High-temperature-resistant and high-voltage-resistant lithium cobalt oxide positive electrode material and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant and high-voltage lithium cobalt oxide positive electrode material and a preparation method thereof, and relates to the technical field of lithium ion batteries, the positive electrode material comprises a lithium cobalt oxide matrix and a coating layer coating the surface of the lithium cobalt oxide matrix; a doping agent containing Mg and rare earth elements is doped in the lithium cobalt oxide matrix, and the lithium cobalt oxide matrix comprises a large-particle matrix and a small-particle matrix; the coating layer is a fast ion coating layer of a garnet phase of Li < 6.75 > La < 3 > Zr < 1.75 > Ta0. 25O12; the surface of a lithium cobalt oxide matrix doped with a dopant is coated with a fast ion coating layer of a Li < 6.75 > La < 3 > Zr < 1.75 > Ta0. 25O12 garnet phase, the dopant contains Mg and rare earth elements, the rare earth elements are introduced outside the doped element Mg for doping, the ion radius of the rare earth elements and doping sites (Li < + > vacancies and CO3 < + > substitution sites) in lithium cobalt oxide crystal lattices have good space adaptability, and the doping performance of the lithium cobalt oxide matrix is improved. And crystal lattices can be effectively embedded without excessive lattice distortion, so that the structural stability of the lithium cobalt oxide crystal in charging and discharging is improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a high-temperature and high-voltage resistant lithium cobalt oxide cathode material and its preparation method. Background Technology

[0002] Lithium cobalt oxide is a commonly used cathode material for lithium-ion batteries. It has advantages such as a high voltage operating platform, high volumetric energy density, high tap density, and ease of large-scale synthesis, and is widely used in various portable electronic devices. However, with the trend of thinner and lighter consumer electronics such as smart devices and wearable devices and the demand for longer battery life, the market demand for battery energy density has further increased. This requires lithium cobalt oxide to increase its charging voltage to obtain higher specific capacity and energy density. For example, the operating voltage of conventional lithium cobalt oxide is usually below 4.5V. By using interface modification technology to build a high-voltage olivine structure coating on the surface of lithium cobalt oxide, the charging cutoff voltage is increased from 4.5V to 4.7V to improve its specific capacity and energy density. When the operating voltage exceeds 4.55V and above, lithium cobalt oxide is under high operating voltage conditions.

[0003] However, under high operating voltage conditions, the crystal structure of lithium cobalt oxide is severely damaged, especially when the cutoff voltage reaches a value relative to Li / Li. + At high voltages of approximately 4.55V, the material undergoes a phase transition, leading to problems such as lattice slip, grain cracking, and lattice deformation, which disrupt lithium-ion migration channels and cause a decline in the material's electrical properties. Furthermore, high operating voltages generate harmful surface transformations and interfacial side reactions. Highly delithiated LiCoO2 is thermodynamically unstable, prone to oxygen loss and transition metal migration, forming a spinel phase, Co3O4, which is detrimental to lithium-ion migration. Simultaneously, the oxygen released during charging to high voltages and the highly catalytic Co... 4+ This will exacerbate electrolyte decomposition, forming an unstable CEI film, further deteriorating electrical performance and affecting battery reliability. Summary of the Invention

[0004] The purpose of this invention is to provide a high-temperature and high-voltage resistant lithium cobalt oxide cathode material and its preparation method, which can improve the stability of lithium cobalt oxide material under high temperature and high voltage and the reliability of basket batteries, thereby solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A high-temperature and high-voltage resistant lithium cobalt oxide cathode material includes a lithium cobalt oxide matrix and a coating layer covering the surface of the lithium cobalt oxide matrix;

[0007] The lithium cobalt oxide matrix is ​​doped with dopants containing Mg and rare earth elements, and the lithium cobalt oxide matrix includes large particle matrix and small particle matrix.

[0008] The coating layer is Li 6.75 La3Zr 1.75 Ta 0.25 O 12 Fast ion coating of garnet phase.

[0009] Preferably, the rare earth elements are Y, La and Ce, and the mass ratio of Mg and rare earth elements is 200-2000 ppm of the total mass of the lithium cobalt oxide matrix.

[0010] Preferably, the mass ratio of the large particle matrix to the small particle matrix is ​​2-4:1, the particle size of the large particle matrix is ​​15-20 μm, and the particle size of the small particle matrix is ​​4-8 μm.

[0011] Preferably, during the preparation of the lithium cobalt oxide matrix, the dopant is provided by magnesium oxide (Mg element), and the rare earth elements are provided by lanthanum oxide (Y), cerium oxide (La), and yttrium oxide (Ce element), respectively. The dopant is embedded into the lithium cobalt oxide matrix by high-temperature sintering.

[0012] Preferably, the lithium cobalt oxide matrix is ​​prepared using lithium carbonate and large-particle aluminum-doped cobalt tetroxide and small-particle aluminum-doped cobalt tetroxide with an aluminum doping concentration of 8000-10000 ppm as raw materials. The large-particle aluminum-doped cobalt tetroxide and small-particle aluminum-doped cobalt tetroxide provide the cobalt source, and lithium carbonate provides the lithium source. The molar ratio of the lithium source to the cobalt source is 1.02-1.1:1.

[0013] Preferably, the preparation process of the large particle matrix is ​​as follows:

[0014] A1. Place large particles of aluminum-doped cobalt tetroxide, lithium carbonate, magnesium oxide, lanthanum oxide, cerium oxide, and yttrium oxide with a particle size of 14-18μm into a self-sealing bag for initial premixing;

[0015] A2. After premixing, transfer the mixture to a ball mill jar and ball mill at 300 rpm for 3 hours to obtain a uniform mixture.

[0016] A3. Load the uniform mixture into the box and place it in the muffle furnace. Heat it to 1020℃-1060℃ at a heating rate of 3℃ / min, and sinter at this temperature for 8-12 hours.

[0017] A4. After sintering, allow the material to cool naturally to room temperature with the furnace. Take out the cooled sintered material and crush it to finally obtain a large-particle lithium cobalt oxide matrix with a particle size of 15μm-20μm.

[0018] Preferably, the preparation process of the small particle matrix is ​​as follows:

[0019] B1. Small particles with a particle size of 3-7μm, doped with aluminum cobalt tetroxide, lithium carbonate, magnesium oxide, lanthanum oxide, cerium oxide and yttrium oxide are placed together in a self-sealing bag for preliminary premixing;

[0020] B2. After premixing, transfer the mixture to a ball mill jar and ball mill at 300 rpm for 3 hours to obtain a uniform mixture.

[0021] B3. Load the uniform mixture into the box and place it in the muffle furnace. Heat it to 980℃-1030℃ at a heating rate of 3℃ / min, and sinter at this temperature for 8-12 hours.

[0022] A4. After sintering, allow the material to cool naturally to room temperature with the furnace. Take out the cooled sintered material and crush it to finally obtain small-particle lithium cobalt oxide matrix with a particle size of 4μm-8μm.

[0023] Preferably, the coating layer is prepared according to Li 6.75 La3Zr 1.75 Ta 0.25 O 12 The stoichiometric ratio is achieved by using lithium source, lanthanum oxide, zirconium oxide and tantalum pentoxide as raw materials of corresponding mass, wherein the lithium source is lithium carbonate or lithium hydroxide.

[0024] Preferably, the preparation process of the coating layer is as follows:

[0025] C1. Prepare the following raw materials: lithium source, lanthanum oxide, zirconium oxide, tantalum pentoxide and isopropanol;

[0026] C2, according to Li 6.75 La3Zr 1.75 Ta 0.25 O 12 The prepared raw materials are added together to a sand mill according to the stoichiometric ratio. Isopropanol is added and the mixture is then sand-milled until a uniform slurry A is formed.

[0027] C3. Transfer slurry A to a grinder for further grinding. After grinding, place it in a forced-air drying oven to dry until slurry A is completely dry and forms powder A.

[0028] C4. After grinding powder A again, it is placed into a muffle furnace and sintered at 800-1200℃ for 8-10 hours. After sintering, the material is taken out and crushed to obtain powder B.

[0029] C5. Add isopropanol to powder B, transfer it to a sand mill again, and sand mill it according to the parameters of feed concentration 300-600g / L, zircon bead particle size 0.4-2mm, filling rate 65-85%, and speed 1500-3500rpm to finally obtain nanoscale coating slurry.

[0030] Based on the above description of a high-temperature, high-voltage resistant lithium cobalt oxide cathode material, this invention also provides a method for preparing the high-temperature, high-voltage resistant lithium cobalt oxide cathode material, comprising the following steps:

[0031] S1. Prepare the lithium cobalt oxide substrate and the slurry-like coating layer respectively;

[0032] S2. Mix the lithium cobalt oxide matrix with the slurry-like coating layer and dispersant, and the mass ratio of lithium cobalt oxide matrix, dispersant and coating layer is 12.5-50:6.75-26:1;

[0033] S3. Sinter the mixed material in a muffle furnace at a temperature of 600-1000℃ for 8-10 hours.

[0034] S4. After sintering, the material is cooled to room temperature in the muffle furnace. The cooled sintered material is then taken out, crushed, filtered, and screened to obtain coatings for large particle matrix and small particle matrix.

[0035] S5. Mix the coatings of the large particle matrix and the coatings of the small particle matrix in a ratio of 2-4:1 to obtain the final high-temperature and high-voltage lithium cobalt oxide cathode material.

[0036] The high-temperature and high-voltage resistant lithium cobalt oxide cathode material and its preparation method proposed in this invention have the following advantages compared with the prior art:

[0037] 1. This invention uses Li 6.75 La3Zr 1.75 Ta 0.25 O 12 A fast-ion coating of garnet phase is deposited on the surface of a doped lithium cobalt oxide matrix. The dopant contains Mg and rare earth elements. In addition to Mg, rare earth elements are introduced for doping. The ionic radius of the rare earth elements is related to the dopant sites (LI) in the lithium cobalt oxide lattice. + Vacancy, CO 3+ Substitution sites possess excellent spatial adaptability, enabling them to effectively embed into the crystal lattice without excessively inducing lattice distortion, thereby increasing the structural stability of lithium cobalt oxide crystals during charging and discharging. Furthermore, the doping of rare earth elements can stabilize CO through charge compensation and electron cloud shielding effects. 3+ / CO 4+ The reduction pair inhibits the dissolution of cobalt under high voltage. In addition, the coating layer on the surface of lithium cobalt oxide increases the Li+ insertion / extraction rate, improves the conductivity of the cathode material, and also improves the rate performance.

[0038] 2. This invention improves the stability of lithium cobalt oxide under high temperature and high voltage through multiple mechanisms such as rare earth ion stabilization of the crystal lattice, interface barrier of composite oxide, and regulation of lithium ion conductivity, thus solving the problem that lithium cobalt oxide is difficult to balance high capacity and cycle stability under high temperature and high voltage. Attached Figure Description

[0039] Figure 1 A flowchart illustrating the preparation process of a large particle matrix according to an embodiment of the present invention is shown;

[0040] Figure 2 A flowchart illustrating the preparation process of a small particle matrix according to an embodiment of the present invention is shown;

[0041] Figure 3 A flowchart illustrating the preparation process of the coating layer according to an embodiment of the present invention is shown;

[0042] Figure 4 A flowchart illustrating the preparation process of the cathode material according to an embodiment of the present invention is shown;

[0043] Figure 5 A scanning electron microscope image according to an embodiment of the present invention is shown;

[0044] Figure 6 A graph showing the relationship between capacity and voltage in the first cycle according to an embodiment of the present invention is shown;

[0045] Figure 7 The diagram shows the relationship between capacity retention and number of cycles in embodiments and comparative examples 1-2 according to the present invention. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] This invention provides, for example Figure 1-3 The high-temperature and high-voltage lithium cobalt oxide cathode material shown includes a lithium cobalt oxide matrix and a coating layer covering the surface of the lithium cobalt oxide matrix; the lithium cobalt oxide matrix is ​​doped with dopants containing Mg and rare earth elements, and the lithium cobalt oxide matrix includes a large particle matrix and a small particle matrix.

[0048] The mass ratio of the large particle matrix to the small particle matrix is ​​2-4:1, the particle size of the large particle matrix is ​​15-20 μm, and the particle size of the small particle matrix is ​​4-8 μm.

[0049] During the preparation of the lithium cobalt oxide matrix, the dopant is provided by magnesium oxide (Mg element), and the rare earth elements are provided by lanthanum oxide (Y), cerium oxide (La element), and yttrium oxide (Ce element). The dopant is embedded into the lithium cobalt oxide matrix by high-temperature sintering.

[0050] The lithium cobalt oxide matrix is ​​prepared using lithium carbonate and large-particle aluminum-doped cobalt tetroxide and small-particle aluminum-doped cobalt tetroxide with an aluminum doping concentration of 8000-10000ppm as raw materials. The large-particle aluminum-doped cobalt tetroxide and small-particle aluminum-doped cobalt tetroxide provide the cobalt source, and lithium carbonate provides the lithium source. The molar ratio of the lithium source to the cobalt source is 1.02-1.1:1.

[0051] The preparation process of the large particle matrix is ​​as follows:

[0052] A1. Place large aluminum-doped cobalt tetroxide particles with a particle size of 14-18μm, lithium carbonate with a purity greater than 99.9%, magnesium oxide, lanthanum oxide, cerium oxide and yttrium oxide into a self-sealing bag for preliminary premixing;

[0053] A2. After premixing, transfer the mixture to a ball mill jar and ball mill at 300 rpm for 3 hours to obtain a uniform mixture.

[0054] A3. Load the uniform mixture into the box and place it in the muffle furnace. Heat it to 1020℃-1060℃ at a heating rate of 3℃ / min, and sinter at this temperature for 8-12 hours.

[0055] A4. After sintering, allow the material to cool naturally to room temperature with the furnace. Take out the cooled sintered material and crush it to finally obtain a large-particle lithium cobalt oxide matrix with a particle size of 15μm-20μm. Mg and rare earth elements Y, La and Ce have been embedded into the matrix lattice through high-temperature sintering to achieve bulk doping.

[0056] The preparation process of the small particle matrix is ​​as follows:

[0057] B1. Small particles of aluminum-doped cobalt tetroxide with a particle size of 3-7μm, lithium carbonate with a purity greater than 99.9%, magnesium oxide, lanthanum oxide, cerium oxide and yttrium oxide are placed together in a self-sealing bag for preliminary premixing;

[0058] B2. After premixing, transfer the mixture to a ball mill jar and ball mill at 300 rpm for 3 hours to obtain a uniform mixture.

[0059] B3. Load the uniform mixture into the box and place it in the muffle furnace. Heat it to 980℃-1030℃ at a heating rate of 3℃ / min, and sinter at this temperature for 8-12 hours.

[0060] A4. After sintering, allow the material to cool naturally to room temperature with the furnace. Take out the cooled sintered material and crush it to obtain small-particle lithium cobalt oxide matrix with a particle size of 4μm-8μm. Mg and rare earth elements Y, La and Ce are doped in bulk through sintering.

[0061] The coating layer is Li 6.75 La3Zr 1.75 Ta 0.25 O 12 Fast ion coating of garnet phase;

[0062] The coating layer is prepared according to Li 6.75 La3Zr 1.75 Ta 0.25 O 12 The stoichiometric ratio is obtained by using lithium source, lanthanum oxide, zirconium oxide and tantalum pentoxide as raw materials of corresponding mass, wherein the lithium source is lithium carbonate or lithium hydroxide;

[0063] Taking the preparation of 1 mol of coating layer as an example, according to Li 6.75 La3Zr 1.75 Ta 0.25 O 12 The method for calculating the amount of each raw material using stoichiometry is as follows:

[0064] Li source: If LiOH is used, 6.75 mol * (1 + 10% ~ 20%) is required; if Li2CO3 is used, 3.37 mol * (1 + 10% ~ 20%) is required.

[0065] Lanthanum oxide (La₂CO₃): 1 mol of La₂O₃ provides 2 mol of La. 3+ Satisfying 3mol La 3+ The demand necessitates 1.5 mol.

[0066] Zirconia (ZrO2): 1.75 mol required, 1.75 mol of Zr is provided directly. 4+ ;

[0067] Tantalum pentoxide (Ta₂O₅): Because 1 mol of Ta₂O₅ provides 2 mol of Ta. 5+ Satisfying 0.25 mol Ta 5+ Therefore, 0.125 mol is required;

[0068] The preparation process of the coating layer is as follows:

[0069] C1. Prepare the following raw materials: lithium source, lanthanum oxide, zirconium oxide, tantalum pentoxide and isopropanol, with isopropanol as a dispersant;

[0070] C2, according to Li 6.75 La3Zr1.75 Ta 0.25 O 12 The prepared raw materials are added together to the sand mill according to the stoichiometric ratio. Isopropanol is added and the mixture is then sand milled. The sand milling conditions are: feed concentration 300-600g / L, zircon bead particle size 0.4-2mm, filling rate 65-85%, and rotation speed 1500-3500rpm until a uniform slurry A is formed.

[0071] C3. Transfer slurry A to a grinder for further grinding. After grinding, place it in a forced-air drying oven to dry until slurry A is completely dry and forms powder A.

[0072] C4. After grinding powder A again, it is placed into a muffle furnace and sintered at 800-1200℃ for 8-10 hours. After sintering, the material is taken out and crushed to obtain powder B.

[0073] C5. Add isopropanol to powder B, transfer it to a sand mill again, and sand mill it according to the parameters of feed concentration 300-600g / L, zircon bead particle size 0.4-2mm, filling rate 65-85%, and speed 1500-3500rpm to finally obtain nanoscale coating slurry.

[0074] By Li 6.75 La3Zr 1.75 Ta 0.25 O 12 A fast-ion coating of garnet phase is deposited on the surface of a doped lithium cobalt oxide matrix. The dopant contains Mg and rare earth elements. In addition to Mg, rare earth elements are introduced for doping. The ionic radius of the rare earth elements is related to the dopant sites (LI) in the lithium cobalt oxide lattice. + Vacancy, CO 3+ Substitution sites possess excellent spatial adaptability, enabling them to effectively embed into the crystal lattice without excessively inducing lattice distortion, thereby increasing the structural stability of lithium cobalt oxide crystals during charging and discharging. Furthermore, the doping of rare earth elements can stabilize CO through charge compensation and electron cloud shielding effects. 3+ / CO 4+ The reduction pair inhibits the dissolution of cobalt under high voltage. In addition, the coating layer on the surface of lithium cobalt oxide increases the Li+ insertion / extraction rate, improves the conductivity of the cathode material, and also improves the rate performance.

[0075] The coating layer uses Li 6.75 La3Zr 1.75 Ta 0.25 O 12 Garnet-phase fast ion conductors can block direct contact between the electrolyte and the lithium cobalt oxide substrate, avoiding the vicious cycle of oxygen release and electrolyte decomposition under high voltage, reducing the formation of unstable CEL films, and the coating film itself has excellent Li... +It has good conductivity and does not hinder lithium ion insertion / extraction, thus resolving the contradiction between coating protection and ion conduction.

[0076] The raw materials used for dopants and coatings are all common in the chemical industry, which are easy to obtain and cost-controllable. The preparation process uses conventional equipment such as sand milling, ball milling and muffle furnace sintering, which does not require special preparation and lowers the threshold for industrialization.

[0077] Based on the above description of a high-temperature, high-voltage resistant lithium cobalt oxide cathode material, this invention also provides a method for preparing such a material, as follows: Figure 4 As shown, it includes the following steps:

[0078] S1. Prepare the lithium cobalt oxide substrate and the slurry-like coating layer respectively;

[0079] S2. Mix the lithium cobalt oxide matrix with the slurry-like coating layer and dispersant, and the mass ratio of lithium cobalt oxide matrix, dispersant and coating layer is 12.5-50:6.75-26:1;

[0080] S3. Sinter the mixed material in a muffle furnace at a temperature of 600-1000℃ for 8-10 hours.

[0081] S4. After sintering, the material is cooled to room temperature in the muffle furnace. The cooled sintered material is then taken out, crushed, filtered, and screened to obtain coatings for large particle matrix and small particle matrix.

[0082] S5. Mix the coatings of the large particle matrix and the coatings of the small particle matrix in a ratio of 2-4:1 to obtain the final high-temperature and high-voltage lithium cobalt oxide cathode material.

[0083] To further verify the performance of the lithium cobalt oxide cathode material prepared by the above-described method for preparing a high-temperature, high-voltage resistant lithium cobalt oxide cathode material, the following examples are provided:

[0084] I. Raw material preparation:

[0085] 1. Cobalt source: Large-particle cobalt tetroxide with an aluminum content of 9000ppm and a particle size of 16μm; Small-particle cobalt tetroxide with an aluminum content of 9000ppm and a particle size of 3.5μm.

[0086] 2. Lithium source: Lithium carbonate with a purity of ≥99.9%;

[0087] 3. Dopants: Magnesium oxide, lanthanum oxide, cerium oxide, and yttrium oxide with a purity ≥ 99.5%;

[0088] 4. Coating layer: Lithium hydroxide, lanthanum oxide, zirconium oxide, and tantalum pentoxide with a purity ≥ 99.5%;

[0089] 5. Dispersant: Isopropanol;

[0090] 6. Battery manufacturing auxiliary materials: conductive carbon, PVDF (polyvinylidene fluoride), NMP (N-methylpyrrolidone), aluminum foil, lithium metal anode sheet, separator, electrolyte mixed solvent, 2032 coin cell casing, wherein the electrolyte mixed solvent is 1 mol / L LiPF6 dissolved in EC / DEC, with a volume ratio of 1:1;

[0091] II. Preparation process:

[0092] 1. Preparation of large-particle lithium cobalt oxide matrix

[0093] 1) Weigh out large-particle aluminum-doped cobalt tetroxide and lithium carbonate at a Li / Co molar ratio of 1:1.08, and add magnesium oxide, lanthanum oxide, cerium oxide and yttrium oxide at the same time, so that the mass percentages of magnesium, lanthanum, cerium and yttrium in the lithium cobalt oxide matrix are 1200ppm, 500ppm, 500ppm and 1600ppm respectively.

[0094] 2) Place the above raw materials in a self-sealing bag and premix for 15 minutes, then transfer them to a ball mill jar and ball mill at 300 rpm for 3 hours to obtain a uniform mixture;

[0095] 3) Load the mixture into a sagger, place it in a muffle furnace, raise the temperature to 1050°C at a rate of 3°C / min, hold for sintering for 10 hours, and then cool it to room temperature with the furnace.

[0096] 4) Remove the cooled sintered material, crush it to obtain a large-particle lithium cobalt oxide matrix with Dv50=18μm.

[0097] 2. Preparation of small-particle lithium cobalt oxide matrix

[0098] 1) Weigh out small-particle aluminum-doped cobalt tetroxide and lithium carbonate according to a Li / Co molar ratio of 1:1.048, and add the same type of dopant as the large-particle matrix, wherein the mass percentages of magnesium, lanthanum, cerium and yttrium are 1200ppm, 500ppm, 500ppm and 1200ppm respectively.

[0099] 2) After premixing in self-sealing bags and ball milling at 300 rpm for 3 hours, the mixture is placed in a sagger and placed in a muffle furnace. The temperature is increased to 1015℃ at a rate of 3℃ / min, and sintered at that temperature for 10 hours. The mixture is then cooled to room temperature in the furnace.

[0100] 3) The sintered material was crushed and cooled to obtain a small-particle lithium cobalt oxide matrix with a Dv50 of 7μm.

[0101] 3. Preparation of the coating layer slurry:

[0102] 1) Press Li 6.75 La3Zr 1.75 Ta 0.25 O12 Weigh out lithium hydroxide, lanthanum oxide, zirconium oxide, and tantalum pentoxide according to the stoichiometric ratio, with lithium hydroxide in 15% excess. Place them in a sand mill and add isopropanol to form slurry A.

[0103] 2) Transfer slurry A into a grinding mill and grind it at 3000 rpm. The zircon beads used have a particle size of 1.8 mm and a filling rate of 80%. After grinding, transfer it into a forced-air drying oven to dry it and obtain powder A.

[0104] 3) After grinding powder A again, it was put into a muffle furnace and sintered at 900°C for 8 hours. The sintered material was then taken out and crushed to obtain powder B.

[0105] 4) Add isopropanol to powder B, load it into a grinder at a feed concentration of 400 g / L, grind at 2000 rpm, with zirconium bead particle size of 1.8 mm and filling rate of 75%, and finally obtain the coating slurry, namely LLZTO nano slurry.

[0106] III. Preparation of High-Temperature and High-Voltage Lithium Cobalt Oxide Cathode Material:

[0107] 1. Take large particle matrix and small particle matrix separately, mix the large particle matrix and small particle matrix with LLZTO nano slurry and isopropanol at a mass ratio of 40:20:1, transfer to a ball mill jar and ball mill at 300 rpm for 3 hours.

[0108] 2. Transfer the mixed slurry into a vacuum drying oven and dry for 3 hours until completely dry;

[0109] 3. The dried mixture is placed into a sagger and sintered in a muffle furnace at 900℃ for 8 hours. After sintering, it is cooled to room temperature with the furnace, crushed and sieved to obtain large-particle coated lithium cobalt oxide and small-particle coated lithium cobalt oxide, respectively.

[0110] 4. Mix large-particle coated lithium cobalt oxide and small-particle coated lithium cobalt oxide at a mass ratio of 4:1 to obtain the finished high-temperature and high-voltage resistant lithium cobalt oxide cathode material.

[0111] IV. Comparative Design:

[0112] 1. Comparative Example 1: The preparation process is the same as in the example, except that the coating layer is replaced with titanium oxide and cobalt hydroxide coating. The mass percentages of titanium and cobalt in the lithium cobalt oxide matrix are 600 ppm and 12000 ppm, respectively.

[0113] 2. Comparative Example 2: The preparation process is the same as in the Example, except that the Mg, La, Ce and Y multi-component doping is replaced with Mg doping alone. The Mg mass percentage is the same as in the Example, which is 1200 ppm.

[0114] V. Battery fabrication:

[0115] The positive electrode materials of the examples and comparative examples were mixed with conductive carbon and PVDF in NMP at a mass ratio of 90:5:5 to form a homogenate, which was then uniformly coated onto aluminum foil. After drying in a forced-air oven at 80°C, the mixture was cut into circular positive electrode sheets with a diameter of 14 mm and vacuum dried at 120°C for 2 hours. CR2032 button half-cells were assembled in a glove box, with lithium metal as the negative electrode and a mixed electrolyte solvent as the electrolyte.

[0116] VI. Performance Testing and Results

[0117] 1. Test conditions:

[0118] Capacity testing: voltage window 3.0-4.58V, discharge rate 0.1C, test temperature 25℃;

[0119] Cyclic performance test: voltage window 3.0-4.58V, charge / discharge rate 0.5C / 1C, test temperature 45℃, 50 cycles.

[0120] 2. The number of tests is shown in Table 1 below:

[0121] Table 1

[0122] category First discharge capacity (mAh / g) First-efficacy (%) Capacity retention rate at 50th lap (%) Example 196.08 94.80 94.51 Comparative Example 1 194.95 94.92 93.06 Comparative Example 2 198.15 94.95 87.46

[0123] From the data in Table 1, we can conclude that:

[0124] The first-cycle discharge capacity of the example is basically the same as that of Comparative Examples 1 and 2, illustrating the high capacity characteristics of the multi-doped material and the LLZTO-coated non-sacrificial material in this scheme. Figure 6 The figure shows the first cycle voltage-capacity curve of the CR2032 button half-cell as the test object in the embodiment, under the conditions of 25℃, 3.0-4.58V voltage window, and 0.1C charge-discharge rate. The first cycle discharge capacity of the material reached 196.08mAh / g, with an initial efficiency of 94.80%. The curve is smooth without obvious abnormal plateaus, indicating that the material can fully de-intercalate and de-intercalate lithium at high voltage (4.58V) and has excellent specific capacity. Moreover, there are few side reactions and no additional capacity loss peaks during the first charge-discharge process. The crystal structure is intact and the interface compatibility is good, which verifies that the electrochemical activity of the material is not damaged by Mg, rare earth element doping and LLZTO coating.

[0125] like Figure 5The image shows a scanning electron microscope (SEM) image of the cathode material prepared in the example, demonstrating the microstructure of the high-temperature and high-voltage lithium cobalt oxide cathode material. It clearly shows the mixed state of large and small lithium cobalt oxide particles, as well as the coverage of the LLZTO coating layer on the surface. From the image, it can be seen that the material particles have regular morphology, uniform distribution of large and small particles, and small particles fill the gaps between large particles, conforming to a 2-4:1 ratio design between large and small particle substrates. The LLZTO coating layer is dense and uniformly covers the substrate surface, with no obvious peeling or exposed areas, proving that the coating process is stable and reliable, providing a structural basis for interface protection and lithium-ion conduction.

[0126] The first-charge efficiency of the example reached 94.80%, close to the 94.92%-94.95% of the comparative examples, indicating high material crystallinity, fewer side reactions during the first charge-discharge process, and low energy loss. After 50 cycles at 45°C, the capacity retention of the example was significantly higher than that of Comparative Examples 1 and 2. Figure 7 As shown, the design of LLZTO coating with Mg and rare earth elements as multi-doped components can effectively suppress structural damage and interfacial side reactions under high temperature and high voltage, and significantly improve cycle stability.

[0127] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-temperature, high-voltage resistant lithium cobalt oxide cathode material, characterized in that: Including a lithium cobalt oxide substrate and a coating layer covering the surface of the lithium cobalt oxide substrate; The lithium cobalt oxide matrix is ​​doped with dopants containing Mg and rare earth elements, and the lithium cobalt oxide matrix includes large particle matrix and small particle matrix. The coating layer is Li 6.75 La3Zr 1.75 Ta 0.25 O 12 Fast ion coating of garnet phase.

2. The high-temperature and high-voltage resistant lithium cobalt oxide cathode material according to claim 1, characterized in that: The rare earth elements are Y, La and Ce, and the mass ratio of Mg and rare earth elements is 200-2000 ppm of the total mass of the lithium cobalt oxide matrix.

3. The high-temperature and high-voltage resistant lithium cobalt oxide cathode material according to claim 2, characterized in that: The mass ratio of the large particle matrix to the small particle matrix is ​​2-4:1, the particle size of the large particle matrix is ​​15-20 μm, and the particle size of the small particle matrix is ​​4-8 μm.

4. The high-temperature and high-voltage resistant lithium cobalt oxide cathode material according to claim 3, characterized in that: During the preparation of the lithium cobalt oxide matrix, the dopant is provided by magnesium oxide (Mg element), and rare earth elements are provided by lanthanum oxide (Y), cerium oxide (La), and yttrium oxide (Ce element). The dopant is embedded into the lithium cobalt oxide matrix by high-temperature sintering.

5. The high-temperature and high-voltage resistant lithium cobalt oxide cathode material according to claim 4, characterized in that: The lithium cobalt oxide matrix is ​​prepared using lithium carbonate and large-particle aluminum-doped cobalt tetroxide and small-particle aluminum-doped cobalt tetroxide with an aluminum doping concentration of 8000-10000ppm as raw materials. The large-particle aluminum-doped cobalt tetroxide and small-particle aluminum-doped cobalt tetroxide provide the cobalt source, and lithium carbonate provides the lithium source. The molar ratio of the lithium source to the cobalt source is 1.02-1.1:

1.

6. The high-temperature and high-voltage resistant lithium cobalt oxide cathode material according to claim 5, characterized in that: The preparation process of the large particle matrix is ​​as follows: A1. Place large particles of aluminum-doped cobalt tetroxide, lithium carbonate, magnesium oxide, lanthanum oxide, cerium oxide, and yttrium oxide with a particle size of 14-18μm into a self-sealing bag for initial premixing; A2. After premixing, transfer the mixture to a ball mill jar and ball mill at 300 rpm for 3 hours to obtain a uniform mixture. A3. Load the uniform mixture into the box and place it in the muffle furnace. Heat it to 1020℃-1060℃ at a heating rate of 3℃ / min, and sinter at this temperature for 8-12 hours. A4. After sintering, allow the material to cool naturally to room temperature with the furnace. Take out the cooled sintered material and crush it to finally obtain a large-particle lithium cobalt oxide matrix with a particle size of 15μm-20μm.

7. The high-temperature and high-voltage resistant lithium cobalt oxide cathode material according to claim 6, characterized in that: The preparation process of the small particle matrix is ​​as follows: B1. Small particles with a particle size of 3-7μm, doped with aluminum cobalt tetroxide, lithium carbonate, magnesium oxide, lanthanum oxide, cerium oxide and yttrium oxide are placed together in a self-sealing bag for preliminary premixing; B2. After premixing, transfer the mixture to a ball mill jar and ball mill at 300 rpm for 3 hours to obtain a uniform mixture. B3. Load the uniform mixture into the box and place it in the muffle furnace. Heat it to 980℃-1030℃ at a heating rate of 3℃ / min, and sinter at this temperature for 8-12 hours. A4. After sintering, allow the material to cool naturally to room temperature with the furnace. Take out the cooled sintered material and crush it to finally obtain small-particle lithium cobalt oxide matrix with a particle size of 4μm-8μm.

8. The high-temperature and high-voltage resistant lithium cobalt oxide cathode material according to claim 1, characterized in that: The coating layer is prepared according to Li 6.75 La3Zr 1.75 Ta 0.25 O 12 The stoichiometric ratio is achieved by using lithium source, lanthanum oxide, zirconium oxide and tantalum pentoxide as raw materials of corresponding mass, wherein the lithium source is lithium carbonate or lithium hydroxide.

9. The high-temperature and high-voltage resistant lithium cobalt oxide cathode material and its preparation method according to claim 8, characterized in that: The preparation process of the coating layer is as follows: C1. Prepare the following raw materials: lithium source, lanthanum oxide, zirconium oxide, tantalum pentoxide and isopropanol; C2, according to Li 6.75 La3Zr 1.75 Ta 0.25 O 12 The prepared raw materials are added together to a sand mill according to the stoichiometric ratio. Isopropanol is added and the mixture is then sand-milled until a uniform slurry A is formed. C3. Transfer slurry A to a grinder for further grinding. After grinding, place it in a forced-air drying oven to dry until slurry A is completely dry and forms powder A. C4. After grinding powder A again, it is placed into a muffle furnace and sintered at 800-1200℃ for 8-10 hours. After sintering, the material is taken out and crushed to obtain powder B. C5. Add isopropanol to powder B, transfer it to a sand mill again, and sand mill it according to the parameters of feed concentration 300-600g / L, zircon bead particle size 0.4-2mm, filling rate 65-85%, and speed 1500-3500rpm to finally obtain nanoscale coating slurry.

10. A method for preparing a high-temperature, high-voltage lithium cobalt oxide cathode material, comprising preparing the high-temperature, high-voltage lithium cobalt oxide cathode material according to any one of claims 1-9, characterized in that: Includes the following steps: S1. Prepare the lithium cobalt oxide substrate and the slurry-like coating layer respectively; S2. Mix the lithium cobalt oxide matrix with the slurry-like coating layer and dispersant, and the mass ratio of lithium cobalt oxide matrix, dispersant and coating layer is 12.5-50:6.75-26:1; S3. Sinter the mixed material in a muffle furnace at a temperature of 600-1000℃ for 8-10 hours. S4. After sintering, the material is cooled to room temperature in the muffle furnace. The cooled sintered material is then taken out, crushed, filtered, and screened to obtain coatings for large particle matrix and small particle matrix. S5. Mix the coatings of the large particle matrix and the coatings of the small particle matrix in a ratio of 2-4:1 to obtain the final high-temperature and high-voltage lithium cobalt oxide cathode material.

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