt (Co), iron ( Fe), nickel (Ni), manganese (Mn), zinc (Zn), calcium (Ca), vanadium (V) and alloys thereof. Metal oxides and sulfides include metal oxides and metal sulfides containing the above metals. Including but not limited to.

According to a preferred embodiment of the invention, the solvent used in the reaction is a polar solvent. The polar solvent includes, but is not limited to, DMF, DMSO, HMPA, Dioxane, THF, MeCN, acetone, DCM, EA, water, methanol, ethanol, propanol, formic acid, HF or ammonia. More preferably, the polar solvent uses a polar aprotic solvent of DMF, DMSO, HMPA, Dioxane, THF, MeCN, acetone, DCM, EA, and most preferably DMF.

According to a preferred embodiment of the present invention, the flow rate of step (ii) is 0.1-3 ml / h. More preferably the flow rate is 0.5-1.5 ml / h.

According to a preferred embodiment of the invention, the voltage is carried out at 0.001-50 kV. More preferably the voltage is at 10-25 kV.

According to a preferred embodiment of the present invention, itaconic acid or methacrylate is additionally added to the mixture. Itaconic acid or methacrylate makes the structure of the shell more uniform and facilitates size control during the carbonization process.

According to a preferred embodiment of the present invention, the heat treatment step of 300 ℃ or more is carried out in the presence of an inert gas (nitrogen or argon). More preferably the heat treatment step is carried out at 700-2000 ° C.

The inert gas is composed of helium, neon, argon, krypton, xenon, radon, more preferably the inert gas is carried out in the presence of argon.

According to a preferred embodiment of the present invention, the present invention provides a negative electrode material for a lithium battery prepared by the method for producing a negative electrode material for a lithium battery.

According to a preferred embodiment of the present invention, the present invention provides a lithium battery comprising a negative electrode material for a lithium battery manufactured using the method for producing a negative electrode material for a lithium battery.

Hereinafter, the present invention will be described in detail through specific examples, and the scope of the present invention is not limited to these examples.

Example  One : Coaxial  Preparation of Core / Shell Nanofibers by Electrospinning Process

In the present invention, the shell portion is a polyacrylonitrile (PAN, molecular weight 200,000 Misui chemical), which is a precursor of a carbon anode material, and acrylonitrile, which is the same unit as a core, as a unit, while having excellent thermal stability, thereby forming a structure but eventually thermally decomposing copolymerization. The chain styrene acrylonitrile (SAN, molecular weight 120,000, Cheil Industries) was used as a carrier to disperse nanoparticles such as Si, SnO ₂ and Sn which are excellent in electrochemical properties. , N-dimethylformamide was dissolved (FIG. 1).

Utilizing the coaxial electrospinning process, the core is Si 5 wt% + SAN 30 wt% in DMF, the shell is PAN 20 wt% in DMF solution, voltage 18 kV, spinning distance 15 cm, core flow rate 0.5 ml / h, shell flow rate Solid precursors prepared at 15 kV, spinning distance 10 cm and flow rate 0.5 ml / h using a core / shell precursor spun at 1 ml / h and a 5 wt% Si + 20 wt% in DMF solution were prepared under an air atmosphere. Si / C composite nanofibers were prepared by stabilizing at 270-300 ° C. for 1 hour and heat treatment at 1000 ° C. for 1 hour under N ₂ atmosphere (FIG. 2). Table 1 below describes the electrospinning process conditions.

The composite nanofibers, PVDF (binder polymer) and acetylene black (AB, filler) were fabricated at 9: 0.5: 0.5 and 200 mA / g for 0.01-1.5 V voltage range using Li metal as a counter electrode. Evaluation of electrochemical properties was carried out with a current density of (Fig. 5).

Example  2: carbonization process by heat treatment process

PAN, which is a shell polymer, forms a ring and interconnection network by heat to form a mismatched structure of a graphene layer, and undergoes one continuous heat treatment process to remove the carrier, SAN. From the stabilization process corresponding to 270-300 ° C., acrylonitrile of PAN forms a ladder by dehydrogenation reaction and cyclization reaction between nitriles (conversion from -C≡N to -C = NC), and SAN Silver forms a molten structure, and after the stabilization process, the carbonization process is started, and the SAN starts pyrolysis at 400 ° C. or higher, and the PAN carbonizes at 700 ° C. or higher (FIG. 3). Since the microstructure of the PAN carbide is changed according to the heat treatment temperature, the capacity can be controlled according to the heat treatment temperature, and since the phase of the nanoparticles is changed to the metal / metal oxide according to the gas atmosphere, the electrochemical characteristics can be controlled.

As shown in the following Table 2, the microstructure incompleteness is improved according to the control of the carbonization temperature that proceeds at 700 ℃ or more, the size and thickness of the grains at 1.28 nm, 1.16 nm, and 1000 ℃ at 800 ℃, respectively At 4.54 nm, 1.56 nm, and 1200 ° C., they grew to 5.83 nm and 1.73 nm, respectively (FIG. 7).

Due to such a microstructure change, the space between the grains and between the grains is narrowed, and the initial capacity of the overall storage capacity of lithium ions is 850 mAh / g at 800 ° C, 720 mAh / g at 1000 ° C, and 460 mAh at 1200 ° C. Although decreased to / g, the initial reversible dose increased to 51, 54, 62% respectively (Figs. 8-10).

Comparative example  1: Preparation of a Single Nozzle of Silicon / Carbon

Electrochemical properties of Si / C were compared with those of nanofibers prepared through a single nozzle for 20% by weight of PAN + 5% by weight of SAN (FIG. 6).

Comparative example  2: carbon Shell To the cathode  Electrochemical Properties to Identify Properties

Since the shell part also becomes the active material of the negative electrode material, the electrochemical properties were also evaluated for the heat treatment temperature of the hollow carbon nanofibers to show that the electrochemical properties can be controlled according to the temperature change (FIGS. 11 to 13).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the present invention. It is therefore intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims (11)

(i) 20-45% by weight of acrylonitrile-based copolymer as the material of the core, 10-40% by weight of acrylonitrile-based copolymer not equal to the material of the core as the material of the shell, metal or metal oxide or metal sulfide 1 Feeding -35% by weight, a mixture of 30-65% by weight of a solvent or a mixture in a molten state;
(ii) applying a voltage to the mixture to form a core / shell composite
(iii) a method of producing a negative electrode material for a lithium battery, comprising the step of carbonizing and graphitizing the composite with a core / shell at 700-3000 ° C.
The acrylonitrile-based copolymer as a material of the core or shell is styrene acrylonitrile (SAN), polyacrylonitrile (PAN), acrylonitrile butadiene styrene (ABS), acrylonitrile A method comprising selecting two different kinds of styrene acrylate (ASA) or acrylonitrile butadiene (NBR) independently of each other.
The method of claim 1, wherein the metal is silicon (Si), tin (Sn), germanium (Ge), antimony (Sb), titanium (Ti), indium (In), copper (Cu), zirconium (Zr), cobalt (Co), iron (Fe), nickel (Ni), manganese (Mn), zinc (Zn), calcium (Ca), vanadium (V) and alloys thereof, and metal oxides and sulfides containing these metals. A metal oxide and a metal sulfide.
The method of claim 1 wherein the solvent is a polar solvent.
The method of claim 4, wherein the polar solvent is DMF, DMSO, HMPA, Dioxane, THF, MeCN, Acetone, DCM, EA, Water, Methanol, Ethanol, Propanol, Formic Acid, HF or Ammonia.
The method of claim 1 wherein the feed is 0.1-3 ml / h.
The method of claim 1 wherein the voltage is 0.01-50 kV.
The method of claim 1 wherein the mixture comprises itaconic acid or methacrylate as a copolymer.
The method of claim 1 wherein the heat treatment step is performed in the presence of nitrogen or an inert gas.
The negative electrode material for lithium batteries manufactured using the method of any one of Claims 1-9.
The lithium battery containing the negative electrode material for lithium batteries manufactured using the method of any one of Claims 1-9.

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