Negative electrode active material for lithium secondary battery and lithium secondary battery comprising same

Abstract

A negative electrode active material for a lithium secondary battery according to the present invention comprises: a graphite-based base material; a low-crystallinity carbon coating layer positioned on the surface of the graphite-based base material; and a conductive material included in the coating layer, wherein the content of the low crystalline carbon is 1.0 to 10 wt %, and the content of the conductive material is 0.1 to 1.0 wt %.

Description

Negative active material for lithium secondary batteries and lithium secondary batteries containing the same

[0001] The present invention relates to a negative electrode active material for a lithium secondary battery and a lithium secondary battery including the same.

[0002] This application claims the benefit of Korean Patent Application No. 10-2024-0117613, filed on August 30, 2024, and Korean Patent Application No. 10-2024-0117614, filed on August 30, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] As technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, are being commercialized and widely used.

[0005] In addition, as interest in environmental issues grows, interest in electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels, such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, is increasing, and research is actively being conducted to use lithium secondary batteries as a power source for the electric vehicles and hybrid electric vehicles.

[0006] Lithium secondary batteries generally consist of a positive electrode containing a positive active material, a negative electrode containing a negative active material, a separator, and an electrolyte, and charge and discharge are performed by the intercalation and decalation of lithium ions. The lithium secondary batteries have the advantages of high energy density, large electromotive force, and high capacity, and are therefore applied in various fields.

[0007] Materials such as metallic lithium anode active materials, carbon-based anode active materials, or silicon oxide (SiOx) are used as the above-mentioned anode active materials. The carbon-based anode active materials exhibit excellent capacity retention characteristics and efficiency. Since the carbon-based anode active materials used as the anodes of lithium secondary batteries have an electrode potential close to that of lithium metal, the change in crystal structure during the insertion and deintercalation process of ionic lithium is small. In addition, the carbon-based anode active materials enable continuous and repeated oxidation and reduction reactions at the electrode, thereby enabling lithium secondary batteries to exhibit high capacity and excellent lifespan.

[0008] As the above carbon-based negative electrode active material, various types of materials are used, such as crystalline carbon-based materials such as natural graphite and artificial graphite, or amorphous carbon-based materials such as hard carbon and soft carbon. Among the above carbon-based negative electrode active materials, graphite-based negative electrode active materials are the most widely used because they have excellent reversibility and can improve the life characteristics of lithium secondary batteries. Since the graphite-based negative electrode active material has a low discharge voltage of -0.2 V compared to lithium, a battery using the graphite-based active material can exhibit a high discharge voltage of 3.6 V, which has an excellent advantage in terms of energy density of lithium secondary batteries.

[0009] The above-mentioned crystalline carbon-based material, artificial graphite, has a more stable crystal structure than the natural graphite because it forms a graphite crystal structure by applying high heat energy of 2,700℃ or more, and the change in the crystal structure is small even with repeated charging and discharging of lithium ions, so the artificial graphite has an advantage of a lifespan that is about 2 to 3 times longer than the natural graphite. The above-mentioned amorphous carbon-based materials, soft carbon and hard carbon, whose crystal structures are not stabilized, have the characteristic of smoother entry and exit of lithium ions, and can increase the charging and discharging speeds, so they can be used in electrodes that require high-speed charging. Therefore, it is common to mix and use the above-mentioned carbon-based materials at a certain ratio in consideration of the lifespan characteristics and output characteristics of the lithium secondary battery to be used.

[0010] Among the graphite-based materials, which are the above-mentioned negative active materials, artificial graphite is also used as a negative active material for rapid charging, but there is a problem that the filling density decreases when the particle size is reduced or the degree of assembly is improved to improve the rapid charging performance.

[0011]

[0012] One object of the present invention is to provide a negative electrode active material for a lithium secondary battery capable of implementing excellent battery characteristics with excellent output characteristics, and a lithium secondary battery including the same.

[0013]

[0014] According to one embodiment of the present invention, a negative active material for a lithium secondary battery comprises: a graphite-based base material; a low-crystalline carbon coating layer positioned on the surface of the graphite-based base material; and a conductive material included in the coating layer; wherein the low-crystalline carbon content is 1.0 to 10 wt%, and the acid conductive material content is 0.1 to 1.0 wt%.

[0015] The weight ratio of the above-mentioned conductive material and low-crystalline carbon (conductive material: low-crystalline carbon) is in the range of 1:1 to 1:30.

[0016] The average particle diameter (D50) of the above negative active material is in the range of 10.0 to 20.0 μm.

[0017] The specific surface area (SSA) of the above negative active material is 0.5 to 1.5 m 2 / g is the range.

[0018] The tap density of the above negative active material is 0.8 to 1.10 g / cm 3 It's a range.

[0019] The pellet density of the above cathode active material is 1.40 g / cc to 1.50 g / cc.

[0020] The minimum particle size (Dmin) of the above negative active material is greater than 3.0㎛.

[0021] The D90 / D10 of the above negative active material is 2.0 to 3.0.

[0022] The above negative active material satisfies the following relationship 1.

[0023] [Relationship 1]

[0024] 6.0 ≤ D50 / (ρ*SSA) ≤ 25.0

[0025] (Here, D50 is the average particle size of the negative electrode active material (unit: ㎛), ρ is the tap density of the negative electrode active material (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.)

[0026] The above negative active material satisfies the following relationship 2:

[0027] [Relationship 2]

[0028] 0.820 ≤ Span*ρ / SSA ≤ 1.1

[0029] (Here, Span is (D90-D10) / D50, ρ is the tap density of the negative electrode active material (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.)

[0030] The above negative active material satisfies the following relationship 3.

[0031] [Relationship 3]

[0032] 10.0 ≤ D50 / ρ ≤ 20.0

[0033] (Here, D50 is the average particle size of the negative electrode active material (unit: ㎛), ρ is the tap density of the negative electrode active material (unit: g / cm 3 )am.)

[0034] The above negative active material has an orientation (I) in XRD analysis 004 / I 110 ) values ​​are between 1.5 and 3.0.

[0035] According to another embodiment of the present invention, a negative electrode for a lithium secondary battery comprises a current collector; and a negative electrode active material layer disposed on the current collector, wherein the negative electrode active material layer includes the negative electrode active material and satisfies the following relational expression 4.

[0036] [Relationship 4]

[0037] 7.0 ≤ AS / (ρ*SSA) ≤ 20.0

[0038] (Here, AS is the adhesive strength between the current collector and the negative electrode active material layer (unit: gf / cm), and ρ is the tap density of artificial graphite (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.)

[0039] The adhesive strength between the above-mentioned collector and the negative electrode active material layer is 7.0 to 20.0 gf / cm.

[0040] A lithium secondary battery according to another embodiment of the present invention includes a negative electrode including the negative electrode active material; a positive electrode; and an electrolyte.

[0041]

[0042] A method for manufacturing artificial graphite according to one embodiment of the present invention can secure excellent output characteristics of a lithium secondary battery to which the method is applied by controlling the physical properties such as particle size and specific surface area of ​​artificial graphite powder manufactured by treating the surface of artificial graphite in two steps.

[0043] A method for manufacturing artificial graphite according to one embodiment of the present invention can produce artificial graphite for a lithium secondary battery by omitting an assembly process step for a graphitization process, thereby simplifying the production process, reducing production costs, and improving overall production efficiency.

[0044]

[0045] Figure 1 is a schematic diagram showing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0046] Figure 2 shows an SEM image of artificial graphite manufactured in Manufacturing Example 3.

[0047] Figure 3 shows an SEM image of artificial graphite manufactured in Manufacturing Example 4.

[0048] Figure 4 shows an SEM image of artificial graphite manufactured in Manufacturing Example 5.

[0049] Figure 5 shows an SEM image of artificial graphite manufactured in Example 5.

[0050] Figure 6 shows an SEM image of artificial graphite manufactured in Example 6.

[0051]

[0052] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, 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.

[0053] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0054] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0055] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0056] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0057] In this specification, the term "combination(s) thereof" described in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including any one or more selected from the group consisting of said components.

[0058] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0059]

[0060] According to one embodiment of the present invention, a negative active material for a lithium secondary battery comprises: a graphite-based base material; a low-crystalline carbon coating layer positioned on the surface of the graphite-based base material; and a conductive material included in the coating layer; wherein the low-crystalline carbon content is 1.0 to 10 wt%, and the acid conductive material content is 0.1 to 1.0 wt%.

[0061]

[0062] Hereinafter, a negative electrode active material for a lithium secondary battery and a negative electrode for a lithium secondary battery according to one embodiment of the present invention are described.

[0063]

[0064] 1-1. Negative active material

[0065] Figure 1 is a schematic diagram of a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0066] Referring to FIG. 1, a negative active material for a lithium secondary battery according to one embodiment of the present invention includes a graphite-based base material; a low-crystalline carbon coating layer positioned on the surface of the graphite-based base material; and a conductive material included in the coating layer.

[0067] The above graphite-based base material may be at least one of amorphous carbon materials such as natural graphite, artificial graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, petroleum coke, resin sintered body, carbon fiber, and pyrolytic carbon. Specifically, the graphite-based base material may be natural graphite or artificial graphite, and more specifically, artificial graphite.

[0068] The coating layer may be at least partially coated on the surface of the graphite-based base material by a coating material. Specifically, the coating layer may be coated on part or all of the surface of the graphite-based base material.

[0069] The above coating layer may be a layer composed of an amorphous carbon layer, a soft carbon layer, or a combination thereof.

[0070] The above coating layer may be formed by heat-treating a carbon material including at least one selected from among petroleum pitch, coal pitch, mesophase pitch, heavy oil, light oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, phenol resin, furan resin, furfuryl alcohol, polyacrylonitrile, cellulose, styrene, polyimide, epoxy resin, and glucose, and specifically, may be formed by heat-treating at least one selected from among petroleum pitch and coal pitch to a carbon material.

[0071] An amorphous carbon layer can be formed from the above carbon material at a carbonization temperature of 1,200°C or lower, and a soft carbon layer with mixed crystalline and amorphous phases can be formed in the range of 1,250 to 2,700°C. Accordingly, the coating layer can be a mixture of amorphous and crystalline phases.

[0072] The above coating layer may contain 1.0 to 10.0 wt% of a coating material (low-crystalline carbon) based on the weight of the negative active material, and specifically, 2.0 to 5.0 wt%, 2.5 to 3.5 wt%. The content of the coating material was measured through TGA analysis.

[0073] If the content of the coating material exceeds the upper limit, the coating layer becomes thick, which inhibits the movement of lithium ions and causes irreversibility, which reduces the initial efficiency and initial capacity, resulting in a deterioration of the battery life. If the content of the coating material exceeds the lower limit, the formation of the coating layer becomes uneven, which prevents the edges of the graphite from being sufficiently coated, causing a side reaction with the electrolyte, which results in a deterioration of the battery life.

[0074] The above coating layer may include a conductive material.

[0075] The conductive material may include at least one selected from the group consisting of carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives.

[0076] The conductive material may be included in an amount of 0.1 to 1.0 wt%, specifically 0.2 to 1.0 wt%, or 0.5 to 1.0 wt%, based on the total weight of the above negative active material.

[0077] In addition, the conductive material and the coating material (low-crystalline carbon) may be included in a weight ratio of 1:1 to 1:30, and specifically, may be included in a weight ratio of 1:1 to 1:20, 1:1 to 1:15, 1:1 to 1:10, 1:1 to 1:5, and 1:3 to 1:4.

[0078] If the content of the conductive material and the weight ratio of the conductive material and the coating material exceed the upper limit, the coating layer containing the conductive material becomes thick, which reduces the movement of lithium ions and deteriorates the lifespan of the battery. If the content of the conductive material exceeds the lower limit, it is difficult to achieve the desired effect of improving the conductivity and the resulting output characteristics of the battery.

[0079] The conductive material may be composed of at least one cluster. The cluster refers to a group of grains, and the conductive material may have the form of a single grain or a group of grains. Since the conductive material is composed of at least one cluster, it has the advantage of forming a conductive chain, thereby ensuring excellent electrical conductivity.

[0080] The above-mentioned conductive material may be positioned on the carbon coating layer, and may also be positioned partially on the graphite-based base material.

[0081] In one embodiment of the present invention, the negative active material may include at least one secondary particle.

[0082] The average particle diameter (D50) of the above negative active material may be in the range of 10.0 to 20.0 μm, and specifically, may be in the range of 15.0 to 20.0 μm, 15.0 to 18.5 μm, or 15.0 to 17.0 μm.

[0083] If the above D50 range exceeds the upper limit, there is a problem that dispersion occurs in the dispersion, and the electrode quality, such as the electrode rolling characteristics, is adversely affected, resulting in a deterioration of the electrochemical characteristics. In addition, the movement path of lithium ions within the negative electrode active material structure becomes longer, which reduces the rapid charging characteristics of the negative electrode active material, thereby offsetting the effect of improving electrical conductivity by the conductive agent. If the above D50 range exceeds the lower limit, there is a problem that the yield is reduced during the pulverization process, causing process problems.

[0084] The minimum particle size (Dmin) of the above negative active material may be 4.0 ㎛ or more, and specifically, may be 5.0 ㎛ or more, and may be in the range of 5.0 to 6.5 ㎛.

[0085] The D90 of the above cathode active material may be 20.0㎛ or more, and specifically may be in the range of 20.0 to 30.0㎛, 20.0 to 28.0㎛.

[0086] If the above D90 range exceeds the upper limit, there is a problem that dispersion occurs in the dispersion, which adversely affects electrode quality, such as electrode rolling characteristics, and thus electrochemical properties deteriorate. If the above D90 range exceeds the lower limit, there is a problem that yields in the pulverization process or sieving process are reduced.

[0087] The D90 / D10 of the above cathode active material may be in the range of 2.0 to 3.0, and specifically in the range of 2.4 to 2.7.

[0088] If the above D90 / D10 values ​​exceed the upper limit, the difference in particle size between the coarse and fine particles becomes excessively large, which causes problems in controlling uniform dispersion. If the above lower limit, the difference in particle size between the coarse and fine particles becomes excessively small, which causes problems in maintaining uniform contact between the particles.

[0089] In one embodiment, the specific surface area (SSA) of the negative active material is 0.5 to 1.5 m 2 / g range, specifically 0.6 to 1.3 m 2 / g, 0.8 to 1.2 m 2 / g, 0.8 to 1.1 m 2 / g can be in the range.

[0090] The above SSA surface area is determined by the shape of the graphite substrate and the properties of the surface coating layer. If the SSA surface area is too small, the affinity with the binder during electrode manufacturing is reduced, which reduces the stability of the electrode. If the SSA surface area is too large, the irreversible capacity increases, which may adversely affect the initial efficiency and discharge capacity. Since the SSA surface area affects the speed of the surface reaction when lithium ions enter and exit the carbon structure, it is desirable to control it within the above range.

[0091] In one embodiment, the tap density of the negative active material is 0.8 to 1.10 g / cm 3 Range, specifically 0.9 to 1.0 g / cm 3 , 0.92 to 1.0 g / cm 3 , 0.94 to 1.0 g / cm 3 It could be.

[0092] If the tap density of the above-mentioned negative active material is less than the lower limit, the rolling characteristics of the electrode are impaired, making it difficult to achieve the target energy density. If the tap density exceeds the upper limit, there is insufficient space for the electrolyte to be impregnated between the negative active materials after the electrode is rolled, which may result in a decrease in the discharge capacity and rapid charge characteristics.

[0093] In one embodiment, the pellet density of the negative active material may be 1.40 g / cc to 1.50 g / cc, specifically 1.42 g / cc to 1.50 g / cc, 1.44 g / cc to 1.50 g / cc.

[0094] By ensuring that the pellet density of the negative active material satisfies the above range, the electrochemical performance of the battery can be improved.

[0095] In one embodiment, the negative active material may satisfy the following relationship 1.

[0096] [Relationship 1]

[0097] 15.0 ≤ D50 / (ρ*SSA) ≤ 25.0

[0098] The D50 / (ρ*SSA) value of the above relational expression 1 may be 15.0 to 25.0, and specifically, 15.5 to 24.0, 16.0 to 23.5, 16.5 to 23.0, and 19.5 to 22.0.

[0099] Since the negative active material satisfies the range of the above relational expression 1, the average particle diameter, tap density, and specific surface area of ​​the negative active material are appropriately controlled, so that the electrochemical performance of the battery to which it is applied can be improved, which is desirable.

[0100] In one embodiment, the Id / Ig of the Raman spectrum measurement value of the negative active material may be 1.40 to 1.50, specifically 1.42 to 1.50, 1.44 to 1.48.

[0101] The above Id / Ig value is a measure of relative crystallinity, and is found in the range of 1580 to 1600 cm in Raman spectroscopy. -1 1350 to 1380 cm for the intensity value (Ig) of the peak in the absorption region -1 It is calculated as the ratio of the intensity values ​​(Id) of the peaks in the absorption region.

[0102] The crystallinity of the graphite negative electrode active material can be determined based on the intensity and width of the above two regions. The D peak is related to the amorphous state of the carbon structure, and the G peak indicates the graphite crystal structure of the sp2 hybrid orbital bond.

[0103] That is, as the Id / Ig value increases, the relative crystallinity decreases. That is, the crystallinity decreases because the amorphous structure of the graphite negative electrode active material increases (Id increases) and the crystalline molecular structure decreases (Ig decreases).

[0104]

[0105] The method for manufacturing the above negative active material may be as follows.

[0106] Specifically, it may include a step of preparing a graphite raw material; a first processing step of mixing the graphite raw material and a first additive to obtain an artificial graphite intermediate; and a second processing step of mixing the artificial graphite intermediate and a second additive to obtain artificial graphite.

[0107] First, the step of preparing the above graphite raw material may include the steps of pulverizing a carbonaceous material, shaping the pulverized carbonaceous material, and then graphitizing the pulverized carbonaceous material.

[0108] The above carbon-based material may be specifically one or more selected from coal-based coke, petroleum-based coke, metallurgical coke, and pitch coke.

[0109] The step of pulverizing the carbon-based material may be a step of pulverizing the carbon-based material to control the particle size of the carbon-based material. Specifically, the step of pulverizing the carbon-based material may be controlled by physical impact. The physical impact may utilize equipment that utilizes physical impact, such as a jet mill, an air classifier mill, or a roller mill. The jet mill directly pulverizes particles by utilizing collisions between particles, the air classifier pulverizes particles by utilizing air currents, and the roller mill pulverizes particles by introducing, compressing, and pulverizing particles between two or more rollers that rotate in opposite directions.

[0110] In one embodiment, the step of crushing the carbon-based material may include at least one crushing step. For example, the step of crushing the carbon-based material may include a coarse crushing step, a medium crushing step, and a fine crushing step. Including the at least one crushing step allows for more precise control of the particle size of the carbon-based material.

[0111] In one embodiment, the crushing step can crush the carbonaceous material to an average particle size (D50) of 1 mm or less, specifically 0.5 mm or less.

[0112] In one embodiment, the fine grinding step can grind the average particle size (D50) of the ground material that has gone through the coarse grinding step into a range of 2 to 30 μm, specifically 2 to 20 μm.

[0113] In this way, by controlling the particle size of the carbonaceous material within the aforementioned range, there is an advantage of realizing artificial graphite with appropriate physical properties and excellent electrochemical characteristics.

[0114] The step of graphitizing the above-mentioned pulverized carbonaceous material can be performed at a temperature of 2,800°C or higher, specifically, in a temperature range of 2,800 to 3,200°C. Specifically, the pulverized carbonaceous material with a controlled particle size can be graphitized within the aforementioned temperature range. If the graphitizing step is performed outside the above-mentioned range, there are problems of poor electrochemical properties and thermal shock to the equipment.

[0115] In one embodiment, the graphitizing step may be performed for a time period of at least 1 hour, specifically at least 2 hours. The graphitizing step may employ a heat treatment method using a known high-temperature furnace, such as an Acheson furnace, for example. After the graphitization process is completed, a small amount of oversized particles formed by agglomeration of the granulated product during the high-temperature graphitization process may be removed by sieving. By separating the oversized particles, it is possible to prevent them from affecting the processing performance of the material, such as slurry stability and coating performance.

[0116] In one embodiment, the step of graphitizing the pulverized carbonaceous material may include a pre-carbonization step of calcining at a lower temperature than the graphitizing step. The pre-carbonization step is a heat treatment step performed before the graphitization step.

[0117] In one embodiment, the preliminary carbonization step may be performed at a temperature range of 800 to 1,500°C. Specifically, the preliminary carbonization step may be performed at a temperature of 1,050 to 1,300°C, more specifically, 1,050 to 1,250°C. By performing the preliminary carbonization step within the aforementioned range, moisture and volatile matter within the pulverized carbon-based material are removed, thereby improving particle flowability and thereby improving density.

[0118] If the temperature range of the above-mentioned preliminary carbonization step exceeds the upper limit, the process time becomes longer, which leads to a decrease in productivity. If the temperature range of the above-mentioned preliminary carbonization step exceeds the lower limit, the specific surface area increases, the tap density decreases, and sufficient volatile matter may not be removed.

[0119] In one embodiment, the preliminary carbonization step may be performed for 2.0 hours or longer. Specifically, the preliminary carbonization step may be performed for 3 hours or longer, and more specifically, for 5.0 hours or longer. The preliminary carbonization time may refer to the maintenance time of the preliminary carbonization. By controlling the preliminary carbonization maintenance time within the aforementioned range, there is an advantage in that the apparent density and the tap density of the artificial graphite are improved. If the preliminary carbonization maintenance time is outside the aforementioned range, there is a problem in that the apparent density and the tap density of the finally manufactured artificial graphite are lowered.

[0120] In one embodiment, the pre-carbonization step may be performed at a heating rate ranging from 5 to 20°C / min. Specifically, the pre-carbonization step may be performed at a heating rate ranging from 5 to 15°C / min. More specifically, the pre-carbonization step may be performed at a heating rate ranging from 5 to 10°C / min.

[0121] When the above-mentioned temperature increase rate range satisfies the aforementioned range, there is an advantage of a reduced specific surface area. When the above-mentioned temperature increase rate range does not satisfy the aforementioned range, there is a problem of an increased specific surface area, resulting in a decrease in powder flowability between processes and an increase in process time.

[0122]

[0123] Next, a step of treating the surface of the graphite raw material can be performed.

[0124] In one embodiment of the present invention, the step of treating the surface of the graphite raw material may include a first treatment step of mixing the graphite raw material with a first additive to obtain an artificial graphite intermediate; and a second treatment step of mixing the artificial graphite intermediate with a second additive to obtain artificial graphite.

[0125] The first additive is a binder, and the second additive is a conductive agent.

[0126] The above binder may include at least one selected from petroleum pitch, coal pitch, mesophase pitch, heavy oil, light oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, phenol resin, furan resin, furfuryl alcohol, polyacrylonitrile, cellulose, styrene, polyimide, epoxy resin, and glucose.

[0127] The above binder can be mixed in a range of 0.1 to 20.0 wt% based on the total weight of the graphite raw material and the binder, and specifically, can be mixed in a range of 1 to 10 wt%, 1 to 6 wt%.

[0128] The conductive material may include at least one selected from the group consisting of carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. Meanwhile, the conductive material may be a particle-shaped material, and may have an average particle size of 0.03 to 3 μm, specifically 0.1 to 1 μm.

[0129] The above conductive material can be mixed in a range of 0.1 to 1.0 wt%, specifically 0.2 to 1.0 wt%, 0.5 to 1.0 wt%, based on the total weight of the graphite raw material and the conductive material.

[0130]

[0131] When the above binder and the above conductive material are mixed within the above weight range, it is preferable to produce the artificial graphite desired in the present invention.

[0132]

[0133] In the present invention, the graphite raw material, artificial graphite intermediate, and conductive material may be particle materials, and their specific characteristics will be described in detail later.

[0134] Meanwhile, the average particle size of the graphite raw material may be 10 to 15 μm, and specifically, may be about 13 μm. When the average particle size of the graphite raw material satisfies the above conditions, it is preferable because it can improve the electrochemical performance, such as the output, of the battery using the final graphite-based negative electrode active material.

[0135]

[0136] In one embodiment of the present invention, the first processing step may be a step of mixing a binder as a first additive with a graphite raw material to obtain an artificial graphite intermediate, and the second processing step may be a step of mixing a conductive agent as a second additive with the artificial graphite intermediate to obtain artificial graphite.

[0137] In another embodiment of the present invention, the first processing step is a step of mixing and stirring a mixture of a graphite raw material and the binder, thereby coating the binder on the surface of the graphite raw material. Specifically, a shear stress is applied to the graphite raw material and the binder to form a binder coating layer, thereby forming an artificial graphite precursor.

[0138] In another embodiment of the present invention, the first processing step may be performed by one or more methods selected from a high speed mixer, Air Classifying milling, Spheronizing milling, Grinding milling, Mechanofusion milling, Planetary milling, Hybridization milling, or Shape milling.

[0139] In another embodiment of the present invention, the first treatment step may be performed at a stirring speed in the range of 2000 to 3000 rpm for 10 to 30 minutes.

[0140] In another embodiment of the present invention, after completion of the first treatment step, a heat treatment step of heating the obtained material may be further included. The heat treatment may be performed in a reducing atmosphere consisting of hydrogen, nitrogen, argon, or a mixed gas thereof at a temperature of 600 to 1500°C, thereby forming an artificial graphite precursor.

[0141] In another embodiment of the present invention, the second processing step may utilize equipment that is mounted on a rotor and has rotating blades that apply shear force to the particles to induce fusion between particle surfaces.

[0142] In another embodiment of the present invention, the process may be performed by one or more methods selected from nobilta milling, mechanofusion milling, shaker milling, planetary milling, attritor milling, disk milling, shape milling, nauta milling, or high speed mixing.

[0143] In another embodiment of the present invention, the second treatment step may be performed by mixing at a first stirring speed and then increasing the stirring speed to a second stirring speed.

[0144] In one embodiment of the present invention, the first stirring speed may be in the range of 200 to 500 rpm, specifically 250 to 350 rpm, and the second stirring speed may be in the range of 600 to 1000 rpm, specifically 700 to 900 rpm.

[0145] In one embodiment of the present invention, mixing may also be performed at the first stirring speed for 2 to 5 minutes, and at the second stirring speed for 6 to 15 minutes.

[0146] In another embodiment of the present invention, in the second processing step, if the stirring speed and / or time range is lower than the above, it is difficult for the conductive material to be effectively coated on the surface of the graphite raw material, and if the stirring speed and / or time range is higher than the above, cracks and breakage of the graphite raw material and conductive material particles may occur.

[0147]

[0148] 2-1. Cathode for lithium secondary batteries

[0149] The present inventors have conducted repeated research to improve the output characteristics of batteries. As a result, they have discovered that the battery characteristics can be improved by sufficiently increasing the adhesive strength between the negative electrode current collector and the negative electrode active material layer, and additionally appropriately controlling various related physical properties. Furthermore, they have discovered that the adhesive strength and various related physical properties can be easily derived by appropriately controlling the physical properties of the negative electrode active material, and in particular, by using a carbon-based conductive material. Thus, the present invention has been completed.

[0150] A negative electrode for a lithium secondary battery according to another embodiment of the present invention comprises a current collector; and a negative electrode active material layer disposed on the current collector, wherein the negative electrode active material layer comprises the above-described negative electrode active material.

[0151] The above negative electrode for a lithium secondary battery satisfies the following relationship 4.

[0152] [Relationship 4]

[0153] 10.0 ≤ AS / (ρ*SSA) 20.0

[0154] Here, AS is the adhesion between the current collector and the negative electrode active material layer (unit: gf / cm), and ρ is the tap density of artificial graphite (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.

[0155] The AS / (ρ*SSA) value of the above relational expression 4 may be 10.0 to 20.0, and specifically, 10.5 to 20.0, 11.0 to 20.0, or 12.5 to 20.0.

[0156] Meanwhile, the adhesive strength between the current collector and the negative electrode active material layer may be 7.0 to 20.0 gf / cm, and specifically, 7.0 to 18.0 gf / cm, 8.5 to 17.5 gf / cm, or 10.0 to 16.0 gf / cm.

[0157] The inventors of the present invention have repeatedly studied the optimal relationship between a positive electrode active material and a negative electrode that can improve the characteristics of a battery, such as the charging output, when artificial graphite is used as a negative electrode active material. As a result, they have found that when the adhesive strength, tap density of the active material, and specific surface area satisfy the range of the above relational expression 4, the battery characteristics are significantly improved.

[0158] This appears to be because, by placing a conductive material with improved conductivity on the graphite surface, the conductive material and binder within the electrode can be uniformly distributed during the pressing process, which improves electrode adhesion and electrical conductivity, thereby further improving the bonding strength between the current collector and the negative electrode active material layer.

[0159] In this specification, the adhesive strength (gf / mm) between the current collector and the negative electrode active material layer is a value derived by performing an adhesive strength test under a compression density range of 1.4 g / cc to 1.8 g / cc of a negative electrode for a lithium secondary battery using the following method.

[0160] First, the manufactured cathode was cut into a size of 20 mm in width and 100 mm in length and prepared. Double-sided tape with an area of ​​18 mm in width and 80 mm in length was attached to a slide glass with an area of ​​25 mm in width and 100 mm in length. After attaching the prepared electrode onto the double-sided tape, it was lightly pressed 10 times with a hand roller and mounted on a UTM (1 kgf load cell) to peel off the current collector and measure the 90-degree peel strength.

[0161]

[0162] Hereinafter, the remaining configuration of the negative electrode for a lithium secondary battery according to one embodiment of the present invention will be described in more detail.

[0163] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0164] The above negative active material layer also includes a binder and may optionally further include a conductive material.

[0165] The above binder serves to improve the adhesion between negative electrode active material particles and the adhesive strength between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the negative electrode active material layer.

[0166] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the negative electrode active material layer.

[0167] A negative electrode for a lithium secondary battery according to one embodiment of the present invention can be manufactured according to a conventional negative electrode manufacturing method, except that the negative electrode active material described above is used.

[0168] Specifically, the composition for forming a negative electrode active material layer, including the aforementioned negative electrode active material and optionally a binder, a conductive agent, and a solvent, can be applied onto a negative electrode current collector, followed by rolling and drying. At this time, the types and contents of the negative electrode active material, binder, and conductive agent are as described above.

[0169] The solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the negative electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the negative electrode.

[0170] Alternatively, the negative electrode may be manufactured by casting the composition for forming the negative electrode active material layer on a separate support, then peeling the film from the support and laminating the resulting film on a negative electrode current collector.

[0171]

[0172] According to another embodiment of the present invention, a negative active material for a lithium secondary battery comprises a graphite-based base material; a low-crystalline carbon coating layer positioned on the surface of the graphite-based base material; and a conductive material included in the coating layer, and satisfies the following equation 2:

[0173] [Relationship 2]

[0174] 0.820 ≤ Span*ρ / SSA ≤ 1.1

[0175] (Here, Span is (D90-D10) / D50, ρ is the tap density of the negative electrode active material (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.)

[0176]

[0177] Hereinafter, a negative electrode active material for a lithium secondary battery and a negative electrode for a lithium secondary battery according to another embodiment of the present invention are described.

[0178]

[0179] 1-2. Negative active material

[0180] Descriptions of the graphite-based base material, coating layer, and conductive material of the negative electrode active material for a lithium secondary battery according to another embodiment of the present invention are as described above, and therefore will be omitted.

[0181] The above-mentioned conductive material and the above-mentioned coating material (low-crystalline carbon) may be included in a weight ratio of 1:1 to 1:5, and specifically, may be included in a weight ratio of 1:1 to 1:4, 1:2 to 1:4, or 1:3 to 1:4.

[0182] If the content of the conductive material and the weight ratio of the conductive material and the coating material exceed the upper limit, the coating layer containing the conductive material becomes thick, which reduces the movement of lithium ions and deteriorates the lifespan of the battery. If the content of the conductive material exceeds the lower limit, it is difficult to achieve the desired effect of improving the conductivity and the resulting output characteristics of the battery.

[0183] In one embodiment, the negative active material may satisfy the following relationship 2.

[0184] [Relationship 2]

[0185] 0.820 ≤ Span*ρ / SSA ≤ 1.1

[0186] (Here, Span is (D90-D10) / D50, ρ is the tap density of the negative electrode active material (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.)

[0187] The Span*ρ / SSA value of the above relational expression 2 may be 0.820 to 1.1, and specifically, 0.820 to 1.08, 0.820 to 1.04, and 0.821 to 1.0.

[0188] Since the negative active material satisfies the range of the above relational expression 2, the span, tap density, and specific surface area of ​​the negative active material are appropriately controlled, so that the electrochemical performance of the battery to which it is applied can be improved, which is desirable.

[0189] The above negative active material can satisfy the following relationship 1.

[0190] [Relationship 1]

[0191] 6.0 ≤ D50 / (ρ*SSA) ≤ 20.0

[0192] (Here, D50 is the average particle size of the negative electrode active material (unit: ㎛), ρ is the tap density of the negative electrode active material (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.)

[0193] The D50 / (ρ*SSA) value of the above relational expression 1 may be 6.0 to 20.0, and specifically, 8.0 to 19.0, 9.0 to 18.0, or 9.5 to 17.5.

[0194] The above negative active material can satisfy the following relationship 3.

[0195] [Relationship 3]

[0196] 10.0 ≤ D50 / ρ ≤ 20.0

[0197] (Here, D50 is the average particle size of the negative electrode active material (unit: ㎛), ρ is the tap density of the negative electrode active material (unit: g / cm 3 )am.)

[0198] The D50 / ρ value of the above relational expression 3 may be 10.0 to 20.0, and specifically, 11.0 to 19.0, 11.5 to 18.5, and 12.0 to 18.0.

[0199] It is preferable that the negative active material satisfies the range of the above equation 1 and / or equation 3, so that the average particle diameter, tap density, and specific surface area of ​​the negative active material are appropriately controlled, thereby improving the electrochemical performance of a battery to which it is applied.

[0200] In one embodiment of the present invention, the negative active material may include at least one secondary particle.

[0201] The average particle diameter (D50) of the above negative active material may be in the range of 10.0 to 20.0 μm, and specifically, may be in the range of 10.5 to 18.0 μm, 11.0 to 17.0 μm, or 11.2 to 17.0 μm.

[0202] If the above D50 range exceeds the upper limit, there is a problem that dispersion occurs in the dispersion, which adversely affects electrode quality, such as electrode rolling characteristics, and thus deteriorates electrochemical properties. If the above D50 range exceeds the lower limit, there is a problem that yield is reduced during the pulverization process, which causes process problems.

[0203] The specific surface area (SSA) of the above negative active material is 0.5 to 1.5 m 2 / g range, specifically 0.7 to 1.4 m 2 / g, 0.8 to 1.4 m 2 / g, 0.9 to 1.4 m 2 / g can be in the range.

[0204] The above-mentioned specific surface area is determined by the shape of the graphite base material and the properties of the surface coating layer. If the SSA specific surface area is too small, the affinity with the binder during electrode manufacturing is reduced, which compromises the stability of the electrode. If it is too large, the irreversible capacity increases, which may adversely affect the initial efficiency and discharge capacity. Since the SSA specific surface area affects the speed of the surface reaction when lithium ions enter and exit the carbon structure, it is desirable to control it within the above range.

[0205] The tap density of the above negative active material is 0.8 to 1.10 g / cm 3 It may range from 0.85 to 1.05 g / cm2 specifically. 3 , 0.87 to 1.00 g / cm 3It could be.

[0206] If the tap density of the above-mentioned negative active material is less than the lower limit, the rolling characteristics of the electrode are impaired, making it difficult to achieve the target energy density. If the tap density exceeds the upper limit, there is insufficient space for the electrolyte to be impregnated between the negative active materials after the electrode rolling, which may result in a decrease in the discharge capacity and rapid charge characteristics.

[0207] The orientation of the above negative active material (I 004 / I 110 ) may be 1.5 to 3.0, specifically 1.5 to 2.8, 1.7 to 2.5. The orientation refers to the ratio of the peak intensity of the (110) plane of the graphite crystal to the orientation peak intensity of the (004) plane in the XRD pattern obtained from X-ray diffraction measurement.

[0208] If the orientation degree exceeds the upper limit of the aforementioned range, it may hinder smooth impregnation of the electrolyte, increase mobility, and hinder smooth insertion and de-insertion of lithium ions, which may result in a reduction in battery life. If the orientation degree exceeds the lower limit of the aforementioned range, the disordered orientation of the negative active material during electrode formation may increase, hindering the smooth insertion and de-insertion of lithium ions, which may result in a reduction in discharge capacity.

[0209] The minimum particle size (Dmin) of the above negative active material may be greater than 3.0 μm, and specifically may be 3.5 μm or more, and in the range of 3.5 to 6.5 μm.

[0210] The D90 of the above negative active material may be 20.0㎛ or more, and specifically may be in the range of 20.0 to 30.0㎛, 20.0 to 28.5㎛.

[0211] If the above D90 range exceeds the upper limit, there is a problem that dispersion occurs in the dispersion, which adversely affects the electrode quality, such as the electrode rolling characteristics, and thus the electrochemical characteristics deteriorate. If the above D90 range exceeds the lower limit, there is a problem that the yield in the pulverization process or the sieving process decreases.

[0212] D of the above cathode active material 90 -D 10 The silver may be in the range of 11.0 to 18.0 μm, and specifically in the range of 12.0 to 17.5 μm, 12.5 to 17.5 μm, or 13.5 to 17.5 μm.

[0213] Above D 90 -D 10 If the value of D exceeds the upper limit, there is a problem in controlling the dispersion so that it is uniform when the difference in particle size between the particles and fine particles is excessively large. 90 - D 10 If the value exceeds the lower limit, the particle size difference between the coarse and fine particles becomes excessively small, causing problems in maintaining uniform contact between the particles.

[0214]

[0215] The method for manufacturing the above negative active material may be as follows.

[0216] Specifically, it may include a step of preparing a graphite raw material; a first processing step of mixing the graphite raw material and a first additive to obtain an artificial graphite intermediate; and a second processing step of mixing the artificial graphite intermediate and a second additive to obtain artificial graphite.

[0217] First, the step of preparing the above graphite raw material may include the steps of pulverizing a carbonaceous material, shaping the pulverized carbonaceous material, and then graphitizing the pulverized carbonaceous material.

[0218] Descriptions of the step of pulverizing the carbonaceous material, the step of graphitizing the pulverized carbonaceous material, and the preliminary carbonization step of firing at a lower temperature than the graphitizing step prior to the step of graphitizing the pulverized carbonaceous material are as described above, and therefore will be omitted.

[0219]

[0220] Next, a step of treating the surface of the graphite raw material can be performed.

[0221] In one embodiment of the present invention, the step of treating the surface of the graphite raw material may include a first treatment step of mixing the graphite raw material and a first additive to obtain an artificial graphite intermediate; and a second treatment step of mixing the artificial graphite intermediate and a second additive to obtain artificial graphite.

[0222] The first additive and the second additive are at least one selected from among a conductive material and a binder, the first additive and the second additive are different materials, and the first additive and the second additive are neither a conductive material nor a binder at the same time.

[0223] Specifically, in the present invention, when the first additive is a conductive agent, the second additive may be a binder, and when the first additive is a binder, the second additive may be a conductive agent.

[0224] Descriptions of the types and weights of the above binders and conductive materials are as described above, so they will be omitted.

[0225]

[0226] In the present invention, the graphite raw material, artificial graphite intermediate, and conductive material may be particle materials, and their specific characteristics will be described in detail later.

[0227]

[0228] In one embodiment of the present invention, the first processing step may be a step of mixing a conductive agent as a first additive with a graphite raw material to obtain an artificial graphite intermediate, and the second processing step may be a step of mixing a binder as a second additive with the artificial graphite intermediate to obtain artificial graphite.

[0229] In one embodiment of the present invention, specifically, in the first treatment step, the conductive material may be coated on part or all of the surface of the graphite raw material to form an artificial graphite intermediate, and in the second treatment step, the binder may be coated on part or all of the surface of the artificial graphite intermediate.

[0230] In one embodiment of the present invention, the first processing step is a step of applying shear stress to a mixture including a graphite raw material and the conductive material, thereby inducing fusion between the surfaces of the graphite raw material particles and the conductive material particles. The graphite raw material and the conductive material may be mixed by loading them into equipment such as a milling machine or a mixer and stirring them.

[0231] In one embodiment of the present invention, the first processing step may utilize equipment that is mounted on a rotor and has a rotating blade that applies a shear force to the particles to induce fusion between particle surfaces.

[0232] In one embodiment of the present invention, the process may be performed by one or more methods selected from nobilta milling, mechanofusion milling, shaker milling, planetary milling, attritor milling, disk milling, shape milling, nauta milling, or high speed mixing.

[0233] In one embodiment of the present invention, the first processing step can be performed by mixing at a rotation speed of the first blade and then increasing the rotation speed of the blade to a rotation speed of the second blade.

[0234] In one embodiment of the present invention, the rotation speed of the first blade may be in the range of 200 to 500 rpm, specifically 250 to 350 rpm, and the rotation speed of the second blade may be in the range of 600 to 1000 rpm, specifically 700 to 900 rpm.

[0235] In one embodiment of the present invention, mixing may also be performed for 2 to 5 minutes at the rotation speed of the first blade, and for 6 to 15 minutes at the rotation speed of the second blade.

[0236] In one embodiment of the present invention, in the first processing step, if the rotation speed and / or time range of the blade is lower than the above range, it is difficult for the conductive material to be effectively coated on the surface of the graphite raw material, and if the rotation speed and / or time range of the blade is higher than the above range, cracks and breakage of the graphite raw material and conductive material particles may occur.

[0237] In one embodiment of the present invention, the second treatment step is a step of mixing and stirring a mixture of an artificial graphite intermediate and the binder, thereby coating the binder on the surface of the artificial graphite intermediate. Specifically, a shear stress is applied to the artificial graphite intermediate and the binder to form a binder coating layer.

[0238] In one embodiment of the present invention, the second processing step may be performed by one or more methods selected from a high speed mixer, Air Classifying milling, Spheronizing milling, Grinding milling, Mechanofusion milling, Planetary milling, Hybridization milling, or Shape milling.

[0239] In one embodiment of the present invention, the second processing step may be performed for 10 to 30 minutes at a rotation speed of the blade in the range of 2000 to 3000 rpm.

[0240] In one embodiment of the present invention, after completion of the second treatment step, a heat treatment step of heating the obtained material may be further included. The heat treatment may be performed in a reducing atmosphere consisting of hydrogen, nitrogen, argon, or a mixed gas thereof, at a temperature of 600 to 1500°C.

[0241]

[0242] In another embodiment of the present invention, the first processing step may be a step of mixing a binder as a first additive with a graphite raw material to obtain an artificial graphite intermediate, and the second processing step may be a step of mixing a conductive agent as a second additive with the artificial graphite intermediate to obtain artificial graphite.

[0243] In another embodiment of the present invention, the first processing step is a step of mixing and stirring a mixture of a graphite raw material and the binder, thereby coating the binder on the surface of the graphite raw material. Specifically, a shear stress is applied to the graphite raw material and the binder to form a binder coating layer, thereby forming an artificial graphite precursor.

[0244] In another embodiment of the present invention, the first processing step may be performed by one or more methods selected from a high speed mixer, Air Classifying milling, Spheronizing milling, Grinding milling, Mechanofusion milling, Planetary milling, Hybridization milling, or Shape milling.

[0245] In another embodiment of the present invention, the first treatment step may be performed for 10 to 30 minutes at a rotational speed of the blade in the range of 2000 to 3000 rpm.

[0246] In another embodiment of the present invention, after completion of the second treatment step, a heat treatment step of heating the obtained material may be further included. The heat treatment may be performed in a reducing atmosphere consisting of hydrogen, nitrogen, argon, or a mixed gas thereof at a temperature of 600 to 1500°C, thereby forming an artificial graphite precursor.

[0247] In another embodiment of the present invention, the second processing step may utilize equipment that is mounted on a rotor and has rotating blades that apply shear force to the particles to induce fusion between particle surfaces.

[0248] In another embodiment of the present invention, the process may be performed by one or more methods selected from nobilta milling, mechanofusion milling, shaker milling, planetary milling, attritor milling, disk milling, shape milling, nauta milling, or high speed mixing.

[0249] In another embodiment of the present invention, the second processing step can be performed by mixing at the rotation speed of the first blade and then increasing the rotation speed of the blade to the rotation speed of the second blade.

[0250] In one embodiment of the present invention, the rotation speed of the first blade may be in the range of 200 to 500 rpm, specifically 250 to 350 rpm, and the rotation speed of the second blade may be in the range of 600 to 1000 rpm, specifically 700 to 900 rpm.

[0251] In one embodiment of the present invention, mixing may also be performed for 2 to 5 minutes at the rotation speed of the first blade, and for 6 to 15 minutes at the rotation speed of the second blade.

[0252] In another embodiment of the present invention, in the second processing step, if the rotation speed and / or time range of the blade is lower than the above range, it is difficult for the conductive material to be effectively coated on the surface of the graphite raw material, and if the rotation speed and / or time range of the blade is higher than the above range, cracks and breakage of the graphite raw material and conductive material particles may occur.

[0253]

[0254] 2-2. Cathode for lithium secondary batteries

[0255] According to another embodiment of the present invention, a negative electrode for a lithium secondary battery comprises a current collector; and a negative electrode active material layer disposed on the current collector, wherein the negative electrode active material layer comprises the above-described negative electrode active material, and the negative electrode for a lithium secondary battery satisfies the following relational expression 4.

[0256] [Relationship 4]

[0257] 7.0 ≤ AS / (ρ*SSA) ≤ 15.0

[0258] (Here, AS is the adhesive strength between the current collector and the negative electrode active material layer (unit: gf / cm), and ρ is the tap density of artificial graphite (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.)

[0259] The AS / (ρ*SSA) value of the above relational expression 4 may be 7.0 to 15.0, and specifically, 7.5 to 13.0, 7.8 to 12.5, and 8.0 to 12.0.

[0260] Meanwhile, the adhesive strength between the current collector and the negative electrode active material layer may be 7.0 to 20.0 gf / cm, and specifically, 8.0 to 16.0 gf / cm, 9.0 to 13.0 gf / cm.

[0261] The inventors of the present invention have repeatedly studied the optimal relationship between a positive electrode active material and a negative electrode that can improve the characteristics of a battery, such as the charging output, when artificial graphite is used as a negative electrode active material. As a result, they have found that when the adhesive strength, tap density of the active material, and specific surface area satisfy the range of the above relational expression 4, the battery characteristics are significantly improved.

[0262] This appears to be because, by placing a conductive material with improved conductivity on the graphite surface, the conductive material and binder within the electrode can be uniformly distributed during the pressing process, which improves electrode adhesion and electrical conductivity, thereby further improving the bonding strength between the current collector and the negative electrode active material layer.

[0263] In this specification, the adhesive strength (gf / mm) between the current collector and the negative electrode active material layer is a value derived by performing an adhesive strength test under a compression density range of 1.4 g / cc to 1.8 g / cc of the negative electrode for a lithium secondary battery, and a description of the specific method for this is omitted as it is as described above.

[0264]

[0265] 3. Lithium secondary battery

[0266] Another embodiment of the present invention provides a lithium secondary battery comprising the aforementioned negative electrode. The lithium secondary battery according to another embodiment of the present invention exhibits excellent output and lifespan characteristics due to the inclusion of the aforementioned negative electrode.

[0267] The lithium secondary battery may more specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0268] The above cathode is as described above.

[0269] In addition, the lithium secondary battery may optionally further include a battery container that houses an electrode assembly of a positive electrode, a negative electrode, and a separator, and a sealing member that seals the battery container.

[0270] The above positive electrode includes a current collector and a positive electrode active material layer formed on the current collector.

[0271] As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used. Specifically, one or more of a composite oxide of lithium and a metal such as cobalt, manganese, nickel, or a combination thereof can be used, and a specific example thereof is a compound represented by one of the following chemical formulas. Li a A 1-b R bD2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li a E 1-b R b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE 2-b R b O 4-c D c (In the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b R c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c Co b R c O 2-α Z α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Co b R c O 2-α Z2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-b-c Mn b R c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α ≤ 2); Li a Ni 1-b-c Mn b R c O 2-α Z α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Lia Ni 1-b-c Mn b R c O 2-α Z2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni b E c G d O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5 and 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d G e O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1); Li a NiG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); and LiFePO4.

[0272] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0273] The compound having a coating layer on the surface thereof may be used, or a compound having the compound and a coating layer may be mixed and used. The coating layer may include, as a coating element compound, an oxide, a hydroxide, an oxyhydroxide, an oxycarbonate, or a hydroxycarbonate of the coating element of the coating element. The compounds forming the coating layer may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer forming process may use any coating method as long as it can coat the compound with these elements without adversely affecting the properties of the positive electrode active material (for example, spray coating, dipping, etc.), and since this is well understood by those working in the relevant field, a detailed description thereof will be omitted.

[0274] The above positive electrode active material layer also includes a binder and a conductive material.

[0275] The binder improves the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof, but is not limited thereto. The above binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0276] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types may be used among these, but the present invention is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0277] The above anode can be manufactured according to a conventional anode manufacturing method.

[0278] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, including a positive electrode active material and optionally a binder, a conductive agent, or a solvent, onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0279] The solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0280] Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the resulting film on a positive electrode current collector by peeling it off from the support.

[0281] The above separator separates the positive and negative electrodes and provides a passage for lithium ions to move. Any separator commonly used as a separator in lithium secondary batteries can be used without any particular restrictions. In particular, a separator having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0282] The above electrolyte may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0283] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0284] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0285] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0286] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0287]

[0288] Hereinafter, embodiments of the present invention will be described in more detail through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0289]

[0290] Experimental Example 1

[0291] (Manufacturing of artificial graphite)

[0292] Manufacturing Example 1 (graphite raw material)

[0293] (Crushing / Formulating Stage)

[0294] Coal-based coke was coarsely crushed with a pin mill and finely crushed with a crusher to produce coke powder.

[0295] For the coke powder obtained after the above crushing, a sizing process was performed to form particles and remove fine powder, thereby manufacturing sizing coke with an average particle size of approximately 13 μm.

[0296]

[0297] (graphitization stage)

[0298] The above-mentioned standardized coke was placed in a crucible, placed in a graphitization furnace, heated to 2,800°C or higher, and ultra-high temperature graphitization was performed to manufacture artificial graphite with controlled average particle size.

[0299]

[0300] Manufacturing Example 2 (B13_M3%, graphite raw material coated with pitch)

[0301] The artificial graphite material having an average particle diameter (D50) of 13 μm manufactured in the above Manufacturing Example 1 was mixed with petroleum-based pitch. Here, the artificial graphite material and the petroleum-based pitch were mixed so that the residual carbon content of the final obtained artificial graphite product was 3 wt%.

[0302] In the present invention, the amount of residual carbon in the final product artificial graphite was measured through TGA analysis.

[0303] The above artificial graphite material and petroleum-based needle pitch mixture were placed in a high speed mixer and stirred at a stirring speed of approximately 2700 rpm for 20 minutes to produce artificial graphite coated with petroleum-based needle pitch.

[0304]

[0305] Example 1 (B13_M3%_S0.8)

[0306] The petroleum-based needle pitch-coated artificial graphite manufactured in the above Manufacturing Example 2 was mixed with carbon black. Here, the carbon black was mixed to be 0.8 wt% based on the total weight.

[0307] A mixture of graphite material and carbon black was placed in a nobilta milling machine and stirred at a stirring speed of 300 rpm for 3 minutes, then the stirring speed was changed to 800 rpm and stirred for 10 minutes. Next, heat treatment was performed at 1200°C under a reducing atmosphere to produce the final product, artificial graphite.

[0308]

[0309] Example 2 (B13_M3%_S0.6)

[0310] Artificial graphite was manufactured in the same manner as in Example 1, except that the carbon black was used in an amount of 0.6 wt% based on the total weight.

[0311]

[0312] Example 3 (B13_M3%_S0.4)

[0313] Artificial graphite was manufactured in the same manner as in Example 1, except that the carbon black was used in an amount of 0.4 wt% based on the total weight.

[0314]

[0315] Example 4 (B13_M3%_S0.2)

[0316] Artificial graphite was manufactured in the same manner as in Example 1, except that the carbon black was used in an amount of 0.2 wt% based on the total weight.

[0317]

[0318] (Manufacturing of cathode)

[0319] A slurry of an anode active material was prepared by mixing 95.6 wt% of the artificial graphite manufactured in the above manufacturing example or example, 1.1 wt% of carboxymethyl cellulose, 2.3 wt% of styrene butadiene rubber, and 1 wt% of Super P conductive agent in a distilled water solvent. The slurry of the anode active material was applied to a copper (Cu) current collector, dried at 80°C for 5 minutes, and pressed in a roll press. Thereafter, the slurry was vacuum-dried in a vacuum oven at 100 to 120°C for 12 hours, thereby preparing an anode in which a layer of the anode active material was formed on the current collector. After vacuum-drying, the electrode density of the anode was set to 1.55 g / cc.

[0320]

[0321] (Manufacturing of lithium secondary batteries)

[0322] Lithium metal (Li-Metal) was used as the negative electrode and counter electrode manufactured by the above-mentioned method, and as the electrolyte, a solution of 1 mol of LiPF6 dissolved in ethylene carbonate (EC) : ethyl methyl carbonate (EMC) at a volume ratio of 2:8 and vinylene carbonate (0.5 wt%) was used.

[0323] Using each of the above components, a half coin cell of the 2032 coin cell type was manufactured according to a conventional manufacturing method.

[0324]

[0325] <Evaluation Example 1>: Analysis of the physical properties of artificial graphite

[0326] (1) Size analysis

[0327] The particle sizes Dmin, D10, D50, D90, and Dmax of the artificial graphite manufactured in the above manufacturing examples and examples were measured using the laser diffraction method, and were the particle sizes corresponding to the minimum, 10%, 50%, 90%, and maximum values ​​of the accumulated volume of the artificial graphite, respectively.

[0328] The results of particle size analysis are shown in Table 1.

[0329] (2) Tap density (g / cm) 3 )

[0330] The tap density of the artificial graphite manufactured in the above manufacturing examples and examples was measured using the BeDensi T3 model from Betersize. 15 g of the sample was measured using a scale, filled into a chamber, and the weight was input to obtain the weight-to-volume ratio.

[0331] The results of the tap density analysis are shown in Table 1.

[0332] (3) Specific Surface Area (SSA) (m 2 / g)

[0333] The specific surface area refers to the total surface area of ​​a material per unit mass, and was measured using the SSA method (Surface Area and Porosity Analyzer) (Micromeritics, TriStar 3030 Plus).

[0334] The results of the specific surface area analysis of the artificial graphite manufactured in the above manufacturing examples and examples are shown in Table 1.

[0335] (4) Pellet density analysis

[0336] Pellet density was measured using Carver 4350. For pellet density analysis, 1 g of sample was placed in a pellet die (Φ12.94), 2 tons of pressure was applied, and the pellet die height was measured after 30 seconds to calculate the pellet density.

[0337] The results of pellet density analysis are shown in Table 1.

[0338]

[0339] <Evaluation Example 2>: Evaluation of cathode properties

[0340] (1) Measurement of adhesion between the current collector and the negative electrode active material layer

[0341] The adhesive strength between the current collector and the negative electrode active material layer of the negative electrode manufactured using the artificial graphite manufactured in the above manufacturing examples and examples was measured.

[0342] To measure the adhesive strength more specifically, first, the manufactured negative electrode was cut into a size of 20 mm in width and 100 mm in length and prepared. Double-sided tape with an area of ​​18 mm in width and 80 mm in length was attached to a slide glass with an area of ​​25 mm in width and 100 mm in length. After attaching the prepared electrode on the double-sided tape, it was lightly pressed 10 times with a hand roller, and this was mounted on a UTM (1 kgf load cell) and the current collector was peeled off at a speed of 300 mm / min, and the 90-degree peel strength was measured. The results are shown in Table 1 below.

[0343] Microtrac particle size (㎛)Tap density SSAPellet density Adhesion ~5μm Dmin D1 D10 D50 D90 Dmax Span D90 / D10 (g / cc) (㎡ / g) g / cc gf / cm Manufacturing example 1 (graphite raw material) 1.14.24.97.512.519.839.01.02.61.210.91.556.6 Manufacturing example 2 (B13_M3%) 0.06.06.810.816.627.262.21.02.60.950.91.4210.6 Example 1(B13_M3%_S0.8%)066.210.416.927.762.21.022.660.9911.4811.5Example 2(B13_M3%_S0.6%)056.69.815.523.8440.92.430.980.81.4610.1Example 3(B13_M3%_S0.4%)066.910.516.726.962.20.982.560.980.81.4615.6Example 4(B13_M3%_S0.2%)067.410.615.521.9370.732.070.960.81.487.7

[0344]

[0345] Referring to Table 1 above, it can be confirmed that the artificial graphite manufactured in Examples 1 to 4 has a relatively large average particle diameter (D50) of 15.5 to 16.9 ㎛ compared to Manufacturing Example 1, a minimum particle diameter (Dmin) of 5.0 ㎛ or more, and a small tap density and specific surface area.

[0346] In addition, it can be confirmed that Examples 1 and 3 have relatively larger average particle diameters (D50) than Manufacturing Example 2, and Examples 2 to 4 have smaller specific surface areas than Manufacturing Example 2.

[0347]

[0348] The calculated values ​​of equations 1 to 4 considering the adhesive strength of the artificial graphite manufactured in the above manufacturing examples and examples and the negative electrode using the same are shown in Table 2 below.

[0349] Relationship 1 Relationship 4D50[㎛] / (ρ[g / cm 3 ]*SSA[m 2 / g])AS[gf / cm] / (ρ[g / cm3 ]*SSA[m 2 / g]) Manufacturing example 1 (graphite raw material) 11.486.06 Manufacturing example 2 (B13_M3%) 19.4212.40 Example 1 (B13_M3%_S0.8%) 17.0711.62 Example 2 (B13_M3%_S0.6%) 19.7712.88 Example 3 (B13_M3%_S0.4%) 21.3019.90 Example 4 (B13_M3%_S0.2%) 20.1810.03

[0350]

[0351] Referring to Table 2 above, it can be confirmed that in the case of the example, the values ​​of relational expressions 1 and 4 are greater than those of manufacturing example 1, and the scope of the present invention is satisfied.

[0352]

[0353] Experimental Example 2

[0354] (Manufacturing of artificial graphite)

[0355] Manufacturing Example 3 (graphite raw material)

[0356] (Crushing / Formulating Stage)

[0357] Coal-based coke was coarsely crushed with a pin mill and finely crushed with a crusher to produce coke powder.

[0358] For the coke powder obtained after the above crushing, a sizing process was performed to form particles and remove fine powder, thereby manufacturing sizing coke having an average particle diameter (D50) of approximately 10 μm.

[0359]

[0360] (graphitization stage)

[0361] The above-mentioned standardized coke was placed in a crucible, placed in a graphitization furnace, heated to 2,800°C or higher, and ultra-high temperature graphitization was performed to manufacture artificial graphite with controlled average particle size.

[0362]

[0363] Manufacturing Example 4 (B10_S, graphite raw material surface-treated with a conductive agent)

[0364] The artificial graphite material having an average particle diameter (D50) of 10 μm manufactured in the above Manufacturing Example 3 was mixed with carbon black. Here, the carbon black was mixed so that each was 0.8 wt% based on the total weight of the artificial graphite material and carbon black.

[0365] The above artificial graphite material and carbon black mixture was placed in a nobilta milling machine and stirred at a stirring speed of 300 rpm for 3 minutes, then the stirring speed was changed to 800 rpm and stirred for 10 minutes. Then, heat treatment was performed while maintaining the temperature at 1200°C in a reducing atmosphere, thereby producing artificial graphite surface-treated with carbon black.

[0366]

[0367] Manufacturing Example 5 (B10_M3%, graphite raw material coated with pitch)

[0368] The artificial graphite material having an average particle diameter (D50) of 10 μm manufactured in the above Manufacturing Example 3 was mixed with petroleum-based needle pitch. Here, the artificial graphite material and the petroleum-based needle pitch were mixed, and the residual carbon content of the final obtained product artificial graphite was 3 wt%.

[0369] In the present invention, the amount of residual carbon in the final product artificial graphite was measured through TGA analysis.

[0370] The above artificial graphite material and petroleum-based needle pitch mixture were placed in a high-speed mixer and stirred at a stirring speed of approximately 2,700 rpm for 20 minutes. Then, heat treatment was performed while maintaining the temperature at 1,200°C in a reducing atmosphere to produce artificial graphite coated with petroleum-based needle pitch.

[0371]

[0372] Manufacturing Example 6 (B13_M3%, graphite raw material coated with pitch)

[0373] Artificial graphite coated with petroleum-based needle pitch was manufactured in the same manner as in Manufacturing Example 5, except that in Manufacturing Example 3, a standardized coke having an average particle diameter (D50) of about 13 ㎛ was used, and an artificial graphite material having an average particle diameter (D50) of 13 ㎛ manufactured through a graphitization step was used.

[0374]

[0375] Example 5 (B10_S_M3%)

[0376] Artificial graphite surface-treated with carbon black manufactured in the above manufacturing example 4 and petroleum-based needle pitch were mixed, and the residual carbon content of the final obtained product artificial graphite was set to 3 wt%.

[0377] The above graphite material and petroleum-based needle pitch mixture were placed in a high-speed mixer and stirred at a stirring speed of approximately 2,700 rpm for 20 minutes. Then, heat treatment was performed while maintaining the temperature at 1,200°C in a reducing atmosphere to produce the final product, artificial graphite.

[0378]

[0379] Example 6 (B10_M3%_S)

[0380] The petroleum-based needle pitch-coated artificial graphite manufactured in the above Manufacturing Example 5 was mixed with carbon black. Here, the carbon black was mixed to be 0.8 wt% based on the total weight.

[0381] A mixture of graphite material and carbon black was placed in a nobilta milling machine and stirred at a stirring speed of 300 rpm for 3 minutes, then the stirring speed was changed to 800 rpm and stirred for 10 minutes. Next, heat treatment was performed at a temperature of 1200°C under a reducing atmosphere to produce the final product, artificial graphite.

[0382]

[0383] Example 7 (B13_M3%_S)

[0384] Artificial graphite was manufactured in the same manner as in Example 6, except that the petroleum-based needle pitch-coated artificial graphite manufactured in Manufacturing Example 6 was used.

[0385]

[0386] (Manufacturing of cathode)

[0387] A slurry of an anode active material was prepared by mixing 95.6 wt% of the artificial graphite manufactured in the above manufacturing example or example, 1.1 wt% of carboxymethyl cellulose, 2.3 wt% of styrene butadiene rubber, and 1 wt% of Super P conductive agent in a distilled water solvent. The slurry of the anode active material was applied to a copper (Cu) current collector, dried at 80°C for 5 minutes, and pressed in a roll press. Thereafter, the slurry was vacuum-dried in a vacuum oven at 100 to 120°C for 12 hours, thereby preparing an anode in which a layer of the anode active material was formed on the current collector. After vacuum-drying, the electrode density of the anode was set to 1.55 g / cc.

[0388]

[0389] (Manufacturing of lithium secondary batteries)

[0390] Lithium metal (Li-Metal) was used as the negative electrode and counter electrode manufactured by the above-mentioned method, and as the electrolyte, a solution of 1 mol of LiPF6 dissolved in ethylene carbonate (EC) : ethyl methyl carbonate (EMC) at a volume ratio of 2:8 and vinylene carbonate (0.5 wt%) was used.

[0391] Using each of the above components, a half coin cell of the 2032 coin cell type was manufactured according to a conventional manufacturing method.

[0392]

[0393] <Evaluation Example 1>: Analysis of the physical properties of artificial graphite

[0394] (1) SEM analysis

[0395] In order to observe the surface characteristics of the artificial graphite manufactured in the above manufacturing examples and examples, SEM images were taken.

[0396] FIG. 2 is an SEM image of artificial graphite manufactured in Manufacturing Example 3, FIG. 3 is an SEM image of artificial graphite manufactured in Manufacturing Example 4, FIG. 4 is an SEM image of artificial graphite manufactured in Manufacturing Example 5, FIG. 5 is an SEM image of artificial graphite manufactured in Example 5, and FIG. 6 is an SEM image of artificial graphite manufactured in Example 6.

[0397] Referring to Figure 2, it can be confirmed that most of the artificial graphite manufactured in Manufacturing Example 3 is in the form of primary particles.

[0398] Referring to Figure 3, it can be confirmed that dot-shaped fine particles are located on the surface of the artificial graphite manufactured in Manufacturing Example 4.

[0399] Referring to Fig. 4, it can be confirmed that the artificial graphite manufactured in Manufacturing Example 5 has a coating layer formed on the surface of the primary particles and some of them are aggregated to form large secondary particles.

[0400] Referring to Figure 5, it can be seen that the artificial graphite manufactured in Example 5 has secondary particles formed by entangling multiple primary particles and microparticles.

[0401] Referring to FIG. 6, the artificial graphite manufactured in Example 6 can be confirmed to have secondary particles formed by entangling multiple primary particles and microparticles, with microparticles being positioned in a grafted shape between some primary particles having a coating layer formed on the surface.

[0402] (2) Particle size analysis

[0403] The particle sizes Dmin, D10, D50, D90, and Dmax of the artificial graphite manufactured in the above manufacturing examples and examples were measured using the laser diffraction method, and were the particle sizes corresponding to the minimum, 10%, 50%, 90%, and maximum values ​​of the accumulated volume of the artificial graphite, respectively.

[0404] The results of particle size analysis are shown in Table 3.

[0405] (3) Tap density (g / cm) 3 )

[0406] The tap density of the artificial graphite manufactured in the above manufacturing examples and examples was measured using the BeDensi T3 model from Betersize. 15 g of the sample was measured using a scale, filled into a chamber, and the weight was input to obtain the weight-to-volume ratio.

[0407] The results of the tap density analysis are shown in Table 3.

[0408] (4) Specific Surface Area (SSA) (m 2 / g)

[0409] The specific surface area refers to the total surface area of ​​a material per unit mass, and was measured using the SSA method (Surface Area and Porosity Analyzer) (Micromeritics, TriStar 3030 Plus).

[0410] The results of the specific surface area analysis of the artificial graphite manufactured in the above manufacturing examples and examples are shown in Table 3.

[0411] (5) Orientation (I) 004 / I 110 )

[0412] Using a D8 ADVACE model XRD device from Bruker, the XRD peak intensity values ​​of the 004 and 110 planes of artificial graphite were measured, and then the peak intensity value of the 004 plane was divided by the peak intensity value of the 110 plane.

[0413] The results of the orientation analysis of the artificial graphite manufactured in the above manufacturing examples and examples are shown in Table 3.

[0414]

[0415] <Evaluation Example 2>: Evaluation of cathode properties

[0416] (1) Measurement of adhesion between the current collector and the negative electrode active material layer

[0417] The adhesive strength between the current collector and the negative electrode active material layer of the negative electrode manufactured using the artificial graphite manufactured in the above manufacturing examples and examples was measured.

[0418] To measure the adhesive strength more specifically, first, the manufactured negative electrode was cut into a size of 20 mm in width and 100 mm in length and prepared. Double-sided tape with an area of ​​18 mm in width and 80 mm in length was attached to a slide glass with an area of ​​25 mm in width and 100 mm in length. After attaching the prepared electrode on the double-sided tape, it was lightly pressed 10 times with a hand roller, and this was mounted on a UTM (1 kgf load cell) and the current collector was peeled off at a speed of 300 mm / min, and the 90-degree peel strength was measured. The results are shown in Table 3 below.

[0419] Microtrac particle size (㎛)Tap densitySSA powder orientationAdhesion ~5μmDminD1D10D50D90DmaxSpanD90-D10(g / cc)(㎡ / g)I 004 / I 110 gf / cm Manufacturing Example 3 (graphite raw material) 5.03.03.75.99.716.137.01.110.21.181.66.66.6 Manufacturing Example 4 (B10_S) 5.93.03.65.79.415.937.01.110.21.142.19.616.6 Example 5 (B10_S_M3%) 6.02.53.25.911.521.444.01.415.50.901.32.09.8 Example 6 (B10_M3%_S) 2.53.64.36.711.720.652.31.213.90.891.32.312.2 Example 7(B13_M3%_S)066.210.416.927.762.21.0217.30.9912.511.5

[0420]

[0421] Referring to Table 3 above, it can be confirmed that the artificial graphite manufactured in Examples 5 to 7 has a relatively large average particle diameter (D50) and a small tap density and specific surface area compared to Manufacturing Examples 3 and 4.

[0422] The calculated values ​​of equations 1 to 4 considering the adhesive strength of the artificial graphite manufactured in the above manufacturing examples and examples and the negative electrode using the same are shown in Table 4 below.

[0423] Relationship 1 Relationship 2 Relationship 3 Relationship 4 D50[㎛] / (ρ[g / cm 3 ]*SSA[m 2 / g])(Span * ρ[g / cm 3 ]) / SSA[m 2 / g]D50[㎛] / ρ[g / cm 3 ]AS[gf / cm] / (ρ[g / cm 3 ]*SSA[m 2 / g]) Manufacturing example 3 (graphite raw material) 5.140.8118.223.50 Manufacturing example 4 (B10_S) 3.930.5978.256.93 Example 5 (B10_S_M3%) 9.830.96912.788.38 Example 6 (B10_M3%_S) 10.110.82213.1510.55 Example 7 (B13_M3%_S) 17.070.99017.0711.62

[0424]

[0425] Referring to Table 4 above, it was confirmed that the artificial graphite manufactured in Examples 5 to 7 had a value of relational expression 2 of 0.822 to 0.990.

[0426] It was confirmed that the value of relational expression 1 of the artificial graphite manufactured in Examples 5 to 7 was 9.83 to 17.07, and the value of relational expression 3 was 12.78 to 17.07.

[0427] On the other hand, the value of relation 1 of the artificial graphite manufactured in Manufacturing Examples 3 and 4 was less than 6, and the value of relation 3 was less than 9.

[0428] In addition, the value of equation 4 of the negative electrode using the artificial graphite manufactured in Examples 5 to 7 was found to be 8.38 to 11.62.

[0429]

[0430] <Evaluation Example 2>: Electrochemical Performance Analysis

[0431] (1) Evaluation of charging output characteristics

[0432] The final obtained negative electrode active material was applied to a half-cell and tested.

[0433] After charging the battery to SOC (State of Charge) of 10, 20, and 30% (when the battery is charged and discharged at 3.0 V to 4.5 V, the battery is charged to 10, 20, 30, and 40% of its total charge capacity when the battery is charged to 100%) in 4 cycles, the voltage was measured 5 times using the ETH-HC0105R device, and then the average voltage value was measured. A higher average voltage means better charge characteristics of the negative active material.

[0434] The results of the charging characteristics analysis are shown in Table 5 below.

[0435] SOC(%)Voltage (V)#1#2#3#4#5AverageManufacturing Example 3 (Graphite Raw Material)10-0.13-0.11-0.11-0.11-0.11-0.12Manufacturing Example 4 (B10_S)10-0.101-0.106-0.103-0.09-0.093-0.10Manufacturing Example 5 (B10_M3%)10-0.093-0.103-0.08-0.129-0.103-0.10Example 5 (B10_S_M3%)10-0.048-0.043-0.047-0.047-0.061-0.05Example 6 (B10_M3%_S)10-0 .043-0.048-0.056-0.052-0.031-0.05Example 7 (B13_M3%_S) 10-0.057-0.048-0.041-0.045-0.046-0.05Manufacturing Example 3 (Graphite Raw Material) 20-0.17-0.16-0.16-0.16-0.15-0.16Manufacturing Example 4 (B10_S) 20-0.149-0.151-0.154-0.144-0.149-0.15Manufacturing Example 5 (B10_M3%) 20-0.143-0.158-0.138-0.183-0.15-0.16 Example 5 (B10_S_M3%) 20-0.119-0.107-0.108-0.109-0.121-0.11Example 6 (B10_M3%_S) 20-0.103-0.105-0.11-0.104-0.084-0.11Example 7 (B13_M3%_S) 20-0.113-0.105-0.097-0.102-0.103-0.10Preparation Example 3 (Graphite Raw Material) 30-0.18-0.18-0.17-0.17-0.17-0.17Preparation Example 4 (B10_S) 30-0.169-0.167-0.1 73-0.169-0.174-0.17 Manufacturing Example 5 (B10_M3%) 30-0.174-0.184-0.173-0.186-0.175-0.18 Exemplary Example 5 (B10_S_M3%) 30-0.157-0.148-0.147-0.152-0.157-0.15 Exemplary Example 6 (B10_M3%_S) 30-0.145-0.148-0.144-0.138-0.117-0.14 Exemplary Example 7 (B13_M3%_S) 30-0.151-0.144-0.133-0.138-0.142-0.14

[0436] Referring to Table 5 above, it can be confirmed that the lithium secondary battery using the artificial graphite manufactured in the example has excellent charging output characteristics.

[0437]

[0438] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

[0439] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Graphite base material; A low-crystalline carbon coating layer located on the surface of the graphite-based base material; and Contains a conductive material included in the above coating layer; The above low-crystalline carbon content is 1.0 to 10 wt%, The content of the above-mentioned conductive agent is 0.1 to 1.0 wt%, Negative active material for lithium secondary batteries.

2. In paragraph 1, The weight ratio of the above-mentioned conductive material and low-crystalline carbon (conductive material: low-crystalline carbon) is in the range of 1:1 to 1:

30. Negative active material for lithium secondary batteries.

3. In paragraph 1, The average particle diameter (D50) of the above negative active material is in the range of 10.0 to 20.0㎛. Negative active material for lithium secondary batteries.

4. In paragraph 1, The specific surface area (SSA) of the above negative active material is 0.5 to 1.5 m 2 / g range, Negative active material for lithium secondary batteries.

5. In paragraph 1, The tap density of the above negative active material is 0.8 to 1.10 g / cm 3 It is a range, Negative active material for lithium secondary batteries.

6. In paragraph 1, The pellet density of the above negative active material is 1.40 g / cc to 1.50 g / cc, Negative active material for lithium secondary batteries.

7. In paragraph 1, The minimum particle size (Dmin) of the above negative active material is greater than 3.0㎛, Negative active material for lithium secondary batteries.

8. In paragraph 1, The D90 / D10 of the above negative active material is 2.0 to 3.

0. Negative active material for lithium secondary batteries.

9. In paragraph 1, The above negative active material satisfies the following relationship 1: Negative active material for lithium secondary batteries. [Relationship 1] 6.0 ≤ D50 / (ρ*SSA) ≤ 25.0 (Here, D50 is the average particle size of the negative electrode active material (unit: ㎛), ρ is the tap density of the negative electrode active material (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.) 10. In paragraph 1, The above negative active material satisfies the following relationship 2: Negative active material for lithium secondary batteries. [Relationship 2] 0.820 ≤ Span*ρ / SSA ≤ 1.1 (Here, Span is (D90-D10) / D50, ρ is the tap density of the negative electrode active material (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.) 11. In paragraph 1, The above negative active material satisfies the following relationship 3: Negative active material for lithium secondary batteries. [Relationship 3] 10.0 ≤ D50 / ρ ≤ 20.0 (Here, D50 is the average particle size of the negative electrode active material (unit: ㎛), ρ is the tap density of the negative electrode active material (unit: g / cm 3 )am.) 12. In paragraph 1, The above negative active material has an orientation (I) in XRD analysis 004 / I 110 ) whose value is between 1.5 and 3.0, Negative active material for lithium secondary batteries.

13. The entire house; and It includes a negative active material layer disposed on the above-mentioned collector, The above negative electrode active material layer includes a negative electrode active material according to any one of claims 1 to 12, It satisfies the following relational expression 4, Cathode for lithium secondary batteries. [Relationship 4] 7.0 ≤ AS / (ρ*SSA) ≤ 20.0 (Here, AS is the adhesion between the current collector and the negative electrode active material layer (unit: gf / cm), and ρ is the tap density of artificial graphite (unit: g / cm 3 ), SSA is the specific surface area of ​​artificial graphite (unit: m 2 / g) is.) 14. In paragraph 13, The adhesive strength between the above-mentioned collector and the negative electrode active material layer is 7.0 to 20.0 gf / cm. Cathode for lithium secondary batteries.

15. A negative electrode comprising a negative electrode active material according to any one of claims 1 to 12; Bipolar; and A lithium secondary battery comprising an electrolyte.

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