Positive electrode active material, method for preparing same, and positive electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode active material and a method for preparing same, the positive electrode active material comprising a single particle-type lithium nickel-based oxide which comprises nickel, cobalt, and manganese, the content of nickel being 90 mol % or more among all metals excluding lithium, and includes 1-30 nodules, wherein D50 is 5㎛ to 7㎛, and a maximum value of a heat flow rate measured by a differential scanning calorimeter (DSC) is 15.0% / g or less while a coin-half cell, prepared by using the positive electrode active material, is charged up to 4.25 V, and then the temperature is raised from room temperature to 380℃ under a heating condition of 10℃ / min.

Description

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

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0105927, filed August 11, 2023, the entire contents of which are incorporated herein by reference.

[0002]

[0003] The present invention relates to a cathode active material, a cathode including the same, and a lithium secondary battery, and more particularly, to a single particle type cathode active material containing 90 mol% or more of Ni and having excellent thermal stability, and a cathode including the same and a lithium secondary battery.

[0004] A lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode include an active material capable of intercalating and deintercalating lithium ions.

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compound (LiFePO4) have been used as cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the high price of cobalt, which is the raw material, and its supply are unstable, making it difficult to commercially apply it to large-capacity batteries. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient cycle life characteristics. Meanwhile, lithium manganese oxide has excellent stability but has the problem of poor capacity characteristics. Therefore, lithium composite transition metal oxides containing two or more transition metals have been developed to complement the problems of lithium transition metal oxides containing only Ni, Co, or Mn. Among these, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0006] Conventional lithium nickel cobalt manganese oxides are typically in the form of spherical secondary particles formed by agglomeration of tens to hundreds of primary particles. However, in the case of lithium nickel cobalt manganese oxides formed by agglomeration of many primary particles in this way, there is a problem in that the primary particles are easily broken during the rolling process during the manufacture of the positive electrode, and cracks occur inside the particles during the charge and discharge process. When the positive electrode active material particles are broken or cracked, the contact area with the electrolyte increases, which increases the problem of gas generation and active material degradation due to side reactions with the electrolyte.

[0007] Meanwhile, in the electric vehicle field, lithium secondary batteries with high energy density are required to extend the single-charge driving distance, and accordingly, the nickel content of the cathode active material is gradually increasing.

[0008] However, in the case of high-Ni cathode active materials with high nickel content, high capacity can be achieved, but when charge and discharge are repeated, the highly reactive Ni +4 There is a problem that a large amount of ions are generated, causing structural collapse of the positive electrode active material, which increases the rate of deterioration of the positive electrode active material, resulting in a decrease in life characteristics and low thermal stability, which reduces battery safety.

[0009] Therefore, there is a need for the development of a cathode active material that can simultaneously achieve high capacity and high thermal stability.

[0010] The present invention is intended to solve the above-mentioned problems, and to provide a cathode active material having a high Ni content of 90 mol% or more among all metals excluding lithium and excellent thermal stability, and a method for manufacturing the same.

[0011] In addition, the present invention seeks to provide a positive electrode including the positive electrode active material and a lithium secondary battery including the positive electrode having excellent thermal stability and excellent high-temperature and high-voltage continuous charging characteristics.

[0012] According to one embodiment, the present invention has a content of Ni of 90 mol% or more among all metal elements, and D 50 This is 5㎛ to 8㎛, D 50 The ratio of the BET surface area to the surface area (BET / D) 50 ) is 0.5 to 2, preferably 0.8 to 1.5, and a lithium raw material are mixed and calcined to produce a single particle type lithium nickel-based oxide.

[0013] At this time, the precursor is D 50 The silver may preferably be 5 ㎛ to 7 ㎛, more preferably 5 ㎛ to 6.5 ㎛.

[0014] The BET surface area of ​​the above precursor is 5 m 2 / g to 10m 2 / g, preferably 5m 2 / g to 8m2 / g more preferably 5m 2 / g to 7m 2 / g may be.

[0015] Specifically, the precursor may be nickel cobalt manganese hydroxide having a Ni content of 90 mol% or more among all metal elements, and more specifically, may be represented by the following [chemical formula 1].

[0016] [Chemical Formula 1]

[0017] Ni a Co b Mn c M 1 d (OH)2

[0018] In the above chemical formula 1, M 1 is at least one 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≤0.05이다.

[0019] Meanwhile, the firing may be performed at 800°C to 900°C, preferably 820°C to 880°C, and more preferably 820°C to 870°C.

[0020] Meanwhile, the lithium nickel-based oxide may contain lithium by-products in an amount of 1 mol% to 5 mol%, preferably 1 mol% to 3 mol%.

[0021] Meanwhile, the method for manufacturing a cathode active material according to the present invention may further include a step of mixing and heat-treating the single-particle lithium nickel-based oxide and a coating raw material after the step of manufacturing the single-particle lithium nickel-based oxide.

[0022] At this time, the coating raw material may include 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.

[0023] Meanwhile, the heat treatment temperature may be performed at an appropriate temperature depending on the type of element included in the coating layer. For example, the heat treatment may be performed at a temperature of 300°C to 800°C, preferably 400°C to 800°C, and more preferably 500°C to 800°C.

[0024] According to another embodiment, the present invention provides a cathode active material comprising a single-particle lithium nickel-based oxide comprising nickel, cobalt and manganese, the nickel content being 90 mol% or more among all metals excluding lithium, and comprising 1 to 30 nodules.

[0025] At this time, D of the positive electrode active material 50 It may be 5 ㎛ to 8 ㎛, preferably 5 ㎛ to 7 ㎛, and more preferably 5 ㎛ to 6.5 ㎛.

[0026] In addition, when a coin-half cell manufactured using the above-described positive electrode active material is charged to 4.25 V and then heated from room temperature to 380°C at a temperature increasing rate of 10°C / min, the maximum value of the heat flow measured using a differential scanning calorimeter (DSC) may 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.

[0027] In addition, when a coin-half cell manufactured using the above positive electrode active material is charged to 4.25 V, the charge capacity may be 240 mAh / g or more, preferably 240 mAh / g to 245 mAh / g, and more preferably 240 mAh / g to 243 mAh / g.

[0028] Additionally, the positive electrode active material may have a cation mixing ratio of 0.9 at% to 1.5 at%, preferably 1 at% to 1.5 at%.

[0029] Meanwhile, the single particle lithium nickel oxide may be a lithium nickel oxide having a Ni content of 90 mol% or more among all metal elements excluding lithium, and more specifically, may be represented by the following [chemical formula 2].

[0030] [Chemical Formula 2]

[0031] Li x [Ni a Co b Mn c M 1 d ]O2

[0032] In the above chemical formula 2, M 1 is at least one 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≤0.05이다.

[0033] Meanwhile, the positive electrode active material may further include a coating layer formed on the single particle lithium nickel oxide, and the coating layer may include 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.

[0034] Preferably, the coating layer may include Co, and at this time, the content of Co included 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 included in the entire positive electrode active material.

[0035] According to another embodiment, the present invention provides a positive electrode comprising a positive electrode active material according to the present invention and a lithium secondary battery comprising the positive electrode.

[0036] D as in the present invention 50When a single particle lithium nickel oxide is manufactured using a precursor having a surface area ratio satisfying a specific range, a cathode active material having excellent thermal stability can be manufactured even though the nickel content is high at 90 mol% or more.

[0037] The cathode active material according to the present invention contains nickel in an amount of 90 mol% or more, thereby realizing a high capacity, while at the same time having thermal stability equivalent to that of a cathode active material having a nickel content of less than 90 mol%.

[0038] Therefore, when the cathode active material according to the present invention is applied to a lithium secondary battery, both high capacity and high thermal stability can be achieved simultaneously. Furthermore, a lithium secondary battery using the cathode active material according to the present invention can exhibit excellent continuous charging performance under high temperature and high voltage conditions.

[0039] Figure 1 is a graph showing the heat flow rate according to temperature of a coin-half cell using the positive electrode active materials of Examples 1 to 2 and Comparative Examples 1 to 4.

[0040] Figure 2 is a graph showing the continuous charging performance of coin-half cells using the positive electrode active materials of Examples 1 to 2 and Comparative Examples 3 to 4.

[0041] Hereinafter, the present invention will be described in more detail.

[0042] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0043] In the present invention, “single particle type” means a particle composed of 30 or fewer nodules, and is a concept that includes a single particle composed of one nodule and a pseudo-single particle which is a composite of 2 to 30 nodules.

[0044] The above “nodule” is a sub-particle unit that constitutes a single particle and a pseudo-single particle, and may be a single crystal without a crystalline grain boundary, or a polycrystal with no apparent grain boundary when observed under a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0045] In the present invention, "secondary particle" refers to a particle formed by agglomeration of a plurality of primary particles, for example, tens to hundreds of primary particles. Specifically, the secondary particle may be an aggregate of 50 or more primary particles.

[0046] In the present invention, “particle” is a concept including any one or all of a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0047] In the present invention, the average particle diameter (D) of the nodules or primary particles mean ) means the arithmetic mean value calculated after measuring the particle size of nodules or primary particles observed in scanning electron microscope images.

[0048] In the present invention, "average particle diameter D 50 " refers to the particle size corresponding to 50% of the volume cumulative particle size distribution of the target powder, and can be measured using the laser diffraction method. For example, after dispersing the target powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then calculating the particle size corresponding to 50% of the volume cumulative amount.

[0049] In the present invention, the “BET specific surface area” is measured by the BET method, and specifically, can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-mino II of BEL Japan.

[0050] The inventors of the present invention have conducted repeated research to develop a cathode active material with high capacity characteristics and excellent thermal stability, and as a result, they have found that the content of Ni is 90 mol% or more and the BET specific surface area is D 50 The rain of (D 50 / BET) has been found that when a cathode active material is manufactured using a precursor satisfying a specific range, both capacity characteristics and thermal stability can be excellently implemented, thereby completing the present invention.

[0051]

[0052] Method for manufacturing positive electrode active material

[0053] The method for manufacturing a positive electrode active material according to the present invention is characterized in that the content of Ni among all metal elements is 90 mol% or more, and D 50 The ratio of the BET surface area to the surface area (BET / D) 50 ) comprises a step of mixing and calcining a precursor and a lithium raw material having a content of 0.5 to 2, preferably 0.8 to 1.5, to produce a single-particle lithium nickel-based oxide.

[0054] According to the research of the present inventors, in the case of an ultra-high nickel positive electrode active material having a Ni content of 90 mol% or more, unlike a positive electrode active material having a Ni content of less than 90 mol%, the D of the precursor used in manufacturing 50 The ratio of the BET surface area to the surface area (BET / D) 50 ) was found to be closely related to thermal stability. Specifically, when manufacturing an ultra-high nickel positive electrode active material with a Ni content of 90 mol% or more, D 50 The ratio of the BET surface area to the surface area (BET / D) 50) was found to improve thermal stability and significantly reduce heat generation when exposed to high temperatures compared to when using a precursor that falls outside the above range. The average particle diameter of the precursor D 50 The average particle diameter D of the positive electrode active material 50 D of the positive electrode active material affects 50 As it becomes smaller, the deterioration of the positive electrode active material occurs quickly when exposed to high temperatures, resulting in a decrease in thermal stability. In addition, the lower the BET surface area of ​​the precursor, the higher the reactivity with lithium during firing, and accordingly, the cation mixing ratio of the synthesized single-particle positive electrode active material decreases, and the degree of completion of the crystal structure of the positive electrode active material increases. If the degree of completion of the crystal structure of the positive electrode active material becomes too high, the side reaction with the electrolyte increases on the surface of the positive electrode active material, resulting in a decrease in thermal stability. Therefore, in the present invention, the ratio of the BET surface area to the average particle diameter D50 (BET / D 50 ) The average particle diameter D of the positive electrode active material synthesized using a precursor satisfying the range of 0.5 to 2 50 And the degree of crystal structure completion can be controlled to an appropriate range. As in the present invention, BET / D 50 When a precursor with a value of 0.5 or higher is used, the degree of completion of the crystal structure of the positive electrode active material decreases, increasing the electrical and chemical inactivity of the surface of the positive electrode active material. As a result, the side reaction with the electrolyte is reduced, and the thermal stability is improved. Meanwhile, BET / D 50 If this exceeds 2, the D of the positive electrode active material 50 It was found that when this becomes too small or the BET specific surface area of ​​the positive electrode active material becomes too high, side reactions with the electrolyte increase, the effect of improving thermal stability decreases, and the resistance increases, deteriorating the electrochemical properties of the positive electrode active material.

[0055] Meanwhile, the precursor may be nickel cobalt manganese hydroxide having a Ni content of 90 mol% or more among all metal elements, and more specifically, may be represented by the following [chemical formula 1].

[0056] [Chemical Formula 1]

[0057] Ni a Co b Mn c M 1 d (OH)2

[0058] In the above chemical formula 1, M 1 It may be at least one selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and preferably at least one selected from the group consisting of Al, Zr, Y, Ti, Sr, and Nb.

[0059] The above a represents the molar fraction of nickel among the metal elements in the precursor, and may be 0.90≤a<1, 0.90≤a≤0.99, or 0.90≤a≤0.99.

[0060] The above b represents the mole fraction of Co among the metal elements in the precursor, 0 <b<0.1, 0.01≤b<0.1, 또는 0.02≤b<0.1일 수 있다.

[0061] The above c represents the molar fraction of Mn among the metal elements in the precursor, and may be 0.005≤c<0.1, or 0.01≤c≤0.08.

[0062] The above d is M among the metal elements in the precursor 1 It represents the mole fraction of an element, and can be 0≤d≤0.05, 0≤d≤0.02, or 0≤d≤0.01.

[0063]

[0064] Meanwhile, the precursor is D 50 This may be 5㎛ to 8㎛, preferably 5㎛ to 7㎛, more preferably 5㎛ to 6.5㎛. D of the precursor50 When this above range is satisfied, a more excellent thermal stability improvement effect can be obtained while minimizing the increase in resistance of the positive electrode active material manufactured using it. D 50 When using this too small precursor, the effect of improving the thermal stability of the positive electrode active material is minimal, and D 50 Using a precursor that is too large can increase the initial resistance and negatively affect the electrochemical properties of the cathode active material.

[0065]

[0066] In addition, the BET surface area of ​​the precursor is 5 m 2 / g to 10m 2 / g, preferably 5m 2 / g to 8m 2 / g more preferably 5m 2 / g to 7m 2 / g may be. When manufacturing a positive electrode active material using a precursor having a BET specific surface area that satisfies the above range, the surface crystal structure of the positive electrode active material is formed to an appropriate level of perfection, thereby reducing side reactions with the electrolyte and improving thermal stability. When using a precursor having too small a BET specific surface area, the layered crystal structure is overly developed on the surface of the positive electrode active material, thereby increasing side reactions with the electrolyte and reducing stability when exposed to high temperatures. In addition, when using a precursor having too large a BET specific surface area, too many inactive crystal structures are formed on the surface of the positive electrode active material, thereby increasing resistance and deteriorating electrochemical properties.

[0067]

[0068] Next, as the lithium raw material, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide may be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or a mixture thereof may be used.

[0069]

[0070] Meanwhile, the lithium raw material and the precursor may be mixed so that the molar ratio of Li: total metal in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1, 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 cathode active material having excellent capacity characteristics and thermal stability can be manufactured. At this time, if necessary, M may be added to the lithium raw material and the precursor. 1 Metal-containing raw materials can be mixed and fired together.

[0071]

[0072] Meanwhile, the sintering may be performed at 800°C to 900°C, preferably 820°C to 880°C, and more preferably 820°C to 870°C. When the sintering temperature satisfies the above range, a single-particle lithium nickel-based oxide having excellent electrochemical properties can be produced. If the sintering temperature is too low, a secondary particle lithium nickel-based oxide rather than a single-particle lithium nickel-based oxide is produced, and if the sintering temperature is too high, a thick inactive phase such as a rock salt phase is formed on the particle surface, resulting in a deterioration in resistance, output, and capacity characteristics.

[0073] Meanwhile, the firing may be performed under an oxygen atmosphere for 5 to 35 hours, preferably 10 to 30 hours, and more preferably 10 to 20 hours. As used herein, the term "oxygen atmosphere" refers to an atmosphere containing oxygen sufficient for firing, including an air atmosphere. In particular, it is preferable to perform the firing in an atmosphere with a higher oxygen partial pressure than an air atmosphere.

[0074]

[0075] Meanwhile, the lithium nickel-based oxide manufactured by the above method may include lithium by-products such as lithium hydroxide and lithium carbonate on the particle surface, and the content of the lithium by-product is preferably 1 mol% to 5 mol%, preferably 1 mol% to 4 mol%, and more preferably 1.5 mol% to 3 mol%. When the lithium nickel-based oxide includes the lithium by-product in the above range, a coating layer can be uniformly formed in the coating process described later. If the content of the lithium by-product is too low, the coating layer may be formed unevenly, and if the content of the lithium by-product is too high, the electrolyte and the lithium by-product may react, increasing gas generation and deteriorating the life characteristics.

[0076]

[0077] Meanwhile, the method for manufacturing a cathode active material according to the present invention may further include, if necessary, a step of mixing and heat-treating the single-particle lithium nickel-based oxide and the coating raw material after the step of manufacturing the single-particle lithium nickel-based oxide.

[0078]

[0079] At this time, 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, and more specifically, may be an oxide, hydroxide, carbide, chloride, carbonate, sulfate, etc. containing the above elements. Preferably, the coating raw material may contain Co. In the case of single-particle lithium nickel-based oxide, since it is fired at a relatively high temperature, a lot of electrically inactive phases such as a rock salt structure are formed on the particle surface, resulting in high resistance, and in particular, when a precursor having a relatively large particle size is used, there is a problem that the resistance increase is further aggravated. However, when a Co-containing coating layer is formed on the surface of the single-particle lithium nickel-based oxide, a part of the inactive phase on the surface is recrystallized during the heat treatment process, resulting in a change in the layered structure, thereby reducing the resistance.

[0080]

[0081] Meanwhile, the above mixing may be performed as a solid mixing or a liquid mixing, and the heat treatment may be performed at an appropriate temperature depending on the coating raw material. For example, the heat treatment of the above coating process may be performed 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.

[0082]

[0083] positive electrode active material

[0084] Next, the positive electrode active material according to the present invention will be described.

[0085] The positive electrode active material according to the present invention may be manufactured by the above-described method for manufacturing a positive electrode active material.

[0086] The cathode active material according to the present invention comprises a single particle lithium nickel-based oxide containing nickel, cobalt and manganese, having a nickel content of 90 mol% or more among all metals excluding lithium, and having 1 to 30 nodules.

[0087] When a single particle lithium nickel oxide having a high nickel content as described above is included, a high capacity can be realized, side reactions with the electrolyte are suppressed, gas generation is suppressed, and excellent life characteristics can be realized.

[0088] In the case of secondary particle-type lithium nickel-based oxides in which 31 to hundreds of primary particles are aggregated, side reactions with the electrolyte frequently occur because the contact area with the electrolyte is large, and gases are generated during the side reactions. In particular, the amount of gas generated further increases under high temperature and / or high voltage conditions, which causes rapid cell degradation. In contrast, single-particle lithium nickel-based oxides have a smaller number of nodules constituting the particles, which reduces the intra-particle interface and thus the contact area with the electrolyte, resulting in less side reactions with the electrolyte than secondary particles, and consequently, significantly less gas generation. Therefore, when single-particle lithium nickel-based oxides are applied as cathode active materials, excellent cycle characteristics can be obtained even under high temperature and / or high voltage conditions.

[0089]

[0090] Specifically, the single particle lithium nickel oxide may be a lithium nickel oxide having a Ni content of 90 mol% or more among all metal elements excluding lithium, and more specifically, may be represented by the following [chemical formula 2].

[0091] [Chemical Formula 2]

[0092] Li x [Ni a Co b Mn c M 1 d ]O2

[0093] In the above chemical formula 2, M 1 It may be at least one selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and preferably at least one selected from the group consisting of Al, Zr, Y, Ti, Sr, and Nb.

[0094] The above x represents the molar fraction of lithium in the lithium nickel-based oxide, and may be 0.8≤x≤1.2, 0.9≤x≤1.1, or 1.0≤x≤1.1.

[0095] The above a represents the mole fraction of nickel among the metal elements excluding lithium in the lithium nickel-based oxide, and may be 0.90≤a<1, 0.90≤a≤0.99, or 0.90≤a≤0.99.

[0096] The above b represents the mole fraction of Co among the metal elements excluding lithium in the lithium nickel oxide, 0 <b<0.1, 0.01≤b<0.1, 또는 0.02≤b<0.1일 수 있다.

[0097] The above c represents the mole fraction of Mn among the metal elements excluding lithium in the lithium nickel-based oxide, and may be 0.005≤c<0.1, or 0.01≤c≤0.08.

[0098] The above d represents the mole fraction of the M1 element among the metal elements excluding lithium in the lithium nickel-based oxide, and may be 0≤d≤0.05, 0≤d≤0.02, or 0≤d≤0.01.

[0099]

[0100] Meanwhile, it is preferred that the single particle lithium nickel-based oxide comprises no more than 30 nodules, preferably 1 to 25 nodules, and more preferably 1 to 15 nodules. If the number of nodules constituting the lithium nickel-based oxide exceeds 30, particle breakage increases during electrode manufacturing, and internal cracks occur more frequently due to volume expansion / contraction of the nodules during charge / discharge, which may deteriorate the effect of improving high-temperature life characteristics and high-temperature storage characteristics.

[0101]

[0102] Meanwhile, the nodules may 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 breakage is minimized during electrode manufacturing, and resistance increase can be more effectively suppressed. At this time, the average particle size of the nodules refers to a value obtained by measuring the particle sizes of nodules observed in SEM images obtained by analyzing the positive electrode active material powder with a scanning electron microscope, and then calculating the arithmetic mean of the measured values.

[0103]

[0104] Meanwhile, the cathode active material according to the present invention may further include a coating layer formed on the single particle lithium nickel-based oxide, and the coating layer may include 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.

[0105] Preferably, the coating layer may include Co, and at this time, the content of Co included 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 included in the entire 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 the capacity can also be excellently implemented.

[0106]

[0107] Meanwhile, the positive electrode active material according to the present invention is D 50 It may be 5㎛ to 8㎛, preferably 5㎛ to 7㎛, more preferably 5㎛ to 6.5㎛. In the case of an ultra-high nickel positive electrode active material having a Ni content of 90 mol% or more, D 50 If it is less than 5㎛, the effect of improving thermal stability is minimal, and D 50 If this 8㎛ is exceeded, the resistance becomes too large and the capacity and output characteristics deteriorate.

[0108]

[0109] Meanwhile, the cationic mixing ratio of the positive active material may be 0.9 at% to 1.5 at%, preferably 1 at% to 1.5 at%. When the cationic mixing ratio of the positive active material satisfies the above range, the side reaction with the electrolyte at the particle surface is reduced, thereby achieving the effect of reducing the leakage current during high-temperature, high-voltage continuous charging.

[0110]

[0111] The positive electrode active material of the present invention as described above has excellent capacity characteristics and thermal stability.

[0112] Specifically, when a coin-half cell manufactured using the positive electrode active material of the present invention is charged to 4.25 V and then heated from room temperature to 380°C at a temperature increasing rate of 10°C / min, the maximum value of the heat flow measured using a differential scanning calorimeter (DSC) may 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.

[0113] In addition, when a coin-half cell manufactured using the above positive electrode active material is charged to 4.25 V, the charge capacity may be 240 mAh / g or more, preferably 240 mAh / g to 245 mAh / g, and more preferably 240 mAh / g to 243 mAh / g.

[0114]

[0115] anode

[0116] Next, the anode of the present invention will be described.

[0117] The positive electrode according to the present invention comprises the positive electrode active material according to the present invention described above, and may further comprise a positive electrode conductive material and a positive electrode binder, if necessary. Specifically, the positive electrode comprises a positive electrode current collector, 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 comprises a positive electrode active material, a positive electrode conductive material, and a positive electrode binder. Meanwhile, since the positive electrode active material is the same as described above, a detailed description thereof will be omitted.

[0118]

[0119] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0120]

[0121] Meanwhile, the positive electrode active material may be included in an amount of 93 wt% to 99 wt%, preferably 95 wt% to 98 wt%, and more preferably 95 wt% to 97 wt%, based on the total weight of the positive electrode active material layer, i.e., the total amount of the positive electrode active material, the positive electrode conductive material, and the positive electrode binder. When the content of the positive electrode active material satisfies the above range, a high energy density can be realized.

[0122]

[0123] Next, the positive electrode conductive material is used to provide conductivity to the positive electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. 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, summer black, carbon fiber, carbon nanotube, etc.; metal powder or metal fiber such as copper, nickel, aluminum, silver, etc.; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, etc., and one of these may be used alone or a mixture of two or more may be used.

[0124] The above-mentioned positive electrode conductive material may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 8 wt%, and more preferably 1 to 5 wt%, based on the total weight of the positive electrode active material layer.

[0125] Next, the positive electrode binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used.

[0126] The above positive electrode binder may be included in an amount of 0.5 wt% to 5 wt%, preferably 1 wt% to 4 wt%, and more preferably 1 wt% to 3 wt%, based on the total weight of the positive electrode active material layer.

[0127]

[0128] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method. 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 manufacture a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling the resulting film, or by casting the positive electrode slurry onto a separate support, and then peeling the resulting film from the support and laminating the resulting film onto a positive electrode current collector.

[0129] Meanwhile, solvents commonly used in the art may be used as the solvent for the positive electrode slurry, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water, which may be used alone or in combination of two or more. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0130]

[0131] lithium secondary battery

[0132] Next, a lithium secondary battery according to the present invention will be described.

[0133]

[0134] The lithium secondary battery of the present invention comprises the positive electrode according to the present invention. Specifically, the lithium secondary battery comprises 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, wherein the positive electrode is as described above.

[0135] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0136]

[0137] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0138] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0139] The above negative electrode active material layer optionally includes a negative electrode binder and a negative electrode conductive material together with the negative electrode active material.

[0140] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may 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 alloy, Sn alloy, or Al alloy; SiO β (0 <β< 2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used.

[0141] In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0142] The above-described negative electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. 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 nanotube; 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, and the like. One type alone or a mixture of two or more types of these may be used. The negative electrode conductive material may typically be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0143] The above negative electrode binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above negative electrode binder may be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0144] The above-described negative electrode active material layer may be manufactured by, for example, applying and drying a negative electrode slurry containing a negative electrode active material, and optionally a negative electrode binder and a negative electrode conductive material, onto a negative electrode current collector, or by casting the negative electrode slurry onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling it off from the support.

[0145]

[0146] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0147]

[0148] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0149]

[0150] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0151] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0152]

[0153] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 5.0 M, and preferably 0.1 to 3.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0154]

[0155] In addition to the electrolyte components, the electrolyte may further include additives for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. For example, the additives may include haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, either singly or in mixtures, but are not limited thereto. The additives may be included in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolyte.

[0156]

[0157] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0158] 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.

[0159] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0160] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0161]

[0162] Example 1

[0163] D 50 This is 5.6㎛, and BET is 5.6m 2 / g, and a nickel cobalt manganese hydroxide precursor having a molar ratio of Ni: Co: Mn of 92:6:2 and lithium hydroxide were mixed so that the molar ratio of Li / (Ni+Co+Mn) was 1.02, and then calcined at 860°C for 12 hours to produce a lithium nickel-based oxide in the form of single particles. Then, the lithium nickel-based oxide and cobalt hydroxide were mixed, and then heat-treated at 750°C to produce a positive electrode active material having a Co-containing coating layer formed. D of the manufactured positive electrode active material 50 was 5.5㎛, and the molar ratio of Ni:Co:Mn in the entire positive electrode active material was 91:7:2.

[0164]

[0165] Example 2

[0166] D 50 This is 5.5㎛ and BET is 6.16m 2 / g, and a nickel cobalt manganese hydroxide precursor having a molar ratio of Ni: Co: Mn of 92:6:2 was used, and a cathode active material was manufactured in the same manner as in Example 1. D of the manufactured cathode active material 50 was 5.4㎛, and the molar ratio of Ni:Co:Mn in the entire positive electrode active material was 91:7:2.

[0167]

[0168] Comparative Example 1

[0169] D 50 This is 3.5㎛ and BET is 8.75m 2 / g, and the nickel cobalt manganese hydroxide precursor having a molar ratio of Ni: Co: Mn of 86:6:8 and lithium hydroxide were mixed so that the molar ratio of Li / (Ni+Co+Mn) was 1.02, and then calcined at 880°C for 12 hours to produce a lithium nickel-based oxide in the form of single particles. Then, the lithium nickel-based oxide and cobalt hydroxide were mixed, and then heat-treated at 750°C to produce a positive electrode active material having a Co-containing coating layer formed. D of the manufactured positive electrode active material 50was 3.5㎛, and the molar ratio of Ni:Co:Mn in the entire positive electrode active material was 85:7:8.

[0170]

[0171] Comparative Example 2

[0172] D 50 This is 3.8㎛ and BET is 8.74m 2 / g, and a nickel cobalt manganese hydroxide precursor having a molar ratio of Ni: Co: Mn of 92:6:2 was used, and a cathode active material was manufactured in the same manner as in Example 1. D of the manufactured cathode active material 50 was 3.8㎛, and the molar ratio of Ni:Co:Mn in the entire positive electrode active material was 91:7:2.

[0173]

[0174] Comparative Example 3

[0175] D 50 This is 5.4㎛ and BET is 1.944m 2 / g, and a nickel cobalt manganese hydroxide precursor having a molar ratio of Ni: Co: Mn of 92:6:2 was used, and a cathode active material was manufactured in the same manner as in Example 1. D of the manufactured cathode active material 50 was 5.4㎛, and the molar ratio of Ni:Co:Mn in the entire positive electrode active material was 91:7:2.

[0176]

[0177] Comparative Example 4

[0178] D 50 This is 5.5㎛ and BET is 2.585m 2 / g, and a nickel cobalt manganese hydroxide precursor having a molar ratio of Ni: Co: Mn of 92:6:2 was used, and a cathode active material was manufactured in the same manner as in Example 1. D of the manufactured cathode active material 50 was 5.5㎛, and the molar ratio of Ni:Co:Mn in the entire positive electrode active material was 91:7:2.

[0179]

[0180] Precursor active substance D 50 (㎛)BET(m 2 / g)BET / D 50 Ni:Co:Mn(molar ratio)D 50 (㎛)Ni:Co:Mn(molar ratio)Example 15.65.61.0092:6:25.591:7:2Example 25.56.161.1392:6:25.491:7:2Comparative Example 13.58.752.5086:6:83.585:7:8Comparative Example 23.88.742.2992:6:23.891:7:2Comparative Example 35.41.9440.3692:6:25.491:7:2Comparative Example 45.52.5850.4792:6:25.591:7:2

[0181]

[0182] Experimental Example 1

[0183] The lithium nickel-based oxides manufactured by the methods of Examples 1 to 2 and Comparative Examples 1 to 4 were collected, and the masses of LiOH and LiCO3 were measured by pH titration, and then the lithium byproduct content (mol%) in the lithium nickel-based oxides before the formation of the Co coating layer was measured by converting the masses into mol%.

[0184] In addition, the cation mixing ratio of the positive electrode active materials manufactured in Examples 1 to 2 and Comparative Examples 1 to 4 was measured through XRD analysis. The XRD analysis was performed using an X-ray diffractometer (Bruker AXS D4-Endeavor XRD), using a Cu Ka light source, and under 10 kV acceleration voltage conditions.

[0185] The measurement results are shown in [Table 2] below.

[0186] Lithium byproduct (mol%) Cation mixing ratio (at%) Example 12.4 1.0 Example 22.7 1.2 Comparative example 11.8 0.6 Comparative example 22.0 0.7 Comparative example 31.4 0.5 Comparative example 42.0 0.8

[0187] As shown in the above [Table 2], BET / D 50 For lithium nickel oxides of Examples 1 and 2 manufactured using precursors having a BET / D of 0.5 to 2, 50 Compared to the lithium nickel oxides of Comparative Examples 1 to 4 manufactured using precursors having a lithium byproduct content of less than 0.5 or more than 2, the lithium byproduct content was higher.

[0188] In addition, the positive electrode active materials manufactured in Examples 1 to 2 showed a higher cation mixing ratio than the positive electrode active materials manufactured in Comparative Examples 1 to 4, which indicates that the structural completeness of the surface of the positive electrode active materials of Examples 1 to 2 is lower than that of the positive electrode active materials of Comparative Examples 1 to 4.

[0189]

[0190] Experimental Example 2: Heat Flow Analysis

[0191] Each of the positive electrode active materials, carbon nanotubes, and PVDF binders manufactured in Examples 1 to 2 and Comparative Examples 1 to 4 were added to N-methylpyrrolidone at a weight ratio of 96:2:2 to manufacture a positive electrode slurry. The positive electrode slurry was applied onto an aluminum current collector, dried, and then rolled to manufacture a positive electrode.

[0192] An electrode assembly was manufactured by stacking the positive electrode and the lithium metal counter electrode manufactured as described above with a separator interposed between them, and the electrode assembly was then placed in a battery case and an electrolyte was injected to manufacture a coin-half cell.

[0193] The above coin-half cell was charged to 4.25 V in 0.1 C constant current mode and then the charge capacity was measured.

[0194] Then, the charged coin-half cell was placed in a heating chamber, and the heat flow was measured according to temperature using a differential scanning calorimeter (DSC) while the temperature was increased from room temperature to 380°C at a temperature increasing rate of 10°C / min.

[0195] The measurement results are shown in Fig. 1 and [Table 3].

[0196] Charging capacity (mAh)DSC heating main peak temperature (℃)DSC heating main peak intensity (W / g)Example 1242226.813.1Example 2240225.812.3Comparative example 1232226.311.8Comparative example 2242221.715.8Comparative example 3243226.319.1Comparative example 4242226.516.1

[0197] As shown in Table 3 and Fig. 1, in the case of the coin-half cell manufactured using the positive electrode active materials of Examples 1 to 2, it can be confirmed that the temperature of the main peak of heat generation is higher and the intensity is lower, indicating excellent thermal stability, compared to the coin-half cell manufactured using the positive electrode active materials of Comparative Examples 2 to 4 having the same composition.

[0198] In addition, it can be confirmed that the positive electrode active materials of Examples 1 and 2 have thermal stability equivalent to that of the positive electrode active material of Comparative Example 1 containing 85 mol% of Ni, even though they contain 90 mol% or more of Ni, and have superior charging capacity compared to the positive electrode active material of Comparative Example 1.

[0199]

[0200] Experimental Example 3: Continuous Charging Performance Evaluation

[0201] In Experimental Example 2, each coin-half cell manufactured using the positive electrode active materials of Examples 1 to 2 and Comparative Examples 3 to 4 was charged in constant current mode at 50°C to 4.7 V, and then, when 4.7 V was reached, the amount of leakage current generated was measured while charging in constant voltage mode. The measurement results are shown in Fig. 2.

[0202] As shown in Fig. 2, it can be confirmed that the coin-half cell manufactured using the positive electrode active materials of Examples 1 and 2 has a smaller leakage current when maintaining a high voltage at high temperature compared to the coin-half cell manufactured using the positive electrode active materials of Comparative Examples 3 and 4. This is believed to be because the positive electrode active materials of Examples 1 and 2 have a lower surface structural perfection than the positive electrode active materials of Comparative Examples 3 and 4, resulting in less side reactions with the electrolyte.

Claims

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

2. In paragraph 1, The above precursor is D 50 The ratio of the BET surface area to the surface area (BET / D) 50 ) is 0.8 to 1.

5.

3. In paragraph 1, The above precursor is D 50 A method for manufacturing a positive electrode active material having a diameter of 5 μm to 7 μm.

4. In paragraph 1, The above precursor has a BET surface area of ​​5 m 2 / g to 10m 2 / g Method for manufacturing a positive electrode active material.

5. In paragraph 1, A method for producing a positive electrode active material, wherein the precursor is represented by the following [chemical formula 1]. [Chemical Formula 1] Ni a What b Mn c M 1 d (OH)2 In the above chemical formula 1, M 1 is at least one 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≤0.05임.

6. In paragraph 1, A method for producing a positive electrode active material, wherein the above-mentioned calcination is performed at 800°C to 900°C.

7. In paragraph 1, A method for producing a positive electrode active material, wherein the lithium nickel-based oxide contains a lithium byproduct in an amount of 1 mol% to 5 mol%.

8. In paragraph 1, A method for producing a cathode active material, further comprising a step of mixing and heat-treating the single-particle lithium nickel-based oxide and a coating raw material after the step of producing the single-particle lithium nickel-based oxide.

9. In paragraph 8, A method for producing a positive electrode active material, wherein the above coating raw material comprises at least one element selected from the group consisting of Co, Al, W, B, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, and Mo.

10. In paragraph 8, A method for producing a positive electrode active material wherein the heat treatment temperature is 300°C to 800°C.

11. A cathode active material comprising a single particle lithium nickel oxide containing nickel, cobalt and manganese, having a nickel content of 90 mol% or more among all metals excluding lithium, and having 1 to 30 nodules. D of the above positive electrode active material 50 This is 5㎛ to 8㎛, A positive electrode active material having a maximum heat flow of 15.0 W / g or less, measured using a differential scanning calorimeter (DSC) while charging a coin-half cell manufactured using the above positive electrode active material to 4.25 V and then heating from room temperature to 380°C at a heating rate of 10°C / min.

12. In paragraph 11, A positive electrode active material having a charge capacity of 240 mAh / g or more when a coin-half cell manufactured using the above positive electrode active material is charged to 4.25 V.

13. In paragraph 11, The above positive electrode active material is a positive electrode active material having a cation mixing ratio of 0.9 at% to 1.5 at%.

14. In paragraph 11, The above single particle lithium nickel oxide is a positive electrode active material represented by the following [chemical formula 2]. [Chemical Formula 2] Li x [Ni a Co b Mr c M 1 d ]O2 In the above chemical formula 2, M 1 is at least one 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≤0.05임.

15. In paragraph 11, The above positive electrode active material further includes a coating layer formed on the single particle lithium nickel oxide, The above coating layer is a positive electrode active material comprising at least one element selected from the group consisting of Co, Al, W, B, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, and Mo.

16. In paragraph 15, A positive electrode active material, wherein the coating layer comprises Co, and the content of Co included in the coating layer is 0.5 mol% to 2 mol% based on the total number of moles of transition metal included in the entire positive electrode active material.

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

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

Images