Positive electrode active material for secondary battery

Abstract

A positive electrode active material particle according to one aspect of the present application includes a bulk region and a coating region, the coating region contains cobalt (Co), the coating region covers a part of the surface of the bulk region, when a unit coating region is defined as a closed coating region on the surface of the bulk region not connected to other coating regions, the positive electrode active material particle includes more than one unit coating region, when a shortest side drawn from the surface of the bulk region on a side of the unit coating region is called a hypotenuse in a scanning electron microscope (SEM) image of the surface of the positive electrode active material particle measured using Image J, for an average length (S) of the hypotenuse, 40 nm ≤ S ≤ 70 nm.

Description

Technical Field

[0001] The present invention relates to positive electrode active material particles and a positive electrode active material for secondary batteries including the same, and more specifically, to a positive electrode active material which, by controlling the composition, coating method, coating morphology and the like of a cobalt (Co)-containing coating material on a lithium composite oxide, significantly improves the stability, cycle life and output performance of a secondary battery when applied thereto. Background Art

[0002] With the development of portable mobile electronic devices such as smartphones, MP3 players and tablet computers, the demand for secondary batteries capable of storing electrical energy has been growing explosively. In particular, with the emergence of electric vehicles, medium-to-large energy storage systems and portable devices requiring high energy density, the demand for lithium secondary batteries has been increasing continuously.

[0003] As the lithium composite oxide contained in the positive electrode active material, the most prominent material in recent years is lithium nickel (manganese / aluminum) cobalt oxide Li(Ni x Co y (Mn / Al) z )O2 (wherein x, y and z are respectively the atomic fractions of each independent constituent element of the oxide, 0<x≤1, 0<y≤1, 0<z≤1 and 0<x+y+z≤1). This positive electrode active material has the advantage of enabling high capacity because it is used at a higher voltage than LiCoO2, which has been actively studied and used as a positive electrode active material to date, and also has the advantage of low cost because its cobalt content is relatively low.

[0004] However, such lithium composite oxides undergo volume changes during charge and discharge along with the intercalation and deintercalation of lithium ions. There are the following problems: the primary particles of the lithium composite oxide undergo drastic volume changes during charge and discharge, cracks generate in secondary particles along with repeated charge and discharge, or collapse or phase transition of the crystal structure occurs.

[0005] To compensate for these drawbacks, as a positive electrode active material for secondary batteries, demand for high-nickel positive electrode active materials having a high nickel content relative to the total metal content excluding lithium (Li) has started to increase. Summary of the Invention

[0006] Technical Problem

[0007] The purpose of this invention is to provide a positive electrode active material that, by controlling the composition, coating method, and coating morphology of the cobalt (Co)-containing coating material, can significantly improve the stability, lifespan, and output performance of secondary batteries when applied to them.

[0008] In particular, the purpose of this invention is to provide a positive electrode active material with controlled coating morphology that can improve battery performance when using a non-water-washed cobalt (Co) coating method, in order to overcome the disadvantages of water-washed coating with coating liquid.

[0009] Technical solution

[0010] According to one aspect of the present invention, the positive electrode active material particles include a body region and a coating region, the coating region comprising cobalt (Co), the coating region covering a portion of the surface of the body region.

[0011] As a more preferred aspect, when a unit coating region is defined as a closed coating region on the surface of the body region that is not connected to other coating regions, the positive electrode active material particle may include more than one unit coating region.

[0012] As a more preferred aspect, when measuring the scanning electron microscope (SEM) image of the positive electrode active material particle surface using Image J, when the shortest side drawn from the surface of the bulk region on the side of the unit coating area is called the hypotenuse, the average length (S) of the hypotenuse can be 40nm≤S≤70nm.

[0013] As a more preferred aspect, when a right triangle is drawn with the hypotenuse as the hypotenuse and the portion that connects to the surface of the body region as the base, the average length (W) of the base and the average length (H) of the height of the right triangle can be 0.58 ≤ H / W ≤ 2.75.

[0014] As a more preferred aspect, it can be 30nm≤W≤60nm.

[0015] As a more preferred aspect, it can be 20nm≤H≤50nm.

[0016] As a more preferred aspect, in a scanning electron microscope (SEM) image of one surface of the positive electrode active material particle, the coverage area ratio of the coating region relative to the total area of ​​the surface can be 50% to 98%.

[0017] As a more preferred aspect, in the positive electrode active material particles, the average coating area per unit coating region can be 2.0 μm. 2 Up to 8.0μm 2 .

[0018] As a more preferred aspect, the coating region may further include one or more of aluminum (Al), zirconium (Zr), boron (B), tungsten (W), yttrium (Y) and titanium (Ti).

[0019] As a more preferred aspect, the body region may be doped with one or more elements selected from cobalt (Co), zirconium (Zr), barium (Ba), strontium (Sr), aluminum (Al) and titanium (Ti).

[0020] As a more preferred aspect, the average particle size (D50) of the positive electrode active material particles may be from 2.0 μm to 6.0 μm.

[0021] As a more preferred aspect, the positive electrode active material particles may consist of a single particle or be composed of two to eight single particles aggregated together.

[0022] According to one aspect of the present invention, the positive electrode active material may comprise said positive electrode active material particles.

[0023] Beneficial effects

[0024] As an effect, the present invention provides a positive electrode active material that, in order to reduce the amount of gas generated that directly affects the lifespan reduction, further increases stability and strengthens the bulk structure and coating structure while suppressing direct contact between the surface and the electrolyte.

[0025] As an effect, the present invention provides a positive electrode active material that significantly improves the stability, lifespan and output performance of secondary batteries. Attached Figure Description

[0026] Figure 1 This is a SEM image of the surface of positive electrode active material particles according to an embodiment of the present invention.

[0027] Figure 2 This is a SEM image of the surface of positive electrode active material particles according to an embodiment of the present invention. Detailed Implementation

[0028] The use of expressions such as “comprising” in this specification should be understood as open-ended terms that include the possibility of other constituent elements.

[0029] As used in this specification, "preferred" and "most suitable" refer to embodiments of the invention that provide specific advantages under specific conditions. However, it is not intended to exclude other embodiments from the scope of the invention.

[0030] Furthermore, the singular form used in the specification and appended claims is intended to include the plural form unless otherwise indicated in the context. That is, a technical feature referring to any one particle may refer to technical features for multiple particles, or may be intended to refer to the average technical features for multiple particles.

[0031] The numerical ranges used in this specification include lower and upper limits, as well as all values ​​within that range, increments logically derived within the defined form and width of the range, all values ​​with double constraints, and all possible combinations of upper and lower limits of numerical ranges that are constrained by different forms.

[0032] Unless otherwise defined, values ​​outside the defined range that may occur due to experimental errors or rounding are also included in the defined range.

[0033] The meanings of '≤', 'above', or 'below' as described in this specification can be replaced by the meanings of '<', 'exceed', or 'less than', respectively.

[0034] Furthermore, the technical features described below relate to one aspect of achieving the effects desired by the invention described above.

[0035] That is, the positive electrode active material according to one aspect of the present invention, by including the technical features according to one aspect described below, thereby further strengthens the bulk structure and coating structure of the particles and can significantly improve the stability, lifespan and output performance of the secondary battery.

[0036] This invention relates to positive electrode active material particles for secondary batteries and positive electrode active materials comprising a plurality of such particles.

[0037] The type of secondary battery of the present invention is not limited as long as it is a battery that converts external electrical energy into chemical energy for storage and reuse. As an example, the present invention may relate to positive electrode active materials for lithium-ion secondary batteries.

[0038] According to one aspect of the present invention, the positive electrode active material particles include a bulk region and a coating region.

[0039] First, the body region will be described.

[0040] As one aspect, the body region may be a lithium composite oxide.

[0041] As one aspect, the body region may be a lithium composite oxide containing nickel (Ni).

[0042] As one aspect, the body region may be a lithium composite oxide comprising nickel (Ni) and cobalt (Co).

[0043] In one respect, the lithium composite oxide can be represented by the following chemical formula 1.

[0044] Li a Ni x M1 y M2 1-x-y O2

[0045] In the chemical formula 1, M1 is selected from the group consisting of cobalt (Co), manganese (Mn), aluminum (Al) and combinations thereof, and M2 is selected from the group consisting of Zr, Mn, Al, B, S, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Na, K, Hf, Ta, Cu and combinations thereof, and 0.9≤a≤1.2, 0.1≤x<1.0, 0.0≤y≤0.5, and 0.0≤1-xyz≤0.5.

[0046] As one aspect, in the chemical formula 1, a, which represents the molar percentage of lithium (Li) relative to the molar percentage of all transition metals other than lithium (Li), may be 0.9 or more, 1.0 or more, 1.2 or less, 1.1 or less, or 1.05 or less.

[0047] In one aspect, in the aforementioned chemical formula 1, x, representing the molar percentage of nickel (Ni) relative to the molar percentage of all transition metals other than lithium (Li), can be 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. In particular, the present invention can be a high-nickel (high-Ni) oxide with x of 0.5 or more. Such a high-nickel cathode active material has the advantage of high energy density. On the other hand, due to the high Li / M ratio during the manufacture of the cathode active material, the residual lithium content in the cathode active material after firing is high, thus causing difficulties in cell manufacturing due to gelation during the manufacture of the electrode slurry. Therefore, although a water washing process is introduced to remove residual lithium, the following problem exists: the cathode surface is damaged during the water washing process, leading to a decrease in battery characteristics.

[0048] Furthermore, the high Ni content makes the structure unstable, increasing the reaction with the electrolyte at the particle surface and interface, which releases a large amount of gas during repeated charge and discharge processes, thus reducing the lifetime characteristics. This invention is particularly able to solve such problems that are further aggravated in high-Ni cathode active materials.

[0049] As one aspect, in the chemical formula 1, when y represents the molar percentage of cobalt (Co) relative to the molar percentage of all transition metals other than lithium (Li), y may be less than 0.5, less than 0.4, less than 0.3, less than 0.2, or less than 0.1.

[0050] As one aspect, in the chemical formula 1, when y represents the molar percentage of Al and / or Mn relative to the molar percentage of all transition metals other than lithium (Li), y may be less than 0.5, less than 0.4, less than 0.3, less than 0.2, less than 0.1, more than 0.1, more than 0.2, or more than 0.3.

[0051] As a more preferred aspect, the body region may be doped with one or more elements selected from cobalt (Co), zirconium (Zr), barium (Ba), strontium (Sr), titanium (Ti), aluminum (Al), niobium (Nb), vanadium (V), molybdenum (Mo), boron (B), yttrium (Y), tungsten (W), magnesium (Mg), zinc (Zn), iron (Fe), tantalum (Ta), silicon (Si), and fluorine (F).

[0052] More preferably, the body region may be doped with one or more elements selected from cobalt (Co), zirconium (Zr), barium (Ba), strontium (Sr), aluminum (Al) and titanium (Ti).

[0053] In manufacturing the positive electrode active material of the present invention, a lithium composite oxide can be produced by heat-treating the hydroxide precursor and the lithium compound. In this case, by heat-treating the dopant element together, it can be uniformly doped into the lattice structure of the primary particles.

[0054] In another aspect, when coating lithium composite oxide particles according to one aspect of the present invention, a portion of the coating element may be present within the crystal lattice structure of the primary particles contained within the lithium composite oxide particles. In this case, the coating element is doped into the lithium composite oxide particles.

[0055] Furthermore, the lithium composite oxide particles in the bulk region are defined as regions containing such doping.

[0056] As one aspect, cobalt (Co) is a coating element that is coated after the production of lithium composite oxides and is doped during the coating heat treatment so that it can exist within the lattice structure of the primary particles.

[0057] As one aspect, aluminum (Al) is a coating element that is coated after the production of lithium composite oxides and is doped during the coating heat treatment so that it can exist within the lattice structure of the primary particles.

[0058] In one aspect, zirconium (Zr) is a coating element coated after the lithium composite oxide is produced, and may be doped during coating heat treatment to exist in the lattice structure of primary particles.

[0059] As described above, the present invention can further strengthen the coating structure by controlling the dopant and the bulk composition, and further improve the stability, cycle life and output performance of a secondary battery.

[0060] Next, the coating region will be described.

[0061] In one aspect, the coating region may be a region distinct from the lithium composite oxide particles serving as the bulk region.

[0062] When coating the lithium composite oxide particles according to one aspect of the present invention, a part of the coating element can form a coating region where a coating material is present. Such coating material may exist on the surface of secondary particles of the lithium composite oxide particles and / or at grain boundaries between primary particles of the lithium composite oxide. Herein, the grain boundaries between primary particles refer to a region including both the spaces between primary particles and the surfaces of said primary particles.

[0063] In a more preferred aspect, the coating region may comprise cobalt (Co).

[0064] In one aspect, said cobalt (Co) in the coating region may be present in the form of LiCoO2, Li 1+a CoO2 (1<a<0.1), Li 1- b CoO2 (1<b<0.1), Co q O r (0<q<10, 0<r<10) and / or Co(OH)2, etc.

[0065] In one aspect, for the coating region on the surface of the positive electrode active material particles, an electron beam irradiated at an acceleration voltage of 1 kV is used to measure the average concentration of elements from the surface of the positive electrode active material particles to the penetration depth of the electron beam. The average concentration of cobalt (Co) element measured by such EP-EDS (Energy Profiling-Energy Dispersive X-Ray Spectroscopy) can be 20 at% or more, 30 at% or more, 40 at% or more, 50 at% or more, 80 at% or less, 70 at% or less, 60 at% or less, 50 at% or less, 40 at% or less, or 30 at% or less.

[0066] As a more preferred aspect, the coating region may contain, in addition to cobalt (Co), any one or more of the following: aluminum (Al), titanium (Ti), zirconium (Zr), magnesium (Mg), zinc (Zn), molybdenum (Mo), iron (Fe), nickel (Ni), barium (Ba), tungsten (W), strontium (Sr), yttrium (Y), niobium (Nb), vanadium (V), boron (B), tantalum (Ta), silicon (Si), and fluorine (F).

[0067] More preferably, the coating region may contain, in addition to cobalt (Co), one or more of aluminum (Al), zirconium (Zr), boron (B), tungsten (W), yttrium (Y) and titanium (Ti).

[0068] More preferably, the coating region may contain, in addition to cobalt (Co), one or more elements selected from aluminum (Al), zirconium (Zr) and boron (B).

[0069] More preferably, the coating region may contain two or more elements selected from aluminum (Al), zirconium (Zr), and boron (B) in addition to cobalt (Co).

[0070] More preferably, the coating region may also include aluminum (Al), zirconium (Zr) and boron (B) in addition to cobalt (Co).

[0071] In addition, as an example, the molar content of the coating element and / or doping element contained in the positive electrode active material may be less than 5.0 mol%, less than 3.0 mol%, or less than 1.0 mol%.

[0072] For example, when aluminum (Al) is included in the positive electrode active material, the content of aluminum (Al) relative to the total content of the positive electrode active material may be 1.0 mol% to 2.0 mol%.

[0073] For example, when zirconium (Zr) is included in the positive electrode active material, the zirconium (Zr) content relative to the total content of the positive electrode active material can be from 0.1 mol% to 1.0 mol%.

[0074] For example, when the positive electrode active material contains barium (Ba), the content of barium (Ba) relative to the total content of the positive electrode active material can be from 0.05 mol% to 0.15 mol%.

[0075] As described above, this invention can further enhance the coating structure and further improve the stability, lifespan, and output performance of the secondary battery by controlling the coating composition.

[0076] The covering area can cover a portion of the surface of the body area.

[0077] In one respect, the positive electrode active material particles may contain more than one 'unit coating region'.

[0078] The unit coverage area refers to a closed coverage area on the surface of the body area that is not connected to other coverage areas.

[0079] As a more preferred aspect, when measuring the surface of the positive electrode active material particles using a scanning electron microscope (SEM) with ImageJ, the average length (S) of the bevel can be 40 nm or more, 45 nm or more, 48 nm or more, 70 nm or less, 60 nm or less, 55 nm or less, or 52 nm or less, more preferably 40 nm to 60 nm. By adjusting the average length (S) of the bevel to the aforementioned range, the present invention can further enhance the coating structure and further improve the stability, lifespan, and output performance of the secondary battery.

[0080] In this invention, 'hypotenuse' refers to the shortest side drawn from the surface of the body region on the side of the unit covered area (see reference). Figure 1 ).

[0081] In this invention, the 'average length (S) of the hypotenuse' refers to the average value of the lengths of 10 to 15 hypotenuses in any selected 2 to 3 unit coverage areas. Furthermore, in this invention, if the average value of the lengths of 10 to 15 hypotenuses in any selected 2 to 3 unit coverage areas meets the stated numerical range, it can be interpreted as belonging to that range.

[0082] As a more preferred aspect, when a right triangle is drawn with the hypotenuse as the hypotenuse and the portion connecting to the surface of the body region as the base, the ratio H / W for the average length (W) of the base and the average length (H) of the height of the right triangle can be 0.58 or more, 0.70 or more, 0.84 or more, 1.00 or more, 1.19 or more, 2.75 or less, 2.14 or less, or 1.73 or less, and more preferably 1.19 to 2.14. By satisfying the above numerical range, the present invention can further strengthen the encapsulation structure and further improve the stability, lifespan, and output performance of the secondary battery.

[0083] At this time, the length of the bottom edge (W) refers to the length of the portion that connects to the surface of the body region, and the length of the height (H) refers to the length of the portion perpendicular to the bottom edge (see reference). Figure 1 ).

[0084] In this invention, the 'average length (W) of the base edge' refers to the average value of 10 to 15 base edge lengths in any selected 2 to 3 unit coverage areas. Furthermore, in this invention, if the average value of 10 to 15 base edge lengths in any selected 2 to 3 unit coverage areas meets the stated numerical range, it can be interpreted as belonging to that range.

[0085] In this invention, the 'average height (H)' refers to the average height of arbitrarily selected 10 to 15 height lengths within arbitrarily selected 2 to 3 unit coverage areas. Furthermore, in this invention, if the average height of arbitrarily selected 10 to 15 height lengths within arbitrarily selected 2 to 3 unit coverage areas satisfies the aforementioned numerical range, it can be interpreted as belonging to that range.

[0086] As a more preferred aspect, W can be 30nm or more, 35nm or more, 38nm or more, 60nm or less, 50nm or less, 45nm or less, or 42nm or less, and more preferably 30nm to 50nm. By adjusting the average length (W) of the bottom edge to the aforementioned numerical range, the present invention can further strengthen the coating structure and further improve the stability, lifespan, and output performance of the secondary battery.

[0087] As a more preferred aspect, H can be 20nm or more, 25nm or more, 28nm or more, 50nm or less, 40nm or less, 35nm or less, or 32nm or less, and more preferably 20nm to 40nm. By adjusting the high average length (H) to the aforementioned numerical range, the present invention can further enhance the coating structure and further improve the stability, lifespan, and output performance of the secondary battery.

[0088] As a more preferred aspect, in a scanning electron microscope (SEM) image of one surface of the positive electrode active material particles, the coverage area ratio of the coated region relative to the total area of ​​the surface can be 50% or more, 60% or more, 70% or more, 80% or more, 98% or less, or 95% or less, more preferably 80% to 96%. By adjusting the coverage area ratio to the aforementioned range, the present invention can further enhance the coating structure and further improve the stability, lifespan, and output performance of the secondary battery.

[0089] In this invention, the coating area ratio is measured using ImageJ software in a scanning electron microscope (SEM) image of one surface of the positive electrode active material particle. Furthermore, in this invention, if the coating area ratio measured on any selected surface of the positive electrode active material particle meets the stated numerical range, it can be interpreted as belonging to that range.

[0090] As a more preferred aspect, the number of unit coating regions in the positive electrode active material particles can be 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, less than 10, less than 9, less than 8, less than 7, less than 6, less than 5, less than 4, less than 3, or less than 2. By adjusting the number of unit coating regions to the aforementioned range, the present invention can further strengthen the coating structure and further improve the stability, lifespan, and output performance of the secondary battery.

[0091] As a more preferred aspect, the average area of ​​the unit coating region in the positive electrode active material particles can be 2.0 μm. 2 Above, 3.0μm 2 Above, 8.0μm 2 Below, 7.0μm 2 Below, 6.0μm 2 Below or 5.0μm 2 More preferably, it can be 3.0μm 2 Up to 5.0μm 2 This invention, by adjusting the area of ​​the unit coating region to the aforementioned numerical range, can further strengthen the coating structure and further improve the stability, lifespan, and output performance of the secondary battery.

[0092] In this invention, the average area of ​​the unit coverage region is calculated by averaging the areas of arbitrarily selected 2 to 5 unit coverage regions in a scanning electron microscope (SEM) image. Furthermore, in this invention, if the average area of ​​arbitrarily selected 2 to 5 unit coverage regions meets the stated numerical range, it can be interpreted as belonging to that range.

[0093] In addition, unlike the wet process of immersing active substance particles in a coating solution, the present invention can adjust the coating content, heat treatment temperature and time, particle size, etc. through a dry coating process during secondary heat treatment without a water washing process, thereby achieving the coating area and morphology.

[0094] In particular, in order to overcome the disadvantages of water-washing coating using coating liquid, the present invention controls the composition, coating method, and coating morphology of the coating material when applying a non-water-washing coating method, so as to further improve battery characteristics.

[0095] According to one aspect of the present invention, the average particle size (D50) of the positive electrode active material particles may be 2.0 μm or more, 2.5 μm or more, 3.0 μm or more, 6 μm or less, 5.5 μm or less, 5 μm or less, or 4.5 μm or less, more preferably 3.0 μm to 4.0 μm.

[0096] In this invention, the average diameter (D50) is the particle size at 50% of the cumulative area distribution that varies with particle size, and it can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device to measure the difference in diffraction pattern as the particles pass through the laser beam, thereby calculating the particle size distribution.

[0097] Furthermore, the bulk region of the positive electrode active material particles can be a particle formed by the contact of at least one or more individual particles. Here, an individual particle refers to a primary particle.

[0098] As a more preferred aspect, the bulk material may consist of a single particle, or may be comprised of 8 or fewer, 7 or fewer, 6 or fewer, 5 or fewer, 4 or fewer, 3 or fewer, or 2 or fewer single particles connected together.

[0099] In one aspect, when the body region is composed of a single particle, the average particle size (D50) may be 2.0 μm or more, 2.5 μm or more, 3.0 μm or more, 6 μm or less, 5.5 μm or less, 5 μm or less, or 4.5 μm or less, and more preferably, it may be composed of a single particle with a particle size of 3.0 μm to 4.0 μm.

[0100] In one aspect, when the body region is comprised of 2 to 8 individual particles connected together, it may be comprised of 2 to 8 individual particles of 1 μm or larger, 3 μm or smaller, or 2 μm or smaller connected together.

[0101] In one respect, the aspect ratio (longest major axis / shortest minor axis) of the single particle can be greater than 1, greater than 2, less than 3, less than 2, less than 1.5, less than 1.2, or less than 1.1.

[0102] According to one aspect of the present invention, the positive electrode active material may comprise a plurality of said positive electrode active material particles.

[0103] According to one aspect of the present invention, the positive electrode comprises the positive electrode active material.

[0104] In addition to using the aforementioned positive electrode active material, the positive electrode may have a known structure and may be manufactured according to known manufacturing methods. The binder, conductive agent, and solvent are not particularly limited as long as they are suitable for use on the positive electrode current collector of a secondary battery.

[0105] A secondary battery according to one aspect of the present invention comprises the positive electrode active material.

[0106] The secondary battery may specifically include a positive electrode, a negative electrode opposite to the positive electrode, and an electrolyte located between the positive electrode and the negative electrode, but there are no particular limitations as long as it can be used as a secondary battery.

[0107] The embodiments of the present invention will now be described in more detail.

[0108] Manufacturing of positive electrode active materials

[0109] <Manufacturing Examples 1-10>

[0110] A NiCoMn(OH)2 hydroxide precursor of lithium complex oxide (Ni:Co:Mn = 95:2:3 (at%)) was synthesized by using a known co-precipitation method with nickel sulfate, cobalt sulfate and manganese sulfate.

[0111] Lithium composite oxides are produced by uniformly mixing 1.02 mol% LiOH·H2O, 0.5 mol% Al(OH)3, 0.2 mol% ZrO2 and 0.1 mol% Ba(OH)2 into the precursor and heat-treating (single firing) at 800°C to 840°C for 24 hours in an oxygen-filled box furnace.

[0112] Subsequently, the lithium composite oxide was broken down using a jet mill to produce single-particle lithium composite oxides.

[0113] Next, under an O2 atmosphere and at 700°C, 0.5 to 4.3 mol% Co(OH)2, 0.2 mol% ZrO2, and 0.5 mol% Al2O3 were mixed and heat-treated (secondary calcination) in an oxygen atmosphere for 12 hours to produce positive electrode active material with a particle size of 3 μm to 4 μm.

[0114] <Manufacturing Example 11>

[0115] Lithium composite oxide in single-particle form was manufactured using the same method as in Manufacturing Examples 1 to 10. Then, distilled water was added to the manufactured lithium composite oxide for a first water wash, and a 3.0 mol% cobalt sulfate aqueous solution was added and stirred for 5 minutes for a second water wash, while cobalt (Co) coating was performed.

[0116] Next, the washed lithium composite oxide is dried in an O2 atmosphere at 300°C.

[0117] Next, ZrO2 0.1 mol% and Al(OH)3 0.1 mol% were mixed in an O2 atmosphere at 700 °C and then heat-treated (secondary calcination) in an oxygen atmosphere for 12 hours to produce positive electrode active material with a particle size of 3 μm to 4 μm.

[0118] Manufacturing of lithium secondary batteries

[0119] A positive electrode slurry was prepared by dispersing 96 wt% of the positive electrode active material, 2 wt% of artificial graphite, and 2 wt% of PVDF binder, all prepared according to the manufacturing example, in 8 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was then uniformly coated onto an aluminum foil with a thickness of 15 μm and vacuum dried at 135 °C to manufacture a positive electrode for lithium secondary batteries.

[0120] For the positive electrode, a lithium foil is used as the counter electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) is used as the separator, and an electrolyte consisting of LiPF6 at a concentration of 1.15 M in a solvent containing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7 is used to manufacture a button cell.

[0121] <Experimental Example 1> SEM Analysis and Measurement

[0122] For the surface of the positive electrode active material particles containing 3.0 mol% Co(OH)₂ in Manufacturing Examples 1 to 10, FE-SEM images of the particle surface were obtained using a JSM-7610FPlus (JEOL) at a voltage of 2 kV, and then shown. Figure 1 and Figure 2 middle.

[0123] In addition, the lengths of the hypotenuses at 10 points were measured using Image J on the SEM images of the surface of the positive electrode active material particles, as shown in Table 1 below.

[0124] Furthermore, a right triangle is drawn with the hypotenuse as the hypotenuse and the part that connects to the surface of the body region as the base. The length of the height (H) and the length of the base (W) are then recorded in Table 1 below.

[0125] Table 1

[0126] <Experimental Example 2> Coverage area, unit coverage area, and number of units covered

[0127] The coating area was measured using ImageJ program in scanning electron microscope (SEM) images of one surface of the positive electrode active material particles according to manufacturing Examples 1 to 10, and is shown in Table 2 below.

[0128] In scanning electron microscope (SEM) images of one surface of the positive electrode active material particles, the average area of ​​arbitrarily selected 2 to 5 unit coated regions was measured, as shown in Table 2 below.

[0129] In addition, scanning electron microscope (SEM) images of all surfaces of the positive electrode active material particles were analyzed to measure the number of unit coated regions, as shown in Table 2 below.

[0130] Table 2

[0131] <Experimental Example 3> Lifetime Characteristics

[0132] For the lithium secondary battery manufactured according to the above example, 50 charge / discharge cycles were performed at 1C / 1C conditions within a driving voltage range of 2.0V to 4.6V at 25°C. The ratio of the discharge capacity to the initial discharge capacity in the 50th cycle (cycle capacity retention) was then measured, as shown in Table 3 below.

[0133] <Experimental Example 4> C-rate Measurement

[0134] For the lithium secondary battery manufactured according to the above-described manufacturing example, the output efficiency (C-rate) at 1.0C / 0.1C was measured using an electrochemical analysis apparatus (Toyo, Toscat-3100) through a charge-discharge experiment at 25°C, a voltage range of 2.5V to 4.25V, and a discharge rate of 0.1C to 1.0C, as shown in Table 3 below.

[0135] Table 3

Claims

1. A positive electrode active material particle, characterized in that, include: Body region; and the covered area, The coated region contains cobalt (Co). The covering area covers a portion of the surface of the body area. When a unit coating region is defined as a closed coating region on the surface of the bulk region that is not connected to other coating regions, the positive electrode active material particle includes more than one unit coating region. When measuring the surface of positive electrode active material particles using a scanning electron microscope (SEM) using Image J, the average length (S) of the hypotenuse is 40 nm ≤ S ≤ 70 nm, where the shortest side drawn from the surface of the bulk region on the side of the unit coated area is called the hypotenuse.

2. The positive electrode active material particles according to claim 1, characterized in that, When a right triangle is drawn with the hypotenuse as the hypotenuse and the part that connects to the surface of the body region as the base, the average length (W) of the base and the average length (H) of the height of the right triangle are 0.58 ≤ H / W ≤ 2.

75.

3. The positive electrode active material particles according to claim 2, characterized in that, 30nm≤W≤60nm.

4. The positive electrode active material particles according to claim 2, characterized in that, 20nm≤H≤50nm.

5. The positive electrode active material particles according to claim 1, characterized in that, In a scanning electron microscope (SEM) image of one surface of the positive electrode active material particle, the coverage area of ​​the coated region is 50% to 98% relative to the total area of ​​the surface.

6. The positive electrode active material particles according to claim 1, characterized in that, The coating region also includes one or more of aluminum (Al), zirconium (Zr), boron (B), tungsten (W), yttrium (Y), and titanium (Ti).

7. The positive electrode active material particles according to claim 1, characterized in that, The body region is doped with one or more elements selected from cobalt (Co), zirconium (Zr), barium (Ba), strontium (Sr), aluminum (Al), and titanium (Ti).

8. The positive electrode active material particles according to claim 1, characterized in that, The average particle size (D50) of the positive electrode active material particles is 2.0 μm to 6.0 μm.

9. The positive electrode active material particles according to claim 1, characterized in that, The positive electrode active material particles consist of a single particle or are composed of two to eight aggregated single particles.

10. A positive electrode active material, characterized in that, It contains the positive electrode active material particles according to claim 1.

Images