Lithium-nickel composite oxides as cathode 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 cathode active material for rechargeable lithium-ion batteries. More specifically, the present invention relates to a cathode active material comprising lithium (Li), M', and oxygen, where M' comprises niobium (Nb) and 80 at% or more of nickel (Ni). The cathode active material is coated with boron (B) and has a specific surface area. The present invention also relates to a method for producing the cathode active material, a battery including the cathode active material, and the use of the battery including the cathode active material in an electric vehicle or hybrid electric vehicle. [Background technology]

[0002] Rechargeable lithium-ion batteries containing Ni-rich (i.e., containing more than 80 at% Ni) cathode active materials have been known to have the advantages of high specific energy capacity and high operating voltage. Furthermore, Yehonatan Levartovsky et al., ACS Appl. Mater. Interface 2021, 13, 34145-34156, reported that electrodes containing Nb and 85 at% Ni cathode active materials have a slightly higher initial discharge capacity (DQ1). However, Figure 3 in Chinese Patent Application Publication No. 106505195(A) shows experimental results showing that lithium-ion batteries containing Nb-containing cathode active materials have a large capacity fade. Capacity fade, or capacity loss, is a phenomenon observed in the use of rechargeable batteries, in which the amount of charge a battery can deliver at its rated voltage decreases with use. While Nb is advantageous for Ni-rich cathode active materials in terms of DQ1, it is undesirable in terms of capacity fade. Furthermore, the inclusion of Nb alone does not resolve the increased gas evolution and DC resistance after full-cell testing. Therefore, there is a need for a Ni-rich positive electrode active material containing Nb that has low capacity fade, high DQ1, and lower gas evolution and DC resistance after full-cell testing. [Prior art documents] [Patent documents]

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

[0004] [Non-Patent Document 1] Yehonatan Levartovsky et al.,ACS Appl.Mater.Interface 2021,13,34145-34156 Summary of the Invention [Problem to be solved by the invention]

[0005] A first object of the present invention is to provide a positive electrode active material containing Nb and 80 at % or more of Ni, which has improved electrochemical properties such as high DQ1 and low capacity fade.

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

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

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

[0009] A first object is to provide a cathode active material for a rechargeable lithium ion battery, the cathode active material comprising Li, M', and oxygen, wherein M' is: Ni with a content x of 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, 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 contains - 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). A The cathode active material has a B content B. B It has B. B B is determined by XPS analysis. 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 achieved by providing a cathode active material that is 0.50 m 2 / g or more and 1.50 m 2 / g or less.

[0010] The second object is a method for manufacturing the cathode active material, which comprises 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) mixing the dry powder with a B-containing compound to obtain a second mixture; 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 object is achieved by providing a battery containing the positive electrode active material.

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

[0013] The cathode active material of the present invention increases DQ1 and reduces capacity fade when used in rechargeable lithium ion batteries. [Brief explanation of the drawings]

[0014] [Figure 1] This is the B1s peak in the XPS spectrum of EX2. [Figure 2] 1 is a STEM-EDS line scan graph of EX1 (A and B each show a different primary particle). [Figure 3] DQ1 vs. capacitance decay for EX1, EX2, and CEX1 to CEX6. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following detailed description describes preferred embodiments in detail to enable the practice of the invention. While the invention has been described with reference to these specific preferred embodiments, it will be understood that the invention is not limited to these preferred embodiments. To the contrary, the invention includes numerous alternatives, modifications, and equivalents, as will become apparent upon consideration of the following detailed description.

[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 a 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 %, with respect to M′.

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

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

[0021] In a preferred embodiment, z≧1.0 at %, preferably z≧1.5 at %, 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 %, with respect to M′.

[0023] In a preferred embodiment, 0.1≦a≦3.5 at %, preferably 0.1≦a≦2.5 at %, and more preferably 0.1≦a≦1.0 at %, with respect to M′.

[0024] In a preferred embodiment, 0.1≦b≦3.5 at %, preferably 0.1≦b≦2.5 at %, and more preferably 0.1≦b≦1.5 at %, with respect to M′.

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

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

[0027] In a preferred embodiment, for M’, 0.1 ≦ e ≦ 3.5 at%, preferably 0.1 ≦ e ≦ 2.0 at%, more preferably 0.1 ≦ e ≦ 1.0 at%.

[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 the 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 are achieved by the positive electrode active material according to the present invention. Specifically, the inventors of the present invention have found that the positive electrode 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 have found that rechargeable lithium-ion batteries containing cathode active materials with specific surface areas in the range of 0.15 to 0.25 μm / g exhibit increased DQ1 and reduced capacity fade.

[0033] B coating is B B / B A It is calculated by the ratio of B B / B A If the value is greater than 10.0, it is considered to have a B coating. A and B B is defined as the atomic content of Ni, Co, Mn, B, Nb, Al, and Zr 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 Ni, Co, Mn, B, Nb, Al, and Zr contents in the B B The contents of Ni, Co, Mn, B, Nb, Al, and Zr in the alloy are measured by XPS analysis.

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

[0037] [Table 1]

[0038] The present inventors found that the DQ1 of a rechargeable lithium-ion battery containing CAM1 was lower than that of a rechargeable lithium-ion battery containing CAM2, but the capacity fade of CAM2 was much greater than that of CAM1. That is, when Nb was further added to the transition metal composite precursor of CAM1, the DQ1 improved, but the capacity fade became much worse. The present inventors also found that the capacity fade of CAM3 was much smaller than that of CAM2, and the DQ1 of CAM3 was higher than that of CAM2. That is, forming a B coating layer on CAM2 improved the DQ1 and capacity fade overall. Furthermore, the present inventors found that the capacity fade of CAM3 was comparable to or worse than that of a rechargeable lithium-ion battery containing CAM4. Surprisingly, for active cathode materials prepared by a method comprising heating a mixture comprising a Li source and a transition metal composite precursor, and then mixing the resulting heated material with an aqueous solution, the presence of Nb in combination with a B coating results in an overall improvement in capacity fade and DQ1, even though the capacity fade of rechargeable lithium-ion batteries containing CAM2 in which only Nb is present is worse.

[0039] The inventors of the present invention have also reported that the positive electrode active material contains Al, Nb, and B coating, and the BET is 0.50m 2 / g~1.50m 2 / g, the DC resistance after a full cell test and the amount of gas generated by the reaction between the charged positive electrode and the electrolyte were all improved, and it was found that this could be achieved by mixing the lithiated transition metal composite material with an aqueous solution.

[0040] In a preferred embodiment, the active cathode material may be Zr-free, i.e., e=0.0 at% relative to M'. The DQ1 and capacity fade of a rechargeable lithium-ion battery including an active cathode material without Zr in CAM3 may be improved compared to the DQ1 and capacity fade of a rechargeable lithium-ion battery including an active cathode material with Zr in CAM3.

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

[0042] In a preferred embodiment, the ratio B B / B A is less than 300.0 because B is higher than 300.0 B / B A This is because a positive electrode active material having the formula (I) can have a DQ1 lower than the DQ1 of the positive electrode active material of the present invention.

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

[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 includes at least one primary particle, and the Nb concentration at the surface of the primary particle relative to the total atomic content of Ni, Mn, Co, and Nb, as measured by cross-sectional TEM-EDS analysis, is higher than the Nb concentration at the center of the primary particle relative to the total atomic content of Ni, Mn, Co, and Nb. The cross section has the outer boundary of the primary particle, also referred to as the "surface." The center of the primary particle is the midpoint of the longest line formed by connecting any two points on the surface of the primary particle and passing through the cross section. When the Nb concentration at the surface of the primary particle is higher than the Nb concentration at the center of the primary particle, the high Li conductivity resulting from the Nb enrichment at the surface accelerates Li ion migration at the surface of the primary particle, thereby increasing the capacity of the rechargeable lithium-ion battery.

[0046] Method for producing positive electrode active material In a second aspect, the present invention provides a method for producing a cathode active material according to the first aspect, comprising the following successive steps: Step 1) mixing a Li 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) heating the first mixture at a temperature of 600°C to 900°C to obtain a first heated substance; step 3) mixing the first heated material with water to obtain a slurry, filtering, and then drying the slurry to obtain a dry powder; step 4) mixing the dry powder with a B-containing compound to obtain a second mixture; 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 at 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 cathode 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, such as the specific composition of the cathode active material, B B / B A >10.0, 0.50m 2 / g~1.50m 2 A specific surface area in the range of 100 ppm to 500 ppm / g and a 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 an active cathode material according to the first aspect.

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

[0053] As will be appreciated by those skilled in the art, all embodiments relating to the cathode active material according to the first aspect can be applied mutatis mutandis to the second, third and fourth aspects.

[0054] Experimental Analysis Used in the Examples In the examples, the following analytical methods are used:

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

[0056] B) Specific surface area analysis The specific surface area of ​​the positive electrode active material is measured by the Bruenauer-Emmett-Teller (BET) method using a Micromeritics Tristar II 3020. To remove adsorbed species, the powder sample is heated at 300°C for 1 hour before measurement under nitrogen (N2) gas. The dried powder is placed in a sample tube. The sample is then degassed at 30°C for 10 minutes. The nitrogen adsorption test is performed at 77K with this instrument. The m 2 The total specific surface area of ​​the sample in units of / g is derived.

[0057] C) Carbon analysis The carbon content of the cathode active material powder is measured using a Horiba Emia-Expert carbon / sulfur analyzer. 1 gram of cathode active material powder is placed in a ceramic crucible in a high-frequency induction furnace. 1.5 grams of tungsten and 0.2 grams of tin as promoters are added to the crucible. The powder is heated at a programmable temperature, and the gases produced during combustion are then analyzed using an infrared detector. The carbon concentration is determined by CO2 and CO analysis.

[0058] D) X-ray photoelectron spectroscopy (XPS) measurement The surface of the positive electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS). In XPS measurements, signals are obtained 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 the positive electrode active material powder particles, XPS measurements were performed using a Thermo K-α+ spectrometer (Thermo Scientific, https: / / www.thermofisher.com / order / catalog / product / IQLAADGAAFFACVMAHV). Monochromatic Al Kα radiation (hν = 1486.6 eV) was used with a spot size of 400 μm and a measurement angle of 45°. A broad survey scan to identify the elements present on the surface was performed with a pass energy of 200 eV. The C1s peak with maximum intensity (or center) at a binding energy of 284.8 eV was used as the calibration peak position after data collection. Then, for each identified element, at least 10 precise narrow scans were performed at 50 eV to determine the exact surface composition.

[0060] Curve fitting was performed using CasaXPS version 2.3.19PR1.0 (Casa Software, http: / / www.casaxps.com / ) using Shirley-type background processing and Scofield sensitivity coefficients. Fitting parameters are according to Table 2a. The line shape GL(30) is the Gaussian / Lorentzian product equation, including the 70% Gaussian line and the 30% Lorentzian line. LA(α, β, m) is the asymmetric line shape, where α and β define the tail broadening of the peak and m defines the width.

[0061] [Table 2]

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

[0063] [Table 3]

[0064] The surface content of B (B B ) 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. It is calculated as follows:

[0065]

number

[0066] The XPS peak position information can be easily obtained in the area and component report specifications after fitting has been performed. The XPS graph of EX2 B is shown in Figure 1.

[0067] E) Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive X-ray Spectroscopy (EDS) measurements Electron microscopy images were obtained by sectioning the particles to obtain cross-sectional images using a Thermo Fisher Helios FIB-SEM, followed by 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 on an aberration-corrected FER titanium transmission electron microscope at 300 kV using a Super X detector.

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

[0069] F-2) Test method The test method is a conventional "constant cutoff voltage" test. Conventional coin cell testing 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 in the 4.3V to 3.0V / Li metal window range. The capacity fade rate (QF) is calculated 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) Preparation of full cells A 2000 mAh pouch-type cell was prepared as follows: Positive electrode active material powder, Super-P (Imerys Graphite & Carbon) as a positive electrode conductive agent, and polyvinylidene fluoride (PVDF S5130, Solvay) as a positive electrode binder were added to N-methyl-2-pyrrolidone (NMP) as a dispersion medium so that the mass ratio of the positive electrode active material powder, the positive electrode conductive agent Super P, and the positive electrode binder was 95:3:2. The positive electrode active material powder was a mixture of 70 wt% CEX7 or EX2 and 30 wt% single-crystal lithium transition metal oxide. The single-crystal lithium transition metal oxide had a D50 of 3.7 μm and contained Ni, Mn, and Co in an atomic ratio of 88:5:7, and also contained Al, B, W, and Zr. The mixture was then kneaded to prepare a positive electrode mixed slurry. The resulting positive electrode mixed slurry was then applied to both sides of a 20 μm thick aluminum foil positive electrode current collector. The width of the applied area was 88.5 mm and the length was 425 mm. The typical loading weight of the positive electrode active material was about 14.8±1 mg / cm. 2The electrode is then dried and calendered using a pressure of 4.5 MPa. An aluminum plate is arc-welded to the end of the positive electrode to serve as the positive electrode current collector tab.

[0074] A commercially available negative electrode is used. Briefly, a mixture of artificial graphite, carbon (Super P (Imerys)), sodium carboxymethyl cellulose, 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 end of the negative electrode. The typical loading weight of the negative electrode active material is about 10±1 mg / cm. 2 is.

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

[0076] The positive electrode sheet, the negative electrode sheet, and a microporous polymer separator sheet (13 μm) sandwiched 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 producing 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 dried battery was soaked in the non-aqueous electrolyte solution for 8 hours at room temperature. The battery was precharged to 14% of its theoretical capacity at a current of 0.25 C and aged at room temperature for 1 day. The battery was then degassed for 30 seconds using a pressure of -760 mmHg, and the aluminum pouch was sealed. During the measurement, the pouch was assembled in a press jig equipped with a silicone pad.

[0078] The battery is charged at a current of 0.2 C in CC mode (constant current) to 4.2 V and in CV mode (constant voltage) until the C / 20 cutoff current is reached. The battery is discharged at a current of 0.2 C in CC mode until it drops to 2.7 V. It is then fully charged at a current of 0.50 C in CC mode to 4.2 V and in CV mode until the C / 20 cutoff current is reached.

[0079] The cell is then discharged in CC mode at a current of 0.50 C down to 2.7 V. It is charged again in CC mode to 4.2 V and in CV mode at a current of 0.5 C until the cutoff current of C / 20 is reached. The final charging step is performed at 25° C.

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

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

[0082] The internal resistance or direct current resistance (DCR) is measured at 1.5 C for 10 seconds at the start of every 100 cycles and at the end of the 600th cycle. [Example]

[0083] The present invention is further illustrated in the following examples. Example 1 The positive electrode active material EX1 is obtained by the following steps: 1) Preparation of a 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 a first mixture. 2) First heating: The first mixture obtained from step 1) is heated at 740° C. for 12 hours in an oxygen atmosphere to obtain a first heated material. 3) Preparation of slurry and drying: The first heated material is mixed with 5 liters of deionized water and stirred for 10 minutes. After stirring, the mixture is filtered to prepare a cake, and then the slurry is dried under vacuum at 140°C for 10 hours. 4) Preparation of the second mixture: 1.0 kilogram of the dried material is mixed homogeneously with 6.0 grams of H3BO3 to obtain the second mixture. 5) Second heating: The second mixture obtained in step 4) is heated at 300° C. for 8 hours in an oxygen atmosphere and 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 steps: 1) Preparation of first mixture: 272.0 grams LiOH, 3.0 grams Al2O3, and 1.0 kilogram Ni0.94 Mn 0.03 Co 0.03 (OH)2 is mixed homogeneously to obtain a first mixture. 2) First heating: The first mixture obtained from step 1) is heated at 720° C. for 12 hours in an oxygen atmosphere and cooled to room temperature to obtain a first heated material. 3) Preparation of slurry and drying: The first heated material is mixed with 5 liters of deionized water and stirred for 10 minutes. After stirring, the mixture is filtered to prepare a cake, and then the slurry is dried under vacuum 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 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 steps: 1) Preparation of a 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 a first mixture. 2) First heating: The first mixture obtained from step 1) is heated at 720° C. for 12 hours in an oxygen atmosphere and cooled to room temperature to obtain a first heated material. 3) Preparation of slurry and drying: The first heated material is mixed with 5 liters of deionized water and stirred for 10 minutes. After stirring, the mixture is filtered to prepare a cake, and then the slurry is dried under vacuum at 140°C for 10 hours. 4) Preparation of the second mixture: 1.0 kilogram of the dried material is mixed homogeneously 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 in an oxygen atmosphere and then cooled to room temperature to obtain a positive electrode active material CEX2.

[0086] Comparative Example 3 The positive electrode active material CEX3 is obtained by the following steps: 1) Preparation of a 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 a first mixture. 2) First heating: The first mixture obtained from step 1) is heated at 740° C. for 12 hours in an oxygen atmosphere and cooled to room temperature to obtain a first heated material. 3) Preparation of slurry and drying: The first heated material is mixed with 5 liters of deionized water and stirred for 10 minutes. After stirring, the mixture is filtered to prepare a cake, and then the slurry is dried under vacuum 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 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 steps: 1) Preparation of a first mixture: 274.0 grams LiOH, 3.0 grams Al2O3, 7.0 grams Nb2O5, 10.0 grams ZrO2, and 1.0 kilogram Ni 0.94 Mn 0.03 Co 0.03 (OH)2 is mixed homogeneously to obtain a first mixture. 2) First heating: The first mixture obtained from step 1) is heated at 740° C. for 12 hours in an oxygen atmosphere and cooled to room temperature to obtain a first heated material. 3) Preparation of slurry and drying: The first heated material is mixed with 5 liters of deionized water and stirred for 10 minutes. After stirring, the mixture is filtered to prepare a cake, and then the slurry is dried under vacuum at 140°C for 10 hours. 4) Preparation of the second mixture: 1.0 kilogram of the dried material is mixed homogeneously with 6.0 grams of H3BO3 to obtain the second mixture. 5) Second heating: The second mixture obtained in step 4) is heated at 300° C. for 8 hours in an oxygen atmosphere and cooled to room temperature to obtain a positive electrode active material EX2.

[0088] Comparative Example 4 The positive electrode active material CEX4 is obtained by the following steps: 1) Preparation of a 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 a first mixture. 2) First heating: The first mixture obtained from step 1) is heated at 745° C. for 12 hours in an oxygen atmosphere and cooled to room temperature to obtain a first heated material. 3) Preparation of slurry and drying: The first heated material is mixed with 5 liters of deionized water and stirred for 10 minutes. After stirring, the mixture is filtered to prepare a cake, and then the slurry is dried under vacuum 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 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 steps: 1) Preparation of a 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 a first mixture. 2) First heating: The first mixture obtained from step 1) is heated at 715° C. for 12 hours in an oxygen atmosphere and cooled to room temperature to obtain a first heated material. 3) Preparation of slurry and drying: The first heated material is mixed with 5 liters of deionized water and stirred for 10 minutes. After stirring, the mixture is filtered to prepare a cake, and then the slurry is dried under vacuum at 140°C for 10 hours. 4) Preparation of the second mixture: 1.0 kilogram of the dried material is mixed homogeneously 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 in an oxygen atmosphere and then cooled to room temperature to obtain a positive electrode active material CEX5.

[0090] Comparative Example 6 The positive electrode active material CEX6 is obtained by the following steps: 1) Preparation of a 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 a first mixture. 2) First heating: The first mixture obtained from step 1) is heated at 740° C. for 12 hours in an oxygen atmosphere and cooled to room temperature to obtain a first heated material. 3) Preparation of slurry and drying: The first heated material is mixed with 5 liters of deionized water and stirred for 10 minutes. After stirring, the mixture is filtered to prepare a cake, and then the slurry is dried under vacuum 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 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 steps: 1) Preparation of a first mixture: 272.0 grams of LiOH, 7.0 grams of NbO, and 10.0 grams of ZrO, and 1.0 kilogram of Ni 0.92 Mn 0.03 Co 0.05 (OH)2 is mixed homogeneously to obtain a first mixture. 2) First heating: The first mixture obtained from step 1) is heated at 770° C. for 12 hours in an oxygen atmosphere and cooled to room temperature to obtain a first heated material. 3) Preparation of slurry and drying: The first heated material is mixed with 5 liters of deionized water and stirred for 10 minutes. After stirring, the mixture is filtered to prepare a cake, and then the slurry is dried under vacuum at 140°C for 10 hours. 4) Preparation of the second mixture: 1.0 kilogram of the dried material is mixed homogeneously 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 in an oxygen atmosphere and then cooled to room temperature to obtain a positive electrode active material CEX7.

[0092] [Table 5]

[0093] Table 4 summarizes the chemical properties for 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 shows B B / B A The ratio, carbon content, and electrochemical properties such as DQ1 and capacity fade are summarized.

[0096] Table 5 shows the XPS analysis results of B for EX1, EX2, and CEX5 (B B ) is the ICP-OES result of B (B A ) compared with B greater than 0. B The results of (a) and (b) indicate that B is present on the surface of the positive electrode active material, in conjunction with the XPS measurements where the signal is acquired from the first few nanometers (e.g., 1 nm to 10 nm) of the sample. On the other hand, the B calculated from the ICP-OES results Ais the B content of the whole particle. Therefore, the ratio of the XPS result to the ICP-OES result, e.g., B B / B A is greater than 1, this indicates that the B is mainly present on the surface of the positive electrode active material. B / B A Higher values ​​correspond to more B present on the surface of the positive electrode active material. B / B A The values ​​are all higher than 10.0, which confirms the presence of B on the surface of the particles according to the present invention. Figure 1 is a representative XPS spectrum showing the B1s peak of EX2.

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

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

[0099] Comparing the experimental results of CEX1 and CEX3 with those of CEX3 (see Figure 3), the presence of Nb deteriorates the QF. Therefore, Nb is not considered advantageous from the perspective of electrochemical stability. However, the experimental results of EX1 demonstrate an unexpected synergistic effect: the inclusion of Nb, B coating, and the mixing process with an aqueous solution improves both the QF and DQ1. Specifically, 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 also observed that EX2 exhibits the highest electrochemical stability among EX2, CEX4, CEX5, and CEX6, with a DQ1 of 229.7 mAh / g and a QF of 20.7% / 100 cycles, which is lower than those of CEX4 and CEX6 and comparable to CEX5.

[0100] CEX7 is essentially identical to EX2, except that CEX7 does not contain Al. The DQ1 and QF of CEX7 are similar to those of EX2. However, Table 6 below, which shows the full cell results for EX2 and CEX7 in terms of % increase in cell thickness after 20 hours and DCR after 600 cycles, shows that EX2 has significantly improved full cell results over CEX7.

[0101] [Table 7]

[0102] Specifically, the cell thickness of EX2 after 20 hours of full-cell cycling increased by 34.3%, which is smaller than that of CEX7. The smaller increase in cell thickness indicates less gas is concomitantly produced during cycling. The DCR of EX2 after 600 cycles is 114.3%, which is lower than that of CEX7. Therefore, it is possible to confirm that the positive electrode active material contains Al, Nb, and B coatings and the BET is 0.50m. 2 / g~1.50m 2 / g, the QF, DQ1 and the above full cell test results are all improved, confirming that this can be obtained by mixing the lithiated transition metal complex material with an aqueous solution.

Claims

1. 1. A cathode active material for a rechargeable lithium ion battery, the cathode active material comprising Li, M′, and oxygen, wherein M′ is: Ni with a content x with 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, with a content a of 0.0≦a≦5.0 at% relative to M′, being 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.% relative to M′, Nb with a content c of 0.0<c≦4.0 at.% relative to M′, Al with a content d of 0.0≦d≦4.0 at% relative to M′, and Zr with a content 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 B defined as b / (x+y+z+b+c+d+e). Ａ and the positive electrode active material has a B content B Ｂ and B Ｂ was determined by XPS analysis, and B Ｂ 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 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 1.50m ２ / g or less.

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

3. The ratio B Ｂ / B Ａ 3. The cathode active material according to claim 1, wherein the σ is at least 35.0, preferably at least 50.0, and more preferably at least 70.

0.

4. The specific surface area of ​​the positive electrode active material is 0.60 m ２ / g to 1.40m ２ / g, preferably 0.65m ２ / g to 1.35m ２ The positive electrode active material according to any one of claims 1 to 3, wherein the SiO2 content is 1 / g.

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

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

7. 7. The positive electrode active material according to claim 1, wherein x≧82.0 at %, preferably x≧84.0 at %, relative to M′.

8. 8. The positive electrode active material according to claim 1, wherein x≦99.0 at %, preferably x≦97.0 at %, relative to M'.

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

10. A method for producing the positive electrode active material according to any one of claims 1 to 9, comprising the following consecutive steps: Step 1) mixing a Li 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) heating the first mixture at a temperature of 600°C to 900°C to obtain a first heated material; Step 3) mixing the first heated material with an aqueous solution to obtain a slurry, filtering, and then drying the slurry to obtain a dry powder; Step 4) mixing the dry powder with a B-containing compound to obtain a second mixture; 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 of claim 10, wherein the second mixture is heated at a temperature of from 250°C to 450°C.

12. 11. The method of 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. 11. 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 according to any one of claims 1 to 9.

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

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