Negative electrode plate for rechargeable lithium battery and rechargeable lithium battery comprising the same

Abstract

Disclosed are a negative electrode plate for a rechargeable lithium battery and a rechargeable lithium battery including the same. The negative electrode plate includes a negative electrode active material. The negative electrode active material includes a mixture of a first negative electrode active material, a second negative electrode active material, and a third negative electrode active material. The first negative electrode active material includes natural graphite including secondary particles each formed of primary particles, and an amorphous carbon coating layer surrounding the secondary particles, and the first negative electrode active material has an orientation degree of 90 or less and a d002 of 3.356 Å to 3.360 Å. The second negative electrode active material is graphite. The binder includes a (meth)acrylic-based binder.

Description

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2024-0175706, filed on November 29, 2024, Korean Patent Application No. 10-2024-0175707, and Korean Patent Application No. 10-2024-0175711, 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 plate for a rechargeable lithium battery and a rechargeable lithium battery including the negative electrode plate. Background Technology

[0003] 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 capacity has increased rapidly. Therefore, research and development to improve the performance of rechargeable lithium batteries is actively underway.

[0004] A rechargeable lithium battery includes a positive electrode and a negative electrode containing active materials capable of inserting and deintercalating lithium ions. The secondary battery generates electrical energy through oxidation and reduction reactions as lithium ions are deintercalated from the positive electrode and inserted into the negative electrode, and vice versa. Summary of the Invention

[0005] This disclosure aims to provide a negative electrode plate for rechargeable lithium batteries that exhibits high energy density and boost charging performance.

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

[0007] According to an aspect of this disclosure, a negative electrode plate for a rechargeable lithium battery is provided, the negative electrode plate comprising a negative electrode active material and a binder, wherein the negative electrode active material comprises a mixture of a first negative electrode active material, a second negative electrode active material, and a third negative electrode active material, the first negative electrode active material comprising natural graphite, the natural graphite comprising secondary particles all formed of primary particles, and a coating layer surrounding the secondary particles and comprising amorphous carbon, and the negative electrode active material having an orientation degree of 90 or less and a d002 of 3.356 Å to 3.360 Å, the second negative electrode active material being graphite, and the third negative electrode active material comprising one or more of the following negative electrode active materials (i), (ii), and (iii): The negative electrode active material (i) includes: a core comprising silicon nanoparticles and amorphous carbon; and an amorphous carbon coating layer surrounding the core and comprising amorphous carbon. The negative electrode active material (ii) comprises: a composite of silicon and crystalline carbon; and an amorphous carbon coating layer formed on the surface of the composite and comprising amorphous carbon; and The negative electrode active material (iii) comprises silicon nanoparticles and an amorphous carbon coating layer disposed on the surface of the silicon nanoparticles, and the negative electrode active material (iii) has a sphericity of 0.9 to 1.0; and Adhesives include (meth)acrylic adhesives.

[0008] According to another aspect of this disclosure, a rechargeable lithium battery is provided, the rechargeable lithium battery including a negative electrode plate and a positive electrode for the rechargeable lithium battery. Attached Figure Description

[0009] The features and advantages of this disclosure will become more apparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings.

[0010] 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 third negative electrode active material according to an embodiment; Figure 3 This is a conceptual diagram of the interparticle distance of the third negative electrode active material according to an embodiment; Figure 4 This is a conceptual diagram of the third negative electrode active material according to an embodiment; and Figures 5 to 8 This is a schematic cross-sectional view of a rechargeable lithium battery according to an embodiment. Detailed Implementation

[0011] Embodiments of this disclosure will be described in detail below. However, the embodiments are given by way of example, and this disclosure is not limited to the examples.

[0012] 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 it is “directly on” the other component, but also the case where there is another component in between.

[0013] Unless otherwise stated herein, the singular may also include the plural. Furthermore, unless otherwise stated, “A or B” may mean “including A,” “including B,” or “including both A and B.”

[0014] In this specification, “combination of them” may mean mixtures, laminates, complexes, copolymers, alloys, blends and reaction products of the components.

[0015] Unless otherwise defined herein, particle size can refer to the average particle diameter. Alternatively, particle size refers to the average particle size (D50), which is the diameter of particles representing 50 vol% of the cumulative volume in a particle size distribution. The average particle size (D50) can be measured using methods known to those skilled in the art, such as particle size analyzers, transmission electron microscopy, or scanning electron microscopy. Alternatively, the average particle size can be measured using a measuring device utilizing 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, the average particle size can be measured using laser diffraction. When measuring average particle size by laser diffraction, more specifically, the target particles can be dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size measurement device (such as the MT 3000 from Microtrac), and irradiated with ultrasound at an output of 60W at approximately 28kHz. The average particle size (D50) can then be calculated based on 50% of the particle size distribution.

[0016] When the particles are spherical, size can refer to diameter.

[0017] Particle size can be measured using a particle size analyzer (Beckman Coulter, LS 13 320 XR).

[0018] According to an exemplary embodiment, the negative electrode plate for a rechargeable lithium battery can provide long lifespan, high energy density, and boost charging performance.

[0019] A negative electrode plate for a rechargeable lithium-ion battery according to an exemplary embodiment includes a negative electrode active material and a binder, wherein the negative electrode active material includes a mixture of a first negative electrode active material, a second negative electrode active material, and a third negative electrode active material; the first negative electrode active material includes: natural graphite, comprising secondary particles assembled from primary particles; and an amorphous carbon coating layer surrounding the secondary particles; the first negative electrode active material has an orientation degree of 90 or less and a d002 of 3.356 Å to 3.360 Å; the second negative electrode active material is graphite; the third negative electrode active material includes: a core, comprising silicon nanoparticles and amorphous carbon; and an amorphous carbon coating layer surrounding the core and comprising amorphous carbon; and the binder includes a (meth)acrylic acid binder. When the negative electrode plate for a rechargeable lithium-ion battery includes a mixture as the negative electrode active material, the negative electrode plate provides high capacity retention and can also provide high energy density, boost charging performance, long lifespan, and low swelling rate. When the negative electrode plate used in rechargeable lithium batteries comprises a mixture of negative electrode active materials and a (meth)acrylic binder as a binder, the negative electrode plate can be highly effective in providing energy density, boost charging and long lifespan, as well as low expansion rate.

[0020] In one embodiment, the mixture may be included in an amount of 95% by weight or greater (e.g., 95% to 100% by weight, 99% to 100% by weight, or 100% by weight) based on the total weight of the negative electrode active material in the negative electrode plate. Within these ranges, the effects of the aforementioned negative electrode plate can be readily achieved.

[0021] In other embodiments, the mixture of negative electrode active materials may be included in the negative electrode plate in an amount of 90% to 99.5% by weight (e.g., 95% to 99.5% by weight or 90% to 99% by weight). Within these ranges, capacity improvement effects can be achieved.

[0022] When the first negative electrode active material is absent from the mixture, the density of the negative electrode plate may decrease, making it difficult to provide battery cells with high energy density, and the boost charging effect may be reduced. When the second negative electrode active material is absent from the mixture, the lifespan effect under high temperature environments may be reduced. When the third negative electrode active material is absent from the mixture, the capacity per unit volume may decrease.

[0023] In some embodiments, the first negative electrode active material may be present in an amount ranging from 20% to 75% by weight (e.g., 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%, 48%, 49%, 50%, 51%, 52%, 53%, 54%). The second negative electrode active material may be included in the mixture in amounts of 20% to 65% (e.g., 20% to 65% by weight, or 20% to 60% by weight) from 55% to 75% by weight (e.g., 20% to 75% by weight, 55% to 65% by weight, 56% to 57% by weight, 58% to 79% by weight, 60% to 60% by weight, 61% to 62% by weight, 63% to 64% by weight, 65% to 66% by weight, 67% to 68% by weight, 69% to 70% by weight, 71% to 72% to 73% to 74% to 75% by weight, or 20% to 60% by weight). 9% by weight, 30% by weight, 31% by weight, 32% by weight, 33% by weight, 34% by weight, 35% by weight, 36% by weight, 37% by weight, 38% by weight, 39% by weight, 40% by weight, 41% by weight, 42% by weight, 43% by weight, 44% by weight, 45% by weight, 46% by weight, 47% by weight, 48% by weight, 49% by weight, 50% by weight, 51% by weight, 52% by weight, 53% by weight, 54% by weight, 55% by weight, 56% by weight, 57% by weight, 58% by weight, 59% by weight, 60% by weight, 61% by weight, 62% by weight, 63% by weight, 64% by weight, 65% by weight, 66% by weight, 67% by weight, 68% by weight, 69% by weight The third negative electrode active material may be included in an amount of 1% to 20% (e.g., 1% to 20% by weight, 70% by weight, 71% by weight, 72% by weight, 73% by weight, 74% by weight, 75% by weight, 20% to 65% by weight or 20% to 60% by weight), and may be included in an amount of 1% to 20% by weight (e.g., 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 1% to 15% by weight, 1% to 10% by weight or 5% to 7% by weight).Within these ranges, high energy density can be easily achieved, providing boost charging performance and improving boost charging lifespan.

[0024] In one specific embodiment, the amount of the third negative electrode active material in the mixture can be from 1 wt% to 15 wt% (e.g., 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 1 to 10 wt%), and the total amount of the first and second negative electrode active materials can be in the range of 85 wt% to 99 wt% (e.g., 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 99 wt%, or 90 to 99 wt%). Within these ranges, boost charging effect and boost charging life improvement effect can be achieved.

[0025] In one embodiment, the third negative electrode active material may be included with a specific capacity of 500 mAh / g or less.

[0026] Based on a total of 100 parts by weight of the first negative electrode active material and the second negative electrode active material, the weight ratio of the first negative electrode active material and the second negative electrode active material can be in the range of 10:90 to 90:10 (e.g., 25:75 to 75:25, 40:60 to 60:40, or 50:50). Within these ranges, boost charging effect and boost charging life improvement effect can be achieved.

[0027] In one specific embodiment, the negative electrode plate can have a density of 1.3 g / cc to 1.7 g / cc (e.g., 1.3 g / cc to 1.68 g / cc). Within these ranges, high energy density and easy boost charging can be achieved.

[0028] The components of the first negative electrode active material will be described in detail below.

[0029] (1) Active material of the first negative electrode The first negative electrode active material comprises: natural graphite, including secondary particles assembled from primary particles; and a coating layer surrounding the secondary particles and comprising amorphous carbon, wherein the first negative electrode active material has an orientation degree of 90 or less and a d002 of 3.356 Å to 3.360 Å.

[0030] In this disclosure, the term "orientation degree" 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 Cuα rays.

[0031] In this specification, the term "d002" may refer to the interplanar spacing of the (002) plane of the first negative electrode active material, as measured by X-ray diffraction analysis using Cuα rays.

[0032] Natural graphite is generally advantageous as a negative electrode active material in batteries; however, it suffers from poor charging characteristics due to its high resistivity. Furthermore, the numerous internal pores in natural graphite can lead to side reactions that negatively impact cycle life and expansion rate.

[0033] The first negative electrode active material can be prepared by significantly reducing the average particle size of secondary particles of natural graphite to a small particle form to provide low resistance. Furthermore, the efficiency reduction caused by the increased specific surface area of ​​the secondary particles is offset by calcining the secondary particles at the temperatures described below, thereby reducing the specific surface area and providing high efficiency.

[0034] The first negative electrode active material may include natural graphite and a coating layer comprising amorphous carbon, and satisfies the aforementioned orientation degree and d002. Therefore, the first negative electrode active material can improve battery capacity and significantly increase the charge rate (C-rate), thereby enhancing the boost charging performance of rechargeable lithium batteries. Although the first negative electrode active material includes natural graphite, it can significantly reduce resistance, provide high energy density, suppress side reactions with the electrolyte, and has improved lifespan.

[0035] The lower the orientation degree, the more randomly oriented the edge planes of natural graphite become, which increases the random orientation of the first negative electrode active material. Therefore, it promotes the insertion and extraction of lithium ions into and from the secondary particles of natural graphite, thereby improving the capacity characteristics of the rechargeable lithium battery. In the example, the orientation degree can be 80 or less, for example, 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, 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. Orientation can be achieved by controlling the average particle size D50 of the secondary particles and the long axis length of the primary particles. In the first negative electrode active material, the average particle size D50 of the secondary particles is significantly reduced to improve the high resistivity of natural graphite.

[0036] As described below, the average particle size D50 of the secondary particles in the first negative electrode active material is significantly smaller than the long axis length of the primary particles. The secondary particles can be manufactured by wrinkling the primary particles. The first negative electrode active material comprises amorphous carbon and can have a high degree of graphitization when it is produced by heat treatment at 2,500°C or higher as described below. A high degree of graphitization can help improve the capacity of the first negative electrode active material and can prevent efficiency reduction due to the decrease in average particle size and the increase in the specific surface area of ​​the secondary particles. In this respect, the d002 of the first negative electrode active material is 3.356 Å to 3.360 Å. Within this range, the decrease in battery efficiency due to the increase in specific surface area of ​​the first negative electrode active material, which includes secondary particles with a relatively small average particle size D50, can be offset, thereby providing 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.

[0037] According to embodiments, the first 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 0.06 mL / g). Within these ranges, significantly higher efficiency of the first negative electrode active material can be achieved due to the small pores (i.e., empty spaces) inside the first negative electrode active material and the appropriate amount of amorphous carbon inside the first negative electrode active material. Furthermore, the internal area of ​​the first negative electrode active material reacting with the electrolyte is not too large, and a density level that allows for good impregnation of the electrolyte can be maintained, thereby maintaining an appropriate lifetime without excessive side reactions. Although the first negative electrode active material comprises small particles of natural graphite, the Hg cumulative pore volume can be a characteristic of the first negative electrode active material produced by the manufacturing method described below to reduce the specific surface area.

[0038] According to an exemplary embodiment, the first negative electrode active material may have a sphericity S of 0.85 or greater, according to the following Equation 1: [Equation 1] Sphericity S = 4π × A / B 2 Where A represents the area of ​​the active material of the first negative electrode, and B represents the perimeter of the shape of the first negative electrode active material. In an exemplary embodiment, B may be the perimeter of the actual shape of the first negative electrode active material.

[0039] The sphericity of the first negative electrode active material can be a value obtained by projecting three-dimensional particles onto a two-dimensional plane. For example, sphericity can be the ratio of the boundary of the actual particle shape to the boundary of a circle with the same area.

[0040] In Equation 1 above, the area value A refers to the area of ​​a circle with the same perimeter as B, which is calculated after obtaining a scanning electron microscope (SEM) image of the electrode profile using controlled pressure scanning electron microscopy (CP-SEM SEM) and calculating the actual perimeter (B) of the particle from the profile image using the ImageJ program. In embodiments, the actual perimeter can refer not only to the perimeter when the particle has a spherical shape, but also to the length obtained along the perimeter even when the particle is not spherical and has non-uniform regions.

[0041] The first negative electrode active material can have a sphericity of 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 is within these ranges, the expansion rate during charging and discharging can be suppressed more effectively.

[0042] The first 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 first negative electrode active material and side reactions with the electrolyte can be reduced, thereby improving its lifetime characteristics. For example, the particle density can be from 1.60 g / cc to 1.80 g / cc, 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, or in the range of 1.70 to 1.80 g / cc.

[0043] The active material of the first negative electrode can 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, 0.9...). Tap densities of 8 g / cc, 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, and 0.75 g / cc to 1.0 g / cc or 0.95 g / cc to 1.20 g / cc can be achieved. Within these ranges, the internal porosity of the first negative electrode active material and side reactions with the electrolyte can be reduced, thereby improving lifetime characteristics. Tap density can be determined by using a conversion factor of 0.2907 cm⁻¹. 3 The specific gravity of the GeoPyc 1360 specific gravity bottle (Micromeritics Instruments) with a chamber diameter of 19.1 mm was obtained by applying a pressure of 108 N three times and calculating the average value.

[0044] The active material of the first negative electrode can have 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, 7.5m 2 / g、8m 2 / g, 8.5m 2 / g、9m 2 / g, 9.5m 2 / g, 10m 2 / g, or 1m 2 / g to 10m 2 The specific surface area ( / g) is considered. Within these ranges, the internal porosity of the first negative electrode active material and 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 Ltd.).

[0045] The internal porosity of the first negative electrode active material can be 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%, 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 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 can be quantitatively measured using a BJH (Barrett-Joyner-Halenda) analytical apparatus.

[0046] The active material of the first negative electrode will be described in detail below.

[0047] The first negative electrode active material includes: natural graphite, including secondary particles assembled from primary particles; and a coating layer surrounding the secondary particles, wherein the coating layer includes amorphous carbon.

[0048] Natural graphite can be in the form of flakes (needle-like, scaly, or sheet-like).

[0049] Primary particles can 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, 1 The primary particle has a major axis length of 20 μm, 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, 200 μm, 10 μm to 100 μm, 30 μm to 60 μm, or 20 μm to 50 μm. Within these ranges, assembly into secondary particles can be facilitated, and the ratios described below can be readily achieved. Here, the term "major axis length" refers to the length of the longest axis between opposite sides when the primary particle is plate-shaped. In some embodiments, the primary particle is plate-shaped, but this disclosure is not limited thereto.

[0050] Secondary particles can have an average particle size D50 of 30 μm or less. Within this range, the ratios described below can be easily achieved. For example, secondary particles can have an average particle size D50 of 5 μm or more and 10 μm or less (5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or 6 μm or more and 8 μm or less). Within these ranges, the aforementioned orientation and sphericity can be easily achieved.

[0051] Secondary particles can be spherical, but this disclosure is not limited thereto.

[0052] In one specific embodiment, 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 can remain unchanged and the boost charging performance can remain undegraded. For example, this 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, 10, 3 to 6, 4 to 6, or 5 to 6. Within these ranges, the orientation and sphericity described above can be easily achieved.

[0053] Amorphous carbon can be incorporated into a coating layer surrounding the surface of secondary particles. Amorphous carbon can reduce the internal porosity of the first negative electrode active material and suppress side reactions between the first negative electrode active material and the electrolyte, thereby improving the charge / discharge rate characteristics. The coating layer, including amorphous carbon, can 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, 50 nm, 10 nm to 50 nm, or 20 nm to 50 nm). Within these ranges, side reactions with the electrolyte can be suppressed, and charge / discharge rate characteristics can be improved.

[0054] Amorphous carbon can be one or more mixtures selected from soft carbon, hard carbon, mesophase pitch carbides, and calcined coke. Amorphous carbon may further exist on the surface of primary particles.

[0055] Based on a total of 100 parts by weight of natural graphite and amorphous carbon in the first negative electrode active material, the natural graphite and amorphous carbon may 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). Within these ranges, side reactions with the electrolyte can be effectively suppressed, and charge / discharge rate characteristics can be improved.

[0056] The method for preparing the first negative electrode active material will be described below.

[0057] (1) Primary particles with the aforementioned long axis length are obtained by grinding natural graphite raw materials whose average particle size D50 is 120 μm or greater. In one embodiment, the natural graphite raw materials can be ground by applying an air jet milling method. The air jet milling method may include grinding at 5 kg / cm² at room temperature. 2 Up to 20kg / cm 2 Natural graphite raw materials are ground under certain conditions.

[0058] (2) Use a spheroidizing device to assemble primary particles into secondary particles.

[0059] Assembly is designed to achieve a sphericity of 0.85 or higher and can be performed 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 controlled by varying pressure, shear rate, etc.

[0060] (3) Mix the prepared secondary particles with the amorphous carbon precursor.

[0061] There are no restrictions on amorphous carbon precursors, as long as they are materials that form carbides. For example, precursors may include one or more of phenolic resins, furan resins, epoxy resins, polyacrylonitrile resins, polyamide resins, polyimide resins, polyamide-imide resins, pitch carbon, synthetic pitch, petroleum pitch, coal tar, and coal tar.

[0062] In the mixing process, natural graphite and amorphous carbon can be added to the final product (i.e., the first negative electrode active material) so that natural graphite and amorphous carbon can exist in the above weight ratio.

[0063] (4) The first negative electrode active material is obtained by calcination and heat treatment of the mixture obtained by mixing.

[0064] Heat treatment can be performed at 2,500°C or higher (e.g., 2,500°C to 3,500°C, for example, 2,500°C to 3,000°C). Within these ranges, the first negative electrode active material comprising secondary particles satisfying the above ratios can be heat-treated to readily achieve the aforementioned orientation, d002, and sphericity.

[0065] The heat treatment can be maintained for 1 to 5 hours (e.g., 1 to 4 hours, 1 to 3 hours, or 2 to 3 hours).

[0066] Figure 1 This is a conceptual diagram of the first negative electrode active material according to an embodiment.

[0067] Reference Figure 1 The first negative electrode active material includes: natural graphite, comprising secondary particles 3 formed from a plurality of primary particles 1; amorphous carbon 5, present on the surface of the primary particles 1; and a coating layer 7, surrounding the secondary particles 3 and comprising the amorphous carbon 5. (See reference...) Figure 1 Because the secondary particles 3 are assembled by shaping the spherical primary particles 1 into a curved shape, natural graphite has a smaller size and a denser internal structure. This minimizes internal porosity, reduces side reactions with the electrolyte, and improves cycle life.

[0068] (2) Active material of the second negative electrode The second negative electrode active material can be graphite. In one embodiment, the second negative electrode active material can be one or more of natural graphite and artificial graphite. For example, the second negative electrode active material can be artificial graphite.

[0069] Artificial graphite can have an average particle size D50 of 10 μm to 20 μm (e.g., 13 μm to 18 μm or 15 μm to 20 μm). Within these ranges, the specific surface area may not increase significantly, thereby suppressing the increase of side reactions with the electrolyte and preventing degradation of boost charging performance. In some embodiments, artificial graphite can have a maximum particle size of 30 μm to 40 μm.

[0070] In some embodiments, the artificial graphite may have a lower particle density than the particle density of the first negative electrode active material. For example, the artificial graphite may have a particle density of 1.1 g / cc to 1.6 g / cc or 1.1 g / cc to 1.5 g / cc.

[0071] In some embodiments, the artificial graphite may have a tap density lower than that of the first negative electrode active material. For example, the artificial graphite may have a tap density of 0.5 g / cc to 1.0 g / cc or 0.5 g / cc to 0.9 g / cc.

[0072] In some embodiments, artificial graphite may have a density of 10 μm. 2 / g or less (e.g., 1m) 2 / g to 10m 2 The specific surface area is ( / g). Specific surface area can be the BET specific surface area.

[0073] In some embodiments, artificial graphite may have an orientation degree of 90 or greater. For example, artificial graphite may have an orientation degree of 90 to 100 or greater than 90 and 100 or less.

[0074] Artificial graphite can have, but is not limited to, a spherical shape. Artificial graphite can be one or more of single particles, primary particles, secondary particles assembled from primary particles, and tertiary particles assembled from secondary particles. In one specific embodiment, the secondary particles may also include a coating layer comprising amorphous carbon on their surface.

[0075] (3) Active material of the third negative electrode The third negative electrode active material may be a silicon-based negative electrode active material, and includes one or more of the following negative electrode active materials (i), (ii), and (iii): The negative electrode active material (i) includes: a core comprising silicon nanoparticles and amorphous carbon; and an amorphous carbon coating layer surrounding the core and comprising amorphous carbon. The negative electrode active material (ii) comprises a composite of silicon and crystalline carbon; and an amorphous carbon coating layer formed on the surface of the composite and comprising amorphous carbon; and The negative electrode active material (iii) includes silicon nanoparticles and an amorphous carbon coating layer formed on the surface of the silicon nanoparticles, and the negative electrode active material (iii) has a sphericity of 0.9 to 1.0.

[0076] Negative electrode active material (i) The negative electrode active material (i) includes a core comprising silicon nanoparticles and amorphous carbon, and an amorphous carbon coating layer surrounding the core and comprising amorphous carbon.

[0077] In one embodiment, the negative electrode active material (i) may be a binary negative electrode active material comprising silicon and amorphous carbon.

[0078] In the negative electrode active material (i), the interparticle distance between the silicon nanoparticles included in the core can be 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, or 35 nm or less. When the interparticle distance between the silicon nanoparticles falls within these ranges, the size of the pores and the total pore volume included in the core can be reduced. When the interparticle distance between the silicon nanoparticles is within these ranges, the volume of the pores present in the negative electrode active material (i) can be reduced, thereby preventing electrolyte from permeating into the core during battery operation. As a result, side reactions between the electrolyte and the negative electrode active material (i) can be suppressed, thereby improving battery life.

[0079] Here, the interparticle distance between silicon nanoparticles refers to the distance between the centers of the silicon nanoparticles. (See reference...) Figure 3 The silicon nanoparticles 2 have a short axis length a and a long axis length b. Therefore, in this case, the interparticle distance d is the distance between the centers of the silicon nanoparticles 2 as depicted. The number of silicon nanoparticles having interparticle distances within the above range is 50% to 100% (e.g., 60% to 100%, 70% to 100%, or 80% to 100%) of the total number of silicon nanoparticles included in the core.

[0080] Silicon nanoparticles can have an average particle size D50 of 50 nm to 150 nm (e.g., 50 nm or larger, 60 nm or larger, 70 nm or larger, or 80 nm or larger and 150 nm or smaller, 140 nm or smaller, 130 nm or smaller, or 115 nm or smaller). When the average particle size D50 of silicon nanoparticles falls within these ranges, side reactions with the electrolyte can be suppressed, and the expansion of silicon nanoparticles can be reduced, thereby improving initial efficiency and lifetime characteristics.

[0081] Silicon nanoparticles can exhibit a full width at half maximum (FWHM) of 0.3° to 7° at an X-ray diffraction angle (2θ) on the (111) plane using CuKα rays. This property can be utilized to improve lifetime. The FWHM of silicon nanoparticles at the X-ray diffraction angle (2θ) on the (111) plane using CuKα rays can be controlled by adjusting the size of the silicon particles or changing the manufacturing process of the silicon nanoparticles.

[0082] Silicon nanoparticles can have an aspect ratio of 2 to 8 (e.g., 2 to 6), and can have a minor axis length a of 20 nm to 50 nm and a major axis length b of 50 nm to 300 nm. When the aspect ratio, major axis length b, and minor axis length a of the silicon nanoparticles fall within these ranges, side reactions between the negative electrode active material (i) and the electrolyte can be suppressed, and the expansion of the silicon nanoparticles can be reduced, thereby improving initial efficiency and lifetime characteristics.

[0083] Based on the total weight of the negative electrode active material (i), silicon nanoparticles can be included in amounts of 20 wt% to 80 wt%, 30 wt% to 70 wt%, 30 wt% to 60 wt%, or 30 wt% to 50 wt%. When the amount of silicon nanoparticles is within these ranges, the battery capacity can be improved.

[0084] The amorphous carbon included in the core can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a combination thereof. When amorphous carbon is included in the core, the pore volume of the negative electrode active material (i) can be reduced, thereby suppressing side reactions with the electrolyte. Furthermore, it can buffer the expansion of silicon nanoparticles within the negative electrode active material (i), thereby suppressing battery swelling. Additionally, amorphous carbon can act as a binder, thus mitigating the cracking of the negative electrode active material (i) and maintaining its shape.

[0085] The coating layer may include amorphous carbon and may have a thickness of 1 nm to 900 nm (e.g., 5 nm to 800 nm). Such a thickness can reduce the specific surface area of ​​the negative electrode active material (i) and prevent the electrolyte from being introduced into the negative electrode active material (i). As a result, side reactions with the electrolyte can be minimized, and the battery life characteristics can be improved.

[0086] The amorphous carbon included in the coating layer can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a combination thereof, and can be the same as or different from the amorphous carbon included in the core.

[0087] Based on the total weight of the negative electrode active material (i), amorphous carbon can be included in an amount of 20 wt% to 80 wt% (e.g., 20 wt% to 70 wt%, 20 wt% to 60 wt%, 20 wt% to 50 wt%, or 20 wt% to 40 wt%). When the amount of amorphous carbon is within these ranges, side reactions between the negative electrode active material (i) and the electrolyte can be suppressed.

[0088] According to one embodiment, the negative electrode active material (i) can have an average particle size D50 of 2 μm to 15 μm (e.g., 3 μm to 13 μm or 5 μm to 10 μm). When the average particle size of the negative electrode active material (i) is within these ranges, lithium ions can easily diffuse into the negative electrode active material (i), thereby improving battery resistance and C-rate characteristics. Furthermore, by suppressing an excessive increase in the specific surface area of ​​the negative electrode active material (i), side reactions with the electrolyte can be reduced.

[0089] The average particle size D50 of the negative electrode active material (i) can be appropriately adjusted by controlling the disintegration and grinding conditions during the manufacturing of the negative electrode active material (i).

[0090] In the negative electrode active material (i), pores with a size of 200 nm or smaller can have a diameter of 3.0 × 10⁻⁶. -2 cm 3 / g or less (e.g., 2.5 × 10⁶ g) -2 cm 3 / g or less, 2.3×10 -2 cm 3 / g or less, 2.0×10 -2 cm 3 / g or less, 1.9×10 -2 cm 3 / g or less, 1.8×10 -2 cm 3 / g or less, 1.7×10 -2 cm 3 / g or less, 1.6×10 -2 cm 3 / g or less, 1.5×10 -2 cm 3 / g or less, 1.4×10 -2 cm 3 / g or less, 1.3×10 -2 cm 3 / g or less, 1.2×10 -2 cm 3 / g or less, 1.1×10 -2 cm 3 / g or less, 1.0×10 -2cm 3 / g or less, 0.9×10 -2 cm 3 / g or less, 0.8×10 -2 cm 3 / g or less, 0.7×10 -2 cm 3 / g or less, 0.6×10 -2 cm 3 / g or less or 0.5×10 -2 cm 3 Total pore volume ( / g or less). Within these ranges, side reactions between the electrolyte and silicon nanoparticles can be suppressed, thereby improving initial efficiency and lifetime characteristics.

[0091] The total pore volume of pores with a size of 200 nm or smaller can be quantitatively measured using the BJH (Barrett-Joyner-Halenda) analytical apparatus.

[0092] The negative electrode active material (i) can have a pore size of 200 nm or smaller (e.g., 170 nm or smaller, 150 nm or smaller, 130 nm or smaller, 100 nm or smaller, or 50 nm or smaller). When the pore size is within these ranges, side reactions between the electrolyte and silicon nanoparticles can be reduced, and batteries with improved initial efficiency and lifetime characteristics can be obtained.

[0093] The negative electrode active material (i) can have 10m 2 A BET specific surface area of ​​ / g or less. When the BET specific surface area is within this range, side reactions with the electrolyte can be suppressed, thereby improving the efficiency characteristics of the battery.

[0094] In the negative electrode active material (i), based on a total of 100 parts by weight of silicon nanoparticles and amorphous carbon, the silicon nanoparticles and amorphous carbon can be included in a weight ratio of 80:20 to 20:80 (e.g., 70:30 to 30:70, 70:30 to 40:60, or 70:30 to 50:50). When the silicon nanoparticles and amorphous carbon are within these ranges, the internal pore volume can be reduced, and the amorphous carbon can be uniformly dispersed in the interior and on the surface of the negative electrode active material (i). As a result, side reactions with the electrolyte can be suppressed, and the performance of the negative electrode active material (i) can be improved.

[0095] A method for preparing the negative electrode active material (i) according to embodiments of the present disclosure will be described.

[0096] The method for preparing the negative electrode active material (i) includes: mixing and dispersing silicon nanoparticles and amorphous carbon to prepare a mixture; spraying, drying and pressing the mixture to manufacture a molded body; and heat-treating the molded body.

[0097] Silicon nanoparticles and amorphous carbon were mixed and dispersed to prepare a mixture. The silicon nanoparticles and amorphous carbon were as described above.

[0098] The prepared mixture is sprayed, dried, and then pressed to produce a molded body.

[0099] Drying can be performed at temperatures ranging from 50°C to 150°C using a spray dryer.

[0100] Pressing can be performed at pressures ranging from 50 MPa to 150 MPa (e.g., 75 MPa to 150 MPa or 75 MPa to 125 MPa). When the molded body is pressed within these pressure ranges, the spacing between silicon nanoparticles can be appropriately maintained, and the volume of pores formed within the negative electrode active material (i) can be controlled, thereby suppressing side reactions between the electrolyte and silicon nanoparticles and improving initial efficiency and lifetime characteristics.

[0101] The molded body is heat-treated to prepare the negative electrode active material (i). The heat treatment can be performed at temperatures ranging from 700°C to 1,100°C (e.g., 800°C to 1,050°C or 900°C to 1,000°C). When heat treatment is performed within these temperature ranges, the strength of the negative electrode active material (i) can be enhanced as the amorphous carbon is carbonized. Furthermore, the conductivity of the negative electrode active material (i) can be improved, and the initial efficiency of the battery can be enhanced.

[0102] Heat treatment can be performed in a furnace under a nitrogen (N2) atmosphere.

[0103] In one embodiment, the negative electrode active material (i) may have a sphericity of 0.7 or greater and 0.7 or greater and 1.0 or less. Here, sphericity refers to the ratio (Lb / La) of the minor axis length (Lb) to the major axis length (La) when the negative electrode active material (i) has a circular or elliptical shape.

[0104] In some embodiments, the negative electrode active material (i) may have an elliptical or circular cross-section. Therefore, a sphericity of 1.0 means that the negative electrode active material (i) is substantially a perfect sphere. Thus, it should be understood that the maximum value of sphericity is 1.0 (and may not exceed 1.0).

[0105] When the sphericity of the negative electrode active material (i) is 0.7 or greater, the surface area of ​​the negative electrode active material (i) can be reduced. Therefore, since the area where the negative electrode active material (i) contacts the electrolyte or the area where the negative electrode active material (i) reacts with lithium is reduced, side reactions with the electrolyte and reactions with lithium can be reduced. Furthermore, volume expansion can be reduced through uniform expansion of the negative electrode active material (i) in the negative electrode.

[0106] When the BET specific surface area of ​​the negative electrode active material (i) is 10m² 2 / g or less (e.g., 0.5m) 2 / g to 10m 2 When the BET specific surface area of ​​the negative electrode active material (i) is 10 m² / g, this surface area reduction effect is more effective. 2 / g or less (e.g., 0.5m) 2 / g to 10m 2 When the concentration is / g), improved performance can exist and the initial efficiency can be enhanced by reducing contact with the electrolyte to suppress side reactions. That is, because the negative electrode active material (i) according to one embodiment has a sphericity of 0.7 or greater and 10m 2 With a BET specific surface area of ​​ / g or less, the negative electrode active material (i) can be an active material in which side reactions with the electrolyte are reduced and reactions with lithium are also reduced.

[0107] In the negative electrode active material (i), silicon nanoparticles are primary particles, and these primary particles can be included in the silicon-carbon composite as secondary particles formed from at least one primary particle. Therefore, the silicon-carbon composite can include secondary particles assembled from Si nanoparticles.

[0108] In some embodiments, silicon nanoparticles may be sheet-like, spherical, etc. However, this disclosure is not limited to these examples. Furthermore, secondary particles assembled from one or more primary particles may have a spherical shape.

[0109] Amorphous carbon can be configured to cover the surface of the secondary particles. That is, the negative electrode active material (i) can include a core comprising silicon nanoparticles, and according to one example, can include a secondary particle core assembled from one or more primary particles that are silicon nanoparticles, with amorphous carbon surrounding the core. Here, the core refers to a region disposed within the negative electrode active material (i). More specifically, the core refers to a region that is substantially not exposed to the outside because the core is surrounded by amorphous carbon. Therefore, the core can be referred to as a region disposed within the amorphous carbon surrounding the core.

[0110] Amorphous carbon can fill the spaces between primary particles, thus covering the surface of the primary particles. When amorphous carbon fills the spaces between primary particles, it can reduce the pore volume of the negative electrode active material (i), thereby suppressing side reactions with the electrolyte. Furthermore, when the primary particles expand, the amorphous carbon can buffer this expansion. Additionally, when the amorphous carbon filling the spaces between primary particles acts as a binder, it can prevent the negative electrode active material (i) particles from breaking and improve conductivity.

[0111] Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbides, calcined coke, or a combination thereof.

[0112] Silicon nanoparticles can be sheet-like. That is, silicon nanoparticles can have a sheet shape with both a long axis and a short axis. The long axis / short axis ratio (e.g., width / thickness ratio) of the silicon particles can be in the range of 5 to 20. When the long axis / short axis ratio of the silicon particles falls within this range, the expansion of the Si nanoparticles can be reduced, thereby improving the initial efficiency and lifetime characteristics of the battery including the negative electrode active material (i).

[0113] Silicon nanoparticles can have a particle size ranging from 10 nm to 200 nm. The particle size can be the average particle size. Here, the average particle size can refer to the particle size D50 measured by cumulative volume. Unless otherwise defined in this disclosure, the particle size D50 refers to the average particle size D50 representing the diameter of particles whose cumulative volume is 50% of the total volume in the particle size distribution. When the size of the Si nanoparticles falls within the above range, side reactions between the negative electrode active material (i) and the electrolyte can be suppressed, and the expansion of the Si nanoparticles can be reduced, thereby improving the initial efficiency and lifespan characteristics of the battery.

[0114] When silicon nanoparticles are secondary particles assembled from one or more primary particles, the secondary particles can have a particle size of 2 μm to 15 μm or 5 μm to 10 μm. Furthermore, the primary particles can have a particle size of 10 nm to 200 nm. When the average particle size of the negative electrode active material (i) is within these ranges, lithium ions can easily diffuse into the negative electrode active material (i), and the resistance and C-rate characteristics can be improved.

[0115] In one embodiment, the full width at half maximum (FWHM) (111) of the diffraction peak on the (111) plane of the silicon nanoparticle, as measured by X-ray diffraction using CuKα rays, can be from 0.3 degrees (°) to 7 degrees (°). When the FWHM (111) of the Si nanoparticle falls within this range, the battery life characteristics can be improved.

[0116] X-ray diffraction measurements can be performed using CuKα rays as the target ray. In this case, measurements are performed under the following conditions: 2θ = 40° to 50°, scan rate (° / s) of 0.04 to 0.06, and step size (° / step) of 0.01 to 0.03.

[0117] The mixing ratio of silicon nanoparticles to amorphous carbon can be from 8:2 to 2:8 by weight, and can be from 7:3 to 5:5 by weight. In one embodiment, since the silicon nanoparticles exist in the negative electrode active material (i) in the form of secondary particles assembled from primary particles, the mixing ratio of silicon nanoparticles to amorphous carbon can be regarded as the mixing ratio of secondary particles to amorphous carbon. When the mixing ratio of silicon nanoparticles to amorphous carbon falls within the above range, it can have better capacity (specifically, higher capacity) compared to crystalline carbon negative electrode active materials.

[0118] Amorphous carbon can exist as a coating layer on the surface of secondary particles, or it can fill between primary particles. Regardless of whether amorphous carbon is filled between primary particles, exists as a coating layer, or exists in any other form, the total amount of amorphous carbon included in the negative electrode active material (i) can be from 20% to 80% by weight, based on a total of 100% by weight of negative electrode active material (i).

[0119] In one embodiment, when amorphous carbon is present as a coating layer surrounding the surface of the secondary particles, the amorphous carbon can be present on the surface of the secondary particles with a thickness of 1 nm to 1,000 nm (e.g., 30 nm to 200 nm). When the thickness of the amorphous carbon layer falls within these ranges, the conductivity of the negative electrode active material (i) can be further improved, and contact with the electrolyte can be reduced, thereby effectively suppressing the increase in resistance due to the generation of by-reaction products.

[0120] In one embodiment, the negative electrode active material (i) may have a particle size of 40 μm or smaller (e.g., a particle size of 2 μm to 15 μm). When the particle size of the negative electrode active material (i) falls within these ranges, lithium ions can easily diffuse into the negative electrode active material (i) and can improve battery resistance and C-rate characteristics.

[0121] According to one embodiment, the negative electrode active material (i) can be prepared by the following process.

[0122] First, silicon particles are prepared. These silicon particles can be nanoparticles and can have a particle size of 10 nm to 200 nm. These nanoscale silicon particles can be obtained by conventional processes for preparing nanoparticles, such as grinding processes. For example, the full width at half maximum (FWHM) (111) of the diffraction peaks on the (111) plane of silicon nanoparticles, as measured by X-ray diffraction using CuKα rays, can be 0.3 degrees to 7 degrees.

[0123] Silicon particles are dispersed in a solvent to prepare a silicon particle solution. Any alcohol that readily evaporates without oxidizing the silicon particles can be used as the solvent. For example, isopropanol, ethanol, methanol, butanol, or combinations thereof can be used as the solvent. The concentration of the silicon particle solution is set to between 10% and 30% by weight.

[0124] The prepared silicon particle solution is spray-dried. This process assembles nanoscale silicon particles (primary particles) to prepare micron-sized spherical Si secondary particles. The secondary particles may include internal pores (i.e., gaps between primary particles). The sphericity of the manufactured negative electrode active material (i) can be controlled based on the type of nozzle and the atmosphere used. Specifically, a two-fluid nozzle capable of forming fine particles by mixing two fluids (liquid and gas) is desirable. When using a two-fluid nozzle, fine and spherical particles can be formed. Because the formed particles are small, no additional grinding process is required. Therefore, the spherical shape can be maintained. When a disc-shaped nozzle that sprays while rotating is used as the nozzle, large particles are formed, and an additional grinding process is required due to the large particle size. Furthermore, the formation of particles with various shapes (such as spherical, elliptical, and annular shapes) is undesirable.

[0125] Preferably, the spray drying process is carried out under an N2 atmosphere, for example, by blowing N2 at a flow rate of 40 L / min to 50 L / min or 30 L / min to 40 L / min. When the N2 flow rate falls within these ranges in the spray drying process, spherical microparticles of suitable size can be formed. When the N2 flow rate is less than 30 L / min, the sprayed product may aggregate, leading to an increase in particle size, which is undesirable. On the other hand, when the N2 flow rate is greater than 50 L / min, there may be a problem of the manufactured particles being too small and generating a large amount of fine powder.

[0126] Spray drying can be performed at temperatures ranging from 120°C to 170°C. When spray drying is performed within this temperature range, the temperature is sufficiently higher than the boiling point of the solvent. Therefore, it is desirable that micron-sized spherical Si particles can be thoroughly dried through rapid evaporation.

[0127] The resulting primary Si nanoparticles, assembled into spherical, micron-sized secondary Si particles, are mixed with an amorphous carbon precursor. The mixing ratio of the secondary particles to the amorphous carbon precursor can be 80:20 to 20:80 by weight, or 60:40 to 50:50 by weight.

[0128] The amorphous carbon precursor can be polyimide resin, furan resin, phenolic resin, polyvinyl alcohol resin, poly(meth)acrylic acid resin, polyurethane resin, cellulose resin, epoxy resin, polystyrene resin, petroleum asphalt, coal tar pitch, raw coke, mesophase pitch, kerosene, heavy petroleum oil, coke, or a combination thereof.

[0129] The resulting mixture is pressed and molded. This pressing and molding process can be performed under pressure that maintains the spherical shape of the micron-sized Si secondary particles. The pressure can be, for example, from 20 MPa to 150 MPa. Furthermore, the pressing and molding process can be performed for 1 to 5 minutes. When the pressing and molding process is performed, the micron-sized spherical Si secondary particles and the amorphous carbon precursor can adhere firmly to each other, and the amorphous carbon precursor can easily insert between the primary particles. Therefore, since the amorphous carbon precursor inserts into the pores formed inside the secondary particles, amorphous carbon can exist in the final negative electrode active material (i) between the primary particles in an appropriate amount (appropriate thickness). As a result, a coating layer can be formed on the surface of the secondary particles, giving the amorphous carbon an appropriate thickness. When the pressing and molding process is not performed, the micron-sized spherical secondary particles and the amorphous carbon precursor may not adhere firmly to each other, and the amorphous carbon precursor is not easily inserted between the primary particles, but rather mainly settles on the surface of the secondary particles. As a result, the amorphous carbon in the final negative electrode active material (i) exists on the surface of the secondary particles with an excessively thick thickness, which is undesirable.

[0130] The resulting pressed and molded product is heat-treated to manufacture a negative electrode active material (i) for a rechargeable lithium battery. The heat treatment process can be performed at 400°C to 1,200°C or 700°C to 1,000°C. When the heat treatment process is performed within these temperature ranges, the shape of the negative electrode active material (i) can be maintained as a spherical shape. Furthermore, since the amorphous carbon is carbonized, the conductivity of the negative electrode active material (i) can be improved, and the initial efficiency of the battery can be improved. The heat treatment process can be performed under an N2 atmosphere. When the amorphous carbon precursor is converted to amorphous carbon through this heat treatment process, the amorphous carbon precursor is included as amorphous carbon in the negative electrode active material (i).

[0131] Figure 2 This is a conceptual diagram of the negative electrode active material (i) according to an embodiment.

[0132] Reference Figure 2 The negative electrode active material (i) comprises: a core 4, comprising amorphous carbon and silicon nanoparticles 2; and a coating layer 6 surrounding the core 4. In the depicted embodiment, a pore 8 is included in the core.

[0133] Negative electrode active material (ii) The negative electrode active material (ii) comprises a composite of silicon and crystalline carbon. An amorphous carbon coating is formed on the surface of the composite and comprises amorphous carbon.

[0134] In one embodiment, the negative electrode active material (ii) may be a ternary negative electrode active material comprising silicon, crystalline carbon, and amorphous carbon.

[0135] In one embodiment, the negative electrode active material (ii) may include a composite core of silicon and crystalline carbon and an amorphous carbon coating layer formed on the surface of the core. The amorphous carbon may be present in the core and may be in contact with each of the silicon and crystalline carbon in the core.

[0136] The negative electrode active material (ii) can have an aspect ratio of 1 to 2.5 (e.g., 1 to 2). Within this range, the negative electrode active material (ii) can expand in a more uniform direction, and the expansion of the negative electrode active material (ii) in the negative electrode can be effectively reduced. The aspect ratio can be measured by photographs taken using controlled pressure scanning electron microscopy (CP-SEM). The aspect ratio refers to the ratio of the maximum major axis length to the maximum minor axis length of the negative electrode active material (ii).

[0137] The composite of silicon and crystalline carbon can have an aspect ratio of 1 to 2.5 (e.g., 1 to 2). Within these ranges, the negative electrode active material (ii) can expand in a more uniform direction, and the expansion of the negative electrode active material (ii) in the negative electrode can be effectively reduced. The aspect ratio can be measured by photographs taken using CP-SEM. The aspect ratio refers to the ratio of the maximum major axis length to the maximum minor axis length of the composite.

[0138] The silicon and crystalline carbon composite can include pores. These pores can be tubular or plate-like, and can also form a network within the core. In the silicon and crystalline carbon composite, the porosity can be appropriately controlled. For example, the porosity (total pore volume) can range from 2% to 50% by volume.

[0139] The negative electrode active material (ii) may include a porous crystalline carbon core, an amorphous carbon shell formed on the surface of the core, silicon particles dispersed in the pores, and amorphous carbon present in the pores.

[0140] Based on a total of 100 parts by weight of silicon and crystalline carbon, the weight ratio of silicon to crystalline carbon in the silicon-crystalline carbon composite can range from 10:90 to 90:10. Within these ranges, better capacity (specifically, higher capacity) can be provided compared to negative electrode active materials made from crystalline carbon. For example, the weight ratio can be from 50:50 to 80:20, and higher capacity can be exhibited within this range.

[0141] Silicon can be spherical and has an average particle size D50 of 10 nm to 150 nm (e.g., 40 nm to 120 nm). Within these ranges, the cycle life characteristics of the battery can be improved.

[0142] Silicon can be silicon (Si) particles.

[0143] Crystalline carbon can have a major axis length of 5 μm to 20 μm (e.g., 5 μm to 10 μm) and an aspect ratio of 4 to 10 (e.g., 4 to 8). Within these ranges, the cycle life characteristics of the battery can be improved, and swelling does not occur because the negative electrode plate does not undergo excessive volume expansion during the charging and discharging of the rechargeable lithium battery. The aspect ratio can be measured using the CP-SEM method. The aspect ratio is the ratio of the maximum major axis length to the maximum minor axis length.

[0144] Crystalline carbon can be natural graphite, artificial graphite, or a combination thereof.

[0145] Crystalline carbon can take the form of rods with an elliptical cross-section.

[0146] Amorphous carbon coatings can be formed on the surface of the composite to improve its conductivity, thereby further enhancing its performance. The amorphous carbon coating on the surface of the composite can also reduce the direct contact between silicon and the electrolyte, effectively suppressing the increase in resistance caused by the formation of by-reaction products.

[0147] Amorphous carbon coatings can have thicknesses ranging from 5 nm to 1,000 nm (e.g., 5 nm to 30 nm). Within these ranges, the thickness level of the layer can be such that electron transfer resistance is not a problem.

[0148] The amorphous carbon in the amorphous carbon coating and the amorphous carbon present in the core can be petroleum pitch, coal pitch, or a combination thereof.

[0149] The amount of amorphous carbon coating in the negative electrode active material (ii) can be in the range of 10% to 60% by weight. Within this range, the performance of the battery can be improved.

[0150] The negative electrode active material (ii) may comprise 20% to 70% by weight of silicon, 3% to 50% by weight of crystalline carbon, and 20% to 50% by weight of amorphous carbon. Within this range, the expansion of the negative electrode active material due to charging and discharging can be effectively suppressed, and cycle life and output characteristics can be improved.

[0151] Figure 4 This is a conceptual diagram of the negative electrode active material (ii) according to an embodiment.

[0152] Reference Figure 4The negative electrode active material (ii) includes silicon particles 11, crystalline carbon 13, and amorphous carbon 15. Amorphous carbon 15 is present between silicon particles 11 and crystalline carbon 13. Amorphous carbon 15 may also be present in a coating layer surrounding silicon particles 11 and crystalline carbon 13.

[0153] The method for preparing the negative electrode active material (ii) will be described below.

[0154] The negative electrode active material (ii) can be prepared by mixing silicon particles, artificial graphite, and amorphous carbon in a solvent to prepare a mixed solution, and then spray-drying and heat-treating the mixed solution. The solvent can be isopropanol, ethanol, methanol, or a combination thereof. Spray drying can be performed at 90°C to 120°C, and heat treatment can be performed at 900°C to 1,000°C in a nitrogen atmosphere, argon atmosphere, hydrogen atmosphere, or a combination thereof.

[0155] Negative electrode active material (iii) The negative electrode active material (iii) includes silicon nanoparticles and an amorphous carbon coating layer disposed on the surface of the silicon nanoparticles.

[0156] In one embodiment, because the negative electrode active material (iii) has a spherical shape, it can be well dispersed throughout the negative electrode plate, thereby reducing the expansion rate of the negative electrode plate during charging and discharging. Furthermore, when the negative electrode active material (iii) is mixed with and used with crystalline carbon (i.e., the first negative electrode active material), the spherical negative electrode active material (iii) can more easily insert itself between the crystalline carbon molecules. Therefore, the first negative electrode active material can be better dispersed throughout the negative electrode.

[0157] According to Equation 1 above, the negative electrode active material (iii) can have a sphericity S of 0.9 to 1.0. Within this range, the expansion rate of the negative electrode plate during charging and discharging can be easily reduced.

[0158] The negative electrode active material (iii) according to one embodiment may also have a sphericity of 0.92 to 0.98 or 0.92 to 0.95. When the sphericity of the negative electrode active material (iii) falls within this range, the expansion rate of the negative electrode plate can be suppressed more effectively during charging and discharging.

[0159] The negative electrode active material (iii) may include pores, and the pores may include mesopores. Here, mesopores refer to pores with a size of 2 nm to 50 nm. When the negative electrode active material (iii) includes mesopores, the effect of the negative electrode plate according to this disclosure can be significant.

[0160] When the first negative electrode active material is mixed with the second negative electrode active material, the negative electrode active material (iii) having the above-mentioned sphericity and mesopore can easily provide long life, high energy density and boost charging effect at the same time.

[0161] In one embodiment, the negative electrode active material (iii) may also include macropores with a pore size greater than 50 nm as pores. Since pores with a pore size greater than 50 nm are classified as macropores, there is no need to limit the maximum size of the macropores; rather, the pore size can be as high as 500 nm. It is desirable that such macropores be included in an amount of 1% by volume or less based on the total pore volume. In this case, macropores may be present in an amount of at least 0% by volume. That is, macropores may not actually be present within the negative electrode active material (iii).

[0162] In one embodiment, the negative electrode active material (iii) may further include micropores with a pore size greater than 0 nm and less than 2 nm as pores. The micropores included in the negative electrode active material (iii) may correspond to the volume of the total pore volume (%) excluding mesopores, or, when the pores also include macropores, to the volume excluding both mesopores and macropores.

[0163] Here, the term "hole size" refers to the diameter of a hole with a circular cross-section, or, when the cross-section of the hole is not circular, the length of the longest axis on the cross-section.

[0164] In one embodiment, the ratio of the mesopore volume of the negative electrode active material (iii) to the total pore volume of the negative electrode active material (iii) ((mesopore volume / total pore volume) × 100) can be in the range of 30% or greater and less than 70%. Within this range, long lifetime, high energy density, and boost charging performance can be further improved. For example, this ratio can be from 30% to 68%.

[0165] The total pore volume can be the total volume of the pores formed in the negative electrode active material (iii), regardless of the pore size. In one embodiment, the total pore volume can be 0.001 cm³. 3 / g to 0.01cm 3 Within the range of / g, or even within 0.005cm 3 / g to 0.05cm 3 Within the range of / g.

[0166] Both total pore volume and mesopore volume can be quantitatively measured using a BJH (Barrett-Joyner-Halenda) analytical apparatus.

[0167] According to Equation 2 below, the negative electrode active material (iii) can have a value ranging from 1.1 to 1.6: [Equation 2] Span = (D90 - D10) / D50 in: D10 represents the particle size of the negative electrode active material particles that constitute 10% of the cumulative volume in the particle size distribution. D50 represents the particle size of the negative electrode active material particles that constitute 50% of the cumulative volume in the particle size distribution. D90 indicates the particle size of the negative electrode active material particles that account for 90% of the cumulative volume in the particle size distribution.

[0168] The detailed methods for measuring D10, D50, and D90 are as described above.

[0169] In one embodiment, the span value can be in the range of 1.1 to 1.55, or it can be in the range of 1.1 to 1.5. When the span value of the negative electrode active material (iii) is in this range, the negative electrode active material (iii) is substantially free of fine particles. That is, because the negative electrode active material (iii) is almost entirely free of irregularly shaped fine particles with a size of 1 μm or smaller, the negative electrode active material (iii) can exhibit a low specific surface area, thereby reducing side reactions with the electrolyte and improving lifetime.

[0170] In one embodiment, the negative electrode active material (iii) can have a low specific surface area. The specific surface area can be as low as 0.5 m². 2 / g to 2m 2 / g, 0.8m 2 / g to 2m 2 / g or 0.8m 2 / g to 1.5m 2 Within the range of / g. This specific surface area is lower than the specific surface area approximately 3m². 2 / g of the specific surface area of ​​the active material of a conventional silicon-carbon composite negative electrode.

[0171] Silicon nanoparticles can have a particle size of 10 nm to 1,000 nm, and according to another embodiment, they can have a particle size of 10 nm to 200 nm or 20 nm to 150 nm. When the particle size of silicon nanoparticles is within these ranges, excessive volume expansion that occurs during charging and discharging can be suppressed, and the interruption of conductive paths due to particle fragmentation during charging and discharging can be prevented.

[0172] Silicon nanoparticles can be assembled to form secondary silicon particles. According to one embodiment, the secondary silicon particles can have an average particle size D50 of 1 μm to 15 μm. For example, the average particle size D50 of the secondary silicon particles can be in the range of 1 μm to 10 μm (e.g., 6 μm to 8 μm).

[0173] In the amorphous carbon coating, the amorphous carbon can be soft carbon or hard carbon, mesophase pitch carbides, calcined coke, or a combination thereof. The amorphous carbon coating can have a thickness of 1 nm to 2 μm, 1 nm to 500 nm, 10 nm to 300 nm, or 20 nm to 200 nm. When the thickness of the amorphous carbon coating is within these ranges, silicon volume expansion during charging and discharging can be effectively suppressed.

[0174] In the negative electrode active material (iii), based on a total of 100 wt% of the negative electrode active material (iii), the amount of silicon nanoparticles can range from 55 wt% to 64 wt% or from 58 wt% to 62 wt%. Based on a total of 100 wt% of the negative electrode active material (iii), the amount of amorphous carbon coating can range from 36 wt% to 45 wt% or from 38 wt% to 42 wt%. Within these ranges, the capacity of the negative electrode plate can be improved and the particle stability can be enhanced.

[0175] The negative electrode active material (iii) may also include a polymer layer disposed on the amorphous carbon coating.

[0176] The polymer layer may include a copolymer of polyvinyl alcohol and polyacrylic acid. The copolymer may be a crosslinked copolymer in which polyvinyl alcohol and polyacrylic acid are crosslinked. When the negative electrode active material (iii) also includes a polymer layer, the volume expansion of the negative electrode active material (iii) during charging and discharging can be more effectively suppressed.

[0177] Because the polymer layer comprises polyvinyl alcohol and polyacrylic acid, it prevents the electrolyte from permeating into the negative electrode active material (iii) during charging and discharging (specifically, preventing the electrolyte from permeating into the empty spaces (such as pores) of the negative electrode active material (iii)). Therefore, the polymer layer can more effectively suppress side reactions between the negative electrode active material (iii) and the electrolyte.

[0178] Polyvinyl alcohol and polyacrylic acid can be environmentally friendly water-based polymers.

[0179] In one embodiment, the polymer layer comprises a copolymer of polyvinyl alcohol and polyacrylic acid, for example, a crosslinked polymer or crosslinked copolymer in which polyvinyl alcohol and polyacrylic acid are crosslinked. That is, the polymer can be a crosslinked polymer of polyvinyl alcohol and polyacrylic acid. When polyvinyl alcohol and polyacrylic acid are crosslinked and included as a crosslinked polymer in the polymer layer, the polymer layer may be insoluble in solvents (such as water) used to prepare the negative electrode active material layer.

[0180] In the negative electrode active material (iii), which is referred to as a silicon-carbon composite, both silicon nanoparticles and an amorphous carbon coating, the amount of polymer layer can be in the range of 0.01 parts by weight to 3 parts by weight or in the range of 1.2 parts by weight to 2.1 parts by weight, based on 100 parts by weight of the silicon-carbon composite. When the amount of polymer layer is within these ranges, the effect produced by the formation of the polymer layer can be further enhanced.

[0181] In the polymer layer, based on a total of 100 parts by weight of polyvinyl alcohol and polyacrylic acid, the mixing ratio of polyvinyl alcohol to polyacrylic acid can be 3:97 to 40:60, 6:94 to 40:60, or 6:94 to 20:80. When the mixing ratio of polyvinyl alcohol to polyacrylic acid falls within these ranges (i.e., when the amount of polyacrylic acid is higher than the amount of polyvinyl alcohol), cycle life characteristics can be further improved.

[0182] In one embodiment, it is also desirable to appropriately control the ratio of functional groups contained in polyvinyl alcohol and polyacrylic acid included in the polymer layer. Based on a total of 100 moles of OH groups and COOH groups, the molar ratio of OH groups in polyvinyl alcohol to COOH groups in polyacrylic acid can be from 5:95 to 50:50, and can be from 10:90 to 30:70. When the molar ratio of functional groups meets these ranges, the effects resulting from the formation of the polymer layer can be further improved, and the cycle life characteristics can be further improved.

[0183] The negative electrode active material can be prepared by the following process (iii).

[0184] Milling micron-sized silicon particles produces nano-sized primary silicon particles. The milling process can be performed using conventional methods such as ball milling. Dispersants can be used in the milling process. Stearic acid, boron nitride (BN), MgS, polyvinylpyrrolidone (PVP), or combinations thereof can be used as dispersants. The amount of dispersant used is sufficient as long as it enables the milling process of the silicon particles. Therefore, there are no limitations on the amount of dispersant.

[0185] Primary silicon particles can have particle sizes ranging from 1 nm to 1,000 nm, 10 nm to 200 nm, or 20 nm to 150 nm.

[0186] For example, a mixture obtained by spray drying is used. Spray drying can produce a dried product with particles having a more uniform particle size and spherical shape, and can form secondary particles from primary particles. When the dried product has particles with a uniform particle size and spherical shape, the subsequently formed amorphous carbon coating can be formed more uniformly across the entire surface of the secondary particles.

[0187] The dried product is mixed with an amorphous carbon precursor. Petroleum coke, coal coke, petroleum pitch, coal pitch, raw coke, or combinations thereof can be used as the amorphous carbon precursor.

[0188] The resulting mixture is then pressed and molded. The resulting product can undergo further pressing and molding. This pressing and molding process reduces the porosity within the negative electrode active material (iii), thereby effectively suppressing side reactions.

[0189] The compression molding process can be performed at a level that maintains the spherical shape of the resulting product (specifically, the negative electrode active material (iii) used in the final product). The compression molding process can be performed at pressures, for example, greater than 0 MPa and 30 MPa or less, greater than 0 MPa and 200 MPa or less, or 5 MPa to 20 MPa.

[0190] Cold isostatic pressing (CIP) can be used to perform the compression molding process. When compression molding is performed within the pressure range described above, porosity can be appropriately reduced while maintaining a spherical shape without producing fine particles.

[0191] Next, the resulting pressed molded product is carbonized. The carbonization process can be performed at temperatures ranging from 600°C to 1,000°C. Dispersants can be removed during this carbonization process. Alternatively, the carbonization process can be performed in an N2 atmosphere, a helium atmosphere, or a combination thereof. Through this carbonization process, the amorphous carbon precursor is converted into amorphous carbon, and an amorphous carbon coating layer is formed around the surface of the pressed molded product.

[0192] When the carbonization process is performed within the aforementioned temperature range, the excessive growth of Si particles can be suppressed, the formation of SiC can be inhibited, and the electronic conductivity of amorphous carbon can be improved. Furthermore, when some of the amorphous carbon is inserted into the pores formed between the primary particles and disposed on the surface of the primary particles, the amorphous carbon surrounds the surface of the primary particles. When the atmosphere of the carbonization process meets the above conditions, amorphous carbon can be effectively formed while suppressing silicon oxidation and SiC formation, thereby reducing the resistance of the negative electrode active material (iii).

[0193] Instead of mixing the dried product with the amorphous carbon precursor, a vapor-phase coating process using an amorphous carbon precursor gas can be performed on the dried product. In this case, an amorphous carbon coating layer can be formed on the surface of the product without performing a separate carbonization process. Therefore, a pressing process can be performed after the vapor-phase coating process. The conditions for the pressing process are as described above.

[0194] When the negative electrode active material layer (iii) according to one embodiment further includes a polymer layer, a process of mixing the negative electrode active material (iii) (referred to as silicon-carbon composite) and the polymer solution, drying the resulting mixture, and then heat-treating the mixture can be further performed.

[0195] Polymer solutions can be prepared by mixing polyvinyl alcohol and polyacrylic acid in a solvent. The solvent can be water, ethanol, or a combination thereof.

[0196] The mixing ratio of the silicon-carbon composite and the polymer solution can be adjusted to achieve the above-mentioned polymer amount in the negative electrode active material (iii) and the mixing ratio of polyvinyl alcohol and polyacrylic acid.

[0197] A condensation reaction occurs between the OH groups of polyvinyl alcohol and the COOH groups of polyacrylic acid using a heat treatment process. As a result, polyvinyl alcohol and polyacrylic acid can be crosslinked to form a crosslinked polymer.

[0198] The heat treatment process can be performed at temperatures ranging from 150°C to 200°C. When the heat treatment process is performed within this temperature range, condensation reactions (i.e., crosslinking reactions) can easily occur, thereby promoting the formation of crosslinked polymers.

[0199] The heat-treated product is subjected to a grading process. This grading process can be performed using a sieve to achieve a span value (defined by Equation 2 above) of 1.1 to 1.6 for the negative electrode active material (iii). The grading process can be performed to obtain negative electrode active material (iii) with a particle size that results in a span value of 1.1 to 1.6 for the D10, D50, and D90 of the negative electrode active material (iii).

[0200] In addition to the first negative electrode active material, the second negative electrode active material and the third negative electrode active material mentioned above, the negative electrode plate may further include a negative electrode active material (a fourth negative electrode active material) that is different from the first to the third negative electrode active materials mentioned above.

[0201] The fourth negative electrode active material may also include materials capable of reversibly inserting / deintercalating lithium ions, lithium metal, lithium and metal alloys, materials capable of doping and dedoping lithium, or transition metal oxides.

[0202] 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. Examples of crystalline carbon include graphite, such as amorphous, tabular, flake, spherical, or fibrous natural or synthetic graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbides, calcined coke, etc.

[0203] As an alloy of lithium and a metal, 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 can be used.

[0204] As a material capable of doping and de-doping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), a Si-Q alloy, or a combination thereof. In the formula Si-Q, 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 be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0205] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in the form of silicon particles coated with amorphous carbon on their surfaces. For example, the composite can include secondary particles (cores) assembled from primary particles and an amorphous carbon coating layer (shells) provided on the surfaces of the secondary particles. Amorphous carbon can be provided between the primary particles of silicon such that the primary particles of silicon can be coated with amorphous carbon. The secondary particles can be dispersed in an amorphous carbon matrix.

[0206] The silicon-carbon composite can further 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 provided on the surface of the core.

[0207] 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.

[0208] adhesive The binder can include a (meth)acrylic binder. The (meth)acrylic binder can provide improved swelling characteristics.

[0209] According to one embodiment, the (meth)acrylic binder can be included in an amount of 95 wt% or more (e.g., 95 wt% to 100 wt% or 100 wt%) of the total binder in the negative electrode plate. Within these ranges, the effects of the above negative electrode plate can be easily achieved.

[0210] When the (meth)acrylic binder is applied to the negative electrode plate including the mixture of the negative electrode active material, the (meth)acrylic binder can improve the charging performance and extend the life. In addition, the (meth)acrylic binder can provide a long life due to its excellent surface protection function for the third negative electrode active material.

[0211] (Meth)acrylic adhesives can be copolymers comprising a mixture of monomers including one or more (meth)acrylic monomers known to those skilled in the art. The (meth)acrylic monomers may include one or more of the following: (meth)acrylic monomers having a cyano group, (meth)acrylic monomers having a carboxylic acid group, (meth)acrylic monomers having a hydroxyl group, (meth)acrylic monomers having an amide group, aromatic vinyl monomers, and unsaturated alkyl carboxylic acid ester monomers.

[0212] In one example, a (meth)acrylic binder may comprise units derived from (meth)acrylic monomers having a carboxylic acid group (e.g., units derived from (meth)acrylic monomers) and units derived from (meth)acrylic monomers having a cyano group. When the (meth)acrylic binder is applied to a negative electrode plate comprising a mixture of negative electrode active materials, the (meth)acrylic binder can improve charging performance and provide a long lifespan.

[0213] Compared to (meth)acrylic adhesives, units derived from (meth)acrylic monomers having carboxylic acid groups may be included in an amount of 35 mol% to 65 mol%. Units derived from (meth)acrylic monomers having cyano groups may be included in an amount of 35 mol% to 65 mol%.

[0214] Compared to (meth)acrylic binders, when the amount of units derived from (meth)acrylic monomers with carboxylic acid groups is less than 35 mol%, the (meth)acrylic binders may be insoluble in water, which is undesirable as it may reduce the dispersibility of the negative electrode active material and degrade the storage stability of the negative electrode slurry. Compared to (meth)acrylic binders, when the amount of units derived from (meth)acrylic monomers with carboxylic acid groups exceeds 65 mol%, cracks may appear in the electrode (negative electrode) during the application and drying of the negative electrode slurry, making it difficult to manufacture the negative electrode.

[0215] Compared to (meth)acrylic binders, when the amount of units derived from cyano-containing (meth)acrylic monomers is less than 35 mol%, the adhesion between the mixture layer of negative electrode active material and the substrate decreases. Compared to (meth)acrylic binders, when the amount of units derived from cyano-containing (meth)acrylic monomers exceeds 65 mol%, the (meth)acrylic binder may be water-insoluble, which is undesirable as it may reduce the dispersibility of the negative electrode active material and potentially degrade the storage stability of the negative electrode slurry.

[0216] Units derived from (meth)acrylic acid monomers can be represented by the following chemical formulas 1, 2, and 3, or combinations thereof: [Chemical Formula 1]

[0217] [Chemical Formula 2]

[0218] [Chemical Formula 3]

[0219] in: R 1 To R 6 Both are independently hydrogen or methyl, and in chemical formula 2, M is an alkali metal.

[0220] Alkali metals can be, for example, lithium, sodium, potassium, calcium, magnesium, rubidium, or cesium.

[0221] The monomer of (meth)acrylic acid is preferably at least one selected from (meth)acrylic acid, an alkali metal salt of (meth)acrylic acid, and an ammonium salt of (meth)acrylic acid. Here, (meth)acrylic acid refers to acrylic acid or methacrylic acid. Alkali metal salts of (meth)acrylic acid include sodium acrylate, lithium acrylate, potassium acrylate, calcium acrylate, magnesium acrylate, sodium methacrylate, lithium methacrylate, potassium methacrylate, calcium methacrylate, etc., preferably sodium acrylate. Ammonium salts of (meth)acrylic acid include ammonia neutralized products of (meth)acrylic acid, monoethanolamine neutralized products, diethanolamine neutralized products, hydroxylamine neutralized products, etc., preferably ammonia neutralized products of acrylic acid.

[0222] Units derived from (meth)acrylic acid monomers having a cyano group can be represented, for example, by the following chemical formula 4: [Chemical Formula 4]

[0223] in: R 7 and R 8 Each is independently hydrogen or C1 to C3 alkyl, L 1 The values ​​are -C(=O)-, -C(=O)O-, -OC(=O)-, -O-, or -C(=O)NH-, where x is an integer from 0 to 2, and L 2 The y is a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a substituted or unsubstituted C3 to C20 heterocyclic group, where y is an integer from 0 to 2.

[0224] The cyano-containing structural unit can be derived from (meth)acrylonitrile, olefin nitrile, (meth)acrylic cyanoalkyl ester, or 2-(ethoxy)alkane nitrile. Here, the olefin can be a C2 to C20 olefin, a C2 to C10 olefin, or a C2 to C6 olefin, and the alkyl can be a C1 to C20 alkyl, a C1 to C10 alkyl, or a C1 to C6 alkyl. Furthermore, the alkane can be a C1 to C20 alkane, a C1 to C10 alkane, or a C1 to C6 alkane.

[0225] Olefin nitrile can be, for example, allyl cyanide, 4-pentenonitrile, 3-pentenonitrile, 2-pentenonitrile, 5-hexenonitrile, etc. (Meth)acrylate cyanoalkyl ester can be, for example, (meth)acrylate methyl cyanoacrylate, (meth)acrylate ethyl cyanoacrylate, (meth)acrylate propyl cyanoacrylate, (meth)acrylate octyl cyanoacrylate, etc. 2-(ethoxy)alkane nitrile can be, for example, 2-(ethoxy)acetonitrile or 2-(ethoxy)propionitrile.

[0226] The negative electrode plate includes a binder comprising units derived from (meth)acrylic acid monomers having carboxylic acid groups and units derived from (meth)acrylic acid monomers having cyano groups. Such a binder further improves the characteristics of the rechargeable battery.

[0227] In addition to units derived from (meth)acrylic acid monomers having carboxylic acid groups and units derived from (meth)acrylic acid monomers having cyano groups, (meth)acrylic adhesives may also include units derived from another monomer (i.e., comonomer) that is copolymerizable with the monomer. The comonomer may include hydroxyl-containing monomers or amide-containing monomers. Hydroxyl-containing monomers include, for example, 2-hydroxyethyl (meth)acrylic acid, 2-hydroxypropyl (meth)acrylic acid, 4-hydroxybutyl (meth)acrylic acid, 2-hydroxyhexyl (meth)acrylic acid, 6-hydroxyhexyl (meth)acrylic acid, 8-hydroxyoctyl (meth)acrylic acid, 10-hydroxydecyl (meth)acrylic acid, 12-hydroxylauryl (meth)acrylic acid, 4-hydroxymethylcyclohexyl methacrylate, N-hydroxymethyl (meth)acrylamide, N-hydroxy (meth)acrylamide, vinyl alcohol, allyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, etc. Monomers containing amide groups include, for example, acrylamide, methacrylamide, diethyl (meth)acrylamide, N-vinylpyrrolidone, N-vinyl-2-pyrrolidone, N-(meth)acryloylpyrrolidone, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N,N'-methylenebisacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, etc.

[0228] Units derived from the comonomer may be included in the binder in amounts greater than 0 mol% and 20 mol% or less. The binder may be a water-soluble copolymer used to stabilize the dispersion of the polymer. The binder (e.g., a (meth)acrylic binder) may be included in the negative electrode plate in amounts from 0.5 wt% to 5 wt% (e.g., 1 wt% to 3 wt%). Within this range, the effects of the aforementioned negative electrode plate can be readily achieved.

[0229] According to one embodiment, based on 100 parts by weight of the mixture of negative electrode active materials, a binder (e.g., a (meth)acrylic binder) may be included in an amount of 1 to 15 parts by weight. Within this range, the effects of the aforementioned negative electrode plate can be easily achieved.

[0230] Adhesives may also include adhesives other than (meth)acrylic adhesives.

[0231] Non-aqueous adhesives, water-based adhesives, dry adhesives, or combinations thereof can be used.

[0232] Non-aqueous adhesives may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0233] Waterborne adhesives may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluorinated elastomers, 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.

[0234] When using an aqueous binder as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may also be included. Such a cellulose-based compound may be one or more mixtures of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts. Na, K, or Li may be used as the alkali metal.

[0235] The dry binder can be a fibrous polymer material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof. In other words, the negative electrode can be a dry negative electrode plate.

[0236] conductive materials The negative electrode plate for a rechargeable lithium battery may also include a conductive material. The conductive material may be included in the negative electrode plate in an amount greater than 0% by weight and 5% by weight or less.

[0237] Conductive materials are used to impart conductivity to electrodes, and any material can be used as long as it is electronically conductive and does not cause undesirable chemical changes in the battery to be constructed. Examples of conductive materials include: carbon-based materials such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, carbon nanotubes, etc.; 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.

[0238] The negative electrode current collector can also be stacked on at least one surface of the negative electrode plate.

[0239] As the negative electrode current collector, any of the following can be used: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0240] Another exemplary embodiment provides a rechargeable lithium battery including a negative electrode plate for a rechargeable lithium battery. The rechargeable lithium battery may include a negative electrode plate and a positive electrode for the rechargeable lithium battery. The negative electrode plate is as described above.

[0241] 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. The positive electrode may also include additives that can be used as a sacrificial positive electrode.

[0242] 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 and metals selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0243] The composite oxide can be a lithium transition metal composite oxide. Specific examples of composite oxides include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free lithium nickel manganese oxides, or combinations thereof. As an example, the following compounds represented by any one 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-g G g PO4 (0.90 ≤ a ≤ 1.8, and 0 ≤ g ≤ 0.5); Li (3-f) Fe2(PO4)3 (0≤f≤2); or Li aFePO4 (0.90≤a≤1.8). In these 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.

[0244] 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 composite oxide. The high-nickel positive electrode active material has a nickel content 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 applied to high-capacity, high-density rechargeable lithium batteries.

[0245] 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.

[0246] The binder is used to adhere the positive electrode active material particles to each other and also to adhere the positive electrode active material to the current collector. Examples of binders may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including 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. However, this disclosure is not limited to these examples.

[0247] Conductive materials can be used to impart conductivity (e.g., electrical conductivity) to electrodes. Any material that does not cause undesirable chemical changes and conducts electrons can be used in a battery, particularly in a rechargeable lithium-ion battery. Examples of conductive materials 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 fibers; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0248] Aluminum can be used as a current collector. However, this disclosure is not limited to aluminum.

[0249] electrolyte Rechargeable lithium batteries may also include an electrolyte. The electrolyte may include a non-aqueous organic solvent and a lithium salt.

[0250] Non-aqueous organic solvents can be used as media for transporting ions that participate in the electrochemical reactions of a battery. Non-aqueous organic solvents can be carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0251] 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.

[0252] Esters can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc. Ethers can include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Ketones can include cyclohexanone, etc. Alcohols 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.

[0253] Non-aqueous organic solvents can be used alone or in combination of two or more.

[0254] Additionally, when using carbonate solvents, cyclic carbonates and chain carbonates can be mixed and used. Cyclic carbonates and chain carbonates can be mixed in a volume ratio of approximately 1:1 to approximately 1:9.

[0255] 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 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+1Lithium trifluoromethane sulfonate (where x and y are integers from 1 to 20), lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalate) phosphate (LiDFBOP), and lithium bis(oxalate) borate (LiBOB).

[0256] diaphragm Rechargeable lithium batteries may also include a separator. Depending on the type of rechargeable lithium battery, the separator may be present between the positive and negative electrodes. The separator may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof, for example, it may be a hybrid multilayer film (such as a polyethylene / polypropylene bilayer separator, a polyethylene / polypropylene / polypropylene trilayer separator, a polypropylene / polypropylene / polypropylene trilayer separator, etc.).

[0257] 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.

[0258] Porous substrates can be polymer membranes formed from polymers, such as polyolefins (e.g., polyethylene and polypropylene), polyesters (e.g., 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 (PTFE). ® (or copolymers or mixtures of two or more of them.)

[0259] Organic materials may include polyvinylidene fluoride polymers or (meth)acrylic acid polymers.

[0260] Inorganic materials may include 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. However, this disclosure is not limited to these examples.

[0261] Organic and inorganic materials can be mixed in a single coating layer. In other embodiments, coating layers comprising organic materials and coating layers comprising inorganic materials can be stacked.

[0262] Rechargeable lithium batteries Depending on their shape, rechargeable lithium batteries can be cylindrical, prismatic, pouch-shaped, or coin-shaped, etc.

[0263] Figures 5 to 8 This is a schematic diagram illustrating a rechargeable lithium battery according to an embodiment. Figure 5 A cylindrical battery is shown. Figure 6 A prismatic battery is shown. Figure 7 and Figure 8 A pouch-type battery is shown. (See reference) Figures 5 to 8 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 the electrode assembly 40 is housed within the housing 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 5 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of the sealed housing 50. Figure 6 In this context, the rechargeable lithium battery 100 may include a positive electrode lead connector 14, a positive terminal 12, a negative electrode lead connector 21, and a negative terminal 22. For example... Figure 7 and Figure 8 As shown, the rechargeable lithium battery 100 may include electrode terminals 70 forming an electrical path for guiding current formed in the electrode assembly 40 to the outside of the battery. The electrode terminals 70 may be, for example, a positive electrode terminal 71 and a negative electrode terminal 72.

[0264] 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.

[0265] Electronic devices or electric vehicles may contain rechargeable lithium batteries.

[0266] Examples and comparative examples of this disclosure will be described below. However, it should be understood that the following examples are merely illustrative, and this disclosure is not limited to these examples.

[0267] Example 1 (1) Preparation of the active material of the first negative electrode Flake-shaped natural graphite raw material with an average particle size D50 of 120 μm was 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, and the mixture was then heat-treated in a sintering furnace at 3,000 °C for 2 hours to prepare the first negative electrode active material. The addition of pitch carbon resulted in a weight ratio of natural graphite to amorphous carbon of 90:10 in the first negative electrode active material.

[0268] (2) Active material of the second negative electrode Artificial graphite (spherical, average particle size D50: 15μm, particle density: 1.5g / cc, tap density: 0.9g / cc, BET specific surface area: 1.5m²) was used. 2 / g, orientation degree: 100) is used as the active material for the second negative electrode. Artificial graphite exists in the form of secondary particles formed from primary particles.

[0269] (3) Preparation of the active material of the third negative electrode Silicon nanoparticles (aspect ratio: 5, average particle size: approximately 100 nm) and petroleum asphalt (amorphous carbon) were mixed in isopropanol solvent at a weight ratio of 70:30, and the mixture was dispersed using a homogenizer to prepare a dispersion. The prepared dispersion was spray-dried at 120 °C using a spray dryer. The resulting spray-dried product (precursor) was pressurized to 50 MPa using a powder press, and then heat-treated in a furnace at 1,000 °C under a N2 atmosphere to produce a reaction product comprising a core containing amorphous carbon and silicon nanoparticles, and a coating layer formed on the surface of the core, the coating layer comprising amorphous carbon. The resulting reaction product was ground and classified using a 325-mesh sieve to prepare a third negative electrode active material (C-1).

[0270] The prepared third negative electrode active material has a size of 200 nm or smaller and a volume of 2.95 × 10⁻⁶. 2 cm 3 / g pores, with an interparticle distance of 65nm between silicon nanoparticles, an average particle size D50 of 8.3μm, and a pore size of 200nm or smaller.

[0271] The interparticle distance between silicon nanoparticles is measured by analyzing the cross-section of the silicon nanoparticles using TEM and calculating the distance between the centers of the silicon nanoparticles.

[0272] Pore ​​volume was measured using the following steps: silicon nanoparticles were placed in a porosity measuring device (ASAP series manufactured by Micromeritics Instruments), heated to 623 K at 10 K / min, and pretreated for 2 to 10 hours (vacuum pressure: 100 mmHg or less). Then, the pore volume was measured under relative pressure (P / P). o The orifice volume was controlled to be 0.01 or less in liquid nitrogen. Specifically, nitrogen adsorption was measured at 32 points with relative pressures ranging from 0.01 to 0.995, followed by nitrogen desorption at 24 points with a relative pressure of 0.14. BET calculations can typically be performed down to the relative pressure (P / P o The point with a value of 0.1.

[0273] (4) Based on a mixture of 100 parts by weight of negative electrode active material, 47 parts by weight of the first negative electrode active material, 47 parts by weight of the second negative electrode active material and 6 parts by weight of the third negative electrode active material are mixed to prepare a mixture of negative electrode active materials.

[0274] A slurry of negative electrode active material was prepared by mixing 97.5% by weight of the mixture of the prepared negative electrode active material and 2.5% by weight of (meth)acrylic binder (a copolymer of acrylic acid and acrylonitrile) and styrene-butadiene rubber (SBR) (1.5% by weight and 1% by weight, respectively) in distilled water.

[0275] The negative electrode active material slurry is applied to a copper current collector, dried, and then rolled to manufacture a negative electrode plate.

[0276] A half-cell is constructed using a negative electrode plate, a lithium metal counter electrode, and an electrolyte. The electrolyte is a mixed solvent (3:7 volume ratio) of ethylene carbonate and dimethyl carbonate containing 1M LiPF6.

[0277] Example 2 Except for changing the spheroidization conditions in Example 1, the first negative electrode active material was prepared in the same manner as in Example 1. The prepared first negative electrode active material was used to manufacture the negative electrode and the half-cell in the same manner as in Example 1.

[0278] Example 3 Except for changing the spheroidization conditions in Example 1, the first negative electrode active material was prepared in the same manner as in Example 1. The prepared first negative electrode active material was used to manufacture the negative electrode and the half-cell in the same manner as in Example 1.

[0279] Examples 4 to 6 Except for changing the weight ratio of each component in Example 1 as shown in Table 1 below, the negative electrode plate and half cell are manufactured in the same manner as in Example 1.

[0280] Comparison Example 1 The first negative electrode active material is prepared in the same manner as in Example 1, except that pitch carbon is not added when preparing the first negative electrode active material in Example 1. The prepared first negative electrode active material is used to manufacture a negative electrode and a half-cell in the same manner as in Example 1.

[0281] Comparison Example 2 Flake-shaped natural graphite raw materials with an average particle size D50 of 120 μm or larger were ground into fine primary particles with a plate-like shape and a long axis 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. Pitch carbon was added to the secondary particles, mixed, and then heat-treated in a sintering furnace at 1200 °C for 2 hours to prepare the first negative electrode active material. The addition of pitch carbon resulted in a weight ratio of natural graphite to amorphous carbon of 90:10 in the first negative electrode active material.

[0282] The prepared first negative electrode active material is used to manufacture the negative electrode and half cell in the same manner as in Example 1.

[0283] Comparison Example 3 Flake-shaped natural graphite raw material with an average particle size D50 of 80 μm was ground into primary particles with a plate-like shape and a major axis 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. Pitch carbon was added to the secondary particles, mixed, and then heat-treated in a sintering furnace at 1200 °C for 2 hours to prepare the first negative electrode active material. The addition of pitch carbon resulted in a weight ratio of natural graphite to amorphous carbon of 90:10 in the first negative electrode active material.

[0284] The prepared first negative electrode active material is used to manufacture the negative electrode and half cell in the same manner as in Example 1.

[0285] Compare Example 4 The negative electrode plate and half cell are manufactured in the same manner as in Example 1, except that carboxymethyl cellulose (CMC) is used instead of the (meth)acrylic binder in Example 1.

[0286] Compare Example 5 The negative electrode plate and half cell are manufactured in the same manner as in Example 1, except that carboxymethyl cellulose is used instead of the (meth)acrylic binder in Example 1 and the weight ratio of each component is changed as shown in Table 1 below.

[0287] Experimental Example 1: Evaluation of the active material of the first negative electrode Particle density (g / cc) Particle density was measured using a Carver 4350.L (CARVER Ltd.) as a particle density meter. Particle density was measured by placing 1.0 g of the first negative electrode active material from each of the example and comparative examples into a mold and holding the first negative electrode active material under a pressure of 2.0 tons for 30 seconds.

[0288] Orientation degree: The orientation degree was measured using an X'Pert Pro (PANalytical) X-ray diffraction (XRD) analyzer. For the first negative electrode active material of the example and comparative examples, 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 XRD analysis using CuKα rays, was calculated.

[0289] d002（Å） d002 was measured using an X'Pert Pro (PANalytical) XRD analysis apparatus. For the first negative electrode active material in the example and comparative examples, the interplanar spacing of the (002) plane was measured using CuKα XRD analysis.

[0290] Mercury accumulation pore volume (mL / g) For the first negative electrode active material in the example and comparative examples, the accumulated pore volume of mercury was measured using a micromeritics (AutoPore V) mercury intrusion porosimeter. The first negative electrode active material was placed in a special sample cup such that mercury surrounded it, and a pressure ranging from 0.2 psi to 60,000 psi was applied to force the mercury into the material. The mercury porosity was then measured by measuring the volume change of the reduced mercury in the capillary rod reservoir. Pore sizes that could be measured in this way ranged from 0.01 μm to 100 μm. In the first negative electrode active material, pores with sizes from 0.01 μm to 5 μm were identified as pores in the first negative electrode active material.

[0291] Sphericity: Sphericity was measured using a Morphologi 4 (Malvern Ltd.) as a sphericity analyzer. For the first negative electrode active material in the example and comparative examples, values ​​A and B in Equation 1 above were calculated, and then the sphericity was calculated according to Equation 1.

[0292] Experimental Example 2: Evaluation of Battery Characteristics The half-cell was charged and discharged at 0.1C to measure the charge and discharge capacity. The measured discharge capacity is shown in Table 1 below. In addition, the coulombic efficiency (discharge capacity / charge capacity ratio × 100%) was measured.

[0293] A half-cell was subjected to one cycle of 0.2C constant current (CC) / constant voltage (CV) charging and 0.2C discharging, one cycle of 0.5C CC 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. The charging conditions were a 10mV cutoff at the CC stage and a 15-hour cutoff at the CV stage, with a 1.5V cutoff at the discharging stage. Charging characteristics were measured at each C rate. The charging characteristics were expressed as the ratio of the 2C CC charging capacity to the 0.2C CC charging capacity.

[0294] Energy density (Wh / L): (Battery capacity (Ah) × Average battery voltage (V)) / Battery volume (L) Energy density is a value obtained by multiplying the discharge capacity calculated by discharging the battery cell at a C-rate of 0.1C to 1C within the operating voltage range of the battery cell by the average voltage of the corresponding battery cell, and then dividing the product by the volume of the battery cell.

[0295] Boost charging time (seconds): Boost charging time refers to the time taken to charge from 8% SOC (State of Charge) to 80% SOC (State of Charge) using constant current charging. Boost charging time is evaluated by identifying charging modes that do not reach the upper limit voltage of 4.2V during charging.

[0296] Boost charging life (cycles): Once the boost charging time is determined, a cycle evaluation of the large battery cell is performed, charging from 8% SOC to 80% SOC and discharging at a discharge voltage of 2.8V and a constant current of 0.33C until the SOH (state of health) reaches 80%.

[0297] Expansion rate (%) The expansion rate was measured using the Thickness Monitoring System (TMS) method.

[0298] Under conditions of a charging voltage of 4.35V and a discharging voltage of 2.8V, the thickness of battery cells manufactured according to the example and comparative examples was evaluated in real time during charging / discharging (0.5C / 0.5C) at 45°C, in order to evaluate the increase in thickness after 50 cycles relative to the thickness after 1 cycle. The expansion rate was then calculated as follows: Expansion rate (%) = (Cell thickness after 50 cycles - Cell thickness after 1 cycle) / Cell thickness after 1 cycle × 100 [Table 1]

[0299] In Table 1: C-1: Silicon-carbon composite D-1: (Meth)acrylic adhesive D-2: CMC D-3: SBR Weight ratio: The weight ratio of the first negative electrode active material to the second negative electrode active material to the third negative electrode active material based on 100 parts by weight of negative electrode active material.

[0300] As shown in Table 1 above, the example negative electrode plate for rechargeable lithium batteries achieves high energy density while simultaneously providing boost charging and long lifespan characteristics. Furthermore, the use of (meth)acrylic binders maximizes lifespan, overcoming the inherent high expansion rate of the third negative electrode active material.

[0301] On the other hand, because Comparative Example 1, which does not include the first negative electrode active material of this disclosure, has a high expansion rate and a long boost charging time, it is inferior in terms of boost charging and electrode plate expansion. Because Comparative Examples 2 and 3, which do not include the first negative electrode active material of this disclosure, are not inferior in terms of boost charging time and boost charging lifetime, they have inferior boost charging performance. Comparative Examples 4 and 5, which do not include the binder of this disclosure, are inferior in terms of electrode plate expansion and boost charging lifetime.

[0302] Example 7 (1) Preparation of the active material of the first negative electrode Flake-shaped natural graphite raw material with an average particle size D50 of 120 μm was 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 then heat-treated in a sintering furnace at 3,000 °C for 2 hours to prepare the first negative electrode active material. The addition of pitch carbon resulted in a weight ratio of natural graphite to amorphous carbon of 90:10 in the first negative electrode active material.

[0303] (2) Active material of the second negative electrode Artificial graphite (spherical, average particle size D50: 15μm, particle density: 1.5g / cc, tap density: 0.9g / cc, BET specific surface area: 1.5m²) was used. 2 / g, orientation degree: 100) is used as the active material for the second negative electrode. The artificial graphite exists in the form of secondary particles, which are all composed of primary particles.

[0304] (3) Preparation of the active material of the third negative electrode Artificial graphite with an average particle size D50 of 3 μm to 5 μm and an aspect ratio of 4 to 10, silicon nanoparticles with an average particle size D50 of 100 nm, and amorphous carbon from petroleum pitch were mixed in a weight ratio of 40:40:20 and dispersed in an isopropyl solvent. The mixture was then dispersed using a homogenizer to prepare a dispersion. The dispersion was spray-dried at 120 °C using a spray dryer. The resulting spray-dried product was heat-treated in a furnace at 1,000 °C under a nitrogen atmosphere to form a silicon-carbon composite core of artificial graphite and silicon particles and an amorphous carbon layer formed on the surface of the core. The resulting product was milled and classified using a 400-mesh sieve to prepare a third negative electrode active material (C-1) having a silicon-carbon composite core of artificial graphite and silicon particles and an amorphous carbon coating layer formed on the surface of the core.

[0305] The third negative electrode active material comprises a composite core of silicon and artificial graphite, and an amorphous carbon shell formed on the surface of the core. The weight ratio of silicon particles to artificial graphite in the third negative electrode active material is 5:5, the amorphous carbon coating layer has a thickness of 30 nm, and the third negative electrode active material has an aspect ratio of 1 to 2.5. The silicon particles, artificial graphite, and amorphous carbon included in the third negative electrode active material are 40% by weight, 40% by weight, and 20% by weight, respectively.

[0306] (4) Based on a mixture of 100 parts by weight of negative electrode active material, 47 parts by weight of the first negative electrode active material, 47 parts by weight of the second negative electrode active material and 6 parts by weight of the third negative electrode active material are mixed to prepare a mixture of negative electrode active materials.

[0307] A slurry of negative electrode active material was prepared by mixing 97.5% by weight of the mixture of the prepared negative electrode active material and 2.5% by weight of a mixture of (meth)acrylic binder (a copolymer of acrylic acid and acrylonitrile) and styrene-butadiene rubber (SBR) (1:1 by weight) in distilled water.

[0308] The negative electrode active material slurry is applied to the copper current collector, dried, and then rolled to manufacture the negative electrode plate.

[0309] 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 dissolved in 1M LiPF6 (volume ratio 3:7).

[0310] Example 8 Except for changing the spheroidization conditions in Example 7, the first negative electrode active material is prepared in the same manner as in Example 7. The prepared first negative electrode active material is used to manufacture the negative electrode and the half-cell in the same manner as in Example 7.

[0311] Example 9 Except for changing the spheroidization conditions in Example 7, the first negative electrode active material is prepared in the same manner as in Example 7. The prepared first negative electrode active material is used to manufacture the negative electrode and the half-cell in the same manner as in Example 7.

[0312] Examples 10 to 13 Except for changing the weight ratio of each of the components in Example 7 as shown in Table 2-1 below, the negative electrode plate and half cell are manufactured in the same manner as in Example 7.

[0313] Example 14 As in Example 1, 97.5% by weight of the prepared negative electrode active material mixture and 2.5% by weight of a mixture of (meth)acrylic binder, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) (1:1:1 by weight ratio) were mixed in distilled water to prepare a negative electrode active material slurry.

[0314] Comparison Example 6 Except that pitch carbon is not added when preparing the first negative electrode active material in Example 7, the first negative electrode active material is prepared in the same manner as in Example 7. The prepared first negative electrode active material is used to manufacture the negative electrode and the half-cell in the same manner as in Example 7.

[0315] Compare Example 7 Flake-shaped natural graphite raw materials with an average particle size D50 of 120 μm or larger were ground into fine primary particles with a plate-like shape and a long axis 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. Pitch carbon was added to the secondary particles, mixed, and then heat-treated in a sintering furnace at 1200 °C for 2 hours to prepare the first negative electrode active material. The addition of pitch carbon resulted in a weight ratio of natural graphite to amorphous carbon of 90:10 in the first negative electrode active material.

[0316] The prepared first negative electrode active material is used to manufacture the negative electrode and half cell in the same manner as in Example 7.

[0317] Compare Example 8 Flake-shaped natural graphite raw material with an average particle size D50 of 80 μm was ground into primary particles with a plate-like shape and a major axis 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. Pitch carbon was added to the secondary particles, mixed, and then heat-treated in a sintering furnace at 1200 °C for 2 hours to produce the first negative electrode active material. The addition of pitch carbon resulted in a weight ratio of natural graphite to amorphous carbon of 90:10 in the first negative electrode active material.

[0318] The prepared first negative electrode active material is used to manufacture the negative electrode and half cell in the same manner as in Example 7.

[0319] Compare Example 9 The negative electrode plate and half cell are manufactured in the same manner as in Example 7, except that carboxymethyl cellulose is used instead of the (meth)acrylic binder in Example 7.

[0320] Experimental Example 3: Evaluation of the Active Material of the First Negative Electrode Particle density (g / cc); orientation; d002 (Å); sphericity; and mercury accumulation pore volume (mL / g) were evaluated in the same manner as in Experimental Example 1.

[0321] Experimental Example 4: Evaluation of Battery Characteristics Capacity (mAh / g) and Charging C-rate (%) The half-cell was charged and discharged at 0.1C, and the discharge capacity was measured. The measured discharge capacities are shown in Table 1. The charge-discharge efficiency (discharge capacity / charge capacity %) was also measured.

[0322] The half-cell was subjected to 0.2C constant current (CC) and constant voltage (CV) charging and one 0.2C discharge, 0.5C constant current (CC) charging and one 0.2C discharge, 1C constant current (CC) charging and one 0.2C discharge, and 2C constant current (CC) charging and one 0.2C discharge. Charging characteristics were calculated using the following conditions: a 10mV cutoff for the CC (constant current) phase and a 15-hour cutoff for the CV (constant voltage) phase. The discharge condition was a 1.5V cutoff. Charging characteristics were measured at each C rate. The charging characteristic results were calculated and expressed as the ratio of the 2CCC charging capacity to the 0.2C CC charging capacity.

[0323] DC internal resistance (DC-IR, unit: Ω) Half-cells manufactured according to the example and comparative examples were charged at 25°C with a constant current / constant voltage of 0.2C, a cutoff condition of 10mV, and a stop condition of 0.01C, and allowed to stand for 10 minutes. They were then discharged with a constant current of 0.2C, a cutoff condition of 1.5V, and allowed to stand for 10 minutes. One charge / discharge cycle was performed under these conditions. The voltage drop (voltage drop, V) was measured at SOC50 (when the total charge capacity is 100%, the battery is charged to 50% of its total charge capacity) for 1 second at a current of 3C. The resistance value was obtained from the measured voltage drop and the applied current (3C), and the result is expressed as DC internal resistance (DC-IR).

[0324] Energy density (Wh / L): Energy density is a value obtained by multiplying the discharge capacity (calculated by discharging the battery cell at a C-rate of 0.1C to 1C within its operating voltage range) by the average voltage of the corresponding battery cell, and then dividing the product by the volume of the battery cell. Energy density can be calculated using the formula: (Battery cell capacity (Ah) × Average battery cell voltage (V)) / Battery cell volume (L) Boost charging time (seconds): Boost charging time refers to the time taken to charge from 8% SOC to 80% SOC using constant current charging, and is evaluated by identifying charging modes that do not reach the upper limit voltage of 4.2V during charging.

[0325] Boost charging life (cycles): Once the boost charging time is determined, a cycle evaluation of the large battery cell is performed, charging from 8% SOC (State of Charge) to 80% SOC (State of Charge), and discharging at a discharge voltage of 2.8V and a constant current of 0.33C until the SOH (State of Health) reaches 80%.

[0326] Expansion rate (%) The expansion rate was measured using the Thickness Monitoring System (TMS) method.

[0327] Under the conditions of charging voltage of 4.35V and discharging voltage of 2.8V, the thickness of the battery cells manufactured according to the example and comparative example was evaluated in real time while being charged / discharged at 45°C (0.5C / 0.5C) to evaluate the increase in thickness after 50 cycles relative to after 1 cycle.

[0328] The expansion rate is calculated as follows: Expansion rate (%) = (Cell thickness after 50 cycles - Cell thickness after 1 cycle) / Cell thickness after 1 cycle × 100 [Table 2-1]

[0329] [Table 2-2]

[0330] In Tables 2-1 and 2-2: C-1: Silicon-carbon composite D-1: (Meth)acrylic adhesive D-2: Carboxymethyl cellulose (CMC) D-3: Styrene-butadiene rubber (SBR) Weight ratio: The weight ratio of the first negative electrode active material to the second negative electrode active material to the third negative electrode active material based on 100 parts by weight of negative electrode active material.

[0331] As shown in Tables 2-1 and 2-2, when the negative electrode plate includes a (meth)acrylic binder, the example negative electrode plates for rechargeable lithium batteries exhibit high energy density, long lifetime, and boost charging characteristics. Furthermore, regarding boost charging lifetime, it can be seen that when only a conventional CMC binder is added, Example 13, which includes a large amount (3%) of a (meth)acrylic binder, has the longest lifetime, Comparative Example 8 has the highest orientation degree, and Comparative Example 9 has the poorest lifetime. Increasing the silicon content may be advantageous in terms of capacity and energy density, but disadvantageous in terms of lifetime. When a (meth)acrylic binder is included, electrode plate expansion can be suppressed, thereby reducing the lifetime reduction effect.

[0332] Example 15 (1) Preparation of the active material of the first negative electrode Flake-shaped natural graphite raw material with an average particle size D50 of 120 μm was 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 then heat-treated in a sintering furnace at 3,000 °C for 2 hours to prepare the first negative electrode active material. The addition of pitch carbon resulted in a weight ratio of natural graphite to amorphous carbon of 90:10 in the first negative electrode active material.

[0333] (2) Active material of the second negative electrode Artificial graphite (spherical, average particle size D50: 15μm, particle density: 1.5g / cc, tap density: 0.9g / cc, BET specific surface area: 1.5m²) was used. 2 / g, orientation degree: 100) is used as the active material for the second negative electrode. Artificial graphite exists in the form of secondary particles, uniformly formed from primary particles.

[0334] (3) Preparation of the active material of the third negative electrode Silicon particles with an average particle size of 8 μm were ball-milled to prepare primary particles with an average particle size D50 of 100 nm. The primary particles were mixed with stearic acid at a weight ratio of 20:80, and the resulting mixture was spray-dried to produce secondary particles containing pores and with an average particle size D50 of 27 μm.

[0335] The prepared secondary particles and petroleum asphalt were mixed at a weight ratio of 60:40, and the resulting mixture was subjected to a cold isostatic pressing process at a pressure of 10 MPa. Subsequently, the resulting pressed product was carbonized at a temperature of 1,000°C under a nitrogen atmosphere.

[0336] The carbonization products were graded using a sieve to achieve a span value of 1.1 in Equation 2 above, in order to prepare the third negative electrode active material. The third negative electrode active material is a silicon-carbon composite with secondary particles having an average particle size D50 of 7 μm. The secondary particles are assembled from primary silicon particles coated with a 30 nm thick layer of soft carbon and having an average particle size D50 of 100 nm. A soft carbon coating layer is then applied to the secondary particles. Based on the total weight of the third negative electrode active material, the amount of silicon nanoparticles is 60 wt%, and the amount of soft carbon is 40 wt%. Furthermore, the D10, D50, and D90 of the negative electrode active material were measured using a particle analyzer (trade name: LS 13 320, manufacturer: Beckman Coulter), and the span value was calculated according to Equation 2 above.

[0337] Furthermore, the sphericity was calculated from the cross-sectional images measured by CP-SEM using the ImageJ program. The sphericity was found to be 0.98. Additionally, the total pore volume and mesopore volume of the prepared third negative electrode active material were measured using a BJH (Barrett-Joyner-Halenda) analytical apparatus.

[0338] The BJH (model name: ASAP 2020, manufacturer: Micromeritics) analytical apparatus was used to measure the adsorption / desorption of the active material of the third negative electrode adsorbed on the sample by using nitrogen gas to change the pressure from 0 mHg to 950 mmHg at liquid nitrogen temperature (-198°C).

[0339] The prepared third negative electrode active material (C-1) has a sphericity of 0.98, a mesopore volume / total pore volume ratio of 68%, and a micrometer diameter of 0.8 μm. 2 Specific surface area per g, 0.007 cm² 3 / g of total BJH pore volume, 4.7μm D10, 8.2μm D50 and 13.7μm D90 and span value of 1.1 as calculated by Equation 2 above.

[0340] (4) Based on a mixture of 100 parts by weight of negative electrode active material, a mixture of negative electrode active material is prepared by mixing 47 parts by weight of first negative electrode active material, 47 parts by weight of second negative electrode active material and 6 parts by weight of third negative electrode active material.

[0341] A slurry of negative electrode active material was prepared by mixing 97.5% by weight of the mixture of the prepared negative electrode active material and 2.5% by weight of (meth)acrylic binder (a copolymer of acrylic acid and acrylonitrile) (D-1) as a binder in distilled water.

[0342] The negative electrode active material slurry is applied to the copper current collector, dried, and then rolled to manufacture the negative electrode plate.

[0343] 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 dissolved in 1M LiPF4 (volume ratio 3:7).

[0344] Example 16 Except for changing the spheroidization conditions in Example 15, the first negative electrode active material is prepared in the same manner as in Example 15. The prepared first negative electrode active material is used to manufacture the negative electrode and the half-cell in the same manner as in Example 15.

[0345] Example 17 Except for changing the spheroidization conditions in Example 15, the first negative electrode active material is prepared in the same manner as in Example 15. The prepared first negative electrode active material is used to manufacture the negative electrode and the half-cell in the same manner as in Example 15.

[0346] Examples 18 and 19 Except for changing the weight ratio of each of the components in Example 15 as shown in Table 3-1 below, the negative electrode plate and half cell are manufactured in the same manner as in Example 15.

[0347] Example 20 (1) Preparation of the active material of the third negative electrode The mixture of secondary particles prepared in Example 1 and petroleum asphalt was subjected to a cold isostatic pressing process at a pressure of 30 MPa, followed by a grading process to achieve a span of 1.5. As a result, a silicon-carbon composite with a span of 1.5 and a sphericity of 0.92 was prepared.

[0348] A polymer solution was prepared by mixing 6% by weight of polyvinyl alcohol and 94% by weight of polyacrylic acid in distilled water. The molar ratio of OH groups in polyvinyl alcohol to COOH groups in polyacrylic acid was 10:90.

[0349] The prepared silicon-carbon composite was mixed with a polymer solution, and the resulting mixture was stirred and then dried. The mixing ratio of the silicon-carbon composite to the polymer solution was adjusted to 97.1 wt% silicon-carbon composite and 2.9 wt% polymer. The dried mixture was heat-treated at 150 °C to prepare the third negative electrode active material (C-2).

[0350] In the prepared third negative electrode active material, based on 100 parts by weight of silicon-carbon composite, the amount of polymer is approximately 3 parts by weight, the mixing ratio of polyvinyl alcohol and polyacrylic acid is 6:94 by weight, and the molar ratio of OH groups contained in polyvinyl alcohol to COOH groups contained in polyacrylic acid is 10:90. Furthermore, the prepared third negative electrode active material (C-2) has a sphericity of 0.95, a mesopore volume / total pore volume ratio of 30%, and a micropore size of 1.2 μm. 2 Specific surface area per g, such as 0.015 cm² as determined by BJH. 3 The total pore volume is / g, the D10 is 4.1μm, the D50 is 7.9μm, the D90 is 15.9μm, and the span value is 1.5.

[0351] Except that the prepared third negative electrode active material is used as the third negative electrode active material in Example 15, the negative electrode plate and half cell are manufactured in the same manner as in Example 15.

[0352] Compare Example 10 Except that pitch carbon is not added when preparing the first negative electrode active material in Example 15, the first negative electrode active material is prepared in the same manner as in Example 15. The prepared first negative electrode active material is used to manufacture a negative electrode and a half-cell in the same manner as in Example 15.

[0353] Compare Example 11 Flake-shaped natural graphite raw materials with an average particle size D50 of 120 μm or larger were ground into fine primary particles with a plate-like shape and a long axis 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. Pitch carbon was added to the secondary particles, mixed, and then heat-treated in a sintering furnace at 1200 °C for 2 hours to prepare the first negative electrode active material. The addition of pitch carbon resulted in a weight ratio of natural graphite to amorphous carbon of 90:10 in the first negative electrode active material.

[0354] The prepared first negative electrode active material is used to manufacture the negative electrode and half cell in the same manner as in Example 15.

[0355] Compare Example 12 Flake-shaped natural graphite raw material with an average particle size D50 of 80 μm was ground into primary particles with a plate-like shape and a major axis 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. Pitch carbon was added to the secondary particles, mixed, and then heat-treated in a sintering furnace at 1200 °C for 2 hours to prepare the first negative electrode active material. The addition of pitch carbon resulted in a weight ratio of natural graphite to amorphous carbon of 90:10 in the first negative electrode active material.

[0356] The prepared first negative electrode active material is used to manufacture the negative electrode and half cell in the same manner as in Example 15.

[0357] Compare Example 13 The negative electrode plate and half cell are manufactured in the same manner as in Example 15, except that carboxymethyl cellulose (CMC) (D-2) is used instead of the (meth)acrylic binder in Example 15.

[0358] Compare Example 14 The negative electrode plate and half cell were manufactured in the same manner as in Comparative Example 13, except that carboxymethyl cellulose was used instead of the (meth)acrylic binder in Example 15 and the weight ratio of each component was changed as shown in Table 3-2 below.

[0359] Experimental Example 5: Evaluation of the Active Material of the First Negative Electrode Particle density (g / cc); orientation; d002 (Å); sphericity; and mercury accumulation pore volume (mL / g) were evaluated in the same manner as in Experimental Example 1.

[0360] Experimental Example 6: Evaluation of Battery Characteristics The half-cell was charged and discharged at 0.1C, and the discharge capacity was measured. The measured discharge capacities are shown in Table 1. The charge-discharge efficiency (discharge capacity / charge capacity %) was also measured.

[0361] The half-cell was subjected to 0.2C constant current (CC) and constant voltage (CV) charging and one 0.2C discharge, 0.5C constant current (CC) charging and one 0.2C discharge, 1C constant current (CC) charging and one 0.2C discharge, and 2C constant current (CC) charging and one 0.2C discharge. Charging characteristics were calculated using the following conditions: a 10mV cutoff for the CC (constant current) phase and a 15-hour cutoff for the CV (constant voltage) phase. The discharge condition was a 1.5V cutoff. Charging characteristics were measured at each C rate. The charging characteristic results were calculated and expressed as the ratio of the 2CCC charging capacity to the 0.2C CC charging capacity.

[0362] Energy density (Wh / L): Energy density is obtained by multiplying the discharge capacity (calculated by discharging the battery cell at a C-rate of 0.1C to 1C within its operating voltage range) by the average voltage of the corresponding battery cell, and then dividing by the volume of the battery cell. Energy density can be calculated as follows: (Battery cell capacity (Ah) × Average battery cell voltage (V)) / Battery cell volume (L) Boost charging time (seconds): Boost charging time refers to the time taken to charge from 8% SOC to 80% SOC using constant current charging, and is evaluated by identifying charging modes that do not reach the upper limit voltage of 4.2V during charging.

[0363] Boost charging life (cycles): Once the boost charging time is determined, a cycle evaluation of the large battery cell is performed, charging from 8% SOC (State of Charge) to 80% SOC (State of Charge), and discharging at a discharge voltage of 2.8V and a constant current of 0.33C until the SOH (State of Health) reaches 80%.

[0364] Expansion rate (%) The expansion rate was measured using the Thickness Monitoring System (TMS) method.

[0365] Under the conditions of charging voltage of 4.35V and discharging voltage of 2.8V, the thickness of the battery cells manufactured according to the example and comparative example was evaluated in real time while being charged / discharged at 45°C (0.5C / 0.5C) to evaluate the increase in thickness after 50 cycles relative to after 1 cycle.

[0366] The expansion rate is calculated using the formula: Expansion rate (%) = (Cell thickness after 50 cycles - Cell thickness after 1 cycle) / Cell thickness after 1 cycle × 100 [Table 3-1]

[0367] [Table 3-2]

[0368] In Tables 3-1 and 3-2: C-1: Silicon-carbon composite C-2: Silicon-carbon composite D-1: (Meth)acrylic adhesive D-2: Carboxymethyl cellulose Weight ratio: The weight ratio of the first negative electrode active material to the second negative electrode active material to the third negative electrode active material based on 100 parts by weight of negative electrode active material.

[0369] As shown in Table 3-1 above, the example negative electrode plate exhibits high energy density, low boost charging time and expansion rate, and long boost charging lifetime. Therefore, the example demonstrates high energy density, long lifetime, high C-rate charging characteristics, and improved electrode plate expansion characteristics.

[0370] However, as shown in Table 3-2 above, Comparative Example 10, which does not include the first negative electrode active material of this disclosure, has poor electrode plate expansion characteristics and is poor in terms of boost charge lifetime and boost charge time. Comparative Examples 11 and 12, which do not include the first negative electrode active material of this disclosure, have poor boost charge lifetime. Comparative Examples 13 and 14, which do not include the (meth)acrylic binder of this invention, have poor electrode plate expansion characteristics and poor boost charge lifetime.

[0371] The negative electrode plate for a rechargeable lithium battery according to embodiments of the present disclosure can provide high energy density, long life and boost charging effect, and thus exhibits excellent rechargeable lithium battery performance.

[0372] While preferred embodiments of the present disclosure have been described above, the disclosure is not limited to these examples. Therefore, it should be understood that various changes and modifications can be made within the scope of the detailed description of the present disclosure.

Claims

1. A negative electrode plate for a rechargeable lithium battery, the negative electrode plate comprising a negative electrode active material and a binder, in, The negative electrode active material comprises a mixture of a first negative electrode active material, a second negative electrode active material, and a third negative electrode active material. The first negative electrode active material comprises natural graphite, which includes secondary particles formed from primary particles, and an amorphous carbon coating layer surrounds the secondary particles. Furthermore, the first negative electrode active material has an orientation degree of 90° or less and a d0O2 of 3.356 Å to 3.360 Å. The second negative electrode active material is graphite. The third negative electrode active material includes one or more of the following negative electrode active materials (i), (ii), and (iii): The negative electrode active material (i) includes a core comprising silicon nanoparticles and amorphous carbon, and an amorphous carbon coating layer surrounds the core; The negative electrode active material (ii) comprises a composite of silicon and crystalline carbon, and an amorphous carbon coating layer is formed on the surface of the composite and comprises amorphous carbon; and The negative electrode active material (iii) comprises silicon nanoparticles and an amorphous carbon coating layer disposed on the surface of the silicon nanoparticles, and the negative electrode active material (iii) has a sphericity of 0.9 to 1.

0. The adhesive includes (meth)acrylic adhesives.

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

5. The negative electrode plate 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 plate according to claim 1, wherein, The primary particles have a plate-like shape, and the secondary particles have a spherical shape.

7. The negative electrode plate according to claim 1, wherein, The primary particles have a major axis length of 10 μm to 200 μm.

8. The negative electrode plate according to claim 1, wherein, The secondary particles have an average particle size D50 of 30 μm or less.

9. The negative electrode plate according to claim 1, wherein, Amorphous carbon forms on the surface of the primary particles.

10. The negative electrode plate according to claim 1, wherein, Amorphous carbon is one or more of soft carbon, hard carbon, mesophase pitch carbides and calcined coke.

11. The negative electrode plate according to claim 9, wherein, In the first negative electrode active material, natural graphite and amorphous carbon are included in a weight ratio of 90:10 to 75:25, based on a total of 100 parts by weight.

12. The negative electrode plate according to claim 1, wherein, The second negative electrode active material has an average particle size D50 of 10 μm to 20 μm, a particle density of 1.1 g / cc to 1.6 g / cc, and a particle size of 10 μm. 2 Artificial graphite with a specific surface area of ​​ / g or less and an orientation degree of 90 or greater.

13. The negative electrode plate according to claim 1, wherein, The interparticle distance between the silicon nanoparticles included in the core of the negative electrode active material (i) is 100 nm or less.

14. The negative electrode plate according to claim 1, wherein, The average particle size D50 of the silicon nanoparticles in the negative electrode active material (i) is 50 nm to 150 nm.

15. The negative electrode plate according to claim 1, wherein, The negative electrode active material (i) has pores with a size of 200 nm or smaller, and the pores have a diameter of 3.0 × 10⁻⁶. -2 cm 3 / g or less of total pore volume.

16. The negative electrode plate according to claim 1, wherein, In the negative electrode active material (i), silicon nanoparticles and amorphous carbon are included in a weight ratio of 80:20 to 20:80, based on a total of 100 parts by weight.

17. The negative electrode plate according to claim 1, wherein, The negative electrode active material (ii) has an aspect ratio of 1 to 2.

5.

18. The negative electrode plate according to claim 1, wherein, In the negative electrode active material (ii), silicon is included in an amount of 20% to 70% by weight, crystalline carbon is included in an amount of 3% to 50% by weight, and amorphous carbon is included in an amount of 20% to 50% by weight.

19. The negative electrode plate according to claim 1, wherein, The negative electrode active material (iii) includes pores, and the pores include mesopores.

20. The negative electrode plate according to claim 19, wherein, The third negative electrode active material (iii) has a ratio of 30% or more and less than 70% of the mesopore volume to the total pore volume of the third negative electrode active material.

21. The negative electrode plate according to claim 1, wherein, The negative electrode active material (iii) has a range of values ​​from 1.1 to 1.6 according to the following equation 2: [Equation 2] Span = (D90 - D10) / D50 in: D10 represents the particle size of the negative electrode active material (iii) with a cumulative volume of 10% in the particle size distribution. D50 represents the particle size of the negative electrode active material (iii) with a cumulative volume of 50% in the particle size distribution, and D90 represents the particle size of the negative electrode active material (iii) whose cumulative volume is 90% in the particle size distribution.

22. The negative electrode plate according to claim 1, wherein, The negative electrode active material (iii) also includes a polymer layer disposed on the amorphous carbon coating layer.

23. The negative electrode plate according to claim 22, wherein, The polymer layer comprises polyvinyl alcohol and polyacrylic acid.

24. The negative electrode plate according to claim 1, wherein, The first negative electrode active material is included in an amount of 20% to 75% by weight, the second negative electrode active material is included in an amount of 20% to 75% by weight, and the third negative electrode active material is included in an amount of 1% to 20% by weight.

25. The negative electrode plate according to claim 1, wherein, The (meth)acrylic adhesive comprises units derived from (meth)acrylic monomers and units derived from (meth)acrylic monomers having cyano groups.

26. The negative electrode plate according to claim 1, wherein, The (meth)acrylic binder is included in the negative electrode plate in an amount of 0.5% to 5% by weight.

27. A rechargeable lithium battery, the rechargeable lithium battery comprising a negative electrode plate and a positive electrode for a rechargeable lithium battery according to any one of claims 1 to 26.

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