A lithium-cobalt composite oxide, its preparation method and application

Abstract

This invention provides a lithium-cobalt composite oxide, its preparation method, and its application, belonging to the field of lithium-ion battery technology. The general formula of the lithium-cobalt composite oxide of this invention is: Li c Co 1d e‑ f M d Q e E f O2·r Li a Co 1‑b T b O 4 / 3 (a×r+c) / (1+r)≤1; M, Q, and E are each independently selected from at least one of Mg, Al, Ni, Mn, Y, La, Zr, F, P, B, Ti, Cu, and Na; T is at least one of Y, Al, B, Ni, and Mn. This invention introduces elements with different doping forms, utilizing in-situ precursor doping, self-doping, and coating. The synergistic effect of various elements suppresses the irreversible phase transition of cobalt-containing cathode materials coated with T-element materials under high voltage, improving the structural stability of the cathode material, thereby achieving good electrochemical performance with good cycle performance under high voltage.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium-cobalt composite oxide, its preparation method, and its application. Background Technology

[0002] Rechargeable lithium-ion batteries are a new generation of green energy storage batteries, boasting outstanding advantages such as high power density, high voltage, high energy density, no memory effect, stable cycle life, and long lifespan. They are widely used in products such as mobile phones, computers, new energy vehicles, smart networks, and distributed energy storage. Lithium-ion batteries come in many varieties, mainly composed of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel oxide, and lithium nickel cobalt manganese oxide. Among these, lithium cobalt oxide has the highest theoretical density, resulting in superior tap density and compaction density in practical applications compared to other existing materials. Its volumetric energy density remains unmatched by any other cathode material.

[0003] With the deepening research on lithium cobalt oxide, its charging voltage has gradually increased from 4.2V to 4.35V, and further to 4.4V, 4.45V, and even higher. The first generation of lithium cobalt oxide batteries used a voltage between 4.2 and 4.3V. The second generation, introduced in 2013, used 4.35V. The subsequent third and fourth generation lithium-ion batteries used voltages of 4.4V and 4.45V respectively, with specific capacities reaching 180-185 mAh / g. Lithium cobalt oxide is one of the most ideal cathode materials in the 3C (computer, communication, and consumer electronics) field. With the development of electronic technology and the increasingly frequent updates and replacements of 3C products, the trend towards "thinner and more durable" 3C products places higher demands on the energy density of lithium-ion batteries.

[0004] The volumetric energy density of a lithium-ion battery = discharge capacity × discharge voltage plateau × compaction density. Currently, the energy density of lithium cobalt oxide batteries is improved by increasing compaction density and cutoff voltage. Improving compaction density through particle size gradation has reached its limit, with very little room for further improvement. Increasing the cutoff voltage further increases the discharge specific capacity, but as the charging voltage rises, more lithium ions are extracted from the crystal lattice, causing structural instability. Increased delithiation on the material surface leads to structural phase transitions extending from the surface to the interior of the particles. High-valence cobalt is unstable, exhibits strong oxidizing properties, and readily reacts with the electrolyte. Cobalt extraction is accompanied by oxygen extraction, which easily leads to gas generation. All these factors shorten cycle life, reduce safety, and hinder the practical application of high-voltage lithium cobalt oxide.

[0005] Current mainstream optimization methods include doping, coating, improved synthesis, and process optimization. Excess lithium during sintering promotes particle growth, but excess lithium in the crystal lattice affects cycle performance and increases the risk of gas generation at high temperatures, compromising safety. Coating with micro / nano cobalt atoms allows for high-temperature sintering to absorb excess lithium and reduce residual lithium, improving high-temperature safety and reducing gas generation. However, under high voltage conditions, as the number of lithium ions released increases, the valence state of cobalt tends to rise, making it prone to side reactions with the electrolyte, leading to decreased cycle performance, capacity, and storage capacity.

[0006] Therefore, there is a need for a lithium cobalt composite oxide material with fewer interfacial side reactions and good cycling performance at voltages of 4.45V / 4.48V / 4.50V or even higher. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a lithium cobalt composite oxide with fewer interfacial side reactions and good cycle performance at voltages of 4.45V / 4.48V / 4.50V or even higher.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned lithium cobalt composite oxide.

[0009] Another object of the present invention is to provide the application of the above-mentioned lithium cobalt composite oxide as a cathode material for lithium-ion batteries.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A lithium-cobalt composite oxide, with the general formula: Li c Co 1 d e-f M d Q e E f O2·r Li a Co 1-b T b O 4 / 3 Where 0.001≤r≤0.05, 0≤a≤0.02, 0.006≤b≤0.03, 0.98≤c≤1.01, 0.005≤d≤0.02, 0.002≤e≤0.015, 0.006≤f≤0.03, and (a×r+c) / (1+r)≤1;

[0012] M, Q, and E are each independently selected from at least one of Mg, Al, Ni, Mn, Y, La, Zr, F, P, B, Ti, Cu, and Na;

[0013] The T is at least one of Y, Al, B, Ni, and Mn.

[0014] The lithium-cobalt composite oxide of the present invention includes a substrate and a coating layer, wherein Li c Co 1 d e-f M d Q e E f O2 is the general formula for the substrate, Li a Co 1-b T b O 4 / 3 This is the general formula for a coating layer. In the substrate, M is a self-doped element, Q is a coating element, and E is an in-situ precursor doped element. In the coating layer, T is an in-situ coating precursor doped element.

[0015] This invention introduces elements M, Q, E, and T. M and E elements replace Co or Li sites in the cathode material, suppressing Co valence state changes and O release when combined with Co; and improving lithium-ion insertion / extraction capabilities when combined with Li sites. Q element significantly enhances interface stability. Through in-situ precursor doping, self-doping, and coating, this invention utilizes the synergistic effect of various elements to suppress irreversible phase transitions in cobalt-containing cathode materials coated with T elements under high voltage, thereby improving the structural stability of these materials.

[0016] The lithium-cobalt composite oxide of the present invention has excess cobalt remaining, and the excess cobalt is in the form of Li a Co 1-b T b O 4 / 3 The form exists as a coexistence of spinel phase and layered phase; excess Co at high temperature will consume excess lithium in the layered material, thereby improving cycle performance and reducing gas production.

[0017] When lithium-cobalt composite oxide is used as a cathode material for lithium-ion batteries, nano-sized Li... a Co 1-b T b O 4 / 3 As a coating layer, the compound can delay or inhibit the oxygen reduction reaction between the electrolyte and the surface of the cathode material, suppress the change of Co valence state in the cathode material, reduce Co dissolution, and improve Li a Co 1-b T b O 4 / 3 The surface structure stability of the material-coated cathode material under high voltage and long cycle is improved, thus enhancing the cycling, storage, and gas generation performance of the Co-containing material-coated cathode material.

[0018] In addition, the introduction of M, Q, E, and T elements can suppress the formation of microcracks on the surface of the cathode material, thereby improving the electrical performance of the cathode material under high voltage.

[0019] In the lithium-cobalt composite oxide of the present invention, a, r, and c should satisfy the following relationship: (a×r+c) / (1+r)≤1. The inventors have found that when (a×r+c) / (1+r)>1, the cycle performance of the lithium-cobalt composite oxide cannot be guaranteed.

[0020] Preferably, (a×r+c) / (1+r) is 0.985 to 0.995.

[0021] The above-mentioned coating layer Li a Co 1-b T b O 4 / 3 In the case where a equals 0 < a ≤ 0.01, cobalt is expressed as Co. 1-b T b O 4 / 3 And Li a Co 1-b T b O 4 / 3 It exists, and its content can be quantitatively detected and analyzed.

[0022] The above-mentioned coating layer Li a Co 1-b T b O 4 / 3 In the context, when a equals 0, cobalt is expressed as Co. 1-b T b O 4 / 3 It exists in form, and its content can be quantitatively detected and analyzed.

[0023] In the lithium-cobalt composite oxide of the present invention, Co 1-b T b O 4 / 3 It exists in the form of spinel phase; the Li a Co b T 1- b O 4 / 3 The phases consist of both spinel and layered phases. The lithium-cobalt composite oxide exists as single crystals or near-single crystal particles.

[0024] Preferably, in the lithium-cobalt composite oxide, the ratio of the sum of the molar amounts of Co, M, Q, E, and T elements to the molar amount of Li element is denoted as m1, where 0.98 ≤ m1 ≤ 1.1. More preferably, 1.02 ≤ m1 ≤ 1.0.

[0025] The inventors discovered that sintering using the above ratio can produce a material with balanced capacity, circulation, gas production, and storage performance.

[0026] Preferably, M is at least one selected from Mg, Al, Ni, Mn, Y, La, Zr, F, P, and B. More preferably, M is at least one selected from Mg, Al, Mn, Y, La, and Zr. Even more preferably, M is at least one selected from Mg, Al, Y, La, and Zr.

[0027] The Q is at least one of Mg, Al, Ti, Cu, Y, La, Zr, F, P, and B. More preferably, the Q is at least one of Al, Ti, Y, Zr, F, and P. Even more preferably, the Q is at least one of Al, Ti, Zr, F, and P.

[0028] More preferably, Q is F.

[0029] When the Q element in the lithium cobalt composite oxide of the present invention is F, the doping occupies the O site, reducing the overall P band Fermi level, which matches the reduction of the driving force for carbonate dehydrogenation; during the process of F replacing the O site, the Co element is reduced, which raises the energy barrier from the electrolyte electron conduction, reduces interfacial side reactions, and improves gas production.

[0030] The E is at least one selected from Mg, Al, Ti, Y, Zr, Ni, Mn, Na, Cu, and B. More preferably, the E is at least one selected from Mg, Al, Ni, and Mn.

[0031] Preferably, T is at least one of Y, Al, Mn, and B. More preferably, T is at least one of Y, Al, and Mn.

[0032] This invention also protects a method for preparing the above-mentioned lithium-cobalt composite oxide, comprising the following steps:

[0033] S1. Mix the Li-containing precursor, the E-doped Co-containing precursor (denoted as Al), and the M-containing precursor, and sinter them to obtain the E- and M-doped matrix.

[0034] S2. The doped matrix obtained in step S1, the Co-containing precursor doped with T element (denoted as A2), and the Q-containing precursor are mixed and sintered to obtain lithium cobalt composite oxide.

[0035] In the preparation method of this invention, M is a precursor element added during sintering, serving as a dopant; E is an element doped into the Co-containing precursor, with doping occurring within the Co-containing precursor, serving as in-situ doping; Q and / or T are added in step S2, serving as a coating element and eliminating excess lithium. Q exists in the form of a composite, optimizing the surface structure and reducing gas generation while maintaining high specific capacity and high-temperature safety performance, thus improving storage.

[0036] In step S2, the addition of a slight excess of doped element Co (T) reacts with the excess Li (Li) from step S1 during sintering to generate a doped hexagonal lithium-cobalt composite oxide. Its main structure is similar to the internal layered structure, which reduces excess lithium within the layered structure and also reduces residual lithium on the surface. The surface-generated doped hexagonal phase is more stable than the traditional undoped hexagonal phase; this can improve the material's high-temperature cycling performance, storage performance, and safety performance, while reducing gas generation.

[0037] Under high voltage conditions, doped Li a Co b T 1-b O 4 / 3 While maintaining the material's high specific capacity and high-temperature safety performance, its cycle performance can also be improved.

[0038] Preferably, in step S1, the molar ratio m2 of Li to Co is adjusted to: 1.0 ≤ m2 ≤ 1.10. More preferably, 1.03 ≤ m2 ≤ 1.07.

[0039] In step S1, when the E element in the Co precursor substitutes for the Co site, additional lithium is added according to the Co site. When the E element has a +n valence, the molar ratio E:Co = 1:n / 3 is used to add lithium. The total amount of lithium added is the sum of m2 and the amount of additional lithium added.

[0040] Controlling the amount of lithium or adding a flux during sintering can promote particle growth, make the particles fuller, eliminate secondary grain boundaries between particles, compensate for lithium loss during sintering, improve material processing performance, compaction density, reduce defects, and lower sintering temperature.

[0041] Preferably, the D50 particle size of the Co-containing precursor is ≤1.0 μm.

[0042] Preferably, the Co-containing precursor is at least one of Co(OH)2, CoCO3, and Co3O4.

[0043] Preferably, in step S1, the Li-containing precursor is at least one of lithium carbonate, lithium carbonate, lithium hydroxide, lithium nitrate, and lithium chloride.

[0044] Preferably, in step S1, the precursor containing element M is an oxide of element M.

[0045] Preferably, in step S2, the precursor containing Q element is at least one of an oxide containing Q element, a salt containing Q element, and an acid containing Q element.

[0046] Preferably, in step S1, the sintering temperature is 900–1100°C, the time is 8–12 hours, and the sintering is carried out in an oxygen-containing atmosphere.

[0047] Preferably, in step S2, the sintering temperature is 800–1000°C, the time is 8–12 hours, and the sintering is carried out in an oxygen-containing atmosphere.

[0048] This invention also protects the application of the above-mentioned lithium cobalt composite oxide as a cathode material for lithium-ion batteries.

[0049] Compared with the prior art, the beneficial effects of the present invention are:

[0050] This invention develops a lithium-cobalt composite oxide, comprising a substrate and a coating layer, with the general formula Li. c Co 1 d e- f M d Q e E f O2·r Li a Co 1-b T b O 4 / 3 By introducing elements with different doping forms, utilizing in-situ precursor doping, self-doping, and coating, and through the synergistic effect of various elements, the irreversible phase transition of the cobalt-containing cathode material coated with T element is suppressed under high voltage, and the structural stability of the cobalt-containing cathode material coated with T element is improved. This results in electrochemical performance with fewer interfacial side reactions and good cycling performance under high voltage. Attached Figure Description

[0051] Figure 1 The image shown is the XRD pattern of the sample obtained in Example 1.

[0052] Figure 2 SEM image of sample 9 in Example 9;

[0053] Figure 3 The test cycle curves for samples from Examples 1-2 and Comparative Examples 1-2 at 3.0-4.65V / 0.5C are shown.

[0054] Figure 4 The test cycle curves for samples from Examples 4-5 and Examples 10-11 are shown at 3.0-4.65V / 0.5C. Detailed Implementation

[0055] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0056] Example 1

[0057] This embodiment provides a lithium-cobalt composite oxide, and the preparation method is as follows:

[0058] S1. Based on the chemical formula Li 0.99 Co 0.96 Mg 0.01 Al 0.03 The molar ratio of O2 is as follows: Li-containing precursor (lithium carbonate), E-doped Co-containing precursor (aluminum-doped cobalt tetroxide), and M-containing precursor (magnesium oxide) are weighed and placed in a three-dimensional mixing device with a ball-to-material mass ratio of 1.5:1. The mixture is mixed for 3 hours to obtain a mixed powder. The mixed powder is calcined at 1100℃ for 10 hours. After natural cooling and crushing, it is pulverized and sieved to obtain modified lithium cobalt oxide primary powder, i.e., the doped matrix (denoted as LCO-Al).

[0059] S2. According to the chemical formula (Li 0.99 Co 0.955 Mg 0.01 Al 0.03 Ti 0.005 O2)·0.005Li 0.01 Co 0.96 Zr 0.03 O 4 / 3 The molar ratio of LCO-A1, a precursor containing Q (titanium oxide), and a precursor containing Co (doped with Zr cobalt tetroxide, with a particle size of 0.5 μm) were weighed and placed in a three-dimensional mixer with a ball-to-material mass ratio of 1:1. The mixture was mixed for 1.5 hours to obtain a mixed powder. The mixed powder was calcined at 850℃ for 8 hours. After natural cooling and sieving, the modified lithium cobalt oxide finished powder, namely lithium cobalt composite oxide (denoted as LCO-A2), was obtained.

[0060] Example 2

[0061] This embodiment provides a lithium-cobalt composite oxide, and the preparation method is as follows:

[0062] S1. Based on the chemical formula Li 0.99 Co 0.960 Mg 0.01 Al 0.03 La 0.005 The molar ratio of O2 is as follows: Li-containing precursor (lithium carbonate), E-doped Co-containing precursor (aluminum-doped cobalt tetroxide), and M-containing precursor (magnesium oxide and lanthanum oxide) are weighed and placed in a three-dimensional mixing device with a ball-to-material mass ratio of 1.5:1. The mixture is mixed for 3 hours to obtain a mixed powder. The mixed powder is calcined at 1100℃ for 10 hours. After natural cooling and crushing, it is pulverized and sieved to obtain modified lithium cobalt oxide primary powder, i.e., the doped matrix (denoted as LCO-B1).

[0063] S2. From the chemical formula (Li 0.99 Co0.950 Mg 0.01 Al 0.03 La 0.005 Ti 0.005 O2)·0.01Li 0.01 Co 0.96 Zr 0.03 O 4 / 3 The molar ratio of LCO-B1, a precursor containing Q (titanium oxide), and a precursor containing Co (doped with Zr cobalt tetroxide, with a particle size of 0.5 μm) were weighed and placed in a three-dimensional mixer with a ball-to-material mass ratio of 1:1. The mixture was stirred for 1.5 hours to obtain a mixed powder. The mixed powder was calcined at 850℃ for 8 hours. After natural cooling and sieving, the modified lithium cobalt oxide finished powder, namely lithium cobalt composite oxide (denoted as LCO-B2), was obtained.

[0064] Example 3

[0065] This embodiment provides a lithium-cobalt composite oxide, and the preparation method is as follows:

[0066] S1. Based on the chemical formula Li 0.99 Co 0.96 Mg 0.01 Al 0.035 The molar ratio of O2 is as follows: Li-containing precursor (lithium carbonate), E-doped Co-containing precursor (aluminum-doped cobalt tetroxide), and M-containing precursor (magnesium oxide) are weighed and placed in a three-dimensional mixing device with a ball-to-material mass ratio of 1.3:1. The mixture is mixed for 3 hours to obtain a mixed powder. The mixed powder is calcined at 1100℃ for 10 hours. After natural cooling and crushing, it is pulverized and sieved to obtain modified lithium cobalt oxide primary powder, i.e., the doped matrix (denoted as LCO-Cl).

[0067] S2. From the chemical formula (Li 0.99 Co 0.950 Mg 0.01 Al 0.035 Ti 0.005 O2)·0.005Li 0.015 Co 0.97 Zr 0.03 O 4 / 3 The molar ratio of LCO-C1, a precursor containing Q (titanium oxide), and a precursor containing Co (doped with T, cobalt carbonate) were weighed and placed in a three-dimensional mixer with a ball-to-material mass ratio of 1:1. The mixture was stirred for 1.5 hours to obtain a mixed powder. The mixed powder was calcined at 850℃ for 8 hours. After natural cooling and sieving, the modified lithium cobalt oxide finished powder, namely lithium cobalt composite oxide (denoted as LCO-C2), was obtained.

[0068] Example 4

[0069] This embodiment provides a lithium-cobalt composite oxide, and the preparation method is as follows:

[0070] S1. Based on the chemical formula Li 0.99 Co 0.96 Mg 0.01 Al 0.035 The molar ratio of O2 is as follows: Li-containing precursor (lithium carbonate), E-doped Co-containing precursor (aluminum-doped cobalt tetroxide), and M-containing precursor (magnesium oxide) are weighed and placed in a three-dimensional mixing device with a ball-to-material mass ratio of 1.3:1. The mixture is mixed for 3 hours to obtain a mixed powder. The mixed powder is calcined at 1100℃ for 10 hours. After natural cooling and crushing, it is pulverized and sieved to obtain modified lithium cobalt oxide primary powder, i.e., the doped matrix (denoted as LCO-D1).

[0071] S2. By (Li) 0.99 Co 0.950 Mg 0.01 Al 0.035 Ti 0.005 O 1.995 F 0.005 0.005Li 0.01 Co 0.97 Zr 0.03 O 4 / 3 The chemical formulas of LCO-D1, Q-containing precursors (lithium fluoride, titanium dioxide), and T-doped Co-containing precursors (Zr-doped cobalt carbonate) were weighed out in a three-dimensional mixer with a ball-to-material mass ratio of 1:1. The mixture was stirred for 1.5 hours to obtain a mixed powder. The mixed powder was calcined at 850℃ for 8 hours. After natural cooling and sieving, the modified lithium cobalt oxide finished powder, namely lithium cobalt composite oxide (denoted as LCO-D2), was obtained.

[0072] Example 5

[0073] This embodiment provides a lithium-cobalt composite oxide, and the preparation method is as follows:

[0074] S1. Based on the chemical formula Li 0.99 Co 0.96 Mg 0.01 Al 0.035 The molar ratio of O2 is as follows: Li-containing precursor (lithium carbonate), E-doped Co-containing precursor (magnesium-doped cobalt tetroxide), and M-containing precursor (alumina) are weighed and placed in a three-dimensional mixing device with a ball-to-material mass ratio of 1.3:1. The mixture is mixed for 3 hours to obtain a mixed powder. The mixed powder is calcined at 1100℃ for 10 hours. After natural cooling and crushing, it is pulverized and sieved to obtain modified lithium cobalt oxide primary powder, i.e., the doped matrix (denoted as LCO-E1).

[0075] S2. By (Li) 0.99 Co 0.950 Mg 0.01 Al 0.035 Ti 0.005 O 1.995 P 0.005 0.005Li 0.01 Co 0.97 Zr 0.03 O 4 / 3 The chemical formulas of LCO-E1, Q-containing precursors (metaphosphate, titanium dioxide), and T-doped Co-containing precursors (Zr-doped cobalt carbonate) were weighed out in a three-dimensional mixer with a ball-to-material mass ratio of 1:1. The mixture was mixed for 1.5 hours to obtain a mixed powder. The mixed powder was calcined at 850℃ for 8 hours. After natural cooling and sieving, the modified lithium cobalt oxide finished powder, namely lithium cobalt composite oxide (denoted as LCO-E2), was obtained.

[0076] Example 6

[0077] This embodiment provides a lithium-cobalt composite oxide, and the preparation method is as follows:

[0078] S1. Based on the chemical formula Li 0.99 Co 0.955 Mg 0.01 Al 0.035 La 0.005 The molar ratio of O2 is as follows: Li-containing precursor (lithium carbonate), E-doped Co-containing precursor (magnesium-aluminum cobalt tetroxide), and M-containing precursor (lanthanum oxide) are weighed and placed in a three-dimensional mixing device with a ball-to-material mass ratio of 1.3:1. The mixture is mixed for 3 hours to obtain a mixed powder. The mixed powder is calcined at 1100℃ for 10 hours. After natural cooling and crushing, it is pulverized and sieved to obtain modified lithium cobalt oxide primary powder, i.e., the doped matrix (denoted as LCO-F1).

[0079] S2. From the chemical formula (Li 0.99 Co 0.950 Mg 0.01 Al 0.035 Ti 0.005 O2)·0.005Li 0.01 Co 0.97 Al 0.03 O 4 / 3The chemical formulas of LCO-F1, a precursor containing Q (titanium oxide), and a precursor containing Co (doped Al cobalt tetroxide) were weighed out in a three-dimensional mixer with a ball-to-material mass ratio of 1:1. The mixture was mixed for 1.5 hours to obtain a mixed powder. The mixed powder was calcined at 850℃ for 8 hours. After natural cooling and sieving, the modified lithium cobalt oxide finished powder, namely lithium cobalt composite oxide (denoted as LCO-F2), was obtained.

[0080] Example 7

[0081] This embodiment provides a lithium-cobalt composite oxide, the preparation method of which differs from that of Example 1 in that...

[0082] In step S1, based on the chemical formula Li 1.0 Co 0.96 Mg 0.02 Al 0.025 The molar ratio of O2 is determined by weighing a Li-containing precursor (lithium carbonate), an E-doped Co-containing precursor (aluminum-doped cobalt tetroxide), and a M-containing precursor (magnesium oxide).

[0083] In step S2, according to (Li) 1.0 Co 0.94 Mg 0.02 Al 0.025 Ti 0.015 O2)·0.01Li 0.02 Co 0.975 Zr 0.025 O 4 / 3 Weigh the doped matrix, the Q-containing precursor (titanium oxide), and the T-doped Co-containing precursor (Zr-doped cobalt tetroxide) according to the chemical formula molar ratio.

[0084] Example 8

[0085] This embodiment provides a lithium-cobalt composite oxide, the preparation method of which differs from that of Example 1 in that...

[0086] In step S1, based on the chemical formula Li 0.98 Co 0.98 Mg 0.005 Al 0.006 The molar ratio of O2 is determined by weighing a Li-containing precursor (lithium carbonate), an E-doped Co-containing precursor (aluminum-doped cobalt tetroxide), and a M-containing precursor (magnesium oxide).

[0087] In step S2, according to (Li) 0.98 Co 0.987 Mg 0.005 Al 0.006 Ti 0.002 O2)·0.0001Co 0.994 Zr0.006 O 4 / 3 Weigh the doped matrix, the Q-containing precursor (titanium oxide), and the T-doped Co-containing precursor (Zr-doped cobalt tetroxide) according to the chemical formula molar ratio.

[0088] Example 9

[0089] This embodiment provides a lithium-cobalt composite oxide, the preparation method of which differs from that of Example 1 in that...

[0090] In-situ doping with aluminum oxide, nickel oxide, and manganese oxide, and doping with magnesium oxide and lanthanum oxide, coated with titanium oxide, Mg cobalt tetroxide, and lithium fluoride, and after sieving, modified lithium cobalt oxide powder LCO-I2 is obtained.

[0091] Example 10

[0092] This embodiment provides a lithium-cobalt composite oxide, the preparation method of which differs from that of Example 4 in that...

[0093] In step S2, the precursors containing Q are all titanium oxide and do not contain lithium fluoride.

[0094] Example 11

[0095] This embodiment provides a lithium-cobalt composite oxide, the preparation method of which differs from that of Example 5 in that...

[0096] In step S2, all precursors containing the Q element are titanium oxide and do not contain metaphosphoric acid.

[0097] Comparative Example 1

[0098] This comparative example provides a lithium-cobalt composite oxide, the preparation method of which differs from that of Example 1 in that:

[0099] Step S2 involves replacing the doped Zr cobalt tetroxide with undoped cobalt tetroxide.

[0100] Comparative Example 2

[0101] This comparative example provides a lithium-cobalt composite oxide, the preparation method of which differs from that of Example 2 in that:

[0102] Step S2 involves replacing the doped Zr cobalt tetroxide with undoped cobalt tetroxide.

[0103] Comparative Example 3

[0104] This comparative example provides a lithium-cobalt composite oxide, the preparation method of which differs from that of Example 1 in that: in step S2,

[0105] According to the chemical formula (Li 0.99 Co 0.955 Mg 0.01 Al 0.03Ti 0.005 O2)·0.015Li 0.01 Co 0.96 Zr 0.03 O 4 / 3 Weigh out all the materials.

[0106] Comparative Example 4

[0107] This comparative example provides a lithium-cobalt composite oxide. The preparation method differs from that of Example 1 in that it uses conventional doping and coating. The specific method is as follows:

[0108] S1. Based on the chemical formula Li 0.99 Co 0.955 Mg 0.01 Al 0.035 La 0.005 The molar ratio of O2 was determined by weighing a Li precursor (lithium carbonate), an undoped Co precursor (cobalt tetroxide), a M precursor (lanthanum oxide), a Mg compound, and an Al compound, and placing them in a three-dimensional mixing device with a ball-to-material mass ratio of 1.3:1. The mixture was mixed for 3 hours to obtain a mixed powder. The mixed powder was then calcined at 1100℃ for 10 hours. After natural cooling and crushing, it was pulverized and sieved to obtain a primary powder, i.e., the doped matrix.

[0109] S2. From the chemical formula (Li 0.99 Co 0.950 Mg 0.01 Al 0.035 Ti 0.005 O2)·0.005Li 0.01 Co 0.97 Al 0.03 O 4 / 3 The chemical formula molar ratio is determined by weighing the doped matrix, Q-containing precursor (titanium oxide), undoped Co-containing precursor (cobalt tetroxide), and Al-containing compound from step S1, placing them in a three-dimensional mixer with a ball-to-material mass ratio of 1:1. The three-dimensional mixer is then mixed for 1.5 hours to obtain a mixed powder. The mixed powder is then calcined at 850℃ for 8 hours. After natural cooling and sieving, the modified lithium cobalt oxide finished powder, i.e., lithium cobalt composite oxide, is obtained.

[0110] Performance testing

[0111] The lithium-cobalt composite oxides obtained in the above embodiments and comparative examples are as follows:

[0112] The lithium cobalt composite oxides prepared in the examples or comparative examples were used as positive electrode materials to prepare lithium-ion batteries: lithium cobalt composite oxides, polyvinylidene fluoride, and conductive carbon were mixed in a mass ratio of 90:5:5, NMP (N-methylpyrrolidone) was added, and the mixture was stirred to form a slurry. The slurry was then coated onto aluminum foil and dried at 80°C to form a positive electrode sheet. The positive electrode sheet, lithium sheet, electrolyte, and separator were used as raw materials to assemble CR2430 coin cells in a glove box.

[0113] Capacity Testing: Four batteries prepared above were used as parallel samples. At room temperature (25°C), they were charged at a constant current rate of 0.1C to voltage V1. Further charging was performed under constant voltage condition V1 until the current dropped below 0.05C, bringing them to a fully charged state (V1). Then, they were discharged at a constant current rate of 0.1C to V2 to obtain the discharge capacity. The specific capacity at 0.1C was calculated using the following formula: Specific capacity = Discharge capacity / Mass of positive electrode material. Cycling tests were conducted at 3.0–4.65V / 0.5C.

[0114] The XRD image of the lithium-cobalt composite oxide obtained in Example 1 is shown below. Figure 1 As shown, the XRD pattern indicates a pure phase with no extraneous peaks.

[0115] SEM image of the lithium-cobalt composite oxide prepared in Example 9 is shown below. Figure 2 As shown, the surface of the lithium cobalt composite oxide is relatively smooth and dense.

[0116] The test results for each embodiment and comparative example are shown in Table 1.

[0117] Table 1

[0118]

[0119] Based on the test results of Examples 1-2 and Comparative Examples 1-3: Examples 1 and 2 were Co3O4-doped coatings, while Comparative Examples 1 and 2 were undoped ordinary Co3O4. The comparison shows that when the coating amount is small, the surface layer is dominated by Co and Li. a Co b T 1-b O 4 / 3 The doped Co3O4 exists in a form where layered and spinel structures coexist. The doped Co3O4 coating has little impact on the capacity of the resulting sample, indicating that the overall capacity change is minimal after doping with a small amount of elements. When the coating layer accounts for a large proportion and the total Zr-Co3O4 coating is large, as in Example 1 and Comparative Example 3, the capacity of the lithium cobalt composite oxide decreases significantly. A significant amount of residual doped Co3O4 lacks electrochemical activity during charge and discharge, thus reducing the capacity.

[0120] Figure 3The figures show the cycle curves of the samples from Examples 1-2 and Comparative Examples 1-2 at 3.0–4.65V / 0.5C. It can be seen that when the charge / discharge rate is 0.5C at 3.0–4.65V, the cycle retention rate of the Zr-Co3O4 coating significantly increases. This is because, under higher cutoff voltage conditions, the doped Co3O4 reacts with lithium in the material to form Li. 0.005 Co 0.96 Zr 0.03 O 4 / 3 Its stability is superior to Li 0.005 Co 0.96 O 4 / 3 Undoped LCO exhibits surface instability under high voltage, and its surface structure is prone to changes, particularly affecting the Co content. 4+ Side reactions can occur between the material and the electrolyte, which can lead to poor structural stability. Zr-Co3O4 coating improves the material's cycling performance.

[0121] Based on the test results of Examples 4-5 and 10-11, it can be seen that coating with a small amount of F and M to replace the O positions results in a small change in overall capacity and has a low impact on the overall capacity. This indicates that a small amount of negative ions replacing the O positions has a small impact on the insertion and extraction of lithium ions.

[0122] Figure 4 The following are the cycle curves of samples 4-5 and 10-11 at 3.0-4.65V / 0.5C. It can be seen that at a charge / discharge rate of 0.5C and at 3.0-4.65V, a small amount of F or M coating replacing the O sites can suppress Co dissolution and O precipitation, stabilize the structure, and significantly improve cycle performance.

[0123] Active materials, conductive agents, binders, and dispersants were dispersed and stirred in a certain proportion, and coated as the positive electrode, with graphite as the negative electrode. The positive electrode sheet, negative electrode sheet, and separator were taken and wound to form a soft-pack battery. Formation and capacity testing were performed. The resulting battery was tested for storage and gas production at 4.5V / 1.0C. The test results of Examples 1, 4, 9, and 10 and Comparative Examples 1 and 4 are shown in Table 2.

[0124] Table 2

[0125] serial number Gas generation during storage at 70℃ Store at 60℃ Example 1 30 days 1.2% 30 days 83.2% Comparative Example 1 30 days 2.7% 30 days 76.3% Comparative Example 4 30 days 6.5% 30 days 20.2% Example 4 30 days 0.83% 30 days 85.2% Example 10 30 days 1.1% 30 days 66.3% Example 9 30 days 0.83% 30 days 88.6%

[0126] As shown in Table 3, in Example 1 and Comparative Example 1, the doped cobalt tetracoating is superior to the undoped cobalt tetracoating in terms of storage and gas generation. This is because the doped cobalt tetracoating can react with excess lithium in the substrate to generate Li. a Co b T 1-b O 4 / 3The resulting lithium-cobalt composite oxide exhibits a coexistence of layered and spinel structures, with other proportions determined by the amount of excess lithium and added cobalt in the substrate structure. Examples 1 and 4 show that in conventional doping coatings, all elemental components are mixed together, resulting in arbitrary elemental doping methods in the prepared lithium-cobalt composite oxide. However, the lithium-cobalt composite oxide prepared by combining different doping methods of this invention exhibits significantly better storage and gas generation performance than conventional doping coatings. This indicates that by following the steps of this invention, different elements act at different positions, stabilizing the layered structure and significantly improving storage and gas generation. Examples 4 and 10 show that shallow F doping can replace the position of O, improving the shallow band structure, suppressing valence state changes of O, suppressing oxygen release, improving surface structure stability, and significantly improving gas generation, while storage improvement is not significant. Example 9 shows that multi-element doping coating, with different elements occupying different positions, results in a synergistic effect that significantly improves storage and gas generation.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium-cobalt composite oxide, characterized in that, The general formula of the lithium-cobalt composite oxide is: Where 0.001≤r≤0.05, 0≤a≤0.02, 0.006≤b≤0.025, 0.98≤c≤1.12, 0.005≤d≤0.02, 0.002≤e≤0.015, 0.006≤f≤0.025, and (a×r+c) / (1+r)≤1; M, Q, and E are each independently selected from at least one of Mg, Al, Ni, Mn, Y, La, Zr, F, P, B, Ti, Cu, and Na; The T is at least one of Zr and Al; The preparation method of the lithium-cobalt composite oxide includes the following steps: S1. Mix the Li-containing precursor, the E-doped Co-containing precursor, and the M-doped precursor, and sinter them to obtain an E-doped and M-doped matrix. S2. The doped matrix obtained in step S1, the Co-containing precursor doped with T element, and the Q-containing precursor are mixed and sintered to obtain a lithium cobalt composite oxide.

2. The lithium-cobalt composite oxide according to claim 1, characterized in that, M is at least one of Mg, Al, Ni, Mn, Y, La, Zr, F, P, and B.

3. The lithium-cobalt composite oxide according to claim 1, characterized in that, Q is at least one of Mg, Al, Ti, Cu, Y, La, Zr, F, P, and B.

4. The lithium-cobalt composite oxide according to claim 1, characterized in that, The E is at least one of Mg, Al, Ti, Y, Zr, Ni, Mn, Na, Cu, and B.

5. The lithium-cobalt composite oxide according to claim 1, characterized in that, The ratio of the sum of the molar amounts of Co, M, Q, E, and T to the molar amount of Li is 0.98 to 1.1:

1.

6. The lithium-cobalt composite oxide according to claim 1, characterized in that, (a×r+c) / (1+r) is 0.985~0.

995.

7. The method for preparing the lithium-cobalt composite oxide according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Mix the Li-containing precursor, the E-doped Co-containing precursor, and the M-doped precursor, and sinter them to obtain an E-doped and M-doped matrix. S2. The doped matrix obtained in step S1, the Co-containing precursor doped with T element, and the Q-containing precursor are mixed and sintered to obtain a lithium cobalt composite oxide.

8. The preparation method according to claim 7, characterized in that, In step S1, the molar ratio of Li to Co is adjusted to 1~1.1∶1.

9. The preparation method according to claim 8, characterized in that, The molar ratio of Li to Co is 1.03 to 1.07:

1.

10. The preparation method according to claim 7, characterized in that, The Co-containing precursor is at least one of Co(OH)2, CoCO3, and Co3O4.

11. The preparation method according to claim 7, characterized in that, The Li-containing precursor is at least one of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium chloride.

12. The preparation method according to claim 7, characterized in that, The precursor containing element M is an oxide of element M.

13. The preparation method according to claim 7, characterized in that, The precursor containing Q element is at least one of the following: an oxide containing Q element, a salt containing Q element, or an acid containing Q element.

14. The preparation method according to claim 7, characterized in that, In step S1, the sintering temperature is 900~1100℃ and the time is 8~12h, and the sintering is carried out in an oxygen-containing atmosphere; in step S2, the sintering temperature is 800~1000℃ and the time is 8~12h, and the sintering is carried out in an oxygen-containing atmosphere.

15. The application of the lithium cobalt composite oxide according to any one of claims 1 to 6 as a cathode material for lithium-ion batteries.

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