Positive electrode active material, method for producing the same, and lithium secondary battery including the same

Abstract

The present invention relates to a cathode active material, the cathode active material including a particulate cathode active material and a coating layer formed on a surface of the particulate cathode active material, the coating layer including aluminum oxide doped with phosphorus (P), and a thickness of the coating layer being 0.1 nm to 2.0 nm, a manufacturing method thereof, and a cathode and a lithium secondary battery including the same.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0174108, filed December 7, 2021, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material, a method for producing the same, and a positive electrode and a lithium secondary battery including the same. [Background technology]

[0003] Recently, with the advancement of technologies such as electric vehicles, the need for high-capacity secondary batteries is increasing, and as a result, active research is being conducted on positive electrodes using high-nickel (High Ni) positive electrode active materials with excellent capacity characteristics.

[0004] The high oxidation potential of the positive electrode causes the electrolyte to decompose on the surface, generating gas and causing the lithium secondary battery to expand. Furthermore, the structure becomes unstable during the process of lithium ion insertion and extraction, causing metal elution from the positive electrode and degradation. This problem is particularly severe with high-nickel (High Ni) positive electrode active materials, causing a sudden drop in the remaining capacity of the lithium secondary battery and reducing its safety.

[0005] To solve these problems, a method of forming a coating layer on the surface of high-nickel positive electrode active material particles has been proposed. However, positive electrode active materials formed into a structure of secondary particles formed by aggregation of primary particles have complex surface morphologies, and pores of various sizes are distributed within the secondary particles, making it difficult to form a thin, uniform coating layer inside these pores.

[0006] For example, forming a boron-based coating layer on a positive electrode active material is known to form a relatively uniform coating layer along the surface, but the glassy properties of boron can reduce the rolling density, resulting in lower energy density, or cause severe particle cracking during over-rolling. Furthermore, forming an inorganic or organic coating layer on a positive electrode active material improves the stability of the positive electrode active material, but can also reduce lithium ion conductivity, resulting in increased interfacial resistance and cell resistance. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Korean Patent Publication No. 10-2016-0026306 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been devised to solve the above-mentioned problems of the conventional art, and aims to provide a cathode active material having a coating layer formed thereon, which can improve the stability of the cathode active material, prevent a decrease in rolling density, and prevent an increase in resistance.

[0009] Another object of the present invention is to provide a positive electrode active material having a coating layer formed thereon, which can improve the life and energy density of a positive electrode active material having a high energy density and prevent a decrease in output characteristics.

[0010] Another object of the present invention is to provide a method for producing the positive electrode active material, a positive electrode including the positive electrode active material, and a lithium secondary battery including the same. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides a positive electrode active material, a method for producing the same, and a positive electrode and a lithium secondary battery including the same.

[0012] (1) The present invention provides a cathode active material comprising a particulate cathode active material and a coating layer formed on the surface of the particulate cathode active material, the coating layer comprising aluminum oxide doped with phosphorus (P), and a thickness of the coating layer ranging from 0.1 nm to 2.0 nm.

[0013] (2) The present invention provides the positive electrode active material according to (1) above, wherein the coating layer has a thickness of 0.2 nm or more and 1.0 nm or less.

[0014] (3) The present invention provides a positive electrode active material according to (1) or (2), wherein the phosphorus (P)-doped aluminum oxide is represented by the following Chemical Formula 1: [Chemical formula 1] AlO m P n In the above chemical formula 1, m is 1.7 or more and 2.6 or less, and n is 0.01 or more and 0.4 or less.

[0015] (4) The present invention provides a positive electrode active material according to the above (3), wherein m is 2.0 or more and 2.5 or less, and n is 0.15 or more and 0.30 or less.

[0016] (5) The present invention provides a positive electrode active material according to any one of (1) to (4), wherein the content of phosphorus (P) in the coating layer is 1% by weight or more and 15% by weight or less.

[0017] (6) The present invention provides a positive electrode active material according to any one of (1) to (5), wherein the content of phosphorus (P) in the coating layer is 8% by weight or more and 12% by weight or less.

[0018] (7) The present invention provides a positive electrode active material according to any one of the above (1) to (6), wherein the particulate positive electrode active material contains a lithium transition metal composite oxide represented by the following chemical formula 2: [Chemical formula 2] Li a Ni b Coc Mn d M 1 e O2 In the above chemical formula 2, M 1 is one or more selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P and S, and 0.9≦a≦1.2, 0 <b<1、0<c<1、0<d<1、0≦e<0.2、b+c+d+e=1である。

[0019] (8) The present invention provides a method for manufacturing a cathode active material, comprising: a step (S1) of loading a particulate cathode active material into a reaction chamber for performing atomic layer deposition; and a step (S2) of forming a coating layer on a surface of the cathode active material by performing a unit process including the following steps (S10) to (S30) multiple times, wherein the thickness of the coating layer formed by the step (S2) is 0.1 nm to 2.0 nm. (S10) injecting a vapor phase aluminum precursor into a reaction chamber and injecting a purge gas; (S20) injecting a gaseous reaction gas into the reaction chamber and injecting a purge gas; (S30) A step of injecting a gas-phase phosphorus (P)-containing precursor into the reaction chamber and injecting a purge gas.

[0020] (9) The present invention provides a method for producing a positive electrode active material according to (8), wherein the unit process including steps (S10) to (S30) of step (S2) is represented by formula 1 or 2 below. [Formula 1] [{(S10)-(S20)} x -{(S30)-(S20)} y ] z [Formula 2] [{(S30)-(S20)} y -{(S10)-(S20)} x ] z In the formulas 1 and 2, "-" indicates the execution order of the unit process, x is the number of times {(S10)-(S20)} is repeated, and is an integer selected from 1 to 5; y is the number of times that {(S30)-(S20)} is repeated, and is an integer selected from 1 to 5; z is [{(S10)-(S20)} x -{(S30)-(S20)} y ] or [{(S30)-(S20)} y -{(S10)-(S20)} x ] is the number of times to repeat the above, and is an integer selected from 1 to 20.

[0021] (10) The present invention provides a method for producing a positive electrode active material according to (8) or (9), wherein the aluminum precursor is one or more selected from the group consisting of trimethylaluminum, triethylaluminum, aluminum ethoxide, and tris(diethylamido)aluminum.

[0022] (11) The present invention provides the method for producing a positive electrode active material according to any one of (8) to (10), wherein the reactive gas is at least one selected from the group consisting of gas-phase water vapor (HO), ozone (O), and oxygen plasma.

[0023] (12) The present invention provides the method for producing a positive electrode active material according to any one of (8) to (11), wherein the phosphorus (P)-containing precursor is at least one selected from the group consisting of trimethylphosphate and triethylphosphate.

[0024] (13) The present invention provides a positive electrode containing the positive electrode active material according to any one of (1) to (7) above.

[0025] (14) The present invention provides a lithium secondary battery including the positive electrode according to (13). [Effects of the Invention]

[0026] The positive electrode active material of the present invention includes aluminum oxide doped with phosphorus (P) and has a thin and uniform coating layer, thereby improving the lifespan and stability and preventing an increase in interface resistance and cell resistance.

[0027] Furthermore, the positive electrode active material of the present invention has superior rolling characteristics compared to conventional coating layers containing boron, and therefore can improve the energy density of the positive electrode.

[0028] Furthermore, according to the method for producing a positive electrode active material of the present invention, it is possible to form a thin and uniform coating layer on the surface of the particulate positive electrode active material.

[0029] Furthermore, a lithium secondary battery containing the positive electrode active material of the present invention has improved cycle characteristics, a superior capacity retention rate, and a low rate of resistance increase due to degradation, thereby suppressing a decrease in output power. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a graph showing the rolling density of positive electrode active materials produced in Examples 1 to 3 of the present invention and Comparative Examples 1 and 3 according to different rolling loads. [Figure 2] 1 is a graph showing the discharge capacity of lithium secondary batteries including the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 and 3 according to the number of cycles. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0032] The terms and words used in the description of the present invention and the claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best describe their inventions.

[0033] In the present invention, the term "primary particle" means the smallest particle unit that can be distinguished as a single mass when a cross section of a positive electrode active material is observed through a scanning electron microscope (SEM), and may consist of multiple crystal grains.

[0034] In the present invention, the term "secondary particles" refers to secondary structures formed by aggregation of a plurality of primary particles. The average particle size of the secondary particles can be measured using a particle size analyzer.

[0035] In the present invention, the term "average particle size (D 50 )" means the particle diameter at the 50% point of the volume cumulative distribution of particle diameters. The average particle diameter is determined by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., S3500 manufactured by Microtrac), measuring the difference in the diffraction pattern depending on the particle diameter when the particles pass through a laser beam, and calculating the particle size distribution. The particle diameter at the 50% point of the volume cumulative distribution of particle diameters in the measuring device is then calculated. 50 can be measured.

[0036] positive electrode active material The present invention provides a positive electrode active material.

[0037] According to one embodiment of the present invention, the positive electrode active material includes a particulate positive electrode active material and a coating layer formed on a surface of the particulate positive electrode active material, the coating layer including aluminum oxide doped with phosphorus (P), and a thickness of the coating layer may be from 0.1 nm to 2.0 nm.

[0038] According to one embodiment of the present invention, the coating layer may be formed by atomic layer deposition according to the method for manufacturing a cathode active material described below, thereby forming a thin and uniform coating layer on the surface of the particulate cathode active material. That is, the coating layer may be formed to a uniform thickness across the entire surface of the particulate cathode active material by atomic layer deposition. Therefore, the thickness of the coating layer may be an arithmetic average thickness of the entire coating layer formed on the surface of the particulate cathode active material. Furthermore, the coating layer may have the same thickness regardless of the surface of the cathode active material including the coating layer.

[0039] According to one embodiment of the present invention, the thickness of the coating layer may be 0.1 nm or more, 0.2 nm or more, 0.3 nm or more, 0.4 nm or more, or 0.5 nm or more, or may be 2.0 nm or less, 1.9 nm or less, 1.8 nm or less, 1.7 nm or less, 1.6 nm or less, 1.5 nm or less, 1.4 nm or less, 1.3 nm or less, 1.2 nm or less, 1.1 nm or less, 1.0 nm or less, 0.9 nm or less, 0.8 nm or less, or 0.7 nm or less. Within this range, an increase in interfacial resistance is suppressed and rolling characteristics are excellent, thereby improving the energy density of the positive electrode.

[0040] According to one embodiment of the present invention, the phosphorus (P)-doped aluminum oxide may be represented by the following Chemical Formula 1. Here, the following Chemical Formula 1 may be a composition formula showing an average composition of the phosphorus (P)-doped aluminum oxide.

[0041] [Chemical formula 1] AlO m P n

[0042] In the above chemical formula 1, m is 1.7 or more and 2.6 or less, and n is 0.01 or more and 0.4 or less.

[0043] To produce the phosphorus-doped aluminum oxide coating layer using atomic layer deposition (ALD), as in the cathode active material manufacturing method described below, an aluminum precursor in which ligands are bonded to aluminum as a central element and a phosphorus-containing precursor in which ligands are bonded to phosphorus (P) as a central element are required. Phosphorus (P) has many valence electrons, and due to steric hindrance caused by the ligands, the reactivity of the phosphorus-containing precursor with hydroxyl groups present on the surface of the deposition target is lower than the reactivity of the aluminum-containing precursor with hydroxyl groups. Furthermore, even after the aluminum precursor reacts with a reactive gas (e.g., water), the ligands bonded to aluminum are not completely removed and remain, further exacerbating the steric hindrance effect, further reducing the surface reactivity of the phosphorus-containing precursor. Therefore, when forming phosphorus (P)-doped aluminum oxide represented by Chemical Formula 1 by atomic layer deposition, the efficiency of the "(S30)-(S20)" process for forming phosphorus (P) oxide (the rate of central element remaining in the deposition layer) is lower than the "(S10)-(S20)" process for forming aluminum oxide in the manufacturing method of a cathode active material described below. Furthermore, even if the number of "(S30)-(S20)" processes (y) is increased relative to the number of "(S10)-(S20)" processes (x) within a unit process, the rate of increase in the value of n with the increase in the number of "(S30)-(S20)" processes (y) significantly decreases when the value of n in the composition formula exceeds 0.4. Therefore, considering the effect of increasing the phosphorus (P) content in the phosphorus (P)-doped aluminum oxide and the number of atomic layer deposition processes and the resulting cost efficiency, n is preferably 0.4 or less.

[0044] According to one embodiment of the present invention, in Formula 1, m may be 1.7 or more, 1.8 or more, 1.9 or more, 2.0 or more, or 2.1 or more, and may be 2.6 or less, 2.5 or less, 2.4 or less, 2.3 or less, 2.25 or less, or 2.21 or less. Furthermore, in Formula 1, n may be 0.01 or more, 0.05 or more, 0.10 or more, 0.15 or more, 0.16 or more, 0.17 or more, or 0.18 or more, and may be 0.40 or less, 0.35 or less, 0.30 or less, or 0.25 or less. Within these ranges, the cycle characteristics of a lithium secondary battery including the positive electrode active material may be further improved, resulting in a more excellent capacity retention rate and a lower rate of resistance increase due to degradation, thereby suppressing output degradation.

[0045] According to one embodiment of the present invention, the phosphorus (P) content in the coating layer may be 1 wt % or more, 2 wt % or more, 3 wt % or more, 4 wt % or more, 5 wt % or more, 6 wt % or more, 7 wt % or more, or 8 wt % or more, and may be 15 wt % or less, 14 wt % or less, 13 wt % or less, or 12 wt % or less. Within these ranges, the stability of the positive electrode active material and the life of a lithium secondary battery including the same may be improved.

[0046] According to one embodiment of the present invention, the particulate positive electrode active material may include a lithium transition metal composite oxide represented by the following Chemical Formula 2:

[0047] [Chemical formula 2] Li a Ni b Co c Mn d M 1 e O2

[0048] In the above chemical formula 2, M 1 is one or more selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P and S, and 0.9≦a≦1.2, 0 <b<1、0<c<1、0<d<1、0≦e<0.2、b+c+d+e=1である。

[0049] According to one embodiment of the present invention, in Formula 2, M 1 is a doping element that can be contained in the lithium transition metal composite oxide, and can be appropriately selected as needed.

[0050] According to one embodiment of the present invention, in Formula 2, a represents a molar ratio of lithium to transition metal in the lithium transition metal composite oxide, and may be 0.9 or more, 0.95 or more, or 1.0 or more, and may be 1.2 or less, 1.1 or less, 1.07 or less, 1.05 or less, or 1.03 or less.

[0051] According to one embodiment of the present invention, in Formula 2, b, c, d, and e are transition metals such as nickel (Ni), cobalt (Co), manganese (Mn), and a doping element (M 1 ) in the transition metals. As a specific example, b is the mole fraction of nickel (Ni) in the transition metals, and may be greater than 0, 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, or 0.8 or more, and may be less than 1.0, 0.95 or less, 0.9 or less, or 0.85 or less. c is the mole fraction of cobalt (Co) in the transition metals, and may be greater than 0, 0.05 or more, or 0.1 or more, and may be less than 1, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, or 0.2 or less. The d is a molar fraction of manganese (Mn) among the transition metals, and may be greater than 0, 0.05 or greater, or 0.1 or greater, or may be less than 1, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, or 0.2 or less. The e is a molar fraction of manganese (Mn) among the transition metals. 1), and can be 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, 0.16 or more, 0.17 or more, 0.18 or more, or 0.19 or more. and can be less than 0.20, 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, 0.10 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less.

[0052] According to one embodiment of the present invention, the lithium transition metal composite oxide may be a high-nickel lithium transition metal composite oxide containing nickel (Ni) at 60 mol % or more among the transition metals. In this case, the high nickel content can ensure high energy density, and the coating layer can prevent a decrease in the stability of the positive electrode active material due to the high nickel content.

[0053] According to an embodiment of the present invention, the particulate positive electrode active material may be secondary particles formed by aggregation of primary particles. For example, the positive electrode active material may have an average particle size (D 50 ) can be 0.5 μm or more, 1 μm or more, 1.5 μm or more, or 2 μm or more, and can be 20 μm or less, 18 μm or less, 16 μm or less, 14 μm or less, or 12 μm or less. Within this range, excellent initial charge / discharge efficiency and reduced resistance can be achieved. 50 ) may refer to the average particle size of secondary particles formed by aggregation of the primary particles.

[0054] According to one embodiment of the present invention, the positive electrode active material has a rolled density measured under a load of 2,000 kgf using a powder resistivity measurement device (Powder Resistivity Measurement System, manufactured by Loresta) of 2.85 g / cc or more, 2.86 g / cc or more, 2.87 g / cc or more, 2.88 g / cc or more, 2.89 g / cc or more, 2.90 g / cc or more, 2.91 g / cc or more, 2.92 g / cc or more, 2.93 g / cc or more, 2.94 g / cc or more, 2.95 g / cc or more, 2.96 g / cc or more, 2.97 g / cc or more, 2.98 g / cc or more, 2.99 g / cc or more, 3.00 g / cc or more, 3.01 g / cc or more, 3.02 g / cc or more, 3.03 g / cc or more, 3.04 g / cc or more, 3.05 g / cc or more, 3.06 g / cc or more, 3.07 g / cc or more, 3.08 g / cc or more, 3.09 g / cc or more, 3.10 g / cc or more, 3.11 g / cc or more, 3.12 g / cc or more, 3.13 g / cc or more, 3.14 g / cc or more, 3.15 g / cc or more, 3.16 g / cc or more, 3.17 g / cc or more, 3.18 g / cc or more, 3.19 g / cc or more, 3.20 g / cc or more, 3.21 g / cc or more, 3.22 g / cc or more, 3.23 g / cc or more, 3.24 g / cc or more, 3.25 g / cc or more, 3.2 The viscosity may be 0.03 g / cc or more, 3.04 g / cc or more, 3.05 g / cc or more, 3.06 g / cc or more, 3.07 g / cc or more, 3.08 g / cc or more, 3.09 g / cc or more, 3.10 g / cc or more, 3.11 g / cc or more, 3.12 g / cc or more, 3.13 g / cc or more, 3.14 g / cc or more, 3.15 g / cc or more, 3.16 g / cc or more, or 3.17 g / cc or more, and may be 3.50 g / cc or less, 3.40 g / cc or less, 3.30 g / cc or less, or 3.20 g / cc or less. When the rolled density of the positive electrode active material measured under a load of 2,000 kgf is equal to or greater than the lower limit, the positive electrode active material has a high energy density and prevents particle cracking during rolling, thereby improving the life and stability of a lithium secondary battery containing the positive electrode active material and preventing increases in interface resistance and cell resistance.

[0055] Method for producing positive electrode active material The present invention provides a method for producing a positive electrode active material.

[0056] According to one embodiment of the present invention, the method for preparing the positive electrode active material may be a method for preparing the positive electrode active material described above. As a specific example, the method may be a method for forming a coating layer including aluminum oxide doped with phosphorus (P) on a surface of a particulate positive electrode active material, the coating layer having a thickness of 0.1 nm to 2.0 nm.

[0057] According to one embodiment of the present invention, the method for preparing a positive electrode active material includes: (S1) loading a particulate positive electrode active material into a reaction chamber for atomic layer deposition (ALD); and (S2) forming a coating layer on a surface of the positive electrode active material by performing a plurality of unit processes including the following steps (S10) to (S30), wherein the thickness of the coating layer formed in step (S2) may be 0.1 nm to 2.0 nm.

[0058] (S10) injecting a vapor phase aluminum precursor into the reaction chamber and injecting a purge gas; (S20) injecting a gaseous reaction gas into the reaction chamber and injecting a purge gas; (S30) A step of injecting a gas-phase phosphorus (P)-containing precursor into the reaction chamber and injecting a purge gas.

[0059] According to one embodiment of the present invention, step (S1) is a step of loading a particulate cathode active material to be coated into a reaction chamber of an ALD system, and may be performed by placing the particulate cathode active material obtained in a powder state in the reaction chamber. Here, the particulate cathode active material may be the same as the particulate cathode active material described above in the positive electrode active material section.

[0060] According to one embodiment of the present invention, atomic layer deposition (ALD) is a self-limiting surface treatment method that forms a thin film layer by layer with an atomic-scale thickness. Unlike chemical vapor deposition (CVD), which deposits a thin film by thermal decomposition and gas-phase reaction of a reactant gas, ALD involves a reaction in which one reactant chemically reacts with the surface of a substrate to form a thin film, followed by the addition of a second or third reactant, which then chemically adsorbs onto the substrate to form a thin film. That is, ALD is a method of forming a thin film by chemical adsorption through the periodic supply of reactants. This method allows for atomic-level deposition without reacting reactants with each other, allowing for atomic-level deposition. Furthermore, because a thin film is formed on all exposed surfaces during ALD, a uniform coating can be formed on the entire surface of the particulate cathode active material when coating the particulate cathode active material according to the method for manufacturing a cathode active material of the present invention.

[0061] According to an embodiment of the present invention, step (S2) may be a step of injecting a precursor and / or a reactant gas into a reaction chamber and performing atomic layer deposition on a surface of a particulate positive electrode active material to form a coating layer.

[0062] According to an embodiment of the present invention, the atomic layer deposition (ALD) step (S2) can easily form a coating layer at a lower temperature than chemical vapor deposition (CVD), which deposits particles formed by a chemical reaction of gases on the surface of a substrate. Specifically, the ALD can be performed at a temperature of 60°C to 240°C. More specifically, the ALD can be performed at a temperature of 70°C or higher, 80°C or higher, 90°C or higher, 100°C or higher, 110°C or higher, 120°C or higher, 130°C or higher, or 140°C or higher, or 230°C or lower, 220°C or lower, 210°C or lower, 200°C or lower, 190°C or lower, 180°C or lower, 170°C or lower, or 160°C or lower. Within these temperature ranges, the reaction can proceed smoothly and / or a coating layer can be formed uniformly. The phosphorus (P) content in the coating layer can be maintained at an appropriate level. Furthermore, a high-temperature process above 400°C is not required, preventing deterioration of the physical properties of the positive electrode active material.

[0063] According to one embodiment of the present invention, the unit process including steps (S10) to (S30) of step (S2) can be expressed by the following formula 1 or 2.

[0064] [Formula 1] [{(S10)-(S20)} x -{(S30)-(S20)} y ] z

[0065] [Formula 2] [{(S30)-(S20)} y -{(S10)-(S20)} x ] z

[0066] In the formulas 1 and 2, "-" indicates the execution order of the unit process, In the formulas 1 and 2, "-" indicates the order in which the unit steps are performed. That is, an expression such as "(S10)-(S20)" means that step (S10) is performed followed by step (S20).

[0067] In addition, in the formulas 1 and 2, x represents the number of times {(S10)-(S20)} are repeated. The x may be an integer selected from 1 to 5, specifically an integer selected from 1 to 3, and more specifically, 1 or 2.

[0068] Furthermore, in Formulas 1 and 2, y represents the number of times that {(S30)-(S20)} is repeated. The y may be an integer selected from 1 to 5, and specifically, an integer selected from 1 to 3. As described above, even if the number of times that {(S30)-(S20)} is repeated is increased according to y, the content of phosphorus (P) doped into the coating layer does not increase proportionally, and therefore, within the above range, the process efficiency can be further improved.

[0069] According to one embodiment of the present invention, the ratio of x and y can be adjusted to dope aluminum oxide with phosphorus (P) within a desired content range.

[0070] In addition, in the formulas 1 and 2, z is [{(S10)-(S20)} x -{(S30)-(S20)} y ] or [{(S30)-(S20)} y -{(S10)-(S20)} x The z may be an integer selected from 1 to 20, and specifically may be an integer selected from 1 to 15, 2 to 12, 3 to 10, 4 to 8, or 5 to 7. The thickness of the coating layer may be adjusted to an appropriate level within this range.

[0071] According to an embodiment of the present invention, the step (S10) included in the unit process may be a step for atomic layer deposition of aluminum from an aluminum precursor, and the aluminum precursor may be an aluminum compound represented by the following Chemical Formula 3:

[0072] [Chemical formula 3] AlR 1 R 2 R 3

[0073] In the above chemical formula 3, R 1 ~R 3 can each be an organic group bonded to Al, and specific examples include R 1 ~R 3 are each independently hydrogen, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a halogen group, or an amino group, and the amino group may be a secondary amino group or a tertiary amino group substituted with an alkyl group having 1 to 10 carbon atoms. 1 ~R 3 may each independently represent an alkyl group having 1 to 5 carbon atoms; an alkoxy group having 1 to 5 carbon atoms; a halogen group; or a secondary amino group or a tertiary amino group substituted with an alkyl group having 1 to 5 carbon atoms. 1 ~R 3 may each independently be an alkyl group having 1 to 3 carbon atoms; an alkoxy group having 1 to 3 carbon atoms; a halogen group; or a tertiary amino group substituted with an alkyl group having 1 to 3 carbon atoms.

[0074] According to an embodiment of the present invention, the aluminum precursor may be at least one selected from the group consisting of trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, aluminum ethoxide, dimethylaluminum chloride, diethylaluminum chloride, di-n-propylaluminum chloride, di-n-butylaluminum chloride, tris(dimethylamino)aluminum, and tris(diethylamino)aluminum. As a specific example, the aluminum precursor may be at least one selected from the group consisting of trimethylaluminum, triethylaluminum, aluminum ethoxide, and tris(diethylamido)aluminum.

[0075] According to one embodiment of the present invention, in step (S10), the aluminum precursor may be injected into the reaction chamber in a state filled in a steel container maintained at 10° C. to 50° C., 10° C. to 40° C., 10° C. to 30° C., or 15° C. to 25° C. When injected into the reaction chamber, the aluminum precursor may be injected in a vaporized state under reduced pressure without using a separate carrier gas, or may be injected using an inert gas as a carrier gas.

[0076] According to one embodiment of the present invention, the step (S20) may be a step for oxidizing an aluminum precursor and / or a phosphorus (P)-containing precursor from a reaction gas, and the reaction gas may include, as an oxidant, one or more selected from the group consisting of water vapor (HO), ozone (O), and oxygen plasma.

[0077] According to one embodiment of the present invention, in step (S20), the reaction gas may be injected into the reaction chamber in a state filled in a steel container maintained at 0° C. to 40° C., 0° C. to 30° C., 10° C. to 20° C., or 12° C. to 18° C. When injected into the reaction chamber, the reaction gas may be injected in a state vaporized by depressurization without using a separate carrier gas, or may be injected using an inert gas as a carrier gas.

[0078] According to an embodiment of the present invention, the step (S30) may be a step of doping aluminum oxide with phosphorus by atomic layer deposition from a phosphorus (P)-containing precursor, and the phosphorus (P)-containing precursor may be a phosphate-based compound represented by the following Chemical Formula 4 (Chemical Formula 1).

[0079] [ka]

[0080] In the above chemical formula 4, R 4 ~R 6 may each independently represent hydrogen or an alkyl group having 1 to 10 carbon atoms. 4 ~R 6 may each independently be an alkyl group having 1 to 8 carbon atoms. 4 ~R 6 may each independently be an alkyl group having 1 to 4 carbon atoms.

[0081] According to one embodiment of the present invention, the phosphorus (P)-containing precursor may be at least one selected from the group consisting of trimethylphosphate and triethylphosphate.

[0082] According to one embodiment of the present invention, in step (S30), the phosphorus-containing precursor may be injected into the reaction chamber in a state filled in a steel container maintained at 50° C. to 100° C., 60° C. to 100° C., 70° C. to 100° C., or 80° C. to 90° C. When injected into the reaction chamber, the phosphorus-containing precursor may be injected in a vaporized state under reduced pressure without using a separate carrier gas, or may be injected using an inert gas as a carrier gas.

[0083] According to one embodiment of the present invention, the purge gas injected during the purging steps (S10) to (S30) may be at least one selected from inert gases such as Ar, N2, He, Ne, and / or Kr, and preferably Ar or N2.

[0084] positive electrode The present invention provides a positive electrode containing the positive electrode active material.

[0085] According to an embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material.

[0086] According to one embodiment of the present invention, the positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to the positive electrode active material layer and is non-reactive within the voltage range of the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel whose surfaces are surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and the surface of the current collector may be micro-irregularized to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0087] According to one embodiment of the present invention, the positive electrode active material layer may optionally include a conductive material and a binder in addition to the positive electrode active material. The positive electrode active material may be included in an amount of 80 wt % to 99 wt %, more specifically, 85 wt % to 98.5 wt %, based on the total weight of the positive electrode active material layer. Within this range, excellent capacity characteristics can be exhibited.

[0088] According to one embodiment of the present invention, the conductive material is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations as long as it does not cause chemical changes in the resulting battery and has electronic conductivity. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 wt % to 15 wt % based on the total weight of the positive electrode active material layer.

[0089] According to an embodiment of the present invention, the binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof. These may be used alone or in combination. The binder may be contained in an amount of 0.1% by weight to 15% by weight based on the total weight of the positive electrode active material layer.

[0090] According to one embodiment of the present invention, the positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode can be manufactured by coating a positive electrode active material layer-forming composition, which is prepared by dissolving or dispersing the positive electrode active material and, optionally, a binder, a conductive material, and a dispersant in a solvent, on a positive electrode current collector, followed by drying and rolling, or by casting the positive electrode active material layer-forming composition on a separate support, peeling it from the support, and laminating the resulting film on a positive electrode current collector.

[0091] According to one embodiment of the present invention, the solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for manufacturing a positive electrode.

[0092] According to an embodiment of the present invention, the positive electrode active material layer may have a porosity of 35% or less, and specific examples thereof include 35% or less, 34% or less, 33% or less, 32% or less, 31% or less, 30% or less, 29% or less, 28% or less, 27% or less, 26% or less, or 25% or less, and may also be 1% or more, 5% or more, 10% or more, 15% or more, 20% or more, 21% or more, 22% or more, 23% or more, or 24% or more. The porosity of the positive electrode active material layer may be the porosity after rolling and may be a value calculated by the following Equation 1:

[0093] [Formula 1] Porosity=(1-filling density / true density)×100

[0094] According to an embodiment of the present invention, the true density in Equation 1 may refer to the theoretical density of a composition for forming a positive electrode active material layer, excluding the solvent, when no voids are present. For a specific example, the true density may be calculated by taking into account the weight ratio of each material other than the solvent contained in the composition for forming a positive electrode active material layer and / or the true density of each material. For a more specific example, the true density may be a value calculated using Equation 2 below.

[0095] [Formula 2] True density=1 / (Σ(P i / D i ))

[0096] In the above formula 2, P i may mean the weight ratio of each component contained in the composition for forming a positive electrode active material layer other than the solvent, and D i " may refer to the true density of each component contained in the composition for forming a positive electrode active material layer, excluding the solvent. Specifically, the true density may refer to the reciprocal of the sum of the weight ratio of the positive electrode active material divided by the true density of the positive electrode active material, the weight ratio of the binder divided by the true density of the binder, and / or the weight ratio of the conductive material, etc. divided by the true density of the conductive material. The true density may be measured, for example, using a known true density measuring device.

[0097] According to an embodiment of the present invention, in Equation 1, the packing density may refer to the density of the positive electrode active material layer after a rolling process. Specifically, the packing density may be calculated by sampling an arbitrary point after rolling the positive electrode active material layer formed on the positive electrode current collector, and dividing the amount of the positive electrode active material layer per unit area (loading amount) by the thickness of the positive electrode active material layer. Therefore, the porosity of the positive electrode active material layer may be controlled by the components of the positive electrode active material layer, the loading amount per area of ​​the positive electrode active material layer, and / or the thickness of the positive electrode active material layer.

[0098] According to one embodiment of the present invention, when the components of the positive electrode active material layer and the loading amount per area of ​​the positive electrode active material layer are the same, the porosity can be reduced as the thickness of the positive electrode active material layer is reduced (i.e., the pressing gap is reduced), and the porosity can be increased as the thickness of the positive electrode active material layer is increased (i.e., the pressing gap is increased). The pressing gap can be appropriately adjusted in consideration of the desired porosity of the positive electrode active material layer.

[0099] Lithium secondary battery The present invention provides a lithium secondary battery including the positive electrode.

[0100] According to an embodiment of the present invention, the lithium secondary battery may include the positive electrode, the negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The lithium secondary battery may also optionally include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0101] According to an embodiment of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0102] According to one embodiment of the present invention, the negative electrode current collector may be made of any material that does not cause chemical changes in the battery and has high conductivity. Examples of such materials include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, the current collector may have a finely textured surface to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be made in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0103] According to an embodiment of the present invention, the negative electrode active material layer may optionally include a binder and a conductive material in addition to the negative electrode active material.

[0104] According to an embodiment of the present invention, the negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO β Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); and composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. These may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Representative examples of low-crystalline carbon include soft carbon and hard carbon, while representative examples of high-crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbon such as petroleum or coal tar pitch-derived cokes. The negative electrode active material may be included in an amount of 80 wt% to 99 wt% of the total weight of the negative electrode active material layer.

[0105] According to one embodiment of the present invention, the binder in the negative electrode active material layer is a component that helps bind the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10 wt % based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0106] According to one embodiment of the present invention, the conductive material in the negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 10 wt % or less, preferably 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material may be any conductive material that does not cause chemical changes in the battery and has conductivity. Examples of such conductive materials include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0107] According to one embodiment of the present invention, the negative electrode may be fabricated by coating a negative electrode active material layer-forming composition, prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, on a negative electrode current collector and drying the coating. Alternatively, the negative electrode active material layer-forming composition may be fabricated by casting the negative electrode active material layer-forming composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0108] According to one embodiment of the present invention, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitation. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification capability is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be selectively used in a single-layer or multi-layer structure.

[0109] According to an embodiment of the present invention, the electrolyte may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which can be used in manufacturing a lithium secondary battery. As a specific example, the electrolyte may include an organic solvent and a lithium salt.

[0110] According to an embodiment of the present invention, the organic solvent may be any solvent capable of acting as a medium through which ions involved in the electrochemical reaction of the battery can migrate. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0111] According to one embodiment of the present invention, the lithium salt may be any compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the anion of the lithium salt may be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within a range of 0.1M to 2.0M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0112] According to one embodiment of the present invention, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethyl alcohol amine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. Here, the additives may be included in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0113] A lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent capacity characteristics, output characteristics, and life characteristics, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0114] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0115] The lithium secondary battery according to the present invention can be used as a battery cell used as a power source for a small device, and can also be preferably used as a unit battery in a medium- to large-sized battery module including a large number of battery cells.

[0116] Therefore, according to one embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0117] According to one embodiment of the present invention, the battery module or battery pack may be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and an electric vehicle (PHEV), including a plug-in hybrid electric vehicle; or a power storage system.

[0118] Although the present invention may be embodied in many different forms, it is to be understood that the invention is not limited to the embodiments set forth herein, and that the invention may be embodied in various different forms, without departing from the spirit or scope of the present invention.

[0119] Examples and Comparative Examples Example 1 Average particle size (D 50 ) is a secondary particle with an average composition of LiNi 0.8 Mn 0.1 Co 0.1 A particulate cathode active material (GL80, manufactured by LG Chem) was loaded into an ALD system (Lucida C200-PL, manufactured by NCD Tech) with the substrate temperature maintained at 150°C. Next, the following unit processes (ALD first unit process) were performed in the order of Scheme 1-1 below: (S11), (S21), and (S31). The ALD first unit process was performed a total of six times to produce a cathode active material coated with phosphorus (P)-doped aluminum oxide.

[0120] [Formula 1-1] (S11)-(S21)-(S31)-(S21)

[0121] (S11) Trimethylaluminum was injected into the ALD system as an aluminum precursor for 1 second. The aluminum precursor was filled in a steel container maintained at 20°C, and the aluminum precursor was vaporized under reduced pressure and injected into the system without the use of a separate carrier gas. Purging was then performed for 50 seconds using the inert gas Ar.

[0122] (S21) Water vapor (water) was injected as a reaction gas into the ALD system for 1 second. The reaction gas was filled in a steel container maintained at 14°C, and the reaction gas was vaporized under reduced pressure and injected into the system without the use of a separate carrier gas. Next, purging was performed for 50 seconds using an inert gas, Ar.

[0123] (S31) Trimethyl phosphate, a phosphorus (P)-containing precursor, was injected into the ALD system for 1 second. The phosphorus-containing precursor was filled in a steel container maintained at 85°C, and the vaporized phosphorus-containing precursor was injected into the system under reduced pressure without the use of a separate carrier gas. Purging was then performed for 50 seconds using the inert gas Ar.

[0124] Example 2 A cathode active material coated with phosphorus (P)-doped aluminum oxide was prepared in the same manner as in Example 1, except that the unit processes (ALD third unit process) of steps (S11), (S21), and (S31) in Example 1 were performed in the order of Schemes 1-3 below, and the ALD third unit process was performed a total of six times.

[0125] [Formula 1-3] (S11)-(S21)-{(S31)-(S21)}3

[0126] Example 3 A cathode active material coated with phosphorus (P)-doped aluminum oxide was prepared in the same manner as in Example 1, except that the unit processes (ALD fourth unit process) of steps (S11), (S21), and (S31) in Example 1 were performed in the order of Schemes 1-4 below, and the ALD fourth unit process was performed twice in total.

[0127] [Formula 1-4] {(S11)-(S21)}3-(S31)-(S21)

[0128] Comparative Example 1 Average particle size (D 50 ) is a secondary particle with an average composition of LiNi 0.8 Mn 0.1 Co 0.1 A particulate positive electrode active material (GL80, manufactured by LG Chem) was dried at 130° C. for 5 hours in a vacuum oven without a separate coating process to prepare a positive electrode active material.

[0129] Comparative Example 2 An aluminum oxide-coated cathode active material was prepared in the same manner as in Example 1, except that the unit process (ALD 5 unit process) of steps (S11) and (S21) in Example 1 was performed in the order of Scheme 3 below, and the ALD 5 unit process was performed a total of 6 times.

[0130] [Formula 3] (S11)-(S21)

[0131] Comparative Example 3 A cathode active material coated with phosphorus (P)-doped aluminum oxide was prepared in the same manner as in Example 1, except that the unit processes (ALD third unit process) of steps (S11), (S21), and (S31) in Example 1 were performed in the order of Schemes 1-3 below, and the ALD third unit process was performed a total of 30 times.

[0132] [Formula 1-3] (S11)-(S21)-{(S31)-(S21)}3

[0133] Experimental example Experimental Example 1: Confirmation of aluminum oxide coating layer components with and without phosphorus (P) doping A silicon wafer was loaded into an ALD system (NCDTech, Lucida C200-PL) with the substrate temperature maintained at 150°C. Next, the following unit steps (S11), (S21), and (S31) were performed in the order of formulas 1-1, 1-2, 1-3, 1-4, and 3 (Formula 1-1: ALD 1st unit step; Formula 1-2: ALD 2nd unit step; Formula 1-3: ALD 3rd unit step; Formula 1-4: ALD 4th unit step; Formula 3: ALD 5th unit step). The ALD 1st unit step through the ALD 5th unit step were performed so that the "(S11)-(S21)" steps were performed a total of 300 times. That is, the ALD 1st unit process to the ALD 3rd unit process and the ALD 5th unit process were performed a total of 300 times, and the ALD 4th unit process was performed a total of 100 times to form an atomic layer deposition film corresponding to an aluminum oxide coating layer doped or undoped with phosphorus (P).

[0134] [Formula 1-1] (S11)-(S21)-(S31)-(S21)

[0135] [Formula 1-2] (S11)-(S21)-{(S31)-(S21)}2

[0136] [Formula 1-3] (S11)-(S21)-{(S31)-(S21)}3

[0137] [Formula 1-4] {(S11)-(S21)}3-(S31)-(S21)

[0138] [Formula 3] (S11)-(S21)

[0139] (S11) Trimethylaluminum was injected as an aluminum precursor into the ALD system for 1 second. The aluminum precursor was filled in a steel container maintained at 20°C, and the aluminum precursor was vaporized under reduced pressure and injected into the system without the use of a separate carrier gas. Purging was then performed for 50 seconds using the inert gas Ar.

[0140] (S21) Water vapor was injected as a reaction gas into the ALD system for 1 second. The reaction gas was filled in a steel container maintained at 14°C, and the reaction gas was vaporized under reduced pressure and injected into the system without the use of a separate carrier gas. Next, purging was performed for 50 seconds using an inert gas, Ar.

[0141] (S31) Trimethyl phosphate, a phosphorus (P)-containing precursor, was injected into the ALD system for 1 second. The phosphorus-containing precursor was filled in a steel container maintained at 85°C, and the vaporized phosphorus-containing precursor was injected into the system under reduced pressure without the use of a separate carrier gas. Purging was then performed for 50 seconds using the inert gas Ar.

[0142] Next, an ellipsometer (MK-2000, manufactured by J.A. Woolam) was used to measure the thickness of the deposited film by fitting psi and delta measurements from 380 nm to 780 nm using the Cauchy model. The deposited film was then irradiated with a monochromatic Al K-α X-ray source using X-ray photoelectron spectroscopy (XPS) (K-Alpha+, Thermo Fisher Scientific Inc.) to analyze the components of the deposited film, the results of which are shown in Table 1 below. Based on the analysis results, the composition ratios of phosphorus (P)-doped and undoped aluminum oxides, represented by Chemical Formula 1 below, for the positive electrode active materials coated with phosphorus (P)-doped and undoped aluminum oxides prepared in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 2 below.

[0143] [Table 1]

[0144] [Table 2]

[0145] As shown in Table 1, when atomic layer deposition was performed using the first, second, and third ALD unit processes, a deposited film was formed with a deposition thickness of about 0.1 nm per unit process. When atomic layer deposition was performed using the fourth ALD unit process, a deposited film was formed with a deposition thickness of about 0.3 nm per unit process. Each deposited film was also confirmed to contain phosphorus (P) in a content of 4.2 wt % to 11.1 wt %. On the other hand, when atomic layer deposition was performed using the fifth ALD unit process, a deposited film was formed with a deposition thickness of about 0.1 nm per unit process, confirming that the deposited film did not contain phosphorus (P).

[0146] Therefore, the cathode active material prepared in Example 1 was subjected to the ALD first unit process a total of six times, and it was estimated that a coating layer having a thickness of 0.576 nm was formed on the surface of the particulate cathode active material, and the phosphorus (P) content in the coating layer was 8.2 wt %.

[0147] In addition, the cathode active material prepared in Example 2 was subjected to the ALD third unit process a total of six times, resulting in a coating layer having a thickness of 0.630 nm formed on the surface of the particulate cathode active material, and the phosphorus (P) content in the coating layer was estimated to be 11.1 wt %.

[0148] In addition, the cathode active material prepared in Example 3 was subjected to the ALD fourth unit process twice in total, and it was estimated that a coating layer having a thickness of 0.612 nm was formed on the surface of the particulate cathode active material, and the phosphorus (P) content in the coating layer was 4.2 wt %.

[0149] In addition, the positive electrode active material prepared in Comparative Example 2 was subjected to the ALD fifth unit process a total of six times, and it was predicted that a coating layer having a thickness of 0.714 nm was formed on the surface of the particulate positive electrode active material, and that the coating layer did not contain phosphorus (P).

[0150] In addition, the cathode active material prepared in Comparative Example 3 was subjected to the ALD third unit process a total of 30 times, resulting in a coating layer having a thickness of 3.150 nm formed on the surface of the particulate cathode active material, and the phosphorus (P) content in the coating layer was estimated to be 11.1 wt%.

[0151] Experimental Example 2: Measurement of rolling density The rolled densities of the positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 3 were measured using a powder resistivity measurement device (Powder Resistivity Measurement System, manufactured by Loresta) under loads of 400 kgf, 800 kgf, 1,200 kgf, 1,600 kgf, and 2,000 kgf, respectively, and are shown in FIG. 1. The rolled densities under a load of 2,000 kg are shown in Table 2 below.

[0152] [Table 3]

[0153] As shown in Table 3, when a coating layer formed on the surface of the particulate positive electrode active material was included, it was confirmed that the rolling density was improved compared to Comparative Example 1, which did not include a coating layer.

[0154] Experimental example 3: Charge / discharge evaluation Using each of the positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 3, carbon black (DenkaBlack, manufactured by Denka Corporation) as a conductive material and PVdF (KF1300, manufactured by Kureha Corporation) as a binder were added to a solvent (N-methylpyrrolidone (NMP), manufactured by Oi Chemical Industries, Ltd.) in a weight ratio of 97.5:1:1.5 (positive electrode active material:conductive material:binder), to produce a composition for forming a positive electrode active material layer.

[0155] Each of the prepared positive electrode active material layer-forming compositions was coated on one side of an aluminum foil current collector with a thickness of 12 μm and dried at 135° C. for 3 hours to form a positive electrode active material layer. The positive electrode active material layer was then rolled using a roll pressing method to prepare a positive electrode having a porosity of 25% in the positive electrode active material layer after rolling.

[0156] A polypropylene separator (WL20C, manufactured by W-Scope) was placed between each of the prepared positive electrodes and a 300 μm-thick lithium metal thin film as the negative electrode, and a coin-type half cell was fabricated using an organic electrolyte of ethylene carbonate (EC) / dimethyl carbonate (DMC) / LiPF6 (Merck Battery grade, EC / DMC=1 / 1, 1M LiPF6).

[0157] The coin-shaped half cell thus fabricated was activated and then charged and discharged. Specifically, 30 cycles of charge / discharge were performed at 45°C under the conditions of a charge cut-off voltage of 4.4V, a discharge cut-off voltage of 2.5V, and a current of 0.3C / 0.3C. The discharge capacity and discharge resistance at 60 seconds were measured for the first and 30th cycles. The discharge capacity retention rate and discharge resistance increase rate (at 60 seconds) at 30 cycles were measured relative to the initial discharge capacity and discharge resistance, and are shown in Table 4 below.

[0158] [Table 4]

[0159] As shown in Table 4, when the positive electrode active materials prepared in Examples 1 to 3 of the present invention were included, the capacity retention rate was improved and the resistance increase rate was significantly reduced compared to when the positive electrode active material of Comparative Example 1, which did not include a coating layer, was included.

[0160] In particular, from the results of Examples 1 and 2 and Example 3, it was confirmed that when the phosphorus (P) content in the aluminum oxide contained in the coating layer was maintained at a predetermined level, as in Examples 1 and 2, the capacity retention rate was further improved and the resistance increase rate was further reduced.

[0161] On the other hand, when the positive electrode active material prepared in Comparative Example 2, in which a coating layer was formed only with aluminum oxide without doping with phosphorus (P), was included, the capacity retention rate and resistance increase rate were improved compared to when the positive electrode active material of Comparative Example 1, which did not include a coating layer, but the improvement was not as significant as when the positive electrode active material prepared in Examples 1 to 3 was included.

[0162] In addition, in the case of the cathode active material of Comparative Example 3, in which the ALD third unit process was performed 30 times and a coating layer of 3.150 nm in thickness was formed on the surface of the particulate cathode active material, it was confirmed that not only did the initial discharge capacity decrease sharply due to the increased thickness of the coating layer, but rather the improvement in the resistance increase rate was minimal.

[0163] From these results, it was confirmed that the cathode active material of the present invention includes aluminum oxide doped with phosphorus (P) formed by atomic layer deposition and includes a thin and uniform coating layer, thereby improving the lifespan and stability and preventing increases in interface resistance and cell resistance. As a result, it was confirmed that the cycle characteristics of the lithium secondary battery are improved, the capacity retention rate is excellent, and the rate of increase in resistance due to degradation is low, thereby suppressing a decrease in output.

Claims

1. a particulate positive electrode active material; and a coating layer formed on the surface of the particulate positive electrode active material, the coating layer includes aluminum oxide doped with phosphorus (P), the thickness of the coating layer is 0.1 nm or more and 2.0 nm or less; the thickness of the coating layer is an arithmetic average thickness of the total thickness of the coating layer formed on the surface of the particulate positive electrode active material, The phosphorus (P)-doped aluminum oxide is represented by the following formula 1: [Chemical formula 1] AlO m P n In the above chemical formula 1, m is 1.7 or more and 2.6 or less, and n is 0.01 or more and 0.4 or less.

2. The cathode active material according to claim 1 , wherein the coating layer has a thickness of 0.2 nm to 1.0 nm.

3. 2. The positive electrode active material according to claim 1, wherein in Chemical Formula 1, m is 2.0 or more and 2.5 or less, and n is 0.15 or more and 0.30 or less.

4. The cathode active material of claim 1 , wherein the coating layer has a phosphorus (P) content of 1% by weight to 15% by weight.

5. The cathode active material of claim 1 , wherein the coating layer has a phosphorus (P) content of 8 wt % to 12 wt %.

6. The particulate positive electrode active material includes a lithium transition metal composite oxide represented by the following chemical formula 2: [Chemical formula 2] Li ａ Ni ｂ Co ｃ Mn ｄ M １ ｅ O ２ In the above chemical formula 2, M １ is one or more elements selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S, and 0.9≦a≦1.2, 0<b<1, 0<c<1, 0<d<1, 0≦e<0.2, and b+c+d+e=1.

7. A step (S1) of loading a particulate positive electrode active material into a reaction chamber for performing atomic layer deposition; and (S2) forming a coating layer on the surface of the positive electrode active material by performing the unit process including the following steps (S10) to (S30) multiple times, The thickness of the coating layer formed in step (S2) is 0.1 nm or more and 2.0 nm or less; (S10) injecting a vapor phase aluminum precursor into the reaction chamber and injecting a purge gas; (S20) injecting a gas phase reaction gas into the reaction chamber and injecting a purge gas; (S30) injecting a gaseous phosphorus (P)-containing precursor into a reaction chamber and injecting a purge gas.

8. The unit process including steps (S10) to (S30) of step (S2) is represented by the following formula 1 or formula 2: [Formula 1] [{(S10)-(S20)} ｘ -{(S30)-(S20)} ｙ ] ｚ [Formula 2] [{(S30)-(S20)} ｙ -{(S10)-(S20)} ｘ ] ｚ In the formulas 1 and 2, "-" indicates the execution order of the unit process, x is the number of times {(S10)-(S20)} is repeated, and is an integer selected from 1 to 5; y is the number of times {(S30)-(S20)} is repeated, and is an integer selected from 1 to 5; z is [{(S10)-(S20)} ｘ -{(S30)-(S20)} ｙ ] or [{(S30)-(S20)} ｙ -{(S10)-(S20)} ｘ 8. The method for producing a positive electrode active material according to claim 7, wherein the number of times the above step (2) is repeated is an integer selected from 1 to 20.

9. 8. The method for producing a positive electrode active material according to claim 7, wherein the aluminum precursor is at least one selected from the group consisting of trimethylaluminum, triethylaluminum, aluminum ethoxide, and tris(diethylamido)aluminum.

10. The reaction gas is water vapor (H ２ O), ozone (O ３ 8. The method for producing a positive electrode active material according to claim 7, wherein the oxygen plasma is at least one selected from the group consisting of oxygen plasma and oxygen plasma.

11. The method for producing a positive electrode active material according to claim 7 , wherein the phosphorus (P)-containing precursor is at least one selected from the group consisting of trimethyl phosphate and triethyl phosphate.

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

13. A lithium secondary battery comprising the positive electrode according to claim 12.

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