Positive electrode active material for lithium secondary battery and method for producing the positive electrode active material

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery and a manufacturing method thereof, the positive electrode active material comprising a first positive electrode active material and a second positive electrode active material having different average particle sizes, the first positive electrode active material comprising a lithium metal oxide having a large particle size and a coating layer disposed on the large particle size lithium metal oxide and containing 1.0 to 7.0 wt% of boron, and the second positive electrode active material comprising a lithium metal oxide having a small particle size and a coating layer disposed on the small particle size lithium metal oxide and containing 3.0 to 12.0 wt% of cobalt.

Description

[Technical Field]

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

[0002] Secondary batteries are widely used in a wide range of devices, from small electronic devices such as mobile phones and laptops to large devices such as electric vehicles (EVs) and energy storage systems (ESSs). Layered lithium transition metal oxides (LiMO2, M = Ni, Co, Mn, etc.) are mainly used as the positive electrode active material for these secondary batteries, and research into improving their performance is actively underway.

[0003] Among the currently available layered cathode active materials, the materials with the highest capacity are LiNiO2 and high-nickel cathode active materials. Conventional high-nickel cathode active materials have been used as multi-particle large-particle cathode materials and small-particle single-particle cathode materials, but these have led to problems such as reduced performance and gas generation in lithium secondary batteries, and solutions to these problems are needed. Summary of the Invention [Problem to be solved by the invention]

[0004] The technical problem to be solved by the present invention is to provide a cathode active material that solves the problem of low life characteristics, which is a drawback of existing high-nickel (High-Ni) multi-particle cathode materials, and improves the drawbacks of small particle size mono-particle cathode materials, such as low capacity, efficiency, and DC-IR resistance.

[0005] Another technical problem to be solved by the present invention is to provide a method for producing a positive electrode active material having the above-mentioned advantages. [Means for solving the problem]

[0006] According to one embodiment of the present invention, a positive electrode active material for a lithium secondary battery includes a first positive electrode active material and a second positive electrode active material having different average particle sizes, the first positive electrode active material including a lithium metal oxide having a large particle size and a coating layer disposed on the large particle size lithium metal oxide and containing 1.0 to 7.0 wt% boron, and the second positive electrode active material including a lithium metal oxide having a small particle size and a coating layer disposed on the small particle size lithium metal oxide and containing 3.0 to 12.0 wt% cobalt. In one embodiment, the positive electrode active material for a lithium secondary battery may satisfy the following formula 1:

[0007] <Expression 1> 1.0≦([B] / )×([Co] / <co>)×[DC-IR]≦2.5

[0008] (In the above formula 1, [B] and [Co] and <co>are the surface concentration and coverage of the boron-containing coating layer and the cobalt-containing coating layer, respectively, and [DC-IR] is the DC-IR resistance value.

[0009] In one embodiment, the coverage of the boron-containing coating layer may be 5 to 40%.

[0010] In one embodiment, the coverage of the cobalt-containing coating layer may be 8.5 to 32.5%.

[0011] In one embodiment, the large particle size lithium metal oxide may have an average particle size (D50) of 12 to 17 μm, and in one embodiment, the small particle size lithium metal oxide may have an average particle size (D50) of 2 to 6 μm.

[0012] In one embodiment, the second positive electrode active material and the first positive electrode active material may be mixed in a ratio of 1:9 to 4:6. In one embodiment, the first positive electrode active material may contain Zr or Al as a dopant. In one embodiment, the second positive electrode active material may contain Zr as a dopant.

[0013] According to another embodiment of the present invention, a method for manufacturing a cathode active material may include the steps of: mixing a large particle size lithium metal oxide with 100 to 1100 ppm of boron source material and heat-treating the mixture to manufacture a first cathode active material; mixing a small particle size lithium metal oxide with 4000 to 20000 ppm of cobalt source material and heat-treating the mixture to manufacture a second cathode active material; and mixing the first and second cathode active materials to manufacture a cathode active material. In one embodiment, the large particle size lithium metal oxide may have an average particle size (D50) of 12 to 17 μm.

[0014] In one embodiment, the small particle size lithium metal oxide may have an average particle size (D50) of 2 to 6 μm. In one embodiment, the step of preparing the positive electrode active material by mixing the first positive electrode active material and the second positive electrode active material may involve mixing the second positive electrode active material to the first positive electrode active material in a ratio of 1 / 9 to 4 / 6.

[0015] In one embodiment, the boron source may be H3BO3 or B2O3. In one embodiment, the cobalt source may be Co3O4 and Co(OH)2. In one embodiment, the step of preparing the first positive electrode active material or the step of preparing the second positive electrode active material may be performed by injecting oxygen at a rate of 30 to 50 L / min during a heat treatment step.

[0016] In one embodiment, the step of preparing the first positive electrode active material or the step of preparing the second positive electrode active material may include a two-stage heat treatment process in the heat treatment step, wherein the first heat treatment step is performed at a temperature in the range of 400 to 600°C, and the second heat treatment step is performed at a temperature in the range of 900 to 950°C.

[0017] In one embodiment, the step of preparing the first positive electrode active material or the step of preparing the second positive electrode active material may include a heat treatment step, in which the heat treatment is performed at a temperature increase rate of 1 to 5° C. / min. [Effects of the Invention]

[0018] The positive electrode active material for a lithium secondary battery according to one embodiment of the present invention provides a positive electrode active material with improved electrochemical properties such as discharge capacity, lifespan, and initial DC-IR resistance by controlling the content of large particle diameter boron coating and the content of small particle diameter cobalt coating.

[0019] A method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery having the above-mentioned advantages. [Brief explanation of the drawings]

[0020] [Figure 1a] 1 is an SEM photograph of a positive electrode active material according to an example of the present invention. [Figure 1b] 1 is an SEM photograph of a positive electrode active material according to an example of the present invention. [Figure 2a] 1 is an SEM photograph of a positive electrode active material according to a comparative example of the present invention. [Figure 2b] 1 is an SEM photograph of a positive electrode active material according to a comparative example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Terms such as 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 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 can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0022] The terminology used herein is for the purpose of referring to particular embodiments only 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 context clearly dictates otherwise. As used herein, the term "comprising" refers to the inclusion of particular 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.

[0023] When a part is referred to as being "on" or "above" another part, it means that it is exactly on or above the other part, and 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.

[0024] Although not defined differently, all terms, including technical and scientific terms used herein, have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or overly formal sense unless otherwise defined. Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0025] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the technical field to which the present invention pertains can easily implement them. However, the present invention can be embodied in various different forms and is not limited to the embodiments described herein.

[0026] The positive electrode active material for a lithium secondary battery according to an embodiment of the present invention includes a first positive electrode active material and a second positive electrode active material having different average particle diameters. The first positive electrode active material may be a large-particle-size lithium metal oxide produced from a large-particle-size positive electrode active material precursor, and the second positive electrode active material may be a small-particle-size lithium metal oxide produced from a small-particle-size positive electrode active material precursor. The positive electrode active material precursor may be, for example, a precursor having an NCM composition (NixCoyMnz(OH)2, 0.7 < x < 1, 0 < y < 0.5, and 0 < z < 0.5).

[0027] In one embodiment, the large-particle-size lithium metal oxide may have an average particle diameter (D50) of 12 to 17 μm. The average particle diameter (D50) means a size corresponding to 50% of the maximum value in the cumulative distribution. Specifically, the average particle diameter (D50) may be 13 to 15 μm. By satisfying the above-described range, the electrode density can be increased, and when outside the above-described range, there is a problem that the electrochemical characteristics deteriorate.

[0028] In one embodiment, the first positive electrode active material can include a coating layer containing boron. Specifically, the coating layer containing boron can be disposed on the large-particle-size lithium metal oxide of the first positive electrode active material.

[0029] In one embodiment, the boron-containing coating layer may contain 1.0 to 7.0 wt% of boron, more specifically, 1.8 to 6.2 wt%, more specifically, 3.6 to 4.5 wt% of boron.

[0030] If the boron content is outside the upper limit of the above range, there is a problem that the initial capacity is reduced and the initial resistance is increased, and if the boron content is outside the lower limit of the above range, there is a problem that the life characteristics are reduced.

[0031] In one embodiment, the boron-containing coating layer may have a coverage of 5 to 40%. The coverage refers to the percentage of the surface of the positive electrode material that is covered with the boron compound. Specifically, the coverage may be 20 to 25%.

[0032] If the coverage is outside the upper limit of the above range, the resistance due to the boron compound increases, resulting in a decrease in initial capacity.If the coverage is outside the lower limit of the above range, a side reaction occurs between the electrolyte and the cathode material, resulting in a decrease in lifespan characteristics.

[0033] In one embodiment, the small particle size lithium metal oxide may have an average particle size (D50) of 2 to 6 μm. Specifically, it may be 3 to 5 μm. By satisfying the above range, there are advantages in improving the electrode density and increasing the initial charge and discharge efficiency. However, if the above range is not met, there are problems in that the density decreases and the efficiency decreases.

[0034] In one embodiment, the first positive electrode active material may include Zr or Al as a dopant. Specifically, the first positive electrode active material may be co-doped with Zr and Al. By including the dopant in the first positive electrode active material, the electrical characteristics of the battery, such as charge and discharge performance and efficiency, may be improved.

[0035] In one embodiment, the content of the dopant in the first positive electrode active material may be 0.01 to 0.03 mol. Specifically, the content of the dopant may be 0.02 to 0.025 mol. More specifically, when the dopant is simultaneously doped with Zr and Al, the content of the Zr-containing dopant may be in the range of 0.001 to 0.0050 mol, and the content of the Al-containing dopant may be in the range of 0.01 to 0.03 mol.

[0036] If the content of the dopant is outside the upper limit of the above range, there is a problem of a decrease in initial capacity, and if the content of the dopant is outside the lower limit of the above range, there is a problem of a decrease in life characteristics and an increase in grain size.

[0037] In one embodiment, the second positive electrode active material may include a coating layer containing cobalt. Specifically, the coating layer containing cobalt may be disposed on the small particle size lithium metal oxide of the second positive electrode active material.

[0038] In one embodiment, the cobalt-containing coating layer may contain 1.0 to 7.0 wt% of cobalt, more specifically, 1.8 to 6.2 wt%, more specifically, 3.6 to 4.5 wt% of cobalt.

[0039] If the cobalt content is outside the upper limit of the above range, the capacity may decrease and the cost may increase due to an increase in unnecessary cobalt compounds, and if the cobalt content is outside the lower limit of the above range, the life characteristics may decrease.

[0040] In one embodiment, the cobalt-containing coating layer may have a coverage of 5 to 40%. The coverage refers to the extent to which the surface of the positive electrode material is covered with the cobalt compound. Specifically, the coverage may be 20 to 25%.

[0041] If the coverage is outside the upper limit of the above range, the initial capacity may be reduced due to the cobalt compound, and if the coverage is outside the lower limit of the above range, side reactions on the surface may not be suppressed, resulting in reduced life characteristics.

[0042] In one embodiment, the second positive electrode active material may include Zr as a dopant. By including the dopant, the second positive electrode active material may improve the electrical characteristics of the battery, such as charge and discharge performance and efficiency. Specifically, by including the dopant, the second positive electrode active material may facilitate the insertion and extraction of Li, thereby increasing the efficiency of the small particle size.

[0043] In one embodiment, the second positive electrode active material may include a dopant in a range of 0.0001 to 0.0003 mol. If the content of the dopant is outside the upper limit, costs may increase and initial capacity may decrease, while if the content of the dopant is outside the lower limit, charge and discharge efficiency may decrease.

[0044] In one embodiment, the second positive electrode active material may be mixed with the first positive electrode active material at a ratio of 1:9 to 4:6. Specifically, the first positive electrode active material:the second positive electrode active material may be mixed at a ratio of 1:9 to 4:6. More specifically, the first positive electrode active material:the second positive electrode active material may be mixed at a ratio of 1:9 to 3:7, and the second positive electrode active material may be mixed with the first positive electrode active material at a ratio of 1:9 to 3:7.

[0045] When the mixing ratio of the second positive electrode active material to the first positive electrode active material satisfies the above-described range, the first positive electrode active material having a large particle size including a boron coating layer and the second positive electrode active material having a small particle size including a cobalt coating layer are uniformly mixed, thereby producing a positive electrode active material having a bimodal particle size distribution.

[0046] Regarding the mixing ratio of the second positive electrode active material to the first positive electrode active material, if the ratio of the first positive electrode active material is too high and deviates from the lower limit, the electrode density may be reduced and the lifespan may be deteriorated.If the ratio of the second positive electrode active material is too high and deviates from the upper limit, the electrode density may be reduced and the slurry viscosity may be increased, making it difficult to manufacture the electrode.

[0047] In one embodiment, a positive electrode active material for a lithium secondary battery that satisfies the following formula 1 may satisfy the following formula 1.

[0048] <Expression 1> 1.0≦([B] / )×([Co] / <co>)×[DC-IR]≦2.5

[0049] (In the above formula 1, [B] and [Co] and <co>are the surface concentration and coverage of the boron-containing coating layer and the cobalt-containing coating layer, respectively, and [DC-IR] is the DC-IR resistance value.

[0050] The formula (1) represents the product of the surface concentration and coverage ratio of the boron-containing coating layer of the first positive electrode active material, the surface concentration and coverage ratio of the cobalt-containing coating layer of the second positive electrode active material, and the DC-IR resistance, and quantifies the relationship between the boron and cobalt contents and the DC-IR resistance. The formula (1) can be 1.0 to 2.5, specifically 2.0 to 2.3.

[0051] If the upper limit of the formula 1 is exceeded, the initial resistance value becomes high, which may cause the battery to malfunction. If the lower limit of the formula 1 is exceeded, the boron compound and the cobalt compound cannot suppress side reactions, which may result in a decrease in lifespan.

[0052] A method for manufacturing a cathode active material according to another embodiment of the present invention may include the steps of: mixing a large particle size lithium metal oxide with a boron source and heat-treating the mixture to manufacture a first cathode active material; mixing a small particle size lithium metal oxide with a cobalt source and heat-treating the mixture to manufacture a second cathode active material; and mixing the first and second cathode active materials to manufacture a cathode active material. Detailed descriptions of the first and second cathode active materials are the same as those described above to the extent that they are not inconsistent.

[0053] In one embodiment, the step of preparing the first positive electrode active material by mixing the large particle size lithium metal oxide with a boron source and heat-treating the mixture may include mixing the large particle size lithium metal oxide with 100 to 1100 ppm of boron source and heat-treating the mixture.

[0054] In one embodiment, the boron source may be HBO or BO. In one embodiment, the boron source may be contained in an amount of 100 to 1100 ppm by weight. Specifically, the boron source may be contained in an amount of 250 to 900 ppm by weight.

[0055] If the boron source is outside the upper limit of the range, there is a problem that the initial resistance increases and the capacity decreases, and if the boron source is outside the lower limit of the range, there is a problem that the life characteristics decrease.

[0056] In one embodiment, the cobalt source may be Co3O4 and Co(OH)2. The cobalt source may be contained in an amount of 4000 to 20000 ppm by weight. Specifically, the cobalt source may be contained in an amount of 6000 to 18000 ppm by weight.

[0057] If the cobalt raw material is outside the upper limit of the range, there are problems such as increased costs and reduced capacity due to excessive cobalt compound, and if the cobalt raw material is outside the lower limit of the range, there are problems such as reduced initial efficiency and reduced capacity.

[0058] In one embodiment, in the step of preparing a positive electrode active material by mixing the first positive electrode active material and the second positive electrode active material, the first positive electrode active material and the second positive electrode active material may be mixed in a ratio of 1:9 to 4:6, the details of which are the same as those described above.

[0059] In one embodiment, Zr oxide or Al oxide may be used as a dopant in the step of preparing the first positive electrode active material. In one embodiment, Zr oxide may be used as a dopant in the step of preparing the second positive electrode active material. The Zr oxide may be, for example, ZrO2, and the Al oxide may be, for example, Al(OH)3.

[0060] For a detailed description of the dopant, please refer to the above-mentioned dopant material.

[0061] In one embodiment, the step of preparing the first positive electrode active material or the step of preparing the second positive electrode active material may be performed by supplying oxygen at a rate of 30 to 50 L / min during the heat treatment step. Specifically, the oxygen may be supplied at a rate of 35 to 45 L / min.

[0062] If the oxygen inflow rate is outside the upper limit, it becomes difficult to control the crystal grain size, and if the oxygen inflow rate is outside the lower limit, it becomes difficult to stabilize the structure due to a decrease in the oxygen partial pressure inside the firing furnace.

[0063] In one embodiment, the heat treatment step in the step of preparing the first positive electrode active material or the step of preparing the second positive electrode active material may include a two-stage heat treatment process. In one embodiment, the first heat treatment step in the two-stage heat treatment process may be performed at a temperature in the range of 400 to 600°C. By performing the first heat treatment step within the above range, there is an advantage in that the weight of the precursor, lithium, and dopant is reduced, thereby increasing productivity. However, if the first heat treatment step is performed outside the above range, there is a problem in that the electrochemical properties may be reduced due to damage to the positive electrode material caused by the high-temperature heat treatment.

[0064] In one embodiment, the second-stage heat treatment process can be performed at a temperature in the range of 800 to 950° C. When the second-stage heat treatment is performed within the above range, there is an advantage in that the initial efficiency is increased and the electrochemical properties are improved, but when the second-stage heat treatment is performed outside the above range, there is a problem in that the electrochemical properties are deteriorated due to non-crystallization and excessive crystallization.

[0065] In one embodiment, the heat treatment step of the first or second positive electrode active material preparation step may be performed at a temperature increase rate of 1 to 5° C. / min. If the temperature increase rate is outside the upper limit, there is a problem that electrochemical properties may be deteriorated due to non-crystallization caused by a sudden temperature change.

[0066] A lithium secondary battery according to another embodiment of the present invention may include a positive electrode, a negative electrode, and an electrolyte, and the positive electrode may include the above-described positive electrode active material. The positive electrode may include a current collector and a positive electrode active material layer disposed on the current collector. The positive electrode active material layer may include a positive electrode active material, and the positive electrode active material may include the above-described positive electrode active material.

[0067] In one embodiment, the content of the positive electrode active material in the positive electrode active material layer may be 90 wt% to 99 wt% based on the total weight of the positive electrode active material layer. The positive electrode active material layer may include a binder and / or a conductive material. The contents of the binder and the conductive material may be 1 wt% to 5 wt% each based on the total weight of the positive electrode active material layer.

[0068] The binder can bind the positive electrode active material particles together and adhere the positive electrode active material to a current collector. Examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, an epoxy resin, and nylon.

[0069] The conductive material may be a material used to impart conductivity to the electrode. The conductive material is not limited as long as it does not undergo chemical changes and is an electronically conductive material. Non-limiting examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based materials such as metal powder or metal fiber of copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives, and mixtures thereof. The positive electrode current collector may be, for example, aluminum foil, nickel foil, or a combination thereof.

[0070] The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer contains a negative electrode active material. The negative electrode active material can include a material capable of reversibly inserting / desorbing (Intercalation / Deintercalation) lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0071] As the material capable of reversibly inserting / desorbing lithium ions, any of the carbon-based negative electrode active materials generally used in lithium-ion secondary batteries can be used. For example, crystalline carbon, amorphous carbon, or both of them can be used.

[0072] As the alloy of lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0073] Examples of the material capable of doping and dedoping lithium include Si, SiOx (0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof and is not Sn), and the like.

[0074] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like. The negative electrode active material layer may also contain a binder and may further selectively contain a conductive material.

[0075] The binder may serve to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector. The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive and does not cause chemical changes in the battery that is constructed therefrom may be used.

[0076] The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0077] The negative electrode and the positive electrode are fabricated by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the composition on a current collector. Since this electrode fabrication method is widely known in the art, a detailed description thereof will be omitted. Examples of the solvent include, but are not limited to, N-methylpyrrolidone.

[0078] The electrolyte includes a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can migrate. The lithium salt dissolves in the organic solvent and acts as a source of lithium ions within the battery, enabling basic lithium secondary battery operation and facilitating the migration of lithium ions between the positive and negative electrodes.

[0079] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. Such separators may be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more of these materials, such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator.

[0080] Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, into cylindrical, prismatic, coin, pouch, etc. types depending on the shape, and into bulk and thin film types depending on the size. The structure and manufacturing method of these batteries are widely known in this field, so a detailed description will be omitted. [Example]

[0081] Specific examples of the present invention will be described below. However, the following examples are merely specific examples of the present invention, and the present invention is not limited to the following examples.

[0082] <Experimental Example 1> - Large particle size with B0pm coating, small particle size with Co12000ppm coating - Comparative Example 1

[0083] "Method for producing large particle size precursor" Prior to cathode material production, a large particle size precursor with a composition of (NixCoyMnz)(OH)2 was prepared by the coprecipitation method of the present invention for 40 hours (x = 0.92, y = 0.4, z = 0.4). The resulting precursor with a composition of (NixCoyMnz)(OH)2 was grown to an average particle size of approximately 14.5 μm.

[0084] The precursor solution was prepared by dissolving NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O in DI water, and NH4(OH) was added as a coprecipitating chealing agent, and NaOH was used to adjust the pH. N2 was purged to prevent oxidation of Ni during coprecipitation, and the reactor temperature was maintained at 50°C.

[0085] The prepared precursor was filtered, washed with DI water, and then dried in an oven at 110°C for 24 hours. The pH range of the co-precipitation step was maintained between 11.0 and 12.0, and the total co-precipitation time was 40 hours. The precursor was prepared through a concentration process. The flow rate of the metal sulfate solution was maintained at 10 L / hr.

[0086] The large particle size metal hydroxide precursor was then mixed uniformly with 0.0035 mol of ZrO2 and 0.02 mol of Al(OH)3 as dopants in a 1:1.06 molar ratio with LiOH·H2O (Samjeon Chemical, Battery Grade) and then calcined at high temperature to produce lithium metal oxide cathode material. The mixture was then mixed uniformly with the lithium raw material in a mixer and placed in a box furnace where it was calcined with oxygen flowing in at 40 L / min. The calcination conditions were 480°C for 5 hours, then 700-780°C for 12 hours, with a temperature increase rate of 2.5°C / min.

[0087] Then, 4 kg of the large particle size cathode material was added to 4 kg of distilled water and stirred for 10 minutes to prepare a slurry, which was then filtered through a filter press and dried in a vacuum oven at 100°C for 12 hours. The 4 kg of washed cathode active material was heated in a firing furnace at a rate of 3°C / min and subjected to a heat treatment process at 300°C for 6 hours.

[0088] "Method for producing small particle size precursors" (Ni x Co y Mn z A precursor with a small particle size was prepared by coprecipitation for 40 hours using a precursor with the composition of (Ni)(OH)2 (x = 0.88, y = 0.5, z = 0.7). x Co y Mn z A precursor having a composition of )(OH)2 was grown to an average particle size diameter of approximately 3.5 μm.

[0089] The precursor solution was prepared by dissolving NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O in DI water, and NH4(OH) was added as a coprecipitating chealing agent, and NaOH was used to adjust the pH. N2 was purged to prevent oxidation of Ni during coprecipitation, and the reactor temperature was maintained at 50°C.

[0090] The prepared precursor was filtered, washed with DI water, and then dried in an oven at 110°C for 24 hours. The pH range of the co-precipitation step was maintained between 11.0 and 12.0, and the total co-precipitation time was 40 hours. The precursor was prepared through a concentration process. The flow rate of the metal sulfate solution was maintained at 10 L / hr.

[0091] The large particle size metal hydroxide precursor was then uniformly mixed with 0.0002 moles of ZrO2 as a dopant in a 1:1.01 molar ratio with LiOH·H2O (Samjeon Chemical, Battery Grade) and then calcined at high temperature to produce lithium metal oxide cathode material. The lithium raw material and the mixture were simultaneously fed into a mixer and mixed uniformly, then placed in a box furnace and calcined with oxygen flowing in at 40 L / min. The calcination conditions were 480°C for 5 hours, then 900-950°C for 12 hours, with a temperature increase rate of 2.5°C / min.

[0092] Then, 4 kg of the calcined small particle size positive electrode active material was mixed with 12,000 ppm cobalt hydroxide (Co(OH)2) in a mixer for 3 minutes, and then the temperature was increased at a rate of 3°C / min in a calcination furnace, and a heat treatment process was performed at a temperature of 680°C for 6 hours.

[0093] "Method of manufacturing positive electrode active material" The large particle size positive active material precursor and the small particle size positive active material precursor were uniformly mixed in a ratio of 8:2 by ball milling to prepare a bimodal positive electrode material.

[0094] "Method of manufacturing lithium secondary batteries" The cathode active material was then electrochemically evaluated using a CR2032 coin cell. The cathode:conductive material (Denka Black):binder (PVDF, KF1100) slurry was 96.5:1.5:2 wt%, and the slurry viscosity was adjusted by adding NMP (N-Methyl-2-pyrrolidone) to achieve a solid content of approximately 30%.

[0095] The prepared slurry was coated on a 20 μm thick aluminum foil using a doctor blade, dried, and then rolled. The electrode loading was 15.8 mg / cm. 2 The rolling density is 3.7 g / cm 3 The electrolyte was 1M LiPF6 in EC:DMC:EMC = 3:4:3 (vol%), and a coin cell was made using a PP separator and a lithium anode (300 μm, Neba Korea), and then aged at room temperature for 10 hours, after which charge and discharge tests were performed.

[0096] Capacity evaluation was performed with 200mAh / g as the reference capacity, under charge-discharge conditions of CC / CV 3.0-4.3V with a 1 / 20C cut-off. The initial capacity was measured by charging at 0.1C / discharging at 0.1C, followed by charging at 0.33C / discharging at 0.33C. Room temperature cycle life characteristics were calculated at room temperature (25°C), and high temperature cycle life characteristics were calculated at high temperature (45°C) by applying a discharge current at 4.25V (100%) and measuring the voltage 60 seconds later.

[0097] The resistance increase rate was measured by measuring the resistance at a high temperature (45°C) in the same manner as the initial resistance measurement method after 30 cycles, and the increase rate was converted into a percentage (%) and recorded.

[0098] <Experimental Example 2> - B1150ppm coating large particle size, Co12000ppm coating small particle size - Comparative Example 2 The manufacturing method was the same as in Experimental Example 1, except that a coating process was added to the large particle diameter cathode active material precursor, and 4 kg of the washed cathode active material was stirred with 1150 ppm of boric acid (H3BO3) in a mixer for 1 minute, and then the temperature was increased at a rate of 3°C / min in a firing furnace and heat-treated at 300°C for 5 hours.

[0099] <Experimental Example 3> - B1300ppm coating large particle size, Co12000ppm coating small particle size - Comparative Example The same procedure as in Experimental Example 2 was carried out, except that the large particle size positive electrode active material precursor was coated with 1300 ppm boric acid (H3BO3).

[0100] <Experimental Example 4> - B 250 ppm coating large particle size, Co 12000 ppm coating small particle size - Example The same procedure as in Experimental Example 2 was carried out, except that the large particle size positive electrode active material precursor was coated with 250 ppm boric acid (H3BO3).

[0101] <Experimental Example 5> - B 400 ppm coating large particle size, Co 12000 ppm coating small particle size - Example The same procedure as in Experimental Example 2 was carried out, except that the large particle size positive electrode active material precursor was coated with 400 ppm boric acid (H3BO3).

[0102] <Experimental Example 6> - B 500 ppm coating large particle size, Co 12000 ppm coating small particle size - Example The same procedure as in Experimental Example 2 was carried out, except that the large particle size positive electrode active material precursor was coated with 500 ppm boric acid (H3BO3).

[0103] <Experimental Example 7> - B 600 ppm coating large particle size, Co 12000 ppm coating small particle size - Example The same procedure as in Experimental Example 2 was carried out, except that the large particle size positive electrode active material precursor was coated with 600 ppm boric acid (H3BO3).

[0104] <Experimental Example 8> - B 650 ppm coating large particle size, Co 12000 ppm coating small particle size - Example The same procedure as in Experimental Example 2 was carried out, except that the large particle size positive electrode active material precursor was coated with 650 ppm boric acid (H3BO3).

[0105] <Experimental Example 9> - B 800 ppm coating large particle size, Co 12000 ppm coating small particle size - Example The same procedure as in Experimental Example 2 was carried out, except that the large particle size positive electrode active material precursor was coated with 800 ppm boric acid (H3BO3).

[0106] <Experimental Example 10> - B 900 ppm coating large particle size, Co 12000 ppm coating small particle size - Example The same procedure as in Experimental Example 2 was carried out, except that the large particle size positive electrode active material precursor was coated with 900 ppm boric acid (H3BO3).

[0107] <Experimental Example 11> - B 600 ppm coating large particle size, Co 0 ppm coating small particle size - Comparative Example The same procedure as in Experimental Example 7 was carried out, except that cobalt hydroxide (Co(OH)2) was not mixed into the small particle size positive electrode active material precursor.

[0108] <Experimental Example 12> - B 600 ppm coating large particle size, Co 3000 ppm coating small particle size - Comparative Example The same procedure as in Experimental Example 7 was carried out, except that the small particle size positive electrode active material precursor was coated with 3000 ppm of cobalt hydroxide (Co(OH)2).

[0109] <Experimental Example 13> - B 600 ppm coating large particle size, Co2 1000 ppm coating small particle size - Comparative Example The same procedure as in Experimental Example 7 was carried out, except that the small particle size positive electrode active material precursor was coated with 21,000 ppm of cobalt hydroxide (Co(OH)2).

[0110] <Experimental Example 14> - B 600 ppm coating large particle size, Co 6000 ppm coating small particle size - Example The same procedure as in Experimental Example 7 was carried out, except that the small particle size positive electrode active material precursor was coated with 6000 ppm of cobalt hydroxide (Co(OH)2).

[0111] <Experimental Example 15> - B 600 ppm coating large particle size, Co 9000 ppm coating small particle size - Example The same procedure as in Experimental Example 7 was carried out, except that the small particle size positive electrode active material precursor was coated with 3000 ppm of cobalt hydroxide (Co(OH)2).

[0112] <Experimental Example 16> - B 600 ppm coating large particle size, Co 15000 ppm coating small particle size - Example The same procedure as in Experimental Example 7 was carried out, except that the small particle size positive electrode active material precursor was coated with 15,000 ppm of cobalt hydroxide (Co(OH)2).

[0113] <Experimental Example 17> - B 600 ppm coating large particle size, Co 18000 ppm coating small particle size - Example The same procedure as in Experimental Example 7 was carried out, except that the small particle size positive electrode active material precursor was coated with 18,000 ppm of cobalt hydroxide (Co(OH)2).

[0114] Table 1 below shows the electrochemical properties of the positive electrode active material depending on the B coating content of the large particle size positive electrode active material precursor or the Co coating content of the small particle size positive electrode active material.

[0115] [Table 1]

[0116] As seen in Table 1, in Comparative Examples 1 to 3, the boric acid content was outside the range of the present invention, and therefore the coating layer content on the cathode material was outside the range of the present invention, and therefore the value of Equation 1 was not satisfied, resulting in decreased charge and discharge capacity, efficiency, and cycle retention, and high DC-IR resistance.In Comparative Examples 4 and 5, the cobalt hydroxide content was outside the range of the present invention, and therefore the coating layer content on the cathode material was outside the range of the present invention, and therefore the value of Equation 1 was not satisfied, resulting in decreased charge and discharge capacity, efficiency, and cycle retention, and high DC-IR resistance.

[0117] 1a and 1b are SEM photographs of a positive electrode active material according to one embodiment of the present invention.

[0118] 1a and 1b are SEM photographs of the positive electrode active material according to Example 4 of the present invention.

[0119] Referring to Figures 1a and 1b, the matrix is ​​76.4% and the B coating coverage is 23.6%. The boron compound and cobalt compound cover the large and small particle surfaces in appropriate amounts, protecting the surface layer of the positive electrode active material from various side reactions, which has been confirmed to have the effect of improving life characteristics. In addition, the high electrical conductivity of the cobalt compound has the effect of increasing efficiency and reducing initial resistance.

[0120] 2a and 2b are SEM photographs of a positive electrode active material according to a comparative example of the present invention.

[0121] Figure 2a is an SEM image of the positive electrode active material of Comparative Example 1, and Figure 2b is an SEM image of the positive electrode active material of Comparative Example 4. Referring to Figures 2a and 2b, the coating layer is thin, which may result in a large area of ​​the positive electrode active material that may be subject to side reactions with the electrolyte, and the positive electrode material may be damaged over time by HF generated in the electrolyte. This results in a rapid deterioration in lifespan characteristics and a lack of increased electrical conductivity due to the cobalt compound, resulting in high initial resistance.

[0122] As described above, by satisfying the contents of boric acid and cobalt hydroxide in the cathode material manufacturing process, the content of the coating layer on the cathode material satisfies the range of the present invention, thereby resolving the shortcomings of high-nickel (High-Ni) multi-particle cathode materials, such as low life characteristics, and improving the shortcomings of small particle size mono-particle cathode materials, such as low capacity, efficiency, and DC-IR resistance.

[0123] The present invention is not limited to the above-described embodiments and / or examples, and may be manufactured in various different forms, and those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical concept or essential characteristics of the present invention. Therefore, it should be understood that the above-described embodiments and / or examples are illustrative in all respects and are not limiting.< / co> < / co> < / co> < / co>

Claims

1. a first positive electrode active material and a second positive electrode active material having different average particle sizes; the first positive electrode active material includes a large particle size lithium metal oxide and a coating layer disposed on the large particle size lithium metal oxide and including 1.0 to 7.0 wt % of boron; The second positive electrode active material is a positive electrode active material for a lithium secondary battery, comprising: a lithium metal oxide having a small particle size; and a coating layer disposed on the lithium metal oxide having a small particle size and containing 3.0 to 12.0 wt % of cobalt.

2. The positive electrode active material for a lithium secondary battery according to claim 1, which satisfies the following formula 1: <Formula 1> 1.0≦([B] / )×([Co] / <Co>)×[DC-IR]≦2.5 (In the above formula 1, [B] and [Co], and and <Co> respectively represent the surface concentration and coverage of the coating layer containing boron and the coating layer containing cobalt, and [DC-IR] represents the DC-IR resistance value.)

3. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coverage of the coating layer containing boron is 5 to 40%.

4. 10. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the coverage of the cobalt-containing coating layer is 8.5 to 32.5%.

5. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the large particle size lithium metal oxide has an average particle size (D50) of 12 to 17 μm.

6. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the small particle size lithium metal oxide has an average particle size (D50) of 2 to 6 μm.

7. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the second positive electrode active material is mixed with the first positive electrode active material in a ratio of 1 / 9 to 4 / 6.

8. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the first positive electrode active material contains Zr or Al as a dopant.

9. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the second positive electrode active material contains Zr as a dopant.

10. mixing the large particle size lithium metal oxide with 100 to 1100 ppm of boron raw material and heat treating the mixture to prepare a first positive electrode active material; Mixing small particle size lithium metal oxide with 4000 to 20000 ppm of cobalt raw material and heat treating the mixture to prepare a second positive electrode active material; and A method for manufacturing a positive electrode active material for a lithium secondary battery, comprising: mixing the first positive electrode active material and the second positive electrode active material to manufacture a positive electrode active material.

11. 11. The method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the large particle size lithium metal oxide has an average particle size (D50) of 12 to 17 μm.

12. 11. The method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the small particle size lithium metal oxide has an average particle size (D50) of 2 to 6 μm.

13. 11. The method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the step of mixing the first positive electrode active material and the second positive electrode active material comprises mixing the second positive electrode active material to the first positive electrode active material in a ratio of 1 / 9 to 4 / 6.

14. The boron source is H ３ BO ３ or B ２ O ３ The method for producing a positive electrode active material for a lithium secondary battery according to claim 10,

15. The cobalt raw material is Co ３ O ４ and Co(OH) ２ The method for producing a positive electrode active material for a lithium secondary battery according to claim 10,

16. The step of preparing the first positive electrode active material or the step of preparing the second positive electrode active material includes: The method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the heat treatment step is carried out by flowing oxygen at 30 to 50 L / min.

17. The method of claim 10 , wherein the heat treatment step of the step of producing the first positive electrode active material or the step of producing the second positive electrode active material comprises a two-stage heat treatment process.

18. In the two-stage heat treatment step, The first-stage heat treatment is carried out in the temperature range of 400 to 600°C, The method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the two-stage heat treatment is carried out at a temperature in the range of 900 to 950°C.

19. The step of preparing the first positive electrode active material or the step of preparing the second positive electrode active material includes:

11. The method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the heat treatment is carried out at a temperature increase rate of 1 to 5° C. / min in the heat treatment step.

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