Positive electrode active material and method for preparing same

Abstract

The present invention provides a positive electrode active material, a method for preparing same, and a positive electrode and lithium secondary battery comprising the positive electrode active material, the positive electrode active material comprising: a lithium nickel cobalt manganese composite oxide which has, among the metals excluding lithium, a nickel content of at least 90 mol%; and a metal element M1 doped into the lithium nickel cobalt manganese composite oxide, wherein the metal element M1 includes two or more elements selected from the group consisting of Al, Zr, and Ti and essentially includes Al, the weight of Al is equal to or greater than 8,000 ppm with respect 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 with respect to the total weight of the positive electrode active material.

Description

Positive electrode active material and method for producing the same

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0117305, filed September 4, 2023, and No. 10-2024-0006915, filed January 16, 2024, the entire contents of which are incorporated herein by reference.

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

[0003] The recent rapid proliferation of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity secondary batteries. In particular, lithium secondary batteries, with their lightweight design and high energy density, are attracting attention as power sources for portable devices. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0004] Lithium secondary batteries produce electrical energy through oxidation and reduction reactions when lithium ions are inserted / deintercalated between the positive and negative electrodes, which are made of active materials capable of intercalating and deintercalating lithium ions, while charging an organic electrolyte or polymer electrolyte between them.

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), lithium iron phosphate compound (LiFePO4), etc. have been used as positive active materials for lithium secondary batteries. In addition, as a method to improve the low thermal stability of LiNiO2 while maintaining the excellent reversible capacity, lithium composite metal oxides (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxides') in which some of the nickel (Ni) is replaced with cobalt (Co) and manganese (Mn) have been developed. However, the conventionally developed NCM-based lithium composite transition metal oxides have insufficient capacity characteristics, which limits their application.

[0006] To address these issues, recent research has focused on increasing the nickel content in NCM lithium composite transition metal oxides. However, high-nickel (High-Ni) cathode active materials with high nickel content suffer from the following problems: Due to the high reactivity of nickel, they generate large amounts of gas during charge / discharge processes, exhibit significant lattice structural instability due to cation mixing and oxygen desorption, and increase the content of lithium impurities remaining on the surface.

[0007] Therefore, there is a need to develop a cathode material that has excellent capacity and structural stability while including a high nickel content.

[0008] The present invention aims to provide a positive electrode active material with improved structural stability and a method for producing the same, and a positive electrode and a lithium secondary battery with improved capacity, resistance, and lifespan characteristics by including the positive electrode active material.

[0009] The present invention relates to a lithium nickel cobalt manganese composite oxide having a nickel content of 90 mol% or more among metals other than lithium; and

[0010] As a positive electrode active material comprising a metal element M1 doped into the above lithium nickel cobalt manganese composite oxide,

[0011] The above metal element M1 is two or more selected from the group consisting of Al, Zr and Ti, but must include Al,

[0012] The weight of the above Al is 8,000 ppm or more based on the total weight of the positive electrode active material,

[0013] A cathode active material is provided, wherein the total weight of the metal element M1 is 9,000 ppm to 12,000 ppm based on the total weight of the cathode active material.

[0014]

[0015] In addition, the present invention provides a method for producing the above-described positive electrode active material, comprising the step of mixing a nickel-cobalt-manganese composite precursor having a nickel content of 90 mol% or more among metals other than lithium, a lithium raw material, and a doping raw material containing a metal element M1, and firing the mixture at 650°C to 850°C.

[0016]

[0017] In addition, 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 includes the positive electrode active material described above.

[0018]

[0019] In addition, the present invention provides a lithium secondary battery including the above-described positive electrode; a negative electrode including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

[0020] The cathode active material according to the present invention has a high nickel content, thus providing excellent capacity, and can reduce the amount of cobalt used, thereby being advantageous in terms of material supply and price.

[0021] In addition, since Zr and / or Ti are included as doping elements together with Al, the effects of improving crystal structure and improving particle strength, etc., can all be achieved by including each of the above doping elements.

[0022] In particular, since the above doping elements are contained in a total content of 9,000 to 12,000 ppm, and among them, Al is contained in a content of 8,000 ppm or more, the limitations of high-nickel, low-cobalt positive electrode active materials, specifically, the disadvantages of large volume change during charge and discharge, which is detrimental to resistance and lifespan, can be effectively resolved.

[0023] In addition, since the positive electrode active material contributes to lowering the charge / discharge efficiency during the initial charge / discharge without deteriorating other performances, it can compensate for capacity loss due to an irreversible reaction in combination with a negative electrode including a silicon-based negative electrode material.

[0024] Therefore, a lithium secondary battery including the above positive electrode active material has the advantages of excellent capacity, resistance, and lifespan characteristics.

[0025] Figure 1 shows the results of obtaining c / 2√6a by analyzing the positive electrode active materials manufactured in Example 1, Example 4, and Comparative Example 5 of the present invention by XRD.

[0026] Hereinafter, the present invention will be described in detail.

[0027]

[0028] In the present invention, the content of the doping element can be measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). Specifically, this means that 0.03 g of the cathode active material to be analyzed is dispersed and dissolved in 1 mL of hydrochloric acid, a small amount of hydrogen peroxide and hydrofluoric acid is added, the result is diluted with 50 mL of ultrapure water, and then analyzed using an Avio series (PerkinElmer, Inc) device.

[0029] In the present invention, “D50” refers to a particle size corresponding to 50% of the volume cumulative particle size distribution of the target powder, and can be measured using a laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S-3500) and irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then finding the particle size at the point where the volume cumulative amount is 50% from the obtained graph.

[0030] In the present invention, "crystallite" refers to a particle unit having substantially the same crystal orientation, which can be confirmed through EBSD (Electron Backscatter Diffraction) analysis. Specifically, it refers to the smallest particle unit displayed in the same color in an IPF map obtained by EBSD analysis of a cross-section of a positive electrode active material cut through ion milling.

[0031] Meanwhile, in the present invention, the “average crystallite size”, “length of the crystallite in the a-axis direction”, and “length of the crystallite in the c-axis direction” can be quantitatively analyzed using X-ray diffraction analysis (XRD) using Cu Kα X-rays. Specifically, the crystallite size can be quantitatively analyzed by putting the particles to be measured in a holder, irradiating the particles with X-rays, and analyzing the diffraction grating that comes out. Sampling was prepared by putting the powder sample of the particles to be measured into the groove in the center of a general powder holder, smoothing the surface using a slide glass, and ensuring that the sample height is the same as the edge of the holder. Then, X-ray diffraction analysis was performed using a Bruker D8 Endeavor (light source: Cu Kα, λ=1.54Å) equipped with a LynxEye XE-T position sensitive detector, under the conditions of a FDS of 0.5°, a step size of 0.02°, and a total scan time of approximately 20 minutes in the range of 2θ=15° to 90°. For the measured data, Rietveld refinement was performed considering the charge (+3 for metal ions at transition metal sites, +2 for Ni ions at Li sites) and cation mixing at each site. When analyzing the crystallite size, instrumental brodadening was considered using the Fundamental Parameter Approach (FPA) implemented in the Bruker TOPAS program, and the entire peaks of the measurement range were used for fitting. The peak shape was fitted using only the Lorenzian contribution as the First Principle (FP) among the peak types available in TOPAS, and strain was not considered at this time.

[0032] However, in the c-axis length change rate according to Equation 1 below, the c-axis length is measured by manufacturing a separate battery for performing in-situ Operando XRD analysis, and specifically, a Mo target X-ray is used as a light source simultaneously with charging, and XRD analysis is performed in the 2-θ scan method in the transmission mode. 1 st slit is 1 / 4°, Soller slit (1 st , 2 nd All) is 0.02 rad, 2 nd The mask is 1.68 mm, and the 2-θ area of ​​7° to 30° is measured every 0.014° for approximately 6 minutes per scan.

[0033]

[0034]

[0035] Hereinafter, each component of the present invention will be described in more detail.

[0036]

[0037] <Cathode active material>

[0038] The present invention relates to a positive electrode active material, and more particularly, to a positive electrode active material for a lithium secondary battery.

[0039] 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 is at least two selected from the group consisting of Al, Zr, and Ti, and necessarily includes Al, and the weight of the Al is 8,000 ppm or more based on 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 based on the total weight of the positive electrode active material.

[0040] As mentioned above, increasing the nickel content in NCM oxides can secure higher capacity, but it also comes with the problem of reduced structural stability. Specifically, high-nickel cathode active materials suffer from significant changes in lattice constants, i.e., changes in volume within the unit cell. These volume changes can cause cracks within the active material particles. These cracks can lead to voids within the active material, which can degrade battery performance.

[0041] In addition, as the nickel content is high, the phenomenon of cation mixing between lithium ions and nickel ions occurs frequently, which hinders the movement of lithium ions when the battery is operated, causing an increase in battery resistance and a deterioration in lifespan.

[0042] Accordingly, the inventors of the present invention solved the above problem by controlling the type and content of doping elements in an ultra-high nickel positive electrode active material having a nickel content of 90 mol% or more.

[0043] Specifically, in lithium nickel cobalt manganese composite oxides having a Ni content of 90 mol% or more, Al increases the length of the c-axis relative to the a-axis in the crystal structure of primary particles, thereby enhancing the completeness of the layered structure and alleviating discontinuity during the phase change from H2 to H3 during charging. Therefore, rapid volume changes in particles and the resulting crack occurrence can be reduced, thereby improving the lifespan of the battery.

[0044] Zr can improve lithium ion intracrystalline mobility during charge and discharge by reducing cation mixing between Li and Ni ions, ultimately contributing to improved battery life. Ti prevents crystal size from growing beyond a certain level, mitigating volume changes during charge and discharge, thereby reducing resistance and improving battery life.

[0045] Additionally, Ti has a stronger bonding affinity with oxygen than Ni, Co, and Mn in the lithium nickel cobalt manganese composite oxide, and thus can increase particle strength when doped. As a result, particle breakage is improved, which can lead to improved battery life.

[0046] In the case of high-nickel, low-cobalt cathode materials, it is difficult to have a high-quality crystal structure and the volume change during charge and discharge is extreme, so the battery performance is greatly deteriorated. Therefore, in order to alleviate this, it is necessary to dope with such doping elements at 10,000 ppm or more. In particular, by doping Al and Zr and / or Ti together, the various shortcomings of the cathode material can be supplemented.

[0047] In addition, since the positive electrode active material according to the present invention can lower the initial charge / discharge efficiency through the doping, there is an advantage in that it can compensate for the irreversible capacity of the negative electrode when combined with a negative electrode including a negative electrode active material such as SiO or Si, which has a high lithium ion loss rate due to initial irreversibility.

[0048] Meanwhile, in the case of a positive electrode active material having a Ni content of less than 90 mol%, doping in this manner may be disadvantageous in terms of achieving energy density because the capacity may be reduced due to excessive doping, but in the case of the present invention having a Ni content of 90 mol% or more, the impact of the capacity reduction due to doping on the energy density loss of the entire active material is relatively small.

[0049]

[0050] In one embodiment of the present invention, the total weight of the metal element M1 may 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, based on the total weight of the positive electrode active material. When M1 is included in an amount of 9,000 ppm or more, the above-described effect can be achieved, but when it exceeds 12,000 ppm, it is not preferable in that undoped residue is generated on the surface of the active material, which causes an increase in surface resistance and a decrease in expressed capacity.

[0051]

[0052] In one embodiment of the present invention, the metal element M1 includes Al, and the weight of the Al may be 8,000 ppm or more, 8,500 ppm or more, or 8,700 ppm or more, and may be 10,000 ppm or less, 9,500 ppm or less, or 9,300 ppm or less, based on the total weight of the positive electrode active material. When the content of Al is 8,000 ppm or more, it is preferable in that the above-described effect of Al can be realized. However, in consideration of the fact that no undoped residue should remain, it is preferable that it is 10,000 ppm or less.

[0053] In one embodiment of the present invention, the metal element M1 includes Zr, and the weight of the Zr may be 1,000 ppm or more, 1,100 ppm or more, or 1,200 ppm or more, and may be 4,000 ppm or less, 3,000 ppm or less, 2,000 ppm or less, or 1,500 ppm or less, based on the total weight of the positive electrode active material. When the content of Zr is 1,000 ppm or more, it is preferable in that the above-described effect of Zr can be realized. However, in consideration of the fact that no undoped residue should remain, it is preferable that it is 4,000 ppm or less.

[0054] In one embodiment of the present invention, the metal element M1 includes Ti, and the content of Ti based on the total weight of the positive electrode active material may be 300 ppm or more, 400 ppm or more, or 500 ppm or more, and may be 4,000 ppm or less, 3,000 ppm or less, 2,000 ppm or less, or 1,000 ppm or less. When the content of Ti is 300 ppm or more, it is preferable in that the effect of Ti described above can be implemented. However, in consideration of the fact that no undoped residue should remain, and that excessive addition of Ti may rapidly reduce the crystal size and increase the resistance, it is preferable that it is 4,000 ppm or less.

[0055] In one embodiment of the present invention, the metal element M1 may include Al and Zr, in which case, a crystal state of a highly complete layered structure with a large ratio of the c-axis length to the a-axis length and reduced Li / Ni cation mixing can be obtained. When a highly complete crystal structure is realized in this way, it is preferable in that volume change can be alleviated during charge and discharge. At this time, the weight ratio of Al and Zr may be 1.5:1 to 9:1, preferably 5:1 to 9:1, and more preferably 7:1 to 9:1.

[0056] Most preferably, the metal element M1 may include all of Al, Zr, and Ti, which is preferable because it can improve life performance by reducing the crystal size and increasing the particle strength. In this case, the weight ratio of Al:Zr:Ti may be 10 to 20:1 to 5:1, preferably 14 to 16:1 to 3:1.

[0057]

[0058] 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 metals other than lithium. This is preferable in that high capacity can be achieved.

[0059] In addition, the lithium nickel cobalt manganese composite oxide may have a cobalt content 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% among metals other than lithium. That is, in the present invention, the lifespan, resistance, and output characteristics are improved by controlling the doping conditions while minimizing the content of expensive cobalt.

[0060] Specifically, the lithium nickel cobalt manganese composite oxide may have a composition represented by the following chemical formula 1.

[0061] [Chemical Formula 1]

[0062] Li 1+x (Ni a Co b Mn c M1 d M2 e )O2

[0063] In the above chemical formula 1,

[0064] M1 is two or more selected from the group consisting of Al, Zr and Ti,

[0065] M2 is at least one 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,

[0066] 1+x, a, b, c, d and e are the atomic fractions of independent elements, respectively.

[0067] -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, a+b+c+d+e=1이다.

[0068]

[0069] The above 1+x represents the molar ratio of lithium in the lithium nickel cobalt manganese composite oxide, and may be -0.1≤x≤0.2, or 0≤x≤0.2. When the molar ratio of lithium satisfies the above range, the crystal structure can be formed stably.

[0070] The above a represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel cobalt manganese composite oxide, and may be 0.92≤a<1, 0.93≤a<1, or 0.95≤a<1. When the molar ratio of nickel satisfies the above range, a high energy density is exhibited, enabling high capacity implementation.

[0071] The above b represents the molar ratio of cobalt among all metals excluding lithium in the lithium nickel cobalt manganese composite oxide, and is 0. <c≤0.009, 0.002≤c≤0.008, 또는 0.004≤c≤0.008일 수 있다. 코발트의 몰비가 상기 범위를 만족할 때, 양호한 저항 특성 및 출력 특성을 구현할 수 있다.

[0072] The above c represents the molar ratio of manganese among all metals excluding lithium in the lithium nickel oxide, and is 0. <c≤0.080, 0<c≤0.060, 또는 0.010≤c≤0.050일 수 있다. 망간의 몰비가 상기 범위를 만족할 때, 양극 활물질의 구조 안정성이 우수하게 나타난다.

[0073] The above d represents the molar ratio of the M1 element among all metals excluding lithium in the lithium nickel oxide, and the above d is 0. <d≤0.045, 0.010≤d≤0.045, 또는 0.020≤d≤0.040일 수 있다.

[0074] The above e represents the molar ratio of the M2 element among all metals excluding lithium in the lithium nickel oxide, and can be appropriately adjusted as needed.

[0075]

[0076] In one embodiment of the present invention, the average crystallite size of the positive electrode active material may 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 in that excellent long-term life performance can be secured.

[0077] In one embodiment of the present invention, when the a-axis direction length of the crystallite of the positive electrode active material is a and the c-axis direction length is c, c / 2√6a may be 1.0075 or more, preferably 1.0080 or more, more preferably 1.0085 or more, and may be 1.0200 or less. This means that the layered structure of the crystallite is well formed by the M1 and the interlayer distance is sufficiently secured, and in this case, there is an advantage of being able to reduce resistance and improve lifespan.

[0078] Meanwhile, the c-axis length change rate of the positive electrode active material according to the following equation 1 may be 7.0% or less, preferably 6.5% or less, and more preferably 6.0% or less.

[0079] [Formula 1]

[0080] Rate of change in c-axis length (%) = {(C max -C min ) / C min} × 100

[0081] In the above equation 1,

[0082] C max is the maximum value of the c-axis length,

[0083] C min is the minimum value of the c-axis length,

[0084] The above c-axis length was obtained by performing in-situ operando XRD analysis while charging a battery including a positive electrode including the positive electrode active material. At this time, the charging can be performed in a manner such that CC charging is performed up to 4.35 V at 0.1 C and then CV state is maintained until the current density becomes 0.05 C.

[0085] Specifically, the battery may be manufactured in a pouch shape including the positive electrode material for in-situ XRD analysis, and more specifically, it may be a pouch-type full cell manufactured by manufacturing an electrode assembly by interposing a porous polyethylene separator between a positive electrode including the positive electrode active material and a negative electrode including graphite as an negative electrode active material, and then positioning the electrode assembly inside a battery case, and then injecting an electrolyte into the case. The electrolyte may be a 1M concentration LiPF in a mixed organic solvent in which ethylene carbonate / dimethyl carbonate / diethyl carbonate are mixed in a volume ratio of 3:4:3. 6　 It may be manufactured by dissolving .

[0086]

[0087] <Method for manufacturing positive electrode active material>

[0088] Meanwhile, the method for manufacturing the positive electrode active material includes a step of mixing a nickel-cobalt-manganese composite precursor having a nickel content of 90 mol% or more among metals other than lithium, a lithium raw material, and a doping raw material containing a metal element M1, and firing the mixture at 650°C to 850°C.

[0089]

[0090] Specifically, the firing can be performed at 700°C to 800°C for 15 to 24 hours.

[0091] Meanwhile, the method for producing the positive electrode active material may further include a step 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 a step of supplying the transition metal-containing solution, an ammonium cation complex forming agent, and a basic compound while performing a co-precipitation reaction 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 co-precipitation reaction.

[0092] Meanwhile, the transition metal precursor may be an acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. of each transition metal.

[0093] Specifically, the nickel precursor may be at least one selected from the group consisting of NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, and nickel sulfide, and the cobalt precursor may be at least one selected from the group consisting of Co(OH)2, Co3O4, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, and Co(SO4)2·7H2O. In addition, the manganese precursor may be at least one selected from the group consisting of Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, and manganese sulfide.

[0094] Meanwhile, the lithium raw material may be an oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate, or sulfate containing lithium. More specifically, the lithium raw material may be at least one selected from the group consisting of Li2CO3, LiNO3, LiNO2, LiOH, LiOH H2O, LiH, LiF, LiCl, LiBr, LiI, Li2O, Li2SO4, CH3COOLi, and Li3C6H6O7.

[0095] At this time, the input amount of each transition metal precursor can be determined by considering the molar ratio of the transition metal in the positive electrode active material to be ultimately produced.

[0096] Meanwhile, the ammonium cation complex forming agent may include at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. At this time, the solvent may be water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water.

[0097] The basic compound may be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. At this time, the solvent may be water, or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water.

[0098] As described above, when a transition metal-containing solution, an ammonium cation complex forming agent, and a basic compound are introduced into a reactor and stirred, the transition metals in the transition metal-containing solution coprecipitate, generating precursor particles in the form of transition metal hydroxides.

[0099] At this time, the transition metal-containing solution, ammonium cation complex forming agent, and basic compound are added in an amount such that the pH of the reaction solution becomes within the desired range.

[0100] Once precursor particles are formed in the above manner, they are separated from the reaction solution to obtain the precursor. For example, the precursor can be separated from the reaction solution by filtering the reaction solution, and then the separated precursor can be washed and dried to obtain the precursor. Processes such as grinding and / or classification may also be performed as needed.

[0101]

[0102] A nickel-cobalt-manganese composite precursor manufactured in this manner and a doping raw material containing a lithium raw material and a metal element M1 are mixed and fired to manufacture a lithium nickel-cobalt-manganese composite oxide.

[0103] As the lithium raw material, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide may be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or a mixture thereof may be used.

[0104] Meanwhile, the lithium raw material and the nickel-cobalt-manganese composite precursor may be mixed so that the molar ratio of Li: total metal in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1. 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 is well developed, so that a cathode active material with excellent capacity characteristics and structural stability can be manufactured.

[0105] In addition, the doping raw material containing the metal element M1 contains the metal element M1. It may contain oxides, hydroxides, oxyhydroxides, halides, nitrates, carbonates, acetates, oxalates, citrates or sulfates.

[0106] When additionally doping with metal element M2, the type and amount of the metal element M2 can be controlled by considering the type and content of the metal element M2 included in the positive electrode active material described above.

[0107]

[0108] Bipolar

[0109] A 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.

[0110] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to by the positive electrode active material layer and does not react within the voltage range of the battery. The positive electrode current collector may be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0111] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, the positive electrode slurry containing the positive electrode active material can be applied onto a positive electrode current collector, followed by drying and rolling, or the positive electrode slurry can be cast onto a separate support, and then the film obtained by peeling it off from the support can be laminated onto a positive electrode current collector.

[0112] In one embodiment of the present invention, the positive electrode includes a positive electrode active material layer formed by coating positive electrode slurry containing the positive electrode active material on at least one surface of a positive electrode current collector.

[0113] Meanwhile, the positive electrode slurry may include the positive electrode active material, a binder, a conductive material, and a solvent.

[0114] Specifically, the binder may be at least one selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, 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 preferably polyvinylidene fluoride.

[0115] The binder may be included in an amount of 0.5 wt% to 3 wt%, preferably 1 wt% to 3 wt%, and more preferably 1.5 wt% to 2.5 wt%, based on the total weight of the solid content in the positive electrode slurry. When the binder content is within the above range, sufficient adhesion to the current collector and bonding between particles can be secured, thereby improving the durability of the positive electrode while maintaining a low initial resistance.

[0116] The conductive material may be at least one 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 summer 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, and preferably carbon nanotubes or carbon black, and most preferably carbon nanotubes.

[0117] The conductive agent may be included in an amount of 0.1 wt% to 2.5 wt%, preferably 0.5 wt% to 2 wt%, and more preferably 1 wt% to 2 wt%, based on the total weight of the solid content in the positive electrode slurry. When the content of the conductive agent is within the above range, it is preferable in that the dead volume can be reduced while maintaining conductivity between active materials.

[0118] In addition, the above cathode slurry may optionally further include a dispersant, and the dispersant may be hydrogenated nitrile butadiene rubber (HNBR).

[0119] Meanwhile, the solvent of the positive electrode slurry may be a solvent generally used in the art, and examples thereof include N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, dimethyl formamide (DMF), acetone, water, or a mixture of two or more thereof. The solvent may be used by adjusting the above-described positive electrode slurry to have an appropriate viscosity. For example, the solvent may be included so that the concentration of solid content in the positive electrode slurry is 60 wt% or more, preferably 60 wt% to 90 wt%, and more preferably 60 wt% to 80 wt%.

[0120]

[0121] Lithium secondary battery

[0122] Next, a lithium secondary battery according to the present invention will be described.

[0123] The lithium secondary battery specifically includes a positive electrode, a negative electrode including a negative electrode active material, and a separator and electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as described above, a detailed description will be omitted, and only the remaining components will be described in detail below.

[0124] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0125] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0126] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0127] The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0128] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β (0 <β< 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used.

[0129] In one embodiment of the present invention, the negative electrode active material may be graphite, the Si-containing material, or a mixture thereof, and specifically, may be graphite, and more specifically, a mixture of artificial graphite and natural graphite. In addition, a metallic lithium thin film may be used as the negative electrode active material. The negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0130] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0131] The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include 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 fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0132] The above negative electrode active material layer can be manufactured by applying and drying a negative electrode composite prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, or by casting the negative electrode composite on a separate support and then laminating the obtained film by peeling it off from the support on a negative electrode current collector.

[0133] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0134] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0135] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0136] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0137] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. 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 can be. More specifically, the lithium salt may be at least one 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 and LiB(C2O4)2. It is preferable to use the concentration of the lithium salt within the range of 0.1M to 4.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0138] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0139]

[0140] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent resistance characteristics and life characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0141] 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.

[0142] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0143] There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0144] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0145] Examples of the above medium and large devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0146]

[0147] Hereinafter, the present invention will be described in more detail through specific examples.

[0148] [Example: Preparation of positive electrode active material]

[0149] Example 1.

[0150] After adding 4 liters of distilled water to a co-precipitation reactor (capacity 20 L), maintaining the temperature at 50°C, 100 mL of an ammonia aqueous solution with a concentration of 28 wt% was added. Then, a transition metal solution mixed with NiSO4, CoSO4, and MnSO4 such that the molar ratio of Ni:Co:Mn was 97.0:0.5:2.5, an ammonia aqueous solution, and a sodium hydroxide solution were added to the co-precipitation reactor, and a co-precipitation reaction was performed to form a precursor. The precursor particles were separated, washed, and dried in an oven at 130°C to prepare a precursor.

[0151] Next, the precursors synthesized by the above coprecipitation reaction, LiOH, Al(OH)3, ZrO2, and TiO2 were mixed. At this time, 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.

[0152] After this, Li[Ni was heat treated at 720℃ for 20 hours in an oxygen atmosphere. 0.9364 Co 0.0048 Mn 0.0241 Al 0.0322 Ti 0.0012 Zr 0.0013 ]A positive electrode active material having a composition of O2 was manufactured.

[0153]

[0154] Example 2.

[0155] Li[Ni] was prepared in the same manner as in Example 1, except that TiO2 was not added in Example 1. 0.9375 Co 0.0048 Mn 0.0242 Al 0.0322 Zr 0.0013 ]A positive electrode active material having a composition of O2 was manufactured.

[0156]

[0157] Example 3.

[0158] Li[Ni] was prepared in the same manner as in Example 1, except that ZrO2 was not added in Example 1. 0.9376 Co 0.0048 Mn 0.0242 Al 0.0322 Ti 0.0012 ]A positive electrode active material having a composition of O2 was manufactured.

[0159]

[0160] Comparative Example 1.

[0161] A positive electrode active material was manufactured using the same process as in Example 1, except that AlO3(OH), ZrO2, and TiO2 were not added in Example 1.

[0162]

[0163] Comparative Example 2.

[0164] A positive electrode active material was manufactured using the same process as in Example 1, except that AlO3(OH) was not added in Example 1.

[0165]

[0166] Comparative Example 3.

[0167] A positive electrode active material was manufactured using the same process as in Example 1, except that AlO3(OH) and TiO2 were not added in Example 1.

[0168]

[0169] Comparative Example 4.

[0170] A positive electrode active material was manufactured using the same process as in Example 1, except that AlO3(OH) and ZrO2 were not added in Example 1.

[0171]

[0172] Comparative Example 5.

[0173] A positive electrode 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 positive electrode active material.

[0174]

[0175] Comparative Example 6.

[0176] A cathode active material was manufactured using the same process as in Example 1, except that TiO2 was added in an amount such that the weight of Ti was 2,000 ppm relative to the total weight of the cathode active material.

[0177]

[0178] Comparative Example 7.

[0179] A positive electrode active material was manufactured using the same process as in Example 1, except that ZrO2 and TiO2 were added in an amount such that the weight of Zr and Ti was 2,000 ppm each relative to the total weight of the positive electrode active material.

[0180]

[0181] Comparative Example 8.

[0182] After adding 4 L of distilled water to a co-precipitation reactor (capacity 20 L), maintaining the temperature at 50°C, 100 mL of an ammonia aqueous solution with a concentration of 28 wt% was added. Then, a transition metal solution mixed with NiSO4, CoSO4, and MnSO4 in a molar ratio of Ni:Co:Mn of 8:1:1, an ammonia aqueous solution, and a sodium hydroxide solution were added to the co-precipitation reactor, and a co-precipitation reaction was performed to form a precursor. The precursor particles were separated, washed, and dried in an oven at 130°C to prepare a precursor.

[0183] Next, the precursors synthesized by the above coprecipitation reaction, LiOH, AlO3(OH), ZrO2, and TiO2 were mixed. At this time, 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.

[0184] Afterwards, the positive electrode active material was manufactured by heat treatment at 720°C for 20 hours in an oxygen atmosphere.

[0185]

[0186] Comparative Example 9.

[0187] Li[Ni] was prepared in the same manner 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 Mn 0.0242 Al0.0276 Ti 0.0012 Zr 0.0013 ]A positive electrode active material having a composition of O2 was manufactured.

[0188]

[0189] [Experimental Example]

[0190] Experimental Example 1. Confirmation of doping content

[0191] For the positive electrode active materials manufactured in the above examples and comparative examples, the Al content based on the total weight of each positive electrode active material was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES; Optima 7300DV, PerkinElmer) and is shown in Table 1 below.

[0192]

[0193] Experimental Example 2. XRD Analysis

[0194] The results of measuring c / 2√6a using X-ray diffraction analysis (XRD) using Cu Kα X-rays for the positive electrode active materials manufactured in Example 1, Example 4, and Comparative Example 5 using the above-described method are shown in Fig. 1.

[0195]

[0196] Experimental Example 3. Capacity and Life Evaluation

[0197] (3-1) Battery manufacturing

[0198] Each of the positive electrode active materials manufactured in the above examples and comparative examples, SuperC as a conductive material, and PVDF as a binder were mixed in a weight ratio of 96.5:1.5:2.0 in N-methylpyrrolidone (NMP) to manufacture a positive electrode slurry having a solid content of 60 wt%.

[0199] The manufactured cathode slurry was loaded with 16 mg / cm 2 The anode was manufactured by applying the coating to both sides of a 15㎛ thick aluminum current collector, drying at 130℃, and then rolling between two rolling rolls.

[0200] A mixture of natural graphite and artificial graphite as negative active materials in a weight ratio of 50:50, SBR and CMC as binders, and SuperC as a conductive material were mixed in a weight ratio of 95.6:1.1:2.3:1.0 in water as a solvent to prepare a negative electrode slurry having a solid content of 60 wt%. The negative electrode slurry had a loading capacity of 4.63 mAh / cm 2 The negative electrode was manufactured by applying the coating to both sides of a 10㎛ thick copper current collector, drying at 130℃, and then rolling between two rolling rolls.

[0201] An electrode assembly was manufactured by interposing a 15 μm thick porous polyethylene separator between the manufactured positive and negative electrodes, and then inserted into a pouch-type battery case and an electrolyte was injected to manufacture a secondary battery. At this time, a solution of 1 M LiPF6 dissolved in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a volume ratio of 1:2 was used as the electrolyte.

[0202]

[0203] (3-2) Initial resistance measurement

[0204] For each of the manufactured cells, an activation (formation) process was performed, and then the cells were charged under CC-CV conditions at 0.2C rate at 25℃ to 4.25V using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd.), discharged at 0.2C rate to reach 50% SOC, and then the voltage drop that occurred while applying a discharge pulse at a constant current of 2.5C for 10 seconds was measured to obtain the initial resistance value. When the initial resistance value measured in Comparative Example 1 was set to 100%, the relative initial resistance value of each cell was calculated and shown in Table 1 below.

[0205]

[0206] (3-3) Measurement of initial capacity and capacity retention rate

[0207] Each cell for which the above initial resistance measurement was completed was charged under CC-CV conditions at 25°C at a 0.2C rate to 4.25 V, and then CC discharged to 2.5 V at a 0.2C rate to measure the initial discharge capacity.

[0208] The charge / discharge above was considered as one cycle, and the same charge / discharge was repeated 30 times. Then, the capacity retention rate and resistance increase rate were measured using the following formula. The measurement results are shown in Table 1 below.

[0209] - Capacity retention rate (%) = (discharge capacity after 30 cycles / initial discharge capacity) × 100

[0210] - Resistance increase rate (%) = {(Resistance after 30 cycles - Initial resistance) / Initial resistance} × 100

[0211] Experimental Example 1 Experimental Example 3Al content (ppm)Zr content (ppm)Ti content (ppm)Al+Zr+Ti total (ppm)Initial resistance (%)Capacity retention rate (%)Resistance increase rate (%)Example 19,0001,20060010,80088.196.740.5Example 29,0001,200-10,20091.695.859.1Example 39,000-6009,60092.595.167.3Comparative Example 1----100 (Reference)80.3148.9Comparative Example 2-20060080097.188.094.9Comparative Example 3-1,200-1,20099.187.9100.1Comparative Example 4--60060098.687.7105.8Comparative example 53,0001,2006004,80095.891.885.0Comparative example 69,0001,2002,00012,20095.485.1111.0Comparative example 79,0002,0002,00013,00098.482.6121.1Comparative example 89,0001,20060010,80099.383.9135.0Comparative example 97,7001,2006009,50094.194.972.5

[0212] As shown in Table 1 above, in the case of a cathode active material including an NCM oxide having a nickel content of 90 mol% or more, when Al and Ti; Al and Zr; or a combination of Al, Ti, and Zr are included as doping elements in a content of 9,000 to 12,000 ppm, and when the Al content is 8,000 ppm or more, it can be confirmed that the resistance and life characteristics are superior to those that are not included. Among them, it can be confirmed that when Al, Ti, and Zr are all included as in Example 1, the initial resistance and resistance increase rate are the lowest, while the capacity retention rate is the best.

[0213] On the other hand, even if a combination of Al+Ti+Zr is included as a doping element, it can be confirmed that when it exceeds 12,000 ppm, as in Comparative Examples 6 and 7, the initial resistance and resistance increase rate rather increase and the capacity retention rate decreases.

[0214] Meanwhile, in the case of NCM oxide having 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 lower than in Example 1 even though the type and content of the doping element are the same as in Example 1. This is because the positive electrode active material of Comparative Example 8 having a Ni content of 80 mol% has a much greater impact on the energy density loss of the entire active material due to capacity reduction due to doping than the positive electrode active material of Example 1 having a Ni content of 97 mol%, and the Ni content is not sufficient to compensate for the loss.

[0215]

[0216] Experimental Example 4. Evaluation of C-axis length change rate and high-voltage performance

[0217] (4-1) Battery manufacturing

[0218] Each of the positive electrode active materials manufactured in Example 1 and Comparative Example 9, SuperC as a conductive material, and PVDF as a binder were mixed in a weight ratio of 96.5:1.5:2.0 in N-methylpyrrolidone (NMP) to manufacture a positive electrode slurry having a solid content of 70 wt%.

[0219] The manufactured cathode slurry was loaded with 16 mg / cm 2 The anode was manufactured by applying the coating to both sides of a 20㎛ thick aluminum current collector, drying at 130℃, and then rolling between two rolling rolls.

[0220] A mixture of natural graphite and artificial graphite as negative active materials in a weight ratio of 50:50, SBR and CMC as binders, and SuperC as a conductive material were mixed in a weight ratio of 95.6:1.1:2.3:1.0 in water as a solvent to prepare a negative electrode slurry having a solid content of 60 wt%. The negative electrode slurry had a loading capacity of 4.63 mAh / cm 2 The negative electrode was manufactured by applying the coating to both sides of a 10㎛ thick copper current collector, drying at 130℃, and then rolling between two rolling rolls.

[0221] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes, and then positioned inside a battery case, and an electrolyte was injected into the case to manufacture a pouch-type full cell. The electrolyte was a 1M concentration LiPF in a mixed organic solvent of ethylene carbonate / dimethyl carbonate / diethyl carbonate in a volume ratio of 3:4:3. 6　 It was manufactured by dissolving .

[0222]

[0223] (4-2) Measurement of change rate of c-axis length

[0224] Operando XRD analysis was performed in real time (in-situ) while charging the cell manufactured in the above (4-1). A Mo target X-ray was used as a light source during XRD analysis, and the analysis was performed in transmission mode using a 2-θ scan method. 1 st slit is 1 / 4°, Soller slit (1 st , 2 nd All) is 0.02 rad, 2 nd A mask of 1.68 mm was used. The 2-θ area of ​​7° to 30° was measured every 0.014° for approximately 6 minutes per scan.

[0225] The above charging was performed by charging CC to 4.35 V at 0.1 C and then maintaining CV until the current density reached 0.05 C. A high-energy XRD Empyrean was used as the measuring equipment.

[0226] Based on the change in c-axis length during charging obtained from the above analysis, the rate of change in c-axis length according to Equation 1 was calculated and recorded in Table 2 below.

[0227]

[0228] (4-3) Measurement of capacity retention rate and resistance increase rate

[0229] For each cell manufactured in the above (4-1), an activation (formation) process was performed, and then the cell was charged at 0.2C rate at 25°C under CC-CV conditions to 4.35V using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd.), discharged at 0.2C rate to 2.5V, and then the initial discharge capacity and initial resistance were measured.

[0230] The charge / discharge above was considered as one cycle, and the same charge / discharge was repeated 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.

[0231] - Capacity retention rate (%) = (discharge capacity after 30 cycles / initial discharge capacity) × 100

[0232] - Resistance increase rate (%) = {(Resistance after 30 cycles - Initial resistance) / Initial resistance} × 100

[0233] Experimental Example 4C-axis length change rate (%) Capacity retention rate (%) Resistance increase rate (%) Example 15.8094.367.3 Comparative example 97.4191.590.1

[0234] Looking at the results in Table 2 above, it can be seen that even if the total amount of Al, Ti, and Zr is 9,000 ppm or more as doping elements, the performance is poor when driven at high voltage when the Al content is less than 8,000 ppm.

[0235] Specifically, it can be confirmed that the positive electrode active material of Example 1 with an Al content of 9,000 ppm has a small change in the c-axis length during charging, so that the volume change of the positive electrode material during charging and discharging is small and durability is excellent, and thus the capacity retention rate and resistance increase rate are excellent even when operated under high voltage conditions.

[0236] On the other hand, it can be confirmed that the cathode active material of Comparative Example 9 with an Al content of 7,700 ppm has a higher rate of change in c-axis length and a larger volume change than the cathode active material of Example 1, and accordingly, its lifespan and resistance characteristics are also worse than those of Example 1.

Claims

1. A lithium nickel cobalt manganese composite oxide having a nickel content of 90 mol% or more among metals other than lithium; and As a positive electrode active material comprising a metal element M1 doped into the above lithium nickel cobalt manganese composite oxide, The above metal element M1 is two or more selected from the group consisting of Al, Zr and Ti, but must include Al, The weight of the above Al is 8,000 ppm or more based on the total weight of the positive electrode active material, A cathode active material, wherein the total weight of the metal element M1 is 9,000 ppm to 12,000 ppm based on the total weight of the cathode active material.

2. In claim 1, A cathode active material, wherein the weight of the above Al is 8,000 ppm or more and 10,000 ppm or less based on the total weight of the above cathode active material.

3. In claim 1, The above metal element M1 contains Zr, A cathode active material, wherein the weight of the above Zr is 1,000 ppm or more and 4,000 ppm or less based on the total weight of the above cathode active material.

4. In claim 1, The above metal element M1 contains Ti, A cathode active material, wherein the weight of the above Ti is 300 ppm or more and 4,000 ppm or less based on the total weight of the above cathode active material.

5. In claim 1, A positive electrode active material, wherein the above metal element M1 includes all of Al, Zr and Ti.

6. In claim 1, The above lithium nickel cobalt manganese composite oxide is a cathode active material having a nickel content of 95 mol% to 99 mol% among metals other than lithium.

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

8. In claim 1, The above lithium nickel cobalt manganese composite oxide is a positive electrode active material having a composition of the following chemical formula 1: [Chemical Formula 1] Li 1+x (Ni a Co b Mr c M1 d M2 e )O2 In the above chemical formula 1, M1 is two or more selected from the group consisting of Al, Zr and Ti, but must include Al, M2 is at least one 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, respectively. -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, a+b+c+d+e=1이다.

9. In claim 1, A cathode active material having an average crystallite size of 80 nm to 160 nm.

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

11. In claim 1, A positive electrode active material having a change rate of the c-axis length according to the following formula 1 of the positive electrode active material of 7.0% or less: [Formula 1] Rate of change in c-axis length (%) = {(C max -C min ) / C min } × 100 In the above equation 1, C max is the maximum value of the c-axis length, C min is the minimum value of the c-axis length, The above c-axis length was obtained by performing in-situ Operando XRD analysis while charging a battery including a positive electrode including the positive electrode active material.

12. A method for producing a cathode active material according to claim 1, comprising the step of mixing a nickel-cobalt-manganese composite precursor having a nickel content of 90 mol% or more among metals other than lithium, a lithium raw material, and a doping raw material containing a metal element M1, and firing the mixture at 650°C to 850°C.

13. Anode current collector; and Including a positive electrode active material layer provided on at least one surface of the positive electrode current collector, A positive electrode, wherein the positive electrode active material layer comprises the positive electrode active material according to claim 1.

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

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