Anode active material for lithium secondary battery, method for manufacturing same, and lithium secondary battery comprising same

Abstract

The present embodiments relate to an anode active material for a lithium secondary battery, a method for manufacturing same, and a lithium secondary battery comprising same. The anode active material of the present invention comprises coarse carbon particles and fine carbon particles and satisfies expression 1 below. <Expression 1> 0.45 ≤ tap density (g / cc) / BET specific surface area (m2 / g) ≤ 0.72 (where, tap density and BET specific surface area represent the tap density and the BET specific surface area of the anode active material, respectively).

Description

Negative active material for lithium secondary battery, method for producing same, and lithium secondary battery including same

[0001] These examples relate to lithium secondary batteries, and more particularly, to a negative electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same.

[0002] Social concern over the depletion of fossil fuels and the resulting environmental pollution is growing, and eco-friendly energy sources are attracting attention as a solution. Among these eco-friendly energy sources, interest in electric energy is growing, and lithium secondary batteries are particularly gaining attention.

[0003] Lithium secondary batteries are increasingly being used in a wide range of applications, from small electronic devices and portable IT devices to electric vehicles and energy storage systems. As the scope of lithium secondary batteries expands, the development of new materials for high capacity and high output is becoming increasingly important. Among the components of lithium secondary batteries, the anode material stores lithium ions and is a key factor in determining their capacity and lifespan.

[0004] Various carbon-based materials, including artificial graphite, natural graphite, and hard carbon, which enable lithium insertion and de-insertion, have been used as anode materials. Graphite has a low discharge voltage of 0.2 V compared to lithium, so batteries using graphite as an anode active material exhibit a high discharge voltage of 3.6 V, offering advantages in energy density for lithium secondary batteries. Furthermore, its excellent reversibility ensures the long life of lithium secondary batteries, making it the most widely used anode material.

[0005] Natural graphite has the advantage of being inexpensive and exhibiting electrochemical properties similar to those of artificial graphite, making it highly useful as an anode material. However, natural graphite has a plate-like shape, so its surface area is large and its edges are exposed, which poses a problem in that electrolyte penetration or decomposition reactions occur when applied as an anode active material. Because of this, the edges are likely to peel off or be destroyed, causing a significant irreversible reaction. In addition, when manufacturing it into an electrode plate, the graphite material is flatly pressed and oriented on the current collector, making it difficult for the electrolyte to be impregnated, which can deteriorate the charge-discharge characteristics.

[0006] To address this, natural graphite is undergoing post-processing, such as spheroidization, to smooth its surface shape and reduce irreversible reactions and improve electrode processability. Commercialized graphite as an anode material exhibits minimal change in crystal structure during lithium ion insertion and deintercalation, allowing continuous oxidation and reduction reactions to occur, resulting in excellent cycle life and high theoretical capacity. However, graphite can only accommodate one lithium ion per six carbon atoms, resulting in a limited theoretical capacity, for example, approximately 372 mAh / g, limiting its ability to meet the demands of high power and capacity.

[0007] Furthermore, lithium ion mobility is typically much slower in solids than in electrolytes. In this case, smaller particle sizes increase lithium ion mobility, shortening the solid diffusion distance, which is advantageous for charging, particularly rapid charging.

[0008] Likewise, research is ongoing into ways to utilize fine-grained products.

[0009] The technical problem to be solved by the present invention is to provide an anode active material having excellent orientation characteristics and output characteristics, which has high mobility of lithium ions during charging and discharging of a lithium secondary battery, thus providing an advantageous rapid charging characteristic, reduces cost by utilizing a waste fine powder product with a small particle size, and provides an anode active material having excellent orientation characteristics and output characteristics.

[0010] Another technical problem to be solved by the present invention is to provide a method for manufacturing a negative electrode active material having the above advantages.

[0011] Another technical problem to be solved by the present invention is to provide a lithium secondary battery including a negative electrode active material having the above advantages.

[0012] According to one embodiment of the present invention, a negative electrode active material for a lithium secondary battery includes coarse carbon particles and fine carbon particles, and can satisfy the following equation 1.

[0013] <Formula 1>

[0014] 0.45 ≤ tap density (g / cc) / BET surface area (m 2 / g) ≤ 0.72

[0015] According to another embodiment of the present invention, a lithium secondary battery may include the aforementioned negative electrode for a lithium secondary battery, a positive electrode including a positive electrode active material, and an electrolyte.

[0016] According to another embodiment of the present invention, a method for manufacturing a negative electrode active material includes the steps of preparing at least one coarse carbon particle having an average particle diameter (D50) of 8 to 15 μm and at least one fine carbon particle having an average particle diameter (D50) of 7 μm or less, the steps of assembling and carbonizing the coarse carbon particles and the fine carbon particles, the step of graphitizing the carbonized assemblage, and the step of coating the graphitized graphitized product, wherein the step of assembling and carbonizing the coarse carbon particles and the fine carbon particles may include a step of mixing the fine carbon particles in an amount of 5 to 30 wt% based on the total amount of the coarse carbon particles and the fine carbon particles.

[0017] According to one embodiment of the present invention, a negative electrode active material for a lithium secondary battery comprising both fine particles and coarse particles is provided, so that when charging and discharging a lithium secondary battery, the mobility of lithium ions is high, which is advantageous for rapid charging characteristics, and by utilizing waste fine particles with small particle sizes, the cost is reduced, and an negative electrode active material with excellent orientation characteristics and output characteristics can be provided.

[0018] A lithium secondary battery according to another embodiment of the present invention can provide a lithium secondary battery applicable to rapid charging by including the above-described negative electrode active material.

[0019] According to another embodiment of the present invention, a method for producing a negative electrode active material for a lithium secondary battery can provide a method for producing a negative electrode active material for a lithium secondary battery having the advantages described above.

[0020] FIG. 1 illustrates a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0021] FIG. 2 illustrates a negative electrode active material for a lithium secondary battery according to another embodiment of the present invention.

[0022] Figure 3 is a flowchart of a method for manufacturing a negative electrode active material according to one embodiment of the present invention.

[0023] Figures 4a to 4c are 1,000x magnification tissue photographs of the negative active materials of Comparative Example 1, Example 1, and Example 2, respectively.

[0024] FIGS. 5A to 5C are 5,000x magnification tissue photographs of negative electrode active materials for lithium secondary batteries according to examples and comparative examples of the present invention.

[0025] Figures 6a to 7c are photographs of the structure of negative electrode active materials for lithium secondary batteries according to examples and comparative examples of the present invention.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and the present invention is not limited thereto, and the present invention is defined solely by the scope of the claims set forth below.

[0031] FIG. 1 illustrates a negative electrode active material (100) for a lithium secondary battery according to one embodiment of the present invention.

[0032] Referring to FIG. 1, the negative active material (100) for a lithium secondary battery may include at least one coarse carbon particle (110) and at least one fine carbon particle (120). The coarse carbon particle (110) may be a carbon particle having a larger diameter than the fine carbon particle (120).

[0033] In one embodiment, the coarse carbon particles (110) and the fine carbon particles (120) may be artificial graphite, natural graphite, or a combination thereof. Specifically, the coarse carbon particles (110) and the fine carbon particles (120) may be artificial graphite.

[0034] In one embodiment, the coarse carbon particles (110) and the fine carbon particles (120) may be amorphous, flaky, angular, plate-like, spherical, fibrous, dot-like, or a combination thereof. In one embodiment, the coarse carbon particles (110) and the fine carbon particles (120) may be derived from coal-based needle calcined, needle green, isostatic calcined, isostatic green, petroleum-based needle calcined, needle green, normal calcined, normal green, or a combination thereof. Specifically, the coarse carbon particles (110) and the fine carbon particles (120) may be derived from green coke (raw coke). More specifically, the fine carbon particles (120) may be a product of waste fines. By mixing the product of the waste fines with the coarse carbon particles, there is an advantage of being able to reduce the cost.

[0035] The above green coke refers to a coke manufactured from coal, petroleum residue, or processed product pitch through a coking reaction under high pressure and high temperature conditions. Specifically, depending on the composition of the raw materials and the coking process conditions, anisotropic or needle coke with a high degree of carbonaceous tissue orientation in a uniaxial direction or isotropic or pitch coke with a low degree of carbonaceous tissue orientation is obtained. Specifically, green refers to a state obtained immediately after the coking process, without undergoing heat treatment such as calcination or carbonization, and thus containing a certain fraction of volatile matter.

[0036] In one embodiment, the green coke may include needle coke, isotropic coke, pitch coke, or a combination thereof. Using the green coke can provide a negative active material for a lithium secondary battery with a low expansion rate and excellent fast charge and discharge characteristics. Furthermore, using the green coke can offer excellent price competitiveness because it eliminates the need for a separate heat treatment process to remove volatile matter, as is the case with calcined coke.

[0037] FIG. 2 illustrates a negative electrode active material (100) for a lithium secondary battery according to another embodiment of the present invention.

[0038] Referring to FIG. 2, the negative active material (100) for a lithium secondary battery may include at least one coarse carbon particle (110) and at least one fine carbon particle (120A, 120B). The coarse carbon particle (110) may be a carbon particle having a larger diameter than the fine carbon particle (120).

[0039] In one embodiment, the coarse carbon particles (110) and fine carbon particles (120A, 120B) may be artificial graphite, natural graphite, or a combination thereof. Specifically, the coarse carbon particles (110) and fine carbon particles (120A, 120B) may be artificial graphite.

[0040] The coarse carbon particles (110) and fine carbon particles (120, 120A, 120B) refer to a state in which the coarse carbon particles and fine carbon particles described later in FIG. 3 are mixed and graphitized together and coated with a coating material such as pitch. For information on the green coke, reference can be made to the coarse carbon particles and fine carbon particles described later.

[0041] Referring again to FIGS. 1 and 2, in one embodiment, the coarse carbon particles (110) may have an average particle diameter in the range of 8 to 15 μm. Specifically, the coarse carbon particles (110) may have an average particle diameter in the range of 8 to 12 μm, and more specifically, in the range of 9 to 11 μm.

[0042] If the particle size range of the coarse carbon particles (110) exceeds the upper limit of the above range, there is a problem of reduced efficiency characteristics and reduced output characteristics. If the particle size range of the coarse carbon particles (110) exceeds the lower limit of the above range, the effect of improving electrochemical characteristics by mixing fine carbon particles is not realized, and there may be a problem of increased specific surface area, decreased tap density, and increased electrode expansion rate.

[0043] In one embodiment, the particulate carbon particles (120) may have an average particle diameter of less than 7 μm. Specifically, the particulate carbon particles (120) may have an average particle diameter of 3 to 7 μm, more specifically, 4 to 6 μm.

[0044] If the particle size range of the fine carbon particles (120) exceeds the upper limit of the above range, there is a problem in that they are not uniformly distributed among the coarse carbon particles (110), and thus the effect of mixing is not realized. If the particle size range of the fine carbon particles (120) exceeds the lower limit of the above range, there are problems in that the charge / discharge capacity decreases, the specific surface area increases, the tap density decreases, and the electrode expansion rate increases.

[0045] In this way, since the coarse carbon particles (110) and fine carbon particles (120) satisfy the above particle size range, the fine carbon particles (120) can be uniformly distributed among the coarse carbon particles (110), and an anode active material having improved orientation characteristics and excellent output characteristics can be provided.

[0046] Specifically, the first particulate carbon particles (120A) may have an average particle diameter of 3 to 7 μm. More specifically, the first particulate carbon particles (120A) may have an average particle diameter of 4 to 6 μm.

[0047] If the particle size range of the first fine carbon particles (120A) exceeds the upper limit of the above range, there is a problem in that it is difficult to apply to rapid charging. If the particle size range of the first fine carbon particles (120A) exceeds the lower limit of the above range, there is a problem in terms of density, life characteristics, and initial efficiency.

[0048] In one embodiment, the second particulate carbon particles (120B) may have an average particle diameter of 3 μm or less. Specifically, the second particulate carbon particles (120B) may have an average particle diameter of 1 to 3 μm, or 1.5 to 2.5 μm.

[0049] If the particle size range of the second fine carbon particles (120A) exceeds the upper limit of the above range, there is a problem of difficulty in rapid charging. If the particle size range of the second fine carbon particles (120A) exceeds the lower limit of the above range, there are problems with density, life characteristics, and initial efficiency.

[0050] In this way, the negative electrode active material for a lithium secondary battery of the present invention simultaneously contains coarse carbon particles (110) and fine carbon particles (120A, 120B), and since the coarse carbon particles (100) and fine carbon particles (120A, 120B) satisfy the above-described range, there are excellent advantages in terms of rapid charging, density, lifespan, and initial efficiency of the battery.

[0051] In one embodiment, the average particle diameter (D50) of the negative active material may have an average particle diameter in the range of 8.0 to 20.0 μm. Specifically, the average particle diameter may be in the range of 10.0 to 16.0 μm, more specifically, the average particle diameter may be in the range of 12.5 to 16.0 μm, more specifically, 13.0 to 15.5 μm, and more specifically, 13.0 to 15.0 μm.

[0052] If the particle size of the negative active material exceeds the upper limit of the above range, there is a problem of reduced efficiency characteristics and reduced output characteristics. If the particle size of the negative active material exceeds the lower limit of the above range, the effect of improving electrochemical characteristics by mixing coarse and fine carbon particles is not realized, and there may be a problem of increased specific surface area, decreased tap density, and increased electrode expansion rate.

[0053] In one embodiment, the weight of the particulate carbon particles (120 or 120A, 120B) relative to the total amount of the coarse carbon particles (110) and the particulate carbon particles (120 or 120A, 120B) may range from 5 to 30 wt%. Specifically, the range may be from 10 to 25 wt%, more specifically, from 13 to 23 wt%, and even more specifically, from 15 to 19 wt%.

[0054] When the weight of the fine carbon particles (120 or 120A, 120B) satisfies the above range, it has the advantages of a large specific surface area and excellent orientation. If it exceeds the upper limit of the above range, there are problems of reduced tap density and increased electrode expansion rate, and if it exceeds the lower limit of the above range, there is a problem of reduced price competitiveness.

[0055] In one embodiment, each of the coarse carbon particles (110) and the fine carbon particles (120, 120A, or 120B) includes a coating layer on the particle surface, and the coating layer may have a thickness of 5 to 100 nm. Specifically, the coating layer may have a thickness of 20 to 80 nm.

[0056] If the coating layer exceeds the upper limit, there is a problem of reduced capacity. If the coating layer exceeds the lower limit, there is a problem of reduced charging speed.

[0057] The coating layer is developed from a covering material, and may be manufactured from a carbon precursor including, for example, sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, or vinyl chloride resin, coal pitch, petroleum pitch, polyvinyl chloride, mesophase pitch, tar, block copolymer, low molecular weight heavy oil, or a mixture thereof.

[0058] In one embodiment, the negative active material (100) may satisfy the following equation 1.

[0059] <Formula 1>

[0060] 0.45 ≤ tap density (g / cc) / BET surface area (m 2 / g) ≤ 0.72

[0061] (In the above formula 1, the tap density and the BET specific surface area mean the tap density and BET specific surface area of ​​the negative electrode active material)

[0062]

[0063] The above equation 1 is a value obtained by dividing the tap density of the negative active material (100) by the specific surface area, and may be an indicator of energy density and electrochemical characteristics. The above equation 1 may satisfy 0.45 to 0.72, specifically, 0.55 to 0.70, more specifically, 0.60 to 0.65, more specifically, 0.61 to 0.63, and more specifically, 0.61 to 0.62.

[0064] If the above equation 1 exceeds the upper limit of the aforementioned range, there is a problem of difficulty in rapid charging. If the above equation 1 exceeds the lower limit of the aforementioned range, there is a problem of inferior life characteristics.

[0065] In one embodiment, the negative active material may satisfy the following equation 2.

[0066] <Formula 2>

[0067] 9.50 ≤ (I (004) / I (110) ) / (D90-D10) ≤ 15.00

[0068] (In the above equation 2, I (004) and I (110) is the intensity of the XRD peak values ​​on the 004 and 110 planes, and D10 and D90 mean the particle sizes when the negative active material particles with various particle sizes are accumulated up to 10% and 90% by volume, respectively.

[0069]

[0070] The above formula 2 is a value obtained by dividing the orientation index of the negative active material by the difference between D90 and D10 of the negative active material, and may be an index of charging characteristics and density. The above formula 2 may be 9.50 or more, specifically, 9.50 to 15.00, more specifically, 9.50 to 12.5, more specifically, 10.00 to 11.00, and more specifically, 10.00 to 10.50.

[0071] By satisfying the aforementioned range, Equation 2 has the advantage of realizing optimal rapid charging characteristics and energy density. If Equation 2 exceeds the upper limit of the aforementioned range, there is a problem of reduced density. If Equation 2 exceeds the lower limit of the aforementioned range, there is a problem of difficulty in rapid charging.

[0072] In one embodiment, the ratio of the transverse size (La) to the vertical size (Lc) of the graphite crystallites of the negative active material (100) (La / Lc) may be 2.45 to 2.75. Specifically, the ratio may be 2.50 to 2.75, and more specifically, 2.65 to 2.75.

[0073] In one embodiment, the lateral size (La) of the graphite crystallites of the negative active material (100) may be 1940 nm or more. Specifically, the lateral size (La) of the graphite crystallites may be 1940 to 2000 nm, more specifically, 1940 to 1955 nm.

[0074] In one embodiment, the vertical size (Lc) of the graphite crystallites of the negative active material (100) may be 690 to 725 nm. Specifically, the vertical size (Lc) of the graphite crystallites may be 700 to 720 nm, more specifically, 710 to 718 nm.

[0075] If the vertical size (Lc) of the graphite crystallites is outside the upper limit of the aforementioned range, there is a problem in terms of initial efficiency and capacity. If the vertical size (Lc) of the graphite crystallites is outside the lower limit of the aforementioned range, there is a problem in that it is difficult to apply to rapid charging. In one embodiment, the Span value of the negative active material (100) may be 0.7 to 2.0. Specifically, the Span value may be 1.0 to 1.3, more specifically, 1.150 to 1.270 or less.

[0076] The above Span value refers to a value obtained by using the formula (D90-D10) / D50 using D10, D50, and D90, which are indicators indicating the particle size. Specifically, the D10, D50, and D90 particle sizes refer to the particle sizes when active material particles having various particle sizes are accumulated up to 10%, 50%, and 90% by volume, respectively.

[0077] If the above Span value is outside the upper limit of the above range, there is a problem that the non-uniformity of the particle size distribution of the negative electrode active material (100) increases. If fine carbon particles (120 or 120A, 120B) are mixed and coated, the Span value decreases compared to coarse carbon particles (110), but if it is outside the lower limit of the above range, it is expected that more uniform electrochemical characteristic values ​​can be obtained.

[0078] In one embodiment, the specific surface area (BET) of the negative active material (100) is 1.15 m 2 / g or more. Specifically, the specific surface area (BET) is 1.2 m 2 / g or more, more specifically, 1.2 to 2.0 m 2 / g, more specifically, 1.2 to 1.5 m 2 / g could be.

[0079] In one embodiment, the tap density of the negative active material (100) may be 0.82 g / cc or less. Specifically, the tap density may be 0.80 g / cc or less, more specifically, 0.70 to 0.80 g / cc.

[0080] In one embodiment, the orientation (I) of the negative active material (100) 004 / I 001) may be 1.85 or less. The orientation is an indicator indicating the degree of orientation of the hexagonal network plane in the thickness direction of the electrode. The orientation can be determined using the JCPDS (ASTM) data as a standard data by X-ray diffraction, and means the peak intensity ratio of the (004) plane and the (001) plane after measuring the (004) plane and the (001) plane of the negative active material by XRD. The orientation (I 004 / I 001 ) may be 1.85 or less, specifically, 1.5 to 1.85, and more specifically, 1.6 to 1.7.

[0081] If the orientation exceeds the upper limit of the above range, electrode swelling may become severe during battery charging. If the orientation exceeds the lower limit of the above range, swelling may increase and charging characteristics may deteriorate.

[0082] In one embodiment, the negative active material (100) may have a point of inflection when the voltage value according to the SOC % is measured, and the point of inflection may be SOC 30% or higher. Specifically, the point of inflection may be SOC 45%, more specifically, SOC 48%, more specifically, SOC 49%, and even more specifically, SOC 50% or higher. Since the inflection point appears above the above-described range, there is an advantage in that it can be utilized as a negative active material for rapid charging. More specifically, in the case of the negative active material (100) including the first particulate carbon particles (120A) and the second particulate carbon particles (120B), the SOC may be 49% or higher.

[0083] In one embodiment, the negative active material (100) of the present invention can satisfy the following equation 3.

[0084] <Formula 3>

[0085] 0.65 ≤ ([SOC 50 %] - [SOC 20 %]) / [SOC 20 %] ≤ 2.00

[0086] (In the above formula 3, [SOC 20%] and [SOC 50%] mean the average voltage values ​​when SOC is 20% and 50%, respectively)

[0087] The above formula 3 is an index for a fast-charging negative electrode active material. The above formula 3 can satisfy 0.65 to 2.00, specifically 0.75 to 1.50, more specifically 0.80 to 1.5, and even more specifically 0.80 to 1.00.

[0088] When the above equation 3 satisfies the aforementioned range, the negative active material can be utilized for rapid charging. If the above equation 3 falls outside the aforementioned range, there is a problem in that the negative active material cannot be utilized for rapid charging.

[0089] In one embodiment, a negative electrode for a lithium secondary battery including a negative electrode active material (100) may be provided. The negative electrode for a lithium secondary battery may include a negative electrode active material (100), a thickener, and a binder. The negative electrode active material (100) may refer to the negative electrode active material (100) described above, as long as it does not contradict the above-described negative electrode active material.

[0090] The above thickener is an additive for increasing the viscosity of the negative electrode material, and may include, for example, at least one of carboxymethyl cellulose (CMC), guar gum, non-crosslinked polyacrylic acid, uncrosslinked polyacrylic acid, and polyvinyl alcohol.

[0091] The binder can make the particles constituting the negative electrode material adhere well to each other and make it easy for the negative electrode material to be attached to the current collector, and can include, for example, at least one of polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethylmethacrylate, polyethylene, and cellulose nitrate.

[0092] In one embodiment, a lithium secondary battery including a negative electrode active material (100) may be provided. In one embodiment, the lithium secondary battery may include a negative electrode including a negative electrode active material (100), a positive electrode including a positive electrode active material, and an electrolyte. Specifically, the lithium secondary battery may further include a separator disposed between the positive electrode and the negative electrode.

[0093] The above negative electrode can be manufactured by mixing a negative electrode active material, a binder, and optionally a conductive material manufactured according to one embodiment of the present invention to manufacture a composition for forming a negative electrode active material layer, and then applying the composition to a negative electrode current collector. The negative electrode current collector can use copper foil.

[0094] The above binder may be, but is not limited to, polyvinyl alcohol, carboxymethyl cellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or polypropylene.

[0095] The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and specifically, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or summer black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorinated carbon, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used. The conductive material can be mixed in an amount of 0.1 wt% to 30 wt% based on the total amount of the composition for forming the negative electrode active material layer.

[0096] The above positive electrode can be manufactured by mixing a positive electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a positive electrode active material layer, and then applying this composition to a positive electrode current collector. At this time, the binder and conductive material are used in the same manner as in the case of the negative electrode described above.

[0097] The above anode is LiCoO2, LiNiO2, LiNi x Mn y O2, Li 1+z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z Any one of the group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, LiFeO2, LiFePO4, and combinations thereof, wherein x is 0.3 to 0.8, y is 0.1 to 0.45, and z may independently be 0 to 0.2. The positive electrode may be more specifically LiFePO4, LiCoO2, NCM811, and NCM622.

[0098] The positive electrode current collector may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium.

[0099] As the electrolyte to be filled in the above lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte, etc., may be used, and a lithium salt dissolved therein may be used. The lithium salt may be, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiSbF6, LiAlO4, LiAlCl4, LiCl, and LiI.

[0100] Examples of the solvent for the non-aqueous electrolyte include, but are not limited to, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; nitriles such as acetonitrile; and amides such as dimethylformamide. These may be used singly or in combination. In particular, a mixed solvent of a cyclic carbonate and a chain carbonate can be preferably used.

[0101] As the electrolyte, a gel polymer electrolyte impregnated with an electrolyte in a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li3N may be used. The separator may be an olefin polymer such as polypropylene that is chemically resistant and hydrophobic; a sheet or non-woven fabric made of glass fiber, polyethylene, or the like. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also function as a separator.

[0102] Figure 3 is a flowchart of a method for manufacturing a negative electrode active material according to one embodiment of the present invention.

[0103] Referring to FIG. 3, the method for manufacturing a negative electrode active material includes a step (S100) of preparing at least one coarse carbon particle having an average particle diameter (D50) of 8 to 15 ㎛ and at least one fine carbon particle having an average particle diameter (D50) of 7 ㎛ or less, a step (S200) of assembling and carbonizing the coarse carbon particle and the fine carbon particle, a step (S300) of graphitizing the carbonized assemblage, and a step (S400) of coating the graphitized graphitized product.

[0104] The coarse carbon particles and fine carbon particles described above may be used as carbon raw materials for manufacturing negative electrode active materials. Specifically, the coarse carbon particles and fine carbon particles may be the green coke described above in FIG. 1, and detailed descriptions thereof may refer to the green coke described in FIG. 1 to the extent that they do not contradict each other.

[0105] The step (S100) of preparing at least one coarse carbon particle having an average particle diameter (D50) of 8 to 15 ㎛ and at least one fine carbon particle having an average particle diameter (D50) of 7 ㎛ or less prepares the coarse carbon particle and the fine carbon particle separately. At this time, the fine carbon particle may be the fine carbon particle (120) described above in FIG. 1, and may also be the first fine carbon particle (120A) and the second fine carbon particle (120B) described above in FIG. 2.

[0106] The step (S200) of assembling and carbonizing the coarse carbon particles and the fine carbon particles may include a step of mixing and assembling the coarse carbon particles and the fine carbon particles, and thereafter, a step of carbonizing the assembled assembly. In the step of carbonizing the assembly, secondary particles may be manufactured by mixing 3 to 30 parts by weight of a covering material based on 100 parts by weight of the assembly. Specifically, the content of the covering material may be 5 parts by weight or more, specifically, 5 to 15 parts by weight, and more specifically, 8 to 13 parts by weight. By mixing the covering material to manufacture secondary particles, the secondary particles may be utilized to convert primary particles into secondary particles.

[0107] By assembling the coarse carbon particles and the fine carbon particles before graphitization, the process is shortened and economical compared to carbonizing the coarse carbon particles and the fine carbon particles separately, and the content of the coating material to be introduced is reduced, and there is an advantage in securing uniformity for the product.

[0108] The step (S300) of graphitizing the carbonized assembly may 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 assembly may be graphitized within the aforementioned temperature range. If the graphitizing step is performed outside the aforementioned range, there are problems such as poor electrochemical properties and thermal shock to the equipment.

[0109] In one embodiment, the step (S300) of graphitizing the carbonized assembly may be performed for a time period of 1 hour or more, specifically, 2 hours or more.

[0110] In one embodiment, the step of coating a graphitized graphite product may include a step of preparing a coating product by mixing a coating material into the graphitized product in an amount of 1 to 10 parts by weight, specifically, 1 to 5 parts by weight, based on the graphitized product. The step of coating the graphitized graphite product is a step of coating the coating material in a state where the coarse carbon particles and the fine carbon particles are mixed. By going through the coating step, the coating material can form a soft carbon layer.

[0111] In the step (S100) of mixing at least one coarse carbon particle and at least one fine carbon particle, the coarse carbon particle may have a larger diameter than the fine carbon particle. In one embodiment, the coarse carbon particle may have a particle diameter in the range of 8 to 15 μm. Specifically, the range may have a particle diameter in the range of 8 to 12 μm.

[0112] Beyond the upper limit of the above range, there are problems with rapid charging applications. Beyond the lower limit, there are problems with reduced capacity and increased specific surface area.

[0113] In one embodiment, the particulate carbon particles may have a particle diameter in a range of 7 μm or less. Specifically, the range may have a particle diameter in a range of 6 μm or less. In another embodiment, the particulate carbon particles may include first particulate carbon particles and second particulate carbon particles. The first particulate carbon particles may have an average particle diameter of 3 to 7 μm, specifically, an average particle diameter of 4 to 6 μm. The second particulate carbon particles may have an average particle diameter of 3 μm or less. Specifically, the second particulate carbon particles may have an average particle diameter of 1 to 3 μm, 1.5 to 2.5 μm. If the upper limit of the above range is exceeded, there is a problem that it is difficult to apply to rapid charging, and if the lower limit of the above range is exceeded, there is a problem that the capacity is reduced and the specific surface area is increased.

[0114] In one embodiment, the step of assembling and carbonizing at least one coarse carbon particle and at least one fine carbon particle includes a step of mixing the coarse carbon particle and the fine carbon particle, and the weight of the fine carbon particle can be mixed in a range of 5 to 30 wt%, specifically, 10 to 25 wt%, more specifically, 15 to 25 wt%, and even more specifically, 18 to 22 wt%, based on the total amount of the coarse carbon particle and the fine carbon particle.

[0115] Beyond the upper limit of the above range, there are problems such as a decrease in density and an increase in specific surface area. Beyond the lower limit of the above range, there are problems such as difficulty in applying it to rapid charging.

[0116] In this way, since the coarse carbon particles and the fine carbon particles satisfy the particle diameters of the above range, and the weight of the fine carbon particles relative to the total amount of the coarse carbon particles and the fine carbon particles satisfies the above range, an anode active material having excellent orientation characteristics and excellent output characteristics can be manufactured.

[0117] In one embodiment, the coarse carbon particles and the fine carbon particles may be green coke. The green coke may be coal-based bed calcined, bed green, isostatic calcined, isostatic green, petroleum-based bed calcined, bed green, conventional calcined, conventional green, or a combination thereof, the detailed description of which is the same as that described above with reference to FIGS. 1 and 2.

[0118] In one embodiment, the step (S100) of mixing at least one coarse carbon particle and at least one fine carbon particle may include the step of crushing and pulverizing the coarse carbon particle and the fine carbon particle. The step of crushing and pulverizing may be performed by selecting any one of ball milling, mechanofusion milling, shaker milling, planetary milling, attritor milling, disk milling, shape milling, nauta milling, nobilta milling, or a combination thereof. Through the step of crushing and pulverizing, the coarse carbon particle and the fine carbon particle within the above-described range may be manufactured.

[0119] The following examples are only examples of the present invention, and the present invention is not limited to the following examples.

[0120]

[0121] <Experimental Example 1>: Coarse carbon particles and first fine carbon particles

[0122] <Example 1>

[0123] 1. Method for manufacturing negative active material

[0124] Preparation of coarse and fine carbon particles

[0125] Green coke was used as a carbon raw material. Specifically, the green coke was pulverized using a pulverizer to have average particle sizes of 9.5 μm and 5.4 μm, respectively. Each pulverized particle can be classified into coarse carbon particles and fine carbon particles.

[0126]

[0127] Carbonization and assembly of coarse and fine carbon particles

[0128] Afterwards, coarse carbon particles and fine carbon particles and pitch having a softening point of 250°C were mixed in an amount of 8 to 13 parts by weight using a mixer for 10 minutes. Afterwards, secondary particles were manufactured through mixing and carbonization for 9 hours using a heatable mixing mixer.

[0129] At this time, the coarse carbon particles and fine carbon particles were mixed and assembled in a ratio of 80:20, and in the carbonization step, 8 parts by weight of pitch was additionally added based on 100 parts by weight of coarse carbon particles and fine carbon particles.

[0130]

[0131] Manufacturing of graphite products

[0132] Afterwards, the secondary particles of each of the coarse carbon particles and fine carbon particles were heated to 3,000°C and a graphitization step was performed for 7 hours to produce artificial graphite.

[0133]

[0134] Manufacturing of coating products

[0135] Afterwards, based on 100 parts by weight of the manufactured graphite product, 3 parts by weight of pitch having a softening point of 250°C was mixed, and then carbonized in an inert atmosphere at 1,200°C for 2 hours to manufacture an artificial graphite coating product, thereby manufacturing an anode active material for a lithium secondary battery.

[0136]

[0137] 2. Manufacturing method of lithium secondary battery

[0138] A slurry of negative active material was prepared by mixing 95.6 wt% of the negative active material manufactured in Table of Contents 1 above, 3.4 wt% of a binder including carboxymethyl cellulose and styrene butadiene rubber, and 1.0 wt% of a Super P conductive material in a distilled water solvent.

[0139] The above-mentioned negative active material slurry was applied to a copper (Cu) current collector, dried at 100°C for 10 minutes, and pressed using a roll press. Thereafter, the negative electrode was manufactured by vacuum drying in a 100°C vacuum oven for 12 hours. After vacuum drying, the electrode density of the negative electrode was set to 1.55 g / cc.

[0140] Lithium metal (Li-metal) was used as the counter electrode, and 1 mol of LiPF6 solution dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 2:8 was used as the electrolyte.

[0141] Using each of the above components, a half coin cell of the 2032 coin cell type was manufactured according to a conventional manufacturing method.

[0142]

[0143] <Example 2>

[0144] Example 2 was performed in the same manner as Example 1, except that the content of pitch was changed to 13 parts by weight in the carbonization and assembly steps.

[0145]

[0146] <Comparative Example 1>

[0147] Comparative Example 1 was performed in the same manner as Example 1, except that fine carbon particles were not mixed with coarse carbon particles.

[0148]

[0149] <Characteristics of primary particles as raw materials>

[0150] Table 1 below shows the particle size and tap density of the primary particles, which are coarse carbon particles and fine carbon particles, which are raw materials. The particle size and tap density in Table 1 below were measured using the following measurement method.

[0151] Particle size (㎛): D1, D10, D50, D90, and Dmax are particle sizes corresponding to 1%, 10%, 50%, 90%, and the maximum value of the accumulated volume of the negative active material measured using the Laser Diffraction Method, respectively. In addition, Span refers to the value calculated as (D90-D10) / D50, and can be an indicator of particle uniformity.

[0152] Tapped density (g / cc): The tapped density measurement method is based on ASTM-B527. 15 g of powder was placed in a 50 mL container and tapped for 3000 cycles to measure the packing density.

[0153]

[0154] Primary particle size, ㎛Tap density -5 ㎛(%)D1D10D50D90DMaxSpang / ccCoarse carbon particles 13.91.64.49.516.2251.20.56Fine carbon particles 46.10.41.85.411.2201.70.43

[0155] Looking at Table 1 above, it was confirmed that the average particle size (D50) of coarse carbon particles was approximately 9.5 ㎛, and the average particle size (D50) of fine carbon particles was approximately 5.4 ㎛.

[0156]

[0157] <Characteristics of graphite products>

[0158] Tables 2 and 3 below show the particle size, physical properties, XRD characteristics, and electrochemical characteristics of graphitized products obtained by assembling the coarse carbon particles and fine carbon particles of Table 1 and graphitizing them at 3,000°C. The particle size and physical properties of the graphitized products in Table 2 below and the XRD characteristics and electrochemical characteristics in Table 3 below are measured by the following methods.

[0159] Specific surface area: The specific surface area was measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0160] XRD measurement method: Using Bruker's XRD equipment, the XRD peak intensity values ​​of the 004 and 110 planes of the negative active material were measured, and then the peak intensity value of the 110 plane was divided by the peak intensity value of the 004 plane.

[0161] - Target: Cu(Ka-ray) graphite monochromator

[0162] - Slit: Diverging slit = 1 degree, Receiving slit = 0.1 mm, Scatter slit = 1 degree

[0163] The above 2Θ refers to the diffraction angle, and the above XRD measurement is a non-limiting example, and other measurement methods may be used.

[0164] D002: The distance at which carbon hexagonal meshwork is stacked is measured by XRD diffraction analysis.

[0165] Lc, La: The Lc value represents the vertical size of the graphite crystallite, and the La value represents the horizontal size of the graphite crystallite.

[0166] Capacity (mAh / g) and Efficiency (%) Evaluation: After manufacturing half-cells of lithium secondary batteries, they were aged at 25℃ for 30 hours and then subjected to charge-discharge tests. For the initial capacity evaluation, 350 mAh / g was used as the reference capacity, and the battery was charged to 0.01 V at a constant current of 0.1 C, then switched to a constant voltage and charged until the end current reached 0.005 C. After a 10-minute rest time after charging, the battery was discharged to 1.5 V at a constant current of 0.1 C, using 350 mAh / g as the reference capacity.

[0167] Degree of Graphitization (%): The degree of graphitization refers to the degree to which a carbon material transforms from a non-graphitic carbon state to a graphitic carbon-like state during high-temperature or secondary heating. The degree of graphitization of a carbon material can be obtained using the following method. The degree of graphitization (Gr) of a carbon material is calculated according to the formula.

[0168] Gr = (0.344-d002) / 0.086 × 100%

[0169]

[0170] Pitch content particle size physical properties [weight parts] - 5 ㎛ (%) D1 D10 D50 D90 Dmax Span tap density [g / cc] specific surface area [g / cc] Comparative example 1 - 0.95.18.013.924.162.21.20.961.8 Example 1 88.22.15.412.221.336.01.30.911.9 Example 2 131.15.07.814.528.074.01.40.891.5

[0171] XRD Characteristics Electrochemical Characteristics D002 (nm) Lc (nm) La (nm) Orientation (I 004 / I 110 ) Graphitization degree (%) La / Lc Initial efficiency (%) Capacity (mAh / g) Comparative example 13.36 1742 189 22.49 22.69 4348.1 Example 13.36 269 217 49 2.69 12.59 4347.3 Example 23.36 17 18 18 542.39 22.69 3348.3

[0172] Looking at Tables 2 and 3 above, it can be confirmed that although fine particles are included, the graphitization degree, capacity, efficiency, and other characteristics of the graphitized product are at similar levels. Specifically, Examples 1 and 2 have differences in orientation, particle size, physical properties, and orientation compared to Comparative Example 1, and it was confirmed that the values ​​of Equations 1 and 2 are included in the scope of the present invention.

[0173]

[0174] <Coating product characteristics>

[0175] Table 4 below shows the particle size, physical properties, XRD characteristics, and electrochemical properties of Comparative Example 1, Example 1, and Example 2 coated with the graphite product of Table 2 above.

[0176] Particle size properties XRD Electrochemical properties Formula 1 Formula 2 -5 ㎛ (%) D 1 D 10 D 50 D 90 D max Span Tap density (g / cc) Specific surface area (m 2 / g)Orientation (I 004 / I 110 ) Initial efficiency (%) Capacity (mAh / g) Comparative example 10.16.39.8 16.73 0.37 4.01.20.84 1.11.99 335 0.20.76 9.27 Exemplary example 12.34.37 113.02 2.95 2.31.20.79 1.31.69 234 2.50.61 10.13 Exemplary example 20.16.19.115.22 6.06 2.21.10.76 1.21.79 134 6.60.63 10.06 Formula 1: Tap density / specific surface area Formula 2: Orientation (I 004 / I 110 ) / (D90-D10)

[0177] Referring to Table 4 above, it was confirmed that the tap density, specific surface area, and orientation of the comparative examples were outside the scope of the present invention. In addition, it was confirmed that, in Equations 1 and 2 of the present invention, Examples 1 and 2 were included in the scope of the present invention, but Comparative Example 1 was not included.

[0178]

[0179] <Rapid charging performance evaluation>

[0180] Table 5 below shows the average voltage values ​​at SOC 10 to 60% of Comparative Example 1 and Examples 1 and 2.

[0181] SOC(State of Charge)(%): The negative active materials of Examples 1 and 2 and Comparative Example 1 were applied to half cells and tested. Specifically, the cells were charged and discharged three times at 3.0 V to 4.5 V, and when the total charge capacity of the cells was 100%, the charge capacity value, SOC (State of Charge), was charged to 10 to 60%, and the average voltage value was measured using ETH-HC0105R equipment.

[0182] SOC [%] Average voltage value [V] Inflection point appearance point [%] Formula 3 Comparative example 110-0.04494430.6320-0.1036330-0.1414340-0.1664650-0.1690660-0.1716 Exemplary example 110-0.03239510.8420-0.091130-0.1220740-0.1505450-0.1679360-0.17516 Exemplary example 210-0.04271490.9720-0.1000930-0.1381340-0.1743750-0.1976360-0.204 Formula 4: (SOC 50%-SOC 20%) / SOC 20%

[0183] Looking at Table 5 above, in the case of the comparative example, it was confirmed that the inflection point appeared at 43% in the voltage value according to SOC %, which is lower than that of Example 1 at 51% and Example 2 at 49%. In the graph of voltage change according to increase in SOC %, the larger the SOC value at the point where the inflection point appears, the more advantageous it is for rapid charging. Therefore, it can be confirmed that the examples are advantageous for rapid charging compared to Comparative Example 1, and that Example 1 is advantageous for rapid charging compared to Example 2. Accordingly, it can be confirmed that the negative active material of the present invention has excellent output characteristics. FIGS. 3A to 3C are tissue photographs of negative active materials for lithium secondary batteries according to examples and comparative examples of the present invention. FIGS. 4A to 4C are tissue photographs at 1,000x magnification of the negative active materials of Comparative Example 1, Example 1, and Example 2, respectively.

[0184] FIGS. 5A to 5C are 5,000x magnification tissue photographs of negative electrode active materials for lithium secondary batteries according to examples and comparative examples of the present invention.

[0185]

[0186] Referring to FIGS. 4a to 4c and 5a to 5c, the fine particles and the degree of particle assembly can be confirmed.

[0187]

[0188] <Experimental Example 2>: Mixture of coarse carbon particles, first fine carbon particles, and second fine carbon particles

[0189] <Example 3>

[0190] 1. Method for manufacturing negative active material

[0191] Preparation of coarse and fine carbon particles

[0192] Green coke was used as a carbon raw material. Specifically, the green coke was pulverized using a pulverizer so that the average particle sizes of the green coke were 9.5 μm, 5.4 μm, and 2.0 μm, respectively. Each of the pulverized particles can be classified into coarse carbon particles, first fine carbon particles, and second fine carbon particles.

[0193]

[0194] Carbonization and assembly of coarse and fine carbon particles

[0195] Thereafter, coarse carbon particles and first and second fine carbon particles were mixed with 15.5 parts by weight of pitch having a softening point of 250°C for 10 minutes using a mixer. Thereafter, secondary particles were manufactured through mixing and carbonization for 9 hours using a heatable mixing mixer.

[0196] At this time, the coarse carbon particles and the first and second fine carbon particles were mixed and assembled in a ratio of 70:17.5:12.5.

[0197]

[0198] Manufacturing of graphite products

[0199] Afterwards, the coarse carbon particles and the secondary particles of each of the first and second fine carbon particles were heated to 3,000°C and a graphitization step was performed for 7 hours to produce artificial graphite.

[0200]

[0201] Manufacturing of coating products

[0202] Afterwards, based on 100 parts by weight of the manufactured graphite product, 3 parts by weight of pitch having a softening point of 250°C was mixed, and then carbonized in an inert atmosphere at 1,200°C for 2 hours to manufacture an artificial graphite coating product, thereby manufacturing an anode active material for a lithium secondary battery.

[0203]

[0204] 2. Manufacturing method of lithium secondary battery

[0205] A slurry of negative active material was prepared by mixing 95.6 wt% of the negative active material manufactured in Table of Contents 1 above, 3.4 wt% of a binder including carboxymethyl cellulose and styrene butadiene rubber, and 1.0 wt% of a Super P conductive material in a distilled water solvent.

[0206] The above-mentioned negative active material slurry was applied to a copper (Cu) current collector, dried at 100°C for 10 minutes, and pressed using a roll press. Thereafter, the negative electrode was manufactured by vacuum drying in a 100°C vacuum oven for 12 hours. After vacuum drying, the electrode density of the negative electrode was set to 1.55 g / cc.

[0207] Lithium metal (Li-metal) was used as the counter electrode, and 1 mol of LiPF6 solution dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 2:8 was used as the electrolyte.

[0208] Using each of the above components, a half coin cell of the 2032 coin cell type was manufactured according to a conventional manufacturing method.

[0209]

[0210] <Comparative Example 2>

[0211] Comparative Example 2 was performed in the same manner as Example 3, except that the first fine carbon particles and the second fine carbon particles were not included and the content of pitch during carbonization was suggested to be 8 parts by weight.

[0212]

[0213] <Comparative Example 3>

[0214] Comparative Example 3 was performed in the same manner as Example 3, except that the coarse carbon particles and the first fine carbon particles were mixed in a ratio of 80:20 and the content of pitch during carbonization was changed to 15.5 parts by weight.

[0215]

[0216] <Characteristics of primary particles as raw materials>

[0217] Table 6 below shows the particle size and tap density of the primary particles, which are coarse carbon particles and fine carbon particles, which are raw materials. The particle size and tap density in Table 6 below were measured using the same measurement method as in Experimental Example 1 described above.

[0218] Primary particle size, ㎛Tap density-5㎛(%)D1D10D50D90DMaxSpang / ccCoarse carbon particles13.91.64.49.516.2251.20.56First fine carbon particles46.10.41.85.411.2201.70.43Second fine carbon particles91.10.00.82.34.98.01.80.25

[0219] Looking at Table 6 above, it was confirmed that the average particle size (D50) of the coarse carbon particles was about 9.5 ㎛, the average particle size (D50) of the first fine carbon particles was about 5.4 ㎛, and the average particle size (D50) of the second fine carbon particles was about 2.3 ㎛.

[0220]

[0221] <Characteristics of graphite products>

[0222] Tables 7 and 8 below show the particle size, physical properties, XRD characteristics, and electrochemical characteristics of graphitized products obtained by assembling the coarse carbon particles and the first and second fine carbon particles of Table 6 above and graphitizing them at 3,000°C. The particle size and physical properties of the graphitized products in Table 7 below and the XRD characteristics and electrochemical characteristics in Table 8 below were measured using the same method as in Experimental Example 1 described above.

[0223] Specific surface area: The specific surface area was measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0224] XRD measurement method: Using Bruker's XRD equipment, the XRD peak intensity values ​​of the 004 and 110 planes of the negative active material were measured, and then the peak intensity value of the 110 plane was divided by the peak intensity value of the 004 plane.

[0225] - Target: Cu(Ka-ray) graphite monochromator

[0226] - Slit: Diverging slit = 1 degree, Receiving slit = 0.1 mm, Scatter slit = 1 degree

[0227] The above 2Θ refers to the diffraction angle, and the above XRD measurement is a non-limiting example, and other measurement methods may be used.

[0228] D002: The distance at which carbon hexagonal meshwork is stacked is measured by XRD diffraction analysis.

[0229] Lc, La: The Lc value represents the vertical size of the graphite crystallite, and the La value represents the horizontal size of the graphite crystallite.

[0230] Capacity (mAh / g) and Efficiency (%) Evaluation: After manufacturing half-cells of lithium secondary batteries, they were aged at 25℃ for 30 hours and then subjected to charge-discharge tests. For the initial capacity evaluation, 350 mAh / g was used as the reference capacity, and the battery was charged to 0.01 V at a constant current of 0.1 C, then switched to a constant voltage and charged until the end current reached 0.005 C. After a 10-minute rest time after charging, the battery was discharged to 1.5 V at a constant current of 0.1 C, using 350 mAh / g as the reference capacity.

[0231] Degree of Graphitization (%): The degree of graphitization refers to the degree to which a carbon material transforms from a non-graphitic carbon state to a graphitic carbon-like state during high-temperature or secondary heating. The degree of graphitization of a carbon material can be obtained using the following method. The degree of graphitization (Gr) of a carbon material is calculated according to the formula.

[0232] Gr = (0.344-d002) / 0.086 × 100%

[0233] Particle size properties - 5 ㎛ (%) D1 D10 D50 D90 Dmax Span Tap density [g / cc] Specific surface area [g / cc] Comparative example 20.9 5.18.0 13.9 24.16 2.21.20.96 1.8 Comparative example 31.15.07.8 14.5 28.07 4.01.4 0.89 1.5 Example 31.05.07.9 14.6 27.5 74.01.30.88 1.7

[0234] XRD Characteristics Electrochemical Characteristics D002 (nm) Lc (nm) La (nm) Orientation (I 004 / I 110 ) Graphitization degree (%) La / Lc Initial efficiency (%) Capacity (mAh / g) Comparative example 23.36 17 42 18 9 22.49 22.69 434 8.1 Comparative example 33.36 17 18 18 5 42.39 22.69 334 8.3 Example 33.16 0 42 8 12 18 1.79 22.89 234 3.9

[0235] Looking at Tables 7 and 8 above, it can be confirmed that in Example 3, Comparative Example 2, and Comparative Example 3, the Example has a better effect than the Comparative Example depending on the orientation.

[0236]

[0237] <Coating product characteristics>

[0238] Tables 9 and 10 below show the particle size, physical properties, XRD characteristics, and electrochemical properties of Comparative Examples 2, 3, and 3, which were prepared by coating the graphite product of Table 7 with a coating material.

[0239] Particle size properties - 5 ㎛ (%) D1D10D50D90DmaxSpanTap density (g / cc)Specific surface area (m 2 / g) Comparative Example 20.16.39.816.730.374.01.20.841.1 Comparative Example 30.16.19.115.226.062.21.10.761.2 Exemplary Example 30.65.48.415.326.762.21.20.761.4

[0240] XRD characteristics Electrochemical characteristics D002 (nm) Lc (nm) La (nm) Orientation (I) 004 / I 110) Graphitization degree (%) La / Lc Initial efficiency (%) Capacity (mAh / g) Comparative example 23.36 1688 1939 1.99 22.89 335 0.2 Comparative example 33.36 172 7168 21.79 22.39 134 6.6 Example 33.36 1715 1948 1.79 12.79 034 3.8

[0241]

[0242] <Rapid charging performance evaluation>

[0243] Table 11 below shows the average voltage values ​​at SOC 10 to 60% of Comparative Example 2, Comparative Example 3, and Example 3.

[0244] SOC(State of Charge)(%): The negative active materials of Comparative Example 2, Comparative Example 3, and Example 3 were applied to half cells and tested. Specifically, the cells were charged and discharged three times at 3.0 V to 4.5 V, and when the total charge capacity of the cell was 100%, the charge capacity value, SOC (State of Charge), was charged to 10 to 60%, and the average voltage value was measured using ETH-HC0105R equipment.

[0245] SOC [%] Average voltage value [V] Inflection point appearance point [%] Formula 3 Comparative example 210-0.04494430.6320-0.1036330-0.1414340-0.1664650-0.1690660-0.1716 Comparative example 310-0.04271480.9720-0.1000930-0.1381340-0.1743750-0.1976360-0.204 Exemplary example 310-0.03725501.0220-0.0913830-0.1266340-0.1647250-0.1846360-0.18911 Formula 3: (SOC 50%-SOC 20%) / SOC 20%

[0246] Looking at Table 11 above, in the case of Comparative Examples 2 and 3, it was confirmed that the inflection points in the voltage values ​​according to SOC % were different at 43% and 48%, compared to Example 3 at 50%. In the graph of voltage change according to increase in SOC %, the larger the SOC value at the point where the inflection point appears, the more advantageous it is for rapid charging. Therefore, it can be confirmed that Example 3 is advantageous for rapid charging compared to Comparative Examples 2 and 3. Accordingly, it can be confirmed that the negative active material of the present invention has excellent output characteristics. FIGS. 6A to 7C are photographs of the structures of negative active materials for lithium secondary batteries according to Examples and Comparative Examples of the present invention.

[0247] Figures 6a to 6c are 1,000x magnification tissue photographs of the negative active materials of Comparative Example 2, Comparative Example 3, and Example 3, respectively.

[0248] FIGS. 7A to 7C are 5,000x magnification tissue photographs of negative electrode active materials for lithium secondary batteries according to Comparative Examples 2, 3, and 3 of the present invention.

[0249] Referring to FIGS. 6a to 6c and FIGS. 7a to 7c, the degree of fine particles and particle assembly can be confirmed.

[0250] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Contains coarse carbon particles and fine carbon particles, A negative electrode active material for a lithium secondary battery satisfying the following equation 1. <Formula 1> 0.45 ≤ tap density (g / cc) / BET surface area (m 2 / g) ≤ 0.72 (In the above formula 1, the tap density and the BET specific surface area mean the tap density and BET specific surface area of ​​the negative electrode active material) 2. In paragraph 1, A negative electrode active material for a lithium secondary battery satisfying the following equation 2. <Formula 2> 9.50 ≤ (I(004) / I(110)) / (D90-D10) ≤ 15.00 (In the above formula 2, I(004) and I(110) are the intensities of the XRD peak values ​​of the 004 plane and the 110 plane, and D10 and D90 mean the particle sizes when the negative active material particles with various particle sizes are accumulated up to 10% and 90% by volume, respectively.) 3. In paragraph 1, A negative electrode active material for a lithium secondary battery, wherein the weight of the fine carbon particles is 5 to 30 wt% based on the total amount of the coarse carbon particles and the fine carbon particles.

4. In paragraph 1, A negative electrode active material for a lithium secondary battery, wherein the point at which an inflection point appears in the measured voltage value according to SOC % is SOC 30% or higher.

5. In paragraph 1, A negative electrode active material for a lithium secondary battery satisfying the following equation 3. <Formula 3> 0.65 ≤ ([SOC 50 %] - [SOC 20 %]) / [SOC 20 %] ≤ 2.00 (In the above formula 3, [SOC 20%] and [SOC 50%] mean the average voltage values ​​when SOC is 20% and 50%, respectively) 6. In paragraph 1, The above coarse carbon particles and the above fine carbon particles are negative active materials for lithium secondary batteries, which are artificial graphite, natural graphite, or a combination thereof.

7. In paragraph 1, A negative electrode active material for a lithium secondary battery having an average particle diameter (D50) of 8.0 to 20.0 ㎛.

8. In paragraph 1, The specific surface area (BET) is 1.15 m 2 / g or more negative electrode active material for lithium secondary batteries.

9. In paragraph 1, A negative electrode active material for a lithium secondary battery having a tap density of 0.82 g / cc or less.

10. In paragraph 1, Orientation (I 004 / I 001 ) A negative electrode active material for a lithium secondary battery having a value of 1.85 or less. (Above I 004 and I 001 (represents the peak intensity ratio of the (004) and (001) planes, respectively) 11. In paragraph 1, The above fine carbon particles include first fine carbon particles and second fine carbon particles, The above first fine carbon particles are a negative active material for a lithium secondary battery, wherein the average particle diameter (D50) of the above first fine carbon particles is larger than that of the above second fine carbon particles.

12. In paragraph 11, A negative electrode active material for a lithium secondary battery, wherein the average particle diameter (D50) of the first fine carbon particles is 3 to 7 μm.

13. In paragraph 11, A negative electrode active material for a lithium secondary battery, wherein the average particle diameter (D50) of the second fine carbon particles is 3 ㎛ or less.

14. A negative electrode for a lithium secondary battery comprising 96 to 99 wt% of a negative electrode active material of any one of claims 1 to 13, 0.5 to 1.5 wt% of a thickener, and the remainder of a binder; a cathode comprising a cathode active material; and A lithium secondary battery containing an electrolyte. A step of preparing at least one coarse carbon particle having an average particle diameter (D50) of 15.8 to 15 ㎛ and at least one fine carbon particle having an average particle diameter (D50) of 7 ㎛ or less; A step of assembling and carbonizing the coarse carbon particles and the fine carbon particles; a step of graphitizing the carbonized assembly; and Comprising a step of coating a graphitized graphite product, In the step of assembling and carbonizing the coarse carbon particles and the fine carbon particles, A method for producing a negative electrode active material for a lithium secondary battery, comprising a step of mixing the fine carbon particles in an amount of 5 to 30 wt% based on the total amount of the coarse carbon particles and the fine carbon particles.

16. In paragraph 15, In the step of assembling and carbonizing the coarse carbon particles and the fine carbon particles, A method for producing a negative electrode active material for a lithium secondary battery, wherein the content of the covering material is mixed in an amount of 3 to 30 parts by weight based on 100 parts by weight of the combined amount of the coarse carbon particles and the fine carbon particles.

17. In paragraph 15, A method for producing a negative electrode active material for a lithium secondary battery, wherein the coarse carbon particles and the fine carbon particles are coal-based needle-like calcined carbon, needle-like green carbon, isotropic calcined carbon, isotropic green carbon, petroleum-based needle-like calcined carbon, needle-like green carbon, general calcined carbon, general green carbon, or a combination thereof.

18. In paragraph 15, In the step of preparing at least one coarse carbon particle having an average particle diameter (D50) of 8 to 15 ㎛ and at least one fine carbon particle having an average particle diameter (D50) of 7 ㎛ or less, A method for producing a negative electrode active material for a lithium secondary battery, comprising a step of crushing the coarse carbon particles to have a particle size of 8 to 15 ㎛.

19. In paragraph 15, The step of coating the above graphitized graphite product is A method for producing a negative electrode active material for a lithium secondary battery, comprising a step of mixing 1 to 5 parts by weight of a covering material based on the above graphite product.

20. In paragraph 15, In the step of preparing at least one coarse carbon particle having an average particle diameter (D50) of 8 to 15 ㎛ and at least one fine carbon particle having an average particle diameter (D50) of 7 ㎛ or less, A method for manufacturing a negative electrode active material for a lithium secondary battery, wherein the above-mentioned fine carbon particles include at least one first fine carbon particle having an average particle diameter (D50) of 4 to 7 ㎛ and at least one second fine carbon particle having an average particle diameter (D50) of 3 ㎛ or less.

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