Method for manufacturing positive electrode active material for lithium secondary battery and positive electrode active material

Abstract

A method for manufacturing a positive electrode active material for a lithium secondary battery, according to the present invention, comprises the steps of: introducing an over-lithiated manganese-based transition metal oxide into an atomic layer deposition reactor; and forming an oxide protective layer on the surface of the over-lithiated manganese-based transition metal oxide through atomic layer deposition (ALD).

Description

Method for manufacturing a positive electrode active material for a lithium secondary battery and a positive electrode active material

[0001] The present invention relates to a method for manufacturing a positive electrode active material for a lithium secondary battery and a positive electrode active material.

[0002] Lithium secondary batteries generally consist of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive and negative electrodes contain active materials capable of lithium ion intercalation and deintercalation. Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics; however, it is difficult to apply commercially to high-capacity batteries due to the high cost and unstable supply of cobalt, which serves as the raw material. Lithium nickel oxide is difficult to achieve sufficient lifespan characteristics due to its poor structural stability.

[0003] Meanwhile, lithium manganese oxide has the problem of having excellent stability but poor capacity characteristics. Accordingly, lithium composite transition metal oxides containing two or more transition metals have been developed to compensate for the problems of lithium transition metal oxides containing Ni, Co, or Mn alone. Among these, lithium nickel cobalt manganese oxide (hereinafter referred to as "high-lithium manganese transition metal oxide"), in which the Mn content is higher than that of other metals excluding lithium, has been found to be a high-capacity active material capable of securing high energy density per unit volume, and research on this is emerging.

[0004] However, in the case of lithium-excessive manganese-based transition metal oxides containing an excess of lithium, they have a structure in which a layered phase (LiM'O2) and a rock salt phase (Li2MnO3) are mixed. During the initial activation process, the rock salt phase is activated, generating an excess amount of lithium ions. Additionally, during the activation process of the rock salt phase, an oxygen-redox reaction occurs, which generates a large amount of gas. Consequently, there is a problem in that the degradation of the cathode is exacerbated due to the occurrence of internal cracks in the active material and the collapse of the crystal structure, thereby degrading the lifespan characteristics.

[0005] On the other hand, lithium-rich manganese-based transition metal oxides have the problem of degraded rate characteristics. This is because when the Co content is decreased while the Mn content is increased, Ni 2 + As the ratio of Li increases + Ni in the layer 2 + It is presumed that this is because resistance increases as the diffusion rate of lithium ions slows down due to this substituting cation mixing.

[0006] One aspect of the present invention for solving the above-mentioned problem is to provide a method for manufacturing a positive electrode active material for a lithium secondary battery and a positive electrode active material having excellent electrochemical properties, with excellent ion conductivity and improved surface stabilization effect, by forming an oxide protective layer on the surface of a lithium manganese-based transition metal oxide using atomic layer deposition (ALD).

[0007] The technical problems to be solved in this document are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which this invention belongs from the description below.

[0008] To achieve the above objective, a method for manufacturing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention may include the step of introducing a lithium-over-manganese-based transition metal oxide into an atomic layer deposition reactor; and the step of forming an oxide protective layer on the surface of the lithium-over-manganese-based transition metal oxide using atomic layer deposition (ALD).

[0009] The step of forming the oxide protective layer according to one embodiment of the present invention may include: supplying a metal precursor into an atomic layer deposition reactor into which the lithium-over-manganese-based transition metal oxide is introduced; supplying a first purge gas into the atomic layer deposition reactor; supplying an oxidizing agent into the atomic layer deposition reactor; and supplying a second purge gas into the atomic layer deposition reactor.

[0010] According to one embodiment of the present invention, the atomic layer deposition reactor may be maintained at a temperature of 100°C to 350°C.

[0011] The metal precursor according to one embodiment of the present invention may include one or more selected from aluminum (Al), titanium (Ti), silicon (Si), zirconium (Zr), vanadium (V), niobium (Nb), magnesium (Mg), tantalum (Ta), boron (B), zinc (Zr), tin (Sn), hafnium (Hf), erbium (Er), lanthanum (La), indium (In), yttrium (Y), cerium (Ce), scandium (Sc), and tungsten (W).

[0012] The metal precursor according to one embodiment of the present invention may include one or more of trimethylaluminum (TMA), triethylaluminum (TEA), tris(diethylamido)aluminum (TBTDET), titanium isopropoxide (titanium(IV) tetraisopropoxide (TTIP), tetrakis(dimethylamido)tin (TDMASn), tetrakis(dimethylamido)titanium (TDMAT), titanium tetrachloride (TiCl4), tin(IV) chloride (SnCl4), and TBTDEN ((tert-butylimino)tris(diethylamino)niobium).

[0013] The metal precursor according to one embodiment of the present invention may be supplied for 10 to 90 seconds.

[0014] According to one embodiment of the present invention, the oxidizing agent may include one or more of water vapor (H2O), ozone (O3), and oxygen (O2).

[0015] According to one embodiment of the present invention, the oxidizing agent may be supplied at a flow rate of 10 sccm to 200 sccm for 0.1 seconds to 90 seconds.

[0016] According to one embodiment of the present invention, the first purge gas or the second purge gas may include one or more of nitrogen (N2), argon (Ar), helium (He), neon (Ne), and krypton (Kr).

[0017] According to one embodiment of the present invention, the first purge gas or the second purge gas may be supplied at a flow rate of 50 sccm to 100 sccm for 60 seconds to 120 seconds.

[0018] The thickness of the oxide protective layer can be formed to be 0.1 nm to 10 nm.

[0019] The atomic layer deposition (ALD) according to one embodiment of the present invention can be performed 1 to 100 times.

[0020] The overlithium manganese-based transition metal oxide according to one embodiment of the present invention can be represented by the following chemical formula 1.

[0021] [Chemical Formula 1]

[0022] Li 1+a (Ni x Co y Mn z W b M c ) 1-a O 2-d A d

[0023] (In the above Chemical Formula 1, 0.1≤a≤0.3, 0.35≤x≤0.45, 0≤y≤0.05, 0.45≤z≤0.65, 0.001≤b≤0.13, 0≤c≤0.1, 0≤d≤0.1, x+y+z+b+c=1, M is one or more of B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, and Ir, and A is one or more of PO4, BO3, CO3, NO3, F, Cl, Br, and I)

[0024] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention may include an over-lithium manganese-based transition metal oxide represented by Chemical Formula 1 and an oxide protective layer formed on the surface of the over-lithium manganese-based transition metal oxide.

[0025] According to one embodiment of the present invention, the thickness of the oxide protective layer may be 0.1 nm to 10 nm.

[0026] According to the present invention, by forming an oxide protective layer on the surface of a lithium manganese-based transition metal oxide using atomic layer deposition (ALD), a method for manufacturing a positive electrode active material for a lithium secondary battery and a positive electrode active material having excellent electrochemical properties with excellent ion conductivity and improved surface stabilization effect can be provided.

[0027] The effects obtainable from the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present invention belongs from the description below.

[0028] FIG. 1 is a diagram showing a transmission electron microscope (TEM) image of an anode active material in which an oxide protective layer is formed using atomic layer deposition (100°C) according to one embodiment of the present invention.

[0029] FIG. 2 is a diagram showing a transmission electron microscope (TEM) image of an anode active material in which an oxide protective layer is formed using atomic layer deposition (200°C) according to one embodiment of the present invention.

[0030] Figure 3 is a diagram showing the results of the analysis of Al element content on the surface of the positive electrode active material according to the number of atomic layer depositions according to one embodiment of the present invention.

[0031] FIG. 4 is a diagram showing the change in the oxidation state of Mn in an anode active material according to atomic layer deposition (100°C) in accordance with one embodiment of the present invention.

[0032] FIG. 5 is a diagram showing the change in the oxidation state of Mn in an anode active material according to atomic layer deposition (200°C) in accordance with one embodiment of the present invention.

[0033] Figure 6 is a diagram showing the change in the Mn oxidation state in the positive active material of Comparative Example 1.

[0034] FIG. 7 is a diagram showing the initial discharge capacity of an anode active material depending on whether an oxide protective layer is formed by atomic layer deposition according to one embodiment of the present invention.

[0035] FIG. 8 is a diagram showing the internal resistance of an anode active material depending on whether an oxide protective layer is formed by atomic layer deposition according to one embodiment of the present invention.

[0036] Preferred embodiments of the present invention are described below. However, embodiments of the present invention may be modified in various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field.

[0037] The terms used in this application are used merely to describe specific examples. For this reason, singular expressions include plural expressions unless the context clearly requires them to be singular. Additionally, it should be noted that terms such as “comprising” or “comprising” used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the existence of other features, steps, functions, components, or combinations thereof.

[0038] Meanwhile, unless otherwise defined, all terms used in this specification shall be understood to have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Accordingly, unless explicitly defined in this specification, specific terms should not be interpreted in an overly ideal or formal sense. For instance, singular expressions in this specification include plural expressions unless the context clearly indicates an exception.

[0039] Additionally, terms such as "about," "substantially," etc., in this specification are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the said sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content in which precise or absolute values ​​are mentioned to aid in understanding the invention.

[0040] The present invention relates to a method for manufacturing a positive electrode active material for a lithium secondary battery in which an oxide protective layer is formed by atomic layer deposition (ALD) on the surface of a lithium manganese-based transition metal oxide, and to a positive electrode active material for a lithium secondary battery manufactured therefrom.

[0041] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention will be described in detail.

[0042] A method for manufacturing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention may include the step of introducing a lithium-over-manganese-based transition metal oxide into an atomic layer deposition reactor and the step of forming an oxide protective layer on the surface of the lithium-over-manganese-based transition metal oxide using atomic layer deposition.

[0043] Each step is explained in detail below.

[0044] First, a lithium manganese-based transition metal oxide is introduced into an atomic layer deposition reactor.

[0045] The above-mentioned lithium manganese-based transition metal oxide may be a compound represented by the following chemical formula 1.

[0046] [Chemical Formula 1]

[0047] Li 1+a (Ni x Co y Mn z W b M c ) 1-a O 2-d A d

[0048] (In the above Chemical Formula 1, 0.1≤a≤0.3, 0.35≤x≤0.45, 0≤y≤0.05, 0.45≤z≤0.65, 0.001≤b≤0.13, 0≤c≤0.1, 0≤d≤0.1, x+y+z+b+c=1, M is one or more of B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, and Ir, and A is one or more of PO4, BO3, CO3, NO3, F, Cl, Br, and I)

[0049] The lithium manganese-based transition metal oxide represented by the above chemical formula 1 contains Mn as an essential transition metal, and is a type of lithium transition metal oxide that has a higher content of Mn than other metals excluding lithium and exhibits a large capacity when overcharged at high voltage.

[0050] Mn, which is included as an essential transition metal in the above-mentioned lithium manganese-based transition metal oxide, is included in a larger amount than the metals excluding lithium, and it is desirable to include it in an amount of 50 mol% or more, preferably 50 to 80 mol%, and more preferably 45 to 65 mol% based on the total amount of the metals excluding lithium. When the Mn content is within the above range, it is possible to ensure stability while suppressing an excessive increase in manufacturing costs, and at the same time, secure excellent electrochemical properties. Preferably, the metals excluding lithium may be included in a molar ratio of Ni:Co:Mn of 40:2:58.

[0051] Next, a step is performed to form an oxide protective layer on the surface of the lithium-and-manganese-based transition metal oxide using atomic layer deposition.

[0052] The step of forming the oxide protective layer can be performed using an atomic layer deposition reactor.

[0053] The above atomic layer deposition is a surface treatment method that forms thin film layers layer by layer with an atomic thickness, and when an oxide protective layer is formed by the above atomic layer deposition, the oxide protective layer can be formed thinly and uniformly.

[0054] The above atomic layer deposition is a method for forming a thin film through chemical adsorption via the periodic supply of each reactant, in which reactions occur only on the surface of the reactant and the substrate (e.g., the anode active material layer), and reactions do not occur between the reactants, thereby enabling deposition at the atomic level.

[0055] The pressure of the atomic layer deposition reactor can be maintained at 0.01 torr to 10 Torr. In addition, the temperature inside the atomic layer deposition reactor can be maintained at 100°C to 350°C, preferably 100°C to 200°C. When the temperature inside the atomic layer deposition reactor is within the above range, the oxide protective layer can be uniformly formed through the smooth performance of atomic layer deposition.

[0056] Specifically, the step of forming the oxide protective layer may be performed by including: a step of supplying a metal precursor into an atomic layer deposition reactor into which the lithium-over-manganese-based transition metal oxide is introduced; a step of supplying a first purge gas into the atomic layer deposition reactor; a step of supplying an oxidizing agent into the atomic layer deposition reactor; and a step of supplying a second purge gas into the atomic layer deposition reactor.

[0057] The metal precursor may include one or more metals selected from aluminum (Al), titanium (Ti), silicon (Si), zirconium (Zr), vanadium (V), niobium (Nb), magnesium (Mg), tantalum (Ta), boron (B), zinc (Zr), tin (Sn), hafnium (Hf), erbium (Er), lanthanum (La), indium (In), yttrium (Y), cerium (Ce), scandium (Sc), and tungsten (W).

[0058] Specifically, the metal precursor may include one or more of trimethylaluminum (TMA), triethylaluminum (TEA), tris(diethylamido)aluminum (TBTDET), titanium isopropoxide (titanium(IV) tetraisopropoxide (TTIP), tetrakis(dimethylamido)tin (TDMASn), tetrakis(dimethylamido)titanium (TDMAT), titanium tetrachloride (TiCl4), tin(IV) chloride (SnCl4), and TBTDEN ((tert-butylimino)tris(diethylamino)niobium).

[0059] The above metal precursor can be supplied into an atomic layer deposition reactor into which a lithium-over-manganese oxide is introduced for 10 to 90 seconds, preferably for 30 to 90 seconds.

[0060] The first purge gas may be one or more selected from nitrogen (N2), argon (Ar), helium (He), neon (Ne), and krypton (Kr), and preferably may be N2 or Ar.

[0061] The first purge gas can be supplied for 60 to 120 seconds at a flow rate of 50 sccm to 100 sccm.

[0062] The above oxidizing agent may be one or more selected from water vapor (H2O), ozone (O3), and oxygen (O2).

[0063] The above oxidizing agent can be supplied for 0.1 to 90 seconds at a flow rate of 10 sccm to 200 sccm.

[0064] The step of forming the oxide protective layer may be performed by sequentially carrying out the steps of introducing a metal precursor, introducing a first purge gas, and introducing an oxidizing agent to form the oxide protective layer, and then purging may be performed by introducing a second purge gas to remove excess oxidizing agent that did not participate in the reaction. At this time, the second purge gas may be the same as the first purge gas.

[0065] Specifically, when an oxidizing agent is introduced into an atomic layer deposition reactor into which the metal precursor and the first purge gas have been introduced, the methyl groups (-CH3) present in the metal precursor are replaced with -OH groups. Once all the methyl groups of the metal precursor have been replaced with -OH groups, a second purge gas is supplied to perform purging in order to remove the remaining oxidizing agent that does not participate in the reaction, thereby forming a metal oxide. Through the above series of processes, the metal precursor reacts with the -OH groups present on the surface of the positive electrode active material layer to form a metal oxide protective layer on the surface of the positive electrode active material.

[0066] That is, the step of forming the oxide protective layer can form an oxide protective layer on the surface of a lithium manganese-based transition metal oxide through atomic layer deposition (ALD) in which a metal precursor is introduced, a first purge gas is introduced, an oxidizing agent is introduced, and a second purge gas is introduced sequentially.

[0067] A series of processes including the introduction of the metal precursor, the introduction of a first purge gas, the introduction of an oxidizing agent, and the introduction of a second purge gas constitutes one cycle of atomic layer deposition (ALD), and in the present invention, the atomic layer deposition cycle can be repeated from 1 to 100 times. Preferably, the atomic layer deposition can be performed 2 to 100 times, 4 to 80 times, or 6 to 60 times.

[0068] When the above atomic layer deposition is performed once, the thickness of the oxide protective layer can be formed to a level of about 0.1 nm. That is, since it is a known fact that the thickness is formed uniformly in the case of atomic layer deposition, it is possible to form an oxide protective layer of a desired thickness by adjusting the number of repetitions of the atomic layer deposition cycle.

[0069] The thickness of the oxide protective layer formed as described above may be 0.1 nm to 10 nm, and preferably 0.1 nm to 5 nm.

[0070] Next, a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described.

[0071] According to another embodiment of the present invention, a positive electrode active material for a lithium secondary battery is provided, manufactured according to the method for manufacturing a positive electrode active material for a lithium secondary battery described above.

[0072] The positive electrode active material for the lithium secondary battery may include an over-lithium manganese-based transition metal oxide represented by the above chemical formula 1 and an oxide protective layer formed on the surface of the over-lithium manganese-based transition metal oxide.

[0073] The thickness of the oxide protective layer may be 0.1 nm to 10 nm, and preferably 0.1 nm to 5 nm.

[0074] When the thickness of the oxide protective layer is within the above range, the lithium on the surface of the lithium manganese-based transition metal oxide reacts sufficiently with the metal precursor to form an oxide protective layer, and accordingly, while having high ionic conductivity, the effect of the surface coating layer is sufficiently displayed to improve electrochemical properties.

[0075] In addition, the present invention provides a positive electrode for a lithium secondary battery comprising the above positive electrode active material.

[0076] Specifically, the anode comprises an anode current collector and an anode active material layer formed on the anode current collector and comprising the anode active material described above.

[0077] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0078] At least one surface of the above-mentioned current collector comprises a positive active material layer comprising one or more of a conductive material and a binder as needed.

[0079] At this time, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98% by weight, based on the total weight of the positive active material layer, and when included within the above range, it may exhibit excellent capacity characteristics.

[0080] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specifically, graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives may be used. The above conductive material may be included in an amount of 0.5% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0081] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specifically, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof may be used. The above binder may be included in an amount of 1% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, based on the total weight of the positive active material layer.

[0082] The above-described anode may be manufactured according to a conventional anode manufacturing method, except for using the anode active material described above. For example, the above-described anode may be manufactured by preparing an anode slurry by dissolving or dispersing the above-described anode active material and optionally at least one of a binder and a conductive material in a solvent, applying the anode slurry to at least one surface of an anode current collector, and then drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0083] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0084] Alternatively, the anode may be manufactured by casting the anode slurry onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0085] In addition, the present invention may provide a lithium secondary battery comprising the above-mentioned positive electrode, negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is the same as previously described, a detailed description is omitted, and only the remaining components are described in detail below.

[0086] The above lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0087] The above cathode includes a cathode current collector and a cathode active material layer located on at least one surface of the cathode current collector.

[0088] The above-mentioned negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative electrode current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0089] The above-mentioned negative electrode active material layer includes a negative electrode active material and, if necessary, may further include one or more of a binder and a conductive material.

[0090] For example, the above-mentioned negative electrode active material layer may be manufactured by applying and drying a negative electrode slurry that includes a negative electrode active material on a negative electrode current collector and, if necessary, further includes one or more of a binder and a conductive material, or by casting the negative electrode slurry onto a separate support and then laminating the film obtained by peeling off from the support onto the negative electrode current collector.

[0091] As the above-mentioned cathode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ βMetal oxides capable of doping and dedoping lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, may be used.

[0092] In addition, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, carbon materials such as low-crystallinity carbon and high-crystallinity carbon may all be used. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0093] In addition, the binder and conductive material mentioned above may be the same as those previously described in the anode.

[0094] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator commonly used in lithium secondary batteries may be used without special restrictions, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0095] In addition, the electrolyte used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0096] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0097] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent is an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether-based solvent such as dibutyl ether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; or an aromatic hydrocarbon-based solvent such as benzene or fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to 1:9 can result in excellent performance of the electrolyte.

[0098] The above lithium salt can be used without special limitations as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1M to 5.0M, more preferably 0.1M to 3.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0099] In addition to the electrolyte components, the above electrolyte may further include additives for the purpose of improving the lifespan characteristics of the battery, suppressing the reduction of battery capacity, and improving the discharge capacity of the battery. For example, the above additives may include haloalkylene carbonate compounds such as difluoroethylene carbonate; pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1% to 10.0% by weight, preferably 0.1% to 5.0% by weight, based on the total weight of the electrolyte.

[0100] The present invention will be explained in more detail below through the following examples. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited thereto.

[0101] Example 1

[0102] Lithium peroxide manganese-based transition metal oxide (Li1 . 099 Ni0 . 358 Co0 . 018 Mn0 .520 W 0. 005O2 ) was introduced into an atomic layer deposition reactor in which the internal temperature was maintained at 100°C. Trimethylaluminum (TMA) was supplied into the atomic layer deposition reactor as a metal precursor for 30 seconds. Subsequently, purging was performed by supplying N2 gas, an inert gas, at a flow rate of 50 sccm for 90 seconds, followed by supplying steam for 0.1 seconds. Afterward, purging was performed by injecting N2 gas, an inert gas, at a flow rate of 50 sccm for 90 seconds to produce an anode active material with an oxide protective layer formed on the surface of a lithium-ion manganese-based transition metal oxide (Fig. 1).

[0103] Example 2

[0104] The above Example 1 was carried out in the same manner as Example 1, except that the internal temperature of the atomic layer deposition reactor was maintained at 200℃ (Fig. 2).

[0105] Comparative Example 1

[0106] In Example 1 above, a lithium manganese-based transition metal oxide without an oxide protective layer was used.

[0107] Experimental Example 1. Observation of Anode Active Material

[0108] Figures 1 and 2 show photographs of the positive electrode active material prepared in Examples 1 and 2 above, observed using a transmission electron microscope (TEM).

[0109] As shown in Figures 1 and 2, in the case of the positive electrode active materials of Examples 1 and 2 in which an oxide protective layer is formed by atomic layer deposition, it was confirmed that an oxide protective layer with a thickness of 1 to 2 nm is formed on the surface of the lithium-over-manganese-based transition metal oxide.

[0110] Experimental Example 2. Analysis of Al Elemental Content by Atomic Layer Deposition

[0111] In Examples 1 and 2 above, atomic layer deposition was repeated 100 times to form an oxide coating layer, and then the Al element content of the surface of the anode material on which the oxide coating layer was formed was analyzed by XPS, and the results are shown in Figure 3.

[0112] As shown in Fig. 3, in both Example 1, in which the temperature inside the atomic layer deposition reactor was maintained at 100°C, and Example 2, in which the temperature was maintained at 200°C, the content of Al elements was confirmed on the surface of the positive electrode active material, and it was found that this result was caused by the formation of a metal oxide protective layer on the surface of the positive electrode active material. In particular, in the case of Example 2, in which the temperature inside the atomic layer deposition reactor was maintained at 200°C, the content of Al elements was found to be higher, and from these results, it was found that the oxide protective layer is formed better when the temperature inside the atomic layer deposition reactor is higher.

[0113] Experimental Example 3. Analysis of Changes in Mn Oxidation Number Due to Atomic Layer Deposition

[0114] During atomic layer deposition for the formation of an Al2O3 oxide protective layer, TMA preferentially binds to oxygen on the surface of lithium-over-manganese transition metal oxides, and depending on electronic affinity, the Mn of the transition metal oxide 4 + Ga Mn 3 +It is reduced to. That is, the increasing trend of the coating range of Al2O3 on the surface of the cathode active material can be inferred from the change in the oxidation state of Mn. Accordingly, in this experimental example, the change in the oxidation state of Mn was analyzed using the cathode active materials of Examples 1 and 2 and the comparative example, and the results are shown in Figures 4 to 6.

[0115] As shown in FIGS. 4 to 6, in the case of Example 2, where the temperature inside the atomic layer deposition reactor was maintained at 200°C, Mn 3 + The ratio was found to be the highest, and through these results, it could be inferred that the diffusion of the deposition gas is promoted when atomic layer deposition is performed at high temperatures.

[0116] Experimental Example 4. Electrochemical Evaluation

[0117] (1) Coin-type half-battery manufacturing

[0118] After manufacturing a CR2032 coin cell using the positive electrode active material prepared as described above, an electrochemical evaluation was conducted.

[0119] Specifically, the positive active material, conductive material (Denka Black), and polyvinylidene fluoride binder (product name: KF1100) prepared in Example 2 and Comparative Example 1 were mixed in a weight ratio of 92.5:3.5:4, respectively, and the mixture was added to an N-methyl-2-pyrrolidone solvent to produce a positive active material slurry with a solid content of approximately 30% by weight.

[0120] The above positive active material slurry was coated onto an aluminum foil (Al foil, thickness: 15㎛) serving as a positive current collector using a doctor blade, dried, and then rolled to produce a positive electrode. The loading amount of the positive electrode was approximately 14.5 mg / cm², and the rolling density was approximately 2.75 g / cc.

[0121] A 2032 coin-type half-cell was manufactured using the above-mentioned positive electrode, lithium metal negative electrode (thickness 300 μm, MTI), electrolyte, and polypropylene separator in a conventional manner. The electrolyte was prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (mixing ratio EC:EMC = 3:7 volume%) to prepare a mixed solution.

[0122] (2) Evaluation of charge / discharge characteristics

[0123] After aging the coin-type half battery manufactured in (1) above at room temperature (25℃) for 10 hours, a charge / discharge test was performed.

[0124] The capacity evaluation was based on a reference capacity of 200 mAh / g, and the charge / discharge conditions applied were a constant current (CC) / constant voltage (CV) of 2.5 V to 4.45 V and a 1 / 20 C cut-off. The initial capacity was measured by performing a 0.1 C charge / 0.1 C discharge followed by a 0.33 C charge / 0.33 C discharge, and the internal resistance before and after charging was measured, with the results shown in Figures 7 and 8.

[0125] As shown in Figures 7 and 8, in the case of Example 2 of the present invention, in which an Al2O3 oxide protective layer is formed by atomic layer deposition, compared to Comparative Example 1 in which an oxide protective layer is not formed, it was confirmed that the ion conductivity and surface stabilization effect are increased, the initial discharge capacity is excellent, and the internal resistance is reduced, resulting in excellent electrochemical characteristics.

[0126] Although embodiments of the invention disclosed above have been illustrated and described, the disclosed invention is not limited to the specific embodiments described above, and various modifications may be made by those skilled in the art to which the disclosed invention belongs without departing from the essence claimed in the claims.

Claims

1. A step of introducing a lithium-over-manganese-based transition metal oxide into an atomic layer deposition reactor; and A method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the step of forming an oxide protective layer on the surface of the lithium-over-manganese-based transition metal oxide using atomic layer deposition (ALD).

2. In Paragraph 1, The step of forming the oxide protective layer above is, A step of supplying a metal precursor into an atomic layer deposition reactor into which the above-mentioned lithium manganese-based transition metal oxide is introduced; A step of supplying a first purge gas into the atomic layer deposition reactor; A step of supplying an oxidizing agent into the atomic layer deposition reactor; and A method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the step of supplying a second purge gas into the atomic layer deposition reactor.

3. In Paragraph 1, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the atomic layer deposition reactor is maintained at a temperature of 100°C to 350°C.

4. In Paragraph 2, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the metal precursor comprises one or more selected from aluminum (Al), titanium (Ti), silicon (Si), zirconium (Zr), vanadium (V), niobium (Nb), magnesium (Mg), tantalum (Ta), boron (B), zinc (Zr), tin (Sn), hafnium (Hf), erbium (Er), lanthanum (La), indium (In), yttrium (Y), cerium (Ce), scandium (Sc), and tungsten (W).

5. In Paragraph 2, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the metal precursor comprises one or more of trimethylaluminum (TMA), triethylaluminum (TEA), tris(diethylamido)aluminum (TBTDET), titanium isopropoxide (titanium(IV) tetraisopropoxide (TTIP), tetrakis(dimethylamido)tin (TDMASn), tetrakis(dimethylamido)titanium (TDMAT), titanium tetrachloride (TiCl4), tin(IV) chloride (SnCl4), and TBTDEN ((tert-butylimino)tris(diethylamino)niobium).

6. In Paragraph 2, A method for manufacturing a positive electrode active material for a lithium secondary battery in which the above metal precursor is supplied for 10 to 90 seconds.

7. In Paragraph 2, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the oxidizing agent comprises one or more of water vapor (H2O), ozone (O3), and oxygen (O2).

8. In Paragraph 2, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above-mentioned oxidizing agent is supplied at a flow rate of 10 sccm to 200 sccm for 0.1 seconds to 90 seconds.

9. In Paragraph 2, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the first purge gas or the second purge gas comprises one or more of nitrogen (N2), argon (Ar), helium (He), neon (Ne), and krypton (Kr).

10. In Paragraph 2, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the first purge gas or the second purge gas is supplied at a flow rate of 50 sccm to 100 sccm for 60 seconds to 120 seconds.

11. In Paragraph 1, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the thickness of the oxide protective layer is formed to be 0.1 nm to 10 nm.

12. In Paragraph 1, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above atomic layer deposition (ALD) is performed 1 to 100 times.

13. In Paragraph 1, The above-mentioned lithium manganese-based transition metal oxide is a method for manufacturing a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1. [Chemical Formula 1] Li 1+a (Ni x Co y Mr z W b M c ) 1-a O 2-d A d (In the above Chemical Formula 1, 0.1≤a≤0.3, 0.35≤x≤0.45, 0≤y≤0.05, 0.45≤z≤0.65, 0.001≤b≤0.13, 0≤c≤0.1, 0≤d≤0.1, x+y+z+b+c=1, M is one or more of B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, and Ir, and A is one or more of PO4, BO3, CO3, NO3, F, Cl, Br, and I) 14. A positive electrode active material for a lithium secondary battery comprising: a lithium-over-manganese-based transition metal oxide represented by the following chemical formula 1; and an oxide protective layer formed on the surface of the lithium-over-manganese-based transition metal oxide. [Chemical Formula 1] Li 1+a (Ni x Co y Mr z W b M c ) 1-a O 2-d A d (In the above Chemical Formula 1, 0.1≤a≤0.3, 0.35≤x≤0.45, 0≤y≤0.05, 0.45≤z≤0.65, 0.001≤b≤0.13, 0≤c≤0.1, 0≤d≤0.1, x+y+z+b+c=1, M is one or more of B, Ti, Cr, Zr, Al, Y, Mg, Nb, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, Sn, Sb, Zn, Cu, Ge, Ru, and Ir, and A is one or more of PO4, BO3, CO3, NO3, F, Cl, Br, and I) 15. In Paragraph 14, A positive electrode active material for a lithium secondary battery, wherein the thickness of the oxide protective layer is 0.1 nm to 10 nm.

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