Doped and coated modified lithium cobalt oxide positive electrode material and preparation method thereof

Abstract

The invention discloses a doped and coated modified lithium cobalt oxide positive electrode material. The doped and coated modified lithium cobalt oxide positive electrode material comprises a lithium cobalt oxide matrix, a doping element uniformly doped in the lithium cobalt oxide matrix, and a cobalt-based coating layer coated on the surface of the lithium cobalt oxide matrix, the doping element is selected from one or more of La, Al, Zr and Y. The cobalt-based coating layer is formed by reaction of stannous chloride and the lithium cobalt oxide matrix at high temperature. Through synergistic modification of the bulk phase and the surface, the crystal structure stability and the interface stability of the material are synchronously improved, the process is simple, the cost is controllable, and the method is suitable for large-scale production of high-energy-density lithium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials technology, specifically to a doped and coated modified lithium cobalt oxide cathode material and its preparation method. Background Technology

[0002] Lithium-ion batteries are core energy storage components in consumer electronics and new energy vehicles, and their energy density, cycle life, and safety performance directly determine the user experience of end products. Among many lithium-ion battery cathode materials, lithium cobalt oxide (LiCoO2) has become one of the most mature and widely used lithium-ion battery cathode materials due to its outstanding advantages such as a high operating voltage of 3.6V, a first-cycle coulombic efficiency of over 90%, excellent cycle stability, and high volumetric energy density.

[0003] However, with the continuous increase in charging cutoff voltage, the performance problems of lithium cobalt oxide materials under high voltage have become increasingly prominent. Although increasing the charging voltage can significantly improve the specific capacity of lithium cobalt oxide, its cycle performance decreases accordingly. The main reasons are: on the one hand, the amount of lithium ions extracted from the lithium cobalt oxide lattice increases under high voltage, leading to structural instability, a higher degree of delithiation on the material surface, and the structural phase transition extending from the material surface to the interior of the particles; on the other hand, high-valence cobalt has strong oxidizing properties and is easily reacted with the electrolyte to be extracted, accompanied by the release of oxygen, which increases safety hazards.

[0004] To address the performance issues of lithium cobalt oxide under high voltage, researchers and industry have developed various modification techniques, among which bulk doping and surface coating are the two most widely used methods. Bulk doping introduces heterogeneous elements (such as Al, Mg, Zr, La, etc.) into the lithium cobalt oxide lattice, utilizing the differences in ionic radii and valence characteristics of these heterogeneous elements to adjust lattice parameters and suppress lattice distortion during lithium-ion insertion / extraction, thereby improving crystal structure stability. For example, CN111924885A discloses a modification method for high-performance lithium cobalt oxide cathode materials. This method includes pretreating cobalt tetroxide to prepare a cobalt tetroxide composite; preparing a lithium cobalt oxide matrix using the cobalt tetroxide composite and a lithium source; and coating and modifying the lithium cobalt oxide matrix to obtain the lithium cobalt oxide cathode material. This method is simple and efficient, and easy to achieve large-scale product conversion. However, this patent still has the problem that the amount and ratio of modifiers and dopants need further optimization.

[0005] CN116161710A discloses a modified lithium cobalt oxide cathode material and its preparation method. The material comprises a mixed sintered cobalt tetroxide precursor, an M oxide, and a lithium source, wherein the cobalt tetroxide precursor is modified cobalt tetroxide doped with lanthanum and N, and N is at least one selected from manganese, yttrium, zirconium, fluorine, boron, aluminum, and magnesium. This modified lithium cobalt oxide cathode material exhibits high specific capacity, high cycle life, high storage performance, and high safety performance. However, this patent still has the issue that the preparation method of the cobalt tetroxide precursor needs further optimization.

[0006] In summary, existing modification technologies for lithium cobalt oxide cathode materials still have significant shortcomings in terms of doping uniformity, coating quality, process cost, and overall high-voltage performance. Developing a novel modification method that can simultaneously improve crystal structure stability and interface stability, with a simple process and controllable cost, is of vital importance for promoting the development of high-energy-density lithium-ion batteries. Summary of the Invention

[0007] The present invention aims to provide a doped and coated modified lithium cobalt oxide cathode material and its preparation method, thereby solving the problems of unstable crystal structure, poor cycle performance, and insufficient interface stability of lithium cobalt oxide materials under high voltage in the prior art.

[0008] To achieve the above objectives, this application provides the following technical solution: A doped and coated modified lithium cobalt oxide cathode material includes a lithium cobalt oxide matrix, doping elements uniformly doped in the lithium cobalt oxide matrix, and a cobalt-based coating layer coated on the surface of the lithium cobalt oxide matrix; the doping elements are selected from one or more of La, Al, Zr, and Y, and the cobalt-based coating layer is formed by reacting stannous chloride with the lithium cobalt oxide matrix at high temperature.

[0009] As a preferred embodiment, the total amount of the doping elements added is 0.1 to 2.0% of the mass of the lithium cobalt oxide matrix.

[0010] Another technical solution of this application discloses a method for preparing lithium cobalt oxide cathode material, characterized by comprising the following steps: Step 1: Mixing cobalt tetroxide raw material with lithium-containing source material, calcining under an inert gas or reducing gas atmosphere, and then ball milling to obtain a cobalt tetroxide composite; Step 2: Mixing the cobalt tetroxide composite with a dopant, synthesizing under high temperature solid-state in an inert gas atmosphere, and then wet milling to obtain a uniformly doped lithium cobalt oxide matrix; Step 3: Mixing the lithium cobalt oxide matrix with lithium-containing source material, calcining under an inert gas atmosphere, and then pulverizing and sieving to obtain a preliminary product with a particle size of less than 300 mesh; Step 4: Placing the preliminary product in a solution containing stannous chloride for surface coating, then synthesizing under high temperature solid-state in an inert gas atmosphere, and finally cooling and washing to obtain the lithium cobalt oxide cathode material.

[0011] As a preferred embodiment, the lithium-containing source material is selected from Li₂CO₃, LiOH, Li₂O, and Li₄Ti₅O. 12 One or more of CH3COOLi.

[0012] As a preferred embodiment, the dopant in step 2 is selected from one or more of La2O3, Al2O3, ZrO2, and Y2O3; As a preferred embodiment, the amount of lithium-containing source material added in step 3 is 1.0% to 3.0% of the mass of the lithium cobalt oxide matrix. As a preferred embodiment, the concentration of the stannous chloride solution in step 4 is 0.25–2.0 mol / L.

[0013] As a preferred embodiment, the cooling rate in step 4 is 2–5 °C / min. The coating temperature is 300–500℃.

[0014] Another technical solution of this application is a lithium-ion battery comprising the aforementioned lithium cobalt oxide cathode material.

[0015] Working principle and beneficial effects of the present invention: Compared with existing technologies, it has the following beneficial effects: 1. By uniformly incorporating rare earth elements into the lithium cobalt oxide matrix through solid-phase doping technology, the crystal structure stability of the material is significantly improved, effectively solving the problem of lithium ions being extracted from the lithium cobalt oxide lattice under high voltage, and effectively preventing the problem of excessive delithiation on the material surface and the structural phase transition extending from the material surface to the particle interior. 2. By employing high-temperature solid-state synthesis and dry coating technology, a uniform cobalt coating layer is formed on the surface of lithium cobalt oxide material, which effectively improves the electrochemical performance of the material under high voltage, enhances the capacity retention and rate performance of the material, and meets the market demand for high energy density and long cycle life. 3. Pretreatment of cobalt tetroxide composites, as a key precursor for the synthesis of high-performance 5B type lithium cobalt oxide, optimizes the microstructure of the material, improves its density and stability, and effectively enhances its interfacial stability and structural integrity. 4. The preparation method of the present invention is simple to operate, the process is controllable, the cost is moderate, and it is easy to realize industrial production, overcoming the problems of complex process and high cost in the prior art; 5. By rationally selecting the types and proportions of doping elements, this invention achieves the synergistic effect of each component, effectively improving the overall performance of the material and solving the problem that the proportion of doping elements is not optimal in the prior art. Detailed Implementation

[0016] The following detailed description illustrates the specific implementation method: Example 1: A method for preparing a doped and coated modified lithium cobalt oxide cathode material, comprising the following steps: 1. Preparation of cobalt tetroxide composite precursor: Cobalt tetroxide raw material was mixed with lithium carbonate and lithium hydroxide at a mass ratio of Li:Co=0.8:1; the temperature was increased to 500℃ at 2℃ / min under nitrogen atmosphere and held for 2h; then ball milled at 300rpm for 4h to obtain cobalt tetroxide composite.

[0017] 2. Preparation of lithium cobalt oxide matrix: The above cobalt tetroxide composite was mixed with lanthanum oxide at a mass ratio of La:Co = 0.05:100; the temperature was increased to 700℃ at 5℃ / min under an inert gas atmosphere and held for 4h; then it was mixed with deionized water at a mass ratio of H2O:Co = 10:1 and ultrasonically dispersed for 30min to obtain a uniformly doped lithium cobalt oxide matrix.

[0018] 3. Preparation of preliminary lithium cobalt oxide cathode material: The above matrix is ​​mixed with lithium carbonate and lithium hydroxide at a mass ratio of Li:Co=1.2:1; the temperature is increased to 800℃ at 3℃ / min under an inert gas atmosphere and held for 3h; after crushing and sieving, the product with a particle size of less than 200 mesh is taken.

[0019] 4. Surface modification treatment: The preliminary product was placed in a 0.8 mol / L stannous chloride solution and stirred for 2 h; the temperature was increased to 400 °C at 4 °C / min under a nitrogen atmosphere and held for 2 h; the temperature was cooled to room temperature at 3 °C / min, filtered and washed to obtain the final product.

[0020] Example 2: A method for preparing a doped and coated modified lithium cobalt oxide cathode material, the steps of which are as follows: 1. Preparation of cobalt tetroxide composite precursor: Cobalt tetroxide raw material was mixed with anhydrous ethanol and hydrated lithium acetate at a mass ratio of Li:Co=0.6:1; the temperature was increased to 600℃ at 3℃ / min under argon atmosphere and held for 3h; then ball milled at 350rpm for 6h to obtain cobalt tetroxide composite.

[0021] 2. Preparation of lithium cobalt oxide matrix: The above cobalt tetroxide composite was mixed with cerium oxide at a mass ratio of Ce:Co = 0.08:100; the temperature was increased to 750℃ at 6℃ / min under an inert gas atmosphere and held for 5h; then it was mixed with ethanol at a mass ratio of C2H5OH:Co = 15:1 and ultrasonically dispersed for 45min to obtain a uniformly doped lithium cobalt oxide matrix.

[0022] 3. Preparation of preliminary lithium cobalt oxide cathode material: The above matrix is ​​mixed with lithium carbonate and lithium hydroxide at a mass ratio of Li:Co=1.5:1; the temperature is increased to 900℃ at 4℃ / min under an inert gas atmosphere and held for 2.5h; after crushing and sieving, the product with a particle size of less than 250 mesh is taken.

[0023] 4. Surface modification treatment: The preliminary product was placed in a 1.0 mol / L stannous chloride solution and stirred for 3 h; the temperature was increased to 450 °C at 5 °C / min under a nitrogen atmosphere and held for 2.5 h; the temperature was then cooled to room temperature at 4 °C / min, filtered and washed to obtain the final product.

[0024] Blank Example: 1. Cobalt tetroxide raw material was mixed with lithium carbonate and lithium hydroxide at a mass ratio of Li:Co=0.8:1, consistent with the precursor preparation parameters in Example 1; 2. Calcination synthesis: The temperature was raised to 500℃ at 2℃ / min under a nitrogen atmosphere and held for 2h, followed by ball milling at 300rpm for 4h to obtain cobalt tetroxide composite; 3. Matrix synthesis: The composite was mixed with lithium carbonate and lithium hydroxide at a mass ratio of Li:Co=1.2:1, and the temperature was raised to 800℃ at 3℃ / min under an inert gas atmosphere and held for 3h, without any doping steps; 4. Post-processing: The product with a particle size <200 mesh was obtained by crushing and sieving, without any surface coating steps.

[0025] Comparative Example 1: Bulk-doped control group: ① The precursor preparation, matrix synthesis (addition of La / Ce doping) and preliminary product preparation steps were exactly the same as in Example 1 / 2, except that the surface modification treatment step was omitted (i.e., no stannous chloride coating, high-temperature reaction and cooling washing were performed); products with qualified particle size were taken as the doped control sample.

[0026] Comparative Example 2:1 Bulk Doping Control Group (Taking Example 1 La Doping as an Example): ① Experimental Scheme: The steps of precursor preparation (Li:Co=0.8:1), matrix synthesis (La:Co=0.05:100, 700℃ for 4h) and preliminary product preparation (800℃ for 3h, particle size <200 mesh) are exactly the same as in Example 1, except that the surface modification treatment step is deleted.

[0027] Comparative Example 3: Surface Coating Control Group Only: ① Experimental Procedure: No La / Ce dopants were added during precursor preparation and preliminary product preparation. Other process parameters (lithium-cobalt ratio, calcination temperature, ball milling parameters, etc.) were the same as in Example 1 / 2. The surface modification treatment steps (stannous chloride concentration, stirring time, coating temperature, etc.) were completely matched to Example 1 / 2.

[0028] Examples 1, 2, the blank group, and Comparative Examples 1 to 3 were used; the same electrochemical testing system (CR2032 coin cell, lithium sheet as counter electrode, 1 mol / L LiPF6 / EC+DMC+EMC electrolyte) and characterization equipment (XRD: CuKα target; EIS: frequency range 10) were employed. -2 -10 5 Hz; ICP-OES: detection limit 0.01 mg / L), the following data were obtained: Example 1: ① Electrochemical performance: 186 mAh / g initial discharge specific capacity at 4.5V / 0.1C, 96% initial coulombic efficiency; 179 mAh / g initial discharge specific capacity at 1C; 92% capacity retention after 500 cycles; Rct=55Ω before cycling, Rct=116Ω after cycling; 165 mAh / g discharge specific capacity at 5C (88% retention at 0.1C baseline); ② Structure and safety performance: No spinel phase impurity peaks were observed after XRD cycling, and the layered structure matched the standard card (JCPDS 05-0605); TEM showed a 30 nm thick continuous cobalt-based coating layer, and EDS mapping showed uniform La element distribution; the particles remained intact and did not pulverize after SEM cycling; the cobalt dissolution was measured to be 2.0 mg / L by ICP-OES; the DSC thermal decomposition onset temperature was 255℃, and the exothermic peak was 280 J / g; ③ Process data: Product yield was 92%, and energy consumption per unit mass was 0.85 kWh / kg.

[0029] Example 2: ① Electrochemical performance: 192 mAh / g initial discharge specific capacity at 4.5V / 0.1C, 95% initial coulombic efficiency; 185 mAh / g initial discharge specific capacity at 1C; 94% capacity retention after 500 cycles; Rct=52Ω before cycling, Rct=108Ω after cycling; 172 mAh / g discharge specific capacity at 5C rate (89% retention at 0.1C baseline); ② Structural and safety performance: intact layered structure with no impurity peaks after XRD cycling; 40 nm thick dense cobalt-based coating layer observed by TEM; uniform Ce element distribution in the matrix shown by EDS mapping; regular particle morphology with no corrosion traces after SEM cycling; cobalt dissolution measured by ICP-OES as 1.8 mg / L; thermal decomposition onset temperature of 260℃ and exothermic peak of 265 J / g by DSC; ③ Process data: product yield 90%, energy consumption per unit mass 0.92 kWh / kg.

[0030] Blank Example: ① Electrochemical Performance: Initial discharge specific capacity at 4.5V / 0.1C is 142mAh / g, initial coulombic efficiency is 89%; initial discharge specific capacity at 1C is 135mAh / g; capacity retention after 500 cycles is 52%; Rct=85Ω before cycling, Rct=320Ω after cycling; discharge specific capacity at 5C rate is 88mAh / g (0.1C baseline retention is 61%); ② Structure and Safety Performance: XRD shows obvious spinel phase (2θ=31.7°) impurity peaks after cycling; SEM observation shows severe particle pulverization after cycling; ICP-OES shows cobalt dissolution is 12.5mg / L; DSC shows thermal decomposition initiation temperature is 185℃, and exothermic peak is 580J / g; ③ Process Data: Product yield is 88%, energy consumption per unit mass is 0.80kWh / kg.

[0031] Comparative Example 1: ① Electrochemical performance: Initial discharge specific capacity at 4.5V / 0.1C was 182mAh / g, initial coulombic efficiency was 94%; initial discharge specific capacity at 1C was 175mAh / g; capacity retention after 500 cycles was 80%; Rct = 68Ω before cycling, Rct = 225Ω after cycling; discharge specific capacity at 5C rate was 148mAh / g (0.1C baseline retention 81%); ② Structure and safety performance: XRD showed intact layered structure after cycling, with no spinel phase impurities; SEM showed no obvious pulverization of particles after cycling, but surface corrosion marks were present; EDS mapping showed uniform distribution of Ce; ICP-OES measured cobalt dissolution of 6.2mg / L; DSC thermal decomposition onset temperature was 210℃, and exothermic peak was 430J / g; ③ Process data: product yield was 91%, and energy consumption per unit mass was 0.88kWh / kg.

[0032] Comparative Example 2: ① Electrochemical performance: Initial discharge specific capacity at 4.5V / 0.1C was 178mAh / g, initial coulombic efficiency was 93%; initial discharge specific capacity at 1C was 170mAh / g; capacity retention after 500 cycles was 78%; Rct = 72Ω before cycling, Rct = 210Ω after cycling; discharge specific capacity at 5C rate was 142mAh / g (0.1C baseline retention 80%); ② Structure and safety performance: No impurity peaks were observed after XRD cycling, and the layered structure was intact; particle integrity was good after SEM cycling, with slight surface corrosion; EDS mapping showed uniform La element dispersion; cobalt dissolution was measured to be 5.8mg / L by ICP-OES; thermal decomposition onset temperature was 205℃, and exothermic peak was 420J / g; ③ Process data: Product yield was 90%, and energy consumption per unit mass was 0.86kWh / kg.

[0033] Comparative Example 3: Corresponding to the process of Example 1 (0.8 mol / L stannous chloride coating): ① Electrochemical performance: 155 mAh / g initial discharge specific capacity at 4.5V / 0.1C, 94% initial coulombic efficiency; 148 mAh / g initial discharge specific capacity at 1C; 65% capacity retention after 500 cycles; Rct=68Ω before cycling, Rct=150Ω after cycling; 105 mAh / g specific capacity at 5C rate (68% retention at 0.1C baseline); ② Structure and safety performance: weak spinel phase (2θ=31.7°) impurity peaks appeared after XRD cycling; intact particle surface but microcracks inside after SEM cycling; 30 nm thick continuous coating layer was observed by TEM; cobalt dissolution was measured to be 2.1 mg / L by ICP-OES; thermal decomposition onset temperature was 230℃, and exothermic peak was 350 J / g; ③ Process data: product yield 89%, energy consumption per unit mass 0.83 kWh / kg.

[0034] In summary, this application addresses the problems of unstable crystal structure, poor cycle performance, and insufficient interface stability of lithium cobalt oxide materials under high voltage in the prior art.

[0035] It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solution of this invention. These modifications and improvements should also be considered within the scope of protection of this invention, and will not affect the effectiveness of the invention or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A doped and coated lithium cobalt oxide cathode material, characterized in that, It includes a lithium cobalt oxide matrix, a dopant element uniformly doped in the lithium cobalt oxide matrix, and a cobalt-based coating layer covering the surface of the lithium cobalt oxide matrix; the dopant element is selected from one or more of La, Al, Zr, and Y, and the cobalt-based coating layer is formed by reacting stannous chloride with the lithium cobalt oxide matrix at high temperature.

2. The lithium cobalt oxide cathode material according to claim 1, characterized in that, The total amount of dopant added is 0.1 to 2.0% of the mass of the lithium cobalt oxide matrix.

3. The method for preparing the lithium cobalt oxide cathode material according to claim 1 or 2, characterized in that, Includes the following steps: Step 1: Mix cobalt tetroxide raw material with lithium-containing source material, calcine under an inert gas or reducing gas atmosphere, and then ball mill to obtain cobalt tetroxide composite. Step 2: Mix the cobalt tetroxide composite with a dopant, synthesize at high temperature under an inert gas atmosphere, and then wet grind to obtain a uniformly doped lithium cobalt oxide matrix. Step 3: Mix the lithium cobalt oxide matrix with lithium-containing source material, calcine under an inert gas atmosphere, and then pulverize and sieve to obtain a preliminary product with a particle size of less than 300 mesh. Step 4: Place the preliminary product in a solution containing stannous chloride for surface coating, then synthesize at high temperature under an inert gas atmosphere, cool and wash to obtain lithium cobalt oxide cathode material.

4. The preparation method according to claim 3, characterized in that, The lithium-containing source material is selected from Li2CO3, LiOH, Li2O, and Li4Ti5O. 12 One or more of CH3COOLi.

5. The preparation method according to claim 4, characterized in that, The dopant mentioned in step 2 is selected from one or more of La2O3, Al2O3, ZrO2, and Y2O3.

6. The preparation method according to claim 5, characterized in that, The amount of lithium-containing source material added in step 3 is 1.0 to 3.0% of the mass of the lithium cobalt oxide matrix.

7. The preparation method according to claim 6, characterized in that, The concentration of the stannous chloride solution in step 4 is 0.25–2.0 mol / L.

8. The preparation method according to claim 7, characterized in that, The cooling rate described in step 4 is 2–5 °C / min. The coating temperature is 300–500℃.

9. A lithium-ion battery, characterized in that, Includes the lithium cobalt oxide cathode material as described in claim 1 or 2.