Positive electrode active material for rechargeable lithium battery, method for manufacturing the same, and rechargeable lithium battery including the same

Abstract

Provided is a positive electrode active material for a rechargeable lithium battery, the positive electrode active material comprising a nickel-based composite oxide containing a nickel content greater than or equal to 60 mol % relative to the total amount of metals excluding lithium, and a coating provided on a surface of the nickel-based composite oxide, wherein the coating comprises lithium fluoride (LiF) and a metal fluoride generated by burning the metal oxide and a fluorine-based organic material.

Description

Technical Field

[0001] Disclosed are a positive active material for a rechargeable lithium battery, a method for preparing the positive active material, and a rechargeable lithium battery including the positive active material. Background Art

[0002] With the development of portable electronic devices, communication devices, etc., there is a need to develop rechargeable lithium batteries with high energy density.

[0003] A rechargeable lithium battery includes a positive electrode and a negative electrode, each of which includes an electrode active material layer formed on an electrode current collector. The positive electrode active material is mainly an intercalation material of lithium ions and may be a lithium cobalt oxide (LiCoO) or a lithium ion battery. x CoO2), lithium nickel oxide (Li x NiO2), lithium nickel cobalt oxide (Li x (NiCoMn)O2), lithium nickel cobalt manganese oxide (Li x (NiCoMn)O2), spinel lithium manganese oxide (Li x Mn2O4), manganese dioxide (MnO2), or oxides such as lithium iron phosphate (Li x FePO4), lithium manganese phosphate (Li x MnPO4) and other olivine or NASICON phosphates, silicates, polymer materials, etc.

[0004] The negative electrode active material can be a compound capable of intercalating metallic lithium, its alloys or lithium ions, and can be a polymer material or a carbon material, for example, a graphite-based material such as artificial or natural graphite, non-graphitized carbon, or graphitized carbon, carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon nanowalls (CNWs). Summary of the Invention

[0005] [Technical Issues]

[0006] Embodiments provide a positive active material for a rechargeable lithium battery that can promote intercalation / deintercalation of lithium during charge and discharge and has excellent cycle-life characteristics and a low inventory of residual lithium on the surface.

[0007] Another embodiment provides a method of preparing a positive active material for a rechargeable lithium battery.

[0008] Another embodiment provides a rechargeable lithium battery including the positive active material for a rechargeable lithium battery.

[0009] [Technical solution]

[0010] According to an embodiment, a positive electrode active material for a rechargeable lithium battery includes a nickel-based composite oxide and a coating on the surface of the nickel-based composite oxide. The nickel-based composite oxide has a nickel content of 60 mol% or more based on the total amount of metals other than lithium.

[0011] The coating includes lithium fluoride (LiF); and metal fluorides produced by burning metal oxides and fluorine-containing organic materials.

[0012] The nickel-based composite oxide may be a composite oxide represented by Chemical Formula 1.

[0013] [Chemical Formula 1]

[0014] Li a (Ni 1-x-y-z Co x Mn y M z )O2

[0015] In Chemical Formula 1, M is an element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al).

[0016] 0.95 ≤ a ≤ 1.3, x ≤ (1 - x - y - z), y ≤ (1 - x - y - z), 0 < x < 1, 0 ≤ y < 1, and 0 ≤ z < 1.

[0017] The lithium fluoride and the metal fluorides may exist in the form of nano-sized particles.

[0018] The coating may include 10 wt% to 90 wt% of lithium fluoride and 10 wt% to 90 wt% of metal fluorides.

[0019] The metal oxide may be an oxide including an element selected from transition metals other than nickel, a Group 13 element capable of reacting with fluorine, and a Group 14 element capable of reacting with fluorine.

[0020] The metal oxide may be selected from alumina, titanium oxide, zirconium oxide, and combinations thereof.

[0021] The fluorine-containing organic material may have a melting point of 150°C to 400°C.

[0022] The fluorine-based organic material may be a polymer or a mixture thereof prepared by polymerizing at least one monomer selected from vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, ethylene fluoride, trifluoroethylene, hexafluoroisobutylene, perfluorobutylethylene, perfluoropropyl vinyl ether, perfluoroethyl vinyl ether, perfluoromethyl vinyl ether, perfluoro-2,2-dimethyl-1,3-dioxolane and perfluoro-2-methylene-4-methyl-1,3-dioxolane.

[0023] The nickel-based composite oxide may include secondary particles in which a plurality of primary particles are aggregated, wherein the secondary particles have a predetermined arrangement structure in which the (003) planes of the primary particles are aligned in a vertical direction relative to a tangent line at a point (P) where the (003) planes of the primary particles intersect with the surface of the secondary particles.

[0024] 50% or more of the primary particles may be aligned in a vertical direction with respect to a tangent line at a point (P) where the (003) plane intersects the surface of the secondary particle.

[0025] The length in the thickness direction of the primary particle (the length in the c-axis direction) may range from 100 nm to 200 nm.

[0026] The secondary particles may have a radial array structure having one center or a multi-core radial array structure having multiple centers.

[0027] The pore volume fraction of micropores less than or equal to 10 nm of the secondary particle may be greater than or equal to 10% of the total pore volume.

[0028] According to another embodiment, a method for preparing a positive active material for a rechargeable lithium battery includes: heat-treating a mixture of a metal oxide and a fluorine-based organic material in an oxidizing atmosphere at a temperature equal to or higher than the melting point of the fluorine-based organic material in the presence of a nickel-based composite oxide having a nickel content greater than or equal to 60 mol% relative to the total amount of metals other than lithium.

[0029] The metal fluoride may be prepared by mixing the metal oxide and the fluorine-based organic material in a weight ratio of 30:70 to 70:30 and then burning them.

[0030] According to another embodiment, a rechargeable lithium battery includes the aforementioned positive electrode, negative electrode, and electrolyte.

[0031] [Beneficial Effects]

[0032] A positive active material for a rechargeable lithium battery can promote intercalation / deintercalation of lithium during charge and discharge and effectively remove lithium present on the surface of the positive active material, thereby providing a rechargeable lithium battery with improved charge / discharge efficiency and cycle-life characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram of a positive active material for a rechargeable lithium battery according to an embodiment.

[0034] Figure 2 is a view schematically showing primary particles constituting a nickel-based composite oxide arranged according to an embodiment.

[0035] Figure 3 is an exploded perspective view schematically showing a typical structure of a rechargeable lithium battery according to an embodiment.

[0036] Figure 4 is a view showing the results of X-ray diffraction analysis of a product obtained by burning alumina and polyvinylidene fluoride (PVDF) at 650°C.

[0037] Figure 5 : is a graph showing the results of evaluating the cycle-life characteristics of the coin batteries manufactured according to Examples 7 and 8 and Comparative Examples 3 and 4. DETAILED DESCRIPTION

[0038] Hereinafter, the embodiments will be described in detail so that those skilled in the art can easily implement them. However, the embodiments may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0039] In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity.

[0040] The problem with composite oxides with high nickel content is that the safety of the battery is deteriorated because the side reactions of the remaining lithium on the surface produce gas. By supplying a compound that can react with this residual lithium, the residual lithium can be removed. When fluorine is supplied as this type of compound, lithium fluoride can be produced by the reaction of fluorine and residual lithium. However, because the lithium fluoride produced by this reaction interferes with the insertion / deinsertion of lithium and cannot effectively suppress the side reaction with the electrolyte solution, the effect of improving the cycle life characteristics may not be expected. In addition, when the nickel-based composite oxide is coated with a metal oxide, the side reaction with the electrolyte solution can be prevented to a certain extent, but metal fluoride can be produced by reacting with HF in the electrolyte solution. When the nickel-based composite oxide is coated with a metal fluoride, the metal fluoride does not have reactivity with the electrolyte solution and is therefore the most stable, but greatly deteriorates the conductivity and therefore interferes with the insertion / deinsertion of lithium. In addition, it is difficult to form nano-scale particles and therefore a uniform coating cannot be obtained. Therefore, one embodiment of the present invention can provide a positive electrode active material that does not interfere with lithium insertion / deinsertion but exhibits improved cycle life characteristics and reduces residual lithium on its surface by forming a coating layer, the coating layer including lithium fluoride produced by the reaction of residual lithium with fluorine in a fluorine-based organic material and a metal fluoride produced by burning the fluorine-based organic material and a metal oxide.

[0041] Hereinafter, a positive active material for a rechargeable lithium battery according to embodiments is described with reference to the accompanying drawings. Figure 1 is a schematic diagram of a positive active material for a rechargeable lithium battery according to an embodiment.

[0042] According to an embodiment, a positive active material 1 for a rechargeable lithium battery includes a nickel-based composite oxide 3 having a nickel content greater than or equal to 60 mol % relative to the total amount of metals excluding lithium, and a coating layer 5 on the nickel-based composite oxide 3 .

[0043] The coating 5 includes lithium fluoride (LiF) and metal fluoride produced by burning metal oxides and fluorine-based organic materials.

[0044] The nickel-based composite oxide 3 may be a metal composite oxide represented by Chemical Formula 1.

[0045] [Chemical Formula 1]

[0046] Li a (Ni 1-x-y-z Co x Mn y M z )O2

[0047] In Chemical Formula 1, M is an element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al).

[0048] 0.95 ≤ a ≤ 1.3, x ≤ (1 - x - y - z), y ≤ (1 - x - y - z), 0 < x < 1, 0 ≤ y < 1, and 0 ≤ z < 1.

[0049] In Chemical Formula 1, the range of a can be 0.95 ≤ a ≤ 1.3, for example, 1.0 ≤ a ≤ 1.1, and the range of x can be 0 < x ≤ 0.33, for example, 0.1 ≤ a ≤ 0.33, and the range of y can be 0 ≤ y ≤ 0.5, for example, 0.05 ≤ y ≤ 0.3, and the range of z can be 0 ≤ z ≤ 0.05, 0.33 ≤ (1 - x - y - z) ≤ 0.95. For example, in Chemical Formula 1, 0.33 ≦ (1 - x - y - z) ≦ 0.95.

[0050] In addition, in Chemical Formula 1, 0 ≤ z ≤ 0.05, 0 < x ≤ 0.33, and 0 ≤ y ≤ 0.33. In Chemical Formula 1, z can be 0. In Chemical Formula 1, when the range of x is 0 < z ≤ 0.05, M can be aluminum.

[0051] For example, the nickel-based composite oxide can be LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.33 [[ID=2�]]Co 0.33 Mn 0.33 O2, LiNi 0.8 Co 0.1 Mn[[ID=ģ5]] 0.1 O2 or LiNi 0.85 Co 0.1 Al 0.05 O2.

[0052] In Coating 5, lithium fluoride and metal fluoride can exist in the form of nanoscale particles. The size of these particles can be greater than or equal to 5 nm, for example, greater than or equal to 6 nm, or greater than or equal to 7 nm, and less than or equal to 50 nm, less than or equal to 45 nm, or less than or equal to 40 nm. When the particles of the coating have a size within this range, lithium can be easily intercalated / deintercalated during charging and discharging. In addition, the surface of the active material can be protected from side reactions of the electrolyte solution, thereby achieving a uniform coating.

[0053] In the coating layer 5, the metal of the metal fluoride may be included in an amount of 0.001 mol or more, 0.01 mol or more, or 0.1 mol or more and 1 mol or less (e.g., 0.5 mol or less) based on 100 mol of the transition metal (Ni + Co + Mn) of the nickel-based composite oxide 3. Within this range, the cycle life characteristics of the positive electrode active material can be improved.

[0054] In the coating layer 5, fluorine included in lithium fluoride and metal fluoride may be included in an amount of 0.001 mol or more, 0.01 mol or more, or 0.1 mol or more and 1 mol or less (e.g., 0.5 mol or less) based on 100 mol of the transition metal (Ni + Co + Mn) of the nickel-based composite oxide 3. Within this range, the cycle life characteristics of the positive electrode active material can be improved.

[0055] In the coating layer 5, lithium fluoride may be included in an amount of greater than or equal to 10 wt% (e.g., greater than or equal to 15 wt%, or greater than or equal to 20 wt%) and less than or equal to 90 wt% (e.g., less than or equal to 85 wt%, or less than or equal to 80 wt%). In the coating layer 5, metal fluoride may be included in an amount of greater than or equal to 10 wt% (e.g., greater than or equal to 15 wt%, or greater than or equal to 20 wt%) and less than or equal to 90 wt% (e.g., less than or equal to 85 wt%, or less than or equal to 80 wt%). Within this range, the cycle life characteristics of the positive electrode active material can be improved, and the stability can also be enhanced.

[0056] The metal fluoride can be obtained by heat-treating a metal oxide and a fluorine-based organic material at a melting point greater than or equal to the melting point of the fluorine-based organic material. For example, a fluorine-based polymer can be heat-treated at a temperature greater than or equal to 350° C. (e.g., greater than or equal to 400° C.) and less than or equal to 650° C. (e.g., less than or equal to 550° C.). In this regard, a fluorine-based organic material having a melting point of 150° C. to 400° C. can be used.

[0057] When the metal oxide and the fluorine-based organic material are burned, the fluorine generated by the burning of the fluorine-based organic material combines with some or all of the metal oxide, thereby producing metal fluoride. When the fluorine combines with some of the metal oxide and produces metal fluoride, the metal oxide may be present on the surface of the nickel-based composite oxide, and the metal fluoride may be present on the surface of the metal oxide and / or at the interface between the nickel-based composite oxide and the metal oxide. When the metal oxide is additionally present in the coating layer, the conductivity of the coating layer 5 can be improved.

[0058] The metal fluoride may be prepared by mixing the metal oxide and the fluorine-based organic material in a weight ratio of 30:70 to 70:30 and then burning.

[0059] The metal oxide may be an oxide including an element selected from transition metals other than nickel, a Group 13 element capable of reacting with fluorine, and a Group 14 element capable of reacting with fluorine. For example, the metal oxide may be selected from aluminum oxide, titanium oxide, zirconium oxide, and combinations thereof.

[0060] A fluorine-based organic material can be used without limitation as long as it is a polymer capable of supplying fluorine, for example, a polymer prepared by polymerizing at least one monomer selected from vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, fluorinated ethylene, trifluoroethylene, hexafluoroisobutylene, perfluorobutylethylene, perfluoropropyl vinyl ether, perfluoroethyl vinyl ether, perfluoromethyl vinyl ether, perfluoro-2,2-dimethyl-1,3-dioxole and perfluoro-2-methylene-4-methyl-1,3-dioxolane, or a mixture thereof.

[0061] In an embodiment, the nickel-based composite oxide 3 may include secondary particles in which a plurality of primary particles are aggregated, wherein the secondary particles have a predetermined arrangement structure in which the (003) planes of the primary particles are aligned in a vertical direction relative to a tangent line at a point (P), where the (003) planes of the primary particles intersect with the surface of the secondary particles.

[0062] In the following, reference will be made to Figure 2 The nickel-based composite oxide having the above structure is described.

[0063] Figure 2 is a view schematically showing primary particles constituting a nickel-based composite oxide arranged according to an embodiment.

[0064] Figure 2 Only a secondary particle consisting of two primary particles is shown, but it is obvious that three or more primary particles can coalesce to form a secondary particle. Figure 2 , the primary particles are aligned vertically to the tangent at point (P1, P2), where the long axis (a-axis) of the (003) plane of the primary particle 10 intersects with the surface of the secondary particle, thus forming a specific arrangement structure. Figure 2 The primary particles are shown to be aligned so that the major axis (a-axis) is perpendicular to the tangent at point (P1, P2), where they intersect with the surface of the secondary particle (indicated by the dotted line), but so that the minor axis (b-axis) may be perpendicular to the tangent at point (P1, P2), where they intersect with the surface of the secondary particle.

[0065] In this article, surface refers to the circle or elliptical surface formed by the connection point of the major axis (a-axis) or minor axis (b-axis) of adjacent primary particles and the edge intersection of primary particles. In addition, vertical direction means that the major axis (a-axis) or minor axis (b-axis) of the (003) plane intersects with the tangent line of the point (P1, P2) at which the major axis (a-axis) or minor axis (b-axis) intersects with the surface of secondary particles at an angle of 90 ° ± 10 ° (for example, 90 ° ± 5 °).

[0066] Greater than or equal to 50%, for example, greater than or equal to 60% or greater than or equal to 70%, of the primary particles may be vertically aligned with the tangent line at the point where their (003) planes intersect the surface of the secondary particle.

[0067] The primary particle 10 may have a plate shape, wherein the thickness of the primary particle (the length in the c-axis direction) may be less than the thickness in the planar direction (major axis (a-axis) or minor axis (b-axis)). The (003) plane of the primary particle 10 may have a rectangular, elliptical, hexagonal sheet or amorphous shape in which the major axis (a-axis) and the minor axis (b-axis) are different from each other, or a circular or square shape in which the major axis (a-axis) and the minor axis (b-axis) are identical to each other, but is not limited thereto.

[0068] The average length in the planar direction (long axis (a-axis) or short axis (b-axis)) may range from 150 nm to 500 nm, for example, from 200 nm to 380 nm, particularly from 290 nm to 360 nm. The average length in the planar direction represents the average length of the long length and the short length.

[0069] The length (length in the c-axis direction) of the thickness direction of the primary particle 10 can be in the range of 100 nm to 200 nm, for example, 120 nm to 180 nm, particularly 130 nm to 150 nm. In this way, because the thickness of the primary particle 10 is small, cracks that may occur during contraction and expansion are reduced, cycle life characteristics are improved, and resistance increase is suppressed.

[0070] The ratio of the long side to the short side of the plane perpendicular to the (003) plane of the primary particle 10 may range from 1:2 to 1:10, for example, from 1:2.1 to 1:5, and particularly from 1:2.3 to 1:2.9.

[0071] The primary particles 10 aligned as described above are coalesced with each other to form the secondary particles 20. For example, a plurality of primary particles 10 are coalesced one after another, thereby providing a secondary particle having a radially arranged structure.

[0072] The particle size of the secondary particles 20 may be 2 μm to 18 μm, for example 8 μm to 15 μm, and particularly 9 μm to 12 μm. Herein, when the secondary particles 20 are spherical, the particle size refers to the average diameter. When the secondary particles 20 are elliptical, rod-shaped, amorphous, etc., the particle size refers to the length of the major axis.

[0073] When primary particle 10 is aligned vertically to a tangent line at a point (P1, P2) where its (003) plane intersects the surface of secondary particle 20, relatively more lithium diffusion paths between grain boundaries can be provided toward the surface portion of secondary particle 20, and crystal planes capable of lithium diffusion are more exposed, thereby ensuring high initial efficiency and capacity. In addition, cracks can be suppressed by suppressing stress according to the volume change of secondary particle 20 during charge and discharge.

[0074] In this specification, the “surface portion” refers to a region that is 30% (length) to 50% (length) (for example, 40% (length)) from the outermost surface of the secondary particle 20, or a region within 2 μm from the outermost surface of the secondary particle 20. In addition, the “central portion” refers to a region that is 50% (length) to 70% (length) (for example, 60% (length)) from the center of the secondary particle 20, of the total distance from the center of the secondary particle 20 to the outermost surface of the secondary particle 20, or other regions except the region within 2 μm from the outermost surface of the secondary particle 20.

[0075] In addition, when Figure 2 When the primary particles 10 shown in FIG. 1 are aligned in contact with each other, pores formed between the primary particles 10 exist on the surface portion of the secondary particle 20 , promoting the diffusion of lithium from the surface.

[0076] The plurality of primary particles 10 are aligned to form surface contact toward one center along the c-axis (thickness) direction of the primary particles 10 , thereby providing the secondary particle 20 having a radially arranged structure.

[0077] In another embodiment, the secondary particle 20 may have a multi-center radially arranged structure having multiple centers.

[0078] In this manner, when the secondary particle 20 has a single-center or multi-center radial arrangement structure as described above, lithium is easily intercalated / deintercalated into / from the center of the secondary particle 20 .

[0079] In one embodiment, the pore volume fraction of micropores having a size of 10 nm or less of the secondary particle 20 may be greater than or equal to 10% based on the total volume of the pores. Micropores having a size of 10 nm or less may be located on the surface portion of the secondary particle 20. The primary particles 10 aligned in surface contact enable uniform contraction and expansion during lithium intercalation and deintercalation, and the micropores exist toward the surface portion of the secondary particle 20 toward which the primary particles 10 also expand during lithium intercalation and deintercalation, thereby acting as a buffer.

[0080] In addition, in the central portion of the secondary particle 20, pores of a larger size than in the surface portion thereof may be formed. Here, there is an effect of shortening the diffusion distance of lithium ions to the central portion. The pores in the central portion of the secondary particle 20 may have a pore size ranging from 150 nm to 1 μm, for example, 150 nm to 550 nm. Herein, when the pores are spherical or circular, "pore size" refers to the average diameter of the pores. When the pores are elliptical, etc., the pore size refers to the length of the major axis. The secondary particle 20 includes a plurality of micropores of the order of several nm between the primary particles in the surface portion, and through these micropores, the lithium transfer from the electrolyte solution to the positive electrode active material is maximized.

[0081] The positive electrode active material has a total porosity of 1% to 8%, for example, 1.5% to 7.3%. The positive electrode active material has a smaller porosity at the surface than at the center. The porosity at the center may range from 2% to 20%, for example, 3.3% to 16.5%, and the porosity at the surface may range from 0.3% to 0.7%. In this specification, porosity is equivalent to pore volume fraction and is expressed as the ratio of pore area to total area.

[0082] According to one embodiment, the nickel-based composite oxide includes a plurality of secondary particles 20, and greater than or equal to 50%, for example, greater than or equal to 60% or greater than or equal to 70%, of the plurality of secondary particles 20 may have a certain arrangement structure, for example, a radial arrangement structure. In this manner, when the secondary particles have a constant arrangement structure, lithium diffusion can be promoted, thereby providing a rechargeable lithium battery with improved cycle life characteristics.

[0083] The nickel-based composite oxide may be prepared by mixing a lithium precursor and a metal hydroxide precursor at a predetermined molar ratio and heat-treating the mixture under an oxidizing atmosphere.

[0084] The lithium precursor may be, for example, lithium hydroxide, lithium fluoride, lithium carbonate, or a mixture thereof. As a metal hydroxide precursor, Me(OH)2 may be used, wherein Me includes nickel, cobalt, manganese, and optionally M in Chemical Formula 1 may be used.

[0085] In an embodiment, the metal hydroxide precursor may be a compound represented by Chemical Formula 2.

[0086] [Chemical Formula 2]

[0087] (Ni 1-x-y-z Co x Mn y M z )(OH)2

[0088] In Chemical Formula 2, M is an element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al),

[0089] x ≤ (1 - x - y - z), y ≤ (1 - x - y - z), 0 < x < 1, 0 ≤ y < 1, and 0 ≤ z < 1.

[0090] In Chemical Formula 2, 0 < x ≤ 0.33, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.05, and 0.33 ≤ (1 - x - y - z) ≤ 0.95.

[0091] In Chemical Formula 2, 0.5 ≤ (1 - x - y - z) ≤ 0.95.

[0092] For example, the metal hydroxide precursor of Chemical Formula 2 may be Ni 0.6 Co 0.2 Mn 0.2 (OH)2, Ni 0.5 Co 0.2 Mn 0.3 (OH)2, Ni 0.33 Co 0.33 Mn 0.33 (OH)2, or Ni 0.8 Co 0.1 Mn 0.1 (OH)2.

[0093] The mixing ratio of the lithium precursor and the metal hydroxide precursor can be stoichiometrically adjusted to prepare the nickel-based composite oxide of Chemical Formula 1.

[0094] The mixing may be dry mixing and can be carried out using a mixer or the like.

[0095] Dry mixing can be carried out by grinding. In this article, the grinding of the pulverization of the metal hydroxide precursor such as the starting material hardly causes modification. For this reason, the size of the lithium precursor mixed with the metal hydroxide precursor needs to be controlled in advance. The size (average particle size) of the lithium precursor can range from 5 μm to 20 μm, for example, about 10 μm. The lithium precursor and the metal hydroxide precursor are mixed by grinding at 300 rpm to 3,000 rpm.

[0096] In the aforementioned grinding process, when the internal temperature of the mixer rises to 30° C. or more, a cooling process of maintaining the internal temperature within room temperature (20° C. to 25° C.) may be performed.

[0097] The heat treatment for preparing the nickel-based composite oxide is carried out in an oxidizing atmosphere. The oxidizing atmosphere may use an oxidizing gas such as oxygen or air. In one embodiment, the oxidizing gas may be composed of 10% (volume) to 30% (volume) oxygen, 70% (volume) to 90% (volume) inert gas, for example, 10% (volume) to 20% (volume) oxygen or air and 80% (volume) to 90% (volume) inert gas.

[0098] The heat treatment process can be performed at, for example, 600° C. to 800° C. (e.g., 650° C. to 800° C.). During the heat treatment, the temperature is increased at 1° C. / min to 5° C. / min (e.g., 3° ​​C. / min). The heat treatment time at a high temperature or the like varies depending on the heat treatment temperature, but can be, for example, 3 hours to 10 hours.

[0099] According to another embodiment, a method for preparing a positive active material for a rechargeable lithium battery includes: heat-treating a mixture of a metal oxide and a fluorine-based organic material in an oxidizing atmosphere at a temperature equal to or higher than the melting point of the fluorine-based organic material in the presence of a nickel-based composite oxide having a nickel content greater than or equal to 60 mol% relative to the total amount of metals other than lithium.

[0100] The nickel-based composite oxide, the metal oxide, and the fluorine-based organic material are the same as explained above.

[0101] The heat treatment process can be performed at a temperature greater than or equal to the melting point of the fluorine-based organic material, for example, greater than or equal to 350°C (for example, greater than or equal to 400°C) and less than or equal to 650°C (for example, less than or equal to 550°C). Within this range, metal fluoride can be effectively generated from the metal oxide and the fluorine-based organic material, and residual lithium can be effectively removed. In addition, when the heat treatment process is performed at a temperature less than or equal to 550°C, the metal oxide can be present in the coating layer, thereby improving the conductivity of the coating layer.

[0102] The oxidizing atmosphere may be oxygen or an air atmosphere, and the air atmosphere may be a decarburized air atmosphere.

[0103] The embodiment provides a rechargeable lithium battery including a positive active material. The rechargeable lithium battery includes a positive electrode including the positive active material, a negative electrode, an electrolyte, and a separator.

[0104] The positive electrode and the negative electrode are manufactured by applying each of a composition for forming a positive active material layer and a composition for forming a sub-active material layer on a current collector, and drying the compositions.

[0105] The composition forming the positive electrode active material layer is formed by mixing a positive electrode active material, a conductive agent, a binder, and a solvent, and the positive electrode active material is as described above.

[0106] The binder is a component that helps bond the active material to the conductive agent and the current collector. The binder is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the positive electrode active material. When the binder amount is within the above range, the adhesion of the active material layer to the current collector is improved.

[0107] Non-limiting examples of the binder may be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers.

[0108] The conductive agent may not be particularly limited as long as it has electronic conductivity without causing chemical changes in the battery, and may be, for example, 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, etc.; conductive fibers such as carbon fibers or metal fibers; carbon fluoride; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives.

[0109] The amount of the conductive agent may be 2 to 5 parts by weight based on 100 parts by weight of the positive electrode active material. When the amount of the conductive agent is within the above range, the conductivity of the finally obtained electrode is improved.

[0110] Non-limiting examples of the solvent include N-methylpyrrolidone and the like.

[0111] The amount of the solvent is 1 to 10 parts by weight based on 100 parts by weight of the positive electrode active material. When the amount of the solvent is within this range, the active material layer is easily formed.

[0112] The positive electrode current collector is 3 μm to 500 μm thick and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and can be, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The current collector may have fine concave and convex shapes formed on its surface to enhance the adhesion of the positive electrode active material, and can be in various forms such as a film, sheet, foil, mesh, porous body, foam, and non-woven fabric body.

[0113] Separately, a composition for forming a negative electrode active material layer is prepared by mixing a negative electrode active material, a binder, a conductive agent, and a solvent.

[0114] The negative electrode active material may be a material capable of intercalating and releasing lithium ions. Non-limiting examples of the negative electrode active material include carbon materials such as graphite or carbon, lithium metal, alloys thereof, and silicon oxide materials. According to an embodiment of the present invention, silicon oxide may be used.

[0115] The binder is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the negative electrode active material. Non-limiting examples of such a binder may be the same type of material as that of the positive electrode.

[0116] The conductive agent is added in an amount of 1 to 5 parts by weight based on 100 parts by weight of the negative electrode active material. When the amount of the conductive agent is within this range, the conductivity characteristics of the final electrode are improved.

[0117] The amount of the solvent is 1 to 10 parts by weight based on 100 parts by weight of the negative electrode active material. When the amount of the solvent is within this range, the negative electrode active material layer is easily formed.

[0118] The conductive agent and solvent may be the same type of material as that of the positive electrode.

[0119] The negative electrode current collector may have a thickness of 3 μm to 500 μm. This negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and it may be, for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. In addition, the negative electrode current collector may have fine concave and convex portions formed on its surface to enhance the adhesion of the negative electrode active material, and may be in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabric bodies, like the positive electrode current collector.

[0120] The separator is disposed between the positive electrode and the negative electrode according to the process.

[0121] The separator has a pore diameter of 0.01 μm to 10 μm and a thickness of 5 μm to 300 μm. Specific examples include olefin polymers such as polypropylene and polyethylene; or sheets made of glass fiber or non-woven fabric. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also serve as the separator.

[0122] The electrolyte may be a non-aqueous electrolyte including a non-aqueous solvent and a lithium salt, an organic solid electrolyte, an inorganic solid electrolyte, or the like.

[0123] The non-aqueous solvent may be, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, N,N-dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, etc. The lithium salt is a material dissolved in the non-aqueous electrolyte, and non-limiting examples thereof may be LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborate, lower aliphatic lithium carboxylate, lithium tetraphenylborate, imide, etc.

[0124] Non-limiting examples of the organic solid electrolyte may be polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and the like.

[0125] Non-limiting examples of inorganic solid electrolytes may be Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, and the like.

[0126] Figure 3 is an exploded perspective view schematically showing a typical structure of a rechargeable lithium battery according to an embodiment.

[0127] refer to Figure 3The rechargeable lithium battery 31 includes a positive electrode 33 containing a positive active material according to an embodiment, a negative electrode 32, and a separator 34. The positive electrode 33, negative electrode 32, and separator 34 are wound or folded and housed in a battery case 35. An organic electrolyte solution is then injected into the battery case 35 and sealed with a cap assembly 36 to complete the rechargeable lithium battery 31. The battery case 35 can be cylindrical, prismatic, thin-film, or the like. For example, the rechargeable lithium battery 30 can be a large thin-film battery. The rechargeable lithium battery can be a lithium-ion battery. A separator can be positioned between the positive and negative electrodes to form a battery structure. After the battery structures are stacked in a bi-cell configuration, they are impregnated with an organic electrolyte, and the resulting product is housed in a pouch and sealed to complete a lithium-ion polymer battery. Furthermore, multiple battery structures can be stacked to form a battery pack, which can be used in all devices requiring high capacity and high output. For example, it can be used in laptops, smartphones, electric vehicles, and the like.

[0128] Furthermore, rechargeable lithium batteries have excellent storage stability at high temperatures, cycle life characteristics, and high rate characteristics, and therefore can be used in electric vehicles (EVs), for example, hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs).

[0129] The present invention is explained in more detail in the following Examples and Comparative Examples. However, it will be understood that the Examples are for illustrative purposes and should not be construed as limiting the present invention.

[0130] Preparation Example 1: Preparation of Metal Hydroxide Precursors

[0131] Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent at a molar ratio of 6:2:2 as positive electrode active material to prepare a mixed solution. Ammonia (NH4OH) was prepared as a diluent and sodium hydroxide (NaOH) as a precipitant to form a composite compound.

[0132] Subsequently, the metal raw material mixed solution, ammonia and sodium hydroxide were continuously added to a batch reactor containing ammonia (NH4OH) diluent at the top of the reactor. In order to maintain the pH inside the reactor, sodium hydroxide was placed by using a pH regulator. After the reaction was carried out while stirring the reactor for about 20 hours, the addition of raw material solution was stopped.

[0133] The slurry solution in the reactor was filtered, washed with distilled water having high purity, and dried in a hot air oven for 24 hours to obtain a metal hydroxide precursor (Ni 0.6 Co 0.2 Mn 0.2 (OH)2) powder.

[0134] Preparation Example 2: Preparation of Metal Hydroxide Precursors

[0135] A metal hydroxide precursor (Ni(II)) was obtained by the same method as in Preparation Example 1 except that the contents of nickel sulfate, cobalt sulfate, and manganese sulfate were changed and the reaction was carried out for 25 hours. 0.5 Co 0.2 Mn 0.3 (OH)2).

[0136] Preparation Example 3: Preparation of Metal Hydroxide Precursor

[0137] A metal hydroxide precursor (Ni(OH)2O) was obtained by the same method as in Preparation Example 1 except that the contents of nickel sulfate, cobalt sulfate, and manganese sulfate were changed and the reaction was carried out for 25 hours. 0.8 Co 0.1 Mn 0.1 (OH)2).

[0138] Preparation Example 4: Preparation of Metal Hydroxide Precursor

[0139] A metal hydroxide precursor (NiSO4.6H2O) was obtained according to the same method as Preparation Example 1, except that nickel sulfate (NiSO4.6H2O), cobalt sulfate (CoSO4.7H2O) and aluminum nitrate (Al(NO3)3.9H2O) were mixed in a molar ratio of 85:10:5 and then reacted for 18 hours. 0.85 Co 0.1 Al 0.05 (OH)2).

[0140] Preparation Example 5: Preparation of Metal Hydroxide Precursor

[0141] The metal hydroxide precursor (Ni(II)) was obtained by the same method as in Preparation Example 1 except that the contents of nickel sulfate, cobalt sulfate, and manganese sulfate were changed and the reaction was carried out for 28 hours. 0.33 Co 0.33 Mn 0.33 (OH)2).

[0142] Example 1: Preparation of positive electrode active material

[0143] The metal hydroxide precursor (Ni 2 O 2 ) prepared in Preparation Example 1 was dry-mixed at a molar ratio of 1:1 using a high-speed mixer at 2,000 rpm. 0.6 Co 0.2 Mn 0.2 (OH)2) and lithium hydroxide (LiOH·H2O) having an average particle size of about 15 μm, and heat-treating the mixture at about 850°C for 8 hours in an oxygen atmosphere in a furnace to synthesize a nickel-based composite oxide (LiNi 0.6 Co0.2 Mn 0.2 O2).

[0144] The obtained nickel composite oxide, aluminum oxide, and PVDF were mixed to prepare a mixture. Here, aluminum oxide and PVDF were mixed to include aluminum and fluorine elements, and the amounts of aluminum and fluorine elements were 0.2 mol and 0.5 mol, respectively, based on 100 mol of transition metal elements (Ni+Co+Nn) of the nickel composite oxide. The mixture was heat-treated at 350° C. for 6 hours under an oxygen atmosphere to prepare a positive electrode active material having a coating on the surface of the nickel composite oxide, the coating including lithium fluoride, aluminum oxide, and aluminum fluoride.

[0145] Example 2: Preparation of positive electrode active material

[0146] The nickel composite oxide of Example 1, titanium oxide, and PVDF were mixed to prepare a mixture. Here, titanium oxide and PVDF were mixed to include titanium and fluorine elements, and the amounts of titanium and fluorine elements were 0.2 mol and 0.5 mol, respectively, based on 100 mol of the transition metal elements (Ni + Co + Nn) of the nickel composite oxide. The mixture was heat-treated at 350° C. for 6 hours under an oxygen atmosphere to prepare a positive electrode active material having a coating on the surface of the nickel composite oxide, the coating including lithium fluoride, titanium oxide, and titanium fluoride.

[0147] Example 3: Preparation of positive electrode active material

[0148] The nickel composite oxide of Example 1, aluminum oxide, and PVDF were mixed to prepare a mixture. Here, the aluminum oxide and PVDF were mixed to include aluminum and fluorine elements, and the amounts of aluminum and fluorine elements were 0.2 mol and 0.5 mol, respectively, based on 100 mol of the transition metal elements (Ni+Co+Nn) of the nickel composite oxide. The mixture was heat-treated at 450° C. for 6 hours under an oxygen atmosphere to prepare a positive electrode active material having a coating on the surface of the nickel composite oxide, the coating including lithium fluoride, aluminum oxide, and aluminum fluoride.

[0149] Example 4: Preparation of positive electrode active material

[0150] The nickel composite oxide of Example 1, titanium oxide, and PVDF were mixed to prepare a mixture. Here, titanium oxide and PVDF were mixed to include titanium and fluorine elements, and the amounts of titanium and fluorine elements were 0.2 mol and 0.5 mol, respectively, based on 100 mol of the transition metal elements (Ni + Co + Nn) of the nickel composite oxide. The mixture was heat-treated at 450° C. for 6 hours under an oxygen atmosphere to prepare a positive electrode active material having a coating on the surface of the nickel composite oxide, the coating including lithium fluoride, titanium oxide, and titanium fluoride.

[0151] Example 5: Preparation of positive electrode active material

[0152] The nickel composite oxide of Example 1, aluminum oxide, and PVDF were mixed to prepare a mixture. Here, the aluminum oxide and PVDF were mixed to include aluminum and fluorine elements, with the amounts of aluminum and fluorine being 0.2 mol and 0.5 mol, respectively, based on 100 mol of the transition metal element (Ni+Co+Nn) of the nickel composite oxide. The mixture was heat-treated at 650° C. for 6 hours under an oxygen atmosphere to prepare a positive electrode active material having a coating on the surface of the nickel composite oxide, the coating including lithium fluoride, aluminum oxide, and aluminum fluoride.

[0153] Example 6: Preparation of positive electrode active material

[0154] The nickel composite oxide of Example 1, titanium oxide, and PVDF were mixed to prepare a mixture. Here, titanium oxide and PVDF were mixed to include titanium and fluorine elements, with the amounts of titanium and fluorine being 0.2 mol and 0.5 mol, respectively, based on 100 mol of the transition metal element (Ni + Co + Nn) of the nickel composite oxide. The mixture was heat-treated at 650° C. for 6 hours under an oxygen atmosphere to prepare a positive electrode active material having a coating on the surface of the nickel composite oxide, the coating including lithium fluoride, titanium oxide, and titanium fluoride.

[0155] Comparative Example 1: Preparation of positive electrode active material

[0156] A positive active material coated with lithium fluoride was prepared according to the same method as in Example 1, except that only PVDF was mixed with the nickel-based composite oxide to include 0.5 mol of fluorine element based on 100 mol of the transition metal element (Ni+Co+Nn).

[0157] Comparative Example 2: Preparation of positive electrode active material

[0158] A positive electrode active material was prepared according to the same method as in Example 1, except that alumina and PVDF were not used.

[0159] Evaluation of residual lithium

[0160] The amounts of residual Li 2 O 3 and residual LiOH and the concentration of residual Li of the positive active materials according to Examples 1 and 2 and Comparative Example 2 were measured, and the results are shown in Table 1.

[0161] (Table 1)

[0162]

[0163] Referring to Table 1, compared with the residual lithium of the positive electrode active material of Comparative Example 2, the residual lithium of the positive electrode active materials of Examples 1 and 2 was effectively reduced.

[0164] Coating analysis

[0165] In order to confirm the reactivity of the metal oxide and the fluorine-based organic material used in the examples, alumina and PVDF were dry mixed at an element ratio of Al:F=1:3, and then heat treated at 650°C for 6 hours in an oxygen atmosphere. Subsequently, X-ray diffraction analysis (XRD) was performed on the obtained product. The results were as follows: Figure 4 Shown in. Figure 4 Shown are the results of X-ray diffraction analysis of a product obtained by burning alumina and PVDF at 650° C. The diffraction analysis was performed by using an X'PERT apparatus from 10 degrees to 90 degrees at 1 degree per minute.

[0166] Figure 4 The diffraction analysis results showed that aluminum oxide and metal fluoride (eg, AlF3) were generated.

[0167] Example 7: Fabrication of coin cells

[0168] A mixture of 96 g of the positive active material according to Example 1, 2 g of polyvinylidene fluoride, 137 g of N-methylpyrrolidone as a solvent, and 2 g of carbon black as a conductive agent was treated with a mixer to remove bubbles to prepare a uniformly dispersed slurry for a positive active material layer.

[0169] The slurry for the positive active material layer was applied to a thin electrode plate formed on an aluminum foil with a doctor blade, dried at 135° C. for 3 hours or more, and then, compressed and vacuum-dried to manufacture a positive electrode.

[0170] A coin half-cell was fabricated using a positive electrode and lithium metal as a counter electrode. A porous polyethylene (PE) film (thickness: approximately 16 μm) was placed between the positive electrode and the lithium metal counter electrode as a separator, and an electrolyte solution was injected into the membrane to create the coin cell. The electrolyte solution was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 3:5 volume ratio and dissolving 1.1 M LiPF6 in the mixture.

[0171] Examples 8 to 10 and Comparative Examples 3 and 4: Production of Coin Cells

[0172] Each coin cell was manufactured according to the same method as in Example 1, except that the positive electrode active materials according to Examples 2 to 6 and Comparative Examples 1 and 2 were used instead of the positive electrode active material according to Example 1.

[0173] Evaluation of battery cell characteristics

[0174] Coin cells according to Examples 7 and 8 and Comparative Examples 3 and 4 were charged and discharged once at 0.1C (18 mAh / g) for formation, and then charged and discharged once at 0.2C for initial charge and discharge. The discharge capacity, charge and discharge efficiency, and 0.2C discharge capacity of the initial charge and discharge were evaluated. The results of Examples 7 and 8 and Comparative Example 3 are shown in Table 2.

[0175] (Table 2)

[0176]

[0177] Referring to Table 2, the batteries (Example 7 and Example 8) including the positive active materials according to Example 1 and Example 2, respectively, exhibited excellent charge and discharge efficiency and capacity compared to the battery (Comparative Example 3) including the positive active material according to Comparative Example 1.

[0178] The cycle life characteristics of the coin cells according to Examples 7 and 8 and Comparative Examples 3 and 4 were evaluated as follows. The battery was charged and discharged once at 0.1C (18 mAh / g) for formation, and then repeatedly charged and discharged 50 times at 0.1C (18 mAh / g) at 45°C to examine the cycle characteristics. Charging was set to start in CC (constant current) mode, then changed to CV (constant voltage) mode, cut off at 4.3V and 0.05C, and discharging was set to start in CC (constant current) mode, cut off at 3.0V. The results were as follows. Figure 5 Shown in. Figure 5 is a graph showing cycle-life characteristic results of coin batteries according to Examples 7 and 8 and Comparative Examples 3 and 4.

[0179] refer to Figure 5 Compared to the battery (Comparative Example 3) including the positive electrode active material including only the fluorine-based organic material of Comparative Example 1 and the battery (Comparative Example 4) including the positive electrode active material without the coating of Comparative Example 2, the batteries (Examples 7 and 8) respectively including the positive electrode active material having the coating including lithium fluoride, aluminum oxide, and aluminum fluoride of Example 1 and the positive electrode active material having the coating including lithium fluoride and aluminum fluoride of Example 2, wherein the metal oxide and / or metal fluoride reduced the side reaction during the reaction of the nickel-based composite oxide with the electrolyte solution, exhibited long-term cycle life characteristics. Therefore, for the positive electrode active materials of Examples 1 and 2, it is believed that the coating effectively protects the surface of the nickel-based composite oxide.

[0180] The above embodiments have been described with reference to the accompanying drawings and examples, but these are merely exemplary and those skilled in the art will appreciate that various modifications and other equivalent embodiments are possible. Therefore, the scope of protection of the present invention should be determined by the appended claims.

[0181] [Explanation of symbols]

[0182] 1: Positive electrode active material 3: Nickel composite oxide

[0183] 5: coating 10: primary particles

[0184] 20: Secondary particles 31: Rechargeable lithium batteries

[0185] 32: Negative electrode 33: Positive electrode

[0186] 34: separator 35: battery housing

[0187] 36: Cover assembly

Claims

1. A positive electrode active material for a rechargeable lithium battery, comprising: a nickel-based composite oxide having a nickel content of 60 mol% or more relative to the total amount of metals other than lithium, and a coating on the surface of the nickel-based composite oxide, wherein the coating comprises: lithium fluoride (LiF); and a metal fluoride produced by burning a metal oxide and a fluorine-based organic material, wherein the lithium fluoride and the metal fluoride are present in the form of nanoscale particles, based on 100 mol of the transition metals of the nickel-based composite oxide, comprising the metal of the metal fluoride in an amount of 0.001 mol or more and 0.5 mol or less, and based on 100 mol of the transition metals of the nickel-based composite oxide, comprising the fluorine included in the lithium fluoride and the metal fluoride in an amount of 0.001 mol or more and 0.5 mol or less.

2. The positive electrode active material according to claim 1, wherein the nickel-based composite oxide is a metal composite oxide represented by Chemical Formula 1: [Chemical Formula 1] Li a (Ni 1-x-y-z Co x Mr y M z )O2 in, In Chemical Formula 1, M is an element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al), 0.95 ≤ a ≤ 1.3, x ≤ (1 - x - y - z), y ≤ (1 - x - y - z), 0 < x < 1, 0 ≤ y < 1, and 0 ≤ z < 1.

3. The positive electrode active material according to claim, wherein the coating has a thickness of 20 nm to 70 nm.

4. The positive electrode active material according to claim 1, wherein the metal oxide is an oxide comprising an element selected from transition metals other than nickel, a Group 13 element capable of reacting with fluorine, and a Group 14 element capable of reacting with fluorine.

5. The positive electrode active material according to claim 1, wherein the metal oxide is selected from aluminum oxide, titanium oxide, zirconium oxide, and combinations thereof.

6. The positive electrode active material according to claim 1, wherein the fluorine-based organic material is a polymer having a melting point of 150°C to 400°C.

7. The positive electrode active material according to claim 1, wherein the fluorine-based organic material is a polymer or a mixture thereof prepared by polymerizing at least one monomer selected from vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, fluoroethylene, trifluoroethylene, hexafluoroisobutene, perfluorobutylethylene, perfluoropropyl vinyl ether, perfluoroethyl vinyl ether, perfluoromethyl vinyl ether, perfluoro-2,2-dimethyl-1,3-dioxolane, and perfluoro-2-methylene-4-methyl-1,3-dioxolane.

8. The positive electrode active material according to claim 1, wherein the coating further comprises a metal oxide.

9. The positive electrode active material according to claim 1, wherein the nickel-based composite oxide includes secondary particles in which a plurality of primary particles are aggregated, wherein the secondary particles have a predetermined arrangement structure, in which the (003) planes of the primary particles are aligned in a vertical direction relative to a tangent line at a point P, where the (003) planes of the primary particles intersect with the surface of the secondary particles. 10 . The positive electrode active material according to claim 9 , wherein 50% or more of the primary particles are arranged in a vertical direction with respect to the tangent line at the point P where the (003) plane intersects the surface of the secondary particle. 11 . The positive electrode active material according to claim 10 , wherein the length of the primary particle in the c-axis direction ranges from 100 nm to 200 nm. 12 . The positive electrode active material according to claim 10 , wherein the secondary particles have a radial array structure with one center or a multi-core radial array structure with multiple centers. 13 . The positive active material according to claim 10 , wherein the pore volume fraction of micropores smaller than or equal to 10 nm of the secondary particles is greater than or equal to 10% of the total pore volume.

14. A method for preparing a positive active material for a rechargeable lithium battery, comprising: A method of preparing a positive electrode active material for a rechargeable lithium battery according to claim 1, wherein the mixture of the metal oxide and the fluorine-based organic material is heat-treated in an oxidizing atmosphere at a temperature equal to or higher than the melting point of the fluorine-based organic material in the presence of a nickel-based composite oxide having a nickel content of 60 mol% or more relative to the total amount of metals other than lithium, wherein the metal of the metal fluoride is included in an amount greater than or equal to 0.001 mol and less than or equal to 0.5 mol based on 100 mol of the transition metal of the nickel-based composite oxide, and The lithium fluoride and fluorine included in the metal fluoride are included in an amount of greater than or equal to 0.001 mol and less than or equal to 0.5 mol based on 100 mol of the transition metal of the nickel-based composite oxide.

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