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

Abstract

The present invention comprises nickel, cobalt, and manganese, wherein the nickel content of the total metals other than lithium is 90 mol% or more, and includes single-particle lithium nickel oxide containing 1 to 30 nodules, D 50 The present invention relates to a positive electrode active material and a method for producing the same, wherein the particle size is 5 μm to 8 μm, and the maximum value of the heat flow measured by a differential scanning calorimeter (DSC) while charging a coin half cell manufactured using the positive electrode active material to 4.25 V, and then heating it from room temperature to 380 °C at a heating rate of 10 °C / min, is 15.0 W / g or less.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0105927 filed on August 11, 2023, and all the contents disclosed in the document of the Korean Patent Application are incorporated herein by reference. The present invention relates to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery. More specifically, the present invention relates to a single-particle type positive electrode active material containing 90 mol% or more of Ni and having excellent thermal stability, a positive electrode including the same, and a lithium secondary battery.

Background Art

[0002] A lithium secondary battery generally includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode include active materials capable of intercalating and deintercalating lithium ions.

[0003] As the positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (such as LiMnO_2 or LiMnO_4), lithium iron phosphate compound (LiFePO_4), etc. have been used. Among these, lithium cobalt oxide has the advantages of a high operating voltage and excellent capacity characteristics, but the price of cobalt as a raw material is high, the supply is unstable, and it is difficult to apply commercially to large-capacity batteries. Lithium nickel oxide has poor structural stability and it is difficult to achieve sufficient life characteristics. On the other hand, lithium manganese oxide is excellent in stability but has a problem of inferior capacity characteristics. Therefore, in order to complement the problems of lithium transition metal oxides containing Ni, Co, or Mn alone, lithium composite transition metal oxides containing two or more transition metals have been developed. Among them, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the battery field of electric vehicles.

[0004] Conventional lithium nickel cobalt manganese oxide typically consists of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles. However, in the case of lithium nickel cobalt manganese oxide with this secondary particle form, particle cracking occurs during the rolling process in the manufacturing of the positive electrode, causing primary particles to detach, and cracks to form inside the particles during the charge-discharge process. When particle cracking or cracking occurs in the positive electrode active material, the contact area with the electrolyte increases, leading to increased gas generation due to side reactions with the electrolyte and increased degradation of the active material.

[0005] On the other hand, in the electric vehicle sector, there has recently been a demand for lithium-ion batteries with high energy density to extend the driving range on a single charge, and consequently, the nickel content of the positive electrode active material has been gradually increasing.

[0006] However, while high capacity can be achieved with high-nickel (high-Ni) cathode active materials, repeated charging and discharging can lead to high reactivity of the nickel. +4 The generation of a large amount of ions causes the structure of the positive electrode active material to break down, which increases the degradation rate of the positive electrode active material, reduces its lifespan, and leads to problems with low thermal stability and poor battery stability.

[0007] Therefore, there is a need to develop cathode active materials that can simultaneously achieve high capacity and high thermal stability. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention aims to solve the above-mentioned problems and provides a positive electrode active material and a method for producing the same, which has a high Ni content of 90 mol% or more among the total metals other than lithium and has excellent thermal stability.

[0009] Furthermore, the present invention provides a lithium secondary battery that has excellent thermal stability due to the inclusion of the positive electrode active material and excellent continuous charging characteristics at high temperatures and high voltages.

Means for Solving the Problem

[0010] According to one embodiment, the present invention has a Ni content of 90 mol% or more among the total metal elements, and D 50 is 5 μm to 8 μm, and the ratio of the BET specific surface area to D 50 (BET / D 50 ) is 0.5 to 2, preferably 0.8 to 1.5. A method for producing a cathode active material is provided, which includes mixing a precursor and a lithium raw material substance and firing them to produce a single-particle type lithium nickel-based oxide.

[0011] Here, the precursor is such that D 50 can preferably be 5 μm to 7 μm, more preferably 5 μm to 6.5 μm.

[0012] The BET specific surface area of the precursor is 5 m 2 / g to 10 m 2 / g, preferably 5 m 2 / g to 8 m 2 / g, more preferably 5 m 2 / g to 7 m 2 / g.

[0013] Specifically, the precursor can be nickel cobalt manganese hydroxide having a Ni content of 90 mol% or more among the total metal elements, and more specifically, it can be represented by the following [Chemical Formula 1]. [Chemical Formula 1] Ni a Co b Mn c M 1 d (OH)2 In the above Chemical Formula 1, M 1 is one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.90 ≦ a < 1, 0 < b < 0.1, 0 < c < 0.1, 0 ≦ d ≦ 0.05.

[0014] On the other hand, the firing can be carried out at 800°C to 900°C, preferably 820°C to 880°C, and more preferably 820°C to 870°C.

[0015] On the other hand, the lithium nickel oxide may contain lithium by-products in an amount of 1 mol% to 5 mol%, preferably 1 mol% to 3 mol%.

[0016] On the other hand, the method for producing a positive electrode active material according to the present invention may further include, after the step of producing the single-particle lithium nickel-based oxide, the step of mixing the single-particle lithium nickel-based oxide with a coating raw material and heat-treating it.

[0017] Here, the coating raw material may contain one or more elements selected from the group consisting of Co, Al, W, B, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, and Mo.

[0018] On the other hand, the heat treatment temperature can be appropriate depending on the type of elements contained in the coating layer. For example, the heat treatment can be performed at 300°C to 800°C, preferably 400°C to 800°C, and more preferably 500°C to 800°C.

[0019] According to other embodiments, the present invention provides a positive electrode active material comprising a single-particle lithium nickel-based oxide containing nickel, cobalt, and manganese, wherein the nickel content of the total metals other than lithium is 90 mol% or more, and the oxide contains 1 to 30 nodules.

[0020] Here, the D of the positive electrode active material 50 However, the particle size can be 5 μm to 8 μm, preferably 5 μm to 7 μm, and more preferably 5 μm to 6.5 μm.

[0021] Furthermore, after charging a coin half-cell manufactured using the positive electrode active material to 4.25V, the maximum value of the heat flow measured by a differential scanning calorimeter (DSC) while raising the temperature from room temperature to 380°C under a heating rate of 10°C / min can be 15.0 W / g or less, preferably 5 W / g to 15.0 W / g, and more preferably 7 W / g to 15.0 W / g.

[0022] Furthermore, when a coin half-cell manufactured using the positive electrode active material is charged to 4.25V, the charging capacity can be 240mAh / g or more, preferably 240mAh / g to 245mAh / g, and more preferably 240mAh / g to 243mAh / g.

[0023] Furthermore, the positive electrode active material may have a cation mixing rate of 0.9 at% to 1.5 at%, preferably 1 at% to 1.5 at%.

[0024] On the other hand, the single-particle lithium nickel oxide can be a lithium nickel oxide in which the Ni content among the total metal elements other than lithium is 90 mol% or more, and more specifically, it can be represented by the following [Chemical Formula 2]. [Chemical formula 2] Li x [Ni a Co b Mn c M 1 d ]O2 In the above chemical formula 2, M 1 x is one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.8≦x≦1.2, 0.9≦a<1, 0 <b<0.1、0<c<0.1、0≦d≦0.05である。

[0025] On the other hand, the positive electrode active material may further include a coating layer formed on the single-particle lithium nickel oxide, and the coating layer may contain one or more elements selected from the group consisting of Co, Al, W, B, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, and Mo.

[0026] Preferably, the coating layer may contain Co, where the Co content in the coating layer may be 0.5 mol% to 4 mol%, preferably 0.5 mol% to 3 mol%, and more preferably 1 mol% to 2 mol%, based on the total number of moles of transition metal contained in the positive electrode active material.

[0027] In further embodiments, the present invention provides a positive electrode containing the positive electrode active material according to the present invention and a lithium secondary battery containing the positive electrode. [Effects of the Invention]

[0028] As in the present invention, D 50 When single-particle lithium nickel oxide is produced using a precursor whose ratio of specific surface area to specific surface area satisfies a specific range, a cathode active material with excellent thermal stability can be produced despite a high nickel content of 90 mol% or more.

[0029] The positive electrode active material according to the present invention achieves high capacity because it contains 90 mol% or more nickel, and has the same level of thermal stability as positive electrode active materials with a nickel content of less than 90 mol%.

[0030] Therefore, when the positive electrode active material according to the present invention is applied to a lithium secondary battery, high capacity and high thermal stability can be achieved simultaneously. Furthermore, a lithium secondary battery to which the positive electrode active material according to the present invention is applied can achieve excellent continuous charging performance under high temperature and high voltage conditions. [Brief explanation of the drawing]

[0031] [Figure 1]This graph shows the heat flow rate with respect to temperature in coin half-cells to which the positive electrode active materials of Examples 1-2 and Comparative Examples 1-4 are applied. [Figure 2] This graph shows the continuous charging performance of coin half-cells using the positive electrode active materials of Examples 1-2 and Comparative Examples 3-4. [Modes for carrying out the invention]

[0032] The present invention will be described in more detail below.

[0033] The terms and words used herein and in the claims shall not be interpreted to be limited to their ordinary or dictionary meanings, but rather to be interpreted in a way that is consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0034] In this invention, "single-particle type" refers to a particle consisting of 30 or fewer nodules, and is a concept that includes single particles consisting of one nodule and pseudo-single particles which are composites of 2 to 30 nodules.

[0035] The aforementioned "nodule" is a lower particle unit that constitutes a single particle or a pseudo-single particle, and can be a single crystal without crystalline grain boundaries, or a polycrystalline material in which no grain boundaries appear to exist when observed with a scanning electron microscope at a field of view of 5,000 to 20,000 times magnification.

[0036] In this invention, "secondary particle" refers to a particle formed by the aggregation of multiple primary particles, for example, several tens to several hundred primary particles. Specifically, a secondary particle may be an aggregate of 50 or more primary particles.

[0037] In this invention, "particle" is a concept that includes one or all of the following: single particles, pseudo-single particles, primary particles, nodules, and secondary particles.

[0038] In the present invention, the average particle size (D) of the nodule or primary particle mean ) refers to the arithmetic mean of these values ​​calculated after measuring the particle sizes of nodules or primary particles observed in scanning electron microscope images.

[0039] In this invention, "average particle size D 50 "50% of the volume of the cumulative particle size distribution of the powder being measured" refers to the particle size corresponding to 50% of the cumulative volume, and can be measured using the laser diffraction method. For example, after dispersing the powder to be measured in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiated with ultrasound at approximately 28 kHz at an output of 60 W, and then measured by obtaining a volume cumulative particle size distribution graph and determining the particle size corresponding to 50% of the cumulative volume.

[0040] In this invention, the "BET specific surface area" is measured by the BET method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan.

[0041] The inventors have diligently conducted research to develop a positive electrode active material that has high capacity characteristics and excellent thermal stability. As a result, they have found a material with a Ni content of 90 mol% or more and a specific surface area of ​​D 50 The ratio (D 50 We have discovered that when producing a cathode active material using a precursor that satisfies a specific range of (BET), excellent capacitance characteristics and thermal stability can be achieved simultaneously, thus completing the present invention.

[0042] Method for manufacturing positive electrode active material The method for producing a positive electrode active material according to the present invention is such that the Ni content among the total metal elements is 90 mol% or more, and D 50 The ratio of the specific surface area of ​​BET to (BET / D 50The process includes the step of mixing a precursor having a ratio of 0.5 to 2, preferably 0.8 to 1.5, with a lithium raw material and calcining to produce a single-particle lithium nickel oxide.

[0043] According to our research, in the case of ultra-high nickel cathode active materials with a Ni content of 90 mol% or more, unlike cathode active materials with a Ni content of less than 90 mol%, the precursor D used during manufacturing is 50 The ratio of the specific surface area of ​​BET to (BET / D 50 It was found that ) is closely related to thermal stability. Specifically, when manufacturing ultra-high nickel cathode active materials with a Ni content of 90 mol% or more, D 50 The ratio of the specific surface area of ​​BET to (BET / D 50 When using a precursor that satisfies 0.5 to 2, thermal stability was improved and the amount of heat generated during high-temperature exposure was significantly reduced compared to when using a precursor that deviates from the above range. Average particle size D of the precursor 50 The average particle size D of the positive electrode active material is 50 It affects the D of the positive electrode active material. 50 The smaller the average particle size D, the faster the positive electrode active material degrades when exposed to high temperatures, and the lower its thermal stability. Furthermore, the lower the BET specific surface area of ​​the precursor, the higher the reactivity with lithium during calcination. This results in a lower cation mixing rate of the synthesized single-particle positive electrode active material, leading to a higher degree of crystal structure completion in the positive electrode active material. However, if the crystal structure of the positive electrode active material is too perfect, side reactions with the electrolyte increase on the surface of the positive electrode active material, reducing thermal stability. Therefore, in this invention, the average particle size D is... 50 The ratio of the specific surface area of ​​BET to (BET / D 50 Using a precursor that satisfies the range of 0.5 to 2, the average particle size D of the synthesized positive electrode active material was determined. 50 Furthermore, the degree of perfection of the crystal structure can be adjusted to an appropriate range. As in the present invention, BET / D 50 When using a precursor with a value of 0.5 or higher, the degree of perfection of the crystal structure of the positive electrode active material decreases, increasing the electrical and chemical inertness of the positive electrode active material surface. Consequently, side reactions with the electrolyte decrease, and the thermal stability is improved. On the other hand, BET / D50 If the value exceeds 2, the D of the positive electrode active material 50 It was observed that either the BET specific surface area of ​​the positive electrode active material becomes excessively small, or the BET specific surface area of ​​the positive electrode active material becomes excessively high, leading to an increase in side reactions with the electrolyte, a decrease in the effect of improving thermal stability, an increase in resistance, and a decrease in the electrochemical properties of the positive electrode active material.

[0044] On the other hand, the precursor can be nickel-cobalt-manganese hydroxide having a Ni content of 90 mol% or more of the total metal elements, and more specifically, it can be represented by the following [Chemical Formula 1].

[0045] [Chemical formula 1] Ni a Co b Mn c M 1 d (OH)2

[0046] In the above chemical formula 1, M 1 This can be one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and preferably one or more elements selected from the group consisting of Al, Zr, Y, Ti, Sr, and Nb.

[0047] The above 'a' represents the mole fraction of nickel among the metal elements in the precursor, and can be 0.90 ≤ a < 1, 0.90 ≤ a ≤ 0.99, or 0.90 ≤ a ≤ 0.99.

[0048] The above b represents the mole fraction of Co among the metal elements in the precursor, and 0 <b<0.1、0.01≦b<0.1、または0.02≦b<0.1であることができる。

[0049] The aforementioned c represents the mole fraction of Mn among the metal elements in the precursor, and can be 0.005 ≤ c < 0.1 or 0.01 ≤ c ≤ 0.08.

[0050] The above d is M among the metal elements in the precursor. 1This represents the mole fraction of an element and can be 0≦d≦0.05, 0≦d≦0.02, or 0≦d≦0.01.

[0051] On the other hand, the precursor is D 50 The particle size can be 5 μm to 8 μm, preferably 5 μm to 7 μm, and more preferably 5 μm to 6.5 μm. Precursor D 50 If the above range is satisfied, the increase in resistance of the positive electrode active material manufactured using it can be minimized, and a better improvement in thermal stability can be obtained. 50 When using a precursor with excessively small values, the effect of improving the thermal stability of the positive electrode active material is minimal, D 50 Using a precursor with an excessively large resistance can increase the initial resistance, potentially negatively affecting the electrochemical properties of the positive electrode active material.

[0052] Furthermore, the BET specific surface area of ​​the precursor is 5m². 2 / g~10m 2 / g, preferably 5m 2 / g~8m 2 / g, comfortably 5m 2 / g~7m 2 It can be / g. When a positive electrode active material is manufactured using a precursor whose BET specific surface area satisfies the above range, the surface crystal structure of the positive electrode active material is formed to an appropriate level, side reactions with the electrolyte are reduced, and thermal stability is improved. If a precursor with an excessively small BET specific surface area is used, a layered crystal structure develops excessively well on the surface of the positive electrode active material, increasing side reactions with the electrolyte and reducing stability when exposed to high temperatures. If a precursor with an excessively large BET specific surface area is used, an excessive amount of inert crystal structure is formed on the surface of the positive electrode active material, increasing resistance and reducing electrochemical properties.

[0053] Next, as the lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides can be used. For example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof can be used.

[0054] On the other hand, the lithium raw material and the precursor can be mixed such that the molar ratio of Li to total metal in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1, and more preferably 1:1 to 1.05:1. When the mixing ratio of the lithium raw material and the metal in the precursor satisfies the above range, a positive electrode active material with excellent capacity characteristics and thermal stability can be produced. Here, if necessary, M can be added to the lithium raw material and the precursor. 1 Metal-containing raw materials may be mixed together and fired.

[0055] On the other hand, the firing can be carried out at 800°C to 900°C, preferably 820°C to 880°C, and more preferably 820°C to 870°C. When the firing temperature is within the above range, single-particle lithium nickel oxide with excellent electrochemical properties can be produced. If the firing temperature is too low, lithium nickel oxide in secondary particle form will be produced instead of single-particle lithium nickel oxide, and if the firing temperature is too high, a thick inert phase, such as a rock salt-type structural phase, will form on the surface of the particles, resulting in a decrease in resistance, power, and capacitance characteristics.

[0056] On the other hand, the firing can be carried out in an oxygen atmosphere for 5 to 35 hours, preferably 10 to 30 hours, and more preferably 10 to 20 hours. In this specification, an oxygen atmosphere means an atmosphere containing an amount of oxygen sufficient for firing, including an atmospheric atmosphere. In particular, it is preferable to carry out the firing in an atmosphere in which the partial pressure of oxygen is higher than that of an atmospheric atmosphere.

[0057] On the other hand, lithium nickel oxide produced by the method described above may contain lithium by-products such as lithium hydroxide and lithium carbonate on the surface of the particles, and the content of the lithium by-products is preferably 1 mol% to 5 mol%, preferably 1 mol% to 4 mol%, and more preferably about 1.5 mol% to 3 mol%. When the lithium nickel oxide contains lithium by-products within the above range, a uniform coating layer can be formed in the coating process described later. If the lithium by-product content is too low, the coating layer may be formed unevenly, and if the lithium by-product content is too high, the electrolyte and lithium by-products will react, increasing gas generation and potentially degrading the lifetime characteristics.

[0058] On the other hand, the method for producing a positive electrode active material according to the present invention may, if necessary, further include, after the step of producing the single-particle lithium nickel-based oxide, the step of mixing the single-particle lithium nickel-based oxide with a coating raw material and heat-treating it.

[0059] Here, the coating raw material can contain one or more elements selected from the group consisting of Co, Al, W, B, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, and Mo, and more specifically, it can be an oxide, hydroxide, carbide, chloride, carbonate, sulfate, etc. containing the element. Preferably, the coating raw material can contain Co. In the case of single-particle lithium nickel oxide, since it is fired at a relatively high temperature, a large amount of electrically inert phases, such as a rock salt type structure, are formed on the surface of the particles, resulting in high resistance. In particular, when a precursor with a relatively large particle size is used, the increase in resistance becomes even more severe. However, when a Co-containing coating layer is formed on the surface of a single-particle lithium nickel oxide, a portion of the inert phase on the surface recrystallizes during the heat treatment process, changing the layered structure and reducing resistance.

[0060] On the other hand, the mixing can be carried out as a solid-phase or liquid-phase mixing, and the heat treatment can be carried out at an appropriate temperature depending on the coating raw material. For example, the heat treatment in the coating step can be carried out at a temperature of 300°C to 800°C, preferably 400°C to 800°C, and more preferably 500°C to 800°C, but is not limited thereto.

[0061] positive electrode active material Next, the positive electrode active material according to the present invention will be described.

[0062] The positive electrode active material according to the present invention can be manufactured by the method for manufacturing the positive electrode active material described above.

[0063] The positive electrode active material according to the present invention contains nickel, cobalt, and manganese, with nickel content being 90 mol% or more of the total metals other than lithium, and includes single-particle type lithium nickel oxide containing 1 to 30 nodules.

[0064] As described above, when a single-particle lithium nickel oxide with a high nickel content is included, a high capacity can be achieved, side reactions with the electrolyte are suppressed, gas generation is suppressed, and excellent life characteristics can be realized.

[0065] In the case of lithium nickel oxides in secondary particle form, where 31 to several hundred primary particles aggregate, the large contact area with the electrolyte leads to numerous side reactions with the electrolyte, generating gas during these side reaction processes. In particular, under high temperature and / or high voltage conditions, the amount of gas generated increases further, causing rapid degradation of the cell. In contrast, single-particle lithium nickel oxides have fewer nodules constituting the particles, resulting in fewer interfaces within the particles and a smaller contact area with the electrolyte. Therefore, compared to secondary particles, there are fewer side reactions with the electrolyte, and consequently, the amount of gas generated is significantly less. Consequently, when single-particle lithium nickel oxides are used as positive electrode active materials, excellent lifetime characteristics can be obtained even under high temperature and / or high voltage conditions.

[0066] Specifically, the single-particle lithium nickel oxide can be a lithium nickel oxide in which the Ni content among the total metal elements other than lithium is 90 mol% or more, and more specifically, it can be represented by the following [Chemical Formula 2].

[0067] [Chemical formula 2] Li x [Ni a Co b Mn c M 1 d ]O2

[0068] In the above chemical formula 2, M 1 This can be one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and preferably one or more elements selected from the group consisting of Al, Zr, Y, Ti, Sr, and Nb.

[0069] The aforementioned x represents the mole fraction of lithium in the lithium nickel oxide, and can be 0.8 ≤ x ≤ 1.2, 0.9 ≤ x ≤ 1.1, or 1.0 ≤ x ≤ 1.1.

[0070] The above 'a' represents the mole fraction of nickel among the metal elements other than lithium in the lithium nickel oxide, and can be 0.90 ≤ a < 1, 0.90 ≤ a ≤ 0.99, or 0.90 ≤ a ≤ 0.99.

[0071] The above b represents the mole fraction of Co among the metal elements other than lithium in the lithium nickel oxide, and 0 <b<0.1、0.01≦b<0.1、または0.02≦b<0.1であることができる。

[0072] The aforementioned c represents the mole fraction of Mn among the metal elements other than lithium in the lithium nickel oxide, and can be 0.005 ≤ c < 0.1 or 0.01 ≤ c ≤ 0.08.

[0073] The above d is M, which is a metallic element other than lithium in lithium nickel oxide. 1 This represents the mole fraction of an element and can be 0≦d≦0.05, 0≦d≦0.02, or 0≦d≦0.01.

[0074] On the other hand, the single-particle lithium nickel oxide preferably contains 30 or fewer nodules, preferably 1 to 25, and more preferably 1 to 15. This is because if the number of nodules constituting the lithium nickel oxide exceeds 30, particle cracking increases during electrode manufacturing, and the occurrence of internal cracks due to the expansion / contraction of nodule volume increases during charging and discharging, which can reduce the improvement effect on high-temperature lifetime characteristics and high-temperature storage characteristics.

[0075] On the other hand, the nodules can have an average particle size of 0.8 μm to 4.0 μm, preferably 0.8 μm to 3 μm, and more preferably 1.0 μm to 2.0 μm. When the average particle size of the nodules satisfies the above range, particle cracking can be minimized during electrode manufacturing, and the increase in resistance can be suppressed more effectively. Here, the average particle size of the nodules refers to the value obtained by measuring the particle size of each nodule observed from the SEM image obtained by analyzing the positive electrode active material powder with a scanning electron microscope, and then calculating the arithmetic mean of the measured values.

[0076] On the other hand, the positive electrode active material according to the present invention may further include a coating layer formed on the single-particle lithium nickel oxide, the coating layer may contain one or more elements selected from the group consisting of Co, Al, W, B, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, and Mo.

[0077] Preferably, the coating layer may contain Co, where the Co content in the coating layer may be 0.5 mol% to 4 mol%, preferably 0.5 mol% to 3 mol%, and more preferably 1 mol% to 2 mol%, based on the total number of moles of transition metal contained in the positive electrode active material. When the Co content in the coating layer satisfies the above range, the resistance reduction effect of the positive electrode active material is excellent, and excellent capacity can be achieved.

[0078] On the other hand, the positive electrode active material according to the present invention is D 50 The particle size can be 5 μm to 8 μm, preferably 5 μm to 7 μm, and more preferably 5 μm to 6.5 μm. In the case of an ultra-high nickel cathode active material with a Ni content of 90 mol% or more, D 50 If it is small, less than 5 μm, the improvement effect on thermal stability is minimal, D 50 If the capacitance exceeds 8 μm, the resistance becomes excessively large, resulting in a decrease in capacitance and output characteristics.

[0079] On the other hand, the positive electrode active material can have a cation mixing rate of 0.9 at% to 1.5 at%, preferably 1 at% to 1.5 at%. When the cation mixing rate of the positive electrode active material satisfies the above range, side reactions with the electrolyte on the surface of the particles are reduced, thereby providing the effect of reducing the leakage current during high-temperature, high-voltage continuous charging.

[0080] The positive electrode active material of the present invention, as described above, exhibits excellent capacitance characteristics and thermal stability.

[0081] Specifically, after charging a coin half-cell manufactured using the positive electrode active material of the present invention to 4.25V, the maximum value of the heat flow measured by a differential scanning calorimeter (DSC) while raising the temperature from room temperature to 380°C under a heating rate of 10°C / min can be 15.0 W / g or less, preferably 5 W / g to 15.0 W / g, and more preferably 7 W / g to 15.0 W / g.

[0082] Furthermore, when a coin half-cell manufactured using the positive electrode active material is charged to 4.25V, the charging capacity can be 240mAh / g or more, preferably 240mAh / g to 245mAh / g, and more preferably 240mAh / g to 243mAh / g.

[0083] positive electrode Next, the positive electrode of the present invention will be described.

[0084] The positive electrode according to the present invention includes the positive electrode active material according to the present invention as described above, and may further include a positive electrode conductive material and a positive electrode binder as needed. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a positive electrode conductive material and a positive electrode binder. On the other hand, the positive electrode active material is as described above, and a detailed explanation is omitted.

[0085] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0086] On the other hand, the positive electrode active material can be included in an amount of 93% to 99% by weight, preferably 95% to 98% by weight, and more preferably 95% to 97% by weight, based on the total weight of the positive electrode active material layer, i.e., the total amount of the positive electrode active material, positive electrode conductive material, and positive electrode binder combined. When the content of the positive electrode active material satisfies the above range, a high energy density can be achieved.

[0087] Next, the positive electrode conductive material is used to impart conductivity to the positive electrode and can be used without particular limitations in a battery that does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Of these, one or more can be used individually or in mixtures of two or more.

[0088] The positive electrode conductive material can be included in an amount of 0.1 to 10% by weight, preferably 0.5% to 8% by weight, and more preferably 1% to 5% by weight, relative to the total weight of the positive electrode active material layer.

[0089] Next, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these can be used.

[0090] The positive electrode binder may be present in an amount of 0.5% to 5% by weight, preferably 1 to 4% by weight, and more preferably 1 to 3% by weight, relative to the total weight of the positive electrode active material layer.

[0091] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode. For example, the positive electrode can be manufactured by mixing a positive electrode active material, a positive electrode binder, and / or a positive electrode conductive material in a solvent to produce a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling it; or by casting the positive electrode slurry onto another support, peeling it off the support, and laminating the resulting film onto the positive electrode current collector.

[0092] On the other hand, the solvent for the positive electrode slurry can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, used individually or in combination of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode, taking into consideration the coating thickness and manufacturing yield of the slurry.

[0093] Lithium-ion battery Next, the lithium secondary battery according to the present invention will be described.

[0094] The lithium secondary battery of the present invention includes the positive electrode according to the present invention. Specifically, the lithium secondary battery includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, where the positive electrode is as described above.

[0095] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0096] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0097] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector can usually have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0098] The negative electrode active material layer may selectively include a negative electrode binder and a negative electrode conductive material together with the negative electrode active material.

[0099] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include metal oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these mixtures can be used.

[0100] Furthermore, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Typical low-crystallinity carbons include soft carbon and hard carbon, while typical high-crystallinity carbons include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0101] The negative electrode conductive material is used to provide conductivity to the electrode and can be used without particular limitations as long as it does not cause chemical changes and has electronic conductivity in the battery it is used in. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Of these, one or more can be used. The negative electrode conductive material can usually be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0102] The negative electrode binder plays a role in improving the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more can be used. The negative electrode binder may be present in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0103] The negative electrode active material layer can be manufactured, for example, by applying a negative electrode slurry containing a negative electrode active material and selectively a negative electrode binder and a negative electrode conductive material onto a negative electrode current collector and drying it, or by casting the negative electrode slurry onto another support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0104] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0105] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0106] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0107] The aforementioned organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group, which can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0108] The lithium salt can be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 5.0 M, more preferably 0.1 to 3.0 M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0109] In addition to the components of the electrolyte, the electrolyte may further contain additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity. For example, the additives may include, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride, either alone or in combination. The additives may be present in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, relative to the total weight of the electrolyte.

[0110] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0111] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0112] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0113] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0114] Example 1 D 50 The thickness is 5.6 μm, and the BET is 5.6 μm 2 A nickel-cobalt-manganese hydroxide precursor with a molar ratio of Ni:Co:Mn of 92:6:2 was mixed with lithium hydroxide to a molar ratio of Li / (Ni+Co+Mn) of 1.02, and then calcined at 860°C for 12 hours to produce a lithium nickel-based oxide in single-particle form. Next, the lithium nickel-based oxide was mixed with cobalt hydroxide and then heat-treated at 750°C to produce a positive electrode active material with a Co-containing coating layer. 50The diameter was 5.5 μm, and the molar ratio of Ni:Co:Mn in the overall positive electrode active material was 91:7:2.

[0115] Example 2 D 50 The thickness is 5.5 μm, and the BET is 6.16 μm. 2 The positive electrode active material was prepared in the same manner as in Example 1, except that a nickel-cobalt-manganese hydroxide precursor was used, which was 1 / g and had a Ni:Co:Mn molar ratio of 92:6:2. 50 The diameter was 5.4 μm, and the molar ratio of Ni:Co:Mn in the overall positive electrode active material was 91:7:2.

[0116] Comparative Example 1 D 50 The thickness is 3.5 μm, and the BET is 8.75 μm 2 A nickel-cobalt-manganese hydroxide precursor with a molar ratio of Ni:Co:Mn of 86:6:8 was mixed with lithium hydroxide to a molar ratio of Li / (Ni+Co+Mn) of 1.02, and then calcined at 880°C for 12 hours to produce a lithium nickel-based oxide in single-particle form. Next, the lithium nickel-based oxide was mixed with cobalt hydroxide and then heat-treated at 750°C to produce a positive electrode active material with a Co-containing coating layer. 50 The diameter was 3.5 μm, and the molar ratio of Ni:Co:Mn in the overall positive electrode active material was 85:7:8.

[0117] Comparative Example 2 D 50 The thickness is 3.8 μm, and the BET is 8.74 μm 2 The positive electrode active material was prepared in the same manner as in Example 1, except that a nickel-cobalt-manganese hydroxide precursor was used, which was 1 / g and had a Ni:Co:Mn molar ratio of 92:6:2. 50 The diameter was 3.8 μm, and the molar ratio of Ni:Co:Mn in the overall positive electrode active material was 91:7:2.

[0118] Comparative Example 3 D 50 The thickness is 5.4 μm, and the BET is 1.944 μm2 is / g, and the positive electrode active material was produced in the same manner as in Example 1 except that a nickel cobalt manganese hydroxide precursor with a molar ratio of Ni:Co:Mn of 92:6:2 was used. The D of the produced positive electrode active material 50 was 5.4 μm, and the molar ratio of Ni:Co:Mn in the total positive electrode active material was 91:7:2.

[0119] Comparative Example 4 D 50 was 5.5 μm, and the BET was 2.585 m 2 / g, and the positive electrode active material was produced in the same manner as in Example 1 except that a nickel cobalt manganese hydroxide precursor with a molar ratio of Ni:Co:Mn of 92:6:2 was used. The D of the produced positive electrode active material 50 was 5.5 μm, and the molar ratio of Ni:Co:Mn in the total positive electrode active material was 91:7:2.

[0120]

Table 1

[0121] Experimental Example 1 The lithium nickel-based oxides produced by the methods of Examples 1 to 2 and Comparative Examples  1 to 4 were collected, and after measuring the masses of LiOH and LiCO3 by pH titration method (pH Titration), the content (mol%) of lithium by-products in the lithium nickel-based oxides before the formation of the Co coating layer was measured by converting this into mol%.

[0122] Also, by XRD analysis, the cation mixing ratio of the positive electrode active materials produced in Examples 1 to 2 and Comparative Examples 1 to 4 was measured. The XRD analysis was carried out using an X-ray diffractometer (Bruker AXS D4-Endeavor XRD), and was performed under the accelerating voltage condition of 10 kV using a Cu Ka light source.

[0123] The measurement results are shown in the following [Table 2].

[0124]

Table 2

[0125] As shown in [Table 2] above, BET / D 50 In the case of lithium nickel oxides of Examples 1 and 2, which were produced using precursors with a ratio of 0.5 to 2, BET / D 50 The lithium by-product content was higher compared to the lithium nickel oxides of Comparative Examples 1-4, which were produced using precursors with a ratio of less than 0.5 or greater than 2.

[0126] Furthermore, the positive electrode active materials produced in Examples 1-2 had a higher cation mixing rate than the positive electrode active materials produced in Comparative Examples 1-4, indicating that the surface structure of the positive electrode active materials in Examples 1-2 was lower than that of the positive electrode active materials in Comparative Examples 1-4.

[0127] Experimental Example 2: Analysis of Heat Flow The positive electrode active materials, carbon nanotubes, and PVDF binders produced in Examples 1-2 and Comparative Examples 1-4 were added to N-methylpyrrolidone in a weight ratio of 96:2:2 to produce a positive electrode slurry. The positive electrode slurry was applied to an aluminum current collector, dried, and then rolled to produce a positive electrode.

[0128] As described above, the positive electrode and lithium metal counter electrode were stacked with a separator in between to produce an electrode assembly. After placing the electrode assembly in a battery case, an electrolyte solution was injected to produce a coin half-cell.

[0129] The aforementioned coin half-cell was charged to 4.25V in a constant current mode of 0.1C, and then its charge capacity was measured.

[0130] Next, the charged coin half-cell was placed in a heating chamber, and the heat flow was measured using a differential scanning calorimeter (DSC) while the temperature was increased from room temperature to 380°C under a heating rate of 10°C / min.

[0131] The measurement results are shown in Figure 1 and Table 3.

[0132] [Table 3]

[0133] As shown in Table 3 and Figure 1 above, in the case of coin half cells manufactured using the positive electrode active materials of Examples 1-2, it can be confirmed that the temperature of the main exothermic peak is higher, the intensity is lower, and the thermal stability is superior compared to coin half cells manufactured using the positive electrode active materials of Comparative Examples 2-4, which have the same composition.

[0134] Furthermore, despite containing 90 mol% or more of Ni, the positive electrode active materials of Examples 1 and 2 exhibit a level of thermal stability equivalent to that of the positive electrode active material of Comparative Example 1, which contains 85 mol% Ni, and demonstrate superior charging capacity compared to the positive electrode active material of Comparative Example 1.

[0135] Experiment Example 3: Evaluation of Continuous Charging Performance In Experimental Example 2, each coin half-cell manufactured using the positive electrode active materials of Examples 1-2 and Comparative Examples 3-4 was charged to 4.7V in constant current mode at 50°C. After reaching 4.7V, the leakage current was measured while charging in constant voltage mode. The measurement results are shown in Figure 2.

[0136] As shown in Figure 2, in the case of coin half cells manufactured using the positive electrode active materials of Examples 1 and 2, it can be confirmed that the leakage current is smaller when maintaining high voltage at high temperatures compared to coin half cells manufactured using the positive electrode active materials of Comparative Examples 3 and 4. This is judged to be because the positive electrode active materials of Examples 1 and 2 have a lower degree of surface structural completion and fewer side reactions with the electrolyte compared to the positive electrode active materials of Comparative Examples 3 and 4.

Claims

1. The Ni content among the total metallic elements is 90 mol% or more, D ５０ The size is 5 μm to 8 μm, D ５０ The ratio of BET specific surface area to (BET / D) ５０ A method for producing a cathode active material, comprising the step of mixing a precursor having a ratio of 0.5 to 2 with a lithium raw material and firing the mixture to produce a single-particle lithium nickel-based oxide.

2. The aforementioned precursor is D ５０ The ratio of BET specific surface area to (BET / D) ５０ A method for producing a positive electrode active material according to claim 1, wherein the ratio is 0.8 to 1.

5.

3. The aforementioned precursor is D ５０ A method for producing a positive electrode active material according to claim 1, wherein the particle size is 5 μm to 7 μm.

4. The aforementioned precursor has a BET specific surface area of ​​5 m². ２ / g to 10m ２ A method for producing a positive electrode active material according to claim 1, wherein the amount is / g.

5. The method for producing a positive electrode active material according to claim 1, wherein the precursor is represented by the following [Chemical Formula 1]. [Chemical formula 1] Ni ａ Co ｂ Mn ｃ M １ ｄ (OH) ２ In the above chemical formula 1, M １ is one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.90 ≤ a < 1, 0 < b < 0.1, 0 < c < 0.1, 0 ≤ d ≤ 0.

05.

6. The method for producing a positive electrode active material according to claim 1, wherein the firing is performed at 800°C to 900°C.

7. The method for producing a positive electrode active material according to claim 1, wherein the lithium nickel-based oxide contains lithium by-products in an amount of 1 mol% to 5 mol%.

8. A method for producing a positive electrode active material according to claim 1, further comprising the step of mixing the single-particle lithium nickel oxide with a coating raw material and heat-treating it, after the step of producing the single-particle lithium nickel oxide.

9. The method for producing a positive electrode active material according to claim 8, wherein the coating raw material contains one or more elements selected from the group consisting of Co, Al, W, B, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, and Mo.

10. The method for producing a positive electrode active material according to claim 8, wherein the temperature of the heat treatment is 300°C to 800°C.

11. A positive electrode active material containing nickel, cobalt, and manganese, wherein the nickel content of the total metals other than lithium is 90 mol% or more, and which contains single-particle lithium nickel oxide containing 1 to 30 nodules, The D of the positive electrode active material ５０ The size is 5 μm to 8 μm. A positive electrode active material wherein, after charging a coin half cell manufactured using the positive electrode active material to 4.25V, the maximum value of the heat flow measured by a differential scanning calorimeter (DSC) while increasing the temperature from room temperature to 380°C under a temperature increase condition of 10°C / min is 15.0 W / g or less.

12. The positive electrode active material according to claim 11, wherein when a coin half cell manufactured using the positive electrode active material is charged to 4.25V, the charging capacity is 240mAh / g or more.

13. The positive electrode active material according to claim 11, wherein the positive electrode active material has a cation mixing rate of 0.9 at% to 1.5 at%.

14. The single-particle lithium nickel oxide is the positive electrode active material according to claim 11, represented by the following [Chemical Formula 2]. [Chemical formula 2] Li ｘ [Ni ａ Co ｂ Mn ｃ M １ ｄ ]O ２ In the above chemical formula 2, M １ x is one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and the following conditions apply: 0.8 ≤ x ≤ 1.2, 0.9 ≤ a < 1, 0 < b < 0.1, 0 < c < 0.1, 0 ≤ d ≤ 0.

05.

15. The positive electrode active material further comprises a coating layer formed on the single-particle lithium nickel oxide, The positive electrode active material according to claim 11, wherein the coating layer contains one or more elements selected from the group consisting of Co, Al, W, B, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, and Mo.

16. The positive electrode active material according to claim 15, wherein the coating layer contains Co, and the Co content in the coating layer is 0.5 mol% to 2 mol%, based on the total number of moles of transition metals contained in the positive electrode active material.

17. A positive electrode comprising the positive electrode active material according to any one of claims 11 to 16.

18. A lithium secondary battery comprising the positive electrode described in claim 17.

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