Cathode active material for lithium secondary battery, manufacturing method of the same and lithium secondary battery comprising the same

Abstract

The present invention comprises a lithium transition metal oxide in the form of a single particle containing 80 mol% or more of nickel based on the total molar amount of the transition metal, and The average number of primary particles within the above single particle is 1.5 or less, and The above lithium transition metal oxide relates to a positive electrode active material for a lithium secondary battery having an electrode composite density of 3.68 g / cc or higher. [Equation 2] 1.52 μm ≤ Dv50 - Dn50 ≤ 1.7 μm In the above Equation 2, Dv50 is the average particle size of the lithium transition metal oxide based on volume, and Dn50 is the average particle size of the lithium transition metal oxide based on number.

Description

Technology Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same. More specifically, the invention relates to a method for manufacturing a positive electrode active material for a lithium secondary battery in the form of a single particle, a positive electrode active material manufactured therefrom, and a lithium secondary battery including the same. Background Technology

[0003] In a lithium secondary battery, electrical energy is produced by oxidation and reduction reactions when lithium ions are inserted into or removed from the positive and negative electrodes, which are composed of active materials capable of lithium ion intercalation and deintercalation, with an organic or polymer electrolyte charged between them.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as cathode active materials for lithium-ion batteries. Among these, lithium cobalt oxide (LiCoO2) is widely used and applied as a cathode active material for high-voltage applications due to its advantages of high operating voltage and excellent capacity characteristics. However, due to the rising price and supply instability of cobalt (Co), there are limitations to its mass use as a power source in fields such as electric vehicles, leading to the emergence of a need for the development of cathode active materials that can replace it.

[0005] Accordingly, a nickel-cobalt-manganese-based lithium composite transition metal oxide (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxide') was developed in which a portion of the cobalt (Co) was replaced with nickel (Ni) and manganese (Mn). However, the conventionally developed NCM-based lithium composite transition metal oxide generally has a secondary particle form in which primary particles are aggregated, and has a large specific surface area, low particle strength, and high lithium byproduct content, resulting in a large amount of gas generated during cell operation and consequently a decrease in lifespan and stability.

[0006] Accordingly, development of cathode active materials in the form of single particles, rather than the existing secondary particle form, is underway. The problem to be solved

[0008] One objective of the present invention is to provide a positive electrode active material for a lithium secondary battery that is a lithium transition metal oxide in the form of a single particle, which can improve high-temperature life characteristics of the battery as well as improve capacity characteristics and electrode energy density by reducing the number of primary particles within the single particle, a method for manufacturing the same, and a lithium secondary battery including the same. means of solving the problem

[0010] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery comprising a lithium transition metal oxide in the form of a single particle containing 80 mol% or more of nickel based on the total molar amount of the transition metal, wherein the average number of primary particles within the single particle is 1.5 or less and satisfies Formula 1 below.

[0011] [Equation 1]

[0012] 1.5 ≤ Dv50 / Dn50 ≤ 1.8

[0013] In the above Equation 1, Dv50 is the average particle size of the lithium transition metal oxide based on volume, and Dn50 is the average particle size of the lithium transition metal oxide based on number.

[0015] The above positive electrode active material for a lithium secondary battery can satisfy the following Equation 2.

[0016] [Equation 2]

[0017] 1.2 μm ≤ Dv50 - Dn50 ≤ 1.7 μm

[0018] In the above Equation 2, Dv50 is the average particle size of the lithium transition metal oxide based on volume, and Dn50 is the average particle size of the lithium transition metal oxide based on number.

[0020] The volume-based average particle size (Dv50) of the above lithium transition metal oxide may be 3.4 to 4.5 μm.

[0021] The average particle size (Dn50) based on the number of lithium transition metal oxides above may be 2.0 to 2.6 μm.

[0022] The above lithium transition metal oxide may have an electrode composite density of 3.68 g / cc or higher.

[0023] The above lithium transition metal oxide can be represented by the following chemical formula 1.

[0024] [Chemical Formula 1]

[0025] Li a [Ni x Co y Mn z M w ]O2

[0026] In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0028] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a transition metal precursor containing 80 mol% or more of nickel based on the total molar amount of the transition metal; mixing the transition metal precursor and a lithium raw material and then calcining to form a lithium transition metal oxide; and forming a lithium transition metal oxide in the form of a single particle by first disintegrating and second disintegrating the lithium transition metal oxide, wherein the second disintegration is performed at a grinding pressure of 3.0 to 4.0 bar.

[0029] The above firing can be performed in a first firing and a second firing, and the first firing and the second firing can be performed in an oxygen (O2) atmosphere.

[0030] The above first disintegration can be performed at a stirring speed of 15,000 to 20,000 rpm.

[0031] The above first firing temperature may be higher than the above second firing temperature.

[0032] The above first firing time may be shorter than the above second firing time.

[0033] The above first firing temperature may be 810 to 890℃.

[0034] The above secondary firing temperature may be 720 to 800℃.

[0036] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0037] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode for the lithium secondary battery. Effects of the invention

[0039] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention has a single particle form, and the average number of primary particles within the single particle is reduced, thereby improving the high-temperature life characteristics of the battery. In addition, the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention can improve the capacity characteristics and electrode energy density of the battery by appropriately controlling the ratio of the average particle size based on volume to the average particle size based on number. Brief explanation of the drawing

[0041] Figure 1 is an SEM image of the positive electrode active material prepared according to Example 1. Figure 2 is an SEM image of the positive electrode active material prepared according to Example 3. Figure 3 is an SEM image of the positive electrode active material prepared according to Example 5. Figure 4 is an SEM image of the positive electrode active material prepared according to Comparative Example 1. Figure 5 is an SEM image of the positive electrode active material prepared according to Comparative Example 3. Figure 6 is an SEM image of the positive electrode active material prepared according to Comparative Example 5. Specific details for implementing the invention

[0042] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0043] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0044] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0045] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0046] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0047] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0048] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0050] 1. Cathode active material

[0051] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises a lithium transition metal oxide in the form of a single particle. The active material in the form of a single particle has a smaller specific surface area compared to conventional secondary particles, which reduces the amount of gas generated due to side reactions with the electrolyte. Additionally, it has a higher particle strength, which can suppress particle breakage during rolling and reduce the occurrence of cracks due to repeated charging and discharging. Accordingly, it has the advantage of superior lifespan and safety compared to secondary particles, and can achieve high energy density of the electrode.

[0052] In this specification, “single particle” is a term used to distinguish from a positive active material particle in the form of a secondary particle formed by the aggregation of tens to hundreds of primary particles that were conventionally used, and is a concept that includes a single particle consisting of one primary particle and an aggregate particle of 30 or fewer primary particles.

[0053] In addition, “secondary particles” refers to aggregates formed by the aggregation of tens to hundreds of primary particles through physical or chemical bonding between primary particles without any intentional aggregation or assembly process of the primary particles, i.e., secondary structures.

[0054] In addition, “primary particle” refers to the smallest particle unit that is distinguished as a single mass when the cross-section of the positive active material is observed through a scanning electron microscope (SEM), and it may consist of a single crystal grain or multiple crystal grains.

[0055] Meanwhile, the lithium transition metal oxide according to the present invention contains 80 mol% or more of nickel based on the total molar amount of the transition metal, and more specifically, may contain 85 mol%, 90 mol%, or 94 mol% or more of nickel. By containing such a high amount of nickel, the lithium transition metal oxide can achieve high capacity characteristics.

[0056] However, even with the same transition metal composition, single-particle lithium transition metal oxides, which have a higher calcination temperature compared to multi-particles, have high particle strength and are difficult to break down, making it difficult to achieve a single-particle form. Even if a single-particle form is achieved, the number of primary particles within the single particle ranges from as few as 3 to 9 to as many as several tens. Consequently, the advantages of a single particle, namely the improvement in lifespan and safety due to enhanced structural stability, may be negligible.

[0057] On the other hand, the lithium transition metal oxide according to the present invention may have an average number of primary particles within a single particle of 1.5 or less, and more specifically, 1.4 or 1.3 or less. This means that most of the lithium transition metal oxide particles according to the present invention are single particles (one body) consisting of only one primary particle, and occasionally have particles consisting of two or more primary particles mixed in. Accordingly, the structural stability of the lithium transition metal oxide particles is improved, and lifespan characteristics, more specifically high-temperature lifespan characteristics, can be improved.

[0058] Meanwhile, the average number of primary particles within the above single particle can be derived by calculating the average value of the number of primary particles within at least 30 arbitrary particles when observing a 2D image of 20 μm × 20 μm in size at 10,000x magnification of the anode active material powder using an SEM (scanning electron microscope).

[0059] However, generally, as lithium transition metal oxide particles approach a single-body form like this, there is a problem in that capacity and initial efficiency decrease as the lithium ion migration distance increases.

[0060] On the other hand, the positive electrode active material according to the present invention satisfies the following Equation 1 or additionally the following Equation 2, so that even though it is close to a one-body form, not only high-temperature life characteristics but also capacity and initial efficiency can be improved.

[0061] [Equation 1]

[0062] 1.5 ≤ Dv50 / Dn50 ≤ 1.8

[0063] In Equation 1 above, Dv50 is the volume-based average particle size of the lithium transition metal oxide, and Dn50 is the number-based average particle size of the lithium transition metal oxide. More specifically, the volume-based average particle size (Dv50) can be defined as the particle size corresponding to 50% of the volume-cumulative amount in the particle size distribution curve. The number-based average particle size (Dn50) can be defined as the particle size corresponding to 50% of the number-cumulative amount in the particle size distribution curve. The volume-based average particle size (Dv50) and the number-based average particle size (Dn50) can be measured, for example, using a laser diffraction method.

[0064] More specifically, the above Dv50 / Dn50 value may be 1.6 to 1.75.

[0065] [Equation 2]

[0066] 1.2 μm ≤ Dv50 - Dn50 ≤ 1.7 μm

[0067] In the above Equation 2, Dv50 is the average particle size of the lithium transition metal oxide based on volume, and Dn50 is the average particle size of the lithium transition metal oxide based on number.

[0068] More specifically, the above Dv50 - Dn50 values ​​may be 1.3 to 1.6 μm.

[0069] The fact that the cathode active material satisfies Equation 1 or Equation 2 implies that, within the overall particle size distribution, the number of small-diameter particles is relatively greater than the number of medium-diameter or large-diameter particles, but is not excessively large. Accordingly, when implemented as a cathode in an actual battery, small-diameter particles can be present in an appropriate content between medium-diameter or large-diameter particles. Consequently, the electrode rolling density can be improved, and as the pores within the electrode are reduced, the diffusion path length of lithium ions is shortened, thereby improving the diffusion rate of lithium ions. As a result, excellent electrode energy density, battery capacity, and initial efficiency can be achieved.

[0071] More specifically, the volume-based average particle size (Dv50) of the lithium transition metal oxide may be 3.4 to 4.5 μm, and more specifically, 3.5 to 4.0 μm. If the volume-based average particle size (Dv50) is too small, the electrode rolling density decreases, which may degrade the electrode energy density. If the volume-based average particle size (Dv50) is too large, the crystal grain and particle size become too large, causing the lithium ion migration length to become too long, which may degrade the capacity and output characteristics. In addition, as described in the manufacturing method described below, the particle size distribution of the lithium transition metal oxide particles can be determined by controlling the process conditions of the final disintegration step. At this time, when the volume-based average particle size (Dv50) is controlled to the above range during the disintegration process, the cathode active material can more easily satisfy the physical properties of Equations 1 and 2 mentioned above.

[0072] In addition, the number-based average particle size (Dn50) of the lithium transition metal oxide may be 2.0 to 2.6 μm. When the number-based average particle size (Dn50) of the lithium transition metal oxide satisfies the above range, Equation 1 or Equation 2 can be more easily satisfied when considering the range of the volume-based average particle size (Dv50) according to the present invention. Accordingly, the aforementioned electrode energy density, battery capacity, and initial efficiency can be more preferably realized.

[0073] In addition, the lithium transition metal oxide may have an electrode composite density of 3.68 g / cc or higher. As the electrode composite density satisfies the above range, the electrode energy density can be maximized. The electrode composite density can be measured by the following method. After pressing the electrode with a roll press gap of 0.1 μm, the electrode is pierced in a circular shape around the 14Ψ circumference, the weight of the electrode is measured, the weight of the current collector is subtracted, and the weight of the active material is calculated by multiplying by the active material concentration of 95%. The electrode composite density can be calculated by measuring the width and thickness of the electrode and dividing the result by the volume value.

[0075] Meanwhile, the above lithium transition metal oxide can be represented more specifically by the following chemical formula 1.

[0076] [Chemical Formula 1]

[0077] Li a [Ni x Co y Mn z M w ]O2

[0078] In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0079] In the lithium transition metal oxide of Chemical Formula 1 above, lithium may be included in an amount corresponding to a, i.e., 0.8 ≤ a ≤ 1.2. If a is too small, the capacity may decrease, and if a is too large, the strength of the calcined cathode active material may increase, making it difficult to grind, and the amount of gas generated may increase due to an increase in lithium by-products. Considering the effect of improving the capacity characteristics of the cathode active material by controlling the lithium content and the balance of sinterability during the manufacture of the active material, the lithium may more preferably be included in an amount of 0.9 ≤ a ≤ 1.1.

[0080] In the lithium transition metal oxide of Chemical Formula 1 above, nickel may be included in an amount corresponding to x, i.e., 0.8≤x<1 or 0.85≤x<1, 0.90≤x<1, or 0.94≤x<1. If the nickel content is too low, it may be difficult to achieve high capacity of the battery, and if the nickel content is too high, the battery life and thermal safety may decrease due to reduced structural stability of the active material, and manufacturing costs may increase.

[0081] In the lithium transition metal oxide of Chemical Formula 1 above, cobalt may be included in an amount corresponding to y, i.e., 0≤y≤0.2 or 0.01≤y≤0.1. If the cobalt content is too low, it may be difficult to simultaneously achieve sufficient rate characteristics and high powder density of the active material. If the cobalt content is too high, the cost of raw materials increases overall and the reversible capacity may decrease.

[0082] In the lithium transition metal oxide of Chemical Formula 1 above, manganese may be included in an amount corresponding to z, i.e., 0≤z≤0.2 or 0.1≤z≤0.1. If the manganese content is too low, the production cost may increase and the stability of the active material may decrease. If the manganese content is too high, the capacity and output characteristics of the battery may decrease.

[0083] In the lithium transition metal oxide of Chemical Formula 1 above, M may be included in an amount corresponding to w, i.e., 0≤w≤0.2 or 0≤w≤0.1. At this time, M may be a doping element and may be Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0085] 2. Method for manufacturing positive electrode active material

[0086] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a transition metal precursor containing 80 mol% or more of nickel based on the total molar amount of the transition metal; mixing the transition metal precursor and a lithium raw material and then calcining to form a lithium transition metal oxide; and forming a lithium transition metal oxide in the form of a single particle by first disintegrating and second disintegrating the lithium transition metal oxide, wherein the second disintegration is performed at a grinding pressure of 3.0 to 4.0 bar.

[0087] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described step by step.

[0089] First, prepare a transition metal precursor containing at least 80 mol% of nickel based on the total molar amount of the transition metal.

[0090] The above transition metal precursor may be a transition metal hydroxide.

[0091] The above transition metal hydroxide may be prepared by co-precipitating a transition metal-containing solution containing a nickel raw material and optionally a cobalt raw material or a manganese raw material by adding a complexing agent-containing solution and a pH adjusting agent-containing solution to the transition metal-containing solution.

[0092] The above nickel raw material is not particularly limited as long as it is used in the industry for manufacturing a cathode active material precursor. For example, the above nickel raw material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, it may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, nickel fatty acid salt, nickel halide, or a combination thereof, but is not limited thereto.

[0093] The above-mentioned cobalt raw material is not particularly limited as long as it is used in the industry for the manufacture of cathode active material precursors. For example, the above-mentioned cobalt raw material may be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, CoSO₄ 4, It may be CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or a combination thereof, but is not limited thereto.

[0094] The above manganese raw material is not particularly limited as long as it is used in the industry for the manufacture of cathode active material precursors. For example, the above manganese raw material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. Specifically, it may be a manganese salt such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid, manganese oxide such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0095] The above transition metal-containing solution may be prepared by adding a nickel raw material and optionally a cobalt raw material or a manganese raw material to a solvent, specifically water, or a mixture of water and an organic solvent that can be uniformly mixed with water (e.g., alcohol).

[0096] The above-mentioned complexing agent-containing solution performs the role of forming a complex, and may include, for example, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof as the complexing agent, but is not limited thereto. Meanwhile, the above-mentioned complexing agent-containing solution may be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent that is uniformly miscible with water (e.g., alcohol, etc.) may be used as the solvent.

[0097] The above pH-adjusting solution acts as a precipitating agent or a pH adjuster and may include alkali compounds such as hydroxides of alkali metals or alkaline earth metals like NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof. Meanwhile, the above pH-adjusting solution may also be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent that is uniformly miscible with water (e.g., alcohol) may be used as the solvent. In this case, the above pH-adjusting solution may be added in an amount such that the pH of the reaction solution becomes 11 to 13.

[0098] The above co-precipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon, at a temperature of 30 to 70°C, and at a pH of 11 to 13.

[0099] By the above process, particles of nickel-cobalt-manganese (-doping element) hydroxide are generated and precipitated in the reaction solution. The precipitated precursor particles can be separated by conventional methods, washed, and dried to obtain a precursor. The precursor may be a secondary particle formed by the aggregation of primary particles.

[0100] At this time, the molar ratio of nickel, cobalt, and manganese in the precursor can be controlled by adjusting the concentrations of the nickel raw material, cobalt raw material, and manganese raw material.

[0101] Accordingly, the nickel content in the transition metal precursor may be 80 mol% or more based on the total molar amount of the transition metal. The technical significance of controlling the nickel content in the transition metal precursor is as described above and is therefore omitted.

[0103] Next, the above transition metal precursor and lithium raw material are mixed and then calcined to form a lithium transition metal oxide.

[0104] At this time, the above calcination can be performed in a first calcination and a second calcination. Conventionally, a first calcination at a high temperature for a long time was generally performed to form a lithium transition metal oxide in the form of a single particle; however, in this case, there was a problem in which the electrochemical properties of the active material deteriorated due to nickel cation mixing and the formation of rocksalt impurity phases caused by over-calcination. On the other hand, the manufacturing method according to the present invention can prevent the above problems by performing the calcination in two stages, improve the particle strength of the active material, and increase production yield.

[0105] In addition, the first and second calcinations can be performed in an oxygen (O2) atmosphere. As the first and second calcinations are performed in an oxygen atmosphere, a layered structure within the lithium transition metal oxide containing a high amount of nickel can be well developed.

[0106] More specifically, the oxygen atmosphere may have an oxygen partial pressure of 90%, 95%, or 96% or higher.

[0107] In addition, the first firing temperature may be higher than the second firing temperature. Accordingly, there may be an advantage in single crystal growth.

[0108] More specifically, the first calcination temperature may be 810 to 890°C or 820 to 880°C. If the first calcination temperature is too low, there may be a problem in that lithium ions are not fully inserted into the precursor. If the first calcination temperature is too high, there may be a problem in that the production speed is reduced due to difficulty in disintegration caused by over-calcination.

[0109] More specifically, the secondary firing temperature may be 720 to 800°C or 730 to 790°C. If the secondary firing temperature is too low, there may be a problem of having electrochemically inferior performance due to insufficient heat for annealing. If the secondary firing temperature is too high, there may be a problem of reduced production speed due to difficulty in disintegration caused by over-firing.

[0110] More specifically, the first calcination time may be 1 to 5 hours or 2 to 4 hours. If the first calcination time is too short, there may be a problem in that lithium ions are not fully inserted into the precursor. If the first calcination time is too long, there may be a problem of capacity reduction due to over-calcination.

[0111] More specifically, the second sintering time may be performed for 7 to 15 hours or 8 to 13 hours. If the second sintering time is too short, the single particle shape is not fully formed, and there may be a problem of electrochemically inferior performance due to insufficient annealing time to have a layered structure. If the second sintering time is too long, there may be a problem of capacity reduction due to under-sintering.

[0113] Next, the lithium transition metal oxide is first broken down and second broken down to form a lithium transition metal oxide in the form of a single particle.

[0114] By dividing the disintegration process into primary and secondary disintegration, the aggregation of strongly aggregated secondary particles of high-nickel lithium transition metal oxide can be efficiently broken down, and the particle size of particles that have been excessively enlarged by calcination can be appropriately reduced. Accordingly, the average number of primary particles within a single particle can be reduced to the range according to the present invention, thereby approaching a single particle form. In addition, the average particle size based on volume (Dv50) and the average particle size based on number (Dn50) can be appropriately controlled, so that physical properties such as Dv50 / Dn50 can be appropriately obtained within the range according to the present invention.

[0115] At this time, the secondary disintegration is performed at a grinding pressure of 3.0 to 4.0 bar, and more specifically, at a grinding pressure of 3.2 to 3.8 bar. When the grinding pressure during secondary disintegration satisfies the above range, the secondary disintegration is performed with appropriate force, thereby allowing for appropriate control of particles of small diameter, i.e., the fine powder ratio. Accordingly, physical properties such as Dv50 / Dn50 of the lithium transition metal oxide can be appropriately obtained within the range according to the present invention.

[0116] The above secondary disintegration can be performed using disintegration equipment commonly used in the industry. For example, the above secondary disintegration can be performed using a jet mill, but is not necessarily limited thereto.

[0117] The above primary crushing can be performed using crushing equipment commonly used in the industry. For example, the above primary crushing can be performed using a rotor mill, but is not necessarily limited thereto.

[0118] At this time, the first disintegration can be performed at a stirring speed of 15,000 to 20,000 rpm, and more specifically, at a stirring speed of 16,000 to 20,000 rpm. When the stirring speed during the first disintegration satisfies the above range, the first disintegration is performed with appropriate force, thereby allowing for appropriate control of the ratio of fine particles, i.e., particles of small particle size. Accordingly, physical properties such as Dv50 / Dn50 of the lithium transition metal oxide can be appropriately obtained within the range according to the present invention.

[0120] Through the above series of manufacturing methods, a lithium transition metal oxide in the form of a single particle according to the present invention can be formed, and the obtained lithium transition metal oxide can be obtained with properties such as Dv50 / Dn50 within the range according to the present invention while approaching a single particle form. Accordingly, not only can high-temperature life characteristics be improved, but electrode energy density, capacity, and initial efficiency can also be improved.

[0122] 3. Anodes and Lithium Secondary Batteries

[0123] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0124] More specifically, the anode may include an anode current collector and an anode active material layer disposed on the anode current collector and comprising the aforementioned anode active material.

[0125] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes 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 above positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0126] The above positive active material layer may include a binder and / or a conductive material together with the aforementioned positive active material.

[0127] At this time, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive 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. One of these alone or a mixture of two or more may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 weight% based on the total weight of the positive active material layer.

[0128] In addition, the conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that possesses electronic conductivity without causing chemical changes may be used without any particular limitations. 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, and carbon fibers; 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. One of these alone or a mixture of two or more may be used, but is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 weight percent relative to the total weight of the positive electrode active material layer.

[0129] The above-mentioned anode can be manufactured according to a conventional anode manufacturing method, except for using the above-mentioned anode active material.

[0130] Specifically, the anode can be manufactured by applying a composition for forming an anode active material layer, comprising the aforementioned anode active material and optionally a binder, conductive material, or solvent as needed, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0131] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0132] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support, and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0134] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode for a lithium secondary battery as described above.

[0135] More specifically, the above lithium secondary battery may include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0136] The above lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0137] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0138] The above-mentioned negative 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., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0139] The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material. The above-mentioned cathode active material layer may be manufactured, as an example, by applying a composition for forming a cathode active material layer, comprising a cathode active material and optionally a binder and a conductive material, onto a cathode current collector and drying it, or by casting the composition for forming a cathode onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0140] As the above-mentioned 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 alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, the carbon material may include both low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, 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.

[0141] The binder and conductive material mentioned above may be the same as those previously described in the anode.

[0143] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0145] The above electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited to these.

[0146] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0147] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, 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 low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0148] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may 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. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0149] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexamethylphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0150] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0151] Accordingly, another embodiment of the present invention provides a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same.

[0152] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0154] The embodiments of the present invention will be described in more detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited by the following examples.

[0156] Example 1

[0157] (1) Manufacturing of positive electrode active material

[0158] (Mixed) Ni 0.95 Co 0.02 Mn 0.03 A mixture was formed by introducing LiOH·H2O and Al(OH)3 into a mixer and mechanically mixing them such that the molar ratio (Li / M) of lithium to the transition metal of the (OH)2 precursor and the (OH)2 precursor was 1.02.

[0159] After the (first firing), the mixture was heated to 850°C through heat treatment in an oxygen (O2) atmosphere with an oxygen partial pressure of 99.5%, then fired at a constant temperature of 850°C for 3 hours, and then cooled naturally. Afterward, the first fired product was crushed using a rotor mill.

[0160] After (secondary calcination), the above-mentioned crushed primary calcined product was heated to 760°C through heat treatment in an oxygen (O2) atmosphere with an oxygen partial pressure of 99.5%, then subjected to secondary calcination at a constant temperature of 760°C for 11 hours, and then naturally cooled to form a lithium transition metal oxide.

[0161] After (first disintegration), the lithium transition metal oxide was first disintegrated using a rotor mill at a stirring speed of 18,000 rpm.

[0162] After (secondary disintegration), a lithium transition metal oxide in the form of single particles was formed by secondary disintegration using a jet mill at a grinding pressure of 3.5 bar.

[0163] The composition of the finally obtained lithium transition metal oxide is Li 1.02 Ni 0.95 Co 0.02 Mn 0.02 Al 0.01 It was O2.

[0164] (2) Lithium secondary battery manufacturing

[0165] The slurry for electrode manufacturing was prepared by mixing the above-prepared cathode active material, conductive material (carbon black, Denka black), and binder (PVDF, KF9700) in a ratio of 95.0 : 2.0 : 3.0 wt%, and adding NMP (N-Methyl-2-pyrrolidone) to adjust the viscosity so that the solid content was approximately 60%. The prepared slurry was coated onto a 20 µm thick Al foil using a doctor blade and then dry-rolled. The electrode loading amount was 16.0 mg / cm². 2It was, and the rolled density (25 ℃, 20 kN) was 3.5 g / cm³ 3 It was.

[0166] A coin cell was manufactured using an electrolyte of 1M LiPF6 in EC:DMC:DEC=1:2:1 (vol%) with 2.0 vol% of VC added relative to the total amount of the electrolyte, a PP separator, and a lithium anode (400 μm, Niba metal).

[0168] Example 2

[0169] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that in the first and second firing steps, the firing was performed under an oxygen (O2) atmosphere with an oxygen partial pressure of 96%.

[0171] Example 3

[0172] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that in the second calcination step, the second calcination was performed for 10 hours.

[0174] Example 4

[0175] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that in the second firing step, the second firing was performed for 10 hours, and in the first and second firing steps, the firing was performed under an oxygen (O2) atmosphere with an oxygen partial pressure of 96%.

[0177] Example 5

[0178] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that in the mixing step, LiOH·H2O was added so that the molar ratio of lithium to the transition metal of the precursor (Li / M) was 1.025.

[0180] Example 6

[0181] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that in the mixing step, LiOH·H2O was added so that the molar ratio of lithium to the transition metal of the precursor (Li / M) was 1.025, and in the first and second calcination steps, the calcination was performed under an oxygen (O2) atmosphere with an oxygen partial pressure of 96%.

[0183] Comparative Example 1

[0184] A positive electrode active material and a lithium secondary battery were prepared by carrying out the same procedure as in Example 1, except that secondary disintegration was not performed.

[0186] Comparative Example 2

[0187] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that the first and second firing steps were performed without secondary disintegration and underwent firing in an oxygen (O2) atmosphere with an oxygen partial pressure of 96%.

[0189] Comparative Example 3

[0190] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that secondary disintegration was not performed and secondary calcination was performed for 10 hours during the secondary calcination step.

[0192] Comparative Example 4

[0193] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that secondary disintegration was not performed, secondary calcination was performed for 10 hours in the secondary calcination step, and in the first and second calcination steps, calcination was performed under an oxygen (O2) atmosphere with an oxygen partial pressure of 96%.

[0195] Comparative Example 5

[0196] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that a second disintegration was not performed and LiOH·H2O was added in the mixing step so that the molar ratio of lithium to the transition metal of the precursor (Li / M) was 1.025.

[0198] Comparative Example 6

[0199] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that secondary disintegration was not performed, LiOH·H2O was added so that the molar ratio of lithium to the transition metal of the precursor (Li / M) was 1.025, and in the first and second calcination steps, the calcination was performed under an oxygen (O2) atmosphere with an oxygen partial pressure of 96%.

[0201] Table 1 below summarizes the process conditions of the examples and comparative examples.

[0202] 1st firing temperature (°C) First firing time (h) Second firing temperature (°C) Second firing time (h) O2 partial pressure (%) during 1st and 2nd firing Li / M ratio Primary disintegration equipment Primary disintegration stirring speed (rpm) Secondary dismantling equipment Secondary crushing pressure (bar) Comparative Example 1 850 3 760 11 99.5 1.02 Rotor mill 18000 - - Comparative Example 2 850 3 760 11 96 1.02 Rotor mill 18000 - - Comparative Example 3 850 3 760 10 99.5 1.02 Rotor mill 18000 - - Comparative Example 4 850 3 760 10 96 1.02 Rotor mill 18000 - - Comparative Example 5 850 3 760 11 99.5 1.025 Rotor mill 18000 - - Comparative Example 6 850 3 760 11 96 1.025 Rotor mill 18000 - - Example 1 850 3 760 11 99.5 1.02 Rotor mill 18000 Jet mill 3.5 Example 2 850 3 760 11 96 1.02 Rotor mill 18000 Jet mill 3.5 Example 3 850 3 760 10 99.5 1.02 Rotor mill 18000 Jet mill 3.5 Example 4 850 3 760 10 96 1.02 Rotor mill 18000 Jet mill 3.5 Example 5 850 3 760 11 99.5 1.025 Rotor mill 18000 Jet mill 3.5 Example 6 850 3 760 11 96 1.025 Rotor mill 18000 Jet mill 3.5

[0203] Experimental Example 1: SEM image of cathode active material

[0204] SEM images of the cathode active materials prepared according to Examples 1, 3, and 5 and Comparative Examples 1, 3, and 5 were observed and are shown in Figures 1 to 6, respectively.

[0205] Referring to FIGS. 1 to 6, it was confirmed that the number of primary particles within the single particle of the positive active material of the example was significantly reduced compared to the comparative example, and that it was close to a single particle form.

[0207] Experimental Example 2: Evaluation of Physical Properties of Anode Active Material

[0208] The properties of the cathode active materials of the examples and comparative examples were evaluated using the method below, and are shown in Table 2.

[0209] (1) Dv50 and Dn50, Dv50 / Dn50, Dv50 - Dn50 evaluation

[0210] The average particle size based on volume (Dv50) was measured by using the laser diffraction method to determine the particle size corresponding to 50% of the volume accumulation, and the average particle size based on number (Dn50) was measured by determining the particle size corresponding to 50% of the number accumulation. Subsequently, Dv50 / Dn50 and Dv50 - Dn50 were calculated using these values.

[0211] (2) Evaluation of the average number of primary particles in a single particle

[0212] Meanwhile, the average number of primary particles within the above single particle was derived by calculating the average value of the number of primary particles within at least 30 arbitrary particles when observing a 2D image of 20 μm × 20 μm in size at 10,000x magnification of the cathode active material powder using an SEM (scanning electron microscope).

[0213] (3) Evaluation of electrode mixture density

[0214] After pressing the electrode with a roll press gap of 0.1 μm, the electrode was pierced in a circular shape around the circumference of 14 Ψ to weigh the electrode, subtract the weight of the current collector, and then multiply by the active material concentration of 95% to obtain the weight of the active material. The density of the electrode composite was evaluated by measuring the width and thickness of the electrode and dividing the result by the volume value.

[0215] Dv50(um) Dn50(um) Dv50 / Dn50 Dv50 - Dn50(um) Average number of primary particles in a single particle Electrode mixture density (g / cc) Comparative Example 1 7.85 4.04 1.94 3.81 5.3 3.65 Comparative Example 2 8.01 3.95 2.03 4.06 5.4 3.58 Comparative Example 3 7.9 3.93 2.01 3.97 4.8 3.64 Comparative Example 4 8.35 4.04 2.07 4.31 5.0 3.58 Comparative Example 5 7.91 4.01 1.97 3.9 5.8 3.63 Comparative Example 6 7.58 3.76 2.02 3.82 5.9 3.66 Example 1 3.81 2.34 1.63 1.47 1.3 3.69 Example 2 3.63 2.18 1.66 1.45 1.3 3.82 Example 3 3.69 2.17 1.7 1.52 1.2 3.84 Example 4 3.73 2.2 1.69 1.53 1.1 3.84 Example 5 3.69 2.19 1.69 1.5 1.3 3.74 Example 6 3.54 2.19 1.61 1.35 1.2 3.73

[0216] Referring to Table 2, it was confirmed that in the case of the example, the Dv50 / Dn50 value, Dv50 - Dn50 value, etc. were appropriately obtained within the range according to the present invention, and it was confirmed that the average number of primary particles within the single particle was low and the electrode composite density was high. At this time, in the case of the example, the electrode composite density was high, so an effect of improving electrode energy density was predicted. On the other hand, in the case of the comparative example, it was confirmed that the Dv50 / Dn50 value, Dv50 - Dn50 value, etc. were outside the range according to the present invention, the average number of primary particles within the single particle was high, and the electrode composite density was low.

[0218] Experimental Example 3: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0219] The electrochemical characteristics of the lithium secondary batteries of the examples and comparative examples were evaluated using the method below, and are shown in Table 3.

[0220] (1) Evaluation of initial capacity and initial efficiency

[0221] After fabricating a lithium secondary battery half cell, it was aged at 25°C for 12 hours, and then a charge-discharge test was performed at 25°C. To evaluate the initial capacity, the reference capacity was set to 200 mAh / g, and the battery was charged to 4.4V with a constant current of 0.1C. Then, the voltage was switched to a constant voltage, and charging continued until the terminal current reached 0.05C. After a 10-minute rest time following charging, the battery was discharged with a reference capacity of 200 mAh / g and a constant current of 0.1C until it reached 2.5V.

[0222] (2) Evaluation of high-temperature life characteristics (high-temperature capacity retention rate) (45℃, 50 cycles)

[0223] After fabricating a lithium secondary battery half cell, it was charged to 4.4V at 45°C with a constant current of 0.5C, then switched to a constant voltage and charged until the termination current reached 0.05C. After a 10-minute rest time following charging, it was discharged with a constant current of 1.0C until it reached 2.5V. Fifty charge-discharge cycles were performed under these conditions, and the capacity retention rate of the 50th cycle was calculated relative to the first cycle.

[0224] charge Discharge Efficiency Retention @50 th mAh / g mAh / g % % Comparative Example 1 244.4 212.9 87.10% 85.60% Comparative Example 2 245.9 212.5 86.40% 88.30% Comparative Example 3 246.9 215.2 87.20% 85.90% Comparative Example 4 245.5 211.3 86.10% 87.40% Comparative Example 5 246.8 213.6 86.60% 87.20% Comparative Example 6 245.9 212.7 86.50% 86.40% Example 1 247.7 218 88.00% 89.70% Example 2 247.3 216.2 87.40% 90.60% Example 3 247.5 217.6 87.90% 90.30% Example 4 248.1 215.5 86.90% 90.60% Example 5 247.9 217.6 87.80% 90.10% Example 6 247.1 215.7 87.30% 89.90%

[0225] Referring to Table 3, in the case of an example where the average number of primary particles within a single particle of the positive electrode active material is low and the Dv50 / Dn50 value satisfies the range according to the present invention, it was confirmed that not only are excellent high-temperature life characteristics realized, but the initial charge capacity, initial discharge capacity, and initial efficiency are also improved. On the other hand, in the case of a comparative example where the average number of primary particles within a single particle of the positive electrode active material is high and the Dv50 / Dn50 value falls outside the range according to the present invention, it was confirmed that the high-temperature life characteristics, initial charge capacity, initial discharge capacity, and initial efficiency are all lower than those of the example.

[0227] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0228] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

Claim 1 A positive electrode active material for a lithium secondary battery comprising a lithium transition metal oxide in the form of a single particle containing 80 mol% or more of nickel based on the total molar amount of the transition metal, wherein the average number of primary particles within the single particle is 1.5 or less, and the lithium transition metal oxide has an electrode composite density of 3.68 g / cc or more, and satisfies the following Equation 2. [Equation 2] 1.52 μm ≤ Dv50 - Dn50 ≤ 1.7 μm In the above Equation 2, Dv50 is the average particle size based on the volume of the lithium transition metal oxide, and Dn50 is the average particle size based on the number of the lithium transition metal oxide. Claim 2 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the volume-based average particle size (Dv50) of the lithium transition metal oxide is 3.4 to 4.5 μm. Claim 3 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the number-based average particle size (Dn50) of the lithium transition metal oxide is 2.0 to 2.6 μm. Claim 4 delete Claim 5 In claim 1, the lithium transition metal oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1]Li a [Ni x Co y Mn z M w ]O2 In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Mo, Ce, Hf, Ta, La, Sr or a combination thereof. Claim 6 A positive electrode for a lithium secondary battery comprising a positive electrode active material according to any one of paragraphs 1 to 3 and 5. Claim 7 A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to claim 6.

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