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

Abstract

A negative electrode active material, a method of preparing the same, a negative electrode, and a rechargeable lithium battery including the negative electrode are disclosed. Embodiments of the present disclosure include a negative electrode active material including a spherical core including silicon nanoparticles and sulfur, and an amorphous carbon coating layer on a surface of the spherical core, in which the negative electrode active material has a span value in a range of about 1.1 to about 1.6, and exhibits high efficiency, high capacity, and long cycle life characteristics.

Description

Technical Field

[0001] Disclosed are a negative electrode active material, a method for preparing the negative electrode active material, and a negative electrode and a rechargeable lithium battery including the negative electrode active material. Background Art

[0002] Rechargeable lithium batteries generally have high electrochemical capacity and operating potential as well as desired or improved charge / discharge cycle characteristics, and therefore are widely included in, for example, portable information terminals, portable electronic devices, small household power storage devices, motorcycles, electric vehicles, hybrid electric vehicles, etc. With the popularization of rechargeable lithium batteries, improved safety and higher performance are demanded.

[0003] An example of a method for increasing the capacity of a rechargeable lithium battery includes using a silicon-containing active material for the negative electrode. When a silicon-containing active material having a larger lithium insertion / deinsertion amount than a conventional carbon-based active material is used for the negative electrode, an improvement in battery capacity can be expected. However, because silicon-based active materials generally have a large volume change accompanying lithium insertion / deinsertion, the negative electrode active material layer may expand and contract violently during charging and discharging, which may be a challenge. To address this challenge, it may be advantageous to change the structure or composition of the silicon-based negative electrode active material. However, there may be limitations such as difficulty in practical application, failure to improve cycle-life characteristics, and failure to sufficiently reduce or suppress electrode expansion. Summary of the Invention

[0004] Some example embodiments include negative electrode active materials that exhibit improved expansion properties and desirable or improved cycle-life characteristics.

[0005] Some example embodiments include a negative electrode including the negative electrode active material and a rechargeable lithium battery.

[0006] According to some example embodiments, a negative electrode active material includes a spherical core including silicon nanoparticles and sulfur, and an amorphous carbon coating on a surface of the core, wherein the negative electrode active material has a span value determined according to Equation 1 below, which is a standard deviation around a mean value, in a range of about 1.1 to about 1.6.

[0007] Equation 1: Span value = (D 90 -D 10 ) / D 50 In Equation 1, D 10 is the particle size of particles that account for 10% of the cumulative volume in the particle size distribution, D 50 is the particle size of particles with a cumulative volume of 50% by volume in the particle size distribution, D90 It is the particle size at which 90% of the particles in the cumulative volume of the particle size distribution are concentrated.

[0008] According to some example embodiments, a method of preparing a negative electrode active material includes: (i) pulverizing silicon to produce nano-sized silicon particles; (ii) preparing a composition including the silicon particles, a sulfur precursor, and ethanol; (iii) spray-drying the composition to produce a dried product; and (iv) forming an amorphous carbon coating using the dried product and an amorphous carbon precursor, wherein the negative electrode active material has a span value according to the following Equation 1 in a range of about 1.1 to about 1.6.

[0009] Equation 1: Span value = (D 90 -D 10 ) / D 50 In Equation 1, D 10 is the particle size of particles that account for 10% of the cumulative volume in the particle size distribution, D 50 is the particle size of particles with a cumulative volume of 50% by volume in the particle size distribution, D 90 It is the particle size at which 90% of the particles in the cumulative volume of the particle size distribution are concentrated.

[0010] According to some example embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material.

[0011] According to some example embodiments, a rechargeable lithium battery includes the negative electrode, a positive electrode, and an electrolyte.

[0012] Negative electrode active materials according to some example embodiments may exhibit high efficiency, high capacity, and long cycle-life characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figures 1 to 4 is a schematic diagram illustrating a rechargeable lithium battery according to some example embodiments. DETAILED DESCRIPTION

[0014] Hereinafter, example embodiments are described in detail so that those skilled in the art can easily implement the example embodiments. However, the present disclosure may be implemented in many different forms and is not to be construed as limited to the example embodiments set forth herein.

[0015] The terms used herein are for describing example embodiments only and are not intended to limit the present disclosure. Unless the context clearly dictates otherwise, expressions in the singular include expressions in the plural.

[0016] As used herein, "combinations thereof" refers to mixtures, stacks, composites, copolymers, alloys, blends, reaction products, and the like, of the components.

[0017] Here, it should be understood that terms such as "include", "comprising" or "having" are intended to indicate the presence of the embodied features, quantities, steps, elements (components) or combinations thereof, but these terms do not exclude the possibility of the presence or addition of one or more other features, quantities, steps, elements (components) or combinations thereof.

[0018] In the drawings, the thickness of layers, films, panels, regions, etc., is exaggerated for clarity, and like reference numerals denote like elements throughout the specification. It is understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present.

[0019] In addition, the "layer" here includes not only a shape formed on the entire surface when viewed from a plan view but also a shape formed on a part of the surface.

[0020] Here, “or” is not to be interpreted in an exclusive sense; for example, “A or B” is to be interpreted as including A, B, A+B, etc.

[0021] As used herein, when no definition is provided otherwise, a particle size or particle size may be an average particle size. The average particle size refers to the average value of the particle sizes according to the cumulative volume in the particle size distribution of the particles included in the negative electrode active material. The particle size distribution can be measured by methods well known to those skilled in the art, for example, by a particle size analyzer, or by a transmission electron microscope image or a scanning electron microscope image. Alternatively, the average particle size value can be obtained by measuring in the following manner: using dynamic light scattering, performing data analysis, counting the number of particles in each particle size range, and calculating this.

[0022] Soft carbon refers to a carbon material that can be graphitized and is easily graphitized by heat treatment at high temperatures (for example, about 2800° C.) Hard carbon refers to a carbon material that cannot be graphitized or is only slightly graphitized by heat treatment.

[0023] When the term "about" or "substantially" is used in conjunction with a numerical value in this specification, it means that the relevant numerical value includes 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%.

[0024] Negative electrode active material In some example embodiments, a negative electrode active material for a rechargeable lithium battery includes a spherical core including silicon nanoparticles and sulfur and an amorphous carbon coating on a surface of the core, wherein the negative electrode active material has a span value as defined in Equation 1 in a range of about 1.1 to about 1.6.

[0025] Equation 1: Span value = (D 90 -D 10 ) / D 50 In Equation 1, D 10 is the particle size of particles that account for 10% of the cumulative volume in the particle size distribution, D 50 is the particle size of particles with a cumulative volume of 50% by volume in the particle size distribution, D 90 It is the particle size at which 90% of the particles in the cumulative volume of the particle size distribution are concentrated.

[0026] The negative electrode active material according to some example embodiments includes silicon nanoparticles in the core. The theoretical capacity of graphite included in the negative electrode of a general rechargeable lithium battery is limited to about 372 mAh / g, and the negative electrode active material according to some example embodiments includes silicon nanoparticles with a theoretical capacity of about 4,200 mAh / g in order to overcome the limitation of graphite in the negative electrode. The silicon nanoparticles may exist as silicon nanoparticles themselves or in a partially oxidized form, and in this case, the atomic content ratio of Si:O indicating the degree of oxidation may be in the range of about 99: 1 to about 34: 66 by weight. That is, the silicon nanoparticles may be Si or SiO x , and in this case, SiO x The range of x in can be greater than about 0 and less than about 2.

[0027] According to some exemplary embodiments, the negative electrode active material includes sulfur in the core in addition to silicon nanoparticles. Sulfur has strong nucleophilicity and can therefore induce a nucleophilic reaction with vinylene carbonate and / or fluoroethylene carbonate included in the electrolyte as an additive to form an artificial SEI film in situ on the surface of the silicon particles. Furthermore, the sulfur protects the surface of the silicon nanoparticles and prevents the electrolyte from damaging the negative electrode active material, thereby improving energy density and extending cycle life. Furthermore, the inclusion of sulfur in the core improves ion and electron transport properties, thereby improving conductivity, which has the advantage of enabling rapid charging.

[0028] In some example embodiments, the weight of sulfur may be in the range of about 20 ppm to about 200 ppm, for example, about 50 ppm to about 200 ppm, about 90 ppm to about 200 ppm, about 90 ppm to about 150 ppm, or about 90 ppm to about 120 ppm, based on the total weight of the core. When the sulfur content satisfies any of the above ranges, the cycle life can be extended by protecting the surface of the silicon nanoparticles and preventing the electrolyte from damaging the negative electrode active material, and the ion or electron migration performance can be improved, which has the advantage of improving conductivity.

[0029] In some example embodiments, the average particle size of sulfur (D 50 ) can be in the range of about 5 nm to about 15 nm, for example, about 5 nm to about 12 nm, about 7 nm to about 12 nm, or about 7 nm to about 9 nm. 50 ) When any of the above ranges is met, the cycle life can be extended by protecting the surface of the silicon nanoparticles and preventing the electrolyte from damaging the negative electrode active material, and the ion or electron migration performance can be improved, thereby improving the conductivity.

[0030] The core of the negative electrode active material according to some example embodiments is substantially spherical and has a spherical shape, so that the negative electrode active material can be fully dispersed throughout the negative electrode, thereby reducing the expansion rate during charging and discharging. In addition, when the negative electrode active material is mixed with crystalline carbon, the substantially spherical negative electrode active material can be better inserted into the crystalline carbon and thus can be better dispersed throughout the negative electrode.

[0031] The negative electrode active material according to some example embodiments has a span value represented by Equation 1 in the range of about 1.1 to about 1.6, for example, about 1.1 to about 1.55 or about 1.1 to about 1.5. When the span value of the negative electrode active material is within any of the above ranges, it means that the negative electrode active material contains almost no fine powder. That is, the size is about 1 μm or less and almost no amorphous fine powder is included overall, so that the negative electrode active material can exhibit a low specific surface area, thereby reducing side reactions of the electrolyte and improving cycle life.

[0032] Equation 1: Span value = (D 90 -D 10 ) / D 50 In Equation 1, D 10 is the particle size of the negative electrode active material particles whose cumulative volume accounts for 10% by volume in the particle size distribution, D 50 is the particle size of the negative electrode active material particles that accounts for 50% by volume of the cumulative volume in the particle size distribution, D 90It is the particle size of the negative electrode active material particles whose cumulative volume accounts for 90% by volume in the particle size distribution.

[0033] The negative electrode active material according to some example embodiments may have a sphericity (S) expressed by Equation 2 in the range of about 0.9 to about 1.0, for example, about 0.92 to about 0.98 or about 0.92 to about 0.95, indicating that the negative electrode active material is spherical or substantially spherical. When the sphericity of the negative electrode active material is within any of the above ranges, the expansion rate during charge and discharge can be more effectively reduced or suppressed.

[0034] Equation 2: Sphericity (S) = 4π × A / B 2 In Equation 2, A is the area of ​​the negative electrode active material, and B is the perimeter of the shape of the negative electrode active material.

[0035] Explaining sphericity in more detail, the sphericity of the negative electrode active material can be obtained by projecting a three-dimensional particle onto a two-dimensional plane. For example, sphericity can be the ratio of the boundary of a circle having the same area as the actual particle. Here, area A can be obtained by obtaining a scanning electron microscope (SEM) image of the electrode cross-section using CP-SEM (controlled pressure scanning electron microscopy), using the cross-sectional image to obtain the actual particle perimeter B using the Image J program, and using perimeter B to find a circle with the same perimeter as B and calculate the area of ​​that circle. In some exemplary embodiments, in addition to perfectly spherical shapes, the actual perimeter can also be the perimeter of any particle with a non-perfectly spherical shape (i.e., an uneven area).

[0036] In some example embodiments, the average particle size (D 50 ) can be in the range of about 10 nm to about 1000 nm, for example, about 10 nm to about 900 nm, about 10 nm to about 800 nm, about 10 nm to about 700 nm, about 10 nm to about 600 nm, about 10 nm to about 500 nm, about 10 nm to about 400 nm, or about 10 nm to about 300 nm. When the spherical core has an average particle size (D) within any of the above ranges, 50 ), there may be advantages in reducing or suppressing the volume expansion generated during charge and discharge, and reducing or preventing the disconnection of the conductive path due to particle breakage during charge and discharge. Here, the average particle size of the spherical core (D 50 ) can be obtained by the following steps: measuring the sizes of about 20 particles randomly selected from a scanning electron microscope image (measuring the diameter of round particles and measuring the length of the major axis of non-round particles) to obtain a particle size distribution, and taking the diameter of particles with a cumulative volume of 50% by volume from the particle size distribution as the average particle size.

[0037] The negative electrode active material according to some example embodiments may include an amorphous carbon coating located on the core surface. In the amorphous carbon coating, the amorphous carbon may be or include soft carbon or hard carbon, a mesophase pitch carbonization product, coke, or a combination thereof. The thickness of the amorphous carbon coating may be in the range of about 1 nm to about 2 μm, for example, about 1 nm to about 500 nm, about 10 nm to about 300 nm, or about 20 nm to about 200 nm. When the amorphous carbon coating has a thickness within this range, the volume expansion of silicon during charge and discharge can be significantly reduced or suppressed.

[0038] In some example embodiments, based on the total 100 wt % of the negative electrode active material, the content of the core may be in the range of about 55 wt % to about 64 wt %, for example, about 56 wt % to about 63 wt % or about 58 wt % to about 62 wt %. In addition, based on the total 100 wt % of the negative electrode active material, the content of the amorphous carbon coating may be in the range of about 36 wt % to about 45 wt %, for example, about 37 wt % to about 43 wt % or about 36 wt % to about 45 wt %. When the contents of the core and the amorphous carbon coating respectively meet any of the above ranges, the excessive volume expansion generated during charge and discharge can be reduced or suppressed, and the disconnection of the conductive path caused by particle rupture during charge and discharge can be reduced or prevented.

[0039] Method for preparing negative electrode active material Methods of preparing a negative electrode active material according to some example embodiments include (i) pulverizing silicon to produce nano-sized silicon particles; (ii) preparing a composition including the silicon particles, a sulfur precursor, and ethanol; (iii) spray-drying the composition to produce a dried product; and (iv) forming an amorphous carbon coating using the dried product and an amorphous carbon precursor, wherein the negative electrode active material has a span value according to Equation 1 in the range of about 1.1 to about 1.6.

[0040] Equation 1: Span value = (D 90 -D 10 ) / D 50 In Equation 1, D 10 is the particle size of particles that account for 10% of the cumulative volume in the particle size distribution, D 50 is the particle size of particles with a cumulative volume of 50% by volume in the particle size distribution, D 90 It is the particle size at which 90% of the particles in the cumulative volume of the particle size distribution are concentrated.

[0041] In some example embodiments, nano-sized silicon particles are produced by pulverizing micron-sized silicon. The pulverization process can be performed using conventional processes such as ball milling. During the pulverization process, a dispersant can be used. The dispersant can be or include at least one of stearic acid, boron nitride (BN), MgS, polyvinyl pyrrolidone (PVP), or a combination thereof. Since an appropriate amount is sufficient to perform the grinding process of the silicon particles, the amount of the dispersant does not need to be limited. The average particle size (D) of the primary silicon particles is 1 / 4 of the particle diameter. 50 ) can be in the range of about 10 nm to about 1000 nm, for example, about 10 nm to about 900 nm, about 10 nm to about 800 nm, about 10 nm to about 700 nm, about 10 nm to about 600 nm, about 10 nm to about 500 nm, about 10 nm to about 400 nm, or about 10 nm to about 300 nm.

[0042] In some example embodiments, a composition including silicon particles, a sulfur precursor, and ethanol is prepared. Sulfate or polysulfide may be included as the sulfur precursor. The weight ratio of the silicon particles to the sulfur precursor may be in the range of about 2:1 to about 20:1, for example, about 2:1 to about 17:1, about 5:1 to about 17:1, about 5:1 to about 14:1, about 8:1 to about 14:1, or about 11:1 to about 14:1. When the weight ratio of the silicon particles to the sulfur precursor satisfies any of the above ranges, the cycle life can be extended by protecting the surface of the silicon nanoparticles and preventing the electrolyte from damaging the negative electrode active material, and the ion or electron migration performance can be improved, thereby improving the conductivity.

[0043] In some example embodiments, a composition comprising silicon particles, a sulfur precursor, and ethanol is dried to produce a dried product. The drying process may be performed using a spray drying process. By performing the drying process using the spray drying process, a dried product having more uniform particle size and spherical particles can be formed. When the dried product is spherical particles having a uniform particle size, the amorphous carbon layer formed thereafter can be more uniformly formed over substantially the entire surface.

[0044] In some example embodiments, the amorphous carbon coating is formed using the dried product and an amorphous carbon precursor, which may be or include at least one of petroleum coke, coal coke, petroleum pitch, coal pitch, green coke, or a combination thereof.

[0045] In some exemplary embodiments, when forming an amorphous carbon coating using a dried product and an amorphous carbon precursor, the mixture of the dried product and the amorphous carbon precursor may be compression molded. The compression molding process can reduce the pores within the negative electrode active material, thereby effectively reducing or inhibiting side reactions. The compression molding process can be performed at a pressure sufficient to maintain a substantially spherical shape of the obtained product (or, for example, the final product, the negative electrode active material), and can be performed, for example, at a pressure within a range of greater than about 0 MPa and less than or equal to about 30 MPa, greater than about 0 MPa and less than or equal to about 200 MPa, or from about 5 MPa to about 20 MPa. The compression molding process can be performed, for example, by cold isostatic pressing (CIP). When compression molding is performed within the above-mentioned pressure range, the spherical shape can be maintained while appropriately reducing the pores without generating fine powder.

[0046] After compression molding is performed, the obtained compression molded product can be carbonized. The carbonization process can be performed at a temperature in the range of about 600°C to about 1,000°C, can be performed in an N2 atmosphere, a helium atmosphere, or a combination thereof, and the dispersant can be removed during the carbonization process. In addition, according to the carbonization process, the amorphous carbon precursor is converted into amorphous carbon and is formed as an amorphous carbon coating around the surface of the compression molded product. When the carbonization process is performed within the above-mentioned temperature range, the problem of excessive growth of silicon particles can be reduced or suppressed, SiC formation can be reduced or suppressed, and the conductivity of the amorphous carbon can be improved. In addition, some amorphous carbon can be inserted into the pores formed between the silicon particles, can be located on the surface of the silicon particles, and surround the surface of the silicon particles. When the atmosphere of the carbonization process is included in the above-mentioned conditions, the oxidation of silicon and the generation of SiC can be reduced or suppressed while effectively forming amorphous carbon, thereby reducing the resistance of the active material.

[0047] Instead of mixing the dried product and the amorphous carbon precursor, the dried product may be subjected to a vapor coating process using an amorphous carbon precursor gas. In this case, an amorphous carbon coating can be formed on the surface of the product without a separate carbonization process. Therefore, a compression molding process may be performed after the vapor coating process. The conditions of the compression molding process may be as described above.

[0048] Subsequently, a screening process of the heat-treated product may be performed. The screening process may be performed using a sieve so that the span value (defined by Equation 1) of the negative electrode active material may be in the range of about 1.1 to about 1.6. For example, the screening process may be performed to obtain an active material having a certain particle size such that the active material D 10 、D 50 and D 90 The span values ​​obtained may be in the range of about 1.1 to about 1.6.

[0049] negative electrode The negative electrode for a rechargeable lithium battery includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector. The negative electrode active material layer includes the aforementioned negative electrode active material, may optionally further include other types of negative electrode active materials, and may also include a binder and / or a conductive material.

[0050] For example, the negative electrode according to some example embodiments may include the aforementioned negative electrode active material as a first negative electrode active material, and may include a second negative electrode active material containing crystalline carbon. Here, based on 100 wt% of the total of the first negative electrode active material and the second negative electrode active material, the second negative electrode active material may be included in an amount within a range of about 1 wt% to about 60 wt%, about 1 wt% to about 50 wt%, about 3 wt% to about 30 wt%, or about 3 wt% to about 10 wt%, and may be appropriately mixed according to the desired capacity.

[0051] binder The binder is configured to adhere the negative electrode active material particles to each other and also to adhere the negative electrode active material to the current collector.The binder can be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0052] The non-aqueous binder may 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.

[0053] The aqueous binder may 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.

[0054] When an aqueous binder is included as the binder for the negative electrode, a cellulose compound that can impart viscosity may be further included. The cellulose compound may include one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be or include at least one of Na, K, or Li.

[0055] The dry binder may be or include a polymer material capable of becoming fibers, and may be or include, for example, at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0056] Conductive materials The conductive material may be included to provide electrode conductivity, and any electrically conductive material may be included as the conductive material unless the electrically conductive material causes chemical changes in or to the battery. Examples of the conductive material include: carbon-based materials such as or including at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, and the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0057] Negative electrode current collector The negative electrode current collector may be or 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.

[0058] Rechargeable lithium battery In some example embodiments, a rechargeable lithium battery includes the negative electrode, the positive electrode, and an electrolyte. Here, the electrolyte may be or include a liquid electrolyte or a solid electrolyte.

[0059] For example, some example embodiments may include a rechargeable lithium battery comprising the above-described negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, and an electrolyte. Some example embodiments may include an all-solid-state rechargeable lithium battery comprising the above-described negative electrode, a positive electrode, and a solid electrolyte layer between the negative electrode and the positive electrode.

[0060] Hereinafter, a rechargeable lithium battery using an electrolyte is described as an example.

[0061] Rechargeable lithium batteries may be classified according to shape into cylindrical, prismatic, pouch-shaped, coin-shaped, and the like. Figures 1 to 4 is a schematic diagram illustrating a rechargeable lithium battery according to some example embodiments, wherein Figure 1 A cylindrical battery is shown, Figure 2 A prismatic cell is shown, Figure 3 and Figure 4 Shows a pouch cell. Figures 1 to 4 , the rechargeable lithium battery 100 includes an electrode assembly 40 having a separator 30 disposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is accommodated. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 1 As shown in FIG, the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. Figure 2In the embodiment, the rechargeable lithium battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. Figure 3 and Figure 4 As shown in FIG, the rechargeable lithium battery 100 includes Figure 4 The electrode tab 70 shown in Figure 3 The positive electrode tab 71 and the negative electrode tab 72 shown in FIG. 7 , the electrode tabs 70 / 71 / 72 form an electrical path for inducing current formed in the electrode assembly 40 to the outside of the rechargeable lithium battery 100 .

[0062] 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.

[0063] The positive electrode active material may be or include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). For example, one or more composite oxides of lithium and a metal such as or including at least one of cobalt, manganese, nickel, and combinations thereof may be used.

[0064] 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, lithium nickel manganese-based oxides not containing cobalt, or combinations thereof.

[0065] As an example, a compound represented by any one of the following chemical formulae can be used. 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 O2-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); and Li a FePO4 (0.90≤a≤1.8).

[0066] 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 1 It is or includes at least one of Mn, Al or a combination thereof.

[0067] As an example, the positive electrode active material may be or include a high-nickel positive electrode active material having a nickel content of greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%, based on 100 mol% of metals other than lithium in the lithium transition metal composite oxide. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density rechargeable lithium batteries.

[0068] Based on the total weight of the positive electrode active material layer, the amount of the positive electrode active material may be in the range of about 90 wt % to about 98 wt %, for example, about 90 wt % to about 95 wt %. Based on the total weight of the positive electrode active material layer, the amount of the binder and / or the conductive material may be in the range of about 1 wt % to about 5 wt %.

[0069] The binder is configured to improve the bonding properties between the positive electrode active material particles and the bonding properties between the positive electrode active material particles and the current collector, and examples thereof may 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, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0070] The conductive material is configured to provide electrode conductivity and may include any electrically conductive material as the conductive material unless the electrically conductive material causes chemical changes in or to the battery, and examples thereof may include: carbon-based materials such as or including at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, etc.; metal-based materials including metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0071] An aluminum foil may be included as the positive electrode current collector, but the positive electrode current collector is not limited thereto.

[0072] electrolyte The electrolyte may include a non-aqueous organic solvent and a lithium salt.

[0073] The non-aqueous organic solvent may constitute a medium for transporting ions participating in the electrochemical reaction of the battery.

[0074] The non-aqueous organic solvent may be or include at least one of a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent, or a combination thereof.

[0075] Carbonate solvents 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), and butylene carbonate (BC). Ester solvents may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonolactone, valerolactone, and caprolactone. Ether solvents may include at least one of dibutyl ether, tetraglyme, diglyme, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Ketone solvents may include cyclohexanone, and the like. The alcohol solvent may include at least one of ethanol, isopropanol, etc., and the aprotic solvent may include at least one of nitrile (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)), amide (such as dimethylformamide), dioxolane (such as 1,3-dioxolane, 1,4-dioxolane, etc.), sulfolane, etc.

[0076] The non-aqueous organic solvent may be used alone or in combination of two or more solvents.

[0077] When the carbonate-based solvent is used, the cyclic carbonate and the chain carbonate may be mixed, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0078] The lithium salt dissolved in the organic solvent is configured to supply lithium ions in the battery to enable basic operation of the rechargeable lithium battery and improve the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts may include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiN(C F 2x+1 SO2)(C y F 2y+2 SO2) (wherein x and y are integers in the range of 1 to 20), at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP) and lithium bis(oxalato)borate (LiBOB).

[0079] diaphragm Depending on the type of rechargeable lithium battery, a separator may be present between the positive electrode and the negative electrode. The separator may include polyethylene, polypropylene, polyvinylidene fluoride, or at least one of a multilayer or mixed multilayer structure of two or more layers thereof (e.g., a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0080] 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.

[0081] The porous substrate may be or include a polymer film formed from or including any one 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 (TEFLON) and polytetrafluoroethylene, or copolymers or mixtures of two or more thereof.

[0082] The organic material may include at least a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0083] The inorganic material may include inorganic particles such as or include at least one of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but is not limited thereto.

[0084] An organic material and an 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.

[0085] Examples and comparative examples of the present disclosure are described below. However, the following examples are merely examples of the present disclosure, and the present disclosure is not limited to the following examples.

[0086] Example 1 Silicon particles with an average particle size of 8 μm were mixed with stearic acid and ball-milled to an average particle size (D 50 ) is 100 nm, and the primary silicon particles are mixed with polysulfide to prepare a mixture. The mixture is mixed with ethanol and spray-dried to prepare an average particle size (D 50 ) are secondary particles having a particle size of 7 μm and including pores, wherein the weight ratio of sulfur to the secondary particles is designed to be 50 ppm.

[0087] The prepared secondary particles were mixed with petroleum pitch at a weight ratio of 60:40 and compression molded at a pressure of 10 MPa in a cold isostatic pressing method. Subsequently, the compression molded product was carbonized at 1,000°C under an N2 atmosphere.

[0088] Subsequently, the carbonized product was sieved with a sieve so that the span value of Equation 1 was 1.1, thereby preparing a carbonized product having an average particle size (D 50 ) is a silicon-carbon composite of secondary particles of 7 μm as the negative electrode active material. In the silicon-carbon composite, the average particle size of the primary silicon particles (D 50 ) was 100 nm, and a 30 nm thick carbon coating was formed on the secondary particles. Here, the content of the secondary particles was 60 wt % and the content of amorphous carbon was 40 wt % based on the total weight of the negative electrode active material. Furthermore, the D 10 、D 50 and D 90 The negative electrode active material was analyzed and the results are shown in Table 1 below.

[0089] In addition, when a cross-sectional image of the negative electrode active material photographed with CP-SEM was analyzed by the Image J program, it was found that the sphericity was 0.98.

[0090] The negative electrode active material prepared as the first negative electrode active material and natural graphite as the second negative electrode active material were mixed in a weight ratio of 90:10, and 97.5 wt % of the mixed negative electrode active material, 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.

[0091] The negative electrode active material layer slurry was coated on a Cu foil current collector, followed by drying and compression to form a negative electrode active material layer, thereby manufacturing a negative electrode.

[0092] A half-cell was fabricated using a conventional method using the negative electrode, a lithium metal counter electrode, and an electrolyte prepared by dissolving 1 M LiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate (3:7 by volume).

[0093] In addition, by using 96 wt% of LiNi as the positive electrode active material 0.88 Co0. 11 Al 0.01O2, 2 wt % of polyvinylidene fluoride as a binder, and 2 wt % of Ketjen black as a conductive material were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material layer slurry, and the positive electrode active material layer slurry was coated on an Al foil current collector, and then the positive electrode active material layer slurry was dried and compressed to form a positive electrode active material layer to manufacture a positive electrode.

[0094] Coin-type and pouch-type full cells were fabricated using conventional methods using the negative and positive electrodes along with an electrolyte solution prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate (3:7 by volume).

[0095] Example 2 A negative electrode, a half-cell, a coin-type full cell, and a pouch-type full cell were manufactured in substantially the same manner as in Example 1, except that a negative electrode active material having a span value of 1.5 and a sphericity of 0.92 was prepared by designing the weight ratio of sulfur to secondary particles to be 100 ppm and performing a screening process so that the span value of Equation 1 can be 1.5.

[0096] Example 3 Negative electrodes, half cells, coin-type full cells, and pouch-type full cells were manufactured in substantially the same manner as in Example 1, except that a negative electrode active material having a sphericity of 0.95 was prepared by designing a weight ratio of sulfur to secondary particles to be 150 ppm and performing a screening process so that the span value of Equation 1 could be 1.3.

[0097] Comparative Example 1 Negative electrodes, half cells, coin-type full cells, and pouch-type full cells were manufactured in substantially the same manner as in Example 1, except that a negative electrode active material having a sphericity of 0.95 was prepared by performing a screening process so that the span value of Equation 1 could be 1.0 without performing a compression molding process of a mixture of secondary particles and petroleum asphalt.

[0098] Comparative Example 2 Negative electrodes, half cells, coin-type full cells, and pouch-type full cells were manufactured in substantially the same manner as in Example 1, except that a screening process was performed so that the span value of Equation 1 could be 1.7 and a mixture of secondary particles and petroleum asphalt was cold isostatically pressed at a pressure of 35 MPa to prepare a negative electrode active material having a sphericity of 0.95.

[0099] Comparative Example 3 A negative electrode, a half cell, a coin-type full cell, and a pouch-type full cell were manufactured in substantially the same manner as in Example 1, except that a sieving process was performed so that the span value of Equation 1 could be 1.1 and a mixture of secondary particles and petroleum asphalt was cold isostatically pressed at a pressure of 150 MPa to prepare a negative electrode active material having a sphericity of 0.85 (i.e., not having a spherical shape).

[0100] Comparative Example 4 A negative electrode, a half-cell, a coin-type full cell, and a pouch-type full cell were manufactured in substantially the same manner as in Example 1, except that a negative electrode active material having a sphericity of 0.85 (i.e., not having a spherical shape) was prepared by performing a screening process so that the span value of Equation 1 could be 1.5 and cold isostatically pressing a mixture of secondary particles and petroleum asphalt at a pressure of 150 MPa.

[0101] Comparative Example 5 A negative electrode, a half cell, a coin-type full cell, and a pouch-type full cell were manufactured in substantially the same manner as in Example 1, except that polysulfide was not used to manufacture the core.

[0102] Comparative Example 6 Negative electrodes, half cells, coin-type full cells, and pouch-type full cells were manufactured in substantially the same manner as in Example 1, except that the weight ratio of sulfur to secondary particles was designed to be 300 ppm.

[0103] For ease of understanding, the designs of the negative electrode active materials of Examples and Comparative Examples are briefly shown in Table 1 below.

[0104] Table 1:

[0105] Evaluation Example 1: Evaluation of charge and discharge efficiency The half cells according to Examples 1 to 3 and Comparative Examples 1 to 6 were charged and discharged once at 0.1 C in the range of 0.01 V to 1.5 V to measure the charge capacity and discharge capacity, and the ratio of the charge capacity to the discharge capacity was calculated. The results are shown in Table 2 as the charge rate.

[0106] Evaluation Example 2: Evaluation of Cycle Life Characteristics Coin-type full batteries according to Examples 1 to 3 and Comparative Examples 1 to 6 were charged and discharged once at 0.1C, once at 0.2C, and then 500 times at 1C within the range of 2.5V to 4.2V. After the first charge / discharge cycle, the initial DC-IR (direct current internal resistance) was measured and is shown in Table 2 below. The charge and discharge and cutoff conditions are as follows.

[0107] Charging: Constant current - constant voltage, 4.2V / 0.01C cut-off Discharge: constant voltage, 2.5V cut-off The ratio of the discharge capacity at the 500th cycle to the discharge capacity at the 1st cycle was calculated, and the results are shown as cycle life in Table 2 below.

[0108] Evaluation Example 3: Evaluation of Expansion Performance The pouch-type full cells according to Examples 1 to 3 and Comparative Examples 1 to 6 were charged and discharged once at 0.1 C for formation, and then charged and discharged 25 times at 1 C. The ratio of the battery thickness at the 25th charge and discharge to the battery thickness after formation charge and discharge was calculated, and the results are provided as expansion ratios in Table 2 below.

[0109] Charging: Constant current - constant voltage, 4.2V / 0.01C cut-off Discharge: constant voltage, 2.5V cut-off In addition, the negative electrode active materials according to Examples 1 to 3 and Comparative Examples 1 to 6 were pulverized, collected, and the powder conductivity of the negative electrode active materials was measured using a powder resistor.

[0110] Table 2:

[0111] Referring to Table 2, Examples 1 to 3 having span values ​​within the range of 1.1 to 1.6 exhibited improved cycle-life characteristics and reduced expansion ratios compared to Comparative Examples 1 and 2 having span values ​​outside the range of 1.1 to 1.6 according to Equation 1.

[0112] In addition, compared with Comparative Examples 3 and 4 having sphericity outside the range of 0.9 to 1.0 according to Equation 2, Examples 1 to 3 having sphericity within the range of 0.9 to 1.0 according to Equation 2 exhibited improved cycle-life characteristics and reduced expansion ratio.

[0113] In addition, compared with Comparative Example 5 in which no sulfur was included in the negative electrode active material, Examples 1 to 3 including sulfur in the negative electrode active material showed desirable or improved trends in powder conductivity, charge rate, expansion rate, and cycle life characteristics.

[0114] In addition, compared with Comparative Example 6 in which the weight ratio of sulfur to secondary particles is outside the range of 20 ppm to 200 ppm, Examples 1 to 3 in which the weight ratio of sulfur to secondary particles is within the range of 20 ppm to 200 ppm show desired or improved trends in powder conductivity, DC resistance, charge rate, expansion ratio and cycle life characteristics.

[0115] Although example embodiments of the present disclosure have been described above, the present disclosure is not limited thereto and may be implemented with various modifications within the scope of the claims, the specification of the present disclosure, and the drawings, and these modifications also fall within the scope of the present disclosure.

[0116] Description of Reference Numerals: 100: Rechargeable lithium battery 10: Positive electrode 11: Positive electrode lead lug 12: Positive electrode terminal 20: Negative electrode 21: Negative electrode lead lug 22: Negative electrode terminal 30: Diaphragm 40: Electrode assembly 50: Shell 60: Sealing component 70: Electrode terminal 71: Positive electrode terminal 72: Negative electrode terminal.

Claims

1. A negative electrode active material, comprising: spherical cores, including silicon nanoparticles and sulfur; as well as an amorphous carbon coating on the surface of the spherical core, wherein the negative electrode active material has a span value defined in Equation 1 in the range of 1.1 to 1.6: Equation 1: Span value = (D 90 -D 10 ) / D 50 Where, in Equation 1, D 10 is the particle size of particles that account for 10% of the cumulative volume in the particle size distribution, D 50 is the particle size of particles with a cumulative volume of 50% by volume in the particle size distribution, D 90 It is the particle size at which 90% of the particles in the cumulative volume of the particle size distribution are concentrated.

2. The negative electrode active material according to claim 1, wherein The weight of sulfur is in the range of 20 ppm to 200 ppm based on the total weight of the spherical core.

3. The negative electrode active material according to claim 1, wherein Average particle size of sulfur D 50 In the range of 5nm to 15nm.

4. The negative electrode active material according to claim 1, wherein The negative electrode active material has a span value in the range of 1.1 to 1.

5.

5. The negative electrode active material according to claim 1, wherein: The negative electrode active material has a sphericity S according to Equation 2 in the range of 0.9 to 1.0: Equation 2: Sphericity S=4π×A / B 2 Wherein, in Equation 2, A is the area of ​​the negative electrode active material, and B is the perimeter of the shape of the negative electrode active material.

6. The negative electrode active material according to claim 5, wherein The negative electrode active material has a sphericity in the range of 0.92 to 0.

95.

7. The negative electrode active material according to claim 1, wherein The average particle size D of the spherical core 50 In the range of 10nm to 1000nm.

8. The negative electrode active material according to claim 1, wherein The thickness of the amorphous carbon coating is in the range of 1 nm to 2 μm.

9. The negative electrode active material according to claim 1, wherein The content of the spherical core is in the range of 55 wt % to 64 wt % based on the total 100 wt % of the negative electrode active material.

10. A method for preparing a negative electrode active material, the method comprising: (i) pulverizing silicon to produce nano-sized silicon particles; (ii) preparing a composition comprising the pulverized silicon particles, a sulfur precursor, and ethanol; (iii) spray drying the composition to produce a dried product; and (iv) forming an amorphous carbon coating using the dried product and an amorphous carbon precursor, wherein the negative electrode active material has a span value defined in Equation 1 in the range of 1.1 to 1.6: Equation 1: Span value = (D 90 -D 10 ) / D 50 Where, in Equation 1, D 10 is the particle size of particles that account for 10% of the cumulative volume in the particle size distribution, D 50 is the particle size of particles with a cumulative volume of 50% by volume in the particle size distribution, D 90 It is the particle size at which 90% of the particles in the cumulative volume of the particle size distribution are concentrated.

11. The method according to claim 10, wherein: The sulfur precursor includes at least one of sulfate and polysulfide.

12. The method according to claim 10, wherein: A weight ratio of the silicon particles to the sulfur precursor is in a range of 2:1 to 20:

1.

13. A negative electrode, comprising: negative electrode current collector; as well as Negative electrode active material layer, on the negative electrode current collector, The negative electrode active material layer comprises the negative electrode active material according to any one of claims 1 to 9.

14. A rechargeable lithium battery, comprising: The negative electrode according to claim 13; positive electrode; as well as electrolytes.

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