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

Abstract

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

Description

Technical Field

[0001] This invention relates to negative electrode active materials, negative electrodes containing the same, and secondary batteries. Background Technology

[0002] With increasing concern about environmental issues, research is underway on electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace vehicles using fossil fuels, such as gasoline and diesel vehicles, which are a major cause of air pollution. Secondary batteries for EVs serve as the power source for both EVs and HEVs. Currently commercially available secondary batteries for EVs include nickel-cadmium (NiCd), nickel-metal hydride (NiMH), nickel-zinc (NiZn), and lithium-ion (Li-ion) batteries. Among these, lithium-ion batteries have been extensively studied due to their advantages, including a substantially lower memory effect compared to nickel-based batteries, resulting in greater freedom of charge and discharge, lower self-discharge rate, and exhibiting high energy density, high discharge voltage, and output stability. Summary of the Invention

[0003] Technical issues

[0004] One aspect of the present invention provides a negative electrode active material for lithium secondary batteries that prevents or suppresses the reduction of discharge capacity, while preventing or suppressing surface peeling (stripping) of artificial graphite-based negative electrode active materials and the resulting electrolyte side reaction defects, thereby improving initial efficiency, maintaining discharge capacity and improving the fast charging performance of secondary batteries.

[0005] Another aspect of the present invention provides a negative electrode comprising the above-described negative electrode active material.

[0006] Another aspect of the present invention provides a lithium secondary battery comprising the above-described negative electrode.

[0007] Technical solution

[0008] [1] The present invention provides a negative electrode active material comprising: artificial graphite particles; and nitrogen, oxygen and hydrogen elements present on the surface, inside or on the surface and inside of the artificial graphite particles, wherein the nitrogen content is 80 mg to 180 mg per 1 kg of the negative electrode active material.

[0009] [2] The present invention provides a negative electrode active material according to [1] above, wherein the oxygen content is 650 mg to 1,000 mg per kg of the negative electrode active material, and the hydrogen content is 300 mg to 500 mg per kg of the negative electrode active material.

[0010] [3] The present invention provides a negative electrode active material according to at least one of [1] to [2] above, wherein the weight ratio of the nitrogen element in the negative electrode active material to the weight of the oxygen element in the negative electrode active material is 0.12 or more.

[0011] [4] The present invention provides a negative electrode active material according to at least one of [1] to [3] above, wherein the weight ratio of the hydrogen element in the negative electrode active material to the weight of the oxygen element in the negative electrode active material is 0.47 or more.

[0012] [5] The present invention provides a negative electrode active material according to at least one of [1] to [4] above, wherein the ratio of the total weight of the nitrogen element and the hydrogen element in the negative electrode active material to the weight of the oxygen element in the negative electrode active material is 0.5 or more.

[0013] [6] The present invention provides a negative electrode active material according to at least one of [1] to [5] above, wherein the total weight of the nitrogen, oxygen and hydrogen elements present in the negative electrode active material is 1,000 mg to 1,600 mg per kg of the negative electrode active material.

[0014] [7] The present invention provides a negative electrode active material according to at least one of [1] to [6] above, wherein the artificial graphite particles are in the form of secondary particles formed by the aggregation of two or more primary particles.

[0015] [8] The present invention provides a negative electrode active material according to at least one of [1] to [7] above, wherein the degree of graphitization of the negative electrode active material is 90% to 99%.

[0016] [9] The present invention provides a negative electrode active material according to at least one of [1] to [8] above, wherein the negative electrode active material has a 1m 2 / g to 8m 2 / g BET specific surface area.

[0017]

[10] The present invention provides a negative electrode active material according to at least one of [1] to [9] above, the negative electrode active material further comprising: an amorphous carbon coating on the artificial graphite particles.

[0018]

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

[10] above.

[0019]

[12] In addition, the present invention provides a negative electrode according to

[11] above; a positive electrode disposed facing the negative electrode; a diaphragm inserted between the negative electrode and the positive electrode; and a non-aqueous electrolyte.

[0020] Beneficial effects

[0021] The negative electrode active material according to the present invention comprises artificial graphite particles, and nitrogen, oxygen, and hydrogen elements. The nitrogen, oxygen, and hydrogen elements may be present or doped into the artificial graphite particles. The nitrogen element is contained in the negative electrode active material in a specific amount. The range of nitrogen content present in the negative electrode active material can be interpreted as an indicator of the degree of graphitization on the surface of the negative electrode active material. According to the present invention, by adjusting the nitrogen content present in the negative electrode active material to a specific range, the degree of graphitization on the surface of the negative electrode active material can be reduced to an appropriate level. Therefore, the negative electrode active material according to the present invention can prevent or suppress stripping due to organic solvents contained in non-aqueous electrolytes, while simultaneously exhibiting the desired level of discharge capacity. Attached Figure Description

[0022] The accompanying drawings illustrate embodiments of the invention and, together with the detailed description below, serve to further understand the technical concept of the invention. Therefore, the invention should not be construed as limited to what is described in these drawings.

[0023] Figure 1 This is a flowchart illustrating the artificial graphite preparation process according to one embodiment of the present invention. Detailed Implementation

[0024] The terms or words used in this specification and claims should not be construed as limited to their general and dictionary meanings, but should be interpreted as meanings and concepts corresponding to the technical concept of the invention, based on the principle that the inventors are allowed to properly define terms so as to best interpret their invention.

[0025] The terminology used in this specification is for describing exemplary embodiments only and is not intended to limit the invention. Unless the context otherwise indicates, the singular form is intended to include the plural form.

[0026] In this specification, the terms “comprising,” “including,” or “having” are intended to indicate the presence of features, figures, steps, constituent elements, or combinations thereof in the implementation, but should not be construed as precluding the possibility of the presence or addition of one or more other features, figures, steps, constituent elements, or combinations thereof.

[0027] In this specification, the average particle size (D) 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the volumetric accumulation in the particle size distribution curve. 50Particle sizes can be measured using methods such as laser diffraction. Laser diffraction is typically capable of measuring particle sizes ranging from submicron to millimeters (mm) and can yield results with high reproducibility and high resolution.

[0028] In this specification, "primary particle" refers to a single particle, and "secondary particle" refers to a collection of multiple primary particles that have been agglomerated through an intentional aggregation or bonding process.

[0029] As used in this specification, taking into account inherent manufacturing and material tolerances, “about,” “approximately,” and “substantially” are used as categories of numerical or degree, or meanings close to them.

[0030] A lithium secondary battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode and the negative electrode are prepared by the following operations: mixing positive and negative active materials with a binder respectively, dispersing them in a solvent to prepare a slurry, applying the slurry to the surface of an electrode current collector, and drying the slurry to form an electrode active material layer.

[0031] Regarding the negative electrode active material, carbonaceous active materials that allow reversible insertion and extraction of lithium ions while maintaining structural and electrical properties can be used. Various types of carbonaceous materials have been used, such as artificial graphite, natural graphite, and hard carbon. Among these, graphite-based active materials, which ensure the lifespan characteristics of lithium-ion secondary batteries due to their high reversibility, have been widely used. Because graphite-based active materials have a relatively low discharge voltage of -0.2V compared to lithium, batteries using these materials can exhibit, for example, a high discharge voltage of about 3.6V, thus providing many advantages in terms of energy density for lithium-ion batteries.

[0032] Among the carbon-based active materials, synthetic graphite exhibits relatively low orientation during electrode calendering compared to natural graphite and possesses excellent lithium-ion inflow / outflow properties, thus offering advantages in terms of superior fast-charging performance and excellent lifetime characteristics due to low expansion during charge and discharge. Synthetic graphite is prepared by heat-treating amorphous carbon, such as coke, at high temperatures (e.g., 2,500°C to 3,200°C), and differs from natural graphite in that it is artificially synthesized. Due to the high-temperature heat treatment, synthetic graphite exhibits a high degree of graphitization, but a drawback is that its surface can peel off upon contact with organic solvents (e.g., ethyl methyl carbonate) in non-aqueous electrolytes. Surface peeling of synthetic graphite can cause various defects, such as increased electrolyte side reactions, low initial efficiency, energy density loss, and gas generation. On the other hand, excessively reducing the graphitization of synthetic graphite to prevent or suppress such defects may itself reduce capacity.

[0033] The invention will be described in detail below.

[0034] Negative electrode active materials

[0035] This invention relates to a negative electrode active material, such as a negative electrode active material for lithium secondary batteries.

[0036] The negative electrode active material comprises artificial graphite particles; and nitrogen (N), oxygen (O) and hydrogen (H) elements present on the surface, inside, or on the surface and inside the artificial graphite particles, wherein the nitrogen content is approximately 80 mg to 180 mg per 1 kg of the negative electrode active material.

[0037] The negative electrode active material according to the present invention comprises the artificial graphite particles, the nitrogen element, the oxygen element, and the hydrogen element. The nitrogen element, the oxygen element, and the hydrogen element may be present in or doped into the artificial graphite particles. The nitrogen element is contained in the negative electrode active material in a specific amount. The range of nitrogen element content present in the negative electrode active material can be interpreted as an indicator of the degree of graphitization on the surface of the negative electrode active material. According to the present invention, by adjusting the nitrogen element content present in the negative electrode active material to a specific range, the degree of graphitization on the surface of the negative electrode active material can be reduced to an appropriate level. Therefore, the negative electrode active material according to the present invention can prevent or suppress stripping due to organic solvents contained in non-aqueous electrolytes, while simultaneously exhibiting the desired level of discharge capacity.

[0038] Typically, graphite can be artificially prepared through a series of complex processes that transform raw materials into a highly ordered crystalline structure. For example, to prepare such artificial graphite, coke and graphite are pulverized and mixed with a binder (e.g., bitumen) to form a homogeneous block. The mixture is then shaped using techniques such as isotropic pressing, extrusion, or molding. Subsequently, the shaped material undergoes a carbonization process at approximately 1,000°C in an oxygen-free environment, and in the next step of the graphitization process, the material is heat-treated in an inert atmosphere to a temperature of approximately 2,500°C to 3,200°C, thereby partially or completely converting amorphous or non-crystalline carbon into graphite. The graphitization process in the preparation of artificial graphite is one of the main steps in the carbon-graphite process. For example, the high-temperature treatment in the graphitization process causes carbon atoms to align in the characteristic layered structure of graphite, thereby improving properties such as strength and electrical conductivity. The degree of graphitization is a measure used to determine how closely the carbon atoms resemble the densely arranged hexagonal crystal structure of graphite. An ideal graphite crystal structure is represented by a dense hexagonal arrangement with lattice constants a = 0.2461 nm and c = 0.6708 nm. Generally, the closer the lattice size is to the ideal graphite lattice constant, the higher the degree of graphitization is considered to be.

[0039] The negative electrode active material comprises the artificial graphite particles. The artificial graphite particles are prepared by heat-treating amorphous carbon at high temperatures (e.g., 2,500°C to 3,200°C), and differ from natural graphite in that the artificial graphite particles are synthetically produced graphite.

[0040] The artificial graphite particles can be in the form of primary particles or secondary particles formed by the aggregation of two or more primary particles. For example, the artificial graphite particles can be in the form of secondary particles formed by the aggregation of two or more primary particles. The primary particles contained in the artificial graphite particles can refer to artificial graphite in the form of primary particles.

[0041] When the artificial graphite particles are in the form of secondary particles, pores can be formed within the artificial graphite particles. These pores can be empty spaces formed between the primary particles, and can be amorphous, with two or more pores present.

[0042] When the artificial graphite particles are in the form of secondary particles, they can be prepared by mixing primary-particle artificial graphite particles with a binder material (e.g., pitch), and then mechanically grinding, shaping or spheroidizing, and heat-treating them to agglomerate the primary-particle artificial graphite particles into secondary particles. Alternatively, when the artificial graphite particles are in the form of secondary particles, they can be prepared by mixing a carbon precursor and a binder material, performing mechanical grinding (or shaping) and agglomeration processes to produce an intermediate in the form of secondary particles, and then heat-treating the intermediate at a temperature above 3,000°C to graphitize it. In this case, the carbon precursor can be heavy oil derived from coal, heavy oil derived from petroleum, tar, pitch, or coke, and can be at least one selected from, for example, needle coke, mosaic coke, and coal tar pitch. The preparation method is not particularly limited, as long as the nitrogen content range present in the negative electrode active material is met.

[0043] The negative electrode active material may contain nitrogen, oxygen, and hydrogen elements present on the surface, inside, or both on and inside the artificial graphite particles. According to one embodiment of the invention, the nitrogen, oxygen, and hydrogen elements may be doped into the artificial graphite particles.

[0044] In this invention, the nitrogen content in the artificial graphite particles can be approximately 80 mg to 180 mg per 1 kg of the negative electrode active material.

[0045] The nitrogen, oxygen, and hydrogen elements may be introduced into or present in the artificial graphite particles during processes such as crushing, mechanical grinding, or agglomeration. Typically, during processes such as graphitization, the nitrogen element is usually removed or present at low levels. On the other hand, when the artificial graphite is sufficiently graphitized as required, the nitrogen content contained in the artificial graphite particles becomes quite low. In this case, surface peeling of the artificial graphite may occur during the impregnation and introduction of an electrolyte component such as ethyl methyl carbonate (EMC) into the artificial graphite. This surface peeling causes side reactions between the non-aqueous electrolyte and the surface of the artificial graphite, and leads to the problem of continuous consumption of the organic solvent in the non-aqueous electrolyte. Furthermore, to prevent this problem, when the overall degree of graphitization of the artificial graphite decreases, the discharge capacity itself decreases, making it difficult to achieve the target energy density.

[0046] In this respect, in this invention, by adjusting the nitrogen content present in the artificial graphite particles to a specific range, electrolyte side reactions are prevented or suppressed, and discharge capacity is improved. The reason for this effect is understood to be that when the nitrogen content present or introduced during the graphitization process of the artificial graphite particles meets a specific range, the degree of graphitization on the surface of the artificial graphite particles is reduced to an appropriate level, thus significantly reducing surface stripping due to organic solvents in the non-aqueous electrolyte. Furthermore, the negative electrode active material according to the invention can prevent or suppress the electrolyte side reactions without reducing the overall degree of graphitization of the artificial graphite particles, thus achieving a high level of discharge capacity.

[0047] When the nitrogen content in the artificial graphite particles is adjusted to a specific range, local electrochemical active sites are generated based on the doping of the nitrogen element, thereby improving the fast charging performance of the negative electrode active material.

[0048] According to the described embodiment, the nitrogen content contained in the artificial graphite particles can be approximately 80 mg to 180 mg per 1 kg of the negative electrode active material, for example, approximately 100 mg to 170 mg, or approximately 110 mg to 160 mg, or approximately 120 mg to 140 mg. Within this range, the effects of improving initial efficiency and discharge capacity, as well as preventing electrolyte side reactions, can be exhibited at a superior level.

[0049] In this invention, the oxygen content in the negative electrode active material can be from about 650 mg to 1,000 mg per 1 kg of the negative electrode active material, for example, from about 650 mg to 900 mg, or from about 680 mg to 850 mg, or from about 700 mg to 800 mg. Furthermore, the hydrogen content in the negative electrode active material can be from about 300 mg to 500 mg per 1 kg of the negative electrode active material, for example, from about 310 mg to 480 mg, or from about 320 mg to 450 mg, or from about 350 mg to 420 mg.

[0050] The total weight of the nitrogen, oxygen 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.

[0051] The weight ratio of nitrogen to oxygen in the negative electrode active material can be about 0.12 or more, for example, 0.15 or more, or 0.16 or more. The weight ratio of nitrogen to oxygen in the negative electrode active material can be, for example, about 0.20 or less, or about 0.19 or less. The weight ratio of nitrogen to oxygen in the negative electrode active material can be about 0.12 to 0.20, for example, about 0.15 to 0.20, or about 0.16 to 0.19, or about 0.165 to 0.185.

[0052] The weight ratio of hydrogen to oxygen in the negative electrode active material can be more than about 0.47, for example, about 0.47 to 0.55, or for example, about 0.48 to 0.51.

[0053] The ratio of the total weight of nitrogen and hydrogen in the negative electrode active material to the weight of oxygen in the negative electrode active material can be about 0.5 or more, for example, 0.55 or more, or 0.6 or more. The ratio of the total weight of nitrogen and hydrogen in the negative electrode active material to the weight of oxygen in the negative electrode active material can be about 0.75 or less. For example, the ratio of the total weight of nitrogen and hydrogen in the negative electrode active material to the weight of oxygen in the negative electrode active material can be about 0.5 to 0.75, for example, 0.6 to 0.72, or 0.65 to 0.70.

[0054] By controlling the content of nitrogen, oxygen, and hydrogen, and the relationship between their contents, it is possible to improve initial efficiency and discharge capacity, as well as prevent or suppress electrolyte side reactions.

[0055] The content of nitrogen, oxygen, and / or hydrogen can be measured using an ONH analyzer. For example, a 0.1g sample of the negative electrode active material can be placed in a crucible and introduced into an ONH analyzer to measure the content of nitrogen, oxygen, and / or hydrogen. For example, the ONH analyzer could be a NOH836 analyzer (LECO Korea Co., Ltd.). To determine the content of nitrogen, oxygen, and / or hydrogen, three identical negative electrode active material samples can be prepared and analyzed three times using the ONH analyzer. The average value obtained can then be defined as the content of nitrogen, oxygen, and / or hydrogen.

[0056] In this invention, the content of nitrogen, oxygen, and hydrogen in the negative electrode active material can be adjusted by controlling the conditions of the preparation steps of the artificial graphite particles, such as the crushing step, the forming step performed by, for example, mechanical grinding, the agglomeration step, the graphitization step, and the additional forming step. According to the embodiment, for the negative electrode active material according to the invention, by performing an additional forming step, such as mechanical grinding or spheroidization, after the graphitization step used to prepare the artificial graphite particles, and by controlling the mechanical grinding or spheroidization conditions at this time, the content of nitrogen, oxygen, and hydrogen in the negative electrode active material can be adjusted. In this case, the mechanical grinding or spheroidization conditions can be controlled by considering, for example, the size of the reactor or the weight of the precursor to be introduced.

[0057] Figure 1 This is a flowchart illustrating a process 100 for preparing artificial graphite according to an embodiment of the present invention.

[0058] In step S110, a crushing process is first performed to crush the coke, which is the raw material for artificial graphite, into the desired size. In this process, the size of the coke is adjusted by regulating the revolutions per minute (RPM) of the grinding equipment, such as an air classifier, roller mill, or hammer mill.

[0059] In step S120, a primary forming process is performed. In this primary forming process, the surface of the coke, which has been reduced to the desired size through the previous crushing process, is smoothed without any unevenness, and it is also formed in a non-pointed shape. This primary forming process can use the same equipment as the crushing process or different equipment.

[0060] In step S130, an agglomeration process is performed. For artificial graphite, this agglomeration process is the preparation of secondary particles, which are formed by agglomerating multiple primary particles that have already been prepared by crushing coke using an additive such as pitch. The agglomeration process is carried out using a vertical or horizontal granulator, which is a device for mixing primary particles, as crushed coke, with an additive such as pitch, and the mixing ratio with the additive can be adjusted by regulating the RPM of the device to form the desired particle size.

[0061] In step S140, a graphitization process is performed. According to the embodiment, an Acheson furnace is used in the graphitization process to heat-treat coke at a temperature of, for example, about 3,000°C to produce graphite.

[0062] In step S150, a secondary forming process is performed, which is an additional forming process that can intentionally damage the graphite surface. In this secondary forming process, the equipment used in the previous forming and crushing processes can be used. However, compared to the previous forming and crushing processes, the RPM or process time is significantly reduced, resulting in, for example, relatively weak grinding.

[0063] The degree of graphitization of the negative electrode active material can be approximately 90% to 99%, for example, approximately 92% to 99%, or approximately 92% to 96%, or approximately 92% to 94%. When the degree of graphitization falls within the above range, the overall degree of graphitization of the negative electrode active material can be increased to a certain level to ensure excellent initial efficiency and discharge capacity, while preventing or suppressing electrolyte side reactions caused by surface peeling of the negative electrode active material.

[0064] The degree of graphitization of the negative electrode active material can be calculated by measuring the interplanar spacing d002 of the graphite (002) facets obtained from XRD data using Bragg's law.

[0065] For example, the degree of graphitization can be obtained from Equation 1 below.

[0066] [Formula 1]

[0067] Degree of graphitization (%) = (3.44 - d002) / (0.086) × 100

[0068] In Equation 1, d002 is the interplanar spacing (nm) of the (002) facets of the artificial graphite particles present in the negative electrode active material.

[0069] The average particle size (D) of the negative electrode active material 50 The diameter can be from about 10 μm to 30 μm, for example, from about 12 μm to 25 μm.

[0070] The specific surface area of ​​the negative electrode active material (Brunauer, Emmett, Teller) can be approximately 1 m². 2 / g to 8m 2 / g, for example, about 1.2m 2 / g to 5m 2 / g, or approximately 1.4m 2 / g to 3.2m 2 / g, or approximately 1.6m 2 / g to 2.5m 2 / g. When the BET specific surface area falls within the above range, the movement path of lithium ions is easily ensured, thereby exhibiting excellent initial efficiency and discharge capacity, and improving electrolyte side reactions by reducing the degree of graphitization on the surface of the negative electrode active material. The BET specific surface area can be measured, for example, using a BEL adsorption instrument (BEL Japan).

[0071] The negative electrode active material may further include an amorphous carbon coating on the surface of the artificial graphite particles. The amorphous carbon coating can help improve the structural stability of the artificial graphite particles and prevent or suppress side reactions between the negative electrode active material and the electrolyte.

[0072] Based on the total weight of the negative electrode active material, the amorphous carbon coating can be formed in an amount from about 0.1% by weight (% by weight) to 10% by weight, for example, from about 1% by weight to 5% by weight. The presence of the amorphous carbon coating can improve the structural stability of the negative electrode active material. On the other hand, excessive formation of the amorphous carbon coating may lead to a decrease in initial efficiency due to the increase in specific surface area during negative electrode calendering, and may also lead to a decrease in high-temperature storage performance. Therefore, the carbon coating can be formed in an amount within the above-mentioned range.

[0073] The amorphous carbon coating can be formed by providing the artificial graphite particles with a carbon coating precursor and then heat-treating it.

[0074] The carbon coating precursor may comprise at least one selected from polymer resins and bitumen. For example, the polymer resin may comprise at least one selected from: sucrose, phenolic resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, vinyl chloride resin, and polyvinyl chloride. The bitumen may comprise at least one selected from: coal-derived bitumen, petroleum-derived bitumen, and mesophase bitumen. The heat treatment process for forming the amorphous carbon coating may be performed at about 1,000°C to 1,500°C to promote the uniform formation of the amorphous carbon coating.

[0075] negative electrode

[0076] The present invention provides a negative electrode, for example, a negative electrode for a lithium secondary battery. The negative electrode may include the above-mentioned negative electrode active material.

[0077] According to the embodiment, the negative electrode may include a negative electrode current collector; and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer may include the above-mentioned negative electrode active material.

[0078] Regarding the negative electrode current collector, any negative electrode current collector commonly used in the art may be used without limitation as long as it has high conductivity and does not cause chemical changes in the lithium secondary battery. For example, the negative electrode current collector may include at least one selected from the following: copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum cadmium alloy, and may be copper according to one embodiment.

[0079] The negative electrode current collector may form fine concavities and convexities on the surface to enhance the bonding force of the negative electrode active material, and may be used in various forms such as a film, sheet, foil, net, porous body, foam, and non-woven fabric.

[0080] The negative electrode current collector generally may have a thickness of about 3 μm to 500 μm.

[0081] The negative electrode active material layer is provided on at least one surface of the negative electrode current collector. For example, the negative electrode active material layer may be provided on one surface or both surfaces of the negative electrode current collector.

[0082] The negative electrode active material layer may include the above-mentioned negative electrode active material.

[0083] Based on including the above-mentioned negative electrode active material, the negative electrode active material layer may further include a silicon-based active material.

[0084] The silicon-based active material may include, for example, at least one of silicon (Si), silicon oxide (SiO x , 0 < x < 2), and silicon-carbon composite.

[0085] The content of the negative electrode active material or the mixture of the negative electrode active material and the silicon-based active material in the negative electrode active material layer may be about 80% by weight to 99% by weight, for example, about 88% by weight to 98% by weight.

[0086] The description of the negative electrode active material is as described above.

[0087] Based on including the above-mentioned negative electrode active material, the negative electrode active material layer may further include a binder, a conductive material, and / or a thickening agent.

[0088] The adhesive is a component that facilitates the bonding between the active material and / or the current collector, and its content in the negative electrode active material layer can typically be from about 1% to 30% by weight, for example, from about 1% to 10% by weight.

[0089] The adhesive may contain at least one selected from the following: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, for example, at least one selected from polyvinylidene fluoride and styrene-butadiene rubber.

[0090] Regarding the thickener, any thickener used in conventional lithium secondary batteries can be used, and examples of the thickener include carboxymethyl cellulose (CMC).

[0091] The conductive material is a component used to further improve the conductivity of the negative electrode active material, and its content in the negative electrode active material layer can be from about 1% to 30% by weight, for example, from about 1% to 10% by weight.

[0092] The conductive material is not particularly limited, as long as it is conductive and will not cause chemical changes in the battery. Examples of conductive materials that can be used include graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; metal powders, such as nickel powder or aluminum powder; fluorocarbons; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives. Examples of commercially available conductive materials include the acetylene black series such as products manufactured by Chevron Chemical Company or Denka Black manufactured by Denka Singapore private limited, products manufactured by Gulf Oil Company, Ketjen Black, the EC series manufactured by Armak Company, Vulcan XC-72 manufactured by Cabot Company, and Super P manufactured by Timcal Company.

[0093] The thickness of the negative electrode active material layer can be from about 10 μm to 300 μm, for example from about 50 μm to 200 μm, but is not limited thereto.

[0094] The negative electrode active material layer can be manufactured by applying a negative electrode slurry, prepared by selectively adding a negative electrode active material, optionally a binder, a thickener, and / or a conductive material to a solvent, to the negative electrode current collector, and then calendering and drying the negative electrode slurry applied to the negative electrode current collector. In this case, the solvent may contain water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be, for example, water.

[0095] Secondary batteries

[0096] The present invention provides a secondary battery comprising the above-described negative electrode, and provides, for example, a lithium secondary battery.

[0097] The secondary battery may include the negative electrode; a positive electrode facing the negative electrode; a separator inserted between the negative electrode and the positive electrode; and an electrolyte.

[0098] The positive electrode can face the negative electrode.

[0099] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.

[0100] Regarding the positive electrode current collector, any positive electrode current collector commonly used in the art can be used without limitation, as long as it has relatively high conductivity without causing chemical changes in the lithium secondary battery. For example, the positive electrode current collector may contain at least one selected from the following: copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy, and according to one embodiment, it may be aluminum.

[0101] The positive electrode current collector can form fine irregularities on its surface to enhance the bonding force of the positive electrode active material, and can be used in various forms such as membranes, sheets, foils, meshes, porous bodies, foams and nonwoven fabrics.

[0102] The positive current collector can typically have a thickness of about 3 μm to 500 μm.

[0103] The positive electrode active material layer may contain a positive electrode active material.

[0104] The positive electrode active material is a compound that allows reversible insertion and extraction of lithium ions, and may include, for example, a lithium composite metal oxide comprising lithium and at least one metal such as cobalt, manganese, nickel, or aluminum. According to the embodiment, the lithium composite metal oxide may be a lithium-manganese oxide (e.g., LiMnO2 or LiMn2O4), a lithium-cobalt oxide (e.g., LiCoO2), a lithium-nickel oxide (e.g., LiNiO2), or a lithium-nickel-manganese oxide (e.g., LiNi...). 1-Y Mn YO2 (where 0 < Y < 1) or LiMn 2-z Ni z O4 (where 0 < z < 2)), lithium-nickel-cobalt oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1)), lithium-manganese-cobalt oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1) or LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2)), lithium-nickel-manganese-cobalt oxide (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 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2)), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from 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)), and the lithium composite metal oxide may contain more than one compound of these oxides. Among them, in terms of improving the capacity characteristics and stability of the battery, the lithium composite metal oxide may be LiCoO2, LiMnO2, LiNiO2, lithium-nickel-manganese-cobalt oxide (e.g., 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) or lithium-nickel-cobalt-aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2). Considering the significance of the improvement effect obtained by controlling the element type and content ratio of the lithium composite metal oxide, the lithium composite metal oxide may be Li(Ni 0.6 Mn 0.2 Co0.2 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, and one or more of them can be used in mixture.

[0105] The content of the positive electrode active material in the positive electrode active material layer can be from about 80% to 99% by weight.

[0106] The positive electrode active material layer may further include at least one selected from adhesives and conductive materials, in addition to the positive electrode active material.

[0107] The adhesive is a component that facilitates the bonding of the active material to the conductive material and to the current collector, and is typically added in an amount of 1% to 30% by weight based on the total weight of the positive electrode mixture. Examples of the adhesive may include at least one selected from the following: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene trimer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber.

[0108] The amount of the adhesive in the positive electrode active material layer can be from about 1% to 30% by weight.

[0109] The conductive material is not particularly limited, as long as it is conductive and will not cause chemical changes in the battery. Examples of conductive materials that can be used include graphite, such as natural or synthetic graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked black; conductive fibers, such as carbon fibers or metal fibers; metal powders, such as nickel powder or aluminum powder; fluorocarbons; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives. Examples of commercially available conductive materials include acetylene black series such as products manufactured by Chevron Chemicals, or Danka Black manufactured by Danka Pte Ltd, Singapore, products manufactured by Gulf Oil, Ketjen black, the EC series manufactured by Armach, Vulcan XC-72 manufactured by Cabot Corporation, and Super P manufactured by TMI Corporation.

[0110] The amount of conductive material added to the positive electrode active material layer can be from about 1% by weight to 30% by weight.

[0111] The separator separates the negative electrode and the positive electrode and provides a channel for lithium ion movement. Those commonly used as separators in lithium secondary batteries can be used without any particular limitation; for example, those with excellent electrolyte retention capabilities and low resistance to ion migration in the electrolyte can be used. According to the embodiments described, porous polymer membranes can be used alone, such as porous polymer membranes prepared from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures having two or more layers can be used. Furthermore, common porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used in single-layer or multi-layer structures.

[0112] The electrolyte used in this invention may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0113] For example, the electrolyte may contain an organic solvent and a lithium salt.

[0114] The organic solvents can be used without any particular restrictions, as long as they can serve as a medium through which ions participating in the electrochemical reactions of the battery can move. For example, as organic solvents, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic solvents such as benzene or fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); alcohol solvents such as ethanol or isopropanol; nitrile solvents such as R-CN (R is a linear, branched, or cyclic C2 to C20 hydrocarbon group, and may contain double-bonded aromatic rings or ether bonds); amide solvents such as dimethylformamide; dioxolane solvents such as 1,3-dioxolane; or sulfolane solvents can be used. According to the described embodiment, a carbonate-based solvent can be used, and a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) can be used, which can increase the charge / discharge performance of the battery. In this case, by using a mixture of cyclic carbonates and linear carbonates in a volume ratio of about 1:1 to about 1:9, the electrolyte can exhibit excellent performance.

[0115] The lithium salt can be used without any particular restrictions, as long as it is a compound capable of providing lithium ions for use in lithium secondary batteries. For example, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt can be in 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 have suitable conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can move efficiently.

[0116] Because the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, fast charging characteristics, and capacity retention, it can be used in portable devices such as mobile phones, laptops, or digital cameras, as well as in electric vehicles such as hybrid electric vehicles (HEVs). For example, the lithium secondary battery can be used as a constituent battery in medium to large-sized battery modules. Therefore, the present invention provides a medium to large-sized battery module comprising the above-described secondary battery as a unit cell.

[0117] The medium-to-large battery modules can be used as power sources for electric vehicles, hybrid electric vehicles, or power storage devices that require relatively high power and relatively large capacity.

[0118] Embodiments of the present invention will be described in detail below, so that those skilled in the art can readily implement the invention. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0119] Examples and Comparative Examples

[0120] Example 1

[0121] The coke raw material is pulverized and subjected to air classification and mechanical grinding to prepare a carbon precursor in primary particle form. The carbon precursor is then mixed with pitch and placed in an agglomeration device with blades, where it is mechanically ground at 400°C to 800°C while mixing, thereby producing an intermediate in secondary particle form. The intermediate is then heat-treated in a graphitization furnace with a capacity of approximately 100 kg at 3,000°C for 2 hours to graphitize it.

[0122] The graphitized product was further mechanically ground at 30 Hz at room temperature in the agglomeration device. This produced artificial graphite particles in the form of secondary particles formed by the aggregation of two or more primary artificial graphite particles, which were then used as a negative electrode active material.

[0123] The average particle size (D) of the negative electrode active material 50 Its thickness is 17 μm, and its BET specific surface area is 1.4 m². 2 / g.

[0124] Example 2

[0125] Except for additional mechanical grinding at room temperature at a speed of 40 Hz, which is higher than 30 Hz in Example 1 above, after graphitization, the negative electrode active material was prepared in the same manner as in Example 1.

[0126] The average particle size (D) of the negative electrode active material 50 Its thickness is 16 μm, and its BET specific surface area is 1.8 m². 2 / g.

[0127] Example 3

[0128] Except for additional mechanical grinding at room temperature at a speed of 50 Hz, which is higher than 40 Hz in Example 2 above, after graphitization, the negative electrode active material was prepared in the same manner as in Example 1.

[0129] The average particle size (D) of the negative electrode active material 50 Its thickness is 15 μm, and its BET specific surface area is 3.2 m². 2 / g.

[0130] Comparative Example 1

[0131] The negative electrode active material was prepared in the same manner as in Example 1, except that no additional mechanical grinding was performed after graphitization.

[0132] The average particle size (D) of the negative electrode active material 50 Its thickness is 19 μm, and its BET specific surface area is 1.2 m². 2 / g.

[0133] Comparative Example 2

[0134] The negative electrode active material was prepared in the same manner as in Example 1, except that the heat treatment time during graphitization was adjusted to 3 hours and no additional mechanical grinding was performed after graphitization.

[0135] The average particle size (D) of the negative electrode active material 50 Its thickness is 19 μm, and its BET specific surface area is 1.0 m². 2 / g.

[0136] Comparative Example 3

[0137] The negative electrode active material was prepared in the same manner as in Example 1, except that the heat treatment time during the graphitization was adjusted to 1 hour and no additional mechanical grinding was performed after the graphitization.

[0138] The average particle size (D) of the negative electrode active material 50 Its thickness is 20 μm, and its BET specific surface area is 3.5 m². 2 / g.

[0139] [Table 1]

[0140] 1) Analysis of the content of nitrogen, oxygen and hydrogen elements.

[0141] A 0.1 g sample of the negative electrode active material was placed in a crucible and introduced into an ONH analyzer (NOH836 analyzer from LECO Corporation, Korea) to measure the content of nitrogen, oxygen, and / or hydrogen. Three samples from each example and each comparative example were prepared, and the measurement tests were performed three times. The average values ​​obtained are recorded in Table 1.

[0142] 2) Degree of graphitization

[0143] The degree of graphitization of the negative electrode active material is calculated by measuring the interplanar spacing d002 of the graphite (002) facets obtained from XRD data using Bragg's law, according to Equation 1 above.

[0144] 3) Average particle size (D) 50 )

[0145] The particle size distribution curve of the particles was obtained by laser diffraction, and then the average particle size (D) of the negative electrode active material was calculated by calculating the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. 50 The particle size corresponding to 50% of the volumetric accumulation is defined as the average particle size (D) of the negative electrode active material. 50 ).

[0146] 4) BET specific surface area

[0147] The BET specific surface area of ​​the negative electrode active material was measured using a BEL adsorption instrument (BEL Japan).

[0148] Experimental Example

[0149] Experimental Example 1: Evaluation of Initial Efficiency and Discharge Capacity

[0150] (Manufacturing of lithium secondary batteries)

[0151] To prepare the negative electrode slurry, the negative electrode active material prepared according to Example 1, carbon black as a conductive material, styrene-butadiene rubber as a binder, and CMC as a thickener were added 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 calendered to manufacture the negative electrode.

[0152] Prepare lithium metal as the counter electrode of the negative electrode.

[0153] A porous polyethylene separator is inserted between the negative electrode and the lithium metal counter electrode to manufacture an electrode assembly. The electrode assembly is placed inside a housing, a non-aqueous electrolyte is injected into the housing, and the housing is sealed to manufacture the lithium secondary battery of Example 1.

[0154] The non-aqueous electrolyte is obtained by dissolving LiPF6 at a concentration of 1.0 M in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 20:80.

[0155] The lithium secondary batteries of Examples 2 to 3 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the negative electrode active materials of Examples 2 to 3 and Comparative Examples 1 to 3 were used.

[0156] (Evaluation of initial efficiency and discharge capacity)

[0157] The lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3 prepared above were charged at 25°C in CC / CV mode at 0.1C (0.005V, 0.005C cutoff) and discharged in CC mode at 0.1C to confirm the initial efficiency and discharge capacity.

[0158] The results are shown in Table 2 below.

[0159] [Table 2]

[0160] Referring to Table 2, it can be confirmed that the lithium secondary batteries comprising the negative electrode active material according to the present invention in Examples 1 to 3 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 are 91.2%, 93.8%, and 92.2%, respectively, which are higher than those of Comparative Examples 1, 2, and 3 (88.6%, 78.3%, and 84.2%, respectively). In terms of discharge capacity, Examples 1, 2, and 3 exhibit 347 mAh / g, 350 mAh / g, and 345 mAh / g, respectively, which are higher than those of Comparative Examples 1, 2, and 3 (336 mAh / g, 343 mAh / g, and 320 mAh / g, respectively).

[0161] Although the invention has been described above with reference to embodiments thereof, those skilled in the art or those with ordinary knowledge in the art will understand that various modifications and changes can be made to the invention without departing from the technical scope of the various embodiments described in the claims below. Therefore, the technical scope of the invention is not limited to the specific embodiments described in this specification, but should be defined by the patent claims.

Claims

1. A negative electrode active material, said negative electrode active material comprising: Artificial graphite particles; and Nitrogen, oxygen, and hydrogen elements are present on the surface, inside, or on the surface and inside the artificial graphite particles. The nitrogen content is 80 mg to 180 mg per 1 kg of the negative electrode active material.

2. The negative electrode active material according to claim 1, wherein the oxygen content is 650 mg to 1,000 mg per 1 kg of the negative electrode active material, and The hydrogen content is 300 mg to 500 mg per 1 kg of the negative electrode active material.

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

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

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

6. The negative electrode active material according to claim 1, wherein the total weight of the nitrogen, oxygen 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. The negative electrode active material according to claim 1, wherein the artificial graphite particles are in the form of secondary particles formed by the aggregation of two or more primary particles.

8. The negative electrode active material according to claim 1, wherein the degree of graphitization of the negative electrode active material is 90% to 99%.

9. The negative electrode active material according to claim 1, wherein the negative electrode active material has a 1m 2 / g to 8m 2 / g BET specific surface area.

10. The negative electrode active material according to claim 1, wherein the negative electrode active material further comprises: An amorphous carbon coating located on the artificial graphite particles.

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

12. A lithium secondary battery, the lithium secondary battery comprising: The negative electrode according to claim 11; The positive electrode is positioned facing the negative electrode; A diaphragm inserted between the negative electrode and the positive electrode; and Non-aqueous electrolyte.

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