Negative electrode active material for lithium secondary batteries, method for manufacturing the same, and lithium secondary battery containing the same

Abstract

The present invention relates to a negative electrode active material for lithium secondary batteries, comprising natural graphite, wherein the natural graphite satisfies the following formula 1. [Formula 1] P 1.7 -P 1.3 ≥1200 kg·f / cm 2 In the above equation 1, P 1.7 This is the applied pressure when the pellet density of the negative electrode active material is 1.7 g / cc, and P 1.3 This is the applied pressure when the pellet density of the negative electrode active material is 1.3 g / cc.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material for lithium secondary batteries, a method for producing the same, and a lithium secondary battery containing the same, and more specifically, to a negative electrode active material for lithium secondary batteries containing natural graphite, a method for producing the same, and a lithium secondary battery containing the same. [Background technology]

[0002] As the depletion of fossil fuels leads to rising energy prices and growing concern about environmental pollution, environmentally friendly alternative energy sources are becoming an essential factor for future life.

[0003] In particular, as technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source has been rapidly growing, and recently, the use of secondary batteries as a power source for electric vehicles (xEVs) and energy storage systems (ESS) has become a reality.

[0004] While conventional lithium metal was used as the negative electrode in the aforementioned secondary batteries, the formation of dendrites led to short circuits and the risk of explosion, which became a problem. As a result, the use of carbon-based active materials that allow for reversible insertion and removal of lithium ions while maintaining structural and electrical properties is gaining prominence.

[0005] As the carbon-based active material, various forms of carbon-based materials such as artificial graphite, natural graphite, and hard carbon are used. Among these, graphite-based active materials, which have excellent reversibility and can guarantee the lifespan characteristics of lithium secondary batteries, are the most widely used. Since the discharge voltage of the graphite-based active material to lithium is low at -0.2V, batteries using graphite-based active materials can exhibit a high discharge voltage of 3.6V, thus offering many advantages in terms of the energy density of lithium batteries.

[0006] Among these, natural graphite, in particular, exhibits higher output and capacity compared to other carbon-based active materials such as artificial graphite. It also has excellent adhesive properties, which allows for a reduction in the amount of binders used, thus enabling the realization of high-capacity, high-density anodes.

[0007] In particular, lithium-ion batteries used in electric vehicles require rapid charging characteristics that allow for quick charging, and long-life characteristics that maintain good discharge capacity even after repeated charging and discharging. Therefore, there is a need to develop technologies that can further improve the charging output characteristics and long-life characteristics of existing natural graphite negative electrode active materials. [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, one objective of the present invention is to provide a negative electrode active material for lithium secondary batteries with improved charging output characteristics and lifespan characteristics, a method for producing the same, and a lithium secondary battery containing the same. [Means for solving the problem]

[0009] One embodiment of the present invention provides a negative electrode active material for a lithium secondary battery, comprising natural graphite, wherein the natural graphite satisfies the following formula 1.

[0010] [Formula 1] P 1.7 -P 1.3 ≥1200 kg·f / cm 2

[0011] In the above equation 1, P 1.7 This is the applied pressure when the pellet density is 1.7 g / cc, and P 1.3 This is the applied pressure when the pellet density is 1.3 g / cc.

[0012] The aforementioned natural graphite can satisfy the following equation 2.

[0013] [Formula 2] P 1.6 -P 1.3≧850 kg·f / cm 2

[0014] In the above formula 2, P 1.6 is the applied pressure when the pellet density is 1.6 g / cc, and P 1.3 is the applied pressure when the pellet density is 1.3 g / cc.

[0015] The natural graphite can satisfy the following formula 3.

[0016] [Formula 3] P 1.5 -P 1.3 ≧550 kg·f / cm 2

[0017] In the above formula 3, P 1.5 is the applied pressure when the pellet density is 1.5 g / cc, and P 1.3 is the applied pressure when the pellet density is 1.3 g / cc.

[0018] The natural graphite can satisfy the following formula 4.

[0019] [Formula 4] P 1.4 -P 1.3 ≧250 kg·f / cm 2

[0020] In the above formula 4, P 1.4 is the applied pressure when the pellet density is 1.4 g / cc, and P 1.3 is the applied pressure when the pellet density is 1.3 g / cc.

[0021] The natural graphite may have an orientation peak intensity ratio (I110 / I004) of 0.50 or more during XRD pattern analysis.

[0022] The natural graphite may have a spheroidization degree of 0.85 or more.

[0023] The negative electrode active material for the lithium secondary battery is disposed on the natural graphite and may further include a low-crystallinity carbon material-containing coating layer.

[0024] The low-crystalline carbon material may be easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), or a combination thereof.

[0025] The content of the coating layer may be 1 to 20% by weight based on the total weight of the natural graphite.

[0026] The aforementioned negative electrode active material for lithium secondary batteries has a tap density of 1.1 g / cm³. 3 That's fine too.

[0027] The negative electrode active material for the lithium secondary battery may have a SPAN value of 1 to 1.5.

[0028] The negative electrode active material for the lithium secondary battery may have an average particle size D50 of 12 to 20 μm.

[0029] Another embodiment of the present invention provides a method for producing a negative electrode active material for a lithium secondary battery, comprising the steps of: preparing natural graphite powder; oxidizing the natural graphite powder; and forming the oxidized natural graphite powder into high-density spheres.

[0030] The oxidation treatment may be carried out at a temperature of 500 to 700°C.

[0031] The oxidation treatment may be carried out for 1 to 5 hours.

[0032] The oxidation treatment may be carried out in an air or oxygen atmosphere.

[0033] The aforementioned high-density spheroidization may be carried out by a mechanical spheroidization method.

[0034] The mechanical spheroidizing method may be carried out through one or more methods selected from the group consisting of ACM milling (Air Classifying milling), Spheronizing milling, Grinding milling, Mechanofusion milling, Planetary milling, Hybridization milling, Shape milling, and High-speed milling.

[0035] The process may further include the step of forming a low-crystallinity carbon material-containing coating layer by heat-treating a mixture of the oxidized natural graphite powder into high-density spheres, followed by the step of mixing it with a low-crystallinity carbon material precursor.

[0036] The low-crystalline carbon material precursor may be petroleum-based pitch, coal-based pitch, mesophase pitch, heavy oil, light oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, phenol resin, furan resin, furfuryl alcohol, polyacrylonitrile, cellulose, styrene, polyimide, epoxy resin, glucose, or a combination thereof.

[0037] Another embodiment of the present invention provides a negative electrode for a lithium secondary battery containing the negative electrode active material described above.

[0038] Another embodiment of the present invention provides a lithium secondary battery including the negative electrode. [Effects of the Invention]

[0039] A negative electrode active material for a lithium secondary battery according to one embodiment of the present invention can improve the charging output characteristics and lifespan characteristics of the battery. [Modes for carrying out the invention]

[0040] The terms first, second, third, etc., are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used solely to distinguish one part, component, region, layer, or section from other parts, components, regions, layers, or sections. 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 exceeding the scope of the present invention.

[0041] The technical terms used herein are for the sole purpose of referring to specific embodiments and are not intended to limit the invention. The singular forms used herein also include plural forms unless the text explicitly indicates otherwise. The meaning of “including” as used in this specification does not mean to embody a particular characteristic, area, integer, step, operation, element, and / or component, thereby excluding the presence or addition of other characteristics, areas, integers, steps, operations, elements, and / or components.

[0042] When one part is described as being "on top of" another part, it means that it is either directly on top of the other part or that the other part is in between. In contrast, when one part is described as being "directly on top of" another part, there is no other part in between.

[0043] Although not defined differently, all terms used herein, including technical and scientific terms, have the same meaning as those generally understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are additionally interpreted as having the meaning consistent with the relevant technical literature and the present disclosure, and are not interpreted in their ideal or highly formal sense unless otherwise defined.

[0044] Also, unless otherwise specified, % means weight percent, and 1 ppm is 0.0001 weight percent.

[0045] In this specification, the term “these combinations” as used in a maxi expression means one or more mixtures or combinations selected from the group of components described in the maxi expression, and includes one or more of the components selected from the group of components.

[0046] The embodiments of the present invention will be described below in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0047] 1.Negative electrode active material The inventors of the present invention have conducted extensive research to improve both the charging output and lifespan characteristics of natural graphite anode active materials. As a result, they have discovered that the above effects can be favorably realized when the anode active material satisfies physical properties such as those shown in Formula 1 below, and have completed the present invention.

[0048] One embodiment of the present invention provides a negative electrode active material for a lithium secondary battery, comprising natural graphite, wherein the natural graphite satisfies the following formula 1.

[0049] [Formula 1] P 1.7 -P 1.3 ≥1200 kg·f / cm 2

[0050] In the above equation 1, P 1.7 This is the applied pressure when the pellet density of the negative electrode active material is 1.7 g / cc, and P 1.3 This is the applied pressure when the pellet density of the negative electrode active material is 1.3 g / cc.

[0051] In this specification, "pellet density" refers to the density of the active material powder measured when a load is applied in the vertical direction to apply pressure after a specific mass and area of ​​the active material powder sample has been placed in a cylinder. In other words, Equation 1 above represents the additional pressure required to increase the pellet density of the active material powder from 1.3 g / cc to 1.7 g / cc, and the greater such additional pressure, the stronger the rigidity of the active material powder. In other words, the natural graphite-silver particle strength according to the present invention is very high.

[0052] By satisfying Equation 1, the negative electrode active material for a lithium secondary battery according to one embodiment of the present invention can improve both the charging output characteristics and lifespan characteristics of the battery.

[0053] More specifically, the inventors have found that natural graphite active materials with a particle strength large enough to satisfy Formula 1 can be more easily obtained by oxidizing natural graphite powder and then shaping it to a high density.

[0054] When natural graphite powder is oxidized, carbon atoms on the graphite surface react with oxygen to form carbon dioxide, and a portion of the layered structure of the natural graphite is decomposed, creating new lithium ion channels. This allows lithium ions to move both through the lithium ion channels parallel to the layered structure (which are the original lithium ion movement pathways) and through the newly formed lithium ion channels, thereby improving the battery's charging output characteristics. Furthermore, when the natural graphite is made into high-density spheres, the directionality of the graphite layer edges within the graphite particles can be diversified, allowing for smoother lithium ion movement. This, in turn, improves the battery's charging output characteristics.

[0055] On the other hand, the inventors have found that by satisfying Equation 1 above, the charging output characteristics of the battery, as well as its lifespan characteristics, are improved. This is thought to be because the oxidation-high-density spheroidization process maximizes the benefits of high-density spheroidization and minimizes the porosity inside the graphite, thereby reducing the irreversible consumption of lithium due to additional SEI formation between the electrolyte / graphite interface during the battery's lifespan, which is known to be the main mechanism of lifespan degradation.

[0056] The value in formula 1 for the aforementioned natural graphite is, more specifically, 1250 kg·f / cm². 2 That's fine too.

[0057] In one embodiment, the natural graphite can satisfy the following formula 2.

[0058] [Formula 2] P 1.6 -P 1.3 ≥850 kg·f / cm 2

[0059] In the above equation 2, P 1.6 This is the applied pressure when the pellet density is 1.6 g / cc, and P 1.3 This is the applied pressure when the pellet density is 1.3 g / cc.

[0060] The value of Equation 2 for natural graphite is, more specifically, 870 kg·f / cm². 2 That's fine too.

[0061] In one embodiment, the natural graphite can satisfy the following formula 3.

[0062] [Formula 3] P 1.5 -P 1.3 ≥550 kg·f / cm 2

[0063] In the above equation 3, P 1.5 This is the applied pressure when the pellet density is 1.5 g / cc, and P 1.3 This is the applied pressure when the pellet density is 1.3 g / cc.

[0064] The value in Equation 3 for natural graphite is, more specifically, 570 kg·f / cm². 2 That's fine too.

[0065] In one embodiment, the natural graphite can satisfy the following formula 4.

[0066] [Formula 4] P 1.4 -P 1.3 ≥250 kg·f / cm 2

[0067] In the above equation 4, P 1.4 This is the applied pressure when the pellet density is 1.4 g / cc, and P 1.3 This is the applied pressure when the pellet density is 1.3 g / cc.

[0068] The value in Equation 4 for the aforementioned natural graphite is, more specifically, 280 kg·f / cm². 2 That's fine too.

[0069] The technical significance of the negative electrode active material satisfying equations 2 through 4 is the same as that of equation 1 described above, and therefore will be omitted.

[0070] On the other hand, the natural graphite may have an orientation peak intensity ratio (I110 / I004) of 0.50 or higher during XRD pattern analysis, more specifically, it may be 0.51 or higher, or 0.70 or lower.

[0071] In this specification, the orientational peak intensity ratio (I110 / I004) refers to the ratio of the areas obtained by integrating the peak intensities of the (110) and (004) planes of a graphite particle after measuring them by XRD. Specifically, the (110) plane is in the range of 76.5 degrees < 2θ < 78.5 degrees, and the (004) plane is in the range of 53.5 < 2θ < 56.0 degrees, where 2θ is the diffraction angle.

[0072] By satisfying the aforementioned range for the orientation peak intensity ratio I110 / I004 of natural graphite, the orientation of the graphite layer edge portion within the graphite particles can be diversified, allowing for smoother lithium ion movement, thereby improving the battery's charging output characteristics.

[0073] The aforementioned natural graphite may have a spheroidization degree of 0.85 or higher, and more specifically, 0.90 or higher.

[0074] In this specification, spheroidization is a numerical representation of the degree to which a particle is close to being spherical, and refers to the value obtained by dividing the circumference of a circle having the same area as the particle projection shape by the actual circumference of the particle projection shape, using a flow-type particle analyzer. Such spheroidization can be measured using an analyzer for obtaining optical images (Fluid Imaging Technologies, Flowcam 8100) and analytical software (visual spreadsheet).

[0075] When natural graphite satisfies the aforementioned range of spheroidization, both the density and orientation of the spherical natural graphite particles increase. When this is applied as a negative electrode active material, a uniform surface coating becomes possible, improving the electrode energy density and thus the output characteristics of the battery.

[0076] The aforementioned orientation peak intensity ratio (I110 / I004) and spheroidization range can be more easily obtained through a high-density spheroidization process in the manufacturing method.

[0077] The negative electrode active material for the lithium secondary battery is placed on the natural graphite and may further include a low-crystallinity carbon material-containing coating layer. The inclusion of the coating layer on the natural graphite surface suppresses side reactions of the natural graphite with the electrolyte, reducing irreversible reactions and improving lithium ion conductivity, thereby improving electrochemical properties such as battery output and lifespan.

[0078] The low-crystalline carbon material is not particularly limited. For example, the low-crystalline carbon material may be, but is not limited to, easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), or a combination thereof. The easily graphitizable carbon may be an amorphous carbon-based material produced by carbonizing coke, needle coke, coal-based pitch, petroleum-based pitch, mesophase pitch, or a combination thereof. The difficult-to-graphitize carbon may be an amorphous carbon-based material obtained by thermally decomposing phenol resin, furan resin, furfuryl alcohol, polyacrylonitrile, styrene, polyimide, epoxy resin, or a combination thereof.

[0079] The content of the coating layer may be 1 to 20% by weight based on the total weight of the natural graphite, and more specifically, it may be 2 to 16% by weight, 3 to 12% by weight, or 4 to 10% by weight. By satisfying the above range for the content of the coating layer, the natural graphite and the coating layer can be effectively bonded, reducing side reactions and improving lithium ion conductivity, thereby improving the output and life characteristics of the lithium secondary battery.

[0080] The aforementioned negative electrode active material for lithium secondary batteries has a tap density of 1.1 g / cm³. 3 The above range is also acceptable. By satisfying the above range for the tap density of the negative electrode active material, the electrode energy density can be improved. In this specification, tap density is a method for measuring the degree of filling of a sample per unit volume, and can be measured by methods commonly used in the industry. For example, it may be the density (sample weight / volume) calculated from the change in volume after a measuring container containing the sample is mechanically dropped (tapped) from a certain height a predetermined number of times in accordance with the measuring instruments and methods specified in ASTM B527.

[0081] The negative electrode active material for the lithium secondary battery may have a SPAN value of 1 to 1.5. Satisfying the SPAN value of the negative electrode active material within this range may offer advantages such as reduced electrode resistance due to fine and coarse particles and improved expansion characteristics due to reduced electrode expansion. More specifically, if the SPAN value of the negative electrode active material is excessively small, problems such as localized electrode expansion may occur due to a relatively wide particle size distribution, and if the SPAN value of the negative electrode active material is excessively large, problems such as reduced electrode rollability and increased porosity within the electrode may occur. In this specification, the SPAN value refers to the value obtained by calculating particle size [particle size D90 - particle size D10] / particle size D50, where particle size D90, particle size D50, and particle size D10 can be defined as particle sizes corresponding to 90%, 50%, and 10% of the cumulative volume in the particle size distribution curve, respectively. Each of these particle sizes can be measured, for example, using the laser diffraction method.

[0082] The negative electrode active material for the lithium secondary battery may have an average particle size D50 of 12 to 20 μm. Satisfying the above range for the average particle size of the negative electrode active material may be advantageous in ensuring maximum electrode adhesion and rollability, as well as ensuring electrochemically reversible capacity and achieving initial efficiency. More specifically, if the average particle size of the negative electrode active material is excessively small, there may be a problem of decreased initial charge / discharge Coulomb efficiency due to an increase in specific surface area, and if the average particle size of the negative electrode active material is excessively large, there may be a problem of increased electrode resistance and electrode expansion rate. In this specification, the average particle size D50 can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve.

[0083] 2. Method for producing negative electrode active material Another embodiment of the present invention provides a method for producing a negative electrode active material for a lithium secondary battery, comprising the steps of: preparing natural graphite powder; oxidizing the natural graphite powder; and forming the oxidized natural graphite powder into high-density spheres.

[0084] The following describes, step by step, a method for producing a negative electrode active material for a lithium secondary battery according to another embodiment of the present invention.

[0085] First, prepare the natural graphite powder.

[0086] In this case, the prepared natural graphite may be natural graphite raw material powder that has been primary sphericalized.

[0087] The aforementioned primary spheroidization may be carried out using a general method for spheroidizing plate-shaped natural graphite raw material powder in order to use spheroidized graphite material during the production of the negative electrode active material.

[0088] Next, the natural graphite powder is subjected to an oxidation treatment.

[0089] Through the aforementioned oxidation treatment, carbon atoms and oxygen atoms on the graphite surface react to produce carbon dioxide, and a portion of the layers forming the graphite structure are decomposed, allowing new lithium ion channels to be formed. Furthermore, as will be described in the high-density spheroidization process later, this process also plays a role in further improving the particle strength of the active material.

[0090] The oxidation treatment may be carried out at a temperature of 500 to 700°C. If the oxidation treatment temperature is too low, the oxidation reaction will not proceed, which may result in a negligible oxidation effect. If the oxidation treatment temperature is too high, excessive oxidation of the graphite surface layer may increase the surface roughness and specific surface area, which may lead to a decrease in reversible discharge capacity and initial charge / discharge cooling efficiency.

[0091] The oxidation treatment may be carried out for 1 to 5 hours. If the oxidation treatment time is too short, the aforementioned oxidation effect may be negligible, and if the oxidation treatment time is too long, excessive oxidation of the graphite surface layer may increase the surface roughness and specific surface area, which may lead to a decrease in reversible discharge capacity and initial charge / discharge cooling efficiency.

[0092] The oxidation treatment may be carried out in an air or oxygen atmosphere.

[0093] Next, the oxidized natural graphite powder is made into high-density spheres.

[0094] The aforementioned high-density spheroidization may be carried out by a mechanical spheroidization method.

[0095] The mechanical spheroidizing method may be carried out through one or more methods selected from the group consisting of ACM milling (Air Classifying milling), Spheronizing milling, Grinding milling, Mechanofusion milling, Planetary milling, Hybridization milling, Shape milling, and High-speed milling.

[0096] The secondary respheroidizing step may be performed at a rotational speed of 500 to 4000 rpm, more specifically, at 700 to 2000 rpm or 800 to 1500 rpm. By performing spheroidizing at rotational speeds within this range, cracking and fracture of the graphite raw material can be minimized, and natural graphite with an appropriate degree of spheroidization can be formed.

[0097] The aforementioned secondary respheroidizing step may be carried out for 5 to 40 minutes, and more specifically, for 8 to 25 minutes or 10 to 20 minutes. By performing spheroidizing for the duration described above, natural graphite with an appropriate degree of spheroidization can be formed.

[0098] In particular, the method for producing the negative electrode active material according to the present invention allows for even greater particle strength of the negative electrode active material compared to the case where only high-density spheroidization is performed, as high-density spheroidization progresses after the oxidation treatment. This allows for a more dense formation of the inside of the graphite particles. As a result, the values ​​of the aforementioned equations 1 to 4 may become even larger. This is thought to be because the oxidation treatment decomposes some of the planes that make up the layered structure of the graphite, and the graphite with shorter planes aggregates more densely through high-density spheroidization.

[0099] Through the oxidation treatment and high-density spheroidization process, the physical properties of the obtained negative electrode active material, such as formulas 1 to 4, orientation peak intensity ratio (I110 / I004), and degree of spheroidization, can be appropriately obtained within the range of the present invention.

[0100] Next, the process may further include the step of forming a high-density sphere from the oxidized natural graphite powder, followed by the step of heat-treating a low-crystallinity carbon material precursor to form a low-crystallinity carbon material-containing coating layer.

[0101] The low-crystalline carbon material precursor may be petroleum-based pitch, coal-based pitch, mesophase pitch, heavy oil, light oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, phenol resin, furan resin, furfuryl alcohol, polyacrylonitrile, cellulose, styrene, polyimide, epoxy resin, glucose, or a combination thereof.

[0102] The mixing may be carried out by a mechanical mixing method. In this case, the mechanical mixing method may be one or more methods selected from the group consisting of ball milling, mechanofusion milling, shaker milling, planetary milling, attritor milling, shape milling, nauta milling, nobilta milling, high-speed mixing, paddle mixing, ribbon mixing, Henschel mixing, cone type mixing, thinky mixing, homo mixing, and a stirrer.

[0103] The mechanical mixing method may be carried out at a rotational speed of 500 to 3000 rpm.

[0104] The heat treatment may be carried out in an atmosphere of hydrogen, nitrogen, argon, or a mixture thereof, at a temperature of 600 to 1500°C.

[0105] 3. Negative electrode and lithium secondary battery Another embodiment of the present invention provides a negative electrode for a lithium secondary battery containing the negative electrode active material described above.

[0106] A negative electrode for a lithium secondary battery according to yet 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 containing the aforementioned negative electrode active material for a lithium secondary battery.

[0107] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. 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 can be used. The negative electrode current collector can also typically have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0108] The negative electrode active material layer may selectively include a binder and / or a conductive material together with the negative electrode active material.

[0109] The binder plays a role in improving 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 can be used. The binder may be present in an amount of 1 to 30% by weight relative to the total weight of the negative electrode active material layer.

[0110] The conductive material is used to impart conductivity to the electrodes and can be used without special limitations as long as it has electronic conductivity without causing chemical changes in the battery it is configured in. 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 fiber; 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. One of these alone or a mixture of two or more can be used. The conductive material may usually be included in an amount of 1 to 30% by weight relative to the total weight of the negative electrode active material layer.

[0111] A negative electrode for a lithium secondary battery according to one embodiment of the present invention can be manufactured by a conventional negative electrode manufacturing method, except that the negative electrode active material described above is used.

[0112] Specifically, it can be manufactured by applying a negative electrode active material layer-forming composition, which includes the aforementioned negative electrode active material and selectively contains a binder, conductive material, and 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.

[0113] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these can be used alone or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the negative electrode active material, conductive material, and binder, taking into consideration the coating thickness and yield of the slurry, and to have a viscosity that allows for excellent thickness uniformity during subsequent coating for the manufacture of the negative electrode.

[0114] Alternatively, the negative electrode may be manufactured by casting the negative electrode active material layer forming composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0115] Another embodiment of the present invention provides a lithium secondary battery including the negative electrode.

[0116] A lithium secondary battery according to yet another embodiment of the present invention may more specifically include a positive electrode, a negative electrode located opposite the positive electrode, a separator interposed between the positive and negative electrodes, and an electrolyte.

[0117] The negative electrode is as described above.

[0118] Furthermore, the lithium secondary battery may selectively further include a battery container for housing an electrode assembly comprising a positive electrode, a negative electrode, and a separator, and a sealing member for sealing the battery container.

[0119] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer may include a positive electrode active material.

[0120] The positive electrode current collector is not particularly limited as long as it is conductive without causing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can also typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0121] As the positive electrode active material, a compound capable of reversibly intercalating and deintercalating lithium (a lithium-intercalated compound) can be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used, and a concrete example thereof is a compound represented by any one of the following chemical formulas.

[0122] Li a A 1-b B b D2 (In the above equation, 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 equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE 2-b B b O 4-c D c (In the above equation, 0≦b≦0.5 and 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, and 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, and 0 < α < 2); Li a Ni 1-b-c Co b B c O 2-α T2(In the above equation, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2);Li a Ni 1-b-c Mn b B c D α(In the above formula, 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 formula, 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 (In the above formula, 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 (In the above formula, 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 d GeO2 (In 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 formula, 0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a CoG b O2 (In the above formula, 0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a MnG b O2 (In the above formula, 0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a Mn2G b O4 (In the above formula, 0.90 ≦ a ≦ 1.8, 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.

[0123] 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, rare earth elements 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; J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0124] Of course, it is also possible to use a compound having a coating layer on its surface, or to use a mixture of the compound and a compound having a coating layer.

[0125] The coating layer may contain at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxys of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers may be amorphous or crystalline. The coating elements included in the coating layer may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer formation step may use any coating method (e.g., spray coating, immersion method, etc.) that does not adversely affect the physical properties of the positive electrode active material using such elements, and this is a matter that will be well understood by those engaged in this field, so a detailed explanation will be omitted.

[0126] The positive electrode active material layer may further include a binder and / or a conductive material along with the positive electrode active material described above.

[0127] The binder plays a role in improving adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive 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 can be used individually or in mixtures of two or more of these, but is not limited thereto. The binder may be present in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0128] The conductive material is used to impart conductivity to the electrodes and can be used without special limitations as long as it has electronic conductivity without causing chemical changes in the battery it is configured in. 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 fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these can be used alone or a mixture of two or more, but it is not limited to these. The conductive material may usually be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0129] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode.

[0130] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, which optionally contains a positive electrode active material and a binder, conductive material, or solvent, onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0131] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these can be used alone or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into consideration the coating thickness and yield of the slurry, and to have a viscosity that allows for excellent thickness uniformity during subsequent coating for the manufacture of the positive electrode.

[0132] Alternatively, the positive electrode may be manufactured by casting the positive electrode active material layer forming composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0133] The separator separates the positive and negative electrodes and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances to ensure heat resistance or mechanical strength may be used, and may be selectively used as torticultural or multilayer structures.

[0134] The aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0135] Specifically, the organic liquid electrolyte may contain an organic solvent and a lithium salt.

[0136] The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, without any special limitations. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; tolyls such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2 to C20, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9 can produce an electrolyte with excellent performance.

[0137] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any special limitations. Specifically, the lithium salt can 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, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0138] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte. [Examples]

[0139] Example 1 (1) Manufacturing of negative electrode active material

[0140] (Preparation of natural graphite powder) Primary spheroidized natural graphite powder with an average particle size D50 of 16 μm was prepared.

[0141] (Oxidation treatment) Subsequently, the natural graphite powder was subjected to oxidation treatment in a continuous rotary kiln at 600°C for 3 hours in an air atmosphere.

[0142] (High-density spheroidization) Subsequently, the oxidized natural graphite powder was subjected to high-density spheroidization treatment at 1000 rpm for 25 minutes in a spheronizer, and fine and coarse particles were removed through airflow classification and sieving.

[0143] (Coating) Afterwards, using the high-density spherical natural graphite powder as a base material, petroleum-based pitch was mixed in a weight ratio of 100:8, and then mechanically mixed in a high-speed stirrer at 2000 rpm for 10 minutes to form a homogeneous mixture. The mixture was placed in a container and heat-treated in a nitrogen atmosphere at 1200°C for 5 hours, and then classified using a 75 μm sieve to produce natural graphite with a coating layer formed on top.

[0144] (2) Manufacturing of the negative electrode The negative electrode active material produced above was mixed with a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethylcellulose (CMC) as a thickener in a mass ratio of 96.6:1:1.3:1.1. The mixture was then dispersed in ion-removed distilled water to produce a negative electrode active material layer composition. The composition was applied to a copper foil current collector, then dried and rolled to obtain electrode densities of 1.50±0.05 and 1.70±0.05 g / cm³. 3 We manufactured the negative electrode.

[0145] (3) Manufacturing of lithium secondary batteries A coin-type 2032 half-cell was fabricated using the aforementioned negative electrode as the working electrode and metallic lithium as the counter electrode. In this case, a separator made of porous polypropylene film was inserted between the working electrode and the counter electrode, and the electrolyte used was a mixed solution of diethyl carbonate (DEC) and ethylene carbonate (EC) in a volume ratio of 7:3, in which 1M LiPF6 was dissolved.

[0146] Example 2 A negative electrode active material, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that natural graphite powder was used as the base material and petroleum-based pitch was mixed in a weight ratio of 100:8.8.

[0147] Comparative Example 1 The negative electrode active material, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1, except that the high-density spheroidization and coating steps were omitted.

[0148] Comparative Example 2 The negative electrode active material, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1, except that the high-density spheroidization step was omitted.

[0149] Comparative Example 3 The negative electrode active material, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1, except that the oxidation treatment step was omitted.

[0150] Comparative Example 4 The negative electrode active material, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1, except that the oxidation treatment and high-density spheroidization steps were omitted.

[0151] Table 1 below summarizes the manufacturing process of the positive electrode active materials for the examples and comparative examples.

[0152] [Table 1]

[0153] Experimental Example 1: Evaluation of Active Material Properties The physical properties of the negative electrode active materials produced according to the examples and comparative examples were evaluated as follows, and the results are shown in Tables 2 and 3.

[0154] (1) Evaluation of particle size D10, D50, D90, Dmax and SPAN value For the active material powder, particle sizes D10, D50, D90, Dmax, and SPAN values ​​were determined using the laser diffraction method. The SPAN value was calculated as [particle size D90 - particle size D10] / particle size D50. Particle sizes Dmax, D90, D10, and D50 can be defined as the particle sizes corresponding to 100%, 90%, 10%, and 50% of the cumulative volume in the particle size distribution curve, respectively.

[0155] (2) Evaluation of specific surface area The specific surface area of ​​the active material powder was measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0156] (3) Evaluation of tap density Based on ASTM B527, 15 g of active material powder was placed in a 50 mL container, then tapped at 3000 cycles @ 284 cycles / min, and the packing density was measured.

[0157] (4) Evaluation of the degree of orientation In the XRD pattern obtained from X-ray diffraction measurements, the area ratio (I110 / I004) was calculated by integrating the peak intensities of the XRD spectra to which the (110) and (004) planes of the graphite crystal belong. More specifically, the XRD measurement conditions were as follows:

[0158] -Target: Cu(Kα-ray) graphite monochromatization device - Slit: Divergent slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree -Measurement area and step angle / measurement time: -(110) plane: 76.5 degrees < 2θ < 78.5 degrees, 0.1 degrees / 4.2 seconds -(004) plane: 53.5 degrees < 2θ < 56.0 degrees, 0.1 degrees / 4.2 arcseconds, where 2θ represents the diffraction angle.

[0159] (5) Evaluation of the degree of spheroidization Using a flow-type particle analyzer, the degree of spheroidization was evaluated by dividing the area around the particle projection shape by the actual area around the particle projection shape. This measurement was performed using an analyzer (Fluid Imaging Technologies, Flowcam 8100) and an analysis software (visual spreadsheet) to obtain optical images.

[0160] (6) Evaluation of pellet density by applied pressure, evaluation by formulas 1 to 4 The pellet density of the active material powder was measured under applied pressure.

[0161] [Table 2]

[0162] [Table 3]

[0163] Referring to Tables 2 and 3, it was confirmed that in Examples 1 and 2, where both oxidation treatment and high-density spheroidization processes were performed, the degree of orientation and spheroidization was excellent, and the tap density was high. Furthermore, the values ​​of Equations 1 to 4 were all large, confirming excellent particle rigidity. In contrast, in Comparative Examples 1, 2, and 4, where the high-density spheroidization process was not performed, it was confirmed that the degree of orientation was inferior and the degree of spheroidization was small. Furthermore, the values ​​of Equations 1 to 4 were small, confirming that the particle rigidity was inferior.

[0164] On the other hand, in Comparative Example 3, which underwent a high-density spheroidization process but not an oxidation treatment process, the degree of orientation, degree of spheroidization, and tap density were good, at a similar level to the examples. However, it was confirmed that the values ​​of Equations 1 to 4 were not at the level of the examples, indicating that the particle rigidity was somewhat inferior.

[0165] Experimental Example 2: Evaluation of the electrochemical properties of lithium secondary batteries The electrochemical properties of lithium secondary batteries manufactured according to the examples and comparative examples were evaluated and are shown in Table 4 below.

[0166] (1) Evaluation of charging output characteristics (SOC 10% → 80%) After the manufactured lithium secondary battery was charged at 0.1C to 4.2V / 0.005C under constant current / constant voltage (CC / CV) conditions at 25°C, and then discharged at 0.1C to 2.5V under constant current (CC) conditions to complete the chemical conversion process, it was charged at a rate of 0.1C to 10% of the cell capacity (SOC 10%). From this point, it was charged at various C rates (2.0C, 2.5C, 3.0C, 3.5C, 4.0C, 4.5C, 5.0C, 6.0C) under constant current / constant voltage (CC / CV) conditions, and the time taken to charge to 80% of the cell capacity (SOC 80%) was measured.

[0167] (2) Evaluation of life characteristics (3C / 0.5C) After the manufactured lithium secondary battery was charged at 25°C under constant current / constant voltage (CC / CV) conditions to 4.2V / 0.005C at 0.1C, and then discharged under constant current (CC) conditions to 2.5V at 0.1C to complete the conversion process, it was then charged at a 3C rate under constant current / pre-voltage (CC / CV) conditions to 4.2V / 0.005C, and then discharged under constant current (CC) conditions to 2.5V at 0.5C to measure the discharge capacity retention rate of the 100th cycle cell.

[0168] [Table 4]

[0169] Referring to Table 4, it was confirmed that in Examples 1 and 2, where the physical properties of the negative electrode active material, such as those in Formula 1, were sufficiently large, the charging output characteristics and lifespan characteristics at high rates of 2C or higher were both excellent. In contrast, in Comparative Examples 1 to 4, where the physical properties of the negative electrode active material, such as those in Formula 1, were small, it was confirmed that the charging output characteristics and lifespan characteristics were inferior to those of the Examples.

[0170] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and these also naturally fall within the scope of the present invention.

[0171] Therefore, the substantial scope of the present invention should be defined by the appended claims and their equivalents.

Claims

1. Contains natural graphite, The aforementioned natural graphite is a negative electrode active material for lithium secondary batteries that satisfies the following formula 1. [Formula 1] P １．７ -P １．３ ≧1200kg・f / cm ２ In the above equation 1, P １．７ This is the applied pressure when the pellet density of the negative electrode active material is 1.7 g / cc, and P １．３ This is the applied pressure when the pellet density of the negative electrode active material is 1.3 g / cc.

2. The aforementioned natural graphite satisfies the following formula 2, wherein it is a negative electrode active material for a lithium secondary battery according to claim 1. [Formula 2] P １．６ -P １．３ ≧850kg・f / cm ２ In the above formula (2), P １．６ is the applied pressure when the pellet density of the negative electrode active material is 1.6 g / cc, and P １．３ is the applied pressure when the pellet density of the negative electrode active material is 1.3 g / cc.

3. The aforementioned natural graphite satisfies the following formula 3, wherein it is a negative electrode active material for a lithium secondary battery according to claim 1. [Formula 3] P １．５ -P １．３ ≧550kg・f / cm ２ In the above equation 3, P １．５ This is the applied pressure when the pellet density of the negative electrode active material is 1.5 g / cc, and P １．３ This is the applied pressure when the pellet density of the negative electrode active material is 1.3 g / cc.

4. The aforementioned natural graphite satisfies the following formula 4, wherein it is a negative electrode active material for a lithium secondary battery according to claim 1. [Formula 4] P １．４ -P １．３ ≧250kg・f / cm ２ In the above equation 4, P １．４ This is the applied pressure when the pellet density of the negative electrode active material is 1.4 g / cc, and P １．３ This is the applied pressure when the pellet density of the negative electrode active material is 1.3 g / cc.

5. The natural graphite has an orientation peak intensity ratio (I110 / I004) of 0.50 or more when analyzed by XRD, as described in claim 1, for a negative electrode active material for a lithium secondary battery.

6. The natural graphite has a spheroidization degree of 0.85 or higher, as described in claim 1, for a negative electrode active material for a lithium secondary battery.

7. The negative electrode active material for a lithium secondary battery according to claim 1, wherein the natural graphite is oxidized.

8. The negative electrode active material for a lithium secondary battery according to claim 1, further comprising a coating layer containing a low-crystallinity carbon material, disposed on the aforementioned natural graphite.

9. The negative electrode active material for a lithium secondary battery according to claim 8, wherein the content of the coating layer is 1 to 20% by weight based on the total weight of the natural graphite.

10. Tap density is 1.1 g / cm³ ３ The negative electrode active material for a lithium secondary battery according to claim 1.

11. The negative electrode active material for a lithium secondary battery according to claim 1, wherein the SPAN value is 1 to 1.

5.

12. The negative electrode active material for a lithium secondary battery according to claim 1, wherein the average particle size D50 is 12 to 20 μm.

13. Steps to prepare natural graphite powder; The steps of oxidizing the aforementioned natural graphite powder; and The step includes forming the oxidized natural graphite powder into high-density spheres, A method for producing a negative electrode active material for lithium secondary batteries.

14. The method for producing a negative electrode active material for a lithium secondary battery according to claim 13, wherein the oxidation treatment is carried out at a temperature of 500 to 700°C.

15. The method for producing a negative electrode active material for a lithium secondary battery according to claim 13, wherein the oxidation treatment is performed for 1 to 5 hours.

16. The method for producing a negative electrode active material for a lithium secondary battery according to claim 13, wherein the oxidation treatment is carried out in an air or oxygen atmosphere.

17. After the step of forming the oxidized natural graphite powder into high-density spheres, A method for producing a negative electrode active material for a lithium secondary battery according to claim 13, further comprising the step of heat-treating a mixture of low-crystallinity carbon material precursors to form a low-crystallinity carbon material-containing coating layer.

18. A negative electrode for a lithium secondary battery, comprising the negative electrode active material described in any one of claims 1 to 12.

19. A lithium secondary battery comprising the negative electrode for a lithium secondary battery as described in claim 18.

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