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

Abstract

The positive electrode active material of the present invention comprises a lithium nickel-based composite oxide including secondary particles formed by aggregation of primary particles, in which some cations and some anions in the lithium nickel-based composite oxide are substituted with cations (M') and fluorine anions (F-) contained in a fluorine-based compound, and the average Ni occupancy rate in the Li 3a site obtained by Rietveld analysis using X-ray diffraction of the secondary particles is 1.1% to 1.5%.

Description

Technical Field

[0001] The present invention relates to a lithium nickel-based composite oxide and a positive electrode active material for a secondary battery containing the same, and more particularly to a positive electrode active material in which cation and anion sites in a crystal structure within a polycrystalline type lithium nickel-based composite oxide are simultaneously substituted with a fluorine-based compound.

Background Art

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

[0003] In recent years, the most spotlighted substance as a lithium composite oxide contained in a positive electrode active material is lithium nickel manganese cobalt oxide Li(Ni x Co y Mn z [[ID=]](where 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 higher capacity than LiCoO2, which has been actively studied and used as a positive electrode active material so far, and has the advantage of being inexpensive because the Co content is relatively low.

[0004]

[0005] However, such a lithium composite oxide comes to be accompanied by a volume change due to intercalation and deintercalation of lithium ions during charge and discharge. As a result, there is a problem that the volume of the primary particles of the lithium composite oxide changes rapidly during charge and discharge, cracks occur in the secondary particles due to repeated charge and discharge, or crystal structure collapse or crystal structure phase transition occurs.To address these shortcomings, demand for high-nickel systems, or nickel-rich systems with a nickel content of 60% or more, as positive electrode active materials for secondary batteries has begun to grow. However, while these nickel-rich systems offer the advantage of high capacity, they also suffer from problems such as increased structural instability due to Li / Ni cation mixing, physical separation of internal particles due to microcracks, and increased electrolyte loss, resulting in rapid deterioration of lifespan characteristics at room and high temperatures. Summary of the Invention [Problem to be solved by the invention]

[0006] In the present invention, the cations and anions in the lithium nickel composite oxide are replaced with the cations (M') and fluorine anions (F - ) to provide a positive electrode active material in which the Ni occupancy in the Li 3a site is adjusted.

[0007] Another object of the present invention is to provide a positive electrode active material that simultaneously exhibits the effect of inhibiting cation mixing and the effect of strengthening the structure by fluorine substituting for oxygen.

[0008] The present invention also provides a positive electrode active material in which lattice defects and residual lithium generated during high-temperature reactions are significantly reduced.

[0009] Another object of the present invention is to provide a positive electrode active material that improves the life of a battery and significantly suppresses gas generation during high-temperature storage.

[0010] The present invention also provides a positive electrode active material that significantly improves battery characteristics such as battery capacity / efficiency and c-rate. [Means for solving the problem]

[0011] The positive electrode active material of the present invention includes a lithium nickel-based composite oxide containing secondary particles formed by aggregation of primary particles, and some cations and some anions in the lithium nickel-based composite oxide are substituted with cations (M') and fluorine anions (F) contained in a fluorine-based compound. - ), and the average Ni occupancy in the Li 3a site obtained from Rietveld analysis by X-ray diffraction of the secondary particles is 1.1% to 1.5%.

[0012] In one embodiment, the average length of the c-axis obtained from Rietveld analysis by X-ray diffraction of the secondary particles may be 14.184 Å to 14.186 Å.

[0013] In one embodiment, when the lithium nickel-based composite oxide is analyzed by XRD, the FWHM corrected by the following relational expression 1 補正(104) can be 0.16° to 0.19° (2θ).

[0014] (Equation 1) FWHM 補正(104) =FWHM 測定(104) -FWHM Si powder (220)

[0015] In the above-mentioned relational expression 1, FWHM 測定(104) means the half-width of the (104) peak observed at 44.5±1.0° (2θ) in XRD analysis of the lithium nickel-based composite oxide, and the FWHM Si(220) means the half-width of the (220) peak observed near 47.3±1.0° (2θ) in the XRD measurement of Si powder.

[0016] In one aspect, the average aspect ratio of the primary particles at the surface of the secondary particles may be greater than the average aspect ratio of the primary particles at the interior.

[0017] In one embodiment, the secondary particles may include a surface portion and an interior portion, and the average particle size of the primary particles in the surface portion of the secondary particles may be larger than the average particle size of the primary particles in the interior portion.

[0018] In one embodiment, primary particles having a particle size of 200 nm or more and less than 500 nm within the secondary particles may account for 50% to 100% by volume of the primary particles constituting the secondary particles.

[0019] In one embodiment, primary particles having a particle size of 500 nm to 10.0 μm at the surface of the secondary particles may account for 50% to 100% by volume of the primary particles constituting the secondary particles.

[0020] In one embodiment, 50% or more of the primary particles in the surface region of the secondary particles may be formed such that the major axis direction of the primary particles has an angle of ±30° or less with respect to a line connecting the surface and center of the secondary particle.

[0021] In one aspect, the primary particles, which are 50% or more of the primary particles in the surface region of the secondary particles, may be formed such that the lithium ion diffusion paths formed within the primary particles have an angle of ±30° or less with a line connecting the surface and center of the secondary particle.

[0022] In one aspect, the secondary particles may exhibit the greatest peak intensity at 684.3 eV to 685.0 eV in fluorine 1s binding energy analysis obtained through XPS (X-ray Photoelectron Spectrometer) measurement.

[0023] In one embodiment, the positive electrode active material may further include a coating oxide occupying at least a portion of at least one of surfaces of the secondary particles, grain boundaries between the primary particles, and surfaces of the primary particles.

[0024] The positive electrode of the present invention contains the positive electrode active material.

[0025] The secondary battery of the present invention includes the positive electrode. [Effects of the Invention]

[0026] As one effect, the present invention can provide a positive electrode active material that simultaneously exhibits the effect of inhibiting cation mixing and the effect of strengthening the structure by fluorine substituting for oxygen.

[0027] As one effect, the present invention can provide a positive electrode active material in which lattice defects and residual lithium that occur during high-temperature reactions, particularly in high-nickel positive electrode active materials, are significantly reduced.

[0028] As one effect, the present invention can provide a positive electrode active material that improves the life of a battery and significantly suppresses gas generation during high-temperature storage.

[0029] As an effect, the present invention can provide a positive electrode active material that significantly improves battery characteristics such as battery capacity / efficiency and C-rate. [Brief explanation of the drawings]

[0030] [Figure 1] 10 is a cross-sectional SEM image of the positive electrode active materials according to comparative examples and examples of the present invention.

[0031] [Figure 2] 1 is a graph showing the average Ni occupancy in the Li 3a site for positive electrode active materials according to comparative examples and examples of the present invention.

[0032] [Figure 3] 1 is a graph showing the c-axis lengths of positive electrode active materials according to comparative examples and examples of the present invention.

[0033] [Figure 4] FIG. 1 is a diagram showing the results of FWHM(104) analysis of positive electrode active materials according to comparative examples and examples of the present invention.

[0034] [Figure 5] FIG. 2 is a diagram showing the results of XPS analysis of positive electrode active materials according to comparative examples and examples of the present invention.

[0035] [Figure 6] FIG. 10 is a diagram showing the analysis results of the reaction initiation temperature during the production of positive electrode active materials according to comparative examples and examples of the present invention.

[0036] [Figure 7] FIG. 10 is a graph showing the analysis results of gas generation during storage at 90° C. in batteries according to comparative examples and examples of the present invention.

[0037] [Figure 8] FIG. 1 is a diagram showing the results of C-rate analysis of batteries according to comparative examples and examples of the present invention.

[0038] [Figure 9] FIG. 1 is a diagram showing the analysis results of LiOH content for positive electrode active materials according to comparative examples and examples of the present invention.

[0039] [Figure 10] FIG. 10 is a diagram showing the analysis results of Li2CO3 content for positive electrode active materials according to comparative examples and examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0040] As used herein, expressions such as "comprises" should be understood as open-ended terms that encompass the possibility of including other features.

[0041] As used herein, the terms "preferred" and "preferably" refer to embodiments of the invention that may offer certain benefits, under certain circumstances, but are not intended to exclude other embodiments from the scope of the invention.

[0042] Also, as used in the specification and the appended claims, the singular forms "a," "an," and "the" can also include the plural forms unless the context clearly dictates otherwise.

[0043] Meanwhile, the technical features described below relate to one aspect of the present invention for achieving the intended effects described above.

[0044] That is, the positive electrode active material according to one embodiment of the present invention can significantly improve battery characteristics by including the technical features according to one embodiment described below.

[0045] A positive electrode active material according to one embodiment of the present invention includes secondary particles formed by aggregation of primary particles.

[0046] In one aspect, the primary particles can include one or more crystallites.

[0047] The secondary particles may be in the form of multiparticles or polycrystals containing two or more primary particles, and more preferably, in the form of multiparticles or polycrystals containing 20 or more primary particles aggregated together.

[0048] In a more preferred embodiment, the secondary particles may have a grain boundary density of 0.85 or more, or 0.90 or more.

[0049] In the present invention, the "grain boundary density" is calculated by the following formula 1 for a primary particle placed on a straight line uniaxially crossing the center of the secondary particle 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.

[0050] (Formula 1) Grain boundary density = Number of grain boundaries between primary particles placed on the line / Number of primary particles placed on the line

[0051] For example, in the case of a single particle that is not aggregated and is made up 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 aggregate of two primary particles, the grain boundary density calculated by the above formula 1 may be 0.5.

[0052] In this case, the grain boundary density means the average value for ten randomly drawn straight lines.

[0053] In one embodiment, the average particle size of the secondary particles may be 1 μm to 30 μm, more preferably 8 μm to 20 μm.

[0054] Meanwhile, in the present invention, "average particle size" refers to the average diameter (D50) when the particles are spherical, and refers to the average length of the major axis when the particles are non-spherical. In the present invention, the average particle size of secondary particles was measured using a particle size analyzer (Cilas) and SEM. Furthermore, the particle size of primary particles was calculated by measuring the length of the major axis of the rod-shaped primary particles in the SEM image, and the average diameter was calculated when the particles were spherical. Furthermore, the crystallite size was measured by calculating the half-width and θ value obtained by XRD analysis using the Scherrer equation.

[0055] The present invention may be a unimodal type positive electrode active material. In another aspect, the positive electrode active material may be a bimodal type positive electrode active material further including secondary particles of a lithium composite oxide having an average particle size of 7 μm or less, the average particle size being different from that of the secondary particles.

[0056] A positive electrode active material according to one embodiment of the present invention includes a lithium-nickel composite oxide containing lithium, nickel, and oxygen.

[0057] In one embodiment, the lithium nickel-based composite oxide may further include cobalt.

[0058] In one embodiment, the lithium nickel-based composite oxide may contain lithium, nickel, and aluminum.

[0059] In one embodiment, the lithium nickel-based composite oxide may contain lithium, nickel, and manganese.

[0060] In one embodiment, the nickel may be a high-nickel lithium composite oxide containing 0.5 mol% or more, 0.6 mol% or more, 0.7 mol% or more, 0.8 mol% or more, or 0.9 mol% or more of nickel relative to the total molar content of transition metals.

[0061] In one aspect, some cations and some anions in the lithium nickel-based composite oxide according to one aspect of the present invention are simultaneously replaced with cations (M') and fluorine anions contained in a fluorine-based compound. The cations (M') and fluorine anions of the fluorine-based compound may simultaneously exist in the lattice structure of the primary particles contained in the lithium nickel-based composite oxide particles, which can be expressed as being doped with the fluorine-based compound, or the fluorine-based compound acting as a dopant.

[0062] In the present invention, a fluorine-based compound simultaneously substitutes for the cation and anion sites of a lithium nickel-based composite oxide, thereby maximizing battery characteristics such as lifespan and high-temperature storage. More specifically, fluorine has a higher electronegativity than oxygen, which strengthens the bond with transition metals such as Ni, improving structural stability and maximizing battery characteristics. The cations of fluorine-based compounds have a cation mixing suppression effect, and the present invention simultaneously achieves these effects, thereby maximizing battery characteristics such as lifespan and high-temperature storage.

[0063] In one embodiment, the cation (M') of the fluorine-based compound may be at least one selected from the group consisting of cations of alkali metals, alkaline earth metals, transition metals, and rare earth metals.

[0064] More preferably, the fluorine-based compound may be LiF, CaF2, MgF2, AlF3 or ZrF4.

[0065] Most preferably, the fluorine-based compound may be LiF or CaF2. In the case of LiF, the excess Li inhibits cation mixing, and the fluorine that replaces oxygen strengthens the structure, suppressing gas generation during high-temperature storage. In the case of CaF2, the large ionic radius of Ca mainly occupies the lithium site, enhancing thermal stability.

[0066] This effect also has a significant impact on the doping content of the fluorine-based compound, and the inventors have been able to dramatically improve the life characteristics and high-temperature storage characteristics by controlling all of the specific processes, doping materials, and doping content of the present invention.

[0067] The lithium nickel-based composite oxide according to one embodiment of the present invention can be represented by the following Chemical Formula 1 by being doped with a fluorine-based compound.

[0068] [ka]

[0069] In the 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 M' is at least one selected from the group consisting of cations of alkali metals, alkaline earth metals, transition metals, and rare earth metals, and is within the range of 0.9≦a≦1.3, 0.5≦x<1.0, 0.0≦y≦0.2, 0.0≦z≦0.2, 0.0 <q≦0.1である。

[0070] In one embodiment, the nickel-based lithium composite oxide may be represented by the following Chemical Formula 2:

[0071] [ka]

[0072] In the formula 2, M1 is Al or Mn, 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 M' is at least one selected from the group consisting of cations of alkali metals, alkaline earth metals, transition metals, and rare earth metals, and is within the range of 0.9≦a'≦1.3, 0.5≦x'≦1.0, 0.0≦y'≦0.2, 0.0≦z'≦0.2, 0.0≦t'≦0.2, 0.0 <q’≦0.1である。

[0073] In one embodiment, a and a' may be 0.9 to 1.2 or 0.9 to 1.1.

[0074] More preferably, the M and / or M' may be any one or more selected from Li, Ca, Mg, Al and Zr.

[0075] More preferably, q and / or q' may be 0.001 or more, 0.002 or more, 0.003 or more, 0.004 or more, 0.005 or more, 0.05 or less, 0.04 or less, 0.03 or less, or 0.02 or less, and may be 0.003 to 0.03, 0.005 to 0.02, or 0.01 to 0.02.

[0076] More preferably, the fluorine-based compound may be contained in an amount of 0.1 mol% or more, 0.2 mol% or more, 0.3 mol% or more, 0.4 mol% or more, 0.5 mol% or more, 5 mol% or less, 4 mol% or less, 3 mol% or less, or 2 mol% or less, relative to the molar percentage of all metals excluding lithium, and may be contained in an amount of 0.3 mol% or more to 3 mol% or less, 0.5 mol% or more to 2 mol% or less, or 1 mol% or more to 2 mol% or less.

[0077] The present invention has confirmed that by controlling the doping content to the above-mentioned level in conjunction with a specific process and a specific doping substance, it has been possible to achieve significantly improved effects such as suppressing cation mixing, strengthening the structure by fluorine substituting for oxygen, and suppressing gas generation during high-temperature storage.

[0078] In a positive electrode active material according to one embodiment of the present invention, the average Ni occupancy rate in the Li 3a site, as determined by Rietveld analysis using X-ray diffraction of secondary particles, may be 1.1% to 1.5%, 1.2% to 1.4%, or 1.2% to 1.3%. The present invention allows for the Ni occupancy rate in the Li 3a site to be adjusted by adjusting the doping content along with a specific process and a specific doping material, thereby controlling the degree of cation mixing.

[0079] In one embodiment of the present invention, the average c-axis length of the cathode active material obtained by Rietveld analysis using X-ray diffraction of secondary particles may be 14.184 Å to 14.186 Å. The present invention allows for the c-axis length to be controlled by adjusting the doping content along with a specific process and a specific doping material, thereby controlling the degree of cation mixing.

[0080] In one embodiment, when the lithium nickel-based composite oxide is analyzed by XRD, the FWHM corrected by the following relational expression 1 補正(104) can be 0.16° to 0.19° 2θ, or 0.17° to 0.19° 2θ.

[0081] (Equation 1) FWHM 補正(104) =FWHM 測定(104) -FWHM Si powder (220)

[0082] In this case, FWHM(104) means the full width at half maximum (FWHM; deg., 2θ) of the (104) peak in the XRD peak defined by a hexagonal lattice having the R-3m space group.

[0083] In the above-mentioned relational expression 1, FWHM 測定(104) means the half-width of the (104) peak observed at 44.5±1.0° (2θ) in XRD analysis of the lithium nickel composite oxide, and the FWHM Si(220) means the half-width of the (220) peak observed near 47.3±1.0° (2θ) in the XRD measurement of Si powder.

[0084] The full width at half maximum (FWHM) of the lithium nickel-based composite oxide according to the present invention was corrected to the full width at half maximum (FWHM) of Si powder as a standard sample according to the above Relation 1, since deviations and errors occur in the measured value of the full width at half maximum (FWHM) during XRD analysis due to various variables such as the condition of the analysis equipment, the X-ray source, and the measurement conditions.

[0085] FWHM (104)and FWHM for Si powder (220) The measurement is calculated by fitting a Gaussian function, and fitting a Gaussian function for FWHM measurement can be performed using a variety of academic / public / commercial software known to those skilled in the art.

[0086] On the other hand, the Si powder used was Si powder (product number 215619) manufactured by Sigma-Aldrich.

[0087] In one aspect, the secondary particles include a surface region and an interior region. The present invention provides a lithium nickel-based composite oxide in which the surface region and interior region of the secondary particles are differentiated by the technical features described below, by controlling the doping content to a specific content using a specific process and a specific doping material. When a specific doping compound is doped in a specific content at a specific heat treatment temperature and reaction time, the surface region of the secondary particles may be doped mainly with a fluorine-based compound.

[0088] Here, the surface portion of the secondary particle refers to a section of 2 μm to 3 μm from the outermost periphery of the secondary particle, and the interior of the secondary particle refers to a section excluding the surface portion of the secondary particle.

[0089] In one embodiment, the average particle size of the primary particles at the surface of the secondary particles may be larger than the average particle size of the primary particles in the interior.

[0090] In one embodiment, primary particles having a particle size of 200 nm or more and less than 500 nm within the secondary particles may account for 50% to 100% by volume of the primary particles constituting the secondary particles.

[0091] In one embodiment, primary particles having a particle size of 200 nm or more and less than 300 nm within the secondary particles may account for 50% to 100% by volume of the primary particles constituting the secondary particles.

[0092] In one embodiment, the average particle size of the primary particles within the secondary particles may be 200 nm to 500 nm, 200 nm to 300 nm, or 200 nm to 250 nm.

[0093] In one embodiment, the primary particles having a particle size of more than 500 nm and less than 10 μm at the surface of the secondary particles may account for 50% to 100%, 70% to 100%, or 100% by volume of the primary particles constituting the secondary particles.

[0094] In one embodiment, the primary particles having a particle size of 1 μm to 10 μm at the surface of the secondary particles may account for 50% to 100%, 70% to 100%, or 100% by volume of the primary particles constituting the secondary particles.

[0095] In one embodiment, the average particle size of the primary particles at the surface portion of the secondary particles may be 500 nm to 2 μm, 800 nm to 1.5 μm, or 1.0 μm to 1.2 μm.

[0096] In one embodiment, the average particle size of the primary particles at the surface of the secondary particles may be 1.2 times, 1.5 times, 2.0 times, or 3.0 times or more larger than the average particle size of the primary particles at the interior.

[0097] In one aspect, the average aspect ratio of the primary particles at the surface of the secondary particles may be greater than the average aspect ratio of the primary particles at the interior.

[0098] In this specification, the aspect ratio means the length of the longest axis / the length of the shortest axis.

[0099] In one embodiment, the average aspect ratio of the primary particles at the surface portions of the secondary particles may be 2.0 or more, 2.4 or more, 2.7 or more, 3.0 or more, or 20.0 or less.

[0100] In one embodiment, the average aspect ratio of the primary particles within the secondary particles may be 1.0 or greater, more than 1.0, 1.2 or greater, more than 1.2, less than 2.0, 1.5 or less, or less than 1.5.

[0101] In one embodiment, the average aspect ratio of the primary particles at the surface of the secondary particles may be 2.0 times or more, 2.4 times or more, or 10.0 times or less than the average aspect ratio of the primary particles at the interior of the secondary particles.

[0102] In the lithium nickel-based composite oxide according to one embodiment of the present invention, the concentration of the doped fluorine anions may exhibit a gradient in the surface portion of the secondary particles.

[0103] In one embodiment, 50% or more of the primary particles in the surface region of the secondary particles may be formed such that the major axis direction of the primary particles has an angle of ±30° or less with respect to a line connecting the surface and center of the secondary particle.

[0104] In one embodiment, the primary particles, which are 50% or more of the primary particles in the surface portion of the secondary particles, may be formed such that the lithium ion diffusion paths formed within the primary particles have an angle of ±30° with a line connecting the surface and center of the secondary particle.

[0105] In the present invention, the lithium ion diffusion paths formed within the primary particles of the lithium nickel-based composite oxide are parallel to the major axis direction of the primary particles, thereby improving the diffusion ability of the lithium ions through the lithium nickel-based composite oxide.

[0106] In one aspect, the secondary particles exhibit the greatest peak intensity at 684.3 eV to 685.0 eV in fluorine 1s binding energy analysis obtained through XPS (X-ray Photoelectron Spectrometer) measurement. The XPS analysis results confirm that F is primarily present in the surface region of the secondary particles. In particular, the binding energy analysis results confirm that F appropriately substitutes for O sites.

[0107] Meanwhile, the cause of deterioration of life characteristics or battery characteristics during high-temperature storage is directly related to the phenomenon of oxygen desorption from nickel-based positive electrode active materials, particularly high-nickel positive electrode active materials. The XPS analysis results show that the present invention can be effective in improving life characteristics or suppressing oxygen desorption during high-temperature storage.

[0108] Meanwhile, lithium, the main raw material for cathode active materials, exhibits high volatility at high temperatures. Therefore, when reacting at high temperatures for long periods to manufacture cathode active materials, the stoichiometric ratio of lithium to transition metals changes, inducing various types of lattice defects, which can result in reduced capacity, lifespan, and other characteristics. In particular, high-nickel batteries, which contain a large amount of Ni for high capacity, experience numerous defects during high-temperature firing. This is related to the reduction of Ni's oxidation state from +3 to +2 when the amount of Li in the structure changes during firing. Therefore, to resolve this issue, the firing temperature must be lowered as much as possible, and the lithium reaction initiation temperature must be lowered as much as possible. Lowering the lithium reaction initiation temperature can also reduce the residual lithium content.

[0109] The present invention reduces the lithium reaction initiation temperature and the content of residual lithium (Li) present in the form of LiOH and Li2CO3 by adjusting the content of a specific fluorine-based compound to fall within a specific range.

[0110] In one embodiment, the content of residual lithium (Li) present in the form of LiOH on the surface of the secondary particles may be 11,300 ppm or less, or 11,000 ppm or less.

[0111] In one embodiment, the content of residual lithium (Li) present on the surface of the secondary particles in the form of Li2CO3 may be 6000 ppm or less, 5000 ppm or less, or 3000 ppm or less.

[0112] In one embodiment, the positive electrode active material may further include a coating oxide occupying at least a portion of at least one of surfaces of the secondary particles, grain boundaries between the primary particles, and surfaces of the primary particles.

[0113] In one embodiment, the coating oxide can be represented by the following Chemical Formula 3:

[0114] [ka]

[0115] 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。

[0116] For example, in Formula 3, M3 represents a coating element, and the coating oxide may be an oxide of lithium and an element represented by M3 combined together, or an oxide of M3.

[0117] In one example, the coating oxide may be 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 Or , 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 can be, but is not limited to this.

[0118] 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.

[0119] 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 or increase 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.

[0120] In addition, the concentration gradient portion may decrease or increase in a direction from the surface of the primary particle that forms the outermost periphery of the secondary particle toward the center of the primary particle.

[0121] 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, the concentration gradient portion may decrease or increase in a direction from the surface of the primary particle toward the center of the primary particle.

[0122] Meanwhile, the technical characteristics of the primary particles or secondary particles of the lithium nickel-based composite oxide described above may be average characteristics of a plurality of particles.

[0123] Furthermore, the meanings of "≦", "greater than or equal to" or "less than or equal to" described in the present invention can be replaced with the meanings of "<", "greater than" or "less than".

[0124] A positive electrode according to one embodiment of the present invention includes the positive electrode active material.

[0125] Except for the use of the above-described positive electrode active material, the positive electrode may have a known structure and may be manufactured by a known manufacturing method. The binder, conductive material, and solvent are not particularly limited as long as they are usable on a positive electrode current collector of a secondary battery.

[0126] A secondary battery according to one embodiment of the present invention includes the positive electrode active material.

[0127] 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. [Example]

[0128] Examples of the present invention will be described in more detail below.

[0129] Manufacturing of positive electrode active materials

[0130] Example 1

[0131] First, nickel sulfate, cobalt sulfate, and manganese sulfate were prepared and subjected to a coprecipitation reaction to synthesize a precursor of NiCoMn(OH)2 hydroxide (Ni:Co:Mn=90:8:2 (at%)).

[0132] Lithium composite oxides were prepared by adding LiOH (Li / (Ni+Co+Mn) molar ratio = 1.04) and fluorine-based compounds to the synthesized precursor in various amounts and then calcining the mixture. In this case, LiOH and fluorine-based compounds were mixed into the precursor, and the temperature was increased at 2°C per minute while maintaining an O2 atmosphere in a calcination furnace. The mixture was then heat-treated at 665°C for 10 hours and then naturally cooled.

[0133] The fluorine-based compounds added in the above examples were LiF, CaF2, AlF3, MgF2, NH4F, and ZrF4, and each was added in various amounts up to 0.2 mol%, 0.5 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, and 5 mol% based on the molar content of all metals excluding lithium.

[0134] <Example 2>

[0135] The positive electrode active material prepared in Example 1 was mixed with TiO2, Al2O3, and ZrO2 in amounts of 0.6 mol%, 0.6 mol%, and 0.1 mol%, respectively, and then the mixture was heated at a rate of 4.4°C per minute while maintaining an O2 atmosphere in a firing furnace, and then heat-treated at 675°C for 8 hours, followed by natural cooling to obtain a lithium composite oxide.

[0136] Distilled water was added to the obtained lithium composite oxide, and then the lithium composite oxide was washed with water for 1 hour. The washed lithium composite oxide was filtered and then dried.

[0137] Next, the dried lithium composite oxide and a B-containing raw material (H3BO3) were mixed together using a mixer. The B-containing raw material (H3BO3) was mixed so that the content was 0.235 wt% based on the total weight of the lithium composite oxide. In the same calcination furnace, an O2 atmosphere was maintained and the temperature was increased at 4.4°C per minute. The mixture was then heat-treated at 300°C for 8 hours and then naturally cooled.

[0138] <Comparative Example 1>

[0139] A positive electrode active material was prepared in the same manner as in Example 1, except that no fluorine-based compound was added.

[0140] <Comparative Example 2>

[0141] A positive electrode active material was prepared in the same manner as in Example 2, except that TiO2, Al2O3, and ZrO2 were mixed with the positive electrode active material prepared in Comparative Example 1, which did not contain a fluorine-based compound.

[0142] Lithium secondary battery manufacturing

[0143] 94 wt% of the positive electrode active material prepared in the Examples and Comparative Examples, 3 wt% of artificial graphite, and 3 wt% of PVDF binder were dispersed in 3.5 g of N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was applied to a 15 μm-thick aluminum (Al) thin film as a positive electrode current collector, dried, and roll-pressed to prepare a positive electrode. The loading level of the positive electrode was 7 mg / cm. 2 The electrode density is 3.2 g / cm 3 It was.

[0144] For the positive electrode, lithium foil was used as a counter electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as a separator, and a liquid electrolyte containing LiPF6 at a concentration of 1.5 M in a solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 3:7 was used. A coin battery was fabricated using a commonly known manufacturing process.

[0145] <Experimental Example>

[0146] (1) Cross-sectional SEM image

[0147] The cathode active materials according to Example 1 and Comparative Example 1 were processed using a cross-section polisher at a current of 380 μA for 1 hour and 30 minutes to obtain cross sections. FE-SEM was performed using a JSM-7610FPlus (JEOL) at a voltage of 2 kV to obtain cross-sectional SEM images of the lithium composite oxides, which are shown in FIG.

[0148] (2)Ni occupancy rate

[0149] The occupancy of Ni inserted into the Li 3a site of the positive electrode active materials of Example 1 and Comparative Example 1 was measured by Rietveld analysis using X-ray diffraction, and the results are shown in Figure 2. XRD analysis was performed using a Bruker D8 Advance diffractometer using Cu-Kα radiation (1.540598 Å) in the 2θ range of 10-80° (2θ) at 0.02° step intervals.

[0150] (3) c-axis length

[0151] The c-axis lengths of the positive electrode active materials according to Example 1 and Comparative Example 1 were measured by Rietveld analysis using X-ray diffraction, and are shown in Figure 3. XRD analysis was performed using a Bruker D8 Advance diffractometer with Cu-Kα radiation (1.540598 Å) in the 2θ range of 10-80° (2θ) at 0.02° step intervals.

[0152] (4) Measurement of half-width

[0153] X-ray diffraction (XRD) analysis was performed on the positive electrode active materials according to Example 1 and Comparative Example 1, and peaks attributed to the crystalline plane of the lithium composite oxide contained in the positive electrode active materials were detected and shown in Figure 4. XRD analysis was performed using a Bruker D8 Advance diffractometer with Cu-Kα radiation (1.540598 Å) in the 2θ range of 10-80° (2θ) at 0.02° step intervals.

[0154] (5)XPS analysis XPS analysis was performed on the positive electrode active materials according to Example 1 and Comparative Example 1. The XPS analysis was performed using Nexsa (Thermo Fisher) (minimum analysis area: 10 μm to 200 μm) using Al-Kα radiation, and the fluorine 1s binding energy contained in the lithium composite oxide was shown in FIG.

[0155] (6) Analysis of reaction initiation temperature

[0156] The reaction initiation temperatures of lithium for the positive electrode active materials according to Example 1 and Comparative Example 1 were analyzed and are shown in FIG.

[0157] (7) Analysis of gas generation amount

[0158] The lithium secondary batteries according to Example 2 and Comparative Example 2 were charged to 4.25 V at a constant current of 0.2 C and then stored at 60° C. for 80 hours. The volume change of the lithium secondary batteries due to gas generation in the lithium secondary batteries was measured to determine the volume increase rate, which is an index of gas generation, and the results are shown in FIG. 7.

[0159] (8) Efficiency analysis of C rate

[0160] For the lithium secondary batteries according to Example 2 and Comparative Example 2, the C-rate efficiency of 5.0C / 0.1C was measured using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, in the voltage range of 3.0V to 4.3V, and at a discharge rate of 0.1C to 5.0C, and the results are shown in FIG. 8.

[0161] (9) Analysis of residual lithium Residual lithium was measured by pH titration using the amount of 0.1M HCl used until the pH reached 4. First, 5 g of the positive electrode active materials according to Example 1 and Comparative Example 1 were placed in 100 mL of DIW, stirred for 15 minutes, and filtered to obtain 50 mL of the filtered solution. 0.1M HCl was added to the filtered solution, and the amount of HCl consumed due to the change in pH was measured to determine Q1 and Q2. Unreacted LiOH and Li2CO3 were calculated using the following equations, which are shown in Figures 9 and 10.

[0162] M1=23.95(LiOH Molecular weight)

[0163] M2=73.89(Li2CO3Molecular weight)

[0164] SPL Size=(Sample weight×Solution Weight) / Water Weight

[0165] LiOH(wt%)=[(Q1-Q2)×C×M1×100] / (SPL Size X1000)

[0166] Li2CO3(wt%)=[2XQ2XCXM2 / 2X100] / (SPL Size X1000)

Claims

1. The lithium nickel composite oxide includes secondary particles formed by aggregation of primary particles, some cations and some anions in the lithium nickel-based composite oxide are substituted with cations (M') and fluorine anions (F-) contained in a fluorine-based compound, The positive electrode active material, wherein the average Ni occupancy rate in the Li 3a site obtained by Rietveld analysis using X-ray diffraction of the secondary particles is 1.1% to 1.5%.

2. The positive electrode active material according to claim 1 , wherein the secondary particles have an average c-axis length of 14.184 Å to 14.186 Å as determined by Rietveld analysis using X-ray diffraction.

3. During XRD analysis of the lithium nickel-based composite oxide, the FWHM was corrected according to the following relational expression 1: 補正（１０４） is 0.16° to 0.19° (2θ): [Relationship 1] FWHM 補正（１０４） =FWHM 測定（１０４） -FWHM Ｓｉ ｐｏｗｄｅｒ (220) In the above-mentioned relational expression 1, FWHM 測定（１０４） means the half-width of the (104) peak observed at 44.5±1.0° (2θ) during XRD analysis of the lithium nickel-based composite oxide, and the FWHM Ｓｉ（２２０） means the half-width of the (220) peak observed near 47.3±1.0° (2θ) in the XRD measurement of Si powder.

4. The secondary particles include a surface portion and an interior portion, The positive electrode active material according to claim 1 , wherein the average particle size of the primary particles at the surface portions of the secondary particles is larger than the average particle size of the primary particles at the interior portions.

5. The cathode active material according to claim 4 , wherein primary particles having a particle size of 200 nm or more and less than 500 nm inside the secondary particles account for 50 to 100% by volume of the primary particles constituting the secondary particles.

6. The cathode active material according to claim 4 , wherein the primary particles having a particle size of 500 nm to 10 μm at the surface of the secondary particles account for 50% to 100% by volume of the primary particles constituting the secondary particles.

7. The positive electrode active material according to claim 4 , wherein an average aspect ratio of the primary particles at the surface portions of the secondary particles is larger than an average aspect ratio of the primary particles in the interior thereof.

8. 5. The cathode active material of claim 4, wherein 50% or more of the primary particles in the surface regions of the secondary particles are formed such that the major axis directions of the primary particles form an angle of ±30° or less with a line connecting the surface and center of the secondary particle.

9. 5. The positive electrode active material of claim 4, wherein the primary particles, which account for 50% or more of the primary particles in the surface regions of the secondary particles, are formed such that the lithium ion diffusion paths formed within the primary particles form an angle of ±30° with a line connecting the surface and center of the secondary particle.

10. 5. The cathode active material of claim 4, wherein the secondary particles exhibit the greatest peak intensity at 684.3 eV to 685.0 eV in a fluorine 1s binding energy analysis result obtained through X-ray Photoelectron Spectrometer (XPS) measurement.

11. The cathode active material of claim 1 , further comprising a coating oxide occupying at least a portion of at least one of surfaces of the secondary particles, grain boundaries between the primary particles, and surfaces of the primary particles.

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

13. A secondary battery comprising the positive electrode of claim 12.

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