Lithium composite oxides and positive electrode active materials for secondary batteries 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 x [ Co y [ Mn z [ )O2 (where x, y, and z are the atomic fractions of independent oxide composition elements, 0 < x = y = 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, and is inexpensive because the Co content is relatively low.

[0004]

[0005] ​To complement such drawbacks, as a positive electrode active material for a secondary battery, the demand for a nickel-rich system (Ni rich system) with a Ni content of 60% or more has begun to increase. However, while the active material of such a nickel-rich system has excellent advantages of high capacity, as the Ni content increases, there are problems such as an increase in structural instability due to Li / Ni cation mixing, physical disconnection of internal particles due to microcracks, and deepening of electrolyte depletion, resulting in a sharp deterioration of the life characteristics at normal temperature and high temperature. Summary of the Invention Problems to be Solved by the Invention

[0006] The present invention aims to provide a positive electrode active material in which cations and anions in a lithium nickel-based composite oxide are simultaneously replaced by cations M' contained in a fluorine-based compound and fluorine anions (F - ), so that the cation mixing suppression effect and the structure strengthening effect by fluorine substituting oxygen appear simultaneously.

[0007] In addition, the present invention aims to provide a positive electrode active material in which the growth of primary particles is regulated inside and on the surface of secondary particles.

[0008] In addition, the present invention aims to provide a positive electrode active material in which the growth of primary particles is controlled in a specific direction on the surface portion distinguished from the inside of secondary particles.

[0009] In addition, the present invention aims to provide a positive electrode active material in which lattice defects and residual lithium generated during high-temperature reaction are significantly reduced.

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

[0011] In addition, the present invention aims to provide 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 comprises a lithium nickel-based composite oxide containing secondary particles formed by the aggregation of primary particles, wherein some of the cations and some of the anions in the lithium nickel-based composite oxide are cations M' and fluorine anions (F) contained in the fluorine-based compound. - ) is replaced by.

[0013] In one embodiment, the fluorine-based compound may be one or more selected from LiF, CaF2, MgF2, AlF3, and ZrF4.

[0014] In one embodiment, the secondary particles include a surface portion and an interior portion, and the average size of the primary particles on 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 with a size of 200 nm or more and less than 500 nm may constitute 50 to 100% by volume of the primary particles that make up the interior of the secondary particles.

[0016] In one embodiment, primary particles with 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 constituting the surface of the secondary particles.

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

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

[0019] In one embodiment, 50% or more of the primary particles on the surface of the secondary particles can be formed such that the lithium ion diffusion pathways formed within the primary particles have an angle of ±30° or less with respect to a line connecting the surface and the 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 that occupies at least one or more 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 includes 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 a cation mixing suppression effect and a structural strengthening effect by fluorine replacing oxygen.

[0024] As one effect, the present invention provides a positive electrode active material in which lattice defects and residual lithium generated during high-temperature reactions are significantly reduced, particularly in high-nickel positive electrode active materials.

[0025] As one effect, the present invention provides a positive electrode active material that extends the lifespan of a battery and significantly suppresses gas generation during high-temperature storage.

[0026] As one effect, the present invention provides a positive electrode active material that significantly improves battery characteristics such as battery capacity / efficiency and c-rate. [Brief explanation of the drawing]

[0027] [Figure 1] These are cross-sectional SEM images of the positive electrode active material according to comparative examples and examples of the present invention. [Figure 2] This graph shows the crystallite size analysis results for the positive electrode active material according to comparative examples and examples of the present invention. [Figure 3] This graph shows the XPS analysis results for the positive electrode active material according to comparative examples and examples of the present invention. [Figure 4] This graph shows the results of the reaction initiation temperature analysis during the production of positive electrode active material according to comparative examples and examples of the present invention. [Figure 5] This graph shows the results of the 90°C storage gas generation analysis of batteries according to comparative examples and examples of the present invention. [Figure 6] This graph shows the c-rate analysis results of batteries according to comparative examples and examples of the present invention. [Figure 7] This graph shows the results of LiOH content analysis for the positive electrode active material according to comparative examples and examples of the present invention. [Figure 8] This graph shows the results of Li2CO3 content analysis of the positive electrode active material according to comparative examples and examples of the present invention. [Modes for carrying out the invention]

[0028] Expressions such as “including” used herein should be understood as open-ended terms that may include other components.

[0029] As used herein, "preferred" and "preferred" indicate embodiments of the present invention that can provide certain advantages under certain conditions. However, this is not intended to exclude other embodiments from the scope of the present invention.

[0030] Furthermore, the singular form used in the specification and the attached claims should be understood to include plural forms unless otherwise indicated in the context.

[0031] On the other hand, the technical features described later relate to one aspect of achieving the effects intended by the present invention as described above.

[0032] In other words, the positive electrode active material according to one aspect of the present invention, by including the technical features of one aspect described later, can significantly improve the characteristics of the battery.

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

[0034] In one embodiment, the primary particle may contain one or more crystallites.

[0035] The secondary particles may have a multiparticle form containing two or more primary particles or a polycrystalline form. More preferably, the secondary particles may have a multiparticle form in which 20 or more primary particles are aggregated or a polycrystalline form.

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

[0037] In this invention, the "grain boundary density" is calculated using the following formula 1 for primary particles placed on a straight line that crosses the center of the secondary particles in the short axis direction in an SEM image obtained by scanning an electron microscope (SEM) after cross-sectional processing of the secondary particles. (Formula 1) Grain boundary density = Number of grain boundaries between primary particles placed on the aforementioned line / Number of primary particles placed on the aforementioned line

[0038] To illustrate with an example, in the case of a single, unaggregated primary particle, the grain boundary density calculated by Equation 1 would be 0. Furthermore, if two primary particles aggregate, the grain boundary density calculated by Equation 1 would be 0.5.

[0039] Here, the grain boundary density refers to the average value with respect to any 10 lines drawn along those 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] In this invention, "average particle size" refers to the average diameter (D50) if the particles are spherical, and the average length of the major axis if the particles are non-spherical. In this invention, the size of secondary particles was measured using a particle size analyzer (CILAS) and a scanning electron microscope (SEM) to obtain the average value. For primary particles, in the case of rod-shaped particles, the length of the major axis of the primary particle was measured in the SEM image and the average value was calculated; for spherical particles, the average diameter was calculated. The crystallite size was measured using Scherrer's 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 embodiment, the positive electrode active material may be a bimodal type positive electrode active material further comprising lithium composite oxide secondary particles of 7 μm or less, in which the secondary particle size and the average particle size differ. A positive electrode active material according to one aspect 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-based composite oxide may include lithium, nickel, and aluminum.

[0045] In one embodiment, the lithium nickel-based composite oxide may 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, relative to the total molar content of the transition metal.

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

[0048] This invention maximizes battery characteristics such as lifespan and high-temperature storage by simultaneously substituting cation and anion sites of lithium nickel-based composite oxides with fluorine-based compounds. More specifically, because fluorine has a higher electronegativity than oxygen, it further strengthens the bonding force with transition metals such as Ni, improving structural safety and thus maximizing battery characteristics. Furthermore, the cations of fluorine-based compounds have a cation mixing suppression effect. By simultaneously obtaining these effects, this 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 one or more selected from 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 can be LiF or CaF₂. In the case of LiF, the effect of suppressing cation mixing by excess Li and the effect of strengthening the structure by fluorine substituting oxygen are high, and gas generation can be suppressed during high-temperature storage. In the case of CaF₂, Ca has a large ionic radius and mainly enters the lithium site, which has the effect of enhancing thermal safety.

[0052] Such effects are also highly influenced by the doping content of the fluorine-based compound. The inventors were able to significantly improve the lifespan and high-temperature storage characteristics by controlling all of the specific processes, doping substances, and doping content of the present invention.

[0053] The lithium nickel-based composite oxide according to one aspect of the present invention can be represented by the following Chemical Formula 1 when doped with a fluorine-based compound. (Chemical Formula 1) Li a Ni x Co y M z M’ 1-x-y-z O 2-q F q

[0054] In Chemical Formula 1, M is selected from the group consisting of Al, Mn, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, and combinations thereof, M’ is any one or more selected from 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.

[0055] As one aspect, the nickel-based lithium composite oxide can be represented by the following Chemical Formula 2. [[ID=​​​​​​​​​​​​​​​2-q’ F q’

[0056] In the above chemical 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 one or more selected from alkali metals, alkaline earth metals, transition metals and rare earth metal cations, with 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, a and / or a' may be 0.9 to 1.2 or 0.9 to 1.1.

[0058] More preferably, M and / or M' may be one or more selected from Li, Ca, Mg, Al, and Zr.

[0059] More preferably, q and / or q' can 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 can 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 included in amounts 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 the metal excluding lithium. It may also be included in amounts 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] This invention confirms that by controlling the doping content to the aforementioned level in conjunction with specific processes and specific doping substances, there are significantly improved effects in suppressing cation mixing, strengthening the structure with fluorine as an alternative to oxygen, and suppressing gas generation during high-temperature storage.

[0062] In one embodiment, the average size of 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 unit volume and improve battery characteristics such as lifespan by growing the crystallite size through a specific process and a specific doping substance, along with controlling the doping content to the aforementioned content.

[0063] In one embodiment, the secondary particles include a surface and an interior. The present invention has made it possible to obtain a lithium nickel-based composite oxide in which the surface and interior of the secondary particles are separated by the technical features described later, by controlling the doping content to a specific content, along with a specific process and a specific doping substance. When a specific doping compound is doped at a specific content at a specific heat treatment temperature and reaction time, the surface of the secondary particles can be mainly doped with a fluorine-based compound.

[0064] Here, the surface portion of the secondary particle refers to the area from 2 μm to 3 μm from the outermost edge of the secondary particle, and the interior portion of the secondary particle refers to the area excluding the surface portion of the secondary particle.

[0065] In one embodiment, the average size of the primary particles on the surface of the secondary particles can be larger than the average size of the primary particles inside.

[0066] In one embodiment, primary particles with a size of 200 nm or more and less than 500 nm may constitute 50 to 100% by volume, 70 to 100% by volume, or 100% by volume of the primary particles that make up the interior of the secondary particles.

[0067] In one embodiment, primary particles with a size of 200 nm or more and less than 300 nm may constitute 50 to 100% by volume, 70 to 100% by volume, or 100% by volume of the primary particles that make up the interior of the secondary particles.

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

[0069] In one embodiment, primary particles with a size of 500 nm to 10 μm on the surface of the secondary particles may constitute 50 to 100% by volume, 70 to 100% by volume, or 100% by volume of the primary particles constituting the surface of the secondary particles.

[0070] In one embodiment, primary particles with a size of 1 μm to 10 μm on the surface of the secondary particles may constitute 50 to 100% by volume, 70 to 100% by volume, or 100% by 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 on the surface 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 on the surface of the secondary particles can 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 inside.

[0073] In one embodiment, the average aspect ratio of the primary particles on the surface of the secondary particles can be greater than the average aspect ratio of the primary particles inside.

[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 on the surface of the secondary particles may be 2.0 or greater, 2.4 or greater, 2.7 or greater, 3.0 or greater, or 20.0 or less.

[0076] In one embodiment, the average aspect ratio of the primary particles inside the secondary particle may be 1.0 or greater, greater than 1.0, 1.2 or greater, greater 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 primary particles on the surface of the secondary particle may be 2.0 times or more, 2.4 times or more, or 10.0 times or less the average aspect ratio of primary particles inside the secondary particle.

[0078] In one aspect of the present invention, the lithium nickel-based composite oxide can have a gradient in the concentration of fluorine anions doped on the surface of the secondary particles.

[0079] Furthermore, in one embodiment, 50% or more of the primary particles on the surface of the secondary particles can be formed such that the longitudinal axis of the primary particles has an angle of ±30° or less with respect to the line connecting the surface and the center of the secondary particle.

[0080] In one embodiment, more than 50% of the primary particles on the surface of the secondary particles can be formed such that the lithium ion diffusion pathways formed within the primary particles have an angle of ±30° or less with respect to the line connecting the surface and the center of the secondary particle.

[0081] The present invention improves the diffusion capacity of lithium ions mediated by the lithium nickel-based composite oxide by forming lithium ion diffusion pathways within the primary particles of the lithium nickel-based composite oxide parallel to the long axis direction of the primary particles.

[0082] In one embodiment, the secondary particles can 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. From the XPS analysis results, it can be confirmed that fluorine (F) is mainly present on the surface of the secondary particles. In particular, the binding energy analysis results can be confirmed that fluorine (F) has appropriately substituted for oxygen (O) sites.

[0083] On the other hand, the reason why battery life deteriorates or battery characteristics degrade during high-temperature storage is directly related to the phenomenon of oxygen desorption from nickel-based cathode active materials, particularly high-nickel cathode active materials. The XPS analysis results indicate that the present invention is efficient in suppressing oxygen desorption during battery life deterioration or high-temperature storage.

[0084] On the other hand, lithium, the main raw material for the positive electrode active material, is highly volatile at high temperatures. Therefore, when the reaction is carried out at high temperatures for a long time to manufacture the positive electrode active material, the stoichiometric ratio of lithium / transition metal changes, causing various lattice defects, which can result in a decrease in properties such as capacity and lifetime. In particular, high-nickel materials with a high Ni content for high capacity are prone to many defects due to such high-temperature firing. A change in the amount of Li in the structure during firing is related to the reduction of the oxidation value state of Ni from +3 to +2. Therefore, to solve this problem, the firing maintenance temperature must be kept as low as possible, and the lithium reaction initiation temperature must be kept as low as possible. A lower lithium reaction initiation temperature can also result in a lower residual lithium content.

[0085] This invention reduces the residual lithium (Li) content, which exists in the form of LiOH and Li2CO3, by adjusting the content of a specific fluorine-based compound to be within a specific range and thereby lowering the lithium reaction initiation temperature.

[0086] In one embodiment, the residual lithium (Li) content present on the surface of the secondary particles in the form of LiOH may be 11,300 ppm or less, or 11,000 ppm or less. In one embodiment, the residual lithium (Li) content 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 that occupies at least one or more 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 above chemical formula 3, M3 is one or more 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 the above chemical formula 3, M3 represents a coating element, and the coating oxide may be an oxide formed by a combination of lithium and the element represented by M3, or an oxide of M3.

[0091] As an example, the coating oxide is Li p Co q O r Li p W q O r Li p Zr q O r Li p Ti q O r Li p Ni q O r Li p Al 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 is possible, but it is not the only possibility.

[0092] The coating oxide may include a concentration gradient portion in which the molar concentrations of the elements contained within the coating oxide change. For example, if the coating oxide contains lithium, the molar concentration of lithium may change. Also, for example, the molar concentration of one or more of the M3 elements contained in the coating oxide may change.

[0093] In one embodiment, when the coating oxide occupies at least a portion of the surface area of ​​the primary particle forming the outermost edge of the secondary particle, the concentration gradient portion may decrease, increase, or increase and then decrease in the direction from the surface of the primary particle forming the outermost edge of the secondary particle toward the center of the secondary particle.

[0094] Furthermore, the concentration gradient portion can decrease, increase, or increase and then decrease in the direction from the surface of the primary particle forming the outermost outermost of the secondary particle toward the center of the primary particle.

[0095] In one embodiment, if the coating oxide occupies at least a portion of the surface area of ​​the primary particle that does not form the outermost edge of the secondary particle, the amount can decrease, increase, or increase and then decrease in the direction from the surface of the primary particle toward the center of the primary particle.

[0096] On the other hand, the technical characteristics of the lithium nickel-based composite oxides described above for primary or secondary particles may relate to the average characteristics of multiple particles.

[0097] Furthermore, the meanings of "≦", "greater than or equal to", or "less than or equal to" as described in this invention can be replaced with the meanings of "<", "greater than", or "less than".

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

[0099] Except for using the positive electrode active material 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 a secondary battery.

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

[0101] The secondary battery may specifically include a positive electrode, a cathode positioned opposite the positive electrode, and an electrolyte between the positive electrode and the cathode, but is not particularly limited as long as it is usable as a secondary battery.

[0102] The following describes embodiments of the present invention in more detail.

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

[0104] Lithium composite oxides were produced by adding LiOH (Li / (Ni+Co+Mn) molar ratio = 1.04) and fluorine-based compounds in various concentrations to the synthesized precursor, followed by calcination. In this case, after mixing LiOH and the fluorine-based compound with the precursor, the furnace was heated at 2°C per minute while maintaining an O2 atmosphere, and then heat-treated at 665°C for 10 hours before being allowed to cool naturally.

[0105] In the above examples, the fluorine-based compounds added were LiF, CaF2, AlF3, MgF2, NH4F, and ZrF4, each added in various concentrations of 0.2 mol%, 0.5 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, and 5 mol% relative to the total molar content of the metals excluding lithium.

[0106] <Example 2> In the positive electrode active material produced in Example 1, TiO2, Al2O3, and ZrO2 were mixed in amounts of 0.6, 0.6, and 0.1 mol%, respectively. Then, the mixture was heated in a firing furnace at 4.4°C per minute while maintaining an O2 atmosphere, and heat-treated at 675°C for 8 hours, followed by natural cooling to obtain a lithium composite oxide.

[0107] After adding distilled water to the obtained lithium composite oxide, it was washed with water for 1 hour, filtered, and then dried.

[0108] Subsequently, the dried lithium composite oxide and the B-containing raw material (H3BO3) were mixed together using a mixer. The B-containing raw material (H3BO3) was mixed to a concentration of 0.235% by weight relative to the total weight of the lithium composite oxide. In the same firing furnace, while maintaining an O2 atmosphere, the temperature was increased at 4.4°C per minute, and the mixture was heat-treated at 300°C for 8 hours, after which it was allowed to cool naturally.

[0109] <Comparative Example 1> The positive electrode active material was prepared in the same manner as in Example 1, except that a fluorine-based compound was not added.

[0110] <Comparative Example 2> The positive electrode active material was produced in the same manner as in Example 2, except that TiO2, Al2O3, and ZrO2 were mixed with the positive electrode active material produced in Comparative Example 1, in which no fluorine-based compounds were added.

[0111] Manufacturing of lithium-ion batteries A cathode slurry was prepared by dispersing 94 wt% of the cathode active material, 3 wt% of artificial graphite, and 3 wt% of the PVDF binder produced according to the above examples and comparative examples in 3.5 g of N-methyl-2-pyrrolidone (NMP). The cathode slurry was applied to a 15 μm thick aluminum (Al) thin film, which served as the cathode current collector, and dried. The cathode was then manufactured by roll pressing. The loading level of the cathode was 7 mg / cm². 2 The electrode density is 3.2 g / cm³. 3 That was the case.

[0112] A coin cell was manufactured using a lithium foil as the counter electrode for the positive electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) as the separation membrane, and a liquid electrolyte containing ethylene carbonate and ethylene carbonate mixed in a volume ratio of 3:7 with LiPF6 present at a concentration of 1.5 M, following a commonly known manufacturing process.

[0113] <Example of experiment> (1) Cross-sectional SEM image Cross-sections were obtained from the positive electrode active materials of Example 1 and Comparative Example 1 by applying a current of 380 μA for 1 hour and 30 minutes through a cross-section polisher. A JSM-7610FPlus (JEOL) FE-SEM was used to obtain a cross-sectional SEM image of the lithium composite oxide at a voltage of 2 kV, which is shown in Figure 1.

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

[0115] (Relationship 1) FWHM 補正(104) =FWHM 測定(104) -FWHM Si 粉末 (220) Here, FWHM(10⁴) represents the full width at half maximum (FWHM; deg., 2θ) of the (10⁴) peak in the XRD peak defined by a hexagonal lattice with an R-3m space group.

[0116] In the above relational equation 1, FWHM 測定(104) This refers to the full width at half maximum (FWHM) of the (10⁴) peak observed at 44.5±1.0°(2θ) during XRD analysis of the lithium nickel-based composite oxide. Si粉末(220) This represents the full width at half maximum of the (220) peak observed around 47.3±1.0°(2θ) in XRD measurements 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 using the FWHM of Si powder as a standard sample, as shown in relation to the FWHM of 104 and FWHM of Si powder. This is because, during XRD analysis, the measured value of the FWHM is subject to deviation and error due to various variables such as the condition of the analytical equipment, the X-ray source, and the measurement conditions. (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, publicly available, and commercial software known to those skilled in the art.

[0118] On the other hand, as the silicon powder, we used silicon powder from Sigma-Aldrich (product number 215619).

[0119] (3)XPS analysis XPS analysis was performed on the positive electrode active materials of Example 1 and Comparative Example 1. The XPS analysis measured the fluorine 1s bond energy contained in the lithium composite oxide using Nexsa (Thermo fisher) with Al-Kα radiation (minimum analysis area: 10-200 μm), and the results are shown in Figure 3.

[0120] (4) Analysis of reaction initiation temperature The reaction initiation temperature of lithium for the positive electrode active materials used in Example 1 and Comparative Example 1 was analyzed and is shown in Figure 4.

[0121] (5) Analysis of gas generation The lithium secondary batteries of Example 2 and Comparative Example 2 were charged to 4.25V with a constant current of 0.2C and then stored at 60°C for 80 hours. The volume change of the lithium secondary batteries due to gas generation was measured, and the volume increase rate, which is an indicator of gas generation, was measured and is shown in Figure 5.

[0122] (6) C-rate efficiency analysis For the lithium secondary batteries of Example 2 and Comparative Example 2 described above, an electrochemical analyzer (Toyo, Toscat-3100) was used to measure the C-rate efficiency of 5.0C / 0.1C at 25°C, applying a discharge rate of 0.1C to 5.0C with a voltage range of 3.0V to 4.3V, and the results are shown in Figure 6.

[0123] (7) Analysis of residual lithium Residual lithium was measured by the amount of 0.1M HCl used until the pH reached 4 by pH titration. First, 5g of the positive electrode active material from Example 1 and Comparative Example 1 was placed in 100ml of DIW and stirred for 15 minutes. After filtering, 50ml of the filtered solution was taken, and 0.1M HCl was added to it. Q1 and Q2 were determined by measuring the amount of HCl consumed due to the pH change, and the unreacted LiOH and Li2CO3 were calculated using the following formula, which are shown in Figures 7 and 8.

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

Claims

1. It contains a lithium nickel-based composite oxide that includes secondary particles formed by the aggregation of primary particles, Some of the cations and some of the anions in the aforementioned lithium nickel-based composite oxide are cations M' and fluorine anions (F) contained in the fluorine-based compound. － ) is replaced by, The secondary particle includes a surface portion and an interior portion. A positive electrode active material characterized in that the average aspect ratio of primary particles on the surface of the secondary particles is greater than the average aspect ratio of primary particles inside the secondary particles.

2. The fluorine-based compounds mentioned above are LiF and CaF ２ MgF ２ AlF ３ and ZrF ４ The positive electrode active material according to claim 1, which is one or more selected from among the following.

3. The positive electrode active material according to claim 1, wherein primary particles with a size of 200 nm or more and less than 500 nm constitute 50 to 100% by volume of the primary particles that make up the interior of the secondary particles.

4. The positive electrode active material according to claim 3, wherein primary particles with a size of 500 nm to 10.0 μm constitute 50 to 100% by volume of the primary particles that make up the surface portion of the secondary particles.

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

6. The positive electrode active material according to claim 3, wherein 50% or more of the primary particles on the surface of the secondary particles are formed such that the lithium ion diffusion pathways formed within the primary particles have an angle of ±30° or less with respect to a line connecting the surface and the center of the secondary particle.

7. The positive electrode active material according to claim 3, wherein the secondary particles show 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 according to claim 1, further comprising a coating oxide occupying at least one or more parts of the surface of the secondary particles, the grain boundaries between the primary particles, and the surface of the primary particles.

9. A positive electrode comprising the positive electrode active material described in claim 1.

10. A secondary battery comprising the positive electrode described in claim 9.

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