Negative electrode for lithium secondary battery, lithium secondary battery comprising same, and method for manufacturing same

Abstract

To provide a negative electrode for a lithium secondary battery capable of minimizing a non-wetting region by including negative electrode active material layers having different densities.SOLUTION: The negative electrode includes a negative electrode collector and a negative electrode active material layer on the negative electrode collector, the negative electrode active material layer has a major axis in a first direction, and the negative electrode active material layer includes first negative electrode active material layers (AML2a) spaced apart from each other in a second direction crossing the first direction and second negative electrode active material layers (AML2a) between the first negative electrode active material layers (AML2b). A ratio of the specific capacitance of the first anode active material layer AML2b to the specific capacitance of the second anode active material layer AML2a may be 0.75 to 0.95.SELECTED DRAWING: Figure 6A

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for a lithium secondary battery, a lithium secondary battery including the same, and a method for producing the same. [Background technology]

[0002] Recently, the demand for high-energy-density, high-capacity secondary batteries has been increasing rapidly due to the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles. Therefore, research and development to improve the performance of lithium secondary batteries has been actively conducted.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, which contain active materials that allow the intercalation and deintercalation of lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted / deintercalated at the cathode and anode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-131297 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a negative electrode for a lithium secondary battery that includes negative electrode active material layers having different densities, thereby minimizing non-wetted regions.

[0006] Another object of the present invention is to provide a lithium secondary battery including the same. [Means for solving the problem]

[0007] According to one embodiment of the present invention, there is provided a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector; and a negative electrode active material layer on the negative electrode current collector, the negative electrode active material layer having a major axis in a first direction; the negative electrode active material layer including first negative electrode active material layers spaced apart in a second direction intersecting the first direction; and a second negative electrode active material layer between the first negative electrode active material layers, wherein a ratio of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer is 0.75 to 0.95.

[0008] A lithium secondary battery according to one embodiment of the present invention includes a positive electrode including a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, the negative electrode active material layer having a major axis in a first direction and including a separator between the positive electrode and the negative electrode, the negative electrode active material layer including first negative electrode active material layers spaced apart in a second direction intersecting the first direction and a second negative electrode active material layer between the first negative electrode active material layers, a specific capacity of the second negative electrode active material layer being greater than a specific capacity of the first negative electrode active material layer, and a ratio of a width of the second negative electrode active material layer in the second direction to a width of the negative electrode current collector in the second direction being 5% to 20%.

[0009] A method for manufacturing a lithium secondary battery according to an embodiment of the present invention includes preparing a first negative electrode active material slurry and a second negative electrode active material slurry, and applying the first negative electrode active material slurry and the second negative electrode active material slurry to a negative electrode current collector in a first direction to form a first negative electrode active material layer and a second negative electrode active material layer, respectively, wherein a ratio of a specific capacity of the first negative electrode active material layer to a specific capacity of the second negative electrode active material layer is 0.75 to 0.95. [Effects of the Invention]

[0010] A negative electrode according to an embodiment of the present invention and a lithium secondary battery including the same may have excellent capacity, efficiency, energy density, and lifespan. Furthermore, according to an embodiment of the present invention, by including a negative electrode active material layer with a relatively low density in the center of the negative electrode, the electrolyte can penetrate to the center of the negative electrode. This minimizes the non-wetted area of ​​the negative electrode. As a result, the electrical characteristics of the secondary battery can be improved. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the lithium secondary battery having a cylindrical battery shape. [Figure 3] 1 is a cross-sectional view showing a lithium secondary battery according to an embodiment. [Figure 4] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the battery having a prismatic shape. [Figure 5] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, in the form of a pouch-shaped battery. [Figure 6A] 1 is a plan view of a negative electrode for a lithium secondary battery according to an embodiment of the present invention. [Figure 6B] 1 is a cross-sectional view of a negative electrode for a lithium secondary battery according to an embodiment of the present invention. [Figure 7] 6B is an enlarged view of the negative electrode active material layer according to region M in FIG. 6A. FIG. [Figure 8] 1 is a diagram illustrating a method for manufacturing a lithium secondary battery according to an embodiment of the present invention; [Figure 9] 9 is a cross-sectional view taken along line AA' of FIG. 8, illustrating a method for manufacturing a lithium secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be realized in various forms and can be modified in various ways. The description of the present embodiments is provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains.

[0013] In this specification, when a certain component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component can be interposed therebetween. Also, in the drawings, the thickness of the components is exaggerated for the sake of efficient explanation of the technical content. Parts designated with the same reference numerals throughout the specification refer to the same components.

[0014] The embodiments described herein are described with reference to cross-sectional views and / or plan views that are idealized examples of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for efficient explanation of the technical content. Therefore, the regions illustrated in the drawings have schematic attributes, and the patterns of the regions illustrated in the drawings are intended to illustrate the specific shapes of the regions of the device and are not intended to limit the scope of the invention. In various embodiments of the present specification, terms such as "first," "second," and "third" are used to describe various components, but these components should not be limited by such terms. These terms are merely used to distinguish one component from another. The embodiments described and illustrated herein also include their complementary embodiments.

[0015] The terms used in this specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless otherwise specified in the context. The terms "comprises" and / or "comprising" used in this specification do not exclude the presence or addition of one or more other components in the secondary battery having the described configuration.

[0016] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0017] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0018] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with the electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in the electrolyte solution ELL.

[0019] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can pass through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0020] positive electrode 10 The positive electrode 10 for a lithium secondary 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 includes a positive electrode active material and may further include a binder and / or a conductive material.

[0021] For example, the positive electrode 10 may further include an additive that can act as a sacrificial positive electrode.

[0022] The content of the positive electrode active material in the positive electrode active material layer AML1 may be 90 wt % to 99.5 wt % relative to 100 wt % of the positive electrode active material layer AML1, and the contents of the binder and conductive material may be 0.5 wt % to 5 wt % each relative to 100 wt % of the positive electrode active material layer AML1.

[0023] The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector COL1. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0024] The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive without causing a chemical change in the battery that is constructed can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0025] The current collector COL1 can be made of Al, but is not limited to this.

[0026] positive electrode active material The positive electrode active material in the positive electrode active material layer AML1 may be a compound capable of reversibly intercalating and deintercalating lithium (lithiated intercalation compound). Specifically, one or more compounds selected from the group consisting of cobalt, manganese, nickel, and combinations thereof, and composite oxides of lithium and the metals may be used.

[0027] The composite oxide is a lithium transition metal composite oxide, and specific examples thereof include lithium nickel-based oxide, lithium cobalt-based oxide, lithium manganese-based oxide, lithium iron phosphate-based compound, cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0028] As an example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b O 2-c D c (0.90≦a≦1.8,0≦b≦0.5,0≦c≦0.05);Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8,0≦b≦0.5,0≦c≦0.05);Li a Ni 1-b-c Co b X c O 2-α D α (0.90≦a≦1.8,0≦b≦0.5,0≦c≦0.5,0<α<2);Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8,0≦b≦0.5,0≦c≦0.5,0<α<2);Li a Ni b Co c L 1 d G e O2(0.90≦a≦1.8,0≦b≦0.9,0≦c≦0.5,0≦d≦0.5,0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8,0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8,0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8,0.001≦b≦0.1);Lia Mn2G b O4(0.90≦a≦1.8,0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8,0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4(0.90≦a≦1.8).

[0029] 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 L1 is Mn, Al, or a combination thereof.

[0030] For example, the positive electrode active material may be a high-nickel-based positive electrode active material in which the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more but 99 mol% or less relative to 100 mol% of metals excluding lithium in a lithium transition metal composite oxide. The high-nickel-based positive electrode active material can achieve high capacity and is therefore applicable to high-capacity, high-density lithium secondary batteries.

[0031] negative electrode 20 The negative electrode 20 for a lithium secondary battery includes 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 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0032] For example, the negative electrode active material layer AML2 may contain 90 to 99 wt % of the negative electrode active material, 0.5 to 5 wt % of the binder, and 0 to 5 wt % of the conductive material.

[0033] The binder serves to firmly adhere the negative active material particles to each other and to firmly adhere the negative active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0034] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0035] The water-based binder may be selected from styrene-styrene rubber, (meth)acrylate styrene-styrene rubber, (meth)acrylonitrile-styrene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0036] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0037] The dry binder may be a polymeric material that can be fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0038] The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive without causing a chemical change in the battery may be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0039] The current collector COL2 may be made of a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0040] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0041] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0042] As the alloy of the lithium metal, an alloy of 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 can be used.

[0043] As the substance capable of doping and undoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (where Q is selected from 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), or a combination of these. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination of these.

[0044] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in a form in which amorphous carbon is coated on the surface of silicon particles. For example, it can include secondary particles (cores) formed by aggregation of primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon can also be located between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0045] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0046] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by being mixed with a carbon-based negative electrode active material.

[0047] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. As such separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and it goes without saying that mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0048] Separator 30 can include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0049] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0050] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0051] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0052] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

[0053] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0054] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0055] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0056] Examples of the carbonate solvent that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0057] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0058] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0059] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0060] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0061] The lithium salt is dissolved in an organic solvent and acts as a lithium ion source in the battery, enabling basic lithium secondary battery operation and promoting the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0062] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to embodiments, with FIG. 2 illustrating a cylindrical type, FIG. 3 illustrating a cross-sectional view, FIG. 4 illustrating a prismatic type, and FIG. 5 illustrating a pouch type. Referring to FIGS. 2 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 2. Also, as shown in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0063] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0064] The anode 20 according to an embodiment of the present invention will now be described in more detail.

[0065] Fig. 6A is a plan view of a negative electrode 20 according to an embodiment of the present invention. Fig. 6B is a cross-sectional view of a negative electrode 20 according to an embodiment of the present invention.

[0066] 6A and 6B, a negative electrode 20 for a lithium secondary battery includes a negative electrode current collector COL2 and a negative electrode active material layer AML2 disposed on the negative electrode current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0067] The negative electrode current collector COL2 may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0068] Negative electrode active material layer AML2 6A and 6B, the negative electrode active material layer AML2 may include a first negative electrode active material layer AML2a and a second negative electrode active material layer AML2b. The negative electrode active material layer AML2 may have a major axis extending in a first direction D1.

[0069] The first and second negative electrode active material layers AML2a and AML2b may extend in the first direction D1 on the current collector COL2. The first and second negative electrode active material layers AML2a may be spaced apart from each other in the second direction D2. A second negative electrode active material layer AML2b may be interposed between adjacent first negative electrode active material layers AML2a. The first negative electrode active material layer AML2a may be provided on both sides of the second negative electrode active material layer AML2b in the second direction D2. The height of the first negative electrode active material layer AML2a in the third direction D3 may be substantially the same as the height of the second negative electrode active material layer AML2b in the third direction D3.

[0070] The negative electrode active material layer AML2 may have a first width WD1 in the second direction D2. The first negative electrode active material layer AML2a may have a second width WD2 in the second direction D2. The second negative electrode active material layer AML2b may have a third width WD3 in the second direction D2. The first width WD1 may be greater than the sum of the second width WD2 and the third width WD3.

[0071] The second width WD2 may be larger than the third width WD3. The ratio of the third width WD3 to the first width WD1 may be 5% to 20%. For example, the first width WD1 may be 60 mm to 80 mm. The third width WD3 may be 3 mm to 15 mm.

[0072] The negative electrode active material layer AML2 may have a non-wetting area NWA. The non-wetting area NWA may be an area of ​​the negative electrode active material layer AML2 that is not wetted by the electrolyte solution ELL shown in FIG. 1. The area other than the non-wetting area NWA may be wetted by the electrolyte solution ELL. The non-wetting area NWA may be multiple. As another example, the non-wetting area NWA may not be formed.

[0073] 7 is an enlarged view of the negative electrode active material layer according to an embodiment of the present invention, the first negative electrode active material layer AML2a and the second negative electrode active material layer AML2b will be described in more detail with reference to FIG.

[0074] Each of the first and second negative electrode active material layers AML2a and AML2b may include a silicon-carbon composite. The silicon-to-carbon ratio in the first negative electrode active material layer AML2a may be different from the silicon-to-carbon ratio in the second negative electrode active material layer AML2b. The silicon content in the second negative electrode active material layer AML2b may be greater than the silicon content in the first negative electrode active material layer AML2a. The carbon content in the second negative electrode active material layer AML2b may be less than the carbon content in the first negative electrode active material layer AML2a. Accordingly, the specific capacity of the first negative electrode active material layer AML2a may be different from the specific capacity of the second negative electrode active material layer AML2b. For example, the specific capacity of the second negative electrode active material layer AML2b may be greater than the specific capacity of the first negative electrode active material layer AML2a. The ratio of the specific capacity of the first negative electrode active material layer AML2a to the specific capacity of the second negative electrode active material layer AML2b may be 0.75 to 0.95.

[0075] As another example, the first and second negative electrode active material layers AML2a and AML2b may contain at least one of natural graphite, artificial graphite, and a combination thereof. The first and second negative electrode active material layers AML2a and AML2b may not contain silicon.

[0076] If the ratio of the specific capacity of the first negative electrode active material layer AML2a to the specific capacity of the second negative electrode active material layer AML2b is less than 0.75, the difference in expansion coefficient between the first negative electrode active material layer AML2a and the second negative electrode active material layer AML2b may result in a poor appearance of the secondary battery.If the ratio of the specific capacity of the first negative electrode active material layer AML2a to the specific capacity of the second negative electrode active material layer AML2b is more than 0.95, the difference in density between the first negative electrode active material layer AML2a and the second negative electrode active material layer AML2b is small, which may result in no improvement in the non-wetted area NWA or may result in a poor appearance of the secondary battery.

[0077] The density of the first negative electrode active material layer AML2a and the density of the second negative electrode active material layer AML2b may be different from each other. For example, the density of the first negative electrode active material layer AML2a may be greater than the density of the second negative electrode active material layer AML2b. The porosity of the second negative electrode active material layer AML2b may be greater than the porosity of the first negative electrode active material layer AML2a.

[0078] The first negative electrode active material layer AML2a may include a first negative electrode active material AM2a, and the second negative electrode active material layer AML2 may include a second negative electrode active material AM2b. The first and second negative electrode active materials AM2a and AM2b may be the silicon-carbon composite described above. The first negative electrode active material AM2a in the first negative electrode active material layer AML2 may be more widely distributed than the second negative electrode active material AM2b in the second negative electrode active material layer AML2b.

[0079] Because the first negative electrode active material layer AML2a has a smaller specific capacity and a larger density than the second negative electrode active material layer AML2b, the capacity per volume of the first negative electrode active material layer AML2a may be substantially the same as the capacity per volume of the second negative electrode active material layer AML2b, i.e., the total capacity of the first negative electrode active material layer AML2a may be the same as the total capacity of the second negative electrode active material layer AML2b.

[0080] The negative electrode active material layer AML2 of the negative electrode 20 according to the present invention may include a first negative electrode active material layer AML2a and a second negative electrode active material layer AML2b having different specific capacities. By including the second negative electrode active material layer AML2b, which has a high specific capacity (i.e., a low density), in the center of the negative electrode 20, the electrolyte ELL can penetrate to the center of the negative electrode 20. This minimizes the size of the non-wetted regions NWA of the negative electrode 20. Minimizing the non-wetted regions NWA can prevent lithium deposition problems due to the non-wetted regions NWA and the resulting degradation of secondary battery performance. As a result, the electrical characteristics of the secondary battery 100 can be improved.

[0081] Lithium secondary battery manufacturing method Figure 8 is a view illustrating a method for manufacturing a lithium secondary battery according to an embodiment of the present invention. Figure 9 is a view illustrating a method for manufacturing a lithium secondary battery according to an embodiment of the present invention, and is a cross-sectional view taken along line A-A' in Figure 8. Hereinafter, the method for manufacturing a lithium secondary battery will be described with reference to Figures 8 and 9. Technical features that overlap with those in Figures 6A to 7 described above will be omitted.

[0082] A method for manufacturing a lithium secondary battery may include preparing a positive electrode, preparing a negative electrode, and combining the positive electrode and the negative electrode to manufacture a battery. More specifically, the method for manufacturing the negative electrode may include preparing first and second negative electrode active material slurries SL1 and SL2, and coating the first and second negative electrode active material slurries SL1 and SL2 on a current collector COL2 to form first and second negative electrode active material layers AML2a and AML2b, respectively.

[0083] Preparing the first negative electrode active material slurry SL1 may include mixing a first negative electrode active material AM2a, a binder, and a conductive material. Preparing the second negative electrode active material slurry SL2 may include mixing a second negative electrode active material AM2b, a binder, and a conductive material. The first negative electrode active material AM2a and the second negative electrode active material AM2b may be the silicon-carbon composite described above. The ratio of silicon to carbon in the first negative electrode active material slurry SL1 may be different from the ratio of silicon to carbon in the second negative electrode active material slurry SL2. Accordingly, the specific capacity of the first negative electrode active material slurry SL1 may be different from the specific capacity of the second negative electrode active material slurry SL2. For example, the specific capacity of the second negative electrode active material slurry SL2 may be greater than the specific capacity of the first negative electrode active material slurry SL1.

[0084] 8, first and second negative electrode active material slurries SL1 and SL2 may be applied onto a current collector COL2 using a slurry coating device DEV. The first and second negative electrode active material slurries SL1 and SL2 may be provided in an interior space of the slurry coating device DEV. The first and second negative electrode active material slurries SL1 and SL2 may be separated from each other in a second direction D2 by a partition PTT. The first and second negative electrode active material slurries SL1 and SL2 may not be mixed due to the partition PTT. Within the slurry coating device DEV, the second negative electrode active material slurries SL2 may be provided between the first negative electrode active material slurries SL1. This may require multiple partition PTTs.

[0085] The current collector COL2 may pass under the slurry coating device DEV. The slurry coating device DEV may apply first and second negative electrode active material slurries SL1 and SL2 onto the current collector COL2 through a nozzle. The first and second negative electrode active material slurries SL1 and SL2 may be applied side by side along a first direction D1. The first and second negative electrode active material slurries SL1 and SL2 may be in a flowing state.

[0086] 9, a first anode coating layer CTL1 may be formed by coating a first anode active material slurry SL1 on a current collector COL2, and a second anode coating layer CTL2 may be formed by coating a second anode active material slurry SL2 on the current collector COL2. The first anode coating layers CTL1 may be spaced apart in the second direction D2 by the second anode coating layer CTL2. A height HE1 of the first anode coating layer CTL1 in the third direction D3 may be greater than a height HE2 of the second anode coating layer CTL2 in the third direction D3. The level of the top surface of the first anode coating layer CTL1 may be higher than the level of the top surface of the second anode coating layer CTL2.

[0087] 6B, the first and second negative electrode coating layers CTL1 and CTL2 may be subjected to a drying process and a rolling process, so that the height HE1 of the first negative electrode coating layer CTL1 may be substantially equal to the height HE2 of the second negative electrode coating layer CTL2.

[0088] The present invention will be described in more detail below through examples. However, these examples are for illustrative purposes only and the scope of the present invention is not limited to these examples.

[0089] Example 1 First and second negative electrode active material slurries were prepared. The second negative electrode active material slurry had a higher silicon content than the first negative electrode active material slurry. The first and second negative electrode active material slurries were applied to a negative electrode current collector and dried to form first and second negative electrode active material layers. The width of the negative electrode current collector in the second direction D2 was 66 mm. The width of the second negative electrode active material layer in the second direction D2 was 3.3 mm.

[0090] The specific capacity of the first negative electrode active material layer is 470 mAh / g, and the specific capacity of the second negative electrode active material layer is 588 mAh / g. The ratio of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer is 0.8. The density of the first negative electrode active material layer is 1.70 g / cc, and the density of the second negative electrode active material layer is 1.36 g / cc. The porosity of the first negative electrode active material layer is 18.5%, and the porosity of the second negative electrode active material layer is 27.9%.

[0091] The negative electrode, separator, and positive electrode prepared as above were combined together, and an electrolyte was used to fabricate a lithium secondary battery.

[0092] Example 2 The second negative electrode active material layer was prepared in the same manner as in Example 1, except that the width of the second negative electrode active material layer in the second direction D2 was 13 mm.

[0093] Example 3 The specific capacity of the second negative electrode active material layer was 495 mAh / g. The ratio of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer was 0.95. The density of the second negative electrode active material layer was 1.62 g / cc. The porosity of the first negative electrode active material layer was 17.9%, and the porosity of the second negative electrode active material layer was 20.5%. Except for this, the same method as in Example 1 was used for preparation.

[0094] Example 4 The second negative electrode active material layer had a specific capacity of 495 mAh / g. The ratio of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer was 0.95. The second negative electrode active material layer had a density of 1.62 g / cc. The first negative electrode active material layer had a porosity of 17.7%, and the second negative electrode active material layer had a porosity of 20.9%. The second negative electrode active material layer had a width of 13 mm in the second direction D2. Except for this, the same method as in Example 1 was used for preparation.

[0095] Comparative Example 1 The second negative electrode active material layer was omitted, and the negative electrode active material layer was prepared using only the first negative electrode active material slurry. Except for this, the negative electrode active material layer was prepared in the same manner as in Example 1.

[0096] Comparative Example 2 The second negative electrode active material layer had a specific capacity of 671 mAh / g. The ratio of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer was 0.7. The second negative electrode active material layer had a density of 1.19 g / cc. The second negative electrode active material layer had a porosity of 32.8%. The second negative electrode active material layer had a width of 13 mm in the second direction D2. Except for this, the second negative electrode active material layer was prepared in the same manner as in Example 1.

[0097] Comparative Example 3 The porosity of the first negative electrode active material layer was 18.7%, and the porosity of the second negative electrode active material layer was 28.6%. The width of the second negative electrode active material layer in the second direction D2 was 2 mm. Except for this, the same method as in Example 1 was used for preparation.

[0098] Comparative Example 4 The porosity of the first negative electrode active material layer was 17.7%, and the porosity of the second negative electrode active material layer was 27.7%. The width of the second negative electrode active material layer in the second direction D2 was 16.5 mm. Except for this, the same method as in Example 1 was used for preparation.

[0099] Comparative Example 5 The second negative electrode active material layer had a specific capacity of 495 mAh / g. The ratio of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer was 0.95. The second negative electrode active material layer had a density of 1.62 g / cc. The first negative electrode active material layer had a porosity of 17.3%, and the second negative electrode active material layer had a porosity of 20.8%. The second negative electrode active material layer had a width of 16.5 mm in the second direction D2. Except for this, the same method as in Example 1 was used for preparation.

[0100] The negative electrode active material layers according to Examples 1 to 4 and Comparative Examples 1 to 5 are compared in Table 1 below.

[0101] [Table 1]

[0102] Experimental Example 1: Analysis of non-wetted area width and cell appearance defects The width of the non-wetted region of the negative electrode and the occurrence of cell appearance defects were analyzed according to Examples 1 to 4 and Comparative Examples 1 to 5. The results are shown in Table 2 below.

[0103] [Table 2]

[0104] Referring to Table 2, it was confirmed that, in Examples 1 and 2, when the ratio (X / Y) of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer was 0.8, the width (A) of the non-wetted region decreased regardless of the width (Z) of the second negative electrode active material layer. In Examples 3 and 4, when the ratio (X / Y) of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer was 0.95, the width (A) of the non-wetted region decreased as the width (Z) of the second negative electrode active material layer increased.

[0105] In Comparative Example 1, the second negative electrode active material layer was omitted, and the width (A) of the non-wetted region was 24 mm, which was wider than in the Examples. In Comparative Example 2, the width (A) of the non-wetted region was reduced, but poor cell appearance was observed. Therefore, it was confirmed that if the ratio (X / Y) of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer was less than 0.75, poor cell appearance would occur due to expansion of the second negative electrode active material layer.

[0106] In Comparative Example 3, the width A of the non-wetted region was 23 mm, which was wider than that of the Examples. Therefore, it was confirmed that if the width of the second negative electrode active material layer was less than 3 mm, the effect of reducing the non-wetted region was small. In Comparative Examples 4 and 5, poor cell appearance was found. Therefore, it was confirmed that if the width of the second negative electrode active material layer was greater than 15 mm, poor cell appearance occurred.

[0107] Referring to the examples and comparative examples, it was confirmed that when the ratio (X / Y) of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer is in the range of 0.75 to 0.95 and the width (Z) of the second negative electrode active material layer is in the range of 3 mm to 15 mm, the non-wetted area of ​​the negative electrode is reduced.

[0108] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention may be embodied in other specific forms without changing the technical spirit or essential features thereof. Therefore, it should be understood that the embodiments described above are illustrative in all respects and are not limiting. [Explanation of symbols]

[0109] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab AML1 positive electrode active material layer AML2 negative electrode active material layer AML2a 1st negative electrode active material layer AML2b 2nd negative electrode active material layer

Claims

1. a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, the negative electrode active material layer having a major axis in a first direction; The negative electrode active material layer is first negative electrode active material layers spaced apart from each other in a second direction intersecting the first direction; a second negative electrode active material layer between the first negative electrode active material layers, A ratio of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer is 0.75 to 0.

95.

2. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the width of the second negative electrode active material layer in the second direction is 3 mm to 15 mm.

3. The negative electrode for a lithium secondary battery according to claim 1 , wherein the width of the first negative electrode active material layer in the second direction is greater than the width of the second negative electrode active material layer in the second direction.

4. The negative electrode of claim 1 , wherein the silicon content in the second negative electrode active material layer is greater than the silicon content in the first negative electrode active material layer.

5. The negative electrode for a lithium secondary battery according to claim 1 , wherein the porosity of the second negative electrode active material layer is greater than the porosity of the first negative electrode active material layer.

6. The negative electrode for a lithium secondary battery according to claim 1 , wherein the density of the first negative electrode active material layer is greater than the density of the second negative electrode active material layer.

7. each of the first and second negative electrode active material layers includes a silicon-carbon composite; The negative electrode of claim 1 , wherein a ratio of silicon to carbon in the first negative electrode active material layer is different from a ratio of silicon to carbon in the second negative electrode active material layer.

8. 2 . The negative electrode for a lithium secondary battery according to claim 1 , wherein a ratio of a width of the second negative electrode active material layer in the second direction to a width of the negative electrode current collector in the second direction is 5% to 20%.

9. a positive electrode including a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector; a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector; the negative electrode active material layer has a major axis in a first direction, a separator between the positive electrode and the negative electrode, The negative electrode active material layer is first negative electrode active material layers spaced apart from each other in a second direction intersecting the first direction; a second negative electrode active material layer between the first negative electrode active material layers, the specific capacity of the second negative electrode active material layer is greater than the specific capacity of the first negative electrode active material layer; A lithium secondary battery, wherein a ratio of the width of the second negative electrode active material layer in the second direction to the width of the negative electrode current collector in the second direction is 5% to 20%.

10. 10. The lithium secondary battery of claim 9, wherein a ratio of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer is 0.75 to 0.

95.

11. The lithium secondary battery of claim 9 , wherein the porosity of the second negative electrode active material layer is greater than the porosity of the first negative electrode active material layer.

12. The lithium secondary battery of claim 9 , wherein the density of the first negative electrode active material layer is greater than the density of the second negative electrode active material layer.

13. each of the first and second negative electrode active material layers contains a silicon-carbon composite; The lithium secondary battery of claim 9 , wherein a ratio of silicon to carbon in the first negative electrode active material layer is different from a ratio of silicon to carbon in the second negative electrode active material layer.

14. preparing a first negative electrode active material slurry and a second negative electrode active material slurry; applying the first and second negative electrode active material slurries to a negative electrode current collector in a first direction to form a first negative electrode active material layer and a second negative electrode active material layer, respectively; A method for manufacturing a lithium secondary battery, wherein a ratio of the specific capacity of the first negative electrode active material layer to the specific capacity of the second negative electrode active material layer is 0.75 to 0.

95.

15. each of the first and second negative electrode active material slurries contains a silicon-carbon composite; 15. The method of claim 14, wherein a ratio of silicon to carbon in the first negative electrode active material slurry is different from a ratio of silicon to carbon in the second negative electrode active material slurry.

16. forming the first and second negative electrode active material layers may include applying the first and second negative electrode active material slurries to the negative electrode current collector while being spaced apart from each other in a second direction intersecting the first direction; The method of claim 14, wherein the first and second negative electrode active material layers extend in the first direction.

17. 17. The method of claim 16, wherein the width of the first negative electrode active material layer in the second direction is greater than the width of the second negative electrode active material layer in the second direction.

18. 18. The method of claim 17, wherein a height of the first negative electrode active material slurry coated on the negative electrode current collector is greater than a height of the second negative electrode active material slurry coated on the negative electrode current collector.

19. The forming of the first and second negative electrode active material layers may further include performing a drying process and a rolling process on the applied first and second negative electrode active material slurries, 15. The method for manufacturing a lithium secondary battery according to claim 14, wherein the heights of the first and second negative electrode active material layers are substantially the same.

20. 15. The method of claim 14, wherein a ratio of a width of the second negative electrode active material layer in the second direction to a width of the negative electrode current collector in the second direction intersecting the first direction is 5% to 20%.

Images