Positive electrode active material for lithium secondary battery and lithium secondary battery comprising same

Abstract

The positive electrode active material for a lithium secondary battery according to an embodiment of the present invention contains lithium-nickel metal oxide particles, and has an expanded phase ratio of 30 to 40%, a contracted phase ratio of 35 to 45%, and a Ni content of 90 to 99 mol% in a metal element other than lithium, as measured in a voltage region of 3.75 to 4.15 V by in-situ X-ray diffraction (XRD) analysis. The life characteristics of a lithium secondary battery including the positive electrode active material can be improved.

Description

Technical Field

[0001] The present invention provides a positive electrode active material for a lithium secondary battery and a lithium secondary battery comprising the positive electrode active material. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged. With the development of the information communications and display industries, secondary batteries are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop computers. Furthermore, battery packs containing secondary batteries are being developed in recent years as power sources for environmentally friendly vehicles such as hybrid cars.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and weight reduction, and are therefore being actively researched and developed.

[0004] A lithium secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator (separator); and an electrolyte impregnated with the electrode assembly. The lithium secondary battery may also include an outer packaging material, such as a pouch-shaped outer packaging material, to house the electrode assembly and the electrolyte.

[0005] Lithium-nickel metal oxide can be used as a positive electrode active material for lithium secondary batteries. Examples of the lithium-nickel metal oxide include nickel-based lithium metal oxide.

[0006] As the application range of lithium secondary batteries expands, longer life, high capacity and working stability are required. In the case of lithium-nickel metal oxide used as the positive electrode active material, when the chemical structure heterogeneity increases due to the distortion of the crystal structure, it may be difficult to achieve a lithium secondary battery with the desired capacity and life. In addition, when the lithium-nickel metal oxide structure is deformed or damaged during repeated charge and discharge, the life stability and capacity retention characteristics may be reduced.

[0007] For example, Korean Patent Publication No. 10-2017-0093085 discloses a positive electrode active material including a transition metal compound and an ion-adsorbing binder, but has limitations in ensuring sufficient lifespan characteristics and stability.

[0008]

Prior art literature

[0009] [Patent Literature]

[0010] Korean Patent Publication No. 10-2017-0093085. Summary of the Invention

[0011] Technical issues

[0012] An object of the present invention is to provide a positive electrode active material for a lithium secondary battery having improved lifespan characteristics and a lithium secondary battery including the same.

[0013] Technical Solution

[0014] According to an exemplary embodiment, a positive electrode active material for a lithium secondary battery is provided, comprising lithium-nickel metal oxide particles having a Ni content of 90 mol % to 99 mol % among metal elements other than lithium, wherein a peak of a (113) plane of the lithium-nickel metal oxide particles measured by in-situ X-ray diffraction analysis (in-situ XRD) is separated into a main phase peak having the highest peak intensity in the voltage region of 3.75 V to 4.15 V, an expansion phase peak appearing at a first diffraction angle less than the main diffraction angle at which the main phase peak appears, and a contraction phase peak appearing at a second diffraction angle greater than the main diffraction angle, wherein a ratio of an integrated area of ​​the expansion phase peak to the sum of the integrated areas of the main phase peak, the expansion phase peak, and the contraction phase peak is 30 to 40%, and a ratio of an integrated area of ​​the contraction phase peak to the sum of the integrated areas of the main phase peak, the expansion phase peak, and the contraction phase peak is 35 to 45%.

[0015] According to an exemplary embodiment, the difference between the main diffraction angle and the first diffraction angle may be greater than 0 and less than 1°, and the difference between the main diffraction angle and the second diffraction angle may be greater than 0 and less than 1°.

[0016] According to exemplary embodiments, the lithium-nickel metal oxide particles may include at least one doping element.

[0017] According to an exemplary embodiment, the lithium-nickel metal oxide particles may be represented by the following Chemical Formula 1:

[0018] [Chemical Formula 1]

[0019] Li x Ni a Co b Mn c M d O 2+y

[0020] In Chemical Formula 1, M includes at least one of Ti, Zr, Al, Mg, Sr, and W, and 0.8 <x<1.5、0.90≤a≤0.99、0≤b≤0.10、0≤c≤0.10、0≤d≤0.05、0.98≤a+b+c≤1.02、-0.1≤y≤0.1。

[0021] According to an exemplary embodiment, in the Chemical Formula 1, 0.94≤a≤0.98 may be satisfied.

[0022] According to an exemplary embodiment, in the Chemical Formula 1, 0≤b≤0.05 may be satisfied.

[0023] According to an exemplary embodiment, in the Chemical Formula 1, 0≤c≤0.05 may be satisfied.

[0024] According to an exemplary embodiment, in the Chemical Formula 1, c≦b may be satisfied.

[0025] According to an exemplary embodiment, in the Chemical Formula 1, M may include two or more of Ti, Zr, Al, Mg, Sr, and W.

[0026] According to an exemplary embodiment, the change amount of the d value of the lithium-nickel metal oxide particles measured by in-situ X-ray diffraction analysis (in-situ XRD) in a voltage region exceeding 4.15 V and not exceeding 4.18 V may be 0.1 to 0.15.

[0027] According to an exemplary embodiment, the lattice constants of the lithium-nickel metal oxide particles measured by in-situ X-ray diffraction (in-situ XRD) may have an a-axis lattice constant variation of 0.05 to 0.08 Å, and a c-axis lattice constant variation of 0.8 to 1.2 Å.

[0028] According to an exemplary embodiment, a lithium secondary battery is provided, including: a positive electrode including the positive electrode active material for a lithium secondary battery; and a negative electrode opposite to the positive electrode.

[0029] Effects of the Invention

[0030] The positive active material for a lithium secondary battery according to an exemplary embodiment of the present disclosure includes a high content of Ni to satisfy a content of Ni of 90 mol % or more in metal elements other than lithium, thereby realizing a high-capacity lithium secondary battery.

[0031] The ratio of the expansion phase and the contraction phase of the positive electrode active material for the lithium secondary battery measured by in-situ XRD in a low voltage band, such as a voltage region of 3.75V to 4.15V, meets a predetermined range, and the crystal structure of the positive electrode can be maintained without collapse during repeated charge and discharge of the lithium secondary battery.

[0032] Therefore, even when the lithium secondary battery is repeatedly charged and discharged, the battery capacity can be maintained without reduction, and the generation of gas caused by the side reaction with the electrolyte due to the collapse of the crystal structure of the positive electrode can be prevented.

[0033] Furthermore, in some embodiments, the positive electrode active material for lithium secondary batteries includes a doping metal, thereby further mitigating the drastic change in the crystal structure. Therefore, even with an increased Ni content, a reduction in the lifespan of the lithium secondary battery and battery swelling can be prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 and Figure 2 are respectively a schematic plan view and a cross-sectional view illustrating a lithium secondary battery according to an exemplary embodiment;

[0035] Figures 3 to 5 is an in-situ XRD graph showing a peak change of the (003) plane of the lithium secondary battery according to the embodiment;

[0036] Figures 6 to 11 This is an in-situ XRD contour plot showing the peak change of the (113) plane of the lithium secondary battery of the example.

[0037] Description of Reference Numerals

[0038] 100: Positive

[0039] 105: Positive electrode current collector

[0040] 107: Positive lead

[0041] 110: Positive electrode active material layer

[0042] 120: Negative electrode active material layer

[0043] 125: Negative electrode current collector

[0044] 127: Negative lead

[0045] 130: Negative electrode

[0046] 140: Diaphragm

[0047] 150: Electrode assembly

[0048] 160: Shell DETAILED DESCRIPTION

[0049] Embodiments of the present disclosure provide a positive electrode active material including lithium-nickel metal oxide particles and a lithium secondary battery including the same.

[0050] Hereinafter, embodiments of the present disclosure will be described in detail. However, these are merely exemplary embodiments, and the present disclosure is not limited to the specific embodiments described exemplarily.

[0051] In an exemplary embodiment, the positive electrode active material may include lithium-nickel metal oxide particles. For example, the lithium-nickel metal oxide particles may have a single crystal or polycrystalline structure.

[0052] The positive electrode active material may include particles of the lithium-nickel metal oxide. For example, the amount of the lithium-nickel metal oxide particles may be 50% by weight or greater of the total weight of the positive electrode active material. Preferably, the amount of the lithium-nickel metal oxide particles may be 60% by weight or greater, 70% by weight or greater, 80% by weight or greater, or 90% by weight or greater of the total weight of the positive electrode active material.

[0053] In one embodiment, the positive electrode active material may consist essentially of particles of the lithium-nickel based composite oxide.

[0054] According to some embodiments, the lithium-nickel metal oxide particles contain nickel (Ni), and may further contain at least one of cobalt (Co) and manganese (Mn), and may further contain other doping metal elements.

[0055] Ni can be provided as a transition metal related to the power and capacity of lithium secondary batteries. Therefore, by using a high-nickel (High-Ni) composition for the lithium-nickel metal oxide particles, a high-power positive electrode and a high-power lithium secondary battery can be provided.

[0056] However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or secondary battery at high temperatures may be relatively reduced. However, according to exemplary embodiments, the conductivity can be maintained by including Co, while the life stability and capacity retention characteristics can be improved by using Mn.

[0057] According to some embodiments, in the lithium-nickel metal oxide particles, the content of Ni in the metal elements other than lithium may be 90 mol % to 99 mol %.

[0058] For example, in the lithium-nickel metal oxide particles, the content of Ni in Ni, Co, and Mn other than lithium may be 90 mol% to 99 mol%. In some embodiments, in the lithium-nickel metal oxide particles, the content of Ni in the metal elements other than lithium may be 92 mol% to 99 mol%, 94 mol% to 99 mol%, or 94 mol% to 98 mol%.

[0059] When the content of Ni included in the lithium-nickel metal oxide particles is within the above range, a high-capacity lithium secondary battery can be realized while ensuring structural stability and lifespan characteristics of the lithium secondary battery.

[0060] When the Ni content of the lithium-nickel metal oxide particles is less than 90 mol%, the battery capacity may not be sufficiently ensured. Furthermore, when the Ni content of the lithium-nickel metal oxide particles exceeds 99 mol%, the crystal structure of the particles becomes excessively unstable, causing damage or swelling in a short period of time during repeated charge and discharge of the battery, which may reduce the battery's lifespan.

[0061] According to an exemplary embodiment, the lithium-nickel metal oxide particles may include at least one doping element. The doping element may be included to prevent cracks that may be generated in the lithium-nickel metal oxide particles. For example, the lithium-nickel metal oxide particles may include one doping element, two doping elements, or three doping elements.

[0062] The type of the doping element is not particularly limited, but in terms of stabilizing the positive electrode active material, it can be one or more selected from Ti, Zr, Al, Mg, Sr and W.

[0063] For example, the lithium-nickel metal oxide particles may have a secondary particle structure including a plurality of primary particles.

[0064] For example, as lithium secondary batteries charge and discharge, the lattice structure within primary particles contained in lithium-nickel metal oxide particles or between primary particles may be distorted. In this case, the distortion of the lattice structure and / or crystal structure may cause peak shifts and / or width changes when measured by X-ray diffraction (XRD).

[0065] For example, changes in the lattice structure and / or crystal structure according to the charge and discharge state of the lithium secondary battery can be confirmed by in-situ XRD analysis.

[0066] According to an exemplary embodiment, the change of each crystal face of the lithium-nickel metal oxide particle can be confirmed by in-situ X-ray diffraction analysis (in-situ X-ray Diffraction, in-situ XRD) through the change of peak morphology and position.

[0067] For example, in situ XRD analysis can be performed by using the lithium-nickel metal oxide as the positive electrode active material to manufacture a cell, and irradiating the cell with X-rays while charging / discharging at about 0.1C to continuously obtain an in situ XRD pattern. Thus, the position and intensity data of the peaks of each XRD pattern can be obtained. A contour plot can be displayed based on the data of the position and intensity changes of the continuous peaks obtained. Through the contour plot, the intensity and position changes of the peaks and whether the peaks are separated can be confirmed.

[0068] In some embodiments, in-situ XRD can confirm that the peak corresponding to each crystal plane in the low voltage region before the phase transition region of the lithium-nickel metal oxide particle is separated into two or more peaks.

[0069] In an exemplary embodiment, the in situ XRD can confirm changes in peaks corresponding to the (003) plane, (101) plane, (105) plane, (107) plane, (113) plane, etc. of the lithium-nickel metal oxide particles.

[0070] In an exemplary embodiment, the peak of the (113) plane of the lithium-nickel metal oxide particles measured by in-situ X-ray diffraction analysis (in-situ XRD) can be separated into three peaks in the low voltage region. For example, the low voltage region can be a voltage region of 3.75V to 4.15V.

[0071] In an exemplary embodiment, in the voltage region of 3.75V to 4.15V, the peak of the (113) face can be separated into a main phase peak, an expansion phase peak, and a contraction phase peak. The main phase peak can be the peak with the highest peak intensity when the peak of the (113) face is separated into three peaks. The expansion phase peak can be a peak that appears at a first diffraction angle that is smaller than the main diffraction angle at which the main phase peak appears. The contraction phase peak can be a peak that appears at a second diffraction angle that is larger than the main diffraction angle.

[0072] The main diffraction angle, the first diffraction angle, and the second diffraction angle correspond to the 2θ value of the horizontal axis of the in-situ XRD analysis result spectrum, and the unit may be ° (degree).

[0073] During the charging process of a battery comprising lithium-nickel metal oxide, the crystal structure of the lithium-nickel metal oxide particles changes, and the separation of the corresponding peaks can be observed by in situ XRD.

[0074] According to an exemplary embodiment, the ratio of the integrated area of ​​the expansion phase peak to the sum of the integrated areas of the main phase peak, the expansion phase peak, and the contraction phase peak may be 30% to 40%. In some embodiments, the ratio of the integrated area of ​​the expansion phase peak to the sum of the integrated areas of the main phase peak, the expansion phase peak, and the contraction phase peak may be 32% to 40%, 32% to 38%, 34% to 38%, or 34% to 36%.

[0075] According to an exemplary embodiment, the ratio of the integrated area of ​​the contraction phase peak to the sum of the integrated areas of the main phase peak, the expansion phase peak, and the contraction phase peak may be 35% to 45%. In some embodiments, the ratio of the integrated area of ​​the contraction phase peak to the sum of the integrated areas of the main phase peak, the expansion phase peak, and the contraction phase peak may be 37% to 45%, 38% to 44%, 39% to 44%, or 39% to 43%.

[0076] When the ratio is within the above range, the lithium-nickel metal oxide particles can maintain a stable crystal structure even during charge and discharge, thereby improving the lifespan characteristics of the lithium secondary battery. In addition, the generation of gas can be prevented by preventing side reactions with the electrolyte of the lithium secondary battery, thereby suppressing the volume expansion of the battery.

[0077] When the ratio of the integral area of ​​the expansion phase peak to the total integral area of ​​the peaks exceeds the above range, or the ratio of the integral area of ​​the contraction phase peak to the total integral area of ​​the peaks exceeds the above range, the crystal structure of the lithium-nickel metal oxide will be excessively distorted or undergo irreversible changes, so the capacity of the lithium secondary battery may be greatly reduced during repeated charging and discharging.

[0078] According to an exemplary embodiment, the difference between the main diffraction angle and the first diffraction angle at which the expansion phase peak appears may be greater than 0 and less than 1°, and the difference between the main diffraction angle and the second diffraction angle at which the contraction phase peak appears may be greater than 0 and less than 1°. For example, when the main phase peak is observed at a 2θ value of approximately 68.5°, the expansion phase peak may be observed within a 2θ value range of approximately 67.5° to less than 68.5°, and the contraction phase peak may be observed within a 2θ value range of approximately greater than 68.5° to less than 69.5°.

[0079] The d-value (d-spacing) of the expansion phase peak can be greater than the d-value of the main phase peak, and the d-value of the contraction phase peak can be smaller than the d-value of the main phase peak. The d-value can refer to the lattice spacing measured by XRD analysis. That is, the crystal lattice is relatively expanded, so the expansion phase can have a d-value greater than the d-value of the main phase, and the crystal lattice is relatively contracted, so the contraction phase can have a d-value less than the d-value of the main phase.

[0080] When the shrinkage phase ratio of the lithium-nickel metal oxide particles measured by in-situ X-ray diffraction (in-situ XRD) in the voltage region of 3.75 V to 4.15 V exceeds 45%, the lithium-nickel metal oxide particles are excessively unstable during charge and discharge, and thus the life characteristics of the lithium secondary battery may be reduced.

[0081] As described above, the lattice structure and / or crystal structure of the lithium-nickel metal oxide particles may change during battery charge and discharge. For example, the (003) plane of the crystal planes of the lithium-nickel metal oxide particles may undergo a phase transition between an H2 phase and an H3 phase during charge and discharge. During this phase transition, the shift of the H2 peak to the H3 peak can be confirmed by in situ XRD.

[0082] In this case, there may be an intermediate peak during the phase transition between the H2 peak and the H3 peak of the (003) plane. The intermediate peak may appear between the positions of the H2 peak and the H3 peak. For example, the intermediate peak may appear between the H2 peak at approximately 18.5° and the H3 peak at approximately 19.5°, i.e., between 18.5° and 19.5°.

[0083] The peak intensity of the intermediate peak is likely weaker than that of the H2 and H3 peaks. Therefore, in the in-situ XRD analysis results, a slight decrease in peak intensity and a peak shift can be confirmed during the phase transition process.

[0084] According to an exemplary embodiment, the lithium-nickel metal oxide particles may have a peak median intensity ratio of the (003) plane measured by in-situ X-ray diffraction analysis and defined by the following formula 1 of 50% or more. Alternatively, the lithium-nickel metal oxide particles may have a peak median intensity ratio of the (003) plane defined by the following formula 1 of 60% or more.

[0085] [Formula 1]

[0086] The peak intensity ratio of (003) plane (%) = 100*(I 003,H2-H3 / I 003,H2 )

[0087] In formula 1, I 003,H2 is the maximum peak intensity of the H2 phase of the (003) plane of the lithium-nickel metal oxide particles measured by in-situ XRD, I 003,H2-H3 is the minimum peak intensity during the H2-H3 phase transition of the (003) plane of the lithium-nickel metal oxide particles measured by in-situ XRD.

[0088] The lithium-nickel metal oxide particles have a high intermediate peak intensity during the H2-H3 phase transition of the (003) plane, so the peak change pattern can be gentle (smooth). Therefore, the crystal structure of the positive electrode active material can be more stable during charge and discharge, and a positive electrode active material and a lithium secondary battery with improved life characteristics can be achieved. According to an exemplary embodiment, the lithium-nickel metal oxide particles can be represented by the following chemical formula 1:

[0089] [Chemical Formula 1]

[0090] Li x Ni a Co b Mn c M d O 2+y

[0091] In Chemical Formula 1, M may include at least one of Ti, Zr, Al, Mg, Sr, and W, and 0.8 <x<1.5,0.90≤a≤0.99,0≤b≤0.10,0≤c≤0.10,0≤d≤0.05,0.98≤a+b+c≤1.02,-0.1≤y≤0.1。

[0092] According to an exemplary embodiment, in the Chemical Formula 1, 0.94≤a≤0.98 may be satisfied.

[0093] According to an exemplary embodiment, in the Chemical Formula 1, 0≤b≤0.05 may be satisfied.

[0094] According to an exemplary embodiment, in the Chemical Formula 1, 0≤c≤0.05 may be satisfied.

[0095] According to an exemplary embodiment, in the chemical formula 1, c≤b may be satisfied. In some embodiments, the content of Co may be greater than the content of Mn. For example, the content of Mn (c) may be 0, and the content of Co (b) may be greater than 0 and less than 0.05, or greater than 0 and less than 0.02.

[0096] According to an exemplary embodiment, in the chemical formula 1, M may refer to a doping metal. The doping metal (M) may include two or more of Ti, Zr, Al, Mg, Sr, and W. Preferably, the doping metal (M) may include three or more of Ti, Zr, Al, Mg, Sr, and W.

[0097] According to an exemplary embodiment, a change amount of a d value of the lithium-nickel metal oxide particles measured by in-situ X-ray diffraction analysis in a voltage region exceeding 4.15 V and below 4.18 V may be 0.1 to 0.15.

[0098] For example, the lithium-nickel metal oxide particles may undergo a phase transition in a high voltage band, for example, in a voltage range of 4.16 V to 4.18 V. When the phase transition occurs, the crystal structure within the particles may change, and thus the d value (d-spacing) measured by in situ X-ray diffraction analysis may change.

[0099] The variation of the d value may be the difference between the minimum and maximum d values ​​measured by in-situ X-ray diffraction analysis during the charge and discharge process of the lithium secondary battery.

[0100] When the d value is within the above range, the layered structure of the lithium-nickel metal oxide particles does not change excessively during charge and discharge, thereby improving the stability of the positive electrode active material.

[0101] According to an exemplary embodiment, the lattice constant of the lithium-nickel metal oxide particles can be measured by in-situ X-ray diffraction analysis (in-situ XRD). For example, the lattice constant of the lithium-nickel metal oxide particles can be measured by analyzing the crystal structure according to the Rietveld method in a space group R-3m crystal structure analyzed by in-situ X-ray diffraction analysis.

[0102] According to an exemplary embodiment, the variation of the a-axis lattice constant of the lithium-nickel metal oxide particles measured by in-situ X-ray diffraction (in-situ XRD) may be 0.05 to 0.08 Å. In some embodiments, the variation of the a-axis lattice constant may be 0.05 to 0.07 Å.

[0103] According to an exemplary embodiment, the change in the c-axis lattice constant of the lithium-nickel metal oxide particles measured by in-situ X-ray diffraction (in-situ XRD) may be 0.8 to 1.2 Å. In some embodiments, the change in the c-axis lattice constant may be 0.8 to 1.1 Å.

[0104] The variation of the a-axis lattice constant and the variation of the c-axis lattice constant may be the difference between the minimum value and the maximum value of the a-axis lattice constant and the c-axis lattice constant respectively measured by in-situ X-ray diffraction analysis during the charge and discharge process of the lithium secondary battery.

[0105] When the variation of the a-axis lattice constant and the variation of the c-axis lattice constant are within the above ranges, the crystal structure distortion of the lithium-nickel metal oxide caused by battery charge and discharge can be reduced, thereby improving the long-term stability of the lithium secondary battery.

[0106] Below, reference Figure 1 and Figure 2 , provides a lithium secondary battery including a positive electrode containing the above-mentioned positive electrode active material for lithium secondary batteries.

[0107] Reference Figure 1 and Figure 2 The lithium secondary battery may include: a positive electrode 100 including a positive electrode active material including a coating layer including the lithium-sulfur compound and a metal hydroxide; and a negative electrode 130 facing the positive electrode 100 .

[0108] The positive electrode 100 may include a positive active material layer 110 formed by coating a positive active material including the above-mentioned lithium-transition metal oxide particles on a positive current collector 105 .

[0109] For example, the slurry can be prepared by mixing and stirring the positive electrode active material prepared according to the above preparation method with a binder, a conductive material and / or a dispersing material in a solvent. The positive electrode 100 can be manufactured by coating the slurry on at least one side of the positive electrode current collector 105, drying and pressing.

[0110] The positive electrode current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably, may include aluminum or an aluminum alloy.

[0111] The adhesive may include, for example, an organic adhesive such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a water-based adhesive such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0112] For example, a PVDF-based binder can be used as the binder for forming the positive electrode. In this case, the amount of binder used to form the positive active material layer 110 can be reduced and the amount of positive active material can be relatively increased, thereby improving the power and capacity of the secondary battery.

[0113] The conductive material may be included to promote electron migration between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes, and / or metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3 perovskite materials.

[0114] The negative electrode 130 may include a negative electrode collector 125 and a negative electrode active material layer 120 formed by coating a negative electrode active material on at least one side of the negative electrode collector 125 .

[0115] The negative electrode active material can be used without particular limitation as long as it is a negative electrode active material known in the art that can intercalate and deintercalate lithium ions. For example, carbon series materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, lithium alloys, silicon or tin, etc. can be used. Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) sintered below 1500°C, mesophase pitch-based carbon fibers (MPCF), etc. Examples of crystalline carbon include natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. Examples of graphite-based carbon include elements such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, and indium.

[0116] The negative electrode current collector 125 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably, may include copper or a copper alloy.

[0117] In some embodiments, the slurry may be prepared by mixing and stirring the negative active material with a binder, a conductive material, and / or a dispersing material in a solvent. The negative electrode 130 may be manufactured by coating the slurry on the negative current collector, drying the coating, and pressing the coating.

[0118] The binder and the conductive material may be substantially the same or similar to the above-mentioned materials. In some embodiments, for compatibility with the carbon series active material, the binder used to form the negative electrode may include a water-based binder such as styrene-butadiene rubber (SBR) and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0119] In some embodiments, a separator 140 may be inserted between the positive electrode 100 and the negative electrode 130. The separator 140 may include a porous polymer film made from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. The separator 140 may also include a non-woven fabric formed from high-melting-point glass fibers, polyethylene terephthalate fibers, or the like.

[0120] According to an exemplary embodiment, an electrode cell is defined by a positive electrode 100, a negative electrode 130, and a separator 140. A plurality of the electrode cells may be stacked to form, for example, an electrode assembly 150 in the form of a jelly roll. For example, the electrode assembly 150 may be formed by winding, laminating, or folding the separator 140.

[0121] The electrode assembly is housed in a housing 160 together with an electrolyte, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte may use a non-aqueous electrolyte.

[0122] The non-aqueous electrolyte may contain a lithium salt as an electrolyte and an organic solvent. The lithium salt may be, for example, Li + X - Represented, and as the anion of the lithium salt (X - ), we can exemplify F - 、Cl - Br - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - wait.

[0123] The organic solvent may be, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0124] like Figure 1 As shown, the electrode tabs (positive electrode tabs and negative electrode tabs) can protrude from the positive electrode current collector 105 and the negative electrode current collector 125 belonging to each electrode cell and extend to one side of the shell 160. The electrode tabs can be fused with the one side of the shell 160 to form electrode leads (positive electrode lead 107 and negative electrode lead 127) extending to the outside of the shell 160 or exposed to the outside of the shell 160.

[0125] The lithium secondary battery may be manufactured in a cylindrical type, a prismatic type, a pouch type, a coin type, or the like using a can, for example.

[0126] The following further illustrates the embodiments of the present disclosure with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and are not intended to limit the scope of the appended claims. Various modifications and variations of the embodiments can be made within the scope and technical concept of the present disclosure, which will be apparent to those skilled in the art, and it is natural that such modifications and variations fall within the scope of the appended claims.

[0127] Example 1

[0128] (1) Preparation of lithium-nickel metal oxide particles

[0129] NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.94:0.05:0.01 in distilled water that had been bubbled with N2 for 24 hours to remove dissolved oxygen to prepare a solution. The solution was added to a reactor at 50°C and co-precipitated using NaOH and NH3H2O ​​as precipitants and chelating agents for 48 hours to obtain Ni as a transition metal precursor. 0.94 Co 0.05 Mn 0.01 (OH) 2. The obtained precursor was dried at 80°C for 12 hours and then dried again at 110°C for 12 hours.

[0130] Lithium hydroxide and the transition metal precursor were added to a dry high-speed mixer at a ratio of 1.03:1, and then uniformly mixed for 5 minutes to prepare a mixture.

[0131] The mixture was placed in a calcining furnace, heated to about 750°C at a rate of 2°C / min, and maintained at about 750°C for 10 hours. During the heating and holding period, oxygen was continuously introduced at a flow rate of 20 L / min. After the calcination was completed, it was naturally cooled to room temperature, pulverized and classified to obtain Li 1.03 Ni 0.94 Co 0.05 Mn 0.01 Lithium-nickel metal oxide particles composed of O2.

[0132] (2) Manufacturing of lithium secondary batteries

[0133] A lithium secondary battery was manufactured using the obtained lithium-nickel metal oxide particles as a positive electrode active material.

[0134] Specifically, the positive electrode active material, acetylene black (Denka Black) as a conductive material, and PVDF as a binder were mixed in a mass ratio of 97:2:1 to prepare a positive electrode mixture. The prepared positive electrode mixture was coated on an aluminum current collector, dried, and pressed to produce a positive electrode.

[0135] A negative electrode slurry was prepared, comprising 93% by weight of natural graphite as the negative electrode active material, 5% by weight of KS6 (a flake-type conductive material) as the conductive material, 1% by weight of styrene-butadiene rubber (SBR) as the binder, and 1% by weight of carboxymethyl cellulose (CMC) as the thickener. The negative electrode slurry was coated on a copper substrate, dried, and pressed to produce a negative electrode.

[0136] The positive and negative electrodes prepared above were notched and stacked, with a separator (polyethylene, 25 μm thick) inserted between them to form an electrode cell. The tabs of the positive and negative electrodes were then welded. 3 mm diameter holes were punched on the top, bottom, and center surfaces (spacers) of the coin cell, and imide tape was applied to the punched areas to block contact with external oxygen.

[0137] The welded positive electrode / separator / negative electrode assembly is placed in a coin cell, electrolyte is injected, and the cell is clamped to seal the cell, followed by immersion for more than 12 hours.

[0138] At this time, an electrolyte prepared by the following method was used: LiPF6 was dissolved in a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio) to give a LiPF6 concentration of 1 M, and then 1 wt% of vinylene carbonate (VC), 0.5 wt% of 1,3-propylene sultone (PRS) and 0.5 wt% of lithium bis(oxalatoborate) (LiBOB) were added.

[0139] The secondary battery fabricated as described above was then pre-charged at a current equivalent to 0.25C (5A) for 36 minutes. After one hour, it was degassed and aged for at least 24 hours. The battery then underwent formation charge-discharge (charging conditions: CC-CV 0.2C 4.2V 0.05C cut-off; discharging conditions: CC 0.2C 2.5V cut-off).

[0140] Example 2

[0141] A lithium secondary battery was manufactured by the same method as in Example 1, except that NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.96:0.03:0.01 to obtain a lithium secondary battery having a Li 1.03 Ni 0.96 Co 0.03 Mn 0.01 Lithium-nickel metal oxide particles composed of O2.

[0142] Example 3

[0143] A lithium secondary battery was manufactured by the same method as in Example 1, except that NiSO4 and CoSO4 were mixed in a ratio of 0.98:0.02 to obtain a lithium secondary battery having a Li 1.03 Ni 0.98 Co 0.02 Lithium-nickel metal oxide particles composed of O2.

[0144] Example 4

[0145] A lithium secondary battery was manufactured by the same method as in Example 1, except that NiSO4 and CoSO4 were mixed in a ratio of 0.98:0.02 to obtain Ni as a transition metal precursor. 0.9 8Co 0.02 (OH)2, lithium hydroxide and the transition metal precursor are added to a dry high-speed mixer at a ratio of 1.03:1, and zirconium oxide (ZrO2) is added to 4000ppm of Zr relative to the total molar number of Ni and Co, and then uniformly mixed for 5 minutes and sintered to obtain a Li 1.03 (Ni0.98 Co 0.02 ) 0.996 Zr 0.004 Lithium-nickel metal oxide particles composed of O2.

[0146] Example 5

[0147] A lithium secondary battery was manufactured by the same method as in Example 1, except that NiSO4 and CoSO4 were mixed in a ratio of 0.98:0.02 to obtain Ni as a transition metal precursor. 0.98 Co 0.02 (OH)2, lithium hydroxide and the transition metal precursor are added to a dry high-speed mixer at a ratio of 1.03:1, and zirconium oxide (ZrO2) and strontium hydroxide (Sr(OH)3) are added to the total molar number of Ni and Co so that Zr and Sr are 2000ppm respectively, and then uniformly mixed for 5 minutes and sintered to obtain Li 1.03 (Ni 0.98 Co 0.02 ) 0.996 Zr 0.002 Sr 0.002 Lithium-nickel metal oxide particles composed of O2.

[0148] Example 6

[0149] A lithium secondary battery was manufactured by the same method as in Example 1, except that NiSO4 and CoSO4 were mixed in a ratio of 0.98:0.02 to obtain Ni as a transition metal precursor. 0.98 Co 0.02 (OH)2, lithium hydroxide and the transition metal precursor are added to a dry high-speed mixer at a ratio of 1.03:1, and aluminum hydroxide (Al(OH)3), titanium hydroxide (Ti(OH)2) and strontium hydroxide (Sr(OH)3) are added to the total molar number of Ni and Co so that Al, Ti and Sr reach 1000ppm, 2000ppm and 700ppm respectively, and then uniformly mixed for 5 minutes and sintered to obtain a Li 1.03 (Ni 0.98 Co 0.02 ) 0.9963 Al 0.001 Ti 0.002 Sr 0.0007 Lithium-nickel metal oxide particles composed of O2.

[0150] Comparative Example 1

[0151] A lithium secondary battery was manufactured by the same method as in Example 1, except that NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.88:0.09:0.03 to obtain a lithium secondary battery having a Li 1.03 Ni 0.88 Co 0.09 Mn 0.03 Lithium-nickel metal oxide particles composed of O2.

[0152] Comparative Example 2

[0153] A lithium secondary battery was manufactured by the same method as in Example 1, except that Ni(NO3)2, Co(NO3)2, and Mn(NO3)2 were mixed in a ratio of 0.94:0.05:0.01 in distilled water that had been bubbled with N2 for 24 hours to remove dissolved oxygen to prepare a solution. Citric acid was added to the solution and stirred at 120°C, and then ammonia was added to adjust the pH of the solution to about 8.5. Subsequently, the solution was dried in an oven at 110°C for 12 hours to obtain Ni as a transition metal precursor. 0.94 Co 0.05 Mn 0.01 (OH) 2. Lithium hydroxide and the transition metal precursor were added to a dry high-speed mixer at a ratio of 1.03:1, and then uniformly mixed for 5 minutes to prepare a mixture.

[0154] The mixture was placed in a calcining furnace and maintained at about 750°C at a rate of 2°C / min for 10 hours. Oxygen was continuously introduced at a flow rate of 20 L / min during the heating and holding period. After the calcination was completed, it was naturally cooled to room temperature and pulverized and classified to obtain Li 1.03 Ni 0.94 Co 0.05 Mn 0.01 Lithium-nickel metal oxide particles composed of O2.

[0155] Experimental example

[0156] (1) In situ XRD analysis of lithium-transition metal oxide particles

[0157] 1) Analysis of crystal phase

[0158] The coin cells of the examples and comparative examples were charged (CC-CV 0.1C 4.3V 0.05C cutoff) and discharged (CC 0.1C 3V cutoff) once each to perform a chemical formation process. In-situ XRD was then performed using PANalytical's X'PertPRO and Empyren instruments under the following conditions.

[0159] -Anode material: Cu

[0160] -K-α1 wavelength: 1.540598 Å

[0161] -Generator voltage: 45kV

[0162] -Tube current: 40mA

[0163] -Scan Range: 10~120°

[0164] -Scan Step Size: 0.0065°

[0165] -Divergence slit: 1 / 4°

[0166] -Antiscatter slit: 1°

[0167] The coin cell was placed in in-situ XRD and charged (CC-CV 0.1C 4.3V 0.05C cut-off) and discharged (CC 0.1C 3V cut-off) once each. During each charge and discharge process, XRD was measured once every 1 minute to measure the integrated area ratio and d value (d-spacing) of the peaks of the expansion phase, main phase and contraction phase of the (113) plane in the voltage region of 3.75V to 4.18V.

[0168] 2) Analysis of lattice constant changes

[0169] The lithium secondary batteries of the embodiment and comparative example were respectively placed in the above-mentioned in-situ XRD equipment in 1), and XRD was measured once after charge and discharge to measure the lattice constant, and the change in the lattice constant was calculated by the difference between the maximum and minimum values.

[0170] The measured values ​​are shown in Table 1.

[0171] 3) Confirmation of the phase transition state of the (003) surface peak

[0172] The lithium secondary batteries of Example and Comparative Example were respectively placed in the above-mentioned in-situ XRD apparatus in 1), and XRD was measured once after charge and discharge to confirm the change of the (003) plane peak.

[0173] Figures 3 to 5 1 and 2 show in-situ XRD graphs showing peak changes of the (003) plane of the lithium secondary batteries of Examples 1 to 3, respectively.

[0174] from Figures 3 to 5 The peak middle intensity ratio according to Formula 1 was calculated and shown in Table 2.

[0175] [Formula 1]

[0176] The peak intensity ratio of (003) plane (%) = 100*(I 003,H2-H3 / I 003,H2 )

[0177] In formula 1, I 003,H2 is the maximum peak intensity of the H2 phase of the (003) plane of the lithium-nickel metal oxide particles measured by in-situ XRD, I 003,H2-H3 is the minimum value of the peak intensity during the H2-H3 phase transition of the (003) plane of the lithium-nickel metal oxide particles measured by in-situ XRD.

[0178] Although the in-situ XRD graphs of the peak changes of the (003) plane of Examples 4 to 6 and Comparative Example are not included in this specification, the peak intermediate intensity ratio was calculated by the same method as above and is shown in Table 2.

[0179] 4) Confirmation of peak separation during phase transition of (113) surface

[0180] The lithium secondary batteries of the examples and comparative examples were respectively subjected to the above-mentioned in-situ XRD in 1) and subjected to one XRD to confirm changes in the peak of the (113) plane.

[0181] Figures 6 to 11 3 and 4 show contour plots of in-situ XRD showing peak changes of the (113) plane of the lithium secondary batteries of Examples 1 to 6, respectively.

[0182] (2) Evaluation of lithium secondary battery efficiency

[0183] The lithium secondary batteries of the examples and comparative examples were charged, and the battery efficiency was calculated by measuring the charge capacity and discharge capacity, respectively, and dividing the discharge capacity by the charge capacity. The discharge capacity, charge capacity, and efficiency are shown in Table 3.

[0184] (3) Measurement of volume change of lithium secondary batteries

[0185] The lithium secondary batteries of the embodiment and the comparative example were placed in a 60 ° C chamber for 4 weeks. After that, they were placed at room temperature for 30 minutes and placed in a chamber for measuring the amount of gas generated. After forming a vacuum in the chamber, nitrogen was filled to form normal pressure. At this time, the nitrogen volume (V0) and the internal pressure (P0) of the chamber were measured. After forming a vacuum inside the chamber again, a hole was punched on the battery, and the internal pressure (P1) of the chamber was measured, and the gas generation was calculated according to the following formula 2. The gas generation is shown in Table 3.

[0186] [Formula 2]

[0187] Gas production (mL) = (V0 / P0)*P1

[0188] (4) Measurement of capacity retention during repeated charge and discharge of lithium secondary batteries

[0189] The lithium secondary batteries according to the examples and comparative examples were charged (CC / CV 0.5C 4.3V 0.05C cutoff) and discharged (CC 1.0C 3.0V cutoff) 500 times at 25°C. The capacity retention was evaluated as the percentage of the 500th discharge capacity divided by the first discharge capacity. The capacity retention is shown in Table 3.

[0190] [Table 1]

[0191]

[0192] [Table 2]

[0193]

[0194] [Table 3]

[0195]

[0196] Referring to Table 1, in the lithium-nickel metal oxide of the lithium secondary battery according to the embodiment, the integrated area ratio of the expansion phase peak measured by in-situ XRD in the voltage region of 3.75 V to 4.15 V is 30% to 40%, and the integrated area ratio of the contraction phase peak is 35% to 45%.

[0197] Therefore, referring to Table 2, it can be confirmed that the lithium secondary battery of the embodiment has high charge and discharge capacity, the battery efficiency and the capacity remain high after 500 cycles, and the amount of gas generated is small.

[0198] In particular, it was confirmed that Example 3, in which the Ni content among metal elements other than lithium was 98 mol%, and Examples 4 to 6, which were doped with metal elements, had small changes in lattice constants, improved capacity retention, and thus improved lifespan characteristics and reduced gas generation. Furthermore, it was confirmed that a greater number of doped metals resulted in a lithium secondary battery with further improved characteristics.

[0199] In addition, see Figures 3 to 5 The results confirm that the (003) peak of the lithium-nickel metal oxide contained in the lithium secondary battery according to the embodiment undergoes a phase transition from H2 to H3 along the arrow during charge and discharge. Specifically, an intermediate peak is observed as it moves from the H2 peak at approximately 18.5° to the H3 peak at approximately 19.5° at a rate of approximately 0.71° / 1.8 minutes.

[0200] At this point, it was confirmed that the more gradual the change in the intensity of the intermediate peak, the less drastic it is. This indicates that the battery has improved lifespan characteristics. For example, the intermediate peaks in Examples 4 to 6 are higher, and the peak changes occur more gradually than in Example 3, confirming that the crystal structure does not undergo drastic changes during charge and discharge.

[0201] See also Figures 6 to 11 , it can be confirmed that the peak of the (113) surface is separated into three peaks in the low voltage band (scan number of the vertical axis is about 70 to 200). For example, see Figure 9 , it can be confirmed that one peak observed when the scan number is approximately less than 70 is separated into three peaks within the range of approximately 70 to 200 scan numbers. Figure 9 In the graph, a main phase peak indicated by a solid ellipse, an expansion phase peak indicated by a dotted ellipse on the left side of the main phase peak, and a contraction phase peak indicated by a dotted ellipse on the right side of the main phase peak can be confirmed.

[0202] On the other hand, the battery of Comparative Example 1 contains a positive electrode active material having a low nickel content, and thus provides a low-capacity battery.

[0203] Furthermore, in Comparative Example 2, the proportion of the contraction phase peak measured by in-situ XRD in the voltage region of 3.75V to 4.15V was low, while the proportion of the expansion phase peak was high, resulting in a decrease in charge and discharge capacity and a decrease in capacity retention. Furthermore, the expansion and contraction phases of the positive electrode active material particles varied over an excessively wide range, increasing the amount of change in the crystal structure of the particles and, consequently, increasing gas generation. Therefore, the battery of Comparative Example 2 did not have a high capacity even though it contained a positive electrode active material having a high nickel content, and exhibited significantly reduced electrochemical properties.

Claims

1. A positive electrode active material for a lithium secondary battery, comprising lithium-nickel metal oxide particles in which the content of Ni among metal elements other than lithium is 90 mol % to 99 mol %, in, The peak of the (113) plane of the lithium-nickel metal oxide particles measured by in-situ X-ray diffraction analysis (in-situ XRD) is separated into a main phase peak with the highest peak intensity in the voltage region of 3.75 V to 4.15 V, an expansion phase peak appearing at a first diffraction angle smaller than the main diffraction angle at which the main phase peak appears, and a contraction phase peak appearing at a second diffraction angle greater than the main diffraction angle. The ratio of the integrated area of ​​the expansion phase peak to the sum of the integrated areas of the main phase peak, the expansion phase peak and the contraction phase peak is 30 to 40%, and the ratio of the integrated area of ​​the contraction phase peak to the sum of the integrated areas of the main phase peak, the expansion phase peak and the contraction phase peak is 35 to 45%.

2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The difference between the main diffraction angle and the first diffraction angle is greater than 0 and less than 1°, The difference between the main diffraction angle and the second diffraction angle exceeds 0 and is less than 1°.

3. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The lithium-nickel metal oxide particles contain at least one doping element.

4. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The lithium-nickel metal oxide particles are represented by the following chemical formula 1: [Chemical Formula 1] Li x Ni a Co b Mr c M d O 2+y In Chemical Formula 1, M includes at least one of Ti, Zr, Al, Mg, Sr, and W, and 0.8 <x<1.5、0.90≤a≤0.99、0≤b≤0.10、0≤c≤0.10、0≤d≤0.05、0.98≤a+b+c≤1.02、-0.1≤y≤0.1。 5. The positive electrode active material for lithium secondary batteries according to claim 4, wherein In the chemical formula 1, 0.94≤a≤0.

98.

6. The positive electrode active material for lithium secondary batteries according to claim 4, wherein In the chemical formula 1, 0≤b≤0.

05.

7. The positive electrode active material for lithium secondary batteries according to claim 4, wherein In the chemical formula 1, 0≤c≤0.

05.

8. The positive electrode active material for lithium secondary batteries according to claim 4, wherein In the chemical formula 1, c≤b.

9. The positive electrode active material for lithium secondary batteries according to claim 4, wherein In the chemical formula 1, M includes two or more of Ti, Zr, Al, Mg, Sr, and W.

10. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The lithium-nickel metal oxide particles have a d value whose variation, measured by in-situ X-ray diffraction (in-situ XRD) in a voltage region exceeding 4.15 V and below 4.18 V, of 0.1 to 0.

15.

11. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The lattice constants of the lithium-nickel metal oxide particles measured by in-situ X-ray diffraction (in-situ XRD) show that the variation of the a-axis lattice constant is 0.05 to 0.08 Å, and the variation of the c-axis lattice constant is 0.8 to 1.2 Å.

12. A lithium secondary battery comprising: A positive electrode comprising the positive electrode active material for a lithium secondary battery according to claim 1; as well as A negative electrode is opposite to the positive electrode.

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