Negative electrode active material for rechargeable lithium battery and rechargeable lithium battery comprising the same

Abstract

Disclosed are a negative electrode active material for a rechargeable lithium battery and a rechargeable lithium battery including the same. The negative electrode active material includes a mixture of a first negative electrode active material and a second negative electrode active material, the first negative electrode active material includes natural graphite and a coating layer, the natural graphite includes secondary particles in which primary particles are disposed, the coating layer includes amorphous carbon and surrounds the secondary particles, the first negative electrode active material has an orientation degree of 90 or less and a d002 value of 3.356 Å to 3.360 Å, and the second negative electrode active material includes rod-like artificial graphite.

Description

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2024-0175699, filed on November 29, 2024, with the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] An aspect of the present invention relates to a negative electrode active material for a rechargeable lithium battery and a rechargeable lithium battery comprising the negative electrode active material. Background Technology

[0003] Recently, with the rapid proliferation of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for secondary batteries with high energy density and high capacity is increasing rapidly. Therefore, research and development to improve the performance of rechargeable lithium batteries is actively underway.

[0004] A rechargeable lithium battery is a battery that includes a positive electrode and a negative electrode, the positive electrode and the negative electrode containing active materials capable of inserting and deintercalating lithium ions, and generating electrical energy through oxidation and reduction reactions when lithium ions are deintercalated from the negative electrode and inserted into the positive electrode and deintercalated from the positive electrode and inserted into the negative electrode. Summary of the Invention

[0005] According to an embodiment of the present invention, a negative electrode active material for a rechargeable lithium battery is provided, which exhibits the effects of boost charging, enhanced charge rate characteristics, improved electrolyte impregnation, and suppression of electrode plate expansion.

[0006] According to another aspect of the present invention, a rechargeable lithium battery comprising a negative electrode active material is provided.

[0007] According to one or more embodiments of the present invention, a negative electrode active material for a rechargeable lithium battery comprises a mixture of a first negative electrode active material and a second negative electrode active material, wherein the first negative electrode active material comprises natural graphite and a coating layer, the natural graphite comprising secondary particles in which primary particles are arranged, the coating layer comprising amorphous carbon and surrounding the secondary particles, the first negative electrode active material having an orientation degree of 90 or less and a d002 value of 3.356 Å to 3.360 Å, and the second negative electrode active material comprises rod-shaped artificial graphite.

[0008] According to one or more embodiments of the present invention, a rechargeable lithium battery includes a negative electrode and a positive electrode, wherein the negative electrode includes the negative electrode active material described above for a rechargeable lithium battery. Attached Figure Description

[0009] The above and other aspects, objects, features, and advantages of the present invention will become more apparent to those skilled in the art from further detailed description of some embodiments of the invention with reference to the accompanying drawings, in which: Figure 1 This is a conceptual diagram of the first negative electrode active material according to an embodiment; Figure 2 This is a conceptual diagram of the second negative electrode active material according to an embodiment; and Figures 3 to 6 This is a schematic cross-sectional view of a rechargeable lithium battery according to an embodiment of the present invention. Detailed Implementation

[0010] Some embodiments of the present invention will be described in further detail herein. However, these embodiments are presented by way of example, and the invention is not limited thereto, and is to be defined by the scope of the appended claims.

[0011] Unless otherwise stated herein, when a component such as a layer, film, region, plate, etc. is referred to as being “on” another component, it includes not only the case where the component is “directly on” the other component, but also the case where there are one or more other components between them.

[0012] Unless otherwise stated herein, the singular may also include the plural. Additionally, unless otherwise stated, “A or B” may mean “including A,” “including B,” or “including both A and B.”

[0013] In this specification, "combination thereof" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product.

[0014] Unless otherwise defined herein, particle size can refer to average particle size. Alternatively, particle size refers to the average particle size (D50) of particles whose cumulative volume is 50 vol% in a particle size distribution. Average particle size (D50) can be measured using methods known to those skilled in the art (e.g., using a particle size analyzer, transmission electron microscopy, or scanning electron microscopy). Alternatively, average particle size can be measured using a measuring device employing dynamic light scattering, and the average particle size (D50) value can be obtained by performing data analysis, counting the number of particles within each particle size range, and then calculating the D50 value. Optionally, laser diffraction can be used to determine the average particle size. When measuring average particle size by laser diffraction, more specifically, the average particle size (D50) can be calculated based on a 50% particle size distribution after dispersing the target particles in a dispersion medium, introducing the particles into a commercially available laser diffraction particle size measuring device (such as the MT 3000 from Microtrac), and irradiating the particles with ultrasound at an output of approximately 28 kHz at 60 W.

[0015] When the particles are spherical, size can refer to diameter.

[0016] The negative electrode active material for rechargeable lithium batteries according to embodiments can provide low resistance, high energy density, boost charging performance, and improved charge rate characteristics. Although natural graphite is included in the negative electrode active material, it can provide significantly low resistance, high energy density, and boost charging performance by overcoming the inherent high resistance problem of natural graphite. The negative electrode active material also includes a first negative electrode active material and a second negative electrode active material described below, which significantly reduces the overall orientation, thereby enhancing electrolyte impregnation, improving charging characteristics, and significantly reducing electrode plate expansion.

[0017] The negative electrode active material for a rechargeable lithium battery according to an embodiment includes a mixture of a first negative electrode active material and a second negative electrode active material, wherein the first negative electrode active material includes natural graphite and a coating layer, the natural graphite including secondary particles formed by the aggregation of primary particles, the coating layer comprising amorphous carbon and surrounding the secondary particles, the first negative electrode active material having an orientation degree of 90 or less and a d002 value of 3.356 Å to 3.360 Å, and the second negative electrode active material is rod-shaped artificial graphite.

[0018] The negative electrode active material for rechargeable lithium batteries can provide low resistance, high energy density and boost charging, improved charge rate characteristics, enhanced electrolyte impregnation and the effect of suppressing electrode plate expansion by including a mixture.

[0019] The negative electrode active material according to an embodiment includes a first negative electrode active material and a second negative electrode active material. The first negative electrode active material is substantially spherical and has a sphericity described below, while the second negative electrode active material has an elongated rod-like shape. The inclusion of the first negative electrode active material can significantly improve boost charging and long-life characteristics, and the inclusion of the second negative electrode active material can significantly reduce volume expansion and resistance during charging / discharging and improve high-rate characteristics. In a negative electrode plate comprising only the second negative electrode active material, the second negative electrode active material can be sequentially arranged only in a direction parallel to the current collector. However, when the first negative electrode active material is also included, the second negative electrode active material can also be oriented perpendicularly to the current collector due to the first negative electrode active material described below, thereby providing a negative electrode active material with a lower degree of orientation. It is known that a lower degree of orientation enhances electrolyte impregnation and suppresses electrode plate expansion.

[0020] In the embodiments, the content of the mixture may be 95 wt% or more of the negative electrode active material, for example, 95 wt% to 100 wt%, 99 wt% to 100 wt% or 100 wt% of the negative electrode active material.

[0021] If the mixture does not include the first negative electrode active material, the battery may exhibit reduced capacity and low charge rate characteristics, as well as excessively high orientation in the negative electrode active material, leading to reduced electrolyte impregnation and increased electrode plate expansion. The first negative electrode active material can significantly reduce the orientation of the negative electrode active material, including the second negative electrode active material.

[0022] In the example, when determined by X-ray diffraction analysis using Cu α radiation, the negative electrode active material (i.e., the mixture) can have a peak intensity ratio I(002) / I(110) (orientation degree) of 200 or less. Within this range, electrolyte impregnation can be improved, thereby enhancing the charging rate characteristics and significantly suppressing electrode plate expansion. In embodiments, for example, the orientation degree can be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, or 200, and in embodiments, 110 or less, for example, 80 to 110. Within this range, the mixture of the first negative electrode active material and the second negative electrode active material can significantly enhance electrolyte impregnation and suppress electrode plate expansion.

[0023] In embodiments, for example, the negative electrode active material (i.e., the mixture) can have an average particle size (D50) of 10 μm to 20 μm, for example, having an average particle size (D50) of 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, or 20 μm. Within this range, improved charging rate characteristics can be achieved.

[0024] In embodiments, for example, the negative electrode active material (i.e., the mixture) may have a particle density of 1.50 g / cc to 1.60 g / cc, such as 1.50 g / cc, 1.51 g / cc, 1.52 g / cc, 1.53 g / cc, 1.54 g / cc, 1.55 g / cc, 1.56 g / cc, 1.57 g / cc, 1.58 g / cc, 1.59 g / cc, or 1.60 g / cc. Within this range, improved charging rate characteristics can be achieved.

[0025] In embodiments, for example, the mixture may include 10 wt% to 80 wt% (e.g., 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%). The first negative electrode active material comprises 20 wt% to 80 wt% of the following amounts: 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 56 wt%, 57 wt%, 58 wt%, 59 wt%, 60 wt%, 61 wt%, 62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, or 80 wt%. In the embodiments, it comprises 20 wt% to 50 wt% of the following amounts: t%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, 69 wt%, 70 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, or 80 wt%. The first negative electrode active material is % of the total active material, and in embodiments, the mixture may include 20wt% to 90wt% (e.g., 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt%, 46wt%, 47wt%, 48wt%, 49wt%, 50wt%, 51wt%, 52wt%, 53wt%). The second negative electrode active material comprises (54wt%, 55wt%, 56wt%, 57wt%, 58wt%, 59wt%, 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, 69wt%, 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, 89wt% or 90wt%), and in the embodiments,It includes 50 wt% to 80 wt% of a second negative electrode active material. Within this range, the mixture can readily provide boost charging performance and improve lifetime under fast charging conditions.

[0026] Here, the individual components of the negative electrode active material will be described in further detail.

[0027] (1) Active material of the first negative electrode The first negative electrode active material includes natural graphite and a coating layer, wherein the natural graphite includes secondary particles in which primary particles aggregate, the coating layer contains amorphous carbon and surrounds the secondary particles, and the first negative electrode active material has an orientation degree of 90 or less and a d002 value of 3.356 Å to 3.360 Å.

[0028] When combined with the second negative electrode active material described below, the orientation degree and d002 value of the first negative electrode active material can synergistically exhibit the effects of boost charging, capacity improvement, and fast charging life improvement.

[0029] In this specification, "orientation degree" refers to the ratio of the diffraction peak intensity [I(002)] of the (002) plane to the diffraction peak intensity [I(110)] of the (110) plane when measured by X-ray diffraction analysis using Cu α radiation, and is expressed as I(002) / I(110).

[0030] In this specification, "d002" may refer to the interplanar spacing of the (002) plane of the first negative electrode active material when measured by X-ray diffraction analysis using Cu α radiation.

[0031] Natural graphite is generally advantageous as a negative electrode active material for batteries, but its high resistance may lead to poor charging characteristics, and its internal porosity may cause side reactions, thus negatively affecting long-term durability and expansion rate.

[0032] The first negative electrode active material addresses this issue by significantly reducing the average particle size of the secondary particles of natural graphite to a fine particle form, thereby effectively reducing resistance. To offset the efficiency reduction caused by the increase in the specific surface area of ​​the secondary particles, the first negative electrode active material is calcined at the temperatures described below, thereby reducing the specific surface area while maintaining high efficiency.

[0033] In this embodiment, the first negative electrode active material comprises natural graphite, amorphous carbon, and a coating layer, and satisfies the aforementioned orientation degree and d002. Therefore, the first negative electrode active material can increase battery capacity and significantly improve the charge rate characteristic, thereby enhancing the fast-charging performance of the rechargeable lithium battery. Although the first negative electrode active material comprises natural graphite, it can significantly reduce resistance and provide high energy density, suppress side reactions with the electrolyte, and improve battery life.

[0034] Lower orientation results in a more random arrangement of edge planes in natural graphite, which increases the disordered orientation of the first negative electrode active material. This facilitates the insertion and extraction of lithium ions into / from the secondary particles of natural graphite, thereby improving the capacity characteristics of rechargeable lithium batteries using them. In embodiments, for example, the orientation degree can be 80 or less, e.g., 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47. The values ​​are 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, or 80, and in the embodiments, 10 to 80, 20 to 80, 30 to 80, 40 to 80, or 50 to 80. Orientation can be achieved by adjusting the average particle size (D50) of the secondary particles and the long axis length of the primary particles. The first negative electrode active material significantly reduces the average particle size (D50) of the secondary particles to address the high resistivity problem of natural graphite.

[0035] In an embodiment, as described below, the D50 of the secondary particles in the first negative electrode active material is substantially smaller than the long axis length of the primary particles. In an embodiment, the secondary particles are formed by wrinkling the primary particles. In an embodiment, the first negative electrode active material comprises amorphous carbon and can be prepared by heat treatment at a temperature of 2500°C or higher, as described below, to achieve a high degree of graphitization. This high degree of graphitization enhances the capacity of the negative electrode active material while mitigating the efficiency reduction caused by the reduced average particle size (D50) of the secondary particles and the increased specific surface area. In an embodiment, the first negative electrode active material has a d002 value of 3.356 Å to 3.360 Å. Within this range, a first negative electrode active material comprising secondary particles with a relatively small average particle size (D50) can offset the efficiency reduction caused by the increased specific surface area, thereby achieving high capacity. For example, d002 could be 3.356 Å, 3.3561 Å, 3.3562 Å, 3.3563 Å, 3.3564 Å, 3.3565 Å, 3.3566 Å, 3.3567 Å, ​​3.3568 Å, 3.3569 Å, 3.357 Å, 3.3571 Å, 3.3572 Å, 3.3573 Å, 3.3574 Å, 3.3575 Å, 3.3576 Å, 3.3577 Å, 3.3578 Å, 3.3579 Å. Å, 3.358Å, 3.3581Å, 3.3582Å, 3.3583Å, 3.3584Å, 3.3585Å, 3.3586Å, 3.3587Å, 3.3588Å, 3.3589Å, 3.359Å, 3.3591Å, 3.3592Å, 3.3593Å, 3.3594Å, 3.3595Å, 3.3596Å, 3.3597Å, 3.3598Å, 3.3599Å, or 3.360Å According to embodiments, the first negative electrode active material can have a mercury (Hg) cumulative pore volume of 0.01 mL / g to 0.06 mL / g, for example, 0.01 mL / g, 0.02 mL / g, 0.03 mL / g, 0.04 mL / g, 0.05 mL / g, 0.06 mL / g, 0.02 mL / g to 0.06 mL / g, 0.03 mL / g to 0.06 mL / g, or 0.03 mL / g to 0.05 mL / g. Within this range, the first negative electrode active material has minimal internal pores (i.e., empty spaces) and an appropriate amorphous carbon content, resulting in excellent efficiency of the negative electrode active material. Furthermore, the negative electrode active material can maintain an optimal density to enable effective electrolyte impregnation while controlling the internal area reacting with the electrolyte to a level that is not excessive, thereby suppressing side reactions and ensuring sufficient lifetime. The cumulative pore volume of Hg can be a characteristic of negative electrode active materials, which include finely ground natural graphite and are prepared by the preparation methods described below to minimize or reduce the specific surface area.

[0036] In an embodiment, the first negative electrode active material may have a sphericity (S) of 0.85 or greater, as defined in Equation 1 below: Equation 1 Sphericity (S) = 4π × A / B 2 , Where A is the area of ​​the first negative electrode active material and B is the perimeter of the shape of the first negative electrode active material.

[0037] In the embodiments, B may refer to the perimeter of the actual particle shape of the negative electrode active material.

[0038] The sphericity of the negative electrode active material can be determined by projecting a three-dimensional particle onto a two-dimensional plane. For example, sphericity can be defined as the ratio of the circumference of a circle with the same area as the projected particle to the actual circumference of the particle boundary.

[0039] In Equation 1, the area (A) is calculated by acquiring a cross-sectional SEM image of the negative electrode active material using controlled pressure scanning electron microscopy (CP-SEM) and measuring the actual perimeter (B) of the particle boundary using ImageJ software based on the cross-sectional image. The area (A) refers to the area of ​​a circle with a perimeter equal to (B). In this embodiment, B may represent the total length measured along the particle boundary, regardless of whether the shape is a perfect sphere or a non-spherical shape with an irregular surface.

[0040] In embodiments, the first negative electrode active material may have a sphericity of 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 1.0, and in embodiments, may have a sphericity of 0.90 to 1.0, 0.90 to 0.98, or 0.90 to 0.95. When the sphericity is within this range, expansion during charge / discharge cycles can be effectively suppressed.

[0041] In the embodiments, the first negative electrode active material may have a particle density of 1.60 g / cc to 1.80 g / cc. Within this range, the first negative electrode active material may exhibit reduced internal porosity and suppressed side reactions with the electrolyte, thereby improving lifetime characteristics. For example, the aggregate density can be 1.60 g / cc, 1.61 g / cc, 1.62 g / cc, 1.63 g / cc, 1.64 g / cc, 1.65 g / cc, 1.66 g / cc, 1.67 g / cc, 1.68 g / cc, 1.69 g / cc, 1.70 g / cc, 1.71 g / cc, 1.72 g / cc, 1.73 g / cc, 1.74 g / cc, 1.75 g / cc, 1.76 g / cc, 1.77 g / cc, 1.78 g / cc, 1.79 g / cc, or 1.80 g / cc, and in the examples, it is 1.70 g / cc to 1.80 g / cc.

[0042] In the embodiments, the first negative electrode active material may have a concentration of 0.75 g / cc to 1.20 g / cc (e.g., 0.75 g / cc, 0.76 g / cc, 0.77 g / cc, 0.78 g / cc, 0.79 g / cc, 0.80 g / cc, 0.81 g / cc, 0.82 g / cc, 0.83 g / cc, 0.84 g / cc, 0.85 g / cc, 0.86 g / cc, 0.87 g / cc, 0.88 g / cc, 0.89 g / cc, 0.90 g / cc, 0.91 g / cc, 0.92 g / cc, 0.93 g / cc, 0.94 g / cc, 0.95 g / cc, 0.96 g / cc, 0.97 g / cc, 0.98 g / cc). The tap density is 0.99 g / cc, 1.00 g / cc, 1.01 g / cc, 1.02 g / cc, 1.03 g / cc, 1.04 g / cc, 1.05 g / cc, 1.06 g / cc, 1.07 g / cc, 1.08 g / cc, 1.09 g / cc, 1.10 g / cc, 1.11 g / cc, 1.12 g / cc, 1.13 g / cc, 1.14 g / cc, 1.15 g / cc, 1.16 g / cc, 1.17 g / cc, 1.18 g / cc, 1.19 g / cc, or 1.20 g / cc, and in the examples, it has a tap density of 0.75 g / cc to 1.0 g / cc or 0.95 g / cc to 1.20 g / cc. Within this range, the negative electrode active material can exhibit reduced internal porosity and suppressed side reactions with the electrolyte, thereby improving lifetime characteristics. Tap density was measured using a GeoPyc1360 specific gravity bottle from Micromeritics, equipped with a 19.1 mm diameter chamber and a 0.2907 cm⁻¹ specific gravity. 3 The conversion factor is / mm. The process involves applying a pressure of 108N three times and calculating the average of the results.

[0043] In an embodiment, the first negative electrode active material may have a 10m 2 / g or less (e.g., 1m) 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g、5m 2 / g, 5.5m 2 / g、6m 2 / g, 6.5m 2 / g、7m 2 / g, 7.5m2 / g、8m 2 / g, 8.5m 2 / g、9m 2 / g, 9.5m 2 / g or 10m 2 The specific surface area is 1 m² / g, and in the embodiments, it has a specific surface area of ​​1 m² / g. 2 / g to 10m 2 The specific surface area is measured in g. Within this range, the first negative electrode active material can exhibit reduced internal porosity and suppressed side reactions with the electrolyte, thereby improving lifetime characteristics. Specific surface area can be the BET specific surface area. The BET specific surface area can be measured using a Macsorb HM Model-1208 analyzer from Mountech Co., Ltd.

[0044] In embodiments, the first negative electrode active material may have an internal porosity of 2% or less (e.g., 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%), and in embodiments, has an internal porosity of 1.8% or less, 1.5% or less, 1.0% to 1.5%, or 1.0% to 1.3%. Within this range, side reactions between the first negative electrode active material and the electrolyte can be suppressed, thereby improving the lifespan of the rechargeable lithium battery. The total pore volume and mesopore volume within the pores can be quantitatively measured using Barrett-Joyner-Halenda (BJH) analysis.

[0045] Here, the composition of the active material of the first negative electrode is described in further detail.

[0046] The first negative electrode active material includes natural graphite and a coating layer. The natural graphite includes secondary particles formed by the aggregation of primary particles, and the coating layer contains amorphous carbon and surrounds the secondary particles.

[0047] Natural graphite can be in the form of flakes or sheets (e.g., scaly sheets).

[0048] In the embodiments, the primary particles may have a size from 10 μm to 200 μm (e.g., 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm, 115 μm, 120 μm, ...). The major axis lengths are 125 μm, 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, 155 μm, 160 μm, 165 μm, 170 μm, 175 μm, 180 μm, 185 μm, 190 μm, 195 μm, or 200 μm, and in the embodiments, they have major axis lengths of 10 μm to 100 μm, 30 μm to 60 μm, or 20 μm to 50 μm. Within this range, it is easy to aggregate into secondary particles, and the target proportions described below can be easily achieved.

[0049] When the primary particles are plate-shaped, the "major axis length" refers to the length of the longest axis between two opposing surfaces.

[0050] In the embodiments, the primary particles may be plate-shaped, but are not limited thereto.

[0051] In embodiments, the secondary particles may have an average particle size (D50) of 30 μm or less. Within this range, the target proportions described below can be easily achieved. For example, the secondary particles may have an average particle size (D50) of 5 μm or more and 10 μm or less (e.g., 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm), and in embodiments, an average particle size (D50) of 6 μm or more and less than 8 μm. Within this range, the aforementioned orientation and sphericity can be easily achieved.

[0052] In this embodiment, the primary particles may be spherical, but are not limited thereto.

[0053] In embodiments, the ratio of the major axis length of the primary particles to the average particle size (D50) of the secondary particles can be greater than 2 and 10 or less. Within this range, the resistance of the active material does not increase, and the boost charging performance does not decrease. For example, the ratio can be 2.1, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 10, and in embodiments, it is 3 to 6, for example, 4 to 6 or 5 to 6. Within this range, the aforementioned orientation and sphericity can be easily achieved.

[0054] Amorphous carbon is contained in a coating layer surrounding the surface of the secondary particles. Amorphous carbon can reduce the porosity within the first negative electrode active material and suppress side reactions between the negative electrode active material and the electrolyte, thereby improving charge / discharge rate characteristics.

[0055] In the embodiments, the coating layer containing amorphous carbon may have a thickness of 5 nm to 50 nm (e.g., 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, 40 nm, 41 nm, 42 nm, 43 nm, 44 nm, 45 nm, 46 nm, 47 nm, 48 nm, 49 nm, or 50 nm), and in the embodiments, it has a thickness of 10 nm to 50 nm or 20 nm to 50 nm. Within this range, side reactions with the electrolyte can be suppressed, and charge / discharge rate characteristics can be improved.

[0056] Amorphous carbon can be one or more of soft carbon, hard carbon, mesophase pitch carbides, and calcined coke.

[0057] Amorphous carbon can also exist on the surface of the primary particles.

[0058] In an embodiment, the natural graphite and amorphous carbon in the first negative electrode active material, based on a total of 100 parts by weight, can be included in a weight ratio of 99:1 to 75:25 (e.g., 90:10 to 75:25, 90:10 to 80:20, 90:10 to 85:15, or 90:10 to 88:12). Within this range, side reactions with the electrolyte can be effectively suppressed, and charge / discharge rate characteristics can be improved.

[0059] Here, a method for preparing the first negative electrode active material according to an embodiment is described.

[0060] (1) Natural graphite raw material with an average particle size (D50) of 120 μm or greater is pulverized to obtain primary particles with the above-mentioned major axis length. In a specific example, the natural graphite raw material can be pulverized using an air jet milling method. Air jet milling can include 5 kg / cm² milling. 2 Up to 20kg / cm 2 Natural graphite raw materials are pulverized at room temperature under pressure.

[0061] (2) Use a spheroidizing device to aggregate primary particles into secondary particles.

[0062] The agglomeration process aims to achieve a sphericity of 0.85 or greater and can be performed using a high-intensity mixer equipped with a high-speed rotating rotor and stator. The average particle size (D50) of the secondary particles can be controlled by adjusting parameters such as pressure and shear rate during the spheroidization process.

[0063] (3) Mix the prepared secondary particles with the amorphous carbon precursor.

[0064] There are no particular restrictions on amorphous carbon precursors, as long as they form carbides. For example, precursors may include one or more of the following: phenolic resins, furan resins, epoxy resins, polyacrylonitrile resins, polyamide resins, polyimide resins, polyamide-imide resins, synthetic bitumen, petroleum bitumen, coal tar, and coal tar.

[0065] During mixing, precursors can be added to achieve the aforementioned weight ratio of natural graphite and amorphous carbon in the final product (i.e., the negative electrode active material).

[0066] (4) The mixture obtained by mixing is calcined and heat-treated to obtain the negative electrode active material.

[0067] Heat treatment can be performed at temperatures of 2500°C or higher (e.g., 2500 to 3500°C, or 2500 to 3000°C). Within this range, negative electrode active materials comprising secondary particles meeting the above proportions can readily achieve the above-mentioned orientation, d002, and sphericity.

[0068] The heat treatment can last from 1 hour to 5 hours, for example, 1 hour to 4 hours, 1 hour to 3 hours, or 2 hours to 3 hours.

[0069] Figure 1 This is a conceptual diagram of the first negative electrode active material according to an embodiment.

[0070] Reference Figure 1 The first negative electrode active material includes natural graphite, which comprises secondary particles 3 formed by the aggregation of primary particles 1, amorphous carbon 5 present on the surface of the primary particles 1, and a coating layer 7 containing amorphous carbon 5 and surrounding the secondary particles 3. (Refer to...) Figure 1 The secondary particles 3 are formed by spherizing the bent primary particles 1 into an aggregated structure. This structure reduces the size of natural graphite while forming a dense internal structure that minimizes or reduces internal porosity, thereby suppressing side reactions with the electrolyte and enhancing cycle life.

[0071] (2) Active material of the second negative electrode The second negative electrode active material can be artificial graphite. When the second negative electrode active material is artificial graphite, it can exhibit improved discharge / discharge efficiency and cycle life characteristics compared to when the second negative electrode active material is natural graphite.

[0072] In this embodiment, the second negative electrode active material is rod-shaped crystalline carbon with an elongated structure in one direction. For example... Figure 2 As shown, rod-shaped carbon has a long axis A and a short axis B. "Rod-shaped" refers to a solid rod-shaped structure with a filled interior. Even though hollow tubular or fibrous carbon types have long and short axes, solid rod-shaped structures are distinguished from hollow tubular or fibrous carbon types.

[0073] "Rod-shaped" refers to a structure with an aspect ratio (long axis length / short axis length) greater than 1. In the embodiments, the second negative electrode active material can have an aspect ratio of 2 to 100 or 4 to 20, and can be a carbon-based material. When the aspect ratio of the second negative electrode active material is within the above range, it can further reduce the volume expansion and resistance of the negative electrode during charging / discharging, while further improving high-rate characteristics.

[0074] In the embodiments, the average major axis length of the second negative electrode active material can be 40 μm to 120 μm, or 50 μm to 120 μm. When the major axis length of the second negative electrode active material is within the above range, the volume expansion and resistance of the negative electrode during charge / discharge cycles can be further reduced, thereby further improving high-rate characteristics.

[0075] "Major axis length" refers to the average length of the major axis. For example, in Figure 2 In the long axis A and short axis B of the rod-shaped (e.g., strip-shaped) carbon shown, "long axis length" refers to the dimension of long axis A.

[0076] In the negative electrode active material according to the embodiment, the area percentage of the second negative electrode active material can be 10% to 40% or 20% to 30% of the total area (100%) of the negative electrode active material. The area percentage is measured using a particle size analyzer, and the area percentage indicates the area percentage of the second negative electrode active material per unit area of ​​negative electrode active material.

[0077] Here, a method for preparing the second negative electrode active material according to an embodiment is described.

[0078] The second negative electrode active material can be prepared by pulverizing a conductive material (such as calcined coke) for graphitization to produce a precursor with an average particle size (D50) of 20 μm or smaller, mixing the precursor with pitch, and then heat-treating the mixture.

[0079] The negative electrode plate for a rechargeable lithium battery according to another embodiment includes the negative electrode active material for a rechargeable lithium battery described above according to the embodiment.

[0080] In an embodiment, the negative electrode plate may include the aforementioned negative electrode active material for rechargeable lithium batteries in an amount of 95 wt% or greater (e.g., 95 wt% to 100 wt% or 100 wt% of the total weight of the negative electrode active material).

[0081] The negative electrode plate may also include one or more of an adhesive and a conductive material. The adhesive and conductive material are described below.

[0082] According to another embodiment, the rechargeable lithium battery includes a negative electrode active material for a rechargeable lithium battery.

[0083] In an embodiment, the rechargeable lithium battery may include a negative electrode and a positive electrode, wherein the negative electrode includes a negative electrode active material for the rechargeable lithium battery.

[0084] negative electrode The negative electrode for a rechargeable lithium battery may include a current collector and a layer of negative electrode active material on the current collector. The negative electrode active material layer may include a negative electrode active material and may also include a binder and / or a conductive material (e.g., an electrically conductive material).

[0085] In an embodiment, for example, the negative electrode active material layer may include about 90 wt% to about 99 wt% of negative electrode active material, about 0.5 wt% to about 5 wt% of binder, and about 0 wt% to about 5 wt% of conductive material.

[0086] The negative electrode active material layer includes the negative electrode active material according to the above embodiments. In the embodiments, the content of the negative electrode active material according to the above embodiments can be 95 wt% or more of the total negative electrode active material in the negative electrode active material layer (e.g., 95 wt% to 100 wt% or 100 wt%).

[0087] In addition to the negative electrode active material according to the above embodiments, the negative electrode active material layer may also include a material that can reversibly insert / deintercalate lithium ions, lithium metal, lithium metal alloy, a material capable of doping / dedoping lithium, or a transition metal oxide.

[0088] Materials that can reversibly insert / deintercalate lithium ions can include carbon-based negative electrode active materials, such as crystalline carbon, amorphous carbon, or combinations thereof. Crystalline carbon can be graphite (such as irregular, plate-like, sheet-like, spherical, or fibrous), natural graphite, or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0089] In an embodiment, the lithium metal alloy includes an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0090] The material capable of doping / dedoping lithium can be a Si-based negative electrode active material or a Sn-based negative electrode active material. The Si-based negative electrode active material can include silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof). The Sn-based negative electrode active material can include Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0091] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to an embodiment, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite can include secondary silicon particles (cores) aggregated from primary silicon particles and an amorphous carbon coating layer (shells) on the surface of the secondary silicon particles. Amorphous carbon can also be between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary silicon particles can exist in a form dispersed in an amorphous carbon matrix.

[0092] The silicon-carbon composite can also include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer on the surface of the core.

[0093] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0094] The binder can adhere the negative electrode active material particles to each other well and can also adhere the negative electrode active material well to the current collector.

[0095] The binder can include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0096] The non-aqueous binder can include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0097] Waterborne adhesives may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0098] If an aqueous binder is used as the negative electrode binder, it may further include a cellulose compound capable of imparting viscosity. The cellulose compound may include at least one of carboxymethyl cellulose, hydroxypropyl methylcellulose, methylcellulose, and their alkali metal salts. In embodiments, the alkali metal may include Na, K, or Li.

[0099] Dry binders can be fibrous polymer materials. For example, dry binders can be polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0100] Conductive materials can impart conductivity (e.g., electrical conductivity) to electrodes. Any suitable material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in rechargeable lithium batteries) and conducts electrons can be used in batteries. Some non-limiting examples may include carbon-based materials (such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes), metallic materials including copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers, conductive polymers (such as polyphenylene derivatives), or mixtures thereof.

[0101] The negative electrode current collector may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, or a combination thereof.

[0102] positive electrode The positive electrode for a rechargeable lithium-ion battery may include a current collector and a layer of positive electrode active material on the current collector. The positive electrode active material layer may include positive electrode active material and may also include a binder and / or a conductive material. For example, the positive electrode may also include additives that can be used as a sacrifice for positive electrode function.

[0103] Positive electrode active material The positive electrode active material may include compounds capable of intercalating and deintercalating lithium (lithiation intercalation compounds). In embodiments, at least one composite oxide of lithium with a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0104] The composite oxide can be a lithium transition metal composite oxide. Examples of composite oxides may include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free lithium nickel-manganese oxides, or combinations thereof.

[0105] As an example, a compound represented by any of the following chemical formulas can be used: Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Ni b Co c L 1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0≤e≤0.1); Li a NiG b O2 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a CoG b O2 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1-b G b O2 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn2G b O4 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1-gG g PO4 (0.90 ≤ a ≤ 1.8 and 0 ≤ g ≤ 0.5); Li (3-f) Fe2(PO4)3 (0≤f≤2); and Li a FePO4 (0.90≤a≤1.8).

[0106] In the above chemical formulas, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 It is Mn, Al, or a combination thereof.

[0107] The positive electrode active material can be, for example, a high-nickel positive electrode active material, based on 100 mol% of metals other than lithium in a lithium transition metal complex oxide. The high-nickel positive electrode active material has a nickel content of greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, greater than or equal to about 94 mol%, and less than or equal to about 99 mol%. High-nickel positive electrode active materials can achieve high capacity and can be applied to high-capacity, high-density rechargeable lithium batteries.

[0108] In an embodiment, based on a 100wt% positive electrode active material layer, the amount of positive electrode active material can be from about 90wt% to about 99.5wt%. In an embodiment, based on a 100wt% positive electrode active material layer, the amounts of binder and conductive material can be from about 0.5wt% to about 5wt%, respectively.

[0109] The binder enables the positive electrode active material particles to adhere well to each other and also enables the positive electrode active material to adhere well to the current collector. As a non-limiting example, examples of binders may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin, nylon, etc.

[0110] Conductive materials can impart conductivity (e.g., electrical conductivity) to electrodes. Any suitable material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in rechargeable lithium batteries) and conducts electrons can be used in batteries. Examples of conductive materials can include carbon-based materials (such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes), metallic materials comprising metal powders or fibers of copper, nickel, aluminum, silver, etc., conductive polymers (such as polyphenylene derivatives), or mixtures thereof.

[0111] In the embodiments, A1 can be used as a current collector, but is not limited thereto.

[0112] Rechargeable lithium batteries may also include an electrolyte solution.

[0113] Electrolyte solution Electrolyte solutions used in rechargeable lithium batteries may include non-aqueous organic solvents and lithium salts.

[0114] Non-aqueous organic solvents can be used as media for transporting ions that participate in the electrochemical reactions of a battery.

[0115] Non-aqueous organic solvents can be carbonates, esters, ethers, ketones, alcohols, aprotic solvents, or combinations thereof.

[0116] Carbonate solvents may include any one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), etc.

[0117] Ester solvents may include any one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc.

[0118] Ether solvents may include any one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Additionally, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc. Aprotic solvents may include nitriles (such as R-CN (where R is a C2 to C20 straight-chain, branched, or cyclic chain, and includes double bonds, aromatic rings, or ether bonds, etc.)), amides (such as dimethylformamide), dioxolane (such as 1,3-dioxolane, 1,4-dioxolane, etc.), sulfolane, etc.

[0119] Non-aqueous organic solvents can be used alone or in combination of two or more.

[0120] Alternatively, if carbonate solvents are used, cyclic carbonates and chain carbonates can be mixed and used, and cyclic carbonates and chain carbonates can be mixed in a volume ratio of about 1:1 to about 1:9.

[0121] Lithium salts dissolved in organic solvents supply lithium ions in batteries, enabling basic operation of rechargeable lithium batteries and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 At least one of the following: (SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0122] Rechargeable lithium batteries may also include a separator.

[0123] diaphragm Depending on the type of rechargeable lithium battery, a separator can be present between the positive and negative electrodes. The separator can include multilayer membranes of polyethylene, polypropylene, polyvinylidene fluoride, or two or more layers thereof, as well as hybrid multilayer membranes (such as polyethylene / polypropylene two-layer membranes, polyethylene / polypropylene / polyethylene three-layer membranes, polypropylene / polyethylene / polypropylene three-layer membranes, etc.).

[0124] The membrane may include a porous substrate and a coating layer on one or both or opposite surfaces of the porous substrate, the coating layer including organic materials, inorganic materials or combinations thereof.

[0125] The porous substrate can be a polymer film formed from any one or a copolymer or mixture of two or more of the following polymers: polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (e.g., Teflon).

[0126] Organic materials may include polymers such as polyvinylidene fluoride or (meth)acrylic acid polymers.

[0127] In the embodiments, the inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite and combinations thereof.

[0128] Organic and inorganic materials can be mixed in a coating layer, or a coating layer containing organic materials and a coating layer containing inorganic materials can be stacked.

[0129] Rechargeable lithium batteries Based on their shape, rechargeable lithium batteries can be classified into any of the following types: cylindrical batteries, prismatic batteries, pouch batteries, and coin-shaped batteries.

[0130] Figures 3 to 6 This is a schematic diagram illustrating a rechargeable lithium battery according to an embodiment. Figure 3 A cylindrical battery is shown; Figure 4 A prismatic battery is shown; and Figure 5 and Figure 6 A pouch-type battery is shown. (See reference) Figures 3 to 6 The rechargeable lithium battery 100 may include an electrode assembly 40 and a housing 50. The electrode assembly 40 includes a separator 30 between a positive electrode 10 and a negative electrode 20, and is included in the housing 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte solution (not shown). Figure 3 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of the sealed housing 50. Figure 4 In this context, the rechargeable lithium battery 100 may include a positive electrode lead connector 11, a positive terminal 12, a negative electrode lead connector 21, and a negative terminal 22. For example... Figure 5 and Figure 6 As shown, the rechargeable lithium battery 100 may include electrode terminals 70, which serve as electrical paths for guiding current formed in the electrode assembly 40 to the outside. The electrode terminals 70 may be, for example, a positive electrode terminal 71 and a negative electrode terminal 72.

[0131] As a non-limiting example, the rechargeable lithium battery according to the embodiments can be used in automobiles, mobile phones and / or various types of electronic devices.

[0132] Some examples and comparative examples of the present invention have been described herein. However, the following examples are provided as illustrative examples of the present invention, and the present invention is not limited to these examples.

[0133] Example 1 (1) Preparation of the active material of the first negative electrode Thin flakes of natural graphite with an average particle size (D50) of 120 μm were pulverized using an air jet mill to obtain plate-shaped primary particles with a long axis length of 20 μm to 30 μm. The primary particles were then aggregated into secondary particles with an average particle size (D50) of 7 μm using a spheroidizing device. The secondary particles were mixed with petroleum asphalt and heat-treated in a calcining furnace at 3000 °C for 2 hours to prepare the first negative electrode active material. The amount of carbon added to the asphalt was adjusted to achieve a weight ratio of natural graphite to amorphous carbon of 90:10 in the negative electrode active material.

[0134] (2) Heat-treated coke with a length of 10 cm is pulverized into a precursor with an average particle size of 20 μm. The precursor is mixed with pitch and heat-treated to produce rod-shaped artificial graphite (containing amorphous carbon) as the active material for the second negative electrode. The rod-shaped artificial graphite has a major axis length of 80 μm and an aspect ratio of 4 to 20.

[0135] (3) Mix 50 parts by weight of the first negative electrode active material and 50 parts by weight of the second negative electrode active material to prepare a mixture of negative electrode active materials.

[0136] (4) A negative electrode active material slurry was prepared by mixing 97.5 wt% of the prepared negative electrode active material mixture, 1.5 wt% of styrene-butadiene rubber as a binder and 1.0 wt% of carboxymethyl cellulose as an additive in distilled water.

[0137] The negative electrode active material slurry is applied to the copper current collector, dried, and rolled to manufacture the negative electrode.

[0138] A half-cell is constructed using a negative electrode, a lithium metal counter electrode, and an electrolyte. The electrolyte is a mixed solvent (volume ratio 3:7) in which ethylene carbonate and dimethyl carbonate, each containing 1 M LiPF4, are dissolved.

[0139] Example 2 The negative electrode plate was prepared in the same manner as in Example 1, except that 20 parts by weight of the first negative electrode active material and 80 parts by weight of the second negative electrode active material were mixed to prepare a mixture of negative electrode active materials.

[0140] Example 3 The first negative electrode active material was prepared by changing the spheroidization conditions in Example 1.

[0141] Using the first negative electrode active material, a mixture of 50 parts by weight of the first negative electrode active material and 50 parts by weight of the second negative electrode active material was prepared. Then, a negative electrode plate was manufactured in the same manner as in Example 1.

[0142] Comparison Example 1 The negative electrode plate is prepared in the same manner as in Example 1, except that only the second negative electrode active material is used instead of the first negative electrode active material.

[0143] Comparison Example 2 The first negative electrode active material was prepared in the same manner as in Example 1, except that pitch carbon was not added. Using the prepared first negative electrode active material, a negative electrode and a half-cell were fabricated in the same manner as in Example 1.

[0144] Comparison Example 3 Thin sheets of natural graphite with an average particle size (D50) of 120 μm were pulverized using an air jet mill to obtain primary particles with a D50 of 120 μm. These primary particles were then aggregated into secondary particles with an average particle size (D50) of 20 μm using a spheroidizing device. The secondary particles were mixed with pitch carbon and heat-treated in a calcining furnace at 1200 °C for 2 hours to prepare the first negative electrode active material. The amount of pitch carbon added was adjusted so that the weight ratio of natural graphite to amorphous carbon in the first negative electrode active material was 90:10.

[0145] The half-cell was fabricated in the same manner as in Example 1 using the prepared first negative electrode active material.

[0146] Compare Example 4 Thin flakes of natural graphite with an average particle size (D50) of 80 μm were pulverized using an air jet mill to obtain primary particles with a long axis length of 7 μm. The primary particles were then aggregated into secondary particles with an average particle size (D50) of 15.6 μm using a spheroidizing device. The secondary particles were mixed with pitch carbon and heat-treated in a calcining furnace at 1200 °C for 2 hours to prepare the first negative electrode active material. The amount of pitch carbon added was adjusted so that the weight ratio of natural graphite to amorphous carbon in the first negative electrode active material was 90:10.

[0147] The half-cell was fabricated in the same manner as in Example 1 using the prepared first negative electrode active material.

[0148] (Experimental Example 1) [Active Material of the First Negative Electrode] Particle density (unit: g / cc) Particle density was measured using a Carver 4350.L apparatus from Carver, Inc. To determine powder density, 1.0 g of the first negative electrode active material from both the example and comparative examples was placed in a mold and compressed for 30 seconds under a pressure of 2.0 tons.

[0149] Orientation Orientation was measured using an XRD analyzer (X'Pert Pro from Malvern Panalytical). For the individual first negative electrode active materials of the example and comparative examples, the ratio of diffraction peak intensities I(002) / I(110) was calculated using X-ray diffraction analysis utilizing Cu α radiation.

[0150] d002 (unit: Å) The interplanar spacing of the d002 planes was measured using an XRD analyzer (X'Pert Pro from Malvern Panalytical). For the individual first negative electrode active materials of the example and comparative examples, the interplanar spacing of the (002) planes was determined by X-ray diffraction analysis using Cu α radiation.

[0151] Mercury cumulative pore volume (unit: mL / g) For each of the first negative electrode active materials in the example and comparative examples, the cumulative Hg pore volume was determined using an Hg intrusion porosimeter (from Micromeritics' AutoPore V). The negative electrode active material was placed in a specialized sample cup and surrounded by mercury, then pressures ranging from 0.2 to 60,000 psi were applied to force the mercury into the negative electrode active material. The resulting change in mercury volume within the capillary rod container was measured to determine the pore volume. This method can measure pore sizes ranging from 0.01 to 100 μm, and in negative electrode active materials, pores with a size of 0.01 μm or larger and 5 μm or smaller are generally considered to be internal pores in the active material.

[0152] sphericity Sphericity was measured using a Morphologi 4 analyzer from Malvern Panalytical. For each of the first negative electrode active materials in the example and comparative examples, values ​​A and B in Equation 1 above were obtained, and sphericity was calculated according to Equation 1.

[0153] (Experimental Example 2) [Electrode Plates and Half-Cell] Average particle size D50 (unit: μm) The average particle size (D50) of the mixture of the first and second negative electrode active materials was measured using a laser diffraction particle size analyzer (LS 13 320 XR from Beckman Coulter).

[0154] Particle density (unit: g / cc) The agglomeration density was measured using a Carver 4350.L apparatus from Carver Corporation. A mixture of 1.0 g each of the first and second negative electrode active materials from the example and comparative examples was placed in a mold and then compressed under a pressure of 2.0 tons for 20 seconds to determine the agglomeration density.

[0155] Capacity (unit: mAh / g) and rate capability (unit: %) Half-cells manufactured in the example and comparative examples were subjected to one charge / discharge cycle at 0.1C and two charge / discharge cycles at 0.2C, and the 0.2C charge capacity was then measured. Subsequently, they were charged at 2.0C with a 0.01V cutoff. Then, charging continued under constant voltage conditions until the 0.01C cutoff was reached. The half-cells were then discharged under constant current conditions at 0.2C with a 1.5V cutoff to determine the 2C charge capacity. Rate performance was evaluated by calculating the ratio of the 2C charge capacity to the 0.2C charge capacity.

[0156] Orientation of the mixture Orientation was measured using an XRD analyzer (X'Pert Pro from Malvern Panalytical). For the individual negative electrode active materials of the example and comparative examples, the ratio of diffraction peak intensities I(002) / I(110) was calculated using X-ray diffraction analysis.

[0157] Table 1

[0158] As shown in Table 1 above, the example negative electrode active material can improve initial efficiency and enhance rate performance. Although not shown in Table 1, the example negative electrode active material comprising both the first and second negative electrode active materials of the present invention is expected to exhibit a low orientation degree of 200 or less, thereby enhancing electrolyte impregnation and reducing expansion of the negative electrode plate.

[0159] However, as shown in Table 1, Comparative Example 1, which includes only the second negative electrode active material and lacks the first negative electrode active material, exhibits low initial efficiency and rate characteristics. Furthermore, Comparative Example 1 shows a significantly higher degree of orientation compared to the examples, indicating that improvements in electrolyte impregnation and electrode plate expansion may be significantly reduced. As shown in Table 1, Comparative Examples 2 to 4, which do not include the first negative electrode active material of the present invention, also exhibit low initial efficiency and rate characteristics. Since Comparative Examples 2 to 4 fail to meet the orientation range specified in the present invention, improvements in electrolyte impregnation and electrode plate expansion in Comparative Examples 2 to 4 are expected to be significantly reduced.

[0160] The negative electrode active material for rechargeable lithium batteries according to embodiments of the present invention can exhibit excellent rechargeable lithium battery performance by providing boost charging, improved charge rate characteristics, enhanced electrolyte impregnation, and suppression of electrode plate expansion.

[0161] Although some exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and it will be understood that various modifications can be made within the scope of the claims, detailed description and drawings of the present invention, and such modifications also fall within the scope of the present invention.

Claims

1. A negative electrode active material, said negative electrode active material comprising a mixture of a first negative electrode active material and a second negative electrode active material, in, The first negative electrode active material comprises natural graphite and a coating layer, wherein the natural graphite includes secondary particles in which primary particles are arranged, and the coating layer comprises amorphous carbon surrounding the secondary particles. The first negative electrode active material has an orientation degree of 90 or less and a d002 value of 3.356 Å to 3.360 Å, and The second negative electrode active material includes rod-shaped artificial graphite.

2. The negative electrode active material according to claim 1, wherein, The first negative electrode active material has a mercury accumulation pore volume of 0.01 mL / g to 0.06 mL / g.

3. The negative electrode active material according to claim 1, wherein, The first negative electrode active material has a particle density of 1.60 g / cc to 1.80 g / cc.

4. The negative electrode active material according to claim 1, wherein, The first negative electrode active material has a sphericity of 0.85 or greater.

5. The negative electrode active material according to claim 1, wherein, The ratio of the major axis length of the primary particle to the average particle size of the secondary particle is greater than 2 and less than or equal to 10.

6. The negative electrode active material according to claim 1, wherein, The primary particles are plate-shaped, and the secondary particles are spherical.

7. The negative electrode active material according to claim 1, wherein, The primary particles have a major axis length of 10 μm to 200 μm, and the secondary particles have an average particle size of 30 μm or less.

8. The negative electrode active material according to claim 1, wherein, The natural graphite includes flake-shaped natural graphite.

9. The negative electrode active material according to claim 1, wherein, The amorphous carbon includes one or more types of mixtures selected from soft carbon, hard carbon, mesophase pitch carbides and calcined coke.

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

11. The negative electrode active material according to claim 1, wherein, The amorphous carbon is also present on the surface of the primary particles.

12. The negative electrode active material according to claim 1, wherein, Based on a total of 100 parts by weight of the natural graphite and the amorphous carbon in the first negative electrode active material, the natural graphite and the amorphous carbon are included in a weight ratio of 99:1 to 75:

25.

13. The negative electrode active material according to claim 1, wherein, The second negative electrode active material has an aspect ratio of 2 to 100.

14. The negative electrode active material according to claim 1, wherein, The second negative electrode active material has an average major axis length of 40 μm to 120 μm.

15. The negative electrode active material according to claim 1, wherein, When measured by X-ray diffraction analysis, the mixture has a peak intensity ratio of 200 or less, I(002) / I(110).

16. The negative electrode active material according to claim 1, wherein, The mixture comprises 10 wt% to 80 wt% of the first negative electrode active material and 20 wt% to 90 wt% of the second negative electrode active material.

17. The negative electrode active material according to claim 1, wherein, The negative electrode active material is used in rechargeable lithium batteries.

18. A rechargeable lithium battery, said rechargeable lithium battery comprising: The negative electrode comprises the negative electrode active material according to any one of claims 1-16; as well as Positive electrode.

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