Cathode active material, cathode and lithium secondary battery comprising same, and method for evaluating quality of lithium secondary battery

Abstract

The present invention relates to a cathode active material, a cathode and lithium secondary battery comprising same, and a method for evaluating the quality of a lithium secondary battery, and provides a cathode active material, and a cathode and a lithium secondary battery, both comprising same, wherein the cathode active material comprises a lithium composite transition metal oxide and has a ratio of Gaussian Lorentzian full width at half maximum (Strain L / G) of 1.6 or less as defined by Mathematical Formula 1 described in the present specification in an XRD peak pattern measured through XRD analysis. Also provided is a method for evaluating the quality of a lithium secondary battery comprising a cathode including the lithium composite transition metal oxide, an anode, and a separator disposed between the anode and the cathode, the method comprising the steps of: calculating a ratio of Gaussian Lorentzian full width at half maximum (Strain L / G) as defined by mathematical formula 1 described in the present specification in an XRD peak pattern of the cathode active material; and determining the battery as acceptable if the ratio of Gaussian Lorentzian full width at half maximum (Strain L / G) is 1.6 or less or as defective if the ratio exceeds 1.6.

Description

Positive electrode active material, positive electrode and lithium secondary battery including the same, and method for evaluating the quality of a lithium secondary battery

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0026418, filed February 23, 2024, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a cathode active material, a cathode and a lithium secondary battery including the cathode active material, and a method for evaluating the quality of a lithium secondary battery.

[0005]

[0006] As technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used.

[0007] Lithium-composite transition metal oxides are used as cathode active materials in lithium secondary batteries. Among these, lithium-cobalt composite metal oxides (LiCoO2) are primarily used due to their high operating voltage and superior capacity characteristics. However, LiCoO2 suffers from poor thermal properties due to crystal structure instability following delithiation, and its high cost limits its widespread use as a power source in fields such as electric vehicles.

[0008] As materials to replace LiCoO2, lithium manganese composite metal oxides (such as LiMnO2 or LiMn2O4), lithium iron phosphate compounds (such as LiFePO4), or lithium nickel composite metal oxides (such as LiNiO2) have been developed. Among these, research and development are actively being conducted on lithium nickel composite metal oxides, which have a high reversible capacity of approximately 200 mAh / g and can easily implement large-capacity batteries. However, LiNiO2 has poor thermal stability compared to LiCoO2, and there is a problem that if an internal short circuit occurs due to external pressure while charged, the positive electrode active material itself decomposes, causing the battery to rupture and catch fire.

[0009] Accordingly, as a method to improve the low thermal stability while maintaining the excellent reversible capacity of LiNiO2, a nickel-cobalt-manganese lithium composite metal oxide (hereinafter simply referred to as 'NCM lithium oxide') was developed in which some of the Ni was replaced with Mn and Co.

[0010] However, due to the recent rise in the price of cobalt (Co), development of lithium-rich NCM cathode active materials that can meet high capacity while containing relatively low cobalt (Co) content is underway.

[0011]

[0012] [Prior Art Literature]

[0013] [Patent Document]

[0014] (Patent Document 1) KR 10-2293046 B1 (Publication Date: August 24, 2021)

[0015]

[0016] The present invention is intended to solve the above problems, and aims to provide a cathode active material that can improve the discharge capacity characteristics and energy density of a secondary battery when applied to the battery.

[0017] In addition, the present invention aims to provide a positive electrode and a lithium secondary battery including the positive electrode active material.

[0018] In addition, the present invention provides a method for evaluating the quality of a lithium secondary battery, which can evaluate the quality of a lithium secondary battery using the positive electrode active material based on the properties of the positive electrode active material.

[0019]

[0020] To solve the above problem, the present invention provides a cathode active material, a cathode and a lithium secondary battery including the cathode active material, and a method for evaluating the quality of a lithium secondary battery.

[0021]

[0022] (1) The present invention provides a cathode active material comprising a lithium composite transition metal oxide, and having a Gaussian Lorentzian half-maximum width ratio (Strain L / G) defined by the following mathematical formula 1 in an XRD peak pattern measured through XRD analysis of 1.6 or less:

[0023] [Mathematical Formula 1]

[0024] Gaussian Lorentzian full width at half maximum ratio (Strain L / G) = L FWHM / G FWHM

[0025] In the above mathematical expression 1, L FWHM is the full width at half maximum in the Lorentzian region in the XRD peak pattern, and G FWHM is the full width at half maximum in the Gaussian region in the XRD peak pattern.

[0026] (2) The present invention provides a positive electrode active material having a Gaussian Lorentzian half-maximum width ratio (Strain L / G) of 0.95 or more and 1.6 or less in (1).

[0027] (3) The present invention provides a positive electrode active material having a full width at half maximum in the Lorentzian region of 0.25° or more and 0.45° or less in (1) or (2).

[0028] (4) The present invention provides a positive electrode active material in any one of the above (1) to (3), wherein the full width at half maximum in the Gaussian region is 0.24° or more and 0.40° or less.

[0029] (5) The present invention provides a positive electrode active material having a crystal size of 150 nm to 350 nm as measured through XRD analysis in any one of the above (1) to (4).

[0030] (6) The present invention provides a positive electrode active material in any one of the above (1) to (5), wherein the lithium composite transition metal oxide is in the form of secondary particles in which a plurality of primary particles are aggregated.

[0031] (7) The present invention provides a positive electrode active material according to any one of the above (1) to (6), wherein the lithium composite transition metal oxide includes nickel and manganese.

[0032] (8) The present invention provides a positive electrode active material in any one of the above (1) to (7), wherein the lithium composite transition metal oxide contains Mn in an amount of 50 mol% or more among transition metals other than lithium.

[0033] (9) The present invention provides a positive electrode active material in any one of the above (1) to (8), wherein the lithium composite transition metal oxide is represented by the following chemical formula 1:

[0034] [Chemical Formula 1]

[0035] Li x [Mn a1 Ni b1 M 1 c1 Co d1 ]O2

[0036] In the above chemical formula 1, 1.1 <x<1.3, 0.5≤a1<1, 0<b1<0.4, 0≤c1≤0.1, 0≤d1≤0.05, x+a1+b1+c1+d1=2이고, M 1is at least one selected from the group consisting of Al, Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

[0037] (10) The present invention provides a positive electrode for a secondary battery comprising a positive electrode active material according to any one of (1) to (9).

[0038] (11) The present invention provides a lithium secondary battery including a positive electrode according to (10).

[0039] (12) The present invention includes a method for evaluating the quality of a lithium secondary battery, including a positive electrode including a positive electrode active material including a lithium composite transition metal oxide; a negative electrode, and a separator interposed between the positive electrode and the negative electrode, the method comprising the steps of: calculating a Gaussian Lorentzian half-maximum width ratio (Strain L / G) defined by the following mathematical formula 1 from an XRD peak pattern of the positive electrode active material; and determining a product as good if the Gaussian Lorentzian half-maximum width ratio (Strain L / G) is 1.6 or less, and determining a product as defective if it is greater than 1.6.

[0040] [Mathematical Formula 1]

[0041] Gaussian Lorentzian full width at half maximum ratio (Strain L / G) = L FWHM / G FWHM

[0042] In the above mathematical expression 1, L FWHM is the full width at half maximum in the Lorentzian region in the XRD peak pattern, and G FWHM is the full width at half maximum in the Gaussian region in the XRD peak pattern.

[0043]

[0044] The cathode active material according to the present invention has the effect of improving the capacity characteristics and energy density of a lithium secondary battery when applied to the battery by satisfying the defined Gaussian Lorentzian full width at half maximum ratio (Strain L / G).

[0045] The method for evaluating the quality of a lithium secondary battery according to the present invention has the advantage of being able to predict the characteristics of a lithium secondary battery (e.g., capacity characteristics, energy density, etc.) by measuring the XRD peak pattern of a positive electrode active material, and of being able to determine the characteristics without assembling the battery.

[0046]

[0047] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0048] Terminology

[0049] In the present invention, the term 'primary particle' means a particle unit that has no apparent grain boundary when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope (SEM).

[0050] In the present invention, the term 'secondary particle' refers to an aggregate formed by the agglomeration of multiple primary particles, i.e., a secondary structure.

[0051] In the present invention, the term 'crystallite size' refers to the size of particles measured by XRD analysis. Specifically, particles refer to micro-sized grains, which can be distinguished into grains with a crystalline form when observed under magnification, and when this is further magnified, a distinct area in the form of a lattice structure of atoms in a certain direction can be confirmed, which is called a crystallite. The size of such crystals can be estimated through XRD analysis.

[0052]

[0053] measurement method

[0054] In the present invention, the ratio of the Gaussian Lorentzian full width at half maximum (Strain L / G) was calculated using XRD (Bruker, D8 ENDEAVOR). The X-ray source of XRD is Cu, and has a wavelength of λ=1.54056Å. The goniometer radius is 200.5mm, and the optics divergence slit is 0.5°. Data was collected using a LynxEye detector, which has 192 detector channels, a channel size of 0.075mm, a detector angle of 4.1°, and a detector slit of 14.325mm. The XRD peak pattern of the positive electrode active material was obtained under the conditions of 40 kV / 40 mA X-ray beam intensity, 2θ=15°~95°, step size=0.01°, and time / step=0.2, and the full width at half maximum (FWHM) in the Lorentzian region and the full width at half maximum (FWHM) in the Gaussian region were obtained from the peak pattern and then calculated using the following mathematical formula 1. At this time, the sample for XRD measurement can be prepared by placing the positive electrode active material powder on the XRD holder and then smoothing it flat with a slide glass to match the height of the XRD holder.

[0055] [Mathematical Formula 1]

[0056] Gaussian Lorentzian full width at half maximum ratio (Strain L / G) = L FWHM / G FWHM

[0057] In the above mathematical expression 1, L FWHM is the full width at half maximum in the Lorentzian region in the XRD peak pattern, and G FWHM is the full width at half maximum in the Gaussian region in the XRD peak pattern.

[0058] In the present invention, the crystal size is a value calculated using the full width at half maximum method from XRD analysis.

[0059]

[0060] The present invention provides a cathode active material, a cathode and a lithium secondary battery including the cathode active material, and a method for evaluating the quality of a lithium secondary battery.

[0061] Hereinafter, the present invention will be described in more detail.

[0062]

[0063] positive electrode active material

[0064] The present invention provides a positive electrode active material capable of improving charge / discharge capacity and energy density by controlling the ratio of Gaussian Lorentzian full width at half maximum (Strain L / G) defined by mathematical equation 1.

[0065] The cathode active material according to one embodiment of the present invention includes a lithium composite transition metal oxide, and is characterized in that the ratio of Gaussian Lorentzian full width at half maximum (Strain L / G) defined by the following mathematical formula 1 in an XRD peak pattern measured through XRD analysis is 1.6 or less.

[0066] [Mathematical Formula 1]

[0067] Gaussian Lorentzian full width at half maximum ratio (Strain L / G) = L FWHM / G FWHM

[0068] In the above mathematical expression 1, L FWHMis the full width at half maximum in the Lorentzian region in the XRD peak pattern, and G FWHM is the full width at half maximum in the Gaussian region in the XRD peak pattern.

[0069]

[0070] The shape of the XRD peak is expressed by the Voigt function, which is a combination of the Lorentzian function and the Gaussian function, as shown below.

[0071] - Lorentzian function: L(x) = (1 / π) × (Γ / ((x - x0) 2 + Γ 2 ))

[0072] (x: independent variable, x0: center location, Γ: width at half height of peak)

[0073] - Gaussian function: G(x) = exp( - (x - μ) 2 / (2σ 2 ))

[0074] (x: independent variable, μ: mean, σ: standard deviation)

[0075] Meanwhile, since Mn-rich cathode materials contain a large amount of Mn, if the synthesis is not successful, the XRD peak pattern may contain impurity phases such as LiMn2O4 spinel phase and Li2MnO3 monoclinic phase. The XRD peak positions of the impurity phases are similar to those of the Mn-rich cathode materials, resulting in overlapping peaks.

[0076] Example 1) (003) peak position of Mn-rich: 18.65°, (111) peak position of LiMn2O4 spinel: 18.66°, (001) peak position of Li2MnO3 monoclinic: 18.68°

[0077] Example 2) Mn-rich (104) peak position: 44.30°, LiMn2O4 spinel phase (400) peak position: 44.00°, Li2MnO3 monoclinic phase (131) peak position: 44.76°

[0078] Meanwhile, as the amount of impurity increases, the number of overlapping peaks increases, which may change the shape of the peaks, and accordingly, the ratio of the Lorentzian region and the Gaussian region may change.

[0079] The inventors of the present invention have confirmed that when the Gaussian Lorentzian full width at half maximum (Strain L / G) defined by the above mathematical formula 1 is 1.60 or less, not only is the capacity at 0.33 C-rate high, but the energy density is also high, and thus the present invention has been completed. When the Gaussian Lorentzian full width at half maximum (Strain L / G) defined by the above mathematical formula 1 is 1.60 or less, the layered phase and the monoclinic phase of the positive electrode active material can be well formed at an appropriate ratio without impurities.

[0080] Meanwhile, when the Gaussian Lorentzian full width at half maximum ratio (Strain L / G) exceeds 1.6, there is a problem that the monoclinic phase ratio becomes too low and the capacity decreases.

[0081]

[0082] Specifically, the Gaussian Lorentzian full width at half maximum ratio (Strain L / G) may be 0.95 or more and 1.6 or less, and more specifically, may be 0.95 or more and 1.56 or less, 1.57 or less, 1.58 or less, 1.59 or less, or 1.60 or less. For reference, when the Gaussian Lorentzian full width at half maximum ratio (Strain L / G) is less than 0.95, there may be a problem of capacity reduction due to the layered phase ratio being too low.

[0083] At this time, the full width at half maximum of the Lorentzian region may be 0.25° or more and 0.45° or less, and more specifically, may be 0.25° or more, 0.26° or more, or 0.27° or more, and 0.44° or less, or 0.45° or less. And, the full width at half maximum of the Gaussian region may be 0.24° or more and 0.40° or less, and more specifically, may be 0.24° or more, 0.36° or less, 0.37° or less, 0.38° or less, 0.39° or less, or 0.45° or less.

[0084] The full width at half maximum (FWHM) in the Lorentzian or Gaussian region is affected by the degree of phase formation, but varies inversely with the firing temperature. The ratio of the Gaussian to Lorentzian full width at half maximum (FWHM) is thought to be more desirable for assessing the degree of phase formation, as it changes simultaneously with the firing temperature.

[0085]

[0086] In addition, the cathode active material may have a crystal size measured through XRD analysis of 150 nm to 350 nm, specifically, 150 nm or more, 151 nm or more, 152 nm or more, 153 nm or more, 154 nm or more, 155 nm or more, 156 nm or more, 157 nm or more, 158 nm or more, or 159 nm or more, and 320 nm or less, 325 nm or less, 330 nm or less, 335 nm or less, 340 nm or less, 345 nm or less, or 350 nm or less.

[0087] Similar to the ratio of full width at half maximum, the crystal size also increases with increasing impurity phase content. This is not due to an actual increase in crystal size; rather, the fitting value jumps due to peaks overlapping with the impurity phase. When the phase is well formed, the value ranges from 150 nm to 350 nm, demonstrating high capacitance characteristics.

[0088]

[0089] By satisfying the ratio of the Gaussian Lorentzian full width at half maximum according to one embodiment of the present invention, the capacity characteristics and energy density of a lithium secondary battery to which it is applied can be improved.

[0090] Impurity phases such as LiMn2O4 spinel phase and Li2MnO3 monoclinic phase have lower capacity characteristics than Mn-rich cathode materials, so they can exhibit higher capacity characteristics when the presented conditions are met.

[0091]

[0092] In addition, the lithium composite transition metal oxide may be in the form of secondary particles in which a plurality of primary particles are aggregated. That is, the lithium composite transition metal oxide may be in the form of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles, and the primary particles may have a length measured through an SEM image of tens to hundreds of nm and may be in an intermediate form between a needle shape and a rod shape with a large aspect ratio. In this case, there is an advantage in that the specific surface area increases, thereby promoting active electron transfer and improving reactivity.

[0093]

[0094] And, the lithium composite transition metal oxide may include nickel and manganese.

[0095] Specifically, the lithium composite transition metal oxide may contain 50 mol% or more or 60 mol% or more of Mn among transition metals other than lithium.

[0096] More specifically, the lithium composite transition metal oxide may be a lithium-rich manganese oxide, represented by the following chemical formula 1. In this case, since the manganese content is high, more lithium can be added, and accordingly, more lithium can be desorbed, thereby increasing the charge / discharge capacity.

[0097] [Chemical Formula 1]

[0098] Li x [Mn a1 Ni b1 M 1 c1 Co d1 ]O2

[0099] In the above chemical formula 1, 1.1 <x<1.3, 0.5≤a1<1, 0<b1<0.4, 0≤c1≤0.1, 0≤d1≤0.05, x+a1+b1+c1+d1=2이고, M 1 is at least one selected from the group consisting of Al, Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

[0100] The above x may be specifically 1.1 or more, 1.105 or more, 1.110 or more, 1.115 or more, 1.120 or more, or 1.125 or more, and may be 1.135 or less, 1.140 or less, 1.150 or less, 1.200 or less, 1.250 or less, or 1.300 or less. In this case, lithium is present in excess, enabling activation and operation at a high operating voltage.

[0101] The above a1 is a ratio of the number of moles of manganese to the total number of moles of metals excluding lithium included in the lithium composite transition metal oxide, and is 0.50 or more and less than 1.0. Specifically, the above a1 may be 0.50 or more, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, or 0.55 or more, and may be 0.60 or less, 0.65 or less, 0.70 or less, 0.80 or less, 0.90 or less, or less than 1.0. The lithium composite transition metal oxide according to the present invention has a high manganese content, so that more lithium can be added, and accordingly, more lithium can be desorbed, thereby increasing the charge / discharge capacity.

[0102] The above b1 is a ratio of the number of moles of nickel to the total number of moles of metals excluding lithium included in the lithium composite transition metal oxide, and is greater than 0 and less than 0.40. Specifically, the above b1 may be greater than 0, 0.10 or more, 0.20 or more, or 0.30 or more, and may be 0.35 or less, or less than 0.40. The lithium composite transition metal oxide according to the present invention includes nickel but satisfies the content range described above, in which case the initial efficiency and discharge capacity retention rate of the battery can be further improved.

[0103] The above c1 is M for the total number of moles of metals excluding lithium included in the lithium composite transition metal oxide. 1 The mole ratio of the elements is 0 or more and 0.1 or less. The above c1 may be 0 or more, and 0.01 or less, 0.02 or less, 0.03 or less, 0.04 or less, 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, or 0.10 or less. In this case, the charge / discharge capacity, initial efficiency, and discharge capacity retention rate of the battery can be further improved.

[0104] The above d1 is a ratio of the number of moles of cobalt to the total number of moles of metals excluding lithium included in the lithium composite transition metal oxide, and is 0 or more and 0.05 or less. The above d1 may be 0 or more, and may be 0.01 or less, 0.02 or less, 0.03 or less, 0.04 or less, or 0.05 or less. In this case, cobalt is contained in an amount similar to an impurity, so that the performance of the battery is not deteriorated, and the effects according to the present invention can be realized. In particular, when c is 0, that is, when the lithium composite transition metal oxide is a cobalt-free lithium composite transition metal oxide that does not contain expensive cobalt, there is an economical advantage in that the cost is reduced.

[0105]

[0106] The cathode active material according to the present invention can be manufactured by mixing a cathode active material precursor and a lithium raw material and then calcining them, but is not limited thereto.

[0107] The above-described positive electrode active material precursor may include a transition metal hydroxide, and the transition metal hydroxide may include Ni and Mn. In addition, the transition metal hydroxide may include Mn in an amount of 50 mol% or more, or 60 mol% or more, among the transition metals.

[0108] Additionally, the transition metal hydroxide may be represented by the following chemical formula 2.

[0109] [Chemical Formula 2]

[0110] [Mn a2 Ni b2 M 2 c2 Co d2 ](OH)2

[0111] In the above chemical formula 2, 0.5≤a2<1, 0 <b2<0.4, 0≤c2≤0.1, a2+b2+c2=1이고, M 2 is at least one selected from the group consisting of Al, Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

[0112] The above a2 is a ratio of the number of moles of manganese to the total number of moles of metal included in the above transition metal hydroxide, and is 0.50 or more and less than 1.0. Specifically, the above a2 may be 0.50 or more, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, 0.55 or more, 0.56 or more, 0.57 or more, 0.58 or more, 0.59 or more, 0.60 or more, or 0.65 or more, and may be 0.70 or less, 0.80 or less, 0.90 or less, or less than 1.0.

[0113] The above b2 is a ratio of the number of moles of nickel to the total number of moles of metal included in the above transition metal hydroxide, and is greater than 0 and less than 0.40. Specifically, the above b2 may be greater than 0, 0.10 or more, 0.20 or more, or 0.30 or more, and may be 0.35 or less, or less than 0.40.

[0114] The above c2 is M for the total number of moles of metal included in the above transition metal hydroxide. 2 The mole ratio of the element is 0 or more and 0.1 or less. The above c2 may be 0 or more, and 0.01 or less, 0.02 or less, 0.03 or less, 0.04 or less, 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, or 0.10 or less.

[0115] The above d2 is a ratio of the number of moles of cobalt to the total number of moles of metal included in the above transition metal hydroxide, and is 0 or more and 0.05 or less. The above d2 may be 0 or more, and may be 0.01 or less, 0.02 or less, 0.03 or less, 0.04 or less, or 0.05 or less.

[0116] The above transition metal hydroxide may not contain Co for cost reduction purposes.

[0117]

[0118] The above lithium raw material may include lithium-containing carbonates (e.g., lithium carbonate, etc.), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide, etc.), nitrates (e.g., lithium nitrate (LiNO3)), chlorides (e.g., lithium chloride (LiCl)), etc., and one of these may be used alone or a mixture of two or more may be used.

[0119] Meanwhile, the mixing of the positive electrode active material precursor and the lithium raw material may be performed by solid-state mixing, and the mixing ratio of the positive electrode active material precursor and the lithium raw material may be determined in a range that satisfies the mole fraction of each component in the positive electrode active material to be finally manufactured. More specifically, the positive electrode active material precursor and the lithium raw material may be mixed so that the molar ratio of the positive electrode active material precursor and the lithium raw material in the lithium element is 1:1.2 to 1:1.6. In addition, the mixing may be performed using an acoustic mixer at a strength of 10G to 80G (G: gravitational acceleration) for 15 to 35 minutes.

[0120] In addition, although not essential, raw materials for doping some of the transition metals and / or oxygen of the positive electrode active material may be additionally included in addition to the positive electrode active material precursor and the lithium raw material during the mixing. For example, the above-described M may be included during the mixing. 1 A raw material containing X or a raw material containing X to be described later may be additionally mixed. At this time, the raw material containing X may be, for example, Na3PO4, K3PO4, Mg3(PO4)2, AlF3, NH4F, LiF, etc., but is not limited thereto. When a part of the oxygen is replaced by the X element as described above, the effect of suppressing oxygen desorption and reaction with the electrolyte during charging and discharging of the secondary battery can be obtained.

[0121] Meanwhile, the firing may be performed at a temperature of 700°C to 1000°C, specifically 750°C to 950°C, and the firing time may be 5 to 30 hours, specifically 8 to 15 hours, but is not limited thereto. In addition, the firing may be performed under an air atmosphere.

[0122] Meanwhile, after the calcination, additional washing and drying steps may be performed to remove lithium byproducts. The washing step may be performed, for example, by adding the prepared cathode active material to ultrapure water and stirring it. At this time, the washing temperature may be 20°C or lower, specifically 10°C to 20°C, and the washing time may be approximately 10 minutes to 1 hour. When the washing temperature and washing time satisfy the above ranges, lithium byproducts can be effectively removed.

[0123]

[0124] Cathode and lithium secondary batteries

[0125] The positive electrode active material according to the present invention can be usefully used in manufacturing a positive electrode for a secondary battery.

[0126] Specifically, the positive electrode for a secondary battery according to the present invention includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material.

[0127] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above positive electrode active material is used. For example, the positive electrode can be manufactured by dissolving or dispersing components constituting the positive electrode active material layer, i.e., the positive electrode active material, a conductive agent, and / or a binder, etc., in a solvent to manufacture a positive electrode composite, applying the positive electrode composite to at least one surface of a positive electrode current collector, and then drying and rolling the positive electrode composite, or by casting the positive electrode composite onto a separate support, and then laminating the film obtained by peeling it from the support onto a positive electrode current collector.

[0128] At this time, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 µm to 500 µm, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0129] A positive electrode active material layer comprising a positive electrode active material according to the present invention is positioned on at least one surface of the above-described collector, and optionally further comprising at least one of a conductive material and a binder, if necessary.

[0130] The above positive electrode active material may be included in an amount of 80 to 99 wt%, more specifically 85 to 98 wt%, based on the total weight of the positive electrode active material layer. When included in the above-mentioned content range, excellent capacity characteristics may be exhibited.

[0131] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types of these may be used. The conductive material may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0132] In addition, the binder plays a role of improving the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0133] Meanwhile, the solvent used in the manufacture of the positive electrode composite may be a solvent commonly used in the relevant technical field, and for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water may be used alone or in a mixture thereof. The amount of the solvent used may be appropriately adjusted in consideration of the coating thickness of the slurry, manufacturing yield, viscosity, etc.

[0134]

[0135] In addition, a lithium secondary battery according to the present invention includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode according to the present invention described above.

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

[0137] In the above secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on at least one surface of the negative electrode current collector.

[0138] The above negative electrode can be manufactured according to a conventional negative electrode manufacturing method generally known in the art. For example, the negative electrode can be manufactured by dissolving or dispersing components constituting the negative electrode active material layer, i.e., the negative electrode active material, a conductive material, and / or a binder, etc., in a solvent to manufacture a negative electrode composite, applying the negative electrode composite to at least one surface of a negative electrode current collector, and then drying and rolling the same, or by casting the negative electrode composite onto a separate support, and then peeling the support to obtain a film and laminating the film onto a negative electrode current collector.

[0139] The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. 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.

[0140] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO v(0 <v<2), SnO2, 바나듐 산화물, 리튬 바나듐 산화물과 같이 리튬을 도프 및 탈도프할 수 있는 금속산화물; 또는 Si-C 복합체 또는 Sn-C 복합체과 같이 상기 금속질 화합물과 탄소질 재료를 포함하는 복합물 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다. 또한, 상기 음극활물질로서 금속 리튬 박막이 사용될 수도 있다. 또, 탄소재료는 저결정 탄소 및 고결정성 탄소 등이 모두 사용될 수 있다. 저결정성 탄소로는 연화탄소 (soft carbon) 및 경화탄소 (hard carbon)가 대표적이며, 고결정성 탄소로는 무정형, 판상, 인편상, 구형 또는 섬유형의 천연 흑연 또는 인조 흑연, 키시흑연 (Kish graphite), 열분해 탄소 (pyrolytic carbon), 액정피치계 탄소섬유 (mesophase pitch based carbon fiber), 탄소 미소구체 (meso-carbon microbeads), 액정피치 (Mesophase pitches) 및 석유와 석탄계 코크스 (petroleum or coal tar pitch derived cokes) 등의 고온 소성탄소가 대표적이다.

[0141] Additionally, the binder and the conductive material may be the same as those described above for the positive electrode.

[0142] Meanwhile, in the 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 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 absorption 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, may 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. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0143] Meanwhile, the electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a secondary battery.

[0144] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0145] 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 Ra-CN (where Ra 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, etc., 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.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to 9.

[0146] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1M to 2.0M. 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.

[0147] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate; or pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, 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.

[0148]

[0149] As described above, a secondary battery including a positive electrode active material according to the present invention has excellent capacity characteristics and energy density, and can be usefully applied to portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0150] In addition, the secondary battery according to the present invention can be used as a unit cell of a battery module, and the battery module can be applied to a battery pack. The 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 including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0151]

[0152] Quality assessment method for lithium secondary batteries

[0153] The present invention provides a method for evaluating the quality of a lithium secondary battery, which can evaluate the quality of a lithium secondary battery using the positive electrode active material based on the properties of the positive electrode active material.

[0154] A method for evaluating the quality of a lithium secondary battery according to an embodiment of the present invention comprises: a lithium secondary battery comprising a positive electrode including a positive electrode active material including a lithium composite transition metal oxide; an anode, and a separator interposed between the positive electrode and the negative electrode, the method comprising: calculating a Gaussian Lorentzian half-maximum width ratio (Strain L / G) defined by the following mathematical formula 1 from an XRD peak pattern of the positive electrode active material; and determining the battery as a good product if the Gaussian Lorentzian half-maximum width ratio (Strain L / G) is 1.6 or less, and determining the battery as a defective product if it exceeds 1.6. Specifically, the method for evaluating the quality of a lithium secondary battery may include a step of determining the battery as a good product if the Gaussian Lorentzian half-maximum width ratio (Strain L / G) is 0.95 to 1.6 or less, and determining the battery as a defective product if it exceeds 1.6 or is less than 0.95.

[0155] [Mathematical Formula 1]

[0156] Gaussian Lorentzian full width at half maximum ratio (Strain L / G) = L FWHM / G FWHM

[0157] In the above mathematical expression 1, L FWHM is the full width at half maximum in the Lorentzian region in the XRD peak pattern, and G FWHM is the full width at half maximum in the Gaussian region in the XRD peak pattern.

[0158]

[0159] Currently, the only way to assess the capacity of a cathode active material is to directly assemble a coin cell. While this method is the most accurate way to determine capacity, it takes at least a day for the capacity to develop, making it difficult to quickly assess battery performance.

[0160] To address this, the inventors of the present invention have derived factors related to the capacity of the positive electrode active material. Specifically, the inventors of the present invention have confirmed that when the ratio of the Gaussian Lorentzian full width at half maximum (Strain L / G), defined by Equation 1 above, in the XRD peak pattern of the positive electrode active material is 1.6 or less, the phase of the positive electrode active material is well formed without impurities, and a high capacity at 0.33 C-rate can be secured.

[0161] According to the present invention, there is an advantage in that the characteristics of a lithium secondary battery (e.g., capacity characteristics, energy density, etc.) can be predicted by measuring the XRD peak pattern of a positive electrode active material, and the characteristics can be determined without assembling the battery.

[0162]

[0163] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0164]

[0165] Examples and Comparative Examples

[0166] Example 1

[0167] Positive electrode active material precursor (Mn 0.65 Ni 0.35 (OH)2) and LiOH were mixed so that the molar ratio of transition metals (Ni and Mn) in the precursor and Li in LiOH was 1:1.32, and then calcined at 910°C for 9 hours in an air atmosphere to obtain a cathode active material (Li). 1.13 Mn 0.57 Ni 0.30 O2) was manufactured. At this time, the mixing was performed using an acoustic mixer (LMTECH, Resodyn Acoustic Mixer LabRAM II) and was performed at a strength of 20G (G: gravitational acceleration) for 34 minutes.

[0168]

[0169] Example 2

[0170] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 33 minutes at a strength of 20 G (G: gravitational acceleration), and the positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0171]

[0172] Example 3

[0173] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 32 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0174]

[0175] Example 4

[0176] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 31 minutes at a strength of 20 G (G: gravitational acceleration), and the positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0177]

[0178] Example 5

[0179] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 30 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0180]

[0181] Example 6

[0182] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 29 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0183]

[0184] Example 7

[0185] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 28 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0186]

[0187] Example 8

[0188] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 27 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0189]

[0190] Example 9

[0191] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 26 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0192]

[0193] Example 10

[0194] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 25 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30O2) was manufactured.

[0195]

[0196] Example 11

[0197] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 24 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0198]

[0199] Example 12

[0200] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 23 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0201]

[0202] Example 13

[0203] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 22 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0204]

[0205] Example 14

[0206] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 21 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0207]

[0208] Example 15

[0209] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 20 minutes at a strength of 20G (G: gravitational acceleration) to obtain a positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0210]

[0211] Comparative Example 1

[0212] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 13 minutes at a strength of 20 G (G: gravitational acceleration), and the positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0213]

[0214] Comparative Example 2

[0215] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 12 minutes at a strength of 20 G (G: gravitational acceleration), and the positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0216]

[0217] Comparative Example 3

[0218] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 11 minutes at a strength of 20 G (G: gravitational acceleration), and the positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30 O2) was manufactured.

[0219]

[0220] Comparative Example 4

[0221] In the above Example 1, the mixing was performed in the same manner as Example 1 except that the mixing was performed for 10 minutes at a strength of 20 G (G: gravitational acceleration), and the positive electrode active material (Li 1.13 Mn 0.57 Ni 0.30O2) was manufactured.

[0222]

[0223] Experimental example

[0224] Experimental Example 1

[0225] The particle characteristics of each positive electrode active material manufactured in the examples and comparative examples were analyzed, and the results are shown in Table 1 below.

[0226] Specifically, the crystal structure, crystal size, and lattice strain were analyzed through XRD analysis.

[0227] XRD analysis was performed using D8 ENDEAVOR (Bruker) under the following conditions: Cu source, λ=1.54056Å, 2θ=15°~95°, step size=0.01°, time / step=0.2. The sample for measurement was prepared by placing the positive active material powder on the XRD holder and then smoothing it flat with a slide glass to match the height of the XRD holder.

[0228]

[0229] Crystal structure (a=b≠c, α,β=90°, γ=120°) Crystal size (nm) Lattice strain a(Å)c(Å)c / aL FWHM (°)G FWHM(°)Strain L / G Example 12.872614.28364.9723159.50000.27170.28400.9567 Example 22.872414.28224.9723205.00000.35950.36000.9986 Example 32.872414.28384.9728176.60000.31390.28001.1211 Example 42.872414.28274.9725182.30000.31430.27701.1347 Example 52.872714.28274.9719192.30000.32300.27701.1661 Example 62.872414.28334.9726212.00000.33910.27401.2376 Example 72.872314.28264.9725197.20000.35780.28301.2643 Example 82.872714.28264.9719194.00000.34300.26601.2895 Example 92.872414.28284.9725199.00000.36550.27601.3243 Example 102.872514.28314.9723232.00000.34370.25401.3531 Example 112.872514.28204.9720320.00000.43770.30501.4351 Example 122.872714.28334.9720258.00000.37770.25601.4754 Example 132.872714.28304.9720254.00000.36750.24701.4879 Example 142.872514.28424.9728217.00000.38380.25701.4934 Example 152.872314.28284.9727229.00000.39510.25401.5555 Comparative Example 12.872914.28414.9721250.00000.38450.24021.6008 Comparative Example 22.872014.28244.9730230.00000.40590.24301.6704Comparative example 32.872214.28334.9730262.00000.42040.24301.7300Comparative example 42.872614.28454.9727309.00000.39970.21001.9033

[0230] Referring to Table 1, it can be confirmed that in the case of the positive electrode active materials of Examples 1 to 15, the ratio of the Gaussian Lorentzian full width at half maximum (Strain L / G) defined by the mathematical formula 1 described herein is 0.95 or more and 1.6 or less, whereas in the case of the positive electrode active materials of Comparative Examples 1 to 4, the ratio of the Gaussian Lorentzian full width at half maximum (Strain L / G) defined by the mathematical formula 1 described herein is more than 1.6.

[0231]

[0232] Experimental Example 2

[0233] After manufacturing a cathode and a lithium secondary battery using each cathode active material manufactured in the examples and comparative examples, a battery performance evaluation was conducted.

[0234] (1) Manufacturing of anode

[0235] Each of the above-mentioned manufactured positive electrode active materials, carbon black conductive agent, and PVdF binder were mixed in a weight ratio of 92.5:3.0:4.5 in an N-methylpyrrolidone solvent to manufacture a positive electrode composite (viscosity: 5000 mPa·s), which was then applied to one surface of an aluminum current collector, dried at 130°C, and rolled to manufacture a positive electrode.

[0236]

[0237] (2) Manufacturing of lithium secondary batteries

[0238] Lithium metal was used as the cathode.

[0239] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes manufactured above, and the electrode assembly was placed inside a case, and then an electrolyte was injected into the case to manufacture a lithium secondary battery. At this time, the electrolyte was manufactured by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate (EC / EMC mixing volume ratio = 3 / 7).

[0240] For each lithium secondary battery half-cell manufactured as described above, it was charged at 0.1C in CCCV mode at 45℃ until 4.65 V, and discharged at 0.1C constant current until 2.0 V. Then, it was charged at 0.1C in CCCV mode at 25℃ until 4.4 V, and discharged at 0.1C constant current until 2.5 V. Then, it was charged at 0.33C in CCCV mode at 25℃ until 4.4 V, and discharged at 0.33C constant current until 2.5 V. Among these, the 0.33C charge / discharge capacity, average discharge voltage, and energy density were measured. The results are shown in Table 2 below.

[0241] Classification 0.33C charge capacity (mAh / g) 0.33C discharge capacity (mAh / g) Average discharge voltage (V) Energy density (mWh / g) Example 1 216.4 205.600 3.69 375 9.200 Example 2 215.6 205.500 3.67 47 54.800 Example 3 213.9 202.100 3.68 07 43.700 Example 4 214.2 202.300 3.68 47 44.900 Example 5 214.1 203.100 3.67 87 46.800 Example 6 212.4 201.000 3.67 9 700 Example 7212.5202.0003.671741.600 Example 8212.2201.6003.681741.800 Example 9212.0201.5003.670739.400 Example 10213.2201.3003.678740.300 Example 11212.5202.4003.661741.100 Example 12212.2201.8003.672740.900 Example 13212.1201.0003.673738.200 Example 14211.3200.5003.668735.434 Example 15211.4200.7003.667736.000Comparative Example 1210.6199.8003.674734.000Comparative Example 2210.3199.6003.666731.700Comparative Example 3210.5199.6003.664731.400Comparative Example 4211.4199.8003.673733.700

[0242] Referring to Tables 1 and 2, it can be confirmed that the positive electrode active materials of Examples 1 to 15 having a Gaussian Lorentzian full width at half maximum ratio (Strain L / G) of 1.6 or less have superior discharge capacity and energy density compared to the positive electrode active materials of Comparative Examples 1 to 4 having a Gaussian Lorentzian full width at half maximum ratio (Strain L / G) of more than 1.6.

[0243] In conclusion, it can be seen that the positive electrode active material according to the present invention has the effect of improving the capacity characteristics and energy density of a lithium secondary battery when applied to the battery, since the Gaussian Lorentzian full width at half maximum ratio (Strain L / G) defined by mathematical equation 1 described herein satisfies 1.6 or less. In addition, it can be seen that the capacity characteristics and energy density of a lithium secondary battery can be predicted by measuring the XRD peak pattern of the positive electrode active material even without assembling the battery.

Claims

1. Contains a lithium composite transition metal oxide, A cathode active material having a Gaussian Lorentzian half-maximum width ratio (Strain L / G) of 1.6 or less, as defined by the following mathematical formula 1, in an XRD peak pattern measured through XRD analysis: [Mathematical Formula 1] Gaussian Lorentzian full width at half maximum ratio (Strain L / G) = L FWHM / G FWHM In the above mathematical expression 1, L FWHM is the full width at half maximum in the Lorentzian region in the XRD peak pattern, and G FWHM is the full width at half maximum in the Gaussian region in the XRD peak pattern.

2. In paragraph 1, A positive electrode active material having a Gaussian Lorentzian full width at half maximum ratio (Strain L / G) of 0.95 or more and 1.6 or less.

3. In paragraph 1, A positive electrode active material having a full width at half maximum in the Lorentzian region of 0.25° or more and 0.45° or less.

4. In paragraph 1, A positive electrode active material having a full width at half maximum in the above Gaussian region of 0.24° or more and 0.40° or less.

5. In paragraph 1, A cathode active material having a crystal size of 150 nm to 350 nm as measured by XRD analysis.

6. In paragraph 1, The above lithium composite transition metal oxide is a cathode active material in the form of secondary particles in which a plurality of primary particles are aggregated.

7. In paragraph 1, The above lithium composite transition metal oxide is a cathode active material containing nickel and manganese.

8. In paragraph 1, The above lithium composite transition metal oxide is a cathode active material containing 50 mol% or more of Mn among transition metals other than lithium.

9. In paragraph 1, The above lithium composite transition metal oxide is a positive electrode active material represented by the following chemical formula 1: [Chemical Formula 1] Li x [Mr a1 Ni b1 M 1 c1 Co d1 ]O2 In the above chemical formula 1, 1.1 <x<1.3, 0.5≤a1<1, 0<b1<0.4, 0≤c1≤0.1, 0≤d1≤0.05, x+a1+b1+c1+d1=2이고, M 1 is at least one selected from the group consisting of Al, Cu, Fe, Mg, B, Cr, V, Ti, Ta, Nb, Mo, Y, W, and Zr.

10. A positive electrode comprising a positive electrode active material according to paragraph 1.

11. A lithium secondary battery comprising a positive electrode according to Article 9.

12. A lithium secondary battery comprising a cathode including a cathode active material including a lithium composite transition metal oxide; a cathode and a separator interposed between the cathode and the cathode, A step of calculating the ratio of Gaussian Lorentzian full width at half maximum (Strain L / G) defined by the following mathematical formula 1 from the XRD peak pattern of the above positive electrode active material; and A method for evaluating the quality of a lithium secondary battery, comprising a step of determining a good product if the Gaussian Lorentzian full width at half maximum ratio (Strain L / G) is 1.6 or less, and determining a bad product if it is greater than 1.

6. [Mathematical Formula 1] Gaussian Lorentzian full width at half maximum ratio (Strain L / G) = L FWHM / G FWHM In the above mathematical expression 1, L FWHM is the full width at half maximum in the Lorentzian region in the XRD peak pattern, and G FWHM is the full width at half maximum in the Gaussian region in the XRD peak pattern.