Coated modified lithium cobalt oxide positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of positive electrode materials, and particularly relates to a coated modified lithium cobalt oxide positive electrode material as well as a preparation method and application thereof. The preparation method provided by the invention comprises the following steps: 1) mixing and grinding lithium cobalt oxide and a metal oxide, and then carrying out first sintering to obtain a lithium cobalt oxide positive electrode material; (2) putting the lithium cobalt oxide positive electrode material obtained in the step (1) into a phosphorus source solution, carrying out first stirring impregnation, filtering and drying, and then putting the lithium cobalt oxide positive electrode material into a halide solution, carrying out second stirring impregnation, filtering and drying to obtain a pre-coated lithium cobalt oxide positive electrode material; and 3) carrying out secondary sintering and crushing on the pre-coated lithium cobalt oxide positive electrode material obtained in the step 2) to obtain the coated modified lithium cobalt oxide positive electrode material.The coated modified lithium cobalt oxide positive electrode material prepared by the method has high first efficiency and high cycle stability under high voltage.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, specifically relating to a coated and modified lithium cobalt oxide cathode material, its preparation method, and its application. Background Technology

[0002] Lithium cobalt oxide, as a cathode material for lithium-ion batteries, has become an important choice for consumer electronics and some military products due to its high energy density. Compared to commercially available lithium iron phosphate cathode materials, lithium cobalt oxide materials have a higher voltage plateau and capacity. To further improve its capacity, most methods involve increasing the operating voltage, such as expanding the charge / discharge voltage range to 3-4.6V, with an actual specific capacity reaching over 220mAh / g (0.1C). However, lithium cobalt oxide materials are prone to degradation under long-term high-voltage conditions. In particular, the dissolution of cobalt ions during high-voltage operation can lead to the collapse of the overall structure. In addition, irreversible surface phase transitions also accelerate the capacity decay of the battery.

[0003] Faced with this dilemma, traditional methods include doping lithium cobalt oxide materials with trace amounts of elements such as Ti, Mg, and Al to stabilize the transition metal layer structure, or coating the surface with oxides (such as Al2O3) to inhibit the dissolution of cobalt ions. However, these doping and coating techniques have limited effect on improving the initial efficiency and long-term cycle stability of battery materials at a high voltage of 4.6V, and cannot meet the high-performance requirements of lithium cobalt oxide batteries. The initial efficiency and cycle stability of existing lithium cobalt oxide materials still need to be further improved. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the shortcomings of existing lithium cobalt oxide materials in terms of initial efficiency and cycle stability, thereby providing a coated modified lithium cobalt oxide cathode material, its preparation method and application.

[0005] This invention provides a method for preparing a coated and modified lithium cobalt oxide cathode material, comprising the following steps: 1) Lithium cobalt oxide and metal oxide are mixed, ground, and then subjected to a first sintering process to obtain lithium cobalt oxide cathode material; 2) The lithium cobalt oxide cathode material obtained in step 1) is placed in a phosphorus source solution and impregnated by first stirring, filtered, and dried. Then it is placed in a halide solution and impregnated by second stirring, filtered, and dried to obtain a pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material obtained in step 2) is subjected to a second sintering and crushed to obtain the coated modified lithium cobalt oxide cathode material.

[0006] Preferably, the metal oxide in step 1) is selected from at least one of aluminum oxide, magnesium oxide, zirconium oxide, and lanthanum oxide; The lithium cobalt oxide mentioned in step 1) is a highly crystalline material, and the crystallinity of the lithium cobalt oxide is above 96%; The molar ratio of the metal oxide to lithium cobalt oxide in step 1) is (0.1-0.5):100; The grinding speed mentioned in step 1) is 350-400℃, and the grinding time is more than 3 hours; Preferably, the grinding time is 3-12 hours; Optionally, the grinding step described in step 1) may be preceded by pre-grinding for 20-30 minutes. Optionally, the pre-grinding may be carried out by traditional manual grinding.

[0007] Preferably, in step 1), the first sintering temperature is 600-900℃ and the first sintering time is 10-12h; In step 1), the first sintering is carried out in an oxygen-containing atmosphere; Optionally, the oxygen-containing atmosphere may include an air atmosphere.

[0008] Preferably, the phosphorus source in the phosphorus source solution in step 2) includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium phosphate, aluminum phosphate, and iron phosphate; The molar concentration of phosphorus source in the phosphorus source solution mentioned in step 2) is 0.05-0.2 mol / L.

[0009] Preferably, the ratio of lithium cobalt oxide cathode material to phosphorus source solution in step 2) is (40-55):(20-30), in g / mL; In step 2), the first stirring and impregnation speed is 400-600 r / min, and the first stirring and impregnation time is 30-35 min.

[0010] Preferably, the halide in the halide solution in step 2) is selected from at least one of NH4F, LiCl, and MgF; The molar concentration of the halide in the halide solution is 0.05-0.2 mol / L; In step 2), the second stirring and impregnation speed is 400-600 r / min, and the second stirring and impregnation time is 30-35 min.

[0011] Preferably, the volume ratio of the phosphorus source solution to the halide solution in step 2) is (20-30):(12-25); Step 2) includes a grinding step after the second stirring and impregnation, filtration, and drying steps in the halide solution.

[0012] Preferably, in step 3), the second sintering temperature is 800-900℃ and the second sintering time is 5-6h; In step 3), the second sintering is carried out in an oxygen-containing atmosphere; Optionally, the oxygen-containing atmosphere includes at least one of an air atmosphere and an oxygen atmosphere.

[0013] This invention provides a coated modified lithium cobalt oxide cathode material, which is prepared by the above-described method for preparing coated modified lithium cobalt oxide cathode materials.

[0014] The present invention also provides an application of the above-described coated modified lithium cobalt oxide cathode material in lithium-ion batteries.

[0015] The technical solution of this invention has the following advantages: 1. The preparation method of the coated modified lithium cobalt oxide cathode material provided by the present invention includes the following steps: 1) mixing lithium cobalt oxide and metal oxide, grinding, and then sintering in a first stage to obtain a lithium cobalt oxide cathode material; 2) placing the lithium cobalt oxide cathode material obtained in step 1) into a phosphorus source solution for a first stirring and impregnation, filtering, and drying, and then placing it into a halide solution for a second stirring and impregnation, filtering, and drying to obtain a pre-coated lithium cobalt oxide cathode material; 3) subjecting the pre-coated lithium cobalt oxide cathode material obtained in step 2) to a second sintering and crushing to obtain the coated modified lithium cobalt oxide cathode material. The present invention employs a triple coating strategy—oxide coating, then phosphate coating, and then halide coating—to jointly suppress the capacity decay of the lithium cobalt oxide cathode material under high voltage conditions. Oxides inhibit cobalt migration by forming a spinel layer, phosphates primarily suppress interfacial side reactions and stabilize the surface structure, and halides work synergistically with phosphates to optimize interfacial lithium-ion transport and neutralize residual alkali on the surface. The combined effect of these three components allows lithium cobalt oxide materials to maintain stable operation over long cycles while improving capacity and initial efficiency at high voltages. The multi-step coating process forms a denser protective layer on the surface of the lithium cobalt oxide material, simultaneously stabilizing the interface, optimizing ion transport channels, and reducing cobalt dissolution, thus enabling better cycle performance under high voltage conditions. The coated and modified lithium cobalt oxide cathode material prepared by this invention exhibits high initial efficiency and high cycle stability at high voltages.

[0016] 2. The preparation method of the coated modified lithium cobalt oxide cathode material provided by the present invention, wherein the molar concentration of the phosphorus source in the phosphorus source solution in step 2) is 0.05-0.2 mol / L; the first stirring and impregnation speed in step 2) is 400-600 r / min, and the first stirring and impregnation time is 30-35 min. The halide in the halide solution in step 2) is selected from at least one of NH4F, LiCl, and MgF; the molar concentration of the halide in the halide solution is 0.05-0.2 mol / L; the second stirring and impregnation speed in step 2) is 400-600 r / min, and the second stirring and impregnation time is 30-35 min. The present invention provides various parameters for controlling the coating step, wherein the phosphorus source or halide is first dissolved in a solvent to form a true solution at the molecular or ionic level. By means of stirring, the ions containing coating elements in these solutions can be uniformly dispersed and adsorbed on the surface of lithium cobalt oxide particles. The use of solution coating can form a uniform, dense, ultrathin and firmly bonded nanoscale coating layer with a thickness of about 2-5 nm with each immersion. This further enhances the synergistic effect of triple coating of oxide, phosphate, and halide, so that the coated modified lithium cobalt oxide cathode material prepared by this invention has higher initial efficiency and higher cycle stability under high voltage.

[0017] 3. The preparation method of the modified lithium cobalt oxide cathode material provided by the present invention, with its layered coating design of inner and outer layers, breaks through the technical bottleneck of traditional single coating and provides a new idea for extending the service life of lithium cobalt oxide batteries while maintaining energy density. Detailed Implementation

[0018] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0019] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0020] Example 1 This embodiment provides a method for preparing a coated modified lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity is 97%) and 0.20g of alumina were placed in a mortar and manually ground for 20 minutes. Then, they were added to a high-speed ball mill and dry-ground for 3 hours at a speed of 400r / min. After that, they were placed in a muffle furnace and sintered at 600℃ for 10 hours in an air atmosphere. The mixture was then crushed and sieved to obtain lithium cobalt oxide cathode material. 2) Add 48.94g of the lithium cobalt oxide cathode material obtained in step 1) to 25mL of ammonium dihydrogen phosphate solution and stir at 500r / min for 30min. The molar concentration of ammonium dihydrogen phosphate in the ammonium dihydrogen phosphate solution is 0.1mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Then add 20mL of lithium chloride solution and stir at 500r / min for 30min. The molar concentration of lithium chloride in the lithium chloride solution is 0.05mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Remove and grind manually for 2h to obtain the pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material was placed in a muffle furnace and sintered at 900°C for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0021] Example 2 This embodiment provides a method for preparing a coated modified lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity of 97%) and 0.08g of magnesium oxide were placed in a mortar and manually ground for 20 minutes. Then, they were added to a high-speed ball mill and dry-ground for 3 hours at a speed of 400r / min. After that, they were placed in a muffle furnace and sintered at 600℃ for 10 hours in an air atmosphere. The mixture was then crushed and sieved to obtain lithium cobalt oxide cathode material. 2) Add 48.94g of the lithium cobalt oxide cathode material obtained in step 1) to 25mL of lithium phosphate solution and stir at 500r / min for 30min. The molar concentration of lithium phosphate in the lithium phosphate solution is 0.1mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Then add 20mL of ammonium fluoride solution and stir at 500r / min for 30min. The molar concentration of ammonium fluoride in the ammonium fluoride solution is 0.05mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Remove and manually grind for 2h to obtain the pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material was placed in a muffle furnace and sintered at 800°C for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0022] Example 3 This embodiment provides a method for preparing a coated modified lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity is 97%) and 0.25g of zirconium oxide were placed in a mortar and manually ground for 20 minutes. Then, they were added to a high-speed ball mill and dry-ground for 3 hours at a speed of 400r / min. After that, they were placed in a muffle furnace and sintered at 700℃ for 10 hours in an air atmosphere. The mixture was then crushed and sieved to obtain lithium cobalt oxide cathode material. 2) Add 48.94g of the lithium cobalt oxide cathode material obtained in step 1) to 25mL of diammonium hydrogen phosphate solution and stir at 500r / min for 30min. The molar concentration of diammonium hydrogen phosphate in the diammonium hydrogen phosphate solution is 0.1mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Then add 20mL of magnesium fluoride solution and stir at 500r / min for 30min. The molar concentration of magnesium fluoride in the magnesium fluoride solution is 0.05mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Remove and manually grind for 2h to obtain the pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material was placed in a muffle furnace and sintered at 900°C for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0023] Example 4 This embodiment provides a method for preparing a coated modified lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity is 97%) and 0.652g of lanthanum oxide were placed in a mortar and manually ground for 20 minutes. Then, they were added to a high-speed ball mill and dry-ground for 3 hours at a speed of 400r / min. After that, they were placed in a muffle furnace and sintered at 800℃ for 10 hours in an air atmosphere. The mixture was then crushed and sieved to obtain lithium cobalt oxide cathode material. 2) Add 48.94g of the lithium cobalt oxide cathode material obtained in step 1) to 25mL of aluminum phosphate solution and stir at 500r / min for 30min. The molar concentration of aluminum phosphate in the aluminum phosphate solution is 0.1mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Then add 20mL of lithium chloride solution and stir at 500r / min for 30min. The molar concentration of lithium chloride in the lithium chloride solution is 0.05mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Remove and grind manually for 2h to obtain the pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material was placed in a muffle furnace and sintered at 800°C for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0024] Example 5 This embodiment provides a method for preparing a coated modified lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity is 97%) and 0.20g of alumina were placed in a mortar and manually ground for 20 minutes. Then, they were added to a high-speed ball mill and dry-ground for 3 hours at a speed of 400r / min. After that, they were placed in a muffle furnace and sintered at 600℃ for 10 hours in an air atmosphere. The mixture was then crushed and sieved to obtain lithium cobalt oxide cathode material. 2) Add 48.94g of the lithium cobalt oxide cathode material obtained in step 1) to 25mL of aluminum phosphate solution and stir at 500r / min for 30min. The molar concentration of aluminum phosphate in the aluminum phosphate solution is 0.1mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Then add 20mL of lithium chloride solution and stir at 500r / min for 30min. The molar concentration of lithium chloride in the lithium chloride solution is 0.05mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Remove and grind manually for 2h to obtain the pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material was placed in a muffle furnace and sintered at 900°C for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0025] Example 6 This embodiment provides a method for preparing a coated modified lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity of 97%) and 0.08g of magnesium oxide were placed in a mortar and manually ground for 20 minutes. Then, they were added to a high-speed ball mill and dry-ground for 3 hours at a speed of 400r / min. After that, they were placed in a muffle furnace and sintered at 600℃ for 10 hours in an air atmosphere. The mixture was then crushed and sieved to obtain lithium cobalt oxide cathode material. 2) Add 48.94g of the lithium cobalt oxide cathode material obtained in step 1) to 25mL of ammonium dihydrogen phosphate solution and stir at 500r / min for 30min. The molar concentration of ammonium dihydrogen phosphate in the ammonium dihydrogen phosphate solution is 0.1mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Then add 20mL of lithium chloride solution and stir at 500r / min for 30min. The molar concentration of lithium chloride in the lithium chloride solution is 0.05mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Remove and grind manually for 2h to obtain the pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material was placed in a muffle furnace and sintered at 900°C for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0026] Comparative Example 1 This comparative example provides a method for preparing a lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity is 97%) was placed in a mortar and manually ground for 20 minutes. Then it was dry ground in a high-speed ball mill for 3 hours at a speed of 400r / min. Then it was placed in a muffle furnace and sintered at 600℃ for 10 hours in air atmosphere, and then sintered at 900℃ for 5 hours in air atmosphere. After that, it was crushed and sieved to obtain lithium cobalt oxide cathode material.

[0027] Comparative Example 2 This comparative example provides a method for preparing a coated and modified lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity is 97%) was placed in a mortar and manually ground for 20 minutes. Then it was added to a high-speed ball mill and dry ground for 3 hours at a speed of 400r / min. Then it was placed in a muffle furnace and sintered at 600℃ for 10 hours in an air atmosphere. After crushing and sieving, lithium cobalt oxide cathode material was obtained. 2) Add 48.94g of the lithium cobalt oxide cathode material obtained in step 1) to 25mL of ammonium dihydrogen phosphate solution and stir at 500r / min for 30min. The molar concentration of ammonium dihydrogen phosphate in the ammonium dihydrogen phosphate solution is 0.1mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Then add 20mL of lithium chloride solution and stir at 500r / min for 30min. The molar concentration of lithium chloride in the lithium chloride solution is 0.05mol / L. After stirring evenly, filter, rinse, and dry in an oven at 120℃ for 5h. Remove and grind manually for 2h to obtain the pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material was placed in a muffle furnace and sintered at 900°C for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0028] Comparative Example 3 This comparative example provides a method for preparing a coated and modified lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity is 97%) and 0.20g of alumina were placed in a mortar and manually ground for 20 minutes. Then, they were added to a high-speed ball mill and dry-ground for 3 hours at a speed of 400r / min. After that, they were placed in a muffle furnace and sintered at 600℃ for 10 hours in an air atmosphere. The mixture was then crushed and sieved to obtain lithium cobalt oxide cathode material. 2) Add 48.94g of the lithium cobalt oxide cathode material obtained in step 1) to 20mL of lithium chloride solution and stir at a constant speed of 500r / min for 30min. The molar concentration of lithium chloride in the lithium chloride solution is 0.05mol / L. After stirring evenly, filter, rinse, dry in an oven at 120℃ for 5h, take it out and grind manually for 2h to obtain the pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material was placed in a muffle furnace and sintered at 900°C for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0029] Comparative Example 4 This comparative example provides a method for preparing a coated and modified lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity is 97%) and 0.20g of alumina were placed in a mortar and manually ground for 20 minutes. Then, they were added to a high-speed ball mill and dry-ground for 3 hours at a speed of 400r / min. After that, they were placed in a muffle furnace and sintered at 600℃ for 10 hours in an air atmosphere. The mixture was then crushed and sieved to obtain lithium cobalt oxide cathode material. 2) Add 48.94g of the lithium cobalt oxide cathode material obtained in step 1) to 25mL of ammonium dihydrogen phosphate solution and stir at a constant speed of 500r / min for 30min. The molar concentration of ammonium dihydrogen phosphate in the ammonium dihydrogen phosphate solution is 0.1mol / L. After stirring evenly, filter, rinse, dry in an oven at 120℃ for 5h, take it out and grind manually for 2h to obtain the pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material was placed in a muffle furnace and sintered at 900°C for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0030] Comparative Example 5 This comparative example provides a method for preparing a coated and modified lithium cobalt oxide cathode material, including the following steps: 97.87g of lithium cobalt oxide (highly crystalline, with a crystallinity of 97%), 0.20g of alumina, 0.29g of ammonium dihydrogen phosphate, and 0.04g of lithium chloride were placed in a mortar and manually ground for 20 minutes. Then, they were dry-milled in a high-speed ball mill for 3 hours at a speed of 400 r / min. The mixture was then sintered in a muffle furnace at 900℃ for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0031] Comparative Example 6 This comparative example provides a method for preparing a coated and modified lithium cobalt oxide cathode material, including the following steps: 1) 97.87g of lithium cobalt oxide (high crystallinity, crystallinity is 97%) and 0.20g of alumina were placed in a mortar and manually ground for 20 minutes. Then, they were added to a high-speed ball mill and dry-ground for 3 hours at a speed of 400r / min. After that, they were placed in a muffle furnace and sintered at 600℃ for 10 hours in an air atmosphere. The mixture was then crushed and sieved to obtain lithium cobalt oxide cathode material. 2) Mix 25 mL of ammonium dihydrogen phosphate solution and 20 mL of lithium chloride solution to form a mixed solution. Then add 48.94 g of lithium cobalt oxide cathode material obtained in step 1) to the mixed solution and stir at a constant speed of 500 r / min for 30 min. The molar concentration of ammonium dihydrogen phosphate in the ammonium dihydrogen phosphate solution is 0.1 mol / L and the molar concentration of lithium chloride in the lithium chloride solution is 0.05 mol / L. After stirring evenly, filter, rinse, dry in an oven at 120℃ for 5 h, take it out and grind manually for 2 h to obtain pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material was placed in a muffle furnace and sintered at 900°C for 5 hours in an air atmosphere. After crushing and sieving, the coated modified lithium cobalt oxide cathode material was obtained.

[0032] Test case The coated and modified lithium cobalt oxide cathode materials prepared in Examples 1-6 or the lithium cobalt oxide cathode materials prepared in Comparative Examples 1-6 were used as the main cathode materials to fabricate lithium-ion batteries (CR2032 type button half-cells). The specific preparation method of the lithium-ion batteries is as follows: The main material, polyvinylidene fluoride (PVDF), and acetylene black were mixed in N-methylpyrrolidone solvent at a mass ratio of 86:7:7. After homogenization, coating, drying, and cutting, the cathode sheet was formed (the areal density of the cathode material is 8.0 mg / cm³). 2 A Celgard 2500 separator, lithium metal sheets as the negative electrode, and LBC3021C011 electrolyte were used. The battery was assembled in a glove box under an argon atmosphere, following the order of negative electrode, electrolyte, separator, electrolyte, and positive electrode. The prepared batteries were then subjected to electrical performance tests using a Blue Electric testing system. Specifically, the batteries were charged at 0.2C to 4.6V at 25°C, then discharged at 0.2C to 3.0V, constituting one cycle. The charge / discharge capacity of this cycle was the initial charge / discharge specific capacity. The initial efficiency was calculated as (initial discharge specific capacity / initial charge specific capacity × 100%). After two cycles, 50 cycles were performed at 1C. The charge / discharge capacity of the third and fifth cycles was recorded. The cycle capacity retention rate was calculated as (fifty-second cycle / third cycle discharge capacity × 100%). The test results are shown in Table 1.

[0033] Table 1

[0034] The first discharge specific capacity, first efficiency, and cycle capacity retention of the coated and modified lithium cobalt oxide cathode materials prepared in Examples 1-6 of this invention are all superior to those prepared in Comparative Examples 1-6. Compared to Example 1, Comparative Example 1 did not have coating with metal oxide, phosphorus source, or halide; Comparative Example 2, compared to Example 1, only lacked coating with metal oxide; Comparative Example 3, compared to Example 1, only lacked coating with phosphorus source; and Comparative Example 4, compared to Example 1, only lacked coating with halide. According to the data in Table 1, the improvement in first discharge specific capacity, first efficiency, and cycle capacity retention of the coated and modified lithium cobalt oxide cathode material of Example 1 compared to Comparative Example 1 is significantly higher than the sum of the improvements in first discharge specific capacity, first efficiency, and cycle capacity retention of Comparative Example 2, Comparative Example 3, and Comparative Example 4 compared to Comparative Example 1. This indicates that the triple coating of metal oxide, phosphorus source, and halide in this invention has a synergistic effect, synergistically improving the first discharge specific capacity, first efficiency, and cycle capacity retention of the coated and modified lithium cobalt oxide cathode material. Compared with Example 1, Comparative Example 5 differs only in that it simultaneously grinds the metal oxide, phosphorus source, and halide with lithium cobalt oxide to achieve a one-step solid coating, and its effect is significantly worse than that of Example 1. Comparative Example 6 differs from Example 1 only in that it simultaneously performs wet coating on the phosphorus source and halide, without stepwise coating, and its effect is also significantly worse than that of Example 1. It can be seen that the coated modified lithium cobalt oxide cathode material prepared by the stepwise coating process of the three substances in the embodiments of the present invention can achieve uniform dispersion of each coated ion and form a denser and stronger protective layer, further improving the first discharge specific capacity, first efficiency, and cycle capacity retention of the lithium cobalt oxide cathode material.

[0035] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a coated and modified lithium cobalt oxide cathode material, characterized in that, Includes the following steps: 1) Lithium cobalt oxide and metal oxide are mixed, ground, and then subjected to a first sintering process to obtain lithium cobalt oxide cathode material; 2) The lithium cobalt oxide cathode material obtained in step 1) is placed in a phosphorus source solution and impregnated by first stirring, filtered, and dried. Then it is placed in a halide solution and impregnated by second stirring, filtered, and dried to obtain a pre-coated lithium cobalt oxide cathode material. 3) The pre-coated lithium cobalt oxide cathode material obtained in step 2) is subjected to a second sintering and crushed to obtain the coated modified lithium cobalt oxide cathode material.

2. The method for preparing the coated modified lithium cobalt oxide cathode material according to claim 1, characterized in that, The metal oxide mentioned in step 1) is selected from at least one of aluminum oxide, magnesium oxide, zirconium oxide, and lanthanum oxide; The crystallinity of the lithium cobalt oxide mentioned in step 1) is above 96%; The molar ratio of the metal oxide to lithium cobalt oxide in step 1) is (0.1-0.5):100; The grinding speed mentioned in step 1) is 350-400℃, and the grinding time is more than 3 hours; Preferably, the grinding time is 3-12 hours; Optionally, the grinding step described in step 1) may be preceded by pre-grinding for 20-30 minutes.

3. The method for preparing the coated modified lithium cobalt oxide cathode material according to claim 1 or 2, characterized in that, In step 1), the first sintering temperature is 600-900℃, and the first sintering time is 10-12h; In step 1), the first sintering is carried out in an oxygen-containing atmosphere; Optionally, the oxygen-containing atmosphere may include an air atmosphere.

4. The method for preparing the coated modified lithium cobalt oxide cathode material according to any one of claims 1-3, characterized in that, The phosphorus source in the phosphorus source solution mentioned in step 2) includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium phosphate, aluminum phosphate, and iron phosphate. The ratio of lithium cobalt oxide cathode material to phosphorus source solution in step 2) is (40-55):(20-30), with units of g / mL.

5. The method for preparing the coated modified lithium cobalt oxide cathode material according to any one of claims 1-4, characterized in that, The molar concentration of the phosphorus source in the phosphorus source solution mentioned in step 2) is 0.05-0.2 mol / L; In step 2), the first stirring and impregnation speed is 400-600 r / min, and the first stirring and impregnation time is 30-35 min.

6. The method for preparing the coated modified lithium cobalt oxide cathode material according to any one of claims 1-5, characterized in that, The halide in the halide solution described in step 2) is selected from at least one of NH4F, LiCl, and MgF; The molar concentration of the halide in the halide solution is 0.05-0.2 mol / L; In step 2), the second stirring and impregnation speed is 400-600 r / min, and the second stirring and impregnation time is 30-35 min.

7. The method for preparing the coated modified lithium cobalt oxide cathode material according to any one of claims 1-6, characterized in that, The volume ratio of the phosphorus source solution to the halide solution in step 2) is (20-30):(12-25); Step 2) includes a grinding step after the second stirring and impregnation, filtration, and drying steps in the halide solution.

8. The method for preparing the coated modified lithium cobalt oxide cathode material according to any one of claims 1-7, characterized in that, In step 3), the second sintering temperature is 800-900℃, and the second sintering time is 5-6 hours. In step 3), the second sintering is carried out in an oxygen-containing atmosphere; Optionally, the oxygen-containing atmosphere includes at least one of an air atmosphere and an oxygen atmosphere.

9. A coated and modified lithium cobalt oxide cathode material, characterized in that, It is prepared by the method for preparing the coated modified lithium cobalt oxide cathode material according to any one of claims 1-8.

10. The application of the coated modified lithium cobalt oxide cathode material according to claim 9 in lithium-ion batteries.

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