KR20220127985A - Mesoporous carbon-carbon wire structure for anode materials of lithium-ion battery, producing method thereof and lithium secondary battery using it - Google Patents

Abstract

The present invention relates to: a mesoporous carbon-carbon wire structure for anode materials of a lithium secondary battery, which includes a carbon structure containing mesopores with an average pore size of 3-5 nm and a carbon wire grown from the carbon structure containing the mesopores, and has a particle size of 80-800 nm; a method for producing the same; and a lithium secondary battery using the same. The mesoporous carbon-carbon wire structure for anode materials of a lithium secondary battery, according to the present invention, has effects of: forming a spherical carbon nanostructure with developed mesopores by using a silicon dioxide nanostructure, thereby supporting a large number of active materials in the mesopores, which are empty spaces formed therein; interconnecting and supporting carbon particles when the carbon wire grown from mesoporous carbon particles is used to charge and discharge lithium to and from carbon particles; and improving lithium-ion transfer characteristics and electron transfer characteristics. Therefore, when the mesoporous carbon-carbon wire structure of the present invention is used for anode materials in a lithium secondary battery, excellent electrical conductivity is achieved, and the charge/discharge cycle characteristics of the lithium secondary battery are improved.

Description

Mesoporous carbon-carbon wire structure for anode materials of lithium-ion battery, producing method thereof and lithium secondary battery using it}

The present invention relates to a medium-pore carbon-carbon wire structure for a negative electrode material for a lithium secondary battery, and more particularly, to a medium-pore carbon-carbon wire structure for a lithium secondary battery negative electrode material manufactured using medium-pore carbon, a method for manufacturing the same, and a method for using the same It relates to a lithium secondary battery.

In the era of smartization, rechargeable batteries are attracting attention as core technologies that can actively control electricity demand, such as smart cars, which are represented by electric vehicles, and smart grids, which are the core of energy storage technology.

A secondary battery is a battery that converts chemical energy into electrical energy to supply power to an external circuit, receives external power when discharged, and converts electrical energy into chemical energy to store electricity. It is a chemical cell that can repeat charging and discharging using mutual change.

Commercially available secondary batteries include lead-acid batteries, nickel/cadmium batteries, nickel/hydrogen batteries, and lithium secondary batteries. Among them, lithium secondary batteries use lithium ions, which are light and have a high electrochemical standard potential, as an active material and have the highest operating voltage. indicates

The material initially studied as an anode material for lithium secondary batteries is lithium metal, and the standard electrode potential of lithium metal is -3.04V and the theoretical capacity is 3,860mAh/g, which shows a higher energy density than other anode materials, but in organic electrolytes. It is thermodynamically unstable and has the characteristic of growing into dendritic phases when charging and discharging are repeated. The dendrites generated by repeated charging and discharging are separated from lithium metal to reduce charge and discharge efficiency and capacity, and to prevent internal short circuits through direct contact with the positive electrode. This directly affects the stability of the battery.

The oxidation-reduction reaction of lithium metal is a process in which lithium ions are reduced and electrodeposited as lithium metal on the electrode surface, and lithium metal is oxidized and eluted into the electrolyte in the form of lithium ions. Since these reactions occur on the electrode surface, the interface phenomenon between lithium metal and electrolyte is very important. .

The SEI layer has lithium ion conduction properties and prevents the electrolyte from contacting lithium, thereby preventing the corrosion of lithium by the electrolyte. The reason why a primary battery using a lithium metal anode can exhibit excellent shelf-life is because a stable SEI is formed. Since the composition and structure of SEI vary greatly depending on the type of electrolyte, electrolyte design for SEI control is one of the most important technologies for stabilizing the lithium metal anode. However, when lithium is electrodeposited on the lithium metal on which SEI is formed, a phenomenon in which lithium electrodeposition is locally concentrated occurs without uniform lithium electrodeposition.

Also, dendrite lithium grows and causes an internal short circuit of the battery. The non-uniform electrodeposition of lithium increases the contact with the electrolyte, forming a new SEI layer by a side reaction between the electrolyte and lithium, and causing depletion of the electrolyte and lithium. In the process of lithium eluting, lithium metal is separated to form 'dead' lithium that is electrically short-circuited. If this process is repeated, a porous layer (porous layer) in which reaction products with electrolyte are accumulated on the lithium surface ) is formed, which increases the resistance of the battery and accelerates the non-uniformity of the electrode reaction.

The reasons for the non-uniform electrodeposition of lithium can be roughly divided into three categories. First, when the lithium electrodeposition reaction rate is high, depletion of lithium ions on the surface of lithium metal occurs and the concentration is reduced to 0, the electrode reaction corresponds to a diffusion controlled regime, and interfacial instability increases. In order to reduce the overvoltage for the lithium electrodeposition reaction, a needle-like structure with a large surface area that can improve diffusion flux at the lithium metal interface grows in a vertical direction.

The second is due to the non-uniformity of the generated SEI layer. If the SEI layer is not uniform, lithium electrodeposition/elution is concentrated on a region or defect having a relatively low resistance among the SEI layer.

Third, lithium has a high activation energy for self-diffusion. Lithium is a material with very high surface energy, and it is thermodynamically advantageous to reduce the surface energy by forming a uniform interface. However, since the activation energy for diffusion of lithium in the surface lattice is high, a uniform interface cannot be formed. That is, lithium metal has a very high activation energy (0.14 to 0.41 eV), and thus exhibits a characteristic that the non-uniform surface structure of lithium is maintained as it is.

In addition, lithium metal has a very low standard oxidation-reduction potential {-3.04vs SHE (Standarded Hydrogen Electrode)}, which means that the tendency to oxidation is very large. Therefore, when lithium metal comes into contact with the electrolyte, oxidation occurs while reducing the electrolyte.

On the other hand, the lower the LUMO (lowest unoccupied molecular orbital) level of the electrolyte component, the more accelerated the reduction, so that the component with the lower LUMO level reacts with lithium first to form the SEI layer. Therefore, if the LUMO level of the electrolyte component is controlled, a reaction between a specific material and lithium can be induced, and the composition and structure of the SEI layer can be controlled. Since it is difficult to completely block the chemical reaction between electrolyte and lithium, research is being conducted in the direction of designing an electrolyte that forms a stable SEI layer or introducing a protective film that blocks the reaction between electrolyte and lithium.

In order to overcome the low charge and discharge efficiency and stability of lithium metal, research on carbon-based materials and metal-based materials that can react with lithium in an ionic state has been conducted. was used

Carbon-based materials have been most widely used since lithium secondary batteries were first commercialized. Graphite, which has a high reversible capacity and a low production cost, is the most used carbon-based material. The theoretical capacity of graphite is limited to 372 mAh/g, and its high crystallinity structural characteristics have poor output characteristics. It has disadvantages in that it deteriorates and thermal stability is poor.

In the graphite crystal in the carbon material, carbon atoms of sp2-hybrid orbitals are bonded to each other in a hexagonal plane to form a carbon hexagonal network (graphene layer), and π electrons located above and below the carbon network are obtained by bonding these meshes. Since π electrons can move relatively freely between the carbon hexagonal planes, graphite has excellent electron conductivity. The π bond bonding these graphite layers forms a weak van der Waals bond, but the bond in the hexagonal carbon plane is a very strong covalent bond, showing anisotropy. Lithium ions are intercalated and deintercalated between these graphite layers. Graphite undergoes a reduction reaction during the charging reaction, and lithium ions are inserted into the layered structure of graphite to form a Li _x C compound. During discharge, an oxidation reaction occurs in graphite and lithium ions are desorbed. In these charging and discharging reactions, electrochemical characteristics such as reaction potential and lithium storage capacity appear differently depending on the crystallinity, microstructure, particle shape, etc. of the carbon material. Due to the phenomenon that the layer structure is peeled off due to the simultaneous insertion of the salt of the electrolyte during the lithium ion insertion process, graphite coated on the surface of amorphous carbon is mainly used as the anode material currently used.

Among electrode active materials, highly crystalline carbon materials, which are most often used as negative electrode materials, exhibit high crystallinity only when graphitized at about 2000°C or higher. Among the four major components of secondary batteries, the cathode active material, the anode active material, the separator, and the electrolyte, the import dependence of the anode active material is absolutely high. Graphite-based anode active materials currently mainly used are mainly manufactured by Japanese companies, and domestic companies are conducting research on their own anode active materials such as graphite and silicon-based anode active materials, but they are not showing clear results.

R&D on anode active materials that can increase energy storage capacity is being actively conducted around the world. In connection with serious natural environmental problems, eco-friendly energy and storage systems are more demanded. R&D is also expanding. This energy storage/conversion performance is closely related to the characteristics of the materials constituting the electrode. When lithium secondary batteries were first commercialized by Sony in Japan in the early 1990s, the electrode active material was composed of micrometer-sized powder, and the electrolyte was also It was entrapped in the membrane micrometer pores.

Recently, as the use of lithium secondary batteries has been expanded from portable power devices to power tools, EVs, ESSs, etc., the demand for the development of high-capacity, high-output, and high-safety lithium secondary batteries is increasing. The need for the development of new materials that can be used is increasing.

Lithium secondary batteries of the current level of technology have higher energy efficiency than conventional nickel-cadmium secondary batteries or nickel-hydrogen secondary batteries, but due to the limitation of the transfer rate of lithium ions in the solid, the charging and discharging rates are relatively slow and low output. In order to improve the performance of communication devices, electric vehicles, and large-capacity energy storage devices, materials with improved lithium ion charging and discharging are required.

If a nanometer-concept nanomaterial is used as an electrode active material as a technology to solve this problem, it is expected that the charge/discharge capacity can be increased while complementing the shortcomings of the carbon anode material according to the fast lithium ion transport characteristics.

The advantage of nanomaterials is that the material composed of micrometer-sized particles is not generated by the electrode reaction, and the lithium ion transfer within the particles is achieved at a short distance, which greatly increases the lithium insertion/desorption rate. In addition, the large surface area allows a large contact area with the electrolyte, which in turn increases the flow of lithium ions through the interface, and can change the chemical potential of lithium ions and electrons, thereby changing the potential of the electrode. In addition, in nanoparticles, the composition range in which lithium ions exist can be further expanded, so that deformations related to lithium ion insertion are much better accommodated. On the other hand, when applying nanomaterials, the disadvantages are that nanoparticles are difficult to synthesize and the size (dimension) is difficult to control, and if the surface area between the electrolyte/electrode is large, a lot of side reactions with the electrolyte occur and it becomes more difficult to maintain contact between the particles. Also, the density of the nanopowder is lower than that of the same material composed of micrometer particles. Therefore, for the same mass of material, the volume of the electrode increases, which in turn reduces the energy density per volume.

In order to use the carbon anode material more efficiently, research to make anode material by mixing carbon such as tube-type and wire-type material is also being actively conducted, mainly methods such as sol-gel, CVD, sputtering, etc. However, low specific surface area, reduced efficiency, and high cost are problems. Fibrous carbon has a higher electron diffusivity than general powders or thin films because the surface of the fibrous carbon rapidly transfers electrons from the outside to suppress recombination of electrons and holes and maximize reaction efficiency.

Since the discovery of carbon nanotubes, interest in nanotube-shaped materials has been amplified, and research on the production of fibrous carbon also started in earnest from the late 1990s, typically in nanotubes with dimensions of 100 nm or less. Structural materials have recently been developed in the form of elongated nanotubes, nanosheets, and nanofibers.

Recently, in relation to a lithium secondary battery, the development of a hybrid type anode material having both the advantages of a graphite-based material and a non-graphite-based material is required.

Korean Patent Registration No. 10-0744832 Korean Patent Publication No. 10-2008-0111809 Korean Patent Publication No. 10-2009-0001316 Korean Patent Publication No. 10-2008-0006898 Korean Patent Publication No. 10-2009-0112542

In order to solve the above problems, the present invention is a medium pore carbon-carbon by complexing a carbon wire that is easy to move electrons and can be manufactured relatively economically compared to carbon nanotubes in a medium pore carbon structure prepared using a porous silica structure. An object of the present invention is to provide a negative electrode material for a lithium secondary battery that can be manufactured at a relatively low cost and has excellent charge and discharge characteristics while compensating for the disadvantages of each of the conventional carbon particles and carbon wires by manufacturing the wire structure.

In order to achieve the above object, the present invention comprises the steps of preparing a porous silica structure; preparing a porous silica-carbon structure by coating and heat-treating a carbon-containing polymer material on the surface of the porous silica structure; Growing a carbon wire on the porous silica-carbon structure to prepare a porous silica-carbon-carbon wire structure; and removing the silica from the porous silica-carbon-carbon wire structure to prepare a medium-pore carbon-carbon wire structure, comprising a step of preparing a medium-pore carbon-carbon wire structure for a lithium secondary battery negative electrode material. It provides a method of manufacturing a carbon wire structure.

In the manufacturing method, the porous silica structure is 2 to 10% by weight of TEOS (Tetraethyl orthosilicate) based on the total weight of the composition, 2 to 15% by weight of ammonia water at a concentration of 20 to 35% by weight, 3 to 25% by weight of distilled water, TEOS volume It is preferable to prepare using a composition containing 0.14 to 0.5 times the volume of organosilane, and the remainder being a solvent selected from among ethanol and methanol.

In the manufacturing method,

The porous silica structure,

A step of synthesizing a mixture of ammonia water, distilled water, organosilane and TEOS at a concentration of 20 to 35% by weight in a solvent and stirring for at least 5 hours; removing the liquid portion, separating the solid portion, and drying at 90 to 110° C. for 12 hours or more; And it is preferably prepared by a method comprising the step of heat-treating at 500 ~ 600 ℃ for 4 to 6 hours.

In the manufacturing method, it is preferable that the porous silica structure has a spherical shape with a particle size of 80 to 700 nm.

In the manufacturing method, the carbon-containing-polymer material is a thermoplastic resin selected from phenol resin, polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC) and polystyrene (PS). , it is preferably a mixture of cellulose.

In the manufacturing method, the thermoplastic resin and cellulose are preferably mixed in a weight ratio of 6:4 to 8:2.

In the manufacturing method, the porous silica-carbon structure,

Dissolving a carbon-containing polymer material having a weight of 0.2 to 0.5 times the weight of the porous silica structure in distilled water 2.5 to 3.5 times the weight of the porous silica structure; coating the carbon-containing polymer material on the porous silica structure by dissolving the carbon-containing polymer material and then adding the porous silica structure and leaving it to stand for 1 hour or more; Evaporating and drying the carbon-containing-polymer material-coated porous silica structure at 100 to 120° C. for 12 hours or more; Oxidation treatment for 1 to 5 hours after heating the dried structure to 180 ~ 220 ℃ at a temperature increase rate of 1 ℃ / min in an air atmosphere; After heating the oxidation-treated structure to 800 ~ 1,000 ℃ at a heating rate of 5 ℃ / min, heat treatment for 5 ~ 25 hours to carbonize the carbon-containing polymer material; And it is preferably prepared by a method comprising the step of natural cooling to room temperature.

In the manufacturing method, it is preferable to further include the step of aging the porous silica structure for 12 hours or more at 75 ~ 85 ℃ after the step of coating the carbon-containing polymer material.

In the manufacturing method, the porous silica-carbon-carbon wire structure,

mixing the porous silica-carbon structure with 4 to 5% by weight of magnesium (Mg) powder based on the weight of the carbon structure; Heat-treating the powder in which magnesium is mixed in the porous silica-carbon structure at 600-700° C. for 5-7 hours in a nitrogen atmosphere; And after pulverizing the heat-treated sample, it is preferably prepared by a method comprising the step of obtaining a porous silica-carbon-carbon wire structure, which is a powder that has passed through a sieve having a size of 150 to 250 mesh.

In the manufacturing method, the medium pore carbon-carbon wire structure,

porous silica-carbon-carbon wire structure 8 to 12 times the weight of the solid content weight of distilled water is placed in a reaction vessel, and hydrofluoric acid is slowly injected into the distilled water to prepare a 15-25 wt% hydrofluoric acid solution; dissolving the silica material in the porous silica-carbon-carbon wire structure by slowly injecting the porous silica-carbon-carbon wire structure into the hydrofluoric acid solution, sealing the structure, and reacting for 12 hours or more; The solution is removed by filtration and the solid is washed 3 to 5 times with distilled water; And it is preferably prepared by a method comprising the step of drying the separated solid content at 90 ~ 110 ℃ for 10 ~ 14 hours.

In the manufacturing method, the mesoporous carbon-carbon wire structure preferably includes mesopores having an average pore size of 3 to 5 nm and the particle size is 80 to 800 nm.

In addition, the present invention provides a carbon structure comprising mesopores having an average pore size of 3 to 5 nm; It provides a medium-pore carbon-carbon wire structure for a negative electrode material for a lithium secondary battery, including a carbon wire grown from the carbon structure including the mesopores, and having a particle size of 80 to 800 nm.

The medium pore carbon-carbon wire structure for the negative electrode material of the lithium secondary battery is preferably manufactured by the method of any one of claims 1 to 10.

In addition, the present invention provides a lithium secondary battery comprising: a carbon structure including mesopores having an average pore size of 3 to 5 nm; It provides a lithium secondary battery comprising a carbon wire grown from the carbon structure including the mesopores, and comprising a medium-pore carbon-carbon wire structure having a particle size of 80 to 800 nm as an anode material.

In the lithium secondary battery, the medium pore carbon-carbon wire structure is preferably manufactured by the method of any one of claims 1 to 10.

The medium pore carbon-carbon wire structure for a lithium secondary battery negative electrode material of the present invention uses a silicon dioxide nanostructure to form a spherical carbon nanostructure with developed mesopores. The carbon wire grown from the mesoporous carbon particles has the effect of interconnecting and supporting the carbon particles when charging and discharging lithium to the carbon particles, while improving the lithium ion transport properties and electron transport properties.

Therefore, the medium-pore carbon-carbon wire structure of the present invention has excellent electrical conductivity when using a negative electrode material for a lithium secondary battery and has the effect of improving the charge/discharge cycle characteristics of a lithium secondary battery.

1 is a SEM image of a porous silica structure.
2 is an SEM image of a porous silica-carbon structure.
3 is a SEM image of the mesoporous carbon structure.
4 is a SEM image of the mesoporous carbon-carbon wire structure.
5 is an SEM image confirming the size of the silica core of the porous silica structure according to the reaction time. The reaction times are (A) 1 hour, (B) 2 hours and (C) 5 hours.
6 is a SEM image confirming the size of the silica core of the porous silica structure according to the amount of the reaction catalyst. The amount of the reaction catalyst is (A) 2% by weight, (B) 5% by weight, (C) 9% by weight, and (D) 15% by weight.
7 is an SEM image confirming the size of the silica core of the porous silica structure according to the amount of distilled water. The amount of distilled water is (A) 3% by weight, (B) 7% by weight, (C) 11% by weight, (D) 15% by weight and (E) 23% by weight.
8 is a SEM image confirming the size of the silica core of the porous silica structure according to the amount of TEOS. The amount of TEOS is (A) 2% by weight, (B) 6% by weight and (C) 10% by weight.
9 shows the results of confirming the silica core size change of the porous silica structure according to the reaction conditions.
10 shows the nitrogen isotherm and pore distribution of the porous silica structure according to the size of the silica core.
11 shows the results of confirming the physical properties of the porous silica structure according to the size of the silica core.
12 is an SEM image showing the result of confirming the core-shell structure of the porous silica structure according to the type of surfactant.
13 shows the nitrogen isotherm of the core-shell of the porous silica structure according to the type of surfactant.
14 shows the pore distribution of the core-shell of the porous silica structure according to the type of surfactant.
15 is an SEM image confirming the core-shell structure of the porous silica structure according to the ratio of organosilane.
16 shows the core-shell nitrogen isotherm and pore distribution of the porous silica structure according to the ratio of organosilane.
17 is an SEM image of the mesoporous carbon structure according to the organosilane ratio. The organosilane/TEOS volume ratio is (A) 0.125, (B) 0.375, and (C) 1.
18 is a nitrogen isotherm of a mesoporous carbon structure according to an organosilane ratio.
19 is a pore distribution curve of the mesoporous carbon structure according to the organosilane ratio.
20 is a result of confirming the physical properties of the mesoporous carbon structure according to the organosilane ratio.
21 is a nitrogen isotherm of the mesoporous carbon structure according to the carbon-containing-polymer ratio.
22 is a pore distribution curve of the mesoporous carbon structure according to the carbon-containing-polymer ratio.
23 is a comparison of the physical properties of the mesoporous carbon structure according to the carbon-containing-polymer ratio.
24 is a SEM image confirming the structure of the mesoporous carbon structure according to the particle size. The particle sizes are (A) 80 nm, (B) 300 nm and (C) 500 nm.
25 is a result of confirming the nitrogen isotherm, pore distribution, and physical properties of the mesoporous carbon structure according to the particle size.
26 is an SEM image confirming the structure of the mesoporous carbon structure according to the heat treatment temperature. (A) shows the case where the organosilane/TEOS volume ratio is 0.125, (B) is 0.375, and (C) is 1.
27 is a result of confirming the nitrogen isotherm, pore distribution and physical properties of the mesoporous carbon structure according to the heat treatment temperature.
28 is a result of confirming the nitrogen isotherm, pore distribution, and physical properties of the mesoporous carbon structure according to the heat treatment time.
29 is a result of confirming the particle size distribution of the mesoporous carbon structure according to the heat treatment time.
30 is an evaluation of the adhesion properties of the mesoporous carbon-carbon wire structure. The left is PAA-SBR, the right is PVdF, and the thickness is 30 μm.
31 is an evaluation of the adhesion properties of the medium-pore carbon-carbon wire structure for each coating thickness. The coating thickness is 30 μm on the left, 50 μm in the middle, and 60 μm on the right.
32 is a result of confirming the electrical capacity characteristics of the medium pore carbon-carbon wire structure at a current density of 50 mA / g.
33 is a result of confirming the electrical capacity characteristics of the medium pore carbon-carbon wire structure at a current density of 100 mA / g.
34 is a result of confirming the electrical capacity characteristics of the medium pore carbon-carbon wire structure at a current density of 200 mA / g.
35 is a result of analyzing the charge/discharge life performance of the medium pore carbon structure at a current density of 40 mA/g.
36 is a result of analyzing the charge and discharge characteristics of the mesoporous carbon structure according to the heat treatment temperature.

The present invention comprises the steps of preparing a porous silica structure; preparing a porous silica-carbon structure by coating and heat-treating a carbon-containing polymer material on the surface of the porous silica structure; Growing a carbon wire on the porous silica-carbon structure to prepare a porous silica-carbon-carbon wire structure; and removing silica from the porous silica-carbon-carbon wire structure to prepare a medium-pore carbon-carbon wire structure.

In addition, the present invention provides a carbon structure comprising mesopores having an average pore size of 3 to 5 nm; It includes a carbon wire grown from the carbon structure including the mesopores, and the particle size is 80-800nm, medium-pore carbon for a lithium secondary battery negative electrode material - relates to a carbon wire structure.

In addition, the present invention provides a lithium secondary battery comprising: a carbon structure including mesopores having an average pore size of 3 to 5 nm; It includes a carbon wire grown from the carbon structure including the mesopores, and a medium-pore carbon-carbon wire structure having a particle size of 80 to 800 nm as an anode material. It relates to a lithium secondary battery.

Hereinafter, the present invention will be described in detail.

1. Preparation of porous silica structures

The porous silica structure is prepared by a sol-gel reaction using a composition in which a silica (SiO ₂ ) raw material, a solvent, a catalyst, distilled water for hydrolysis, and a surfactant are mixed.

As a raw material for silica, TEOS (Tetraethyl orthosilicate) is used. TEOS is preferably used in an amount of 2 to 10% by weight based on the total weight of the composition.

Ethanol or methanol is used as a solvent for providing a space for silica synthesis.

As a catalyst for silica synthesis, aqueous ammonia, hydrochloric acid, nitric acid or sulfuric acid is used. It is more preferable to use ammonia water. As ammonia water, it is preferable to use ammonia water having a concentration of 20 to 35% by weight, more preferably to use ammonia water having a concentration of 25 to 30% by weight, and particularly preferably to use ammonia water having a concentration of 28% by weight.

Distilled water is used for the hydrolysis reaction. Distilled water is preferably used in an amount of 3 to 25% by weight based on the total weight of the composition.

Surfactants are used for pore expansion. As surfactant, organosilane {C ₁₈ -TMS(Trimethoxy(octadecyl)silane}), CTAB(Cetyltrimethylammoniumbromide), CTAC(Cetyltrimethylammoniumchloride), divinylbenzene, cellulose, phenol resin, polyvinyl Alcohol (Polyvinylalcohol) can be used, etc. It is particularly preferable to use an organosilane. The organosilane is preferably used in an amount such that the volume ratio of organosilane/TEOS is 0.14 to 0.5, and an amount such as 0.3 to 0.4 It is more preferable to use it, and it is especially preferable to use the amount which becomes 0.375.

A porous silica structure is synthesized by mixing aqueous ammonia, organosilane, and TEOS with solvent ethanol or methanol and reacting with stirring for at least 5 hours. It is more preferable to synthesize by reacting for 5 to 7 hours, and particularly preferably to react for 5 hours.

The synthesized silica structure is dried at 90~110°C for more than 12 hours by removing the liquid part, separating the solid part. It is more preferable to dry at 100° C. for 12 to 14 hours. It is preferable to remove the liquid part using a centrifuge.

The dried silica structure is heat-treated at a temperature of 500 to 600° C. for 4 to 6 hours to remove organic materials present therein to obtain a porous silica structure.

The porous silica structure is a spherical material having a particle size (diameter) of 80 to 700 nm and is used as a template for manufacturing a medium pore carbon-carbon wire negative electrode material. The particle size of the porous silica structure is preferably 80 to 100 nm, particularly preferably 80 nm, because pores formed between small particles affect physical properties.

2. Preparation of porous silica-carbon structures

The porous silica structure is coated with a carbon-containing polymer material and heat-treated to prepare a porous silica-carbon structure.

As a carbon-containing polymer material to be coated on the silica surface, a thermoplastic resin selected from phenol resin, PVA (polyvinyl alcohol), PAN (polyacrylonitrile), PE (polyethylene), PP (polypropylene), PVC (polyvinylchloride) and PS (polystyrene) and , a mixture of cellulose is used. It is more preferable to use a mixture of phenol resin and cellulose.

The thermoplastic resin and cellulose are preferably mixed in a weight ratio of 6:4 to 8:2, and more preferably used by mixing in a weight ratio of 7:3.

Dissolve a carbon-containing-polymer material having a weight of 0.2 to 0.5 times the weight of the porous silica structure in distilled water 2.5 to 3.5 times the weight of the porous silica structure. It is more preferable to use a carbon-containing-polymer material with a weight of 0.2 to 0.3 times the weight of the porous silica structure, and it is particularly preferable to use a carbon-containing-polymer material with a weight of 0.23 times the weight of the porous silica structure.

After dissolving the carbon-containing-polymer material in distilled water, the porous silica structure is added while stirring, and left to stand for 1 hour or more, more preferably 1 to 3 hours, to coat the carbon-containing-polymer material on the porous silica structure.

It is more preferable that the porous silica structure further comprises a process of coating the polymer material containing carbon on the porous silica structure and then aging at 75 to 85° C. for 3 hours or more, more preferably 3 to 5 hours.

The carbon-containing-polymer material-coated porous silica structure is evaporated and dried at 100 to 120° C. for at least 12 hours, more preferably for 12 to 14 hours.

The dried structure is subjected to oxidation treatment by raising the temperature to 180 to 220° C., more preferably to 200° C. at a temperature increase rate of 1° C./min in an air atmosphere in order to increase crosslinking of the carbon-containing polymer material, and then maintaining it for 1 to 5 hours. do.

The oxidized structure is heat-treated and carbonized. It is preferable to carbonize it by charging it into a kiln in which nitrogen is purged. The structure is heated to 800 to 1,000° C., more preferably to 900° C. at a temperature increase rate of 5° C./min, and then heat-treated for 5 to 25 hours to carbonize the carbon-containing polymer material. It is more preferable to heat-treat for 20-25 hours.

After carbonization, it is cooled naturally to room temperature to prepare a porous silica-carbon structure in which a carbon-containing polymer material is carbonized.

3. Preparation of porous silica-carbon-carbon wire structure

A carbon wire is grown on the porous silica-carbon structure to prepare a porous silica-carbon-carbon wire structure.

First, the porous silica-carbon structure is mixed with 4-5 wt% of magnesium (Mg) powder based on the weight of the porous silica-carbon structure. Magnesium serves as a catalyst for pyrolyzing carbon materials in a porous silica-carbon structure to grow them in a wire form. Magnesium is oxidized at the same time as reducing silica and converted into MgOx.

The powder in which magnesium is mixed with the porous silica-carbon structure is heat treated at 600-700° C. for 5-7 hours in a nitrogen atmosphere.

After the heat-treated sample is pulverized, a porous silica-carbon-carbon wire structure, which is a powder that has passed through a sieve of 150 to 250 mesh size, is obtained. It is more preferable to use a 200 mesh sieve.

4. Preparation of medium pore carbon-carbon wire structure

The porous silica-carbon-carbon wire structure by removing the silica from the mesoporous carbon-carbon wire structure is prepared.

As a material for removing silica, strong alkali such as hydrofluoric acid (HF), sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide {Ca(OH) ₂ } is used. It is more preferable to use hydrofluoric acid.

Porous silica-carbon-carbon wire structure Put distilled water 8 to 12 times the weight of the solid content into the reaction vessel, and slowly inject a material for removing silica into the distilled water to prepare a hydrofluoric acid solution or strong alkali solution with a concentration of 15 to 25 wt% . It is more preferable to prepare a solution with a concentration of 20% by weight.

After slowly injecting and sealing the porous silica-carbon-carbon wire structure into the prepared solution, it is reacted for at least 12 hours, more preferably for 12 to 14 hours to dissolve the silica material in the porous silica-carbon-carbon wire structure. The reaction is preferably carried out while vibrating using a vibrating stirrer.

When stirring is complete, the solution is removed by filtration, and the solid is washed 3 to 5 times with distilled water. The separated solid is dried at 90 to 110° C. for 10 to 14 hours to prepare a medium pore carbon-carbon wire structure.

The medium pore carbon-carbon wire structure preferably includes mesopores having an average pore size of 3 to 5 nm, and the particle size is 80 to 800 nm. It is more preferable that the particle size is 80 to 500 nm.

The medium-pore carbon-carbon wire structure prepared as described above is used as an anode material in a lithium secondary battery. The medium-pore carbon-carbon wire structure for a negative electrode material for a lithium secondary battery can be mixed with a conductive material, a binder and a solvent to prepare a negative electrode plate for a lithium secondary battery.

As a binder, PAA-SBR (polyacrylic acid - styrene butadiene rubber), PVDF (polyvinylidene difluoride), etc. can be used, and when PAA-SBR is used as a binder, the adhesive strength is better.

The medium pore carbon-carbon wire structure and the binder are preferably mixed in a weight ratio of 80:15 to 25, and particularly preferably mixed in a weight ratio of 82:20.

When the medium pore carbon-carbon wire structure of the present invention is used as an anode material, the discharge capacity is superior to that of graphite that is currently commercially available.

The present invention will be described in detail with reference to the following examples. These examples illustrate the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

Preparation of medium pore carbon-carbon wire structure

(1) Preparation of porous silica structure

In a reactor loaded with 1000 g of ethanol, 2 ml of 28 wt% ammonia water, 80 ml of distilled water, 15 ml of organosilane, and 60 ml of TEOS were quantitatively added and stirred for 5 hours or more to synthesize a porous silica structure.

The synthesized silica structure was dried in a drying oven at 100° C. for 12 hours or more after removing the liquid part using a centrifuge.

The dried silica structure was placed in a kiln and heat-treated at 550° C. for 5 hours to remove organic materials present therein to obtain a porous silica structure.

The SEM image of the porous silica structure having an average diameter of 500 nm prepared as described above is shown in FIG. 1 .

(2) Preparation of porous silica-carbon structure

The prepared porous silica structure was coated with a carbon-containing polymer material to prepare a porous silica-carbon structure.

As a carbon-containing polymer material to be coated on the silica surface, a mixture of phenol resin and cellulose in a weight ratio of 7:3 was used.

A carbon-containing polymer material having a weight of 0.23 times the weight of the porous silica structure was dissolved in distilled water three times the weight of the porous silica structure.

After dissolving the carbon-containing polymer material, the porous silica structure was added while stirring and aged at 80° C. for at least 3 hours to uniformly coat the carbon-containing polymer material on the surface of the porous silica structure.

The carbon-containing-polymer-coated porous silica structure was evaporated and dried at 100-120° C. for 12 hours or more.

The dried structure was heated to 200° C. at a temperature increase rate of 1° C./min in an air atmosphere in order to increase cross-linking of the carbon-containing polymer material, and then oxidized for 1 hour.

The oxidized structure was charged into a kiln in which nitrogen was purged, and the temperature was raised to 900°C at a temperature increase rate of 5°C/min, followed by heat treatment for 5 hours to carbonize.

After carbonization, it was naturally cooled to room temperature to obtain a porous silica-carbon structure in which a carbon-containing polymer material was carbonized.

The SEM image of the porous silica-carbon structure having an average diameter of 500 nm prepared as described above is shown in FIG. 2 .

(3) Preparation of porous silica-carbon-carbon wire structure

A silica-carbon-carbon wire structure was prepared by growing a carbon wire on the porous silica-carbon structure.

First, magnesium (Mg) powder in an amount of 4.5% by weight based on the weight of the porous silica-carbon structure was mixed. The magnesium-mixed powder was charged into a kiln and then heat-treated at 650° C. for 6 hours in a nitrogen atmosphere.

After the heat-treated sample was pulverized, it was sieved using a 200 mesh sieve to obtain a porous silica-carbon-carbon wire structure that was passed through a mesh network.

(4) Preparation of porous carbon-carbon wire structure

A porous carbon-carbon wire structure was prepared from the prepared porous silica-carbon-carbon wire structure.

After preparing distilled water 10 times the weight of the solid content of the porous silica-carbon-carbon wire structure in a reaction vessel, hydrofluoric acid (Sigma-aldrich, HF 48wt% in H ₂ O, ≥99.99% trace metals basis) was slowly injected into the distilled water 20 A hydrofluoric acid solution of weight % was prepared. The porous silica-carbon-carbon wire structure was slowly injected into the hydrofluoric acid solution, sealed using a Teflon tape, and then left in a vibrating stirrer for more than 12 hours to dissolve the silica material in the porous silica-carbon-carbon wire structure.

After stirring, the reaction material was filtered with filter paper in a plastic separator to remove the solution, and then washed 4 times with distilled water. The separated solid was placed in a drying oven and dried at 100° C. for 12 hours to prepare a medium pore carbon-carbon wire structure.

<Example 2>

Preparation of porous silica structures

In a reactor loaded with 1000 g of ethanol, 2 ml of 28 wt% ammonia water, 80 ml of distilled water, 15 ml of organosilane, and 60 ml of TEOS were quantitatively added and stirred for 5 hours or more to synthesize a porous silica structure.

The synthesized silica structure was dried in a drying oven at 100° C. for 12 hours or more after removing the liquid part using a centrifuge.

The dried silica structure was placed in a kiln and heat-treated at 550° C. for 5 hours to remove organic materials present therein to obtain a porous silica structure.

<Example 3>

Preparation of medium pore carbon structure

A porous silica-carbon structure was prepared in the same manner as in Example 1.

After preparing distilled water 10 times the weight of the silica-carbon structure solid content in the reaction vessel, hydrofluoric acid (Sigma-aldrich, HF 48 weight in H ₂ O, ≥99.99% trace metals basis) was slowly injected into the distilled water to obtain a concentration of 20% by weight. A hydrofluoric acid solution was prepared. The porous silica-carbon structure was slowly injected into the prepared 20% hydrofluoric acid solution, sealed using a Teflon tape, and reacted with stirring in a vibrating stirrer for at least 12 hours to dissolve the silica material in the porous silica-carbon structure.

After the stirring was completed, the solution was removed using filter paper in a plastic funnel, and then washed 4 times with distilled water. The separated solid was dried in a drying oven at 100° C. for 12 hours to obtain a mesoporous carbon structure.

The SEM image of the medium-pore carbon structure having an average diameter of 500 nm prepared as described above is shown in FIG. 3 . As shown in FIG. 3, the outer shape of the mesoporous carbon structure was composed of spherical particles agglomerated.

[Experimental example]

Experimental method

By BET (Brunauer, Emmett, Teller) analysis, the physical properties of the structure, such as specific surface area, pore volume and pore size, nitrogen adsorption/desorption characteristics, and pore distribution, were confirmed.

<Experimental Example 1>

Structure and physical properties of medium pore carbon-carbon wire structure

The structure of the medium-pore carbon-carbon wire structure prepared in Example 1 was confirmed, and the resultant medium-pore carbon-SEM image of the carbon wire structure was shown in FIG. 4 .

In addition, the physical properties of the prepared mesoporous carbon-carbon wire structure were compared with the properties of the mesoporous carbon structure and are shown in Table 1 below.

characteristic unit Medium pore carbon structure Medium pore carbon-carbon wire structure specific surface area m ² /g 967 960 gun skin g/cm ³ 1.64 1.76 average pore size nm 6.68 4.26

As shown in Table 1, the physical properties of the mesoporous carbon-carbon wire structure were similar to those of the mesoporous carbon structure of Example 3, and the specific surface area and pore volume were similar, and the average pore size was slightly decreased.

<Experimental Example 2>

Confirmation of characteristics of porous silica structure according to reaction conditions

The characteristics of the porous silica structure according to various reaction conditions were confirmed as follows.

(1) Confirmation of core size of porous silica structure by reaction time

A porous silica structure was prepared in the same manner as in Example 2, except that the reaction times for the synthesis of the porous silica structure were 1 hour, 2 hours, and 5 hours, respectively.

The silica core size of the prepared three types of porous silica structures was confirmed, and the resulting SEM image is shown in FIG. 5 . In FIG. 5, (A) is a core size of 100 nm as a result of reacting for 1 hour, (B) is a core size of 300 nm as a result of reacting for 2 hours, (C) is a reaction for 5 hours As a result, the core size was 300 nm.

(2) Confirmation of the size of the porous silica structure according to the amount of the reaction catalyst

A porous silica structure was prepared in the same manner as in Example 2, except that the amount of ammonia water as a reaction catalyst was 2 wt%, 5 wt%, 9 wt%, and 15 wt%.

The silica core size of the prepared four types of porous silica structures was confirmed, and the resulting SEM image is shown in FIG. 6 . In FIG. 6 (A) is 2 wt%, (B) is 5 wt%, (C) is 9 wt%, (D) is a result when 15 wt%, and the core size was 300 nm.

(3) Confirmation of the size of the porous silica structure according to the amount of distilled water

A porous silica structure was prepared in the same manner as in Example 2, except that the amounts of distilled water were 3% by weight, 7% by weight, 11% by weight, 15% by weight, and 23% by weight.

The silica core size of the prepared five porous silica structures was confirmed, and the resulting SEM image is shown in FIG. 7 . 7, (A) is the result when the core size is 150 nm as a result of 3% by weight, (B) is the result when the core size is 230 nm when it is 7% by weight, (C) is the result when the result is 11% by weight The raw core size is 300 nm, (D) is the result when the core size is 15% by weight, the core size is 300nm, (E) is the core size as the result when the 23% by weight is 300nm.

(4) Confirmation of the size of the porous silica structure according to the amount of TEOS

A porous silica structure was prepared in the same manner as in Example 2, except that the amount of TEOS was 2 wt%, 6 wt%, and 10 wt%.

The silica core size of the prepared three types of porous silica structures was confirmed, and the resulting SEM image is shown in FIG. 8 . In FIG. 8, (A) is the result when the core size is 2% by weight, and the core size is 80nm, (B) is the result when the core size is 6% by weight, and the core size is 300nm, (C) is the result when the result is 10% by weight The raw core size was 500 nm.

The result of confirming the silica core size change of the porous silica structure according to the reaction conditions for the synthesis as described above is shown in FIG. 9 .

<Experimental Example 3>

Characterization of the porous silica structure according to the size of the silica core

The characteristics of the porous silica structure according to the silica core size were confirmed.

The nitrogen adsorption/desorption characteristics, pore distribution and physical properties of the porous silica structures having core sizes of 80 nm, 300 nm and 500 nm, respectively, were confirmed.

The resultant nitrogen isotherm and pore distribution are shown in FIG. 10, and the results of checking the physical properties are shown in FIG. 11 and Table 2 below.

Item unit Silica Core Size 80 300 500 specific surface area m ² /g 296 140 140 pore volume cc/g 0.64 0.37 0.36 pore size nm 8.63 10.49 10.24

As shown in the above results, the specific surface area and pore volume properties of the porous silica structure having the smallest size of the silica core of 80 nm were the best. It is considered that the pores formed between the small particles affect the physical properties of the porous silica structure.

<Experimental Example 4>

Characteristics of the porous silica structure according to the type of surfactant

The characteristics of the porous silica structure according to the type of surfactant used for pore expansion during the preparation of the porous silica structure were confirmed as follows.

As surfactants for the synthesis of porous silica structures, organosilane, CTAB (Cetyltrimethylammoniumbromide), CTAC (Cetyltrimethylammoniumchloride), divinylbenzene, cellulose, phenol resin, and polyvinylalcohol are used, respectively. A porous silica structure was prepared using the same method as in Example 2 and used as a sample.

(1) Confirmation of the core-shell structure of the porous silica structure

The core-shell structure of the porous silica structure was confirmed, and the resulting SEM image is shown in FIG. 12 .

As can be seen in FIG. 12 , the shape of the structure was most uniform when organosilane was used as the surfactant.

(2) Confirmation of the characteristics of the porous silica structure

Among the porous silica structures, nitrogen adsorption/desorption characteristics, pore distribution and physical properties of the porous silica structures prepared using organosilane (C ₁₈ TMS), CTAB, and CTAC were confirmed. A 300 nm silica core was used for comparison.

The nitrogen isotherm of the core-shell of the porous silica structure is shown in FIG. 13 and the pore distribution is shown in FIG. 14 .

In addition, the results of confirming the physical properties of the core-shell of the porous silica structure prepared using organosilane (C ₁₈ TMS), CTAB, and CTAC are shown in Table 3 below.

Item unit Silica Core-Shell C ₁₈ TMS CTAB CTAC specific surface area m ² /g 472 441 270 pore volume cc/g 0.48 0.36 0.22 pore size nm 4.1 3.2 3.2

As shown in the above results, the physical properties of the porous silica structure prepared using organosilane as a surfactant were the best.

<Experimental Example 5>

Confirmation of characteristics of porous silica structure according to organosilane ratio

The characteristics of the porous silica structure according to the organosilane ratio used in the preparation of the porous silica structure were confirmed.

A porous silica structure was prepared in the same manner as in Example 2, except that organosilane was used so that the organosilane/TEOS volume ratio was 0.125, 0.375, and 1, respectively.

(1) Confirmation of the core-shell structure of the porous silica structure

An SEM image obtained by confirming the core-shell structure of the porous silica structure is shown in FIG. 15 .

As can be seen in FIG. 15 , when the ratio of organosilane was 0.375, the core-shell structure of the porous silica structure was the best.

(2) Confirmation of the characteristics of the porous silica structure

The nitrogen adsorption/desorption characteristics, pore distribution and physical characteristics of the porous silica structure were confirmed.

The results of confirming the nitrogen isotherm and pore distribution of the core-shell of the porous silica structure are shown in FIG. 16, and the results of confirming the physical properties of the core-shell of the porous silica structure are shown in Table 4 below.

Item unit Silica core-shell (organosilane/TEOS) 0.125 0.375 One specific surface area m ² /g 237 470 397 pore volume cc/g 0.22 0.42 0.38 pore size nm 3.58 4.58 3.65

As shown in the above results, when the volume ratio of organosilane/TEOS was 0.375, the physical properties of the porous silica structure were the best.

<Experimental Example 6>

Confirmation of characteristics of mesoporous carbon structure according to organosilane ratio

The characteristics of the mesoporous carbon structure according to the mixing ratio of the organosilane were confirmed as follows.

Example 3 except that organosilane was used so that the organosilane/TEOS volume ratio was 0.125, 0.375, and 1, respectively, and 50 wt% of carbon-containing-polymer materials (phenolic resin and cellulose) were used based on the weight of the porous silica structure. Three medium-pore carbon structures were prepared in the same manner as described above and used as samples.

(1) Confirmation of structure of mesoporous carbon structure according to organosilane ratio

The SEM image of the medium pore carbon structure sample is shown in FIG. 17 . In FIG. 17, (A) shows a case where the organosilane/TEOS volume ratio is 0.125, (B) is 0.375, and (C) is 1.

As shown in FIG. 17, the outer shape of the mesoporous carbon structure is composed of spherical particles agglomerated. In the case of a mesoporous carbon structure with a volume ratio of organosilane/TEOS of 1, it can be seen that particles having a particle size smaller than that of the silica template are uniformly mixed, and the agglomeration phenomenon is more dense. In addition, when less organosilane was used compared to TEOS, the surface of the mesoporous carbon structure was uniform and concise, but as the ratio increased, the appearance surface was rough and the frequency of irregular shapes was high.

(2) Confirmation of nitrogen adsorption/desorption characteristics of medium pore carbon structure according to organosilane ratio

Using the sample, the nitrogen adsorption/desorption characteristics of the mesoporous carbon structure according to the organosilane ratio were confirmed.

The nitrogen isotherm of the mesoporous carbon structure according to the resulting organosilane ratio is shown in FIG. 18 .

As shown in the results of FIG. 18 , the isothermal shapes of the mesoporous carbon structures prepared for each organosilane ratio were similar to each other. Similar results were also obtained in the porous silica structure, indicating that the mesoporous carbon structure was composed of mesopores and had the form of a porous silica structure that determines the shape of carbon.

(3) Confirmation of pore distribution of mesoporous carbon structure according to organosilane ratio

The pore distribution of the mesoporous carbon structure according to the ratio of organosilane was confirmed using the sample.

The pore distribution curve of the mesoporous carbon structure according to the resulting organosilane ratio is shown in FIG. 19 .

From the result of FIG. 19 , it was confirmed that the adsorbed volume further increased in the pore distribution of 10 nm or more. This can be considered to be the effect of mesopores of 10 nm or more formed when the mesoporous carbon structure is manufactured based on the porous silica structure, and the part composed of silica is melted out during the etching process.

(4) Confirmation of physical properties of mesoporous carbon structure according to organosilane ratio

Using the sample, the physical properties of the mesoporous carbon structure according to the ratio of organosilane were confirmed as follows.

20 is a graph showing the comparison of physical properties of the mesoporous carbon structure, such as specific surface area, pore volume, and pore size.

It can be seen from the graph of FIG. 20 that the pore size is maintained constant even when the ratio of organosilane is increased. This phenomenon is due to the effect of the pores formed while the silica is removed during the etching process, and it can be seen that the silica structures forming the walls within the structure provide an average pore size of 3 to 5 nm.

As a result, the mesoporous carbon structure includes not only the pores of the silica structure used as a template, but also the pores generated by the removal of the silica material, so that the pore volume per unit weight is more than 10 times that of the silica structure. . Such an abundant pore volume provides favorable conditions for supporting the negative electrode active material.

The physical properties of the mesoporous carbon structures derived from the BET analysis results are shown in Table 5 below.

Item unit Medium pore carbon structure (organosilane/TEOS volume ratio) 0.125 0.375 One specific surface area m ² /g 1517 1459 1148 pore volume cc/g 1.16 1.28 1.03 pore size nm 2.98 3.44 3.52

As shown in the results of Table 5, it can be confirmed that when the ratio of organosilane application is 0.375 compared to TEOS, it is the most advantageous structure for supporting the active material when the specific surface area, pore volume, and pore size are all taken into consideration.

<Experimental Example 7>

Characterization of medium-pore carbon structure according to the amount of carbon-containing-polymer material added

The properties of the mesoporous carbon structure according to the amount of the carbon-containing polymer material to be coated on the porous silica structure were confirmed as follows.

As the carbon-containing-polymer material, a mixture of phenol resin and cellulose in a weight ratio of 7:3 was used.

Three kinds of mesoporous carbon structures were prepared and used as samples in the same manner as in Example 3, except that carbon-containing-polymer materials were used in weight ratios of 0.23, 0.5, and 1, respectively, based on the solid content of the porous silica structure.

(1) Confirmation of nitrogen adsorption/desorption characteristics of medium pore carbon structure according to the amount of carbon-containing-polymer material added

Using the sample, the nitrogen adsorption/desorption characteristics of the mesoporous carbon structure according to the amount of carbon-containing-polymer material added were confirmed.

The resultant carbon-containing-nitrogen isotherm of the mesoporous carbon structure according to the addition amount of the polymer material is shown in FIG. 21 .

From the results of FIG. 21 , it can be seen that the carbon-containing-the smaller the amount of the polymer material added, the greater the nitrogen adsorption capacity of the mesoporous carbon structure. In particular, when the polymer addition ratio is 1, it can be seen that the nitrogen adsorption capacity of the hollow carbon structure is significantly reduced.

This result is confirmed to be because the physical properties of the mesoporous carbon structure are greatly affected depending on the amount of the carbon-containing polymer material to be coated in the porous silica structure.

(2) Confirmation of pore distribution of medium-pore carbon structure according to the amount of carbon-containing-polymer material added

Using the sample, the pore distribution of the mesoporous carbon structure according to the amount of carbon-containing-polymer material added was confirmed.

The resulting carbon-containing-pore distribution curve of the mesoporous carbon structure according to the addition amount of the polymer material is shown in FIG. 22 .

Looking at the pore distribution for each sample in the results of FIG. 22, the carbon-containing-medium pore carbon structures having the addition amount of the polymer material of 0.23 and 0.5 have similar pore distributions, but when the amount of the carbon-containing polymer material is 1, the pore volume is is rapidly decreasing.

That is, when the carbon-containing polymer material is added in an amount of 0.23 and 0.5, it can be seen that when the amount of carbon-containing polymer material added is small, pores of 2 nm or less are decreased while pores of 10 nm or more are enlarged. When the addition amount of the carbon-containing-polymer material was 1, the overall pore distribution was similar to that of the case where the addition amount of the carbon-containing-polymer material was 0.5, but the volume decreased sharply.

This phenomenon is that if the amount of the carbon-containing polymer material coated on the porous silica structure is 0.5 or more, it is excessively supported than the pore volume provided by the porous silica structure, and the excessively supported polymer is transferred to the outside surface in addition to the inside of the pores of the porous silica structure. It seems that this is because the resin layer is formed thick and converted into a carbon body with no pores developed.

(3) Confirmation of physical properties of mesoporous carbon structure according to carbon-containing-polymer addition amount

Using the sample, the physical properties of the mesoporous carbon structure according to the amount of carbon-containing-polymer material added were confirmed.

A graph comparing the specific surface area, pore volume, and pore size, which are the physical properties of the resulting mesoporous carbon structure, is shown in FIG. 23 .

As shown in the graph of FIG. 23, the specific surface area of the mesoporous carbon structure is highest when the amount of carbon-containing-polymer material added is 0.5, but the pore volume and pore size show the highest characteristics when the amount of carbon-containing-polymer material added is small. have.

In view of this trend, it is assumed that micropores are further developed when the amount of carbon-containing polymer material is half compared to the silica solid content in the stage where the carbon-containing polymer material is coated and carbonized in the pores of the porous silica structure to form a carbon body. can do.

That is, when the addition amount of the carbon-containing-polymer material is 1, it is determined that the carbon-containing-polymer material does not completely fill the pore volume and is coated on the pore wall to a thickness of 2 nm or less. However, when the amount of the carbon-containing-polymer material is less than this, it can be estimated that the carbon-containing-polymer material is coated more thinly on the pore walls to expand the pore volume.

The physical properties of the mesoporous carbon structures derived from the BET analysis results are shown in Table 6 below.

characteristic unit
(unit) Medium-pore carbon structure (polymer material/silica weight ratio) 0.23 0.5 One surface area m ² /g 967 1459 586 pore volume cc/g 1.64 1.28 0.33 pore size nm 6.68 3.4 2.3

From the results of Table 6, it can be seen that the physical properties are generally decreased as the content of carbon-containing polymer material, that is, carbon, increases, compared to the porous silica structure, and the pore volume, which is the physical property of the provided template, is not effectively utilized. can be found

In order to prepare an optimal mesoporous carbon structure for supporting the anode active material for a secondary battery, more favorable conditions may be provided in terms of pore volume and pore size than physical properties of specific surface area.

From these results, it can be seen that the optimal condition of the mesoporous carbon structure for supporting the active material is that the ratio of the polymer material is about 0.23 compared to the silica structure. Under these conditions, it can be confirmed that the pore volume of the carbon structure is 1.64, which can support an active material that is 1.5 times or more of the weight of carbon.

<Experimental Example 8>

Confirmation of characteristics of mesoporous carbon structure according to particle size

The characteristics of the mesoporous carbon structure according to the particle size were confirmed.

The structure, nitrogen adsorption/desorption characteristics, pore distribution and physical properties were confirmed for the mesoporous carbon structures having particle sizes of 80 nm, 300 nm and 500 nm, respectively.

The SEM image as a result of confirming the structure is shown in FIG. 24 . 24, (A) is a medium pore carbon structure having a particle size of 80 nm, (B) is a medium pore carbon structure having a particle size of 300 nm, (C) is a SEM image of a medium pore carbon structure having a particle size of 500 nm.

In addition, the results of checking the nitrogen isotherm and pore distribution are shown in FIG. 25, and the results of checking the physical properties are shown in FIG. 25 and Table 7 below.

Item unit Particle size of mesoporous carbon structure 80 300 500 surface area m ² /g 936 958 967 pore volume cc/g 1.67 1.31 1.64 pore size nm 7.19 5.5 6.68 Pore 2~10nm nm 1.03 0.39 0.79

As shown in the above results, the properties of the mesoporous carbon structure having the smallest size of the silica core of 80 nm were the best.

<Experimental Example 9>

Confirmation of characteristics of medium pore carbon structure according to heat treatment temperature

The characteristics of the mesoporous carbon structure according to the heat treatment temperature were confirmed.

The structure, nitrogen adsorption/desorption characteristics, pore distribution and physical properties were confirmed for the mesoporous carbon structures prepared by heat treatment at 110° C., 400° C., 700° C. and 900° C. for 1 hour, respectively.

The SEM image as a result of confirming the structure is shown in FIG. 26 . 26, (A) is a medium pore carbon structure heat treated at 110 ℃, (B) is a medium pore carbon structure heat treated at 400 ℃, (C) is a medium pore carbon structure heat treated at 700 ℃, (D) is 900 It is an SEM image of the mesoporous carbon structure heat-treated at ℃.

In addition, the results of checking the nitrogen isotherm and pore distribution are shown in FIG. 27, and the results of checking the physical properties are shown in FIG. 27 and Table 8 below.

temperature ℃ 110 400 700 900 surface area m ² /g 936 978 999 1021 pore volume cc/g 1.67 1.84 1.92 2 pore size nm 7.19 7.53 7.7 7.77

As shown in the above results, when the heat treatment temperature was 900° C., the physical properties of the mesoporous carbon structure were the best.

When the heat treatment temperature is increased, there is no change in the external shape of the structure and the distribution of the nitrogen isotherm and the pores are similar, but the specific surface area, pore volume, and physical properties of the pores increase, and the pores expand due to the thermal decomposition of carbon forming the walls of the pores.

<Experimental Example 10>

Confirmation of characteristics of mesoporous carbon structure according to heat treatment time

The characteristics of the mesoporous carbon structure were confirmed during the heat treatment time.

A mesoporous carbon structure was prepared in the same manner as in Example 3, except that heat treatment was performed at 900° C. for 5 hours, 10 hours, 15 hours, 20 hours, and 25 hours. Nitrogen adsorption/desorption characteristics, pore distribution, physical characteristics and particle size distribution were confirmed for the prepared mesoporous carbon structure.

(1) Characteristics according to heat treatment time

The results of checking the nitrogen isotherm and pore distribution according to the heat treatment time are shown in FIG. 28, and the results of checking the physical properties are shown in FIG. 28 and Table 9 below.

characteristic unit Heat treatment time at 900℃ 5 10 15 20 25 specific surface area m ² /g 999 1052 1085 1098 1119 pore volume cc/g 1.93 2.06 2.18 2.24 2.33 pore size nm 7.66 7.78 7.98 8.09 8.25

As shown in the above results, when the heat treatment time was 25 hours, the physical properties of the mesoporous carbon structure were the best.

(2) Characteristics of particle size distribution according to heat treatment time

The result of confirming the particle size distribution of the mesoporous carbon structure according to the heat treatment time is shown in FIG. 29 .

29, D[3.2] is the surface area moment mean, D[4.3] is the volume moment mean, D[1.0] is the number length mean, Dv[10] ] is the maximum particle size of 10% of the sample volume, Dv[50] is the maximum particle size of 50% of the sample volume, and Dv[90] is the maximum particle size of 90% of the sample volume.

As shown in the results of FIG. 29 , the average particle volume showed a tendency to decrease according to the heat treatment time.

<Experimental Example 11>

Confirmation of adhesion properties for electrode fabrication

In order to select a binder for electrode fabrication and to set the amount of application of the medium-pore carbon-carbon wire structure as an anode material, the adhesive strength characteristics of the medium-pore carbon-carbon wire structure were confirmed as follows. As a sample, the medium pore carbon-carbon wire structure of Example 1 was used.

(1) Binder selection

In order to find a binder suitable for copper foil and electrode material (carbon black), the adhesive strength characteristics of the medium-pore carbon-carbon wire structure were evaluated using two types of binders as follows.

First, for sludge production, 80% by weight of the medium pore carbon-carbon wire structure, which is an anode material, 10% by weight of a conductive material, and 10% by weight of a binder were mixed and stirred sufficiently to be uniformly prepared.

As binders, PVDF (Polyvinylidene Fluoried, Solef5130, Solvay Korea) [8% in NMP (1-methyl-2pyrrolinone)] and PAA (polyacrylic acid)-SBR (styrene butadiene rubber) were used to compare their properties. In addition, an appropriate amount of NMP (1-methyl pyrrolidinone, Sigma-Aldrich) was added to control the viscosity.

The obtained slurry was evenly coated on a copper current collector to a thickness of 50 μm using an applicator to prepare an electrode.

The electrode was dried in a forced circulation oven maintained at 80° C. for about 12 hours to completely evaporate moisture and solvent.

3M tape was repeatedly applied 2-3 times to the surface of the electrode prepared as described above, and then removed to measure the thickness of the negative electrode material attached to the electrode surface.

The results are shown in FIG. 30 . In FIG. 30, the left side is PAA-SBR, the right side is PVdF, and the thickness is 30 μm.

As shown in FIG. 30, when PAA-SBR, which is a water-based binder, was used, higher adhesion was exhibited than when PVdF binder was used.

(2) Carbon-carbon wire application amount setting

The capacity of the battery is directly proportional to the amount of application (thickness). An increase in the amount of application (coating thickness) is an important factor when making a battery because it accompanies an increase in the capacity of the battery. Adhesion test was performed as follows.

First, for sludge production, 80% by weight of the medium pore carbon-carbon wire structure, which is an anode material, 10% by weight of a conductive material, and 10% by weight of a binder were mixed and stirred sufficiently to be uniformly prepared.

Acetylene Black was used as a conductive material, and PAA-SBR was used as a binder. In addition, an appropriate amount of NMP (1-methyl pyrrolidinone, Sigma-Aldrich) was added to control the viscosity.

The obtained slurry was uniformly coated on a copper current collector to a constant thickness using an applicator to prepare an electrode.

The electrode was dried in a forced circulation oven maintained at 80° C. for about 12 hours to completely evaporate moisture and solvent.

The results of evaluating the adhesive strength characteristics for each thickness of the medium pore carbon-carbon wire structure using the electrode prepared as described above are shown in FIG. 31 . In FIG. 31, the left side shows the results when the thickness of the mesoporous carbon-carbon wire structure is 30 μm, the middle is 50 μm, and the right side shows the results when the thickness is 60 μm.

As shown in FIG. 31, when the medium-pore carbon-carbon wire structure was applied thicker than 30 μm, the carbon was weakly attached to the copper foil or the uppermost side was weakly attached to the extent that the role of the binder was meaningless. Therefore, it is preferable to set the thickness of the medium pore carbon-carbon wire structure to 30㎛.

<Experimental Example 12>

electrochemical properties

In order to investigate the electric capacity characteristics of the secondary battery of the medium-pore carbon-carbon wire structure, a half-cell was fabricated and tested.

The ratio of the medium pore carbon-carbon wire structure and the binder used in the electrode was set to a weight ratio of 80:20, and the electrode was manufactured by coating it with a thickness of 30 μm. The experiment was conducted with three coin cells to increase reliability.

The electric capacity characteristics of the carbon-carbon wire structure according to the current density were confirmed by setting the current density to 50 mA/g, 100 mA/g or 200 mA/g. The results are shown in FIGS. 32 to 34 .

32 shows the results of analyzing the charge/discharge characteristics for 30 cycles at a current density of 50 mA/g. In the results of FIG. 32 , when the charging and discharging characteristics were analyzed for 30 cycles at a current density of 50 mA/g, it can be seen that the initial discharge capacity exceeded 1,200 mAh/g, but gradually decreased and maintained at 700 mAh/g. The initial high capacity is presumed to be the result of pores of 10 nm or more developed in the carbon structure, and after 10 cycles, the capacity stabilized to 700 mAh/g. Also, the difference between the charge capacity and the discharge capacity was high, which is expected to be influenced by pores or surface area.

33 shows the experimental results by increasing the current density to 100 mA/g. In the results of FIG. 33 , when the current density was increased to 100 mA/g, the discharge capacity was about 400 mAh/g, and the discharge capacity was lower than when the experiment was performed at 50 mA/g. However, since there is almost no difference between the charge capacity and the discharge capacity, it is assumed that the higher the current density, the smaller the effect on the pores or the surface area.

34 shows the experimental results at a current density of 200 mA/g. From the result of FIG. 34 , it was confirmed that the discharge capacity and the charge capacity were almost identical at a current density of 200 mA/g, but the discharge capacity decreased to 200 mAh/g.

The electrochemical characteristic evaluation results are summarized in Table 10 below and the discharge capacity of the mesoporous carbon structure.

sample current density
(50mA/g) current density
(100mA/g) current density
(200mA/g) discharge capacity Medium pore carbon structure 320 - - Medium pore carbon-carbon wire structure 700 400 200

As shown in the results of Table 4, the medium pore carbon structure has a discharge capacity of 320 mAh/g, which shows performance almost similar to that of graphite, which is currently commercially available, and the medium pore carbon-carbon wire structure manufactured from the medium pore carbon structure is discharged. The capacity rose to 700 mAh/g.

As a result of increasing the current density in the medium-pore carbon-carbon wire structure, the discharge capacity decreased similarly to the characteristics of a general anode material, but even at a current density of 100 mA/g, higher performance than commercial graphite was realized.

The increase in the electric capacity of the mesoporous carbon-carbon wire structure is judged by the carbon wire connecting the particles of the mesoporous carbon structure to increase electron transfer during lithium ion charging and discharging, thereby improving the capacity utilization of the carbon structure. do.

<Experimental Example 13>

Confirmation of electrochemical properties

A half-cell using a medium-pore carbon structure as an anode material was fabricated and the charge/discharge characteristics of the anode material were analyzed.

(1) Production of half-cell

In order to evaluate the electrochemical properties, the mesoporous carbon structure synthesized in Example 3 was used as a negative electrode material.

First, in order to prepare sludge, it was prepared by mixing 80% by weight of the negative electrode active material, 10% by weight of the conductive material, and 10% by weight of the binder, and stirring enough to be uniformly mixed. Acetylene Black was used as a conductive material, and PVDF (Polyvinylidene Fluoried, Solef5130, Solvay Korea) [8% in NMP (1-methyl-2pyrrolinone)] was used as a binder. In addition, an appropriate amount of NMP (1-methyl pyrrolidinone, Sigma-Aldrich) was added to control the viscosity.

The obtained slurry was evenly coated on a copper current collector to a thickness of 50 μm using an applicator to prepare an electrode.

The electrode was dried in a forced circulation oven maintained at 80° C. for about 12 hours to completely evaporate moisture and solvent.

The battery was assembled in a glove box filled with Ar gas. A half-cell was manufactured as a CR2032 type coin cell, and lithium metal was used as a counter electrode.

20㎛ PE (poly-ethylene, W-SCOPE KOREA, COD 20A) was used as the separator, and the electrolyte was 1.15M LiPF ₆ salt dissolved in EC (ethylene carbonate): EMC (ehthyl-methyl carbonate) (3: 7, v/v, Panax-Etch) was used.

(2) Charging/discharging performance analysis

Using the half-cell prepared as described above, it was charged with a constant current (CC) to 0.005V (vs. Li/Li+) at a current value of 0.2C with respect to the weight of the negative electrode active material, and then 0.005V (vs. Li/Li+) Li+) while maintaining a voltage of 0.01C, a constant voltage (CV) charging was performed in which the charging was terminated. The discharge was a constant current discharge terminated at 2V (vs. Li/Li+) with a current value of 0.1C.

At this time, assuming that the 1C value was 400 mA/g, the charge/discharge experiment was performed in the above method, and then the 1C value of each sample was obtained.

The lifetime test was conducted after the activation process was performed under the above conditions. The life test was performed with the current value of charging and discharging being 40 mA/g and other conditions being the same. The charge/discharge experiment was measured using WBS-3000L of Won-A Tech.

In the analysis stage, in order to analyze the charge/discharge curve, output characteristics, and lifespan characteristics of the battery, the analysis was performed based on the theoretical capacity of graphite at a cut-off voltage of 0.01~2.5V, and the output characteristics were at 40mA/g. Measurements were repeated 50 cycles. The results of analyzing the charge/discharge performance of the mesoporous carbon structure are shown in FIG. 35 .

As shown in FIG. 35 , the discharge capacity was about 320 mAh/g in 50 cycles, and the charge/discharge efficiency was about 95%. It can be seen that as the charge/discharge cycle is repeated, it is slightly continuously decreased.

<Experimental Example 14>

Confirmation of electrochemical properties according to heat treatment temperature of medium pore carbon structure

A half-cell using a medium-pore carbon structure with a particle size of 80 nm as an anode material was fabricated, and the charge and discharge characteristics of the anode material were analyzed.

As the anode material, a medium-pore carbon structure having a particle size of 80 nm and heat-treated at 110°C and 400°C, respectively, was used.

The results of confirming the manufacturing conditions of the half-cell and the charging/discharging performance of the produced half-cell are shown in FIG.

As shown in Fig., the sample that was heat treated at 400,400 °C for 5 hours had the best discharge performance at about 700 mAh/g at a current density of 50 mA.

Claims (15)

preparing a porous silica structure;
preparing a porous silica-carbon structure by coating and heat-treating a carbon-containing polymer material on the surface of the porous silica structure;
Growing a carbon wire on the porous silica-carbon structure to prepare a porous silica-carbon-carbon wire structure; and
The porous silica-carbon-carbon wire structure by removing silica from the medium-pore carbon-carbon wire structure comprising the step of preparing a carbon wire structure, a medium-pore carbon for a lithium secondary battery negative electrode material - Method of manufacturing a carbon wire structure. The method of claim 1,
The porous silica structure is based on the total weight of the composition TEOS (Tetraethyl orthosilicate) 2 to 10% by weight, 20 to 35% by weight of ammonia water at a concentration of 2 to 15% by weight, distilled water 3 to 25% by weight, 0.14 to 0.5 times the volume of TEOS A process according to claim 1, characterized in that it is prepared using a composition comprising a volume of the organosilane and the remainder being a solvent selected from among ethanol and methanol. 3. The method of claim 2,
The porous silica structure,
A step of synthesizing a mixture of ammonia water, distilled water, organosilane and TEOS at a concentration of 20 to 35% by weight in a solvent and stirring for at least 5 hours;
removing the liquid portion, separating the solid portion, and drying at 90 to 110° C. for 12 hours or more; and
A manufacturing method, characterized in that it is prepared by a method comprising the step of heat treatment at 500 ~ 600 ℃ for 4 ~ 6 hours. According to claim 1,
The porous silica structure is a manufacturing method, characterized in that the spherical particle size of 80 ~ 700nm. According to claim 1,
The carbon-containing-polymer material is a mixture of phenolic resin, polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC) and polystyrene (PS) selected from among a thermoplastic resin and cellulose A manufacturing method, characterized in that. 6. The method of claim 5,
The thermoplastic resin and cellulose are mixed in a weight ratio of 6:4 to 8:2. The method of claim 1,
The porous silica-carbon structure,
Dissolving a carbon-containing polymer material in an amount of 0.2 to 0.5 times the weight of the porous silica structure in distilled water 2.5 to 3.5 times the weight of the porous silica structure;
coating the carbon-containing polymer material on the porous silica structure by dissolving the carbon-containing-polymer material and then adding the porous silica structure and leaving it to stand for at least 1 hour;
Evaporating and drying the carbon-containing-polymer material-coated porous silica structure at 100 to 120° C. for 12 hours or more;
Oxidation treatment for 1 to 5 hours after heating the dried structure to 180 ~ 220 ℃ at a temperature increase rate of 1 ℃ / min in an air atmosphere;
After heating the oxidation-treated structure to 800 ~ 1,000 ℃ at a heating rate of 5 ℃ / min, heat treatment for 5 ~ 25 hours to carbonize the carbon-containing polymer material; and
A manufacturing method, characterized in that manufactured by a method comprising the step of natural cooling to room temperature. 8. The method of claim 7,
After the carbon-containing polymer material is coated on the porous silica structure, the method further comprises the step of aging at 75 to 85° C. for 3 hours or more. According to claim 1,
The porous silica-carbon-carbon wire structure,
mixing the porous silica-carbon structure with 4 to 5% by weight of magnesium (Mg) powder based on the weight of the carbon structure;
Heat-treating the powder in which magnesium is mixed in the porous silica-carbon structure at 600-700° C. for 5-7 hours in a nitrogen atmosphere; and
A method comprising the step of obtaining a porous silica-carbon-carbon wire structure, which is a powder that has passed through a 150-250 mesh size sieve after pulverizing the heat-treated sample. According to claim 1,
The medium pore carbon-carbon wire structure,
porous silica-carbon-carbon wire structure 8 to 12 times the weight of the solid content weight of distilled water is placed in a reaction vessel, and hydrofluoric acid is slowly injected into the distilled water to prepare a 15-25 wt% hydrofluoric acid solution;
dissolving the silica material in the porous silica-carbon-carbon wire structure by slowly injecting the porous silica-carbon-carbon wire structure into the hydrofluoric acid solution, sealing the structure, and reacting for 12 hours or more;
The solution is removed by filtration and the solid is washed 3 to 5 times with distilled water; and
A manufacturing method, characterized in that it is prepared by a method comprising the step of drying the separated solid content at 90 ~ 110 ℃ for 10 ~ 14 hours. According to claim 1,
The medium pore carbon-carbon wire structure is a manufacturing method, characterized in that the average pore size is 3 ~ 5nm containing mesopores and the particle size is 80 ~ 800nm. a carbon structure including mesopores having an average pore size of 3 to 5 nm;
Containing a carbon wire grown from the carbon structure including the mesopores,
A medium-pore carbon-carbon wire structure for a lithium secondary battery negative electrode material having a particle size of 80 to 800 nm. 13. The method of claim 12,
The medium-pore carbon-carbon wire structure for a negative electrode material for a lithium secondary battery is characterized in that it is prepared by the method of any one of claims 1 to 10, wherein the medium-pore carbon-carbon wire structure for a lithium secondary battery negative electrode material. In the lithium secondary battery,
a carbon structure including mesopores having an average pore size of 3 to 5 nm; A lithium secondary battery comprising; a carbon wire grown from the carbon structure including the medium pores; and a medium pore carbon-carbon wire structure having a particle size of 80 to 800 nm as an anode material. 15. The method of claim 14,
The medium pore carbon-carbon wire structure is a lithium secondary battery, characterized in that it is manufactured by the method of any one of claims 1 to 10.

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