Negative electrode active material, and negative electrode and secondary battery comprising same

Abstract

The present invention relates to a negative electrode active material. Specifically, the negative electrode active material comprises: artificial graphite particles; and a nitrogen element, an oxygen element, and a hydrogen element present on the surface of, inside, or both on the surface of and inside the artificial graphite particles, wherein the content of the nitrogen element is 80 to 180 mg per kg of the negative electrode active material.

Description

Negative active material, negative electrode and secondary battery containing the same The present invention relates to a negative electrode active material, a negative electrode including the same, and a secondary battery. As interest in environmental issues grows, research is being conducted on electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace vehicles that use fossil fuels, such as gasoline and diesel vehicles, which are a major cause of air pollution. Secondary batteries for electric vehicles are used as the power source for these electric vehicles (EVs) and hybrid electric vehicles (HEVs). Currently, commercialized secondary batteries for electric vehicles include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, and lithium-ion batteries. Among these secondary batteries for electric vehicles, lithium-ion batteries have the advantages of having almost no memory effect compared to nickel-based batteries, allowing free charging and discharging, a low self-discharge rate, high energy density, high discharge voltage, and output stability, and therefore, various studies are being conducted on them. One object of the present invention is to provide an anode active material capable of preventing a decrease in discharge capacity, while preventing surface peeling of an artificial graphite-based anode active material and the resulting electrolyte side reaction problems, thereby achieving an effect of improving initial efficiency and maintaining discharge capacity, and having improved rapid charging performance. In addition, another object of the present invention is to provide a negative electrode comprising the above-described negative electrode active material. In addition, another object of the present invention is to provide a lithium secondary battery including the aforementioned negative electrode. [1] The present invention provides a negative electrode active material, wherein the negative electrode active material comprises artificial graphite particles; and nitrogen elements, oxygen elements, and hydrogen elements present on the surface, inside, or both of the surface and inside of the artificial graphite particles, wherein the nitrogen element is present in an amount of 80 mg to 180 mg per 1 kg of the negative electrode active material. [2] The present invention provides a negative electrode active material according to [1], wherein the content of the oxygen element is 650 mg to 1,000 mg per 1 kg of the negative electrode active material, and the hydrogen element is included in an amount of 300 mg to 500 mg per 1 kg of the negative electrode active material. [3] The present invention provides a negative electrode active material in which the ratio of the weight of nitrogen element in the negative electrode active material to the weight of oxygen element in the negative electrode active material is 0.12 or more, in at least one of [1] to [2]. [4] The present invention provides an anode active material, wherein the ratio of the weight of hydrogen element in the anode active material to the weight of oxygen element in the anode active material is 0.47 or more, in one or more of the above [1] to [3]. [5] The present invention provides an anode active material in which the ratio of the total weight of nitrogen elements and hydrogen elements in the anode active material to the weight of oxygen elements in the anode active material is 0.5 or more, in at least one of [1] to [4]. [6] The present invention provides a negative electrode active material in which the total weight of nitrogen elements, oxygen elements, and hydrogen elements present in the negative electrode active material is 1,000 mg to 1,600 mg per 1 kg of the negative electrode active material, in at least one of [1] to [5]. [7] The present invention provides a negative electrode active material in one or more of the above [1] to [6], wherein the artificial graphite particles are in the form of secondary particles assembled from two or more primary particles. [8] The present invention provides a negative electrode active material having a graphitization degree of 90% to 99% in at least one of the above [1] to [7]. [9] The present invention is characterized in that in at least one of the above [1] to [8], the BET specific surface area of ​​the negative active material is 1 m 2 / g to 8m 2 / g provides a negative electrode active material.

[0010] The present invention provides an anode active material according to at least one of the above [1] to [9], wherein the anode active material further includes an amorphous carbon coating layer positioned on the artificial graphite particles.

[0011] The present invention provides a negative electrode comprising a negative electrode active material according to at least one of the above [1] to

[0010] .

[0012] In addition, the present invention provides a lithium secondary battery including a negative electrode according to

[0011] ; a positive electrode opposing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and a non-aqueous electrolyte. The negative active material according to the present invention includes artificial graphite particles and nitrogen, oxygen and hydrogen elements. The nitrogen, oxygen and hydrogen elements may be present in or doped in the artificial graphite particles. The nitrogen element is contained in the negative active material in a specific content. The content range of the nitrogen element present in the negative active material can be interpreted as an indicator of the degree of graphitization of the surface of the negative active material, and the present invention can lower the degree of graphitization of the surface of the negative active material to an appropriate level by controlling the content of the nitrogen element present in the negative active material to a specific range. Accordingly, the negative active material according to the present invention can prevent or suppress the peeling phenomenon caused by an organic solvent included in a non-aqueous electrolyte, and at the same time, can exhibit a required level of discharge capacity. The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description of the invention described below, serve to further understand the technical idea of ​​the present invention; therefore, the present invention should not be interpreted as being limited to matters described in such drawings. Figure 1 is a flow chart explaining a process for manufacturing a negative active material according to one embodiment of the present invention. The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as having meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best manner. The terminology used in this specification is for the purpose of describing exemplary embodiments only and is not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, it should be understood that the terms “comprise,” “include,” or “have,” etc., are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof. In this specification, the average particle diameter (D 50 ) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D 50 ) can be measured, for example, using a laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain results with high reproducibility and high resolution. In this specification, 'primary particle' means a single particle, i.e., one particle, and 'secondary particle' means an aggregate in which multiple primary particles are aggregated through an intentional assembly or bonding process. As used herein, the terms “about,” “approximately,” and “substantially” are used to mean a range of or approximation to a numerical value or degree, taking into account inherent manufacturing and material tolerances. A lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode and the negative electrode are manufactured by mixing a positive electrode active material and a negative electrode active material with a binder or the like, dispersing them in a solvent to prepare a slurry, applying the slurry to the surface of an electrode current collector, and drying it to form an electrode active material layer. As a negative active material, a carbon-based active material that allows reversible lithium ion intercalation and deintercalation and maintains structural characteristics and electrical properties can be used. Various forms of carbon-based materials such as artificial graphite, natural graphite, and hard carbon have been used as carbon-based active materials, and among these, graphite-based active materials that can guarantee the life characteristics of lithium secondary batteries due to excellent reversibility are widely used. Since graphite-based active materials have a relatively low discharge voltage of -0.2 V compared to lithium, a battery using graphite-based active materials can exhibit a high discharge voltage of, for example, approximately 3.6 V, and thus provide many advantages in terms of energy density of lithium batteries. Among carbon-based active materials, artificial graphite has the advantage of excellent rapid charging performance of the battery due to its relatively low orientation during electrode rolling compared to natural graphite, which improves the inflow / outflow characteristics of lithium ions, and excellent life characteristics due to its low degree of expansion during charge / discharge. Artificial graphite is manufactured by heat-treating amorphous carbon such as coke at a high temperature (e.g., 2,500°C to 3,200°C), and is distinguished from natural graphite in that it is artificially synthesized graphite. Such artificial graphite has a high degree of graphitization due to the high-temperature heat treatment, and has a problem in that the surface is peeled off due to contact with an organic solvent (e.g., ethyl methyl carbonate, etc.) in a non-aqueous electrolyte. Such surface peeling of artificial graphite can cause various problems, such as an increase in electrolyte side reactions, low initial efficiency, loss of energy density, and gas generation. On the other hand, if the degree of graphitization of artificial graphite is excessively lowered in order to prevent or suppress such problems, the capacity itself may be reduced. Hereinafter, the present invention will be described in detail. Negative active material The present invention relates to a negative electrode active material, for example, a negative electrode active material for a lithium secondary battery. The above negative active material comprises artificial graphite particles; and nitrogen element (N), oxygen element (O), and hydrogen element (H) present on the surface, inside, or both of the surface and inside of the artificial graphite particles, and the nitrogen element is characterized in that it is included in an amount of about 80 mg to 180 mg per 1 kg of the negative active material. The negative active material according to the present invention includes artificial graphite particles and nitrogen, oxygen and hydrogen elements. The nitrogen, oxygen and hydrogen elements may be present in the artificial graphite particles or may be doped therein. The nitrogen element is contained in the negative active material in a specific content. The content range of the nitrogen element present in the negative active material can be interpreted as an indicator of the degree of graphitization of the surface of the negative active material, and the present invention can lower the degree of graphitization of the surface of the negative active material to an appropriate level by controlling the content of the nitrogen element present in the negative active material to a specific range. Accordingly, the negative active material according to the present invention can prevent or suppress a peeling phenomenon caused by an organic solvent included in a non-aqueous electrolyte, and at the same time, can exhibit a required level of discharge capacity. Graphite can generally be artificially manufactured through a series of complex processes that transform raw materials into highly ordered crystal structures. For example, to manufacture such artificial graphite, coke and graphite are pulverized and mixed with a binder (e.g., pitch) to form a homogeneous mass, and then the mixture can be shaped using techniques such as isotropic pressing, extrusion, or die molding. The shaped material is then subjected to a carbonization process in an oxygen-free environment at about 1000°C, and in the next step, the graphitization process, the material is heat-treated by heating it to a temperature of about 2500°C to 3200°C in an inert atmosphere, thereby partially or completely converting the amorphous or non-crystalline carbon into graphite. The graphitization process in such an artificial graphite manufacturing process is a major process of the carbon-graphite process, and for example, the high-temperature treatment in the graphitization process aligns the carbon atoms into the characteristic layered structure of graphite, thereby improving properties such as strength and conductivity. The degree of graphitization is a measure of how close carbon atoms are to forming a tightly packed hexagonal graphite crystal structure, with the ideal graphite crystal structure being a closely packed hexagonal arrangement with lattice constants a = 0.2461 nm and c = 0.6708 nm. In general, the closer the lattice dimensions are to the ideal graphite lattice constants, the higher the degree of graphitization. The above negative active material includes artificial graphite particles. Artificial graphite particles are manufactured by heat-treating amorphous carbon at a high temperature (e.g., 2,500°C to 3,200°C), and are distinguished from natural graphite in that they are artificially synthesized graphite. The above artificial graphite particles may be in the form of primary particles, or may be in the form of secondary particles assembled from two or more primary particles. For example, the artificial graphite particles may be in the form of secondary particles assembled from two or more primary particles. The primary particles included in the artificial graphite particles may mean artificial graphite in the form of primary particles. When the artificial graphite particles are in the form of secondary particles, pores may be formed within the artificial graphite particles, and the pores may be empty spaces formed between primary particles, may be amorphous, and may exist in two or more forms. When the artificial graphite particles are in the form of secondary particles, the artificial graphite particles can be manufactured by a method of mixing primary artificial graphite particles with a binder material (e.g., pitch), mechanical milling, shaping or spheroidizing, and heat-treating to agglomerate the primary artificial graphite particles to form secondary particles. Alternatively, when the artificial graphite particles are in the form of secondary particles, the artificial graphite particles can be manufactured by mixing a carbon precursor and a binder material, performing mechanical milling (or shaping) and assembling processes to manufacture an intermediate in the form of secondary particles, and heat-treating the intermediate at a temperature of 3,000° C. or higher to graphitize it. At this time, the carbon precursor can be coal-based heavy oil, petroleum-based heavy oil, tar, pitch, coke, and the like, and can be, for example, at least one selected from the group consisting of needle coke, mosaic coke, and coal tar pitch. The manufacturing method is not particularly limited as long as the content range of nitrogen element present in the above negative active material is satisfied. The above negative active material may include nitrogen elements, oxygen elements and hydrogen elements present on the surface, inside or both the surface and inside of the artificial graphite particles. According to one embodiment, the nitrogen elements, oxygen elements and hydrogen elements may be doped into the artificial graphite particles. In the present invention, the content of nitrogen element present in the artificial graphite particles may be about 80 mg to 180 mg per 1 kg of the negative electrode active material. The above nitrogen element, oxygen element, and hydrogen element may be introduced or present in the artificial graphite particles, for example, during the manufacturing process of the artificial graphite particles, such as during the process of pulverization, mechanical milling, and assembly. Normally, the nitrogen element, etc. are removed or are generally present at a low content level during the manufacturing process of the artificial graphite particles, for example, during the graphitization process. On the other hand, if the graphitization of the artificial graphite is sufficiently performed as necessary, the content of the nitrogen element included in the artificial graphite particles becomes relatively low, and in this case, the surface of the artificial graphite may be peeled off during the process of impregnating and introducing an electrolyte component such as ethyl methyl carbonate (EMC) into the artificial graphite. This peeling off of the surface of the artificial graphite causes a side reaction between the non-aqueous electrolyte and the surface of the artificial graphite, and causes a problem in that the organic solvent in the non-aqueous electrolyte is continuously consumed. On the other hand, in order to prevent this problem, if the degree of graphitization of the entire artificial graphite is lowered, the discharge capacity itself is reduced, making it difficult to achieve the desired energy density. In this regard, in the present invention, by controlling the content of nitrogen elements present in the artificial graphite particles to a specific range, electrolyte side reactions are prevented or suppressed while also improving the discharge capacity. The reason for the expression of such an effect is understood to be that when the content of nitrogen elements present or introduced during the graphitization process of the artificial graphite particles satisfies a specific range, the degree of graphitization of the surface of the artificial graphite particles is reduced to an appropriate level, thereby significantly reducing surface exfoliation by a non-aqueous electrolyte organic solvent. In addition, since the negative active material according to the present invention can prevent or suppress electrolyte side reactions without lowering the degree of graphitization of the entire artificial graphite particles, it may also be possible to implement a high level of discharge capacity. In addition, when the content of nitrogen element present in the artificial graphite particles is controlled within a specific range, an improvement in the rapid charging performance of the negative electrode active material can also be expected by creating local electrochemically active sites according to nitrogen element doping. According to one embodiment, the content of nitrogen element present in the artificial graphite particles may be about 80 mg to 180 mg per 1 kg of the negative active material, for example, about 100 mg to 170 mg, or about 110 mg to 160 mg, or about 120 mg to 140 mg, and within this range, the effects of improving initial efficiency and discharge capacity and preventing electrolyte side reactions may be exhibited at a more excellent level. In the present invention, the content of oxygen element present in the negative electrode active material may be about 650 mg to 1,000 mg per 1 kg of the negative electrode active material, for example, about 650 mg to 900 mg, or about 680 mg to 850 mg, or about 700 mg to 800 mg. In addition, the content of hydrogen element present in the negative electrode active material may be about 300 mg to 500 mg per 1 kg of the negative electrode active material, for example, about 310 mg to 480 mg, or about 320 mg to 450 mg, or about 350 mg to 420 mg. The total weight of nitrogen elements, oxygen elements, and hydrogen elements present in the negative electrode active material may be about 1,000 mg to 1,600 mg per 1 kg of the negative electrode active material, for example, about 1,050 mg to 1,500 mg, or about 1,110 mg to 1,460 mg, or about 1,200 mg to 1,400 mg. The ratio of the weight of nitrogen element in the negative electrode active material to the weight of oxygen element in the negative electrode active material may be about 0.12 or greater, for example, 0.15 or greater, or 0.16 or greater. The ratio of the weight of nitrogen element in the negative electrode active material to the weight of oxygen element in the negative electrode active material may be, for example, about 0.20 or less, or about 0.19 or less. The ratio of the weight of nitrogen element in the negative electrode active material to the weight of oxygen element in the negative electrode active material may be about 0.12 to 0.20, for example, about 0.15 to 0.20, or 0.16 to 0.19, or about 0.165 to 0.185. The ratio of the weight of hydrogen element in the negative electrode active material to the weight of oxygen element in the negative electrode active material may be about 0.47 or more, for example, about 0.47 to 0.55, for example, about 0.48 to 0.51. The ratio of the sum of the weights of nitrogen and hydrogen elements in the negative electrode active material to the weight of oxygen element in the negative electrode active material may be about 0.5 or greater, for example, 0.55 or greater, or 0.6 or greater. The ratio of the sum of the weights of nitrogen and hydrogen elements in the negative electrode active material to the weight of oxygen element in the negative electrode active material may be about 0.75 or less. For example, the ratio of the sum of the weights of nitrogen and hydrogen elements in the negative electrode active material to the weight of oxygen element in the negative electrode active material may be about 0.5 to 0.75, for example, 0.6 to 0.72, or 0.65 to 0.70. Through the contents of the nitrogen element, oxygen element, and hydrogen element described above and the relationship between the contents thereof, the effects of improving the initial efficiency and discharge capacity and the effects of preventing or suppressing electrolyte side reactions can be implemented. The contents of the above nitrogen element, oxygen element and / or hydrogen element can be measured by an ONH analyzer. For example, 0.1 g of a negative electrode active material sample can be placed in a crucible and placed in an ONH analyzer to measure the contents of the nitrogen element, oxygen element and / or hydrogen element. For example, the NOH836 Analyzer of LECO Korea can be used as the ONH analyzer. In the case of the contents of the above nitrogen element, oxygen element and / or hydrogen element, three identical negative electrode active material samples are prepared, analyzed three times using the ONH analyzer, and the average value obtained therefrom can be defined as the contents of the nitrogen element, oxygen element and / or hydrogen element. In the present invention, the content of nitrogen, oxygen and hydrogen elements present in the negative electrode active material can be controlled by controlling the conditions of the manufacturing process of artificial graphite particles, such as shaping by grinding, mechanical milling, etc., assembly, graphitization, and additional shaping processes. According to one embodiment, the negative electrode active material according to the present invention can control the content of nitrogen, oxygen and hydrogen elements present in the negative electrode active material by controlling the conditions of the mechanical milling or spheroidization process while performing an additional shaping process, such as mechanical milling or spheroidization process, after the graphitization process for manufacturing artificial graphite particles. At this time, the mechanical milling or spheroidization conditions can be controlled by considering, for example, the size of the reactor, the weight of the precursor to be introduced, and the like. FIG. 1 is a flow chart illustrating an artificial graphite manufacturing process (100) according to one embodiment. In step S110, a crushing process is first performed to crush coke, which is a raw material for artificial graphite, into a desired size. In this process, the size of the coke is controlled by controlling the rotation speed per minute (RPM) of milling equipment such as an air classifier mill, a roll mill, or a hammer mill. In step S120, a first shaping process is performed. The first shaping process is a process for making the surface of the coke, which has been reduced to a desired size through the previous crushing process, smooth and non-uneven, as well as shaping it into a non-pointed shape. The first shaping process may use the same equipment as the crushing process, or may use different equipment. In step S130, an assembly process is performed. In the case of artificial graphite, the assembly process is a process of manufacturing secondary particles in the form of agglomerating multiple primary particles by using an additive such as pitch to primary particles manufactured by crushing coke. The assembly process is performed using a vertical or horizontal granulator, which is equipment that mixes primary particles, which are crushed coke, with additives such as pitch, and the mixing ratio with the additives can be controlled to form a desired particle size by controlling the RPM of the equipment, etc. In step S140, a graphitization process is performed. According to one embodiment, the graphitization process uses an Acheson furnace to heat-treat coke at a temperature of, for example, about 3,000° C. to produce graphite. In step S150, a secondary shaping process is performed, which is an additional shaping process that can artificially damage the surface of the graphite. In the secondary shaping process, the equipment used in the previously performed shaping and crushing processes can be used. However, compared to the previously performed shaping and crushing processes, the RPM or process time is significantly reduced, so that, for example, relatively weak milling is performed. The degree of graphitization of the above negative active material may be about 90% to 99%, for example, about 92% to 99%, or about 92% to 96%, or about 92% to 94%. When in the above range, the degree of graphitization of the entire negative active material is increased to a certain level, thereby securing excellent levels of initial efficiency and discharge capacity, and at the same time, electrolyte side reactions due to exfoliation of the negative active material surface may be prevented or suppressed. The degree of graphitization of the above negative active material can be calculated by measuring the interplanar spacing d002 of the graphite (002) plane obtained through Bragg's Law from XRD data. For example, the graphitization degree can be derived from Equation 1 below. [Formula 1] Graphitization degree (%) = (3.44 - d002) / (0.086) × 100 (In the above formula 1, d002 is the interplanar spacing (nm) of the (002) plane of the artificial graphite particles present in the negative active material.) The average particle diameter (D) of the above negative active material 50 ) may be about 10 μm to 30 μm, for example about 12 μm to 25 μm. The BET (Brunauer, Emmett, Teller) specific surface area of ​​the above negative active material is approximately 1 m 2 / g to 8m 2 / g, for example, about 1.2m 2 / g to 5m 2 / g, or about 1.4m 2 / g to 3.2m 2 / g, or about 1.6 m 2 / g to 2.5m 2 / g, and when it is in the above range, the movement path of lithium ions is smoothly secured, so that excellent initial efficiency and discharge capacity can be exhibited, and the effect of improving electrolyte side reactions can be implemented by lowering the graphitization degree of the surface of the negative electrode active material. The above BET specific surface area can be measured using, for example, a BEL Sorption device (BEL Japan). The above negative active material may further include an amorphous carbon coating layer positioned on the surface of the artificial graphite particles. The amorphous carbon coating layer may contribute to improving the structural stability of the artificial graphite particles and preventing or suppressing side reactions between the negative active material and the electrolyte. The amorphous carbon coating layer may be formed in an amount of about 0.1 wt% to 10 wt%, for example, about 1 wt% to 5 wt%, based on the total weight of the negative active material. The presence of the amorphous carbon coating layer can improve the structural stability of the negative active material, but excessive formation of the amorphous carbon coating layer may cause a decrease in initial efficiency due to an increase in the specific surface area during negative electrode rolling and may cause a deterioration in high-temperature storage performance. Therefore, the carbon coating layer is formed in an amount within the above-described range. The above amorphous carbon coating layer can be formed by providing a carbon coating layer precursor to artificial graphite particles and then performing heat treatment. The above carbon coating layer precursor may include at least one selected from the group consisting of a polymer resin and a pitch. For example, the polymer resin may include at least one selected from the group consisting of sucrose, a phenol resin, a naphthalene resin, a polyvinyl alcohol resin, a furfuryl alcohol resin, a polyacrylonitrile resin, a polyamide resin, a furan resin, a cellulose resin, a styrene resin, a polyimide resin, an epoxy resin, a vinyl chloride resin, and a polyvinyl chloride. The pitch may include at least one selected from the group consisting of a coal-based pitch, a petroleum-based pitch, and a mesophase pitch. The heat treatment process for forming the above amorphous carbon coating layer can be performed at about 1,000°C to 1,500°C in order to promote uniform formation of the amorphous carbon coating layer. cathode The present invention provides an anode, for example, an anode for a lithium secondary battery. The anode may be an anode comprising the anode active material described above. According to one embodiment, the negative electrode includes a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; wherein the negative electrode active material layer may include the above-described negative electrode active material. The negative electrode current collector may be any negative electrode current collector generally used in the art without limitation, and is not particularly limited as long as it has high conductivity without causing a chemical change in a lithium secondary battery. For example, the negative electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and an aluminum-cadmium alloy, and, in one embodiment, copper. The above negative electrode current collector can form fine roughness on the surface to strengthen the bonding strength of the negative electrode active material, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, and non-woven fabric. The above negative electrode collector may generally have a thickness of about 3 μm to 500 μm. The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. For example, the negative electrode active material layer may be disposed on one surface or both surfaces of the negative electrode current collector. The above negative electrode active material layer may include the above-described negative electrode active material. The above-described negative electrode active material layer may further include a silicon-based active material together with the above-described negative electrode active material. The above silicon-based active material includes, for example, silicon (Si), silicon oxide (SiO). x , 0 <x<2) 및 실리콘-탄소 복합체 중 적어도 1종을 포함할 수 있다. The negative electrode active material or the mixture of the negative electrode active material and the silicon-based active material may be included in the negative electrode active material layer in an amount of about 80 wt% to 99 wt%, for example, about 88 wt% to 98 wt%. In addition, the description of the negative active material is as described above. The above-described negative electrode active material layer may further include a binder, a conductive agent, and / or a thickener in addition to the above-described negative electrode active material. The above binder is a component that assists in bonding between the active material and / or the current collector, and may typically be included in the negative electrode active material layer at about 1 wt% to 30 wt%, for example, about 1 wt% to 10 wt%. The above binder may include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber and fluororubber, for example, at least one selected from the group consisting of polyvinylidene fluoride and styrene-butadiene rubber. Any thickener conventionally used in lithium secondary batteries can be used as the thickener, and an example is carboxymethyl cellulose (CMC). The above-mentioned conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be included in the negative electrode active material layer at about 1 wt% to 30 wt%, for example, 1 wt% to 10 wt%. The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorinated carbon, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used. Examples of commercially available challenging agents include acetylene blacks (Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company), Ketjenblack, the EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal). The thickness of the negative active material layer may be about 10 ㎛ to 300 ㎛, for example, about 50 ㎛ to 200 ㎛, but is not limited thereto. The above negative electrode active material layer can be manufactured by applying, rolling, and drying a negative electrode slurry manufactured by selectively adding a negative electrode active material, optionally a binder, a thickener, and / or a conductive agent to a solvent, to the negative electrode current collector. At this time, the solvent can include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and can be, for example, water. Secondary battery In addition, the present invention provides a secondary battery including the above-described negative electrode, for example, a lithium secondary battery. The secondary battery may include the above-mentioned negative electrode; a positive electrode opposite to the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte. The above anode can be opposed to the above cathode. The above positive electrode may include a positive electrode current collector; and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode current collector may be any negative electrode current collector generally used in the art without limitation, and is not particularly limited as long as it has relatively high conductivity without causing a chemical change in the secondary battery. For example, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and an aluminum-cadmium alloy, and, in one embodiment, aluminum. The above positive electrode current collector can form fine irregularities on the surface to strengthen the bonding strength of the positive electrode active material, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric. The above positive electrode current collector may generally have a thickness of about 3 μm to 500 μm. The above positive electrode active material layer may include a positive electrode active material. The above cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and may include, for example, a lithium composite metal oxide including lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. According to one embodiment, the lithium composite metal oxide is a lithium-manganese oxide (for example, LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (for example, LiCoO2, etc.), a lithium-nickel oxide (for example, LiNiO2, etc.), a lithium-nickel-manganese oxide (for example, LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-z Ni zO4 (wherein, 0<Z<2) etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-z1 Co z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2(where, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2) etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2(wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of independent elements, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1), etc.), and one or more compounds of these may be included. Among these, the lithium composite metal oxide may be LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (for example, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1)O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), and considering the remarkable improvement effect according to the control of the type and content ratio of the constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide may be Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc., and one or a mixture of two or more of these may be used. The above-mentioned positive electrode active material may be included in the positive electrode active material layer at about 80 wt% to 99 wt%. The above-mentioned positive electrode active material layer may further include at least one selected from the group consisting of a binder and a conductive material together with the above-mentioned positive electrode active material. The above binder is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and is typically added in an amount of 1 to 30 wt% based on the total weight of the positive electrode mixture. Examples of such binders may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber. The above binder may be included in the positive electrode active material layer at about 1 wt% to 30 wt%. The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used. Examples of commercially available challenging agents include acetylene blacks (Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company), Ketjenblack, the EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal). The above-mentioned challenging agent can be added in an amount of about 1 wt% to 30 wt% in the above-mentioned positive electrode active material layer. The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. If it is a separator that is usually used in lithium secondary batteries, it can be used without any special restrictions. For example, one that has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity can be used. According to one embodiment, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof can be used. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. can be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can be optionally used in a single-layer or multi-layer structure. In addition, examples of the electrolyte used in the present invention 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. For example, the electrolyte may include an organic solvent and a lithium salt. As the organic solvent, any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. For example, the organic solvent may include: ester solvents such as methyl acetate, ethyl acetate, gamma-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon element solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a linear, branched or cyclic hydrocarbon group having C2 to C20, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. According to one embodiment, a carbonate solvent may be used among these, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant capable of improving charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) may be used. In this case, when the cyclic carbonate and the linear carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent. The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. For example, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the concentration of the lithium salt within the range of about 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively. As described above, the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, rapid charge characteristics, and capacity retention rate, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs), and in particular, can be used as a component battery of a medium- or large-sized battery module. Accordingly, the present invention also provides a medium- or large-sized battery module including the above-described secondary battery as a unit battery. These medium and large-sized battery modules can be applied to power sources that require relatively high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices. Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. Examples and Comparative Examples Example 1 Coke raw material was crushed, air-classified, and mechanically milled to produce a carbon precursor in the form of primary particles. The carbon precursor and pitch were mixed and placed into a granulating facility having blades inside, and mechanically milled at 400 to 800°C while mixing to produce an intermediate in the form of secondary particles. The intermediate was heat-treated at 3,000°C for 2 hours in a graphitization furnace having a capacity of about 100 kg to be graphitized. The product obtained after the above graphitization was further mechanically milled at room temperature and a speed of 30 Hz in an assembly facility. Through this, artificial graphite particles in the form of secondary particles in which two or more primary artificial graphite particles were assembled were manufactured, and this was used as a negative electrode active material. The average particle diameter (D) of the above negative active material 50 ) was 17㎛, and the BET surface area was 1.4m 2 / g was. Example 2 A negative active material was manufactured in the same manner as in Example 1, except that additional mechanical milling after graphitization was performed at room temperature and at a speed of 40 Hz, which is higher than 30 Hz in Example 1 described above. The average particle diameter (D) of the above negative active material 50 ) was 16㎛, and the BET surface area was 1.8m 2 / g was. Example 3 A negative active material was manufactured in the same manner as in Example 1, except that additional mechanical milling after graphitization was performed at room temperature and at a speed of 50 Hz, which is higher than the 40 Hz of Example 2 described above. The average particle diameter (D) of the above negative active material 50 ) was 15㎛, and the BET surface area was 3.2m 2 / g was. Comparative Example 1 A negative active material was prepared in the same manner as in Example 1, except that no additional mechanical milling was performed after graphitization. The average particle diameter (D) of the above negative active material 50 ) was 19㎛, and the BET surface area was 1.2m 2 / g was. Comparative Example 2 A negative active material was manufactured in the same manner as in Example 1, except that the heat treatment time during graphitization was adjusted to 3 hours and additional mechanical milling after graphitization was not performed. The average particle diameter (D) of the above negative active material 50 ) was 19㎛, and the BET surface area was 1.0m 2 / g was. Comparative Example 3 A negative active material was manufactured in the same manner as in Example 1, except that the heat treatment time during graphitization was adjusted to 1 hour and additional mechanical milling after graphitization was not performed. The average particle diameter (D) of the above negative active material 50 ) was 20㎛, and the BET surface area was 3.5m 2 / g was. Oxygen element (O) content in the negative active material (mg / kg, based on 1kg of negative active material)Nitrogen element (N) content in the negative active material (mg / kg, based on 1kg of negative active material)Hydrogen element (H) content in the negative active material (mg / kg, based on 1kg of active material weight)Graphitization degree (%)Average particle size (D 50 )(㎛)BET specific surface area(m 2 / g)Example 168011032094171.4Example 273013037093161.8Example 385016045092153.2Comparative Example 12805528094181.2Comparative Example 22203522098181.0Comparative Example 3110020566084203.5 1) Analysis of the content of nitrogen, oxygen and hydrogen elements A 0.1 g sample of the negative active material was placed in a crucible and placed in an ONH analyzer (NOH836 Analyzer of LECO Korea) to measure the content of nitrogen, oxygen, and / or hydrogen elements. At this time, three samples of each example and comparative example were prepared, the measurement test was performed three times, and the average values ​​are recorded in Table 1. 2) Graphitization The degree of graphitization of the negative active material was calculated according to Equation 1 above by measuring the interplanar spacing d002 of the graphite (002) plane obtained through Bragg's Law from XRD data. 3) Average particle diameter (D) 50 ) Average particle size of negative active material (D 50 ) obtains the particle size distribution curve using laser diffraction, and then calculates the particle size corresponding to 50% of the volume accumulation, and uses this as the average particle size (D) of the negative active material. 50 ) was defined as follows. 4) BET surface area The BET surface area of ​​the negative active material was measured using a BEL Sorption device (BEL Japan). Experimental example Experimental Example 1: Evaluation of Initial Efficiency and Discharge Capacity (Manufacturing of lithium secondary batteries) The negative electrode slurry was prepared by adding the negative electrode active material manufactured according to Example 1, carbon black as a conductive material, styrene-butadiene rubber as a binder, and CMC as a thickener to water as a solvent in a weight ratio of 95.6:1.0:1.1:2.3. The negative electrode slurry was applied to a copper current collector, dried at 130°C, and rolled to prepare a negative electrode. Lithium metal was prepared as a counter electrode to the above cathode. An electrode assembly was manufactured by interposing a porous polyethylene separator between the negative electrode and the lithium metal counter electrode, the electrode assembly was positioned inside a case, and a non-aqueous electrolyte was injected into the case and sealed to manufacture a lithium secondary battery of Example 1. The above non-aqueous electrolyte is LiPF in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a volume ratio of 20:80. - 6 was used after dissolving it at a concentration of 1.0 M. Lithium secondary batteries of Examples 2 to 3 and Comparative Examples 1 to 4 were manufactured in the same manner as in Example 1, except that the negative active materials of Examples 2 to 3 and Comparative Examples 1 to 3 were used. (Evaluation of initial efficiency and discharge capacity) The lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 above were charged at 25°C in CC / CV mode at 0.1C (cut-off of 0.005 V, 0.005C), and discharged at 0.1C in CC mode to confirm the initial efficiency and discharge capacity. The results are shown in Table 2 below. Initial Efficiency (%)Discharge Capacity (mAh / g)Example 191.2347Example 293.8350Example 392.2345Comparative Example 188.6336Comparative Example 278.3343Comparative Example 384.2320 Referring to Table 2, it can be confirmed that the lithium secondary batteries of Examples 1 to 3 including the negative active material according to the present invention have superior initial efficiency and discharge capacity compared to Comparative Examples 1 to 3. For example, the initial efficiencies of Examples 1, 2, and 3 were 91.2%, 93.8%, and 92.2%, respectively, which were higher than 88.6%, 78.3%, and 84.2% of Comparative Examples 1, 2, and 3. In the case of discharge capacity, Examples 1, 2, and 3 were 347 mAh / g, 350 mAh / g, and 345 mAh / g, respectively, which were higher than 336 mAh / g, 343 mAh / g, and 320 mAh / g of Comparative Examples 1, 2, and 3. Although the present disclosure has been described above with reference to embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that various modifications and changes may be made to the various embodiments of the present disclosure without departing from the technical scope of the various embodiments of the present disclosure as set forth in the claims below. Accordingly, the technical scope of the various embodiments of the present disclosure should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims

1. As a negative active material, The above negative active material comprises artificial graphite particles; and nitrogen elements, oxygen elements and hydrogen elements present on the surface, inside, or both the surface and inside of the artificial graphite particles. A negative electrode active material wherein the nitrogen element is contained in an amount of 80 mg to 180 mg per 1 kg of the negative electrode active material.

2. In claim 1, The content of the above oxygen element is 650 mg to 1,000 mg per 1 kg of the negative electrode active material, A negative electrode active material wherein the hydrogen element is contained in an amount of 300 mg to 500 mg per 1 kg of the negative electrode active material.

3. In claim 1, A negative electrode active material, wherein the ratio of the weight of nitrogen element in the negative electrode active material to the weight of oxygen element in the negative electrode active material is 0.12 or more.

4. In claim 1, A negative electrode active material, wherein the ratio of the weight of hydrogen element in the negative electrode active material to the weight of oxygen element in the negative electrode active material is 0.47 or more.

5. In claim 1, A negative electrode active material, wherein the ratio of the total weight of nitrogen elements and hydrogen elements in the negative electrode active material to the weight of oxygen elements in the negative electrode active material is 0.5 or more.

6. In claim 1, A negative electrode active material wherein the total weight of nitrogen elements, oxygen elements, and hydrogen elements present in the negative electrode active material is 1,000 mg to 1,600 mg per 1 kg of the negative electrode active material.

7. In claim 1, The above artificial graphite particles are negative active materials in the form of secondary particles assembled from two or more primary particles.

8. In claim 1, A negative electrode active material having a graphitization degree of 90% to 99%.

9. In claim 1, The BET surface area of ​​the above negative active material is 1 m 2 / g to 8m 2 / g negative active material.

10. In claim 1, The above negative active material further comprises an amorphous carbon coating layer positioned on the artificial graphite particles.

11. A negative electrode comprising a negative active material according to claim 1.

12. A cathode according to claim 11; An anode opposite to the cathode; A separator interposed between the cathode and the anode; and A lithium secondary battery comprising a non-aqueous electrolyte.

Images