Negative electrode active material composite and preparation method, negative electrode, and rechargeable lithium battery

Abstract

Provided are a negative electrode active material composite, a method for preparing the negative electrode active material composite, a negative electrode including the negative electrode active material composite, and a rechargeable lithium battery. Specifically, in an embodiment, the negative electrode active material composite for a rechargeable lithium battery includes: compound particles represented by SiO x (0 < x ≤ 2.0); silicon nanoparticles having an average particle size (D50) of less than or equal to about 200 nm (provided that it is greater than about 0 nm); and amorphous carbon, wherein the internal pore volume of the negative electrode active material composite is less than or equal to about 5.0×10 ‑2 cm 3 / g (provided that it is greater than about 0 cm 3 / g).

Description

[0001] This application claims priority and the benefit of Korean Patent Application No. 10-2021-0148941, filed with the Korean Intellectual Property Office on November 2, 2021, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention discloses a negative electrode active material composite, a method for preparing the negative electrode active material composite, a negative electrode including the negative electrode active material composite, and a rechargeable lithium battery. Background Art

[0003] Rechargeable lithium batteries have received attention as power sources for driving medium- and large-sized devices such as hybrid vehicles and battery vehicles, and small-sized devices such as mobile phones, laptop computers, and smartphones.

[0004] As a negative electrode active material for rechargeable lithium batteries, various types of carbon-based negative electrode active materials (including artificial graphite, natural graphite, hard carbon, etc.) capable of intercalating / deintercalating lithium ions are widely used. Recently, research on non-carbon-based negative electrode active materials (such as silicon and tin) has been actively conducted to obtain higher capacities.

[0005] However, non-carbon-based negative electrode active materials have a large volume change due to charging and discharging, so the cycle life of rechargeable lithium batteries is shortened compared to carbon-based negative electrode active materials. Summary of the Invention

[0006] The present disclosure relates to a negative electrode active material composite, a method for preparing the negative electrode active material composite, a negative electrode including the negative electrode active material composite, and a rechargeable lithium battery that can simultaneously ensure the initial efficiency, cycle life, etc. of a rechargeable lithium battery including the negative electrode active material composite.

[0007] In an embodiment, a negative electrode active material composite for a rechargeable lithium battery includes: compound particles represented by SiO x , 3 ,

[0008] , (0 < x ≤ 2.0); silicon nanoparticles having an average particle diameter (D50) of less than or equal to about 200 nm (provided that it is greater than about 0 nm); and amorphous carbon, wherein the internal pore volume of the negative electrode active material composite is less than or equal to about 5.0 × 10 -2 cm 3 / g (provided that it is greater than about 0 cm 3 / g).

[0008] In another embodiment, a method for preparing a negative electrode active material composite for a rechargeable lithium battery includes: spray drying a mixture including a solvent, SiO xA solution of compound particles represented by (0 < x ≤ 2.0) and silicon nanoparticles; compression molding a mixture including the product obtained by spray drying and an amorphous carbon precursor within a pressure range greater than about 10 MPa; and heat treating the product obtained by compression molding.

[0009] In another embodiment, the negative electrode for a rechargeable lithium battery includes a current collector and a negative electrode active material layer on the current collector, wherein the negative electrode active material layer includes the negative electrode active material composite of this embodiment.

[0010] In another embodiment, a rechargeable lithium battery includes a positive electrode, a negative electrode, and an electrolyte, and the negative electrode is the negative electrode of this embodiment.

[0011] The negative electrode active material composite of the embodiment can achieve a rechargeable lithium battery that exhibits excellent initial efficiency, cycle life, etc. Description of the Drawings

[0012] Figure 1 is a schematic diagram of the negative electrode active material composite according to the embodiment. Detailed Description of the Embodiments

[0013] Hereinafter, specific embodiments will be described in detail so that those of ordinary skill in the art can easily implement them. However, the present disclosure can be embodied in many different forms and is not to be construed as limited to the example embodiments set forth herein.

[0014] The terms used herein are for the purpose of describing embodiments only and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, singular expressions also include plural expressions.

[0015] As used herein, "a combination thereof" refers to a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, a reaction product, etc.

[0016] Here, it should be understood that terms such as "comprising," "including," or "having" are intended to indicate the presence of the recited features, numbers, steps, elements, or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, elements, or combinations thereof.

[0017] In the drawings, for clarity, the thicknesses of layers, films, panels, regions, etc. are exaggerated, and throughout the specification, like reference numerals denote like elements. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, no intervening elements are present.

[0018] In addition, the "layer" here not only includes the shape formed on the entire surface when observed from a plan view, but also includes the shape formed on a partial surface.

[0019] In addition, the "particle size" or "average particle size" can be measured by methods well known to those skilled in the art. For example, it can be measured by a particle size analyzer, or can be measured by transmission electron microscopy or scanning electron microscopy. Optionally, the average particle size value can be obtained by the following steps: measuring using dynamic light scattering method, performing data analysis, counting the number of particles in each particle size range and thus calculating. Unless otherwise defined, the average particle size may refer to the diameter (D50) of the particles having a cumulative volume of 50% by volume in the particle size distribution.

[0020] The "thickness" can be measured by photos taken with an optical microscope (such as a scanning electron microscope).

[0021] (Negative electrode active material)

[0022] In an embodiment, the negative electrode active material composite for a rechargeable lithium battery includes: compound particles represented by SiO x (0 < x ≤ 2.0); silicon nanoparticles having an average particle size (D50) less than or equal to about 200 nm (provided that it is greater than about 0 nm); and amorphous carbon, wherein the internal pore volume of the negative electrode active material composite is less than or equal to about 5.0×10 -2 cm 3 / g (provided that it is greater than about 0 cm 3 / g).

[0023] Prior to the negative electrode active material composite according to the embodiment, SiO (silicon monoxide), SiC (silicon carbide), etc. have been proposed in order to suppress the volume change of non-carbon-based negative electrode active materials (such as silicon, tin, etc.) and improve the low capacity of carbon-based negative electrode active materials (such as artificial graphite, natural graphite, hard carbon, etc.), thereby ensuring cycle life characteristics.

[0024] Compared with carbon-based negative electrode active materials, both SiO and SiC can increase the capacity of a rechargeable lithium battery. However, SiO is a negative electrode active material with high resistance and needs to be used by making its size smaller, which will slightly reduce the initial efficiency of the rechargeable lithium battery, but can ensure cycle life characteristics; SiC is a negative electrode active material that increases the initial efficiency of the rechargeable lithium battery, but is somewhat disadvantageous in ensuring cycle life characteristics. Therefore, there is a trade-off relationship between the capacity, initial efficiency, and cycle life of a rechargeable lithium battery: it is very difficult to increase the initial efficiency and cycle life uniformly (or balance).

[0025] As Figure 1As shown, the negative electrode active material composite of the embodiment is a composite of compound particles 1 represented by SiO x (0 < x ≤ 2.0), silicon nanoparticles 2, and amorphous carbon 3, which can compensate for the respective disadvantages of SiO and SiC while leveraging their advantages. In addition, the negative electrode active material composite of the embodiment can have a specific surface area limited within an appropriate range by restricting the D50 particle size of the silicon nanoparticles to about 200 nm or less (provided that it is greater than about 0 nm) and simultaneously restricting the internal pore volume of the composite to about 5.0×10 -2 cm 3 / g or less (provided that it is greater than about 0 cm 3 / g), thereby ensuring both the initial efficiency and cycle life of the rechargeable lithium battery at the same time.

[0026] Hereinafter, the negative electrode active material composite of the embodiment will be described in detail.

[0027] Silicon nanoparticles

[0028] In the negative electrode active material composite of the embodiment, the silicon nanoparticles are a component that helps increase the capacity of the rechargeable lithium battery.

[0029] The average particle size (D50) of the silicon nanoparticles can be less than or equal to about 200 nm (provided that it is greater than about 0 nm), and the maximum particle size (D max ) can be less than or equal to about 300 nm (provided that it is greater than about 0 nm). For example, the average particle size (D50) of the silicon nanoparticles can be greater than or equal to about 50 nm, greater than or equal to about 60 nm, greater than or equal to about 70 nm, or greater than or equal to about 80 nm, and less than or equal to about 200 nm, less than or equal to about 150 nm, less than or equal to about 140 nm, less than or equal to about 130 nm, or less than or equal to about 115 nm. Additionally, the maximum particle size (D max ) of the silicon nanoparticles can be greater than or equal to about 80 nm, greater than or equal to about 90 nm, greater than or equal to about 100 nm, or greater than or equal to about 110 nm, and less than or equal to about 300 nm, less than or equal to about 250 nm, less than or equal to about 240 nm, less than or equal to about 230 nm, or less than or equal to about 215 nm. Within these ranges, the side reaction between the silicon nanoparticles and the electrolyte can be suppressed, and the expansion of the silicon nanoparticles can be reduced, thereby improving the initial efficiency and cycle life characteristics of the rechargeable lithium battery.

[0030] The short-axis length (a) of the silicon nanoparticles can be from about 5 nm to about 50 nm, and the long-axis length (b) of the silicon nanoparticles can be from about 50 nm to about 300 nm. The aspect ratio (b / a) of the silicon nanoparticles can be from about 4 to about 20. For example, the aspect ratio of the silicon nanoparticles can be greater than or equal to about 4, greater than or equal to about 5, greater than or equal to about 6, or greater than or equal to about 7, and less than or equal to about 20, less than or equal to about 18, less than or equal to about 16, or less than or equal to about 14. When the long-axis length (b), short-axis length (a), and aspect ratio (b / a) of the silicon nanoparticles all fall within the above ranges, side reactions between the silicon nanoparticles and the electrolyte can be inhibited, and expansion of the silicon nanoparticles can be reduced, such that the initial efficiency and cycle life characteristics of the rechargeable lithium battery can be improved.

[0031] The full width at half maximum (FWHM) of the X-ray diffraction angle (2θ) using CuKα radiation at the (111) plane of the silicon nanoparticles can be from about 0.3° to about 1.5°. Within this range, the cycle life characteristics of the rechargeable lithium battery can be improved. The full width at half maximum (FWHM) of the X-ray diffraction angle (2θ) using CuKα radiation at the (111) plane of the silicon nanoparticles can be achieved by adjusting the particle size of the silicon nanoparticles or changing the silicon nanoparticle preparation process.

[0032] Compound particles represented by SiO x (0 < x ≤ 2.0)

[0033] In the negative electrode active material composite of the embodiment, the compound particles represented by SiO x (0 < x ≤ 2.0) are components that contribute to ensuring the cycle life characteristics of the rechargeable lithium battery.

[0034] The compound particles represented by SiO x (0 < x ≤ 2.0, such as SiO, SiO2, etc.) are materials with high resistance. When applied to the negative electrode, the average particle size (D50) and the maximum particle size (D max ) of the compound particles can be reduced to lower the resistance. Specifically, the average particle size (D50) of the compound particles represented by SiO x (0 < x ≤ 2.0) can be from about 1 μm to about 10 μm, and the maximum particle size (D max ) can be from about 5 μm to about 20 μm. For example, the average particle size (D50) of the compound particles represented by SiO x (0 < x ≤ 2.0) can be greater than or equal to about 1 μm, greater than or equal to about 2 μm, greater than or equal to about 3 μm, or greater than or equal to about 4 μm, and less than or equal to about 10 μm, less than or equal to about 9 μm, less than or equal to about 8 μm, less than or equal to about 7 μm, or less than or equal to about 6 μm. Additionally, for SiO x(0 < x ≤ 2.0) represents the maximum particle size (D max ) of the compound particles can be greater than or equal to about 5 μm, greater than or equal to about 6 μm, greater than or equal to about 7 μm, or greater than or equal to about 8 μm, and less than or equal to about 20 μm, less than or equal to about 18 μm, less than or equal to about 16 μm, less than or equal to about 14 μm, or less than or equal to about 12 μm. Within these ranges, when the compound particles represented by SiO x (0 < x ≤ 2.0) are applied to the negative electrode, the resistance of the compound particles represented by SiO x (0 < x ≤ 2.0) can be minimized.

[0035] Amorphous carbon

[0036] In the negative electrode active material composite of the embodiment, amorphous carbon surrounds the outer surface of the silicon nanoparticles, so that the conductivity of the negative electrode active material can be further improved, and the contact between the silicon nanoparticles and the electrolyte can be inhibited to reduce the side reactions between them, and the cycle life characteristics of the rechargeable lithium battery can be ensured. In addition, amorphous carbon acts as a binder for bonding the silicon nanoparticles to each other, thereby preventing the composite from breaking and maintaining its shape well.

[0037] The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonized product, calcined coke, or a combination thereof. Compared with crystalline carbon, amorphous carbon effectively penetrates between the silicon nanoparticles during the heat treatment process to reduce the internal pores, thereby improving the conductivity and effectively inhibiting the side reactions of the electrolyte.

[0038] Complex

[0039] As described above, the negative electrode active material composite of the embodiment (i.e., the composite of the compound particles represented by SiO x (0 < x ≤ 2.0), silicon nanoparticles, and amorphous carbon) can compensate for the respective disadvantages of SiO and SiC while utilizing their advantages, thereby ensuring both the initial efficiency and the cycle life of the rechargeable lithium battery.

[0040] The composite can include the compound particles represented by SiO x and silicon nanoparticles in a weight ratio (SiO x (0 < x ≤ 2.0): silicon) of about 8:2 to about 2:8 (specifically about 7:3 to about 3:7, for example about 6:4 to about 4:6). Within the above ranges, the effect of improving the capacity of the rechargeable lithium battery by the silicon nanoparticles and the effect of ensuring the cycle life of the rechargeable lithium battery by the compound particles represented by SiO x (0 < x ≤ 2.0) can be coordinated.

[0041] In addition, based on the total weight of the negative electrode active material composite, it may include compound particles represented by SiO x (0 < x ≤ 2.0) in an amount of about 5 wt% to about 90 wt% (specifically about 10 wt% to about 70 wt%, more specifically about 20 wt% to about 60 wt%, for example about 30 wt% to about 50 wt%); it may include silicon nanoparticles in an amount of about 10 wt% to about 95 wt% (specifically about 20 wt% to about 75 wt%, more specifically about 20 wt% to about 60 wt%, for example about 30 wt% to about 50 wt%); and the balance may be amorphous carbon. Within the above ranges, the effect of improving the capacity of the rechargeable lithium battery by the silicon nanoparticles and the effect of ensuring the cycle life of the rechargeable lithium battery by the compound particles represented by SiO x (0 < x ≤ 2.0) and amorphous carbon can be coordinated.

[0042] The average particle diameter (D50) of the negative electrode active material composite may be about 2 μm to about 15 μm, and the maximum particle diameter (D max ) may be about 5 μm to about 40 μm. For example, the average particle diameter (D50) of the composite may be greater than or equal to about 2 μm, greater than or equal to about 3 μm, greater than or equal to about 4 μm, or greater than or equal to about 5 μm, and less than or equal to about 15 μm, less than or equal to about 14 μm, less than or equal to about 13 μm, less than or equal to about 12 μm, or less than or equal to about 11 μm. In addition, the maximum particle diameter (D max ) may be greater than or equal to about 5 μm, greater than or equal to about 7 μm, greater than or equal to about 10 μm, greater than or equal to about 11 μm, greater than or equal to about 12 μm, or greater than or equal to about 13 μm, and less than or equal to about 40 μm, less than or equal to about 38 μm, less than or equal to about 36 μm, less than or equal to about 34 μm, or less than or equal to about 32 μm. Within these ranges, an excessive increase in the specific surface area of the negative electrode active material composite can be suppressed to reduce side reactions with the electrolyte, improve rate performance, and suppress the resistance of the rechargeable lithium battery.

[0043] The interior of the negative electrode active material composite includes pores having a diameter less than or equal to about 330 nm (provided that it is greater than about 0 nm), and the volume of the internal pores having this diameter is less than or equal to about 5.0×10 -2 cm 3 / g (provided that it is greater than about 0 cm 3 / g). For example, the diameter of the internal pores within the negative active material composite may be greater than 0 nm, greater than or equal to about 10 nm, greater than or equal to about 20 nm, greater than or equal to about 30 nm, greater than or equal to about 40 nm, greater than or equal to about 50 nm, greater than or equal to about 60 nm, greater than or equal to about 70 nm, greater than or equal to about 80 nm, greater than or equal to about 90 nm, or greater than or equal to about 100 nm, and less than or equal to about 330 nm, less than or equal to about 300 nm, less than or equal to about 250 nm, less than or equal to about 200 nm, less than or equal to about 180 nm, less than or equal to about 160 nm, less than or equal to about 140 nm, or less than or equal to about 120 nm. In addition, the volume of the internal pores having the above diameters may be greater than about 0 cm 3 / g, greater than or equal to about 0.1×10 -2 cm 3 / g is greater than or equal to about 0.2×10 -2 cm 3 / g, greater than or equal to about 0.3×10 -2 cm 3 / g, greater than or equal to about 0.4×10 -2 cm 3 / g, greater than or equal to about 0.5×10 -2 cm 3 / g, greater than or equal to about 0.6×10 -2 cm 3 / g, greater than or equal to about 0.8×10 -2 cm 3 / g or greater than or equal to about 1.0×10 -2 cm 3 / g, and less than or equal to about 5.0×10 -2 cm 3 / g, less than or equal to about 4.5×10 -2 cm 3 / g, less than or equal to about 4.0×10 -2 cm 3 / g, less than or equal to about 3.5×10 -2 cm 3 / g or less than or equal to about 3.0×10 -2 cm 3 When the diameter and volume of the internal pores inside the composite satisfy the aforementioned ranges, side reactions between the silicon nanoparticles included in the composite and the electrolyte can be suppressed, and the expansion of the silicon nanoparticles can be reduced, so that the initial efficiency and cycle life characteristics of the rechargeable lithium battery can be improved.

[0044] As a reference, as described above, the volume of internal pores having a diameter of nanometers (nm) can be quantitatively measured using a BJH (Barrett-Joyner-Halenda) analysis facility.

[0045] Meanwhile, the BET specific surface area of the negative electrode active material composite can be from about 0.1 cm 2 / g to about 10 cm 2 / g. For example, the BET specific surface area of the composite can be greater than or equal to about 0.1 cm 2 / g, greater than or equal to about 0.5 cm 2 / g, greater than or equal to about 1 cm 2 / g, greater than or equal to about 1.5 cm 2 / g, greater than or equal to about 2 cm 2 / g, greater than or equal to about 2.5 cm 2 / g or greater than or equal to about 3 cm 2 / g, and less than or equal to about 10 cm 2 / g, less than or equal to about 9 cm 2 / g, less than or equal to about 8 cm 2 / g, less than or equal to about 7 cm 2 / g, less than or equal to about 5 cm 2 / g, less than or equal to about 3 cm 2 / g or less than or equal to about 2.5 cm 2 / g. Within these ranges, an excessive increase in the specific surface area of the negative electrode active material composite can be suppressed to reduce side reactions with the electrolyte, and the rate performance can be improved while suppressing the resistance of the rechargeable lithium battery.

[0046] The negative electrode active material composite can include a matrix containing silicon nanoparticles and amorphous carbon and compound particles represented by SiO x (0 < x ≤ 2.oo). Specifically, the matrix can include secondary particles in which the silicon nanoparticles are aggregated and a coating that surrounds the outer surface of the secondary particles and the outer surface of the silicon nanoparticles and includes amorphous carbon. When such a structure is achieved, while achieving the effect of improving the capacity of the rechargeable lithium battery by the silicon nanoparticles and ensuring the cycle life of the rechargeable lithium battery by the compound particles represented by SiO x (0 < x ≤ 2.oo), the coating including amorphous carbon surrounds the outer surface of the secondary particles and the outer surface of the silicon nanoparticles to maintain a dense structure, thereby reducing side reactions with the electrolyte and further improving the cycle life of the rechargeable lithium battery.

[0047] The coating may have a thickness of about 1 nm to about 900 nm (e.g., about 5 nm to about 800 nm). Within these ranges, the internal pore size and volume of the composite can be controlled, the degree of electrolyte penetration into the composite can be controlled, and side reactions between the electrolyte and the negative electrode active material composite can be minimized to improve the cycle life characteristics of the rechargeable lithium battery.

[0048] (Method for preparing negative electrode active material)

[0049] In an embodiment, a method for preparing a negative electrode active material composite for a rechargeable lithium battery includes: spray-drying a solution including a solvent, compound particles represented by SiO x (0 < x ≤ 2.0) and silicon nanoparticles; compression-molding (or "compression molding") a mixture including the product obtained by spray-drying and an amorphous carbon precursor within a pressure range greater than about 10 MPa; and heat-treating the product obtained by compression-molding.

[0050] Through the above series of processes, the negative electrode active material composite of the foregoing embodiment can be obtained. Hereinafter, descriptions overlapping with the above will be omitted, and each process will be described.

[0051] spray drying

[0052] First, in an embodiment, spray-drying is performed on a slurry including a solvent, compound particles represented by SiO x (0 < x ≤ 2.0) and silicon nanoparticles.

[0053] The solvent is not particularly limited as long as it is a solvent capable of dispersing both the compound particles represented by SiO x (0 < x ≤ 2.0) and silicon nanoparticles, but may include isopropyl alcohol (IPA), ethanol (ETOH), etc.

[0054] When preparing the solution, the weight ratio (SiO x (0 < x ≤ 2.0): silicon) of the compound particles represented by SiO x to silicon nanoparticles can be controlled to be about 8:2 to about 2:8, specifically about 7:3 to about 3:7, for example about 6:4 to about 4:6. Thus, the weight ratio of the compound particles represented by SiO x (0 < x ≤ 2.0) to silicon nanoparticles in the product obtained by spray-drying and the final product according to the embodiment can be determined.

[0055] Spray drying can be carried out at about 120°C to about 170°C. The product obtained by spray drying may include secondary particles in which silicon nanoparticles are aggregated and compound particles represented by SiO x (0 < x ≤ 2.0).

[0056] Compression molding

[0057] In an embodiment, the product obtained by spray drying is mixed with an amorphous carbon precursor and compression molded.

[0058] The amorphous carbon precursor may include pitches such as coal-based pitch and petroleum-based pitch, resins such as phenolic resin and furan resin, and / or hydrocarbons having 1 to 10 carbon atoms. Among them, pitch can be used from the viewpoints of economy and the like.

[0059] Compression molding can be carried out within a pressure range greater than about 10 MPa and less than or equal to about 150 MPa (specifically, about 15 MPa to about 150 MPa, for example, about 20 MPa to about 125 MPa). When the product obtained by spray drying is compressed within this range, the initial efficiency and cycle life characteristics of a rechargeable lithium battery can be improved by appropriately maintaining the gaps between silicon nanoparticles and controlling the pore volume inside the product obtained by compression molding to suppress side reactions between the electrolyte solution and silicon nanoparticles.

[0060] The product obtained by compression molding may include a matrix precursor containing silicon nanoparticles and an amorphous carbon precursor and compound particles represented by SiO x (0 < x ≤ 2.0). Specifically, the matrix precursor may include secondary particles in which silicon nanoparticles are aggregated and a coating that surrounds the outer surface of the secondary particles and the outer surface of the silicon nanoparticles and includes an amorphous carbon precursor.

[0061] Heat treatment

[0062] In an embodiment, the product obtained by compression molding can be heat treated.

[0063] Heat treatment can be carried out at about 700°C to about 1100°C (specifically, about 800°C to about 1050°C, for example, about 900°C to about 1000°C). Within this range, the amorphous carbon precursor in the product obtained by spray drying can be carbonized. Therefore, the amorphous carbon precursor is converted into amorphous carbon, and the product obtained by compression molding is converted into the composite of the foregoing embodiment, thereby improving the strength, conductivity, etc. of the rechargeable lithium battery, and thus improving the initial efficiency of the rechargeable lithium battery.

[0064] The heat treatment may be performed in a furnace under a nitrogen (N2) atmosphere.

[0065] (negative electrode)

[0066] In an embodiment, a negative electrode for a rechargeable lithium battery includes a current collector and a negative active material layer on the current collector, wherein the negative active material layer includes the negative active material composite according to the aforementioned embodiment.

[0067] Since the negative electrode of the above embodiment includes the negative electrode active material composite of the aforementioned embodiment, the capacity, initial efficiency and cycle life of the rechargeable lithium battery can be simultaneously ensured. Hereinafter, the description overlapping with the above will be omitted, and the configuration other than the negative electrode active material composite will be described.

[0068] current collector

[0069] The current collector may include one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0070] Negative electrode active material layer

[0071] The negative electrode active material layer generally includes the negative electrode active material composite of the aforementioned embodiment, and may optionally further include a negative electrode active material different from the composite of the aforementioned embodiment.

[0072] A negative electrode active material different from the composite of the aforementioned embodiment may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0073] The material that reversibly intercalates / deintercalates lithium ions may include, for example, crystalline carbon, amorphous carbon, or a combination thereof as a carbon-based negative electrode active material. The crystalline carbon may be natural graphite or artificial graphite in an unshaped or flake, flaky, spherical, or fibrous form. The amorphous carbon may be soft carbon, hard carbon, a mesophase pitch carbonization product, calcined coke, or the like.

[0074] Lithium metal alloys include alloys 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.

[0075] The material capable of doping / undoping lithium can be a Si-based negative electrode active material or a Sn-based negative electrode active material. The Si-based negative electrode active material can include silicon, silicon-carbon composite, SiO x(0 < x < 2), a Si-Q alloy (where Q is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition metal, rare earth element, and combinations thereof, but not Si), and the Sn-based negative electrode active material may include Sn, SnO₂, a Sn-R alloy (where R is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition metal, rare earth element, and combinations thereof, but not Sn). At least one of these materials may be mixed with SiO₂. The elements Q and R may be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof. [[ID=**1**]] [[ID=**2**]]

[0076] [[ID=**3**]]The silicon-carbon composite may be, for example, a silicon-carbon composite including a core containing crystalline carbon and silicon particles and an amorphous carbon coating provided on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon precursor may be coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or a polymer resin (such as a phenol resin, furan resin, or polyimide resin). In this case, based on the total weight of the silicon-carbon composite, the content of silicon may be about 10 wt% to about 50 wt%. Additionally, based on the total weight of the silicon-carbon composite, the content of crystalline carbon may be about 10 wt% to about 70 wt%, and based on the total weight of the silicon-carbon composite, the content of amorphous carbon may be about 20 wt% to about 40 wt%. Additionally, the thickness of the amorphous carbon coating may be about 5 nm to about 100 nm. The average particle diameter (D50) of the silicon particles may be about 10 nm to about 20 μm. The average particle diameter (D50) of the silicon particles may be preferably about 10 nm to about 200 nm. The silicon particles may exist in an oxidized form, and in this case, the Si:O atomic content ratio indicating the degree of oxidation in the silicon particles may be a weight ratio of about 99:1 to about 33:66. The silicon particles may be SiO[[ID=**4**]] x [[ID=**5**]]particles, and in this case, x in SiO[[ID=**6**]] x [[ID=**7**]]may have a range greater than about 0 and less than about 2. As used herein, when no other definition is provided, the average particle diameter (D50) represents the diameter of the particles with a cumulative volume of about 50 volume% in the particle distribution. [[ID=**8**]] [[ID=**9**]]

[0077] The Si-based negative electrode active material or the Sn-based negative electrode active material can be mixed with the carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are mixed and used, the mixing ratio can be about 1:99 to about 90:10 by weight.

[0078] In the negative active material layer, the negative active material may be included in an amount of about 95 wt % to about 99 wt % based on the total weight of the negative active material layer.

[0079] In an embodiment, the negative electrode active material layer further includes a binder and may optionally further include a conductive material. Based on the total weight of the negative electrode active material layer, the content of the binder in the negative electrode active material layer may be about 1 wt% to about 30 wt%. In addition, when a conductive material is also included, the negative electrode active material layer may include about 50 wt% to about 98 wt% of the negative electrode active material, about 1 wt% to about 30 wt% of the binder, and about 1 wt% to about 30 wt% of the conductive material.

[0080] The binder is used to adhere the negative active material particles to each other and also to adhere the negative active material to the current collector. The binder can be a non-water-soluble binder, a water-soluble binder, or a combination thereof.

[0081] Examples of non-water-soluble binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, ethylene propylene copolymers, polystyrene, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0082] The water-soluble binder may include a rubber binder or a polymer resin binder. The rubber binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0083] When a water-soluble binder is used as the negative electrode binder, a cellulose compound that can impart viscosity may also be included. As the cellulose compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts may be mixed and used. As the alkali metal, Na, K, or Li may be used. The amount of such a thickener used may be about 0.1 to about 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0084] A conductive material is included to provide electrode conductivity. Any conductive material can be used as the conductive material unless it causes a chemical change. Examples of the conductive material include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanotubes, etc.; metal-based materials including metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0085] The negative electrode current collector may include one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0086] (Rechargeable lithium battery)

[0087] In another embodiment, a rechargeable lithium battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is the negative electrode of the above embodiment.

[0088] Since the rechargeable lithium battery of the embodiment includes the negative electrode of the aforementioned embodiment, the capacity, initial efficiency and cycle life of the rechargeable lithium battery can be ensured at the same time. Hereinafter, descriptions overlapping with the above description will be omitted, and the configuration other than the negative electrode will be described.

[0089] positive electrode

[0090] The positive electrode includes a current collector and a positive active material layer on the current collector. According to an embodiment, the positive electrode may have a structure in which the current collector, the positive active material layer, the functional layer, and the adhesive layer are stacked in this order.

[0091] The positive active material layer may include a positive active material, and may further include a binder and / or a conductive material.

[0092] The positive electrode active material may include a lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions. Examples of the positive electrode active material may include a compound represented by any one of the following chemical formulas:

[0093] Li a A 1-b X b D2(0.90≤a≤1.8, 0≤b≤0.5);

[0094] Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);

[0095] Li a E 1-b Xb O 2-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05);

[0096] Li a HAVE BEEN 2-b X b O 4-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05);

[0097] Li a Ni 1-b-c Co b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α≤2);

[0098] Li a Ni 1-b-c Co b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);

[0099] Li a Ni 1-b-c Co b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);

[0100] Li a Ni 1-b-c Mr b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α≤2);

[0101] Li a Ni 1-b-c Mr b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);

[0102] Li a Ni 1-b-c Mr b X c O 2-αT2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);

[0103] The a Nor b E c G d O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0.001≤d≤0.1);

[0104] The a Nor b Co c Mn d G e O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0≤d≤0.5,0.001≤e≤0.1);

[0105] The a NiG b O2(0.90≤a≤1.8,0.001≤b≤0.1);

[0106] The a CoG b O2(0.90≤a≤1.8,0.001≤b≤0.1);

[0107] The a Mn 1-b G b O2(0.90≤a≤1.8,0.001≤b≤0.1);

[0108] The a Mn2G b O4(0.90≤a≤1.8,0.001≤b≤0.1);

[0109] The a Mn 1-g G g PO4(0.90≤a≤1.8,0≤g≤0.5);

[0110] QO2;QS2;LiQS2;

[0111] V2O5;LiV2O5;

[0112] LiZO2:

[0113] LiNiVO4;

[0114] The (3-f) J2(PO4)3(0≤f≤2);

[0115] The (3-f)Fe2(PO4)3(0≤f≤2); and

[0116] Li a FePO4(0.90≤a≤1.8).

[0117] In the chemical formula, A is selected from Ni, Co, Mn, and combinations thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from O, F, S, P, and combinations thereof; E is selected from Co, Mn, and combinations thereof; T is selected from F, S, P, and combinations thereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from Ti, Mo, Mn, and combinations thereof; Z is selected from Cr, V, Fe, Sc, Y, and combinations thereof; and J is selected from V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

[0118] The compound may have a coating on the surface, or may be mixed with another compound having a coating. The coating may include at least one coating element compound selected from an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound for the coating may be amorphous or crystalline. The coating elements included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a combination thereof. In the coating formation process, a method that does not adversely affect the physical properties of the positive active material may be used, for example, spraying, dipping, etc.

[0119] The positive active material may include, for example, a lithium nickel composite oxide represented by Chemical Formula 11.

[0120] [Chemical Formula 11]

[0121] Li a11 Ni x11 M 11 y11 M 12 1-x11-y12 O2

[0122] In Chemical Formula 11, 0.9≤a11≤1.8, 0.3≤x11≤1, 0≤y11≤0.7, and M 11 and M 12 are independently Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr or a combination thereof.

[0123] In Chemical Formula 11, 0.4≤x11≤1 and 0≤y11≤0.6, 0.5≤x11≤1 and 0≤y11≤0.5, 0.6≤x11≤1 and 0≤y11≤0.4, 0.7≤x11≤1 and 0≤y11≤0.3, 0.8≤x11≤1 and 0≤y11≤0.2, or 0.9≤x11≤1 and 0≤y11≤0.1.

[0124] As a specific example, the positive active material may include a lithium nickel cobalt composite oxide represented by Chemical Formula 12.

[0125] [Chemical Formula 12]

[0126] Li a12 Ni x12 Co y12 M 13 1-x12-y12 O2

[0127] In Chemical Formula 12, 0.9≤a12≤1.8, 0.3≤x12≤1, 0≤y12≤0.7, and M 13 is Al, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof.

[0128] In Chemical Formula 12, 0.3≤x12≤0.99 and 0.01≤y12≤0.7, 0.4≤x12≤0.99 and 0.01≤y12≤0.6, 0.5≤x12≤0.99 and 0.01≤y12≤0.5, 0.6≤x12≤0.99 and 0.01≤y12≤0.4, 0.7≤x12≤0.99 and 0.01≤y12≤0.3, 0.8≤x12≤0.99 and 0.01≤y12≤0.2, or 0.9≤x12≤0.99 and 0.01≤y12≤0.1.

[0129] As a specific example, the positive active material may include a lithium nickel cobalt composite oxide represented by Chemical Formula 13.

[0130] [Chemical Formula 13]

[0131] Li a13 Ni x13 Co y13 M 14 z13 M 15 1-x13-y13-z13 O2

[0132] In Chemical Formula 13, 0.9≤a13≤1.8, 0.3≤x13≤0.98, 0.01≤y13≤0.69, 0.01≤z13≤0.69, M 14is Al, Mn or a combination thereof, and M 15 is B, Ce, Cr, F, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, or a combination thereof.

[0133] In Chemical Formula 13, 0.4≤x13≤0.98, 0.01≤y13≤0.59 and 0.01≤z13≤0.59; 0.5≤x13≤0.98, 0.01≤y13≤0.49 and 0.01≤z13≤0.49; 0.6≤x13≤0.98, 0.01≤y13≤0.39 and 0.01≤z13≤0. 39; 0.7≤x13≤0.98, 0.01≤y13≤0.29 and 0.01≤z13≤0.29; 0.8≤x13≤0.98, 0.01≤y13≤0.19 and 0.01≤z13≤0.19; or 0.9≤x13≤0.98, 0.01≤y13≤0.09 and 0.01≤z13≤0.09.

[0134] The positive electrode active material may be present in an amount of about 90 wt % to about 98 wt % based on the total weight of the positive electrode active material layer, or, for example, about 90 wt % to about 95 wt %. The binder and the conductive material may each be present in an amount of about 1 wt % to about 5 wt % based on the total weight of the positive electrode active material layer.

[0135] The binder improves the bonding between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples thereof may include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon.

[0136] A conductive material is included to provide electrode conductivity. Any conductive material can be used as the conductive material unless it causes a chemical change. Examples of the conductive material include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0137] Aluminum foil may be used as the positive electrode current collector, but is not limited thereto.

[0138] diaphragm

[0139] The separator separates the positive electrode and the negative electrode and provides a transmission channel for lithium ions, and can be any separator commonly used in lithium ion batteries. In other words, the separator can have low ion transmission resistance and excellent electrolyte impregnation. For example, the separator can be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene and combinations thereof. The separator can have the form of a non-woven fabric or a woven fabric. For example, in lithium ion batteries, polyolefin polymer separators such as polyethylene and polypropylene are mainly used. In order to ensure heat resistance or mechanical strength, a separator comprising a coating of a ceramic component or a polymer material can be used. Optionally, the separator can have a single-layer or multi-layer structure.

[0140] electrolytes

[0141] The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0142] Non-aqueous organic solvents serve as a medium for transporting ions involved in the electrochemical reaction of the battery. Non-aqueous organic solvents can be carbonate, ester, ether, ketone, or alcohol solvents, or aprotic solvents. Carbonate solvents can include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, mevalonolactone, caprolactone, etc. Ether solvents can include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents can include cyclohexanone, etc. In addition, the alcohol solvent can be ethanol, isopropanol, etc., and the aprotic solvent can be a nitrile such as R-CN (wherein R is a C2 to C20 linear, branched or cyclic hydrocarbon group, and can include a double bond, an aromatic ring or an ether bond), an amide such as dimethylformamide, a dioxolane such as 1,3-dioxolane, cyclopentane, etc.

[0143] The non-aqueous organic solvent can be used alone or in a mixture. When the organic solvent is used in a mixture, the mixing ratio can be controlled according to the desired battery performance.

[0144] In addition, in the case of carbonate solvents, a mixture of cyclic carbonate and chain carbonate can be used. In this case, when the cyclic carbonate and chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte can exhibit excellent performance.

[0145] In addition to the carbonate-based solvent, the non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

[0146] As the aromatic hydrocarbon solvent, an aromatic hydrocarbon compound represented by Chemical Formula I may be used.

[0147] [Chemical Formula I]

[0148]

[0149] In Chemical Formula I, R 4 ~R 9 are the same or different and are selected from hydrogen, halogen, C1-C10 alkyl, halogenated alkyl and combinations thereof.

[0150] Specific examples of aromatic hydrocarbon organic solvents can be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorobenzene, Toluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0151] The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound of Chemical Formula II to improve the cycle life of the battery.

[0152] [Chemical Formula II]

[0153]

[0154] In Chemical Formula II, R 10 and R 11 are the same or different and are selected from hydrogen, halogen, cyano, nitro and fluorinated C1-C5 alkyl, provided that R 10 and R 11 At least one of them is selected from halogen, cyano, nitro and fluorinated C1-C5 alkyl, but R 10 and R 11 Neither is hydrogen.

[0155] Examples of ethylene carbonate compounds may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of the additive for improving cycle life may be used within an appropriate range.

[0156] The lithium salt dissolved in the non-organic solvent supplies lithium ions in the battery, enables the basic operation of the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode.

[0157] Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein, x and y are natural numbers, for example, integers of 1 to 20), at least one supporting salt selected from lithium difluoro(bisoxalato)phosphate, LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalato)borate; LiBOB) and lithium difluoro(oxalato)borate (LiDFOB).

[0158] The lithium salt may be used in a concentration range of about 0.1 M to about 2.0 M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0159] Rechargeable lithium batteries can be classified as lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries, depending on the presence of a separator and the type of electrolyte used therein. Rechargeable lithium batteries can have a variety of shapes and sizes, including cylindrical, prismatic, button-type (coin), or pouch-type batteries, and can be thin-film batteries or quite bulky in size. The structure and manufacturing methods of the lithium ion batteries of the present disclosure are well known in the art.

[0160] Hereinafter, examples and comparative examples of the present invention are described. However, it will be understood that the examples are for illustrative purposes and should not be construed as limiting the present disclosure.

[0161] [Internal pores of the negative electrode active material composite]

[0162] Example 1

[0163] (1) Preparation of negative electrode active material composite

[0164] A mixed solvent consisting of IPA and ETOH at a volume ratio of 3:7 was prepared as a solvent. 5 g of the silicon nanoparticles (D50: 100 nm) and 5 g of SiO particles (D50: 3 μm) listed in Table 1 were added to 80 g of the mixed solvent and then dispersed therein. Thus, a solution was obtained in which the silicon nanoparticles and SiO particles were uniformly dispersed in the mixed solvent.

[0165] The solution was spray-dried by using a spray dryer at 150° C. and a spray rate of 60 g / min.

[0166] 6 g of the product obtained by spray drying was mixed with 6 g of petroleum-based pitch as a type of amorphous carbon, and the mixture was compression-molded at a pressure of 20 MPa for 3 minutes.

[0167] The obtained compression-molded product was heat-treated at 1000° C. under an N 2 atmosphere to prepare a negative electrode active material composite.

[0168] (2) Manufacturing of negative electrode

[0169] A negative electrode active material slurry was prepared by mixing 70 wt% of the negative electrode active material composite, 15 wt% of a conductive material (Super-P), and 15 wt% of a binder (polyacrylic acid (PAA)) in water as a solvent. The negative electrode active material slurry was applied to one surface of a copper foil having a length of 76.5 mm, a width of 48.0 mm, and a thickness of 10 μm, followed by drying and compression to produce a negative electrode. The negative electrode active material slurry was applied using a die coating method.

[0170] (3) Manufacturing of positive electrode

[0171] A positive electrode active material slurry was prepared by mixing 95 wt% of LiCoO2 (the positive electrode active material), 3 wt% of polyvinylidene fluoride (PVDF) (the binder), and 2 wt% of Ketjen Black (the conductive material) in N-methylpyrrolidone solvent. The slurry was applied to one surface of an aluminum current collector measuring 74.5 mm in length, 45.0 mm in width, and 12 μm in thickness, followed by drying and compression to produce the positive electrode. The slurry was applied using a die coating method.

[0172] (4) Manufacturing of battery cells

[0173] A polyethylene separator having a length of 76.5 mm, a width of 48.0 mm, and a thickness of 14 μm was prepared and then inserted between the negative electrode and the positive electrode, and then assembled together. Here, the coated surface of the negative electrode was in contact with the separator.

[0174] The electrode assembly was housed in a pouch, and an electrolyte solution prepared by adding 1.10M LiPF6 lithium salt and 10% FEC (fluoroethylene carbonate) to a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 50:50 was injected therein, thereby manufacturing a rechargeable lithium battery cell.

[0175] Example 2

[0176] By changing the compression molding pressure to 30 MPa, a negative active material composite was prepared in the same manner as in Example 1. Subsequently, a negative electrode and a rechargeable lithium battery cell of Example 2 were manufactured in the same manner as in Example 1 except that the negative active material composite was used.

[0177] Example 3

[0178] By changing the compression molding pressure to 50 MPa, a negative active material composite was prepared in the same manner as in Example 1. Subsequently, a negative electrode and a rechargeable lithium battery cell of Example 3 were manufactured in the same manner as in Example 1 except that the negative active material composite was used.

[0179] Example 4

[0180] By changing the compression molding pressure to 100 MPa, a negative active material composite of Example 4 was prepared in the same manner as in Example 1. Subsequently, a negative electrode and a rechargeable lithium battery cell of Example 4 were manufactured in the same manner as in Example 1 except that the negative active material composite was used.

[0181] Comparative Example 1

[0182] 5 g of SiO particles (D50: 3.0 μm) and 5 g of SiC particles (D50: 8.4 μm) were mixed to prepare the negative active material of Comparative Example 1. The negative electrode and rechargeable lithium battery cell of Comparative Example 1 were manufactured in the same manner as in Example 1 except that the negative active material composite was used.

[0183] Comparative Example 2

[0184] By changing the compression molding pressure to 1 MPa, a negative active material composite of Comparative Example 2 was prepared in the same manner as in Example 1. Subsequently, a negative electrode and a rechargeable lithium battery cell of Comparative Example 2 were manufactured in the same manner as in Example 1 except that the negative active material composite was used.

[0185] Comparative Example 3

[0186] By changing the compression molding pressure to 10 MPa, a negative active material composite of Comparative Example 3 was prepared in the same manner as in Example 1. Subsequently, a negative electrode and a rechargeable lithium battery cell of Comparative Example 3 were manufactured in the same manner as in Example 1 except that the negative active material composite was used.

[0187] (Table 1)

[0188]

[0189] Specifically, the negative active material composites having a SiO@SiC structure according to Examples 1 to 4 and Comparative Examples 2 and 3 were prepared by using the same raw materials (such as silicon nanoparticles, etc.) but changing the compression molding pressure. On the other hand, Comparative Example 1 used a simple mixture of SiO particles and SiC particles.

[0190] Evaluation Example 1: Evaluation of Properties of Negative Electrode Active Material Composite

[0191] Each of the negative active material composites according to Examples 1 to 4 and Comparative Examples 1 to 3 was evaluated according to the following method, and the results are shown in Table 2.

[0192] (1) Internal pore volume and BET specific surface area: The volume of internal pores was quantitatively measured by using a BJH (Barrett-Joyner-Halenda) analysis apparatus.

[0193] Take each electrode plate portion of the unreacted area of ​​the rechargeable lithium battery cell that was charged and discharged once at 0.1C and put it into a hole measurement device (equipment name: ASAP series, manufacturer: Micromeritics Instrument Corp.), and then heat it to 623K at 10K / min and keep it for 2 hours to 10 hours (vacuum: 100mmHg or less) for pretreatment. Here, the temperature and time can be appropriately adjusted according to the negative active material composite powder.

[0194] Subsequently, the pore volume is measured in liquid nitrogen controlled to have a relative pressure (P / Po) of 0.01 or less. Specifically, the pore volume is measured by absorbing nitrogen at 32 points at a relative pressure of 0.01 to 0.995, and then desorbing nitrogen at 24 points at a relative pressure of 0.14. Here, the pore volume can generally be measured using BET at a relative pressure (P / Po) of 0.1.

[0195] (2) D50: The average particle size (D50) of the negative electrode active material complex was measured by using PSA (Particle Size Analyzer, Beckman Coulter, Inc.).

[0196] (Table 2)

[0197]

[0198] In Table 2, unlike the negative active material composites according to Comparative Examples 2 and 3, the negative active material composites of Examples 1 to 4 showed a value of 5.0×10 -2 cm 3 / g or less of internal pore volume (provided that it is greater than about 0cm 3 / g). Specifically, referring to Examples 1 to 4 and Comparative Examples 2 and 3, the internal pore volume and BET specific surface area of ​​the negative electrode active material composite changed according to the compression molding pressure. More specifically, when the compression molding pressure was set to greater than 10 MPa (specifically, 20 MPa or greater), the negative electrode active material composite ensured a pore volume of 5.0×10 -2 cm 3 / g or less of internal pore volume (provided that it is greater than about 0 cm 3 In addition, as the compression molding pressure increases to 20 MPa or more, the internal pore volume and BET specific surface area of ​​the negative electrode active material composite tend to decrease.

[0199] On the other hand, Comparative Example 1 used a simple mixture of SiO particles and SiC particles, wherein each particle had a particle size of 5.0×10 -2 cm 3 / g or less (provided that it is greater than about 0cm 3 / g).

[0200] Evaluation Example 2: Evaluation of electrochemical characteristics of rechargeable lithium battery cells

[0201] Regarding electrochemical characteristics, each of the rechargeable lithium battery cells of Examples 1 to 4 and Comparative Examples 1 to 3 was evaluated in the following method, and the results are shown in Table 3.

[0202] (1) Initial efficiency: Regarding the initial charge and discharge efficiency, the rechargeable lithium battery cells were charged and discharged once at 0.1 C and evaluated, and the results are shown in Table 3.

[0203] (2) Cycle life characteristics: The rechargeable lithium battery cell was charged and discharged 100 times at 0.5 C at 25° C. The ratio of the discharge capacity at the first cycle to the discharge capacity at the 100th cycle was calculated, and the results are shown in Table 3.

[0204] (Table 3)

[0205]

[0206] In Table 3, different from the rechargeable lithium battery cells manufactured by using the negative electrode active material mixture of Comparative Example 1 and the negative electrode active material composites of Comparative Examples 2 and 3, the rechargeable lithium battery cells manufactured by using the negative electrode active material composites of Examples 1 to 4 maintained a discharge capacity of 80% or higher after 100 cycles. First, Comparative Example 1 using a simple mixture of SiO particles and SiC particles showed that the average internal pore volume per particle was in the range of 5.0×10 -2 cm 3 / g or less (provided that it was greater than about 0 cm 3 / g), but failed to overcome the drawbacks of the SiC particles, resulting in deterioration of the cycle life of the rechargeable lithium battery cell.

[0207] Compared with the negative electrode active material mixture of Comparative Example 1, each of the negative electrode active material composites according to Examples 1 to 4 and Comparative Examples 2 and 3 (as composites including compound particles represented by SiO x (0 < x ≤ 2.0), silicon nanoparticles, and amorphous carbon) improved the cycle life of the rechargeable lithium battery cell.

[0208] However, each of the negative electrode active material composites of Comparative Examples 2 and 3 showed an internal pore volume greater than 5.0×10 - 2 cm 3 / g, and maintained a discharge capacity of about 70% of the rechargeable lithium battery cell after 100 cycles.

[0209] In contrast, each of the negative electrode active material composites of Examples 1 to 4 showed an internal pore volume of 5.0×10 -2 cm 3 / g or less (provided that it was greater than about 0 cm 3 / g), and ensured a discharge capacity of 80% or more of the rechargeable lithium battery cell even after 100 cycles.

[0210] Therefore, in order to improve the cycle life and initial efficiency of the rechargeable lithium battery cell, a negative electrode active material should be used as a composite including compound particles represented by SiO x (0 < x ≤ 2.0), silicon nanoparticles, and amorphous carbon and having an internal pore volume of 5.0×10 -2 cm 3 / g or less (provided that it was greater than about 0 cm 3 / g).

[0211] [D50 particle size of silicon nanoparticles]

[0212] Example 5

[0213] The negative active material composite of Example 5 was prepared by using silicon nanoparticles under the conditions described in Table 4. The negative electrode and the rechargeable lithium battery cell of Example 5 were manufactured in the same manner as in Example 2, except that the negative active material composite of Example 5 was used.

[0214] Example 6

[0215] The negative active material composite of Example 6 was prepared by using silicon nanoparticles under the conditions described in Table 4. The negative electrode and the rechargeable lithium battery cell of Example 6 were manufactured in the same manner as in Example 2, except that the negative active material composite of Example 6 was used.

[0216] Example 7

[0217] The negative active material composite of Example 7 was prepared by using silicon nanoparticles under the conditions described in Table 4. The negative electrode and the rechargeable lithium battery cell of Example 7 were manufactured in the same manner as in Example 2, except that the negative active material composite of Example 7 was used.

[0218] Comparative Example 4

[0219] The negative active material composite of Comparative Example 4 was prepared by using silicon nanoparticles under the conditions described in Table 4. The negative electrode and the rechargeable lithium battery cell of Comparative Example 4 were manufactured in the same manner as in Example 2, except that the negative active material composite of Comparative Example 4 was used.

[0220] Comparative Example 5

[0221] The negative active material composite of Comparative Example 5 was prepared by using silicon nanoparticles under the conditions described in Table 4. The negative electrode and the rechargeable lithium battery cell of Comparative Example 5 were manufactured in the same manner as in Example 2, except that the negative active material composite of Comparative Example 5 was used.

[0222] (Table 4)

[0223]

[0224] Specifically, in Examples 2 and 5 to 7 and Comparative Examples 4 and 5, a negative active material composite having a SiO@SiC structure was prepared under the same compression molding pressure but by changing the D50 particle size and XRD half maximum full width of silicon nanoparticles.

[0225] Evaluation Example 3: Evaluation of Properties of Negative Electrode Active Material Composite

[0226] Each of the negative active material composites according to Examples 2 and 5 to 7 and Comparative Examples 4 and 5 was evaluated in the same method as in Evaluation Example 1, and the evaluation results are shown in Table 5.

[0227] (Table 5)

[0228]

[0229] In Table 5, each of the negative active material composites of Examples 2 and 5 to 7 and Comparative Examples 4 and 5 exhibited almost equal internal pore volumes. Therefore, the internal pore volume of the negative active material composite was shown to be more dependent on the compression molding pressure than the D50 particle size of the silicon nanoparticles.

[0230] Evaluation Example 4: Evaluation of electrochemical characteristics of rechargeable lithium battery cells

[0231] Regarding electrochemical characteristics, each of the rechargeable lithium battery cells of Examples 2 and 5 to 7 and Comparative Examples 4 and 5 was evaluated in the same method as in Evaluation Example 2, and the results are shown in Table 6.

[0232] (Table 6)

[0233]

[0234] In Table 6, the rechargeable lithium battery cells manufactured by using each of the negative active material composites of Examples 2 and Examples 5 to 7 and Comparative Examples 4 and 5 exhibited almost equal initial efficiency but different cycle life characteristics. Specifically, each of the negative active material composites of Examples 2 and Examples 5 to 7 and Comparative Examples 4 and 5 exhibited 5.0×10 -2 cm 3 / g or less of internal pore volume (provided that it is greater than 0cm 3 / g), regardless of the D50 particle size of the silicon nanoparticles, and ensured an initial efficiency of a rechargeable lithium battery cell of 87% or higher.

[0235] However, each of the negative active material composites of Comparative Examples 4 and 5 used silicon nanoparticles having a D50 particle size of greater than 200 nm and maintained less than 70% of the discharge capacity of the rechargeable lithium battery cell after 100 cycles.

[0236] Therefore, in order to improve the cycle life and initial efficiency of rechargeable lithium battery cells, it is necessary to use a xA composite of compound particles represented by (0 < x ≤ 2.0), silicon nanoparticles (where the silicon nanoparticles have a D50 particle size of 200 nm or less (provided that it is greater than 0 nm)), and amorphous carbon, and having an internal pore volume of 5.0 × 10 -2 cm 3 / g or less (provided that it is greater than 0 cm 3 / g) of the negative electrode active material.

[0237] Although the present disclosure has been described in connection with presently considered to be practical exemplary embodiments, it will be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the claims.

[0238] <Explanation of Reference Numerals>

[0239] 1: Compound particles represented by SiO x (0 < x ≤ 2.0)

[0240] 2: Silicon nanoparticles

[0241] 3: Amorphous carbon

Claims

1. A negative electrode active material composite for a rechargeable lithium battery, the negative electrode active material composite comprising: Compound particles represented by SiO x where 0 < x ≤ 2.0; and A matrix comprising silicon nanoparticles and amorphous carbon, said silicon nanoparticles having an average particle size D50 less than or equal to 200 nm, provided that said average particle size D50 is greater than 0 nm, Wherein, the SiO x represents the compound particles in said matrix, The internal pore volume of the negative electrode active material composite is less than or equal to 5.0×10 -2 cm 3 / g, provided that the internal pore volume is greater than 0cm 3 / g, and The negative electrode active material composite includes SiO x Representing the compound particles and the silicon nanoparticles.

2. The negative electrode active material composite according to claim 1, wherein The average particle size D50 of the silicon nanoparticles is 50 nm to 200 nm.

3. The negative electrode active material composite according to claim 1, wherein The aspect ratio of the silicon nanoparticles is 4-20.

4. The negative electrode active material composite according to claim 1, wherein The full width at half maximum of the X-ray diffraction angle using CuKα rays at the (111) plane of the silicon nanoparticles is 0.3°~1.5°.

5. The negative electrode active material composite according to claim 1, wherein The SiO x The average particle size D50 of the compound particles represented is 1 μm to 10 μm.

6. The negative electrode active material composite according to claim 1, wherein The amorphous carbon is soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke or a combination thereof.

7. The negative electrode active material composite according to claim 1, wherein Based on the total weight of the negative electrode active material composite, the amount of SiO x The compound particles represented by α-HgCl2 include the silicon nanoparticles in an amount of 10 wt % to 95 wt %, and the remainder includes the amorphous carbon.

8. The negative electrode active material composite according to claim 1, wherein The average particle size D50 of the negative electrode active material composite is 2 μm to 15 μm.

9. The negative electrode active material composite according to claim 1, wherein The internal pore diameter of the negative electrode active material complex is less than or equal to 330 nm, provided that the internal pore diameter of the negative electrode active material complex is greater than 0 nm.

10. The negative electrode active material composite according to claim 1, wherein The BET specific surface area of ​​the negative electrode active material composite is 0.1 cm 2 / g~10cm 2 / g.

11. The negative electrode active material composite according to claim 1, wherein The matrix includes secondary particles in which the silicon nanoparticles are aggregated; and a coating layer surrounding outer surfaces of the secondary particles and outer surfaces of the silicon nanoparticles and including the amorphous carbon.

12. A method for preparing a negative active material composite for a rechargeable lithium battery, the method comprising: Spray drying includes solvent, SiO x Represents a solution of compound particles and silicon nanoparticles, wherein 0 <x≤2.0; compression molding a mixture of the obtained product and an amorphous carbon precursor including spray drying at a pressure greater than 10 MPa; and The compression-molded product is heat-treated to obtain the negative electrode active material composite according to claim 1 .

13. The method according to claim 12, wherein: The spray drying is performed in a temperature range of 120°C to 170°C.

14. The method according to claim 12, wherein: The compression molding is performed within a pressure range of greater than 10 MPa and less than or equal to 150 MPa.

15. The method according to claim 12, wherein: The heat treatment is performed in a temperature range of 700°C to 1100°C.

16. A negative electrode for a rechargeable lithium battery, the negative electrode comprising: a current collector and a negative electrode active material layer on the current collector, Wherein, the negative electrode active material layer comprises the negative electrode active material composite according to any one of claims 1 to 11.

17. The negative electrode according to claim 16, wherein The negative electrode active material layer further includes a conductive material, a binder or a combination thereof.

18. A rechargeable lithium battery, comprising: positive electrode, negative electrode and electrolyte, The negative electrode is the negative electrode according to claim 16.

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