Positive electrode active material and method for producing the same

Abstract

The present invention relates to a positive electrode active material having high capacity and high rate characteristics and a manufacturing method thereof. The positive electrode active material of the present invention includes lithium transition metal oxide particles having a composition represented by the following Chemical Formula 1, and the (003) d-spacing on the surface of the lithium transition metal oxide particles is larger than the (003) d-spacing inside the particles. [Chemical formula 1] Li a [Ni x Co y Mn z M 1 w ]O2 In the above formula 1, 0.8≦a≦1.2, 0.6≦x<1, 0 <y<0.4、0<z<0.4、0≦w≦0.1であり、M 1 is one or more selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0061000, filed May 11, 2021, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material and a method for producing the same, and more particularly to a high-capacity positive electrode active material having high-rate characteristics that enable rapid charging, and a method for producing the same. [Background technology]

[0003] With the increasing demand for mobile devices, battery-powered vehicles, etc., the demand for secondary batteries as an energy source is rapidly increasing, and among secondary batteries, lithium secondary batteries, which have high energy density and low self-discharge rates, have been commercialized and widely used. In particular, with the recent rapid expansion of the electric vehicle market, the demand for high-capacity secondary batteries is increasing, and there is a need to develop lithium secondary batteries with excellent high-rate characteristics that enable rapid charging.

[0004] To improve the capacity characteristics of secondary batteries, lithium composite transition metal oxides containing two or more transition metals, such as NCM and NCMA, have been developed and used as positive electrode active materials. Conventionally, lithium composite transition metal oxides have been prepared by dissolving a transition metal source material, such as nickel sulfate, cobalt sulfate, or manganese sulfate, in water to prepare a transition metal aqueous solution. The transition metal aqueous solution, a cation complex, and a basic compound are then added to a reactor to perform a coprecipitation reaction to prepare a hydroxide-form transition metal precursor. The transition metal precursor is then mixed with a lithium source material and calcined. However, conventional lithium composite transition metal oxides prepared by these methods have had difficulty achieving sufficient capacity and high-rate performance.

[0005] Therefore, there is a need to develop a positive electrode active material that has high capacity and high rate characteristics. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve the above problems, and aims to provide a cathode active material in which the (003) d-spacing on the surface of the cathode active material is larger than the (003) d-spacing inside the cathode active material, thereby increasing capacity and maintaining high capacity even during high-rate charge / discharge, and a method for manufacturing such a cathode active material. [Means for solving the problem]

[0007] According to one embodiment, the present invention provides a positive electrode active material comprising lithium transition metal oxide particles having a composition represented by the following Chemical Formula 1, wherein the (003) d-spacing at the surface of the lithium transition metal oxide particles is larger than the (003) d-spacing inside the particles: [Chemical formula 1] Li a [Ni x Co y Mn z M 1 w ]O2 In the above chemical formula 1, 0.8≦a≦1.2, 0.6≦x<1, 0 <y<0.4、0<z<0.4、0≦w≦0.1であり、M 1 is one or more elements selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S.

[0008] According to another embodiment, the present invention provides a method for manufacturing a cathode active material, the method including: preparing a precursor for a cathode active material having a multilayer structure in which two or more elements selected from nickel, cobalt, and manganese are precipitated in different regions; and mixing the precursor for the cathode active material with a lithium source material and then calcining the mixture to prepare a lithium transition metal oxide.

[0009] According to still another embodiment, there is provided a positive electrode including the positive electrode active material according to the present invention, and a lithium secondary battery including the positive electrode. [Effects of the Invention]

[0010] In the method for producing a cathode active material according to the present invention, nickel, cobalt, and manganese elements are not simultaneously coprecipitated during the preparation of a precursor for the cathode active material, but two or more elements of nickel, cobalt, and manganese are added separately to produce a precursor for the cathode active material having a multilayer structure in which two or more elements of nickel, cobalt, and manganese are precipitated in different regions. The precursor for the cathode active material is then mixed with a lithium source material and calcined to produce a cathode active material.

[0011] In the cathode active material of the present invention prepared by the above method, the distance between (003) planes (d-spacing) on ​​the surface of the lithium transition metal oxide particles is greater than the distance between (003) planes (d-spacing) inside the particles. The increased distance between (003) planes on the surface of the lithium transition metal oxide widens the lithium ion migration path, facilitating the insertion and extraction of lithium ions. Therefore, the cathode active material of the present invention has superior capacity characteristics and high-rate performance compared to conventional cathode active materials that have a constant distance between (003) planes throughout the particle. Therefore, when the cathode active material of the present invention is applied to a lithium secondary battery, excellent capacity characteristics and rapid charging performance can be achieved. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be specifically described below.

[0013] The present inventors conducted extensive research to develop a cathode active material that exhibits minimal capacity degradation even during rapid charging. As a result, they discovered that by separately precipitating two or more elements from nickel, cobalt, and manganese rather than simultaneously coprecipitating nickel, cobalt, and manganese during the preparation of a precursor for the cathode active material, it is possible to prepare a cathode active material in which the distance between (003) planes (d-spacing) is relatively larger on the surface than in the interior of lithium transition metal oxide particles. They also discovered that when such a cathode active material is applied to a lithium secondary battery, high capacity can be maintained even at high charge and discharge rates, leading to the completion of the present invention.

[0014] Method for producing positive electrode active material First, the method for producing the positive electrode active material of the present invention will be described.

[0015] The method for manufacturing a positive electrode active material according to the present invention includes the steps of: (1) preparing a precursor for a positive electrode active material having a multilayer structure in which two or more elements selected from nickel, cobalt, and manganese are precipitated in different regions; and (2) mixing the precursor for the positive electrode active material with a lithium source material and then calcining the mixture to prepare a lithium transition metal oxide.

[0016] (1) Manufacturing steps for the precursor of the positive electrode active material First, a precursor for a positive electrode active material having a multi-layer structure in which two or more elements selected from nickel, cobalt, and manganese are precipitated in different regions is prepared.

[0017] In the past, to prepare a precursor for a positive electrode active material containing nickel, cobalt, and manganese, a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material were mixed together to prepare a composite transition metal solution containing nickel, cobalt, and manganese, and the composite transition metal solution was then added to a reactor with an ammonium cation complex-forming agent and a basic compound to cause a coprecipitation reaction. Using this conventional method, nickel-cobalt-manganese hydroxide was prepared in which nickel, cobalt, and manganese were uniformly distributed throughout the precursor particles.

[0018] In contrast, the present invention is characterized by preparing a cathode active material precursor by incorporating two or more elements selected from nickel, cobalt, and manganese into separate solutions at different times and introducing them into a reactor. The method of the present invention produces a multilayered cathode active material precursor in which two or more elements selected from nickel, cobalt, and manganese are precipitated in different regions. Using such a multilayered precursor, it is possible to produce a cathode active material having different (003) d-spacing values ​​on the particle surface and in the particle interior.

[0019] Specifically, the multilayered positive electrode active material precursor in which two or more elements selected from nickel, cobalt, and manganese are precipitated in different regions can be prepared by any one of the following methods (I) to (III).

[0020] (I) Method: First, a nickel-cobalt metal solution, an ammonium cation complexing agent, and a basic compound are mixed together, and then a coprecipitation reaction is carried out to form nickel-cobalt hydroxide particles.

[0021] Here, the coprecipitation reaction can be carried out, for example, by carrying out the reaction for a predetermined time under conditions where the pH of the reaction solution is 11.5 to 12.5, preferably 11.8 to 12.3, to form hydroxide particle nuclei, and then lowering the pH of the reaction solution and carrying out an additional reaction to grow the hydroxide particles.

[0022] Meanwhile, the nickel-cobalt metal solution can be prepared by dissolving a nickel source material and a cobalt source material in a solvent such as water.

[0023] Here, the nickel source material may be nickel acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, and specifically may be, but is not limited to, NiO, NiCO3·2Ni(OH)2·4H2O, NiCO2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halides, or combinations thereof.

[0024] The cobalt source material may be a cobalt metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, and specifically may be, but is not limited to, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0025] On the other hand, the nickel-cobalt metal solution may be optionally 1 It may further contain raw materials. 1 is one or more selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and M 1 The raw materials contained are M 1 It can be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, or the like.

[0026] The ammonium cation complexing agent may be at least one selected from the group consisting of NHOH, (NH)SO, NHNO, NHCl, CHCOONH, and NHCO, and may be introduced into the reactor in the form of a solution in a solvent, which may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0027] The basic compound may be at least one selected from the group consisting of NaOH, KOH, and Ca(OH)2, and may be added to the reactor in the form of a solution in a solvent, which may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0028] Co-precipitation of nickel and cobalt as described above results in nickel-cobalt hydroxide particles with constant concentrations of nickel and cobalt throughout the particle.

[0029] Next, the addition of the nickel-cobalt metal solution is stopped, and a manganese metal solution, an ammonium cation complexing agent, and a basic compound are added to the reaction solution containing the nickel-cobalt hydroxide particles to carry out a precipitation reaction.

[0030] Here, the manganese precipitation reaction is preferably carried out under conditions where the pH of the reaction solution is 11.0 or less, preferably 10.0 to 11.0. When the pH of the reaction solution satisfies the above range, manganese precipitation proceeds smoothly.

[0031] The manganese metal solution can be prepared by dissolving a manganese source material in a solvent such as water. The manganese source material can be manganese metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, such as, but not limited to, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, or a combination thereof.

[0032] On the other hand, the manganese metal solution may contain, as needed, M 1 It may further contain raw materials. 1 is one or more selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and M 1The raw materials contained are M 1 It can be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, or the like.

[0033] On the other hand, the ammonium cation complex-forming agent and the basic compound are as described above.

[0034] By the precipitation reaction, manganese hydroxide is precipitated on the surfaces of the hydroxide particles in which nickel and cobalt have been coprecipitated, and a precursor for a positive electrode active material having a two-layer structure in which manganese hydroxide is precipitated on nickel-cobalt hydroxide can be formed.

[0035] (II) Method: First, a nickel metal solution, an ammonium cation complexing agent, and a basic compound are added to carry out a precipitation reaction to form nickel hydroxide.

[0036] Here, the nickel precipitation reaction is preferably carried out under the condition that the pH of the reaction solution is 11.4 to 11.8. When the pH of the reaction solution is in this range, nickel precipitation can be carried out smoothly.

[0037] Meanwhile, the nickel metal solution can be prepared by dissolving a nickel source material in a solvent such as water. The nickel source material can be nickel acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, such as, but not limited to, NiO, NiCO3·2Ni(OH)2·4H2O, NiCO2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halides, or combinations thereof.

[0038] On the other hand, the nickel metal solution may be optionally 1 It may further contain raw materials. 1 is one or more selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and M1 The raw materials contained are M 1 It can be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, or the like.

[0039] On the other hand, the ammonium cation complex-forming agent and the basic compound are as described above.

[0040] Next, the addition of the nickel metal solution is stopped, and a cobalt metal solution, an ammonium cation complex-forming agent, and a basic compound are added to the reaction solution in which the nickel hydroxide has been formed, to carry out a precipitation reaction, thereby forming nickel-cobalt hydroxide particles in which cobalt hydroxide is precipitated on the nickel hydroxide.

[0041] The cobalt precipitation reaction is preferably carried out under conditions where the pH of the reaction solution is 11.0 to 11.4. When the pH of the reaction solution is in this range, cobalt precipitation can be carried out smoothly.

[0042] Meanwhile, the cobalt metal solution may be prepared by dissolving a cobalt source material in a solvent such as water. The cobalt source material may be acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of cobalt metal, such as, but not limited to, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0043] On the other hand, the cobalt metal solution may contain, as needed, M 1 It may further contain raw materials. 1 is one or more selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and M 1 The raw materials contained are M 1 It can be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, or the like.

[0044] On the other hand, the ammonium cation complex-forming agent and the basic compound are as described above.

[0045] Next, the addition of the cobalt metal solution is stopped, and a manganese metal solution, an ammonium cation complexing agent, and a basic compound are added to the reaction solution containing the nickel-cobalt hydroxide to carry out a precipitation reaction.

[0046] Here, the manganese precipitation reaction is preferably carried out under conditions where the pH of the reaction solution is 11.0 or less, preferably 10.0 to 11.0. When the pH of the reaction solution satisfies the above range, manganese precipitation proceeds smoothly.

[0047] The manganese metal solution can be prepared by dissolving a manganese source material in a solvent such as water. The manganese source material can be manganese metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, such as, but not limited to, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, or a combination thereof.

[0048] On the other hand, the manganese metal solution may contain, as needed, M 1 It may further contain raw materials. 1 is one or more selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and M 1 The raw materials contained are M 1 It can be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, or the like.

[0049] On the other hand, the ammonium cation complex-forming agent and the basic compound are as described above.

[0050] By the above method, a three-layered nickel-cobalt-manganese hydroxide can be prepared in which nickel hydroxide, cobalt hydroxide, and manganese hydroxide are precipitated in this order.

[0051] (III) Method: First, a nickel metal solution, an ammonium cation complexing agent, and a basic compound are added to carry out a precipitation reaction to form nickel hydroxide.

[0052] Here, the nickel precipitation reaction is preferably carried out under the condition that the pH of the reaction solution is 11.4 to 11.8. When the pH of the reaction solution is in this range, nickel precipitation can be carried out smoothly.

[0053] Meanwhile, the nickel metal solution can be prepared by dissolving a nickel source material in a solvent such as water. The nickel source material can be nickel acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, such as, but not limited to, NiO, NiCO3·2Ni(OH)2·4H2O, NiCO2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halides, or combinations thereof.

[0054] On the other hand, the nickel metal solution may be optionally 1 It may further contain raw materials. 1 is one or more selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and M 1 The raw materials contained are M 1 It can be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, or the like.

[0055] On the other hand, the ammonium cation complex-forming agent and the basic compound are as described above.

[0056] Next, the addition of the nickel metal solution is stopped, and a manganese metal solution, an ammonium cation complex-forming agent, and a basic compound are added to the reaction solution in which the nickel hydroxide has been formed, to carry out a precipitation reaction, thereby forming a nickel-manganese hydroxide in which manganese hydroxide is precipitated on the nickel hydroxide.

[0057] Here, the manganese precipitation reaction is preferably carried out under conditions where the pH of the reaction solution is 11.0 or less, preferably 10.0 to 11.0. When the pH of the reaction solution satisfies the above range, manganese precipitation proceeds smoothly.

[0058] The manganese metal solution can be prepared by dissolving a manganese source material in a solvent such as water. The manganese source material can be manganese metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, such as, but not limited to, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, or a combination thereof.

[0059] On the other hand, the manganese metal solution may contain, as needed, M 1 It may further contain raw materials. 1 is one or more selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and M 1 The raw materials contained are M 1 It can be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, or the like.

[0060] On the other hand, the ammonium cation complex-forming agent and the basic compound are as described above.

[0061] Next, the addition of the manganese metal solution is stopped, and a precipitation reaction is carried out while adding a cobalt metal solution, an ammonium cation complexing agent, and a basic compound to the reaction solution containing the nickel-manganese hydroxide.

[0062] The cobalt precipitation reaction is preferably carried out under conditions where the pH of the reaction solution is 11.0 to 11.4. When the pH of the reaction solution is in this range, cobalt precipitation can be carried out smoothly.

[0063] Meanwhile, the cobalt metal solution may be prepared by dissolving a cobalt source material in a solvent such as water. The cobalt source material may be acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of cobalt metal, such as, but not limited to, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0064] On the other hand, the cobalt metal solution may contain, as needed, M 1 It may further contain raw materials. 1 is one or more selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and M 1 The raw materials contained are M 1 It can be a metal acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide, or the like.

[0065] On the other hand, the ammonium cation complex-forming agent and the basic compound are as described above.

[0066] By using the method (I), (II), or (III), a precursor having a multilayer structure in which at least two metal elements selected from nickel, cobalt, and manganese are precipitated in different regions can be produced. When the precursor particles grow to a desired particle size, the reaction is terminated, and the precursor for the positive electrode active material is separated from the reaction solution, washed, and dried to obtain the precursor for the positive electrode active material.

[0067] (2) Lithium transition metal oxide production steps Next, the precursor for the positive electrode active material prepared by the above method is mixed with a lithium source material and then calcined to prepare a lithium transition metal oxide.

[0068] Examples of the lithium source material include lithium-containing carbonates (e.g., lithium carbonate, etc.), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide, etc.), nitrates (e.g., lithium nitrate (LiNO3), etc.), and chlorides (e.g., lithium chloride (LiCl)), and any of these may be used alone or in combination.

[0069] Meanwhile, the positive electrode active material precursor and the lithium source material may be mixed by solid-phase mixing, and the mixing ratio of the positive electrode active material precursor and the lithium source material may be determined so as to satisfy the atomic fraction of each component in the final positive electrode active material. For example, the positive electrode active material precursor and the lithium source material may be mixed in amounts such that the molar ratio of transition metal to Li is 1:0.8 to 1:1.2, preferably 1:0.85 to 1:1.15, and more preferably 1:0.9 to 1:1.1. When the precursor and the lithium source material are mixed in this range, a positive electrode active material exhibiting excellent capacity characteristics can be produced.

[0070] If necessary, a doping element M 1 The doping element M may be further mixed. 1 can be, for example, one or more selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and the doping element M 1 The raw material contains the doping element M 1 The compound may be at least one selected from the group consisting of acetates, sulfates, sulfides, hydroxides, oxides, and oxyhydroxides, including

[0071] The firing may be carried out at a temperature of 600 to 1000°C, preferably 700 to 900°C, and the firing time may be 5 to 30 hours, preferably 8 to 15 hours, but is not limited thereto.

[0072] positive electrode active material Next, the positive electrode active material according to the present invention will be described.

[0073] The cathode active material according to the present invention includes lithium transition metal oxide particles having a (003) d-spacing at the particle surface that is larger than the (003) d-spacing in the particle interior, where the "interior" refers to a region at a distance of 500 nm or more from the surface of the cathode active material particle, and the "surface" refers to a region at a distance of 500 nm or less from the surface of the cathode active material particle.

[0074] The lithium transition metal oxide particles may have a composition represented by the following Chemical Formula 1, for example.

[0075] [Chemical formula 1] Li a [Ni x Co y Mn z M 1 w ]O2

[0076] Said M 1 is at least one selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and preferably at least one selected from the group consisting of Al, Zr, B and W. 1 When the element is further contained, the effect of improving the capacity characteristics, life characteristics, etc. of the positive electrode active material can be obtained.

[0077] The a represents the molar ratio of lithium in the lithium transition metal oxide and may be 0.8≦a≦1.2, 0.85≦a≦1.15, or 0.9≦a≦1.1. When the molar ratio of lithium in the lithium transition metal oxide satisfies this range, a layered crystal structure is well developed, resulting in a positive electrode active material with excellent electrochemical properties.

[0078] The x represents the molar ratio of nickel among metal components other than lithium in the lithium transition metal oxide, and may be 0.6≦x<1, 0.8≦x<1, or 0.85≦x<1. When the molar ratio of nickel satisfies this range, high capacity characteristics can be achieved.

[0079] The y represents the molar ratio of cobalt among the metal components other than lithium in the lithium transition metal oxide, and is 0 <y<0.4、0<y<0.2または0<y<0.15であることができる。

[0080] The z represents the molar ratio of manganese among the metal components other than lithium in the lithium transition metal oxide, and is 0 <z<0.4、0<z<0.2または0<z<0.15であることができる。

[0081] The w is M among the metal components other than lithium in the lithium transition metal oxide. 1 It represents the molar ratio of the elements and can be 0≦w≦0.1, 0≦w≦0.05, or 0≦w≦0.02.

[0082] The lithium transition metal oxide has a (003) d-spacing (distance between planes) at the surface of the particle that is larger than the (003) d-spacing (distance between planes) inside the particle. As the distance between the (003) planes at the surface of the particle increases, the thickness of the Li layer increases, thereby improving lithium mobility.

[0083] The difference between the (003) d-spacing on the surface of the lithium transition metal oxide particles and the (003) d-spacing inside the particles can be 0.005 nm or more, preferably 0.005 nm to 0.02 nm, and more preferably 0.005 nm to 0.015 nm. When the difference between the (003) d-spacing on the surface of the particles and the inside of the particles satisfies this range, excellent capacity characteristics and high-rate characteristics can be improved.

[0084] Specifically, the (003) d-spacing on the surface of the lithium transition metal oxide particles can be 0.46 nm to 0.50 nm, preferably 0.465 nm to 0.50 nm, and more preferably 0.465 nm to 0.490 nm.

[0085] The (003) d-spacing inside the lithium transition metal oxide particles can be 0.45 nm to 0.50 nm, preferably 0.45 nm to 0.49 nm, and more preferably 0.46 nm to 0.485 nm.

[0086] positive electrode Next, the positive electrode according to the present invention will be described.

[0087] The positive electrode according to the present invention includes the positive electrode active material of the present invention. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material of the present invention.

[0088] Since the positive electrode active material has been described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0089] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to the positive electrode active material layer and is non-reactive within the battery voltage range. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0090] The positive electrode active material layer may optionally contain a conductive material and a binder in addition to the positive electrode active material, as required.

[0091] The positive electrode active material may be contained in an amount of 80 to 99 wt %, more specifically 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when contained in this range.

[0092] The conductive material is used to impart conductivity to the electrode. Any material that does not cause chemical changes in the resulting battery and has electronic conductivity can be used without particular limitations. 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 fibers, such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0093] The binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof. These may be used alone or in combination. The binder may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0094] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode can be manufactured by applying a positive electrode mixture, which is manufactured by dissolving or dispersing the positive electrode active material and, if necessary, a binder, a conductive material, and a dispersant in a solvent, onto a positive electrode current collector, followed by drying and rolling, or by casting the positive electrode mixture onto a separate support, peeling it from the support, and laminating the resulting film onto a positive electrode current collector.

[0095] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for manufacturing a positive electrode.

[0096] Lithium secondary battery Next, the lithium secondary battery according to the present invention will be described.

[0097] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is as described above, detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0098] The lithium secondary battery may further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0099] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0100] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector can be formed with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0101] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0102] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. β Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. These may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. The negative electrode active material may be present in an amount of 80 wt % to 99 wt % of the total weight of the negative electrode active material layer.

[0103] The binder is a component that facilitates bonding between the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0104] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 10 wt % or less, specifically 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0105] The negative electrode active material layer can be produced by coating a negative electrode composite, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, on a negative electrode current collector and drying the coating. Alternatively, the negative electrode composite can be produced by casting the negative electrode composite on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0106] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to ion movement in the electrolyte and excellent humidification ability for the electrolyte solution is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be selectively used in a single-layer or multi-layer structure.

[0107] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0108] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0109] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0110] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the anion of the lithium salt can be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 4.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0111] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0112] As described above, the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0113] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0114] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and an electric vehicle (PHEV), including a plug-in hybrid electric vehicle; or a power storage system.

[0115] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0116] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also as a unit battery in a medium- to large-sized battery module including a large number of battery cells.

[0117] Examples of the medium to large size devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0118] The present invention will now be described in more detail with reference to specific examples.

[0119] Example 1 A 2.4M solution of the first metal was prepared by adding NiSO4 and CoSO4 to distilled water in amounts that would result in a Ni:Co molar ratio of 95:5. A 2.4M solution of the second metal was prepared by adding MnSO4 to distilled water. In addition, an 8.0M NaOH solution and a 5.1M NH4OH solution were prepared.

[0120] After 13 L of deionized water, 0.013 L of the aqueous NaOH solution, and 0.64 L of the aqueous NH4OH solution were charged into the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor.

[0121] The first metal solution was then added to the reactor at a rate of 3.8 L / hr, the NaOH aqueous solution at 2.3 L / hr, and the NH4OH aqueous solution at 0.54 L / hr, and a precipitation reaction was carried out for 10 minutes at pH 11.9 to form nickel-cobalt hydroxide particle nuclei. Next, the stirring speed was gradually decreased, and NaOH was added using a pH sensor to adjust the pH of the reaction solution to 11.2-11.6. After that, the first metal solution was added at a rate of 3.8 L / hr, the NaOH aqueous solution at 2.3 L / hr, and the NH4OH aqueous solution at 0.54 L / hr, and a co-precipitation reaction was carried out for 48 hours to produce nickel-cobalt hydroxide particles.

[0122] Next, the addition of the first metal solution was stopped, and NaOH was added using a pH sensor to adjust the pH of the reaction solution to 10.7-11.2. The second metal solution was then added at a rate of 3.8 L / hr, the NaOH aqueous solution at 2.3 L / hr, and the NH4OH aqueous solution at 0.54 L / hr, while stirring and allowing the precipitation reaction to proceed for 4 hours. This produced a cathode active material precursor in which manganese hydroxide precipitated on the surfaces of nickel-cobalt hydroxide particles. The molar ratio of Ni:Co:Mn in the entire cathode active material precursor particles was 88:5:7.

[0123] The cathode active material precursor, LiOH·H2O, and Al(OH)3 prepared as above were mixed so that the molar ratio of Ni+Co+Mn:Li:Al was 0.98:1.05:0.02, and then calcined at 765°C for 13 hours to prepare the cathode active material. The molar ratio of Ni:Co:Mn:Al in the prepared cathode active material was 86:5:7:2.

[0124] Example 2 A first metal solution with a concentration of 2.4 M was prepared by adding NiSO4 to distilled water. A second metal solution with a concentration of 2.4 M was prepared by adding CoSO4 to distilled water. A third metal solution with a concentration of 2.4 M was prepared by adding MnSO4 to distilled water.

[0125] After adding deionized water to the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. An 8.0 M NaOH solution and a 5.1 M NH4OH solution were added to the reactor to prepare a reaction mother liquor with a pH of 12.

[0126] Thereafter, the first metal solution was added to the reactor at a rate of 3.8 L / hr, the NaOH aqueous solution at 2.3 L / hr, and the NH4OH aqueous solution at 0.54 L / hr, and the precipitation reaction was carried out for 42.2 hours, while maintaining the pH of the reaction solution at 11.6.

[0127] Next, the addition of the first metal solution was stopped, and NaOH was added using a pH sensor to adjust the pH of the reaction solution to 11.4. Then, the second metal solution was added at a rate of 3.8 L / hr, the NaOH aqueous solution at 2.3 L / hr, and the NH4OH aqueous solution at 0.54 L / hr, and the precipitation reaction was carried out for 2.4 hours.

[0128] The addition of the second metal solution was then stopped, and NaOH was added using a pH sensor to adjust the pH of the reaction solution to a range of 10.8-11.0. The third metal solution was then added at a rate of 3.8 L / hr, followed by an aqueous NaOH solution at 2.3 L / hr and an aqueous NH4OH solution at 0.54 L / hr. The precipitation reaction was carried out for 3.4 hours to produce a cathode active material precursor. The molar ratio of Ni:Co:Mn in the entire cathode active material precursor particles was 88:5:7.

[0129] The cathode active material precursor, LiOH·H2O, and Al(OH)3 prepared as above were mixed so that the molar ratio of Ni+Co+Mn:Li:Al was 0.98:1.05:0.02, and the mixture was calcined at 765°C for 13 hours to prepare the cathode active material. The molar ratio of Ni:Co:Mn:Al in the prepared cathode active material was 86:5:7:2.

[0130] Example 3 A first metal solution with a concentration of 2.4 M was prepared by adding NiSO4 to distilled water. A second metal solution with a concentration of 2.4 M was prepared by adding MnSO4 to distilled water. A third metal solution with a concentration of 2.4 M was prepared by adding CoSO4 to distilled water.

[0131] After adding deionized water to the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. An 8.0 M NaOH solution and a 5.1 M NH4OH solution were added to the reactor to prepare a reaction mother liquor with a pH of 12.

[0132] Thereafter, the first metal solution was added to the reactor at a rate of 3.8 L / hr, the NaOH aqueous solution at 2.3 L / hr, and the NH4OH aqueous solution at 0.54 L / hr, and the precipitation reaction was carried out for 42.2 hours, while maintaining the pH of the reaction solution at 11.6.

[0133] Next, the addition of the first metal solution was stopped, and NaOH was added using a pH sensor to adjust the pH of the reaction solution to 10.8-11.0. Then, the second metal solution was added at a rate of 3.8 L / hr, NaOH aqueous solution at 2.3 L / hr, and NH4OH aqueous solution at 0.54 L / hr, and the precipitation reaction was carried out for 3.4 hours.

[0134] The addition of the second metal solution was then stopped, and the pH of the reaction solution was adjusted to 11.4 by adding NaOH via a pH sensor. The third metal solution was then added at a rate of 3.8 L / hr, followed by an aqueous NaOH solution at 2.3 L / hr and an aqueous NH4OH solution at 0.54 L / hr, and a precipitation reaction was carried out for 2.4 hours to produce a cathode active material precursor. The molar ratio of Ni:Co:Mn in the entire cathode active material precursor particles was 88:5:7.

[0135] The cathode active material precursor, LiOH·H2O, and Al(OH)3 prepared as above were mixed so that the molar ratio of Ni+Co+Mn:Li:Al was 0.98:1.05:0.02, and the mixture was calcined at 765°C for 13 hours to prepare the cathode active material. The molar ratio of Ni:Co:Mn:Al in the prepared cathode active material was 86:5:7:2.

[0136] Comparative Example 1 NiSO4, CoSO4, and MnSO4 were mixed in distilled water in amounts such that the nickel:cobalt:manganese molar ratio was 88:5:7 to prepare a metal solution with a concentration of 2.4 M.

[0137] After adding deionized water to the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. An 8.0 M NaOH solution and a 5.1 M NH4OH solution were added to the reactor to prepare a reaction mother liquor.

[0138] The metal solution was then added to the reactor at a rate of 3.8 L / hr, an aqueous NaOH solution at 2.3 L / hr, and an aqueous NH4OH solution at 0.54 L / hr, and the pH of the reaction solution was maintained at 11.2 to 11.9 while a coprecipitation reaction was carried out for 48 hours to produce a cathode active material precursor. The molar ratio of Ni:Co:Mn in the entire cathode active material precursor particles was 88:5:7.

[0139] The cathode active material precursor, LiOH·H2O, and Al(OH)3 prepared as above were mixed so that the molar ratio of Ni+Co+Mn:Li:Al was 0.98:1.05:0.02, and the mixture was calcined at 765°C for 13 hours to prepare the cathode active material. The molar ratio of Ni:Co:Mn:Al in the prepared cathode active material was 86:5:7:2.

[0140] Experimental Example 1 The cathode active materials prepared in Examples 1 to 3 and Comparative Example 1 were coated with carbon or platinum and then irradiated with an ion beam using a focused ion beam (FIB) device (Helios NanoLab 450, FEI) to prepare thin film samples (approximately 100 nm thick) that allowed for particle cross-section observation. The thin film samples were placed on a transmission electron microscope (TEM) grid, and HR-TEM images of the thin film samples were obtained using a high-resolution transmission electron microscopy (HR-TEM) device. The HR-TEM images were converted into diffraction patterns using Gatan software (Digital Micrograph). The inter-point distances of 5 to 10 points in the diffraction pattern were then measured, and the average of these inter-point distances was calculated. The reciprocal of this average was used to calculate the (003) d-spacing. The measurement results are shown in Table 1 below.

[0141] [Table 1] [Table 1]

[0142] As shown in Table 1, in the case of the cathode active materials prepared in Examples 1 to 3, the (003) d-spacing on the particle surface was larger than the (003) d-spacing inside the particle by 0.005 nm or more, whereas in the cathode active material of Comparative Example 1 prepared by the conventional method, the (003) d-spacing on the particle surface was at the same level as that inside the particle.

[0143] Experimental Example 2 The positive electrode active materials prepared in Examples 1 to 3 and Comparative Example 1, the conductive material (carbon black), and the binder (PVdF) were mixed in a weight ratio of 97.5:1:1.5 in N-methyl-2-pyrrolidone (NMP) solvent to prepare positive electrode slurries. The positive electrode slurries were applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare positive electrodes.

[0144] A separator was interposed between each of the positive and negative electrodes to prepare an electrode assembly, which was then placed inside a battery case. An electrolyte solution was then injected into the battery case to prepare a 2032-type coin cell lithium secondary battery.

[0145] Here, a lithium metal disk was used as the negative electrode, and the electrolyte was prepared by dissolving 1M LiPF6 in an organic solvent made by mixing ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3:3:4.

[0146] Each of the lithium secondary batteries prepared as described above was charged in CC / CV mode (CV 0.05C) at 25°C with a constant current of 0.1C up to 4.25V, and then discharged in CC mode down to 3V to measure the initial charge capacity and discharge capacity. The measurement results are shown in Table 2 below.

[0147] [Table 2] [Table 2]

[0148] From Table 2, it can be seen that the lithium secondary batteries employing the cathode active materials of Examples 1 to 3, in which the (003) d-spacing on the surface of the particles is larger than the (003) d-spacing inside the particles, have superior capacity characteristics compared to the lithium secondary battery employing the cathode active material of Comparative Example 1.

[0149] Experimental Example 3 The lithium secondary batteries prepared in Experimental Example 2 were each discharged at discharge currents of 0.33 C, 0.5 C, and 2 C, and then the discharge capacity was measured. The measurement results are shown in Table 3.

[0150] [Table 3] [Table 3]

[0151] As shown in Table 3, the lithium secondary batteries employing the cathode active materials of Examples 1 to 3, in which the (003) d-spacing on the particle surface is larger than the (003) d-spacing inside the particle, maintained higher capacities during high-rate discharge than the lithium secondary battery employing the cathode active material of Comparative Example 1.

Claims

1. The lithium transition metal oxide particles have a composition represented by the following chemical formula 1: the (003) d-spacing at the surface of the lithium transition metal oxide particles is larger than the (003) d-spacing in the interior of the particles; the (003) d-spacing on the surface of the lithium transition metal oxide particles is 0.46 nm to 0.50 nm; the (003) d-spacing within the lithium transition metal oxide particles is 0.45 nm to 0.49 nm; The positive electrode active material has a difference between the (003) d-spacing on the surface of the lithium transition metal oxide particle and the (003) d-spacing inside the particle of 0.005 nm to 0.010 nm. [Chemical formula 1] Li ａ [Ni ｘ Co ｙ Mn ｚ M １ ｗ ]O ２ In the above Chemical Formula 1, 0.8≦a≦1.2, 0.6≦x<1, 0<y<0.4, 0<z<0.4, 0≦w≦0.1, M １ is one or more elements selected from the group consisting of Al, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S.

2. The positive electrode active material according to claim 1 , wherein in the formula (1), 0.8≦x<1, 0<y<0.2, and 0<z<0.

2.

3. preparing a multi-layered precursor for a positive electrode active material in which two or more elements selected from nickel, cobalt, and manganese are precipitated in different regions; The method for producing a positive electrode active material according to claim 1 , further comprising the step of mixing the positive electrode active material precursor and a lithium source material and then calcining the mixture.

4. The step of preparing the positive electrode active material precursor includes a step of conducting a coprecipitation reaction by adding a nickel-cobalt metal solution, an ammonium cation complexing agent, and a basic compound to form hydroxide particles in which nickel and cobalt are coprecipitated; and carrying out a precipitation reaction by adding a manganese metal solution, an ammonium cation complex-forming agent, and a basic compound to a reaction solution containing the nickel and cobalt coprecipitated hydroxide particles, thereby precipitating manganese hydroxide on the nickel and cobalt coprecipitated hydroxide particles.

5. The step of preparing a precursor for a positive electrode active material includes: conducting a precipitation reaction while introducing a nickel metal solution, an ammonium cation complexing agent, and a basic compound to form nickel hydroxide; a step of carrying out a precipitation reaction while adding a cobalt metal solution, an ammonium cation complex-forming agent, and a basic compound to the reaction solution containing the nickel hydroxide to form a nickel-cobalt hydroxide in which cobalt hydroxide is precipitated on the nickel hydroxide; and conducting a precipitation reaction while adding a manganese metal solution, an ammonium cation complex-forming agent, and a basic compound to the reaction solution containing the nickel-cobalt hydroxide, thereby forming nickel-cobalt-manganese hydroxide particles in which nickel hydroxide, cobalt hydroxide, and manganese hydroxide are precipitated in this order.

6. The step of preparing a precursor for a positive electrode active material includes: conducting a precipitation reaction while introducing a nickel metal solution, an ammonium cation complexing agent, and a basic compound to form nickel hydroxide; a manganese metal solution, an ammonium cation complex-forming agent, and a basic compound are added to the reaction solution containing the nickel hydroxide to cause a precipitation reaction, thereby forming a nickel-manganese hydroxide in which manganese hydroxide is precipitated on the nickel hydroxide; and conducting a precipitation reaction while adding a cobalt metal solution, an ammonium cation complex-forming agent, and a basic compound to the reaction solution containing the nickel-manganese hydroxide, thereby forming nickel-manganese-cobalt hydroxide particles in which nickel hydroxide, manganese hydroxide, and cobalt hydroxide are precipitated in this order.

7. A positive electrode comprising the positive electrode active material according to claim 1 or 2.

8. A lithium secondary battery comprising the positive electrode according to claim 7.

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