Anode active materil for lithium secondary battery, manufacturing method of the same and lithium secondary battery comprising the same

Abstract

The present invention relates to a method for manufacturing a negative electrode active material for a lithium secondary battery, comprising the steps of: graphitizing a carbon precursor to produce a graphitide; introducing a low-crystallinity carbon material into the graphitide and performing a coating heat treatment; and crushing the coated graphitide with an impact mill and drying it.

Description

Technology Field

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

[0002] The electronics and information and communications industries are experiencing rapid development through the portability, miniaturization, lightweighting, and high performance of electronic devices. Consequently, there is a surging demand for lithium-ion batteries, which can provide high capacity and performance as power sources for these devices. By repeatedly charging and discharging through the intercalation and deintercalation of lithium ions, lithium-ion batteries are establishing themselves as essential power sources for medium-to-large devices, such as electric vehicles, as well as portable electronic devices for information and communications.

[0003] Recently, as improving high-temperature performance—such as high-temperature storage and cycling characteristics—while preserving existing capacity is a critical challenge for lithium-ion batteries, the role of the negative electrode active material, which is responsible for storing lithium ions during charging, is becoming increasingly important.

[0004] As a negative electrode active material in a lithium secondary battery, a metallic lithium negative electrode active material, a carbon-based negative electrode active material, or silicon oxide (SiO₂) x Materials such as ) are used. Since carbon-based cathode active materials have a potential close to the electrode potential of lithium metal, the change in crystal structure during the insertion and extraction process of lithium in an ionic state is small, and the higher the crystallinity of the particles, the better the capacity retention characteristics.

[0005] However, if the carbon-based anode active material contains fine and coarse particles, the particle size distribution widens, which can lead to a decrease in slurry phase stability due to the aggregation of fine particles and cause line formation during electrode coating due to coarse particles; therefore, the particle size distribution of the carbon-based anode active material can have a significant impact on the discharge capacity and energy density of lithium secondary batteries. Colloid mills are mainly used during disintegration to control the particle size distribution of the carbon-based anode active material. Colloid mills are primarily used in wet processes, allowing for very fine grinding of particles, and because they operate in a liquid state, they can uniformly control the dispersion and density of the carbon-based anode active material.

[0006] However, colloid mills are not suitable for mass production because they operate in a wet manner, resulting in a slow processing speed. Additionally, due to centrifugal motion, the flow rate of colloid mills is not constant, and because the variation in flow rate is large depending on the viscosity of the active material, it may be difficult to easily control the particle size.

[0007] Accordingly, there is a need for research on a process capable of fast processing speed and uniform particle size distribution during the disintegration of carbon-based cathode active materials. The problem to be solved

[0008] A method for manufacturing a negative electrode active material according to one embodiment of the present invention provides a method for manufacturing a negative electrode active material having excellent tap density, specific surface area, and particle size distribution. means of solving the problem

[0009] A method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises: a step of graphitizing a carbon precursor to produce a graphitide; a step of adding a low-crystallinity carbon material to the graphitide and performing a coating heat treatment; and a step of crushing the coated graphitide with an impact mill and drying it.

[0010] The impact amount of the above impact mill may be calculated using the following Equation 1.

[0011] [Equation 1]

[0012] Hits (ea·m / s) = A x B

[0013] (A is the linear velocity, and B is the number of pins.)

[0014] The impact force of the above impact mill may be 14,500 to 60,000 ea·m / s.

[0015] The linear velocity of the above impact mill may be 40 to 150 m / s.

[0016] The number of pins of the above impact mill may include 300 to 500.

[0017] The rotational speed of the above impact mill may be 3,500 to 12,500 rpm.

[0018] The above carbon precursor may be one or more selected from sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, vinyl chloride resin, coal-based pitch, petroleum-based pitch, polyvinyl chloride, mesophase pitch, tar, low molecular weight heavy oil, needle coke, ordinary coke, isotropic coke, and anthracite.

[0019] The above low-crystallinity carbon material may be soft carbon, hard carbon, or a combination thereof.

[0020] In the above graphitization step, the graphitization temperature may be 2800 to 3300℃.

[0021] In the above coating heat treatment step, the coating heat treatment temperature may be 1000 to 1400℃. Effects of the invention

[0022] A method for manufacturing a negative electrode active material according to one embodiment of the present invention can improve the electrochemical characteristics of a lithium secondary battery by using a particle size mill during crushing, thereby ensuring a uniform particle size distribution and excellent tap density and specific surface area. Brief explanation of the drawing

[0023] Figure 1 is a graph showing the D50 measurement according to the rotational speed of the impact mill during graphite disintegration according to one embodiment and a comparative example of the present invention. Figure 2 is a graph of D90 measurements according to the rotational speed of the impact mill during graphite disintegration according to one embodiment and a comparative example of the present invention. Specific details for implementing the invention

[0024] In this specification, terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the invention.

[0025] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0026] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other part is interposed in between.

[0027] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0028] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0029] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0030] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0031] Method for manufacturing negative electrode active material

[0032] As mentioned above, colloid mills are not suitable for mass production because they operate in a wet manner when grinding carbon-based cathode active materials, resulting in a slow processing speed. Additionally, colloid mills may have the problem of being difficult to easily control particle size because the flow rate is inconsistent due to centrifugal motion and there is a large variation in flow rate depending on the viscosity of the active material.

[0033] However, in this embodiment, this problem was solved by controlling the particle size distribution of the cathode active material during the disintegration process.

[0034] In this specification, Dmax represents the particle size corresponding to the maximum value of the volume accumulation of the negative electrode active material measured using the Laser Diffraction Method.

[0035] In this specification, D1, D10, D50, and D90 represent particle sizes corresponding to 1%, 10%, 50%, and 90% of the maximum value of the cumulative particle size distribution of the cathode active material measured using the Laser Diffraction Method.

[0036] Embodiments of the present invention will be described in detail below. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0037] A method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises: a step of graphitizing a carbon precursor to produce a graphitide; a step of adding a low-crystallinity carbon material to the graphitide and performing a coating heat treatment; and a step of crushing the coated graphitide with an impact mill and drying it.

[0038] In the above-mentioned coating heat treatment step, the low-crystallinity carbon material may be coated on at least a portion of the graphitide surface. Specifically, the carbon material graphitide may be coated on a portion or the entire surface of the graphitide.

[0039] In a method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention, the impact amount of the impact mill may be calculated by the following Equation 1.

[0040] [Equation 1]

[0041] Hits (ea·m / s) = A x B

[0042] (A is the linear velocity, and B is the number of pins.)

[0043] For example, if the number of pins is 400 and the linear velocity is 130 m / s, the impact amount of the impact mill can be 52,000 ea·m / s.

[0044] In a method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention, the impact amount of the impact mill may be 14,500 to 60,000 ea·m / s, preferably 16,000 to 56,000 ea·m / s, and more preferably 17,000 to 53,000 ea·m / s. When the impact amount of the impact mill satisfies the above range, the negative electrode active material is ground into a uniform particle size, and the classification yield of the negative electrode active material can be improved compared to when ground using a colloid mill. On the other hand, if the impact amount of the impact mill deviates from the above range, the particle size of the ground negative electrode active material is non-uniform, which may cause a problem of degraded electrochemical properties when applied to a lithium secondary battery.

[0045] In a method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention, the linear velocity of the impact mill may be 40 to 150 m / s, preferably 45 to 140 m / s, and more preferably 47 to 130 m / s. When the linear velocity of the impact mill satisfies the above range, the negative electrode active material can be ground into uniform particle sizes without aggregation during impact milling. On the other hand, if the linear velocity of the impact mill deviates from the above range, the particle size of the negative electrode active material may be non-uniform, which may cause a problem of degraded electrochemical properties when applied to a lithium secondary battery.

[0046] In a method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention, the number of pins of the impact mill may be 300 to 500, preferably 350 to 450, and more preferably 400 to 425. When the number of pins of the impact mill satisfies the above range, graphite is supplied from the high-speed rotating grinding rotor and the center of the stator and diffuses along with the airflow, and as the circumferential speed of the pins increases sequentially, a strong impact force is applied so that the negative electrode active material is ground into a uniform particle size distribution and then sorted and discharged. On the other hand, if the number of pins of the impact mill deviates from the above range, a problem may arise where it is difficult to control the particle size and shape of the negative electrode active material during grinding.

[0047] In a method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention, the rotational speed of the impact mill may be 3,500 to 12,500 rpm, preferably 4,000 to 12,000 rpm, and more preferably 8,000 to 11,000 rpm. When the rotational speed of the impact mill satisfies the above range, the negative electrode active material can be uniformly ground into smaller particles due to the impact force generated by the rotation of the impeller inside the impact mill. On the other hand, if the rotational speed of the impact mill deviates from the above range, the negative electrode active material may exhibit a wide particle size distribution including fine particles and coarse particles, and the slurry phase stability may be reduced due to the aggregation of fine particles. Furthermore, if the coarse particles are generated, line formation may occur during electrode coating, which may lead to a problem of reduced discharge capacity and energy density of the lithium secondary battery.

[0048] In a method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention, the carbon precursor may be one or more selected from sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, vinyl chloride resin, coal-based pitch, petroleum-based pitch, polyvinyl chloride, mesophase pitch, tar, low molecular weight heavy oil needle coke, general coke, isotropic coke, and anthracite, but is not limited thereto, and any material that can be used as a negative electrode active material as a carbon precursor may be used.

[0049] In a method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention, the low-crystallinity carbon material may be soft carbon, hard carbon, or a combination thereof, but is not limited thereto, and any low-crystallinity carbon material capable of coating a graphitide may be used.

[0050] In a method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention, in the step of graphitizing the mixture, the graphitization temperature may be 2,800 to 3,300°C, preferably 2,850 to 3,250°C, and more preferably 2,900 to 3,200°C. If the graphitization temperature of the mixture satisfies the above range, the aforementioned carbon precursor mixture can be graphitized. On the other hand, if the graphitization temperature of the mixture deviates from the above range, the electrochemical characteristics of the lithium secondary battery may deteriorate, and problems such as thermal shock to the equipment may occur. In the graphitization step, the graphitization time may be performed in a range of at least 1 hour, specifically at least 2 hours. The graphitization step may be carried out by a heat treatment method using a known high-temperature furnace, such as an Etchison furnace, for example, or by using a continuous graphitization furnace. After the graphitization treatment is completed, a small amount of excess particles formed by the aggregation of aggregated products during the high-temperature graphitization process may be removed by sieving. By separating the above-mentioned excess particles, it is possible to prevent them from affecting the processing performance of the material, such as slurry stability and coating performance. Additionally, a preliminary carbonization step may be included, in which the material is calcined at a temperature lower than the calcination temperature prior to the step of obtaining the graphitized material by calcination. The preliminary carbonization step may be a heat treatment step performed prior to the graphitization step of the carbon precursor mixture.

[0051] In a method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention, the coating heat treatment temperature in the coating heat treatment step may be 1000 to 1400°C, preferably 1100 to 1300°C, and more preferably 1150 to 1250°C. When the coating heat treatment temperature satisfies the above range, a low-crystallinity carbon material can be appropriately coated on part or all of the graphitized surface. On the other hand, if the coating heat treatment temperature exceeds 1400°C, a problem may arise in which process costs increase and economic feasibility decreases. In addition, if the coating heat treatment temperature is less than 1000°C, a performance reduction problem may occur due to side reactions with the electrolyte caused by functional groups remaining on the surface of the negative electrode active material.

[0052] Cathode and lithium secondary battery

[0053] Another embodiment of the present invention provides a negative electrode for a lithium secondary battery comprising the aforementioned negative electrode active material.

[0054] A negative electrode for a lithium secondary battery according to another embodiment of the present invention may more specifically include a negative electrode current collector; and a negative electrode active material layer located on the negative electrode current collector and comprising the aforementioned negative electrode active material for a lithium secondary battery.

[0055] The above-mentioned negative 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., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0056] The above-mentioned cathode active material layer may optionally include a binder and / or a conductive material together with the cathode active material.

[0057] The above binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, 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 alone or a mixture of two or more may be used. The above binder may be included in an amount of 1 to 30 weight% based on the total weight of the negative electrode active material layer.

[0058] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special restrictions as long as it possesses electronic conductivity without causing chemical changes. 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, thermal black, and carbon fibers; metal powders or metal fibers 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 one of these alone or a mixture of two or more may be used. The above conductive material may typically be included in an amount of 1 to 30 weight% relative to the total weight of the negative electrode active material layer.

[0059] 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 for using the negative electrode active material described above.

[0060] Specifically, it can be manufactured by applying a composition for forming a negative electrode active material layer, comprising the aforementioned negative electrode active material and optionally a binder, a conductive material, and a solvent, 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 material are as described above.

[0061] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the cathode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for cathode manufacturing.

[0062] Alternatively, the cathode may be manufactured by casting the composition for forming the cathode active material layer onto a separate support, and then laminating the film obtained by peeling off from the support onto a cathode current collector.

[0064] Another embodiment of the present invention provides a lithium secondary battery comprising the negative electrode.

[0065] A lithium secondary battery according to another embodiment of the present invention may, more specifically, include a positive electrode, a negative electrode positioned opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0066] The above cathode is as described above.

[0067] Additionally, the lithium secondary battery may optionally further include a battery container housing an electrode assembly of a positive electrode, a negative electrode, and a separator, and a sealing member sealing the battery container.

[0069] The above positive electrode may include a positive current collector and a positive active material layer disposed on the positive current collector, and the positive active material layer may include a positive active material.

[0070] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0071] As the above-mentioned cathode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used, and specific examples thereof may include compounds represented by any one of the following chemical formulas:

[0072] Li a A 1-b B b D2(wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li a E 1-b B b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE 2-b B b O 4-c D c (In the above equation, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B c D α(In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Co b B c O 2-α T α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b B c O 2-α T2(wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c D α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mn b B c O 2-α T α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c O 2-α T2(wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c G d O2(wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn dGeO2(wherein the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2(in the above equation, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O2(in the above equation, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a MnG b O2(in the above equation, 0.90 ≤ a ≤ 1.8, 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; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); and LiFePO4.

[0073] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; B 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; T 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; I is Cr, V, Fe, Sc, Y, or a combination thereof; and J may be V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0074] Of course, the compound having a coating layer on its surface or the compound having a coating layer may also be used in combination.

[0075] The above coating layer may include at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers may be amorphous or crystalline. As coating elements included in the above coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof may be used. For the coating layer formation process, any coating method may be used as long as the compound can be coated using these elements in a way that does not adversely affect the physical properties of the cathode active material (e.g., spray coating, immersion method, etc.), and since this is a matter that is well understood by those engaged in the relevant field, a detailed explanation will be omitted.

[0076] The above positive active material layer may further include a binder and / or a conductive material together with the aforementioned positive active material.

[0077] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more may be used, but is not limited thereto. The above binder may be included in an amount of 1 to 30 weight% based on the total weight of the positive active material layer.

[0078] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. 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, thermal black, and carbon fibers; 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; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used, but is not limited thereto. The above conductive material may typically be included in an amount of 1 to 30 weight% relative to the total weight of the positive electrode active material layer.

[0079] The above anode can be manufactured according to a conventional anode manufacturing method.

[0080] Specifically, the anode can be manufactured by applying a composition for forming an anode active material layer, comprising an anode active material and optionally a binder, conductive material, or solvent as needed, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0081] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that allows for the dissolution or dispersion of the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0082] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support, and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0083] The above separator separates the positive and negative electrodes and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0084] The above electrolytes may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited thereto.

[0085] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0086] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, 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 low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0087] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0088] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexamethylphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0090] The embodiments of the present invention will be described in more detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited by the following examples.

[0092] Preparation Example 1

[0093] (Grinding / Shaping Step)

[0094] Coal-based coke was fed in, and the raw material was crushed using a roller mill to obtain coke powder. The raw material was crushed to a target particle size of approximately 6 to 20 μm in center diameter. The coke powder obtained after crushing was subjected to a shaping process to form particles and a treatment to remove fine powder to produce shaped coke.

[0095] (Graphitization stage)

[0096] The above-mentioned standardized coke was loaded into a crucible, placed in a graphitizing furnace, and heated to over 2,800°C to produce artificial graphite through ultra-high temperature graphitization. After producing the above-mentioned artificial graphite, petroleum-based pitch was mixed with a low-crystallinity carbon material and coated with heat treatment at a temperature of 1,200°C for 12 hours to produce artificial graphite coated with a low-crystallinity carbon material.

[0097] Example 1

[0098] 1-1 Preparation of Cathode Active Material

[0099] Coal-based coke was introduced, and the raw material was crushed using a roller mill. The raw material was crushed to a target particle size with a central particle diameter of approximately 6 to 20 μm. After crushing, the mixture obtained was subjected to a shaping process to form particles and remove fine powder, and then the material was aggregated under an inert gas atmosphere to obtain an aggregate. Subsequently, the aggregate was placed in a crucible and placed in a graphitization furnace, and heated to over 2,800°C to produce artificial graphite through ultra-high temperature graphitization. After producing the artificial graphite, petroleum-based pitch was mixed with a low-crystallinity carbon material and subjected to a coating heat treatment at 1,200°C for 12 hours to produce artificial graphite coated with the low-crystallinity carbon material. The coated artificial graphite was then crushed using an impact mill at a rotational speed of approximately 4,000 rpm and an impact force of approximately 18,933 ea·m / s to produce a cathode active material.

[0100] 1-2 Method for manufacturing a lithium secondary battery

[0101] A negative electrode active material slurry was prepared by mixing 95.6% by weight of the negative electrode active material prepared in Example 1-1, 3.4% by weight of a binder containing carboxymethyl cellulose and styrene butadiene rubber, and 1.0% by weight of Super P conductive material in a distilled water solvent.

[0102] The above cathode active material slurry was applied to a copper (Cu) current collector, dried at 100°C for 10 minutes, and then compressed in a roll press. Afterward, the cathode was manufactured by vacuum drying in a vacuum oven at 100°C for 12 hours. After vacuum drying, the electrode density of the cathode was set to 1.55 g / cc.

[0103] Lithium metal (Li-metal) was used as the counter electrode, and 1 mol of LiPF6 solution was dissolved in a mixed solvent with a volume ratio of ethylene carbonate (EC) to dimethyl carbonate (DMC) of 2:8 as the electrolyte.

[0104] A half coin cell of the 2032 coin cell type was manufactured using each of the above components according to a conventional manufacturing method.

[0105] Examples 2 to 5

[0106] The process was carried out in the same manner as in Example 1, except that the rotational speed of the impact mill and the impact amount during crushing were performed under the conditions listed in Table 1 below.

[0107] Comparative Examples 1 to 5

[0108] The cathode active material was prepared using a colloid mill instead of an impact mill during disintegration, and the experiment was repeated 5 times under the same conditions.

[0109] Reference Examples 1 and 2

[0110] The procedure was performed in the same manner as Example 1, except that the impact mill was used to crush the material under the conditions listed in Table 1 below.

[0111] Experimental Example 1 Particle Size Analysis

[0112] The particle sizes Dmin, D10, D50, D90, and Dmax of the negative electrode active materials prepared in the embodiments, comparative examples, and reference examples of the present invention were measured using the Laser Diffraction Method, corresponding to the minimum, 1%, 10%, 50%, 90%, and maximum values ​​of the volume accumulation of artificial graphite, respectively, and the results are shown in Table 2.

[0113] Experimental Example 2 Tap Density

[0114] The tap density of the cathode active material prepared in the examples, comparative examples, and reference examples of the present invention was measured using the BeDensi T3 model of Bettersize, and 15g of the sample was weighed and filled into the chamber, and the weight was entered to obtain the ratio of weight to volume, and the results are shown in Table 2.

[0115] Experimental Example 3 Specific Surface Area (BET)

[0116] 2g of the cathode active material samples prepared in the examples, comparative examples, and reference examples of the present invention were placed in a cylinder, pretreated at 300°C for 1 hour under vacuum, cooled at room temperature for 30 minutes, and then measured using the BET method (Surface Area and Porosity Analyzer) (Micromeritics, TriStar 3030 Plus), and the results are shown in Table 2.

[0118] Reference Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 Reference Example 2 Rotational speed (RPM) 3000 4000 8000 9000 10000 11000 13000 Number of Pins 400 400 400 400 400 400 400 linear velocity (m / s) 36 47 95 107 118 130 154 Rotating motion pin impact amount (ea·m / s) 14200 18933 37867 42600 47333 52067 61533

[0119] Table 1 above shows the rotary impact mill diameter, rotational speed, number of pins, linear speed, and impact amount when the impact mills of Examples 1 to 5 and Reference Examples 1 and 2 are crushed.

[0120] Particle Size (PSD) Physical properties ~5um D1 D10 D50 D90 Dmax Dmin Span Tap density (g / cc) Specific surface area (m²) 2 / g) Preparation Example 1 0.00 8.04 10.90 15.50 23.86 418.6 7.13 0.84 - - Example 1 0.58 5.65 9.90 15.17 22.77 44.00 4.24 0.85 1.08 1.10 Example 2 0.52 5.75 9.90 14.95 22.16 44.00 4.24 0.82 1.08 1.06 Example 3 0.39 5.98 10.00 15.06 22.25 44.00 4.24 0.81 1.08 1.08 Example 4 0.24 8.06 9.97 15.07 22.09 44.00 4.24 0.75 1.08 - Example 5 0.53 5.76 10.05 15.07 22.20 44.00 4.24 0.81 1.07 - Comparative Example 1 0.14 6.38 10.45 16.03 24.08 44.00 5.04 0.85 1.04 0.91 Comparative Example 2 0.16 6.20 10.19 15.61 23.99 52.30 5.04 0.88 1.05 0.98 Comparative Example 3 0.14 6.38 10.57 16.08 24.67 52.30 5.04 0.88 1.05 0.91 Comparative Example 4 0.27 6.09 10.27 15.80 23.95 52.30 4.24 0.80 1.04 - Comparative Example 5 0.40 5.93 10.25 15.73 24.22 52.30 4.24 0.89 1.05 0.97 Reference Example 1 0.14 6.42 10.47 15.87 24.64 74.00 5.04 0.89 1.06 1.16 Reference Example 2 1.11 4.87 9.26 14.40 21.38 44.00 3.57 0.84 1.04

[0121] Referring to Table 2 above, it can be confirmed that Examples 1 to 5, in which artificial graphite was disintegrated using an impact mill, exhibited superior specific surface area and tap density compared to Comparative Examples 1 to 5, in which the graphite was disintegrated using a colloid mill. Additionally, it was confirmed that the D90 of Examples 1 to 5 was 23 μm or less, indicating more effective control compared to Comparative Examples 1 to 5. Furthermore, it was confirmed that Examples 1 to 5, in which artificial graphite was disintegrated using an impact mill, had a more uniform particle size distribution compared to Preparation Example 1, in which the disintegration step was not performed. Referring to Figures 1 and 2, When the rotational speed range of the impact mill is 4,000 to 11,000 rpm, it was confirmed that D50 showed a relatively uniform particle size distribution compared to the comparative example, with D50 being approximately 14.95 to 15.17 and D90 being approximately 22.09 to 22.77.

[0122] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0123] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

Claim 1 A method for manufacturing a negative electrode active material for a lithium secondary battery, comprising: a step of graphitizing a carbon precursor to produce a graphitide; a step of adding a low-crystallinity carbon material to the graphitide and performing a coating heat treatment; and a step of crushing the coated graphitide with an impact mill and drying it, wherein the impact amount of the impact mill is 14,500 to 60,000 ea·m / s. Claim 2 A method for manufacturing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the impact amount of the impact mill is calculated by the following Equation 1. [Equation 1] Impact amount (ea·m / s) = A x B (A is linear velocity, B is the number of pins.) Claim 3 delete Claim 4 A method for manufacturing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the linear velocity of the impact mill is 40 to 150 m / s. Claim 5 A method for manufacturing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the number of pins of the impact mill comprises 300 to 500. Claim 6 A method for manufacturing a negative electrode active material for a lithium secondary battery, wherein, in claim 1, the rotational speed of the impact mill is 3,500 to 12,500 rpm. Claim 7 A method for manufacturing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the carbon precursor is one or more selected from sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, vinyl chloride resin, coal-based pitch, petroleum-based pitch, polyvinyl chloride, mesophase pitch, tar, low molecular weight heavy oil, needle coke, ordinary coke, isotropic coke, and anthracite. Claim 8 A method for manufacturing a negative electrode active material for a lithium secondary battery, wherein, in claim 1, the low-crystallinity carbon material is soft carbon, hard carbon, or a combination thereof. Claim 9 A method for manufacturing a negative electrode active material for a lithium secondary battery, wherein, in the graphitizing step of claim 1, the graphitization temperature is 2800 to 3300℃. Claim 10 A method for manufacturing a negative electrode active material for a lithium secondary battery, wherein, in claim 1, the coating heat treatment temperature in the coating heat treatment step is 1000 to 1400℃.

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