Graphite-based negative electrode material and method for producing the same

Abstract

The present embodiment relates to a graphite-based negative electrode material, a manufacturing method thereof, a negative electrode including the same, and a lithium secondary battery including the same. The graphite-based negative electrode material according to one embodiment includes a graphite oxide obtained by oxidizing the surface of a first graphite; and a graphite coating including a second graphite and low-crystalline carbon located on the surface of the second graphite, and the ratio of the graphite coating to the graphite oxide is 1 / 9 to 1 / 3.

Description

[Technical Field]

[0001] The present embodiment relates to a lithium secondary battery, and more particularly to a graphite-based negative electrode material and a method for producing the same. [Background technology]

[0002] As social concern grows over the depletion of fossil fuels and the environmental pollution caused by their use, attention is being paid to environmentally friendly energy sources as a means of solving these problems. Among these environmentally friendly energy sources, electrical energy has been attracting increasing attention, and lithium secondary batteries in particular have been attracting attention.

[0003] The range of applications for lithium secondary batteries is expanding, from small electronic devices and portable IT devices to electric vehicles and energy storage systems. As the range of applications for lithium secondary batteries expands, the development of new materials for high capacity and high output is becoming increasingly important. The negative electrode material, which stores lithium ions, is a factor related to the capacity and lifespan of lithium secondary batteries.

[0004] Various types of carbonaceous materials, including artificial graphite, natural graphite, and hard carbon, which are capable of lithium insertion / extraction, have been used as anode materials. Graphite has a lower discharge voltage of 0.2V compared to lithium, and batteries using graphite as the anode active material exhibit a high discharge voltage of 3.6V, offering advantages in terms of energy density for lithium secondary batteries. Its excellent reversibility also ensures the long life of lithium secondary batteries, making it the most widely used.

[0005] Natural graphite has the advantage of being inexpensive yet exhibiting electrochemical properties similar to those of artificial graphite, making it highly useful as an anode material. However, natural graphite has a plate-like shape with a large surface area and exposed edges, which can lead to electrolyte penetration and decomposition reactions when used as an anode active material. As a result, the edges peel off or break, causing significant irreversible reactions. When this material is manufactured into an electrode plate, the graphitized material is pressed flat and oriented on the current collector, making it difficult for the electrolyte to penetrate, resulting in reduced charge / discharge performance.

[0006] To solve this problem, efforts are being made to transform natural graphite into a smooth surface shape through post-processing such as spheroidization in order to reduce irreversible reactions and improve the processability of the electrode.

[0007] Graphite, which has been commercialized as an anode material, undergoes minimal changes in its crystalline structure during the insertion and desorption of lithium ions, allowing oxidation and reduction reactions to occur continuously, resulting in excellent lifespan characteristics and high theoretical capacity. However, graphite can only accommodate one lithium ion per six carbon atoms, ensuring a limited theoretical capacity of, for example, 372 mAh / g, which places a limit on the requirements for high power and high capacity.

[0008] Research into new anode materials to overcome the limitations of graphite is ongoing, with interest in silicon-based anode materials growing in particular. Silicon is not only abundant worldwide, but also has the advantages of a higher theoretical capacity of approximately 4,200 mAh / g compared to graphite, a low reaction potential with lithium, and being an environmentally friendly material.

[0009] However, silicon-based anode materials have irregular shapes because they are made by mechanically crushing bulk silicon. The irregular shapes can lead to irregular volume expansion and contraction during the charge and discharge process of silicon, resulting in reduced battery performance. In addition, non-uniform electrodes can be manufactured during electrode fabrication, resulting in reduced battery performance. Summary of the Invention [Problem to be solved by the invention]

[0010] The technical problem to be solved by the present invention is to provide a carbon-based anode material that can suppress volume expansion and contraction that occur during the charging and discharging process of a battery, and can also provide a graphite-based anode material that can suppress non-uniformity during electrode manufacturing, thereby preventing a decrease in battery performance.

[0011] Another technical problem to be solved by the present invention is to provide a method for producing a graphite-based negative electrode material having the above advantages. [Means for solving the problem]

[0012] According to one embodiment of the present invention, the graphite-based negative electrode material includes a graphite oxide formed by oxidizing the surface of a first graphite, and a graphite coating including a second graphite and low-crystalline carbon located on the surface of the second graphite, wherein the ratio of the graphite coating to the graphite oxide is 1 / 9 to 1 / 3. In one embodiment, the graphite-based negative electrode material may have a D50 in the range of 17.5 μm to 19.5 μm.

[0013] In one embodiment, the graphite-based negative electrode material has a tap density of 0.80 g / cm 3 ~0.86g / cm 3 In one embodiment, the specific surface area of ​​the graphite-based negative electrode material may be in the range of 4.57 m 2 / g~5.50m 2 In one embodiment, the oil absorption of the graphite-based negative electrode material may be in the range of 51 ml / 100 g to 56 ml / 100 g.

[0014] According to another embodiment of the present invention, the negative electrode for a lithium secondary battery can contain 96 to 99 wt % of the graphite-based negative electrode material described above, 0.5 to 1.5 wt % of a thickener, and the balance being a binder. In one embodiment, the electrode density of the negative electrode for a lithium secondary battery is 1.2 g / m 3 ~1.8g / m 3 may be.

[0015] According to yet another embodiment of the present invention, a lithium secondary battery may include the above-described negative electrode for lithium secondary batteries, a positive electrode including a positive electrode active material, and an electrolyte, and the electrolyte may have an ethylene methyl carbonate (EMC) to ethylene carbonate (EC) ratio of 7 / 3 to 6 / 4.

[0016] According to yet another embodiment of the present invention, a method for manufacturing a graphite-based negative electrode material may include oxidizing a surface of a first graphite to prepare a graphite oxide, mixing a second graphite with low-crystalline carbon to prepare a graphite coating material, and mixing the graphite coating material with the graphite oxide in a ratio of 1 / 9 to 1 / 3. In one embodiment, the step of preparing the graphite oxide may include heating the first graphite at a temperature in the range of 550°C to 650°C.

[0017] In one embodiment, preparing the graphite coating may include preparing a homogeneous mixture by mixing the second graphite and low crystalline carbon at a ratio of 3 / 100 to 4 / 100. In another embodiment, firing the homogeneous mixture at a temperature of 1,100° C. or higher. In one embodiment, the method for preparing the graphite-based negative electrode material may include providing the graphite-based negative electrode material with an oil absorption of 51 ml / 100 g to 56 ml / 100 g. [Effects of the Invention]

[0018] According to one embodiment, the negative electrode material includes a graphite oxide obtained by oxidizing the surface of a first graphite, a second graphite, and a graphite coating obtained by disposing low-crystalline carbon on the surface of the second graphite. The ratio of the graphite coating to the graphite oxide is 1 / 9 to 1 / 3, thereby providing a carbon-based negative electrode material with a small specific surface area and high tap density. This suppresses volume expansion and contraction that occur during the charging and discharging process of a battery, and suppresses non-uniformity during electrode manufacturing, thereby preventing a decrease in battery performance. [Brief explanation of the drawings]

[0019] [Figure 1A]1 is a photograph of the structure of graphite oxide, showing the structure of a graphite-based negative electrode material according to one embodiment of the present invention. [Figure 1B] 1 is a structure photograph of a graphite coating material, which is a graphite-based negative electrode material according to an embodiment of the present invention. [Figure 2] 1 is a flowchart illustrating a method for manufacturing a graphite-based negative electrode material according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] Terms such as "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0021] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0022] When we say that a part is "on" another part, it means that it is exactly on top of the other part, or there may be other parts between them. In contrast, when we say that a part is "directly above" another part, there are no other parts between them.

[0023] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless otherwise defined.

[0024] DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the present invention is provided by way of example only and is not intended to limit the scope of the present invention, which is defined solely by the scope of the claims that follow.

[0025] 1A and 1B are structural photographs of graphite oxide and graphite coating, respectively, showing the structure of a graphite-based negative electrode material according to one embodiment of the present invention.

[0026] 1A and 1B, FIG. 1A is a scanning electron microscope (SEM) photograph showing the state of graphite oxide particles, and FIG. 1B is a SEM photograph of graphite-coated particles. The graphite-based negative electrode material may include graphite oxide and a graphite coating. The graphite oxide may be obtained by oxidizing the surface of a first graphite, and the graphite coating may include a graphite coating that is a mixture of a second graphite and low-crystalline carbon.

[0027] In one embodiment, the first graphite and the second graphite may be, as a non-limiting example, natural graphite. The natural graphite may be, for example, spherical natural graphite. The natural graphite is plate-shaped and highly oriented, which can make it difficult to apply to batteries, such as by reducing the output of electrode plates. Therefore, the first graphite and the second graphite of the present invention may be spherical graphite.

[0028] In one embodiment, the graphite oxide may be obtained by oxidizing graphite. The first graphite is oxidized in an oxidizing atmosphere, whereby carbon (C) on the surface of the first graphite reacts with oxygen (O) to produce and emit carbon dioxide (CO).

[0029] In one embodiment, the graphite oxide may have an average particle size (D50) of 12 μm to 20 μm, specifically 15 μm to 18 μm. The D50 is defined as the cumulative median diameter and is part of the volume cumulative particle size distribution. The volume cumulative particle size distribution is determined by assuming a single powder aggregate. When a cumulative curve is determined in the particle size distribution with the total volume of the powder aggregate as 100%, the particle sizes at the points where the cumulative curve is 10%, 50%, and 0% are expressed as the 10% diameter, 50% diameter, and 90% diameter (μm), respectively.

[0030] In one embodiment, when the graphite oxide is within the above range, a stable anode material can be produced during electrode fabrication, and a high-density electrode can be fabricated using the anode material, improving the lifespan and safety of the battery. However, this is a non-limiting example, and it is clear that the graphite oxide can be appropriately classified as needed.

[0031] In one embodiment, the graphite coating may include a second graphite and low-crystalline carbon located on the surface of the second graphite. The second graphite may be, for example, spherical natural graphite, and the low-crystalline carbon material may be petroleum pitch, coal pitch, mesophase pitch carbide, low-molecular-weight heavy oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, calcined coke, or a combination thereof, or specifically, a pitch with a softening point of 250.

[0032] In one embodiment, the graphite coating material may be made by mixing the low-crystalline carbon material with the second graphite at a ratio of 3 / 100 to 4 / 100. Specifically, the second graphite and the low-crystalline carbon material may be mixed at a weight ratio of 100:3 to 100:4, specifically 94:6 to 98:2, and more specifically 95:5 to 97:3. By mixing the low-crystalline carbon material at a weight ratio within this range, a coating layer can be formed that is uniformly coated on the surface of the spherical graphite.

[0033] In one embodiment, the graphite coating material may have an average particle size (D50) of 17.5 to 19.5 μm, specifically 18 to 19 μm. Within this range, a stable negative electrode material can be produced during electrode fabrication, and high-density electrodes can be manufactured using the negative electrode material, improving the lifespan and safety of the battery. However, this is a non-limiting example, and it is clear that the graphite coating material can be appropriately classified as needed.

[0034] In one embodiment, the ratio of the graphite oxide to the graphite coating is 1 / 9 to 1 / 3. Specifically, the graphite oxide and the graphite coating may be in a weight ratio of 90:10 to 75:25. By utilizing a graphite-based negative electrode material mixed in this weight ratio range, excellent initial capacity, efficiency, and life characteristics of a secondary battery can be manufactured. More specifically, the ratio of the graphite oxide to the graphite coating may be 85:15 to 80:20. Within this weight ratio range, a content ratio with high tap density, low specific surface area, and excellent cycle characteristics can be obtained.

[0035] As the ratio of the graphite coating material increases, the specific surface area decreases, the tap density increases, the electrical conductivity of the lithium secondary battery decreases, the impregnation of the electrolyte decreases, and the cycle characteristics decrease.As the ratio of the graphite oxide increases, the specific surface area increases, the tap density decreases, the electrical conductivity of the lithium secondary battery increases, the impregnation of the electrolyte increases, and the cycle characteristics improve.

[0036] If the ratio of the graphite oxide is too high, the tap density becomes too low, which causes a decrease in packing density and may cause a limit in rolling the electrode. Therefore, when the ratio of the graphite coating to the graphite oxide in the graphite-based negative electrode material is 1 / 9 to 1 / 3, specifically 3 / 17 to 1 / 4, a graphite-based negative electrode material having advantages of high tap density, low specific surface area, and excellent cycle characteristics can be provided.

[0037] In one embodiment, the graphite-based negative electrode material may have a D50 in the range of 18.5 μm to 20.5 μm, or more specifically, in the range of 18.5 μm to 19 μm.

[0038] In one embodiment, the graphite-based negative electrode material has a tap density of 0.80 g / cm 3 ~0.90g / cm 3 The tap density of the graphite-based negative electrode material may be in the range of 0.82 g / cm. 3 ~0.86g / cm 3 If the tap density of the graphite-based negative electrode material is below the lower limit, the ratio of oxide is increased, and pores formed on the outer surface of the oxide result in excessively high viscosity during slurry preparation, ultimately resulting in a decrease in the absolute amount of active material disposed on the current collector and a low packing density. If the tap density of the graphite-based negative electrode material is above the upper limit, the particle size is varied, resulting in relatively few particle voids, which hinders electrolyte penetration and reduces ionic conductivity, resulting in poor processability during electrode preparation and poor cycle characteristics of lithium secondary batteries.

[0039] In one embodiment, the specific surface area of ​​the graphite-based negative electrode material is 4.57 m 2 / g~5.50m 2 The specific surface area of ​​the graphite-based negative electrode material may be in the range of 4.60 m / g. 2 / g~5.10m 2The specific surface area of ​​the graphite-based negative electrode material decreases as the ratio of the graphite coating material increases, and the graphite coating material contains about 3% amorphous carbon, so its irreversible capacity is greater than that of graphite oxide.

[0040] If the specific surface area is below the lower limit, there is a problem that the irreversible capacity may increase, and if the specific surface area is above the upper limit, there is a problem that the oxidation of the oxidized product is insufficient, and therefore channels cannot be formed well on the surface of the graphite-based negative electrode material, resulting in low oil absorption and poor electrolyte impregnation.

[0041] In one embodiment, the oil absorption of the graphite-based negative electrode material may be in the range of 51 ml / 100 g or more. Specifically, the oil absorption of the graphite-based negative electrode material may be in the range of 51.0 ml / 100 g to 56.0 ml / 100 g. More specifically, the oil absorption of the graphite-based negative electrode material may be in the range of 51.5 ml / 100 g to 55.0 ml / 100 g. The oil absorption may be, for example, the oil absorption of linseed oil. If the oil absorption of the graphite-based negative electrode material exceeds the upper limit, the viscosity may increase and the slurry properties may deteriorate. If the oil absorption of the graphite-based negative electrode material exceeds the lower limit, the impregnation of the electrolyte and the lithium ion conductivity may decrease, resulting in problems such as reduced capacity and cycle characteristics of the lithium secondary battery.

[0042] When the oil absorption of the graphite-based negative electrode material satisfies the range of 51 ml / 100 g or more, it has the advantage of increasing the electrolyte impregnation and lithium ion conductivity, thereby improving cycle characteristics. When the oil absorption of the graphite-based negative electrode material exceeds the upper limit of the range, the surface of the graphite oxide in the graphite-based negative electrode material becomes rough and increases porosity, which can cause a problem of clumping during electrode manufacturing using the graphite-based negative electrode material.

[0043] In one embodiment, the viscosity of the graphite-based negative electrode material may be in the range of 11,750 to 13,500 cP. Specifically, the viscosity may be in the range of 12,000 to 13,000 cP. If the viscosity exceeds the upper limit, the slurry becomes too thick. When used in the manufacture of an electrode, the slurry may solidify, resulting in a deterioration in the properties of the slurry and the electrode. If the viscosity exceeds the lower limit, the electrical conductivity may decrease during the manufacture of the electrode.

[0044] In one embodiment, the graphite-based negative electrode material has an electrical conductivity of 276.0 S / cm or more. Specifically, the electrical conductivity may be 280.0 S / cm or more. The electrical conductivity may be 700 kgf / cm or more. 2 The higher the electrical conductivity, the higher the ionic conductivity, since electrons must flow in order for ions to be conducted.

[0045] In one embodiment, a negative electrode for a lithium secondary battery may be provided, the negative electrode for the lithium secondary battery including the graphite-based negative electrode material. The negative electrode for the lithium secondary battery may include the graphite-based negative electrode material, a thickener, and a binder. The graphite-based negative electrode material may refer to the graphite-based negative electrode material described above to the extent that it is not inconsistent.

[0046] The thickener is an additive for increasing the viscosity of the negative electrode material, and may include, for example, at least one of carboxymethyl cellulose (CMC), guar gum, non-crosslinked polyacrylic acid, uncrosslinked polyacrylic acid, and polyvinyl alcohol.

[0047] The binder can effectively bond particles constituting the negative electrode material to each other and facilitate adhesion of the negative electrode material to the current collector, and can include, for example, at least one of polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethylmethacrylate, polyethylene, and cellulose nitrate.

[0048] In one embodiment, the negative electrode for a lithium secondary battery comprises 96 to 99 wt % of a graphite-based negative electrode material, 0.5 to 1.5 wt % of a thickener, and the balance being a binder. In one embodiment, the negative electrode for a lithium secondary battery has an electrode density of 1.2 g / m 3 ~1.8g / m 3 In this range of electrode density, the initial capacity, efficiency, and life characteristics of the lithium secondary battery can be improved when electrodes are manufactured in the future.

[0049] In one embodiment, a lithium secondary battery including the graphite-based negative electrode material can be provided. In one embodiment, the lithium secondary battery can include a negative electrode including the graphite-based negative electrode material, a positive electrode including a positive electrode active material, and an electrolyte. The graphite-based negative electrode material and the negative electrode are the same as those described above, and the positive electrode can refer to a positive electrode used in a conventional lithium secondary battery. In one embodiment, the electrolyte may contain ethylene carbonate (EC) and ethylene methyl carbonate (EMC) in a ratio of 7:3 to 6:4. Specifically, the electrolyte may contain the ethylene carbonate and the ethylene methyl carbonate in a weight ratio of 30:70 to 40:60. By including the graphite-based negative electrode material, the lithium secondary battery can have physical properties such as an initial capacity of 360 mAh / g or more, specifically 363 mAh / g or more, an efficiency of 93.0% or more, specifically 94.0% or more, and a lifespan characteristic of 88% or more, specifically 91% or more.

[0050] FIG. 2 is a flowchart showing a method for producing a graphite-based negative electrode material according to one embodiment of the present invention.

[0051] 2, a method for manufacturing a graphite-based negative electrode material according to one embodiment of the present invention may include step S100 of oxidizing the surface of a first graphite to prepare a graphite oxide, step S200 of mixing a second graphite with low-crystalline carbon to prepare a graphite coating material, and step S300 of mixing the graphite coating material with the graphite oxide in a ratio of 1 / 9 to 1 / 3. For a detailed description of the first graphite, the second graphite, the graphite oxide, the low-crystalline carbon, and the graphite coating material, please refer to FIG. 1.

[0052] Step S100 of producing graphite oxide by oxidizing the surface of the first graphite may be performed under gaseous or solid oxidation conditions containing a substance capable of oxidizing the first graphite. Under the oxidation conditions, the graphite oxide oxidizes the first graphite, e.g., spheroidal graphite, thereby partially or completely removing defects in the crystalline structure of the spheroidal graphite. The gaseous or solid may contain, for example, oxygen. As a result, carbon (C) within the spheroidal graphite, e.g., on the surface, reacts with oxygen (O2), producing and discharging carbon dioxide (CO2).

[0053] In one embodiment, the step of preparing the graphite oxide may include heating the first graphite at a temperature ranging from 550° C. to 700° C. The graphite oxide is prepared by heat-treating the first graphite at a temperature ranging from 500° C. to 700° C., specifically, at a temperature ranging from 550° C. to 650° C. This allows side reaction-inducing organic substances to be removed from the surface of the graphite oxide, and increases the number of voids, e.g., channels, generated by the removal of the side reaction-inducing organic substances, thereby facilitating the movement of lithium ions.

[0054] The step S200 of mixing the second graphite and the low-crystalline carbon to prepare a graphite-coated material may include mixing and stirring the second graphite and the low-crystalline carbon. The step of preparing the graphite-coated material may include mixing the second graphite and the low-crystalline carbon in a weight ratio of 3:97 to 2:98. Specifically, the step may include mixing the second graphite and the low-crystalline carbon in a weight ratio of 97:3 to 98:2 to prepare a uniform mixture.

[0055] In one embodiment, the mixing and stirring is performed by a mechanical mixing process, which is performed after spheroidizing the second graphite by selecting any one of ball milling, mechanofusion milling, shaker milling, planetary milling, attritor milling, disk milling, shape milling, nauta milling, nobilta milling, or a combination thereof.

[0056] In one embodiment, the mechanical mixing treatment can be carried out at a rotation speed of 300 to 2000 rpm. In another embodiment, the mechanical mixing treatment can be carried out in a two-stage treatment. Specifically, the two-stage treatment can involve a first stage of rotation at a rotation speed of 300 to 1000 rpm, followed by a second stage of rotation at a rotation speed of 1000 rpm to 2000 rpm. By carrying out the two-stage treatment, the second graphite and the low-crystalline carbon can be uniformly mixed and stirred.

[0057] In one embodiment, preparing the homogeneous mixture may further include calcining the homogeneous mixture at a temperature of 1,100°C or higher. In one embodiment, the calcining is performed in a gas atmosphere. The gas atmosphere may be nitrogen (N2), argon (Ar), helium (He), hydrogen (H2), or a mixture thereof. The calcining may produce a graphite coating in which low-crystalline carbon is uniformly coated on the surface of the second graphite. In one embodiment, preparing the homogeneous mixture may further include classifying the homogeneous mixture through a 45 μm sieve.

[0058] In step S300, the graphite oxide and the graphite coating material may be mixed at a weight ratio of 1:9 to 1:3, inclusive. By mixing the graphite oxide and the graphite coating material in this range, a graphite-based anode material having a low tap density and a high specific surface area can be manufactured. Therefore, by incorporating the graphite-based anode material, a lithium secondary battery having excellent initial capacity, high efficiency, and excellent lifespan characteristics can be manufactured. [Example]

[0059] Examples of the present invention and comparative examples are shown in Figures 1 and 2. The following examples and comparative examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0060] To measure the tap density of the following examples and comparative examples, 15 g of powder was filled into a 50 ml cylinder and tapped and rotated simultaneously 3,000 times using a tap density measuring device (Quantachrome's Autotap). To measure the oil absorption, 30 g of powder was placed in the mixing unit of an oil absorption measuring device (ASAHI SOUKEN's S-500), and linseed oil was added and rotated simultaneously to measure the oil absorption per 100 g of sample.

[0061] Example 1 1. Graphite oxide manufacturing method Spherical natural graphite with an average particle size of 18 μm was oxidized in an air atmosphere at 600°C for 3 hours in a continuous rotary kiln. The physical properties of the oxidized natural graphite were measured, and the average particle size was 18.5 μm and the tap density was 0.78 g / cm. 3 , specific surface area is 5.4m 2 The oil absorption of linseed oil is 58.3 ml / 100 g. The natural graphite oxide is classified using a 45 μm sieve.

[0062] 2. Manufacturing method of graphite coating Spherical natural graphite with an average particle size of 17.5 μm and pitch were mixed in a weight ratio of 96:4 and mechanically mixed for 10 minutes at 1,500 rpm using a high-speed stirrer to prepare a homogeneous mixture. The homogeneous mixture was then calcined in a nitrogen atmosphere at 1,200°C for 12 hours to produce a natural graphite-low crystalline carbon composite. The physical properties of the oxidized natural graphite were measured, revealing an average diameter of 17.9 μm and a tap density of 1.09 g / cm. 3 , specific surface area is 2.7m 2 / g, and the oil absorption capacity of linseed oil is 42.7 ml / 100 g.

[0063] 3. Manufacturing method of graphite-based negative electrode material The natural graphite oxide and the natural graphite coating were mixed in a weight ratio of 90:10.

[0064] 4. Negative electrode manufacturing method The composite for the negative electrode material was mixed with carboxymethyl cellulose (CMC) as a thickener and styrene butadiene rubber (SBR) as a binder in a mass ratio of 98:1:1, and then dispersed in deionized distilled water to prepare a negative electrode active material layer composition. This was applied to a copper foil, dried, and rolled to produce an electrode with a density of 1.4 g / m. 3 The negative electrode was manufactured so that

[0065] 5. Lithium secondary battery manufacturing method A lithium secondary battery was fabricated by inserting a polypropylene separator between the negative electrode and the counter electrode into a battery container and injecting an electrolyte solution, which consisted of 1M LiPF6 dissolved in a mixed solution of ethylene carbonate (EC):ethylene methyl carbonate (EMC) in a 3:7 ratio and containing 0.5 wt% vinylidene carbonate (VC).

[0066] <Example 2> The same procedure as in Example 1 was carried out, except that the graphite oxide was used in an amount of 85 wt % and the graphite coating material was used in an amount of 15 wt %.

[0067] Example 3 The same procedure as in Example 1 was carried out, except that the graphite oxide was used in an amount of 80 wt % and the graphite coating material was used in an amount of 20 wt %.

[0068] Example 4 The same procedure as in Example 1 was carried out, except that the graphite oxide was used in an amount of 75 wt % and the graphite coating material was used in an amount of 25 wt %.

[0069] <Comparative Examples 1 to 5> Comparative Example 1 was carried out in the same manner as Example 1, except that 70 wt % of the graphite oxide and 30 wt % of the graphite-coated material were used; Comparative Example 2 was used in 65 wt % of the graphite oxide and 35 wt % of the graphite-coated material; Comparative Example 3 was used in 60 wt % of the graphite oxide and 40 wt % of the graphite-coated material; Comparative Example 4 was used in 55 wt % of the graphite oxide and 45 wt % of the graphite-coated material; and Comparative Example 5 was used in 50 wt % of the graphite oxide and 50 wt % of the graphite-coated material.

[0070] <Comparative Examples 6 to 8> Comparative Example 6 was carried out in the same manner as Example 1, except that 100% of the raw material was used, 100% of the graphite oxide was used, and 100% of the graphite coating was used in Comparative Example 7.

[0071] The physical properties of Examples 1 to 4 and Comparative Examples 1 to 8 can be confirmed from Table 1 below.

[0072] [Table 1]

[0073] As can be seen from Table 1, the ratio of graphite oxide to graphite coating was 1 / 9 to 1 / 3. Specifically, the graphite oxide to graphite coating weight ratio ranged from 90:10 to 75:25, and it was confirmed that the tap density was low, the specific surface area was high, the viscosity was high, and the electrical conductivity was high. Specifically, it was confirmed that the graphite-based negative electrode materials of Examples 1 to 4 and Comparative Examples 1 to 5 decreased in tap density as the ratio of mixed graphite oxide increased, and increased in tap density as the ratio of graphite coating increased. Furthermore, it was confirmed that the graphite-based negative electrode materials of Examples 1 to 4 and Comparative Examples 1 to 5 increased in oil absorption as the ratio of mixed graphite oxide increased, and increased in oil absorption as the ratio of graphite coating decreased.

[0074] It was confirmed that the oxidation of the graphite surface increased the oil absorption in the graphite-based anode materials of Comparative Examples 6 and 7, and that the low-crystalline carbon coating reduced the oil absorption in the graphite-based anode materials of Comparative Examples 7 and 8. This confirms that the initial capacity, efficiency, and lifespan characteristics of secondary batteries using the graphite-based anode materials containing the graphite coating and the graphite oxide mixture as anode materials are excellent.

[0075] The present invention is not limited to the above-described embodiments, and can be manufactured in various different forms. Those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical concept or essential characteristics of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not limiting.

Claims

1. a graphite oxide obtained by oxidizing the surface of the first graphite; and a graphite coating including second graphite and low-crystalline carbon located on a surface of the second graphite; the graphite coating to the graphite oxide is 1 / 9 to 1 / 3; The graphite-based negative electrode material has a specific surface area in the range of 4.57 m 2 / g to 5.50 m 2 / g.

2. 2. The graphite-based negative electrode material according to claim 1, wherein the graphite-based negative electrode material has a D50 in the range of 17.5 to 19.5 μm.

3. The tap density of the graphite-based negative electrode material is 0.80 g / cm ３ ~0.86 g / cm ３ The graphite-based negative electrode material according to claim 1, wherein the carbon black content is in the range of

4. 2. The graphite-based negative electrode material according to claim 1, wherein the oil absorption of the graphite-based negative electrode material is in the range of 51 ml / 100 g to 56 ml / 100 g.

5. 5. A negative electrode for a lithium secondary battery comprising 96 to 99 wt % of the graphite-based negative electrode material according to claim 1, 0.5 to 1.5 wt % of a thickener, and the balance being a binder.

6. Electrode density is 1.2 g / m ３ ~1.8g / m ３ 6. The negative electrode for a lithium secondary battery according to claim 5, wherein

7. The negative electrode for a lithium secondary battery according to claim 5 or 6; a positive electrode including a positive electrode active material; and Contains electrolytes, The electrolyte is a lithium secondary battery in which the ratio of ethylene methyl carbonate (EMC) to ethylene carbonate (EC) is 7 / 3 to 6 / 4.

8. oxidizing the surface of the first graphite to produce graphite oxide; mixing the second graphite with low-crystalline carbon to prepare a graphite coating; and 1. A method for manufacturing a graphite-based negative electrode material, comprising: mixing the graphite oxide and the graphite coating material in a ratio of 1 / 9 to 1 / 3; The method for producing a graphite-based negative electrode material, wherein the specific surface area of ​​the graphite-based negative electrode material is in the range of 4.57 m 2 / g to 5.50 m 2 / g.

9. 9. The method of claim 8, wherein the step of preparing the graphite oxide comprises heating the first graphite at a temperature in the range of 550°C to 650°C.

10. 10. The method of claim 8, wherein the preparing the graphite coating comprises mixing the second graphite and low crystalline carbon in a ratio of 3 / 100 to 4 / 100 to prepare a uniform mixture.

11. The method for producing a graphite-based negative electrode material according to claim 10, further comprising the step of firing the homogeneous mixture at a temperature of 1,100°C or higher.

12. The method for producing a graphite-based negative electrode material according to claim 8, wherein the graphite-based negative electrode material has an oil absorption in the range of 51 ml / 100 g to 56 ml / 100 g.

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