Precursor for positive electrode active material for secondary battery and positive electrode active material

Abstract

To provide a precursor for a positive electrode active material for a secondary battery and a positive electrode active material manufactured from the precursor and to control the physical properties of precursor particles of the positive electrode active material to control the physical properties of the positive electrode active material manufactured therefrom, thereby applying the positive electrode active material to a secondary battery to improve the life characteristics.SOLUTION: The precursor for a positive electrode active material contains multiple hydroxide particles. An X-ray diffraction (XRD) analysis result using CuKα rays and an XRD pattern obtained by Rietveld fitting satisfy the following formula 1. (Formula 1) 0.82≤FWHM(102)≤1.22 In the above Formula 1, FWHM(102) denotes the full width at half maximum (FWHM (deg., 2θ)) of the (102) plane in the XRD peak defined by the hexagonal lattice with the R-3m space group.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cathode active material precursor for a secondary battery and a cathode active material produced from the cathode active material precursor, and more particularly to those in which the cathode active material precursor is a precursor in the form of a hydroxide and a precursor in the form of an oxide.

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-scale 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 cathode 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 the independent oxide composition elements, respectively, 0 < x ≤ 1, 0 < y ≤ 1, 0 < z ≤ 1, and 0 < x + y + z ≤ 1). This cathode 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 cathode active material, and it has the advantage of being inexpensive because the Co content is relatively low.

[0004] However, such a lithium composite oxide will undergo 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, there is an increasing demand for high-nickel positive active materials, or nickel-rich systems, in which the nickel (Ni) content is 50 mol% or more relative to the total transition metal content excluding lithium (Li), as positive active materials for secondary batteries.

[0006] However, although such nickel-rich positive electrode active materials have the advantage of high energy density, the increased Ni content causes problems such as increased structural instability due to Li / Ni cation mixing, physical disconnection of internal particles due to microcracks, and deepening electrolyte depletion, resulting in rapid deterioration of life characteristics at room and high temperatures. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to control the physical properties of the positive electrode active material precursor particles, thereby controlling the physical properties of the positive electrode active material produced from them, and to apply the positive electrode active material to a secondary battery to improve its life characteristics. [Means for solving the problem]

[0008] A positive electrode active material precursor according to one embodiment of the present invention is a precursor including a plurality of hydroxide particles, and as a result of X-ray diffraction (XRD) analysis using CuKα radiation, the following Relational Expression 1 can be satisfied in an XRD pattern obtained by Rietveld fitting. (Equation 1) 0.82≦FWHM (102) ≦1.22

[0009] In the above-mentioned Relational Formula 1, the FWHM (102) means the full width at half maximum (FWHM (deg., 2θ)) of the (102) plane in the XRD peak defined by a hexagonal lattice having the R-3m space group. In addition, a positive electrode active material precursor according to one embodiment of the present invention is a precursor including a plurality of oxide particles, and as a result of X-ray diffraction (XRD) analysis using CuKα radiation, the following Relational Expression 2 can be satisfied in an XRD pattern obtained by Rietveld fitting. (Equation 2) 127≦XRD peak Integral breadth / 4tanθ≦137

[0010] In the above Relation 2, the XRD peak integral breadth is the value obtained by dividing the "area of ​​the XRD peak" by the "height of the XRD peak", and θ is the Bragg angle of the peak.

[0011] In one embodiment, the particles contained in the positive electrode active material may be first particles having an average particle size (D50) of 8 μm or more, and may further include second particles having an average particle size (D50) of 7 μm or less.

[0012] In one embodiment, the positive electrode active material precursor including the oxide particles can be produced from the positive electrode active material precursor including the hydroxide particles.

[0013] In one embodiment, the average porosity A of the positive electrode active material particles contained in the positive electrode active material may be 5%≦A≦7%.

[0014] In one embodiment, the positive electrode active material particles contained in the positive electrode active material may be first particles having an average particle size (D50) of 8 μm or more, and may further include second particles having an average particle size (D50) of 7 μm or less.

[0015] In one aspect, the positive electrode active material particles included in the positive electrode active material may include 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. A positive electrode according to an embodiment of the present invention may include the positive electrode active material. A secondary battery according to an embodiment of the present invention may include the positive electrode active material. Effect of the Invention

[0016] As one effect, the present invention controls the physical properties of the positive electrode active material precursor particles, thereby controlling the physical properties of the positive electrode active material produced from the particles, and the positive electrode active material can be applied to a secondary battery to improve its life characteristics. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a cross-sectional SEM image of positive electrode active materials according to examples and comparative examples of the present invention. [Diagram 2] FIG. 2 is a diagram showing the results of measuring the particle strength of oxide precursors according to examples of the present invention and comparative examples. [Diagram 3] FIG. 2 is a graph showing the results of measuring the rate of change in average particle size (D50) after pressing of oxide precursors according to examples of the present invention and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] As used herein, terms such as "comprises" should be understood as open-ended terms that encompass the possibility of including other configurations.

[0019] 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.

[0020] 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.

[0021] Meanwhile, the technical features described below relate to one aspect for achieving the effects aimed at by the present invention as described above.

[0022] That is, the cathode active material precursor particles and the cathode active material particles according to one embodiment of the present invention include technical features according to one embodiment described below, and thus when applied to a secondary battery, the battery characteristics can be significantly improved.

[0023] The present invention relates to a positive electrode active material precursor and a positive electrode active material for a secondary battery, and the secondary battery of the present invention is not limited to a particular type as long as it is a battery that converts external electrical energy into a form of chemical energy, stores it, and can be reused. 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.

[0024] First, the positive electrode active material precursor particles of the present invention will be described. Meanwhile, in this specification, a positive electrode active material precursor containing a plurality of hydroxide particles is referred to as a "hydroxide precursor", and a positive electrode active material precursor containing a plurality of oxide particles is referred to as an "oxide precursor".

[0025] A positive electrode active material precursor according to one embodiment of the present invention is a precursor including a plurality of hydroxide particles, and as a result of X-ray diffraction (XRD) analysis using CuKα radiation, the following Relational Expression 1 can be satisfied in an XRD pattern obtained by Rietveld fitting. (Equation 1) 0.82≦FWHM (102) ≦1.22,

[0026] In the above-mentioned Relational Formula 1, the FWHM (102) means the full width at half maximum (FWHM (deg., 2θ)) of the (102) plane in the XRD peak defined by a hexagonal lattice having the R-3m space group. 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.

[0027] In the present invention, the corundum disc used was a NIST corundum disc.

[0028] 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 0.01° / step and a measurement time per step of 0.05 s / step.

[0029] In one embodiment, in the above-mentioned relation 1, FWHM (102) can be 0.9 or more or 1.1 or less.

[0030] In one embodiment, the hydroxide particles can include nickel (Ni).

[0031] In one embodiment, the hydroxide particles may further include at least one selected from the group consisting of cobalt (Co), aluminum (Al), and manganese (Mn).

[0032] In one embodiment, the hydroxide particles can be represented by the following Chemical Formula 1: (chemical formula 1) Ni x Co y M 1-x-y (OH)2

[0033] 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 0.5≦x≦1.0, 0.0≦y≦0.4, and 0.0≦1-xy≦0.4.

[0034] In one embodiment, the hydroxide particles can be represented by the following Formula 1-1: (Chemical formula 1-1) Ni x’ Co y’ M1 z’ M2 1-x’-y’-z’ (OH)2

[0035] 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, 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.

[0036] In one embodiment, x and / or x', which means nickel (Ni) mole % relative to the total transition metal mole %, 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 hydroxide having 0.8 or more, or 0.9 or more.

[0037] In one embodiment, in Formula 1 and / or Formula 1-1, y and / or y', which represent the mole percent of cobalt (Co) relative to the mole percent of all transition metals, may be 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0038] A positive electrode active material precursor according to one embodiment of the present invention is a precursor including a plurality of oxide particles, and as a result of X-ray diffraction (XRD) analysis using CuKα radiation, the following Relational Expression 2 can be satisfied in an XRD pattern obtained by Rietveld fitting. (Equation 2) 127≦XRD peak Integral breadth / 4tanθ≦137

[0039] In the above-mentioned Relational Formula 2, the XRD peak integral breadth is a value obtained by dividing the "area of ​​the XRD peak" by the "height of the XRD peak."

[0040] In the above-mentioned Relation 2, since the value of "XRD peak Integral breadth / 4tanθ" is derived as an inherent value of the sample, any peak for any plane of the sample may be selected and measured. As an example, the value of "XRD peak Integral breadth / 4tanθ" may be a value measured at a peak for the (200) plane.

[0041] The "XRD peak area" and "XRD peak height" refer to values ​​corrected by subtracting the background, and the background correction is performed by a commonly performed method.

[0042] The θ is the Bragg angle of the peak.

[0043] In one embodiment, in the above Relational Formula 2, "XRD peak integral breadth / 4tanθ" may be 129 or more or 135 or less.

[0044] In one embodiment, the oxide particles may include nickel (Ni).

[0045] In one embodiment, the oxide particles may further include at least one selected from the group consisting of cobalt (Co), aluminum (Al), and manganese (Mn).

[0046] In one embodiment, the oxide particles can be represented by the following Formula 2: (Chemical formula 2) Ni x Co y M 1-x-yO2

[0047] In the formula 2, 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.

[0048] In one embodiment, the oxide particles can be represented by the following Formula 2-1. (Chemical formula 2-1) Ni x’ Co y’ M1 z’ M2 1-x’-y’-z’ O2

[0049] In the above Chemical Formula 2-1, 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 0.5≦x'≦1.0, 0.0≦y'≦0.4, 0.0≦z'≦0.4, 0.0≦1-x'-y'-z'≦0.4.

[0050] In one embodiment, in Formula 2 and / or Formula 2-1, x and / or x', which means nickel (Ni) mole % relative to the total transition metal mole %, 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 hydroxide having 0.8 or more, or 0.9 or more.

[0051] In one embodiment, in Formula 2 and / or Formula 2-1, y and / or y', which represent the mole percent of cobalt (Co) relative to the mole percent of all transition metals, may be 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0052] Meanwhile, the oxide precursor may be prepared by oxidizing the hydroxide precursor. More specifically, the oxide precursor may be produced by oxidizing the hydroxide precursor through heat treatment, in which case the heat treatment temperature may be 300°C to 500°C. In one embodiment, the positive electrode active material precursor may be unimodal, and the positive electrode active material precursor particles may have an average particle size (D50) of 1 to 30 μm, more preferably 8 to 20 μm.

[0053] In another more preferred embodiment, in the positive electrode active material precursor of the present invention, the hydroxide particles and / or oxide particles contained in the positive electrode active material precursor may be in a bimodal form, further including first particles having an average particle size (D50) of 8 μm or more, or 10 μm or more, and second particles having an average particle size (D50) of 7 μm or less, or 5 μm or less.

[0054] In this specification, D 50 is the particle size at the 50% point of the cumulative area distribution by particle size, which can be measured by the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer. When the particles pass through a laser beam, the difference in the diffraction pattern due to the particle size is measured, and the particle size distribution can be calculated.

[0055] In one embodiment, when the positive electrode active material precursor is bimodal, a weight of a first particle contained in the positive electrode active material precursor is referred to as w1, and a weight of a second particle contained in the positive electrode active material precursor is referred to as w2, and w1 / w2 may be 1.5 to 9.0, or 2.0 to 4.0.

[0056] Next, the positive electrode active material of the present invention will be described. The positive electrode active material according to one embodiment of the present invention may be prepared from the hydroxide precursor and / or oxide precursor described above.

[0057] In one embodiment, the positive electrode active material may be prepared by mixing the hydroxide precursor with a lithium compound and then heat treating the mixture.

[0058] The positive electrode active material can be prepared by mixing the oxide precursor with a lithium compound and then heat treating the mixture.

[0059] Meanwhile, the positive electrode active material may include a plurality of lithium composite oxide particles.

[0060] In one embodiment, the lithium composite oxide particles can contain nickel (Ni).

[0061] In one embodiment, the lithium composite oxide particles may further include at least one selected from the group consisting of cobalt (Co), aluminum (Al), and manganese (Mn).

[0062] In one embodiment, the lithium composite oxide particles can be represented by the following Formula 3. (Chemical formula 3) Li a Ni x Co y M 1-x-y O2

[0063] In the 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 0.9≦a≦1.2, 0.5≦x≦1.0, 0.0≦y≦0.4, and 0.0≦1-xy≦0.4.

[0064] In one embodiment, the lithium composite oxide particles can be represented by the following Formula 3-1. (Chemical formula 3-1) Li a’ Ni x’ Co y’ M1 z’ M2 1-x’-y’-z’ O2

[0065] 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, and 0.9≦a'≦1.2, 0.5≦x'≦1.0, 0.0≦y'≦0.4, 0.0≦z'≦0.4, 0.0≦1-x'-y'-z'≦0.4.

[0066] In one aspect, in Formula 3 and / or Formula 3-1, a and / or a', which represent the mol% of lithium (Li) relative to the total mol% of transition 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.

[0067] In one embodiment, x and / or x', which means nickel (Ni) mole % relative to the total transition metal mole % excluding lithium (Li) in Formula 3 and / or Formula 3-1, 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.

[0068] In one embodiment, in Formula 3 and / or Formula 3-1, y and / or y', which means the mole percent of cobalt (Co) relative to the mole percent of all transition metals excluding lithium (Li), may be 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0069] The crystal structure of the positive electrode active material particles according to one embodiment of the present invention may be a hexagonal α-NaFeO2 (R-3m space group).

[0070] In one embodiment, the average porosity A of the positive electrode active material particles contained in the positive electrode active material may be 5%≦A≦7%, or 5%≦A≦6%.

[0071] In the present invention, porosity is defined as "void area / total particle cross-sectional area."

[0072] The "total particle cross-sectional area" refers to the cross-sectional area passing through the center of a secondary particle, and is measured including both material regions and void regions.

[0073] The "void area" means the area of ​​the "void" on a cross section passing through the center of a secondary particle.

[0074] The term "void" refers to the space between primary particles constituting a secondary particle and / or the space between crystallites, and includes both open and closed voids.

[0075] On the other hand, the inventors of the present invention have (102) It has been confirmed that the average porosity of the positive electrode active material particles contained in the positive electrode active material can be controlled by controlling the value.

[0076] In addition, the inventors of the present invention have confirmed that the average porosity of the positive electrode active material particles contained in the positive electrode active material can be controlled by controlling the value of "XRD peak integral breadth / 4tanθ" of the oxide precursor.

[0077] Furthermore, the inventors of the present invention have confirmed that, when a hydroxide precursor satisfies the above-mentioned Relational Formula 1 and an oxide precursor produced by oxidizing the hydroxide precursor satisfies the above-mentioned Relational Formula 2, the life characteristics of a battery can be significantly improved by controlling the average porosity of the positive electrode active material particles contained in the positive electrode active material produced from the oxide precursor.

[0078] The positive electrode active material particles contained in the positive electrode active material may be secondary particles formed by agglomeration of a plurality of primary particles.

[0079] In one aspect, the primary particles can include one or more crystallites.

[0080] The secondary particles may be in multiparticulate or polycrystalline form comprising two or more primary particles.

[0081] In a more preferred embodiment, the secondary particles may have a grain boundary density calculated by the following Equation 1 of 0.50 or more, 0.60 or more, 0.70 or more, 0.80 or more, 0.90 or more, or 0.95 or more.

[0082] (Formula 1) Grain boundary density = number of grain boundaries between primary particles on the line / number of primary particles on the line

[0083] The "grain boundary density" is calculated for primary particles and grain boundaries between primary particles that are placed on a straight line that passes through the center of a secondary particle and crosses the minor axis direction in a cross-sectional image of the particle taken with a scanning electron microscope (SEM).

[0084] For example, in the case of a non-agglomerated single particle consisting of a single primary particle, the grain boundary density calculated by the above formula 1 may be 0. In addition, in the case of an agglomeration of two primary particles, the grain boundary density calculated by the above formula 1 may be 0.5.

[0085] Here, the grain boundary density means an average value for 10 randomly drawn straight lines.

[0086] In one embodiment, the positive electrode active material may be unimodal, and the positive electrode active material particles may have an average particle size (D50) of 1 to 30 μm, more preferably 8 to 20 μm.

[0087] In another more preferred embodiment, the positive electrode active material of the present invention may be a bimodal form, further including first particles having an average particle size (D50) of 8 μm or more or 10 μm or more, and second particles having an average particle size (D50) of 7 μm or less or 5 μm or less.

[0088] In one embodiment, when the positive electrode active material is bimodal, the weight of the first particles contained in the positive electrode active material is referred to as w1, and the weight of the second 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 can increase the energy density by the small particles existing in the gaps between the large particles, while solving 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.

[0089] In one embodiment, when the cathode active material of the present invention has a bimodal form, the first particles, which are large particles, may be secondary particles formed by agglomeration of primary particles.

[0090] In one embodiment, the primary particles of the first particles, which are the large particles, can include one or more crystallites.

[0091] The secondary particles of the large first particles may be in a multi-particle or polycrystalline form including a plurality of primary particles.

[0092] In one embodiment, the first particles of the large particles may have a grain boundary density calculated by Equation 1 of 0.95 or more.

[0093] In one embodiment, the small secondary particles may be in the form of a single particle including one primary particle, and when the primary particle is composed of one crystallite, the secondary particles may be in the form of a single crystal.

[0094] In one embodiment of another aspect, the second particles, which are small particles, may be in a multiparticulate or polycrystalline form including two or more primary particles.

[0095] In one embodiment, the second particles, which are small particles, may have a grain boundary density calculated by the following Equation 1 of 0.98 or less, 0.95 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less.

[0096] In one aspect, the positive electrode active material particles included in the positive electrode active material may include 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.

[0097] In one embodiment, the coating oxide can be represented by the following Chemical Formula 4: (Chemical formula 4) Li p M3 q O r

[0098] In the formula 4, 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。

[0099] For example, in Formula 4, 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.

[0100] 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.

[0101] The coating oxide may include a concentration gradient portion in which the molar concentration of an element contained in the coating oxide changes. For example, when the coating oxide includes lithium, the molar concentration of lithium may change. Also, for example, the molar concentration of any one or more of M3 contained in the coating oxide may change.

[0102] In one aspect, when the coating oxide occupies at least a portion of a surface region of a primary particle that constitutes an outermost portion of the secondary particle, the concentration gradient portion may decrease, increase, or increase and then decrease from the surface of the primary particle that constitutes the outermost portion of the secondary particle toward the center of the secondary particle.

[0103] In addition, the concentration gradient portion may decrease, increase, or increase and then decrease from a surface of a primary particle that forms the outermost periphery of the secondary particle toward the center of the primary particle.

[0104] In one aspect, when the coating oxide occupies at least a portion of a surface region of a primary particle that does not form the outermost portion of the secondary particle, it may decrease, increase, or increase and then decrease from the surface of the primary particle in a direction toward the center of the primary particle.

[0105] The coating oxide according to an embodiment of the present invention improves the output characteristics of a battery due to its high ionic conductivity, and improves the lifespan of the battery by protecting the surface of the lithium composite oxide. In addition, the coating oxide effectively reduces the residual lithium present on the surface of the lithium composite oxide, thereby preventing side reactions caused by unreacted residual lithium.

[0106] As long as the method for producing a cathode active material precursor and a cathode active material according to an embodiment of the present invention has the above technical features, the method is not limited thereto. However, as a more preferred embodiment, the cathode active material can be produced as follows.

[0107] First, a hydroxide precursor can be prepared. The hydroxide precursor thus prepared may then be heat-treated to prepare an oxide precursor. The prepared oxide precursor may then be mixed with a lithium compound and heat-treated to prepare a positive electrode active material.

[0108] Meanwhile, the technical characteristics of the positive electrode active material precursor described above may be average technical characteristics of a plurality of positive electrode active material precursor particles contained in the positive electrode active material precursor.

[0109] In addition, the technical characteristics of the positive electrode active material described above may be average technical characteristics of a plurality of positive electrode active material particles contained in the positive electrode active material.

[0110] 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".

[0111] A positive electrode according to one embodiment of the present invention includes the positive electrode active material described above. 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. A secondary battery according to an embodiment of the present invention includes the above-described positive electrode active material. 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.

[0112] Examples of the present invention will now be described more specifically. <Example 1> (a) Preparation of hydroxide precursor The seeds of the large hydroxide precursor and the small hydroxide precursor designed with an atomic ratio of Ni:Co:Al=95:4:1 (at%) were synthesized by the co-precipitation method using nickel sulfate, cobalt sulfate, and aluminum sulfate, respectively. During the synthesis of the large hydroxide precursor seeds, the mixture was stirred at 400 rpm, and then the reactor was transferred and stirred at 600 rpm.

[0113] (b) Preparation of oxide precursors The prepared large hydroxide precursor and small hydroxide precursor were heated at 2° C. per minute and oxidized by calcination at 400° C. for 6 hours to convert them into oxide precursors. The converted oxide large particle precursor had an average particle size (D50) of 15.0 μm, and the produced oxide small particle precursor had an average particle size (D50) of 3.0 μm.

[0114] (c) Manufacturing of cathode materials The large oxide precursor and the small oxide precursor were weighed out to a weight ratio of 70:30, and 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 sintering furnace, and heat-treated for 12 hours.

[0115] Distilled water was added to the lithium composite oxide produced by the heat treatment, and NaOH was added at 1.5 wt% relative to the lithium composite oxide. Then, a 5.0 wt% aqueous solution of cobalt sulfate was added while stirring so that the aqueous solution of cobalt sulfate contained 3.0 mol% relative to the metal elements (Ni+Co+Al) of the lithium composite oxide excluding lithium, to coat the surface of the lithium composite oxide particles. After the reaction was completed, the mixture was dried at 120°C for 12 hours.

[0116] The dried product was heated to 700° C. at a rate of 2° C. per minute in a sintering furnace while maintaining an O 2 atmosphere, and was heat-treated at 700° C. for 12 hours to obtain a bimodal type positive electrode active material.

[0117] <Comparative Example 1> A positive electrode active material was obtained in the same manner as in Example 1, except that in step (a) of Example 1, the reactor was not moved during the synthesis of the large hydroxide precursor seed, and the reactor was stirred at 600 rpm.

[0118] <Comparative Example 2> A positive electrode active material was obtained in the same manner as in Example 1, except that in step (a) of Example 1, the reactor was not moved during the synthesis of the large hydroxide precursor seed, and the reactor was stirred at 400 rpm.

[0119] Manufacture of lithium secondary batteries A positive electrode slurry was prepared by dispersing 92 wt% of the positive electrode active material prepared according to the examples and comparative examples, 4 wt% of artificial graphite, and 4 wt% of PVDF binder in 30 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. 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.

[0120] <Experimental Example 1> The cross-sections of the positive active materials according to the examples and comparative examples were obtained by polishing them with a cross-section polisher at a current of 380 μA for 1 hour and 30 minutes. The FE-SEM was performed using a JSM-7610FPlus (JEOL) at a voltage of 2 kV to obtain cross-sectional SEM images of the positive active material particles, which are shown in FIG.

[0121] <Experimental Example 2> For the hydroxide precursors according to the examples and comparative examples, FWHM (102) The value (X) was measured by the method described above.

[0122] In addition, the XRD peak broadening / 4tanθ value (Y) was calculated for the oxide precursors according to the examples and comparative examples. The measurement method was as described above.

[0123] The average porosity of the positive electrode active materials according to the examples and comparative examples was calculated by taking a cross-sectional SEM image of a particle after cross-section processing through the center of the particle using an FIB (Ga-ion source), and measuring the area of ​​the dark areas indicating voids in the SEM image.

[0124] The results are shown in Table 1 below. [Table 1]

[0125] <Experimental Example 3> The battery characteristics measured for the lithium secondary batteries according to the examples and comparative examples are shown in Table 2 below.

[0126] The charge and discharge capacity was measured using an electrochemical analyzer (Toyo, Toscat-3100) by performing a charge and discharge experiment at 25° C., voltage range of 3.0 V to 4.25 V, and discharge rate of 0.2 C. The initial charge capacity and initial discharge capacity were measured, and the efficiency was calculated.

[0127] For the life measurement, the same lithium secondary battery was charged and discharged 50 times at 1C / 1C at 45°C within the driving voltage range of 3.0V to 4.3V, and then the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity (cycle capacity retention) was measured.

[0128] In the DC-IR analysis, the battery was charged and discharged at 45°C based on SOC 100%, and the resistance was measured after charging and discharging 50 times in the same manner as in the life measurement, and the resistance was measured under the same measurement conditions.

[0129] The CCCV analysis measured the charging time by charging at 45℃ at 1C in CC (Constant Current) mode to the maximum driving voltage of -0.05V, and then measuring the charging time by fully charging in CV (Constant Voltage) mode until the maximum driving voltage was reached. After that, 50 charge / discharge cycles were performed in the same manner as in the lifespan measurement, and the charging time was measured under the same measurement conditions.

[0130] Here, the CCCV value is (CC charging time) / (CC charging time+CV charging time)*100(%). [Table 2]

[0131] From Table 2, it can be seen that the life characteristics of Example 1 are significantly improved compared to Comparative Examples 1 and 2. This is because the FWHM of the hydroxide precursor (102)It can be understood that the life characteristics of the lithium secondary battery are improved by controlling the porosity of the positive electrode active material by controlling the XRD peak integral breadth / 4tanθ value (X) of the oxide precursor and controlling the XRD peak integral breadth / 4tanθ value (Y).

[0132] <Experimental Example 4> The particle strength of the oxide precursors according to the examples and comparative examples was measured, and the results are shown in FIG. The particle strength was measured by dropping oxide precursor particles onto a glass plate, gradually applying pressure with a particle strength measuring device, and measuring the force at which the particle broke.

[0133] 2, it can be seen that the particle strength of Example 1 is significantly improved compared to Comparative Examples 1 and 2. This is because the FWHM of the hydroxide precursor (102) It can be understood that the stability of the crystal structure is ensured and the particle strength is improved by controlling the XRD peak integral breadth / 4tanθ value (X) of the oxide precursor and controlling the XRD peak integral breadth / 4tanθ value (Y) of the oxide precursor.

[0134] <Experimental Example 5> The oxide precursors according to the examples and comparative examples were pressed, and then the rate of change in particle size (D50) was measured. The results are shown in FIG.

[0135] The particle size change rate was measured as follows. Particle size change rate = (P0-P1) / P0*100(%)

[0136] In the above formula, P0 is the D50 of the oxide precursor particles, and P1 is the D50 measured after pressing the oxide precursor particles at 8.5 tons for 30 seconds.

[0137] 3, it can be seen that the rate of change in particle size (D50) after pressing is larger in the case of Example 1 than in Comparative Examples 1 and 2. This is because the FWHM of the hydroxide precursor (102)It can be understood that by controlling the XRD peak integral breadth / 4tanθ value (X) of the oxide precursor and controlling the XRD peak integral breadth / 4tanθ value (Y) of the oxide precursor, the stability of the crystal structure is ensured, and the rate of change in particle size (D50) increases after the oxide precursor is pressed while cracking without shrinking into space due to pressure above the limit strength.

Claims

1. comprising a plurality of hydroxide particles; A positive electrode active material precursor, 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. (Relationship 1) 0.82≦FWHM （１０２） ≦1.22 In the above-mentioned Relational Formula 1, the FWHM （１０２） means the full width at half maximum (FWHM (deg., 2θ)) of the (102) plane in an XRD peak defined by a hexagonal lattice having an R-3m space group.

2. comprising a plurality of oxide particles; A positive electrode active material precursor, which satisfies the following relational expression 2 in an XRD pattern obtained by Rietveld fitting as a result of X-ray diffraction (XRD) analysis using CuKα radiation. (Relationship 2) 127≦XRD peak Integral breadth / 4tanθ≦137 In the above Relation 2, the XRD peak integral breadth is a value obtained by dividing the "area of ​​the XRD peak" by the "height of the XRD peak", and θ is the Bragg angle of the peak.

3. The particles are first particles having an average particle size (D50) of 8 μm or more, The positive electrode active material precursor according to claim 1 , further comprising second particles having an average particle size (D50) of 7 μm or less.

4. A positive electrode active material produced from the positive electrode active material precursor according to claim 1 or 2.

5. The positive electrode active material according to claim 4 , wherein an average porosity A of positive electrode active material particles contained in the positive electrode active material satisfies 5%≦A≦7%.

6. The positive electrode active material particles contained in the positive electrode active material are first particles having an average particle size (D50) of 8 μm or more, The positive electrode active material according to claim 4 , further comprising second particles having an average particle size (D50) of 7 μm or less.

7. 5. The positive electrode active material of claim 4, wherein the positive electrode active material particles comprise a coating oxide occupying at least a portion of at least one of a surface of a secondary particle, a grain boundary between primary particles, and a surface of a primary particle.

8. A positive electrode comprising the positive electrode active material according to claim 4.

9. A secondary battery comprising the positive electrode active material according to claim 4.

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