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

Abstract

The present invention provides a high-nickel positive electrode active material that has improved stability and initial capacity and suppresses the occurrence of cracks at the interface between primary particles, a method for producing the same, and a positive electrode and a lithium secondary battery including the same. The present invention also provides a high-nickel positive electrode active material that can reduce the content of lithium impurities and omit a water washing process, a method for producing the same, and a positive electrode 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. 10-2021-0037588 filed on Mar. 23, 2021, and all of the contents disclosed in the document of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a positive electrode active material including a high-Ni (high-nickel) based lithium transition metal oxide and a method for manufacturing the same.

Background Art

[0003] Recently, with the development of technologies such as electric vehicles, the demand for high-capacity secondary batteries has been increasing, and accordingly, research on high-Ni (high-nickel) based positive electrode active materials having excellent capacity characteristics has been actively conducted.

[0004] The positive electrode active material is generally manufactured by mixing a lithium-containing raw material substance and a transition metal hydroxide and then firing. When manufacturing a high-Ni based positive electrode active material having a high nickel content, a low firing temperature is required. Therefore, when manufacturing a high-Ni based positive electrode active material having a high nickel content, the residual amount of lithium by-products such as lithium carbonate and lithium hydroxide increases. Such lithium by-products react with the electrolyte in the secondary battery, causing problems of deteriorating the battery performance and generating gas, and causing a gelling phenomenon during the manufacture of the electrode slurry.

[0005] Therefore, generally, when manufacturing a high-Ni based positive electrode active material, after the firing step, a water washing step is performed to remove lithium by-products such as lithium carbonate and lithium hydroxide remaining on the surface of the particles. Further, after the water washing step, boron coating is usually performed to ensure the stability and initial performance of the positive electrode active material. However, when boron coating is performed, cracks occur between the primary particles of the lithium transition metal oxide, causing problems such as gas generation and deterioration of the cycle characteristics of the battery when the positive electrode active material is applied to the battery.

[0006] In order to solve this problem, a method of forming a coating layer made of lithium cobalt oxide has been proposed. However, in this case, it is difficult to reduce the cost due to the high raw material unit price. Also, when forming a coating layer made of lithium manganese oxide, there is a drawback that the initial capacity decreases.

[0007] Also, as described above, when performing the water washing step, although lithium by-products are removed, lithium ions inside the positive electrode active material are detached, and NiO, NiOOH, etc. are formed on the surface portion of the positive electrode active material, resulting in a change in the structure of the lithium transition metal oxide. Therefore, there is a problem that the capacity of the lithium secondary battery decreases.

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention is for solving the above problems, and aims to provide a high-nickel-based positive electrode active material capable of improving the stability and initial capacity of a lithium secondary battery and suppressing the generation of cracks at the interface between primary particles, a method for manufacturing the same, a positive electrode including the same, and a lithium secondary battery.

[0009] Also, the present invention aims to provide a method for manufacturing a high-nickel-based positive electrode active material capable of suppressing the content of lithium by-products to a low level and omitting the water washing step, a positive electrode active material manufactured thereby, a positive electrode including the same, and a lithium secondary battery.

Means for Solving the Problems

[0010] In order to solve the above problems, the present invention provides a positive electrode active material, a method for manufacturing the positive electrode active material, a positive electrode, and a lithium secondary battery.

[0011] (1) The present invention provides a cathode active material which is in the form of secondary particles aggregated from a plurality of primary particles, and includes a lithium transition metal oxide in which the content of nickel among metal elements other than lithium is 80 atm% or more; a first coating layer which is formed on the surface of the secondary particles of the lithium transition metal oxide and on the surface of some or all of the plurality of primary particles, contains nickel and manganese, and has a layered structure; and a second coating layer which is formed on the outer surface of the first coating layer and contains boron.

[0012] (2) In the above (1), the present invention provides a cathode active material in which the lithium transition metal oxide has a composition represented by the following Chemical Formula 1. [Chemical Formula 1] Li a Ni b Co c M 1 d M 2 e O 2 In the above Chemical Formula 1, M 1 is one or more selected from Mn and Al, M 2 is one or more selected from the group consisting of Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y, 0.9 ≦ a ≦ 1.3, 0.8 ≦ b < 1.0, 0 < c ≦ 0.2, 0 < d ≦ 0.2, 0 ≦ e ≦ 0.1.

[0013] (3) In the above (1) or (2), the present invention provides a cathode active material in which the average particle diameter of the primary particles is 0.1 μm to 0.5 μm.

[0014] (4) In any one of the above (1) to (3), the present invention provides a cathode active material in which the average particle diameter (D 50 ) of the secondary particles is 8 μm to 15 μm.

[0015] (5) The present invention provides a positive electrode active material in any one of (1) to (4) above, wherein the average thickness of the first coating layer is 10 nm to 200 nm.

[0016] (6) The present invention provides a positive electrode active material in any one of (1) to (5) above, wherein the first coating layer has a composition represented by the following Chemical Formula 2. [Chemical Formula 2] Li x [Ni z Mn w y O 2 In Chemical Formula 2, 0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0.1 ≦ z ≦ 0.9, and 0.1 ≦ w ≦ 0.9.

[0017] (7) The present invention provides a positive electrode active material in any one of (1) to (6) above, wherein the molar ratio of nickel to manganese contained in the first coating layer is 1:9 to 9:1.

[0018] (8) The present invention provides a positive electrode active material in any one of (1) to (7) above, wherein the molar ratio of nickel to manganese contained in the first coating layer is 5:5 to 9:1.

[0019] (9) The present invention provides a positive electrode active material in any one of (1) to (8) above, wherein the first coating layer is contained in an amount of 1 part by weight to 5 parts by weight with respect to 100 parts by weight of the lithium transition metal oxide.

[0020] (10) The present invention provides a positive electrode active material in any one of (1) to (10) above, wherein the second coating layer contains one or more selected from the group consisting of lithium borate and borate.

[0021] (11) The present invention provides a positive electrode active material in any one of (1) to (10) above, wherein the second coating layer is contained in an amount of 0.01 part by weight to 1 part by weight with respect to 100 parts by weight of the lithium transition metal oxide. ​

[0022] (12) The present invention provides a positive electrode active material in any one of (1) to (11) above, wherein the content of lithium by-products remaining on the surface is 1% by weight or less based on the total weight of the positive electrode active material.

[0023] (13) The present invention includes a step of preparing a lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated, and the content of nickel among metal elements other than lithium is 80 atm% or more; a step of mixing the lithium transition metal oxide with a solution containing a nickel raw material substance and a manganese raw material substance, and then performing a first heat treatment to form a first coating layer having a layered structure and containing nickel and manganese on the surface of the secondary particles of the lithium transition metal oxide and on the surface of some or all of the plurality of primary particles; and a step of mixing the lithium transition metal oxide having the first coating layer formed thereon with a boron raw material substance and performing a second heat treatment to form a second coating layer containing boron on the outer surface of the first coating layer.

[0024] (14) The present invention provides a method for manufacturing a positive electrode active material according to (13) above, wherein the step of preparing the lithium transition metal oxide is performed by mixing a lithium raw material substance and a positive electrode active material precursor and then firing.

[0025] (15) The present invention provides a method for manufacturing a positive electrode active material according to any one of (13) or (14) above, wherein the step of preparing the lithium transition metal oxide does not include a water washing step.

[0026] (16) The present invention provides a method for manufacturing a positive electrode active material according to any one of (13) to (15) above, wherein the nickel raw material substance is nickel nitrate and the manganese raw material substance is manganese nitrate.

[0027] (17) The present invention provides a method for manufacturing a positive electrode active material according to any one of (13) to (16) above, wherein the first heat treatment is performed at 650°C to 850°C.

[0028] (18) The present invention provides a method for manufacturing a positive electrode active material, in any one of (13) to (17) above, wherein the boron raw material substance is boric acid.

[0029] (19) The present invention provides a method for manufacturing a positive electrode active material, in any one of (13) to (18) above, wherein the second heat treatment is performed at 150°C to 500°C.

[0030] (20) The present invention provides a positive electrode including the positive electrode active material according to any one of (1) to (12).

[0031] (21) The present invention provides a lithium secondary battery including the positive electrode according to (20), a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

Effects of the Invention

[0032] The high-nickel-based positive electrode active material according to the present invention can improve the stability and initial capacity of a lithium secondary battery, suppress the generation of cracks at the interface between primary particles, and also improve the cycle characteristics of the battery.

[0033] In addition, according to the method for manufacturing a high-nickel-based positive electrode active material of the present invention, the content of lithium by-products can be suppressed low, the water washing process can be omitted, the problems caused by the water washing process can be solved, and the equipment and process costs can be reduced.

[0034] Therefore, the high-nickel-based positive electrode active material according to the present invention can be applied to a positive electrode and usefully used in a lithium secondary battery.

Brief Description of the Drawings

[0035]

Figure 1

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BEST MODE FOR CARRYING OUT THE INVENTION

[0036] The terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. In accordance with the principle that the inventors can appropriately define the concepts of the terms in order to explain their invention in the best way, they should be construed in meanings and concepts consistent with the technical idea of the present invention.

[0037] In this specification, terms such as "comprising", "including" or "having" are used to specify the presence of implemented features, numbers, steps, components or combinations thereof, and it should be understood that they do not preclude in advance the presence or possibility of addition of one or more different features, numbers, steps, components or combinations thereof.

[0038] Hereinafter, the present invention will be described in more detail.

[0039] In the present invention, the "primary particle" means the smallest particle unit that can be distinguished as a single mass when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and it can consist of one crystal grain or a plurality of crystal grains.

[0040] In the present invention, the average particle diameter of the primary particles is the arithmetic mean value of the numerical values obtained by measuring the respective primary particle diameters distinguished from the cross-sectional SEM image of the positive electrode active material particles obtained using a scanning electron microscope (SEM) with the Image J program.

[0041] In the present invention, "secondary particles" means a secondary structure formed by aggregation of a plurality of primary particles.

[0042] In the present invention, the average particle diameter (D 50 ) of the secondary particles is the particle diameter corresponding to 50% of the volume cumulative amount in the particle size distribution curve. The average particle diameter (D 50 ) of the secondary particles can be obtained using the laser diffraction method. Specifically, the average particle diameter (D 50 ) of the secondary particles is obtained by dispersing the positive electrode active material particles in a dispersion medium (e.g., distilled water) and then introducing them into a laser diffraction particle size measuring device (Microtrac S3500). When the particles pass through the laser beam, the difference in the diffraction pattern due to the particle diameter is measured, and it is the particle diameter at the point where the volume cumulative amount reaches 50% in the obtained particle size distribution curve.

[0043] Positive electrode active material The positive electrode active material according to the present invention is in the form of secondary particles in which a plurality of primary particles are aggregated, and includes a lithium transition metal oxide in which the content of nickel among metal elements other than lithium is 80 atm% or more, and a first coating layer formed on the surface of the secondary particles of the lithium transition metal oxide and on the surface of some or all of the plurality of primary particles, containing nickel and manganese and having a layered structure, and a second coating layer formed on the outer surface of the first coating layer and containing boron.

[0044] The positive electrode active material according to the present invention can be in the form of secondary particles in which a plurality of primary particles are aggregated, and includes a lithium transition metal oxide in which the content of nickel among metal elements other than lithium is 80 atm% or more.

[0045] Specifically, the lithium transition metal oxide contained in the positive electrode active material of the present invention can have a composition represented by the following Chemical Formula 1.

[0046] [Chemical Formula 1] Li a Ni b Co c M 1 d M 2 e O 2

[0047] In the Chemical Formula 1, M 1 can be one or more selected from Mn and Al, and preferably can be Mn or a combination of Mn and Al.

[0048] In the Chemical Formula 1, M 2 can be one or more selected from the group consisting of Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y.

[0049] The a represents the molar ratio of lithium in the lithium transition metal oxide, and can be 0.9 ≦ a ≦ 1.3, 0.9 ≦ a ≦ 1.2, or 1.0 ≦ a ≦ 1.1.

[0050] The b represents the molar ratio of nickel among the metal elements other than lithium in the lithium transition metal oxide, and can be 0.80 ≦ b < 1.0, 0.80 ≦ b ≦ 0.98, or 0.80 ≦ b ≦ 0.95. When the nickel content satisfies the above range, high capacity characteristics can be realized.

[0051] The c represents the molar ratio of cobalt among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 < c ≦ 0.2, 0 < c ≦ 0.15, or 0.01 ≦ c ≦ 0.10.

[0052] The d represents M among the metal elements other than lithium in the lithium transition metal oxide 1shows the molar ratio, and can be 0 < d ≦ 0.2, 0 < d ≦ 0.15, or 0.01 ≦ d ≦ 0.10.

[0053] Said e represents the molar ratio of metal elements other than lithium in the lithium transition metal oxide among M 2 and can be 0 ≦ e ≦ 0.1 or 0 ≦ e ≦ 0.05.

[0054] The lithium transition metal oxide contained in the positive electrode active material of the present invention can have an average primary particle diameter of 0.1 μm to 0.5 μm, preferably 0.1 μm to 0.3 μm. When the average primary particle diameter satisfies the above range, sufficient capacity of the secondary battery can be ensured.

[0055] The lithium transition metal oxide contained in the positive electrode active material of the present invention has an average secondary particle diameter (D 50 ) that can be 8 μm to 15 μm, preferably 9 μm to 12 μm. When the average secondary particle diameter (D 50 ) is smaller than the above range, there is a problem that the gas reaction due to the side reaction with the electrolyte becomes too much in the manufactured secondary battery, and when the average secondary particle diameter (D 50 ) is larger than the above range, there is a problem that the electrode current collector is broken when coating the positive electrode active material on the electrode.

[0056] The positive electrode active material according to the present invention can include a first coating layer formed on the surface of the secondary particles of the lithium transition metal oxide and on the surface of some or all of the plurality of primary particles, containing nickel and manganese, and having a layered structure.

[0057] Since the first coating layer has a layered structure and thus has a crystal structure such as that of a lithium transition metal oxide, it is considered that the stability and initial charge-discharge characteristics of the positive electrode active material can be improved compared to a coating layer having a spinel structure.

[0058] The first coating layer can be formed on the surface of the secondary particles of the lithium transition metal oxide and on the surface of some or all of the plurality of primary particles inside the secondary particles. The first coating layer can be formed so as to be interconnected and fill all the gaps between the primary particles. Preferably, the first coating layer is formed on the entire surface of the plurality of primary particles and can be formed so as to fill all the gaps between the primary particles.

[0059] The average thickness of the first coating layer can be 10 nm to 200 nm, preferably 30 nm to 100 nm. When the average thickness of the first coating layer satisfies the above range, the generation of cracks at the interface between the primary particles can be suppressed, and the stability and initial capacity can be improved.

[0060] The first coating layer according to the present invention can contain manganese and nickel. By containing the manganese and nickel, the first coating layer according to the present invention can have a layered structure, and thus, it is considered that the stability and initial charge-discharge characteristics of the positive electrode active material can be improved as compared with a coating layer having a spinel structure containing only manganese.

[0061] The first coating layer according to the present invention can contain lithium-nickel manganese oxide when lithium in the lithium transition metal oxide diffuses during heat treatment.

[0062] Specifically, the first coating layer can have a composition represented by the following Chemical Formula 2.

[0063] [Chemical Formula 2] Li x Ni y Mn z O 2

[0064] The x represents the molar ratio of lithium in the first coating layer, and can be 0.8 ≦ x ≦ 1.2, preferably 1.00 ≦ x ≦ 1.02.

[0065] Wherein y represents the molar ratio of nickel in the first coating layer, and 0.1 ≦ y ≦ 0.9, preferably 0.2 ≦ y ≦ 0.8.

[0066] Wherein z represents the molar ratio of manganese in the first coating layer, and 0.1 ≦ z ≦ 0.9, preferably 0.2 ≦ z ≦ 0.8.

[0067] Specifically, the molar ratio of nickel:manganese contained in the first coating layer can be 1:9 to 9:1, preferably 5:5 to 9:1, and more preferably 6:4 to 8:2. When the molar ratio of nickel:manganese contained in the first coating layer is less than 1:9, since the first coating layer exists in a spinel structure, sufficient initial charge and discharge capacity cannot be obtained. When the molar ratio of nickel:manganese contained in the first coating layer is greater than 9:1, the content of nickel is high and the capacity retention rate decreases, and the cycle characteristics may not be favorable.

[0068] The first coating layer according to the present invention can be contained in an amount of 1 part by weight to 5 parts by weight, preferably 1 part by weight to 3 parts by weight, and more preferably 1.5 parts by weight to 2.5 parts by weight with respect to 100 parts by weight of the lithium transition metal oxide. When the content of the first coating layer satisfies the above range, generation of cracks at the interface between primary particles can be suppressed, and stability and initial capacity can be improved.

[0069] The positive electrode active material according to the present invention can include a second coating layer containing boron, which is formed on the outer surface of the first coating layer. The first coating layer having the layered structure can improve the problem of deterioration of initial charge and discharge characteristics, which is a drawback of the coating having a spinel structure, but a phenomenon of deterioration of cycle characteristics appears. Therefore, by forming a second coating layer containing boron on the outer surface of the first coating layer having a layered structure, the cycle characteristics can be improved.

[0070] Specifically, the second coating layer according to the present invention can contain boron in the form of amorphous boron compounds such as lithium borate and borate. For example, the second coating layer can include LiBO 2 、Li 2 B 4 O 7 、LiB 3 O 5 、B 2 O 3 and the like. Different from crystalline compounds that can only form particulate and discontinuous coatings, the amorphous boron compound can form a continuous coating in the form of a film, an island, or a mixture thereof.

[0071] The second coating layer can be contained in an amount of 0.01 part by weight to 1 part by weight, preferably 0.05 part by weight to 0.5 part by weight, and more preferably 0.1 part by weight to 0.3 part by weight, based on 100 parts by weight of the lithium transition metal oxide. When the content of the second coating layer satisfies the above range, the cycle characteristics can be improved.

[0072] The content of lithium by-products remaining on the surface of the positive electrode active material according to the present invention can be 1% by weight or less, specifically 0.6% by weight or less, based on the total weight of the positive electrode active material.

[0073] Method for manufacturing positive electrode active material The method for manufacturing a positive electrode active material according to the present invention can include steps of preparing a lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated, and having a nickel content of 80 atm% or more among metal elements other than lithium; mixing the lithium transition metal oxide with a solution containing a nickel raw material substance and a manganese raw material substance, and then performing a first heat treatment to form a first coating layer containing nickel and manganese on the surface of the secondary particles of the lithium transition metal oxide and on the surface of some or all of the plurality of primary particles, the first coating layer having a layered structure; and mixing the lithium transition metal oxide having the first coating layer formed thereon with a boron raw material substance, and performing a second heat treatment to form a second coating layer containing boron on the outer surface of the first coating layer.

[0074] First, it is possible to prepare a lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated, and having a nickel content of 80 atm% or more among metal elements other than lithium.

[0075] The lithium transition metal oxide can be purchased as a commercially available product and used, or can be manufactured using a method for manufacturing a lithium transition metal oxide well-known in the art. For example, the lithium transition metal oxide can be manufactured by mixing a lithium raw material substance and a positive electrode active material precursor, and then firing them.

[0076] The positive electrode active material precursor can be represented by, for example, the following [Chemical Formula A] or [Chemical Formula B].

[0077] [Chemical Formula A] [Ni p Co q M 1 r M 2 s (OH) 2

[0078] [Chemical Formula B] [Ni p Co q M 1 rM 2 s O·OH

[0079] In the chemical formulas A and B, M 1 can be one or more selected from Mn and Al, and preferably can be Mn or a combination of Mn and Al.

[0080] In the chemical formulas A and B, M 2 can be one or more selected from the group consisting of Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y.

[0081] The p represents the molar ratio of nickel among the metal elements in the precursor, and can be 0.80 ≦ p < 1.0, 0.80 ≦ p ≦ 0.98, or 0.80 ≦ p ≦ 0.95.

[0082] The q represents the molar ratio of cobalt among the metal elements in the precursor, and can be 0 < q ≦ 0.2, 0 < q ≦ 0.15, or 0.01 ≦ q ≦ 0.10.

[0083] The r represents the molar ratio of the M 1 element among the metal elements in the precursor, and can be 0 < r ≦ 0.2, 0 < r ≦ 0.15, or 0.01 ≦ r ≦ 0.1.

[0084] The s represents the molar ratio of the M 2 element among the metal elements in the precursor, and can be 0 ≦ s < 0.1, or 0 ≦ s ≦ 0.05.

[0085] The lithium raw material substance is, for example, lithium carbonate (Li 2 CO 3 ), lithium hydroxide (LiOH·H 2 O), lithium hydroxide anhydride (LiOH), LiNO 3 , CH 3 COOLi, and Li 2 (COO) 2It can be at least one or more selected from the group consisting of, preferably lithium carbonate (Li 2 CO 3 ), lithium hydroxide (LiOH·H 2 O) or a combination thereof.

[0086] During the production of the positive electrode active material, the positive electrode active material precursor and the lithium raw material can be mixed so that the molar ratio of Li:transition metal is 1:1 to 1.3:1, preferably 1:1 to 1.1:1. When the mixing ratio of the positive electrode active material precursor and the lithium raw material satisfies the above range, the crystal structure of the positive electrode active material develops smoothly, and a positive electrode active material with excellent physical properties can be produced. If the content of the lithium raw material is too small, the crystal structure cannot develop properly. If it is too large, unreacted Li remains as a by-product, which may cause a decrease in capacity and gas generation.

[0087] On the other hand, the firing can be carried out at a temperature of 700°C to 1000°C, preferably 700°C to 900°C, more preferably 700°C to 850°C. When the firing temperature is less than 700°C, raw material substances may remain in the particles due to insufficient reaction, which may reduce the high-temperature stability of the battery, and the bulk density and crystallinity may decrease, resulting in a decrease in structural stability. On the other hand, when the firing temperature exceeds 1000°C, non-uniform growth of particles may occur, it may be difficult to crush the particles, and a decrease in capacity may occur.

[0088] The firing can be carried out for 5 hours to 24 hours, preferably 10 hours to 24 hours. When the firing time is less than 5 hours, the reaction time may be too short to obtain a highly crystalline positive electrode active material. When it exceeds 24 hours, the particle size may become too large, resulting in a decrease in production efficiency.

[0089] When producing a positive electrode active material by the production method according to the present invention, in the process of forming the first coating layer and the second coating layer, lithium by-products on the surface of the lithium transition metal oxide are consumed. Therefore, even when using a lithium transition metal oxide that has not undergone a water washing process, the residual amount of lithium by-products in the finally produced positive electrode active material is small. Specifically, the positive electrode active material according to the present invention can have a content of lithium by-products remaining on the surface of 1% by weight or less, specifically 0.6% by weight or less, based on the total weight of the positive electrode active material. Therefore, the step of preparing the lithium transition metal oxide of the present invention may not include a water washing process. Thus, according to the production method of the high-nickel positive electrode active material according to the present invention, the water washing process can be omitted, problems caused by the water washing process can be solved, and equipment and process costs can be reduced.

[0090] Next, after mixing the prepared lithium transition metal oxide with a solution containing a nickel raw material substance and a manganese raw material substance, it is heat-treated for the first time to form a first coating layer having a layered structure and containing nickel and manganese on the surface of the secondary particles of the lithium transition metal oxide and on the surface of some or all of the plurality of primary particles.

[0091] Specifically, the step of forming the first coating layer can be carried out, for example, by mixing the lithium transition metal oxide with a solution containing a nickel raw material substance and a manganese raw material substance, stirring it, filtering and separating it, and then performing the first heat treatment in an oxygen atmosphere.

[0092] In the step of forming the first coating layer, it is considered that the solution containing the nickel raw material substance and the manganese raw material substance penetrates into the interface of the primary particles inside the lithium transition metal oxide, and the first coating layer can be coated not only on the secondary particles but also on the interface of the primary particles. Thereby, in the positive electrode active material according to the present invention, the generation of cracks between the primary particles is suppressed, and the high-temperature cycle characteristics can be improved.

[0093] The nickel raw material substance and the manganese raw material substance can be mixed so as to be 0.5 parts by weight to 10 parts by weight, preferably 1 part by weight to 8 parts by weight, and more preferably 2 parts by weight to 8 parts by weight, respectively, based on 100 parts by weight of the lithium transition metal oxide. The amounts of the nickel raw material substance and the manganese raw material substance are adjusted so that the formed first coating layer contains 1 part by weight to 5 parts by weight based on 100 parts by weight of the lithium transition metal oxide in the positive electrode active material. When the contents of the nickel raw material substance and the manganese raw material substance satisfy the above range, the generation of cracks at the interface between the primary particles can be suppressed, and the stability and the initial capacity can be improved.

[0094] As the nickel raw material substance, for example, nickel acetate, nickel sulfate, nickel chloride, nickel nitrate, etc. can be used.

[0095] As the manganese raw material substance, for example, manganese acetate, manganese sulfate, manganese chloride, manganese nitrate, etc. can be used.

[0096] On the other hand, the solution containing the nickel raw material substance and the manganese raw material substance can be produced by dissolving the nickel raw material substance and the manganese raw material substance in a solvent such as water or ethanol.

[0097] After adding and mixing the lithium transition metal oxide into the solution containing the nickel raw material substance and the manganese raw material substance and then stirring, nickel and manganese contained in the solution adhere to the surface of the lithium transition metal oxide.

[0098] After filtering and separating this, it is heat-treated for the first time to obtain a lithium transition metal oxide powder having a first coating layer formed thereon.

[0099] Here, the filtration can be performed by putting filter paper in a filter flask and performing vacuum decompression, and the drying can be performed at 50°C to 200°C, preferably 80°C to 150°C, for 2 hours to 20 hours, preferably 5 hours to 15 hours.

[0100] The first heat treatment is performed to fix nickel and manganese on the surface of the lithium transition metal oxide to form a first coating layer, and can be performed at a temperature of 650°C to 850°C, preferably 650°C to 750°C. When the heat treatment temperature is less than 650°C, a first coating layer with a spinel structure rather than a layered structure can be obtained. On the other hand, when the heat treatment temperature exceeds 850°C, the strength of the particles increases excessively due to necking between the particles, and when performing subsequent processes, it is necessary to add a step of further pulverizing the particle mass densely, or there is a problem that the capacity decreases during charge and discharge during the manufacture of the secondary battery.

[0101] The first heat treatment can be performed for 1 hour to 10 hours, preferably 3 hours to 7 hours. When the heat treatment time is within the above range, an appropriate first coating layer can be formed, and the production efficiency can be improved.

[0102] Through the above process, when the first coating layer is formed, the lithium transition metal oxide with the first coating layer formed is mixed with a boron raw material substance and subjected to a second heat treatment to form a second coating layer containing boron on the outer surface of the first coating layer.

[0103] Specifically, the step of forming the second coating layer can be performed by a method of dry-mixing a boron raw material substance such as boric acid with the lithium transition metal oxide on which the first coating layer is formed and then performing a second heat treatment.

[0104] When the second coating layer is formed on the first coating layer, not only the phenomenon of deterioration of the cycle characteristics due to the formation of the first coating layer is improved, but also the migration barrier energy of lithium ions can be lowered by boron which is its constituent element. In addition, the generated second coating layer can suppress the direct reaction between the electrolyte and the lithium transition metal oxide, and the stability of the positive electrode active material and the life characteristics of the secondary battery using the positive electrode active material can be improved.

[0105] The boron raw material substance can be a powder containing amorphous compound particles containing boron. For example, boric acid, B 2 O 3 and the like can be mentioned.

[0106] The boron raw material substances can be mixed so as to be 0.0001 part by weight to 10 parts by weight, preferably 0.001 part by weight to 5 parts by weight, and more preferably 0.01 part by weight to 1 part by weight, respectively, based on 100 parts by weight of the lithium transition metal oxide. The amount of the boron raw material substance is an amount adjusted so that the formed second coating layer contains 0.01 part by weight to 1 part by weight based on 100 parts by weight of the lithium transition metal oxide in the positive electrode active material. When the content of the boron raw material substance satisfies the above range, the direct reaction between the electrolytic solution and the lithium transition metal oxide can be suppressed, and the stability of the positive electrode active material and the life characteristics of the secondary battery using the positive electrode active material can be improved.

[0107] The second heat treatment is performed to solidify the boron-containing compound adhered to the outer surface of the first coating layer of the lithium transition metal oxide on which the first coating layer is formed to form the second coating layer, and can be performed at a temperature of 150°C to 500°C, preferably 300°C to 400°C. When the heat treatment temperature is less than 150°C, since it is below the melting point of the boron-containing compound, coating is impossible. On the other hand, when the heat treatment temperature exceeds 500°C, there is a problem that the boron layer crystallizes and the coating is not well performed.

[0108] The second heat treatment can be performed for 1 hour to 10 hours, preferably 3 hours to 7 hours. When the heat treatment time is within the above range, an appropriate second coating layer can be formed, and the production efficiency can be improved.

[0109] On the other hand, the second heat treatment is preferably performed in an oxygen atmosphere.

[0110] By the second heat treatment, a second coating layer containing boron is formed on the outer surface of the first coating layer. Here, the second coating layer can contain boron in the form of an amorphous boron compound such as lithium borate or boric oxide. For example, the second coating layer can contain LiBO 2 、Li 2 B 4 O 7 、LiB 3 O 5 、B 2 O 3 and so on.

[0111] Positive electrode The positive electrode according to the present invention includes the positive electrode active material of the present invention described above. Specifically, the positive electrode includes 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 includes the positive electrode active material according to the present invention. Since the positive electrode active material has been described above, specific description is omitted, and only the remaining configuration will be specifically described below.

[0112] The positive electrode current collector can include a metal with high conductivity, and the positive electrode active material layer can easily adhere thereto. At this time, it is not particularly limited as long as it is not reactive within the voltage range of the battery. The positive electrode current collector can be, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. Further, the positive electrode current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0113] The positive electrode active material layer can selectively include a conductive material and a binder, if necessary, together with the positive electrode active material.

[0114] Here, the positive electrode active material can be contained in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive electrode active material layer. When contained within the above content range, excellent capacity characteristics can be exhibited.

[0115] The conductive material is used to impart conductivity to the electrode and can be used without particular limitation as long as it does not cause a chemical change and has electron conductivity in the configured battery. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers 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; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds can be used. The conductive material can be contained in an amount of 0.1% to 15% by weight based on the total weight of the positive electrode active material layer.

[0116] The binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the current collector. Specific examples 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, and polymers in which hydrogen thereof is substituted with Li, Na, or Ca, or various copolymers thereof, etc. One of these alone or a mixture of two or more thereof can be used. The binder can 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.

[0117] The above positive electrode can be manufactured by the usual positive electrode manufacturing method except that the above positive electrode active material is used. Specifically, the positive electrode is obtained by applying a composition for forming a positive electrode active material layer, which is prepared by dissolving or dispersing the above positive electrode active material and, optionally, a binder, a conductive material, and a dispersant in a solvent, onto a positive electrode current collector, followed by drying and rolling, or by casting the composition for forming a positive electrode active material layer on another support and then laminating the film obtained by peeling off this support onto the positive electrode current collector.

[0118] As the solvent, it can be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone or water, etc. Among these, one kind alone or a mixture of two or more kinds can be used. The amount of the solvent used is considered in view of the coating thickness of the slurry and the production yield, so as to dissolve or disperse the positive electrode active material, conductive material, binder and dispersant, and then, when coating for the production of the positive electrode, it is sufficient if it has a viscosity that can show excellent thickness uniformity.

[0119] Electrochemical device Next, the electrochemical device according to the present invention will be described. The electrochemical device according to the present invention includes the positive electrode of the present invention described above. Specifically, the electrochemical device can be a battery, a capacitor, etc., and more specifically, it can be a lithium secondary battery.

[0120] The lithium secondary battery specifically includes a positive electrode, a negative electrode located opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is as described above, specific description is omitted, and hereinafter, only the remaining configurations will be specifically described.

[0121] In addition, the lithium secondary battery can selectively further include a battery container for housing the electrode assembly of the positive electrode, negative electrode and separator, and a sealing member for sealing the battery container.

[0122] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0123] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those obtained by surface treatment of copper or stainless steel with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. Further, the negative electrode current collector can usually have a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0124] The negative electrode active material layer selectively contains a binder and a conductive material together with the negative electrode active material.

[0125] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, 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, or Al alloys; SiO β (0 < β < 2), SnO 2Metal oxides such as vanadium oxides and lithium vanadium oxides that can be doped and undoped with lithium; or composites containing the metallic compound and a carbonaceous material such as Si-C composites or Sn-C composites, etc. may be mentioned, and mixtures of any one or two or more of these can be used. Further, as the negative electrode active material, a thin film of metallic lithium can also be used. Further, as the carbonaceous material, both low-crystalline carbon and high-crystalline carbon can be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, Mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0126] The negative electrode active material can be contained in an amount of 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0127] The binder is a component that facilitates the bonding between the conductive material, the active material, and the current collector, and can usually be added in an amount of 0.1% by weight to 10% by weight 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, various copolymers thereof, etc.

[0128] The conductive material is a component for further improving the conductivity of the negative electrode active material, and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

[0129] The negative electrode is produced by applying and drying a composition for forming a negative electrode active material layer, which is 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, or by casting the composition for forming a negative electrode active material layer on another support and then laminating a film obtained by peeling the support on the negative electrode current collector.

[0130] On the one hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any separator that can be used in a lithium secondary battery can be used without particular limitation. In particular, those with low resistance to ion migration of the electrolyte and excellent moisture retention ability of the electrolyte solution are preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, for ensuring heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and optionally, it can be used as a single-layer or multilayer structure.

[0131] Also, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used during the manufacture of lithium secondary batteries.

[0132] Specifically, the electrolyte can contain an organic solvent and a lithium salt.

[0133] As the organic solvent, any substance can be used without particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. 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 or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), , E ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, aromatic ring, or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can enhance the charge and discharge performance of the battery, and a linear carbonate compound with low viscosity (e.g., ethylmethylcarbonate, dimethylcarbonate, or diethylcarbonate) is more preferred.

[0134] The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, as the anion of the lithium salt, F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , CF 3 CF 2 , SO 3 - , (CF 3 , SO 2 ) 2 , N - , (FSO 2 ) 2 , N - , CF 3 CF 2 (CF 3 ) 2 , CO - , (CF 3 , SO 2 ) 2 , CH - , (SF 5 ) 3 , C - , (CF 3 , SO 2 ) 3 , C - , CF 3 (CF 2 ) 7 , SO 3 - , CF 3 , CO 2 - , CH 3 , CO 2 - , SCN - and (CF 3 CF 2 , SO 2 ) 2 , N - can be one or more selected from the group consisting of, and the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF4 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiCl, LiI, or LiB(C 2 O 4 ) 2 etc. can be used. The concentration of the lithium salt is preferably in the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0135] In addition to the constituent components of the electrolyte, for the purpose of improving the life characteristics of the battery, suppressing the capacity reduction of the battery, improving the discharge capacity of the battery, etc., the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexa Sali minic acid triamide, nitrobenzene derivatives, sulfur, quinonimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride. At this time, the additive can be contained in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

[0136] As described above, since the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, it is useful in portable devices such as mobile phones, notebook computers, digital cameras, and the like, and in the field of electric vehicles such as hybrid electric vehicles (HEV).

[0137] Therefore, according to another embodiment of the present invention, there are provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

[0138] The battery module or battery pack can be used as a power source for any one or more medium to large-sized devices such as power tools; electric vehicles including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); or power storage systems.

[0139] The outer shape of the lithium secondary battery of the present invention is not particularly limited, and can be, for example, a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0140] The lithium secondary battery according to the present invention can be preferably used not only as a battery cell used as a power source for a small device, but also as a unit battery in a medium to large-sized battery module including a large number of battery cells.

[0141] Examples of the medium to large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0142] Hereinafter, embodiments of the present invention will be described in detail so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0143] Example 1 LiNi 0.86 Co 0.05 Mn 0.07 Al 0.02 O 2 A lithium transition metal oxide having the composition of and having a form of secondary particles in which a plurality of primary particles are aggregated was prepared.

[0144] 50 g of the lithium transition metal oxide was added to a solution in which 3.96 g of nickel nitrate and 1.06 g of manganese nitrate were dissolved in 15.0 g of ultrapure water (DI water) (the molar ratio of nickel:manganese in the solution = 8:2), mixed at 100 °C for 1 hour, and then dried in an oven at 130 °C. Next, the dried product was first heat-treated at 750 °C in an oxygen atmosphere to form a first coating layer.

[0145] 30 g of the product with the first coating layer formed and 0.18 g of boric acid powder were mixed, then second heat-treated at 300 °C for 5 hours in an air atmosphere to form a second coating layer, and then the sintered body was pulverized and classified to obtain a positive electrode active material for a lithium secondary battery.

[0146] Example 2 A positive electrode active material was produced in the same manner as in Example 1, except that the lithium transition metal oxide was added to a solution in which 2.97 g of nickel nitrate and 2.12 g of manganese nitrate were dissolved in 15.0 g of ultrapure water (DI water) (the molar ratio of nickel:manganese in the solution = 6:4) to form a first coating layer.

[0147] Example 3 A positive electrode active material was produced in the same manner as in Example 1, except that 1.98 g of nickel nitrate and 3.18 g of manganese nitrate were dissolved in 15.0 g of ultrapure water (DI water) (molar ratio of nickel:manganese in the solution = 4:6), and the lithium transition metal oxide was added thereto to form a first coating layer.

[0148] Example 4 A positive electrode active material was produced in the same manner as in Example 1, except that 0.99 g of nickel nitrate and 4.24 g of manganese nitrate were dissolved in 15.0 g of ultrapure water (DI water) (molar ratio of nickel:manganese in the solution = 2:8), and the lithium transition metal oxide was added thereto to form a first coating layer.

[0149] Comparative Example 1 A positive electrode active material was produced in the same manner as in Example 1, except that only 5.29 g of manganese nitrate was dissolved in 15.0 g of ultrapure water (DI water), and the lithium transition metal oxide was added thereto to form a first coating layer.

[0150] <Analysis of the Structure of the First Coating Layer> Figure 1 shows the results of EPMA (Electron Probe Micro-Analysis) for particles of a lithium transition metal oxide in the form of secondary particles aggregated from a plurality of primary particles after forming the first coating layer according to Example 1 (before forming the second coating layer). In Figure 1, a region rich in manganese (Mn-rich) was observed at the interface of the primary particles. Thus, it can be confirmed that the raw material substances introduced to form the first coating layer were coated at the interface of the primary particles to form the first coating layer.

[0151] Figure 2 is a TEM (Transmission Electron Microscope) image of the particles after forming the first coating layer according to Example 1 (before forming the second coating layer). The image represented by 1 in Figure 2 is an image of the lithium transition metal oxide, and the image represented by 2 in Figure 2 is an image of the first coating layer. From the images represented by 1 and 2 in Figure 2, since FFT (Fast Fourier Transfrom) patterns observed in a layered structure were observed in both cases, it was confirmed that both the lithium transition metal oxide and the first coating layer of Example 1 have a layered structure.

[0152] Figure 3 is a TEM (Transmission Electron Microscope) image of the particles after forming the first coating layer according to Comparative Example 1 on the lithium transition metal oxide which is a secondary particle (before forming the second coating layer). A in Figure 3 is an image of the first coating layer. In the image represented by A in Figure 3, an FFT pattern of a spinel structure was observed. That is, it was confirmed that the first coating layer of Comparative Example 1 has a spinel structure.

[0153] <Analysis of Whether the Second Coating Layer Contains Boron> Figure 4 shows the XPS (X-ray Photoelectron Spectroscopy) results for the cathode active material on which the first coating layer and the second coating layer were formed according to Example 1. As shown in the graph of Figure 4, it was confirmed that boron is contained in the second coating layer located on the outermost surface of the cathode active material.

[0154] <Measurement of the Particle Sizes of Primary Particles and Secondary Particles> Using SEM, the average particle size of the primary particles of the lithium transition metal oxide used in Examples 1 to 4 and Comparative Example 1 was measured, and using the laser diffraction method, the average particle size (D 50 ) of the secondary particles of the lithium transition metal oxide used in Examples 1 to 4 and Comparative Example 1 was measured.

[0155] The measurement result shows that the average particle size of the primary particles is 0.15 μm, and the average particle size (D 50 ) of the secondary particles was 10 μm.

[0156] <Measurement of the Content of the Second Coating Layer> ICP-MS (Inductively Coupled Plasma-Mass Spectrometer) analysis was performed to measure the content of boron contained in the second coating layer of Example 1.

[0157] As a result of calculating the content of lithium borate or borate contained in the second coating layer from the measured boron content, in Example 1, the content of the second coating layer was calculated to be 0.1% by weight based on 100 parts by weight of the lithium transition metal oxide.

[0158] <Measurement of the Average Thickness of the First Coating Layer> The thickness of the first coating layer of Example 1 was measured using a TEM image. Specifically, three arbitrary locations of the positive electrode active material of Example 1 were observed by TEM to determine the thickness of the first coating layer, and the average value of these was calculated.

[0159] The measurement result shows that in Example 1, the average thickness of the first coating layer was measured to be 80 nm.

[0160] Experimental Example 1 - Measurement of the Content of Lithium By-Products Remaining on the Surface of the Positive Electrode Active Material The content of lithium by-products remaining on the surface of each positive electrode active material produced in Examples 1 to 4 was measured.

[0161] Specifically, 5 g of the positive electrode active materials produced in Examples 1 to 4 and Comparative Example 1 were stirred with 100 mL of ultrapure water for 5 minutes, filtered, and then the filtered solution was titrated with 0.1 N HCl. After obtaining the titration curve using a Metrohm pH meter, from the titration curve, LiOH and Li 2 CO 3The equivalent point was determined, and the content of lithium by-products remaining on the surface of the positive electrode active material was calculated. The results are shown in Table 1 below.

[0162] For comparison, the content of lithium by-products remaining on the surface of the lithium transition metal oxide before forming the first coating layer in Examples 1 to 4 is also shown in Table 1.

[0163]

Table 1

[0164] Referring to Table 1, it can be confirmed that the positive electrode active materials of Examples 1 to 4 had sufficiently reduced residual lithium despite not having undergone a water washing process.

[0165] Experimental Example 2 - Evaluation of Initial Discharge Capacity 92.5% by weight of each of the positive electrode active materials produced in Examples 1 to 4 and Comparative Example 1, 3.5% by weight of carbon black as a conductive material, and 4% by weight of polyvinylidene fluoride as a binder were mixed in an N-methylpyrrolidone solvent to produce a positive electrode slurry. After applying the positive electrode slurry to one side of an aluminum current collector, it was dried at 130 °C and then rolled to produce a positive electrode.

[0166] Li metal was used as the counter electrode for the positive electrode, and an electrode assembly was produced with a porous PE separator interposed between the positive electrode and the negative electrode. This was placed inside a case, and an electrolytic solution in which ethylene carbonate (EC) / ethylmethylcarbonate (EMC) / diethylcarbonate (DEC) were mixed at a volume ratio of 3:4:3 was injected to produce a coin-type half cell.

[0167] For each of the batteries manufactured as described above, after charging to 4.25 V at a constant current of 0.1C at 25 °C, discharging was performed at a constant current of 0.1C to 3.00 V, and the initial discharge capacity was measured. The results are shown in Table 2 below.

[0168]

Table 2

[0169] Referring to Table 2, it can be confirmed that the secondary batteries applying the cathode active materials of Examples 1 to 4 have a higher initial discharge capacity than the secondary battery applying the cathode active material of Comparative Example 1.

[0170] Experimental Example 3 - Evaluation of Cycle Characteristics Regarding each of the batteries manufactured in the above Experimental Example 2, charging up to 4.25 V at a constant current of 0.33 C at 45°C and discharging at a constant current of 0.33 C to 3.00 V were taken as one cycle, and after performing 30 cycles of charge and discharge, the capacity retention rate with respect to the initial capacity after 30 cycles was measured. The results are shown in Table 3 below.

[0171]

Table 3

[0172] Referring to Table 3, it can be confirmed that the secondary batteries applying the cathode active materials of Examples 1 to 4 are superior in high-temperature cycle characteristics to the secondary battery applying the cathode active material of Comparative Example 1.

Claims

1. A lithium transition metal oxide in the form of secondary particles aggregated from a plurality of primary particles, wherein the content of nickel among metal elements other than lithium is 80 atm% or more, and a first coating layer formed on the surface of the secondary particles of the lithium transition metal oxide and on the surface of some or all of the plurality of primary particles, containing nickel and manganese and having a layered structure, and a second coating layer formed on the outer surface of the first coating layer and containing boron, and the molar ratio of nickel:manganese contained in the first coating layer is 5:5 to 9:1, and the first coating layer has a composition represented by the following Chemical Formula 2, a positive electrode active material: 【Chemical Formula 2】 Li x [Ni z Mn w ] y O 2 In the Chemical Formula 2, 0.8 ≦ x ≦ 1.2, 0.8 ≦ y ≦ 1.2, 0.1 ≦ z ≦ 0.9, 0.1 ≦ w ≦ 0.

9.

2. The lithium transition metal oxide has a composition represented by the following Chemical Formula 1, the positive electrode active material according to Claim 1. 【Chemical Formula 1】 Li ａ Ni ｂ Co ｃ M １ ｄ M ２ ｅ O ２ In the Chemical Formula 1, M １ is one or more selected from Mn and Al, M ２ is one or more selected from the group consisting of Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y, 0.9 ≦ a ≦ 1.3, 0.8 ≦ b < 1.0, 0 < c ≦ 0.2, 0 < d ≦ 0.2, 0 ≦ e ≦ 0.

1.

3. The average particle size of the primary particles is 0.1 μm to 0.5 μm, the positive electrode active material according to Claim 1 or 2.

4. The average particle size (D ５０ ) of the secondary particles is 8 μm to 15 μm. The positive electrode active material according to any one of claims 1 to 3.

5. The average thickness of the first coating layer is 10 nm to 200 nm, the positive electrode active material according to any one of Claims 1 to 4.

6. The first coating layer is contained in an amount of 1 part by weight to 5 parts by weight based on 100 parts by weight of the lithium transition metal oxide, the positive electrode active material according to any one of Claims 1 to 5.

7. The second coating layer contains one or more selected from the group consisting of lithium borate and borate, the positive electrode active material according to any one of Claims 1 to 6.

8. The second coating layer is contained in an amount of 0.01 part by weight to 1 part by weight based on 100 parts by weight of the lithium transition metal oxide, the positive electrode active material according to any one of Claims 1 to 7.

9. The content of lithium by-products remaining on the surface is 1% by weight or less based on the total weight of the positive electrode active material, and the lithium by-products remaining on the surface are Li 2 CO 3 and LiOH, the positive electrode active material according to any one of Claims 1 to 8.

10. After mixing a lithium raw material substance and a cathode active material precursor, firing is performed to obtain a lithium transition metal oxide in the form of secondary particles in which a plurality of primary particles are aggregated, and the content of nickel among metal elements other than lithium is 80 atm% or more. The steps of preparing are as follows: After mixing the lithium transition metal oxide with a solution containing a nickel raw material substance and a manganese raw material substance, performing a first heat treatment to form a first coating layer having a layered structure and containing nickel and manganese on the surface of the secondary particles of the lithium transition metal oxide and on the surface of some or all of the plurality of primary particles. The method includes the steps of mixing the lithium transition metal oxide having the first coating layer formed thereon with a boron raw material substance and performing a second heat treatment to form a second coating layer containing boron on the outer surface of the first coating layer. The step of preparing the lithium transition metal oxide does not include a water washing step. A method for manufacturing a cathode active material, wherein the molar ratio of nickel to manganese contained in the first coating layer is 5:5 to 9:

1.

11. The method for manufacturing a cathode active material according to claim 10, wherein the nickel raw material substance is nickel nitrate and the manganese raw material substance is manganese nitrate.

12. The method for manufacturing a cathode active material according to claim 10 or 11, wherein the first heat treatment is performed at 650°C to 850°C.

13. The method for manufacturing a cathode active material according to any one of claims 10 to 12, wherein the boron raw material substance is boric acid.

14. The method for manufacturing a cathode active material according to any one of claims 10 to 13, wherein the second heat treatment is performed at 150°C to 500°C.

15. A cathode comprising the cathode active material according to any one of claims 1 to 9.

16. A lithium secondary battery comprising the cathode according to claim 15, an anode, a separator interposed between the cathode and the anode, and an electrolyte.

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