KR20240034570A - Producing method of mesoporous hollow carbon-oxidized metal-carbon complex for anode materials of lithium-ion battery - Google Patents

Abstract

The present invention relates to a method of manufacturing a mesoporous carbon-metal oxide-carbon composite for a negative electrode material of a lithium secondary battery. In particular, the present invention relates to a method of manufacturing a mesoporous carbon-metal oxide-carbon composite in a mesoporous carbon structure and introducing a carbon material with excellent electrical conductivity to produce a negative electrode of a lithium secondary battery. This relates to a method of manufacturing a mesoporous carbon-metal oxide-carbon composite that can develop a discharge capacity of 400 mAh/g or more when used as an active material. The manufacturing method of the present invention includes manufacturing a porous silica structure; Preparing a porous silica-carbon composite by coating the surface of the porous silica structure with a carbon-containing polymer material and heat treating it; removing silica from the porous silica-carbon composite to produce a mesoporous carbon structure; Preparing a mesoporous metal oxide (Fe ₂ O ₃ )-carbon composite by coating the mesoporous carbon structure with a metal and heat treating it; And a step of coating the mesoporous metal oxide-carbon composite with a carbon-containing polymer material and heat treating the mesoporous carbon-metal oxide-carbon composite to produce a mesoporous carbon-metal oxide-carbon composite. The mesoporous carbon-metal oxide-carbon composite of the present invention can be used as a negative electrode active material for lithium secondary battery negative electrodes and can develop a discharge capacity of 400 mAh/g or more, and suppresses the movement of metal oxides in the negative electrode to the electrolyte to reduce capacity loss and It reduces the increase in resistance, protects the cathode interface, increases stability, and surpasses the theoretical capacity of graphite, which is used as a conventional cathode active material, and is also competitive in terms of unit cost.

Description

{Producing method of mesoporous hollow carbon-oxidized metal-carbon complex for anode materials of lithium-ion battery}

The present invention relates to a method of manufacturing a mesoporous carbon-metal oxide-carbon composite for a negative electrode material of a lithium secondary battery. In particular, the present invention relates to a method of manufacturing a mesoporous carbon-metal oxide-carbon composite in a mesoporous carbon structure and introducing a carbon material with excellent electrical conductivity to produce a negative electrode of a lithium secondary battery. This relates to a method of manufacturing a mesoporous carbon-metal oxide-carbon composite that can develop a discharge capacity of 400 mAh/g or more when used as an active material.

In the era of smartization, secondary batteries are attracting attention as a core technology that can actively control electricity demand, such as smart cars, represented by electric vehicles, and smart grid, 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, and when discharged, receives external power and converts electrical energy into chemical energy to store electricity. It is a reversible battery of chemical and electrical energy. It is a chemical battery that can repeat charging and discharging using mutual changes.

Secondary batteries that have been commercialized to date include lead acid batteries, nickel/cadmium batteries, nickel/hydrogen batteries, and lithium secondary batteries. Among these, lithium secondary batteries are lightweight and use lithium ion, which has a high electrochemical standard potential, as an active material and has the highest operating voltage. represents.

The material initially studied as a negative electrode material for lithium secondary batteries is lithium metal. The standard electrode potential of lithium metal is -3.04V and the theoretical capacity is 3,860 mAh/g, showing a higher energy density than other negative electrode materials. However, it is thermodynamically unstable in the organic electrolyte and has the characteristic of growing into dendrites when charging/discharging is repeated. The dendrites generated by repeated charging/discharging are separated from the lithium metal, reducing charge/discharging efficiency and capacity, and are not directly connected to the anode. Contact causes an internal short circuit, which directly affects the stability of the battery.

The redox reaction of lithium metal is a process in which lithium ions are reduced and electrodeposited into 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 surface of lithium metal is formed by a solid electrolyte interface (SEI) layer made by accumulation of decomposition products formed due to a chemical reaction with the electrolyte solution. .

The SEI layer has lithium ion conduction properties and prevents corrosion of lithium by the electrolyte by preventing contact between the electrolyte and lithium. The reason why primary batteries using lithium metal anodes can exhibit excellent shelf life is because stable SEI is formed. Since the composition and structure of SEI varies greatly depending on the type of electrolyte, electrolyte design for SEI control is one of the very important technologies for stabilizing lithium metal anodes. However, when lithium is electrodeposited on lithium metal with SEI formed, uniform lithium electrodeposition is not achieved and lithium electrodeposition is concentrated locally.

Additionally, dendrite lithium may grow and cause an internal short circuit of the battery. Non-uniform electrodeposition of lithium increases contact with the electrolyte, forming a new SEI layer due to a side reaction between the electrolyte and lithium, causing depletion of the electrolyte and lithium. In the process of lithium elution, lithium metal falls off and forms electrically short-circuited 'dead' lithium. When this process is repeated, a porous layer in which reaction products with the electrolyte accumulate on the lithium surface. ) is formed, which increases the resistance of the battery and accelerates the non-uniformity of the electrode reaction.

The reasons why uneven electrodeposition of lithium occurs can be broadly divided into three categories.

First, when the rate of lithium electrodeposition reaction is high, lithium ions are depleted from the surface of lithium metal and the concentration decreases to 0, the electrode reaction falls into a diffusion controlled regime and interfacial instability increases. do. In order to reduce the overvoltage for the lithium electrodeposition reaction, the lithium metal interface grows vertically in a needle-like structure with a large surface area that can improve diffusion flux.

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 in areas or defects with relatively low resistance in the SEI layer.

Thirdly, 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 surface energy by forming a uniform interface. However, the activation energy for diffusion of lithium in the surface lattice is high, so a uniform interface cannot be formed. In other words, lithium metal has a very high activation energy (0.14 ~ 0.41 eV), showing the characteristic that the structure of the non-uniform lithium surface is maintained as is.

Additionally, lithium metal has a very low standard oxidation-reduction potential {-3.04 vs SHE (Standard Hydrogen Electrode)}, which means that it has a very high tendency to be oxidized. Therefore, when lithium metal comes into contact with an electrolyte, oxidation occurs while reducing the electrolyte.

Meanwhile, the lower the LUMO (lowest unoccupied molecular orbital) level of the electrolyte component, the faster the reduction, so the component with the lower LUMO level reacts with lithium first to form an SEI layer. Therefore, by controlling the LUMO level of the electrolyte component, 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 to design an electrolyte that forms a stable SEI layer or to introduce a protective film that blocks the reaction between electrolyte and lithium.

In order to overcome the low charge/discharge efficiency and stability of lithium metal, research has been conducted on carbon-based materials and metal-based materials that can react with lithium in an ion state, and carbon-based materials are used as anode materials in the first commercialized lithium secondary battery. was used as

Carbon-based materials have been the most widely used since lithium secondary batteries were first commercialized. Graphite, which has a high reversible capacity and low production cost, is the most widely used carbon-based material. The theoretical capacity of graphite is limited to 372 mAh/g, the output characteristics are poor due to the structural characteristics of high crystallinity, and the long life characteristics are poor due to side reactions with the electrolyte. It has the disadvantage of being deteriorated and having poor thermal safety.

Graphite crystals in carbon materials are obtained by combining carbon atoms in sp2-hybridized orbitals with each other in hexagonal planes to form a carbon hexagonal layer (graphene layer), and π electrons located above and below this carbon layer combine these layers. Graphite has excellent electronic conductivity because π electrons can move relatively freely between carbon hexagonal planes. The π bonds connecting these graphite layers form weak van der Waals bonds, but the bonds within the carbon hexagonal network are very strong covalent bonds, showing anisotropy. Lithium ions are inserted and desorbed between these graphite layers. Graphite undergoes a reduction reaction while the charging reaction progresses, 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 the graphite and lithium ions are desorbed. In these charging and discharging reactions, electrochemical properties such as reaction potential and lithium storage capacity appear differently depending on the crystallinity, microstructure, and particle shape of the carbon material. Because the salt of the electrolyte is simultaneously inserted during the insertion of lithium ions and the layered structure is peeled off, the cathode material currently used is mainly graphite with amorphous carbon coated on the surface.

Among electrode active materials, highly crystalline carbon materials, which are most commonly used as anode materials, must be graphitized at over 2000°C to exhibit high crystallinity. However, due to problems such as production costs, they cannot be manufactured domestically with mass production facilities, so all lithium must be imported. Among the four major components of secondary batteries, positive electrode active material, negative electrode active material, separator, and electrolyte, the dependence on imports of negative electrode active material is absolutely high. Currently, the mainly used graphite-based anode active materials are mainly products of Japanese companies, and domestic companies are conducting research on their own anode active materials such as graphite-based and silicon-based and are currently producing them domestically, but are not showing clear results.

Research and development on cathode active materials that can increase energy storage capacity are actively underway around the world. In connection with the increasingly serious natural environment problems, eco-friendly energy and storage systems are increasingly required, and thus, low-cost and eco-friendly energy technology is being developed. Research and development is also expanding. The performance of this energy storage/conversion is closely related to the characteristics of the materials that make up 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 was captured within the micrometer pores of the separator.

Recently, as the use area of lithium secondary batteries has expanded from portable power devices to power tools, EVs, ESS, etc., the demand for development of high-capacity, high-output, high-safety lithium secondary batteries has increased, leading to improvements in graphite and alternatives to it. The need for the development of new materials that can be used is increasing.

Lithium secondary batteries at the current level of technology have higher energy efficiency than existing nickel-cadmium secondary batteries or nickel-hydrogen secondary batteries, but due to limitations in the transfer speed of lithium ions in solids, charge/discharge speeds are relatively slow, resulting in low output. In order to improve the performance of communication devices, electric vehicles, and large-capacity energy storage devices, materials with improved charging/discharging of lithium ions are needed.

Among several candidates for use as a negative electrode material for lithium secondary batteries, metal oxide-carbon composite negative electrode material is a system that uses low-cost metal oxide as a negative electrode active material. The metal oxide-carbon composite anode material is based on the high theoretical capacity of metal oxide (Fe ₂ O ₃ , 1,005 mAh/g), so it produces a very high current that is approximately 3 times the theoretical capacity of conventionally used graphite (372 mAh/g). There is an advantage in that density is possible. However, although the metal oxide-carbon composite cathode material system has many advantages, the structural problems to achieve theoretical high energy density have not been solved, and capacity degradation occurs rapidly as the lifespan progresses. So far, it has not been commercialized. is having difficulty with In metal oxide-carbon composite anode materials, lithium-metal oxide, an intermediate product generated during charge/discharge reactions, is leached into the electrolyte, making it difficult to commercialize metal oxide-carbon composite anode materials. To control this problem, the most promising method is to use conductive porous carbon that has sufficient internal space to contain metal. Carbon materials for supporting metal oxides have high porosity to support metal oxides, high electrical conductivity to allow electrons generated by electrochemical reactions of metal oxides to move, and volume expansion due to electrochemical reactions of metal oxides. Requirements such as mechanical strength that can be suppressed and distribution of pores of various sizes that can prevent the elution of lithium-metal oxide, an intermediate product, are required, so the development of a carbon composite that can satisfy these requirements is required.

As research on nanoscale metal active materials began, research on the manufacture of nanoscale iron oxide structures also began in earnest in the late 1990s. Nanostructured iron oxide structures, which typically have dimensions of 100 nm or less, have recently been developed in the form of nanorods, nanosheets, and nanofibers. Among these, the production of nanotubes by alkaline hydrothermal synthesis is relatively more economical than carbon nanotubes, which has accelerated its development. Nanorod-shaped particles have excellent output characteristics and cycle stability, but are known to cause a serious decrease in the charge density or energy density of the electrode plate when manufacturing electrodes compared to spherical particles. This is a unique characteristic of spiral particles in which more vacancies are formed between particles compared to spherical particles. Therefore, a new concept of active material structure is needed that can take advantage of the output characteristics of these structural materials while maintaining high energy density and high filling density in the electrode plate.

Republic of Korea Patent Registration No. 10-0744832 Republic of Korea Patent Publication No. 10-2008-0111809 Republic of Korea Patent Publication No. 10-2009-0001316 Republic of Korea Patent Publication No. 10-2008-0006898 Republic of Korea Patent Publication No. 10-2009-0112542

The purpose of the present invention is to provide a method for producing a mesoporous carbon-metal oxide-carbon composite with high porosity, high electrical conductivity, mechanical strength, and pore distribution of various sizes for use as a negative electrode active material in lithium secondary batteries. Do it as

Specifically, the present invention is a conductive polymer material that can suppress the elution and diffusion of lithium-metal oxide by supporting metal oxide in a mesoporous carbon structure manufactured using silica as a template and introducing a carbon material with excellent electrical conductivity into the metal oxide. The purpose is to provide a mesoporous carbon-metal oxide-carbon composite coated with carbon.

In particular, the present invention can be used as a negative electrode active material for lithium secondary batteries to develop a discharge capacity of 400 mAh/g or more, and suppresses the movement of metal oxides in the negative electrode into the electrolyte to reduce capacity loss and resistance increase and protect the negative electrode interface. The aim is to provide a mesoporous carbon-metal oxide-carbon composite that can increase stability.

In order to achieve the above object, in the present invention,

Preparing a porous silica structure; Preparing a porous silica-carbon composite by coating the surface of the porous silica structure with a carbon-containing polymer material and heat treating it; removing silica from the porous silica-carbon composite to produce a mesoporous carbon structure; Preparing a mesoporous metal oxide (Fe ₂ O ₃ )-carbon composite by coating the mesoporous carbon structure with a metal and heat treating it; And preparing a mesoporous carbon-metal oxide-carbon composite by coating the mesoporous metal oxide-carbon composite with a carbon-containing polymer material and heat treating it to produce a mesoporous carbon-metal oxide-carbon composite. A method for manufacturing a carbon composite is provided.

The manufacturing method may further include heat treating the manufactured mesoporous carbon structure. Preferably, the heat treatment at this time includes heat treatment at 400 to 900°C for 3 to 8 hours.

The manufacturing method may further include heat treating the prepared mesoporous metal oxide-carbon composite. Preferably, the heat treatment at this time includes heat treatment at 400 to 900°C for 3 to 8 hours.

In the above manufacturing method, the porous silica structure contains 2 to 10% by weight of TEOS, 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, and 0.14 to 0.5% by weight of TEOS based on the total weight of the composition. It is preferably prepared using a composition comprising twice the weight of the organosilane, and the remainder in a solvent selected from ethanol and methanol.

In the above manufacturing method, the porous silica structure is,

Synthesizing by mixing ammonia water, distilled water, organosilane and TEOS at a concentration of 20 to 35% by weight in a solvent and stirring for 2 to 7 hours; Removing the liquid part, separating only the solid content, and drying it at 90-110°C for more than 12 hours; and heat treatment at 500-600°C for 4-6 hours.

In the above manufacturing method, the porous silica-carbon composite,

Dissolving the carbon-containing polymer material in distilled water; coating the porous silica structure with the carbon-containing polymer material by supporting the porous silica structure on the carbon-containing polymer material dissolved in distilled water for more than 5 hours; Drying the porous silica structure coated with the carbon-containing polymer material at 100-120°C for more than 12 hours; After drying, oxidation treatment at 180~220℃ for 1~2 hours; and oxidation treatment followed by heat treatment at 400 to 900°C for 2 to 8 hours in a nitrogen atmosphere.

In the above manufacturing method, the mesoporous carbon structure preferably has a particle size of 100 to 500 nm.

In the above manufacturing method, the mesoporous metal oxide-carbon composite,

Dissolving ferrous chloride (FeCl ₂ ) in distilled water; Preparing a mesoporous carbon-ferrous chloride composite by supporting the mesoporous carbon structure in the ferrous chloride solution dissolved in distilled water, coating the mesoporous carbon structure with ferrous chloride and drying it; and heat-treating the mesoporous carbon-ferrous chloride composite at 450-550°C for 4-6 hours in a nitrogen atmosphere.

In the above manufacturing method, the mesoporous carbon-metal oxide-carbon composite,

Dissolving the carbon-containing polymer material in distilled water; Supporting the mesoporous metal oxide-carbon composite on the carbon-containing-polymer material dissolved in distilled water for more than 5 hours to coat the mesoporous metal oxide-carbon composite with the carbon-containing-polymer material; and heat-treating the mesoporous metal oxide-carbon composite coated with the carbon-containing polymer material at 850-950°C for 4-6 hours.

In the above manufacturing method, the content of metal oxide in the mesoporous carbon-metal oxide-carbon composite is preferably 10 to 50% by weight.

According to the manufacturing method of the present invention, the metal oxide is supported in the mesoporous carbon structure and carbon with excellent electrical conductivity is introduced to the surface, thereby suppressing the elution and diffusion of lithium-metal oxide and increasing the electrical conductivity in the electrode to prevent the metal oxide from forming. It is possible to manufacture a mesoporous carbon-metal oxide-carbon composite that can increase utilization rate.

The mesoporous carbon-metal oxide-carbon composite of the present invention can be used as a negative electrode active material for lithium secondary batteries and can develop a discharge capacity of 400 mAh/g or more, and suppresses the movement of metal oxide in the negative electrode to the electrolyte, reducing capacity loss and resistance. Stability can be increased by reducing the increase and protecting the cathode interface. In addition, it surpasses the theoretical capacity of graphite, which is conventionally used as a negative electrode active material, and is competitive in terms of unit cost.

Figure 1 is an SEM image of a porous silica core synthesized according to reaction time. (A) is the result at a reaction time of 1 hour, (B) is a reaction time of 2 hours, and (C) is a result at a reaction time of 5 hours.
Figure 2 is an SEM image of the silica core according to the amount of ammonia water. The amount of ammonia water relative to the weight of ethanol is (A) 2% by weight, (B) 5% by weight, (C) 9% by weight, and (D) 15% by weight.
Figure 3 is an SEM image of the silica core according to the amount of water (water in distilled water + ammonia water). The amount of water relative to the weight of ethanol is (A) 3% by weight, (B) 7% by weight, (C) 11% by weight, (D) 18% by weight, and (E) 23% by weight.
Figure 4 is an SEM image of silica core depending on the amount of TEOS. The amounts of TEOS are (A) 2% by weight, (B) 6% by weight, and (C) 10% by weight.
Figure 5 shows the change in size of the silica core according to various reaction conditions (reaction time, reaction catalyst, amount of distilled water and TEOS).
Figure 6 is an SEM image of porous silica cores with particle sizes of 80 nmn, 300 nm, and 500 nm.
Figure 7 is a nitrogen isotherm of porous silica cores with particle sizes of 80 nm, 300 nm, and 500 nm.
Figure 8 is a pore distribution curve of porous silica cores with particle sizes of 80 nm, 300 nm, and 500 nm.
Figure 9 shows the results of comparing the physical properties of porous silica cores according to size.
Figure 10 is an SEM image, nitrogen isotherm, and pore distribution curve of a porous silica core-shell manufactured using organosilane.
Figure 11 is an SEM image, nitrogen isotherm, and pore distribution curve of a porous silica core-shell prepared using CTAB.
Figure 12 is an SEM image, nitrogen isotherm, and pore distribution curve of a porous silica core-shell prepared using CTAC.
Figure 13 is an SEM image of a porous silica core-shell structure manufactured using various carbon-containing polymer materials, (A) divinylbenzene resin, (B) cellulose, (C) phenol resin, (D) is polyvinyl acrylic.
Figure 14 is an SEM image of porous silica core-shell according to the application ratio of organosilane. The ratio of organosilane (organosilane/TEOS) is (A) 0.125, (B) 0.375, and (C) 1.
Figure 15 is a nitrogen isotherm of porous silica core-shell prepared with organosilane ratios (organosilane/TEOS) of 0.125, 0.375, and 1.
Figure 16 is a pore distribution curve of porous silica core-shell according to organosilane ratio.
Figure 17 is a graph comparing the physical properties of porous silica core-shell according to organosilane ratio.
Figure 18 shows thermogravimetric analysis (TGA) results of a phenolic resin and a silica-resin composite coated with it on the silica surface.
Figure 19 is an SEM image of a porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ).
Figure 20 is a nitrogen isotherm and pore distribution curve of porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ).
Figure 21 is an SEM image of a porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C).
Figure 22 is a nitrogen isotherm and pore distribution curve of porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C).
Figure 23 shows the EDS analysis results of porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C).
Figure 24 shows silica (SiO ₂ ), silica-metal oxide complex (Fe ₂ O ₃ @SiO ₂ ) and the XRD diffraction pattern of silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C).
Figure 25 shows the results of a charge/discharge test for lithium ions of a porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C).
Figure 26 is an SEM image and XRD diffraction pattern of a porous silicon oxide-carbon composite (SiOx@Carbon).
Figure 27 is a nitrogen isotherm of porous silica-carbon composite (SiO ₂ @Carbon) and porous silicon oxide-carbon composite (SiOx@Carbon).
Figure 28 is a pore distribution curve of porous silica-carbon composite (SiO ₂ @Carbon) and porous silicon oxide-carbon composite (SiOx@Carbon).
Figure 29 shows the charge/discharge performance of porous silicon oxide-carbon composite (SiOx@Carbon) at 400 mA/g.
Figure 30 is an SEM image, nitrogen isotherm, and pore distribution curve of a porous silica structure.
Figure 31 is an SEM image, nitrogen isotherm, and pore distribution curve of a porous silica-carbon composite.
Figure 32 is an SEM image, nitrogen isotherm, and pore distribution curve of a mesoporous carbon structure.
Figure 33 is an SEM image of a mesoporous carbon structure with organosilane application ratios of 0.125, 0.375, and 1.
Figure 34 is a nitrogen isotherm of mesoporous carbon structures according to organosilane application ratio.
Figure 35 is a pore distribution curve of a mesoporous carbon structure according to the organosilane application ratio.
Figure 36 compares the physical properties of mesoporous structures by organosilane application ratio.
Figure 37 is a nitrogen isotherm of a mesoporous carbon structure according to the application ratio of carbon-containing polymer material.
Figure 38 is a pore distribution curve of a mesoporous carbon structure according to the application ratio of carbon-containing polymer material.
Figure 39 compares the physical properties of mesoporous carbon structures according to the application ratio of carbon-containing polymer materials.
Figure 40 is an SEM image of a mesoporous carbon structure manufactured with particle sizes of 100 nm, 500 nm, and 700 nm.
Figure 41 is a nitrogen isotherm and pore distribution curve of a mesoporous carbon structure manufactured with particle sizes of 100 nm, 500 nm, and 700 nm.
Figure 42 is a nitrogen isotherm for each heat treatment temperature of a mesoporous carbon structure heat-treated at 110°C, 400°C, 700°C, and 900°C.
Figure 43 is a pore distribution curve by heat treatment temperature for a mesoporous carbon structure heat-treated at 110°C, 400°C, 700°C, and 900°C.
Figure 44 compares the physical properties of mesoporous carbon structures heat-treated at 110°C, 400°C, 700°C, and 900°C according to heat treatment temperature.
Figure 45 is an SEM image of a mesoporous carbon structure heat-treated at 900°C for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours.
Figure 46 is a nitrogen isotherm of a mesoporous carbon structure heat-treated at 900°C for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours.
Figure 47 is a pore distribution curve of a mesoporous carbon structure manufactured by heat treatment at 900°C for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours.
Figure 48 compares the physical properties of mesoporous carbon structures.
Figure 49 is a particle distribution curve of a mesoporous carbon structure according to heat treatment time (1 to 5 hours).
Figure 50 shows the charge/discharge battery performance of a mesoporous carbon structure heat-treated for 1 hour at heat treatment temperatures of 110°C, 450°C, and 700°C.
Figure 51 shows the charge/discharge performance of a mesoporous carbon structure heat-treated at a heat treatment temperature of 900°C for 1 hour and 5 hours.
Figure 52 shows the charge/discharge performance of the mesoporous carbon structure when the current density is 50 mA/g, 100 mA/g, and 200 mA/g.
Figure 53 is a report on the results of an experiment conducted at the Korea Testing and Research Institute.
Figure 54 is an SEM image of a mesoporous metal oxide-carbon composite containing 4% by weight, 10% by weight, and 20% by weight of iron oxide in the mesoporous carbon structure.
Figure 55 shows the results of XRD diffraction pattern analysis of a mesoporous metal oxide-carbon composite containing 4% by weight, 10% by weight, and 20% by weight of iron oxide in the mesoporous carbon structure.
Figure 56 is a nitrogen isotherm of a mesoporous metal oxide-carbon composite containing 4%, 10%, and 20% by weight of iron oxide in the mesoporous carbon structure.
Figure 57 is a pore distribution curve of a mesoporous metal oxide-carbon composite containing 4% by weight, 10% by weight, and 20% by weight of iron oxide in the mesoporous carbon structure.
Figure 58 compares the physical properties of mesoporous metal oxide-carbon composites.
Figure 59 shows the charge/discharge performance of the mesoporous metal oxide-carbon composite.
Figure 60 is an SEM image of pure carbon carbonized by heat treatment of a carbon-containing polymer material.
Figure 61 is an SEM image of a mesoporous carbon-metal oxide-carbon composite containing 10% by weight of metal oxide.
Figure 62 is an SEM image of a mesoporous carbon-metal oxide-carbon composite containing 30% by weight of metal oxide.
Figure 63 is an SEM image of a metal oxide sample heat-treated without coating a carbon-containing polymer material.
Figure 64 shows a mesoporous carbon structure (carbon) coated with carbon on a mesoporous carbon structure containing no metal, a mesoporous carbon-metal oxide-carbon composite (F10C) containing 10% by weight of metal oxide (iron oxide), and oxidation These are the thermogravimetric analysis results of a mesoporous carbon-metal oxide-carbon composite (F30C) containing 30% by weight of metal (iron oxide) and a structure using only iron oxide (F100).
Figure 65 shows a carbon structure (carbon) coated with carbon on a mesoporous carbon structure containing no metal, a mesoporous carbon-metal oxide-carbon composite (F10C) containing 10% by weight of metal oxide (iron oxide), and a metal oxide ( This is a comparison of the final yield calculated from the thermogravimetric analysis results of the mesoporous carbon-metal oxide-carbon composite (F30C) containing 30% by weight of iron oxide and the structure using only iron oxide (F100).
Figure 66 is a nitrogen isotherm of mesoporous carbon-metal oxide-carbon composites.
Figure 67 is a pore distribution curve of mesoporous carbon-metal oxide-carbon composites.
Figure 68 shows a mesoporous carbon-metal oxide-carbon composite (F10C) containing 10% by weight of metal oxide (iron oxide) and a mesoporous carbon-metal oxide-carbon composite (F30C) containing 30% by weight of metal oxide (iron oxide). , XRD diffraction patterns and particle distribution curves of a mesoporous carbon-metal oxide-carbon composite (F50C) containing 50% by weight of metal oxide (iron oxide) and a structure using only iron oxide (F100).
Figure 69 shows the charge/discharge performance of a mesoporous carbon-metal oxide-carbon composite (F10C) containing 10% by weight of iron oxide at 100 mA/g.
Figure 70 shows the charge/discharge performance at 100 mA/g of a mesoporous carbon-metal oxide-carbon composite (F30C) containing 30% by weight of iron oxide.
Figure 71 shows the charge/discharge performance at 100 mA/g of an iron oxide sample without a carbon-containing polymer material coating.
Figure 72 is a report on the results of an experiment conducted at the Korea Testing and Research Institute.
Figure 73 is an SEM image of nanoscale iron oxide (F0) manufactured by hydrothermal synthesis.
Figure 74 is an SEM image of a nano-scale metal oxide-carbon composite (CF3) coated with 3% by weight of carbon on the surface of iron oxide prepared by hydrothermal synthesis.
Figure 75 is an SEM image of a nanoscale metal oxide-carbon composite (CF10) prepared by hydrothermal synthesis and coated with 10% by weight of carbon on the surface of iron oxide.
Figure 76 is an SEM image of a nanoscale metal oxide-carbon composite (CF30) produced by hydrothermal synthesis and coated with 30% by weight of carbon on the surface of iron oxide.
Figure 77 is an SEM image of a nanoscale metal oxide-carbon composite (CF50) coated with 50% by weight of carbon on the surface of iron oxide prepared by hydrothermal synthesis.
Figure 78 graphically shows the results of thermogravimetric analysis of nanoscale iron oxide and iron oxide-carbon composites.
Figure 79 shows the results of X-ray diffraction pattern analysis of nanoscale iron oxide and iron oxide-carbon complexes.
Figure 80 shows the initial charge and discharge performance of nanoscale metal oxide-carbon composites coated with 3% by weight and 10% by weight of carbon.
Figure 81 shows the initial charge and discharge performance of nanoscale metal oxide-carbon composites coated with 30% and 50% by weight of carbon.
Figure 82 shows the discharge performance and charge/discharge efficiency of nanoscale metal oxide-carbon composites coated with 3% by weight and 10% by weight of carbon according to the number of charge/discharge times.
Figure 83 shows the discharge performance and charge/discharge efficiency according to the number of charge/discharge of nanoscale metal oxide-carbon composites coated with 30% and 50% by weight of carbon.
Figure 84 compares the results of analyzing discharge performance according to the content of metal oxide in the nanoscale metal oxide-carbon composite.

The present invention relates to a method of manufacturing a mesoporous carbon-metal oxide-carbon composite for a negative electrode material of a lithium secondary battery. The manufacturing method of the present invention includes the steps of manufacturing a porous silica structure; Preparing a porous silica-carbon composite by coating the surface of the porous silica structure with a carbon-containing polymer material and heat treating it; removing silica from the porous silica-carbon composite to produce a mesoporous carbon structure; Preparing a mesoporous metal oxide (Fe ₂ O ₃ )-carbon composite by coating the mesoporous carbon structure with a metal and heat treating it; And a step of coating the mesoporous metal oxide-carbon composite with a carbon-containing polymer material and heat treating the mesoporous carbon-metal oxide-carbon composite to produce a mesoporous carbon-metal oxide-carbon composite.

Hereinafter, the present invention will be described in detail for each step.

1. Preparation of porous silica structure

The porous silica structure is manufactured through a sol-gel reaction using a mixture of silica (SiO ₂ , Dioxide Silicon) raw materials, a solvent, a catalyst, distilled water for hydrolysis, and a surfactant.

TEOS (Tetraethyl orthosilicate) is used as the silica raw material. It is preferable to use 2 to 10% by weight of TEOS based on the total weight of the composition.

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

Ammonia water, hydrochloric acid, nitric acid, or sulfuric acid are used as catalysts for silica synthesis. It is more preferable to use ammonia water. As ammonia water, it is preferable to use ammonia water with a concentration of 20 to 35% by weight, and it is more preferable to use ammonia water with a concentration of 25 to 30% 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 to expand pores. Surfactants include organosilanes [C ₁₈ -TMS{Trimethoxy(octadecyl)silane}], CTAB (Cetyltrimethylammoniumbromide), CTAC (Cetyltrimethylammoniumchloride), Divinylbenzene, Cellulose, Phenol resin, and poly. Vinyl alcohol (polyvinylalcohol), etc. can be used. Particular preference is given to using organosilanes.

It is preferable to use the surfactant in an amount such that the weight ratio of surfactant/TEOS is 0.14 to 0.5, more preferably 0.3 to 0.4, and especially preferably 0.375.

It is particularly preferable to use an organosilane in a weight of 0.14 to 0.5 times the weight of TEOS.

The porous silica structure consists of 2 to 10% by weight of TEOS, 2 to 15% by weight of ammonia water with a concentration of 20 to 35% by weight, 3 to 25% by weight of distilled water, and an organosilane with a weight of 0.14 to 0.5 times the weight of TEOS, based on the total weight of the composition. and the remainder is preferably prepared using a composition comprising a solvent selected from ethanol and methanol.

A porous silica structure is synthesized by mixing ammonia water, organosilane, and TEOS in ethanol or methanol as a solvent and reacting with stirring for 2 to 7 hours or more. It is more preferable to react for 2 to 6 hours, and it is especially preferable to react for 5 hours.

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

The dried silica structure is heat-treated at 500-600°C for 4-6 hours to remove organic substances present inside, thereby obtaining a porous silica structure.

The porous silica structure is a spherical material with a particle size (diameter) of 80 to 700 nm and is used as a template for manufacturing mesoporous carbon-metal oxide-carbon composites used as structures for cathode materials. The particle size of the porous silica structure is preferably 200 to 600 nm, and more preferably 300 to 500 nm.

The size of the porous silica structure does not have a significant effect on the volume and distribution of pores formed between silica particles or particles. As the size of the core increases, the size of the pores formed between particles expands and macropores develop more. It is confirmed that it does.

2. Preparation of porous silica-carbon composite

A porous silica-carbon composite is prepared by coating the porous silica structure with carbon.

Carbon-containing polymer materials are selected from divinylbenzene resin, cellulose, phenol resin, and polyvinyl alcohol. It is more preferable to use phenol resin.

Carbon-containing polymer materials are dissolved in distilled water. It is desirable to dissolve the carbon-containing polymer material in distilled water 2 to 4 times the weight of the porous silica structure.

The porous silica structure is supported on a carbon-containing polymer material dissolved in distilled water, and the carbon-containing polymer material is coated on the porous silica structure. It is preferable to hold for more than 5 hours, and more preferably for 5 to 7 hours.

The carbon-containing polymer material dries the porous silica structure at 100~120℃ for more than 12 hours. It is more preferable to dry for 12 to 14 hours.

After drying, oxidize at 180~220℃ for 1~2 hours. Oxidation treatment at 200°C for 1 hour is particularly preferred. At this time, it is desirable to raise the temperature to 180~220℃ at a rate of 1℃/min in an air atmosphere.

After oxidation treatment, it is carbonized by heat treatment at 400~900℃ for 2~8 hours. Heat treatment at 900°C for 5 hours is particularly preferred. At this time, it is desirable to raise the temperature to 400-900°C at a rate of 5°C/min in a nitrogen atmosphere.

Once heat treatment is complete, cool to room temperature.

In the above process, a porous silica-carbon structure is obtained in which carbon is coated on the surface of the porous silica structure.

3. Fabrication of mesoporous carbon structures

Silica is removed from the porous silica-carbon composite to produce a mesoporous hollow carbon structure.

Preferably, the removal of silica includes mixing distilled water and a silica removal material to prepare a silica removal solution with a concentration of 15 to 25% by weight; Gradually injecting the porous silica-carbon composite into the silica removal solution, sealing it, and reacting for more than 12 hours to dissolve the silica in the porous silica-carbon composite; Dissolving the silica and then filtering to remove the solution and washing the solids; And drying the washed solids at 90-110°C for 10-14 hours.

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

First, prepare a silica removal solution with a concentration of 15 to 25% by weight by mixing distilled water and a silica removal material. It is preferable to prepare a silica removal solution with a concentration of 15 to 25% by weight by placing 8 to 12 times the weight of the solid content of the porous silica-carbon composite in a reaction vessel and slowly injecting the silica removal material into the distilled water.

The porous silica-carbon composite is slowly injected into the prepared silica removal solution, sealed, and reacted for more than 12 hours to dissolve the silica in the porous silica-carbon composite. It is preferable to react for 12 to 14 hours. The reaction is preferably carried out while vibrating and stirring using a vibrating stirrer.

When the reaction is complete, the solution is removed by filtration and the solid content is washed. It is desirable to wash solids 3 to 5 times using distilled water.

The washed solids are dried at 90 to 110°C for 10 to 14 hours to produce a mesoporous carbon structure.

The mesoporous carbon structure preferably has a particle size of 100 to 500 nm.

The physical properties of the mesoporous carbon structure can be improved by heat treating the prepared mesoporous carbon structure. The mesoporous carbon structure is preferably heat treated at 400 to 900°C for 3 to 8 hours, and more preferably at 700 to 900°C for 4 to 5 hours.

4. Preparation of mesoporous metal oxide-carbon composites

A metal is coated on the mesoporous carbon structure and oxidized to produce a mesoporous metal oxide-carbon composite.

As a raw material for metal oxide, ferrous chloride (FeCl ₂ ) is used to obtain iron oxide (Fe ₂ O ₃ ).

Ferrous chloride (FeCl ₂ ) is dissolved in distilled water. It is preferable to dissolve 8 to 15% by weight of ferrous chloride (FeCl ₂ ) in distilled water 8 to 15 times the weight of the mesoporous carbon structure. It is more preferable to dissolve 10% by weight of ferrous chloride (FeCl ₂ ) reagent in 10 times the weight of distilled water.

The mesoporous carbon structure is soaked in a ferrous chloride solution dissolved in distilled water for 3 to 5 hours, the mesoporous carbon structure is coated with ferrous chloride, and then dried. Evaporation to dryness is preferred.

Dried ferrous chloride (FeCl ₂ )-carbon powder is charged into a sintering furnace and heat-treated at 450-550°C for 4-6 hours in a nitrogen atmosphere to obtain a mesoporous metal oxide (Fe ₂ O ₃ )-carbon composite. Heat treatment at 500°C for 5 hours is more preferable.

The physical properties of the mesoporous metal oxide-carbon composite can be improved by heat treating the prepared mesoporous metal oxide-carbon composite. The mesoporous metal oxide-carbon composite is preferably heat treated at 400 to 900°C for 3 to 8 hours, and more preferably at 700 to 900°C for 4 to 5 hours.

5. Preparation of mesoporous carbon-metal oxide-carbon composite

A mesoporous carbon-metal oxide-carbon composite is prepared by coating the mesoporous metal oxide-carbon composite with a carbon-containing polymer material.

Carbon-containing polymer materials can be selected from divinylbenzene resin, cellulose, phenol resin, and polyvinyl alcohol. It is more preferable to use phenol resin.

Carbon-containing polymer materials are dissolved in distilled water. It is desirable to dissolve the carbon-containing polymer material in distilled water at a weight of 2 to 4 times the weight of the mesoporous metal oxide-carbon composite.

The mesoporous metal oxide-carbon composite is supported on a carbon-containing-polymer material dissolved in distilled water, and the carbon-containing-polymer material is coated on the mesoporous metal oxide-carbon composite. It is preferable to hold for more than 5 hours, and more preferably for 5 to 7 hours.

The mesoporous metal oxide-carbon composite coated with the carbon-containing polymer material is heat-treated at 850-950°C for 4-6 hours in a nitrogen atmosphere.

In the above process, a mesoporous carbon-metal oxide-carbon composite in which carbon is coated on the surface of the mesoporous metal oxide-carbon composite is obtained.

The content of metal oxide in the mesoporous carbon-metal oxide-carbon composite is preferably 10 to 50% by weight, more preferably 20 to 40% by weight, and especially preferably 30%.

The mesoporous carbon-metal oxide-carbon composite prepared as described above is used as a negative electrode material in lithium secondary batteries. The mesoporous carbon-metal oxide-carbon composite for lithium secondary battery negative electrode material can be mixed with a conductive material, binder, and solvent to produce a negative electrode plate for lithium secondary battery.

As a binder, PAA-SBR (polyacrylic acid-styrene butadiene rubber), PVDF (polyvinylidene fluoride or polyvinylidene difluoride), etc. can be used. Adhesion is superior when PAA-SBR is used as a binder.

It is preferable to mix the mesoporous carbon-metal oxide-carbon composite and the binder at a weight ratio of 80:15 to 25, and especially preferably at a weight ratio of 82:20.

When the mesoporous carbon-metal oxide-carbon composite of the present invention is used as a negative electrode material, the discharge capacity is superior to that of currently commercialized graphite.

The present invention will be described in more detail below through examples and experimental examples. These are illustrative of the present invention and the scope of the present invention is not limited thereto.

<Example 1>

Preparation of porous silica core

As raw materials for manufacturing the porous silica core, anhydrous ethanol (Sigma-Aldrich), aqueous ammonia solution (28%, Sigma-Aldrich), distilled water (Sigma-Aldrich), and TEOS (99.99%, Sigma-Aldrich) were used.

Anhydrous ethanol was added to the synthesis reactor. 4% by weight of ammonia water was added compared to the weight of ethanol. Next, 10% by weight of distilled water compared to the weight of ethanol was added and strongly stirred to ensure that each substance was uniformly mixed. Afterwards, TEOS, a silica raw material, was added at 6% by weight based on the weight of ethanol, and then reacted for 5 hours while strongly stirring.

When the reaction reached the end stage, the silica solid was separated using a centrifuge and dried at 100°C to prepare a porous silica core.

<Experimental Example 1>

Check manufacturing conditions of porous silica core

The manufacturing conditions for controlling the size of the porous silica core were confirmed as follows.

In order to manufacture various cores made of silica materials, silica cores were manufactured using the materials input during the manufacturing process as a variable. The production of the silica core was carried out as follows.

Raw materials for manufacturing the porous silicon core include anhydrous ethanol (Sigma-Aldrich), ammonia solution (28%, Sigma-Aldrich), distilled water (Nuclease-Free Water, Sigma-Aldrich), and TEOS (99.99%, Sigma-Aldrich). was used.

After a certain amount of anhydrous ethanol was added to the synthesis reactor, a certain amount of ammonia water was added based on the weight of ethanol. Then, a certain amount of distilled water was added and stirred vigorously for a certain period of time to ensure that each substance was mixed evenly. Afterwards, a certain amount of TEOS, a silica raw material, was added, and the reaction proceeded for a certain period of time while vigorously stirring.

As the synthesis reaction progresses, the transparent solution becomes opaque, and these opaque particles are SiO ₂ molecules continuously bonded together. When the reaction reached the end stage, the silica solid content was separated using a centrifuge, dried at 100°C, and then analyzed using an analysis device such as an SEM. At this time, since the amount of each input material relative to the weight of ethanol is a factor that determines the size of the silica core, we attempted to derive the manufacturing conditions necessary for core manufacturing by using this as an experimental variable.

(One) Size control of porous silica core according to reaction time

A porous silica core was prepared by using the reaction time after adding TEOS as a variable during the sol-gel synthesis process to prepare the porous silica core.

At this time, the amount of input raw materials was fixed at a constant level, and the silica sol was centrifuged for each reaction time to analyze the size of the porous silica core. The materials and composition used in the experiment are as follows.

As raw materials, 85% by weight of anhydrous ethanol, 3% by weight of aqueous ammonia solution, 7% by weight of distilled water, and 5% by weight of TEOS were used.

To check the effect of reaction time in the sol-gel synthesis process, TEOS was added, the reaction solution was centrifuged at 1 hour, 2 hours, and 5 hours after the reaction time, and the size of the core was confirmed using SEM images. did.

SEM images of the porous silica core synthesized at different reaction times are shown in Figure 1. In Figure 1, the reaction times are (A) 1 hour, (B) 2 hours, and (C) 5 hours.

As shown in Figure 1, when the reaction time for synthesis was 1 hour, the size of the core was about 200 nm, and when the reaction time was 2 hours, the size of the core was about 300 nm, which is the porous silica core when the reaction time was 1 hour. It increased by about 100 nm from the size of 200 nm. However, after 2 hours of reaction time elapsed, the size of the silicon core did not change even after the reaction time had elapsed.

Therefore, the reaction time for synthesizing the silicon core is set by adding the reaction stabilization time to the reaction end time, and was set to a minimum of 5 hours to induce completion of the micro-reaction of Theos.

(2) Adjustment of the size of the porous silica core according to the amount of reaction catalyst

In order to check the effect of ammonia, which acts as a catalyst to promote the process of changing TEOS to silica (SiO ₂ ) in the sol-gel synthesis process to manufacture a porous silica core, the amount of other raw materials input was fixed constant and ammonia water was used. The experiment was conducted by controlling only the amount.

The reaction was conducted for 5 hours using 2 to 15% by weight of ammonia aqueous solution, 11% by weight of distilled water, and 8% by weight of TEOS relative to the weight of anhydrous ethanol. After the reaction, the silica sol was centrifuged and the size of the porous silica core was analyzed.

Porous silica core prepared under conditions where the amount of ammonia water was 2% by weight (A), 5% by weight (B), 9% by weight (C), and 15% by weight (D), respectively, relative to the weight of ethanol, and the reaction time was 5 hours. The SEM image is shown in Figure 2. As shown in Figure 2, the outer diameter of the porous silica core was found to be 300 nm on average under all conditions even when the amount of ammonia water added was changed. According to these results, the amount of ammonia, which acts as a catalyst, did not affect the size of the silicon core.

(3) Adjustment of the size of the porous silica core according to the amount of distilled water

To check the effect of the amount of water involved in the condensation polymerization reaction during the conversion of TEOS to silica during the sol-gel synthesis process to produce a porous silica core, an experiment was conducted by fixing the amount of other raw materials input to a constant level and controlling only the amount of distilled water. did.

The reaction was conducted for 5 hours using 4% by weight of ammonia aqueous solution, 0-20% by weight of distilled water, and 8% by weight of TEOS relative to the weight of anhydrous ethanol. After the reaction, the silica sol was centrifuged and the size of the porous silica core was analyzed.

The total amount of water (water in distilled water + ammonia water) is 3% by weight (A), 7% by weight (B), 11% by weight (C), 18% by weight (D), and 23% by weight (E) by weight, respectively, relative to the weight of ethanol. The SEM image of the porous silica core prepared under the condition of a reaction time of 5 hours is shown in Figure 3.

In Figure 3, the size of the porous silica core is an average of 50 to 80 nm when the total amount of water is 3% by weight, an average of 230nm when the total amount of water is 7% by weight, an average of 300nm when the total amount of water is 11% by weight, and an average of 300nm and 23% by weight when the total amount of water is 18% by weight. %, the average was 300 nm.

According to these results, the size of the porous silica core can be adjusted depending on the amount of water molecules that provide oxygen, which serves as a link for silicon during the condensation polymerization reaction using TEOS.

(4) Adjustment of the size of the porous silica core according to the amount of TEOS

In order to check the effect of the amount of TEOS involved in the condensation polymerization reaction in the process of converting TEOS to silica during the sol-gel synthesis process to manufacture a porous silica core, the amount of other raw materials input was fixed constant and only the amount of TEOS was adjusted. Experimented.

The reaction was conducted for 5 hours using 4% by weight of ammonia aqueous solution, 11% by weight of distilled water, and 2-10% by weight of TEOS relative to the weight of anhydrous ethanol. After the reaction, the silica sol was centrifuged and the size of the porous silica core was analyzed.

In this experimental condition, 11% by weight of distilled water was used to ensure a sufficient amount of water in order to exclude the influence of water molecules necessary for the condensation reaction and to check the change in core size purely due to the change in the amount of TEOS.

The SEM image of the porous silica core prepared under conditions where the amount of TEOS was 2% by weight (A), 6% by weight (B), and 10% by weight (C) and the reaction time was 5 hours is shown in Figure 4.

In Figure 4, it can be seen that when the amount of TEOS is 2% by weight, the size of the porous silica core is 80nm on average, when the amount of TEOS is 6% by weight, it is 300nm on average, and when the amount of TEOS is 10% by weight, it is 500nm on average.

(5) Manufacturing conditions of porous silica core

The change in size of the porous silica core according to the reaction time, reaction catalyst, distilled water, and amount of TEOS confirmed in the experiment as described above is shown in Figure 5.

From the results in Figure 5, it can be seen that the factor that has the greatest influence on the size change of the porous silica core is TEOS, a silica raw material.

<Experimental Example 2>

Determination of physical properties of porous silica core

The physical properties according to the size of the porous silica core, which has the greatest influence on the pore volume of the mesoporous metal oxide-carbon composite, were analyzed as follows.

Samples include a porous silica core with a size of 300 nm, which is relatively easy to manufacture among various silica cores and has the highest uniformity in the shape or diameter size of the silica core, a porous silica core with an average diameter of 80 nm with a size smaller than 300 nm, and a porous silica core with an average size larger than 300 nm. Physical properties were analyzed and compared using a porous silica core with a diameter of 500 nm.

The sample porous silica core was prepared as follows.

2,542 g of anhydrous ethanol (99.99%, Sigma aldrich) was injected into a reactor with an internal volume of 5 liters, and then 120 g of ammonia water (28%, Sigma aldrich) was added and vigorously stirred. Then, 240 g of distilled water was added and stirred for 30 minutes. After stirring, 30 g, 180 g, and 300 g of TEOS (98%, Sigma-aldrich) were added, respectively, and the reaction proceeded for 5 hours. At this time, the total amount of reaction solution is 2,932g, 3,082g, and 3202g, respectively, and the raw materials are ethanol, TEOS, NH ₄ OH (ammonia water), and H ₂ O at 86.69 : 1.02 : 4.09 : 8.18 and 82.47 : 5.84 : 3.89 : 7.78 and 79.38, respectively. It was composed of a weight ratio of : 9.36 : 3.74 : 7.49.

SEM images of the prepared porous silica cores with particle sizes of 80 nmn, 300 nm, and 500 nm are shown in Figure 6.

BET (Brunauer-Emmett-Teller) analysis was performed to analyze the physical properties of the prepared porous silica core, such as specific surface area, pore volume, and pore size.

First, the nitrogen isotherm (N ₂ -isotherm) of the porous silica core with sizes of 80 nm, 300 nm, and 500 nm is shown in Figure 7.

As shown in Figure 7, the porous silica core manufactured under the above conditions exhibits a hysteresis phenomenon in which the shape of the nitrogen isotherm is different.

Additionally, the pore distribution curves of porous silica cores with sizes of 80 nm, 300 nm, and 500 nm are shown in Figure 8.

As a result of BET analysis of a porous silica core with a particle diameter of 80 nm, the nitrogen isotherm showed that the curve shape and nitrogen adsorption capacity according to particle diameter were similar to those of a 300 nm porous silica core, but the adsorption distribution curve according to pore volume was different. It was taking shape.

In addition, as a result of BET analysis of a porous silica core with a particle diameter of 500 nm, the shape of the curve and nitrogen adsorption capacity according to particle diameter in the nitrogen isotherm were found to be similar to those of a porous silica core with a particle diameter of 300 nm, and the adsorption distribution curve also showed a similar shape. It was showing.

From these results, it can be seen that the size of the porous silica core does not significantly affect the pore volume and distribution composed of silica particles or between particles, but the larger the size of the porous silica core, the more macropores there are, as shown in the pore distribution curve. ) is developing further. This phenomenon can be judged to occur because as the size of the core increases, the size of the pores formed between particles expands. This does not mean that the characteristics of the pores provided within the porous silica core change, but rather that the pores formed between the spherical cores are made of macropores, and these pores develop further as the particle size increases.

The results of comparing the physical properties according to the size of the porous silica core are shown in Figure 9 and Table 1 below.

characteristic Porous silica core size (nm) 80 300 500 specific surface area ^m2 /g 296 140 140 Pore volume cc/g 0.64 0.37 0.36 Pore size nm 8.63 10.49 10.24

From the results in Table 1 above, the specific surface area of the porous silica core was found to be wider as the size of the core was smaller, and the pore volume also showed similar results. In the case of pore size, the core size of 300 nm was found to be the largest.

The porous silica core with a diameter of 300 nm has a specific surface area of 140 m ² /g, a pore volume of 0.37 cc/g, and a pore size of 10 nm. Compared to the physical properties of activated carbon, a representative porous material, in the case of commercial activated carbon, if the pore volume is 0.3 cc/g or more, the specific surface area is an average of 700 m ² /g and the average pore size is about 2 to 4 nm. Therefore, it can be determined that the porous silica core is a material composed mostly of pores. Using a structure composed of such pores as a template is advantageous for manufacturing a porous structure.

<Example 2>

Preparation of porous silica core-shell

A porous silica core was manufactured with a size of 300 nm.

In ethanol, 4% by weight of ammonia water as a catalyst, 8% by weight of distilled water, and 10% by weight of TEOS are mixed with ethanol, and the organosilane C ₁₈ -TMS as a surfactant is mixed with TEOS at a weight ratio of 0.37 (C ₁₈ -TMS/TEOS). did.

The mixture was reacted for 5 hours using a sol-gel synthesis method to form a silica shell on the surface of the porous silica core. When the reaction was completed, the porous silica core-shell was prepared by firing at 550°C for 5 hours.

<Experimental Example 3>

Confirmation of porous silica core-shell characteristics according to type of surfactant

A porous silica core-shell is manufactured by forming a porous silica shell on the surface of the porous silica core, which serves as a template for the mesoporous carbon form, to provide pores for the mesoporous carbon manufactured to support metal oxides. did.

To confirm the characteristics of the porous silica core-shell according to the type of surfactant used, the following experiment was performed.

In the sol-gel synthesis process, the reaction time is 5 hours, and the amount of catalyst added is 4% by weight of ethanol. The amount of distilled water added was fixed at 8% based on the weight of ethanol, the amount of TEOS added was fixed at 10% based on the weight of ethanol, and the amount of surfactant added was varied from 1 to 4% based on the weight of ethanol.

(1) Characteristics of porous silica core-shell prepared using organosilane

The characteristics of the porous silica core-shell prepared using organosilane as a surfactant were confirmed as follows.

The size of the porous silica core was manufactured to 300 nm, and then the surfactant organosilane C ₁₈ -TMS (Octadecyltrimethoxysilane) and TEOS were added to the surface at a weight ratio of 0.37 (C ₁₈ -TMS/TEOS) to form a silica shell. . The prepared porous silica core-shell was used as a reference sample.

The SEM image, nitrogen isotherm, and pore distribution curve of the porous silica core-shell calcined at 550°C for 5 hours after sol-gel synthesis are shown in Figure 10.

As shown in Figure 10, the porous silica core-shell maintained a constant spherical shape, and the average diameter of each particle was 500 nm. Since the size of the porous silica core provided to form the shell is 300 nm, it can be confirmed that the thickness of the shell formed on the surface of the porous silica core is 100 nm. The nitrogen isotherm showed hysteresis, a phenomenon that occurs in porous silica cores. From these results, it can be inferred that even in the porous silica core-shell, spaces are formed inside the pore volume larger than the pores developed on the surface.

Table 2 below shows the physical properties of porous silica core-shell with a particle size of 500 nm manufactured using C ₁₈ -TMS, an organosilane.

characteristic unit value specific surface area ^m2 /g 472 Total pore volume cc/g 0.48 Pore size nm 4.1

Compared to a porous silica core with a particle size of 500 nm, it can be seen that the specific surface area and pore volume increase, but the pore size decreases. The reason why the specific surface area of the porous silica core-shell, which consists of a porous shell on the porous silica core, increases is that the physical properties are changed by the porous shell developed on the surface of the silica core, considering that the particle size is the same as 500 nm.

(2) Characteristics of porous silica core-shell prepared using CTAB

The properties of the porous silica core-shell prepared using CTAB as a surfactant were confirmed as follows.

The size of the porous silica core was manufactured to 300 nm, and then surfactants CTAB and TEOS were added to the surface at a weight ratio of 0.37 (CTAB/TEOS) to form a silica shell. The prepared porous silica core-shell was used as a reference sample.

The SEM image, nitrogen isotherm, and pore distribution curve of the porous silica core-shell manufactured using CTAB are shown in Figure 11.

Silica spheres manufactured using CTAB maintained a constant shape, and the particle diameter was 500 nm on average. The surface state showed denser cracks than spheres using organosilane, which is presumed to be a characteristic of the added surfactant.

In addition, looking at the nitrogen isotherm and pore distribution curve of the porous silica core-shell manufactured using CTAB, it is a structure with developed mesoporosity of 2~30 nm, and compared to the sample manufactured using organosilane, the hysteresis history in the nitrogen isotherm is low. A curve that does not appear is appearing. In other words, it can be confirmed that the shape of the pore entrance is similar in size to the pores existing inside the structure.

This difference in structure is due to the difference in the surfactant used in sample preparation. As mentioned in the SEM image above, the fact that cracks appear less on the surface is due to the difference between the pore size inside the silica structure and the pore entrance in the space derived from the outer wall of the surface. It is assumed to provide similar figures.

Table 3 below shows the physical properties of the porous silica core-shell with a particle size of 500 nm manufactured using CTAB.

characteristic unit value specific surface area ^m2 /g 441 Total pore volume cc/g 0.36 Average pore size nm 3.2

From the results in Table 3, the specific surface area and pore volume of the porous silica core-shell manufactured using CTAB were found to be overall reduced compared to the porous silica core-shell manufactured using organosilane. In addition, it was analyzed that the average pore size decreased by about 1 nm.

(3) Characteristics of porous silica core-shell prepared using CTAC

The properties of the porous silica core-shell prepared using CTAC as a surfactant were confirmed as follows.

The size of the porous silica core was manufactured to 300 nm, and then surfactants CTAC and TEOS were added to the surface at a weight ratio of 0.37 (CTAC/TEOS) to form a silica shell. The prepared porous silica core-shell was used as a reference sample.

The SEM image, nitrogen isotherm, and pore distribution curve of the porous silica core-shell manufactured using CTAC are shown in Figure 12.

The silica spheres maintained a constant shape and the average particle diameter was 350 nm. The surface condition showed excessive aggregation between particles compared to the structure using organosilane and CTAB. As can be seen from the nitrogen isotherm and pore distribution, it showed a structure with developed mesopores of about 3 nm, and the nitrogen isotherm showed a curve without hysteresis phenomenon. In other words, it can be confirmed that the shape of the pore entrance is of a similar size to the pores existing inside the structure.

Table 4 below shows the physical properties of the porous silica core-shell with a particle size of 500 nm manufactured using CTAC compared with the structure manufactured using C ₁₈ TMS and CTAB, which are organosilane.

characteristic unit Porous silica core-shell C ₁₈ TMS CTAB CTAC specific surface area ^m2 /g 472 441 270 Pore volume cc/g 0.48 0.36 0.22 Pore size nm 4.1 3.2 3.2

The physical properties of the porous silica core-shell manufactured using CTAC as a surfactant showed that the specific surface area was reduced by approximately 200 m ² /g compared to the structure manufactured using other surfactants, and the pore size was similar to that of the structure manufactured using CTAB. . Considering that the most important physical property of the carbon structure for supporting metal oxide is pore volume, it was confirmed that the pore volume provided by the surfactant was significantly reduced compared to organosilane.

(4) Characteristics of porous silica core-shell prepared using various polymers

In addition to the applied surfactants, silica core-shells using various polymers were manufactured to control the physical properties within the silica structure that determine the pore volume and pore size of carbon, and their physical properties were compared.

Divinylbenzene resin, cellulose, phenol resin, and polyvinyl alcohol were used as polymers.

SEM images of porous silica core-shell manufactured using various polymers are shown in Figure 13. In Figure 13, (A) is divinylbenzene resin, (B) is cellulose, (C) is phenol resin, and (D) is polyvinyl alcohol.

As shown in Figure 13, most of the porous silica core-shells manufactured using various polymers were found to collapse in shape and show agglomeration. It is presumed that the carbon-containing polymer materials added during the silica synthesis process reduce the repulsive force between silica particles in the ethanol solvent that provides the synthesis space, causing them to clump together.

(5) As shown in the above analysis results, in order to manufacture the optimal mesoporous carbon-metal oxide-carbon structure for supporting metal oxide, a porous silica core-shell manufactured using an organosilane containing a silane group as a surfactant is optimal. It is a substance of

<Experimental Example 4>

Characteristics of porous silica core-shell according to organosilane application ratio

The properties of the porous silica core-shell were analyzed according to the application ratio of organosilane, which affects the pore characteristics of the shell, as follows.

The shell using organosilane as a variable was manufactured under the following conditions. The core used a spherical silica solid with a diameter of 300 nm, the organosilane used C ₁₈ -TMS and TEOS at a weight ratio of 0.125, 0.375, and 1 (C18-TMS/TEOS), and 4 wt% of TEOS was used compared to the weight of ethanol. did.

Figure 14 shows SEM analysis images of porous silica core-shell prepared by varying the application ratio of organosilane. In Figure 14, the application ratio of organosilane (organosilane/TEOS) is (A) 0.125, (B) 0.375, and (C) 1.

As shown in Figure 14, the porous silica core-shell had an average particle diameter of 500 nm regardless of the application ratio of organosilane. In samples with an organosilane/TEOS ratio of 1, unreacted silica substances such as impurities appear on the surface of the structure. When an excessive amount of organosilane was added, it appears that residues that failed to form a structure were exposed on the external surface of the structure during the reaction of the organosilane with TEOS.

Figure 15 shows the nitrogen isotherm of the porous silica core-shell manufactured according to the application ratio of organosilane (organosilane/TEOS).

As shown in Figure 15, the nitrogen isotherms for each material showed similar shapes, and the isotherms all showed curves containing mesopores. This phenomenon indicates that the distribution of organosilane present in the shell structure created by TEOS is constant. However, the smaller the amount of organosilane, the smaller the pore volume caused by the surfactant in the shell. If it is excessive, it cannot exist inside the shell and is bound to the outer shell. The surfactant that did not participate in the formation of this structure will sublime and be discharged during firing. will be.

The pore distribution curve of the porous silica core-shell according to the organosilane application ratio derived from the BET results is shown in Figure 16.

In Figure 16, it was confirmed that the porous silica core-shell to which a small amount of organosilane was applied developed pores of 2 nm, but the total pore volume was smaller than that of other structures. The structure in which organosilane was applied at a ratio of 0.375 to 1 showed a similar pore distribution. Therefore, the most appropriate application ratio of the organosilane added to form the porous shell is a weight ratio of 0.37 to TEOS.

Figure 17 shows a graph comparing the physical properties of the porous silica core-shell.

From the results in Figure 17, the specific surface area of the porous silica core-shell increases depending on the application ratio of the organosilane, but the pore volume and pore size show the largest values when the application ratio of the organosilane is 0.375, and the application of the organosilane It was found that as the ratio increased, it decreased again.

The physical properties derived from BET analysis of the porous silica core-shell according to the organosilane application ratio are shown in Table 5 below.

characteristic unit Porous silica core-shell (C18/TEOS) 0.125 0.375 One specific surface area ^m2 /g 237 470 397 Pore volume cc/g 0.22 0.42 0.38 Pore size nm 3.56 4.58 3.65

As shown in Table 5, the highest pore volume is shown when the application ratio of organosilane, a surfactant that plays an important role in pore formation of the porous silica core-shell structure, is 0.375.

Therefore, since the pore volume of the carbon structure is proportional to the pore volume of the silica structure that serves as the template, it is difficult to manufacture a mesoporous carbon structure that contains a large amount of metal oxide in the mesoporous carbon and provides contact and space for the electrolyte into the cathode material. The most suitable silica structure is one with an organosilane application ratio of 0.375.

<Experimental Example 5>

Thermogravimetric analysis of silica-resin composites

Thermogravimetric analysis (TGA) of phenol resin, a carbon-containing polymer material used as a carbon raw material, and silica-resin (SiO ₂ -resin) composite coated on the silica surface was performed as follows.

The analysis conditions were a temperature increase rate of 1°C/min in an inert atmosphere using nitrogen, and weight loss was analyzed during the final increase to 900°C.

The results of thermogravimetric analysis of phenol resin, a carbon-containing polymer material used as a carbon raw material, and the silica-resin composite coated on the silica surface are shown in Figure 18.

As shown in the results of Figure 18, the final yield of the pure phenol resin was about 36%, and the final yield of the silica-resin complex was about 70%.

The high yield of the composite is due to the influence of silica, an inorganic material that is not removed by thermal decomposition, and when carbonized on the surface of silica, the yield is lower compared to the form in which the resin itself is aggregated.

In addition, the influence of the resin thickness present during carbonization can be considered. The resin coated in silica is uniformly distributed along the porous silica surface with a thickness of approximately 1 to 2 nm, so it is more thermally affected. When manufacturing a silica-resin composite, silica consists of approximately 66% by weight and resin consists of approximately 33% by weight. Based on the calculation results of thermal analysis of the resin during final carbonization, the carbon present on the silica surface is approximately 22% by weight compared to silica.

On the other hand, when the weight was quantified at each stage when preparing the sample, the weight of the silica-resin composite composed of 30 g of silica and 15 g of phenol resin was analyzed to be about 33.4 g after carbonization and about 3.2 g after etching. According to these results, about 9% by weight of carbon exists in the silica structure.

The reason for this difference is that when pure resin is carbonized, there is no moisture present in the resin or inorganic substances that can additionally thermally decompose the resin, so the crosslinked pure carbon yield appears, and in the case of silica-resin composite, the synthetic process It is believed that the yield was lowered due to various oxidizing substances that may be present in the resin, the effect of the silica surface that increases heat transfer to the resin, and the nano-level thickness effect compared to pure resin lumps.

<Example 3>

Preparation of porous silica-metal oxide composite

A porous silica-metal oxide composite was prepared as follows.

FeCl ₂ ·6H ₂ O (Sigma aldrich) was used as a raw material to produce Fe ₂ O ₃ , a metal oxide, in a porous silica-metal oxide complex.

1000 ml of ethanol (Sigma aldrich, 99.8%), 40 ml of ammonia water (Sigma aldrich, 28% in H ₂ O, purity > 99.99%), 100 ml of TEOS (Sigma aldrich, 99.0%, Tetraethyl orthosilicate), H ₂ O (Sigma 80 ml of aldrich, Nuclease-Free Water, for Molecular Biology) and 15 ml of C18-TMS (Sigma aldrich, Octadecyltrimethoxysilane; OTMS) were added to a 2L reaction vessel and stirred at a speed of 100 rpm for 5 hours to react.

Afterwards, the prepared sol solution was treated in a centrifuge at 10,000 rpm for more than 1 hour to separate the solution and silica sol, and then dried in a drying oven at 100°C for more than 12 hours. The dried silica sol was fired at 550°C for 5 hours using a kiln, then naturally cooled and stored.

Metal oxide was coated on the prepared porous silica structure as follows. First, 10% by weight of FeCl ₂ ·6H ₂ O compared to the weight of silica was dissolved in distilled water 10 times the weight of silica, and the porous silica structure was added to the solution in which the metal was dissolved, and then heated at 80°C for more than 3 hours while slowly stirring. did. Afterwards, the solution and solid were separated using a filter, and the solid was dried at 100°C for more than 12 hours. The dried sample was heat-treated at 550°C for 5 hours in a sintering furnace to convert the metal on the silica surface into metal oxide to prepare a porous silica-metal oxide composite.

<Example 4>

Preparation of porous silica-metal oxide-carbon composite

A porous silica-metal oxide-carbon composite was prepared as follows.

To improve the conductivity of the metal oxide bound to the silica surface of the porous silica-metal oxide composite prepared in Example 3, carbon coating was applied to prepare a porous silica-metal oxide-carbon composite.

For the carbon coating, 30% by weight of phenol resin (Sigma aldrich, Phenol-formaldehyde polymer, average Mn ~ 345) based on the weight of the solid sample was used as the raw material.

The phenolic resin was dissolved in distilled water 10 times the weight of the porous metal oxide-silica solid content, and then the solid sample was added while constantly stirring. After addition, the mixture was stirred for more than 3 hours to ensure uniform coating of the solid sample and phenol resin. The solution was then filtered and dried in a drying oven at 100°C for 12 hours. The dried sample was heat treated in a furnace at 250°C for 1 hour to induce crosslinking of the polymer coated on the surface of the porous silica-metal oxide composite. When the crosslinking reaction was completed, the final porous silica-metal oxide-carbon composite was prepared by heat treatment at 900°C for 5 hours in an inert atmosphere.

<Experimental Example 6>

Determination of physical properties of porous silica-metal oxide composite and porous silica-metal oxide-carbon composite

A porous silica-metal oxide composite coated with iron oxide (Fe ₂ O ₃ ), a metal oxide, on a porous silica structure that serves as a template for mesoporous carbon, and a porous silica-metal oxide-carbon coated with carbon on a porous silica-metal oxide composite. The physical properties of the composite were confirmed as follows.

This is to determine the characteristics of the structure before the silica material is removed by the etching process in order to identify the characteristics of the composite in which metal oxides exist in the porous mesoporous carbon, and ultimately contribute to improving the electrical properties by the core and mesopores. This is to check.

The experimental samples were the porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ) prepared in Example 3 and the porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C) prepared in Example 4. ) was used.

Figure 19 shows an SEM image of the porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ). As shown in Figure 19, each particle is uniformly distributed with a certain shape and size. As a result of enlarging this to a particle size of 1㎛ or less, the average particles are in the form of a cluster where spherical bodies of about 500nm are gathered together, providing constant space between particles.

Figure 20 shows the nitrogen isotherm and pore distribution curve based on BET analysis of the porous silica-metal oxide composite.

Looking at the nitrogen isotherm in Figure 20, it shows a type V isotherm curve in which a mesopore shape is developed, and shows a hysteresis phenomenon that does not match the adsorption isotherm during desorption. In general, hysteresis phenomenon, which is a hysteresis phenomenon that occurs during gas adsorption/desorption, is involved in the shape of the internal pores of the adsorbent. In other words, this phenomenon occurs when the size or volume of the inner pores where the gas is fixed is larger than the size or volume of the pores on the surface where the gas flows during adsorption. In other words, it can be explained as a bottleneck phenomenon in which the speed when gas is adsorbed into the pore is faster than the speed when it is desorbed, and conversely, the release speed of gas is relatively slow during desorption.

As shown in the pore distribution curve in Figure 20, most of the pore structures involved in nitrogen adsorption are distributed at 2 to 4 nm. In addition, pores larger than 20 nm can be viewed as pores formed between particles as shown in the SEM image.

Therefore, the prepared porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ) does not completely block the mesoporous pores formed in the shell during the production of the silica structure, but is uniformly coated on the surface of the silica pore wall, forming the existing It can be judged to be a composite structure in which metal oxide is added while maintaining pores.

This can be explained by comparing it to the porous silica core-shell. Most of the pore distribution curves shown in the porous silica core-shell are concentrated at an average of 4 nm, but the pore distributions shown in the porous silica core-shell coated with metal oxide are There are differences evenly distributed from 2nm to 4nm.

This difference can be assumed to be due to the fact that pores of 4 nm in size were solidified in a reduced size form by the metal oxide distributed on the surface within the pores in the step of coating the metal oxide on the porous silica.

Table 6 below shows the physical properties of the porous silica-metal oxide composite and the porous silica core-shell derived from BET analysis.

characteristic unit value porous silica Silica-metal oxide complex specific surface area ^m2 /g 347 303 Total pore volume cc/g 0.42 0.33 Average pore size nm 4.58 4.29

As shown in Table 6, the specific surface area and pore volume of the porous silica-metal oxide composite with added metal oxide decreases compared to the porous silica core-shell, but the average pore size shows almost similar values. This phenomenon confirms that the metal oxide is uniformly distributed and coated on the silica structure as described above.

Figure 21 shows the prepared porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ) coated with carbon on the porous silica-metal oxide composite (Fe ₂ O 3 @SiO 2 ). ₃ @SiO ₂ @C) SEM image is shown.

As shown in Figure 21, the porous silica-metal oxide-carbon composite coated with carbon on a conventional porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ) has the shape and size of the particles similar to those of the porous silica- before coating the carbon. It showed a similar form to a metal oxide complex. From these results, it can be confirmed that the carbon coated on the porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ) is uniformly coated without changing the shape of the structure.

During carbon coating, 30% by weight of phenol resin, which is a raw material for carbon materials, was used based on the weight of the porous silica-metal oxide composite. In general, the yield of phenol resin upon carbonization is reported to be about 30%, so the amount of carbon remaining after carbonization is estimated to be about 9% by weight compared to the composite. Since a small amount of carbon material is formed along the surface of the structure with a thickness of approximately 2 to 4 nm, the particle appears to have not changed significantly in appearance.

Figure 22 shows the nitrogen isotherm and pore distribution curve derived from the BET analysis results of the porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C).

As shown in Figure 22, in the case of the nitrogen isotherm, the hysteresis phenomenon, which is a hysteresis phenomenon due to differences in pore shape, appears more clearly than in the silica-metal oxide complex (Fe ₂ O ₃ @SiO ₂ ), and the shape of the curve is also influenced by the macropores. The relative pressure (>0.8=P/Po) changed even more differently.

This change in the isotherm can be explained in the pore distribution curve. Compared to the silica-metal oxide composite, the pore volume of mesopores of 2 to 5 nm decreased, but the decrease in pore volume of 10 nm or more was relatively small, and pores of about 15 nm were reduced. Because it has developed. In other words, compared to the decrease in the medium pores of the composite, pores larger than 10 nm decreased relatively little, so it appears that they are more greatly influenced by macropores when analyzing nitrogen adsorption/desorption.

Table 7 below shows the physical properties of the porous silica structure (SiO ₂ ), porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ), and porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C). is shown for comparison.

characteristic unit value SiO ₂ Fe ₂ O ₃ ＠SiO ₂ Fe ₂ O ₃ ＠SiO ₂ ＠C specific surface area ^m2 /g 347 303 106 Total pore volume cc/g 0.42 0.33 0.14 Average pore size nm 4.58 4.29 5.5

From the results in Table 7, it can be seen that compared to the porous silica-metal oxide composite before carbon coating, the specific surface area and pore volume of the porous silica-metal oxide-carbon composite coated with carbon decrease, while the pore size increases. .

This phenomenon seems to be because the average pore size increased numerically as the proportion of pores larger than 10 nm increased, which was a phenomenon shown in the pore distribution curve. In the case of a porous silica-metal oxide-carbon composite coated with carbon, during the carbon coating manufacturing step, the carbon material fills some pores on the surface of the metal oxide and silica or increases the thickness of the pore wall, and is uniformly distributed in the space within the pores of 10 nm or more. It is assumed to be distributed.

Figure 23 shows the EDS analysis results of the porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C).

As a result of EDS analysis, carbon was 31.9%, silicon was 10.3%, iron was 5.99%, and oxygen atoms were more than 50%. The high oxygen fraction appears to be the effect of oxides existing in oxidized structures in the form of SiO ₂ and Fe ₂ O ₃ . At this time, Pt is a material coated during pretreatment to improve sample image clarity during SEM/EDS analysis.

If silica is removed from the composite, the iron content is about 6.68% by weight, which when converted to iron oxide is about 10% by weight. Considering these results, it is believed that the metal oxide-carbon structure to be finally manufactured can easily support more than 10% by weight of metal oxide.

In addition, if subsequent heat treatment is performed to develop carbon pores, the proportion of metal oxides is expected to increase further.

Figure 24 shows porous silica (SiO ₂ ) and porous silica-metal oxide complex (Fe ₂ O ₃ @SiO ₂ ). and the XRD diffraction pattern of porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C).

As shown in Figure 24, the porous silica-metal oxide composite coated with metal on the silica surface showed a clear crystalline peak, and in the porous silica-metal oxide-carbon composite coated with carbon on the surface of this composite, most of the crystalline peaks were observed. Although the peak disappeared, compared to the amorphous silica pattern, diffraction influenced by crystalline particles appears at about 45°.

<Example 5>

Manufacturing of half cells

In order to confirm the electrochemical properties of porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ) and porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C), a half-cell using them as anode material (half-cell) was prepared.

As the negative electrode active material, the porous silica-metal oxide composite prepared in Example 3 and the porous silica-metal oxide-carbon composite prepared in Example 4 were used.

First, to prepare sludge, 80% by weight of negative electrode active material, 10% by weight of conductive material, and 10% by weight of binder were mixed and thoroughly stirred to ensure uniform mixing.

Acetylene Black was used as a conductive material, and PVDF (Solef5130, Solvay Korea) [8% in NMP (N- Methylpyrrolidone)] was used as a binder. To control viscosity, an appropriate amount of NMP (Sigma-Aldrich) was added.

An electrode was manufactured by coating the obtained slurry evenly on a copper current collector to a thickness of 50 μm using an applicator.

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

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

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

<Experimental Example 7>

Charging/discharging performance analysis of half-cell

The electrochemical properties of the porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ) and the porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C) were confirmed as follows.

Electrochemical properties were confirmed by analyzing the charge/discharge performance of lithium ions, and the analysis conditions and methods are as follows.

As samples for evaluating electrochemical properties, the two half-cells prepared in Example 5 were used.

Using the manufactured half-cell, charge it with a constant current (CC) up to 0.005V (vs. Li/Li+) at a current value of 0.2C relative to the weight of the active material, and then charge it with a constant current (CC) of 0.005V (vs. Li/Li+). Constant voltage (CV) charging was performed, with charging ending at a current value of 0.01C while maintaining .

The discharge was a constant current discharge that ended at 2V (vs. Li/Li+) with a current value of 0.1C. At this time, assuming that the 1C value was 350 mA/g, a charge/discharge experiment was performed using the above method, and then the 1C value of each sample was obtained.

After the activation process was performed under the above conditions, only the charge/discharge current value was set to 0.1C and the lifespan experiment was performed with the remaining conditions remaining the same.

All charge/discharge experiments were measured using WBS-3000L from Won-A Tech. As a result of charge/discharge performance analysis, the porous silica-metal oxide composite (Fe ₂ O ₃ @SiO ₂ ) did not show any electrical properties.

In general, silica is reported to be unable to transfer electrons to the cathode during the discharge process when lithium ions are charged/discharged because the inactive phase Li ₂ O and lithium silicate are formed during the reaction with lithium, resulting in an irreversible reaction. [H. Yoon and WS Kim, “High capacity and rate capability of core-shell structured nano-Si/C anode for Li-ion batteries”, Electrochimica Acta 71, 201-205 (2012)]

Figure 25 shows the results of a charge/discharge test for lithium ions of a porous silica-metal oxide-carbon composite (Fe ₂ O ₃ @SiO ₂ @C).

As shown in Figure 25, the discharge performance of the composite acting as a cathode material was about 100 mAh/g in the initial cycle, and gradually increased as the cycle progressed, reaching about 180 mAh/g at 100 cycles, and tending to continuously increase. It was showing.

The charge/discharge efficiency characteristics started at about 70% in the initial cycle and showed an efficiency of about 98% or more after 20 cycles. This phenomenon is believed to be because the activity of Fe ₂ O ₃ , a metal oxide coated with carbon, toward lithium ions continues to increase as charge and discharge are repeated.

This is presumed to be a process in which the metal oxide bound to the surface of silica is separated from the bond with silica during the bonding and desorption process of lithium ions and moves to the carbon body and is immobilized.

In light of this, as charging and discharging of the porous silica-metal oxide-carbon composite continues, the metal oxides are continuously inserted into the carbon layer and become fixed, and this repetitive phenomenon results in a physical structure in which the metal oxides are uniformly distributed within the carbon porous layer. It is expected to have a positive effect. It can be indirectly confirmed that the metal oxide can be stably supported within the carbon layer without being eluted. In addition, considering the weight ratio of silica, which is not involved in the lithium ion reaction, it is estimated that if the sample was from which silica was ideally removed, the charge/discharge performance would be significantly higher.

Therefore, the metal oxide-carbon anode material sample is expected to achieve stable performance beyond the theoretical capacity of carbon.

<Example 6>

Preparation of porous silica-carbon composites

After adding 1,000 g of ethanol to the synthesis reactor, 40 g of ammonia water (28%) to act as a catalyst for the synthesis reaction, 80 g of distilled water for the hydrolysis reaction, 5 to 40 g of organosilane (C18-TMS) for pore formation, and TEOS as a silica raw material. After weighing 60g, it was reacted for more than 5 hours.

The liquid part of the synthesized silica was removed using a centrifuge, and the solid content was dried in a drying oven at 100°C for more than 12 hours.

The dried porous silica structure was heat-treated at 550°C for 5 hours in a firing furnace to remove organic substances present inside, and then prepared as a sample for carbon coating.

A porous silica-carbon composite was prepared using the prepared porous silica structure. As a carbon-containing polymer material, a phenolic resin was used and coated on the silica surface.

A certain weight of phenol resin compared to the weight of silica was dissolved in distilled water three times the weight of silica, and then silica was added while stirring and left for more than 5 hours.

Silica coated with phenol resin was evaporated and dried in a drying oven at 110°C for more than 12 hours.

The dried solid sample was oxidized by raising the temperature to 200°C in an air atmosphere at a rate of 1°C/min and maintaining it for 1 hour to increase crosslinking of the polymer resin.

The oxidized porous silica (carbon-containing polymer material) was charged into a calcination furnace in which a nitrogen atmosphere was created to heat-treat and carbonize it. Under the condition of a temperature increase rate of 5℃/min, the temperature is raised to a maintenance temperature of 900℃ and maintained for 5 hours, then naturally cooled to room temperature, and the silica-(carbon-containing-polymer material) is heat-treated to form silica-carbon where the carbon-containing-polymer material is carbonized. A composite was prepared.

<Experimental Example 8>

Characterization of porous silica-carbon composites

To produce a mesoporous carbon _structure , a porous silica-carbon composite (SiO ₂ -C) applied as a precursor and a porous silicon oxide-carbon composite (SiO The characteristics were analyzed.

The porous silicon-carbon structure prepared in Example 6 and magnesium were mixed at a weight ratio of 7:3, reduced by reacting in a sintering furnace in a nitrogen atmosphere at 400°C for 5 hours, and then washed with an aqueous sulfuric acid solution to form a porous silicon oxide-carbon composite. Manufactured.

Figure 26 shows the SEM image and XRD diffraction pattern of the porous silicon oxide-carbon composite. In the SEM image of the porous silicon oxide-carbon composite, the surface of the composite showed partial cracks in the coated carbon due to high heat generation during the reduction process. In the diffraction pattern, silica peaks appeared clearly, unlike the amorphous pattern of the porous silica-carbon composite.

Figure 27 shows a comparison of the nitrogen isotherms of the porous silica-carbon composite and the porous silicon oxide-carbon composite. As can be seen in Figure 27, the isotherm shapes of the two materials were similar.

Figure 28 shows the pore distribution curves of the porous silica-carbon composite and the porous silicon oxide-carbon composite. From the results in Figure 28, it can be seen that the two materials before and after reduction have similar pore shapes and structures, which are physical characteristics.

These results are shown in Table 8 below.

characteristic unit _SiO2 -C _SiOx -C specific surface area ^m2 /g 140 139 Pore volume cc/g 0.36 0.35 Pore size nm 10.4 10.2

As shown in the results in Table 8 above, the specific surface area, pore volume, and pore size of the samples were almost similar even after reduction, and the very slight decrease was within the error range of analysis.

Therefore, it can be seen that the physical properties of the porous silica-carbon composite manufactured by coating the surface of the nanoscale porous silica composite with carbon are maintained constant.

Figure 29 shows the charge/discharge performance of the porous silicon oxide-carbon composite at 400 mA/g.

The initial battery performance of the porous silicon oxide-carbon composite was about 1,100 mAh/g, which is 300 mAh/g lower than the theoretical capacity of silicon, which is 1,400 mAh/g.

As the number of charge/discharge cycles progressed, the capacity gradually decreased, and the discharge performance was approximately 700 mAh/g around 170 cycles. This indicates that the lifespan characteristics are maintained at more than 60%.

The results are shown in Table 9 below.

Anode Battery performance (Capacity) Current density Cycle Efficiency unit mAh/g mA/g times % SiOx-C 696 400 171 96.9 SiOx-C 715 400 174 97.0

As can be seen in Table 9 above, the porous silicon oxide-carbon sample prepared in Example 6 exhibits a battery performance of about 2 times more than that of the conventional graphite negative electrode active material, and considering the current density, the battery performance is about 5 times more than that of the conventional graphite negative electrode active material. will be.

<Example 7>

Fabrication and characterization of mesoporous carbon structures

A porous silica structure that determines the shape and pore characteristics of carbon is manufactured, a carbon-containing polymer material, which is a carbon raw material, is coated on the surface of the porous silica structure, and then heat treated and carbonized to produce a porous silica-carbon composite using hydrofluoric acid. A mesoporous carbon structure was prepared by etching silica from the porous silica-carbon composite, and its physical properties were confirmed.

(1) Preparation and characterization of porous silica structure

The porous silica structure, which serves as a template for the carbon structure, was manufactured using TEOS, a silica (SiO ₂ ) raw material. The synthesis reaction was carried out using a sol-gel reaction, and ethanol was used as a solvent to provide a space for silica synthesis.

After adding 1,000 g of ethanol to the synthesis reactor, 40 g of ammonia water (28%) to act as a catalyst for the synthesis reaction, 80 g of distilled water for the hydrolysis reaction, 5 to 40 g of organosilane (C18-TMS) for pore formation, and TEOS as a silica raw material. After weighing 60g, it was reacted for more than 5 hours.

The liquid part of the synthesized silica was removed using a centrifuge, and the solid content was dried in a drying oven at 100°C for more than 12 hours.

The dried porous silica structure was heat-treated at 550°C for 5 hours in a firing furnace to remove organic substances present inside, and then prepared as a sample for carbon coating.

Figure 30 shows the SEM image, nitrogen isotherm, and pore distribution of the porous silica structure prepared as above, and Table 10 below shows the BET analysis results confirming the physical properties.

characteristic unit silica specific surface area ^m2 /g 362 Pore volume cc/g 0.42 Pore size nm 4.58

As shown in Table 10, the pore volume of the porous silica structure is similar to that of general activated carbon. This confirms that the silica structure is a low-density material even though it is a material with a heavier specific gravity than the carbon material, and this volume provides favorable conditions for polymer coating.

The shape of the nitrogen isotherm shows the type IV, which appears in a structure with mesopores, and it can be seen that the structure has a pore size of 2 to 5 nm.

(2) Preparation and characterization of porous silica-carbon composite

A porous silica-carbon composite was prepared using the prepared porous silica structure. As a carbon-containing polymer material, a phenolic resin was used and coated on the silica surface.

A certain weight of phenol resin compared to the weight of silica was dissolved in distilled water three times the weight of silica, and then the porous silica structure was added while stirring and left for more than 5 hours.

The porous silica structure coated with phenol resin was evaporated to dryness at 110°C for more than 12 hours in a drying oven.

The dried solid sample was oxidized by raising the temperature to 200°C in an air atmosphere at a rate of 1°C/min and maintaining it for 1 hour to increase crosslinking of the polymer resin.

The oxidized silica-phenol resin was heat-treated and charged into a furnace in which a nitrogen atmosphere was created to carbonize it. Under the condition of a temperature increase rate of 5°C/min, the temperature was raised to a holding temperature of 900°C and maintained for 5 hours to carbonize the silica-phenol resin, and then naturally cooled to room temperature to prepare a porous silica-carbon composite in which the carbon-containing polymer material was carbonized. .

Figure 31 shows the SEM image, nitrogen isotherm, and pore distribution of the porous silica-carbon composite prepared as above. In Figure 31, the average size of the porous silica-carbon composite was 500 nm, which is the same size as the diameter of the silica structure, and it can be seen that carbon was consistently coated on the surface of the porous silica and into the pores. The nitrogen isotherm shows the development of pores of 10 nm or more, which are believed to be pores that exist between particles, and the size appears to be 10 to 20 nm as shown in the pore distribution curve.

Table 11 below shows the results of BET analysis confirming the physical properties of the porous silica-carbon composite.

characteristic unit Silica-carbon composite specific surface area ^m2 /g 140 Pore volume cc/g 0.37 Pore size nm 10.49

As shown in Table 11, the specific surface area of the porous silica-carbon composite was reduced by more than 200 m ² /g compared to the porous silica structure, but the pore volume was slightly reduced by about 0.1 cc/g. This is believed to be because the carbon coating within the pores of the porous silica structure does not fill the inside of the pores because carbon is coated with a thin film on the silica pore walls.

(3) Fabrication and characterization of mesoporous carbon structures

Mesoporous carbon structures were prepared from porous silica-carbon composites as follows.

After preparing 10 times the weight of distilled water compared to the solid content of the porous silica-carbon composite in a reaction vessel, hydrofluoric acid (Sigma-aldrich, HF 48% by weight in H2O, ≥99.99% trace metals basis) was slowly injected into the distilled water to form a 20% hydrofluoric acid solution. prepared.

The solid content was slowly injected into the hydrofluoric acid solution, sealed using Teflon tape, and left in a vibrating stirrer for more than 12 hours to remove silica substances in the solid content.

After complete stirring, the reaction material was washed 3 to 5 times with distilled water after removing the solution using filter paper in a plastic funnel. The separated solid was dried in a drying oven at 100°C for 12 hours to prepare a sample.

To analyze the physicochemical properties of the manufactured mesoporous carbon structure, SEM/EDS, BET, and XRD instrumental analyzes were performed to determine the physical properties.

Figure 32 shows the SEM image, nitrogen isotherm, and pore distribution of the mesoporous carbon structure prepared as above.

The external appearance of the mesoporous carbon structure maintained the same shape as that of silica, and its size was also the same. In the SEM image, particles with partially visible internal shapes are visible, which appears to have been ruptured and cut due to overheating during the hydrofluoric acid etching process.

The internal shape shows a hollow shape with empty space. This appears to have developed as silica lumps were first formed from TEOS, a silica raw material, during the sol-gel synthesis process, and then particles in the form of a combination of organosilane and silica were formed on the surface.

The polymer infiltrates the silica formed in this way into the space where the pores are formed, is coated, and is then carbonized and converted to carbon. Therefore, the mesoporous carbon structure, which is the final step in the manufacturing process, takes the form of a replica of silica.

Since carbon coats the pore surface in silica, the pores of the mesoporous carbon structure form pores in the pores provided by silica and the spaces created by etching. Therefore, the porosity of mesoporous carbon structures is determined by the ratio of organosilane and TEOS in silica production.

The isotherm line and pore distribution indicate a medium-porous carbon form, and the pore volume is 1.28 cc/g, which is about twice as high as that of commercial activated carbon. It is believed that this pore volume will provide favorable conditions for lithium ion charging/discharging.

Table 12 below shows BET results confirming the physical properties of the prepared mesoporous carbon structure.

characteristic unit Carbon specific surface area ^m2 /g 1491 Pore volume cc/g 1.28 Pore size nm 3.44

The mesoporous carbon structure forms a spherical carbon structure with developed mesopores. A large amount of lithium ions can be inserted into the pores, which are the inner space of the structure, and the outer carbon wall plays a role in the movement of electrons during discharge.

<Experimental Example 9>

Characteristics of mesoporous carbon structures according to organosilane ratio

In order to confirm the conditions for controlling the pore volume of the mesoporous carbon structure, the differences in characteristics of the carbon structure manufactured using porous silica structures prepared at different organosilane application ratios were confirmed as follows.

A silica structure prepared by applying organic silane at a volume ratio of 0.125, 0.375, and 1 compared to TEOS was used as a template. The mold was coated with 50% by weight of phenol resin, a carbon material, based on the solid weight of the porous silica structure, and then oxidized for 1 hour in an air atmosphere at 200°C to increase crosslinking of the chains within the polymer. The oxidized porous silica-polymer composite was carbonized by heat treatment at 900°C for 5 hours in a nitrogen atmosphere to prepare a porous silica-carbon composite.

The porous silica-carbon composite was etched using a 20% hydrofluoric acid solution and then dried in a drying oven at 110°C for 12 hours to prepare a mesoporous carbon structure.

Figure 33 shows SEM images of the mesoporous carbon structures prepared above according to the organosilane application ratio. In Figure 33, the outer appearance of the carbon structure is composed of spherical particles agglomerated. In the case of carbon with an organosilane ratio of 1, the particles are composed of a uniform mixture of particles whose size is smaller than that of the silica template.

As shown in the SEM analysis results, when the proportion of organosilane is small, the external appearance of the mesoporous carbon structure shows a constant and simple surface, but as the proportion of organosilane increases, the surface becomes rough and the frequency of irregular shapes increases.

Looking at the cross section of a particle damaged due to overheating and expansion during the etching process, the thickness of the composed carbon layer is about 100 nm. Considering that the pore size inside the carbon is about 300 nm, it can be seen that the thickness of pore formation in silica is about 100 nm.

Figure 34 shows nitrogen isotherms using BET analysis of mesoporous carbon structures by organosilane application ratio. As shown in Figure 34, the isotherm line of the mesoporous carbon structure shows a curve containing mesopores. The isotherms of the carbon structures manufactured at different organosilane application ratios show similar shapes, and it can be confirmed that they are structures composed of mesopores.

This similar type of isothermal curve indicates that the pores developed within each carbon have a similar shape, and it appears that pores of a certain type are formed regardless of the applied organosilane ratio.

Figure 35 shows the pore distribution curve of the mesoporous carbon structure according to the organosilane application ratio. In the pore distribution curve of Figure 35, the pore volume increased depending on the organosilane ratio. This is because the porous silica structure, which determines the structure of carbon, provides more abundant mesopores as the proportion of organosilane increases. In the pore distribution curve, the volume of 3nm or less increased as the ratio of organosilane decreased. This means that the size of the pores formed by organosilane is 2nm on average, and as the amount of organosilane increases, the size of the pores formed by organosilane increases. It is judged that

Figure 36 shows a graph comparing the physical properties of mesoporous carbon structures prepared at different organosilane application ratios. In the graph of Figure 36, the specific surface area decreased as the organosilane application rate increased, and the pore volume was the largest in the mesoporous carbon structure with an organosilane application rate of 0.375, but the average pore size increased with the organosilane application rate.

As explained above, this phenomenon can be judged to be due to the effect of pores formed when the silica that forms pores is removed during the etching process. In other words, the pores formed by organosilane in silica have an average size of 2 to 5 nm, and the polymer is supported in the pores. During the carbonization process, carbon is formed along the inner wall of the pores and exists in the form of pores in silica. Pores larger than 10 nm are considered to be pores provided by etched silica.

Carbon not only contains the pores of the porous silica structure used as a template but also includes pores that occur due to the removal of silica, forming a pore volume per unit weight that is more than twice that of the porous silica structure.

Table 13 below shows the physical properties of the mesoporous carbon structure by organosilane application ratio.

characteristic unit Carbon structure (C18TEM/TEOS) 0.125 0.375 One specific surface area ^m2 /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 Table 13 above, the specific surface area decreased as the organosilane application rate increased, and the pore volume showed the largest value when the organosilane application rate was 0.375. The pore size increased in proportion to the organosilane application rate.

This phenomenon appears to be due to the formation of large pores in the mesopore region when the application rate of organosilane in the porous silica structure increases, and the development of pores of 3 nm or less when the application rate of organosilane is low.

From these results, it can be assumed that the mesoporous carbon structure made of carbon-containing polymer material does not completely fill the pores provided by the porous silica structure during the carbonization process, but is formed by leaving the center of the pores empty.

This is because the amount of polymer applied compared to the porous silica structure is the same in the production of the mesoporous carbon structure according to the organosilane application ratio, so when the organosilane application ratio is small, the pore volume in the porous silica structure decreases and the density of the filled polymer relatively increases. Therefore, it appears that the pore size within the mesoporous carbon structure formed after carbonization has become relatively small.

<Experimental Example 10>

Characteristics of mesoporous carbon structures according to the amount of carbon-containing polymer material added

The characteristics of the mesoporous carbon structure according to the amount of carbon-containing polymer material filled in the porous silica structure were confirmed as follows.

Phenol resin was used as the carbon-containing polymer material. The amount of carbon-containing polymer material was charged at a weight ratio of 0.23, 0.5, and 1, respectively, relative to the solid weight of the porous silica structure, and then carbonized by heat treatment to prepare a porous silica-carbon composite. The prepared porous silica-carbon composite was etched using a hydrofluoric acid solution, dried at 110°C for 12 hours, and then used as an experimental sample.

Figure 37 shows the nitrogen isotherm of the mesoporous carbon structure according to the application ratio of the carbon-containing polymer material. As shown in Figure 37, the nitrogen adsorption capacity was greater as the application ratio of the carbon-containing polymer material decreased. When the carbon-containing polymer material application ratio was 1, the adsorption capacity was significantly reduced.

From these results, it can be seen that the amount of carbon-containing polymer material supported or coated in silica has a significant effect on the physical properties of mesoporous carbon.

Figure 38 shows the pore distribution curve of the carbon structure according to the application ratio of carbon-containing polymer material.

Looking at the pore distribution of carbon, the pore distribution of the carbon structures manufactured when the carbon-containing polymer material application ratio was 0.23 and 0.5 was similar, but when the application ratio was 1, the pore volume decreased sharply.

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

From these results, it can be seen that if the application ratio of the carbon-containing polymer material coated on silica is more than 0.5, the pore volume is excessively charged compared to the pore volume provided by silica. This is because the excessively charged carbon-containing polymer material forms a thick resin layer on the outer surface in addition to the inside of the pores of the mesoporous carbon structure, forming a mesoporous carbon structure with undeveloped pores.

In Figure 39, the physical properties of mesoporous carbon structures according to the application ratio of carbon-containing polymer materials are compared graphically.

As shown in the graph of Figure 39, the specific surface area of the mesoporous carbon structure was highest when the carbon-containing-polymer material application ratio was 0.5, but the pore volume and pore size were the highest when the carbon-containing-polymer material application ratio was low. It was the highest.

This trend shows that in the step of forming a carbon structure by carbonizing silica by coating and heat treatment within the pores, when the amount of carbon-containing polymer material is half of the silica solid weight, the most micropores, which have the greatest impact on the specific surface area, are formed. This is a result that can be confirmed. It is believed that within the pores, where the average pore size of silica is 4.58 nm, the carbon material does not completely fill the pore volume and is coated on the pore walls with a thickness of less than 2 nm. If the amount of carbon-containing polymer material is less than this, it can be assumed that the carbon material is coated more thinly on the pore walls, expanding the pore volume.

Table 14 below shows a comparison of the physical characteristics of the mesoporous carbon structures according to the application ratio of the carbon-containing polymer material.

characteristic unit mesoporous carbon
(Carbon-containing polymer material application ratio compared to silica weight) 0.23 0.5 One specific surface area ^m2 /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 in Table 14 above, it can be seen that as the content of carbon-containing polymer material, that is, carbon, increases compared to silica, physical properties other than surface area decrease overall, and the pore volume, which is a physical property of the provided mold, is not effectively utilized. there is.

In order to use it as a negative electrode active material, lithium ions must be effectively inserted, so the volume and size of pores provide more advantageous conditions than the physical properties of specific surface area.

From the above results, it is judged that the optimal specification of the carbon structure for inserting lithium ions is when the ratio of carbon-containing polymer material is about 0.23 compared to silica. Under these conditions, the pore volume is 1.64, which allows insertion of about 1.5 times more lithium ions than the weight of carbon.

<Experimental Example 11>

Physical properties of medium-porous carbon structures according to particle size

Changes in physical properties of the mesoporous carbon structure according to particle size were confirmed as follows.

Mesoporous carbon structures with particle sizes of 100 nm, 500 nm, and 700 nm were manufactured and their physical properties were analyzed.

Figure 40 shows SEM images of mesoporous carbon structures manufactured with particle sizes of 100 nm, 500 nm, and 700 nm.

Figure 41 shows nitrogen isotherms by particle size of mesoporous carbon structures manufactured with particle sizes of 100 nm, 500 nm, and 700 nm.

As shown in Figure 41, the shape of the nitrogen isotherm shows the type IV isotherm that appears in mesoporous materials. All nitrogen isotherms show a hysteresis phenomenon in which adsorption and desorption do not coincide. This phenomenon occurs in adsorbents with pores of 1 nm or more. In the mesoporous carbon structure, mesopores develop and induce condensation of nitrogen. It is judged.

Figure 41 shows the pore distribution curves of mesoporous carbon structures manufactured with particle sizes of 100 nm, 500 nm, and 700 nm.

When the particle size is 700 nm, it can be seen that macropores of more than 10 nm are expanding. This appears to be caused by a larger volume ratio due to the empty mesopore structure inside the carbon structure compared to the volume of mesopores developed inside the carbon wall.

Table 15 below numerically shows the physical properties of the mesoporous carbon structures manufactured with particle sizes of 100 nm, 500 nm, and 700 nm.

characteristic unit Mesoporous carbon structure size nm 100 500 700 specific surface area ^m2 /g 936 1491 985 Pore volume cc/g 1.68 1.28 1.65 Pore size nm 7.19 3.44 6.69

From the results in Table 15 above, the specific surface area of the mesoporous carbon structure shows the highest value in the mesoporous carbon structure with a particle size of 500 nm, but the pore volume shows the highest value in the mesoporous carbon structure with a particle size of 100 nm. . The pore volume of the mesoporous carbon structure with a particle size of 700 nm is judged to be unsuitable as a structure for metal support due to the high proportion of macropores.

Therefore, it is desirable that the mesoporous carbon structure for supporting metal have a particle size of 100 nm.

<Experimental Example 12>

Confirmation of physical property changes in mesoporous carbon structures according to heat treatment temperature

The change in physical properties of the mesoporous carbon structure according to the heat treatment temperature of the mesoporous carbon structure was confirmed as follows.

As a heat treatment sample, a mesoporous carbon structure manufactured with a particle size of 100 nm was used.

Heat treatment was carried out in a kiln in a nitrogen gas atmosphere containing 10% air. The heat treatment temperature was set to 110°C, 400°C, 700°C, and 900°C, respectively, and the heat treatment time was constant at 1 hour.

Figure 42 shows the nitrogen isotherm for each heat treatment temperature of the mesoporous carbon structure heat-treated at 110°C, 400°C, 700°C, and 900°C. Comparing the isotherms in Figure 42, it can be seen that the shape of the nitrogen isotherm of the mesoporous carbon structure is similar even when the heat treatment temperature increases.

Figure 43 shows the pore distribution curve of the mesoporous carbon structure heat-treated at 110°C, 400°C, 700°C, and 900°C by heat treatment temperature. In Figure 43, it can be seen that pores of about 5 to 7 nm are expanding as the heat treatment temperature increases. This shows that as the heat treatment temperature increases, the pore size expands due to activation of carbon, that is, oxidation of the pore walls within the carbon.

Figure 44 shows a graph comparing changes in physical properties such as specific surface area, pore volume, and pore size according to heat treatment temperature of mesoporous carbon structures heat-treated at 110°C, 400°C, 700°C, and 900°C.

Table 16 below shows the physical properties of the mesoporous carbon structures heat-treated at 110°C, 400°C, 700°C, and 900°C by heat treatment temperature.

characteristic unit Mesoporous carbon structure temperature ℃ 110 400 700 900 specific surface area ^m2 /g 936 979 999 1032 Pore volume cc/g 1.68 1.84 1.92 2.01 Pore size nm 7.19 7.54 7.71 7.78

From the results in Table 16, it can be seen that all physical properties of the mesoporous carbon structure increase as the heat treatment temperature increases. This shows that the pore volume for metal support in a mesoporous carbon structure can be expanded using heat treatment.

<Experimental Example 13>

Confirmation of physical properties of mesoporous carbon structures according to heat treatment time

The change in physical properties of the mesoporous carbon structure according to the heat treatment time of the mesoporous carbon structure was confirmed as follows.

The heat treatment temperature was set at 900°C, and the heat treatment time was set to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours to heat treat the mesoporous carbon structure.

Figure 45 shows SEM images of the mesoporous carbon structure heat-treated at 900°C for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours.

From the results in Figure 45, it can be seen that almost no change in the appearance of the mesoporous carbon structure occurred even as the heat treatment time increased.

Figure 46 shows the nitrogen isotherm of the mesoporous carbon structure manufactured by heat treatment at 900°C for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours. As shown in Figure 46, there is no clear change in the nitrogen isotherm even as the heat treatment time increases.

Figure 47 shows the pore distribution curve of the mesoporous carbon structure manufactured by heat treatment at 900°C for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours. As shown in Figure 47, the pore volume in the 5 to 7 nm range of the mesoporous carbon structure shows a similar shape when the heat treatment time is 3 hours.

Figure 48 shows a graph comparing changes in the physical characteristics identified above, such as specific surface area, pore volume, and pore size. As shown in Figure 48, the specific surface area and pore volume excluding pore size showed the highest values when the heat treatment time was 5 hours, and the physical properties decreased thereafter. From the results in Figure 48, it can be seen that 5 hours is the most effective heat treatment time for improving the physical properties of the mesoporous carbon structure.

Since this is limited to the experimental conditions of a nitrogen atmosphere with an air ratio of 10%, the optimal conditions will change if the ratio is changed or the composition contains other activators.

In the process of manufacturing a mesoporous carbon structure, pore volume expansion by heat treatment may be subject to various conditions, but the improvement of the physical properties of the mesoporous carbon structure by heat treatment is achieved at a heat treatment temperature of 900°C in a nitrogen atmosphere containing 10% air. Heat treatment for 5 hours is preferable to improve the physical properties of the mesoporous carbon structure.

Table 17 below shows the physical properties of the mesoporous carbon structure prepared by heat treatment at 900°C for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours.

characteristic unit Mesoporous carbon structure hour time (hr) One 2 3 4 5 6 7 8 specific surface area ^m2 /g 999 1052 1085 1098 1119 1046 994 1084 Pore volume cc/g 1.93 2.06 2.18 2.24 2.33 2.07 2.05 2.24 Pore size nm 7.66 7.76 7.98 8.09 8.25 7.91 8.26 8.28

Figure 49 shows the particle distribution curve of the mesoporous carbon structure for each heat treatment time (1 to 5 hours). Looking at the curve showing the distribution of particle size, the overall distribution did not change, but it was confirmed that particles larger than about 100 nm did not appear after 3 hours of heat treatment. This is believed to be a phenomenon caused by the destruction of the carbon connections in the cluster form, which is composed of basic units of nanoscale particles and connected between carbons, due to thermal decomposition during the heat treatment process.

Table 18 below shows the particle size distribution analysis results of the mesoporous carbon structure according to heat treatment time (1 to 5 hours).

sample area D[3,2] D[4,3] D[1,0] Dv(10) Dv(50) Dv(90) unit ^m2 /kg ㎛ ㎛ ㎛ ㎛ ㎛ ㎛ MHC900C1H 472.8 12.7 77.4 1.2 5.47 33.4 111 MHC900C2H 408.4 14.7 52.3 1.59 6.48 34.4 99.2 MHC900C3H 412.2 14.6 43.3 1.59 6.47 33.8 94.5 MHC900C4H 403.1 14.9 44.7 1.58 6.69 34.7 97.2 MHC900C5H 437.6 13.7 42 1.41 6.09 32.8 92

<Example 8>

Manufacturing and analysis conditions for batteries using medium-porous carbon structures as anode active materials

A half-cell was manufactured by applying the mesoporous carbon structure of Example 7 as a negative electrode active material, and the electrochemical properties of the manufactured battery were confirmed.

First, to prepare a slurry, 80% by weight of the active material, 10% by weight of the conductive material, and 10% by weight of the binder were mixed uniformly. Acetylene black was used as a conductive material, and PVDF (Solef5130, Solvay Korea) [8% in NMP] was used as a binder. To control viscosity, an appropriate amount of NMP (Sigma-Aldrich) was added.

An electrode was manufactured by coating the obtained slurry evenly on a copper current collector to a thickness of 50 μm using an applicator. The electrode was dried in a forced circulation oven maintained at 80°C for about 12 hours to completely evaporate the moisture and solvent.

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

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

The manufactured half-cell was charged with a constant current (CC) up to 0.005V (vs. Li/Li+) at a current of 0.2C relative to the weight of the active material, and then maintained at a voltage of 0.005V (vs. Li/Li+). Constant voltage (CV) charging was performed, with charging ending at a current of 0.01C.

The discharge was a constant current discharge that ended at 2V (vs. Li/Li+) with a current of 0.1C. At this time, assuming the 1C value was 400 mA/g, a charge/discharge experiment was performed using the above method, and then the 1C value of each sample was obtained.

The lifespan experiment was conducted after the activation process was performed under the above conditions. A lifespan test was conducted by setting only the charge/discharge current to 0.1C and keeping the remaining conditions the same. The charge/discharge experiment was measured using WBS-3000L from Won-A Tech.

<Experimental Example 14>

Verification of battery performance according to heat treatment temperature of medium-porous carbon structure

For the battery manufactured in Example 8, the effect of the heat treatment temperature of the mesoporous carbon structure on battery performance was confirmed as follows.

The charge/discharge battery performance of the mesoporous carbon structures heat-treated for 1 hour at heat treatment temperatures of 110°C, 450°C, and 700°C, respectively, was confirmed.

Figure 50 shows the charge/discharge battery performance of mesoporous carbon structures that were heat-treated for 1 hour at heat treatment temperatures of 110°C, 450°C, and 700°C, respectively.

Table 19 below shows the battery performance and efficiency at 30 charge/discharge cycles of the mesoporous carbon structures that were heat-treated for 1 hour at heat treatment temperatures of 110°C, 450°C, and 700°C, respectively.

Evaluation items unit Mesoporous carbon structure temperature ℃ 110 450 700 Battery performance mAh/g 255 412 531 efficiency % 95 93 97 cycle episode 30 30 30

From the results in Table 19 above, it can be seen that the battery performance improves as the heat treatment temperature increases at a current density of 50 mA/g and 30 cycles.

In the results of Experimental Example 13, it was confirmed that the pore volume increased as the heat treatment temperature increased. It was believed that this increase in pore volume increased the amount of lithium ion charge.

It can be confirmed that these results are similar to the results from a study using porous carbon black as a negative electrode active material [H. Zhao, J. Ren., X. He, J. Li, C. Jiang, and C. Wan, Purification and carbon-film-coating of natural graphite as anode materials for Li-ion batteries, Electrochim. Acta, 52, 6006-6011 (2007)].

<Experimental Example 15>

Check battery performance according to heat treatment time of medium-porous carbon structure

For the battery manufactured in Example 8, the effect of heat treatment time on the mesoporous carbon structure on battery performance was confirmed as follows.

The charge/discharge performance of the mesoporous carbon structure heat-treated at 900°C for 1 hour and 5 hours was confirmed.

The results of confirming the charge/discharge performance of the mesoporous carbon structure heat-treated at 900°C for 1 hour and 5 hours are shown in Figure 51 and Table 20.

Evaluation items unit 900℃, 1 hour 900℃, 5 hours cycle episode 40 40 100 electric current mA/g 50 50 50 Performance mAh/g 569 577 742 efficiency % 95 96 97

As shown in Table 20, the difference in battery performance depending on heat treatment time was slight based on 40 charge/discharge cycles. In addition, the mesoporous carbon structure heat-treated for 5 hours improved the battery performance at 100 cycles by about 180 mAh/g compared to the battery performance at 40 cycles.

From the results in Figure 51, it can be seen that the battery performance of the mesoporous carbon structure is improved in proportion to the increase in the number of charge/discharge cycles. This is believed to be due to the formation of an SEI layer on the carbon surface.

<Experimental Example 16>

Check battery performance according to current density

For the battery prepared in Example 8, the effect of current density on battery performance analysis of the mesoporous carbon structure was confirmed as follows.

Charge/discharge experiments on the mesoporous carbon structure were conducted at current densities of 50 mA/g, 100 mA/g, and 200 mA/g, respectively.

Figure 52 shows the results of charge/discharge experiments on the mesoporous carbon structure at current densities of 50 mA/g, 100 mA/g, and 200 mA/g.

From the results in Figure 52, it can be seen that the discharge performance is rapidly decreasing as the current density, which is a condition for analyzing battery performance, increases. This phenomenon occurs in most negative electrode active materials, but appears more clearly in porous carbon materials.

Table 21 below shows the performance and efficiency at 30 charge/discharge cycles obtained from the above experimental results.

Evaluation items unit Medium porous carbon structure heat treated at 900℃ for 1 hour electric current mA/g 50 100 200 Performance mAh/g 600 380 120 efficiency % 93 91 94 cycle episode 30 30 30

From the results in Table 21 above, the mesoporous carbon structure showed performance that exceeded the theoretical capacity of graphite, 372 mAh/g, by about 1.5 times at a current density of 50 mA/g, and showed a value higher than the theoretical capacity even at a current density of 100 mA/g. .

<Experimental Example 17>

Verification of battery performance of mesoporous carbon structure

For the battery prepared in Example 8, the battery performance of the mesoporous carbon structure for metal complexation was confirmed as follows.

In Experimental Example 16, the performance of about 600 mAh/g was confirmed at a current density of 50 mA/g, and based on this, the mesoporous carbon structure manufactured under the same conditions was commissioned to the Korea Testing and Research Institute, an official test report institution, and the mesoporous carbon as a negative electrode active material was obtained. The performance of the structure was verified.

The original result report of the experiment conducted at the Korea Testing and Research Institute is shown in Figure 53, and the results are shown numerically in Table 22.

Evaluation items unit measurements Cathode discharge capacity mAh/g 592.5 cathode energy density mAh/cc 88.8 Charge/discharge efficiency % 14.5

As shown in Table 22 above, the discharge capacity of the carbon structure was confirmed to be 592 mAh/g, and this value is similar to the self-evaluated value.

<Example 9>

Preparation of mesoporous metal oxide-carbon composites

Mesoporous metal oxide-carbon composites containing 4%, 10%, and 20% by weight of iron oxide in the mesoporous carbon structure were prepared as follows.

A certain amount of FeCl ₂ reagent relative to the weight of the mesoporous carbon structure was dissolved in distilled water, loaded on the mesoporous carbon structure, and then evaporated to dryness. The dried carbon-FeCl ₂ powder was placed in a sintering furnace and heat-treated for 5 hours at a sintering temperature of 500°C under a nitrogen atmosphere to obtain a mesoporous metal oxide (Fe ₂ O ₃ )-carbon composite. The obtained mesoporous metal oxide-carbon composite powder was sieved using a 200 mesh mesh.

<Experimental Example 18>

Determination of physical properties of mesoporous metal oxide-carbon composites

The physical properties of the mesoporous metal oxide-carbon composite prepared in Example 9 were confirmed as follows.

SEM images of mesoporous metal oxide-carbon composites containing 4% by weight, 10% by weight, and 20% by weight of iron oxide in the mesoporous carbon structure are shown in Figure 54.

In addition, the results of XRD diffraction pattern analysis of the mesoporous metal oxide-carbon composite containing 4%, 10%, and 20% by weight of iron oxide in the mesoporous carbon structure are shown in Figure 55. In the results of Figure 55, all mesoporous metal oxide-carbon composites showed crystalline peaks, and when comparing each pattern, the intensity increased as the contained metal material increased. These analysis results can be inferred that the metal material is uniformly contained within the mesoporous carbon structure.

Figure 56 shows nitrogen isotherms of mesoporous metal oxide-carbon composites containing 4% by weight, 10% by weight, and 20% by weight of iron oxide in the mesoporous carbon structure. The nitrogen isotherm of the mesoporous metal oxide-carbon composite is similar to the shape of the porous carbon structure and appears to be largely influenced by the carbon structure. However, compared to the porous carbon structure, the macropores are more developed, which can be judged to be the effect of the metal contained in the composite. That is, it is presumed that in the heat treatment step that occurs after combining the porous carbon structure and the metal precursor, the thermal decomposition of carbon is promoted by the metal with excellent heat transfer and macropores are formed in the space.

Figure 57 shows the pore distribution curves of mesoporous metal oxide-carbon composites containing 4% by weight, 10% by weight, and 20% by weight of iron oxide in the porous carbon structure. The pore distribution of the mesoporous metal oxide-carbon composite is similar in shape to that of the porous carbon structure.

Figure 58 shows a graph comparing the physical properties of mesoporous metal oxide-carbon composites. As the ratio of metal in the mesoporous metal oxide-carbon composite increased, the specific surface area and pore volume decreased, but the pore size increased.

This result can be judged to be because the metal present in carbon promoted thermal decomposition of carbon during the heat treatment process.

Table 23 below shows the physical properties of mesoporous metal oxide-carbon composites containing 4%, 10%, and 20% by weight of iron oxide in the porous carbon structure.

characteristic unit Mesoporous metal oxide-carbon composite sample MC_F4% MC_F10% MC_F20% specific surface area ^m2 /g 885 756 582 Pore volume cc/g 1.96 1.75 1.37 Pore size nm 8.83 9.26 9.40

From the results in Table 23, it was confirmed that as the metal content in the composite increased, the specific surface area and pore volume decreased and the pore size increased, which was related to the result of breaking the shape of the carbon in the SEM image of Figure 54. It is judged that

<Experimental Example 19>

Electrochemical properties of mesoporous metal oxide-carbon composites

The battery performance of the mesoporous metal oxide-carbon composite was confirmed as follows.

A half-cell using the mesoporous metal oxide-carbon composite of Example 9 was manufactured and a charge/discharge experiment was performed, and the results are shown in Figure 59 and Table 24.

half cell Furtherance Slurry (70%) Conductive material (10%)
Binder (20%) active material Performance current density active material Mesoporous metal oxide-carbon composite HC_F4 107mAh/g 100 mA/g conductive material acetylene black HC_F10 91Ah/g 100 mA/g bookbinder PAA:SBR = 6:1 wt% HC_F20 71Ah/g 100 mA/g Electrode thickness 40㎛ Electrode diameter 16Ø operating voltage 0.01~2.5V

As shown in the results in Table 24 above, as the metal content increases, battery performance actually decreases. This is presumed to be related to the decrease in the physical properties of the mesoporous metal oxide-carbon composite compared to the porous carbon structure.

The role of carbon in the mesoporous metal oxide-carbon composite is to stably preserve the battery performance of the metal oxide material and improve conductivity. However, as a result of analyzing the physical properties, it was confirmed that the porous carbon structure was rapidly damaged, and the carbon material was found to be rapidly damaged. As the surfaces were damaged, conductivity decreased rapidly and it is believed that metal material leaked into the electrolyte through the damaged space.

Due to this phenomenon, the inherent battery performance of carbon, which serves as a support for the mesoporous metal oxide-carbon composite, decreased rapidly, and at the same time, the performance possessed by the metal material was not realized.

<Example 10>

Preparation of mesoporous carbon-metal oxide-carbon composites

The mesoporous metal oxide-carbon composite prepared in Example 9 was heat-treated at 900°C for 5 hours under an air atmosphere.

Phenol resin was used as the carbon-containing polymer material. The phenol resin was dissolved in distilled water three times the weight of the mesoporous metal oxide-carbon composite.

The mesoporous metal oxide-carbon composite was supported on a carbon-containing-polymer material dissolved in distilled water, and the carbon-containing-polymer material was coated on the mesoporous metal oxide-carbon composite for 5 hours.

A mesoporous metal oxide-carbon composite coated with a carbon-containing polymer material was heat-treated at 900°C for 5 hours in a nitrogen atmosphere to prepare a mesoporous carbon-metal oxide-carbon composite.

<Experimental Example 20>

Determination of physical properties of mesoporous carbon-metal oxide-carbon composite

In order to improve the battery performance of the mesoporous metal oxide-carbon composite, the mesoporous carbon-metal oxide-carbon composite was prepared and its physical properties were confirmed as follows.

The mesoporous carbon-metal oxide-carbon composite prepared in Example 10 was used as an experimental sample. For comparison, a metal oxide sample coated with a carbon-containing polymer material and heat treated was used.

Figure 60 shows an SEM image of pure carbon carbonized by heat treatment of the carbon-containing polymer material used in the production of the mesoporous carbon-metal oxide-carbon composite. When a carbon-containing polymer material, which is a precursor of carbon for coating metal oxide, is heat treated and carbonized, the surface becomes smooth and dense.

Figure 61 is an SEM image of a mesoporous carbon-metal oxide-carbon composite manufactured by setting the weight ratio of metal oxide to 10% by weight in the manufacturing stage. In the case of a mesoporous carbon-metal oxide-carbon composite containing 10% by weight of metal oxide, the carbon-containing polymer material was manufactured in a tightly aggregated shape during the carbonization process by heat treatment.

Figure 62 is an SEM image of a mesoporous carbon-metal oxide-carbon composite manufactured by setting the weight ratio of metal oxide to 30% by weight in the manufacturing stage. In the case of a mesoporous carbon-metal oxide-carbon composite containing 30% by weight of metal, the amount of carbon coating is relatively small, so the material develops into a relatively spherical shape, and the overall particles are made up of clusters of small granular materials.

Figure 63 is an SEM image of a metal oxide sample that was heat-treated without coating a carbon-containing polymer material in the manufacturing stage.

When a mesoporous carbon-metal oxide composite is oxidized and heat-treated at a high temperature, the shape is spherical and the surface is a porous material with fine spaces developed. Due to this shape, if 70% or less of carbon is coated on the surface, a spherical porous material is formed.

From these results, in the case of manufacturing a mesoporous carbon-metal oxide-carbon composite by heat-treating the mesoporous carbon-metal oxide composite and coating it with carbon, the mesoporous carbon-metal oxide composite is manufactured and then oxidized and heat-treated to form only the metal oxide material. It is desirable to prepare a mesoporous carbon-metal oxide-carbon composite by manufacturing and controlling the amount of carbon on the surface.

<Experimental Example 21>

Confirmation of metal content in mesoporous carbon-metal oxide-carbon complex

The metal content in the mesoporous carbon-metal oxide-carbon composite was confirmed as follows.

Samples include a mesoporous carbon structure (carbon) coated with carbon on a metal-free mesoporous carbon structure, a mesoporous carbon-metal oxide-carbon composite (F10C) containing 10% by weight of metal oxide (iron oxide), and oxidation Thermogravimetric analysis was performed under an air atmosphere using a mesoporous carbon-metal oxide-carbon composite (F30C) containing 30% by weight of metal (iron oxide) and a structure using only iron oxide (F100), and the results are shown in Figure 64. .

From the results in Figure 64, it can be seen that the higher the metal content, the higher the final yield. This is because the analysis conditions are conducted in an air atmosphere, so carbon materials react with oxygen and are oxidized and lost. Therefore, since the final yield would have consisted only of metal oxides, it can be assumed that the final yield is the ratio of the metal material contained in carbon.

Figure 65 shows a carbon structure (carbon) coated with carbon on a mesoporous carbon structure containing no metal, a mesoporous carbon-metal oxide-carbon composite (F10C) containing 10% by weight of metal oxide (iron oxide), and a metal oxide ( The final yield of each material calculated from the thermogravimetric analysis results of the mesoporous carbon-metal oxide-carbon composite (F30C) containing 30% by weight of iron oxide (iron oxide) and the structure using only iron oxide (F100) is shown.

In the results of Figure 65, the final yield of the sample (F100) containing 100% metal was 97%, which appears to have reduced the organic substances and moisture remaining in the sample. For the mesoporous carbon-metal oxide-carbon composite sample (F10C) containing 10% of metal, the final yield was about 8.1%, and for the mesoporous carbon-metal oxide-carbon composite sample (F30C) containing 30% of metal. The final yield was about 35%. This is believed to be due to minor errors in the sample manufacturing process. The final yield of pure carbon sample was 0.8%.

Based on the numerical values of the analysis results, it can be assumed that there are minutely inorganic impurities in the carbon sample, and this problem can be solved by acid washing after manufacturing a mesoporous carbon-metal oxide-carbon composite.

<Experimental Example 22>

Analysis of physical properties of mesoporous carbon-metal oxide-carbon composites

The physical properties of the mesoporous carbon-metal oxide-carbon composite were analyzed as follows.

Samples include a mesoporous carbon-metal oxide-carbon composite (F10C) containing 10% by weight of metal oxide (iron oxide), and a mesoporous carbon-metal oxide-carbon composite (F30C) containing 30% by weight of metal oxide (iron oxide). , a mesoporous carbon-metal oxide-carbon composite (F50C) containing 50% by weight of metal oxide (iron oxide) and a structure using only iron oxide (F100) were used, and the physical properties were confirmed by BET analysis.

Figure 66 shows the nitrogen isotherm of the mesoporous carbon-metal oxide-carbon composite.

As shown in Figure 66, compared to the mesoporous carbon-metal oxide-carbon composite sample containing 10% by weight of metal oxide, the curve of the mesoporous carbon-metal oxide-carbon composite, which is a sample containing more metal, shows that the mesopores have significantly disappeared. It shows the shape of the adsorption isotherm type I.

The hysteresis phenomenon commonly occurs when the pores are expanded inward or the pores are formed within the structure, and the phenomenon is clearly visible in the isothermal curve of metal oxide.

These results show that the causes of the hysteresis phenomenon occurring in carbon structures and the hysteresis phenomenon occurring in composites are different. In other words, during the manufacturing process of the mesoporous carbon-metal oxide-carbon composite, a significant portion of the mesopores developed in the carbon disappear, but it is believed that new pores are developing due to the metal oxide.

Figure 67 shows the pore distribution curves of mesoporous carbon-metal oxide-carbon composites.

As shown in the pore distribution in Figure 67, in the mesoporous carbon-metal oxide-carbon composite sample loaded with 30% by weight of metal oxide, most of the pores of about 5 nm or larger developed in the structure loaded with 10% by weight were reduced, affecting the physical properties. It has decreased to an unattainable level. In addition, in the mesoporous carbon-metal oxide-carbon composite sample containing 50% by weight of metal oxide, pores of about 20 nm or more increase. From these results, it can be seen that as the metal content increases, the pores in the macropore region develop.

Table 25 below shows the physical properties of the mesoporous carbon-metal oxide-carbon composites.

characteristic unit Mesoporous carbon-metal oxide-carbon composite Metal content % 10 30 50 100 specific surface area ^m2 /g 658 341 278 0 Pore volume cc/g 1.27 0.19 0.18 0.00 Pore size nm 7.64 2.20 2.58 21.53

As shown in the results in Table 25 above, as the content of metal oxide increased, the specific surface area, pore volume, and pore size decreased.

Comparing the pore sizes, it can be seen that the pore size of metal oxide is approximately 20 nm. It can be inferred that in the heat-treated sample of the mesoporous carbon-metal composite, most of the pores of the metal oxide disappeared, but pores were formed between particles. In this mesoporous carbon-metal oxide-carbon composite coated with carbon on metal oxide, it can be seen from the pore distribution curve that mesopores have developed again.

The formation of these mesopores can be explained as follows. In the step of coating the polymer onto the metal oxide, the carbon-containing polymer material penetrates into the interior of the metal material and is uniformly distributed, and during the carbonization process, a structure is formed with the carbon material in the form of pores under the influence of the metal.

Additionally, when the metal content increases to 50%, large pores are formed along with mesopores. This can be seen as the effect of the space formed inside the metal oxide and the thickness of the carbon film becoming thinner as the metal content increases.

Figure 68 shows a mesoporous carbon-metal oxide-carbon composite (F10C) containing 10% by weight of metal oxide (iron oxide) and a mesoporous carbon-metal oxide-carbon composite (F30C) containing 30% by weight of metal oxide (iron oxide). , XRD diffraction patterns and particle distribution curves of a mesoporous carbon-metal oxide-carbon composite (F50C) containing 50% by weight of metal oxide (iron oxide) and a structure using only iron oxide (F100) were shown.

As shown in the diffraction pattern of Figure 68, crystalline peaks can be confirmed in each complex, and as the metal content increases, more peaks appear.

In the case of particle distribution, the complex is distributed in the range of about 1 to 90㎛, and the D[4, 3] value, which is the volume moment mean that reflects the size of the particles that occupy most of the sample volume, is 20. It was found to be ~25㎛. This level of particle size distribution can present favorable conditions for electrode manufacturing.

<Experimental Example 23>

Electrochemical properties of mesoporous carbon-metal oxide-carbon composites

The electrochemical properties of the mesoporous carbon-metal oxide-carbon composite were analyzed as follows.

Samples include a mesoporous carbon-metal oxide-carbon composite (F10C) containing 10% by weight of metal oxide (iron oxide), and a mesoporous carbon-metal oxide-carbon composite (F30C) containing 30% by weight of metal oxide (iron oxide). and a structure using only iron oxide (F100).

In Figure 69, the charging/discharging performance of the composite composed of 10% by weight of iron oxide in the mesoporous carbon-metal oxide-carbon composite is analyzed and shown in a graph, and in Figure 70, the iron oxide in the mesoporous metal oxide-carbon composite is 30% by weight. The charge/discharge performance of the composite composed of % weight was analyzed and presented in a graph.

Comparing the graphs of Figures 69 and 70, the charge/discharge capacity of both composites decreases up to the 25th initial cycle and then increases again, and shows a slight increase even after 150 cycles or more.

A similar phenomenon can be found in the results of researchers related to the development of negative electrode active materials using iron oxide. In most cases, these results show that the metal oxide deactivated during the initial charge/discharge process can react with lithium ions due to repetitive electron transfer. It is assumed that it is activated in a form that can be used [W. Wei, W. Zhaohui, Y. Taekyung, J. Changzhong, K. Woo-Sik, Sci. Technol. Adv. Mater. 2015, 16, 02350].

In Figure 71, the charge/discharge performance of the iron oxide sample heat-treated without coating with the carbon-containing polymer material among the composites was analyzed at 100 mA/g and shown in a graph.

As shown in the results of Figure 71, iron oxide, a metal oxide produced by heat treatment of a mesoporous carbon-metal oxide composite, initially shows high performance, but then rapidly decreases, showing a constant value of battery capacity at about 200 mAh/g.

Comparing these results with those of the mesoporous carbon-metal oxide-carbon composite, in the case of carbon-coated iron oxide, the battery capacity increased by at least two times. This can be seen as because the active material was stabilized by carbon. It can be judged that the surface-coated carbon improves electrical conductivity, which is a disadvantage of iron oxide, and at the same time suppresses the volume expansion of the metal that occurs during charging/discharging.

Table 26 below shows the experimental results confirming the battery performance of the mesoporous carbon-metal oxide-carbon composite at 160 charge/discharge cycles.

cathode Performance cycle electric current efficiency cycle efficiency unit mAh/g episode mA/g % % F100 209 160 100 98.4 46.2 F30C 499 160 100 99.1 107.8 F10C 387 160 100 99.0 102.2

As shown in the results in Table 26 above, the performance of the mesoporous carbon-metal oxide-carbon composite with 30% iron oxide content after 160 cycles at a current density of 100 mA/g is about 499 mAh/g, which is 1007 mAh, which is the theoretical capacity of iron oxide. Equivalent to 50% of /g.

In the case of the structure (F100) using only iron oxide, the initial performance was higher than that of the mesoporous carbon-metal oxide-carbon composite with 30% iron oxide content, but the performance rapidly decreased thereafter. This is believed to be because the carbon coating is not uniform.

<Experimental Example 24>

Confirmation of charge/discharge performance of mesoporous carbon-metal oxide-carbon composite

The battery performance of the mesoporous carbon-metal oxide-carbon composite was confirmed as follows.

Among the mesoporous metal oxide-carbon composites of Example 10, a coin cell was manufactured using a composite composed of 30% by weight of iron oxide as a negative electrode active material, and the battery performance thereof was requested from the Korea Testing & Research Institute, a certified testing institute, to determine the total charge/resistance. Battery performance was confirmed at 100 discharge cycles.

The original experimental result report conducted at the Korea Testing & Research Institute of Chemical Technology is shown in Figure 72, and the results are shown in Table 27.

Evaluation items unit measurements Cathode discharge capacity mAh/g 485.5 cathode energy density mAh/cc 722.0 Charge/discharge efficiency % 103.1

As shown in the results in Table 27 above, the discharge capacity of the mesoporous carbon-metal oxide-carbon composite conducted by the Korea Testing and Research Institute, an accredited institution, shows similar values to the discharge capacity conducted by the performing institution.

<Example 11>

Preparation of nanoscale metal oxide-carbon composites

6H₂O) 분말을 사용하였고, 나노분말을 수열 합성하는 용액인 강알칼리성 수용액은 10M의 NaOH 수용액을 사용하였다.The raw material powder is ferric chloride (FeCl ₃

6H ₂ O) powder was used, and a 10M NaOH aqueous solution was used as a strong alkaline aqueous solution for hydrothermal synthesis of nanopowders.

Ferric chloride powder sieved to 325 mesh was mixed in 10M NaOH aqueous solution, which is a strong alkaline aqueous solution. The mixture was stirred and subjected to hydrothermal synthesis at 180°C for more than 5 hours using a hydrothermal synthesis reactor to prepare a nanoscale iron oxide negative electrode active material with a one-dimensional structure.

After hydrothermal synthesis, the synthesized powder was washed and filtered to adjust the pH to neutral. At this time, the washing was done first with a dilute aqueous hydrochloric acid solution and second with distilled water and ethanol.

The sample whose pH value was adjusted to neutral was dried at 80°C for 12 hours before heat treatment and then treated at 110°C for 12 hours to obtain nanoscale iron oxide.

A nanoscale metal oxide-carbon composite was prepared by coating carbon on the particle surface of the nanoscale iron oxide as follows.

First, a certain amount of carbon-containing polymer material was stirred and mixed relative to the weight of nanoscale iron oxide. At this time, the carbon-containing polymer material was used in an amount to coat 3% by weight, 10% by weight, 30% by weight, and 50% by weight of carbon on the surface of iron oxide prepared by hydrothermal synthesis. Iron oxide and carbon-containing polymer material were heated to 200°C at a temperature increase rate of 1°C/min under an air atmosphere and then oxidized at 200°C for 1 hour.

The oxidized composite was heated to 900°C at a rate of 5°C/min under a nitrogen atmosphere and then carbonized by heat treatment at 900°C for 1 hour.

The carbonized composite was ground using a ball mill at 250 rpm for 5 hours and separated by sieving through a 200 mesh standard sieve to obtain a nanoscale metal oxide-carbon composite.

<Experimental Example 25>

Confirmation of properties of nanoscale metal oxide-carbon composites

A nano-scale metal oxide-carbon composite coated with nano-sized iron oxide and carbon in different weight ratios was manufactured, and the physical properties were confirmed as follows.

As an experimental sample, the nanoscale metal oxide-carbon composite prepared in Example 11 was used, and for comparison, nanoscale iron oxide prepared by hydrothermal synthesis without carbon coating was used. Each experimental sample was nanoscale iron oxide (F0) manufactured by applying a hydrothermal synthesis method, a nanoscale metal oxide-carbon composite (CF3) coated with 3% by weight of carbon on the surface of the iron oxide manufactured by hydrothermal synthesis, and a nanoscale metal oxide-carbon composite (CF3) manufactured by hydrothermal synthesis. Nanoscale metal oxide-carbon composite (CF10) coated with 10% by weight of carbon on the surface of iron oxide, nanoscale metal oxide-carbon composite (CF30) coated with 30% by weight of carbon on the surface of iron oxide manufactured by hydrothermal synthesis, manufactured by hydrothermal synthesis It is a nanoscale metal oxide-carbon composite (CF50) in which 50% by weight of carbon is coated on the surface of the manufactured iron oxide.

(1) Image analysis

The samples were analyzed using FE-SEM as an analysis equipment, and SEM images, which are enlarged images of the complex, were analyzed at the Chungbuk National University Joint Practice Center and the Korea Research Institute of Chemical Technology's Instrument Analysis Laboratory, which are analysis institutions.

As a result, the SEM image of the nanoscale iron oxide (F0) manufactured by applying the hydrothermal synthesis method is shown in Figure 73, and the nanoscale metal oxide-carbon composite (CF3) coated with 3% by weight of carbon on the surface of the iron oxide manufactured by hydrothermal synthesis. ) is shown in Figure 74, and in Figure 75 is an SEM image of a nanoscale metal oxide-carbon composite (CF10) coated with 10% by weight of carbon on the surface of iron oxide prepared by hydrothermal synthesis. Figure 76 shows the SEM image of the nanoscale metal oxide-carbon composite (CF30) coated with 30% by weight of carbon, and the nanoscale metal oxide-carbon composite (CF50) coated with 50% by weight of carbon on the surface of iron oxide prepared by hydrothermal synthesis. The SEM image of is shown in Figure 77.

Hydrothermally synthesized nanoscale iron oxide is rod-shaped with an average thickness of about 20 nm, but as the amount of carbon coated on the iron oxide increases, it is converted into a spherical shape. Since the shape of the anode active material is spherical, such as graphite, which is advantageous for electrode performance, a spherical composite coated with carbon will achieve better performance than iron oxide.

As a result of BET analysis of the above materials, the specific surface area was on average 50 m ² /g or less.

(2) Thermogravimetric analysis (TGA)

For the above samples, TGA was used as an analysis equipment, and thermogravimetric analysis was performed at the Chungbuk National University Joint Practice Center, an analysis institution.

Thermogravimetric analysis was performed on a 3.82 mg sample by raising the temperature from an initial temperature of 30°C to a final temperature of 1000°C at a temperature increase rate of 10°C/min under an air atmosphere using TG209F1 (Al2O3 support) as an analysis equipment.

Figure 78 shows a graph of the thermogravimetric analysis results of nanoscale iron oxide and nanoscale metal oxide-carbon composites coated with carbon on iron oxide, and Table 28 shows the thermogravimetric analysis results numerically.

sample transference number(%) CF3 4.38 CF10 10.50 CF30 31.29 CF50 54.19

As a result of the analysis, the final yield for each sample shows a value similar to the amount of metal supported during the carbon coating process. These results show that the design range for coating carbon on the iron oxide surface is manufactured reproducibly even in the actual sample manufacturing stage.

(3) X-ray diffraction pattern analysis

For the above samples, XRD was used as an analysis equipment, and the X-ray diffraction pattern, which is an enlarged image of the composite, was analyzed at the joint practice center of Chungbuk National University, an analysis institute.

Figure 79 graphically shows the results of X-ray diffraction pattern analysis of nanoscale iron oxide and nanoscale metal oxide-carbon composites.

In Figure 79, a nanoscale metal oxide-carbon composite (CF50) coated with 50% by weight of carbon on the iron oxide surface shows a clear crystalline peak. This is highly likely because the thickness of the carbon coated on the iron oxide surface is thin or the iron oxide is partially exposed.

Nanoscale metal oxide-carbon composite (CF30) coated with 30% by weight of carbon on the surface of iron oxide, nanoscale metal oxide-carbon composite (CF10) coated with 10% by weight of carbon on the surface of iron oxide, and 3% by weight of carbon on the surface of iron oxide. In the case of coated nanoscale metal oxide-carbon composite (CF3), the amount of carbon in the composite is more than 70%, and most peaks show a carbon material composed of amorphous material.

The above results show that when manufacturing a nanoscale metal oxide-carbon composite by coating the surface of iron oxide, the carbon content in the composite must be 70% or more to ensure that the metal in the metal oxide-carbon composite is not exposed to the outside and the metal oxide-carbon composite is stable. It shows that it is manufactured with .

<Experimental Example 26>

Confirmation of properties of nanoscale metal oxide-carbon composites

A coin shell, a half-cell, was manufactured using a nano-scale metal oxide-carbon composite coated with iron oxide, a nano-sized metal oxide, and carbon, as a negative electrode active material, and its electrochemical properties were confirmed.

As an experimental sample, the nanoscale metal oxide-carbon composite prepared in Example 11 was used, and for comparison, nanoscale iron oxide prepared by hydrothermal synthesis without carbon coating was used.

(1) Manufacturing of half-cells

A coin shell, a half-cell, was manufactured as follows.

A slurry was prepared by mixing the negative electrode active material, conductive material, and binder at a weight ratio of 70:20:10. The nanoscale metal oxide-carbon composite prepared above was used as the negative electrode active material. Acetylene black was used as a conductive material, and as a binder, PAA and SRB were mixed at a weight ratio of 8:2 and then mixed with distilled water.

The prepared slurry was applied to a thickness of 50㎛ on copper foil using a doctor blade, dried at room temperature for 24 hours, and then dried in a vacuum oven at 85°C for 24 hours.

A CR2032 type coin shell was manufactured by assembling it in a glove box filled with Ar gas. As the electrolyte, 1.15M LiPF ₆ salt with 10% by weight of FEC added at EC:EMC=3:7 (v/v) was used.

(2) Confirmation of electrochemical properties

WBCS-3000L (Won-A Tech. Co.) was used as analysis equipment, and the electrode was analyzed under the conditions of operating voltage of 0.01~3.0 V and current density of 100 mA/g.

Figure 80 shows a graph showing the initial charge and discharge performance of nanoscale metal oxide-carbon composites coated with 3% and 10% by weight of carbon. From the results of FIG. 80, the initial performance of the nanoscale metal oxide-carbon composite (CF3) coated with 3% by weight of carbon is about 95 mAh/g, and the initial performance of the nanoscale metal oxide-carbon composite (CF10) coated with 10% by weight of carbon is about 95 mAh/g. The initial performance was found to be about 1050mAh/g.

Figure 81 graphically shows the initial charge and discharge performance of nanoscale metal oxide-carbon composites coated with 30% and 50% by weight of carbon. From the results of FIG. 81, the initial performance of the nanoscale metal oxide-carbon composite (CF30) coated with 30% by weight of carbon is about 1050 mAh/g, and the initial performance of the nanoscale metal oxide-carbon composite (CF50) coated with 50% by weight of carbon is about 1050 mAh/g. The initial performance was found to be about 1050mAh/g.

Initial performance results show nanoscale metal oxide-carbon composites coated with 10 wt% carbon (CF10), nanoscale metal oxide-carbon composites coated with 30 wt% carbon (CF30), and nanoscale metal oxide-carbon composites coated with 50 wt% carbon. The initial performance of the metal oxide-carbon composite (CF50) samples was similar, but this value was slightly lower than the theoretical capacity of iron oxide. Therefore, it can be confirmed that the nanoscale metal oxide-carbon composite sample of the present invention was manufactured to sufficiently express the capacity of iron oxide as a negative electrode active material.

Figure 82 graphs the discharge performance and charge/discharge efficiency according to the number of charge/discharge of nanoscale metal oxide-carbon composites coated with 3% and 10% by weight of carbon.

In the results of Figure 82, the initial discharge performance of the metal oxide-carbon composite (CF3) coated with 3% by weight of carbon gradually decreases with the number of cycles from 900 mAh/g, reaching a level of 400 mAh/g at 100 cycles. Nanoscale metal oxide-carbon composite (CF10) coated with 10% by weight carbon gradually decreased from an initial discharge performance of over 1000 mAh/g to less than 500 mAh/g at about 90 times.

Figure 83 shows a graph showing the discharge performance and charge/discharge efficiency according to the number of charge/discharge of nanoscale metal oxide-carbon composites coated with 30% and 50% by weight of carbon. In the results of Figure 83, the nanoscale metal oxide-carbon composite (CF30) coated with 30% by weight of carbon gradually decreased from an initial discharge performance of 1000 mAh/g or more, reaching about 600 mAh/g at about 90 times, and the carbon content was 50 mAh/g. The weight percent coated nanoscale metal oxide-carbon composite (CF50) gradually decreased from an initial discharge performance of more than 1000 mAh/g, reaching about 580 mAh/g in 100 cycles.

Among the above samples, the nano-scale metal oxide-carbon composite (CF30) coated with 30% by weight carbon had the lowest capacity, but its performance remained constant after 80 cycles or more, and the other samples continued to increase as the cycle was repeated. It is decreasing and the final performance can be estimated to reach around 400mAh/g.

These results show that iron oxide manufactured by controlling the size at the nanoscale has superior initial performance and lifespan performance compared to metallic carbon manufactured at the microscale, but is expected to show similar capacity over 300 cycles.

This is presumed to be because the initial capacity of the metal, which is manufactured in a small size during manufacturing, has a higher particle size than micro-sized materials and thus has a high contact efficiency with lithium ions in the electrolyte.

Figure 84 shows a graph showing the results of analyzing discharge performance according to the content of metal oxide in the nanoscale metal oxide-carbon composite, and Table 29 shows the results of comparing discharge performance. At this time, the discharge performance represents the performance at 88 cycles.

sample cycle Performance efficiency FeOx(%) CF3 88 412.1 97.4 3 CF10 88 484.9 99.6 10 CF30 88 634.0 98.7 30 CF50 88 581.2 99.2 50

From the results of Figure 84 and Table 29, when the number of cycles that can determine the battery life is 88, the discharge capacity of the nanoscale metal oxide-carbon composite (CF30) with an iron oxide content of 30% by weight is the best and the charge/discharge efficiency is It is confirmed that this represents more than 98%. This shows that the battery capacity of the composite is closely related to the carbon content, although the interaction between iron oxide and lithium is the dominant factor.

In the study on the micro-sized metal oxide-carbon composite, it was confirmed that the initial performance was high for a sample composed only of iron oxide, but the discharge capacity rapidly decreased as charge/discharge was repeated. This can be judged because although the amount of bonds formed between iron oxide and lithium during charging is large, the detachment of lithium ions from iron oxide during discharging decreases rapidly compared to the charging amount.

This desorption problem can be compensated for by carbon, which is believed to improve the electrical conductivity of the carbon body when lithium ions are desorbed, thereby facilitating the release of lithium ions into the electrolyte. However, if the carbon content is too low compared to the weight of iron oxide, the volume occupied by iron oxide in the electrode increases excessively, reducing the effect of ion transfer, and if the content is too high, the charging capacity for storing lithium ions decreases. appears to be decreasing.

Therefore, a composite containing a microscale iron oxide content of 30% by weight and a coated carbon body content of 70% by weight is preferable.

[Assignment information]

Project name: Technology development (R&D) support for secondary battery materials and components

Project name: Development of nanoscale mesoporous/hollow carbon anode material containing Fe ₂ O ₃

Project period: 2020.03.01. ~ 2022.10.31. (32 months)

Dedicated organization: Chungbuk Techno Park (Foundation)

Host organization: Wifinetech Co., Ltd.

Claims (11)

Preparing a porous silica structure;
Preparing a porous silica-carbon composite by coating the surface of the porous silica structure with a carbon-containing polymer material and heat treating it;
removing silica from the porous silica-carbon composite to produce a mesoporous carbon structure;
Preparing a mesoporous metal oxide (Fe ₂ O ₃ )-carbon composite by coating the mesoporous carbon structure with a metal and heat treating it; and
Mesoporous carbon-metal oxide-carbon for negative electrode material of a lithium secondary battery, comprising the step of coating the mesoporous metal oxide-carbon composite with a carbon-containing-polymer material and heat treating it to produce a mesoporous carbon-metal oxide-carbon composite. Manufacturing method of composite. According to paragraph 1,
The manufacturing method further includes the step of heat treating the manufactured mesoporous carbon structure. According to paragraph 1,
The manufacturing method further includes the step of heat treating the prepared mesoporous metal oxide-carbon composite. According to paragraph 2 or 3,
The heat treatment step includes heat treatment at 400 to 900°C for 3 to 8 hours. According to paragraph 1,
The porous silica structure includes 2 to 10% by weight of TEOS, 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, and organosilane with a weight of 0.14 to 0.5 times the weight of TEOS, based on the total weight of the composition. , and the remainder is prepared using a composition containing a solvent selected from ethanol and methanol. According to clause 5,
The porous silica structure,
Synthesizing by mixing ammonia water, distilled water, organosilane and TEOS at a concentration of 20 to 35% by weight in a solvent and stirring for 2 to 7 hours;
Removing the liquid part, separating only the solid content, and drying it at 90-110°C for more than 12 hours; and
A manufacturing method characterized in that it is manufactured by a method comprising the step of heat treatment at 500 to 600 ° C. for 4 to 6 hours. According to paragraph 1,
The porous silica-carbon composite,
Dissolving the carbon-containing polymer material in distilled water;
coating the porous silica structure with the carbon-containing polymer material by supporting the porous silica structure on the carbon-containing polymer material dissolved in distilled water for more than 5 hours;
Drying the porous silica structure coated with the carbon-containing polymer material at 100-120°C for more than 12 hours;
After drying, oxidation treatment at 180~220℃ for 1~2 hours; and
A manufacturing method characterized in that it is manufactured by a method including the step of heat treatment for 2 to 8 hours at 400 to 900 ° C. in a nitrogen atmosphere after oxidation treatment. According to paragraph 1,
A manufacturing method wherein the mesoporous carbon structure has a particle size of 100 to 500 nm. According to paragraph 1,
The mesoporous metal oxide-carbon composite,
Dissolving ferrous chloride (FeCl ₂ ) in distilled water;
Preparing a mesoporous carbon-ferrous chloride composite by supporting the mesoporous carbon structure in the ferrous chloride solution dissolved in distilled water, coating the mesoporous carbon structure with ferrous chloride and drying it; and
A manufacturing method, characterized in that it is manufactured by a method comprising the step of heat treating the mesoporous carbon-ferrous chloride composite at 450 to 550 ° C. for 4 to 6 hours in a nitrogen atmosphere. According to paragraph 1,
The mesoporous carbon-metal oxide-carbon composite,
Dissolving the carbon-containing polymer material in distilled water;
Supporting the mesoporous metal oxide-carbon composite on the carbon-containing-polymer material dissolved in distilled water for more than 5 hours to coat the mesoporous metal oxide-carbon composite with the carbon-containing-polymer material; and
A manufacturing method comprising the step of heat treating a mesoporous metal oxide-carbon composite coated with a carbon-containing polymer material at 850-950°C for 4-6 hours. According to paragraph 1,
A manufacturing method, characterized in that the content of metal oxide in the mesoporous carbon-metal oxide-carbon composite is 10 to 50% by weight.