Positive electrode active material and method for manufacturing the same

Abstract

The present invention provides a positive electrode active material comprising a lithium nickel cobalt manganese composite oxide having a nickel content of 90 mol% or more among metals other than lithium, and a metal element M1 doped into the lithium nickel cobalt manganese composite oxide, wherein the metal element M1 consists of two or more elements selected from the group consisting of Al, Zr, and Ti, and always contains Al, the weight of Al is 8,000 ppm or more relative to the total weight of the positive electrode active material, and the total weight of the metal element M1 is 9,000 ppm to 12,000 ppm relative to the total weight of the positive electrode active material, a method for producing the same, a positive electrode containing the positive electrode active material, and a lithium secondary battery.

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Application No. 10-2023-0117305 dated September 4, 2023, and Korean Patent Application No. 10-2024-0006915 dated January 16, 2024, and all content disclosed in the documents of the said Korean patent applications is incorporated herein by reference.

[0002] This invention relates to a positive electrode active material, a method for producing the same, a positive electrode, and a lithium secondary battery. [Background technology]

[0003] Recently, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for rechargeable batteries that are small, lightweight, and relatively high-capacity has been rapidly increasing. In particular, lithium-ion batteries are attracting attention as a power source for portable devices due to their light weight and high energy density. As a result, research and development efforts to improve the performance of lithium-ion batteries are being actively pursued.

[0004] Lithium-ion secondary batteries produce electrical energy through oxidation and reduction reactions that occur when lithium ions are inserted into and removed from the positive and negative electrodes, with an organic electrolyte or polymer electrolyte filled between the positive and negative electrodes, which are made of an active material that allows for the insertion and removal of lithium ions.

[0005] As the positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (such as LiMnO2 or LiMn2O4), lithium iron phosphate (LiFePO4), etc. have been used. Also, as a method for maintaining the excellent reversible capacity of LiNiO2 and improving its low thermal stability, a lithium composite metal oxide in which a part of nickel (Ni) is substituted with cobalt (Co) and manganese (Mn) (hereinafter, simply referred to as "NCM-based lithium composite transition metal oxide") has been developed. However, the conventionally developed NCM-based lithium composite transition metal oxides have insufficient capacity characteristics and limitations in application.

[0006] In order to improve such problems, recently, research has been conducted to increase the Ni content in NCM-based lithium composite transition metal oxides. However, high-nickel (High-Ni) positive electrode active materials with a high nickel content have problems such as generating a large amount of gas during charge and discharge due to the high reactivity of nickel, significant instability of the lattice structure due to cation mixing and oxygen desorption, and an increase in the content of lithium impurities remaining on the surface.

[0007] Therefore, in a situation where it is necessary to develop a positive electrode material that has excellent capacity due to its high nickel content and ensures structural stability.

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention provides a positive electrode active material with improved structural stability and a method for manufacturing the same, a positive electrode and a lithium secondary battery in which the capacity, resistance, and life characteristics are improved by including the positive electrode active material.

Means for Solving the Problems

[0009] The present invention relates to a lithium nickel cobalt manganese-based composite oxide in which the content of nickel among metals other than lithium is 90 mol% or more, and A positive electrode active material comprising a metallic element M1 doped into the lithium nickel cobalt manganese composite oxide, The aforementioned metal element M1 is two or more elements selected from the group consisting of Al, Zr, and Ti, and must include Al. The weight of Al is 8,000 ppm or more relative to the total weight of the positive electrode active material. The present invention provides a positive electrode active material in which the total weight of the metal element M1 is 9,000 ppm to 12,000 ppm relative to the total weight of the positive electrode active material.

[0010] Furthermore, the present invention provides a method for producing the above-mentioned positive electrode active material, comprising the step of mixing a nickel-cobalt-manganese composite precursor having a nickel content of 90 mol% or more, a lithium raw material, and a doping raw material containing the metal element M1, and firing at 650°C to 850°C.

[0011] Furthermore, the present invention provides a positive electrode comprising a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer contains the above-mentioned positive electrode active material.

[0012] Furthermore, the present invention provides a lithium secondary battery comprising the above-described positive electrode, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0013] The positive electrode active material according to the present invention has excellent capacity due to its high nickel content, which in turn reduces the amount of cobalt used, making it advantageous in terms of material supply and demand and price.

[0014] Furthermore, since it contains Zr and / or Ti as doping elements along with Al, it can achieve all of the effects of improving crystal structure and particle strength that come from including each of the aforementioned doping elements.

[0015] In particular, since the doping elements are contained in a total of 9,000 to 12,000 ppm, and among them Al is contained in a concentration of 8,000 ppm or more, the limitations of high-nickel, low-cobalt cathode active materials, specifically the disadvantages in resistance and lifespan due to large volume changes during charging and discharging, can be effectively overcome.

[0016] Furthermore, since the positive electrode active material helps to reduce the charge-discharge efficiency during initial charging and discharging without any degradation of other performance, it can compensate for capacity loss due to irreversible reactions when combined with a negative electrode containing a silicon-based negative electrode material.

[0017] Therefore, lithium secondary batteries containing the aforementioned positive electrode active material have the advantage of superior capacity, resistance, and lifespan characteristics. [Brief explanation of the drawing]

[0018] [Figure 1] This shows the results of determining c / 2√6a by XRD analysis of the positive electrode active materials produced in Example 1, Example 4 and Comparative Example 5 of the present invention. [Modes for carrying out the invention]

[0019] The present invention will be described in detail below.

[0020] In this invention, the doping element content can be measured by inductively coupled plasma optical emission spectrometry (ICP-OES). Specifically, this means that 0.03 g of the cathode active material to be analyzed was dispersed and dissolved in 1 mL of hydrochloric acid, then a small amount of hydrogen peroxide and hydrofluoric acid were added, followed by dilution with 50 mL of ultrapure water, and then analyzed using an Avio series instrument (PerkinElmer, Inc.).

[0021] In the present invention, "D 50"50% of the volume cumulative particle size distribution of the powder being measured" refers to the particle size corresponding to 50% of the volume cumulative amount, and can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S-3500), irradiated with ultrasound at approximately 28 kHz with an output of 60 W, and then a volume cumulative particle size distribution graph is obtained. The particle size at the point where the volume cumulative amount is 50% in the obtained graph can then be determined.

[0022] In this invention, "crystallite" refers to a particle unit having substantially the same crystal orientation, which can be confirmed by EBSD (Electron Backscatter Diffraction) analysis. Specifically, it refers to the smallest particle unit represented by the same hue in the IPF (Inverse Pole Figure) map obtained by EBSD analysis of a cross-section of a positive electrode active material cut by ion milling.

[0023] On the other hand, in the present invention, the "average crystallite size," the "a-axis length of the crystallite," and the "c-axis length of the crystallite" can be quantitatively analyzed using X-ray diffraction analysis (XRD) with Cu Kα X-rays. Specifically, the crystallite size can be quantitatively analyzed by placing the particle to be measured in a holder, irradiating the particle with X-rays, and analyzing the resulting diffraction pattern. Sampling is performed by placing the powder sample of the target particles into the central recessed groove of a general powder holder, leveling the surface using a glass slide, and ensuring the sample height is the same as the edge of the holder. Next, X-ray diffraction analysis is performed using a Bruker D8 Endeavor (light source: Cu Kα, λ=1.54Å) equipped with a LynxEye XE-T position-sensitive detector, in the region of FDS 0.5°, 2θ=15°~90°, with a step size of 0.02° and a total scan time of approximately 20 minutes. Rietveld refinement is then performed on the measured data, taking into account the charge at each site (metal ions at transition metal sites are +3, Ni ions at Li sites are +2) and cation mixing. During crystallite size analysis, instrumental brodening is performed using a Bruker The TOPAS program implements a Fundamental Parameter Approach (FPA), and during fitting, the entire peak range of the measurement is used. The peak shape is First Principle (FP) among the peak types available in TOPAS, and only the Lorenzian contribution is used for fitting, without considering strain.

[0024] However, in the c-axis length change rate calculated using Equation 1 below, the c-axis length is measured by creating a separate battery for in-situ operando XRD analysis. Specifically, simultaneously with charging, Mo target X-rays are used as the light source, and XRD analysis is performed in transmission mode using the 2θ scanning method. st The slit is 1 / 4°, Solar slit (1 st , 2 nd Both are 0.02rad, 2 nd A 1.68 mm mask is used, and measurements are taken in the 2θ = 7° to 30° region, with each scan taking approximately 6 minutes, at intervals of 0.014°.

[0025] The various components of the present invention will be described in more detail below.

[0026] <Cathode active material> This invention relates to a positive electrode active material, specifically a positive electrode active material for lithium secondary batteries.

[0027] The positive electrode active material of the present invention comprises a lithium nickel cobalt manganese composite oxide having a nickel content of 90 mol% or more among metals other than lithium, and a metal element M1 doped into the lithium nickel cobalt manganese composite oxide, wherein the metal element M1 consists of two or more elements selected from the group consisting of Al, Zr, and Ti, and always contains Al, the weight of Al is 8,000 ppm or more relative to the total weight of the positive electrode active material, and the total weight of the metal element M1 is 9,000 ppm to 12,000 ppm relative to the total weight of the positive electrode active material.

[0028] As mentioned above, increasing the nickel content in NCM oxides can ensure high capacity, but it comes with the problem of reduced structural stability. Specifically, high-nickel cathode active materials have the disadvantage of significant changes in the lattice constant, i.e., changes in the volume within the unit cell. Such volume changes can cause crack formation within the active material particles. These cracks can lead to the formation of voids within the active material, potentially resulting in a decrease in battery performance.

[0029] Furthermore, the higher the nickel content, the more cation mixing occurs between lithium ions and nickel ions. This hinders the movement of lithium ions during battery operation, leading to increased battery resistance and reduced battery life.

[0030] Therefore, the inventors have solved the above-mentioned problems by adjusting the type and content of doping elements in an ultra-high nickel cathode active material having a nickel content of 90 mol% or more.

[0031] Specifically, in lithium nickel-cobalt-manganese composite oxides with a Ni content of 90 mol% or more, Al enhances the completeness of the layered structure by increasing the length of the c axis relative to the a axis in the crystal structure of the primary particles, and mitigates discontinuities in the phase change process from H2 to H3 during charging. Therefore, it is possible to reduce rapid volume changes of particles and the resulting crack formation, thereby improving battery life.

[0032] In the case of Zr, reducing cation mixing between Li and Ni ions can improve the mobility of lithium ions within the crystal during charging and discharging, ultimately contributing to improved battery life. In the case of Ti, preventing the crystal size from growing beyond a certain limit mitigates volume changes during charging and discharging, which helps reduce resistance and improve battery life.

[0033] Furthermore, since Ti has a stronger binding affinity to oxygen than Ni, Co, and Mn in the lithium nickel cobalt manganese composite oxide, it can increase the strength of the particles during doping. As a result, particle cracking is improved, which can lead to an improvement in battery life.

[0034] In the case of high-nickel, low-cobalt cathode materials, it is difficult to achieve a highly complete crystal structure, and the volume changes during charging and discharging are severe, leading to a significant degradation of battery performance. To mitigate this, it is necessary to dope the material with such doping elements at a concentration of 10,000 ppm or more. In particular, doping with Al, Zr, and / or Ti together can compensate for the various disadvantages of such cathode materials.

[0035] Furthermore, the positive electrode active material according to the present invention can reduce the initial charge-discharge efficiency through the doping process, and in combination with a negative electrode containing a negative electrode active material such as SiO or Si, which has a high lithium ion loss rate due to initial irreversibility, it has the advantage of being able to compensate for the irreversible capacity of the negative electrode.

[0036] On the other hand, in the case of a cathode active material with a Ni content of less than 90 mol%, doping in this manner may actually lead to a decrease in capacity due to excessive doping, which can be disadvantageous in terms of achieving energy density. However, as in the present invention, when the Ni content is 90 mol% or more, the decrease in capacity due to doping has a relatively small impact on the loss of overall energy density of the active material.

[0037] In one embodiment of the present invention, the total weight of the metal element M1 can be 9,500 ppm or more, 10,000 ppm or more, or 10,500 ppm or more, and 11,500 ppm or less, or 11,000 ppm or less, relative to the total weight of the positive electrode active material. When M1 is present in a concentration of 9,000 ppm or more, the above-mentioned effects can be achieved, but when it exceeds 12,000 ppm, undoped residue is generated on the surface of the active material, which is undesirable as it causes an increase in surface resistance and a decrease in expressed capacity.

[0038] In one embodiment of the present invention, the metal element M1 includes Al, and the weight of Al can be 8,000 ppm or more, 8,500 ppm or more, or 8,700 ppm or more, and 10,000 ppm or less, 9,500 ppm or less, or 9,300 ppm or less, relative to the total weight of the positive electrode active material. An Al content of 8,000 ppm or more is preferable in that it can realize the effects of Al described above. However, considering that no undoped residue should remain, it is preferable that the Al content be 10,000 ppm or less.

[0039] In one embodiment of the present invention, the metal element M1 contains Zr, and the weight of Zr can be 1,000 ppm or more, 1,100 ppm or more, or 1,200 ppm or more, and 4,000 ppm or less, 3,000 ppm or less, 2,000 ppm or less, or 1,500 ppm or less, relative to the total weight of the positive electrode active material. A Zr content of 1,000 ppm or more is preferable in that it can realize the effects of Zr described above. However, considering that no undoped residue should remain, it is preferable that the content be 4,000 ppm or less.

[0040] In one embodiment of the present invention, the metal element M1 includes Ti, and the Ti content relative to the total weight of the positive electrode active material can be 300 ppm or more, 400 ppm or more, or 500 ppm or more, and can be 4,000 ppm or less, 3,000 ppm or less, 2,000 ppm or less, or 1,000 ppm or less. A Ti content of 300 ppm or more is preferable in that it can realize the effects of Ti described above. However, since no undoped residue should remain, and considering that adding an excess of Ti can cause a rapid decrease in crystal size and an increase in resistance, a Ti content of 4,000 ppm or less is preferable.

[0041] In one embodiment of the present invention, the metal element M1 may include Al and Zr. In this case, the ratio of the length of the c axis to the length of the a axis is large, and a highly complete layered crystalline structure with reduced Li / Ni cation mixing can be obtained. Achieving such a highly complete crystalline structure is preferable because it can mitigate volume changes during charging and discharging. Here, the weight ratio of Al to Zr can be 1.5:1 to 9:1, preferably 5:1 to 9:1, and more preferably 7:1 to 9:1.

[0042] Most preferably, the metal element M1 can include all of Al, Zr, and Ti, which is preferable because it can improve lifetime performance by reducing crystal size and increasing particle strength. Here, the weight ratio of Al:Zr:Ti can be 10-20:1-5:1, preferably 14-16:1-3:1.

[0043] In one embodiment of the present invention, the lithium nickel cobalt manganese composite oxide may have a nickel content of 92 mol% or more, preferably 93 mol% or more, and more preferably 95 mol% to 99 mol% among the metals other than lithium. This is preferable in that it enables the realization of high capacity.

[0044] Furthermore, the lithium nickel cobalt manganese composite oxide can contain cobalt among the metals other than lithium in an amount of 0.1 mol% to 1.0 mol%, preferably 0.2 mol% to 0.9 mol%, and more preferably 0.4 mol% to 0.8 mol%. In other words, the present invention minimizes the amount of expensive cobalt and improves lifetime, resistance, and output characteristics by adjusting the doping conditions.

[0045] Specifically, the lithium nickel cobalt manganese composite oxide may have the composition of the following chemical formula 1.

[0046] [Chemical formula 1] Li 1+x (Nia Co b Mn c M1 d M2 e )O2

[0047] In Chemical Formula 1 above, M1 is two or more selected from the group consisting of Al, Zr, and Ti, M2 is any one or more selected from the group consisting of W, Cu, Fe, V, Cr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, 1+x, a, b, c, d, and e are atomic fractions of independent elements, -0.2 ≦ x ≦ 0.2, 0.90 ≦ a < 1, 0 < b < 0.01, 0 < c < 0.10, 0 < d ≦ 0.05, 0 ≦ e ≦ 0.05, and a + b + c + d + e = 1.

[0048] The 1+x represents the lithium molar ratio in the lithium nickel cobalt manganese composite oxide, and it can be -0.1 ≦ x ≦ 0.2 or 0 ≦ x ≦ 0.2. When the lithium molar ratio satisfies the above range, the crystal structure can be stably formed.

[0049] The a represents the nickel molar ratio among all the metals other than lithium in the lithium nickel cobalt manganese composite oxide, and it can be 0.92 ≦ a < 1, 0.93 ≦ a < 1, or 0.95 ≦ a < 1. When the nickel molar ratio satisfies the above range, it shows a high energy density and enables the realization of a high capacity.

[0050] The b represents the cobalt molar ratio among all the metals other than lithium in the lithium nickel cobalt manganese composite oxide, and it can be 0 < c ≦ 0.009, 0.002 ≦ c ≦ 0.008, or 0.004 ≦ c ≦ 0.008. When the cobalt molar ratio satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0051] The c represents the molar ratio of manganese among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 < c ≤ 0.080, 0 < c ≤ 0.060, or 0.010 ≤ c ≤ 0.050. When the molar ratio of manganese satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0052] The d represents the molar ratio of the M1 element among all the metals other than lithium in the lithium nickel-based oxide, and the d can be 0 < d ≤ 0.045, 0.010 ≤ d ≤ 0.045, or 0.020 ≤ d ≤ 0.040.

[0053] The e represents the molar ratio of the M2 element among all the metals other than lithium in the lithium nickel-based oxide, and can be appropriately adjusted as needed.

[0054] In one embodiment of the present invention, the average crystallite size of the positive electrode active material can be 80 nm to 160 nm, preferably 85 nm to 150 nm, and more preferably 90 nm to 150 nm. When the average crystallite size is within the above range, there is an advantage that excellent long-term life performance can be ensured.

[0055] In one embodiment of the present invention, when the length of the a-axis of the crystallite of the positive electrode active material is a and the length of the c-axis is c, c / 2√6a can be 1.0075 or more, preferably 1.0080 or more, and more preferably 1.0085 or more, and can be 1.0200 or less. This means that the layered structure of the crystal is well formed by the M1 and the interlayer distance is sufficiently ensured. In this case, there is an advantage that the reduction of resistance and the improvement of life are possible.

[0056] On the other hand, the change rate of the length of the c-axis of the positive electrode active material according to the following formula 1 can be 7.0% or less, preferably 6.5% or less, and more preferably 6.0% or less.

[0057] [Formula 1] Change rate of the length of the c-axis (%) = {(C max -C min ) / Cmin}×100

[0058] In the above formula 1, C max This is the maximum value of the c-axis length, C min This is the minimum value of the c-axis length, The length of the c-axis is obtained by charging a battery containing the positive electrode containing the positive electrode active material and performing operando XRD analysis in situ. Here, the charging can be performed by charging with a constant current (CC) at 0.1C up to 4.35V, and then maintaining a constant voltage (CV) state until the current density reaches 0.05C.

[0059] Specifically, the battery can be manufactured in a pouch type containing the positive electrode material for in-situ XRD analysis, and more specifically, it can be a pouch-type full cell manufactured by interposing a porous polyethylene separator between a positive electrode containing the positive electrode active material and a negative electrode containing graphite as the negative electrode active material, then positioning this assembly inside a battery case, and finally injecting an electrolyte into the case. The electrolyte can be manufactured by dissolving 1M LiPF6 in a mixed organic solvent of ethylene carbonate / dimethyl carbonate / diethyl carbonate in a volume ratio of 3:4:3.

[0060] <Method for manufacturing positive electrode active material> On the other hand, the method for producing the positive electrode active material includes the step of mixing a nickel-cobalt-manganese composite precursor having a nickel content of 90 mol% or more, a lithium raw material, and a doping raw material containing the metal element M1, and firing it at 650°C to 850°C.

[0061] Specifically, the firing process can be carried out at 700°C to 800°C for 15 to 24 hours.

[0062] On the other hand, the method for producing the positive electrode active material may further include the steps of: dissolving a nickel precursor, a cobalt precursor, and a manganese precursor in a solvent in a reactor to produce a transition metal-containing solution; and coprecipitation reaction while supplying the transition metal-containing solution, an ammonium cation complex-forming agent, and a basic compound to form a nickel-cobalt-manganese composite precursor having a nickel content of 90 mol% or more. If necessary, an oxidizing agent or oxygen gas may be further added during the coprecipitation reaction.

[0063] On the other hand, the transition metal precursor can be an acetate, carbonate, nitrate, sulfate, halide, or sulfide of each transition metal.

[0064] Specifically, the nickel precursor can be one or more selected from the group consisting of NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, and nickel sulfide. The cobalt precursor can be one or more selected from the group consisting of Co(OH)2, Co3SO4, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, and Co(SO4)2·7H2O. The manganese precursor can be one or more selected from the group consisting of Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, and manganese sulfide.

[0065] On the other hand, the lithium raw material can be an oxide, hydroxide, oxyhydroxide, halide salt, nitrate, carbonate, acetate, oxalate, citrate, or sulfate containing lithium. More specifically, the lithium raw material can be one or more selected from the group consisting of Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, Li2O, Li2SO4, CH3COOLi, and Li3C6H6O7.

[0066] Here, the amount of each transition metal precursor added can be determined by considering the molar ratio of the transition metal in the cathode active material that is ultimately to be produced.

[0067] On the other hand, the ammonium cation complex-forming agent may contain at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and the compound may be introduced into the reactor in the form of a solution in which it is dissolved in a solvent. Here, the solvent may be water, or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol, etc.).

[0068] The basic compound can be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and the compound can be introduced into the reactor in the form of a solution in which it is dissolved in a solvent. Here, the solvent can be water, or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol, etc.).

[0069] As described above, when the transition metal-containing solution, ammonium cation complex-forming agent, and basic compound are added to the reactor and stirred, the transition metal in the transition metal-containing solution co-precipitates, and precursor particles in the form of transition metal hydroxide are generated.

[0070] Here, the transition metal-containing solution, the ammonium cation complex-forming agent, and the basic compound are added in amounts such that the pH of the reaction solution falls within the desired range.

[0071] Once precursor particles are formed by the method described above, they are separated from the reaction solution to obtain the precursor. For example, the reaction solution can be filtered to separate the precursor, and then the separated precursor can be washed with water and dried to obtain the precursor. Here, if necessary, steps such as grinding and / or classification may be performed.

[0072] The nickel-cobalt-manganese composite precursor produced in this manner is mixed with a lithium raw material and a doping raw material containing the metal element M1, and then calcined to produce a lithium-nickel-cobalt-manganese composite oxide.

[0073] As the lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides can be used. For example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof can be used.

[0074] On the other hand, the lithium raw material and the nickel-cobalt-manganese composite precursor can be mixed such that the molar ratio of Li to total metal in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1. When the mixing ratio of the lithium raw material and the metal in the precursor satisfies the above range, the layered crystal structure of the lithium-nickel-cobalt-manganese composite oxide develops well, and a positive electrode active material with excellent capacity characteristics and structural stability can be produced.

[0075] Furthermore, the doping material containing the metal element M1 may be an oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate, or sulfate containing the metal element M1.

[0076] For example, when doping with additional metal element M2, the type and amount of metal element M2 added can be adjusted considering the type and content of metal element M2 contained in the positive electrode active material described above.

[0077] <Positive electrode> The positive electrode according to the present invention comprises a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material described above.

[0078] The positive electrode current collector is not particularly limited as long as it contains a highly conductive metal, allows for easy adhesion of the positive electrode active material layer, and is unreactive within the battery voltage range. Examples of materials that can be used for the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0079] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material described above. Specifically, it can be manufactured by applying a positive electrode slurry containing the positive electrode active material onto a positive electrode current collector, followed by drying and rolling, or by casting the positive electrode slurry onto another support, peeling it off the support, and laminating the resulting film onto the positive electrode current collector.

[0080] In one embodiment of the present invention, the positive electrode includes a positive electrode active material layer formed by coating at least one surface of a positive electrode current collector with a positive electrode slurry containing the positive electrode active material.

[0081] On the other hand, the positive electrode slurry may contain the positive electrode active material, binder, conductive material, and solvent.

[0082] Specifically, the binder can be one or more selected from the group consisting of 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, and various copolymers thereof, and is preferably polyvinylidene fluoride.

[0083] The binder can be included in the positive electrode slurry in an amount of 0.5% to 3% by weight, preferably 1% to 3% by weight, and more preferably 1.5% to 2.5% by weight, relative to the total weight of the solid content. When the binder content is within this range, sufficient adhesion to the current collector and interparticle bonding are ensured, thereby improving the durability of the positive electrode and maintaining a low initial resistance.

[0084] The conductive material can be one or more selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; carbon-based materials such as carbon fibers and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. Preferably, it can be carbon nanotubes or carbon black, and most preferably, carbon nanotubes.

[0085] The conductive material can be included in the positive electrode slurry in an amount of 0.1% to 2.5% by weight, preferably 0.5% to 2% by weight, and more preferably 1% to 2% by weight, relative to the total weight of the solid content. When the content of the conductive material is within the above range, it is preferable in that it is possible to maintain conductivity between the active materials and reduce dead volume.

[0086] In addition, the positive electrode slurry may further selectively contain a dispersant, which may be hydrogenated nitrile butadiene rubber (HNBR).

[0087] On the other hand, the solvent of the positive electrode slurry can be a solvent commonly used in the art, such as N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, dimethylformamide (DMF), acetone, water, or a mixture of two or more of these. The solvent can be adjusted to ensure that the positive electrode slurry has an appropriate viscosity. For example, the solvent can be included such that the concentration of solids in the positive electrode slurry is 60% by weight or more, preferably 60% to 90% by weight, and more preferably 60% to 80% by weight.

[0088] <Lithium-ion secondary battery> Next, the lithium secondary battery according to the present invention will be described.

[0089] The lithium secondary battery specifically includes a positive electrode, a negative electrode containing a negative electrode active material, a separator interposed between the positive and negative electrodes, and an electrolyte. The positive electrode is as described above, and a detailed explanation will be omitted; only the remaining components will be described in detail below.

[0090] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0091] In the lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0092] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0093] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0094] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include metal oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more mixtures of these can be used.

[0095] In one embodiment of the present invention, the negative electrode active material may be graphite, a substance containing Si, or a mixture thereof, and more specifically, graphite, or more specifically, a mixture of artificial graphite and natural graphite. Alternatively, a metallic lithium thin film may be used as the negative electrode active material. The negative electrode active material may be present in an amount of 80% to 99% by weight relative to the total weight of the negative electrode active material layer.

[0096] The binder is a component that helps to bond the conductive material, active material, and current collector, and is usually added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0097] The conductive material is a component for further improving the conductivity of the negative electrode active material and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, relative to the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0098] The negative electrode active material layer can be manufactured by coating a negative electrode composite material, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode composite material onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0099] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0100] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0101] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0102] The aforementioned organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0103] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt is F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - Or (CF3CF2SO2)2N - It may also be one or more selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, 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 M to 4.0 M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0104] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride. Here, the additive may be present in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0105] As described above, lithium secondary batteries containing the positive electrode active material according to the present invention exhibit excellent resistance characteristics and stable life characteristics, making them useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0106] 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.

[0107] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0108] The external shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, rectangular, pouch-shaped, or coin-shaped, using a can.

[0109] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0110] Examples of the aforementioned medium- and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0111] The present invention will be described in more detail below with reference to specific examples.

[0112] [Example: Production of positive electrode active material] Example 1. Four liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and then 100 mL of a 28 wt% aqueous ammonia solution was added while maintaining a temperature of 50°C. Subsequently, a transition metal solution (NiSO4, CoSO4, and MnSO4 mixed in a Ni:Co:Mn molar ratio of 97.0:0.5:2.5), aqueous ammonia solution, and sodium hydroxide solution were added to the coprecipitation reactor to form a precursor. The precursor particles were separated and washed, then dried in an oven at 130°C to produce the precursor.

[0113] Next, the precursor synthesized by the coprecipitation reaction, LiOH, Al(OH)3, ZrO2, and TiO2 were mixed. Here, LiOH was added in an amount such that the molar ratio of Li:(Ni+Co+Mn) was 1:0.968, and AlO3(OH), ZrO2, and TiO2 were added in amounts such that the weights of Al, Zr, and Ti were 9,000 ppm, 1,200 ppm, and 600 ppm, respectively, relative to the total weight of the positive electrode active material.

[0114] Next, the Li[Ni 0.9364 Co 0.0048 Mn 0.0241 Al 0.0322 Ti 0.0012 Zr0.0013 A positive electrode active material having the composition of ]O2 was manufactured.

[0115] Example 2. Except for not adding TiO2 as in Example 1, the process is the same as in Example 1, but with the same process as in Example 1. 0.9375 Co 0.0048 Mn 0.0242 Al 0.0322 Zr 0.0013 A positive electrode active material having the composition of ]O2 was manufactured.

[0116] Example 3. Except for not adding ZrO2 as in Example 1, the process is the same as in Example 1, but with the addition of Li[Ni 0.9376 Co 0.0048 Mn 0.0242 Al 0.0322 Ti 0.0012 A positive electrode active material having the composition of ]O2 was manufactured.

[0117] Comparative Example 1. The cathode active material was produced using the same process as in Example 1, except that AlO3(OH), ZrO2, and TiO2 were not added.

[0118] Comparative Example 2. The cathode active material was manufactured using the same process as in Example 1, except that AlO3(OH) was not added.

[0119] Comparative Example 3. The cathode active material was produced using the same process as in Example 1, except that AlO3(OH) and TiO2 were not added.

[0120] Comparative Example 4. The cathode active material was produced using the same process as in Example 1, except that AlO3(OH) and ZrO2 were not added.

[0121] Comparative Example 5. The cathode active material was manufactured using the same process as in Example 1, except that AlO3(OH) was added in an amount such that the weight of Al was 3,000 ppm relative to the total weight of the cathode active material.

[0122] Comparative Example 6. The cathode active material was manufactured using the same process as in Example 1, except that the amount of TiO2 added was such that the weight of Ti was 2,000 ppm relative to the total weight of the cathode active material.

[0123] Comparative Example 7. The cathode active material was manufactured using the same process as in Example 1, except that ZrO2 and TiO2 were added in amounts such that the weights of Zr and Ti were 2,000 ppm each relative to the total weight of the cathode active material.

[0124] Comparative Example 8. Four liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and then 100 mL of a 28 wt% aqueous ammonia solution was added while maintaining a temperature of 50°C. Subsequently, a transition metal solution (NiSO4, CoSO4, and MnSO4 mixed in a Ni:Co:Mn molar ratio of 8:1:1), aqueous ammonia solution, and sodium hydroxide solution were added to the coprecipitation reactor to form a precursor. The precursor particles were separated and washed, and then dried in an oven at 130°C to produce the precursor.

[0125] Next, the precursor synthesized by the coprecipitation reaction, LiOH, AlO3(OH), ZrO2, and TiO2 were mixed. Here, LiOH was added in an amount such that the molar ratio of Li:(Ni+Co+Mn) was 1:0.968, and AlO3(OH), ZrO2, and TiO2 were added in amounts such that the weights of Al, Zr, and Ti were 9,000 ppm, 1,200 ppm, and 600 ppm, respectively, relative to the total weight of the positive electrode active material.

[0126] Next, the cathode active material was produced by heat treatment in an oxygen atmosphere at 720°C for 20 hours.

[0127] Comparative Example 9. Li[Ni] was added in the same process as in Example 1, except that AlO3(OH) was added in an amount such that the weight of Al was 7,700 ppm relative to the total weight of the positive electrode active material. 0.9409 Co 0.0048 Mn0.0242 Al 0.0276 Ti 0.0012 Zr 0.0013 A positive electrode active material having the composition of ]O2 was manufactured.

[0128] [Example of experiment] Experimental Example 1: Confirmation of Doping Content The Al content relative to the total weight of each positive electrode active material produced in the above examples and comparative examples was measured using an inductively coupled plasma atomic emission spectrometer (ICP-OES; Optima 7300DV, PerkinElmer), and is shown in Table 1 below.

[0129] Experimental Example 2. XRD Analysis Figure 1 shows the results of measuring c / 2√6a for the positive electrode active materials produced in Examples 1, 4 and Comparative Example 5 using Cu Kα X-ray X-ray diffraction analysis (XRD) by the method described above.

[0130] Experimental Example 3. Evaluation of Capacity and Lifespan (3-1) Battery manufacturing The positive electrode active materials produced in the above examples and comparative examples, SuperC as the conductive material and PVDF as the binder, were mixed in N-methylpyrrolidone (NMP) in a weight ratio of 96.5:1.5:2.0 to produce a positive electrode slurry with a solid content of 60% by weight.

[0131] The manufactured positive electrode slurry was loaded at a rate of 16 mg / cm³. 2 Accordingly, the material was applied to both sides of a 15 μm thick aluminum current collector, dried at 130°C, and then rolled between two rolling rollers to produce the positive electrode.

[0132] A negative electrode slurry was prepared by mixing a mixture of natural graphite and artificial graphite in a 50:50 weight ratio as the negative electrode active material, SBR and CMC as the binder, and SuperC as the conductive material in a weight ratio of 95.6:1.1:2.3:1.0 with water as the solvent, resulting in a solid content of 60% by weight. The negative electrode slurry was then loaded at a rate of 4.63 mAh / cm³. 2Accordingly, the material was applied to both sides of a 10 μm thick copper current collector, dried at 130°C, and then rolled between two rolling rollers to produce the negative electrode.

[0133] An electrode assembly was manufactured by interposing a 15 μm thick porous polyethylene separator between the manufactured positive and negative electrodes. This assembly was then inserted into a pouch-type battery case, and an electrolyte was injected to produce a secondary battery. As the electrolyte, a solution of 1 M LiPF6 dissolved in an organic solvent, which was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2, was used.

[0134] (3-2) Measurement of initial resistance After performing an activation process on each of the manufactured cells, the initial resistance was obtained by measuring the voltage drop that appeared when a discharge pulse of 2.5C was applied for 10 seconds, using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd.). The initial resistance was calculated by charging to 4.25V at 25°C at a rate of 0.2C under CC-CV conditions, discharging at a rate of 0.2C to match the state of charge (SOC) of 50%, and then charging to 4.25V at a rate of 0.2C. The initial resistance was then calculated and is shown in Table 1 below, with the initial resistance measured in Comparative Example 1 set to 100%.

[0135] (3-3) Measurement of initial capacity and capacity retention rate Each cell, after the initial resistance measurement was completed, was charged to 4.25V at a rate of 0.2C under CC-CV conditions at 25°C, discharged to 2.5V at a rate of 0.2C, and its initial discharge capacity was measured.

[0136] The above charge / discharge cycle was considered one cycle, and after repeating the same charge / discharge 30 times, the capacity retention rate and resistance increase rate were measured using the following formula. The measurement results are shown in Table 1 below.

[0137] - Capacity retention rate (%) = (Discharge capacity after 30 cycles / Initial discharge capacity) × 100 - Resistance increase rate (%) = {(Resistance after 30 cycles - Initial resistance) / Initial resistance} × 100

[0138] [Table 1]

[0139] Referring to Table 1 above, it can be confirmed that when a positive electrode active material containing an NCM oxide with a nickel content of 90 mol% or more contains Al and Ti; Al and Zr; or a combination of Al, Ti, and Zr as doping elements, with a total content of 9,000 to 12,000 ppm and an Al content of 8,000 ppm or more, it exhibits superior resistance and lifetime characteristics compared to cases without these elements. In particular, as in Example 1, when Al, Ti, and Zr are all included, it can be confirmed that the initial resistance and resistance increase rate are the lowest, and the capacitance retention rate is the best.

[0140] On the other hand, even when the combination of Al+Ti+Zr is included as a doping element, as in Comparative Examples 6 and 7, it can be confirmed that when the concentration exceeds 12,000 ppm, the initial resistance and resistance increase rate actually increase, while the capacity retention rate decreases.

[0141] On the other hand, in the case of NCM oxides with a Ni content of less than 90 mol%, as in Comparative Example 8, it can be confirmed that the resistance characteristics and capacity retention rate are significantly inferior to those of Example 1, even though the type and content of the doping element are the same as in Example 1. This is because, in the positive electrode active material of Comparative Example 8, which has a Ni content of 80 mol%, the reduction in capacity due to doping has a much greater impact on the loss of energy density of the entire active material compared to the positive electrode active material of Example 1, which has a Ni content of 97 mol%, and the Ni content is not sufficient to compensate for that loss.

[0142] Experimental Example 4. Evaluation of the rate of change of the c-axis length and high-voltage performance. (4-1) Battery manufacturing The positive electrode active materials produced in Example 1 and Comparative Example 9, SuperC as the conductive material and PVDF as the binder, were mixed in N-methylpyrrolidone (NMP) in a weight ratio of 96.5:1.5:2.0 to produce a positive electrode slurry with a solid content of 70% by weight.

[0143] The manufactured positive electrode slurry was loaded at a rate of 16 mg / cm³. 2 Accordingly, the material was applied to both sides of a 20 μm thick aluminum current collector, dried at 130°C, and then rolled between two rolling rollers to produce the positive electrode.

[0144] A negative electrode slurry was prepared by mixing a mixture of natural graphite and artificial graphite in a 50:50 weight ratio as the negative electrode active material, SBR and CMC as the binder, and SuperC as the conductive material in a weight ratio of 95.6:1.1:2.3:1.0 with water as the solvent, resulting in a solid content of 60% by weight. The negative electrode slurry was then loaded at a rate of 4.63 mAh / cm³. 2 Accordingly, the material was applied to both sides of a 10 μm thick copper current collector, dried at 130°C, and then rolled between two rolling rollers to produce the negative electrode.

[0145] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes. After this assembly was placed inside a battery case, an electrolyte solution was injected into the case to produce a pouch-type full cell. The electrolyte solution was prepared by dissolving 1M LiPF6 in a mixed organic solvent consisting of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 3:4:3.

[0146] (4-2) Measurement of the rate of change of the length of the c axis Simultaneously with charging the cell manufactured in (4-1) above, real-time (in-situ) operando XRD analysis was performed. During the XRD analysis, Mo target X-rays were used as the light source, and the analysis was performed in transmission mode using a 2θ scanning method. stThe slit is 1 / 4°, Solar slit (1 st , 2 nd Both are 0.02rad, 2 nd A 1.68 mm mask is used, and measurements are taken in the 2θ = 7° to 30° region at intervals of 0.014°, with each scan taking approximately 6 minutes.

[0147] The charging process was performed by first charging at 0.1C to 4.35V using a CC (converter-charge) method, and then maintaining a CV (converter-charge) state until the current density reached 0.05C. A high-energy XRD Empyrean was used as the measuring device.

[0148] Based on the change in the length of the c-axis during charging obtained from the above analysis, the rate of change in the length of the c-axis was calculated using Equation 1 and is shown in Table 2 below.

[0149] (4-3) Measurement of capacitance retention rate and resistance increase rate After performing an activation process on each of the cells manufactured in (4-1) above, they were charged to 4.35V at 25°C at a rate of 0.2C using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd.) under CC-CV conditions, discharged at a rate of 0.2C to 2.5V, and then the initial discharge capacity and initial resistance were measured.

[0150] The above charge / discharge cycle was considered one cycle, and after repeating the same charge / discharge 30 times, the capacity retention rate and resistance increase rate were measured using the following formula. The measurement results are shown in Table 2 below.

[0151] - Capacity retention rate (%) = (Discharge capacity after 30 cycles / Initial discharge capacity) × 100 - Resistance increase rate (%) = {(Resistance after 30 cycles - Initial resistance) / Initial resistance} × 100

[0152] [Table 2]

[0153] Referring to the results in Table 2 above, it can be confirmed that even if the doping elements include a combination of Al, Ti, and Zr, and the total is 9,000 ppm or more, if the Al content is less than 8,000 ppm, the performance will be poor when driven at high voltage.

[0154] Specifically, the positive electrode active material of Example 1, which has an Al content of 9,000 ppm, exhibits excellent durability because, during charging, the rate of change in the length of the c-axis is small, resulting in minimal volume change of the positive electrode material during charging and discharging. Therefore, it can be confirmed that it shows excellent capacity retention and resistance increase rates even when operated under high voltage conditions.

[0155] On the other hand, the positive electrode active material of Comparative Example 9, which has an Al content of 7,700 ppm, shows a higher rate of change in the c-axis length and a larger change in volume compared to the positive electrode active material of Example 1. Consequently, its lifespan and resistance characteristics are also not as good as those of Example 1.

Claims

1. A lithium nickel cobalt manganese composite oxide in which the nickel content among metals other than lithium is 90 mol% or more, A positive electrode active material comprising a metallic element M1 doped into the lithium nickel cobalt manganese composite oxide, The aforementioned metal element M1 is two or more elements selected from the group consisting of Al, Zr, and Ti, and must contain Al. The weight of Al is 8,000 ppm or more relative to the total weight of the positive electrode active material. A positive electrode active material in which the total weight of the metal element M1 is 9,000 ppm to 12,000 ppm relative to the total weight of the positive electrode active material.

2. The positive electrode active material according to claim 1, wherein the weight of Al is 8,000 ppm or more and 10,000 ppm or less relative to the total weight of the positive electrode active material.

3. The aforementioned metal element M1 includes Zr, The positive electrode active material according to claim 1, wherein the weight of Zr is 1,000 ppm or more and 4,000 ppm or less relative to the total weight of the positive electrode active material.

4. The aforementioned metal element M1 includes Ti, The positive electrode active material according to claim 1, wherein the weight of Ti is 300 ppm or more and 4,000 ppm or less relative to the total weight of the positive electrode active material.

5. The positive electrode active material according to claim 1, wherein the metal element M1 comprises all of Al, Zr, and Ti.

6. The lithium nickel cobalt manganese composite oxide is a positive electrode active material according to claim 1, wherein the nickel content among the metals other than lithium is 95 mol% to 99 mol%.

7. The lithium nickel cobalt manganese composite oxide is a positive electrode active material according to claim 1, wherein the cobalt content among the metals other than lithium is 0.1 mol% to 1.0 mol%.

8. The aforementioned lithium nickel cobalt manganese composite oxide has the composition of the following chemical formula 1, [Chemical formula 1] Li １＋ｘ (N ａ Co ｂ Mn ｃ M1 ｄ M2 ｅ )O ２ In the aforementioned chemical formula 1, M1 consists of two or more elements selected from the group consisting of Al, Zr, and Ti, and must include Al. M2 is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. 1 + x, a, b, c, d, and e are the atomic fractions of independent elements. The positive electrode active material according to claim 1, wherein -0.2 ≤ x ≤ 0.2, 0.90 ≤ a < 1, 0 < b < 0.01, 0 < c < 0.10, 0 < d ≤ 0.05, 0 ≤ e ≤ 0.05, and a + b + c + d + e = 1.

9. The positive electrode active material according to claim 1, wherein the average crystallite size of the positive electrode active material is 80 nm to 160 nm.

10. The positive electrode active material according to claim 1, wherein when the length of the crystallite in the a-axis direction of the positive electrode active material is a and the length in the c-axis direction is c, c / 2√6a is 1.0075 or more.

11. The rate of change of the c-axis length of the positive electrode active material according to the following formula 1 is 7.0% or less. [Formula 1] Change rate (%) of the length of the c-axis = { (C ｍａｘ - C ｍｉｎ ) / C ｍｉｎ} × 100 In the above formula 1, C ｍａｘ This is the maximum value of the length of the c-axis, C ｍｉｎ This is the minimum value of the length of the c-axis, The length of the c-axis is obtained by charging a battery containing the positive electrode containing the positive electrode active material and performing operando X-ray diffraction analysis in a situ manner, as described in claim 1.

12. A method for producing the positive electrode active material described in claim 1, A manufacturing method comprising the step of mixing a nickel-cobalt-manganese composite precursor having a nickel content of 90 mol% or more, a lithium raw material, and a doping raw material containing metal element M1, and firing at 650°C to 850°C.

13. Positive electrode current collector and The positive electrode current collector includes a positive electrode active material layer provided on at least one surface of the positive electrode current collector, The positive electrode comprises the positive electrode active material layer described in claim 1.

14. The positive electrode according to claim 13, A negative electrode containing a negative electrode active material, A separator interposed between the positive electrode and the negative electrode, A lithium secondary battery containing an electrolyte.

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