Positive electrode active material precursor, method for producing the same, and method for producing positive electrode active material using the same

Abstract

The present invention relates to a cathode active material precursor that can realize a cathode active material in a single particle form even when heat-treated at a low temperature. Specifically, the present invention relates to a cathode active material precursor that has a composition represented by Chemical Formula 1 described in the present specification and contains a composite transition metal in a single particle form, a method for producing the same, and a method for producing a cathode active material using the same.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2020-00165676, filed December 1, 2020, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material precursor, a method for producing the same, and a method for producing a positive electrode active material using the same. [Background technology]

[0003] Recently, with the technological development and increasing demand for mobile devices and electric vehicles, the demand for secondary batteries as energy sources has been rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Lithium transition metal oxides such as lithium cobalt oxides (LiCoO2), lithium nickel oxides (LiNiO2), lithium manganese oxides (LiMnO2 or LiMn2O4), and lithium iron phosphate oxides (LiFePO4) have been developed as positive electrode active materials for lithium secondary batteries. a Co b Mn c ]O2, Li[Ni a Co b Al c ]O2, Li[Ni a Co b Mn c Al d Lithium composite transition metal oxides containing two or more transition metals, such as ]O2, have been developed and are widely used.

[0005] Lithium transition metal oxides developed to date are generally prepared by co-precipitation of ammonia water as a chelating agent and aqueous sodium hydroxide solution as a basic solution into a solvent containing a mixture of transition metal-containing raw materials, such as nickel sulfate, cobalt sulfate, and manganese sulfate, followed by mixing the lithium transition metal hydroxide with a lithium-containing raw material and optionally a doping raw material, followed by high-temperature heat treatment.

[0006] As described above, when producing a lithium transition metal hydroxide, a lithium transition metal hydroxide having the form of spherical secondary particles formed by aggregation of primary particles of several nm to several tens of nm is formed as a positive electrode active material precursor. In order to produce a positive electrode active material in the form of a single particle using this, a high-temperature heat treatment of 900°C or higher is required.

[0007] However, when high-temperature heat treatment above 900°C is performed to produce a single-particle cathode active material, a phase change occurs in the rock salt structure of the NiO phase, resulting in problems such as a decrease in the capacity and life characteristics of batteries containing the cathode active material and an increase in the rate of increase in resistance.On the other hand, when heat treatment is performed below 900°C, the material exists in the form of over-baked secondary particles, resulting in problems such as less improvement in life and gas generation than expected with single particles.

[0008] Therefore, research is being conducted to develop a positive electrode active material precursor that does not require high-temperature heat treatment at 900° C. or higher even when manufacturing a single particle positive electrode active material. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a cathode active material precursor containing a composite transition metal in a single particle form, which can realize a cathode active material in a single particle form even when heat-treated at a low temperature.

[0010] Another object of the present invention is to provide a method for producing the positive electrode active material precursor.

[0011] Another object of the present invention is to provide a method for producing a positive electrode active material, which can obtain a positive electrode active material in the form of a single particle even when heat-treated at a low temperature by using the positive electrode active material precursor during production of the positive electrode active material. [Means for solving the problem]

[0012] The present invention provides a positive electrode active material precursor having a composition represented by the following Chemical Formula 1 and containing a composite transition metal in the form of a single particle. [Chemical formula 1] Ni a M 1 b Mn c M 2 d In the above Chemical Formula 1, M 1 is one or more selected from Co and Al, M 2 is one or more selected from Nb, Ti, Mg, Ta, Zr, W and Sc, 0.6≦a<1, 0 <b≦0.4、0≦c≦0.4、0≦d≦0.2である。

[0013] The present invention also provides a method for preparing a reaction solution by (A) dissolving a transition metal (M) source material in a reaction solvent, and (B) adding a ligand (L) that forms a complex compound with the transition metal to the reaction solution to form a complex compound (ML). x , 1≦x≦6), and (C) adding a basic aqueous solution to a solution containing the complex compound to form a composite transition metal in the form of a single particle, wherein the transition metal (M) source material is a nickel-containing source material and M 1 The present invention provides a method for producing a cathode active material precursor containing a raw material containing at least one element selected from Co and Al.

[0014] The present invention also provides a method for producing a cathode active material, comprising the steps of mixing a cathode active material precursor according to the present invention with a lithium-containing raw material, and then heat-treating the mixture at 700°C to 820°C to obtain a lithium transition metal oxide in the form of a single particle. [Effects of the Invention]

[0015] Since the cathode active material precursor according to the present invention contains a composite transition metal in a single particle form, a cathode active material in a single particle form can be obtained even if the cathode active material precursor is heat-treated at a low temperature during production of the cathode active material.

[0016] According to the method for preparing a positive electrode active material precursor according to the present invention, a positive electrode active material precursor containing a composite transition metal in the form of a single particle can be prepared in a simple manner.

[0017] The cathode active material manufactured by the manufacturing method of the cathode active material according to the present invention can realize excellent capacity characteristics, life characteristics, resistance characteristics, and a significant reduction in gas generation when applied to a secondary battery. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows SEM images of a positive electrode active material precursor and a positive electrode active material of Example 1. [Figure 2] 1 shows SEM images of a positive electrode active material precursor and a positive electrode active material of Example 2. [Figure 3] 10 is an SEM image of a positive electrode active material precursor and a positive electrode active material of Example 3. [Figure 4] 1 shows SEM images of a positive electrode active material precursor and a positive electrode active material of Comparative Example 1. [Figure 5] 10 is an SEM image of a positive electrode active material precursor and a positive electrode active material of Comparative Example 2. [Figure 6] 1 shows XRD data of a positive electrode active material precursor according to the temperature during heat treatment in Example 1. [Figure 7] 1 shows XRD data of the positive electrode active material precursor of Example 1. [Figure 8]1 is a graph showing the volume change rates of batteries using the positive electrode active materials produced in Example 2 and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0019] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0020] In this specification, the terms "comprises," "includes," "has," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but are not intended to preclude the possible presence or addition of one or more different features, numbers, steps, components, or combinations thereof.

[0021] In this specification, D 50 and can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (graph curve of particle size distribution degree). 50 can be measured using, for example, a laser diffraction method, which generally allows measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0022] In this specification, the term "on" refers not only to a case where one structure is formed immediately on top of another structure, but also to a case where a third structure is interposed between the structures.

[0023] In this specification, the term "single particle form" refers to a concept that contrasts with the spherical secondary particle form formed by the aggregation of tens to hundreds of primary particles produced by conventional methods, and includes a form in which particles are separated and / or dispersed to form independent and / or distinct phases, or a form in which 2 to 10 particles are attached to each other.

[0024] Positive electrode active material precursor The cathode active material precursor according to the present invention includes a composite transition metal in a single particle form having a composition represented by the following Chemical Formula 1. According to the present invention, the cathode active material precursor may be the composite transition metal itself in a single particle form having a composition represented by the following Chemical Formula 1. Meanwhile, the cathode active material precursor may be a composite transition metal in a single particle form having a composition represented by the following Chemical Formula 1, the surface of which has been surface-modified into an oxide, hydrate, or the like by reacting with oxygen or moisture in the air.

[0025] [Chemical formula 1] Ni a M 1 b Mn c M 2 d

[0026] In the above Chemical Formula 1, M 1 is one or more selected from Co and Al, M 2 is one or more selected from Nb, Ti, Mg, Ta, Zr, W and Sc, 0.6≦a<1, 0 <b≦0.4、0≦c≦0.4、0≦d≦0.2である。

[0027] The present inventors have conducted extensive research to develop a positive electrode active material that can achieve excellent life characteristics and resistance characteristics. As a result, they have found that when a positive electrode active material precursor containing a composite transition metal in a single particle form is used as the positive electrode active material precursor, the capacity characteristics, life characteristics, resistance characteristics, and high-temperature storage characteristics of a secondary battery containing the positive electrode active material produced using this can be improved, and have completed the present invention.

[0028] First, when using a cathode active material precursor having the form of secondary particles formed by aggregation of existing primary particles, a high-temperature heat treatment of 900°C or higher is required to produce a cathode active material in the form of a single particle, whereas when using a cathode active material precursor in the form of a single particle as in the present invention, a cathode active material in the form of a single particle can be produced even by heat treatment at less than 900°C. Therefore, phase transformation of the NiO phase to a rock salt structure, which can occur when undergoing high-temperature heat treatment at 900°C or higher, does not occur, and as a result, a cathode active material with excellent performance can be produced.

[0029] Furthermore, since the positive electrode active material precursor according to the present invention is an isotropic transition metal rather than an anisotropic transition metal hydroxide, the particles grow uniformly regardless of the growth direction and are more likely to be formed into single particles than hydroxide precursors.

[0030] The a represents the atomic fraction of nickel among the metal elements in the precursor, and may be 0.6≦a<1, 0.6≦a≦0.98, or 0.7≦a≦0.95.

[0031] The b is M among the metal elements in the precursor. 1 means the atomic fraction of 0 <b≦0.4、0.01≦b≦0.4または0.01≦b≦0.3であることができる。

[0032] The c represents the atomic fraction of manganese among the metal elements in the precursor, and may be 0≦c≦0.4, 0.01≦c≦0.4, or 0.01≦c≦0.3.

[0033] The d is the number of metal elements in the precursor, M 2 means the atomic fraction of an element and can be 0≦d≦0.2, 0≦d≦0.1, or 0≦d≦0.05.

[0034] According to the present invention, the positive electrode active material precursor may contain nickel and cobalt in order to improve the resistance characteristics of a battery, and may have a composition represented by the following Chemical Formula 1-1:

[0035] [Chemical formula 1-1] Ni a Co x Al y Mn c M 2 d

[0036] In the above chemical formula 1-1, M 2 is one or more selected from Nb, Ti, Mg, Ta, Zr, W and Sc, 0.6≦a<1, 0 <x≦0.4、0≦y≦0.4、0≦c≦0.4、0≦d≦0.2である。

[0037] According to the present invention, the positive electrode active material precursor has an average particle size (D 50 ) can be 0.1 μm to 10 μm, specifically 0.5 μm to 5 μm, and more specifically 0.5 μm to 3 μm. When the average particle size of the positive electrode active material precursor is within the above range, the number of lithium paths in contact with the electrolyte increases, resulting in an increase in reversibly usable lithium ions, and thus high capacity and output characteristics can be exhibited.

[0038] According to the present invention, the positive electrode active material precursor may have a face-centered cubic crystalline structure. When the positive electrode active material precursor has a face-centered cubic crystalline structure, a large amount of positive electrode active material can be produced from a precursor with a small volume and weight due to the close-packed face-centered cubic structure, thereby improving processability.

[0039] Method for producing a positive electrode active material precursor The method for producing a cathode active material precursor according to the present invention includes the steps of: (A) dissolving a surface stabilizer and a transition metal (M) raw material in a reaction solvent to prepare a reaction solution; (B) adding a ligand (L) that forms a complex compound with the transition metal to the reaction solution to prepare a complex compound (ML) x, 1≦x≦6), and (C) adding a basic aqueous solution to the solution containing the complex compound to form a composite transition metal in the form of a single particle, wherein the transition metal (M) source material is a nickel-containing source material and M 1 (One or more selected from Co and Al)-containing raw material.

[0040] The cathode active material precursor prepared by the method for preparing a cathode active material precursor may be the cathode active material precursor according to the present invention. Specifically, it may include a composite transition metal in a single particle form having a composition represented by Chemical Formula 1. According to the present invention, the cathode active material precursor may be a composite transition metal in a single particle form having a composition represented by Chemical Formula 1 below, but the surface may be modified to an oxide, hydrate, or the like by reacting with oxygen or moisture in the air.

[0041] Each step of the method for producing a positive electrode active material precursor will be specifically described below.

[0042] (A) Step The step (A) is a step of preparing a reaction solution by dissolving a transition metal (M) source material in a reaction solvent. The transition metal (M) source material includes a nickel-containing source material and M 1 The transition metal (M) source material includes a source material containing at least one metal selected from Co and Al. 2 It may further contain a raw material containing one or more elements selected from Nb, Ti, Mg, Ta, Zr, W, and Sc.

[0043] The reaction solution may further include a surface stabilizer. The surface stabilizer may prevent aggregation of transition metal ions or transition metal particles contained in the transition metal source material. Furthermore, the surface stabilizer may stabilize the surface of the cathode active material precursor to be produced, thereby preventing excessive aggregation between precursor particles due to soft magnetic properties. Furthermore, when calcined to produce the cathode active material, the surface stabilizer may prevent aggregation between active material particles, which may occur due to high surface energy caused by small particle diameters.

[0044] The reaction solvent may be deionized water, distilled water, industrial water, general water, etc. Specifically, the reaction solvent may be deionized water or distilled water. In this case, the content of impurities may be low, and as a result, the purity of the cathode active material precursor produced may be high.

[0045] According to the present invention, the surface stabilizer can include one or more selected from a compound containing a citrate, a compound containing a dodecyl sulfate salt, and a compound containing polyvinylpyrrolidone. Specifically, the surface stabilizer can be a compound containing a citrate, and the citrate-containing compound can include one or more selected from sodium citrate, potassium citrate, and triethyl citrate. Specifically, the citrate-containing compound can be sodium citrate or potassium citrate. In this case, the particle surface can be stabilized to suppress aggregation between particles, resulting in a uniform particle size distribution.

[0046] The surface stabilizer may be added in an amount of 100 mol % to 200 mol % based on the total number of moles of transition metal ions contained in the transition metal source material.

[0047] The transition metal (M) source material is a nickel-containing source material and M 1 The material necessarily contains a (one or more selected from Co and Al)-containing source material, and may optionally further contain a cobalt-containing source material, a niobium-containing source material, a titanium-containing source material, a magnesium-containing source material, a tantalum-containing source material, a zirconium-containing source material, a tungsten-containing source material, a scandium-containing source material, or a combination thereof.

[0048] The nickel-containing source material may be a nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, fatty acid nickel salts, nickel halides (specifically, NiCl2), or combinations thereof.

[0049] The manganese-containing source material may be a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, MnCl, MnO, MnO, MnCO, Mn(NO), MnSO, ​​manganese acetate, manganese dicarboxylate, manganese citrate, manganese fatty acid salt, manganese oxyhydroxide, manganese chloride, or a combination thereof.

[0050] The aluminum-containing source material may be an aluminum-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, AlCl, AlO, aluminum hydroxide, aluminum sulfate, aluminum nitrate, aluminum acetate, or a combination thereof.

[0051] The cobalt-containing source material may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, CoCl2, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or a combination thereof.

[0052] M 2 (One or more selected from Nb, Ti, Mg, Ta, Zr, W and Sc)-containing raw material is M2 The oxide may be, but is not limited to, an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide containing one or more of Nb, Ti, Mg, Ta, Zr, W, and Sc.

[0053] (B) Step The step (B) is a step of adding a ligand (L) that forms a complex compound with a transition metal to the reaction solution to form a complex compound (ML x , 1≦x≦6).

[0054] According to the present invention, the ligand may include one or more selected from hydrazine, sodium borohydride, lithium aluminum hydride, oxalic acid, formic acid, ascorbic acid, and hydrogen peroxide. Specifically, the ligand may be hydrazine or lithium aluminum hydride. In this case, since the ligand is a strong reducing agent as well as a ligand, it may be advantageous for producing a uniform transition metal precursor.

[0055] The complex compound can be Ni(N2H4)2, Ni(N2H4)3, Co(N2H4)2, Co(N2H4)3, Mn(N2H4)2, Mn(N2H4)3, Al(N2H4)2, Al(N2H4)3, etc.

[0056] According to the present invention, the ligand may be added in an amount such that the molar ratio of the transition metal to the ligand contained in the reaction solution is 1:2 to 1:12. The ligand may be added in an amount such that the molar ratio of the transition metal to the ligand contained in the reaction solution is specifically 1:2 to 1:8, more specifically 1:2 to 1:6. This has an advantageous effect in producing a uniform transition metal precursor in terms of particle size and composition.

[0057] According to the present invention, step (B) may be carried out at a temperature of 25° C. to 80° C., specifically 40° C. to 60° C., and more specifically 50° C. to 60° C. When step (B) is carried out within this range, the viscosity of the solution and the reaction rate can be controlled to synthesize particles of uniform composition and size, and unnecessary side reactions can be suppressed.

[0058] (C) Step The step (C) is a step of adding a basic aqueous solution to a solution containing the complex compound to form a composite transition metal in the form of a single particle.

[0059] When a basic aqueous solution is added to a solution containing the complex compound, a transition metal hydroxide is first formed, and then the transition metal is produced by reducing the transition metal hydroxide.

[0060] For example, when the complex compound is Ni(N2H4)2 and the basic aqueous solution contains NaOH, the following reaction occurs:

[0061] [Reaction Scheme 1] Ni(N2H4)2+2NaOH→Ni(OH)2+2N2H4+2Na +

[0062] [Reaction Scheme 2] 2Ni(OH)2+N2H4→2Ni+N2(g)+4H2O

[0063] According to the present invention, the basic aqueous solution may be added in an amount such that the molar ratio of the transition metal to the basic aqueous solution contained in the reaction solution is 1:2 to 1:12. The basic aqueous solution may be added in an amount such that the molar ratio of the transition metal to the basic aqueous solution contained in the reaction solution is specifically 1:2 to 1:10, 1:2 to 1:8, or more specifically 1:2 to 1:6. In this case, a uniform size distribution can be achieved, the hydroxide ratio can be suppressed, and a pure transition metal precursor can be produced. Furthermore, the number of crystal grains and defects within the particles can be reduced.

[0064] Method for producing positive electrode active material The method for producing the cathode active material according to the present invention includes the steps of mixing the cathode active material precursor according to the present invention with a lithium-containing raw material, and then heat-treating the mixture at 700°C to 820°C to obtain a lithium transition metal oxide in the form of a single particle.

[0065] In a conventional method for producing a cathode active material using a cathode active material precursor, a high-temperature heat treatment at 900°C or higher is required to obtain a cathode active material in a single particle form. However, according to the present invention, a composite transition metal in a single particle form is used in the production of the cathode active material, so that a cathode active material in a single particle form can be obtained even by heat treatment at a low temperature of 700°C to 820°C. In other words, because the precursor is in a single particle form, a cathode active material in a single particle form can be obtained even by heat treatment at a low temperature of 700°C to 820°C instead of a high-temperature heat treatment of 900°C or higher.

[0066] The lithium-containing raw material may include at least one selected from lithium hydroxide hydrate, lithium carbonate, lithium nitrate, and lithium oxide. Specifically, the lithium-containing raw material may be lithium hydroxide hydrate, more specifically, LiOH·H2O. In this case, the reactivity of the lithium-containing raw material with a precursor having a high atomic fraction of nickel among the metal elements in the precursor may be improved.

[0067] When preparing the positive electrode active material, the positive electrode active material precursor and the lithium-containing raw material may be mixed in a molar ratio of 1:1.02 to 1:1.2, specifically 1:1.02 to 1:1.1, and more specifically 1:1.02 to 1:1.07. If the lithium-containing raw material is mixed in an amount less than this range, the capacity of the resulting positive electrode active material may be reduced. If the lithium-containing raw material is mixed in an amount greater than this range, unreacted Li may remain as a by-product, resulting in reduced capacity and separation of positive electrode active material particles after firing (causing agglomeration of the positive electrode active material).

[0068] The heat treatment temperature can be 700°C to 820°C, specifically 720°C to 820°C, and more specifically 750°C to 820°C. When the heat treatment temperature is within the above range, the crystallinity of the particles can be increased, and Ni 2+ This can suppress the phenomenon of ions entering the Li layer, thereby achieving excellent electrochemical properties when applied to batteries.

[0069] The heat treatment can be carried out in an oxygen atmosphere, which can increase the reactivity, uniformly sinter the particles, and increase the crystallinity.

[0070] The heat treatment can be carried out for 5 to 20 hours. Specifically, the heat treatment can be carried out for 8 to 18 hours, more specifically, 10 to 16 hours. When the heat treatment time is within this range, the lithium source reacts for a sufficient time, which increases the crystallinity through atomic rearrangement and reduces defects.

[0071] In the method for preparing the positive electrode active material, a doping element-containing material may be mixed with a positive electrode active material precursor and a lithium-containing raw material, and the mixture may be heat-treated to prepare a positive electrode active material doped with the doping element.

[0072] In addition, the method for manufacturing the positive electrode active material may include mixing the prepared single particle lithium transition metal oxide with a raw material containing a coating element, and then performing a secondary heat treatment to manufacture a positive electrode active material having a coating layer formed on the lithium transition metal oxide.

[0073] The positive electrode active material prepared by the method for preparing the positive electrode active material is a lithium transition metal oxide in the form of a single particle, and may have a composition represented by the following Chemical Formula 2:

[0074] [Chemical formula 2] Li e [Ni a’ M 1 b’ Mn c’ M 3 d’ ]O2-f A f

[0075] In the above Chemical Formula 2, M 1 is one or more elements selected from Co and Al, M 3 is one or more selected from B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta, Sc, and W, A is one or more selected from F, Cl, Br, I and S; 0.9≦e≦1.2, 0.6≦a'<1, 0 <b'≦0.4、0≦c'≦0.4、0≦d'≦0.2、a’+b’+c’+d’=1、0≦f≦0.2である。

[0076] The a' represents the atomic fraction of nickel among the metal elements in the positive electrode active material, and may be 0.6≦a'<1, 0.6≦a'≦0.98, or 0.7≦a'≦0.95.

[0077] The b' is M among the metal elements in the positive electrode active material. 1 means the atomic fraction of an element, 0 <b'≦0.4、0.01≦b'≦0.4または0.01≦b'≦0.3であることができる。

[0078] The c' represents the atomic fraction of manganese among the metal elements in the positive electrode active material, and may be 0≦c'≦0.4, 0.01≦c'≦0.4, or 0.01≦c'≦0.3.

[0079] The d' is the M of the metal elements in the positive electrode active material. 3 It means the atomic fraction of an element and can be 0≦d′≦0.2, 0≦d′≦0.1, or 0≦d′≦0.05.

[0080] According to the present invention, the positive electrode active material may contain nickel and cobalt, for example, may have a composition represented by the following Chemical Formula 2-1.

[0081] [Chemical formula 2-1] Li e [Ni a’ Co x’ Al y’ Mn c’ M 2 d’ ]O 2-f A f

[0082] In the above chemical formula 2-1, M 3 is one or more selected from B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta, Sc, and W, A is one or more selected from F, Cl, Br, I and S; 0.9≦e≦1.2, 0.6≦a'<1, 0 <x'≦0.4、0≦y'≦0.4、0≦c'≦0.4、0≦d'≦0.2、a’+b’+c’+d’=1、0≦f≦0.2である。

[0083] On the other hand, lithium ions (Li + When transition metal cations with similar size to the lithium layer exist, the transition metal cations are mixed into the lithium layer, which is called cation mixing. In the case of lithium nickel cobalt oxide, Ni 3+ , Co 3+ Ions such as Li + However, the nickel ion has a +2 oxidation state, so there is little possibility of cation mixing occurring. 2+ The ions have a size similar to that of lithium ions, making cation mixing more likely to occur. 2+ When ions are mixed in the lithium layer, the layered crystal structure cannot develop properly, which reduces the structural stability of the active material. 2+The presence of ions inhibits the movement of lithium ions, resulting in a decrease in battery performance. In particular, when a cathode active material is sintered at a high temperature of 900°C or higher, the rate of phase transformation from a stable LiNO2 layered structure to a NiO phase increases, resulting in a significant increase in the degree of cation mixing. However, the cathode active material prepared by the method for preparing a cathode active material of the present invention can be sintered at a temperature of 820°C or lower, thereby suppressing the phase transformation and reducing the degree of cation mixing. Specifically, the degree of cation mixing can be 1% or less. Therefore, batteries including the cathode active material prepared by the method for preparing the cathode active material can achieve excellent electrochemical performance.

[0084] positive electrode The present invention also provides a positive electrode for a lithium secondary battery, which contains the positive electrode active material produced by the above-described method.

[0085] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector and including the positive electrode active material.

[0086] The positive electrode current collector may be any conductive material that does not cause chemical changes in the battery, and may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0087] The positive electrode active material layer may contain a conductive material and a binder in addition to the positive electrode active material.

[0088] The positive electrode active material may be included in an amount of 80 wt % to 99 wt %, more specifically 85 wt % to 98 wt %, based on the total weight of the positive electrode active material layer. When included in this range, excellent capacity characteristics can be exhibited.

[0089] 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 powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be present in an amount of 1 wt % to 30 wt % based on the total weight of the positive electrode active material layer.

[0090] The binder functions to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used alone or in combination. The binder may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0091] The positive electrode can be fabricated by a conventional method for fabricating a positive electrode, except for using the positive electrode active material described above. Specifically, the positive electrode can be fabricated by coating a positive electrode active material layer-forming composition prepared by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent onto the entire positive electrode assembly, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0092] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity during subsequent application to fabricate a positive electrode, taking into consideration the coating thickness of the slurry and manufacturing yield.

[0093] Alternatively, the positive electrode can be produced by casting the composition for forming a positive electrode active material layer on a separate support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0094] Lithium secondary battery The present invention also provides an electrochemical device including the positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0095] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is as described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0096] 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.

[0097] 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.

[0098] The negative electrode current collector may be any material that does not cause chemical changes in the battery and has high conductivity, and examples of such materials include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloys. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the current collector may have a surface with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0099] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0100] 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. βExamples 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); and 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 carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0101] The negative electrode active material may be contained in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0102] 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 wt % 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0103] 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.

[0104] 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.

[0105] 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 electrolyte ion movement and excellent electrolyte humidification 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.

[0106] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel 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.

[0107] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0108] 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 suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a hydrocarbon group having 2 to 20 carbon atoms, 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 low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred, as they have high ionic conductivity and a high dielectric constant, which can enhance the charge / discharge performance of batteries. In this case, the cyclic carbonate and linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, which allows the electrolyte to exhibit excellent performance.

[0109] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(CF, SO), LiCl, LiI, and LiB(CO). The lithium salt is preferably used in a concentration range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0110] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid 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 loss, and improve battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0111] 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 capacity retention rate, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0112] Therefore, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0113] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0114] 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.

[0115] 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 for a medium- to large-sized battery module including a large number of battery cells.

[0116] While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms without departing from the spirit or scope of the present invention.

[0117] Examples and Comparative Examples Example 1 A reaction solution was prepared by dissolving 147.50 g of sodium citrate (Na3C6H5O7) in 300 ml of deionized water at 60°C, followed by dissolving 106.96 g of NiCl2, 9.52 g of CoCl2, and 2.40 g of AlCl3, respectively, so that the molar ratio of transition metals Ni:Co:Al was 90:8:2, and adding deionized water until the total volume of the solution reached 500 ml.

[0118] Hydrazine (N2H4) was added to the reaction solution so that the molar ratio of Ni+Co+Al:N2H4 was 1:4 to form a transition metal-N2H4 complex.

[0119] A 50% by mass aqueous solution of sodium hydroxide was added to the solution containing the transition metal-N2H4 complex so that the molar ratio of Ni+Co+Al:NaOH was 1:6 to form a composite transition metal in the form of a single particle, which was then washed and dried to form a Ni 0.9 Co 0.08 Al 0.02 The positive electrode active material precursor A was prepared as a composite transition metal in the form of a single particle. 50 ) was 800 nm.

[0120] The positive electrode active material precursor A and LiOH were mixed so that the molar ratio of Ni+Co+Al:Li was 1:1.05, and the temperature was increased from room temperature to 760°C at a rate of 20°C / hour, followed by heat treatment at 760°C for 16 hours to obtain Li[Ni 0.9 Co 0.08 Al 0.02 ]O2, and a single particle form positive electrode active material I was prepared.

[0121] Example 2 A reaction solution was prepared by dissolving 147.50 g of sodium citrate (Na3C6H5O7) in 300 ml of deionized water at 60°C, followed by dissolving 50.51 g of NiCl2 and 8.92 g of CoCl2, respectively, so that the molar ratio of transition metals Ni:Co was 85:15, and adding deionized water until the total volume of the solution reached 500 ml.

[0122] Hydrazine (N2H4) was added to the reaction solution so that the molar ratio of Ni+Co:N2H4 was 1:6 to form a transition metal-N2H4 complex.

[0123] A 50% by mass aqueous solution of sodium hydroxide was added to the solution containing the transition metal-N2H4 complex so that the molar ratio of Ni+Co:NaOH was 1:4 to form a composite transition metal in the form of a single particle, which was then washed and dried to obtain Ni 0.85 Co 0.15 The positive electrode active material precursor B was prepared as a composite transition metal in the form of a single particle. 50 ) was 1 μm.

[0124] The positive electrode active material precursor B and LiOH were mixed so that the molar ratio of Ni+Co:Li was 1:1.05, and the temperature was increased from room temperature to 760°C at a rate of 20°C / hour, followed by heat treatment at 760°C for 16 hours to obtain Li[Ni 0.85 Co 0.15 ]O2, and a single particle form positive electrode active material II was prepared.

[0125] Example 3 A reaction solution was prepared by dissolving 147.50 g of sodium citrate (Na3C6H5O7) in 300 ml of deionized water at 60°C, followed by dissolving 56.45 g of NiCl2 and 3.06 g of AlCl3 in the molar ratio of transition metals Ni:Al of 95:5, and adding deionized water until the total volume of the solution reached 500 ml.

[0126] Hydrazine (N2H4) was added to the reaction solution so that the molar ratio of Ni+Al:N2H4 was 1:6 to form a transition metal-N2H4 complex.

[0127] A 50% by mass aqueous solution of sodium hydroxide was added to the solution containing the transition metal-N2H4 complex so that the molar ratio of Ni+Al:NaOH was 1:4 to form a composite transition metal in the form of a single particle, which was then washed and dried to obtain Ni 0.95 Al 0.05 The positive electrode active material precursor C was prepared as a composite transition metal in the form of a single particle. 50 ) was 1 μm.

[0128] The positive electrode active material precursor C and LiOH were mixed so that the molar ratio of Ni+Al:Li was 1:1.05, and the temperature was increased from room temperature to 760°C at a rate of 20°C / hour, followed by heat treatment at 760°C for 16 hours to obtain Li[Ni 0.95 Al 0.05 ]O2, and a single particle form positive electrode active material III was prepared.

[0129] Comparative Example 1 Ni(SO3)2 and Co(SO3)2 were mixed in deionized water in amounts such that the Ni:Co molar ratio was 92:8 to prepare a 2.29 M transition metal aqueous solution 1. Furthermore, Al(NO3)2 was mixed with deionized water to prepare a 2.29 M transition metal aqueous solution 2.

[0130] After adding deionized water to the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen from the water and create a non-oxidizing atmosphere inside the reactor. Next, 6M NaOH was added to maintain the pH inside the reactor at 12.5.

[0131] Next, the transition metal aqueous solution 1 was added to the reactor at a rate of 11.76 mL / min, and the transition metal aqueous solution 2 was added at a rate of 0.48 mL / min, the NaOH aqueous solution at 7.2 mL / min, and the NH4OH aqueous solution at 1.8 mL / min, while the reaction was carried out for 48 hours under the conditions of a reaction temperature of 58°C, pH 11.4, and a stirring speed of 350 rpm, to obtain Ni. 0.9 Co 0.08 Al 0.02 A cathode active material precursor D having the form of spherical secondary particles formed by aggregation of primary particles represented by (OH)2 was prepared. The average particle size (D 50 ) was 4 μm.

[0132] The positive electrode active material precursor D and LiOH were mixed so that the molar ratio of Ni+Co+Al:Li was 1:1.05, and the mixture was heat-treated at 1000°C for 10 hours to obtain Li[Ni 0.9 Co 0.08 Al 0.02 ]O2 was produced.

[0133] Comparative Example 2 Ni(SO3)2 and Co(SO3)2 were mixed in deionized water in amounts such that the molar ratio of Ni:Co was 85:15 to prepare a transition metal aqueous solution 3 with a concentration of 2.29 M.

[0134] After adding deionized water to the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen from the water and create a non-oxidizing atmosphere inside the reactor. Next, 6M NaOH was added to maintain the pH inside the reactor at 12.5.

[0135] Next, the transition metal aqueous solution 3 was added to the reactor at a rate of 11.76 mL / min, and the NaOH aqueous solution and the NH4OH aqueous solution were added at a rate of 7.2 mL / min and 1.8 mL / min, respectively, while the reaction was carried out for 48 hours under the conditions of a reaction temperature of 58°C, pH 11.4, and a stirring speed of 350 rpm, to obtain Ni. 0.85 Co 0.15 A cathode active material precursor E having the form of spherical secondary particles formed by aggregation of primary particles represented by (OH)2 was prepared. The average particle size (D 50 ) was 4 μm.

[0136] The positive electrode active material precursor E and LiOH were mixed so that the molar ratio of Ni+Co:Li was 1:1.05, and the mixture was heat-treated at 1000°C for 10 hours to obtain Li[Ni 0.85 Co 0.15 ]O2 was produced.

[0137] Experimental example Experimental Example 1: Analysis of Positive Electrode Active Material Precursor and Positive Electrode Active Material SEM images were taken of the cathode active material precursor and cathode active material of Example 1, and are shown in FIGS. 1(A) and 1(B), respectively. SEM images were taken of the cathode active material precursor and cathode active material of Example 2, and are shown in FIGS. 2(A) and 2(B), respectively. SEM images were taken of the cathode active material precursor and cathode active material of Example 3, and are shown in FIGS. 3(A) and 3(B), respectively. SEM images were taken of the cathode active material precursor and cathode active material of Comparative Example 1, and are shown in FIGS. 4(A) and 4(B), respectively. SEM images were taken of the cathode active material precursor and cathode active material of Comparative Example 2, and are shown in FIGS. 5(A) and 5(B), respectively.

[0138] 1 to 5, it can be seen that the cathode active material precursors of Examples 1 to 3 can be produced in a single particle form without a high-temperature heat treatment at 900°C or higher during the production of the cathode active material in a single particle form. In contrast, it can be seen that the cathode active material precursors of Comparative Examples 1 and 2 can be produced in a single particle form when a high-temperature heat treatment at 1000°C or higher is performed in a secondary particle form formed by aggregation of primary particles.

[0139] Using an in-situ XRD (Malvern PANalytical, BV EMPYREAN, Cu Target), XRD data of the positive electrode active material precursor as a function of temperature was measured while heat treatment was being performed in Example 1, and the results are shown in FIG.

[0140] Referring to FIG. 6, it can be seen that a layered cathode active material can be prepared, similar to conventional cathode active materials, even when the cathode active material precursor of Example 1 is mixed with a lithium-containing raw material and then heat-treated.

[0141] The XRD data of the positive electrode active material precursor of Example 1 was measured using an XRD (manufactured by Bruker, D4 Endeavor, Cu Target) and is shown in FIG.

[0142] 7, it can be seen that the positive electrode active material precursor of Example 1 has a face-centered cubic structure and is a mixed metal of Ni, Co, and Al.

[0143] Experimental Example 2: Evaluation of capacitance and resistance characteristics Lithium secondary batteries were produced using the positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 and 2, and the initial charge capacity, initial discharge capacity, capacity retention rate, and resistance increase rate of each lithium secondary battery were evaluated.

[0144] The positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 and 2, a conductive material (FX35), and a 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 slurry. The positive electrode slurry was applied to one side of an aluminum current collector, dried, and rolled to prepare a positive electrode. An electrode assembly was fabricated by interposing a separator between the positive electrode and Li metal, and then placed inside a battery case and injected with an electrolyte to fabricate a lithium secondary battery. The electrolyte used was 1M LiPF6 dissolved in an organic solvent mixture of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate in a volume ratio of 3:3:4.

[0145] Thereafter, the secondary batteries were charged at a constant current of 0.1 C at 25° C. to 4.25 V. Then, they were discharged at a constant current of 0.1 C to 3 V, and the initial charge capacity and the initial discharge capacity were measured. The results are shown in Table 1 below.

[0146] The capacity of the lithium secondary battery was measured by repeating 30 charge-discharge cycles at 45°C and a constant current of 0.33 C in the range of 3.0 to 4.25 V, and in particular, the ratio of the discharge capacity at the 30th cycle to the discharge capacity at the first cycle was taken as the capacity retention rate, which is shown in Table 1 below. The resistance increase rate was also taken as the ratio of DCIR, which was calculated by dividing the voltage drop (ΔV) for 60 seconds at the 30th discharge cycle by the current, to DCIR, which was calculated by dividing the voltage drop (ΔV) for 60 seconds at the first discharge cycle by the current, which is shown in Table 1 below.

[0147] [Table 1]

[0148] Experimental Example 3: Evaluation of Volume Change Rate Lithium secondary batteries were manufactured using the positive electrode active materials manufactured in Example 2 and Comparative Example 2, and the volume change rate of each lithium secondary battery when left at high temperature was evaluated.

[0149] The positive electrode active material prepared in Example 2 and Comparative Example 2, a conductive material (FX35), and a binder (PVDF) were mixed in a weight ratio of 97.5:1:1.5 in N-methyl-2-pyrrolidone (NMP) solvent to prepare a positive electrode slurry. The positive electrode slurry was applied to one side of an aluminum current collector, dried, and rolled to prepare a positive electrode. The negative electrode active material (artificial graphite), a conductive material (Super C-65), and a binder (PVDF) were mixed in a ratio of 95.6:2.1:2.3 in water (HO) to prepare a negative electrode slurry. The negative electrode slurry was applied to one side of a copper current collector, dried, and rolled to prepare a negative electrode. An electrode assembly was fabricated by interposing a separator between the positive and negative electrodes, and then placed inside a battery case. An electrolyte was then injected to fabricate a lithium secondary battery. In this case, the electrolyte used was an organic solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3:7, and in which 0.7M LiPF6 and 0.3M LiFSI were dissolved.

[0150] The amount of gas generated was measured immediately after production of the secondary battery and every week while storing it at 60°C for 8 weeks, and the ratio of the amount of gas generated each week to the amount of gas generated immediately after production was taken as the volume change rate of the battery, which is shown in Table 2 below and Figure 8. The amount of gas generated was measured using Archimedes' principle.

[0151] [Table 2]

[0152] 8, it can be seen that batteries including cathode active materials prepared using cathode active material precursors according to the present invention have excellent capacity characteristics, excellent life characteristics at high temperatures, and a small rate of increase in resistance at high temperatures. Furthermore, it can be seen that batteries including cathode active materials prepared using cathode active material precursors according to the present invention have a significantly smaller rate of volume change when left at high temperatures for a long period of time, compared to batteries including cathode active materials prepared using cathode active material precursors having the form of secondary particles formed by aggregation of primary particles.

Claims

1. It has a composition represented by the following chemical formula 1 and contains a composite transition metal in a single particle form, The average particle size (D 50 ) is 0.1 μm to 10 μm, The crystal structure is a face-centered cubic structure, [Chemical formula 1] Ni ａ M １ ｂ Mn ｃ M ２ ｄ In the above Chemical Formula 1, M １ is one or more selected from Co and Al, M ２ is one or more selected from Nb, Ti, Mg, Ta, Zr, W and Sc, A positive electrode active material precursor, wherein 0.6≦a≦0.95, 0<b≦0.4, 0≦c≦0.4, and 0≦d≦0.

2.

2. A method for producing the positive electrode active material precursor according to claim 1, comprising: (A) preparing a reaction solution by dissolving a transition metal (M) source material in a reaction solvent; (B) Adding a ligand (L) that forms a complex compound with a transition metal to the reaction solution to form a complex compound (ML ｘ , 1≦x≦6); (C) adding a basic aqueous solution to the solution containing the complex compound to form a composite transition metal in the form of a single particle, The transition metal (M) source material is a nickel-containing source material and M １ A method for producing a positive electrode active material precursor, comprising a raw material containing at least one element selected from Co and Al.

3. The method for producing a positive electrode active material precursor according to claim 2 , wherein the reaction solution further comprises a surface stabilizer.

4. 4. The method for producing a positive electrode active material precursor according to claim 3, wherein the surface stabilizer comprises at least one selected from the group consisting of a compound containing a citrate salt, a compound containing a dodecyl sulfate salt, and a compound containing polyvinylpyrrolidone.

5. 5. The method for producing a positive electrode active material precursor according to claim 4, wherein the citrate-containing compound includes at least one selected from the group consisting of sodium citrate, potassium citrate, and triethyl citrate.

6. 6. The method for producing a positive electrode active material precursor according to claim 2, wherein the ligand comprises at least one selected from the group consisting of hydrazine, sodium borohydride, oxalic acid, formic acid, ascorbic acid, and hydrogen peroxide.

7. 7. The method for producing a positive electrode active material precursor according to claim 2, wherein the ligand is added in an amount such that a molar ratio of the transition metal to the ligand contained in the reaction solution is 1:2 to 1:

12.

8. The method for producing a positive electrode active material precursor according to any one of claims 2 to 7, wherein the step (B) is carried out at a temperature of 25°C to 80°C.

9. 9. The method for producing a positive electrode active material precursor according to claim 2, wherein the basic aqueous solution contains NaOH and is added in an amount such that a molar ratio of the transition metal contained in the reaction solution to NaOH is 1:2 to 1:

12.

10. 10. A method for producing a positive electrode active material, comprising: mixing the positive electrode active material precursor of claim 1 with a lithium-containing raw material, and then heat-treating the mixture at 700°C to 820°C to obtain a lithium transition metal oxide in the form of a single particle.

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