Positive active material, method of preparing same, and rechargeable lithium battery including same

Abstract

Disclosed are a positive active material for a rechargeable lithium battery, a method of preparing the same, and a rechargeable lithium battery including the same. A positive electrode active material for a rechargeable lithium battery includes a lithium nickel-based metal composite oxide, in which the positive electrode active material includes secondary particles in which a plurality of primary particles are aggregated, the positive electrode active material includes a first boron coating portion present on a surface of the secondary particles and a second boron coating portion present on a surface of the primary particles within the secondary particles, and a weight of the first boron coating portion is greater than a weight of the second boron coating portion.

Description

[0001] This application is a divisional application of the invention patent application with the application date of November 9, 2021, the application number of 202111318837.7, and the invention name of "Cathode active material, method for preparing the same, and rechargeable lithium battery including the same". TECHNICAL FIELD

[0002] Disclosed are a cathode active material for a rechargeable lithium battery, a method for preparing the same, and a rechargeable lithium battery including the same. BACKGROUND

[0003] Portable information devices, such as mobile phones, notebook computers, and smart phones, etc., or electric vehicles have used rechargeable lithium batteries having high energy density and easy portability as a driving power source. Recently, active research has been conducted to use rechargeable lithium batteries having high energy density as a driving power source or an energy storage power source for a hybrid vehicle or an electric vehicle.

[0004] Various cathode active materials have been researched to achieve the application purpose of rechargeable lithium batteries. Among them, the use of nickel-based cathode active materials achieving high capacity is increasing. In particular, in order to increase the capacity of the battery, research to increase the nickel content in lithium composite metal oxides is being conducted.

[0005] However, as the nickel content increases, the capacity is considerably deteriorated due to an increase in a cation mixing phenomenon in which Ni2+ ions occupy lithium sites, or the battery cycle life is deteriorated due to impurities such as NiO hindering the diffusion of lithium ions. In addition, there can be a battery safety problem due to a side reaction between impurities on the surface of the cathode active material and the electrolyte. Therefore, methods to improve the capacity characteristics and cycle life characteristics of the battery, and to increase the nickel content in lithium composite metal oxides while securing the safety of the battery, are being actively researched. SUMMARY

[0006] Provided are a cathode active material for a rechargeable lithium battery having improved cycle life characteristics while achieving high capacity, a method for preparing the same, and a rechargeable lithium battery including the same.

[0007] In an embodiment, a cathode active material for a rechargeable lithium battery includes a lithium nickel-based metal composite oxide, wherein the cathode active material includes secondary particles in which a plurality of primary particles are aggregated, the cathode active material includes a first boron coating portion present on the surface of the secondary particles and a second boron coating portion present on the surface of the primary particles within the secondary particles, and the weight of the first boron coating portion is greater than the weight of the second boron coating portion.

[0008] In another embodiment, a method for preparing a positive electrode active material for a rechargeable lithium battery includes mixing a nickel-based metal composite hydroxide, a lithium raw material, and a boron raw material, and heat-treating the mixture to obtain the positive electrode active material.

[0009] In another embodiment, a rechargeable lithium battery is provided, comprising a positive electrode containing a positive electrode active material, a negative electrode, and an electrolyte.

[0010] The positive electrode active material for rechargeable lithium batteries manufactured according to the embodiments, and the rechargeable lithium batteries including the same, can exhibit excellent cycle life characteristics while achieving high capacity. Attached Figure Description

[0011] Figure 1 This is a schematic view showing a rechargeable lithium battery according to an embodiment.

[0012] Figure 2 The diagram schematically illustrates the voltage versus capacity curves during the initial discharge of the battery cells of Comparative Example 1 and Examples 1 to 3.

[0013] Figure 3 The diagram schematically illustrates the voltage versus capacity curves during the initial discharge of the battery cells in Comparative Examples 2 to 5.

[0014] <Symbol Description>

[0015] 100: Rechargeable lithium battery; 112: Negative electrode

[0016] 113: Diaphragm; 114: Positive electrode

[0017] 120: Battery casing; 140: Sealing element Detailed Implementation

[0018] Specific implementations will be described in detail below so that those skilled in the art can readily implement them. However, this disclosure may be embodied in many different forms and is not to be construed as limited to the exemplary implementations set forth herein.

[0019] The terminology used herein is for descriptive purposes only and is not intended to limit the invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0020] As used in this article, “combination of” means mixtures of components, laminates, complexes, copolymers, alloys, blends, and reaction products, etc.

[0021] In this document, it should be understood that terms such as “comprises,” “includes,” or “have” are intended to indicate the features, quantities, steps, elements, or combinations thereof presented, but do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0022] In the accompanying drawings, for clarity, the thicknesses of layers, films, plates, regions, etc., are enlarged, and the same reference numerals are used throughout the drawings to label the same elements as in the specification. It will be understood that when an element, such as a layer, film, region, or substrate, is referred to as being "on" another element, it may be directly on the other element or an intervening element may be present. Conversely, when an element is referred to as being "directly on" another element, no intervening element is present.

[0023] In addition, the term "layer" in this article includes not only the shape formed on the entire surface when viewed from a plan view, but also the shape formed on a portion of the surface.

[0024] Alternatively, the average particle size can be measured using methods well known to those skilled in the art, for example, by a particle size analyzer, or by analysis using a transmission electron microscope or scanning electron microscope. Optionally, the average particle size value may be obtained by measuring using a dynamic light scattering method, performing data analysis, calculating the number of particles for each particle size range, and thus calculating the average particle size. Unless otherwise defined, the average particle size may mean the diameter (D50) of the particles having a cumulative volume of 50% of the particle size distribution.

[0025] Positive electrode active material

[0026] In one embodiment, the positive electrode active material for a rechargeable lithium-ion battery comprises a lithium-nickel metal composite oxide, wherein the positive electrode active material includes secondary particles in which multiple primary particles are aggregated, and the positive electrode active material includes a first boron coating portion present on the surface of the secondary particles and a second boron coating portion present on the surface of the primary particles within the secondary particles, wherein the weight of the first boron coating portion is greater than the weight of the second boron coating portion. Such a positive electrode active material can exhibit improved cycle life characteristics while achieving high capacity.

[0027] The second boron coating is partially present within the interior portion of the secondary particles rather than on the surface, and it is coated along the interface between the primary particles within the secondary particles; therefore, it can be described as being coated at the grain boundaries. Here, the interior portion of the secondary particles means the entire interior except for the surface, for example, it could mean the entire interior from a depth of approximately 2 μm from the outer surface. It can also be described as the portion that distilled water cannot reach when the secondary particles of the positive electrode active material are rinsed with distilled water.

[0028] Conventionally, when coating boron onto a positive electrode active material, a method is typically used where the boron raw material is heat-treated by wet or dry mixing after the preparation of a lithium metal composite oxide. However, in this case, boron acts as a surface resistivity of the positive electrode active material, degrading capacity and cycle life. On the other hand, according to an embodiment, when a lithium source is added to a nickel-based metal composite hydroxide, which serves as a precursor for the positive electrode active material, boron raw material is added together, and the mixture is heat-treated to obtain a positive electrode active material, wherein boron is coated on the surface of the positive electrode active material and at its internal grain boundaries. By simultaneously coating appropriate amounts of boron at the grain boundaries within the positive electrode active material and on its surface, boron no longer acts as a resistivity, ensuring the structural stability of the positive electrode active material, and the initial discharge capacity of the battery is not reduced while improving cycle life characteristics.

[0029] The first boron coating portion and the second boron coating portion each include a boron-containing compound, specifically boron oxide, lithium boron oxide, or combinations thereof, such as B2O2, B2O3, B4O3, B4O5, LiBO2, Li2B4O7, Li3BO3, or combinations thereof.

[0030] Based on the total amount of the first boron coating portion and the second boron coating portion, the amount of the second boron coating portion can be from about 2 wt% to about 30 wt%, and specifically from about 2 wt% to about 20 wt%, from about 2 wt% to about 15 wt%, from about 2 wt% to about 10 wt%, or from about 5 wt% to about 20 wt%, and the amount of the first boron coating portion can be from about 70 wt% to about 98 wt%, from about 85 wt% to about 98 wt%, from about 90 wt% to about 98 wt%, or from about 80 wt% to about 95 wt%. For example, the weight ratio of the first boron coating portion to the second boron coating portion can be from about 70:30 to about 98:2, for example, from about 80:20 to about 95:5. When the weights of the first boron coating portion and the second boron coating portion are as described, boron does not act as a resistor in the positive electrode active material and can be used to improve performance, and the positive electrode active material including such a boron coating portion can exhibit improved cycle life characteristics while achieving high capacity.

[0031] Based on the positive electrode active material, the content of the first boron coating portion can be, for example, about 200 ppm to about 5000 ppm, about 300 ppm to about 5000 ppm, or about 500 ppm to about 4000 ppm. Based on the positive electrode active material, the content of the second boron coating portion can be, for example, about 10 ppm to about 500 ppm, about 10 ppm to about 400 ppm, about 10 ppm to about 300 ppm, or about 30 ppm to about 200 ppm, but is not limited thereto. When the contents of the first and second boron coating portions based on the positive electrode active material are as described above, boron does not act as a resistor in the positive electrode active material, and the positive electrode active material including it can exhibit high capacity and excellent cycle life characteristics.

[0032] In this article, ppm can be a unit expressed in weight, that is, 1 ppm can mean 10 -4 Therefore, based on the positive electrode active material, the content of the first boron coating portion may be about 0.02 wt% to about 0.5 wt%, about 0.03 wt% to about 0.5 wt%, or about 0.05 wt% to about 0.4 wt%, and based on the positive electrode active material, the content of the second boron coating portion may be about 0.001 wt% to about 0.05 wt%, about 0.001 wt% to about 0.04 wt%, about 0.001 wt% to about 0.03 wt%, or about 0.003 wt% to about 0.02 wt%.

[0033] Based on 100 mol% of the positive electrode active material, the total amount of the first boron coating portion and the second boron coating portion can be from about 0.1 mol% to about 5 mol%, for example, from about 0.1 mol% to about 4 mol%, from about 0.1 mol% to about 3 mol%, from about 0.1 mol% to about 2.9 mol%, from about 0.1 mol% to about 2.5 mol%, from about 0.1 mol% to about 2 mol%, from about 0.1 mol% to about 1.5 mol%, from about 0.1 mol% to about 1.3 mol%, or from about 0.5 mol% to about 1.3 mol%.

[0034] When the total amount of the first boron coating and the second boron coating is not within the predetermined range, the initial discharge capacity can be reduced and the cycle life characteristics can be degraded. In particular, if the amount of the first boron coating on the surface of the secondary particles of the positive electrode active material is too high, the initial discharge capacity will be greatly reduced because boron acts as a resistor.

[0035] Lithium-nickel metal composite oxides can be, for example, high-nickel metal oxides with a high nickel content. For instance, in lithium-nickel metal composite oxides, based on the total amount of metals other than lithium, the nickel content can be greater than or equal to about 60 mol%, greater than or equal to about 70 mol%, greater than or equal to about 80 mol%, greater than or equal to about 83 mol%, greater than or equal to about 90 mol%, or greater than or equal to about 92 mol%, and less than or equal to about 99.9 mol%, less than or equal to about 99 mol%, or less than or equal to about 98 mol%. Therefore, high-capacity batteries can be achieved when the nickel content is high.

[0036] However, as the nickel content increases, due to Ni 2+ The mixing of cations occupying lithium sites also increases, thus significantly reducing capacity. Alternatively, lithium-ion diffusion may be hindered by impurities such as NiO, leading to a deterioration in battery cycle life. Furthermore, battery safety issues arise due to side reactions between impurities on the surface of the positive electrode active material and the electrolyte. To address these problems, when boron is coated only on the surface of the active material using conventional methods, boron acts as a resistor and actually reduces capacity and worsens cycle life. In contrast, even when using high-nickel materials, because the positive electrode active material according to the embodiment is coated with an appropriate amount of boron on the surface of the secondary particles of the positive electrode active material and to the grain boundaries therein, the problems caused by high nickel concentration can be improved, achieving high capacity while improving cycle life characteristics without deteriorating the initial discharge capacity.

[0037] Lithium-nickel metal composite oxides can be represented, for example, by chemical formula 1.

[0038] [Chemical Formula 1]

[0039] Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O2

[0040] In chemical formula 1, 0.9 ≤ a1 ≤ 1.8, 0.6 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.4, and M 1 and M 2 Each is independently selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and their combinations.

[0041] In Chemical Formula 1, x1 and y1 can be, for example, within the following ranges: 0.65 ≤ x1 < 1 and 0 ≤ y1 ≤ 0.35, 0.70 ≤ x1 < 1 and 0 ≤ y1 ≤ 0.30, 0.80 ≤ x1 < 1 and 0 ≤ y1 ≤ 0.20, or 0.92 ≤ x1 < 1 and 0 ≤ y1 ≤ 0.08. In this case, the positive electrode active material including the same can achieve high capacity and exhibit excellent battery characteristics.

[0042] As a specific example, the lithium nickel-based metal composite oxide can be represented by Chemical Formula 2 or Chemical Formula 3.

[0043] [Chemical Formula 2]

[0044] Li a2 Ni x2 Co y2 Al z2 M 3 1-x2-y2-z2 O2

[0045] In Chemical Formula 2, 0.9 ≤ a2 ≤ 1.8, 0.6 ≤ x2 < 1, 0 < y2 < 0.4, 0 < z2 < 0.4, and M 3 is selected from B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

[0046] [Chemical Formula 3]

[0047] Li a3 Ni x3 Co y3 M 4 1-x3-y3 O2

[0048] In Chemical Formula 3, 0.9 ≤ a3 ≤ 1.8, 0.6 ≤ x3 < 1, 0 < y3 ≤ 0.4, and M 4 is selected from B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

[0049] When the lithium nickel-based metal composite oxide is a compound represented by Chemical Formula 2 or Chemical Formula 3, the effect of improving battery performance according to the first boron coating portion and the second boron coating portion can be higher, that is, while achieving high capacity, the initial discharge capacity is not reduced, and the effect of improving the cycle life characteristics can be obtained.

[0050] In Chemical Formula 2, x2, y2, and z2 can, for example, be in the following ranges: 0.70 ≤ x2 < 1, 0 < y2 < 0.30, and 0 < z2 < 0.30; 0.8 ≤ x2 < 1, 0 < y2 < 0.2, and 0 < z2 < 0.2; or 0.93 ≤ x2 < 1, 0 < y2 < 0.07, and 0 < z2 < 0.07. Additionally, in Chemical Formula 3, x3 and y3 can, for example, be in the following ranges: 0.70 ≤ x3 < 1 and 0 < y3 ≤ 0.30; 0.8 ≤ x3 < 1 and 0 < y3 ≤ 0.2; or 0.90 ≤ x3 ≤ 0.99 and 0.01 ≤ y3 ≤ 0.10.

[0051] In an embodiment, a method for preparing a positive electrode active material for a rechargeable lithium battery includes mixing a nickel-based metal composite hydroxide, a lithium raw material, and a boron raw material to obtain a mixture, and heat-treating the mixture to obtain the positive electrode active material described above.

[0052] Conventionally, when boron is coated on a positive electrode active material, a lithium raw material is usually mixed with a nickel-based metal composite hydroxide, and then the mixture is heat-treated to prepare a lithium nickel-based metal composite oxide, and the boron raw material is mixed with it by a wet or dry method, and then heat-treatment is performed again. In this case, only the surface of the positive electrode active material is coated with boron, and thus boron acts as a resistance, reducing the capacity and cycle life. According to the embodiment, a positive electrode active material can be obtained in which not only the surface of the positive electrode active material is coated with a boron compound but also the grain boundaries within the positive electrode active material are coated with a boron compound.

[0053] In the preparation method, the nickel-based metal composite hydroxide is a precursor of the positive electrode active material and can be prepared by a general co-precipitation method and can, for example, be represented by Chemical Formula 11.

[0054] [Chemical Formula 11]

[0055] Ni x11 M 11 y11 M 12 1-x11-y11 (OH)2

[0056] In Chemical Formula 11, 0.6 ≤ x11 ≤ 1, 0 ≤ y11 ≤ 0.4, and M 11 and M 12 are each independently selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

[0057] As a specific example, the nickel-based metal composite hydroxide can be represented by Chemical Formula 12 or Chemical Formula 13.

[0058] [Chemical Formula 12]

[0059] Ni x12 Co y12 Al z12 M 13 1-x12-y12-z12 (OH)2

[0060] In Chemical Formula 12, 0.6 ≤ x12 < 1, 0 < y12 < 0.4 and 0 < z12 < 0.4, and M 13 is selected from B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

[0061] [Chemical Formula 13]

[0062] Ni x13 Co y13 M 14 1-x13-y13 (OH)2

[0063] In Chemical Formula 13, 0.6 ≤ x13 < 1, 0 < y13 ≤ 0.4, and M 14 is selected from B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

[0064] In the preparation method, the lithium raw material can be, for example, lithium hydroxide, etc., and can be mixed at a ratio of about 0.9 moles to about 1.8 moles, or about 0.8 moles to about 1.2 moles, based on 1 mole of the nickel-based metal composite hydroxide.

[0065] The boron raw material can be a boron-containing compound, for example, H3BO3, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, (C3H7O)3B, C3H9B3O6, C 13 H 19BO3 or combinations thereof. Based on 100 mol% nickel-based metal complex hydroxide, the boron feedstock content can be from about 0.1 mol% to about 5 mol%, for example, from about 0.1 mol% to about 4 mol%, from about 0.1 mol% to about 3 mol%, from about 0.1 mol% to about 2.9 mol%, from about 0.1 mol% to about 2.5 mol%, from about 0.1 mol% to about 2 mol%, from about 0.1 mol% to about 1.5 mol%, or from about 0.5 mol% to about 1.3 mol%. When the boron feedstock content meets the above ranges, boron does not act as a resistor in the positive electrode active material and can be used to improve battery performance, thereby improving battery capacity and cycle life characteristics. When the boron feedstock content is excessive, the content of the first boron coating portion increases excessively, and boron acts as a resistor in the positive electrode active material, thereby reducing battery capacity and cycle life.

[0066] The mixture can be heat-treated, for example, at a temperature of about 650°C to about 850°C, or about 690°C to about 780°C. In this case, a positive electrode active material having a stable structure comprising both a first boron coating portion and a second boron coating portion can be prepared.

[0067] Furthermore, the heat treatment of the mixture can be carried out for approximately 5 to approximately 15 hours, for example, approximately 8 to approximately 12 hours. In this case, a positive electrode active material having a stable structure comprising both a first boron coating portion and a second boron coating portion is prepared.

[0068] Positive electrode

[0069] The positive electrode for a rechargeable lithium battery may include a current collector and a layer of positive electrode active material on the current collector. The positive electrode active material layer may include a positive electrode active material and may further include a binder and / or a conductive material.

[0070] The binder improves the adhesion properties between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic styrene-butadiene rubber, epoxy resin, and nylon, but are not limited to these.

[0071] Based on the total amount of the positive electrode active material layer, the content of the binder in the positive electrode active material layer can be from about 1 wt% to about 5 wt%.

[0072] Conductive materials are included to provide electrode conductivity. Any electrically conductive material can be used as a conductive material unless it causes a chemical change. Examples of conductive materials may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers; metallic materials including metal powders or fibers of copper, nickel, aluminum, and silver; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0073] Based on the total amount of the positive electrode active material layer, the content of conductive material in the positive electrode active material layer can be from about 1 wt% to about 5 wt%.

[0074] Aluminum foil can be used as a current collector, but is not limited to this.

[0075] Negative electrode

[0076] The negative electrode for a rechargeable lithium battery includes a current collector and a layer of negative electrode active material on the current collector. The negative electrode active material layer may include a negative electrode active material and may further include a binder and / or a conductive material.

[0077] The negative electrode active material may include materials that can reversibly insert / deintercalate lithium ions, lithium metal, lithium metal alloys, materials that can be doped / dedoped with lithium, or transition metal oxides.

[0078] Materials capable of reversibly inserting / deintercalating lithium ions may include, for example, crystalline carbon, amorphous carbon, or combinations thereof as carbon-based anode active materials. Crystalline carbon may be amorphous, or in the form of flakes, sheets, spheres, or fibers, natural or artificial graphite. Amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization products, and calcined coke, etc.

[0079] Lithium metal alloys include alloys of lithium with metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0080] Materials capable of lithium doping / de-doping can be Si-based or Sn-based anode active materials. Si-based anode active materials can include silicon, silicon-carbon composites, and SiO₂. x(0 < x < 2), Si-Q alloy (where Q is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition metal, rare earth element, and combinations thereof, but not Si), and the Sn-based negative electrode active material may include Sn, SnO2, Sn-R alloy (where R is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition metal, rare earth element, and combinations thereof, but not Sn). At least one of these materials may be mixed with SiO2. Element Q and element R may be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0081] The silicon-carbon composite may be, for example, a silicon-carbon composite including a core containing crystalline carbon and silicon particles and an amorphous carbon coating provided on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon precursor may be coal tar pitch, mesophase pitch, petroleum pitch, coal oil, petroleum heavy oil, or a polymer resin such as phenolic resin, furan resin, or polyimide resin. In this case, based on the total amount of the silicon-carbon composite, the content of silicon may be about 10 wt% to about 50 wt%. Additionally, based on the total amount of the silicon-carbon composite, the content of crystalline carbon may be about 10 wt% to about 70 wt%, and based on the total amount of the silicon-carbon composite, the content of amorphous carbon may be about 20 wt% to about 40 wt%. Further, the thickness of the amorphous carbon coating may be about 5 nm to about 100 nm. The average particle size (D50) of the silicon particles may be about 10 nm to about 20 μm. The average particle size (D50) of the silicon particles may preferably be about 10 nm to about 200 nm. The silicon particles may exist in an oxidized form, and in this case, the atomic content ratio of Si:O indicating the degree of oxidation in the silicon particles may be about 99:1 to about 33:67. The silicon particles may be SiO x particles, and in this case, SiO x in which the range of x may be greater than about 0 and less than about 2. In this specification, unless otherwise defined, the average particle size (D50) indicates the diameter of the particles with a cumulative volume of about 50 volume% in the particle distribution.

[0082] Si-based or Sn-based anode active materials can be mixed with carbon-based anode active materials. When Si-based or Sn-based anode active materials and carbon-based anode active materials are mixed and used, the mixing ratio can be from about 1:99 to about 90:10 by weight.

[0083] In the negative electrode active material layer, the amount of negative electrode active material included, based on the total weight of the negative electrode active material layer, can be from about 95 wt% to about 99 wt%.

[0084] In one embodiment, the negative electrode active material layer further includes a binder and optionally further includes a conductive material. Based on the total amount of the negative electrode active material layer, the binder content in the negative electrode active material layer can be from about 1 wt% to about 5 wt%. Alternatively, when further including a conductive material, the negative electrode active material layer may include about 90 wt% to about 98 wt% of negative electrode active material, about 1 wt% to about 5 wt% of binder, and about 1 wt% to about 5 wt% of conductive material.

[0085] The binder is used to ensure good adhesion between the negative electrode active material particles and also to adhere the negative electrode active material to the current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0086] Examples of water-insoluble adhesives include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, ethylene propylene copolymers, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0087] Water-soluble adhesives may include rubber adhesives or polymeric resin adhesives. Rubber adhesives may be selected from styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. Polymeric resin adhesives may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0088] When a water-soluble binder is used as a negative electrode binder, it may further include a cellulose compound capable of imparting viscosity. As a cellulose compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts may be mixed and used. As an alkali metal, Na, K, or Li may be used. Based on 100 parts by weight of the negative electrode active material, the amount of thickener used may be from about 0.1 parts by weight to about 3 parts by weight.

[0089] Conductive materials are included to provide electrode conductivity. Any electrically conductive material can be used as a conductive material unless it causes a chemical change. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers; metallic materials including metal powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0090] The current collector may include one of the following: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0091] Rechargeable lithium battery

[0092] Another embodiment provides a rechargeable lithium battery including a positive electrode, a negative electrode, a separator between the positive and negative electrodes, and an electrolyte. Here, the electrodes can be a positive electrode and a negative electrode.

[0093] Figure 1 This is a schematic diagram illustrating a rechargeable lithium battery according to an embodiment. See also... Figure 1 According to an embodiment of the present invention, a rechargeable lithium battery 100 includes a battery cell, the battery cell including a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 between the positive electrode 114 and the negative electrode 112, and an electrolyte for a rechargeable lithium battery impregnating the positive electrode 114, the negative electrode 112 and the separator 113; a battery housing 120 for housing the battery cell; and a sealing member 140 for sealing the battery housing 120.

[0094] Electrolytes include non-aqueous organic solvents and lithium salts.

[0095] Non-aqueous organic solvents are used as media for transporting ions involved in the electrochemical reactions of a battery. Non-aqueous organic solvents can be carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, or proton-inert solvents. Examples of carbonate solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene glycol carbonate (EC), propylene glycol carbonate (PC), and butylene glycol carbonate (BC). Examples of ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, mevalonate lactone, and caprolactone. Ether solvents can be dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran, etc., and ketone solvents can be cyclohexanone, etc. Additionally, alcohol solvents can be ethanol, isopropanol, etc., and proton-inert solvents can be nitriles, such as R-CN (where R is a C2 to C20 straight-chain, branched, or cyclic hydrocarbon group and may include double bonds, aromatic rings, or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; and sulfolane, etc.

[0096] Non-aqueous organic solvents can be used alone or in mixtures. When organic solvents are used in mixtures, the mixing ratio can be controlled according to the desired battery performance.

[0097] Alternatively, in the case of carbonate solvents, a mixture of cyclic carbonates and chain carbonates can be used. In this case, the electrolyte exhibits excellent performance when the cyclic carbonates and chain carbonates are mixed in a volume ratio of about 1:1 to about 1:9.

[0098] In addition to carbonate solvents, non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. In this case, carbonate solvents and aromatic hydrocarbon organic solvents may be mixed in a volume ratio of about 1:1 to about 30:1.

[0099] Aromatic hydrocarbon solvents can be aromatic hydrocarbon compounds represented by chemical formula I.

[0100] [Chemical Formula I]

[0101]

[0102] In chemical formula I, R 4 To R 9 They may be the same or different and are selected from hydrogen, halogen, C1 to C10 alkyl, haloalkyl and combinations thereof.

[0103] Specific examples of aromatic hydrocarbon solvents can be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, and fluorotoluene. 2,3-Difluorotoluene, 2,4-Difluorotoluene, 2,5-Difluorotoluene, 2,3,4-Trifluorotoluene, 2,3,5-Trifluorotoluene, Chlorotoluene, 2,3-Dichlorotoluene, 2,4-Dichlorotoluene, 2,5-Dichlorotoluene, 2,3,4-Trichlorotoluene, 2,3,5-Trichlorotoluene, Iodotoluene, 2,3-Diiodotoluene, 2,4-Diiodotoluene, 2,5-Diiodotoluene, 2,3,4-Triiodotoluene, 2,3,5-Triiodotoluene, Xylene and combinations thereof.

[0104] The electrolyte may further include vinylene carbonate or ethylene glycol carbonate compounds represented by Formula II to improve the cycle life of the battery.

[0105] [Chemical Formula II]

[0106]

[0107] In chemical formula II, R 10 and R 11 The same or different, and selected from hydrogen, halogen, cyano, nitro and fluorinated C1 to C5 alkyl groups, under the condition that R 10 and R 11 At least one of them is a halogen, cyano, nitro, or fluorinated C1 to C5 alkyl group, and R 10 and R 11 They are not both hydrogen.

[0108] Examples of ethylene carbonate compounds may be ethylene glycol difluorocarbonate, ethylene glycol chlorocarbonate, ethylene glycol dichlorocarbonate, ethylene glycol bromocarbonate, ethylene glycol dibromocarbonate, ethylene glycol nitrocarbonate, ethylene glycol cyanocarbonate, or ethylene glycol fluorocarbonate. The amount of additives used to improve cycle life may be used within appropriate limits.

[0109] Lithium salts dissolved in non-aqueous organic solvents supply lithium ions to the battery, ensuring the basic operation of rechargeable lithium batteries and improving the transport of lithium ions between the positive and negative electrodes.

[0110] Examples of lithium salts include at least one supported salt selected from the following: LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2), where x and y are natural numbers, for example, integers ranging from 1 to 20, lithium difluoro(bis(oxalic acid)phosphate), LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalic acid)borate: LiBOB) and lithium difluoro(oxalic acid)borate (LiDFOB).

[0111] Lithium salts can be used at concentrations ranging from about 0.1 M to about 2.0 M. When lithium salts are included within the above concentration range, the electrolyte exhibits excellent performance and lithium-ion mobility due to optimal electrolyte conductivity and viscosity.

[0112] Separator 113 separates the positive electrode 114 and the negative electrode 112 and provides a transport channel for lithium ions, and can be any separator commonly used in lithium-ion batteries. In other words, it can have low resistance to ion transport and excellent impregnation properties for the electrolyte. For example, the separator can be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene, or combinations thereof. It can be in the form of non-woven or woven fabric. For example, in lithium-ion batteries, polyolefin polymer separators, such as polyethylene and polypropylene, are mainly used. To ensure heat resistance or mechanical strength, coated separators including ceramic components or polymer materials can be used. Optionally, it can have a single-layer structure or a multi-layer structure.

[0113] Depending on the presence or absence of a separator and the type of electrolyte used, rechargeable lithium batteries can be classified as lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries. Rechargeable lithium batteries can have various shapes and sizes, including cylindrical, prismatic, button-shaped, or pouch-shaped batteries, and can be thin-film batteries or quite large in size. The structures and methods of manufacturing lithium-ion batteries disclosed herein are well known in the art.

[0114] Embodiments and comparative examples of the present invention are described below. However, these embodiments are exemplary, and the present disclosure is not limited thereto.

[0115] Example 1

[0116] 1. Preparation of positive electrode active material precursor

[0117] First, 0.25 M ammonia solution was poured into the reactor. The metal feedstock and complexing agent were reacted at 142 ml / min and 34 ml / min respectively at 50°C and 3.0 kW / m³. 3 The reaction began with the addition of stirring power. Nickel sulfate, cobalt sulfate, and aluminum nitrate were used as the metal raw materials. NaOH was added to maintain the pH, and the reaction proceeded for 30 hours. The reaction was terminated when the average size of the obtained core particles reached 4 µm. After rinsing the obtained product, it was dried with hot air at approximately 150°C for 24 hours to obtain a nickel-based metal hydroxide (Ni...). 0.945 Co 0.04 Al 0.015 (OH)2), which is a precursor of positive electrode active material.

[0118] 2. Preparation of positive electrode active material

[0119] A nickel-based metal composite oxide (LiNi) obtained by mixing nickel hydroxide and LiOH, which serve as precursors for the positive electrode active material, in a 1:1 molar ratio, was mixed with 0.5 mol% boric acid based on 100 mol% of the positive electrode active material precursor, and then heat-treated at 725°C for 10 hours in an oxygen atmosphere to obtain a lithium-nickel composite oxide (LiNi) coated with boron compounds at the inner grain boundaries and on the surface. 0.945 Co 0.04 Al 0.015 O2).

[0120] 3. Manufacture of positive electrode

[0121] A positive electrode active material slurry was prepared by mixing 95 wt% of the obtained positive electrode active material, 3 wt% of polyvinylidene fluoride binder, and 2 wt% of Ketjen Black conductive material in an N-methylpyrrolidone solvent. The positive electrode active material slurry was applied to an aluminum current collector, dried, and then compressed to manufacture the positive electrode.

[0122] 4. Manufacture of rechargeable lithium battery cell

[0123] A button half-cell is manufactured by placing a separator with a polyethylene-polypropylene multilayer structure between a manufactured positive electrode and a lithium metal counter electrode, and injecting an electrolyte solution, wherein the electrolyte solution is a solvent in which 1.0 M LiPF6 lithium salt is added, and the solvent is in which ethylene glycol ester and diethyl carbonate are mixed in a volume ratio of 50:50.

[0124] Example 2

[0125] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Example 1, except that 1.0 mol% of boric acid was added in the preparation of the positive electrode active material in Example 1.

[0126] Example 3

[0127] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Example 1, except that 1.5 mol% of boric acid was added in the preparation of the positive electrode active material in Example 1.

[0128] Example 4

[0129] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Example 1, except that 3.0 mol% of boric acid was added in the preparation of the positive electrode active material in Example 1.

[0130] Example 5

[0131] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Example 1, except that 5.0 mol% of boric acid was added in the preparation of the positive electrode active material in Example 1.

[0132] Comparative Example 1

[0133] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Example 1, except that boric acid was not added in the preparation of the positive electrode active material in Example 1.

[0134] Comparative Example 2

[0135] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Comparative Example 1, except that the positive electrode active material was prepared in the same manner as in Comparative Example 1 and then subjected to additional heat treatment at 350°C in an oxygen atmosphere for 8 hours.

[0136] Comparative Example 3

[0137] The positive electrode active material was prepared in the same manner as in Comparative Example 1, and then coated with a boron compound using conventional methods. In other words, the positive electrode active material of Comparative Example 1 was mixed with 0.5 mol% boric acid based on 100 mol% of the positive electrode active material precursor, and then heat-treated at 350°C in an oxygen atmosphere for 8 hours to obtain a nickel-based metal composite oxide (LiNi) coated with a boron compound on its surface. 0.945 Co 0.04 Al 0.015 O2). The positive electrode and battery cell were manufactured in the same manner as in Example 1, except that the positive electrode active material was used.

[0138] Comparative Example 4

[0139] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Comparative Example 3, except that boric acid was added in an amount of 1.0 mol%.

[0140] Comparative Example 5

[0141] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Comparative Example 3, except that boric acid was added in an amount of 1.5 mol%.

[0142] Comparative Example 6

[0143] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Comparative Example 3, except that boric acid was added in an amount of 3.0 mol%.

[0144] Example 6

[0145] 1. Preparation of positive electrode active material precursor

[0146] First, 0.25 M ammonia solution was poured into the reactor. The metal feedstock and complexing agent were reacted at 142 ml / min and 34 ml / min respectively at 50°C and 3.0 kW / m³. 3 The reaction began simultaneously with the addition of the stirring power. Nickel sulfate and cobalt sulfate were used as the metal raw materials. The reaction proceeded for 23 hours while NaOH was added to maintain the pH. As a result, the reaction was terminated when the average size of the obtained core particles reached 3 µm. After rinsing the obtained product, it was dried with hot air at approximately 150°C for 24 hours to obtain a nickel-based metal composite hydroxide (Ni...). 0.9 Co 0.1 (OH)2), which is a precursor of positive electrode active material.

[0147] 2. Preparation of positive electrode active material

[0148] A nickel-based metal composite oxide (LiNi) obtained by mixing nickel hydroxide and LiOH, which serve as precursors for the positive electrode active material, in a 1:1 molar ratio, was mixed with 0.5 mol% boric acid based on 100 mol% of the positive electrode active material precursor, and then heat-treated at 725°C for 10 hours in an oxygen atmosphere to obtain a lithium-nickel composite oxide (LiNi) coated with boron compounds at the inner grain boundaries and on the surface. 0.9 Co 0.1 O2).

[0149] Subsequently, the positive electrode and battery cell were manufactured in the same manner as in Example 1.

[0150] Example 7

[0151] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Example 6, except that 1.0 mol% of boric acid was added in the preparation of the positive electrode active material in Example 6.

[0152] Example 8

[0153] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Example 6, except that 1.5 mol% of boric acid was added in the preparation of the positive electrode active material in Example 6.

[0154] Example 9

[0155] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Example 6, except that 3.0 mol% of boric acid was added in the preparation of the positive electrode active material in Example 6.

[0156] Comparative Example 7

[0157] The positive electrode active material, positive electrode, and battery cell were manufactured in the same manner as in Example 6, except that boric acid was not added in the preparation of the positive electrode active material in Example 6.

[0158] Table 1 below summarizes the design content of the examples and comparative examples, where NCA is nickel-cobalt-aluminum and NC is nickel-cobalt.

[0159] [Table 1]

[0160]

[0161] Evaluation Example 1: Evaluation of boron content at intracrystalline boundaries of positive electrode active material

[0162] The boron content of the positive electrode active materials according to Examples 1 to 5 and 7 and Comparative Examples 1, 4 and 6 was measured by ICP (Inductively Coupled Plasma) emission spectroscopy. 10 g of each positive electrode active material was added to 100 g of distilled water, and the mixture was stirred for 30 minutes. The positive electrode active material was then filtered through a filter. This washing process removed all boron present on the surface of the positive electrode active material. The recovered positive electrode active material was dried at 130°C for 24 hours and analyzed by ICP emission spectroscopy to measure the remaining boron content in the positive electrode active material, expressed as the boron content present inside the positive electrode active material (i.e., at grain boundaries). Furthermore, the difference in boron content obtained by subtracting the boron content after washing from the boron content before washing, i.e., the boron content removed by washing, is expressed as the boron content present on the surface of the positive electrode active material. In Table 2 below, ppm is based on weight, and 1 ppm is 10 -4 wt%, and ND means not detected.

[0163] [Table 2]

[0164]

[0165] Referring to Table 2, in the positive electrode active material of Comparative Example 1, which was not boron coated, boron was absent at the grain boundaries and on the surface. In contrast, in the positive electrode active materials of Comparative Examples 4 and 6, which were boron coated using conventional methods, no boron remained; that is, boron was not coated to the grain boundaries but only on the surface. In contrast, in the positive electrode active materials of Examples 1 to 5 and 7, boron remained even after all the boron on the surface was removed during cleaning of the positive electrode active material; that is, the coating even reached the grain boundaries within the positive electrode active material that distilled water could not reach.

[0166] Evaluation Example 2: Evaluation of battery performance

[0167] The button half-cells according to Examples 1 to 7 and Comparative Examples 1 to 7 were charged at 25°C with a constant current of 0.2 C until a voltage of 4.25 V was reached, and the capacity was measured relative to the initial charge. They were then discharged at 0.2 C to a discharge cutoff voltage of 3.0 V, and the initial discharge capacity was measured. The ratio of the initial discharge capacity to the initial charge capacity was calculated as the efficiency. Additionally, the button half-cells were charged at 45°C with a constant current of 1 C to an upper limit voltage of 4.3 V and discharged at 1 C to a discharge cutoff voltage of 3.0 V. The initial discharge capacity was measured, and the discharge capacity was also measured. After 50 consecutive charge and discharge cycles, the capacity retention rate after the 50th charge and discharge cycle was evaluated.

[0168] [Table 3]

[0169]

[0170] [Table 4]

[0171]

[0172] Referring to Tables 3 and 4, compared to the examples in which boron coating was performed in the same amount, Comparative Examples 1, 2, and 7, in which no boron coating was performed, showed extremely low capacity retention, while Comparative Examples 3 to 6, in which boron coating was performed only on the surface of the positive electrode active material, showed low capacity retention and low discharge capacity. This is because the boron compound coated on the surface of the positive electrode active material only acts as a resistor. In contrast, Examples 1 to 7, in which boron compounds were coated on the surface of the positive electrode active material and at its grain boundaries, exhibited comprehensively improved discharge capacity and capacity retention.

[0173] Figure 2 and Figure 3 The diagram schematically illustrates the capacity versus voltage curves of the button-type half-cells of Examples 1 to 3 and Comparative Examples 1 to 5 during the initial discharge period. Figure 2 This is a graph showing the curves of Comparative Example 1 and Examples 1 to 3. Figure 3 These are the graphs for comparative examples 2 to 5. See also... Figure 2 and Figure 3 , Figure 2 Examples 1 to 3 and Figure 2 Comparative Example 1 and Figure 3 Compared to Comparative Examples 2 to 5, it exhibits higher capacity at the same voltage, indicating that a larger number of lithium ions move at the same voltage, meaning that lithium ions can move more smoothly. Figure 3 As shown in Comparative Examples 2 to 5, the boron compound coated only on the surface of the positive electrode active material acts as a resistor and thus inhibits the migration of lithium ions.

[0174] Although the invention has been described in conjunction with exemplary embodiments now regarded as practice, it should be understood that the invention is not limited to the disclosed embodiments. Rather, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A positive electrode active material for rechargeable lithium batteries, comprising lithium nickel-based metal composite oxides, in, The positive electrode active material includes secondary particles in which multiple primary particles are aggregated. The positive electrode active material includes a first boron coating portion existing on the surface of the secondary particles and a second boron coating portion existing on the surface of the primary particles within the secondary particles, and The weight of the first boron coating portion is greater than the weight of the second boron coating portion, and Wherein, based on 100 mol% of the positive electrode active material, the total amount of the first boron coating portion and the second boron coating portion is 1 mol% to 3 mol%. Wherein, based on the total amount of the first boron coating portion and the second boron coating portion, the amount of the first boron coating portion is 70 wt% to 98 wt% and the amount of the second boron coating portion is 2 wt% to 30 wt%, and The lithium-nickel metal composite oxide is represented by chemical formula 2 or chemical formula 3: [Chemical Formula 2] Li a2 Ni x2 Co y2 Al z2 M 3 1-x2-y2-z2 O2 Among them, in Chemical Formula 2, 0.9 ≤ a2 ≤ 1.8, 0.6 ≤ x2 < 1, 0 < y2 < 0.4, 0 < z2 < 0.4, and M 3 is selected from B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof. [Chemical Formula 3] Li a3 Ni x3 Co y3 M 4 1-x3-y3 O2 Among them, in Chemical Formula 3, 0.9 ≤ a3 ≤ 1.8, 0.6 ≤ x3 < 1, 0 < y3 ≤ 0.4, and M 4 is selected from B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and combinations thereof.

2. The positive electrode active material as described in claim 1, wherein, The first boron coating portion and the second boron coating portion each comprise boron oxide, lithium boron oxide, or a combination thereof.

3. The positive electrode active material as described in claim 1, wherein, Based on the total amount of the first boron coating portion and the second boron coating portion, the amount of the first boron coating portion included is 90 wt% to 98 wt% and the amount of the second boron coating portion included is 2 wt% to 10 wt%.

4. The positive electrode active material as described in claim 1, wherein, Based on the total amount of the first boron coating portion and the second boron coating portion, the amount of the first boron coating portion included is 80 wt% to 95 wt% and the amount of the second boron coating portion included is 5 wt% to 20 wt%.

5. The positive electrode active material as described in claim 1, wherein, Based on the positive electrode active material, the content of the first boron coating portion is from 200 ppm to 5000 ppm.

6. The positive electrode active material as described in claim 1, wherein, Based on the positive electrode active material, the content of the second boron coating portion is from 10 ppm to 500 ppm.

7. The positive electrode active material as described in claim 1, wherein, In the lithium-nickel metal composite oxide, the nickel content is greater than or equal to 60 mol, based on the total amount of metals other than lithium.

8. A method for preparing a positive electrode active material for a rechargeable lithium battery, comprising: A mixture is obtained by mixing nickel-based metal composite hydroxides, lithium feedstocks, and boron feedstocks, and Heat treatment of the mixture yields the positive electrode active material according to any one of claims 1 to 7. Based on 100 mol% of the nickel-based metal complex hydroxide, the boron raw material content is from 1 mol% to 3 mol%.

9. The method of claim 8, wherein, The heat treatment of the mixture is carried out at a temperature of 650°C to 850°C.

10. The method of claim 8, wherein, The heat treatment of the mixture is carried out for 5 to 15 hours.

11. A rechargeable lithium battery, comprising The positive electrode, negative electrode, and electrolyte for the rechargeable lithium battery, wherein the positive electrode comprises the positive electrode active material according to any one of claims 1 to 7.

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