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

Abstract

Disclosed are a positive electrode active material for a rechargeable lithium battery, a method of preparing the same, and a positive electrode and a rechargeable lithium battery including the same. The positive electrode active material includes: a nickel-based active material; a cobalt-containing coating layer on a surface of the nickel-based active material; and a boron-containing coating layer on a surface of the cobalt-containing coating layer, wherein the positive electrode active material has a specific surface area of 0.45 m2 / g to 0.60 m2 / g.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority and the benefit of Korean Patent Application No. 10 - 2023 - 0178972, filed with the Korean Intellectual Property Office on December 11, 2023, the entire contents of which are incorporated herein by reference. Technical field

[0003] The present disclosure relates to a positive electrode active material for a rechargeable lithium battery, a method for preparing the same, and a positive electrode and a rechargeable lithium battery including the same. Background art

[0004] In recent years, with the rapid popularization of battery - powered electronic devices (such as mobile phones, laptop computers, and electric vehicles), the demand for high - energy - density and high - capacity rechargeable lithium batteries has increased rapidly. Therefore, active research and development have been carried out to improve the performance of rechargeable lithium batteries.

[0005] A rechargeable lithium battery includes a positive electrode and a negative electrode (each containing an active material capable of allowing the insertion and extraction of lithium ions) and an electrolyte. If lithium ions are inserted into and extracted from the positive electrode and the negative electrode (for example, when lithium ions are inserted into and extracted from the positive electrode and the negative electrode), the rechargeable lithium battery generates electricity through oxidation and reduction reactions.

[0006] Nickel - based active materials can be used as positive electrode active materials for rechargeable lithium batteries. Since nickel - based active materials may suffer from performance degradation due to inter - particle growth and side reactions with the electrolyte during charging and discharging, it is necessary to improve the performance of nickel - based active materials. Summary of the invention

[0007] According to one or more aspects of embodiments of the present disclosure, there is provided a positive electrode active material for a rechargeable lithium battery, which ensures (for example, guarantees) an excellent improvement in high - temperature life (also referred to as high - temperature life characteristics), and at the same time suppresses ignition by increasing the gas evolution amount when overcharged to 4.8 V or higher (for example, when overcharged to 4.8 V or higher).

[0008] According to one or more aspects of embodiments of the present disclosure, there is provided a positive electrode active material for a rechargeable lithium battery, which ensures (for example, guarantees) an increase in charge efficiency / discharge efficiency, an improvement in capacity, suppression of side reactions (such as gas evolution), and a reduction in resistance.

[0009] According to one or more aspects of embodiments of the present disclosure, there is provided a method for preparing a positive electrode active material for a rechargeable lithium battery.

[0010] Aspects according to one or more embodiments of the present disclosure relate to a rechargeable lithium battery, including a positive electrode active material for a rechargeable lithium battery as described above.

[0011] Other aspects will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the presented embodiments of the disclosure.

[0012] According to one or more embodiments of the present disclosure, a positive electrode active material for a rechargeable lithium battery includes: a nickel-based active material; a cobalt-containing coating on the surface of the nickel-based active material; and a boron-containing coating on the surface of the cobalt-containing coating, wherein the positive electrode active material has a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g.

[0013] In some embodiments, the nickel-based active material may be a nickel-based active material represented by Formula 1:

[0014] Formula 1

[0015] Li a (Ni 1-x-y-z Co x M y M’ z )O 2-δ ,

[0016] wherein M represents at least one selected from Mn and Al;

[0017] M’ represents at least one element selected from the group consisting of: boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); and

[0018] a, x, y, z, and δ satisfy the following relationships: 0.95 ≤ a ≤ 1.3, x ≤ (1 - x - y - z), y ≤ (1 - x - y - z), z ≤ (1 - x - y - z), 0 < x < 1, 0 ≤ y < 1, 0 ≤ z < 1, and 1.98 ≤ 2 - δ ≤ 2.

[0019] In some embodiments, the boron-containing coating may be formed integrally with the cobalt-containing coating.

[0020] In some embodiments, based on all metal elements other than lithium in the positive electrode active material in a total of 100 mol%, the positive electrode active material may have a nickel content of 70 mol% or more.

[0021] In some embodiments, the nickel-based active material may include secondary particles formed by physical aggregation and / or chemical aggregation of primary particles.

[0022] In some embodiments, the cobalt-containing coating may be present on the surface of the secondary particles and at the grain boundaries of the primary particles.

[0023] In some embodiments, the nickel-based active material may include at least one of (i) a first secondary particle, (ii) a particle having a single crystal structure, and (iii) an integral particle.

[0024] In some embodiments, the nickel-based active material may be a mixture of (i) a first secondary particle and (ii) a particle having a single crystal structure.

[0025] In some embodiments, with respect to 100 parts by weight of the mixture, (i) the amount of the first secondary particle present may be 60 to 90 parts by weight, and (ii) the amount of the particle having a single crystal structure present may be 10 to 40 parts by weight.

[0026] In some embodiments, (i) the first secondary particle may have a size of 14 μm to 18 μm, and (ii) the particle having a single crystal structure may have a size of 1 μm to 7 μm.

[0027] In some embodiments, if charging from 2.8 V to 5 V, in the dQ / dV curve, the peak in the region of 4.1 V to 4.2 V is referred to as I1, and the peak in the region of 4.7 V to 4.9 V is referred to as I2 (for example, when charging from 2.8 V to 5 V, in the dQ / dV curve, the peak in the region of 4.1 V to 4.2 V is referred to as I1, and the peak in the region of 4.7 V to 4.9 V is referred to as I2), the ratio of I1 / I2 may be greater than or equal to 20.

[0028] In some embodiments, the nickel-based active material may include Li 1.01 Ni 0.8 Co 0.1 Al 0.1 O 2 、Li 1.01 Ni 0.8 Co 0.05 Al 0.15 O 2 、Li 1.01 Ni 0.8 Co 0.15 Al 0.05 O 2 、LiNi 0.95 Co 0.04 Al 0.01 O 2 or a combination thereof.

[0029] According to one or more embodiments of the present disclosure, a method for preparing a positive electrode active material for a rechargeable lithium battery includes: preparing a first positive electrode active material from a mixture including a nickel-based active material, a cobalt compound, and a solvent, wherein the cobalt compound is wet-coated on the surface of the nickel-based active material; preparing a second positive electrode active material by dry-coating a boron compound on the surface of the first positive electrode active material; and preparing a positive electrode active material for a rechargeable lithium battery by heat-treating the second positive electrode active material at 700 °C to 750 °C, wherein based on all metal elements other than lithium in the nickel-based active material in a total of 100 mol%, the amount of boron from the boron compound is 0.25 mol% to 0.5 mol%.

[0030] According to one or more embodiments of the present disclosure, a positive electrode includes a positive electrode active material for a rechargeable lithium battery.

[0031] According to one or more embodiments of the present disclosure, a rechargeable lithium battery includes: a positive electrode including a positive electrode active material for a rechargeable lithium battery; a negative electrode; and an electrolyte.

[0032] Embodiments of the present disclosure provide a positive electrode active material for a rechargeable lithium battery, which ensures (e.g., guarantees) an excellent improvement in high-temperature life while suppressing ignition by increasing the amount of outgassing if overcharged to 4.8 V or higher (e.g., when overcharged to 4.8 V or higher). In addition, embodiments of the present disclosure provide a positive electrode active material for a rechargeable lithium battery, which ensures (e.g., guarantees) an increase in charge efficiency / discharge efficiency, an improvement in capacity, suppression of side reactions (such as outgassing), and a reduction in resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated into and constitute a part of this specification. The drawings illustrate embodiments of the present disclosure and, together with the description, are used to explain the principles of the present disclosure.

[0034] Figure 1 It is a schematic illustration of a cylindrical battery according to one or more embodiments of the present disclosure.

[0035] Figure 2 It is a schematic illustration of a prismatic battery according to one or more embodiments of the present disclosure.

[0036] Figure 3 It is a schematic illustration of a pouch-type or kind of battery according to one or more embodiments of the present disclosure.

[0037] Figure 4 It is a schematic illustration of a pouch-type or kind of battery according to one or more embodiments of the present disclosure.

[0038] Figure 5 Scanning electron micrograph (SEM) image of a positive electrode prepared using the positive electrode active material of Example 1.

[0039] Figure 6 is Figure 5 SEM image at a greater magnification of the portion shown within the frame of

[0040] Figure 7 Graph depicting the high-temperature life evaluation results of rechargeable lithium batteries of the examples and comparative examples.

[0041] Figure 8 Graph depicting the outgassing evaluation results of rechargeable lithium batteries of the examples and comparative examples after being placed at 80 °C.

[0042] Figure 9 Graph depicting the outgassing evaluation results of rechargeable lithium batteries of the examples and comparative examples when overcharged from 2.8 V to 5 V.

[0043] Figure 10 Graph depicting the charge curve (time vs. voltage) of rechargeable lithium batteries of the examples and comparative examples when overcharged to 5 V.

[0044] Figure 11 Graph depicting the charge curve dQ / dV of rechargeable lithium batteries of the examples and comparative examples when overcharged to 5 V, where the x-axis represents voltage and the y-axis represents the derivative graph of the relationship between capacity change / voltage change, the voltage is distributed in the range of 3.0 V to 4.2 V, and the maximum peak (H2-H3 phase transition) is in the range of 4.1 V to 4.2 V (usually occurring in positive electrodes with high Ni (Ni ≥ 80)).

[0045] Figure 12 Graph depicting the charge curve dQ / dV of rechargeable lithium batteries of the examples and comparative examples when overcharged to 5 V, where the x-axis represents voltage and the y-axis represents the derivative graph of the relationship between capacity change / voltage change, and the voltage is distributed in the range of 4.5 V to 5.0 V, which indirectly confirms the outgassing caused by the boron coating in the high-voltage range.

[0046] In Figure 7 , Figure 8 and Figures 10 to 12 the solid line indicates Example 1, the dashed line indicates Example 2, the dotted line indicates Comparative Example 1, and the double-dotted line indicates Comparative Example 2. Detailed Description of the Invention

[0047] Hereinafter, exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. However, it should be understood that the following embodiments are provided by way of illustration, and the present disclosure is not limited thereto and is only defined by the claims and their equivalents.

[0048] The terms used herein are for the purpose of describing embodiments of the present disclosure and are not intended to limit the present disclosure. Throughout the specification, unless otherwise indicated, each element may be singular or plural.

[0049] As used herein, the term "a combination thereof" may refer to a mixture, stack, composite, copolymer, alloy, blend, and reaction product of components.

[0050] It will be further understood that the terms "includes", "including", "comprises", and / or "comprising" when used in this specification, indicate the presence of the recited features, integers, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0051] In the drawings, for clarity of illustration, the thicknesses of various elements, layers, regions, etc. may be exaggerated, and throughout the specification, the same elements are denoted by the same reference numerals. Additionally, when any element is referred to as being "on" (or "under") or "above" (or "below") a component (or located in a component or positioned in a component), it may mean that any element is placed in contact with the upper surface (or lower surface) of the component, and may also mean that another component may be inserted between the component and any element that is on (or under) the component (or located in the component or positioned in the component).

[0052] As used herein, the term "layer" includes not only features formed on the entire surface but also features formed on the surface in a plan view.

[0053] As used herein, the term "specific surface area" may be a value measured by the BET measurement method. The MOUNTECH Macsorb HM Model-1208 may be used to measure the BET surface area.

[0054] As used herein, to represent a specific numerical range, "X to Y" refers to a value greater than or equal to X and less than or equal to Y (X ≤ and ≤ Y).

[0055] As a high-capacity positive electrode active material, a nickel-based active material having a high nickel content may be used, for example, a nickel-based active material having a nickel content of 50 mol% or more, 70 mol% or more, or 80 mol% or more.

[0056] A nickel-based active material can be prepared, for example, by coprecipitation. In this method, doping elements such as cobalt (Co), aluminum (Al), manganese (Mn), zirconium (Zr), titanium (Ti), and / or magnesium (Mg) can be uniformly distributed in nickel used as the main component. The nickel-based active material prepared by this method can be prepared in the form of secondary particles.

[0057] The nickel-based active material prepared in the form of secondary particles may suffer from crack growth and side reactions with the electrolyte during repeated charge and discharge. As a result, a rechargeable lithium battery provided with a positive electrode including the nickel-based active material may suffer from deterioration of its life (e.g., service life). For example, the nickel-based active material can reduce the high-temperature life of the rechargeable lithium battery. Accordingly, a nickel-based active material capable of improving the high-temperature life of the rechargeable lithium battery is desired.

[0058] On the other hand, even when a rechargeable lithium battery operates stably at a normal driving voltage (e.g., 2.8 V to less than 4.8 V), the rechargeable lithium battery generates gas through a chemical reaction when overcharged to a high voltage of 4.8 V or higher (e.g., a voltage of 5.0 V or higher). Therefore, it is necessary or desirable for the rechargeable lithium battery to activate an overcharge fire-resistant component (e.g., a fire protection component) during overcharge. During overcharge, the overcharge fire-resistant component can be activated by the internal pressure and can include, for example, a current interruption device (CID), a vent fitting, etc. The fire protection component is a safety device for the rechargeable lithium battery and can significantly reduce the possibility of the rechargeable lithium battery catching fire during overcharge.

[0059] Accordingly, the inventors of the present application have developed a positive electrode active material that includes a cobalt-containing coating and a boron-containing coating on the surface of the nickel-based active material, and can improve the high-temperature life characteristics of the rechargeable lithium battery, while generating gas to operate (e.g., activate) the overcharge fire-resistant component when overcharged to 4.8 V or higher. If the specific surface area of the outermost surface of the positive electrode active material is controlled to be 0.45 m 2 / g to 0.60 m 2 / g (e.g., when the specific surface area of the outermost surface of the positive electrode active material is controlled to be 0.45 m 2 / g to 0.60 m 2 / g), the positive electrode active material can improve the high-temperature life characteristics of the rechargeable lithium battery and can generate gas to operate the overcharge fire-resistant component when overcharged to 4.8 V or higher, thereby improving the safety of the rechargeable lithium battery.

[0060] According to some embodiments, the positive electrode active material for a rechargeable lithium battery includes a nickel-based active material; a cobalt-containing coating on the surface of the nickel-based active material; and a boron-containing coating on the surface of the cobalt-containing coating, wherein the outermost surface of the positive electrode active material has 0.45 m 2 / g to 0.60 m 2 / g of specific surface area.

[0061] The positive electrode active material having a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g may include a coating having a desired or optimal combination of boron and cobalt. If the positive electrode active material has a specific surface area greater than 0.60 m 2 / g, the cobalt-containing coating may be formed in a higher amount on the surface of the secondary particles than on the grain boundaries of the primary particles, and side reactants may be formed during the life (e.g., during the operation of the battery over its life), thereby hindering or reducing the improvement of life (e.g., service life). If the positive electrode active material has a specific surface area less than 0.45 m 2 / g, the boron-containing coating may be almost absent from the positive electrode active material, and thus degassing may be disadvantageous in the overcharge voltage region (4.8 V or higher). The inventors of the present application have found (and confirmed) that the positive electrode active material capable of improving the high-temperature life characteristics and activating the overcharge fire-resistant component during overcharge has a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g.

[0062] In addition, if the specific surface area of the outermost surface of the positive electrode active material is less than 0.45 m 2 / g, the positive electrode active material cannot provide improvements in charge efficiency / discharge efficiency and high-temperature life, and a small amount (e.g., an insufficient amount) of gas may be generated during overcharge, thereby preventing the proper operation of the overcharge fire-resistant component. If the specific surface area of the outermost surface of the positive electrode active material is greater than 0.60 m 2 / g, compared to the positive electrode active material having a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g (e.g., 0.60 m 2 / g) for the outermost surface, the positive electrode active material may suffer from deterioration of charge capacity / discharge capacity and efficiency, and the positive electrode active material may provide insufficient improvement in high-temperature life.

[0063] According to some embodiments, the nickel-based active material may include secondary particles formed by physical aggregation and / or chemical aggregation of primary particles.

[0064] According to some embodiments, the nickel-based active material may be, for example, a nickel-based active material represented by Formula 1:

[0065] Formula 1

[0066] Li a (Ni 1-x-y-z Co x M y M’ z )O 2-δ ,

[0067] wherein M represents at least one selected from Mn and Al;

[0068] M’ represents at least one element selected from the group consisting of: boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum (Al); and

[0069] a, x, y, z, and δ satisfy the following relationships: 0.95 ≤ a ≤ 1.3, x ≤ (1 - x - y - z), y ≤ (1 - x - y - z), z ≤ (1 - x - y - z), 0 < x < 1, 0 ≤ y < 1, 0 ≤ z < 1, and 1.98 ≤ 2 - δ ≤ 2. For example, a may be 1, 1.01, or 1.03.

[0070] The nickel-based active material of Formula 1 has a nickel content higher than the content of each of cobalt, M, and M’.

[0071] According to one embodiment, in Formula 1, x, y, and z satisfy the following relationships: 0.3 ≤ 1 - x - y - z ≤ 0.99, 0.5 < 1 - x - y - z ≤ 0.99, 0.6 < 1 - x - y - z ≤ 0.99, 0.8 ≤ 1 - x - y - z ≤ 0.99, or 0.8 ≤ 1 - x - y - z ≤ 0.95.

[0072] The nickel-based active material of Formula 1 may include a nickel-based active material represented by Formula 1-1.

[0073] Formula 1-1

[0074] Li a (Ni 1-x-y-z Co x Al y M z )O 2-δ ,

[0075] Where M represents at least one selected from the group consisting of: boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr); and a, x, y, z, and δ satisfy the following relationships: 0.95 ≤ a ≤ 1.3, x ≤ (1 - x - y - z), y ≤ (1 - x - y - z), z ≤ (1 - x - y - z), 0 < x < 1, 0 ≤ y < 1, 0 ≤ z < 1, and 1.98 ≤ 2 - δ ≤ 2.

[0076] In Formula 1-1, x, y, and z satisfy the following relationships: 0.3 ≤ 1 - x - y - z ≤ 0.99, 0.5 < 1 - x - y - z ≤ 0.99, 0.6 < 1 - x - y - z ≤ 0.99, 0.8 ≤ 1 - x - y - z ≤ 0.99, or 0.8 ≤ 1 - x - y - z ≤ 0.95. In Formula 1-1, x, y, and z satisfy the following relationships: 0.001 ≤ x ≤ 0.5, for example, 0.001 ≤ x ≤ 0.334; 0.001 ≤ y ≤ 0.5, for example, 0.001 ≤ y ≤ 0.334; 0 ≤ z < 1, for example, z = 0.

[0077] According to some embodiments, the nickel-based active material may include Li 1.01 Ni 0.8 Co 0.1 Al 0.1 O 2 、Li 1.01 Ni 0.8 Co 0.05 Al 0.15 O 2 、Li 1.01 Ni 0.8 Co 0.15 Al 0.05 O 2 、LiNi 0.95 Co 0.04 Al 0.01 O 2 or a combination thereof.

[0078] According to some embodiments, the nickel-based active material may include at least one of (i) a first secondary particle, (ii) a particle having a single crystal structure, and (iii) an integral particle. Here, (i) the first secondary particle is a particle having a larger size than (ii) the particle having a single crystal structure.

[0079] For example, the nickel-based active material may be a mixture of (i) a first secondary particle; and (ii) a particle having a single crystal structure. According to one embodiment, with respect to 100 parts by weight of the mixture, the amount of the first secondary particle present in (i) may be 60 to 90 parts by weight, for example, 60 to 80 parts by weight, and the amount of the particle having a single crystal structure present in (ii) may be 10 to 40 parts by weight, for example, 20 to 40 parts by weight.

[0080] The first secondary particle may be a secondary particle having a size of 13 μm to 20 μm and is formed by physical aggregation and / or chemical aggregation of primary particles having a size of 1 μm or less. Within this size range, the first secondary particle can ensure (for example, guarantee) the effect of maximizing or enhancing the density of the electrode plate. For example, the first secondary particle may have a size of 14 μm to 18 μm or 14 μm to 17 μm.

[0081] In the first secondary particle, the primary particle has an average particle diameter of 0.01 μm to 1 μm, 0.02 μm to 0.8 μm, 0.03 μm to 0.5 μm, 0.04 μm to 0.1 μm, or 0.05 μm to 0.07 μm (50 nm to 70 nm). According to one embodiment, the first secondary particle may have a polycrystalline structure. As used herein, the term "polycrystalline" refers to an aggregate structure of multiple crystalline particles.

[0082] In this document, if the particle is spherical (e.g., when the particle is spherical), the term "size" refers to the average particle diameter of the nickel-based active material particle. If the nickel-based active material particle is not spherical (e.g., when the nickel-based active material particle is not spherical), the term "size" refers to the maximum value of the major axis length obtainable from the cross-section of the particle.

[0083] The average particle diameter can be measured by, for example, a particle size distribution (PSD) tool or SEM. Unless otherwise defined, the average particle diameter refers to the particle diameter (D 50 ) which refers to the diameter of the particle corresponding to 50% cumulative volume in the particle size distribution. The major axis length can be measured by, for example, SEM, etc.

[0084] In this document, the term "integral particle" refers to a structure in which the particles form morphologically distinct phases that do not aggregate with each other. In contrast to integral particles, there is a particle structure in which small particles (primary particles) physically aggregate and / or chemically aggregate to form relatively larger particles (secondary particles).

[0085] "Single crystal" has a structure in which many crystalline particles are dispersed and / or separated from each other such that each crystalline particle forms an independent and / or distinct phase rather than an aggregated phase, and may also include a structure in which 10 or fewer particles are attached to each other.

[0086] (ii) Each of the particles having a single crystal structure and (iii) the integrated particles may have a size of 1 μm to 7 μm. According to one embodiment, the nickel-based active material may include integrated particles containing primary particles having a size of 1 μm to 7 μm. According to another embodiment, the nickel-based active material may include particles having a single crystal structure with a size of 1 μm to 7 μm.

[0087] According to some embodiments, the nickel-based active material may have a size of 10 μm to 20 μm.

[0088] According to some embodiments, the positive electrode active material includes a cobalt-containing coating formed on the surface of the secondary particles; and a boron-containing coating formed on the cobalt-containing coating.

[0089] The cobalt-containing coating can improve the thermal stability at high temperatures by protecting the nickel-based active material.

[0090] According to some embodiments, the cobalt-containing coating may be present on the surface of the secondary particles and also at the grain boundaries (surfaces) of the primary particles constituting the secondary particles. The cobalt-containing coating can prevent or substantially prevent the secondary particles from cracking at high temperatures, and even if cracking occurs, it can inhibit or reduce side reactions caused by the cracking while improving the lifespan.

[0091] According to some embodiments, the cobalt-containing coating may be formed of a lithium cobalt compound.

[0092] According to some embodiments, the cobalt-containing coating may have a thickness of 100 nm or less, for example, 1 nm to 100 nm, 1 nm to 50 nm, or 5 nm to 50 nm. Within these ranges, the cobalt-containing coating can ensure (e.g., guarantee) a good improvement in the stability of the positive electrode active material.

[0093] The boron-containing coating can reduce the resistance by improving the conductivity of the nickel-based active material while improving the charge efficiency / discharge efficiency.

[0094] According to some embodiments, the boron-containing coating may be integrally formed with the cobalt-containing coating. As used herein, the term "integrally formed" means that by wet-coating a cobalt compound on the surface of the nickel-based active material, then dry-coating a boron compound and performing heat treatment at 700 °C to 750 °C, the cobalt-containing coating and the boron-containing coating are formed simultaneously or synchronously. That is, the wet-coated cobalt compound is not heated separately, and immediately after wet-coating the cobalt compound, the boron compound is directly dry-coated on the wet-coated cobalt compound. Then the wet-coated cobalt-containing coating and the dry-coated boron-containing coating are heat-treated together (simultaneously).

[0095] According to some embodiments, the boron-containing coating may be a different layer independent of the cobalt-containing coating.

[0096] According to some embodiments, the boron-containing coating may be formed from a lithium boron compound.

[0097] According to some embodiments, the boron-containing coating may have a thickness of 100 nm or less, for example, 1 nm to 100 nm, 1 nm to 50 nm, or 5 nm to 50 nm. Within these ranges, the boron-containing coating can ensure (e.g., guarantee) good improvement in the stability of the positive electrode active material.

[0098] Based on all the metal elements other than lithium in the positive electrode active material, in total 100 mol%, the positive electrode active material may have, for example, a nickel content of 70 mol% or more, 70 mol% to 95 mol%, or 80 mol% to 95 mol%.

[0099] According to some embodiments, a positive electrode active material having a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g can be prepared by the method for preparing a positive electrode active material described below.

[0100] Method for preparing a positive electrode active material for a rechargeable lithium battery

[0101] Hereinafter, the method for preparing a positive electrode active material for a rechargeable lithium battery will be described in more detail.

[0102] The preparation method includes: preparing a first positive electrode active material from a mixture including a nickel-based active material, a cobalt compound, and a solvent, wherein the cobalt compound is wet-coated on the surface of the nickel-based active material;

[0103] preparing a second positive electrode active material by dry-coating a boron compound on the surface of the first positive electrode active material; and

[0104] preparing a positive electrode active material for a rechargeable lithium battery by heat-treating the second positive electrode active material at 700 °C to 750 °C,

[0105] wherein the boron compound is dry-coated on the surface of the first positive electrode active material to provide 0.25 mol% to 0.5 mol% of boron based on all the metal elements other than lithium in the nickel-based active material, in total 100 mol%.

[0106] (1) First, a mixture is prepared by mixing a nickel-based active material, a cobalt compound, and a solvent. The nickel-based active material may be a compound represented by Formula 1.

[0107] The cobalt compound may include, for example, cobalt hydroxide, cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt carbonate, cobalt citrate, cobalt acetate, or a combination thereof.

[0108] Cobalt compounds may be present in the mixture to provide 1 mol% to 3 mol% of cobalt based on the total content of all metal elements other than lithium in the nickel-based active material. The cobalt content of 1 mol% to 3 mol% may facilitate the preparation of the positive electrode active material having the above specific surface area range with the coating amount of the boron compound described below and at the heat treatment temperature described below.

[0109] The solvent may be any suitable solvent capable of dissolving or dispersing the nickel-based active material and the cobalt compound, and may include, for example, distilled water, ethanol, methanol, isopropanol, butanol, pentanol, or a combination thereof. For example, the solvent may be an aqueous solvent, such as distilled water.

[0110] (2) Next (or as a result of operation (1)), a first positive electrode active material is prepared in which the cobalt compound is wet-coated on the surface of the nickel-based active material. The wet coating can be carried out by mixing the nickel-based active material, the cobalt compound, and the solvent with each other.

[0111] (3) Next, a second positive electrode active material is prepared by dry-coating a boron compound on the surface of the first positive electrode active material. The dry coating can be carried out by mixing the first positive electrode active material with the boron compound.

[0112] The boron compound may include boron trioxide (B 2 O 3 ), sodium borohydride (NaBH 4 ), sodium cyanoborohydride (NaCNBH 3 ), sodium cyanoborohydride acetate (NaCNBH 3 OAc), or a mixture thereof.

[0113] The boron compound is present in the mixture to provide 0.25 mol% to 0.5 mol% of boron based on the total 100 mol% of all metal elements other than lithium in the nickel-based active material, and the boron compound is dry-coated.

[0114] If the boron content is less than 0.25 mol%, the positive electrode active material may exhibit insufficient improvement in high-temperature life and generate an insufficient amount of gas during overcharge, whereby the fire protection assembly cannot operate properly. If the boron content is greater than 0.5 mol%, the positive electrode active material may exhibit insufficient improvement in high-temperature life, and the excessive boron content in the boron-containing coating may increase the resistance while reducing the charge capacity / discharge capacity and efficiency.

[0115] (4) The second positive electrode active material is heat-treated at 700 °C to 750 °C to prepare a positive electrode active material for a rechargeable lithium battery. Within this temperature range, it is beneficial to prepare a positive electrode active material having 0.45 m 2 / g to 0.60 m 2The positive electrode active material with a specific surface area of / g.

[0116] Rechargeable lithium battery

[0117] According to some embodiments, a rechargeable lithium battery includes: a positive electrode including a positive electrode active material for the rechargeable lithium battery; a negative electrode; and an electrolyte.

[0118] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode 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.

[0119] In one embodiment, the positive electrode may further include a component capable of acting as a sacrificial positive electrode.

[0120] Based on 100 wt% of the positive electrode active material layer, the amount of the positive electrode active material present may be 90 wt% to 99 wt%, and based on 100 wt% of the positive electrode active material layer, the amount of each of the binder and the conductive material present may be 0.5 wt% to 5 wt%.

[0121] The positive electrode active material layer includes a positive electrode active material according to one or more embodiments of the present disclosure.

[0122] In addition to the positive electrode active material according to the embodiment, the positive electrode active material layer may further include a different positive electrode active material for the rechargeable lithium battery.

[0123] A different positive electrode active material for the rechargeable lithium battery according to one embodiment may include at least one metal selected from cobalt, manganese, nickel, and combinations thereof and a composite oxide of lithium.

[0124] The composite oxide may be a lithium transition metal composite oxide. For example, the composite oxide may include lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, cobalt-free lithium manganese oxide, or a combination thereof.

[0125] By way of example, the composite oxide may be a compound represented by any of the following chemical formulas: Li a A 1- b X b O 2-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Mn 2-b X b O 4-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Lia Ni 1-b-c Co b X c O 2-α D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α < 2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α < 2); Li a Ni b Co c L 1 d G e O 2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0 ≤ e ≤ 0.1); Li a NiG b O 2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O 2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O 2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 2 G b O 4 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO 4 (0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); Li (3-f) Fe 2 (PO 4 ) 3 (0 ≤ f ≤ 2); and Li a FePO 4 (0.90 ≤ a ≤ 1.8).

[0126] In the above formula, A is Ni, Co, Mn, or a combination thereof; X represents Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 is Mn, Al, or a combination thereof.

[0127] In some embodiments, the positive electrode active material may be a high-nickel-content positive electrode active material, which contains 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% to 99 mol% of nickel based on all the metal elements other than lithium in the lithium transition metal composite oxide. The high-nickel-content positive electrode active material can achieve high capacity and thus can be applied to high-capacity / high-energy-density rechargeable lithium batteries.

[0128] The binder is used to attach the positive electrode active material particles to each other and at the same time attach the positive electrode active material particles to the positive electrode current collector. The binder may include, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate esterified styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc., but is not limited thereto.

[0129] The conductive material is used to impart conductivity to the electrode and can be any conductive material that does not cause chemical changes in the constructed battery cell. The conductive material may include, for example, carbon materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.); metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers (such as polyphenylene derivatives, etc.); and mixtures thereof.

[0130] The positive electrode current collector may be Al foil, but is not limited thereto.

[0131] The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0132] For example, based on 100 wt% of the negative electrode active material layer, the negative electrode active material layer may include 90 wt% to 99 wt% of the negative electrode active material, 0.5 wt% to 5 wt% of the binder, and 0 wt% to 5 wt% of the conductive material.

[0133] The negative electrode active material includes a material capable of allowing reversible insertion / extraction of lithium ions, lithium metal, a lithium metal alloy, a material into which lithium can be doped and from which it can be de-doped, or a transition metal oxide.

[0134] The material capable of allowing reversible insertion / extraction of lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Crystalline carbon may include, for example, graphite (such as natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fibrous), and amorphous carbon may include, for example, soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0135] As the lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0136] The material into which lithium can be doped and from which it can be de-doped may be a Si-based negative electrode active material or a Sn-based negative electrode active material. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, Group XIII elements, Group XIV elements (excluding Si), Group XV elements, Group XVI elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material may be Sn, SnO x (0 < x ≤ 2), for example, SnO 2 ), a Sn alloy, or a combination thereof.

[0137] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be prepared in the form of silicon particles having an amorphous carbon coating formed on their surface. For example, the silicon-carbon composite may include secondary particles (cores) composed of primary silicon particles and an amorphous carbon coating (shells) formed on the surface of the secondary particles. Amorphous carbon may also be placed between the primary silicon particles such that, for example, the primary silicon particles are coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0138] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating formed on the core.

[0139] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used in combination with the carbon-based negative electrode active material.

[0140] The binder is used to attach the negative electrode active material particles to each other while attaching the negative electrode active material particles to the negative electrode current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0141] The non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0142] The aqueous binder may be selected from the group consisting of: styrene-butadiene rubber, (meth)acrylate esterified styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluorinated rubber, polyethylene oxide, polyvinylpyrrolidone, epichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and a combination thereof.

[0143] If the aqueous binder is used as a binder in the negative electrode active material layer (for example, when the aqueous binder is used as a binder in the negative electrode active material layer), a cellulose compound capable of imparting viscosity (for example, providing appropriate viscosity) may be further included. The cellulose compound may be a mixture of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0144] The dry binder may be a fibrous polymer material and may include, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0145] The conductive material is used to impart conductivity to the electrode and may be any conductive material that does not cause chemical changes in the constructed battery cell. Specifically, the conductive material may include, for example, carbon materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.); metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers (such as polyphenylene derivatives, etc.); or a mixture thereof.

[0146] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0147] The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0148] The non-aqueous organic solvent serves as a medium through which ions participating in the electrochemical reaction of the battery cell can move.

[0149] The non-aqueous organic solvent may include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or a combination thereof.

[0150] The carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC) and / or butylene carbonate (BC).

[0151] The ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc.

[0152] The ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Additionally, the ketone solvents may include cyclohexanone, etc. The alcohol solvents may include ethanol, isopropanol, etc., and the aprotic solvents may include nitriles (such as, R-CN, where R is a straight-chain hydrocarbon group, branched-chain hydrocarbon group or cycloalkyl group having 2 to 20 carbon atoms and may include double bonds, aromatic rings or ether bonds); amides (such as, dimethylformamide); dioxolanes (such as, 1,3-dioxolane, 1,4-dioxolane, etc.); sulfolane, etc.

[0153] The non-aqueous organic solvents can be used alone or in mixtures thereof.

[0154] When using carbonate solvents, a mixture of cyclic carbonate and chain carbonate can be used, and the cyclic carbonate and the chain carbonate can be mixed at a volume ratio of 1:1 to 1:9.

[0155] The lithium salt is a substance soluble in non-aqueous organic solvents and serves as a source of lithium ions in the battery, ensuring the basic operation of the rechargeable lithium battery while facilitating the transfer of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt may include those selected from LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiPO 2 F 2 , LiCl, LiI, LiN(SO 3 C 2 F 5 ) 2 , Li(FSO 2 ) 2 N (lithium bis(fluorosulfonyl)imide (LiFSI)), LiC 4 F 9 SO 3, LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 )(wherein x and y are each an integer from 1 to 20), at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro bis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0156] Depending on the type of rechargeable lithium battery, a separator can be inserted between the positive electrode and the negative electrode. For such a separator, a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, or at least two layers thereof (such as a polyethylene / polypropylene bilayer separator, a polyethylene / polypropylene / polyethylene trilayer separator, a polyethylene / polyethylene / polypropylene trilayer separator, etc.) can be used.

[0157] The separator can include a porous substrate and a coating including an organic material, an inorganic material, or a combination thereof on one surface or both surfaces of the porous substrate.

[0158] The porous substrate can be a polymer layer formed from a polymer selected from polyolefins (such as polyethylene, polypropylene, etc.), polyesters (such as polyethylene terephthalate, polybutylene terephthalate, etc.), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyarylether ketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cycloolefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (e.g., Teflon), copolymers thereof, or mixtures thereof.

[0159] The organic material can include a polyvinylidene fluoride polymer or a (meth)acrylic polymer. The inorganic material can include inorganic particles selected from Al 2 O 3 , SiO 2 , TiO 2 , SnO 2 , CeO 2 , MgO, NiO, CaO, GaO, ZnO, ZrO 2 , Y 2 O 3 , SrTiO 3 , BaTiO 3 , Mg(OH) 2 , boehmite, and combinations thereof, but not limited thereto.

[0160] The organic material and the inorganic material can exist in a mixed state in one coating or can be in the form of a stacked structure including a coating including the organic material and a coating including the inorganic material.

[0161] Based on the shape of the rechargeable lithium battery, the rechargeable lithium battery can be classified into a cylindrical battery, a prismatic battery, a pouch-type battery, a coin-type battery, etc. Figures 1 to 4 FIG. is a schematic view of a rechargeable lithium battery according to an embodiment of the present disclosure, in which Figure 1 a cylindrical battery is shown, Figure 2 a polyhedron (e.g., prismatic) battery is shown, and Figure 3 and Figure 4 a pouch-type battery is shown. Referring to Figures 1 to 4 , the rechargeable lithium battery 100 may include an electrode assembly 40 in which a separator 30 is inserted between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is accommodated. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolyte. As Figure 1 shown in Figure 2 , the rechargeable lithium battery 100 may include a sealing member 60 for sealing the case 50. Additionally, as Figure 2 shown in Figure 3 and Figure 4 , the rechargeable lithium battery 100 may include electrode tabs 70 that serve as a circuit path for guiding the current generated in the electrode assembly 40 to the outside, i.e., a positive electrode tab 71 and a negative electrode tab 72.

[0162] The rechargeable lithium battery according to an embodiment of the present disclosure may be applied to a vehicle, a mobile phone, and / or various other electronic devices, but is not limited thereto.

[0163] Next, the present disclosure will be described in more detail with reference to embodiments. However, it should be understood that these embodiments are provided only for illustration and should not be construed as limiting the present disclosure in any way.

[0164] Example 1: Preparation of a positive electrode active material for a rechargeable lithium battery

[0165] (1) Mix an aluminum precursor Al 2 (SO 4 ) 3 ·18H 2 O with NaOH, NH 4 OH, and water to prepare an aqueous solution of the aluminum precursor.

[0166] Additionally, mix a nickel precursor NiSO 4 ·6H 2 O with water to prepare an aqueous solution of the nickel precursor, and mix a cobalt precursor CoSO 4 ·7H 2 O with water to prepare an aqueous solution of the cobalt precursor.

[0167] An aqueous solution of an aluminum precursor is placed in a reactor, and aqueous solutions of a nickel precursor and a cobalt precursor are added dropwise to the reactor to obtain a reaction mixture, and then the reaction mixture is stirred for 10 to 20 hours. Control the content of each of the nickel precursor, cobalt precursor, and aluminum precursor in the reaction mixture according to stoichiometry until the molar ratio of nickel, manganese, and aluminum reaches 95:4:1.

[0168] An aqueous solution of sodium hydroxide is added to the reaction mixture to adjust the pH of the reaction mixture to 10 to 12. The product obtained by filtering and rinsing the resulting precipitate is dried in vacuo at 100 °C to prepare nickel cobalt aluminum hydroxide powder (Ni 0.95 Co 0.04 Al 0.01 (OH) 2 ).

[0169] After mixing nickel cobalt aluminum hydroxide with lithium hydroxide (LiOH) as a lithium precursor in a bowl, the mixture is placed in a furnace and then subjected to a first heat treatment at 750 °C for 20 hours while supplying O 2 to prepare a nickel-based active material. Control the content of each of the nickel cobalt aluminum hydroxide and the lithium precursor so that the molar ratio of the transition metals (nickel, cobalt, and aluminum metals) to lithium reaches 1:1.

[0170] The prepared nickel-based active material is in the form of (i) first secondary particles (NCA, LiNi 0.95 Co 0.04 Al 0.01 O 2 ) with an average particle size of 14 μm.

[0171] (2) Prepare particles (NCA, LiNi 0.95 Co 0.04 Al 0.01 O 2 ) having a single crystal structure in substantially the same manner as in (1), except that the reaction mixture for obtaining nickel cobalt aluminum hydroxide is stirred for 30 hours to control the precursor size and the first heat treatment is carried out at 850 °C instead of 750 °C, and then grinding and heat treatment are carried out at 750 °C. (ii) The particles having a single crystal structure have an average particle size of 3 to 4 μm.

[0172] (3) With respect to 100 parts by weight of (i) first secondary particles and (ii) particles having a single crystal structure, a nickel-based active material is prepared by mixing 70 parts by weight of (i) first secondary particles and 30 parts by weight of (ii) particles having a single crystal structure.

[0173] (4) By mixing a nickel-based active material, cobalt hydroxide (Co(OH) as a cobalt compound2 ) and water as a solvent to prepare a composition for a positive electrode active material, the positive electrode active material including a nickel-based active material wet-coated with a cobalt compound on its surface. Cobalt hydroxide is added to the mixture such that, based on the total content of all metal elements other than lithium in the nickel-based active material, the nickel-based active material prepared in (4) has a cobalt content of 3 mol%.

[0174] (5) Next, under a nitrogen atmosphere, B 2 O 3 as a boron compound is added to the composition of (4), and mixed at 25 °C for 2 hours. Then, the boron compound is dry-coated on the surface of the nickel-based active material wet-coated with the cobalt compound, and a secondary heat treatment is carried out at 725 °C for 12 hours to prepare the desired positive electrode active material. The boron compound is added to the composition such that, based on the total content of all metal elements other than lithium in the nickel-based active material, the nickel-based active material prepared in (5) has a boron content of 0.25 mol%.

[0175] Example 2: Preparation of positive electrode active material

[0176] The positive electrode active material is prepared in substantially the same manner as in Example 1, except that in (5) of Example 1, a boron compound is added such that, based on the total content of all metal elements other than lithium in the nickel-based active material, the nickel-based active material prepared in (5) has a boron content of 0.5 mol%.

[0177] Comparative Example 1: Preparation of positive electrode active material

[0178] Steps (1) to (4) of Example 1 are carried out in the same manner. Then, the positive electrode active material is obtained by carrying out a secondary heat treatment at 725 °C for 12 hours.

[0179] Comparative Example 2: Preparation of positive electrode active material

[0180] The positive electrode active material is prepared in substantially the same manner as in Example 1, except that a boron compound is added such that, based on the total content of all metal elements other than lithium in the nickel-based active material, the nickel-based active material prepared in (5) has a boron content of 0.75 mol%.

[0181] Preparation of rechargeable lithium battery

[0182] A rechargeable lithium battery is prepared using the positive electrode active materials prepared in the examples and comparative examples as follows.

[0183] A positive electrode active material slurry with uniform dispersion is prepared by mixing a positive electrode active material, carbon black as a conductive material, polyvinylidene fluoride as a binder, and N-methylpyrrolidone as a solvent in a mixer to remove air bubbles. In the positive electrode active material slurry, based on a total of 100 parts by weight, the weight ratio of the positive electrode active material, carbon black, and polyvinylidene fluoride is 97.7:1.0:1.3, and the amount of the solvent present is about 50 parts by weight relative to 90 parts by weight of the positive electrode active material.

[0184] The prepared positive electrode active material slurry is coated on an aluminum foil using a doctor blade to form a thin electrode plate, and then dried at 135 °C for 3 hours or longer, rolled, and dried in vacuo to prepare a positive electrode.

[0185] Graphite powder (Japan Carbon) as a negative electrode active material and a mixture of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) with a weight ratio of 1:1 are mixed at a weight ratio of 98:2 to prepare a negative electrode active material slurry.

[0186] The prepared negative electrode active material slurry is coated on a copper foil current collector with a thickness of 8 μm at a loading level of 19.5 mg / cm 2 . The coated electrode plate is dried at 100 °C for 1 hour or longer, and then rolled to prepare a negative electrode with a composite density of 1.60 g / cm 3 .

[0187] A rechargeable lithium battery with a capacity of 30 mAh is prepared using the positive electrode and the negative electrode together with a polyethylene separator (separator, STAR 20, Asahi) and an electrolytic solution (in which 1.15 M LiPF 6 is dissolved in a mixed solvent of EC (ethylene carbonate), EMC (ethyl methyl carbonate), and DMC (dimethyl carbonate) (volume ratio 3:3:4)).

[0188] Evaluation Example 1: Scanning electron microscope (SEM)

[0189] The cross-section of the positive electrode prepared using the positive electrode active material prepared in Example 1 is measured by SEM, and the results are shown in Figure 5 . In addition, SEM images at a higher magnification of the outer peripheral portion (the portion shown within the frame) of the positive electrode active material in Figure 6 are shown in Figure 5 .

[0190] As shown in Figure 5 , it can be seen that the positive electrode active material prepared in Example 1 is uniformly coated with a coating material on its nickel-based active material.

[0191] AsFigure 6 As shown in Figure 6 , the visible bright area represents cobalt, indicating that the grain boundaries of the primary particles of the nickel-based active material are uniformly coated with cobalt.

[0192] Evaluation Example 2: Specific surface area of the positive electrode active material

[0193] The specific surface area of the positive electrode active material prepared in each of the Examples and Comparative Examples was measured by the BET measurement method, and the results are shown in Table 1. As shown in Table 1, it can be seen that the positive electrode active material of the Example in which 0.25 mol% and 0.5 mol% of boron are coated relative to 3 mol% of cobalt has a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g. However, the positive electrode active material of the Comparative Example in which boron is not coated or 0.75 mol% of boron is coated relative to 3 mol% of cobalt has a specific surface area outside the range of 0.45 m 2 / g to 0.60 m 2 / g.

[0194] Evaluation Example 3: Charge capacity / discharge capacity and efficiency

[0195] For each of the rechargeable lithium batteries of the Examples and Comparative Examples, the initial charge capacity and the initial discharge capacity were measured as follows: at 25 °C, charging was carried out at a constant current of 0.2C from 2.8V to the upper limit voltage of 4.2V, and the rechargeable lithium battery was charged until the current dropped to the end condition of 0.05C, and then discharged at 0.2C to the discharge termination voltage of 2.8V. The results are shown in Table 1.

[0196] As shown in Table 1, compared with the positive electrode active material of the Comparative Example, the positive electrode active material of the Example having a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g shows significantly improved efficiency (i.e., the percentage of the initial discharge capacity to the charge capacity).

[0197] Evaluation Example 4: High-temperature life

[0198] Each of the rechargeable lithium batteries prepared in the Examples and Comparative Examples was charged at a constant current of 0.2C from 2.8V to the upper limit voltage of 4.2V at 45 °C, and then charged at a constant voltage until the current dropped to 0.05C while maintaining the voltage at 4.2V. Then, the battery was discharged at a constant current of 0.2C until the voltage dropped to 2.8V (formation stage).

[0199] Each of the rechargeable lithium batteries undergoing the formation stage was charged at a constant current of 1C at 45 °C until the voltage reached 4.2V, and then charged at a constant voltage until the current dropped to 0.05C while maintaining the voltage at 4.2V. Then, it was discharged at a constant current of 1C until the voltage dropped to 2.8V. The above charge / discharge cycle was repeated 100 times. The discharge capacity of each cycle was measured, and the high-temperature life was evaluated by the ratio of the discharge capacity of each cycle to the first discharge capacity.

[0200] The results are shown in Figure 7 As shown in Figure 7 As shown in, it can be seen that compared with the rechargeable lithium battery prepared using the positive electrode active material of the comparative example, the rechargeable lithium battery prepared using the positive electrode active material of the example having a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g exhibits significantly improved high-temperature life. In particular, it can be seen that compared with the rechargeable lithium battery prepared using the positive electrode active material of Comparative Example 1 having a specific surface area of 0.41 m 2 / g and the positive electrode active material of Comparative Example 2 having a specific surface area of 0.76 m 2 / g, the rechargeable lithium battery prepared using the positive electrode active material of the example having a specific surface area of 0.45 m 2 / g to 0.60 m 2 / g exhibits significantly improved high-temperature life.

[0201] Evaluation Example 5: Outgassing amount after being placed at 80 °C

[0202] The rechargeable lithium batteries of the examples and comparative examples were placed in a chamber at a constant temperature of 80 °C for a predetermined time to evaluate the outgassing amount per unit weight of the positive electrode active material in the battery. The outgassing amount was evaluated by the Archimedes measurement method. The results are shown in Figure 8 As shown in

[0203] As shown in Figure 8 As shown in, it can be seen that the outgassing amount of the positive electrode active material of the example is much lower than that of the positive electrode active material of Comparative Example 1 without the boron coating after being placed at high temperature (e.g., stored).

[0204] Evaluation Example 6: Outgassing amount in the overcharged state of 2.8V to 5V

[0205] Each of the rechargeable lithium batteries of the examples and comparative examples was charged from 2.8V to 5V at a constant current of 0.2C at 25 °C, and then cut off in a constant voltage mode at 0.1C. Here, the outgassing amount per unit weight of the positive electrode active material in the rechargeable lithium battery was measured, and the results are shown in Figure 9 As shown in

[0206] As Figure 9 shown, it can be seen that, compared with the rechargeable lithium battery prepared using the positive electrode active material of Comparative Example 1, in the overcharged state, the outgassing amount per unit weight of the positive electrode active material in the rechargeable lithium battery prepared using the positive electrode active material of the Example is higher. Accordingly, it is considered that the positive electrode active material of the Example can ensure (for example, guarantee) safety by quickly activating the safety device in the case of overcharging.

[0207] Evaluation Example 7: Free lithium content

[0208] The free lithium (residual lithium) of the positive electrode active materials of the Examples and Comparative Examples was evaluated. 100 g of deionized water was added to 10 g of the positive electrode active material sample, and then stirred at about 250 rpm for 30 minutes. The resulting solution was filtered, and then titrated with a 0.1 M hydrochloric acid aqueous solution. After the titration, as Figure 12 shown, two inflection points were generated, and the content of free lithium was calculated by examining the added amount of the hydrochloric acid aqueous solution at each inflection point. The results are shown in Table 1. As shown in Table 1, it can be seen that the higher the content of the boron compound, the higher the measured value of free lithium.

[0209] Evaluation Example 8: Curve analysis evaluation during overcharging from 2.8 V to 5 V

[0210] Each of the rechargeable lithium batteries of the Examples and Comparative Examples was charged from 2.8 V to 5 V at a constant current of 0.5 C at 25 °C, and cut off in a constant voltage mode at 0.1 C.

[0211] Figure 10 A comparison of the curves showing the relationship between time and voltage during charging to 5 V is shown. It can be seen that as the boron content on the surface of the positive electrode active material increases, the curve stretches in the region of 4.8 V or higher, indicating that a phase change and a chemical reaction have occurred. The expected chemical reaction is the generation of O 2 gas and other gases due to the chemical decomposition of the lithium boron coating at high voltage. As the amount of the chemical reaction increases and more gas is generated, the curve further stretches into a flat shape.

[0212] Figure 11 and Figure 12Graph showing the relationship between voltage (x-axis) and dQ / dV during charging to 5V. Generally, a high-Ni (Ni 80 or higher) positive electrode active material shows a flat region with a curve stretch when charged in the range of 4.1V to 4.2V, and a peak is generated in the dQ / dV graph. If the peak in the corresponding region (4.1V to 4.2V) is set as I1, and the peak in the region of 4.7V to 4.9V that occurs during overcharging is set as I2 (for example, when the peak in the corresponding region (4.1V to 4.2V) is set as I1, and the peak in the region of 4.7V to 4.9V that occurs during overcharging is set as I2), a ratio (I1 / I2) of 20 or greater satisfies the optimal cobalt and boron coating conditions.

[0213] Table 1

[0214]

[0215]

[0216] As used herein, the terms "use", "using", and "used" may be considered synonymous with the terms "utilize", "utilizing", and "utilized", respectively. As used herein, phrases such as "at least one of...", "one of...", and "selected from...", when before / after a list of elements, modify the entire list of elements and do not modify an individual element of the list. For example, "at least one selected from a, b, and c" and "at least one of a, b, and c" may indicate only a, only b, only c, both a and b (e.g., a and b simultaneously), both a and c (e.g., a and c simultaneously), both b and c (e.g., b and c simultaneously), all of a, b, and c, or variants thereof.

[0217] When describing embodiments of the inventive concept, the use of "may" refers to "one or more embodiments of the inventive concept".

[0218] As used herein, the terms "about" and similar terms are used as approximate terms and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by a person of ordinary skill in the art. As used herein, "about" includes the recited value and means within an acceptable deviation range determined for a particular value by a person of ordinary skill in the art considering the measurements discussed and the errors associated with the particular quantity of measurements (i.e., the limitations of the measurement system). For example, "about" may mean within one or more standard deviations of the recited value, or within ±30%, ±20%, ±10%, or ±5% of the recited value.

[0219] Also, any numerical range recited herein is intended to include all sub-ranges of the same numerical precision falling within the recited range. For example, a range of "1.0 to 10.0" is intended to include between the minimum value of 1.0 and the maximum value of 10.0 recited (and including 1.0 and 10.0), i.e., all sub-ranges having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limit recited herein is intended to include all lower numerical limits falling therein and any minimum numerical limit recited in this specification is intended to include all higher numerical limits falling therein. Accordingly, the applicant reserves the right to amend this specification (including the claims) to expressly recite any sub-range falling within the ranges expressly recited herein.

[0220] Here, unless otherwise specified, steps, tasks, or acts listed in a particular order do not necessarily mean that the invention or claim requires that particular order. That is, the general rule is that unless the steps, tasks, or acts of a method (e.g., method claims) actually recite an order, these steps, tasks, or acts should not be construed as requiring an order.

[0221] The battery manufacturing apparatus, battery management system (BMS) apparatus, and / or any other related apparatus or components according to embodiments of the present invention described herein can be implemented using any suitable hardware, firmware (e.g., application specific integrated circuit), software, or a combination of software, firmware, and hardware. For example, the various components of the apparatus can be formed on one integrated circuit (IC) chip or on separate IC chips. Further, the various components of the apparatus can be implemented on a flexible printed circuit film, tape carrier package (TCP), or printed circuit board (PCB), or formed on a substrate. Further, the various components of the apparatus can be processes or threads running on one or more processors in one or more computing devices, executing computer program instructions and interacting with other system components to perform the various functions described herein. The computer program instructions are stored in a memory, which can be implemented in a computing device using standard storage devices, such as, for example, random access memory (RAM). The computer program instructions can also be stored in other non-transitory computer-readable media, such as, for example, CD-ROM, flash drive, etc. And, those skilled in the art should recognize that, without departing from the scope of the present disclosure, the functions of various computing devices can be combined or integrated into a single computing device, or the functions of a dedicated computing device can be distributed over one or more other computing devices.

[0222] Although the present disclosure has been described with reference to some embodiments and the accompanying drawings, it should be understood that the present disclosure is not limited thereto, and various modifications, changes, variations, and equivalent embodiments may be made by those skilled in the art without departing from the spirit and scope of the present disclosure as set forth in the claims and their equivalents.

Claims

1. A positive electrode active material for a rechargeable lithium battery, comprising: a nickel-based active material; a cobalt-containing coating on the surface of the nickel-based active material; and a boron-containing coating on the surface of the cobalt-containing coating, The positive electrode active material has a 0.45 m 2 / g~0.60m 2 / g specific surface area.

2. The positive electrode active material according to claim 1, wherein the nickel-based active material is represented by Formula 1: Formula 1 Li a (Ni 1-x-y-z Co x M y m' z )O 2-δ , wherein M is at least one selected from Mn and Al; M' is at least one element selected from the group consisting of boron, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, iron, copper, zirconium, and aluminum; and 0.95 ≤ a ≤ 1.3, x ≤ (1 - x - y - z), y ≤ (1 - x - y - z), z ≤ (1 - x - y - z), 0 < x < 1, 0 ≤ y < 1, 0 ≤ z < 1 and 1.98 ≤ 2 - δ ≤ 2.

3. The positive electrode active material according to claim 1, wherein the boron-containing coating is integrally formed with the cobalt-containing coating.

4. The positive electrode active material according to claim 1, wherein based on all metal elements other than lithium in the positive electrode active material in a total of 100 mol%, the positive electrode active material has a nickel content of 70 mol% or more.

5. The positive electrode active material according to claim 1, wherein the nickel-based active material includes secondary particles formed by physical aggregation and / or chemical aggregation of primary particles.

6. The positive electrode active material according to claim 5, wherein the cobalt-containing coating is present on the surface of the secondary particles and at the grain boundaries of the primary particles.

7. The positive electrode active material according to claim 1, wherein the nickel-based active material includes at least one of (i) a first secondary particle, (ii) a particle having a single crystal structure, and (iii) an integral particle.

8. The positive electrode active material according to claim 7, wherein the nickel-based active material is a mixture of (i) the first secondary particle and (ii) the particle having a single crystal structure.

9. The positive electrode active material according to claim 8, wherein with respect to 100 parts by weight of the mixture, (i) the amount of the first secondary particle is 60 to 90 parts by weight, and (ii) the amount of the particle having a single crystal structure is 10 to 40 parts by weight.

10. The positive electrode active material according to claim 7, wherein (i) the first secondary particle has a size of 14 to 18 μm, and (ii) the particle having a single crystal structure has a size of 1 to 7 μm.

11. The positive electrode active material according to claim 1, wherein when charging from 2.8V to 5V, in the dQ / dV curve, when the peak in the region of 4.1V to 4.2V is referred to as I1, and the peak in the region of 4.7V to 4.9V is referred to as I2, the ratio of I1 / I2 is greater than or equal to 20.

12. The positive electrode active material according to claim 1, wherein the nickel-based active material comprises Li 1.01 Ni 0.8 Co 0.1 Al 0.1 O2、Li 1.01 Ni 0.8 Co 0.05 Al 0.15 O2、Li 1.01 Ni 0.8 Co 0.15 Al 0.05 O2、LiNi 0.95 Co 0.04 Al 0.01 O2 or a combination thereof.

13. A method for preparing a positive electrode active material for a rechargeable lithium battery, the method comprising: preparing a first positive electrode active material from a mixture comprising a nickel-based active material, a cobalt compound, and a solvent, wherein the cobalt compound is wet-coated on the surface of the nickel-based active material; preparing a second positive electrode active material by dry coating a boron compound on a surface of the first positive electrode active material; as well as preparing a positive electrode active material for a rechargeable lithium battery by heat-treating the second positive electrode active material at 700° C. to 750° C., The amount of boron from the boron compound is 0.25 mol % to 0.5 mol % based on 100 mol % of all metal elements except lithium in the nickel-based active material. 14 . A positive electrode comprising the positive electrode active material according to claim 1 or the positive electrode active material prepared by the method according to claim 13 .

15. A rechargeable lithium battery comprising: A positive electrode comprising the positive electrode active material according to any one of claims 1 to 12 or a positive electrode active material prepared by the method according to claim 13; a negative electrode; and Electrolyte.

Images