Expanded carbon for improving the output of secondary batteries and its manufacturing method

Abstract

The present invention relates to expanded carbon for improving the output of a secondary battery and a method for manufacturing the same. The present invention comprises a method for manufacturing expanded carbon for enhancing the output of a secondary battery, wherein the method comprises the steps of: mixing lithium metal into a water-soluble oil and then mixing carbon to produce a mixture; reacting the mixture at 200 to 450°C while applying pressure to produce a lithium-carbon compound in which lithium is incorporated between carbon layers; and heat-treating the lithium-carbon compound to produce expanded carbon in which lithium is detached and removed from the lithium-carbon compound, thereby expanding the carbon layers; wherein the heat treatment is characterized by rapidly heating the lithium-carbon compound to 450 to 1,000°C by passing an electric current through it. The technical gist of the invention is the expanded carbon produced thereby.

Description

Technology Field

[0001] The present invention relates to expanded carbon for improving the output of a secondary battery and a method for manufacturing the same. Background Technology

[0002] Lithium-ion batteries are energy storage devices that realize capacity through chemical reactions between lithium ions and positive and negative electrode active materials. While they offer high energy density, they have the disadvantage of reduced output characteristics and long-term reliability due to long-term degradation caused by these chemical reactions.

[0003] The internal resistance of lithium-ion batteries is primarily influenced by the intercalation and deintercalation reactions of lithium ions, but it is also significantly affected by constituent components such as electrode composition, thickness, and density, as well as process design.

[0004] Since the positive electrode of a lithium-ion battery uses lithium metal oxides such as lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium iron phosphate oxide as active materials, not only is the electrical resistance of the electrode high, but the diffusion resistance caused by lithium ions increases as the electrode thickness and density increase.

[0005] There are cases where output characteristics have been improved by adding activated carbon to the anode to reduce these resistance components. When activated carbon is added to replace some lithium metal oxides, the electrical conductivity of the anode is improved by the activated carbon, which has excellent electrical conductivity.

[0006] Furthermore, the output characteristics of the anode can be improved through the electric double layer capacity formed on the surface of the activated carbon or by the role of the pores distributed within the activated carbon as reservoirs for the lithium electrolyte. There are instances where output characteristics are enhanced by a hybrid combination of the anode's electric double layer capacitor capacity and the lithium-ion battery capacity, or by rapidly supplying the lithium electrolyte contained within the activated carbon's pores to adjacent lithium metal oxides.

[0007] However, there is a high possibility that the performance of the battery will deteriorate due to acidic functional groups such as carboxyl groups and phenolic hydroxyl groups, as well as residual moisture on the inner and outer surfaces of the activated carbon, along with many micropores during the manufacturing process.

[0008] Since activated carbon is activated using non-graphitizable carbon or digraphitizable carbon in the stage prior to interlayer crystallization, acidic functional groups are easily formed on the exposed edges, and moisture also adheres readily. These acidic functional groups and residual moisture cause irreversible side reactions with organic electrolytes, reducing battery performance through capacity degradation and increased internal resistance.

[0009] Expanded graphite can be considered as a porous carbon that excludes micropores and acidic functional groups; however, conventional expanded graphite is manufactured using a mixture of sulfuric acid and an oxidizing agent, and has the problem of reduced density due to rapid expansion.

[0010] This expanded graphite is manufactured by oxidizing graphite with a mixture of sulfuric acid and oxidizing agents, such as sulfuric acid and nitric acid, sulfuric acid and potassium permanganate, or sulfuric acid and perchloric acid, then washing and drying it with water, and finally rapidly heating it to expand the graphite. However, during the manufacturing process, sulfur remains inside the graphite and corrodes the contents of the battery during the charging and discharging process or generates sulfur reaction gas through reaction with the electrolyte.

[0011] In addition, expanded graphite has a severe degree of expansion, ranging from 0.003 to 0.2 g / cm³ 3 When an electrode is manufactured by mixing it with the active material of a battery, it has a density that reduces the charge capacity due to the low electrode density, so there is an urgent need for research on technology development to improve this. Prior art literature

[0012] Korean Patent Publication No. 10-0769567, registered on October 17, 2007. Korean Patent Publication No. 10-1775544, registered on August 31, 2017. The problem to be solved

[0013] The present invention was developed to resolve the aforementioned problems, and its technical objective is to provide a method for manufacturing expanded carbon through lithium incorporation to improve the output characteristics of a lithium-ion battery or lithium-ion supercapacitor using a lithium electrolyte and to reduce irreversible capacity.

[0014] Furthermore, the technical challenge is to simultaneously resolve the issues of acidic functional groups and residual moisture in commercial activated carbon and the issue of residual sulfur in the interlayers of commercial expanded graphite by incorporating lithium into carbon and expanding it, and to provide expanded carbon with a high meso-pore fraction as pores that supply lithium ions. means of solving the problem

[0015] To solve the above technical problem, the present invention provides a method for manufacturing expanded carbon for improving the output of a secondary battery, comprising the steps of: mixing lithium metal into a water-soluble oil and then mixing carbon to prepare a mixture; reacting the mixture at 200 to 450°C while applying pressure to produce a lithium-carbon compound in which lithium is incorporated between carbon layers; and heat-treating the lithium-carbon compound to produce expanded carbon in which lithium is detached and removed from the lithium-carbon compound, thereby expanding the carbon layers; wherein the heat treatment is characterized by rapidly heating the lithium-carbon compound to 450 to 1,000°C by passing an electric current through it.

[0016] In the present invention, the step of manufacturing the expanded carbon is characterized by pressurizing the lithium-carbon compound to form a compact, then bringing the compact into contact with an electrode and applying current at a power density of 5 to 100 W / g.

[0017] In the present invention, the expanded carbon is characterized by forming mesopores in which the mesopores constitute 30% or more of the total pore volume fraction within the carbon through the electric current and rapid heating.

[0018] In the present invention, the expanded carbon has a specific surface area of ​​10 to 200 m² 2 It is characterized by being / g.

[0019] In the present invention, the carbon in the step of preparing the mixture is interlayer distance (d 002 It is characterized by being one or more selected from the group consisting of graphite having a thickness of 0.335 to 0.36 nm and digraphitic carbon.

[0020] In order to solve the other technical problems mentioned above, the present invention provides expanded carbon for improving the output of a secondary battery, characterized by being manufactured by the above method and having a mesopore volume fraction of 30% or more of the total pore volume fraction within the carbon. Effects of the invention

[0021] According to the expanded carbon for improving secondary battery output and the method for manufacturing the same according to the means for solving the above problem of the present invention, the carbon interlayer distance (d 002 By using digraphitic carbon or graphite with a thickness in the range of 0.335 to 0.36 nm, it is possible to have a porous structure with a volume fraction of mesopores of 30% or more during the process of incorporating lithium between carbon layers and expanding.

[0022] This overcomes the impurity issues associated with commercial activated carbon and expanded graphite using sulfuric acid, thereby having the effect of improving the output characteristics and long-term reliability of lithium-ion batteries or lithium-ion supercapacitors. Brief explanation of the drawing

[0023] FIG. 1 is a flowchart showing a method for manufacturing expanded carbon according to the present invention. Figure 2 is an SEM image showing Example 3 and Comparative Example 1. Figure 3 is a graph showing the isothermal adsorption curves of Example 3 and Comparative Example 1. Figure 4 is a graph showing the AC impedance results of Example 3 and Comparative Example 1. FIG. 5 is a graph showing the capacity retention rate (%) for the C-rate of Example 3 and Comparative Example 1. Specific details for implementing the invention

[0024] The present invention will be described in detail below.

[0025] However, the volume fraction described in this specification refers to the fraction of the volume of mesopores in the total volume of expanded carbon.

[0027] The present invention relates to a method for manufacturing expanded carbon for improving the output of a secondary battery. As shown in FIG. 1, which illustrates the method for manufacturing expanded carbon according to the present invention as a flowchart, the method for manufacturing expanded carbon according to the present invention comprises the steps of: mixing lithium metal with water-soluble oil and then mixing carbon to produce a mixture (S10); reacting the mixture while applying pressure at 200 to 450°C to produce a lithium-carbon compound in which lithium is incorporated between carbon layers (S20); and heat-treating the lithium-carbon compound to produce expanded carbon in which lithium is detached and removed from the lithium-carbon compound, thereby expanding the carbon layers.

[0029] According to the above manufacturing method, first, lithium metal is mixed with water-soluble oil, and then carbon is mixed to prepare a mixture (S10).

[0030] Before explaining, carbon can be used in various ways as long as it incorporates lithium between the layers and pores can be formed at the carbon interlayer or carbon grain interface during the rapid heating process, for example, it may be one or more selected from the group consisting of digraphitic carbon, (002) graphite with a developed interlayer structure.

[0031] At this time, one or more types of graphite may be selected from the group consisting of natural graphite, aliphatic polymer compounds such as vinyl chloride resins and polyacrylonitrile, aromatic polymer compounds such as mesophase pitch and polyimide, coal-based pitch, petroleum coke, coal coke, mesocarbon micro beads, mesophase pitch spinnerets, artificial graphite, and composite graphite materials thereof. As for the crystal structure of this graphitizable carbon or graphite, depending on the type of carbon, the interlayer distance (d 002 Although it varies, typically the distance between floors (d) 002 It is preferable that ) be in the range of 0.335 to 0.36 nm.

[0032] Accordingly, the present step is a step of preparing a mixture by mixing carbon into a lithium-oil mixture in which lithium metal and water-soluble oil are mixed, wherein the lithium metal may be included in an amount of 10 to 50 weight percent of the lithium-oil mixture composed of lithium metal and water-soluble oil.

[0033] If lithium metal is included in an amount of less than 10% by weight of 100% by weight of the lithium-oil mixture, the amount of lithium that can be incorporated between the carbon layers is small, making it impossible to increase the volume fraction of mesopores in the expanded carbon to more than 30%. On the other hand, if lithium metal is included in an amount exceeding 50% by weight, the amount of lithium metal is too large, which may lead to the formation of macropores in addition to mesopores within the expanded carbon, resulting in the disadvantage of the expanded carbon becoming too large in volume. Furthermore, if lithium metal exceeds 50% by weight, it becomes difficult to achieve uniform mixing with carbon. Accordingly, it is preferable that the lithium metal be in the range of 10 to 50% by weight of 100% by weight of the lithium-oil mixture.

[0034] It is preferable to use such lithium metal that maintains a melting point of 186°C and has a purity of 99.9% or higher so that no metal other than lithium exists between the carbon layers. However, the form (powder, etc.) of the lithium metal mixed into the water-soluble oil is not restricted.

[0035] In the case of water-soluble oil, it is intended to prevent the phenomenon of lithium metal igniting when exposed to the atmosphere, and may be included in a range of 50 to 90 weight percent of 100 weight percent of the lithium-oil mixture. If the water-soluble oil is less than 50 weight percent, it is insufficient to completely block the ignition of lithium metal, and if it exceeds 90 weight percent, the amount of water-soluble oil becomes too large, which has the disadvantage of lowering process efficiency.

[0036] As water-soluble oils, one or more of mineral oils and vegetable oils may be used, but are not limited to the types mentioned above; any oil having water-soluble properties may be used in various ways.

[0037] Here, the mixing of the lithium-oil mixture with carbon is not limited to the container used or the mixing method, such as rotary mixing, ball mixing, and jet mill methods. The reason the mixing method of the lithium-oil mixture with carbon is not limited is that water-soluble oil prevents the oxidation of lithium metal, so there is no need to control the mixing atmosphere.

[0038] In the mixing process of the lithium-oil mixture and carbon in this step, if the carbon content is less than 10% by weight of 100% by weight of solids, there is a possibility that an excessive number of pores may be formed during the expansion process due to the excessive incorporation of lithium metal, or that the carbon powder may be crushed during the expansion process. Conversely, if the carbon content exceeds 90% by weight, there is a disadvantage in that the amount of lithium incorporated decreases and the amount of pores inside the carbon decreases. For this reason, it is preferable that the carbon be included in the range of 10 to 90% by weight of 100% by weight of solids. In the case of lithium metal, it may consist of the remaining remainder of 10 to 90% by weight of 100% by weight of solids.

[0040] Next, the mixture is reacted under pressure at 200 to 450°C to produce a lithium-carbon compound in which lithium is incorporated between the carbon layers (S20).

[0041] The step for forming an interlayer compound in carbon is characterized by the ability to form a lithium interlayer compound using lithium metal and water-soluble oil, unlike conventional methods that use oxidizing agents or strong acids.

[0042] To facilitate the formation of lithium interlayer compounds, a mixture prepared by mixing a lithium-oil solution and carbon powder is introduced into a reactor and homogeneously mixed under constant pressure at 200 to 450°C to incorporate or insert lithium into the carbon. For this purpose, 250 to 350 kg / cm² 3 React for 5 to 7 hours under pressure.

[0043] If the reaction temperature is below 200℃, there is a disadvantage that the lithium may remain in a solid state and the reaction may not proceed sufficiently, and if it exceeds 450℃, there is a disadvantage that the water-soluble oil is denatured or lost.

[0044] The reaction pressure is 250 kg / cm² 3 If it is less than 350 kg / cm², a sufficient reaction does not occur, and 3If it exceeds, an excessive amount of lithium is incorporated, making it difficult to control the size and porosity of the pores within the carbon to the desired size, i.e., mesopores.

[0045] Regarding the reaction time, if it is less than 5 hours, there is a problem that the reaction is not sufficiently completed, and maintaining reaction conditions exceeding 7 hours is unnecessary, highlighting the inefficiency of the process.

[0047] Finally, a lithium-carbon compound is heat-treated to produce expanded carbon in which lithium is defused and removed from the lithium-carbon compound, thereby expanding the carbon layers (S30).

[0048] Pores can be formed in the carbon by loading a lithium-carbon compound into a cylindrical or rectangular insulating apparatus and pressing it into a compactor, contacting it with electrodes of conductive materials placed above and below the compactor, and applying a current at a power density of 5 to 100 W / g per weight of the lithium-carbon compound powder to rapidly heat it to 450 to 1,000°C. At this time, rapid heating can be carried out at a rate of 10 to 50°C / min; if the rate is less than 10°C / min, it is inefficient in terms of process because too much time is consumed to detach lithium from the lithium-carbon compound, and if it exceeds 50°C / min, it is undesirable because the excessively high heating rate may cause a deterioration in the physical properties of the expanded carbon.

[0049] The insulator may be a conventional oxide, nitride, etc., that does not conduct electricity, and it is preferable that it be a material that does not melt or corrode at high temperatures of 1,000°C or higher. The insulator mechanism is not limited as long as it is a structure capable of carrying a lithium-carbon compound and allowing current to flow up and down.

[0050] The compact of the lithium-carbon compound loaded into the insulating device may be a pre-formed compact, or the lithium-carbon compound may be introduced into an insulating device that is open at the top and bottom, and the electrodes of the conductive material may be pressed against the upper and lower parts, and then pressure may be applied to the central area to form the compact.

[0051] It is preferable to use stainless steel for the electrodes of the conductive body, which has excellent conductivity and excellent corrosion resistance to toxic gases emitted from the compacted body, and pores capable of inhaling or releasing gas may be formed in the electrodes during the process of energizing the compacted body.

[0052] When current is applied through electrodes in close contact with the upper and lower parts of a compact of a lithium-carbon compound, Joule heating occurs due to the instantaneous power supply, and as a result, a rapid temperature change occurs, the lithium interlayer oxide formed between the layers of the lithium-carbon compound is discharged, and pores are formed inside the carbon.

[0053] The temperature of the compacted body by Joule heating can be controlled according to the current being passed, and can be passed at a power density of 5 to 100 W / g per weight of the lithium-carbon compound powder, at which time the temperature of the compacted body is rapidly heated to a temperature range of 450 to 1,000℃.

[0054] If the power density is less than 5 W / g, the heating rate of the compact is slow, making it difficult to form pores between the layers of carbon, and if the power density exceeds 100 W / g, there is a high possibility that carbon will be crushed due to the rapid discharge of lithium interlayer compounds, so caution is required.

[0055] Gas generated during the expansion process of the lithium-carbon compound is not only discharged to the outside through the pores of the conductive electrodes placed above and below the compact, but gas can also be injected into the compact from the outside if necessary for the process.

[0056] During the expansion process of lithium-carbon compounds, structural defects are prone to occur at the inter-carbon layer or grain interfaces, and the edge surfaces resulting from these structural defects are susceptible to exposure to pores.

[0057] Since one or more acidic functional groups among carbonyl groups, carboxyl groups, and ketone groups are prone to attaching to the edge surface, a gas containing nitrogen (N) can be injected to remove them.

[0058] By passing a gas containing nitrogen (N) through the expanded carbon, carbon structures such as pyrydone, pyrrolic, pyrydinic, and quaternary are formed on the edge surface of the expanded carbon. These carbon structures containing nitrogen elements are adsorbed into the pores, which suppresses the reformation of acidic functional groups, increases the polarization and charge density of the carbon, thereby suppressing degradation with electrolyte ions and increasing the electric double layer capacity.

[0059] Here, gases containing the element nitrogen include nitrogen gas (N2), nitric oxide (NO), nitrogen dioxide (NO2), and ammonia (NH3), and these gases can be obtained by heating nitrogen-containing polymers. For example, heating melamine (C3N6H6) at 350°C or higher produces carbon nitride (C3N4) and -CN x It decomposes into nitrogen molecules at temperatures above 800°C, and nitrogen molecules are bonded to carbon.

[0060] Expanded carbon formed by passing an electric current through a compact has mesopores formed within the carbon with a volume fraction of 30% or more, and a specific surface area of ​​10 to 200 m² 2 It exhibits the characteristic of / g. Preferably, the volume fraction is in the range of 30 to 60%, and if it is less than 30%, the development of micropores is present, and if it exceeds 60%, the output characteristics of expanded carbon may not be satisfied.

[0061] Specific surface area of ​​5 to 10 m² 2 When non-graphitized carbon or graphite with a specific surface area of ​​1 / g is expanded, the specific surface area increases due to pores formed within the carbon, and the volume fraction of mesopores increases mainly due to the formation of pores between graphene layers.

[0062] The specific surface area of ​​expanded carbon can be controlled by lithium incorporation and current application conditions, and the specific surface area is 10m² 2 If it is less than / g, the total pore volume is small, resulting in less space to store the electrolyte, and the specific surface area is 200m² 2 If it exceeds / g, micropores develop and the volume fraction of mesopores decreases to less than 30%. However, as previously mentioned, the volume fraction is defined as the ratio of the volume of mesopores to the total volume of expanded carbon.

[0063] In the present invention, mesopores refer to pores with an average diameter of 2 to 50 nm. However, if heat treatment is performed by simply introducing the material into a furnace, the pores formed within the carbon may include not only mesopores but also macropores with an average diameter exceeding 50 nm or micropores with an average diameter of less than 2 nm, which is undesirable.

[0064] In expanded carbon manufactured in this way, some lithium may remain between the carbon layers during the expansion process. In this case, the weight fraction of lithium must be 5% or less, because if the weight fraction of lithium exceeds 5%, there is a concern that it may act as an impurity within the expanded carbon. In other words, if the weight fraction of lithium remaining between the carbon layers of the expanded carbon exceeds 5%, it may hinder the incorporation of the electrolyte into the expanded carbon during the formation process of the energy storage device, potentially preventing it from functioning as a pore.

[0065] Since the lithium remaining between the carbon layers can provide additional lithium ions during the charging and discharging process of lithium-ion batteries or lithium-ion supercapacitors using lithium ions, it can replenish the lithium ions consumed by irreversible reactions during the repeated charging and discharging process of these energy storage devices.

[0067] In summary, the present invention relates to expanded carbon for improving the output of a secondary battery and a method for manufacturing the same. The invention is characterized by mixing lithium metal with water-soluble oil and then mixing carbon to produce a mixture, reacting the mixture while applying pressure at 200 to 450°C to produce a lithium-carbon compound in which lithium is incorporated between the carbon layers, and heat-treating the lithium-carbon compound thus produced to produce expanded carbon in which lithium is detached and removed from the lithium-carbon compound, thereby expanding the carbon layers, and rapidly heating the lithium-carbon compound to 450 to 1,000°C by passing an electric current through it.

[0068] According to these characteristics, the volume fraction of mesopores within the carbon is 30% or more, and the specific surface area is 10 to 200 m² 2 Since expanded carbon can be manufactured at a density of 1 / g, utilizing it as an active material or additive for lithium-ion batteries or lithium-ion supercapacitors using lithium electrolytes solves the problems associated with commercial activated carbon or commercial expanded graphite. Furthermore, as the mesopores of the expanded carbon store electrolyte and reduce diffusion resistance, there is an advantage in that the output characteristics of energy storage devices can be improved.

[0070] The embodiments of the present invention will be described in more detail below. However, the following embodiments are provided merely to aid in understanding the present invention and do not limit the scope of the present invention.

[0071] <Example 1>

[0072] A lithium-oil mixture containing 60 wt% lithium in paraffin oil was mixed with natural graphite at a ratio of 10:90 wt% and dispersed for 2 hours. This mixture was placed in a reactor at 250°C and 300 kg / cm² 3 Lithium was incorporated or inserted into the carbon by mixing for 6 hours under pressure. The reaction-completed lithium-carbon compound was loaded into a cylindrical insulating apparatus and compacted by applying pressure. This compacted body was rapidly heated to a temperature of 800°C for 10 minutes by applying a power density of 65 W / g through electrodes positioned above and below. The lithium-carbon compound thus prepared was used as an electrode active material.

[0073] <Example 2>

[0074] A lithium-oil mixture containing 60 wt% lithium in paraffin oil was mixed with natural graphite at a ratio of 20:80 wt% and dispersed for 2 hours. This mixture was placed in a reactor at 250°C and 300 kg / cm² 3 Lithium was incorporated or inserted into the carbon by mixing for 6 hours under pressure. The reaction-completed lithium-carbon compound was loaded into a cylindrical insulating apparatus and compacted by applying pressure. This compacted body was rapidly heated to a temperature of 800°C for 10 minutes by applying a power density of 65 W / g through electrodes positioned above and below. The lithium-carbon compound thus prepared was used as an electrode active material.

[0075] <Example 3>

[0076] A lithium-oil mixture containing 60 wt% lithium in paraffin oil was mixed with natural graphite at a ratio of 30:70 wt% and dispersed for 2 hours. This mixture was placed in a reactor at 250°C and 300 kg / cm² 3Lithium was incorporated or inserted into the carbon by mixing for 6 hours under pressure. The reaction-completed lithium-carbon compound was loaded into a cylindrical insulating apparatus and compacted by applying pressure. This compacted body was rapidly heated to a temperature of 800°C for 10 minutes by applying a power density of 65 W / g through electrodes positioned above and below. The lithium-carbon compound thus prepared was used as an electrode active material.

[0077] <Comparative Example 1>

[0078] The process was carried out in the same manner as in the example, but natural graphite was used as the electrode active material.

[0080] Here, FIG. 2 shows SEM images of Example 3 and Comparative Example 1. FIG. 2(a) shows an SEM image of Example 3, confirming that an interlayer expansion structure is present. On the other hand, FIG. 2(b) shows an SEM image of Comparative Example 1, confirming that a typical plate-like natural graphite shape is present.

[0082] <Test Example 1>

[0083] In this test example, we decided to analyze the discharge capacity and rate characteristics using the electrode active materials according to Examples 1 to 3 and Comparative Example 1.

[0084] Sample preparation

[0085] (a) Preparation of slurry electrode

[0086] 13g of CMC (carboxymethyl cellulose) dispersed in 2 wt% distilled water and 1.2g of SBR (styrene butadiene rubber) dispersed in 48 wt% distilled water were added to a reactor, and then stirred at 1,800 rpm for 10 minutes using a dispersion device (Thinky mixer). 0.3g of carbon black, a conductive material, was added to the reactor and subjected to ultrasonic treatment for 10 minutes, followed by mixing using a dispersion device (Thinky mixer) at 1,800 rpm for 10 minutes. Finally, 19g of active material was added to the reactor, and a slurry was prepared by stirring at 1,800 rpm for 10 minutes and degassing for 5 minutes using a dispersion device.

[0087] (b) Preparation of electrodes

[0088] A slurry electrode was coated onto the surface of a Cu current collector with a uniform thickness using an applicator. The coated electrode was hot-air dried at a temperature of 100°C, then compressed using a roll press (roll surface temperature: 80°C) until the electrode thickness reached 40 μm and the electrode density reached 1.5 g / cc, and then vacuum dried at a temperature of 150°C for 24 hours to manufacture the electrode.

[0089] (c) Preparation of a half cell

[0090] A lithium-carbon compound and a natural graphite electrode were each cut to a size of 2.5 × 2.5 cm², and one end of the current collector, to which no electrode was attached, was cut lengthwise to be used as a terminal, and these carbon electrodes were used as negative electrodes. Meanwhile, the positive electrode was manufactured by cutting a 300 μm thick Li foil to the same size as each carbon electrode. After stacking the carbon electrode, separator (Celgard 3501), and Li foil in that order, the assembly was impregnated with an electrolyte solution in which 1.0 M LiPF6 (lithium hexafluorophosphate) was dissolved in a co-solvent of EC (ethylene carbonate), DEC (diethyl carbonate), and EMC (ethyl methyl carbonate) in a weight ratio of 1:1:1 using an electrolyte injector capable of vacuum pressure reduction and increase, and then vacuum-packed.

[0091] Characteristic analysis

[0092] (a) Discharge capacity (mAh / g)

[0093] The charge and discharge characteristics of the cell fabricated using a Li-carbon compound and a natural graphite electrode were tested using a charge / discharge tester (MACCOR, model name MC-4). The test was conducted under 0.2C conditions at a driving voltage of 0.005 to 1.5V. The specific capacity per weight of the Li-carbon compound and the natural graphite electrode was expressed as the value obtained by dividing the capacity measured during the third constant current discharge by the weight of the Li-carbon compound and the natural graphite electrode.

[0094] (b) Rate characteristics (C-rate)

[0095] After performing a third 0.2C charge and discharge of a cell manufactured using a Li-carbon compound and a natural graphite electrode, a fourth 0.2C charge and 1, 5, and 10C discharges were performed, and the rate characteristics were calculated using Equation 1 below.

[0096] [Equation 1]

[0097] Rate Characteristic (%) = Discharge Capacity @ x C / Discharge Capacity @ 0.2 C × 100 (x=0.2, 1, 5, 10)

[0098] The specific surface area (m) obtained from the isothermal adsorption curves of Examples 1 to 3 and Comparative Example 1 according to this. 2 The cell resistance (mΩ@1kHz), discharge capacity (mAh / g), and capacity retention rate (%) at 10C obtained from AC impedance and charge / discharge results are shown in Table 1.

[0099] Specific surface area (m²) 2 / g) Cell resistance @ 1kHz (mΩ) Discharge capacity @ 5th (mAh / g) Capacity retention rate @ 10C (%) Example 1 7.9 2.3 350 82.2 Example 2 9.3 2.3 360 83.9 Example 3 15.2 1.8 360 90.3 Comparative Example 1 6.2 2.5 357 74.4

[0100] Referring to Table 1, the specific surface area increased from Comparative Example 1 to Example 1, Example 2, and Example 3, and the highest specific surface area was observed in Example 3. The phenomenon of the specific surface area increasing from Example 1 to Example 2 and Example 3 implies that pores are formed by the detachment of Li compounds between the graphite layers during the rapid heat treatment process.

[0101] In this regard, FIG. 3 is a graph showing the isothermal adsorption curves of Example 3 and Comparative Example 1. Referring to FIG. 3, which shows the isothermal adsorption curves of Example 3 and Comparative Example 1, it can be confirmed that the fraction of mesopores in Example 3 has increased compared to Comparative Example 1.

[0102] Figure 4 is a graph showing the AC impedance results of Example 3 and Comparative Example 1. Referring to Figure 4, the AC impedance results according to Example 3 and Comparative Example 1 can be observed, and it can be seen that the internal resistance of Example 3 shows a reduced value compared to Comparative Example 1.

[0103] Figure 5 is a graph showing the capacity retention rate (%) for the C-rate of Example 3 and Comparative Example 1. Referring to Figure 5, the capacity retention rate (%) for the C-rate according to Example 3 and Comparative Example 1 is shown, and it can be seen that the output characteristics of Example 3 are improved compared to Comparative Example 1.

[0105] Based on the results of the above-described examples and test examples, the present invention relates to expanded carbon for improving the output of a secondary battery and a method for manufacturing the same, characterized in that when lithium is incorporated into natural graphite and heated by applying an electric current, expanded carbon containing mesopores between layers is produced by the delamination of lithium compounds during the rapid heating process.

[0106] This feature can be achieved by mixing lithium metal into a water-soluble oil and then mixing carbon to produce a mixture, reacting the mixture under pressure at 200 to 450°C to produce a lithium-carbon compound in which lithium is incorporated between the carbon layers, and then passing an electric current through the lithium-carbon compound to rapidly heat it to 450 to 1,000°C, thereby causing lithium to be detached and removed from the lithium-carbon compound and expanding the carbon layers.

[0107] In addition, according to the electrochemical results of the half-cell using expanded carbon of the present invention, it can be seen that the pores play a role in improving output characteristics, and this is due to the pores reducing the diffusion resistance of lithium ions.

[0108] Therefore, it is expected that the output characteristics and long-term reliability of lithium-ion batteries or lithium-ion supercapacitors can be improved by overcoming the impurity problems associated with commercial activated carbon and expanded graphite using sulfuric acid.

[0110] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not to limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments. The scope of protection of the present invention shall be interpreted by the claims, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

Claim 1 A method for manufacturing expanded carbon for improving the output of a secondary battery, comprising: a step of preparing a mixture by mixing lithium metal into a water-soluble oil and then mixing carbon; a step of preparing a lithium-carbon compound in which lithium is incorporated between carbon layers by reacting the mixture while applying pressure at 200 to 450°C; and a step of preparing expanded carbon in which lithium is detached and removed from the lithium-carbon compound and the carbon layers are expanded by heat treatment; wherein the heat treatment involves rapidly heating the lithium-carbon compound to 450 to 1,000°C by passing an electric current through it, and the step of preparing the expanded carbon involves pressurizing the lithium-carbon compound to form a compact, then contacting the compact to an electrode and passing an electric current by applying a power density of 5 to 100 W / g. Claim 2 delete Claim 3 A method for manufacturing expanded carbon for improving secondary battery output according to claim 1, characterized in that the expanded carbon forms mesopores in which the mesopores constitute 30% or more of the total pore volume fraction within the carbon through the electric current and rapid heating. Claim 4 In claim 1, the expanded carbon has a specific surface area of ​​10 to 200 m² 2 A method for manufacturing expanded carbon for improving secondary battery output, characterized by having a value of / g. Claim 5 In claim 1, the carbon in the step of preparing the mixture is the interlayer distance (d 002 A method for manufacturing expanded carbon for improving secondary battery output, characterized by being one or more selected from the group consisting of graphite having a thickness of 0.335 to 0.36 nm and digraphitic carbon. Claim 6 Expanded carbon characterized by being manufactured by the method of any one of claims 1, 3 to 5, and having a mesopore volume fraction of 30% or more of the total pore volume fraction within the carbon.

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