Negative electrode for lithium secondary battery and lithium secondary battery including the same

Abstract

To provide a negative electrode for a lithium secondary battery in which the growth of lithium dendrites is suppressed.SOLUTION: The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same, and the negative electrode includes a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a carrier disposed on the negative electrode active material layer and containing LiNO3 and a binder.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, each containing an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated at the cathode and anode.

[0004] However, during charging of a lithium secondary battery, lithium crystalline nuclei are formed on the surface of the negative electrode, and lithium dendrites may grow around the lithium crystalline nuclei. These lithium dendrites are considered to be the main cause of reduced life and safety of lithium secondary batteries (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Korean Patent No. 10-0686848 Summary of the Invention [Problem to be solved by the invention]

[0006] One embodiment provides a negative electrode for a lithium secondary battery in which the growth of lithium dendrites is suppressed. Another embodiment provides a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0007] One embodiment provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector; a negative electrode active material layer located on the negative electrode current collector; and a protective layer located on the negative electrode active material layer and comprising LiNO.

[0008] Another embodiment provides a lithium secondary battery including: a negative electrode according to the above embodiment; a positive electrode; and a separator between the negative electrode and the positive electrode. [Effects of the Invention]

[0009] In the anode according to one embodiment, a stable SEI (Solid electrolyte interphase) film is formed by the LiNO3, which inhibits the growth of lithium dendrites and improves the life of the lithium secondary battery. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the present invention is given by way of example only, and the present invention is not limited thereto, but is defined only by the scope of the claims that follow.

[0012] Unless otherwise specified in this specification, when a layer, film, region, plate, or other part is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between.

[0013] Unless otherwise specified herein, the singular can also include the plural, and unless otherwise specified, "A or B" can mean "including A, including B, or including A and B."

[0014] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0015] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope or scanning electron microscope. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. When measuring by the laser diffraction method, more specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac's MT3000) and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W, and the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0016] As used herein, "(meth)acrylic" means that both acrylic and methacrylic are possible.

[0017] (Negative electrode) One embodiment provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector; a negative electrode active material layer located on the negative electrode current collector; and a protective layer located on the negative electrode active material layer and comprising LiNO3.

[0018] LiNO 3 LiNO3 is insoluble in non-aqueous organic solvents (poorly soluble), has excellent ionic conductivity, and can react with non-aqueous organic solvents to form a stable SEI (Solid electrolyte interphase) film on the surface of the negative electrode.

[0019] Therefore, a lithium secondary battery using a negative electrode with a protective layer containing LiNO3 can have a longer life at room temperature and high temperature than a negative electrode without a protective layer.

[0020] Meanwhile, lithium secondary batteries using anodes with a protective layer containing LiCl instead of LiNO3 may show improved performance compared to anodes without a protective layer, but may still exhibit reduced lifespan compared to anodes with a protective layer containing LiNO3. This may indicate that a more stable SEI film is formed when LiNO3 is used compared to LiCl.

[0021] Although it is possible to use a binder in the protective layer, it is also possible to form a protective layer consisting of only LiNO3.

[0022] Generally, the binder can serve to allow the particles to adhere well to each other and to the negative electrode active material layer.

[0023] However, when LiNO3 is present, the binders may clump together, and if the binder is a polymeric material, it may act as a resistor on the electrode.

[0024] In contrast, when the protective layer is formed using only LiNO3, LiNO3 can form a stable SEI film on the surface of the negative electrode during the first cycle of the lithium secondary battery.

[0025] Therefore, in one embodiment, when manufacturing the negative electrode, it is preferable to form the protective layer using only LiNO3 without using a binder. For example, methods for forming the protective layer using only LiNO3 include a spray method and a vapor deposition method.

[0026] The life of the lithium secondary battery can be controlled by the amount of LiNO3 used.

[0027] For example, LiNO3 can be contained in an amount of 0.01 to 10 parts by weight, or 0.1 to 5 parts by weight, based on 100 parts by weight of the total amount of the negative electrode active material layer.

[0028] Furthermore, the amount of LiNO3 can be 5 to 100 wt %, 20 to 99 wt %, or 50 to 95 wt % relative to the total amount of the protective layer.

[0029] Within this range, as the amount of LiNO3 used increases, a more stable SEI (Solid electrolyte interphase) film can be formed by LiNO3.

[0030] binder Of course, in one embodiment, the protective layer may further comprise a binder.

[0031] 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)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, and the like.

[0032] For example, when a binder is included, it may be 0 to 20% by weight, 0 to 2% by weight, or 0.1 to 1% by weight (but greater than 0% by weight) relative to the total weight of the protective layer.

[0033] Within this range, the binder can uniformly coat the LiNO3 salt, and when inorganic particles are added, can effectively adhere the inorganic particles to the negative electrode active material layer, and can uniformly coat and adhere the LiNO3 and inorganic particles to the surface of the negative electrode active material layer.

[0034] inorganic particles The protective layer may further include inorganic particles.

[0035] Generally known lithium secondary batteries use a polyolefin-based substrate as a separator to prevent short circuits between the positive and negative electrodes, but the polyolefin-based substrate has a drawback in that it has poor heat resistance.

[0036] When inorganic particles are coated on the surface of the negative electrode active material layer, the inclusion of Li-Me-O bonds allows the formation of a more stable SEI film, which effectively suppresses side reactions. Furthermore, the coating has high ionic conductivity, which contributes to improving the performance of lithium secondary batteries.

[0037] Furthermore, since inorganic particles have excellent heat resistance, a protective layer further containing inorganic particles can complement the heat resistance of the polyolefin-based substrate.

[0038] The inorganic particles can be Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, or a combination thereof.

[0039] The average particle size (D50) of the inorganic particles can be 10 to 3,000 nm, 100 to 2,000 nm, or 300 to 1,500 nm.

[0040] The inorganic particles may be present in an amount of 5 to 70% by weight, 10 to 50% by weight, or 15 to 30% by weight based on the total weight of the protective layer.

[0041] Within this range, an SEI film with excellent ion conductivity is formed on the surface of the negative electrode active material layer, thereby increasing the life of the negative electrode and complementing the heat resistance of the polyolefin-based substrate.

[0042] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0043] The material capable of reversibly inserting / extracting lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0044] As an alloy of 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.

[0045] As a substance capable of doping and undoping 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 alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations 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.

[0046] 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 where silicon particles are coated with amorphous carbon on the surface. For example, it can include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surface of these secondary particles. 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.

[0047] The silicon-carbon composite can further contain 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 this core.

[0048] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0049] negative electrode The negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive agent.

[0050] For example, the negative electrode active material layer can contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive agent.

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

[0052] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0053] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene 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.

[0054] 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.

[0055] The dry binder is a fiberizable polymeric material, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0056] The conductive agent is used to impart conductivity to the electrode, and any electron-conductive material that does not undergo chemical change in the battery that is constructed can 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.

[0057] The negative electrode current collector 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.

[0058] (lithium secondary battery) Another embodiment provides a lithium secondary battery including: a negative electrode according to the above embodiment; a positive electrode; and a separator between the negative electrode and the positive electrode.

[0059] The lithium secondary battery according to an embodiment may have an improved lifespan because it includes the anode according to the embodiment described above.

[0060] Hereinafter, a lithium secondary battery according to an embodiment will be described in detail, excluding redundant description of the negative electrode.

[0061] positive electrode active material The positive electrode active material may be a compound capable of reversibly inserting and extracting lithium (lithiated insertion compound). Specifically, one or more of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0062] The composite oxide may be 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.

[0063] 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 L1 d G e O2(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4(0.90≦a≦1.8) In the 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; L 1 is Mn, Al or a combination thereof.

[0064] For example, the positive electrode active material may be a high-nickel 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 positive electrode active material can realize high capacity and therefore can be applied to high-capacity, high-density lithium secondary batteries.

[0065] positive electrode A positive electrode for a lithium secondary battery can include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer includes a positive electrode active material and can further include a binder and / or a conductive agent.

[0066] As an example, the positive electrode may further include an additive that can act as a sacrificial positive electrode.

[0067] The content of the positive electrode active material may be 90% by weight to 99.5% by weight relative to 100% by weight of the positive electrode active material layer, and the contents of the binder and conductive agent may each be 0.5% by weight to 5% by weight relative to 100% by weight of the positive electrode active material layer.

[0068] The binder serves to effectively adhere the positive electrode active material particles to each other and to effectively adhere the positive electrode active material to the current collector. Representative examples of the binder 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)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0069] The conductive agent is used to impart conductivity to the electrode, and any electron-conductive material that does not undergo chemical change in the battery that is constructed can be used. Examples of conductive agents 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 containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0070] The current collector may be made of Al, but is not limited thereto.

[0071] electrolyte The electrolyte for the lithium secondary battery contains a non-aqueous organic solvent and a lithium salt.

[0072] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate.

[0073] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0074] Examples of carbonate solvents 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), butylene carbonate (BC), etc. 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, caprolactone, etc. 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.

[0075] The non-aqueous organic solvents can be used alone or in combination of two or more kinds.

[0076] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0077] Lithium salts are substances dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. 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+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0078] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. Such a separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these materials. Of course, 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.

[0079] The separator 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.

[0080] 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.

[0081] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0082] 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.

[0083] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a form in which a coating layer containing an organic material and a coating layer containing an inorganic material are stacked.

[0084] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams illustrating a lithium secondary battery according to an embodiment, with FIG. 1 illustrating a cylindrical battery, FIG. 2 illustrating a prismatic battery, and FIGS. 3 and 4 illustrating pouch battery types. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween, and a case 50 housing the electrode assembly 40. 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. 1. Also, as shown in FIG. 2, 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. 3 and 4, 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 the current generated in the electrode assembly 40 to the outside.

[0085] 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.

[0086] Examples and comparative examples of the present invention will be described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0087] Example 1 (1) Manufacturing of the negative electrode The negative electrode active material was a 5:5 blend of artificial graphite and natural graphite, mixed with 14.8% Si-C composite. A composition containing 97.5 wt% of the negative electrode active material, 1.0 wt% of carboxymethyl cellulose (CMC), and 1.5 wt% of styrene butadiene rubber (SBR) was mixed in an aqueous solvent to prepare a negative electrode active material slurry. The resulting negative electrode active material slurry was applied to a copper current collector, dried, and rolled to form a negative electrode active material layer.

[0088] The Si-C composite used had a core containing artificial graphite and silicon particles, and the surface of the core was coated with carbide of coal-based pitch.

[0089] Thereafter, 0.5 parts by weight of LiNO3 was sprayed onto 100 parts by weight of the composition, and then dried to form a protective layer.

[0090] As a result, in the final negative electrode obtained, the thickness of the negative electrode active material layer was 85 μm, and the thickness of the protective layer was about 1 μm.

[0091] (2) Manufacturing of the positive electrode LiNi 1※y Al x Co y A positive electrode active material slurry was prepared by mixing 97.2 wt% O2, 0.5 wt% carbon nanotubes, and 1.1 wt% polyvinylidene fluoride in N-methylpyrrolidone solvent. The resulting positive electrode active material slurry was applied to an Al current collector, dried, and rolled to prepare a positive electrode.

[0092] (3) Manufacture of lithium secondary batteries The positive and negative electrodes prepared as described above were assembled with a 10 μm thick polyethylene separator to prepare an electrode assembly, and an electrolyte solution was injected into the assembly to prepare a lithium secondary battery.

[0093] The electrolyte used was a solution of 1.15M LiPF6 dissolved in a solvent made by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 30:40:40.

[0094] Example 2 A negative electrode and a lithium secondary battery were produced in the same manner as in Example 1, except for the method of forming the protective layer.

[0095] Specifically, LiNO3 was applied by spraying in an amount of 1 part by weight to 100 parts by weight of the composition of Example 1, and then dried to form a protective layer.

[0096] Example 3 A negative electrode and a lithium secondary battery were produced in the same manner as in Example 1, except for the method of forming the protective layer.

[0097] Specifically, 5 parts by weight of LiNO3 was applied to 100 parts by weight of the composition of Example 1 by spraying, and then dried to form a protective layer.

[0098] Example 4 A negative electrode and a lithium secondary battery were produced in the same manner as in Example 1, except for the method of forming the protective layer.

[0099] Specifically, a protective layer composition containing 399% by weight of LiNO and 1% by weight of CMC (carboxymethyl cellulose) binder was prepared. 1 part by weight of the protective layer composition was spray-coated for 100 parts by weight of the composition of Example 1, and then dried to form a protective layer.

[0100] Example 5 A negative electrode and a lithium secondary battery were produced in the same manner as in Example 1, except for the method of forming the protective layer.

[0101] Specifically, a protective layer composition containing 94 wt% LiNO3, 5 wt% Al2O3 inorganic particles (D50: 2 μm), and 1 wt% CMC (carboxymethyl cellulose) binder was prepared. 1 part by weight of this protective layer composition was spray-coated for 100 parts by weight of the composition of Example 1, and then dried to form a protective layer.

[0102] Example 6 A negative electrode and a lithium secondary battery were produced in the same manner as in Example 1, except for the method of forming the protective layer.

[0103] Specifically, a protective layer composition containing 86.5 wt% LiNO3, 12.5 wt% Al2O3 inorganic particles (D50: 2 μm), and 1 wt% CMC (carboxymethyl cellulose) binder was prepared. 1 part by weight of this protective layer composition was spray-coated for 100 parts by weight of the composition of Example 1, and then dried to form a protective layer.

[0104] Comparative Example 1 A negative electrode and a lithium secondary battery were produced in the same manner as in Example 1, except that no protective layer was formed.

[0105] Comparative Example 2 A negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 100% by weight of the binder was used in preparing the protective layer composition.

[0106] Comparative Example 3 A negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the protective layer composition was prepared using 86.5 wt% LiCl, 12.5 wt% AlO (D50: 2,000 nm) inorganic particles, and 1 wt% CMC as a binder.

[0107] Evaluation example 1: Evaluation of room temperature characteristics of lithium secondary batteries Each lithium secondary battery in the Examples and Comparative Examples was cycled 50 times in total, with one cycle consisting of 2.0 C charge (CC / CV, 4.53 V, 0.025 C cut-off) and 1.0 C discharge (CC, 3 V cut-off) at 25°C, and the capacity retention rate was evaluated using the following mathematical formula 1. The evaluation results are shown in Table 1 below. [Formula 1] Capacity retention rate (%) = 100 * [discharge capacity after 50 charge / discharge cycles / discharge capacity after 1 charge / discharge cycle]

[0108] Evaluation example 2: Evaluation of high-temperature characteristics of lithium secondary batteries Each lithium secondary battery in the Examples and Comparative Examples was cycled 50 times in total, with one cycle consisting of 2.0 C charge (CC / CV, 4.53 V, 0.025 C cut-off) and 1.0 C discharge (CC, 3 V cut-off) at 45° C., and the capacity retention rate was evaluated using Equation 1. The evaluation results are shown in Table 1 below.

[0109] [Table 1]

[0110] In Table 1, "content in negative electrode" indicates the weight of the protective layer in "parts by weight" when the total weight of the negative electrode active material layer is 100 parts by weight. Table 1 also shows the weight ratio of lithium salt:binder:inorganic particles in the protective layer.

[0111] Table 1 shows that the lithium secondary batteries using negative electrodes with protective layers containing LiNO3 (Examples 1 to 6) have improved lifespans at room temperature and high temperatures compared to the negative electrodes without protective layers (Comparative Example 1).

[0112] Here, we can see that LiNO3 forms a stable SEI film and inhibits the growth of lithium dendrites. Although a binder can be used (Examples 4 to 6), a protective layer consisting of LiNO3 alone can also be formed (Examples 1 to 3), and the life of the lithium secondary battery can be controlled by the amount of LiNO3 used. Furthermore, when inorganic particles are added to form a protective layer (Examples 5 and 6), the heat resistance is improved, resulting in an improved high-temperature life.

[0113] On the other hand, a lithium secondary battery using an anode coated only with a binder (Comparative Example 2) lacked ionic conductivity and was unable to operate as a lithium secondary battery, and an anode using an anode with a protective layer containing LiCl instead of LiNO3 (Comparative Example 3) showed an improvement over Comparative Example 1 but a shorter lifespan than Examples 1 to 6. This may indicate that a more stable SEI film is formed when LiNO3 is used compared to LiCl.

[0114] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is to be understood that these modifications also fall within the scope of the present invention. [Explanation of symbols]

[0115] 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: Case 60: Sealing material 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. Negative electrode current collector; a negative electrode active material layer located on the negative electrode current collector; and LiNO 3 a protective layer comprising The LiNO 3 is contained in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the total amount of the negative electrode active material layer. Negative electrode for lithium secondary batteries.

2. The LiNO 3 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the protective layer contains 5 to 100% by weight of the protective layer.

3. The negative electrode for a lithium secondary battery according to claim 1 , wherein the protective layer further comprises a binder, inorganic particles, or a combination thereof.

4. 4. The negative electrode for a lithium secondary battery according to claim 3, wherein the binder is polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, an epoxy resin, a (meth)acrylic resin, a polyester resin, nylon, or a combination thereof.

5. the binder is contained in an amount of 0 to 20% by weight (but not more than 0% by weight) based on the total amount of the protective layer; The inorganic particles are Al 2 O 3 , SiO 2 , TiO 2 , SnO 2 , CeO 2 , MgO, NiO, CaO, GaO, ZnO, ZrO 2 , Y 2 O 3 , SrTiO 3 , BaTiO 3 , Mg(OH) 2 4. The negative electrode for a lithium secondary battery according to claim 3, wherein the negative electrode is a SiO2-based material, a SiO2-based material, a boehmite material, or a combination thereof.

6. 4. The negative electrode for a lithium secondary battery according to claim 3, wherein the inorganic particles are contained in an amount of 5 to 70% by weight based on the total amount of the protective layer.

7. the negative electrode active material layer contains a negative electrode active material, The negative electrode for a lithium secondary battery according to claim 1 , wherein the negative electrode active material comprises a carbon-based negative electrode active material, a Si-based negative electrode active material, or a combination thereof.

8. The negative electrode according to any one of claims 1 to 7; a positive electrode; and a separator between the negative electrode and the positive electrode; Lithium secondary battery.

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