Negative active material, method of preparing same, and rechargeable lithium battery including same

Abstract

Disclosed are a negative active material, a method of preparing the same, and a rechargeable lithium battery including the same. The negative electrode active material includes secondary particles including aggregated primary particles including a substrate in which pores are formed, the pores being filled with amorphous Si, and an amorphous carbon coating layer on a surface of the secondary particles, in which the primary particles have a size in a range of about 1 [mu] m to about 15 [mu] m, and the negative electrode active material has a porosity within a range of about 2% or less.

Description

Technical Field

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

[0002] With the increasing use of battery-based electronic devices, such as mobile phones, laptop computers, electric vehicles, etc., there is an increasing demand for smaller, lighter, and relatively high-capacity rechargeable lithium batteries. Therefore, it may be advantageous to improve the performance of rechargeable lithium batteries.

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

[0004] One or more example embodiments include a negative active material exhibiting desirable or improved cycle-life characteristics.

[0005] Another example embodiment includes a method of preparing a negative active material.

[0006] Yet another example embodiment includes a rechargeable lithium battery including a negative active material.

[0007] One or more example embodiments include a negative electrode active material, the negative electrode active material including: secondary particles in which primary particles are aggregated, the primary particles including a base in which pores are formed, and amorphous Si filling the pores; and an amorphous carbon coating layer on surfaces of the secondary particles, wherein the primary particles have a size in a range of about 1 μm to about 15 μm, and the negative electrode active material has a porosity of about 2% or less.

[0008] Another example embodiment includes a method for preparing a negative active material, the method comprising the steps of: vapor-coating Si on a porous substrate having pores formed therein to prepare primary particles in which amorphous Si is filled in the pores; aggregating the primary particles to prepare secondary particles; and forming an amorphous carbon coating layer on the secondary particles.

[0009] Another example embodiment includes a rechargeable lithium battery including a negative electrode including a negative active material, a positive electrode, and an electrolyte.

[0010] The negative active material according to one or more example embodiments may exhibit high strength and desired or improved dynamic properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram illustrating a negative active material according to one or more example embodiments.

[0012] Figures 2 to 5 is a cross-sectional view schematically illustrating a rechargeable lithium battery according to some example embodiments. DETAILED DESCRIPTION

[0013] Hereinafter, exemplary embodiments are described in detail. However, these embodiments are examples, and the present disclosure is not limited thereto, and the present disclosure is defined by the scope of the claims.

[0014] The terms used in the specification are for explaining example embodiments and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, an expression in the singular includes an expression in the plural.

[0015] The term "combinations thereof" may include mixtures, laminates, composites, copolymers, alloys, blends, reactants of the components.

[0016] The terms "include", "comprising" or "having" are intended to indicate the presence of a certain characteristic, quantity, step, constituent element or combination thereof, but it should be understood that the possibility of the presence or addition of one or more other characteristics, quantities, steps, constituent elements or combinations is not precluded.

[0017] The drawings are shown with exaggerated thickness to clearly illustrate various layers and regions, and the same reference numerals are used throughout the specification to designate similar components (portions). When an element, such as a layer, film, region, or plate, is referred to as being "on" or "over" another element, this may include being "directly on" the other element as well as intervening elements. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present.

[0018] Here, when viewed from a plan view, the "layer" includes a shape formed entirely on the entire surface or a shape formed on a part of the surface.

[0019] Here, “or” should not be interpreted as exclusive, for example, “A or B” is interpreted as including A, B, A+B, etc.

[0020] As used herein, unless otherwise defined, particle diameter or particle size may refer to an average particle diameter. The average particle diameter represents the average value of the diameters of the particles, based on the cumulative volume of 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 (e.g., using a particle size analyzer or using transmission electron microscopy or scanning electron microscopy images). In some exemplary embodiments, data analysis is performed using a dynamic light scattering measurement device, and the number of particles in each size range is counted, allowing the average particle diameter (D50) value to be readily obtained by calculation.

[0021] According to one or more example embodiments, a negative active material includes: secondary particles in which primary particles are aggregated, the primary particles including a base having pores formed therein and amorphous Si filled in the pores; and an amorphous carbon coating layer on surfaces of the secondary particles, wherein the primary particles have a size in a range of about 1 μm to about 15 μm, and the negative active material has a porosity of about 2% or less.

[0022] When the term "about" or "substantially" is used in conjunction with a numerical value in this specification, it is intended that the relevant numerical value include a tolerance of ±10% around the stated numerical value. When a range is specified, the range includes all values ​​therebetween, such as increments of 0.1%.

[0023] Figure 1 Schematically illustrates a negative active material according to one or more example embodiments. Figure 1 As shown in FIG, the negative electrode active material 1 includes primary particles 15 including a substrate 11 having pores formed therein and amorphous Si 13, and secondary particles 16 in which the primary particles 15 are aggregated. An amorphous carbon coating layer 17 is on the surface of the secondary particles.

[0024] In an example, the negative active material has a porosity of about 2% or less (e.g., in a range of about 0.1% to about 2.0%) (which is low porosity). This low porosity of the negative active material indicates that silicon is sufficiently filled in the pores of the substrate. A porosity of about 1% or less indicates that the interiors of the pores formed in the substrate are substantially and almost filled with silicon, indicating that there is almost no empty space in the substrate.

[0025] If the porosity of the negative active material is about 2% or less (eg, the negative active material includes a dense structure), enhanced cycle-life characteristics may be exhibited.

[0026] The porosity of the negative electrode active material can be determined by measuring the pore volume of the negative electrode active material using a specific surface area measurement device and multiplying the pore volume by the true density to calculate the pore volume fraction (%) of the secondary particles. This physical property is also maintained in batteries using the negative electrode active material.

[0027] This can be obtained by separating the negative electrode active material from the negative electrode separated from the disassembled battery after formation charge and discharge, removing the binder and organic material, etc. from the negative electrode active material, drying the negative electrode active material to obtain negative electrode active material powder, and measuring the porosity of the powder through the above steps.

[0028] In one or more exemplary embodiments, the Si is amorphous and may exhibit reduced volume expansion during charge and discharge and improved cycle life characteristics compared to crystalline Si. In one or more exemplary embodiments, amorphous Si may be confirmed by measuring TEM or X-ray diffraction (XRD) peaks. In the case of TEM measurements, Si exhibiting no lattice fringes may indicate amorphous silicon. In the case of XRD measurements using CuKα radiation as the target radiation, the presence of broad peaks may indicate amorphous silicon. The Si filling the pores may be or include elemental Si.

[0029] The size of the primary particles may be in the range of about 1 μm to about 15 μm, about 3 μm to about 14 μm, or about 4 μm to about 13 μm. Since the size of the primary particles is small in any of the above ranges, silicon can be substantially completely filled in the pores even if the pores are located in the middle of the porous substrate.

[0030] In the negative active material according to one or more example embodiments, the size of the primary particles is relevant, and the size of the secondary particles may be appropriately adjusted.

[0031] The negative electrode active material according to one or more example embodiments includes secondary particles in which at least one such primary particle is aggregated. Because the negative electrode active material includes secondary particles in which one or more primary particles are aggregated, silicon can be substantially uniformly distributed in the center (e.g., the middle region) of the negative electrode active material, compared to unaggregated single particles. This enables high capacity and improved long-term cycling performance. The silicon is positioned by filling the pores of the substrate, and some of the silicon may be exposed outwardly, which can be covered with the amorphous carbon precursor used in the aggregation, thereby substantially reducing or preventing direct contact between the silicon and the electrolyte. Therefore, the generation of H2 gas due to direct contact between the silicon and the electrolyte can be reduced or prevented.

[0032] The size of the pores formed in the substrate may be in the range of about 1 nm to about 100 nm, about 10 nm to about 100 nm, about 1 nm to about 80 nm, or about 1 nm to about 50 nm. If the size of the pores formed in the substrate is within any of the above ranges, the size of the silicon filled in the pores is within the nanometers within the above ranges, thereby reducing the absolute volume value expanded during charge and discharge. This makes it possible to reduce or suppress the loss of capacity and efficiency and improve cycle life characteristics. The size of the pores may be an average size.

[0033] The porosity of the substrate may be in the range of about 30% to about 90%, about 40% to about 80%, or about 50% to about 70%. If the porosity of the substrate is within any of the above ranges, the amount of silicon filled inside increases, thereby exhibiting a substantially higher capacity. The porosity of the substrate refers to the porosity of the substrate before amorphous Si is filled therein.

[0034] In one or more example embodiments, the amount of amorphous Si may be in a range of about 19 wt % to about 70 wt %, about 30 wt % to about 60 wt %, or about 40 wt % to about 50 wt % based on 100 wt % of the negative electrode active material. If amorphous Si is included in any of the above ranges, the amount of Si exposed to the surface of the negative electrode active material and causing side reactions with the electrolyte can be effectively reduced or eliminated.

[0035] The substrate may include at least one of Al2O3, ZrO2, SiO2, TiO2, SiC, C (carbon), or a combination thereof. For example, the substrate may be or include at least one of activated carbon, silica gel, or zeolite.

[0036] Based on 100 wt % of the negative electrode active material, the amount of the substrate may be in the range of about 29 wt % to about 80 wt %, about 40 wt % to about 70 wt %, or about 50 wt % to about 60 wt %. If the amount of the substrate is within any of the above ranges, Si deposition can be appropriately performed and a significantly higher capacity can be ensured after deposition.

[0037] In the amorphous carbon coating layer, the amorphous carbon may be or include at least one of pitch carbon, soft carbon, hard carbon, mesophase pitch carbide, sintered coke, carbon fiber, or a combination thereof.

[0038] The thickness of the amorphous carbon coating layer may be greater than about 0 nm and about 2 μm or less, within a range of about 1 nm to about 2000 nm or about 1 nm to about 1000 nm. The thickness refers to the thickness of the amorphous carbon on the surface of the core. If the amorphous carbon is unevenly distributed, the thickness may refer to the length of the thickest amorphous carbon. In one or more example embodiments, the thickness may be an average thickness. If the thickness of the amorphous carbon coating layer is within any of the above ranges, the charge and discharge efficiency and rate characteristics may be enhanced.

[0039] The secondary particles may also include amorphous carbon.

[0040] In the negative electrode active material according to one or more example embodiments, the amount of amorphous carbon may be in the range of about 1 wt % to about 25 wt %, about 2 wt % to about 20 wt %, or about 3 wt % to about 15 wt % based on 100 wt % of the negative electrode active material. The amount of amorphous carbon may be or include the amount of amorphous carbon included in the amorphous carbon coating layer. In another example embodiment, when the secondary particles further include amorphous carbon, the amount of amorphous carbon may be the total amount included in the amorphous carbon coating layer and the secondary particles. For example, the amount may be or include the amount of amorphous carbon included in the negative electrode active material, regardless of whether the amorphous carbon is included in any position.

[0041] If the amount of amorphous carbon satisfies any of the above ranges, positioning of silicon in the pores outside the support can be reduced or prevented, generation of H2 gas by a side reaction of silicon with the electrolyte can be reduced or prevented, and long-term cycle performance can be enhanced.

[0042] A negative active material according to one or more example embodiments may be prepared through the following example steps.

[0043] Prepare a porous substrate with a small particle size. The porous substrate with a small particle size may be a substrate having an average particle size (D50) in the range of about 3 μm to about 20 μm, or may be formed by pulverizing a porous substrate with a large average particle size (D50) to prepare a porous substrate having an average particle size in the range of about 3 μm to about 20 μm.

[0044] The porous substrate is a substrate having pores formed therein, and the porosity may be in the range of about 30% to about 90%, about 40% to about 80%, or about 50% to about 70%. The size of the pores may be about 1 nm to about 100 nm, about 1 nm to about 80 nm, or about 1 nm to about 50 nm.

[0045] The porous substrate may be or include a commercially available porous substrate, or may be used through an aerogel step or a spray drying step. In another exemplary embodiment, the porous substrate may be or include at least one of activated carbon, silica gel, or zeolite. The porous substrate may further be subjected to a sieving step using a sieve.

[0046] The aerogel or spray drying step is described below.

[0047] In the aerogel step, water glass containing SiO2 is diluted with water to prepare a water glass solution containing SiO2. In addition to SiO2, the water glass may further include at least one of Na2O, K2O, and Fe2O3. In the water glass, the amount of SiO2 may be in the range of about 20wt% to about 40wt% based on the total 100wt% of the water glass, and in the diluted water glass solution containing SiO2, the amount of SiO2 may be in the range of about 3wt% to about 6wt% based on the total 100wt% of the diluted water glass solution containing SiO2. If the amount of SiO2 included in the water glass is within any of the above ranges, the internal pores can be freely controlled.

[0048] In one or more example embodiments, among the components included in the water glass, the amount of compounds other than SiO 2 may be appropriately adjusted.

[0049] A water glass solution is mixed with an acid solution to produce a silica sol. Mixing with the acid solution removes the sodium component in the water glass solution. Without mixing the water glass solution with the acid solution (e.g., without neutralization with the acid solution), the strongly alkaline water glass may not be able to produce a silica sol, and thus, the desired negative electrode active material cannot be produced. For example, preparing a porous support with sufficient pores can be challenging, and thus filling the pores of the porous support with sufficient silicon can be challenging.

[0050] The acid solution may be or include a solution containing at least one acid such as hydrochloric acid, nitric acid, sulfuric acid, acetic acid, fluoric acid, or a combination thereof, and may include water as a solvent. The acid solution may have a concentration in the range of about 0.2M to about 3M.

[0051] A mixing ratio of the water glass solution and the acid solution may be in the range of about 8:2 to about 6:2 by volume ratio, or in the range of about 6:1 to about 6:0.5 by volume ratio.

[0052] Thereafter, alcohol is added to the silica sol and stirred to achieve gelation, thereby obtaining a wet gel. The alcohol may be added in an amount corresponding to a range of approximately 40% to approximately 60% based on the volume of the silica sol. When the alcohol is used in an amount within the above range, more uniform gelation can be induced. The wet gel may further be washed.

[0053] The wet gel can be modified to have a hydrophobic surface using a non-polar organic solvent and an organosilane compound. Modification can be performed by mixing the wet gel with the non-polar organic solvent and the organosilane compound. The mixing can be performed for a period of time ranging from about 2 hours to about 4 hours. During this mixing, a solvent substitution reaction can occur, and the surface of the gel can be modified to be hydrophobic.

[0054] The individually collected wet gels may be further washed before mixing.

[0055] The non-polar organic solvent may be or include a solvent capable of modifying the surface of the target material into a hydrophobic surface. The solvent may be or include at least one of isopropyl alcohol, n-hexane, n-heptane, xylene, trimethylsilyl chloride, cyclohexane, or a combination thereof.

[0056] The organosilane compound may include at least one of trimethylchlorosilane, hexamethyldisilazane, methyltrimethoxysilane, trimethylethoxysilane, ethyltriethoxysilane, phenyltriethoxysilane, or a combination thereof.

[0057] In the mixing, a mixing ratio of the wet gel, the nonpolar organic solvent, and the organosilane compound may be in a range of about 1:1:1 to about 1:1:0.5 by volume, or about 1:0.5:0.5 by volume to about 1:0.5:0.25 by volume.

[0058] Thereafter, the prepared surface-modified gel is dried to prepare a porous inorganic support. Drying can be performed at a temperature of about 50° C. to about 180° C., or about 70° C. to about 160° C. Drying can be performed for a period of about 1 to 5 hours, or about 1 to about 3 hours.

[0059] In another exemplary embodiment, drying may be performed in two steps including low-temperature drying and high-temperature drying. Low-temperature drying may be performed at a temperature in the range of about 50° C. to about 80° C. for about 1 hour to about 2 hours, and high-temperature drying may be performed at about 140° C. to about 170° C. for about 1 hour to about 3 hours.

[0060] Drying can be carried out at atmospheric pressure.

[0061] The porous substrate is vapor-coated with Si to prepare primary particles in which amorphous Si is filled in the pores. The vapor coating may be vapor deposition using a silicon source material. The silicon source material may be or include at least one of SiH4 gas, Si2H6 gas, Si3H8 gas, or a combination thereof.

[0062] The vapor deposition may be chemical vapor deposition (CVD).

[0063] Vapor deposition can be performed at a temperature (e.g., in the range of about 400°C to about 700°C) at which the deposited silicon is converted into amorphous Si (a-Si). If vapor deposition is performed at a temperature above about 700°C, the deposited silicon crystallizes, thereby increasing volume expansion during charge and discharge and degrading cycle life characteristics, which is undesirable. If vapor deposition is performed at a temperature below about 400°C, the silicon raw material does not decompose easily, and the silicon raw material remains in the porous support and forms impurities, which is undesirable.

[0064] In vapor deposition, the flow rate of the gas as the silicon source material may be in the range of about 1 sccm to about 500 sccm, about 10 sccm to about 400 sccm, or about 50 sccm to about 300 sccm. sccm is standard cc per minute and represents 2.7×10 19 The gas flow rate of the molecular particles is measured at about 0°C and about 1 atm. Silicon can be filled in the pores of the porous substrate through a vapor deposition process.

[0065] Deposition may be performed for a period of time in the range of about 0.5 hours to about 5 hours, or for about 0.5 hours to about 3 hours.

[0066] The particle size of the primary particles prepared by the steps may be in the range of about 1 μm to about 15 μm, about 3 μm to about 14 μm, or about 4 μm to about 13 μm.

[0067] The prepared primary particles are aggregated to prepare secondary particles. Aggregation can be performed using an amorphous carbon precursor. For example, the primary particles are mixed with the amorphous carbon precursor and heat-treated. The heat treatment temperature can be in the range of about 600° C. to about 1000° C.

[0068] The amorphous carbon precursor is not particularly limited as long as it is a material for producing amorphous carbon by heat treatment, but may include at least one of petroleum coke, coal coke, petroleum pitch, coal pitch, green coke, or a combination thereof.

[0069] The amount of the amorphous carbon precursor used may be in the range of about 1 wt % to about 15 wt %, about 1 wt % to about 13 wt %, or about 2 wt % to about 10 wt %, based on 100 wt % of the primary particles. If the amount of the amorphous carbon precursor used is within any of the above ranges, the primary particles are sufficiently aggregated, thereby appropriately preparing the secondary particles.

[0070] Thereafter, an amorphous carbon coating layer is formed on the prepared secondary particles. The formation of the amorphous carbon coating layer can be performed by vapor coating with an amorphous carbon precursor gas, or by mixing the secondary particles with an amorphous carbon precursor and performing a heat treatment.

[0071] The amorphous carbon precursor gas may be or include methane (CH4) gas, ethylene (C2H4) gas, acetylene (C2H2) gas, propane (C3H8) gas, propylene (C3H6) gas, or a combination thereof, and the amorphous carbon precursor may be or include at least one of petroleum coke, coal coke, petroleum pitch, coal pitch, green coke, or a combination thereof.

[0072] The vapor deposition can be performed by chemical vapor deposition (CVD), which can be thermal chemical vapor deposition, plasma enhanced chemical vapor deposition, or low pressure chemical vapor deposition.

[0073] The vapor coating step may be performed at a temperature in a range of about 700°C to about 1000°C or about 700°C to about 900°C.

[0074] According to the carbon coating, an amorphous carbon coating layer is formed on the surface of the secondary particles.

[0075] If the secondary particles are mixed with the amorphous carbon precursor, a mixing ratio of the secondary particles to the amorphous carbon precursor may be in the range of about 95:5 to about 30:70 by weight or about 90:10 to about 40:60 by weight.

[0076] The heat treatment may be performed at a temperature in a range of about 600° C. to about 1,000° C. During the heat treatment, the amorphous carbon precursor may be converted into amorphous carbon, thereby preparing an amorphous carbon coating layer.

[0077] Rechargeable lithium battery Another example embodiment includes a rechargeable lithium battery including a negative electrode, a positive electrode, and an electrolyte.

[0078] Negative electrode: The negative electrode includes a negative current collector and a negative active material layer formed on the negative current collector and including the negative active material according to one or more example embodiments. The negative active material layer includes the negative active material and may further include a binder and / or a conductive material.

[0079] According to one or more example embodiments, the negative electrode active material is included as a first negative electrode active material, and crystalline carbon may be included as a second negative electrode active material. The mixing ratio of the first negative electrode active material to the second negative electrode active material may be about 80:20 to about 90:10 by weight. In another example embodiment, the negative electrode active material may include the first negative electrode active material and the second negative electrode active material in a weight ratio ranging from about 85:15 to about 90:10.

[0080] In the negative electrode active material layer, the amount of the negative electrode active material may be in the range of 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 in the range of about 1 wt % to about 5 wt % based on the total 100 wt % of the negative electrode active material layer. When a conductive material is also included, the amount of the binder may be in the range of 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 in the range of about 0.5 wt % to about 5 wt % based on the total 100 wt % of the negative electrode active material layer.

[0081] The binder improves the bonding properties between the negative electrode active material particles and between the negative electrode active material particles and the current collector. The binder can be or include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0082] The non-aqueous binder may be or include at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0083] The aqueous binder may be or include at least one of 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.

[0084] When an aqueous binder is used as a negative electrode binder, a cellulose compound may be further used to increase 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 or include at least one of Na, K, or Li.

[0085] The dry binder can be or include a polymer material that can be fibrous. For example, the dry binder can be or include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0086] A conductive material is included to provide electrode conductivity, and any electrically conductive material can be used as the conductive material unless it causes chemical changes in the battery. Examples of the conductive material may include or include: a carbon-based material such as or including at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; a metal-based material including metal powder or metal fiber of at least one of copper, nickel, aluminum, silver, etc.; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

[0087] The negative electrode current collector may include at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0088] Positive electrode: The positive electrode may include a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and may further include a binder and / or a conductive material.

[0089] For example, the positive electrode may further include additives that may constitute a sacrificial positive electrode.

[0090] The amount of the positive active material may be in the range of 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 %, respectively, based on 100 wt % of the positive active material layer.

[0091] The positive active material may include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). In some example embodiments, at least one composite oxide of lithium and a metal such as or including at least one of cobalt, manganese, nickel, or a combination thereof may be used.

[0092] The composite oxide may be or include a lithium transition metal composite oxide, and examples thereof may include at least one of lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free lithium nickel manganese-based oxides, or combinations thereof.

[0093] For example, the following compounds represented by any one of the following chemical formulae can be used: 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); Li a Ni b Co c L 1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 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).

[0094] In the above chemical formula, A is or includes at least one of Ni, Co, Mn, or a combination thereof; X is or includes at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is or includes at least one of O, F, S, P, or a combination thereof; G is or includes at least one of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1It is or includes at least one of Mn, Al or a combination thereof.

[0095] For example, the positive electrode active material may be or include a high-nickel positive electrode active material, wherein the high-nickel positive electrode active material has 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 the metal other than lithium in the lithium transition metal composite oxide. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density rechargeable lithium batteries.

[0096] The binder improves the bonding properties between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of the binder may include or include at least one of 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, nylon, etc., but are not limited thereto.

[0097] A conductive material is included to provide electrode conductivity, and any electrically conductive material can be used as the conductive material unless it causes chemical changes in the battery. Examples of the conductive material may include: a carbonaceous material such as or including at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; a metal-based material including metal powder or metal fiber of at least one of copper, nickel, aluminum, silver, etc.; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

[0098] The positive electrode current collector may include Al, but is not limited thereto.

[0099] Electrolyte: The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0100] The non-aqueous organic solvent may be a medium for transporting ions participating in the electrochemical reaction of the battery.

[0101] The non-aqueous organic solvent may include at least one of a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, or an aprotic solvent.

[0102] The carbonate solvent may include at least one of 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), etc.

[0103] The ester solvent may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonolactone, valerolactone, caprolactone, and the like.

[0104] Ether solvents may include at least one of dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, and the like. Ketone solvents may include cyclohexanone, and the like. Alcohol solvents may include at least one of ethanol and isopropanol, and aprotic solvents may include at least one of the following: 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); amides, such as dimethylformamide; dioxolanes, such as 1,3-dioxolane and 1,4-dioxolane; and sulfolane.

[0105] The non-aqueous organic solvent may be used alone or as a mixture of two or more solvents.

[0106] If a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be used together with each other, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9.

[0107] Lithium salts dissolved in organic solvents supply lithium ions to the battery, operate rechargeable lithium batteries, and improve the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include one or at least two supporting electrolyte salts, including 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), at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0108] 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 include at least one of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer having two or more layers thereof, and may be or include 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, and the like.

[0109] The separator may include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof on one or both surfaces of the porous substrate.

[0110] The porous substrate may be or include a membrane formed from any one or more of 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 sulfide, polyethylene naphthalate, glass fibers, Teflon (polytetrafluoroethylene), or copolymers or mixtures of two or more thereof.

[0111] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acryl-based polymer.

[0112] The inorganic material may be or include inorganic particles, the inorganic particles including at least one of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite or a combination thereof, but is not limited thereto.

[0113] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer including an organic material and a coating layer including an inorganic material may be stacked.

[0114] Rechargeable lithium batteries may be classified into cylindrical batteries, prismatic batteries, pouch-type batteries, coin-type batteries, etc., according to their shapes. Figures 2 to 5 is a schematic diagram illustrating a rechargeable lithium battery according to example embodiments, and 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. Figures 2 to 5The rechargeable lithium battery 100 may include an electrode assembly 40 and a case 50 in which the electrode assembly 40 is accommodated. The electrode assembly 40 includes a separator 30 between a positive electrode 10 and a negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The rechargeable lithium battery 100 may include a sealing member 60 that seals the case 50, such as Figure 2 As shown in . Figure 3 In the embodiment, the rechargeable lithium battery 100 may include a positive electrode lead tab 11a and a positive terminal 12, a negative electrode lead tab 21 and a negative terminal 22. Figure 4 and Figure 5 As shown in FIG, the rechargeable lithium battery 100 may include Figure 5 The electrode tab 70 shown in FIG. 1 may form an electrical path for guiding the current formed in the electrode assembly 40 to the outside of the rechargeable lithium battery 100 and Figure 4 Also shown in FIG. 7 are a positive electrode tab 71 and a negative electrode tab 72 that form an electrical path for guiding current formed in the electrode assembly 40 to the outside of the rechargeable lithium battery 100 .

[0115] As non-limiting examples, rechargeable lithium batteries according to example embodiments may be applied to, for example, automobiles, mobile phones, and / or various types of electronic devices.

[0116] The following examples and comparative examples are provided to emphasize the characteristics of one or more example embodiments, but it will be understood that the examples and comparative examples will not be interpreted as limiting the scope of the example embodiments, nor will the comparative examples be interpreted as being outside the scope of the example embodiments. Furthermore, it will be understood that the example embodiments are not limited to the specific details described in the examples and comparative examples.

[0117] Example 1 A porous substrate (SiO2) with an average particle size (D50) of 4 μm was prepared. The pore size of the porous substrate was 20 nm, and the porosity was 75%.

[0118] Chemical vapor deposition (primary deposition) was performed on the porous substrate at 400°C for 1 hour using SiH₄ gas at a gas flow rate of 100 sccm (measured at 0°C and 1 atm) to fill the interior of the pores of the porous substrate with Si, thereby preparing primary particles (average particle size (D50) of the primary particles: 5 μm) in which Si filled the interior of the pores of the porous substrate. The SiH₄ gas was used so that the weight ratio of the porous substrate to Si was 30:70.

[0119] The primary particles were mixed with petroleum asphalt at a weight ratio of 100:10 and agglomerated by heat treatment in an agglomeration device. The agglomeration produced secondary particles (average particle size (D50) of the secondary particles: 13 μm).

[0120] The secondary particles were subjected to chemical vapor deposition (second deposition) at 700°C using C₂H₂ gas to form a soft carbon coating layer on the surface of the secondary particles, thereby preparing a negative electrode active material. The prepared negative electrode active material had a porosity of 1%, and the soft carbon coating layer had a thickness of 10 nm. The porosity of the negative electrode active material was obtained by measuring the pore volume of the negative electrode active material using a specific surface area measurement device (available from Micromeritics Instruments) and multiplying the resulting pore volume by the true density of the negative electrode active material.

[0121] The negative electrode active material is used as the first negative electrode active material, and 97.5 wt % of a mixed negative electrode active material (the mixed negative electrode active material is the first negative electrode active material and natural graphite (the second negative electrode active material), and the mixing ratio of the first negative electrode active material to the second negative electrode active material = a weight ratio of 90:10), 1.5 wt % of carboxymethyl cellulose and 1 wt % of styrene butadiene rubber are mixed in an aqueous solvent to prepare a negative electrode active material layer slurry.

[0122] The negative active material layer slurry was coated on a Cu foil current collector, dried and pressed under general steps to prepare a negative electrode including the Cu foil current collector and the negative active material layer formed on the Cu foil current collector.

[0123] 96wt% LiNi 0.8 Co 0.1 Mn 0.1 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.

[0124] The positive active material slurry was coated on an Al foil current collector, dried and pressed to prepare a positive electrode.

[0125] A half-cell was fabricated using a negative electrode, a lithium metal counter electrode, and an electrolyte by general steps.

[0126] A full battery is fabricated using the negative electrode, positive electrode, and electrolyte via general steps.

[0127] 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.

[0128] Example 2: Half cells and full cells were manufactured by the same steps as in Example 1, except that a porous substrate having an average particle size of 7 μm was used to prepare a negative electrode active material having an average primary particle size (D50) of 8 μm and a porosity of 1%.

[0129] Example 3: Half cells and full cells were fabricated by the same steps as in Example 1, except that the first deposition was performed for 120 minutes to prepare a negative active material having an average primary particle size (D50) of 5 μm and a porosity of 0.1%.

[0130] Example 4: Half cells and full cells were fabricated by the same steps as in Example 2, except that the first deposition was performed for 120 minutes to prepare a negative active material having an average primary particle size (D50) of 8 μm and a porosity of 0.1%.

[0131] Comparative Example 1: Half cells and full cells were fabricated by the same steps as in Example 1, except that the first deposition was performed for 30 minutes to prepare a negative active material having an average primary particle size (D50) of 5 μm and a porosity of 2.1%.

[0132] Comparative Example 2: Half cells and full cells were fabricated by the same steps as in Example 2, except that the first deposition was performed for 30 minutes to prepare a negative active material having an average primary particle size (D50) of 8 μm and a porosity of 2.1%.

[0133] Comparative Example 3: A porous substrate (SiO2) having an average particle size (D50) of 15 μm was subjected to chemical vapor deposition (primary deposition) using SiH4 gas at a gas flow rate of 100 sccm (measured at 0°C and 1 atm) at 400°C for 1 hour to fill the interior of the pores of the porous substrate with Si, thereby preparing large particles in which Si was filled in the interior of the pores of the porous substrate (average particle size (D50) of the primary particles: 16 μm).

[0134] The secondary particles were chemically vapor deposited using C2H2 gas at 700°C to form a soft carbon coating on the surface of the large particles, thereby preparing a negative electrode active material. The prepared negative electrode active material had a porosity of 1% and a soft carbon coating thickness of 10 nm.

[0135] A negative electrode, a half cell, and a full cell were manufactured through the same steps as those in Example 1, except that the negative electrode active material was used.

[0136] Experimental Example 1) Evaluation of Specific Capacity The half cells according to Examples 1 to 4 and Comparative Examples 1 to 3 were charged and discharged once at 0.1 C to measure the specific capacity. The results are shown in Table 1.

[0137] Experimental Example 2) Efficiency Evaluation The full batteries according to Examples 1 to 4 and Comparative Examples 1 to 3 were charged and discharged once at 0.1 C, and the ratio of the measured discharge capacity to the measured charge capacity was calculated. The results are shown in Table 1 as efficiency.

[0138] Experimental Example 3) Evaluation of cycle life characteristics The half-cells of Examples 1 to 4 and Comparative Examples 1 to 3 were charged and discharged for 400 cycles at 1C. The ratio of the capacity at each cycle to the first discharge capacity was measured. If the capacity ratio (e.g., capacity retention) reached 80%, the cycle number at which the cycle life sharply decreased was recorded in Table 1.

[0139] Table 1

[0140] As shown in Table 1, Examples 1 to 4 exhibit high specific capacity and efficiency as well as desirable or improved cycle-life characteristics.

[0141] However, Comparative Examples 1 and 2 including negative active materials having a porosity greater than 2% exhibited deteriorated cycle-life characteristics, and Comparative Example 3 including a negative active material composed of large primary particles having a particle size of 16 μm exhibited drastically deteriorated efficiency and cycle-life characteristics.

[0142] While the present disclosure has been described in connection with what are presently considered to be practical example embodiments, it is to be understood that the disclosure is not limited to the disclosed example embodiments, but on the contrary is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A negative electrode active material, comprising: Secondary particles comprising aggregated primary particles, the primary particles comprising a base formed with pores, the pores being filled with amorphous Si; and an amorphous carbon coating layer on the surface of the secondary particle, wherein the primary particles have a size in the range of 1 μm to 15 μm, and The porosity of the negative electrode active material is within a range of 2% or less.

2. The negative electrode active material according to claim 1, wherein The size of the pores ranges from 1 nm to 100 nm.

3. The negative electrode active material according to claim 1, wherein The substrate has a porosity in the range of 30% to 90%.

4. The negative electrode active material according to claim 1, wherein The porosity of the negative electrode active material is in the range of 0.1% to 2%.

5. The negative electrode active material according to claim 1, wherein The primary particles have a size in the range of 3 μm to 14 μm.

6. The negative electrode active material according to claim 1, wherein The amount of the amorphous Si is in the range of 19 wt % to 70 wt % based on 100 wt % of the negative electrode active material.

7. The negative electrode active material according to claim 1, wherein An amount of the base is in the range of 29 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 amount of the amorphous carbon is in the range of 1 wt % to 25 wt % based on 100 wt % of the negative active material.

9. The negative electrode active material according to claim 1, wherein The amorphous carbon coating layer has a thickness greater than 0 nm and equal to or less than 2 μm.

10. The negative electrode active material according to claim 1, wherein The secondary particles also include amorphous carbon.

11. The negative electrode active material according to claim 1, wherein The substrate includes at least one of Al2O3, ZrO2, SiO2, TiO2, SiC and C.

12. A method for preparing a negative electrode active material, the method comprising the following steps: Vapor-coating Si onto a porous substrate having pores to prepare primary particles in which amorphous Si is filled in the pores; agglomerating the primary particles to form secondary particles; as well as An amorphous carbon coating layer is formed on the secondary particles.

13. The method for preparing a negative electrode active material according to claim 12, wherein: The porous substrate has a porosity in the range of 30% to 90%.

14. The method for preparing a negative electrode active material according to claim 12, wherein: The size of the pores ranges from 1 nm to 100 nm.

15. The method for preparing a negative electrode active material according to claim 12, wherein: The vapor coating is performed using a Si-containing gas including at least one of SiH 4 gas, Si 2 H 6 gas, and Si 3 H 8 gas.

16. The method for preparing a negative electrode active material according to claim 12, wherein: The step of aggregating is performed by using an amorphous carbon precursor.

17. The method for preparing a negative electrode active material according to claim 12, wherein: The step of forming the amorphous carbon coating layer is performed by using an amorphous carbon precursor gas.

18. A rechargeable lithium battery, comprising: A negative electrode comprising the negative electrode active material according to any one of claims 1 to 11; positive electrode; as well as electrolyte.

Images