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

Abstract

To provide a positive electrode active material that simultaneously exhibits an effect of suppressing cation mixing and an effect of enhancing the strength of structure due to fluorine replacing oxygen.SOLUTION: A positive electrode active material includes a lithium nickel-based composite oxide including secondary particles formed by aggregation of primary particles, where a part of cations and a part of anions in the lithium nickel-based composite oxide are substituted, respectively, with cations M' and fluorine anions (F-) contained in a fluorine-based compound.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a lithium composite oxide and a positive electrode active material for a secondary battery containing the same, and more particularly to a positive electrode active material in which cations and anions are simultaneously substituted with a fluorine-based compound in the crystal structure of a polycrystalline type lithium nickel-based composite 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-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 most spotlighted substance recently is lithium nickel manganese cobalt oxide Li(Ni , ,

[0004] ,

[0005] , Co<00000​​​​​​​​​​To overcome these drawbacks, demand for high-nickel systems, or Ni-rich systems with a Ni content of 60% or more, as positive electrode active materials for secondary batteries has begun to grow. However, while such Ni-rich active materials have the advantage of high capacity, as the Ni content increases, they also suffer from problems such as increased structural instability due to the mixing of Li / Ni cations, physical disconnection of internal particles due to microcracks, and deepening electrolyte depletion, resulting in a rapid deterioration of life characteristics at room and high temperatures. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention uses a cation and anion in a lithium nickel-based composite oxide as a cation M' and a fluorine anion (F - ) to simultaneously provide a positive electrode active material that exhibits the effect of inhibiting cation mixing and the effect of strengthening the structure by fluorine substituting for oxygen.

[0007] The present invention also provides a positive electrode active material in which the growth of primary particles is controlled inside and on the surface of secondary particles.

[0008] The present invention also provides a positive electrode active material in which the growth of primary particles is controlled in a specific direction at the surface of the secondary particles, distinct from the interior of the secondary particles.

[0009] Another object of the present invention is to provide a positive electrode active material in which lattice defects and residual lithium generated during high-temperature reactions are significantly reduced.

[0010] Another object of the present invention is to provide a positive electrode active material that extends the life of a battery and significantly suppresses gas generation during high-temperature storage.

[0011] 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]

[0012] 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 cations M' and fluorine anions (F) contained in a fluorine-based compound. - ) is replaced by

[0013] In one embodiment, the fluorine-based compound may be at least one selected from the group consisting of LiF, CaF2, MgF2, AlF3, and ZrF4.

[0014] In one embodiment, the secondary particles may include a surface portion and an interior portion, and the average size of the primary particles in the surface portion of the secondary particles may be larger than the average size of the primary particles in the interior portion.

[0015] In one embodiment, primary particles having a size of 200 nm or more and less than 500 nm inside the secondary particles may account for 50 to 100% by volume of the primary particles constituting the interior of the secondary particles.

[0016] In one embodiment, primary particles having a size of 500 nm to 10.0 μm on the surface of the secondary particles may account for 50 to 100% by volume of the primary particles that make up the surface of the secondary particles.

[0017] In one embodiment, the average aspect ratio of the primary particles at the surface portion of the secondary particles may be greater than the average aspect ratio of the primary particles at the interior portion.

[0018] In one embodiment, 50% or more of the primary particles on the surface of the secondary particle may be formed so that the major axis direction of the primary particle has an angle of ±30° or less with respect to a line connecting the surface and center of the secondary particle.

[0019] In one aspect, 50% or more of the primary particles in the surface region of the secondary particles may be formed such that the lithium ion diffusion path formed within the primary particle has an angle of ±30° or less with respect to a line connecting the surface and center of the secondary particle.

[0020] In one embodiment, the secondary particles can exhibit a maximum peak intensity at 684.3 eV to 685.0 eV as a result of Fluorine 1s binding energy analysis obtained by XPS (X-ray Photoelectron Spectrometer) measurement. In one embodiment, the positive electrode active material may further include a coating oxide occupying at least a portion of at least one of the surfaces of the secondary particles, the grain boundaries between the primary particles, and the surfaces of the primary particles.

[0021] The positive electrode of the present invention contains the positive electrode active material.

[0022] The secondary battery of the present invention includes the positive electrode. [Effects of the Invention]

[0023] As one effect, the present invention provides 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.

[0024] As one effect, the present invention provides 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.

[0025] As one advantage, the present invention provides a positive electrode active material that extends the battery life and significantly reduces gas evolution during high temperature storage.

[0026] As an advantage, the present invention provides a cathode active material that significantly improves battery characteristics such as battery capacity / efficiency and c-rate. [Brief explanation of the drawings]

[0027] [Figure 1] 10A and 10B are cross-sectional SEM images of positive electrode active materials according to comparative examples and examples of the present invention. [Figure 2] 1 is a graph showing the results of crystallite size analysis of positive electrode active materials according to comparative examples and examples of the present invention. [Figure 3] 1 is a graph showing XPS analysis results for positive electrode active materials according to comparative examples and examples of the present invention. [Figure 4] 1 is a graph showing the analysis results of reaction initiation temperatures during the preparation of positive electrode active materials according to comparative examples and examples of the present invention. [Figure 5] 1 is a graph showing the results of gas generation analysis when batteries according to comparative examples and examples of the present invention are stored at 90° C. [Figure 6] 1 is a graph showing the c-rate analysis results of batteries according to comparative examples and examples of the present invention. [Figure 7] 1 is a graph showing the results of analyzing LiOH content for positive electrode active materials according to comparative examples and examples of the present invention. [Figure 8] 1 is a graph showing the results of analyzing the Li2CO3 content of positive electrode active materials according to comparative examples and examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] As used herein, expressions such as "comprises" should be understood as open-ended terms that may include other configurations.

[0029] As used herein, the terms "preferred" and "preferably" refer to embodiments of the invention that may provide certain benefits, under certain circumstances, but are not intended to exclude other embodiments from the scope of the invention.

[0030] Also, as used in the specification and the appended claims, the singular forms "a," "an," and "the" are to be understood as including the plural forms as well, unless the context clearly dictates otherwise.

[0031] On the other hand, the technical features described below relate to one aspect for achieving the effects aimed at by the present invention.

[0032] That is, the cathode active material according to one aspect of the present invention can significantly improve the battery characteristics by incorporating the technical features according to one aspect described below.

[0033] A positive electrode active material according to one embodiment of the present invention includes secondary particles formed by aggregation of primary particles.

[0034] In one embodiment, the primary particles can include one or more crystallites.

[0035] The secondary particles may have a multi-particle or polycrystalline form containing two or more primary particles, and more preferably, the secondary particles may have a multi-particle or polycrystalline form containing an aggregation of 20 or more primary particles.

[0036] In a more preferred embodiment, the secondary particles may have a grain boundary density of 0.85 or more, or 0.90 or more.

[0037] In the present invention, the "grain boundary density" is calculated by the following Equation 1 for primary particles placed on a line crossing the center of the secondary particle in the minor axis direction in an SEM image obtained by photographing a cross section of the lithium composite oxide using a scanning electron microscope (SEM) after cross-section processing of the secondary particle. (Formula 1) Grain boundary density = Number of grain boundaries between primary particles placed on the line / Number of primary particles placed on the line

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

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

[0040] In one embodiment, the average particle size of the secondary particles may be 1 to 30 μm, more preferably 8 to 20 μm.

[0041] Meanwhile, in the present invention, "average particle size" refers to the average diameter (D50) when the particles are spherical, and refers to the average major axis length when the particles are non-spherical. In the present invention, the size of secondary particles was measured as an average value using a particle size analyzer (Cilas) and SEM. In addition, the primary particle size was calculated by measuring the major axis length of the primary particles in the SEM image when they were rod-shaped, and calculating the average diameter when they were spherical. In addition, the crystallite size was measured using the Scherrer equation from the full width at half maximum and θ value obtained by XRD analysis.

[0042] The present invention may be a unimodal type positive electrode active material. In yet another aspect, the positive electrode active material may be a bimodal type positive electrode active material further including lithium composite oxide secondary particles having an average particle size of 7 μm or less, the secondary particle size being different from the average particle size. A positive electrode active material according to one embodiment of the present invention includes a lithium-nickel composite oxide containing lithium, nickel, and oxygen.

[0043] In one embodiment, the lithium nickel-based composite oxide may further contain cobalt.

[0044] In one embodiment, the lithium nickel composite oxide can contain lithium, nickel, and aluminum.

[0045] In one embodiment, the lithium nickel composite oxide can contain lithium, nickel, and manganese.

[0046] 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.

[0047] In accordance with one aspect of the present invention, some cations and some anions in the lithium nickel-based composite oxide are simultaneously replaced with cations M' and fluorine anions contained in the fluorine-based compound. The cations M' and fluorine anions of the fluorine-based compound can simultaneously exist within the lattice structure of the primary particles contained in the lithium nickel-based composite oxide particles. This can be expressed as being doped with the fluorine-based compound, or as the fluorine-based compound acting as a dopant.

[0048] The present invention maximizes battery characteristics such as lifespan and high-temperature storage by simultaneously substituting cation and anion sites of a lithium nickel-based composite oxide with a fluorine-based compound. More specifically, fluorine has a higher electronegativity than oxygen, which further strengthens its bonding with transition metals such as Ni, improving structural stability and further maximizing battery characteristics. The cations of the fluorine-based compound also have the effect of suppressing cation mixing. By simultaneously achieving these effects, the present invention maximizes battery characteristics such as lifespan and high-temperature storage.

[0049] 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.

[0050] More preferably, the fluorine-based compound may be LiF, CaF2, MgF2, AlF3 or ZrF4.

[0051] Most preferably, the fluorine-based compound may be LiF or CaF2. In the case of LiF, excess Li has a high effect of suppressing cation mixing, and fluorine substitutes for oxygen to strengthen the structure, thereby suppressing gas generation during high-temperature storage. In the case of CaF2, Ca has a large ionic radius and mainly occupies the lithium site, thereby enhancing thermal stability.

[0052] The doping content of the fluorine-based compound also has a very important effect on this effect, and the inventors have been able to dramatically improve the lifespan and high-temperature storage characteristics by controlling the specific process, doping material, and doping content of the present invention.

[0053] 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. (chemical 1) Li a Ni x Co y M z M' 1-x-y-z O 2-q F q

[0054] 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, 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 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。

[0055] In one embodiment, the nickel-based lithium composite oxide can be represented by the following Chemical Formula 2: (Case 2) Li a’ Ni x’ Co y’ M1 z’ M2 t 'M' 1-x’-y’-z’-t 'O2-q’ F q’

[0056] 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, 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。

[0057] In one embodiment, the a and / or a' may be 0.9 to 1.2 or 0.9 to 1.1.

[0058] More preferably, the M and / or M' may be at least one selected from the group consisting of Li, Ca, Mg, Al and Zr.

[0059] 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.

[0060] 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 total mol% of 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.

[0061] The present invention has confirmed that by controlling the doping content to the above-mentioned level along with a specific process and a specific doping material, it is possible to achieve significantly improved effects of suppressing cation mixing, strengthening the structure by fluorine substituting for oxygen, and suppressing gas generation during high-temperature storage.

[0062] In one embodiment, the average size of the crystallites in the lithium nickel-based composite oxide may be 40 nm or more, 41 nm or more, 42 nm or more, 43 nm or more, or 50 nm or less. The present invention can increase the energy density per volume and improve battery characteristics such as lifespan by growing the crystallite size through controlling the doping content to the above range using a specific process and a specific doping substance.

[0063] In one embodiment, 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 level using a specific process and a specific doping material. When a specific doping compound is doped at a specific content at a specific heat treatment temperature and reaction time, the fluorine-based compound can be primarily doped in the surface region of the secondary particles.

[0064] Here, the surface portion of the secondary particle means a section of 2 μm to 3 μm from the outermost periphery of the secondary particle, and the interior of the secondary particle means a section excluding the surface portion of the secondary particle.

[0065] In one embodiment, the average size of the primary particles in the surface portion of the secondary particles may be larger than the average size of the primary particles in the interior portion.

[0066] In one embodiment, primary particles having a size of 200 nm or more and less than 500 nm inside the secondary particles may account for 50 to 100 volume %, 70 to 100 volume %, or 100 volume % of the primary particles constituting the interior of the secondary particles.

[0067] In one embodiment, primary particles having a size of 200 nm or more and less than 300 nm inside the secondary particles may account for 50 to 100 volume %, 70 to 100 volume %, or 100 volume % of the primary particles constituting the interior of the secondary particles.

[0068] In one embodiment, the average size of the primary particles within the secondary particles may be 200 to 500 nm, 200 to 300 nm, or 200 to 250 nm.

[0069] In one embodiment, primary particles having a size of 500 nm to 10 μm on the surface of the secondary particles may account for 50 to 100 volume %, 70 to 100 volume %, or 100 volume % of the primary particles that make up the surface of the secondary particles.

[0070] In one embodiment, primary particles having a size of 1 μm to 10 μm on the surface of the secondary particles may account for 50 to 100 volume %, 70 to 100 volume %, or 100 volume % of the primary particles that make up the surface of the secondary particles.

[0071] In one embodiment, the average size of the primary particles in the surface portion of the secondary particles may be 500 nm or more and 2 μm or less, 800 nm or more and 1.5 μm or less, or 1.0 μm or more and 1.2 μm or less.

[0072] In one embodiment, the average size of the primary particles in the surface portion 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 size of the primary particles in the interior portion.

[0073] In one embodiment, the average aspect ratio of the primary particles in the surface region of the secondary particles may be greater than the average aspect ratio of the primary particles in the interior region.

[0074] In this specification, the aspect ratio means the length of the longest axis / the length of the shortest axis.

[0075] 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.

[0076] 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.

[0077] In one embodiment, the average aspect ratio of the primary particles in the surface portion 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 in the interior of the secondary particles.

[0078] In the lithium nickel-based composite oxide according to an embodiment of the present invention, the concentration of the doped fluorine anions may have a gradient at the surface of the secondary particles.

[0079] In one embodiment, 50% or more of the primary particles on the surface of the secondary particle may be formed so that the major axis direction of the primary particle has an angle of ±30° or less with respect to a line connecting the surface and center of the secondary particle.

[0080] In one embodiment, 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 respect to a line connecting the surface and center of the secondary particle.

[0081] The present invention enables the lithium ion diffusion ability to be improved through the lithium nickel-based composite oxide by forming lithium ion diffusion paths in the primary particles of the lithium nickel-based composite oxide that are parallel to the long axis direction of the primary particles.

[0082] In one embodiment, the secondary particles may have a maximum peak intensity at 684.3 eV to 685.0 eV as a result of Fluorine 1s binding energy analysis obtained by XPS (X-ray Photoelectron Spectrometer) measurement. The XPS analysis result confirms that F is mainly present in the surface region of the secondary particles. In particular, the binding energy analysis result confirms that F is appropriately substituted for O sites.

[0083] Meanwhile, the deterioration of battery performance during lifespan or 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 demonstrate that the present invention is effective in suppressing oxygen desorption during lifespan or high-temperature storage.

[0084] Meanwhile, lithium, the main raw material for cathode active materials, is highly volatile 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, causing various lattice defects, which can result in reduced capacity, lifespan, and other characteristics. High-temperature firing, especially in high-nickel batteries with a high Ni content for high capacity, can often cause defects. The change in the amount of Li in the structure during firing is related to the reduction of the Ni oxidation state from +3 to +2. Therefore, to resolve this issue, the firing temperature must be kept as low as possible, and the lithium reaction initiation temperature must be kept as low as possible. Lowering the lithium reaction initiation temperature can also reduce the residual lithium content.

[0085] In the present invention, the content of a specific fluorine-based compound is adjusted to be within a specific range, thereby lowering the lithium reaction initiation temperature and thereby reducing the content of residual lithium (Li) present in the form of LiOH and Li2CO3.

[0086] 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. 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.

[0087] In one embodiment, the positive electrode active material may further include a coating oxide occupying at least a portion of at least one of the surfaces of the secondary particles, the grain boundaries between the primary particles, and the surfaces of the primary particles.

[0088] In one embodiment, the coating oxide can be represented by the following Chemical Formula 3: (3) Li p M3 q O r

[0089] 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。

[0090] 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 in combination, or an oxide of M3.

[0091] 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 qO r , Li p Mo q O r , Co q O r , Al q O r , W q O r , Zr q O r , Ti q O r , B q O r , Li p (W / Ti) q O r , Li p (W / Zr) q O r , Li p (W / Ti / Zr) q O r , or Li p (W / Ti / B) q O r It can be, but is not limited to this.

[0092] 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.

[0093] In one aspect, when the coating oxide occupies at least a portion of the surface region of a primary particle that forms the outermost periphery of the secondary particle, the concentration gradient portion may decrease, increase, or increase and then decrease in a direction from the surface of the primary particle that forms the outermost periphery of the secondary particle toward the center of the secondary particle.

[0094] In addition, the concentration gradient portion may decrease, increase, or increase and then decrease in a direction from the surface of the primary particle forming the outermost periphery of the secondary particle toward the center of the primary particle.

[0095] In one aspect, when the coating oxide occupies at least a portion of the surface region of the primary particle that does not form the outermost periphery of the secondary particle, it may decrease, increase, or increase and then decrease in a direction from the surface of the primary particle toward the center of the primary particle.

[0096] Meanwhile, the technical characteristics of the primary particles or secondary particles of the lithium nickel-based composite oxide may be related to the average characteristics of a plurality of particles.

[0097] Furthermore, the meanings of "≦", "greater than", and "less than" described in the present invention can be replaced with the meanings of "<", "more than", and "less than".

[0098] A positive electrode according to one aspect of the present invention includes the positive electrode active material.

[0099] Except for the use of the above-described positive electrode active material, the positive electrode has a known structure and can be manufactured by a known manufacturing method. The binder, conductive material, and solvent are not particularly limited as long as they can be used on a positive electrode current collector of a secondary battery.

[0100] A secondary battery according to one aspect of the present invention includes the positive electrode active material.

[0101] 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.

[0102] Examples of the present invention will be described in more detail below.

[0103] Manufacturing of positive electrode active materials Example 1 First, nickel sulfate, cobalt sulfate, and manganese sulfate were prepared and coprecipitation reaction was carried out to synthesize NiCoMn(OH)2 hydroxide precursor (Ni:Co:Mn=90:8:2 (at%)).

[0104] Lithium composite oxides were prepared by adding various amounts of LiOH (Li / (Ni+Co+Mn) molar ratio = 1.04) and fluorine-based compounds to the synthesized precursor and then calcining. In this case, after mixing LiOH and fluorine-based compounds with the precursor, the temperature was increased at a rate of 2°C per minute while maintaining an O2 atmosphere in a calcination furnace, and the mixture was heat-treated at 665°C for 10 hours and then naturally cooled.

[0105] Here, the fluorine-based compounds added in the above examples were LiF, CaF2, AlF3, MgF2, NH4F, and ZrF4, and each was added in various amounts of 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.

[0106] <Example 2> The positive electrode active material prepared in Example 1 was mixed with 0.6, 0.6, and 0.1 mol% of TiO, AlO, and ZrO, respectively, and then heated at a rate of 4.4°C per minute while maintaining an O atmosphere in a firing furnace. The mixture was then heat-treated at 675°C for 8 hours and then naturally cooled to obtain a lithium composite oxide.

[0107] 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.

[0108] The dried lithium composite oxide was then mixed with a B-containing raw material (H3BO3) using a mixer. The B-containing raw material (H3BO3) was mixed in an amount of 0.235 wt% based on the total weight of the lithium composite oxide. In the same calcination furnace, the temperature was increased at a rate of 4.4°C per minute while maintaining an O2 atmosphere, and the mixture was heat-treated at 300°C for 8 hours, followed by natural cooling.

[0109] <Comparative Example 1> A positive electrode active material was produced in the same manner as in Example 1, except that no fluorine-based compound was added.

[0110] <Comparative Example 2> 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.

[0111] Lithium secondary battery manufacturing A positive electrode slurry was prepared by dispersing 94 wt% of the positive electrode active material prepared according to the examples and comparative examples, 3 wt% of artificial graphite, and 3 wt% of PVDF binder in 3.5 g of N-methyl-2-pyrrolidone (NMP). 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 and the electrode density is 3.2 g / cm 3 It was.

[0112] A lithium foil was used as a counter electrode for the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) was used as a separator, and a liquid electrolyte solution of 1.5M LiPF6 in a solvent of ethylene carbonate and ethylene carbonate mixed in a volume ratio of 3:7 was used. A coin battery was fabricated according to a commonly known manufacturing process.

[0113] <Experimental Example> (1) Cross-sectional SEM image The cathode active materials according to Example 1 and Comparative Example 1 were polished 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.

[0114] (2) Average crystallite size The average crystallite size of the positive electrode active materials according to Example 1 and Comparative Example 1 was measured and is shown in FIG. 2. To measure the crystallite size, X-ray diffraction (XRD) analysis was performed to detect peaks due to the crystal plane of the lithium composite oxide contained in the positive electrode active material. The XRD analysis was performed using a Bruker D8 Advance diffractometer with Cu-Kα radiation (1.540598 Å) in 2θ ranges of 10-80° (2θ) at 0.02° intervals, and the FWHM was corrected according to the following equation: 補正(104) After obtaining the above, it was converted into the crystallite size by the Scherrer equation, which is shown in FIG.

[0115] (Equation 1) FWHM 補正(104) =FWHM 測定(104) -FWHM Si 粉末 (220) Here, 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.

[0116] In the above-mentioned relational expression 1, FWHM 測定(104) means the full width at half maximum of the (104) peak observed at 44.5±1.0° (2θ) in the XRD analysis of the lithium nickel composite oxide, and the FWHM Si粉末(220) means the full width at half maximum of the (220) peak observed near 47.3±1.0° (2θ) in the XRD measurement of Si powder.

[0117] The full width at half maximum (FWHM) of the lithium nickel-based composite oxide according to the present invention is corrected by the full width at half maximum (FWHM) of Si powder as a standard sample, as shown in the above relational expression 1, since the measured value of the full width at half maximum (FWHM) during XRD analysis may have deviations and errors due to various variables such as the condition of the analysis equipment, the X-ray source, and the measurement conditions. FWHM(104) and FWHM of 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.

[0118] On the other hand, the Si powder used was Si powder (product number 215619) manufactured by Sigma-Aldrich.

[0119] (3)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 a Nexsa (Thermo Fisher) (minimum analysis area: 10-200 μm) using Al-Kα radiation to measure the Fluorine 1s binding energy contained in the lithium composite oxide, and the results are shown in FIG.

[0120] (4) Reaction initiation temperature analysis 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.

[0121] (5) Gas generation rate analysis 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. 5.

[0122] (6) C-rate efficiency analysis The lithium secondary batteries according to Example 2 and Comparative Example 2 were subjected to measurement of the C-rate efficiency at 5.0C / 0.1C using an electrochemical analyzer (Toyo, Toscat-3100) at 25°C, with a voltage range of 3.0V to 4.3V and a discharge rate of 0.1C to 5.0C. The results are shown in FIG. 6.

[0123] (7) Residual lithium analysis 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. 50 ml of the filtered solution was taken, to which 0.1M HCl was added, 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 FIGS. 7 and 8.

[0124] M1=23.95 (LiOH molecular weight) M2=73.89(Li2CO3 molecular weight) SPL size = (sample weight x solution weight) / water weight LiOH (wt%) = [(Q1-Q2) x C x M1 x 100] / (SPL size x 1000) Li2CO3 (wt%) = [2 x Q2 x C x M2 / 2 x 100] / (SPL size x 1000)

Claims

1. The lithium nickel composite oxide includes secondary particles formed by aggregation of primary particles, A part of the cations and a part of the anions in the lithium nickel-based composite oxide are cations M' and fluorine anions (F － ) and The secondary particles include a surface portion and an interior portion, A positive electrode active material, wherein an average aspect ratio of the primary particles in the surface portions of the secondary particles is greater than an average aspect ratio of the primary particles in the interiors of the secondary particles.

2. The fluorine-based compound is LiF, CaF ２ , MgF ２ , AlF ３ and ZrF ４ The positive electrode active material according to claim 1 , wherein the positive electrode active material is at least one selected from the following:

3. 2. The positive electrode active material according to claim 1, wherein primary particles having a 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 interior of the secondary particles.

4. 4. The positive electrode active material according to claim 3, wherein primary particles having a size of 500 nm to 10.0 μm on the surface portions of the secondary particles account for 50 to 100% by volume of the primary particles constituting the surface portions of the secondary particles.

5. 4. The positive electrode active material according to claim 3, wherein 50% or more of the primary particles in the surface portions of the secondary particles are formed such that the major axis direction of the primary particle forms an angle of ±30° or less with respect to a line connecting the surface and the center of the secondary particle.

6. 4. The cathode active material of claim 3, wherein 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° or less with respect to a line connecting the surface and the center of the secondary particle.

7. 4. The cathode active material of claim 3, wherein the secondary particles exhibit a maximum peak intensity at 684.3 eV to 685.0 eV as a result of Fluorine 1s binding energy analysis obtained by XPS (X-ray Photoelectron Spectrometer) measurement.

8. The positive electrode active material of claim 1 , further comprising 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.

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

10. A secondary battery comprising the positive electrode according to claim 9.

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