Positive electrode active material for lithium secondary battery, method for producing the same, and lithium secondary battery including the same

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery, comprising: a core including a layered lithium transition metal oxide containing 60 mol % or more of nickel (Ni) based on the total moles of transition metals; and a coating layer disposed on the core and including cobalt (Co), aluminum (Al), or a combination thereof, the coating layer being composed of single particles, and being an island type.

Description

[Technical Field]

[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, and more specifically to a positive electrode active material for a lithium secondary battery consisting of single particles, a method for producing the same, and a lithium secondary battery including the same. [Background technology]

[0002] Recently, due to the explosive demand for electric vehicles and the demand for increased driving distances, the development of secondary batteries having high capacity and high energy density to meet this demand has been actively promoted worldwide.

[0003] In particular, to meet these requirements, high-nickel NCM (nickel-cobalt-manganese) cathode materials with a high nickel content should be used. However, the increased nickel content reduces particle strength, causing microcracks during charging and discharging. This increases the specific surface area, which increases side reactions with the electrolyte, increasing gas generation and structural instability, resulting in unstable Ni. 3+ Ni is stable 2+ The stable NiO increases the cation mixing phenomenon, making it difficult to use this as a positive electrode active material for actual electric vehicles or lithium-ion batteries for energy storage.

[0004] As a result, there is an increasing demand for single-crystalline active materials, which maximize the size of primary particles by breaking away from the polycrystalline structure in which primary particles aggregate to form secondary particles. Single-crystalline active materials have the advantage of having a smaller specific surface area than polycrystalline active materials, which inhibits side reactions with the electrolyte and significantly reduces gas generation.

[0005] However, single particles have a problem in that a resistive layer of nickel oxide is present on the surface during the manufacturing process, which increases the initial resistance and reduces the lifespan characteristics. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, one object of the present invention is to provide a single-particle positive electrode active material that can reduce initial resistance, thereby improving the capacity and output characteristics of a battery and improving life characteristics, a method for manufacturing the same, and a lithium secondary battery including the same. [Means for solving the problem]

[0007] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, comprising: a core including a layered lithium transition metal oxide containing 60 mol % or more of nickel (Ni) based on the total moles of transition metals; and a coating layer disposed on the core and including cobalt (Co), aluminum (Al), or a combination thereof, the coating layer being composed of single particles, and the coating layer being an island type.

[0008] The content of nickel may be 85 mol % or more based on the total number of moles of transition metals.

[0009] The coating layer further includes lithium and may be an oxide.

[0010] The coating layer may be in the form of protrusions or hemispheres of a coating material that are discontinuously disposed on the core.

[0011] The coating layer may be a layered crystalline structure.

[0012] The coating layer may be connected to the core in a layered crystal structure.

[0013] The coating layer contains cobalt and aluminum, and the molar ratio of cobalt to aluminum (Co / Al) can be 3 to 18.

[0014] The content of the coating layer can be 1 to 3% by weight based on the total weight of the positive electrode active material for the lithium secondary battery.

[0015] The lithium transition metal oxide can further contain zirconium (Zr), aluminum (Al), or a combination thereof.

[0016] The lithium transition metal oxide can be represented by the following Chemical Formula 1.

[0017] [Chemical Formula 1] Li a [Ni x Co y Mn z M1 w1 M2 w2 O2

[0018] In Chemical Formula 1, 0.8 ≦ a ≦ 1.2, 0.6 ≦ x ≦ 0.97, 0 ≦ y ≦ 0.2, 0 < z ≦ 0.2, 0 ≦ w1 ≦ 0.1, 0 ≦ w2 ≦ 0.1, M1 is Zr, Al, or a combination thereof, and M2 is Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0019] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, including the steps of preparing a transition metal hydroxide containing nickel; forming a mixture containing the transition metal hydroxide and a lithium raw material substance, and then firing at a temperature of 710 to 930 °C to form a lithium transition metal oxide; and mixing the lithium transition metal oxide and a coating raw material substance, and then heat treating at a temperature of 670 to 740 °C to form a coating layer, wherein the coating raw material substance contains a cobalt raw material substance, an aluminum raw material substance, or a combination thereof.

[0020] In the step of forming the lithium transition metal oxide, the mixture may further include a doping source material, and the doping source material may include a zirconium source material, an aluminum source material, or a combination thereof.

[0021] In forming the coating layer, the content of the coating raw material may be 1 to 3 wt % based on the total weight of the lithium transition metal oxide and the coating raw material.

[0022] The coating raw material may be fine particles having an average particle size (D50) of 200 to 500 nm.

[0023] Another embodiment of the present invention provides a positive electrode including the above-described positive electrode active material for a lithium secondary battery.

[0024] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte disposed therebetween, wherein the positive electrode includes the above-described positive electrode active material for a lithium secondary battery. [Effects of the Invention]

[0025] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention includes a coating layer containing cobalt, aluminum, or a combination thereof as single particles. The coating layer is an island type, which reduces initial resistance, thereby improving the capacity and output characteristics of the battery and improving the life characteristics.

[0026] In another embodiment of the present invention, a method for manufacturing a positive electrode active material for a lithium secondary battery can easily manufacture a positive electrode active material having an island-type coating layer as a single particle by appropriately adjusting the calcination temperature during the formation of a lithium transition metal oxide and the heat treatment temperature during the formation of a coating layer. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a schematic diagram of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram of a conventional positive electrode active material for a lithium secondary battery. [Figure 3] 1 is an SEM image of the surface of a single particle of the positive electrode active material prepared in Example 1-1. [Figure 4] 1 is an SEM image of the surface of a single particle of the positive electrode active material prepared in Comparative Example 1. [Figure 5] 1 is an image of the positive electrode active material prepared in Example 1-1 after FIB (Focused Ion Milling). [Figure 6] 1 is an image of the positive electrode active material prepared according to Comparative Example 1 after FIB (Focused Ion Milling). [Figure 7] 1 is an element mapping image of the positive electrode active material prepared in Example 1-1 after FIB (Focused Ion Milling). [Figure 8] 1 is a graph showing the results of EDS line scan measurement from the inside to the outside of an image of region 1 of a positive active material prepared according to Example 1-1 after FIB (Focused Ion Milling). [Figure 9] 1 is a graph showing the results of EDS line scanning from the inside to the outside of an image of region 2 of a positive electrode active material prepared according to Example 1-1 after FIB (Focused Ion Milling).

[0028] [Figure 10] 1 is a graph showing the results of EDS line scanning from the inside to the outside of an image of region 1 of a positive electrode active material prepared according to Comparative Example 1 after FIB (Focused Ion Milling). [Figure 11] 1 is a graph showing the results of EELS measurement of a coating layer of a positive electrode active material prepared in Example 1-1. [Figure 12]1 is a TEM image of a cross section of a positive electrode active material prepared in Example 1-1. [Figure 13] 1 shows SAED pattern analysis images of the core and coating layer regions of the positive electrode active material prepared in Example 1-1. DETAILED DESCRIPTION OF THE INVENTION

[0029] Terms such as first, second, and third 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. Therefore, 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 merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the phrase clearly indicates otherwise. As used in the specification, the term "comprising" means to embody certain features, regions, integers, steps, operations, elements, and / or components, and 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" another part, it may be on top of the other part or there may be other parts between them. In contrast, when a part is referred to as being "directly on top of" another part, there are no other parts between them.

[0032] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Terms defined in dictionaries are generally interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted as having an ideal or very formal meaning unless otherwise defined.

[0033] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0034] In this specification, the term "combination(s) thereof" used in a maxi-format expression means a mixture or combination of one or more components selected from the group of components described in the maxi-format expression, and includes any one or more components selected from the group of components.

[0035] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art can easily understand and practice the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments set forth herein.

[0036] 1.Cathode active material One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, comprising: a core including a layered lithium transition metal oxide containing 60 mol % or more of nickel (Ni) based on the total moles of transition metals; and a coating layer disposed on the core and including cobalt (Co), aluminum (Al), or a combination thereof, the coating layer being composed of single particles, and the coating layer being an island type.

[0037] FIG. 1 is a schematic diagram of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0038] Referring to FIG. 1, a positive electrode active material 100 for a lithium secondary battery according to one embodiment of the present invention has a structure of a core 10 and a coating layer 20 disposed on the core.

[0039] In this case, the positive electrode active material 100 for a lithium secondary battery according to one embodiment of the present invention is composed of single particles.

[0040] More specifically, positive electrode active materials can be classified into unassembled primary particles and secondary particles formed by agglomeration of multiple primary particles, depending on whether the primary particles, which are unit particles, are assembled. Such primary particles refer to the smallest particle unit distinguishable as a single mass when a cross section of the positive electrode active material is observed through a scanning electron microscope (SEM), and may consist of one crystal grain or multiple crystal grains.

[0041] The cathode active material according to the present invention is composed of single particles, which solves the problems associated with secondary particles, such as a large specific surface area that increases the risk of side reactions with the electrolyte, and the occurrence of fine cracks between primary particles with repeated charge and discharge, which reduces structural stability and reduces lifespan characteristics. Furthermore, the rolling density can be increased during electrode fabrication, thereby improving the energy density of the electrode.

[0042] However, the single particle positive electrode active material has unstable Ni 3+ , Ni 4+ The ions create a nickel oxide resistive layer on the surface, which increases the initial resistance and slightly reduces the lifespan.

[0043] To solve this problem, the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention includes a coating layer 20 containing cobalt, aluminum, or a combination thereof on a lithium transition metal oxide core.

[0044] By including a coating layer containing cobalt, aluminum, or a combination thereof in the active material, the formation of the nickel oxide resistance layer can be suppressed, the initial resistance can be reduced, and the capacity, output characteristics, and life characteristics of the battery can be improved. Furthermore, the residual lithium in the lithium transition metal oxide during the coating layer formation process can be reduced, and the deterioration of battery performance due to the residual lithium can be suppressed.

[0045] FIG. 1 is a schematic diagram of an island coating type positive electrode active material according to one embodiment of the present invention, and FIG. 2 is a schematic diagram of a conformal coating type positive electrode active material.

[0046] In particular, the positive electrode active material coating layer according to the present invention is of an island type.

[0047] More specifically, the form of the positive electrode active material coating layer can be divided into a conformal coating that uniformly and continuously covers the entire surface of the positive electrode material, and an island coating that surrounds the surface in a discontinuous dot pattern.

[0048] The coating layer morphology may vary depending on the coating material, and may result in an optimum morphology that can improve battery performance.

[0049] Through extensive research, the inventors have found that the island coating method is more effective in improving battery performance when using a coating material containing cobalt, aluminum, or a combination thereof. This is believed to be because coating materials containing cobalt, aluminum, or a combination thereof form a composite oxide-based material containing lithium and oxygen during heat treatment to form a coating layer. In this case, if such an oxide-based material is used to completely surround the cathode material, resistance increases when lithium is inserted into or extracted from the core. This reduces the initial resistance of the battery, improving its capacity and output characteristics and lifespan.

[0050] Specifically, the coating layer may further contain lithium and may be an oxide. More specifically, the coating layer may be a composite oxide containing lithium and cobalt, aluminum, or a combination thereof. This is the result of a reaction between the raw material coating material and the remaining lithium remaining on the surface during the formation of the lithium transition metal oxide during the manufacturing process.

[0051] More specifically, the coating layer may be in the form of a plurality of protrusions or hemispheres of a coating material that are discontinuously arranged on the core.

[0052] In this case, the size of each of the protrusions or hemispherical coating materials may be 50 to 400 nm. When the size of each of the protrusions or hemispherical coating materials satisfies this range, there is an advantage that an island-type random coating is obtained.

[0053] The arrangement and size of the coating material can be confirmed by observing the surface of the positive electrode active material with a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0054] In particular, the coating layer may have a layered crystalline structure. That is, both the core and the coating layer of the cathode active material according to the present invention may have a layered crystalline structure. Therefore, unlike conventional coating layers that block the path of lithium ions to the core due to a typical inorganic coating layer, the layered coating layer of the present invention has the advantage of acting as a path through which lithium ions can pass. The layered structure of the coating layer can be confirmed by a selected area electron diffraction (SAED) pattern analysis of the active material.

[0055] In this case, the coating layer may be connected to the core in a layered crystalline structure, thereby maximizing the lithium ion conductivity improvement effect. This can be confirmed by EDS line scanning of the boundary region between the core and the coating layer.

[0056] Meanwhile, the coating layer may contain only cobalt, only aluminum, or both cobalt and aluminum. More specifically, when the coating layer contains both cobalt and aluminum, the battery performance improvement effect can be preferably achieved.

[0057] When the coating layer contains both cobalt and aluminum, the molar ratio of cobalt to aluminum (Co / Al) may be 3 to 18, more specifically, 4 to 17. This allows the battery performance improvement effect to be more effectively achieved.

[0058] The content of the coating layer may be 1 to 3 wt %, more specifically 1.2 to 2.8 wt %, based on the total weight of the positive electrode active material for a lithium secondary battery. If the content of the coating layer is too small, the reduction in initial resistance and the improvement effects of capacity, output, and life characteristics due to the coating may be minimal. If the content of the coating layer is too large, the content of the core may be too small, resulting in a decrease in battery capacity.

[0059] Meanwhile, the core includes a layered lithium transition metal oxide. The nickel content may be 60 mol% or more, more specifically, 85 mol% or more, based on the total moles of the transition metals. A higher nickel content can increase capacity, but can also lead to reduced structural stability due to cation mixing. The positive electrode active material according to the present invention is composed of single particles and includes a coating layer containing cobalt, aluminum, or a combination thereof, as described above, allowing for a high nickel content while ensuring battery stability.

[0060] The lithium transition metal oxide may further include zirconium (Zr), aluminum (Al), or a combination thereof as a doping element, which may improve the structural stability of the active material and further maximize the battery life characteristics.

[0061] More specifically, Zr ions occupy the Li site, acting as a kind of filler (pillar), mitigating the contraction of the lithium ion path during the charge / discharge process and stabilizing the layered structure. This phenomenon reduces cation mixing, increases the lithium diffusion coefficient, and can extend cycle life.

[0062] In addition, the Al ions move to the tetragonal lattice site, suppressing the deterioration of the layered structure into a spinel structure in which the movement of lithium ions is not smooth relatively.

[0063] As the doping element, it can contain only Zr, can contain only Al, or can contain all of Zr and Al. Preferably, when containing all of Zr and Al as the doping element, the effect of improving the battery life characteristics can be maximized.

[0064] The content of the Zr can be 0.1 to 1 mol% based on the total number of moles of the transition metals, and more specifically, can be 0.16 to 0.64 mol%.

[0065] The content of the Al can be 0.1 to 4 mol% based on the total number of moles of the transition metals, and more specifically, can be 0.4 to 2.8 mol%.

[0066] More specifically, the lithium transition metal oxide can be represented by the following Chemical Formula 1.

[0067] [Chemical Formula 1] Li a [Ni x Co y M nz M1 w1 M2 w2 O2

[0068] In Chemical Formula 1, 0.8 ≦ a ≦ 1.2, 0.6 ≦ x ≦ 0.97, 0 ≦ y ≦ 0.2, 0 < z ≦ 0.2, 0 ≦ w1 ≦ 0.1, 0 ≦ w2 ≦ 0.1, M1 is Zr, Al, or a combination thereof, and M2 is Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0069] In the lithium transition metal oxide of Chemical Formula 1, lithium may be contained in a content corresponding to a, that is, 0.8 ≤ a ≤ 1.2. If a is too small, the capacity may decrease. If a is too large, the strength of the fired cathode active material becomes high and it becomes difficult to pulverize, and the amount of gas generation may increase due to an increase in lithium by-products. When considering the effect of improving the capacity characteristics of the cathode active material by controlling the lithium content and the balance of sinterability during the production of the active material, the lithium may more preferably be contained in a content of 0.9 ≤ a ≤ 1.1.

[0070] In the lithium transition metal oxide of Chemical Formula 1, nickel may be contained in a content corresponding to x, that is, 0.6 ≤ x ≤ 0.97 or 0.85 ≤ x ≤ 0.97. If the nickel content is too low, it may be difficult to achieve a high capacity of the battery. If the nickel content is too high, the battery life and safety may decrease due to a decrease in the stability of the active material structure.

[0071] In the lithium transition metal oxide of Chemical Formula 1, cobalt may be contained in a content corresponding to y, that is, 0 ≤ y ≤ 0.2. If the cobalt content is too low, it may be difficult to simultaneously achieve sufficient rate characteristics and a high powder density of the active material. If the cobalt content is too high, the cost of the raw material substances may increase as a whole, and the reversible capacity may decrease.

[0072] In the lithium transition metal oxide of Chemical Formula 1, manganese may be contained in a content corresponding to z, that is, 0 < z ≤ 0.2. If the manganese content is too low, the production cost may increase and the stability of the active material may decrease. If the manganese content is too high, the capacity and output characteristics of the battery may decrease.

[0073] In the lithium transition metal oxide of Chemical Formula 1, M1 may be contained in a content corresponding to w1, that is, 0 ≤ w1 ≤ 0.1. M1 is a doping element Zr, Al, or a combination thereof.

[0074] In the lithium transition metal oxide of Chemical Formula 1, M2 may be included in an amount corresponding to w2, i.e., 0≦w2≦0.1, and M2 is another doping element such as Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0075] 2. Manufacturing method of positive electrode active material The present inventors have conducted extensive research into a method for easily producing a positive electrode active material having an island-type coating layer while being a single particle, and as a result, have discovered that it is important to adjust the heat treatment temperature for forming the coating layer, and have thus completed a method for producing an active material.

[0076] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, the method comprising: preparing a transition metal hydroxide containing nickel; forming a mixture containing the transition metal hydroxide and a lithium source material, and then firing the mixture at a temperature of 710 to 930°C to form a lithium transition metal oxide; and mixing the lithium transition metal oxide with a coating source material, and then heat-treating the mixture at a temperature of 670 to 740°C to form a coating layer, wherein the coating source material includes a cobalt source material, an aluminum source material, or a combination thereof.

[0077] Hereinafter, a method for preparing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described step by step.

[0078] First, a transition metal hydroxide containing nickel is prepared.

[0079] The transition metal hydroxide is a precursor of the positive electrode active material.

[0080] In this case, the doping element can be doped during the preparation stage of the positive electrode active material precursor.

[0081] For example, the precursor may be prepared by introducing an ammonia solution and a caustic soda solution into a transition metal-containing solution containing a nickel source material, a manganese source material, and optionally a doping source material including Zr, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof, to cause a co-precipitation reaction.

[0082] The nickel source material is not particularly limited as long as it is one commonly used in the art for preparing a cathode active material precursor. For example, the nickel source material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, such as NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiCO2·2H2O, Ni(NO3)2·6H2O, a fatty acid nickel salt, a nickel halide, or a combination thereof, but is not limited thereto.

[0083] The manganese source material is not particularly limited as long as it is a material commonly used in the art for preparing a cathode active material precursor. For example, the manganese source material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, specifically, but not limited to, manganese salts such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, and fatty acid manganese salts, manganese oxides such as Mn2O3, MnO2, and Mn3O4, oxyhydroxides, manganese chloride, or a combination thereof.

[0084] The ammonia solution may contain, but is not limited to, a complexing agent such as NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof. Meanwhile, the ammonia solution may be used in the form of an aqueous solution, and the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0085] The caustic soda solution may contain, as a precipitant or pH adjuster, an alkali metal or alkaline earth metal hydroxide, a hydrate thereof, or a combination thereof, such as NaOH, KOH, or Ca(OH)2. The caustic soda solution may also be used in the form of an aqueous solution, in which case the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0086] The co-precipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon.

[0087] The temperature inside the reactor during the coprecipitation reaction may be 30 to 70°C, specifically 40 to 60°C, more specifically 45 to 55°C.

[0088] Through this process, nickel-manganese (-doping element) hydroxide particles are produced and precipitated in the reaction solution. The precipitated precursor particles are separated and dried by a conventional method to obtain the precursor. The precursor may be secondary particles formed by aggregation of primary particles.

[0089] In this case, the concentrations of the nickel-containing raw material and the manganese-containing raw material can be adjusted to produce a precursor having a nickel (Ni) content of 60 mol % or more or 85 mol % or more of the total metal content. In other words, the nickel content of the transition metal hydroxide can be 60 mol % or more or 85 mol % or more based on the total number of moles of the transition metals, thereby achieving a high capacity battery.

[0090] Next, a mixture containing the transition metal hydroxide and a lithium source material is formed, and then fired at a temperature of 730 to 900° C. to form a lithium transition metal oxide.

[0091] In this case, the mixture may further include a doping source material, and the doping source material may include a zirconium source material, an aluminum source material, or a combination thereof.

[0092] The doping source material may also include other doping source materials including Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or combinations thereof.

[0093] In particular, the firing temperature is 710 to 930° C., more specifically, 720 to 920° C. If the firing temperature is too low, it may be difficult to form a positive electrode active material in a single particle form, and particle size growth may not occur sufficiently. If the firing temperature is too high, the structural stability of the positive electrode active material may be reduced, and the reversible capacity may be reduced.

[0094] The calcination time may be 2 to 36 hours, more specifically, 20 to 30 hours. If the calcination time is too short, the synthesis reaction may not be completed and the crystal structure may not be sufficiently developed, whereas if the calcination time is too long, productivity may be poor.

[0095] The firing can be carried out in an oxygen atmosphere. When a high-Ni-content (Ni-rich) positive electrode active material is fired at a high temperature for a long time, Ni is deposited in the lithium layer in the layered crystalline structure during the firing process. 2+ In order to prevent this, it is preferable to synthesize the positive electrode active material in an oxygen atmosphere.

[0096] The firing can be carried out in two steps, a first firing and a second firing, if necessary.

[0097] Next, the lithium transition metal oxide and the coating raw material are mixed, and then heat-treated at a temperature of 670 to 740° C. to form a coating layer.

[0098] In this case, the coating source material includes a cobalt source material, an aluminum source material, or a combination thereof.

[0099] The coating source material may further include a lithium source material.

[0100] The cobalt source material is not particularly limited as long as it is a cobalt-containing material, and may preferably be Co(OH)2.

[0101] The aluminum source material is not particularly limited as long as it is an aluminum-containing material, and may preferably be Al(OH)3.

[0102] The lithium source material is not particularly limited as long as it is a lithium-containing material, and may be preferably LiOH·H2O.

[0103] In particular, the heat treatment temperature during coating layer formation may be 670 to 740°C, more specifically 680 to 730°C. If the heat treatment temperature is too low, the coating layer may not be formed easily. If the heat treatment temperature is too high, a conformal coating layer may be formed instead of an island-type coating layer, or the coating raw material Co or Al may be excessively diffused into the interior rather than on the surface of the cathode material, resulting in minimal improvement in battery performance due to the coating.

[0104] The content of the coating raw material may be 1 to 3 wt %, more specifically 1.2 to 2.8 wt %, based on the total weight of the lithium transition metal oxide and the coating raw material. If the content of the coating raw material is too low, the coating content may be too low, and the initial resistance reduction and life characteristic improvement effects due to the coating may be minimal. If the content of the coating raw material is too high, the coating content may be too high and the core content may be too low, which may result in a decrease in battery capacity.

[0105] More specifically, the content of the cobalt source material may be 1 to 2 wt % based on the total weight of the lithium transition metal oxide and the coating source material.

[0106] The content of the aluminum raw material may be 0.2 to 0.8 wt % based on the total weight of the lithium transition metal oxide and the coating raw material.

[0107] Meanwhile, the coating raw material may be fine particles with an average particle size (D50) of 200 to 500 nm. If the fine particles are too small, aggregation may occur during dry mixing of the coating raw material, resulting in an inconsistent coating. If the fine particles are too large, the coating particles may be too large, resulting in increased resistance.

[0108] 3. Cathode and lithium secondary battery Another embodiment of the present invention provides a positive electrode including the above-described positive electrode active material for a lithium secondary battery.

[0109] Specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector and including the above-described positive electrode active material.

[0110] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0111] The positive electrode active material layer may include a binder and / or a conductive material in addition to the positive electrode active material.

[0112] The binder improves adhesion between positive electrode active material particles and between the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One or a mixture of two or more of these may be used, but the binder is not limited thereto. The binder may be present in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0113] The conductive material is used to impart conductivity to the electrode and can be any material that has electronic conductivity without causing chemical changes in the resulting battery. 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, summer 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; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may typically be present in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0114] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material.

[0115] Specifically, the positive electrode may be manufactured by applying a composition for forming a positive electrode active material layer containing the positive electrode active material described above and, optionally, a binder, a conductive material, or a solvent onto a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0116] The solvent may be a solvent commonly used in the art, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into consideration the coating thickness of the slurry and the production yield, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a positive electrode.

[0117] Alternatively, the positive electrode may be produced by casting the positive electrode active material layer-forming composition on a separate support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0118] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode, the positive electrode including the positive electrode active material described above.

[0119] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is as described above.

[0120] The lithium secondary battery may further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0121] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0122] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc. may be used. The negative electrode current collector may typically have a thickness of 3 to 500 μm. As with the positive electrode current collector, the current collector surface may be formed with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0123] The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. For example, the negative electrode active material layer may be fabricated by coating a negative electrode active material layer-forming composition containing the negative electrode active material and, optionally, the binder and the conductive material on a negative electrode current collector and drying the coating, or by casting the negative electrode-forming composition on a separate support and peeling it off from the support to obtain a film, which may then be laminated on the negative electrode current collector.

[0124] The negative electrode active material may be a compound capable of reversible lithium intercalation and deintercalation. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ(0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; and composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of any one or two of these may also be used. Alternatively, a metallic lithium thin film may be used as the negative electrode active material. Carbon materials may include both low-crystalline carbon and high-crystalline carbon. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0125] The binder and conductive material may be the same as those described above for the positive electrode.

[0126] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular limitations. It is particularly preferable that the separator has low resistance to electrolyte ion movement and excellent electrolyte humidification ability. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can be used, and it can be selectively used in a single-layer or multi-layer structure.

[0127] In addition, in the lithium secondary battery, examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used when manufacturing a lithium secondary battery, but are not limited to these.

[0128] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0129] The organic solvent may be any solvent capable of acting as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a C2 to C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constants, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the linear carbonate may be mixed in a volume ratio of about 1:1 to about 1:9 to obtain excellent electrolyte performance.

[0130] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(CF, SO), LiCl, LiI, or LiB(CO) . The lithium salt concentration is preferably in the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0131] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, improving battery discharge capacity, etc. In this case, the additives may be included in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0132] As described above, a lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in the fields of portable devices such as mobile phones, laptops, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0133] Accordingly, another embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0134] The battery module or battery pack may be used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems. [Example]

[0135] The present invention will be described in more detail with reference to the following examples, which are merely preferred examples of the present invention and are not intended to limit the scope of the present invention.

[0136] Example 1-1 (1) Manufacturing of positive electrode active material (Preparation of precursor) The precursor was spherical transition metal hydroxide particles produced by coprecipitation. The synthesis raw materials were prepared by dissolving NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O in DI water. NH4(OH) was added as a co-precipitation chelating agent, and NaOH was used to adjust the pH. N2 was purged to prevent oxidation of Ni during co-precipitation, and the reactor temperature was maintained at 50°C. The prepared precursor was filtered, washed with DI water, and then dried in an oven at 100°C for 24 hours. The average particle size (D50) of the metal hydroxide precursor prepared in this way was approximately 3 to 5 μm. The metal composition of the precursor prepared in this way was (Ni 0.88 Co 0.07 Mn 0.05 )(OH)2.

[0137] (Production of lithium transition metal oxides) Then, the precursor and the lithium source LiOH·H2O were mixed uniformly in a stoichiometric ratio so that the Li / Me ratio was slightly greater than 1. At this time, for structural stability and long life, 0.003 mol of Zr and 0.01 mol of Al were added and the mixture was fired at 890°C for 24 hours to obtain LiNi 0.87 Co 0.07 Mn 0.05 Al 0.01 A single particle cathode material in the form of a lithium transition metal oxide with a composition of O2 was synthesized. The amount of Zr added was so small that it was not included in the composition.

[0138] (Formation of coating layer) The prepared lithium transition metal oxide was then dry-mixed with Co(OH)2 as a cobalt source material, Al(OH)3 as an aluminum source material, and LiOH·H2O as a lithium source material. The Co(OH)2 content was 1.5 wt% based on the total weight of the lithium transition metal oxide, cobalt source material, aluminum source material, and lithium source material. The Al(OH)3 content was 0.5 wt% based on the total weight of the lithium transition metal oxide, cobalt source material, aluminum source material, and lithium source material. The LiOH·H2O content was 0.1 wt% based on the total weight of the lithium transition metal oxide, cobalt source material, aluminum source material, and lithium source material. Both Co(OH)2 and Al2O3 were used as fine particles with a size of 200 to 500 nm. The mixture was then heat-treated at 710°C to form a coating layer, thereby producing a cathode active material. At this time, the Co / Al molar ratio of the formed coating layer was 4, and the content of the formed coating layer was 1.5 wt % relative to the positive electrode active material.

[0139] (2) Manufacture of lithium secondary batteries The slurry for electrode plate manufacturing was prepared by mixing the prepared positive electrode active material, conductive material (carbon black), and binder (PVDF, KF1120) in a ratio of 96.5:1.5:2 wt%, and adjusting the slurry viscosity to about 30% solids by adding NMP (N-Methyl-2-pyrrolidone). The prepared slurry was coated on a 15 μm thick aluminum foil using a doctor blade, then dried and rolled. The electrode loading was 14.6 mg / cm. 2 and the rolling density (25°C, 20kN) is 3.7g / cm 3 It was. The electrolyte was 1M LiPF6 in EC:DMC:EMC = 3:4:3 (vol%). A coin cell was fabricated using a PP separator and a lithium anode (300 μm, MTI), and then aged at room temperature for 10 hours.

[0140] Example 1-2 The same lithium transition metal oxide as in Example 1-1 was used, but the coating layer preparation conditions were different. The Co(OH)2 content was 1.8 wt% based on the total weight of the lithium transition metal oxide, cobalt source material, aluminum source material, and lithium source material. The Al(OH)3 content was 0.05 wt% based on the total weight of the lithium transition metal oxide, cobalt source material, aluminum source material, and lithium source material. The LiOH·H2O content was 0.1 wt% based on the total weight of the lithium transition metal oxide, cobalt source material, aluminum source material, and lithium source material. Both Co(OH)2 and Al2O3 were fine particles with a size of 200 to 500 nm. A coating layer was then formed by heat treatment at 710°C to prepare a cathode active material. The Co / Al molar ratio of the formed coating layer was 17, and the content of the formed coating layer was 2.0 wt% relative to the cathode active material.

[0141] Example 2 The composition of the produced precursor is Ni 0.92 Co 0.05 Mn 0.03(OH)2, and the calcination temperature during the production of lithium transition metal oxide was set at 770°C. 0.91 Co 0.05 Mn 0.03 Al 0.01 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that a lithium transition metal oxide having an O2 composition (the doping amount of Zr was so small that it is not listed in the composition) was formed.

[0142] Example 3 The composition of the produced precursor is Ni 0.96 Co 0.03 Mn 0.01 (OH)2, and the calcination temperature during the production of lithium transition metal oxide was set at 750°C. 0.95 Co 0.03 Mn 0.01 Al 0.01 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that a lithium transition metal oxide having an O2 composition (the doping amount of Zr was so small that it is not listed in the composition) was formed.

[0143] Example 4 The composition of the produced precursor is Ni 0.98 Co 0.01 Mn 0.01 (OH)2, and the calcination temperature during the production of lithium transition metal oxide was set at 730°C. 0.97 Co 0.01 Mn 0.01 Al 0.01 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that a lithium transition metal oxide having an O2 composition (the doping amount of Zr was so small that it is not listed in the composition) was formed.

[0144] Example 5 The composition of the produced precursor is Ni 0.86 Co 0.09 Mn 0.05 (OH)2, and the calcination temperature during the production of lithium transition metal oxide was set at 910°C. 0.85 Co 0.09 Mn 0.05 Al0.01 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that a lithium transition metal oxide having an O2 composition (the doping amount of Zr was so small that it is not listed in the composition) was formed.

[0145] Comparative Example 1 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that the heat treatment temperature during the formation of the coating layer was set to 760°C.

[0146] Comparative Example 2 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 2, except that the heat treatment temperature during the formation of the coating layer was set to 760°C.

[0147] Comparative Example 3 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 3, except that the heat treatment temperature during the coating layer formation was 760°C.

[0148] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 4, except that the heat treatment temperature during the formation of the coating layer was set to 760°C.

[0149] Comparative Example 5 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 5, except that the heat treatment temperature during the formation of the coating layer was set to 760°C.

[0150] Reference example 1 A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that no aluminum source material was added when forming the coating layer, the Co(OH) content was mixed to be 1.5% based on the total weight of the lithium transition metal oxide, cobalt source material, and lithium source material, and the LiOH·HO content was mixed to be 0.07% based on the total weight of the lithium transition metal oxide, cobalt source material, and lithium source material.

[0151] Reference example 2 A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that the cobalt source material was not added when forming the coating layer, the Al(OH) content was mixed to be 1.5% based on the total weight of the lithium transition metal oxide, the aluminum source material, and the lithium source material, and the LiOH·HO content was mixed to be 0.07% based on the total weight of the lithium transition metal oxide, the aluminum source material, and the lithium source material.

[0152] Reference example 3 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that the coating layer was formed such that the Co / Al molar ratio of the coating layer was 2 by adjusting the weight ratio between the contents of Co(OH)2, Al(OH)3, and LiOH·HO during the formation of the coating layer.

[0153] Reference example 4 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that the coating layer was formed such that the Co / Al molar ratio of the coating layer was 1 by adjusting the weight ratio between the contents of Co(OH)2, Al(OH)3, and LiOH·HO during the formation of the coating layer.

[0154] Reference example 5 A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that the weight ratios of the Co(OH)2 content, the Al(OH)3 content, and the LiOH·HO content were maintained constant during the formation of the coating layer, and the contents of the respective coating raw materials were reduced so that the content of the formed coating layer was 0.8 wt% relative to the cathode active material.

[0155] Reference example 6 A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1-1, except that the weight ratios of the Co(OH)2 content, the Al(OH)3 content, and the LiOH·HO content were maintained constant during the formation of the coating layer, and the contents of the respective coating raw materials were increased so that the content of the formed coating layer was 3.2 wt % relative to the cathode active material.

[0156] Table 1 below is a summary of the positive electrode active materials and process conditions of Examples 1-1 to 1-5, Comparative Examples 1 to 1-5, and Reference Examples 1 to 1-6.

[0157] [Table 1]

[0158] Experimental Example 1: Active material SEM image analysis Scanning electron microscope (SEM) images of the positive electrode active materials prepared in Example 1-1 and Comparative Example 1 were taken, and the results are shown in FIG. 3 (Example 1-1) and FIG. 4 (Comparative Example 1).

[0159] 3 and 4, in Example 1-1, it was confirmed that protrusions or hemispherical coating materials with a size of 100 to 300 nm were discontinuously present on the surface of the lithium transition metal oxide, indicating that an island-type coating layer was formed.

[0160] On the other hand, in the case of Comparative Example 1, it was confirmed that the coating layer was spread over the entire surface and had a very smooth coating layer.

[0161] Experimental Example 2: Image analysis after active material FIB (Focused Ion Milling) Images of the positive electrode active materials prepared in Example 1-1 and Comparative Example 1 after FIB (Focused Ion Milling) were taken, and the results are shown in FIG. 5 (Example 1-1) and FIG. 6 (Comparative Example 1).

[0162] 5 and 6, in Example 1-1, it was confirmed that coating particles were discontinuously present on the surface of the lithium transition metal oxide matrix.

[0163] On the other hand, in the case of Comparative Example 1, it was confirmed that the coating particles were continuously and uniformly coated on the surface.

[0164] Experimental example 3: Element mapping analysis of images after active material FIB (Focused Ion Milling) The image of the positive electrode active material prepared in Example 1-1 after FIB (Focused Ion Milling) was subjected to element mapping, and the result is shown in FIG.

[0165] Referring to Figure 7, it was confirmed that nickel, manganese, and the doping element zirconium were distributed throughout the lithium transition metal oxide, while the coating elements cobalt and aluminum were mainly present on the surface of the lithium transition metal oxide.

[0166] Experimental Example 4: EDS line scan analysis of images after active material FIB (Focused Ion Milling) An EDS line scan was performed from the inside to the outside of region 1 of the image of the cathode active material prepared according to Example 1-1 after FIB (Focused Ion Milling), and the results are shown in Figure 8. An EDS line scan was performed from the inside to the outside of region 2 of the image of the cathode active material prepared according to Comparative Example 1 after FIB (Focused Ion Milling), and the results are shown in Figure 9. In addition, an EDS line scan was performed from the inside to the outside of region 1 of the image of the cathode active material prepared according to Comparative Example 1 after FIB (Focused Ion Milling), and the results are shown in Figure 10.

[0167] 8 and 9, in the case of Example 1-1, it was confirmed that cobalt and aluminum were present in both regions 1 and 2, which is consistent with the element mapping analysis image in Figure 7. It was also confirmed that the concentration gradient of cobalt and aluminum continued continuously, and it was confirmed that the layered crystal structure of the coating layer and the core was connected without any twisting of the crystal structure.

[0168] 10, it was confirmed that the amount of cobalt was small and almost no aluminum was detected in Comparative Example 1, unlike Example 1-1. This can be interpreted as a result of cobalt and aluminum diffusing into the cathode material due to the high temperature during the coating heat treatment, which reduced the coating effect.

[0169] Experimental Example 5: ELLS analysis of active material coating layer The coating layer of the positive electrode active material prepared in Example 1-1 was subjected to ELLS (Electron Energy Loss Spectroscopy) analysis, and the results are shown in FIG.

[0170] 11, it was confirmed that lithium was present in the coating layer, and that the coating layer had a lithium-cobalt-aluminum composite oxide composition due to the reaction of the remaining lithium remaining in the formation of the lithium transition metal oxide with the coating raw materials cobalt and aluminum.

[0171] Experimental Example 6: TEM image analysis of cross section of active material The cross section of the positive electrode active material prepared in Example 1-1 was analyzed by TEM (transmission electron microscope) image analysis, and the results are shown in FIG.

[0172] Referring to FIG. 12, it was confirmed that the positive electrode active material of Example 1-1 had a lithium transition metal oxide core and an island-shaped coating layer formed thereon.

[0173] Experimental Example 7: SAED pattern analysis of active material core and coating layer The positive electrode active material prepared in Example 1-1 was subjected to a Selected Area Electron Diffraction (SAED) pattern analysis, and the results are shown in Figure 13. Figure 13(a) shows the SAED pattern analysis result of the core region, and Figure 13(b) shows the SAED pattern analysis result of the coating layer region.

[0174] 13, it was confirmed that the positive electrode active material of Example 1-1 had a well-formed layered structure in both the core and the coating layer, and that the coating layer had a layered structure composed of lithium, cobalt, and aluminum composite oxide.

[0175] Experimental Example 8: Evaluation of the electrochemical properties of lithium secondary batteries

[0176] The electrochemical characteristics of the lithium secondary batteries manufactured in Examples 1-1 to 1-5, Comparative Examples 1 to 1-5, and Reference Examples 1 to 1-4 were evaluated, and the results are shown in Table 2. The specific experimental method is as follows.

[0177] (1) Initial discharge capacity and initial efficiency evaluation The capacity evaluation was performed with 200 mAh / g as the reference capacity, and the charge / discharge conditions were CC / CV 2.5 to 4.25 V with a 1 / 20 C cut-off. The initial capacity was measured by 0.1 C charge / 0.1 C discharge.

[0178] (2) Initial resistance evaluation (25°C) The room temperature resistance (DC-iR) was calculated by measuring the voltage 60 seconds after applying a discharge current at 4.25 V with 100% charge at 25°C.

[0179] (3) Lifespan characteristics evaluation (50 cycles) at high temperature (45°C) and normal temperature (25°C) High temperature life characteristics were measured 50 times at 45°C under 0.3C charge / 0.3C discharge conditions. The room temperature life characteristics were measured 50 times at 25°C under the conditions of 0.3C charge / 0.3C discharge.

[0180] (4) Evaluation of high temperature resistance increase rate The high temperature resistance increase rate was evaluated by measuring the resistance after 50 cycles of the cycle life in the same manner as the initial resistance measurement method at 45°C, and converting the increase rate into a percentage (%).

[0181] (5) Differential Scanning Calorimetry (DSC) Thermal Analysis For DSC analysis, the coin cell was initially charged to 4.25 V at 0.1 C charging conditions, then the cell was disassembled to separate the positive electrode, which was then washed five times with DMC. During DSC measurement, the electrode plate was immersed in the electrolyte in a DSC crucible, and measurements were taken while increasing the temperature. The DSC equipment used for the measurements was a Mettler Toledo DSC1 Star system.

[0182] (6) Output characteristics evaluation (2C / 0.1C) The output characteristics were evaluated by dividing the capacity at 2C by the capacity at 0.1C and converting the result into a percentage (%).

[0183] [Table 2]

[0184] Referring to Table 2, Examples 1-1 to 1-5 exhibited superior battery capacity, initial efficiency, initial resistance, high-temperature and room-temperature life characteristics, high-temperature resistance increase rate, DSC peak temperature characteristics, and output characteristics compared to Comparative Examples 1 to 5, which fabricated active materials and lithium secondary batteries using different heat treatment temperatures during coating layer formation. This can be interpreted as a result of the island-type coating layers in Examples 1-1 to 1-5, while the conformal-type coating layers in Comparative Examples 1 to 1-5 resulted in excessive diffusion of cobalt and aluminum into the active material, resulting in reduced coating effectiveness. Furthermore, despite the increased Co content and reduced Al content in Example 1-2 compared to Example 1-1, the excellent electrical conductivity and improved life characteristics of Co were found to compensate for the degradation of characteristics, particularly life characteristics, caused by insufficient Al content.

[0185] Meanwhile, it was confirmed that Reference Example 1 had lower high-temperature and room-temperature life characteristics, high-temperature resistance increase rate, and DSC peak temperature characteristics than Example 1-1. Also, it was confirmed that Reference Example 2 had lower battery capacity, initial efficiency, initial resistance, high-temperature and room-temperature life characteristics, high-temperature resistance increase rate, DSC peak temperature characteristics, and output characteristics than Example 1-1. This confirmed that it is preferable for the coating layer element to contain heterogeneous elements, Co and Al, rather than a single element, Co or Al.

[0186] On the other hand, in the cases of Reference Examples 3 and 4, it was confirmed that the battery capacity, initial efficiency, initial resistance, high temperature and room temperature life characteristics, high temperature resistance increase rate, and output characteristics, excluding the DSC peak temperature characteristics, were lower than those of Example 1-1, confirming that a too small Co / Al molar ratio in the coating layer leads to poor battery performance.

[0187] Meanwhile, in Reference Example 5, it was confirmed that the high temperature and room temperature life characteristics, high temperature resistance increase rate, DSC peak temperature characteristics, and output characteristics were lower than those in Example 1-1, and in Reference Example 6, it was confirmed that the battery capacity, initial efficiency, initial resistance, high temperature resistance increase rate, DSC peak temperature characteristics, and output characteristics were lower than those in Example 1-1. This confirmed that if the coating layer content was too small or too large, the battery performance was inferior.

[0188] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is of course understood that these modifications also fall within the scope of the present invention.

[0189] Therefore, the true scope of the present invention is to be defined by the appended claims and their equivalents. [Explanation of symbols]

[0190] 100: Positive electrode active material 10: Core 20: Coating layer

Claims

1. A core including a layered lithium transition metal oxide containing 60 mol% or more of nickel (Ni) based on the total moles of transition metals; and a coating layer disposed on the core and including cobalt (Co), aluminum (Al), or a combination thereof; A positive electrode active material for a lithium secondary battery, comprising a single particle, and wherein the coating layer is of an island type.

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of the nickel is 85 mol% or more based on the total moles of the transition metals.

3. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the coating layer further contains lithium and is an oxide.

4. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating layer is in the form of protrusions or hemispheres of the coating material discontinuously arranged on the core.

5. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the coating layer has a layered crystal structure.

6. The positive electrode active material for a lithium secondary battery according to claim 5 , wherein the coating layer is connected to the core in a layered crystal structure.

7. 2 . The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the coating layer comprises cobalt and aluminum, and a molar ratio of the cobalt to the aluminum (Co / Al) is 3 to 18.

8. 10. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of the coating layer is 1 to 3 wt% based on the total weight of the positive electrode active material for a lithium secondary battery.

9. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium transition metal oxide further comprises zirconium (Zr), aluminum (Al), or a combination thereof.

10. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium transition metal oxide is represented by the following chemical formula 1: [Chemical formula 1] Li ａ [Ni ｘ Co ｙ Mn ｚ M1 ｗ１ M2 ｗ２ ]O ２ In Chemical Formula 1, 0.8≦a≦1.2, 0.6≦x≦0.97, 0≦y≦0.2, 0<z≦0.2, 0≦w1≦0.1, 0≦w2≦0.1, M1 is Zr, Al, or a combination thereof, and M2 is Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

11. providing a transition metal hydroxide comprising nickel; forming a mixture containing the transition metal hydroxide and a lithium source material, and then calcining the mixture at a temperature of 710 to 930°C to form a lithium transition metal oxide; and and mixing the lithium transition metal oxide and a coating raw material, and then heat-treating the mixture at a temperature of 670 to 740° C. to form a coating layer. The coating raw material comprises a cobalt raw material, an aluminum raw material, or a combination thereof.

12. In the step of forming the lithium transition metal oxide, 12. The method of claim 11, wherein the mixture further comprises a doping source material, and the doping source material comprises a zirconium source material, an aluminum source material, or a combination thereof.

13. In the step of forming the coating layer, 12. The method of claim 11, wherein the content of the coating raw material is 1 to 3 wt % based on the total weight of the lithium transition metal oxide and the coating raw material.

14. The method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the coating raw material is a fine particle having an average particle size (D50) of 200 to 500 nm.

15. A positive electrode comprising the positive electrode active material according to claim 1 .

16. A lithium secondary battery comprising a positive electrode, the positive electrode comprising the positive electrode active material according to claim 1 .

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