Lithium nickel-based composite oxides as positive electrode active materials for rechargeable lithium-ion batteries

Abstract

The present invention relates to a positive electrode active material for a rechargeable lithium-ion battery, comprising Li, Ni, optionally Co, and optionally transition metals such as Mn and Nb, coated with B, and having a specific surface area of ​​0.50 m / g or more and 1.50 m / g or less.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for rechargeable lithium-ion batteries. More specifically, the present invention relates to a positive electrode active material comprising lithium (Li), M', and oxygen, wherein M' comprises niobium (Nb) and 80 at% or more nickel (Ni). The positive electrode active material is coated with boron (B) and has a certain specific surface area. The present invention also relates to a method for producing a positive electrode active material, a battery containing the positive electrode active material, and the use of a battery containing the positive electrode active material in electric vehicles or hybrid electric vehicles. [Background technology]

[0002] Rechargeable lithium-ion batteries containing Ni-rich (i.e., containing more than 80 at% Ni) cathode active materials are already known to have advantages such as high specific energy capacity and high operating voltage. Furthermore, Yehonatan Levartovsky et al., ACS Appl. Mater. Interface 2021, 13, 34145-34156, describes that electrodes containing Nb and 85 at% Ni cathode active materials have a slightly higher initial discharge capacity (DQ1). However, Figure 3 of Chinese Patent Application Publication No. 106505195(A) shows experimental results that lithium-ion batteries containing Nb cathode active materials have significant capacity decay. Capacity decay, or capacity loss, is a phenomenon observed in the use of rechargeable batteries where the amount of charge that the battery can supply at its rated voltage decreases with use. While Nb is advantageous to Ni-rich cathode active materials in terms of DQ1, it is undesirable in terms of capacity decay. Furthermore, simply including Nb does not eliminate the increase in gas generation and DC resistance after full-cell testing. Therefore, there is a need for a Ni-rich cathode active material containing Nb that exhibits small capacitance decay, high DQ1, and lower gas generation and DC resistance after full-cell testing. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Chinese Patent Application Publication No. 106505195 Specification [Non-patent literature]

[0004] [Non-Patent Document 1] Yehonatan Levartovsky et al.,ACS Appl.Mater.Interface 2021,13,34145-34156 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The first object of the present invention is to provide a positive electrode active material that contains Nb and 80 at% or more Ni, and has improved electrochemical properties such as high DQ1 and small capacitance decay.

[0006] A second object of the present invention is to provide a method for producing the above-described positive electrode active material.

[0007] A third object of the present invention is to provide a battery containing a positive electrode material.

[0008] A fourth object of the present invention is to provide a battery containing a positive electrode active material for use in electric vehicles or hybrid electric vehicles. [Means for solving the problem]

[0009] The first objective is a positive electrode active material for a rechargeable lithium-ion battery, wherein the positive electrode active material contains Li, M', and oxygen, and M' is Ni with content x ≥ 80.0 at% for -M', For -M', Co with a content y of 0.0 ≤ y ≤ 20.0 at% For -M', Mn of content z such that 0.0 ≤ z ≤ 20.0 at% - D which has a content a of 0.0 ≦ a ≦ 5.0 at% with respect to M', and is at least one element selected from the group consisting of Ba, Ca, Cr, Fe, Mg, Mo, S, Si, Sr, Ti, Y, V, W, and Zn, - B which has a content b of 0.0 < b ≦ 4.0 at% with respect to M', - Nb which has a content c of 0.0 < c ≦ 4.0 at% with respect to M', - Al which has a content d of 0.0 ≦ d ≦ 4.0 at% with respect to M', and - Zr which has a content e of 0.0 ≦ e ≦ 4.0 at% with respect to M', and includes, - x, y, z, a, b, c, d, and e are measured by ICP - OES, - x + y + z + a + b + c + d + e is 100.0 at%, The cathode active material has a B content B defined as b / (x + y + z + b + c + d + e) , , , , and the cathode active material has a B content B B and B B is determined by XPS analysis, and B B is expressed as the atomic content with respect to the total atomic content of Ni, Co, Mn, B, Nb, Al, and Zr measured by XPS analysis, and the ratio B B / B A > 10.0, The specific surface area of the cathode active material is 0.50 m 2 / g or more and 1.50 m 2 / g or less, which is achieved by providing the cathode active material.

[0010] The second object is a method for manufacturing the cathode active material, comprising the following continuous steps: Step 1) A step of mixing a lithium source and a transition metal composite precursor containing Ni, optionally Co, and optionally Mn with a Nb - containing compound to obtain a first mixture; Step 2) A step of heating the first mixture at a temperature of 600 °C to 900 °C to obtain a first heated substance; Step 3) A step of mixing the first heated substance with water to obtain a slurry, filtering it, and then drying the slurry to obtain a dry powder; Step 4) A step of mixing the dried powder with the B-containing compound to obtain a second mixture, This is achieved by providing a method comprising step 5) heating the second mixture at a temperature of 250°C to 500°C to obtain a positive electrode active material powder.

[0011] The third objective is achieved by providing a battery containing the positive electrode active material.

[0012] The fourth objective is achieved by providing the use of the battery containing the positive electrode active material in an electric vehicle or a hybrid electric vehicle.

[0013] When the positive electrode active material according to the present invention is used in a rechargeable lithium-ion battery, DQ1 increases and capacity decay is reduced. [Brief explanation of the drawing]

[0014] [Figure 1] This is the B1s peak in the XPS spectrum of EX2. [Figure 2] This is a STEM-EDS line scan graph of EX1 (A and B show different primary particles). [Figure 3] This is the DQ1 versus capacitance attenuation for EX1, EX2, and CEX1-CEX6. [Modes for carrying out the invention]

[0015] In the following embodiments for carrying out the invention, preferred embodiments are described in detail to enable the implementation of the invention. Although the invention is described with reference to these specific preferred embodiments, it will be understood that the invention is not limited to these preferred embodiments. In contrast, the invention includes a number of substitutes, variations and equivalents, which will become apparent when considering the following embodiments for carrying out the invention.

[0016] positive electrode active material In a first aspect, the present invention relates to a positive electrode active material for a rechargeable lithium ion battery, the positive electrode active material containing Li, M', and oxygen, where M' is - Ni with a content x of x ≥ 80.0 at% with respect to M', - Co with a content y of 0.0 ≤ y ≤ 20.0 at% with respect to M', - Mn with a content z of 0.0 ≤ z ≤ 20.0 at% with respect to M', - D with a content a of 0.0 ≤ a ≤ 5.0 at% with respect to M', where D is at least one element selected from the group consisting of Ba, Ca, Cr, Fe, Mg, Mo, S, Si, Sr, Ti, Y, V, W, and Zn, - B with a content b of 0.0 < b ≤ 4.0 at% with respect to M', - Nb with a content c of 0.0 < c ≤ 4.0 at% with respect to M', - Al with a content d of 0.0 ≤ d ≤ 4.0 at%, preferably 0.0 < d ≤ 4.0 at% with respect to M', and - Zr with a content e of 0.0 ≤ e ≤ 4.0 at% with respect to M', and - x, y, z, a, b, c, d, and e are measured by ICP - OES, - x + y + z + a + b + c + d + e is 100.0 at%, The positive electrode active material has a B content B defined as b / (x + y + z + b + c + d + e), A The positive electrode active material has the B content B, B where B B is determined by XPS analysis, and B B is expressed as the atomic content with respect to the total atomic content of Ni, Co, Mn, B, Nb, Al, and Zr measured by XPS analysis, and the ratio B B / B A > 10.0, The specific surface area of the positive electrode active material is 0.50 m 2 / g or more and 1.50 m 2 / g or less. This relates to the positive electrode active material.

[0017] In a preferred embodiment, x ≥ 82.0 at% with respect to M', preferably x ≥ 84.0 at%.

[0018] In a preferred embodiment, x ≤ 99.0 at%, preferably x ≤ 97.0 at%, relative to M'.

[0019] In a preferred embodiment, y ≥ 1.0 at%, preferably y ≥ 1.5 at%, and more preferably y ≥ 2.0 at% relative to M'.

[0020] In a preferred embodiment, y ≤ 15.0 at%, preferably y ≤ 13.0 at%, and more preferably y ≤ 10.0 at% relative to M'.

[0021] In a preferred embodiment, z ≥ 1.0 at%, preferably z ≥ 1.5 at%, and more preferably z ≥ 2.0 at% relative to M'.

[0022] In a preferred embodiment, z ≤ 15.0 at%, preferably z ≤ 13.0 at%, and more preferably z ≤ 10.0 at% relative to M'.

[0023] In a preferred embodiment, with respect to M', the range is 0.1 ≤ a ≤ 3.5 at%, preferably 0.1 ≤ a ≤ 2.5 at%, and more preferably 0.1 ≤ a ≤ 1.0 at%.

[0024] In a preferred embodiment, with respect to M', the range is 0.1 ≤ b ≤ 3.5 at%, preferably 0.1 ≤ b ≤ 2.5 at%, and more preferably 0.1 ≤ b ≤ 1.5 at%.

[0025] In a preferred embodiment, with respect to M', c is 0.1 ≤ c ≤ 3.5 at%, preferably 0.1 ≤ c ≤ 2.5 at%, and more preferably 0.1 ≤ c ≤ 1.0 at%.

[0026] In a preferred embodiment, with respect to M', 0.1 ≤ d ≤ 3.5 at%, preferably 0.1 ≤ d ≤ 2.0 at%, and more preferably 0.1 ≤ d ≤ 1.0 at%.

[0027] In a preferred embodiment, 0.1 ≦ e ≦ 3.5 at%, preferably 0.1 ≦ e ≦ 2.0 at%, more preferably 0.1 ≦ e ≦ 1.0 at% with respect to M'.

[0028] In a preferred embodiment, the positive electrode active material is represented by the following formula Li f Ni x1 Mn y1 Co z1 D a1 B b1 Nb c1 Al d1 Zr e1 (O)2 (where f is 0.90 ≦ f ≦ 1.10, preferably 0.95 ≦ f ≦ 1.05, more preferably 0.98 ≦ f ≦ 1.02, most preferably about 1.00, x1 is 0.80 ≦ x1 ≦ 0.99, preferably 0.82 ≦ x1 ≦ 0.97, more preferably 0.84 ≦ x1 ≦ 0.95, most preferably about 0.94, y1 is 0.00 ≦ y1 ≦ 0.20, preferably 0.01 ≦ y1 ≦ 0.15, more preferably 0.02 ≦ y1 ≦ 0.13, most preferably about 0.03, z1 is 0.00 ≦ z1 ≦ 0.20, preferably 0.01 ≦ z1 ≦ 0.15, more preferably 0.02 ≦ z1 ≦ 0.13, most preferably about 0.03, a1 is 0.000 ≦ a1 ≦ 0.050, preferably 0.001 ≦ a1 ≦ 0.035, more preferably 0.001 ≦ a1 ≦ 0.010, most preferably about 0.000, b1 is 0.000 < b1 ≦ 0.040, preferably 0.001 ≦ b1 ≦ 0.035, more preferably 0.001 ≦ b1 ≦ 0.010, most preferably about 0.010, c1 is 0.000 < c1 ≦ 0.040, preferably 0.001 ≦ c1 ≦ 0.035, more preferably 0.001 ≦ c1 ≦ 0.010, most preferably about 0.005, d1 is 0.000 < d1 ≦ 0.040, preferably 0.001 ≦ d1 ≦ 0.035, more preferably 0.001 ≦ d1 ≦ 0.010, most preferably, about 0.006, e1 is 0.000 < e1 ≦ 0.040, preferably 0.001 ≦ e1 ≦ 0.035, more preferably 0.001 ≦ e1 ≦ 0.010, and most preferably about 0.004, and is based on (x1 + y1 + z1 + a1 + b1 + c1 + d1 + e1 = 1.00).

[0029] In the framework of the present invention, at% means atomic percentage. The at% or "atomic percent" of a given element means the percentage of the atoms of that element among all the atoms in the claimed composition.

[0030] ICP - OES provides the weight percentage (wt%) of each element contained in the substance whose composition is determined by this technique. The conversion from wt% to at% is as follows. The at% (E at1 ) of the first element E1 in the substance can be converted from a given wt% (E wt1 ) of the first element E1 in the substance by applying the following formula.

[0031]

Equation

[0032] The inventors of the present invention have found that both an increase in DQ1 and a reduction in capacity decay of a rechargeable lithium-ion battery can be achieved by the cathode active material according to the present invention. Specifically, the inventors of the present invention have found that the cathode active material according to the present invention contains Nb and 80 at% or more of Ni, is coated with B, and has a value of 0.50 m 2 / g to 1.50 m 2We found that rechargeable lithium-ion batteries containing a positive electrode active material with a specific surface area in the range of / g exhibit increased DQ1 and reduced capacity decay.

[0033] B coating is B B / B A It can be determined by the ratio of B. B / B A If the value exceeds 10.0, it is considered that B coating has been applied. A and B B It is defined as the atomic content relative to the total atomic content of Ni, Co, Mn, B, Nb, Al, and Zr, and is expressed as follows:

[0034]

number

[0035] B A The content of Ni, Co, Mn, B, Nb, Al, and Zr in was measured by ICP-OES, and B B The content of Ni, Co, Mn, B, Nb, Al, and Zr is measured by XPS analysis.

[0036] Table 1 shows some symbols for positive electrode active materials to illustrate the technical effects of the present invention.

[0037] [Table 1]

[0038] The inventors of the present invention have found that the DQ1 of a rechargeable lithium-ion battery containing CAM1 is lower than that of a rechargeable lithium-ion battery containing CAM2, but the capacity decay of CAM2 is much greater than that of CAM1. That is, when Nb is further included in the transition metal composite precursor of CAM1, the DQ1 is improved, but the capacity decay worsens considerably. The inventors of the present invention have also found that the capacity decay of CAM3 is much smaller than that of CAM2, and the DQ1 of CAM3 is higher than that of CAM2. That is, when a B coating layer is formed on CAM2, both the DQ1 and the capacity decay are improved overall. Furthermore, the inventors of the present invention have found that the capacity decay of CAM3 is equivalent to or worse than that of a rechargeable lithium-ion battery containing CAM4. Surprisingly, with respect to a positive electrode active material prepared by a method comprising heating a mixture containing a Li source and a transition metal composite precursor, and then mixing the heated material obtained from that mixture with an aqueous solution, the combination of the presence of Nb and a B coating improves overall capacity decay and DQ1, even in cases where the capacity decay of a rechargeable lithium-ion battery containing CAM2 with only the presence of Nb worsens.

[0039] The inventors of this invention also state that the positive electrode active material comprises Al, Nb, and B coating, and the BET is 0.50 m 2 / g~1.50m 2 When the values ​​are within the range of / g, the DC resistance after the full-cell test and the amount of gas generated by the reaction between the charged positive electrode and the electrolyte are generally improved. We found that this can be achieved by mixing a lithiated transition metal composite with an aqueous solution.

[0040] In a preferred embodiment, the positive electrode active material does not have to contain Zr, i.e., e = 0.0 at% relative to M'. The DQ1 and capacity decay of a rechargeable lithium-ion battery containing a positive electrode active material in CAM3 that does not contain Zr can be improved compared to the DQ1 and capacity decay of a rechargeable lithium-ion battery containing a positive electrode active material in CAM3 that contains Zr.

[0041] In a preferred embodiment, ratio B B / B A This can be at least 35.0, preferably at least 50.0, and more preferably at least 70.0.

[0042] In a preferred embodiment, ratio B B / B A It is less than or equal to 300.0. This is because B is higher than 300.0. B / B A This is because a positive electrode active material having [specific characteristic] may have a lower DQ1 than the positive electrode active material in the present invention.

[0043] In a preferred embodiment, the specific surface area of ​​the positive electrode active material is 0.60 m². 2 / g~1.40m 2 / g, preferably 0.65m 2 / g~1.35m 2 / g is also acceptable.

[0044] In a preferred embodiment, the positive electrode active material has a carbon content of at least 100 ppm and at most 500 ppm, as measured by the carbon combustion method.

[0045] In a preferred embodiment, the positive electrode active material comprises at least one primary particle, wherein the concentration of Nb relative to the total atomic content of Ni, Mn, Co, and Nb at the surface of the primary particle, as measured by cross-sectional TEM-EDS analysis, is higher than the concentration of Nb relative to the total atomic content of Ni, Mn, Co, and Nb at the center of the primary particle. The cross-section has an outer boundary of the primary particle, also called the "surface." The center of the primary particle is the midpoint of the longest straight line passing through the cross-section, formed by connecting any two points on the surface of the primary particle. When the concentration of Nb at the surface of the primary particle is higher than the concentration of Nb at the center of the primary particle, the high Li conductivity resulting from the Nb enrichment at the surface accelerates the movement of Li ions at the surface of the primary particle, thereby increasing the capacity of the rechargeable lithium-ion battery.

[0046] Method for manufacturing positive electrode active material In a second aspect, the present invention relates to a method for producing a positive electrode active material according to the first aspect, comprising the following sequential steps: Step 1) A step of mixing a Li source and a transition metal composite precursor containing Ni, optionally Co, and optionally Mn with an Nb-containing compound to obtain a first mixture. Step 2) A step of heating the first mixture at a temperature of 600°C to 900°C to obtain the first heated substance, Step 3) Mixing the first heated substance with water to obtain a slurry, filtering it, and then drying the slurry to obtain a dried powder, Step 4) A step of mixing the dried powder with the B-containing compound to obtain a second mixture, The present invention relates to a method comprising step 5) heating the second mixture at a temperature of 250°C to 500°C to obtain a positive electrode active material powder.

[0047] In a preferred embodiment, the second mixture is heated to a temperature of 250°C to 450°C.

[0048] In a preferred embodiment, the Nb-containing compound in step 1) is at least one selected from the group consisting of niobic acid, niobium oxide, and lithium niobium oxide.

[0049] In a preferred embodiment, the B-containing compound in step 4) is at least one selected from the group consisting of boric acid, boron oxide, and lithium boron oxide.

[0050] The positive electrode active material according to the first aspect of the present invention is obtained by the method according to the second aspect of the present invention. In particular, the technical features of the first aspect of the present invention, for example, the specific composition of the positive electrode active material, B B / B A >10.0, 0.50m 2 / g~1.50m 2 The specific surface area in the range of / g and the carbon content in the range of 100 ppm to 500 ppm are achieved by the method according to the second aspect of the present invention.

[0051] battery In a third aspect, the present invention relates to a battery comprising a positive electrode active material according to the first aspect.

[0052] Battery usage In a fourth aspect, the present invention relates to the use of a battery according to the third aspect.

[0053] As will be understood by those skilled in the art, all embodiments relating to the positive electrode active material according to the first embodiment can be applied mutatis mutandis to the second, third, and fourth embodiments.

[0054] Experimental analysis used in the examples In this embodiment, the following analysis method is used.

[0055] A) Inductively coupled plasma emission spectrometry (ICP-OES) measurement The amounts of Li, Ni, Co, Mn, B, Nb, Al, and Zr in the positive electrode active material powder are measured by inductively coupled plasma atomic emission spectroscopy (ICP-OES) using Agilent ICP 720-ES (Agilent Technologies). In an Erlenmeyer flask, 2 grams of the powder sample are dissolved in 10 mL of high-purity hydrochloric acid (at least 37 wt% HCl relative to the total weight of the solution). The flask is covered with glass and heated on a hot plate at 380°C until the precursor is completely dissolved. After cooling to room temperature, the solution in the Erlenmeyer flask is poured into a 250 mL volumetric flask. The volumetric flask is then filled with deionized water to the 250 mL mark and then completely homogenized.

[0056] B) Specific surface area analysis The specific surface area of ​​the positive electrode active material is measured using the Bruanauer-Emmett-Teller (BET) method with Micromeritics Tristar II 3020. To remove adsorbed species, the powder sample is heated under nitrogen (N2) gas at 300°C for 1 hour before measurement. The dried powder is placed in the sample tube. The sample is then degassed at 30°C for 10 minutes. In this apparatus, nitrogen adsorption tests are performed at 77K. By obtaining the nitrogen isothermal adsorption / desorption curve, m 2 Derive the total specific surface area of ​​the sample in units of gram.

[0057] C) Carbon analysis The carbon content of the positive electrode active material powder is measured using a Horiba Emia-Expert carbon / sulfur analyzer. One gram of positive electrode active material powder is placed in a ceramic crucible in a high-frequency induction electric furnace. 1.5 grams of tungsten and 0.2 grams of tin are added to the crucible as accelerators. The powder is heated at a programmable temperature, and the gas produced during combustion is then analyzed using an infrared detector. The carbon concentration is determined by the analysis of CO2 and CO.

[0058] D) X-ray photoelectron spectroscopy (XPS) measurement The surface of the positive electrode active material is analyzed using X-ray photoelectron spectroscopy (XPS). In XPS measurements, the signal is acquired from the top of the sample, i.e., the first few nanometers (e.g., 1 nm to 10 nm) of the surface layer. Therefore, all elements measured by XPS are contained in the surface layer.

[0059] For surface analysis of cathode active material powder particles, XPS measurements are performed using a ThermoK-α+ spectrometer (Thermo Scientific, https: / / www.thermofisher.com / order / catalog / product / IQLAADGAAFFACVMAHV). Monochromatic Al Kα line (hν=1486.6eV) is used with a spot size of 400 μm and a measurement angle of 45°. A broad survey scan is performed at a pass energy of 200 eV to identify elements present on the surface. The C1s peak with maximum intensity (or center) at a binding energy of 284.8 eV is used as the calibration peak position after data acquisition. Subsequently, for each identified element, at least 10 precise narrow scans are performed at 50 eV to determine the accurate surface composition.

[0060] Curve fitting is performed using CasaXPS version 2.3.19PR1.0 (Casa Software, http: / / www.casaxps.com / ) with Shirley-type background processing and Schofield sensitivity coefficients. The fitting parameters are as shown in Table 2a. The linear shape GL(30) is a Gauss / Lorentz product equation containing 70% Gaussian lines and 30% Lorentz lines. LA(α, β, m) is an asymmetric linear shape, where α and β define the tail spread of the peak and m defines the width.

[0061] [Table 2]

[0062] For the Al, Mn, and Co peaks, restrictions are set for each defined peak according to Table 2b. All related Ni3p peaks, including Ni3p3, Ni3p1, Ni3p3 satellite, and Ni3p1 satellite, are not quantified.

[0063] [Table 3]

[0064] Surface content of B determined by XPS (B B This is expressed as the atomic content of B in the surface layer of a particle divided by the total content of Ni, Co, Mn, B, Nb, Al, and Zr in that surface layer. This is calculated as follows:

[0065]

number

[0066] XPS peak location information can be easily obtained in the region and component report specifications after fitting. The XPS graph of EX2B is shown in Figure 1.

[0067] E) Scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) measurements Electron microscope images were obtained by thinning the particles using a Thermo Fisher Helios FIB-SEM to acquire cross-sectional images, and then measured using scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray spectroscopy (EDS) were performed at 300 kV using a Super X detector with an aberration-corrected FER titanium transmission electron microscope.

[0068] F) Coin cell test F-1) Coin cell fabrication For the preparation of the positive electrode, a slurry containing positive electrode active material powder, conductive agent (Super P, Timcal), and binder (KF#9305, Kureha) in a weight ratio of 96.5:1.5:2.0 in solvent (NMP, Mitsubishi) is prepared using a high-speed homogenizer. The homogenized slurry is spread onto one side of an aluminum foil using a doctor blade coater with a 170 μm gap. The slurry-coated foil is dried in an oven at 120°C and then pressed using a calendering tool. It is then dried again in a vacuum oven to completely remove any residual solvent from the electrode film. The coin cell is assembled in a glove box filled with argon. A separator (Celgard 2320) is placed between the positive electrode and the lithium foil piece to be used as the negative electrode. 1M LiPF6 in EC / DMC (1:2) is used as the electrolyte and is dropped between the separator and the electrode. Next, the coin cell is completely sealed to prevent electrolyte leakage.

[0069] F-2) Test Method The test method is the conventional "constant cutoff voltage" test. The conventional coin cell test in this invention follows the schedule shown in Table 3. Each cell is cycled at 25°C using a Toscat-3100 computer-controlled galvanostatic cycling station (manufactured by Toyo).

[0070] The schedule uses a 1C current definition of 220mA / g within the 4.3V to 3.0V / Li metal window range. The capacitance decay rate (QF) is obtained by the following formula, where DQ1 is the discharge capacity of the first cycle.

[0071]

number

[0072] [Table 4]

[0073] G) Full Cell Test G-1) Full cell preparation A 2000mAh pouch-type cell is prepared as follows: Positive electrode active material powder, Super-P (Super-P,Imerys Graphite & Carbon) as a positive electrode conductive agent, and polyvinylidene fluoride (PVDF S5130,Solvay) as a positive electrode binder are added to N-methyl-2-pyrrolidone (NMP) as a dispersion medium such that the mass ratio of the positive electrode active material powder, the positive electrode conductive agent Super-P, and the positive electrode binder is 95:3:2. The positive electrode active material powder is a mixture of 70 wt% CEX7 or EX2 and 30 wt% single-crystal lithium transition metal oxide, the single-crystal lithium transition metal oxide having a D50 of 3.7 μm and containing Ni, Mn, and Co in an atomic ratio of 88:5:7, and also containing Al, B, W, and Zr. The mixture is then kneaded to prepare a positive electrode mixed slurry. Next, the resulting positive electrode slurry is applied to both sides of a positive electrode current collector made of 20 μm thick aluminum foil. The width of the application area is 88.5 mm and the length is 425 mm. The typical load weight of the positive electrode active material is approximately 14.8 ± 1 mg / cm³. 2Next, the electrodes are dried and calendered using a pressure of 4.5 MPa. Additionally, an aluminum plate, which will function as a positive electrode current collector tab, is arc-welded to the end of the positive electrode.

[0074] A commercially available negative electrode is used. In short, a mixture of artificial graphite, carbon (Super P(Imerys)), sodium carboxymethylcellulose, and styrene-butadiene rubber in a mass ratio of 95.0 / 1 / 1.5 / 2.5 is applied to both sides of a copper foil. A nickel plate, which functions as a negative electrode current collector tab, is arc-welded to the ends of the negative electrode. The typical load weight of the negative electrode active material is approximately 10 ± 1 mg / cm³. 2 That is the case.

[0075] A non-aqueous electrolyte is obtained by dissolving lithium hexafluorophosphate (LiPF6) salt at a concentration of 1.2 mol / L in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1. This electrolyte contains 1.0 wt.% lithium difluorophosphate (LiPO2F2) and 1.0 wt.% vinylene carbonate (VC) as additives.

[0076] A positive electrode sheet, a negative electrode sheet, and a microporous polymer separator sheet (13 μm) inserted between them are spirally wound using a winding core rod to obtain a spirally wound electrode assembly. The assembly and electrolyte are then placed in an aluminum laminated pouch in an air-drying chamber with a dew point of -50°C, thereby fabricating a flat pouch-type lithium secondary battery. The design capacity of the secondary battery is 2000 mAh when charged to 4.20 V. The full cell test procedure uses a 1C current definition of 2000 mA / g.

[0077] G-2) Cycle Life Test A. Pre-charging and Formation The prepared, dried batteries are impregnated in a non-aqueous electrolyte solution at room temperature for 8 hours. The batteries are pre-charged to 14% of their theoretical capacity with a current of 0.25C and aged at room temperature for 1 day. The batteries are then degassed using a pressure of -760 mmHg for 30 seconds and sealed in an aluminum pouch. During measurement, the pouch is assembled in a press jig equipped with a silicone pad.

[0078] Charge the battery with a current of 0.2C in CC mode (constant current) until it reaches 4.2V, and in CV mode (constant voltage) until the cutoff current of C / 20 is reached. Discharge the battery with a current of 0.2C in CC mode until it drops to 2.7V. Then fully charge it with a current of 0.50C in CC mode until it reaches 4.2V, and in CV mode until the cutoff current of C / 20 is reached.

[0079] Next, discharge the cell in CC mode with a current of 0.50C until the voltage drops to 2.7V. Then, recharge it in CC mode until the voltage reaches 4.2V, and then in CV mode with a current of 0.5C until the cutoff current of C / 20 is reached. The final charging process is performed at 25°C.

[0080] B. Expansion Test A 2000mAh pouch-type battery, prepared using the method described above, is fully charged to 4.2V and placed in an oven heated to 90°C, where it is left for 20 hours. The charged positive electrode reacts with the electrolyte at 90°C, generating gas. This gas causes expansion. After 20 hours, the increase in thickness ((thickness after storage - thickness before storage) / thickness before storage × 100%) is measured.

[0081] C. Cycle Life Test A lithium secondary full-cell battery is continuously charged and discharged at 45°C under the following conditions, and its charge-discharge cycle performance is determined. - Charge in CC mode at a 1C rate until 4.2V, then in CV mode until C / 20 is reached. - Next, set the cell to pause for 10 minutes. - Discharge in CC mode at a 1C rate until the voltage drops to 2.7V. - Next, set the cell to pause for 10 minutes. - Perform up to 600 charge-discharge cycles. Every 100 cycles, discharge in CC mode at a rate of 0.1C until the voltage drops to 2.7V.

[0082] The internal resistance or DC resistance (DCR) is measured at 1.5C for 10 seconds at the start of each 100-cycle cycle and at the end of the 600th cycle. [Examples]

[0083] The present invention will be further explained in the following examples. Example 1 The positive electrode active material EX1 is obtained by the following process: 1) Preparation of the first mixture: 274.0 grams of LiOH, 3.0 grams of Al2O3, 7.0 grams of Nb2O5, and 1.0 kilogram of Ni 0.94 Mn 0.03 Co 0.03 (OH)2 is mixed homogeneously to obtain the first mixture. 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 740°C for 12 hours to obtain the first heated substance. 3) Preparation and drying of slurry: Mix the first heated substance with 5 liters of deionized water and stir for 10 minutes. After stirring, filter the mixture to prepare a cake, and then dry the slurry under a vacuum atmosphere at 140°C for 10 hours. 4) Preparation of the second mixture: 1.0 kilogram of the dried substance is homogeneously mixed with 6.0 grams of H3BO3 to obtain the second mixture. 5) Second heating: The second mixture obtained from step 4) is heated at 300°C for 8 hours under an oxygen atmosphere and then cooled to room temperature to obtain the positive electrode active material EX1.

[0084] Comparative Example 1 The positive electrode active material CEX1 is obtained by the following process: 1) Preparation of the first mixture: 272.0 grams of LiOH, 3.0 grams of Al2O3, and 1.0 kilogram of Ni0.94 Mn 0.03 Co 0.03 (OH)2 is mixed homogeneously to obtain the first mixture. 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 720°C for 12 hours and then cooled to room temperature to obtain the first heated substance. 3) Preparation and drying of slurry: Mix the first heated substance with 5 liters of deionized water and stir for 10 minutes. After stirring, filter the mixture to prepare a cake, and then dry the slurry under a vacuum atmosphere at 140°C for 10 hours. 4) Second heating: The dried material obtained from step 3) is heated at 300°C for 8 hours in an oxygen atmosphere and then cooled to room temperature to obtain the positive electrode active material CEX1.

[0085] Comparative Example 2 The positive electrode active material CEX2 is obtained by the following process: 1) Preparation of the first mixture: 272.0 grams of LiOH, 3.0 grams of Al2O3, and 1.0 kilogram of Ni 0.94 Mn 0.03 Co 0.03 (OH)2 is mixed homogeneously to obtain the first mixture. 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 720°C for 12 hours and then cooled to room temperature to obtain the first heated substance. 3) Preparation and drying of slurry: Mix the first heated substance with 5 liters of deionized water and stir for 10 minutes. After stirring, filter the mixture to prepare a cake, and then dry the slurry under a vacuum atmosphere at 140°C for 10 hours. 4) Preparation of the second mixture: 1.0 kilogram of the dried substance is homogeneously mixed with 6.0 grams of H3BO3 to obtain the second mixture. 5) Second heating: The second mixture obtained from step 4) is heated at 300°C for 8 hours under an oxygen atmosphere and then cooled to room temperature to obtain the positive electrode active material CEX2.

[0086] Comparative Example 3 The positive electrode active material CEX3 is obtained by the following process: 1) Preparation of the first mixture: 274.0 grams of LiOH, 3.0 grams of Al2O3, 7.0 grams of Nb2O5, and 1.0 kilogram of Ni 0.94 Mn 0.03 Co 0.03 (OH)2 is mixed homogeneously to obtain the first mixture. 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 740°C for 12 hours and then cooled to room temperature to obtain the first heated substance. 3) Preparation and drying of slurry: Mix the first heated substance with 5 liters of deionized water and stir for 10 minutes. After stirring, filter the mixture to prepare a cake, and then dry the slurry under a vacuum atmosphere at 140°C for 10 hours. 4) Second heating: The dried material obtained from step 3) is heated at 300°C for 8 hours in an oxygen atmosphere and then cooled to room temperature to obtain the positive electrode active material CEX3.

[0087] Example 2 The positive electrode active material EX2 is obtained by the following process: 1) Preparation of the first mixture: 274.0 grams of LiOH, 3.0 grams of Al2O3, 7.0 grams of Nb2O5, 10.0 grams of ZrO2, and 1.0 kilogram of Ni 0.94 Mn 0.03 Co 0.03 (OH)2 is mixed homogeneously to obtain the first mixture. 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 740°C for 12 hours and then cooled to room temperature to obtain the first heated substance. 3) Preparation and drying of slurry: Mix the first heated substance with 5 liters of deionized water and stir for 10 minutes. After stirring, filter the mixture to prepare a cake, and then dry the slurry under a vacuum atmosphere at 140°C for 10 hours. 4) Preparation of the second mixture: 1.0 kilogram of the dried substance is homogeneously mixed with 6.0 grams of H3BO3 to obtain the second mixture. 5) Second heating: The second mixture obtained from step 4) is heated at 300°C for 8 hours under an oxygen atmosphere and then cooled to room temperature to obtain the positive electrode active material EX2.

[0088] Comparative Example 4 The positive electrode active material CEX4 is obtained by the following process: 1) Preparation of the first mixture: 272.0 grams of LiOH, 3.0 grams of Al2O3, 10.0 grams of ZrO2, and 1.0 kilogram of Ni 0.94 Mn 0.03 Co 0.03 (OH)2 is mixed homogeneously to obtain the first mixture. 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 745°C for 12 hours and then cooled to room temperature to obtain the first heated substance. 3) Preparation and drying of slurry: Mix the first heated substance with 5 liters of deionized water and stir for 10 minutes. After stirring, filter the mixture to prepare a cake, and then dry the slurry under a vacuum atmosphere at 140°C for 12 hours. 4) Second heating: The dried material obtained from step 3) is heated at 300°C for 8 hours in an oxygen atmosphere and then cooled to room temperature to obtain the positive electrode active material CEX4.

[0089] Comparative Example 5 The positive electrode active material CEX5 is obtained by the following process: 1) Preparation of the first mixture: 272.0 grams of LiOH, 3.0 grams of Al2O3, 10.0 grams of ZrO2, and 1.0 kilogram of Ni 0.94 Mn 0.03 Co 0.03 (OH)2 is mixed homogeneously to obtain the first mixture. 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 715°C for 12 hours and then cooled to room temperature to obtain the first heated substance. 3) Preparation and drying of slurry: Mix the first heated substance with 5 liters of deionized water and stir for 10 minutes. After stirring, filter the mixture to prepare a cake, and then dry the slurry under a vacuum atmosphere at 140°C for 10 hours. 4) Preparation of the second mixture: 1.0 kilogram of the dried substance is homogeneously mixed with 6.0 grams of H3BO3 to obtain the second mixture. 5) Second heating: The second mixture obtained from step 4) is heated at 300°C for 8 hours under an oxygen atmosphere and cooled to room temperature to obtain the positive electrode active material CEX5.

[0090] Comparative Example 6 The positive electrode active material CEX6 is obtained by the following process: 1) Preparation of the first mixture: 272.0 grams of LiOH, 3.0 grams of Al2O3, 7.0 grams of Nb2O5, and 10.0 grams of ZrO2, and 1.0 kilogram of Ni 0.94 Mn 0.03 Co 0.03 (OH)2 is mixed homogeneously to obtain the first mixture. 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 740°C for 12 hours and then cooled to room temperature to obtain the first heated substance. 3) Preparation and drying of slurry: Mix the first heated substance with 5 liters of deionized water and stir for 10 minutes. After stirring, filter the mixture to prepare a cake, and then dry the slurry under a vacuum atmosphere at 140°C for 10 hours. 4) Second heating: The dried material obtained from step 3) is heated at 300°C for 8 hours in an oxygen atmosphere and then cooled to room temperature to obtain the positive electrode active material CEX6.

[0091] Comparative Example 7 The positive electrode active material CEX7 is obtained by the following process: 1) Preparation of the first mixture: 272.0 grams of LiOH, 7.0 grams of Nb2O5, 10.0 grams of ZrO2, and 1.0 kilogram of Ni 0.92 Mn 0.03 Co 0.05 (OH)2 is mixed homogeneously to obtain the first mixture. 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 770°C for 12 hours and then cooled to room temperature to obtain the first heated substance. 3) Preparation and drying of slurry: Mix the first heated substance with 5 liters of deionized water and stir for 10 minutes. After stirring, filter the mixture to prepare a cake, and then dry the slurry at 140 °C for 10 hours under a vacuum atmosphere. 4) Preparation of the second mixture: Homogeneously mix 1.0 kilogram of the dried substance with 6.0 grams of H3BO3 to obtain the second mixture. 5) Second heating: Heat the second mixture obtained from step 4) at 300 °C for 8 hours under an oxygen atmosphere, and cool it to room temperature to obtain the positive electrode active material CEX7.

[0092]

Table 5

[0093] Table 4 summarizes the chemical properties of the examples and comparative examples, such as the composition analyzed by ICP-OES and the specific surface area (SSA) analyzed by the BET method.

[0094]

Table 6

[0095] Table 5 summarizes the B B / B ratio, carbon content, and electrochemical properties such as DQ1 and capacity decay.

[0096] In Table 5, for EX1, EX2, and CEX5, the XPS analysis results of B (B B ) are compared with the ICP-OES results of B (B A ). The result of B greater than 0 B indicates that the B exists on the surface of the positive electrode active material in relation to the XPS measurement where the signal is obtained from the first few nanometers (e.g., 1 nm to 10 nm) at the top of the sample. On the other hand, B calculated from the ICP-OES results Ais the B content of the entire particle. Therefore, the ratio of the XPS result to the ICP-OES result, for example, B B / B A being greater than 1 indicates that the B is mainly present on the surface of the positive electrode active material. The B B / B A value increasing corresponds to an increase in the presence of B on the surface of the positive electrode active material. The B B / B A values in EX1, EX2, and CEX5 are all higher than 10.0, which confirms the presence of B on the surface of the particles according to the present invention. FIG. 1 is a representative XPS spectrum showing the B1s peak of EX2.

[0097] FIG. 2 is a STEM-EDS line scan graph between the surfaces of two primary particles for EX1, and A and B represent different primary particles respectively. It is clearly observed that the Nb concentration on the surface of the primary particle is higher than that inside the primary particle.

[0098] CEX1 is a substance containing Ni, Mn, Co, and Al but not containing B and Nb. CEX3 is a substance containing Nb in addition to the elements of CEX1. The discharge capacity (DQ1) of CEX3 in the first cycle is 228.7 mAh / g, which is higher than the DQ1 of CEX1 having a value of 209.9 mAh / g. However, when comparing the capacity decay rate (QF), the electrochemical cell containing CEX3 having QF of 41.2% / 100 cycles shows worse stability than the electrochemical cell containing CEX1 having QF of 28.1% / 100 cycles.

[0099] Referring to Figure 3, a comparison of the experimental results for CEX1 and CEX3 shows that the presence of Nb worsens the QF. Therefore, Nb is not considered advantageous from the standpoint of electrochemical stability. However, the experimental results for EX1 show an unexpected synergistic effect in which both QF and DQ1 are improved by including the mixing process with Nb, B coating, and aqueous solution. In detail, it is clearly observed that the electrochemical cell containing EX1 has the highest DQ1 and best electrochemical stability among EX1, CEX1, CEX2, and CEX3, with a DQ1 of 230.9 mAh / g and a QF of 16.5% / 100 cycles. Regarding EX2, it is observed that EX2 exhibits electrochemical stability with the highest DQ1 of 229.7 mAh / g and a QF of 20.7% / 100 cycles among EX2, CEX4, CEX5, and CEX6, which is lower than that of CEX4 and CEX6 and equivalent to CEX5.

[0100] CEX7 is substantially identical to EX2, except that it does not contain Al. The DQ1 and QF of CEX7 are approximately the same as those of EX2. However, Table 6 below, which shows the full cell results for the percentage increase in cell thickness after 20 hours and the DCR after 600 cycles for EX2 and CEX7, shows that EX2 shows a significant improvement in full cell results compared to CEX7.

[0101] [Table 7]

[0102] In detail, the cell thickness of EX2 after a full 20-hour cell cycle increased by 34.3%, which is smaller than the increase in cell thickness of CEX7, and a smaller increase in cell thickness indicates less gas is produced during the cycle. The DCR of EX2 after 600 cycles is 114.3%, which is lower than the DCR of CEX7. Therefore, the positive electrode active material contains Al, Nb, and B coating, and the BET is 0.50m 2 / g~1.50m 2When the values ​​are within the range of / g, the QF, DQ1, and the full-cell test results described above are generally improved, confirming that this can be achieved by mixing the lithiated transition metal composite with an aqueous solution.

Claims

1. A positive electrode active material for a rechargeable lithium-ion battery, wherein the positive electrode active material contains Li, M' and oxygen, and M' is - Ni content x such that x ≥ 80.0 at% relative to M', - Co with a content y of 0.0 ≤ y ≤ 20.0 at% relative to M', - Mn with a content z of 0.0 ≤ z ≤ 20.0 at% relative to M', - D having an content a of 0.0 ≤ a ≤ 5.0 at% relative to M', where D is at least one element selected from the group consisting of Ba, Ca, Cr, Fe, Mg, Mo, S, Si, Sr, Ti, Y, V, W, and Zn, - B is the content b of M', where b is 0.0 < b ≤ 4.0 at%. - Nb with a content c of 0.0 < c ≤ 4.0 at% relative to M', - Al with a content of d such that 0.0 ≤ d ≤ 4.0 at% relative to M', and - Contains Zr with a content of e of 0.0 ≤ e ≤ 4.0 at% relative to M', - x, y, z, a, b, c, d, and e are measured by ICP-OES. - x + y + z + a + b + c + d + e is 100.0 at%, The positive electrode active material has a B content defined as b / (x+y+z+b+c+d+e). Ａ The positive electrode active material has a B content of B Ｂ It has B Ｂ However, B is determined by XPS analysis. Ｂ However, it is expressed as the atomic content relative to the total atomic content of Ni, Co, Mn, B, Nb, Al, and Zr measured by XPS analysis, and ratio B Ｂ / B Ａ > 10.0, The specific surface area of ​​the positive electrode active material is 0.50 m². ２ / g or more and 1.50m ２ A positive electrode active material that is less than or equal to / g.

2. The positive electrode active material according to claim 1, wherein e = 0.0 at% relative to M'.

3. The ratio B Ｂ / B Ａ is at least 35.0, at least 50.0, or at least 70.0, and the positive electrode active material according to claim 1.

4. The specific surface area of ​​the positive electrode active material is 0.60 m². ２ / g ~ 1.40m ２ / g, or 0.65m ２ / g to 1.35m ２ The positive electrode active material according to claim 1, wherein the value is / g.

5. The positive electrode active material according to claim 1, having a carbon content of at least 100 ppm and at most 500 ppm when measured by the carbon combustion method.

6. The positive electrode active material according to claim 1, comprising primary particles, wherein the concentration of Nb relative to the total atomic content of Ni, Mn, Co, and Nb on the surface of the primary particles is higher than the concentration of Nb relative to the total atomic content of Ni, Mn, Co, and Nb at the center of the primary particles, and the concentration of Nb is measured by cross-sectional STEM-EDS analysis.

7. The positive electrode active material according to claim 1, wherein x ≥ 82.0 at% or x ≥ 84.0 at% relative to M'.

8. The positive electrode active material according to claim 1, wherein x ≤ 99.0 at% or x ≤ 97.0 at% with respect to M'.

9. The positive electrode active material according to claim 1, wherein y ≤ 15.0 at%, y ≤ 13.0 at%, or y ≤ 10.0 at% relative to M'.

10. A method for producing a positive electrode active material according to any one of claims 1 to 9, comprising the following sequential steps: Step 1) A step of mixing a Li source and a transition metal composite precursor containing Ni, optionally Co, and optionally Mn with an Nb-containing compound to obtain a first mixture, Step 2) A step of heating the first mixture at a temperature of 600°C to 900°C to obtain the first heated substance, Step 3) The first heated substance is mixed with an aqueous solution to obtain a slurry, which is then filtered, and the slurry is dried to obtain a dried powder. Step 4) A step of mixing the dried powder with a B-containing compound to obtain a second mixture, A method comprising step 5) heating the second mixture at a temperature of 250°C to 500°C to obtain a positive electrode active material powder.

11. The method according to claim 10, wherein the second mixture is heated to a temperature of 250°C to 450°C.

12. The method according to claim 10, wherein the Nb-containing compound in step 1) is at least one selected from the group consisting of niobic acid, niobium oxide, and lithium niobium oxide.

13. The method according to claim 10, wherein the B-containing compound in step 4) is at least one selected from the group consisting of boric acid, boron oxide, and lithium boron oxide.

14. A battery comprising the positive electrode active material described in any one of claims 1 to 9.

15. Use of the battery according to claim 14 in an electric vehicle or a hybrid electric vehicle.

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