Positive electrode active material for secondary battery

Abstract

To provide a positive electrode active material particle, a positive electrode active material, a positive electrode and a secondary battery that enable control of physical properties of a positive electrode active material to be produced and enable application of the positive electrode active material to a secondary battery to improve the lifespan characteristics by controlling the content of a coating element on a surface portion of a positive electrode active material particle and coating a grain boundary in a manner in which problems of a conventional grain boundary coating method are remedied.SOLUTION: A positive electrode active material particle according to one aspect of the present invention may include a lithium composite oxide particle and a coating material including a coating element, in which the lithium composite oxide particle is a secondary particle formed by aggregation of two or more primary particles, the coating material is included on a surface of the secondary particle, the coating material is included in a grain boundary between the primary particles, calcium (Ca) is included in the positive electrode active material particle, and a calcium (Ca) content X included in the positive electrode active material satisfies 0.003 mol%≤X≤0.03 mol%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a secondary battery, and more particularly, to positive electrode active material particles containing lithium composite oxide particles and a coating material, and a positive electrode active material containing the same.

Background Art

[0002] 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.

[0003] As the 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 (wherein x, y, and z are 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 has the advantage of being inexpensive because the Co content is relatively small.

[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 that the primary particles of the lithium composite oxide rapidly change in volume, cracks occur in the secondary particles due to repeated charge and discharge, or the crystal structure collapses or a phase transition of the crystal structure occurs.

[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 improve the problems of the existing grain boundary coating method by adding calcium (Ca) as a dopant in a specific content and manufacturing method during the manufacture of a positive electrode active material, diffusing the coating element into the positive electrode active material particles, controlling the concentration of the coating element on the surface of the positive electrode active material particles, and performing grain boundary coating between primary particles of lithium composite oxide, thereby improving the life performance of the battery. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a positive electrode active material particle including lithium composite oxide particles and a coating material including a coating element, the lithium composite oxide particles being secondary particles formed by agglomeration of two or more primary particles, the coating material being included on surfaces of the secondary particles, the coating material being included in grain boundaries between the primary particles, calcium (Ca) being included in the positive electrode active material particles, and a calcium (Ca) content X included in the positive electrode active material may be 0.003 mol%≦X≦0.03 mol%.

[0009] In one embodiment, the positive electrode active material particles include the coating element, and an average concentration Y of the coating element measured by Energy Profiling-Energy Dispersive X-ray Spectroscopy (EP-EDS) that measures an average concentration of an element from the surface of the positive electrode active material particle to a depth penetrated by the electron beam using an electron beam irradiated to the surface of the positive electrode active material particle at an accelerating voltage of 3 kV may be 32 at%≦Y≦37 at%.

[0010] In one embodiment, the coating element may be cobalt (Co) and the coating material may be cobalt (Co) oxide.

[0011] In one embodiment, the positive electrode active material particles include cobalt (Co), and an average concentration Y of cobalt (Co) measured by Energy Profiling-Energy Dispersive X-ray Spectroscopy (EP-EDS) that measures an average concentration of an element from the surface of the positive electrode active material particles to a depth penetrated by the electron beam using an electron beam irradiated to the surface of the positive electrode active material particles at an accelerating voltage of 3 kV may be 32 at%≦Y≦37 at%.

[0012] In one embodiment, the calcium (Ca) may be included in the positive electrode active material particles in the form of calcium (Ca) oxide on the surfaces of the secondary particles.

[0013] In one embodiment, the calcium (Ca) may be included in the positive electrode active material particles in the form of calcium (Ca) oxide at the grain boundaries between the primary particles.

[0014] According to an embodiment of the present invention, the positive electrode active material may include a plurality of the positive electrode active material particles.

[0015] In one embodiment, the positive electrode active material contained in the positive electrode active material may be the first positive electrode active material particles having an average particle size (D50) of 8 μm or more, and the positive electrode active material may further include second positive electrode active material particles having an average particle size (D50) of 7 μm or less.

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

[0017] A positive electrode according to an embodiment of the present invention may include the positive electrode active material particles.

[0018] A secondary battery according to an embodiment of the present invention may include the positive electrode active material particles. Effect of the Invention

[0019] One advantage of the present invention is that the content of coating elements on the surface of positive electrode active material particles is controlled, and grain boundary coating is performed in a manner that overcomes the problems of the existing grain boundary coating method, thereby improving the life performance of a battery. [Brief description of the drawings]

[0020] [Figure 1] FIG. 2 illustrates a calcium (Ca) doping method according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing cross-sectional EDS images of positive electrode active material particles according to comparative examples and examples of the present invention. [Diagram 3] FIG. 2 is a diagram showing the results of X-ray diffraction (XRD, X-ray diffraction) analysis using CuKα radiation for positive electrode active material particles according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] As used herein, terms such as "comprises" should be understood as open-ended terms that encompass the possibility of including other configurations.

[0022] 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.

[0023] 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.

[0024] Meanwhile, the technical features described below relate to one aspect for achieving the effects aimed at by the present invention as described above.

[0025] That is, the positive electrode active material particles according to one embodiment of the present invention include the technical features according to one embodiment described below, and thus when applied to a secondary battery, the battery characteristics can be significantly improved.

[0026] The present invention relates to a positive electrode active material particle for a secondary battery and a positive electrode active material including a plurality of the particles, and the type of the secondary battery of the present invention is not limited as long as the secondary battery is a battery manufactured to convert external electric 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 for a lithium ion secondary battery.

[0027] In nickel-based positive electrode active materials, especially high-nickel (High-Ni) positive electrode active materials, coating can improve battery performance such as life and resistance, and especially in the case of grain boundary coating between primary particles, these advantages can be maximized.

[0028] For this grain boundary coating, a method of diffusing the coating material into the inside of the particles at a specific heat treatment temperature has been implemented, but there are problems with changing the heat treatment temperature for carrying out the grain boundary coating and with deterioration of battery performance due to changes in physical properties such as deformation of the primary particles.

[0029] In order to improve the problem of grain boundary coating, the present invention adds calcium (Ca) as a dopant in a specific content and in a specific manufacturing method, and the coating element, especially cobalt (Co), is diffused into the inside of the positive electrode active material particles to coat the grain boundaries between the primary particles, and the content of the coating element on the surface of the positive electrode active material particles is adjusted to improve the battery performance.

[0030] One positive electrode active material particle according to one embodiment of the present invention can include one lithium composite oxide particle.

[0031] The lithium composite oxide particles may be secondary particles formed by agglomeration of two or more primary particles.

[0032] In addition, the positive electrode active material particles may include a coating material including a coating element.

[0033] Meanwhile, in this specification, a distinction is made between the lithium composite oxide particles and the coating material.

[0034] When the lithium composite oxide particles according to an 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 particles are defined to include all of the doped regions.

[0035] In another aspect, when the lithium composite oxide particles according to an embodiment of the present invention are subjected to a coating treatment, a portion of the coating element may form a coating material. Such a coating material may be present on the surface of the secondary particles of the lithium composite oxide particles and / or at the grain boundaries between the primary particles of the lithium composite oxide.

[0036] Here, the grain boundary between primary particles means a region including the space between the primary particles and the entire surface of the primary particles.

[0037] That is, in this specification, the doping region within the lattice structure of the lithium composite oxide primary particles of the positive electrode active material particles, the surface of the lithium composite oxide secondary particles, and the grain boundary region between the lithium composite oxide primary particles are all distinct regions.

[0038] Meanwhile, in this specification, the elements calcium (Ca) and cobalt (Co) are interpreted as including both the zero-valent state and the ionic state.

[0039] In one embodiment, the lithium composite oxide particles can contain nickel (Ni).

[0040] 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).

[0041] In one embodiment, the lithium composite oxide particles can be represented by the following Formula 1: (chemical 1) Li a Ni x Co y M 1-x-y O2

[0042] 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.

[0043] In one embodiment, the lithium composite oxide particles can be represented by the following formula 1-1. (Chem.1-1) Li a’ Ni x’ Co y’ M1 z’ M2 1-x’-y’-z’ O2

[0044] 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.

[0045] In one embodiment, in Formula 3 and / or Formula 1-1, 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.

[0046] 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.

[0047] In one embodiment, in Formula 3 and / or Formula 1-1, 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.

[0048] The crystal structure of the lithium composite oxide particles according to one embodiment of the present invention may be a hexagonal α-NaFeO2 (R-3m space group).

[0049] Next, the positive electrode active material particles according to an embodiment of the present invention include a coating material including a coating element.

[0050] As an example, the coating material may be a coating oxide.

[0051] In one embodiment, the coating material can be represented by the following Chemical Formula 2: (chemical 2) Li p M3 q O r

[0052] 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。

[0053] 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.

[0054] 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) qO 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.

[0055] 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.

[0056] In one embodiment, the coating material may be included on the surfaces of the lithium composite oxide secondary particles and in the grain boundaries between the lithium composite oxide primary particles.

[0057] Meanwhile, in one embodiment, the coating element may be included in a coating material contained on the surface of the lithium composite oxide secondary particles.

[0058] In addition, as one embodiment, the coating element may be contained in a coating material contained in the grain boundaries between the primary particles of the lithium composite oxide.

[0059] In addition, in one embodiment, the coating element may be doped and contained in the lattice structure of the lithium composite oxide primary particles, which is not a coating material.

[0060] In a more preferred embodiment, the positive electrode active material particles include the coating element, and the average concentration Y of the coating element measured by EP-EDS (Energy Profiling-Energy Dispersive X-ray Spectroscopy) in which an electron beam is irradiated to a surface of the positive electrode active material particle at an acceleration voltage of 3 kV to measure an average concentration of the element from the surface of the positive electrode active material particle to a depth penetrated by the electron beam may be 32 at% or more, 33 at% or more, 34 at% or more, 35 at% or more, 37 at% or less, or 36 at% or less.

[0061] In the present invention, calcium (Ca) is added as a dopant in a specific content and in a specific manufacturing method to diffuse the coating element into the positive electrode active material particles, and the concentration of the coating element on the surface of the positive electrode active material particles is adjusted to 32at%≦Y≦37at%, thereby improving the life performance of the battery.

[0062] In a more preferred embodiment, the coating element is cobalt (Co), and the coating material is cobalt (Co) oxide.

[0063] Meanwhile, in this specification, a coating oxide is an oxide containing a coating element, and includes all cases in which other elements are further contained, and a cobalt (Co) oxide is an oxide containing cobalt (Co), and includes all cases in which other elements are further contained.

[0064] As an example, the cobalt (Co) oxide is Li p Co q O r , Co q O r , and / or an LCO-like structure. Meanwhile, the LCO-like structure is an intermediate that may exist in the process of forming the cobalt (Co) oxide of LiCoO2, and may be, for example, amorphous and may have a spinel structure.

[0065] In one embodiment, the cobalt (Co) oxide may be contained on the surfaces of the lithium composite oxide secondary particles and in the grain boundaries between the lithium composite oxide primary particles.

[0066] On the other hand, as one embodiment, cobalt (Co) can be contained in cobalt (Co) oxide contained on the surface of the lithium composite oxide secondary particles.

[0067] In addition, in one embodiment, cobalt (Co) may be contained in a coating material contained in the grain boundaries between the primary particles of the lithium composite oxide.

[0068] In addition, in one embodiment, cobalt (Co) may be doped and included in the lattice structure of the lithium composite oxide primary particles, which is not a coating material.

[0069] In a more preferred embodiment, the positive electrode active material particles contain the cobalt (Co), and an average concentration Y of the cobalt (Co) measured by EP-EDS (Energy Profiling-Energy Dispersive X-ray Spectroscopy) in which an electron beam is irradiated to a surface of the positive electrode active material particle at an acceleration voltage of 3 kV to measure an average concentration of an element from the surface of the positive electrode active material particle to a depth penetrated by the electron beam may be 32 at% or more, 33 at% or more, 34 at% or more, 35 at% or more, 37 at% or less, or 36 at% or less.

[0070] In the present invention, calcium (Ca) is added as a dopant in a specific content and in a specific manufacturing method, and cobalt (Co) is diffused into the positive electrode active material particles, and the concentration of cobalt (Co) on the surface of the positive electrode active material particles is adjusted to 32at%≦Y≦37at%, thereby improving the life performance of the battery.

[0071] Next, calcium (Ca) can be contained in the positive electrode active material particles by being added to a dopant.

[0072] In one aspect, the calcium (Ca) may be present in one or more regions selected from a doping region in a lattice structure of a lithium composite oxide primary particle, a surface of a lithium composite oxide secondary particle, and a grain boundary region between the lithium composite oxide primary particles.

[0073] In one embodiment, when present in the grain boundary region between primary particles of the lithium composite oxide, it may exist as calcium (Ca) ions themselves.

[0074] In one embodiment, when present on the surface of the lithium composite oxide secondary particles and in the grain boundary region between the lithium composite oxide primary particles, it may exist in the form of calcium (Ca) oxide, i.e., in various forms of oxides containing calcium (Ca). For example, it may exist as an amorphous calcium (Ca) composite oxide.

[0075] In one embodiment, the content X of calcium (Ca) contained in the positive electrode active material particles may be 0.003 mol% or more, 0.005 mol% or more, 0.03 mol% or less, or 0.025 mol% or less. By containing calcium (Ca) in the positive electrode active material particles at this content, the present invention can improve battery performance by diffusing a coating element, particularly cobalt (Co), into the positive electrode active material particles to coat the grain boundaries between the lithium composite oxide primary particles and controlling the concentration of the coating element, particularly cobalt (Co), on the surface of the positive electrode active material particles.

[0076] According to an embodiment of the present invention, the positive electrode active material may include a plurality of the positive electrode active material particles.

[0077] The positive electrode active material according to one embodiment of the present invention 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.

[0078] In this specification, D 50is 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.

[0079] In one embodiment, when the positive electrode active material has a unimodal form, the lithium composite oxide particles are secondary particles formed by agglomeration of a plurality of primary particles, and the primary particles may include one or more crystallites.

[0080] In one embodiment, the secondary particles may be in a multiparticulate or polycrystalline form including 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. (Formula 1) Grain boundary density = number of grain boundaries between primary particles on the line / number of primary particles on the line

[0082] The "grain boundary density" is calculated for primary particles and grain boundaries between primary particles that are placed on a straight line that crosses the minor axis direction through the center of a secondary particle in a cross-sectional image of the particle taken with a scanning electron microscope (SEM).

[0083] 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.

[0084] Here, the grain boundary density means an average value for 10 randomly drawn straight lines.

[0085] In yet another more preferred embodiment, the positive electrode active material particles contained in the positive electrode active material may be the first positive electrode active material particles having an average particle size (D50) of 8 μm or more, and the positive electrode active material may be a bimodal type further including the second positive electrode active material particles having an average particle size (D50) of 7 μm or less.

[0086] 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 w1, and the weight of the second positive electrode active material particles is 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 existing 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.

[0087] In one aspect, when the positive electrode active material of the present invention is in a bimodal form, the first lithium composite oxide particles in the first positive electrode active material particles, which are the large particles, are secondary particles formed by aggregation of primary particles, and the primary particles of the first lithium composite oxide particles may include one or more crystallites.

[0088] In one embodiment, the secondary particles of the first lithium composite oxide particles may have a multiparticle form or a polycrystalline form including a plurality of primary particles.

[0089] In one embodiment, the first lithium composite oxide particles may have a grain boundary density calculated by Equation 1 of 0.95 or more.

[0090] In one embodiment, the second lithium composite oxide particles in the second positive electrode active material particles, which are small particles, may have a single particle form including one primary particle, and when the primary particle is composed of one crystallite, the second lithium composite oxide particles may have a single crystal form.

[0091] In yet another embodiment of the present invention, the second lithium composite oxide particles may be in a multiparticulate form or a polycrystalline form including two or more primary particles.

[0092] In one embodiment, the second lithium composite oxide particles may have a grain boundary density calculated by 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.

[0093] As long as the method for producing the positive electrode active material particles and the positive electrode active material according to one embodiment of the present invention has the above technical features, the method is not limited thereto, but as a more preferred embodiment, the positive electrode active material can be produced as follows.

[0094] First, a hydroxide precursor can be prepared.

[0095] Then, the hydroxide precursor thus prepared can be heat-treated to prepare an oxide precursor, where the heat treatment temperature can be 300°C to 500°C.

[0096] Next, the prepared oxide precursor is mixed with a lithium compound and heat-treated to prepare a lithium composite oxide, where the heat-treatment temperature may be 750°C to 850°C.

[0097] Next, the heat-treated lithium composite oxide is washed with a washing solution, and then an aqueous cobalt (Co) solution and an aqueous calcium (Ca) solution are added and stirred, and then the oxide is dried (see FIG. 1).

[0098] Next, the structure can be heat-treated to produce a positive electrode active material, in which case the heat treatment temperature can be 680°C to 720°C.

[0099] In the method for producing the positive electrode active material particles and the positive electrode active material according to an embodiment of the present invention, cobalt (Co) wet coating and calcium (Ca) wet doping are simultaneously performed during the washing step of the lithium composite oxide, thereby diffusing cobalt (Co) into the inside of the particles to coat the grain boundaries between the primary particles, and controlling the content of the coating elements on the surfaces of the lithium composite oxide secondary particles, thereby improving the performance of the battery.

[0100] In addition, the above-mentioned technical features of the positive electrode active material particles may be average technical features of a plurality of positive electrode active material particles contained in the positive electrode active material.

[0101] 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".

[0102] A positive electrode according to one embodiment of the present invention includes the positive electrode active material particles described above.

[0103] Except for the use of the positive electrode active material particles described above, 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.

[0104] A secondary battery according to an embodiment of the present invention includes the above-described positive electrode active material particles.

[0105] 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.

[0106] Examples of the present invention will now be described more specifically. Manufacture of positive electrode active material <Example 1> (a) Preparation of hydroxide precursor A large hydroxide precursor and a small hydroxide precursor designed with an atomic ratio of Ni:Co:Al=95:4:1 (at%) were synthesized by a known co-precipitation method using nickel sulfate, cobalt sulfate, and aluminum sulfate.

[0107] (b) Preparation of oxide precursors The synthesized hydroxide large particle precursor and hydroxide small particle precursor were heated at 2° C. per minute and oxidized by calcination at 400° C. for 6 hours to convert them into oxide large particle precursor and oxide small particle precursor, respectively.

[0108] The large oxide particle precursor had an average particle size (D50) of 15.0 μm, and the small oxide particle precursor had an average particle size (D50) of 3.0 μm.

[0109] (c) Manufacturing of positive electrode active material 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 to produce an intermediate product.

[0110] Distilled water was added to the intermediate product, and NaOH was added at 1.5 wt% relative to the lithium composite oxide. Then, a 5.0 wt% aqueous cobalt sulfate solution was added so that the cobalt derived from the aqueous cobalt sulfate solution was 3.0 mol% relative to the metal elements (Ni+Co+Al) of the intermediate product excluding lithium, and a 0.5 wt% aqueous calcium nitrate solution was added so that the calcium derived from the aqueous calcium nitrate solution was 0.01 mol% relative to the elements (Ni+Co+Al) of the intermediate product excluding lithium, while stirring to coat the surface of the intermediate product with cobalt. After the reaction was completed, the product was dried at 120°C for 12 hours.

[0111] The dried material was heated to 700° C. at a rate of 2° C. per minute in a sintering furnace while maintaining an O 2 atmosphere, and then heat-treated at 700° C. for 12 hours to obtain a bimodal type positive electrode active material.

[0112] <Example 2> A positive electrode active material was obtained in the same manner as in Example 1, except that in step (c), a 0.5 wt % calcium nitrate aqueous solution was added so that the calcium from the calcium nitrate aqueous solution was 0.02 mol % relative to the metal elements (Ni+Co+Al) excluding lithium in the intermediate product.

[0113] <Example 3> A positive electrode active material was obtained in the same manner as in Example 1, except that in step (c), a 0.5 wt % calcium nitrate aqueous solution was added so that the calcium from the calcium nitrate aqueous solution was 0.03 mol % relative to the metal elements (Ni+Co+Al) excluding lithium in the intermediate product.

[0114] <Comparative Example 1> A positive electrode active material was obtained in the same manner as in Example 1, except that the 0.5 wt % calcium nitrate aqueous solution was not added in step (c).

[0115] <Comparative Example 2> A positive electrode active material was obtained in the same manner as in Example 1, except that in step (c), a 0.5 wt % calcium nitrate aqueous solution was added so that the calcium from the calcium nitrate aqueous solution was 0.33 mol % relative to the metal elements (Ni+Co+Al) excluding lithium in the intermediate product.

[0116] Manufacture of lithium secondary batteries A positive electrode slurry was prepared by dispersing 92 wt% of the positive electrode active materials 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.

[0117] 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.

[0118] <Experimental Example 1> Analysis of surface cobalt (Co) content The surfaces of the positive electrode active material particles according to the examples and comparative examples were irradiated with an electron beam at an accelerating voltage of 3 kV, and the average concentration of the element was measured from the surface of the positive electrode active material particles to the depth penetrated by the electron beam by EP-EDS (Energy Profiling-Energy Dispersive X-ray Spectroscopy). The results of the measurement of the average concentration of cobalt (Co) were shown in Table 1 below.

[0119] The EP-EDS (Energy Profiling-Energy Dispersive X-ray Spectroscopy) measurement was performed by scanning an electron beam accelerated at a voltage of 3 kV on the surface of the positive electrode active material particles using a scanning electron microscope (SEM; Hitachi Co.) to perform EDS component analysis. [Table 1]

[0120] <Experimental Example 2> The battery characteristics measured for the lithium secondary batteries according to the examples and comparative examples are shown in Table 2 below.

[0121] 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.

[0122] 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. [Table 2]

[0123] From Table 2, it can be seen that the charge / discharge capacity and life characteristics are significantly improved in the examples compared to the comparative examples.

[0124] <Experimental Example 3> Measurement of cross-sectional EDS image FIG. 2 shows cross-sectional EDS images of large particles contained in the positive electrode active materials according to the examples and comparative examples.

[0125] From FIG. 2, it can be seen that cobalt (Co) and calcium (Ca) are diffused into the positive electrode active material particles by the calcium (Ca) wet coating, thereby controlling the cobalt (Co) concentration at the surface of the positive electrode active material particles.

[0126] <Experimental Example 4> XRD Measurement FIG. 3 shows the results of X-ray diffraction (XRD) analysis using CuKα radiation for the positive electrode active materials according to the examples and comparative examples.

[0127] In the present invention, X-ray diffraction (XRD) analysis was performed using a Bruker D8 Advance diffractometer using 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.

[0128] According to FIG. 3, the intensity of the Co-rich peak becomes weaker as the content of added calcium (Ca) increases, which confirms that calcium (Ca) is doped into the primary particle lattice structure.

Claims

1. A positive electrode active material particle including a lithium composite oxide particle and a coating material including a coating element, The lithium composite oxide particles are secondary particles formed by agglomeration of two or more primary particles, the coating material is included on a surface of the secondary particles; the coating material is included in the grain boundaries between the primary particles; calcium (Ca) is contained in the positive electrode active material particles; The positive electrode active material particles have a calcium (Ca) content X in the positive electrode active material particles, which is 0.003 mol%≦X≦0.03 mol%.

2. 2. The cathode active material particle according to claim 1, wherein an average concentration Y of the coating element measured by EP-EDS (Energy Profiling-Energy Dispersive X-ray Spectroscopy) in which an electron beam is irradiated onto a surface of the cathode active material particle at an accelerating voltage of 3 kV to measure an average concentration of the element from the surface of the cathode active material particle to a depth penetrated by the electron beam is 32 at %≦Y≦37 at %.

3. The positive electrode active material particles according to claim 1 , wherein the coating element is cobalt (Co) and the coating material is cobalt (Co) oxide.

4. The positive electrode active material particles contain cobalt (Co), 2. The cathode active material particle according to claim 1, wherein an average concentration Y of cobalt (Co) measured by EP-EDS (Energy Profiling-Energy Dispersive X-ray Spectroscopy) in which an electron beam is irradiated onto a surface of the cathode active material particle at an accelerating voltage of 3 kV to measure an average concentration of an element from the surface of the cathode active material particle to a depth penetrated by the electron beam is 32 at %≦Y≦37 at %.

5. The positive electrode active material particle according to claim 1 , wherein the calcium (Ca) is contained in the form of calcium (Ca) oxide on the surface of the secondary particles within the positive electrode active material particle.

6. The positive electrode active material particle according to claim 1 , wherein the calcium (Ca) is contained in the form of calcium (Ca) oxide at grain boundaries between the primary particles within the positive electrode active material particle.

7. A positive electrode active material comprising a plurality of the positive electrode active material particles according to claim 1 .

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

9. 9. The positive electrode active material according to claim 8, wherein w1 / w2 is 1.5 to 9.0, where w1 is a weight of the first positive electrode active material particles and w2 is a weight of the second positive electrode active material particles.

10. A positive electrode comprising the positive electrode active material particles according to claim 1 .

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

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