Positive electrode active material for lithium secondary batteries, method for manufacturing the same, and lithium secondary battery containing the same

Abstract

The present invention relates to a positive electrode active material for lithium secondary batteries, comprising a core containing a boron-doped lithium transition metal oxide; and a coating layer disposed on the core and containing boron and cobalt, wherein the total boron content, including the boron doped into the lithium transition metal oxide and the boron contained in the coating layer, is 1200 ppm or less based on the total weight of the positive electrode active material, and is composed of single particles.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for lithium secondary batteries, a method for producing the same, and a lithium secondary battery containing the same, and more specifically, to a single-particle positive electrode active material for lithium secondary batteries, a method for producing the same, and a lithium secondary battery containing the same. [Background technology]

[0002] With the increasing adoption of electric vehicles for carbon neutrality and the surge in demand for energy storage systems such as ESS (Energy Storage Systems) for renewable energy use, lithium-ion batteries are becoming an irreplaceable core energy storage element. In particular, since the characteristics of lithium-ion batteries are greatly influenced by the cathode material, research on cathode materials accounts for the largest proportion of research in lithium-ion battery studies.

[0003] Among cathode materials, research on NCM cathode materials, in which cobalt and manganese are replaced in a layered nickel-based cathode active material, is actively being conducted. However, conventionally, much of the research focused on secondary particle active materials formed by the aggregation of primary particles. But such secondary particle active materials have a large specific surface area and low particle strength, leading to problems such as cracking and life degradation due to gas generation. Therefore, in the case of small-particle active materials, development is shifting towards single-particle cathode materials composed of primary particles.

[0004] However, such single-particle cathode materials have a problem in that the electrochemical properties related to lithium diffusion (i.e., capacitance, initial efficiency, resistance characteristics, etc.) are inevitably inferior to those of secondary particles because the distance over which lithium ions must diffuse within the cathode material is longer. [Overview of the project] [Problems that the invention aims to solve]

[0005] Therefore, one objective of the present invention is to provide a positive electrode active material for lithium secondary batteries that has excellent capacity, initial efficiency, and resistance characteristics as a single particle, a method for producing the same, and a lithium secondary battery containing the same. [Means for solving the problem]

[0006] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery comprising a core containing a boron-doped lithium transition metal oxide; and a coating layer disposed on the core and containing boron and cobalt, wherein the total boron content, including the boron doped into the lithium transition metal oxide and the boron contained in the coating layer, is 1200 ppm or less based on the total weight of the positive electrode active material, and is composed of single particles.

[0007] The boron doped into the lithium transition metal oxide can be present in a region within a distance of 5 nm from the surface of the core in the inward direction.

[0008] The coating layer may contain lithium boron oxide.

[0009] When XPS analysis is performed at a depth of 5 nm from the outermost surface of the positive electrode active material, the weight ratio of boron contained in the boron oxide to the boron contained in the lithium boron oxide in the coating layer may be 15% by weight or less.

[0010] When XPS analysis is performed at a depth of 5 nm from the outermost surface of the positive electrode active material, the boron content of the lithium boron oxide may be 85% by weight or more, based on the total boron content in the coating layer.

[0011] When XPS analysis is performed at a depth of 5 nm from the outermost surface of the positive electrode active material, the boron content of the boron oxide may be 15% by weight or less, based on the total boron content in the coating layer.

[0012] The coating layer can further contain aluminum.

[0013] The coating layer can further contain lithium.

[0014] The lithium transition metal oxide can contain 60 mol% or more of nickel based on the total number of moles of transition metals.

[0015] The lithium transition metal oxide can be represented by the following Chemical Formula 1.

[0016] [Chemical Formula 1] Li a [Ni x Co y Mn z B w1 M w2 O2

[0017] In Chemical Formula 1, 0.8 ≦ a ≦ 1.2, 0.60 ≦ x < 1, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, 0 < w1 ≦ 0.2, 0 ≦ w2 ≦ 0.2, x + y + z + w1 + w2 = 1, and M is Zr, Al, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0018] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, including: preparing a transition metal hydroxide; forming a single particle lithium transition metal oxide by subjecting a mixture containing the transition metal hydroxide and a lithium raw material to primary firing and secondary firing; forming a first mixture containing the lithium transition metal oxide and a cobalt raw material, and then subjecting the first mixture to a first heat treatment; and forming a second mixture containing the result of the first heat treatment and a boron raw material, and then subjecting the second mixture to a second heat treatment.

[0019] The first mixture can further contain an aluminum raw material.

[0020] ]] The first mixture can further contain a lithium raw material.

[0021] The first heat treatment can be performed at a temperature of 600 to 720°C.

[0022] The second heat treatment can be performed at a temperature of 250 to 350°C.

[0023] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery using the aforementioned positive electrode active material.

[0024] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for a lithium secondary battery.

Effects of the Invention

[0025] The positive electrode active material for a lithium secondary battery according to an embodiment of the present invention can achieve excellent capacity, initial efficiency, and resistance characteristics by coating and doping boron and coating cobalt.

Brief Description of the Drawings

[0026] [Figure 1] It is a SEM image of the positive electrode active material manufactured according to Example 4. [Figure 2] It is a SEM image of the positive electrode active material manufactured according to Example 4. [Figure 3] It is a TOF-SIMS analysis graph of the positive electrode active material manufactured according to Example 4. [Figure 4] It is a SEM image of the positive electrode active material manufactured according to Comparative Example 4. [Figure 5] It is a SEM image of the positive electrode active material manufactured according to Comparative Example 4. [Figure 6] It is a TOF-SIMS analysis graph of the positive electrode active material manufactured according to Comparative Example 4. [Figure 7] It is a SEM image of the positive electrode active material manufactured according to Comparative Example 5. [Figure 8] It is a SEM image of the positive electrode active material manufactured according to Comparative Example 5. [Figure 9] This is a TOF-SIMS analysis graph of the positive electrode active material produced by Comparative Example 5. [Figure 10] This is a graph showing the XPS analysis results of the positive electrode active material produced according to Example 4. [Figure 11] This is a graph showing the XPS analysis results of the positive electrode active material produced by Comparative Example 4. [Figure 12] This is a graph showing the XPS analysis results of the positive electrode active material produced by Comparative Example 5. [Figure 13] This shows the TEM image and outer EELS analysis results graph of the positive electrode active material produced according to Example 4. [Figure 14] This graph shows the capacity characteristics of lithium secondary batteries manufactured according to Example 4, Comparative Example 4, and Comparative Example 5, as the cycle progresses. [Figure 15] This is a voltage-dQ / dV curve analysis graph of the lithium secondary batteries manufactured according to Example 4, Comparative Example 4, and Comparative Example 5. [Modes for carrying out the invention]

[0027] The terms first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used solely to distinguish one part, component, region, layer, or section from other parts, components, regions, layers, or sections. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the invention.

[0028] The technical terms used herein are for the sole purpose of referring to specific embodiments and are not intended to limit the invention. The singular forms used herein also include plural forms unless the wording explicitly indicates otherwise. The meaning of “including” as used in this specification embodies certain characteristics, areas, integers, stages, operations, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, stages, operations, elements, and / or components.

[0029] When we say that one part is "on top of" another part, it means that it is either directly above the other part, or that another part may be in between them. In contrast, when we say that one part is "directly above" another part, it means that no other part is in between them.

[0030] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as those generally understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have the meaning corresponding to the relevant technical literature and the present disclosures, and are not interpreted in their ideal or highly formal sense unless otherwise defined.

[0031] Also, unless otherwise specified, % means weight percent, and 1 ppm is 0.0001 weight percent.

[0032] In this specification, the term “these combinations” as described in the Markush expression means one or more mixtures or combinations selected from the group of components described in the Markush expression, and including one or more of the selected components.

[0033] The embodiments of the present invention will be described in detail below so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be embodied in a variety of different forms and is not limited to the embodiments described herein.

[0034] 1.Cathode active material One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery comprising a core containing a boron-doped lithium transition metal oxide; and a coating layer disposed on the core and containing boron and cobalt, wherein the total boron content, including the boron doped into the lithium transition metal oxide and the boron contained in the coating layer, is 1200 ppm or less based on the total weight of the positive electrode active material, and is composed of single particles.

[0035] In this case, the lithium transition metal oxide may have a layered crystalline structure.

[0036] Furthermore, the lithium transition metal oxide may contain 60 mol% or more of nickel based on the total number of moles of the transition metal, and more specifically, it may contain 70, 80, or 90 mol% or more of nickel. When the nickel content meets the above range, high capacity characteristics can be achieved.

[0037] The positive electrode active material for a lithium secondary battery according to one embodiment of the present invention is composed of single particles.

[0038] In this specification, “single particle” is a term used to distinguish it from positive electrode active material particles in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles, which have been commonly used in the past. The term includes both single particles consisting of one primary particle and aggregate particles of 30 or fewer primary particles. The “secondary particle” refers to an aggregate, i.e., a secondary structure, formed by the aggregation of primary particles through physical or chemical bonding between primary particles without any intentional aggregation or granulation process for the primary particles.

[0039] The aforementioned "primary particle" refers to the smallest particle unit that can be distinguished as a single mass when a cross-section of the positive electrode active material is observed using a scanning electron microscope (SEM), and may consist of one crystal grain or multiple crystal grains.

[0040] In one embodiment of the present invention, the positive electrode active material for a lithium secondary battery is composed of single particles, which increases particle strength and suppresses particle cracking during rolling. This prevents cracks from occurring between primary particles as charging and discharging cycles are repeated, and the small specific surface area reduces the amount of gas generated by side reactions with the electrolyte. Furthermore, the rolling density can be increased during electrode manufacturing, thereby improving the energy density of the electrode.

[0041] However, in the case of single-particle cathode active materials, the distance over which lithium ions must diffuse within the cathode material becomes longer, resulting in electrochemical properties related to lithium diffusion (i.e., capacity and power characteristics) that are inferior to those of secondary particles. Furthermore, structural defects occur, such as an increase in the amount of nickel cations occupying lithium sites during high-temperature firing for particle growth.

[0042] Therefore, the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises a lithium transition metal oxide core doped with boron and a coating layer containing boron and cobalt. By coating and doping with boron and coating with cobalt in this manner, excellent capacity, initial efficiency, and resistance characteristics can be achieved.

[0043] More specifically, the boron doped into the lithium transition metal oxide can be present in a region within a distance of 5 nm from the surface of the core in the inward direction. The boron can be present in the lithium transition metal oxide core in a manner that is uniform throughout all regions of the core, or locally present only in the outer periphery of the core. In this case, when the boron is locally doped only in the outer periphery of the core, as in one embodiment of the present invention, improvements in capacity, initial efficiency, and resistance characteristics can be more favorably achieved compared to when the boron is uniform throughout all regions of the core. This is believed to be because it suppresses structural collapse during charging and discharging.

[0044] The doping region of boron within such lithium transition metal oxides can be confirmed by dispersing the active material powder in epoxy, molding it to create a protective layer, slicing the layer, and then performing ion milling pretreatment. The doping region can then be confirmed by boron EELS (electron energy loss spectroscopy) peak analysis using TEM (transmission electron microscope) imaging of the oxide outer layer.

[0045] On the other hand, in order for boron to be locally doped only in the outer casing of the core, it is more appropriate to dope the boron by mixing and heat-treating the boron raw material after the production of the lithium transition metal oxide, rather than doping during the coprecipitation process for the production of the transition metal hydroxide precursor or during the calcination process for the production of the lithium transition metal oxide. The reason why the boron is doped in a form that is locally present only in the outer casing of the core is thought to be that, after the NCM layered structure has already been formed, the boron has been heat-treated at a low temperature and therefore cannot easily diffuse into the interior. More specific methods for boron coating and doping will be explained in more detail in the production method of the positive electrode active material described later.

[0046] In particular, the total boron content, including the boron doped into the lithium transition metal oxide and the boron contained in the coating layer, is 1200 ppm or less based on the total weight of the positive electrode active material, more specifically, it may be 1100 or 1000 ppm or less, and may be 200 ppm, 300 ppm, 400 ppm, or 500 ppm or more. If the boron content is excessively low, the improvement in capacity, initial efficiency, and resistance characteristics by coating and doping with boron may be minimal. If the boron content is excessively high, the content of boron oxides, which are boron compounds in an undesirable form for battery performance, in the coating layer increases, which may actually degrade battery performance. More specifically, as mentioned above, boron can be locally doped and present only in the outer region, which is within a distance of 5 nm from the core surface. In this case, when the boron content in the active material increases, up to a certain level, boron is doped in a form that is uniformly present in the outer region of the core, improving battery performance. However, any excess boron exceeding a certain level will not be further doped into the core casing and will remain within the coating layer. This excess doping within the coating layer forms boron oxides, which can actually degrade battery performance. The boron-containing compounds within the coating layer will be explained in more detail below.

[0047] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention includes a coating layer containing boron and cobalt.

[0048] The boron contained in the coating layer may exist within the coating layer in the form of a boron-containing compound.

[0049] More specifically, the boron-containing compound may include lithium boron oxide, and may further include boron oxide as a by-product.

[0050] At this time, when XPS analysis is performed at a depth of 5 nm from the outermost surface of the positive electrode active material, the weight ratio of boron contained in the boron oxide to the boron contained in the lithium boron oxide in the coating layer may be 15% by weight or less. In other words, the more lithium boron oxide and the less boron oxide the boron-containing compound in the coating layer contains, the more favorably improvements in capacity, initial efficiency, and resistance characteristics can be achieved. This is thought to be because the conductivity of lithium boron oxide is higher than that of boron oxide.

[0051] More specifically, when XPS analysis is performed at a depth of 5 nm from the outermost surface of the positive electrode active material, the boron content of the lithium boron oxide may be 85% by weight or more, based on the total boron content in the coating layer.

[0052] The lithium-boron oxide is not particularly limited as long as it is a lithium and boron-containing oxide. For example, the lithium-boron oxide may be LiBO2, but is not necessarily limited to this.

[0053] More specifically, when XPS analysis is performed at a depth of 5 nm from the outermost surface of the positive electrode active material, the boron content of the boron oxide may be 15% by weight or less, based on the total boron content in the coating layer.

[0054] The lithium-boron oxide is not particularly limited as long as it is a lithium and boron-containing oxide. For example, the lithium-boron oxide may be LiBO2, but is not necessarily limited to this.

[0055] On the other hand, the content of lithium boron oxide and boron oxide as boron-containing compounds in the coating layer can be determined by the content of boron introduced into the positive electrode active material, and a more detailed explanation of this is given above.

[0056] The coating layer can further selectively contain aluminum if necessary. When the coating layer contains all of boron, cobalt, and aluminum, the improvement effects on capacity, initial efficiency, and resistance characteristics can be more preferably realized.

[0057] The coating layer can further contain lithium. The lithium can be derived from a lithium raw material substance introduced during the formation of the coating layer, as described in the manufacturing method below.

[0058] On the other hand, as described above, the lithium transition metal oxide according to the present invention can contain nickel at a high content of 60, 80, or 90 mol% or more. The higher the nickel content, the more sensitively the influence of the battery chemical characteristics according to the selection of the doping element, coating element, and coating layer compound and the adjustment of their contents is reflected. Therefore, when it is a high-content nickel active material, it is particularly important to appropriately realize doping and coating.

[0059] Such a lithium transition metal oxide can be more specifically represented by the following Chemical Formula 1.

[0060] [Chemical Formula 1] Li a [Ni x Co y Mn z [[ID=I26]]B w1 M w2 O2

[0061] In Chemical Formula 1, 0.8 ≦ a ≦ 1.2, 0.60 ≦ x < 1, 0 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, 0 < w1 ≦ 0.2, 0 ≦ w2 ≦ 0.2, x + y + z + w1 + w2 = 1, and M is Zr, Al, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0062] In the lithium transition metal oxide of chemical formula 1, lithium may be present in an amount corresponding to a, i.e., 0.8 ≤ a ≤ 1.2. If a is too small, the capacity may decrease, and if a is too large, the strength of the calcined positive electrode active material may increase, making it difficult to pulverize, and the amount of gas generated may increase due to an increase in lithium byproducts. Considering the effect of improving the capacity characteristics of the positive electrode active material according to the control of lithium content and the balance of sinterability during the manufacture of the active material, the lithium may more preferably be present in an amount of 0.9 ≤ a ≤ 1.1.

[0063] In the lithium transition metal oxide of chemical formula 1, nickel may be present in a content corresponding to x, i.e., 0.6 ≤ x < 1, 0.6 ≤ x ≤ 0.97, 0.7 ≤ x ≤ 0.97, 0.80 ≤ x ≤ 0.97, or 0.90 ≤ x ≤ 0.97. If the nickel content is too low, it may be difficult to increase the capacity of the battery, and if the nickel content is too high, the structural stability of the active material may decrease, which may reduce the battery life and safety.

[0064] In the lithium transition metal oxide of chemical formula 1, cobalt may be present in a content corresponding to y, i.e., 0 ≤ y ≤ 0.4, 0 ≤ y ≤ 0.3, 0 ≤ y ≤ 0.2, or 0 ≤ y ≤ 0.1. If the cobalt content is too low, it may be difficult to simultaneously achieve sufficient rate characteristics and high powder density of the active material. If the cobalt content is too high, the overall cost of the raw materials may increase and the reversible capacity may decrease.

[0065] In the lithium transition metal oxide of chemical formula 1, manganese may be present in an amount corresponding to z, i.e., 0 ≤ z ≤ 0.4. 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.

[0066] In the lithium transition metal oxide of Chemical Formula 1, boron may be contained in a content corresponding to w1, that is, 0 < w1 ≤ 0.2. If the boron content is excessively low, the effects of improving capacity, initial efficiency, and resistance characteristics may be negligible. If the boron content is excessively high, excessive formation of boron oxide in the coating layer may occur.

[0067] In the lithium transition metal oxide of Chemical Formula 1, M may be contained in a content corresponding to w2, that is, 0 ≤ w2 ≤ 0.2. At this time, M is a doping element other than boron, and is Zr, Al, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0068] 2. Method for manufacturing a positive electrode active material 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; forming a mixture including the transition metal hydroxide and a lithium raw material substance, and then performing primary firing and secondary firing to form single-particle lithium transition metal oxide; forming a first mixture including the lithium transition metal oxide and a cobalt raw material substance, and then performing a first heat treatment; and forming a second mixture including the result of the first heat treatment and a boron raw material substance, and then performing a second heat treatment.

[0069] Hereinafter, the method for manufacturing a positive electrode active material for a lithium secondary battery according to an embodiment of the present invention will be described in detail step by step.

[0070] First, a transition metal hydroxide is prepared.

[0071] The transition metal hydroxide may be produced as a positive electrode active material precursor by, for example, adding a complexing agent-containing solution and a pH adjuster-containing solution to a transition metal-containing solution including a nickel raw material substance and selectively a cobalt raw material substance or a manganese raw material substance, and performing a coprecipitation reaction.

[0072] The nickel raw material is not particularly limited as long as it is used in the industry during the production of cathode active material precursors. For example, the nickel raw material may be nickel-containing sulfates, acetates, nitrates, halogen compounds, sulfides, hydroxides, oxides or oxyhydroxides, and may specifically be, but not limited to, NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salts, nickel halides or combinations thereof.

[0073] The aforementioned cobalt raw material is not particularly limited as long as it is used in the industry in the production of cathode active material precursors. For example, the cobalt raw material may be cobalt-containing sulfates, acetates, nitrates, halogen compounds, sulfides, hydroxides, oxides or oxyhydroxides, and may specifically be, but not limited to, CoSO4, CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O or combinations thereof.

[0074] The manganese raw material is not particularly limited as long as it is used in the industry in the production of cathode active material precursors. For example, the manganese raw material may be manganese-containing sulfates, acetates, nitrates, halogen compounds, sulfides, hydroxides, oxides, oxyhydroxides or combinations thereof, and may, but is not limited to, manganese salts such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate salts, manganese citrate and manganese fatty acid salts, manganese oxides such as Mn2O3, MnO2, and Mn3O4, oxyhydroxides, manganese chloride or combinations thereof.

[0075] The transition metal-containing solution may be prepared by adding a nickel raw material and, selectively, a cobalt raw material or a manganese raw material to a solvent, specifically water, or a mixture of water and an organic solvent (e.g., alcohol) that is homogeneously miscible with water.

[0076] The complexing agent-containing solution plays a role in complex formation, and the complexing agent may include, but is not limited to, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or combinations thereof. On the other hand, the complexing agent-containing solution can be used in aqueous solution form, in which case water or a mixture of water and an organic solvent that can be homogeneously mixed with water (e.g., alcohol) can be used as the solvent.

[0077] The pH adjusting agent-containing solution may serve as a precipitating agent or pH adjuster and may include alkali metal or alkaline earth metal hydroxides such as NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof. Alternatively, the pH adjusting agent-containing solution may also be used in aqueous solution form, in which case water or a mixture of water and an organic solvent that is homogeneously miscible with water (e.g., alcohol) may be used as the solvent. In this case, the pH adjusting agent-containing solution may be added in an amount that brings the pH of the reaction solution to 11-13.

[0078] The aforementioned coprecipitation reaction may be carried out under an inert atmosphere such as nitrogen or argon, at a temperature of 30-70°C, and at a pH of 11-13.

[0079] Through the process described above, nickel-cobalt-manganese (-doping element) hydroxide particles are generated and precipitate in the reaction solution. The precipitated precursor particles can be separated by conventional methods, washed with water, and dried to obtain the precursor. The precursor may be secondary particles formed by the aggregation of primary particles.

[0080] At this time, the molar ratio of nickel, cobalt, and manganese in the precursor can be adjusted by controlling the concentrations of the nickel raw material, cobalt raw material, and manganese raw material.

[0081] On the other hand, in addition to boron, other doping elements can be added during the lithium transition metal oxide formation stage. In this case, the doping element can be added to the lithium transition metal oxide by further adding the doping raw material during the formation of the mixture and then calcining it.

[0082] Next, a mixture containing the transition metal hydroxide and lithium raw material is formed, and then subjected to main calcination and post-calcination to form single-particle lithium transition metal oxide.

[0083] The lithium raw material can be lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halogen compounds, hydroxides, or oxyhydroxides, and is not particularly limited as long as it is soluble in water. Specifically, the lithium raw material may be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or combinations thereof.

[0084] The aforementioned firing process may be carried out at a temperature of 800-900°C for 2-5 hours.

[0085] The aforementioned post-firing process may be carried out at a temperature of 700-820°C for 5-13 hours.

[0086] The firing process can be carried out in an oxygen or air atmosphere. When firing is performed in the aforementioned atmosphere, the local oxygen partial pressure increases, which can improve the crystallinity of the positive electrode active material.

[0087] On the other hand, in addition to boron, other doping elements can be added during the lithium transition metal oxide formation stage. In this case, the doping element can be added to the lithium transition metal oxide by further adding the doping raw material during the formation of the mixture and then calcining it.

[0088] Next, a first mixture containing the lithium transition metal oxide and cobalt raw material is formed, and then subjected to a first heat treatment.

[0089] The aforementioned cobalt raw material is not particularly limited as long as it is a cobalt-containing compound, for example, Co3O4, Co(OH)2, Co(NO3) 2、 C4H6CoO 4、 It could be CoSO4 or a combination of these.

[0090] The first mixture may further contain an aluminum raw material. In this case, the aluminum raw material is not particularly limited as long as it is an aluminum-containing compound, for example, Al2O3, Al(OH)3, Al2(SO4) 3、 It may be Al(NO3)3, AlCl3, or a combination thereof.

[0091] The first mixture may further contain a lithium raw material. In this case, the lithium raw material is not particularly limited as long as it is a lithium-containing compound, but may be, for example, LiOH, LiOH(H2O), Li2CO3, LiF, or a combination thereof.

[0092] The first heat treatment can be performed at a temperature of 600 to 720°C. If the first heat treatment temperature is too low, there is a problem in that the coating layer may not be formed properly, and if the first heat treatment temperature is too high, there is a problem in that doping occurs rather than coating layer formation, resulting in deterioration of surface properties.

[0093] Next, a second mixture containing the first heat-treated product and the boron raw material is formed and then subjected to a second heat treatment. This allows the boron to be coated and doped as in the embodiments described above.

[0094] The boron raw material is not particularly limited as long as it is a boron-containing compound, but may be, for example, B2O3, H3BO3, or a combination thereof.

[0095] The second heat treatment can be performed at a temperature of 250 to 350°C. If the second heat treatment temperature is too low, there is a problem in that the coating layer may not be formed properly, and if the second heat treatment temperature is too high, there is a problem in that doping occurs rather than coating layer formation, resulting in deterioration of surface properties.

[0096] The second heat treatment may be carried out in an oxygen or air atmosphere.

[0097] On the other hand, as described above, the method for producing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention involves sequentially coating with cobalt, cobalt / aluminum, or cobalt / aluminum / lithium first, and then coating with boron. This has the advantage of reducing surface degradation of the active material because the concentration of Ni is high in the NCM core, and the concentration of Ni decreases towards the outside, while the concentrations of Co and B increase.

[0098] 3. Positive electrode and lithium secondary battery Another embodiment of the present invention provides a positive electrode for a lithium secondary battery containing the positive electrode active material described above.

[0099] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0100] The lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0101] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0102] 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, which contains the positive electrode active material described above.

[0103] The positive electrode current collector is not particularly limited as long as it is conductive but does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can also typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0104] The positive electrode active material layer may include a binder and / or conductive material together with the positive electrode active material described above.

[0105] At this time, the binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these can be used, but are not limited to these. The binder may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0106] The conductive material is used to impart conductivity to the electrodes and can be used without special restrictions in the battery in which it is constructed, as long as it has electronic conductivity that does not cause chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used, but is not limited to these. The conductive material can usually be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0107] The positive electrode can be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used.

[0108] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, which includes the positive electrode active material described above and optionally a binder, conductive material, or 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.

[0109] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the cathode active material, conductive material, and binder, taking into account the coating thickness and production yield of the slurry, and to have a viscosity that allows for excellent thickness uniformity during subsequent coating for cathode manufacturing.

[0110] Alternatively, the positive electrode can also be manufactured by casting the positive electrode active material layer forming composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0111] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0112] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery but has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treatments with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector can also typically have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0113] The negative electrode active material layer may selectively include a binder and a conductive material together with the negative electrode active material. The negative electrode active material layer can also be manufactured, for example, by applying a negative electrode active material layer forming composition, which includes the negative electrode active material and selectively a binder and a conductive material, onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0114] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metallic oxides capable of doping and dedoping with lithium, such as SiOβ (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. One or more mixtures of these can be used. Furthermore, a metallic lithium thin film can also be used as the negative electrode active material. In addition, all types of carbon materials, including low-crystallinity carbon and high-crystallinity carbon, can be used. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

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

[0116] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

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

[0118] Specifically, the organic liquid electrolyte may contain an organic solvent and a lithium salt.

[0119] The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, without any special limitations. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the performance of the electrolyte may be improved by mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9.

[0120] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any special limitations. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0121] In addition to the electrolyte components, the electrolyte may also contain one or more additives for purposes such as improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0122] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0123] To that end, yet 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.

[0124] The aforementioned battery module or battery pack may be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems. [Examples]

[0125] Embodiments of the present invention will be described in more detail below through the examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0126] Example 1 (Boron 500 ppm) (1) Manufacturing of positive electrode active material (Firing) Ni 0.95 5Co 0.02 Mn 0.02 Al 0.005 (OH)2 transition metal hydroxide was prepared. Then, the prepared transition metal hydroxide and LiOH·H2O were placed in a mixer and mechanically mixed. After that, a first calcination process was carried out at 850°C for 3.75 hours under an oxygen atmosphere, followed by a second calcination process at 790°C for 9.75 hours to form single-particle lithium transition metal oxide.

[0127] (First heat treatment) Subsequently, based on the total number of moles of the lithium transition metal oxide, the cobalt raw material was mixed so that it amounted to 2 mol% Co(OH)2, the aluminum raw material so that it amounted to 0.5 mol% Al(OH)3, and the lithium raw material so that it amounted to 0.1 mol% LiOH·H2O to form the first mixture, which was then subjected to the first heat treatment at 680°C for 5 hours.

[0128] (Second heat treatment) Subsequently, the product obtained from the first heat treatment was mixed with H3BO3 as a boron raw material so that the boron content in the active material was 500 ppm to form a second mixture, and then subjected to a second heat treatment at 280°C for 5 hours under an oxygen atmosphere.

[0129] (2) Manufacturing of lithium secondary batteries The slurry for manufacturing the electrode plate was prepared by mixing the manufactured positive electrode active material, conductive material (carbon black, denka black), and binder (PVDF, KF1100) in a ratio of 96.25:1.65:2.1 wt%, and adjusting the viscosity by adding NMP (N-Methyl-2-pyrrolidone) so that the solid content was approximately 30%. The manufactured slurry was coated onto 15 μm thick aluminum foil using a doctor blade, and then dried and rolled. The electrode loading amount was 14.6 mg / cm². 2 The rolling density (25°C, 20kN) is 3.5g / cm³. 3 That was the case.

[0130] The electrolyte used was 1M LiPF6in EC:DMC:EMC=3:4:3 (vol%) with 3.0 vol% VC added relative to the total electrolyte volume. Coin cells were manufactured using a PP separation membrane and a lithium anode (200 μm, Honzo metal).

[0131] Example 2 (Boron 1,000 ppm) The cathode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of boron raw material added was adjusted in the second heat treatment stage so that the boron content in the active material was 1000 ppm.

[0132] Comparative Example 1 The positive electrode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment was performed without adding boron raw material in the second heat treatment stage.

[0133] Comparative Example 2 A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the second heat treatment step was omitted.

[0134] Comparative Example 3 (Boron 1,300 ppm) The cathode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of boron raw material added was adjusted in the second heat treatment stage so that the boron content in the active material was 1300 ppm.

[0135] Comparative Example 4 (Boron 5,000 ppm) The cathode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of boron raw material added was adjusted in the second heat treatment stage so that the boron content in the active material was 1300 ppm.

[0136] Comparative Example 5 (Boron 10,000 ppm) The cathode active material and lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of boron raw material added was adjusted in the second heat treatment stage so that the boron content in the active material was 1300 ppm.

[0137] Experimental Example 1: Evaluation of Active Material SEM Images and TOF-SIMS Graphs SEM (scanning electron microscope) images and TOF-SIMS (time-of-flight secondary ion mass spectrometry) graphs of the cathode active materials produced in Example 4, Comparative Example 4, and Comparative Example 5 are shown in Figures 1 to 3 (Example 4), Figures 4 to 6 (Comparative Example 4), and Figures 7 to 9 (Comparative Example 5).

[0138] Referring to Figures 1 to 9, it was confirmed that the positive electrode active materials produced by the examples and comparative examples were in single-particle form.

[0139] On the other hand, in Example 4, which contained an appropriate amount of boron, it was confirmed that the lithium transition metal oxide surface was smoothly coated. However, in Comparative Examples 4 and 5, which contained excessive amounts of boron, it was confirmed that the surface was not smooth and that many by-products were formed. Furthermore, it was confirmed that the surface became less smooth as the boron content increased beyond a certain amount.

[0140] On the other hand, by referring to the TOF-SIMS graph, it was confirmed that the higher the boron content, the greater the amount of B detected on the surface.

[0141] Experimental Example 2: Evaluation of the components of the coating layer To evaluate the types and content of boron-containing compounds in the coating layer of the positive electrode active materials produced by the examples and comparative examples, XPS (X-ray photoelectron spectroscopy) analysis was performed at a depth of 5 nm from the outermost surface of the active material. The results are shown in Figure 10 (Example 4), Figure 11 (Comparative Example 4), and Figure 12 (Comparative Example 5). In addition, the types of boron-containing compounds in the coating layer and the content ratio of each boron-containing compound relative to the total weight of the coating layer were evaluated based on the XPS analysis results and are shown in Table 1 below.

[0142] [Table 1]

[0143] Referring to Figures 10 to 12 and Table 1, it was confirmed that in the examples containing an appropriate amount of boron, LiBO2 was mainly detected in the coating layer, and BO3 was not detected.

[0144] On the other hand, in the comparative example containing an excessive amount of boron, it was confirmed that LiBO2 decreased and BO3 increased. More specifically, it was confirmed that when the boron content exceeded a certain amount (approximately 1000-1200 ppm), the amount of BO3 compounds increased as the boron content increased. This can be interpreted as a result of the fact that when the boron content exceeds a certain amount, it no longer dops the lithium transition metal oxide and remains in the coating layer, forming BO3 compounds as byproducts.

[0145] Experimental Example 3: Evaluation of Active Material TEM Imaging and EELS TEM (transmission electron microscope) images of the positive electrode active material produced in Example 4 and EELS (electron energy loss spectroscopy) peak evaluations of the outer region of the lithium transition metal oxide on the TEM images are shown in Figure 13.

[0146] More specifically, the active material powder was dispersed in epoxy, molded to create a protective layer, and then the EELS boron peak was measured using an ion milling method after the layer was sliced.

[0147] Referring to Figure 13, it was confirmed that boron is not only present within the coating layer, but also doped in a region within a distance of 5 nm from the transition metal oxide surface inward.

[0148] Experimental Example 4: Evaluation of Battery Electrochemical Properties The electrochemical properties of the positive electrode active materials produced by the examples and comparative examples were evaluated, and the results are shown in Table 2 and Figures 14-15 below. The specific experimental methods are as follows.

[0149] (1) Evaluation of initial charge and discharge capacity and initial efficiency The coin-type half-cells manufactured in the examples and comparative examples were aged at room temperature (25°C) for 10 hours, and then subjected to charge-discharge tests.

[0150] Capacity evaluation was performed using a baseline capacity of 200 mAh / g, with charge / discharge conditions of constant current (CC) / constant voltage (CV) of 3.0V to 4.25V and a 1 / 20C cutoff applied. Initial charge and discharge capacity and initial efficiency at 0.2C were evaluated.

[0151] (2) Evaluation of resistance characteristics (DC-IR) The initial resistance at room temperature (DC-IR (Direct current internal resistance)) was calculated by performing one 0.1C charge and 0.1C discharge cycle on the battery at 25°C under constant current-constant voltage conditions of 2.5V to 4.25V and 1 / 20C cutoff. The voltage value was measured 60 seconds after the discharge current was applied when the battery was charged to 100% at 4.25V, and then the initial resistance at room temperature (DC-IR (Direct current internal resistance)) was calculated.

[0152] (3) Evaluation of lifespan characteristics (50 cycles) The lifespan characteristics of the positive electrode active material were evaluated after 50 cycles under high temperature (45°C) and 0.5C charge / 1C discharge conditions.

[0153] (4) Evaluation of voltage-dQ / dV characteristics The voltage curves obtained after initial charging and discharging at 0.2C were differentiated to evaluate the voltage-dQ / dV characteristics, which are shown in Figure 15.

[0154] [Table 2]

[0155] Referring to Table 2 and Figure 14, it was confirmed that in examples where the coating layer contained boron, cobalt, and aluminum, but the boron content in the active material was appropriately adjusted, the initial capacity, efficiency, resistance characteristics, and lifetime characteristics were generally very good.

[0156] In Comparative Examples 1 and 2, where the coating layer contained Co and Al but lacked boron, we were able to confirm that the initial volume and efficiency were significantly inferior.

[0157] On the other hand, in Comparative Examples 3-5, where the coating layer contained boron, cobalt, and aluminum, but the boron content was excessive, the initial capacity, efficiency, resistance characteristics, and lifetime characteristics were inferior. Specifically, it was confirmed that these characteristics tended to deteriorate as the boron content increased.

[0158] Referring to Figure 15, it can be seen that the average charge and discharge voltage itself changes between 4.1 and 4.2 V as the boron content increases from 0 ppm to 1000 ppm. This can be interpreted as a result of the composition of the lithium transition metal oxide itself changing as the boron content increases, leading to an increase in the amount of boron doped into the lithium transition metal oxide.

[0159] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto. It can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and these variations naturally also fall within the scope of the present invention.

[0160] Therefore, the substantial scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A positive electrode active material comprising: a core containing a boron-doped lithium transition metal oxide; and a coating layer disposed on the core and containing boron and cobalt; The total boron content, including the boron doped into the lithium transition metal oxide and the boron contained in the coating layer, is 1200 ppm or less based on the total weight of the positive electrode active material. A positive electrode active material for lithium secondary batteries, composed of single particles.

2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the boron doped to the lithium transition metal oxide is present in a region within a distance of 5 nm from the surface of the core in the inward direction.

3. The coating layer comprises lithium boron oxide, as described in claim 1, for a positive electrode active material for a lithium secondary battery.

4. The positive electrode active material for a lithium secondary battery according to claim 3, wherein when XPS analysis is performed at a depth of 5 nm from the outermost surface of the positive electrode active material, the weight ratio of boron contained in the boron oxide to the boron contained in the lithium boron oxide in the coating layer is 15% by weight or less.

5. The positive electrode active material for a lithium secondary battery according to claim 3, wherein when XPS analysis is performed at a depth of 5 nm from the outermost surface of the positive electrode active material, the boron content contained in the lithium boron oxide is 85% by weight or more based on the total boron content in the coating layer.

6. The positive electrode active material for a lithium secondary battery according to claim 4, wherein when XPS analysis is performed at a depth of 5 nm from the outermost surface of the positive electrode active material, the boron content contained in the boron oxide is 15% by weight or less based on the total boron content in the coating layer.

7. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating layer further comprises aluminum.

8. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating layer further comprises lithium.

9. The lithium transition metal oxide contains 60 mol% or more nickel based on the total number of moles of the transition metal, as described in claim 1.

10. The lithium transition metal oxide is represented by the following chemical formula 1, wherein the lithium secondary battery positive electrode active material is as described in claim 1. [Chemical formula 1] Li ａ [Ni ｘ Co ｙ Mn ｚ B ｗ１ M ｗ２ ]O ２ (In the above chemical formula 1, 0.8 ≤ a ≤ 1.2, 0.60 ≤ x < 1, 0 ≤ y ≤ 0.4, 0 ≤ z ≤ 0.4, 0 < w1 ≤ 0.2, 0 ≤ w2 ≤ 0.2, x + y + z + w1 + w2 = 1, and M is Zr, Al, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.)

11. The step of preparing transition metal hydroxides; The step of forming a mixture containing the transition metal hydroxide and lithium raw material, followed by a main calcination and a post-calcination to form single-particle lithium transition metal oxide; The first step is to form a first mixture containing the lithium transition metal oxide and cobalt raw material, and then perform a first heat treatment; and The process includes a step of performing a second heat treatment after forming a second mixture containing the result of the first heat treatment and the boron raw material, A method for producing positive electrode active material for lithium secondary batteries.

12. The method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the first mixture further comprises an aluminum raw material.

13. The method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the first mixture further comprises a lithium raw material.

14. The method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the first heat treatment is performed at a temperature of 600 to 720°C.

15. The method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the second heat treatment is performed at a temperature of 250 to 350°C.

16. The method for producing a positive electrode active material for a lithium secondary battery according to claim 11, wherein the second heat treatment is carried out in an oxygen atmosphere.

17. A positive electrode for a lithium secondary battery comprising the positive electrode active material according to any one of claims 1 to 10.

18. A lithium secondary battery comprising a positive electrode for a lithium secondary battery as described in claim 17.

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