Negative electrode for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

Disclosed are a negative electrode and a rechargeable lithium battery including the same. The negative electrode comprises a negative electrode current collector; and a negative electrode active material layer on the negative electrode current collector. The negative electrode active material layer includes a first active material layer, a second active material layer, and a third active material layer sequentially stacked on the negative electrode current collector. The first active material layer, the second active material layer, and the third active material layer include first crystalline carbon, second crystalline carbon, and third crystalline carbon, respectively. The first active material layer is a random alignment layer having a divergence (DD) value of about 5 to about 20. The third active material layer may be an alignment layer having a DD value of about 20 to about 60.

Description

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0050838, filed on April 16, 2024, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] Embodiments of the disclosure relate to a negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same, for example, to a multi-layered negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same. BACKGROUND

[0003] Recently, as electronic devices using batteries, such as mobile phones, laptop computers, and electric vehicles, rapidly spread, interest in rechargeable batteries having high energy density and high capacity has rapidly increased. Accordingly, intensive research has been conducted to improve the performance of rechargeable lithium batteries.

[0004] A rechargeable lithium battery includes a positive electrode, a negative electrode, and an electrolyte, the positive electrode and the negative electrode including active materials in which lithium ions can be intercalated and deintercalated, and generating electric energy caused by oxidation and reduction reactions when intercalating and deintercalating lithium ions. SUMMARY

[0005] Embodiments of the disclosure provide a negative electrode for a rechargeable lithium battery having large capacity, high charge / discharge efficiency, and stability.

[0006] Embodiments of the disclosure provide a rechargeable lithium battery having large capacity, high charge / discharge efficiency, and stability.

[0007] According to embodiments of the disclosure, a negative electrode for a rechargeable lithium battery can include a negative electrode current collector; and a negative electrode active material layer on the negative electrode current collector. The negative electrode active material layer can include a first active material layer, a second active material layer, and a third active material layer sequentially stacked on the negative electrode current collector. The first active material layer, the second active material layer, and the third active material layer can include first crystalline carbon, second crystalline carbon, and third crystalline carbon, respectively. The first active material layer can be a random orientation layer having a divergence degree (DD) value defined by Equation 1 of about 5 to about 20. The third active material layer can be an orientation layer having a DD value defined by Equation 1 of about 20 to about 60.

[0008] Equation 1 DD (Divergence Degree) = (I a / I 总 ) × 100 In Equation 1, I aThe I can be a sum of peak intensities at non-plane angles in an X-ray diffraction (XRD) measurement using Cu Kα rays, and I 总 The I can be a sum of peak intensities at all angles in an XRD measurement using Cu Kα rays.

[0009] According to an embodiment of the disclosure, a negative electrode for a rechargeable lithium battery can include: a negative electrode current collector; and a negative electrode active material layer on the negative electrode current collector. The negative electrode active material layer can include a first active material layer, a second active material layer, and a third active material layer sequentially stacked on the negative electrode current collector. The first active material layer, the second active material layer, and the third active material layer can include first crystalline carbon, second crystalline carbon, and third crystalline carbon, respectively. A ratio of a DD value of the third active material layer defined by Equation 1 to a DD value of the first active material layer defined by Equation 1 can be in a range of about 2.2 to about 7.

[0010] According to an embodiment of the disclosure, a rechargeable lithium battery can include: the negative electrode discussed above; a positive electrode; and an electrolyte between the negative electrode and the positive electrode. BRIEF DESCRIPTION OF DRAWINGS

[0011] The accompanying drawings, together with the specification, illustrate embodiments of the disclosed subject matter and serve to explain the principles of embodiments of the disclosed subject matter.

[0012] Figure 1 is a simplified conceptual view illustrating a rechargeable lithium battery according to an embodiment of the disclosure.

[0013] Figures 2 to 5 is a view illustrating a rechargeable lithium battery according to an embodiment of the disclosure.

[0014] Figure 6 is a cross-sectional view illustrating a rechargeable lithium battery according to an embodiment of the disclosure.

[0015] Figure 7 is an enlarged cross-sectional view illustrating a cross-section M of Figure 6

[0016] Figures 8A to 8C is a simplified conceptual view illustrating first crystalline carbon to third crystalline carbon, respectively.

[0017] Figure 9 is an enlarged cross-sectional view illustrating a cross-section M of Figure 6

[0018] Figures 10 to 11 is a cross-sectional view illustrating a method of manufacturing a negative electrode according to an embodiment of the disclosure.

[0019] ​​Figure 12 is a cross-sectional view illustrating a method of manufacturing a negative electrode according to another embodiment of the disclosure.

[0020] Figure 13 is a cross-sectional view illustrating a method of manufacturing a negative electrode according to a comparative example of the disclosure. DETAILED DESCRIPTION

[0021] In order to fully understand the construction and effects of the subject matter of the disclosure, some embodiments of the disclosure will be described with reference to the accompanying drawings. However, it should be noted that the disclosure is not limited to the following example embodiments and can be implemented in various suitable forms. Rather, the example embodiments are provided only to disclose the subject matter of the disclosure and to enable those skilled in the art to fully understand the scope of the disclosure.

[0022] In the present specification, it will be understood that, if an element is referred to as being "on" another element, it can be directly on the other element or intervening elements can be present therebetween. In the drawings, the thickness of some components can be exaggerated for effective explanation of the technical content. Throughout the specification, like reference numerals refer to like elements.

[0023] Unless specifically stated otherwise in the specification, expressions of a singular form can include expressions of a plural form. In the embodiments, unless specifically stated otherwise, the phrase "A or B" can mean "A but not B," "B but not A," and "A and B." The terms "include / including" and / or variations thereof used in the specification do not exclude the presence or addition of one or more other components.

[0024] As used herein, the term "combination thereof" can refer to a mixture, a stack, a composite, a copolymer, an alloy, a blend, and / or a reaction product.

[0025] Figure 1 is a simplified conceptual diagram illustrating a rechargeable lithium battery according to an embodiment of the disclosure. Referring to Figure 1 The rechargeable lithium battery can include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0026] The positive electrode 10 and the negative electrode 20 can be spaced apart from each other with the separator 30 therebetween. The separator 30 can be between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 can be in contact with the electrolyte ELL. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated with the electrolyte ELL.

[0027] The electrolyte ELL can be a medium through which lithium ions are transferred between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can move toward one selected from among the positive electrode 10 and the negative electrode 20 through the separator 30.

[0028] Positive electrode 10 The positive electrode 10 for the rechargeable lithium battery can include a positive electrode current collector COL1 and a positive electrode active material layer AML1 on the positive electrode current collector COL1. The positive electrode active material layer AML1 can include a positive electrode active material, and further include a binder and / or a conductive material (e.g., an electrically conductive material).

[0029] For example, the positive electrode 10 can further include an additive that can be used as a sacrificial positive electrode.

[0030] The amount of the positive electrode active material in the positive electrode active material layer AML1 can be about 90 wt% to about 99.5 wt% with respect to 100 wt% of the positive electrode active material layer AML1. The amount of each of the binder and the conductive material can be about 0.5 wt% to about 5 wt% with respect to 100 wt% of the positive electrode active material layer AML1.

[0031] The binder can be used to improve the adhesion of the positive electrode active material particles to each other, and can also be used to improve the adhesion of the positive electrode active material to the positive electrode current collector COL1. The binder can include, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and / or nylon, but the present disclosure is not limited thereto.

[0032] The conductive material can be used to provide conductivity (e.g., electrical conductivity) to the electrode, and any suitable conductive material that does not cause chemical changes in the battery (e.g., does not cause undesirable chemical changes in the rechargeable lithium battery) can be used as the conductive material constituting the battery. The conductive material can include, for example, a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and / or carbon nanotube; a metal powder and / or a metal fiber including one or more of copper, nickel, aluminum, and silver; a conductive polymer (e.g., an electrically conductive polymer) such as a polyphenylene derivative; or a mixture thereof.

[0033] Aluminum (Al) can be used as the positive electrode current collector COL1, but the present disclosure is not limited thereto.

[0034] Positive electrode active material The positive electrode active material in the positive electrode active material layer AML1 can include a compound that can reversibly intercalate and deintercalate lithium (e.g., a lithiated intercalation compound). For example, the positive electrode active material can include at least one complex oxide including lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof.

[0035] The complex oxide can include a lithium transition metal complex oxide, for example, a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free lithium nickel manganese-based oxide, or combinations thereof.

[0036] For example, the positive electrode active material can include a compound represented by one selected from the following chemical formulas: a A 1-b X b O 2-c D c (wherein, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Mn 2-b X b O 4-c D c (wherein, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, and 0<α<2); Li a Ni 1-b-c Co b X c O 2-α D α (wherein, 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 (wherein, 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(wherein, 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(wherein, 0.90≤a≤1.8 and 0.001≤b≤0.1); Li a CoG b O2(wherein, 0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn1-b G b O2 (where 0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn2G b O4 (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); and Li a FePO4 (where 0.90≤a≤1.8).

[0037] In the above chemical formula, A is Ni, Co, Mn or a combination thereof, X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof, D is O, F, S, P or a combination thereof, G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof, and L 1 It is Mn, Al or a combination thereof.

[0038] For example, the positive electrode active material may be a high-nickel positive electrode active material having a nickel content of about 80 mol% or more, about 85 mol% or more, about 90 mol% or more, about 91 mol% or more, or about 94 mol% or more and about 99 mol% or less relative to 100 mol% of metals other than lithium in the lithium transition metal composite oxide. The high-nickel positive electrode active material can achieve high capacity and can therefore be applied to rechargeable lithium batteries with high capacity and high energy density.

[0039] Negative electrode 20 The negative electrode 20 for a rechargeable lithium battery may include a negative electrode current collector COL2 and a negative electrode active material layer AML2 on the negative electrode 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 (e.g., an electrically conductive material).

[0040] For example, the negative electrode active material layer AML2 may include about 90 wt % to about 99 wt % of a negative electrode active material, about 0.5 wt % to about 5 wt % of a binder, and about 0 wt % to about 5 wt % of a conductive material (eg, an electrically conductive material).

[0041] The binder can be used to improve the adhesion of the negative electrode active material particles to each other, and can also be used to improve the adhesion of the negative electrode active material to the negative electrode current collector COL2. The binder can include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0042] The non-aqueous binder can include polyvinyl chloride, carboxylated polyvinyl chloride, polyfluoroethylene, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or a combination thereof.

[0043] The aqueous binder can include styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluorine-containing elastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0044] If the aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of providing or increasing viscosity can also be included. The cellulose-based compound can include one or more selected from carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof. The alkali metal can include Na, K, and / or Li.

[0045] The dry binder can include a fibrillatable polymeric material, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0046] The conductive material can be used to provide electrical conductivity (e.g., electrical conductivity) to the electrode, and any suitable conductive material that does not cause chemical changes in the battery (e.g., does not cause undesirable chemical changes in a rechargeable lithium battery) can be used as the conductive material constituting the battery. For example, the conductive material can include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and / or carbon nanotube; metal powder and / or metal fiber including one or more of copper, nickel, aluminum, and silver; electrically conductive polymer (e.g., electrically conductive polymer) such as polyphenylene derivative; or a mixture thereof.

[0047] The negative electrode current collector COL2 can include a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0048] The negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 can include a material that can reversibly intercalate and deintercalate lithium ions, lithium metal, a lithium metal alloy, a material that can dope and undope lithium, and / or a transition metal oxide.

[0049] The material that can reversibly intercalate and deintercalate lithium ions can include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. For example, the crystalline carbon can include graphite (such as unformed, flaky, flake-like, spherical, and / or fibrous natural graphite and / or artificial graphite), and the amorphous carbon can include soft carbon, hard carbon, meso-phase pitch carbon, and / or calcined coke.

[0050] The lithium metal alloy can include lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0051] The material that can dope and undope lithium can include a Si-based negative electrode active material and / or a Sn-based negative electrode active material. The Si-based negative electrode active material can include silicon, a silicon-carbon composite, SiO x (wherein, 0 < x < 2), a Si-Q alloy (wherein Q is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (except Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, or a combination thereof), or a combination thereof. The Sn-based negative electrode active material can include Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0052] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to an embodiment, 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 can include secondary particles (core) in which primary silicon particles are assembled and an amorphous carbon coating layer (shell) on the surface of the secondary particles. Amorphous carbon can also be present between the primary silicon particles, for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be present dispersed in an amorphous carbon matrix.

[0053] The silicon-carbon composite can further include crystalline carbon. For example, the silicon-carbon composite can include a core including crystalline carbon and silicon particles, and can further include an amorphous carbon coating layer on the surface of the core.

[0054] The Si-based negative electrode active material and / or the Sn-based negative electrode active material can be used in combination with the carbon-based negative electrode active material.

[0055] The separator 30 The separator 30 can exist between the positive electrode 10 and the negative electrode 20 based on the type (or kind) of the rechargeable lithium battery. The separator 30 can include one or more selected from polyethylene, polypropylene, and polyvinylidene fluoride, and can have a multi-layer separator (such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene triple-layer separator, and a polypropylene / polyethylene / polypropylene triple-layer separator) selected from one or more of polyethylene, polypropylene, and polyvinylidene fluoride.

[0056] The separator 30 can include a porous substrate and a coating layer on one or opposite two surfaces of the porous substrate, the coating layer including an organic material, an inorganic material, or a combination thereof.

[0057] The porous substrate can be a polymeric layer including one selected from polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyarylether ketones, polyetherimides, polyamideimides, polybenzimidazoles, polyether sulfones, polyphenylene ethers, cyclic olefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, and Teflon (polytetrafluoroethylene), or can be a copolymer or a mixture including two or more of the above materials.

[0058] The organic material can include a polyvinylidene fluoride-based copolymer and / or a (meth)acrylic copolymer.

[0059] The inorganic material can include inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof, but the disclosure is not limited thereto.

[0060] The organic material and the inorganic material can exist mixed together in one coating layer, or can exist as a stack of a coating layer including the organic material and a coating layer including the inorganic material.

[0061] Reference will be made to Figure 6 The negative electrode active material layer AML2 according to the embodiment of the disclosure will be further discussed in more detail with reference to FIG. 8.

[0062] Electrolyte ELL The electrolyte ELL for the rechargeable lithium battery can include a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent can serve as a medium to transport ions participating in an electrochemical reaction of the battery. The non-aqueous organic solvent can include a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0063] Carbonate-based solvents can include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and / or fluoroethylene carbonate (FEC).

[0064] Ester-based solvents can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, methyl hydroxyvalerate lactone, valerolactone, and / or caprolactone.

[0065] Ether-based solvents can include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and / or tetrahydrofuran. Ketone-based solvents can include cyclohexanone. Alcohol-based solvents can include ethanol and / or isopropanol. Aprotic solvents can include: nitriles such as R-CN (where R is a hydrocarbon group having a C2 to C20 linear, branched, or cyclic structure, and can include double bonds, aromatic rings, and / or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and / or 1,4-dioxolane; and / or sulfolanes.

[0066] The non-aqueous organic solvent can be used alone or in a mixture of two or more substances.

[0067] In embodiments, if a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be mixed together and used, and the cyclic carbonate and the chain carbonate can be mixed together in a volume ratio of about 1:1 to about 1:9.

[0068] The lithium salt can be a material that is dissolved in the non-aqueous organic solvent to serve as a supply source of lithium ions in the battery, and functions to enable the rechargeable lithium battery to operate substantially and to facilitate movement of lithium ions between the positive electrode and the negative electrode. The lithium salt can include, for example, at least one selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N, lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (where x and y are integers between 1 and 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOB), and lithium bis(oxalato)borate (LiBOB).

[0069] The rechargeable lithium battery Based on the shape of the rechargeable lithium battery, the rechargeable lithium battery can be classified into a cylindrical shape, a prismatic shape, a pouch shape (or the like), and / or a coin shape (or the like). Figures 2 to 5 is a simplified diagram illustrating a rechargeable lithium battery according to an embodiment, Figure 2 illustrates a cylindrical battery, Figure 3 illustrates a prismatic battery, and Figures 4 to 5 illustrates a pouch battery. Referring to Figures 2 to 4 The rechargeable lithium battery 100 can include an electrode assembly 40 in which a separator 30 is between a positive electrode 10 and a negative electrode 20, and can further include a case 50 in which the electrode assembly 40 is accommodated. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated with an electrolyte. As Figure 2 indicated in Figure 3 , the rechargeable lithium battery 100 can include a sealing member 60 that seals the case 50. In an embodiment, as Figures 4 to 5 indicated in Figure 5 , the rechargeable lithium battery 100 can include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As Figure 4 indicated in , the rechargeable lithium battery 100 can include an electrode tab 70 (or a positive electrode tab 71 and a negative electrode tab 72)

[0070] , which functions as an electrical path for inducing an electric current generated in the electrode assembly 40 to the outside.

[0071] Figure 6 is a cross-sectional view illustrating a rechargeable lithium battery according to an embodiment of the disclosure. Figure 7 is an enlarged cross-sectional view illustrating a cross section M of Figure 6 .

[0072] Referring to Figures 6 to 7 , as discussed above with reference to Figure 1 , the rechargeable lithium battery according to the disclosure can include a positive electrode 10, a negative electrode 20, and a separator 30 between the positive electrode 10 and the negative electrode 20. In an embodiment, the rechargeable lithium battery according to the disclosure can further include an electrolyte ELL. The separator 30 can be impregnated with the electrolyte ELL.

[0073] The positive electrode 10 can include a positive electrode current collector COL1 and a positive electrode active material layer AML1 on the positive electrode current collector COL1. The negative electrode 20 can include a negative electrode current collector COL2 and a negative electrode active material layer AML2 on the negative electrode current collector COL2. The separator 30 can be between the positive electrode active material layer AML1 and the negative electrode active material layer AML2.

[0074] The negative electrode active material layer AML2 according to embodiments of the disclosure can have a multi-layer structure. For example, the negative electrode active material layer AML2 can include a first active material layer NAL1, a second active material layer NAL2, and a third active material layer NAL3, which are sequentially stacked. The first active material layer NAL1 can be directly on the negative electrode current collector COL2. The second active material layer NAL2 can be between the first active material layer NAL1 and the third active material layer NAL3.

[0075] The first active material layer NAL1 to the third active material layer NAL3 can include respective negative electrode active materials different from each other. The first active material layer NAL1 to the third active material layer NAL3 can have respective compositions different from each other. Each of the first active material layer NAL1 to the third active material layer NAL3 can include a carbon-based negative electrode active material such as crystalline carbon, amorphous carbon, or any combination thereof. Detailed descriptions thereof can be the same as those of the negative electrode active material.

[0076] The first active material layer NAL1 can include a first crystalline carbon LGR. The second active material layer NAL2 can include a second crystalline carbon MGR and silicon-containing particles SCP. The third active material layer NAL3 can include a third crystalline carbon UGR. Each of the first crystalline carbon LGR, the second crystalline carbon MGR, and the third crystalline carbon UGR can be natural graphite, artificial graphite, or any suitable mixture thereof.

[0077] In an embodiment, in the first crystalline carbon LGR of the first active material layer NAL1, the natural graphite can have a ratio of about 0 wt% to about 100 wt%, about 50 wt% to about 100 wt%, or about 80 wt% to about 100 wt%. In the first crystalline carbon LGR, the remaining component other than the natural graphite can be artificial graphite. In the first crystalline carbon LGR of the first active material layer NAL1, the ratio of the natural graphite can be greater than the ratio of the artificial graphite.

[0078] In embodiments of the disclosure, in the third crystalline carbon UGR of the third active material layer NAL3, the artificial graphite can have a ratio of about 0 wt% to about 100 wt%, about 50 wt% to about 100 wt%, or about 80 wt% to about 100 wt%. In the third crystalline carbon UGR, the remaining component other than the artificial graphite can be natural graphite. In the third crystalline carbon UGR of the third active material layer NAL3, the ratio of the artificial graphite can be greater than the ratio of the natural graphite. For example, in an embodiment, the first active material layer NAL1 can include natural graphite, the third active material layer NAL3 can include artificial graphite, and the second active material layer NAL2 can include a mixture of natural graphite and artificial graphite.

[0079] In an embodiment of the disclosure, the second crystalline carbon MGR of the second active material layer NAL2 can include a mixture of natural graphite and artificial graphite. The ratio of the natural graphite to the artificial graphite of the second crystalline carbon MGR can be in a range of about 1:9 to about 9:1.

[0080] In another embodiment of the disclosure, the second active material layer NAL2 can not include the second crystalline carbon MGR. The second active material layer NAL2 can include amorphous carbon and silicon particles. The second active material layer NAL2 can include a silicon-carbon composite as the silicon-containing particle SCP, which will be further discussed below.

[0081] The second active material layer NAL2 can include carbon (C) and silicon (Si). The silicon (Si) can be derived from the silicon-containing particle SCP. The carbon (C) can be derived from at least one of carbon selected from the second crystalline carbon MGR, the amorphous carbon, and the silicon-containing particle SCP in the second active material layer NAL2.

[0082] The silicon (Si) in the second active material layer NAL2 can have a ratio of about 5 wt% to about 99 wt%, about 5 wt% to about 30 wt%, or about 5 wt% to about 10 wt%. The silicon-containing particle SCP can include silicon, a silicon-carbon composite, SiO x (wherein, 0 < x < 2), a Si-Q alloy (wherein Q is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element (except Si), a group 15 element, a group 16 element, a transition metal, a rare earth element, or any combination thereof), or any combination thereof.

[0083] Each of the first active material layer NAL1 to the third active material layer NAL3 can further include a binder. The binder in each of the first active material layer NAL1 to the third active material layer NAL3 can have an amount of about 1 wt% to about 10 wt%. In an embodiment of the disclosure, the binder of the second active material layer NAL2 including the silicon-containing particle SCP can have a larger amount than the amount of the binder of each of the first active material layer NAL1 and the third active material layer NAL3 including only the crystalline carbon (for example, including only carbon and a binder, or not including silicon such as in the case of the silicon-containing particle). A large amount of the binder in the active material layer can cause a problem of a reduced moving speed of lithium ions.

[0084] The first active material layer NAL1 can have a first thickness TK1, the second active material layer NAL2 can have a second thickness TK2, and the third active material layer NAL3 can have a third thickness TK3. In an embodiment of the disclosure, the second thickness TK2 can be greater than the first thickness TK1. The second thickness TK2 can be greater than the third thickness TK3.

[0085] Since the second active material layer NAL2 includes the silicon-containing particles SCP, the second active material layer NAL2 can have an increased volume during charging of the rechargeable lithium battery. For example, if the rechargeable lithium battery is charged, the second thickness TK2 of the second active material layer NAL2 can increase. However, the first active material layer NAL1 and the third active material layer NAL3 including only crystalline carbon (e.g., including only carbon and a binder, or excluding silicon such as exemplified by the silicon-containing particles) can not have a large change in volume (or thickness). While the present disclosure is not limited by any particular mechanism or theory, it is believed that the foregoing can arise from the fact that the silicon-containing particles SCP intercalate lithium ions more than crystalline carbon if the rechargeable lithium battery is charged. The first active material layer NAL1 and the third active material layer NAL3 can act as buffer layers to reduce the change in volume (or thickness) of the second active material layer NAL2 during charge and discharge of the rechargeable lithium battery.

[0086] Referring back to Figure 7 , each of the first active material layer NAL1 to the third active material layer NAL3 can have a value of divergence (DD) defined by Equation 1 below.

[0087] Equation 1 DD (divergence) = (I a / I 总 ) x 100 In Equation 1, I a may represent the sum of peak intensities at non-plane angles in an X-ray diffraction (XRD) measurement using CuKα rays. In an embodiment, I 总 may represent the sum of peak intensities at all angles in the XRD measurement using CuKα rays.

[0088] In the XRD measurement using CuKα rays, the non-plane angles can be 2θ = 42.4 ± 0.2°, 43.4 ± 0.2°, 44.6 ± 0.2°, and 77.5 ± 0.2°. For example, these angles 42.4 ± 0.2°, 43.4 ± 0.2°, 44.6 ± 0.2°, and 77.5 ± 0.2° can represent (100) planes, (101)R planes, (101)H planes, and (110) planes, respectively. In general, based on the stacking order of graphene layers, graphite can be classified as a hexagonal structure and a rhombohedral structure having an ABAB type stacking order. The R planes can represent the rhombohedral structure, and the H planes can represent the hexagonal structure.

[0089] In the XRD measurement using CuKα rays, all of the angles can be 2θ = 26.5±0.2°, 42.4±0.2°, 43.4±0.2°, 44.6±0.2°, 54.7±0.2°, and 77.5±0.2°. For example, these angles 26.5±0.2°, 42.4±0.2°, 43.4±0.2°, 44.6±0.2°, 54.7±0.2°, and 77.5±0.2° can represent (002) plane, (100) plane, (101)R plane, (101)H plane, (004) plane, and (110) plane, respectively. The peak appearing at 2θ = 43.4±0.2° can be seen as an overlap of the peak corresponding to the (100)R plane of the carbon-based material and the peak corresponding to the (111) plane of the current collector or Cu.

[0090] The peak intensity value can mean a height value of a peak or an integral value of a peak. In an embodiment, the peak intensity value can be an integral value of a peak.

[0091] In an embodiment of the disclosure, the XRD measurement can be performed using CuKα rays as target rays. The target rays can be extracted by using a monochromator to improve the peak intensity resolution. The measurement can be performed under the condition of 2θ = 10° to 80°, a scan speed (° / s) of 0.044 to 0.089, and a step of 0.026° / step.

[0092] The DD value according to an embodiment of the disclosure can be obtained by measuring the XRD of the negative electrode active material layer AML2, which is obtained by fully charging and discharging the rechargeable lithium battery shown in FIG. 1 and then disassembling the battery in a fully discharged state. The charging and discharging can be performed one or two times at 0.1C to 0.2C. Figure 6

[0093] If the negative electrode active material layer AML2 undergoes the XRD measurement using CuKα rays, the peak intensity ratio (I (004) / I (002) ) of the (004) plane to the (002) plane can be equal to or greater than about 0.04 or be about 0.04 to about 0.07. If the I (004) / I (002) of the negative electrode active material layer AML2 is equal to or greater than about 0.04, the rate characteristics (e.g., high rate characteristics) and cycle life characteristics can be improved without increasing the direct current internal resistance.

[0094] The DD value can be a physical property that is maintained even during or after charging and discharging. The DD value of the active material layers NAL1 to NAL3 according to an embodiment of the disclosure can represent the degree of orientation at a constant angle of the crystalline carbon in the active material layers NAL1 to NAL3. For ease of description, Figure 7 ​The elliptical graphite particles are depicted as crystalline carbon, but the present disclosure is not limited thereto.

[0095] According to embodiments of the present disclosure, the DD value of the first active material layer NAL1 can be in the range of about 5 to about 25 (e.g., about 5 to about 20). The DD value of the second active material layer NAL2 can be in the range of about 15 to about 50. The DD value of the third active material layer NAL3 can be in the range of about 20 to about 60. The DD value of the second active material layer NAL2 can be greater than the DD value of the first active material layer NAL1. The DD value of the third active material layer NAL3 can be greater than the DD value of the second active material layer NAL2.

[0096] The difference between the DD value of the third active material layer NAL3 and the DD value of the first active material layer NAL1 can be equal to or greater than about 10. The difference between the DD value of the third active material layer NAL3 and the DD value of the first active material layer NAL1 can be in the range of about 10 to about 50.

[0097] According to embodiments of the present disclosure, the ratio of the DD value of the third active material layer NAL3 to the DD value of the first active material layer NAL1 can be in the range of about 1.2 to about 10, about 1.5 to about 8, or about 2.2 to about 7. Within the above ratio range, the negative electrode active material layer AML2 can have both excellent lithium ion conductivity and excellent adhesion to the negative electrode current collector COL2.

[0098] The third active material layer NAL3 can have a relatively large DD value. For example, the third crystalline carbon UGR in the third active material layer NAL3 can be oriented at a set or specific angle. The third crystalline carbon UGR in the third active material layer NAL3 can be erected at a set or specific angle with respect to the top surface of the negative electrode current collector COL2. Since the third crystalline carbon UGR is oriented in an upright posture, lithium ions can easily move in the third active material layer NAL3.

[0099] The first active material layer NAL1 can have a relatively small DD value. For example, the first crystalline carbon LGR in the first active material layer NAL1 can be randomly oriented. The first crystalline carbon LGR in the first active material layer NAL1 can be laid horizontally with respect to the top surface of the negative electrode current collector COL2. Since the first crystalline carbon LGR is randomly oriented in a lying posture, the contact area between the first crystalline carbon LGR and the top surface of the negative electrode current collector COL2 can increase.

[0100] Figures 8A to 8C are simplified conceptual diagrams respectively illustrating the first crystalline carbon to the third crystalline carbon. Referring to Figure 7 and Figure 8ASome of the first crystalline carbon LGR in the first active material layer NAL1 can be representatively illustrated. In an embodiment, the first crystalline carbon LGR can include a first lower particle LGR1, a second lower particle LGR2, and a third lower particle LGR3. Each of the first lower particle LGR1 to the third lower particle LGR3 can have a long axis MAA in a longitudinal direction thereof. A first angle θ1 can be formed between the long axis MAA of the first lower particle LGR1 and the top surface of the negative electrode current collector COL2. A second angle θ2 can be formed between the long axis MAA of the second lower particle LGR2 and the top surface of the negative electrode current collector COL2. A third angle θ3 can be formed between the long axis MAA of the third lower particle LGR3 and the top surface of the negative electrode current collector COL2. The first angle θ1 to the third angle θ3 can be the same as or different from each other.

[0101] An average value of the first angle θ1 to the third angle θ3 can be defined as an average angle of the first crystalline carbon LGR. For example, the average angle of the first crystalline carbon LGR can be in a range of about 0° to about 40°. Since the first crystalline carbon LGR has the average angle of about 0° to about 40°, the first crystalline carbon LGR can be regarded as being randomly oriented.

[0102] Referring to Figure 7 and Figure 8B Some of the second crystalline carbon MGR in the second active material layer NAL2 can be representatively illustrated. In an embodiment, the second crystalline carbon MGR can include a first intermediate particle MGR1, a second intermediate particle MGR2, and a third intermediate particle MGR3. Each of the first intermediate particle MGR1 to the third intermediate particle MGR3 can have a long axis MAA in a longitudinal direction thereof. A fourth angle θ4 can be formed between the long axis MAA of the first intermediate particle MGR1 and the top surface of the negative electrode current collector COL2. A fifth angle θ5 can be formed between the long axis MAA of the second intermediate particle MGR2 and the top surface of the negative electrode current collector COL2. A sixth angle θ6 can be formed between the long axis MAA of the third intermediate particle MGR3 and the top surface of the negative electrode current collector COL2. The fourth angle θ4 to the sixth angle θ6 can be the same as or different from each other.

[0103] An average value of the fourth angle θ4 to the sixth angle θ6 can be defined as an average angle of the second crystalline carbon MGR. For example, the average angle of the second crystalline carbon MGR can be in a range of about 20° to about 60°. In an embodiment, the average angle of the second crystalline carbon MGR can be greater than the average angle of the first crystalline carbon LGR.

[0104] Referring to Figure 7 and Figure 8CSome of the third crystalline carbon UGRs in the third active material layer NAL3 can be representatively illustrated. In an embodiment, the third crystalline carbon UGRs can include a first upper particle UGR1, a second upper particle UGR2, and a third upper particle UGR3. Each of the first to third upper particles UGR1 to UGR3 can have a long axis MAA in a longitudinal direction thereof. A seventh angle Θ7 can be formed between the long axis MAA of the first upper particle UGR1 and a top surface of the negative electrode current collector COL2. An eighth angle Θ8 can be formed between the long axis MAA of the second upper particle UGR2 and the top surface of the negative electrode current collector COL2. A ninth angle Θ9 can be formed between the long axis MAA of the third upper particle UGR3 and the top surface of the negative electrode current collector COL2. The seventh to ninth angles Θ7 to Θ9 can be the same as or different from each other.

[0105] An average value of the seventh to ninth angles Θ7 to Θ9 can be defined as an average angle of the third crystalline carbon UGR. For example, the average angle of the third crystalline carbon UGR can be in a range of about 50° to about 89°. In an embodiment, the average angle of the third crystalline carbon UGR can be greater than the average angle of the second crystalline carbon MGR. Since the third crystalline carbon UGR has an average angle of about 50° to about 89°, the third crystalline carbon UGR can be regarded as being almost vertically oriented.

[0106] Referring again to Figure 7 , the third crystalline carbon UGRs of the third active material layer NAL3 can have a relatively large DD value and a relatively large average angle. For example, the third crystalline carbon UGRs can be oriented in an upright posture. Since the third crystalline carbon UGRs are oriented in the upright posture, the third active material layer NAL3 can have a relatively small tortuosity and a relatively large porosity. Since a movement path of lithium ions in the third active material layer NAL3 is reduced, the lithium ions can move easily in the third active material layer NAL3. In an embodiment, the third active material layer NAL3 can improve ion conductivity.

[0107] The first crystalline carbon LGR of the first active material layer NAL1 can have a relatively small DD value and a relatively small average angle. For example, the first crystalline carbon LGR can be randomly oriented in a lying posture. The first active material layer NAL1 can have a relatively large tortuosity and a relatively small porosity. For example, the porosity of the third active material layer NAL3 can be greater than the porosity of the first active material layer NAL1.

[0108] The random orientation of the first crystalline carbon LGR may increase the contact area between the first crystalline carbon LGR and the top surface of the negative electrode current collector COL2, increase the friction between the first active material layer NAL1 and the negative electrode current collector COL2, and improve the adhesion between the first active material layer NAL1 and the negative electrode current collector COL2.

[0109] The second active material layer NAL2 and the third active material layer NAL3 can be stably physically supported by the first active material layer NAL1. If the negative electrode active material layer AML2 is rolled, the negative electrode active material in the second active material layer NAL2 and the third active material layer NAL3 can stably maintain its orientation even if the negative electrode active material (or crystalline carbon) is compressed.

[0110] The first active material layer NAL1 may have reduced ion mobility (or conductivity) compared to the third active material layer NAL3. However, the first active material layer NAL1 may help stabilize the adhesion between the negative electrode active material layer AML2 and the negative electrode current collector COL2 and stably physically support the second active material layer NAL2 and the third active material layer NAL3.

[0111] In the following embodiments, the above reference may not be repeated. Figures 6 to 8C The technical features of the discussed rechargeable lithium battery repeat the detailed description of the technical features, and the differences thereof will be discussed in more detail.

[0112] Figure 9 A diagram showing a rechargeable lithium battery according to another embodiment of the present disclosure is shown. Figure 6 An enlarged sectional view of section M in FIG. Figure 9 The first crystalline carbon LGR in the first active material layer NAL1 may include carbon particles GRP and a coating layer CTL. The coating layer CTL may encapsulate the surface of the carbon particles GRP. The coating layer CTL may include a magnetic substance. The coating layer CTL may be configured such that the carbon particles GRP are arranged horizontally by magnetic force.

[0113] In an embodiment, the coating layer CTL may allow the first crystalline carbon LGR to have a Figure 7 The coating layer CTL may make the first active material layer NAL1 have an average angle smaller than the average angle of the first crystalline carbon LGR shown in FIG. Figure 7 The DD value of the first active material layer NAL1 shown in FIG is a small DD value.

[0114] Figures 10 to 11 is a cross-sectional view illustrating a method of manufacturing a negative electrode according to an embodiment of the present disclosure.

[0115] Reference Figure 10The wound negative electrode current collector COL2 can be unwound and provided to a coating process. The traveling negative electrode current collector COL2 can be transferred along the first direction D1 by the support roller SRL and coated. The negative electrode current collector COL2 can be subjected to the coating process on the support roller SRL.

[0116] The coating mold CTD can be adjacent to the support roller SRL. The coating mold CTD can include three holes for slurry injection. The three slurry injection holes can be provided with a first negative electrode slurry NSL1, a second negative electrode slurry NSL2, and a third negative electrode slurry NSL3. The coating mold CTD can provide the first negative electrode slurry NSL1, the second negative electrode slurry NSL2, and the third negative electrode slurry NSL3 sequentially coated on the negative electrode current collector COL2.

[0117] For example, the first negative electrode slurry NSL1 can include a first crystalline carbon LGR, a binder, and a solvent. The second negative electrode slurry NSL2 can include a second crystalline carbon MGR, silicon-containing particles SCP, a binder, and a solvent. The third negative electrode slurry NSL3 can include a third crystalline carbon UGR, a binder, and a solvent. Each of the first crystalline carbon LGR, the second crystalline carbon MGR, and the third crystalline carbon UGR can be natural graphite, artificial graphite, or any suitable mixture thereof. For example, the first negative electrode slurry NSL1 can include a majority (e.g., as a main component) of natural graphite. The third negative electrode slurry NSL3 can include a majority (e.g., as a main component) of artificial graphite.

[0118] The solvent in the slurry can be any suitable solvent generally used in the art, for example, can include at least one selected from dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl pyrrolidone (NMP), acetone, water, and combinations thereof.

[0119] The first negative electrode slurry NSL1, the second negative electrode slurry NSL2, and the third negative electrode slurry NSL3 coated on the negative electrode current collector COL2 can be formed into the first active material layer NAL1, the second active material layer NAL2, and the third active material layer NAL3, respectively, discussed above with reference to Figure 6 The negative electrode active material layer AML2 can be composed of the first active material layer NAL1, the second active material layer NAL2, and the third active material layer NAL3 sequentially stacked on the negative electrode current collector COL2.

[0120] A magnetic orientation graphite anode (MOGA) process can be performed on the negative electrode active material layer AML2. The MOGA process can refer to a technique of increasing a vertical orientation ratio by applying a magnetic force to graphite particles having a diamagnetic property.

[0121] For example, the negative electrode current collector COL2 and the negative electrode active material layer AML2 can travel along the first direction D1. In an embodiment, the direction of travel MD of the negative electrode active material layer AML2 can be parallel to the first direction D1.

[0122] A magnet MAG can be disposed on the third active material layer NAL3 of the negative electrode active material layer AML2. The magnet MAG can apply a magnetic force MGF toward the negative electrode active material layer AML2. For example, the magnet MAG can have a magnetic field with a strength of about 4,000 Gauss. The magnetic force MGF can strongly act on the third active material layer NAL3 close to the magnet MAG. The magnetic force MGF can weakly act on the first active material layer NAL1 away from the magnet MAG.

[0123] In an embodiment, a magnetic flux caused by the magnet MAG can be formed in a direction perpendicular (or substantially perpendicular) to the top surface of the negative electrode current collector COL2, but due to the speed of travel, the magnetic force MGF can act in a vector direction of the magnetic field direction and the direction of travel MD (in the opposite direction of the third direction D3). For example, the direction of the magnetic force MGF can be inclined at a set or specific angle without being completely perpendicular to the top surface of the negative electrode current collector COL2. Accordingly, the third graphitic carbon UGR can be oriented at an average angle of less than about 90° (see Figure 8C ).

[0124] Since the magnetic force MGF weakly acts on the first active material layer NAL1, unlike the third graphitic carbon UGR, the first graphitic carbon LGR can be oriented randomly rather than upright. Accordingly, an increased contact area between the negative electrode current collector COL2 and the first graphitic carbon LGR of the first active material layer NAL1 can be maintained.

[0125] The magnetic force MGF acting on the second active material layer NAL2 can be weaker than the magnetic force acting on the third active material layer NAL3 and stronger than the magnetic force acting on the first active material layer NAL1. Accordingly, the second graphitic carbon MGR in the second active material layer NAL2 can be oriented at an average angle of about 20° to about 60°.

[0126] Thereafter, a drying process can be performed on the negative electrode active material layer AML2 that has undergone the MOGA process. After the negative electrode active material layer AML2 is dried, the negative electrode 20 can sequentially undergo a roll-pressing process, a slitting process, and a grooving process. The negative electrode 20, the separator 30, and the positive electrode 10 can be stacked, and then the electrolyte ELL can be provided to manufacture a rechargeable lithium battery according to the present disclosure.

[0127] Figure 12 is a cross-sectional view illustrating a method of manufacturing a negative electrode according to another embodiment of the present disclosure. Referring to Figure 12The first crystalline carbon LGR can include carbon particles GRP and a coating layer CTL. The coating layer CTL can include a magnetic substance. The coating layer CTL can be affected by the magnetic force MGF to make the first crystalline carbon LGR randomly oriented. The first crystalline carbon LGR can be horizontally placed on the top surface of the negative electrode current collector COL2.

[0128] Figure 13 A cross-sectional view illustrating a method of manufacturing a negative electrode according to a comparative example of the disclosure is shown. Referring to FIG. 2, Figure 13 The method of manufacturing a negative electrode according to the comparative example of the disclosure can include positioning a magnet MAG adjacent to the first active material layer NAL1. For example, according to the comparative example, the magnet MAG can be positioned under the negative electrode current collector COL2. The magnetic force MGF can strongly act on the first active material layer NAL1 close to the magnet MAG. The magnetic force MGF can weakly act on the third active material layer NAL3 far from the magnet MAG.

[0129] Since the magnetic force MGF strongly acts on the first active material layer NAL1, the first crystalline carbon LGR can be vertically oriented. The vertical orientation of the first crystalline carbon LGR can cause a reduction in the contact area between the first crystalline carbon LGR and the top surface of the negative electrode current collector COL2. Accordingly, the adhesion between the first active material layer NAL1 and the negative electrode current collector COL2 can be reduced, thereby causing a problem in which the negative electrode active material layer AML2 is easily detached from the negative electrode current collector COL2. Accordingly, it can be required to increase the amount of a binder in the first active material layer NAL1 to improve the adhesion, and this can cause a problem in which the energy density is reduced.

[0130] Since the magnetic force MGF weakly acts on the third active material layer NAL3, the third crystalline carbon UGR can be randomly oriented. The movement path of lithium ions in the third active material layer NAL3 can increase, and the lithium ions can be difficult to move in the third active material layer NAL3. In this sense, the ion conductivity of the third active material layer NAL3 can be reduced.

[0131] The following description will focus on some embodiments of the disclosure. The following embodiments are provided to help understand the disclosure and are not intended to limit the scope of the disclosure.

[0132] Manufacture of a negative electrode: Embodiment 1 A first negative electrode slurry was prepared by mixing together 68 wt% of natural graphite, 30 wt% of artificial graphite, 0.8 wt% of carboxymethyl cellulose, and 1.2 wt% of styrene-butadiene rubber in pure water. A second negative electrode slurry was prepared by mixing together 44 wt% of natural graphite, 44 wt% of artificial graphite, 9 wt% of silicon nanoparticles, 0.8 wt% of carboxymethyl cellulose, and 2.2 wt% of styrene-butadiene rubber in pure water. A third negative electrode slurry was prepared by mixing together 68 wt% of artificial graphite, 30 wt% of natural graphite, 0.8 wt% of carboxymethyl cellulose, and 1.2 wt% of styrene-butadiene rubber in pure water.

[0133] The first negative electrode slurry, the second negative electrode slurry, and the third negative electrode slurry were sequentially coated on a copper current collector to form first, second, and third active material layers, respectively. A magnet was disposed on the third active material layer. The negative electrode active material layers were passed along one direction through the magnet. The magnet can have a magnetic field with a strength of about 4,000 Gauss.

[0134] After the MOGA process of applying a magnetic force to the first to third active material layers was completed, the negative electrode active material layers were first dried at 80°C, and then roll-pressed. The negative electrode active material layers were second dried at 120°C under vacuum conditions. Thus, the negative electrode of Example 1 was manufactured.

[0135] Example 2 The natural graphite and the artificial graphite in the first negative electrode slurry were coated with a magnetic substance (see Figure 12 ). Except for the above-mentioned, the negative electrode of Example 2 was manufactured according to the same method as in Example 1.

[0136] Comparative Example 1 Except for omitting the MOGA process, the negative electrode of Comparative Example 1 was manufactured according to the same method as in Example 1.

[0137] Comparative Example 2 A magnet was disposed under the negative electrode current collector (see Figure 13 ). Except for the magnet being positioned close to the first active material layer, the negative electrode of Comparative Example 2 was manufactured according to the same method as in Example 1.

[0138] Comparative Example 3 The magnet was adjusted to have a magnetic field with a strong strength of about 8,000 Gauss. Except for the above-mentioned, the negative electrode of Comparative Example 3 was manufactured according to the same method as in Example 1.

[0139] Manufacture of a half-single body The prepared negative electrode was wound into a circular shape having a diameter of 12 mm, and then a 2032-type coin half-cell was manufactured using lithium metal as a counter electrode. An organic electrolyte in which 1.3 M LiPF6was dissolved in a mixture solvent including a mixture of ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate mixed together in a weight ratio of 2:6:2 was used.

[0140] Evaluation 1: Orientation degree of graphite in the first to third active material layers The negative electrodes according to Example 1 and Example 2 and Comparative Examples 1 to 3 were disassembled to measure a divergence degree (DD) value of each of the first to third active material layers.

[0141] A scanning electron microscope (SEM) image of the negative electrode was used to measure an average angle of graphite particles in each of the first to third active material layers. For example, among the graphite particles in the image, 50 particles were randomly selected from each layer to calculate their average angle.

[0142] The results are listed in Table 1 below.

[0143] Table 1

[0144] Referring to Table 1, in Example 1 and Example 2, the third active material layer has the greatest (e.g., largest) DD value and the greatest (e.g., largest) average angle. In Example 1 and Example 2, the first active material layer has the smallest (e.g., least) DD value and the smallest (e.g., least) average angle. In contrast, in Comparative Example 2, the first active material layer has the greatest (e.g., largest) DD value and the greatest (e.g., largest) average angle. In Comparative Example 1, the third active material layer has the smallest (e.g., least) DD value and the smallest (e.g., least) average angle.

[0145] In Comparative Example 3, the third active material layer has the greatest (e.g., largest) DD value. In Comparative Example 3, the ratio of the DD value of the third active material layer to the DD value of the first active material layer is about 2.15, which is less than the DD value ratio (2.25) of the third active material layer to the first active material layer in Example 1 and the DD value ratio (6.5) of the third active material layer to the first active material layer in Example 2.

[0146] In the negative electrode according to Embodiment 1 and Embodiment 2, since the crystalline carbon of the first active material layer in contact with the current collector is randomly oriented, excellent adhesion can be provided between the first active material layer and the current collector. In the negative electrode according to Embodiment 1 and Embodiment 2, since the crystalline carbon of the third active material layer at the top position is vertically oriented, excellent lithium ion conductivity can be achieved.

[0147] Evaluation 2: Specific capacity characteristics of the half-monoblocs and charge characteristics for various rates of the rechargeable lithium battery The coin half-monoblocs using the negative electrode according to Embodiment 1 and Embodiment 2 and Comparative Example 1 to Comparative Example 3 were charged at 0.2 C under the condition of constant current and cut off at 0.01 V under the condition of constant voltage, and discharged at 0.2 C under the condition of constant current and cut off at 1.5 V under the condition of constant voltage. The discharge capacity at the first charge / discharge was obtained to evaluate the specific capacity characteristics of the half-monoblocs, and the results are listed in Table 2 below.

[0148] The coin full-monoblocs using the negative electrode according to Embodiment 1 and Embodiment 2 and Comparative Example 1 to Comparative Example 3 were subjected to one charge / discharge, in which the coin full-monoblocs were charged at 0.2 C under the condition of constant current and cut off at 4.25 V under the condition of constant voltage, and cut off at 0.05 C under the condition of constant voltage and discharged at 2.8 V under the condition of constant current, and then discharged at 0.05 C under the condition of constant voltage and cut off at 4.25 V under the condition of constant voltage, while maintaining discharge at 0.2 C under the condition of constant current and cut off at 2.8 V under the condition of constant voltage, and the charge C rate was changed to 0.5 C, 1.0 C, and 2.0 C under the condition of constant current.

[0149] The ratio of the charge capacity at each C rate to the charge capacity of the first cycle at 0.2 C was calculated from the measurement results, and the calculation results are listed in Table 2 below.

[0150] Table 2

[0151] Referring to Table 2, in Comparative Example 1 and Comparative Example 2, since the crystalline carbon in the third active material layer is randomly oriented, a decrease in ion conductivity to reduce the charge efficiency can be observed. In Comparative Example 2 and Comparative Example 3, since the crystalline carbon in the first active material layer has an orientation, the amount of the binder added for adhesion of the electrode plate is increased. Therefore, it can be determined that the specific capacity is decreased. If the orientation of the crystalline carbon in the first active material layer to the third active material layer is generally increased (Comparative Example 3), a significant decrease in the specific capacity and the charge efficiency can be observed.

[0152] In contrast, in Embodiment 1 and Embodiment 2, it can be observed that the crystalline carbon in the third active material layer is smoothly oriented to increase ion conductivity and charging efficiency. In Embodiment 1 and Embodiment 2, the crystalline carbon in the first active material layer is randomly oriented to increase adhesion of the electrode plate and reduce the amount of the addition of the binder. Therefore, it can be determined that the specific capacity is increased.

[0153] The negative electrode for a rechargeable lithium battery according to an embodiment of the disclosure can have excellent adhesion between the first active material layer and the current collector. Since the third active material layer of the negative electrode includes vertically oriented crystalline carbon, lithium ion conductivity can be excellent. As a result, the rechargeable lithium battery according to the disclosure can have excellent capacity and excellent charging / discharging efficiency.

[0154] While the subject matter of the disclosure has been described in connection with what is presently considered to be the exemplar}' embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments, and is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims and their equivalents, and accordingly, the foregoing embodiments are to be regarded as illustrative in nature, and not restrictive in any way.

Claims

1. A negative electrode for a rechargeable lithium battery, the negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer on the negative electrode current collector, wherein the negative electrode active material layer comprises a first active material layer, a second active material layer, and a third active material layer sequentially stacked on the negative electrode current collector, wherein the first active material layer, the second active material layer, and the third active material layer each comprise first crystalline carbon, second crystalline carbon, and third crystalline carbon, wherein the first active material layer is a random orientation layer having a divergence value defined by Equation 1 of 5 to 20, wherein the third active material layer is an orientation layer having a divergence value defined by Equation 1 of 20 to 60, Equation 1 divergence = (I a / I 总 ) x 100 wherein, in Equation 1, I a is the sum of the peak intensities at non-planar angles in XRD measurements using Cu Ka radiation, and I 总 is the sum of the peak intensities at all angles in the XRD measurement using Cu Ka radiation.

2. The negative electrode according to claim 1, wherein the divergence value of the second active material layer defined by Equation 1 is in the range of 15 to 50, wherein the divergence value of the second active material layer is greater than the divergence value of the first active material layer and less than the divergence value of the third active material layer.

3. The negative electrode according to claim 1, wherein a difference between the divergence value of the third active material layer and the divergence value of the first active material layer is in the range of 10 to 50.

4. The negative electrode according to claim 1, wherein a ratio of the divergence value of the third active material layer to the divergence value of the first active material layer is in the range of 2.2 to 7.

5. The negative electrode according to claim 1, wherein the second active material layer further comprises silicon-containing particles. 6.The negative electrode of claim 1, wherein: a proportion of natural graphite in the first crystalline carbon is greater than a proportion of artificial graphite in the first crystalline carbon, and a proportion of artificial graphite in the third crystalline carbon is greater than a proportion of natural graphite in the third crystalline carbon.

7. The negative electrode according to claim 1, wherein an average angle between long axes of the first crystalline carbon and a top surface of the negative electrode current collector is in the range of 0° to 40°.

8. The negative electrode according to claim 1, wherein an average angle between long axes of the second crystalline carbon and a top surface of the negative electrode current collector is in the range of 20° to 60°.

9. The negative electrode according to claim 1, wherein an average angle between long axes of the third crystalline carbon and a top surface of the negative electrode current collector is in the range of 50° to 89°.

10. The negative electrode according to claim 1, wherein the first crystalline carbon comprises carbon particles and a coating layer on surfaces of the carbon particles, wherein the coating layer comprises a magnetic substance.

11. The negative electrode according to claim 1, wherein a porosity of the third active material layer is greater than a porosity of the first active material layer. 12.A negative electrode for a rechargeable lithium battery, the negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer on the negative electrode current collector, wherein the negative electrode active material layer comprises a first active material layer, a second active material layer, and a third active material layer sequentially stacked on the negative electrode current collector, wherein the first active material layer, the second active material layer, and the third active material layer each comprise first crystalline carbon, second crystalline carbon, and third crystalline carbon, and wherein a ratio of a divergence value of the third active material layer defined by Equation 1 to a divergence value of the first active material layer defined by Equation 1 is in the range of 2.2 to 7, Equation 1 divergence = (I a / I 总 ) x 100 wherein, in Equation 1, I a is the sum of the peak intensities at non-planar angles in XRD measurements using Cu Ka radiation, and I 总 is the sum of the peak intensities at all angles in the XRD measurement using Cu Ka radiation.

13. The negative electrode according to claim 12, wherein, The divergence value defined by Equation 1 of the second active material layer is greater than the divergence value of the first active material layer and is less than the divergence value of the third active material layer.

14. The negative electrode according to claim 12, wherein, The second active material layer further includes silicon-containing particles.

15. The negative electrode according to claim 12, wherein, The proportion of natural graphite in the first crystalline carbon is greater than the proportion of artificial graphite in the first crystalline carbon.

16. The negative electrode according to claim 12, wherein The proportion of artificial graphite in the third crystalline carbon is greater than the proportion of natural graphite in the third crystalline carbon.

17. The negative electrode according to claim 12, wherein: an average angle between a long axis of the first crystalline carbon and a top surface of the negative electrode current collector is in a range of 0° to 40°, an average angle between a long axis of the second crystalline carbon and the top surface of the negative electrode current collector is in a range of 20° to 60°, and an average angle between a long axis of the third crystalline carbon and the top surface of the negative electrode current collector is in a range of 50° to 89°.

18. The negative electrode according to claim 12, wherein, The first crystalline carbon includes carbon particles and a coating layer on surfaces of the carbon particles, wherein the coating layer includes a magnetic substance.

19. The negative electrode of claim 12, wherein, The porosity of the third active material layer is greater than the porosity of the first active material layer.

20. A rechargeable lithium battery, the rechargeable lithium battery comprising: the negative electrode according to claim 1; a positive electrode; and an electrolyte between the negative electrode and the positive electrode.

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