Positive electrode for rechargeable lithium batteries and rechargeable lithium batteries including the positive electrode.

Abstract

A positive electrode for a rechargeable lithium-ion battery and a rechargeable lithium-ion battery including the positive electrode are disclosed. The positive electrode for the rechargeable lithium-ion battery includes a substrate and a positive electrode active material layer on the substrate. The positive electrode active material layer includes MXene, a solid electrolyte, and the positive electrode active material. The distribution of the solid electrolyte increases from the bottom to the top 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 can have an energy density three times or more higher per unit weight than conventional lead-acid, nickel-cadmium, nickel-metal hydride, and nickel-zinc batteries. Rechargeable lithium-ion batteries can also be charged at high rates and therefore can be commercially manufactured for use in, for example, laptops, cell phones, power tools, and electric bicycles. Providing additional energy density to rechargeable lithium-ion batteries can be advantageous.

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

[0004] When a solid electrolyte is applied to the positive electrode, the R of the positive electrode can be reduced. ct (Charge transfer resistance), reduces or suppresses lithium deposition and side reactions, and reduces electrolyte consumption.

[0005] However, since solid electrolytes are generally known to be materials with low conductivity and do not exhibit high capacity, applying solid electrolytes to the positive electrode may reduce the output, capacity and cycle life of rechargeable lithium batteries. Summary of the Invention

[0006] Some example embodiments include a positive electrode for a rechargeable lithium battery that overcomes the disadvantage of low conductivity while having the advantages of a solid electrolyte.

[0007] Some example embodiments include a positive electrode for a rechargeable lithium-ion battery, the positive electrode comprising a substrate and a layer of positive electrode active material on the substrate. The positive electrode active material layer comprises MXene, a solid electrolyte, and the positive electrode active material. The solid electrolyte has an increasing distribution from the lower portion of the positive electrode active material layer near the substrate to the upper portion away from the substrate.

[0008] Some example embodiments include a rechargeable lithium battery comprising a positive electrode according to the foregoing example embodiments.

[0009] The positive electrode for a rechargeable lithium battery according to the foregoing example embodiments can take advantage of the solid electrolyte while compensating for the disadvantage of low conductivity.

[0010] Therefore, a rechargeable lithium battery including a positive electrode according to the foregoing example embodiments can exhibit desired or improved cycle life characteristics, stability, output characteristics, etc. Attached Figure Description

[0011] Figure 1 This is a schematic diagram illustrating a positive electrode active material layer for a rechargeable lithium battery according to some example embodiments.

[0012] Figures 2 to 5 This is a schematic diagram illustrating a rechargeable lithium battery according to some example embodiments. Detailed Implementation

[0013] 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.

[0014] 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.

[0015] 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”.

[0016] As used herein, “combination of them” can mean a mixture, stack, complex, copolymer, alloy, blend or reaction product of the components.

[0017] 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 that constitute 50% of the total volume in a particle size distribution. The average particle size (D50) can be measured by methods known to those skilled in the art, for example, 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 to count the number of particles in each particle size range. Thus, the average particle size (D50) value can be readily obtained by calculation. Optionally, the average particle size 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 measuring device (e.g., Microtrac MT 3000), and irradiated with ultrasound at approximately 28 kHz at a 60 W output to calculate the average particle size (D50) based on 50% of the particle size distribution in the measuring device.

[0018] 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 it, such as increments of 0.1%.

[0019] Positive electrode: Some example embodiments include a positive electrode for a rechargeable lithium-ion battery, the positive electrode comprising a substrate and a layer of positive electrode active material on the substrate. The positive electrode active material layer comprises MXene, a solid electrolyte, and the positive electrode active material. The solid electrolyte has an increasing distribution from the lower portion of the positive electrode active material layer near the substrate to the upper portion away from the substrate.

[0020] (1) The positive electrode for a rechargeable lithium battery according to the foregoing example embodiments includes a solid electrolyte.

[0021] As mentioned above, when a solid electrolyte is applied to the positive electrode, the amount of liquid electrolyte required is reduced, which can improve the low-temperature cycle life and battery stability of rechargeable lithium batteries.

[0022] (2) The positive electrode for a rechargeable lithium battery according to the foregoing example embodiments includes MXene.

[0023] In addition, "Maxene" (also known as MXene) is a two-dimensional nanomaterial in which transition metal layers and carbon layers are stacked (e.g., stacked alternately) and can exhibit desired or improved conductivity compared to commonly known conductive materials (e.g., carbon, graphene, etc.).

[0024] In some example embodiments, commonly known conductive materials are replaced with or combined with MXene. Therefore, the insufficient conductivity of solid electrolytes can be compensated for.

[0025] (3) In the positive electrode of the rechargeable lithium battery according to the foregoing example embodiment, the distribution of solid electrolyte increases from the lower part of the positive electrode active material layer near the substrate to the upper part away from the substrate.

[0026] Therefore, at the upper part of the positive electrode that is in direct contact with the electrolyte, it is possible to achieve effects such as reducing R. ct While achieving the effects of (charge transfer resistance), reducing or suppressing lithium deposition and side reactions, and reducing electrolyte consumption, it can also increase the amount of highly conductive MXene and / or positive electrode active material, which are capacity-generating materials, at the lower part of the positive electrode that is not in direct contact with the electrolyte.

[0027] The distribution of each of MXene and the positive electrode active material is described below.

[0028] In the following text, the portion of the positive electrode active material layer near the substrate is referred to as the "lower portion," and the portion away from the substrate is referred to as the "upper portion." The positive electrode according to the foregoing example embodiment is described in detail below.

[0029] solid electrolyte Based on a total positive electrode active material layer of 100 wt%, the total amount of solid electrolyte distributed in the lower and upper parts of the positive electrode active material layer can be in the range of about 0.1 wt% to about 5 wt%, about 0.2 wt% to about 3 wt%, or about 0.5 wt% to about 2 wt%.

[0030] The amount of solid electrolyte distributed in the lower part of the positive electrode active material layer can be in the range of about 0 wt% to about 5 wt%, 0 wt% to about 3 wt%, or 0 wt% to about 2 wt%; and the amount of solid electrolyte distributed in the upper part of the positive electrode active material layer can be in the range of about 0.5 wt% to about 2 wt%.

[0031] Solid electrolytes may not be distributed in the lower part of the positive electrode active material layer.

[0032] For example, at the lower part of the positive electrode active material layer, the ratio of solid electrolyte to MXene can be in the range of about 0:100 to about 50:50, about 0:100 to about 40:60, or about 0:100 to about 30:70; and at the upper part of the positive electrode active material layer, the ratio of solid electrolyte to MXene can be in the range of about 10:90 to about 50:50, about 20:80 to about 50:50, or about 30:70 to about 50:50, and the distribution of solid electrolyte can increase from the lower part to the upper part of the positive electrode active material layer. Here, the ratio can be expressed as a weight ratio.

[0033] The amount of solid electrolyte at the boundary between the lower and upper portions of the positive electrode active material layer can be increased (e.g., intermittently). For example, the boundary between the lower and upper portions of the positive electrode active material layer can be located in the range of about 30% to about 70%, about 40% to about 60%, or about 50% of the total thickness (100% of the total thickness) of the positive electrode active material layer.

[0034] In the above, the amount of solid electrolyte in the lower part of the positive electrode active material layer is "0 wt%" and the ratio of solid electrolyte to MXene is "0:100", which means that solid electrolyte may not be included in the lower part of the positive electrode active material layer.

[0035] When the above ranges are met, the effects of solid electrolyte, MXene, and positive electrode active material can be coordinated.

[0036] Solid electrolytes can be or include oxide-based solid electrolytes.

[0037] The oxide-based solid electrolyte may be or include at least one of the following: Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 < x < 2, 0 ≤ y < 3), BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT) (0 ≤ x < 1, 0 ≤ y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 (PMN - PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3 (0 < x < 2, 0 < y < 3), Li x Al y Ti z (PO4)3 (0 < x < 2, 0 < y < 1, 0 < z < 3) (LATP), Li 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1), Li x La y TiO3 (0 < x < 2, 0 < y < 3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O - Al2O3 - SiO2 - P2O5 - TiO2 - GeO2, Li 3+x La3M2O 12 (M = Te, Nb or Zr, 0 ≤ x ≤ 10) or a combination thereof.

[0038] For example, the oxide-based solid electrolyte may be or include Li x Al y Ti z (PO4)3 (0 < x < 2, 0 < y < 1, 0 < z < 3) (LATP) having a NASICON structure, because this oxide-based solid electrolyte has the advantages of high ionic conductivity and a wide potential window compared to other oxide-based solid electrolytes and is suitable for application in high-voltage, high-power batteries.

[0039] MXene Based on the total amount of 100wt% of the positive electrode active material layer, the total amount of MXene distributed in the lower and upper parts can be in the range of about 0.1wt% to about 10wt%, about 0.5wt% to about 5wt%, or about 1wt% to about 4wt%.

[0040] In addition, MXene can be uniformly or substantially uniformly distributed in the lower and upper parts of the positive electrode active material layer.

[0041] When MXene is distributed uniformly or substantially uniformly in the lower and upper parts of the positive electrode active material layer in the stated amount, it has the effect of uniformly or substantially uniformly compensating for the conductivity in the lower and upper parts of the positive electrode active material layer.

[0042] MXene can be represented by the following chemical formula 1.

[0043] Chemical Formula 1: (M 1 ) m (X 1 ) n T s ; In chemical formula 1, X 1 It can be located in M 1 Within the octahedral array.

[0044] M 1 It may include at least one of the group IIIB metals, group IVB metals, group VB metals, group VIB metals, and combinations thereof.

[0045] X 1 It can include either C or N.

[0046] m can be an integer in the range of 1 to 3, and n can be an integer in the range of 0 to 3.

[0047] 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.

[0048] For example, MXene can be or includes Ti3C2(OH)2.

[0049] 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.

[0050] Chemical Formula 11: Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 .

[0051] 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 of them independently is or includes at least 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.

[0052] 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.

[0053] Chemical formula 12: Li a2 Co x2 M 3 y2 O 2-b2 X b2 .

[0054] 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 X 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.

[0055] Chemical formula 13: Li a3 Fe x3 M 4 y3PO 4-b3 X b3 。

[0056] 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.

[0057] Chemical Formula 14: Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4 。

[0058] 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.

[0059] The positive electrode active material may be composed only of a lithium iron phosphate compound or may only include a lithium iron phosphate compound, or may include a mixture of a lithium iron phosphate compound and at least one composite oxide of lithium and a metal (such as or including at least one of cobalt, manganese, nickel, and combinations thereof).

[0060] 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) and a lithium iron phosphate compound may be distributed in the lower part of the positive electrode active material layer. For example, only the lithium iron phosphate compound may be distributed in the upper part of the positive electrode active material layer.

[0061] Based on 100 mol% of the metal excluding lithium, the composite oxide of lithium and a metal (such as or including at least one of cobalt, manganese, nickel, and combinations thereof) may have a nickel content of greater than or equal to about 80 mol%.

[0062] The complex oxide of lithium and metal (such as or including at least one of cobalt, manganese, nickel and combinations thereof) may be or include a compound represented by formula 11, and lithium iron phosphate compounds may be or include a compound represented by formula 13.

[0063] 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.

[0064] The positive electrode active material layer may include the positive electrode active material, and may also include a binder and / or a conductive material.

[0065] For example, the positive electrode may also include additives that can constitute a sacrificial positive electrode.

[0066] 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% or about 94wt% to about 98.5wt%, and based on a 100wt% positive electrode active material layer, the amount of each of the binder and conductive material can be in the range of about 0.5wt% to about 5wt%.

[0067] The binder improves the adhesion properties between the positive electrode active material particles and 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.

[0068] 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 fibers, carbon nanofibers, carbon nanotubes, etc.; metallic materials, such as metal powders or metal fibers, including at least one of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0069] Rechargeable lithium batteries: Some example embodiments include a rechargeable lithium battery, which includes a positive electrode, a negative electrode, and a separator between the positive and negative electrodes as described in the foregoing example embodiments.

[0070] Since the rechargeable lithium battery includes the positive electrode of the foregoing exemplary embodiments, it can exhibit desired or improved cycle life characteristics, stability, output characteristics, and the like.

[0071] Hereinafter, rechargeable lithium batteries of some exemplary embodiments will be described in detail, excluding any descriptions that are repeated above.

[0072] Negative electrode active material The negative electrode active material may include at least one of a material that reversibly embeds / extracts lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, or a transition metal oxide.

[0073] The material that reversibly embeds / extracts lithium ions may include, for example, crystalline carbon, amorphous carbon, or a combination thereof as a carbon-based negative electrode active material. The crystalline carbon may be natural graphite or artificial graphite that is irregular or in the form of flakes, platelets, spheres, or fibers. The amorphous carbon may be or include at least one of soft carbon, hard carbon, mesophase pitch carbonized product, calcined coke, and the like.

[0074] The lithium metal alloy includes an alloy of lithium and a metal (such as at least one of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn).

[0075] The material capable of doping / dedoping lithium may be or include a Si-based negative electrode active material or a Sn-based negative electrode active material. The Si-based negative electrode active material may include silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), a 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 a combination 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, and a combination thereof.

[0076] The silicon-carbon composite may be or include a composite of silicon and amorphous carbon. According to some exemplary 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 (shell) 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.

[0077] Silicon-carbon composites may also include crystalline carbon. For example, a silicon-carbon composite may include a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating layer on the surface of the core.

[0078] Si-based or Sn-based negative electrode active materials can be mixed with carbon-based negative electrode active materials.

[0079] negative electrode The negative electrode for a rechargeable lithium battery includes a current collector and a layer of negative electrode active material on the current collector. The negative electrode active material layer includes negative electrode active material and may also include a binder and / or a conductive material.

[0080] For example, the negative electrode active material layer may include about 90 wt% to about 99 wt% of negative electrode active material, about 0.5 wt% to about 5 wt% of binder and about 0.5 wt% to about 5 wt% of conductive material.

[0081] The binder causes the negative electrode active material particles to adhere to each other and to adhere the negative electrode active material to the current collector. The binder can be or includes non-aqueous binders, aqueous binders, dry binders, or combinations thereof.

[0082] Non-aqueous adhesives may include at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0083] 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.

[0084] When using an aqueous binder as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may also be included. As a cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts may be mixed and used. The alkali metal may be or include at least one of Na, K, or Li.

[0085] 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.

[0086] 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 such as metal powders or metal fibers, including at least one of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0087] The negative electrode current collector may include at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, and combinations thereof.

[0088] electrolyte Electrolytes used in rechargeable lithium batteries include non-aqueous organic solvents and lithium salts.

[0089] Non-aqueous organic solvents constitute the medium for transporting ions that participate in the electrochemical reactions of the battery.

[0090] Non-aqueous organic solvents may be or include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents or alcohol solvents, aprotic solvents or combinations thereof.

[0091] 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, and caprolactone. Ether solvents may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Additionally, ketone solvents may include cyclohexanone. Alcohol solvents may include ethanol and isopropanol. Aprotic solvents may include at least one of the following: nitriles, such as R-CN (wherein R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group, and may include double bonds, aromatic rings or ether groups, etc.); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane, etc.

[0092] Non-aqueous organic solvents can be used alone or in mixtures of two or more types of solvents.

[0093] 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.

[0094] The electrolyte 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.

[0095] 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 may 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 At 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), lithium difluoro(oxalate)borate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0096] 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 polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, and may include mixed multilayer films (such as polyethylene / polypropylene bilayer separators, polyethylene / polypropylene / polypropylene trilayer separators, polypropylene / polypropylene / polypropylene trilayer separators, etc.).

[0097] 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.

[0098] The porous substrate may be or include a polymer membrane, which is formed or includes any one of the following polymers or copolymers or mixtures of two or more of them, such as polyolefins (e.g., polyethylene and polypropylene), polyesters (e.g., 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 (e.g., TEFLON). ® At least one of the following.

[0099] Organic materials may include polyvinylidene fluoride polymers or (meth)acrylic acid polymers.

[0100] Inorganic materials may include, but are not limited to, 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).

[0101] 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.

[0102] Rechargeable lithium batteries Based on their shape, rechargeable lithium batteries can be classified as cylindrical batteries, prismatic batteries, pouch batteries, or coin-shaped batteries, etc. Figures 2 to 5 This is a schematic diagram illustrating a rechargeable lithium battery according to some example embodiments, wherein, Figure 2 A cylindrical battery is shown. Figure 3 A prismatic battery is shown. Figure 4 and Figure 5 A pouch-shaped battery is shown. (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 (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 3In 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 is 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.

[0103] The rechargeable lithium batteries 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.

[0104] 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.

[0105] Example 1 (1) Manufacturing of the positive electrode Prepare an aluminum foil with a thickness of 10 μm as the positive electrode current collector.

[0106] The active materials for the mixed positive electrode are LiFePO4 and LiNi mixed in a weight ratio of 50:50. 0.88 Co 0.08 Al 0.04 O2 (positive electrode active material), Li as a solid electrolyte x Al y Ti z (PO4)3 (x=1.4, y=0.4, z=1.6) (LATP), MXene (chemical formula = Ti3C2(OH)2) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed in a weight ratio of 94:0.5:3:2.5 and dispersed in N-methyl-2-pyrrolidone to prepare a first positive electrode slurry.

[0107] The first positive electrode slurry is coated onto an aluminum foil, dried, and then pressed to form the lower part of the positive electrode active material layer (thickness: 45 μm).

[0108] LiFePO4 as the single positive electrode active material and Li as the solid electrolyte x Al y Ti z(PO4)3 (x=1.4, y=0.4, z=1.6) (LATP), MXene (chemical formula = Ti3C2(OH)2) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed in a weight ratio of 93:1.5:3:2.5 and dispersed in N-methyl-2-pyrrolidone to prepare a second positive electrode slurry.

[0109] The second positive electrode slurry is coated on the lower part of the positive electrode active material layer, dried, and then pressed to form the upper part of the positive electrode active material layer (thickness: 45 μm).

[0110] When the solid content in the first positive electrode slurry is referred to as the first solid content, and the solid content in the second positive electrode slurry is referred to as the second solid content, the weight ratio of the first solid content to the second solid content is 50:50. Therefore, based on the total thickness (100%) of the positive electrode active material layer, the thickness of each of the lower and upper portions of the positive electrode active material layer is set to 50%.

[0111] (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 the negative electrode active material, 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.

[0112] 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.

[0113] An electrolyte was prepared by mixing 1.5 M lithium salt (LiPF6) in a carbonate solvent comprising ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) in a volume ratio of 20:40:40.

[0114] The positive and negative electrodes are assembled to manufacture an electrode assembly, which is then housed in a housing and injected with electrolyte to manufacture a 2023 coin-shaped rechargeable lithium battery cell.

[0115] Example 2 The positive electrode and rechargeable lithium battery cell are manufactured in the same manner as in Example 1, except that the weight ratio of the positive electrode active material, solid electrolyte, MXene and binder is changed to 93.3:0.2:3:2.5 when preparing the first positive electrode slurry, and the weight ratio of the positive electrode active material, solid electrolyte, MXene and binder is changed to 92.7:1.8:3:2.5 when preparing the second positive electrode slurry.

[0116] 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, solid electrolyte, MXene and binder was changed to 94.5:0:3:2.5 when preparing the first positive electrode slurry, and the weight ratio of the positive electrode active material, solid electrolyte, MXene and binder was changed to 92.5:2:3:2.5 when preparing the second positive electrode slurry.

[0117] Example 4 When the solid content in the first positive electrode slurry is referred to as the first solid content, and the solid content in the second positive electrode slurry is referred to as the second solid content, the first solid content and the second solid content are set to a weight ratio of 30:70. Therefore, based on the total thickness of 100% of the positive electrode active material layer, the thicknesses of the lower and upper parts of the positive electrode active material layer are 30% and 70%, respectively.

[0118] Using the above differences, the positive electrode and rechargeable lithium battery cell of Example 4 are manufactured in the same manner as in Example 3.

[0119] Example 5 When the solid content in the first positive electrode slurry is referred to as the first solid content, and the solid content in the second positive electrode slurry is referred to as the second solid content, the weight ratio of the first solid content to the second solid content is set to 40:60. Therefore, based on the total thickness of the 100% positive electrode active material layer, the thicknesses of the lower and upper parts of the positive electrode active material layer are 40% and 60%, respectively.

[0120] Utilizing the above differences, the positive electrode and rechargeable lithium battery cell of Example 5 are manufactured in the same manner as in Example 3.

[0121] Example 6 When the solid content in the first positive electrode slurry is referred to as the first solid content, and the solid content in the second positive electrode slurry is referred to as the second solid content, the first solid content and the second solid content are set to a weight ratio of 60:40. Therefore, based on the total thickness of the 100% positive electrode active material layer, the thicknesses of the lower and upper parts of the positive electrode active material layer are 60% and 40%, respectively.

[0122] Utilizing the above differences, the positive electrode and rechargeable lithium battery cell of Example 6 are manufactured in the same manner as in Example 3.

[0123] Example 7 When the solid content in the first positive electrode slurry is referred to as the first solid content, and the solid content in the second positive electrode slurry is referred to as the second solid content, the first solid content and the second solid content are set to a weight ratio of 70:30. Therefore, based on the total thickness of 100% of the positive electrode active material layer, the thicknesses of the lower and upper parts of the positive electrode active material layer are 70% and 30%, respectively.

[0124] Utilizing the above differences, the positive electrode and rechargeable lithium battery cell of Example 7 are manufactured in the same manner as in Example 3.

[0125] Compare with Example 1 (for reference) The positive electrode and rechargeable lithium battery cell of Comparative Example 1 were manufactured in the same manner as in Example 1, except that carbon black was used as a carbon-based conductive material instead of a solid electrolyte in the preparation of 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, solid electrolyte, MXene and binder was changed to 93.5:1:3:2.5 when preparing the first positive electrode slurry, and the weight ratio of the positive electrode active material, solid electrolyte, MXene and binder was changed to 93.5:1:3:2.5 when preparing the second positive electrode slurry.

[0127] Comparison 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 in which the first positive electrode slurry and the second positive electrode slurry were coated 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] Table 2:

[0131] Evaluation Example 1: Evaluation of the Positive Electrode The following evaluation examples and comparison examples show the R values ​​of each of the positive electrodes. ct (Electron transfer resistance), the results are shown in Tables 3 and 4 below.

[0132] For each of the positive electrodes, a symmetrical cell consisting of two positive electrodes was fabricated to measure SC-EIS (square-wave current electrochemical impedance spectroscopy) with an amplitude Va of 5 mV. The measurement results were used to separate and measure the electron transfer resistance based on the internal resistance of each of the positive electrodes using transmission line model theory.

[0133] Table 3:

[0134] Table 4:

[0135] Evaluation Example 2: Evaluation of Rechargeable Lithium-ion Battery Cells The evaluation results for each of the rechargeable lithium-ion battery cells in the following evaluation examples and comparison examples are shown in Tables 5 and 6 below.

[0136] (1) Formation capacity: The battery is charged and discharged 3 times at 0.1C (25°C) within a voltage range of 2.0V to 3.7V.

[0137] (2) Cycle life: The battery is charged and discharged 100 times at 1C (25°C) within a voltage range of 2.0V to 3.7V.

[0138] (3) Output at various rates: Measure the discharge capacity of the battery cells from 0.1C to 10C within a voltage range of 2.0V to 3.7V (25°C).

[0139] Table 5:

[0140] Table 6:

[0141] Comparative Example 1 uses carbon black as a carbon-based conductive material instead of a solid electrolyte in the preparation of the first and second positive electrode slurries. Compared to Examples 1 to 7, Comparative Example 1 exhibits overall performance degradation, including formation, efficiency, cycle life, and characteristics at various rates.

[0142] Comparative Example 2 includes a solid electrolyte and MXene, but the solid electrolyte exhibits the same distribution in both the upper and lower portions. Compared to Comparative Example 1, Comparative Example 2 shows improved performance, but overall performance is still degraded compared to Examples 1 through 7.

[0143] Comparative Example 3 includes a solid electrolyte and MXene, but the solid electrolyte exhibits a distribution that increases from top to bottom. In other words, this solid electrolyte distribution is the opposite of that in Examples 1 to 7, and therefore, the overall performance is degraded compared to the overall performance of Examples 1 to 7.

[0144] Conversely, the positive electrode for a rechargeable lithium battery according to Examples 1 to 7 comprises a solid electrolyte and MXene, but the solid electrolyte exhibits a distribution that gradually increases from bottom to top. This positive electrode for a rechargeable lithium battery according to an example embodiment, as shown in Examples 1 to 7, not only utilizes the advantages of a solid electrolyte but also compensates for its low conductivity.

[0145] Therefore, a rechargeable lithium battery including a positive electrode according to the foregoing example embodiments can exhibit desired or improved cycle life characteristics, stability, output characteristics, etc.

[0146] While this disclosure has been described in conjunction with what are now considered to be exemplary embodiments, 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.

[0147] Description of reference numerals in the attached figures: 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: Base; as well as Positive electrode active material layer, on the substrate, The positive electrode active material layer comprises: MXene; a solid electrolyte; and the positive electrode active material, and The solid electrolyte has an increasing distribution from the lower part of the positive electrode active material layer near the substrate to the upper part away from the substrate.

2. The positive electrode according to claim 1, wherein, Based on the total amount of the positive electrode active material layer of 100 wt%: The total amount of solid electrolyte distributed in the lower and upper 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 of 100 wt%: The amount of solid electrolyte distributed in the lower part of the positive electrode active material layer is in the range of 0 wt% to 5 wt%, and The amount of solid electrolyte distributed in the upper part of the positive electrode active material layer is in the range of 0.5 wt% to 2 wt%.

4. The positive electrode according to claim 1, wherein: The ratio of solid electrolyte to MXene distributed in the lower part of the positive electrode active material layer is in the range of 0:100 to 50:50 by weight, and The ratio of solid electrolyte to MXene distributed in the upper part of the positive electrode active material layer is in the range of 10:90 to 50:50 by weight.

5. The positive electrode according to claim 1, wherein, At the boundary between the lower and upper portions of the positive electrode active material layer: The amount of solid electrolyte increases intermittently, and The boundary between the lower and upper portions of the positive electrode active material layer is located within the range of 30% to 70% of the total thickness of the positive electrode active material layer.

6. The positive electrode according to claim 1, wherein: Solid electrolytes include oxide-based solid electrolytes, and Oxide solid electrolytes include at least one of the following: Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 0 <x<2,0≤y<3;BaTiO3;Pb(Zr,Ti)O3;Pb 1-x La x Zr 1-y Ti y O3, 0≤x<1, 0≤y<1; Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3; HfO2; SrTiO3; SnO2; CeO2; Na2O; MgO; NiO; CaO; BaO; ZnO; ZrO2; Y2O3; Al2O3; TiO2; SiO2; Li3PO4; Li x Ti y (PO4)3,0 <x<2,0<y<3;Li x Al y Ti z (PO4)3,0 <x<2,0<y<1,0<z<3;Li 1+x+y (Al,Ga) x (Ti,Ge) 2- x Si y P 3-y O 12 , 0≤x≤1, 0≤y≤1; Li x La y TiO3,0 <x<2,0<y<3;Li2O;LiOH;Li2CO3;LiAlO2;Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2;Li 3+x La3M2O 12 M = Te, Nb, or Zr, 0 ≤ x ≤ 10; and combinations thereof.

7. The positive electrode according to claim 1, wherein, Based on the total amount of the positive electrode active material layer of 100 wt%: The total amount of MXene distributed in the lower and upper parts ranges from 1 wt% to 4 wt%.

8. The positive electrode according to claim 1, wherein, MXene is substantially uniformly distributed in the lower and upper parts of the positive electrode active material layer.

9. The positive electrode according to claim 1, wherein, MXene is represented by chemical formula 1: Chemical Formula 1: (M 1 ) m (X 1 ) n T s , In chemical formula 1, X 1 Located in M 1 Within the octahedral array, T s This includes functional groups comprising at least one of alkoxides, carboxylates, halides, hydroxides, hydrides, oxides, low-valent oxides, nitrides, low-valent nitrides, sulfides, thiols, and combinations thereof. M 1 This includes metals derived from at least one of Group IIIB, Group IVB, Group VB, Group VIB, and combinations thereof. X 1 Includes one of C and N, m is an integer in the range of 1 to 3, and n is an integer in the range of 0 to 3.

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

11. The positive electrode according to claim 1, wherein: The positive electrode active material includes only lithium iron phosphate compounds; or 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.

12. The positive electrode according to claim 11, 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 lower part of the positive electrode active material layer, and Only lithium iron phosphate compounds are distributed in the upper part of the positive electrode active material layer.

13. The positive electrode according to claim 11, wherein, Based on 100 mol% of metals 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%.

14. A rechargeable lithium battery, said rechargeable lithium battery comprising: The positive electrode according to any one of claims 1 to 13; negative electrode; as well as A diaphragm is located between the positive electrode and the negative electrode.

15. The rechargeable lithium battery according to claim 14, wherein, The rechargeable lithium battery also includes an electrolyte that impregnates the separator.

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