Cathode active material for lithium secondary battery, method of preparing same, and lithium secondary battery comprising same

Abstract

A cathode active material for a lithium secondary battery, according to the present invention, comprises: a core including a lithium transition metal oxide that does not include cobalt; and an oxide coating layer positioned on the surface of the core, wherein the oxide coating layer is an oxide including lithium (Li) and at least one element selected from the group consisting of titanium (Ti), zirconium (Zr), aluminum (Al), and silicon (Si).

Description

Cathode active material for lithium secondary batteries, method for producing same, and lithium secondary batteries comprising same

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same.

[0002] The recent rapid proliferation of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity secondary batteries. In particular, lithium secondary batteries, with their lightweight design and high energy density, are attracting attention as power sources for portable devices. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0003] In addition, as interest in environmental issues grows, interest in electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels, such as gasoline and diesel vehicles, which are one of the main causes of air pollution, is also increasing, and research is actively being conducted to use lithium secondary batteries as the power source for electric vehicles and hybrid electric vehicles. Lithium secondary batteries are generally composed of a positive electrode containing a positive active material, a negative electrode containing a negative active material, a separator, and an electrolyte, and charging and discharging are performed by the intercalation and decalation of lithium ions. The lithium secondary battery has the advantages of high energy density, large electromotive force, and high capacity, and is therefore applied in various fields.

[0004] Furthermore, active research is being conducted to improve structural stability and suppress interfacial degradation during charge and discharge in lithium secondary batteries. For example, in order to improve electrochemical properties of existing NCM and NCA-based active materials, cathode active materials were manufactured primarily by internally positioning cobalt during the precursor and sintering stages. Furthermore, active research is being conducted to secure stability by applying technologies such as additional coating and doping to improve structural stability and suppress interfacial degradation that occurs during charge and discharge. Furthermore, active research is being conducted on NM materials composed solely of Ni and Mn, as they do not use Co and offer cost savings.

[0005] The solid-state coating method, which is the most commonly used coating method, simply mixes the positive active material and coating material, followed by a heat treatment process to complete the coating. However, since the solid-state reaction is the main mechanism, it is difficult to form a uniform coating layer. If a non-uniform and localized coating layer is formed, the desired effect cannot be properly achieved, and problems such as reduced average voltage and capacity may occur. Furthermore, the commonly used metal oxide coating layer is difficult to help lithium ion diffusion. Therefore, even if it shows improved structural stability and improved interfacial deterioration, it can cause problems with capacity reduction and improved rate characteristics.

[0006] The present invention aims to provide a cathode active material for a lithium secondary battery that can improve structural stability and interface deterioration, as well as discharge capacity and rate characteristics.

[0007] In addition, the present invention seeks to provide a method for manufacturing a positive electrode active material for a lithium secondary battery, which can improve structural stability and interface deterioration, as well as discharge capacity and rate characteristics.

[0008] One aspect of the present invention provides a cathode active material for a lithium secondary battery, comprising a core including a lithium transition metal oxide that does not include cobalt, and an oxide coating layer positioned on the surface of the core, wherein the oxide coating layer is an oxide including lithium (Li) and at least one element selected from the group consisting of titanium (Ti), zirconium (Zr), aluminum (Al), and silicon (Si).

[0009] The content of the metal element or metalloid element of the above oxide may be 300 ppm to 1600 ppm for all metals except lithium.

[0010] The above oxide coating layer is an oxide containing lithium and titanium, and the content of titanium may be 400 ppm to 1200 ppm with respect to the total metal excluding lithium.

[0011] The above core is lithium nickel manganese oxide, and the lithium nickel manganese oxide may contain 60 mol% to 80 mol% of manganese among the total metals excluding lithium.

[0012] The above lithium nickel manganese oxide may have a molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li) (Li / Me) of 1.29 to 1.35.

[0013] The crystal grain size of the above core may be 52 nm to 54 nm.

[0014] In addition, another aspect of the present invention provides a method for producing a positive electrode active material for a lithium secondary battery, comprising the steps of obtaining a lithium transition metal oxide that does not contain cobalt, mixing the lithium transition metal oxide with a molten salt and an oxide to obtain a mixture, and heat-treating the mixture at a temperature higher than the melting point of the molten salt.

[0015] The above molten salt may include at least one selected from the group consisting of lithium chloride, lithium carbonate, and lithium hydroxide.

[0016] The above oxide may include at least one selected from the group consisting of titanium oxide, zirconium oxide, aluminum oxide, and silicon oxide.

[0017] The oxides may be mixed so that the content of the metal element or metalloid element of the oxide is 300 ppm to 1600 ppm with respect to the total metal excluding lithium.

[0018] The above oxide is titanium oxide, and the oxide can be mixed so that the content of titanium is 400 ppm to 1200 ppm with respect to the total metal excluding lithium.

[0019] The step of heat treating the above mixture can be performed at a temperature of 500°C to 800°C.

[0020] The above lithium transition metal oxide is lithium nickel manganese oxide, and the lithium nickel manganese oxide may contain 60 mol% to 80 mol% of manganese among the total metals excluding lithium.

[0021] The above lithium nickel manganese oxide may have a molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li) (Li / Me) of 1.29 to 1.35.

[0022] And, another aspect of the present invention provides a lithium secondary battery including a positive electrode including the positive electrode active material.

[0023] Since the cathode active material for a lithium secondary battery according to the present invention includes an oxide coating layer evenly distributed on the surface of a core made of a lithium transition metal oxide, structural stability and interface deterioration can be improved.

[0024] In addition, since the positive electrode active material for a lithium secondary battery according to the present invention includes a lithium ion conductive oxide coating layer evenly distributed on the surface of a core made of a lithium transition metal oxide, the discharge capacity and rate characteristics of the battery can be improved.

[0025] In addition, the method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention can evenly form an oxide coating layer having lithium ion conductivity on the surface of a core made of a lithium transition metal oxide by forming an oxide coating layer in a molten salt molten state.

[0026] In addition, the method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention can provide a positive electrode active material for a lithium secondary battery in which not only structural stability and interface deterioration are improved, but also discharge capacity and rate characteristics are improved.

[0027] Figures 1 and 2 show the room temperature discharge capacity of positive electrode active materials for lithium secondary batteries manufactured according to embodiments and comparative examples of the present invention.

[0028] Figure 3 shows the high-temperature discharge capacity of the positive electrode active material for a lithium secondary battery manufactured according to the embodiments and comparative examples of the present invention.

[0029] In this specification, the terms first, second, and third, etc. are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0030] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0031] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0032] Although not otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0033] In this specification, the term "combination(s) thereof" described in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including any one or more selected from the group consisting of said components.

[0034] In this specification, “secondary particle” means an aggregate, i.e., a secondary structure, in which tens to hundreds of primary particles are aggregated together by physical or chemical bonding between the primary particles without any intentional aggregation or assembly process for the primary particles.

[0035] “Primary particle” refers to the smallest particle unit that can be distinguished as a single lump when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and may be composed of a single crystal grain or multiple crystal grains.

[0036] In this specification, “crystal grain” means a distinct region in which atoms within a primary particle form a lattice structure with a certain direction.

[0037] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0038] <Cathode active material for lithium secondary batteries>

[0039] One aspect of the present invention relates to a positive electrode active material for a lithium secondary battery, comprising a core including a lithium transition metal oxide that does not include cobalt (Co), and a coating layer positioned on the surface of the core, wherein the coating layer is an oxide including lithium (Li) and at least one element selected from the group consisting of titanium (Ti), zirconium (Zr), aluminum (Al), and silicon (Si).

[0040] Since the positive electrode active material for a lithium secondary battery according to one aspect of the present invention includes an oxide coating layer evenly distributed on the surface of a core made of a lithium transition metal oxide, structural stability and interface deterioration can be improved.

[0041] In addition, since the positive electrode active material for a lithium secondary battery according to one aspect of the present invention includes a lithium ion conductive oxide coating layer evenly distributed on the surface of a core made of a lithium transition metal oxide, the discharge capacity and rate characteristics can be improved.

[0042] A cathode active material for a lithium secondary battery according to one embodiment of the present invention may include lithium nickel manganese oxide that includes nickel (Ni) and manganese (Mn) and does not include cobalt (Co).

[0043] The above lithium nickel manganese oxide may contain manganese (Mn) in an amount of 60 mol% or more among all metals excluding lithium (Li), specifically 60 mol% to 80 mol%, more specifically 60 mol% to 70 mol%, and even more specifically 65 mol%.

[0044] The above lithium nickel manganese oxide may contain nickel (Ni) in an amount of 40 mol% or less among all metals excluding lithium (Li), specifically 20 mol% to 40 mol%, more specifically 30 mol% to 40 mol%, and even more specifically 35 mol%.

[0045] Meanwhile, the lithium nickel manganese oxide may have a molar ratio of nickel (Ni) and manganese (Mn) of Ni:Mn of 20:80, specifically 30:70, and more specifically 35:65.

[0046] A cathode active material for a lithium secondary battery according to one embodiment of the present invention may include an oxide coating layer positioned on the surface of a core made of a lithium transition metal oxide. The oxide coating layer may be an oxide containing lithium (Li) and at least one element selected from the group consisting of titanium (Ti), zirconium (Zr), aluminum (Al), and silicon (Si).

[0047] Among the entire metal (Me) excluding lithium (Li), at least one element of the oxide coating layer may be included in an amount of 0.03 mol% to 0.16 mol% (300 ppm to 1600 ppm).

[0048] For example, the oxide coating layer may be an oxide containing lithium and titanium. For example, the oxide coating layer may be Li2TiO3.

[0049] When the above oxide coating layer is an oxide containing lithium and titanium, titanium (Ti) may be included in an amount of 0.04 mol% to 0.12 mol% (400 ppm to 1200 ppm) among the total metal (Me) excluding lithium (Li).

[0050] By including the metal or metalloid element of the oxide coating layer within the above range, the room temperature and high temperature (45°C) discharge capacity of a secondary battery using the positive electrode active material for a lithium secondary battery can be increased and the rate characteristics can be improved.

[0051] In one embodiment of the present invention, the positive electrode active material for a lithium secondary battery may have a molar ratio of lithium to the total metal (Me) excluding lithium (Li) (Li / Me) of 1 to 1.5, specifically 1.1 to 1.4, and more specifically 1.29 to 1.35.

[0052]

[0053] In one embodiment of the present invention, a positive electrode active material for a lithium secondary battery can be represented by the following chemical formula 1.

[0054] [Chemical Formula 1]

[0055] Li a Ni x Mn y M z O2

[0056] In the above chemical formula 1, 1≤a≤1.5, 0.2 <x<0.4, 0.6<y<0.8, 0.0003≤z≤0.0016, M은 Ti, Zr, Al, 및 Si 중에서 선택되는 1종 이상이다.

[0057]

[0058] In one embodiment of the present invention, the cathode active material for a lithium secondary battery may have a crystallite size of 55 nm or less, and specifically, 48 nm to 54 nm. In the present specification, "crystallite" means at least one crystal growth unit in a crystalline material, and the "crystallite size" can be estimated using peak broadening of XRD data and can be quantitatively calculated using the Scherrer equation.

[0059] In one embodiment of the present invention, the positive electrode active material for a lithium secondary battery may be a secondary particle formed by agglomeration of primary particles, and the center particle diameter (D50) of the secondary particles may be 8.0 µm to 10.0 µm, and specifically, 9.2 µm to 9.6 µm.

[0060] By controlling the central particle diameter (D50) of the positive electrode active material within the above range, the electrode electrolyte and active area can be reduced, thereby improving electrochemical safety. In this specification, the central particle diameter (D50) can be defined as a particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve. The central particle diameter (D50) can be measured using a particle size distribution meter that utilizes, for example, a laser diffraction method.

[0061]

[0062] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention will be described. The present invention is not necessarily limited to the method for manufacturing a positive electrode active material described below, and may be manufactured according to any method for manufacturing a positive electrode active material well known in the art.

[0063] <Method for manufacturing positive electrode active material for lithium secondary batteries>

[0064] Another aspect of the present invention relates to a method for producing a positive electrode active material for a lithium secondary battery, comprising the steps of obtaining a lithium transition metal oxide that does not contain cobalt, mixing the lithium transition metal oxide, a molten salt, and an oxide to obtain a mixture, and heat-treating the mixture at a temperature higher than the melting point of the molten salt.

[0065] The method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention can evenly form an oxide coating layer having lithium ion conductivity on the surface of a core made of a lithium transition metal oxide by forming an oxide coating layer in a molten salt molten state.

[0066] A method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention includes a step of obtaining a lithium transition metal oxide that does not contain cobalt.

[0067] First, a step of preparing a nickel- and manganese-containing transition metal hydroxide precursor is performed.

[0068] A coprecipitation reaction can be performed by introducing nickel-containing raw material, manganese-containing raw material, a chelating agent such as an aqueous ammonia solution, and an alkaline aqueous solution for pH adjustment into a coprecipitation reactor.

[0069] The nickel-containing raw material is not particularly limited as long as it is used in the manufacture of a positive electrode active material precursor in the relevant technical field. As a non-limiting example, the nickel-containing raw material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically, may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salt, nickel halide or a combination thereof.

[0070] The manganese-containing raw material may be, but is not limited to, manganese-containing sulfates, acetates, nitrates, halides, sulfides, hydroxides, oxides, oxyhydroxides or combinations thereof, and specifically, manganese salts such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylic acid salts, manganese citrate and manganese fatty acid salts, manganese oxides such as Mn2O3, MnO2, and Mn3O4, manganese oxyhydroxide, manganese chloride or combinations thereof.

[0071] The ammonia solution may include, as a complexing agent, non-limiting examples thereof, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof. Meanwhile, the ammonia solution may also be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent, such as alcohol, which is uniformly miscible with water, may be used as the solvent.

[0072] The pH adjusting agent may be a caustic soda solution, which may include an alkaline compound such as a hydroxide of an alkali metal or alkaline earth metal, such as NaOH, KOH, or Ca(OH)2, a hydrate thereof, or a combination thereof. The caustic soda solution may also be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent, such as an alcohol that can be uniformly mixed with water, may be used as the solvent.

[0073] The above coprecipitation reaction can be performed under an inert atmosphere such as nitrogen or argon to prevent oxidation of the metal ion. Specifically, the coprecipitation reaction can be performed while injecting nitrogen.

[0074] During the above-described co-precipitation reaction, the temperature within the reactor may be 30°C to 70°C, specifically 40°C to 60°C, and more specifically 45°C to 55°C. By performing the co-precipitation reaction within the above temperature range, particles of nickel-manganese element hydroxide may be generated and precipitated within the reaction solution. The precipitated precursor particles may be separated and dried according to a conventional method to obtain a nickel- and manganese-containing transition metal hydroxide precursor. The precursor may be in the form of secondary particles formed by agglomeration of primary particles.

[0075] At this time, by controlling the concentration of the nickel-containing raw material and the manganese-containing raw material, a precursor having a nickel (Ni) content of 40 mol% or less, specifically 20 mol% to 40 mol%, more specifically 30 mol% to 40 mol%, and even more specifically 35 mol% of the total metal content can be manufactured. That is, the nickel content of the transition metal hydroxide may be 40 mol% or less, specifically 20 mol% to 40 mol%, more specifically 30 mol% to 40 mol%, and even more specifically 35 mol%, based on the total mole number of transition metals.

[0076] In one embodiment, the nickel and manganese containing transition metal hydroxide may be represented by the following chemical formula 2.

[0077] <Chemical Formula 2>

[0078] Ni x1 Mn y1 (OH)2

[0079] 0.2 in the above chemical formula 2 <x1<0.4, 0.6<y1<0.8 이다.

[0080] As shown in the above chemical formula 2, by not including cobalt, there is an advantage of improved structural stability and superior electrochemical properties by replacing cobalt with manganese in the existing NCM precursor.

[0081] Next, a step of forming a mixture containing the nickel and manganese-containing transition metal hydroxide and the lithium raw material and then calcining it to form a lithium transition metal oxide is performed.

[0082] The lithium source material may include, for example, Li2CO3, LiOH, or a combination thereof.

[0083] The mixing ratio of the nickel and manganese-containing metal hydroxide and the lithium raw material can be adjusted according to the composition of the target lithium cathode active material.

[0084] The sintering temperature of the above mixture may be 700°C to 900°C, specifically, 800°C to 900°C, and more specifically, 840°C to 880°C. If the sintering temperature exceeds the upper limit of the above-mentioned range, the structural stability of the positive electrode active material may deteriorate, resulting in a decrease in reversible capacity. If the sintering temperature exceeds the lower limit of the above-mentioned range, there is a problem in that the particle size growth of the positive electrode active material is not sufficiently accompanied.

[0085] The above firing time can be performed for 4 to 20 hours, specifically 8 to 12 hours. The above firing time refers to the time maintained at the firing temperature, excluding the heating and cooling times. If the above firing time is excessively long, there are problems in terms of productivity and economic feasibility, and if the above firing time is excessively short, there are problems in which the synthetic reaction does not occur completely or the crystal structure does not develop sufficiently.

[0086] The obtained lithium transition metal oxide may contain manganese in an amount of 60 mol% to 80 mol% among the total metals excluding lithium, and the molar ratio of lithium (Li) to the total metals (Me) excluding lithium (Li) (Li / Me) may be 1.29 to 1.35.

[0087] The method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention includes a step of mixing the obtained lithium transition metal oxide, molten salt, and oxide to obtain a mixture, and a step of heat-treating the mixture at a temperature higher than the melting point of the molten salt.

[0088] The molten salt may be a lithium salt and may include at least one selected from the group consisting of lithium chloride, lithium carbonate, and lithium hydroxide. The molten salt may be, for example, lithium chloride.

[0089] The oxide may include at least one of a metal oxide and a metalloid oxide. Specifically, the oxide may include at least one selected from the group consisting of titanium oxide, zirconium oxide, aluminum oxide, and silicon oxide. The oxide may be, for example, titanium oxide.

[0090] The oxide may be mixed into the mixture so that the content of the metal element or metalloid element of the oxide is 300 ppm to 1600 ppm with respect to the total metal excluding lithium.

[0091] When the oxide is, for example, titanium oxide, the titanium oxide may be mixed into the mixture so that the content of titanium is 400 ppm to 1200 ppm with respect to the total metal excluding lithium.

[0092] By designing the metal element or metalloid element of the oxide forming the oxide coating layer together with the molten salt to be included in the above-described range, the method for manufacturing a positive electrode active material for a lithium secondary battery according to the present invention can provide a positive electrode active material for a lithium secondary battery in which not only structural stability and interface deterioration are improved, but also discharge capacity and rate characteristics can be improved.

[0093] The step of heat-treating the above mixture may be performed at a temperature of 500°C to 800°C, and may be performed for 1 hour to 12 hours, but is not limited thereto. The heat-treatment temperature may be adjusted depending on the melting point temperature of the molten salt, and may be lower than the sintering temperature. When the molten salt is lithium chloride, the heat-treatment temperature may be 630°C to 670°C, and specifically, 650°C.

[0094]

[0095] Bipolar

[0096] Another aspect of the present invention provides a current collector, and a positive electrode positioned on at least one surface of the current collector and including a positive electrode active material layer.

[0097] The characteristics of the positive electrode active material constituting the positive electrode active material layer are the same as described above. Therefore, a detailed description of the positive electrode active material will be omitted.

[0098] The above-mentioned collector may be, for example, made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0099] Meanwhile, the positive electrode active material layer may include a binder and a conductive material.

[0100] At this time, the binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof, but is not limited thereto. The above binder may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0101] And, the conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include 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, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one type alone or a mixture of two or more types among these may be used, but the present invention is not limited thereto. The conductive material may typically be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0102] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used.

[0103] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, including the positive electrode active material described above and optionally a binder, a conductive agent, or a solvent, on a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0104] The solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied for subsequent positive electrode manufacturing.

[0105] Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the resulting film on a positive electrode current collector by peeling it off from the support.

[0106] The structure and manufacturing method of the positive electrode are not limited in the present invention.

[0107]

[0108] Lithium secondary battery

[0109] Another aspect of the present invention provides a lithium secondary battery comprising the positive electrode. A lithium secondary battery comprising the positive electrode active material described above can have improved discharge capacity and rate characteristics.

[0110] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container that houses an electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0111] In the above lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0112] The 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., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0113] The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. The negative electrode active material layer may be manufactured by, for example, applying a composition for forming a negative electrode active material layer comprising the negative electrode active material and optionally a binder and a conductive material onto a negative electrode current collector and drying the composition, or by casting the negative electrode forming composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a negative electrode current collector.

[0114] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof 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 alloy, Sn alloy, and Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more thereof may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, 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.

[0115] The above binder and conductive material may be the same as those described above for the positive electrode.

[0116] Next, depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof, and mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0117] In addition, in the lithium secondary battery, examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0118] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt. The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used.Among these, a carbonate solvent is preferable, 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 compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable. In this case, the performance of the electrolyte can be excellent when the cyclic carbonate and the linear carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0119] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0120] The structure and manufacturing method of the battery are not limited in the present invention.

[0121]

[0122] Hereinafter, embodiments and comparative examples of the present invention will be described. However, the embodiments are presented as examples and the present invention is not limited thereto.

[0123] Example 1

[0124] A mixture was prepared by uniformly mixing Li2CO3 into a precursor having a composition of Ni0.35Mn0.65(OH)2. At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) was designed to be 1.33.

[0125] Next, the mixture was placed in a kiln in an air atmosphere from which moisture had been removed, and the temperature was raised to 860°C for 10 hours to obtain a lithium transition metal oxide.

[0126] The lithium transition metal oxide was uniformly mixed with coating raw materials LiCl and TiO2, placed in a crucible, and heat-treated at 650°C for 5 hours in a kiln in an air atmosphere from which moisture had been removed, thereby manufacturing a cathode active material in which an oxide coating layer was formed on the surface of the lithium transition metal oxide. At this time, LiCl and TiO2 were mixed in a molar ratio of 2:1, and TiO2 was mixed so that Ti was 500 ppm with respect to the total metal excluding lithium in the final cathode active material. Thereafter, the cathode active material including the lithium transition metal oxide having an oxide coating layer including Li and Ti was manufactured by classifying using a mesh.

[0127] Example 2

[0128] A mixture was prepared by uniformly mixing Li2CO3 into a precursor having a composition of Ni0.35Mn0.65(OH)2. At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) was designed to be 1.33.

[0129] Next, the mixture was placed in a kiln in an air atmosphere from which moisture had been removed, and the temperature was raised to 860°C for 10 hours to obtain a lithium transition metal oxide.

[0130] LiCl and TiO2, which are coating raw materials, were uniformly mixed with the lithium transition metal oxide above, placed in a crucible, and heat-treated at 650°C for 5 hours in a kiln in an air atmosphere from which moisture had been removed, thereby manufacturing a cathode active material in which an oxide coating layer was formed on the surface of the lithium transition metal oxide. At this time, LiCl and TiO2 were mixed in a molar ratio of 2:1, and TiO2 was mixed so that Ti was 1000 ppm with respect to the total metal excluding lithium in the final cathode active material manufactured. Thereafter, a cathode active material including a lithium transition metal oxide having an oxide coating layer including Li and Ti was manufactured by classifying using a mesh.

[0131] Comparative Example 1

[0132] A mixture was prepared by uniformly mixing Li2CO3 into a precursor having a composition of Ni0.35Mn0.65(OH)2. At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) was designed to be 1.33.

[0133] Next, the mixture was placed in a kiln in an air atmosphere from which moisture had been removed, and the temperature was raised to 860°C for 10 hours to obtain a lithium transition metal oxide.

[0134] Comparative Example 1 did not form an oxide coating layer on the surface of the lithium transition metal oxide.

[0135] Comparative Example 2

[0136] A mixture was prepared by uniformly mixing Li2CO3 into a precursor having a composition of Ni0.35Mn0.65(OH)2. At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) was designed to be 1.33.

[0137] Next, the mixture was placed in a kiln in an air atmosphere from which moisture had been removed, and the temperature was raised to 860°C for 10 hours to obtain a lithium transition metal oxide.

[0138] LiCl and TiO2, which are coating raw materials, were uniformly mixed with the lithium transition metal oxide above, placed in a crucible, and heat-treated at 650°C for 5 hours in a kiln in an air atmosphere from which moisture had been removed, thereby manufacturing a cathode active material in which an oxide coating layer was formed on the surface of the lithium transition metal oxide. At this time, LiCl and TiO2 were mixed in a molar ratio of 2:1, and TiO2 was mixed so that Ti was 250 ppm with respect to the total metal excluding lithium in the final cathode active material manufactured. Thereafter, a mesh was used for classification to manufacture a cathode active material including a lithium transition metal oxide having an oxide coating layer including Li and Ti formed thereon.

[0139] Comparative Example 3

[0140] A mixture was prepared by uniformly mixing Li2CO3 into a precursor having a composition of Ni0.35Mn0.65(OH)2. At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) was designed to be 1.33.

[0141] Next, the mixture was placed in a kiln in an air atmosphere from which moisture had been removed, and the temperature was raised to 860°C for 10 hours to obtain a lithium transition metal oxide.

[0142] The lithium transition metal oxide was uniformly mixed with LiCl and TiO2 as coating raw materials, and placed in a crucible, and heat-treated at 650°C for 5 hours in a kiln in an air atmosphere from which moisture had been removed, thereby manufacturing a cathode active material in which an oxide coating layer was formed on the surface of the lithium transition metal oxide. At this time, LiCl and TiO2 were mixed in a molar ratio of 2:1, and TiO2 was mixed so that Ti was 1500 ppm with respect to the total metal excluding lithium in the final cathode active material. Thereafter, a mesh was used for classification to manufacture a cathode active material including a lithium transition metal oxide having an oxide coating layer including Li and Ti formed thereon.

[0143] Comparative Example 4

[0144] A mixture was prepared by uniformly mixing Li2CO3 into a precursor having a composition of Ni0.35Mn0.65(OH)2. At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) was designed to be 1.33.

[0145] Next, the mixture was placed in a kiln in an air atmosphere from which moisture had been removed, and the temperature was raised to 860°C for 10 hours to obtain a lithium transition metal oxide.

[0146] LiCl and TiO2, which are coating raw materials, were uniformly mixed with the lithium transition metal oxide above, placed in a crucible, and heat-treated at 650°C for 5 hours in a kiln in an air atmosphere from which moisture had been removed, thereby manufacturing a cathode active material in which an oxide coating layer was formed on the surface of the lithium transition metal oxide. At this time, LiCl and TiO2 were mixed in a molar ratio of 2:1, and TiO2 was mixed so that Ti was 2000 ppm with respect to the total metal excluding lithium in the final cathode active material manufactured. Thereafter, a mesh was used for classification to manufacture a cathode active material including a lithium transition metal oxide having an oxide coating layer including Li and Ti formed thereon.

[0147] Comparative Example 5

[0148] A mixture was prepared by uniformly mixing Li2CO3 into a precursor having a composition of Ni0.35Mn0.65(OH)2. At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) was designed to be 1.33.

[0149] Next, the mixture was placed in a kiln in an air atmosphere from which moisture had been removed, and the temperature was raised to 860°C for 10 hours to obtain a lithium transition metal oxide.

[0150] LiCl and TiO2, which are coating raw materials, were uniformly mixed with the lithium transition metal oxide above, placed in a crucible, and heat-treated at 650°C for 5 hours in a kiln in an air atmosphere from which moisture had been removed, thereby manufacturing a cathode active material in which an oxide coating layer was formed on the surface of the lithium transition metal oxide. At this time, LiCl and TiO2 were mixed in a molar ratio of 2:1, and TiO2 was mixed so that Ti was 3000 ppm with respect to the total metal excluding lithium in the final cathode active material manufactured. Thereafter, a mesh was used for classification to manufacture a cathode active material including a lithium transition metal oxide having an oxide coating layer including Li and Ti formed thereon.

[0151]

[0152] (1) Crystallite size evaluation

[0153] The crystal grain sizes of the positive electrode active materials manufactured according to the Examples and Comparative Examples were quantitatively calculated using XRD data and the Scherrer equation, and are shown in Table 1. The XRD data of the positive electrode active materials manufactured according to the Examples and Comparative Examples were measured using Rigaku's smart lab equipment. The XRD peak used in the calculation is the (104) peak.

[0154] (2) Evaluation of cation mixing ratio

[0155] For the positive electrode active materials manufactured according to the examples and comparative examples, the cation mixing ratio was measured by dividing the intensity of the (003) peak of the XRD data by the intensity of the (104) peak.

[0156] (3) Tap density evaluation

[0157] The tap density was evaluated by placing 10 g of positive electrode active material in a cylinder with a diameter of 19.1 mm, applying a pressure of 108 N, and measuring the height of the cylinder.

[0158] Ti content ratio (ppm)Crystal grain size (nm)Cation mixing (I 003 / I104 )Tab density (g / ml) Comparative Example 1-57.41.512.03 Comparative Example 2 25051.51.572.12 Example 1 50051.31.552.21 Example 2 100052.61.552.19 Comparative Example 3 150051.51.532.19 Comparative Example 4 200050.81.612.03 Comparative Example 5 300049.01.622.00

[0159] (4) In order to evaluate the electrochemical properties of the positive electrode active material manufactured according to the lithium secondary battery performance evaluation examples and comparative examples, a coin-type half-cell CR2032 coin cell was manufactured as follows.

[0160] Specifically, a positive electrode active material, a conductive agent (acetylene black FX35, Denka), and a polyvinylidene fluoride (PVDF) binder (trade name: KF9709) were mixed in a weight ratio of 96.5:1.5:2.0, and the mixture was added to an N-methyl-2-pyrrolidone solvent so that the solid content was about 65 to 69 wt% to prepare a positive electrode active material slurry.

[0161] The above slurry was coated on an aluminum foil (Al foil, thickness: 20 μm), which is a positive electrode collector, using a doctor blade, dried, and rolled to manufacture a positive electrode. The loading amount of the positive electrode was about 15-16 mg / cm2, and the rolling density was about 3.5 g / cm 3 It was.

[0162] A 2032 coin-type half-cell was manufactured using the above positive electrode, lithium metal negative electrode (400 μm thick, NEBA), electrolyte, and polypropylene polyethylene separator in a conventional manner. The electrolyte was prepared by dissolving 1 M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (mixing ratio EC:DMC:DEC=1:2:1 volume %) to prepare a mixed solution, to which 3 wt% of vinylene carbonate (VC) was added and used.

[0163] After aging the manufactured coin-type half-cells at room temperature (RT, 25℃) for 10 hours, a charge-discharge test was conducted.

[0164] After aging the coin-type half-cell at high temperature (HT, 45℃) for 10 hours, 200 mAh / g was used as the reference capacity for initial capacity evaluation, and the charge / discharge conditions were CC / CV 2.0~4.65 V, 0.05 cut-off. The initial capacity was measured by charging at 0.1C / discharging at high temperature (45℃).

[0165] In addition, for the evaluation of room temperature capacity, the CC / CV was applied at room temperature (RT, 25℃) with a 0.05C cut-off of 2.5V~4.4V and 0.1C / charge and 0.1C / discharge.

[0166] Meanwhile, in order to measure the output characteristics (rate characteristics), a charge / discharge test was conducted at 0.1C and 0.33C with a CC / CV of 2.5 to 4.4 V and a 0.05C cut-off at room temperature, and the ratio of the 0.33C discharge capacity to the 0.1C discharge capacity (rate characteristics, %) is shown in Table 2 below.

[0167] Figures 1 to 3 show the high-temperature discharge capacity of positive electrode active materials for lithium secondary batteries manufactured according to the embodiments and comparative examples of the present invention.

[0168] High temperature charge / discharge testRoom temperature charge / discharge test0.1C charge (mAh / g)0.1C discharge (mAh / g)0.1C charge (mAh / g)0.1C discharge (mAh / g)0.33C Discharge (mAh / g) Rate Characteristics (%) Comparative Example 1 292.4 275.0 227.4 218.4 205.193.9 Comparative Example 2 292.2 275.3 226.0 216.4 206.295.2 Exemplary Example 1 294.4 276.8 230.9 220.2 208.8 94.8 Exemplary Example 2 294.8 276.5 227.6 219.1 208.9 95.3 Comparative Example 3 295.0 275.8 227.6 217.7 207.0 95.1 Comparative Example 4 294.9 270.4 222.1 211.9 204.5 96.5 Comparative Example 5 302.3 269.3 219.9 210.2 200.0 95.1

[0169] Referring to Table 2 and Figures 1 to 3, it can be seen that the electrochemical performance, particularly the discharge capacity, of the examples in which the Ti content ratio of the oxide coating layer is within the range of the present invention when applied to a lithium secondary battery is superior to that of the comparative examples. In particular, it can be seen that the room temperature 0.33C discharge capacity of Examples 1 and 2 is significantly superior to that of the comparative examples. It can be seen that Examples 1 and 2 have superior discharge capacities compared to Comparative Example 1, which does not form an oxide coating layer.

[0170] In the case of Comparative Example 2, an oxide coating layer was formed on the surface of the lithium transition metal oxide, but it can be seen that the Ti content ratio of the oxide coating layer is lower than the range of the present invention, so the discharge capacity is lower than that of the examples.

[0171] In the case of Comparative Examples 3, 4, and 5, an oxide coating layer was formed on the surface of the lithium transition metal oxide, but it was found that the discharge capacity decreased again as the Ti content ratio of the oxide coating layer increased beyond the range of the present invention.

[0172]

[0173] The present invention is not limited to the above embodiments, but can be manufactured in various different forms, and those skilled in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential characteristics of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims

1. A core comprising a lithium transition metal oxide that does not contain cobalt; and An oxide coating layer positioned on the surface of the core; A positive electrode active material for a lithium secondary battery, wherein the oxide coating layer is an oxide containing lithium (Li) and at least one element selected from the group consisting of titanium (Ti), zirconium (Zr), aluminum (Al), and silicon (Si).

2. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the content of a metal element or metalloid element of the above oxide is 300 ppm to 1600 ppm with respect to all metals excluding lithium.

3. In paragraph 1, The above oxide coating layer is an oxide containing lithium and titanium, A cathode active material for a lithium secondary battery, wherein the content of the titanium is 400 ppm to 1200 ppm relative to the total metal excluding lithium.

4. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the core is lithium nickel manganese oxide, and the lithium nickel manganese oxide contains 60 mol% to 80 mol% of manganese among all metals excluding lithium.

5. In paragraph 4, The above lithium nickel manganese oxide is a cathode active material for a lithium secondary battery, wherein the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li) (Li / Me) is 1.29 to 1.

35.

6. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the crystal grain size of the core is 52 nm to 54 nm.

7. A step for obtaining a lithium transition metal oxide that does not contain cobalt; A step of obtaining a mixture by mixing the above lithium transition metal oxide, molten salt and oxide; A method for producing a positive electrode active material for a lithium secondary battery, comprising the step of heat-treating the mixture at a temperature higher than the melting point of the molten salt.

8. In paragraph 7, A method for producing a positive electrode active material for a lithium secondary battery, wherein the molten salt comprises at least one selected from the group consisting of lithium chloride, lithium carbonate, and lithium hydroxide.

9. In paragraph 7, A method for producing a positive electrode active material for a lithium secondary battery, wherein the oxide comprises at least one selected from the group consisting of titanium oxide, zirconium oxide, aluminum oxide, and silicon oxide.

10. In paragraph 9, A method for producing a positive electrode active material for a lithium secondary battery, wherein the oxide is mixed so that the content of a metal element or metalloid element of the oxide is 300 ppm to 1600 ppm with respect to the total metal excluding lithium.

11. In paragraph 9, The above oxide is titanium oxide, A method for producing a positive electrode active material for a lithium secondary battery, wherein the oxide is mixed so that the content of titanium is 400 ppm to 1200 ppm with respect to the total metal excluding lithium.

12. In paragraph 7, A method for producing a positive electrode active material for a lithium secondary battery, wherein the step of heat-treating the above mixture is performed at a temperature of 500°C to 800°C.

13. In paragraph 7, A method for producing a positive electrode active material for a lithium secondary battery, wherein the lithium transition metal oxide is lithium nickel manganese oxide, and the lithium nickel manganese oxide contains 60 mol% to 80 mol% of manganese among all metals excluding lithium.

14. In paragraph 13, A method for producing a positive electrode active material for a lithium secondary battery, wherein the lithium nickel manganese oxide has a molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li) (Li / Me) of 1.29 to 1.

35.

15. A lithium secondary battery comprising a positive electrode including a positive electrode active material according to claims 1 to 6; a negative electrode; and an electrolyte.

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