Anode active material, method for producing the same, anode containing the same, and secondary battery

Abstract

The present invention relates to a negative electrode active material comprising secondary particles formed by agglomeration of two or more primary particles, the primary particles comprising natural graphite particles and an amorphous carbon coating layer located on at least a portion of the natural graphite particles, the negative electrode active material having a void volume of 0.06 mL / g to 0.15 mL / g as measured by a mercury porosimeter measurement method.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0129159, filed on September 29, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference. The present invention relates to a negative electrode active material, a method for producing the same, a negative electrode containing the same, and a secondary battery. [Background technology]

[0002] 2. Description of the Related Art As energy prices rise due to the depletion of fossil fuels and concerns about environmental pollution grow, environmentally friendly alternative energy sources have become an essential factor for future life. In particular, with the increasing technological development and demand for mobile devices, the demand for secondary batteries as an environmentally friendly alternative energy source is rapidly increasing.

[0003] In addition, with growing interest in environmental issues in recent years, much research is being conducted into electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace vehicles that use fossil fuels such as gasoline and diesel, which are one of the main causes of air pollution. Lithium secondary batteries, which have high energy density, high discharge voltage, and stable output, are being primarily researched and used as the power source for such electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0004] Conventionally, secondary batteries have used lithium metal as the negative electrode. However, due to the risk of short circuiting of the battery due to the formation of dendrites and the resulting risk of explosion, the use of carbon-based active materials, which allow reversible intercalation and deintercalation of lithium ions and maintain structural and electrical properties, is becoming more common.

[0005] Various types of carbon-based active materials have been used, including artificial graphite, natural graphite, and hard carbon. Among them, graphite-based active materials are the most widely used because they can ensure the life characteristics of lithium secondary batteries due to their excellent reversibility. Because graphite-based active materials have a lower discharge voltage of -0.2 V compared to lithium, batteries using graphite-based active materials can exhibit a high discharge voltage of 3.6 V, providing many advantages in terms of the energy density of lithium batteries.

[0006] Among these, natural graphite is known to have the advantage of having a high degree of crystallinity and high capacity compared to other carbon-based active materials such as artificial graphite. However, natural graphite has a disadvantage of being highly oriented, resulting in poor fast charging performance for lithium ions. Furthermore, natural graphite is softer than other carbon-based active materials, which can clog internal voids during the rolling process used to manufacture the anode, resulting in poor fast charging performance.

[0007] Therefore, when natural graphite is applied to the negative electrode, it is necessary to develop natural graphite with improved fast charging performance. Japanese Patent Registration No. 4403327 discloses graphite powder for the negative electrode of lithium ion secondary batteries, but fails to provide an alternative to the above-mentioned problems. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 4403327 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a negative electrode active material that has excellent rapid charging performance, prevents swelling, and has excellent high-temperature life performance. Another object of the present invention is to provide a method for producing the above-mentioned negative electrode active material. Another object of the present invention is to provide a negative electrode and a secondary battery containing the above-mentioned negative electrode active material. [Means for solving the problem]

[0010] One embodiment of the present invention provides a negative electrode active material comprising secondary particles formed by agglomeration of two or more primary particles, the primary particles comprising primary natural graphite particles and an amorphous carbon coating layer located on at least a portion of the surface of the primary natural graphite particles, and having a pore volume of 0.06 mL / g to 0.15 mL / g as measured by mercury porosimetry.

[0011] In addition, one embodiment of the present invention provides a method for manufacturing the aforementioned anode active material, the method including: agglomerating two or more primary natural graphite particles to form a primary spheron; forming an amorphous carbon coating layer on at least a portion of the surface of the primary natural graphite particles after the primary spheronization to form an intermediate structure; and a secondary spheronization of the intermediate structure.

[0012] In addition, one embodiment of the present invention provides a negative electrode including: 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 includes the above-described negative electrode active material.

[0013] Furthermore, one embodiment of the present invention provides a secondary battery including the above-described negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. [Effects of the Invention]

[0014] The negative electrode active material of the present invention comprises secondary particles formed by agglomeration of two or more primary particles, the primary particles comprising primary natural graphite particles and an amorphous carbon coating layer disposed on at least a portion of the surface of the primary natural graphite particles, and the pore volume measured by mercury porosimetry is controlled to fall within a specific range. The negative electrode active material having a pore volume measured by mercury porosimetry controlled to fall within the range contains hard amorphous carbon within the negative electrode active material, preventing voids in the negative electrode due to deformation of the negative electrode active material even upon rolling, thereby improving the fast charging characteristics of the negative electrode. The amorphous carbon reduces the degree of orientation of the negative electrode active material, preventing swelling and improving high-temperature life performance.

[0015] In addition, the method for manufacturing the anode active material according to the present invention includes agglomerating two or more primary natural graphite particles to form primary spheroids, forming an amorphous carbon coating layer on the primary natural graphite particles, and then performing secondary spheroidization. This allows amorphous carbon to be distributed in large voids formed between the primary natural graphite particles, resulting in the amorphous carbon with good output characteristics being distributed in the anode active material layer, improving fast charging characteristics. The amorphous carbon reduces the degree of orientation of the anode active material, preventing swelling and improving high-temperature life.

[0016] Therefore, the negative electrode and secondary battery including the above-described negative electrode active material not only have improved fast charging performance, but also minimize swelling and improve high-temperature life performance. DETAILED DESCRIPTION OF THE INVENTION

[0017] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0018] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless otherwise clearly indicated in the context.

[0019] It should be understood that in this specification, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0020] 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 cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0021] As used herein, the term "primary particle" refers to a single particle, and the term "secondary particle" refers to an aggregate formed by agglomerating multiple primary particles through an intentional granulation or bonding process. The present invention will be specifically described below.

[0022] negative electrode active material The present invention relates to a negative electrode active material, specifically to a negative electrode active material for a lithium secondary battery.

[0023] Specifically, the negative electrode active material includes secondary particles formed by agglomeration of two or more primary particles, the primary particles including natural graphite particles and an amorphous carbon coating layer located on at least a portion of the natural graphite particles, and has a pore volume of 0.06 mL / g to 0.15 mL / g measured by mercury porosimetry.

[0024] The negative electrode active material according to the present invention comprises secondary particles formed by agglomeration of two or more primary particles, the primary particles comprising natural graphite particles and an amorphous carbon coating layer disposed on at least a portion of the natural graphite particles, and the pore volume measured by mercury porosimetry is controlled to fall within a specific range. The negative electrode active material, whose pore volume measured by mercury porosimetry is controlled to fall within the range, contains amorphous carbon having hard properties within the negative electrode active material, preventing pore blockage even when the negative electrode active material is rolled, thereby improving fast charging characteristics. For example, the pore size of 100 nm or more is reduced to a desirable level, preventing swelling and improving high-temperature life performance.

[0025] The negative electrode active material includes secondary particles formed by agglomeration of two or more primary particles, each of which includes a primary natural graphite particle and an amorphous carbon coating layer located on at least a portion of the surface of the primary natural graphite particle.

[0026] Two or more of the primary natural graphite particles may be bound together and agglomerated by an amorphous carbon coating layer or a precursor thereof (such as a pitch binder) located on at least a portion of the surface.

[0027] The primary natural graphite particles may be flake natural graphite particles. The flake natural graphite is natural graphite having a scaly particle shape, and may be produced by pulverizing natural graphite in the shape of flakes, plates, crushed particles, tablets, or the like to a desired particle size.

[0028] The average particle size of the primary natural graphite particles (D 50) may be 10 μm to 30 μm, specifically 15 μm to 20 μm, and when it is in the above range, it is preferable in terms of ease of spheronization.

[0029] The negative electrode active material may further include voids formed on the surface, inside, or both the surface and the interior of the primary particles. The voids may be formed on the surface, inside, or both the surface and the interior of the primary particles, or between two or more of the primary particles.

[0030] The amorphous carbon coating layer is located on at least a portion of the surface of the primary natural graphite particles. The amorphous carbon coating layer may aid in the aggregation, granulation, or bonding of the primary natural graphite particles in the negative electrode active material. Furthermore, the amorphous carbon coating layer has a harder characteristic than the primary natural graphite particles. Since the amorphous carbon coating layer is positioned in the spaces between the primary natural graphite particles, the amorphous carbon coating layer may maintain voids in the negative electrode active material even after a rolling process is performed during negative electrode manufacturing, thereby helping to improve fast charging.

[0031] The amorphous carbon coating layer may be formed by agglomerating and spheronizing the primary natural graphite particles, specifically, by agglomerating and primary spheronizing as described below, providing the agglomerated primary natural graphite particles with a carbon precursor, and then heat-treating the agglomerated primary natural graphite particles. Specifically, the carbon precursor may be, but is not limited to, a polymer resin such as sucrose, phenol 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, or polyvinyl chloride; or a pitch such as coal-based pitch, petroleum-based pitch, or mesophase pitch. The heat-treatment temperature may be 1,000°C to 1,800°C.

[0032] In the negative electrode active material of the present invention, the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer may be 75:25 to 99:1, specifically 85:15 to 92:8. When the weight ratio is within this range, the amorphous carbon coating layer can sufficiently fill voids and maintain the shape of the negative electrode active material, improving fast charging performance, preventing swelling, and high-temperature life performance, while eliminating problems such as reduced sphericity and surface unevenness due to excessive formation of the amorphous carbon coating layer.

[0033] The pore volume of the negative electrode active material measured by a mercury porosimeter is 0.06 mL / g to 0.15 mL / g. The mercury porosimetry (Hg porosimetry) method is a measurement method that allows mercury to be adsorbed onto a sample and measures the size, porosity, and pore volume of voids present on the surface of the sample. Unlike the BET nitrogen adsorption method, the mercury porosimetry method adsorbs mercury, rather than gas, onto the sample, allowing it to measure the volume of large voids in a negative electrode active material, specifically voids with sizes on the order of 100 nm to 1,000 nm. In contrast, the BET nitrogen adsorption method measures void volume by adsorbing nitrogen gas onto the sample. This allows it to measure the presence, specific surface area, and pore volume of small voids, specifically voids with sizes on the order of 0.5 nm to 100 nm, but has limitations in measuring voids larger than 100 nm. Therefore, the measurement ranges of voids by the mercury porosimetry and the BET nitrogen adsorption method can be considered to be different.

[0034] The anode active material of the present invention is a secondary particle-form anode active material in which primary particles include the primary natural graphite particles and an amorphous carbon coating layer, and the primary particles are aggregated to form secondary particles. The pore volume measured by mercury porosimetry is adjusted to the above-described level, thereby reducing the proportion, content, or volume of large pores within the particles, e.g., pores with a size of 100 nm or more. When the pore volume measured by mercury porosimetry is adjusted to the above-described level, the amorphous carbon coating layer is preferably positioned between the primary natural graphite particles, so that the anode active material easily maintains its shape and pores even when rolled during anode fabrication, thereby improving the fast charging performance of the anode active material. The presence of the hard amorphous carbon coating layer minimizes swelling and side reactions with the electrolyte, thereby improving high-temperature life performance.

[0035] If the pore volume of a negative electrode active material measured by mercury porosimetry is less than 0.06 mL / g, it can be understood that the internal porosity is reduced, but such a negative electrode active material is not sufficiently spherical, which makes it difficult to ensure voids between the active material particles within the negative electrode.If the pore volume of a negative electrode active material measured by mercury porosimetry is more than 0.15 mL / g, it cannot be determined that the amorphous carbon coating layer is sufficiently distributed between the primary natural graphite particles, which can result in reduced fast charging performance, swelling, and reduced high-temperature life.

[0036] More specifically, the pore volume of the negative electrode active material measured by a mercury porosimeter may be 0.08 mL / g to 0.12 mL / g. When the pore volume is in the above range, the rapid charge performance, prevention of swelling, and high-temperature life performance of the negative electrode active material are further improved.

[0037] The void volume measured by the mercury porosimetry may be adjusted by appropriately disposing an amorphous carbon coating layer between primary natural graphite particles. For example, as described below, a spheronization process is performed twice after the aggregation of primary natural graphite particles. In this case, a process of forming an amorphous carbon coating layer on at least a portion of the surface of the primary natural graphite particles is performed between the primary spheronization and the secondary spheronization. This prevents the amorphous carbon coating layer from concentrating on the outside of the particles and allows it to be disposed between the primary natural graphite particles, thereby adjusting the void volume measured by the mercury porosimetry to a preferred level. In addition, the void volume measured by the mercury porosimetry may be adjusted by adjusting the content of the amorphous carbon coating layer located on at least a portion of the surface of the primary natural graphite particles, the degree of spheronization, and the average particle size (D) of the primary and secondary particles. 50 ) may be realized by adjusting the above, but is not limited thereto.

[0038] In the present invention, the BET specific surface area of ​​the negative electrode active material measured by the BET nitrogen adsorption method is 0.9 m 2 / g~3.0m 2 / g, specifically 1.1m 2 / g~1.8m 2 / g. When the pore volume is in the above range, it is preferable in terms of preventing a side reaction with the electrolyte. The pore volume according to the BET nitrogen adsorption method can be measured using a BEL Sorption instrument (BEL Japan).

[0039] The negative electrode active material may be spherical. When the negative electrode active material is spherical, a void structure is smoothly maintained when the negative electrode active material is contained in the negative electrode, thereby ensuring a diffusion path for lithium ions and improving the output characteristics of the negative electrode. In this specification, the term "spherical" refers to a shape that is not only perfectly spherical, but also includes a shape that is substantially spherical even if it is slightly distorted.

[0040] Specifically, the sphericity of the negative electrode active material may be 0.85 to 1, more specifically, 0.88 to 0.95. When this range is satisfied, the effect of maintaining the pore structure in the negative electrode can be more effectively achieved. The sphericity can be measured by capturing a 2D image of the 3D particles and using a digital image analysis method (for example, using an apparatus called Morphologi4 (Malvern)).

[0041] The average particle size (D 50 ) may be 10 μm to 25 μm, preferably 15 μm to 20 μm. When it is in the above range, it is preferable in terms of simultaneously improving the output characteristics and life characteristics.

[0042] The negative electrode active material may further include an additional amorphous carbon coating layer disposed on the secondary particles, which may improve the structural stability of the negative electrode active material, increase particle strength, and prevent side reactions between the negative electrode active material and the electrolyte.

[0043] The additional amorphous carbon coating layer may be included in the negative electrode active material in an amount of 1 wt % to 15 wt %, preferably 2 wt % to 5 wt %. The presence of the additional amorphous carbon coating layer is preferred because excessive formation of the additional amorphous carbon coating layer may increase side reactions of the electrolyte, thereby reducing thermal stability and output characteristics.

[0044] The additional amorphous carbon coating layer may include amorphous carbon. Specifically, the additional amorphous carbon coating layer may be formed by providing a carbon precursor to the secondary particles and then heat-treating the resulting mixture. Specifically, the carbon precursor may be, but is not limited to, a polymer resin such as sucrose, phenol 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, or polyvinyl chloride; or a pitch such as coal-based pitch, petroleum-based pitch, or mesophase pitch. The heat-treatment temperature may be 1,000°C to 1,800°C.

[0045] When the negative electrode active material further includes an additional amorphous carbon coating layer, the weight ratio of the primary artificial graphite particles to the amorphous carbon coating layer and the additional amorphous carbon coating layer may be 75:25 to 98:2, specifically 85:15 to 92:8.

[0046] Method for producing negative electrode active material The present invention also provides a method for producing a negative electrode active material. Specifically, the method for producing a negative electrode active material may be the method for producing a negative electrode active material described above.

[0047] Specifically, the method for manufacturing the negative electrode active material includes a step of aggregating two or more primary natural graphite particles to form a primary spheroid; a step of forming an amorphous carbon coating layer on at least a portion of the surface of the primary natural graphite particles after the primary spheroidization to form an intermediate structure; and a step of secondary spheroidizing the intermediate structure.

[0048] The method for manufacturing a negative electrode active material according to the present invention is characterized in that, in the process of agglomerating and spheronizing two or more primary natural graphite particles, the spheronization is performed twice, and an amorphous carbon coating layer is formed on at least a portion of the surface of the primary natural graphite particles between the primary and secondary spheronization steps. This method allows the amorphous carbon coating layer to be smoothly disposed on the surface of the primary natural graphite particles and between the primary natural graphite particles, thereby filling large voids between the primary natural graphite particles. Because this amorphous carbon coating layer has hard physical properties, it smoothly maintains its shape even when the negative electrode active material is rolled during the manufacture of the negative electrode, thereby facilitating lithium diffusion, improving fast charging performance, minimizing swelling, preventing side reactions with the electrolyte, and improving high-temperature life.

[0049] The method for producing a negative electrode active material of the present invention includes a step of aggregating two or more primary natural graphite particles to form a primary spheroid. The primary natural graphite particles may be flake natural graphite particles. The flake natural graphite is natural graphite having a scaly particle shape, and may be produced by pulverizing natural graphite in the shape of flakes, plates, crushed particles, tablets, or the like to a desired particle size. The rest of the description regarding the primary natural graphite particles is as described above.

[0050] The primary spheronization may be performed using any spheronization method known in the art, without limitation. For example, the primary spheronization may be performed by applying mechanical treatment such as impact compression, friction, or shear force. The mechanical treatment may be performed using a spheronization device commonly known in the art, such as a pulverizer such as a counter jet mill (Hosokawa Micron, JP), an ACM pulverizer (Hosokawa Micron, JP), or a current jet (Nissin, JP); a granulator such as a SARARA (Kawasaki Heavy Industries, Ltd., JP), a GRANUREX (Freund Corporation, JP), a New Gram Machine (Seishin, JP), or an Agromaster (Hosokawa Micron, JP); a pressure kneader (dispersion kneader), a two-roll mixer, or a compression shear processing device such as a Mechano Micro System, an extruder, a ball mill, a planetary mill, a Mechano Fusion System, a Nobilta, a hybridization system, or a rotary ball mill.

[0051] Specifically, the primary spheronization is performed by feeding the two or more primary natural graphite particles into a spheronization device that applies a mechanical shear force to form a granulated particle core, and then stacking one or more layers of the primary natural graphite particles concentrically on the surface of the granulated particle core, thereby agglomerating the two or more primary natural graphite particles to obtain spherical particles.

[0052] The method for preparing a negative electrode active material of the present invention includes, after the primary spheronization, forming an amorphous carbon coating layer on at least a portion of the surface of the primary natural graphite particles to form an intermediate structure.

[0053] After the primary spheronization, an amorphous carbon coating layer is formed on at least a portion of the surface of the primary natural graphite particles, thereby disposing the amorphous carbon coating layer or amorphous carbon between the primary natural graphite particles agglomerated by the primary spheronization. In the present invention, after the primary spheronization, an amorphous carbon coating layer is formed on the primary natural graphite particles, and then secondary spheronization is performed to complete the spheronization process, thereby disposing the amorphous carbon coating layer smoothly between the primary natural graphite particles. Therefore, in the present invention, the amorphous carbon coating layer can be disposed in large voids (e.g., voids having a size of 100 nm or more) formed between the primary natural graphite particles. Therefore, even when the negative electrode active material is rolled during the manufacture of the negative electrode, its shape can be smoothly maintained. This facilitates lithium diffusion, improves fast charging performance, minimizes swelling, prevents side reactions with the electrolyte, and improves high-temperature life.

[0054] If an amorphous carbon coating layer is formed after the aggregation and spheronization of the primary natural graphite particles are completed, the amorphous carbon coating layer will be concentrated on the particle surfaces and will not be easily distributed between the primary natural graphite particles, making it difficult to adjust the void volume measured by the mercury porosimeter measurement method described above to a desired level, and the effects of fast charge performance, swelling prevention, and high-temperature life performance may be reduced. If an amorphous carbon coating layer is formed on the primary natural graphite particles before the spheronization process is performed, the primary natural graphite particles will become hard and will not be easily spheroidized, which may result in an increase in voids or an increase in swelling due to a side reaction with the electrolyte. This may make it difficult to adjust the void volume measured by the mercury porosimeter measurement method described above to a desired level, making it difficult to adjust the void volume measured by the mercury porosimeter measurement method described above to a desired level, and the effects of fast charge performance, swelling prevention, and high-temperature life performance may be reduced.

[0055] The amorphous carbon coating layer may be formed by providing a carbon precursor to the agglomerate of the primary spheroidized primary natural graphite particles, followed by heat treatment. The primary spheroidized and agglomerated primary natural graphite particles have an open pore structure, so that the carbon precursor can flow into and be disposed between the primary natural graphite particles, and the carbon precursor can form an amorphous carbon coating layer by heat treatment.

[0056] Specifically, the carbon precursor may be, but is not limited to, a polymer resin such as sucrose, phenol 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, or polyvinyl chloride; or pitch such as coal-based pitch, petroleum-based pitch, or mesophase pitch. The heat treatment temperature may be 1,000°C to 1,800°C. The other details regarding the amorphous carbon coating layer are as described above.

[0057] The method for manufacturing a negative electrode active material of the present invention includes a step of secondary spheronizing the intermediate structure. The secondary spheronization process can be completed by secondary spheronizing the intermediate structure manufactured above, and the secondary spheronization process can further reduce voids in the negative electrode active material while increasing the degree of sphericity. The secondary spheronization may be carried out in the same manner as the primary spheronization described above.

[0058] The method for manufacturing a negative electrode active material according to the present invention may further include a step of heat-treating the secondary spheronized intermediate structure, which may be performed to alleviate damage to the negative electrode active material caused by the spheronization process and to reduce the specific surface area of ​​the negative electrode active material. The heat treatment may be carried out at a temperature of 900°C to 1,400°C, specifically 1,000°C to 1,300°C.

[0059] The method for manufacturing a negative electrode active material of the present invention may further include forming an additional amorphous carbon coating layer on the secondary spheroidized intermediate structure. The additional amorphous carbon coating layer may be formed by providing a carbon precursor to the secondary spheroidized intermediate structure and then heat-treating it. Specifically, the carbon precursor may be, but is not limited to, a polymer resin such as sucrose, phenol 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, or polyvinyl chloride; or pitch such as coal-based pitch, petroleum-based pitch, or mesophase pitch. The heat-treatment temperature may be 1,000°C to 1,800°C.

[0060] The method for manufacturing a negative electrode active material of the present invention may further include a step of crushing the secondary spheronized intermediate structural bodies. Crushing can be understood as a process of breaking down, dispersing, and pulverizing agglomerates of the secondary spheronized intermediate structural bodies by applying a relatively weak force.

[0061] negative electrode The present invention also provides a negative electrode, specifically a negative electrode for a lithium secondary battery, which may include the above-described negative electrode active material.

[0062] Specifically, 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, and the negative electrode active material layer includes the above-described negative electrode active material.

[0063] The negative electrode includes the above-described negative electrode active material, thereby exhibiting excellent fast charging performance, minimizing the occurrence of swelling, and improving high-temperature life performance to an excellent level.

[0064] The negative electrode current collector may be any negative electrode current collector commonly used in the art, and is not particularly limited as long as it does not induce chemical changes in the lithium secondary battery and has high conductivity. For example, the negative electrode current collector may include at least one selected from copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and preferably copper.

[0065] The negative electrode current collector may have fine irregularities on its surface to strengthen the binding force of the negative electrode active material, and may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric. The negative electrode current collector may generally have a thickness of 3 μm to 500 μm.

[0066] The negative electrode active material layer may be disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one or both surfaces of the negative electrode current collector.

[0067] The negative electrode active material layer includes the above-described negative electrode active material. The negative electrode active material may be contained in the negative electrode active material layer in an amount of 80% by weight to 99% by weight, preferably 88% by weight to 98% by weight. The other details regarding the negative electrode active material are as described above.

[0068] The negative electrode active material layer may further include a binder, a conductive material, and / or a thickener in addition to the negative electrode active material. The binder is a component that aids in bonding between the active material and / or the current collector, and may generally be contained in the negative electrode active material layer in an amount of 1 to 30% by weight, preferably 1 to 10% by weight.

[0069] The 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, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably at least one selected from polyvinylidene fluoride and styrene-butadiene rubber.

[0070] As the thickener, any thickener used in conventional lithium secondary batteries may be used, and an example thereof is carboxymethyl cellulose (CMC).

[0071] The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be contained in the negative electrode active material layer in an amount of 1 to 30% by weight, preferably 1 to 10% by weight.

[0072] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black-based materials (such as those from Chevron Chemical Company, Denka Singapore Private Limited, and Gulf Oil Company), Ketjenblack, EC-based materials (products from Armak Company), Vulcan XC-72 (products from Cabot Company), and Super P (manufactured by Timcal).

[0073] The orientation index I(004) / I(110) of the negative electrode may be 10 to 25. The orientation index indicates the degree to which the crystalline structure inside the negative electrode is aligned in a certain direction, and can be used to evaluate the orientation of the crystals within the electrode. The orientation index can be measured by X-ray diffraction (XRD). More specifically, the orientation index is the area ratio ((004) / (110)) obtained by measuring the (110) and (004) planes of the negative electrode active material included in the negative electrode by XRD and then integrating the peak intensities of the (110) and (004) planes. More specifically, the XRD measurement conditions are as follows:

[0074] - Target: Cu (Kα line) graphite monochromator -Slit: Divergence slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree -Measurement area and step angle / measurement time: (110) plane: 76.5 degrees < 2θ < 78.5 degrees, 0.01 degrees / 3 seconds (004) plane: 53.5 degrees < 2θ < 56.0 degrees, 0.01 degrees / 3 seconds In the above, 2θ represents the diffraction angle. The XRD measurement is just one example, and other measurement methods may also be used.

[0075] When the orientation index of the negative electrode is within the above range, the rapid charging performance of the negative electrode can be further improved. If the orientation index of the negative electrode is less than 10, it is undesirable in terms of a decrease in initial efficiency due to the formation of initial irreversibility, and if the orientation index of the negative electrode is more than 25, volume expansion during charging and discharging becomes severe, resulting in a shortened lifespan.

[0076] The thickness of the negative electrode active material layer may be 10 μm to 150 μm, specifically 50 μm to 100 μm, but is not limited thereto. The negative electrode active material layer can be manufactured by mixing the above-described negative electrode active material and at least one selected from a binder, a conductive material, and a thickener in a solvent to prepare a negative electrode slurry, and then applying the negative electrode slurry to the negative electrode current collector, rolling, and drying the slurry.

[0077] The solvent may include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a preferred viscosity when containing the negative electrode active material, and optionally a binder, a conductive material, etc. For example, the solvent may be included so that the concentration of solids containing the negative electrode active material, and optionally at least one selected from the binder, thickener, and conductive material, is 50 wt % to 95 wt %, preferably 70 wt % to 90 wt %.

[0078] secondary battery The present invention also provides a secondary battery, more specifically a lithium secondary battery, including the above-described negative electrode.

[0079] The secondary battery may include the above-described negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. The positive electrode can face the negative electrode. The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.

[0080] The positive electrode current collector may be used without limitation as long as it is a negative electrode current collector generally used in the art. For example, it is not particularly limited as long as it does not induce chemical changes in the secondary battery and has high conductivity. For example, the positive electrode current collector may include at least one selected from copper, stainless steel, aluminum, nickel, titanium, fired carbon, and an aluminum-cadmium alloy, preferably aluminum.

[0081] The positive electrode current collector may form fine irregularities on its surface to strengthen the binding force of the positive electrode active material, and may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc. The positive electrode current collector may generally have a thickness of 3 μm to 500 μm.

[0082] The positive electrode active material layer may contain a positive electrode active material. The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it may include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1O2 (where 0 < Y1 < 1, etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2, etc.), lithium-nickel-manganese-cobalt-based 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 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2, etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1, etc.), etc., and any one or two or more of these compounds may be included. Among them, in terms of improving the capacity characteristics and safety of the battery, the lithium composite metal oxide is 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, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05)O2, etc.), and in consideration of the remarkable improvement effect according to the control of the types and content ratios 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 a mixture of any one or more of these may be used. The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80% by weight to 99% by weight.

[0083] The positive electrode active material layer may further contain, in addition to the positive electrode active material, at least one selected from the group consisting of a binder and a conductive material. The binder is a component that aids in bonding the active material and conductive material, etc., and 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 include at least one selected from the group consisting of 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. The binder may be contained in the positive electrode active material layer in an amount of 1% by weight to 30% by weight.

[0084] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and examples thereof include 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 fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black-based materials (e.g., Chevron Chemical Company, Denka Singapore Private Limited, and Gulf Oil Company products), ketjen black, EC-based materials (e.g., Armak Company products), Vulcan XC-72 (e.g., Cabot Company products), and Super P (manufactured by Timcal). The conductive material may be added to the positive electrode active material layer in an amount of 1% by weight to 30% by weight.

[0085] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in lithium secondary batteries can be used without particular limitations. It is particularly preferable for the separator to have low resistance to electrolyte ion migration and excellent electrolyte humidification capacity. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0086] Furthermore, examples of the electrolyte used in the present invention include 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 production of lithium secondary batteries, but are not limited to these.

[0087] Specifically, the electrolyte may include an organic solvent and a lithium salt. The organic solvent may be used without any particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent that may be used include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon 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 C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of a battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, thereby providing excellent electrolyte performance.

[0088] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has suitable conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0089] As described above, the lithium secondary battery according to the present invention exhibits excellent discharge capacity, rapid charging characteristics, and stable capacity retention, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in electric vehicles such as hybrid electric vehicles (HEVs), and is particularly suitable as a component battery of medium- to large-sized battery modules. Accordingly, the present invention also provides a medium- to large-sized battery module including the above-described secondary battery as a unit cell.

[0090] Such a medium- to large-sized battery module can be suitably applied to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices.

[0091] The present invention may be embodied in various different forms and should not be construed as being limited to the embodiments set forth herein, although the present invention may be embodied in various different forms and should not be construed as being limited to the embodiments set forth herein.

[0092] Example Example 1: Preparation of negative electrode active material (1) Primary spheroidization Average particle size (D 50 ) 20 μm flake-like primary natural graphite particles were prepared. The primary natural graphite particles were spheronized using a spheronizing device (Counter Jet Mill, manufactured by Hosokawa Micron Corporation) to aggregate and primarily spheronize the primary natural graphite particles.

[0093] (2) Formation of intermediate structure The primary natural graphite particles, which were agglomerated through primary spheronization, were mixed with liquid pitch as a carbon precursor (weight ratio of primary natural graphite particles to carbon precursor = 90:10), and then heat-treated at 1,300°C for 12 hours to form an intermediate structure in which an amorphous carbon coating layer was formed on at least a portion of the surface of the primary natural graphite particles. At this time, the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer was 90:10.

[0094] (3) Secondary spheroidization The intermediate structure was subjected to secondary spheronization using a spheronization device (Counter Jet Mill, manufactured by Hosokawa Micron Corporation).

[0095] (3) Formation of an additional amorphous carbon coating layer The secondary spheroidized intermediate structure was mixed with liquid pitch as a carbon precursor and heat-treated at 1,300°C for 12 hours to form an additional amorphous carbon coating layer on the intermediate structure. The resulting material was crushed and used as the negative electrode active material of Example 1.

[0096] An additional amorphous carbon coating layer of about 3.3 wt % was formed on the negative electrode active material. In the negative electrode active material, the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer and the additional amorphous carbon coating layer was 87:13.

[0097] The pore volume of the negative electrode active material measured by a mercury porosimeter (instrument used: Autopore V, manufactured by Micromeritics) was 0.09 mL / g, and the BET specific surface area measured by a BET nitrogen adsorption method (instrument used: BEL Sorption, manufactured by BEL Japan) was 1.6 m 2 / g, the sphericity was 0.91, and the average particle size (D 50 ) was 20 μm.

[0098] Example 2: Preparation of negative electrode active material An anode active material was prepared in the same manner as in Example 1, except that: (1) in the step of forming the intermediate structure, the weight ratio of the primary natural graphite particles to the carbon precursor was 98:2, and the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer was 98:2; (2) the additional amorphous carbon coating layer was formed in an amount of about 3.06 wt % of the weight of the anode active material; and (3) the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer and the additional amorphous carbon coating layer was 95:5.

[0099] The pore volume of the negative electrode active material measured by mercury porosimetry was 0.12 mL / g, and the BET specific surface area measured by BET nitrogen adsorption was 1.8 m 2 / g, the sphericity was 0.94, and the average particle size (D 50 ) was 20 μm.

[0100] Example 3: Preparation of negative electrode active material An anode active material was prepared in the same manner as in Example 1, except that (2) in the step of forming the intermediate structure, the weight ratio of the primary natural graphite particles to the carbon precursor was 80:20, the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer was 80:20, (2) the additional amorphous carbon coating layer was formed in an amount of about 3.75 wt % of the weight of the anode active material, and (3) the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer and the additional amorphous carbon coating layer was 77:23.

[0101] The pore volume of the negative electrode active material measured by mercury porosimetry was 0.07 mL / g, and the BET specific surface area measured by BET nitrogen adsorption was 1.1 m 2 / g, the sphericity was 0.88, and the average particle size (D 50 ) was 20 μm.

[0102] Comparative Example 1: Production of negative electrode active material (1) Spheroidization The primary natural graphite particles were aggregated and spheronized in the same manner as in the primary spheronization step of Example 1.

[0103] (2) Formation of an amorphous carbon coating layer The spheroidized primary natural graphite particles were provided with pitch as a carbon precursor (weight ratio of primary natural graphite particles to carbon precursor = 97:3), and then heat-treated at 1,300°C for 12 hours to form an amorphous carbon coating layer, which was used as the negative electrode active material of Comparative Example 1. At this time, the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer was 97:3.

[0104] The pore volume of the negative electrode active material measured by mercury porosimetry was 0.27 mL / g, and the BET specific surface area measured by BET nitrogen adsorption was 2.6 m 2 / g, the sphericity was 0.93, and the average particle size (D 50 ) was 20 μm.

[0105] Comparative Example 2: Production of negative electrode active material (1) Formation of an amorphous carbon coating layer The same primary natural graphite particles as used in Example 1 and a carbon precursor were mixed in a weight ratio of 90:10, and then heat-treated at 1,300°C for 12 hours to form an amorphous carbon coating layer on at least a portion of the surface of the primary natural graphite particles. At this time, the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer was 90:10.

[0106] (3) Spheroidization The primary natural graphite particles on which the amorphous carbon coating layer was formed were spheroidized using a spheroidizing device (Counter Jet Mill, manufactured by Hosokawa Micron Corporation).

[0107] (3) Formation of an additional amorphous carbon coating layer The spheronized primary natural graphite particles were mixed with liquid pitch as a carbon precursor and heat-treated at 1,300°C for 12 hours to form an additional amorphous carbon coating layer. The resulting material was crushed and used as the negative electrode active material of Comparative Example 2. That is, in Comparative Example 2, the negative electrode active material was prepared in the same manner as in Example 1, except that the primary spheronization was not performed.

[0108] An additional amorphous carbon coating layer of about 3.3 wt % was formed on the negative electrode active material. In the negative electrode active material, the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer and the additional amorphous carbon coating layer was 87:13.

[0109] The pore volume of the negative electrode active material measured by mercury porosimetry was 0.67 mL / g, and the BET specific surface area measured by BET nitrogen adsorption was 2.3 m 2 / g, the sphericity was 0.71, and the average particle size (D 50 ) was 20 μm.

[0110] Comparative Example 3: Production of negative electrode active material (1) Spheroidization The primary natural graphite particles were aggregated and spheronized in the same manner as in the primary spheronization step of Example 1.

[0111] (2) Formation of an amorphous carbon coating layer The spheroidized primary natural graphite particles were provided with pitch as a carbon precursor (weight ratio of primary natural graphite particles to carbon precursor = 87:13), and then heat-treated at 1,300°C for 12 hours to form an amorphous carbon coating layer, which was used as the negative electrode active material of Comparative Example 3. At this time, the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer was 87:13.

[0112] The pore volume of the negative electrode active material measured by mercury porosimetry was 0.26 mL / g, and the BET specific surface area measured by BET nitrogen adsorption was 1.7 m 2 / g, the sphericity was 0.89, and the average particle size (D 50 ) was 20 μm.

[0113] Comparative Example 4: Production of negative electrode active material An anode active material was prepared in the same manner as in Example 1, except that (2) in the step of forming the intermediate structure, the weight ratio of the primary natural graphite particles to the carbon precursor was 75:25, the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer was 75:25, (2) the additional amorphous carbon coating layer was formed in an amount of about 4 wt % of the weight of the anode active material, and (3) the weight ratio of the primary natural graphite particles to the amorphous carbon coating layer and the additional amorphous carbon coating layer was 72:28.

[0114] The negative electrode active material had a pore volume of 0.04 mL / g measured by a mercury porosimeter and a BET specific surface area of ​​1.0 m measured by a BET nitrogen adsorption method. 2 / g, the sphericity was 0.79, and the average particle size (D 50 ) was 20 μm.

[0115] [Table 1]

[0116] The orientation index is an area ratio ((004) / (110)) obtained by measuring the (110) plane and the (004) plane of the negative electrode active material contained in the negative electrode by XRD and then integrating the peak intensities of the (110) plane and the (004) plane. More specifically, the XRD measurement conditions are as follows:

[0117] - Target: Cu (Kα line) graphite monochromator -Slit: Divergence slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree -Measurement area and step angle / measurement time: (110) plane: 76.5 degrees < 2θ < 78.5 degrees, 0.01 degrees / 3 seconds (004) plane: 53.5 degrees < 2θ < 56.0 degrees, 0.01 degrees / 3 seconds In the above, 2θ represents the diffraction angle.

[0118] Meanwhile, the sphericity was measured by capturing a 2D image of the prepared negative electrode active material and measuring it by digital image analysis (using a Morphologi4 device manufactured by Malvern).

[0119] Experimental example <Secondary battery manufacturing> The negative electrode active material of Example 1, Super C65 as a conductive material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in a weight ratio of 96.5:1.0:1.3:1.2, and water was added to prepare a negative electrode slurry. The negative electrode slurry was applied to a copper negative electrode current collector, vacuum dried at about 130°C for 10 hours, and rolled to form a negative electrode active material layer, which was used as the negative electrode of Example 1. The negative electrode loading was 3.6 mAh / cm. 2 It was manufactured so that A lithium metal counter electrode was prepared as the positive electrode.

[0120] A polyolefin separator was interposed between the negative electrode and the positive electrode, and then an electrolyte solution was injected to produce a lithium secondary battery of Example 1. The electrolyte solution used was a non-aqueous electrolyte solvent made by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 2:8, to which vinylene carbonate (VC) was added at 0.5 wt % relative to the solvent, and LiPF6 was dissolved at 1 M.

[0121] Lithium secondary batteries of Examples 2 and 3 and Comparative Examples 1 to 4 were manufactured in the same manner as in Example 1, except that the negative electrode active materials of Examples 2 and 3 and Comparative Examples 1 to 4 were used instead of the negative electrode active material of Example 1.

[0122] Experimental example 1: Evaluation of rapid charging performance The lithium secondary battery prepared above was charged and discharged for three cycles at 1 C, and then charged at 3 C for 15 minutes. The charging profiles were first differentiated. The inflection point in the dQ / dV curve was identified, and the lithium plating SOC (Li-Plating SOC, %), which is the SOC at which lithium deposition occurs on the surface of the negative electrode, was quantified. The results are shown in Table 2 below.

[0123] Experimental example 2: Evaluation of high temperature life performance The lithium secondary battery prepared above was charged at 1C to 4.2V / 38mA under constant current / constant voltage (CC / CV) conditions at 45°C, and then discharged at 1C to 2.5V under constant current (CC) conditions to measure the discharge capacity. This cycle was repeated up to 200 times.

[0124] The capacity retention rate after 200 cycles was evaluated using the following formula, and the results are shown in Table 2 below. Capacity retention rate (%) = (discharge capacity at 200th cycle) / (discharge capacity at first cycle) × 100

[0125] Experimental Example 3: Swelling Evaluation The lithium secondary battery fabricated above was charged and discharged over the SOC range of 0 to 95, with the first cycle at 0.1 C, the second cycle at 0.2 C, and the third to 50th cycles at 0.5 C. The swelling ratio was then measured and calculated using the following equation. The results are shown in Table 2 below.

[0126] Swelling ratio (%) = {(t2-t1) / t1} × 100 (t1 is the thickness of the negative electrode for secondary batteries before the first charge-discharge cycle, and t2 is the thickness of the negative electrode for secondary batteries after the 50th charge-discharge cycle)

[0127] [Table 2]

[0128] Referring to Table 2, it can be seen that Examples 1 to 3, in which the pore volume measured by the mercury porosimeter measurement method was preferably adjusted, had excellent fast charging performance, cycle characteristics, and swelling prevention effects compared to the comparative example.

Claims

1. A negative electrode current collector; a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; A negative electrode comprising: The negative electrode active material layer is The secondary particles are formed by agglomerating two or more primary particles, the primary particles include primary natural graphite particles and an amorphous carbon coating layer located on at least a portion of the surface of the primary natural graphite particles; the secondary particles contain the amorphous carbon coating layer at least in their internal voids, a negative electrode active material having a pore volume of 0.06 mL / g to 0.15 mL / g, the pore size of which is 100 nm or more and 1000 nm or less as measured by a mercury porosimeter measurement method; The orientation index I(004) / I(110) of the negative electrode is 10 to 25.

2. The BET specific surface area of ​​the negative electrode active material measured by the BET nitrogen adsorption method was 0.9 m ２ / g to 3.0m ２ The negative electrode according to claim 1 , wherein the anode has a Cr content of 1.0 / g.

3. The negative electrode of claim 1 , wherein the negative electrode active material is spherical.

4. 4. The negative electrode according to claim 1, wherein a weight ratio of the primary natural graphite particles to the amorphous carbon coating layer is from 75:25 to 99:

1.

5. 10. The negative electrode of claim 1, further comprising an additional amorphous carbon coating layer located on the secondary particles.

6. The negative electrode of claim 5 , wherein the additional amorphous carbon coating layer is included in the negative electrode active material in an amount of 1% by weight to 15% by weight.

7. The average particle size (D ５０ 2. The negative electrode according to claim 1, wherein the thickness of the first electrode is 10 μm to 30 μm.

8. The secondary particles are formed by agglomeration of two or more primary particles, the primary particles include primary natural graphite particles and an amorphous carbon coating layer located on at least a portion of the surface of the primary natural graphite particles; A method for producing a negative electrode active material, wherein the pore volume having a diameter of 100 nm or more and 1000 nm or less as measured by a mercury porosimeter measurement method is 0.06 mL / g to 0.15 mL / g, agglomerating two or more primary natural graphite particles into a primary spheroid; After the primary spheronization, forming an amorphous carbon coating layer on at least a portion of the surface of the primary natural graphite particles to form an intermediate structure; Secondary spheronizing the intermediate structure; A method for producing a negative electrode active material, comprising:

9. The method for producing a negative electrode active material according to claim 8 , wherein the primary natural graphite particles are flake natural graphite particles.

10. The method for producing a negative electrode active material according to claim 8 , further comprising the step of crushing the secondary spheroidized intermediate structure.

11. The method for producing a negative electrode active material according to claim 8 , further comprising the step of heat-treating the secondary spheroidized intermediate structure.

12. The method for producing a negative electrode active material according to claim 8 , further comprising forming an additional amorphous carbon coating layer on the secondary spheroidized intermediate structure.

13. The negative electrode according to claim 1 ; A positive electrode and a separator interposed between the negative electrode and the positive electrode; Electrolytes, A secondary battery comprising:

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