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

Abstract

Provided are a negative electrode active material for a rechargeable lithium battery, and a negative electrode plate and a rechargeable lithium battery including the same. The negative electrode active material includes natural graphite and a coating layer, the natural graphite including secondary particles assembled from primary particles, the coating layer surrounding the secondary particles and including amorphous carbon. The negative electrode active material has a d002 value of 3.356 Å to 3.360 Å and an orientation degree of 90 or less.

Description

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2024-0175698, filed on November 29, 2024, with the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] This disclosure relates to a negative electrode active material for a rechargeable lithium battery and a rechargeable lithium battery including 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 rechargeable 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 containing active materials capable of inserting and deintercalating lithium ions, and generates electrical energy through redox reactions when lithium ions are deintercalated from the positive electrode and inserted into the negative electrode or deintercalated from the negative electrode and inserted into the positive electrode. Summary of the Invention

[0005] This disclosure aims to provide a negative electrode active material for rechargeable lithium batteries that exhibits low resistance, high energy density, and fast charging performance.

[0006] This disclosure also aims to provide a negative electrode plate including the negative electrode active material and a rechargeable lithium battery.

[0007] One or more aspects of this disclosure provide a negative electrode active material for a rechargeable lithium battery, the negative electrode active material comprising natural graphite and a coating layer, the natural graphite comprising secondary particles in which primary particles are assembled, the coating layer surrounding the secondary particles and comprising amorphous carbon, wherein the negative electrode active material has an orientation degree of 90 or less and a d002 of 3.356 Å to 3.360 Å.

[0008] One or more aspects of this disclosure provide a negative electrode plate comprising the negative electrode active material for a rechargeable lithium battery.

[0009] One or more aspects of this disclosure provide a rechargeable lithium battery including a negative electrode and a positive electrode, the negative electrode including a negative electrode active material for the rechargeable lithium battery.

[0010] The negative electrode active material for a rechargeable lithium battery according to one or more embodiments includes natural graphite and can exhibit excellent rechargeable lithium battery performance by significantly reducing resistance and providing high energy density and fast charging performance. Attached Figure Description

[0011] The above and other objects, features and advantages of this disclosure will become more apparent to those skilled in the art from the detailed description of exemplary embodiments of this disclosure with reference to the accompanying drawings, in which: Figure 1 This is a schematic diagram of a negative electrode active material for a rechargeable lithium battery according to one or more embodiments.

[0012] Figures 2 to 5 This is a schematic cross-sectional view of a rechargeable lithium battery according to one or more embodiments. Detailed Implementation

[0013] Embodiments of this disclosure will be described in detail below. However, they are provided by way of example, and this disclosure is not limited thereto; rather, it is limited only by the scope of the described claims.

[0014] Unless otherwise stated herein, when a component such as a layer, film, region, plate, etc., is described as being "on" another component, this includes not only the case where the component is "directly on" said other component, but also the case where there is another component between them. In the accompanying drawings, the thickness of some components is exaggerated for the purpose of effectively illustrating the technical content. The same reference numerals always refer to the same elements, and their repeated description may not be provided in the specification.

[0015] Unless otherwise stated in this specification, anything indicated in the singular may include multiples. Furthermore, unless otherwise stated, “A or B” may mean “including A, including B, or including both A and B”.

[0016] As used herein, the term "combination of components" can refer to mixtures, laminates, complexes, copolymers, alloys, blends, and reaction products of the components.

[0017] As used herein, the terms “comprising / including,” “having,” and / or variations thereof are intended to indicate the presence of the embodied aspects, quantities, steps (e.g., actions or tasks), elements, and / or combinations thereof (e.g., any suitable combinations). However, the use of these terms does not prevent or exclude the possibility of the presence and / or addition of one or more other components, features, quantities, steps (e.g., actions or tasks), elements, and / or combinations thereof (e.g., any suitable combinations). Additionally, the terms “comprising,” “including,” “having,” or other similar terms include or support the terms “consisting of,” and “substantially consisting of,” which indicate the presence of the stated features, integers, steps, operations, elements, and / or components, while other features, integers, steps, operations, elements, components, and / or groups thereof are absent or substantially absent. Furthermore, in this document, “substantially consisting of” means that any additional components will not substantially affect the chemical, physical, optical, or electrical properties of the semiconductor film.

[0018] It will be understood that although the terms “first,” “second,” “third,” etc., may be used herein to describe one or more suitable elements, components, regions, layers, and / or parts, these elements, components, regions, layers, and / or parts should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or part from another. Therefore, without departing from the teachings set forth herein, a first element, first component, first region, first layer, or first part described herein may be referred to as a second element, second component, second region, second layer, or second part.

[0019] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of…”, “one of…”, and “selected from…” modify the entire list of elements rather than individual elements of that list if they precede a list of elements (e.g., when preceded by an element). For example, expressions “at least one of a to c”, “at least one of a, b, or c”, and “at least one of a, b, and / or c” can indicate only a, only b, only c, both a and b (e.g., simultaneously), both a and c (e.g., simultaneously), both b and c (e.g., simultaneously), all of a, b, and c, or variations thereof.

[0020] Spatial relative terms such as “below,” “under,” “lower,” “above,” and “upper” can be used here to readily describe the relationship between one element or feature and another. It will be understood that, in addition to covering the orientations shown in the figures, spatial relative terms are also intended to cover different orientations of the device during use or operation. For example, if the device in the figures is flipped (e.g., when the device in the figures is flipped), an element described as “below” or “under” other elements or features will be oriented “above” said other elements or features. Thus, the example term “below” can cover both above and below (e.g., simultaneously). The device can be additionally oriented (rotated 90 degrees or in other orientations), and the spatial relative terms used herein can be interpreted accordingly.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. Unless otherwise defined, all terms used herein (including chemical, technical, and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will also be understood that terms (such as those defined in common dictionaries) should be interpreted as having the same meaning as they have in the relevant field and in the context of this disclosure, and not in an idealized or overly formal sense.

[0022] Example embodiments are described herein with reference to a cross-sectional view as an idealized embodiment. Thus, variations in the illustrated shapes due to, for example, manufacturing techniques and / or tolerances are expected. Therefore, the embodiments described herein should not be construed as limited to the specific shapes of the regions shown herein, but will include, for example, shape deviations caused by manufacturing processes. For example, regions shown or described as flat may generally have rough and / or non-linear characteristics. Furthermore, sharp corners shown may be rounded. Therefore, the regions shown in the figures are schematic in nature, and their shapes are not intended to represent the precise shape of the regions, nor are they intended to limit the scope of the claims.

[0023] The term “may” will be understood to mean “one or more embodiments of this disclosure,” some of which include the described elements, and some of which exclude the element and / or include alternative elements. Similarly, alternative expressions such as “or” refer to “one or more embodiments of this disclosure,” each including the corresponding listed item.

[0024] In the context of this application, unless otherwise defined, the term “use” and its variations may be considered synonymous with the term “utilize” and its variations, respectively.

[0025] Here, the term "particle size / diameter D50" refers to the average particle size / diameter, which is the size / diameter of the particles that constitute 50% of the total volume in the particle size distribution. The particle size distribution can be measured using methods well known to those skilled in the art. For example, it can be measured using a particle size analyzer, transmission electron microscopy, or scanning electron microscopy. In another approach, the D50 value can be obtained by measuring the particle size / diameter using a measuring device that utilizes dynamic light scattering, performing data analysis to count the number of particles within each particle size range, and then calculating the particle size / diameter from this. Alternatively, D50 can be measured using laser diffraction. More specifically, when measured by laser diffraction, after dispersing the particles to be measured in a dispersion medium, the particles can be introduced into a commercially available laser diffraction particle size / diameter measuring device (e.g., Microtrac MT3000) and irradiated with ultrasound at approximately 28 kHz at an output of 60 W, and the D50 based on the 50% particle size / diameter distribution in the measuring device can be calculated.

[0026] Negative electrode active material The negative electrode active material for rechargeable lithium batteries according to one or more embodiments can provide low resistance, high energy density, and fast charging performance. The negative electrode active material includes natural graphite and can provide significantly low resistance, high energy density, and fast charging performance by mitigating the high resistance problem of natural graphite.

[0027] The negative electrode active material for a rechargeable lithium battery according to one or more embodiments includes natural graphite and a coating layer, the natural graphite comprising secondary particles assembled from primary particles, the coating layer surrounding the secondary particles and comprising amorphous carbon, wherein the negative electrode active material has an orientation degree of 90 or less and a d002 of 3.356 Å to 3.360 Å.

[0028] The “orientation degree” used here can refer 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, as measured by X-ray diffraction analysis using CuKα radiation.

[0029] The term "d002" as used here can refer to the interplanar spacing of the (002) plane of the negative electrode active material as measured by X-ray diffraction analysis using CuKα radiation.

[0030] Natural graphite is generally advantageous as a negative electrode active material in batteries, but its high resistivity leads to poor charging characteristics. Furthermore, due to its numerous internal pores, side reactions can adversely affect long cycle life and expansion rate.

[0031] The negative electrode active material is prepared by significantly reducing the average particle size of the secondary particles of natural graphite to a fine particle form to provide low resistance. In order to offset the efficiency reduction caused by the increased specific surface area of ​​the secondary particles, the negative electrode active material is calcined at the following temperature to reduce the specific surface area and provide high efficiency at the same time.

[0032] In this regard, the negative electrode active material for rechargeable lithium batteries includes natural graphite and a coating layer comprising amorphous carbon, and satisfies the above-mentioned orientation degree and d002. Therefore, the negative electrode active material for rechargeable lithium batteries improves battery capacity and significantly increases the charge rate (C-rate), thereby enhancing the fast-charging performance of rechargeable lithium batteries. Although the negative electrode active material for rechargeable lithium batteries includes natural graphite, it can significantly reduce resistance and provide high energy density, suppression of side reactions with the electrolyte, and improved lifespan.

[0033] As the degree of orientation decreases, the edge planes of natural graphite become oriented in random directions, thereby increasing the random orientation of the negative electrode active material. This facilitates the extraction and insertion of lithium ions from or into the natural graphite secondary particles, thus improving the capacity characteristics of the rechargeable lithium battery. For example, the degree of orientation can be 80 or less, such as 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 orientation degrees 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, 80, 10 to 80, 20 to 80, 30 to 80, 40 to 80, or 50 to 80. These orientation degrees can be obtained by adjusting the average particle size (D50) of the secondary particles and the long axis length of the primary particles. In negative electrode active materials, the average particle size (D50) of the secondary particles can be significantly reduced to lower the high resistivity of natural graphite.

[0034] As described below, the average particle size (D50) of the secondary particles in the negative electrode active material is significantly smaller than the long axis length of the primary particles. The secondary particles can be produced by wrinkling the primary particles. The negative electrode active material may include amorphous carbon and can be manufactured by heat treatment at 2500°C or higher, as described below, thereby achieving a high degree of graphitization. A high degree of graphitization can help improve the capacity of the negative electrode active material and prevent efficiency reduction caused by the decrease in the low average particle size of the secondary particles and the increase in specific surface area. In this respect, the d002 of the negative electrode active material is 3.356 Å to 3.360 Å. Within this range, the decrease in battery efficiency caused by the increase in specific surface area of ​​the negative electrode active material, which includes secondary particles with a relatively small average particle size (D50), can be offset, and high capacity can be provided. 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, 3.360Å.

[0035] According to one or more embodiments, the negative electrode active material can have an Hg cumulative pore volume of 0.01 mL / g to 0.06 mL / g (e.g., 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, or 0.03 mL / g to 0.05 mL / g). Within this range, significantly higher negative electrode active material efficiency can be achieved due to the small pores (i.e., voids) in the negative electrode active material and the appropriate amount of amorphous carbon therein. Furthermore, the internal region of the negative electrode active material that reacts with the electrolyte is not excessively large, and a sufficient density is maintained to allow for good electrolyte impregnation, thereby ensuring a suitable lifetime without excessive side reactions. The Hg cumulative pore volume can be a characteristic of the negative electrode active material prepared by the preparation method described below, in order to reduce the specific surface area while including small particles of natural graphite.

[0036] According to one or more embodiments, the negative electrode active material may have a sphericity (S) of 0.85 or greater according to Equation 1 below: Equation 1 Sphericity (S) = 4π × A / B 2 (In Equation 1, A is the area of ​​the negative electrode active material, and B is the perimeter of the negative electrode active material.)

[0037] In one or more embodiments, B may be the perimeter of the actual shape of the negative electrode active material.

[0038] The sphericity of the negative electrode active material can be a value obtained by projecting a three-dimensional particle onto a two-dimensional plane. For example, sphericity can be the ratio of the outline of a real particle to the outline of a circle with the same area as the real particle.

[0039] In Equation 1, area A represents the area of ​​a circle with the same perimeter as the actual perimeter B of the particle, which has been obtained using pressure-controlled scanning electron microscopy (CP-SEM) via SEM images of the electrode profile and calculated from the profile images using the ImageJ program. In one or more embodiments, the actual perimeter may refer not only to the perimeter when the particle has a perfectly spherical shape, but also to the length obtained along the perimeter even when the particle is not perfectly spherical and has non-uniform regions.

[0040] The sphericity of the negative electrode active material can be 0.85 to 1.0, 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, 1.0, 0.90 to 1.0, 0.90 to 0.98, or 0.90 to 0.95. When the sphericity falls within the above range, the expansion rate during charging and discharging can be suppressed more effectively.

[0041] The negative electrode active material can have a particle density of 1.60 g / cc to 1.80 g / cc. Within this range, the internal porosity of the negative electrode active material and side reactions with the electrolyte can be reduced, thereby improving its lifetime characteristics. For example, particle 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, 1.80 g / cc, 1.70 g / cc to 1.80 g / cc.

[0042] The active material for the negative electrode can have a concentration from 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). Tap densities ranging from 0.75 g / cc to 1.0 g / cc, or from 0.95 g / cc to 1.20 g / cc, can be determined within the range of 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, 1.20 g / cc, 0.75 g / cc to 1.0 g / cc, or 0.95 g / cc to 1.20 g / cc. Within these ranges, the internal porosity of the negative electrode active material and side reactions with the electrolyte can be reduced, thereby improving lifetime characteristics. By using a conversion factor of 0.2907 cubic centimeters per millimeter (cm) 3 The tap density can be obtained by performing three cycles of applying 108N pressure to a GeoPyc 1360 micromeritics bottle with a chamber diameter of 19.1mm and a chamber diameter of 19.1mm.

[0043] The active material of the negative electrode can have a concentration of 10 m² / g (m²). 2 / g) or smaller (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, 7.5m 2 / g、8m 2 / g, 8.5m 2 / g、9m 2 / g, 9.5m 2 / g, 10m 2 / g、1m 2 / g to 10m 2 The specific surface area ( / g) can be considered. Within this range, the internal porosity of the negative electrode active material and its side reactions with the electrolyte can be reduced, 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 (MOUNTECH).

[0044] The internal porosity of the negative electrode active material can be 2% or less, for example, 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%, 2%, 1.8% or less, 1.5% or less, 1.0% to 1.5%, or 1.0% to 1.3%. Within these ranges, side reactions between the 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 can be quantitatively measured using a Barrett-Joyner-Halenda (BJH) analytical instrument.

[0045] The composition of the negative electrode active material used in rechargeable lithium batteries will be described in detail below.

[0046] The negative electrode active material includes natural graphite and a coating layer. The natural graphite includes secondary particles in which primary particles are assembled, and the coating layer surrounds the secondary particles and includes amorphous carbon.

[0047] Natural graphite can be in the form of flakes (needle-shaped or scale-shaped).

[0048] Primary particles can have a size from 10 micrometers (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). The major axis lengths are 120μm, 125μm, 130μm, 135μm, 140μm, 145μm, 150μm, 155μm, 160μm, 165μm, 170μm, 175μm, 180μm, 185μm, 190μm, 195μm, 200μm, 10μm to 100μm, 30μm to 60μm, or 20μm to 50μm. Within these ranges, secondary particles can be easily assembled, and the ratios described below can be easily achieved.

[0049] Here, "major axis length" refers to the length of the longest axis between the facing edges when the primary particles are formed into a plate shape.

[0050] In one or more embodiments, the primary particles may be formed in a plate-like shape, but this disclosure is not limited thereto.

[0051] The average particle size (D50) of the secondary particles can be 30 μm or smaller. Within this range, the secondary particles can easily achieve the ratios described below. For example, the average particle size (D50) of the secondary particles can be 5 μm or larger and 10 μm or smaller, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 6 μm or larger and less than 8 μm. Within this range, the secondary particles can easily achieve the above-mentioned orientation and sphericity.

[0052] Secondary particles may be spherical, but this disclosure is not limited thereto.

[0053] In one or more 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 less than or equal to 10. Within this range, the resistance of the negative electrode active material does not increase, and the fast charging performance does not decrease. For example, the ratio can be 2.1 to 10, 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, 10, 3 to 6, 4 to 6, or 5 to 6. Within the above range, the secondary particles can easily achieve the above-mentioned orientation and sphericity.

[0054] Amorphous carbon can be incorporated into a coating layer surrounding the surface of secondary particles. Amorphous carbon can reduce the internal porosity of the negative electrode active material and suppress side reactions between the negative electrode active material and the electrolyte, thereby improving rate performance.

[0055] The thickness of the coating layer containing amorphous carbon can range from 5 nanometers (nm) to 50 nm, for example, 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, 50 nm, 10 nm to 50 nm, or 20 nm to 50 nm. Within this range, side reactions with the electrolyte can be suppressed, and rate performance can be improved.

[0056] Amorphous carbon can be one or a mixture of soft carbon (e.g., pitch carbon), hard carbon, mesophase pitch carbides, and calcined coke.

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

[0058] The natural graphite and amorphous carbon in the negative electrode active material can be included in a weight ratio of 90:10 to 75:25 (e.g., 90:10 to 80:20, 90:10 to 85:15, or 90:10 to 88:12) relative to 100 parts by weight of the total amount of natural graphite and amorphous carbon. Within this range, side reactions with the electrolyte can be suppressed, and rate performance can be improved.

[0059] The method for preparing the negative electrode active material will be described below.

[0060] (1) Grinding natural graphite raw material with an average particle size (D50) of 120 μm or greater to obtain primary particles with the above-mentioned major axis length. In one or more embodiments, the natural graphite raw material can be ground by applying an air jet milling method. Air jet milling may include grinding at room temperature at 5 kg / cm². 2 Up to 20 kg / cm 2 Grinding natural graphite raw materials under certain conditions.

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

[0062] Assembly is a process to achieve a sphericity of 0.85 or greater, and can be achieved using a high-intensity mixer equipped with a high-speed rotating rotor and stator. In the sphericification process, the average particle size (D50) of the secondary particles can be adjusted by changing the pressure, shear rate, etc.

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

[0064] There are no particular limitations on the amorphous carbon precursor, as long as it is a material that forms a carbide. For example, the precursor may include one or more of phenolic resin, furan resin, epoxy resin, polyacrylonitrile resin, polyamide resin, polyimide resin, polyamide-imide resin, synthetic bitumen, petroleum bitumen, coal tar, and coal tar.

[0065] During mixing, natural graphite and amorphous carbon in the final product (i.e., the negative electrode active material) can be added in the manner described above in weight ratio.

[0066] (4) The negative electrode active material is obtained by calcination and heat treatment of the mixture obtained by mixing.

[0067] Heat treatment can be performed at temperatures of 2500°C or higher (e.g., 2500°C to 3500°C, or 2500°C to 3000°C). Within these ranges, negative electrode active materials comprising secondary particles satisfying the aforementioned ratios can readily achieve the aforementioned orientation, d002, and sphericity.

[0068] The heat treatment can be maintained for 1 to 5 hours, for example, 1 to 4 hours, 1 to 3 hours, or 2 to 3 hours.

[0069] Figure 1 This is a schematic diagram of the negative electrode active material according to one or more embodiments.

[0070] Reference Figure 1 The negative electrode active material includes natural graphite, amorphous carbon 5, and a coating layer 7. The natural graphite includes secondary particles 3 in which multiple primary particles 1 are assembled. The amorphous carbon 5 is present on the surface of the primary particles. The coating layer 7 surrounds the secondary particles 3 and includes the amorphous carbon 5. (Refer to...) Figure 1 Since the secondary particles 3 are assembled by forming the primary particles 1 into a curved shape in a spherical manner, natural graphite has a small size and a dense internal structure, which minimizes internal pores, reduces side reactions with electrolytes, and improves cycle life.

[0071] The negative electrode plate for a rechargeable lithium battery according to another embodiment includes a negative electrode active material for a rechargeable lithium battery according to one or more embodiments.

[0072] In one or more embodiments, the negative electrode plate may include 95 wt% or more (e.g., 95 wt% to 100 wt%, or 100 wt%) of the aforementioned negative electrode active material for rechargeable lithium batteries in the negative electrode active material.

[0073] The negative electrode plate may also include one or more of a binder and a conductive material. The binder and conductive material will be described below.

[0074] According to yet another embodiment, the rechargeable lithium battery includes a negative electrode active material for a rechargeable lithium battery.

[0075] In one or more embodiments, the rechargeable lithium battery may include a negative electrode and a positive electrode, the negative electrode including the negative electrode active material described above for the rechargeable lithium battery.

[0076] 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).

[0077] 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.

[0078] The negative electrode active material includes the negative electrode active material according to the above embodiments. In a specific example, the negative electrode active material according to the above embodiments may be included in the negative electrode active material layer in an amount of 95 wt% or more (e.g., 95 wt% to 100 wt%, or 100 wt%) of the total negative electrode active material.

[0079] In addition to including 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.

[0080] Materials capable of reversibly inserting / deintercalating 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 amorphous, flake, sheet, spherical, or fibrous natural or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0081] 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.

[0082] 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, Sn-based alloys, or combinations thereof.

[0083] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to the 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 particles (cores) in which primary silicon particles are assembled, and an amorphous carbon coating layer (shells) on the surface of the secondary particles. Amorphous carbon can also be between the primary silicon particles. For example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can exist dispersed in an amorphous carbon matrix.

[0084] 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.

[0085] 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.

[0086] A binder can be used to make the negative electrode active material particles adhere well to each other and also to make the negative electrode active material adhere well to the current collector.

[0087] The binder can include a non-aqueous binder, an aqueous binder, a dry binder, or combinations thereof.

[0088] 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 combinations thereof.

[0089] 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.

[0090] When an aqueous binder is used as the negative electrode binder, it may also include a cellulose compound capable of imparting viscosity. The cellulose compound may include at least one of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may include Na, K, or Li.

[0091] Dry adhesives can be polymeric materials capable of taking the form of fibers. For example, dry adhesives can be polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0092] Conductive materials can be used to impart conductivity (e.g., electrical conductivity) to electrodes. Any 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 the battery. Non-limiting examples of conductive materials 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 in the form of metal powders or fibers, including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0093] The negative electrode current collector may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0094] positive electrode The positive electrode for a rechargeable lithium 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 conductive material. For example, the positive electrode may also include additives that can be used as a sacrificial positive electrode.

[0095] Positive electrode active material The positive electrode active material may include compounds capable of intercalating and deintercalating lithium (lithium-intercalating compounds). Specifically, at least one of the composite oxides of lithium with metals selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0096] The composite oxide can be a lithium transition metal composite oxide. Specific 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.

[0097] As an example, the following compounds, 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, 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, 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, 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, 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, 0≤e≤0.1); Li a NiG b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn1-g G g PO4 (0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3 (0≤f≤2); or Li a FePO4 (0.90≤a≤1.8).

[0098] 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; L 1 It is Mn, Al, or a combination thereof.

[0099] The positive electrode active material can be, for example, a high-nickel positive electrode active material. Based on 100 mol% of the metals other than lithium in the lithium transition metal composite 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%, or 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 used in high-capacity, high-density rechargeable lithium batteries.

[0100] 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%. Based on the 100wt% positive electrode active material layer, the amounts of binder and conductive material can be from about 0.5wt% to about 5wt%, respectively.

[0101] The binder is used to ensure good adhesion between the positive electrode active material particles and also to ensure good adhesion of the positive electrode active material to the current collector. 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.

[0102] Conductive materials can be used to impart conductivity (e.g., electrical conductivity) to electrodes. Any material that does not cause chemical changes in the battery (e.g., does not cause undesirable chemical changes in rechargeable lithium batteries) and conducts electrons can be used. 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 in the form of metal powders or fibers, including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0103] Al can be used as a current collector, but is not limited to this.

[0104] Rechargeable lithium batteries may also include an electrolyte.

[0105] electrolyte Electrolytes used in rechargeable lithium batteries may include non-aqueous organic solvents and lithium salts.

[0106] Non-aqueous organic solvents can be used as a medium for transporting ions that participate in the electrochemical reactions of a battery.

[0107] Non-aqueous organic solvents can be carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0108] Carbonate solvents can include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), etc.

[0109] Ester solvents can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc.

[0110] Ether solvents can include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents can include cyclohexanone, etc. Alcohol solvents can include ethanol, isopropanol, etc. Aprotic solvents can include: nitriles, such as R-CN (where R is a C2 to C20 straight-chain, branched, or cyclic hydrocarbon group, and may include double bonds, aromatic rings, or ether bonds, etc.); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane, etc.

[0111] Non-aqueous organic solvents can be used alone or in combination of two or more.

[0112] In addition, when using carbonate solvents, 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.

[0113] 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).

[0114] Rechargeable lithium batteries may also include a separator.

[0115] diaphragm Depending on the type of rechargeable lithium battery, a separator can be present between the positive and negative electrodes. The separator can include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof, such as hybrid multilayer films (e.g., polyethylene / polypropylene bilayer separators, polyethylene / polypropylene / polypropylene trilayer separators, polypropylene / polypropylene / polypropylene trilayer separators, etc.).

[0116] The membrane may include a porous substrate and a coating layer on one or both surfaces of the porous substrate, comprising organic materials, inorganic materials, or combinations thereof.

[0117] Porous substrates can be made from a selection of polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyetherketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (e.g., TEFLON). ® A polymer film formed from any one of the substances mentioned above, or a copolymer or mixture of two or more of the aforementioned substances.

[0118] Organic materials may include polyvinylidene fluoride polymers or (meth)acrylic acid polymers.

[0119] Inorganic materials may include, but are 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.

[0120] Organic and inorganic materials can be mixed in a single coating layer, or coating layers comprising organic materials and coating layers comprising inorganic materials can be stacked.

[0121] Rechargeable lithium batteries Rechargeable lithium batteries can be classified according to their shape, such as cylindrical batteries, prismatic batteries, pouch batteries, or coin-shaped batteries.

[0122] Figures 2 to 5 This is a schematic diagram illustrating a rechargeable lithium battery according to an embodiment. Figure 2 A cylindrical battery is shown. Figure 3 A prismatic battery is shown. Figure 4 and Figure 5 A pouch-type battery is shown. (See reference) Figures 2 to 5 The rechargeable lithium battery 100 may include an electrode assembly 40 and a housing 50 therein housing the electrode assembly 40, the electrode assembly 40 including a separator 30 between a positive electrode 10 and a negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 2 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of the sealed housing 50. Figure 3 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 4 and Figure 5 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.

[0123] 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.

[0124] Terms such as “substantially,” “about,” and “approximately” are used as relative terms rather than terms of degree and are intended to account for inherent deviations in measured or calculated values ​​that would be recognized by one of ordinary skill in the art. Taking into account the limitations and errors associated with the measurement of a quantity, terms such as “substantially,” “about,” and “approximately” can include deviations from the stated value and from an acceptable range as determined by one of ordinary skill in the art. For example, “about” can refer to one or more standard deviations, or ±30%, ±20%, ±10%, ±5% of the stated value.

[0125] The numerical ranges disclosed herein include, and are intended to include, all subranges having the same numerical precision. For example, the range “1.0 to 10.0” includes all subranges having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0 (such as 2.4 to 7.6). The applicant therefore reserves the right to amend this specification and the claims to expressly describe any subranges included within the range expressly described herein.

[0126] Examples and comparative examples of this disclosure will be described below. However, the following examples are merely exemplary, and this disclosure is not limited thereto.

[0127] Example Example 1 Thin flakes of natural graphite with an average particle size (D50) of 120 μm were ground into primary particles with a plate-like shape and a long axis length of 30 μm using an air jet milling method. The primary particles were then assembled into spherical secondary particles with an average particle size (D50) of 7 μm using a spheroidizing device. Pitch carbon was added to the secondary particles, mixed, and heat-treated in a furnace at 3000 °C for 2 hours to prepare the negative electrode active material. The addition of pitch carbon resulted in a natural graphite:amorphous carbon weight ratio of 90:10 in the first negative electrode active material.

[0128] A negative electrode active material slurry was prepared by mixing 97.5 wt% of the prepared negative electrode active material, 1.5 wt% of styrene-butadiene rubber as a binder, and 1.0 wt% of carboxymethyl cellulose as an additive in distilled water.

[0129] The negative electrode is manufactured by coating a copper current collector with a negative electrode active material slurry, and then drying and rolling the slurry-coated current collector.

[0130] A half-cell is constructed using a negative electrode plate, a lithium metal counter electrode, and an electrolyte. The electrolyte is a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 3:7) containing 1M LiPF6.

[0131] Example 2 Except for changing the spheroidization conditions in Example 1, the negative electrode active material was prepared in the same manner as in Example 1, and then the negative electrode and half cell were manufactured.

[0132] Example 3 Except for changing the spheroidization conditions in Example 1, the negative electrode active material was prepared in the same manner as in Example 1, and then the negative electrode and half cell were manufactured.

[0133] Example 4 The negative electrode and half cell are manufactured in the same manner as in Example 1, except that 1.5 wt% of polyvinylidene fluoride (PVDF) is used instead of 1.5 wt% of styrene-butadiene rubber as a binder used in Example 1.

[0134] Example 5 The negative electrode active material is prepared in the same manner as in Example 1. The prepared negative electrode active material is used to manufacture a negative electrode plate for a dry electrode.

[0135] Specifically, 97.5 wt% of the prepared negative electrode active material and 2.5 wt% of polytetrafluoroethylene (PTFE) as a binder were placed in a solvent-free mixer and mixed at 10,000 rpm for 1 minute to obtain a mixture. The resulting mixture was then placed in a kneader and kneaded at 110°C and 60 rpm for 5 minutes to obtain a blended material. The blended material was then placed in a mixer and pulverized at 10,000 rpm for 40 seconds to obtain electrode powder. Subsequently, the electrode powder was repeatedly pressed using a calendering roller (roller diameter: 200 mm, roller temperature: 80°C) to obtain an active material layer (thickness: 150 μm). The prepared active material layer was laminated onto a copper current collector with a primer layer and rolled to manufacture a negative electrode. A half-cell was manufactured using the manufactured negative electrode in the same manner as in Example 1.

[0136] Comparison Example 1 Except for not adding the pitch carbon as in Example 1, the negative electrode active material, negative electrode, and half cell are manufactured in the same manner as in Example 1.

[0137] Comparison Example 2 Natural graphite raw material with an average particle size (D50) greater than 120 μm was pulverized into primary particles with an elongation length of 120 μm using an air jet milling method. The primary particles were then assembled into spherical secondary particles with an average particle size (D50) of 20 μm using a spheroidizing device. The negative electrode active material was prepared by adding pitch carbon to the secondary particles, mixing them, and then heat-treating the resulting mixture in a furnace at 1200 °C for 2 hours. The addition of pitch carbon resulted in a natural graphite:amorphous carbon weight ratio of 90:10 in the first negative electrode active material.

[0138] The prepared negative electrode active material is used to manufacture the negative electrode and half cell in the same manner as in Example 1.

[0139] Comparison Example 3 Artificial graphite with an average particle size (D50) of 15 μm was used as the negative electrode active material, and the negative electrode active material slurry, negative electrode and half cell were manufactured in the same manner as in Example 1.

[0140] Compare Example 4 Natural graphite raw material with an average particle size (D50) of 80 μm was pulverized into primary particles with an elongation length of 7 μm using an air jet milling method. The primary particles were then assembled into spherical secondary particles with an average particle size (D50) of 15.6 μm using a spheroidizing device. The negative electrode active material was prepared by adding pitch carbon to the secondary particles, mixing them, and then heat-treating the resulting mixture in a furnace at 1200 °C for 2 hours. The addition of pitch carbon resulted in a natural graphite:amorphous carbon weight ratio of 90:10 in the first negative electrode active material.

[0141] The prepared negative electrode active material is used to manufacture the negative electrode and half cell in the same manner as in Example 1.

[0142] Experimental Example Particle density (unit: grams per cubic centimeter (g / cc)) Particle density was measured using a Carver 4350.L (CARVER) particle density meter. The powder density was measured after 1.0 g of each of the example and comparative example negative electrode active materials were added to the mold, while the mold was held under a pressure of 2.0 tons for 30 seconds.

[0143] Orientation Orientation was measured using an XRD analyzer X'Pert Pro (PANalytical). The ratio of the diffraction peak intensity I(002) of the (002) plane to the diffraction peak intensity I(110) of the (110) plane was measured for each of the negative electrode active materials of the example and comparative examples by using X-ray diffraction analysis of CuKα radiation.

[0144] d002 (unit: Å) d002 was measured using an XRD analyzer X'PertPro (PANalytical). The interplanar spacing of the (002) plane was measured in each of the negative electrode active materials of the example and comparative examples using X-ray diffraction analysis with CuKα radiation.

[0145] Hg cumulative pore volume (unit: ml / g) The cumulative Hg pore volume in each of the example and comparative negative electrode active materials was measured using an AutoPore V (Micromeritics) mercury porosimeter. The negative electrode active material was placed in a dedicated sample cup, surrounded by mercury, and pressures ranging from 0.2 psi to 60,000 psi were applied to allow the mercury to penetrate the material. The cumulative Hg pore volume was then measured by monitoring changes in the mercury volume in the capillary reservoir, and the mercury porosity was calculated based on the measured cumulative Hg pore volume. Pore sizes ranging from 0.01 μm to 100 μm can be determined using this method. Generally, pores with a size of 0.01 μm or larger and 5 μm or smaller are considered pores in the negative electrode active material.

[0146] Sphericity: Sphericity was measured using a Morphologi 4 (Malvern) sphericity analyzer. For each of the negative electrode active materials in the example and comparative examples, values ​​A and B in Equation 1 were obtained, and then sphericity was calculated according to Equation 1.

[0147] Capacity (unit: mAh / g) and charging C-rate (unit: %) The manufactured half-cells were charged and discharged at 0.1C to measure their charge and discharge capacities. The measured discharge capacities are shown in Table 1 below, and the coulombic efficiency (discharge capacity / charge capacity × 100%) was measured.

[0148] The manufactured half-cells were subjected to one cycle of 0.2C constant current (CC) / constant voltage (CV) charging and 0.2C discharging, one cycle of 0.5CCC charging and 0.2C discharging, one cycle of 1C CC charging and 0.2C discharging, and one cycle of 2C CC charging and 0.2C discharging, and then the charging characteristics were calculated. Here, the charging conditions were a 10mV cutoff for the CC phase and a 15-hour cutoff for the CV phase, and the discharging condition was a 1.5V cutoff. The charging characteristics were measured at each C rate. The charging characteristics were evaluated by calculating the ratio of the 2C CC charging capacity to the 0.2C CC charging capacity.

[0149] DC internal resistance (DC-IR, unit: ohms (Ω)) Each of the half-cells manufactured according to the example and comparative examples was subjected to one charge / discharge cycle under the following conditions: charging at a constant current / constant voltage (CC / CV) of 0.2C with a cutoff condition of 10mV and 0.01C; resting for 10 minutes; discharging at a constant current (CC) of 0.2C with a cutoff condition of 1.5V; and resting for 10 minutes. Subsequently, the voltage drop (V) was measured while a 3C current was applied for 1 second at SOC50 (where SOC50 refers to a cell's charge being 50% of its capacity, meaning the cell is 50% discharged in the discharge state). The resistance value was calculated from the measured voltage drop and the applied current (3C), and the result was expressed as DC internal resistance (DC-IR).

[0150] Rion (unit: ohms (Ω)): The fabricated negative electrode plate is used to create symmetrical monomers to measure EIS, from which Rion can be calculated using the Nyquist plot.

[0151] The evaluation results are shown in Table 1 below.

[0152] Table 1

[0153] As shown in Table 1, each of the example negative electrode active materials for rechargeable lithium batteries provides high energy density and fast-charging performance. Each example negative electrode active material has a low DC-IR, which helps prevent lithium plating during high-rate charging. Additionally, each example negative electrode active material has a low Rion (representing ion resistance), which facilitates lithium-ion movement within the electrode plate and is therefore expected to benefit fast charging. Furthermore, compared to each comparative example negative electrode active material, each example negative electrode active material has a small size, thus allowing for the fabrication of thin-film electrode plates, which is advantageous for manufacturing batteries suitable for fast charging. Therefore, the example negative electrode active materials can provide fast-charging performance and long cycle life.

[0154] However, as shown in Table 1, compared with the example negative electrode active material, the comparative example negative electrode active material not only has lower rate performance, but also higher DC-IR and higher Rion, demonstrating that the fast charging performance and long cycle life are significantly reduced compared with the example negative electrode active material.

[0155] While one or more embodiments of this disclosure have been described above, this disclosure is not limited thereto, and various modifications can be made within the scope of the claims and their equivalents, the detailed description of this disclosure, and the accompanying drawings. Clearly, these modifications also fall within the scope of this disclosure.

Claims

1. A negative electrode active material, said negative electrode active material comprising: Natural graphite, including secondary particles assembled from primary particles; as well as A coating layer surrounds the secondary particles and comprises amorphous carbon. The negative electrode active material has a d002 value of 3.356 Å to 3.360 Å and an orientation degree of 90 or less. The negative electrode active material is used in rechargeable lithium batteries.

2. The negative electrode active material according to claim 1, wherein, The negative electrode active material has an Hg cumulative pore volume of 0.01 mL / g to 0.06 mL / g.

3. The negative electrode active material according to claim 1, wherein, The 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 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 D50 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 flake-shaped, and the secondary particles are spherical.

7. The negative electrode active material according to claim 1, wherein, The major axis length of the primary particles is in the range of 10 μm to 200 μm.

8. The negative electrode active material according to claim 1, wherein, The average particle size D50 of the secondary particles is 30 μm or smaller.

9. The negative electrode active material according to claim 1, wherein, The natural graphite mentioned is in the form of thin flakes.

10. The negative electrode active material according to claim 1, wherein, The amorphous carbon is a mixture selected from at least one of soft carbon, hard carbon, mesophase pitch carbide and calcined coke.

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

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

13. The negative electrode active material according to claim 1, wherein, The total amount of natural graphite and amorphous carbon in the negative electrode active material is 100 parts by weight, and the weight ratio of natural graphite to amorphous carbon is 90:10 to 75:

25.

14. A negative electrode plate comprising the negative electrode active material according to claim 1 for a rechargeable lithium battery.

15. A rechargeable lithium battery, said rechargeable lithium battery comprising: The negative electrode includes the negative electrode active material according to claim 1 for use in a rechargeable lithium battery; as well as Positive electrode.

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