Positive electrode active material and method of manufacturing positive electrode active material

Abstract

To provide a positive electrode active material capable of improving a battery performance such as lifespan, capacity and the like, when a positive electrode active material with increased production volume, improved safety, and reduced residual lithium is manufactured and the positive electrode active material is applied to a secondary battery.SOLUTION: A positive electrode active material according to one aspect of the present invention is a lithium composite oxide, and may satisfy relational expression 1 below in an XRD pattern obtained through Rietveld fitting as a result of X-ray diffraction (XRD) analysis using a CuKα ray. (Relational expression 1) 0.110≤FWHM(104)≤0.170 A method of manufacturing a positive electrode active material according to one aspect of the present invention may include the steps of: preparing an oxide precursor; and manufacturing a first lithium composite oxide by primarily heat-treating a first mixture including the prepared oxide precursor, a lithium-containing compound, and a first cobalt-containing compound.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode active material and a method for manufacturing the same, and more particularly to a positive electrode active material for a secondary battery manufactured from an oxide precursor and a method for manufacturing the positive electrode active material.

Background Art

[0002] With the development of portable mobile electronic devices such as smartphones, MP3 players, and tablet PCs, the demand for secondary batteries capable of storing electrical energy has increased explosively. In particular, with the emergence of electric vehicles, medium and large-sized energy storage systems, and portable devices that require high energy density, the demand for lithium secondary batteries is increasing.

[0003] As a lithium composite oxide contained in the positive electrode active material, the substance that has received the most attention in recent years is lithium nickel manganese cobalt oxide Li(Ni x Co y Mn z )O2 (where x, y, and z are the atomic fractions of independent oxide composition elements, respectively, 0 < x ≤ 1, 0 < y ≤ 1, 0 < z ≤ 1, and 0 < x + y + z ≤ 1). This positive electrode active material has the advantage of having a high capacity because it is used at a higher voltage than LiCoO2, which has been actively studied and used as a positive electrode active material, and it is inexpensive because the Co content is relatively low.

[0004] However, such a lithium composite oxide undergoes volume changes due to the intercalation and deintercalation of lithium ions during charge and discharge. During charge and discharge, there are problems such as the primary particles of the lithium composite oxide rapidly changing in volume, cracks occurring in the secondary particles due to repeated charge and discharge, or the collapse of the crystal structure or a phase transition of the crystal structure occurring.

[0005] To make up for these shortcomings, the demand for nickel-rich systems (high nickel-based positive active materials) with nickel (Ni) content of 50 mol% or more relative to the total transition metal content excluding lithium (Li) as positive active materials for secondary batteries has increased, making it necessary to increase production.

[0006] However, high nickel-based positive electrode active materials have the drawback of reduced safety and lifespan due to the high Ni content. In addition, due to the high Li / M ratio during manufacturing, the residual lithium content is high after sintering, making cell manufacturing difficult due to gelation during electrode slurry manufacturing. Therefore, a water washing process is introduced to remove the residual lithium, but the surface of the positive electrode is damaged during the water washing process, resulting in poor battery performance. Summary of the Invention [Problem to be solved by the invention]

[0007] In the case of existing positive electrode active materials, hydroxide precursors are produced by heat treatment with lithium-containing compounds, but this has limitations in improving productivity. Therefore, the present invention aims to increase production by 10% or more by using oxide precursors when producing positive electrode active materials, and therefore it was necessary to develop a technology to apply this.

[0008] The present inventors attempt to improve battery performance, such as the life span and capacity, when applying this to a secondary battery by controlling the full width at half maximum (FWHM (deg., 2θ)) of the (104) plane and / or the full width at half maximum (FWHM (deg., 2θ)) of the (003) plane in the XRD pattern obtained by Rietveld fitting based on the results of X-ray diffraction (XRD) analysis using CuKα radiation.

[0009] In addition, the present inventors intend to manufacture a cathode active material having improved safety and reduced residual lithium by applying a specific process in the step of performing a first heat treatment and / or a second heat treatment on an oxide precursor together with a lithium-containing compound, and to improve battery performance such as lifespan and capacity when the cathode active material is applied to a secondary battery. [Means for solving the problem]

[0010] A positive electrode active material according to one embodiment of the present invention includes a lithium composite oxide, and as a result of X-ray diffraction (XRD) analysis using CuKα radiation, the following Relational Formula 1 can be satisfied in an XRD pattern obtained by Rietveld fitting.

number

[0011] In the above-mentioned Relational Formula 1, the FWHM (104) means the full width at half maximum (FWHM (deg., 2θ)) of the (104) plane in the XRD peak defined by a hexagonal lattice having the R-3m space group.

[0012] In one embodiment, the positive electrode active material may satisfy the following Relational Expression 2 in an X-ray diffraction (XRD) pattern obtained by Rietveld fitting as a result of X-ray diffraction analysis using CuKα radiation.

number

[0013] In the above-mentioned Relational Formula 2, the FWHM (003) means the full width at half maximum (FWHM (deg., 2θ)) of the (003) plane in the XRD peak defined by a hexagonal lattice having the R-3m space group.

[0014] As one embodiment, the a-axis lattice constant of the positive electrode active material may be 2.860 to 2.890.

[0015] As one embodiment, the c-axis lattice constant of the positive electrode active material may be 14.190 to 14.200.

[0016] As one embodiment, the positive electrode active material may be in a bi-modal form including first positive electrode active material particles having an average particle diameter (D50) of 8 μm or more and second positive electrode active material particles having an average particle diameter (D50) of 7 μm or less.

[0017] A method for manufacturing a positive electrode active material according to one embodiment of the present invention includes preparing an oxide precursor, and first heat-treating a first mixture including the prepared oxide precursor, a lithium-containing compound, and a first cobalt-containing compound to produce a first lithium composite oxide.

[0018] As one embodiment, after the step of producing the first lithium composite oxide, the method may further include a step of second heat-treating a second mixture including the produced first lithium composite oxide and a second cobalt-containing compound to produce a second lithium composite oxide.

[0019] As one embodiment, in the step of producing the first lithium composite oxide, when the molar percentage of cobalt contained in the first cobalt-containing compound is A based on the total metal of the prepared oxide precursor, and in the step of producing the second lithium composite oxide, when the molar percentage of cobalt contained in the second cobalt-containing compound is B based on the total metal excluding lithium of the produced first lithium composite oxide, 0.1 ≦ A / B ≦ 0.5 may be satisfied.

[0020] As one embodiment, the first cobalt-containing compound may be Co3O4. As one embodiment, the second cobalt-containing compound may be Co3O4.

[0021] As one embodiment, the second heat treatment temperature Y may satisfy 690°C < Y < 720°C.

[0022] The positive electrode active material according to one embodiment of the present invention can be produced by the method for producing a positive electrode active material.

[0023] A positive electrode according to an embodiment of the present invention may include the positive electrode active material.

[0024] A secondary battery according to an embodiment of the present invention may include the positive electrode active material. Effect of the Invention

[0025] One advantage of the present invention is that a positive electrode active material having increased productivity, improved safety, and reduced residual lithium can be produced, and when the positive electrode active material is applied to a secondary battery, the battery performance such as lifespan and capacity can be improved. [Brief description of the drawings]

[0026] [Figure 1] FIG. 4 is a diagram showing the effect of reducing nickel vacancies after a first heat treatment and the effect of removing residual lithium after a second heat treatment according to a manufacturing method according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a graph showing a comparison of (104) shift changes after a first heat treatment and a second heat treatment according to a manufacturing method of an embodiment of the present invention, as a result of X-ray diffraction (XRD) analysis using CuKα radiation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] As used herein, terms such as "comprises" should be understood as open-ended terms that encompass the possibility of including other configurations.

[0028] As used herein, the terms "preferred" and "preferably" refer to embodiments of the invention that may provide certain advantages, under certain circumstances, but are not intended to exclude other embodiments from the scope of the invention.

[0029] Additionally, as used in the specification and the appended claims, the singular forms "a," "an," and "the" can be intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0030] Meanwhile, the technical features described below relate to one aspect for achieving the effects aimed at by the present invention as described above.

[0031] That is, the positive electrode active material and the method for manufacturing the positive electrode active material according to one embodiment of the present invention include technical features according to one embodiment described below, and thus, when the positive electrode active material and the method for manufacturing the positive electrode active material according to one embodiment of the present invention are applied to a secondary battery, the battery characteristics can be significantly improved.

[0032] The present invention relates to a positive electrode active material and a positive electrode active material for a secondary battery, and the type of the secondary battery is not limited as long as the secondary battery is a battery manufactured to convert external electrical energy into a form of chemical energy, store it, and reuse it. As a more preferred example, the present invention may relate to a positive electrode active material precursor and a positive electrode active material for a lithium ion secondary battery.

[0033] First, the positive electrode active material precursor particles of the present invention will be described.

[0034] The positive electrode active material according to one embodiment of the present invention may include a lithium composite oxide.

[0035] In one embodiment, the positive electrode active material may include nickel (Ni).

[0036] In one embodiment, the positive electrode active material may further include at least one selected from the group consisting of cobalt (Co), aluminum (Al), and manganese (Mn).

[0037] In one embodiment, the positive electrode active material may be represented by the following Chemical Formula 1: [ka]

[0038] In the above Chemical Formula 1, M is selected from the group consisting of Zr, Mn, Al, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, and combinations thereof, and 0.9≦a≦1.2, 0.5≦x≦1.0, 0.0≦y≦0.4, and 0.0≦1-xy≦0.4.

[0039] In one embodiment, the positive electrode active material may be represented by the following Formula 1-1: [ka]

[0040] In the above Chemical Formula 1-1, M1 is Al or Mn, and M2 is selected from the group consisting of Zr, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, and combinations thereof, and 0.9≦a'≦1.2, 0.5≦x'≦1.0, 0.0≦y'≦0.4, 0.0≦z'≦0.4, and 0.0≦1-x'-y'-z'≦0.4.

[0041] In one aspect, in Formula 1 and / or Formula 1-1, a and / or a', which represent the mol% of lithium (Li) relative to the total mol% of metals excluding lithium (Li), may be 0.9 or more, 1.0 or more, 1.2 or less, 1.1 or less, or 1.05 or less.

[0042] In one embodiment, x and / or x', which means nickel (Ni) mole % relative to the total metal mole % excluding lithium (Li) in Formula 1 and / or Formula 1-1, may be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. In particular, x and / or x' may be a high nickel-based oxide, which is 0.8 or more, or 0.9 or more.

[0043] In one embodiment, in Formula 1 and / or Formula 1-1, y and / or y', which means the cobalt (Co) mole percent relative to the total metal mole percent excluding lithium (Li), may be 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0044] In one embodiment, the crystal structure of the positive electrode active material may be hexagonal α-NaFeO2 (R-3m space group).

[0045] In one aspect, the positive electrode active material may satisfy the following Relational Expression 1 in an X-ray diffraction (XRD) pattern obtained by Rietveld fitting as a result of X-ray diffraction analysis using CuKα radiation.

number

[0046] In the above-mentioned Relational Formula 1, the FWHM (104) means the full width at half maximum (FWHM (deg., 2θ)) of the (104) plane in the XRD peak defined by a hexagonal lattice having the R-3m space group.

[0047] In one embodiment, the FWHM (104) may be 0.110 or more, 0.120 or more, 0.130 or more, 0.170 or less, 0.160 or less, 0.150 or less, or 0.140 or less.

[0048] In the present invention, in the XRD analysis, the full width at half maximum (FWHM) value is subject to deviation and error depending on various variables such as the condition of the analysis equipment, the X-ray source, and the measurement conditions, so it was corrected using the full width at half maximum (FWHM) of a corundum disc as a standard sample.

[0049] In the present invention, the corundum disc used was a NIST corundum disc.

[0050] In the present invention, X-ray diffraction (XRD) analysis was performed using a Bruker D8 Advance diffractometer with CuKα radiation (1.540598 Å) at a step size (° / step) of 0.02° / step and a measurement time per step of 0.1 s / step.

[0051] In one aspect, the positive electrode active material may satisfy the following Relational Expression 1 in an X-ray diffraction (XRD) pattern obtained by Rietveld fitting as a result of X-ray diffraction analysis using CuKα radiation.

number

[0052] In the above-mentioned Relational Formula 2, the FWHM (003) is an XRD peak defined by a hexagonal lattice with the R-3m space group. (003) FWHM (deg., 2θ) means the full width at half maximum of the surface.

[0053] In one embodiment, the FWHM (003) may be 0.080 or more, 0.090 or more, 0.100 or more, 0.130 or less, 0.120 or less, or 0.110 or less.

[0054] In one embodiment, the a-axis lattice constant of the positive electrode active material may be 2.860 or more, 2.870 or more, 2.871 or more, 2.872 or more, 2.873 or more, 2.890 or less, 2.880 or less, 2.875 or less, or 2.874 or less.

[0055] In one embodiment, the c-axis lattice constant of the positive electrode active material may be 14.185 or more, 14.190 or more, 14.192 or more, 14.193 or more, 14.200 or less, 14.195 or less, or 14.194 or less.

[0056] In the present invention, the a-axis lattice parameter and the c-axis lattice parameter are values ​​calculated by indexing XRD measurement data by the Rietveld refinement method.

[0057] In one embodiment, the positive electrode active material may include a plurality of positive electrode active material particles.

[0058] In one embodiment, the positive electrode active material particles may be secondary particles formed by agglomeration of one or more primary particles.

[0059] In one aspect, the primary particles can include one or more crystallites.

[0060] In one embodiment, the secondary particles may be in a multiparticulate or polycrystalline form including two or more primary particles.

[0061] In one embodiment, the positive electrode active material may be in a unimodal form including positive electrode active material particles having an average particle size (D50) of 1 μm to 30 μm.

[0062] In the present invention, the average particle size (D50) is the particle size at 50% of the cumulative area distribution of particle sizes, which can be measured by a laser diffraction method.

[0063] In another more preferred embodiment, the positive electrode active material may be in a bimodal form including first positive electrode active material particles having an average particle size (D50) of 8 μm or more and second positive electrode active material particles having an average particle size (D50) of 7 μm or less.

[0064] In one embodiment, when the positive electrode active material is bimodal, the weight of the first positive electrode active material particles contained in the positive electrode active material is referred to as w1, and the weight of the second positive electrode active material particles contained in the positive electrode active material is referred to as w2, and w1 / w2 may be 1.5 to 9.0, or 2.0 to 4.0. In the bimodal type positive electrode active material having such a mixing ratio, the present invention increases the energy density by the small particles present in the gaps between the large particles, while resolving the problem of deterioration of battery characteristics due to the change in the deviation of the average particle size of the large particles and the small particles.

[0065] In one embodiment, when the positive electrode active material of the present invention is bimodal, the first positive electrode active material particles, which are large particles, may be secondary particles formed by agglomeration of primary particles.

[0066] In one embodiment, the primary particles of the first positive electrode active material particles, which are the large particles, can include one or more crystallites.

[0067] In one embodiment, the secondary particles of the first positive electrode active material particles, which are large particles, may have a multi-particle form or a polycrystalline form including a plurality of primary particles.

[0068] In one embodiment, the second positive electrode active material particles, which are small particles, may be in a single particle form including one primary particle, and when the primary particle is composed of one crystallite, may be in a single crystal form.

[0069] In another embodiment of the present invention, the second positive electrode active material particles, which are small particles, may be in a multi-particle form or a polycrystalline form including two or more primary particles.

[0070] In addition, when preparing the positive active material, the cobalt inputted in the first heat treatment and / or the second heat treatment according to the method for preparing the positive active material described below may be present in the form of cobalt oxide on the surface of the secondary particles of the positive active material and / or on the grain boundaries between the primary particles, in addition to being present in the lattice structure of the primary particles of the positive active material. The cobalt oxide may be a composite oxide of lithium and cobalt, or an oxide of cobalt.

[0071] In one aspect, the cobalt oxide may include a concentration gradient portion in which the molar concentration of cobalt varies. For example, when the cobalt oxide includes lithium, the molar concentration of lithium may vary. Also, for example, the molar concentration of the cobalt may vary.

[0072] In one embodiment, the positive electrode active material may have an element other than the cobalt present in the lattice structure of the primary particles, such as one or more selected from aluminum (Al), titanium (Ti), zirconium (Zr), magnesium (Mg), zinc (Zn), boron (B), molybdenum (Mo), iron (Fe), nickel (Ni), barium (Ba), and tungsten (W).

[0073] Meanwhile, in this specification, "element" is interpreted as including both the zero-valent state and the ionic state.

[0074] In a further aspect, the positive electrode active material may further include a coating oxide of another element formed on the surfaces of the secondary particles and / or on the grain boundaries between the primary particles.

[0075] In one embodiment, the coating oxide can be represented by the following Chemical Formula 2: [ka]

[0076] In the formula 2, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd, and Nd; 0≦p≦10, 0 <q≦8、2≦r≦13である。

[0077] For example, in Formula 2, M3 represents a coating element, and the coating oxide may be an oxide of lithium and an element represented by M3 in combination, or an oxide of M3.

[0078] In one example, the coating oxide is Li p Co q O r , Li p W q O r , Li p Zr q O r , Li p Ti q O r , Li p Ni q O r , Li p Al q O r , Li p Mo q O r , Co q O r , Al q O r , W q O r , Zr q O r , Ti q O r , B q O r , Li p (W / Ti) q O r , Li p (W / Zr) q O r , Li p (W / Ti / Zr) q O r , Li p (W / Ti / B)q O r It may be, but is not limited to this.

[0079] In one aspect, the coating oxide includes an element that may be included in the first mixture and / or the second mixture in the manufacturing method of the positive electrode active material described below, and may be an element-containing coating oxide selected from aluminum (Al), titanium (Ti), zirconium (Zr), magnesium (Mg), zinc (Zn), boron (B), molybdenum (Mo), iron (Fe), nickel (Ni), barium (Ba), and tungsten (W).

[0080] Meanwhile, the technical characteristics of the positive electrode active material may be average technical characteristics of a plurality of positive electrode active material particles contained in the positive electrode active material.

[0081] Meanwhile, the meanings of "≦", "greater than or equal to" and "less than or equal to" described in the present invention can be replaced with the meanings of "<", "more than" and "less than".

[0082] Next, a method for producing a positive electrode active material according to one embodiment of the present invention will be described.

[0083] First, a method for manufacturing a positive electrode active material according to an embodiment of the present invention may include a step of preparing an oxide precursor.

[0084] The positive electrode active material according to one embodiment of the present invention can be prepared from an oxide precursor.

[0085] In one embodiment, the oxide precursor can include nickel (Ni).

[0086] In one embodiment, the oxide precursor may further include at least one selected from the group consisting of cobalt (Co), aluminum (Al), and manganese (Mn).

[0087] In one embodiment, the oxide precursor can be represented by Formula 3 below. [ka]

[0088] In Formula 3, M is selected from the group consisting of Zr, Mn, Al, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, and combinations thereof, and 0.5≦x≦1.0, 0.0≦y≦0.4, and 0.0≦1-xy≦0.4.

[0089] In one embodiment, the oxide precursor may be represented by the following Formula 3-1: [ka]

[0090] In the above Chemical Formula 3-1, M1 is Al or Mn, and M2 is selected from the group consisting of Zr, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, and combinations thereof, where 0.5≦x′≦1.0, 0.0≦y′≦0.4, 0.0≦z′≦0.4, and 0.0≦1-x′-y′-z′≦0.4.

[0091] In one embodiment, in Formula 3 and / or Formula 3-1, x and / or x', which means nickel (Ni) mole percent relative to the total metal mole percent, may be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. In particular, x and / or x' may be a high nickel-based oxide, which is 0.8 or more, or 0.9 or more.

[0092] In one embodiment, in Formula 3 and / or Formula 3-1, y and / or y', which represent the mole percent of cobalt (Co) relative to the total metal mole percent, may be 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0093] Meanwhile, the oxide precursor may be prepared by oxidizing a hydroxide precursor.

[0094] More specifically, the oxide precursor may be produced by oxidizing a hydroxide precursor through heat treatment, in which case the heat treatment temperature may be 300°C to 500°C, or 350°C to 450°C.

[0095] Then, a first mixture including the prepared oxide precursor, the lithium-containing compound, and the first cobalt-containing compound may be subjected to a first heat treatment to prepare a first lithium composite oxide.

[0096] In a more preferred embodiment, the first cobalt-containing compound may be Co3O4, which may be effective not only in improving battery performance such as life and capacity, but also in removing residual lithium by reacting with the residual lithium on the surface of the particles.

[0097] In a further embodiment, the first mixture may further include one or more element-containing compounds selected from aluminum (Al), titanium (Ti), zirconium (Zr), magnesium (Mg), zinc (Zn), boron (B), molybdenum (Mo), iron (Fe), nickel (Ni), barium (Ba), and tungsten (W). More preferably, the first mixture may also include aluminum (Al).

[0098] In one embodiment, the first heat treatment temperature may be 690° C. or more, 700° C. or more, 720° C. or less, or 710° C. or less.

[0099] In the method for preparing a positive electrode active material according to an embodiment of the present invention, after the step of preparing the first lithium composite oxide, the water washing step may not be performed.

[0100] Positive electrode active materials, especially high nickel positive electrode active materials, have a high content of residual lithium after sintering due to their high Li / M ratio during production, which makes it difficult to manufacture cells due to gelation during electrode slurry production. Therefore, to remove the residual lithium, a water washing process is introduced in which the particles are put into distilled water, etc., but there is a problem that the positive electrode surface is damaged during the water washing process, resulting in a decrease in battery characteristics.

[0101] In the present invention, when the oxide precursor is subjected to the first heat treatment and / or the second heat treatment, a cobalt-containing compound such as Co3O4 is added, so that the residual lithium can be effectively removed without performing a water washing process for removing the residual lithium, and damage to the positive electrode surface, etc. can be reduced.

[0102] In addition, the present invention optimizes the ratio of the cobalt input content and / or the second heat treatment temperature condition in each heat treatment step, thereby effectively removing residual lithium without performing a water washing process for removing residual lithium, and reducing damage to the positive electrode surface, etc.

[0103] In one embodiment, after the step of preparing the first lithium composite oxide, a step of preparing a second lithium composite oxide by subjecting the prepared first lithium composite oxide and a second mixture including a second cobalt-containing compound to a second heat treatment may be further performed.

[0104] In a more preferred embodiment, the second cobalt-containing compound may be Co3O4. Co3O4 may be effective not only in improving battery performance such as life and capacity, but also in removing residual lithium by reacting with the residual lithium on the particle surface.

[0105] In a further embodiment, the second mixture may further include one or more element-containing compounds selected from aluminum (Al), titanium (Ti), zirconium (Zr), magnesium (Mg), zinc (Zn), boron (B), molybdenum (Mo), iron (Fe), nickel (Ni), barium (Ba), and tungsten (W). More preferably, the second mixture may further include titanium (Ti) and zirconium (Zr).

[0106] Meanwhile, in the present invention, in the step of preparing the first lithium composite oxide, the mol % of cobalt contained in the first cobalt-containing compound based on the total metal of the prepared oxide precursor is defined as A.

[0107] In addition, in the step of preparing the second lithium composite oxide, the mol % of cobalt contained in the second cobalt-containing compound is defined as B based on the total metals excluding lithium of the prepared first lithium composite oxide.

[0108] Here, A / B can be 0.1 or more, 0.2 or more, 0.3 or more, 0.5 or less, or 0.4 or less.

[0109] The present inventors newly recognized that the effects of the cobalt added in the first heat treatment step and the second heat treatment step of the oxide precursor are different, and optimized the content of cobalt added in each heat treatment step.

[0110] More specifically, it was confirmed that the doping effect in the final cathode active material is maintained depending on the amount of cobalt added during the first heat treatment, but the doping effect due to the amount of cobalt added during the second heat treatment is not significant.

[0111] Meanwhile, when the oxide precursor is subjected to the first and second heat treatments, the residual lithium in the positive active material decreases as the cobalt content increases. However, even if the total cobalt content input is the same, it was found that the content of cobalt input during the second heat treatment has a greater effect on the reduction of residual lithium (Figure 1).

[0112] Therefore, the present inventors have recognized the need to optimize the ratio of the cobalt content added in each step, taking into consideration the different effects of the cobalt added in the first heat treatment and the second heat treatment.

[0113] Therefore, even if the total cobalt content is the same, when the cobalt content added in the step of preparing the first lithium composite oxide is 0.1 to 0.5 of the cobalt content added in the step of preparing the second lithium composite oxide, it is possible to maximize the doping effect and the synergistic effect of removing residual lithium and further improve the battery performance.

[0114] In one aspect, A, which is related to the content of cobalt added in the preparation of the first lithium composite oxide, may be 0.5 mol% or more, 0.8 mol% or more, 3.5 mol% or less, 3.0 mol% or less, 2.5 mol% or less, 2.0 mol% or less, 1.5 mol% or less, or 1.2 mol% or less.

[0115] In one embodiment, B, which is related to the cobalt content added in the preparation of the second lithium composite oxide, may be 0.5 mol% or more, 1.0 mol% or more, 1.5 mol% or more, 2.0 mol% or more, 2.5 mol% or more, 4.0 mol% or less, or 3.5 mol% or less.

[0116] In one aspect, the total cobalt content A+B (mol % of cobalt added based on all metals excluding lithium) added in the step of preparing the positive active material may be 2.5 mol % or more, 3.0 mol % or more, 4.5 mol % or less, or 4.0 mol % or less.

[0117] In a more preferred embodiment, the second heat treatment temperature Y may be 690° C. or more, more than 690° C., 700° C. or more, 720° C. or less, less than 720° C., or 710° C. or less.

[0118] The present inventors optimized the amount of cobalt added in the first heat treatment and the second heat treatment, and optimized the temperature of the second heat treatment for the optimized amount of cobalt.

[0119] As a result, it was confirmed that when the second heat treatment temperature Y was within the above range, the battery performance was further improved.

[0120] The positive electrode active material according to an embodiment of the present invention may be prepared by the method for preparing a positive electrode active material described above.

[0121] The positive electrode active material may include the technical features of the positive electrode active material described above.

[0122] A positive electrode according to an embodiment of the present invention may include the positive electrode active material.

[0123] Except for the use of the above-mentioned positive electrode active material, the positive electrode has a known structure and can be manufactured by a known manufacturing method. The binder, conductive material, and solvent are not particularly limited as long as they can be used on the positive electrode current collector of the secondary battery.

[0124] A secondary battery according to an embodiment of the present invention may include the positive electrode active material.

[0125] Specifically, the secondary battery may include a positive electrode, a negative electrode facing the positive electrode, and an electrolyte between the positive electrode and the negative electrode, but is not particularly limited thereto as long as it can be used as a secondary battery.

[0126] Examples of the present invention will now be described more specifically.

[0127] Manufacture of positive electrode active material

[0128] <Example 1>

[0129] (a) Preparation of hydroxide precursor

[0130] The reactor was charged with an aqueous solution of NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O in a molar ratio of 95:4:1, along with NaOH and NH4OH, and stirred. The temperature inside the reactor was maintained at 45°C, and N2 gas was fed into the reactor to synthesize the hydroxide precursor. After the reaction was completed, the reactor was washed and dehydrated to obtain Ni 0.95 Co 0.04 Mn 0.01 A large hydroxide precursor with the composition (OH)2 was obtained. A small hydroxide precursor was prepared in this manner in a 94:5:1 mole ratio.

[0131] (b) Preparation of oxide precursors

[0132] The hydroxide precursor prepared in step (a) was oxidized in a furnace under an O2 atmosphere at 400° C. for 6 hours to obtain an oxide precursor.

[0133] The average particle size (D50) of the obtained large oxide precursor was 15.0 μm, and the average particle size (D50) of the small oxide precursor was 3.0 μm.

[0134] (C) Preparation of the first lithium composite oxide

[0135] A first mixture was prepared by mixing the oxide large particle precursor and oxide small particle precursor in a weight ratio of 7:3 prepared in step (b), lithium-containing material LiOH (Li / Metal molar ratio=1.015), Co3O4 having a Co content of 0.925 mol% based on the total metal of the oxide precursor, and Al(OH)3 having an Al content of 0.85 mol%. Then, a sintering furnace in an O2 atmosphere was heated to 705° C. for 2 hours and 20 minutes, and the mixture was subjected to a first heat treatment for 8 hours, and then the furnace was cooled and crushed to obtain a first lithium composite oxide.

[0136] (d) Preparation of the second lithium composite oxide

[0137] A second mixture was prepared by mixing the first lithium composite oxide prepared in step (c) and Co3O4 having a Co content of 2.775 mol%, TiO2 having a Ti content of 0.2 mol%, and ZrO2 having a Zr content of 0.1 mol%, based on the total metals of the first lithium composite oxide excluding lithium. Then, a sintering furnace in an air atmosphere was heated to 705° C. for 2 hours and 20 minutes, and the mixture was subjected to a second heat treatment for 8 hours and then cooled in the furnace to prepare a second lithium composite oxide.

[0138] <Example 2>

[0139] A second lithium composite oxide was prepared in the same manner as in Example 1, except that in step (d), the second heat treatment was performed by increasing the temperature of the calciner to 690° C.

[0140] <Example 3>

[0141] A second lithium composite oxide was prepared in the same manner as in Example 1, except that in step (d), the second heat treatment was performed by increasing the temperature of the calciner to 720° C.

[0142] <Example 4>

[0143] A second lithium composite oxide was prepared in the same manner as in Example 1, except that in step (c), Co3O4 having a Co content of 1.85 mol% was mixed, and in step (d), Co3O4 having a Co content of 1.85 mol% was mixed, and a second heat treatment was performed by heating the calcination furnace to 690°C.

[0144] <Example 5>

[0145] A second lithium composite oxide was prepared in the same manner as in Example 1, except that in step (c), Co3O4 having a Co content of 1.85 mol% was mixed, and in step (d), Co3O4 having a Co content of 1.85 mol% was mixed.

[0146] <Example 6>

[0147] A second lithium composite oxide was prepared in the same manner as in Example 1, except that in step (c), Co3O4 having a Co content of 1.85 mol% was mixed, and in step (d), Co3O4 having a Co content of 1.85 mol% was mixed, and the temperature of the calcination furnace was increased to 720° C. to perform a second heat treatment.

[0148] <Example 7>

[0149] A second lithium composite oxide was prepared in the same manner as in Example 1, except that in step (c), Co3O4 having a Co content of 2.775 mol% was mixed, and in step (d), Co3O4 having a Co content of 0.925 mol% was mixed, and the temperature of the calcination furnace was increased to 690° C. to perform a second heat treatment.

[0150] <Example 8>

[0151] A second lithium composite oxide was prepared in the same manner as in Example 1, except that in step (c), Co3O4 having a Co content of 2.775 mol% was mixed, and in step (d), Co3O4 having a Co content of 0.925 mol% was mixed.

[0152] <Example 9>

[0153] A second lithium composite oxide was prepared in the same manner as in Example 1, except that in step (c), Co3O4 having a Co content of 2.775 mol% was mixed, and in step (d), Co3O4 having a Co content of 0.925 mol% was mixed, and the temperature of the calcination furnace was increased to 720° C. to perform a second heat treatment.

[0154] Manufacture of lithium secondary batteries

[0155] A positive electrode slurry was prepared by dispersing 95.5 wt% of the positive electrode active material prepared according to the above example, 2.5 wt% of artificial graphite, and 2 wt% of PVDF binder in 2.7 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on an aluminum thin film having a thickness of 15 μm and dried in a vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0156] A coin battery was fabricated using a lithium foil as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) as a separator, and an electrolyte of LiPF6 at a concentration of 1.15 M in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7.

[0157] <Experimental Example 1> Measurement of full width at half maximum (FWHM (deg., 2θ))

[0158] The full width at half maximum (FWHM (deg., 2θ)) of the second lithium composite oxide according to the embodiment was measured and is shown in Table 1 below.

[0159] In addition, the a-axis lattice constant and the c-axis lattice constant of the second lithium composite oxide according to the embodiment were measured and are shown in Table 1 below.

[0160] The measurement method is as described above. [Table 1]

[0161] <Experimental Example 2> XRD Measurement

[0162] FIG. 2 shows the results of X-ray diffraction (XRD) analysis of the first and second lithium composite oxides according to the above examples.

[0163] X-ray diffraction (XRD) analysis was performed using a Bruker D8 Advance diffractometer with CuKα radiation (1.540598 Å) at a step size (° / step) of 0.02° / step and a measurement time per step of 0.1 s / step.

[0164] Referring to FIG. 2, it can be seen that as the amount of cobalt added during the first heat treatment increases, the amount of (104) shift occurs, but the amount of cobalt added during the second heat treatment does not affect the position change of the (104) shift.

[0165] In addition, it was confirmed that the doping effect in the final cathode active material is maintained depending on the amount of cobalt added during the first heat treatment.

[0166] <Experimental Example 3> Measurement of residual lithium

[0167] The results of measuring the residual lithium in the first and second lithium composite oxides according to the above examples are shown in Table 2 below.

[0168] Residual lithium is measured by the amount of 0.1M HCl used until the pH reaches 4 according to pH adjustment. First, 5g of oxide is placed in 100ml of DIW, stirred for 15 minutes, and then filtered. Next, 50ml of the filtered solution is taken and 0.1M HCl is added to it to measure the amount of HCl consumed due to the change in pH, and Q1 and Q2 are determined. Residual LiOH and Li2CO3 are calculated according to the following formula. M1=23.94 (LiOH molecular weight) M2=73.89(Li2CO3 molecular weight)

number

[0169] Referring to Table 2, it was found that as the amount of cobalt added during the first heat treatment and the second heat treatment increases, the amount of residual lithium in the positive active material decreases. However, even if the total amount of cobalt added is the same, the amount of cobalt added during the second heat treatment has a greater effect on the reduction in residual lithium.

[0170] In addition, the effect of removing residual lithium was confirmed in the final cathode active material manufactured without a water washing process, and in particular, it was confirmed that the effect of removing residual lithium was increased by the addition of cobalt during the second heat treatment.

[0171] Also, it was confirmed that Examples 1, 2 and 3, which had an increased Co content during the second heat treatment, showed the lowest residual lithium values.

[0172] <Experimental Example 4> Evaluation of electrochemical properties

[0173] The electrochemical characteristics of the lithium secondary batteries according to the above examples are shown in Table 3 below.

[0174] The initial charge and discharge capacity was measured using an electrochemical analyzer (Toyo, Toscat-3100) by a charge and discharge experiment at 25° C., voltage range of 2.0 V to 4.25 V, and discharge rate of 0.1 C. The initial charge capacity and initial discharge capacity were measured, and the initial reversible efficiency was calculated.

[0175] The C-rate measurement was performed using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, with a voltage range of 2.5V to 4.25V, and a discharge rate of 0.1C to 10.0C. The output efficiency (C-rate) of 10.0C / 0.1C was measured by a charge-discharge experiment.

[0176] The high temperature life measurement was performed by performing one charge / discharge cycle at 25°C, a voltage range of 2.0V to 4.25V, and 0.1C / 0.1C, and one charge / discharge cycle at a voltage range of 2.5V to 4.25V and 0.2C / 0.2C, and then performing 50 charge / discharge cycles at 45°C, a voltage range of 2.5V to 4.25V, and 1.0C / 5.0C, and then measuring the ratio of the discharge capacity at the 50th cycle to the initial capacity (cycle capacity retention). [Table 3]

[0177] From Table 3, it can be seen that in Examples 1, 5 and 8, where the second heat treatment temperature was 705° C., the initial charge / discharge capacity was the highest.

[0178] In addition, it was confirmed that the ratio of the Co content during the first heat treatment and the second heat treatment was 1 / 3, and in the cases of Examples 1, 2 and 3, the high temperature life characteristics were good.

[0179] Meanwhile, it was confirmed that in Example 1, in which the ratio of Co content during the first heat treatment and the second heat treatment was 1 / 3 and the second heat treatment temperature was 705° C., optimal battery characteristics were realized.

Claims

1. Contains a lithium composite oxide, A positive electrode active material, which satisfies the following relational expression 1 in an XRD pattern obtained by Rietveld fitting as a result of X-ray diffraction (XRD) analysis using CuKα radiation. [0010] In the above-mentioned Relational Formula 1, the FWHM （１０４） means the full width at half maximum (FWHM (deg., 2θ)) of the (104) plane in an XRD peak defined by a hexagonal lattice having an R-3m space group.

2. 2. The positive electrode active material according to claim 1, wherein the positive electrode active material satisfies the following Relational Formula 2 in an XRD pattern obtained by Rietveld fitting as a result of X-ray diffraction (XRD) analysis using CuKα radiation: [0025] In the above-mentioned Relational Formula 2, the FWHM （００３） means the full width at half maximum (FWHM (deg., 2θ)) of the (003) plane in the XRD peak defined by a hexagonal lattice having the R-3m space group.

3. The positive electrode active material according to claim 1, wherein the a-axis lattice constant is 2.860 to 2.

890.

4. The positive electrode active material according to claim 1, wherein the c-axis lattice constant is 14.190 to 14.

200.

5. 2. The positive electrode active material of claim 1, wherein the positive electrode active material is in a bi-modal form including first positive electrode active material particles having an average particle size (D50) of 8 μm or more and second positive electrode active material particles having an average particle size (D50) of 7 μm or less.

6. Providing an oxide precursor; and performing a first heat treatment on a first mixture including the prepared oxide precursor, a lithium-containing compound, and a first cobalt-containing compound to prepare a first lithium composite oxide.

7. 7. The method of claim 6, further comprising, after the step of preparing the first lithium composite oxide, performing a second heat treatment on a second mixture including the prepared first lithium composite oxide and a second cobalt-containing compound to prepare a second lithium composite oxide.

8. 8. The method of claim 7, wherein, in the step of preparing the first lithium composite oxide, a mol % of cobalt contained in the first cobalt-containing compound is A based on the total metal of the prepared oxide precursor, and in the step of preparing the second lithium composite oxide, a mol % of cobalt contained in the second cobalt-containing compound is B based on the total metal excluding lithium of the prepared first lithium composite oxide, and 0.1≦A / B≦0.

5.

9. The first cobalt-containing compound is Co ３ O ４ The method for producing a positive electrode active material according to claim 6 ,

10. The second cobalt-containing compound is Co ３ O ４ The method for producing a positive electrode active material according to claim 7 ,

11. The method of claim 7 , wherein the second heat treatment temperature Y is in the range of 690° C.<Y<720° C.

12. A positive electrode active material produced by the method according to claim 6.

13. A positive electrode comprising the positive electrode active material of claim 1.

14. A secondary battery comprising the positive electrode active material according to claim 1.

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