Negative electrode active material and rechargeable lithium battery including same

Abstract

The present invention relates to a negative electrode active material and a rechargeable lithium battery comprising the same, the negative electrode active material comprising: secondary particles each being a spheroidized aggregate of a plurality of primary particles; tertiary natural graphite particles, each of which is an aggregate of the secondary particles; artificial graphite on the surfaces of the primary particles and the surfaces of the secondary particles; and Nb2O5.

Description

TECHNICAL FIELD

[0001] Disclosed are a negative electrode active material and a rechargeable lithium battery including the same. BACKGROUND

[0002] Recently, rapid replenishment of electronic devices using a battery, such as a mobile phone, a laptop computer, and an electric vehicle, has required a surprising increase in demand for a rechargeable battery having a relatively high capacity and a light weight. In particular, since a rechargeable lithium battery has a light weight and a high energy density, it has recently attracted attention as a driving power source for a portable device. Accordingly, research and development for improving the performance of a rechargeable lithium battery are actively being conducted.

[0003] A rechargeable lithium battery includes a positive electrode and a negative electrode including an active material capable of intercalating and deintercalating lithium ions, and an electrolyte solution, and generates electric energy through oxidation and reduction reactions when lithium ions are intercalated / deintercalated from the positive electrode and the negative electrode. SUMMARY

[0004] TECHNICAL PROBLEM

[0005] One embodiment provides a negative electrode active material exhibiting improved excellent rapid charging characteristics.

[0006] Another embodiment provides a rechargeable lithium battery including the negative electrode active material.

[0007] TECHNICAL SOLUTION

[0008] One embodiment provides a negative electrode active material including secondary particles aggregated and spheroidized from a plurality of primary particles, tertiary particles of natural graphite aggregated from the secondary particles; and artificial graphite on surfaces of the primary particles and the secondary particles, and including Nb2O5.

[0009] Another embodiment provides a rechargeable lithium battery including: a negative electrode including the negative electrode active material; a positive electrode; and an electrolyte.

[0010] ADVANTAGEOUS EFFECTS

[0011] The negative electrode active material according to an embodiment can exhibit rapid charging characteristics. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 FIG. 1 is a schematic view illustrating a structure of a negative electrode active material according to one embodiment.

[0013] Figure 1a is a view illustrating a tertiary particle of natural graphite in the structure of the negative electrode active material illustrated in FIG. 1. Figure 1 is a view illustrating a tertiary particle of natural graphite in the structure of the negative electrode active material illustrated in FIG. 1.

[0014] Figure 2 is a schematic diagram showing a structure of a negative electrode active material according to another embodiment.

[0015] Figure 3 is a schematic diagram showing a structure of a conventional negative electrode active material.

[0016] Figure 3 is a diagram showing products in each process during the preparation process (process) of the negative electrode active material according to the embodiment.

[0017] Figure 4 is a schematic diagram showing a rechargeable lithium battery according to the embodiment. DETAILED DESCRIPTION

[0018] Hereinafter, the embodiments of the present application will be described in detail. However, these embodiments are merely examples, the present application is not limited thereto, and the present application is defined by the scope of the claims.

[0019] As used herein, when a specific definition is not otherwise provided, it will be understood that when an element, such as a layer, film, region, or substrate, is referred to as being "on" another element, it can be directly on the other element or an intervening element can also be present.

[0020] As used herein, when a specific definition is not otherwise provided, a singular expression can also include a plural. In addition, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B".

[0021] In the present specification, when a definition is not otherwise provided, the particle diameter can be an average particle diameter. The particle diameter means an average particle diameter (D50), which means a diameter of a particle having 50% of a cumulative volume in a particle size distribution. The average particle diameter (D50) can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer or by using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). Alternatively, data analysis is performed using a dynamic light scattering measuring device, and the number of particles is counted for each particle size range. Thereby, the average particle diameter (D50) value can be easily obtained by calculation. A laser diffraction method can also be used. When measured by laser diffraction, more specifically, particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (for example, MT 3000 available from Microtrac, Ltd.) using ultrasonic waves of about 28 kHz, and after irradiation with a power of 60 W, the average particle diameter (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0022] The negative electrode active material according to the embodiment includes secondary particles aggregated and spheroidized from a plurality of primary particles, and tertiary particles of natural graphite aggregated from the secondary particles; and artificial graphite on surfaces of the primary particles and the secondary particles, and includes Nb2O5. In the embodiment, Nb2O5may be provided on the tertiary particles of the natural graphite.

[0023] Figure 1 is a schematic diagram showing a structure of such a negative electrode active material. Figure 1 In the drawing, the right side is an enlarged view of the secondary particle 5 corresponding to the dotted line. The negative electrode active material 1 according to the embodiment includes secondary particles 5 aggregated and spheroidized from a plurality of primary particles 3, and tertiary particles of natural graphite aggregated from the secondary particles. In addition, the negative electrode active material includes Nb2O5 15 provided on the tertiary particles of the natural graphite. In addition, the negative electrode active material includes artificial graphite 9 on surfaces of the primary particles 3 and the secondary particles 5.

[0024] In addition, Figure 1a more clearly shows Figure 1 the tertiary particles of the natural graphite in the drawing.

[0025] According to the embodiment, the negative electrode active material can further include an amorphous carbon coating layer (coating) around the tertiary particles of the natural graphite. If the negative electrode active material further includes the amorphous carbon coating layer, as Figure 2 shown in the drawing, the Nb2O5 15 can be provided on the amorphous carbon coating layer 11.

[0026] Crystalline carbon, particularly natural graphite, used as a negative electrode active material has a higher capacity than artificial graphite, and an ideal capacity close to a theoretical capacity can be achieved. However, natural graphite is composed of large particles having 40 μm to 120 μm, and is generally used as a negative electrode active material by spheroidizing it. Figure 3 A structure of a typical natural graphite negative electrode active material 20 is shown, which includes flaky (scale) natural graphite 23 and an amorphous carbon coating layer 27 on surfaces of the flaky natural graphite particles. The negative electrode active material has limited sites for intercalation / deintercalation during charging / discharging, and thus its charging / discharging characteristics, particularly high-rate charging / discharging characteristics, are not suitable.

[0027] The negative electrode active material according to the embodiment includes secondary particles formed by agglomerating and spheroidizing small primary particles of natural graphite, and tertiary particles of the natural graphite formed by re-agglomerating the secondary particles, and includes artificial graphite on the surfaces of the primary particles and the secondary particles, thereby increasing sites of intercalation / deintercalation of lithium ions and facilitating movement of the lithium ions. In addition, the negative electrode active material according to the embodiment includes Nb2O5 in the tertiary particles, which is similar to a pseudo-capacitor, and which absorbs and desorbs lithium ions and is a structurally stable material that does not cause volume expansion during charging and discharging, so that lithium ions can be rapidly absorbed and desorbed during charging and discharging. The negative electrode active material according to the embodiment can exhibit improved rapid charging / discharging characteristics. In addition, in the embodiment, the Nb2O5 can be disposed on the tertiary particles of the natural graphite.

[0028] In one embodiment, the natural graphite can be flaky natural graphite, in which case lithium intercalation can more actively (positively) occur. According to another embodiment, the flaky natural graphite can be small-particle flaky natural graphite. If the natural graphite is in the form of small-particle flakes, the number of sites in which lithium ions can be intercalated and deintercalated increases within the same area, and the path through which lithium ions can move becomes shorter, so that it is more suitable for rapid charging and discharging.

[0029] In addition, because the negative electrode active material according to the embodiment is formed by spheroidizing and bending small primary particles, lithium can be intercalated into the bent portions of the flaky natural graphite and the both ends of the negative electrode active material, in particular. In this way, the negative electrode active material according to the embodiment has an increased number of lithium intercalation sites, and thus can exhibit improved charge rates (charging rates), in particular, improved high-rate charge rates.

[0030] In the embodiment, the amount of Nb2O5 can be 1% to 15%, 2% to 12%, or 2% to 10% by weight, based on 100% by weight of the total negative electrode active material. If the amount of Nb2O5 is within the above range, rapid charging performance can be further improved while maintaining a uniform state, thereby exhibiting excellent battery chemical characteristics.

[0031] In the embodiment, the Nb2O5 can have an orthorhombic (orthorhombic crystal) structure. The Nb2O5 having the orthorhombic structure can be referred to as T-Nb2O5. The Nb2O5 having the orthorhombic structure can have a crystal plane spacing of the (001) plane of 0.390 nm to 0.399 nm.

[0032] Among Nb2Os having a pseudo-hexagonal or monoclinic (monoclinic crystal) structure, Nb2Os having an orthorhombic structure can be preferred. If Nb2Os having an orthorhombic structure is used, lithium ions can have channels through which they can move faster, thereby providing an effect of reducing volume expansion during charging and discharging and improving rate characteristics.

[0033] According to the embodiment having such a configuration, if the X-ray diffraction peaks (JCPDS card No. 30-0873) of the negative electrode active material are analyzed, it can have peaks occurring at 2Θ = 22.7° ± 0.2°, 28.5° ± 0.2°, 36.7° ± 0.2°, 46.2° ± 0.2°, 50.9° ± 0.2°, and 55.1° ± 0.2°. 2Θ = 22.7° ± 0.2°, 28.5° ± 0.2°, 36.7° ± 0.2°, 46.2° ± 0.2°, 50.9° ± 0.2°, 55.1° ± 0.2° represent (001) plane, (180) plane, (181) plane, (002) plane, (380) plane, and (381) plane, respectively. The X-ray diffraction peak analysis can be performed using CuKa rays.

[0034] The primary particles can have a particle diameter of 4 μm to 8 μm. The particle diameter of the primary particles can be, for example, 5 μm to 8 μm, 6 μm to 8 μm, or 6 μm to 7 μm.

[0035] The secondary particles can have a particle diameter of 5 μm to 10 μm. The particle diameter of the secondary particles can be, for example, 6 μm to 10 μm, 6 μm to 8 μm, or 7 μm to 8 μm.

[0036] The tertiary particles can have a particle diameter of 9 μm to 15 μm. For example, it can be 9.2 μm to 15 μm or 9.5 μm to 15 μm.

[0037] If the particle diameter of the primary particles is 4 μm to 8 μm, the preparation thereof can be easier, the cycle life characteristics can be further improved, and the application to a rechargeable lithium battery can be easier. In addition, if the particle diameter of the secondary particles is 5 μm to 10 μm, the tertiary particles can be better prepared and can be more easily applied to a rechargeable lithium battery. In addition, if the particle diameter of the tertiary particles is 9 μm to 15 μm, it can exhibit better initial efficiency and show excellent negative electrode charging / discharging characteristics, making it more suitable for application to a rechargeable lithium battery.

[0038] In the negative electrode active material according to the embodiment, the thickness of the amorphous carbon coating layer can be 5 nm to 50 nm, for example, 10 nm to 50 nm or 20 nm to 50 nm. If the thickness of the amorphous carbon coating layer falls within the above range, the side reaction with the electrolyte can be more effectively suppressed, and the charge / discharge rate characteristics can be improved.

[0039] The particle diameter of the negative electrode active material including the primary particles, the secondary particles, and the tertiary particles having such a particle diameter and the amorphous carbon coating layer having the thickness described above can be 9.05 μm to 16 μm. The particle diameter of the negative electrode active material can be, for example, 9.05 μm to 16 μm, 9.2 μm to 15.5 μm, or 9.5 μm to 15 μm. If the particle diameter of the negative electrode active material is within the above range, the insertion of lithium ions is easy, so that the charge rate characteristics can be improved, and excellent cycle life characteristics can be exhibited due to the improvement of the initial efficiency and the negative electrode processability.

[0040] In the embodiment, the secondary particles are formed by aggregating the primary particles, and the number of the primary particles is not particularly limited as long as it can form the secondary particles, but, for example, 2 to 30, 2 to 20, 2 to 10, or 2 to 4 primary particles can be aggregated to form the secondary particles. Also, the tertiary particles are formed by aggregating the secondary particles, and the number of the secondary particles is not particularly limited as long as they can form the tertiary particles. For example, 2 to 20, 2 to 10, or 2 to 4 secondary particles can be aggregated to form the tertiary particles.

[0041] In the embodiment, the amount of the artificial graphite can be 6% by weight to 16.5% by weight, 6% by weight to 15% by weight, or 10% by weight to 14.5% by weight, based on 100% by weight of the total negative electrode active material. In the embodiment, because the artificial graphite is disposed on the surfaces of the primary particles and the secondary particles, if the amount of the artificial graphite is within the above range, the inside of the negative electrode active material can be in a more dense form. Because the negative electrode active material according to the embodiment includes the secondary particles in which the primary particles are aggregated and spheroidized and the tertiary particles in which the secondary particles are aggregated, the artificial graphite is filled in the spaces that can be formed between the particles, and in particular, is filled in the above amount, so that the spaces can be more sufficiently filled, and as a result, the inside of the final negative electrode active material can be in a more dense form.

[0042] In the embodiment, the amount of the natural graphite can be 74% by weight to 89% by weight, 80% by weight to 88.5% by weight, or 80.5% by weight to 88% by weight, based on 100% by weight of the total negative electrode active material.

[0043] In this way, the negative electrode active material according to the embodiments can have characteristics of high capacity, good pressing properties, and excellent pellet (puck) density due to the use of natural graphite, have improved high-rate chargeability due to increased lithium insertion sites including spherical secondary particles aggregated with small primary particles, and also have high chargeability characteristics of artificial graphite. In addition, an effect of improving charge / discharge rate characteristics by including an amorphous carbon coating layer can also be obtained.

[0044] The amorphous carbon can be any one selected from the group consisting of soft carbon, hard carbon, meso-phase pitch carbonization product, calcined coke, and mixtures thereof. In embodiments, the amount of amorphous carbon can be 1 to 5 weight % based on 100 weight % of the total binder negative electrode active material.

[0045] The negative electrode active material can have a tap density of 0.8 g / cc to 1.1 g / cc, for example, can have a tap density of 0.9 g / cc to 1.1 g / cc. If the tap density of the negative electrode active material falls within the above range, the internal pore volume (volume) of the negative electrode active material and side reactions with the electrolyte are reduced, and thus the cycle life characteristics can be improved. In embodiments, the tap density can be obtained by applying a pressure of 108 N three times and calculating the average value using a GeoPyc 1360 Pycnometer from Micromeritics having a conversion factor of 0.2907 cm 3 / mm and a chamber having a diameter of 19.1 mm.

[0046] According to embodiments, the negative electrode active material can have a Hg cumulative pore volume of 0.01 mL / g to 0.07 mL / g, 0.03 mL / g to 0.07 mL / g, or 0.04 mL / g to 0.07 mL / g. If the mercury cumulative pore volume is within the above range, it means that the pores (i.e., empty spaces) inside the negative electrode active material are small. The pores measured in pore volume can have a particle size of 0.01 μm to 1 μm.

[0047] If the mercury cumulative pore volume is within the above range, the amount of amorphous carbon inside the negative electrode active material is appropriate such that better negative electrode active material efficiency can be obtained. In addition, if the mercury cumulative pore volume is within the above range, the inside of the negative electrode active material can maintain a density sufficient to allow the electrolyte to be well impregnated, while the area reacting with the electrolyte is not excessive (excessive), such that appropriate cycle life characteristics can be exhibited without excessive side reactions.

[0048] In an embodiment, the mercury accumulation pore volume can be obtained by adding mercury to the negative electrode active material, applying a pressure of 0.1 psi to 60,000 psi to press the mercury into the negative electrode active material, and then measuring the change in the volume of the mercury as a function of the pressure. The change in pressure can be performed by controlling the pressure to increase from 0.1 psi to 0.2 psi to a pressure of 50,000 psi to 60,000 psi.

[0049] The negative electrode active material can be prepared by the following method.

[0050] A pulverization and particle size reduction process can be performed to pulverize the natural graphite raw material having a particle size of greater than or equal to 80 μm into primary particles. The natural graphite raw material can be pulverized into primary particles by applying an air flow pulverization method. The air flow pulverization can be performed by air flow pulverizing the natural graphite at room temperature with an air flow of 5 to 20 kg / cm 2 .

[0051] The natural graphite raw material can be a flaky natural graphite.

[0052] The pulverization and particle size reduction process can be performed such that the particle size of the primary particles is 4 μm to 8 μm, for example, 4 μm to 7 μm, 4 μm to 6 μm, or 5 μm to 7 μm.

[0053] The primary particles can be subjected to a spheroidization and aggregation process using a spheroidization apparatus to form secondary particles. The spheroidization and aggregation process can be performed such that the particle size of the secondary particles is 5 μm to 10 μm, for example, 6 μm to 10 μm, 6 μm to 8 μm, or 7 μm to 8 μm.

[0054] Subsequently, the secondary particles and a first amorphous carbon precursor are mixed to prepare a mixed product. This process can make the interior of the secondary particles denser.

[0055] A second amorphous carbon precursor is added to the obtained mixed product and aggregated to produce tertiary particles. The aggregation process can be performed using a conventional aggregation apparatus, but is not limited thereto.

[0056] The first and second amorphous carbon precursors can be the same or different, and can be any one selected from the group consisting of a phenol resin, a furan resin, an epoxy resin, a polyacrylonitrile, a polyamide resin, a polyimide resin, a polyamide-imide resin, a synthetic pitch, a petroleum pitch, a coal pitch, a tar, and combinations thereof.

[0057] Since the first and second amorphous carbon precursors are converted into crystalline carbon (i.e., artificial graphite) in their subsequent heat treatment process, the mixing ratio of the secondary particles to the first and second amorphous carbon precursors can be adjusted to have 10% to 15% by weight of artificial graphite based on 100% by weight of the total negative electrode active material as a final product.

[0058] According to the process, the first and second amorphous carbon precursors can be inserted into the secondary particles and disposed on the surface of the primary particles as well as the surface of the secondary particles.

[0059] The obtained tertiary particles are subjected to a first heat treatment. The first heat treatment can be performed at a suitable high temperature, for example, 2800°C to 3000°C, in which the first and second amorphous carbon precursors are graphitized. The first heat treatment process can be performed for 1 hour to 5 hours, for example, 1 hour to 4 hours or 1 hour to 3 hours. According to the process, the first and second amorphous carbon precursors can be converted into artificial graphite. Thus, the first and second amorphous carbon precursors on the surface of the primary particles and the surface of the secondary particles can be converted into artificial graphite disposed thereon.

[0060] The obtained first heat treatment product is added to a niobium precursor solution. The niobium precursor solution can be prepared by adding a niobium precursor to a solvent. The niobium precursor can include NbCl5, niobium oxalate, or a combination thereof, and the solvent can include ethanol, methanol, dimethylformamide, or a combination thereof. The niobium precursor solution can have a solid content of 0.01 wt% to 1 wt%, 0.01 wt% to 0.5 wt%, or 0.02 wt% to 0.2 wt%. The mixing ratio of the first heat treatment product and the niobium precursor solution is adjusted to have 1 wt% to 15 wt% of Nb2O5 in the final negative electrode active material.

[0061] The obtained mixture is stirred. The stirring process can be performed at 100°C to 150°C, 110°C to 140°C, or 110°C to 130°C for 10 hours to 20 hours or 10 hours to 15 hours.

[0062] Subsequently, the stirred product is subjected to a heat treatment to prepare a negative electrode active material. In the heat treatment process, the niobium precursor is converted into Nb2O5, which is then disposed on the surface of the tertiary particles. The heat treatment process can be performed at 500°C to 1200°C, 600°C to 1000°C, or 700°C to 900°C for 1 hour to 10 hours, 1 hour to 8 hours, or 1 hour to 6 hours.

[0063] After the stirring and heat treatment, a washing process can be further performed. The washing process can be performed with an alcohol, for example, methanol, ethanol, propanol, or the like.

[0064] Before adding the niobium precursor solution, the obtained first heat treatment product can be further coated with a third amorphous carbon precursor. The third amorphous carbon precursor can be a phenol resin, a furan resin, an epoxy resin, a polyacrylonitrile, a polyamide resin, a polyimide resin, a polyamide-imide resin, a synthetic pitch, a petroleum pitch, a coal pitch, a tar, or a combination thereof. The third amorphous carbon precursor can be the same as or different from the first and / or second amorphous carbon precursors.

[0065] In the coating process, the amount of the third amorphous carbon precursor can be appropriately adjusted to form an amorphous carbon coating layer having a thickness in the range of 5 nm to 50 nm in the negative electrode active material (final product), without particular limitation.

[0066] The coated product is subjected to a second heat treatment. The second heat treatment process can be performed at 800°C to 2,000°C, for example, 800°C to 1,800°C, 800°C to 1,600°C, 800°C to 1,400°C, or 1,200°C to 1,300°C. The second heat treatment process can be performed for 1 hour to 5 hours, 1 hour to 4 hours, or 1 hour to 3 hours.

[0067] Another embodiment provides a rechargeable lithium battery including a negative electrode, a positive electrode, and a non-aqueous electrolyte.

[0068] The negative electrode includes a negative electrode active material layer and a current collector supporting (carrying) the negative electrode active material layer, the negative electrode active material layer including the negative electrode active material according to the embodiment, a binder, and optionally a conductive material.

[0069] In the negative electrode active material layer, the amount of the negative electrode active material can be 95% to 99% by weight, based on 100% by weight of the total negative electrode active material layer.

[0070] The amount of the binder can be 1% to 5% by weight, based on 100% by weight of the total negative electrode active material layer.

[0071] If the negative electrode active material layer further includes the conductive material, the amount of the negative electrode active material can be 90% to 99% by weight, based on 100% by weight of the total negative electrode active material layer, and the amounts of the binder and the conductive material can each be 1% to 5% by weight, based on 100% by weight of the total negative electrode active material layer.

[0072] The binder serves to attach the negative electrode active material particles to each other well, and also serves to attach the negative electrode active material to the current collector well. The binder can be a non-aqueous binder, an aqueous binder, or a combination thereof.

[0073] The non-aqueous binder can include an ethylene propylene copolymer, a polyacrylonitrile, a polystyrene, a polyvinyl chloride, a carboxylated polyvinyl chloride, a polyvinyl fluoride, a polyurethane, a polytetrafluoroethylene, a polyvinylidene fluoride, a polyethylene, a polypropylene, a polyamide imide, a polyimide, or a combination thereof.

[0074] Waterborne adhesives may include styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber (ABR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polymers containing ethylene oxide (polymers containing ethylene oxide), polyvinylpyrrolidone, polypropylene, polyepoxychlorohydrin, polyphosphazene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or combinations thereof.

[0075] The negative electrode binder may also include cellulose-based compounds. Additionally, the negative electrode binder may comprise both a cellulose-based compound and an aqueous binder. The cellulose-based compound may be one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts. The alkali metal may be Na, K, or Li. Besides acting as a binder, the cellulose-based compound may also act as a thickener to provide viscosity. Therefore, the cellulose-based compound may be used appropriately within the amount of the binder, and its amount is not limited, but it may be from 0.1 parts by weight to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0076] Conductive materials are included to provide electrode conductivity, and any electrically conductive material can be used as the conductive material unless it causes a chemical change. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials in the form of metal powder or metal fiber such as copper, nickel, aluminum, silver, etc.; and conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0077] The current collector may include, but is not limited to, one of the following: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0078] The positive electrode includes a current collector and a layer of positive electrode active material on the current collector.

[0079] The positive electrode active material can be a compound capable of lithium intercalation and deintercalation (lithiation intercalation compound). Specifically, one or more composite oxides of lithium with metals selected from cobalt, manganese, nickel, and combinations thereof can be used. As a more specific example, a compound represented by any of the following chemical formulas can be used: Li a A 1-b X b D2 (0.90≤a≤1.8, 0≤b≤0.5); Li a A 1-b X b O 2-c D c(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05); Li a HAVE BEEN 1-b X b O 2-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05); Li a HAVE BEEN 2-b X b O 4-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05); Li a Ni 1-b-c Co b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α≤2); Li a Ni 1-b- c Co b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α<2); Li a Ni 1-b-c Co b X c O 2-α T2 (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α<2); Li a Ni 1-b-c Mr b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α≤2); Li a Ni 1-b-c Mr b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α<2);Li a Ni 1-b-c Mr b X c O 2-α T2 (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α<2); Li a Ni b HAVE BEEN c G dO2 (0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0.001≤d≤0.1); The a Nor b Co c L 1 d G e O2 (0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0≤d≤0.5,0≤e≤0.1); The a Nor b Co c Al d G e O2 (0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0≤d≤0.5,0≤e≤0.1); The a Nor b Co c Mn d G e O2 (0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0≤d≤0.5,0.001≤e≤0.1); The a NiG b O2 (0.90≤a≤1.8,0.001≤b≤0.1);Li a CoG b O2 (0.90≤a≤1.8,0.001≤b≤0.1); The a Mn 1-b G b O2 (0.90≤a≤1.8,0.001≤b≤0.1); The a Mn2G b O4 (0.90≤a≤1.8,0.001≤b≤0.1); The a Mn 1-g G g PO4 (0.90≤a≤1.8,0≤g≤0.5); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; The (3-f) J2(PO4)3 (0≤f≤2);Li (3-f) Fe2(PO4)3 (0≤f≤2); The a FePO4 (0.90≤a≤1.8)。

[0080] In the above chemical formulas, A is Ni, Co, Mn, or a combination thereof; X 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; Z is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof; and L 1 It is Mn, Al, or a combination thereof.

[0081] The compound may have a coating layer on its surface, or it may be mixed with another compound having a coating layer. The coating layer may include a compound containing at least one coating element selected from: oxides of the coating element, hydroxides of the coating element, hydroxyoxides of the coating element, oxycarbonates of the coating element, and hydroxycarbonates of the coating element. The compound used for the coating layer may be amorphous or crystalline. The coating element included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer may be formed by using these elements in the compound in a manner that does not adversely affect the properties of the positive electrode active material. For example, the method may include any coating method (e.g., spraying, dipping, etc.), but will not be described in more detail as it is well known to those skilled in the art.

[0082] In the positive electrode, the amount of positive electrode active material can be 90% to 98% by weight, based on the total weight of the positive electrode active material layer.

[0083] In this embodiment, the positive electrode active material layer may further include a binder and a conductive material. In this document, based on the total weight of the positive electrode active material layer, the amounts of binder and conductive material may range from 1% to 5% by weight, respectively.

[0084] The binder is used to ensure good adhesion between the positive electrode active material particles and also to ensure good adhesion of the positive electrode active material to the current collector. Examples of such binders may include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide (polymers containing ethylene oxide), polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0085] Conductive materials are used to impart conductivity to electrodes and can be any material that does not cause chemical changes and conducts electrons in the battery. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials in the form of metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; and conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0086] Al can be used for current collectors, but is not limited to this.

[0087] Electrolytes include non-aqueous organic solvents and lithium salts.

[0088] Non-aqueous organic solvents are used as media for transporting ions that participate in the electrochemical reactions of the battery.

[0089] As the aforementioned non-aqueous organic solvents, carbonate (carbonate-based) solvents, ester (ester-based) solvents, ether (ether-based) solvents, ketone (ketone-based) solvents, alcohol (alcohol-based) solvents, or aprotic solvents may be used.

[0090] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolactone, mevalonolactone, and caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran, etc. Ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles such as R-CN (where R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon, double bond, aromatic ring or ether bond), amides such as dimethylformamide, dioxolane such as 1,3-dioxolane, sulfolane, etc.

[0091] Organic solvents can be used alone or in combination of one or more, and if one or more are used in combination, the mixing ratio can be appropriately adjusted depending on the desired battery performance, as is widely understood by those working in the relevant field.

[0092] Alternatively, in the case of carbonate solvents, a mixture of cyclic and linear carbonates can be used. In this case, cyclic and linear carbonates can be mixed in a volume ratio of 1:1 to 1:9, which improves the performance of the electrolyte.

[0093] In addition to carbonate solvents, organic solvents may further include aromatic hydrocarbon (aromatic hydrocarbon-based) organic solvents. In this article, carbonate solvents and aromatic hydrocarbon organic solvents may be mixed in volume ratios from 1:1 to 30:1.

[0094] Aromatic hydrocarbon organic solvents can be aromatic hydrocarbon compounds of chemical formula 1.

[0095] [Chemical Formula 1]

[0096]

[0097] (In Formula 1, R1 to R6 may be the same or different, and are selected from hydrogen, halogens, C1 to C10 alkyl groups, haloalkyl groups and combinations thereof)

[0098] Specific examples of aromatic hydrocarbon organic solvents can be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, and fluoromethylbenzene. Benzene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene and combinations thereof.

[0099] The electrolyte may further include vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate compounds of formula 2 as cycle life improving additives to improve battery cycle life.

[0100] [Chemical Formula 2]

[0101]

[0102] (Whereinin chemical formula 2, R7 and R8 may be the same or different, and are selected from hydrogen, halogen, cyano (CN), nitro (NO2) and fluorinated C1 to C5 alkyl, provided that at least one of R7 and R8 is halogen, cyano (CN), nitro (NO2) and fluorinated C1 to C5 alkyl, and R7 and R8 are not hydrogen.)

[0103] Examples of ethylene carbonate compounds may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, brominated ethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of cycle life improving additives may be used within appropriate limits.

[0104] Lithium salts dissolved in organic solvents supply lithium ions to the battery, essentially operating a rechargeable lithium battery and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts may include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, and LiN(C x F 2x+1 SO2)(C y F 2y+1 One or two of the following lithium salts are used as the supporting electrolyte: lithium difluoro(bis(oxalate)phosphate) phosphate (where x and y are natural numbers, such as integers from 1 to 20), LiCl, LiI, LiB(C₂O₄)₂ (lithium bis(oxalate)borate: LiBOB), and lithium difluoro(oxalate)borate (LiDFOB). The concentration of the lithium salt can range from about 0.1 to about 2.0 M. If lithium salts are included within the above concentration range, the electrolyte can exhibit excellent performance and lithium-ion mobility due to optimized electrolyte conductivity and viscosity.

[0105] Depending on the type of battery, rechargeable lithium batteries may further include a separator between the negative and positive electrodes. Examples of separator materials include polyethylene, polypropylene, polyvinylidene fluoride, and multilayers having two or more layers, such as polyethylene / polypropylene bilayer separators, polyethylene / polypropylene / polyethylene trilayer separators, and polypropylene / polypropylene / polypropylene trilayer separators.

[0106] Figure 4 An exploded perspective view of a rechargeable lithium battery according to an embodiment of the present invention is shown. The rechargeable lithium battery according to the embodiment is described as prismatic, but the invention is not limited thereto and can be applied to various types of batteries such as cylindrical and pouch cells.

[0107] Reference Figure 4 According to an embodiment, a rechargeable lithium battery 100 may include: an electrode assembly 40 in which a separator 30 is wound between a positive electrode 10 and a negative electrode 20, and a housing 50 therein housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte solution (not shown).

[0108] Mode for carrying out the present invention

[0109] The following describes embodiments and comparative examples of the invention. However, these embodiments are not to be construed as limiting the scope of the invention in any way.

[0110] (Example 1)

[0111] Flake-shaped natural graphite raw materials with a particle size of 80 μm to 120 μm are subjected to air jet milling (air blast milling) to produce small primary particles. The small primary particles are then spheroidized and aggregated using a spheroidizing device to produce secondary particles. The secondary particles are mixed with pitch carbon (a first amorphous carbon precursor) to prepare a mixed product.

[0112] Subsequently, pitch carbon (a second amorphous carbon precursor) is added to the mixture, which is then aggregated to produce tertiary particles.

[0113] The resulting tertiary particles were subjected to a first heat treatment at 2,800°C for 2 hours. During this heat treatment process, all the pitch carbon was graphitized and existed as artificial graphite on the surface of the primary and secondary particles.

[0114] A solution of NbCl5 (solvent: ethanol, solid content: 0.02 wt%) was added to the resulting first heat-treated product, and then the mixture was stirred at 120°C for 20 hours.

[0115] The stirred product was washed several times with ethanol and then dried.

[0116] Subsequently, the dried product was heat-treated at 800°C for 3 hours and then washed with ethanol to prepare the negative electrode active material.

[0117] The prepared negative electrode active material includes natural graphite composed of secondary particles aggregated and spheroidized from primary particles, tertiary particles aggregated from these secondary particles, and artificial graphite on the surface of the primary and secondary particles, and also includes Nb2O5 on the tertiary particles.

[0118] During the preparation process, the amounts of secondary particles and pitch carbon were adjusted so that 100% by weight of the final negative electrode active material contained 88% by weight of natural graphite and 10% by weight of artificial graphite. Additionally, the amount of NbCl5 solution was adjusted so that 100% by weight of the final negative electrode active material contained 2% by weight of Nb₂O₅.

[0119] The average particle size (D50) of the primary particles, the average particle size (D50) of the secondary particles, the average particle size (D50) of the tertiary particles, and the average particle size (D50) and tap density of the negative electrode active material are shown in Table 1.

[0120] A slurry of negative electrode active material was prepared by mixing 97.5% by weight of negative electrode active material, 1.5% by weight of styrene-butadiene rubber binder and 1% by weight of carboxymethyl cellulose thickener in an aqueous solvent.

[0121] A negative electrode active material slurry is coated onto a Cu foil current collector using conventional methods, and then dried and compressed to manufacture a negative electrode comprising a current collector and a layer of negative electrode active material formed on the current collector.

[0122] The negative electrode, along with the lithium metal counter electrode and electrolyte, was used to fabricate a coin-type half-cell. The electrolyte was prepared by dissolving 1.5 M LiPF6 in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (in a volume ratio of 20:10:70).

[0123] (Example 2)

[0124] The negative electrode active material was prepared in the same manner as in Example 1, except that the amounts of secondary particles and pitch carbon were adjusted to have 81% by weight of natural graphite and 9% by weight of artificial graphite based on 100% by weight of the negative electrode active material, and the amount of NbCl5 solution was adjusted to have 10% by weight of Nb2O5 in the final negative electrode active material. The negative electrode and half-cell were manufactured in the same manner as in Example 1, except that the negative electrode active material was used.

[0125] (Example 3)

[0126] The negative electrode active material was prepared in the same manner as in Example 1, except that the amounts of secondary particles and pitch carbon were adjusted to have 85.5% by weight of natural graphite and 9.5% by weight of artificial graphite based on 100% by weight of the negative electrode active material, and the amount of NbCl5 solution was adjusted to have 5% by weight of Nb2O5 in the final negative electrode active material. The negative electrode and half-cell were manufactured in the same manner as in Example 1, except that the negative electrode active material was used.

[0127] (Example 4)

[0128] The first heat-treated product of Example 1 was further coated with pitch carbon and then subjected to a second heat treatment at 1,200°C for 2 hours.

[0129] Subsequently, an NbCl5 solution (solvent: ethanol, solid content: 0.02 wt%) was added to the second heat-treated product, and then stirred at 120°C for 20 hours.

[0130] The stirred product was washed several times with ethanol and then dried.

[0131] Subsequently, the dried product was heat-treated at 800°C for 3 hours and then washed with ethanol to prepare the negative electrode active material.

[0132] The prepared negative electrode active material includes natural graphite composed of secondary particles aggregated and spheroidized from primary particles, tertiary particles aggregated from these secondary particles, and artificial graphite on the surfaces of the primary and secondary particles, and also includes an amorphous carbon coating layer (soft carbon coating layer) and Nb2O5 surrounding the surface of the tertiary particles.

[0133] During the preparation process, the amounts of secondary particles and pitch carbon were adjusted so that 100% by weight of the negative electrode active material contained 85% by weight of natural graphite, 10% by weight of artificial graphite, and 3% by weight of amorphous carbon coating. Additionally, the amount of NbCl5 solution was adjusted so that 100% by weight of the negative electrode active material contained 2% by weight of Nb₂O₅.

[0134] The average particle size (D50) of the primary particles, the average particle size (D50) of the secondary particles, the average particle size (D50) of the tertiary particles, and the average particle size (D50) and tap density of the negative electrode active material are shown in Table 1.

[0135] Except for using the negative electrode active material, the negative electrode and half-cell are manufactured in the same manner as in Example 1.

[0136] (Example 5)

[0137] The negative electrode active material was prepared in the same manner as in Example 2, except that the amounts of secondary particles and pitch carbon were adjusted to have 78% by weight of natural graphite and 9% by weight of artificial graphite based on 100% by weight of the negative electrode active material, and the amount of NbCl5 solution was adjusted to have 10% by weight of Nb2O5 in the final negative electrode active material. The negative electrode and half-cell were manufactured in the same manner as in Example 1, except that the negative electrode active material was used.

[0138] (Comparative Example 1)

[0139] Add flake-shaped natural graphite raw material with a particle size of 11 μm and NbCl5 solution (solvent: ethanol, solid content: 0.02 wt%), and then stir at 120°C for 20 hours.

[0140] The stirred product was washed several times with ethanol and then dried.

[0141] Subsequently, the dried product was heat-treated at 800°C for 3 hours and then washed with ethanol to prepare the negative electrode active material.

[0142] The prepared negative electrode active material comprises a natural graphite core and Nb₂O₅ disposed on the surface of the graphite core. The amount of NbCl₅ solution is adjusted to have 2% by weight of Nb₂O₅ in the final negative electrode active material.

[0143] Since the negative electrode active material of Comparative Example 1 is not in the form of secondary particles aggregated from primary particles, only the average particle size of the negative electrode active material is shown in Table 1.

[0144] (Table 1)

[0145]

[0146] (Table 2)

[0147]

[0148] Experimental Example 1) Evaluation of X-ray Diffraction Analysis

[0149] The negative electrode active materials according to Examples 1 to 5 and Comparative Example 1 were subjected to X-ray diffraction analysis using CuKα rays.

[0150] X-ray diffraction analysis was performed using an X'Pert (Malvern PANalytical Ltd.) as the XRD instrument, but the monochromator equipment was removed to improve peak intensity resolution. Measurements were performed at 2θ = 20° to 80°, a scan rate (° / sec) of 0.06436, and a step size of 0.026° / step.

[0151] The X-ray diffraction analysis results (JCPDS card number 30-0873) are shown in Table 3. In Table 3, if all peaks appear at 2θ = 22.7° ± 0.2°, 28.5° ± 0.2°, 36.7° ± 0.2°, 46.2° ± 0.2°, 50.9° ± 0.2°, and 55.1° ± 0.2°, an O is given; if at least one of them does not appear, an X is given. 2θ = 22.7° ± 0.2°, 28.5° ± 0.2°, 36.7° ± 0.2°, 46.2° ± 0.2°, 50.9° ± 0.2°, and 55.1° ± 0.2° represent the (001), (180), (181), (002), (380), and (381) planes, respectively.

[0152] Experimental Example 2) Evaluation of Charge Acceptability

[0153] The half-cells of Examples 1 to 5 and Comparative Example 1 were charged and discharged once at 0.2 C, and then charged and discharged once at 2 C.

[0154] The ratio of 2 C charging capacity to 0.2 C charging capacity was calculated, and the results are presented in Table 3 as charging rate characteristics.

[0155] Experimental Example 3) Evaluation of DC Internal Resistance (DC-IR)

[0156] The half-cells according to Examples 1 to 5 and Comparative Example 1 were charged and discharged once at 25°C under the following conditions: charged at a constant current / constant voltage of 0.2 C / 0.01 V with a cutoff of 0.01 C, and allowed to rest for 10 minutes; then discharged at a constant current of 0.2 C with a cutoff of 1.5 V, and allowed to rest for 10 minutes; and the voltage drop (V) was measured when the current flowed at 8 C for 10 seconds at SOC50 (where each cell is charged to 50% of its total charge capacity of 100%, which is also 50% discharged in terms of its discharge state). The resistance was calculated using the measured voltage and the applied current (8 C), and the results are shown as DC internal resistance (DC-IR). The results are shown in Table 3.

[0157] Experimental Example 4) Evaluation of Cycle Life Characteristics

[0158] The half-cells of Examples 1 to 5 and Comparative Example 1 were charged and discharged 300 times at 1 C at 25°C. The ratio of the capacity at the 300th discharge to the capacity at the 1st discharge was calculated. The results are shown in Table 3 as cycle life characteristics.

[0159] (Table 3)

[0160]

[0161] As shown in Table 3, Examples 1 to 5 and Comparative Example 1 all exhibited similar X-ray diffraction analysis results. Referring to these results, it was confirmed that the Nb₂O₅ included in the negative electrode active material corresponds to T-Nb₂O₅. Furthermore, the interplanar spacing of the (001) plane of the Nb₂O₅ included in the negative electrode active material was measured to be 0.39 nm.

[0162] As shown in Table 3, the battery cells of Examples 1 to 5, which use Nb2O5 as the negative electrode active material on the surface of aggregated carbon-based materials, particularly tertiary particles, exhibit high capacity, charge rate, and cycle life characteristics, but low resistance.

[0163] In contrast, Comparative Example 1 exhibits a very low charging rate but a very high resistance.

[0164] While the invention has been described with respect to exemplary embodiments which are now considered practical, it will be understood that the invention is not limited to the disclosed embodiments. Rather, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A negative electrode active material comprising: secondary particles aggregated and spheroidized from a plurality of primary particles, and tertiary particles of natural graphite aggregated from the secondary particles; artificial graphite on surfaces of the primary particles and surfaces of the secondary particles, and Nb2O5.

2. The negative electrode active material according to claim 1, wherein the amount of the Nb2O5 is 1 to 15% by weight based on 100% by weight of the total negative electrode active material.

3. The negative electrode active material according to claim 1, wherein the amount of the Nb2O5 is 5 to 10% by weight based on 100% by weight of the total negative electrode active material.

4. The negative electrode active material according to claim 1, wherein the Nb2O5 has an orthorhombic structure.

5. The negative electrode active material according to claim 1, wherein the Nb2O5 has a crystal plane spacing of (001) face of 0.390 nm to 0.399 nm.

6. The negative electrode active material according to claim 1, wherein when analyzing X-ray diffraction peaks of the negative electrode active material, peaks appear at 2Θ = 22.7° ± 0.2°, 28.5° ± 0.2°, 36.7° ± 0.2°, 46.2° ± 0.2°, 50.9° ± 0.2°, and 55.1° ± 0.2°.

7. The negative electrode active material according to claim 1, wherein the Nb2O5 is provided on the tertiary particles of the natural graphite.

8. The negative electrode active material according to claim 1, wherein the negative electrode active material further comprises an amorphous carbon coating layer surrounding the tertiary particles of the natural graphite.

9. The negative electrode active material according to claim 1, wherein the Nb2O5 is provided on the amorphous carbon coating layer.

10. The negative electrode active material according to claim 1, wherein the coating layer has a thickness of 5 nm to 50 nm.

11. The negative electrode active material according to claim 1, wherein the natural graphite is flaky natural graphite.

12. The negative electrode active material according to claim 1, wherein the amount of the artificial graphite is 6 to 16.5% by weight based on 100% by weight of the total negative electrode active material.

13. The negative electrode active material according to claim 1, wherein the amount of the natural graphite is 74 to 89% by weight based on 100% by weight of the total negative electrode active material.

14. The negative electrode active material according to claim 1, wherein the primary particles have a particle diameter of 4 μm to 8 μm.

15. The negative electrode active material according to claim 1, wherein the secondary particles have a particle diameter of 5 μm to 10 μm.

16. The negative electrode active material according to claim 1, wherein the tertiary particles have a particle diameter of 9 μm to 15 μm.

17. The negative electrode active material according to claim 1, wherein the negative electrode active material has a tap density of 0.8 g / cc to 1.1 g / cc.

18. The negative electrode active material according to claim 1, wherein the negative electrode active material has a mercury cumulative pore volume of 0.01 mL / g to 0.07 mL / g.

19. The negative electrode active material according to claim 1, wherein the amorphous carbon comprises soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, and mixtures thereof.

20. A rechargeable lithium battery, comprising: a negative electrode comprising the negative electrode active material of any one of claims 1 to 19; a positive electrode; and an electrolyte. ​

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