Lithium composite oxide and positive electrode active material for secondary battery containing the same

Abstract

To provide a positive electrode active material, capable of significantly improving DC-IR characteristics, capacity characteristics, output characteristics and life characteristics of a battery.SOLUTION: A positive electrode active material according to an embodiment of the present invention includes a first lithium composite oxide particle including a secondary particle formed by aggregation of one or more primary particles, and a coating oxide occupying at least a part of at least one of surfaces of the secondary particle, grain boundaries between the primary particles, or surfaces of the primary particles. The positive electrode active material satisfies an equation of 1.3≤a / b≤3.0 where a represents a max peak intensity at 2θ=44.75° to 44.80° and b represents a max peak intensity at 2θ=45.3° to 45.6° in X-ray diffraction (XRD) analysis using Cu Kα radiation.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a lithium composite oxide and a positive electrode active material for a secondary battery containing the same. As a result of X-ray diffraction (XRD) analysis using CuKα rays, more specifically, it relates to a positive electrode active material in which the ratio of the maximum peak intensity appearing at 2θ 44.75° to 44.80° and the maximum peak intensity appearing at 2θ 45.3° to 45.6° is adjusted.

[0002] Also, as one aspect, it relates to a positive electrode active material in which the maximum peak intensity ratio is adjusted with respect to a bimodal type positive electrode active material in which large particles and small particles with adjusted grain boundary densities are mixed.

Background Art

[0003] With the development of portable mobile electronic devices such as smartphones, MP3 players, and tablet PCs, the demand for secondary batteries that can store 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.

[0004] As the lithium composite oxide contained in the positive electrode active material, the most spotlighted substance recently is lithium nickel manganese cobalt oxide Li(Ni x Co y Mn z )O2 (where x, y, and z are the atomic fractions of the independent oxide composition elements, 0 < x = 1, 0 < y = 1, 0 < z = 1, and 0 < x + y + z = 1). The material of 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 has the advantage of being inexpensive because the Co content is relatively low. However, in particular, in the case of high-nickel (Hi-nickel) positive electrode active materials in which the nickel content is increased to 50 mol% or more to realize high capacity, structural instability occurs due to the mixing of cations as the nickel content increases, which can lead to a rapid deterioration of battery characteristics not only at high temperatures but also at room temperature. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a cathode active material that significantly improves the DC-IR characteristics, capacity characteristics, output characteristics, and life characteristics of a battery by adjusting the ratio of the maximum peak intensity appearing at 2θ 44.75° to 44.80° and the maximum peak intensity appearing at 2θ 45.3° to 45.6° when coating a lithium composite oxide. [Means for solving the problem]

[0006] The cathode active material of the present invention includes first particles of a lithium composite oxide including secondary particles formed by aggregation of at least one or more primary particles, and a coating oxide occupying at least a portion of at least one of the surfaces of the secondary particles, the grain boundaries between the primary particles, and the surfaces of the primary particles. When analyzed by X-ray diffraction (XRD) using CuKα radiation, the maximum peak intensity appearing in the 2θ range of 44.75° to 44.80° is defined as a and the maximum peak intensity appearing in the 2θ range of 45.3° to 45.6° is defined as b, where a / b is a relationship of 1.3≦a / b≦3.0.

[0007] In one embodiment, 400≦a≦1200.

[0008] In one embodiment, 150≦b≦500.

[0009] In one embodiment, the coating oxide can be represented by the following Chemical Formula 3:

[0010] Li p M3 q O r

[0011] In the formula 3, 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, and 0≦p≦10, 0 <q≦8、2≦r≦13である。

[0012] In one embodiment, in a cross-sectional image of the secondary particles taken with a scanning electron microscope (SEM), the grain boundary density calculated by the following Equation 1 for primary particles and grain boundaries between primary particles placed on a line that passes through the center of the secondary particle and crosses the minor axis direction may be 0.85 or more.

[0013] [Formula 1] Grain boundary density = Number of grain boundaries between primary particles placed on the line / Number of primary particles placed on the line

[0014] In one embodiment, the positive electrode active material further includes second particles of a lithium composite oxide including secondary particles formed by aggregation of at least one primary particle, and a coating oxide occupying at least a portion of at least one of the surfaces of the secondary particles of the lithium composite oxide, the grain boundaries between the primary particles, and the surfaces of the primary particles, wherein the average diameter (D50) of the first particles of the lithium composite oxide may be 8 μm or more, and the average diameter (D50) of the second particles of the lithium composite oxide may be 7 μm or less.

[0015] In one embodiment, the grain boundary density of the second particles of the lithium composite oxide may be 0.95 or less.

[0016] In one embodiment, when the weight of the first particles of the lithium composite oxide contained in the positive electrode active material is w1 and the weight of the second particles of the lithium composite oxide is w2, w1 / w2 can be 1.5 to 9.0.

[0017] The positive electrode of the present invention contains the positive electrode active material.

[0018] The secondary battery of the present invention includes the positive electrode. [Effects of the Invention]

[0019] As one effect, the positive electrode active material of the present invention can significantly improve the DC-IR characteristics, capacity characteristics, output characteristics and life characteristics of a battery.

[0020] Another effect is that the problem of large deviation in average particle size or reduced impedance and life characteristics due to simultaneous firing of large and small particles in bimodal type positive electrode active materials can be significantly improved. [Brief explanation of the drawings]

[0021] [Figure 1] 1 shows the results of X-ray diffraction (XRD) analysis using CuKα radiation for a positive electrode active material according to an embodiment of the present invention. [Figure 2] 1 is a diagram illustrating Co doping and Co coating by cation mixing phenomenon. DETAILED DESCRIPTION OF THE INVENTION

[0022] As used herein, expressions such as "comprises" should be understood as open-ended terms that may include other configurations.

[0023] As used herein, the terms "preferred" and "preferably" refer to embodiments of the invention that may provide certain benefits, under certain circumstances, but are not intended to exclude other embodiments from the scope of the invention.

[0024] Also, as used in the specification and the appended claims, the singular forms "a," "an," and "the" are to be understood as including the plural forms as well, unless the context clearly dictates otherwise.

[0025] On the other hand, the technical features described below relate to one aspect for achieving the effects aimed at by the present invention.

[0026] That is, the positive electrode active material according to one aspect of the present invention includes the technical features according to one aspect described below, and can significantly improve the DC-IR characteristics, capacity characteristics, output characteristics, and life characteristics of the battery.

[0027] In this specification, a distinction is made between lithium composite oxides and coating oxides.

[0028] When the lithium composite oxide particles according to one embodiment of the present invention are coated, a portion of the coating element may be present in the lattice structure of the primary particles contained in the lithium composite oxide particles, which is expressed as the coating element being doped into the lithium composite oxide particles, and the lithium composite oxide is defined to include all of the doped regions.

[0029] In yet another aspect, when the lithium composite oxide particles according to one embodiment of the present invention are coated, a portion of the coating element may form a coating oxide, which occupies at least a portion of at least one of the surfaces of secondary particles, the grain boundaries between primary particles, and the surfaces of primary particles contained in the lithium composite oxide particles.

[0030] A positive electrode active material according to one embodiment of the present invention includes first particles of a lithium composite oxide including secondary particles formed by aggregation of at least one or more primary particles.

[0031] When the secondary particle consists of one primary particle, the secondary particle may be the primary particle itself.

[0032] In one embodiment, the primary particles can include one or more crystallites.

[0033] In one embodiment, the first particles of the lithium composite oxide may have a single particle form including one primary particle, and when the primary particle is composed of one crystallite, the first particles may have a single crystal form.

[0034] In yet another aspect, the first particles of the lithium composite oxide may have a multiparticle or polycrystalline form including two or more primary particles, and more preferably, the first particles of the lithium composite oxide may have a multiparticle or polycrystalline form including an aggregation of 20 or more primary particles.

[0035] In a more preferred embodiment, the first particles of the lithium composite oxide may have a grain boundary density of 0.85 or more, or 0.90 or more.

[0036] In the present invention, the "grain boundary density" is calculated by the following Equation 1 for primary particles placed on a line crossing the center of the secondary particle in the minor axis direction in an SEM image obtained by photographing a cross section of the lithium composite oxide using a scanning electron microscope (SEM) after cross-section processing of the secondary particle.

[0037] [Formula 1] Grain boundary density = Number of grain boundaries between primary particles placed on the line / Number of primary particles placed on the line

[0038] To explain this by taking an example, in the case of a single particle that is not agglomerated and is made up of a single primary particle, the grain boundary density calculated by the above formula 1 would be 0. In addition, in the case of an agglomeration of two primary particles, the grain boundary density calculated by the above formula 1 would be 0.5.

[0039] Here, the grain boundary density means the average value for 10 randomly drawn straight lines.

[0040] The average particle size of the primary particles of the lithium composite oxide may be 1 to 30 μm, more preferably 8 to 20 μm.

[0041] Meanwhile, in the present invention, the "average particle size" refers to the average diameter (D50) when the particles are spherical, and refers to the average major axis length when the particles are non-spherical. The particle size can be measured using a particle size analyzer (PSA).

[0042] The present invention can be a unimodal type positive electrode active material.

[0043] In yet another more preferred embodiment, the positive electrode active material may be a bimodal type that further includes, in addition to the first particles of the lithium composite oxide, second particles of the lithium composite oxide, which include secondary particles formed by aggregation of at least one or more primary particles.

[0044] When the second particles are further included, the first particles of lithium composite oxide and the second particles of lithium composite oxide are distinguished from each other in that they have different average particle sizes. More specifically, the average diameter (D50) of the first particles of lithium composite oxide may be 8 μm or more, more preferably 10 to 20 μm, and the average diameter (D50) of the second particles of lithium composite oxide may be 7 μm or less, more preferably 1 to 5.0 μm.

[0045] The positive electrode active material according to one embodiment of the present invention may be a bimodal type in which large particles and small particles are mixed, and the small particles are located in the voids between the large particles, thereby increasing the energy density per unit volume. However, in the case of such a bimodal type, the deviation of the average particle size may increase upon sintering, or the impedance and life characteristics may be reduced.

[0046] One aspect of the present invention is to adjust Ni vacancies in the lattice structure of a lithium composite oxide in a bimodal type positive electrode active material, thereby increasing the energy density by small particles existing in the gaps between large particles, while resolving the problem of deterioration in battery characteristics due to changes in the deviation in the average particle size between large and small particles.

[0047] In a more preferred embodiment, where w1 represents the weight of the first lithium composite oxide particles contained in the positive electrode active material and w2 represents the weight of the second lithium composite oxide particles, the w1 / w2 ratio may be 1.5 to 9.0, more preferably 2.3 to 4. That is, the first and second particles may be mixed in a ratio of 6:4 to 9:1, more preferably 7:3 to 8:2. In the present invention, by adjusting Ni vacancies within the lithium composite oxide lattice structure in a bimodal-type positive electrode active material having such a mixing ratio, the energy density can be increased by small particles existing in the gaps between large particles, while the problem of reduced battery performance due to variations in the average particle size of the large and small particles can be resolved.

[0048] The secondary particles of the lithium composite oxide according to one embodiment of the present invention may have a single particle form including one primary particle, and when the primary particle is composed of one crystallite, the secondary particles may have a single crystal form.

[0049] In yet another embodiment of the present invention, the secondary particles of the lithium composite oxide may have a multi-particle or polycrystalline form including two or more primary particles.

[0050] In a more preferred embodiment, in the bimodal type positive electrode active material, the grain boundary density of the second particles may be 0.95 or less, 0.90 or less, 0.85 or less, 0.80 or less, 0.75 or less, 0.70 or less, 0.65 or less, 0.60 or less, 0.55 or less, or 0.5 or less.

[0051] The lithium composite oxide according to one embodiment of the present invention may be a lithium-nickel based composite oxide containing lithium and nickel.

[0052] In one embodiment, the nickel is Excluding lithium relative to the total molar content of transition metals, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more or 90 The high nickel-based lithium composite oxide may contain at least 100% by mole of nickel.

[0053] In one embodiment, the lithium composite oxide may be a lithium-nickel composite oxide containing lithium, nickel, and aluminum.

[0054] In one embodiment, the lithium composite oxide may be a lithium nickel composite oxide containing lithium, nickel, and manganese.

[0055] In one embodiment, the lithium composite oxide can be represented by the following Chemical Formula 1:

[0056] [C1] Li a Ni x Co y M 1-x-y O2

[0057] In Chemical Formula 1, M is selected from the group consisting of Al, Mn, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, and combinations thereof, and 0.9≦a≦1.3, 0.6≦x≦1.0, 0.0≦y≦0.4, and 0.0≦1−xy≦0.4.

[0058] In one embodiment, the lithium composite oxide can be represented by the following Chemical Formula 2.

[0059] [C2] Li a’ Ni x’ Coy’ M1 z’ M2 1-x’-y’-z’ O2

[0060] In Chemical Formula 2, M1 is Al or Mn, and M2 is selected from the group consisting of B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, and combinations thereof, and 0.9≦a′≦1.3, 0.6≦x′≦1.0, 0.0≦y′≦0.4, 0.0≦z′≦0.4, and 0.0≦1−x′−y′−z′≦0.4.

[0061] Also, a positive electrode active material according to an embodiment of the present invention includes a coating oxide occupying at least a portion of at least one of the surfaces of secondary particles, grain boundaries between primary particles, and surfaces of primary particles.

[0062] In addition, in the case of a bimodal type positive electrode active material, the positive electrode active material may further include a coating oxide occupying at least a portion of at least one of the surfaces of the secondary particles of the second particles of the lithium composite oxide, the grain boundaries between the primary particles, and the surfaces of the primary particles.

[0063] In one embodiment, the coating oxide can be represented by the following Chemical Formula 3:

[0064] [C3] Li p M3 q O r

[0065] In the formula 3, 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, and 0≦p≦10, 0 <q≦8、2≦r≦13である。

[0066] As an example, in Chemical Formula 3, M3 represents a coating element, and the coating oxide can be an oxide in which lithium and the element represented by M3 are combined, or an oxide of M3.

[0067] As an 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 , or Li p (W / Ti / B) q O r and can be, but is not limited to, these.

[0068] In a more preferred embodiment, the coating oxide can be Li p’ Co q’ Or’ (where 0 ≦ p’ ≦ 10, 0 < q’ ≦ 8, 2 ≦ r’ ≦ 13).

[0069] In a more preferred embodiment, the coating oxide may include LiCoO2.

[0070] When the coating oxide occupies at least a portion of the surface of the primary particle, the surface of the primary particle may be a surface region of the primary particle that forms the outermost periphery of the secondary particle, or may be a surface region of the primary particle that does not form the outermost periphery of the secondary particle.

[0071] Here, the surface region of the primary particle forming the outermost periphery of the secondary particle can be interpreted as the surface of the secondary particle.

[0072] The coating oxide may include a concentration gradient portion where the molar concentrations of elements contained in the coating oxide vary. For example, if the coating oxide includes lithium, the molar concentration of lithium may vary. Also, for example, the molar concentrations of one or more of M3 contained in the coating oxide may vary.

[0073] In one aspect, when the coating oxide occupies at least a portion of the surface region of a primary particle that forms the outermost periphery of the secondary particle, the concentration gradient portion may decrease, increase, or increase and then decrease in a direction from the surface of the primary particle that forms the outermost periphery of the secondary particle toward the center of the secondary particle.

[0074] In addition, the concentration gradient portion may decrease, increase, or increase and then decrease in a direction from the surface of the primary particle forming the outermost periphery of the secondary particle toward the center of the primary particle.

[0075] In one aspect, when the coating oxide occupies at least a portion of the surface region of the primary particle that does not form the outermost periphery of the secondary particle, it may decrease, increase, or increase and then decrease in a direction from the surface of the primary particle toward the center of the primary particle.

[0076] In the present invention, X-ray diffraction (XRD) analysis was performed using a Bruker D8 Advance diffractometer with CuKα radiation (1.540598 Å), with a step size (° / step) of 0.01° / step and a measurement time per step of 0.1 s / step.

[0077] In the present invention, the maximum peak intensity means the maximum value of the peak in the region.

[0078] In this specification, the maximum peak intensity appearing at 2θ 44.75° to 44.80° as a result of X-ray diffraction (XRD) analysis using CuKα radiation is referred to as a. In one embodiment, the a may be the maximum peak intensity appearing at 2θ 44.80°.

[0079] In the present invention, the maximum peak intensity a was determined by using the average diffraction peak intensity in the flat section in the 2θ range of 30° to 50° as a background correction value and subtracting the background correction value from the uncorrected maximum peak intensity (max peak intensity) appearing in the 2θ range of 44.75° to 44.80°.

[0080] In this specification, the maximum peak intensity appearing at 2θ 45.3° to 45.6° as a result of X-ray diffraction (XRD) analysis using CuKα rays is defined as b.

[0081] The maximum peak intensity b was calculated by subtracting the average diffraction peak intensity in the flat section in the 2θ range of 30° to 50° as the background correction value from the uncorrected maximum peak intensity (max peak intensity) appearing in the 2θ range of 45.3° to 45.6°.

[0082] Here, the ratio a / b of the maximum peak intensity a to the maximum peak intensity b may be 1.3 or more or 1.5 or more and 3.0 or less or 2.5 or less. The inventors have confirmed that when the ratio a / b of the maximum peak intensity a to the maximum peak intensity b is adjusted to 1.3≦a / b≦3.0, more preferably 1.5≦a / b≦2.5, the output characteristics and life characteristics are significantly improved.

[0083] The maximum peak intensity a appearing at 2θ 44.75° to 44.80° may be due to a phase where the coating element is enriched in a region partially present in the primary particle, as the coating element is doped into the lattice structure of the primary particle contained in the lithium composite oxide particle when the lithium composite oxide particle is coated.

[0084] More specifically, the primary particles contained in the nickel-containing lithium composite oxide particles are Ni 2+ Cation mixing occurs due to the presence of Ni vacancies in the lithium composite oxide lattice structure. In particular, in the case of high-nickel positive electrode active materials, this cation mixing occurs more easily. Here, when lithium composite oxide particles are coated, the Ni vacancies in the lattice structure are easily doped with the coating element, forming regions partially enriched with the coating element.

[0085] The maximum peak intensity b appearing at 2θ of 45.3° to 45.6° may be due to a coating oxide formed by coating the lithium composite oxide particles.

[0086] The Ni vacancy can be controlled by the manufacturing process according to one aspect of the present invention.

[0087] The coating oxide according to one embodiment of the present invention improves the output characteristics of a battery through high ionic conductivity, extends the life of the battery by protecting the surface of the positive electrode active material, and effectively reduces residual lithium on the surface of the lithium composite oxide, thereby preventing side reactions caused by unreacted residual lithium.

[0088] However, if the doping of the coating element is significantly reduced, the amount of Ni in the lattice structure of the lithium composite oxide becomes too large, resulting in Ni 4+ This can be accompanied by electrolyte reactions, which may actually reduce the battery's life characteristics.

[0089] Therefore, the present invention provides a positive electrode active material that can maximize battery performance by controlling the doping of coating elements and the degree of coating oxide formation.

[0090] The ratio a / b can be controlled by adjusting Ni vacancies in the lithium composite oxide lattice, and as will be described later, the Ni vacancies can be controlled by adjusting the washing and coating processes.

[0091] In a more preferred embodiment, the maximum peak intensity a may be 400 or more, 450 or more, and 1200 or less, or 1000 or less.

[0092] In a more preferred embodiment, the maximum peak intensity b may be 150 or more, 200 or more, 250 or more, or 500 or less.

[0093] The positive electrode active material of the present invention may include first particles of a lithium composite oxide having the above-described technical features and a coating oxide thereof, and / or second particles of a lithium composite oxide and a coating oxide thereof.

[0094] In addition, the technical characteristics of the first particles of lithium composite oxide and their coating oxide, and / or the second particles of lithium composite oxide and their coating oxide may relate to average characteristics of a plurality of particles.

[0095] Meanwhile, the meanings of "≦", "greater than", and "less than" described in the present invention can be replaced with the meanings of "<", "more than", and "less than".

[0096] The method for producing a positive electrode active material of the present invention is not limited to a specific method as long as it has the above-described technical features, but as a more preferred embodiment, the positive electrode active material can be produced as follows.

[0097] In particular, in one production embodiment of the present invention, the coating step can be carried out at a pH range of 11 to 13. After producing the lithium composite oxide, and prior to mixing with the coating compound, a washing step can be carried out in which a washing solution is poured into the produced lithium composite oxide and NaOH is added to the washing solution in an amount of 1.1 to 3.4 wt %, 1.3 to 3.2 wt %, or 1.5 to 3.0 wt % relative to the total weight of the lithium composite oxide.

[0098] In one embodiment, the cleaning solution may be distilled water or alcohol, more preferably distilled water.

[0099] The present invention can adjust Ni vacancies by controlling the size, uniformity and rate of coprecipitated particles through the amount of NaOH added to the cleaning solution prior to mixing with the coating compound.

[0100] If the amount of NaOH contained in the cleaning solution is too small, the co-precipitation reaction may not occur well or the co-precipitated particles may be too small, resulting in a / b being less than 1.3.

[0101] Also, if the amount of NaOH contained in the cleaning solution is too large, the coating compound particles mixed therein will become too large, and the ratio a / b may exceed 3.0.

[0102] In addition to the above-described manufacturing process, in one manufacturing embodiment of the present invention, the a / b value is adjusted by adjusting the content of the coating compound, the heat treatment temperature, and the reaction time.

[0103] In a more specific embodiment of the production process, hydroxide precursor particles are first produced.

[0104] Here, when a bimodal type is to be produced, the hydroxide precursor is produced in two forms, large particles and small particles, which have different particle sizes.

[0105] Next, the hydroxide precursor particles are oxidized to produce an oxide precursor.

[0106] Next, the oxide precursor is mixed with a lithium compound and heat-treated to produce a lithium composite oxide.

[0107] In one embodiment, the heat treatment can be carried out by mixing the oxide precursor with a lithium compound, raising the temperature to 750 to 850° C. at a rate of 1 to 3° C. per minute, and then performing heat treatment for 10 to 14 hours.

[0108] In one embodiment, a compound selected from B, Ba, Ce, Cr, F, Mg, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, or Sr can be heat-treated together during this process.

[0109] Next, a cleaning solution is added to the produced lithium composite oxide, and NaOH is added to the cleaning solution in an amount of 1.1 to 3.4 wt % relative to the total wt % of the lithium composite oxide.

[0110] Next, a coating compound in the form of an aqueous solution is added so that the content of the coating elements contained in the coating compound is 2.5 to 10.0 mol % based on the total metal elements excluding lithium, and a coating step is carried out while stirring.

[0111] Next, the coated lithium composite oxide is dried at 100 to 140°C, and then heated to 650 to 750°C at a rate of 1 to 3°C per minute, followed by heat treatment for 10 to 14 hours, thereby producing the lithium composite oxide.

[0112] A positive electrode according to one aspect of the present invention includes the positive electrode active material.

[0113] Except for the use of the above-described 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 a positive electrode current collector of a secondary battery.

[0114] A secondary battery according to one aspect of the present invention includes the positive electrode active material.

[0115] 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.

[0116] Examples of the present invention will be described in more detail below.

[0117] Manufacturing of positive electrode active materials

[0118] Example 1

[0119] (a) Large and small particles of NiCoAl(OH) hydroxide precursors (Ni:Co:Al = 95:4:1 (at%)) were synthesized by the known co-precipitation method using nickel sulfate, cobalt sulfate, and aluminum sulfate, respectively.

[0120] The synthesized NiCoAl(OH)2 hydroxide precursor was converted to an oxide precursor by heating at 400°C for 6 hours at a rate of 2°C per minute.

[0121] The large particle oxide precursor had an average particle size (D50) of 15.0 μm, and the small particle oxide precursor had an average particle size (D50) of 3.0 μm.

[0122] (b) The large particle oxide precursor and the small particle oxide precursor prepared in step (a) were weighed out to a weight ratio of 80:20, and then LiOH (Li / (Ni+Co+Al) molar ratio = 1.05) was added and mixed. The mixture was then heated to 800°C at a rate of 2°C per minute while maintaining an O2 atmosphere in a calciner, and heat-treated for 12 hours to obtain a lithium composite oxide.

[0123] (c) Distilled water was added to the lithium composite oxide produced, and 1.5 wt% of NaOH was added based on the lithium composite oxide. Subsequently, a 5.0 wt% aqueous solution of cobalt sulfate was added while stirring so that the cobalt content of the aqueous solution was 3.0 mol% based on the metal elements (Ni, Co, and Al) of the intermediate product excluding lithium, thereby coating the surface of the lithium composite oxide particles. After the reaction was completed, the product was dried at 120°C for 12 hours.

[0124] (d) The dried product was heated to 700°C at a rate of 2°C per minute in a firing furnace while maintaining an O2 atmosphere, and then heat-treated at 700°C for 12 hours to obtain a positive electrode active material.

[0125] <Example 2>

[0126] A positive electrode active material was obtained in the same manner as in Example 1, except that in step (c), NaOH was added in an amount of 2.0 wt % based on the lithium composite oxide.

[0127] Example 3

[0128] A positive electrode active material was obtained in the same manner as in Example 1, except that in step (c), NaOH was added in an amount of 2.5 wt % based on the lithium composite oxide.

[0129] Example 4

[0130] A positive electrode active material was obtained in the same manner as in Example 1, except that in step (c), NaOH was added in an amount of 3.0 wt % based on the lithium composite oxide.

[0131] <Example 5>

[0132] A cathode active material was prepared in the same manner as in Example 1, except that in step (b), the large particle oxide precursor and the small particle oxide precursor were weighed out to a weight ratio of 80:20, and then mixed with LiOH (Li / (Ni+Co+Al) molar ratio=1.05) and H3BO3 (B / (Ni+Co+Al) molar ratio=0.015), followed by heat treatment.

[0133] Example 6

[0134] A positive electrode active material was prepared in the same manner as in Example 1, except that in step (b), the large particle oxide precursor and the small particle oxide precursor were weighed out to a weight ratio of 80:20, and then mixed with LiOH (Li / (Ni+Co+Al) molar ratio=1.05) and Zr(OH) (Zr / (Ni+Co+Al) molar ratio=0.005), followed by heat treatment.

[0135] <Comparative Example 1>

[0136] A positive electrode active material was obtained in the same manner as in Example 1, except that in step (c), NaOH was added in an amount of 1.0 wt % based on the lithium composite oxide.

[0137] <Comparative Example 2>

[0138] A positive electrode active material was obtained in the same manner as in Example 1, except that in step (c), NaOH was added in an amount of 0.5 wt % based on the lithium composite oxide.

[0139] <Comparative Example 3>

[0140] A positive electrode active material was obtained in the same manner as in Example 1, except that in step (c), NaOH was added in an amount of 3.5 wt % based on the lithium composite oxide.

[0141] <Comparative Example 4>

[0142] A positive electrode active material was obtained in the same manner as in Example 1, except that in step (c), NaOH was added in an amount of 4.0 wt % based on the lithium composite oxide.

[0143] Lithium secondary battery manufacturing

[0144] A positive electrode slurry was prepared by dispersing 92 wt% of the positive electrode active materials prepared in the Examples and Comparative Examples, 4 wt% of artificial graphite, and 4 wt% of a PVDF binder in 30 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was uniformly coated on a 15 μm-thick aluminum foil and dried under vacuum at 135° C. to prepare a positive electrode for a lithium secondary battery.

[0145] 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 solution of 1.15 M LiPF in a solvent of ethylene carbonate and ethyl carbonate mixed in a volume ratio of 3:7.

[0146] <Experimental Example 1> Measurement of maximum peak intensity

[0147] The results of the X-ray diffraction (XRD) analysis are shown in Figure 1. For the positive electrode active materials according to the examples and comparative examples, the maximum peak intensity a appearing at 2θ between 44.75° and 44.80° and the maximum peak intensity b appearing at 2θ between 45.3° and 45.6° were measured, and the a / b values ​​were calculated and shown in Table 1 below.

[0148] The X-ray diffraction (XRD) analysis was performed using a Bruker D8 Advance diffractometer with CuKα radiation (1.540598 Å) at a step size of 0.01° / step and a measurement time per step of 0.1 s / step. The average diffraction peak intensity in the flat section in the 2θ range of 30° to 50° was used as a background correction value, and the maximum peak intensity was calculated by subtracting this background correction value from the measured maximum peak intensity.

[0149] [Table 1]

[0150] <Experimental Example 2> DC-IR characteristic evaluation

[0151] The lithium secondary batteries according to the examples and comparative examples were charged and discharged at 25° C. based on SOC 100% and stored at 60° C. for 7 days, and then the resistance was measured. The results are shown in Table 2 below.

[0152] [Table 2]

[0153] <Experimental Example 3> Initial charge capacity, initial discharge capacity, charge / discharge efficiency

[0154] A charge-discharge experiment was carried out on the lithium secondary batteries according to the examples and comparative examples using an electrochemical analyzer (Toyo, Toscat-3100) at 25° C., a voltage range of 3.0 V to 4.25 V, and a discharge rate of 0.2 C. The initial charge capacity, initial discharge capacity, and charge / discharge efficiency measured are shown in Table 3 below.

[0155] [Table 3]

[0156] <Experimental Example 4> Output characteristics evaluation

[0157] The lithium secondary batteries according to the examples and comparative examples were charged and discharged at 25° C. in a voltage range of 3.0 V to 4.25 V using an electrochemical analyzer (Toyo, Toscat-3100).

[0158] The rate capability (C-rate) measured in this way is shown in Table 4 below.

[0159] [Table 4]

[0160] <Experimental Example 5> Evaluation of life characteristics

[0161] The lithium secondary batteries according to the examples and comparative examples were charged and discharged 50 times at 60°C and 1C / 1C within a driving voltage range of 3.0V to 4.35V, and then the cycle capacity retention at the 50th cycle relative to the initial capacity was measured and shown in Table 5 below.

[0162] [Table 5]

Claims

1. First particles of a lithium composite oxide including secondary particles formed by aggregation of at least one or more primary particles; a coating oxide occupying at least a portion of at least one of the surfaces of the secondary particles, the grain boundaries between the primary particles, and the surfaces of the primary particles; As a result of X-ray diffraction (XRD) analysis using CuKα radiation, when the maximum peak intensity (max peak intensity) appearing at 2θ 44.75° to 44.80° is defined as a and the maximum peak intensity (max peak intensity) appearing at 2θ 45.3° to 45.6° is defined as b, A positive electrode active material in which 1.3≦a / b≦3.0, The lithium composite oxide is a high-nickel lithium composite oxide containing nickel in an amount of 50 mol% or more relative to the total molar content of transition metals excluding lithium, The coating oxide is represented by the following chemical formula 3: [C3] Li ｐ M3 ｑ O ｒ In the formula 3, M3 is Co, and 0≦p≦10, 0<q≦8, and 2≦r≦13.

2. 2. The cathode active material of claim 1, wherein in a cross-sectional image of the secondary particles taken with a scanning electron microscope (SEM), a grain boundary density calculated by Equation 1 below for primary particles and grain boundaries between primary particles located on a line that passes through a center of the secondary particle and crosses the minor axis direction is 0.85 or more: [Formula 1] Grain boundary density = number of grain boundaries between primary particles placed on the line / number of primary particles placed on the line

3. The positive electrode active material is Second particles of a lithium composite oxide including secondary particles formed by aggregation of at least one or more primary particles; a coating oxide occupying at least a portion of at least one of the surfaces of the secondary particles of the second particles of the lithium composite oxide, the grain boundaries between the primary particles, and the surfaces of the primary particles, The average diameter (D50) of the first particles of the lithium composite oxide is 8 μm or more, The positive electrode active material according to claim 1 , wherein the average diameter (D50) of the second particles of the lithium composite oxide is 7 μm or less.

4. The positive electrode active material according to claim 3 , wherein the second particles of the lithium composite oxide have a grain boundary density of 0.95 or less.

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

6. A secondary battery comprising the positive electrode according to claim 5 .

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