KR20030056544A - Nano-sized spherical non-graphitizable carbons, the process of producing said carbons, and lithium secondary batteries comprising said carbons as anodal active materials - Google Patents

Abstract

PURPOSE: A nano-sized spherical and non-graphitizable carbon for use in a secondary cell is provided to improve the processing capability and electro-conductivity in forming an electrode plate. CONSTITUTION: The nano-sized spherical and non-graphitizable carbon is produced by the method comprising the steps of: (a) dissolving a monomer, formaldehyde and a surfactant having a concentration greater than the critical micelle concentration into water in the presence of a polymerization accelerating catalyst and controlling pH to obtain a solution; (b) stirring the solution obtained from the step (a); (c) polymerizing the solution obtained from the step (b) at a temperature of 30 to 200 deg.C to form a spherical polymer; (d) drying the polymer obtained from the step (c); and (e) heat treating the spherical polymer obtained from the step (d) under an inert atmosphere to carbonize it.

Description

Nano-sized spherical non-graphitizable carbon, a method of manufacturing the same, and a lithium secondary battery including the carbon as a negative electrode active material TECHNICAL-SIZED SPHERICAL NON-GRAPHITIZABLE CARBONS ACTIVE MATERIALS}

The present invention relates to a nano-sized spherical non-graphitizable carbon, a method for preparing the same, and a lithium secondary battery including the carbon as a negative electrode active material.

Carbon material is used as a negative electrode active material of a lithium secondary battery. Such a negative electrode active material should have a high lithium ion storage capacity (capacity), high charge and discharge efficiency, excellent workability of the plate forming, high electrical conductivity and compatibility with the electrolyte. For the use of a carbon material as a negative electrode active material of a lithium secondary battery, Japanese Laid-Open Patent Publication No. 63-114056, No. 62-268056, No. 2-82466, No. 2-79153, No. 4 -359862, (Pyung) 5-101818, (Pyung) 7-105936 and the like. Carbon materials currently used in the negative electrode active materials of lithium secondary batteries include graphite materials such as natural graphite and artificial graphite, non-graphitizable carbons, and graphitizable carbons. The most favored product is Graphitized Meso Carbon Microbeads (g-MCMB), a type of artificial graphite. The reason is that the particles are spherical in shape and have advantages such as high packing density of spherical carbon and excellent workability of plate forming. However, graphite carbon, such as g-MCMB, has a reversible capacity of only 300 mAh / g to 400 mAh / g (theoretical capacity of 372 mAh / g), and thus is applied as a negative electrode active material of a lithium secondary battery having a high capacity and a high energy density. There is a limit to.

As an alternative, non-graphitizable carbon materials are used. Non-graphitizable carbon for negative electrode active materials of lithium secondary batteries is disclosed in U.S. Pat. And the like. Non-graphitizable carbon has a reversible capacity of 400 mAh / g or more, since lithium ions are not only intercalated into the graphene layer but also stored in the micro-pore. In addition, while the production of artificial graphite requires a high temperature heat treatment of 2800 ℃ or more, while non-graphitizable carbon is manufactured by carbonizing at 600 ℃ to 1600 ℃ low heat treatment cost. In addition, there is an advantage that can be used as an electrolyte PC (Propylene Carbonate) excellent in low temperature properties.

However, non-graphitizable carbon materials are not widely commercialized in batteries despite these good properties. Non-graphitizable carbon has a low density due to its low crystalline and micropore density compared to graphite carbon, and thus has low energy density per volume when used as a negative electrode active material of a lithium secondary battery. In addition, since non-graphitizable carbon is manufactured in the form of agglomerates, it is required to undergo a grinding process in order to be applied to a battery, and the pulverized carbon has a low filling density and poor processability of the electrode plate molding because the shape of the particles is not uniform and the size is not uniform.

In order to overcome the problems of the prior art, an object of the present invention is to provide a nano-sized spherical non-graphitizable carbon, a method for manufacturing the same and a lithium secondary battery including the carbon as a negative electrode active material. When the non-graphitizable carbon is spherical, even if the density of the non-graphitizable carbon is small, the amount of filling in the battery can be increased, so that the energy density per volume of the battery can be improved, and the workability of the plate forming can be improved. In addition, when the size of the non-graphitizable carbon is a nano size, since the area between the particles is in contact with the electrical conductivity is excellent, there is no need to add a conductive material when forming the electrode plate.

1 is a 10,000 times magnification Scanning Electron Microscopy photograph of the spherical non-graphitizable carbon of Example 1. FIG.

FIG. 2 is a 50,000 × magnification of Transmission Electron Microscopy of the spherical non-graphitizable carbon of Example 2. FIG.

3 is a magnification 2,500 times scanning electron micrograph of the spherical non-graphitizable carbon of Example 3. FIG.

4 is a transmission electron micrograph of 50,000 times the magnification of the spherical non-graphitizable carbon of Example 4. FIG.

5 is a 200,000-fold transmission electron micrograph of the spherical non-graphitizable carbon of Example 5. FIG.

6 is a one-time charge and discharge graph of a lithium secondary battery using spherical non-graphitizable carbon of Example 6 as a negative electrode active material.

7 is a seventh charge and discharge graph of a lithium secondary battery using spherical non-graphitizable carbon of Example 6 as a negative electrode active material.

In order to achieve the above object, the present invention provides a method for producing a nano-size spherical non-graphitizable carbon,

a) dissolving a polymer monomer, formaldehyde, and a surfactant having a critical micelle concentration (CMC) or higher in water in the presence of a catalyst for promoting a polymerization reaction, and then adjusting the pH to prepare a solution;

b) stirring the solution prepared in step a);

c) polymerizing the solution stirred in step b) at 30 ° C. to 200 ° C. to produce a spherical polymer polymer;

d) drying the spherical polymer polymer polymerized in step c); And

e) carbonizing the spherical polymer polymer dried in step d) by heat treatment at a temperature of 500 ° C. to 3000 ° C. under an inert atmosphere.

It provides a method comprising a.

In addition, the present invention provides a lithium secondary battery comprising a nano-sized spherical non-graphitizable carbon prepared by the above method as a negative electrode active material.

The present invention is described in detail below.

The non-graphitizable carbon of the present invention is characterized by being nano-sized and spherical. The diameter of the spherical non-graphitizable carbon particles is generally 1 nm to 900 nm, the smaller the diameter of the particles has excellent characteristics. In the lithium secondary battery, the smaller the diameter of the spherical non-graphitizable carbon particles included as the negative electrode active material, the smaller the diffusion length of lithium ions, so that the rate capability is improved and a higher current can be used. .

In order to obtain nano sized spherical non-graphitizable carbon, a surfactant must be added. Surfactants have the property of making themselves spherical when they are above a certain concentration. This is called self-assembly, and the concentration at which the surfactant begins to form a spherical shape in the solution is called Critical Micelle Concentration (CMC). In more detail, the concentration at the time of making a spherical shape is called CMC 1, and when the concentration is thicker, it has a hexagonal structure, and the concentration at this time is called CMC 2. Since the surfactant forms a sphere through self-assembly above the critical micelle concentration, the addition of the surfactant above the CMC forms a spherical micelle. By controlling the concentration of the surfactant, the size of the micelle can be adjusted to nano size, and when the organic monomer is added to the monomer, the monomer penetrates into the spherical nano-sized surfactant, and the spherical monomer is surrounded by the surfactant. Becomes It may be heated to a temperature of 30 ℃ to 200 ℃ in a closed reactor to polymerize for 1 hour to 20 days to produce a nano-sized spherical polymer. In this case, when ultrasonication is performed in the process of stirring the solution, polymer particles having a smaller size may be synthesized.

The spherical monomer formed by the surfactant undergoes precipitation polymerization and sol-gel polymerization depending on the pH of the solution. When the polymerization is carried out by adjusting the pH to 5 or less, a precipitation polymerization reaction occurs, thereby producing a spherical polymer.

Since the spherical polymer prepared in this way is polymerized in an aqueous solution, it has to go through a drying step to remove water.

In addition, the dried spherical polymer is carbonized by heat treatment at a temperature of 500 ° C. to 3000 ° C. under an inert atmosphere to convert it into spherical non-graphitizable carbon.

Preparation of the polymer used in the present invention proceeds by the following equation.

Monomer + Formaldehyde → Polymer

The reaction proceeds in a spherical organic layer formed by a surfactant and requires a catalyst to promote the polymerization reaction. The catalyst used is sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide and the like.

The monomer used in the present invention may be an organic material including a hydroxyl group or an amine group capable of sol-gel polymerization and precipitation polymerization, and examples thereof include resorcinol, phenol, melamine, furfuryl alcohol, and sucrose. and sucrose.

In addition, the surfactants used in the present invention include alkyltrimethyl ammonium halide-based cationic surfactants; Neutral surfactants such as oleic acid and alkylamine; And anionic surfactants such as sodium alkyl sulfate and sodium alkyl phosphate. In addition, organometallic compounds capable of forming micelles (such as tin (IV) bis (acetylacetonate) dichloride) and the like can be used as surfactants. Representative surfactants include cetyltrimethyl ammonium bromide (CTAB), cetyltrimethyl ammonium chloride (CTAC), dodecyltrimethyl ammonium bromide (CTAB), and the like.

In addition, acids or bases may be added to adjust the pH. If the pH is to be lowered, acid can be added, but any acidic substance such as hydrochloric acid or nitric acid can be used. In addition, since the formaldehyde is acidic, it is possible to control the pH by adjusting the amount of formaldehyde. In order to adjust the pH to 5 or less, the amount of formaldehyde may be added in an equivalent amount (for example, resorcinol: formaldehyde = 1: 2).

In preparing the nano-sized spherical non-graphitizable carbon, the molar mixing ratio of the monomer and the surfactant is 1: 0.01 to 2, the molar mixing ratio of the monomer and the formaldehyde is 1: 1 to 2000, and It is preferable that the molar mixing ratio of the catalyst is 1: 0.001 to 0.1 and the molar mixing ratio of the monomer and water is 1: 0.001 to 20000.

Spherical non-graphitizable carbon prepared by the above method can be used as a lithium secondary battery negative electrode active material. For practical application to the cell, the electrode is prepared as follows. As a method for forming an electrode, a spherical carbon and a binder prepared by the method of the present invention are added to a dispersant in a weight ratio of 10: 0.5 to 2 and stirred to prepare a paste, which is then applied to a current collector of a metal material and compressed. It is dried to prepare a laminate electrode.

In some cases, a conductive material may be added to reduce the resistance of the electrode. Generally, 5% to 20% by weight of carbon black, based on the total weight, is added as the conductive material. Products currently marketed as conductive materials include acetylene black series (Chevron Chemical Company or Gulf Oil Company), and Ketjen Black EC series (Armak Company Company), Vulcan XC-72 (Cabot Company), and Super P (MMM).

Representative examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, and the like. Representative examples of the dispersant include isopropyl alcohol, N-methylpyrrolidone (NMP), Acetone and the like.

The current collector of the metal material is a metal having high conductivity, and any metal can be used as long as the paste of the material is easily adhered and is not reactive in the voltage range of the battery. Representative examples include a mesh or foil of copper or nickel.

The method of apply | coating the paste of an electrode material to a metal material can be selected from a well-known method in consideration of the characteristic of a material, or can be performed by a new suitable method. An example of this is to distribute the paste onto the current collector and then to uniformly disperse it using a doctor blade or the like. In some cases, a method of distributing and dispersing in one process may be used. In addition, a method of die casting, comma coating, screen printing, or the like may be selected. Alternatively, after molding on a separate substrate, it can be bonded to the current collector by pressing or lamination.

An example of a method of drying the applied paste is to dry for 1 to 3 days in a vacuum oven at 50 ℃ to 200 ℃.

A method of constructing a lithium secondary battery using the electrode manufactured by the above method is, for example, using the electrode as a negative electrode, and lithium cobalt oxide (LiCoO 2), lithium nickel oxide (LiNiO 2), lithium manganese oxide (LiMn 2 O 4), and the like. And insert the separator between them. The membrane blocks the internal short circuit of the two electrodes and impregnates the electrolyte, and materials that can be used include polymer, glass fiber mat, and kraft paper. Typical examples of the commercially available membranes include Celgard 2400 and 2300 ( Hoechest Celanese Corp.), polypropylene membrane (manufactured by Ube Industries Ltd. or Pall RAI).

The electrolyte is a system in which a lithium salt is dissolved in an organic solvent, and the lithium salt uses LiClO 4, LiCF 3 SO 3, LiAsF 6, LiBF 4, LiN (CF 3 SO 2) 2, LiPF 6, LiSCN, and LiC (CF 3 SO 2) 3, and the organic solvent is ethylene carbonate ( Ethylene Carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), 1,2-dimethoxyethane, 1,2 1,2-diethoxyethane, gamma-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxoene 1 type, or 2 or more types of 1,3-dioxolane, 4-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, diethylether, and sulfolene Can be mixed and used.

The present invention will be described in more detail with reference to the following examples. However, an Example is for illustrating this invention and is not limited only to these.

EXAMPLE

Example 1

Preparation of Nano-Sized Spherical Non-Graphite Carbon

Resorcinol, formaldehyde, sodium carbonate, cetyltrimethyl ammonium bromide and water were mixed at a molar ratio of 1: 100: 0.02: 0.41: 5.6 × 10 ³ and polymerized at 85 ° C. for 7 days using a closed reactor. The pH of the initial solution was 3.28. The polymer was then dried at 85 ° C. and heat treated at 1000 ° C. for 3 hours at an elevated rate of 10 ° C./min under an argon atmosphere. The carbon thus produced was spherical and had a uniform distribution with a diameter of 300 nm to 350 nm. 1 is a scanning electron micrograph of the nano-sized spherical non-graphitizable carbon prepared as described above.

Example 2

Preparation of Nano-Sized Spherical Carbon

Resorcinol, formaldehyde, sodium carbonate, cetyltrimethyl ammonium bromide and water were mixed at a molar ratio of 1: 1000: 0.02: 0.57: 5.6 × 10 ³ and polymerized at 85 ° C. for 7 days using a closed reactor. The pH of the initial solution was 3.20. The polymer was then dried at 85 ° C. and heat treated at 1000 ° C. for 3 hours at an elevated rate of 10 ° C./min under an argon atmosphere. The carbon thus produced was spherical and had a uniform distribution with a diameter of 200 nm to 300 nm. 2 is a transmission electron micrograph of the nano-sized spherical non-graphitizable carbon prepared as described above.

Example 3

Preparation of Nano-Sized Spherical Non-Graphite Carbon

Phenol, formaldehyde, sodium carbonate, cetyltrimethyl ammonium bromide, and water were mixed at a molar ratio of 1: 1000: 0.02: 0.082: 5.6 × 10 ³ and polymerized at 85 ° C. for 7 days using a sealed reactor. The pH of the initial solution was 3.50. The polymer was then dried at 85 ° C. and heat treated at 1000 ° C. for 3 hours at an elevated rate of 10 ° C./min under an argon atmosphere. The carbon thus produced was spherical and had a uniform distribution with a diameter of 900 nm to 1000 nm. 3 is a scanning electron micrograph of the nano-sized spherical non-graphitizable carbon prepared as described above.

Example 4

Preparation of Nano-Sized Spherical Non-Graphite Carbon

Melamine, formaldehyde, sodium carbonate, cetyltrimethyl ammonium bromide and water were mixed and stirred by sonication in a molar ratio of 1: 1000: 0.02: 0.082: 5.6 × 10 ³ , and polymerization was carried out at 85 ° C. for 7 days using a sealed reactor. It was. The pH of the initial solution was 3.44. The polymer was then dried at 85 ° C. and heat treated at 1000 ° C. for 3 hours at an elevated rate of 10 ° C./min under an argon atmosphere. The carbon thus produced was spherical and had a uniform distribution with a diameter of 100 nm to 200 nm. 4 is a transmission electron micrograph of the nano-sized spherical non-graphitizable carbon prepared as described above.

Example 5

Preparation of Nano-Sized Spherical Non-Graphite Carbon

Resorcinol, formaldehyde, sodium carbonate, cetyltrimethyl ammonium bromide and water are mixed and stirred by sonication in a molar ratio of 1: 1000: 0.02: 0.25: 5.6 × 10 ³ , and the mixture is stirred at 85 ° C. using a sealed reactor. Polymerized daily. The pH of the initial solution was 3.28. The polymer was then dried at 85 ° C. and heat treated at 1000 ° C. for 3 hours at an elevated rate of 10 ° C./min under an argon atmosphere. The carbon thus produced was spherical and had a uniform distribution with a diameter of 50 nm to 100 nm. 5 is a transmission electron micrograph of the nano-sized spherical non-graphitizable carbon prepared as described above.

Example 6

Fabrication and Performance of Lithium Secondary Battery Using Spherical Non-Graphite Carbon as Negative Active Material

A spherical non-graphitizable carbon prepared as in Example 5 was used as a negative electrode active material, and polytetrafluoroethylene (PTFE) was mixed with a binder in a weight ratio of 10: 1 to prepare a paste, and then a working electrode was attached to a copper mesh current collector. It was prepared and dried in a 120 ° C. vacuum oven for at least 10 hours. Using a lithium metal foil as a counter electrode and a reference electrode in a dry box under an argon atmosphere, and using a 1 molar concentration LiClO 4 / EC: DEC (volume ratio 1: 1) as an electrolyte, a beaker type 3-pole cell was used. It was prepared and a constant current constant voltage experiment was performed at 25 ℃ under the following conditions. During charging, a constant current was applied to 0 V ( vs. Li / Li +) at a current density of 30 mA / g, and a constant voltage was applied at 0 V until the current density became 0.5 mA / g or less. At discharge, up to 2 V ( vs. Li / Li +) was performed at a current density of 30 mA / g. A 5 minute pause was given between charge and discharge. Figure 6 is a one-time charge and discharge graph, the charge and discharge showed a reversible capacity of 580 mAh / g, the initial coulombic efficiency was 68.6%. Figure 7 is a charge-discharge reversible graph seven times, it can be seen that since the reversible capacity does not decrease as the number of charge and discharge recovery proceeds showing a stable reversibility.

Since the nano-sized spherical non-graphitizable carbon prepared in the present invention has a large apparent density when used as a negative electrode active material of a lithium secondary battery, the capacity per unit volume of the battery may be increased, and processability of the electrode plate may be improved. In addition, since the particle size is small as the nano-size, the conductivity is improved, it is possible to manufacture the electrode plate without a conductive material.

Claims (16)

As a method for producing nano-sized spherical non-graphitizable carbon, a) dissolving a polymer monomer, formaldehyde and a surfactant at a concentration higher than the critical micelle concentration in water in the presence of a catalyst for promoting a polymerization reaction, and then adjusting the pH to prepare a solution; b) stirring the solution prepared in step a); c) polymerizing the stirred solution in step b) at 30 ° C. to 200 ° C. to produce a spherical polymer; d) drying the spherical polymer polymer polymerized in step c); And e) carbonizing the spherical polymer polymer dried in step d) by heat treatment at 500 ° C. to 3000 ° C. under an inert atmosphere. How to include. The method of claim 1, The spherical non-graphitizable carbon is characterized in that the diameter of 1 nm to 900 nm. The method of claim 1, The molar mixing ratio of the monomer and the surfactant in the step a) is 1: 0.01 to 2. The method of claim 1, The molar mixing ratio of the monomer and formaldehyde in the step a) is 1: 1 to 2000. The method of claim 1, The molar mixing ratio of the monomer and the catalyst in the step a) is 1: 0.001 to 0.1. The method of claim 1, The molar mixing ratio of the monomer and water in step a) is 1: 0.001 to 20000. The method of claim 1, PH of the solution in step a) is adjusted to 5 or less. The method of claim 1, The stirring of the solution in step b) is stirring by sonication. The method of claim 1, The polymerization reaction of step c) is carried out at a temperature of 30 ℃ to 200 ℃ for 1 hour to 20 days. The method of claim 1, The monomer is an organic material comprising a hydroxyl group or an amine group capable of sol-gel polymerization and precipitation polymerization. The method of claim 10, The monomer is selected from the group consisting of resorcinol, phenol, melamine, biphenol, furfuryl alcohol, sucrose. The method of claim 1, Surfactants are cationic surfactants of the alkyltrimethyl ammonium halide series; Neutral surfactants including oleic acid, alkylamines; Anionic surfactants including sodium alkyl sulfates, sodium alkyl phosphates; And an organometallic compound capable of forming a micelle comprising tin (IV) bis (acetylacetonate) dichloride. The method of claim 1, The catalyst is selected from the group comprising sodium carbonate, potassium carbonate, sodium hydroxide and potassium hydroxide. A nano-sized spherical non-graphitizable carbon prepared by any one of claims 1 to 13, which is useful for a negative electrode active material of a lithium secondary battery. A lithium secondary battery comprising a nano-sized spherical non-graphitizable carbon prepared by any one of claims 1 to 13 as a negative electrode active material. The method of claim 15, A lithium secondary battery comprising no conductive material.