Negative electrode for rechargeable lithium battery and rechargeable lithium battery comprising the same

Abstract

Disclosed is a negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same. The negative electrode includes a current collector, a first active material layer including a first active material on the current collector, and a second active material layer including a second active material on the first active material layer. The first active material includes a Si-based active material and the first active material layer is a non-oriented layer, and the second active material is crystalline carbon and the second active material layer is an oriented layer; or the first active material is crystalline carbon and the first active material layer is an oriented layer, and the second active material includes a Si-based active material and the second active material layer is a non-oriented layer.

Description

Technical Field

[0001] A negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the negative electrode are disclosed. Background Technology

[0002] The increasing presence of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, has driven a growing demand for rechargeable batteries with relatively high capacity and light weight. Improving the performance of rechargeable lithium batteries can be advantageous.

[0003] A rechargeable lithium battery includes a positive electrode and a negative electrode containing active materials capable of inserting and deintercalating lithium ions, as well as an electrolyte, and generates electrical energy through redox reactions during the insertion / deintercalation of lithium ions at the positive and negative electrodes. Summary of the Invention

[0004] One or more example embodiments include a negative electrode for a rechargeable lithium battery that exhibits desired or improved high-rate cycle life characteristics.

[0005] Another example embodiment includes a rechargeable lithium battery that includes a negative electrode.

[0006] One or more example embodiments include a negative electrode for a rechargeable lithium battery, the negative electrode comprising: a current collector; a first active material layer on the current collector and including the first active material; and a second active material layer on the first active material layer and including the second active material. The first active material comprises a Si-based active material and the first active material layer is a non-oriented layer, and the second active material is crystalline carbon and the second active material layer is an oriented layer; or the first active material is crystalline carbon and the first active material layer is an oriented layer, and the second active material comprises a Si-based active material and the second active material layer is a non-oriented layer.

[0007] Another example embodiment includes a rechargeable lithium battery comprising: the negative electrode; the positive electrode; and a non-aqueous electrolyte.

[0008] The negative electrode for a rechargeable lithium battery according to one or more example embodiments can exhibit desired or improved high-rate cycle life characteristics. Attached Figure Description

[0009] Figure 1 The negative electrode for a rechargeable lithium battery is schematically shown according to one or more example embodiments.

[0010] Figures 2 to 5 This is a schematic cross-sectional view of a rechargeable lithium battery according to some example embodiments.

[0011] Figure 6 The graph shows the room temperature cycle life characteristics of the half-cells according to Example 1 and Example 2, as well as Comparative Example 1 and Comparative Example 2. Detailed Implementation

[0012] Example embodiments are described in detail below. However, these embodiments are exemplary, and this disclosure is not limited thereto; rather, it is defined by the scope of the appended claims.

[0013] As used herein, unless otherwise specifically defined, it is understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, the element may be “directly on” the other element, or there may be an intervening element present.

[0014] Unless otherwise stated in this specification, things expressed in the singular may also include the plural. In addition, unless otherwise stated, "A or B" may mean "including A, including B, or including both A and B".

[0015] As used herein, the expression “combination of them” can include mixtures, laminates, complexes, copolymers, alloys, blends, and reactants of components.

[0016] In this disclosure, unless otherwise defined, particle size can be the average particle size. Particle size represents the average particle size (D50) of particles that accumulate to approximately 50% of the volume in a particle size distribution. The average particle size (D50) can be measured by methods known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscopy (TEM) images or scanning electron microscopy (SEM) images. In some example embodiments, a dynamic light scattering measurement device can be used to perform data analysis and count the number of particles in each particle size range, thereby easily obtaining the average particle size (D50) value by calculation. Particle size can be measured by laser diffraction. Laser diffraction can be performed by distributing the particles to be measured in a distribution solvent and introducing the distribution solvent into a commercially available laser diffraction particle measurement device (e.g., the MT 3000 available from Microtrac), irradiating with ultrasound at a power of approximately 60 W at approximately 28 kHz, and calculating the average particle size (D50) based on a 50% standard of particle distribution in the measurement device.

[0017] In some example embodiments, the average particle size can be measured using various techniques, such as a particle size analyzer.

[0018] In some example embodiments, thickness can be measured using cross-sectional SEM or TEM images; however, the measurement technique is not limited to these, and any technique can be used to measure thickness, as long as it is applicable to related technologies. The thickness can be the average thickness.

[0019] As used herein, soft carbon refers to graphitizable carbon materials that are easily graphitized by heat treatment at high temperatures (e.g., about 2800°C), while hard carbon refers to non-graphitizable carbon materials that are substantially ungraphitizable or only slightly graphitized by heat treatment. The terms soft carbon and hard carbon may be well known in the relevant fields.

[0020] In some example embodiments, crystalline carbon and amorphous carbon can be distinguished by XRD measurements. Crystalline carbon includes natural graphite and synthetic graphite. Natural graphite can refer to graphite that is naturally produced by separating graphite from minerals, and when measured by XRD, the interplanar spacing (d002) of the (002) facets can be in the range of about 3.350 Å to about 3.360 Å. Synthetic graphite can refer to graphite manufactured by graphitization, and when (e.g., when) measured by XRD, the interplanar spacing (d002) of the (002) facets can be in the range of about 3.355 Å to 3.365 Å. Meanwhile, amorphous carbon can have an interplanar spacing (d002) of the (002) facets in the range of about 3.34 Å or less when measured by XRD. XRD can be measured using CuKα rays as the target ray with an X-ray diffractometer (e.g., product name: X'Pert, manufacturer: Malvern Panalytical) and by removing the monochromator to improve peak intensity resolution. Measurement conditions can be 2θ = 10° to 80°, scan speed (° / s) from 0.044 to 0.089, and step size (° / step) from 0.013 to 0.039.

[0021] In some example embodiments, the weight-average molecular weight can be measured using gel permeation chromatography (GPC).

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

[0023] A negative electrode for a rechargeable lithium battery according to one or more example embodiments includes: a current collector; a first active material layer disposed on the current collector and including the first active material; and a second active material layer disposed on the first active material layer and including the second active material.

[0024] In one or more example embodiments, the first active material layer may be a non-oriented layer, and the second active material layer may be an oriented layer. In another example embodiment, the first active material layer may be an oriented layer, and the second active material layer may be a non-oriented layer. For example, the lower layer may be a non-oriented layer, and the upper layer may be an oriented layer; in another example embodiment, the bottom layer may be an oriented layer, and the upper layer may be a non-oriented layer.

[0025] When the active material layer is a non-oriented layer, the active material includes Si-based active materials, and in other example embodiments, when the active material layer is an oriented layer, the active material is crystalline carbon.

[0026] In one or more example embodiments, when the first active material layer is a non-oriented layer and the first active material comprises a Si-based active material, and the second active material layer is an oriented layer and the second active material is crystalline carbon, lithium ions are rapidly inserted at the top during charging and discharging, while the silicon at the bottom reacts slowly, and high-rate characteristics such as high-rate cycle life characteristics can be improved. Therefore, this configuration is suitable.

[0027] For example, a negative electrode that includes a non-oriented layer (first active material layer) with Si-based active material as the first active material as the bottom and an oriented layer with crystalline carbon as the second active material as the top can exhibit desired or improved high rate performance.

[0028] It is suitable for the negative electrode active material in the alignment layer to consist of or include crystalline carbon, because crystalline carbon enhances the rapid insertion and extraction of lithium ions during charging and discharging through the physical effect of the negative electrode active material standing at a predetermined angle. When other active materials (such as silicon-based active materials or amorphous carbon) are included in the alignment layer, silicon-based active materials, which significantly degrade cycle life characteristics, react and degrade first, making silicon-based active materials unsuitable.

[0029] An oriented layer means that the included negative electrode active material stands substantially perpendicular to the current collector at a predetermined angle, while a non-oriented layer means that the included negative electrode active material is substantially horizontal and parallel to the current collector, or randomly oriented in various orientations.

[0030] Figure 1 The negative electrode 20 is schematically shown, in which the bottom (first active material layer 4) in contact with the current collector 2 is a non-oriented layer 4, and the top (second active material layer 6) is an oriented layer. Figure 1 As shown, in the non-oriented layer 4, the negative electrode active material 10a is positioned relative to the current collector 2 in a random orientation, such as in the horizontal direction or the vertical direction, and in the oriented layer 6, the negative electrode active material 10b exists in a substantially vertical direction relative to the surface of the current collector 2.

[0031] In one or more example embodiments, when X-ray diffraction is measured using CuKα rays, the peak intensity ratio (I002) of the peak intensity at the (002) plane of the alignment layer relative to the peak intensity at the (110) plane is... (002) / I (110) The peak intensity ratio (I) can be in the range of approximately 50 to approximately 200, approximately 100 to approximately 200, or approximately 110 to approximately 200. (002) / I (110) When the values ​​fall within the above range, the performance related to the fast response speed of the orientation layer can be further maximized.

[0032] In one or more example embodiments, when X-ray diffraction is measured using CuKα rays, the peak intensity ratio (I002) of the peak intensity at the (002) plane of the unoriented layer relative to the peak intensity at the (110) plane is... (002) / I (110) () is about 300 or greater, greater than about 300 and less than or equal to 500, or about 350 to about 500.

[0033] XRD can be measured using CuKα rays as the target ray with an X-ray diffractometer (e.g., product name: X'Pert, manufacturer: Malvern Panalytical) and by removing the monochromator to improve peak intensity resolution. Measurement conditions can be 2θ = 10° to 80°, scan speed (° / s) from 0.044 to 0.089, and step size (° / step) from 0.013 to 0.039.

[0034] X-ray diffraction analysis can also be performed on the negative electrode separated from the battery, which is charged once or five times at about 0.1C to about 0.5C and completely discharged at about 0.1C to about 0.5C to about 2.5V to about 3V. Therefore, the peak intensity ratio (I0) of the negative electrode according to one or more example embodiments is... (002) / I (110) It remains essentially unchanged after multiple charge and discharge cycles.

[0035] The peak intensity ratio of the first active material layer (I) (002) / I (110) The result was obtained by peeling off the second active material layer with tape after charging and discharging and performing X-ray diffraction analysis on the active material layer attached to the current collector.

[0036] In one or more example embodiments, the crystalline carbon may be or include artificial graphite, natural graphite, or a combination thereof. In another example embodiment, the crystalline carbon may be or include artificial graphite or a combination of artificial and natural graphite.

[0037] In one or more example embodiments, the negative electrode active material of the non-aligned layer is or includes a Si-based negative electrode active material. The Si-based negative electrode active material may be a silicon-carbon composite.

[0038] Silicon-carbon composites can be or include composites of silicon and amorphous carbon. For example, a silicon-carbon composite may include silicon particles and amorphous carbon coated on the surface of the silicon particles. In one or more example embodiments, the silicon-carbon composite may include secondary particles (cores) in which primary silicon particles aggregate and an amorphous carbon coating layer (shell) on the secondary particles. For example, amorphous carbon may also be present between the primary silicon particles to coat them. For example, the secondary particles may also be distributed within an amorphous carbon matrix. The primary silicon particles may be or include nano-silicon particles. Nano-silicon particles may have an average particle size in the range of about 10 nm to about 900 nm, about 10 nm to about 800 nm, about 10 nm to about 500 nm, about 10 nm to about 300 nm, or about 10 nm to about 200 nm. When the average particle size of the silicon particles is within the above ranges, substantial volume expansion during charging and discharging can be reduced or suppressed, and the breakage of conductive paths due to particle breakage during charging and discharging can be reduced or prevented. In one or more example embodiments, the particle size of the secondary silicon particles is not limited thereto.

[0039] The thickness of the amorphous carbon coating can be adjusted as desired, but for example, it can be in the range of about 2 nm to about 800 nm, about 5 nm to about 600 nm, about 10 nm to about 400 nm, or about 20 nm to about 200 nm. In one or more example embodiments, the thickness of the amorphous carbon coating can be measured by SEM or TEM images of the cross-section of the silicon-carbon composite, but the thickness measurement technique is not limited to this. Therefore, the thickness can be measured by any technique, as long as the thickness of the amorphous carbon coating is measured.

[0040] The average particle size of the silicon-carbon composite can be adjusted as desired, for example, in the range of about 30 μm or smaller, such as in the range of about 1 μm to about 30 μm, about 2 μm to about 25 μm, about 3 μm to about 20 μm, or about 5 μm to about 15 μm.

[0041] Based on a 100 wt% silicon-carbon composite, the amount of silicon particles can range from about 30 wt% to about 70 wt%, or from about 40 wt% to about 65 wt%. Based on a total silicon-carbon composite of 100 wt%, the amount of amorphous carbon can range from about 30 wt% to about 70 wt%, or from about 35 wt% to about 60 wt%. When the amounts of silicon particles and amorphous carbon are within these ranges, higher capacity can be achieved.

[0042] In another example embodiment, the silicon-carbon composite may further include crystalline carbon. In some example embodiments, the silicon-carbon composite may include a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating layer on the surface of the core. For example, the silicon-carbon composite may include a core and an amorphous carbon coating layer on the core, the core comprising secondary particles in which primary silicon particles and crystalline carbon aggregate. The amorphous carbon may be present between primary silicon particles, between crystalline carbon particles, or between primary silicon particles and crystalline carbon, allowing the amorphous carbon to substantially fill the spaces between primary silicon particles, between crystalline carbon particles, or between primary silicon particles and crystalline carbon.

[0043] When the silicon-carbon composite comprises silicon particles, crystalline carbon, and amorphous carbon, based on a total amount of 100 wt% for silicon particles, amorphous carbon, and crystalline carbon, the amount of crystalline carbon may be in the range of about 10 wt% to about 70 wt%, or about 20 wt% to about 60 wt%, the amount of amorphous carbon may be in the range of about 20 wt% to about 40 wt%, or about 20 wt% to about 30 wt%, and the amount of silicon particles may be in the range of about 10 wt% to about 70 wt%, or about 10 wt% to about 60 wt%.

[0044] In some example embodiments, the first or second active material layer, serving as a non-oriented layer, may further comprise a carbon-based negative electrode active material. The carbon-based negative electrode active material may be or includes crystalline carbon, carbon nanotubes, or a combination thereof, and in one or more example embodiments, may be or includes crystalline carbon and carbon nanotubes.

[0045] When the first or second active material layer, serving as a non-oriented layer, comprises a Si-based negative electrode active material and a carbon-based negative electrode active material, based on 100 wt% of the first or second active material layer, the amount of the Si-based negative electrode active material can range from about 2 wt% to about 20 wt%, and the amount of the carbon-based negative electrode active material can range from about 98 wt% to about 80 wt%. In one or more example embodiments, when the first or second active material layer, serving as a non-oriented layer, comprises a Si-based negative electrode active material, crystalline carbon, and carbon nanotubes, based on 100 wt% of the first or second active material layer, the amount of the Si-based negative electrode active material can range from about 2 wt% to about 20 wt%, the amount of crystalline carbon can range from about 97 wt% to about 79.9 wt%, and the amount of carbon nanotubes can range from about 0.01 wt% to about 0.1 wt%.

[0046] In one or more example embodiments, the ratio of the thickness of the first active material layer to the thickness of the second active material layer may be in the range of about 1:1 to about 1:2, or about 1:1 to about 1:1.4.

[0047] Apart from the active material, the first active material layer and the second active material layer have the same composition, as further provided below.

[0048] The first and second active material layers include an adhesive and may also include a conductive material.

[0049] In each of the first and second active material layers, the amount of active material can range from about 95 wt% to about 99 wt%, and the amount of binder can range from about 1 wt% to about 5 wt%. In another example embodiment, the amount of active material can range from about 91.5 wt% to about 99 wt%, the amount of binder can range from about 1 wt% to about 5 wt%, and the amount of conductive material can range from about 0.5 wt% to about 5 wt%.

[0050] The binder is configured to improve the adhesion properties between the negative electrode active material particles and between the negative electrode active material particles and the current collector. The binder may include non-aqueous binders, aqueous binders, dry binders, or combinations thereof.

[0051] In example embodiments, the non-aqueous adhesive may 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 combinations thereof.

[0052] Waterborne adhesives may include at least one of the following: styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0053] When using an aqueous binder as the negative electrode binder, cellulose compounds can also be used to provide viscosity. Cellulose compounds include one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts. The alkali metal can be or includes at least one of Na, K, and Li. Cellulose compounds can be configured as thickeners and can also be configured as aqueous binders.

[0054] Dry adhesives can be or include polymeric materials capable of being fibrous. For example, dry adhesives can be or include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, and combinations thereof.

[0055] The conductive material is included to provide electrode conductivity, and may include any electrically conductive material as the conductive material unless such electrically conductive material causes adverse chemical changes in the battery. Examples of conductive materials may be or include: carbon-based materials, such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metallic materials such as metal powders or metal fibers, including at least one of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0056] The negative electrode current collector may include at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, and combinations thereof.

[0057] Methods for preparing negative electrodes: The negative electrode according to one or more example embodiments can be prepared by the following steps: coating a first active material layer composition onto a current collector and drying the first active material layer composition to prepare a first active material layer; coating a second active material layer composition onto the first active material layer and drying the second active material layer composition to prepare a second active material layer; and compressing the negative electrode.

[0058] In one or more example embodiments, the prepared active material layer can become an oriented layer when a magnetic field is applied between coating and drying. For example, when coating a first active material layer composition, a magnetic field can be applied and the first active material layer composition can be dried, and the first active material layer can become an oriented layer. Optionally, when coating a second active material layer composition, a magnetic field is applied and the second active material layer composition is dried, and the second active material layer can be an oriented layer. According to one or more example embodiments, the first active material layer can be prepared without applying a magnetic field, and the second active material layer can be prepared with a magnetic field applied.

[0059] A magnetic field can be applied by placing a magnet below the current collector. For example, drying can be performed after placing the magnet below the current collector. Therefore, the crystalline carbon negative electrode active material included in the active material layer composition can stand at a predetermined or desired angle relative to the current collector (i.e., can be oriented), and thus the active material layer can be formed as an oriented layer.

[0060] In one or more exemplary embodiments, a first active material layer is prepared, i.e., a non-oriented layer is prepared, and then a second active material layer composition is coated and a magnet is disposed below a current collector. Subsequently, drying is performed to prepare a second active material layer as an oriented layer, followed by compression to prepare a negative electrode.

[0061] In the case where a first active material layer and a second active material layer are formed on both sides of the current collector, the first active material layer is formed on one side of the current collector, and another first active material layer is formed on the other side of the current collector (opposite to the side where the first active material layer is formed), and then a second active material layer is formed on each side of the two first active material layers. In another example embodiment, the first and second active material layers may be formed (e.g., sequentially) on one side of the current collector, and then the first and second active material layers may be formed (e.g., sequentially) on the other side of the current collector.

[0062] The magnet can have a magnetic field in the range of about 1000 Gauss to 10000 Gauss. Furthermore, the negative electrode active material composition can be coated onto the current collector and maintained for a duration in the range of about 3 seconds to about 15 seconds, i.e., exposed to the magnetic field for about 3 seconds to about 15 seconds. In one or more example embodiments, the magnetic field exposure time can be in the range of about 3 seconds to about 12 seconds. The resulting peak intensity ratio (I0) (002) / I (110) It can vary depending on the duration of exposure to the magnetic field.

[0063] The first and second active material layer compositions can be prepared by mixing a negative electrode active material, a binder, and a conductive material in a solvent. The viscosity of the first and second active material layer compositions can be adjusted to a value suitable for coating.

[0064] The solvent may be or include organic solvents (such as N-methylpyrrolidone) or water, and when an aqueous adhesive is included as the adhesive, the solvent may be water.

[0065] Rechargeable lithium batteries: Other example embodiments include a rechargeable lithium battery, which includes the negative electrode, the positive electrode, and a non-aqueous electrolyte.

[0066] Positive electrode: The positive electrode may include a current collector and a layer of positive electrode active material on the current collector. The layer of positive electrode active material includes a positive electrode active material and may also include a binder and / or a conductive material.

[0067] For example, the positive electrode may also include additives that can be configured as a sacrificial positive electrode.

[0068] Based on a 100wt% positive electrode active material layer, the amount of positive electrode active material can be in the range of about 90wt% to about 99.5wt%, and based on a 100wt% positive electrode active material layer, the amounts of binder and conductive material can be in the range of about 0.5wt% to about 5wt%, respectively.

[0069] The positive electrode active material may include compounds capable of reversibly inserting and deintercalating lithium (lithium-intercalating compounds). In some example embodiments, it may include at least one of a composite oxide of lithium and a metal (such as or including at least one of cobalt, manganese, nickel and combinations thereof).

[0070] The composite oxide can be or includes lithium transition metal composite oxides, and examples of lithium transition metal composite oxides can include at least one of lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free lithium nickel manganese oxides, and combinations thereof.

[0071] For example, it may include compounds represented by any of the following chemical formulas. Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NiG b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b Gb 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).

[0072] In the above chemical formulas, 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 It is or includes at least one of Mn, Al and combinations thereof.

[0073] For example, the positive electrode active material can be or includes a high-nickel positive electrode active material. Based on 100 mol% of metals other than lithium in the lithium transition metal complex oxide, the high-nickel positive electrode active material has a nickel content of greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%. High-nickel positive electrode active materials can achieve high capacity and can be applied to high-capacity, high-density rechargeable lithium batteries.

[0074] The binder is configured to improve the adhesion properties between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of binders may be, but are not limited to, at least one of the following: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin, nylon, etc.

[0075] The conductive material is included to provide electrode conductivity, and any suitable electrically conductive material may be included as the conductive material unless it causes adverse chemical changes in the battery. Examples of conductive materials may include: carbon-based materials, such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metallic materials such as metal powders or metal fibers, including at least one of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0076] The current collector may include, but is not limited to, Al.

[0077] Electrolytes: Electrolytes used in rechargeable lithium batteries may include non-aqueous organic solvents and lithium salts.

[0078] Non-aqueous organic solvents are constructed as media for transporting ions that participate in the electrochemical reactions of the battery.

[0079] Non-aqueous organic solvents may include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, and combinations thereof.

[0080] Carbonate solvents may include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC). Esters may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolactone, γ-butyrolactone, mevalonolactone, valproic acid lactone, and caprolactone. Ether solvents may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Ketone solvents may include cyclohexanone. Alcohol solvents may include at least one of ethanol and isopropanol. Aprotic solvents may include at least one of the following: nitriles, such as R-CN (wherein R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group, and may include double bonds, aromatic rings or ether bonds, etc.); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane, etc.

[0081] Organic solvents may be included alone or as a mixture of two or more solvents.

[0082] When carbonate solvents are included, cyclic carbonates and chain carbonates may be included together, and cyclic carbonates and chain carbonates may be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0083] The electrolyte may also include at least one of the following as an additive: vinyl ethyl carbonate, vinylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, and combinations thereof.

[0084] Lithium salts dissolved in organic solvents are configured to supply lithium ions to a battery for operating a rechargeable lithium battery and to improve lithium ion transport between the positive and negative electrodes. Examples of lithium salts include one or at least two supporting electrolyte salts, such as or including at least one of the following: 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 Lithium trifluoromethanesulfonate (SO2) (where x and y are integers in the range of about 1 to about 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0085] Diaphragm: Depending on the type of rechargeable lithium battery, a separator may be present between the positive and negative electrodes. The separator may include at least one of polyethylene, polypropylene, polyvinylidene fluoride, and multilayers having two or more layers (e.g., multilayers mixed together, such as polyethylene / polypropylene bilayer separators, polyethylene / polypropylene / polyethylene trilayer separators, polypropylene / polypropylene / polypropylene trilayer separators, etc.)).

[0086] The membrane may include a porous substrate and a coating layer comprising organic materials, inorganic materials, or combinations thereof on one or both surfaces of the porous substrate (e.g., one or two opposing surfaces).

[0087] The porous substrate may be or comprise a membrane formed of or comprising any polymer, such as polyolefins (e.g., polyethylene, polypropylene, etc.), polyesters (e.g., polyethylene terephthalate, polybutylene terephthalate, etc.), polyacetals, polyamides, polyimides, polycarbonates, polyetherketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (e.g., TEFLON).® ( ) or a copolymer or mixture of two or more of them.

[0088] Organic materials may include polymers such as polyvinylidene fluoride or (meth)acrylic acid polymers.

[0089] Inorganic materials may be or include inorganic particles, such as or including 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 are not limited thereto.

[0090] Organic and inorganic materials can be mixed in a coating layer, or a coating layer containing organic materials and a coating layer containing inorganic materials can be stacked together.

[0091] Based on their shape, rechargeable lithium batteries can be classified into cylindrical, prismatic, pouch-shaped, or coin-shaped batteries, etc. Figures 2 to 5 This is a schematic diagram illustrating 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. (See reference) Figures 2 to 5 The rechargeable lithium battery 100 may include an electrode assembly 40 and a housing 50 therein housing the electrode assembly. The electrode assembly 40 includes a separator 30 between a positive electrode 10 and a negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 2 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of the sealed housing 50. Figure 3 In this context, the rechargeable lithium battery 100 may include a positive electrode lead connector 11 and a positive terminal 12 connected to the positive electrode lead connector 11, a negative electrode lead connector 21 and a negative terminal 22 connected to the negative electrode lead connector 21. For example... Figure 5 As shown, the rechargeable lithium battery 100 may include electrode tabs 70 forming electrical paths for guiding current formed in the electrode assembly 40 to the outside of the battery 100, or as... Figure 4 The positive electrode terminal 71 and the negative electrode terminal 72 are shown.

[0092] As a non-limiting example, the rechargeable lithium battery according to the example embodiment can be used in, for example, automobiles, mobile phones and / or various types (or kinds) of electronic devices.

[0093] The following examples and comparative examples are provided to highlight the characteristics of one or more example embodiments; however, it is 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 being outside the scope of the example embodiments. Furthermore, it is understood that the example embodiments are not limited to the specific details described in the examples and comparative examples.

[0094] Example 1: A first active material layer slurry with a viscosity of 2500 centipoise (cps) to 3000 cps (at 25°C) was prepared by mixing 96 wt% of a mixture of artificial graphite and natural graphite (artificial graphite:natural graphite mixing ratio = 5:5 by weight), 2 wt% of styrene-butadiene rubber binder and 2 wt% of carboxymethyl cellulose thickener in an aqueous solvent.

[0095] A second active material layer slurry with a viscosity of 2500 cps to 3000 cps (at 25°C) was prepared by mixing 96 wt% of Si-type negative electrode active material including a silicon core and a soft carbon amorphous carbon layer on the surface of the core, 2 wt% of styrene-butadiene rubber binder and 2 wt% of carboxymethyl cellulose thickener in an aqueous solvent.

[0096] The first active material layer slurry is coated onto the Cu foil current collector, and then a magnet with a magnetic field of 3000 Gauss is placed below the current collector to expose the first active material layer slurry to the magnetic field for 10 seconds. The first active material layer slurry is then dried to form the first active material layer.

[0097] After removing the magnet, a second active material layer slurry is coated onto the first active material layer and dried to prepare the second active material layer. Subsequently, compression is performed to prepare the negative electrode. In the prepared negative electrode, the thickness of both the first and second active material layers is 100 μm.

[0098] A coin-shaped half-cell was fabricated using a negative electrode, a lithium metal counter electrode, and an electrolyte. 1.5 M LiPF6 was used as the electrolyte, dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (20:10:70 volume ratio).

[0099] Example 2: A first active material layer slurry with a viscosity of 2500 cps to 3000 cps (at 25°C) was prepared by mixing 96 wt% of Si-type negative electrode active material including a silicon core and a soft carbon amorphous carbon layer on the surface of the core, 2 wt% of styrene-butadiene rubber binder and 2 wt% of carboxymethyl cellulose thickener in an aqueous solvent.

[0100] A second active material layer slurry with a viscosity of 2500 cps to 3000 cps (at 25°C) was prepared by mixing 96 wt% of a mixture of artificial graphite and natural graphite (artificial graphite:natural graphite mixing ratio = 5:5 by weight), 2 wt% of styrene-butadiene rubber binder and 2 wt% of carboxymethyl cellulose thickener in an aqueous solvent.

[0101] A first active material layer slurry was coated onto a Cu foil and dried to prepare the first active material layer. A second active material layer slurry was coated onto the first active material layer. The resulting product was placed on a magnet with a magnetic field of 3000 Gauss to expose it to the magnetic field for 10 seconds, and then dried to prepare the second active material layer. Subsequently, the second active material layer was compressed to prepare the negative electrode. In the prepared negative electrode, the thickness of both the first and second active material layers was 100 μm.

[0102] A coin-shaped half-cell was fabricated using a negative electrode, a lithium metal counter electrode, and an electrolyte. 1.5 M LiPF6 was used as the electrolyte, dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (20:10:70 volume ratio).

[0103] Compare with Example 1: 96 wt% artificial graphite, 2 wt% styrene-butadiene rubber binder and 2 wt% carboxymethyl cellulose thickener were mixed in an aqueous solvent to prepare a first active material layer slurry with a viscosity of 2500 cps to 3000 cps (at 25°C).

[0104] A second active material layer slurry with a viscosity of 2500 cps to 3000 cps (at 25°C) was prepared by mixing 96 wt% of Si-type negative electrode active material including a silicon core and a soft carbon amorphous carbon layer on the surface of the core, 2 wt% of styrene-butadiene rubber binder and 2 wt% of carboxymethyl cellulose thickener in an aqueous solvent.

[0105] The first active material layer slurry is coated onto the Cu foil current collector, and then the Cu foil is placed on a magnet with a magnetic field of 3000 Gauss to expose the first active material layer slurry to the magnetic field for 10 seconds. The first active material layer slurry is then dried to form the first active material layer.

[0106] After removing the magnet, a second active material layer slurry is coated onto the first active material layer. A 3000 Gauss magnetic field is then repositioned below the current collector, exposing the second active material layer slurry to the magnetic field for 10 seconds. The slurry is then dried to form the second active material layer. In the prepared negative electrode, both the first and second active material layers have a thickness of 100 μm.

[0107] A coin-shaped half-cell was fabricated using a negative electrode, a lithium metal counter electrode, and an electrolyte. 1.5 M LiPF6 was used as the electrolyte, dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (20:10:70 volume ratio).

[0108] Compare with Example 2: A first active material layer slurry with a viscosity of 2500 cps to 3000 cps (at 25°C) was prepared by mixing 96 wt% of Si-type negative electrode active material including a silicon core and a soft carbon amorphous carbon layer on the surface of the core, 2 wt% of styrene-butadiene rubber binder and 2 wt% of carboxymethyl cellulose thickener in an aqueous solvent.

[0109] 96 wt% artificial graphite, 2 wt% styrene-butadiene rubber binder and 2 wt% carboxymethyl cellulose thickener were mixed in an aqueous solvent to prepare a second active material layer slurry with a viscosity of 2500 cps to 3000 cps (at 25°C).

[0110] The first active material layer slurry is coated onto the Cu foil current collector, and then the Cu foil is placed on a magnet with a magnetic field of 3000 Gauss to expose the first active material layer slurry to the magnetic field for 10 seconds. The first active material layer slurry is then dried to form the first active material layer.

[0111] After removing the magnet, a second active material layer slurry is coated onto the first active material layer. A 3000 Gauss magnetic field is then repositioned below the current collector, exposing the second active material layer slurry to the magnetic field for 10 seconds. The slurry is then dried to form the second active material layer. In the prepared negative electrode, both the first and second active material layers have a thickness of 100 μm.

[0112] A coin-shaped half-cell was fabricated using a negative electrode, a lithium metal counter electrode, and an electrolyte. 1.5 M LiPF6 was used as the electrolyte, dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (20:10:70 volume ratio).

[0113] Experimental Example 1) Evaluation of X-ray diffraction characteristics (XRD) The half-cells according to Examples 1 and 2, as well as Comparative Examples 1 and 2, were charged and discharged twice at 0.1C, and then fully discharged to 2.75V at 0.1C. The fully discharged cell was disassembled to obtain the negative electrode. For the negative electrode, X-ray diffraction was measured using an X'Pert XRD apparatus (available from Malvern Panalytical) with CuKα rays as the target ray and the monochromator removed to improve peak intensity resolution. Here, measurements were performed at 2θ = 10° to 80°, a scan rate (° / s) = 0.06436, and a step size of 0.026° / step.

[0114] In the measurement results, the peak intensity ratio (I002) of the peak intensity at the (002) plane of the second active material layer relative to the peak intensity at the (110) plane was obtained. (002) / I (110) The results are shown in Table 1 below. After removing the second active material layer using tape, the XRD of the first active material layer was measured under the same conditions. The peak intensity ratio (I002) of the peak intensity at the (002) plane of the first active material layer relative to the peak intensity at the (110) plane was obtained. (002) / I (110) The results are shown in Table 1 below.

[0115] Table 1:

[0116] As shown in Table 1, the first active material layer of Example 1 and the second active material layer of Example 2 are orientation layers. Both the first and second active material layers of Comparative Example 1 and Comparative Example 2 are orientation layers.

[0117] Experimental Example 2) Evaluation of Room Temperature Cycling Life Characteristics Batteries from Examples 1 and 2, as well as Comparative Examples 1 and 2, were charged at 0.2C and discharged at 0.2C for 7 cycles at room temperature (25°C) within a range of 1.2V to 0.05V. The ratio of the discharge capacity of each cycle to the discharge capacity of the first cycle was determined. The ratio of the discharge capacity of the battery from Example 1 in the 7th cycle to the discharge capacity of the first cycle was 104.5%, indicating that the room temperature cycle life characteristics of Example 1 are significantly improved compared to those of Comparative Example 1.

[0118] The results of Example 2 and Comparison Example 2 are shown below. Figure 6 In the middle. For example Figure 6 As shown, the room temperature cycle life characteristics of Example 2 are significantly improved compared to those of Comparative Example 2.

[0119] While this disclosure has been described in conjunction with what are now considered to be exemplary embodiments, it will be understood that the disclosure is not limited to the disclosed exemplary embodiments, but rather is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A negative electrode for a rechargeable lithium battery, the negative electrode comprising: current collector; A first active material layer is present on the current collector and includes the first active material. as well as A second active substance layer is formed on the first active substance layer and includes the second active substance. in: The first active material comprises a Si-based active material and the first active material layer is a non-oriented layer, and the second active material comprises crystalline carbon and the second active material layer is an oriented layer; or The first active material comprises crystalline carbon and the first active material layer is an oriented layer, and the second active material comprises a Si-based active material and the second active material layer is a non-oriented layer.

2. The negative electrode for a rechargeable lithium battery according to claim 1, wherein: The first active material includes a Si-based active material, and the first active material layer is a non-oriented layer; and The second active material comprises crystalline carbon, and the second active material layer is an orientation layer.

3. The negative electrode for a rechargeable lithium battery according to claim 1, wherein, The peak intensity ratio of the peak intensity at the (002) plane of the orientation layer to the peak intensity at the (110) plane, as measured by X-ray diffraction, is I. (002) / I (110) In the range of 50 to 200.

4. The negative electrode for a rechargeable lithium battery according to claim 1, wherein, The peak intensity ratio of the peak intensity at the (002) plane of the orientation layer to the peak intensity at the (110) plane, as measured by X-ray diffraction, is I. (002) / I (110) In the range of 100 to 200.

5. The negative electrode for a rechargeable lithium battery according to claim 1, wherein, The peak intensity ratio of the peak intensity at the (002) plane of the orientation layer to the peak intensity at the (110) plane, as measured by X-ray diffraction, is I. (002) / I (110) The range is between 110 and 200.

6. The negative electrode for a rechargeable lithium battery according to claim 1, wherein, The peak intensity ratio I of the peak intensity at the (002) plane of the unoriented layer relative to the peak intensity at the (110) plane, as measured by X-ray diffraction. (002) / I (110) 300 or more.

7. The negative electrode for a rechargeable lithium battery according to claim 1, wherein, The peak intensity ratio I of the peak intensity at the (002) plane of the unoriented layer relative to the peak intensity at the (110) plane, as measured by X-ray diffraction. (002) / I (110) Greater than 300 and less than or equal to 500.

8. The negative electrode for a rechargeable lithium battery according to claim 1, wherein, The peak intensity ratio I of the peak intensity at the (002) plane of the unoriented layer relative to the peak intensity at the (110) plane, as measured by X-ray diffraction. (002) / I (110) In the range of 350 to 500.

9. The negative electrode for a rechargeable lithium battery according to claim 1, wherein, Crystalline carbon includes at least one of artificial graphite, natural graphite, and combinations thereof.

10. The negative electrode for a rechargeable lithium battery according to claim 1, wherein, Si-based active materials include silicon-carbon composites.

11. The negative electrode for a rechargeable lithium battery according to claim 10, wherein, The silicon-carbon composite includes a composite of silicon and amorphous carbon.

12. The negative electrode for a rechargeable lithium battery according to claim 11, wherein, Silicon-amorphous carbon composites include: Silicon particles; and An amorphous carbon coating layer is applied to the surface of the silicon particles.

13. The negative electrode for a rechargeable lithium battery according to claim 10, wherein, The silicon-carbon composite also includes crystalline carbon.

14. The negative electrode for a rechargeable lithium battery according to claim 13, wherein, The silicon-carbon composite includes: The nucleus, including silicon particles and crystalline carbon; and An amorphous carbon coating is applied to the surface of the core.

15. The negative electrode for a rechargeable lithium battery according to claim 1, wherein, The non-oriented layer also includes carbon-based negative electrode active materials.

16. A rechargeable lithium battery, said rechargeable lithium battery comprising: The negative electrode according to any one of claims 1 to 15; Positive electrode; as well as Non-aqueous electrolyte.

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