Negative active material, method for preparing negative active material, negative electrode including negative active material, and rechargeable lithium battery including negative active material

Abstract

Disclosed are a negative active material, a method of preparing the same, and a rechargeable lithium battery including the same. The negative active material includes: a core including a porous support including pores, a carbon layer disposed in the pores, and a silicon layer disposed on the carbon layer; and an amorphous carbon layer disposed on an outer surface of the core. The pores include mesopores having a porosity of from about 50% to about 100% of the total porosity of the porous support.

Description

Technical Field

[0001] Embodiments relate to a negative active material, a method of preparing the negative active material, a negative electrode including the negative active material, and a rechargeable lithium battery including the negative active material. Background Art

[0002] With the rapid popularization of electronic devices using batteries (such as mobile phones, laptop computers and electric vehicles), the demand for smaller, lighter and relatively high-capacity rechargeable lithium batteries has rapidly increased. Therefore, consideration has been given to improving the performance of rechargeable lithium batteries.

[0003] Rechargeable lithium batteries include positive and negative electrodes containing active materials capable of intercalating and deintercalating lithium ions, as well as an electrolyte solution. When lithium ions are intercalated and deintercalated at the positive and negative electrodes, electrical energy is generated through oxidation and reduction reactions. Summary of the Invention

[0004] One or more embodiments provide a negative active material exhibiting high capacity, high efficiency, and excellent cycle-life characteristics.

[0005] Another embodiment provides a method for preparing the negative electrode active material.

[0006] Yet another embodiment provides a negative electrode including the negative active material.

[0007] Yet another embodiment provides a rechargeable lithium battery including the negative electrode active material.

[0008] One or more embodiments provide a negative electrode active material, the negative electrode active material comprising: a core comprising a porous support including pores, a carbon layer disposed in the pores, a silicon layer disposed on the carbon layer; and an amorphous carbon layer disposed on an outer surface of the core, wherein the pores comprise mesopores having a porosity of about 50% to about 100% of the total porosity of the porous support.

[0009] Another embodiment provides a negative electrode active material, the negative electrode active material including: secondary particles, which are aggregates of primary particles, wherein the primary particles include: a core including (i) a porous support containing pores, (ii) a carbon layer disposed in the pores, and (iii) a silicon layer disposed on the carbon layer; and (iv) an amorphous carbon layer disposed on an outer surface of the core, wherein the pores include mesopores having a porosity of about 50% to about 100% of the total porosity of the porous support.

[0010] Another embodiment provides a method for preparing a negative active material, the method comprising: performing a first vapor phase coating with carbon gas on a porous support including pores to form a carbon layer in the pores; performing a second vapor phase coating with silicon gas on the carbon layer to form a silicon layer; and coating the outer surface of the porous support with an amorphous carbon precursor, wherein the pores include mesopores having a porosity of about 50% to about 100% of the total porosity of the porous support.

[0011] Yet another embodiment provides a rechargeable lithium battery, including: a negative electrode including the negative active material; a positive electrode; and an electrolyte.

[0012] The negative active material according to one or more embodiments may exhibit excellent charge and discharge efficiency, high rate characteristics, and excellent cycle-life characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram showing a negative electrode active material according to an embodiment.

[0014] Figures 2 to 5 is a cross-sectional view schematically illustrating a rechargeable lithium battery according to an embodiment. DETAILED DESCRIPTION

[0015] The embodiments are described in detail herein. However, the embodiments are exemplary, and the present disclosure is not limited to the disclosed embodiments.

[0016] The terms used in this specification explain the embodiments, but are not intended to limit the entire scope of the present disclosure. Unless the context clearly indicates otherwise, an expression in the singular includes an expression in the plural.

[0017] The term "combinations thereof" may include mixtures, laminates, composites, copolymers, alloys, blends, reactants of the components.

[0018] The terms "include", "comprising" or "having" are intended to indicate the presence of executed features, quantities, steps, constituent elements or combinations thereof, but it should be understood that the possibility of the presence or addition of one or more other features, quantities, steps, constituent elements or combinations thereof is not excluded.

[0019] The accompanying drawings are shown with exaggerated thickness to clearly illustrate various layers and regions, and the same reference numerals are assigned to similar parts throughout the specification. If an element (such as a layer, film, region, plate, etc.) is referred to as being "on" or "over" another part, this may include the case where the element is "directly on" the other element, as well as the case where another element is present between them. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present.

[0020] Here, when viewed from a plan view, the “layer” includes a shape formed entirely on the entire surface or a shape formed on a portion of the surface.

[0021] Here, “or” is not to be interpreted as exclusive, for example, “A or B” is to be interpreted as including A, B, A+B, etc.

[0022] As used herein, when no other definition is provided, a particle size or particle size may be an average particle size. The average particle size represents the average value of the diameters of the particles according to the cumulative volume in the particle size distribution of the particles included in the negative electrode active material. The average particle size (D50) can be measured by methods well known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscopy or scanning electron microscopy. In some embodiments, data analysis is performed using a dynamic light scattering measurement device, and the number of particles is counted for each particle size range, from which the average particle size (D50) value can be easily obtained by calculation.

[0023] Particle size can be measured by laser diffraction. Laser diffraction can be performed by distributing particles to be measured in a distribution solvent and introducing the particles into a commercially available laser diffraction particle measuring device (e.g., MT 3000 available from Microtrac), irradiating the device with ultrasonic waves of approximately 28 kHz at a power of approximately 60 W, and calculating the average particle size (D50) based on the 50% standard of the particle distribution in the measuring device.

[0024] In some embodiments, the average particle size can be measured by various techniques, such as by a particle size analyzer, for example.

[0025] In some embodiments, the thickness can be measured by scanning electron microscopy (SEM) or transmission electron microscopy (TEM) images of a cross section. However, the present disclosure is not limited to thickness measurements by SEM and TEM, and the thickness can be measured by any other technique known in the relevant art. The thickness can be an average thickness.

[0026] As used herein, soft carbon refers to a graphitizable carbon material that is readily graphitized by heat treatment at high temperatures (e.g., approximately 2800°C). Hard carbon refers to a non-graphitizable carbon material that is substantially not graphitized, or is slightly graphitized, by heat treatment. The terms soft carbon and hard carbon are well known in the relevant art.

[0027] In some embodiments, crystalline carbon and amorphous carbon can be distinguished by X-ray diffraction (XRD) measurement. Crystalline carbon includes natural graphite and artificial graphite. Natural graphite may refer to graphite that can be naturally generated by separating it from a mineral, and if measured by XRD, the interplanar spacing (d002) of the (002) plane may be about 3.350 Å to about 3.360 Å. Artificial graphite may refer to graphite manufactured by graphitization, and if measured by XRD, the interplanar spacing (d002) of the (002) plane may be about 3.355 Å to about 3.365 Å. If measured by XRD, amorphous carbon may have an interplanar spacing (d002) of the (002) plane of about 3.34 Å or less. XRD can be measured using CuKα radiation as a target radiation with an X-ray diffraction analyzer (e.g., product name: X'Pert, manufacturer: Malvern Panalytical) and by removing the monochromator to improve peak density resolution. The measurement conditions may be 2θ=10° to 80°, a scanning speed (° / S) of 0.044 to 0.089, and a step size (° / step size) of 0.013 to 0.039.

[0028] According to one or more embodiments, the negative active material includes: a core including a porous support including pores, a carbon layer located in the pores, and a silicon layer located on the carbon layer; and an amorphous carbon layer on the outer surface of the core, wherein the pores include mesopores and the porosity of the mesopores is about 50% to about 100% based on 100% of the overall porosity of the porous support.

[0029] Figure 1 Schematically shows the negative active material according to one or more embodiments. Figure 1 As shown in FIG, the negative electrode active material 1 includes a core and an amorphous carbon layer 17. The core includes a carrier 14 containing pores, a carbon layer 13 located in the pores, and a silicon layer 15 located on the carbon layer 13. The amorphous carbon layer 17 is located on the outer surface of the core. Figure 1 In FIG. 1 , P represents a hole before the carbon layer 13 and the silicon layer 15 are formed. Figure 1 The dimensions on the left schematically illustrate the dimensions of the holes.

[0030] The carrier according to one or more embodiments is formed with pores, and the pores have various sizes such as micropores, mesopores, or macropores. Among them, mesopores are included in a porosity of about 50% to about 100% of the total porosity. The mesopores may have an average diameter of about 1 nm to about 50 nm. In one or more embodiments, micropores refer to pores with an average diameter of less than about 1 nm, and macropores refer to pores with an average diameter of greater than about 50 nm.

[0031] The porosity of the mesopores may constitute about 60% to about 100% or about 70% to about 100% of the total porosity. The average diameter of the mesopores may be about 1 nm to about 50 nm to allow silicon to be located in the mesopores. Therefore, since silicon having an average diameter of about 1 nm to about 50 nm is located within the pores of the porous support, the volume expansion of silicon can be suppressed, and silicon having an average diameter of about 1 nm to about 50 nm can be appropriately included in the negative electrode active material in proportion to the percentage of the mesopores. If the porosity of the mesopores is less than about 50% of the total porosity, there may not be sufficient area to deposit silicon, and therefore, the designed capacity may not be achieved.

[0032] The overall porosity of the porous support according to one or more embodiments may be from about 30% to about 90%, from about 40% to about 80%, or from about 50% to about 70%. If the overall porosity of the porous support is within these ranges, silicon can be included in the pores in sufficient amounts, thereby exhibiting much higher capacity.

[0033] The bulk porosity and mesoporosity of a porous support can be measured using the Barrett-Joyner-Halenda (BJH) method. For example, porosity can be determined by measuring the pore volume using the BJH method using a N2 adsorption isotherm and dividing the measured pore volume by the volume of the entire porous support. Specifically, the porous support is pretreated by increasing the temperature to approximately 523 K (Kelvin, absolute temperature) at a rate of approximately 10 K / min and maintaining the porous support at this temperature and a pressure of approximately 100 mmHg or less for approximately 2 to 10 hours. Liquid nitrogen, whose relative pressure (P / P0) is adjusted to approximately 0.01 Torr or less, is adsorbed by the porous support at approximately 32 points to a relative pressure of 0.01 Torr to approximately 0.955 Torr and desorbed at approximately 24 points to a relative pressure of approximately 0.14 Torr. Given the volume of the porous support, the porosity can be obtained from the amount of N2 measured using this method.

[0034] In another embodiment, the individual porosities of micropores, mesopores, or macropores and the overall porosity of the porous support can be measured by N2 absorption isotherm using a pore measurement device (ASAP2020 available from Micromeritics Instruments) by the BJH method.

[0035] The negative active material according to the embodiment is located in the pores of the porous support. Therefore, the volume expansion of silicon during charge and discharge can be effectively suppressed, and a high capacity of silicon can be obtained.

[0036] In one or more embodiments, the silicon-containing porous support may include nano-silicon or SiO x(0 ≤ x ≤ 2). Compared to carbon-containing porous supports, this silicon-containing porous support can provide more uniform deposition of silicon within the pores. Consequently, smaller silicon particles can be deposited within the pores of the porous support. This enables more effective suppression of silicon volume expansion.

[0037] Based on 100 wt % of the negative electrode active material, the amount of the porous support may be about 30 wt % to about 70 wt %, about 35 wt % to about 65 wt %, or about 40 wt % to about 60 wt %. If the amount of the porous support satisfies these ranges, the amount of silicon to be deposited can be controlled, and thus the desired capacity can be ensured.

[0038] The negative active material according to the embodiment includes the silicon layer in the pores and the carbon layer between the pores, thereby achieving improved ion conductivity.

[0039] In an embodiment, the carbon layer may include amorphous carbon, crystalline carbon, or a combination thereof. In another embodiment, the carbon layer may include amorphous carbon. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, sintered coke, or a combination thereof. The crystalline carbon may be natural graphite or artificial graphite in an unspecified shape, sheet, flake, spherical, or fibrous form.

[0040] In one or more embodiments, the thickness of the carbon layer may be about 1 nm to about 15 nm, about 1 nm to about 10 nm, or about 1 nm to about 5 nm. If the thickness of the carbon layer is within these ranges, the ionic conductivity may be increased, and the rate characteristics and cycle life characteristics may be improved.

[0041] The silicon layer may include amorphous silicon. If the silicon included in the silicon layer is amorphous silicon, the volume expansion during charge and discharge can be reduced relative to crystalline silicon, and the cycle life characteristics can also be improved. In an embodiment, amorphous Si can be confirmed by using TEM or XRD measurement. In the case of using TEM measurement, silicon that does not show lattice fringes can indicate amorphous silicon. In the case of measuring XRD using CuKα radiation as the target radiation, the appearance of a broad peak can indicate amorphous silicon.

[0042] The silicon located in the pores may be elemental Si (simple Si) or pure Si.

[0043] In one or more embodiments, based on 100 wt % of the negative electrode active material, the amount of silicon may be about 40 wt % to about 80 wt %, about 45 wt % to about 65 wt %, or about 50 wt % to about 60 wt %. If the amount of silicon is within these ranges, higher efficiency and capacity may be exhibited, and cycle life characteristics may be excellent.

[0044] The negative electrode active material according to one or more embodiments includes amorphous carbon located on the core. For example, the negative electrode active material may include an amorphous carbon layer surrounding the outer surface of the core. The amorphous carbon layer may completely surround the surface of the core or may partially surround the surface of the core. The thickness of the amorphous carbon layer may be from about 1 nm to about 100 nm, from about 1 nm to about 50 nm, or from about 1 nm to about 30 nm. If the thickness of the amorphous carbon layer is within these ranges, irreversible reactions may be minimized and resistance may be improved.

[0045] In the amorphous carbon layer, the amorphous carbon may be pitch carbon, soft carbon, hard carbon, mesophase pitch carbide, sintered coke, carbon fiber, or a combination thereof.

[0046] The thickness of the amorphous carbon layer refers to the thickness of the amorphous carbon on the outer surface of the core. If the amorphous carbon is unevenly distributed, it may be the length at the thickest point. In one or more embodiments, the thickness may be an average thickness. If the thickness of the amorphous carbon layer is within the above range, irreversible capacity loss can be reduced, charge and discharge efficiency can be improved, and rate characteristics can be improved.

[0047] According to an embodiment, based on 100 wt% of the negative electrode active material, the amount of carbon may be about 1 wt% to about 30 wt%, about 1 wt% to about 20 wt%, or about 1 wt% to about 15 wt%. The amount of carbon represents the sum of the amount of carbon in the carbon layer located in the pores and the amount of carbon in the amorphous carbon layer located on the core. In one or more embodiments, the total amount of carbon included in the negative electrode active material is meaningful, and there is no need to define the amount of carbon included in the carbon layer and the amount of carbon included in the amorphous carbon layer.

[0048] If the amount of carbon included in the negative active material is within the above range, conductivity may be improved, thereby maximizing capacity.

[0049] In an embodiment, silicon carbide may be located between the carbon layer and the silicon layer. In the negative electrode active material according to one or more embodiments, the presence of silicon carbide between the carbon layer and the silicon layer can be confirmed by X-ray diffraction. Since silicon carbide is located between the carbon layer and the silicon layer, the boundary between the carbon layer and the silicon layer can be clearly identified.

[0050] According to another embodiment, a negative electrode active material includes secondary particles in which at least one primary particle is aggregated, the primary particle including a core and an amorphous carbon layer, the core including a porous support including pores, a carbon layer located in the pores, and a silicon layer located on the carbon layer, and the amorphous carbon layer is located on the outer surface of the core. The pores may include mesopores, and the porosity of the mesopores may be about 50% to about 100%, about 60% to about 100%, or about 70% to about 100%, based on the overall porosity.

[0051] For better understanding and ease of description, the negative active material according to one embodiment is referred to as the negative active material according to the first embodiment and the negative active material according to another embodiment is referred to as the negative active material according to the second embodiment.

[0052] The negative electrode active material according to the second embodiment includes secondary particles in which primary particles (the negative electrode active material according to the first embodiment as primary particles) are aggregated. Therefore, the negative electrode active material according to the second embodiment has the same configuration as the negative electrode active material according to the first embodiment, except that it is in the form of secondary particles formed by aggregating primary particles.

[0053] In one or more embodiments, the average diameter of the primary particles may be about 1 μm to about 20 μm, or about 5 μm to about 15 μm. If the size of the primary particles is within these ranges, the increase in Brunner-Emmett-Teller (BET) specific surface area can be minimized, thereby improving efficiency.

[0054] In the negative active material according to one or more embodiments, the size of the primary particles may be set, and the size of the secondary particles may be appropriately adjusted.

[0055] If the negative active material includes secondary particles in which primary particles are aggregated, the silicon layer may be more uniformly formed in the secondary particles compared to the negative active material according to the first embodiment formed of single particles that are not aggregated.

[0056] [Method for preparing negative electrode active material] According to one or more embodiments, a negative electrode active material is prepared by first vapor-phase coating a porous support including pores with carbon gas to prepare a carbon layer; second vapor-phase coating the carbon layer with silicon gas; and coating the resulting material with an amorphous carbon precursor. The preparation is described below.

[0057] First, a porous carrier is prepared. The porous carrier can be commercially available or can be formed by aerogel preparation or spray drying process. In other embodiments, the porous carrier can be silica gel or zeolite.

[0058] A porous support is first vapor-coated using carbon gas. The pores of the support have various sizes, such as micropores, mesopores, or macropores. Among these pores, mesopores have a porosity of about 50% to about 100% based on the overall porosity. In one or more embodiments, the porosity of the mesopores may be about 60% to about 100%, or about 70% to about 100% of the total porosity. The size of the mesopores may be about 1 nm to about 50 nm.

[0059] The overall porosity of the porous support may be from about 30% to about 90%, from about 40% to about 80%, or from about 50% to about 70%.

[0060] The carbon gas may be methane (CH 4 ) gas, ethylene (C 2 H 4 ) gas, acetylene (C 2 H 2 ) gas, propane (C 3 H 8 ) gas, propylene (C 3 H 6 ) gas, or a combination thereof.

[0061] The first vapor coating may be a chemical vapor deposition process (CVD), which may be thermal chemical vapor deposition, plasma-enhanced chemical vapor deposition, or low-pressure chemical vapor deposition.

[0062] The first vapor coating process may be performed at about 300°C to about 1200°C, for example, about 500°C to about 1200°C, about 600°C to about 1150°C, or about 700°C to about 1100°C.

[0063] In the first vapor coating, the flow rate of the carbon gas may be about 0.3 L / min to about 1 L / min, or about 0.3 L / min to about 0.6 L / min. If the flow rate of the carbon gas is within these ranges, the carbon layer can be sufficiently formed in the pores of the porous support.

[0064] The deposition may be performed for about 0.15 hours to about 5 hours, or about 0.15 hours to about 3 hours.

[0065] Thereafter, a second vapor coating process is performed on the carbon layer using silicon gas to prepare a silicon layer. The silicon gas may be SiH4 gas, Si2H6 gas, Si3H8 gas, or a combination thereof.

[0066] The second vapor coating process can be chemical vapor deposition (CVD). Chemical vapor deposition can be thermal CVD, plasma-enhanced CVD, or low-pressure CVD. Vapor deposition can be performed at a temperature at which the deposited silicon is converted into amorphous Si (a-Si), for example, at temperatures between about 400°C and about 700°C. If the second vapor deposition is performed at temperatures above about 700°C, the deposited silicon crystallizes, increasing volume expansion during charge and discharge and reducing cycle life characteristics. If the second vapor deposition is performed at temperatures below about 400°C, the silicon raw material is less likely to decompose and may remain as impurities in the porous support.

[0067] In the second vapor-phase coating, the flow rate of the gas serving as the silicon source material may be about 0.3 L / min to about 1 L / min, or about 0.3 L / min to about 0.6 L / min. If the second vapor-phase coating is performed using a gas flow rate within these ranges, a silicon layer can be sufficiently formed on the carbon layer of the porous support.

[0068] The second vapor coating may be performed for about 0.5 hours to about 5 hours, or about 0.5 hours to about 3 hours.

[0069] Thereafter, an amorphous carbon layer is formed on the resultant product. The formation of the amorphous carbon layer is performed by vapor coating with an amorphous carbon precursor gas, or by mixing the resultant product with an amorphous carbon precursor and carbonizing the mixture.

[0070] The amorphous carbon precursor gas may be methane (CH4) gas, ethylene (C2H4) gas, acetylene (C2H2) gas, propane (C3H8) gas, propylene (C3H6) gas, or a combination thereof. The vapor coating may be performed by vapor deposition, and the vapor deposition may be chemical vapor deposition. The chemical vapor deposition may be thermal chemical vapor deposition, plasma-enhanced chemical vapor deposition, or low-pressure chemical vapor deposition.

[0071] The vapor coating process may be performed at about 700°C to about 1000°C, or about 700°C to about 900°C.

[0072] The amorphous carbon precursor may be petroleum coke, coal coke, petroleum pitch, coal pitch, mesophase pitch, pitch carbon, synthetic pitch, green coke, or a combination thereof.

[0073] In the case of mixing with the amorphous carbon precursor, a mixing ratio of the resultant product and the amorphous carbon precursor may be about 99:1 to about 90:10 by weight, or about 99:1 to about 95:5 by weight.

[0074] The carbonization may be performed at about 600° C. to about 1,000° C., or about 700° C. to about 1,000° C. The carbonization may be performed under a nitrogen atmosphere, a helium atmosphere, or a combination thereof.

[0075] During carbonization, the amorphous carbon precursor may be converted into amorphous carbon, thereby preparing an amorphous carbon layer.

[0076] <Rechargeable lithium battery> Another embodiment provides a rechargeable lithium battery including a negative electrode, a positive electrode, and an electrolyte.

[0077] [Negative electrode] The negative electrode includes a current collector and a negative active material layer formed on the current collector, and the negative active material layer includes the negative active material according to one or more embodiments. The negative active material layer including the negative active material may further include a binder and a conductive material.

[0078] In the negative electrode active material layer, the amount of the negative electrode active material may be about 90 wt % to about 99 wt % based on the total 100 wt % of the negative electrode active material layer. The amount of the binder may be about 1 wt % to about 5 wt % based on the total 100 wt % of the negative electrode active material layer. If a conductive material is included, the amount of the binder may be about 0.5 wt % to about 5 wt % based on the total 100 wt % of the negative electrode active material layer, and the amount of the conductive material may be about 0.5 wt % to about 5 wt % based on the total 100 wt % of the negative electrode active material layer.

[0079] The binder improves the binding properties between the negative electrode active material particles and between the negative electrode active material particles and the current collector. The binder can be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0080] The non-aqueous binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0081] The aqueous binder can be styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol or a combination thereof.

[0082] If an aqueous binder is used as the negative electrode binder, a cellulose compound may be further used to provide viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0083] The dry binder can be a polymer material that can be in a fibrous form. For example, the dry binder can be polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0084] A conductive material is included to provide electrode conductivity, and any conductive material can be used as long as it does not cause chemical changes. Examples of the conductive material include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, 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 be 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] [Positive electrode] The positive electrode may include a current collector and a positive active material layer on the current collector. The positive active material layer includes a positive active material and may further include a binder and / or a conductive material.

[0087] The positive electrode may also include an additive that acts as a sacrificial positive electrode.

[0088] The amount of the positive active material may be about 90 wt % to about 99.5 wt % based on 100 wt % of the positive active material layer, and the amount of the binder and the conductive material may be 0.5 wt % to 5 wt % based on 100 wt % of the positive active material layer.

[0089] The positive electrode active material may include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). In some embodiments, at least one composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used. The composite oxide may be a lithium-transition metal composite oxide, and examples thereof may include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free lithium nickel manganese oxides, or combinations thereof.

[0090] For example, the following compounds represented by any one of the following chemical formulae can be used as the composite oxide: Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Lia Ni b Co c L 1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NiG b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4 (0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2);Li a FePO4 (0.90≤a≤1.8). In these chemical formulas, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 It is Mn, Al or a combination thereof.

[0091] The positive electrode active material may be a high-nickel positive electrode active material having a nickel content of greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%, based on 100 mol% of metals other than lithium in the lithium transition metal composite oxide. The high-nickel positive electrode active material has a high capacity and can be used in high-capacity, high-density rechargeable lithium batteries.

[0092] 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 of binders include 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, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon. However, the present disclosure is not limited to such examples.

[0093] A conductive material is included to provide electrode conductivity, and any conductive material can be used as long as it does not cause chemical changes. Examples of the conductive material include: carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, carbon nanotubes, etc.; metallic materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0094] The current collector may include Al, but is not limited thereto.

[0095] [Electrolytes] The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0096] The non-aqueous organic solvent is used as a medium for transporting ions participating in the electrochemical reaction of the battery. The non-aqueous organic solvent may include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, or an aprotic solvent.

[0097] The carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like.

[0098] The ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonolactone, valerolactone, caprolactone, and the like.

[0099] Ether solvents may include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc. Aprotic solvents may include: nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group and may include a double bond, an aromatic ring, or an ether bond, etc.); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane, etc.; and sulfolane, etc.

[0100] The non-aqueous organic solvent may be used alone or as a mixture of two or more.

[0101] If a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be used together, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9.

[0102] Lithium salts dissolved in organic solvents provide lithium ions to the battery, enable the rechargeable lithium battery to operate and improve the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein x and y are integers of 1 to 20), one or more supporting electrolyte salts selected from the group consisting of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0103] [Diaphragm] Depending on the type of rechargeable lithium battery, a separator may be provided between the positive electrode and the negative electrode. The separator may be formed of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer having two or more layers thereof, and may be a mixed multilayer such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.

[0104] The separator may include a porous substrate and a coating layer on one or both surfaces of the porous substrate, the coating layer including an organic material, an inorganic material or a combination thereof. The porous substrate may be a material selected from polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyetherketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene oxides, cyclic olefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, TEFLON, ® and polytetrafluoroethylene or a copolymer or mixture of two or more thereof.

[0105] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acryl-based polymer.

[0106] The inorganic material may be inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof. However, the present disclosure is not limited to these examples.

[0107] The organic material and the inorganic material may be mixed in one coating layer, or coating layers including the inorganic material may be stacked.

[0108] According to the shape of the rechargeable lithium battery, the rechargeable lithium battery may be classified into a cylindrical, prismatic, pouch, or coin type, among others. Figures 2 to 5 is a schematic diagram illustrating a rechargeable lithium battery according to an embodiment. Figure 2 shows a cylindrical battery, Figure 3 A prismatic cell is shown, and Figure 4 and Figure 5 A pouch-type battery is shown. The rechargeable lithium battery 100 may include an electrode assembly 40 and a case 50. The electrode assembly 40 includes a separator 30 between a positive electrode 10 and a negative electrode 20. The electrode assembly 40 is accommodated in the case 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 2 As shown in FIG, the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. Figure 3 As shown in , the rechargeable lithium battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. Figure 4 and Figure 5 As shown in FIG, the rechargeable lithium battery 100 may include an electrode tab 70 that may form an electrical path for guiding current formed in the electrode assembly 40 to the outside of the battery. The electrode tab 70 may include a positive electrode tab 71 and a negative electrode tab 72.

[0109] As non-limiting examples, rechargeable lithium batteries according to embodiments may be used in automobiles, mobile phones, and / or various types of electronic devices.

[0110] The following examples and comparative examples are provided to highlight the features of one or more embodiments, but it will be understood that the embodiments and comparative examples do not limit the scope of the embodiments. The comparative examples are not to be construed as being outside the scope of the embodiments. Furthermore, it will be understood that the embodiments are not limited to the specific details described in the examples and comparative examples.

[0111] (Example 1) Chemical vapor deposition (first deposition) was performed at 950°C on a porous SiO2 support having a total porosity of 60%, thereby forming a soft carbon layer in the pores. 95% of the total porosity was mesopores (average diameter of 10 nm to 50 nm). The methane gas flow rate during the chemical vapor deposition was 0.3 L / min, and the chemical vapor deposition was performed for 0.15 hours.

[0112] The porosity was measured using a porosimeter (ASAP2020, Micromeritics Instrument Co., Ltd.) by the BJH method (N2 absorption isotherm).

[0113] The thickness of the soft carbon formed in the pores was 1 nm.

[0114] After that, a chemical vapor deposition process (second deposition) using SiH4 gas was performed on the soft carbon layer at 500° C. to prepare an amorphous silicon layer in the pores. In the chemical vapor deposition, the flow rate of the SiH4 gas was 0.3 L / min, and the chemical vapor deposition was performed for 1 hour.

[0115] The resultant product was provided with petroleum pitch at a weight ratio of 99:1 (ie, a weight ratio of the resultant product to the petroleum pitch), and carbonized at 1000° C. to prepare a negative active material.

[0116] The prepared negative electrode active material includes a core and a soft carbon layer arranged on the outer surface of the core, and the core has a soft carbon layer arranged in the pores of the porous support and a silicon layer arranged on the soft carbon layer. The core also includes silicon carbide arranged between the soft carbon layer and the silicon layer. The thickness of the soft carbon layer arranged in the pores is 1nm, and the thickness of the soft carbon layer arranged on the outer surface of the core is 10nm. Based on 100wt% of the prepared negative electrode active material, the amount of SiO2 porous support is 42wt%, the amount of amorphous silicon is 55wt%, and the amount of soft carbon is 3wt%. XRD using CuKα rays confirmed that silicon is amorphous in the prepared negative electrode active material.

[0117] 97.5 wt % of the prepared negative active material, 1.5 wt % of carboxymethyl cellulose, and 1 wt % of styrene butadiene rubber were mixed in a water solvent to prepare a negative active material layer slurry.

[0118] The negative electrode active material layer slurry was coated on a Cu foil current collector, dried, and pressed under a general process to prepare a negative electrode active material layer. Thus, a negative electrode was prepared.

[0119] 96wt% LiNi 0.8 Co 0.1 Mn 0.1The O2 positive electrode active material, 2 wt % of Ketjen black and 2 wt % of polyvinylidene fluoride were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material layer slurry.

[0120] The positive active material slurry was coated on an Al foil current collector, dried, and pressed to prepare a positive electrode.

[0121] A half-cell was fabricated using a negative electrode, a lithium metal counter electrode, and an electrolyte using a conventional process, and a full cell was fabricated using a negative electrode, a positive electrode, and an electrolyte using a conventional process.

[0122] In both half-cells and full-cells, 1 M LiPF6 dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate (3:7 volume ratio) was used as the electrolyte.

[0123] (Example 2) A negative electrode active material was prepared using the same process as in Example 1, except that the first deposition was performed for 0.3 hours and the second deposition was performed for 1 hour. In the prepared negative electrode active material, the thickness of the soft carbon layer located in the pores was 2 nm. Based on 100 wt % of the prepared negative electrode active material, the amount of the SiO2 porous support was 42 wt %, the amount of amorphous silicon was 53 wt %, and the amount of soft carbon was 5 wt %.

[0124] A half cell and a full cell were manufactured by the same process as that in Example 1 except for the negative electrode active material.

[0125] (Example 3) A negative electrode active material was prepared using the same process as in Example 1, except that the first deposition was performed for 0.4 hours and the second deposition was performed for 1 hour. In the prepared negative electrode active material, the thickness of the soft carbon layer located in the pores was 3 nm. Based on 100 wt % of the prepared negative electrode active material, the amount of the SiO2 porous support was 42 wt %, the amount of amorphous silicon was 51 wt %, and the amount of soft carbon was 7 wt %.

[0126] A half cell and a full cell were manufactured by the same process as that in Example 1 except for the negative electrode active material.

[0127] (Example 4) A negative electrode active material was prepared using the same process as in Example 1, except that the first deposition was performed for 0.7 hours and the second deposition was performed for 1 hour. In the prepared negative electrode active material, the thickness of the soft carbon layer located in the pores was 5 nm. Based on 100 wt % of the prepared negative electrode active material, the amount of the SiO2 porous support was 42 wt %, the amount of amorphous silicon was 46 wt %, and the amount of soft carbon was 12 wt %.

[0128] A half cell and a full cell were manufactured by the same process as that in Example 1 except for the negative electrode active material.

[0129] (Comparative Example 1) A negative electrode active material was prepared using the same process as in Example 1, except that the porous SiO2 support had a porosity of 40% and the porosity of micropores (average diameter less than 1 nm) accounted for 70% of the total porosity. In the prepared negative electrode active material, the soft carbon layer located within the pores had a thickness of 1 nm. Based on 100 wt% of the prepared negative electrode active material, the amount of the porous SiO2 support was 55 wt%, the amount of amorphous silicon was 42 wt%, and the amount of soft carbon was 3 wt%.

[0130] A half cell and a full cell were manufactured by the same process as that in Example 1 except for the negative electrode active material.

[0131] (Comparative Example 2) A negative electrode active material was prepared using the same process as in Example 1, except that the porous SiO2 support had a porosity of 80% and the porosity of macropores (average diameter greater than 50 nm) accounted for 70% of the total porosity. The first deposition was performed for 3 hours, and the second deposition was performed for 1 hour. In the prepared negative electrode active material, the thickness of the soft carbon layer located in the pores was 20 nm. Based on 100 wt% of the prepared negative electrode active material, the amount of the porous SiO2 support was 15 wt%, the amount of amorphous silicon was 42 wt%, and the amount of soft carbon was 43 wt%.

[0132] A half cell and a full cell were manufactured by the same process as that in Example 1 except for the negative electrode active material.

[0133] (Comparative Example 3) A negative electrode active material was prepared by the same process as in Example 1, except that a chemical vapor deposition process using SiH4 gas was performed at 500° C. in a SiO2 porous support having a total porosity of 60% and mesopores (average diameter of 10 nm to 50 nm) whose porosity constituted 95% of the total porosity. In the chemical vapor deposition, the flow rate of the SiH4 gas was 0.3 L / min, and the chemical vapor deposition was performed for 1 hour.

[0134] The obtained product was added to petroleum asphalt at a weight ratio of 99:1 (the weight ratio of the obtained product to the petroleum asphalt was 99:1), and carbonized at 1000° C. to prepare a negative electrode active material.

[0135] The prepared negative electrode active material includes a core having a silicon layer disposed within the pores of a porous support and a soft carbon layer disposed on the outer surface of the core. Furthermore, silicon carbide is disposed between the soft carbon layer and the silicon layer. Based on 100 wt% of the prepared negative electrode active material, the amount of the SiO2 porous support is 42 wt%, the amount of amorphous silicon is 57 wt%, and the amount of soft carbon is 1 wt%.

[0136] A half cell and a full cell were manufactured by the same process as that in Example 1 except for the negative electrode active material.

[0137] (Comparative Example 4) A negative electrode active material was prepared using the same process as in Example 1, except that the first deposition was performed for 1.8 hours and the second deposition was performed for 1 hour. In the prepared negative electrode active material, the thickness of the soft carbon layer disposed in the pores was 20 nm. Based on 100 wt % of the prepared negative electrode active material, the amount of the SiO2 porous support was 42 wt %, the amount of amorphous silicon was 36 wt %, and the amount of soft carbon was 22 wt %.

[0138] A half cell and a full cell were manufactured by the same process as that in Example 1 except for the negative electrode active material.

[0139] (Comparative Example 5) A negative electrode active material was prepared using the same process as in Example 1, except that the first deposition was performed for 3 hours and the second deposition was performed for 1 hour. In the prepared negative electrode active material, the thickness of the soft carbon layer disposed in the pores was 30 nm. Based on 100 wt % of the prepared negative electrode active material, the amount of the SiO2 porous support was 42 wt %, the amount of amorphous silicon was 15 wt %, and the amount of soft carbon was 43 wt %.

[0140] A half cell and a full cell were manufactured by the same process as that in Example 1 except for the negative electrode active material.

[0141] (Comparative Example 6) Nano-silicon and petroleum pitch were mixed in a weight ratio of 60:40, and the mixture was carbonized at 950°C to prepare a negative active material.

[0142] The prepared negative electrode active material includes a core containing nano-silicon and a soft carbon layer located on the surface of the core. Silicon carbide is disposed between the soft carbon layer and the silicon layer. The amount of soft carbon is 40wt% based on 100wt% of the prepared negative electrode active material.

[0143] A half cell and a full cell were manufactured by the same process as that in Example 1 except for the negative electrode active material.

[0144] Experimental Example 1) Evaluation of Specific Capacity The half cells according to Examples 1 to 4 and Comparative Examples 1 to 6 were charged and discharged once at 0.1 C to measure the specific capacity. The results are shown in Table 1.

[0145] Experimental Example 2) Efficiency Evaluation The full cells according to Examples 1 to 4 and Comparative Examples 1 to 6 were charged and discharged once at 0.1 C, and the ratio of the measured discharge capacity to the measured charge capacity was obtained. The results are shown in Table 1 as efficiency %.

[0146] Experimental Example 3) Evaluation of Charging Rate The full batteries according to Examples 1 to 4 and Comparative Examples 1 to 6 were charged and discharged once at 0.2 C and once at 2.0 C, and the ratio of the discharge capacity at 2.0 C to the discharge capacity at 0.2 C was obtained. The results are shown in Table 1 as charge rate %.

[0147] Experimental Example 4) Evaluation of cycle life characteristics The full cells according to Examples 1 to 4 and Comparative Examples 1 to 6 were charged and discharged for 400 cycles at 1C. The ratio of the capacity at each cycle to the discharge capacity at the first cycle was calculated. The cycle number at which the capacity ratio (capacity retention) reached 80% is shown in Table 1, marked as the cycle number at which the cycle life sharply decreased.

[0148] Table 1

[0149] As shown in Table 1, Examples 1 to 4 exhibited high specific capacity and improved efficiency and charge rate, and Examples 1 to 4 also had excellent cycle-life characteristics.

[0150] Comparative Examples 1 and 2, which used porous supports composed primarily of micropores or macropores, exhibited very low specific capacity, slightly low efficiency and charge rate, and significantly degraded cycle-life characteristics. Specifically, Comparative Example 2, which used a porous support composed primarily of macropores, exhibited extremely degraded cycle-life characteristics, as the capacity retention rate rapidly decreased to 80%.

[0151] Comparative Example 3 having no carbon layer in the pores exhibited remarkably low charge rate and cycle life characteristics.

[0152] Among them, Comparative Examples 4 and 5, in which the thickness of the soft carbon layer is thick, exhibit very low specific capacity, efficiency, and cycle life characteristics.

[0153] Comparative Example 6 using the negative active material including the nano-silicon core, the soft carbon layer, and silicon carbide exhibited slightly lower specific capacity, efficiency, and charge rate, and significantly lower cycle-life characteristics.

[0154] While the present disclosure has been described in connection with what are presently considered to be practical example embodiments, the present disclosure is not limited to the disclosed embodiments. Instead, the present disclosure covers various modifications and equivalent arrangements.

Claims

1. A negative electrode active material, comprising: a core comprising a porous support including pores, a carbon layer disposed in the pores, and a silicon layer disposed on the carbon layer; as well as an amorphous carbon layer disposed on an outer surface of the core, The pores include mesopores having a porosity of 50% to 100% relative to the total porosity of the porous support.

2. The negative electrode active material according to claim 1, wherein The carbon layer includes amorphous carbon, crystalline carbon, or a combination thereof.

3. The negative electrode active material according to claim 1, wherein The carbon layer includes amorphous carbon.

4. The negative electrode active material according to claim 1, wherein The silicon layer includes amorphous silicon.

5. The negative electrode active material according to claim 1, wherein The average diameter of the mesopores is 1 nm to 50 nm.

6. The negative electrode active material according to claim 1, wherein The total porosity of the porous support is 30% to 90%.

7. The negative electrode active material according to claim 1, wherein The amount of silicon is 40 wt % to 80 wt % based on 100 wt % of the negative active material.

8. The negative electrode active material according to claim 1, wherein The carbon layer has a thickness of 1 nm to 15 nm.

9. The negative electrode active material according to claim 1, wherein The porous carrier includes nano-silicon or SiO x , where 0≤x≤2. 10 . The negative electrode active material according to claim 1 , further comprising silicon carbide disposed between the carbon layer and the silicon layer.

11. A negative electrode active material, comprising: secondary particles, which are aggregates of primary particles, wherein the primary particle comprises: a core comprising (i) a porous support including pores, (ii) a carbon layer disposed in the pores, and (iii) a silicon layer disposed on the carbon layer; and (iv) an amorphous carbon layer disposed on an outer surface of the core, and The pores include mesopores having a porosity of 50% to 100% relative to the total porosity of the porous support.

12. The negative electrode active material according to claim 11, wherein The carbon layer includes amorphous carbon, crystalline carbon, or a combination thereof.

13. The negative electrode active material according to claim 11, wherein The carbon layer includes amorphous carbon.

14. The negative electrode active material according to claim 11, wherein The silicon layer includes amorphous silicon.

15. The negative electrode active material according to claim 11, wherein The average diameter of the mesopores is 1 nm to 50 nm.

16. The negative electrode active material according to claim 11, wherein The total porosity of the porous support is 30% to 90%.

17. The negative electrode active material according to claim 11, wherein The amount of silicon is 40 wt % to 80 wt % based on 100 wt % of the negative active material.

18. The negative electrode active material according to claim 11, wherein The carbon layer has a thickness of 1 nm to 15 nm.

19. The negative electrode active material according to claim 11, wherein The porous carrier includes nano-silicon or SiO x , where 0≤x≤2. 20 . The negative electrode active material according to claim 11 , further comprising silicon carbide disposed between the carbon layer and the silicon layer.

21. A method for preparing a negative electrode active material, the method comprising the following steps: performing a first vapor-phase coating on a porous support including pores with a carbon gas to form a carbon layer in the pores; performing a second vapor phase coating on the carbon layer using silicon gas to form a silicon layer; as well as coating the outer surface of the porous support with an amorphous carbon precursor, The pores include mesopores having a porosity of 50% to 100% relative to the total porosity of the porous support.

22. The method for preparing a negative electrode active material according to claim 21, wherein: The average diameter of the mesopores is 1 nm to 50 nm.

23. The method for preparing a negative electrode active material according to claim 21, wherein: The total porosity of the porous support is 30% to 90%.

24. The method for preparing a negative electrode active material according to claim 21, wherein: The carbon gas includes methane gas, ethylene gas, acetylene gas, propane gas, propylene gas or a combination thereof.

25. The method for preparing a negative electrode active material according to claim 21, wherein: The silicon gas is SiH4 gas, Si2H6 gas, Si3H8 gas or a combination thereof.

26. The method for preparing a negative electrode active material according to claim 21, wherein: The first vapor coating and the second vapor coating are performed by chemical vapor deposition.

27. The method for preparing a negative electrode active material according to claim 21, wherein: The first vapor coating is performed at 300°C to 1200°C, and the second vapor coating is performed at 400°C to 700°C.

28. The method for preparing a negative electrode active material according to claim 21, wherein: The amorphous carbon precursor includes petroleum coke, coal coke, petroleum pitch, coal pitch, mesophase pitch, pitch carbon, synthetic pitch, green coke or a combination thereof.

29. A rechargeable lithium battery, comprising: A negative electrode comprising a negative electrode active material according to any one of claims 1 to 10; positive electrode; as well as electrolytes.

30. A rechargeable lithium battery, comprising: A negative electrode comprising a negative electrode active material according to any one of claims 11 to 20; positive electrode; as well as electrolytes.

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