KR101429842B1 - Electrode including mixed composites of self―assembled carbon nanotube and sulphur for lithium sulphur battery, and the fabrication method thereof - Google Patents

Abstract

Disclosed is an electrode comprising a self-assembled carbon nanotube and a sulfur hybrid composite used in a lithium sulfur battery, and a method of manufacturing the electrode. The electrode active material is composed of a carbon nanotube aggregate self-assembled into at least one of spherical, elliptical, crushed spherical and squashed elliptical shapes, and sulfur contained in the inner space of the agglomerated carbon nanotube aggregate . ≪ / RTI >

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode comprising a self-assembled carbon nanotube and a sulfur hybrid composite used in a lithium sulfur battery, and a method of manufacturing the same. BACKGROUND ART [0002] Electrodes for electrochemical cells,

Embodiments of the present invention relate to an electrode including a hybrid composite of carbon nanotube aggregates and sulfur coagulated in the form of a porous structure, a lithium sulfur battery using the electrode, and a method of manufacturing the same.

The secondary battery includes a cathode, an anode, an electrolyte, and a separator. In this configuration, the reversible oxidation and reduction reactions between the anode and the cathode enable the rechargeable battery to be used.

Lithium-ion secondary battery, which is widely used now, is widely used as a high-power power source for stably driving an industrial robot and an electric vehicle as well as a power supply source for portable electronic devices because of its excellent energy conversion efficiency. As a result, the lithium ion secondary battery has been expanding its market as a medium and large power source in addition to its application as a small portable power source.

On the other hand, the performance of the battery is determined according to the capacity and output of the battery, depending on how much electric energy can be used and how much electricity can be drawn at a certain speed. Such performance is basically different from selection of the anode and cathode materials do.

Lithium selenium is operated by lithium ions moving in the electrolyte interposed between the anode and the cathode, as in conventional lithium ion secondary batteries. However, since the lithium sulfur battery uses only simple sulfur, unlike the conventional lithium ion secondary battery, in which lithium ions are intercalated between molecules of an electrode active material, the electrode structure is deformed to store energy, unlike the reaction between sulfur and lithium ions , And a reduction reaction. Therefore, the lithium sulfur battery is not limited in electrode structure as compared with the conventional lithium ion secondary battery, and can theoretically have a larger capacity at the same volume. Assuming that the sulfur (S8) having a ring structure reacts completely to lithium polysulfide (Li ₂ S) in a lithium sulfur battery composed of an anode sulfur and an anode lithium metal, the theoretical capacity is 1,675 mAh / g (Ni / MH battery: 450Wh / kg, Li / FeS: 480Wh / kg, Li / MnO ₂ : 1,000Wh / kg, Na / S: 800Wh / kg).

On the other hand, in the conventional transition metal oxide based lithium ion secondary battery, an oxide of nickel (Ni), cobalt (Co), and manganese (Mn) having a density higher than a density of a heavy metal Therefore, it can be evaluated as a battery containing heavy metal pollutants. However, lithium sulphate batteries are environmentally friendly because they use no toxic materials and are excluded from these pollutants. In addition, sulfur as a cathode material is advantageous in that it is rich in resources and is inexpensive in terms of cost.

However, these lithium-sulfur batteries have various advantages including advantages of having a higher energy density than existing batteries, but they are also relatively disadvantageous compared to conventional batteries. For example, the polysulfide produced during the charging / discharging process has a high solubility in the organic electrolyte, resulting in loss of sulfur. This leads to a decrease in capacity during charging / discharging, and since the polysulfide dissolved by the movement through the electrolyte reacts with the lithium metal of the anode to form an insoluble product on the surface, the electrode operation is negatively affected. In addition, due to the nature of sulfur, the diffusion reaction of ions and electrons generated during the oxidation and reduction reaction is relatively slow because of ionic insulators and electrically nonconductive materials, which causes a decrease in output of the battery. In addition, since the operating voltage is operated near 2V, it has a disadvantage that the voltage is low because it replaces the current lithium ion secondary battery.

Therefore, in order to compensate for this, various studies such as complexation with a conductive material, complexation with different sulfur compounds, electrolyte modification, and the like have been actively conducted.

For example, Korean Patent Laid-Open Publication No. 10-2007-0049770 (published on May 14, 2007) entitled " Method for manufacturing composite iron sulfide electrode for positive electrode and lithium secondary sulfide secondary battery " And a transition metal element powder are weighed and then synthesized using a mechanochemical method. The composite iron sulfide produced through the above process is mixed with a carbon powder and a binder to prepare a slurry, and the slurry thus prepared is dried to produce a composite iron sulfide anode have.

However, these methods are still constrained in practical commercial applications. Therefore, it is necessary to develop a structure of an electrode active material capable of improving the low electrical conductivity characteristic of the electrode active material, and a structure capable of maintaining battery performance even at a fast charge and discharge is required. In particular, there is a need for structuring a new electrode active material which can be obtained in an easier way in consideration of commercial applications.

Further, by using a carbon nanotube having a high-crystalline carbon structure, not only is it superior in electric conductivity to other amorphous carbon, but also the sulfur inside the electrode can be mechanically, thermally, electrically, and chemically It is important to develop a thin electrode layer capable of maximizing the output characteristics, durability and reliability of the battery so as to be stably present.

An electrode comprising a hybrid composite of self-assembled carbon nanotubes and sulfur used in a lithium sulfur battery capable of providing an electrode active material with high output characteristics capable of rapidly transferring electrons generated during oxidation and reduction of sulfur, A manufacturing method is provided.

There is provided an electrode comprising a hybrid composite of a self-assembled carbon nanotube and sulfur, which is used in a lithium sulfur battery, which can provide an electrode active material having a high output characteristic with high ion conductivity and rapid permeation of a liquid electrolyte, .

An electrode comprising a hybrid composite of a self-assembled carbon nanotube and sulfur, which is used in a lithium sulfur battery in which sulfur can provide a composite electrode active material that is mechanically, thermally, electrically, and chemically safe at the time of charge and discharge of the battery, and A manufacturing method is provided.

There is provided an electrode comprising a hybrid composite of a self-assembled carbon nanotube and sulfur, which is used in a lithium sulfur battery in which sulfur can be rapidly penetrated in the production of an electrode active material, and a method of manufacturing the electrode.

There is provided an electrode including a hybrid composite of a self-assembled carbon nanotube and sulfur, which is used in a lithium sulphate battery capable of mass production at a high yield, and a method of manufacturing the same.

The electrode active material is composed of a carbon nanotube aggregate self-assembled into at least one of spherical, elliptical, crushed spherical and squashed elliptical shapes, and sulfur contained in the inner space of the agglomerated carbon nanotube aggregate . ≪ / RTI >

According to one aspect of the present invention, the carbon nanotube agglomerate may include a plurality of micropores filled with the sulfur, and the plurality of carbon nanotubes are connected to each other in a network form.

According to another aspect, the aggregates of carbon nanotubes have a size range of 100 nanometers to 10,000 nanometers when agglomerated into spherical and distorted spherical shapes, and when agglomerated into oval and elliptical shapes, 100 nanometers to 10,000 nanometers Meter range and the ratio of the short axis can be in the range of 1 to 5 or less.

According to another aspect, the carbon nanotube may include at least one or more of a single wall, a double wall, and a multiwall carbon nanotube having a diameter of 1 nanometer to 20 nanometers and a length of several micrometers to several hundreds of micrometers It can be complex.

According to another aspect of the present invention, the carbon nanotube aggregates are formed in a network structure in which a plurality of the carbon nanotubes are entangled with each other, and the micropores between the carbon nanotubes are porous aggregates having a size of 0.1 nm to 900 nm .

According to another aspect, the carbon nanotube aggregate and the sulfur may have relative weight ratios of 10: 9 to 5: 5, respectively.

The lithium sulfur battery may be composed of a cathode active material including an aggregate in which a plurality of carbon nanotubes are self-assembled and a sulfur filled in a space inside the aggregate.

A method of manufacturing a lithium sulfur battery includes the steps of forming a carbon nanotube aggregate self-assembled in a network form by spraying a carbon nanotube dispersion solution, heating the self-assembled carbon nanotube aggregate, heating the carbon nanotube aggregate And mixing the carbon nanotube aggregates and the sulfur in a predetermined ratio; and heating the mixed carbon nanotube aggregates and the sulfur to permeate the sulfur into the carbon nanotube aggregates, thereby forming an electrode active material.

The sulfur in the carbon nanotube agglomerate self-assembled in a network form is stably present mechanically, thermally, electrically, and chemically by aggregates of carbon nanotubes, so that lifetime characteristics and safety of the lithium sulfur battery can be greatly improved. Particularly, since the number of polysulfides which can be dissolved in the electrolyte solution during the electrochemical reaction can be reduced, the reduction of the capacity value of the battery can be greatly improved.

Due to the fast electron transfer characteristics of the carbon nanotubes, electron transfer between the agglomerates can be easily performed, and the overall cell cell resistance can be greatly reduced, and excellent high output characteristics can be provided. Particularly, since the aggregate has at least any one form selected from the group consisting of spherical, elliptical and distorted spherical and elliptical shapes, it has aggregate characteristics rather than individual nanoparticles, and the electron transfer and lithium ion transfer characteristics It becomes easy.

Since the carbon nanotube agglomerate contains sulfur constituting the cathode active material, the full cell of the lithium sulfur battery can be provided.

It is possible to improve the charge transfer ability between the agglomerates due to the pressing process and the mixing of the additional conductive carbon and the organic binder, and the adhesion to the metal substrate used as the current collector can be greatly improved. Further, it is possible to manufacture the thin film to the thick film by adjusting the viscosity of the slurry and the thickness of the casting tool.

Since carbon nanotube agglomerates can be easily produced through the process of electric spraying, they have favorable conditions for mass production.

1 is a flow chart showing a method of manufacturing a lithium sulfur battery in an embodiment of the present invention.
FIG. 2 is a schematic view showing a manufacturing process of a carbon nanotube aggregate using an electric spraying method according to an embodiment of the present invention. FIG.
FIG. 3 is a schematic view showing a manufacturing process of melting sulfur in a heating furnace in an embodiment of the present invention, and injecting sulfur into the self-assembled carbon nanotube aggregate. FIG.
4 is a conceptual view of an electrode active material layer in which a self-assembled carbon nanotube aggregate-sulfur composite electrode active material and a conductive carbon black organic binder are formed in the form of a thin layer in an embodiment of the present invention.
5 is a scanning electron microscope (SEM) image of a self-assembled carbon nanotube agglomerate containing a binder and an organic material obtained through electrospray according to an embodiment of the present invention.
Fig. 6 is a scanning electron microscope photograph (X17,000) of Fig. 5 further enlarged.
FIG. 7 is a scanning electron micrograph (X8,000) of a self-assembled carbon nanotube aggregate composed of only pure carbon nanotubes obtained by removing a dispersant and an organic material from a heating furnace in an embodiment of the present invention.
Fig. 8 is a scanning electron microscope photograph (X15, 000) enlarged in Fig.
Fig. 9 shows the interval and the size of pores vacated between the carbon nanotubes by a scanning electron microscope photograph (X100,000) enlarged in Fig.
Fig. 10 shows the diameter of the carbon nanotubes by a scanning electron microscope photograph (X200,000) enlarged in Fig.
FIG. 11 is a graph showing the relationship between sulfur and self-assembled carbon nanotube agglomerates in a ratio of 6: 4, in which sulfur is introduced into the agglomerate, It is a photograph (X10,000).
FIG. 12 is a scanning electron microscope photograph (X30,000) of FIG. 11 further enlarged.
13 is a thermogravimetric analysis diagram of a composite electrode active material in which aggregates of sulfur and self-assembled carbon nanotubes are formed at ratios of 6: 4, 7: 3, and 8: 2, respectively, in one embodiment of the present invention.
FIG. 14 is a graph showing the state of a composite electrode active material in which sulfur is introduced into an aggregate in a composite electrode active material in which sulfur and self-assembled carbon nanotube aggregates are mixed at a ratio of 7: 3, respectively (X10,000). ≪ / RTI >
Fig. 15 is a scanning electron microscope photograph (X50,000) showing a further enlarged view of Fig.
FIG. 16 is a transmission electron microscope photograph of a carbon nanotube aggregate into which sulfur is self-assembled.
17 is a photograph showing the components of the respective elements in a transmission electron microscope and showing a state in which the components of sulfur (S) are uniformly distributed in the carbon nanotubes (C).
18 is a graph showing the state of a composite electrode active material in which sulfur is permeated into an aggregate in a composite electrode active material in which sulfur and self-assembled carbon nanotube agglomerates are mixed at a ratio of 8: 2, (X30,000). ≪ / RTI >
Fig. 19 is a scanning electron microscope photograph (X50,000) showing a further enlarged view of Fig.
FIG. 20 is a scanning electron micrograph (X300) in which sulfur and self-assembled carbon nanotube agglomerates are mixed at a ratio of 9: 1, respectively, in an embodiment of the present invention.
21 is a graph showing changes in voltage with respect to charging and discharging capacity of a lithium-sulfur battery with respect to a self-assembled carbon nanotube aggregate-sulfur composite electrode active material.
22 is a graph showing changes in charging and discharging capacities with respect to the number of cycles of a lithium-sulfur battery with respect to a self-assembled carbon nanotube aggregate-sulfur composite electrode active material.

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

1 is a flow chart showing a method of manufacturing a lithium sulfur battery in an embodiment of the present invention.

The lithium sulfur battery according to the present invention may include an electrode active material composed of agglomerates in which the self-assembled carbon nanotubes are formed in a network form, and sulfur which penetrates into the agglomerates. Here, the aggregate may have any one of spherical, elliptical, and crushed spherical and elliptical shapes, and the carbon nanotube may be any one of a single wall, a double wall, and a multiwall carbon nanotube. have.

In order to manufacture such a lithium sulfur battery, a carbon nanotube dispersion solution, which is an electrode material, is first sprayed on an electrode of a conductive current collector to self-assemble the carbon nanotube dispersion solution on the electrode (conductive substrate) of the conductive current collector, (Network) type carbon nanotube aggregates are formed (110). Then, in order to disperse the carbon nanotubes by heating the carbon nanotube electrode agglomerates self-assembled in the form of a network, an aggregate composed of pure carbon nanotubes is obtained by removing the dispersant and various organic substances contained in the carbon nanotube dispersion solution (120 ).

Thereafter, aggregates of pure carbon nanotubes are separated and collected from a conductive current collector used for electrospinning, and then put into a sulfur dispersion solution to uniformly disperse carbon nanotube aggregates and sulfur particles. Then, the carbon nanotube aggregate is heated by sulfur to dissolve into the liquid carbon nanotube aggregate to form an electrode active material (130).

The lithium sulfur battery according to the present invention can be manufactured through a process of coating the electrode active material formed through the above process on the current collector and a process of pressing the electrode active material (140).

FIG. 2 is a schematic view showing a manufacturing process of carbon nanotube agglomerates using an electrospinning method according to an embodiment of the present invention. FIG. 3 is a schematic view of a carbon nanotube aggregate according to an embodiment of the present invention, A carbon nanotube agglomerate, and a carbon nanotube aggregate. Hereinafter, the process for producing the electrode active material according to the present invention will be described in more detail with reference to FIGS. 2 and 3. FIG.

In order to produce the lithium sulfur battery according to the present invention, an electrode active material must first be prepared. For this purpose, the carbon nanotube dispersion solution 210, which is an electrode material, can be mounted on the electric spraying apparatus and sprayed. 2, the electrospinning apparatus includes a metering pump 220 for quantitatively injecting the carbon nanotube dispersion solution 210, a jet nozzle 230 connected to the metering pump 220, a high voltage generator 240 , A grounded conductive current collector electrode 250, and the like.

The carbon nanotube aggregate 260 formed by self-assembling on the electrode 250 of the conductive current collector as it is sprayed by the electric spraying device may have a size range of 100 nm to 10 μm. The diameter of the carbon nanotubes constituting the self-assembled carbon nanotube aggregate 260 may range from 1 nm to 20 nm, and the length may range from several to several hundreds of micrometers. Here, self-assembly means that nanoparticles and carbon nanotubes aggregate themselves to form an aggregate in order to minimize surface energy.

The self-assembled carbon nanotube aggregates 260 may be networked and connected to each other like a network as shown in FIG. 2, and may be agglomerated into a porous structure. At this time, the spacing between the carbon nanotubes and the size of the pores seen in the porous aggregate structure may have a size of several nanometers to several hundred nanometers (for example, 0.1 nanometer to 900 nanometers). The porous structure having such pores can not only provide a capillary effect to allow liquid sulfur to permeate, but also allows a liquid electrolyte to permeate smoothly during an electrochemical reaction, thereby realizing a high-output lithium sulfur battery with high ion conductivity do.

Meanwhile, in order to disperse the carbon nanotubes in the self-assembled carbon nanotube aggregate 260 through the electric spraying, and to remove the dispersant and various organic substances that have entered the carbon nanotube dispersion solution 210, the self-assembled carbon nanotubes The aggregate (260) can be heated in a heating furnace to obtain aggregates composed of pure carbon nanotubes. At this time, the self-assembled carbon nanotube aggregate 260 may be heated at a temperature between 300 ° C. and 500 ° C. for 10 minutes to 1 hour.

The carbon nanotube agglomerates obtained through such a process can be separated and collected from the conductive current collector used for electrospinning, and then mixed with the sulfur at a certain ratio in the solvent. At this time, the carbon nanotube aggregates and the sulfur may be mixed at predetermined ratios, for example, each ratio may be 1: 9 to 5: 5. As the solvent, any one selected from the group consisting of ethanol, methanol, propanol, butanol, IPA, dimethylformamide (DMF), acetone, tetrahydrofuran, toluene, water, , But the present invention is not limited thereto.

Thereafter, ultrasonic dispersion may be mechanically performed for 10 minutes to 1 hour in order to uniformly disperse the carbon nanotube aggregates and sulfur particles added to the solvent. At this time, it is preferable that the ultrasonic dispersing device is used by adjusting the time so that aggregated carbon nanotubes are not loosened. Further, an additive may be added to the dispersion solution for smooth dispersion. Examples of the additive include acetic acid, stearic acid, adipic acid, ethoxyacetic acid, benzoic acid, nitric acid, and cetyltrimethyl ammonium bromide (CTAB).

For example, the carbon nanotube agglomerates may be impregnated with sulfur in the heating furnace 310 as shown in Fig. At this time, the heating furnace 310 is heated at 100 ° C to 200 ° C, which is a temperature at which sulfur can be dissolved in a liquid state, for 1 hour to 10 hours so that the sulfur can sufficiently penetrate into the carbon nanotube aggregates. Here, the main principle that sulfur enters into the aggregate of carbon nanotubes is that the aggregate is composed of porous nano pores by the capillary phenomenon, so that the sulfur dissolved in the liquid state penetrates into the aggregate. Glass, quartz, alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ) crucibles and the like which can withstand mechanical and chemical conditions even at high temperatures can be used as the crucible (container) There is no restriction on a specific container.

The carbon nanotube agglomerate-sulfur composite electrode active material produced through the above process has excellent conductivity characteristics because the carbon nanotubes penetrate into the interior of the carbon nanotube agglomerate-sulfur composite electrode active material and surround the sulfur particles, And the composite electrode active material having high mechanical, thermal, electrical and chemical safety is constituted by carbon nanotubes.

In order to evaluate the characteristics of the lithium sulfur battery, an organic binder and conductive carbon were added to the carbon nanotube aggregate-sulfur composite electrode active material according to the present invention to form an organic solvent, n-methyl-2-pyrrolidone (NMP) The slurry state can be made together. At this time, the organic solvent does not limit the specific substance unless it causes a chemical reaction with the carbon nanotube aggregate-sulfur composite electrode active material.

The mixing ratio may be selected in the range of 60 to 95 wt%, 5 to 20 wt%, and 5 to 20 wt%, respectively, relative to the electrode active material, the conductive carbon, and the organic binder. If the electrochemical characteristics of the active material can be evaluated, .

The organic binder polymer may be at least one selected from the group consisting of PVDF, styrene-butadiene rubber (SBR), PTEE, polyolefin, polyimide, polyure- You can use one. The conductive carbon may be at least one selected from the group consisting of carbon black, acetylene black, and ketjen black.

For the slurry casting of the present invention, casting is carried out in the form of a film on a charge collector used as an electrode using a casting tool. A doctor blade or a bar coater may be used as the casting tool that can be used at this time. If the casting tool is a tool capable of casting the slurry, a specific tool is not limited.

The lithium sulfur battery of the present invention may include a charge collector and an electrode formed on the charge collector using the composite electrode active material of the present invention. The charge collector may include at least one selected from the group consisting of nickel (Ni), stainless steel (SUS), aluminum (Al), molybdenum (Mo), chromium (Cr), copper (Cu), and titanium Can be used.

4 is a conceptual view of an electrode active material layer in which a carbon nanotube aggregate-sulfur composite electrode active material and a conductive carbon black organic binder are formed in the form of a thin layer in an embodiment of the present invention.

4, since the electrode active material is mixed with the conductive carbon 420 and the organic binder 430, the charge transfer ability between the carbon nanotube aggregates 410 can be improved and high output characteristics can be improved. The adhesion property between the charge collector 440 used as the electrode active material and the electrode active material is improved, so that the mechanical stability, durability, and reliability of the battery can be improved.

The organic solvent added to make the slurry state after the casting can be dried by heating at a temperature of 50 to 120 캜 for 6 to 24 hours. At this time, after drying for about 1 to 3 hours in the drying time, the carbon nanotube agglomerate-sulfur composite electrode active material can be compressed. Such a pressing process can increase the filling density and reduce the contact resistance between the sulfur particles and the sulfur particles and the carbon nanotubes.

The method for manufacturing and evaluating characteristics of a battery according to the present invention is the same as the method for manufacturing and evaluating characteristics of a general secondary battery. In general, the secondary battery is composed of an electric charge collector used as an electrode, an electrode active material (including composite electrode active material), an electrolyte, a separator, a case, and a terminal. The components used in the lithium sulfur battery according to the present invention, May be the same as other components of a general secondary battery. For the electrolyte, an electrolyte salt that may be used in the lithium sulfur battery LiTFSI, LiPF6, LiTF, LiCF ₃ SO _3, LiClO _4, can be used to mix at least one or two or more mixture selected from the group consisting of LiBF ₄ at a constant rate have. As the electrolyte solvent, at least one or at least two compounds selected from the group consisting of TEGDME, TEGDME-DIOX, DME, DIOX, DME-DIOX, EC-EMC, EC-DMC, DOL-DMC, ethyl methyl sulphone and TG- Can be mixed at a certain ratio. At this time, the electrolyte is not limited to a specific substance as long as it is an electrolyte capable of causing an electrochemical reaction with the carbon nanotube aggregate-sulfur composite electrode active material of the present invention.

Hereinafter, a method for producing the electrode active material according to the present invention will be described in more detail. As shown in the schematic view of the manufacturing process of FIGS. 2 and 3, the electrode active material manufacturing method according to the present invention comprises the steps of: (a) forming a carbon nanotube aggregate by self-assembling a carbon nanotube dispersion solution, (B) heating the self-assembled carbon nanotube electrode agglomerates in a heating furnace to remove the dispersant and other organic substances, (c) subjecting the self-assembled carbon nanotube electrode agglomerates to self-assembled carbon nanotubes Collecting the aggregates; (d) dispersing the carbon nanotubes and sulfur mixed in the solution in a predetermined ratio to disperse them in the solution; and (e) heating the carbon nanotubes And penetrating into the agglomerate to form a composite electrode active material.

In addition to sulfur (S) used in a lithium sulfur battery, the composite electrode active material may be a crystalline or amorphous material composed of Si, Sn, Ti, Cu, Al, Ce and La constituent elements, which are electrode active materials capable of dissolving in a liquid state by applying heat Structure, or may contain two or more particle mixed phases. At this time, it is preferable that the liquid phase can be formed at a temperature of 500 DEG C or less, which is a temperature at which the carbon nanotubes are not heated or removed by heat.

In the electrospray process, the conductive current collector may include at least one selected from the group consisting of Pt, Au, Pd, Ir, Ag, Ru, Ni, , consisting of aluminum (Al), molybdenum (Mo), chromium (Cr), copper (Cu), titanium (Ti), tungsten (W), ITO (in doped SnO 2) and FTO (F doped SnO ₂₎ Any one selected from the group can be used. It is also preferable to use a carbon nanotube dispersion solution which is dispersed in a solvent containing 50% or more of a solvent having a boiling point (volatility point) of 80 ° C or lower so that the carbon nanotubes can smoothly aggregate in the electric spraying process .

In the method for producing the composite electrode material of the present invention, the carbon nanotube dispersion solution, which is an electrode material, may have a carbon nanotube content of 0.5 to 20 wt% based on the total solution. At this time, the carbon nanotubes are not limited to single wall, double wall, and multiwall carbon nanotubes. The size of the self-assembled carbon nanotube agglomerates obtained by electrospraying the carbon nanotube dispersion solution is made 100 nm to 10 μm.

Hereinafter, the method for producing the composite electrode active material of the present invention will be described in detail as follows.

By electrospray Carbon nanotubes  Step of preparing electrode material

First, a dispersion solution in which carbon nanotubes are uniformly dispersed is prepared. Depending on the passage of time or the change in temperature and humidity, a uniform dispersion solution with a dispersing agent may agglomerate to some extent and sink into the solution. Generally, aggregated carbon nanotubes are present in solution in the form of agglomerates having a size of several hundred nanometers to several micrometers. This coagulation phenomenon is a direct cause of the nozzle clogging during the electro-spraying process, so that the coagulated powder should not exist. These agglomerates can be easily reconstituted into a homogeneous dispersion solution through an ultrasonic dispersion process. At this time, the time for ultrasonic dispersion is sufficiently added for about 30 minutes to 2 hours to obtain a homogeneous dispersion solution. The carbon nanotube dispersion solution may be composed of at least one dispersion solution selected from a single wall, a double wall, and a multiwall carbon nanotube.

Examples of the solvent constituting the dispersion include ethanol, methanol, propanol, butanol, isopropyl alcohol (IPA), dimethylformamide (DMF), acetone, tetrahydrofuran, toluene, Can be selected. Preferably a solvent having a volatilization temperature of 80 DEG C or lower can be selected.

The carbon nanotube dispersion solution may be injected into the electric spraying apparatus as shown in FIG. The electrospray device may consist of a spray nozzle connected to a metering pump capable of quantitatively introducing the dispersion, a high voltage generator, a grounded conductive substrate, and the like.

In this case, first, the conductive current collector is placed on the grounded conductive substrate. At this time, a grounded conductive substrate is used as a cathode, and a spray nozzle having a pump whose amount of discharge per hour is adjusted is used as an anode. A voltage of 8 to 30 kV is applied and the solution discharge rate is adjusted to 10 to 300 μl / min and the solution is sprayed on the conductive current collector.

When the carbon nanotube dispersion solution is sprayed under a constant electric field, carbon nanotubes discharged from the spray nozzle are observed to be aggregated between particles to minimize surface energy. Since the shape with the lowest surface energy is spherical, when the conditions such as the hole size of the injection nozzle, the discharge speed, the concentration of the nanoparticles of the dispersion solution, the spray distance, and the like are optimized, aggregates having an average particle size of 100 nm to 10 μm are formed. In some cases, it may be formed into an elliptical shape rather than a spherical shape, and spherical and elliptical agglomerates of a distorted shape may be formed because the aggregate itself has a very high porosity.

The sizes of self-assembled spherical and crushed spherical agglomerates have a size range of 100 nm to 10,000 nm, the sizes of self-assembled elliptical and crushed elliptical agglomerates have a size range of 100 nm to 10,000 nm, oval and squal The elliptical agglomerates of the form may have a ratio of the major axis to the minor axis in the range of 1 to 5 or less. In the present invention, aggregates formed by self-assembly of carbon nanotubes have many porous pores and are not restricted to specific shapes provided that they maintain a tightly aggregated shape.

The volatilization rate of the solvent is also very important for the formation of agglomerates after electrospray. (CH ₃ ) ₂ CHOH, 82 ° C), ethanol (CH ₃ CH ₂ -OH, 78 ° C), methanol (CH ₃ -OH, 68 ° C), tetrahydrofuran , 66 ° C), acetone (CH ₃ COCH ₃ , 56.2 ° C), and the dispersion solution sufficiently containing the solvent can be electrospun to form self-assembled aggregates.

Particularly, in the case of using highly volatile ethanol, the nanoparticles are sprayed and the solvent is volatilized at the injection nozzle where the spraying is performed. Therefore, in order to minimize the surface area of the charged particles, spherical, elliptical, At least one nanoparticle aggregate selected from the shape of the nanoparticles. On the other hand, when water having low volatility is used as a solvent, the solvent is not volatilized well until the carbon nanotubes move on the conductive current collector after being sprayed from the injection nozzle. As a result, since water is evaporated while reaching the conductive current collector, a uniform aggregate is not formed well, and the coating is carried out on the conductive current collector in the form of a non-uniform thin layer.

On the other hand, the shape of the agglomerate can be changed depending on the hole size and discharge speed of the spray nozzle through which the submerged solution is discharged at the time of electric spraying. If the discharge speed is excessively high, spherical agglomerates are not formed well.

The self-assembled aggregate particles are preferably spherical in shape and have an average particle size in the range of 100 nm to 10 탆. The particle diameter of the agglomerate particles can be controlled by varying the content of the nanoparticles in the dispersion solution during the electrospray process. When a 1 wt% dispersion solution is used, the size of the self-assembled aggregate particles is as small as 600 nm or less, and when more than 3 wt% of the dispersion solution is used, self-assembled aggregate particles having a size of 1 μm or more can be distributed. The electrode material carbon nanotubes in the whole solution are preferably prepared in a weight ratio of 0.5 to 20 wt% for the electric spraying of the carbon nanotubes. If the carbon nanotubes are present in a large amount in the solution, the size of the aggregate may increase during the spraying process. Since there is a limit of solubility in which carbon nanotubes can be uniformly dispersed, the size of the aggregate can not be infinitely increased, and the size of the self-assembled aggregate is preferably selected within the range of 500 nm to 5 mu m. Aggregates are mostly distributed in spherical shape. It may be formed in an elliptical shape in accordance with the electric spraying conditions, and the shape of the self-assembled secondary aggregate is not particularly limited. However, it is preferable to have a spherical aggregate for high filling conditions.

Carbon nanotubes  Residues in aggregates Dispersant  And removing the organic material

The self-assembled carbon nanotube aggregates after electrospray will contain dispersants and various unnecessary organic materials. These dispersants and organic materials are additives that are added so that the carbon nanotubes are well dispersed in the solvent. However, if the dispersing agent and the organic materials are not removed from the self-assembled carbon nanotube aggregates, the porosity of the agglomerate is reduced. In addition, if electrochemical oxidation and reduction reactions occur later, a side reaction with the electrolyte is caused, . Accordingly, the dispersant and the organic materials can be evaporated as heat using a heating furnace or burned by reaction with oxygen. The heat treatment can be carried out at a temperature range of 300 to 500 DEG C for 10 minutes to 1 hour. If the heat treatment temperature exceeds 500 캜, some of the carbon nanotubes may be removed by pyrolysis to deteriorate the network characteristics between the carbon nanotubes, and consequently, the electrical conduction characteristics may be deteriorated, so that the heat treatment temperature is not excessively increased desirable. In addition, when the heat treatment temperature is as low as 300 캜 or less, the dispersant and organic materials may not be completely removed.

Porous Carbon nanotubes  Collecting aggregates

The pure carbon nanotube aggregates obtained through the heat treatment in the previous step are separated and collected from the conductive current collector used for electrospinning using a sharp blade or the like. This is because in the next step heat treatment with sulfur, the plate of the conductive current collector may cause an unwanted chemical reaction with sulfur.

Adding the agglomerate and the sulfur at a predetermined ratio

The self-assembled carbon nanotubes collected in the previous step are mixed with sulfur at a predetermined ratio into the solvent. At this time, the solvent should be selected so that the sulfur does not dissolve, so as to prevent the loss of sulfur which can be eliminated by the evaporation of the solvent during the heat treatment in the next step. The ratio of self-assembled carbon nanotube aggregates to sulfur can be mixed in a ratio of 1: 9 to 5: 5, respectively. The solvent may be selected from the group consisting of ethanol, methanol, propanol, butanol, IPA, dimethylformamide (DMF), acetone, tetrahydrofuran, toluene, water, There is no restriction on the solvent. Next, the self-assembled carbon nanotube aggregates and sulfur are uniformly dispersed in the solvent. When uniform dispersion is not achieved, a large amount of sulfur is injected into the specific region or less. This leads to a weight variation of the electrode active material during the manufacture of the battery and makes it impossible to perform an accurate electrochemical analysis.

The dispersing agent uniformly disperses the carbon nanotube aggregates and the sulfur particles in the solvent within a time range of 10 minutes to 1 hour by using an ultrasonic dispersing machine. At this time, it is preferable that the use of the ultrasonic dispersing machine is carried out within 30 minutes so that aggregated carbon nanotubes are not loosened.

Porous sulfur Carbon nanotubes  Step of infiltration into the aggregate

The solvent is removed by heat treatment of the carbon nanotube agglomerate and sulfur mixed at a predetermined ratio in the previous step, and the sulfur penetrates into the carbon nanotube agglomerate (see FIG. 3). The melting point of sulfur is 115.21 ° C, which can vary depending on particle size, surface contamination and pressure. At this time, the sulfur injected into the carbon nanotube aggregate having a complex mesh form is in an increased state of internal pressure. Therefore, the temperature of the heating furnace has a temperature range of 100 ° C to 200 ° C, and the liquefied sulfur can sufficiently penetrate into the inside of the agglomerate in a time of 1 hour to 10 hours. At this time, if the substrate is heated to a high temperature of 200 DEG C or more or subjected to a heat treatment for a long period of time of 12 hours or more, sulfur may be vaporized, resulting in loss of sulfur. The porous carbon nanotube aggregates prepared in the previous step have pores of several nanometers to several hundreds of nanometers in size. Therefore, when it is present in the form of liquid sulfur, the sulfur is infiltrated into the aggregate by the capillary phenomenon.

The heat treatment is carried out in an atmosphere of an inert gas to suppress the reaction between sulfur and oxygen as much as possible. As the inert gas, any one selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn) can be selected. The heat treatment is preferably carried out at a gas flow rate of 5 L / min or less in a heating furnace having a volume of 5 L, and if the reaction is not performed between sulfur and oxygen, the volume of the heating furnace and the gas flow It is not subject to restrictions.

The sulfur and the self-assembled carbon nanotube agglomerates may be added in a ratio of 5: 5 to 9: 1, respectively. If the self-assembled carbon nanotube agglomerate can be injected with 100% sulfur, There is no specific limitation on the mixing ratio of the carbon nanotube aggregates.

The carbon nanotube agglomerate-sulfur composite electrode active material enhances the electrical conduction characteristic of the electrically non-conductive sulfur by surrounding the sulfur particles penetrated into the carbon nanotube having excellent conductivity characteristics. At this time, when the porosity of the carbon nanotube agglomerates is uniform, the conductive carbon nanotubes are interposed between the sulfur particles with uniform intervals and are connected to each other to form a network, so that a composite electrode active material having a high output density can be manufactured . On the other hand, the internal sulfur is stably present mechanically, thermally, electrically, and chemically by the agglomerates of carbon nanotubes, thereby greatly improving lifetime characteristics and safety of the lithium sulfur battery. In addition, since the amount of polysulfide that can be dissolved in the electrolyte solution during the electrochemical reaction can be reduced, the capacity reduction of the battery can be greatly suppressed.

Hereinafter, the present invention will be described in more detail with reference to various examples. However, the following examples are presented for the purpose of more clear understanding of the present invention, but the present invention is not limited thereto.

1st Example : Self-assembled Carbon nanotubes  Agglomerate-sulfur in a ratio of 4: 6 Complex Electrode active material  Produce

The uniformly dispersed carbon nanotube dispersion solution was selected, and the carbon nanotube dispersion solution was a solution in which 3 wt% of carbon nanotubes were dispersed in ethanol. At this time, the physical properties of the carbon nanotube dispersion solution were a film having a thickness of 1 m, a resistance value of <30? / Sq and a viscosity of <300 cps. The dispersed carbon nanotube solution was again redispersed for 30 minutes using an ultrasonic disperser. The dispersion solution prepared for preparing the electrode material was transferred to a syringe and mounted on an electric spraying machine. As shown in Fig. At this time, the voltage used for electric injection of the carbon nanotube was 17 kV, the needle size was 23GA, the flow rate was 18 μ / min, and the distance between the tip and the substrate was 12 cm. A stainless steel (SUS) substrate was used as the conductive collector substrate.

FIG. 5 is a scanning electron micrograph (X2,000) of self-assembled carbon nanotube aggregates containing a binder and an organic material obtained by electrospray in one embodiment of the present invention, It is a scanning electron microscope photograph (X17,000).

Referring to FIG. 5, it can be seen that round and elliptical agglomerates of spherical, elliptical (nearly spherical) and squashed forms are well formed, and that agglomerates have a size of 3 to 7 μm, . As described above, the size of the aggregate of the porous carbon nanotubes can be easily controlled.

Referring to FIG. 6, it can be seen that carbon nanotubes having a diameter of 5 nm to 20 nm and a length of several to several hundreds of micrometers are well formed in a spherical shape.

In the first embodiment, the carbon nanotube dispersion solution is discharged from the injection nozzle during the electric spraying process, and ethanol is volatilized. In order to reduce the surface energy, the carbon nanotubes are self-assembled in a spherical or elliptical shape, It happens. At this time, the agglomerated carbon nanotube agglomerates are accelerated in speed as they approach the conductive current collector. When the agglomerate having a large degree of porosity inside is contacted with the conductive current collector, the aggregated carbon nanotube agglomerates are squeezed by a physical force or impact, An elliptical aggregate shape may be formed. Further, in the first embodiment, if the carbon nanotube dispersion solution is sprayed by using one injection nozzle, if the amount of the spray nozzle is increased to several tens to several thousands and the area of the conductive current collector is increased accordingly, It is possible to mass-produce agglomerated structures through possible continuous processes. Also, in the experiment conducted in the first embodiment, since the aggregate yield is close to 100% without loss of the carbon nanotube, it can be a process capable of achieving a high yield even under a mass production system.

As shown in FIGS. 5 and 6, the self-assembled carbon nanotube agglomerates subjected to the electro-spraying process include dispersants and other undesirable organic materials used for smooth dispersion of carbon nanotubes on the surface. The undesired organic substances on the surface cause side reactions with the electrolyte due to the oxidation and reduction action in the electrochemical reaction of the electrode, which can directly cause the performance of the battery to be reduced. Therefore, the dispersing agent and the organic material on the surface were evaporated or burned out through the heat treatment process.

7 is a scanning electron micrograph (X8,000) of a self-assembled carbon nanotube aggregate composed of only pure carbon nanotubes obtained by removing a dispersant and an organic material from a heating furnace in an embodiment of the present invention, 7 is an enlarged scanning electron microscope photograph (X15,000).

In the first embodiment, the heat treatment was performed at 400 ° C. for 30 minutes using a heating furnace. Referring to the scanning electron microscope (X 8,000) image shown in FIG. 7, the binder and the organic material on the surface were cleanly removed Can be confirmed. If the temperature of the heat treatment exceeds 500 ° C., some of the carbon nanotubes may be removed by pyrolysis. If the temperature is lower than 300 ° C., the dispersant and organic materials may not be completely removed. Therefore, it is preferable to conduct the heat treatment in the temperature range of 300 ° C and 500 ° C.

Meanwhile, referring to FIG. 8, it can be seen that the dispersant and the organic materials are cleanly removed from the surface of the carbon nanotube existing inside the small pores.

FIG. 9 is a scanning electron microscope (X100,000) enlarged view of FIG. 8 showing the spacing and size of vacancies between carbon nanotubes, and FIG. 10 is a scanning electron micrograph (X200, 000) shows the diameter of the carbon nanotube.

Referring to FIG. 9, it can be seen that the distance between the locally agglomerated carbon nanotubes is several to several hundred nanometers. That is, it can be seen that a porous electrode material having a uniform pore size is well formed. Such a uniform pore distribution can provide a uniform and stable current value during the electrochemical reaction by allowing the sulfur to uniformly permeate and keeping the interval between the electrodes constant.

On the other hand, FIG. 10 shows the diameter of aggregated carbon nanotubes self-assembled with an enlarged scanning electron microscope photograph (X 200,000) of FIG. 9, and as shown in FIG. 7, an image in which a dispersant and residual organics were completely removed It shows more clearly. Also, it can be confirmed once again that the pores are locally uniform in size as shown in FIG.

Thereafter, the self-assembled carbon nanotube agglomerates subjected to heat treatment were separated and collected from the conductive collector electrodes used in the electrospray process. This is to remove unwanted chemical reactions between the sulfur and the conductive collector in the subsequent process. If the conductive current collector used in the electrospray process is used as it is, the sulfur may be applied to the surface by reaction with sulfur, which may deteriorate the life characteristics and stability of the battery in a later battery reaction.

The collected self-assembled carbon nanotube agglomerates were mixed with sulfuric solvent at a ratio of 6: 4 (sulfur 0.15 g: carbon nanotube agglomerate 0.1 g) to an ethanol solvent and dispersed in an ultrasonic disperser for 30 minutes. Then, a solution in which the carbon nanotubes and the sulfur particles are uniformly dispersed was placed in a heating furnace, and the sulfur was infiltrated into the carbon nanotube aggregates. The heat treatment was carried out at 155 ° C for 6 hours at a temperature at which the liquid sulfur was formed after the heat treatment at 90 ° C for 1 hour at which the ethanol could be evaporated. At this time, argon (Ar) gas, which is an inert gas, was injected into the heating furnace so that the reaction between sulfur and oxygen was suppressed to the utmost, and heat treatment was carried out with a gas flow of 2 L / min in a 3 L heating furnace.

11 is a scanning electron micrograph showing a composite electrode active material in which sulfur and self-assembled carbon nanotube agglomerates are mixed at a ratio of 6: 4, respectively, (X10,000), and Fig. 12 is a scanning electron microscope photograph (X30,000) enlarged in Fig.

Referring to FIG. 11, it can be seen that the sulfur is permeated into the self-assembled carbon nanotube aggregates. As can be seen from the agglomerate shape of FIG. 11, it can be seen that sulfur was not present externally, but all entered the inside of the carbon nanotube aggregates.

Referring to FIG. 12, it can be seen that sulfur is reliably present in the self-assembled carbon nanotube aggregates. Since the sulfur is surrounded by the carbon nanotubes having excellent electrical conductivity at a certain interval, the electric conductivity of the non-conductive sulfur can be improved by the constant and stable current transfer characteristics of the carbon nanotubes, have. In addition, since sulfur exists coexisting in the carbon nanotube agglomerate, a composite electrode active material which is mechanically, thermally, electrically and chemically stable can be produced.

13 is a thermogravimetric analysis diagram of a composite electrode active material in which aggregates of sulfur and self-assembled carbon nanotubes are formed at ratios of 6: 4, 7: 3, and 8: 2, respectively, in one embodiment of the present invention.

Thermogravimetric analysis was performed to confirm that the ratio of the carbon nanotube agglomerate and the sulfur constituting the mixture was in good agreement with the initial ratio. Referring to FIG. 13, it can be seen that aggregates of sulfur and carbon nanotubes are well mixed at a ratio of 6: 4.

Sn, Ti, Cu, Al, Ce, and La, which are electrode active materials capable of dissolving in a liquid state by applying heat in addition to sulfur (S) used for a lithium sulfur battery in the electrode active material particles. An alloy having an amorphous structure, or a mixed phase of two or more particles.

Second Example : Self-assembled Carbon nanotubes  Aggregate-sulfur complexed at a ratio of 3: 7 Electrode active material  Produce

Carbon nanotube agglomerates were prepared by self-assembling the carbon nanotube solution by the same method as in Example 1, and then the dispersant and the organic solvent were removed through a heat treatment process so that the same carbon nanotube agglomerates as in FIGS. 5 to 8 . Thereafter, sulfur and self-assembled carbon nanotube agglomerates were mixed at a ratio of 7: 3 (sulfur: 0.23 g: carbon nanotube agglomerates: 0.1 g) and heat treated. The atmosphere of the heating furnace was the same as in Example 2.

FIG. 14 is a graph showing a composite electrode active material in which sulfur and carbon nanotube aggregates are mixed in a ratio of 7: 3, respectively, according to an embodiment of the present invention. (X10,000), and Fig. 15 is a scanning electron micrograph (X50,000) of Fig.

Referring to FIG. 14, it can be confirmed that sulfur is completely permeated into the aggregate. Referring to FIG. 15, it can be seen that the sulfur impregnated inside is certainly present. The second embodiment shows the possibility of further improving the capacity characteristics per unit volume of the battery by further increasing the amount of sulfur as the electrode active material while maintaining the same characteristics of the composite electrode active material as in the first embodiment.

17 is a photograph showing the components of the respective elements in a transmission electron microscope. Fig. 17 is a photograph showing the composition of sulfur (S) in the carbon nanotube (C). Fig. 16 is a photograph of a transmission electron microscope In which the components are uniformly distributed.

FIG. 16 is a transmission electron microscope photograph showing directly that the sulfur penetrates into the aggregate of carbon nanotubes. In addition, FIG. 17 directly shows that the penetration of sulfur is uniformly distributed by a transmission electron microscope. Thereafter, the electrochemical characteristics proceeded under the same conditions as in the first embodiment.

Third Example : Self-assembled Carbon nanotubes  Agglomerate-sulfur in a ratio of 2: 8 Complex Electrode active material  Produce

Carbon nanotube agglomerates self-assembled by electrospraying the carbon nanotube solution in the same manner as in the first and second embodiments, and then the dispersant and the organic solvent were removed through a heat treatment process, Carbon nanotube agglomerates were obtained. Thereafter, sulfur and self-assembled carbon nanotube agglomerates were mixed at a ratio of 8: 2 (sulfur: 0.4 g: carbon nanotube agglomerates: 0.1 g) and heat treatment was performed. The atmosphere of the heating furnace was changed to the first and second embodiments .

18 is a graph showing the state of a composite electrode active material in which sulfur is permeated into an aggregate in a composite electrode active material in which sulfur and self-assembled carbon nanotube agglomerates are mixed at a ratio of 8: 2, (X30,000), and FIG. 19 is a scanning electron microscope photograph (X50,000) showing a further enlarged view of FIG.

Referring to FIG. 18, it can be confirmed that sulfur is completely penetrated into the aggregate. Also, referring to FIG. 19, it can be seen that the sulfur permeated inside is surely present.

Third Embodiment In addition, by maintaining the same characteristics of the composite electrode active material as in the first and second embodiments and increasing the amount of sulfur as the electrode active material in comparison with the second embodiment, the capacity characteristics per unit volume of the battery can be further improved It can be improved. Thereafter, the electrochemical characteristics were the same as in the first and second embodiments.

Comparative Example : Self-assembled Carbon nanotubes  Agglomerate-sulfur is added at a ratio of 1: 9 to over-add sulfur Electrode active material  Produce

In the comparative example, the amount of sulfur added was greatly increased for comparison with the first to third embodiments, and the experiment was conducted.

Carbon nanotube agglomerates self-assembled by electrospraying the carbon nanotube dispersion solution were prepared in the same manner as in the first to third embodiments, and then the dispersant and the organic solvent were removed through a heat treatment process, Nanotube agglomerates were obtained. Thereafter, sulfur and carbon nanotubes were mixed at a ratio of 9: 1 (sulfur 0.9g: carbon nanotube aggregates 0.1g), and sulfur was over-added to perform heat treatment. The atmosphere of the heating furnace is the same as in the first to third embodiments.

FIG. 20 is a scanning electron micrograph (X300) in which sulfur and self-assembled carbon nanotube agglomerates are mixed at a ratio of 9: 1, respectively, in an embodiment of the present invention.

Referring to FIG. 20, when the sulfur is maintained at 9: 1 wt% with respect to the carbon nanotubes, the structure of the composite electrode active material collapses due to the sulfur particles formed on the outside. The sulfur remaining out of the reactor causes the cohesion between the structures in a liquid state by the heat treatment, and the external sulfur causes the elution into the electrolyte during the electrochemical reaction. Therefore, the lifetime characteristics of the battery can be largely lowered, and an excessive amount of eluted polysulfide may cause a reaction on the surface of the lithium metal, which is the anode, resulting in a serious problem of stability.

Analysis example : Self-assembled Carbon nanotubes  Aggregate-sulfur complex The electrode active material  The lithium- Of sulfur cells  Character rating

The composite electrode active material was prepared by impregnating sulfur into the self-assembled carbon nanotube aggregates formed on the stainless steel substrate according to the first to third embodiments. In order to confirm the characteristics of the cathode active material in the lithium sulfur battery, Cell (CR2032-type coin cell) structure. In the cell structure, a solution of TEGDME / DIOX (1/1 volume%) in which 0.2 M of LiNO ₃ was dissolved was used as an electrolyte. A metal lithium foil having a purity of 99.99% was used as a reference electrode and a counter electrode, and sulfur and carbon nanotube aggregates of the second embodiment were used as working electrodes in a ratio of 7 (sulfur): 3 (carbon nanotube) Composite electrode active material was used.

Next, the composite electrode active material, the conductive carbon super-p, and the PVDF organic binder were mixed at a ratio of 84: 8: 8 wt%, and then an organic solvent, n-methyl-2-pyrrolidone (NMP) And then the film was formed into a thin film through a tape-casting process, followed by drying at 50 ° C. for 12 hours in an atmospheric state. At this time, after about 2 hours in the drying process, the pressing process was performed using the roll press equipment to increase the packing density of the electrode, and further drying was performed. A polypropylene film was used as a separator to prevent an electrical short between the cathode and the anode. The cell was fabricated in an argon (Ar) atmosphere in a VAC company glove box.

The charge / discharge test device used here was a WBCS3000 model of WonATech Co., Ltd., and the change of voltage under a constant current was examined with MPS (Multi Potentiostat System) which can measure 16 channels by adding 16 boards. The current density used for charging / discharging was measured at 100 cycles based on 0.5 C-rate based on the theoretical capacity (1,675 mAh / g) of sulfur, which is an electrode active material. The cut off voltage was 1.5 to 3.0 V.

FIG. 21 is a graph showing a change in voltage with respect to charging and discharging capacity of a lithium selenium battery with respect to a self-assembled carbon nanotube aggregate-sulfur composite electrode active material, and FIG. 22 is a graph showing changes in voltage with respect to charging and discharging capacity of a self-assembled carbon nanotube aggregate- FIG. 5 is a graph showing changes in charging and discharging capacity with respect to the number of cycles of a lithium sulfur battery with respect to an electrode active material. FIG.

21 is a graph showing changes in voltage with respect to charge and discharge capacities when a composite electrode active material in which sulfur and self-assembled carbon nanotube aggregates are mixed at a ratio of 7: 3 as a cathode active material, as in Example 2, -rate. &lt; / RTI &gt; The voltage leveling zone of the discharge voltage polysulfide is present exchange area for 2.4V and Li ₂ S _6, 2V area at the time of _4,2 days when the Li ₂ S _8, which demonstrate that the reaction of lithium and sulfur takes place for sure Giving.

Fig. 22 shows changes in charge and discharge capacities with respect to the number of cycles under the same conditions as in Fig. The initial charge / discharge capacity was 1150 mAh / g, and the capacity was maintained at 800 mAh / g over 100 cycles. It is shown that most of the lithium sulfide molecules generated during the electrochemical oxidation and reduction reactions exist in the self-assembled carbon nanotube aggregates and are stable in mechanical, thermal, electrical and chemical inside the aggregates. In addition, since the polysulfide that can be dissolved in the electrolytic solution can be reduced, the reduction of the capacity value of the battery can be greatly improved.

Therefore, in order to secure excellent electrical, mechanical, and long-term stability without decreasing the capacity, it can be found that the sulfur introduced into the inside should be configured in the form of a network networked by self-assembled carbon nanotube aggregates.

It has been experimentally proved that a very high capacity battery having a capacity of 800 mAh / g or more can be realized by using a composite electrode active material containing a complexed sulfur contained in a self-assembled agglomerate. These high-capacity batteries include very high utility value as next-generation electric vehicles or large-capacity storage batteries.

As can be seen from the above Examples and Experimental Examples, the kinds of the electrode active material used for obtaining the thin layer vary and are not limited to specific materials.

The self-assembled carbon nanotube aggregate-sulfur composite electrode active material prepared according to the present invention enables electron transfer of electrically non-conductive sulfur to occur rapidly due to excellent electrical conduction properties of carbon nanotubes. Particularly, the sulfur present inside the carbon nanotube aggregates is protected by the carbon nanotubes that are networked to each other, and can be stably present mechanically, thermally, electrically, and chemically. Also, the pore structure between the self-assembled carbon nanotube agglomerates is well developed, so that penetration of the liquid electrolyte rapidly occurs, thereby improving the ion transfer ability of the sulfur ion, which is an ion insulator, to provide an electrode active material of lithium sulfur battery having high output, high capacity and high stability. do. In addition, it has the advantage of being mass-produced at a high yield by self-assembly through the electro-spraying method. Such a composite electrode active material can be applied not only to a lithium sulfur battery but also to various energy storage devices such as a lithium ion battery, a fuel cell, and an electrochemical capacitor.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI &gt; or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

210: Carbon nanotube dispersion solution
220: metering pump
230: injection nozzle
240: High voltage generator
250: Conductive collector electrode
260: Self-assembled carbon nanotube aggregate

Claims (18)

Carbon nanotube agglomerates aggregated into at least one of spherical, elliptical, crushed spherical, and distorted elliptical shapes by self assembling the carbon nanotubes; And
The sludge filled in the inner space of the agglomerated carbon nanotube aggregates
And an electrode active material. The method according to claim 1,
The aggregate of carbon nanotubes may be,
Wherein the plurality of carbon nanotubes are connected to each other in a network form and include a plurality of micropores filled with the sulfur. The method according to claim 1,
The aggregate of carbon nanotubes may be,
When agglomerated into spherical or distorted spheres, agglomerated spheres having a diameter in the range of 100 nanometers to 10,000 nanometers, and agglomerated in elliptical or distorted ellipses, the lengths of the long and short axes of the ellipse are 100 nanometers Wherein the length ratio of the major axis to the minor axis is in a range of more than 1 and less than 5 within a size range of from 1 to 10,000 nanometers. The method according to claim 1,
The carbon nanotubes may include,
Wherein the electrode active material is at least one of a single wall, a double wall, and a multiwall carbon nanotube having a diameter of 1 nanometer to 20 nanometers. The method according to claim 1,
The aggregate of carbon nanotubes may be,
Wherein the plurality of carbon nanotubes are formed in a network structure entangled with each other, and the fine pores between the carbon nanotubes are porous aggregates having a size of 0.1 nanometer to 900 nanometers. The method according to claim 1,
The carbon nanotube agglomerates and the sulfur may be,
Each having a relative weight ratio of 10: 9 to 5: 5. Wherein the electrode active material including an aggregate in which a plurality of carbon nanotubes are self-assembled and a sulfur filled in a space inside the aggregate is composed of a cathode active material. A method of manufacturing a lithium sulfur battery,
Forming a carbon nanotube aggregate self-assembled in a network form by electro-spraying the carbon nanotube dispersion solution;
Heating the self-assembled carbon nanotube aggregate;
Mixing the heated carbon nanotube aggregates with sulfur at a predetermined ratio; And
Wherein the mixed carbon nanotube aggregates and the sulfur are heated so that the sulfur penetrates into the carbon nanotube aggregates to form an electrode active material
&Lt; / RTI &gt; 9. The method of claim 8,
The self-assembled carbon nanotube agglomerates are agglomerated into at least one of spherical, elliptical, crushed spherical, and crushed elliptical shapes,
The step of forming the self-assembled carbon nanotube agglomerates includes:
The carbon nanotube dispersion solution is discharged under a predetermined pressure under an electric field and is sprayed onto the conductive substrate to form a spherical or crushed spherical shape having a spherical diameter ranging from 100 nanometers to 10 micrometers, Or an elliptical or distorted elliptical shape having a length ratio of the major axis to the minor axis within a range of from 1 to 5 within a size range of 100 nm to 10,000 nm, Wherein the carbon nanotube aggregates are formed in the shape of a carbon nanotube aggregate. 9. The method of claim 8,
In the carbon nanotube dispersion solution,
A solvent having a volatilization rate higher than that of water and a boiling point lower than that of water. 9. The method of claim 8,
The carbon nanotube dispersion solution may contain,
Wherein the carbon nanotubes have a weight ratio of 0.5 to 20 wt%. 9. The method of claim 8,
The heated carbon nanotube agglomerate may be,
Wherein the positive electrode is heated in a temperature range of 300 to 500 degrees and comprises a plurality of micropores. 9. The method of claim 8,
Wherein the mixing step comprises:
Wherein the heated carbon nanotube aggregates are separated from the conductive substrate and mixed with the sulfur at a predetermined ratio. 9. The method of claim 8,
Wherein the mixing step comprises:
Wherein the heated carbon nanotube agglomerates are mixed by stirring together with sulfur and a solvent in which the sulfur is insoluble,
The step of forming the electrode active material may include:
After the carbon nanotube aggregates and sulfur mixed in the solvent are dispersed through the ultrasonic dispersing device, the liquefied sulfur is heated into the carbon nanotube agglomerate by heating for 1 hour to 10 hours in the temperature range of 100 to 200 degrees Wherein the electrode active material is formed on the electrode. 15. The method of claim 14,
The electrode active material,
Wherein the heat treatment is performed in an atmosphere of an inert gas to suppress the reaction between sulfur and oxygen as much as possible. 9. The method of claim 8,
The self-assembled carbon nanotube agglomerates and the sulfur,
Are mixed at a ratio of 1: 9 to 5: 5, respectively. 9. The method of claim 8,
Coating the current collector with the electrode active material as a cathode active material of a lithium sulfur battery; And
Wherein the current collector coated with the electrode active material is squeezed
Further comprising the steps of: 18. The method of claim 17,
The ratio of the organic binder of the lithium sulfur battery to the conductive carbon of the lithium sulfur battery, as compared to the electrode active material,
Is selected from the range of 60 to 95 wt%, 5 to 20 wt% and 5 to 20 wt%, respectively.

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