Method for producing a positive electrode active material and positive electrode active material

Abstract

This invention relates to a method for preparing a positive electrode active material, a positive electrode active material prepared by the above-described method, and a positive electrode and a lithium secondary battery containing the positive electrode active material. The method for preparing the positive electrode active material includes the following steps: (A) preparing a pre-sintered product by first sintering a mixture of a positive electrode active material precursor having a composition of Formula 1-1 or 1-2 as described in this specification and a lithium-containing raw material; (B) preparing a lithium transition metal oxide having a composition of Formula 2 as described in this specification by mixing the pre-sintered product with an aluminum-containing raw material, performing a second sintering, washing, and drying; and (C) dry mixing the lithium transition metal oxide with a boron-containing raw material and heat-treating it to form a coating.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2021-0003193, filed on January 11, 2021, the disclosure of which is incorporated herein by reference. Technical Field

[0004] This invention relates to a method for preparing a positive electrode active material for lithium secondary batteries, a positive electrode active material prepared by the method, a positive electrode for lithium secondary batteries containing the positive electrode active material, and a lithium secondary battery. Background Technology

[0005] With the technological advancements and increasing demands of mobile devices, the need for secondary batteries as an energy source has grown significantly. Among these secondary batteries, lithium-ion batteries, characterized by high energy density, high voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0006] Lithium transition metal oxides have been used as positive electrode active materials for lithium secondary batteries, and among these oxides, lithium cobalt oxides such as LiCoO2, which have high operating voltage and excellent capacity characteristics, are mainly used. However, because LiCoO2 has very poor thermal properties due to its unstable crystal structure caused by delithiation and is expensive, there are limitations to its use in large quantities as a power source for applications such as electric vehicles.

[0007] Lithium-manganese composite metal oxides (LiMnO2, LiMn2O4, etc.), lithium iron phosphate compounds (LiFePO4, etc.), or lithium-nickel composite metal oxides (LiNiO2, etc.) have been developed as alternatives to LiCoO2. Among these materials, lithium-nickel composite metal oxides have been studied and developed more actively, as they can easily achieve large-capacity batteries due to their high reversible capacity of approximately 200 mAh / g. However, LiNiO2 is limited by its poor thermal stability compared to LiCoO2, and the positive electrode active material decomposes itself when an internal short circuit occurs during charging due to external pressure, leading to battery rupture and fire. Therefore, as a method to improve the low thermal stability while maintaining the excellent reversible capacity of LiNiO2, partially nickel-substituted LiNiO2 has been developed. 1-α Co α O2 (α = 0.1 to 0.3) or lithium-nickel composite metal oxides in which some nickel is replaced by Mn, Co or Al.

[0008] However, a limitation of lithium-nickel composite metal oxides is their low capacity. To improve the capacity of lithium-nickel composite metal oxides, methods to increase the amount of nickel contained in them have been studied. However, in this case, a washing process is necessary due to unreacted residual lithium on the surface, and the washing process causes surface defects in the positive electrode active material, thus degrading the battery's lifespan.

[0009] To overcome this problem, traditionally, the following method has been studied: after washing the positive electrode active material, a coating is formed on the surface of the positive electrode active material at low temperature. However, there are still limitations in improving high-temperature lifetime characteristics, resistance characteristics and high-temperature gas generation characteristics.

[0010] Therefore, there is a need to develop a positive electrode active material with improved high-temperature lifetime characteristics, high-temperature resistance characteristics, high-temperature gas generation characteristics, and high capacity characteristics. Summary of the Invention

[0011] Technical issues

[0012] One aspect of the present invention provides a method for preparing a positive electrode active material and a positive electrode active material therefrom, said positive electrode active material having improved high-temperature lifetime characteristics, high-temperature resistance characteristics, high-temperature gas generation characteristics, and high capacity characteristics.

[0013] However, the purpose of this invention is not limited to the above, and those skilled in the art will clearly understand other purposes not described herein through the following description.

[0014] Technical solution

[0015] According to one aspect of the present invention, a method for preparing a positive electrode active material is provided, the method comprising the following steps:

[0016] (A) A pre-sintered product is prepared by sintering a mixture of a positive electrode active material precursor having a composition of formula 1-1 or 1-2 and a lithium-containing raw material in one step.

[0017] (B) A lithium transition metal oxide having the composition of Formula 2 is prepared by mixing the pre-sintered product with an aluminum-containing raw material, followed by secondary sintering, washing, and drying; and

[0018] (C) The lithium transition metal oxide is dry-mixed with a boron-containing raw material and then heat-treated to form a coating.

[0019] [Equation 1-1]

[0020] Ni a1 Co b1 Mn c1 M 1d1 (OH)2

[0021] [Formula 1-2]

[0022] Ni a1 Co b1 Mn c1 M 1 d1 O·OH

[0023] In Formulas 1-1 and 1-2,

[0024] M 1 is at least one selected from the following: Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and

[0025] 0.7 ≤ a1 ≤ 1.0, 0 ≤ b1 ≤ 0.3, 0 ≤ c1 ≤ 0.3, and 0 ≤ d1 ≤ 0.1,

[0026] [Formula 2]

[0027] Li x Ni a2 Co b2 Mn c2 Al d2 M 1 e2 O2

[0028] In Formula 2,

[0029] M 1 is at least one selected from the following: Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and

[0030] 0.9 ≤ x ≤ 1.12, 0.7 ≤ a2 ≤ 1.0, 0 ≤ b2 ≤ 0.3, 0 ≤ c2 ≤ 0.3, 0 < d2 ≤ 0.2, and 0 ≤ e2 ≤ 0.1.

[0031] According to another aspect of the present invention, there is provided a positive electrode active material comprising: a lithium transition metal oxide represented by Formula 2; and a boron-containing coating formed on the surface of the lithium transition metal oxide, wherein the coating contains a Li-Al-B-O solid solution, and in time-of-flight secondary ion mass spectrometry, the intensity ratio of the peak detected at a mass greater than 27.0 and equal to or less than 27.5 to the intensity of the peak of Al + is in the range of 1:0.5 to 1:1.5.

[0032] [Formula 2]

[0033] Li x Ni a2Co b2 Mn c2 Al d2 M 1 e2 O2

[0034] In Formula 2,

[0035] M 1 is at least one selected from the following: Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and

[0036] 0.9 ≤ x ≤ 1.12, 0.7 ≤ a2 ≤ 1.0, 0 ≤ b2 ≤ 0.3, 0 ≤ c2 ≤ 0.3, 0 < d2 ≤ 0.2, and 0 ≤ e2 ≤ 0.1.

[0037] According to another aspect of the present invention, there is provided a positive electrode for a lithium secondary battery, the positive electrode including the positive electrode active material according to the present invention.

[0038] According to another aspect of the present invention, there is provided a lithium secondary battery, the lithium secondary battery including the positive electrode according to the present invention.

[0039] Advantageous Effects

[0040] According to the present invention, by adding aluminum during the sintering (secondary sintering) step after presintering (primary sintering) and before washing during the preparation of the positive electrode active material to control the doping degree of aluminum present on the outermost surface, the high-temperature life characteristics, high-temperature resistance characteristics, and high-temperature gas generation characteristics of a battery using the positive electrode active material to be prepared can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the cationic spectrum analysis result of various positive electrode active materials of Example 1 and Comparative Example 1;

[0042] Figure 2 is the anionic spectrum analysis result of various positive electrode active materials of Example 1 and Comparative Example 1;

[0043] Figure 3 is a graph showing data on the high-temperature discharge capacity of secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2;

[0044] Figure 4 is a graph showing the high-temperature life characteristics of secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2;

[0045] Figure 5 is a graph showing the high-temperature resistance characteristics of secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2;

[0046] Figure 6 The graph shows the high-temperature gas generation characteristics of the secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2. Detailed Implementation

[0047] The invention will be described in more detail below.

[0048] It should be understood that the words or terms used in the specification and claims should not be interpreted as having the meanings defined in common dictionaries, and it will be further understood that the words or terms should be interpreted as having meanings consistent with their meanings in the context of the relevant field and technical concept of the invention, based on the principle that the inventor can appropriately define the meanings of the words or terms to best interpret the invention.

[0049] The terminology used in this specification is for describing exemplary embodiments only and is not intended to limit the invention. Unless otherwise stated, singular terms may include plural forms.

[0050] It should be further understood that the terms "comprising," "including," or "having" in this specification are used to specify the presence of the described features, quantities, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0051] In this specification, unless otherwise expressly stated, “%” means “weight %”.

[0052] In this specification, the term "on" means not only that a component is formed directly on the upper surface of another component, but also that an intermediary component may be present.

[0053] Methods for preparing positive electrode active materials

[0054] The method for preparing the positive electrode active material according to the present invention will be described in detail below.

[0055] The method for preparing the positive electrode active material according to the present invention includes the following steps:

[0056] (A) A pre-sintered product is prepared by sintering a mixture of a positive electrode active material precursor having a composition of formula 1-1 or 1-2 and a lithium-containing raw material in one step.

[0057] (B) A lithium transition metal oxide having the composition of Formula 2 is prepared by mixing the pre-sintered product with an aluminum-containing raw material, followed by secondary sintering, washing, and drying; and

[0058] (C) The lithium transition metal oxide is dry-mixed with a boron-containing raw material and then heat-treated to form a coating.

[0059] [Formula 1-1]

[0060] Ni a1 Co b1 Mn c1 M 1 d1 (OH)2

[0061] [Formula 1-2]

[0062] Ni a1 Co b1 Mn c1 M 1 d1 O·OH

[0063] In Formulas 1-1 and 1-2,

[0064] M 1 is at least one selected from the following: Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and

[0065] 0.7 ≤ a1 ≤ 1.0, 0 ≤ b1 ≤ 0.3, 0 ≤ c1 ≤ 0.3, and 0 ≤ d1 ≤ 0.1,

[0066] [Formula 2]

[0067] Li x Ni a2 Co b2 Mn c2 Al d2 M 1 e2 O2

[0068] In Formula 2,

[0069] M 1 is at least one selected from the following: Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and

[0070] 0.9 ≤ x ≤ 1.12, 0.7 ≤ a2 ≤ 1.0, 0 ≤ b2 ≤ 0.3, 0 ≤ c2 ≤ 0.3, 0 < d2 ≤ 0.2, and 0 ≤ e2 ≤ 0.1.

[0071] The present inventors have found that by adding aluminum during the secondary sintering (sintering before washing) step rather than the primary sintering (pre-sintering) step during the preparation of the positive electrode active material to adjust the doping degree of aluminum present on the outermost surface to a high level, the high-temperature life characteristics, high-temperature resistance characteristics, and high-temperature gas generation characteristics of the battery using the positive electrode active material to be prepared can be improved.

[0072] In the following, each step will be described in more detail.

[0073] Step (A)

[0074] Step (A) is a step of preparing a pre-sintered product by performing a single sintering on a mixture in which a precursor of a positive electrode active material having a composition of Formula 1-1 or 1-2 and a lithium-containing raw material are mixed.

[0075] [Formula 1-1]

[0076] Ni a1 Co b1 Mn c1 M 1 d1 (OH)2

[0077] [Formula 1-2]

[0078] Ni a1 Co b1 Mn c1 M 1 d1 O·OH

[0079] In Formulas 1-1 and 1-2,

[0080] M 1 is at least one selected from the following: Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and

[0081] 0.7 ≤ a1 ≤ 1.0, 0 ≤ b1 ≤ 0.3, 0 ≤ c1 ≤ 0.3, and 0 ≤ d1 ≤ 0.1.

[0082] a1 represents the atomic fraction of nickel among the metal elements in the precursor, where a1 can satisfy 0.7 ≤ a1 < 1, 0.7 ≤ a1 ≤ 0.98, or 0.7 ≤ a1 ≤ 0.95.

[0083] b1 represents the atomic fraction of cobalt among the metal elements in the precursor, where b1 can satisfy 0 < b1 ≤ 0.3 or 0.01 ≤ b1 ≤ 0.3.

[0084] c1 represents the atomic fraction of manganese among the metal elements in the precursor, where c1 can satisfy 0 < c1 ≤ 0.3 or 0.01 ≤ c1 ≤ 0.3. [[ID=,58]]

[0085] d1 represents the atomic fraction of M 1 in the precursor, where d1 can satisfy 0 ≤ d1 ≤ 0.1 or 0 ≤ d1 ≤ 0.05.

[0086] The lithium-containing feedstock may include at least one selected from: lithium hydroxide hydrate, lithium carbonate, and lithium hydroxide. Specifically, the lithium-containing feedstock may be lithium hydroxide hydrate, such as LiOH·H₂O. In this case, the reactivity between the lithium-containing feedstock and the precursor with a high atomic fraction of nickel in the precursor element can be improved.

[0087] The cathode active material precursor and lithium-containing raw material can be mixed in a molar ratio of 1:1.0 to 1:1.10, particularly 1:1.03 to 1:1.09, and even more particularly 1:1.05 to 1:1.09. When the lithium-containing raw material is mixed in a molar ratio below the above range, there is a problem of reduced capacity in the prepared cathode active material. When the lithium-containing raw material is mixed in a molar ratio above the above range, a large amount of unreacted lithium (Li) remains as a byproduct, and capacity reduction and particle separation of the cathode active material after sintering (leading to agglomeration of the cathode active material) may occur.

[0088] The primary sintering temperature can be in the range of 600℃ to 775℃. Specifically, the primary sintering temperature can be in the range of 620℃ to 760℃, for example, 620℃ to 700℃. When the primary sintering temperature is within the above range, the crystal structure of the pre-sintered product can be controlled, and therefore, the diffusion of aluminum during the secondary sintering can be appropriately controlled.

[0089] One-time sintering can be carried out in an oxygen atmosphere. Under these conditions, pre-sintered products with structurally stable phases can be formed.

[0090] A single sintering process can last from 2 to 15 hours. Specifically, sintering can last from 3 to 10 hours, for example, from 3 to 8 hours. When the sintering time is within the above range, sintering can be carried out well without deviation (uniformly) at each sintering position.

[0091] Residual unreacted lithium is present on the surface of the pre-sintered product, wherein the amount of residual lithium can be minimized by steps (B) and (C) according to the invention.

[0092] Step (B)

[0093] Step (B) is a step of preparing a lithium transition metal oxide having the composition of Formula 2 by mixing the pre-sintered product prepared in step (A) with an aluminum-containing raw material, performing secondary sintering, washing and drying.

[0094] [Equation 2]

[0095] Li x Ni a2 Co b2 Mn c2 Al d2 M1 e2 O2

[0096] In Formula 2,

[0097] M 1 is at least one selected from the following: Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and

[0098] 0.9 ≤ x ≤ 1.12, 0.7 ≤ a2 ≤ 1.0, 0 ≤ b2 ≤ 0.3, 0 ≤ c2 ≤ 0.3, 0 < d2 ≤ 0.2, and 0 ≤ e2 ≤ 0.1.

[0099] a2 represents the atomic fraction of nickel among the metal elements other than lithium in the positive electrode active material, where a2 can satisfy 0.7 ≤ a2 < 1.0, 0.7 ≤ a2 ≤ 0.98, or 0.7 ≤ a2 ≤ 0.95.

[0100] b2 represents the atomic fraction of cobalt among the metal elements other than lithium in the positive electrode active material, where b2 can satisfy 0 < b2 ≤ 0.3 or 0.01 ≤ b2 ≤ 0.3. [[ID=二十]] [[ID=二十一]]

[0101] [[ID=二十二]] [[ID=二十三]]

[0102] [[ID=二十五]]d2 represents the atomic fraction of aluminum among the metal elements other than lithium in the positive electrode active material, where d2 can satisfy 0 ≤ d2 ≤ 0.2, 0 ≤ d2 ≤ 0.1, or 0 ≤ d2 ≤ 0.05. [[ID=二十六]] [[ID=二十七]]

[0103] [[ID=二十八]]e2 represents the atomic fraction of M [[ID=二十九]] 1 [[ID=三十]]in the metal elements other than lithium in the positive electrode active material, where e2 can satisfy 0 ≤ e2 ≤ 0.1 or 0 ≤ e2 ≤ 0.05. [[ID=三十一]] [[ID=三十二]]

[0104] [[ID=三十三]]In the present invention, since an aluminum-rich coating is formed on the surface of the obtained positive electrode active material by mixing an aluminum-containing raw material and performing secondary sintering in step (B), the high-temperature life characteristics, high-temperature resistance characteristics, and high-temperature gas generation characteristics of the secondary battery including the positive electrode active material can be improved. [[ID=三十四]] [[ID=三十五]]

[0105] The aluminum-containing raw material can be at least one selected from the following: Al(OH)3, Al2O3, AlF3, AlBr3, AlPO4, AlCl3, Al(NO3)3, Al(NO3)3·9H2O, Al2(SO4)3·H2O, Al(H2PO4)3, C2H5O4Al, Al2(SO4)3, NaAlO2, Al2CoO4, LaAlO3, and MgAl2O4. Specifically, the aluminum-containing raw material can be Al(OH)3 and Al2O3, more specifically Al(OH)3. In this case, because the aluminum-containing raw material has a low melting point, aluminum can diffuse uniformly, existing in large quantities and uniformly on the surface of the lithium transition metal oxide.

[0106] Compared to pre-sintered products, the amount of aluminum-containing raw material added can be from 1000 ppm to 10000 ppm, particularly from 2000 ppm to 8000 ppm, and even more particularly from 4000 ppm to 6000 ppm. When the amount of aluminum-containing raw material is within the above range, not only can the reduction in battery capacity be prevented when the desired positive electrode active material is used in a battery, but thermal stability can also be improved.

[0107] The secondary sintering temperature can be in the range of 730°C to 900°C. Specifically, the secondary sintering temperature can be in the range of 730°C to 850°C, for example, 750°C to 800°C. When the secondary sintering temperature is within the above range, because an appropriate crystal size is formed, the battery life characteristics can be improved when the prepared positive electrode active material is used in a battery.

[0108] The secondary sintering temperature is higher than the primary sintering temperature, and the difference between the secondary and primary sintering temperatures can be in the range of 10°C to 150°C, particularly 20°C to 150°C, and even more particularly 30°C to 140°C. When the difference between the secondary and primary sintering temperatures is within the above range, the degree of aluminum doping present on the outermost surface can be advantageously controlled.

[0109] Secondary sintering can be performed in an oxygen atmosphere. In this case, because the cation exchange between lithium and nickel is suppressed, the capacity of the battery can be increased when the positive electrode active material to be prepared is used in the battery.

[0110] The secondary sintering can be carried out for 2 to 15 hours. Specifically, the sintering can be carried out for 3 to 10 hours, for example, 3 to 8 hours. When the secondary sintering time is within the above range, sintering can be carried out well without deviation (uniformly) at each sintering position.

[0111] Washing is a process for removing unreacted residual lithium, wherein the washing is performed by mixing the secondary sintering product with a washing liquid and then separating the secondary sintering product from the washing liquid.

[0112] The washing solution can be water or ethanol, but is not limited to these.

[0113] The mixing amount of the washing liquid can be 60 to 200 parts by weight relative to 100 parts by weight of the secondary sintered product, particularly 60 to 150 parts by weight, and even more particularly 80 to 120 parts by weight. When the amount of washing liquid is within the above range, residual lithium present on the surface of the secondary sintered product can be easily removed. When the amount of washing liquid is below the above range, because the amount of residual lithium present on the surface of the secondary sintered product is large, there is a problem of gas generation when the secondary sintered product is used in a battery. Conversely, when the amount of washing liquid is above the above range, because the surface of the lithium transition metal oxide is damaged, the lifespan of the lithium transition metal oxide may be shortened and the rate of increase in resistance may increase when it is used in a battery.

[0114] The process of separating the secondary sintering product from the washing liquid can be carried out in such a way that the water content of the secondary sintering product separated from the washing liquid is in the range of 3% to 15%. Specifically, the process of separating the secondary sintering product from the washing liquid can be carried out in such a way that the water content of the secondary sintering product is in the range of 5% to 12%, for example, 5% to 10%.

[0115] In this context, the moisture content refers to the water content contained in the secondary sintering product after separation from the washing liquid and before drying, wherein the moisture content can be calculated according to Formula 1 below.

[0116] [Formula 1]

[0117] Moisture content (%) = {[(mass of the secondary sintered product before drying) - (mass of the secondary sintered product after drying)] / (mass of the secondary sintered product before drying)} × 100

[0118] In this case, drying can be performed by drying the secondary sintering product separated from the washing liquid at 130°C for 300 minutes.

[0119] When the water content is within the above range, because the surface state, i.e. the surface properties, can be controlled, a coating with uniform composition and uniform thickness can be easily formed on the surface of lithium transition metal oxide.

[0120] The separation can be performed using a vacuum filter with an average pore size of 1 μm to 50 μm. In this case, the secondary sintering products can be separated from the washing liquid in a short time.

[0121] The drying process is used to remove moisture from lithium transition metal oxides that contain water after a washing process. The drying can be carried out at a temperature range of 60°C to 150°C after moisture removal using a vacuum pump. Specifically, the drying process can be carried out at a temperature range of 60°C to 150°C for more than 3 hours.

[0122] Step (C)

[0123] Step (C) involves dry mixing the lithium transition metal oxide prepared in step (B) with a boron-containing raw material and then heat-treating it to form a coating.

[0124] A boron-containing coating is formed on the surface of a lithium transition metal oxide in step (C). Specifically, a coating containing a Li-Al-BO solid solution is formed on the surface of the lithium transition metal oxide. That is, by dry mixing the lithium transition metal oxide with a boron-containing raw material and then heat-treating, a coating containing both Li-Al-BO and Li-BO solid solutions is formed. In this case, because the coating is strengthened, side reactions between the positive electrode active material and the electrolyte can be suppressed more effectively. Furthermore, the coating may also contain aluminum-rich Ni-Co-Mn-Al and aluminum-rich Ni-Co-Mn-Al-B solid solutions. The coating thickness can be in the range of 4 nm to 10 nm. When the coating thickness is within the above range, because surface side reactions can be suppressed, the battery life characteristics can be improved when the positive electrode active material is used in a battery, and gas generation can be suppressed.

[0125] Furthermore, because aluminum is abundant on the outermost surface of lithium transition metal oxides, it is also abundant in the coating. And when analyzing the obtained positive electrode active material, the intensity of the peak detected in time-of-flight secondary ion mass spectrometry at a mass greater than 27.0 and equal to or less than 27.5 is relative to that of Al. + The ratio of peak intensity can be in the range of 1:0.5 to 1:1.5.

[0126] The boron-containing raw material can be at least one selected from the following: H3BO3, B2H4O4, B2O3, LiBO2, Li2B4O7, and AlBO3. Specifically, the boron-containing raw material can be H3BO3 and B2O3, more specifically, H3BO3. In this case, because the boron-containing raw material has a low melting point, a uniform coating can be formed.

[0127] The amount of boron-containing raw material mixed with 100 parts by weight of lithium transition metal oxide can be from 0.1 parts by weight to 1.5 parts by weight, particularly from 0.2 parts by weight to 1.0 parts by weight, and even more particularly from 0.4 parts by weight to 0.8 parts by weight. When the amount of boron-containing raw material is within the above range, not only can a coating be formed uniformly, but a coating with an appropriate thickness can also be formed, thus improving the battery's lifespan characteristics when the positive electrode active material to be prepared is used in a battery.

[0128] Dry mixing of lithium transition metal oxides and boron-containing raw materials has the advantage of minimizing impurities compared to wet mixing.

[0129] The heat treatment temperature can be in the range of 250°C to 400°C. Specifically, the heat treatment temperature can be in the range of 250°C to 350°C, for example, 260°C to 330°C. When the heat treatment temperature is within the above range, because a coating is uniformly formed on the lithium transition metal oxide, the battery life characteristics can be improved when the positive electrode active material is used in a battery. When the heat treatment temperature is below the lower limit of the above range, because the boron-containing raw material has low reactivity, the boron-containing raw material remains on the surface of the lithium transition metal oxide, which may thus act as a resistor. When the heat treatment temperature is above the upper limit of the above range, because the boron-containing raw material and the lithium present on the surface of the lithium transition metal oxide may react excessively, a large amount of lithium may be present in the coating.

[0130] Positive electrode active material

[0131] Furthermore, the positive electrode active material according to the present invention comprises: a lithium transition metal oxide represented by Formula 2; and a boron-containing coating formed on the surface of the lithium transition metal oxide, wherein the coating comprises a Li-Al-BO solid solution, and the intensity of the peak detected in the time-of-flight secondary ion mass spectrometry of the positive electrode active material at a mass greater than 27.0 and equal to or less than 27.5 is relative to Al. + The ratio of peak intensity is in the range of 1:0.5 to 1:1.5.

[0132] [Equation 2]

[0133] Li x Ni a2 Co b2 Mn c2 Al d2 M 1 e2 O2

[0134] In Equation 2,

[0135] M 1is at least one selected from the following: Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and

[0136] 0.9 ≤ x ≤ 1.12, 0.7 ≤ a2 ≤ 1.0, 0 ≤ b2 ≤ 0.3, 0 ≤ c2 ≤ 0.3, 0 < d2 ≤ 0.2, and 0 ≤ e2 ≤ 0.1.

[0137] a2 represents the atomic fraction of nickel among the metal elements other than lithium in the positive electrode active material, where a2 can satisfy 0.7 ≤ a2 < 1.0, 0.7 ≤ a2 ≤ 0.98, or 0.7 ≤ a2 ≤ 0.95.

[0138] b2 represents the atomic fraction of cobalt among the metal elements other than lithium in the positive electrode active material, where b2 can satisfy 0 < b2 ≤ 0.3 or 0.01 ≤ b2 ≤ 0.3.

[0139] c2 represents the atomic fraction of manganese among the metal elements other than lithium in the positive electrode active material, where c2 can satisfy 0 < c2 ≤ 0.3 or 0.01 ≤ c2 ≤ 0.3.

[0140] d2 represents the atomic fraction of aluminum among the metal elements other than lithium in the positive electrode active material, where d2 can satisfy 0 ≤ d2 ≤ 0.2, 0 ≤ d2 ≤ 0.1, or 0 ≤ d2 ≤ 0.05.

[0141] e2 represents the atomic fraction of M 1 among the metal elements other than lithium in the positive electrode active material, where e2 can satisfy 0 ≤ e2 ≤ 0.1 or 0 ≤ e2 ≤ 0.05.

[0142] Since the positive electrode active material is prepared by the above preparation method, it has a coating enhanced due to the presence of a large amount of aluminum on its surface, thereby improving the high-temperature life characteristics, high-temperature resistance characteristics, and high-temperature gas generation characteristics of the secondary battery including the positive electrode active material. The coating may also include an aluminum-rich Ni-Co-Mn-Al solid solution and an aluminum-rich Ni-Co-Mn-Al-B solid solution. The thickness of the coating can be in the range of 4 nm to 10 nm. When the thickness of the coating is within the above range, since the side reaction with the electrolyte can be suppressed, the high-temperature life characteristics and high-temperature resistance characteristics of the battery can be improved when the positive electrode active material is used in the battery, and the generation of gas can be suppressed.

[0143] In the time-of-flight secondary ion mass spectrometry of the positive electrode active material, the intensity of the peak detected at a mass greater than 27.0 and equal to or less than 27.5 relative to Al +The peak intensity ratio is in the range of 1:0.5 to 1:1.5, particularly 1:0.6 to 1:1.3, and even more particularly 1:0.7 to 1:1.2. The peak detected at a mass greater than 27.0 and equal to or less than 27.5 is C2H3. + The peak, where it is the base peak. In this case, the cycle characteristics and capacity characteristics of the battery using the positive electrode active material according to the invention can be improved. In particular, the high-temperature lifetime characteristics of the battery can be improved, and the rate of increase in resistance and the rate of gas generation at high temperatures can be suppressed.

[0144] In the time-of-flight secondary ion mass spectrometry of the positive electrode active material, the ratio of the intensity of the peak detected at mass 182 to 184 to the intensity of the peak detected at mass 172 to 174 can be in the range of 1:0.3 to 1:2, particularly 1:0.4 to 1:1.5, and more particularly 1:0.5 to 1:1.2. In this case, because side reactions that may occur on the surface of the positive electrode active material are suppressed, gas generation in the secondary battery containing the positive electrode active material during charging and discharging can be suppressed, and the rate of increase in resistance of the secondary battery can be improved.

[0145] In the time-of-flight secondary ion mass spectrometry of the positive electrode active material, the ratio of the intensity of the peak detected at mass 182 to 184 to the intensity of the peak detected at mass 197 to 199 can be in the range of 1:0.3 to 1:1.5, particularly 1:0.3 to 1:1.2, and even more particularly 1:0.3 to 1:0.8. In this case, because side reactions that may occur on the surface of the positive electrode active material are suppressed, gas generation in the secondary battery containing the positive electrode active material during charging and discharging can be suppressed, and the rate of increase in resistance of the secondary battery can be improved.

[0146] positive electrode

[0147] Furthermore, the present invention provides a positive electrode for a lithium secondary battery comprising the above-mentioned positive electrode active material. Specifically, the positive electrode for the secondary battery comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to the present invention.

[0148] In this case, since the positive electrode active material is the same as described above, its detailed description will be omitted, and only the remaining structure will be described in detail below.

[0149] There are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause adverse chemical changes in the battery. It can be made of materials such as stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness from 3 μm to 500 μm, and fine irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0150] In addition to the positive electrode active material, the positive electrode active material layer may also contain a conductive material, and optionally, an adhesive, if desired.

[0151] In this case, the content of the positive electrode active material can be 80% to 99% by weight, for example, 85% to 98.5% by weight, relative to the total weight of the positive electrode active material layer. When the content of the positive electrode active material is within the above range, excellent capacity characteristics can be obtained.

[0152] Conductive materials are used to provide conductivity to the electrodes. Any conductive material can be used without particular restriction, provided it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of conductive materials can be: graphite, such as natural or artificial graphite; carbonaceous materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, and carbon fibers; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of them can be used. The content of the conductive material relative to the total weight of the positive electrode active material layer can typically be from 0.1% by weight to 15% by weight.

[0153] The adhesive enhances the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of the adhesive may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. The adhesive content may range from 0.1% by weight to 15% by weight relative to the total weight of the positive electrode active material layer.

[0154] In addition to using the aforementioned positive electrode active materials, positive electrodes can be prepared according to typical methods for preparing positive electrodes. Specifically, a composition for forming a positive electrode active material layer, prepared by dissolving or dispersing the positive electrode active material, along with optional binders and conductive materials, in a solvent, is coated onto a positive electrode current collector. The positive electrode can then be prepared by drying and rolling the coated positive electrode current collector.

[0155] The solvent can be one commonly used in the art. The solvent may include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water, and any one of these or mixtures of two or more thereof may be used. The amount of solvent used may be sufficient if, considering the coating thickness and manufacturing yield of the slurry, the solvent can dissolve or disperse the positive electrode active material, the conductive material, and the binder, and can result in a viscosity that provides excellent thickness uniformity during subsequent coating for the preparation of the positive electrode.

[0156] In addition, as another method, the positive electrode can be prepared by casting the composition for forming the positive electrode active material layer onto a separate carrier, and then pressing the film layer separated from the carrier onto the positive electrode current collector.

[0157] Lithium secondary batteries

[0158] Furthermore, in this invention, an electrochemical device comprising the aforementioned positive electrode can be prepared. Specifically, the electrochemical device can be a battery or a capacitor, for example, a lithium secondary battery.

[0159] The lithium secondary battery specifically includes a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. Since the positive electrode is the same as described above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0160] In addition, the lithium secondary battery may optionally include: a battery container that houses an electrode assembly comprising a positive electrode, a negative electrode, and a separator; and a sealing member that seals the battery container.

[0161] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0162] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause adverse chemical changes in the battery. It can be made of, for example, copper; stainless steel; aluminum; nickel; titanium; calcined carbon; copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.; and aluminum-cadmium alloys. Furthermore, the negative electrode current collector can typically have a thickness from 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on its surface to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0163] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0164] Compounds capable of reversibly inserting and deintercalating lithium can be used as anode active materials. Specific examples of anode active materials can be: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; (semi-metallic) materials capable of forming alloys with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and (semi-metallic) oxides that can be doped or undoped with lithium, such as SiO₂. β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or composite materials containing (semi-)metallic materials and carbonaceous materials, such as Si-C composite materials or Sn-C composite materials, and any one of them or a mixture of two or more thereof can be used. Additionally, lithium metal films can be used as the negative electrode active material. Furthermore, low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Typical examples of low-crystallinity carbon can be soft carbon and hard carbon, and typical examples of high-crystallinity carbon can be irregular, planar, sheet-like, spherical or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature sintered carbon, such as coke derived from petroleum or coal tar pitch.

[0165] The content of the negative electrode active material can be from 80% to 99% by weight relative to the total weight of the negative electrode active material layer.

[0166] Adhesives are components that facilitate bonding between conductive materials, active materials, and current collectors, and are typically added in an amount from 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0167] Conductive materials are components used to further improve the conductivity of the negative electrode active material, wherein the conductive material can be added in an amount of less than 10% by weight, for example, less than 5% by weight, relative to the total weight of the negative electrode active material layer. There are no particular limitations on the conductive material, as long as it is conductive and does not cause adverse chemical changes in the battery. Examples of conductive materials that can be used include: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0168] For example, the negative electrode active material layer can be prepared by coating a composition for forming the negative electrode active material layer, prepared by dissolving or dispersing the negative electrode active material and optionally a binder and conductive material in a solvent, onto a negative electrode current collector and drying the coated negative electrode current collector; or it can be prepared by casting the composition for forming the negative electrode active material layer onto a separate carrier and then pressing the film layer separated from the carrier onto the negative electrode current collector.

[0169] In lithium-ion secondary batteries, a separator is used to separate the negative electrode and the positive electrode and to provide a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used in lithium-ion secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion transfer can be used. Specifically, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers; or laminated structures having two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can optionally be used.

[0170] Furthermore, the electrolyte used in this invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used to prepare lithium secondary batteries, but this invention is not limited thereto.

[0171] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0172] As the organic solvent, any organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the following substances can be used as organic solvents: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic solvents, such as benzene and fluorobenzene; or carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group and may contain double bonds, aromatic rings, or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents can be used. For example, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of the battery, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) can be used. In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0173] Lithium salts can be used without particular restriction, as long as they are compounds capable of providing lithium ions used in lithium secondary batteries. Specifically, the following substances can be used as lithium salts: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. These lithium salts can be used in concentrations ranging from 0.1 M to 2.0 M. When the concentration of the lithium salt is within this range, excellent electrolyte performance can be obtained because the electrolyte can have suitable conductivity and viscosity, and lithium ions can move efficiently.

[0174] To improve battery life, suppress capacity reduction, and increase discharge capacity, in addition to the electrolyte components, the electrolyte may contain at least one additive, such as: haloalkyl carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, and N-substituted compounds. The additives may include oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the content of the additives may be from 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0175] As described above, because lithium secondary batteries containing the positive electrode active material according to the present invention stably exhibit excellent discharge capacity, output characteristics and capacity retention, the lithium secondary batteries are suitable for: portable devices, such as mobile phones, laptops and digital cameras; and electric vehicles, such as hybrid electric vehicles (HEVs).

[0176] Therefore, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit battery and a battery pack comprising the battery module are provided.

[0177] The battery module or the battery pack can be used as a power source for at least one medium to large-sized device: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0178] There are no particular limitations on the shape of the lithium secondary battery of the present invention, but it can be used in the form of a cylindrical can, prismatic can, pouch or coin.

[0179] The lithium secondary battery according to the present invention can be used not only as a battery cell for use as a power source for small devices, but also as a unit battery in medium and large battery modules containing multiple battery cells.

[0180] Preferred implementation scheme

[0181] The invention will now be described in detail with reference to specific embodiments. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these exemplary embodiments are provided so that the description will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0182] Example

[0183] Example 1

[0184] Ni, as a precursor of the positive electrode active material, is used in a manner that ensures a Li:transition metal (Ni+Co+Mn) molar ratio of 1.07:1. 0.88 Co 0.05 Mn 0.07 (OH)₂ and LiOH·H₂O were mixed and sintered at 640°C for 5 hours to prepare a pre-sintered product (containing Ni). 0.88 Co 0.05Mn 0.07 O2).

[0185] The pre-sintered product was mixed with Al(OH)3 to achieve a Ni:Co:Mn:Al molar ratio of 0.86:0.05:0.07:0.02, and then subjected to a secondary sintering at 775°C for 6 hours to prepare a sintered product (containing LiNi). 0.86 Co 0.05 Mn 0.07 Al 0.02 O2). The sintered product and water were mixed at a weight ratio of 1:1.2, and the sintered product was washed for 5 minutes. The washed product was then filtered under reduced pressure to obtain a water content in the range of 5% to 10%, and then dried at 130°C to prepare LiNi. 0.86 Co 0.05 Mn 0.07 Al 0.02 O2 is a lithium transition metal oxide.

[0186] Subsequently, lithium transition metal oxide and H3BO3 were mixed at a weight ratio of 100:0.57 and heat-treated at 300°C for 4 hours to prepare a positive electrode active material having a coating comprising Li-Al-BO solid solution, Li-BO solid solution and BO solid solution formed on its surface.

[0187] Example 2

[0188] Except that the primary sintering temperature in Example 1 was adjusted to 720°C, the positive electrode active material was prepared in the same manner as in Example 1.

[0189] Comparative Example 1

[0190] Ni, as a precursor of the positive electrode active material, is prepared in a manner that makes the molar ratio of Li:Ni:Co:Mn:Al 1.05:0.86:0.05:0.07:0.02. 0.88 Co 0.05 Mn 0.07 The mixture of (OH)2, LiOH·H2O and Al(OH)3 was sintered at 640℃ for 5 hours, followed by a second sintering at 775℃ for 6 hours to prepare the sintered product (containing LiNi). 0.86 Co 0.05 Mn 0.07 Al 0.02 O2).

[0191] The sintered product and water were mixed at a weight ratio of 1:1.2, and the sintered product was washed for 5 minutes. The washed product was then subjected to vacuum filtration to ensure a water content of 5% to 10%. Finally, it was dried at 130°C to prepare LiNi. 0.86 Co 0.05 Mn 0.07 Al 0.02 O2 is a lithium transition metal oxide.

[0192] Subsequently, lithium transition metal oxide and H3BO3 were mixed at a weight ratio of 100:0.57 and heat-treated at 300°C for 4 hours to prepare a positive electrode active material having a coating comprising Li-BO and BO solid solutions formed on its surface.

[0193] Comparative Example 2

[0194] LiNi 0.88 Co 0.05 Mn 0.07 O2 lithium transition metal oxide, H3BO3 and Al(OH)3 are mixed in a weight ratio of 100:0.2:0.3 and heat-treated at 700°C for 4 hours to prepare a positive electrode active material having a coating containing a Li-Al-BO solid solution formed on its surface.

[0195] Experimental Example 1: Confirmation of Coating Formation

[0196] The cation and anion spectra on the surface of the positive electrode active materials prepared in Example 1 and Comparative Example 1 were measured using a time-of-flight secondary ion mass spectrometer (TOF-SIMS5, ION-TOF GmbH), and the results are shown below. Figure 1 and Figure 2 middle.

[0197] first, Figure 1 (a) and (b) are the cation spectrum analysis results of Example 1 and Comparative Example 1, respectively.

[0198] As a result of cation analysis of the outermost surface of the positive electrode active materials prepared in Example 1 and Comparative Example 1, for Example 1, strong Al was observed in the mass range of 26.9 to 27.0. + However, for Comparative Example 1, it can be confirmed that weak Al was observed within the aforementioned range. + The peak. The reason is that, for Example 1, the preparation method was adjusted so that a large amount of aluminum existed on the surface of the positive electrode active material before the coating was formed on the surface of the positive electrode active material.

[0199] Specifically, it can be confirmed that in the cation spectrum of Example 1, the peak (C2H3) detected at a mass greater than 27.0 and equal to or less than 27.1 is... + The intensity of the peak relative to Al + The ratio of peak intensities was 1:0.9. Conversely, it can be confirmed that in the cation spectrum of Comparative Example 1, the peak (C2H3) detected at a mass greater than 27.0 and equal to or less than 27.1 was... + The intensity of the peak relative to Al + The ratio of peak intensity is 1:0.2.

[0200] also, Figure 2 (a) and (b) are the anion spectrum analysis results of Example 1 and Comparative Example 1, respectively.

[0201] As a result of the anion analysis of the outermost surface of the positive electrode active material prepared in Example 1 and Comparative Example 1, for Example 1, strong aluminum-related peaks were observed in the mass range of 172 to 174 and in the mass range of 197 to 198, but for Comparative Example 1, it can be confirmed that weak peaks were observed in the above ranges.

[0202] Specifically, in the anion spectrum of Example 1, it can be confirmed that the intensity ratio of the peak detected at mass 182 to 184 to the intensity ratio of the peak detected at mass 172 to 174 is 1:1.1, and the intensity ratio of the peak detected at mass 182 to 184 to the intensity ratio of the peak detected at mass 197 to 199 is 1:0.5. Conversely, in the anion spectrum of Comparative Example 1, it can be confirmed that the intensity ratio of the peak detected at mass 182 to 184 to the intensity ratio of the peak detected at mass 172 to 174 is 1:0.4, and the intensity ratio of the peak detected at mass 182 to 184 to the intensity ratio of the peak detected at mass 197 to 199 is 1:0.2.

[0203] Experimental Example 2: Evaluation of the capacity and resistance characteristics of lithium secondary batteries

[0204] Lithium-ion batteries were prepared using the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, and the capacity and resistance characteristics of these lithium-ion batteries were examined. In this case, in addition to using the various positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2, various lithium-ion batteries were prepared by using the following method.

[0205] Specifically, various positive electrode active materials, carbon black conductive materials, and polyvinylidene fluoride binders prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were mixed in NMP solvent at a weight ratio of 97.5:1.15:1.35 to prepare a composition for forming the positive electrode. A 12 μm thick Al current collector was coated with the composition for forming the positive electrode, dried, and then rolled to prepare the positive electrode. Various lithium secondary batteries according to Examples 1 and 2 and Comparative Examples 1 and 2 were prepared by stacking the above-prepared positive electrode and lithium metal as the negative electrode using a porous polyethylene separator, placing the stack in a battery case, and injecting an electrolyte in which 1 M LiPF6 and other additives were dissolved in a mixed solvent of ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) in a ratio of 3:4:3.

[0206] Various lithium secondary batteries prepared therefrom were charged to 4.25V (CV 0.05C) at a constant current / constant voltage (CC / CV) mode at 25°C and then discharged to 3V in CC mode to measure the initial charge capacity (in mAh / g) at room temperature (25°C), and the results are shown in Table 1 below.

[0207] [Table 1]

[0208]

[0209] Referring to Table 1, for batteries containing the positive electrode active materials prepared in Examples 1 and 2, it can be confirmed that the initial charge capacity at room temperature is excellent. For reference, in Comparative Example 2, where boron-containing and aluminum-containing raw materials were mixed with a lithium transition metal oxide and then heat-treated at 700°C to form a coating, the diffusion of aluminum and boron was not controlled, and it is understandable that there is a problem of capacity reduction due to reactions, such as the doping of some boron or aluminum into the positive electrode active material at high temperatures.

[0210] Various lithium secondary batteries thus prepared were charged to 4.25V (CV 0.05C) at a constant current of 0.33C in CC / CV mode at 45°C, and then discharged to 3V in CC mode. This charge and discharge behavior was defined as one cycle, and after repeating this cycle 30 times, the initial discharge capacity (mAh / g), capacity retention (%), and resistance increase (%) of the various lithium secondary batteries thus prepared at high temperature (45°C) were measured, and the results are shown in Table 2 below. Figures 3 to 5 middle.

[0211] Figure 3This is a graph showing data on the discharge capacity of the secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 at high temperatures.

[0212] Figure 4 This is a graph showing the high-temperature lifetime characteristics of the secondary batteries prepared in Examples 1 and 2, and Comparative Examples 1 and 2. Specifically, Figure 4 It is a graph showing data on capacity retention at high temperatures.

[0213] Figure 5 The graph shows the high-temperature resistance characteristics of the secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2. Figure 5 It is a graph showing data on the rate of increase in electrical resistance at high temperatures.

[0214] [Table 2]

[0215]

[0216] As shown in Table 2 and Figures 3 to 5 As shown, for the secondary batteries prepared in Examples 1 and 2, it can be confirmed that the high-temperature capacity characteristics, lifetime characteristics, and resistance characteristics are significantly better than those of the secondary batteries prepared in Comparative Examples 1 and 2.

[0217] Experiment Example 3: Evaluation of Gas Production

[0218] Lithium-ion batteries were prepared using the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, and their capacity and resistance characteristics were examined. In this case, in addition to using the various positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2, various lithium-ion batteries were prepared using the following method.

[0219] Specifically, the various positive electrode active materials, carbon black conductive materials, and polyvinylidene fluoride binders prepared in Examples 1 and 2, as well as Comparative Examples 1 and 2, were mixed in NMP solvent at a weight ratio of 97.5:1.15:1.35 to prepare compositions for forming the positive electrode. The compositions for forming the positive electrode were coated onto a 12 μm thick Al current collector, dried, and then rolled to prepare the positive electrode.

[0220] Next, the negative electrode active material (natural graphite), conductive material (carbon black), and binder (SBR+CMC) are mixed in water at a weight ratio of 95:1.5:3.5 to prepare a negative electrode slurry. The negative electrode slurry is then used to coat a copper current collector, dried, and rolled to prepare the negative electrode.

[0221] Electrode assemblies were fabricated by placing a separator between the positive and negative electrodes. These assemblies were then placed in a battery casing, and electrolyte was injected to prepare three single cells with electrode dimensions of 3 cm × 4 cm. In this case, the electrolyte was a solution containing 1 M LiPF6 dissolved in an organic solvent in a volume ratio of ethylene carbonate, ethyl carbonate, and diethyl carbonate of 3:3:4.

[0222] Three single cells were charged to 4.25V (CV 0.05C) at a constant current of 0.33C in CC / CV mode at 45°C, and then the positive electrode was separated. The separated positive electrode was placed in a battery bag, and after additional electrolyte was injected, the battery bag was sealed to prepare the sample. The volume change rate (in %) of the battery was measured while the sample was stored at 60°C for 4 weeks, and the results are shown in Table 3 below. Figure 6 middle.

[0223] [Table 3]

[0224]

[0225] Referring to Table 3, for the batteries containing the positive electrode active materials of Examples 1 and 2, since the battery volume change rate during storage at high temperature is significantly less than that of the batteries containing the positive electrode active materials of Comparative Examples 1 and 2, it can be confirmed that the amount of gas generated is significantly less.

[0226] Therefore, according to the present invention, it is understood that by adding aluminum during the preparation of the positive electrode active material in a sintering step (secondary sintering) after pre-sintering (primary sintering) and before washing to control the degree of aluminum doping present on the outermost surface, the cycle characteristics, particularly high-temperature lifetime characteristics and capacity characteristics of the battery using the prepared positive electrode active material can be improved. Furthermore, it is understood that the increase in resistance and gas generation at high temperatures in the battery using the said positive electrode active material can be suppressed.

Claims

1. A method for preparing a positive electrode active material, the method comprising the following steps: (A) Preparing a pre-sintered product by performing a first sintering on a mixture in which a positive electrode active material precursor having a composition of Formula 1-1 or 1-2 and a lithium-containing raw material are mixed; (B) Preparing a lithium transition metal oxide having a composition of Formula 2 by mixing the pre-sintered product with an aluminum-containing raw material, performing a second sintering, washing, and drying; and (C) Dry-mixing the lithium transition metal oxide with a boron-containing raw material and performing a heat treatment to form a coating, where the second sintering temperature is higher than the first sintering temperature, and the difference between the second sintering temperature and the first sintering temperature is in the range of 10 °C to 150 °C, [Formula 1-1] Ni a1 Co b1 Mn c1 M 1 d1 (OH)2 [Formula 1-2] Ni a1 Co b1 Mn c1 M 1 d1 O·OH in, In Formulas 1-1 and 1-2, M 1 is at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and 0.7 ≤ a1 ≤ 1.0, 0 ≤ b1 ≤ 0.3, 0 ≤ c1 ≤ 0.3, and 0 ≤ d1 ≤ 0.1, [Formula 2] Li x Ni a2 Co b2 Mn c2 Al d2 M 1 e2 O2 where, in Formula 2, M 1 is at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and 0.9 ≤ x ≤ 1.12, 0.7 ≤ a2 ≤ 1.0, 0 ≤ b2 ≤ 0.3, 0 ≤ c2 ≤ 0.3, 0 < d2 ≤ 0.2, and 0 ≤ e2 ≤ 0.

1.

2. The method according to claim 1, wherein the first sintering temperature is in the range of 600 °C to 775 °C.

3. The method according to claim 1, wherein the second sintering temperature is in the range of 730 °C to 900 °C.

4. The method according to claim 1, wherein the aluminum-containing raw material is at least one selected from the following: Al(OH)3, Al2O3, AlF3, AlBr3, AlPO4, AlCl3, Al(NO3)3, Al(NO3)3·9H2O, Al2(SO4)3·H2O, Al(H2PO4)3, C2H5O4Al, Al2(SO4)3, NaAlO2, Al2CoO4, LaAlO3, and MgAl2O4.

5. The method according to claim 1, wherein the heat treatment temperature is in the range of 250 °C to 400 °C.

6. The method according to claim 1, wherein the boron-containing raw material is at least one selected from the following: H3BO3, B2H4O4, B2O3, LiBO2, Li2B4O7, and AlBO3.

7. A positive electrode active material, the positive electrode active material comprising: a lithium transition metal oxide represented by Formula 2; and a boron-containing coating formed on the surface of the lithium transition metal oxide, where the coating contains a Li-Al-B-O solid solution, and In time-of-flight secondary ion mass spectrometry, the ratio of the intensity of the peak detected at a mass greater than 27.0 and equal to or less than 27.5 relative to the intensity of the peak of Al + is in the range of 1 :0.5 to 1 :1.5, [Formula 2] Li x Ni a2 Co b2 Mr c2 Al d2 M 1 e2 O2 in, in Formula 2, M 1 It is selected from at least one of the following: Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.9 ≤ x ≤ 1.12, 0.7 ≤ a2 ≤ 1.0, 0 ≤ b2 ≤ 0.3, 0 ≤ c2 ≤ 0.3, 0 < d2 ≤ 0.2, and 0 ≤ e2 ≤ 0.

1.

8. The positive electrode active material according to claim 7, wherein in the time-of-flight secondary ion mass spectrometry of the positive electrode active material, the ratio of the intensity of the peak detected at a mass of 182 to 184 to the intensity of the peak detected at a mass of 172 to 174 is in the range of 1:0.3 to 1:

2.

9. The positive electrode active material according to claim 7, wherein in the time-of-flight secondary ion mass spectrometry of the positive electrode active material, the ratio of the intensity of the peak detected at mass 182 to 184 to the intensity of the peak detected at mass 197 to 199 is in the range of 1:0.3 to 1:1.

5.

10. A positive electrode for a lithium secondary battery, the positive electrode comprising the positive electrode active material according to claim 7.

11. A lithium secondary battery, the lithium secondary battery comprising the positive electrode for a lithium secondary battery as described in claim 10.

Images