Negative electrode active material for lithium secondary battery comprising magnesium silicate, method for preparing the same, and lithium secondary battery comprising the same

Abstract

The invention provides a negative electrode active material comprising magnesium silicate for lithium secondary batteries, a method for its preparation and lithium secondary batteries comprising the same, the negative electrode active material comprising magnesium silicate and crystalline silicon in a specific weight ratio and optionally magnesium oxide. The negative electrode active material is formed by mixing silicon, silicon monoxide and magnesium hydride followed by a heat treatment to produce a stable magnesium silicate phase while retaining crystalline silicon. This improves the initial efficiency, reduces the irreversible capacity loss and extends the charge-discharge cycle life. The method can further comprise a comminution and optional carbon coating of the heat treated product to adjust the pore structure and electrical conductivity. The obtained electrode material provides a high energy density and good electrical conductivity resulting in better performance of lithium ion batteries.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10 - 2025 - 0022851, filed with the Korean Intellectual Property Office on February 21, 2025, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to a negative electrode active material containing magnesium silicate for a lithium secondary battery, a method for preparing the negative electrode active material, and a lithium secondary battery including the negative electrode active material. Background art

[0004] Lithium secondary batteries are widely used in various applications, from small electronic devices such as smartphones to medium - to - large - scale energy storage devices, including batteries for electric vehicles. In recent years, as a countermeasure against global regulations on CO2 and greenhouse gas emissions, the demand for high - energy - density batteries has been increasing.

[0005] Graphite, which is commonly used as the negative electrode of a lithium secondary battery, has a low theoretical capacity of 372 mAh / g, resulting in limited energy density. To overcome this limitation, various materials are being studied. Among these materials, silicon has a discharge capacity of 3579 mAh / g, which is about 10 times that of graphite, making it a promising next - generation negative electrode active material. However, due to particle fragmentation and electrode delamination caused by high expansion (about 300%) during the charging process, silicon has poor cycle life characteristics. In addition, silicon oxide SiOx (0 < x < 2) has a discharge capacity more than three times that of graphite and exhibits excellent cycle life characteristics compared to silicon, but its initial efficiency is low due to irreversible reactions that occur during the initial charging process.

[0006] To solve these problems, efforts have been made to regulate the oxygen content or silicon content in silicon oxide materials. However, such changes generally result in a shortened cycle life. In addition, composites formed by the reaction of silicon oxide with other metal materials (such as Li (pre - lithiation), Mg, and Ca) have been studied as negative electrode materials for lithium secondary batteries, but these result in a reduced discharge capacity.

[0007] Therefore, there is a need to develop materials that can simultaneously solve various problems of silicon negative electrode active materials to achieve high - energy - density lithium storage materials. Summary of the invention

[0008] Some embodiments of the present invention aim to provide a negative electrode active material for a lithium secondary battery, a method for preparing the negative electrode active material, and a lithium secondary battery including the negative electrode active material, the negative electrode active material exhibiting high efficiency, high capacity, and long cycle life characteristics.

[0009] Some embodiments of the present invention aim to provide a negative electrode active material that can be applied to green technology fields using batteries (e.g., electric vehicles).

[0010] Some embodiments of the present invention may provide a negative electrode active material for lithium secondary batteries, the negative electrode active material comprising magnesium silicate and crystalline silicon, wherein the magnesium silicate comprises one or more selected from Mg2SiO4 and MgSiO3.

[0011] According to one embodiment, the negative electrode active material for a lithium secondary battery may also contain magnesium oxide (MgO).

[0012] Based on 100 parts by weight of crystalline silicon, the negative electrode active material for a lithium secondary battery according to one embodiment may contain 1 to 150 parts by weight of magnesium silicate.

[0013] According to one embodiment, the negative electrode active material for a lithium secondary battery may comprise magnesium silicate and crystalline silicon in a weight ratio of 1:0.5 to 1:1.5.

[0014] Based on 100 parts by weight of crystalline silicon, the negative electrode active material for a lithium secondary battery according to one embodiment may contain 0.5 parts by weight to 5 parts by weight of magnesium oxide.

[0015] According to one embodiment, the crystalline silicon can be polycrystalline silicon, and the polycrystalline silicon can include a first crystalline silicon containing a (111) facet, a second crystalline silicon containing a (220) facet, and a third crystalline silicon containing a (311) facet.

[0016] According to one embodiment, the ratio of the grain size of the first crystalline silicon, the second crystalline silicon, and the third crystalline silicon can be 1:(0.5 to 1):(0.5 to 1).

[0017] Some embodiments of the present invention may provide a method for preparing a negative electrode active material for lithium secondary batteries, the method comprising preparing a mixed powder by mixing silicon (Si), silicon monoxide (SiO) and magnesium hydride (MgH2); and heat-treating the mixed powder to obtain a heat-treated product.

[0018] According to one embodiment, the mixed powder may contain silicon, silicon monoxide (SiO) and magnesium hydride in a weight ratio of 1:(1 to 2):(0.1 to 1).

[0019] According to one implementation scheme, heat treatment can be carried out at 700°C to 1000°C.

[0020] A method for preparing a negative electrode active material for a lithium secondary battery according to one embodiment may further include pulverizing the heat-treated product; and carbon coating the heat-treated product pulverized during pulverization.

[0021] According to one implementation plan, pulverization can be carried out by ball milling.

[0022] According to one implementation, the ball milling process can be carried out for 10 to 36 hours at a ball-to-particle weight ratio (BPR) of 5:1 to 50:1.

[0023] According to one embodiment, carbon coating can be performed in an argon (Ar) atmosphere at 350°C to 1200°C for 0.5 to 10 hours.

[0024] Some embodiments of the present invention may provide a negative electrode for a lithium secondary battery, the negative electrode comprising a negative electrode active material for a lithium secondary battery.

[0025] Some embodiments of the present invention can provide a lithium secondary battery, the lithium secondary battery including a negative electrode, a positive electrode, a separator located between the negative electrode and the positive electrode, and an electrolyte.

[0026] In some embodiments, a negative electrode active material for lithium secondary batteries is provided, wherein the negative electrode active material is obtained by: preparing a mixture of silicon, silicon monoxide and magnesium hydride; heat-treating the mixture at a temperature of about 700°C to 1000°C to form a magnesium silicate phase comprising Mg2SiO4 and / or MgSiO3; and optionally pulverizing and carbon-coating the heat-treated product, wherein the negative electrode active material comprises: a magnesium silicate phase and crystalline silicon.

[0027] Based on 100 parts by weight of crystalline silicon, there may be approximately 1 to 150 parts by weight of magnesium silicate phase.

[0028] Based on 100 parts by weight of crystalline silicon, the negative electrode active material may also contain about 0.5 to 5 parts by weight of magnesium oxide.

[0029] The crystalline silicon can be polycrystalline silicon, which includes a first crystalline silicon with a (111) facet, a second crystalline silicon with a (220) facet, and a third crystalline silicon with a (311) facet.

[0030] The ratio of the average grain size of the first crystalline silicon, the second crystalline silicon, and the third crystalline silicon can be 1:(0.5 to 1):(0.5 to 1).

[0031] The negative electrode active material for lithium secondary batteries according to the present invention can improve capacity by including a high content of silicon.

[0032] Lithium secondary batteries incorporating the negative electrode active material for lithium secondary batteries according to the present invention can exhibit improved cycle life characteristics.

[0033] A lithium secondary battery containing the negative electrode active material for a lithium secondary battery according to the present invention can improve the initial efficiency of the negative electrode through an irreversible phase formation reaction.

[0034] As discussed, the methods and systems appropriately include the use of controllers or processors.

[0035] In another embodiment, a vehicle is provided that includes the device as disclosed herein. Attached Figure Description

[0036] The foregoing and other aspects, features, advantages, and embodiments described below will be better understood when read in conjunction with the accompanying drawings. However, the invention is not intended to be limited to the details shown in the drawings, and various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope of the equivalent forms of the claims. The same reference numerals and names in the various drawings denote the same elements.

[0037] Figure 1 A flowchart illustrating the preparation process of a negative electrode active material for a lithium secondary battery according to some embodiments of the present invention.

[0038] Figure 2 The X-ray diffraction (XRD) analysis results are shown for the negative electrode active material of a lithium secondary battery according to an embodiment of the present invention.

[0039] Figure 3 The results are Raman spectral measurements of the negative electrode active materials according to embodiments and comparative embodiments of the present invention.

[0040] Figure 4 Figure A shows the initial efficiency of a battery comprising the negative electrode active material according to Examples 1 to 3 and Comparative Example 1. Figure 4 B illustrates the cycle life characteristics of batteries containing the negative electrode active materials of Examples 1 to 3 and Comparative Example 1 according to the present invention.

[0041] Figure 5 Figure A shows the initial efficiency of a battery comprising the negative electrode active material according to Example 1 and Comparative Examples 1 to 3 of the present invention. Figure 5 B illustrates the cycle life characteristics of a battery comprising the negative electrode active material according to Embodiment 1 and Comparative Embodiments 1 to 3 of the present invention.

[0042] Figure 6Figure A shows the initial efficiency of a battery comprising the negative electrode active material according to Embodiment 1, Comparative Embodiment 1, and Comparative Embodiment 4 of the present invention. Figure 6 B illustrates the cycle life characteristics of batteries comprising the negative electrode active materials of Embodiment 1, Comparative Embodiment 1, and Comparative Embodiment 4 according to the present invention. Detailed Implementation

[0043] The invention will be described in more detail below. However, the following embodiments and examples are provided by way of reference only for describing the invention in detail, and the invention is not limited thereto and may be implemented in various forms.

[0044] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0045] The terminology used herein is intended only to effectively describe specific embodiments and is not intended to limit the invention. It should be understood that the terms "vehicle" or "of a vehicle" or other similar terms as used herein 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 resources). As mentioned herein, a hybrid vehicle is a vehicle having two or more power sources, such as a vehicle that combines gasoline and electric power.

[0046] 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 “described” are intended to include the plural forms as well. These terms are intended only to distinguish one component from another, and they do not limit the nature, order, or sequence of the components. It should also be understood that, when used in this specification, the terms “comprising” and / or “including” indicate the presence of the stated features, values, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof. As used herein, the term “and / or” includes any and all combinations of one or more of the associated enumerated items. Throughout this specification, unless expressly stated to the contrary, the words “comprising” and variations such as “including” or “containing” are to be understood as implying the inclusion of the stated elements, but not excluding any other elements. Furthermore, the terms “unit,” “component,” “device,” and “module” described herein 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.

[0047] While the exemplary embodiments are described as using multiple units to perform the exemplary processes, it should be understood that the 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.

[0048] Furthermore, the control logic of the present invention can be implemented as a non-transient computer-readable medium on a computer-readable medium, comprising executable program instructions 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-coupled computer system, thereby enabling the computer-readable medium to be stored and executed in a distributed manner, for example, via a telematics server or a controller area network (CAN).

[0049] Unless otherwise stated or obvious from the context, as used herein, the term “about” is understood to mean within the normal tolerance range in the field, such as within 2 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”.

[0050] Unless otherwise stated, all units used in this specification are based on weight. For example, units such as “%” or “ratio” represent weight percentage (wt%) or weight ratio, respectively. Unless otherwise defined, weight percentage (wt%) indicates the proportion of a particular component in the total composition, expressed as a weight percentage.

[0051] Furthermore, the numerical ranges used in this specification may include all values ​​between the lower and upper limits, all values ​​derived logically in ascending order within the shape and width of the defined range, all double-limited values, and all possible combinations of the upper and lower limits of different defined numerical ranges. Unless specifically defined in this specification, values ​​outside the defined numerical range that may occur due to experimental errors or rounding are also included within the defined numerical range.

[0052] The term "magnesium silicate" refers to a compound containing one or more magnesium-silicon-oxygen phases.

[0053] The term "crystalline silicon" refers to silicon with a crystal structure that can be identified by techniques such as X-ray diffraction, Raman spectroscopy, or electron diffraction.

[0054] The term "polycrystalline silicon" refers to silicon composed of multiple grains or domains, each of which exhibits an ordered lattice but may have different orientations.

[0055] A more detailed description of the invention is provided below.

[0056] This invention provides a negative electrode active material for lithium secondary batteries, the negative electrode active material comprising magnesium silicate and crystalline silicon, wherein the magnesium silicate comprises one or more selected from Mg2SiO4 and MgSiO3. The negative electrode active material for lithium secondary batteries comprises an irreversible phase of magnesium silicate that does not react with lithium ions and crystalline silicon, thereby providing improved capacity and initial efficiency, and improved cycle life characteristics.

[0057] In one embodiment, the negative electrode active material for the lithium secondary battery may also contain magnesium oxide (MgO). By meeting this requirement, the initial efficiency and cycle life characteristics of the lithium secondary battery can be further improved.

[0058] In this specification, crystalline silicon may refer to silicon that exists in a three-dimensional structure at the atomic level.

[0059] When the negative electrode active material for lithium secondary batteries of the present invention comprises crystalline silicon, the high theoretical capacity of crystalline silicon enables high-energy-density batteries. Furthermore, crystalline silicon possesses excellent conductivity, enabling rapid charging and discharging of the battery.

[0060] In one embodiment, based on 100 parts by weight of crystalline silicon, the negative electrode active material for a lithium secondary battery may comprise 1 to 150 parts by weight, 4.5 to 125 parts by weight, specifically 50 to 100 parts by weight, and more specifically 80 to 90 parts by weight of magnesium silicate. By meeting this requirement, the capacity, initial efficiency, and cycle life characteristics of the lithium secondary battery can be improved.

[0061] In one embodiment, based on 100 parts by weight of crystalline silicon, the negative electrode active material for a lithium secondary battery may contain 0.5 parts by weight to 5 parts by weight, specifically 1 part by weight to 3 parts by weight, and more specifically 1.2 parts by weight to 2 parts by weight of magnesium oxide. By meeting this requirement, the initial efficiency and cycle life characteristics of the lithium secondary battery can be further improved.

[0062] In one embodiment of the present invention, the crystalline silicon can be polycrystalline silicon, and the polycrystalline silicon can include a first crystalline silicon with a (111) facet, a second crystalline silicon with a (220) facet, and a third crystalline silicon with a (311) facet. By satisfying this requirement, a high energy density battery can be realized, and the charging and discharging rates of the battery can be improved.

[0063] In one embodiment, the ratio of the grain size of the first crystalline silicon, the second crystalline silicon, and the third crystalline silicon can be 1:(0.5 to 1):(0.5 to 1), specifically 1:(0.6 to 0.9):(0.6 to 0.9), more specifically 1:(0.7 to 0.8):(0.8 to 0.85), but is not limited thereto, as long as the purpose of the present invention can be achieved.

[0064] The present invention also provides a method for preparing a negative electrode active material for lithium secondary batteries, the method comprising preparing a mixed powder by mixing silicon (Si), silicon monoxide (SiO) and magnesium hydride (MgH2); and heat-treating the mixed powder to obtain a heat-treated product.

[0065] In one embodiment, the mixed powder may comprise silicon, silicon monoxide (SiO), and magnesium hydride in a weight ratio of 1:(1-2):(0.1-1), specifically 1:(1.3-1.7):(0.2-0.5). Batteries containing negative electrode active materials prepared by satisfying this range can exhibit improved capacity, initial efficiency, and cycle life characteristics.

[0066] In one embodiment, the heat treatment can be carried out at 700°C to 1000°C, specifically 750°C to 900°C. Meeting this range facilitates the formation of magnesium silicate and crystalline silicon.

[0067] In one embodiment, the method for preparing a negative electrode active material for a lithium secondary battery may further include pulverizing a heat-treated product; and carbon coating the heat-treated product pulverized during pulverization. By further including pulverization, larger internal pores can be formed, thereby improving the cycle life characteristics of the battery. Furthermore, by further including carbon coating, the cycle life characteristics, electrochemical properties, and thermal stability of the battery can be improved.

[0068] In one embodiment, pulverization can be carried out by ball milling, high-energy ball milling, grinding, spray milling, or resonant acoustic mixer method, specifically by high-energy ball milling, but not limited to this, as long as the purpose of the present invention can be achieved.

[0069] In one embodiment, the ball-to-material weight ratio (BPR, large balls: small balls) in the ball milling process can be from 1:1 to 10:1, specifically from 2:1 to 5:1. The ball milling process can be carried out for 10 to 36 hours, specifically from 15 to 25 hours. Furthermore, the ball milling speed can be from 50 rpm to 2000 rpm, specifically from 100 rpm to 1000 rpm, but is not limited to these speeds.

[0070] In one embodiment, the carbon coating can be performed in an argon (Ar) atmosphere at 350°C to 1200°C, specifically 600°C to 1000°C, for 0.5 hours to 10 hours, specifically 1 hour to 5 hours, but is not limited thereto.

[0071] Furthermore, the present invention provides a negative electrode for a lithium secondary battery, comprising a negative electrode active material for a lithium secondary battery.

[0072] The description of the negative electrode active material used in lithium secondary batteries is as described above, and therefore will be omitted.

[0073] In one embodiment, the negative electrode for a lithium secondary battery may further comprise an adhesive, and the adhesive may be used without limitation, provided that it is used in the art to manufacture a negative electrode for a lithium secondary battery.

[0074] Furthermore, the present invention provides a lithium secondary battery, which includes a negative electrode, a positive electrode, a separator located between the negative electrode and the positive electrode, and an electrolyte.

[0075] There are no particular limitations on the positive electrode, membrane, and electrolyte, and the present invention can utilize positive electrodes, membranes, and electrolytes known in the art. Specific examples are as follows.

[0076] In one embodiment, the positive electrode can be manufactured by mixing and stirring the negative electrode active material with a solvent and, if necessary, a binder, a conductive material and a dispersant to prepare a mixture, then coating the mixture onto a metal current collector, drying the mixture and pressing the mixture.

[0077] In one embodiment, the positive electrode active material can be any active material commonly used in positive electrodes of lithium secondary batteries. For example, the positive electrode material may include lithium metal oxide particles, which comprise one or more metals selected from Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, B, and combinations thereof.

[0078] In one implementation, common conductive carbon materials can be used as the conductive material without any special limitations.

[0079] In one embodiment, the metal current collector can be any metal with high conductivity, which allows the positive electrode active material mixture to adhere easily and does not react within the voltage range of the battery. As a non-limiting example, the positive electrode current collector can be a foil made of aluminum, nickel, or a combination thereof.

[0080] In one embodiment, the separator can be a separator having micropores through which ions can pass, and by way of non-limiting example, it can be one or more combinations selected from glass fiber, polyester, polyethylene, polypropylene, and polytetrafluoroethylene, and can be in the form of a nonwoven or woven fabric. Specifically, lithium secondary batteries can primarily use polyolefin-based polymer separators, such as polyethylene and polypropylene, but the invention is not limited thereto. Furthermore, to improve heat resistance or mechanical strength, separators coated with compositions comprising ceramic components or polymeric materials can also be used. The separator can optionally have a single-layer or multi-layer structure, and separators known in the art can be used, but the invention is not limited thereto.

[0081] In one embodiment, the electrolyte may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used to manufacture lithium secondary batteries.

[0082] In one embodiment, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0083] In one embodiment, the non-aqueous organic solvent may include, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, diethyl ether, methyl propionate, and ethyl propionate.

[0084] In one embodiment, cyclic carbonates (e.g., ethylene carbonate and propylene carbonate) can preferably be used as high-viscosity organic solvents with high dielectric constants, which can effectively dissociate lithium salts, and when these cyclic carbonates are mixed in appropriate proportions with low-viscosity, low-dielectric-constant linear carbonates (e.g., dimethyl carbonate and diethyl carbonate), an electrolyte with high conductivity can be produced, making their use more preferred.

[0085] In one embodiment, lithium salt can be used as a metal salt, and the lithium salt can be a material that is well soluble in non-aqueous electrolytes. For example, the anion of the lithium salt may include one or more selected from F-, Cl-, I-, NO3-, N(CN)2-, BF4-, ClO4-, PF6-, (CF3)2PF4-, (CF3)3PF3-, (CF3)4PF2-, (CF3)5PF-, (CF3)6P-, CF3SO3-, CF3CF2SO3-, (CF3SO2)2N-, (FSO2)2N-, CF3CF2(CF3)2CO-, (CF3SO2)2CH-, (SF5)3C-, (CF3SO2)3C-, CF3(CF2)7SO3-, CF3CO2-, CH3CO2-, SCN-, and (CF3CF2SO2)2N-.

[0086] In one embodiment, the electrolyte may also contain one or more additives, such as difluoroethylene carbonate or other haloalkyl carbonate compounds, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexaphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride, to improve the cycle life characteristics of the battery, prevent battery capacity reduction, or increase battery discharge capacity.

[0087] In one embodiment, the external shape of the lithium secondary battery is not particularly limited, but can be selected from, for example, cylindrical, square, pouch-shaped or coin-shaped containers.

[0088] Various embodiments and comparative embodiments of the present invention will be described below. However, the following embodiments are merely various embodiments of the present invention, and the present invention is not intended to be limited thereto.

[0089] Example 1

[0090] Example 1 and below Figure 1The same sequence was followed. The mixed powder was prepared as follows: 2.238 g of Si powder and 3.512 g of SiO powder were pulverized by high-energy ball milling at a BPR ratio of 2:1 for 18 hours (S100), and then mixed with 0.911 g of MgH2 powder and 5 g of NaCl powder (S200). The mixed powder was transferred to an alumina crucible, and an additional 3 g of NaCl powder was coated on top. The crucible was then heat-treated in a vertical furnace at 800 °C under an Ar atmosphere for 5 hours at a heating rate of 5 °C / min to obtain a heat-treated product (S300). The heat-treated product was then pulverized in a mortar to obtain a powder. To remove residual salts from the prepared powder, each 1 g of powder was stirred in 50 ml of an aqueous acetic acid solution for 30 minutes, then filtered using a filter (S400), and dried in a convection oven for one day to prepare the negative electrode active material (S500).

[0091] Example 2

[0092] The negative electrode active material was prepared in the same manner as in Example 1, except that the heat treatment temperature was 700°C.

[0093] Example 3

[0094] The negative electrode active material was prepared in the same manner as in Example 1, except that the heat treatment temperature was 750°C.

[0095] Comparative Example 1

[0096] 2.238 g of Si powder and 3.512 g of SiO powder were pulverized by high-energy ball milling for 18 hours under BPR conditions of 20:1 (large ball: small ball = 2:1) and used as negative electrode active materials.

[0097] Comparative Example 2

[0098] Using SiO powder as the negative electrode active material requires no separate treatment.

[0099] Comparative Example 3

[0100] The negative electrode active material was prepared in the same manner as in Example 1, except that 5.75g of SiO powder was used alone as the matrix material and 1.71g of MgH2 powder was used.

[0101] Comparative Example 4

[0102] The negative electrode active material was prepared in the same manner as in Example 1, except that 0.95 g of Mg powder was used instead of 0.911 g of MgH2 powder.

[0103] Experimental Example 1: X-ray Diffraction Analysis

[0104] The negative electrode active materials prepared according to the examples and comparative examples were analyzed by X-ray diffraction, and are shown in the figure. Figure 2 middle.

[0105] The specific X-ray diffraction analysis conditions are as follows:

[0106] i) Equipment: Bruker, D8 Advance

[0107] ii) Condition: Cu Kα radiation

[0108] Figure 2 The X-ray diffraction (XRD) analysis results of the negative electrode active materials according to Examples 1 to 3 of the present invention are shown.

[0109] pass Figure 2 In Examples 1 and 3, the Mg₂SiO₄ phase, the Si phase, and a small amount of the MgO phase were confirmed. In Example 2, the Si phase and a small amount of the Mg₂SiO₄ phase were confirmed, and no MgO-related peaks were observed. This confirms that different products are formed as the heat treatment temperature increases.

[0110] Experimental Example 2: Quantitative Analysis

[0111] To quantify the proportions of Si, Mg2SiO4 and MgO in Examples 1 to 3, Rietveld analysis was performed on the X-ray diffraction results, and the results are listed in Table 1.

[0112] [Table 1]

[0113] Si (%) <![CDATA[Mg2SiO4(%)]]> MgO (%) Example 1 53.7 45.6 0.8 Example 2 95.4 4.6 - Example 3 54.0 45.3 0.7

[0114] As can be seen from Table 1, the proportion of Mg2SiO4 increased in Examples 1 and 3 compared to Example 2.

[0115] Experimental Example 3: Grain Size Measurement

[0116] The grain size of each component contained in the negative electrode active materials of Examples 1 to 3 was calculated using the following Scherrer equation, and the results are shown in Table 2:

[0117] Scherrer's Equation

[0118]

[0119] K (Scherrer constant) = 0.94

[0120] λ (wavelength of X-rays) =

[0121] β = Full width at half maximum (FWHM)

[0122] θ = Bragg angle

[0123] [Table 2]

[0124]

[0125] As can be seen from Table 2, it was confirmed that the c-Si and c-Mg2SiO4 in Example 1 were smaller in size compared to Examples 2 and 3.

[0126] Experimental Example 4: Raman Spectroscopy

[0127] To confirm the extent of reaction progression according to the heat treatment temperature, Raman spectroscopy was performed on Examples 1 to 3 and Comparative Example 1, and the results are shown below. Figure 3 middle.

[0128] Depend on Figure 3 It can be seen that, in Comparative Example 1, the 400 cm⁻¹ values ​​corresponding to a-SiO₂ and a-Si were confirmed, respectively. -1 With and 480cm -1 In contrast, in Examples 1 to 3, the bands corresponding to a-SiO2 and a-Si decreased, and a 520 cm band corresponding to c-Si appeared. -1 Therefore, it was confirmed that the degree of reaction progress varied with increasing heat treatment temperature.

[0129] Experimental Example 5: Evaluation of Initial Efficiency and Cycle Life Characteristics

[0130] Electrochemical evaluation was performed on the negative electrode active materials prepared according to the examples and comparative examples.

[0131] Specifically, a slurry composition was prepared by mixing the prepared negative electrode active material, Super-C as a conductive material, and PAA as a binder in a mass ratio of 8:1:1 and then mixing with deionized water. The composition was coated onto copper foil and then vacuum dried at 120°C for 6 hours to prepare the negative electrode.

[0132] CR2032 coin cells were assembled by using lithium metal as the counter electrode, placing a polyethylene separator between the negative and counter electrodes, and injecting an electrolyte of 1M LiPF6 in an EC:EMC:DEM (2:2:5) mixture containing 10% by weight FEC additive. The assembled coin cells were left to stand at room temperature for 12 hours, followed by charging and discharging.

[0133] The prepared half-cell was subjected to three formation cycles at room temperature (25°C). It was charged with a constant current of 0.1C until the voltage reached 0.01V (vs. Li+ / Li), then charged with a constant voltage while maintaining 0.01V (vs. Li+ / Li) until the current reached the 0.01C cutoff value. It was then discharged with a constant current of 0.1C until the voltage reached 1.5V (vs. Li+ / Li).

[0134] Subsequently, it was charged with a constant current of 0.5C until the voltage reached 0.01V (vs. Li+ / Li), followed by constant voltage charging while maintaining 0.01V (vs. Li+ / Li) until the current reached the 0.01C cutoff value. It was then discharged with a constant current of 0.5C until the voltage reached 1.5V (vs. Li+ / Li). The results are shown in... Figure 4 A and Figure 4 In B and Table 3.

[0135] [Table 3]

[0136]

[0137] Depend on Figure 4 As can be seen from A and Table 3, Examples 1 to 3 show significantly improved initial efficiency compared to Comparative Example 1, and by Figure 4 As can be seen from B, Examples 1 and 3 show improved cycle life characteristics compared to Comparative Example 1.

[0138] Since Example 1 exhibited the best performance in terms of initial efficiency and cycle life characteristics, the same experimental methods were used to compare Example 1 with the remaining comparative examples, and the results are shown below. Figure 5 A and Figure 5 B, Figure 6 A and Figure 6 In B and Table 4.

[0139] [Table 4]

[0140]

[0141]

[0142] Depend on Figure 5 A and Figure 5 B, Figure 6 A and Figure 6 As can be seen from B and Table 4, compared with Comparative Examples 1 to 4, Example 1 shows superior initial efficiency and cycle life characteristics.

[0143] Therefore, it has been confirmed that the negative electrode active material for lithium secondary batteries according to the present invention can simultaneously solve the problems of low initial efficiency and poor cycle life characteristics that occur when using silicon-based materials, thereby realizing a high energy density lithium storage material.

[0144] The features, structures, effects, etc., described in the above exemplary embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to a single embodiment. Furthermore, the features, structures, effects, etc., exemplified in each exemplary embodiment can be combined or modified by those skilled in the art in other embodiments. Therefore, such combinations and modifications should be understood to be within the scope of the present invention.

Claims

1. A negative electrode active material for lithium secondary batteries, the negative electrode active material comprising: Magnesium silicate, wherein the magnesium silicate comprises Mg₂SiO₄ and / or MgSiO₃; and Crystalline silicon.

2. The negative electrode active material for lithium secondary batteries according to claim 1, wherein the negative electrode active material further comprises magnesium oxide.

3. The negative electrode active material for lithium secondary batteries according to claim 1, based on 100 parts by weight of crystalline silicon, wherein the negative electrode active material comprises 1 to 150 parts by weight of magnesium silicate.

4. The negative electrode active material for lithium secondary batteries according to claim 2, based on 100 parts by weight of crystalline silicon, wherein the negative electrode active material comprises 0.5 parts by weight to 5 parts by weight of magnesium oxide.

5. The negative electrode active material for lithium secondary batteries according to claim 1, wherein, The crystalline silicon is polycrystalline silicon, and the polycrystalline silicon includes a first crystalline silicon with a (111) facet, a second crystalline silicon with a (220) facet, and a third crystalline silicon with a (311) facet.

6. The negative electrode active material for lithium secondary batteries according to claim 5, wherein, The ratio of the grain size of the first crystalline silicon, the second crystalline silicon, and the third crystalline silicon is from 1:0.5 to 1:0.5 to 1.

7. A method for preparing a negative electrode active material for a lithium secondary battery, the method comprising: Mixed powders were prepared by mixing silicon, silicon monoxide, and magnesium hydride. and The mixed powder is subjected to heat treatment to obtain a heat-treated product.

8. The method for preparing a negative electrode active material for a lithium secondary battery according to claim 7, wherein, The mixed powder contains silicon, silicon monoxide, and magnesium hydride in a weight ratio of 1:1 to 2:0.1 to 1.

9. The method for preparing a negative electrode active material for a lithium secondary battery according to claim 7, wherein, The heat treatment is carried out at 700°C to 1000°C.

10. The method for preparing a negative electrode active material for a lithium secondary battery according to claim 7, the method further comprising: The heat-treated product is pulverized to obtain the pulverized heat-treated product; and Carbon coating is applied to the pulverized and heat-treated product.

11. The method for preparing a negative electrode active material for a lithium secondary battery according to claim 10, wherein, The pulverization is carried out by ball milling.

12. The method for preparing a negative electrode active material for a lithium secondary battery according to claim 11, wherein, The ball milling process is carried out for 10 to 36 hours at a ball-to-material weight ratio of 5:1 to 50:

1.

13. The method for preparing a negative electrode active material for a lithium secondary battery according to claim 10, wherein, The carbon coating is performed in an argon atmosphere at 350°C to 1200°C for 0.5 to 10 hours.

14. A negative electrode for a lithium secondary battery, the negative electrode comprising a negative electrode active material for a lithium secondary battery according to any one of claims 1 to 6.

15. A lithium secondary battery, the lithium secondary battery comprising: The negative electrode for a lithium secondary battery according to claim 14; Positive electrode; The diaphragm located between the negative electrode and the positive electrode; as well as Electrolytes.

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