Negative electrode active material for lithium secondary battery, method for manufacturing same, negative electrode comprising same, and lithium secondary battery

Abstract

A negative electrode active material for a lithium secondary battery, a method of manufacturing the same, a negative electrode comprising the same, and a lithium secondary battery are described. A negative electrode active material for a lithium secondary battery includes a core portion and a shell portion surrounding the core portion, in which the core portion includes a porous structure including sheet-like silicon particles and amorphous carbon, and the shell portion includes sheet-like silicon particles, amorphous carbon, and crystalline carbon.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0137425, filed with the Korean Intellectual Property Office on October 10, 2024, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to a negative electrode active material for lithium secondary batteries, a method for manufacturing the same, and a negative electrode and a lithium secondary battery comprising the negative electrode active material. Background Technology

[0004] In recent years, the demand for high-energy-density batteries has increased in response to global regulations such as CO2 and greenhouse gas emission regulations. Lithium-ion batteries are the most widely used rechargeable batteries for energy storage devices. Graphite is most commonly used as the active material in the negative electrode of lithium-ion batteries. However, graphite has a low theoretical capacity per unit weight of 372 mAh / g, thus limiting its energy density. Therefore, it cannot meet the high energy density requirements for the driving range of electric vehicles on a single charge. Silicon is a negative electrode active material that has emerged as an alternative to overcome the low capacity of graphite. Silicon has a discharge capacity per unit weight of 3579 mAh / g, approximately 10 times that of graphite, and is therefore attracting attention as a next-generation negative electrode active material. However, silicon also has a drawback: poor cycle life due to particle breakage and electrode detachment caused by the high expansion rate (up to approximately 300%) during a single charge. Therefore, continuous efforts are being made to mitigate the performance degradation caused by the volume expansion of silicon and improve overall cycle life. Summary of the Invention

[0005] The present invention was developed to solve the aforementioned problems in the related art. One aspect of the present invention is to provide a negative electrode active material for lithium secondary batteries, a method for manufacturing the same, and a negative electrode and a lithium secondary battery comprising the negative electrode active material. Compared with conventional inventions, the negative electrode active material has increased particle size to reduce reaction sites at the interface between the negative electrode active material and the electrolyte, thereby exhibiting excellent initial efficiency and lifetime characteristics.

[0006] To achieve this, in one aspect, the negative electrode active material for a lithium secondary battery of the present invention may include a core and a shell portion at least partially surrounding the core. In one aspect, the core may include a porous structure comprising sheet-like silicon particles and amorphous carbon, and the shell portion may include sheet-like silicon particles, amorphous carbon, and crystalline carbon.

[0007] In a preferred aspect, the sheet-like silicon particles and amorphous carbon can be interconnected, for example, by physical aggregation and / or non-covalent and / or covalent bonding. Non-covalent bonds can include polar interactions, such as hydrogen bonds.

[0008] A method for manufacturing a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention may include: preparing a mixture comprising silicon particles and an amorphous carbon precursor, preparing a molded body by spray drying the mixture, preparing a composite material having a core-shell structure by carbonizing the molded body, and controlling the size of the composite material.

[0009] The negative electrode in this embodiment of the invention may include a negative electrode active material located on the current collector, and the negative electrode active material may be a negative electrode active material for lithium secondary batteries according to various embodiments of the invention.

[0010] The lithium secondary battery of this invention may include a positive electrode, a negative electrode according to various embodiments of the invention, and an electrolyte.

[0011] According to the present invention, the negative electrode active material for lithium secondary batteries has an increased particle size compared with conventional inventions, so as to reduce the reaction sites at the interface between the negative electrode active material and the electrolyte.

[0012] Therefore, the rate of resistance increase can be reduced by suppressing the reaction and region that produces SEI.

[0013] Therefore, initial efficiency can be improved, and lifetime characteristics can be excellent.

[0014] Furthermore, unlike conventional inventions, the core may not contain crystalline carbon. Therefore, the aggregation of sheet-like silicon particles can be reduced, allowing the core diameter to be uniform.

[0015] The negative electrode active material for lithium secondary batteries according to the present invention has a porous structure and pores that serve as a buffer layer, thereby mitigating volume changes in silicon during charging and discharging. Furthermore, even after numerous repeated cycles, the amount of cracking can be reduced, thereby improving safety.

[0016] In some embodiments, the negative electrode active material for a lithium secondary battery includes a core and a shell surrounding the core, wherein the core comprises a porous structure in which sheet-like silicon particles are interconnected with amorphous carbon, and the shell comprises sheet-like silicon particles, amorphous carbon, and crystalline carbon.

[0017] The negative electrode active material can have a median diameter (Dv50) of about 9 to 11 micrometers.

[0018] The negative electrode active material can have a SPAN value of approximately 1.6 to 2.2, which is defined as (Dv90-Dv10) / Dv50, where Dv90, Dv10, and Dv50 represent the particle diameters corresponding to 90%, 10%, and 50% of the volume in the particle size distribution, respectively.

[0019] The distance between the points where the major and minor axes of the sheet-like silicon particles in the negative electrode active material intersect can be approximately 20 nanometers to 50 nanometers.

[0020] The anode active material has sheet-like silicon particles with a crystal size of approximately 16 to 18 nanometers.

[0021] The negative electrode active material can have a shell thickness of about 20 nanometers to 300 nanometers.

[0022] The core of the negative electrode active material may contain little or no crystalline carbon.

[0023] In some embodiments, a method for manufacturing a negative electrode active material for lithium secondary batteries includes: preparing a mixture comprising silicon particles and an amorphous carbon precursor, preparing a molded body by spray drying the mixture, preparing a composite material having a core-shell structure by carbonizing the molded body, and controlling the dimensions of the composite material.

[0024] This method may include adding crystalline carbon and amorphous carbon precursors and performing heat treatment when preparing a composite material with a core-shell structure.

[0025] The method may include adding about 47% to 57% by weight of crystalline carbon and about 65% to 75% by weight of amorphous carbon precursor based on the total weight of silicon particles.

[0026] The method may include heat treatment at approximately 900°C to 1100°C.

[0027] In this method, crystalline carbon can be flake graphite with a median volume diameter Dv50 of about 10 micrometers to 100 micrometers.

[0028] In this method, the amorphous carbon precursor can be any one selected from phenolic resin, furan resin, coal tar pitch, petroleum pitch, and combinations thereof.

[0029] In this method, the amorphous carbon precursor can be petroleum bitumen with a median volume diameter Dv50 of about 1 to 10 micrometers.

[0030] This method may include controlling the volume median diameter Dv50 of the composite material to approximately 9 to 11 micrometers.

[0031] The method may include controlling the SPAN value of the composite material to approximately 1.6 to 2.2, wherein the SPAN value is defined as (Dv90-Dv10) / Dv50.

[0032] In the composite material with a core-shell structure produced by this method, the core may contain a porous structure in which lamellar silicon particles and amorphous carbon are interconnected, and the shell may contain lamellar silicon particles, amorphous carbon and crystalline carbon.

[0033] This method can make the core contain little or no crystalline carbon.

[0034] This method can produce shells with a thickness of approximately 20 nanometers to 300 nanometers.

[0035] In some implementations, a negative electrode comprising a negative electrode active material is provided.

[0036] As mentioned herein, in at least some respects, sheet-like silicon particles can be considered as essentially more two-dimensional structures, where dimensions X and Y are much larger than dimension Z (e.g., at least 10%, 20%, 30%, 40%, 50%, 100%, 200%, 300%, 400%, or 500% larger). Sheet-like silicon particles can be considered as sheet-like silicon particles, and in some respects as thin films. Attached Figure Description

[0037] The above and other aspects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0038] Figure 1 This is a schematic diagram of the negative electrode active material for lithium secondary batteries according to the present invention;

[0039] Figure 2 This is a schematic diagram illustrating the porous structure included in the core according to an embodiment of the present invention;

[0040] Figure 3 This is a process flow diagram of the manufacturing method of the negative electrode active material for lithium secondary batteries according to the present invention;

[0041] Figure 4 This is a schematic diagram illustrating a process for manufacturing a negative electrode active material for a lithium secondary battery according to various embodiments of the present invention;

[0042] Figure 5 The XRD results show the dimensions of the sheet-like silicon particles in Example 3;

[0043] Figure 6 This is a SEM image showing the core of Example 3;

[0044] Figure 7This is a graph illustrating the particle size distribution of the embodiments and comparative embodiments;

[0045] Figure 8 These are SEM images of Example 3 and Comparative Example 3, wherein, Figure 8 (a) is a SEM image of Comparative Example 3. Figure 8 (b) is the SEM image of Example 3;

[0046] Figure 9 This is a graph showing the initial capacity and initial efficiency of Example 3;

[0047] Figure 10 This is a graph showing the capacity retention rate after 300 cycles for the embodiments and comparative embodiments;

[0048] Figure 11 This is an image of the negative electrode after 300 cycles, where... Figure 11 (a) is an image of Comparative Example 3. Figure 11 (b) is an image of Example 3; and

[0049] Figure 12 These are cross-sectional SEM images of the negative electrode before and after 300 cycles, where... Figure 12 (a) is the initial SEM image of Comparative Example 3. Figure 12 (b) is the initial SEM image of Example 3. Figure 12 (c) is the SEM image of Comparative Example 3 after 300 cycles. Figure 12 (d) is the SEM image of Example 3 after 300 cycles.

[0050] [Explanation of reference numerals and symbols in the attached figures]

[0051] 1: Negative electrode active material

[0052] 100: Core

[0053] 110: Flake-shaped silicon particles

[0054] 120: Amorphous carbon

[0055] 200: Shell

[0056] D: Distance between the points where the major and minor axes of the sheet-like silicon particle intersect.

[0057] S100: Preparation of mixture

[0058] S200: Preparation of molded body

[0059] S300: Preparation of composite materials

[0060] S310: Contains crystalline carbon and amorphous carbon precursors.

[0061] S320: Heat treatment

[0062] S400: Controls the dimensions of composite materials. Detailed Implementation

[0063] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by those skilled in the art. Terms as defined in commonly used dictionaries should be interpreted as having a meaning that matches the context of the relevant art and should not be interpreted as having an ideal or overly formal meaning, unless otherwise explicitly defined in this invention.

[0064] As used in this invention, terms including "first," "second," etc., can be used to describe various components, but the components are not limited by these terms. These terms are only used to distinguish one component from another. For example, without departing from the scope of this invention, a first component may be named a second component, and similarly, a second component may be named a first component.

[0065] The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. Singular expressions include plural expressions unless otherwise defined in the context. In this invention, it should be understood that the terms "comprising" or "having" indicate the presence of the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0066] It should be understood that, as used herein, the terms “vehicle” or “of a vehicle” or other similar terms generally include motor vehicles, such as passenger vehicles including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, vessels including various boats and ships, aircraft, etc., and include hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from non-petroleum energy sources). As mentioned herein, a hybrid vehicle is a vehicle with two or more power sources, such as a vehicle that combines gasoline and electric power.

[0067] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the / said” are intended to include the plural forms as well. These terms are intended only to distinguish one component from another, and the terms do not limit the nature, order, or sequence of these constitutive components. As used herein, the term “and / or” includes any and all combinations of one or more of the associated enumerations. Furthermore, the terms “unit,” “component,” “device,” and “module” described in this specification refer to a unit for performing at least one function and operation, and may be implemented by hardware components or software components and combinations thereof.

[0068] While exemplary embodiments are described as using multiple units to perform exemplary processes, it should be understood that exemplary processes can also be performed by one or more modules. Furthermore, it should be understood that the term controller / control unit refers to a hardware device including a memory and a processor, specifically programmed to perform the processes described herein. The memory is configured to store modules, and the processor is specifically configured to execute said modules to perform one or more processes further described below.

[0069] Furthermore, the control logic of the present invention can be implemented as a non-volatile computer-readable medium containing executable program instructions that are executed by a processor, controller, etc. Examples of computer-readable media include (but are not limited to) ROM, RAM, optical disc (CD)-ROM, magnetic tape, floppy disk, flash drive, smart card, and optical data storage device. The computer-readable medium can also be distributed across a network-connected computer system, thereby enabling the computer-readable medium to be stored and executed in a distributed manner via, for example, a telematics server or a controller area network (CAN).

[0070] Unless otherwise stated or obvious from the context, the term “about” as used herein is understood to mean within the normal tolerance range in the field, such as within two standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless the context clearly indicates otherwise, all numerical values ​​provided herein are modified by the term “about”.

[0071] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0072] First, refer to Figure 1 and Figure 2 The present invention describes a negative electrode active material 1 for lithium secondary batteries.

[0073] Figure 1 This is a schematic diagram of the negative electrode active material for lithium secondary batteries according to the present invention.

[0074] Figure 2 This is a schematic diagram illustrating the negative electrode active material 1 for a lithium secondary battery according to an embodiment of the present invention and the porous structure contained in the core 100.

[0075] Reference Figure 1 The negative electrode active material 1 for lithium secondary batteries of the present invention may include a core 100 and a shell 200 surrounding the core 100. The core 100 may include sheet-like silicon particles 110 and amorphous carbon 120.

[0076] At this point, the sheet-like silicon particles 110 and the amorphous carbon 120 can be interconnected. In some embodiments of the invention, interconnection refers to the shape in which the amorphous carbon 120 is attached or connected to the plurality of sheet-like silicon particles 110 without a specific regularity, such as... Figure 2 As shown.

[0077] In this invention, sheet-like silicon particles 110 and amorphous carbon 120 can be interconnected to form a porous structure. In this invention, the porous structure may include spaces or pores formed by the interconnection of sheet-like silicon particles 110 and amorphous carbon 120, such as... Figure 2 As shown. Meanwhile, Figure 1 and Figure 2 The sheet-like silicon particles 110, amorphous carbon 120, and the spaces between them are merely examples and are not limited to their shapes.

[0078] In the negative electrode active material 1 for lithium secondary batteries according to the present invention, the core 100 includes a porous structure in which sheet-like silicon particles 110 and amorphous carbon 120 are interconnected to serve as a buffer layer, which mitigates the volume expansion of silicon that occurs during the charging and discharging of the lithium secondary battery. Therefore, even after continuous charging and discharging, the amount of cracks that occur can be reduced, thereby improving safety.

[0079] In various embodiments of the present invention, the distance D between the points where the major and minor axes of the sheet-like silicon particles 110 intersect can be 20 nanometers to 50 nanometers.

[0080] In various embodiments of the present invention, the crystal size of the sheet-like silicon particles 110 can be from 16 nanometers to 18 nanometers. In this case, the crystal size of the particles can be obtained according to the Debye-Scherrer equation via the equation Kλ / FWHM×cosθ. Here, K is the form factor with a value of approximately 0.9, λ represents the X-ray wavelength, FWHM represents the full width at half maximum (FWHM), and θ represents the X-ray incident angle.

[0081] Furthermore, unlike conventional inventions, the core 100 of the negative electrode active material 1 for lithium secondary batteries according to the present invention may not contain crystalline carbon. In some embodiments, the core 100 of the negative electrode active material 1 for lithium secondary batteries according to the present invention may be substantially free of crystalline carbon. As used herein, "substantially free" means that the amount of crystalline carbon present does not substantially affect the properties or performance of the material. For example, "substantially free" may mean that the content of crystalline carbon is less than about 5% by weight, or less than about 1% by weight, or even 0% by weight. Therefore, the aggregation of the flake silicon particles 110 can be reduced, so that the diameter of the core 100 can be uniform. In addition, since relatively coarse crystalline carbon is not contained, the diameter and shape of the core 100 can be uniform.

[0082] The shell portion 200 of the negative electrode active material 1 for lithium secondary batteries according to the present invention may comprise flake silicon particles 110, amorphous carbon 120, and crystalline carbon. In this case, the crystalline carbon may be flake graphite. When flake graphite is included in the shell portion 200, conductivity can be improved by contacting the flake silicon particles 110. In one embodiment, the flake graphite may have a carbon content greater than 99.9%, an oxygen content less than 0.5%, and a moisture content less than 1%.

[0083] In one embodiment of the present invention, the thickness of the housing 200 can be from 20 nanometers to 300 nanometers.

[0084] The median volume diameter D of the negative electrode active material 1 for lithium secondary batteries according to the present invention v The particle size can be from 9 micrometers to 11 micrometers. Compared with conventional inventions, the negative electrode active material 1 for lithium secondary batteries according to the present invention has an increased particle diameter, thereby reducing the reaction sites at the interface between the negative electrode active material 1 and the electrolyte. Therefore, the rate of resistance increase can be reduced by suppressing the reaction and region that generates SEI. Therefore, the initial efficiency can be improved and the lifetime characteristics can be excellent.

[0085] The SPAN value of the negative electrode active material 1 for lithium secondary batteries according to the present invention can be from 1.6 to 2.2. The SPAN value is used as a particle size distribution adjustment index and is defined as (D... v 90-D v 10) / D v 50. Here, D v 90. D v 10 and D v 50 represents the particle diameter corresponding to 90%, 10%, and 50% of the volume in the size distribution, respectively. In other words, the SPAN value indicates the deviation of the diameter of large particles and the diameter of small particles from the median diameter D in the volumetric distribution. vThe SPAN value is 50, and the smaller the value, the more uniform the particle size. The negative electrode active material 1 for lithium secondary batteries according to the invention can have an SPAN value of 1.6 to 2.2, which makes the particle size uniform and the capacity retention excellent.

[0086] In the following text, reference will be made to Figure 3 and Figure 4 Methods for manufacturing negative electrode active materials for lithium secondary batteries according to various embodiments of the present invention are described. Figure 3 This is a process flow diagram of the manufacturing method of the negative electrode active material for lithium secondary batteries according to the present invention. Figure 4 This is a schematic diagram illustrating a process for manufacturing a negative electrode active material for a lithium secondary battery according to various embodiments of the present invention.

[0087] Reference Figure 3 The method for manufacturing the negative electrode active material for lithium secondary batteries according to the present invention may include: preparing a mixture (S100), preparing a molded body (S200), preparing a composite material (S300), and controlling the size of the composite material (S400).

[0088] Specifically, the preparation of the mixture of the present invention (S100) may involve preparing a mixture comprising silicon particles and an amorphous carbon precursor. In the preparation of the mixture (S100), the silicon particles can be pulverized by a grinding process. The grinding process may be wet grinding. For example, wet grinding may be bead milling, but is not limited to any particular type, and can be applied if the process is a conventional wet grinding process.

[0089] In this case, the silicon particles can be flake-shaped silicon particles. In one embodiment, the pulverized flake-shaped silicon particles can be in the form of a slurry.

[0090] The amorphous carbon precursor can be any one selected from phenolic resins, furan resins, coal tar pitch, petroleum pitch, and combinations thereof. In one embodiment, the amorphous carbon precursor can be petroleum pitch, wherein the median volume diameter D of the petroleum pitch is... v 50 represents 1 to 10 micrometers. At this point, the softening point of petroleum asphalt can be between 200°C and 250°C.

[0091] Amorphous carbon precursors can be formed by removing internal organic materials in the heat treatment step (S320) described below.

[0092] Specifically, the preparation of the molded body of the present invention (S200) can be achieved by spray drying the mixture. The molded body can form a porous structure, in which, as described above, sheet-like silicon particles and amorphous carbon are interconnected. In one embodiment, the molded body can be in powder form.

[0093] Specifically, the preparation of the composite material of the present invention (S300) may involve carbonizing the molded body to prepare a composite material having a core-shell structure.

[0094] Reference Figure 4 The preparation of the composite material (S300) may include adding crystalline carbon and amorphous carbon precursors (S310) and performing heat treatment (S320).

[0095] The addition of crystalline carbon and amorphous carbon precursors (S310) can be performed by coating them onto the surface of a molded body. The molded body can form a core structure, and the crystalline carbon and amorphous carbon precursors can be coated onto the surface of the molded body to form a shell structure. In one embodiment, flake-shaped silicon particles can be added together with the crystalline carbon and amorphous carbon precursors used for coating onto the surface of the molded body.

[0096] When crystalline carbon and amorphous carbon precursors are coated on the surface of the molded body, direct contact between the core and the electrolyte can be prevented, volume expansion can be suppressed, and conductivity can be improved.

[0097] The crystalline carbon can be flake graphite with a median volume diameter (Dv50) of 10 to 100 micrometers. In one embodiment, the flake graphite may have a carbon content greater than 99.9%, an oxygen content less than 0.5%, and a moisture content less than 1%.

[0098] The amorphous carbon precursor can be any one selected from phenolic resins, furan resins, coal tar pitch, petroleum pitch, and combinations thereof. In one embodiment, the amorphous carbon precursor can be petroleum pitch, wherein the median volume diameter D of the petroleum pitch is... v 50 represents 1 to 10 micrometers. At this point, the softening point of petroleum asphalt can be between 200°C and 250°C.

[0099] When adding crystalline carbon and amorphous carbon precursors (S310), 47% to 57% wt% crystalline carbon and 65% to 75% amorphous carbon precursors may be added relative to the total weight of silicon particles in the molded body.

[0100] Simultaneously, the heat treatment step (S320) can be performed at 900°C to 1100°C. Through the heat treatment step (S320), the molded body can be finally carbonized. Furthermore, the organic material in the amorphous carbon precursor can be removed to form amorphous carbon. That is, the amorphous carbon precursor contained in the core and shell can be formed into amorphous carbon by removing the organic material therein.

[0101] Meanwhile, the core of the prepared core-shell composite material can contain a porous structure, as described above, in which sheet-like silicon particles and amorphous carbon are interconnected. The shell can contain sheet-like silicon particles, amorphous carbon, and crystalline carbon, and can be in the form of surrounding the core.

[0102] The size control of the composite material of the present invention (S400) can be achieved by shredding and classifying the composite material. Shredding refers to dispersing materials (e.g., particle aggregates or granules) that are aggregated with relatively weak forces during a general crushing process. In controlling the size of the composite material (S400), aggregation of the prepared composite material can be eliminated by shredding.

[0103] In addition, in composite materials prepared by gradation, fine particles exceeding a certain size or coarse particles exceeding a certain size can be removed.

[0104] The dimension control of the composite material of the present invention (S400) enables the median volume diameter D of the composite material having a core-shell structure to be... v The particle size is 9 to 11 micrometers. Composite materials with this controlled-size core-shell structure can have increased particle size compared to conventional inventions, thereby reducing reaction sites at the interface between the negative electrode active material and the electrolyte. Therefore, the rate of resistance increase can be reduced by suppressing the reaction and region that generates SEI. Consequently, initial efficiency can be improved and lifetime characteristics can be excellent.

[0105] The dimension control of the composite material of the present invention (S400) can make the SPAN value of the composite material 1.6 to 2.2.

[0106] The negative electrode of the present invention includes a current collector and a negative electrode active material located on the current collector, and the negative electrode active material can be a negative electrode active material for lithium secondary batteries according to various embodiments of the present invention. There are no particular limitations on the negative electrode current collector, as long as it is conductive and does not cause chemical changes in the lithium secondary battery. For example, the negative electrode current collector can be made of copper, stainless steel, aluminum, nickel, titanium, plastic carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, etc.

[0107] The lithium secondary battery of the present invention may include a positive electrode, a negative electrode according to various embodiments of the present invention, and an electrolyte. The positive electrode may include a positive electrode active material and a current collector. As the positive electrode active material, one or at least two types of lithium-containing transition metal oxides commonly used in lithium secondary batteries may be mixed and used, but are not necessarily limited thereto. For example, a composite oxide of lithium with cobalt, nickel, manganese, etc., may be used as the lithium-containing transition metal oxide. There are no restrictions on the positive electrode current collector used, as long as the positive electrode current collector has good conductivity, can easily adhere to the slurry of the positive electrode active material, and is not reactive within the voltage range of the battery; examples include aluminum (Al), nickel (Ni), etc.

[0108] The electrolyte may contain lithium salts. Lithium salts can act as channels for the movement of lithium ions and can be, but are not limited to, LiPF6, LiBF4, LiBOB, and LiTFSI. Additionally, the electrolyte may contain solvents and additives, but is not limited to any particular type, and any commonly used solvents and additives can be used.

[0109] The present invention will be described in more detail below with reference to embodiments. However, the following embodiments and experimental examples are intended only to describe the invention in more detail, and the scope of the invention is not limited to the following embodiments and experimental examples.

[0110] Examples and Comparative Examples

[0111] To manufacture the negative electrode active material for lithium-ion secondary batteries, a slurry-type mixture comprising flake silicon particles and petroleum pitch was prepared. The mixture was spray-dried to prepare a powder-type molded body. Subsequently, flake graphite, petroleum pitch, and flake silicon particles were coated onto the molded body, and a negative electrode active material with a core-shell structure was obtained by heat treatment at approximately 1000°C. The size of the negative electrode active material was then controlled by fragmentation and classification.

[0112] Meanwhile, during the manufacturing process, different settings were made for the slurry solid content, nozzle injection angle, chamber temperature, injection speed, and air flow rate during spray drying. Additionally, different settings were made for the powder feeding speed, crushing pressure, and air flow rate during the pulverization process. By changing the above conditions, the negative electrode active materials of the embodiments and comparative embodiments were finally obtained, and their physical properties are shown in Table 1 below.

[0113] Meanwhile, in Table 1, D refers to the distance between the points where the major and minor axes of the flake silicon particles intersect.

[0114] [Table 1]

[0115]

[0116] Experimental Example 1

[0117] Morphological observation

[0118] In the experimental embodiments, the morphology of the embodiments and comparative embodiments was analyzed. Figure 5 The image shows the XRD results of the dimensions of the sheet-like silicon particles in Example 3. Figure 6 This is a SEM image showing the core of Example 3. (Refer to...) Figure 5 and Figure 6 The pores can be observed, which confirms the porous structure in which sheet-like silicon particles and amorphous carbon are interconnected. Figure 7 This is a graph illustrating the particle size distribution of the embodiments and comparative embodiments. (Refer to...) Figure 7 As can be seen, the particle size distribution of the embodiment is about 2 micrometers larger than that of the comparative embodiment. Figure 8 These are SEM images of Example 3 and Comparative Example 3. Figure 8 (a) is a SEM image of Comparative Example 3. Figure 8 (b) is the SEM image of Example 3. (Refer to...) Figure 8 It can be observed that the particle size of the embodiment is larger than that of the comparative embodiment. Therefore, it is possible to obtain... Figure 7 The results from the particle size distribution map lead to the same conclusion.

[0119] Experimental Example 2

[0120] Analysis of electrochemical properties

[0121] In the experimental examples, batteries incorporating the negative electrode active materials of the examples and comparative examples were fabricated, and their electrochemical characteristics were analyzed. Initial specific discharge capacity, initial efficiency, and capacity retention after 300 cycles were measured. The results are shown in Table 2 below.

[0122] [Table 2]

[0123]

[0124] Figure 9 This is a graph showing the initial capacity and initial efficiency of Example 3. Figure 10 This is a graph showing the capacity retention rate after 300 cycles for the embodiments and comparative embodiments. Refer to Table 2 and... Figure 9 and Figure 10 As can be seen, in the examples and comparative examples, the initial specific discharge capacity is about 1400 mAh / g and the initial efficiency is 88% to 90%.

[0125] To further study the cycling characteristics, a pouch cell (full cell) containing the negative electrode active material of Example 3 and Comparative Example 3 was manufactured, and the state of the negative electrode after 300 cycles was compared and analyzed.

[0126] Figure 11 This is the image of the negative electrode after 300 cycles. Figure 11 (a) is an image of Comparative Example 3. Figure 11 (b) is an image of Example 3. Figure 12 It is a cross-sectional SEM image of the negative electrode before and after 300 cycles. Figure 12 (a) is the initial SEM image of Comparative Example 3. Figure 12 (b) is the initial SEM image of Example 3. Figure 12 (c) is the SEM image of Comparative Example 3 after 300 cycles. Figure 12 Image (d) is the SEM image of Example 3 after 300 cycles. Refer to Table 2 and... Figures 10 to 12 As can be seen, more cracks appeared in the comparative examples than in the examples, and deterioration that could be observed with the naked eye was also observed. In fact, referring to Table 2, it can be seen that the capacity retention rate was 82% to 86% in the comparative examples, while it was 83% to 93% in the examples.

[0127] This can be presumably because, in the case of the embodiment, the particle size of the negative electrode active material is relatively large, which effectively controls the volume expansion of the negative electrode, thereby improving the lifetime characteristics.

[0128] The present invention has been described above with reference to preferred embodiments. Those skilled in the art will understand that the invention can be implemented in modified forms without departing from its essential characteristics. Therefore, the disclosed embodiments should be considered illustrative rather than restrictive. The scope of the invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of its equivalents should be interpreted as included within the present invention.

Claims

1. A negative electrode active material for lithium secondary batteries, the negative electrode active material comprising: A core and a shell, the shell surrounding at least a portion of the core. in, The core comprises a porous structure, which includes sheet-like silicon particles and amorphous carbon. The shell comprises sheet-like silicon particles, amorphous carbon, and crystalline carbon.

2. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, At least a portion of the sheet-like silicon particles and at least a portion of the amorphous carbon are interconnected.

3. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The median volume diameter D of the negative electrode active material v 50 is 9 to 11 micrometers.

4. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The SPAN value of the negative electrode active material is 1.6 to 2.2, and the SPAN value is defined as (Dv90-Dv10) / Dv50, where Dv90, Dv10 and Dv50 represent the particle diameters corresponding to 90%, 10% and 50% of the volume in the particle size distribution of the negative electrode active material, respectively.

5. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The distance between the points where the major and minor axes of the sheet-like silicon particles intersect is 20 nanometers to 50 nanometers.

6. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The crystal size of the sheet-like silicon particles is 16 to 18 nanometers.

7. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The thickness of the shell is 20 nanometers to 300 nanometers.

8. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The core contains little or no crystalline carbon.

9. A method for manufacturing a negative electrode active material for lithium secondary batteries, the method comprising: Prepare a mixture comprising silicon particles and amorphous carbon precursors; Prepare a molded article containing the mixture; A composite material with a core-shell structure is prepared by carbonizing the molded body. as well as Control the dimensions of the composite material.

10. The manufacturing method according to claim 9, wherein, Preparing a composite material with a core-shell structure by carbonizing the molded body includes: Addition of crystalline carbon and amorphous carbon precursors; and Heat treatment is performed.

11. The manufacturing method according to claim 10, wherein, When adding crystalline carbon and amorphous carbon precursors relative to the total weight of silicon particles, adding 47% to 57% by weight of crystalline carbon; and 65% to 75% by weight of amorphous carbon precursors.

12. The manufacturing method according to claim 9, wherein, The crystalline carbon is flake graphite, and the median volume diameter D of the flake graphite is... v 50 represents 10 to 100 micrometers.

13. The manufacturing method according to claim 9, wherein, The amorphous carbon precursor is selected from any one of phenolic resin, furan resin, coal tar pitch, petroleum pitch, and combinations thereof.

14. The manufacturing method according to claim 9, wherein, The amorphous carbon precursor is petroleum bitumen, and the median volume diameter D of the petroleum bitumen is... v 50 represents 1 to 10 micrometers.

15. The manufacturing method according to claim 9, wherein, When controlling the dimensions of the composite material, the median volume diameter D of the composite material is... v 50 is 9 to 11 micrometers.

16. The manufacturing method according to claim 9, wherein, When controlling the size of the composite material, the SPAN value of the composite material is 1.6 to 2.2, and the SPAN value is defined as (Dv90-Dv10) / Dv50, where Dv90, Dv10 and Dv50 represent the particle diameters corresponding to 90%, 10% and 50% of the volume of the particle size distribution of the negative electrode active material, respectively.

17. The manufacturing method according to claim 9, wherein, In composite materials with a core-shell structure The core comprises a porous structure in which sheet-like silicon particles are interconnected with amorphous carbon. The shell comprises sheet-like silicon particles, amorphous carbon, and crystalline carbon.

18. The manufacturing method according to claim 9, wherein, The core contains little or no crystalline carbon.

19. The manufacturing method according to claim 9, wherein, The thickness of the shell is 20 nanometers to 300 nanometers.

20. A negative electrode comprising the negative electrode active material of claim 1.

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