Negative active material and rechargeable lithium battery including same

Abstract

Disclosed are a negative active material and a rechargeable lithium battery including the same. The negative active material includes crystalline silicon primary particles, amorphous silicon, and an amorphous carbon coating layer.

Description

TECHNICAL FIELD

[0001] Example embodiments relate to a negative active material and a rechargeable lithium battery including the same. BACKGROUND

[0002] As the use of electronic devices using batteries, such as mobile phones, laptop computers, and electric vehicles, for example, is increasing, the demand for rechargeable lithium batteries that are smaller, lighter, and relatively high in capacity is increasing. Accordingly, it can be advantageous to improve the performance of rechargeable lithium batteries.

[0003] A rechargeable lithium battery generally includes a positive electrode and a negative electrode including an active material capable of intercalating and deintercalating lithium ions, and an electrolyte solution, and generates electric energy through oxidation and reduction reactions as lithium ions are intercalated / deintercalated at the positive electrode and the negative electrode. SUMMARY

[0004] One or more example embodiments include a negative active material exhibiting high capacity, high efficiency, and desirable or improved cycle life characteristics.

[0005] Another example embodiment includes a rechargeable lithium battery including the same.

[0006] One or more example embodiments include a negative active material including: a crystalline silicon primary particle; amorphous silicon; and an amorphous carbon coating layer.

[0007] Another example embodiment includes a rechargeable lithium battery including: a negative electrode including the negative active material; a positive electrode; and an electrolyte.

[0008] The negative active material according to one or more example embodiments can exhibit high capacity, high efficiency, and desirable or improved cycle life characteristics. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 FIG. 1 is a schematic diagram illustrating a negative active material according to one or more example embodiments.

[0010] Figures 2 to 5 FIG. 2 is a cross-sectional view schematically illustrating a rechargeable lithium battery according to some example embodiments. DETAILED DESCRIPTION

[0011] Hereinafter, example embodiments are described in detail. However, these example embodiments are exemplary, the present disclosure is not limited thereto, and the present disclosure is defined by the scope of the claims.

[0012] The terms used in the specification are explained by way of example embodiments, but are not intended to limit the present disclosure. The expression in the singular includes the expression in the plural, unless the context clearly dictates otherwise.

[0013] The term "combinations thereof can include mixtures, laminates, composites, copolymers, alloys, blends, reactants of constituent elements.

[0014] The terms "include", "comprise" or "have" are intended to mean that there are the features, numbers, steps, constituent elements or combinations thereof, but it should be understood that the possibility of presence or addition of one or more other features, numbers, steps, constituent elements or combinations thereof is not precluded.

[0015] The accompanying drawings illustrate thicknesses that are exaggerated to clearly show various layers and regions, and the same reference numerals are assigned to similar parts throughout the specification. When an element such as a layer, film, region, plate, etc., is referred to as being "on" or "over" another element, it can include the case where it is "directly on" the other element, as well as the case where another element is interposed therebetween. Conversely, when an element is referred to as being "directly on" another element, there is no intervening element therebetween.

[0016] Here, when viewed from a plan view, a "layer" includes a shape formed entirely on a surface or a shape formed on a partial surface.

[0017] Here, "or" is not to be construed as an exclusive meaning, for example, "A or B" is to be construed to include A, B, A+B, etc.

[0018] As used herein, when no definition is otherwise provided, the particle diameter or particle size can be an average particle diameter. The average particle diameter indicates an average value of diameters of particles according to a cumulative volume in a particle size distribution of particles included in the negative active material. The average particle diameter (D50) can be measured by a method well known to those skilled in the art, for example, by a particle size analyzer or by a transmission electron micrograph image or a scanning electron micrograph image. In some example embodiments, data analysis is performed using a dynamic light scattering measuring device, and the number of particles is counted for each particle size range, whereby the average particle diameter (D50) value can be easily obtained by calculation.

[0019] In some example embodiments, the average particle diameter can be measured by various techniques, for example, can be measured by a particle size analyzer.

[0020] In some example embodiments, the thickness can be measured by an SEM or TEM image for a cross section, but is not limited thereto, and it can be measured by any technique as long as it can measure the thickness in the art. The thickness can be an average thickness.

[0021] When the term "about" or "substantially" is used in the description in connection with a numerical value, it is intended to refer to a value that is within ±10% of the stated value. When a range is specified, the range includes all values within it, such as in increments of 0.1%.

[0022] As used herein, soft carbon refers to a graphitizable carbon material and is easily graphitized by heat treatment at a high temperature (e.g., about 2800°C), and hard carbon refers to a non-graphitizable carbon material and is substantially not or slightly graphitized by heat treatment. The terms "soft carbon" and "hard carbon" can be well known in the art.

[0023] In some example embodiments, crystalline carbon and amorphous carbon can be distinguished by XRD measurement. Crystalline carbon includes natural graphite and artificial graphite. Natural graphite can refer to graphite that can be naturally produced by separation from a mineral, and when measured by XRD, the interplanar spacing (d002) of the (002) plane can be in the range of about 3.350 Å to about 3.360 Å. Artificial graphite can refer to graphite manufactured by graphitization, and when measured by XRD, the interplanar spacing (d002) of the (002) plane can be in the range of about 3.355 Å to about 3.365 Å. For example, amorphous carbon can have an interplanar spacing (d002) of the (002) plane of about 3.34 Å or less when measured by XRD. XRD can be measured with an X-ray diffractometer (e.g., product name: X'Pert, manufacturer: Malvern Panalytical) using CuKα rays as target rays and by removing a monochromator to improve peak density resolution. The measurement conditions can be 2θ = 10° to 80°, a scan speed (° / S) of 0.044 to 0.089, and a step size (° / step) of 0.013 to 0.039.

[0024] The negative active material according to one or more example embodiments includes: crystalline silicon primary particles; amorphous silicon; and an amorphous carbon coating layer.

[0025] In one or more example embodiments, the amorphous silicon can be located on the surface of the crystalline silicon primary particles, for example, the amorphous silicon can be positioned to surround the surface of the crystalline silicon primary particles. For example, the amorphous silicon is positioned to surround the surface of the crystalline silicon primary particles, thus, the surface of the crystalline silicon primary particles can be coated with the amorphous silicon, and the amorphous silicon can be included in the form of a layer that substantially continuously covers the surface of the crystalline silicon primary particles.

[0026] The position of the amorphous silicon on the surface of the crystalline silicon primary particle can slowly convert the crystalline silicon primary particle into amorphous silicon during charge and discharge, thereby enhancing the charge and discharge efficiency. Since amorphous silicon having a low volume expansion surrounds the surface of the crystalline silicon primary particle, volume expansion of the negative active material during charge and discharge can be reduced or inhibited. This can reduce or prevent degradation during charge and discharge, thereby improving the cycle life characteristics. The negative active material includes amorphous silicon having a relatively large critical size than crystalline silicon, and thus, charge and discharge can occur more easily.

[0027] In one or more example embodiments, the amorphous carbon coating layer can be positioned to surround the crystalline silicon primary particle and the amorphous silicon. If the amorphous silicon surrounds the surface of the crystalline silicon primary particle, the amorphous carbon coating layer can be located on the amorphous silicon, thereby surrounding the amorphous silicon.

[0028] In one or more example embodiments, if the crystalline silicon primary particle and the amorphous silicon positioned on the surface of the crystalline silicon primary particle are referred to as a core, the amorphous carbon coating layer can be located on the surface of the core and can fill the inside of the core. For example, the amorphous carbon coating layer can be located between the crystalline silicon primary particles and can surround the surface of the amorphous silicon, and thus, a dense form in which almost no space is present inside the core can be implemented.

[0029] In one or more example embodiments, the crystalline silicon primary particles can be aggregated to prepare secondary particles. For example, the negative active material according to one or more example embodiments can include secondary particles in which at least one crystalline silicon primary particle is aggregated. Here, the amorphous silicon can be located on the surface of the secondary particle to coat the surface of the secondary particle. For example, the amorphous silicon can be in the form of a layer surrounding the surface of the secondary particle.

[0030] The amorphous carbon coating layer can be configured to surround the amorphous silicon.

[0031] For example, the negative active material according to one or more example embodiments can include secondary particles in which at least one crystalline silicon primary particle is aggregated, amorphous carbon is located on the surface of the secondary particle, and an amorphous carbon coating layer surrounds the secondary particle and the amorphous silicon. If the amorphous silicon covers the secondary particle, the amorphous carbon coating layer can be located on the amorphous silicon.

[0032] The amorphous carbon coating layer can be located between the secondary particles, surround the surface of the amorphous silicon, and thus, the inside of the negative active material can become dense. For example, if the secondary particle and the amorphous silicon positioned on the surface of the secondary particle are referred to as a core, the amorphous carbon coating layer fills the inside of the core and is positioned on the amorphous silicon, thereby providing a dense form of the negative active material having substantially almost no empty space inside.

[0033] Thus, the amorphous silicon and amorphous carbon coating layer can provide a dense interior to the negative active material, thereby improving cycle life characteristics.

[0034] The porosity of the negative active material according to one or more example embodiments can be in a range of greater than 0% to about 3%, greater than 0% to about 1.75%, or about 0.20% to about 1.00%. In one or more example embodiments, the porosity can be determined by measuring the volume of pores via BJH (Barrett-Joyner-Halenda) technique and dividing the measured pore volume by the total volume of the active material.

[0035] Figure 1 A schematic structure of the negative active material is shown. In Figure 1 The negative active material 1 includes secondary particles in which crystalline silicon primary particles 3 are aggregated, and amorphous silicon 5 that covers the surface of the secondary particles. The negative active material 1 further includes an amorphous carbon coating layer 7 that substantially completely surrounds the secondary particles and the amorphous silicon 5.

[0036] In one or more example embodiments, the amorphous silicon (amorphous Si) can be confirmed by measuring TEM or X-ray diffraction peaks (XRD). In the case of measuring TEM, Si that does not exhibit a lattice fringe can be referred to as amorphous silicon. In the case of measuring XRD using CuKα rays as target rays, the appearance of a broad peak can indicate amorphous silicon.

[0037] The negative active material according to one or more example embodiments includes both crystalline silicon and amorphous silicon, and thus, both a sharp crystalline peak and a broad amorphous peak can appear in XRD measurement.

[0038] In one or more example embodiments, the mixing ratio of the crystalline silicon primary particles to the amorphous silicon can be in a range of about 95:5 to about 20:80 by weight ratio, about 85:15 to about 40:60 by weight ratio, or about 70:30 to about 50:50 by weight ratio. If the mixing ratio of the crystalline silicon primary particles to the amorphous silicon satisfies the range, the properties of the crystalline silicon and the amorphous silicon can be both improved at the same time or concurrently, resulting in high capacity as well as further improved efficiency and cycle life.

[0039] In one or more example embodiments, the amount of the amorphous silicon can be in a range of about 1 wt% to about 50 wt%, about 5 wt% to about 40 wt%, or about 15 wt% to about 30 wt% based on 100 wt% of the negative active material. If the amount of the amorphous silicon is within any one of the above ranges, the efficiency and cycle life as well as the high capacity can be further enhanced.

[0040] The amount of the crystalline silicon primary particles can be in the range of about 30 wt% to about 80 wt%, about 40 wt% to about 70 wt%, or about 45 wt% to about 60 wt% based on 100 wt% of the negative electrode active material. If the amount of the crystalline silicon primary particles is within any one of the above ranges, high capacity can be maintained, and further enhanced efficiency and cycle life characteristics can be exhibited. In one or more example embodiments, the secondary particles are agglomerates of the crystalline silicon primary particles, and thus, the amount of the primary particles is substantially equal to the amount of the secondary particles.

[0041] In one or more example embodiments, the amount of the amorphous carbon can be in the range of about 19 wt% to about 65 wt%, about 25 wt% to about 60 wt%, or about 30 wt% to about 55 wt% based on 100 wt% of the negative electrode active material. The amount of the amorphous carbon is the amount of the amorphous carbon coating layer, and can be the total amount of the amorphous carbon included in the negative electrode active material.

[0042] In one or more example embodiments, the average particle diameter (D50) of the crystalline silicon primary particles can be in the range of about 50 nm to about 150 nm, about 60 nm to about 120 nm, or about 70 nm to about 100 nm. If the average particle diameter (D50) of the crystalline silicon primary particles is within any one of the above ranges, desirable or improved cycle life attributes can be obtained. In the negative electrode active material according to one or more example embodiments, the average particle diameter (D50) of the crystalline silicon primary particles is important, and the particle diameter of the secondary particles can be appropriately adjusted. In one or more example embodiments, the average particle diameter (D50) can be measured by the above-described techniques, and for example, can be measured by a particle size analyzer.

[0043] In the amorphous carbon coating layer, the amorphous carbon can be or include at least one of pitch carbon, soft carbon, hard carbon, meso-phase pitch carbide, baked coke, carbon fiber, and combinations thereof.

[0044] In one or more example embodiments, the thickness of the amorphous carbon coating layer can be in the range of greater than 0 nm and about 2 μm or less, about 1 nm to about 2000 nm, or about 1 nm to about 1000 nm. The thickness indicates the thickness of the amorphous carbon on the surface of the core. If the amorphous carbon is positioned unevenly, the thickness can indicate the length of the thickest amorphous carbon. In one or more example embodiments, the thickness can be an average thickness. If the thickness of the amorphous carbon coating layer is within the range, the charge and discharge efficiency and rate characteristics can be further enhanced.

[0045] The amorphous silicon can be prepared by vapor deposition. The vapor deposition will be described in the following description.

[0046] The negative electrode active material according to one or more example embodiments can be prepared by the following steps.

[0047] Silicon nanoparticles are prepared. The silicon nanoparticles can have a particle size in a range of about 10 nm to about 200 nm.

[0048] Such silicon nanoparticles can be obtained by performing general steps for preparing nanoparticles, such as pulverization, for example. The pulverization can be performed by mixing with addition of a dispersant. The dispersant can be or include at least one of stearic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid, gallic acid, carboxymethyl cellulose, sucrose, ethylene glycol, citric acid, boron nitride (BN), MgS, and combinations thereof.

[0049] The mixing can be performed by using a bead mill or a ball mill. If the dispersant is mixed, the dispersant can be present in an amount suitable for the silicon nanoparticles to be substantially dispersed in the solvent. For example, a mixing ratio of the dispersant and the silicon nanoparticles can be in a range of about 30:70 to about 90:10 by weight, about 40:60 to about 90:10 by weight.

[0050] The resulting product is dried. The drying can be performed by, for example, spray drying. If the drying is performed by spray drying, a dried product having a substantially uniform particle size can be prepared, and secondary particles in which the silicon nanoparticles (primary particles) are aggregated can be prepared.

[0051] The drying can be performed at a temperature in a range of about 100°C to about 200°C, or about 120°C to about 170°C.

[0052] Accordingly, vapor deposition is performed on the resulting dried product using a Si-containing gas to form amorphous silicon on a surface of the dried product. The amorphous silicon can be positioned to cover the surface of the dried product.

[0053] The vapor deposition can be chemical vapor deposition (CVD). The chemical vapor deposition can be any one or more of thermal chemical vapor deposition, plasma-enhanced chemical vapor deposition, and low-pressure chemical vapor deposition.

[0054] The Si-containing gas can be or include at least one of SiH4 gas, Si2H6 gas, Si3H8 gas, and combinations thereof.

[0055] The vapor deposition can be performed at a temperature at which the deposited silicon is converted to amorphous Si (a-Si), for example, at a temperature in a range of about 300 °C to about 700 °C or about 400 °C to about 600 °C. If the vapor deposition is performed at a temperature greater than about 700 °C, the silicon to be deposited can become crystalline, increasing the volume expansion during charge and discharge, and degrading the cycle life characteristics, which is undesirable. If the vapor deposition is performed at a temperature less than about 300 °C, the silicon feedstock is typically not readily decomposed and remains as a silicon feedstock, becoming an impurity in the porous support, which is also undesirable.

[0056] In the vapor deposition, the flow rate of the gas as the Si-containing gas can be in a range of about 1 seem to about 1000 seem, about 10 seem to about 700 seem, or about 50 seem to about 500 seem. The seem is a standard cc per minute, and represents a gas flow rate of 2.7 x 10 19 The silicon can be filled between the crystalline silicon primary particles by the process.

[0057] The deposition can be performed for a period of time in a range of about 10 minutes to about 5 hours, about 20 minutes to about 4 hours, about 20 minutes to about 3 hours, or about 20 minutes to about 1 hour.

[0058] Thereafter, an amorphous carbon coating layer is formed on the resulting product. The formation of the amorphous carbon coating layer is performed by vapor coating with an amorphous carbon precursor gas or by mixing the resulting product with an amorphous carbon precursor and carbonizing.

[0059] The amorphous carbon precursor gas can be or include at least one of a methane (CH4) gas, an ethylene (C2H4) gas, an acetylene (C2H2) gas, a propane (C3H8) gas, a propylene (C3H6) gas, and combinations thereof. The vapor coating can be performed by vapor deposition, and the vapor deposition can be chemical vapor deposition. The vapor deposition step can be performed at a temperature in a range of about 400 °C to about 1000 °C or about 500 °C to about 700 °C.

[0060] The amorphous carbon precursor can be or include at least one of petroleum coke, coal coke, petroleum pitch, coal pitch, pitch carbon, mesophase pitch, green coke, and combinations thereof.

[0061] If the resulting product is mixed with the amorphous carbon precursor, the mixing ratio of the product and the amorphous carbon precursor can be in a range of about 80:20 by weight to about 35:65 by weight, about 75:25 by weight to about 40:60 by weight, or about 70:30 by weight to about 45:55 by weight.

[0062] The carbonization can be performed at a temperature in a range of about 500°C to about 1,000°C or about 600°C to about 900°C. In the carbonization, the dispersant can be removed. The carbonization can be performed under a N2 atmosphere, a helium atmosphere, or a combination thereof.

[0063] In the heat treatment, the amorphous carbon precursor can be converted into amorphous carbon, thereby including the amorphous carbon in the negative electrode active material. The amorphous carbon can be positioned to surround the crystalline silicon primary particles and the amorphous silicon, and can fill in the inside by intercalating into pores formed between the amorphous silicon and between the crystalline silicon primary particles.

[0064] The amorphous carbon can be arranged to surround the secondary particles in which the crystalline silicon primary particles are aggregated and the amorphous silicon on the surface of the secondary particles, and can fill in the inside by intercalating into pores formed between the amorphous silicon or between the secondary particles.

[0065] According to the carbon coating, an amorphous carbon coating layer is formed on the surface of the secondary particles.

[0066] Rechargeable lithium battery Another example embodiment includes a rechargeable lithium battery including a negative electrode, a positive electrode, and an electrolyte.

[0067] Negative electrode: The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector and including a negative electrode active material according to one or more example embodiments. The negative electrode active material layer includes the negative electrode active material, and can also include a binder and / or a conductive material.

[0068] The negative electrode active material according to one or more example embodiments is included as a first negative electrode active material, and crystalline carbon can be included as a second negative electrode active material. A mixing ratio of the first negative electrode active material to the second negative electrode active material can be in a range of about 20:80 to about 10:90 by weight ratio. In other example embodiments, the negative electrode active material can include the first negative electrode active material and the second negative electrode active material in a weight ratio in a range of about 15:85 to about 10:90.

[0069] In the negative electrode active material layer, an amount of the negative electrode active material can be in a range of about 90wt% to about 99wt% based on a total 100wt% of the negative electrode active material layer. An amount of the binder can be in a range of about 1wt% to about 5wt% based on a total 100wt% of the negative electrode active material layer. If the conductive material is also included, an amount of the binder can be in a range of about 0.5wt% to about 5wt% based on a total 100wt% of the negative electrode active material layer, and an amount of the conductive material can be in a range of about 0.5wt% to about 5wt% based on a total 100wt% of the negative electrode active material layer.

[0070] The binder improves the binding performance between the negative active material particles and between the negative 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.

[0071] The non-aqueous binder can be or include at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, and a combination thereof.

[0072] The aqueous binder can be or include at least one of styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoro rubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and a combination thereof.

[0073] If the aqueous binder is a negative electrode binder, a cellulose-based compound can be further added to provide viscosity. The cellulose-based compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof. The alkali metal can be or include at least one of Na, K, and Li.

[0074] The dry binder can be or include a polymeric 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, and a combination thereof.

[0075] The conductive material is included to provide electrode conductivity, and any electrically conductive material can be the conductive material unless the electrically conductive material causes a chemical change in the battery. Examples of the conductive material can be 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, or the like; a metal-based material of a metal powder or a metal fiber including at least one of copper, nickel, aluminum, silver, or the like; a conductive polymer such as a polyaniline derivative; or a mixture thereof.

[0076] The negative current collector can include one or more of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0077] Positive electrode: The positive electrode can 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 can further include a binder and / or a conductive material.

[0078] For example, the positive electrode can further include an additive that can be a sacrificial positive electrode.

[0079] The amount of the positive active material can 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 amounts of the binder and the conductive material can be 0.5 wt% to 5 wt% respectively based on 100 wt% of the positive active material layer.

[0080] The positive active material can include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). In some example embodiments, at least one of a composite oxide of lithium and a metal including at least one of cobalt, manganese, nickel, and combinations thereof can be used.

[0081] The composite oxide can be or include a lithium transition metal composite oxide, and examples thereof can include at least one of a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a lithium nickel manganese-based oxide not containing cobalt, and combinations thereof.

[0082] For example, the following compounds represented by any one of the following chemical formulas 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 Coc 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).

[0083] In the above chemical formula, A is or includes at least one of Ni, Co, Mn, and combinations thereof; X is or includes at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is or includes at least one of O, F, S, P, and combinations thereof; G is or includes at least one of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; and L 1 is or includes at least one of Mn, Al, and combinations thereof.

[0084] For example, the positive active material can be or include a high-nickel type positive active material having a nickel amount 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 a lithium-transition metal composite oxide. The high-nickel type positive active material can achieve a high capacity, and can be applied to a high-capacity, high-density rechargeable lithium battery.

[0085] 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.

[0086] A conductive material is included to provide electrode conductivity. Any electrically conductive material may be a conductive material unless it causes a chemical change in the battery. Examples of conductive materials may include: carbonaceous materials such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials such as metal powders or metal fibers, including at least one of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0087] The current collector may include Al, but is not limited thereto.

[0088] Electrolytes: The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0089] The non-aqueous organic solvent may be or include a medium for transporting ions participating in the electrochemical reaction of the battery.

[0090] 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, and an aprotic solvent.

[0091] 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.

[0092] 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.

[0093] The ether-based solvent can include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, or the like. The ketone-based solvent can include cyclohexanone or the like. The alcohol-based solvent can include ethanol, isopropyl alcohol, or the like, and the aprotic solvent can include at least one of a nitrile such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and can include a double bond, an aromatic ring, an ether, or the like); an amide such as dimethylformamide; a dioxolane such as 1,3-dioxolane, 1,4-dioxolane, or the like; a sulfolane; or the like.

[0094] The non-aqueous organic solvent can exist alone or in a mixture of two or more solvents.

[0095] When using carbonate-based solvents, cyclic carbonates and chain carbonates can be mixed together, and the cyclic carbonates and the chain carbonates can be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0096] In an example, the lithium salt dissolved in the organic solvent supplies lithium ions to the battery, enables the substantially operation of the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt include one or at least two supporting electrolyte salts such as 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), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium bis(oxalato)borate (LiBOB).

[0097] Separator: The separator can be disposed between the positive electrode and the negative electrode according to the type of the rechargeable lithium battery. The separator can use polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer thereof having two or more layers, and can be or include at least one of a mixed multilayer such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene triple-layer separator, a polypropylene / polyethylene / polypropylene triple-layer separator, or the like.

[0098] The separator can 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.

[0099] The porous substrate can be or include a polymeric film formed of or including any one of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cyclic olefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, TEFLON, and polytetrafluoroethylene or a copolymer or mixture of two or more thereof.

[0100] The organic material can include a polyvinylidene fluoride-based polymer or a (meth)acryl-based polymer.

[0101] The inorganic material can be or include inorganic particles including at least one of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2boehmite, and combinations thereof, but is not limited thereto.

[0102] The organic material and the inorganic material can be mixed in one coating layer, or a coating layer including the inorganic material and a coating layer including the organic material can be stacked.

[0103] The rechargeable lithium battery can be classified into a cylindrical battery, a prismatic battery, a pouch battery, or a coin-type battery, etc. according to a shape thereof. Figures 2 to 5 is a schematic view showing a rechargeable lithium battery according to an example embodiment. Figure 2 A cylindrical battery is shown, Figure 3 A prismatic battery is shown, Figure 4 and Figure 5 A pouch-type battery is shown. Referring to Figures 2 to 5 The rechargeable lithium battery 100 can include an electrode assembly 40 including a separator 30 between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is included. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated with an electrolyte (not shown). As shown in Figure 2 The rechargeable lithium battery 100 can include a sealing member 60 sealing the case 50. In Figure 3In the rechargeable lithium battery 100, the positive electrode lead tab 11 and the positive terminal 12, and the negative electrode lead tab 21 and the negative terminal 22 can be included. As shown in FIG. 1A, the positive electrode lead tab 11 and the negative electrode lead tab 21 can be formed on the same surface of the battery 100. Figure 4 and Figure 5 As shown in FIG. 1B, the rechargeable lithium battery 100 can include Figure 5 As shown in FIG. 1C, the electrode tab 70 that can form an electric path for guiding electric current formed in the electrode assembly 40 to the outside of the battery 100 can be formed. Figure 4 As shown in FIG. 1D, the positive electrode tab 71 and the negative electrode tab 72 can be formed, and the tabs 71, 72 also form an electric path for guiding electric current formed in the electrode assembly 40 to the outside of the battery 100.

[0104] As non-limiting examples, the rechargeable lithium battery according to example embodiments can be applied to automobiles, mobile phones, and / or various types of electrical devices.

[0105] The following examples and comparative examples are provided in order to highlight features of one or more example embodiments, but it will be understood that the examples and comparative examples are not to be construed as limiting the scope of the example embodiments, nor are the comparative examples to be construed as 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.

[0106] Example 1: Si particles were pulverized to prepare Si nanoparticles having an average particle diameter (D50) of 100 nm. Silicon nanoparticles having an average particle diameter (D50) of 100 nm and stearic acid were mixed at a weight ratio of 80:20 in an ethanol solvent at a speed of 1000 rpm for 1 hour using a ball mill to prepare a silicon particle liquid having a solid amount of 11 wt%.

[0107] The silicon particle liquid was spray-dried at 120°C to prepare secondary particles in which silicon nanoparticles (primary particles) were aggregated.

[0108] Chemical vapor deposition was performed on the secondary particles using SiH4 gas at 470°C for 20 minutes (gas flow rate: 100 seem (which is a value measured at 0°C and 1 atm)) to prepare a product including amorphous silicon positioned on the surface of the secondary particles.

[0109] Thereafter, the resulting product and mesophase pitch were mixed at a weight ratio of 62.5:37.5, and the resulting mixture was heat-treated at 700°C to prepare a negative active material.

[0110] The prepared negative electrode active material includes secondary particles in which crystal silicon primary particles are aggregated, amorphous silicon surrounding the surface of the secondary particles, and a soft carbon coating layer on the surface of the secondary particles and the amorphous silicon. In the prepared negative electrode active material, the mixing ratio of the crystal silicon primary particles and the amorphous silicon is 80:20 by weight, the amount of the crystal silicon primary particles is 50.0 wt% based on 100 wt% of the negative electrode active material, the amount of the amorphous silicon is 12.5 wt%, and the amount of the amorphous carbon is 37.5 wt%. The negative electrode active material has a porosity of 0.5%, and the soft carbon coating layer has a thickness of 50 nm.

[0111] The negative electrode active material was used as a first negative electrode active material, and a mixed negative electrode active material of 97.5 wt% of the first negative electrode active material and a natural graphite second negative electrode active material (the mixing ratio of the first negative electrode active material and the second negative electrode active material was equal to 10:90 by weight), 1.5 wt% of carboxymethyl cellulose, and 1 wt% of styrene butadiene rubber were mixed in an aqueous solvent to prepare a negative electrode active material layer slurry.

[0112] The negative electrode active material layer slurry was coated on a Cu foil current collector, dried, and pressed to prepare a negative electrode including the current collector and a negative electrode active material layer formed on the current collector.

[0113] 96 wt% of 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 an N-methylpyrrolidone solvent to prepare a positive electrode active material layer slurry.

[0114] The positive electrode active material slurry was coated on an Al foil current collector, dried, and pressed to prepare a positive electrode.

[0115] A full cell was manufactured by the general procedure using the negative electrode, the positive electrode, and an electrolyte. As the electrolyte, 1M LiPF6dissolved in a mixed solvent (3:7 by volume) of ethylene carbonate and dimethyl carbonate was used.

[0116] Example 2: The negative electrode active material was prepared by the same procedure as in Example 1, except that chemical vapor deposition was performed at 470°C for 34 minutes, in which the mixing ratio of the crystal silicon primary particles and the amorphous silicon was 70:30 by weight, the amount of the crystal silicon primary particles was 50.0 wt% based on 100 wt% of the negative electrode active material, the amount of the amorphous silicon was 21.0 wt%, and the amount of the amorphous carbon was 29.0 wt%. The negative electrode active material had a porosity of 1%, and the soft carbon coating layer had a thickness of 50 nm.

[0117] A negative electrode and a full cell were manufactured by the same steps as in Example 1, except that the negative electrode active material was used as the first negative electrode active material.

[0118] Example 3: A negative electrode active material was prepared by the same steps as in Example 1, except that chemical vapor deposition was performed at 470°C for 32 minutes, and in the negative electrode active material, the mixing ratio of the crystalline silicon primary particles and amorphous silicon was 70:30 by weight, the amount of the crystalline silicon primary particles was 47.0 wt% and the amount of the amorphous silicon was 20.0 wt% based on 100 wt% of the negative electrode active material, and the amount of the amorphous carbon was 33.0 wt%. The negative electrode active material had a porosity of 1%, and the soft carbon coating layer had a thickness of 50 nm.

[0119] A negative electrode and a full cell were manufactured by the same steps as in Example 1, except that the negative electrode active material was used as the first negative electrode active material.

[0120] Example 4: A negative electrode active material was prepared by the same steps as in Example 1, except that chemical vapor deposition was performed at 470°C for 50 minutes, and in the negative electrode active material, the mixing ratio of the crystalline silicon primary particles and amorphous silicon was 60:40 by weight, the amount of the crystalline silicon primary particles was 47.0 wt% and the amount of the amorphous silicon was 31.0 wt% based on 100 wt% of the negative electrode active material, and the amount of the amorphous carbon was 22.0 wt%. The negative electrode active material had a porosity of 0.6%, and the soft carbon coating layer had a thickness of 50 nm.

[0121] A negative electrode and a full cell were manufactured by the same steps as in Example 1, except that the negative electrode active material was used as the first negative electrode active material.

[0122] Comparative Example 1: Si particles were pulverized to prepare Si nanoparticles having an average particle diameter (D50) of 200 nm. Silicon nanoparticles having an average particle diameter (D50) of 200 nm and stearic acid were mixed at a weight ratio of 90:10 in an ethanol solvent at a speed of 1000 rpm for 1 hour using a ball mill to prepare a silicon particle liquid having a solid amount of 11 wt%.

[0123] The silicon particle liquid was spray-dried at 120°C to prepare secondary particles in which the silicon nanoparticles (primary particles) were aggregated.

[0124] The secondary particles were mixed with mesophase carbon (pitch) at a weight ratio of 62.5:37.5, and the mixture was heat-treated at 950°C to prepare a negative electrode active material.

[0125] The prepared negative electrode active material includes secondary particles in which crystal silicon primary particles are aggregated, and a soft carbon coating layer on the surface of the secondary particles. In the prepared negative electrode active material, the amount of the crystal silicon primary particles is 62.5 wt% and the amount of the amorphous carbon is 37.5 wt% based on 100 wt% of the negative electrode active material. The negative electrode active material has a porosity of 3.5% and the soft carbon coating layer has a thickness of 50 nm.

[0126] A negative electrode and a full cell were manufactured by the same steps as in Example 1, except that the negative electrode active material was used as the first negative electrode active material.

[0127] Comparative Example 2: Si particles were pulverized to prepare Si nanoparticles having an average particle diameter (D50) of 200 nm.

[0128] The Si nanoparticles were mixed with meso-carbon, and the resulting mixture was heat-treated at 950°C to prepare an aggregated product of Si nanoparticles and soft carbon, and then chemical vapor deposition was performed on the aggregated product using SiH4 gas at 470°C for 20 minutes (gas flow rate: 100 seem (which is a value measured at 0°C and 1 atm)) to thereby prepare a negative electrode active material including amorphous silicon on the surface of the aggregated product. Here, the weight ratio of the crystal Si nanoparticles, the amorphous carbon, and the amorphous Si on the surface was 50.0:37.5:12.5.

[0129] The prepared negative electrode active material includes an aggregated product of Si nanoparticles and soft carbon, and an amorphous silicon coating layer on the surface of the aggregated product.

[0130] In the prepared negative electrode active material, the mixed ratio of the crystal silicon primary particles and the amorphous silicon was 80:20 by weight, the amount of the crystal silicon primary particles was 50.0 wt% and the amount of the amorphous silicon was 12.5 wt% based on 100 wt% of the negative electrode active material, and the amount of the amorphous carbon was 37.5 wt%. The negative electrode active material had a porosity of 4.7% and the amorphous silicon coating layer had a thickness of 20 nm.

[0131] A negative electrode and a full cell were manufactured by the same steps as in Example 1, except that the negative electrode active material was used as the first negative electrode active material.

[0132] Comparative Example 3: Si particles were pulverized to prepare Si nanoparticles having an average particle diameter (D50) of 200 nm. Silicon nanoparticles having an average particle diameter (D50) of 200 nm and stearic acid were mixed in a weight ratio of 90:10 in an ethanol solvent at a speed of 1000 rpm for 1 hour using a ball mill to prepare a silicon particle liquid having a solid amount of 11 wt%.

[0133] The silicon particle liquid was spray-dried at 120°C to prepare secondary particles in which silicon nanoparticles (primary particles) were aggregated.

[0134] Chemical vapor deposition was performed on the secondary particles using SiH4 gas at 470°C for 32 minutes (gas flow rate: 100 seem (which is a value measured at 0°C and 1 atm)) to prepare a negative active material including amorphous silicon positioned on the surface of the secondary particles.

[0135] The prepared negative active material included secondary particles in which crystalline silicon primary particles were aggregated and amorphous silicon surrounding the surface of the secondary particles. In the prepared negative active material, the mixing ratio of the crystalline silicon primary particles and the amorphous silicon was 80:20 by weight ratio, the amount of the crystalline silicon primary particles was 80 wt% and the amount of the amorphous silicon was 20 wt% based on 100 wt% of the negative active material. The negative active material had a porosity of 11.0%.

[0136] A negative electrode and a full cell were manufactured by the same steps as in Example 1, except that the negative active material was used as the first negative active material.

[0137] Experimental Example 1) Evaluation of X-ray Diffraction With respect to the first negative active materials according to Examples 1 to 4 and Comparative Examples 1 to 3, X-ray diffraction analysis was performed by using Cu Kα rays.

[0138] The X-ray diffraction analysis was measured by using an X'Pert (purchased from PANalytical B.V.) XRD device, but a monochromator device was removed to improve peak intensity resolution. The measurement was performed under conditions of 2θ = 20° to 80°, a scan speed (° / S) = 0.06436, and a step of 0.026° / step.

[0139] Experimental Example 2) Evaluation of Porosity The porosity of the first negative active materials according to Examples 1 to 4 and Comparative Examples 1 to 3 was measured by N2 absorption isotherm by BJH (Barret-Joyner-Halenda) technique. The results are shown in Table 2.

[0140] Experimental Example 3) Evaluation of Discharge Capacity The full cells according to Examples 1 to 4 and Comparative Examples 1 to 3 were charged and discharged once at 1C to measure the discharge capacity. The results are shown in Table 2.

[0141] Experimental Example 4) Evaluation of Efficiency The full cells according to Example 1 to Example 4 and Comparative Example 1 to Comparative Example 3 were charged and discharged at 0.1C once to obtain a ratio of measured discharge capacity to measured charge capacity. The results are shown as efficiency in Table 2.

[0142] Example 5) Evaluation of cycle life characteristics The half cells according to Example 1 to Example 4 and Comparative Example 1 to Comparative Example 3 were charged and discharged at 1C for 400 cycles. The ratio of discharge capacity at the 400th cycle to discharge capacity at the 1st cycle was calculated. The results are shown as capacity retention in Table 2.

[0143] The deposition conditions and the composition of the first negative active material of Example 1 to Example 4 and Comparative Example 1 to Comparative Example 3 are shown in Table 1.

[0144] Table 1

[0145] Table 2

[0146] As shown in Table 2, the battery cells including the negative active material of Example 1 to Example 4 exhibited high discharge capacity and desirable or improved efficiency and capacity retention.

[0147] The battery cell of Comparative Example 1 including the negative active material including only crystalline silicon and an amorphous carbon coating layer exhibited deteriorated discharge capacity, efficiency, and capacity retention overall. The battery cell of Comparative Example 2 including the amorphous silicon coating layer formed on the aggregated product of crystalline silicon and amorphous carbon exhibited slightly improved discharge capacity compared to Comparative Example 1, but significantly deteriorated efficiency and capacity retention. The battery cell according to Comparative Example 3 including the negative active material having no amorphous carbon coating layer exhibited high discharge capacity, but significantly deteriorated efficiency, and the cycle life characteristics can not be measured.

[0148] While the disclosure has been described in connection with what is presently considered to be the 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, the negative electrode active material comprising: crystalline silicon primary particles; amorphous silicon; and an amorphous carbon coating layer. The amorphous silicon is on a surface of the crystalline silicon primary particles.

2. The negative electrode active material according to claim 1, wherein, The amorphous carbon coating layer surrounds the crystalline silicon primary particles and the amorphous silicon.

3. The negative electrode active material according to claim 1, wherein, The amorphous silicon surrounds a surface of the crystalline silicon primary particles.

4. The negative electrode active material according to claim 1, wherein, 5. The negative electrode active material according to claim 1, further comprising secondary particles, wherein: the crystalline silicon primary particles are aggregated to form the secondary particles, the amorphous silicon is on a surface of the secondary particles, and the amorphous carbon coating layer surrounds the amorphous silicon. A mixing ratio of the crystalline silicon primary particles to the amorphous silicon is in a range of 95:5 to 20:80 by weight ratio.

6. The negative electrode active material according to claim 1, wherein An amount of the amorphous silicon is in a range of 1 wt% to 50 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 crystalline silicon primary particles is in a range of 30 wt% to 80 wt% based on 100 wt% of the negative electrode active material.

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

9. The negative electrode active material according to claim 1, wherein The crystalline silicon primary particles have an average particle diameter D50 in a range of 50 nm to 150 nm.

10. The negative electrode active material according to claim 1, wherein The negative electrode active material has a porosity in a range of 0% to 3%.

11. The negative electrode active material according to claim 1, wherein The amorphous silicon is prepared by vapor deposition.

12. The negative electrode active material according to claim 1, wherein The vapor deposition is performed using a Si-containing gas including at least one of SiH4 gas, Si2H6 gas, and Si3H8 gas.

13. The negative electrode active material according to claim 12, wherein The vapor deposition is chemical vapor deposition.

14. The negative electrode active material according to claim 12, wherein In the vapor deposition, a flow rate of the Si-containing gas is in a range of 1 seem to 1000 seem.

15. The negative electrode active material according to claim 13, wherein, The vapor deposition is performed for a period of time in a range of 10 minutes to 5 hours.

16. The negative electrode active material according to claim 12, wherein 17. A rechargeable lithium battery, the rechargeable lithium battery comprising: a negative electrode including the negative electrode active material according to any one of claims 1 to 16; a positive electrode; and an electrolyte. The negative electrode further includes a crystalline carbon negative electrode active material. ​ 18. The rechargeable lithium battery of claim 17, wherein, ​

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