Negative electrode for rechargeable lithium battery, wound-type electrode assembly including the same, and rechargeable lithium battery including the same

Abstract

The present disclosure relates to a negative electrode for a rechargeable lithium battery, a jelly-roll type electrode assembly including the same, and a rechargeable lithium battery including the same. The present disclosure relates to a negative electrode for a lithium battery, the negative electrode including a negative electrode current collector, a first negative electrode active material layer formed on a first surface of the negative electrode current collector, and a second negative electrode active material layer and a third negative electrode active material layer stacked on a second surface of the negative electrode current collector.

Description

[0001] This application claims priority to Korean Patent Application No. 10-2024-0175248, filed on November 29, 2024, with the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] This disclosure relates to a negative electrode for a rechargeable lithium battery, a wound electrode assembly including the negative electrode, and a rechargeable lithium battery including the negative electrode. More specifically, this disclosure relates to a negative electrode for a rechargeable lithium battery wherein a negative electrode active material layer is asymmetrically formed on two surfaces of a negative electrode current collector, a wound electrode assembly including the negative electrode, and a rechargeable lithium battery including the negative electrode. Background Technology

[0003] With the increasing prevalence of battery-powered electronic devices (such as mobile phones, laptops, and electric vehicles), the demand for rechargeable batteries with high energy density and large capacity is growing. Therefore, enhancing the performance of rechargeable lithium batteries can be advantageous.

[0004] Rechargeable lithium-ion batteries typically consist of a positive electrode, a negative electrode, and an electrolyte. Both the positive and negative electrodes contain active materials capable of inserting and deintercalating lithium ions. As lithium ions move between the electrodes during charging and discharging, electrical energy is generated through oxidation and reduction reactions. Summary of the Invention

[0005] Example embodiments of this disclosure include a negative electrode for a rechargeable lithium battery having desired or improved dynamic characteristics, high capacity, and desired or improved lifetime characteristics.

[0006] Example embodiments of this disclosure include a wound electrode assembly having desired or improved dynamic characteristics, high capacity, and desired or improved lifetime characteristics.

[0007] According to an example embodiment of this disclosure, the negative electrode for a rechargeable lithium battery may include a negative electrode current collector, a first negative electrode active material layer on a first surface of the negative electrode current collector, and a second and third negative electrode active material layer stacked (e.g., sequentially stacked) on a second surface of the negative electrode current collector. The first negative electrode active material layer may include a first carbon-based negative electrode active material and a first silicon-based negative electrode active material; the second negative electrode active material layer may include a second carbon-based negative electrode active material and a second silicon-based negative electrode active material; and the third negative electrode active material layer may include a third carbon-based negative electrode active material. The amount of the third carbon-based negative electrode active material in the third negative electrode active material layer may be greater than the amount of the first carbon-based negative electrode active material in the first negative electrode active material layer. The amount of the third carbon-based negative electrode active material in the third negative electrode active material layer may be greater than the amount of the second carbon-based negative electrode active material in the second negative electrode active material layer.

[0008] According to an example embodiment of this disclosure, a wound electrode assembly may include a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. The negative electrode may include a negative electrode current collector, a first negative electrode active material layer on a first surface of the negative electrode current collector, and a second and third negative electrode active material layer stacked (e.g., sequentially stacked) on a second surface of the negative electrode current collector. The first negative electrode active material layer may include a first carbon-based negative electrode active material and a first silicon-based negative electrode active material; the second negative electrode active material layer may include a second carbon-based negative electrode active material and a second silicon-based negative electrode active material; and the third negative electrode active material layer may include a third carbon-based negative electrode active material. The amount of the third carbon-based negative electrode active material in the third negative electrode active material layer may be greater than the amount of the first carbon-based negative electrode active material in the first negative electrode active material layer. The amount of the third carbon-based negative electrode active material in the third negative electrode active material layer may be greater than the amount of the second carbon-based negative electrode active material in the second negative electrode active material layer.

[0009] According to an example embodiment of this disclosure, a rechargeable lithium battery may include the wound electrode assembly. Attached Figure Description

[0010] Figure 1 The illustration shows a conceptual diagram of a rechargeable lithium battery according to an example embodiment of the present disclosure.

[0011] Figures 2 to 5 A simplified diagram illustrating a rechargeable lithium battery according to an example embodiment of the present disclosure is shown.

[0012] Figure 6 The illustration shows a cross-sectional view of a negative electrode according to an exemplary embodiment of the present disclosure.

[0013] Figure 7 The illustration shows a cross-sectional view of a wound electrode assembly according to an exemplary embodiment of the present disclosure.

[0014] Figure 8 The illustration shows a cross-sectional view of the negative electrode of a wound electrode assembly according to an exemplary embodiment of the present disclosure. Detailed Implementation

[0015] To provide a full understanding of the structure and effects of this disclosure, some exemplary embodiments have been described with reference to the accompanying drawings. However, this disclosure is not limited to the following exemplary embodiments and can be implemented in various forms. The exemplary embodiments are provided merely to illustrate this disclosure and to enable those skilled in the art to fully understand its scope.

[0016] In this specification, when an element is described as being "on" another element, the element may be directly on said other element, or one or more intervening elements may be present between them. In the accompanying drawings, certain thicknesses may be exaggerated to better illustrate technical details. Throughout the specification, the same reference numerals denote the same elements.

[0017] Cross-sectional views and / or plan views may be used to illustrate the exemplary embodiments described herein, which are presented as idealized examples of this disclosure. For clarity, the thickness of layers and regions in the figures may be exaggerated. The regions shown in the figures are for illustrative purposes and should not be construed as limiting the scope of this disclosure. Although terms such as “first,” “second,” and “third” may be used to describe various elements, these terms are used only for distinction and do not imply any particular order or hierarchy. The exemplary embodiments described and illustrated herein include complementary variations.

[0018] The terminology used in this specification is for illustrative purposes only and is not intended to limit this disclosure. Unless otherwise expressly stated, the singular form may also include the plural form. The term "comprising / including" and variations thereof do not exclude the presence or addition of one or more other components.

[0019] In this specification, the phrase “combinations thereof” may refer to mixtures, stacks, complexes, copolymers, alloys, blends, or reaction products.

[0020] The phrases “A or B”, “at least one of A and B (species / man)”, “at least one of A or B (species / man)”, “A, B or C”, “at least one of A, B and C (species / man)”, and “at least one of A, B or C (species / man)” include any one of the listed elements or all possible combinations thereof.

[0021] Unless otherwise specifically defined, the term "particle size" refers to the average particle size. Particle size can be expressed as the median particle size (D50) corresponding to the diameter of 50% by volume of particles in the cumulative particle size distribution. The average particle size (D50) can be measured using widely known methods, such as particle size analyzers, transmission electron microscopy (TEM) images, or scanning electron microscopy (SEM) images. Alternatively, dynamic light scattering can be used, in which particles within a size range are counted and analyzed to calculate the average particle size (D50). Additionally, laser scattering can be used, in which target particles are dispersed in a solvent, introduced into a laser scattering particle measurement device (e.g., the MT3000 from Microtrac), irradiated with 28 kHz and 60 W ultrasound, and subsequently analyzed to determine the D50 value based on the 50% cumulative particle size distribution.

[0022] In some example embodiments, the average particle size can be determined by randomly or arbitrarily selecting 100 or more particles from an electron microscope image. Alternatively, the average particle size can be measured using a particle size analyzer and defined as the diameter corresponding to 50% by volume in the cumulative particle size distribution.

[0023] When the terms “about” or “substantially” are used in conjunction with numerical values ​​in this specification, it is intended that the relevant numerical value includes 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%.

[0024] Figure 1 A simplified conceptual diagram illustrating a rechargeable lithium battery according to an example embodiment of the present disclosure is shown. (Refer to...) Figure 1 A rechargeable lithium battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0025] The positive electrode 10 and the negative electrode 20 can be separated from each other by a diaphragm 30. The diaphragm 30 can be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20 and the diaphragm 30 can be in contact with the electrolyte ELL. The positive electrode 10, the negative electrode 20 and the diaphragm 30 can be immersed in the electrolyte ELL.

[0026] The electrolyte ELL can be or includes a medium through which lithium ions transfer between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, lithium ions can move toward one of the positive electrode 10 and the negative electrode 20 through the separator 30.

[0027] Positive electrode 10 The positive electrode 10 for a rechargeable lithium battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 may include a positive electrode active material, and may also include a binder and / or a conductive material.

[0028] For example, the positive electrode 10 may also include additives that can constitute a sacrificial positive electrode.

[0029] The amount of positive electrode active material relative to 100 wt% of the positive electrode active material layer AML1 can range from about 90 wt% to about 99.5 wt%. The amount of each of the binder and conductive material relative to 100 wt% of the positive electrode active material layer AML1 can range from about 0.5 wt% to about 5 wt%.

[0030] The binder can improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector COL1. The binder may include, for example, at least one of 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 and nylon, but this disclosure is not limited thereto.

[0031] Conductive materials can provide conductivity to electrodes and any suitable conductive material that does not cause chemical changes in the battery can be used as a conductive material. For example, conductive materials may include: carbon-based materials, such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal powders or metal fibers, comprising one or more of copper, nickel, aluminum, and silver; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0032] Aluminum (Al) can be used as a current collector COL1, but this disclosure is not limited thereto.

[0033] Positive electrode active material The positive electrode active material in the positive electrode active material layer AML1 may include compounds capable of reversibly inserting and deintercalating lithium (e.g., lithiation intercalation compounds). For example, the positive electrode active material may include at least one composite oxide comprising lithium and a metal, wherein the metal is or includes at least one of cobalt, manganese, nickel, and combinations thereof.

[0034] Composite oxides may include lithium transition metal composite oxides, such as lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free lithium nickel manganese oxides, and combinations thereof, at least one of these.

[0035] For example, the positive electrode active material may include a compound represented by one of the following chemical formulas: Li a A 1- b X b O 2-c D c (Where, 0.90≤a≤1.8, 0≤b≤0.5 and 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (Where, 0.90≤a≤1.8, 0≤b≤0.5 and 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (Where, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5 and 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (Where, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5 and 0<α<2); Li a Ni b Co c L 1 d G e O2 (where 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5 and 0≤e≤0.1); Li a NiG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn2G bO4 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO4 (where 0.90 ≤ a ≤ 1.8 and 0 ≤ g ≤ 0.5); Li (3-f) Fe2(PO4)3 (where 0≤f≤2); Li a FePO4 (where 0.90≤a≤1.8).

[0036] In the above chemical formulas, A can be or include at least one of Ni, Co, Mn, and combinations thereof; X can be or include at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D can be or include at least one of O, F, S, P, and combinations thereof; G can be or include at least one of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; and L 1 It can be or include at least one of Mn, Al and combinations thereof.

[0037] For example, the positive electrode active material can be or includes a high-nickel positive electrode active material, wherein the nickel content of the high-nickel positive electrode active material is equal to or greater than about 80 mol%, equal to or greater than about 85 mol%, equal to or greater than about 90 mol%, equal to or greater than about 91 mol%, or equal to or greater than about 94 mol%, and equal to or less than about 99 mol%, relative to 100 mol% of metals other than lithium in the lithium transition metal complex oxide. High-nickel positive electrode active materials can achieve high capacity and therefore can be used in high-capacity and high-density rechargeable lithium batteries.

[0038] negative electrode 20 The negative electrode 20 for a rechargeable lithium battery may include a current collector COL2 and a negative electrode active material layer AML2 located on the current collector COL2. The negative electrode active material layer AML2 may include a negative electrode active material, and may also include a binder and / or a conductive material.

[0039] For example, the negative electrode active material layer AML2 may include a negative electrode active material in the range of about 90 wt% to about 99 wt%, a binder in the range of about 0.5 wt% to about 5 wt%, and a conductive material in the range of about 0 wt% to about 5 wt%.

[0040] The binder can improve the adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material and the current collector COL2. The binder can include non-aqueous binders, aqueous binders, dry binders, or combinations thereof.

[0041] Non-aqueous adhesives 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.

[0042] Waterborne adhesives may include at least one of styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomers, 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.

[0043] When using an aqueous binder as the negative electrode binder, it may also include a cellulose compound capable of providing viscosity. The cellulose compound may include one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts. The alkali metal may include at least one of Na, K, and Li.

[0044] Dry adhesives may include fibrillable polymeric materials, such as at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, and combinations thereof.

[0045] Conductive materials can provide conductivity to electrodes, and any suitable conductive material that does not cause chemical changes in the battery can be used as the conductive material. For example, conductive materials can include: carbon-based materials, such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal powders or metal fibers, including one or more of copper, nickel, aluminum, and silver; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0046] The current collector COL2 may include at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0047] Negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 may include at least one of the following: materials capable of reversibly inserting and de-intercalating lithium ions, lithium metal, lithium metal alloys, materials capable of doping and de-doping lithium, and transition metal oxides.

[0048] Materials capable of reversibly embedding and de-embedding lithium ions may include carbonaceous negative electrode active materials, for example, crystalline carbon, amorphous carbon, or a combination thereof. For example, crystalline carbon may include graphite, such as natural graphite or artificial graphite in an amorphous shape, sheet-like, flaky, spherical, or fibrous form, and amorphous carbon may include at least one of soft carbon, hard carbon, mesophase pitch carbon, and calcined coke.

[0049] Lithium metal alloys may include alloys of lithium and a metal that is or includes at least one of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0050] Materials capable of doping and de-doping lithium may include Si-based negative electrode active materials or Sn-based negative electrode active materials. Si-based negative electrode active materials may include silicon, silicon-carbon composites, SiO x (where 0 < x ≤ 2), Si-Q alloys (where Q is or includes at least one of alkali metals, alkaline earth metals, group 13 elements, group 14 elements (except Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), and at least one of their combinations. Sn-based negative electrode active materials may include at least one of Sn, SnO2, Sn-based alloys, and their combinations.

[0051] The silicon-carbon composite may be or include a composite of silicon and amorphous carbon. According to an exemplary embodiment, the silicon-carbon composite may have a structure in which amorphous carbon is coated on the surface of silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) in which primary silicon particles are assembled and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, and for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0052] The silicon-carbon composite may also include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and may also include an amorphous carbon coating on the surface of the core.

[0053] Si-based negative electrode active materials or Sn-based negative electrode active materials may be used in combination with carbonaceous negative electrode active materials.

[0054] Diaphragm 30 Depending on the type of rechargeable lithium battery, the separator 30 may be present between the positive electrode 10 and the negative electrode 20. The separator 30 may include one or more of polyethylene, polypropylene, and polyvinylidene fluoride, and may have multiple layers of them, such as at least one of polyethylene / polypropylene bilayer separator, polyethylene / polypropylene / polyethylene trilayer separator, and polypropylene / polypropylene / polypropylene trilayer separator.

[0055] The diaphragm 30 may include a porous substrate and a coating located on one side or opposite sides of the porous substrate, the coating including organic materials, inorganic materials or combinations thereof.

[0056] The porous substrate may be or include a polymer layer comprising one or more of the following: polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene; or the polymer layer may be or include copolymers or mixtures comprising two or more of the above materials.

[0057] Organic materials may include polyvinylidene fluoride copolymers or (meth)acrylic acid copolymers.

[0058] Inorganic materials may include inorganic particles such as or containing 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 this disclosure is not limited thereto.

[0059] Organic and inorganic materials can be mixed in a coating, or they can exist as a stack of coatings containing organic materials and coatings containing inorganic materials.

[0060] Electrolyte ELL Electrolytes (ELLs) used in rechargeable lithium batteries may include non-aqueous organic solvents and lithium salts.

[0061] Non-aqueous organic solvents can serve as media for transporting ions that participate in the electrochemical reactions of a battery.

[0062] 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.

[0063] 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), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC).

[0064] Ester solvents may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, valproic acid lactone, and caprolactone.

[0065] 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 ethanol or isopropanol. Aprotic solvents may include at least one of the following: nitriles, such as R-CN (wherein R is a hydrocarbon group having a C2 to C20 straight-chain structure, branched structure, or cyclic structure, and may include double bonds, aromatic rings, or ether groups); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane or 1,4-dioxolane; and sulfolane.

[0066] Non-aqueous organic solvents can be used alone or in mixtures of two or more solvents.

[0067] In addition, when using carbonate solvents, cyclic carbonates and chain carbonates can be mixed, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0068] Lithium salts can be or include materials that are dissolved in a non-aqueous organic solvent to form a lithium-ion supply source in the battery, and which contribute to the basic operation of the rechargeable lithium battery and facilitate the movement of lithium ions between the positive and negative electrodes. Lithium salts can include, for example, 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 At least one of the following: (SO2) (where x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0069] Rechargeable lithium batteries Based on their shape, rechargeable lithium batteries can be classified into cylindrical, prismatic, pouch, and coin-shaped types. Figures 2 to 5 The illustration shows a simplified diagram of a rechargeable lithium battery according to an example embodiment, wherein, Figure 2 A cylindrical battery is shown. Figure 3 A prismatic battery is shown, and Figure 4 and Figure 5 A pouch-type battery is shown. (See reference) Figures 2 to 4 The rechargeable lithium battery 100 may include an electrode assembly 40 and a housing 50, in which a separator 30 is located between a positive electrode 10 and a negative electrode 20, and the electrode assembly 40 is housed within the housing 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolyte (not shown). Figure 2 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of the sealed housing 50. Additionally, as... Figure 3 As shown, the rechargeable lithium battery 100 may include a positive electrode lead connector 11, a positive electrode terminal 12 connected to the positive electrode lead connector 11, a negative electrode lead connector 21, and a negative electrode terminal 22 connected to the negative electrode lead connector 21. Figure 4 and Figure 5 As shown, the rechargeable lithium battery 100 may include Figure 5 The electrode connector 70 shown, or Figure 4 The positive electrode terminal 71 and negative electrode terminal 72 shown form an electrical path for guiding the current generated in the electrode assembly 40 to the outside.

[0070] The lithium batteries according to exemplary embodiments of this disclosure can be used in, for example, vehicles, mobile phones and / or various types of electronic devices, but are not limited thereto.

[0071] Figure 6 The illustration shows a cross-sectional view of a negative electrode 20 according to an exemplary embodiment of the present disclosure. Figure 7 The illustration shows a cross-sectional view of a wound electrode assembly 40 according to an exemplary embodiment of the present disclosure. Figure 8 The illustration shows a cross-sectional view of a portion of a negative electrode 20 included in a wound electrode assembly according to an exemplary embodiment of the present disclosure. Hereinafter, reference is made to... Figures 6 to 8 The negative electrode 20, the wound electrode assembly 40 including the negative electrode 20, and the rechargeable lithium battery including the negative electrode 20 are described in more detail.

[0072] Reference Figure 6, the negative electrode 20 for a rechargeable lithium battery according to an exemplary embodiment of the present disclosure may include a negative electrode current collector COL2, an inner negative electrode active material layer INAL on a first surface of the negative electrode current collector COL2, and an outer negative electrode active material layer ONAL on a second surface of the negative electrode current collector COL2. The inner negative electrode active material layer INAL may include a first negative electrode active material layer NAL1. The outer negative electrode active material layer ONAL may include a second negative electrode active material layer NAL2 and a third negative electrode active material layer NAL3.

[0073] The ratio of the thickness of the first negative electrode active material layer NAL1 to the thickness of the second negative electrode active material layer NAL2 may be from about 2:1 to about 1:2. The ratio of the thickness of the third negative electrode active material layer NAL3 to the thickness of the second negative electrode active material layer NAL2 may be from about 2:1 to about 1:1.

[0074] The negative electrode 20 for a rechargeable lithium battery according to an exemplary embodiment of the present disclosure may enhance its dynamic characteristics and life characteristics by asymmetrically forming negative electrode active material layers on first and second surfaces facing each other. Hereinafter, each of the negative electrode active material layers NAL1, NAL2, and NAL3 formed on each surface of the negative electrode current collector COL2 will be described in more detail.

[0075] First negative electrode active material layer NAL1 The first negative electrode active material layer NAL1 may include a first carbon-based negative electrode active material CM1 and a first silicon-based negative electrode active material SM1.

[0076] The first carbon-based negative electrode active material CM1 may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. For example, crystalline carbon may include graphite, such as natural graphite or artificial graphite in an irregular shape, sheet, flake, spherical, or fibrous form, and amorphous carbon may include at least one of soft carbon, hard carbon, mesophase pitch carbon, and calcined coke.

[0077] The first silicon-based negative electrode active material SM1 may include silicon, a silicon-carbon composite, SiO x (where 0 < x ≤ 2), a Si-Q alloy (where Q is or includes at least one of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof), and a combination thereof.

[0078] Silicon-carbon composites can be or include composites of silicon and amorphous carbon. According to example embodiments, the silicon-carbon composite can have a structure in which amorphous carbon is coated on the surface of silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) in which primary silicon particles are assembled and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon may also be present between the primary silicon particles; for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed within an amorphous carbon matrix.

[0079] The weight ratio of the first carbon-based negative electrode active material CM1 to the first silicon-based negative electrode active material SM1 in the first negative electrode active material layer NAL1 can be in the range of about 60:40 to about 99:1, about 70:30 to about 98:2, or about 80:20 to about 98:2. When the amount of the first silicon-based negative electrode active material SM1 in the first negative electrode active material layer NAL1 is too small, the capacity of the negative electrode may decrease, and an N / P reversal phenomenon may occur. When the amount of the first silicon-based negative electrode active material SM1 in the first negative electrode active material layer NAL1 is too large, the volume change of the negative electrode active material layer during charging and discharging may increase, leading to a deterioration in the lifetime characteristics of the negative electrode 20. When the weight ratio of the first carbon-based negative electrode active material CM1 to the first silicon-based negative electrode active material SM1 meets the above ranges, the negative electrode 20 can exhibit the desired or improved lifetime characteristics and sufficient capacity.

[0080] The first negative electrode active material layer NAL1 may also include a conductive material. Any suitable conductive material that can provide conductivity to the electrode and does not cause chemical changes in the battery can be used as the conductive material. The conductive material may include, for example, at least one of carbon-based materials, metallic materials, conductive polymers, and combinations thereof.

[0081] The amount of conductive material in the first negative electrode active material layer NAL1 can be less than or equal to about 1 wt% relative to the total weight of the first negative electrode active material layer NAL1. For example, the amount of conductive material in the first negative electrode active material layer NAL1 can be in the range of about 0.01 wt% to about 1 wt%, about 0.02 wt% to about 0.5 wt%, or about 0.03 wt% to about 0.1 wt%. In an example embodiment, the amount of conductive material in the first negative electrode active material layer NAL1 can be about 0.05 wt% relative to the total weight of the first negative electrode active material layer NAL1.

[0082] In example embodiments, linear carbon-based conductive materials may be included as conductive materials. Linear conductive materials refer to conductive materials having a needle-like particle shape. For example, linear conductive materials may refer to conductive materials with an aspect ratio (length to diameter) in the range of about 10 or greater. The aspect ratio of linear carbon-based conductive materials may, for example, be in the range of about 20 to about 700, about 50 to about 600, about 60 to about 300, or about 100 to about 300. For example, linear carbon-based conductive materials may include at least one of carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCFs), carbon nanofibers (CNFs), and combinations thereof.

[0083] When the first negative electrode active material layer NAL1 comprises a linear carbon-based conductive material, its conductivity can be improved and its volume expansion can be mitigated. The first negative electrode active material layer NAL1 comprises a silicon-based negative electrode active material SM1, which has low conductivity and large volume changes during charging and discharging. Since linear carbon-based conductive materials can rapidly transport electrons through their needle-like structure, only a small amount of linear carbon-based conductive material is needed to significantly improve the conductivity of the negative electrode active material layer. Furthermore, the linear carbon-based conductive material can physically compensate for the expansion of silicon particles, thereby stabilizing the structure of the silicon particles and improving the lifetime of the negative electrode.

[0084] In addition to linear carbon-based conductive materials, the first negative electrode active material layer NAL1 may also include spherical carbon-based conductive materials. Spherical carbon-based conductive materials can refer to conductive materials having a generally spherical or elliptical particle shape. Spherical carbon-based conductive materials may include, for example, at least one of carbon black, graphite powder, acetylene black, and combinations thereof.

[0085] The first negative electrode active material layer NAL1 may also include a binder. The binder can improve the adhesion between the negative electrode active material particles and the adhesion of the negative electrode active material to the current collector COL2. The binder may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof. The amount of binder in the first negative electrode active material layer NAL1 relative to the total weight of NAL1 may range from about 0 wt% to about 10 wt%, from about 0.3 wt% to about 7 wt%, or from about 0.5 wt% to about 5 wt%.

[0086] Non-aqueous adhesives 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.

[0087] 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, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, epichlorohydrin, 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. When using the aqueous binder as the negative electrode binder, a cellulose compound capable of providing viscosity may be further included.

[0088] The dry binder may include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, and combinations thereof as polymer materials capable of fibrillating.

[0089] The second negative electrode active material layer NAL2 The second negative electrode active material layer NAL2 may include a second carbon-based negative electrode active material CM2 and a second silicon-based negative electrode active material SM2.

[0090] The second carbon-based negative electrode active material CM2 may be the same as or similar to the above-mentioned first carbon-based negative electrode active material CM1. For example, the second carbon-based negative electrode active material CM2 may include crystalline carbon, amorphous carbon, or combinations thereof. The second silicon-based negative electrode active material SM2 may be the same as or similar to the above-mentioned first silicon-based negative electrode active material SM1. For example, the second silicon-based negative electrode active material SM2 may include silicon, silicon-carbon composite, SiO x (0 < x ≤ 2) and at least one of combinations thereof.

[0091] The weight ratio of the second carbon-based negative electrode active material CM2 to the second silicon-based negative electrode active material SM2 in the second negative electrode active material layer NAL2 may be in the range of about 60:40 to about 99:1, about 70:30 to about 98:2, or about 80:20 to about 98:2.

[0092] The second negative electrode active material layer NAL2 may further include a conductive material. The conductive material may be the same as or similar to the conductive material included in the first negative electrode active material layer NAL1. For example, the conductive material may include a linear carbon-based conductive material.

[0093] The amount of conductive material in the second negative electrode active material layer NAL2 can be less than or equal to about 1 wt% relative to the total weight of the second negative electrode active material layer NAL2. For example, the amount of conductive material in the second negative electrode active material layer NAL2 can be in the range of about 0.01 wt% to about 1 wt%, about 0.02 wt% to about 0.5 wt%, or about 0.03 wt% to about 0.1 wt%. In an example embodiment, the amount of conductive material in the second negative electrode active material layer NAL2 can be about 0.05 wt% relative to the total weight of the second negative electrode active material layer NAL2.

[0094] In addition to the negative electrode active material and the conductive material, the second negative electrode active material layer NAL2 may also include a binder. The binder may be the same as or similar to the binder included in the first negative electrode active material layer NAL1. For example, the binder may include an aqueous binder, such as at least one of styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, and (meth)acrylate rubber, and may also include a cellulose compound capable of providing viscosity.

[0095] The second negative electrode active material layer NAL2 can have the same or similar composition as the first negative electrode active material layer NAL1. That is, each of the first negative electrode active material layer NAL1 and the second negative electrode active material layer NAL2 can include carbon-based and silicon-based negative electrode active materials as negative electrode active materials, and can include linear carbon-based conductive materials as conductive materials. When the first negative electrode active material layer NAL1 and the second negative electrode active material layer NAL2 have the same composition, a single nozzle can be used to form both the first and second negative electrode active material layers, thereby simplifying the manufacturing process of the negative electrode 20.

[0096] The third negative electrode active material layer NAL3 The third negative electrode active material layer NAL3 may include a third carbon-based negative electrode active material CM3. The third carbon-based negative electrode active material CM3 may be the same as or similar to the first carbon-based negative electrode active material CM1 described above. For example, the third carbon-based negative electrode active material CM3 may include crystalline carbon, amorphous carbon, or a combination thereof. In an example embodiment, the third carbon-based negative electrode active material may include graphite, such as shapeless, sheet-like, flake-like, spherical, or fibrous natural or artificial graphite.

[0097] The amount of the third carbon-based negative electrode active material CM3 in the third negative electrode active material layer NAL3 can be greater than the amount of the first carbon-based negative electrode active material CM1 included in the first negative electrode active material layer NAL1, and can be greater than the amount of the second carbon-based negative electrode active material CM2 included in the second negative electrode active material layer NAL2. Relative to the total weight of the third negative electrode active material layer NAL3, the amount of the third carbon-based negative electrode active material in the third negative electrode active material layer NAL3 can be greater than or equal to about 90 wt%. For example, the amount of the third carbon-based negative electrode active material can be in the range of about 90 wt% to about 99 wt% or about 95 wt% to about 98 wt%.

[0098] In addition to the third carbon-based negative electrode active material CM3, the third negative electrode active material layer NAL3 may also include a third silicon-based negative electrode active material. The third silicon-based negative electrode active material may be the same as or similar to the first silicon-based negative electrode active material SM1 described above. For example, the third silicon-based negative electrode active material may be or include at least one of silicon, silicon-carbon composites, and combinations thereof.

[0099] Relative to the total weight of the third negative electrode active material layer NAL3, the amount of the third silicon-based negative electrode active material in the third negative electrode active material layer NAL3 can be less than or equal to about 5 wt%. For example, the amount of the third silicon-based negative electrode active material can be in the range of about 0 wt% to about 5 wt% or about 0 wt% to about 2 wt%. The amount of the third silicon-based negative electrode active material in the third negative electrode active material layer NAL3 can be less than the amount of the first silicon-based negative electrode active material SM1 in the first negative electrode active material layer NAL1, and can be less than the amount of the second silicon-based negative electrode active material SM2 in the second negative electrode active material layer NAL2.

[0100] In other words, the third negative electrode active material layer NAL3 may contain a small amount of silicon-based negative electrode active material, or it may contain no silicon-based negative electrode active material at all. Since the third negative electrode active material layer NAL3 contains about 5 wt% or less of silicon-based negative electrode active material, it can exhibit reduced or minimal volume change during charging and discharging, thereby achieving the desired or improved lifetime characteristics.

[0101] The third negative electrode active material layer NAL3 may also include a conductive material. The conductive material may include, for example, carbon-based materials, metallic materials, conductive polymers, or combinations thereof.

[0102] The amount of conductive material in the third negative electrode active material layer NAL3 relative to the total weight can range from about 0 wt% to about 10 wt%, about 0.01 wt% to about 5 wt%, or about 0.05 wt% to about 3 wt%.

[0103] In addition to the negative electrode active material and the conductive material, the third negative electrode active material layer NAL3 may also include a binder. The binder may be the same as or similar to the binder included in the first negative electrode active material layer NAL1. For example, the binder may include an aqueous binder, such as at least one of styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, and (meth)acrylate rubber, and may also include a cellulose compound capable of providing viscosity.

[0104] Electrode assembly 40 Reference Figure 7 The electrode assembly according to the exemplary embodiments of this disclosure may be or include a wound electrode assembly 40. The wound electrode assembly 40 may refer to an electrode assembly in which a sheet-type negative electrode 20, a sheet-type positive electrode 10, and a sheet-type diaphragm 30 are wound in a spiral shape. For example, the wound electrode assembly 40 may include: a sheet-type negative electrode 20, in which a negative electrode active material layer is loaded on both sides of a negative electrode current collector; a sheet-type positive electrode 10, in which a positive electrode active material layer is loaded on both sides of a positive electrode current collector; and sheet-type diaphragms 32 and 34 disposed between the positive electrode 10 and the negative electrode 20.

[0105] The plate-type negative electrode 20 can be referenced above. Figure 6 The negative electrode described. In other words, the sheet-type negative electrode 20 may include a negative electrode current collector COL2, an inner negative electrode active material layer INAL on a first surface of the negative electrode current collector COL2, and an outer negative electrode active material layer ONAL on a second surface of the negative electrode current collector COL2. The inner negative electrode active material layer INAL may include a first negative electrode active material layer NAL1, and the outer negative electrode active material layer ONAL may include a second negative electrode active material layer NAL2 and a third negative electrode active material layer NAL3.

[0106] The sheet-type positive electrode 10 may include a positive electrode current collector COL1, an inner positive electrode active material layer ICAL on a first surface of the positive electrode current collector COL1, and an outer positive electrode active material layer OCAL on a second surface of the positive electrode current collector COL1.

[0107] The wound electrode assembly 40 may have a structure in which a unit structure consisting of an inner positive electrode active material layer ICAL / positive electrode current collector COL1 / outer positive electrode active material layer OCAL / first diaphragm 32 / inner negative electrode active material layer INAL / negative electrode current collector COL2 / outer negative electrode active material layer ONAL / and second diaphragm 34 is stacked (e.g., sequentially stacked) in such a way that the inner positive electrode active material layer ICAL and the inner negative electrode active material layer INAL face the winding center 80 of the wound electrode structure.

[0108] In the wound electrode assembly 40, the outer positive electrode active material layer OCAL can be positioned further away from the winding center 80 of the electrode assembly than the inner positive electrode active material layer ICAL. In one example embodiment, the loading level of the outer positive electrode active material layer OCAL can be equal to or greater than the loading level of the inner positive electrode active material layer ICAL. For example, the ratio of the loading level of the outer positive electrode active material layer OCAL to the loading level of the inner positive electrode active material layer ICAL can be about 1 to 4, about 1 to 3, or about 1.1 to 2.5. The loading level can refer to the amount of positive electrode active material loaded on the positive electrode and can represent the mass of positive electrode active material per unit area.

[0109] In the wound electrode assembly 40, the outer negative electrode active material layer ONAL can be positioned further away from the winding center 80 of the electrode assembly than the inner negative electrode active material layer INAL. That is, the second negative electrode active material layer NAL2 and the third negative electrode active material layer NAL3 can be positioned further away from the winding center 80 of the electrode assembly than the first negative electrode active material layer NAL1. The third negative electrode active material layer NAL3 can be positioned further away from the winding center 80 of the electrode assembly than the second negative electrode active material layer NAL2. In other words, the first negative electrode active material layer NAL1 can be positioned closest to the winding center 80, and the third negative electrode active material layer NAL3 can be positioned furthest from the winding center.

[0110] The first negative electrode active material layer NAL1 (i.e., the inner negative electrode active material layer INAL) located closest to the winding center 80 of the wound electrode assembly may require a relatively low load level while maintaining the desired or improved capacity.

[0111] The inner negative electrode active material layer INAL can face the outer positive electrode active material layer ONAL, with the first separator 32 situated between them. When the capacity of the inner negative electrode active material layer INAL is insufficient, an N / P reversal phenomenon may occur. When an N / P reversal phenomenon occurs, lithium dendrites may form, leading to a decrease in battery capacity and a reduction in battery thermal stability.

[0112] When increasing the loading level to enhance the capacity of the inner negative electrode active material layer INAL, the increased loading level can help reduce or prevent N / P reversal. However, increasing the loading level may also lead to increased ion diffusion distance and higher electron transport resistance within the negative electrode active material layer, which may degrade the dynamic characteristics of the negative electrode 20. This could result in a decrease in the battery's charging rate and a reduction in reaction uniformity.

[0113] Since the inner negative electrode active material layer INAL according to the example embodiment of this disclosure contains a certain amount of silicon as the negative electrode active material, the inner negative electrode active material layer INAL can exhibit the desired or improved capacity even at a relatively low load level.

[0114] For example, the inner negative electrode active material layer INAL may include a first carbon-based negative electrode active material and a first silicon-based negative electrode active material as negative electrode active materials. The weight ratio of the first carbon-based negative electrode active material to the first silicon-based negative electrode active material may be about 60:40 to about 99:1, about 70:30 to about 98:2, or about 80:20 to about 98:2.

[0115] Reference Figure 8 Because the inner negative electrode active material layer INAL is subjected to stronger compressive stress PR1 compared to the outer negative electrode active material layer ONAL, the volume change of silicon during charging and discharging can be reduced or suppressed even when a certain amount of silicon-based negative electrode active material is included.

[0116] In addition to the negative electrode active material, the inner negative electrode active material layer (INAL) may also include a conductive material. In an example embodiment, the conductive material may include a linear carbon-based conductive material. For example, the linear carbon-based conductive material may include at least one of carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCFs), carbon nanofibers (CNFs), and combinations thereof. The linear carbon-based conductive material can physically compensate for the expansion of silicon particles to stabilize the structure of the silicon particles and improve the lifetime of the negative electrode.

[0117] In example embodiments, the conductive material may include spherical carbon conductive materials and linear carbon conductive materials. Spherical carbon conductive materials may include, for example, carbon black, graphite powder, acetylene black, or combinations thereof.

[0118] Return to reference Figure 8 Positioned at a distance of 80° from the winding center of the wound electrode assembly (in Figure 7The third negative electrode active material layer (NAL3), being the furthest in the middle, experiences the lowest compressive stress (PR1) and the highest tensile stress (PR2), making it more susceptible to cracking and separation than the first and second negative electrode active material layers (NAL1 and NAL2). Since the third negative electrode active material layer (NAL3) contains only a small amount of silicon-based negative electrode active material or none at all, the risk of cracking and separation of the third negative electrode active material layer (NAL3) can be reduced, and its lifespan can be improved.

[0119] The amount of the third carbon-based negative electrode active material in the third negative electrode active material layer NAL3 can be greater than the amount of the first carbon-based negative electrode active material in the first negative electrode active material layer NAL1, and can be greater than the amount of the second carbon-based negative electrode active material in the second negative electrode active material layer NAL2. Relative to the total weight of the third negative electrode active material layer NAL3, the amount of the third carbon-based negative electrode active material in the third negative electrode active material layer NAL3 can be greater than or equal to about 90 wt%. For example, the amount of the third carbon-based negative electrode active material can be in the range of about 90 wt% to about 99 wt% or about 95 wt% to about 98 wt%.

[0120] In addition to the third carbon-based negative electrode active material, the third negative electrode active material layer NAL3 may also include a third silicon-based negative electrode active material. The amount of the third silicon-based negative electrode active material in the third negative electrode active material layer NAL3 may be less than or equal to about 5 wt% of the total weight of the third negative electrode active material layer NAL3. For example, the amount of the third silicon-based negative electrode active material may be in the range of about 0 wt% to about 5 wt% or about 0 wt% to about 2 wt%.

[0121] Return to reference Figure 8 The second negative electrode active material layer NAL2 can be disposed between the negative electrode current collector COL2 and the third negative electrode active material layer NAL3. The second negative electrode active material layer NAL2 may include a second carbon-based negative electrode active material and a second silicon-based negative electrode active material.

[0122] The weight ratio of the second carbon-based negative electrode active material to the second silicon-based negative electrode active material in the second negative electrode active material layer NAL2 can be in the range of about 60:40 to about 99:1, about 70:30 to about 98:2, or about 80:20 to about 98:2. Although the second negative electrode active material layer NAL2 is subjected to a smaller compressive stress PR1 than the first negative electrode active material layer NAL1, the second negative electrode active material layer NAL2 is sandwiched between the structurally stable negative electrode current collector COL2 and the third negative electrode active material layer NAL3. Therefore, even if the second negative electrode active material layer NAL2 contains a certain amount of silicon, the volume change caused by charging and discharging can be reduced or suppressed.

[0123] In addition to the negative electrode active material, the second negative electrode active material layer NAL2 may also include a conductive material. In an example embodiment, the conductive material may include a linear carbon-based conductive material. The linear carbon-based conductive material can physically compensate for the expansion of the silicon particles, thereby stabilizing the structure of the silicon particles and improving the lifetime of the negative electrode. In an example embodiment, the conductive material may also include a spherical carbon-based conductive material.

[0124] The thickness ratio of the first negative electrode active material layer NAL1 to the thickness of the second negative electrode active material layer NAL2 can be approximately 2:1 to approximately 1:2. The thickness ratio of the third negative electrode active material layer NAL3 to the thickness of the second negative electrode active material layer NAL2 can be approximately 1:1 to approximately 2:1.

[0125] When the thickness ratio of the second negative electrode active material layer NAL2 and the third negative electrode active material layer NAL3 meets the above-mentioned range, the outer negative electrode active material layer ONAL can exhibit the desired or improved capacity while reducing or suppressing volume expansion, thus demonstrating improved lifetime characteristics. When the thickness ratio of each negative electrode active material layer meets the aforementioned range, the inner negative electrode active material layer INAL can have a larger capacity than the outer negative electrode active material layer ONAL. By increasing the capacity of the inner negative electrode active material layer INAL in relation to the outer positive electrode active material layer OCAL, which has a high load level, a balance can be achieved between the positive and negative electrode active material layers, thereby improving rate performance and lifetime characteristics.

[0126] The negative electrode 20 included in the wound electrode assembly 40 according to the exemplary embodiments of the present disclosure can exhibit desired or improved capacity and desired or improved dynamic characteristics by including a first negative electrode active material layer NAL1 and a second negative electrode active material layer NAL2 having a relatively high content of silicon-based negative electrode active material. Furthermore, the negative electrode 20 according to the exemplary embodiments of the present disclosure can achieve desired or improved lifetime characteristics by including a third negative electrode active material layer NAL3 that does not contain silicon-based negative electrode active material or contains only a small amount of silicon-based negative electrode active material. That is, in the negative electrode 20 according to the exemplary embodiments of the present disclosure, different negative electrode active material layers can be formed on the two surfaces of the negative electrode current collector COL2, thereby improving or maximizing the charge-discharge characteristics, capacity characteristics, and lifetime characteristics of the negative electrode 20.

[0127] The following description focuses on some exemplary embodiments of this disclosure. These exemplary embodiments are provided to aid in understanding this disclosure and are not intended to limit its scope.

[0128] Example Preparation of the first negative electrode paste: Graphite powder was prepared as the active material for the carbon-based negative electrode, and a silicon-carbon composite (silicon to carbon weight ratio of 6:4) was prepared as the active material for the silicon-based negative electrode. The graphite powder and silicon-carbon composite were mixed at a weight ratio of 86:14 to prepare the negative electrode active material. A mixture obtained by mixing styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) at a weight ratio of 1.2:1 was prepared as a binder, and carbon nanotubes (CNTs) were prepared as a conductive material. The negative electrode active material, binder, and conductive material were mixed at a weight ratio of 97.75:2.20:0.05 to prepare the first negative electrode slurry.

[0129] Preparation of the second negative electrode paste: Graphite powder was prepared as the active material for the carbon-based negative electrode, and a silicon-carbon composite (silicon to carbon weight ratio of 6:4) was prepared as the active material for the silicon-based negative electrode. The graphite powder and silicon-carbon composite were mixed at a weight ratio of 99:1 to prepare the negative electrode active material. A mixture obtained by mixing styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) at a weight ratio of 1.2:1 was prepared as a binder, and carbon black was prepared as a conductive material. The negative electrode active material, binder, and conductive material were mixed at a weight ratio of 97.75:2.20:0.05 to prepare a second negative electrode slurry.

[0130] Manufacturing of the negative electrode: The first negative electrode paste was simultaneously coated onto both surfaces (upper and lower surfaces) of a 10 μm thick copper foil current collector to form a first negative electrode active material layer and a second negative electrode active material layer. The coated electrode plate was dried at 100°C for more than 1 hour. The coating was performed with a thickness ratio of 1:1 between the first negative electrode active material layer (formed on the lower surface) and the second negative electrode active material layer (formed on the upper surface).

[0131] A second negative electrode slurry is coated onto the second negative electrode active material layer to form a third negative electrode active material layer. The coated electrode plate is dried at 100°C for more than 1 hour, and then pressed to form the final negative electrode. In the final negative electrode, the thickness ratio of the third negative electrode active material layer to the thickness of the second negative electrode active material layer is 2:1.

[0132] Manufacturing of the positive electrode: Add positive electrode active material (LiNi) 0.6 Co 0.2 Mn 0.2 The positive electrode slurry is prepared by mixing O2, carbon-based conductive material (Super P), and PVDF (polyvinylidene fluoride) binder solution. The mixing ratio of the positive electrode active material, conductive material, and binder in the positive electrode slurry is 98:1:1 by weight.

[0133] The positive electrode paste was coated onto both surfaces (upper and lower surfaces) of an aluminum current collector with a thickness of 12 μm, dried at 120°C for more than 1 hour, and then pressed to form a positive electrode in which an inner positive electrode active material layer and an outer positive electrode active material layer are formed. The coating was performed with a thickness ratio of 1:1.6 between the inner positive electrode active material layer (formed on the lower surface) and the outer positive electrode active material layer (formed on the upper surface).

[0134] Manufacturing of wound electrode assemblies: A 20 μm thick polyethylene (PE) membrane (manufactured by Celgard) is prepared as the first separator, and a 12 μm thick polyethylene (PE) membrane (manufactured by Celgard) is prepared as the second separator. The first separator is disposed between the outer positive electrode active material layer and the first negative electrode active material layer, and the second separator is disposed on the outer surface of the third negative electrode active material layer. Subsequently, the obtained positive electrode, the first separator, the obtained negative electrode, and the second separator are arranged in the following order: inner positive electrode active material layer / Al current collector / outer positive electrode active material layer / first separator / first negative electrode active material layer / Cu current collector / second negative electrode active material layer / third negative electrode active material layer / second separator. This structure is wound to form a core-type electrode assembly.

[0135] Manufacturing of rechargeable lithium batteries: The manufactured electrode assembly is housed in a cylindrical casing, and an electrolyte solution is injected to form a cylindrical lithium battery. The electrolyte solution is prepared by dissolving 1.5M LiPF6 lithium salt in a solvent mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 2:1:7.

[0136] Comparative Examples Preparation of negative electrode paste: Graphite powder was prepared as the active material for the carbon-based negative electrode, and a silicon-carbon composite (silicon to carbon weight ratio of 6:4) was also prepared as the active material for the silicon-based negative electrode. The graphite powder and silicon-carbon composite were mixed at a weight ratio of 92:8 to prepare the negative electrode active material. A mixture obtained by mixing styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) at a weight ratio of 1.2:1 was prepared as a binder, and carbon nanotubes (CNTs) were prepared as the conductive material. The negative electrode active material, binder, and conductive material were mixed at a weight ratio of 97.75:2.20:0.05 to prepare the negative electrode slurry.

[0137] Manufacturing of the negative electrode: The prepared negative electrode slurry was simultaneously coated onto both surfaces (upper and lower surfaces) of a 10 μm thick copper foil current collector to form a first and a second negative electrode active material layer. The coated electrode plate was dried at 100°C for more than 1 hour. Coating was performed with a thickness ratio of 1:1 between the first negative electrode active material layer (formed on the lower surface) and the second negative electrode active material layer (formed on the upper surface). The dried plate was then pressed to form the final negative electrode.

[0138] Manufacturing of rechargeable lithium batteries: The positive electrode, the wound electrode assembly, and the rechargeable lithium battery were manufactured in the same manner as in Example 1.

[0139] Evaluation Example 1 The following methods were used to evaluate the lifespan characteristics of the lithium batteries manufactured in the examples and comparative examples.

[0140] The rechargeable lithium batteries manufactured in the examples and comparative examples were each charged at 25°C with a constant current at a rate of 0.1C until the voltage reached 4.2V (relative to Li). Subsequently, charging continued in constant voltage mode, maintaining 4.2V while applying a cutoff current at a rate of 0.05C. Next, the batteries were discharged at a constant current at a rate of 0.1C until the voltage reached 2.5V (relative to Li) (formation cycle). The rechargeable lithium batteries that had undergone the formation process were charged at 25°C with a constant current at a rate of 0.33C until the voltage reached 4.2V (relative to Li). Subsequently, the batteries were discharged at a constant current at a rate of 1.0C until the voltage reached 2.5V (relative to Li), and this cycle was repeated under the same conditions until the 100th cycle (100 repetitions). A 10-minute rest period was applied after each charge / discharge cycle. The results of the charge / discharge experiments are shown in Table 1 below. The capacity retention at the 100th cycle is defined by Equation 1 below.

[0141] Equation 1: Capacity retention rate (%) = (Discharge capacity in the 100th cycle / Discharge capacity in the 1st cycle) × 100.

[0142] Table 1:

[0143] Referring to Table 1, it can be observed that the lithium battery according to the embodiment exhibits superior lifespan characteristics compared to the lithium battery according to the comparative embodiment.

[0144] Evaluation Example 2 The rate characteristics of the lithium batteries manufactured in the examples and comparative examples were evaluated using the following methods.

[0145] The rechargeable lithium batteries manufactured in the examples and comparative examples were each charged at 25°C with a constant current at a rate of 0.1C until the voltage reached 4.2V (relative to Li). Subsequently, charging continued in constant voltage mode, maintaining 4.2V, while a cutoff current at a rate of 0.05C was applied. Next, the batteries were discharged at a constant current at a rate of 0.1C until the voltage reached 2.5V (relative to Li) (formation cycle). The rechargeable lithium batteries that had undergone the formation process were charged and discharged once at each C-rate of 0.2C, 0.5C, 1C, 1.5C, and 2C at 25°C (charging voltage: 4.2V, discharging voltage: 2.5V). The discharge capacity at each C-rate was measured. Rate characteristics were evaluated according to Equation 2 below, and the results are shown in Table 2 below.

[0146] Equation 2: Rate characteristic (%) = (Discharge capacity at each C rate / Discharge capacity at 0.2C rate) × 100.

[0147] Table 2:

[0148] Referring to Table 2, it can be observed that the lithium batteries according to the embodiments exhibit desired or improved capacity retention characteristics, which are particularly desirable or improved at high rates.

[0149] By including layers of negative electrode active material with an asymmetric structure on both surfaces of the negative electrode current collector, the negative electrode for a rechargeable lithium battery according to this disclosure can have improved dynamic and lifetime characteristics. The rechargeable lithium battery according to this disclosure can have desired or improved dynamic and lifetime characteristics.

[0150] While this disclosure has been described with reference to exemplary embodiments, it should be understood that these exemplary embodiments are provided for illustrative purposes only and do not limit the scope of this disclosure. Various modifications and equivalent arrangements may be made without departing from the spirit and scope of the appended claims. Therefore, the described embodiments should be considered as examples and not as limitations on this disclosure.

Claims

1. A negative electrode for a rechargeable lithium battery, the negative electrode comprising: Negative electrode current collector; The first negative electrode active material layer is on the first surface of the negative electrode current collector; as well as The second and third negative electrode active material layers are stacked on the second surface of the negative electrode current collector. The first negative electrode active material layer includes a first carbon-based negative electrode active material and a first silicon-based negative electrode active material. The second negative electrode active material layer includes a second carbon-based negative electrode active material and a second silicon-based negative electrode active material. The third negative electrode active material layer includes a third carbon-based negative electrode active material. Wherein, the amount of the third carbon-based negative electrode active material in the third negative electrode active material layer is greater than the amount of the first carbon-based negative electrode active material in the first negative electrode active material layer, and The amount of the third carbon-based negative electrode active material in the third negative electrode active material layer is greater than the amount of the second carbon-based negative electrode active material in the second negative electrode active material layer.

2. The negative electrode according to claim 1, in, The amount of the third carbon-based negative electrode active material in the third negative electrode active material layer is in the range of 90 wt% to 99 wt%.

3. The negative electrode according to claim 1, in, The third negative electrode active material layer further includes a third silicon-based negative electrode active material, and The amount of the third silicon-based negative electrode active material in the third negative electrode active material layer is 2 wt% or less.

4. The negative electrode according to claim 1, in, The weight ratio of the first carbon-based negative electrode active material to the first silicon-based negative electrode active material in the first negative electrode active material layer is in the range of 80:20 to 98:

2.

5. The negative electrode according to claim 1, in, The weight ratio of the second carbon-based negative electrode active material to the second silicon-based negative electrode active material in the second negative electrode active material layer is in the range of 80:20 to 98:

2.

6. The negative electrode according to claim 1, in, Each of the first negative electrode active material layer and the second negative electrode active material layer further includes a conductive material, and The conductive material includes linear carbon-based conductive materials.

7. The negative electrode according to claim 6, in, The amount of the linear carbon-based conductive material in the first negative electrode active material layer is in the range of 0.01 wt% to 1 wt%, and The amount of the linear carbon-based conductive material in the second negative electrode active material layer is in the range of 0.01 wt% to 1 wt%.

8. The negative electrode according to claim 1, in, The ratio of the thickness of the first negative electrode active material layer to the thickness of the second negative electrode active material layer is in the range of 2:1 to 1:

2.

9. The negative electrode according to claim 1, in, The ratio of the thickness of the third negative electrode active material layer to the thickness of the second negative electrode active material layer is in the range of 2:1 to 1:

1.

10. The negative electrode according to claim 1, in, At least one of the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer further includes a binder.

11. A wound electrode assembly, the wound electrode assembly comprising: Positive electrode, negative electrode, and a membrane between the positive electrode and the negative electrode. The negative electrode comprises: a negative electrode current collector; a first negative electrode active material layer on a first surface of the negative electrode current collector; and a second negative electrode active material layer and a third negative electrode active material layer, stacked on a second surface of the negative electrode current collector. The first negative electrode active material layer includes a first carbon-based negative electrode active material and a first silicon-based negative electrode active material. The second negative electrode active material layer includes a second carbon-based negative electrode active material and a second silicon-based negative electrode active material. The third negative electrode active material layer includes a third carbon-based negative electrode active material. Wherein, the amount of the third carbon-based negative electrode active material in the third negative electrode active material layer is greater than the amount of the first carbon-based negative electrode active material in the first negative electrode active material layer, and The amount of the third carbon-based negative electrode active material in the third negative electrode active material layer is greater than the amount of the second carbon-based negative electrode active material in the second negative electrode active material layer.

12. The wound electrode assembly according to claim 11, in, The amount of the third carbon-based negative electrode active material in the third negative electrode active material layer is in the range of 90 wt% to 99 wt%.

13. The wound electrode assembly according to claim 11, in, The third negative electrode active material layer further includes a third silicon-based negative electrode active material, and The amount of the third silicon-based negative electrode active material in the third negative electrode active material layer is 2 wt% or less.

14. The wound electrode assembly according to claim 11, in, The weight ratio of the first carbon-based negative electrode active material to the first silicon-based negative electrode active material in the first negative electrode active material layer is in the range of 80:20 to 98:2, and The weight ratio of the second carbon-based negative electrode active material to the second silicon-based negative electrode active material in the second negative electrode active material layer is in the range of 80:20 to 98:

2.

15. The wound electrode assembly according to claim 11, in, At least one of the first negative electrode active material layer and the second negative electrode active material layer further includes a conductive material, and The conductive material includes linear carbon-based conductive materials.

16. The wound electrode assembly according to claim 11, in, The ratio of the thickness of the first negative electrode active material layer to the thickness of the second negative electrode active material layer is in the range of 2:1 to 1:2, and The ratio of the thickness of the third negative electrode active material layer to the thickness of the second negative electrode active material layer is in the range of 2:1 to 1:

1.

17. The wound electrode assembly according to claim 11, in, The third negative electrode active material layer is positioned further away from the winding center of the electrode assembly than the second negative electrode active material layer, and The second negative electrode active material layer is positioned further away from the winding center of the electrode assembly than the first negative electrode active material layer.

18. The wound electrode assembly according to claim 11, in, The positive electrode includes: Positive electrode current collector; An inner positive electrode active material layer is present on the first surface of the positive electrode current collector; and An external positive electrode active material layer is located on the second surface of the positive electrode current collector. The outer positive electrode active material layer is positioned further away from the winding center of the electrode assembly than the inner positive electrode active material layer.

19. The wound electrode assembly according to claim 17, in, The ratio of the loading level of the outer positive electrode active material layer to the loading level of the inner positive electrode active material layer is in the range of 1 to 4.

20. A rechargeable lithium battery, the rechargeable lithium battery comprising a wound electrode assembly according to any one of claims 11 to 19.

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