Positive electrode for rechargeable lithium batteries and rechargeable lithium battery comprising the same

Abstract

A positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the positive electrode are disclosed. The positive electrode for the rechargeable lithium battery includes a substrate and a positive electrode active material layer on the substrate. The positive electrode active material layer includes MXene and a positive electrode active material. The amount of MXene increases from the top to the bottom of the positive electrode active material layer.

Description

Technical Field

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

[0002] Rechargeable lithium-ion batteries can be recharged, and their energy density per unit weight is three times or more higher than that of traditional lead-acid, nickel-cadmium, nickel-metal hydride, and nickel-zinc batteries. Rechargeable lithium-ion batteries can also be charged at high rates, thus enabling their commercial manufacture for use in laptops, cell phones, power tools, electric bicycles, and more. The increased energy density can be advantageous.

[0003] Rechargeable lithium batteries are typically manufactured by injecting an electrolyte solution into an electrode assembly, which includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode active material capable of inserting / deintercalating lithium ions, and the negative electrode includes a negative electrode active material capable of inserting / deintercalating lithium ions.

[0004] However, during the charging / discharging process of a rechargeable lithium battery, transition metals may be eluted from the positive electrode active material, potentially degrading the SEI (solid electrolyte interface) film at the interface between the positive electrode and the electrolyte solution, and reducing the capacity and stability of the rechargeable lithium battery. Summary of the Invention

[0005] Some example embodiments include a positive electrode for a rechargeable lithium battery that improves conductivity while reducing or inhibiting the elution of transition metals from the positive electrode active material and stably retains an SEI film at the interface between the positive electrode and the electrolyte solution.

[0006] Some example embodiments include a positive electrode for a rechargeable lithium battery, the positive electrode comprising a substrate and a positive electrode active material layer on the substrate. The positive electrode active material layer comprises MXene and a positive electrode active material. The amount of MXene increases from the top to the bottom of the positive electrode active material layer.

[0007] Some example embodiments include a rechargeable lithium battery comprising a positive electrode according to the foregoing example embodiments.

[0008] The positive electrode for a rechargeable lithium battery according to the above example embodiments can improve conductivity while reducing or suppressing the elution of transition metals from the positive electrode active material and stably maintaining it as an SEI film at the interface between the positive electrode and the electrolyte solution.

[0009] Therefore, a rechargeable lithium battery including a positive electrode according to the above example embodiments can exhibit desired or improved cycle life characteristics, stability, etc. Attached Figure Description

[0010] Figure 1 This is a schematic diagram illustrating a positive electrode active material layer for a rechargeable lithium battery according to some example embodiments.

[0011] Figures 2 to 5 This is a schematic diagram illustrating a rechargeable lithium battery according to some example embodiments. Detailed Implementation

[0012] Hereinafter, exemplary embodiments of the present disclosure are described in detail. However, these embodiments are examples, and the present disclosure is not limited thereto, and is defined by the scope of the claims.

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

[0014] As used herein, the singular may also include the plural unless otherwise specifically defined. Additionally, unless otherwise stated, “A or B” may mean “including A, including B, or including both A and B”.

[0015] As used herein, “combination of” can refer to a mixture, stack, complex, copolymer, alloy, blend, or reaction product of the components.

[0016] As used herein, unless otherwise defined, particle size can be the average particle size. Alternatively, particle size can refer to the average particle size (D50), which means the diameter of particles having a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods known to those skilled in the art (e.g., by a particle size analyzer, or by transmission electron microscopy or scanning electron microscopy images). Optionally, data analysis can be performed using a dynamic light scattering measurement device, and the number of particles in each particle size range can be counted. Thus, the average particle size (D50) value can be readily obtained by calculation. Optionally, the average particle size (D50) can be measured using laser diffraction. When measured by laser diffraction, for example, the particles to be measured are dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac MT 3000) and irradiated with ultrasonic waves at approximately 28 kHz and an output of 60 W to calculate the average particle size (D50) based on a particle size distribution of 50% in the measurement device.

[0017] When the terms “about” or “substantially” are used in conjunction with numerical values ​​in this specification, it means that the relevant numerical value includes a tolerance of ±10% around the stated value. When a range is specified, the range includes all values ​​within that range, such as increments of 0.1%.

[0018] Positive electrode: Figure 1 This is a schematic diagram illustrating a positive electrode active material layer for a rechargeable lithium battery according to some example embodiments.

[0019] Some example embodiments include a positive electrode for a rechargeable lithium battery, the positive electrode comprising a substrate and a positive electrode active material layer on the substrate, wherein the positive electrode active material layer comprises MXene 1 and positive electrode active material 2, and the amount of MXene 1 increases from the top to the bottom of the positive electrode active material layer. The positive electrode active material layer may also optionally include a binder 3.

[0020] (1) The positive electrode for a rechargeable lithium battery according to the above example embodiment includes MXene.

[0021] Because Maxene (also known as MXene) is a crystalline material, it can reduce or suppress the elution of transition metals from the positive electrode active material during the charging / discharging process of a rechargeable lithium battery and stably maintain the SEI film at the interface between the positive electrode and the electrolyte solution.

[0022] In addition, "Maxene" is a two-dimensional nanomaterial in which transition metal layers and carbon layers are stacked alternately, and it can exhibit desired or improved conductivity compared to commonly known conductive materials (e.g., carbon, graphene, etc.).

[0023] In some example embodiments, the aforementioned Maxene is used in place of or in combination with commonly known conductive materials. Therefore, the conductivity of the positive electrode can be improved.

[0024] (2) In the positive electrode of a rechargeable lithium battery according to the above example embodiment, the amount of MXene can increase from the upper part to the lower part of the positive electrode active material layer.

[0025] By increasing the amount of MXene in the lower part of the above-mentioned positive electrode active material layer near the substrate, the effect of (2) can be enhanced at the interface with the substrate.

[0026] Meanwhile, by reducing the amount of MXene in the upper part of the positive electrode active material layer that is far from the substrate, the porosity in the upper part can be increased, and the amount of positive electrode active material used as a capacity display material can be increased.

[0027] The positive electrode according to some example embodiments is described in detail below.

[0028] MXene Based on a total positive electrode active material layer of 100 wt%, the total amount of MXene, including in the upper and lower parts of the positive electrode active material layer, may be in the range of about 0.1 wt% to about 5 wt%, about 0.3 wt% to about 3 wt%, or about 0.5 wt% to about 1.5 wt%.

[0029] The amount of MXene included in the lower portion of the positive electrode active material layer can range from about 0.5 wt% to about 5 wt%, about 1 wt% to about 4 wt%, or about 2 wt% to about 3 wt%; and the amount of MXene included in the upper portion of the positive electrode active material layer can range from 0 wt% to about 3 wt%, about 0.1 wt% to about 2.5 wt%, or about 0.2 wt% to about 2 wt%. However, the amount of MXene included in the lower portion of the positive electrode active material layer can be greater than the amount of MXene included in the upper portion.

[0030] Within the aforementioned range, the aforementioned effects of MXene can be enhanced.

[0031] The positive electrode active material layer may have a multilayer structure in which the amount of MXene increases intermittently from the top to the bottom of the positive electrode active material layer; or it may have a monolayer structure in which the amount of MXene increases continuously or substantially continuously from the top to the bottom of the positive electrode active material layer.

[0032] For example, the positive electrode active material layer can have a multilayer structure, and the boundary between the lower and upper parts of the positive electrode active material layer can be located in the range of about 30% to about 70%, or about 40% to about 60% of the total thickness (100% thickness) of the positive electrode active material layer.

[0033] Conversely, the positive electrode active material layer has a monolayer structure; and the amount of MXene relative to the increase in thickness of the positive electrode active material layer from the top to the bottom can be in the range of about 20 wt% to about 30 wt%, or about 0.1 g / μm to about 0.2 g / μm.

[0034] MXene can be represented by chemical formula 1.

[0035] Chemical Formula 1: (M 1 ) n+1 (X 1 ) n T s .

[0036] The description of chemical formula 1 is as follows.

[0037] X 1 It can be located in M 1 Within the octahedral array.

[0038] M 1 It may include at least one metal selected from Group IIIB, Group IVB, Group VB, Group VIB and combinations thereof.

[0039] X can include C or N.

[0040] n can be equal to 1, 2 or 3.

[0041] T s It may include functional groups such as or including at least one of alkoxides, carboxylates, halides, hydroxides, hydrides, oxides, low-valent oxides, nitrides, low-valent nitrides, sulfides, thiols, and combinations thereof.

[0042] For example, MXene can be or includes Ti3C2(OH)2, which is titanium carbide with hydroxyl (-OH) surface functional groups.

[0043] Positive electrode active material The positive electrode active material may be or include at least one of the following: lithium nickel oxide represented by chemical formula 11, lithium cobalt oxide represented by chemical formula 12, lithium iron phosphate compound represented by chemical formula 13, cobalt-free lithium nickel manganese oxide represented by chemical formula 14, or combinations thereof.

[0044] Chemical Formula 11: Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 .

[0045] In chemical formula 11, 0.9 ≤ a1 ≤ 1.8, 0.3 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.7, 0 ≤ z1 ≤ 0.7, 0.9 ≤ x1 + y1 + z1 ≤ 1.1, and 0 ≤ b1 ≤ 0.1, M 1 and M 2 Each is independently one or more of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is or includes one or more of F, P, and S.

[0046] In chemical formula 11, 0.6≤x1≤1, 0≤y1≤0.4, and 0≤z1≤0.4; or 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2.

[0047] Chemical formula 12: Lia2 Co x2 M 3 y2 O 2-b2 X b2 。

[0048] In Chemical Formula 12, 0.9 ≤ a2 ≤ 1.8, 0.7 ≤ x2 ≤ 1, 0 ≤ y2 ≤ 0.3, 0.9 ≤ x2 + y2 ≤ 1.1 and 0 ≤ b2 ≤ 0.1, M 3 is or includes one or more of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is or includes one or more of F, P and S.

[0049] Chemical Formula 13: Li a3 Fe x3 M 4 y3 PO 4-b3 X b3 。

[0050] In Chemical Formula 13, 0.9 ≤ a3 ≤ 1.8, 0.6 ≤ x3 ≤ 1, 0 ≤ y3 ≤ 0.4, and 0 ≤ b3 ≤ 0.1, M 4 is or includes one or more of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is or includes one or more of F, P and S.

[0051] Chemical Formula 14: Li a4 Ni x4 Mn[[ID=……]] y4 M 5 z4 O 2-b4 X b4 。

[0052] In Chemical Formula 14, 0.9 ≤ a4 ≤ 1.8, 0.8 ≤ x4 < 1, 0 < y4 ≤ 0.2, 0 ≤ z4 ≤ 0.2, 0.9 ≤ x4 + y4 + z4 ≤ 1.1 and 0 ≤ b4 ≤ 0.1, M 5 is or includes one or more of Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W and Zr, and X is or includes one or more of F, P and S.

[0053] The positive electrode active material may consist of only lithium iron phosphate compounds or may include only lithium iron phosphate compounds; or may include a mixture of lithium iron phosphate compounds and at least one of lithium and metal (such as or including at least one of cobalt, manganese, nickel and combinations thereof) composite oxides.

[0054] In the distribution of the positive electrode active material, a mixture of at least one composite oxide of lithium and a metal (such as or including at least one of cobalt, manganese, nickel, and combinations thereof) with a lithium iron phosphate compound may be distributed in the upper part of the positive electrode active material layer. For example, the lithium iron phosphate compound may be distributed only in the upper part of the positive electrode active material layer.

[0055] Based on 100 mol% of metal excluding lithium, a composite oxide of lithium and metal (such as or including at least one of cobalt, manganese, nickel and combinations thereof) may have a nickel content greater than or equal to about 80 mol%.

[0056] The complex oxide of lithium and metal (such as at least one of cobalt, manganese, nickel and combinations thereof) may be or include compounds represented by formula 11; and lithium iron phosphate compounds may be or include compounds represented by formula 13.

[0057] positive electrode The positive electrode for a rechargeable lithium battery may include a current collector and a layer of positive electrode active material on the current collector.

[0058] The positive electrode active material layer may include the positive electrode active material, and may also include a binder and / or a conductive material.

[0059] For example, the positive electrode may also include additives that can constitute a sacrificial positive electrode.

[0060] Based on a 100wt% positive electrode active material layer, the amount of positive electrode active material can be in the range of about 90wt% to about 99.5wt%, and based on a 100wt% positive electrode active material layer, the amounts of binder and conductive material can each be in the range of about 0.5wt% to about 5wt%.

[0061] The binder improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material particles and the current collector. Examples of binders may include, but are not limited to, at least one of the following: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin, and nylon.

[0062] Conductive materials are included to provide electrode conductivity, and any electrically conductive material can be used as a conductive material unless it causes an adverse chemical change in the battery. Examples of conductive materials may include carbon-based materials (such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.), metallic materials including at least one of copper, nickel, aluminum, silver, etc., metal powders or metal fibers, conductive polymers (such as polyphenylene derivatives), or mixtures thereof.

[0063] Rechargeable lithium batteries: Some example embodiments include a rechargeable lithium battery comprising a positive electrode, a negative electrode, and a separator between the positive and negative electrodes as described in the foregoing example embodiments.

[0064] Because this configuration includes the positive electrode of the aforementioned example embodiment, it can exhibit desired or improved cycle life characteristics, stability, output characteristics, etc.

[0065] In the following text, except for any descriptions repeated above, some example embodiments of rechargeable lithium batteries are described in detail.

[0066] Negative electrode active material The negative electrode active material may include at least one of the following: materials that can reversibly insert / deintercalate lithium ions, lithium metal, lithium metal alloys, materials capable of doping / dedoping lithium, or transition metal oxides.

[0067] Materials that can reversibly insert / deintercalate lithium ions can include, for example, crystalline carbon, amorphous carbon, or combinations thereof as carbon-based negative electrode active materials. Crystalline carbon can be irregular, or in the form of flakes, scaly, spherical, or fibrous natural or artificial graphite. Amorphous carbon can be or includes at least one of soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0068] Lithium metal alloys include alloys of lithium and metals (such as or including at least one of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn).

[0069] Materials capable of doping / dedoping lithium can be, or include, Si-based or Sn-based negative electrode active materials. Si-based negative electrode active materials can include silicon, silicon-carbon composites, and SiO₂. xwhere \(0 < x\leq2\), at least one of an Si-Q alloy (where Q is an element such as or including at least one of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof) or a combination thereof. The Sn-based negative electrode active material may be or include at least one of Sn, SnO₂, a Sn-based alloy, or a combination thereof.

[0070] The silicon-carbon composite may be or include a composite of silicon and amorphous carbon. According to some example embodiments, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) assembled from silicon primary particles and an amorphous carbon coating layer (shells) on the surface of the secondary particles. Amorphous carbon may also be present between the silicon primary particles. For example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0071] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer on the surface of the core.

[0072] The Si-based negative electrode active material or the Sn-based negative electrode active material may be mixed with a carbon-based negative electrode active material.

[0073] negative electrode The negative electrode for a rechargeable lithium battery includes a current collector and a negative electrode active material layer 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 material.

[0074] For example, the negative electrode active material layer may include from about 90 wt% to about 99 wt% of a negative electrode active material, from about 0.5 wt% to about 5 wt% of a binder, and from about 0.5 wt% to about 5 wt% of a conductive material. [[ID=E19]]

[0075] The binder may bond the negative electrode active material particles to each other and may also bond the negative electrode active material to the current collector. The binder may be or include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0076] The non-aqueous binder may be at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0077] Waterborne adhesives may include at least one of the following: styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or combinations thereof.

[0078] When an aqueous binder is used as the negative electrode binder, it may also include a cellulose-based compound capable of imparting viscosity. As a cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts may be mixed. The alkali metal may be or include at least one of Na, K, or Li.

[0079] Dry adhesives are or include fibrous polymeric materials and may be or include at least one of, for example, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0080] Conductive materials are included to provide electrode conductivity, and any electrically conductive material can be used as a conductive material unless it causes an adverse chemical change in the battery. Examples of conductive materials include carbon-based materials (such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.), metallic materials including at least one of copper, nickel, aluminum, silver, etc., metal powders or metal fibers, conductive polymers (such as polyphenylene derivatives), or mixtures thereof.

[0081] The negative electrode current collector may include at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0082] Electrolyte solution Electrolyte solutions used in rechargeable lithium batteries include non-aqueous organic solvents and lithium salts.

[0083] Non-aqueous organic solvents constitute the medium for transporting ions that participate in the electrochemical reactions of the battery.

[0084] Non-aqueous organic solvents may be or include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0085] Carbonate solvents may include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC). Ester solvents may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolactone, mevalonolactone, valproic acid lactone, caprolactone, etc. Ether solvents may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Additionally, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc. Aprotic solvents may include at least one of nitriles (such as R-CN (where R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group or includes double bonds, aromatic rings or ether groups, etc.)), amides (such as dimethylformamide), dioxolane (such as 1,3-dioxolane, 1,4-dioxolane, etc.), sulfolane, etc.

[0086] Non-aqueous organic solvents can be used alone or in mixtures of two or more types of solvents.

[0087] In addition, when using carbonate solvents, cyclic carbonates and chain carbonates can be mixed, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0088] The electrolyte solution may also include at least one of vinyl ethyl carbonate, vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or combinations thereof as an additive.

[0089] Lithium salts dissolved in organic solvents supply lithium ions in batteries, enabling rechargeable lithium batteries to operate and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts can 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+1At least one of the following: (SO2) (where x and y are integers in the range of 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalate) phosphate (LiDFBOP), and lithium bis(oxalate) borate (LiBOB).

[0090] diaphragm Depending on the type of rechargeable lithium battery, a separator may be present between the positive and negative electrodes. The separator may include at least one of the following: polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer membrane of two or more layers thereof, and may include mixed multilayer membranes (such as polyethylene / polypropylene bilayer membranes, polyethylene / polypropylene / polyethylene trilayer membranes, polypropylene / polyethylene / polypropylene trilayer membranes, etc.).

[0091] The membrane may include a porous substrate and a coating layer on one or both surfaces of the porous substrate, comprising organic materials, inorganic materials or combinations thereof.

[0092] The porous substrate may be or include a polymer membrane, which is formed of or includes any polymer, such as or includes at least one of polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (Teflon) or copolymers or mixtures of two or more of them.

[0093] Organic materials may include polymers such as polyvinylidene fluoride or (meth)acrylic acid polymers.

[0094] Inorganic materials may include inorganic particles, such as or including at least one of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but are not limited thereto.

[0095] Organic and inorganic materials can be mixed in a coating layer, or a coating layer containing organic materials and a coating layer containing inorganic materials can be stacked together.

[0096] Rechargeable lithium batteries Based on their shape, rechargeable lithium batteries can be classified into cylindrical batteries, prismatic batteries, pouch batteries, or coin-shaped batteries, etc. Figures 2 to 5This is a schematic diagram illustrating a rechargeable lithium battery according to some example embodiments, wherein, Figure 2 It is a cylindrical battery. Figure 3 It is a prismatic battery. Figure 4 and Figure 5 It's a pouch battery. (See reference) Figures 2 to 5 The rechargeable lithium battery 100 includes an electrode assembly 40 and a housing 50. The electrode assembly 40 has a separator 30 disposed between a positive electrode 10 and a negative electrode 20. The electrode assembly 40 is housed within the housing 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte solution (not shown). Figure 2 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of the sealed housing 50. Additionally, in Figure 3 In this context, the rechargeable lithium battery 100 may include a positive electrode lead connector 11, a positive electrode terminal 12 connected to the positive electrode lead connector 11, a negative electrode lead connector 21, and a negative electrode terminal 22 connected to the negative electrode lead connector 21. For example... Figure 4 and Figure 5 As shown, the rechargeable lithium battery 100 includes Figure 5 The electrode connector 70 shown, or Figure 4 The positive electrode terminal 71 and negative electrode terminal 72 shown form an electrical path for guiding the current formed in the electrode assembly 40 to the outside of the rechargeable lithium battery 100.

[0097] The rechargeable lithium battery according to some example embodiments can be used in, for example, automobiles, mobile phones and / or various types of electronic devices, but this disclosure is not limited thereto.

[0098] Examples and comparative examples of this disclosure are described below. However, the following examples are merely examples of this disclosure, and this disclosure is not limited to these examples.

[0099] Example 1 (1) Manufacturing of the positive electrode Prepare an aluminum foil with a thickness of 10 μm as the positive electrode current collector.

[0100] LiFePO4 and LiNi will be used as the active materials for the positive electrode. 0.88 Co 0.08 Al 0.04 O2 is mixed in a weight ratio of 50:50 to form a mixed positive electrode active material, MXene (Ti3C2(OH)2) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed in a weight ratio of 97:1.5:1.5 to disperse in N-methyl-2-pyrrolidone, thereby preparing a first positive electrode slurry.

[0101] The first positive electrode slurry is coated onto an aluminum foil, dried, and then compressed to form the lower part of the positive electrode active material layer (thickness: 50 μm).

[0102] A second positive electrode slurry was prepared by mixing LiFePO4 as the single positive electrode active material, MXene (Ti3C2(OH)2) as the conductive material, and polyvinylidene fluoride (PVDF) as the binder in a weight ratio of 97.2:1.3:1.5 and dispersing them in N-methyl-2-pyrrolidone.

[0103] The second positive electrode slurry is coated on the lower part of the positive electrode active material layer, dried, and then compressed to form the upper part of the positive electrode active material layer (thickness: 50 μm).

[0104] Therefore, based on the total thickness (100%) of the positive electrode active material layer, the thickness of each of the lower and upper parts of the positive electrode active material layer is set to 50%.

[0105] (2) Manufacturing of rechargeable lithium battery cells A mixture of artificial graphite and silicon particles in a weight ratio of 93.5:6.5 was used as the negative electrode active material, and a styrene-butadiene rubber binder and carboxymethyl cellulose were mixed and dispersed in distilled water in a weight ratio of 97:1:2 to prepare a negative electrode active material slurry.

[0106] The negative electrode active material slurry was coated onto a 10 μm thick Cu foil, dried at 100 °C, and then pressed to form a negative electrode active material layer.

[0107] An electrolyte solution was prepared by mixing 1.5M lithium salt (LiPF6) with a carbonate solvent comprising ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) in a volume ratio of 20:40:40.

[0108] The manufactured positive and negative electrodes are assembled to obtain an electrode assembly, which is then inserted into a housing and an electrolyte solution is injected therein to manufacture a 2023 coin-shaped rechargeable lithium battery cell.

[0109] Example 2 The positive electrode and rechargeable lithium battery cell of Example 2 were manufactured in the same manner as in Example 1, except that the weight ratio of the positive electrode active material, MXene and binder was changed to 97.5:1:1.5 when preparing the second positive electrode slurry.

[0110] Example 3 The positive electrode and rechargeable lithium battery cell of Example 3 were manufactured in the same manner as in Example 1, except that the weight ratio of the positive electrode active material, MXene and binder was changed to 98:0.5:1.5 when preparing the second positive electrode slurry.

[0111] Example 4 The weight ratio of the first solid component to the second solid component is 30:70. Therefore, based on the total thickness of the positive electrode active material layer (100% total thickness), the thicknesses of the lower and upper parts of the positive electrode active material layer are 30% and 70%, respectively.

[0112] Despite the differences mentioned above, the positive electrode and rechargeable lithium battery cell of Example 4 are manufactured in the same manner as in Example 2.

[0113] Example 5 The weight ratio of the first solid component to the second solid component is 40:60. Therefore, based on the total thickness of the positive electrode active material layer (100% total thickness), the thicknesses of the lower and upper portions of the positive electrode active material layer are 40% and 60%, respectively.

[0114] Despite the differences mentioned above, the positive electrode and rechargeable lithium battery cell of Example 5 are manufactured in the same manner as in Example 2.

[0115] Example 6 The weight ratio of the first solid component to the second solid component is 60:40. Therefore, based on the total thickness of the positive electrode active material layer (100% of the total thickness), the thicknesses of the lower and upper parts of the positive electrode active material layer are 60% and 40%, respectively.

[0116] Despite the differences mentioned above, the positive electrode and rechargeable lithium battery cell of Example 6 are manufactured in the same manner as in Example 2.

[0117] Example 7 The weight ratio of the first solid component to the second solid component is 70:30. Therefore, based on the total thickness of the positive electrode active material layer (100% total thickness), the thicknesses of the lower and upper parts of the positive electrode active material layer are 70% and 30%, respectively.

[0118] Despite the differences mentioned above, the positive electrode and rechargeable lithium battery cell of Example 7 are manufactured in the same manner as in Example 2.

[0119] Example 8 Prepare an aluminum foil with a thickness of 10 μm as the positive electrode current collector.

[0120] LiFePO4 and LiNi will be used as the active materials for the positive electrode. 0.88 Co 0.08 Al 0.04O2 is mixed in a weight ratio of 50:50 to form a mixed positive electrode active material, MXene (Ti3C2(OH)2) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed in a weight ratio of 97:1.5:1.5 to disperse in N-methyl-2-pyrrolidone, thereby preparing a first positive electrode slurry.

[0121] The first positive electrode paste is coated onto an aluminum foil, dried, and then compressed to form the lower part of the positive electrode active material layer (thickness: 100 / 3μm).

[0122] A second positive electrode slurry was prepared by mixing LiFePO4 as the single positive electrode active material, MXene (Ti3C2(OH)2) as the conductive material, and polyvinylidene fluoride (PVDF) as the binder in a weight ratio of 98:0.5:1.5 and dispersing them in N-methyl-2-pyrrolidone.

[0123] A third positive electrode slurry was prepared by mixing LiFePO4 as the single positive electrode active material, MXene (Ti3C2(OH)2) as the conductive material, and polyvinylidene fluoride (PVDF) as the binder in a weight ratio of 97.5:1:1.5 and dispersing them in N-methyl-2-pyrrolidone.

[0124] The third positive electrode slurry and the second positive electrode slurry are coated on the lower part of the positive electrode active material layer, dried, and then compressed to form the middle and upper parts of the positive electrode active material layer (each with a thickness of 100 / 3μm).

[0125] Compare with Example 1 (Ref.) The positive electrode and rechargeable lithium battery cell of Comparative Example 1 were manufactured in the same manner as in Example 3, except that carbon black was used instead of MXene as a carbon-based conductive material when manufacturing each of the first and second positive electrode slurries.

[0126] Comparison Example 2 The positive electrode and rechargeable lithium battery cell of Comparative Example 2 were manufactured in the same manner as in Example 3, except that the weight ratio of the positive electrode active material, MXene and binder was changed to 98:0.5:1.5 when manufacturing the first positive electrode slurry.

[0127] Compare Example 3 The positive electrode and rechargeable lithium battery cell of Comparative Example 3 were manufactured in the same manner as in Example 3, except that the order of applying the first positive electrode slurry and the second positive electrode slurry was changed.

[0128] Tables 1 and 2 below summarize the amounts of each component in the lower part based on 100 parts by weight, the amounts of each component in the upper part based on 100 parts by weight, and the thickness ratio of the lower and upper parts.

[0129] Table 1:

[0130] Example 8 is a structure with an upper part, a middle part, and a lower part, and only the upper part and the lower part are described.

[0131] Table 2:

[0132] Evaluation Example 1: Electrochemical Characteristics of Rechargeable Lithium-ion Battery Cells For the rechargeable lithium-ion battery cells of Examples 1 to 8 and Comparative Examples 1 to 3, the formation capacity, cycle life, and output at each rate were measured as follows. The results are shown in Tables 3 and 4 below.

[0133] (1) Formation capacity: 3 charge and discharge cycles at 0.1C within a voltage range of 2.0V to 3.7V (@25℃).

[0134] (2) Cycle life: 100 charge and discharge cycles at 1C within a voltage range of 2.0V to 3.7V (@25℃).

[0135] (3) Rate output: Confirm discharge capacity from 0.1C to 10C within a voltage range of 2.0V to 3.7V (@25℃).

[0136] Table 3:

[0137] Table 4:

[0138] Evaluation Example 2 For Examples 1 to 8 and Comparative Examples 1 to 3, symmetrical cells were fabricated by inserting a separator between the two positive electrodes, and the lithium-ion migration resistance (Ri) was evaluated. ion The evaluation results are shown in Tables 5 and 6 below.

[0139] When the amount of MXene is high at the top, MXene acts as a resistor for lithium ions during charging and discharging, thereby increasing the resistance to lithium ion movement (R0). ion Therefore, the lithium-ion movement resistance (Ri) measured using symmetrical cells can be evaluated. ion This is used to identify the behavior of lithium ions during charging and discharging.

[0140] Table 5:

[0141] Table 6:

[0142] The positive electrodes for rechargeable lithium batteries represented by Examples 1 to 8 can improve conductivity while reducing or inhibiting the elution of transition metals from the positive electrode active material and stably maintaining an SEI film at the interface between the positive electrode and the electrolyte solution.

[0143] Therefore, a rechargeable lithium battery including a positive electrode according to the above example embodiments can exhibit desired or improved cycle life characteristics, stability, etc.

[0144] While this disclosure has been described in conjunction with exemplary embodiments now considered practical, it will be understood that the disclosure is not limited to the disclosed exemplary embodiments. Rather, the disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0145] Symbol explanation: 1: MXene 2: Positive electrode active material 3: Adhesive 100: Rechargeable lithium battery; 10: Positive electrode 11: Positive electrode lead connector 12: Positive electrode terminal 20: Negative electrode 21: Negative electrode lead connector 22: Negative electrode terminal; 30: Diaphragm 40: Electrode assembly; 50: Housing 60: Sealing component; 70: Electrode terminal piece 71: Positive electrode connector; 72: Negative electrode connector.

Claims

1. A positive electrode for a rechargeable lithium battery, the positive electrode comprising: substrate; as well as A positive electrode active material layer is placed on the substrate. The positive electrode active material layer includes: MXene; and a positive electrode active material, and The amount of MXene increases from the top to the bottom of the positive electrode active material layer.

2. The positive electrode according to claim 1, wherein, Based on the total amount of the positive electrode active material layer, 100wt%: The total amount of MXene included in the upper and lower parts of the positive electrode active material layer is in the range of 0.1 wt% to 5 wt%.

3. The positive electrode according to claim 1, wherein, Based on the total amount of the positive electrode active material layer, 100wt%: The amount of MXene included in the lower part of the positive electrode active material layer is in the range of 0.5 wt% to 5 wt%. The amount of MXene included in the upper part of the positive electrode active material layer is in the range of 0 wt% to 3 wt%, and The amount of MXene included in the lower part of the positive electrode active material layer is greater than the amount of MXene included in the upper part of the positive electrode active material layer.

4. The positive electrode according to claim 1, wherein, The positive electrode active material layer has: A multilayer structure in which the amount of MXene increases intermittently from the top to the bottom of the positive electrode active material layer; or A single-layer structure in which the amount of MXene increases substantially continuously from the top to the bottom of the positive electrode active material layer.

5. The positive electrode according to claim 4, wherein: The positive electrode active material layer has the aforementioned multilayer structure, and The boundary between the lower and upper parts of the positive electrode active material layer is located in the range of 30% to 70% of the total thickness of the positive electrode active material layer.

6. The positive electrode according to claim 4, wherein: The positive electrode active material layer has the monolayer structure, and The amount of MXene increases by 20 wt% to 30 wt% relative to the thickness of the positive electrode active material layer from top to bottom.

7. The positive electrode according to claim 1, wherein, MXene is represented by chemical formula 1: Chemical Formula 1: (M 1 ) n+1 (X 1 ) n T s ; In chemical formula 1, X 1 Located in M 1 Within the octahedral array; M 1 Includes metals selected from at least one of Group IIIB, Group IVB, Group VB, Group VIB, and combinations thereof; and X includes either C or N.

8. The positive electrode according to claim 1, wherein, Based on the total amount of the positive electrode active material layer, 100wt%: The total amount of positive electrode active material distributed in the lower and upper parts ranges from 90 wt% to 99.5 wt%.

9. The positive electrode according to claim 1, wherein, Meet one of the following: The positive electrode active material includes lithium iron phosphate compounds; and The positive electrode active material comprises a mixture of lithium and at least one composite oxide of a metal including at least one of cobalt, manganese, nickel and combinations thereof, and lithium iron phosphate compounds.

10. The positive electrode according to claim 9, wherein, In the distribution of the positive electrode active material: A mixture of lithium and at least one composite oxide of a metal including at least one of cobalt, manganese, nickel and combinations thereof, and lithium iron phosphate compounds is distributed in the upper part of the positive electrode active material layer, and Lithium iron phosphate compounds are only distributed in the upper part of the positive electrode active material layer.

11. The positive electrode according to claim 10, wherein, Based on 100 mol% of metal excluding lithium, the composite oxide of lithium with at least one of metals including cobalt, manganese, nickel and combinations thereof has a nickel content of greater than or equal to 80 mol%.

12. A rechargeable lithium battery, said rechargeable lithium battery comprising: The positive electrode according to any one of claims 1 to 11; negative electrode; as well as A diaphragm is located between the positive electrode and the negative electrode.

13. The rechargeable lithium battery according to claim 12, wherein, The rechargeable lithium battery also includes an electrolyte solution impregnated in the separator.

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